Symmetry-breaking of LiMn6 hexatomic-ring in grain surface of Li2MnO3

LiMn6 hexatomic-rings act as functional units in Li-rich layered oxides (LLOs), which determine the capacity, voltage, and structural stability of LLOs. However, the symmetry of the LiMn6 hexatomic-ring is always broken, especially in the grain surface of LLOs, which will greatly affect its electrochemical performance. Herein, the symmetry-breaking of LiMn6 hexatomic-ring in the grain surface of Li2MnO3 was studied, and their effect on charge compensation mechanism and structure evolution behavior was thoroughly investigated. The results show that the electrochemical activity of the symmetry-broken LiMn6 hexatomic-ring is higher than that of the unbroken LiMn6, and the former is more favorable for spinelization on the grain surface. Furthermore, the exposure proportion of crystallographic planes with different symmetry-broken LiMn6 hexatomic-ring has also been discussed, which can be adjusted by changing the partial pressure of oxygen. The in-depth understanding of the symmetry-breaking of LiMn6 hexatomic-ring will provide more targeted strategies for designing high-performance LLOs cathodes for lithium-ion batteries.