Exceptional supercapacitor performance from optimized oxidation of graphene-oxide

Graphene-based materials are highly desirable for supercapacitors, but vary considerably in reported properties despite being prepared by similar procedures; therefore, a clear route to improve the performance is currently lacking. Here, a direct correlation between the initial oxidation of graphene-oxide precursors and final supercapacitor performance is demonstrated. Building on this significant understanding, the optimized three-dimensional graphene frameworks achieve a superior gravimetric capacitance of 330 F g(-1) in an aqueous electrolyte. This extraordinary performance is also validated in various electrolytes at a device level. In a commercially used organic electrolyte, an excellent volumetric energy density of 51 Wh L-1 can be delivered, which significantly outperforms the state-of-the-art commercial carbon-based devices. Furthermore, solid-state supercapacitor with a gel electrolyte shows an impressive capacitance of 285 F g(-1) with a rate capability of 79% at 20 A g(-1) and capacitance retention of 93% after 20,000 cycles. This study presents a versatile design principle for engineering chemically derived graphene towards diverse applications in energy storage.