Batteries by Design (R. Edwin García)
Modern rechargeable batteries are complex ensembles of particles of electrochemically active material with high charge capacity utilization achieved through the development of optimized chemistries and particle architectures (see Figure 1). Here the research performed by the group led by Prof. Edwin García focuses on the development of thermodynamic and kinetic theories, models, and algorithms to realize improved portable and stationary energy storage technology. In order to incorporate the effects of the mesoscale microstructure and tortuosity, a theoretical framework is being developed to establish processing-property relations that combine the constitutive properties of the individual components into realistic microstructural designs. The developed framework is directly compared against experimental results [1,2,3].
Figure 1. (a) As received imaged cross-section of rechargeable lithium-ion battery. (b) Segmented and digitized cross-section of battery: green phase corresponds to crystallographically anisotropic graphite phase, red to LiCoO2 particles, and black background to electrolyte. (c) Predicted 2D spatial distribution of lithium after a 1C discharge. In anode, darker regions (smaller particle size) in anode correspond lithium-depleted regions. Microstructure cross-section is a courtesy of Dr. Quinn Horn [1].
Our most recent effort is on the generation of spatially-resolved computer representations of battery material microstructures by directly using 3D X-ray CT data (see Figure 2). The effort allows to simulate the local and macroscopic electrochemical response of real battery electrodes as a function of galvanostatic cycling. Through this analysis, the effects of the discharge-rate on deleterious effects, such as dendrite formation and salt precipitation are assessed. A comparison against previously performed two-dimensional work (e.g., see Figure 1) is also carried out to understand the reaches and limitations of low-dimensional (1D and 2D) models. The development of an accurate understanding of the basic physical microstructural mechanisms that occur during battery operation is expected to lead to improved coarse grained (Newman-based) models that will incorporate the richness of behavior of the underlying microstructure.
Figure 2. 50x60x60 micrometers preliminary calculation of discharge sequence of reconstructed, three-dimensionally determined graphite anode.
Figure 3. a) Average hydrostatic stress in intercalated grain as a function of crystallographic orientation. Grain is subjected to a maximum tensile stress of 250MPa when the grain is oriented at approximately 45◦ and a maximum compressive stress of 70MPa when the grain is oriented at 90◦. (b) shows average shear stress as a function of grain orientation. The grain boundary is subjected to maximum shear stress at approximately 40◦ and minimum shear stress at 0◦ and 90◦.
A focus on the basic science on batteries is on modeling existing and emerging battery characterization techniques, such as Electrochemical Strain Microscopy (ESM). Here, numerical techniques are being developed to demonstrate the effect of the relevant transport paths within polycrystalline thin film and the extent of lithium diffusion into the electrode as a function of the ESM-tip-imposed overpotential frequency. Recent results demonstrate that the crystallographic orientation of electrochemically-actuated grains has a significant impact on the entirety of the intercalation process, including effective stored charge, discharge rate, electrochemically induced stresses, and side reactions (see Figure 3). Simulations also demonstrate that continuous battery cycling results in a cumulative capacity loss as a result of successive non-reversible lithium intercalation. Results also demonstrate that ESM has the capability of inferring the local out-of-plane lithium diffusivity and the out-of-plane contributions to Vegard's tensor [4,5].
1. M. C. Smith, R. E. García, and Q. C. Horn. “The Effect of Microstructure on the Galvanostatic Discharge of Graphite Anode Electrodes in LiCoO2-Based Rocking-Chair Rechargeable Batteries.” The Journal of the Electrochemical Society. (156) A896-A904, 2009.
2. R. E. García, Y.-Ming Chiang, W. C. Carter, P. Limthongkul, and C. M. Bishop. “Microstructural Modeling and Design of Rechargeable Lithium-Ion Batteries.” The Journal of the Electrochemical Society. (152) 1, A255-A263, 2005.
3. R. E. García and Y.-M. Chiang. “Spatially-Resolved Modeling of Microstructurally Complex Battery Architectures.'' Journal of the Electrochemical Society (154) A856-A864, 2007.
4. N. Balke, S. Jesse, A.N. Morozovska, E. Eliseev, D.W. Chung, Y. Kim, L. Adamczyk, R.E. García, N. Dudney, and S.V. Kalinin. “Nanometer-Scale Electrochemical Intercalation and Diffusion Mapping of Li-Ion Battery Materials.” Nature Nanotechnology, DOI: 10.1038/NNANO.2010.174, August 2010.
5. D.-W. Chung, N. Balke, S. V. Kalinin, and R. E. García “Virtual Electrochemical Strain Microscopy of Polycrystalline LiCoO2 Films.” The Journal of the Electrochemical Society, 158 (10) A1083-A1089 (2011).