Abstract All‐solid‐state lithium batteries (ASSBs) have received increasing attentions as one promising candidate for the next‐generation energy storage devices. Among various solid electrolytes, sulfide‐based ASSBs combined with layered oxide cathodes have emerged due to the high energy density and safety performance, even at high‐voltage conditions. However, the interface compatibility issues remain to be solved at the interface between the oxide cathode and sulfide electrolyte. To circumvent this issue, we propose a simple but effective approach to magic the adverse surface alkali into a uniform oxyhalide coating on LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) via a controllable gas‐solid reaction. Due to the enhancement of the close contact at interface, the ASSBs exhibit improved kinetic performance across a broad temperature range, especially at the freezing point. Besides, owing to the high‐voltage tolerance of the protective layer, ASSBs demonstrate excellent cyclic stability under high cutoff voltages (500 cycles~94.0 % at 4.5 V, 200 cycles~80.4 % at 4.8 V). This work provides insights into using a high voltage stable oxyhalide coating strategy to enhance the development of high energy density ASSBs.
