VO/vertically-aligned carbon nanotubes as negative electrode for asymmetric supercapacitor in neutral aqueous electrolyte.

Development of aqueous asymmetric supercapacitors (ASCs) is often limited by low specific capacitance of negative electrodes. Herein, a composite electrode with tiny vanadium pentoxide (VO) nanoparticles homogeneously decorated in vertically-aligned carbon nanotube arrays (VACNTs) is prepared by supercritical CO impregnation and subsequent annealing, and used as binder-free negative electrode for aqueous ASCs. Owing to its unique three-dimensional (3D) hierarchical nanostructure, the VO/VACNTs (VN) electrodes exhibit an ideal specific capacitance of 284 F g in the potential range of -1.1 to 0 V vs SCE at 2 A g and outstanding cycling stability in the NaSO aqueous solution. An aqueous ASC device possessing wide potential range of 1.7 V was constructed with pure VACNTs and VN-350 as the positive and negative electrodes, respectively. The ASC delivers a high energy density of 32.3 Wh kg at a power density of 118 W kg and satisfactory cycling life with capacitance retention of 76% after 5000 cycles.