Enhanced Cycling Stability of High‐Voltage Ni‐Rich Cathodes With Autogenous Robust Surfaces for All‐Solid‐State Batteries

ABSTRACT The development of all‐solid‐state batteries (ASSBs) with sulfide‐based solid electrolytes is a promising strategy for realizing safe Li‐ion storage systems with high energy densities. However, the practical implementation of Ni‐rich layered cathode active materials (CAMs) with superior theoretical capacities remains hindered by their interfacial instability in sulfide electrolytes and intrinsic structural degradation caused by cation mixing and oxygen losses. To address these challenges, this study introduces a novel flash‐light sintering (FLS) technique that can rapidly generate a conformal NiO‐like protective surface layer directly from the CAM lattice without using external precursors or extensive thermal treatments. This uniformly engineered nanoscale surface layer undergoes robust chemical and mechanical stabilization by blocking direct contact with the electrolyte, thereby significantly inhibiting parasitic interfacial reactions. Additionally, the NiO‐like shell acts as a rigid structural pillar, effectively preventing cation migration, layered‐to‐rock‐salt phase transitions, and the subsequent lattice collapse, thereby preserving the electrochemically active core. Electrochemical assessments demonstrate significantly enhanced performance; at a charge rate of 0.1 C in the normal voltage window, the capacity retention after 100 cycles improves from 55% with 103.8 mAh g −1 and a Coulombic efficiency of 89.13% for the pristine material to 81% with 152.1 mAh g −1 and a Coulombic efficiency of 99.78% for the treated material. In an extended cut‐off window, the capacity retention improves from 40% with 90.9 mAh g −1 and a Coulombic efficiency of 86.98% to 78% with 166.3 mAh g −1 and a Coulombic efficiency of 98.9%. Owing to its rapid, scalable, and highly controllable nature, FLS offers a compelling approach for practical surface engineering with a substantial potential for improving both the performance and safety of ASSBs and extending their applicability to various functional oxide materials that require precise and efficient surface modifications.