Calendar degradation of Li-ion batteries under high storage temperature based on electrochemical impedance spectroscopy

High temperature accelerates the degradation of Li-ion batteries, but the influences of temperature as high as 70 °C have not been identified. Therefore, calendar degradation of Li-ion batteries under 70 °C was investigated, degradation models on capacity and resistance were developed. The electrochemical impedance spectroscopy (EIS) components, such as Rb, Rct, and RSEI, were analyzed, the degradation behaviors of EIS components with storage time under 70 °C were identified by developed models to describe the influences of high temperature on resistance of Li-ion batteries. The results present that DCR increases with degradation time, whereas the capacity decreases with degradation time, but the EIS components exhibit various changing trends with degradation time. In addition, 0 V open circuit voltage was observed due to internal structure broken by gas generation and was verified by computerized tomography inspection.