Holey Graphene Nanosheets with Surface Functional Groups as High‐Performance Supercapacitors in Ionic‐Liquid Electrolyte

Abstract

Abstract Pores and surface functional groups are created on graphene nanosheets (GNSs) to improve supercapacitor properties in a butylmethylpyrrolidinium–dicyanamide (BMP–DCA) ionic liquid (IL) electrolyte. The GNS electrode exhibits an optimal capacitance of 330 F g −1 and a satisfactory rate capability within a wide potential range of 3.3 V at 25 °C. Pseudocapacitive effects are confirmed using X‐ray photoelectron spectroscopy. Under the same conditions, carbon nanotube and activated carbon electrodes show capacitances of 80 and 81 F g −1 , respectively. Increasing the operation temperature increases the conductivity and decreases the viscosity of the IL electrolyte, further improving cell performance. At 60 °C, a symmetric‐electrode GNS supercapacitor with the IL electrolyte is able to deliver maximum energy and power densities of 140 Wh kg −1 and 52.5 kW kg −1 (based on the active material on both electrodes), respectively, which are much higher than the 20 Wh kg −1 and 17.8 kW kg −1 obtained for a control cell with a conventional organic electrolyte.