Hierarchical vanadium oxide microspheres forming from hyperbranched nanoribbons as remarkably high performance electrode materials for supercapacitors†
Novel hierarchical vanadium oxide microspheres forming from hyperbranched growth of nanoribbons have been successfully synthesized by a solvothermal method. The as-prepared hierarchical microspheres have a diameter of ∼5 μm, in which ∼400 nm long nanoribbons grow as hyperbranches on the clustering nanobelt backbones. These hierarchical microspheres contain 86.2 mass% V6O13 with metallic conductivity and 13.8 mass% VO2. Investigation of the growth mechanism indicates that EG plays an important role in the formation of hierarchical microspheres by regulating the solvent polarity and vanadium valences. The hierarchical microspheres exhibit a specific capacitance as remarkably high as 456 F g−1, with a corresponding volumetric specific capacitance of 3.09 F cm−3, at 0.6 A g−1 in the potential range of 0 to 1.2 V. The maximal energy density and power density achieved are up to 22.8 W h kg−1 (0.16 mW h cm−3) and 1.2 kW kg−1 (8.14 mW cm−3). The high performance of hierarchical vanadium oxide microspheres can be ascribed to the high specific surface area and large amount of mesopores provided by the hierarchical architecture, and the high conductivity and density of V6O13 in a high content in the hierarchical microspheres. This work has provided a new strategy to increase the specific capacitance of transition-metal oxides as electrode materials for the next-generation supercapacitors.