Three-Dimensional\nHierarchically Porous Graphene Fiber-Shaped\nSupercapacitors with High Specific Capacitance and Rate Capability

Abstract

Chemically\nconverted graphene fiber-shaped supercapacitors (FSSCs)\nare highly promising flexible energy storage devices for wearable\nelectronics. However, the ultralow specific capacitance and poor rate\nperformance severely hamper their practical applications. They are\ncaused by severe stacking of graphene nanosheets and tortuous ion\ndiffusion path in graphene-based electrodes; thus, the ultralow utilization\nof graphene has been rarely carefully considered to date. Here, we\naddress these issues by developing three-dimensional hierarchically\nporous graphene fiber with the incorporation of holey graphene for\nefficient utilization of graphene to achieve fast charge diffusion\nand good charge storage capability. Without deterioration in electrical\nbut robust mechanical properties, the optimal graphene fiber shows\nultrahigh specific capacitance of 220.1 F cm^–3 at\ncurrent density of 0.1 A cm^–3 and boosted specific\ncapacitance of 254.3 F cm^–3 at 0.1 A cm^–3 after nitrogen doping. Moreover, the nitrogen-doped 40% holey graphene\nhybrid fiber-assembled FSSC exhibits ultrahigh rate capability (96,\n91, and 87% at current density of 0.5, 1.0, and 2.0 A cm^–3, respectively, and 67% even at ultrahigh current density of 10.0\nA cm^–3) and excellent cycle stability (95.65% capacitance\nretention after 10 000 cycles). The contribution of three-dimensional\ninterconnected hierarchically porous network to the enhanced electrochemical\n(EC) performance is semiquantitatively elucidated by Brunauer–Emmett–Teller\nand energy dispersive spectroscopy mapping. Our work gives insights\ninto the importance of fully utilizing graphene and provides an efficient\nstrategy for high EC performance in chemically converted graphene-based\nFSSCs.