Reduced graphene oxides prepared via mass loading-controlled non-explosive thermal reduction for high volumetric capacitance supercapacitors†

Abstract

Graphene oxide (GO) is known to undergo volume expansion during rapid and high-temperature heat treatment, resulting in a low packing density and thus a poor volumetric capacitance. This paper reports a non-explosive thermal reduction strategy (NET) to prepare compact thermally reduced graphene oxide (NE-TRGO) by controlling the mass loading of the GO film below a typical value (<5 mg cm⁻²). On one hand, the NET strategy effectively inhibits the expansion of graphene sheets, and thus the optimized NE-TRGO exhibits a high packing density of 1.94 g cm⁻³. On the other hand, the NET strategy contributes to preserving the electrochemically active C–OH and CO groups. Due to the high packing density and the abundance of electrochemically active groups, the gravimetric and volumetric capacitance of the optimized NE-TRGO were 314 F g⁻¹ and 609 F cm⁻³ @ 0.1 A g⁻¹, respectively, with excellent rate capability (160 F g⁻¹ and 310 F cm⁻³ @ 10 A g⁻¹) and significant cycling performance (∼99% capacitance retention after 9000 cycling at 5 A g⁻¹). The assembled symmetric supercapacitor delivers an energy density of 9.5 W h L⁻¹ at a power density of 96.7 W L⁻¹ and 1.5 W h L⁻¹ at a power density of 1056.3 W L⁻¹. This NET strategy represents a simple and feasible heat treatment approach to control the packing density and oxygen functional groups of graphene-based materials toward compact energy storage devices.