Investigating capacity degradation of LiFePO4 battery for electric vehicles under different overcharge conditions

When the state of charge (SOC) estimation of the battery management system (BMS) is inaccurate or the battery balance fails, the power battery in the electric vehicle may be overcharged, resulting in the decline of battery capacity and performance. In this paper, and different overcharge paths and overcharge cut-off states of charge (SOCOC) are adopted to study the influence of different overcharge conditions on the performance decay of the commercial large format LiFePO4 battery. The experimental results show that the SOCOC is the main reason for battery performance decay. When charging and discharging at the standard rate (1/3C), it will cause the phenomenon of capacity recovery, constant voltage charging time (TOCVC) and constant voltage charging capacity ratio (CCROCVC) synchronous recovery. The battery discharge capacity overcharged to 110% recovered from 59.7% to 68.4%. One battery overcharged to 105% recovered from 58.2% to 96.5%, and the other recovered from 86% to 97.5%.