Energy storage performance of thin film nanocrystalline vanadium oxide with fluorinated tin oxide current carrier electrode for solid-state transparent supercapacitors based on ionic liquid gel electrolyte

Abstract

Energy-power performance of transparent supercapacitors based on sol gel processed nanometer thin nanocrystalline vanadium oxide film composite with fluorinated tin oxide (FTO) thin film electrode as current collector is investigated. The symmetric supercapacitor device configured in the solid-state form using the BMIMBF4 ionic liquid with LiClO4 dopant gel electrolyte shows high areal capacitance of 310 mFcm−2 attributed to pseudocapacitive energy storage mechanism with minimal ion kinetics limitation. The vanadium oxide electrode forms in the stoichiometric V2O5 and in the multivalent phases depending on the annealing process in film synthesis which impacts the specific energy-power performance. The supercapacitor based on V2O5 with distorted [VO5] pyramids alongside phases with V4+ and mixed V oxidation states exhibited high specific energy 7.7 μWhcm−2 at corresponding specific power of 64.7 μWcm−2 and significantly large specific power of 363.8 μWcm−2 at 1.5 V. High capacitance and energy-power is attributed to simultaneous redox reactions storing charges in the specific potential range to contribute to the pseudocapacitance. The stoichiometric V2O5 films in V5+ valence state show minimum loss of specific energy (1.20–0.89 μWhcm−2) at high power (40–132 μWcm−2) and much stable 75 ± 2% charge-discharge performance for 2000 cycles. The single valent V2O5 electrodes show sequential V5+/V4+ and V4+/V3+ redox processes and lesser stored charge but high cyclic stability. The significantly improved capacitive and specific energy-power parameters pertaining to a high >77% transmittance at 590 nm show the applicability of the V2O5 solid-state ionic liquid electrolyte based supercapacitor energy storage devices in futuristic transparent electronics.