Study on electrochemical impedance spectrum of C-LiFePO4 power battery

Abstract

Electrochemical impedance spectroscopy (EIS) can provide the change of ohmic resistance (Rs), charge transfer impedance (Rct) and diffusion impedance (Zw) in the different charging/discharging states, which is a powerful tool to evaluate the application state of the battery. This paper tested EIS of 60 Ah C/LiFePO4 power battery in different SOC and SOH states, and analyzed the variation tendency of Rs, Rct and Zw with the change of SOC and SOH states. The experimental results showed that Rs value keeps stable while values of Rct and Zw increase apparently at both ends of SOC (0∼25% and 75∼100%) at different SOC states. For different SOH states, the values of Rs, Rct and Zw keep stable in the range of 100∼95% SOH. But when SOH decreases to 90%, it is found that the capacity of 60 Ah battery decreases while the resistant value increases obviously. Therefore, EIS parameters can reflect partially the polarization state of the internal battery, so as to predict the degradation state of the storage lithiumion battery.