High-performance asymmetric supercapacitors containing thick-film electrodes (over 100 mu m thick) made of CNT/V2O5 nanowire composite are designed. The excellent conductivity, high specific capacitance, and a large voltage window of the CNT/V2O5 nanocomposite enable the fabrication of devices with high energy and high power densities. Moreover, the resulting devices exhibit excellent cycling stability. This supercapacitor approach may be attractive for a wide range of device applications.