Research On Modified Sulfur Cathode And Separator For Lithium Sulfur Battery

As a new kind of energy storage system,lithium sulfur battery have attracted considerable attention owing to its theoretical energy density of 2600 Wh/kg.Moreover,the sulfur is environmentally friendly,low cost and abundant.Compared with traditional lithium ion batteries,lithium sulfur battery possesses more advantages.The lithium sulfur battery is still at the laboratory research sta ge,large-scale industrial production faces with a series of problems such as low specific capacity and short cycle life.Researchers analysed the construction and operational principle of lithium sulfur battery,finding these problems are mainly related to insulation of sulfur and solubility of active materials.Particularly,the dissolution of intermediates polysulfide ions in liquid electrolytes,which triggers a shuttling effect.In order to solve the crucial problems,this paper carried out research on the modified sulfur cathode and separator.N ickel coated multiwalled carbon nanotubes?N i-MWNTs?were used as the host material of sulfur.The electrochemical properties of titanium nitride?TiN?/sulfur composite cathode were studied.Modified membrane was prepared by coating Ti₄O₇ powder on the surface of commercial membrane.The main research contents are displayed as follows:The N i-MWNTs/S composite was prepared by melt impregnation method.MWNTs interact with each other to form a three-dimensional conductive network,which has hollow structure can adsorb polysulfide and accommodate the volume change of activities.The nickel particles on the surface of of MWNTs are favorable for reducing the electron transport distance and have a catalytic effect on the sulfur redox reaction,facilitating the conversion of long-chain polysulfides to lithium sulfide.TiN powder was prepared via carbothermal reduction and nitridation method.A sulfur-amine chemistry-based method has been developed to prepare TiN /sulfur composite cathode.TiN possess high conductivity and also can trap polysulfides via a chemical interaction,reduce the shuttling effect during the discharge/charge process.Through CV and EIS analyses,TiN can reduce the charge transfer resistance and promote the electrochemical reaction.TiN/sulfur composite exhibits high reversible capacity of 602 mAh/g at 1 C after 200 cycles.Ti₄O₇ powder was prepared by carbothermal reduction of rutile TiO 2.The Ti₄O₇ slurry was coated on one side of Celgard 2400,the thickness of the coating is 5 ?m.Ti₄O₇ coated separator could act as the upper current collector and physical barrier which can improve the utilization of sulfur and inhibit the diffusion of polysulfides to lithium anode.Compared with the battery using a conventional separator,the battery with Ti₄O₇ modified separator achieved excellent cycling performance and rate capability.The capacity of this cell retains as high as 565 mAh/g after 600 cycles at 1 C.Even at a 5 C rate,the average reversible capacity is 367 mAh/g.