Enhanced differential impedance analysis for SoH estimation of batteries

Electrochemical Impedance spectroscopy (EIS) is a promising method for SoH estimation. However, interpreting EIS data is challenging and requires complex and time-consuming signal processing, which is required in both model-based or data-driven approaches. To overcome these challenges, we propose a new method based on Differential Impedance Analysis (DIA). DIA is a less complex method based on local modeling by directly calculating the Local Operator Model (LOM) parameters for each individual impedance point. This model includes a series resistor (R) connected to an RC circuit. This approach significantly simplifies signal processing and enhances computational efficiency. As the original DIA is highly sensitive to noise, we propose a new formulation of the LOM parameters with limited use of numerical derivations to only the calculation of one parameter. This reduces the influence of derivative-induced noise and make the method very robust and accurate. In this paper, we applied the enhanced DIA for battery SoH assessment. The spectra of four lithium-ion cells were considered in the frequency range from 10 mHz to 1 kHz. The LOM parameters ( R p , R s , and C p ) can be fitted to an exponential model in dependence of the number of cycles. The highest sensitivity to SoH was found for the LOM parameter R p in the frequency range of 50 to 178 Hz (charge transfer region, R 2 > 0 . 98 ). • Novel calculation method the differential impedance analysis overcoming noise effects. • Estimation of state of health of battery cells by differential impedance analysis. • SoH determination without a global model reducing measurement and processing effort.