EIS Based ECM Parameter and SOH Estimation for LiFePO4 Battery Considering SOC Effect

Electrochemical Impedance Spectroscopy (EIS) is a powerful non-destructive detection method, which has been widely used in lithium-ion battery state estimation studies in recent years. Electrochemical impedance spectroscopy is usually resolved by establishing a reasonable Equivalent Circuit Model (ECM), which is crucial for lithium battery state estimation, and the method of identifying the parameters of the equivalent circuit model also directly affects the accuracy and speed of the final estimation. In this paper, firstly, a large amount of impedance spectrum data is obtained by conducting cycle aging experiments on lithium batteries and electrochemical impedance spectrum tests under different cycle times. Subsequently, an equivalent circuit model based on the internal reaction process of the lithium battery was selected, and an algorithm based on the Levenberg-Marquardt nonlinear least-squares method was used to identify the parameters of the equivalent circuit, the reliability of the model was verified by fitting, and the charge transfer resistance was extracted as a characteristic parameter. It is observed from the identification results that the fitting is significant in the range of SOC=60% to SOC=90%, so the State of Health (SOH) estimation model considering State of Charge (SOC) is adopted and the SOH estimation is successfully implemented in this SOC range. The results showed that the SOH estimation was within 3% error for the vast majority of the data.