Theoretical Study On The Adsorption Of Polysulfides By Two-dimensional Materials In Lithium-sulfur Batteries

Lithium sulfur?Li-S?batteries are considered as one of the candidates for the new generation of energy storage materials,because of its high specific capacity?1675mAh g-1?and high theoretical energy density?2600 Wh kg-1?,which can meet the energy storage requirements of energy and large electronic devices that cannot be met by conventional batteries.As the cathode material of lithium-sulfur battery,sulfur is widely concerned for its low cost,environmental friendliness and abundant reserves.However,the commercialization process of lithium-sulfur batteries still faces many challenges,such as rapid decline of capacity and poor coulomb efficiency.One of the key problems is that the intermediate polysulfide produced in the charging and discharging process of lithium-sulfur battery is easily dissolved into the electrolyte,resulting in the"shuttle effect"that affects the battery performance.So scientists are looking for new materials or techniques to solve these problems.In this paper,a variety of two-dimensional materials are selected as the anchoring materials of polysulfide in lithium-sulfur batteries,and their adsorption properties are investigated by applying the first principle calculations to study the their effects for"shuttle effect".The main contents are as follows:Firstly,the metallic sulfide SnS₂ is used as the anchoring material of polysulfide,and its influence on battery performance is explored by applying the first principle.The adsorption energy and charge transfer properties of polysulfide on SnS₂ surface were analyzed,and the integrity of polysulfide adsorption structure on SnS₂ surface was calculated.The results showed that SnS₂ could bind polysulfide with moderate adsorption intensity and maintain the integrity of polysulfide molecular structure in the adsorption process.Therefore,SnS₂ can be used as a candidate material for inhibiting the"shuttle effect"in lithium-sulfur batteries.Secondly,the graphene-like two dimensional materials of IVA group—silene,germanene and stanene were selected as the research objects,exploring the adsorption mechanism of polysulfide on pure,metallic doped and non-metallic doped materials,and the diffusion barrier of polysulfide on the surface was calculated.Based on the comprehensive analysis of the adsorption strength and diffusion behavior,it is concluded that the pure silene,Sn doped germanene,Ge doped stanene and B doped germanene have better performance as polysulfide anchoring materials.Finally,based on density functional theory,the adsorption mechanism of polysulfide on the surface of non-metallic heteroatoms doped phosphene was investigated.The comprehensive evaluation was made from the aspects of adsorption energy,diffusion energy barrier and structural stability,and finally it was concluded that Si doped phosphene had excellent performance in all aspects and became the most potential anchor material for polysulfide.