Highly Durable, Self-Standing Solid-State Supercapacitor Based on an Ionic Liquid-Rich Ionogel and Porous Carbon Nanofiber Electrodes

A high-performance, self-standing solid-state supercapacitor is prepared by incorporating an ionic liquid (IL)-rich ionogel made with 95 wt % IL (1-ethyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­imide) and 5 wt % methyl cellulose, a polymer matrix, into highly interconnected 3-D activated carbon nanofiber (CNF) electrodes. The ionogel exhibits strong mechanical properties with a storage modulus of 5 MPa and a high ionic conductivity of 5.7 mS cm^–1 at 25 °C. The high-surface-area CNF-based electrode (2282 m² g^–1), obtained via an electrospinning technique, exhibits hierarchical porosity generated both in situ during pyrolysis and ex situ via KOH activation. The porous architecture of the CNF electrodes facilitates the facile percolation of the soft but mechanically durable ionogel film, thereby enabling intimate contact between porous nanofibers and the gel electrolyte interface. The supercapacitor demonstrates promising capacitive characteristics, including a gravimetric capacitance of 153 F g^–1, a high specific energy density of 65 W h kg^–1, and high cycling stability, with a capacitance fade of only 4% after 20 000 charge–discharge cycles at 1 A g^–1. Moreover, device-level areal capacitances for the gel IL cell of 122 and 151 mF cm^–2 are observed at electrode mass loadings of 3.20 and 5.10 mg cm^–2, respectively.