Ion Transport Mechanism Of Lithium Solid-state Battery Materials Based On First Principles Study

At present,lithium-ion batteries are considered to be the most potential chemical energy sources.Research on lithium-ion battery materials is the top priority for improving battery performance.This paper uses first-principles calculations based on density functional theory（DFT）The electronic structure of the positive electrode lithium manganate material and the simulation calculation of the extraction and insertion of Li⁺material in the battery charge and discharge state.In addition,the performance of Li_1.4Al_0.4Ti_1.6（PO₄）₃oxide electrolyte material was evaluated and the migration of Li⁺in the bulk phase was simulated,and the stability of the crystal structure was judged in conjunction with the change in the properties of the material.In this paper,DFT is used to simulate the Li_xMn₂O₄（x=0,0.5,1）crystal structure of the three Li atomic ratios to simulate the deintercalation behavior of lithium ions in the system.First,the structure optimization and energy calculation are performed,and the energy band,state Research on density,differential charge density,etc.The results show that the LiMn₂O₄crystal is a direct energy gap semiconductor,which can better exert the properties of ion conduction in the application of batteries.In the LiMn₂O₄-Mn₂O₄system,manganese and oxygen contribute greatly to the states near the Fermi level,and exist as covalent bonds.Due to the disappearance of the Li valence band,the bonding of Mn-O bonds is further strengthened.The distribution of the differential charge density of Li_xMn₂O₄（x=0,0.5,1）shows that the bonding characteristics of LiMn₂O₄materials are a mixture of ionic bonds and covalent bonds,and Li⁺shows a strong locality,showing ionic bonds.From the LiMn₂O₄system to Mn₂O₄,the valence state of Mn atoms in the lattice changes slightly with the deintercalation of Li ions.The average valence state of Mn atoms increases from+0.72 to+0.89.There is no difference in the Mn atoms in the system.In the oxidation state,a covalent bond formed between Mn and O exists in the crystal lattice through the sharing of electron pairs.After the lithium ions are completely removed from the lattice,the Mn₂O₄material can still maintain good stability.In this paper,DFT is used to study the crystal structure characteristics,lattice dynamic stability and Li⁺migration in the bulk phase of the oxide electrolyte Li_1.4Al_0.4Ti_1.6（PO₄）₃material.The results show that the oxide electrolyte Li_1.4Al_0.4Ti_1.6（PO₄）₃exhibits strong ionic crystal characteristics.Bader charge data shows that Li atoms are almost completely ionized into Li⁺,which are combined into solid oxide electrolyte materials by the coulomb force between the atoms.In the stability of lattice dynamics in the system,the phonon frequency is positive and the contributions of different elements of the phonon’s vibrational density to the lattice vibration all indicate that the material is dynamically stable.Afterwards,through the elastic band method（NEB）calculation,it can be seen that the migration barrier of Li⁺in the Li_1.4Al_0.4Ti_1.6（PO₄）₃crystal is very small as 0.23e V.With sufficient vacancies,this migration mode is It is easy to happen,so the migration rate of lithium ions in the bulk phase is determined by the concentration of vacancies.In this paper,the theoretical study of Li_xMn₂O₄（x=0,0.5,1）for the cathode material of lithium-ion batteries was conducted to simulate the deintercalation behavior of lithium ions during the chemical reaction,and the electrolyte material Li_1.4Al_0.4Ti_1.6（PO₄）The internal mechanism of 3 and the migration of lithium vacancies in the system,the material reflected in the theoretical calculation has the characteristics suitable for solid-state batteries,and provides a theoretical basis for the development of solid-state batteries.