Supercapacitor with Ultra-High power and energy density enabled by Nitrogen/Oxygen-Doped interconnected hollow carbon Nano-Onions

A nitrogen/oxygen-codoped interconnected hollow carbon nano-onion structure is synthesized using uniform-sized metal oxide nanocrystals as sacrificing templates. The structural merits enable the ultrafast ion transportation and efficient ion accomodation within the electrode material, which can simultaneously realize high energy density and high power density in supercapacitor. [Display omitted] •Nitrogen/oxygen-codoped interconnected hollow carbon nano-onions have been synthesized as supercapacitor electrode.•The tetrahedron- and octahedron-type pores originated from the closed packing of onion particles build the fast ion transportation tunnel.•A superhigh power density of 400 kW kg−1 was obtained in supercapacitor, with a high energy density of 71 Wh kg−1 achieved meanwhile.•An ultrahigh energy density of 195.6 Wh kg−1 can be reached at 2 kW kg−1 in supercapacitor. Challenge remains in the supercapacitor development for simultaneously realizing high power density and high energy density, hindering its durable power application in renewable energy technologies. Herein, a nitrogen/oxygen-codoped interconnected hollow carbon nano-onion structure (N,O-IHCNO) was synthesized for fast accommodating and releasing large amounts of ionic liquid ions. The novel structure was prepared using monodispersed uniform-sized Fe3O4 nanoparticles as sacrificing templates and oleic acid ligands bounded to the surface as carbon source. The tetrahedron- and octahedron-type pores originated from the closed packing of onion particles build the fast ion transportation tunnel. Three-dimensional covalently interconnected graphitic layers greatly improve the conductivity of the carbon onion structure. Heteroatom doping increases the surface polarity, electrolyte affinity and energy storage capacitance. These merits jointly make the structural advantages of CNOs in energy storage well utilized, resulting in a superhigh power density of 400 kW kg−1 in the supercapacitor based on N,O-IHCNOs in ionic liquid, with a high energy density of 71 Wh kg−1 achieved meanwhile. Moreover, a maximum energy density of 195.6 Wh kg−1 can be reached at 2 kW kg−1. This study provides a strategy for synthesis of high-performance CNOs-based electrode materials for reliable and efficient electricity storage equipment and devices.