Mitigating Reaction Barriers in Ni-Rich Cathodes via Surface-Bulk Coupling Strategy for Fast-Charging

Material degradation in layered oxide cathodes, particularly mechanical degradation, presents a "chicken or egg" dilemma as it may originate from either the surface or the bulk. Surface-only or bulk-only modifications have proven insufficient to resolve these intrinsic issues. While combined surface-bulk strategies can mitigate degradation, they often require complex processes that increase costs and limit scalability. Here, we report a design that couples bulk structural stabilization with the in situ formation of a fast conductive interphase on Ni-rich layered oxides. This dual approach yields a robust bulk framework and a stable surface with accelerated reaction kinetics, enabling a high-rate capability of over 160 mAh g^-1 at the current of 5 C and stable cycling over 200 cycles. Beyond performance gains, our results reveal atomic-scale insights into the interplay between structural evolution, ionic transport, and electrochemical stability, offering a practical pathway to durable high-nickel cathodes for fast-charging batteries.