Optimal structuring of nitrogen-doped hybrid-dimensional nanocarbons for high-performance flexible solid-state supercapacitors

The rapid development of wearable electronics has increased the demand for high-performance flexible power-supply devices for enhancing portability and durability. Flexible solid-state supercapacitors (FSSSCs) could have potential to fulfill this demand, but engineering electrode materials is still a challenging issue. Herein, we demonstrate optimal structuring of nitrogen-doped hybrid-dimensional nanocarbons (N-RGO-CNT-CBNP) for high-performance FSSSCs. Three types of representative nanocarbons including reduced graphene oxide nanosheets, carbon nanotubes and carbon black nanoparticles are explored as building blocks to construct N-RGO-CNT-CBNP synergistically via facile and low-cost solution processing. With melamine as both a structure-directing agent and a highly effective nitrogen source, a highly-porous three-dimensional hierarchical structure and a high nitrogen doping level of 13.8 at% are simultaneously achieved. Such a nanostructured material is employed to fabricate sandwich-structured papers (N-RGO-CNT-CBNP-Ps) with high flexibility, conductivity and mechanical strength. The resulting N-RGO-CNT-CBNP-Ps possess an ultrahigh areal specific capacitance (935 mF cm−2 at 1 mA cm−2), as well as a remarkable rate capability (e.g. 580 mF cm−2 at 100 mA cm−2) and cycling stability (e.g. 91.6% retention even after 40 000 cycles at 50 mA cm−2). An N-RGO-CNT-CBNP-P based FSSSC displays both high energy density and power density, while satisfying operational reliability/durability requirements. The results indicate that the N-RGO-CNT-CBNP-P based FSSSCs hold promise towards their practical applications in wearable electronics. © The Royal Society of Chemistry.