Research On The Construction And Application Of Chemical Sulfur-fixing Binder For Lithium-sulfur Batteries

With the growing concern about environmental issues and the increasingpopularity of portable smart devices,the requirements for highly advanced energy storage systems are increasing,and lithium-ion batteries cannot longer meet the demand.Therefore,it is urgent to develop efficient and advanced energy storage systems.In terms of many advantages such as low cost,environmental friendliness,ultra-high theoretical energy density and so on,lithium-sulfur batteries（Li-Bs）have shown their great potential as a new generation of energy storage system.However,the practical application of Li-Bs is seriously hindered by the low utilization of active matters and poor Coulomb efficiency due to the shuttling of soluble polysulfides between the positive and negative electrodes during the charge and discharge cycles.In order to address the problems aboveof Li-Bs,we havetaken measures that using chemically active binder that can generate strong S-O and C-S covalent bonds by chemical reactions with polysulfidesor direct with sulfur to anchor the generated polysulfides in the sulfur electrode region,inhibit the dissolution of polysulfides,control the shuttle effect,improve the utilization of active material,enhance the cycle life and so on.The main works and results of this paper are as follows:（1）The binder 3M₉₀was prepared by a simple solid-liquid mixing process using 1,1-di-tert-butylperoxy-3,3,5-trimethylcyclohexane（3M）and silica（Si O₂as the main component）.Electrochemical tests showthat the initial discharge specific capacity of 3M₉₀is 1239 m Ah·g^-1and the sulfur utilization rate reaches 74.1%,and at the end of the 100th cycle,the capacity still maintains at 772 m Ah·g^-1with a specific capacity retention rate of 62.3%.It is demonstrated by XPS and other characterizations that the abundant oxygen-containing functional groups of 3M₉₀binder can effectively combine with polysulfide to generate S-O bonds,thus inhibiting the shuttle effect of polysulfide and enhancing the electrochemical performance.（2）Chloroprene rubber（CR）containing vulcanizable double bonds was used as a binder for Li-Bs,and the polysulfide will beanchored in the sulfur cathode region by the reaction of double bond addition and C-Cl substitution.Electrochemical tests showthat the surface capacity of the CR binder could be maintained at 4 m Ah·cm^-2after 120 cycles at a current density of 0.05C with a high sulfur loading,6.6mg·cm^-2.The ability of the CR binder to effectively bond with the polysulfide is demonstrated by XPS and other characterization methods,which is important to suppressthe shuttle effect of Li-Bs and ensure the high surface capacity.（3）To suppress the shuttle effect,the elemental sulfurswas polymerized with long-chain macromolecule Span through C-S bonding and cross-linked into a network polymer S-Span₉-MDx by adding cross-linker.Electrochemical tests for different degrees of polymerization,different degrees of cross-linking shows that the cycling performanceof S-Span₄with 25%degree of polymerization is best,the initial discharge capacity of S-Span₉-MD₂with50%degree of cross-linking reaches at1409 m Ah·g^-1,which is best,and the high sulfur utilization rate of it maintains at 84.3%.Besides,the capacity maintain at 942 m Ah·g^-1after the100th cycle,with a retention rate of 67.1%.The S-Span₉-MD₂electrode exhibits excellent electrochemical performance at both high current density and high sulfur loading,offering the possibility of constructing high energy density Li-Bs for applications.