Regrouping Optimization Method for Retired Batteries based on Particle Swarm Optimization Algorithm

A large number of lithium-ion batteries retired from electric vehicles (EVs) need to be treated because nearly 80% of the capacity remains. However, the retired batteries have inconsistencies in capacity, state of charge (SOC), and internal resistance. If batteries are regrouped directly, the power and energy performance will be restricted. In order to improve the energy performance of the second-use battery pack, this paper studies the regrouping method of retired batteries. A semi-empirical model of LiFePO4 battery is used, and then a capacity fading model for the second-use battery pack considering inconsistencies is established. The maximum available Ah-throughput of the pack after regrouping is set as the optimization goal, and the particle swarm optimization algorithm (PSO) is used to search the optimal regrouping method. Simulation is employed to verify the method and the results show that the value of the maximum available Ah-throughput is about 8.2% larger than that of the traditional method. The proposed method is of great significance for guiding effect on the regrouping of retired batteries.