In-situ conversion of residual alkali into fast-ion conductor coating and synchronously realizing gradient Mo4+ doping to stabilize LiNi0.9Mn0.1O2 cathode

The surficial residual alkali is a key factor that leads to aggravated phase transition and decay in cobalt-free high-nickel cathode. In this paper, we develop a one-step in-situ modification technique to convert the residual alkali on the LiNi0.9Mn0.1O2 (NM91) surface into Li2MoO4 coating. As a fast ionic conductor, Li2MoO4 coating not only facilitate Li+ diffusion, but also inhibits the transition from layered to rock salt phase on the cathode surface. Moreover, the multi-aperture architecture formed in the conversion promotes the high-valent Mo enter-into the lattice and realizes the gradient doping of Mo4+ through thermodynamic diffusion. Due to the pillar effect, Mo doping increases c-axis spacing, mitigates cation mixing, and reduces the irreversible H2-H3 phase transition. As a result, both the Li+ diffusion kinetics and thermodynamic stability are improved. Consequently, the as-prepared Mo modified NM91 exhibits an increased capacity retention from original 62.3% to 75.6% (100 cycles, 0.2C) and enhanced rate capability of 131.96 mAh g-1 at 5.0C. This work provides a facile “reducing alkali” technological process, and lays foundation for the material design and performance optimization of high energy density cathodes in lithium-ion batteries.