Construction Of Highly Stable Lithium Metal Anodes For Lithium-sulfur Batteries Based On Organic Polysulfide Polymers With Different Sulfur Chain Lengths And Sulfur Contents

Due to the advantages of low redox potential（-3.040 V,relative to standard hydrogen electrodes）and high theoretical specific capacity(3860mAh g^-1),metallic lithium is considered to be a very promising anode material.However,when used as the anode of lithium-sulfur batteries,its dendrite growth and lithium corrosion problems during cycling seriously hinder the practical application of lithium-sulfur batteries.In this paper,a series of organic polysulfide compounds with different sulfur chain lengths and sulfur contents were designed,and a stable SEI film was constructed on the surface of the metal lithium anode by using electrolyte additives and artificially constructing a solid-state electrolyte interface film（SEI film）.Effects of sulfur chain length and sulfur content in organic polysulfide compounds on the stability of SEI films.The specific research contents are as follows:（1）Using bis-3-（triethoxysilyl）propyl-disulfide（Si-O-2S）and bis-3-（triethoxysilyl）propyl-tetrasulfide（Si-O-4S）These two organic polysulfur compounds with different sulfur chain lengths were used as electrolyte additives to construct an SEI film on the surface of the lithium anode in situ.It shows better SEI film stability when it is used as an electrolyte additive.Through a series of electrochemical performance and characterization tests,it is found that Si-O-4S as an electrolyte additive can be grafted on the surface of lithium metal by the bridging effect of Si-O bonds.When under electrochemical cycling,it is converted into an organic-inorganic hybrid SEI film,which in turn protects the lithium anode.The organic polysulfides act as"plasticizers"in the inorganic phase,making the SEI film more flexible and stable.Thus,the electrochemical performance of lithium-sulfur batteries can be improved.（2）The sulfides with different sulfur chains were incorporated into amino-terminated polydimethylsiloxane（PDMS）,and three organopolysulfur compounds with different sulfur chain lengths were designed and prepared,which were then coated on the surface of lithium metal respectively.A layer of artificial SEI film was constructed.The study further confirmed that the artificial SEI film constructed by DS-PDMS with long sulfur chain has better cycle stability.Through a series of electrochemical performance and characterization tests,it was found that DS-PDMS can promote lithium metal anode.A stable organic-inorganic hybrid SEI film is generated,which contains various components,such as organic polysulfides,inorganic Li_xSiO_y,Li_xSiS_y,etc.Due to this stable SEI film,uniform deposition of lithium and stable cycling of lithium-sulfur batteries can be achieved.（3）An artificial SEI film was constructed on the surface of lithium anode by in-situ crosslinking of lithium polythiophosphate（LPSP）and chlorine-terminated polydimethylsiloxane（Cl-PDMS-Cl）with different sulfur contents.When the lithium anode is modified with PDMS-LPSP-5with a sulfur content of 9.6%,the SEI film on the surface of the lithium anode has the best performance.The Li-Li symmetrical battery has a current density of 1 mA cm^-2 and an areal specific capacity of 1 mAh cm^-2.The cycle life under condition 2 reaches 400 hours,and the lithium-sulfur battery has a discharge specific capacity of 785.8 mAh g^-1 after 200 cycles at 0.5 C,a capacity retention rate of 85%,and a Coulombic efficiency（CE）of about 99%.