Because of the inconsistency of a battery pack and the fault of a charging device

lithium ion battery will be overcharged during use.In order to explore the influences of overcharge cycling on battery aging and safety

the degradation process and aging mechanism of lithium ion battery under overcharge cycling were studied qualitatively and quantitatively based on electrochemical impedance spectroscopy. In addition

the new and aged lithium ion batteries were overcharged for safety tests. The results show that

compared with the normal cycling

the overcharge cycling will lead to a rapid decline in battery capacity

which will accelerate the battery aging. The loss of lithium inventory has the greatest impact on battery aging

the loss of active material is at a medium level

while the conductivity loss has a negligible impact on capacity fading. As the aging degree deepens

the stability and safety of the battery become worse.After 92%SOH

side reactions occur in the battery during the overcharge tests

which greatly increases the energy released by the battery. The maximum temperature of aging batteries at 79.6%SOH is 68% higher than that of fresh battery

and the aged battery can not be reused after the experiment. The loss of lithium inventory and the loss of active material in batteries are the most correlated factors to cause side effects during overcharge tests. The experimental results can provide references for battery design and battery management system

so as to improve the battery’s tolerance to overcharging and safety.