A black zirconia cathode coating layer enabling facile charge diffusion and surface lattice stabilization for lithium-ion batteries†

Abstract

The conformal surface coating of Ni-rich layered cathode materials is essential for mitigating their interfacial and subsequent structural degradation. The zirconia (ZrO₂) coating effectively enhances the surface stability of the cathode owing to its excellent chemical durability; however, the insulating electrical conductivity of ZrO₂ increases the electrode resistance and triggers efficiency decay. Here, we propose highly conductive oxygen-deficient black ZrO_2−x as a charge-conductive coating material. The black ZrO_2−x is uniformly coated onto the Ni-rich LiNi_0.8Mn_0.1Co_0.1O₂ (NMC) surface via a solvent-free mechanochemical shearing process. Benefiting from the black ZrO_2−x coating layer, black ZrO_2−x coated NMC shows improved cycling characteristics and better rate capability than both bare NMC and ZrO₂ coated NMC. The enhanced electrochemical performance by the conformal coating of black ZrO_2−x mainly results from enhanced charge transfer, reduced gas evolution, and mitigated microstructural cracking. Density functional theory calculations confirm that the defective structure of black ZrO_2−x lowers the energy barrier for Li ion transfer, and strong hybridization between Zr in black ZrO_2−x and O in NMC mitigates oxygen evolution.