Influence Of Defects On Ion Transport Behavior In Transition Metal Halides And Interfacial Problems With Negative Electrodes Based On First-Principles

With the development of the battery industry,it has become a general trend to replace traditional electrolyte batteries with safer and more stable solid-state electrolyte batteries.As an emerging solid electrolyte material,transition metal lithium halide has attracted extensive attention due to its better stability and excellent ionic conductivity.Due to the non-uniform concentration of framework lithium ions in the transition metal lithium halide solid electrolyte,the blocking phenomenon of migration ions is caused,and the side reaction between the transition metal lithium halide solid electrolyte and the lithium metal anode interface occurs to form conductive compounds and induce dendrite growth during the lithium deposition process.Therefore,it is necessary to study the effect of defects on the ion transport behavior of transition metal lithium halide,and to seek methods to improve the interface problem between it and the lithium metal anode.In this paper,Li₃ScCl₆and Li₃InCl₆,which are more representative transition metal halides,are selected as the research objects,and the influence of defects on the transport behavior of structural ions is studied.At the same time,in order to improve the dendrite growth problem between it and the lithium metal anode,a double halide electrolyte interface model was built on the surface of the lithium metal anode.In this thesis,Li₃ScCl₆,Li₃InCl₆and their defect-containing models are simulated by Ab initio molecular dynamics（AIMD）,and the important parameters such as diffusion coefficient,ion mobility,and migration energy barrier are solved.The calculated results of Li₃ScCl₆and Li₃InCl₆were compared with the defect-containing model to explore the influence of lithium site defects on the ion transport behavior of the structure.At the same time,the local migration energy barrier is calculated by the CI-NEB method,and the local lithium ion migration behavior of the defect is explained.In order to improve the problem of dendrite growth between the material and the lithium anode,the Li₃ScCl₆-LiF and Li₃InCl₆-LiF heterostructures were constructed by using the inhibitory effect of LiF on lithium dendrites.The deposition is described by the adsorption of lithium ions on different surfaces.In this thesis,the inhibitory effect of heterostructure on the interfacial Li dendrite growth is explained from another perspective by the calculation of the surface migration energy barrier.Finally,in order to prove the interfacial stability of heterostructures containing defects,the calculations of adhesion work and binding energy were carried out.The calculation proves that the existence of a small amount of lithium site defects in the Li₃ScCl₆and Li₃InCl₆structures is beneficial to improve the lithium ion migration efficiency in the structure,which greatly improves the charge-discharge efficiency of the structure as a solid electrolyte material.Through the calculation of the migration energy barrier,it is determined that the existence of lithium site defects increases the lithium ion migration ability of the overall structure,but the defect locally decreases slightly.In order to ensure the interfacial stability of heterostructures containing lithium site defects,the interfacial adhesion work and binding energy are calculated in this thesis,and the comparison with the defect suppression structure is used to determine the amount of lithium site defects on Li₃ScCl₆and Li₃InCl₆substrates.The introduction does not have a significant effect on the interfacial stability of the heterostructures.To sum up,the introduction of a small amount of lithium site defects into the Li₃ScCl₆and Li₃InCl₆structures can further improve the ion mobility of the Li₃ScCl₆and Li₃InCl₆structures,which already have outstanding ion mobility.At the same time,constructing a heterostructure with LiF can improve the problem of dendrite growth caused by the direct contact of Li₃ScCl₆and Li₃InCl₆with the lithium anode.Its practicality as a solid electrolyte material is greatly improved.