Cyclic Capacity Fade Plots for aging studies of Li-ion cells

摘要

The article introduces a Cyclic Capacity Fade Plot, to depict the deterioration of a lithium-ion cell material, as a graph between a factor based on State of Charge (ΔSOC~*SOC_(mean)) and the % capacity loss per cycle. The plots are generated entirely using experimental data. A variant of this plot is presented as Log(cycle life) vs. ASOC~*SOC_(mean), that is analogous to Stress-Number of Cycles (S-N) type limit curves used in the study of cyclic fatigue of metallic materials. The monotonic variation and in some cases near linear nature of these plots, valid for different temperatures, is noteworthy. These plots provide a wealth of information at a quick glance and are shown to be useful in comparing the performance of different cell materials. The utility of the Cyclic Capacity Fade Plots is demonstrated illustratively for two (Li Manganese Oxide) LMO-graphite cells studied in-house and for an olivine system reported in the literature. These plots are expected to be useful in electrode material development, accelerated testing, battery health management etc.