Effect of charge rate on capacity degradation of LiFePO 4 power battery at low temperature

Limited by the current power battery technology, electric vehicles show extremely poor duration performance and potential risk at low temperature, which is mainly caused by poor charging performance of lithium-ion batteries. To explore the impact of charging process on cycle degradation at low temperatures, a cycle aging experimental scheme with different charging C-rate (0.3C and 0.5C) under −10°C and −20°C was designed for the commercial LiFePO4 battery. The experimental batteries showed severe degradation after a few of cycles. The phenomenon of reduced internal resistance and up-shift of the charging curve was found during the early cycle stages (0th-20th cycle). The influence of low-temperature cycle on battery was analyzed by the increment capacity analysis (ICA); the fast decreasing intensity of ①*II showed sharp loss of lithium ions. Those lithium ions mainly transformed into lithium plating and built up dendrites instead of reintercalating into the anode crystal structure, causing the further degradation of capacity and ohmic resistance. Degradation law was obtained by curve regression analysis in the end.