The Preparation And The Supercapacitive Properties Study Of Manganese Dioxide And Its Composites

Supercapacitors have been widely researched by researchers because of their advantages of long cycle life,high power discharge,fast charge and discharge.According to the energy storage mechanism,the supercapacitor electrode material can be divided into an electrode material of an electric double layer capacitor electrode and a pseudocapacitor electrode.Pseudocapacitive capacitor electrode material has been studied for its energy density,maximum voltage and so on.In the pseudocapacitor electrode material,metal oxides are often studied,such as RuO₂,MnO₂,Co₃O₄ and so on.Due to its wide range of sources,low cost and simple synthesis,MnO2 is regarded as the ideal electrode material for supercapacitors.However,due to its poor conductivity,easy to reunion,poor circulation and other shortcomings restricting the development of its application to MnO₂,therefore,modification of MnO₂ or composite supercapacitors materials has been a keen direction of researchers.In this thesis,MnO2 was prepared by liquid-phase precipitation method using KMnO4and dilute HCl as reactants,and the effect of reaction temperature and time on the morphology and supercapacitance was investigated to obtain an optimum reaction parameter.The MnO2 was composited with Fe2O3 and SnO2 respectively,and the supercapacitive properties of the composites were investigated,then the composites were assembled into supercapacitors to test the practical application of the MnO₂ composites.?1?The KMnO₄ and the dilute HCl were used as reactants,the pure MnO₂ was prepared by liquid-phase precipitation method.The temperature of the water bath and the stirring time of the water bath were controlled respectively as variables.By the testing,it was found that when the water bath temperature is 60?,water bath mixing time of 1 h prepared MnO₂material has the best supercapacitive performance in 1 mol·L^-1 Na₂SO₄ electrolyte solution charge and discharge test,when the current density of 0.2 A·g^-1,the specific capacitance up to224 F·g^-1.?2?Respectively compound the MnO₂ and Fe₂O₃ by chemical compound method and physical grinding method,and controlling the mass fraction of Fe2O3 in MnO2 to prepare a plurality of MnO2@Fe2O3 composite materials.By the morphology test and electrochemical test,it is found that the composite MnO₂@Fe₂O₃?10%-1?prepared by chemical compound method,that is,the prepared Fe₂O₃ material in the synthesis of MnO₂,and the content of Fe₂O₃ accounted for 10%,has the best morphology and supercapacitive properties.The MnO₂ particles agglomeration has been effectively improved,the material has greatly improved the circulatory performance and conductivity.The composite has a specific capacitance up to 232 F·g^-1 at a current density of 0.2 A·g^-1.After 1000 cycles,the specific capacitance retention rate was as high as 91%,which was 11%higher than the 80%retention of pure MnO₂.?3?In order to improve the specific capacitance and cycling performance of MnO₂materials,the SnO₂ materials are used to effectively combine the two.The effects of the composite method and the mass fraction of SnO₂ on MnO₂ on the morphology and the supercapacitor properties of the composites were investigated.The results show that when the SnO₂ and MnO₂ co-grow in the same reaction system and the content of SnO₂ in MnO₂ is0.5%,the prepared MnO₂@SnO₂?0.5%-2?composite has the best morphology and supercapacitance.MnO₂ dispersions have been effectively improved,and the specific capacitance and the cycle performance have been greatly improved.The specific capacitance of the electrolyte is up to 250 F·g^-1 at a current density of 0.2 A·g^-1 in 1 mol·L^-1 Na₂SO₄electrolyte.When the current density was increased to 3 A·g^-1,the specific capacitance was maintained at 207 F·g^-1,while pure MnO₂ had a specific capacitance of only 157 F·g^-1 at this current density.The composite also has excellent cycle performance,after cycling 1000 times,the specific capacitance of it up to 94.3%.?4?Assemble symmetric supercapacitors using MnO₂@SnO₂?0.5%-2?as the electrode active material and 1 mol·L^-1 Na₂SO₄ as the electrolyte solution,to verify the practical application of MnO₂@SnO₂?0.5%-2?in supercapacitors.The power density of the capacitor is 0.08kW·kg^-1,the corresponding energy density is 7.27 Wh·kg^-1 and the supercapacitor has a good multiplying ratio.Therefore,MnO₂@SnO₂?0.5%-2?composite material in the practical application of supercapacitors is more ideal.