Flexible upper cut-off voltage regulation for life extension of lithium-ion batteries

As one of the most expensive components in electric vehicles (EVs), lithium-ion batteries (LIBs) have been paid much attention by buyers in terms of their lifetime. Therefore, it is necessary to slow down the degradation of LIBs and extend their lifetime to reduce the cost for users. Here, we propose a life regulation method for LIBs based on flexible upper cut-off voltage (UCV), in which an UCV of 4.2V and an UCV below 4.2V, are alternately used to obtain a trade-off between life extension and energy density loss. Firstly, non-destructive diagnostic methods are used to analyze the degradation mechanism of LIBs under different UCVs. The internal mechanism of lowering the UCV to retard the battery capacity degradation is emphasized. Then, considering the loss of energy density caused by lowering the UCV, flexible UCVs are alternately used to achieve battery life extension by reducing the increase in internal resistance and the loss of active materials. Finally, the experimental results show that after 400 equivalent cycles, the capacity degradation for the battery after regulation is reduced from 7.43 % to at least 4.09 %, with an impressive life extension effect. This finding provides new ideas and methods for the long-life LIBs in future EVs.