Accurate non-invasive prediction of battery internal temperature to enhance battery safety

Thermal runaway in batteries, driven by uncontrolled temperature rise, remains a critical safety challenge, highlighting limitations in temperature monitoring and management. Here, we report a non-invasive internal temperature evaluation method based on in-operando isothermal calorimetry. The method quantitatively characterizes heat generation and evaluates internal temperature gradients under various operating conditions, demonstrating the existence of thermal hysteresis and its dependence on temperature and charge/discharge rates. Applying heat transfer theory to boundary heat flux data obtained from calorimetry enables the evaluation of the internal temperature distribution, whose validity is confirmed through in situ temperature measurements. A geometric approximation further extends the methodology to thermal management applications lacking direct calorimetry capabilities, enabling estimation of internal temperature during discharge. This non-invasive strategy provides reliable reference internal temperatures for safely profiling internal thermal states and guiding the design of advanced battery thermal management systems.