The Study On Preparation And Performance Of Cathode Materials For Lithium-sulfur Batteries

With the advancement of social science and technology,people’s energy demand has increased,and they have paid more and more attention to environmental protection.Therefore,the research and development of reusable fresh energy has been urgent.Lithium-sulfur battery not only has extremely high energy density and theoretical capacity,but its active substance sulfur has the characteristics of cheap price,abundant reserves and resources and no pollution to the environment.It has become one of the most potential low-cost energy storage systems.However,due to certain characteristics of the active material sulfur,there are still many problems that need to be solved to commercialize lithium-sulfur batteries.The main reasons include the following:the active material sulfur and its product lithium sulfide are not conductive;the sulfur electrode is in the volume expansion during cycling destroys the electrode structure;the "shuttle effect" during charging and discharging causes capacity decay and slow reaction kinetics.Therefore,improving the conductivity of the positive electrode material,designing suitable structural materials for sulfur storage buffer volume expansion,and improving the adsorption reaction of polysulfides while catalyzing and accelerating the conversion reaction kinetics are important to make lithium-sulfur batteries commercially available.problem.The purpose of this paper is to build a three-dimensional porous carbon material,doping heteroatoms to improve the polarity of the surface of the material,etc.The purpose is to improve the conductivity of the sulfur positive electrode,buffer the volume expansion of the sulfur positive electrode,and suppress the dissolution and shuttle effect of polysulfide in the electrolyte.The main research results are as follows:PVDC with abundant reserves is used as the carbon source,melamine is used as the nitrogen source,NaOH is used as the dehalogenating agent,then PVDC dehalogenation is achieved by ball milling,and then a high-temperature calcination is used to prepare a nitrogen-doped porous carbon material.The material’s large specific surface area(～1064 m2 g-1)not only provides storage space for sulfur,but also effectively relieves volume expansion problems.The high electron cloud density of heteroatom N can significantly enhance the adsorption of polysulfides to suppress the "shuttle effect",which can effectively improve the cycle stability.Using a chemical vapor deposition method to construct a cobalt-coated nitrogen-doped carbon nanotube array on a graphene substrate,this material has a strong adsorption capacity and catalytic effect on polysulfides,which can not only effectively suppress the "shuttle effect",but also Significantly enhance the redox kinetics during the reaction.The use of this material as a positive electrode material for lithium-sulfur batteries has a very good specific capacity and cycle stability.