An Approximate Method for Retired Battery Capacity Degradation Model Based on Limited Test Data of SOC Ranges

Facing the peak of electric vehicle power battery decommissioning, the secondary utilization technology of such retired power batteries is of great significance to minimize the battery cost and improve their whole life cycle value of them. To achieve safe, reliable, large-scale, and multi-scenario secondary utilization of retired power batteries, the study on the capacity degradation model of such retired batteries is crucial. In this condition, an approximate method for a retired battery capacity degradation model using limited test data of the state of charge (SOC) ranges, is proposed herein. First, the Gaussian polynomial function is fitted according to the test data of retired batteries with a high state of health (SOH) and hence extended to obtain the approximate model of capacity fade for low SOH of the retired batteries. Then, to fit the capacity degradation of retired batteries with different SOC ranges from the test data of limited SOC ranges, this paper proposes an approximate method for the capacity degradation model of retired batteries. Using the mathematical model of interval number similarity, the weight of the fitting curve can be determined by calculating the interval similarity between each SOC range and the test data SOC range, and the approximate model of retired battery capacity degradation in different SOC ranges is obtained. Finally, through the approximate method proposed herein, the retired battery capacity degradation model’s fitting performance for different SOC ranges is compared with diverse battery test data, which verifies the applicability of the proposed method.