Robust Surface Reconstruction Induced by Subsurface Ni/Li Antisites in Ni-Rich Cathodes

Loss of active materials is a critical problem of layered oxide cathodes for lithium-ion batteries and undermines their long-term electrochemical performance. However, the atomic-scale outward migration mechanism of transition metals and oxygen remains elusive due to a highly localized environment at surface. Here, the robust surface reconstruction of LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) induced by artificially introduced Ni/Li antisites is reported. Using scanning transmission electron microscopy, the outward co-migration process of nickel and oxygen ions is directly revealed at the atomic scale, finally resulting in a stable surface structure. The robust nature of this surface structure originates from the strong linear superexchange interaction between subsurface Ni_Li and surface Ni as supported by first-principles calculations. An idealized subsurface structure with $\frac{1}{3}$ Ni_Li is designed to suppress the outward migration of transition metal and oxygen ions and provide a universal lattice-coherent surface protection strategy for layered lithium transition metal oxide cathodes.