Searching for the optimal current pattern based on grey wolf optimizer and equivalent circuit model of Li-ion batteries

Abstract In this study, a novel method is proposed to search for the optimal charging pattern (OCP) of the five stage constant current charging method. Firstly, a detailed equivalent circuit model of the lithium-ion battery obtained by Electrochemical Impedance Spectroscopy analysis is utilized to derive the mathematical expression of the charging time and the charging loss of the battery. Next, the grey wolf optimization method is utilized to find the optimal charging pattern which simultaneously takes the charging time and charging loss into account. According to the experimental results, the obtained OCP has the lowest temperature rise and the best charging efficiency. Compared with the conventional constant current- constant voltage charging technique with 1C charging current, the charging time, maximum temperature rise, average temperature rise, and charging efficiency are improved by 5.33%, 25.99%, 19.59%, and 0.48%, respectively. Comparing with the result obtained by optimization method which only takes the charging time into account, the maximum temperature rise, average temperature rise, and charging efficiency are improved by 12.54%, 5.74% and 0.21%, respectively. In addition, cycling results also show that the life cycle can be improved by 79.6% and 40.2% compared with the CC-CV charging method and the optimization result obtained by considering only the charging time.