An improvement of equivalent circuit model for state of health estimation of lithium-ion batteries based on mid-frequency and low-frequency electrochemical impedance spectroscopy

•The proposed fusion resistor RSC takes into account the difference between the fitted and real values of the ECM parameters, and this difference is greatly reduced by the proposed MLECM as an approach, and the fitting effect and success rate are optimized and improved.•In this study, the CECM is optimized by discarding the high-frequency region and some of the mid-frequency parts of the circuit components and fusing them to form a completely new resistor. The method for estimating SOH based on the MLECM is obtained, and the model loading of MLECM is reduced by 69.57% relative to ECM.•In this study, two different battery datasets are used, taking into account the variability brought by different SOC, different battery types, different charge/discharge rates and different temperatures for battery aging. The method is applicable to the range of 25–45 °C where the power battery temperature is located during the actual driving of the vehicle, and provides a new idea for the establishment of the EIS ECM for electric vehicle lithium-ion batteries.