Free-radical-initiated strategy aiming for pitch-based dual-doped carbon nanosheets engaged into high-energy asymmetric supercapacitors

Doped quasi-two-dimensional carbons with layer-stacked porous architecture and chemically functionalized surface are strongly appealing for high-energy supercapacitors, but there are daunting challenges to synthesize them through a cost-efficient and eco-friendly path. Herein, N/S dual-doped stacked carbon nanosheets (D-SCN) is first synthesized from coal tar pitch, a cheap coking by-product, beginning with a controlled molecular radical-polymerization initiated by 2,3-dimethyl-2,3-diphenylbutane, followed by a one-step carbonization-activation process in presence of potassium benzoate and N,N'-diphenylthiourea. As-obtained D-SCN with reasonable densification shares a well-designed layer-stacked topology texture, hierarchical interconnected porous structure and N/S dual-doped surface, which work together to harvest high supercapacitive performance. The D-SCN delivers a maximal specific capacitance of 458 F g(-1), which is considerably higher than most of previously reported for other carbon materials. As-assembled asymmetric all-solid-state supercapacitor with a wide voltage range of 0-1.8 V takes on a volumetric energy density of 27 W h L-1 at a power density of 296 W L-1 with fading capacitance of merely 5.9% after 20000 cycles. The route advocated here for preparing pitch-based nanocarbons opens up new horizons in exploring large-scale preparation of electrode materials suitable for narrow spaces.