Nb2O5 Nanoparticles Anchored on an N-Doped Graphene Hybrid Anode for a Sodium-Ion Capacitor with High Energy Density

Abstract

Sodium-ion capacitors (SICs) have gained great interest for mid- to large-scale energy storage applications because of their high energy and high power densities as well as long cycle life and low cost. Herein, a T-Nb2O5 nanoparticles/N-doped graphene hybrid anode (T-Nb2O5/NG) was prepared by solvothermal treating a mixed ethanol solution of graphene oxide (GO), urea, and NbCl5 at 180 °C for 12 h, followed by calcining at 700 °C for 2 h, in which T-Nb2O5 nanoparticles with average size of 17 nm were uniformly anchored on the surface of the nitrogen-doped reduced GO because their growth and aggregation were hindered, and also, the electronic conductivity and the active sites of T-Nb2O5/NG were improved by doping nitrogen. The T-Nb2O5/NG anode showed superior rate capability (68 mA h g-1 even at 2 A g-1) and good cycling life (106 mA h g-1 at 0.2 A g-1 for 200 cycles and 83 mA h g-1 at 1 A g-1 for 1000 cycles) and also showed high-rate pseudocapacitive behavior from kinetics analysis. A novel SIC system had been constructed by using the T-Nb2O5/NG as anode and commercially activated carbon as the cathode; it delivered an energy density of 40.5 W h kg-1 at a power density of 100 W kg-1 and a long-term cycling stability (capacity retention of 63% after 5000 consecutive cycles at a current density of 1 A g-1) and showed a promising application for highly efficient energy storage systems.