Supercapacitors based on nitrogen-enriched crumpled graphene with a high volumetric capacitance and high-mass-loading per area of the electrode

The low volumetric capacity and sluggish diffusion of ions at high mass loadings of active materials per area limit any improvement of the energy and power densities of supercapacitors. A mixture of graphene oxide (GO) and urea in water was treated by an ultrasonic atomizer to form aerosol droplets, which were dried to obtain crumpled GO/urea particles. Crumpled graphene with a nitrogen content of 11.38% was obtained by the thermal shocking of these particles at 600 °C for 50 s. A volumetric capacitance of 384.0 F cm−3 was achieved when the crumpled graphene was used as supercapacitor electrodes. Even at a high current density (10 A g−1) and a high loading (74.3 mg/cm2 electrode), the specific capacitance retention still remained high. It is proposed that N-doping in the forms of pyrrole, imide, lactam and other types of pyridine-like nitrogen, and high surface area of the sample were key factors in improving the capacitance. The crumpled structure provided high mass transfer and high accessibility of ions to the active surface.