Polymer-Engineered Ionogels for Lithium-Based Energy Storage: Interactions, Processing, and Electrode Interfaces

By immobilizing ionic liquids (ILs) within polymer networks, ionogels offer a route to quasi-solid-state electrolytes with liquid-like ion mobility and solid-like dimensional stability. Their practical performance, however, is not determined by IL content or total ionic conductivity alone. Frequently reported limitations include low Li+ transference numbers, polymer–IL demixing, creep, insufficient electrode wetting, and unstable interphases. This review develops a mechanistically informed framework that traces how polymer chemistry and polymer–IL–lithium salt interactions shape process-induced microstructures, which in turn influence ion transport, mechanical response, and electrode interfaces. We examine electrostatic interactions, hydrogen bonding, and competitive Li+ coordination across representative polymer–IL systems, and compare fabrication routes in terms of the confinement, phase connectivity, and electrode contact they generate. The routes considered include solution casting, phase inversion and scaffold impregnation, electrospinning, thermal or photoinitiated in situ polymerization, physical self-assembly, interpenetrating-network and multiple-network formation, hybrid sol–gel processing, and thin-film patterning. The review distinguishes structural evidence from Li+-specific transport evidence and considers differences in measurement and cell conditions. Load-bearing networks and continuous ion-rich domains can mitigate the transport–mechanical trade-off, but their benefits require verification of Li+ transport and interfacial stability under relevant operating conditions. Minimum reporting criteria for meaningful comparison and scale-up are proposed.