The inconsistency of the cells and inadequate charge balancing can result in slight overcharging of some Li-ion battery cells.The impact of this condition on battery capacity has not been fully elucidated.Galvanostatic charging and cycling aging experiments on NCA(LixNi0.80Co0.15Al0.05O2)batteries at different maximum cut-off voltages(4.2V,4.3 V and 4.4 V)are conducted and test methods such as differential voltage analysis and electrochemical impedance spectroscopy(EIS)are used to investigate the effects of high cut-off voltage cycling on battery aging.As the maximum cut-off voltage increases,the rate of battery aging accelerates.After 280 cycles at 2.5 A,the capacity retention at 4.2 V,4.3 V and 4.4 V is 90.30％,88.19％and 86.19％,respectively.Differential voltage analysis reveals that the accelerated capacity decay is due to the loss of cathode active materials and active Li+.EIS test discloses that hte mild overcharging leads to a slight increase in the impedance of the solid electrolyte interphase(SEI)film,and an increase in the charge transfer impedance,the extent of which increase with the increase of the cut-off voltage.
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