Effect of Potential Profile on Battery Capacity Decrease during Continuous Cycling

The origin of the capacity decrease of lithium ion batteries during continuous charge/discharge cycling, as typified by battery operation in electric vehicles, is elucidated using LiNi1/3Co1/3Mn1/3O2 (NCM)-based composite electrodes. Electrochemical cycling tests without any rest process show the capacity decrease only during discharging. Reaction distribution analysis by operando energy -scanning confocal Xray diffraction indicates that considerable reaction inhomogeneity occurs on the lithiation of NCM during discharging, whereas the delithiation during charging proceeds homogeneously. It is shown that the reaction inhomogeneity caused by limited Li' transportation in the composite electrode is relaxed during charging owing to the potential profile of the NCMbased electrode, whereas no such relaxation occurs during discharging. This result demonstrates that the optimization of the electrode potential profile is important for good cydability of the batteries continuous charge/discharge cycling, in addition to improving Li+ transportation within the battery.