A three-dimensional structure of ternary carbon for high performance supercapacitor

In supercapacitor applications, the energy storage capacitance and rate performance of graphene are severely weakened by the restacking of graphene sheets, which is a great challenge to overcome for fully exploring its supercapacitive properties. If one of the current strategies for promoting the ion diffusion of graphene is employed alone, only a limited improvement of supercapacitive performance of graphene can be achieved. Here, we combine three carbon allotropes into an all-carbon structure, and improve the ion diffusion and mitigate graphene restacking using combination of three strategies, including creating in-plane holes, self-assembling into three-dimensional (3D) structure, and adding spacers between graphene sheets. Thus a 3D hybrid-structured ternary-carbon (holey graphene/carbon nanotube/hollow carbon nano-onion, denoted as HG-CNT-HCNO) is synthesized as supercapacitor electrode material through a facile and effective one-step hydrothermal method. The synergistic effect of strategies and the different dimensional carbon allotropes endows the 3D structure with hierarchical porous structure, improved electron/ion transport, and increased energy storage sites. Consequently, the HG-CNT-HCNO exhibits high specific capacitance of 236.5 F g−1, ultrahigh rate capability (capacitance retention of 97.9% as the current density increases from 0.5 to 40 A g−1), and high electrochemical stability. Furthermore, the device with organic electrolyte shows high energy and power densities of 71.3 Wh kg−1 and 7.5 kW kg−1, respectively, demonstrating a high energy storage performance. The ternary-carbon structure may open up a new avenue for electrode performance optimization in the future energy storage systems by involving different dimensional carbon nanomaterials. © 2020 Elsevier B.V.