The Preparation And Electrochemical Performance Of MnO₂-Based Powder For Supercapacitors

In this dissertation,different kinds of manganese oxide-based electrode materials for supercapacitor were prepared by chemical co-precipitation method:modified by doping iron;different reaction methods were used to prepare electrode materials;multi-walled carbon nanotubes?MWCNTs?were added to synthesize MWCNTs-MnO₂ composite electrode materials.The electrode materials were characterized by X-ray diffractometer,nitrogen adsorption-desorption tester,field emission scanning electron microscopy?FESEM?and transmission electron microscopy?TEM?;and the tests of electrochemical performance of electrode materials were conducted.The results showed that:The manganese oxide prepared by the chemical co-precipitation method was poorly crystalline birnessite-type manganese dioxide.The diameter of manganese oxide particles after doping with iron element decreased slightly and the overall morphology changed little.The pure manganese oxide powder prepared by the direct mixing method was composed of smooth spherical particles,while the pure manganese oxide powder prepared by slow dropping method was composed of superficially embroidered spherical particles.The diameter of MWCNTs in the MWCNTs-MnO₂ composite electrode materials was about 50 nm,the multi-walled carbon nanotubes with different lengths and shapes could be uniformly dispersed.With the increasing of iron element,the BET specific surface area of the manganese oxide-based electrode material increased first and then decreased,and the content of 1¹0nm size pores also increased first and then decreased;when iron element was increased to 6 at%of potassium permanganate,the BET specific surface area and the content of 1¹0nm size pores of the manganese oxide-based electrode material reached the maximum at the same time.With the increasing of iron element,the mass specific capacitances of iron-doped manganese oxide-based electrodes measured at 0.2 A/g current density were 144.6 F/g,147.6 F/g,165.3 F/g,and 153.7F/g,respectively.The mass specific capacitances showed the regularity of increasing first and then decreasing,which was consistent with the regularity of the specific surface area.The specific capacitance of the iron-doped manganese oxide electrode material gradually increased with the increasing of the specific surface area and the content of 1¹0nm size pores.The specific capacitance of the MWCNTs-MnO₂ composites prepared by the direct mixing method under the same test conditions was higher than the slow dropping method.The arc radius of Nyquist curve of MWCNTs-MnO₂ composite electrode in the high-frequency region was smaller than pure manganese oxide electrode,which means that the charge transfer resistance reduced after the composite with multi-walled carbon nanotubes;and the arc radius decreased obviously when the more amount of multi-wall carbon nanotubes in the composite materials.With the increasing of the content of manganese oxide,the specific capacitances of MWCNTs-MnO₂ composite electrodes were 111.5 F/g,145.6 F/g,161.1 F/g,167.0 F/g and 144.6F/g?current density of 0.2 A/g?,respectively.The results of galvanostatic charge-discharge tests at different current densities and cyclic voltammetry tests showed that the specific capacitance of MWCNTs-MnO₂ composites increased first and then decreased;when the content of added manganese compound was 66.7 at%,the specific capacitance of MWCNTs-MnO₂ composites reached the highest value.