Interfacial Engineering for Layered Oxide Cathodes in All‐Solid‐State Batteries

All‐solid‐state batteries (ASSBs) have attracted significant attention as promising next‐generation battery systems due to their theoretically high energy density and excellent safety performance compared to liquid electrolyte lithium‐ion batteries. Layered oxide cathodes offer high capacities and operating voltages and are considered among the most suitable cathode candidates for ASSBs due to these properties. However, the unstable interface between layered oxide cathodes and solid electrolytes leads to detrimental electrochemical side reactions such as internal microcracks, contact loss, electrolyte decomposition, gas evolution, and surface impurity, which hinder the practical application of ASSBs. These interfacial issues have prompted extensive research efforts aimed at addressing interfacial instability and its adverse impact on the electrochemical performance of ASSBs. This review first provides a comprehensive overview of the interfacial failure mechanisms occurring between layered oxide cathodes and each type of solid electrolyte, including polymer‐, oxide‐, and sulfide‐based solid electrolytes. Recent advances in interfacial engineering strategies designed to mitigate degradation and improve interfacial compatibility are also summarized for each electrolyte type. Finally, key challenges and future research directions, including emerging halide solid electrolytes, for commercialization of ASSBs are discussed.