Highly Conductive, Ceramic‐Rich Hybrid Ionogel Electrolytes for Room‐Temperature Li‐Metal Batteries

Hybrid solid electrolytes present a promising class for applications in lithium‐metal batteries; however, their practical implementation remains limited by the difficulty of simultaneously achieving high room‐temperature ionic conductivity, mechanical robustness, and stable electrode‐electrolyte interfaces. In this study, we report the development of ceramic‐rich hybrid ionogels (HIGs) formulated by combining a dimethacrylate polymer with a high content of Li6.25Al0.25La3Zr2O12 (LLZO) nanoparticles and imidazolium‐based ionic liquid electrolytes (ILEs). This approach results in a garnet‐rich solid electrolyte matrix intended to balance mechanical integrity and ion‐conducting performance. Four groups of self‐standing HIG electrolyte membranes are fabricated through an in situ solvent‐free thermal polymerization process, where the ILEs feature either single‐ or binary‐anion environments and serve as the reaction media. Comprehensive characterization demonstrates electrolyte membranes with high ionic conductivities (up to 1.93 × 10−3 S cm−1 at 20°C). Among the investigated formulations, the LiTFSI‐EMIFSI‐based HIG exhibits the most favorable electrochemical performance, including a wide electrochemical stability window and stable charge‐discharge cycling with LiFePO4 at room temperature, delivering specific discharge capacities approaching 130 mAh g−1 up to C/5 and coulombic efficiency close to 100%. This work highlights the potential of hybrid ionogel electrolytes, clarifies the role of anion chemistry in enabling practical solid‐state electrolyte designs, and provides a useful strategy for the development of safer and more stable lithium‐metal batteries operating at room temperature.