Lithium ion capacitors fabricated with polyethylene oxide-functionalized polysilsesquioxane hybrid ionogel electrolytes

We present a new polyethylene glycol-functionalized polysilsesquioxane, a ladder-like structured poly(poly(ethylene oxide)-co-methacryloxypropyl)silsesquioxane) (PEO-SQ) hybrid-type polymer gelator to fabricate hybrid ionogel electrolytes for lithium ion capacitors. The organic-inorganic hybrid polymer gelator contains not only an inorganic ladder-like polysilsesquioxane backbone for the thermal and electrochemical stability, but also dual organic pendant groups consisting of free-dangling PEO chains and unsaturated methacryloxypropyl groups for enhanced lithium ion dissociation and thermal curing function, respectively. The successful crosslinking of 1 M LiTFSI in N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMPTFSI) ionic liquid with only a small amount of PEO-SQ hybrid crosslinker (5 wt%) gave non-leaking ionogels with high thermal stability (∼400°C), large ionic conductivities, and excellent lithium ion capacitor C-rate performance and cyclability, comparable to those of neat ionic liquid electrolyte and superior over conventional organic ionogels fabricated with organic crosslinkers without PEO-moeities.