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.