EIS Analysis of Aged Lithium-ion Battery by Comparing RC Parallel Equivalent Circuits

Electrochemical Impedance Spectroscopy (EIS) is a traditional method for the evaluation of electrochemical charac-teristics associated with the aging process of lithium-ion batteries (LiBs). As the LiB ages, the electrode surface undergoes severe degradation, including oxidation/reduction and dendrite formation within the solid electrolyte interface (SEI) layer, resulting in an increase in internal impedance. These chemical processes can be observed by the variations in the signature in impedance of the semi-circles in the EIS measurements. In this paper, the state of the LiB is predicted by comparing the impedance measurements in each cycle with the similarity of the nth-order RC Electrical Equivalent Circuit (EEC) model. The proposed method compares RC parameters as aging indicators in the EIS based on an increase in the number and size of semi-circles in the EEC model as well as considering the order of the RC model as an additional variable. The proposed method can estimate the aging of any LiBs based on EIS by comparing their similarity to RC EEC models.