Atomic Insights into Surface Orientations and Oxygen Vacancies in the LiMn2O4 Cathode for Lithium Storage

Abstract Surface anisotropy of spinel LiMn2O4 crystal is of significance for strengthening the lithium storage. In this work, we investigate the evolutions of surface orientations and oxygen vacancies in the LiMn2O4 cathode materials by the spherical aberration-corrected scanning transmission electron microscopy (Cs-STEM) technique. Firstly, the {111} lattice planes appear in the formed LiMn2O4 octahedra, and then the {110} and {001} crystal planes are observed in the subsequent truncated octahedral at a higher temperature or a longer annealing time. The LiMn2O4 crystals with dominated {111} and {110} planes and an appropriate amount of oxygen vacancies exhibits a superior cycling performance and rate performance, suggesting a synergistic effect of surface orientation and concentration of oxygen vacancies achieves an enhanced electrochemical performance. The introduction of oxygen vacancies can accelerate the diffusion of lithium-ions along {110} plane and strengthen the rate performance of LiMn2O4, as elucidated by the combination of Cs-STEM observation, X-ray photoelectronic spectra analysis and property measurements.