Surface Reconstruction Enables High‐Voltage, Long‐Life All‐Solid‐State Batteries

All‐solid‐state batteries (ASSBs) offer enhanced energy density and improved safety through the utilization of solid electrolytes. Among these, halide‐based electrolytes have emerged as the most promising candidates due to their high oxidative stability and compatibility with layered oxide cathodes. However, current voltage limitations (≤4.3 V) restrict the advancement of energy density, while elevated cut‐off voltages result in structural degradation of layered oxides and deterioration of the cathode electrolyte interface (CEI). In this study, an atomic‐scale surface reconstruction strategy is presented that transforms the LiCoO 2 surface into a perovskite phase nanolayer through limited Li + /La 3+ ion exchange. The engineered interface suppresses lattice oxygen release and stabilizes the CEI, thus preventing both bulk‐phase collapse and decomposition of the Li 3 InCl 6 electrolyte. The engineered batteries demonstrate remarkable performance, exhibiting a high specific capacity of 208 mAh g −1 with an initial coulombic efficiency of 97.4% at 4.6 V and impressive long‐term cycling stability (over 1000 cycles). Furthermore, the capacity retention is found to be 94% even after 200 cycles at high loading (5 mAh cm −2 ). These findings establish surface reconstruction as a promising strategy for the engineering of interfaces in high‐voltage ASSBs, providing insights that will inform the development of next‐generation energy storage systems.