Ionogels: materials design, properties, and emerging applications in advanced electrochemical and bioelectronic systems

Ionogels are hybrid materials formed by immobilizing ionic liquids within polymeric, inorganic, or composite matrices, combining high ionic conductivity and electrochemical stability with the mechanical integrity of solid-like networks. This review examines the fundamental principles governing ionic liquid confinement and the design of polymer-based, inorganic, and nanocomposite ionogels incorporating fillers such as carbon nanotubes, graphene derivatives, MXenes, and metal nanoparticles. Key fabrication strategies, including sol-gel processing, in situ polymerization, physical gelation, and emerging additive manufacturing, are discussed alongside the resulting physicochemical and electrochemical properties. Particular emphasis is placed on how ionic liquid chemistry, matrix architecture, interfacial interactions, and network structure collectively determine ionic conductivity, electrochemical stability, thermal resilience, mechanical performance, and device-level functionality. These properties enable applications spanning lithium- and sodium-ion batteries, metal-air batteries, supercapacitors, fuel cells, flexible and wearable electronics, soft robotics, biosensors, and neural interfaces. Despite substantial progress, challenges remain in balancing conductivity and mechanical robustness, minimizing ionic liquid leakage, ensuring long-term biocompatibility and stability, and achieving scalable, reproducible manufacturing. This review further highlights structure-property-application relationships and identifies key considerations for translating ionogels from material platforms to functional devices. Overall, ionogels represent a versatile and rapidly evolving materials platform with significant potential for next-generation electrochemical, electronic, and bioelectronic technologies.