A method for improving BaF2 fluorine ion conductivity based on K doping and grain boundary regulation

Abstract

This invention discloses a method for improving the fluoride ion conductivity of BaF2 based on K doping and grain boundary modulation, mainly providing a technical solution to the problem of low fluoride ion conductivity at room temperature (300K) in BaF2-based solid electrolytes. Firstly, a first-principles method is used to improve the fluoride ion conductivity of the K-doped BaF2 system (Ba... 1‑x K x F 2‑x Structure screening was conducted, and the relationship between K concentration (x) and its room-temperature fluoride ion conductivity was calculated and analyzed. The optimal K-doped BaF2 crystal (Ba...) was designed. 0.875 K 0.125 F 1.875 Its room temperature fluoride ion conductivity is significantly greater than that of BaF2; in addition, Ba... 0.875 K 0.125 F 1.875 It possesses a wide band gap, excellent mechanical properties, and a wide electrochemical window; finally, Ba was designed using molecular dynamics methods. 0.875 K 0.125 F 1.875 The optimal grain boundary structure (∑9(221)) has a room-temperature fluoride ion conductivity on the order of 10. ‑ 3 S / cm. This invention also provides an effective method for designing solid electrolytes for high-performance fluoride-ion batteries.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of computational materials chemistry, and particularly relates to a method for improving BaF2 fluorine ion conductivity based on K doping and grain boundary regulation. BACKGROUND

[0002] Solid-state fluorine ion batteries have high theoretical voltage, high energy density, good safety performance and other advantages, and have a wide application prospect. However, the cycle life of the solid-state fluorine ion battery is poor at present, which seriously restricts its development, and how to quickly and accurately research and develop fluorine ion solid-state electrolyte with high room temperature (300K) fluorine ion conductivity has become a problem to be solved. In the fluorite-type BaF2 unit cell, Ba ions are in cubic close packing, which are located at the vertices and face centers of the cubic unit cell; F ions occupy all tetrahedral voids, but do not occupy octahedral voids, which lays a foundation for the migration of fluorine ions in BaF2; at the same time, due to the strong binding effect of Ba-F ion bond on fluorine ions, BaF2 has the problem of low room temperature fluorine ion conductivity, and its mechanical properties and electrochemical window still need to be further improved. Based on this problem, the first principle method is used to study the mechanism of K doping regulation of BaF2, to find the optimal partial replacement of K ions to Ba ions, to produce suitable fluorine vacancies and to weaken the Ba-F bond effect, so as to induce the rapid diffusion of fluorine ions in the BaF2 crystal, and to design K-doped BaF2 crystal (Ba 0.875 K 0.125 F 1.875 ) with the highest room temperature fluorine ion conductivity. In order to further design the optimal grain boundary structure of Ba 0.875 K 0.125 F 1.875 , the molecular dynamics method is used to calculate the fluorine ion conductivity corresponding to the ∑3 (111), ∑5 (210) and ∑9 (221) grain boundaries of Ba 0.875 K 0.125 F 1.875 , and through comparison, it can be known that the ∑9 (221) grain boundary of Ba 0.875 K 0.125 F 1.875 has the highest room temperature (300K) fluorine ion conductivity (3.68×10 -3 S / cm), which is significantly greater than the fluorine ion conductivity of BaF2. The application aims to effectively improve the fluorine ion conductivity of BaF2, and based on the method of K doping and grain boundary regulation, the first principle and molecular dynamics method are used to accurately and quickly design BaF2-based fluorine ion battery solid-state electrolyte with high room temperature fluorine ion conductivity. SUMMARY

[0003] The purpose of this invention is to provide a method for improving the fluoride ion conductivity of BaF2 based on K doping and grain boundary modulation, aiming to increase its fluoride ion conductivity. The specific implementation method is carried out according to the following steps:

[0004] Step 1: For Ba 1-x K x F 2-x Structure screening was performed using (x = 0.03125, 0.0625, 0.09375, 0.125, 0.15625); then Ba was calculated. 1-x K x F 2-x The relationship between the formation energy and the K doping concentration (x) was obtained to obtain the effect of the K doping concentration (x) on Ba. 1- x K x F 2-x The influence of stability was investigated to select the optimal K-doped raw material.

[0005] Step 2: Calculate and analyze Ba using ab initio molecular dynamics (AIMD) method. 1-x K x F 2-x The correlation between fluoride ion conductivity and K doping concentration (x) at different temperatures was investigated, and Ba was designed. 0.875 K 0.125 F 1.875 It has the highest fluoride ion conductivity (at a temperature of 300K);

[0006] Step 3: Calculate Ba using VASP software based on first-principles methods. 0.875 K 0.125 F 1.875 The band structure was analyzed to determine its electronic conductivity.

[0007] Step 4: Calculate Ba using VASP software based on first-principles methods. 0.875 K 0.125 F 1.875 The distribution law of Young's modulus along three-dimensional space is analyzed to determine its mechanical properties;

[0008] Step 5: Calculate Ba 0.875 K 0.125 F 1.875 The electrochemical window;

[0009] Step 6: Create Ba 0.875 K 0.125 F 1.875 Three grain boundary structures are identified: ∑3(111), ∑5(210) and ∑9(221), and the grain boundary energies of these three structures are calculated. The stability of ∑3(111), ∑5(210) and ∑9(221) is compared.

[0010] Step 7: Calculate Ba using LAMMPS software based on molecular dynamics methods. 0.875 K 0.125 F 1.875 Fluoride ion conductivity at the ∑3(111), ∑5(210), and ∑9(221) grain boundaries; by comparison, it can be seen that: Ba 0.875 K 0.125 F 1.875 The ∑9(221) grain boundary exhibits the highest fluoride ion conductivity (3.68 × 10⁻⁶) at a temperature of 300 K. -3 S / cm);

[0011] This invention proposes a method for improving the fluoride ion conductivity of BaF2 based on K-doping and grain boundary modulation, thereby enabling precise and rapid design of BaF2-based solid electrolytes for fluoride ion batteries with high fluoride ion conductivity. Firstly, the BaF2... 1-x K x F 2-x Structure screening was performed using (x = 0.03125, 0.0625, 0.09375, 0.125, 0.15625); subsequently, Ba was calculated. 1-x K x F 2-x The formation energies under different chemical potentials and K concentrations were determined to identify Ba with the most stable structure. 1-x K x F 2-x And obtain the optimal K-doped raw material (K3Ba); then calculate Ba 1-x K x F 2-x The fluoride ion conductivity of (x = 0.03125, 0.0625, 0.09375, 0.125, 0.15625) was used to design a K-doped BaF2 structure (Ba) with the highest fluoride ion conductivity. 0.875 K 0.125 F 1.875 ); then calculate and analyze Ba 0.875 K 0.125 F 1.875 The band structure, mechanical properties, and electrochemical window of Ba were analyzed; based on this, the Ba band structure was established using Atomsk software. 0.875 K 0.125 F 1.875 Three grain boundary structures (∑3(111), ∑5(210), and ∑9(221)) were identified, and their grain boundary energies were calculated to obtain their relative stability. Finally, the Ba values ​​were calculated using LAMMPS software. 0.875 K 0.125 F 1.875 The fluoride ion conductivity of the ∑3(111), ∑5(210), and ∑9(221) grain boundaries. The Ba provided by this invention...0.875 K 0.125 F 1.875 It not only possesses a wide band gap, excellent mechanical properties, and a wide electrochemical window, but also Ba 0.875 K 0.125 F 1.875 The ∑9(221) grain boundary exhibits the optimal fluoride ion conductivity (3.68 × 10⁻⁶) at a temperature of 300 K. -3 S / cm). Attached Figure Description

[0012] The following detailed description will focus on the embodiments illustrated in conjunction with the accompanying drawings. The drawings are merely some embodiments of the present invention, in which:

[0013] Figure 1 This is an overall flowchart of a method for improving the fluoride ion conductivity of BaF2 based on K doping and grain boundary modulation.

[0014] Figure 2 (a) The range of relative chemical potentials required to form stable BaF2; Figure 2 (b) is Ba 1-x K x F 2-x The formation energy (E) of (x = 0.03125, 0.0625, 0.09375, 0.125, 0.15625) f (x) (using K3Ba as the doping material);

[0015] Figure 3 (a) is Ba 1-x K x F 2-x The relationship between ln(σT) and K concentration (x) for (x = 0, 0.03125, 0.0625, 0.09375, 0.125, 0.15625), where temperature (T) is 300 K and σ is Ba. 1-x K x F 2-x Fluoride ion conductivity; Figure 3 (b) represents BaF2 and Ba 0.875 K 0.125 F 1.875 The relationship between ln(σT) and 1000 / T, where σ and T are the fluoride ion conductivity and temperature, respectively, and E a Indicates activation energy;

[0016] Figure 4 For BaF2 and Ba 0.875 K 0.125 F 1.875 The distribution of Young's modulus in three-dimensional space and its projection along the x, y and z directions, in GPa;

[0017] Figure 5 For Ba 0.875 K 0.125 F 1.875 Fluoride ion conductivity of the ∑3(111), ∑5(210) and ∑9(221) grain boundaries (at 300 K); Detailed Implementation

[0018] This embodiment provides a method for improving the fluoride ion conductivity of BaF2 based on K doping and grain boundary modulation, including the following steps:

[0019] First, regarding Ba 1-x K x F 2-x Structure screening was performed using (x = 0.03125, 0.0625, 0.09375, 0.125, 0.15625), and then based on the formation of stable Ba... 1-x K x F 2-x Required relative chemical potential conditions, calculate its formation energy, and compare with Ba 1-x K x F 2-x The stability of the material under different K concentrations was investigated, and the optimal K-doped raw material (K3Ba) was obtained. Then, ab initio molecular dynamics (AIMD) was used to calculate the stability of Ba. 1-x K x F 2-x Using fluoride ion conductivity values ​​(x = 0.03125, 0.0625, 0.09375, 0.125, 0.15625), a Ba2O3 substrate with the highest room temperature (300 K) fluoride ion conductivity was designed. 0.875 K 0.125 F 1.875 Crystal; then further calculations of Ba 0.875 K 0.125 F 1.875 The band structure, mechanical properties, and electrochemical window of Ba were studied. Based on this, Ba was constructed. 0.875 K 0.125 F 1.875 The grain boundary structures (∑3(111), ∑5(210), and ∑9(221)) were determined, and their grain boundary energies were calculated to obtain the most stable grain boundary structures. Then, the Ba values ​​were calculated and compared. 0.875 K 0.125 F 1.875 The fluoride ion conductivity of the ∑3(111), ∑5(210), and ∑9(221) grain boundaries at different temperatures was used to design Ba 0.875 K 0.125 F 1.875The optimal grain boundary (∑9(221)) has the highest fluoride ion conductivity (3.68×10⁻⁶) at room temperature (300K). -3 S / cm). Figure 1 The overall process of a method to improve the fluoride ion conductivity of BaF2 based on K doping and grain boundary modulation is presented.

[0020] The specific parameter settings for the first-principles calculations are as follows: the exchange energy is handled using the PBE (Perdew-Burke-Ernzerh) method based on the generalized gradient approximation (GGA), and the projected fused plane wave (PAW) method is used to describe the interaction between electrons and ions. The plane wave cutoff energy and the Monkhorst-Pack type k-point grid are set to 520 eV and 6×6×6, respectively, and the energy and force convergence accuracy are set to 10. -5 eV / atom and

[0021] First, regarding Ba 1-x K x F 2-x Structures were screened using (x = 0.03125, 0.0625, 0.09375, 0.125, 0.15625), and the formation enthalpy of the compounds corresponding to their constituent components was calculated to determine the formation of stable Ba. 1-x K x F 2-x The relative chemical potential conditions required for the constituent elements; then calculate Ba according to equation (1-1). 1-x K x F 2-x (x = 0.03125, 0.0625, 0.09375, 0.125, 0.15625) Formation energy (E) under different relative chemical potentials. f (x)), compare Ba 1-x K x F 2-x The stability of the material under different K concentrations was investigated, and K3Ba was selected as the optimal K-doped raw material.

[0022] E f (x)=E tot (Ba 1-x K x F 2-x )-E tot (bulk)+x(Δμ Ba +μ Ba )+x(Δμ F +μ F )-x(Δμ K +μ K (1-1)

[0023] In equation (1-1), E tot (Ba 1-x K x F 2-x ) and E tot (bulk) represents Ba 1-x K x F 2-x Total energy and total energy of BaF2; μ Ba μ F and μ K Chemical potentials of Ba, F, and K, respectively; Δμ Ba , Δμ F and Δμ K Let be the relative chemical potentials of Ba, F, and K, respectively. To solve Δμ... Ba , Δμ F and Δμ K First, the ICSD (Inorganic Crystal Structure Database) is used to search for potential competing phases. Based on the formation enthalpy of the competing phases, the relative chemical potential (Δμ) is calculated and determined using the CPLAP (Chemical Potential Limits Analysis Program). Ba , Δμ F and Δμ K The range of ) and the calculation results are as follows Figure 2 As shown in (a). In Figure 2 In (a), point A represents the F-rich condition, and point B represents the Ba-rich condition. To maintain the stable structure of BaF2 and avoid the formation of other competing phases, Δμ i (i is Ba or F) should satisfy the following constraints (see Equations (1-2)-(1-3)).

[0024] Δμ Ba +2Δμ F ≤ΔH f (BaF2) (1-2)

[0025] Δμ Ba ≤0Δμ F ≤0 (1-3)

[0026] Based on the formation of stable Ba 1-x K x F 2-x Required relative chemical potential (Δμ) i Under the given conditions, considering six K-based reactants (KF, KF2, KF3, KF5, K3Ba, and KBa3), the relative chemical potential constraints of these six compounds were used to calculate the Ba-based reactants. 1-x K x F 2-xComparing the formation energies (x = 0.03125, 0.0625, 0.09375, 0.125, 0.15625) at the boundary points (points A and B), we can see that: Ba 1-x K x F 2-x At point B (Δμ) Ba = -11.66eV, Δμ F =0 eV) has a low formation energy, and its value is negative. The corresponding K starting material is K3Ba, and its formation energy gradually decreases with increasing K concentration (x) (see Figure 2 (b) shows that Ba 1-x K x F 2-x At point B (Δμ) Ba = -11.66eV, Δμ F It is easier to form under the growth conditions corresponding to K concentration (x) = 0 eV, and the difficulty of its formation gradually decreases with the increase of K concentration (x).

[0027] The ab initio molecular dynamics (AIMD) method was used to calculate and analyze the K concentration (x) and temperature in relation to Ba. 1-x K x F 2-x The correlation between fluoride ion conductivity and conductivity was first calculated. 1-x K x F 2-x The mean square displacement (MSD) in (x = 0.03125, 0.0625, 0.09375, 0.125, 0.15625) is then used to derive the Ba value based on the relationship between the slope of the MSD curve and the diffusion coefficient. 1-x K x F 2-x The fluoride ion diffusion coefficients (x = 0.03125, 0.0625, 0.09375, 0.125, 0.15625) were calculated. Finally, Ba was calculated based on the fluoride ion diffusion coefficients and the Nernst-Einstein equation. 1-x K x F 2-x Fluoride ion conductivity (σ) for (x = 0.03125, 0.0625, 0.09375, 0.125, 0.15625).

[0028] Based on the above method, Ba was obtained. 1-x K x F 2-x Fluoride ion conductivity (x = 0.03125, 0.0625, 0.09375, 0.125, 0.15625); by comparison, it can be seen that: Ba 0.875 K 0.125 F 1.875It has the highest room temperature (300K) fluoride ion conductivity (see Figure 3 (a)).

[0029] According to Ba 0.875 K 0.125 F 1.875 The activation energies of BaF2 and BaF2 are derived from the relationship between their fluoride ion conductivity and temperature (the activation energy of BaF2 is listed for comparison only). The calculation results are as follows: Figure 3 As shown in (b).

[0030] Ba 0.875 K 0.125 F 1.875 Its band gap is 6.03 eV, which indicates that it has excellent electronic insulation properties.

[0031] Ba is calculated based on the relationship between energy and strain. 0.875 K 0.125 F 1.875 The elastic constant of Ba; based on this, and using the mechanical stability criteria of the tetragonal crystal system, it was further proved that Ba... 0.875 K 0.125 F 1.875 It has good mechanical stability.

[0032] According to Ba 0.875 K 0.125 F 1.875 The bulk modulus (B) and shear modulus (G) are derived from the elastic constants. Based on the critical B / G value (1.75), the Ba... 0.875 K 0.125 F 1.875 Whether it exhibits brittleness or toughness. A B / G value greater than 1.75 indicates good ductility; conversely, a lower value indicates brittleness. Ba 0.875 K 0.125 F 1.875 The B / G value is 2.24, indicating that it has good ductility. For example, Ba... 0.875 K 0.125 F 1.875 When used as a solid electrolyte in fluoride-ion batteries, it exhibits strong resistance to stress damage during charging and discharging.

[0033] Calculate and analyze Ba 0.875 K 0.125 F 1.875 The distribution of Young's modulus (E) of BaF2 in three-dimensional space was analyzed (the Young's modulus of BaF2 is listed for comparison only). The projections of these two moduli along the x, y, and z directions were obtained, and the calculation results are as follows: Figure 4 As shown. From Figure 4 It can be known: Ba 0.875 K 0.125F 1.875 The Young's modulus (E) of BaF2 is not only greater than that of BaF2, but the former also exhibits more pronounced isotropy than the latter, indicating that BaF2... 0.875 K 0.125 F 1.875 It has better mechanical properties than BaF2, which helps it maintain good cycle stability during charge and discharge.

[0034] When Ba and K are used as the negative electrode materials in a fluorine-ion battery, calculate Ba. 0.875 K 0.125 F 1.875 The electrochemical window was explored to investigate its electrochemical stability. Based on Ba... 0.875 K 0.125 F 1.875 The chemical reaction equations corresponding to different voltages were used to obtain the variation of Ba(K) reaction amount with voltage.

[0035] Based on the coincident lattice theory (CSL), a Ba system was constructed using Atomsk software. 0.875 K 0.125 F 1.875 The grain boundary structures are (∑3(111), ∑5(210), and ∑9(221)), where ∑ represents the coincidence index, which is equal to the ratio of the coincidence cell volume to the unit cell volume; then Ba is calculated according to equation (1-4). 0.875 K 0.125 F 1.875 The grain boundary energy (γ) corresponding to the grain boundary structures (∑3(111), ∑5(210) and ∑9(221)) GB ).

[0036]

[0037] In equation (1-4), E GB and E bulk Ba 0.875 K 0.125 F 1.875 Grain boundaries (∑3(111), ∑5(210) and ∑9(221)) and Ba 0.875 K 0.125 F 1.875 The total energy of the bulk, where A is the grain boundary area. The grain boundary energies (γ) of ∑3(111), ∑5(210), and ∑9(221) are... GB The values ​​are 0.67 J·m -2 0.55J·m -2 and 0.21 J·m -2 .

[0038] The LAMMPS software was used to analyze Ba. 0.875 K0.125 F 1.875 Molecular dynamics calculations were performed on the ∑3(111), ∑5(210), and ∑9(221) grain boundaries. First, the mean square displacement (MSD) of fluoride ions at these three grain boundaries was calculated; then, the diffusion coefficient of fluoride ions was derived based on the relationship between the MSD slope and the diffusion coefficient; based on this, the Ba values ​​were calculated according to the Nernst-Einstein equation. 0.875 K 0.125 F 1.875 Fluoride ion conductivity (σ) of the ∑3(111), ∑5(210) and ∑9(221) grain boundaries.

[0039] Based on the above methods, calculate Ba respectively 0.875 K 0.125 F 1.875 The room temperature (300K) fluoride ion conductivity of the ∑3(111), ∑5(210), and ∑9(221) grain boundaries of Ba can be compared to show that: 0.875 K 0.125 F 1.875 The ∑9(221) grain boundaries have the highest room temperature (300K) fluoride ion conductivity (3.68×10⁻⁶). -3 S / cm)(see Figure 5 This is significantly greater than the room temperature (300K) fluoride ion conductivity of BaF2.

[0040] Finally, it is necessary to state that the specific embodiments described above are merely illustrative of or explanations of the principles of the present invention, and do not constitute a limitation thereof. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention.

Claims

1. A method for improving the fluoride ion conductivity of BaF2 based on K doping and grain boundary modulation, characterized in that, The method includes the following steps: Step 1: For Ba 1-x K x F 2-x Perform structural screening; then calculate Ba. 1-x K x F 2-x The relationship between the formation energy and the K doping concentration x is obtained to obtain the effect of K doping concentration x on Ba 1-x K x F 2-x The influence of stability was investigated to screen out the optimal K-doped raw materials, where x = 0.03125, 0.0625, 0.09375, 0.125, and 0.15625; Step 2: Calculate and analyze Ba using ab initio molecular dynamics. 1-x K x F 2-x The correlation between fluoride ion conductivity and K doping concentration x at different temperatures was investigated, and Ba was designed. 0.875 K 0.125 F 1.875 It has the highest fluoride ion conductivity at a temperature of 300K; Step 3: Calculate Ba using VASP software based on first-principles methods. 0.875 K 0.125 F 1.875 The band structure was analyzed to determine its electronic conductivity. Step 4: Calculate Ba using VASP software based on first-principles methods. 0.875 K 0.125 F 1.875 The distribution law of Young's modulus along three-dimensional space is analyzed to determine its mechanical properties; Step 5: Calculate Ba 0.875 K 0.125 F 1.875 The electrochemical window; Step 6: Create Ba 0.875 K 0.125 F 1.875 Three grain boundary structures are identified: ∑3(111), ∑5(210) and ∑9(221), and the grain boundary energies of these three structures are calculated. The stability of the ∑3(111), ∑5(210) and ∑9(221) grain boundaries is compared. Step 7: Calculate Ba using LAMMPS software based on molecular dynamics methods. 0.875 K 0.125 F 1.875 Fluoride ion conductivity at the ∑3(111), ∑5(210), and ∑9(221) grain boundaries; by comparison, it can be seen that: Ba 0.875 K 0.125 F 1.875 The ∑9(221) grain boundary exhibits the highest fluoride ion conductivity at a temperature of 300 K, with a value of 3.68 × 10⁻⁶. -3 S / cm.

2. The method for improving the fluoride ion conductivity of BaF2 based on K doping and grain boundary modulation according to claim 1, characterized in that, In step 1, Ba 1-x K x F 2-x Perform structural screening; then calculate Ba. 1-x K x F 2-x The relationship between the formation energy and the K doping concentration x is obtained to obtain the effect of K doping concentration x on Ba 1-x K x F 2-x The influence of stability was investigated to screen for the optimal K-doped raw materials, where x = 0.03125, 0.0625, 0.09375, 0.125, and 0.15625; the specific steps are as follows: Step 1.1: Calculate the chemical potential μ corresponding to each constituent element of BaF2. i and its relative chemical potential Δμ i To obtain the region of relative chemical potential required for BaF2; Step 1.2: Based on the required relative chemical potential region of BaF2 obtained in Step 1.1, calculate and compare the BaF2 system with K-doped BaF2. 1- x K x F 2-x The formation energy was determined, and the effect of K doping concentration x on its structural stability was obtained. Step 1.3: Compare Ba according to Step 1.2 1-x K x F 2-x Based on the formation energy, K3Ba was selected as the optimal K-doped raw material, with x = 0.03125, 0.0625, 0.09375, 0.125, and 0.15625.

3. The method for improving the fluoride ion conductivity of BaF2 based on K doping and grain boundary modulation according to claim 1, characterized in that, In step 2, the ab initio molecular dynamics method is used to calculate and analyze Ba. 1-x K x F 2-x The correlation between fluoride ion conductivity and K doping concentration x at different temperatures was investigated, and Ba was designed. 0.875 K 0.125 F 1.875 It exhibits the highest fluoride ion conductivity at a temperature of 300K; the specific steps are as follows: Step 2.1: Studying fluoride ions in Ba 1-x K x F 2-x The diffusion process in the atmosphere was investigated, and its mean square displacement (MSD) curves under different temperature conditions were obtained, where x = 0.03125, 0.0625, 0.09375, 0.125, and 0.15625. Step 2.2: Based on Ba obtained in Step 2.1 1-x K x F 2-x The fluoride ion conductivity at 300K was derived from the MSD curves under different temperature conditions, where x = 0.03125, 0.0625, 0.09375, 0.125, and 0.15625.

4. The method for improving the fluoride ion conductivity of BaF2 based on K doping and grain boundary modulation according to claim 1, characterized in that, In step 3, VASP software based on first-principles methods is used to calculate Ba. 0.875 K 0.125 F 1.875 The band structure was analyzed, and its electronic conductivity was examined. The specific steps are as follows: Step 3.1: Apply the Ba obtained in step 1 0.875 K 0.125 F 1.875 Static calculations were performed; the Brillouin zone k-point grid and cutoff energy were set to 6×6×6 and 520eV, respectively, based on the Monkhorst-Pack (MP) type. Step 3.2: Use the output file obtained in step 3.1 for Ba 0.875 K 0.125 F 1.875 Band structure calculation.

5. The method for improving the fluoride ion conductivity of BaF2 based on K doping and grain boundary modulation according to claim 1, characterized in that, In step 7, the LAMMPS software, based on molecular dynamics methods, is used to calculate Ba. 0.875 K 0.125 F 1.875 Fluoride ion conductivity at the ∑3(111), ∑5(210), and ∑9(221) grain boundaries; by comparison, it can be seen that: Ba 0.875 K 0.125 F 1.875 The ∑9(221) grain boundary exhibits the highest fluoride ion conductivity at a temperature of 300 K, with a value of 3.68 × 10⁻⁶. -3 S / cm; The specific steps are as follows: Step 7.1: Investigate fluoride ions in Ba 0.875 K 0.125 F 1.875 The diffusion properties of the ∑3(111), ∑5(210) and ∑9(221) grain boundaries were determined, and their MSD curves at different temperatures were obtained. Step 7.2: Based on Ba obtained in Step 7.1 0.875 K 0.125 F 1.875 The slopes of the MSD curves of the ∑3(111), ∑5(210) and ∑9(221) grain boundaries at different temperature environments were used to derive their fluoride ion conductivity at 300K.

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