High-energy density nanofiber-based solid-state supercapacitors

We have developed binder-free solid-state electric double layer supercapacitors using freestanding porous carbon nanofiber electrodes fabricated using electrospinning and silica-based ionic liquid gel electrolytes. To ensure close electrode/electrolyte contact and efficient transport of ions for high power operation, we fabricated our electrodes by uniformly filling freestanding samples of porous carbon nanofiber mats with a blend of silica sol-gel precursor and ionic liquid electrolyte, which were then appropriately dried/gelled to form all-solid supercapacitors. Two different carbon nanofiber samples have been investigated with high specific surface areas of 1218 m² g^-1 and 2282 m² g^-1. The resulting solid-state supercapacitor can operate in a large voltage window of 3.5 V. We achieved specific capacitance (C_sp) and specific energy (E_cell, based on the mass of the two electrodes) of up to 144 F g^-1 and 61 W h kg^-1 respectively, rivaling that of lead-acid batteries, with a high active material (carbon only) loading of 3-5 mg cm^-2.