Research On The Preparation And Electrochemical Properties Of Hollow Sn-doped MnO₂Microsphere For Supercapacitor

Rescently, energy crisis goes worse and worse and fossil fuel is harmful toenvironment. So the society needs new energy resources urgently. Then thesupercapacitor that has big capacitance, high charge and discharge rate and long cyclelife become a hot area of research. Among all the supercapacitorelectrode materials,MnO₂is the most promising one because the energy density of MnO₂is high and it islow cost and environmentally friendly. Thus, this subject choses MnO₂as the researchobject. Sn is doped into MnO₂to improve the electrical conductivityand and MnO₂isprepared to be hollow to increase the specific area. At the same time, the surface ofMnO₂is prepared to be porousto make it be beneficial for the diffusion of electrolyte.Firstly, Sn-MnCO₃/SiO₂shell-core material was prepared via hydration method.Then the precursor was calcined to get porous Sn-MnO₂/SiO₂shell-core material.Finally the SiO₂was etched by NaOH solution and hollow Sn-doped MnO₂wasprepared. During the calcine process, CO₂appeared with the decomposition ofMnCO₃. The CO₂could make the surface of MnO₂porous. The holes made it easy forNaOH to etch SiO₂. And the holes made it easy for the electrolyte to contact MnO₂during electrochemical reaction.Preparation conditions such as the amount of SiO₂, the amount of C₂H₆O₂,reaction temperature, the pH of the reaction solution, calcination temperature, etchperiod, the doping amount of Sn were confirmed by single factor experiment viaconstant current charge-discharge test. And the test results were:SiO₂:MnSO₄=2:4（mol:mol）, C₂H₆O₂:H2O=2:8（ml:ml）, the reaction temperature was30℃, the pH of reaction solution was8, calcination temperature was450℃, the etchperiod was120min, the doping amount of Sn was3mol%（vs. MnSO₄）. TheSn/H-MnO₂electrode under the best preparation conditions got a specific capacity of243F/g while the specific capacity of Pure-MnO₂electrode was only131F/g. Thespecific capacityobservably increased by85.5%. The BET results implied that thespecific area of MnO₂increased from145m2/g to256m2/g. The FT-IR resultsindicated that Sn was successfully doped into MnO₂.Then Pure-MnO₂electrode and Sn/H-MnO₂electrode were characterized cyclicvoltammetry and electrochemical impedance spectroscopy. The CV curves indicatedthat the Sn/H-MnO₂electrode owned better reversibility and maintained goodcapacitance characteristics under high scan rate. And the electrochemical impedancespectroscopy showed that the resistance of charge transfer and electrolyte transfer was much smaller than that of Pure-MnO₂electrode. All those results proved that theSn-doping and hollow structure could improve the electrochemical performance ofMnO₂significantly.In addition, the Sn/H-MnO₂electrode was tested in acid electrolyte, neutralelectrolyte and alkaline electrolyte. The results implied that neutral electrolyte thatcontained SO₄^2-was suitable for MnO₂-based supercapacitor.