Solvent evaporation induced graphene powder with high volumetric capacitance and outstanding rate capability for supercapacitors

Graphene-based electrode materials for supercapacitors usually suffer from poor volumetric performance due to the low density. The enhancement of volumetric capacitance by densification of graphene materials, however, is usually accompanied by deterioration of rate capability, as the huge contraction of pore size hinders rapid diffusion of electrolytes. Thus, it is important to develop suitable pore size in graphene materials, which can sustain fast ion diffusion and avoid excessive voids to acquire high density simultaneously for supercapacitor applications. Accordingly, we propose a simple solvent evaporation method to control the pore size of graphene powders by adjusting the surface tension of solvents. Ethanol is used instead of water to reduce the shrinkage degree of graphene powder during solvent evaporation process, due to its lower surface tension comparing with water. Followed by the assistance of mechanical compression, graphene powder having high compaction density of 1.30 g cm(-3) and a large proportion of mesopores in the pore size range of 2-30 nm is obtained, which delivers high volumetric capacitance of 162 F cm(-3) and exhibits outstanding rate performance of 76% capacity retention at a high current density of 100 A g(-1) simultaneously.