Mechanism of Capacity Fading of Li-Rich Layer-Structured Cathode Materials Based on TEM/Electrochemical Analyses

Recently, Li-rich layer-structured cathode formulated as xLi2MnO3 -(1-x)LiMO2(M = Mn, Ni, Co, etc.) exhibit high reversible capacity for Li-ion battery applications. Although Li-rich layer-structured cathode material show a reversible capacity as high as 250 mAh/g, its electrochemical properties such as capacity loss at first cycle, rate capability and capacity fading upon cycling still need to be investigated. A systematic study on crystal structures and electrochemical testing is employed. In this study, various compositions of xLi2MnO3 -(1-x)LiMO2 (M = Mn, Ni, Co, etc.) were investigated. The electron diffraction pattern of spinel structure was observed from a cycled layer-structured cathode particle. The transition from layered structure to spinel structure may induce a large lattice distortion resulting in lattice breakdown and capacity. Furthermore, the phase transition may be caused by the redox reaction of transition metal ions through repeated cycling tests. Discussion will be carried out based on the results of XRD, SEM, TEM analyses on cycled cathode materials