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

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 (similar to 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.