Numerical analysis of capacity fading for a LiFePO4 battery under different current rates and ambient temperatures

Abstract Understanding of the capacity fading for lithium-ion batteries will contribute to increasing the endurance of electric vehicles and avoiding rapid devaluation. Based on an electrochemical-thermal coupled model, a comprehensive physics-based cycle life model is developed for a LiFePO4 battery. The model takes the solid electrolyte interface (SEI) formation, Li plating and loss of active material (LAM) into consideration. The model can accurately predict the capacity fading of the battery under a wide range of operating temperatures and current rates (C-rates). The effects of C-rates and ambient temperatures on the capacity fading and the aging distribution inside a cell are extensively discussed. As the ambient temperature increases from -10 °C to 50 °C, the capacity fading decreases and then increases, and it can be divided into three stages. The LAM, both the LAM and SEI formation, and the SEI formation dominate the capacity fading in the first stage, the second stage and the third stage, respectively. The capacity fading in the second stage is the minimum and slightly affected by the ambient temperature. When the C-rate of cycles is 1 C, the ambient temperature range corresponding to the second stage is 20 °C ~ 30 °C. As the C-rate increases, the range will migrate to those with higher ambient temperature. When the charging C-rate increases from 4 C to 6 C, the aggravation of capacity fading is insignificant due to the fact that the charging rapidly changes into constant voltage charging. The Li plating primarily occurs in the region near to the separator, and restrains the SEI formation and the LAM in the region. The LAM in the region is more significant, which will be aggravated when the ambient temperature decreases or the C-rate increases.