Synthesis of dense but microporous graphene by Na+ ions intercalation toward high volumetric performance supercapacitors

Abstract

With the rapid development of mobile electronics and electric vehicles, supercapacitors need to store as much energy as possible in relatively limited space. For aqueous-electrolyte supercapacitor, it is particularly important to design the electrode materials with high particle density, appropriate pore size distribution and doping degrees. In this work, we report an efficient approach to simultaneous increase the particle density and doping level of graphene-based electrode material. Through the interaction of oxygen functionalized graphene with NaOH solution, the electrostatic adsorption of sodium ions and oxygen-containing functional groups increases the density of the material while the reaction of hydroxide ions with oxygen-containing functional groups can increase the concentration of oxygen-containing functional groups of graphene. The as-prepared graphene displays both high particle density and pseudocapacitance which contributed from oxygen-containing functional groups. The graphene-based electrode delivers high volumetric capacitance of 469 F cm−3 as well as high rate capability (77% capacitance retention at 30 A g−1). Also, the assembled supercapacitor shows the high volumetric energy density of 24.2 Wh L−1, which is higher than most of the carbon materials in aqueous electrolyte. Therefore, this work provides a method to prepare high density and functionalized graphene, which has potential application in energy storage devices.