Solid‐state electrolytes are widely anticipated to enable the revival of high energy density and safe metallic Li batteries, however, their lower ionic conductivity at room temperature, stiff interfacial contact, and severe polarization during cycling continue to pose challenges in practical applications. Herein, a dual‐composite concept is applied to the design of a bilayer heterostructure solid electrolyte composed of Li+ conductive garnet nanowires (Li6.75La3Zr1.75Nb0.25O12)/polyvinylidene fluoride‐co‐hexafluoropropylene (PVDF‐HFP) as a tough matrix and modified metal organic framework particles/polyethylene oxide/PVDF‐HFP as an interfacial gel. The integral ionic conductivity of the solid electrolyte reaches 2.0 × 10−4 S cm−1 at room temperature. In addition, a chemically/electrochemically stable interface is rapidly formed, and Li dendrites are well restrained by a robust inorganic shield and matrix. As a result, steady Li plating/stripping for more than 1700 h at 0.25 mA cm−2 is achieved. Solid‐state batteries using this bilayer heterostructure solid electrolyte deliver promising battery performance (efficient capacity output and cycling stability) at ambient temperature (25 °C). Moreover, the pouch cells exhibit considerable flexibility in service and unexpected endurance under a series of extreme abuse tests including hitting with a nail, burning, immersion under water, and freezing in liquid nitrogen.

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 (Li6.4La3Zr1.4Ta0.6O12) 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.

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