The Theoretical Design And Prediction Of Anode For Alkali Metal Ion Batteries

In recent years,due to environmental pressures and the traditional energy crisis,the search for high-performance,low-cost,sustainable,low-pollution and energy storage materials has become a important topic in the field of new energy development and material device development.Low-dimensional nanomaterials have unique volume effects,surface effects,macroscopic quantum tunneling effects and dielectric confinement effects,so they have extremely high application prospects in the fields of energy storage materials,catalytic materials and biomedicine.At the same time,because the structure of the material determines the properties of the material,it is very important to simulate and predict the structure of nanomaterials.In this paper,first-principles calculations have been performed to make theoretical designs and predictions of some novel low-dimensional nanomaterials used as electrode materials in alkali metal ion batteries.Besides,structures and properties of potassium ion-doped organic-inorganic perovskite materials have been studied here.The main contents and results are as follows:1.We performed a systematic study and prediction of transition metal dichalcogenides(Transition metal dichalcogenides,TMDs)as the anode material of potassium ion batteries,and twelve TMDs materials which have been successfully synthesized in experiments were studied here.The calculation results showed that potassium ions can be adsorbed stably on the surface of TMDs,and the diffusion energy barrier of potassium ions on monolayer TMDs material is very small,only 0.05 eV,which makes potassium ions almost free to diffuse on the surface.Although the diffusion energy barrier of potassium ions between layers is larger than that in monolayer,the diffusion energy barrier is between 0.13 eV and 0.44 eV,but it is smaller than that of lithium ions and sodium ions between TMDs.Some TMDs materials will phase change with the insertion of potassium ions.After the phase change,the adsorption energy of potassium ions on the 1T phase or 1T' structures will increase,and the diffusion barrier of potassium ions on VS2 and WS2 will be further reduced.Our theoretical calculations indicated that VS2 and TiS2 have the best OCV values(1.20?1.34 eV vs.K+/K),and the theoretical capacity is 278 mA h/g and 282 mA h/g,respectively.Therefore,we recommend two-dimensional VS2 and TiS2 with important application prospects as anode materials for potassium ion batteries.2.We conducted a theoretical study of monolayer ?-MoO3 as an anode material for alkali metal ion batteries and made a systematic comparison with the 3D MoO3.The results of our calculations showed that,unlike that only Li ions in the bulk phase can be stably adsorbed,the three alkali metal ions,Li,Na and K can be adsorbed on monolayer of MoO3 and the adsorption is more stable.For the diffusion barriers,the migration energy barriers of lithium,sodium and potassium are 0.44 eV,0.28 eV and 0.22 eV,respectively,which are significantly lower than the migration energy barriers of alkali metal ions in the 3D MoO3,indicating that the migration and diffusion of alkali metal ions are more likely to occur on the surface of the monolayer MoO3.Therefore,reducing the material dimension to obtain better performance is a new way of thinking about finding more suitable electrode materials for alkali metal ion batteries.3.A new type of two-dimensional perovskite K2PbI4 structure is theoretically predicted.It was proved that the 2D K2PbI4 structure can exist stably since there is no virtual frequency in the simulation of phonon spectrum.We further doped K+in the 3D orthogonal phase MAPbI3,built a 2D/3D interface perovskite structure,and fixed the bottom layer to optimize the surface structure.We found that as the doped K+concentration increases,the Pb-? bond on the surface occurs obviously inclined.From the perspective of bonding and electronic structure,after K+enters the 3D perovskite,it will exist on the surface of the 3D perovskite in the form of 2D K2PbI4,forming a stable interface structure.This calculation is calculated as the future 2D/3D perovskite The experimental study of material interface structure provides a theoretical basis.