Unveiling real-world aging mechanisms of lithium-ion batteries in electric vehicles

This work focuses on understanding the degradation mechanisms of lithium-ion batteries in relation to driving distances of electric vehicles (EVs). Comprehensive electrochemical analysis successfully identified and quantified major degradation mechanisms of EV battery cells including active material loss, Li loss, and cell impedance. Cathode performance was the major limiting factor of the overall cell capacity given the N/P ratio exceeding 1.0. The impact of Li loss and active material loss mechanisms on performance degradation with total driven distance from 0 to 250 k km was visualized by simple, customized electrochemical methods. The Li loss predominantly governed the initial performance degradation of EV cells, while after 150 k km driving distance (i.e,. mileage), active material loss started to dominate the degradation. The degradation mechanism of cell impedance was analyzed using symmetric cell through electrochemical impedance spectroscopy (EIS) and distribution of relaxation times (DRT) techniques. With increasing mileage, the cathode suffered from charge transfer resistance, while the anode suffered from the contact impedance. This work demonstrates effective experimental strategies to reveal Li-ion battery degradation mechanisms in EVs, which can contribute to the continued development of future EV technology. • Li-ion battery degradation mechanisms from real-world EV driving distances analyzed • The Li loss predominantly governed the initial performance degradation of EV cells. • After 150 k km mileage, active material loss started to dominate the degradation. • Cathode and anode, respectively, suffer from charge transfer and contact impedances.