All-Solid-State Asymmetric Supercapacitors with Novel Ionic Liquid Gel Electrolytes

In the past years, all-solid-state supercapacitors, as energy storage devices, have drawn greatest attention in both academic and industrial sectors because of their potential applications, in particular in the wearable and portable electronics. However, poor energy densities of all-solid-state supercapacitors restrict their practical applications. In this study, we first report novel ionic liquid gels composed of poly(vinyl alcohol) (PVA), 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4), and tetrabutylammonium tetrafluoroborate (TBABF4) (PVA:BMIMBF4:TBABF4) as the solid-state electrolytes. It is found that the PVA:BMIMBF4:TBABF4 solid-state electrolytes exhibit dramatically enhanced ionic conductivity. Afterward, we report all-solid-state asymmetric supercapacitors (ASCs) by using MnO2 coated on a carbon cloth (CC) as the positive electrode, reduced graphene oxide coated on a CC as the negative electrode, and novel PVA:BMIMBF4:TBABF4 as the solid-state electrolyte. All-solid-state ASCs exhibit an operational window of 3 V, an energy density of 61.2 W h/kg at the power density of 1049 W/kg, and more than 80% capacitance retention after 3000 charge/discharge cycles. All these results demonstrate that we provide a facile way to develop high-energy-density all-solid-state ASCs with good cycling stability.