A First-Principles Study Of Anchoring And Catalysis Performance Of Two-Dimensional Heterostructure Materials In Lithium-Sulfur Batteries

With the development of modern portable electronic equipment,electric vehicles,aerospace and large-scale energy storage systems,people’s demand for electrochemical energy storage has gradually increased.Traditional lithium-ion batteries are currently unable to meet the demand for high energy density due to the theoretical capacity of electrode materials.Therefore,as a new generation of high energy density rechargeable batteries,lithium-sulfur batteries have become the main research target in the field of energy storage.However,the practical application of lithium-sulfur batteries is greatly hindered due to its low cycle stability and low efficiency,which is mainly due to the dissolution and diffusion of lithium polysulfide in the electrolyte.The development of new sulfur cathode materials is the key to solving these challenges and promoting the commercialization of lithium-sulfur batteries.To tackle these challenges,an asymmetric polar two-dimensional heterostructure material Ti₂CO/WS₂ is constructed as a sulfur cathode additive material for lithium-sulfur batteries.The first-principles calculation of density functional theory including van der Waals force correction（DFT-D3）is used.The performance and mechanism have been studied.We found that Ti₂CO/WS₂ as an electrode additive material has a higher binding energy to high-order polysulfides on the oxygen surface.This anchoring performance helps to inhibit the shuttle effect of polysulfides.At the same time,it was also found that the sulfur surface of Ti₂CO/WS₂ has a lower polysulfide diffusion barrier,which is beneficial to the improvement of the cycle performance of lithium-sulfur batteries.And through the analysis of the electric field distribution inside the material,we find that how the two-dimensional heterostructure material we proposed affects the behavior of polysulfides.It’s worth noting that the analysis of the electronic density of states of Ti₂CO/WS₂ shows the metal properties of the system,which guarantees high conductivity and fast electron transfer.All these features indicate that this asymmetric heterostructure is an excellent anchoring material for lithium-sulfur battery cathodes.We also designed another two-dimensional heterostructure material WS₂/graphene.Through first-principles calculations,the performance of WS₂/graphene as a lithium-sulfur battery cathode composite material is studied.Our density functional theory calculation results show that the binding energy of WS₂/graphene to polysulfides is stronger than the binding energy of electrolyte solvent to polysulfides.This suitable adsorption strength can inhibit the shuttle effect of the intermediate product lithium polysulfide to a certain extent.Moreover,the structure of polysulfide is less deformed during adsorption,so it is not easily broken,which is conducive to the good cycle stability of lithium-sulfur batteries.It is worth noting that WS₂/graphene has excellent electrochemical catalytic performance.The electrocatalytic capability of WS₂/graphene accelerates the transformation process from Li₂S₂ to Li₂S,which is the key rate-limiting step in the entire discharge process,thereby enhancing the kinetic process of battery reaction.Therefore,the two-dimensional heterostructure WS₂/graphene can be used as an advantageous lithium-sulfur battery cathode additive material.