Theoretical Study On The Inhibition Of CaF₂-like Alloys On The Growth Of Lithium Dendrite

With the development of science and technology,lithium batteries have become an indispensable part in people’s daily lives.From intelligent mobile to wearable devices,lithium metal is an ideal anode material due to its higher energy and power density.However,because of its instability in the lithium metal-electrolyte interface during cycling and charge-discharge process,the reliability of lithium metal batteries still faces a series of stern challenge.Lithium dendrites pierce the diaphragm,and cause short circuits in the battery.Therefore,inhibiting the growth of lithium dendrites has become a key issue in the industrialization of lithium batteries.Based on the above problems,the growth mode and inhibition mechanism of lithium dendrite have been studied in depth.In this paper,we performed density functional theory（DFT）calculations to study the theoretical model of CaF₂-like compounds and its inhibition of lithium dendrite growth,which provides theoretical basis and practical design schemes for relevant experiments and research.This paper takes strontium fluoride（Sr F₂）as the starting point to study the thermodynamic and dynamic properties between lithium atoms and the surface of CaF₂-like materials.Studies have shown that the surface with F atom terminations in the（001）direction is the most stable surface for both Sr F₂ and CaF₂.The adsorption energies of a single Li atom on Sr F₂ and CaF₂ surfaces are-7.775 e V and-8.219 e V,respectively,with high diffusion energy barriers.However,lithium atom has a smaller adsorption energy and lower diffusion energy barrier on the pure Li metal surface.Subsequently,the effects of different Li adsorption concentrations on the growth of lithium dendrite were studied.With the increase of adsorption concentration,the adsorption energy gradually increased,but it was still lower than the cohesive energy of lithium metal（-1.606 e V）,indicating that it has an ideal effect on inhibiting the growth of lithium dendrites.The low adsorption energy and high diffusion energy barrier on the surface of CaF₂-like materials cause Li atoms to form a densely uniform lithium deposition,thereby inhibiting the growth of lithium dendrites.The CaF₂-like surfaces are intrinsically magnetic with the outer layer fluoride atoms.With the increase of the Li adsorption concentration,the outer layer fluoride atoms gradually weaken their magnetic properties.In order to clarify the role of fluoride atoms of the outer layer,we studied the growth mechanism of lithium dendrites on the surface of Sr Cl₂ and Sr F₂ materials by replacing outer layer fluoride atoms with Br and Cl,The DFT calculation results showed that the adsorption energy was significantly lower than the surface of Sr F₂ and the surface magnetism is decreased,too.Instead of pure lithium metal,lithium alloys are also commonly used as the negative electrode of batteries to inhibit the growth of lithium dendrites.This paper studies the effect of lithium bismuth alloy on the growth of lithium dendrites,and proposes the mechanism of out-of-plane adsorption and in-plane diffusion competition.A single lithium atom possesses low adsorption energy and high diffusion energy barrier on the surface of lithium bismuth alloy,indicating that it has the effect of inhibiting the growth of lithium dendrites.Bi atoms changes the coordination environment of surrounding atoms and enhances the interaction between Li-p_x,y orbitals and Li-p states in Li adatom.By comparing the adsorption energy and diffusion energy barriers of different Li layers,it is found that the inhibition of lithium dendrite growth is a process of competition between out-of-plane adsorption and in-plane diffusion.Our theoretical studies could provide theoretical basis and practical design schemes for related experiments.