Overlapped T-Nb₂O₅/Graphene Hybrid for a Quasi-Solid-State Asymmetric Supercapacitor with a High Rate Capacity

To utilize the special intercalation pesudocapacitive behavior of T-Nb2O5 and good conductivity of reduced graphene (rGO), a T-Nb2O5/rGO composite with an overlapping structure is developed to meet the demands of energy storage devices with a remarkable electrochemical performance. T-Nb2O5 nanowires (NWs) prepared by a hydrothermal method are assembled layer by layer onto the GO surface by electrostatic interaction to obtain T-Nb2O5/rGO hybrids. The overlapped T-Nb2O5/rGO composites exhibit an outstanding capacitance of 1492 F g-1 at 1 A g-1, which is superior to that of pure T-Nb2O5 NWs, and also present a better cycling stability of 88.6% of the initial capacitance after 3000 charge-discharge cycles in KOH aqueous solution. The supercapacitive performances of an asymmetric supercapacitor (ASC) of T-Nb2O5/rGO//activated carbon (AC) are evaluated in KOH aqueous solution and a quasi-solid KOH/poly(vinyl alcohol) gel. The quasi-solid ASC device of T-Nb2O5/rGO//AC delivers an energy density of 72 Wh kg-1 at 479 W kg-1. Furthermore, the ASC device could power a digital timer and a red light-emitting diode upon fast charging, exhibiting potential applications in future portable electronics.