Study On The Doping Modification And Electrochemical Performance Of Hollow Manganese Dioxide Microsphere Electrode Materials

Manganese dioxide?MnO₂?electrode materials have been recognized as the most potential electrode material for supercapacitors.MnO₂ has attracted more and more attention on account of its extra resources,low prices,high theoretical and non-toxic nature.However,in the practical application,the specific capacitance of MnO₂ far less than its theoretical value.The poor conductivity(10^-5-10^-6 S/cm)and low mechanical stability have greatly restricts its practical electrochemical performance.So,in this paper,we take the?-MnO₂ and?-MnO₂ as the research object,and then enhance the electrochemical properties of MnO₂ with the method of metallic ions(Sn⁴⁺)doping.The purpose of ions doping is to introduce more electrochemical active sites,optimize the transmission route for electrons and ions,improve the conductivity,and enhance the structure strength and stability.For a further research,the effect of rare earth element doping on MnO₂ has been explored and analyzed.In the paper,we prepared the precursor of MnO₂@MnCO₃ microspheres by the chemical precipitating process and redox process at the room temperature.And then,?-MnO₂ and?-MnO₂ hollow microspheres have been prepared by the hydrochloric acid and heat treatment,respectively.The specific capacitance of the?-MnO₂ electrode is 65.4 F/g,and the retention ratio is 67.7%.The?-MnO₂ is 101.2 F/g and 83.2%,respectively.In the first part,Sn⁴⁺have been doped into the?-MnO₂ with the ion form.After doping,the size of?-MnO₂ microsphere decreased from 5?m to 2?m.Also,the surface morphologies of?-MnO₂ have been changed a lot,and been made up of many triangular edges and corners that are also made up of many interconnected nanosheets.The optimized doping ratio?1 at.%?has been selected for the following electrochemical tests after comparing the different doping contents.The specific capacitance of Sn?1 at.%?/?-MnO₂ electrode is the 125.6 F/g?1 A/g?,which increases 92%,and the value can reach to 258.2 F/g at 0.1 A/g.Also,the retention ratio of specific capacitance still remains 93.7%after 1000 cycles,which increases26%.Furthermore,the electrochemical performances at the different temperature and voltage windows have been tested.The result shows that the specific capacitance increased with the temperature improving and voltage windows increasing.At the high temperature and large voltage window,the electrochemical properties of Sn?1at.%?/?-MnO₂ electrode also perform well.The specific capacitance is 161.9 F/g at the high temperature of 85?,and retention ratio is 90.5%.At the large voltage window from-0.2 to 1.2 V,the capacitance and the retention ratio is 130.2 F/g and86.2%,respectively.In the second part,we introduced the Sn⁴⁺into the?-MnO₂ electrode.After doping,the microsphere size of?-MnO₂ decreased to less than 1?m from 1.5?m.The morphologies of the?-MnO₂ microspheres have changed slightly,and the specific surface area of the hollow microsphere increased from 76.6 m²/g to 115.1 m²/g.The electrochemical result shows that the specific capacitance of Sn/?-MnO₂ electrode is122.0 F/g at 1 A/g,which is improved by 21%.And the retention ratio of capacitance is 93.2%,which increased 9%,after 1000 cycles.In the final,we introduced the rare earth element of Er into the?-MnO₂ electrode by the same way.After doping,the morphologies of?-MnO₂ have changed,and a lot of nanoparticles emerged around the microsphere.Also,the specific surface area increased to 121.4 m²/g.The electrochemical result shows that the doping of Er has significant influence on the electrochemical performance of?-MnO₂ electrode.At the current density of 1 A/g,the capacitance of the Er/?-MnO₂ electrode is 153.4 F/g,which is increased by 52%.And after 1000 cycles,the capacitance still remains 93.2%,which improves 10%.