In‐Situ Polymerization Confined PEGDME‐Based Composite Quasi‐Solid‐State Electrolytes for Lithium Metal Batteries

Abstract Solid‐state lithium metal batteries are under development for higher energy density and better safety. A key is to develop new electrolyte systems that are readily processible and capable to improve electrochemical cycling stability. In this study, A quasi‐solid‐state composite electrolyte based on low‐molecular‐weight polyethylene glycol dimethyl ether (PEGDME) in situ confined within polymerized methyl methacrylate (PMMA) backbone is designed and presented. The new design of the polymer matrix, together with Li+‐conducting ceramic fillers and appropriate lithium salts, has satisfactory Li‐ionic conductivity (1.1 × 10−4 S cm−1 at 30 C and 1.0 × 10−3 S cm−1 at 80 °C), good electrochemical stability (>4.7 V vs Li+/Li), and high compatibility with lithium metal anode, enabling room‐temperature operation and stable long‐term cycling of both Li||Li symmetric cells and lithium‐metal full cells (including LiFePO4 or LiCoO2 cathode). This work can extend the design boundaries of composite electrolytes meaningfully, and the idea of in situ polymerization limiting applies to almost all low‐molecular‐weight polymers, high‐molecular‐weight backbones, ceramic fillers, lithium salts, and additives in future development of room‐temperature solid‐state lithium metal batteries.