Freestanding CNT–WO3 hybrid electrodes for flexible asymmetric supercapacitors

Freestanding carbon nanotube (CNT)–tungsten oxide (WO3) hybrid films as the negative electrode of asymmetric supercapacitors (ASCs) are synthesized via a facile vacuum filtration and a subsequent physical vapor deposition method. With pure CNT films as the paired positive electrodes, these flexible ASC devices have been fabricated to demonstrate excellent electrochemical performance. Their cyclic voltammetry curves barely change when the ASC device is flat, bent, or twisted. Their volumetric capacitance reaches a high value of 2.6 F cm−3 at a scan rate of 10 mV s−1. Due to the extended operating voltage of 1.4 V, the ASC device reaches a power density of 30.6 mW cm−3 and an energy density of 0.59 mW h cm−3. After 50 000 cycles, the capacitance retention of the ASC is still 75.8%, which shows its excellent stability and ultra-long lifetime. When these ASC devices are connected in series as power sources, a commercial blue light-emitting diode can be lighted up and a commercial mobile-phone can be charged. In short, the novel ASC device with perfect flexibility and stability can be applied as one of the most promising next-generation power supplies.