Highly Flexible Supercapacitors Based On Cabon Nanotube Films

Along with the gradual advance of modern science and technology, an increasing number of portable and wearable electronics have been brought to our attention, customer electronics are becoming small, lightweight, wearable, flexible, all of these electronics require lightweight, thin and tough energy storage device. Supercapacitors are new type of energy storage devices, it can provide high energy density, high power density, fast charging speed, long-cycle life, wide using temperature range, and they are environment-friendly. Carbon nanotubes(CNT) films are promising electrode materials for supercapacitors as a result of their high conductivity, high thermal conductivity, good corrosion resistance, high temperature stability and excellent mechanical performance. However, charge storage ability of the CNT is limited because of the capacitance of CNT electrochemical capacitor is mainly derived from the double layer capacitance, and the specific surface area of CNT is small. This dissertation adopts a strategy that coupling ploypyrrole(PPy) with flexible and stable CNTs to improve specific capacitance of the film and keep the flexibility of CNT films, PPy is a kind of conductive polymer with pseudo capacitance. Based on the CNT/PPy composite films, we have successfully prepared a film-shaped supercapacitor and a fiber-shaped supercapacitor with excellent capacitance and flexibility.Large area CNT film directly prepared by chemical vapor deposition, according to the research, It is found that the best quality CNT film can be produced when the feed rate of carbon source is 0.4 L/h, and the hydrogen content is 20%. CNT films become hydrophilic after treated by H2O2 and HCl, moreover, impurities can be removed by this method.CNT/PPy composite films can be prepared by electrochemical deposition,according to the research, we know that the CNT/PPy film with 200 s deposition time is most suitable to use as the electrode material of supercapacitors. We have studied the capacitive properties of carbon CNT films with 200 s deposition time, the mass specific capacitance of the film is increased from 6.76 F/g to 241.69 F/g.By using the CNT/PPy films as flexible film electrodes, we have fabricated solid-state film-shaped supercapacitor. The mass specific capacitance of this composite film supercapacitor can reach 69.6 F/g, and the area specific capacitance can reach 13.9 mF/cm2, after 10000 times of galvanostatic charging and discharging, the mass specific capacitance retention rate at 65.6%.In addition, this supercapacitor can be arbitrarily deformed, including in the bending, bending into the "S" type and the twisted state, and the capacitive maintaining stable performance in these deformation conditions.We have prepared CNT/PPy composite fibers by direct spinning method, and by using these composite fibers as flexible fiber electrode, we have fabricated solid-state fiber-shaped supercapacitor. By this method, the PPy not only deposited on the CNT and CNT bundles of the surface of the fiber, but also deposited on the CNT and CNT bundles inside the fiber, the fiber-shaped supercapacitor has a good capacitance, and the mass specific capacitance of the supercapacitor can reach 165.7 F/g. We have studied the flexibility of this kind fiber-shaped supercapacitor, it can be arbitrarily deformed and has good capacitance in these deformation conditions.