Energy and Transport Sciences Lab

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Author - ETSL graduate student

Author - ETSL undergraduate student

Browse through our publications.
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Author - ETSL graduate student	Author - ETSL undergraduate student

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Electrodeposition Stability Landscape for Solid–Solid Interfaces

D. Chatterjee, K.G. Naik, B.S. Vishnugopi and P. P. Mukherjee

Journal Paper Advanced Science, 11, 2307455 (2024)

Abstract

As solid-state batteries (SSBs) with lithium (Li) metal anodes gain increasing traction as promising next-generation energy storage systems, a fundamental understanding of coupled electro-chemo-mechanical interactions is essential to design stable solid-solid interfaces. Notably, uneven electrodeposition at the Li metal/solid electrolyte (SE) interface arising from intrinsic electrochemical and mechanical heterogeneities remains a significant challenge. In this work, the thermodynamic origins of mechanics-coupled reaction kinetics at the Li/SE interface are investigated and its implications on electrodeposition stability are unveiled. It is established that the mechanics-driven energetic contribution to the free energy landscape of the Li deposition/dissolution redox reaction has a critical influence on the interface stability. The study presents the competing effects of mechanical and electrical overpotential on the reaction distribution, and demarcates the regimes under which stress interactions can be tailored to enable stable electrodeposition. It is revealed that different degrees of mechanics contribution to the forward (dissolution) and backward (deposition) reaction rates result in widely varying stability regimes, and the mechanics-coupled kinetics scenario exhibited by the Li/SE interface is shown to depend strongly on the thermodynamic and mechanical properties of the SE. This work highlights the importance of discerning the underpinning nature of electro-chemo-mechanical coupling toward achieving stable solid/solid interfaces in SSBs.

Correlating Lithium Plating Quantification with Thermal Safety Characteristics of Lithium-ion Batteries

H. Zhou, C. Fear, R. Carter, C. Love and P. P. Mukherjee

Journal Paper Energy Storage Materials, 103214 (2024)

Abstract

Lithium plating is one of the most safety-critical side reactions in lithium-ion (Li-ion) batteries. It is likely to occur under overcharge or fast-charge scenarios when the overwhelming Li-ion flux exceeds the intercalation or diffusion limits of the graphite host structure. Adverse lithium plating will cause the loss of lithium inventory to accelerate degradation and reduce the cell safety limits due to high thermal instability. Correlating lithium plating quantification with cell-level thermal safety characteristics remains a critical bottleneck. In this study, we derive correlations between the total plating energy and kinetic parameters of lithium plating induced exothermic reactions. Three-electrode electrochemical analytics of Li-ion pouch cells, under isothermal and thermal gradient conditions, are analyzed based on decoupled anode potential for lithium plating signatures. Post-mortem analysis reveals the distribution, morphology, and chemical state of lithium plating regimes. Accelerating rate calorimetry is employed to evaluate cell thermal hazards, followed by thermos-kinetic analysis to reveal correlations between the safety factor and plating energy. This work reveals the evolution of lithium plating induced early cell exotherm and total heat generation, promoting the development of real-time battery safety monitoring based on the online detection of lithium plating severity.

Mechanistic understanding of thermodynamic metastability of core-shell catalysts in the polymer electrolyte fuel cell catalyst layer durability

N. Goswami, K. Chen, X. Wang, J. S. Spendelow, R. L. Borup and P. P. Mukherjee

Journal Paper Chemical Engineering Journal, 484, 149672 (2024)

Abstract

Core-shell nanoparticles in cathode catalyst layers of Polymer Electrolyte Fuel Cells (PEFCs) are a promising class of electrocatalysts that have received considerable attention owing to their high mass activity when compared to their single metal counterparts. The nature of its bimetallic design offers a potential range of tunable parameters to improve its stability mediated by the long-range interactions arising from the strain effect. In this work, we reveal the emergence of thermodynamic metastability in the surface energetics at a critical design limit of large core diameter and shell thickness when the elastic strain energy of the electrocatalyst exceeds the energy to form dislocations. The progression of degradation events induces a transition in the metastability front in the catalyst layer which can be attributed to the heterogeneous nature of particle aging. We performed a screening of key candidate core materials and found that negative misfit scenarios such as Nickel (Ni), Copper (Cu), Cobalt (Co), and Palladium (Pd) impart durability against the primary mode of electrochemical dissolution. The positively mismatched structures however exhibit a disparate trend where the strain ramp at high lattice misfits is suppressed mechanistically by exerting a pseudo-compressive force field. Consequently, the critical onset of the nanocatalysts to reach a limiting diameter is governed by the property mismatch between the core and the shell, in terms of the bulk moduli and molar volume. The contrariety in the metastability-durability characteristics stemming from a variation in the initial thickness of the protective Pt skin is further delineated.

Probing multiphase reactive transport interactions in the polymer electrolyte fuel cell catalyst layer degradation

N. Goswami, J.B. Grunewald, T.F. Fuller and P.P. Mukherjee

Journal Paper Electrochimica Acta, 486, 144143 (2024)

Abstract

The multiphase, multicomponent reactive transport plays a critical role in the degradation of the cathode catalyst layer in Polymer Electrolyte Fuel Cells. This warrants a fundamental understanding of the pore-scale, mechanistic interactions in the catalyst layer. Herein, the interfacial and transport interactions due to the flooding dynamics in the presence of carbon support corrosion, which is a primary degradation mode in the cathode catalyst layer, are delineated based on a comprehensive mesoscale model. The mechanistic interrogation of the degradation-transport interactions reveals the spatio-temporal heterogeneity of the pristine and aged microstructures. An electrode-averaged saturation front of 80 % unveils a critical limit of percolation which results in an onset of limiting current density. Further, it is observed that the reactant severity is amplified at progressively higher stages of corrosion owing to the appearance of dead pores and a thicker ionomer film. We also shed light on the fluid displacement patterns which reveal the existence of a capillary fingering regime. The interplay of the operating current density and carbon corrosion in governing the substrate-ionomer interaction is described through an electrochemical Damköhler number.

State-of-Charge Implications of Thermal Runaway in Li-ion Cells and Modules

A. Karmakar, H. Zhou, B.S. Vishnugopi, J.A. Jeevarajan and P. P. Mukherjee

Journal Paper Journal of The Electrochemical Society, 171, 010529 (2024)

Abstract

The thermal safety of lithium-ion (Li-ion) batteries for electric vehicles continues to remain a major concern. A comprehensive understanding of the thermal runaway (TR) mechanisms in Li-ion cells and modules due to intrinsic factors such as state-of-charge (SOC) and cell-to-cell arrangement under abuse scenarios such as external heating is critical toward the development of advanced battery thermal management systems. This study presents a hierarchical TR modeling framework to examine the TR behavior of Li-ion cells at various SOCs and probe its implications on the thermal runaway propagation (TRP) in a battery module. We perform accelerating rate calorimetry (ARC) experiments with 3.25 Ah cylindrical Li-ion cells at different SOCs and demonstrate the strong SOC dependence of TR characteristics such as the onset temperature, maximum cell temperature, and self-heating rate. The thermo-kinetic parameters extracted from the ARC experiments are used to develop a TR model that captures the SOC-induced TR response in Li-ion cells. The mechanistic information from the cell-level model is used to examine the pathways for TRP in a battery module consisting of cells with uniform and imbalanced SOCs, thereby demonstrating the underlying role of SOC variability on the resulting TRP under abuse conditions.

Uncertainty Quantification and Propagation in Lithium-ion Battery Electrodes using Bayesian Convolutional Neural Networks

C. Norris, A. Ayyaswamy, B. S. Vishnugopi, C. Martinez, S. A. Roberts and P. P. Mukherjee

Journal Paper Energy Storage Materials, 103251 (2024)

Abstract

The complex nature of manufacturing processes stipulates electrodes to possess high variability with increased heterogeneity during production. X-ray computed tomography imaging has proved to be critical in visualizing the complicated stochastic particle distribution of as-manufactured electrodes in lithium-ion batteries. However, accurate prediction of their electrochemical performance necessitates precise evaluation of kinetic and transport properties from real electrodes. Image segmentation that characterizes voxels to particle/pore phase is often meticulous and fraught with subjectivity owing to a myriad of unconstrained choices and filter algorithms. We utilize a Bayesian convolutional neural network to tackle segmentation subjectivity and quantify its pertinent uncertainties. Otsu inter-variance and Blind/Referenceless Imaging Spatial Quality Evaluator are used to assess the relative image quality of grayscale tomograms, thus evaluating the uncertainty in the derived microstructural attributes. We analyze how image uncertainty is correlated with the uncertainties and magnitude of kinetic and transport properties of an electrode, further identifying pathways of uncertainty propagation within microstructural attributes. The coupled effect of spatial heterogeneity and microstructural anisotropy on the uncertainty quantification of transport parameters is also understood. This work demonstrates a novel methodology to extract microstructural descriptors from real electrode images through quantification of associated uncertainties and discerning the relative strength of their propagation, thus facilitating feedback to manufacturing processes from accurate image based electrochemical simulations.

Revealing hidden predicaments to lithium-ion battery dynamics for electric vertical take-off and landing aircraft

A. Ayyaswamy, B.S. Vishnugopi and P. P. Mukherjee

Journal Paper Joule, 7, 2016 (2023)

Abstract

The future of urbanization engulfs the trident of electrification, increased accessibility, and enhanced productivity. Although electric vertical take-off and landing (eVTOL) aircrafts provide cleaner, faster, and more efficient mobility solutions, they exhibit stringent phase-disparate demands on Li-ion batteries (LIBs). Through our mechanistic modeling framework, we demonstrate that eVTOL architecture, its mission constraints, and electrode design portray complex electrochemical implications in LIBs. Accrescent current densities distinctive to eVTOLs signify landing/balked phases as critical pathways to trigger thermal safety. During cold starts, we identify key limitations arising from the union of initial energy consumption and thermal convection from altitude variation. Cognizant of the mission-specific thermo-electrochemical interactions in LIBs, practical insights into the dynamic response of battery thermal management systems are discussed. The confluence of eVTOL power requirements with its concomitant battery response conveys mechanistic trade-offs pertinent to a spectrum of target applications, including passenger mobility, cargo, and emergency medical services.

Interphases and Electrode Crosstalk Dictate the Thermal Stability of Solid-State Batteries

B.S. Vishnugopi, M.T. Hasan, H. Zhou and P. P. Mukherjee

Journal Paper ACS Energy Letters, 8, 398 (2023)

Abstract

Solid-state batteries, because of their high energy density, are promising candidates for long-range electric vehicles and electric aviation. While the enhanced safety potential of solid-state batteries has been typically ascribed to the nonflammability of solid electrolytes, an extensive interrogation of their thermal stability is still required. In this work, we reveal how the thermal stability in sulfide-based solid-state batteries is critically dependent on the interphase interactions at the solid electrolyte/Li interface, thereby illustrating the drastically different thermal signature of Li10SnP2S12 when compared with Li3PS4 and Li6PS5Cl. Our study shows that thermal runaway occurs even for a pristine Li10SnP2S12/Li interface and is severely exacerbated with cycling, which exhibits a massive thermal spike at the melting point of Li; this shift in thermal response uniquely correlates to the Li10SnP2S12 interphase evolution. On the basis of these distinct thermal signatures, cell-level mechanistic safety maps cognizant of the Li/interphase interaction, cathode/Li crosstalk, and specific energy are delineated.

Asymmetric Contact Loss Dynamics during Plating and Stripping in Solid-State Batteries

B.S. Vishnugopi, K.G. Naik, H. Kawakami, N. Ikeda, Y. Mizuno, R. Iwamura, T. Kotaka, K. Aotani, Y. Tabuchi and P. P. Mukherjee

Journal Paper Advanced Energy Materials, 13, 2203671 (2023)

Abstract

Solid-state batteries (SSBs) hold the potential to improve energy density and offer enhanced safety when compared to lithium-ion batteries. However, the development of practical SSBs faces major challenges, such as filament growth and void formation, which necessitate a comprehensive understanding of the intrinsic solid–solid interfaces and limiting mechanisms. In this work, the underpinning asymmetry in the mechanistic interplay and resulting interface dynamics during Li plating and stripping is demonstrated, illustrating the critical effect of reaction heterogeneity on the contact loss behavior. With increasing stripping rates, the manifestation of solid–solid point contacts is identified as a key descriptor that signifies a transition in electrochemical response from a regime of continuous contact decay to current constriction. It is revealed that contact loss can also occur during plating at the Li/Li6PS5Cl interface; this severity scales with the reaction heterogeneity and is identified as an important challenge toward achieving faster charging rates in SSBs. The distinct nature of competing electrochemical–mechanical interactions that govern void formation during plating/stripping are delineated in this work. Coupled with these intrinsic mechanisms, non-uniformities in external pressure and temperature fields drastically alter the contact dynamics, resulting in disparate void localization patterns.

Heterogeneities affect solid-state battery cathode dynamics

K.G. Naik, B.S. Vishnugopi and P. P. Mukherjee

Journal Paper Energy Storage Materials, 55, 312 (2023)

Abstract

Solid-state batteries hold the promise to improve energy and power densities compared to conventional lithium-ion batteries. Among myriad interface and mechanistic challenges plaguing the solid-state batteries, the composite cathode architecture owing to the underlying microstructural heterogeneity poses a critical bottleneck. The spatial variability of solid-solid point contacts and ionic/electronic percolation pathways govern the underlying reaction-transport dichotomy, and ultimately affect the spatio-temporal dynamics. In this work, we postulate the inherent role of mesoscale interactions and delineate how heterogeneities profoundly affect the spatio-temporal evolution of thermo-electrochemical dynamics subject to physical and operational extremes. This study critically examines the importance of solid-solid point contacts manifesting as singularities in thermo-electrochemical hotspot formation, intercalation cascade, and reaction current localization and establishes these as mechanistic pain points for consideration in the future development of improved solid-state battery cathode architectures.

Dynamics of lithium stripping on graphite electrodes after fast charging

S.P. Rangarajan, C. Fear, T. Adhikary, Y. Barsukov, G. Dadheech and P. P. Mukherjee

Journal Paper Cell Reports Physical Science, 4, 101740 (2023)

Abstract

Safe and reliable fast charging of lithium-ion batteries is contingent upon the development of facile methods of detection and quantification of lithium plating. Among the leading candidates for online lithium plating detection is analysis of the voltage plateau observed during the rest or discharge phase ensuing a charge. In this work, an operando metric, ‘‘S-factor,’’ is developed from electrochemical data to quantitatively analyze the severity of lithium plating over a range of charge rates and temperatures. An in situ visualization method is employed to study the physical mechanisms and phase transitions occurring at the graphite electrode during the voltage plateau. Here, we report that plated electrodes with significant state of charge heterogeneity exhibit multiple voltage plateaus and a higher proportion of irreversible plating. Cell characterization using S-factor and coulombic inefficiency helps in identifying the zone of opportunity with highly reversible lithium plating, facilitating development of safe and reliable fast-charging algorithms.

Electro-Chemo-Mechanical Challenges and Perspective in Lithium Metal Batteries

K. G. Naik, B.S. Vishnugopi, J. Datta, D. Datta and P. P. Mukherjee

Journal Paper Applied Mechanics Reviews, 75, 010802 (2023)

Abstract

The development of next-generation batteries, utilizing electrodes with high capacities and power densities requires a comprehensive understanding and precise control of material interfaces and architectures. Electro-chemo-mechanics plays an integral role in the morphological evolution and stability of such complex interfaces. Volume changes in electrode materials and the chemical interactions of electrode/electrolyte interfaces result in nonuniform stress fields and structurally different interphases, fundamentally affecting the underlying transport and reaction kinetics. The origin of this mechanistic coupling and its implications on degradation is uniquely dependent on the interface characteristics. In this review, the distinct nature of chemo–mechanical coupling and failure mechanisms at solid–liquid interfaces and solid–solid interfaces is analyzed. For lithium metal electrodes, the critical role of surface/microstructural heterogeneities on the solid electrolyte interphase (SEI) stability and dendrite growth in liquid electrolytes, and on the onset of contact loss and filament penetration with solid electrolytes is summarized. With respect to composite electrodes, key differences in the microstructure-coupled electro-chemo-mechanical attributes of intercalation- and conversion-based chemistries are delineated. Moving from liquid to solid electrolytes in such cathodes, we highlight the significant impact of solid–solid point contacts on transport/mechanical response, electrochemical performance, and failure modes such as particle cracking and delamination. Finally, we present our perspective on future research directions and opportunities to address the underlying electro-chemo-mechanical challenges for enabling next-generation lithium metal batteries.

Fluorinated ethylene carbonate as additive to glyme electrolytes for robust sodium solid electrolyte interface

S. Sarkar, M. J. Lefler, B.S. Vishnugopi, R. B. Nuwayhid, C. T. Love, R. Carter and P. P. Mukherjee

Journal Paper Cell Reports Physical Science, 4, 101356 (2023)

Abstract

The utilization of alkali metal anodes is hindered by an inherent instability in organic electrolytes. Sodium is of growing interest due to its high natural abundance, but the carbonate electrolytes popular in lithium systems cannot form a stable solid electrolyte interphase (SEI) with a sodium electrode. Using half-cell and symmetric-cell analysis, we identify specific glyme (chain ether) electrolytes that produce thin, predominantly inorganic SEI at the sodium metal interface, and we study the effect of ethylene carbonate and fluoroethylene carbonate (FEC) additives on the SEI formed in these systems via X-ray photoelectron spectroscopy. Through in situ optical microscopy, we observe the onset and growth of sodium dendrites in these electrolytes. We determine that the SEI formed by glyme alone may not support extensive or extreme cycling conditions, but the addition of FEC provides a more robust SEI to facilitate numerous consistent sodium plating and stripping cycles.

Probing Asymmetric Plating and Stripping Behavior of Symmetric Sodium Metal Batteries

S. Sarkar and P. P. Mukherjee

Journal Paper Journal of The Minerals, Metals & Materials Society (2024)

Abstract

Numerous research endeavors are currently centered around metal-based batteries due to their remarkable attributes of high energy density and theoretical capacity. Sodium (Na) metal, in particular, stands out as an exceptionally appealing choice. Not only does Na possess a high energy density but it is also abundant and cost-effective. Similar to lithium-metal batteries, the selection of cathode materials for Na-metal batteries is made based on specific needs, leading to the inherent achievement of either high capacity or enhanced thermal stability. Consequently, it becomes imperative to explore the failure modes of Na metal for various cathode–metal anode pairs scenarios. In the case of cathodes devoid of Na, the stripping of Na metal occurs, whereas, for cathodes that involve Na as a contributing component, the initial step involves the plating of Na metal. This work aims to unravel the impact of the initial plating and stripping protocols on the behavior of the working electrode, and to establish a correlation between the unique voltage trends and the eventual failure of the cell. Furthermore, this study explores the distinctive plating and stripping dynamics exhibited by the glyme and carbonate mixture, along with the variations in the behavior of the working electrode and counter electrode throughout different cycling stages. This thorough analysis based on comprehensive electrochemical signatures subsequently facilitates the enhancement of electrolyte choices, the formulation of effective cell designs, and the establishment of cycling protocols that can either avert or delay cell failure.

Thermal Runaway Propagation Analytics and Crosstalk in Lithium-Ion Battery Modules

A. Karmakar, H. Zhou, B.S. Vishnugopi and P. P. Mukherjee

Journal Paper Energy Technology, 12, 2300707 (2023)

Abstract

The thermal safety of lithium-ion (Li-ion) batteries continues to remain a critical concern for widespread vehicle electrification. Under abuse scenarios, thermal runaway (TR) of individual energy-dense Li-ion cells can be dominated by various exothermic mechanisms due to interelectrode crosstalk, resulting in an enormous heat generation response that can potentially lead to thermal runaway propagation (TRP) in a battery module. Herein, a hierarchical TRP analytics approach is developed, which includes cell-level thermokinetic and electrode crosstalk interactions derived from accelerating rate calorimetry characteristics of a representative high-energy 18650 cylindrical Li-ion cell with Ni-rich cathodes and Si–C anodes. The hierarchical TRP model, coupled with multimodal heat dissipation, demonstrated for an exemplar energy-dense Li-ion battery module configuration, determines TRP criticality at module level for a wide range of conditions, including ambient temperature, intercell spacing, trigger cell location, external heating power, and heat dissipation coefficients. Potential propagation pathways have been identified, and their underlying attributes in terms of propagation speed, heat release from exothermic reactions, critical thermal energy input, and heat dissipation to surroundings have been quantified. This hierarchical approach, including thermal transfer and chemical interelectrode crosstalk during TR, can provide high-resolution TRP analytics for energy-dense Li-ion battery modules and is scalable to packs.

Li-ion Battery Safety: A Perspective on Hierarchy of Scales

A. Karmakar, H. Zhou, B.S. Vishnugopi and P. P. Mukherjee

Journal Paper Annual Review of Heat Transfer, 26, 11 (2023)

Abstract

Electrochemical energy systems, such as lithium-ion batteries, are leading candidates for applications ranging from portable devices and electric vehicles to large-scale grid storage due to their high energy and power densities. These advanced storage technologies are crucial in achieving sustainable energy and can offer cleaner and more efficient energy options. However, there is a risk of thermal runaway, a phenomenon when a chain of exothermic reactions occurs within the battery under abuse conditions. This can cause the battery's internal temperature to increase rapidly, destabilizing and degrading the intrinsic msaterials, ultimately resulting in a cascading failure. Herein, we describe the state-of-the-art understanding and our perspective on the hierarchical nature of thermal safety interactions in lithium-ion batteries. The material-level thermal instability mechanisms for various anode, cathode, and electrolyte materials are discussed. Notable results are highlighted on the effect of multiple cell factors and operating conditions on the cell-level thermal runaway process, mechanisms, flame characteristics, and gas compositions. The wide range of thermo-electrochemical mechanisms that determine the cell-level thermal runaway under different abuse scenarios are summarized. Lastly, the experimental and numerical findings on the module-level thermal runaway propagation behavior and mitigation strategies are described. The concepts discussed in this perspective are aimed toward enabling a hierarchical understanding of thermal stability and mechanistic thermal management solutions for lithium-ion batteries.

Developing a model for the impact of non-conformal lithium contact on electro-chemo-mechanics and dendrite growth

J. M. Meyer, K. L.Harrison, P. P. Mukherjee and S. A. Roberts

Journal Paper Cell Reports Physical Science, 4, 101364 (2023)

Abstract

Lithium dendrite growth hinders the use of lithium metal anodes in commercial batteries. We present a 3D model to study the mechanical and electrochemical mechanisms that drive microscale plating. With this model, we investigate electrochemical response across a lithium protrusion characteristic of rough anode surfaces, representing the separator as a porous polymer in non-conformal contact with a lithium anode. The impact of pressure on separator morphology and electrochemical response is of particular interest, as external pressure can improve cell performance. We explore the relationships between plating propensity, stack pressure, and material properties. External pressure suppresses lithium plating due to interfacial stress and separator pore closure, leading to inhomogeneous plating rates. For moderate pressures, dendrite growth is completely suppressed, as plating will occur in the electrolyte-filled gaps between anode and separator. In fast-charging conditions and systems with low electrolyte diffusivities, the benefits of pressure are overridden by ion transport limitations.

Structural and electrochemical evolution of alloy interfacial layers in anode-free solid-state batteries

S.E. Sandoval, J.A. Lewis, B.S. Vishnugopi, D.L. Nelson, M.M. Schneider, F.J.Q. Cortes, C.M. Matthews, J. Watt, M. Tian, P. Shevchenko, P. P. Mukherjee and M.T. McDowell

Journal Paper Joule, 7 (2023)

Abstract

“Anode-free” solid-state batteries feature high energy density since there is no anode active material. Although the beneficial effects of interfacial layers at the anode-solid electrolyte interface have been demonstrated, the mechanisms through which they influence lithium plating/stripping are unclear. Here, we reveal the evolution of 100-nm silver and gold interfacial layers during lithium plating/stripping using electrochemical methods, electron microscopy, X-ray microcomputed tomography, and modeling. The alloy layers improve Coulombic efficiency and resistance to short circuiting, even though the alloys form solute regions or particulates that detach from the current collector during plating. In situ electrochemical impedance spectroscopy shows that the alloys return to the interface and mitigate contact loss at the end of stripping, avoiding a critical vulnerability of anode-free cells. Contact retention is driven by even Li thickness that promotes spatially uniform stripping, as well as local alloy delithiation in response to current concentrations that homogenizes current and diminishes voiding.

Influence of Potassium Metal-Support Interactions on Dendrite Growth

P. Liu, D. Yen, B.S. Vishnugopi, V. R. Kankanallu, D. Gürsoy, M. Ge, J. Watt, P. P. Mukherjee, Y. K. Chen-Wiegart and D. Mitlin

Journal Paper Angewandte Chemie, e202300943 (2023)

Abstract

Combined synchrotron X-ray nanotomography imaging, cryogenic electron microscopy (cryo-EM) and modeling elucidate how potassium (K) metal-support energetics influence electrodeposit microstructure. Three model supports are employed: O-functionalized carbon cloth (potassiophilic, fully-wetted), non-functionalized cloth and Cu foil (potassiophobic, nonwetted). Nanotomography and focused ion beam (cryo-FIB) cross-sections yield complementary three-dimensional (3D) maps of cycled electrodeposits. Electrodeposit on potassiophobic support is a triphasic sponge, with fibrous dendrites covered by solid electrolyte interphase (SEI) and interspersed with nanopores (sub-10 nm to 100 nm scale). Lage cracks and voids are also a key feature. On potassiophilic support, the deposit is dense and pore-free, with uniform surface and SEI morphology. Mesoscale modeling captures the critical role of substrate-metal interaction on K metal film nucleation and growth, as well as the associated stress state.

Tuned Reactivity at the Lithium Metal–Argyrodite Solid State Electrolyte Interphase

H. Hao, Y. Liu, S. M. Greene, G. Yang, K. G. Naik, B.S. Vishnugopi, Y. Wang, H. Celio, A. Dolocan, W. Tsai, R. Fang, J. Watt, P. P. Mukherjee, D. J. Siegel and D. Mitlin

Journal Paper Advanced Energy Materials, 13, 2301338 (2023)

Abstract

Thin intermetallic Li2Te–LiTe3 bilayer (0.75 µm) derived from 2D tellurene stabilizes the solid electrolyte interphase (SEI) of lithium metal and argyrodite (LPSCl, Li6PS5Cl) solid-state electrolyte (SSE). Tellurene is loaded onto a standard battery separator and reacted with lithium through single-pass mechanical rolling, or transferred directly to SSE surface by pressing. State-of-the-art electrochemical performance is achieved, e.g., symmetric cell stable for 300 cycles (1800 h) at 1 mA cm−2 and 3 mAh cm−2 (25% DOD, 60 µm foil). Cryo-stage focused ion beam (Cryo-FIB) sectioning and Raman mapping demonstrate that the Li2Te–LiTe3 bilayer impedes SSE decomposition. The unmodified Li–LPSCl interphase is electrochemically unstable with a geometrically heterogeneous reduction decomposition reaction front that extends deep into the SSE. Decomposition drives voiding in Li metal due to its high flux to the reaction front, as well as voiding in the SSE due to the associated volume changes. Analysis of cycled SSE found no evidence for pristine (unreacted) lithium metal filaments/dendrites, implying failure driven by decomposition phases with sufficient electrical conductivity that span electrolyte thickness. DFT calculations clarify thermodynamic stability, interfacial adhesion, and electronic transport properties of interphases, while mesoscale modeling examines interrelations between reaction front heterogeneity (SEI heterogeneity), current distribution, and localized chemo-mechanical stresses.

Intermetallics Based on Sodium Chalcogenides Promote Stable Electrodeposition–Electrodissolution of Sodium Metal Anodes

Y. Wang, H. Dong, N. Katyal, B.S. Vishnugopi, M. K. Singh, H. Hao, Y. Liu, P. Liu, P. P. Mukherjee, G. Henkelman, J. Watt and D. Mitlin

Journal Paper Advanced Energy Materials, 13, 2204402 (2023)

Abstract

Sodiophilic micro-composite films of sodium-chalcogenide intermetallics (Na2Te and Na2S) and Cu particles are fabricated onto commercial copper foam current collectors (Na2Te@CF and Na2S@CF). For the first time a controllable capacity thermal infusion process is demonstrated. Enhanced wetting by the metal electrodeposition leads to state-of-the-art electrochemical performance. For example, Na2Te@CF-based half-cells demonstrate stable cycling at 6 mA cm−2 and 6 mAh cm−2, corresponding to 54 µm of Na electrodeposited/electrodissolved by geometric area. Sodium metal batteries with Na3V2 (PO4)3 cathodes are stable at 30C (7 mA cm−2) and for 10 000 cycles at 5C and 10C. Cross-sectional cryogenic focused ion beam (cryo-FIB) microscopy details deposited and remnant dissolved microstructures. Sodium metal electrodeposition onto Na2Te@CF is dense, smooth, and free of dendrites or pores. On unmodified copper foam, sodium grows in a filament-like manner, not requiring cycling to achieve this geometry. Substrate–metal interaction critically affects the metal–electrolyte interface, namely the thickness and morphology of the solid electrolyte interphase. Density functional theory and mesoscale simulations provide insight into support-adatom energetics, nucleation response, and early-stage morphological evolution. On Na2Te sodium atomic dispersion is thermodynamically more stable than isolated clusters, leading to conformal adatom coverage of the surface.

Stable Anode-Free All-Solid-State Lithium Battery through Tuned Metal Wetting on the Copper Current Collector

Y. Wang, Y. Liu, M. Nguyen, J. Cho, N. Katyal, B.S. Vishnugopi, H. Hao, R. Fang, N. Wu, P. Liu, P. P. Mukherjee, J. Nanda, G. Henkelman, J. Watt and D. Mitlin

Journal Paper Advanced Materials, 35, 2206762 (2023)

Abstract

A stable anode-free all-solid-state battery (AF-ASSB) with sulfide-based solid-electrolyte (SE) (argyrodite Li6PS5Cl) is achieved by tuning wetting of lithium metal on “empty” copper current-collector. Lithiophilic 1 μm Li2Te is synthesized by exposing the collector to tellurium vapor, followed by in situ Li activation during the first charge. The Li2Te significantly reduces the electro-deposition/electrodissolution overpotentials and improves Coulombic effi-ciency (CE). During continuous electrodeposition experiments using half-cells (1 mA cm−2), the accumulated thickness of electrodeposited Li on Li2Te–Cu is more than 70 μm, which is the thickness of the Li foil counter-electrode. Full AF-ASSB with NMC811 cathode delivers an initial CE of 83% at 0.2C, with a cycling CE above 99%. Cryogenic focused ion beam (Cryo-FIB) sec-tioning demonstrates uniform electrodeposited metal microstructure, with no signs of voids or dendrites at the collector-SE interface. Electrodissolution is uniform and complete, with Li2Te remaining structurally stable and adherent. By contrast, an unmodified Cu current-collector promotes inhomogeneous Li electrodeposition/electrodissolution, electrochemically inactive “dead metal,” dendrites that extend into SE, and thick non-uniform solid electrolyte interphase (SEI) interspersed with pores. Density functional theory (DFT) and mesoscale calculations provide complementary insight regarding nucleation-growth behavior. Unlike conventional liquid-electrolyte metal batteries, the role of current collector/support lithiophilicity has not been explored for emerging AF-ASSBs.

Mesoscale Interrogation Reveals Mechanistic Origins of Lithium Filaments along Grain Boundaries in Inorganic Solid Electrolytes

B.S. Vishnugopi, M.B. Dixit, F. Hao, B. Shyam, J.B. Cook, K.B. Hatzell and P. P. Mukherjee

Journal Paper Advanced Energy Materials, 12, 2102825 (2022)

Abstract

Solid-state batteries (SSBs), utilizing a lithium metal anode, promise to deliver enhanced energy and power densities compared to conventional lithium-ion batteries. Penetration of lithium filaments through the solid-state electrolytes (SSEs) during electrodeposition poses major constraints on the safety and rate performance of SSBs. While microstructural attributes, especially grain boundaries (GBs) within the SSEs are considered preferential metal propagation pathways, the underlying mechanisms are not fully understood yet. Here, a comprehensive insight is presented into the mechanistic interactions at the mesoscale including the electrochemical-mechanical response of the GB-electrode junction and competing ion transport dynamics in the SSE. Depending on the GB transport characteristics, a highly non-uniform electrodeposition morphology consisting of either cavities or protrusions at the GB-electrode interface is identified. Mechanical stability analysis reveals localized strain ramps in the GB regions that can lead to brittle fracture of the SSE. For ionically less conductive GBs compared to the grains, a crack formation and void filling mechanism, triggered by the heterogeneous nature of electrochemical-mechanical interactions is delineated at the GB-electrode junction. Concurrently, in situ X-ray tomography of pristine and failed Li7La3Zr2O12 (LLZO) SSE samples confirm the presence of filamentous lithium penetration and validity of the proposed mesoscale failure mechanisms.

Kinetics or transport – whither goes the solid-state battery cathode?

K.G Naik, B.S. Vishnugopi, and P. P. Mukherjee

Journal Paper ACS Applied Materials & Interfaces, 14, 29754 (2022)

Abstract

Solid-state batteries (SSBs) hold the potential to enhance the energy density, power density, and safety of conventional lithium-ion batteries. The theoretical promise of SSBs is predicated on the mechanistic design and comprehensive analysis of various solid−solid interfaces and microstructural features within the system. The spatial arrangement and composition of constituent phases (e.g., active material, solid electrolyte, binder) in the solid-state cathode dictate critical characteristics such as solid−solid point contacts or singularities within the microstructure and percolation pathways for ionic/ electronic transport. In this work, we present a comprehensive mesoscale discourse to interrogate the underlying microstructure-coupled kinetic-transport interplay and concomitant modes of resistances that evolve during electro-chemical operation of SSBs. Based on a hierarchical physics-based analysis, the mechanistic implications of solid−solid point contact distribution and intrinsic transport pathways on the kinetic heterogeneity is established. Toward designing high-energy-density SSB systems, the fundamental correlation between active material loading, electrode thickness and electrochemical response has been delineated. We examine the paradigm of carbon-binder free cathodes and identify design criteria that can facilitate enhanced performance with such electrode configurations. A mechanistic design map highlighting the dichotomy in kinetic and ionic/electronic transport limitations that manifest at various SSB cathode microstructural regimes is established.

Solid Electrolyte–Cathode Interface Dictates Reaction Heterogeneity and Anode Stability

K.G. Naik, D. Chatterjee and P. P. Mukherjee

Journal Paper ACS Applied Materials & Interfaces, 14, 45308 (2022)

Abstract

Solid-state batteries (SSBs) employing a lithium metal anode are a promising candidate for next-generation energy storage systems, delivering higher power and energy densities. Interfacial instabilities due to non-uniform electrodeposition at the anode–solid electrolyte (SE) interface pose major constraints on the safety and endurance of SSBs. In this regard, non-uniform kinetic interactions at the anode–SE interface which are derived from cathode microstructural heterogeneity can have significant impact on anode stability. In this work, we present a comprehensive insight into microstructural heterogeneity-driven cathode–anode cross-talk and delineate the role of cathode architecture and SE separator design in dictating reaction heterogeneity at the anode–SE interface. We show that intrinsic and extrinsic parameters, such as cathode loading, separator thickness, particle morphologies of active material and SE, and temperature can have significant impact on reaction heterogeneity at the anode–SE interface and thus govern anode stability. Tradeoff between energy density and anode stability while achieving higher cathode loading and thinner SE separators is highlighted, and potential strategies to mitigate this problem are discussed. This work provides fundamental insights into cathode–anode cross-talk involving interfacial heterogeneities and enhancement in energy densities of SSBs via electrode engineering.

Polymorphism of garnet solid electrolytes and its implications for grain-level chemo-mechanics

M.B. Dixit, B.S. Vishnugopi, W. Zaman, P. Kenesei, J.S. Park, J. Almer, P. P. Mukherjee and K.B. Hatzell

Journal Paper Nature Materials, 21, 1298 (2022)

Abstract

Understanding and mitigating filament formation, short-circuit and solid electrolyte fracture is necessary for advanced all-solid-state batteries. Here, we employ a coupled far-field high-energy diffraction microscopy and tomography approach for assessing the chemo-mechanical behaviour for dense, polycrystalline garnet (Li7La3Zr2O12) solid electrolytes with grain-level resolution. In situ monitoring of grain-level stress responses reveals that the failure mechanism is stochastic and affected by local microstructural heterogeneity. Coupling high-energy X-ray diffraction and far-field high-energy diffraction microscopy measurements reveals the presence of phase heterogeneity that can alter local chemo-mechanics within the bulk solid electrolyte. These local regions are proposed to be regions with the presence of a cubic polymorph of LLZO, potentially arising from local dopant concentration variation. The coupled tomography and FF-HEDM experiments are combined with transport and mechanics modelling to illustrate the degradation of polycrystalline garnet solid electrolytes. The results showcase the pathways for processing high-performing solid-state batteries.

Plating energy as a universal descriptor to classify accelerated cell failure under operational extremes

S.P. Rangarajan, Y. Barsukov, and P. P. Mukherjee

Journal Paper Cell Reports Physical Science, 3, 100720 (2022)

Abstract

Lithium plating is an anode-centric degradation process occurring in lithium-ion batteries resulting in irreversible capacity loss and cell failure. Temperature plays a critical role in improving the kinetics and transport, reducing lithium plating propensity. This study quantitively probes the evolution of plating with aging under temperature extremes in commercial Li-ion cells. Plating energy is proposed as a unique descriptor to quantify the extent of lithium plating and state of the electrode using operando analytics at any operating condition. Cells operated at temperature extrema (high/low) experience rapid capacity fade accompanied by a significant rise in anode impedance and exhibit plating energies greater than 1 Wh. Unfavorable intercalation kinetics at low temperatures and favorable solid electrolyte interphase (SEI) kinetics at high temperatures exacerbate anode impedance. These kinetically disparate manifestations on anode impedance adversely impact the interfacial overpotential and reversibility of plating, resulting in localized deposits and preferential stripping, ultimately promoting cell failure.

Mechanistic interactions in polymer electrolyte fuel cell catalyst layer degradation

N. Goswami, J.B. Grunewald, T.F. Fuller and P. P. Mukherjee

Journal Paper Journal of Materials Chemistry A, 10, 15101 (2022)

Abstract

Polymer Electrolyte Fuel Cells (PEFCs) exhibit considerable performance decay with cycling owing to the degradation of platinum (Pt) catalysts, resulting in the loss of valuable electrochemically active surface area. Catalyst inventory retention is thus a necessity for sustained cathodic oxygen reduction reaction (ORR) and also to ameliorate the life expectancy of the PEFC. We demonstrate a thermo-kinetic model cognizant of processes like platinum particle dissolution-reprecipitation and oxide formation coupled with an electrochemical reactive transport model to derive mechanistic insights of the deleterious phenomena at the interfacial scale. The heterogeneous nature of particle aging in a catalyst layer environment is delineated through coarsening-shrinking zones and further comprehension about instability signatures are developed from the dissolution affinity of diameter bins through a metric, onset time. The severe degradation at high temperature and fully humidified conditions is intertwined with the local transport resistance and the critical transient where the catalyst nanoparticles reach a limiting diameter stage. We further reveal the degradation-performance characteristics through variation in the ionomer volume fraction and the mean size of the particle distribution in the electrode. It has been found that the kinetic and transport characteristics are crucially dependent on the interplay of two modes – one leading to the depletion of the catalyst nanoparticles and the other that emanates from catalyst coarsening.

State-of-electrode (SOE) analytics of lithium-ion cells under overdischarge extremes

H. Zhou, C. Fear, J.A. Jeevarajan and P. P. Mukherjee

Journal Paper Energy Storage Materials, 54, 60 (2022)

Abstract

Overdischarge is an electrical abuse that may arise in a Li-ion battery module when a voltage imbalance occurs between series-connected cells. Although a wide range of studies has investigated overdischarge-induced aging at the full cell scale, the role of each electrode in degradation mechanisms and impacts of C-rates still require fundamental understanding. While most previous studies focus on copper dissolution, the inter-electrode crosstalk which occurs under an overdischarge scenario remains an open question. To fill these gaps, we deconvolute anode and cathode characteristics from the full cell performance during overdischarge abuses by fabricating Li-ion cells with a reference electrode configuration. Electrode potentials vs. Li/Li+ are measured and interpreted for increasingly severe overdischarge cycles under various C-rates. Deterioration of state of health is tracked by monitoring cell surface temperature, internal resistance, volumetric expansion, capacity retention, and impedance evolution. Surface microscopic characterizations are implemented to explore morphological changes and chemical state variations of electrodeposition with particle deformation. This study reveals the dual effect of the C-rate on explicit anode-centric failure mechanisms and implicit cathode-centric degradation pathways, providing new insights on overdischarge abuse fundamentals and effective mitigation strategies.

Underpinnings of Multiscale Interactions and Heterogeneities in Li-Ion Batteries: Electrode Microstructure to Cell Format

M. Parmananda, B.S. Vishnugopi, H. Garg and P. P. Mukherjee

Journal Paper Energy Technology, 2200691 (2022)

Abstract

Lithium-ion batteries exhibit a coupled set of electrochemical, thermal, and mechanical interactions ranging over different length scales. Microstructure-scale electrode characteristics govern the intrinsic and kinetic processes and lead to distinct signatures in electrochemical performance and degradation (e.g., lithium plating). Accurate prediction of cell response relies on advanced physics-based models that can analyze the spatial heterogeneity in pore-scale and electrode-scale features. Herein, a hierarchical modeling framework that captures the mechanistic interactions stemming from electrode microstructure and systematically connects this to the lithium-ion pouch cell performance/degradation response is developed. In conjunction with the microstructural arrangement, the roles of cell format on spatiotemporal heterogeneity in intercalation/plating dynamics, internal heat generation, and mechanical stresses across the pouch cell that are important aspects for fast charging are analyzed. Based on the cell design and operating conditions, unique attributes with respect to the location of plating onset, presence of thermal/mechanical hotspots, and the manifestation of temperature gradients across the pouch cell. are delineated. This study provides a mechanistic understanding of the multiscale interactions and heterogeneity underlying the electrochemical–thermal–mechanical response of lithium-ion batteries, critical for operational extremes such as fast charging.

The Role of Separator Thermal Stability in Safety Characteristics of Lithium-ion Batteries

H. Zhou, C. Fear, M. Parekh, F. Gray, J. Fleetwood, T. Adams, V. Tomar, V. G. Pol and P. P. Mukherjee

Journal Paper Journal of The Electrochemical Society, 169, 090521 (2022)

Abstract

The thermal instability of polymer separators severely threatens the safety characteristics of lithium-ion (Li-ion) batteries. Separators will melt, shrink, vaporize, and collapse under high temperatures, leading to internal short circuits and thermal runaway catastrophes of the cell. Therefore, the amelioration of battery safety challenges benefits from a fundamental understanding of separator behaviors under thermally abusive scenarios. This work investigates the role of separator thermal stability in modulating Li-ion cell safety performance. Three types of separators made of commercially available cellulose, trilayer polypropylene/polyethylene/polypropylene, standard polypropylene, and an in-house modified graphene-polydopamine coated separator are fabricated in custom single layer pouch cells and subjected to accelerating rate calorimeter (ARC) tests to investigate dynamic thermo-electrochemical interactions. The safety hazards of 18650 cylindrical cells assembled with different types of separators are predicted using a verified ARC computational model to compare the effects of separator heat resistance on cell-level thermal runaway risks. This study reveals the thermally robust mechanisms of diverse separator microstructures, indicating how the in-house modified graphene-polydopamine coated separator significantly enhances the safety limits of Li-ion batteries.

Mesoscale Machine Learning Analytics for Electrode Property Estimation

V. Kabra, B. Birn, I. Kamboj, V. Augustyn, and P. P. Mukherjee

Journal Paper Journal of Physical Chemistry C (2022)

Abstract

The development of next-generation batteries with high areal and volumetric energy density requires the use of high active material mass loading electrodes. This typically reduces the power density, but the push for rapid charging has propelled innovation in microstructure design for improved transport and electrochemical conversion efficiency. This requires accurate effective electrode property estimation, such as tortuosity, electronic conductivity, and interfacial area. Obtaining this information solely from experiments and 3D mesoscale simulations is time-consuming while empirical relations are limited to simplified microstructure geometry. In this work, we propose an alternate route for rapid characterization of electrode microstructural effective properties using machine learning (ML). Using the Li-ion battery graphite anode electrode as an exemplar system, we generate a comprehensive dataset of ~17000 electrode microstructures. These consist of various shapes, sizes, orientations, and chemical compositions, and characterize their effective properties using 3D mesoscale simulations. A low dimensional representation of each microstructure is achieved by calculating a set of comprehensive physical descriptors and eliminating redundant features. The mesoscale ML analytics based on porous electrode microstructural characteristics achieves prediction accuracy of more than 90% for effective property estimation.

Asphericity Can Cause Nonuniform Lithium Intercalation in Battery Active Particles

A. Mistry, T. Heenan, K. Smith, P. Shearing and P. P. Mukherjee

Journal Paper ACS Energy Letters, 7, 1871 (2022)

Abstract

Uniform intercalation is desired to enable next-generation Li-ion batteries. While we expect nonuniformity in materials undergoing a phase change, single-phase intercalation materials such as nickel manganese cobalt oxide are believed to lithiate uniformly at the particle/electrolyte interface. However, recent imaging reveals nonuniform lithiation. Motivated by this discrepancy, we examine if aspherical particle shape can cause such nonuniformity since the conventional belief is based on spherical particle theory. We obtain real particle geometries using rapid lab-based X-ray computed tomography and subsequently perform physics-based calculations accounting for electrochemical reactions at the particle/electrolyte interface and lithium transport inside the particle bulk. The aspherical geometry breaks the symmetry and causes nonuniform reaction distribution. Such nonuniformity is exacerbated as the particle becomes more aspherical. The proposed mechanism represents a fundamental limit on achievable lithiation uniformity in aspherical particles in the absence of other mechanisms causing inhomogeneity, such as grain structure, nonuniform carbon-binder coating, etc.

Multiscale Electrochemomechanics Interaction and Degradation Analytics of Sn Electrodes for Sodium-Ion Batteries

S. Sarkar, H.J. Gonzalez-Malabet, M. Flannagin, A. L'Antigua, P.D. Shevchenko, G.J. Nelson and P. P. Mukherjee

Journal Paper ACS Applied Materials & Interfaces, 14, 29711 (2022)

Abstract

Sodium-ion batteries have emerged as a strong contender among the beyond lithium-ion chemistries due to elemental abundance and the low cost of sodium. Tin (Sn) is a promising alloying electrode with high capacity, redox reversibility, and earth abundance. Tin electrodes, however, undergo a series of intermediate reactions exhibiting multiple voltage plateaus upon sodiation/desodiation. Phase transformations related to incomplete sodiation in tin during cycling, in the presence of a frail solid electrolyte interphase layer, can quickly weaken the structural stability. The structural dynamics and reactivity of the electrode/electrolyte interface, being further dependent on the size and morphology of the active material particle in the presence of different electrolytes, dictate the electrode degradation and survivability during cycling. In this study, we paint a comprehensive picture of the underpinnings of the electrochemical and mechanics coupling and electrode/electrolyte interfacial interactions in alloying Sn electrodes. We elicit the fundamental role of electrode/electrolyte complexations in the Sn electrode structure–property–performance relationship based on multimodal analytics, including electrochemical, microscopy, and tomography analyses.

Probing the Role of Multi-scale Heterogeneity in Graphite Electrodes for Extreme Fast Charging

M. Parmananda, C. Norris, S.A Roberts, and P. P. Mukherjee

Journal Paper ACS Applied Materials & Interfaces, 14, 18335 (2022)

Abstract

Electrode-scale heterogeneity can combine with complex electrochemical interactions to impede lithium-ion battery performance, particularly during fast charging. This study investigates the influence of electrode heterogeneity at different scales on the lithium-ion battery electrochemical performance under operational extremes. We employ image-based mesoscale simulation in conjunction with a three-dimensional electrochemical model to predict performance variability in 14 graphite electrode X-ray computed tomography data sets. Our analysis reveals that the tortuous anisotropy stemming from the variable particle morphology has a dominating influence on the overall cell performance. Cells with platelet morphology achieve lower capacity, higher heat generation rates, and severe plating under extreme fast charge conditions. On the contrary, the heterogeneity due to the active material clustering alone has minimal impact. Our work suggests that manufacturing electrodes with more homogeneous and isotropic particle morphology will improve electrochemical performance and improve safety, enabling electromobility.

Probing the Influence of Multiscale Heterogeneity on Effective Properties of Graphite Electrodes

C. Norris, M. Parmananda, S.A Roberts, and P. P. Mukherjee

Journal Paper ACS Applied Materials & Interfaces, 14, 943 (2022)

Abstract

Graphite electrodes in the lithium-ion battery exhibit various particle shapes, including spherical and platelet morphologies, which influence structural and electrochemical characteristics. It is well established that porous structures exhibit spatial heterogeneity, and the particle morphology can influence transport properties. The impact of the particle morphology on the heterogeneity and anisotropy of geometric and transport properties has not been previously studied. This study characterizes the spatial heterogeneities of 18 graphite electrodes at multiple length scales by calculating and comparing the structural anisotropy, geometric quantities, and transport properties (pore-scale tortuosity and electrical conductivity). We found that the particle morphology and structural anisotropy play an integral role in determining the spatial heterogeneity of directional tortuosity and its dependency on pore-scale heterogeneity. Our analysis reveals that the magnitude of in-plane and through-plane tortuosity difference influences the multiscale heterogeneity in graphite electrodes.

Chemomechanical Interactions Dictate Lithium Surface Diffusion Kinetics in the Solid Electrolyte Interphase

F. Hao, B.S. Vishnugopi, H. Wang and P. P. Mukherjee

Journal Paper Langmuir, 38, 5472 (2022)

Abstract

The solid electrolyte interphase (SEI) plays a pivotal role in enabling fast ionic transport and preserving the battery electrodes from parasitic reactions with solvents. However, due to large volume changes of lithium (Li) electrodes, the SEI layer can potentially undergo mechanical failure, resulting in electrolyte degradation. The mechanical stability of the SEI is a critical aspect that needs to be modulated for designing rechargeable metal batteries with optimal performance. In this work, we perform density functional theory calculations to investigate the mechanical properties of lithium fluoride (LiF) and lithium oxide (Li2O) nanofilms and quantify the Li surface diffusion kinetics over these two SEI materials. Based on our analysis, it is identified that Young’s modulus and the ideal strength of the SEI are strong functions of the nanofilm thickness and crystallographic direction. Interestingly, we find that mechanical strain substantially alters the Li surface diffusion behavior on the SEI. For a strain of 4%, while the Li surface diffusion rate decreases by two orders of magnitude on the stretched Li2O film, it increases two times on the stretched LiF film, indicating critical implications on the morphological stability of the metal anode. A fundamental correlation between inherent SEI properties and Li plating behavior is revealed, suggesting a potential pathway to achieve dendrite-free electrodeposition via SEI modulation.

“Dead” lithium or back from the “dead”? [Commentary]

B.S. Vishnugopi, P. P. Mukherjee

Journal Paper Joule, 6, 291 (2022)

Abstract

The formation and accumulation of “dead” lithium is a major cause of performance decay in lithium metal batteries (LMBs). Writing in Nature, Liu et al. demonstrate how dead lithium can be revived based on its response to the electric field during battery operation.

Celebrating Women in Electrochemical Sciences and Engineering (WIESE) [Energy Focus]

S. Sarkar, D. Chatterjee, N. Goswami and P. P. Mukherjee

Journal Paper ACS Energy Letters, 7, 2105 (2022)

Advancements in extreme fast charging to foster sustainable electrification [Commentary]

X.G. Yang, B.S. Vishnugopi, P. P. Mukherjee, W. Wang, F. Sun and C.Y. Wang

Journal Paper One Earth, 5, 216 (2022)

Abstract

The transition toward electrified mobility is rapidly accelerating, but sustainability challenges associated with batteries, including costs, raw materials, and manufacturing-related emissions, pose barriers. Here, we discuss the role of extreme fast charging in breaking down these barriers and offering a pathway toward a more sustainable battery-powered electric-vehicle market.

Mechanistic Underpinnings of Morphology Transition in Electrodeposition under the Application of Pulsatile Potential

T. Dhara, U.U. Ghosh, A. Ghosh, B.S. Vishnugopi, P. P. Mukherjee and S. DasGupta

Journal Paper Langmuir, 38, 4879 (2022)

Abstract

We quantitatively investigate the role of voltage fluctuation in terms of different waveforms on the electrodeposition dynamics and morphology for varying electrolyte concentrations. Dependent on the electrolyte concentration, a wide range of morphologies ranging from highly branched dendrites to comparatively closed packed electrodeposits has been captured. We mechanistically map the deposition dynamics by image analysis and demonstrate the highly porous dendritic dynamics to be independent of external perturbation. Additionally, comparatively closed packed morphological features show significant sensitivity toward the frequency and nature of the waveforms. The results provide fundamental insights into the correlation between the time scales of voltage fluctuation and growth dynamics. We comprehensively analyze the effect of the waveform nature on the average deposition height and show sinusoidal fluctuation to be preferred over square and pulse for metal batteries for lower deposition heights.

MATBOX: An Open-source Microstructure Analysis Toolbox for microstructure generation, segmentation, characterization, visualization, correlation, and meshing

F.L.E. Usseglio-Viretta, P. Patel, E. Bernhardt, A. Mistry, P. P. Mukherjee, J. Allen, S.J. Cooper, J. Laurencin, K. Smith

Journal Paper SoftwareX, 17, 100915 (2022)

Abstract

MATBOX is an easy-to-use, all-in-one, MATLAB application for microstructure numerical analysis, including microstructure numerical generation, image filtering and microstructure segmentation, microstructure characterization, three-dimensional visualization, microstructure parameters correlation, and microstructure meshing. MATBOX was originally developed to analyse electrode microstructures for lithium-ion batteries; however, the algorithms provided by the toolbox are widely applicable to other heterogeneous materials. The toolbox provides a user-friendly experience thanks to a Graphic-User Interface.

Challenges and Opportunities for Fast Charging of Solid-State Lithium Metal Batteries [Journal Cover]

B.S. Vishnugopi, E. Kazyak, J.A. Lewis, J. Nanda, M.T. McDowell, N.P. Dasgupta and P. P. Mukherjee

Journal Paper ACS Energy Letters, 6, 3734 (2021)

Abstract

In this Perspective, we assess the promise and challenges for solid-state batteries (SSBs) to operate under fast-charge conditions (e.g., <10 min charge). We present the limitations of state-of-the-art lithium-ion batteries (LIBs) and liquid-based lithium metal batteries in context, and highlight the distinct advantages offered by SSBs with respect to rate performance, thermal safety, and cell architecture. Despite the promising fast-charge attributes of SSBs, we must overcome fundamental challenges pertaining to electro-chemo-mechanics interaction, interface evolution, and transport-kinetics dichotomy to realize their implementation. We describe the mechanistic implications of critical features including plating-stripping crosstalk, metallic filament growth, cathode microstructure, and interphase formation on the fast-charge performance of SSBs. Toward achieving the eventual goal of fast-charge in SSBs, we highlight both intrinsic (e.g., interface design, transport properties) and extrinsic (e.g., temperature, pressure) design factors that can favorably modulate the mechanistic coupling and cross-correlations. Finally, a list of key research questions is identified that need to be answered to gain a deeper understanding of the fast-charge capabilities and requirements of SSBs.

Effect of Electrode Crosstalk on Heat Release in Lithium-ion Batteries under Thermal Abuse Scenarios

H. Zhou, M. Parmananda, K.R. Crompton, M.P. Hladky, M.A. Dann, J.K. Ostanek and P. P. Mukherjee

Journal Paper Energy Storage Materials, 44, 326 (2021)

Abstract

Predicting thermal safety events of lithium-ion (Li-ion) batteries is significant in optimizing electrochemical systems with high thermal tolerance. The safety performances of Li-ion batteries are dictated by the thermal stability of their component materials both individually and collectively due to intricate exothermic reactions. Although the heat release of individual battery material has been thoroughly investigated, the safety hazards of inter-electrode chemical crosstalk under thermal abuse scenarios remain elusive and thus need a fundamental understanding. This study carries out a comprehensive thermal analysis of various material samples harvested from a commercial Li-ion cell using differential scanning calorimetry (DSC), complemented with full-cell accelerating rate calorimetry (ARC) and computational modeling. Reaction kinetics of electrolyte, wet cathode, wet anode and DSC-full cell samples imitating cell layered architectures are delineated to reveal substantial thermal interactions between electrodes. High-resolution kinetic parameters of reaction mechanisms are estimated using a synergy of Kissinger's method and mechanism-driven non-linear optimization strategies. A thermal abuse model is built based on the extracted kinetic parameters to simulate the cell-level thermal runaway phenomenon and compared with experimental observations, indicating how interlayer crosstalk effects significantly impact the thermal safety characteristics of Li-ion cell chemistries.

Synergistic Voltage and Electrolyte Mediation Improves Sodiation Kinetics in µ-Sn Alloy-anodes

S. Sarkar and P. P. Mukherjee

Journal Paper Energy Storage Materials, 43, 305 (2021)

Abstract

Alloying electrodes, such as tin (Sn), are promising candidates for sodium-ion batteries because of their high specific capacity, electronic conductivity, and low sodium insertion voltage. However, sizeable volumetric change and electrode-electrolyte interface evolution in Sn preclude prolonged performance. The electrochemical potential window, compounded by the choice of electrolyte and additive combination, plays a critical role in the interface instability which yet remains unresolved. This study, based on a comprehensive set of electrochemical, microscopy and spectroscopic analyses, sheds light into the interface instability and reveals that the use of fluoroethylene carbonate additives in carbonate-based electrolytes can dramatically improve the interface stability of such alloying anodes. Electrochemical and morphological analyses show that without the additive, a higher end-of-charge voltage can cause breakdown and reformation of an unstable passivating layer, leading to rapid electrochemical performance decay. A novel three-electrode-based analytics reveals that superior interphase stability with higher microstructural integrity of the Sn electrode can alleviate the detriments from the upper cut-off voltage restrictions. Addressing the hitherto unresolved role of the electrochemical potential window, this study comprehensively examines and elucidates the causality of interfacial instability and the underpinnings of electrochemical complexations in sodium-alloying anodes.

Co-Electrodeposition Mechanism in Rechargeable Metal Batteries

B.S. Vishnugopi, F. Hao, A. Verma, L. Marbella, V. Viswanathan and P. P. Mukherjee

Journal Paper ACS Energy Letters, 6, 2190 (2021)

Abstract

Metal anode-based batteries, owing to their high energy densities enable long-range electric vehicles and semi-trucks. Controlling the electrodeposition growth during charging at practical rates remains a challenge. Incorporating an additive cation in the electrolyte offers an approach to address this through co-electrodeposition which can tune the nucleation and the surface diffusion processes at the growth front. This opens up new design possibilities to address the dendrite challenge. In this work, we develop a mesoscale formalism to study the co-electrodeposition mechanism and analyze the underlying electrolyte design, material selection and electrochemical complexations governing the composition and morphological evolution. We delineate stable regimes of nucleation and electrodeposition that can be attained by tailoring the surface diffusion and electrochemical reaction kinetics. We believe that this study provides the basis for future experiments to rationalize trends in metal co-electrodeposition.

Preventing lithium plating under extremes: an untold tale of two electrodes [Hot Paper]

A. Bohinsky, S.P. Rangarajan, Y. Barsukov, and P. P. Mukherjee

Journal Paper Journal of Materials Chemistry A, 9, 17249 (2021)

Abstract

Fast charging of lithium-ion cells is key to alleviate range anxiety and improve the commercial viability of electric vehicles, which is, however, limited by the propensity of lithium plating. The plated lithium can grow dendritically and may cause internal short and increase the risk of thermal runaway. In this study, a novel anode potential control strategy using a battery management system (BMS) has been demonstrated to enable fast charging in commercial pouch cells without lithium plating. Operando anode potential measurement using a 3-electrode configuration allows monitoring the occurrence of lithium plating. A novel 3-electrode cell analytics was developed to delineate the irreversible and irretrievable contributions to the total capacity loss and identify electrode-specific degradation mechanisms. The BMS algorithm dictates the charging current to maintain a positive anode potential and prevents lithium plating on the anode but fails to sufficiently control the cathode operating potential leading to irretrievable capacity loss. Operating the cell in conditions favorable to the anode may contrarily lead to cathode degradation and subsequent cell failure. Morphological and electrochemical characterizations reveal minimal anode degradation and a 2x higher cathode-capacity loss in the BMS-controlled cells. The baseline cell, not enabled with the BMS anode potential control strategy, exhibits extensive lithium deposition in the anode resulting in 7x higher anode-capacity loss. This study discovers the role of cathode-induced cell failure even when the anode-centric lithium plating is prevented and suggests pathways toward future BMS algorithm development enabling Li-ion cell operation under extremes.

3ε–A Versatile Operando Analytics Toolbox in Energy Storage

S.P. Rangarajan, S. Sarkar, Y. Barsukov, and P. P. Mukherjee

Journal Paper ACS Omega, 6, 33284 (2021)

Abstract

The performance and safety of lithium-ion batteries are plagued by several diverse, nonlinear aging mechanisms influenced by the electrochemical thermal interactions at the electrodes, usage history, and operating conditions. Understanding and deconvoluting the fundamental reaction mechanisms responsible for electrode degradation are key for developing technologies in Li-ion battery diagnostics and prognostics. Hence, there exists a need for high-precision operando techniques to investigate and characterize distinct electrode degradation modes over a gamut of operational variability. Cells embedded with a stable, nonpolarizable reference electrode offer an in situ and operando tool to decouple the complex electrochemical interplay between the electrode pair by measuring individual electrode responses simultaneously with the cell response in the time and frequency domains. This perspective comprehensively looks at 3-electrode (3ε) analytics as a versatile toolbox, highlighting recent techniques and parameters developed with an emphasis on degradation diagnostics and control strategies that is expected to drive the futuristic design of battery management systems.

Mechanistic Insight into Lithium Electrodeposition in Porous Host Architectures

F. Hao, B.S. Vishnugopi, A. Verma, and P. P. Mukherjee

Journal Paper Journal of Physical Chemistry C, 125, 25369 (2021)

Abstract

Large volumetric changes and dendrite growth are major challenges to achieving enhanced cycling efficiency and safety in lithium (Li) metal batteries. Porous hosts for Li storage can potentially accommodate large volumetric changes and enable stable deposition morphologies. In this study, we mechanistically explore the Li electrodeposition process in porous host architectures that contain well-aligned channels. It is identified that the channel architecture helps regulate Li-ion flux and stabilize Li electrodeposition when the channel size is comparable to the characteristic size of the dendrites. Dendrite growth due to local inhomogeneity in ion flux/reaction kinetics can be alleviated through the confinement effect of vertically aligned channel walls. The critical effect of host architectural features, such as channel patterns, pore size, and connectivity, on the local morphological stability have been quantified. For high-rate applications, vertically aligned channel design with minimal interchannel connectivity is found to be an effective strategy for dendrite suppression when compared to horizontally aligned channels. This study provides fundamental insight into Li morphological growth within porous host architectures, identifying design guidelines to address the interfacial instability challenges in Li metal batteries.

Quantifying Sodiation Kinetics in Alloying Tin Electrodes for Sodium-Ion Batteries

S. Sarkar, A. Verma and P. P. Mukherjee

Journal Paper Journal of The Electrochemical Society, 168, 090550 (2021)

Abstract

Sodium-ion batteries (SIBs) are promising next-generation energy storage devices because of the elemental abundance and low sodium cost. However, the lower storage capacity and short lifespan of SIBs necessitate the need for a fundamental understanding of the sodiation/de-sodiation kinetics complexation due to the inherent electrode materials and electrolyte interactions. This study comprehensively studied the kinetics of the sodium alloying and de-alloying mechanism in tin (Sn) electrodes, a promising anode, relying on GITT-based (galvanostatic intermittent titration technique) analytics. This study includes a limited combinatorial analysis of sodium salts, namely, NaPF6 and NaClO4, in conjunction with different carbonate solvents. This comprehensive analysis elicits a comparative paradigm of diffusivity, charge transfer resistance, intercalation rate constant, and exchange current density for the salt/solvent combinations. Overall, NaClO4 exhibits better kinetic and transport properties as compared to NaPF6. This study further elucidates the variation of ionic mobility and reaction rate with interfacial passivation due to excess fluorine donation from additives. The effect of active particle size reveals that nanoparticles exhibit reduced electrochemical (charge/discharge) hysteresis than microparticles. Overall, this study demonstrates a more considerable sensitivity of the charge transfer resistance, exchange current density, and reaction rate constants compared to the diffusivity.

Microstructure and Pressure-Driven Electrodeposition Stability in Solid-State Batteries

A. Verma, H. Kawakami, H. Wada, A. Hirowatari, N. Ikeda, Y. Mizuno, T. Kotaka, K. Aotani, Y. Tabuchi and P. P. Mukherjee

Journal Paper Cell Reports Physical Science, 2, 100301 (2021)

Abstract

Interfacial deposition stability at the Li-metal-solid electrolyte interface in all solid-state batteries is governed by the stress-transport-electrochemistry coupling in conjunction with the polycrystalline/amorphous solid electrolyte architecture. In this work, we delineate the optimal solid electrolyte microstructure comprising grains, grain boundaries, and voids possessing desirable ionic conductivity and elastic modulus for superior transport and strength. An analytical formalism is provided to discern the impact of external “stack” pressure-induced mechanical stress on electrodeposition stability; the stress magnitudes obtained are in the megapascal range, considerably diminishing the stress-kinetics effects. For experimental stack pressures ranging up to 10 MPa, the impact of stress on reaction kinetics is negligibly small, and electrolyte transport overpotentials dictate electrodeposition stability. High current density operation with stable deposition can be ensured with ample external pressure, high temperature, and low surface roughness operation for a low shear modulus ratio of the solid electrolyte to Li-metal.

Quantifying Negative Effects of Carbon-Binder Networks from Electrochemical Performance of Porous Li-Ion Electrodes

A. Mistry, S. Trask, A. Dunlop, G. Jeka, B. Polzin, P. P. Mukherjee and V. Srinivasan

Journal Paper Journal of The Electrochemical Society, 168, 070536 (2021)

Abstract

Porous Li-ion electrodes contain active particles, ion transporting electrolyte, and carbon-binder networks. While macrohomogeneous models are often used to predict electrode behavior, accurate predictions remain challenging, owing to the incomplete understanding of the critical role of carbon-binder networks and how they affect the electrochemical response. The present study systematically characterizes these effects in terms of effective properties by utilizing macrohomogeneous models to analyze the measured responses for electrodes with different carbon-binder content, electrode thickness, and porosity but with identical materials. We find that the impact of the carbon-binder network is more severe than previously thought. Even for low carbon-binder content (5 %wt. dry electrode), the presence of the network decreases the reaction area and increases the ion transport resistance, negatively impacting electrode performance. These effects scale with not just porosity or active material volume but also with carbon-binder content. The findings underscore the importance of connecting all effective properties to electrode specifications in a full factorial sense to transform the electrode design paradigm.

Effect of crystallite geometries on electrochemical performance of porous intercalation electrodes by multiscale operando investigation

Y. Luo, Y. Bai, A. Mistry, Y. Zhang, D. Zhao, S. Sarkar, J.V. Handy, S. Rezaei, A.C. Chuang, L. Carrillo, K. Wiaderek, M. Pharr, K. Xie, P.P. Mukherjee, B. Xu, S. Banerjee

Journal Paper Nature Materials, 21, 217 (2021)

Abstract

Lithium-ion batteries are yet to realize their full promise because of challenges in the design and construction of electrode architectures that allow for their entire interior volumes to be reversibly accessible for ion storage. Electrodes constructed from the same material and with the same specifications, which differ only in terms of dimensions and geometries of the constituent particles, can show surprising differences in polarization, stress accumulation and capacity fade. Here, using operando synchrotron X-ray diffraction and energy dispersive X-ray diffraction (EDXRD), we probe the mechanistic origins of the remarkable particle geometry-dependent modification of lithiation-induced phase transformations in V2O5 as a model phase-transforming cathode. A pronounced modulation of phase coexistence regimes is observed as a function of particle geometry. Specifically, a metastable phase is stabilized for nanometre-sized spherical V2O5 particles, to circumvent the formation of large misfit strains. Spatially resolved EDXRD measurements demonstrate that particle geometries strongly modify the tortuosity of the porous cathode architecture. Greater ion-transport limitations in electrode architectures comprising micrometre-sized platelets result in considerable lithiation heterogeneities across the thickness of the electrode. These insights establish particle geometry-dependent modification of metastable phase regimes and electrode tortuosity as key design principles for realizing the promise of intercalation cathodes.

Linking void and interphase evolution to electrochemistry in solid-state batteries using operando X-ray tomography

J.A. Lewis, F.J.Q. Cortes, Y. Liu, J.C. Miers, A. Verma, B.S. Vishnugopi, J. Tippens, D. Prakash, T.S. Marchese, S.Y. Han, C. Lee, P.P. Shetty, H.-W. Lee, P. Shevchenko, F. De Carlo, C. Saldana, P.P. Mukherjee, M.T. McDowell

Journal Paper Nature Materials, 20, 503 (2021)

Abstract

Despite progress in solid-state battery engineering, our understanding of the chemo-mechanical phenomena that govern electrochemical behaviour and stability at solid–solid interfaces remains limited compared to at solid–liquid interfaces. Here, we use operando synchrotron X-ray computed microtomography to investigate the evolution of lithium/solid-state electrolyte interfaces during battery cycling, revealing how the complex interplay among void formation, interphase growth and volumetric changes determines cell behaviour. Void formation during lithium stripping is directly visualized in symmetric cells, and the loss of contact that drives current constriction at the interface between lithium and the solid-state electrolyte (Li10SnP2S12) is quantified and found to be the primary cause of cell failure. The interphase is found to be redox-active upon charge, and global volume changes occur owing to partial molar volume mismatches at either electrode. These results provide insight into how chemo-mechanical phenomena can affect cell performance, thus facilitating the development of solid-state batteries.

Quantifying the unknown impact of segmentation uncertainty on image-based simulations

M.C. Krygier, T. LaBonte, C. Martinez, C. Norris, K. Sharma, L.N. Collins, P.P. Mukherjee, S.A. Roberts

Journal Paper Nature Communications, 12, 5414 (2021)

Abstract

Image-based simulation, the use of 3D images to calculate physical quantities, relies on image segmentation for geometry creation. However, this process introduces image segmentation uncertainty because different segmentation tools (both manual and machine-learning-based) will each produce a unique and valid segmentation. First, we demonstrate that these variations propagate into the physics simulations, compromising the resulting physics quantities. Second, we propose a general framework for rapidly quantifying segmentation uncertainty. Through the creation and sampling of segmentation uncertainty probability maps, we systematically and objectively create uncertainty distributions of the physics quantities. We show that physics quantity uncertainty distributions can follow a Normal distribution, but, in more complicated physics simulations, the resulting uncertainty distribution can be surprisingly nontrivial. We establish that bounding segmentation uncertainty can fail in these nontrivial situations. While our work does not eliminate segmentation uncertainty, it improves simulation credibility by making visible the previously unrecognized segmentation uncertainty plaguing image-based simulation.

From material properties to multiscale modeling to improve lithium‑ion energy storage safety

J.C. Hewson, H. Zhou, M. Parmananda, R.C. Shurtz and P.P. Mukherjee

Journal Paper MRS Bulletin, 46, 402 (2021)

Abstract

Energy storage using lithium-ion cells dominates consumer electronics and is rapidly becoming predominant in electric vehicles and grid-scale energy storage, but the high energy densities attained lead to the potential for release of this stored chemical energy. This article introduces some of the paths by which this energy might be unintentionally released, relating cell material properties to the physical processes associated with this potential release. The selected paths focus on the anode–electrolyte and cathode–electrolyte interactions that are of typical concern for current and near-future systems. Relevant material processes include bulk phase transformations, bulk diffusion, surface reactions, transport limitations across insulating passivation layers, and the potential for more complex material structures to enhance safety. We also discuss the development, parameterization, and application of predictive models for this energy release and give examples of the application of these models to gain further insight into the development of safer energy storage systems.

Degradation-Safety Analytics in Lithium-Ion Cells and Modules: Part III. Aging and Safety of Pouch Format Cells

D. Juarez-Robles, S. Azam, J. Jeevarajan and P. P. Mukherjee

Journal Paper Journal of The Electrochemical Society, 168, 110501 (2021)

Abstract

Owing to their versatility in cell formats, lithium-ion cells are widely used in energy storage systems. The pouch format cell architecture allows easy adaptability to a manufacturer's application needs. This study aims to characterize the interplay between cycle life aging and off-nominal conditions. Single pouch cells aged to different capacity fade (CF) levels and modules aged to 20% CF were subjected to overcharge tests. Fresh cells and fresh and aged modules were subjected to external short tests. Under overcharge conditions, fresh cells experienced thermal runaway under 1C overcharge but exhibited only swelling under C/3. Overcharged cells with 10% CF experienced swelling and thermal runaway, while cells with over 15% CF experienced swelling and venting through pouch sidewall rupture. It can be conjectured that cells with over 15% CF did not experience thermal runaway due to the relative loss of active material. Under external short, single cells exhibited slight swelling, charring of the anode tab and crumbling of the cathode. Fresh and aged modules subjected to C/3 overcharge experienced catastrophic thermal runaway. Although aging slightly delays the onset of thermal runaway, the fresh module went into catastrophic thermal runaway under external short, whereas the aged one did not.

Degradation-Safety Analytics in Lithium-Ion Cells and Modules Part II. Overcharge and External Short Circuit Scenarios

D. Juarez-Robles, S. Azam, J. Jeevarajan and P. P. Mukherjee

Journal Paper Journal of The Electrochemical Society, 168, 050535 (2021)

Abstract

Lithium-ion cells can be inadvertently subjected to overcharge or other off-nominal conditions during their use in the field, compromising user safety. Off-nominal tests are typically carried out on fresh cells. The goal of this work is to characterize the interplay between cycle life aging and the off-nominal events. Cylindrical cells aged to 10, 15 and 20% capacity fade (CF) and battery modules aged to 20% CF, both cycled under two operating voltage windows, were subjected to overcharge and external short tests. Additionally, single cells were aged to 20% CF using a drive cycle profile at three temperatures of 10, 25 and 40 oC. Under overcharge conditions, the single fresh cells experience slower activation of the current interrupt device (CID) compared to the aged cells and the cathode displayed severe degradation in spite of the CID activation and the anode exhibited lithium plating on the edges of the electrode. At the module level, the fresh module experiences fire while the aged module shows sequential CID activation with no thermal runaway. No major trends were observed with the external short tests of the aged cells compared to the fresh ones due to protection provided by the positive temperature coefficient (PTC).

Directionality of thermal gradients in lithiumion batteries dictates diverging degradation modes

R. Carter, T. A. Kingston, R. W. Atkinson III, M. Parmananda, M. Dubarry, C. Fear, P. P. Mukherjee and C.T. Love

Journal Paper Cell Reports Physical Science, 2, 100351 (2021)

Abstract

Intentionally applied interelectrode thermal gradients (ITGs) accelerate capacity loss in 35°C cells, and the directionality of the thermal gradient dictates the responsible degradation mode. By simulating cell self-heating at various temperatures and C-rates, we identify 35°C and C/5 as a condition that does not typically exhibit lithium (Li) plating under isothermal conditions but is sensitive to thermal gradients. When subjected to an ITG, we observe 77% capacity fade over 20 cycles when the negative electrode (NE) is warmer than the positive electrode (PE) (ΔTint = +2°C) and 100% capacity fade when the PE is warmer than the NE (ΔTint = −2°C). Incremental capacity analysis diagnoses PE degradation for ΔTint = +2°C and NE degradation for ΔTint = −2°C. Electrochemical impedance spectroscopy and postmortem optical investigation corroborate these findings. We identify ITGs as a means to achieve accelerated aging of Li-ion cells with the capability to dictate a limiting electrode and/or decouple degradation of each electrode.

Two-Phase Dynamics and Hysteresis in the PEM Fuel Cell Catalyst Layer with the Lattice-Boltzmann Method

J.B. Grunewald, N. Goswami, P. P. Mukherjee and T.F. Fuller

Journal Paper Journal of the Electrochemical Society, 168, 024521 (2021)

Abstract

In this work, a Lattice-Boltzmann-Method (LBM) model for simulating hysteresis in a proton exchange membrane fuel cell (PEMFC) electrode is presented. One of the main challenges hindering study of the cathode catalyst layer (CCL) in PEMFCs is the lack of understanding of two-phase transport and how it affects electrochemical performance. Previously, the microstructure details needed to build an accurate mesoscale model to examine such phenomena have eluded researchers; however, with advances in tomography and focused-ion-beam scanning-electron-microscopy (FIB-SEM), reconstruction of the complex porous media has become possible. Using LBM with these representations, the difficult problem of catalyst layer capillary hysteresis can be examined. In two-phase capillary hysteresis, both the equilibrium saturation position as well as its absolute value depends on the wetting history. Based on the models, it is ascertained that at lower capillary numbers, the liquid begins to undergo capillary fingering – only above a capillary pressure of 5 MPa, a regime change into stable displacement is observed. As capillary fingering does not lead to uniform removal of liquid, the prediction is that because high capillary pressures are needed to change to the regime of stable displacement, wicking is not as effective as the primary means of water removal.

Optical Microscopy Reveals the Ambient Sodium−Sulfur Discharge Mechanism

R. Carter, A. NewRingeisen, Daniel Reed, R. W. Atkinson III, P. P. Mukherjee and C.T. Love

Journal Paper ACS Sustainable Chemistry and Engineering, 9, 92 (2021)

Abstract

With growing demand for energy storage, there is renewed interest in ambient sodium–sulfur batteries, which boast raw material costs below $1/kWh owing to the natural abundance and high theoretical energy density of the pairing. As with lithium, sodium electrochemically reacts with sulfur in ether-based electrolytes, and the intermediate discharge products (polysulfides) dissolve in the battery electrolyte. These polysulfide intermediates have distinct colors, from red-brown to yellow. Additionally, when the solvent permits chemical reordering, the S3•– radical is detected with a blue hue. Radicalization hinders the electrochemical reaction by altering charge balance. Since the reaction intermediates exist with distinct colors, their evolution can be identified during electrochemical discharge with an in-situ optical cell. Optical analysis facilitates detection and characterization of intermediate products across a broader concentration range that is not accessed by more complex in-situ UV–vis spectroscopy. We demonstrate the utility of in-situ optical microscopy for comparing the ambient discharge mechanism in electrolytes from the glyme family. These chain-like solvents, from monoglyme (G1) to tetraglyme (G4), have a greater stabilizing effect on sodium electroplating than for lithium, warranting their investigation at the sulfur cathode. Both the in-situ experiment and stoichiometric solutions reveal that G1 results in the lowest polysulfide solubility and the least sulfur radicalization, while G4 has the greatest. G2 falls between them. Image analysis of the electrolyte between the sulfur working electrode and sodium counter allow for the red, green, and blue image pixilation (RGB) and image brightness to be assessed. With this analysis, we can assign the evolution of particular polysulfides to discharge voltage features.

Molar Volume Mismatch: a Malefactor for Irregular Metallic Electrodeposition with Solid Electrolytes

A. Mistry and P. P. Mukherjee

Journal Paper Journal of The Electrochemical Society, 167, 082510 (2020)

Abstract

Regularizing metallic electrodeposition has been a long-standing challenge in energy storage. Leveraging mechanical stresses, solid ion conductors have been proposed to stabilize the evolving interface. Paradoxically softer electrodepositing metals are often found to form penetration fronts under the hypothesized stable conditions. We find that mechanical contributions to energy of the interacting species (i.e., metal and cation) relate to respective molar volumes. The stresses at the electrodepositing interface are correlated, and consequently, localized deposition is energetically favored for larger cationic molar volumes. Electrolyte stresses cause a stress-driven ionic flux away from compressed locations, which proves to be a stabilizing influence. Stability is found to be nonlinearly related to electrolyte stiffness. Material complexities such as interphases, interlayer, and grain boundaries are also examined to proffer guidelines for a stabilized growth.

Corrosion-induced Microstructural Variability Affects Transport-Kinetics Interaction in PEM Fuel Cell Catalyst Layers

N. Goswami, A. Mistry, J.B. Grunewald, T.F. Fuller and P. P. Mukherjee

Journal Paper Journal of The Electrochemical Society, 167, 084519 (2020)

Abstract

The ionomer, which is responsible for proton transport, oxygen accessibility to reaction sites, and binding the carbon support particles, plays a central role in dictating the catalyst layer performance. In this work, we study the effect of ionomer distribution owing to the corrosion induced degradation mode in the catalyst layer based on a combined mesoscale modeling and experimental image-based data. It is observed that the coverage of the ionomer over the platinum-carbon interface is heterogeneous at the pore-scale which in turn can critically affect the electrode-scale performance. Further, an investigation of the response of the pristine as well as degraded microstructures that have been exposed to carbon support corrosion has been demonstrated to highlight the kinetic-transport underpinnings on the catalyst layer performance decay.

Mechanistic Analysis of Microstructural Attributes to Lithium Plating in Fast Charging

V. Kabra, M. Parmananda, C. Fear, F.L.E Usseglio-Viretta, A. Colclasure, K. Smith and P. P. Mukherjee

Journal Paper ACS Applied Materials & Interfaces, 12, 55795 (2020)

Abstract

Metallic lithium deposition on graphite anodes is a critical degradation mode in lithium-ion batteries, which limits safety and fast charge capability. A conclusive strategy to mitigate lithium deposition under fast charging yet remains elusive. In this work, we examine the role of electrode microstructure in mitigating lithium plating behavior under various operating conditions, including fast charging. The multi-length scale characteristics of the electrode microstructure lead to a complex interaction of transport and kinetic limitations that significantly governs the cell performance and the occurrence of Li plating. We demonstrate, based on a comprehensive mesoscale analysis, that the performance and degradation can be significantly modulated via systematic design improvements at the hierarchy of length scales. It is found that the improvement in kinetic and transport characteristics achievable at disparate scales can dramatically affect Li plating propensity.

Mechanistic Underpinnings of Thermal Gradient Induced Inhomogeneity in Lithium Plating

C. Fear, M. Parmananda, V. Kabra, R. Carter, C.T. Love and P. P. Mukherjee

Journal Paper Energy Storage Materials, 35, 500 (2020)

Abstract

In the pursuit to enable the rapid charging of lithium-ion batteries, lithium plating at the anode poses one of the most significant challenges. Additionally, the heat generation that accompanies high rate battery operation in conjunction with non-uniform cooling and localized heating at tabs is known to result in thermal inhomogeneity. Such thermal anomalies in the absence of proper thermal management can instigate accelerated degradation in the cell. In this work, a physics-based interrogation of the link between thermal gradient induced inhomogeneity and lithium plating during charging is presented. The relative importance of in-plane vs. through-plane (inter-electrode) thermal gradients to charging performance and cell degradation is necessary to intelligently design packaging and cooling systems for large-format cells. While in-plane thermal gradients strongly influence active material utilization, the lithium plating severity was found to be very similar to an isothermal case at the same mean temperature. By contrast, interelectrode thermal gradients cause a shifting on the solid phase potential at each electrode during charging, related to the increase or decrease in overpotential due to local temperature variation. When the cathode temperature exceeds the anode temperature, lithium plating is exacerbated, and accelerated degradation occurs.

Degradation - Safety Analytics in Lithium-ion Cells: Part I. Aging under Charge/Discharge Cycling

D. Juarez-Robles, J. Jeevarajan and P. P. Mukherjee

Journal Paper Journal of The Electrochemical Society, 167, 160510 (2020)

Abstract

Disparate degradation modes in lithium-ion cell components due to aging under continuous cycling cause capacity fade and safety concerns under abuse conditions. In this work, the interplay between aging and abuse conditions, namely overcharge and external short, is investigated in fresh and aged cylindrical lithium-ion cells for different degradation conditions and operating windows. The objective, to elicit insights into the potential hazards in an aged cell, is accomplished via a comprehensive and controlled experimental analytics of the electrochemical, thermal and morphological behavior of the cell components. The Part I of the study sets the baseline for the aging induced degradation. According to the results of the aging study, cycle life can be doubled by reducing 200 mV at either ends of the voltage window at the expense of having a 20% reduction in capacity utilization. Differential voltage and temperature analyses revealed a state-of-charge dependence of the internal resistance and heat generation rate. Post-mortem analyses showed that the loss of cyclable lithium inventory due to the solid electrolyte interphase (SEI) formation; and electrochemical deactivation of the cathode owing to delamination and particle cracking, are the primary degradation mechanisms responsible for the cell capacity fade due to aging under continuous cycling.

Energetics Dictates Deposition at Metal/Solid Electrolyte Interfaces

D. Tewari and P. P. Mukherjee

Journal Paper Journal of Physical Chemistry C, 125, 2221 (2020)

Abstract

Solid electrolytes are promising toward utilizing lithium metal anodes with high specific capacity and low redox potential. The solid electrolytes are expected to provide mechanical barrier, thereby dwarfing lithium metal dendrite growth. However, dendrite penetration though solid electrolytes have been reported. In this work, we present a comprehensive description of the role of interface energetics in determining the deposition morphology at the metal/solid electrolyte buried interfaces. If the interaction between the solid electrolyte and metal surfaces at the interface is weak, the morphology of the metal surface is rough after deposition. Conversely, for strongly interacting interface, flat interface is obtained. The energy of the total system is limited to a small region near the interface, and the bulk of the metal away from the interface is free of distortion and has negligible energy. The strength of the energetic interaction at the metal and solid electrolyte interface primarily determines the deposition morphology.

Morphology-Safety Implications of Interfacial Evolution in Lithium Metal Anodes

B.S. Vishnugopi, A. Verma, and P. P. Mukherjee

Journal Paper Journal of Physical Chemistry C, 124, 16784 (2020)

Abstract

Dendrite formation and growth upon cycling pose major concerns toward lithium metal battery performance and safety. Herein, we present an interface-capturing formalism to study the morphological evolution of lithium metal anodes at time scales comparable to typical charging durations. This mesoscale study distinctly captures mossy/fractal growth patterns that manifest depending on the electrochemical environment of the lithium metal battery system and observed in in situ experimental electrodeposition studies. We further develop a safety map (pertaining to short-circuit via direct dendrite propagation) in terms of charged capacity and the limiting current density of the system. Examination of the safety map, in conjunction with the delineated morphological features (growth speed and interfacial area, in particular), allows deriving insights into probable cell failure modes. We deduce that the electrolyte starvation and solid electrolyte interphase reformation are more likely causes for cell failure, that are instigated at higher applied current densities than direct dendrite penetration itself.

In Operando Detection of the Onset and Mapping of Lithium Plating Regimes during Fast Charging of Lithium-ion Batteries

C. Fear, T. Adhikary, R. Carter, A. Mistry, C.T. Love and P. P. Mukherjee

Journal Paper ACS Applied Materials & Interfaces, 12, 30438 (2020)

Abstract

Existing in operando methods for detection of plated lithium can only detect the presence of plating after the charge is complete and irreversible damage has already occurred. In this work, the characteristic potential minimum on the graphite electrode during high rate lithiation is proposed and assessed as an in operando technique for detecting the onset of lithium plating. While other studies have shown that rapid self-heating of a cell can cause this type of “voltage overshoot,” we confirm through temperature-controlled coin cell experiments that such a voltage profile can also be caused by the occurrence of severe lithium plating. In cells which demonstrated voltage overshoot, macroscopically observable lithium plating films were present on the graphite electrodes upon disassembly, resulting in very poor single-cycle Coulombic efficiency. The significance of this voltage characteristic is confirmed through direct observation of the onset of lithium plating in an in-situ optical microscopy cell. We observe that the growth of large metallic lithium deposits within the porous electrode structure can cause swelling and cracking of the graphite electrode, suggesting loss of active material due to mechanical electrode degradation as an important consequence of severe lithium plating.

Anode potential controlled charging prevents lithium plating [Hot Paper]

S.P. Rangarajan, Y. Barsukov, and P. P. Mukherjee

Journal Paper Journal of Materials Chemistry A, 8, 13077 (2020)

Abstract

We report a novel anode potential controlled charging strategy for lithium-ion cells which eliminates lithium plating at most aggressive conditions, such as at low temperatures. This is applicable for lithium-ion cells with graphite anode irrespective of the form factor, capacity or cathode chemistry. This new charging strategy exhibits seven-fold increase in cycle life and concomitant improvement in the electrochemical performance. Conventional charging shows copious footprint of lithium plating swiftly followed by cell failure due to accelerated increase in the anode resistance. The anode potential controlled charging strategy, based on a three-electrode cell construction, exhibits minimal increase in the anode resistance and shows no signs of lithium plating in operational extremes. Optical micrographs and high-resolution scanning electron images confirm that the graphite anode in the conventionally charged Li-ion cell undergoes significant loss in porosity resulting in massive underlithiation and dramatic capacity fade. The degradation rate in the anode is decelerated in the anode potential controlled charging by assuring that plating potential is not reached and improving ion transport in the anode even at low temperatures due to the absence of decomposition products that would have formed during plating.

Double-Edged Effect of Temperature on Lithium Dendrites

B.S. Vishnugopi, F. Hao, A. Verma, and P. P. Mukherjee

Journal Paper ACS Applied Materials & Interfaces, 12, 23931 (2020)

Abstract

Lithium metal, although attracting renewed interest for the next revolution in energy storage, continues to be challenged with the detrimental dendrite formation. Recent experimental reports have demonstrated the contrasting impact of thermal attributes on the electrodeposition morphology, showcasing the alleviation and/or aggravation of dendrite formation. Herein, we present a comprehensive discourse to discern the thermally activated physical mechanisms governing lithium electrodeposition morphology. We report that the synergistic effect of enhanced electrolyte transport and surface self-diffusion under a uniform thermal field (~350K) enables adequate dendrite suppression, even at high reaction rates. However, in contrast to this, a localization of the thermal field substantially increases the exchange current density of the confined region, instigating the growth of needle- dendrites. Based on our mesoscale analysis, we demarcate safety limits for such an event, beyond which dendrite growth is inevitably triggered. Therefore, though the operational strategy of elevating the cell temperature promises to resolve the challenge of stable electrodeposition, it comes along with the caveat. This fundamental study provides a detailed insight into underlying electrochemical-thermal complexations, critical to the performance and safety of metal-based rechargeable batteries.

Surface Diffusion Manifestation in Electrodeposition of Metal Anodes [Hot Paper]

B.S. Vishnugopi, F. Hao, A. Verma, and P. P. Mukherjee

Journal Paper Physical Chemistry Chemical Physics, 22, 11286 (2020)

Abstract

Metal anode-based battery systems have been deemed indispensable towards energy storage renaissance engendering extensive research into strategies countering dendritic growth of metal electrodeposition. Fundamentally, the morphological evolution of a material is uniquely characterized by the heights of its self-diffusion barrier across multiple pathways. Herein, we derive insights into the nucleation and growth of metallic electrodeposits in liquid electrolytes, governed by surface self-diffusion characteristics cognizant of the diverse diffusion routes including terrace, away from step and interlayer pathways. We deconvolve the roles played by each of these surface diffusion mechanisms in conjunction with the electrochemical reaction rate on the deposition morphology regime (film vs mossy vs fractal). We identify interlayer diffusion as the predominant morphology-determining mechanism; dendrite-free deposition even at moderate current rates constrains this diffusion barrier to an upper limit. Additionally, we highlight subtle features amidst the realm of the morphological growth assortment that connect to the cell’s electrochemical performance. Finally, we delineate morphological features of Li, Na, Mg and Al based on their respective surface diffusion barriers and applied overpotentials, and provide a baseline for the interpretation of experimental observations. This fundamental study sheds light on the mesoscale underpinnings of morphological variances in mono-valent and multi-valent metal electrodeposition.

Mesoscale Anatomy of Dead Lithium Formation

D. Tewari, S.P. Rangarajan, P. Balbuena, Y. Barsukov, and P. P. Mukherjee

Journal Paper Journal of Physical Chemistry C, 124, 6502 (2020)

Abstract

Lithium metal anodes are an attractive option for next generation batteries because of high gravimetric and volumetric energy density. The formation of dendritic morphology of electrodeposition during charging, however, poses safety concerns, which in particular been a focus of intense research. The formation of “dead lithium” with successive cycling, on the other hand, has been relatively unexplored as the deterioration in performance is gradual. Dead lithium is the fragment of lithium that is detached from the lithium electrode during electrodissolution or stripping. In this study, the mesoscale underpinnings of dead lithium formation via a synergistic computational and experimental approach is presented. The mechanistic focus centers on morphological evolution of the lithium electrode-electrolyte interface and relative quantification of dead lithium formation under a range of operating temperatures and currents. This study reveals that the amount of dead lithium formed during stripping increases with decreasing current and increasing temperature. This finding is in direct contrast to the operating conditions which lead to dendritic deposition during charging, i.e., at higher currents and lower temperatures. During stripping, more dead lithium is formed when the interface has thin narrow structures. The ionic diffusion and self-diffusion of lithium at the interface play a key role toward the evolution of narrow structures at the interface. Therefore, more dead lithium is formed when diffusive processes are facilitated compared to the oxidative reaction at the interface.

Overdischarge and Aging Analytics of Li-ion Cells

D. Juarez-Robles, A. Vyas, C. Fear, J. Jeevarajan and P. P. Mukherjee

Journal Paper Journal of The Electrochemical Society, 167, 090558 (2020)

Abstract

Overdischarge is a potential problem in large battery packs since cells in a series string are discharged under the same load, despite having different capacities. Although a single overdischarge does not necessarily cause a safety hazard, it forces electrodes outside their safe potential range and adversely affects the integrity of cell components. This work aims to fill the knowledge gap about the combined effect of aging-induced and overdischarge–induced degradation mechanisms. Graphite/LCO pouch cells are cycled at a moderate rate using four lower cutoff voltages: 2.7 V, 1.5 V, 0.0 V, and -0.5 V. The cells aged above the onset of reverse potential have an extended cycle life with aging-induced solid electrolyte interphase (SEI) growth and electrolyte decomposition as the main degradation mechanisms. In contrast, the cells aged under reversal condition (Elower≤ 0.0 V) exhibit fast degradation, dictated by the interplay among lithium plating, cathode particle cracking, and dissolution of Cu current collector. The analysis is complemented with a comparative study of various state of health (SoH) indicators, including an internal resistance based dimensionless SoH descriptor. The results prove that overdischarge induced abuse although benign, may turn into a malignant condition when alternated with continuous charging.

Overcharge and Aging Analytics of Li-ion Cells

D. Juarez-Robles, A. Vyas, C. Fear, J. Jeevarajan and P. P. Mukherjee

Journal Paper Journal of The Electrochemical Society, 167, 090547 (2020)

Abstract

Overcharge presents a serious safety concern for large scale applications of Li-ion batteries. Despite the availability of several studies of aging-induced and overcharge-induced degradation, there still exists a knowledge gap of what would happen if both degradation mechanisms simultaneously occur. In this work, commercial graphite/LCO pouch cells (5Ah) are continuously cycled at different upper cutoff voltages, 4.2 through 4.8 V, to elucidate the cumulative effect of the overcharge process on the long-term cycling. As the upper cutoff voltage is extended, the cell gains a higher initial capacity but the cycle life diminishes significantly. Cells overcharged beyond 4.5 V experience significant volume expansion and a high rate of capacity fade, as well as a considerable increase in the temperature and internal resistance. Lithium plating and electrolyte decomposition are observed in cells charged beyond 4.5 V, with SEM-EDS verifying their presence. Electrochemical evidence of both degradation modes appears as a voltage undershoot in the discharge curves. A comparative study of various State of Health (SoH) estimation parameters is presented with the introduction of a new dimensionless SoH indicator, ΦR, based on internal resistance measurement. The proposed degradation number is found to be a good indicator of aggravated degradation in cells.

Fingerprinting Redox Heterogeneity in Electrodes during Extreme Fast Charging

A. Mistry, F.L.E Usseglio-Viretta, A. Colclasure, K. Smith and P. P. Mukherjee

Journal Paper Journal of The Electrochemical Society, 167, 090542 (2020)

Abstract

Conventionally, battery electrodes are rationalized as homogeneous reactors. It proves to be an erroneous interpretation for fast transients, where mass transport limitations amplify underlying heterogeneities. Given the lack of observability of associated fast spatiotemporal dynamics, redox activity in inhomogeneous electrodes is superficially explored. We resort to a physics-based description to examine extreme fast charging of lithium-ion battery electrodes. Representative inhomogeneity information is extracted from electrode tomograms. We discover such electrodes to undergo preferential intercalation, localized lithium plating and nonuniform heat generation as a result of distributed long- and short-range interactions. The spatial correlations of these events with the underlying inhomogeneity are found to be nonidentical. Investigation of multiple inhomogeneity fields reveals an exponential scaling of plating severity and early onset in contrast to the homogeneous limit. Anode and cathode inhomogeneities couple nonlinearly to grow peculiar electrodeposition patterns. These mechanistic insights annotate the complex functioning of spatially nonuniform electrodes in fast charge extremes.

Stochasticity at Scales Leads to Lithium Intercalation Cascade

A. Mistry, K. Smith, and P. P. Mukherjee

Journal Paper ACS Applied Materials & Interfaces, 12, 16359 (2020)

Abstract

Porous intercalation electrodes are synonymous with the promise of lithium-ion batteries toward electromobility. These electrodes exhibit stochastic geometrical features spanning different length-scales. The implication of microstructural inhomogeneity on the lithium intercalation dynamics is hitherto unknown. Starting from 3D, x-ray tomograms of intercalation electrode microstructures, we characterize the microstructural variability in porous intercalation electrodes. Furthermore, a physics-based analysis of electrochemical response reveals that the stochastic features can cause preferential lithiation fronts.

Fast Charging of Lithium-Ion Batteries via Electrode Engineering

B.S. Vishnugopi, A. Verma, and P. P. Mukherjee

Journal Paper Journal of The Electrochemical Society, 167, 09058 (2020)

Abstract

Vehicular electrification necessitates the need for fast charge of lithium-ion batteries (LIBs) involving high current densities such that the charging durations reach equivalence with internal combustion engine vehicles refueling times. High C-rate performance of LIBs requires overcoming challenges associated with Li plating, thermal excursions and battery shutdown at sub-zero temperatures. In this work, we aim to understand/improve fast charge characteristics by delving into the electrode level microstructural impact on battery performance in terms of delivered capacity, temperature rise and plating propensity. A microstructure-aware physics based electrochemical-thermal model is used to ascertain the performance-safety indicators from sub-zero to standard thermal environments. Fast charge is an anode-centric phenomenon; consequently, optimal anode porosities and operating conditions are ascertained. At sub-zero temperatures, high C-rate operation up to a threshold provides good capacities and low plating propensity through large heat generation induced cell temperature elevation to appreciable levels. Beyond the threshold current, self-shutdown of the cell prevents any degradation. Additionally, standard thermal environment operation is majorly limited by rapid temperature rise beyond safe limits and large plating propensities at low porosities.

Mechano-Electrochemical Interaction in Solid-State Lithium Batteries

F. Hao, W. Wang, and P. P. Mukherjee

Journal Paper Journal of The Electrochemical Society, 167, 080513, (2020)

Abstract

A solid-state lithium (Li) battery primarily consists of Li metal anode, solid electrolyte separator, and a porous cathode. The asymmetrical volumetric changes, originating from ion transport and interfacial Li growth during plating, lead to significant stresses in the layered architecture. In this study, we develop a coupled mechanics-electrochemistry formalism for polymer electrolyte based solid-state batteries, in particular, focusing on the stress effect on electrochemical performance. By means of a mechano-electrochemical coupling coefficient, it is found that stress-assisted ion transport in the electrolyte results in a delayed Sand's time and increased critical current density of unstable electrodeposition, and consequently, alleviates the propensity of dendrite formation. Stress at the Li metal-electrolyte interface affects the electrochemical reaction kinetics, and the influences from the deviatoric stress and hydrostatic pressure vary with Li plating time. In addition, a low restraint stiffness to the layered structure could elastically buffer the volumetric changes and thus reduce the stress during Li plating. This fundamental study provides guidance for the design of solid-state batteries, aimed at stable electrodeposition and mechanical integrity.

Electroanalytical Quantification of Electrolyte Transport Resistance in Porous Electrodes

W. Wang, D. Juarez-Robles, and P. P. Mukherjee

Journal Paper Journal of The Electrochemical Society, 167, 080510, (2020)

Abstract

A generalized, noninvasive technique based on electrochemical impedance spectroscopy is proposed to quantify the electrolyte transport resistance of typical electrode microstructures for lithium ion batteries. The electrolyte transport resistance, representative of the pore network resistance, can be obtained via an impedance analytics approach, thus quantifying the tortuosity of porous electrode microstructures. A characteristic coefficient is defined and estimated for more electronically conductive graphite, lithium cobalt oxide (LCO), and nickel-manganese-cobalt oxide (NMC) electrodes, and for less electronically conductive lithium iron phosphate (LFP) and lithium titanate (LTO) electrodes. The fitting of the electrochemical impedance spectra by the general transmission line model yields unambiguous values by adding an independent determination of the electronic resistance. Such an independent determination of the electronic resistance can be easily done by sandwiching the composite electrode between two ion-blocking electrodes. This would be essential to verify the approach for electrodes with low electronic conductivity, such as LFP and LTO. This method is capable of adequately capturing the influence of particle size and morphology on the pore-scale tortuosity of electrode microstructures.

Mechanistics of Lithium Metal Battery Performance by Separator Architecture Design

W. Wang, F. Hao, and P. P. Mukherjee

Journal Paper ACS Applied Materials & Interfaces, 12, 556 (2020)

Abstract

Lithium (Li) metal anode has attracted renewed research interests due to its high specific capacity and the lowest negative potential. However, Li metal batteries have safety issues and severe capacity fading. In this study, we demonstrate a facile and effective technique by adding an anodic aluminum oxide nano-structured interlayer (AO) onto the commercial polypropylene separator (PP) to create a novel architecture (AP). It is found that AP based symmetric Li-Li cells and Li-NCM523 cells exhibit enhanced cycling performance and delayed capacity decay. Furthermore, compared with the cells with PP, the cells with AP show reduced overpotentials and improved cycle stability at low temperatures and various current densities, implying the wide applications of the designed architecture. The superior performance of AP is ascribed to its high electrolyte retention, high mechanical strength, and precisely ordered architecture, which contribute to uniform Li nucleation and growth. This unique separator architecture provides mechanistic insights into the design of rechargeable lithium metal batteries, which are aimed at high energy density and cycling stability.

Challenges in Lithium Metal Anodes for Solid-State Batteries

K.B. Hatzell, X.C. Chen, C.L. Cobb, N.P. Dasgupta, M.B. Dixit, L.E. Marbella, M.T. McDowell, P.P. Mukherjee, A. Verma et al.

Journal Paper ACS Energy Letters, 5, 922 (2020)

Abstract

The utilization of metallic anodes holds promise for unlocking high gravimetric and volumetric energy densities and is pivotal to the adoption of ‘beyond Li’ battery chemistries. Much of the promise of magnesium batteries stems from claims regarding their invulnerability to dendrite growth. Whilst considerable effort has been invested in the design of novel electrolytes and cathodes, detailed studies of Mg plating are scarce. Using galvanostatic electrodeposition of metallic Mg from Grignard reagents in symmetric Mg-Mg cells, we establish a phase map characterized by disparate morphologies spanning the range from fractal aggregates of 2D nanoplatelets to highly anisotropic dendrites with singular growth fronts and nanowires entangled in the form of mats. The effects of electrolyte concentration, applied current density, and coordinating ligands have been explored. The study demonstrates a complex range of electrodeposited morphologies including canonical dendrites with shear moduli conducive to penetration through typical polymeric separators. We further demonstrate a strategy for mitigating Mg dendrite formation based on the addition of molecular Lewis bases that promote nanowire growth through selective surface coordination.

Mapping Mechanisms and Growth Regimes of Magnesium Electrodeposition at High Current Densities

R. Davidson, A. Verma et al.

Journal Paper Materials Horizons, 7, 843 (2020)

Abstract

Synchrotron Imaging of Pore Formation in Li Metal Solid-State Batteries Aided by Machine Learning

MB. Dixit, A. Verma , W. Zaman, X. Zhong, P. Kenesei, J. S. Park, J. Almer, P. P. Mukherjee, and K. B. Hatzell

Journal Paper ACS Applied Energy Materials (2020)

Abstract

High-rate capable, reversible lithium metal anodes are necessary for next generation energy storage systems. In situ tomography of Li|LLZO|Li cells is carried out to track morphological transformations in Li metal electrodes. Machine learning enables tracking the lithium metal morphology during galvanostatic cycling. Nonuniform lithium electrode kinetics are observed at both electrodes during cycling. Hot spots in lithium metal are correlated with microstructural anisotropy in LLZO. Mesoscale modeling reveals that regions with lower effective properties (transport and mechanical) are nuclei for failure. Advanced visualization combined with electrochemistry represents an important pathway toward resolving non-equilibrium effects that limit rate capabilities of solid-state batteries.

Probing the Thermal Safety of Li Metal Batteries

D. Puthusseri, M. Parmananda, P. P. Mukherjee and V. Pol

Journal Paper Journal of The Electrochemical Society, 167, 120513 (2020)

Abstract

Li metal batteries (LMBs) with high energy density electrodes have emerged as the primary candidate for next-generation batteries owing to its superiority over conventional Li-ion technology. However, the safe operation of these systems under thermal abuse conditions remains a primary concern regardless of tremendous efforts to prevent short circuits through dendrite formation. In this context, we employ differential scanning calorimetry technique to investigate the thermal stability of Li-S and Li-NMC532 metal batteries. The calorimetric measurements identify separator melting together with anode-centric thermal degradation reactions as the primary mechanism of thermal runaway. Separator with poor thermal stability (low melting point), could instigate an internal short circuit that leads to exponential temperature rise due to the rapid release of electrical energy. An in-house physics-based modeling technique utilizes the knowledge of thermal stability at materials level to predict the thermal safety of LMBs for pouch cell configuration. Simulations reveal that the thermal stability of the separator and parasitic reactions at the anode (Li metal) dictate the critical onset temperature of thermal runaway in Li metal batteries. The severity of thermal runaway can be modulated by carefully designing (capacity loading ratio (N/P)) the thickness of metal anode and advanced separator with better thermal stability.

Simulating onset and evolution of thermal runaway in Li-ion cells using a coupled thermal and venting model

J.K. Ostanek, W. Li, P. P. Mukherjee, K.R. Crompton and C. Hacker

Journal Paper Applied Energy, 268, 114972 (2020)

Abstract

A coupled, thermal and gas generation/venting model has been developed for simulating the onset and evolution of thermal runaway in 18650 format Li-ion battery cells. The model simulates heat and gas generation during external heating of an electrically isolated cell that results in thermal runaway. Gas generation within the cell leads to pressure build up until the point at which the vent mechanism opens and relieves the internal pressure. Compressible flow of gases is modeled through the vent cap as a function of pressure ratio across the vent. The energy balance of the battery cell includes: heat generated from decomposition reactions and electrical short, external heat transfer to the surroundings, heat absorbed with vaporization and melting processes, as well as the energy loss as material is vented from the cell. The model was able to capture features of the temperature evolution of the battery cell well and generate detailed information about the progression of thermal runaway. The model was exercised to simulate time-to-venting and time-to-thermal-runaway for various changes in cell design parameters such as: amount of free liquid electrolyte, external convection coefficient, and electrolyte evaporation rate after vent opening.

Decreasing the Ion-Diffusion Pathways for the Intercalation of Multivalent Cations into One-Dimensional TiS2 Nanobelt Arrays

C.G. Hawkins, A. Verma , W. Horbinski, R. Weeks, P. P. Mukherjee, L. Whittaker-Brooks

Journal Paper ACS Applied Materials & Interfaces, 12, 21788 (2020)

Abstract

The sparse selection of available cathode materials that allow for reversible intercalation (de-intercalation) of Al3+ species represents a major hurdle in the development of efficient Al-ion batteries. Herein, we developed cathodes based on TiS2 nanobelts that are capable of withstanding the high charge density of Alion species with minimal host lattice/ion interactions. The fabricated TiS2 nanobelts are highly anisotropic and are directly grown on a carbon current collector yielding a spatially controlled array. The sum of evidence presented in this work indicates that one-dimensional TiS2 nanobelt arrays can reversibly accommodate an unprecedented amount of Al ion species within their layered structure with no significant volume expansion as well as full retention of the nanobelt morphology. Thus, the one-dimensional morphology, nanoscale dimensions, short ion diffusion paths, high electrical conductivity, and absence of additives that hinder ion migration lead to Al-based TiS2 electrochemical devices exhibiting high specific capacity, less capacity fade, and resilience under higher cycling rates at both room temperature and elevated temperatures when compared to TiS2 platelets. We also present the effects of sulfur vacancies on the electrochemical performance of Al-based TiS2-x nanobelt array batteries. Although Al-ion batteries are still in their infancy, we believe our TiS2 nanobelt array cathode insertion hosts may play an important role in addressing the poor kinetics of solid-state Al-ion diffusion to enable efficient alternatives beyond lithium energy storage devices.

In Operando XANES Imaging of High Capacity Intermetallic Anodes for Lithium Ion Batteries

H.J.G. Malabet, D. Juarez-Robles, V. Andrade, P. P. Mukherjee and G.J. Nelson

Journal Paper Journal of The Electrochemical Society, 167, 4, 040523 (2020)

Abstract

In operando 2D X-ray absorption near edge structure (XANES) imaging was performed near the Cu K-edge during cycling of Cu6Sn5 composite anodes for lithium ion batteries. Galvanostatic lithiation and delithiation with intermittent constant voltage holds near reaction plateaus show evolution of absorption spectra for active material particles. XANES spectra obtained from images taken during cycling were compared to standard spectra for Cu, Cu6Sn5, and Li2CuSn. Chemical composition was assessed for Cucontaining phases. Distinct Cu, Cu6Sn5, and Li2CuSn regions were identified for each voltage plateau. Mechanical degradation, electrode particle fracture and expansion were observed during delithiation. Movement of particles during cycling suggests that expansion also impacts the supporting secondary phases and the transport networks therein. These results demonstrate that spectroscopic X-ray imaging methods can clearly distinguish chemically distinct phases in alloy electrodes and have the versatility to observe the evolution of these phases during lithiation and delithiation.

Deconstructing Electrode Pore Network to Learn Transport Distortion

A. Mistry and P. P. Mukherjee

Journal Paper Physics of Fluids, 31, 122005 (2019)

Abstract

The central premise of porous electrodes is to avail more surface area for reactions. However, the convoluted pore network of such reactors exacerbates the transport of reacting species. Tortuosity is a measure of such transport distortion and is conventionally expressed in terms of porosity (the fraction of electrode volume occupied by liquid-filled pores). Such an approach is overly simplistic and falls short of accounting spatial variabilities characteristic of electrode samples. These networks are defined by multiple features such as size distribution, connectivity, and pore morphology, none of which are explicitly considered in a porosity based interpretation, thus limiting predictability. We propose a recourse using a two-point correlation function that deconstructs the pore network into its essential attributes. Such a quantitative representation is mapped to the transport response of these networks. Given the explicit treatment of pore network geometry, this approach provides a consistent treatment of three-dimensionalities like inhomogeneity and anisotropy. Three-dimensional (3D) tomograms of Li-ion battery electrodes are studied to characterize the efficacy of the proposed approach. The proposed approach is applicable to abstracting effective properties related to different transport modes in porous fluid networks.

Thermo-electrochemical Stability Analytics of Electrode Materials

M. Parmananda, B. Ryali, and P. P. Mukherjee

Journal Paper Journal of Physical Chemistry C, 123, 30106 (2019)

Abstract

Thermal safety concerns of lithium-ion batteries continue to be a pervasive impediment toward vehicle electrification, grid storage, and space exploration. The advent of high capacity cathode materials necessitates a clear understanding of the associated reaction kinetics at elevated temperatures. Here, we present a comprehensive thermo-electrochemical analytics approach to study simulated calorimetric experiments and kinetic parameters estimation for understanding material specific thermal stability. In particular, the focus of the present study is on the fundamental understanding of the thermal stability of disparate cathode materials for lithium-ion intercalation chemistry. Unfortunately, stability of high-capacity cathode materials at elevated temperatures is often challenged by undesirable side reactions including oxygen evolution that promotes electrolyte combustion. The electrochemistry coupled thermo-kinetic strategy presented here acknowledges the multiple abuse reactions associated with the cathode active material and electrolyte interaction at elevated temperatures, which is elucidated via thermal runaway potential based on simulated oven test signatures. The proposed thermo-electrochemical analytics could prove decisive in de-convolving the innate thermal instability signatures of electrode-electrolyte pairs in Li-ion battery chemistry.

In Operando Signature and Quantification of Lithium Plating [Hot Paper]

S.P. Rangarajan, Y. Barsukov, and P. P. Mukherjee

Journal Paper Journal of Materials Chemistry A, 7, 20683 (2019)

Abstract

Lithium plating is a critical challenge for lithium intercalation battery chemistry, especially at high charge rates and high states of charge leading to reduced cycle life, capacity loss, and safety concerns. The anode-centric process of metallic lithium deposition can be identified by monitoring the anode potential in a full cell. In this study an in operando, three-electrode Li-ion pouch cell construct is proposed to probe and quantify lithium plating over a gamut of operational variability, combined with a comprehensive analysis including electrochemical, microscopy and spectroscopy signatures. Different regimes of capacity fade over cycling are identified with respect to the relative extent of lithium plating based on the plating energy as a descriptor. This study reveals the existence of a critical rate where the degradation due to lithium plating is minimal, which is a manifestation of the synergy between the kinetic processes and heat generation signatures. Different morphologies of lithium plating were observed, such as, localized agglomeration predominantly at rates exhibiting higher extent of plating, while diffuse characteristics at rates with lower plating. The propensity for lithium plating and plating induced failure are found to increase with aging even at lower charge rates. This study comprehensively proffers the stochastic nature of the lithium plating process with operational variability.

Cationic Shield Mediated Electrodeposition Stability in Metal Electrodes

F. Hao, A. Verma, and P. P. Mukherjee

Journal Paper Journal of Materials Chemistry A, 7, 18442 (2019)

Abstract

High-energy-density rechargeable batteries, comprising metal electrodes, such as the lithium metal anode, are desirable to meet the ever-increasing demands of energy storage. Metallic dendrite formation, however, poses a critical challenge leading to inferior cycling performance and safety concerns. Here, we present a comprehensive analysis of the electrochemical-transport complexations underlying the cationic shield mechanism, attributed to the presence of additive cations which holds promise toward mitigating dendritic electrodeposition. It is found that the dendrite growth is significantly alleviated by the electrostatic shield in the reaction-kinetics-limited regime, while this effect relies on the concentration of additive cations physically adsorbed to dendrite tips. Furthermore, the competition between the reaction rate and transport rate of additive cations plays a pivotal role in dendrite suppression. In the transport-limited regime, the cationic shield mechanism assists in relatively uniform growth of the otherwise dendritic features. This study provides a comprehensive understanding of the cationic shield mechanism and demonstrates its potential toward stable electrodeposition.

Electrodeposition stability of metal electrodes

F. Hao, A. Verma, and P. P. Mukherjee

Journal Paper Energy Storage Materials, 20, 1 (2019)

Abstract

Rechargeable battery chemistries, with high energy densities, are particularly desirable in order to meet the burgeoning demand for energy storage. In this regard, metal electrodes have recently drawn extensive research interest due to the intrinsic energy density boost, while a fundamental study is needed to reveal the underlying mechanisms governing the electrodeposition stability. Here, we explore the mesoscale interactions in nucleation and growth of electrodeposition, with a focus on the competition of ion transport in the electrolyte, electrochemical reactions at the electrolyte-electrode interface, and surface self-diffusion. It is found that lithium (Li) and sodium (Na) metal anodes have the tendency to form dendrites at high local reaction rates, whereas magnesium (Mg) and aluminum (Al) do not, because of the low intrinsic self-diffusion barriers. Nonuniform electrodeposition at low reaction rates is observed, which could be attributed to the spatial inhomogeneities due to separator wetting, solid electrolyte interphase (SEI) formation, and electrode surface roughness. This work provides a fundamental understanding of the mesoscale underpinnings on the electrodeposition stability of various metal electrodes, especially shedding light on pathways toward potentially dendrite-free electrodeposition morphology.

Electrolyte Confinement Alters Lithium Electrodeposition

A. Mistry, C. Fear, R.E. Carter, C.T. Love and P. P. Mukherjee

Journal Paper ACS Energy Letters, 4, 156 (2019)

Abstract

The metastability of lithium electrodeposition continues to be a scientific mystery. Local ionic depletion has been conventionally argued to be a root cause for nonlinear morphological manifestations. Given the bulk nature of electrolyte transport limitation, it should be absent for very small interelectrode separations; however, even under such conditions, sustained electrodeposition is not observed. We find that the passivating film formed due to lithium’s high reactivity alters the surface energies and in turn deposition preference for fresh lithium. This asymmetry in deposition preference leads to nonuniform surface structure growth and traps the electrolyte layer. Such electrolyte confinement causes polarization, even at subcritical currents. The existence of confined electrolyte and associated electrochemical complexations is proved through temperature-controlled electrodeposition experiments.

Non-equilibrium Thermodynamics in Electrochemical Complexation of Li-Oxygen Porous Electrodes [Hot Paper]

A. Mistry, F. Cano-Banda, D. Law, A. Hernandez-Guerrero and P. P. Mukherjee

Journal Paper Journal of Materials Chemistry A, 7, 8882 (2019)

Abstract

The lithium-oxygen conversion chemistry relies on solid – electrolyte interface centered energy storage, rather than bulk considerations in intercalation chemistry. The electrochemical complexations in porous air electrodes are, however, a manifestation of coupled interface-transport-kinetic interactions. The non-equilibrium thermodynamics behind such multi-modal coupling, hitherto unappreciated, forms the central argument of this work. We comprehensively demonstrate the role of reciprocity between electrode architecture and off-equilibrium interactions in Li-O₂ electrochemistry based energy storage.

Controllable Electrode Stochasticity Self-heats Lithium-ion Batteries at Low Temperatures

A. Mistry, A. Verma and P. P. Mukherjee

Journal Paper ACS Applied Materials & Interfaces, 11, 26764 (2019)

Abstract

Cold-start is an ineluctable stipulation for electric vehicle operation under low temperature extremes. It has typically been addressed through cell-level heating strategies. We advocate an electrode-level strategy leveraging pore-scale manifestation of thermal metastability that promotes self-heating. Appropriate controllable stochastic characteristics of porous electrodes are delineated that contribute to the proposed solution at low temperatures. This approach is most conducive to high energy density Li-ion cells and devoid of extrinsic overheads.

In Operando Thermal Signature Probe for Lithium-Ion Batteries

A. Mistry, H.R. Palle and P. P. Mukherjee

Journal Paper Applied Physics Letters, 114, 023901 (2019)

Abstract

Thermal metastability is an inescapable trait of lithium-ion batteries. However, canonically only electrochemical signatures are studied as calorimetry imposes a controlled environment to isolate the self-heating signal. We propose an in operando approach for characterizing the thermal signatures. Using an inverse heat transfer formulation, we deconvolve the self-heating signature from other simultaneous heat transfer modes. Temporal variation of heat generation is subsequently estimated. This approach does not presuppose a particular electrochemical operation and is agnostic to materials used in the Li-ion cells. The generality and simplicity of this experimental approach rely on inverse thermal analysis and concurrent calibration of ambient natural convection response.

Mechanistic Understanding of Electrochemical Plating and Stripping of Metal Electrodes [Hot Paper]

D. Tewari, and P. P. Mukherjee

Journal Paper Journal of Materials Chemistry A, 12, 556 (2019)

Abstract

Lithium metal is an attractive negative electrode material for rechargeable lithium batteries because of its light weight and high electronegative redox potential. However, dendritic deposition of lithium during charging poses a safety concern. During discharging, some of the lithium may strip away from the electrode as the root of the dendrite is electrodissolved. This is referred to as dead lithium since it is not electrochemically active, which may result in low Coulombic efficiency. In this work, a comprehensive understanding of the interface evolution leading to the formation of dead lithium is presented based on a mechanism-driven probabilistic analysis. Nondendritic interface morphology is obtained under reaction and ionic transport controlled scenarios. Otherwise, this may evolve into mossy, dendritic, whisker or needle-like structures with the main characteristic being the propensity for undesirable vertical growth. During discharging, pitted interface may be formed along with bulk dissolution. Surface diffusion is a key determinant controlling the extent of dead lithium formation, including a higher probability of the same when the effect of surface diffusion is comparable to that of ionic diffusion in the electrolyte and interface reaction.

Formation of Magnesium Dendrites during Electrodeposition

R. Davidson, A. Verma et al.

Journal Paper ACS Energy Letters, 4, 375 (2019)

Abstract

We demonstrate the growth of dendritic magnesium deposits with fractal morphologies exhibiting shear moduli in excess of values for polymeric separators upon the galvanostatic electrodeposition of metallic Mg from Grignard reagents in symmetric Mg—Mg cells. Dendritic growth is understood based on the competing influences of reaction rate, electrolyte transport rate, and self-diffusion barrier evaluated using a dimensionless Damköhler ratio as further corroborated by kinetic Monte Carlo simulations.

Mechanistic Elucidation of Si Particle Morphology on Electrode Performance

A. Verma, A. A. Franco and P. P. Mukherjee

Journal Paper Journal of the Electrochemical Society (2019)

Abstract

High specific capacity silicon anodes are limited by immense volumetric expansion making them prone to deleterious capacity fade through particle cracking and disintegration. Nanosized silicon active particles with spherical and rod morphology demonstrate resistance to lithiation induced fracture owing to their smaller size. However, lithium insertion in silicon nanospheres and nanowires exhibit varying characteristics as a function of the morphology. In this work, we contrast the lithiation impact on diffusive transport and reaction kinetics for silicon nanospheres and nanorods cognizant of the volume evolution using a particle formalism. For the same equivalent volume, nanorods surpass nanospheres in rate performance beyond a threshold initial length to initial radius aspect ratio. Nanorods show faster radial growth as compared to nanospheres for the same initial radius, resulting in exacerbated diffusion limitations below the threshold aspect ratio. The mechanistic insight into the morphology dependence on performance is elucidated. Diffusivity and exchange current density values for the silicon anode are computed as well through synergy between experimental dataset and simulation results.

In Operando Impedance Based Diagnostics of Electrode Kinetics in Li-Ion Pouch Cells

S.P. Rangarajan, Y. Barsukov, and P. P. Mukherjee

Journal Paper Journal of the Electrochemical Society, 166, A2131 (2019)

Abstract

A key to understanding the coupled electrochemical and transport processes in Li-ion batteries is to distinguish the complex interactions between the electrode pair. In this study, an in operando impedance based diagnostics for a three-electrode Li-ion pouch cell configuration is presented in order to study the individual electrode kinetics under varying operating temperatures and depths of discharge. The electrochemical processes including intercalation, diffusion, and interfacial reactions occur at different timescales. Impedance analytics allows estimating the resistances and activation energies of different processes to identify the limiting mechanisms in each electrode. It was found that at -5^oC, the effect of staging in the graphite electrode manifests as a piece-wise dependence of the pore resistance and the double layer capacitance in the anode. The dense and highly ordered stages (1,2) of graphite exhibit higher ionic resistance than the disordered (2L,3L, and 4L) stages at -5^oC, due to the added contribution of pore transport resistance at higher depths of discharge.

Drying Temperature and Capillarity Driven Crack Formation in Aqueous Processing of Li-Ion Battery Electrodes

K. Rollag, D. Juarez-Robles, D. Wood and P. P. Mukherjee

Journal Paper ACS Applied Energy Materials, 2, 4464 (2019)

Abstract

Unlike conventional electrode processing for Li-ion batteries, which uses the expensive and highly toxic organic N-methyl-2-pyrrolidone (NMP) solvent, aqueous processing simply employs deionized water as the solvent. However, thick aqueous processed cathodes have been found to crack during drying. In this study, the influence of electrode drying temperature andthickness on cracking was investigated. LiNi_1/3Mn_1/3Co_1/3O₂ cathodes prepared with a hydrophilic binder, modified tyrene-butadiene rubber (SBR), were coated at various thicknesses and dried at temperatures ranging from 20 °C to 70 °C. Experiments revealed cracking worsens with increased electrode thickness, and elevated drying temperatures. Cracks were formed during thecapillarity driven phase during drying. Strong evaporation and weak diffusion played a criticalrole in the non-uniform distribution of the inactive phase. Images of electrode surfaces wereprocessed to quantify crack dimensions and crack intensity factor (CIF). Average crack lengthand width, as well as CIF, increased with drying temperature and electrode thickness.Electrochemical performance revealed a strong and negative correlation between the crackdensity and performance in terms of specific capacity. Transport limitations associated with thepresence of cracks adversely affect the advantage of high volume ratio of active materials in the thick electrodes.

Mesoscale Elucidation of Self-Discharge Induced Performance Decay in Lithium-Sulfur Batteries

F. Hao, P. Balbuena and P. P. Mukherjee

Journal Paper ACS Applied Materials and Interfaces, 11, 13326 (2019)

Abstract

Polysulfide shuttle phenomenon substantially deteriorates the electrochemical performance of lithium-sulfur (Li-S) batteries, resulting in continued self-discharge and capacity fade during cycling. In this study, a mesoscale analysis is presented to explore the mechanisms of self-discharge behavior in the Li-S battery during rest state. It is found that self-discharge rate is determined by the sulfur solubility, desorption capability, diffusion kinetics, and reaction rate on the anode surface. Three regimes have been identified: desorption control, diffusion control, and charge transfer control. Correspondingly, strategies are suggested to increase the capacity retention, such as enhancing the binding of sulfur molecules to the host, reducing dissolved sulfur diffusivity, and improving the chemical stability of active materials with Li metal anode. Furthermore, the use of interlayer with high diffusion barriers can effectively suppress the self-discharge rate due to the confinement effect.

Materials by Design: Tailored Morphology and Structures of Carbon Anodes for Enhanced Battery Safety

R. Adams, A. Mistry, P. P. Mukherjee, and V. Pol

Journal Paper ACS Applied Materials and Interfaces, 11, 13334 (2019)

Abstract

Next generation Li-ion battery technology awaits materials that not only store more electrochemical energy at finite rates but exhibit superior control over side reactions and better thermal stability. Herein, we hypothesize that designing an appropriate particle morphology can provide a well-balanced set of physicochemical interactions. Given the anode-centric nature of primary degradation modes, we investigate three different carbon particles – commercial graphite, spherical, and spiky carbon, and analyze the correlation between particle geometry and functionality. Intercalation dynamics, side reaction rates, self-heating, and thermal abuse behavior have been studied. It is revealed that the spherical particle outperforms an irregular one (commercial graphite) under thermal abuse conditions, as it eliminates unstructured inhomogeneities. A spiky particle with ordered protrusions exhibits smaller intercalation resistance and attenuated side reactions, thus outlining the benefits of controlled stochasticity. Such findings emphasize the importance of tailoring particle morphology to proffer selectivity among multimodal interactions.

Mesoscale Modeling in Electrochemical Devices – a Critical Perspective

E. Ryan and P. P. Mukherjee

Journal Paper Progress in Energy and Combustion Science, 71, 118 (2019)

Abstract

Electrochemical energy systems, such as batteries and fuel cells, are being developed for applications ranging from portable devices and electric vehicles to large-scale grid storage. These advanced energy conversion and storage technologies will be a critical aspect of a sustainable energy future and promise to provide cleaner, more efficient energy. Computational modeling at various scales from nanoscale ab initio modeling to macroscale system and controls level modeling, has been a central part of the electrochemical energy research. Much of the complex interactions due to the electrochemistry coupled transport phenomena occur at the interfaces and within the porous electrode microstructures. This is often referred to as the mesoscale and plays a critical role in the operation and efficiency of electrochemical devices. In this critical perspective, we discuss the state-of-the-art, challenges and path forward in mesoscale modeling of electrochemical energy systems and their application to various design and operational issues in solid oxide fuel cells, polymer electrolyte membrane fuel cells, lithium ion batteries and metal-air batteries. Particular focus is given to particle-based methods and fine-scale computational fluid dynamics based direct numerical simulation techniques, along with the challenges and advantages of these methods. Notable results from mesoscale modeling are presented along with discussions of the advantages, disadvantages and challenges facing mesoscale model development. This in-depth perspective is envisioned to serve as a primer to the critical role mesoscale modeling is poised to play in advancing the science and engineering of electrochemical energy systems.

Mesoscale Physics in the Catalyst Layer of Proton Exchange Membrane Fuel Cells: a Critical Perspective

J.B. Grunewald, A. Mistry, A. Verma, N. Goswami, P. P. Mukherjee, and T.F. Fuller

Journal Paper Journal of Electrochemical Society, 166, F3089 (2019)

Abstract

Proton-exchange membranes fuel-cells (PEMFC) electrochemical performance insights are predicated on a detailed understanding of species transport in the cathode catalyst layer (CCL). Traditionally, CCL microstructure considerations were approached through approximations with unresolved pore-scale features. Such simplifications cause the loss of predictability for improving the economic feasibility via lower Pt-loading or non-noble metal catalysts. With advances in visualization, microstructure resolved mesoscale models become possible. A judicious combination of lattice Boltzmann (LBM) and finite volume (FVM) is an appropriate strategy for direct numerical simulation (DNS) of the physicochemical fields that remain unresolved due to spatiotemporal limitations.

Electrochemical reaction driven interfacial stress in a solid/solid layered architecture

F. Hao, W. Wang and P. P. Mukherjee

Journal Paper Physical Review Applied, 11, 034038 (2019)

Abstract

Reaction driven interfacial growth causes significant strain in layered architectures accompanied by mass transfer and moving boundaries Here, we present an analytical construct of the stress generated in a multi-layer film which incorporates the elastic-plastic strain of the growth layer, which suggests its strong dependence on the mechanical properties and thickness. This analytical formalism is further applied to a layered all-solid-state lithium battery architecture. This study demonstrates that mechanical stability can be enhanced by using a positive electrode material with high stiffness, porous hosts for lithium plating, and small external elastic constraints to buffer the volumetric changes in the electrode material. Our results also reveal that small surface flaws in the solid electrolyte and high internal hydrostatic pressure can alleviate lithium dendrite growth through surface cracks.

Probing spatial coupling of resistive modes in porous intercalation electrodes through impedance spectroscopy

A. Mistry and P. P. Mukherjee

Journal Paper Physical Chemistry Chemical Physics, 21, 3805 (2019)

Abstract

In porous intercalation electrodes, coupled charge and species transport interactions take place at the pore-scale, while often observations are made at the electrode-scale. The physical manifestation of these interactions from pore- to electrode-scale is poorly understood. Moreover, the spatial arrangement of the constituent material phases forming a porous electrode significantly affects the multi-modal electrochemical and transport interplay. In this study, the relation between the electrode specification, resultant porous microstructure, and electrode-scale resistances is delineated based on a virtual deconvolution of the impedance response. Relevant short- and long-range interactions are identified. Without altering the microstructural arrangement, if the electrode thickness is increased, the resistances do not scale linearly with thickness. This dependence is also probed to identify the fundamental origins of thick electrode limitations.

Elucidating Lithium Alloying Induced Degradation Evolution in High Capacity Electrodes

D. Juarez-Robles, H. J. Gonzalez-Malabet, M. L'Antigua, X. Xiao, G.J. Nelson and P. P. Mukherjee

Journal Paper ACS Applied Materials & Interfaces, 11, 563 (2019)

Abstract

Alloy electrode materials offer high capacity in lithium ion batteries, however, exhibit rapid degradation resulting in particle disintegration and electrochemical performance decay. In this study, the evolution of lithium alloying induced degradation due to electrochemo-mechanical interactions is examined based on a multi-pronged electrochemical and microstructural analysis. Copper-tin (Cu6Sn5) is chosen as an exemplar alloy electrode material. Electrodes with compositional variations were fabricated and electrochemical performance was examined under varying conditions, such as voltage window, C-rate, and short- and long-term cycling. Morphology and composition analyses of pristine and cycled electrodes were conducted using micrography and spectroscopy techniques. Alloying induced electrode microstructural evolution was probed using X-ray microtomography. The rapid capacity fading was found to be caused by mechanical degradation of the electrode. Driving the electrode to a lower potential (E ≈ 0.2 V vs. Li/Li+) induced Li-Sn alloy formation, providing the characteristic large capacity; however leading to a large volume expansion and active particle cracking and disintegration. Copper expulsion was found to be a consequence of the alloy formation, however, not the primary contributor to the dramatic electrochemical performance decay.

Quantifying Transport, Geometrical and Morphological Parameters in Li-ion Cathode Phases using X-ray Microtomography

T. Rajendra, A. Mistry, P. Patel, L. Ausderau, X. Xiao, P. P. Mukherjee, and G. Nelson

Journal Paper ACS Applied Materials & Interfaces, 11, 19933 (2019)

Abstract

The charge/discharge capabilities of Li-ion cathodes are influenced by the meso-scale geometry, transport properties and morphological parameters of the constituent phases in the cathode: active material, binder, conductive additive and pore. Electrode processing influences the structure and attendant properties of these constituents. Thus, performance of the battery can be enhanced by correlating various electrode processing techniques with the charge/discharge behavior in the Lithium-ion cathodes. X-ray microtomography was used to image samples obtained from pristine Li(Ni_1/3Mn_1/3Co_1/3)O₂ (NMC) cathodes subjected to distinct processing approaches. Two sample preparation approaches were applied to the samples prior to microtomography. Casting the samples in epoxy yielded only a cathode active material domain. Encapsulating the sample with Kapton tape yielded phase contrast data that permitted segmentation of the active material, combined carbon/binder and pore regions. Geometrical and morphological details of the active material and the secondary phases were characterized and compared between the varied processing approaches. Calendered and ball-milled samples exhibited distinct differences in both geometry and morphology. Drying modes demonstrated variation in the distribution of the secondary and pore phases. Applying phase contrast capabilities, the processing-morphology relationship can be better understood to enhance overall battery performance across multiple scales.

Chemical and Mechanical Degradation and Mitigation Strategies for Si Anodes

D.E. Galvez-Aranda, A. Verma, K. Hankins, J. Seminario P. P. Mukherjee, and P.B. Balbuena

Journal Paper Journal of Power Sources, 419, 208 (2019)

Abstract

Atomistic and mesoscopic models are used to analyze cracking and stresses produced during charge of Si nanoparticles covered by a thin SEI film. Mechanical stresses coupled to chemical effects are investigated with classical molecular dynamics simulations and with a mesoscopic models. Rupture of the surface film is the main cause of capacity fade and damage evolution is strongly influenced by the structure of the solid film. For example, high currents can cause rapid amorphization and help preserving the bond integrity. But large damage occurs after the current is above a threshold. In agreement with the atomistic results, mesoscopic modeling reveals that rupture of the surface film is the primary cause of capacity fading for amorphous silicon exhibiting single phase diffusion. It also suggests that conjugated silicon-film fracture in crystalline silicon with two-phase diffusion further exacerbates this deterioration. Fracture damage is slightly diminished by decreasing the Young's modulus of the brittle coating for both amorphous and crystalline silicon; however, controlling the large volumetric expansion induced stress on surface film is crucial towards improving silicon anodes. Mitigation strategies examined by ab initio molecular dynamics and electronic density functional theory simulations show passivation effects of graphene and graphene oxide on lithiated Si surfaces.

Non-dimensional Analysis of the Criticality of Li-ion Battery Thermal Runaway Behavior

P. Huang, H. Chen, A. Verma, Q. Wang, P. P. Mukherjee, and J. Sun

Journal Paper Journal of Hazardous Materials, 369, 268 (2019)

Abstract

Lithium-ion batteries are the most popular used portable energy storage technology due to the relatively high energy density. While thermal instability induced safety concerns impede the pace of developing large scale applications, the practical applications have no tolerance for the catastrophic failure. To learn more about the characteristics of battery failure, the criticality of battery thermal runaway is studied in this paper. Semenov and Thomas models are employed to analyze the criticality of battery thermal runaway in uniform and nonuniform temperature distribution situations. In order to improve accuracy of prediction, the critical parameters of overall reaction are taken as a weighted average of four exothermic reactions and the critical critera are revised by the consumption of reactants. Results from revised model are consistence with oven model. According to the revised thermal abuse models, the critical criterion (ψ_cr,δ_cr) and critical temperature distribution (θ_cr) are analyzed in different composite materials, convective heat transfer coefficients and cell deformations. Results give the variation of critical criteria and critical temperature with these factors.

Probing the Influence of Confinement and Wettability on Droplet Displacement Behavior: A Mesoscale Analysis

P. Randive, A. Dalal and P. P. Mukherjee

Journal Paper European Journal of Mechanics - B/Fluids, 75, 327 (2019)

Abstract

The influence of confinement and wall wettability on droplet displacment behavior is presented. Two phase lattice Boltzmann Shan and Chen model has been employed to unveil the droplet dynamics. The time evolution of wetted length and wetted area for different confinement configurations is discussed. The effect of confinement on droplet dispalcement behavior has been found to be more pronounced on hydrophobic surface as compared to hydrophilic surface. Furthermore, the droplet morphology shows more deformation on hydrophobic surface as compared to hydrophilic surface for low confinement ratios at low capillary number in paticular.

Mesoscale understanding of capillarity driven two-phase flow in a packed bed architecture

S. Bhardwaj, A. Dalal and P. P. Mukherjee

Journal Paper International Journal of Heat and Mass Transfer (2019)

Abstract

Understanding the displacement dynamics in capillarity driven two-phase flow in packed bed architectures is of fundamental importance. In this work, the role of mesoscale physics due to the underlying capillarity wettability interaction on the two-phase flow in a sphere-packed architecture is presented. The influence of different pore surface wettability, porosity and pressure gradient on the two-phase flow behavior has been studied. The mesoscale study exhibits interesting pattern formations due to the invasion of a non-wetting fluid and surface adherence owing to the underlying wettability-capillarity characteristics. The emergence of finger like invasion pattern in a hydrophobic architecture is observed while a stable fluid front predominates in a hydrophilic structure. This study further reveals that a hydrophilic architecture is prone to elevated saturation limit for the invading fluid, while a larger pressure gradient can promote pronounced finger-like patterns.

Mechanistic Insight into Dendrite-SEI Interactions for Lithium Metal Electrodes

F. Hao, A. Verma and P. P. Mukherjee

Journal Paper Journal of Materials Chemistry A, 6, 19664 (2018)

Abstract

Solid electrolyte interphase (SEI) layer stability and homogeneity are critical toward understanding the root causes behind rapid performance decay and safety concerns with lithium metal electrodes for energy storage. This study focuses on deducing mechanistic insights into the complexations between Li metal electrode and SEI during electrodeposition. It is found that the formation of Li dendrite can be initiated by two distinct mechanisms: (i) aggravated Li-ion depletion near the anode-SEI interface at high reaction rates or low temperatures attributed to transport limitations, and (ii) spatially varying reaction kinetics due to SEI layer inhomogeneity even at low currents. Subsequent mechanical stability analyses reveal that significantly high stress is generated due to nonuniform Li electrodeposition which could lead to crack formation in the existing SEI layer, and consequently exposure of fresh lithium to the electrolyte resulting in enhanced capacity fading. Furthermore, a non-dimensional analysis relating the interfacial stress induced failure propensity to electrochemical Biot number and SEI heterogeneity factor is proposed, which delineates stable lithium deposition regimes.

‘Shuttle’ in Polysulfide Shuttle: Friend or Foe?

A. Mistry and P. P. Mukherjee

Journal Paper Journal of Physical Chemistry C, 122, 23485 (2018)

Abstract

The polysulfide shuttle effect, where sulfur species reach the negative electrode surface and undergo chemical reduction, is believed to be a major bottleneck in lithium-sulfur chemistry. The importance of this phenomenon often judged based on phenomenological arguments, does not account for mesoscale complexations. This work presents a comprehensive investigation of the coupled interactions arising from speciation, concentrated electrolyte solution and reaction time scales. Polysulfide transport consists of diffusion and migration, which determines the net flux. This study demonstrates that the polysulfide shuttle effect can be bounded between reaction-limited and shuttle-limited regimes, depending on the operational extremes. At high sulfur to electrolyte ratio (i.e. lean electrolyte condition), the polysulfide shuttle effect may not necessarily attribute to the cell performance limitation, believed contrarily otherwise.

Mesoscale Complexations in Lithium Electrodeposition

F. Hao, A. Verma and P. P. Mukherjee

Journal Paper ACS Applied Materials and Interfaces, 10, 26320 (2018)

Abstract

Mechanistic understanding of lithium electrodeposition and morphology evolution is critical for lithium metal anodes. In this study, we deduce that Li deposition morphology evolution is determined by the mesoscale complexations that underlie due to local electrochemical reaction, Li surface self-diffusion, and Li-ion transport in the electrolyte. Li-ion depletion at the reaction front for higher reaction rates primarily accounts for dendritic growth with needlelike or fractal morphology. Large Li self-diffusion barrier, on the other hand, may lead to the formation of porous Li film for lower reaction rates. Enhanced ion transport in the electrolyte contributes to homogeneous deposition, thereby avoiding nucleation for Li dendrite formation. This study also demonstrates that the substrate surface roughness strongly affects dendritic growth localization over the protrusive surface features. A nondimensional electrochemical Damkohler number is further proposed, which correlates surface diffusion rate and reaction rate and allows constructing a comprehensive phase map for lithium electrodeposition morphology evolution.

Secondary Phase Stochastics in Lithium-ion Battery Electrodes [Journal Cover]

A. Mistry, K. Smith and P. P. Mukherjee

Journal Paper ACS Applied Materials and Interfaces, 10, 6317 (2018)

Abstract

Lithium-ion battery electrodes exhibit complex interplay among multiple electrochemically coupled transport processes, which rely on the underlying functionality and relative arrangement of different constituent phases. The electrochemically inactive solid phases (e.g., conductive additive and binder, referred to as the secondary phase) while beneficial for improved electronic conductivity and mechanical integrity, may partially block the electrochemically active sites and introduce additional transport resistances in the pore (electrolyte) phase. In this work, the role of mesoscale interactions and inherent stochasticity in porous electrodes is elucidated in the context of short-range (interface) and long-range (transport) characteristics. The electrode microstructure significantly affects kinetically and transport limiting scenarios and thereby the cell performance. The secondary phase morphology is also found to strongly influence the microstructure-transport-kinetics interactions. Apropos, strategies have been proposed for performance improvement via electrode microstructural modifications.

Electrolyte Transport Evolution Dynamics in Lithium–Sulfur Batteries

A. Mistry and P. P. Mukherjee

Journal Paper Journal of Physical Chemistry C, 122, 18329 (2018)

Abstract

The liquid electrolyte is a critical component in the lithium-sulfur battery, which dissolves long-chain intermediate polysulfides, forms electrochemically active interface, and allows species and charge transport. The electrolyte transport dynamics is, however, intricately affected by the underlying evolution of chemical speciation. In this work, a comprehensive description is presented to identify the role of speciation and intra- and interspecies interactions on electrolyte-transport dynamics. The evolutionary presence of different polysulfide species alters the transport characteristics which in turn affects electrochemical complexations. Microstructural changes and electrolyte evolution are concurrently present, and their mutual coupling is discussed. The role of the sulfur to electrolyte ratio, which dictates speciation in the electrolyte phase, and ionic transport limitations are elucidated.

Analysis of Droplet Dynamics in a Partially Obstructed Confinement in a Three-Dimensional Channel [Editor's Choice]

S. Bhardwaj, A. Dalal, G. Biswas and P. P. Mukherjee

Journal Paper Physics of Fluids, 30, 102102 (2018)

Abstract

This study presents droplet dynamics due to capillarity-wettability interaction through a partially obstructed channel confinement based on a mesoscopic, two-phase lattice Boltzmann model. To explore the dynamic behavior of droplet motion past an obstruction, the effects of modified capillary number and surface wettability, including obstruction size and architecture, are elucidated. For this work, a single spherical obstruction, and different spherical agglomerate structures have been considered. The mesoscale simulations exhibit interesting two-phase flow physics and pattern formations due to droplet pinching, break up, and surface adherence owing to the underlying wettability-capillarity characteristics. This study further reveals an interesting trade-off, between the time required for the bulk droplet fluid to pass by and/ or through the obstruction and the fraction of droplet fluid volume adhering to the surface, depending on the combination of the modified capillary number and surface wettability.

Mesoscale Analysis of Conductive Binder Domain Morphology in Lithium-Ion Battery Electrodes [Editor's Choice]

B.L. Trembacki, A. Mistry, D.R. Noble, M.E. Ferraro, P. P. Mukherjee and S.A. Roberts

Journal Paper Journal of The Electrochemical Society, 165, E725 (2018)

Abstract

Typical lithium-ion battery electrodes are porous composites comprised of active material, conductive additives, and polymeric binder, with liquid electrolyte filling the pores. The mesoscale morphology of these constituent phases has a significant impact on both electrochemical reactions and transport across the electrode, which can ultimately limit macroscale battery performance. We reconstruct published X-ray computed tomography (XCT) data from a NMC333 cathode to study mesoscale electrode behavior on an as-manufactured electrode geometry. We present and compare two distinct models that computationally generate a composite binder domain (CBD) phase that represents both the polymeric binder and conductive additives. We compare the effect of the resulting CBD morphologies on electrochemically active area, pore phase tortuosity, and effective electrical conductivity. Both dense and nanoporous CBD are considered, and we observe that acknowledging CBD nanoporosity significantly increases effective electrical conductivity by up to an order of magnitude. Properties are compared to published measurements as well as to approximate values often used in homogenized battery-scale models. All reconstructions exhibit less than 20% of the standard electrochemically active area approximation. Order of magnitude discrepancies are observed between two popular transport simulation numerical schemes (finite element method and finite volume method), highlighting the importance of careful numerical verification.

Resolving the Discrepancy in Tortuosity Factor Estimation for Li-ion Battery Electrodes through Micro-Macro Modeling and Experiment

F.L.E Usseglio-Viretta, A. Colclasure, A. Mistry et al.

Journal Paper Journal of Electrochemical Society, 165, A3403 (2018)

Abstract

Battery performance is strongly correlated with electrode microstructural properties. Of the relevant properties, the tortuosity factor of the electrolyte transport paths through microstructure pores is important as it limits battery maximum charge/discharge rate, particularly for energy-dense thick electrodes. Tortuosity factor however, is difficult to precisely measure, and thus its estimation has been debated frequently in the literature. Herein, three independent approaches have been applied to quantify the tortuosity factor of lithium-ion battery electrodes. The first approach is a microstructure model based on three-dimensional geometries from X-ray computed tomography (CT) and stochastic reconstructions enhanced with computationally generated carbon/binder domain (CBD), as CT is often unable to resolve the CBD. The second approach uses a macro-homogeneous model to fit electrochemical data at several rates, providing a separate estimation of the tortuosity factor. The third approach experimentally measures tortuosity factor via symmetric cells employing a blocking electrolyte. Comparisons have been made across the three approaches for 14 graphite and nickel-manganese-cobalt oxide electrodes. Analysis suggests that if the tortuosity factor were characterized based on the active material skeleton only, the actual tortuosities would be 1.35–1.81 times higher for calendered electrodes. Correlations are provided for varying porosity, CBD phase interfacial arrangement and solid particle morphology.

Electrochemistry Coupled Mesoscale Complexations in Electrodes Lead to Thermo-Electrochemical Extremes

A. Mistry, K. Smith and P. P. Mukherjee

Journal Paper ACS Applied Materials and Interfaces, 10, 28644 (2018)

Abstract

Thermo-electrochemical extremes continue to remain a challenge for lithium-ion batteries. Contrary to the conventional approach, we propose herein that the electrochemistry coupled and microstructure mediated cross-talk between the positive and negative electrodes ultimately dictates the off-equilibrium coupled processes, such as heat generation and the propensity for lithium plating. The active particle morphological differences between the electrode couple foster thermo-electrochemical hysteresis, where difference in heat generation rates change the electrochemical response. The intrinsic asymmetry in electrode microstructural complexations leads to thermo-electrochemical consequences, such as, cathode-dependent thermal excursion; and co-dependent lithium plating otherwise believed to be anode-dependent.

Mesoscale Understanding of Lithium Electrodeposition for Intercalation Electrodes

D. Tewari, Z. Liu, P.B. Balbuena and P. P. Mukherjee

Journal PaperJournal of Physical Chemistry C, 122, 21097 (2018)

Abstract

Stringent performance and operational requirements in electric vehicles can push lithium-ion batteries toward unsafe conditions. Electroplating and possible dendritic growth are a cause for safety concern as well as performance deterioration in such intercalation chemistry-based energy storage systems. There is a need for better understanding of the morphology evolution due to electrodeposition of lithium on graphite anode surface, and the interplay between material properties and operating conditions. In this work, a mesoscale analysis of the underlying multi-modal interactions is presented to study the evolution of morphology due to lithium deposition on typical graphite electrode surfaces. It is found that electrodeposition is a complex interplay between the rate of reduction of Li ion and the intercalation of Li in the graphite anode. The morphology of the electrodeposited film changes from dendritic to mossy structures due to the surface diffusion of lithium on the electrodeposited film.

Mesoscale Analysis of the Electrolyte-Electrode Interface in All-Solid-State Li-Ion Batteries

F. Hao and P. P. Mukherjee

Journal Paper Journal of Electrochemical Society, 165, A1857 (2018)

Abstract

Electrolyte-electrode interface plays a critical role in the electrochemical performance of all-solid-state Li-ion batteries. In this work, a mesoscale study is presented to investigate lithium transport and stress in the solid electrolyte based positive electrode during discharge. It is found that increasing electrolyte-electrode interface contact facilitates Li intercalation into the electrode and alleviates the stresses in both the electrode and the electrolyte. Using small electrode particles helps to improve rate capability and avoid interfacial failures due to the volume change of electrode particles. Interface stress strongly depends on the mechanical properties of the two components. In addition, this study demonstrates the importance of electrolyte network through the porous active particle backbone.

Mechano-Electrochemical Interaction and Degradation in Graphite Electrode with Surface Film

A. Verma, T. Kotaka, Y. Tabuchi and P. P. Mukherjee

Journal Paper Journal of Electrochemical Society, 165, A2397 (2018)

Abstract

Lithium ion batteries (LIBs) exhibit significant capacity and performance degradation with cycling owing to extensive decrepitation of anodes associated with lithiation-delithiation induced volumetric expansion and contraction. Microcrack formation in the active material and solid electrolyte interphase layer contribute to deleterious effects including hindered diffusion, particle isolation, and loss of cyclable Li inventory, with detrimental performance ramifications. In this work, a stochastic computational methodology, utilizing lattice spring formalism, is extended to probe effect of surface film characteristics on diffusion induced damage in graphite anodes with a direct correlation to LIB performance. Film geometric and mechanical properties of interest, with a direct impact on fracture characteristics, are identified and parametric variations are explored to ascertain the relative influence of each property. Reduction of surface film stiffness is found to substantially ameliorate fracture damage inside both active material and film. Film thickness and fracture threshold energy primarily affect the fracture characteristics inside film with a less discernible impact on the anode active material. Extensive damage density data based regression as well as rate performance study is performed to strengthen the hypothesis and desirable film properties are outlined for improved LIB performance, specifically, low stiffness and high fracture threshold energy film with optimal thickness.

Elucidating Copper Dissolution Phenomenon in Li-ion Cells under Overdischarge Extremes

C. Fear, D. Juarez-Robles, J.A. Jeevarajan and P. P. Mukherjee

Journal Paper Journal of Electrochemical Society, 165, A1639 (2018)

Abstract

The mechanisms driving the thermo-electrochemical response of commercial lithium-ion cells under extreme overdischarge conditions (< 0.0 V) are investigated in the context of copper dissolution from the anodic current collector. A constant current discharge with no lower cutoff voltage was used to emulate the effects of forced overdischarge, as commonly experienced by serially connected cells in an unbalanced module. Cells were overdischarged to 200% DOD (depth of discharge) at C/10 and 1C rates to develop an understanding of the overdischarge extremes. Copper dissolution began when a cell reached its minimum voltage level (between −1.3 V and −1.5 V), where the anode potential reached a maximum value of ∼4.8 V vs. Li/Li⁺. Deposition of copper on the cathode, anode, and separator surfaces was observed in all overdischarged cells, verified with EDS/SEM results, which further suggests the formation of internal shorts, although the cell failures proved to be relatively benign. The maximum cell surface temperature during overdischarge was found to be highly rate-dependent, with the 1C-rate cell experiencing temperatures as high as 79°C. Concentration polarization and solid electrolyte interphase (SEI) layer breakdown prior to the initiation of copper dissolution are proposed to be the main sources of heat generation during overdischarge.

Electrochemistry-Mechanics Coupling in Intercalation Electrodes

N. Kotak, P. Barai, A. Verma A. Mistry, and P. P. Mukherjee

Journal Paper Journal of Electrochemical Society, 165, A1064 (2018)

Abstract

Diffusion induced stress, due to repeated intercalation/deintercalation of lithium during cycling, causes mechanical degradation in graphite active particles used as an anode in lithium-ion batteries. The microcracks formed in the active particles hinder diffusion of lithium. On the other hand, flow of electrolyte through the accessible microcracks in the active particles leads to additional electrochemically active surfaces and effectively reduces the diffusion length. In this work, stochastic modeling of electrochemistrymechanics interaction is presented which introduces the influence of electrochemically active microcracks on electrochemical reactions. Enhanced electrochemically active surface area further results in the formation of solid electrolyte interphase (SEI), which decreases the cell capacity due to the consumption of cyclable lithium. This stochastic model successfully predicts the formation of non-uniform and spanning cracks in active particles, which are typically observed in scanning electron micrographs. The impact of coupled electrochemical and mechanical interaction in graphite active particles on capacity fade is elucidated.

Three-electrode Coin Cell Preparation and Electrodeposition Analytics for Lithium-ion Batteries

R. D. Minter, D. Juarez-Robles, C. Fear, Y. Barsukov and P. P. Mukherjee

Journal PaperJournal of Visualized Experiments, 135, e57735 (2018)

Abstract

As lithium-ion batteries find use in high energy and power applications, such as in electric and hybrid-electric vehicles, monitoring the degradation and subsequent safety issues becomes increasingly important. In a Li-ion cell setup, the voltage measurement across the positive and negative terminals inherently includes the effect of the cathode and anode which are coupled and sum to the total cell performance. Accordingly, the ability to monitor the degradation aspects associated with a specific electrode is extremely difficult because the electrodes are fundamentally coupled. A three-electrode setup can overcome this problem. By introducing a third (reference) electrode, the influence of each electrode can be decoupled, and the electrochemical properties can be measured independently. The reference electrode (RE) must have a stable potential that can then be calibrated against a known reference, for example, lithium metal. The three-electrode cell can be used to run electrochemical tests such as cycling, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS). Three-electrode cell EIS measurements can elucidate the contribution of individual electrode impedance to the full cell. In addition, monitoring the anode potential allows the detection of electrodeposition due to lithium plating, which can cause safety concerns. This is especially important for the fast charging of Li-ion batteries in electric vehicles. In order to monitor and characterize the safety and degradation aspects of an electrochemical cell, a three-electrode setup can prove invaluable. This paper aims to provide a guide to constructing a three-electrode coin cell setup using the 2032-coin cell architecture, which is easy to produce, reliable, and cost-effective..

Revealing Reaction Mechanisms of Nanoconfined Li₂S: Implications for Lithium-Sulfur Batteries [Hot Paper]

Z. Liu, H. Deng, W. Hu, F. Gao, S. Zhang, P.B. Balbuena and P. P. Mukherjee

Journal PaperPhysical Chemistry Chemical Physics, 20, 11713 (2018)

Abstract

Li₂S as an active material and designing nanostructured cathode host are considered as promising strategies to improve the performance of lithium-sulfur (Li-S) batteries. In this study, the reaction mechanisms during delithiation of nanoconfined Li₂S as active material, represented by a Li₂₀S₁₀ cluster, are examined by first-principle based calculations and analysis. Local reduction reactions and disproportionation reaction can be observed although the overall delithiation process is an oxidation reaction. Long-chain polysulfides can form as intermediate products, which however can bind to insoluble S_2- via Li atoms as mediators. Activating the charging process only requires an overpotential of 0.37 V if using Li₂₀S₁₀ as the active material. Sulfur allotropes longer than cyclo-S₈ are observed at the end of charge process. Although the discharge voltage of Li₂₀S₁₀ is only 1.27 V, it can still deliver an appreciable theoretical energy density of 1480 Wh/kg. This study also suggests that hole polarons, in Li₂₀S₁₀ and intermediate products, can serve as carriers to facilitate charge transport. This work provides new insights toward revealing detailed reaction mechanisms of nanoconfined Li₂S as an active material in the Li-S battery cathode.

Multiscale model reduction for pore-scale simulation of Li-ion batteries using GMsFEM

M. Vasilyeva, A. Mistry and P. P. Mukherjee

Journal Paper Journal of Computational and Applied Mathematics, 344, 73 (2018)

Abstract

In this work, we consider electrochemical processes for the pore-scale simulation of Lithium-ion batteries (LIBs). Mathematical model consists of the coupled system of the equations for the concentration and electric potential. We develop fine-scale approximation using discontinuous Galerkin approach, where interface condition is imposed weakly. We present novel multiscale model reduction technique based on the GMsFEM, where multiscale basis functions are constructed using information about variation of the medium at the micro level. We present numerical results for two cases of the boundary conditions and compare errors for different coarse grids for testing the proposed computational multiscale method. Numerical results show that the multiscale basis functions can efficiently capture the information of the fine-scale features of the medium with significant dimension reduction of the system and provide accurate solutions.

Roadblocks in Cation Diffusion Pathways: Implications of Phase Boundaries for Li-ion Diffusivity in an Intercalation Cathode Material

Y. Luo, L.R.D. Jesus, J.L. Andrews, A. Parija, N. Fleer, D. Juarez-Robles, P. P. Mukherjee and S. Banerjee

Journal Paper ACS Applied Materials and Interfaces, 10, 30901 (2018)

Abstract

Increasing intercalation of Li-ions brings about distortive structural transformations in several canonical intercalation hosts. Such phase transformations require the energy dissipative creation and motion of dislocations at the interface between the parent lattice and the nucleated Li-rich phase. Phase inhomogeneities within particles and across electrodes give rise to pronounced stress gradients, which can result in capacity fading. How such transformations alter Li-ion diffusivities remains much less explored. In this article, we use layered V2O5 as an intercalation host and examine the structural origins of the evolution of Li-ion diffusivities with phase progression upon electrochemical lithiation. Galvanostatic intermittent titration measurements show a greater than four orders of magnitude alteration of Li-ion diffusivity in V₂O₅ as a function of the extent of lithiation. Pronounced dips in Li-ion diffusivities are correlated with the presence of phase mixtures as determined by Raman spectroscopy and X-ray diffraction, whereas monophasic regimes correspond to the highest Li-ion diffusivity values measured within this range. First-principles density functional theory calculations confirm that the variations in Li-ion diffusivity do not stem from intrinsic differences in diffusion pathways across the different lithiated V₂O₅ phases, which despite differences in the local coordination environments of Li-ions show comparable migration barriers. Scanning transmission X-ray microscopy measurements indicate the stabilization of distinct domains reflecting the phase coexistence of multiple lithiated phases within individual actively intercalating particles. The results thus provide fundamental insight into the considerable ion transport penalties incurred as a result of phase boundaries formed within actively intercalating particles. The combination of electrochemical studies with ensemble structural characterization and single-particle X-ray imaging of phase boundaries demonstrates the profound impact of interfacial phenomena on macroscopic electrode properties.

Super-hierarchical Nickel-Vanadia Nanocomposites for Lithium Storage

Y. Yue, D. Juarez-Robles, P. P. Mukherjee and H. Liang

Journal PaperACS Applied Energy Materials, 1, 2056 (2018)

Abstract

New materials are critically needed for advanced energy storage devices due to the limited performance of currently-used electrode materials. We report an alternative approach to fabricate a novel type of nanostructured cathodes with a three-dimensional configuration that shows superior performance. A super-hierarchical Ni/Porous-Ni/V₂O₅ nanocomposite is designed and synthesized using a simple electrodeposition process followed by a hydrothermal treatment. Hierarchical V₂O₅ nanostructures are deposited directly on a Ni micro-channeled current collector. Morphological characterization shows that two-dimensional V₂O₅ nanosheets are uniformly distributed on the porous Ni substrate. A peony-like V₂O₅ microstructure arises having a diameter of ~4 μm. The super-hierarchical Ni/Porous-Ni/V₂O₅ nanocomposite exhibits superior electrochemical performance as a binder-free cathode. Its maximum reversible discharge capacity reaches 165.6 mAh g−1 at 0.2 C, which is higher than the theoretical capacity of bulk V₂O₅ cathodes. The capacity retains 90.9% and 72.4% after 100 cycles at 0.2 C and 500 cycles at 3.0 C, respectively. The stable rate capability is also confirmed. Our analysis indicates that such high-performance is attributed to the synergistic effects of: the hierarchical structure, micro-channeled Ni current collectors, two-dimensional V₂O₅ nanostructured active materials, and the binder-free processing. This research shows significant promise for use of super-hierarchical structures in future of rechargeable batteries.

Mesoscopic Modeling of Capillarity-Induced Two-Phase Transport in a Microfluidic Porous Structure

P. Randive, A. Dalal and P. P. Mukherjee

Journal Paper Transport in Porous Media, 122, 673 (2018)

Abstract

Mesoscopic modeling at the pore scale offers great promise in exploring the underlying structure transport performance of flow through porous media. The present work studies the fluid flow subjected to capillarity-induced resonance in porous media characterized by different porous structure and wettability. The effects of porosity and wettability on the displacement behavior of the fluid flow through porous media are discussed. The results are presented in the form of temporal evolution of percentage saturation and displacement of the fluid front through porous media. The present study reveals that the vibration in the form of acoustic excitation could be significant in the mobilization of fluid through the porous media. The dependence of displacement of the fluid on physicochemical parameters like wettability of the surface, frequency along with the porosity is analyzed. It was observed that the mean displacement of the fluid is more in the case of invading fluid with wetting phase where the driving force strength is not so dominant.

Vortex generators for active thermal management in lithium-ion battery systems

B. Mondal, C. Lopez, A. Verma, and P. P. Mukherjee

Journal PaperInternational Journal of Heat and Mass Transfer, 124, 800 (2018)

Abstract

The aim of the present study is to determine efficacy of using vortex generators in the cooling channels of a lithium-ion battery thermal management system (BTMS). Numerical simulations of a Li-ion battery module containing 20 prismatic lithium ion cells and associated cooling channels with four different winglet configurations were developed. This study examines the effects of vortex generators on the heat transfer performance of typical battery thermal management solutions. The performance of the BTMS is assessed over a Reynolds number range ( 65⩽Re⩽1650) based on the hydraulic diameter of a rectangular channel. Specialized software designed for studying heat transfer problems in lithium-ion batteries coupled with computational fluid dynamics was used to determine such effects. The performance of the different vortex generator configurations was compared in terms of the Nusselt number, maximum module temperature, and cell-to-cell temperature variation. The addition of vortex generators to the modeled BTMS has shown a significant increase in overall heat transfer of cooling channel, a decrease in the maximum cell temperature, and a lower temperature difference within the cells.

Probing the cooling effectiveness of phase change materials on lithium-ion battery thermal response under overcharge condition

P. Huang, A. Verma, D. Juarez-Robles, Q. Wang, P. P. Mukherjee, and J. Sun

Journal Paper Applied Thermal Engineering, 132, 521 (2018)

Abstract

Usage of phase change materials (PCM) can help reduce the safety risk during LIB operation. This work investigates the cooling effectiveness of PCM on lithium ion battery operation under overcharge scenario. Combined with adiabatic overcharge tests at 0.1, 0.2, 0.5, 1, 2 current rates (C-rate), the relationship of cell thermal performance and cooling efficacy with C-rates, thermal contact resistance, amount and melting temperature of PCM are analyzed by lumped model. Results indicate steep decline of cooling effectiveness with C-rate increase. Temperature difference between cell and PCM is stable below 1C, however, abrupt hikes are observed at higher C-rates. Effectiveness increase with PCM thickness is also seen up to a critical thickness of 3 mm beyond which minimal change is observed while thermal contact resistance is found to enlarge the temperature difference between cell and PCM during the melting process causing wide variability in cooling effectiveness magnitude. For similar latent heat and density material, low melting temperature PCM exhibits superior cooling characteristics as compared to its high temperature counterpart. The results contribute to enhanced understanding of the thermal performance of PCM and LIB during overcharge process under varying conditions.

Precipitation – Microstructure Interactions in the Li-Sulfur Battery Electrode

A. Mistry, and P. P. Mukherjee

Journal Paper Journal of Physical Chemistry C, 121, 26256 (2017)

Abstract

Formation and precipitation of insulating discharge products, such as Li₂S, in the lithium-sulfur (Li-S) battery cathode leads to deleterious performance decay. Physicochemical interactions underlying the cathode microstructure evolution due to precipitation are hitherto poorly understood. In this work, a mesoscale understanding of the microstructure – precipitate interplay owing to surface passivation and pore blockage is presented. Mesoporous, carbon-based cathode microstructures are examined for disparate precipitate morphology and growth. Pore-scale manifestation of the microstructural and transport limitations on the electrochemical performance is elucidated. Surface passivation and pore blockage effects are examined for complexations due to sulfur loading, electrolyte volume, pore size and precipitate morphology. This study provides critical insights into the underlying mesoscale physics and microstructural stochasticity on the Li-S battery performance.

Probing Impedance and Microstructure Evolution in Lithium-Sulfur Battery Electrodes

C.-F. Chen, A. Mistry, and P. P. Mukherjee

Journal Paper Journal of Physical Chemistry C, 121, 21206 (2017)

Abstract

Lithium–sulfur chemistry, despite being a promising candidate for energy storage due to its higher theoretical capacity, is faced with several critical challenges. Practical operation of Li–S batteries demonstrates lower capacity, poor rate capability, and insufficient cycle life, which can be related to the underlying physicochemical interactions at the electrodes. Typical carbon-based porous cathodes undergo coupled electrochemical, chemical, and microstructural evolution during operation. In this work, the mesoscale interaction resulting from the underlying chemical/electrochemical complexations and microstructural evolution is studied in order to elucidate the transient impedance behavior in Li–S battery mesoporous carbon cathodes. The discharge product (e.g., Li₂S) precipitation is shown to affect impedance evolution with correlational dependence on the porous cathode microstructure attributes. This mesoscale impedance analytics can be a valuable virtual probing tool for Li–S battery electrochemical performance.

Mesoscale Elucidation of Solid Electrolyte Interphase Layer Formation in Li-Ion Battery Anode

F. Hao, Z. Liu, P. Balbuena, and P. P. Mukherjee

Journal Paper Journal of Physical Chemistry C, 121, 26233 (2017)

Abstract

Capacity fade in lithium-ion batteries largely originates from the undesired electrolyte decomposition, which results in the formation of solid electrolyte interphase (SEI) and the anode surface passivation. In this work, a mesoscale interfacial modeling approach is developed to investigate the formation and growth of the SEI film on typical graphite based anode over several cycles. It is found that lithium diffusion kinetics in the SEI film significantly affects the SEI growth rate. Lower lithium diffusion barrier leads to higher growth rate. The present model demonstrates that the SEI thickness is a linear function of the square root of the charging time over long-time cycling. Growth of multi-component SEI film is also elucidated. It is found that the heterogeneity of the SEI film may lead to instability in lithium ion concentration distribution.

Mechanistic Analysis of Mechano-electrochemical Interaction in Silicon Electrodes with Surface Film

A. Verma, and P. P. Mukherjee

Journal Paper Journal of the Electrochemical Society, 164, A3570 (2017)

Abstract

High-capacity anode materials for lithium-ion batteries, such as silicon, are prone to large volume change during lithiation/delithiation which may cause particle cracking and disintegration, thereby resulting in severe capacity fade and reduction in cycle life. In this work, a stochastic analysis is presented in order to understand the mechano-electrochemical interaction in silicon active particles along with a surface film during cycling. Amorphous silicon particles exhibiting single-phase lithiation incur lower amount of cracking as compared to crystalline silicon particles exhibiting two-phase lithiation for the same degree of volumetric expansion. Rupture of the brittle surface film is observed for both amorphous and crystalline silicon particles and is attributed to the large volumetric expansion of the silicon active particle with lithiation. The mechanical property of the surface film plays an important role in determining the amount of degradation in the particle/film assembly. A strategy to ameliorate particle cracking in silicon active particles is proposed.

Galvanostatic Intermittent Titration and Performance Based Analysis of LiNi_0.5Co_0.2Mn_0.3O₂ Cathode

A. Verma, K. Smith, S. Santhanagopalan, D. Abraham, K. P. Yao, and P. P. Mukherjee

Journal Paper Journal of Electrochemical Society, 164, A3380 (2017)

Abstract

Galvanostatic intermittent titration technique (GITT) – a popular method for characterizing kinetic and transport properties of battery electrodes – is predicated on the proper evaluation of electrode active area. LiNi_0.5044Co_0.1986Mn_0.2970O₂ (NCM523) material exhibits a complex morphology in which sub-micron primary particles aggregate to form secondary particle agglomerates. This work proposes a new active area formulation for primary/secondary particle agglomerate materials to better mimic the morphology of NCM523 electrodes. This formulation is then coupled with macro-homogeneous models to simulate GITT and half-cell performance of NCM523 electrodes. Subsequently, the model results are compared against the experimental results to refine the area formulation. A single parameter, the surface roughness factor, is proposed to mimic the change in interfacial area, diffusivity and exchange current density simultaneously and detailed modeling results are presented to provide valuable insights into the efficacy of the formulation.

Hole Polaron Diffusion in the Final Discharge Product of Lithium-Sulfur Batteries

Z. Liu, P. Balbuena, and P. P. Mukherjee

Journal Paper Journal of Physical Chemistry C, 121, 17169 (2017)

Abstract

Poor electronic conductivity of bulk lithium sulfide (Li₂S) is a critical challenge for the debilitating performance of the lithium–sulfur battery. This study focuses on investigating the thermodynamic and kinetic properties of native defects in Li₂S based on a first-principles approach. It is found that the hole polaron p⁺ can form in Li₂S by removing a 3p electron from an S^2– anion. The p⁺ diffusion barrier is only 90 meV, which is much lower than the Li vacancy (V_Li^-) diffusion barrier. Hence p⁺ has the potential to serve as a charge carrier in the discharge product. Once the vacancy–polaron complex (V_Li^- – 2p⁺) forms, the charge transport will be hindered due to the relatively higher diffusion barrier of the complex. Heteroatom dopants, which can decrease the p⁺ formation energy and increase V_Li^- formation energy, are expected to be introduced to the discharge product to improve the electronic conductivity.

Mesoscale Elucidation of Surface Passivation in the Lithium-Sulfur Battery Cathode

Z. Liu and P. P. Mukherjee

Journal Paper ACS Applied Materials and Interfaces, 9, 5263 (2017)

Abstract

The cathode surface passivation caused by Li₂S precipitation adversely affects the performance of lithium–sulfur (Li–S) batteries. Li₂S precipitation is a complicated mesoscale process involving adsorption, desorption and diffusion kinetics, which are affected profoundly by the reactant concentration and operating temperature. In this work, a mesoscale interfacial model is presented to study the growth of Li₂S film on carbon cathode surface. Li₂S film growth experiences nucleation, isolated Li₂S island growth and island coalescence. The slow adsorption rate at small S^2- concentration inhibits the formation of nucleation seeds and the lateral growth of Li₂S islands, which deters surface passivation. An appropriate operating temperature, especially in the medium-to-high temperature range, can also defer surface passivation. Fewer Li₂S nucleation seeds form in such an operating temperature range, thereby facilitating heterogeneous growth and potentially inhibiting the lateral growth of the Li₂S film, which may ultimately result in reduced surface passivation. The high specific surface area of the cathode microstructure is expected to mitigate the surface passivation.

Revealing Charge Transport Mechanisms in Li₂S₂ for Li-Sulfur Batteries

Z. Liu, P. Balbuena, and P. P. Mukherjee

Journal Paper Journal of Physical Chemistry Letters, 8, 1324 (2017)

Abstract

Besides lithium sulfide (Li₂S), lithium persulfide (Li₂S₂) is another solid discharge product in lithium–sulfur (Li–S) batteries. Revealing the charge transport mechanism in the discharge products is important for developing an effective strategy to improve the performance of Li–S batteries. Li₂S₂ cannot transport free electrons due to its wide bandgap between the valence band maximum (VBM) and conduction band minimum (CBM). However, electron polarons (p^-) and hole polarons (p⁺) can appear in solid Li₂S₂ due to the unique molecular orbital structure of the S₂^2- anion. The thermodynamic and kinetic properties of native defects are investigated. It is found that negatively charged Li vacancies (V_Li^-) and p⁺ are the main native defects with a low formation energy of 0.77 eV. The predominant charge carrier is p⁺ because p⁺ has a high mobility. The electronic conductivity related to p⁺ diffusion is dependent on temperature, and high temperatures are preferred to increase the conductivity.

Evaporation Induced Nanoparticle – Binder Interaction in Electrode Film Formation

Z. Liu, D. L. Wood III, and P. P. Mukherjee

Journal Paper Physical Chemistry Chemical Physics, 19, 10051 (2017)

Abstract

Processing induced nanoparticle agglomeration and binder distribution affect the electrode microstructure formation and corresponding electrochemical performance in lithium-ion batteries. In the present study, stochastic dynamics computations based on a morphologically detailed mesoscale model are performed to illustrate the microstructural variability of electrode films affected by the evaporation condition (drying temperature) and the binder length (molecular weight). Micropores are observed at the surface of the electrode film when dried at a lower temperature. The pore formation depth tends to increase as the binder length increases. The solvent chemical potential also affects the surface topography of the electrode film. The solvent with higher volatility (more negative chemical potential) tends to produce more micropores. A lower drying temperature is beneficial for improving the electronic conductivity of the porous electrode film due to the better distribution of the conductive additive nanoparticles on and around the active particles, thereby facilitating the electron transport network formation. Agglomeration between active material nanoparticles can also be mitigated at a lower drying temperature. Additionally, better adhesion of the porous electrode film can be achieved due to preferential localization of the binder on the substrate at relatively low-temperature evaporation.

Mechanistic Understanding of the Role of Evaporation in Electrode Processing

M. Stein IV, A. Mistry, and P. P. Mukherjee

Journal Paper Journal of the Electrochemical Society, 164, A1616 (2017).

Abstract

Electrode processing based on the state-of-the-art materials represents a scientific opportunity toward a cost-effective measure for improving the lithium-ion battery performance. In this regard, perhaps the most important is the drying step in a typical non-aqueous based slurry processing which can profoundly impact the electrode microstructure and hence performance. Solvent evaporation during drying plays a critical role in the redistribution of the particulate phases consisting of active particle, conductive additive and binder. In this work, we attempt to provide a mechanistic understanding of the role of solvent evaporation on the electrode characteristics and performance via a combined experimental and theoretical analysis. This study elucidates that a non-uniform distribution of the constituent phases, especially the relatively mobile conductive additive and binder, can develop which depends on the solvent evaporation, particle diffusion and sedimentation attributes. Experimental results and theoretical analysis reveal the impact of evaporation rate on the conductive additive and binder distribution in the electrode microstructure and resulting electrochemical performance. Our analysis has shown that a slower two-stage drying, as opposed to a high-rate single-stage drying, allows for a favorable distribution of binder and conductive additive, thus reducing internal cell resistance and improving electrochemical performance.

Probing the Role of Electrode Microstructure in the Lithium-ion Battery Thermal Behavior

C.-F. Chen, A. Verma, and P. P. Mukherjee

Journal Paper Journal of the Electrochemical Society, 164, E3146 (2017)

Abstract

Safety and performance of lithium-ion batteries over a wide temperature window are of paramount importance, especially for electric vehicles. The safety concerns are predicated on the thermal behavior as the occurrence of local temperature excursions may lead to thermal runaway. In this work, the role of electrode microstructure and implications on the cell thermal behavior are examined. A microstructure-aware electrochemical-thermal coupled model has been proposed, which delineates the electrode-level thermal complexations due to the structure-transport-electrochemistry interactions. Detailed analysis of the spatio-temporal variation of the heat generation rates (ohmic, reaction and reversible contributions) for different electrode microstructural configurations is presented to explain the dominant factors causing temperature rise. The tradeoff between the cell performance and safety is discussed from an electrode-level, bottom-up view point. This study aims to provide valuable insights into potentially tuning electrode-level structural features as an internal safety switch toward limiting the Li-ion cell temperature rise during operation.

Impedance Evolution Characteristics in Lithium-ion Batteries

D. Juarez-Robles, C. F. Chen, Y. Barsukov, and P. P. Mukherjee

Journal Paper Journal of the Electrochemical Society, 164, A837 (2017)

Abstract

A three-electrode cell can be a useful tool for measuring electrode-level and cell-level electrochemical characteristics, such as the impedance response and potential variations in lithium-ion cells. In this paper, a reliable three-electrode coin cell setup is introduced, which improves the stability and accuracy of electrochemical measurements by modifying the electrode alignment and employing Li₄Ti₅O₁₂ as a reference electrode. An important highlight is the ability to obtain impedance evolution characteristics at different depth of discharge (DOD) for an individual electrode and the full cell based on both the frequency response analysis and the carrier function Laplace transform characteristics. The reliability of the proposed modified three-electrode coin cell setup has been validated by analyzing the impedance response of symmetric and full cells, and the voltage profiles of the full cell along with the positive/negative electrode contributions. The importance of the resistance contributions from the negative and positive electrodes to the full cell impedance evolution at different DOD is highlighted.

Mesoscale Physicochemical Interactions in Lithium–Sulfur Batteries: Progress and Perspective

Z. Liu, A. Mistry, and P. P. Mukherjee

Journal Paper Journal of Electrochemical Energy Conversion and Storage, 15, 010802 (2017)

Abstract

The shuttle effect and poor conductivity of the discharge products are among the primary impediments and scientific challenges for lithium–sulfur batteries. The lithium–sulfur battery is a complex energy storage system, which involves multistep electrochemical reactions, insoluble polysulfide precipitation in the cathode, soluble polysulfide transport, and self-discharge caused by chemical reactions between polysulfides and Li metal anode. These phenomena happen at different length and time-scales and are difficult to be entirely gauged by experimental techniques. In this paper, we reviewed the multiscale modeling studies on lithium–sulfur batteries: (1) the atomistic simulations were employed to seek alternative materials for mitigating the shuttle effect; (2) the growth kinetics of Li₂S film and corresponding surface passivation were investigated by the interfacial model based on findings from atomistic simulations; (3) the nature of Li₂S₂, which is the only solid intermediate product, was revealed by the density functional theory simulation; and (4) macroscale models were developed to analyze the effect of reaction kinetics, sulfur loading, and transport properties on the cell performance. The challenge for the multiscale modeling approach is translating the microscopic information from atomistic simulations and interfacial model into the meso-/macroscale model for accurately predicting the cell performance.

Mesoscale Evaluation of Titanium Silicide Monolayer as a Cathode Host Material in Lithium-Sulfur Batteries

Z. Liu, P. Balbuena, and P. P. Mukherjee

Journal Paper Journal of The Minerals, Metals & Materials Society, 69, 1532 (2017)

Abstract

Two-dimensional materials are competitive candidates as cathode materials in lithium–sulfur batteries for immobilizing soluble polysulfides and mitigating the shuttle effect. In this study, a mesoscale modeling approach, which combines first-principles simulation and kinetic Monte Carlo simulation, is employed to evaluate titanium silicide (Ti₂Si and TiSi₂) monolayers as potential host materials in lithium–sulfur batteries. It is found that the Ti₂Si monolayer has much stronger affinities to Li₂S_x (x = 1, 2, 4) molecules than the TiSi₂ monolayer. Also, Ti₂Si can facilitate the dissociation of long-chain Li₂S₄ to LiS₂. On the other hand, TiSi₂ can only provide a weak chemical interaction for trapping soluble Li₂S₄. Therefore, the Ti₂Si monolayer can be considered as the next-generation cathode material for lithium–sulfur batteries. However, the strong interaction between Ti₂Si and Li₂S also causes fast surface passivation. How to control the Li₂S precipitation on Ti₂Si should be answered by further studies.

Exploring the Efficacy of Nanofluids for Lithium-Ion Battery Thermal Management

B. Mondal, C. Lopez, and P. P. Mukherjee

Journal Paper International Journal of Heat and Mass Transfer, 112, 779 (2017)

Abstract

Thermal implications related to heat generation and potential temperature excursions during operation in lithium-ion batteries are of critical importance for electric vehicle safety, performance and life. Concurrently, appropriate thermal management strategies for lithium-ion batteries are crucial to maintain cell temperatures within a desired range. Different battery thermal management strategies have been proposed, each with various advantages and disadvantages depending on the applications. This work proposes the use of nanofluids, colloidal suspensions of nanoparticles in a base fluid, as a heat transfer fluid for active thermal management. To analyze the efficacy of nanofluids for thermal management in lithium-ion batteries, different nanofluids and their effect on the temperature distribution within typical battery modules are investigated for two different flow configurations. In particular, the study is focused on battery performance, heat dissipation capability under high discharge rates and ambient temperatures, and design considerations relevant to electric vehicle applications. This study underscores the potential of this innovative thermal management technique toward effective thermal safety without performance penalty of lithium-ion batteries for vehicle electrification.

Enabling Aqueous Processing for Crack-Free Thick Electrodes

Z. Du, K. Rollag, J. Li, S. J. An, M. Wood, Y. Sheng, P. P. Mukherjee, C. Daniel, and D. L. Wood III

Journal Paper Journal of Power Sources, 354, 200 (2017)

Abstract

Aqueous processing of thick electrodes for Li-ion cells promises to increase energy density due to increased volume fraction of active materials, and to reduce cost due to the elimination of the toxic solvents. This work reports the processing and characterization of aqueous processed electrodes with high areal loading and associated full pouch cell performance. Cracking of the electrode coatings becomes a critical issue for aqueous processing of the positive electrode as areal loading increases above 20–25 mg/cm² (~4 mAh/cm²). Crack initiation and propagation, which was observed during drying via optical microscopy, is related to the build-up of capillary pressure during the drying process. The surface tension of water was reduced by the addition of isopropyl alcohol (IPA), which led to improved wettability and decreased capillary pressure during drying. The critical thickness (areal loading) without cracking increased gradually with increasing IPA content. The electrochemical performance was evaluated in pouch cells. Electrodes processed with water/IPA (80/20 wt%) mixture exhibited good structural integrity with good rate performance and cycling performance.

Transport-Geometry Interactions in Li-Ion Cathode Materials Imaged Using X-ray Nanotomography

G. Nelson, L. Ausderau, J. R. Buckley, S. Y. Shin, A. Mistry, P. P. Mukherjee, and V. De Andrade

Journal Paper Journal of Electrochemical Society, 164, A1412 (2017)

Abstract

Forging a stronger connection between mesoscale geometry, performance, and processing techniques can realize practical approaches for controlling battery performance using mesoscale geometry. To this end, 3D X-ray imaging, microstructural characterization, and computational modeling have been applied to analyze the intercalation behavior of Li(Ni_1/3Mn_1/3Co_1/3)O₂(NMC) cathodes. Samples extracted from pristine cathodes were imaged using X-ray nanotomography. Active material particle geometry was characterized and compared for samples from four cathodes treated with distinct preparation steps. Significant size reduction was observed in calendered and ball milled samples, and distinct differences were observed in particle morphology. Tomographic data for a representative particle was applied in a numerical transport model to assess the effect of particle geometry on intercalation. This assessment proved critical in determining an appropriate estimate of particle size for defining dimensionless parameters that permit rapid estimation of intercalation time. Defining an effective particle radius based on a sphere of equivalent surface area to volume ratio was found to provide the most accurate estimate of intercalation time. Informed by this analysis, dimensionless parameters were used to assess intercalation behavior of the cathode materials. This assessment revealed a substantial change in rate capability connected to particle size reductions achieved in calendering and ball milling.

Hierarchical Structured Cu/Ni/TiO₂ Nanocomposites as Electrodes for Lithium-Ion Batteries

Y. Yue, D. Juarez-Robles, Y. Chen, L. Ma, W. C. H. Kuo, P. P. Mukherjee, and H. Liang

Journal Paper ACS Applied Materials and Interfaces, 9, 28695 (2017)

Abstract

The electrochemical performance of anodes made of transition metal oxides (TMOs) in lithium-ion batteries (LIBs) often suffers from their chemical and mechanical instability. In this research, a novel electrode with a hierarchical current collector for TMO active materials is successfully fabricated. It consists of porous nickel as current collector on a copper substrate. The copper has vertically aligned microchannels. Anatase titanium dioxide (TiO₂) nanoparticles of ∼100 nm are directly synthesized and cast on the porous Ni using a one-step process. Characterization indicates that this electrode exhibits excellent performance in terms of capacity, reliable rate, and long cyclic stability. The maximum insertion coefficient for the reaction product of Li_xTiO₂ is ∼0.85, a desirable value as an anode of LIBs. Cross-sectional SEM and EDS analysis confirmed the uniform and stable distribution of nanosized TiO₂ nanoparticles inside the Ni microchannels during cycling. This is due to the synergistic effect of nano-TiO₂ and the hierarchical Cu/Ni current collector. The advantages of the Cu/Ni/TiO₂ anode include enhanced activity of electrochemical reactions, shortened lithium ion diffusion pathways, ultrahigh specific surface area, effective accommodation of volume changes of TiO₂ nanoparticles, and optimized routes for electrons transport.

State-of-the-Art and Future Research Needs for Multiscale Analysis of Li-Ion Cells

K. Shah, N. Balsara, S. Banerjee, M. Chintapalli, A. P. Cocco, W. K. S. Chiu, I. Lahiri, S. Martha, A. Mistry, P. P. Mukherjee, V. Ramadesigan, C. Sharma, V. Subramanian, S. Mitra, and A. Jain

Journal Paper Journal of Electrochemical Energy Conversion and Storage, 14, 020801 (2017)

Abstract

The performance, safety, and reliability of Li-ion batteries are determined by a complex set of multiphysics, multiscale phenomena that must be holistically studied and optimized. This paper provides a summary of the state of the art in a variety of research fields related to Li-ion battery materials, processes, and systems. The material presented here is based on a series of discussions at a recently concluded bilateral workshop in which researchers and students from India and the U.S. participated. It is expected that this summary will help understand the complex nature of Li-ion batteries and help highlight the critical directions for future research.

Stochastics of Diffusion Induced Damage in Intercalation Materials

P. Barai and P. P. Mukherjee

Journal Paper Materials Research Express, 3, 104001 (2016)

Abstract

Fundamental understanding of the underlying diffusion-mechanics interplay in the intercalation electrode materials is critical toward improved life and performance of lithium-ion batteries for electric vehicles. Especially, diffusion induced microcrack formation in brittle, intercalation active materials, with emphasis on the grain/grain-boundary (GB) level implications, has been fundamentally investigated based on a stochastic modeling approach. Quasistatic damage evolution has been analyzed under lithium concentration gradient induced stress. Scaling of total amount of microcrack formation shows a power law variation with respect to the system size. Difference between the global and local roughness exponent indicates the existence of anomalous scaling. The deterioration of stiffness with respect to microcrack density displays two distinct regions of damage propagation; namely, diffused damage evolution and stress concentration driven localized crack propagation. Polycrystalline material microstructures with different grain sizes have been considered to study the diffusion-induced fracture in grain and GB regions. Intergranular crack paths are observed within microstructures containing softer GB region, whereas, transgranular crack paths have been observed in microstructures with relatively strong GB region. Increased tortuosity of the spanning crack has been attributed as the reason behind attaining increased fracture strength in polycrystalline materials with smaller grain sizes.

Mechano-electrochemical Interaction Gives Rise to Strain Relaxation in Sn Electrodes

P. Barai, B. Huang, S. Dillon, and P. P. Mukherjee

Journal Paper Journal of the Electrochemical Society, 163, A1120 (2016)

Abstract

Tin (Sn) anode active particles were electrochemically lithiated during simultaneous imaging in a scanning electron microscope. Relationships among the reaction mechanism, active particle local strain rate, particle size, and microcrack formation are elucidated to demonstrate the importance of strain relaxation in the mechano-electrochemical interaction in Sn-based electrodes under electrochemical cycling. At low rates of operation, due to significant creep relaxation, large Sn active particles, of size 1 μm, exhibit no significant surface crack formation. Microcrack formation within Sn active particles occurs due to two different mechanisms: (i) large concentration gradient induced stress at the two-phase interface, and (ii) high volume expansion induced stress at the surface of the active particles. From the present study, it can be concluded that majority of the microcracks evolve at or near the particle surface due to high volume expansion induced tension. Concentration gradient induced damage prevails near the center of the active particle, though significantly smaller in magnitude. Comparison with experimental results indicates that at operating conditions of C/2, even 500 nm sized Sn active particles remain free from surface crack formation, which emphasizes the importance of creep relaxation. A phase map has been developed to demonstrate the preferred mechano-electrochemical window of operation of Sn-based electrodes.

Mechanistic Evaluation of Li_xO_y Formation on δ-MnO₂ in Non-Aqueous Li-air Batteries

Z. Liu, L. De Jesus, S. Banerjee, and P. P. Mukherjee

Journal Paper ACS Applied Materials and Interfaces, 8, 23028 (2016)

Abstract

Transition metal oxides are usually used as catalysts in the air cathode of lithium–air (Li–air) batteries. This study elucidates the mechanistic origin of the oxygen reduction reaction catalyzed by δ-MnO₂ monolayers and maps the conditions for Li₂O₂ growth using a combination of first-principles calculations and mesoscale modeling. The MnO₂ monolayer, in the absence of an applied potential, preferentially reacts with a Li atom instead of an O₂ molecule to initiate the formation of LiO₂. The oxygen reduction products (LiO₂, Li₂O₂, and Li₂O molecules) strongly interact with the MnO₂ monolayer via the stabilization of Li–O chemical bonds with lattice oxygen atoms. As compared to the disproportionation reaction, direct lithiation reactions are the primary contributors to the stabilization of Li₂O₂ on the MnO₂ monolayer. The energy profiles of (Li₂O₂)₂ and (Li₂O)₂ nucleation on δ-MnO₂ monolayer during the discharge process demonstrate that Li₂O₂ is the predominant discharge product and that further reduction to Li₂O is inhibited by the high overpotential of 1.21 V. Interface structures have been examined to study the interaction between the Li₂O₂ and MnO₂ layers. This study demonstrates that a Li₂O₂ film can be homogeneously deposited onto δ-MnO₂ and that the Li₂O₂/MnO₂ interface acts as an electrical conductor. A mesoscale model, developed based on findings from the first-principles calculations, further shows that Li₂O₂ is the primary product of electrochemical reactions when the applied potential is smaller than 2.4 V.

An Overview of Degradation Phenomena Modeling in Lithium-ion Battery Electrodes

C.-F. Chen, P. Barai, and P. P. Mukherjee

Journal Paper Current Opinion in Chemical Engineering, 13, 82 (2016)

Abstract

The formation of solid electrolyte interphase and diffusion induced microcrack in the lithium-ion battery electrodes are predominant degradation mechanisms, which cause capacity fade and cell impedance rise. Physics-based degradation models reveal new insights and allow fundamental understanding of the transport–chemistry–mechanics interactions. In addition, simulation-based diagnostics (e.g. electrochemical impedance spectroscopy, acoustic emission characteristics) can enable virtual probing and interrogation of electrode degradation behavior. This short perspective highlights the recent progress in physics-based degradation modeling and virtual diagnostics in lithium-ion battery electrodes.

Modeling of Mesoscale Variability in Biofilm Shear Behavior

P. Barai, A. Kumar, and P. P. Mukherjee

Journal Paper PLOS ONE, 11, e0165593 (2016)

Abstract

Formation of bacterial colonies as biofilm on the surface/interface of various objects has the potential to impact not only human health and disease but also energy and environmental considerations. Biofilms can be regarded as soft materials, and comprehension of their shear response to external forces is a key element to the fundamental understanding. A mesoscale model has been presented in this article based on digitization of a biofilm microstructure. Its response under externally applied shear load is analyzed. Strain stiffening type behavior is readily observed under high strain loads due to the unfolding of chains within soft polymeric substrate. Sustained shear loading of the biofilm network results in strain localization along the diagonal direction. Rupture of the soft polymeric matrix can potentially reduce the intercellular interaction between the bacterial cells. Evolution of stiffness within the biofilm network under shear reveals two regimes: a) initial increase in stiffness due to strain stiffening of polymer matrix, and b) eventual reduction in stiffness because of tear in polymeric substrate.

Analysis of Long-range Interaction in Lithium-ion Battery Electrodes

A. Mistry, D. Juarez-Robles, M. Stein IV, K. Smith, and P. P. Mukherjee

Journal Paper Journal of Electrochemical Energy Conversion and Storage, 13, 031006 (2016)

Abstract

The lithium-ion battery electrode represents a complex porous composite, consisting of multiple phases including active material, conductive additive and polymeric binder. This study proposes a mesoscale model to probe the effects of the cathode composition, e.g. the ratio of active material, conductive additive and binder content, on the electrochemical properties and performance. The results reveal a complex non-monotonic behavior in the effective electrical conductivity as the amount of conductive additive is increased. Insufficient electronic conductivity of the electrode limits the cell operation to lower currents. Once sufficient electron conduction (i.e., percolation) is achieved, the rate performance can be a strong function of ion-blockage effect and pore phase transport resistance. Even for the same porosity, different arrangements of the solid phases may lead to notable difference in the cell performance, which highlights the need for accurate microstructural characterization and composite electrode preparation strategies.

Evaluation of Combined Active and Passive Thermal Management Strategies for Lithium-Ion Batteries

C. Lopez, J. Jeevarajan, and P.P. Mukherjee

Journal Paper Journal of Electrochemical Energy Conversion and Storage, 13, 031007 (2016)

Abstract

Lithium-ion batteries are the most commonly used portable energy storage technology due to their relatively high specific energy and power, but face thermal issues that raise safety concerns, particularly in automotive and aerospace applications. In these environments, there is zero tolerance for catastrophic failures such as fire or cell rupture, making thermal management a strict requirement to mitigate thermal runaway potential. The optimum configurations for such thermal management systems are dependent on both the thermo-electrochemical properties of the batteries and operating conditions/engineering constraints. The aim of this study is to determine the effect of various combined active (liquid heat exchanger) and passive (phase change material) thermal management techniques on cell temperatures and thermal balancing. The cell configuration and volume/weight constraints have important roles in optimizing the thermal management technique, particularly when utilizing both active and passive systems together. A computational modeling study including conjugate heat transfer and fluid dynamics coupled with thermo-electrochemical dynamics is performed to investigate design trade-offs in lithium-ion battery thermal management strategies. It was found that phase change material properties and cell spacing have a significant effect on the maximum and gradient of temperature in a module cooled by combined active and passive thermal management systems.

Probing the Effect of High Energy Ball Milling on the Structure and Properties of LiNi_1/3Mn_1/3Co_1/3O₂ Cathodes for Li-Ion Batteries

M. Stein IV, C.-F. Chen, M. Mullings, D. Jaime, A. Zaleski, P. P. Mukherjee, and C. P. Rhodes

Journal Paper Journal of Electrochemical Energy Conversion and Storage, 13, 031001 (2016)

Abstract

Particle size plays an important role in the electrochemical performance of cathodes for lithium-ion (Li-ion) batteries. High energy planetary ball milling of LiNi_1/3Mn_1/3Co_1/3O₂ (NMC) cathode materials was investigated as a route to reduce the particle size and improve the electrochemical performance. The effect of ball milling times, milling speeds, and composition on the structure and properties of NMC cathodes was determined. X-ray diffraction analysis showed that ball milling decreased primary particle (crystallite) size by up to 29%, and the crystallite size was correlated with the milling time and milling speed. Using relatively mild milling conditions that provided an intermediate crystallite size, cathodes with higher capacities, improved rate capabilities, and improved capacity retention were obtained within 14 μm-thick electrode configurations. High milling speeds and long milling times not only resulted in smaller crystallite sizes but also lowered electrochemical performance. Beyond reduction in crystallite size, ball milling was found to increase the interfacial charge transfer resistance, lower the electrical conductivity, and produce aggregates that influenced performance. Computations support that electrolyte diffusivity within the cathode and film thickness play a significant role in the electrode performance. This study shows that cathodes with improved performance are obtained through use of mild ball milling conditions and appropriately designed electrodes that optimize the multiple transport phenomena involved in electrochemical charge storage materials.

Computational Studies of Interfacial Reactions at Anode Materials: Initial Stages of the Solid-Electrolyte-Interphase Layer Formation

G. Ramos-Sanchez, F. A. Soto, J. M. Martinez de la Hoz, Z. Liu, P. P. Mukherjee, F. El-Mellouhi, J. M. Seminario, and P. B. Balbuena

Journal Paper Journal of Electrochemical Energy Conversion and Storage, 13, 031002 (2016)

Abstract

Understanding interfacial phenomena such as ion and electron transport at dynamic interfaces is crucial for revolutionizing the development of materials and devices for energy-related applications. Moreover, advances in this field would enhance the progress of related electrochemical interfacial problems in biology, medicine, electronics, and photonics, among others. Although significant progress is taking place through in situ experimentation, modeling has emerged as the ideal complement to investigate details at the electronic and atomistic levels, which are more difficult or impossible to be captured with current experimental techniques. Among the most important interfacial phenomena, side reactions occurring at the surface of the negative electrodes of Li-ion batteries, due to the electrochemical instability of the electrolyte, result in the formation of a solid-electrolyte interphase layer (SEI). In this work, we briefly review the main mechanisms associated with SEI reduction reactions of aprotic organic solvents studied by quantum mechanical methods. We then report the results of a Kinetic Monte Carlo method to understand the initial stages of SEI growth.

Poromechanical Effect in the Lithium-Sulfur Battery Cathode

P. Barai, A. Mistry, and P. P. Mukherjee

Journal Paper Extreme Mechanics Letters, 9, 359 (2016)

Abstract

In lithium-sulfur (Li-S) batteries, during discharge, solid sulfur (S_8(s)) gets dissolved and undergoes successive reduction and finally precipitates as lithium sulfide (Li₂S) in a typical carbon-based, porous cathode. Deposition of Li₂S leads to 80% volume expansion compared to solid S_8(s). During the dissolution-precipitation process, the total volume change of the electrolyte in the pore space can be attributed to two factors: (a) precipitation/dissolution of the solid sulfur phase; and (b) the cathode microstructure shrinks or swells to accommodate the changes in the pore volume resulting from the electrolyte induced hydrostatic pressure. Current lithium-sulfur performance models neglect this contribution. In this work, a computational methodology has been developed to quantify the impact of precipitation induced volume change, pore morphology and confinement attributes in a Li-S cathode. Impact of volume expansion on cell voltage has also been analyzed using a performance model. It is found that the poromechanical interaction significantly affects the second voltage plateau. Cathode microstructures with relatively smaller pores tend to experience less volume expansion, for the same operating conditions. It has been found that non-uniform precipitation may lead to significant pore confinement, which has the potential to cause microcrack formation in the pore walls of a typical carbon-based cathode microstructure.

Mechano-Electrochemical Stochastics in High-Capacity Electrodes for Energy Storage

P. Barai and P. P. Mukherjee

Journal Paper Journal of the Electrochemical Society, 163, A1120 (2016)

Abstract

High-capacity anode materials (such as, silicon) are of critical importance for lithium-ion batteries aimed at achieving longer drive range for electric vehicles. Large lithium retention in these alloying materials is, however, accompanied by high volume expansion, which results in severe mechanical degradation and capacity decay. The inherently coupled mechano-electrochemical stochastics is elucidated in this work. A stochastic computational methodology has been developed to capture the large deformation and mechanical degradation in high-capacity anode materials. Lithiation and delithiation in such active particles follow a two-phase diffusive interface formation and propagation. Mechano-electrochemical interactions lead to different tensile forces acting on the active particle that may lead to microcrack formation. In this study, we have demonstrated that: (a) concentration gradient induced stress at the two-phase interface does not lead to severe mechanical degradation; and (b) large volume expansion induced tensile force at the particle surface actually gives rise to multiple spanning crack formation and further propagation during delithiation. Anode materials with higher partial molar volume of the lithiated phase can lead to enhanced mechanical degradation. Functionally graded materials, with reduced elastic modulus near the surface, hold potential for significant reduction in crack formation.

Scaling Relations for Intercalation Induced Damage in Electrodes

C.-F. Chen, P. Barai, K. Smith and P. P. Mukherjee

Journal PaperElectrochimica Acta, 204, 31 (2016)

Abstract

Mechanical degradation, owing to intercalation induced stress and microcrack formation, is a key contributor to the electrode performance decay in lithium-ion batteries (LIBs). The stress generation and formation of microcracks are caused by the solid state diffusion of lithium in the active particles. In this work, scaling relations are constructed for diffusion induced damage in intercalation electrodes based on an extensive set of numerical experiments with particle-level description of microcrack formation under disparate operating and cycling conditions, such as temperature, particle size, C-rate, and drive cycle. The microcrack formation and evolution in active particles is simulated based on a stochastic methodology. A reduced order scaling law is constructed based on an extensive set of data from the numerical experiments. The scaling relations include combinatorial constructs of concentration gradient, cumulative strain energy, and microcrack formation. The reduced order relations are further employed to study the influence of mechanical degradation on cell performance and validated against the high order model for the case of damage evolution during variable current vehicle drive cycle profiles.

Evaluating Silicene as a Potential Cathode Host to Immobilize Polysulfides in Lithium-Sulfur Batteries

Z. Liu, P. Balbuena, and P. P. Mukherjee

Journal Paper Journal of Coordination Chemistry, 69, 11 (2016)

Abstract

The internal shuttle effect caused by polysulfides dissolution and migration negatively impacts the lithium-sulfur battery performance. In this work, a mesoscale simulation strategy, which involves atomistic calculation and coarse-grained molecular modeling, is employed to evaluate silicene as a potential cathode host material to immobilize polysulfides. Adsorption energies of insoluble polysulfides (Li₂S_x with x = 1, 2) and soluble polysulfide Li₂S₄ on pristine and doped silicene sheets are calculated. Results show that the adsorption is thermodynamically favorable and N-doped silicene is helpful in trapping intermediate discharge products, Li₂S₂ and Li₂S₄. The dissociation and reduction of long-chain polysulfides to short-chain polysulfides are observed. Electronic structure analysis shows that Li₂S_x molecules interact with silicene via strong chemical bonds. The atomistic structure evolution of Li₂S layer formation on silicene is also investigated in this study. It is found that Li₂S (110) layer forms first and then it is converted to Li₂S (111) layer by introducing more Li₂S molecules to the substrate. Li₂S (111)/silicene interfacial structure is thermodynamically stable and the interaction is dominated by Li-Si bonds. A coarse-grained model is developed to study and compare the growth of Li₂S on silicene and graphene. It is found that the Li₂S induced surface coverage is faster on silicene than on graphene, which indicates that a silicene-based cathode host will experience more acute surface passivation, which will adversely affect cathode performance.

Li₂S Film Formation on Lithium Anode Surface of Li-S Batteries

Z. Liu, S. Bertolini, P. Balbuena and P. P. Mukherjee

Journal Paper ACS Applied Materials & Interfaces, 8, 4700 (2016)

Abstract

The precipitation of lithium sulfide (Li₂S) on the Li metal anode surface adversely impacts the performance of lithium–sulfur (Li₂S) batteries. In this study, a first-principles approach including density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations is employed to theoretically elucidate the Li₂S/Li metal surface interactions and the nucleation and growth of a Li₂S film on the anode surface due to long-chain polysulfide decomposition during battery operation. DFT analyses of the energetic properties and electronic structures demonstrate that a single molecule adsorption on Li surface releases energy forming chemical bonds between the S atoms and Li atoms from the anode surface. Reaction pathways of the Li₂S film formation on Li metal surfaces are investigated based on DFT calculations. It is found that a distorted Li₂S (111) plane forms on a Li(110) surface and a perfect Li₂S (111) plane forms on a Li(111) surface. The total energy of the system decreases along the reaction pathway; hence Li₂S film formation on the Li anode surface is thermodynamically favorable. The calculated difference charge density of the Li₂S film/Li surface suggests that the precipitated film would interact with the Li anode via strong chemical bonds. AIMD simulations reveal the role of the anode surface structure and the origin of the Li₂S formation via decomposition of Li₂S₈ polysulfide species formed at the cathode side and dissolved in the electrolyte medium in which they travel to the anode side during battery cycling.

Towards Next Generation Lithium-Sulfur Batteries: Non-conventional Carbon Compartments/Sulfur Electrodes and Multi-scale Analysis

A. D. Dysart, J. C. Burgos, A. Mistry, C.-F. Chen, Z. Liu, C. N. Hong, P. Balbuena, P. P. Mukherjee and V. Pol

Journal Paper Journal of the Electrochemical Society, 163, A730 (2016)

Abstract

In this work, a novel heterofunctional, bimodally-porous carbon morphology, termed the carbon compartment (CC), is utilized as a sulfur host within a lithium-sulfur battery cathode. A multi-scale model explores the physics and chemistry of the lithium-sulfur battery cathode. The CCs are synthesized through a rapid, low cost process to improve electrode-electrolyte interfacial contact and accommodate volumetric expansion associated with sulfide formation. The CCs demonstrate controllable sulfur loading and ca. 700 mAh g^-1 (at 47%-wt S) reversible capacity with high coulombic efficiency due to their unique structures. Density functional theory and ab initio molecular dynamics characterize the interface between the C/S composite and electrolyte during the sulfur reduction mechanism. Stochastic realizations of 3D electrode microstructures are reconstructed based on representative SEM micrographs to study the influence of solid sulfur loading and lithium sulfide precipitation on microstructural and electrochemical properties. A macroscale electrochemical performance model is developed to analyze the performance of lithium-sulfur batteries. The combined multi-scale simulation studies explain key fundamentals of sulfur reduction and its relation to the polysulfide shuttle mechanism: how the process is affected due to the presence of carbon substrate, thermodynamics of lithium sulfide formation and deposition on carbon, and microstructural effects on the overall cell performance.

Non-aqueous Electrode Processing and Construction of Lithium-ion Coin Cells

M. Stein IV, C.-F. Chen, D. Juarez-Robles, C. P. Rhodes and P. P. Mukherjee

Journal Paper Journal of Visualized Experiments (108), e53490 (2016)

Abstract

Research into new and improved materials to be utilized in lithium-ion batteries (LIB) necessitates an experimental counterpart to any computational analysis. Testing of lithium-ion batteries in an academic setting has taken on several forms, but at the most basic level lies the coin cell construction. In traditional LIB electrode preparation, a multi-phase slurry composed of active material, binder, and conductive additive is cast out onto a substrate. An electrode disc can then be punched from the dried sheet and used in the construction of a coin cell for electrochemical evaluation. Utilization of the potential of the active material in a battery is critically dependent on the microstructure of the electrode, as an appropriate distribution of the primary components are crucial to ensuring optimal electrical conductivity, porosity, and tortuosity, such that electrochemical and transport interaction is optimized. Processing steps ranging from the combination of dry powder, wet mixing, and drying can all critically affect multi-phase interactions that influence the microstructure formation. Electrochemical probing necessitates the construction of electrodes and coin cells with the utmost care and precision. This paper aims at providing a step-by-step guide of non-aqueous electrode processing and coin cell construction for lithium-ion batteries within an academic setting and with emphasis on deciphering the influence of drying and calendaring.

Probing the Morphological Influence on Solid Electrolyte Interphase and Impedance Response in Intercalation Electrodes

C.-F. Chen and P. P. Mukherjee

Journal Paper Physical Chemistry Chemical Physics, 17, 9812 (2015)

Abstract

Solid electrolyte interphase (SEI) formation, due to the electrochemical reaction between the salt and solvent in the electrolyte, is a key contributor to the electrode performance decay in lithium-ion batteries. The active particle morphology and electrode microstructure affect the side reaction rate and hence the SEI induced interfacial transport and impedance behavior. The change resistance due to the variation of SEI thickness can be inferred from electrochemical impedance spectroscopy. In this study, we proposed a microstructure-aware impedance model to predict the effect of electrode microstructure on impedance response. Our model successfully captures the influence of active particle morphology on the SEI formation and corresponding impedance characteristics. Different electrode realizations with microstructural and compositional variations have been considered. The critical influence of active material morphology, mean particle size, binder and electrolyte volume fractions on the SEI formation and impedance behavior reveals the underlying interdependences of the interfacial and transport resistance modes.

Adsorption of Insoluble Polysulfides Li₂S_x (x = 1, 2) on Li₂S Surfaces

Z. Liu, D. Hubble, P. Balbuena, and P. P. Mukherjee

Journal PaperPhysical Chemistry Chemical Physics, 12, 9032 (2015)

Abstract

In lithium–sulfur batteries, the growth of insulating discharge product Li₂S film affects the cathode microstructure and the related electron as well as lithium ion transport properties. In this study, chemical reactions of insoluble lithium polysulfides Li₂S_x (x = 1, 2) on crystal Li₂S substrate are investigated by a first-principles approach. First-principles atomistic thermodynamics predicts that the stoichiometric (111) and (110) surfaces are stable around the operating cell voltage. Li₂S_x adsorption is an exothermic reaction with the (110) surface being more active to react with the polysulfides than the stoichiometric (111) surface. There is no obvious charge transfer between the adsorbed molecule and the crystal Li₂S substrate. Analysis of the charge density difference suggests that the adsorbate interacts with the substrate via a strong covalent bond. The growth mechanism of thermodynamically stable surfaces is investigated in the present study. It is found that direct Li₂S deposition is energetically favored over Li₂S₂ deposition and reduction process.

Reduced Order Modeling of Mechanical Degradation Induced Performance Decay in Lithium-Ion Battery Porous Electrodes

P. Barai, K. Smith, C.-F. Chen, G.-H. Kim, and P. P. Mukherjee

Journal PaperJournal of the Electrochemical Society, 162, A1751 (2015)

Abstract

A one-dimensional computational framework is developed that can solve for the evolution of voltage and current in a lithium-ion battery electrode under different operating conditions. A reduced order model is specifically constructed to predict the growth of mechanical degradation within the active particles of the carbon anode as a function of particle size and C-rate. Using an effective diffusivity relation, the impact of microcracks on the diffusivity of the active particles has been captured. Reduction in capacity due to formation of microcracks within the negative electrode under different operating conditions (constant current discharge and constant current constant voltage charge) has been investigated. At the beginning of constant current discharge, mechanical damage to electrode particles predominantly occurs near the separator. As the reaction front shifts, mechanical damage spreads across the thickness of the negative electrode and becomes relatively uniform under multiple discharge/charge cycles. Mechanical degradation under different drive cycle conditions has been explored. It is observed that electrodes with larger particle sizes are prone to capacity fade due to microcrack formation. Under drive cycle conditions, small particles close to the separator and large particles close to the current collector can help in reducing the capacity fade due to mechanical degradation.

Characterization of Lithium-Ion Battery Thermal Abuse Behavior Using Experimental and Computational Analysis

C. Lopez, J. Jeevarajan and P. P. Mukherjee

Journal Paper Journal of the Electrochemical Society, 162, A2163 (2015)

Abstract

While the popularity of lithium-ion batteries (LIBs) has increased significantly in recent years, safety concerns due to the high thermal instability of LIBs limit their use in applications with zero tolerance for a catastrophic failure. Industries such as aerospace and automotive must be very stringent in their selection and design of lithium-ion cells and modules to meet safety requirements. A safety issue of particular interest is a scenario called thermal runaway in which one or more exothermic side-reactions occur, leading to elevated temperature ranges that in turn lead to an uncontrollable and excessive release of heat. This work aims to characterize the effect of these reactions by utilizing a thermal abuse model that predicts single-cell behavior when subjected to an elevated-temperature. The experimental test of the thermal safety behavior includes a constant-power heating element to trigger a thermal runaway event. This study takes an existing thermal abuse model and modifies it to emulate the conditions during a constant-power heating test. The result is found to be in agreement with the experimental data for different cell configurations. The influence of convection condition, cell physical configuration, and electrolyte combustion on the cell thermal behavior is also investigated.

Experimental Analysis of Thermal Runaway and Propagation in Lithium-Ion Battery Modules

C. Lopez, J. Jeevarajan and P. P. Mukherjee

Journal Paper Journal of the Electrochemical Society, 162, A1905 (2015)

Abstract

While the energy and power density of lithium-ion batteries (LIBs) are steadily improving, thermal safety continues to remain a critical challenge. Under abuse conditions, exothermic reactions may lead to the release of heat that can trigger subsequent unsafe reactions. The situation worsens in a module configuration, as the released heat from an abused cell can activate a chain of reactions in the neighboring cells, causing catastrophic thermal runaway. This work focuses on experimental elucidation and analysis of different LIB module configurations to characterize the thermal behavior and determine safe practices. The abuse test consists of a heat-to-vent setting where a single cell in a module is triggered into thermal runaway via a heating element. The cell-to-cell thermal runaway propagation behavior has been characterized. Results have shown that increasing the inter-cell spacing in a module containing cylindrical cells significantly decreases the probability of thermal runaway propagation. Additionally, it was determined that appropriate tab configuration combined with cell form factors exhibit a major influence on thermal runaway propagation. Different thermal insulation materials have been analyzed to determine their ability to ameliorate and/or potentially mitigate propagation effects.

Influence of Microstructure on Impedance Response in Intercalation Electrodes

S. Cho, C.-F. Chen and P. P. Mukherjee

Journal PaperJournal of the Electrochemical Society, 162, A1202 (2015)

Abstract

The active particle morphology and microstructure affect the impedance behavior of intercalation electrodes due to the underlying charge transport, active material/electrolyte interfacial surface area, and solid-phase diffusion in lithium-ion batteries (LIB). In order to capture the impact of the electrode microstructural variability on the impedance response, an integrated electrochemical impedance predictive analysis is presented. In the analysis, stochastically reconstructed 3-D microstructures of representative LIB electrodes are considered with variations in the active material morphology and particle size distribution. With the properties evaluated from the virtual 3-D microstructures, the corresponding impedance response is predicted. The concept of electrochemical Sauter mean diameter (ESMD) has been introduced to investigate the effect of active particle morphology, such as particle agglomeration. This integrated analysis is envisioned to offer a virtual impedance response probing framework to elucidate the influence of electrode microstructural variability and underlying electrochemical and transport interactions.

Evaluating Pristine and Modified SnS₂ as a Lithium-ion Battery Anode: A First-Principles Study

Z. Liu, H. Deng and P. P. Mukherjee

Journal Paper ACS Applied Materials and Interfaces, 7, 4000 (2015)

Abstract

Li intercalation and diffusion in pristine and modified SnS₂ interlayer are studied by a first-principles approach. The results predict that the octahedral interstitial site is energetically favored for Li intercalation. The minimum energy path of Li diffusion in SnS₂ interlayer is investigated by climbing image nudged elastic band method. It is found that Li atom diffuses from one energetically favored octahedral interstitial site to the neighbor one via tetrahedral interstitial site. The expansion of interlayer spacing is beneficial for decreasing the diffusion barrier. Ce dopant negatively impacts the Li diffusivity although it can optimize the interlayer spacing. Geometric structures of Li_xSnS₂ (0 < x ≤ 3) are investigated to understand the lithiation-induced volume expansion and atomic structure change. The lithiation process can be divided into two stages. When Li content (x in Li_xSnS₂) is less than 1, the volume expansion is not dramatic and only S atoms capture electrons from Li atoms. When Li content is larger than 1, Sn⁴⁺ cations are significantly reduced, S-Sn-S trilayer gradually decomposes, and Li_xS₂ (1 ≤ x ≤ 3) layer forms between two Sn monolayers. The mechanism of volume expansion is elucidated in this study.

Morphological Influence in Lithium-Ion Battery 3D Electrode Architectures

M. A. Martin, C.-F. Chen , P. P. Mukherjee et al.,

Journal Paper Journal of Electrochemical Society, 162, A991 (2015)

Abstract

The performance of lithium-ion batteries is limited by suboptimal energy density and power capability. A feasible approach is designing 3D electrode architectures where lithium ion transport in the electrolyte and active material can be optimized for improving the energy/power density. In this study, the influence of active material morphology and 3D electrode configurations is investigated with particular emphasis on solid-state transport and resulting implications on the performance. A morphology-detailed computational modeling is presented which simulates lithium transport in disparate 3D electrode configurations. The resulting lithium concentration in the 3D electrode constructs during discharging, relaxation, and charging process reveal a local sate of charge map. This is correlated with the electrode performance. This study demonstrates the role of active particle morphology and 3D architecture on the electrode relaxation behavior, which determines the resulting concentration gradient and performance.

Analysis of the Implications of Rapid Charging on Lithium-Ion Battery Performance

M. Hasan, C.-F. Chen , C. E. Shaffer, and P. P. Mukherjee

Journal Paper Journal of the Electrochemical Society, 162, A1382 (2015)

Abstract

Fast charging is critical for efficient electrical vehicle operation. In this study, the fast charging performance limitations are elucidated with emphasis on the influence of temperature extremes. The role of charging protocols and electrode design parameters on charging time reduction are analyzed. Conventional charging protocol at high C-rate (e.g. at 3C) demonstrates that the performance limitation in rapid charging primarily originates from lithium ion transport in the electrolyte (electrolyte resistance) at moderate and high operating temperatures. However, interfacial kinetics resistance becomes the limiting mechanism for the 1C charging rate at low temperatures. To overcome the low temperature limitation, self-heating has been found to boost the cell performance and coulombic efficiency. An effective charging protocol has been suggested by maximizing lithium concentration at the anode/separator interface. Based on the advantageous combination of charging protocol and temperature, we propose a pulse-charging protocol with adiabatic operation, which can reduce charging time and increase performance. Furthermore, appropriate electrode design, such as reducing the electrode thickness and increasing the porosity, results in improved charging performance.

Mesoscale Elucidation of Laser-Assisted Chemical Deposition of Sn Nanostructured Electrodes

Z. Liu, B. Deng, G. Cheng, H. Deng, and P. P. Mukherjee

Journal PaperJournal of Applied Physics, 117, 214301 (2015)

Abstract

Nanostructured tin (Sn) is a promising high-capacity electrode for improved performance in lithium-ion batteries for electric vehicles. In this work, Sn nanoisland growth for nanostructured electrodes assisted by the pulse laser irradiation has been investigated based on a mesoscale modeling formalism. The influence of pertinent processing conditions, such as pulse duration, heating/cooling rates, and atom flux, on the Sn nanostructure formation is specifically considered. The interaction between the adsorbed atom and the substrate, represented by the adatom diffusion barrier, is carefully studied. It is found that the diffusion barrier predominantly affects the distribution of Sn atoms. For both α-Sn and β-Sn, the averaged coordination number is larger than 3 when the diffusion barrier equals to 0.15 eV. The averaged coordination number decreases as the diffusion barrier increases. The substrate temperature, which is determined by heating/cooling rates and pulse duration, can also affect the formation of Sn nanoislands. For α-Sn, when applied low heating/cooling rates, nanoislands cannot form if the diffusion barrier is larger than 0.35 eV.

Microstructural Analysis of Mass Transport Phenomena in Gas Diffusion Media for High Current Density Operation in PEM Fuel Cells

T. Kotaka, Y. Tabuchi, and P. P. Mukherjee

Journal PaperJournal of Power Sources, 280, 231 (2015)

Abstract

Cost reduction is a key issue for commercialization of fuel cell electric vehicles (FCEV). High current density operation is a solution pathway. In order to realize high current density operation, it is necessary to reduce mass transport resistance in the gas diffusion media commonly consisted of gas diffusion layer (GDL) and micro porous layer (MPL). However, fundamental understanding of the underlying mass transport phenomena in the porous components is not only critical but also not fully understood yet due to the inherent microstructural complexity. In this study, a comprehensive analysis of electron and oxygen transport in the GDL and MPL is conducted experimentally and numerically with three-dimensional (3D) microstructural data to reveal the structure–transport relationship. The results reveal that the mass transport in the GDL is strongly dependent on the local microstructural variations, such as local pore/solid volume fractions and connectivity. However, especially in the case of the electrical conductivity of MPL, the contact resistance between carbon particles is the dominant factor. This suggests that reducing the contact resistance between carbon particles and/or the number of contact points along the transport pathway can improve the electrical conductivity of MPL.

A Silver-nanoparticle Catalyzed Graphite Composite for Electrochemical Energy Storage

X. He, D. Hubble, R. Calzada, A. Ashtamkar, D. Bhatia, S. Cartagena, P. P. Mukherjee and H. Liang

Journal Paper Journal of Power Sources, 275, 688 (2015)

Abstract

A new composite containing silver nanoparticles and graphite is developed in order to improve electrochemical energy storage. The nanocomposite uses silver (Ag) nanoparticles as a catalyst to enhance the electrochemical performance. Results indicate that the graphite composite decorated with Ag shows up to a six-fold improvement in specific capacitance. Electron/charge transfer is enhanced through a shift from double-layer to pseudocapacitive behavior, mediated by Li⁺ intercalation. Decoration with Ag nanoparticles allows for improvements in electrochemical impedance response, ease of electronic/ionic charging, and overall energy storage capability. This research provides a promising alternative solution for the next generation of safe and cost-effective lithium-ion devices.

Wettability Effects on Contact Line Dynamics of Droplet Motion in an Inclined Channel

P. Randive, A. Dalal, K. Sahu, G. Biswas and P. P. Mukherjee

Journal Paper Physical Review E, 91, 053006 (2015)

Abstract

The present work discusses the implications of wall wettability and inclination of the surface on droplet dynamics. In this work, mesoscopic illustration of droplet dynamics in a duct with different inclination angles, based on the two-phase lattice Boltzmann model is reported. Temporal evolution of wetted length, wetted area and maximum height of the droplet for surfaces with different inclination angles and wettabilities is furnished in detail in order to elucidate the droplet displacement dynamics. It has been observed that the effect of inclination of the surface on droplet dynamics is more pronounced on a hydrophobic surface as compared to a hydrophilic surface. The time evolution of height and contact line motion of the droplet shows that higher angle of inclination of substrate affects the dynamics strongly irrespective of wettability.

Mesoscopic Simulation of Blob Resonance in a Model Porous Pathway

P. Randive, A. Dalal and P. P. Mukherjee

Journal Paper Microfluidics and Nanofluidics, 18, 215 (2015)

Abstract

The present work presents the capillarity–wettability interaction of the trapped non-wetting phase in a model pore, characterized by a circular tube with varying constriction. The displacement of a three-dimensional immiscible binary large object (blob) subjects to oscillatory acoustic excitation in a tube of varying radius is examined using the lattice Boltzmann method. The impact of the physicochemical parameters, including radius of the tube, amplitude of the force, wettability, viscosity and frequency on blob dynamics is discussed. The response of the blob with pinned and sliding contact line exhibits underdamped and overdamped characteristics, respectively. It is observed that the mean displacement and frequency response increase with amplitude of the force. The resonance behavior of the blob with different surface wettability and capillary number is discussed. It has been observed that the displacement behavior is not affected to a large extent at high capillary number. However, wettability plays a crucial role in mobilization of trapped blob at low capillary number. The displacement of the blob is greater in case of the surfaces with uniformly wettability as opposed to mixed wettability.

Mesoscale Elucidation of the Influence of Mixing Sequence in Electrode Processing

Z. Liu,V. Battaglia and P. P. Mukherjee

Journal Paper Langmuir, 30, 15102 (2014)

Abstract

Mixing sequence during electrode processing affects the internal microstructure and resultant performance of a lithium-ion battery. In order to fundamentally understand the microstructure evolution during electrode processing, a mesoscale model is presented, which investigates the influence of mixing sequence for different evaporation conditions. Our results demonstrate that a stepwise mixing sequence can produce larger conductive interfacial area ratios than that via a one-step mixing sequence. Small-sized cubical nanoparticles are beneficial for achieving a high conductive interfacial area ratio when a stepwise mixing sequence is employed. Two variants of multistep mixing have been investigated with constant temperature and linearly increasing temperature conditions. It is found that the temperature condition does not significantly affect the conductive interfacial area ratio. The homogeneity of binder distribution in the electrode is also studied, which plays an important role along with the solvent evaporation condition. This study suggests that an appropriate combination of mixing sequence and active particle size and morphology plays a critical role in the formation of electrode microstructures with improved performance.

Mechano-Electrochemical Model for Acoustic Emission Characterization in Intercalation Electrodes

P. Barai and P. P. Mukherjee

Journal Paper Journal of the Electrochemical Society, 161, F3123 (2014)

Abstract

Active particles inside the lithium-ion battery electrode experience diffusion induced stress and volume change during intercalation. High-rate or low-temperature operation can cause large concentration gradients resulting in higher probability of microcrack formation and propagation in the active particles and ultimately performance decay. Acoustic emission is a non-destructive technique for the detection of mechanical degradation. In this work, a computational methodology has been developed, based on a dynamic lattice spring model (DLSM), to study acoustic emission characteristics resulting from intercalation induced microcrack formation in electrodes. This method allows relating the acoustic response with the mechanical damage experienced during lithiation/delithiation in the active particles. Energy released due to brittle fracture is rendered as the major source of acoustic emission response. Predictions from this analysis suggest that during cycling maximum amount of acoustic activity is observed in the first couple of cycles. A phase map has been developed to demonstrate the influence of elastic modulus and damping coefficient on the damage evolution and identify a potential window of reduced mechanical degradation.

Diffusion Induced Damage and Impedance Response in Lithium-Ion Battery Electrodes

C. F. Chen, P. Barai and P. P. Mukherjee

Journal Paper Journal of the Electrochemical Society, 161, A2138 (2014)

Abstract

Mechanical degradation, owing to intercalation induced stress and fracture, is a key contributor to the electrode performance decay in lithium-ion batteries. Solid state diffusion of lithium ions in the active particles causes concentration gradients, which results in stress generation and formation of microcracks or propagation of preexisting cracks. Formation and propagation of microcracks in turn affects the solid state transport of lithium ions and the interfacial charge transfer resistance. In this work, a systematic investigation of the influence of mechanical degradation on the resistance to diffusion and charge transport is provided. In this regard, a modeling approach combining fracture formation and electrochemical impedance is presented, which predicts the mechanical damage induced impedance response and resistance evolution in the electrode. The impact of particle size, charge/discharge rate and operating temperature on the electrode impedance response is illustrated.

Microstructure Evolution in Lithium-Ion Battery Electrode Processing

Z. Liu and P. P. Mukherjee

Journal Paper Journal of the Electrochemical Society, 161, E3248 (2014)

Abstract

The processing induced active particle assembly determines the internal microstructure and resultant performance of the electrode in a lithium-ion battery. A morphology-detailed mesoscale model has been developed to gain fundamental understanding of the influence of active particle morphology, size, volume fraction, solvent evaporation, and multi-phase (active particle, conductive additive, binder and solvent) interaction. Our results demonstrate that smaller isometric active particles tend to form favorable aggregation with conductive additive particles. Two regimes, namely spontaneous aggregation and evaporation induced aggregation, have been identified. Low solvent evaporation rate promotes spontaneous aggregation resulting in an enhanced interfacial area than that in evaporation-induced aggregation. The influence of active material morphology and volume fraction on conducting pathway formation has been conjectured.

Probing the Thermal Implications in Mechanical Degradation of Lithium-ion Battery Electrodes

K. An, P. Barai, K. Smith, and P. P. Mukherjee

Journal Paper Journal of the Electrochemical Society, 161, A1058 (2014)

Abstract

In a lithium-ion cell, heat generation and temperature evolution during operation pose a significant bearing on the mechanical degradation and cell performance. The thermal implications on the electrode mechano-electrochemical behavior have been elucidated. Crack formation due to diffusion-induced stress in the active particles has been analyzed. Temperature dependence of the mechano-physicochemical parameters has been taken into account. Total amount of diffusion-induced damage has been estimated for different current density, ambient temperature and particle size. For subzero temperatures, adiabatic operation can boost the cell performance significantly. Increased mechanical degradation has been observed for high C-rate and larger particle sizes. Decreasing ambient temperature results in aggravated crack formation resulting in severe capacity loss. However, at subzero temperatures and under high C-rate conditions, significant concentration gradient exists near the active particle peripheral region resulting in reduced damage penetration. The cell performance analysis reveals that the impact of mechanical degradation on the capacity loss is most prominent at subzero temperatures. The effect of cycling shows accelerated damage in the first few cycles followed by a plateau in the damage evolution. Existence of a critical particle size for maximum damage has been suggested which depends significantly on the cell temperature.

Abstract

The field of Mechano-Electro-Chemical (MEC) Coupling examines the multi-directional couplings that exist between a material's physico-electro-chemical state and its properties, processing, and structure. While increasing electro-chemical performance (e.g. reaction rates in fuel cell or battery applications) has largely been the focus in energy related materials, its coupling with mechanical properties, as well as mechano-chemical and mechano-electrical coupling, are becoming of increasing interest, as demonstrated by Barai and Mukherjee,¹ Kim and Qi,² Malavé et al.,³ Zenyuk et al.,⁴ Zuev et al.,⁵ and the many other articles in this Focus Issue. Furthermore, as described by the definition above and conceptually highlighted in Fig. 1, MEC coupling also influences material structure and processing. Examples of this include the stress-induced ferroelastic domain switching discussed in Kimura et al.,⁶ and the chemically induced changes in cation diffusion coefficients, and hence sintering kinetics, discussed in Ni et al.⁷

Simulation of the Effect of Interfacial Lithium Flux on Miscibility Gap in Non-equilibrium Phase Transformation of LiFePO₄ Particles

N. A. Siddique, A. M. Allen, P. P. Mukherjee, and F. Liu

Journal Paper Journal of Power Sources, 245, 83 (2014)

Abstract

Non-equilibrium phase transformation and effect of interfacial Li flux on miscibility gap in two-phase transformation of LiFePO₄ have been explored in this study. Our previously developed “Mushy-Zone” (MZ) model, accounting for sluggish Li diffusion across the two-phase interface, has been employed to study the non-equilibrium phase transformation in LiFePO₄ materials of Li-ion batteries. Phase transformation rate, variation of two-phase miscibility gap, and interfacial Li composition profiles have been studied for different particle shapes at varying discharge rates. Sluggish Li flux across the two-phase interface, which is believed to be the origin of the kinetically-induced non-equilibrium phase transformation, has been calculated to explain the obtained results. It is found that small particle sizes (radii of 20 nm) and slow discharge rates tend to create homogenous phase transformation (i.e., shrunk or no miscibility gap). Two-phase transformation is remarkably delayed for spherical particles at low discharge rates, leading to a lower capacity compared to that of plated-shaped particles. However, at higher discharge rates spherical particles show better capacity.

Biofilm Streamer Formation in a Microfluidic Device with Micro-pillars

M. Hassanpourfard, X. Sun, A. Valiei, P. P. Mukherjee, T. Thundat, Y. Liu, and A. Kumar

Journal Paper Journal of Visualized Experiments, 90, e51732 (2014)

Abstract

Several bacterial species possess the ability to attach to surfaces and colonize them in the form of thin films called biofilms. Biofilms that grow in porous media are relevant to several industrial and environmental processes such as wastewater treatment and CO₂ sequestration. We used Pseudomonas fluorescens, a Gram-negative aerobic bacterium, to investigate biofilm formation in a microfluidic device that mimics porous media. The microfluidic device consists of an array of micro-posts, which were fabricated using soft-lithography. Subsequently, biofilm formation in these devices with flow was investigated and we demonstrate the formation of filamentous biofilms known as streamers in our device. The detailed protocols for fabrication and assembly of microfluidic device are provided here along with the bacterial culture protocols. Detailed procedures for experimentation with the microfluidic device are also presented along with representative results.

Lattice Boltzmann Modeling of Two-phase Behavior under Acoustic Excitation: Capillarity-Wettability Interaction

P. Randive, A. Dalal, and P. P. Mukherjee

Journal Paper International Journal of Heat and Mass Transfer, 74, 460 (2014)

Abstract

We report capillarity–wettability interaction of the trapped nonwetting phase. The displacement of immiscible nonwetting phase subject to oscillatory acoustic excitation in a sinusoidal channel is analyzed with the lattice Boltzmann method. The effect of the surface wettability, frequency and geometry of the channel on two-phase behavior is discussed. The effect of capillarity induced resonance on mobilization of trapped nonwetting phase blob is explored for a range of capillary number for uniform and mixed-wet surfaces. It is observed that transport of a nonwetting phase can be achieved by exciting with the frequencies near to the resonant frequency which is vital in mobilization of the trapped nonwetting phase in the application like recovery of oil and two-phase flows.

Probing the Influence of Superhydrophobicity and Mixed Wettability on Droplet Displacement Behavior

P. Randive, A. Dalal, and P. P. Mukherjee

Journal Paper Microfluidics and Nanofluidics, 17, 657 (2014)

Abstract

The importance of fundamental understanding of droplet dynamics and the concomitant implications of wall wettability are critical in the emergent science and technology areas including digital microfluidics and clean energy conversion. In this work, mesoscopic illustration, based on the two-phase lattice Boltzmann model, of droplet dynamics in a microchannel is presented in order to unveil the role of superhydrophobicity and mixed wettability. The impact of critical physicochemical determinants, including capillary number and droplet size, is explored in the context of droplet–wettability interactions. Temporal evolution of wetted length and wetted area for a combination of wettability scenarios is furnished in detail in order to elucidate the droplet displacement dynamics. Capillary number plays an important role with disparate droplet behavioral patterns stemming from superhydrophobic and mixed-wet wall characteristics.

Stochastic Analysis of Diffusion Induced Damage in Lithium-ion Battery Electrodes

P. Barai and P. P. Mukherjee

Journal Paper Journal of the Electrochemical Society, 160, 6 (2013)

Abstract

Fracture due to diffusion induced stress of electrode active particles has been identified as one of the critical factors for capacity fade and impedance rise in lithium-ion batteries. The inherent stochastics underlying the crack formation and propagation in brittle intercalation materials is critical toward fundamental understanding of the degradation phenomena limiting battery life and performance. A stochastic methodology has been developed to characterize the diffusion-induced damage inside lithium-ion battery electrode active particles. Presence of a “critical” initial crack length at which maximum stress occurs has been identified. A damage parameter has been introduced to characterize the impact of fracture on solid state lithium diffusion. The importance of active particle size, concentration dependent elastic moduli and cycling on the fracture stochastics and concomitant electrochemical performance decay has been elucidated along with the concept of a fracture phase-map.

Microscale Confinement Features Can Affect Biofilm Formation

A. Kumar, D. Karig, R. Acharya, S. Neethirajan, P. P. Mukherjee, S. Retterer, and M. J. Doktycz

Journal Paper Microfluidics and Nanofluidics, 14, 895 (2013)

Abstract

The majority of bacteria in nature live in biofilms, where they are encased by extracellular polymeric substances (EPS) and adhere to various surfaces and interfaces. Investigating the process of biofilm formation is critical for advancing our understanding of microbes in their most common mode of living. Despite progress in characterizing the effect of various environmental factors on biofilm formation, work remains to be done in the realm of exploring the inter-relationship between hydrodynamics, microbial adhesion and biofilm growth. We investigate the impact of secondary flow structures, which are created due to semi-confined features in a microfluidic device, on biofilm formation of Shewanella oneidensis MR-1. Secondary flows are important in many natural and artificial systems, but few studies have investigated their role in biofilm formation. To direct secondary flows in the creeping flow regime, where the Reynolds number is low, we flow microbe-laden culture through microscale confinement features. We demonstrate that these confinement features can result in pronounced changes in biofilm dynamics as a function of the fluid flow rate.

Columnar Order in Jammed LiFePO₄ Cathodes: Ion Transport Catastrophe and its Mitigation

K. C. Smith, P. P. Mukherjee, and T. S. Fisher

Journal Paper Physical Chemistry Chemical Physics, 14, 7040 (2012)

Abstract

The high-rate, high-capacity potential of LiFePO₄-based lithium-ion battery cathodes has motivated numerous experimental and theoretical studies aiming to realize such performance through nano-sizing, tailoring of particle shape through synthesis conditions, and doping. Here, a granular mechanics study of microstructures formed by dense jammed packings of experimentally and theoretically inspired LiFePO₄ particle shapes is presented. A strong dependence of the resultant packing structures on particle shapes is observed, in which columnar structures aligned with the [010] direction inhibit diffusion along [010] in anisotropic LiFePO₄. Transport limitations are induced by [010] columnar order and lead to catastrophic performance degradation in anisotropic LiFePO₄ electrodes. Further, judicious mixing of nanoplatelets with additive nanoparticles can frustrate columnar ordering and thereby enhance the rate capability of LiFePO₄ electrodes by nearly an order of magnitude.

Subfreezing Operation of Polymer Electrolyte Fuel Cells: Ice Formation and Cell Performance Loss

Y. Wang, J. Mishler, P. P. Mukherjee, R. Mukundan, and R. L. Borup

Journal Paper Electrochimica Acta, 65, 127 (2012)

Abstract

In this work, we investigate the cold-start operation of polymer electrolyte fuel cells (PEFCs) through high-resolution neutron radiography, experimental testing, theoretical evaluation, and comparison with model prediction. Ice formation location, voltage evolution, and loss of the electro-catalyst surface area (ECSA) are examined. A dimensionless parameter h¯ , characterizing the spatial variation of the reaction rate across the cathode catalyst layer, is discussed at subfreezing temperature using newly determined membrane ionic conductivity. The h¯ evaluation identifies the operating range that the reaction rate can be treated uniform across the catalyst layer, in which the model is valid.

A Web of Streamers: Biofilm Formation in a Porous Microfluidic Device

A. Valiei, A. Kumar, P. P. Mukherjee

Journal Paper Lab on a Chip, 12, 5133 (2012)

Abstract

Using a microfabricated porous media mimic platform, we investigated how fluid flow influences the formation of filamentous structures, known as streamers, between porous media structures. We demonstrate how hydrodynamics govern the formation, morphology and the distribution of these biofilm streamers in the device. Our work establishes that, under favorable hydrodynamic conditions, streamers can often act as precursors to mature microbial structures found in complex geometries, such as those involved in porous media.

Pore-Scale Modeling of Two-Phase Transport in Polymer Electrolyte Fuel Cells - Progress and Perspective

P. P. Mukherjee, Q. Kang, and C. Y. Wang

Journal Paper Energy & Environmental Science (Royal Society of Chemistry), 4, 346 (2011)

Abstract

Recent years have witnessed an explosion of research and development efforts in the area of polymer electrolyte fuel cells (PEFC), perceived as the next generation clean energy source for automotive, portable and stationary applications. Despite significant progress, a pivotal performance/durability limitation in PEFCs centers on two-phase transport and mass transport loss originating from suboptimal liquid water transport and flooding phenomena. Liquid water blocks the porous pathways in the gas diffusion layer (GDL) and the catalyst layer (CL), thus hindering oxygen transport from the flow field to the electrochemically actives sites in the catalyst layer. Different approaches have been examined to model the underlying transport mechanisms in the PEFC with different levels of complexities. Due to the macroscopic nature, these two-phase models fail to resolve the underlying structural influence on the transport and performance. Mesoscopic modeling at the pore-scale offers great promise in elucidating the underlying structure-transport-performance interlinks in the PEFC porous components. In this article, a systematic review of the recent progress and prospects of pore-scale modeling in the context of two-phase transport in the PEFC is presented. Specifically, the efficacy of lattice Boltzmann (LB), pore morphology (PM) and pore network (PN) models coupled with realistic delineation of microstructures in fostering enhanced insight into the underlying liquid water transport in the PEFC GDL and CL is highlighted.

Non-equilibrium Phase Transformation and Particle Shape Effect in LiFePO₄ Materials for Li-Ion Batteries

F. Liu, N. A. Siddique, and P. P. Mukherjee

Journal Paper Electrochemical and Solid State Letters, 14, 1 (2011)

Abstract

The nonequilibrium phase transformation and particle shape effects in LiFePO₄ materials of Li-ion batteries are explored in this work. A continuum model employing the “mushy-zone” (MZ) approach, accounting for sluggish Li diffusion across the two-phase boundary, has been developed to study the kinetically-induced nonequilibrium phenomenon in Li-ion batteries. A theoretical analysis is presented to show that the nonequilibrium miscibility gap expands and shifts to higher Li composition at high discharge rates, due to insufficient compositional readjustments at the two-phase boundary. Furthermore, critical effects of particle shape on nonequilibrium phase transformation and discharge capacity have been discovered by the model.

Electric Field Induced Bacterial Flocculation of Enteroaggregative Escherichia Coli 042

A. Kumar, N. P. Mortensen, P. P. Mukherjee, S. Retterer, and M. J. Doktycz

Journal Paper Applied Physics Letters, 98, 253701 (2011) [Journal Issue Cover Feature; also featured in Virtual Journal of Biological Physics Research, July 2011 Issue]

Abstract

A response of the aggregation dynamics of enteroaggregative Escherichia coli under low magnitude steady and oscillating electric fields is presented. The presence of uniform electric fields hampered microbial adhesion and biofilm formation on a transverse glass surface, but instead promoted the formation of flocs. Extremely heterogenous distribution of live and dead cells was observed among the flocs. Moreover, floc formation was largely observed to be independent of the frequency of alternating electric fields.

Cold Start of Polymer Electrolyte Fuel Cells: Three-Stage Startup Characterization

Y. Wang, P. P. Mukherjee, J. Mishler, R. Mukundan, and R. L. Borup

Journal Paper Electrochimica Acta, 55, 2636 (2010)

Abstract

In this paper, the electrochemical kinetics, oxygen transport and solid water formation within the cathode electrode of polymer electrolyte fuel cells (PEFCs) during cold start is investigated. We specifically evaluate the key parameters that govern the self-startup of PEFCs by considering a wide range of the relevant factors. These parameters include characteristic time scales of cell warm-up, ionomer hydration in the catalyst layer, ice build-up and melting, as well as the ratios of the time constants. Supporting experimental observation using neutron imaging and isothermal cold start experiment is discussed. Gas purge is found to facilitate the PEFC cold start but the improvement may be relatively small compared with other methods such as selecting suitable materials and modifying the cell design. We define a three-step electrode process for cold start and conduct a one-dimensional analysis, which enables the evaluation of the impact of ice volume fraction and temperature variations on the cell cold start performance. The ionic conductivity data of Nafion® 117 membrane at subfreezing temperature, evaluated from experiment, is utilized to analyze the temperature dependence of the ohmic polarization during cold start.

Mesoscopic Modeling of Multi-physicochemical Transport Phenomena in Porous Media

Q. Kang, M. Wang, P. P. Mukherjee, and P. C. Lichtner

Journal Paper Advances in Mechanical Engineering, Article ID 142879, doi:10.1155/2010/142879 (2010)

Abstract

We present our recent progress on mesoscopic modeling of multiphysicochemical transport phenomena in porous media based on the lattice Boltzmann method. Simulation examples include injection of CO₂-saturated brine into a limestone rock, two-phase behavior and flooding phenomena in polymer electrolyte fuel cells, and electroosmosis in homogeneously charged porous media. It is shown that the lattice Boltzmann method can account for multiple, coupled physicochemical processes in these systems and can shed some light on the underlying physics occurring at the fundamental scale. Therefore, it can be a potential powerful numerical tool to analyze multiphysicochemical processes in various energy, earth, and environmental systems.

Mesoscopic Modeling of Two-phase Behavior and Flooding Phenomena in Polymer Electrolyte Fuel Cells

P. P. Mukherjee, C. Y. Wang, and Q. Kang

Journal Paper Electrochimica Acta, 54, 6861 (2009) [Ranked in the Top 25 Most Cited Articles]

Abstract

A key performance limitation in polymer electrolyte fuel cells (PEFC), manifested in terms of mass transport loss, originates from liquid water transport and resulting flooding phenomena in the constituent components. Liquid water covers the electrochemically active sites in the catalyst layer (CL) rendering reduced catalytic activity and blocks the available pore space in the porous CL and fibrous gas diffusion layer (GDL) resulting in hindered oxygen transport to the active reaction sites. The cathode CL and the GDL play a major role in the mass transport loss and hence in the water management of a PEFC. In this work the development of a mesoscopic modeling formalism coupled with realistic microstructural delineation is presented to study the influence of the pore structure and surface wettability on liquid water transport and interfacial dynamics in the PEFC catalyst layer and gas diffusion layer. The two-phase regime transition phenomenon in the capillary dominated transport in the CL and the influence of the mixed wetting characteristics on the flooding dynamics in the GDL are highlighted.

Modeling of Fractal Electrodes in Li-Ion Batteries

G. T. Teixidor, B. Y. Park, P. P. Mukherjee, Q. Kang, and M. J. Madou

Journal Paper Electrochimica Acta, 54, 5928 (2009)

Abstract

This paper presents a first approximation to the theoretical analysis of fractal-like electrodes for lithium-ion batteries, and demonstrates that fractals constitute an optimal electrode configuration for electrochemical energy storage systems. The model considers a generalized description of three-dimensional, non-deterministic branching structures composed of cylindrical elements for the electrode design. Each element is attached to a branch in an iterative process. At every branching step, the “parent” branch divides into N “child” branches (N being a random variable with a defined probability distribution). At the same time, the dimensions of the radii and lengths of the branches are also determined by a stochastic process. With this model, the charge characteristics of several fractal electrodes corresponding to different geometric configurations are simulated, and the optimal parameters are obtained.

Direct Numerical Simulation Modeling of Bi-layer Cathode Catalyst Layers for Polymer Electrolyte Fuel Cells

P. P. Mukherjee and C. Y. Wang

Journal Paper Journal of the Electrochemical Society, 154, B1121 (2007)

Abstract

A pore-scale description of species and charge transport through a bilayer cathode catalyst layer (CL) of a polymer electrolyte fuel cell using a direct numerical simulation (DNS) model is presented. Two realizations of the bilayer catalyst layer structure are generated using a stochastic reconstruction technique with varied electrolyte and void phase volume fractions. The DNS calculations predict that a higher electrolyte phase volume fraction near the membrane–CL interface provides an extended active reaction zone and exhibits enhanced performance. A higher void phase fraction near the gas diffusion layer aids in better oxygen transport. The effects of cell operating conditions in terms of low inlet relative humidity and elevated cell operating temperature on the bilayer CL performance are also investigated. Low humidity and elevated temperature operations exhibit overall poorer performance compared to the high humidity and the low-temperature operations, respectively.

Impact of Gas Diffusion Layer Structure and Wettability on Water Management in Polymer Electrolyte Fuel Cells

P. K. Sinha, P. P. Mukherjee, and C. Y. Wang

Journal Paper Journal of Materials Chemistry (Royal Society of Chemistry), 17, 3089 (2007) [Journal Issue Cover Feature]

Abstract

A key performance limitation in polymer electrolyte fuel cells (PEFC), called the mass transport loss, originates from liquid water transport and resulting flooding phenomena in the constituent components. The cathode gas diffusion layer (GDL) is a primary contributor to mass transport loss owing to the blockage of available pore space by liquid water thereby rendering hindered oxygen transport to the active reaction sites in the electrode. The GDL, typically a fibrous non-woven carbon paper or a woven carbon cloth, thus plays an important role in the water management of a PEFC. This Feature Article provides a systematic description of the development of pore-scale models coupled with realistic microstructural delineation as well as micron-resolution imaging techniques to study the profound influence of the underlying structure and surface wettability on liquid water transport and interfacial dynamics in the fuel cell GDL. A pore-network model and a two-phase lattice Boltzmann model coupled with stochastic generation of GDL microstructures are elaborated. Concurrently, optical diagnostics of water dynamics at GDL interfaces and X-ray micro-tomographic imaging of liquid water distribution inside the GDL of an operating fuel cell are discussed.

Optimization of Polymer Electrolyte Fuel Cell Cathode Catalyst Layers via Direct Numerical Simulation Modeling

G. Wang, P. P. Mukherjee, and C. Y. Wang

Journal Paper Electrochimica Acta, 52, 6367 (2007)

Abstract

The cathode catalyst layer (CL), due to sluggish oxygen reduction reaction and several transport losses therein, plays an important role in the overall performance of polymer electrolyte fuel cells (PEFCs). The relative volume fractions of the constituent phases, i.e. the electronic, electrolyte and void phases, of the cathode CL need to be selected appropriately in order to achieve an optimal balance between oxygen diffusion and proton conduction. In this work, the influence of electrolyte and void phase fractions of the cathode CL on the cell performance is investigated based on a pore-level description of species and charge transport through a random CL microstructure via the direct numerical simulation (DNS) model. Additionally, the effects of inlet relative humidity and net water transport from the anode on the cathode performance have been studied which indicate the interdependence between the CL composition and the cell operating conditions. The results indicate that the low humidity operation benefits the performance by enhancing the oxygen transport especially under high current densities. Finally, the DNS model predicts the volume fractions of 0.4 and 0.26 for the void and electrolyte phases, respectively, as the optimal composition of the catalyst layer for the best performance.

Anisotropic Heat and Water Transport in a PEFC Cathode Gas Diffusion Layer

U. Pasaogullari, P. P. Mukherjee, C. Y. Wang, and K. S. Chen

Journal Paper Journal of the Electrochemical Society, 154, B823 (2007)

Abstract

A nonisothermal, two-phase model was developed to investigate simultaneous heat and mass transfer in the cathode gas diffusion layer (GDL) of a polymer electrolyte fuel cell (PEFC). The model was applied in two-dimensions with the in-plane (i.e., channel-to-land) and through-plane (i.e., catalyst layer-to-channel) directions to investigate the effects of anisotropy of GDL. For the first time, the anisotropy in the GDL properties was taken into account and found to be an important factor controlling the temperature distribution in the GDL. The maximum temperature difference in the GDL was found to be a strong function of GDL anisotropy. A temperature difference of up to 5°C at a cell voltage of 0.4 V was predicted for an isotropic GDL while it reduced to 3°C for an anisotropic GDL. Significant effect of temperature distribution on liquid water transport and distribution was also observed. In addition, the latent heat effects due to condensation/evaporation of water on the temperature and water distributions were analyzed and found to strongly affect the two-phase transport.

Modeling of Two-phase Behavior in the Gas Diffusion Medium of Polymer Electrolyte Fuel Cells via Full Morphology Approach

V. P. Schulz, P. P. Mukherjee, J. Becker, A. Wiegmann, and C. Y. Wang

Journal Paper Journal of the Electrochemical Society, 154, B419 (2007) [5th Most Cited Article]

Abstract

A full morphology (FM) model has been developed for studying the two-phase characteristics of the gas diffusion medium in a polymer electrolyte fuel cell (PEFC). The three-dimensional (3D) fibrous microstructure for the nonwoven gas diffusion layer (GDL) microstructure has been reconstructed using a stochastic technique for Toray090 and SGL10BA carbon papers. The FM model directly solves for the capillary pressure-saturation relations on the detailed morphology of the reconstructed GDL from drainage simulations. The estimated capillary pressure-saturation curves can be used as valuable inputs to macroscopic two-phase models. Additionally, 3D visualization of the water distribution in the gas diffusion medium suggests that only a small number of pores are occupied by liquid water at breakthrough. Based on a reduced compression model, the two-phase behavior of the GDL under mechanical load is also investigated and the capillary pressure-saturation relations are evaluated for different compression levels.

Stochastic Microstructure Reconstruction and Direct Numerical Simulation of the PEFC Catalyst Layer

P. P. Mukherjee and C. Y. Wang

Journal Paper Journal of the Electrochemical Society, 153, A840 (2006)

Abstract

A direct numerical simulation (DNS) model of species and charge transport in the cathode catalyst layer of a polymer electrolyte fuel cell has been developed. The 3D porous microstructure of the catalyst layer has been reconstructed based on a stochastic technique using the low-order statistical information (porosity, two-point correlation function) as obtained from 2D transmission electron microscopy (TEM) micrographs of a real catalyst layer. In this microscopically complex structure, the DNS model solves point-wise accurate conservation equations, thereby obtaining a pore-scale description of concentration and potential fields. DNS predictions are further compared with the one-dimensional macrohomogeneous results to establish appropriate correlations for effective transport properties as input into macroscopic computational fuel cell models. Finally, the utility of the stochastic reconstruction technique coupled with the DNS model is demonstrated through addressing the influence of microstructural inhomogeneity on the fuel cell performance.

Direct Numerical Simulation (DNS) Modeling of PEFC Electrodes: Part I. Regular Microstructure

G. Wang, P. P. Mukherjee, and C. Y. Wang

Journal Paper Electrochimica Acta, 51, 3139 (2006)

Abstract

A direct numerical simulation (DNS) model is developed to achieve pore-level description of polymer electrolyte fuel cell (PEFC) electrodes. The DNS method solves point-wise accurate conservation equations directly on an electrode microstructure comprising of various phases and hence utilizes the intrinsic transport properties of each phase. Idealized two- and three-dimensional regular microstructures are constructed to represent the porous cathode catalyst layer. Various voltage losses identified from the simulation results are compared with experimental observations. This pore-scale model is further applied to study the morphological effects, such as pore size, layer thickness and porosity, on the performance of the cathode catalyst layer.

Direct Numerical Simulation (DNS) Modeling of PEFC Electrodes: Part II. Random Microstructure

G. Wang, P. P. Mukherjee, and C. Y. Wang

Journal Paper Electrochimica Acta, 51, 3151 (2006)

Abstract

The direct numerical simulation (DNS) method, developed for modeling the cathode catalyst layer (CL) of a polymer electrolyte fuel cell (PEFC) in Part I, is further extended wherein the catalyst layer is described as a random three-dimensional porous structure. A random CL microstructure is obtained using a computer-generated random number with specified porosity and pore size as the input structural parameters. Some statistical features of the CL and their dependence on the porosity are identified and demonstrated. The charge and species conservation equations are solved directly on this microscopically complex structure. The results from the DNS calculation are compared with the one-dimensional macrohomogeneous predictions and the Bruggeman factor for transport property correction is evaluated, which can be used as direct input into the macroscopic fuel cell models.

Numerical Experiments in the Simulation of Enhanced Oil Recovery from a Porous Formation

T. Sheorey, K. Muralidhar, and P. P. Mukherjee

Journal Paper International Journal of Thermal Sciences, 40, 981 (2001)

Abstract

A numerical reservoir simulation model for the study of enhanced oil recovery (EOR) from a porous formation has been presented. The resistance to oil movement arises from viscous forces in the fluid phase as well as surface tension. Viscous forces can be lowered by hot water injection into the formation or by raising the formation temperature. These methods have been numerically analyzed in the present study. The role of the operating parameters such as the injection pressure and temperature on oil recovery has been reported. Displacement of oil by water is clearly brought out by the saturation and the temperature profiles.The numerical solution of the EOR problem experiences growth of errors during long time integration, particularly on large regions. Possible reasons are scatter in the constitutive relationship data, inexact outflow boundary condition and round-off errors in the calculation of the matrix inverse. The nature of these errors has been addressed in the present work. To solve the computationally intensive field-scale problems, two domain decomposition algorithms namely, Schwarz's and Uzawa's algorithms have been evaluated.Results show that oil recovery can be improved when the formation temperature is higher, or the injection temperature and pressure are raised. Adverse results can however be obtained when the injection temperature exceeds a critical value. Optimum conditions prevail when the speed of the oil–water interface is matched with that of the thermal front. As a computational tool, the domain decomposition algorithms are conditionally seen to improve the numerical performance of the oil recovery codes.

Cyclic Voltammetry analysis of catalyst degradation modes in Polymer Electrolyte Fuel Cells

N. Goswami and P. P. Mukherjee

Open-Source Repository Purdue University Research Repository (2021)

Establishing standards for battery data and pathways towards its validation

D. Hayman, E. J. Dufek, P. P. Mukherjee, T. Sholklapper and C. T. Love

Editorial Front. Energy Res., 11, 1271196 (2023)

Lithium battery fire safety: State of the art and the future

Q. Duan, P. P. Mukherjee, Z. Wang and Q. Wang

Editorial Journal of Loss Prevention in the Process Industries, 83, 105073 (2023)

Special Section on Mechanics of Electrochemical Energy Storage and Conversion

D. Datta, P. P. Mukherjee and W. K. S. Chiu

Editorial Journal of Electrochemical Energy Conversion and Storage, 18, 040301 (2021)

Mesoscale Interplay in Lithium-ion Batteries and Beyond

P. P. Mukherjee, L. Arava and A. Pandey

Editorial Journal of The Minerals, Metals & Materials Society, 69, 1467 (2017)

Multiphysics Coupling in Energy Storage

P. P. Mukherjee and G. J. Nelson

Editorial Journal of Electrochemical Energy Conversion and Storage, 13, 030301 (2016)

Introduction to Mechano-Electro-Chemical Coupling in Energy Related Materials and Devices

J. D. Nicholas, Y. Qi, S. R. Bishop and P. P. Mukherjee

Editorial Journal of the Electrochemical Society, 161, Y11 (2014)

Electrodics: Mesoscale Physicochemical Interactions in Lithium-ion Batteries

P. P. Mukherjee, C. F. Chen

Conference PaperSPIE Proceedings (2014)

Abstract

Recent years have witnessed an explosion of interest and research endeavor in lithium-ion batteries to enable vehicle electrification. In particular, a critical imperative is to accelerate innovation for improved performance, life and safety of lithium-ion batteries for electric drive vehicles. Lithium ion batteries are complex, dynamical systems which include a multitude of coupled physicochemical processes encompassing electronic/ionic/diffusive transport in solid/electrolyte phases, electrochemical and phase change reactions and diffusion induced stress generation in multi-scale porous electrode microstructures. While innovations in nanomaterials and nanostructures have spurred the recent advancements, fundamental understanding of the electrode processing – microstructure – performance interplay is of paramount importance. In this presentation, mesoscale physicochemical interactions in lithium-ion battery electrodes will be elucidated.

Temperature Dependent Performance of a Lithium-ion Battery Electrode

P. Barai, K. An, P. P. Mukherjee

Conference PaperProceedings of the 11th International and 22nd National ISHMT-ASME Heat and Mass Transfer Conference, IIT Kharagpur, India (2013)

Analysis of Mass Transport Phenomena in Microporous Layer for High Current Density Operation on PEFC for Automobile Application

T. Kotaka, K. Aotani, Y. Tabuchi, and P. P. Mukherjee

Conference PaperProceedings of the 11th ASME International Fuel Cell Science, Engineering, and Technology Conference (2013)

Abstract

Cost reduction is the most important issue for commercialization of Fuel Cell Electric Vehicle (FCEV). High current density operation is one of the solutions for it. In order to realize high current density operation, it is necessary to reduce both of electron and oxygen transport resistance in the porous materials such as gas diffusion layer (GDL) and microporous layer (MPL). However, the impacts of MPL microstructure on their properties are not fully understood yet compared with GDL because of the necessity of higher spatial resolution. In previous study, the transport analysis on the micro-structure which were visualized by Nano X-ray CT and FIB-SEM were conducted for it. However, it was not enough to understand both of the electron and oxygen transport phenomena and find the dominant factors, because there is no study which focused on the comparison of the numerical and experimental results on both of the electron and oxygen transport. In this study, the comprehensive analysis on both of electron and oxygen transport phenomena in GDL and MPL was conducted with experimental and numerical study based on the three-dimensional (3D) micro structure data. As a result, it was found that pore structure, such as a local porosity and/or tortuosity significantly affected the oxygen transport phenomena. On the other hands, especially in the case of electron transport phenomena in MPL, our results suggested that the dominant factor is not the solid structure such as local solid fraction and/or tortuosity but the contact resistance between carbon particles. This fact revealed that it is effective way to reduce the contact resistance between carbon particles and/or the number of contact points in unit length of a transport path in order to improve electrical transport of MPL.

Simulation of Blob Dynamics inside a Channel under Acoustic Excitation

P. Randive, A. Dalal, and P. P. Mukherjee

Conference PaperProceedings of the ASME Summer Heat Transfer Conference (2013)

Abstract

The displacement of a three-dimensional immiscible blob subject to oscillatory acoustic excitation in a channel is studied with the Lattice Boltzmann method. The effects of amplitude of the force, viscosity and frequency on blob dynamics are investigated. The trend for variation of mean displacement of blob and frequency response is in agreement to that of the previous two-dimensional studies reported in literature. The response of the blob with pinned contact line shows underdamped behavior. It is also found that increasing the amplitude of the force increases the mean displacement and frequency response.

Damage and Crack Analysis in a Li-ion Battery Electrode using Random Spring Model

P. Barai, S. Simunovic, and P. P. Mukherjee

Conference PaperProceedings of the ASME International Mechanical Engineering Congress and Exposition (IMECE) (2012)

Abstract

Lithium-ion batteries (LiB) are widely used in the electronics industry (such as, cell phones and laptop computers) because of their very high energy density, which reduced the size and weight of the battery significantly. LiB also serves as a renewable energy source for the transportation industry (see Ref. [1,2]). Graphite and LiCoO₂ are most frequently used as anode and cathode material inside LiB (see Ref. [2,3]). During the charging and discharging process, intercalation and de-intercalation of Li occur inside the LiB electrodes. Non-uniform distributions of Li induce stress inside the electrodes, also known as diffusion induced stress (DIS). Very high charge or discharge rate can lead to generation of significant amount of tensile or compressive stress inside the electrodes, which can cause damage initiation and accumulation (see Ref. [4]). Propagation of these micro-cracks can cause fracture in the electrode material, which impacts the solid electrolyte interface (SEI) (see Ref. [2,3,5]). Concurrent to the reduction of cyclable Li, resistance between the electrode and electrolyte also increases, which affects the performance and durability of the electrode and has a detrimental consequence on the LiB life (see Ref. [6]).

Adhesion and formation of microbial biofilms in complex microfluidic devices

A. Kumar, SD. Karig, S. Neethirajan, A. K. Suresh, B. R. Srijanto, P. P. Mukherjee, S. T. Retterer, M. J. Doktycz

Conference PaperProceedings of ASME 3rd Micro/Nanoscale Heat and Mass Transfer International Conference (2012)

Shewanella oneidensis is a metal reducing bacterium, which is of interest for bioremediation and clean energy applications. S. oneidensis biofilms play a critical role in several situations such as in microbial energy harvesting devices. Here, we use a microfluidic device to quantify the effects of hydrodynamics on the biofilm morphology of S. oneidensis. For different rates of fluid flow through a complex microfluidic device, we studied the spatiotemporal dynamics of biofilms, and we quantified several morphological features such as spatial distribution, cluster formation and surface coverage. We found that hydrodynamics resulted in significant differences in biofilm dynamics. The baffles in the device created regions of low and high flow in the same device. At higher flow rates, a non-uniform biofilm develops, due to unequal advection in different regions of the microchannel. However, at lower flow rates, a more uniform biofilm evolved. This depicts competition between adhesion events, growth and fluid advection. Atomic force microscopy (AFM) revealed that higher production of extra-cellular polymeric substances (EPS) occurred at higher flow velocities.

Non-equilibrium Phase Transformation and Particle Shape Effect in LiFePO₄ Materials for Li-Ion Batteries

Fuqiang Liu, N. A. Siddique and P. P. Mukherjee

Conference Papers Journal of Consumer Psychology, Volume 22, Issue 2, April 2012, Pages 191-194

Abstract

Compression Modeling and Transport Characterization of the PEM Fuel Cell Diffusion Medium

V. P. Schulz, P. P. Mukherjee, and H. Andra

Conference PaperProceedings of ASME FuelCell2011, 9th ASME International Fuel Cell Science, Engineering, and Technology Conference (2011)

Abstract

Despite tremendous progress in recent years, a pivotal performance limitation in PEM fuel cells manifests in terms of mass transport loss owing to liquid water transport and resulting flooding. A key contributor to the mass transport loss is the cathode gas diffusion layer (GDL) due to the blockage of available pore space by liquid water thus rendering hindered oxygen transport to the active reaction sites in the electrode. The GDL, typically a non-woven carbon paper or woven carbon cloth, thus plays an important role in the overall water management in PEM fuel cells. The underlying poremorphology and the pore wetting characteristics have significant influence on the flooding dynamics in the GDL. Another important factor is the role of cell compression on the GDL microstructural change. In this work, we investigate the influence of GDL microstructure change under compression on the transport behavior. We will present an improved compression model based on the micro fini te element approach. The compression of reconstructed GDL microstructures along with effective property estimation and transport characterization are elucidated.

Digital Volume Imaging of the PEFC Gas Diffusion Layer

P. P. Mukherjee, E. Shim, R. Mukundan, and R. L. Borup

Conference PaperECS Transactions (2010)

Abstract

The gas diffusion layer (GDL) plays a key role in the overall performance/durability of a polymer electrolyte fuel cell (PEFC). Of profound importance, especially in the context of water management and flooding phenomena, is the influence of the underlying pore morphology and wetting characteristics of the GDL microstructure. In this article, we present the digital volumetric imaging (DVI) technique in order to generate the 3-D carbon paper GDL microstructure. The internal pore structure and the local microstructural variations in terms of fiber alignment and fiber/binder distributions are investigated using the several 3-D thin sections of the sample obtained from DVI.

Measurement of Water Content in Polymer Electrolyte Membranes Using High Resolution Neutron Imaging

D. Spernjak, P. P. Mukherjee, R. Mukundan, J. R. Davey, D. S. Hussey, D. L. Jacobson, and R. L. Borup

Conference PaperECS Transactions (2010)

Abstract

Sufficient water content within a polymer electrolyte membrane (PEM) is necessary for adequate ionic conductivity. Membrane hydration is therefore a fundamental requirement for fuel cell operation. The hydration state of the membrane affects the water transport within, as both the diffusion coefficient and electro-osmotic drag depend on the water content. Membrane's water uptake is conventionally measured ex situ by weighing free-swelling samples equilibrated at controlled water activity. In the present study, water profiles in Nafion® membranes were measured using high-resolution neutron imaging. The state-of-the-art, 13 μm resolution neutron detector is capable of resolving water distributions across N1120, N1110 and N117 membranes. It provides a means to measure the water uptake and transport properties of fuel cell membranes in situ.

Multi-physics, Multi-scale Modeling in Polymer Electrolyte Fuel Cells

Y. Wang and P. P. Mukherjee

Conference PaperInvited Paper in ASME International Mechanical Engineering Congress and Exposition (IMECE) (2010)

Abstract

In recent years, the polymer electrolyte fuel cell (PEFC) has emerged as a promising clean energy conversion device for various applications. One key research direction requiring significant breakthrough in order to alleviate performance limitations in PEFCs involves enhanced understanding of the coupled multi-physics transport phenomena and interfacial processes catering over multiple length scales in the constituent porous components. Multi-physics, multi-scale modeling is envisioned to hold the key toward enhanced understanding of the underlying structure-transport-performance interactions. In this article, a brief overview of several major aspects pertaining to the multi-physicochemical modeling of electrochemical reaction kinetics, species transport, two-phase heat and water transport, and phase change in the PEFC is presented.

Heat and Water Transport in a Polymer Electrolyte Fuel Cell Electrode

P. P. Mukherjee, D. Ranjan, R. Mukundan, and R. L. Borup

Conference PaperProceedings of the ASME International Heat Transfer Conference (IHTC-14) (2010)

Abstract

In the present scenario of a global initiative toward a sustainable energy future, the polymer electrolyte fuel cell (PEFC) has emerged as one of the most promising alternative energy conversion devices for various applications. Despite tremendous progress in recent years, a pivotal performance limitation in the PEFC comes from liquid water transport and the resulting flooding phenomena. Liquid water blocks the open pore space in the electrode and the fibrous diffusion layer leading to hindered oxygen transport. The electrode is also the only component in the entire PEFC sandwich which produces waste heat from the electrochemical reaction. The cathode electrode, being the host to several competing transport mechanisms, plays a crucial role in the overall PEFC performance limitation. In this work, an electrode model is presented in order to elucidate the coupled heat and water transport mechanisms. Two scenarios are specifically considered: (1) conventional, Nafion® impregnated, three-phase electrode with the hydrated polymeric membrane phase as the conveyer of protons where local electro-neutrality prevails; and (2) ultra-thin, two-phase, nano-structured electrode without the presence of ionomeric phase where charge accumulation due to electro-statics in the vicinity of the membrane-CL interface becomes important. The electrode model includes a physical description of heat and water balance along with electrochemical performance analysis in order to study the influence of electro-statics/electro-migration and phase change on the PEFC electrode performance.

Cold Start Characteristics of Polymer Electrolyte Fuel Cells

Y. Wang, P. P. Mukherjee, J. Mishler, R. Mukundan, and R. L. Borup

Conference PaperProceedings of the ASME International Heat Transfer Conference (IHTC-14) (2010)

Abstract

In this paper, we investigate the electrochemical reaction kinetics, species transport, and solid water dynamics in a polymer electrolyte fuel cell (PEFC) during cold start. A simplified analysis is developed to enable the evaluation of the impact of ice volume fraction on cell performance during cold-start. Supporting neutron imaging data are also provided to reveal the real-time water evolution. Temperature-dependent voltage changes due to the reaction kinetics and ohmic loss are also analyzed based on the ionic conductivity of the membrane at subfreezing temperature. The analysis is valuable for the fundamental study of PEFC cold-start.

Modeling of Durability Effect on the Flooding Behavior in the PEFC Gas Diffusion Layer

P. P. Mukherjee, R. Mukundan, and R. L. Borup

Conference PaperProceedings of ASME FuelCell2010, 8th ASME International Fuel Cell Science, Engineering, and Technology Conference (2010)

Abstract

The gas diffusion layer (GDL) plays a critical role in the overall performance of a polymer electrolyte fuel cell (PEFC), especially in the mass transport control regime due to suboptimal liquid water transport. Liquid water blocks the porous pathways in the catalyst layer and gas diffusion layer thereby causing hindered oxygen transport from the channel to the active reaction sites. This phenomenon is known as “flooding” and is perceived as the primary mechanism leading to the limiting current behavior in the cell performance. The pore morphology and wetting characteristics of the cathode GDL are of paramount importance in the effective PEFC water management. Typical beginning-of-life GDLs exhibit hydrophobic characteristics, which facilities liquid water transport and hence reduces flooding. Experimental data, however, suggest that the GDL loses hydrophobicity over prolonged PEFC operation and becomes prone to enhanced flooding. In this work, we present a pore-scale modeling framework to study the structure-wettability-durability interplay in the context of flooding behavior in the PEFC GDL.

Numerical and Experimental Analysis of Subfreezing Operation in PEM Fuel Cells

J. Mishler, Y. Wang, P. P. Mukherjee, R. Mukundan, and R. L. Borup

Conference PaperProceedings of ASME FuelCell2010, 8th ASME International Fuel Cell Science, Engineering, and Technology Conference (2010)

Abstract

In this work, we present a neutron radiography and analysis, as well as modeling study on cold-start operation of polymer electrolyte membrane (PEM) fuel cells. Fuel cells with Gore™ or LANL MEAs and SGL or E-Tek ELAT GDLs are tested in varying subfreezing temperatures (−40 to 0°C) to determine the time scale of cold-start failure, amount of solid water formation, solid water formation location, and. A higher PTFE-loading in the MPL is found to decrease loss in electrocatalytic surface area in our case. Theoretical analysis is also conducted and model predictions are compared with the experimental data in terms of the cell voltage evolution.

Numerical Modeling of Two-Phase Behavior in the PEFC Gas Diffusion Layer

P. P. Mukherjee, Q. Kang, R. Mukundan, and R. L. Borup

Conference PaperECS Transactions (2010)

Abstract

A critical performance limitation in the polymer electrolyte fuel cell (PEFC) is attributed to the mass transport loss originating from suboptimal liquid water transport and flooding phenomena. Liquid water can block the porous pathways in the fibrous gas diffusion layer (GDL) and the catalyst layer (CL), thus hindering oxygen transport from the flow field to the electrochemically actives sites in the catalyst layer. The cathode GDL is the component primarily responsible for facilitating gas and liquid transport, therefore plays a major role in determining the water management of a PEFC and hence the mass transport loss. The underlying pore morphology and wetting characteristics have significant influence on the flooding dynamics in the GDL. In this paper, the study of the two-phase behavior and the durability implications due to the wetting characteristics in the carbon paper GDL are presented using a pore-scale modeling framework.

Two-Phase Behavior and Effect of Compression in a PEFC Gas Diffusion Medium

P. P. Mukherjee, C. Y. Wang, V. P. Schulz, Q. Kang, J. Becker, and A. Wiegmann

Conference PaperECS Transactions (2009)

Abstract

A key performance limitation in the polymer electrolyte fuel cell (PEFC), manifested in terms of mass transport loss, originates from liquid water transport and resulting flooding phenomena in the constituent components. A key contributor to the mass transport loss is the cathode gas diffusion layer (GDL) due to the blockage of available pore space by liquid water thus rendering hindered oxygen transport to the active reaction sites in the electrode. The GDL, therefore, plays an important role in the overall water management in the PEFC. The underlying pore-morphology and the wetting characteristics have significant influence on the flooding dynamics in the GDL. Another important factor is the role of cell compression on the GDL microstructural change and hence the underlying two-phase behavior. In this article, we present the development of a pore-scale modeling formalism coupled with realistic microstructural delineation and reduced order compression model to study the structure-wettability influence and the effect of compression on two-phase behavior in the PEFC GDL.

High Resolution Neutron Imaging of Water in the Polymer Electrolyte Fuel Cell Membrane

P. P. Mukherjee, R. Mukundan, J. Spendelow, J. R. Davey, R. L. Borup, D. S. Hussey, D. L. Jacobson, and M. Arif

Conference PaperECS Transactions (2009)

Abstract

Water transport in the ionomeric membrane, typically Nafion®, has profound influence on the performance of the polymer electrolyte fuel cell, in terms of internal resistance and overall water balance. In this work, high resolution neutron imaging of the Nafion® membrane is presented in order to measure water content and through-plane gradients in situ under disparate temperature and humidification conditions.

Pseudo One-Dimensional Analysis of Polymer Electrolyte Fuel Cell Cold-Start

Y. Wang<, J. Mishler, P. P. Mukherjee, R. Mukundan, and R. L. Borup

Conference PaperECS Transactions (2009)

Abstract

This paper investigates the electrochemical kinetics, oxygen transport, and solid water formation in polymer electrolyte fuel cell (PEFC) during cold start. Following [Y. Wang, J. Electrochem. Soc., 154 (2007) B1041-B1048.], we develop a pseudo one-dimensional analysis, which enables the evaluation of the impact of ice volume fraction and temperature variations on cell performance during cold-start. The oxygen profile, starvation ice volume fraction, and relevant overpotentials are obtained. This study is valuable for studying the characteristics of PEFC cold-start.

Wetting and Drying Responses of Gas Diffusion Layers and Proton Exchange Membrane to Current Transients

J. R. Davey, R. Mukundan, J. S. Spendelow, P. P. Mukherjee, D. S. Hussey, D. L. Jacobson, and M. Arif, and R. L. Borup

Conference PaperECS Transactions (2009)

Abstract

This study examined the hydration state of the PEM and GDLs in four PEM fuel cells, with various combinations of SGL Carbon carbon paper GDLs with different PTFE loadings, in response to current step up and step down transients. The goal was to determine the effect of these GDLs and their PTFE loadings in the substrates and MPLs on the water dynamics and performance. The fuel cells used GoreTM MEAs and were operated at 80oC with stoich tracking gas flows at 50% inlet RHs. In situ HFR measurements were used for monitoring PEM hydration and in situ neutron imaging of the fuel cells was conducted at NIST with quantitative analysis to determine the liquid water content in the GDLs and channels. High PTFE loadings in the porous, open GDL substrates allow for greater water flux and lower water holding capacity, which facilitates cathode reaction water removal at high currents. In contrast, high PTFE loadings in the less porous, smaller pore size MPLs increase the water barrier attributes and seal in PEM water. Counter flow gas feed results in more even water distribution than co-flow feed. Counter flow feed with cathode air flowing against gravity increases cell hydration in dry operating conditions.

Capillarity, Wettability and Interfacial Dynamics in Polymer Electrolyte Fuel Cells

P. P. Mukherjee

Conference PaperInvited Keynote Paper in Proceedings of the ASME 7th International Conference on Nanochannels, Microchannels and Minichannels, Pohang, South Korea (2009)

Abstract

In the present scenario of a global initiative toward a sustainable energy future, the polymer electrolyte fuel cell (PEFC) has emerged as one of the most promising alternative energy conversion devices for different applications. Despite tremendous progress in recent years, a pivotal performance/durability limitation in the PEFC arises from liquid water transport, perceived as the Holy Grail in PEFC operation. The porous catalyst layer (CL), fibrous gas diffusion layer (GDL) and flow channels play a crucial role in the overall PEFC performance due to the transport limitation in the presence of liquid water and flooding phenomena. Although significant research, both theoretical and experimental, has been performed, there is serious paucity of fundamental understanding regarding the underlying structure-transport-performance interplay in the PEFC. The inherent complex morphologies, micro-scale transport physics involving coupled multiphase, multicomponent, electrochemically reactive phenomena and interfacial interactions in the constituent components pose a formidable challenge. In this paper, the impact of capillary transport, wetting characteristics and interfacial dynamics on liquid water transport is presented based on a comprehensive mesoscopic modeling framework with the objective to gain insight into the underlying electrodics, two-phase dynamics and the intricate structure-transport-interface interactions in the PEFC.

Mesoscopic Modeling of Liquid Water Transport in Polymer Electrolyte Fuel Cells

P. P. Mukherjee and C. Y. Wang

Conference PaperECS Transactions (2008)

Abstract

A key performance limitation in polymer electrolyte fuel cells (PEFC), manifested in terms of mass transport loss, originates from liquid water transport and resulting flooding phenomena in the constituent components. Liquid water leads to the coverage of the electrochemically active sites in the catalyst layer (CL) rendering reduced catalytic activity and blockage of the available pore space in the porous CL and fibrous gas diffusion layer (GDL) resulting in hindered oxygen transport to the active reaction sites. The cathode CL and the GDL therefore play a major role in the mass transport loss and hence in the water management of a PEFC. In this article, we present the development of a mesoscopic modeling formalism coupled with realistic microstructural delineation to study the profound influence of the pore structure and surface wettability on liquid water transport and interfacial dynamics in the PEFC catalyst layer and gas diffusion layer.

Probing Liquid Water Profile in the Polymer Electrolyte Fuel Cell Membrane

P. P. Mukherjee, T. E. Springer, R. Mukundan, D. S. Hussey, D. L. Jacobson, M. Arif, and R. L. Borup

Conference PaperECS Transactions (2008)

Abstract

Water transport in the ionomeric membrane, typically Nafion®, has profound influence on the performance of the polymer electrolyte fuel cell, in terms of internal resistance and overall water balance. In this work, the response of Nafion® membrane water content and the resulting water gradient to fuel cell operational variability are investigated and the results from a theoretical modeling study are furnished along with reference to neutron imaging observations.

One Dimensional Analysis of Subzero Start-Up for Polymer Electrolyte Fuel Cells

J. Chen, Y. Wang, and P. P. Mukherjee

Conference PaperECS Transactions (2008)

Abstract

This paper investigates interaction of the electrochemical kinetics, oxygen transport and solid water formation within polymer electrolyte fuel cell (PEFC) electrode during cold start. Followed by the analysis of Wang [1], we simplify the one-dimensional model of electrode processes, which allows solving the profiles of important quantities and directly relating the ice impact mechanisms to surface overpotential. The key parameters that govern these profiles are evaluated in the range of the relevant factors for a typical fuel cell. We also decouple the mechanisms of solid water impacts and compare their importance. This study is valuable for studying the characteristics of cold-start for PEFCs.

A Catalyst Layer Flooding Model for Polymer Electrolyte Fuel Cells

P. P. Mukherjee and C. Y. Wang

Conference PaperProceedings of ASME FuelCell2008, 6th ASME International Fuel Cell Science, Engineering, and Technology Conference, Denver, CO, USA (2008)

Abstract

It is widely recognized that the performance degradation and the limiting current behavior in polymer electrolyte fuel cells (PEFC) are mainly attributed to the excessive build up of liquid water in the cathode side and the resulting flooding phenomena. Liquid water blocks the open pore space in the catalyst layer (CL) and the gas diffusion layer (GDL) leading to hindered oxygen transport and covers the electrochemically active sites in the CL thereby rendering reduced catalytic activity. The CL flooding therefore plays a crucial role in the overall PEFC performance limitation. In order to elucidate the primary mechanisms of liquid water removal out of the CL, the factors affecting CL flooding and to discern the role and contribution of CL flooding on the overall PEFC voltage loss, a CL flooding model has been developed. The flooding model is based on a simplified structure-wettability representation of the PEFC CL and a physical description of water and heat balance along with electrochemical performance analysis. The model shows that the evaporation mechanism, depending upon the cell operating temperature and the GDL thermal conductivity, plays a crucial role in the CL flooding behavior and the cell performance.

Modeling of Catalyst Layer Surface Coverage and Volume Blockage Owing to Liquid Water in a PEFC

P. P. Mukherjee and C. Y. Wang

Conference PaperECS Transactions (2006)

Abstract

A comprehensive pore-scale modeling framework has been developed for the catalyst layer of a polymer electrolyte fuel cell in order to study the effects of site coverage and volume blockage owing to liquid water. The catalyst layer microstructure is reconstructed using a stochastic generation method. The liquid water distribution is obtained from a two- phase lattice Boltzmann simulation and the catalytic surface coverage leading to reduced electrochemical activity is estimated from the saturation maps. The pore blockage effect due to liquid water is evaluated using a direct numerical simulation model from the reduced oxygen diffusivity owing to the resistance offered by the blocked pores.

Numerical Evaluation of Effective Gas Diffusivity - Saturation Dependence of Uncompressed and Compressed Gas Diffusion Media in PEFCs

V. P. Schulz, P. P. Mukherjee, J. Becker, A. Wiegmann, and C. Y. Wang

Conference PaperECS Transactions (2006)

Abstract

In the current work, we present a comprehensive modeling framework to predict the effective gas diffusivity, as a function of liquid water saturation, based on realistic 3-D microstructures of the uncompressed as well as compressed gas diffusion layer (GDL). The presented approach combines the generation of a virtual microscopic GDL and different physical modeling. We develop a reduced model in order to simulate the compression of the GDL layer since its compression has a strong impact on the material properties such as the water transport or its gas diffusion. Then, we determine the two-phase distribution of a non-wetting fluid, i.e. water, and a wetting fluid, i.e. air, within the GDL for different saturations. This is done using a full morphology (FM) model. Finally, solving the Laplace equation for the partly saturated medium we determine the relative gas diffusion, i.e. the gas diffusion depending on the saturation. In the present work, our approach is applied to a typical GDL medium, a SGL10BA carbon paper.

Effect of Anisotropy of Gas Diffusion Layers on Two-Phase Heat and Mass Transport in Polymer Electrolyte Fuel Cells

U. Pasaogullari, P. P. Mukherjee, C. Y. Wang, and K. S. Chen

Conference PaperECS Transactions (2006)

Abstract

A non-isothermal, two-phase model is applied to a two- dimensional model of GDL to study the heat and mass transport in the in-plane direction (i.e. channel-to-land) and in the through-plane direction (i.e. catalyst layer-to-channel). For the first time, the anisotropy in the GDL thermal conductivity is taken into account, and found to be an important factor governing the temperature distribution in the GDL. The maximum temperature difference in the GDL is found to be a strong function of the GDL anisotropy. A temperature difference of up to 5ºC is predicted, and a significant effect of temperature distribution on the water transport and distribution is observed. In addition, the latent heat effects due to condensation/evaporation of water on the temperature and water distributions are also analyzed and found to strongly affect the two-phase transport.

Numerical Investigation of Heat Transfer Enhancement in Fin-tube Heat Exchangers with Winglet Type Vortex Generators

P. P. Mukherjee, S. Sarkar, and G. Biswas

Conference PaperProceedings of the International Conference on Scientific and Engineering Computation (IC-SEC), Singapore (2002)

Numerical Simulation of Enhanced Oil Recovery from Porous Formations and Fractured Rocks

P. P. Mukherjee, K. Muralidhar, and G. Biswas

Conference PaperProceedings of the 4th ISHMT-ASME Heat and Mass Transfer Conference, 857, Pune, India (2000)

Modeling Transport Phenomena in Porous Media with Applications

M. K. Das, P. P. Mukherjee and K. Muralidhar

Book Ed: F. A. Kulacki, Mechanical Engineering Series, Springer (2017)

Mesoscale Physics based Modeling and Analysis in Electrochemical Energy Systems

V. Kabra, N. Goswami, B.S. Vishnugopi, and P. P. Mukherjee

Chapter in Modern Aspects of Electrochemistry, Ed: S..Santhanagopalan; Springer Nature (2023)

Performance Degradation Modeling in Silicon Anodes

P. P. Mukherjee and A. Verma

Chapter in Silicon Anode Systems for Lithium-Ion Batteries, Ed: P. N. Kumta, A. F. Help, M. K. Datta, and O. I. Velikokhatnyi; Ch. 8, Elsevier (2022)

Multiscale Modeling of Physicochemical Interactions in Lithium-Sulfur Battery Electrodes

P. P. Mukherjee, Z. Liu, F. Hao, and B.S. Vishnugopi

Chapter in Lithium-Sulfur Batteries, Ed: P. N. Kumta, A. F. Help, M. K. Datta, and O. I. Velikokhatnyi; Ch. 4, Elsevier (2022)

Microstructure Reconstruction and Transport Simulation in PEM Fuel Cells

P. P. Mukherjee, V. P. Schulz, J. Becker, E. Glatt, and A. Wiegmann

Chapter Invited Chapter in Polymer Electrolyte Membrane and Direct Methanol Fuel Cell Technology (PEMFCs and DMFCs), Ed: C. Hartnig and C. Roth, Ch. 9, Woodhead Publishing Ltd. (2012)

Multi-scale Modeling of Two-Phase Transport Phenomena in PEM Fuel Cells

J. Hinebaugh, A. Bazylak, and P. P. Mukherjee

Chapter Invited Chapter in Polymer Electrolyte Membrane and Direct Methanol Fuel Cell Technology (PEMFCs and DMFCs), Ed: C. Hartnig and C. Roth, Ch. 10, Woodhead Publishing Ltd., (2012)

Micro/nano Transport in Microbial Energy Harvesting

R. Ghosh, A. Kumar, and P. P. Mukherjee

Chapter in Encyclopedia of Nanotechnology, Ed: B. Bhushan, Article 00421, Springer (2012)

Bacterial electrical conduction; Cellular electronic energy transfer; Microbial electrolysis cell; Microbial fuel cell.

Biofilms in Microfluidic Devices

S. Neethirajan, D. Karig, A. Kumar, P. P. Mukherjee, S. T. Retterer, and M. J. Doktycz

Chapter in Encyclopedia of Nanotechnology, Ed: B. Bhushan, Article 00427, Springer (2012)

Biofilms are aggregations of microbes that are encased by extracellular polymeric substances (EPS) and adhere to surfaces or interfaces. Biofilms exist in a very wide diversity of environments, and microfluidic devices are being increasingly utilized to study and understand their formation and properties.

Modeling and Simulation of Battery Systems

P. P. Mukherjee, S. Pannala, and J. A. Turner

Chapter Invited Chapter in Handbook of Battery Materials, 2nd Edition, Ed. C. Daniel, and J. O. Besenhard, Ch. 25, Wiley-VCH, Weinheim, Germany, (2011)

Electrodics in Electrochemical Energy Conversion Systems

P. P. Mukherjee and Q. Kang

Chapter Invited Chapter in Mechanics over Micro and Nano Scales, Springer, Ed: S. Chakraborty, Ch. 7, Springer (2011)

Modeling of Two-phase Transport Phenomena in Porous Media: Pore-scale Approach

P. K. Sinha and P. P. Mukherjee

Chapter Invited Chapter in Mechanics over Micro and Nano Scales, Springer, Ed: S. Chakraborty, Ch. 3, Springer (2011)

Fundamentals of two-phase transport in a porous medium with emphasis on pore-scale physics are discussed. Lattice Boltzmann modeling and pore network modeling techniques are reviewed and are deployed to study two-phase flow in the engineered porous materials used in a polymer electrolyte fuel cell (PEFC). Computation of fluid distribution, capillary pressure, and relative permeability is discussed. Porous material microstructure–PEFC performance relation is showcased, highlighting the potential of deploying pore-scale modeling to the advancement of fundamental two-phase transport understanding and PEFC porous material development. Additionally, the need for further advancement of pore-scale models is highlighted.

Polymer Electrolyte Fuel Cell Modeling: A Pore-Scale Perspective

P. P. Mukherjee and C. Y. Wang

Chapter Invited Chapter in Progress in Green Energy, Ed: X. Li, Vol. 1, Ch. 5, Springer (2011)

Fuel cells, being highly energy efficient, environmentally benign, and minimally noisy, are widely considered as the 21st century energy-conversion devices for mobile, stationary, and portable power. Unlike the conventional Carnot cycle based energy conversion devices with intermediate heat and mechanical energy generation, fuel cells convert the chemical energy of a fuel directly into electricity. Among the several types of fuel cells, the polymer electrolyte fuel cell (PEFC) has emerged as the most promising power source for a wide range of applications.

Mesoscopic Modeling of Two-Phase Transport in Polymer Electrolyte Fuel Cells

P. P. Mukherjee and C. Y. Wang

Chapter Invited Chapter in Modeling and Diagnostics of Polymer Electrolyte Fuel Cells, special issue of Modern Aspects of Electrochemistry series, Ed. U. Pasaogullari and C. Y. Wang, 49, Ch. 8, Springer (2010)

Fuel cells, owing to their high energy efficiency, environmental friendliness and low noise, are widely considered as the twenty-first century energy-conversion devices for mobile, stationary and portable power. Among the different types of fuel cells, the polymer electrolyte fuel cell (PEFC) has emerged as a promising power source for a wide range of applications.

Perspectives of Micro and Nanofabrication of Carbon for Electrochemical and Microfluidic Applications

R. Martinez-Duarte, G. T. Teixidor, P. P. Mukherjee, Q. Kang, and M. J. Madou

Chapter Invited Chapter in Microfluidics and Microfabricaion, Ed: S. Chakraborty, 181-263, Springer (2010)

This chapter focuses on glass-like carbons, their method of micro and nanofabrication and their electrochemical and microfluidic applications. At first, the general properties of this material are exposed, followed by its advantages over other forms of carbon and over other materials. After an overview of the carbonization process of organic polymers we delve into the history of glass-like carbon. The bulk of the chapter deals with different fabrication tools and techniques to pattern polymers. It is shown that when it comes to carbon patterning, it is significantly easier and more convenient to shape an organic polymer and carbonize it than to machine carbon directly. Therefore the quality, dimensions and complexity of the final carbon part greatly depend on the polymer structure acting as a precursor. Current fabrication technologies allow for the patterning of polymers in a wide range of dimensions and with a great variety of tools. Even though several fabrication techniques could be employed such as casting, stamping or even Computer Numerical Controlled (CNC) machining, the focus of this chapter is on photolithography, given its precise control over the fabrication process and its reproducibility. Next Generation Lithography (NGL) tools are also covered as a viable way to achieve nanometer-sized carbon features. These tools include electron beam (e-beam), Focused-ion beam (FIB), Nano Imprint Lithography (NIL) and Step-and-Flash Imprint Lithography (SFIL). At last, the use of glass-like carbon in three applications, related to microfluidics and electrochemistry, is discussed: Dielectrophoresis, Electrochemical sensors, and Fuel Cells. It is exposed how in these applications glass-like carbon offers an advantage over other materials.

Direct Numerical Simulation of Polymer Electrolyte Fuel Cell Catalyst Layers

P. P. Mukherjee, G. Wang, and C. Y. Wang

Chapter Invited Chapter in Modern Aspects of Electrochemistry, Ed. R. White et al., 40, Ch. 6, Springer, New York (2007)

Fuel cells, due to their high energy efficiency, zero pollution and low noise, are widely considered as the 21st century energy-conversion devices for mobile, stationary and portable power. Among the several types of fuel cells, polymer electrolyte fuel cell (PEFC) has emerged as the most promising power source for a wide range of applications.

Mesoscale Physics of Electrified Interfaces with Metal Electrodes

Bairav Sabarish Vishnugopi

Ph.D. ThesisPurdue University, West Lafayette (2023)

Kinetics and Chemo-Mechanics in Sodium Metal and Alloy Electrodes

Susmita Sarkar

Ph.D. ThesisPurdue University, West Lafayette (2023)

Mesoscale and Interfacial Physics in the Catalyst Layer of Electrochemical Energy Conversion Systems

Navneet Goswami

Ph.D. ThesisPurdue University, West Lafayette (2023)

Physics Based Degradation Analytics in Energy Storage

Venkatesh Kabra

Ph.D. ThesisPurdue University, West Lafayette (2023)

Image Based Electrode Analytics Using Machine Learning

Chance Norris

Ph.D. ThesisPurdue University, West Lafayette (2022)

Mechanistic Role of Thermal Effects on Lithium Plating

Conner Fear

Ph.D. ThesisPurdue University, West Lafayette (2022)

Operando Analytics of Lithium Electrodeposition

Sobana Rangarajan

Ph.D. ThesisPurdue University, West Lafayette (2021)

Interrogating Buried Electrochemical Interfaces

Deepti Tewari

Ph.D. ThesisPurdue University, West Lafayette (2020)

Multimodal Degradation Interactions in Electrodes for Energy Storage

Ankit Verma

Ph.D. ThesisPurdue University, West Lafayette (2020)

Degradation – Safety Analytics in Energy Storage

Daniel Juarez Robles

Ph.D. ThesisPurdue University, West Lafayette (2019)

Mesoscale Interactions in Porous Electrodes

Aashutosh Mistry

Ph.D. ThesisPurdue University, West Lafayette (2019)

Mesoscale Interaction in Electrodes for Energy Storage

Zhixiao Liu

Ph.D. ThesisTexas A&M University, College Station (2016)

Addressing Electrode Degradation and Microstucture Effect in Energy Storage

Chien-Fan Chen

Ph.D. ThesisTexas A&M University, College Station (2016)

Mechano-Electrochemical Interactions and Stochastics in Intercalation Electrodes

Pallab Barai

Ph.D. ThesisTexas A&M University, College Station (2015)

Implications of Off Nominal Conditions on Degradation and Cycle Life of Li-Ion Cells

Maria Terese

M.S. ThesisPurdue University, West Lafayette (2023)

Interrogating Underlying Mechanisms of Room Temperature Sodium Sulfur Cells

Trent James Murray

M.S. ThesisPurdue University, West Lafayette (2022)

Internal Short Circuit in Lithium-ion Batteries

Fahim Vora

M.S. ThesisPurdue University, West Lafayette (2022)

Effect of Electrolytes on Room-Temperature Sodium-Sulfur Battery Performance

Daniel Reed

M.S. ThesisPurdue University, West Lafayette (2022)

Operando Degradation Diagnostics and Fast Charging Analytics in Lithium-Ion Batteries

Amy Bohinsky

M.S. ThesisPurdue University, West Lafayette (2021)

Operando Analysis of Lithium Plating in Lithium-Ion Cells

Tanay Adhikary

M.S. ThesisPurdue University, West Lafayette (2019)

Mechanistic Analysis of Sodiation in Electrodes

Akshay Parag Biniwale

M.S. ThesisPurdue University, West Lafayette (2019)

Degradation Behavior of Lithium-Ion Cells Under Overcharge Extremes

Anjul Arun Vyas

M.S. ThesisPurdue University, West Lafayette (2019)