Preparation Of Porous Material/Sulfur Composites As Cathode Material For Lithium Sulfur Battery And Their Electrochemical Performance

To maintain the sustainable development of the human society,it plays a key role for the clean energy and renewable energy to replace the the traditional fossil energy.As a clean energy,lithium-sulfur batteries have high theoretical specific capacity?1675 mAh/g?and high energy density?2600wh/kg?.Therefore,recently much attention has been paid on the research of lithium-sulfur batteries worldwide.At present,there are two problems to obstacle the application of lithium-sulfur batteries.The first one is that S and Li₂S are difficult to be used as the cathode material due to their insulation property;the second is that polysulfide could be dissolved in electrolyte,resulting in“shuttling effect”.To solve the above problems,various porous material/S composites were studied in this thesis.Firstly,we selected the porous foam nickel for research.Nickel,sulfur and carbon are merged into three-element composite materials plate by tableting.Secondly,we selected cotton as carbon source,and prepared the porous biomass carbon fiber materials by one-step.In this paper,Raman,XRD,BET,SEM and TEM were used to test the materials.The research work of this paper mainly includes the following aspects:?1?Using porous foam nickel as the metal framework,a three element electrode?nickel,sulfur and carbon?was prepared by dissolution,tableting and coating.The results show that when the content of sulfur is 0.42mg/cm²,the initial discharge specific capacity is 1415 mAh/g at 1 C,the discharge specific capacity still hold 800 mAh/g ever after 100 cycles,and the discharge/charge performance remains stable.?2?Using cotton as the source of carbon and potassium hydroxide solution as the pore forming agent,the porous biomass carbon fiber was prepared in a vacuum tube furnace.The result shows the BET surface area of the porous biomass carbon fiber was 1696 m²/g and its pore volume is 0.84cm³/g when the mass ratio of cotton and potassium hydroxide is 1:2 and the carbonization temperature is 850?C.Under 50%percentage of sulfur in the composite and at 0.1 C ratio,the initial discharge capacity is 1237 mAh/g.After 200 cycles,the discharge capacity maintains 813 mAh/g,and the coulomb efficiency reaches 90%.The electrochemical performance was much better than pure sulfur cathode in lithium sulfur battery.?3?Asphalt based porous carbon material was prepared.There exist mesoporous and macroporous in asphalt based porous carbon and it has huge specific surface,strong adsorption and three-dimensional porous structure with highly ordered channel.Under 50%sulfur in the composite and at 0.1 C ratio,the initial discharge capacity is 1096 mAh/g,and the discharge capacity is 612 mAh/g after 60 cycles.