| With the rapid growth of economic,global fossil fuel consumption has increased significantly.At the same time,environmental conditions have also deteriorated drastically.Therefore,it is extremely urgent to develop sustainable energy sources and energy conversion devices with high efficiency.Among various energy storage devices,electrochemical supercapacitors have attracted extensive attention due to long cycle life,high power density,high specific capacity and environmental-friendly.The electrode material is a key component which determines the capacitive performances of supercapacitors.At present,many kinds of electrode materials are studied,including electrochemical double layer capacitor carbon-based materials,Faraday conductive polymers and metal oxides.However,the carbon material owns low specific capacity;the conductive polymer material is prone to volume expansion and contraction during charging and discharging process,thereby causing the structure to collapse,resulting in poor cycle stability;although the metal oxide has a high specific capacity,it has poor conductivity.In comparison with the materials mentioned above,metal sulfides have high capacity and good conductivity simultaneously,and they are expected to realize high performance supercapacitors as electrode materials.As a vital member of metal sulfides,tin sulfides(SnS2)has the advantages of high specific capacity,abundant reserves and environmental friendliness.It not only exhibits good capacitance characteristics in the electrochemical double layer,but also produces Faraday capacitance by allowing a variety of ions to diffuse into the layer due to the large layer spacing,thus playing an important role in charge energy storage.The object of this work is to achieve the controllable synthesis of SnS2 material,systematically study its growth mechanism and its potential application as a supercapacitor,and improve its electrochemical performance by doping and compounding with a conductive carbon cloth substrate.The thesis includes five chapters.The first chapter is the introduction which mainly introduces the classification,energy storage mechanism,electrode materials and their advantages,applications and challenges of supercapacitors.The structure,characteristics,advantages and research progress of SnS2 electrode materials are also discussed.The chapters from two to four are the experiments,results and discussion of this thesis,comprised of the formation mechanism of hollow spherical SnS2,the influence of morphology on the electrochemical performances of SnS2 materials and'the study on the composite materials of Mn-doped SnS2 on carbon cloth and their supercapacitor properties.The fifth chapter is the summary.The main research contents are as follows:1.SnS2 hollow spherical material was suCCessfully synthesized on the surface of F-doped SnO2(FTO)glass using SnCl2 and Na2S2O3 as reactants by a simple one-step solvothermal method.The average size of the as-prepared SnS2 hollow spheres is about 2 ?m and the thickness of the shell is only 300 nm.ACCording to the evolution of morphology with reaction time,a growth mechanism of the template-free hollow sphere is proposed.The difference in surface energy between SnS2 and FTO substrate might be responsible for the formation of hollow spheres.2.SnS2 materials with three kinds of morphologies were prepared by SnCl2,Na2S2O3·5H2O and sulfur as reactants using simple solvothermal method.The different morphologies were realized by adjusting the molar ratio of reactants,and the effects of morphologies on the electrochemical properties of SnS2 were also investigated.When the molar ratios of the three reactants were 1:5:1,1:5:3 and 1:5:5,respectively,the products were in the form of ball-flower-like,flower-like and wrinkle-like morphologies,respectively.The results of the three-electrode electrochemical test exhibited that although the spherical sample had a higher specific capacity of 158 F g-1,its rate performance was poor.The SnS2 sample with wrinkle-like morphology showed the best capacitive performance,and the mass specific capacitances were 115,98,92,85,73 and 62 F g-1 at current densities of 0.2,0.5,1,2,5,and 10 A g-1,respectively.This may be on aCCount of the special wrinkle-like morphology of the SnS2 sample with a larger specific surface area,which provides more active sites for its reaction with electrolyte ions.Nevertheless,compared to other metal sulfides,the prepared-SnS2 material has a lower specific capacity and cannot meet the requirements of electrode materials in high-performance supercapacitors.3.In order to increase the specific capacitance of the SnS2 material,Mn-doped SnS2 nanosheets were grown on a carbon cloth to form a composite by a facile solvothermal method.Firstly,the optimal Mn doping ratio was explored without introducing carbon cloth.The results demonstrated that when the doping ratio of Mn was 0.1,the obtained Sn0.9Mn0.1S2 sample exhibited a specific capacitance of 464 F g-1 at a current density of 0.2 A g-1,which was superior to other doping ratio samples,and it was about three times that of the un-doped sample SnS2(158 F g-1).The elemental valance state and microstructure of the Sn0.9Mn0.1S2 sample were further analyzed by XPS and TEM;the results demonstrated that the valance state and the existing form of Mn element are+2 and MnS,respectively.Subsequently,the CC-Sn0.9Mn0.1S2 sample was suCCessfully prepared on the carbon cloth with the optimal Mn doping ratio.The electrochemical tests of CC-Sn0.9Mn0.1S2 were carried out in a three electrode system and the CC-Sn0.9Mn0.1S2 sample possessed a specific capacitance of 511 F cm-2 at a current density of 1 A cm-2,which showed a great improvement compared with the un-doped CC-SnS2 sample(428 F cm-2).The enhancement in capacitance performance could be attributed to the synergistic effect of uniformly distributed MnS and SnS2,which enabled the CC-Sn0.9Mn0.1S2 sample to have multiple oxidation states and rich redox reactions. |
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