Flash joule heating-induced spinel-phase surface in Ni-rich layered oxide positive electrodes to stabilise lattice oxygen.

High-nickel layered positive electrodes suffer from progressive structural degradation arising from lattice oxygen loss and inherent lattice strain. Although surface coatings are widely used to stabilize lattice-oxygen redox and mitigate electro-chemo-mechanical degradation, achieving coatings with full continuity, robust interfacial bonding, and fast Li+ conductivity remains challenging. Herein, we present a fundamentally different approach to shell formation via a self-derived subtractive strategy, departing from the conventional additive-based coating methods. By accurately applying transient thermal pulses, surface lithium is selectively extracted from layered LiNixCoyMn1-x-yO2 (x = 0.8 ~ 0.9), directly converting the outer region into a coherent spinel-phase shell with tunable thickness. This nanoscale spinel-phase skin forms a robust mortise-and-tenon-like interconnection with the layered bulk, enabling isotropic, high-rate Li+ extraction/insertion while maintaining electronic conductivity throughout cycling. It effectively confines active oxygen intermediates, and suppresses interfacial side reactions and strain evolution under high-potential operation. Therefore, the spinel-phase skin-encapsulated LiNi0.8Co0.1Mn0.1O2 achieves an initial Coulombic efficiency of 95.3% and enables pouch cells with 80.1% capacity retention after 2000 cycles at 180 mA g-1. This strategy is extendable to LiNi0.9Co0.05Mn0.05O2, may open new avenues for advancing nickel-rich positive electrode technologies.