The Preparation Of Layer-by-layer Self-assembled Composite Fiber Membrane And The Performance Of Lithium-sulfur Battery

With the rapid development of electric vehicles,energy storage power supplies,portable electronic products and other fields,the performance of existing secondary batteries is slightly insufficient.The lithium-sulfur battery has a high theoretical energy density?2600 Wh/kg?,which is about 3-5 times that of the current lithium-ion battery,which is the mainstream of the development of high-energy density chemical power in the future.However,lithium-sulfur batteries still face huge challenges.Safety issues caused by the insulation of elemental sulfur and its final discharge products,short cycle life of the battery,and poor stability of the lithium anode are urgent issues to be resolved.For lithium-sulfur batteries,traditional polyolefin separator materials not only have the problems of low safety,poor affinity for electrolytes,and low heat shrinkage deformation temperature?about 110??,but their dual-ion conduction characteristics make the polysulfide ions generated by the reaction The ability to repeatedly pass through the diaphragm,creating a"shuttle effect".In this paper,sulfonated polyether ether ketone?SPEEK?with excellent heat resistance is selected as a functional polymer,and its characteristic functional group-SO₃H is used to achieve the"pass-through"behavior of polysulfide ions.First,a PAN/SPEEK composite fiber membrane was prepared by an electrostatic spinning method.Secondly,a method of combining layers by layers to build dense functional layers?CS/MWNTs-COOH?_nwith different numbers of assembly layers?5,10,15 layers?on the surface of the base film.The experimental results show that compared with the traditional PP separator,the assembled membrane?PEC?has better thermal stability and electrolyte wettability.At a rate of 0.1 C,the capacity retention rate of 10 layers of assembled membrane?PEC?₁₀after 100 cycles is 48.4%;the capacity retention rates of 5 layers?PEC?₅and15 layers?PEC?₁₅are 47.4%and 44.7%respectively,Are higher than the capacity retention rate of PP separator.This may be because the carboxylic acid group and the sulfonic acid group achieve the selective permeability of Li⁺,which prevents the passage of Sn^2-,thereby slowing the"shuttle effect"of lithium-sulfur batteries and improving the cycle life and safety performance of lithium-sulfur batteries.Compared with-COOH,-SO₃H has higher ion selectivity.In order to further improve the cycle stability of lithium-sulfur batteries,poly?4-styrenesulfonic acid?sodium?PSS?was selected as the assembly layer,and the sulfonic acid group was also introduced into the dense layer using the layer-by-layer self-assembly technology.Electrochemical tests showed that the capacity retention rates of assembled films using aminoated carbon nanotubes and sodium poly?4-styrenesulfonate?as the assembly layer after 100 cycles at a rate of 0.1 C were 70.32%,71.48%and 68.1%,both higher than the capacity retention rate of PP?61.33%?,further alleviating the shuttle effect of lithium-sulfur batteries.