In this work, the asymmetric supercapacitor in which spherical porous VN is used as a negative electrode and NiOx as a positive electrode was assembled in 1 M KOH aqueous electrolyte. The spherical porous VN negative material has a specific capacitance of 580 Fig and the NiOx positive electrode a specific capacitance of 680 F/g. The VN/NiOx symmetric supercapacitor shows a sloping voltage profile from 0.5 to 1.45 V with excellent reversibility and delivers a specific capacitance of 139 F/g and an energy density of 63 Wh/kg based on the total weight of the active electrode materials. The VN/NiOx asymmetric supercapacitor shows a good cycling behavior, about 15% specific capacitance decay after 1000 cycles. It also exhibits an excellent rate capability, even at a power density of 2400 W/kg, it has a specific energy 26 Wh/kg compared with 50 Wh/kg at the power density about 365 W/kg. (C) 2012 Elsevier Ltd. All rights reserved.