Controllable adjustment strategies for activated carbon and application in supercapacitors with both ultra-high capacitance and rate performance

Abstract

Pore structure in activated carbons (ACs) is critical for supercapacitors with both high capacitance and rate performance. To obtain ACs with suitable pore structures, many efforts in the exploration of technology have been made. In this work, we found that it is easier to form a developed pore structure when precursor carbon is composed of disordered graphite-like micro-crystals. The gas produced during the activation process could provide the force to separate the neighboring graphite layers. Based on this, we propose a controllable adjustment of the pore structure strategy. A sub-micron scale carbon sphere composed of randomly arranged graphite micro-crystals is chosen as the precursor carbon. After CO 2 activation, a high specific surface area (SSA, ~3300 m 2 g −1 ) AC dominated by micropores is obtained. For KOH activation, a hierarchical porous AC possessing ultra-high SSA (~3400 m 2 g −1 ) is achieved. Benefited from the cross-linked mesopores with the size range of 3 to 5 nm, the fabricated symmetric supercapacitors exhibit high specific capacitances in organic electrolyte (192 F g −1 at 0.01 V s −1 ) and excellent rate performance (110 F g −1 at 30 V s −1 ) that is comparable with the CNTs electrode with the similar areal capacitance (~25 mF cm −2 ). This provides a route to fabricate ACs with both high specific capacitance and rate performance. • A Pressure-space mechanism was proposed for the formation of micropores in ACs. • Controllable adjustment strategies were put forward for pore structure. • Hierarchical porous ACs possessing ultra-high SSA up to 3400 m 2 g −1 • The fabricated EDLC exhibits comparable rate performance with CNTs electrode.