Ab Initio Molecular Dynamics Study On The Disordered Li-Ga-Sn System

Pure Ga and Ga-Sn alloys are used as negative electrodes of liquid metal lithium-ion batteries,which can avoid dendrite growth issue and volume expansion during the operation of batteries.At present,the experiments mainly focus on the morphology and electrochemical properties of Ga-based anodes,but there are few reports on the lithiation mechanism,microstructure and basic thermal properties of liquid Ga-based alloys.Therefore,in this paper,the ab initio molecular dynamics simulation method based on density functional theory is used to study the structure,thermodynamics and atomic diffusivity of unit system,binary system and ternary system in disordered Li-Ga-Sn.The main conclusions of this paper are as follows:（1）Liquid systems Li,Ga and Sn were simulated.The study found that at the same temperature,the basic physical properties of liquid Li,Ga and Sn satisfy the following laws:densityρ_Sn>ρ_Ga>ρ_Li,thermal expansion coefficientα_v（Li）>α_v（Sn）>α_v（Ga）,diffusion coefficient D_Li>D_Ga>D_Sn and viscosityη_Sn>η_Ga>η_Li.In addition,the simulation results are in good agreement with experimental data,which shows the reliability of the calculation parameters and model in this paper.（2）Liquid Ga-Sn and Li-Ga systems were simulated.The study shows that the mixing enthalpy of Ga-Sn is positive and increases with the increase of Sn content,while the mixing enthalpy of Li-Ga system is negative and first decreases and then increases with the increase of Li content.The radial distribution function and Warren-Cowley parameter of the Ga-Sn system reveal that there is no obvious interaction between heterogeneous atoms in the Ga-Sn system,and the Ga atoms and Sn atoms tend to exhibit the properties of pure Ga and pure Sn,which make the density and viscosity increase with the Sn content.In the liquid Li-Ga system,there is a strong attraction between heterogeneous atoms,At 1023K,with the increase of Li content,the Li-Ga ionic bond is gradually saturated,and the diffusion coefficient of Ga atoms decreases due to the strong ionic bond between Li-Ga.（3）The structure,thermodynamics and thermophysical properties of disordered ternary Li-Ga-Sn system were studied.The study shows that the intercalation of Li will cause a strong exothermic behavior of the Ga-Sn system.During the lithiation process,the affinity between Li-Sn is stronger than that between Li-Ga,indicating Li is prone to combine with Sn firstly in the lithiation process of Ga_91.6Sn_8.4.Radial distribution function and diffusion coefficient analysis show that at room-temperature,with increasing Li content,the system transforms from a liquid to a solid-like state,which consistent with the experimental findings.The bond angle distribution function indicates that Li₂Ga₇,Li Ga and some Li-Sn alloys are formed when Li embedded into eutectic Ga-Sn.The above studies on the structure,thermodynamics and thermophysical properties of the disordered Li-Ga-Sn system can provide some theoretical guidance for the research and development of room temperature liquid metals as electrode materials for lithium-ion batteries.