| Garnet-type Solid-state electrolyte Li7La3Zr2O12（LLZO）is a promising solid electrolyte for the next-generation Solid-state Li-ion batteries due to its excellent stability,wide electrochemical window,and high ionic conductivity.However,despite the many advantages of LLZO as a solid-state electrolyte,there are still some problems in its practical application in all-solid-state lithium batteries.The growth of lithium dendrites between the solid electrolyte LLZO and the lithium metal anode leads to battery short circuit,capacity loss,etc.How to inhibit the growth of lithium dendrites is an urgent problem to be solved.Therefore,in this paper,the structure and properties of the surface and grain boundaries of LLZO were studied by combining first-principles calculations and molecular dynamics simulations,and the effects of lithium content on the stability of the surface/grain boundaries,electronic structure and Li ion transport were investigated.The regulation and control of transport properties,the specific work is:（1）The electronic structure,stability,Li-ion transport properties of solid electrolyte LLZO bulk and surface,and the effect of Li concentration on the surface on the stability of the surface structure were systematically studied.The results show that the surface model of LLZO Li-terminated is the most stable.Localized surface states exist in the band gap of the Li-rich surface structure,which provide electronic pathways for the formation of metallic Li on the Li-rich surface.Furthermore,the formation energy of the surface structure is lowest when the Li concentration on the surface is reduced to half of the initial surface Li amount.At this time,the potential barrier of Li+migration path I（Li1→Li3）on the surface decreases from 0.74 e V to 0.70 e V,and that of path II（Li3→Li2）decreases from 0.50 e V to 0.34 e V.Therefore,reducing the Li concentration on the surface is beneficial to improve the stability of the surface structure to a certain extent,while reducing the migration barrier of Li ions on the surface,thereby inhibiting the formation of lithium dendrites.（2）The mechanical properties and transport properties of solid electrolyte LLZO bulk phase andΣ3（112）,Σ5（210）,Σ5（310）andΣ9（114）grain boundary structures,as well as the transport properties of Li concentration in the grain boundary region Impact.The research results show that the Li+migration barrier in the four grain boundary models is higher than that of the bulk,indicating that the existence of grain boundaries hinder the migration of Li ions.The interstitial Li atoms in the grain boundaryΣ3（112）are mainly distributed in the grain boundary region in the equilibrium state,resulting in the aggregation of Li atoms and providing the possibility for the formation of lithium dendrites.Finally,based on the original Li+content in the system,the Li content of+10%,+20%and+30%were set respectively,and three concentration gradient models were constructed.The calculation results show that the activation energy of Li+in the system increases with the increase of Li concentration in the four models.For the grain boundary region,the diffusion rate of Li ions reaches the maximum at+10%concentration,indicating that increasing the lithium concentration is beneficial to the Li+diffusion in the grain boundary region to a certain extent.The main reason is that the number of Li atoms occupying the octahedral 96h sites on the branches of the three-dimensional channel increases at this concentration.The research in this paper clarifies that the lithium content has a certain regulatory effect on the structure and properties of the surface/grain boundary.It provides a theoretical basis for inhibiting the growth of lithium dendrites in inorganic oxide-based solid electrolytes. |
