Low-Cost, High-Performance Flexible Supercapacitors Based on Vanadium Oxynitride Reactively Sputtered on a Porous Polymeric Substrate for Sustainable Energy Storage Applications

This work presents an air bubble method to fabricate a porous poly(vinyl alcohol) (PVA) substrate for a room-temperature (RT) reactively sputtered vanadium oxynitride (VON)-based high-performance, eco-friendly flexible supercapacitor. The air was inserted into the aqueous PVA solution, and controlled stirring was performed to form micrometer-sized air bubbles, which, upon drying in a mold, formed the porous substrate. Further, vanadium pentoxide (V2O5) was reactively sputtered at RT on the Ag current collector-coated plane and porous substrates. The supercapacitor device fabricated on the porous PVA substrate demonstrated drastically enhanced performance in a 1 M Na2SO4 electrolyte due to the remarkably higher surface area. For further improvement, a VON-based supercapacitor was fabricated that exhibited 377 F/g specific capacitance (areal capacitance of 18.9 mF/cm2 and volumetric capacitance of 196.35 F/cm3), 1.2 V potential window, 27.8 Wh/kg energy, and 3.0 kW/kg power density. It demonstrated 100% capacitance retention after 5000 charging–discharging cycles. For real applications, five devices connected in series glowed different colored light-emitting diodes (LEDs) for more than 180 s and 10 red LEDs together for 60 s. Further, it showed no performance degradation upon bending and twisting and illustrated fast disposal in normal water and moist soil. The fabricated materials were studied employing various characterizing tools.