Impact of Internal Temperature Stabilisation on Electrochemical Impedance Spectroscopy Based State‐of‐Health Evaluation of Electric Vehicle Battery Modules for Second‐Life Applications

As second‐life applications for used electric vehicle (EV) batteries receive growing attention, the need for accurate and efficient diagnostics of the state‐of‐health (SOH) of such battery modules becomes increasingly critical. Electrochemical impedance spectroscopy (EIS) stands out as one of the most promising techniques for this purpose, offering comprehensive and non‐destructive analysis of various SOH indicators. However, its pronounced sensitivity to temperature raises concerns regarding the influence of thermal conditions during measurements. This study investigates the thermal stabilisation behaviour of a first‐generation Nissan Leaf battery module subjected to step changes in ambient temperature and evaluates how internal thermal dynamics affect the accuracy and reliability of key EIS parameters. The results show that, at the point when the module casing appears thermally stabilised, the R OHM and Warburg impedance exhibit acceptable accuracy approaching the 2% error benchmark. In contrast, R SEI and R CHT demonstrate large relative errors and require significantly more time to reach thermal equilibrium. These findings highlight that, under the tested conditions, surface temperature monitoring alone is insufficient. This work provides practical insight into reliable EIS‐based SOH diagnostics of used battery modules, with particular emphasis on the impact of ambient temperature variations during the transition from storage to testing facilities.