An integrated surface coating strategy to enhance the electrochemical performance of nickel-rich layered cathodes

Abstract

High-nickel layered oxides, LiNixCoyMnzO2 (0.6 ≤ x < 1), are promising cathode materials for producing batteries with high energy density and working voltage, while their poor cycling performance severely limits their commercial applications. Herein, an integrated surface coating/doping strategy is developed to significantly improve the structural stability and electrochemical performance of LiNi0.88Co0.06Mn0.06O2. The titanium ions from a thin TiNb2O7 coating layer diffuse inward during the high-temperature sintering process and a uniform protective layer forms on the surface of the secondary particles of the material. This protective layer suppresses side reactions, and the Ti4+ doping increases the thickness of the lithium layer and reduces the lithium/nickel mixing, thereby enhancing the diffusion of lithium ions in bulk electrode. The capacity retention of modified material after 200 cycles at 1 C is greatly improved from 59.8% of the pristine material to 87.2%. First-principles calculations confirm the interaction affinity of the TiNb2O7 coating on the layered LiNi0.88Co0.06Mn0.06O2 with Ti ion migration in the interlayer region. Moreover, the enhanced oxygen release energy and electronic conductivity benefiting from Ti4+ doping promote the cycling stability of the integrated cathode. The surface engineering strategy proposed herein is generally effective for the electrochemical improvement of nickel-rich ternary cathode materials.