Degradation and Structural Evolution of xLi2MnO3·(1–x)LiMn1/3Ni1/3Co1/3O2 during Cycling

Abstract

In the present work, the electrochemical degradation and structural evolution of xLi2MnO3·(1–x)LiMn1/3Ni1/3Co1/3O2 (x = 0.3, 0.5, and 0.7) materials and the role of Li2MnO3 component during electrochemical cycling are systematically studied through careful analysis of electrochemical data, ex-situ XRD, and HR-TEM observations. The materials consisting of higher Li2MnO3 content show better cyclic performance with more significant voltage decay compared to that of xLi2MnO3·(1–x)LiMn1/3Ni1/3Co1/3O2 electrodes with low Li2MnO3 content. The electrochemical degradation of xLi2MnO3·(1–x)LiMn1/3Ni1/3Co1/3O2 electrodes upon cycling not only results from the remarkably increase in impedance caused by the damage of the electrode surface, in particular for low Li2MnO3 content; but also arises from structural rearrangement, especially for high Li2MnO3 content. Upon cycling, high Li2MnO3 content in the crystal structure of lithium-rich transition metal oxides can stabilize the electrode\\electrolyte interface at high potentials, facilitates the rapid formation of cracks and porosity in the cycled electrodes, and promotes the distortions and breakdown of the original well-layered lattice.