Internal Temperature Evolution Metrology and Analytics in Li‐Ion Cells

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.