Hierarchical Composite‐Solid‐Electrolyte with High Electrochemical Stability and Interfacial Regulation for Boosting Ultra‐Stable Lithium Batteries

Abstract Solid‐state electrolytes have drawn enormous attention to reviving lithium batteries but have also been barricaded in lower ionic conductivity at room temperature, awkward interfacial contact, and severe polarization. Herein, a sort of hierarchical composite solid electrolyte combined with a “polymer‐in‐separator” matrix and “garnet‐at‐interface” layer is prepared via a facile process. The commercial polyvinylidene fluoride‐based separator is applied as a host for the polymer‐based ionic conductor, which concurrently inhibits over‐polarization of polymer matrix and elevates high‐voltage compatibility versus cathode. Attached on the side, the compact garnet (Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 ) layer is glued to physically inhibit the overgrowth of lithium dendrite and regulate the interfacial electrochemistry. At 25 °C, the electrolyte exhibits a high ionic conductivity of 2.73 × 10 −4 S cm −1 and a decent electrochemical window of 4.77 V. Benefiting from this elaborate electrolyte, the symmetrical Li||Li battery achieves steady lithium plating/stripping more than 4800 h at 0.5 mA cm −2 without dendrites and short‐circuit. The solid‐state batteries deliver preferable capacity output with outstanding cycling stability (95.2% capacity retained after 500 cycles, 79.0% after 1000 cycles at 1 C) at ambient temperature. This hierarchical structure design of electrolyte may reveal great potentials for future development in fields of solid‐state metal batteries.