Asymmetric supercapacitors based on 3D graphene-wrapped V2O5 nanospheres and Fe3O4@3D graphene electrodes with high power and energy densities

Asymmetric supercapacitor (ASC) devices are emerging as effective high-performance energy storage systems. We report on the synthesis of novel and green electrode materials and their use to construct high performance ASCs. The assembled ASCs are based on 3D porous graphene-wrapped V2O5 nanospheres as the positive electrode and Fe3O4@graphene as the negative electrode. The optimal ratio of the V2O5 nanospheres intercalated graphene sheets in the composite electrodes was identified. Compared to all positive electrode formulations, the V2O5@3DGr (33%) hybrid electrode achieved the highest specific capacitance (612.5 Fg−1) at a current density of 1.0 A g−1. Based on the excellent electrochemical behavior of the fabricated electrodes, the assembled asymmetric supercapacitor devices of V2O5@3DGr//Fe3O4@3DGr exhibited a maximum energy density of 54.9 Wh kg−1 with a power density of 898 Wkg−1 with an extended voltage of 1.8 V in 1.0 M Na2SO4 aqueous electrolyte. Furthermore, the ASC device demonstrated excellent cycling stability with 89.6% capacitance retention over 10,000 cycles. The outstanding electrochemical performance of the fabricated electrodes can be attributed to the synergic effect between graphene sheets and metal oxides (V2O5, Fe3O4) sandwich network structures. Interestingly, the proposed asymmetric electrode materials provide a promising strategy for integrating low cost transition metal, green electrolyte, high energy, and power densities of supercapacitor devices and that can bridge the gap with commercial batteries.