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 0.0458Ω to 0.411Ω 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.