Stages assessment of state of health in a lifetime based on the capacity variance of lithium batteries

To avoid the overuse or underutilization of lithium battery in practical applications, the state of health of lithium battery should be assessed in time to ensure safety and maximize utilization. A health indicator is proposed to show the SOH of lithium battery in this paper. Firstly, the degradation mechanism of lithium battery is described based on the working principle and the aging phenomenon of lithium-iron phosphate battery, and the existing problems in the current research on battery aging phenomenon are expounded. Secondly, to deal with the hidden dangers caused by the aging problem of the battery, the variation of capacity variance is selected to construct the health indicator of lithium battery. Finally, the performance degradation state of lithium battery is divided into four stages according to the changing trend of the constructed indicators in the whole lifetime, which are the formation stage of the first solid electrolyte interface film stage, the normal working stage, the new solid electrolyte interface film stage and the internal resistance rise stage. The battery data set from MIT-Stanford-Toyota Research Center is utilized to verify the proposed method. The results show that the performance of lithium batteries will accelerate degradation with temperature rapidly rising in the new solid electrolyte interface film stage; the internal resistance will increase sharply in the internal resistance rise stage, which can easily lead to accidents such as thermal runaway. The proposed health state assessment method compares with other methods, and it is shown that the proposed method helps to ensure safety and maximize the utilization of lithium batteries.