Rational design of coating ions via advantageous surface reconstruction in high-nickel layered oxide cathodes for lithium-ion batteries

The implementation of high-nickel layered oxide cathodes in lithium-ion batteries is hampered by the inherent issues of formation of NiO-like rock-salt phase as well as residual lithium (e.g., LiOH, LiHCO${}_3$, and Li${}_2$CO${}_3$) on the surface. To overcome the challenges, here a rational strategy is presented of interdiffusion-based surface reconstruction via dry coating and the design principles for identifying the optimum coating ions on a LiNi${}_{0.91}$Mn${}_{0.03}$Co${}_{0.06}$O${}_2$ (NMC91) cathode. Notably, the combined approach of theoretical screening, which involves the consideration of superexchange interactions among different oxidation states and density functional theory calculations, along with experimental analyses, which involve the characterization of the decrease in Ni content and residual lithium on the surface of NMC91, demonstrate the effective reduction in rock-salt phase and residual lithium. Among the four ions investigated (Al, Co, Fe, and Ti), cobalt-coated NMC91 is the most effective at reducing the rock-salt phase and residual lithium by successfully reconstructing the surface of NMC91 and exhibits an excellent capacity retention of 85% in a full cell after 300 cycles at 30 °C. (© 2021 Wiley-VCH GmbH)