Predicting the Capacity Fade of Discarded Batteries with Electrochemical Impedance Spectroscopy

To enable the reuse of batteries from discarded battery packs, eligible cells need to be identified. After sourcing qualitative packs, the packs are manually opened, and the cells are carefully removed and tested to assess their suitability for reuse in various applications. Typically, cell testing entails an internal resistance (IR) measurement to sort out cells that no longer function, followed by charging and discharging cycles to determine the State of Health (SoH) and capacity loss. This process requires several hours and dedicated hardware to perform safely. To estimate SoH and capacity loss at the outset and to better define the cell’s SoH in its digital product passport (DPP), the authors propose to perform Electrochemical Impedance Spectroscopy (EIS) prior to battery cycling. With this measurement, various cell deterioration aspects are determined in a two-minute measurement. The proposed method is validated on a dataset of 84 cells with known varying capacity losses. IR and EIS measurements are performed to predict capacity loss. Using Gradient Boosting, an RMSE of 3.71, MAE of 2.47, and R² of 0.98 is achieved. These results indicate that cell SoH and capacity loss could be estimated, facilitating more cost-efficient testing for reuse, and providing valuable data to determine the most suitable application for each cell.