The Structural Stability And Evolution Process Of Li₂Se₂S_x On The Surface Of Graphene By A First Principles Calculation

In recent years,the addition of selenium to the cathode of lithium-sulfurselenium batteries has greatly improved the conductivity of the positive electrode of the battery and has attracted much attention.However,like lithium-sulfur batteries,the shuttle phenomenon that occurs during the charging and discharging process limits the further development of its research.The use of diaphragms is an important way to improve the shuttle effect during battery charging and discharging.Therefore,it is of practical significance to study the influence of the diaphragm on the suppression of the shuttle effect.Researchs have found that graphene is a two-dimensional conductive material with good flexibility and high electron mobility,which can induce and accommodate the uniform growth and deposition of electrode materials while improving the electron and ion transport capabilities.A series of studies have shown that the modification of graphene can significantly improve the anchoring ability of graphene to sulfur atoms.Therefore,doping modification of graphene is one of the effective methods to improve the barrier’s shuttle effect.This article is based on the First-principles based on density functional theory,and studies the stable configuration of lithium-sulfur selenide.Build a lithium-sulfurselenide in which selenium atoms replace two sulfur atoms in the sulfide was established.By comparing the binding energy,bond length and bond angle of the molecules,the stable configuration of the lithium-sulfur-selenide was finally determined.On this basis,study the adsorption strength of graphene and doped graphene for lithium sulfur selenide.Build a model for the adsorption of lithium sulfur selenide by graphene and the nitrogen atom-assisted transition metal single atom co-doped graphene to adsorb lithium sulfur selenide is established.By comparing the size of the adsorption energy,the type of bonding,the differential charge,the amount of Bader transfer,and the electron contribution of the energy state density orbital of the two adsorption models.Graphene co-doped with nitrogen atoms and transition metals titanium,vanadium,and zirconium can anchor lithium-sulfur selenide better than intrinsic graphene.And in the calculation process,it is found that the nitrogen atoms in the doped graphene can adsorb the lithium atoms in the lithium sulfur selenide,which makes the nitrogen atoms that are intended to assist the transition metal single atoms to bond with the graphene have an additional feature that is conducive to adsorption.From this series of theoretical calculations,it can be concluded that the maximum adsorption energy of graphene for each position of lithium sulfur selenide is about 0.4 eV.The graphene co-doped with a nitrogen atom and a transition metal single atom has a maximum adsorption energy of more than 2.0 eV at each position of lithium sulfur selenide,especially the maximum adsorption energy of graphene doped with zirconium atoms is more than 4.0 eV.It shows that doped modified graphene is a feasible research method.These theoretical calculation results have played a good guiding role for the new modified diaphragm,and can provide a theoretical basis for solving the shuttle effect of lithium-sulfur-selenium batteries.