Effects of ambient temperature on the health characteristics of vehicular Li-ion batteries by electrochemical impedance spectroscopy

To widely commercialize electric vehicles (EVs), more efforts to improve their life span seem profoundly inevitable. Thermal conditions have profound the nonlinear effects on the degradation rate, performance, and safety level of an EV battery pack. In the current study, both cycle life and calendar life of a commercial LiFePO4-based cell are investigated experimentally via electrochemical impedance spectroscopy (EIS) for different operating temperatures. This is the first time that the effects of low temperatures such as − 20 °C and − 5 °C on the life of LiFePO4-based cells are investigated via EIS, which is the crucial case during the cold start of EVs in cold climate regions of the world. The results show a considerable increase of solvent resistance for the cell which experienced calendar aging test at 55 °C; this demonstrates a drastic thickening of the SEI for this storage temperature. Moreover, anode cracking is clearly observed at such a high temperature. The results of the cycle aging tests also show that the increase in the solvent resistance is negligible for all other three operating temperatures. Nevertheless, the increasing of SEI thickness at low-temperature condition (− 5 °C) is noticeable. The role of temperature on the degradation level of LiFePO4-based cells has also been discovered via scanning electron microscopy.