Preparation And Electrochemical Performance Of Polypyrrole Coated Sulfur-carbon Composites

Lithium-sulfur battery is a new type of secondary battery,which has a high energy density of 2600 Wh/kg,and the lithium-sulfur battery has a long cycle life,but its active substance sulfur has poor conductivity and volume during circulation.Disadvantages such as expansion and shuttle effect of intermediate products make lithium-sulfur batteries greatly limited in practical applications.For the deficiency of lithium-sulfur battery,the sugar carbon aerogel was prepared by reversed-phase emulsification method and combined with sulfur to make it a carbon substrate material for the positive electrode of lithium-sulfur battery.Secondly,multi-walled carbon nanotubes are doped in a sugar carbon aerogel,and an oxygen-containing group such as a carbonyl group is introduced by high-temperature carbonization to generate a polar adsorption effect on the polysulfide of the lithium-sulfur battery.Finally,the carbon aerogel is doped with graphene oxide,and the rich oxygen-containing functional groups on the surface are used to enhance the adsorption of polysulfide.The main research contents of the thesis are mainly divided into the following three parts:(1)The rotational speeds of 1 kr/min(CA-1),4 kr/min(CA-2),7 kr/min(CA-3)and 10 kr/min(CA-)were prepared by inverse emulsification.4)Four sets of sugar carbon aerogel materials,which are combined with sulfur by hydrothermal method to obtain CAS composite materials.Then assembled the battery to explore the effect of different speeds on the electrochemical performance of lithium-sulfur batteries.At a rate of 0.5 C discharge,CAS-1 was unable to discharge.CAS-2,CAS-3,and CAS-4 have stable discharge curves,and the retention rates of capacity after 100 cycles are 68.53%,63.67%,and 53.42%,respectively.By comparison,CAS-2 has the best electrochemical performance.(2)In view of the problem that polysulfide is easily soluble in electrolyte in lithium-sulfur batteries,the oxygen-containing functional groups generated on the surface of MWCNTs after high-temperature oxidation have strong adsorption characteristics to polysulfides,and carbon is prepared by reverse phase emulsification method.Three sets of multi-walled carbon nanotubes/carbon aerogel composites with nanotube doping amounts of 5%(CAM-1),10%(CAM-2),and 20%(CAM-3),respectively.The capacity retention rates were 87.00%,77.28%,and 73.88% at 0.5 C,respectively.When the doping amount of MWCNTs was 5%,it had relatively good electrochemical performance.(3)In order to alleviate the shuttle effect of lithium-sulfur batteries,we used the inverse oxygenation of the oxygen-containing functional groups on the surface of graphene oxide to prepare the graphene oxide doping amount of 5%(CAG-1),10%(CAG-2)and 20%(CAG-3)graphene oxide/carbon aerogel composites.The results showed that the capacity retention rates of CAGS-1,CAGS-2 and CAGS-3 were 100%,82.04% and 76.66% after 100 cycles at 0.5 C,respectively.When the doping amount of GO was 5%,it has a superior capacity retention rate.