Percolated Sulfide in Salt‐Concentrated Polymer Matrices Extricating High‐Voltage All‐Solid‐State Lithium‐metal Batteries

All‐solid‐state lithium‐metal batteries (ASLMBs) are considered to be remarkably promising energy storage devices owing to their high safety and energy density. However, the limitations of current solid electrolytes in oxidation stability and ion transport properties have emerged as fundamental barriers in practical applications. Herein, a novel solid electrolyte is presented by in situ polymerization of salt‐concentrated poly(ethylene glycol) diglycidyl ether (PEGDE) implanted with a three‐dimensional porous L(10)GeP(2)S(12) skeleton to mitigate these issues. The poly(PEGDE) endows more oxygen atoms to coordinate with Li(+), significantly lowering its highest occupied molecular orbital level. As a consequence, the electro‐oxidation resistance of poly(PEGDE) exceeds 4.7 V versus Li(+)/Li. Simultaneously, the three‐dimensonal porous L(10)GeP(2)S(12) skeleton provides a percolated pathway for rapid Li(+) migration, ensuring a sufficient ionic conductivity of 7.7 × 10(−4) S cm(−1) at room temperature. As the bottlenecks are well solved, 4.5 V LiNi(0.8)Mn(0.1)Co(0.1)O(2)‐based ASLMBs present fantastic cycle performance over 200 cycles with an average Coulombic efficiency exceeding 99.6% at room temperature.