Effect of Fast-Charging and Cycling Window on Lithium-Ion Battery Performance and Aging

The impact of state-of-charge cycling windows and fast-charging on the performance and aging of Graphite/Nickel Cobalt Aluminum oxide 18650 cells has been investigated. Departing from the conventional constant-current constant-voltage fast-charging protocol, a scaled-down equivalent of a 150-kW real-world electric vehicle fast-charging profile was adopted. Unlike the broader state-of-charge range of high current charging typical in conventional protocol, the real-world protocol employs peak power only in a narrow state-of-charge window (10%–40%) and then tapers down. Cycling tests were conducted for two sets of state-of-charge windows: 0%–50% and 0%–100%. Both tests showed similar capacity fade trends but with different underlying causes. Differential voltage and incremental capacity analysis indicated that loss of active negative electrode material and loss of lithium inventory were significant for both, alongside varying loss of positive electrode material. Additionally, low homogeneity of lithium distribution and kinetic rate degradation were evident in the negative electrode. This research underscores the critical role of state-of-charge cycling windows and fast-charging protocols in battery degradation, with non-intrusive differential voltage and incremental capacity analysis revealing distinct degradation pathways. It emphasizes the importance of optimized battery usage to extend lifespan, improve economics, and reduce environmental impact, contributing to sustainable electric vehicle market growth.