High-Energy-Density 3.5 V Carbon Supercapacitor Fabricated with Ionic-Liquid-Incorporated Redox-Active Gel Polymer Electrolyte

Introducing redox-active species in the electrolyte component is an effective approach to improving the energy density of carbon supercapacitors via additional pseudocapacitive redox activities at the electrode-electrolyte interfaces. Herein, we report a quasisolid-state supercapacitor fabricated with symmetrical activated carbon electrodes and an ionic liquid (IL, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, BMPTFSI)-incorporated nonaqueous, redox-active gel polymer electrolyte (R-GPE) added with a redox-additive IL (BMPBr), entrapped in a polymer matrix of poly(vinylidene fluoride-co-hexafluoropropylene). The R-GPE film with an optimum composition of an additive (BMPBr) showing a high mechanical stability (tensile strength similar to 0.32 MPa and elongation at break similar to 154%), a wide thermal stability range (up to similar to 385 degrees C), and excellent electrochemical properties (an ionic conductivity of similar to 1.2 X 10(-3) S cm(-1) at room temperature and an electrochemical stability window of similar to 6.5 V) is found as an excellent substitute of liquid electrolytes in supercapacitors. The quasisolid-state supercapacitor is fabricated from biomass (pollen-cone)-derived activated carbon electrodes separated by the R-GPE film and characterized via electrochemical techniques, namely, electrochemical impedance spectroscopy, cyclic voltammetry, and galvanostatic charge-discharge tests. The BC-related redox activities at the interfaces lead to a significant improvement in specific capacitance (from similar to 164 to similar to 248 F g(-1)), specific energy (from similar to 65 to similar to 105 W h kg(-1)), and maximum power (from similar to 15 to 31 kW kg(-1)). With a moderate rate capability, the supercapacitor demonstrates a good cycling performance with an initial similar to 23% fading in the specific capacitance and a similar to 100% Coulombic efficiency for similar to 10000 charge-discharge cycles.