High-power and high-energy asymmetric supercapacitors based on Li+-intercalation into a T-Nb2O5/graphene pseudocapacitive electrode

The intercalation pseudocapacitance which leads to the extraordinary charge storage properties has been confirmed as an intrinsic capacitive property of orthorhombic Nb2O5 (T-Nb2O5) nanocrystals. However, the poor electronic conductivity of T-Nb2O5 nanocrystals may limit their electrochemical utilization and high-rate performance especially for thick electrodes with high mass loadings. To address this issue, we herein reported a hydrothermal-heat treatment method to anchor T-Nb2O5 nanocrystals on conductive graphene sheets, which form a layer-by-layer integrated electrode with much shortened ion transport paths and results in excellent electrochemical capacitive properties, including high capacitance (626 C g(-1)), excellent rate handling and cyclic stability. Furthermore, asymmetric supercapacitors were constructed by using the high-rate response T-Nb2O5/graphene nanocomposite and mesoporous carbon as the negative and positive electrode, respectively. The asymmetric supercapacitor could deliver a high energy density of 16 W h kg(-1) at an unprecedented power density of 45 kW kg(-1) (discharge time of 1.2 s). The outstanding power properties of the supercapacitors are mainly attributed to the improved high-rate Li-insertion/extraction capability of the T-Nb2O5/graphene electrode and appropriate pairing of the mesoporous carbon electrode.