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Electrochemical Cycling Stability Of Doped Manganese Dioxide

Posted on:2019-11-21Degree:MasterType:Thesis
Country:ChinaCandidate:S G HuangFull Text:PDF
GTID:2392330602456649Subject:Materials engineering
Abstract/Summary:PDF Full Text Request
Supercapacitor with high specific capacity,high power density,long cycle life,environment-friendly and many other features,it is the focus of green energy development.While the electrode material is the main factor that affects the electrochemical performance of the supercapacitor.Among the many electrode materials,manganese dioxide?MnO2?is a perfect electrode material for supercapacitors with high theoretical specific capacity?1370 F/g?,abundant raw materials,low price and various crystal types.However,the semiconductor properties leading to its poor conductivity and cyclic stability,limiting its practical application.Studies have shown that the modification of MnO2 by doping metal ions is conducive to improving its conductivity,thereby increasing its electrochemical properties.The purpose of this paper is to improve the electrochemical performance of MnO2 by different doping of metal-ions,and to reveal the factors that influence its cycling stability through the observation of its morphological evolution during cycling,and further reveal its charge-discharge mechanism by in-situ NMR.The specific research results are as follows:?1?Al-doped MnO2?Al-MO?and pure MnO2?MO?samples were prepared by chemical deposition method.Their crystal forms,morphologies and elemental compositions were also analyzed,the results show that Al elements have been successfully doped into the MnO2 nanoparticles lattice.Compared with the electrochemical performance of the two electrodes,the specific capacity of the Al-MO electrode at the current density of 1 A/g was 264.6 F/g,which was higher than that of the MO electrode?180.6 F/g?.Moreover,the Al-MO electrode has excellent cycle stability at room temperature and high temperature?50°C?at a current density of 10 A/g,the capacitance retention was 100%after 10,000 cycles at both situation.?2?Through the analysis of microstructure of Al-MO electrode during cycles,it is found that Al-MO electrode has the same variation rule at high temperature and room temperature,which is the important reason of its high temperature cycling stability.The structure stability of Al-MO and MO electrodes during charge-discharge was investigated by In-situ NMR technique.It was found that the structure of Al-MO was stable.Combined with the observation of morphology during cycling,we found that the morphology of Al-MO electrode may follow?pulverization-reassembling?process,which is important for studying the charge-discharge mechanism of MnO2electrode material and improving its cycle stability.?3?Sn-doped MnO2?Sn-MnO2?samples were prepared by hydrothermal method.Compared with pure MnO2,Sn-MnO2 showed a new structure:nanorods,indicating that Sn doping has an influence on the morphology of MnO2.The electrochemical properties of Sn-MnO2 and MnO2 electrode materials were analyzed.The specific capacity of Sn-MnO2 electrode was 243.6 F/g at current density of 1 A/g,while MnO2electrode was only 148.6 F/g.At a current density of 10 A/g,the capacitance retention was 95%after 10000 cycles.It was further found that electrode shedding and morphological evolution during Sn-MnO2 electrode cycling were the main reasons for the decay of capacitance,this finding has played a role in guiding the improvement of cycling stability of doped manganese dioxide electrode materials.
Keywords/Search Tags:Supercapacitor, MnO2, Al-MO, in-situ NMR, Sn-MnO2
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