First Principles Study On The Ion Miagration Properties Of Transition Metal Lithium Halide And Its Interaction With Metal Lithium Anode

All-solid-state battery is expected to be the best alternative to current liquid lithium battery due to its high safety and ionic conductivity.The focus of all solid state battery research is how t o choose the appropriate solid electrolyte.Transition metal lithium halide solid electrolyte has m ore than 10^-4 orders of magnitude of ionic conductivity,low barrier of ion migration potential an d high oxidation stability.At present,lithium halide Li₃Er Cl₆ and Li₃YCl₆ with high oxidation r esistance and electrochemical stability are obtained by the synthesis process combined with ball milling and high temperature annealing,which is one of the research directions of inorganic soli d electrolyte materials.In this paper,the first-principles software VASP is used to study the structural stability of t ransition metal halides Li₃Er Cl₆,Li₃YCl₆（Li₃TMCl₆,TM=Er,Y）,including the electronic struct ure properties analysis of the electronic insulation of LTMC,and the simulation of ion motion b ehavior to obtain the corresponding input.These parameters were obtained,and the correspondi ng Sc³⁺,La³⁺and Zr⁴⁺doping structures were constructed and compared with the properties in t he intrinsic LTMC structure to obtain the best doping scheme.In addition,the interface structur e of lithium halide LTMC and lithium metal anode was constructed,and the electron tunneling barrier was obtained based on the electron tunneling effect theory to evaluate the stability of the interface structure,and simulate the process of ion movement at the interface at the picosecond s cale.The results show that the ground state structure of the lithium halide solid electrolyte Li₃T MCl₆ with atomic disorder is a hexagonal close-packed structure,and its lithium atoms are unif ormly distributed.LTMC has excellent electronic properties,and the band gap value of 4.86 e V～5.26 e V has sufficient ability to suppress electronic conduction.In addition,the lithium halide LTMC exhibits high ionic conductivity exceeding 10^-3 S·cm^-1,also maintains good thermal stab ility at a high temperature of 600 K,and the lithium ions are three-dimensionally diffused.The ion transport properties of lithium halide LTMC were regulated by changing the unit c ell parameters and increasing the concentration of lithium ion vacancies.The results show that t he incorporation of a larger radius of the same valent ion La³⁺can increase the unit cell volume and widen the lithium ion diffusion channel.Increase ionic conductivity.However,the incorpor ation of heterovalent Zr⁴⁺reduces the concentration of Li⁺in the unit cell,and its ionic conducti vity is more than one order of magnitude compared with the intrinsic lithium halide LTMC,indi cating that the introduction of a charge compensation mechanism can effectively increase the Li vacancy concentration.The Coulomb repulsion between parts of Li is reduced,and the ionic co nductivity of the structure is improved.In addition,the incorporation of different metal ions wit h similar physical properties does not change the electronic properties of the corresponding lithi um halide LTMC doped structures.Before constructing the Li|LTMC interface model,we consider the different terminal plane s of the LTMC surface model,and the surface energy calculation shows that the stable LTMC{0001}surface has a small proportion of transition metals.The electronic properties of the Li|L TMC interface are calculated and analyzed by DOS and ESP.The electron tunneling barrier at t he interface is generally close to 0 e V.The differential density map indicates that there is a large accumulation of charges at the interface,which are taken up by the transition metal on the surfa ce of the lithium halide.AIMD simulations also demonstrate that transition metals are reduced t o elemental metals due to the electrons received from the interface.These elemental metals are dissolved out and diffused to the negative electrode metal lithium,which further aggravates the electron tunneling phenomenon and makes the interface in an unstable state.Based on the problems of the Li|LTMC interface model,based on the theory of electron tu nneling effect,we propose that the thin film Li Cl is deposited on the lithium halide LTMC solid electrolyte to construct the interface model of the double-layer lithium halide solid electrolyte L i Cl|LTMC and the negative metal lithium,namely Li|Li Cl|LTMC.The results show that the fou r-layer Li Cl atomic layer in the Li|Li Cl|LTMC interface effectively increases the electron tunnel ing barrier to 1.19 e V～1.81 e V,and the differential charge density map shows that the charge at the interface is not transferred to the solid electrolyte region,inhibiting the transition metal Er³⁺,the restoration process of Y³⁺.In addition,AIMD simulations also prove that due to the presenc e of Li Cl,a passivation effect occurs at the interface,which effectively increases the electron tu nneling barrier.Reduce the probability of interface electron tunneling phenomenon and improve interface stability.