A redox additive gel-polymer electrolyte and vanadium oxide hydrate electrode material for quasi-solid state asymmetric supercapacitor.

Herein, we prepared layered vanadium oxide hydrate (VOH), a vanadium pentoxide-based electrode material for supercapacitor applications. The VOH electrode showed a specific capacity of 77.6 C g-1 at 4 A g-1 in a 3 M KOH electrolyte solution. Furthermore, the enhancement of the electrochemical performance of the VOH was achieved by adding K3[Fe(CN)6] to the electrolyte as a redox additive. Among the various concentrations, the VOH electrode showed a specific capacity of 1085.9 C g-1 at 4 A g-1 in a 3 M KOH containing 75 mM K3[Fe(CN)6] electrolyte. The performance enhancement was attributed to the eased diffusion of ferricyanide species into the hydrated, enlarged interlayer structure of the active material. Additionally, the [Fe(CN)6]3-/[Fe(CN)6]4- redox pair contributed to the charge-storing process through reversible redox reactions in the electrolyte. Moreover, a quasi-solid-state asymmetric supercapacitor was constructed by employing VOH as positive electrode, activated charcoal (AC) as negative electrode, and PVA/KOH/K3[Fe(CN)6] as gel-polymer electrolyte (GPE). The constructed device displayed a specific capacity of 105.2 C g-1 at 1 A g-1 and delivered a maximum energy density of 24.8 Wh kg-1 at 850 W kg-1 power density with a cell voltage of 1.7 V. The outcomes of this work suggest a viable strategy for the rational design of next-generation high-performance energy storage systems.