In lithium-ion batteries, appearances can be deceiving: although external sensors may report safe operating temperatures, the interior of the battery may be experiencing extreme heat, leading to unsafe conditions. Purdue University researchers are investigating how to diagnose the “true” temperature of a battery in real time. (AI illustration/Purdue University)

“Most battery thermal management systems use external sensors,” said Anuththara Alujjage, a Ph.D. student in mechanical engineering. “But that doesn’t give the whole picture of what’s actually going on. It may be telling you that your battery is good because the external operating temperature is in range, but something entirely different may be happening inside the battery.”

Alujjage works in the Energy and Transport Sciences Lab with Partha Mukherjee, professor of mechanical engineering. Their team’s research focuses on the fundamental mechanisms that affect the performance, safety, and lifespan of energy storage systems, with an emphasis on battery safety. For example, they have partnered with UL Research Institutes to establish a research hub devoted to the design and operation of batteries and energy storage systems and their impact on safety and resilience.

In order to truly measure what’s happening inside a battery, you have to put sensors inside. But doing that invalidates its real-world performance. So Alujjage chose a hybrid approach: use internal sensors to build a theoretical model of how lithium-ion cells heat up and cool down; and combine that with observed data from external sensors to construct a comprehensive physics-based framework that reflects the true thermal condition of batteries in operation.

For this project, they collaborated with Texas Instruments; their research has been published in Advanced Functional Materials.

“What we found is that internal temperatures follow a non-linear evolution,” Alujjage said. “The further you get through a battery cycle, the more the internal temperature diverges from the surface temperature. We also found that internal heat generation is more pronounced during discharge than charging, with this effect intensifying at higher currents and lower temperatures.”

These extreme temperature gradients are important to understand, as they can accelerate degradation effects such as lithium plating that drastically reduce a battery’s performance. They can even lead to thermal runaway and catastrophic failure, a severe safety risk for any smartphone or electric vehicle.

“To prevent these from happening, we need smarter battery thermal management systems,” Alujjage said. “Our research lays the foundation for the next generation of onboard diagnostics. Using our models we can build digital twins of a battery, and combine its data with external temperature sensors to give a more accurate real-time picture of a battery’s thermal state, whatever its materials or construction.”

“I joined this field because I believe electrification is important to building a sustainable future,” Alujjage said. “If we want people to use electric vehicles and devices, we want to be able to ensure that they are safe. I’m glad to work on a project that contributes to the betterment of all these products, making them safer and more resilient.”

Source: Anuththara Alujjage, aalujjag@purdue.edu

Writer: Jared Pike, jaredpike@purdue.edu, 765-496-0374

Internal Temperature Evolution Metrology and Analytics in Li-Ion Cells
Anuththara S. J. Alujjage, Bairav S. Vishnugopi, Avijit Karmakar, David P. Magee, Yevgen Barsukov, and Partha P. Mukherjee
https://doi.org/10.1002/adfm.202417273
ABSTRACT: Lithium-ion (Li-ion) batteries have become indispensable as the energy landscape shifts toward electrification. Enhancing their cycle life while ensuring optimal safety and performance is predicated on developing advanced thermal management approaches. Most battery thermal management systems rely on external temperature sensors, which do not reflect the true dynamic changes in internal temperatures, especially under operational extremes. This study utilizes a combination of operando thermal sensing and mechanistic modeling to investigate internal temperature evolution and associated thermo-electrochemical interactions during Li-ion cell cycling. Through this analysis, the non-linear progression in cell temperature dynamics at various operating conditions and the underlying difference between the internal and external temperatures are captured. The internal temperature measurements reveal a critical asymmetry in the thermal response during charge and discharge operation, with a strong dependence on the current rate and operating temperature. In synergy with thermal sensing, a physics-based modeling framework is developed to quantify different modes of heat generation within the cell layers and correlate them with the occurrence of degradation mechanisms, including lithium plating and solid electrolyte interphase interactions. This work provides the baseline for developing onboard diagnostic tools capable of detecting internal cell temperatures and monitoring cell safety through integrated thermal sensing and physics-informed digital twins.