Ionic liquid incorporated, redox-active blend polymer electrolyte for high energy density quasi-solid-state carbon supercapacitor

Abstract

Quasi-solid-state carbon supercapacitors offering high power density, flexibility and long cycle life have shown excellent potential for commercial applications. Recently, major focus of research and development on such supercapacitors is towards their improvement in energy density. A latest approach for improvement in energy storage is enhancement of redox-activity at electrode-electrolyte interfaces introducing suitable redox-additive in electrolytes. Here, an ionic liquid (IL)- incorporated redox-active gel polymer electrolyte (GPE) based on polymer blend of poly(vinyl alcohol) (PVA) and poly(vinyl pyrrolidone) (PVP) is presented for application in carbon supercapacitors. The GPE, comprising IL 1-ethyl-3-methylimidazolium hydrogen-sulphate (EMIHSO4), added with redox-additive hydroquinone (HQ), immobilized in PVA/PVP, exhibits excellent flexibility, thermal and electrochemical stability with optimum ionic conductivity of ~9.3 mS cm−1 at room temperature. Quasi-solid-state supercapacitors have been fabricated using GPEs with symmetrical electrodes of multiwalled carbon nanotubes (MWCNTs), graphene nanoplatelets (GNPs) and biomass-derived activated carbon (AC) for comparative studies. AC-electrodes illustrate superior capacitive responses over other carbon-electrodes due to their suitable porous texture with hierarchical porosity. Redox-activity of HQ-incorporated GPE at the interfaces with porous AC-electrodes provides optimum capacitive parameters of the device (Cs ~485 F g−1 and E ~24.3 Wh kg−1) with prolonged cyclic performance up to 5000 charge-discharge cycles.