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Preparation,modification And Electrochemical Performance Of Carbon/Sulfur Composite Cathode Materials For Li-S Batteries

Posted on:2018-09-05Degree:MasterType:Thesis
Country:ChinaCandidate:S Y CaiFull Text:PDF
GTID:2321330518981808Subject:Chemistry
Abstract/Summary:PDF Full Text Request
Accompanying with the development of materials science,especially the flourishing research of nanomaterial science and nanomaterial technology,porous carbon materials have not only received extensive attention from the researchers all over the world,but also acted as a crucial role in the areas of energy storage.Porous carbon materials possess many advantages,such as: the large specific surface area;the large pore volume;the stable chemical property;the excellent electrical conductivity.Therefore,that using porous carbon materials as both conductive framework and host material embedded in sulfur to synthesize porous carbon/sulfur composite is a desirable method to reduce the shuttle effect for lithium-sulfur battery(Li-S)and improve the electrical conductivity of composite.In this research paper,the researches of porous carbon/sulfur composites can be divided into three parts.At the first part,a kind of MOFs-derived mesoporous carbon polyhedron/sulfur composites(MCP-950/S)are deliberately designed and synthesized,which is to analyze the optimization of carbonization temperature and the effect of mesoporous structure for Li-S battery.At the second part,in order to further increase the carbon porosity,based on the MCP-950 carbon material,a novel activated mesoporous carbon polyhedron/sulfur composites(AMCP-950/S)are prepared by KOH activation reaction and sulfur permeation process,which is to analyze the physical absorption effect of abundant micropores structure for Li-S battery.At the the third part,in order to further enhance the polarity of carbon materials,the nitrogen is introduced into carbon as polar functional group,a kind of nitrogen-doped activated microporous carbon sphere/sulfur composites(NAMCS/S)are designed and prepared via a controllable solvothermal method and a liquid phase in-situ sulfur deposition technology,which is to analyze chemical absorption effect of nitrogen functional group for Li-S battery.The main works in this paper is as follows:(1)The MOF-5(Zn4O(BDC)3)as porous carbon precursor are carbonized at three different temperature,three kind of mesoporous carbon polyhedron/sulfur composites are synthesised via the in-situ liquid phase reaction and high-temperature gas-phase reaction.The results show that the MCP-950 possess abundant mesoporous structure,as high as 1464.47 m2 g-1 surface areas,the most suitable average aperture of 5.4497 nm.The sulfur content in MCP-950/S composites is 77.3 wt%,the MCP-950/S composites show an initial capacity of 1196.7 mAh g-1,which still possess 763.9 mAh g-1 after 50 cycles at 0.2 C.These significant performance improvements of Li-S battery can be attributed to that the abundant mesoporous structure provide more polysulfides storehouse,and restrain polysulfide dissolved in the electrolyte.(2)In order to further increase the carbon porosity and research the physical absorption effect of abundant micropores structure for Li-S battery.A novel activated mesoporous carbon polyhedron/sulfur composites(AMCP-950/S)are prepared by KOH activation reaction and sulfur permeation process.The AMCP-950 possess abundant microporous and mesoporous structure,as high as 2211.12 m2 g-1 specific surface areas and 2.62 cm3 g-1 pore volume.The huge surface area can promote electrolyte penetration and ion diffusion.The abundant microporous structure can provide strong physical adsorption,which can effectively reduce the loss of the active material.The abundant mesoporous structure as polysulfides storehouse can provide sufficient sulfur content to improve the specific capacity of composites.The AMCP-950/S composites show 79.0 wt% sulfur content,high initial capacity of 1274.0 mAh g-1and discharge capacity of 1040.9 mAh g-1 after 50 cycles at 0.2 C,with capacity retention of 81.7% and over 95% Coulombic efficiency.(3)In order to further enhance the polarity of carbon materials,the nitrogen is introduced into carbon as polar functional group.The results show that the activated microporous carbon spheres with high adsorption capacity and good conductivity are successfully prepared and used as the excellent cathode host material for Li-S battery.Introduction of the nitrogen as polar functional group in the activated microporous carbon spheres can enhance the chemical interaction,immobilize active material,and restrain diffusion of soluble polysulfides.Combining with the advantage of microporous materials,the nitrogen-doped microporous carbon material can effectively promote the ion diffusion and electron transfer.Particularly,the NAMCS/S composites with sulfur loading of 64.42 wt% exhibit a high initial capacity of 1004.0 mAh g-1 and an excellent cycling ability of 794.4 mAh g-1 after 100 cycles at 0.1 C,a good capacity retention of 79.1% and a remarkably high Coulombic efficiency of over 95%.
Keywords/Search Tags:Lithium-Sulfur Battery, Carbon/Sulfur Composite, KOH Activation, Metal Organic Frameworks, Nitrogen Doping
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