VOLTAGE FADING MECHANISM OF LI-RICH LAYERED OXIDE CATHODE MATERIALS FOR LITHIUM-ION BATTERIES

摘要

In this presentation, we synthesized the Li-rich layered oxidesrnpowders with various primary particle sizes by the co-precipitationrnmethod. The primary particle size substantially increased withrnincreasing the Li/M ratio or heating temperature. The samples with arnlower surface area showed more stable cycle performance but poorerrnrate performance. Through the designed electrochemical experimentsrncombined with ex situ XANES analysis, it is clarified that the poorrnkinetics of Li-rich layered oxides is attributed to the slower kineticsrnof the Li_2MnO_3 crystallite, compared with the kinetics of LiMO_2rncrystallites within the integrated composite structure of the Li-richrnlayered oxides. The poor kinetics of the Li_2MnO_3 crystallite causedrnthe larger polarization of the discharge than that of the charge. Forrnthe explanation of this behavior, we suggest the mediator model forrnthe integrated structure of Li_2MnO_3 and LiMO_2 crystallites.rnMoreover, the polarization of the discharge increased with thernincreased cycle number, resulting in the voltage fading of the Li-richrnlayered oxides during cycling. Therefore, it is required to improvernthe kinetics of the Li2MnO3 crystallite in the composite structure ofrnthe Li-rich layered oxides in order to solve the voltage fadingrnproblem.