Synthesis of activated carbon nanospheres with hierarchical porous structure for high volumetric performance supercapacitors

Activated carbon nanospheres (ACNS) with hierarchical porosity have been synthesized via a low-concentration hydrothermal reaction with phenolic resin as a carbon source and block copolymer F127 as a soft template, followed by subsequent KOH activation. As-obtained ACNS material integrates several advantages, such as a nanoscale particle size, a hierarchical porosity, abundant oxygen-containing functional groups and a high mass density (0.81 g cm^-3). The electrochemical tests in KOH aqueous electrolyte shows superior capacitive performances, i.e. both high gravimetric and volumetric capacitance of 243 F g^-1 and 198 F cm^-3, a large areal capacitance of 25.5 μF cm^-2, an excellent rate capability as well as a superior long-term cycling stability (96.1% capacitance retention over 10000 cycles). Moreover, symmetric supercapacitors based on ACNS electrodes achieve a high volumetric energy density of 6.0 Wh L^-1, which maintains 3.7 Wh L^-1 even at a high power density of 6.6 kW L^-1. Such ACNS thus shows great potential as a promising porous carbon material for high volumetric performance supercapacitors.