Surpercapacitors Based On Directly Grown Carbon Nanotubes

The supercapacitor, also called electrochemical capacitor, is a new type energy storage device. It has great .potential application in electric vehicles; aerospace; digital communications system; defense technology and so on. However, the furtherance of supercapacitor technologies still suffers from some challenges-including a higher self-discharge, low energy density and high production cost. It is great significance of studying the electrode materials, which is a key factor influencing the performance of supercapacitor. In this work, in situ deposit manganese dioxide on foamed nickel with directly grown multi-walled carbon nanotubes by the CVD technique without extra catalyst layer and to prepare the Mn02-MWNT-Ni foam electrode realized by facile hydrothermal method for the flexible supercapacitor applications.Specific studies are as follows:MWNTs with diameters of ?90 nm and lengths of ?20 um were grown uniformly on Ni foam surface, The measured interplanar distance of Mn02 nano flakes is 0.64 nm, The CV curve area of Mn02-MWNT-Ni foam electrode increased about 590% compared with Ni Foam electrodes,attributed to the improvements on electrochemical reaction efficiency,and indicating the best capacitive performance of Mn02-MWNT-Ni foam electrode. The EIS comparison indicates that the charge transfer resistance of MnO₂-MWNT-Ni foam electrode dropped 797.3% from 0.0458? to 0.411? with the Mn02-Ni foam electrode. The as-prepared Mn02-MWNT-Ni foam with a nanocomposite structure presented a high specific capacitance of 1915.8F/g ?2.9F/cm ? at the current density of 6.5A/g. It also exhibited the excellent high rate performance and long-term cyclic stability ?94.9% capacitance retention after 4600 cycles?in three-electrode systems in KOH electrolyte. The power density reached 6398.5W/kg, while a reasonable energy density of 344.8Wh/kg,suggesting excellent cycle stability.Results show that the MnO₂-MWNT-Ni foam composite exhibits a great potential as a low-cost, high specific capacitance, high energy density, power density, long-term cyclic stability and attractive wearable energy storage device, which is promising for various supercapacitor and battery manufacturing applications.