Mechanistic Coupling of Degradation Modes and Impedance Growth of Lithium-Ion Batteries for Kneepoint Prediction

Fast charging of lithium-ion batteries accelerates degradation and can induce lithium plating when the negative electrode potential approaches or falls below 0 V versus Li / Li + . This study investigates the aging of multilayer pouch cells with nickel-rich positive electrodes and graphite negative electrodes under charge profiles with different minimum negative electrode potentials. Non-invasive degradation mode estimation, operando electrochemical impedance spectroscopy, and gas chromatography are combined to identify charge-profile-specific degradation mechanisms. Electrode-specific impedance growth is separated into contributions from loss of active material in the negative electrode, loss of active material in the positive electrode, and side reactions. The impedance increase associated with side reactions exhibits a strong linear correlation with loss of lithium inventory, with a Pearson correlation coefficient > 0.98 across all investigated charge profiles. This relationship is incorporated into a physically motivated equivalent circuit model using degradation-sensitive impedance factors. Parameterized with the first 200 equivalent full cycles, the model predicts electrode capacities, lithium inventory, impedance growth, full-cell voltage response, and minimum negative electrode potential. It also predicts the degradation-induced onset of lithium plating for the critical charge profile, confirmed by gas chromatography. The proposed framework enables mechanistic aging prediction and provides a basis for kneepoint prediction and aging-adaptive fast-charging strategies.