Research On The Preparation And Eclectrochemical Properties Of Manganese Oxides/Nano-carbon Composites

The extensive research of electrode materials for supercapacitors has experienced morethan ten years from carbon materials to metal oxides and conducting polymers. Manganeseoxide （MnO₂） plays a significant role not only in the pseudocapacitor, but also in the capacitorcombined with both electrical double-layer capacitor（EDLC） and pseudocapacitor because ofits abundance, low cost, friendly environmental nature and higher electrochemical activity.However, MnO₂as semiconductor suffers from intrinsically low electrical conductivity, whichlimits its chargeable and dis-chareable ability under higher current, also leads to poor powerdensity. Therefore, we consider to prepare the composite of MnO₂/CNTs as supercapacitorelectrode material, through which way, we can not only improve the the conductive propertiesand frequency response characteristics of MnO₂, but also produce a higher capacitance. Themain contents are as follows:Firstly, MnSO₄·H₂O and K₂S₂O₈were taken as raw material. Using hydrothermaltechnique in the temperature60℃and pH1, under which environment the thorn sphericalmanganese dioxide particles was successfully prepared whose radius is2-4μm. The productswere characterized by XRD, SEM, and they have been proved to be the α-MnO₂in tetragonalsystem; The obtained α-MnO₂was then applied as the electrode material for supercapacitors,electrochemical characterization was carried out using cyclic voltammetry, galvanostaticcharge–discharge cycling and impedance spectroscopy in6M KOH. Its specific capacitance is65F/g at the scan rate of100mV/s, the power density is3.3kW/kg.Secondly, we investigated the impact of reaction temperature and the concentration ofthe reaction solution on the structure and morphology of manganese oxide particles. Resultsshow that the more the volume of water dissolved in reaction, the smaller the diameter ofmanganese dioxide particles, but no thorn spherical would be achieved in40℃.Additionally, we research on the processing method and condition of preparingα-MnO₂/CNTs based on the preparation method mentioned above, as well as effects ofdifferent doping methods, the use of different types of carbon nanotubes and different choiceof electrolyte on the electrochemical performance using α-MnO₂/CNTs as electrode materials.Results show that α-MnO₂/CNTs composites with the mass ratio of5%purified CNTs showsgood capacitance characteristics and obtained the highest specific capacitance in theelectrolyte of6M KOH. The in-situ synthesis is superior to ball milling method by contrast ofdifferent preparing method. The power density of the composite electrode was increased200%compared with α-MnO₂. Finally, aiming at solving the problem of agglomeration of CNTs in α-MnO₂, a fewgraphene oxide was added to α-MnO₂/CNTs in order to prevent adjacent CNTs fromaggregation, TEM was used to analyze the mechanism of GO dispersing CNTs. Results showthat GO with CNTs mass ratio of1:10does promoted the dispersion of CNTs in MnO₂,further improved its electrochemical performance, The power density of the compositeelectrode was increased227%compared with α-MnO₂.