Graphene Nanosphere as Advanced Electrode Material to Promote High Performance Symmetrical Supercapacitor

To get carbon electrode with both excellent gravimetric and volumetric capacitances at high mass loadings is critical to supercapacitors. Herein, cracked defective graphene nanospheres (GNS) well meet above requirements. The morphology and structure of the GNS are controlled by polystyrene sphere template/glucose ratio, microwave heating time, and Fe content. The typical GNS with specific surface area of 2794 m² g^-1 , pore volume of 1.48 cm³ g^-1 , and packing density of 0.74 g cm^-3 performs high gravimetric and volumetric capacitances of 529 F g^-1 and 392 F cm^-3 at 1A g^-1 with a capacitance retention of 62.5% at 100 A g^-1 in a three-electrode system in 6 mol L^-1 KOH aqueous electrolyte. In a two-electrode system, the GNS possesses energy density of 18.6 Wh kg^-1 (13.8 Wh L^-1 ) at the power density of 504 W kg^-1 , which is higher than all reported pure carbon materials in gravimetric energy density and higher than all reported heteroatom-doped carbon materials in volumetric energy density, in aqueous solution, as far as it is known. A structural feature of carbon materials that possess both high energy density and high power density is pointed out here.