Abstract: In this paper, the overcharge behaviors of 30 A·h pouch lithium-ion battery with LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622) cathode for electric vehicles are studied under different overcharge current rates (C-rates). The results indicate that the overcharge process can be divided into four stages. The highest surface temperature position of the cell is not fixed. In most test time, the maximum temperature difference (MTD) is less than 1 °C. It's worth noting that the C-rate has a great influence on the overcharge behaviors of Li-ion batteries. As C-rate increases, so do the maximum temperature and crest voltage, while the overcharge time and state of charge (SOC) value at the end of the test decrease as the C-rate increases. The study can provide a reference for the safety design of nickel-rich lithium-ion batteries and the safety management of the battery management system (BMS) for overcharge fault.

Key words: lithium-ion power battery, overcharge behaviors, thermal runaway, charging rate