Unveiling the role of Ni doping in the electrochemical performance improvement of the LiMn2O4 cathodes

Ni doping is a commonly used strategy to improve the electrochemical performance of LiMn2O4. Uncovering the structural changes of Ni-doped LiMn2O4 during electrochemical cycling, particularly at the atomic level, is important to understand the mechanism of the relationship between Ni doping and performance improvement. Herein, we investigate the chemical and structural evolutions of the Ni-doped LiMn2O4 electrodes before and after 1000 cycles at 10 C with atomic resolution and correlate them with changes in the electrochemical properties. We found that Ni2+ ions doped into the Mn 16d sites to form a more steady LiNixMn2-xO4 phase construction, which can effectively stabilize the spinel structure by hindering Jahn -Teller distortion. Comprehensive atomic imaging demonstrated that Ni doping can suppress the formation of the unexpected Mn3O4, and rock-salt MnO phases on the surface and subsurface of LiMn2O4 during cycling, which is conducive to stabilizing the MnO6 octahedron and inhibiting the migration of Mn. Resultantly, splendid long cycling sta-bility of 88.92 % after 1000 cycles at 10 C (1 C = 148 mAh g-1) for the optimized LiNi0.05Mn1.95O4 sample is presented. Our study provides an ingenious avenue for regulating the surface optimization and reconstruction of electrode materials.