All-solid-state batteries are a potential game changer in the energy storage market; however, their practical employment has been hampered by premature short circuits caused by the lithium dendritic growth through the solid electrolyte. Here, we demonstrate that a rational layer-by-layer strategy using a lithiophilic and electron-blocking multilayer can substantially enhance the performance/stability of the system by effectively blocking the electron leakage and maintaining low electronic conductivity even at high temperature (60°C) or under high electric field (3 V) while sustaining low interfacial resistance (13.4 ohm cm 2 ). It subsequently results in a homogeneous lithium plating/stripping, thereby aiding in achieving one of the highest critical current densities (~3.1 mA cm −2 ) at 60°C in a symmetric cell. A full cell paired with a commercial-level cathode exhibits exceptionally long durability (>3000 cycles) and coulombic efficiency (99.96%) at a high current density (2 C; ~1.0 mA cm −2 ), which records the highest performance among all-solid-state lithium metal batteries reported to date.

Halide solid electrolytes have recently emerged as a promising option for cathode‐compatible catholytes in solid‐state batteries (SSBs), owing to their superior oxidation stability at high voltage and their interfacial stability. However, their day‐ to month‐scale aging at the cathode interface has remained unexplored until now, while its elucidation is indispensable for practical deployment. Herein, the stability of halide solid electrolytes (e.g., Li3InCl6) when used with conventional layered oxide cathodes during extended calendar aging is investigated. It is found that, contrary to their well‐known oxidation stability, halide solid electrolytes can be vulnerable to reductive side reactions with oxide cathodes (e.g., LiNi0.8Co0.1Mn0.1O2) in the long term. More importantly, the calendar aging at a low state of charge or as‐fabricated state causes more significant degradation than at a high state of charge, in contrast to typical lithium‐ion batteries, which are more susceptible to high‐state‐of‐charge calendar aging. This unique characteristic of halide‐based SSBs is related to the reduction propensity of metal ions in halide solid electrolytes and correlated to the formation of an interphase due to the reductive decomposition triggered by the oxide cathode in a lithiated state. This understanding of the long‐term aging properties provides new guidelines for the development of cathode‐compatible halide solid electrolytes.