Fast supercapacitors based on graphene-bridged V₂O₃/VO_x core-shell nanostructure electrodes with a power density of 1 MW kg^-1

Transition metal oxides (TMOs), with their very large pseudocapacitance effect, hold promise for next generation high-energy-density electrochemical supercapacitors (ECs). However, the typical high resistivity of TMOs restricts the reported ECs to work at a low charge-discharge (C-D) rate of 0.1-1 V s^-1. Here, a novel vanadium oxides core/shell nanostructure-based electrode to overcome the resistivity challenge of TMOs for rapid pseudocapacitive EC design is reported. Quasi-metallic V₂O₃ nanocores are dispersed on graphene sheets for electrical connection of the whole structure, while a naturally formed amorphous VO₂ and V₂O₅ (called as VO_x here) thin shell around V₂O₃ nanocore acts as the active pseudocapacitive material. With such a graphene-bridged V₂O₃/VO_x core-shell composite as electrode material, ECs with a C-D rate as high as 50 V s^-1 is demonstrated. This high rate was attributed to the largely enhanced conductivity of this unique structure and a possibly facile redox mechanism. Such an EC can provide 1000 kW kg^-1 power density at an energy density of 10 Wh kg^-1. At the critical 45° phase angle, these ECs have a measured frequency of 114 Hz. All these indicate the graphene-bridged V₂O₃/VO_x core-shell structure is promising for fast EC development. A graphene-bridged V₂O₃/VO_x core-shell nanostructure based supercapacitor demonstrates an extremely high charge-discharge rate (50 V s^-1) and a high-power density performance. In this structure, quasi-metallic V₂O₃ nanocores are dispersed on graphene sheets for electrical connection of the whole structure, while a naturally formed amorphous VO₂ and V₂O₅ (or VO_x) thin shell around the V₂O₃ nanocore acts as the active pseudocapacitive material.