Influence of Cycling on the Electrochemical Impedance Spectroscopy for Lithium Iron Phosphate Batteries

Abstract Electrochemical impedance spectroscopy (EIS) is one of the most effective methods that can be used to study the cycling decay behavior of lithium ion batteries (LIBs) without destruction of the battery. In this paper, in order to understand and to analyse the impedance response of the Lithium iron phosphate (LFP) batteries during various cycling rates, an equivalent circuit model (ECM) is established to investigate the cycling influence on the ECM parameters of LIBs. The influence of the discharging process on the patterns of the ECM was also analysed. The results indicate that the sum ohmic resistance and the Li + diffusion through the SEI layer resistance keep increasing and the charge transfer resistance drop during the cycling when the retention capacities are higher than 90%. While the LFP batteries cycle under 1 C, the charge transfer resistance of them drop at first and then increase significantly after around 200 cycles when the retention capacities are lower than 80%. The results also show that when the LFP batteries are discharged during one single cycle, the sum ohmic resistance, the Li + diffusion through the SEI layer resistance and the charge transfer resistance keep increasing. The results in this study indicate that EIS is a useful tool to obtain information for monitoring the state of health of LIBs.