Early-Warning of Thermal Runaway for Lithium-Ion Batteries via State-Insensitive EIS Features

The early warning of thermal runaway (TR) for lithium-ion batteries (LIBs) remains a critical challenge, particularly because the thermal stability varies with the state of charge (SOC) and state of health (SOH). In this work, electrochemical impedance spectroscopy (EIS) is coupled with the accelerating rate calorimeter (ARC) to screen features that are robust to the cell state, thereby enhancing the performance of early warning. Among others, the phase angle and imaginary impedance exhibit a strong correlation with TR while maintaining robustness to SOC and SOH. The optimal ratio of signal-to-noise and discrimination capability are demonstrated at 627.8 Hz. Moreover, an early-warning framework with three levels is proposed based on two state-insensitive features. As a result, the early warning of TR can be achieved 189–608 s in advance. The proposed method provides new insights into the early warning of TR throughout the lifecycle of the LIBs, thereby enhancing the operational safety of electric vehicles and energy storage systems.