A method for improving the diffusion performance of chloride ions on monolayer Ta2N using biaxial strain

Abstract

The application discloses a method for improving the diffusion performance of chlorine ions on monolayer Ta2N by adopting biaxial strain, and mainly solves the problem of low chlorine ion diffusion performance of monolayer Ta2N as an electrode material of a chlorine ion battery. The application firstly applies different degrees of biaxial strain (epsilon) to the monolayer Ta2N, and then carries out screening and optimization on the monolayer Ta2N by adopting a first principle method; on the basis, the most stable chlorine ion adsorption site is discussed, the structure corresponding to the most stable adsorbed chlorine ion system is obtained, and it is found that when the suitable biaxial strain (epsilon=-4%) is applied to the Ta2N, the Ta2N has the optimal chlorine ion diffusion energy barrier (0.17 eV) and good thermal stability. The application provides a train of thought and a method for designing the electrode material of the chlorine ion battery with excellent chlorine ion diffusion performance.

Description

Technical Field

[0001] This invention belongs to the field of computational materials science, specifically relating to a method for improving the diffusion performance of chloride ions on monolayer Ta2N using biaxial strain. Background Technology

[0002] With the continuous exploitation and utilization of fossil fuels, humanity faces a severe energy crisis and environmental pollution problems. Energy conversion and storage technologies have become a key means to solve this problem. Among them, chloride-ion batteries have advantages such as low cost, high theoretical energy density, and high safety, and have broad application prospects. However, their poor rate performance seriously restricts the further development of chloride-ion batteries. Monolayer Ta₂N, as a typical two-dimensional transition metal nitride, has stable chemical properties, abundant reactive sites, and good electronic conductivity, and has become one of the research hotspots in the field of chloride-ion batteries. The diffusion performance of chloride ions on monolayer Ta₂N still needs to be further improved (the diffusion barrier is 0.59 eV). This invention uses a structural control method with a biaxial strain degree of -4% on monolayer Ta₂N, which significantly reduces its chloride ion diffusion barrier (the diffusion barrier is only 0.17 eV), thereby designing a monolayer Ta₂N-based chloride-ion battery electrode material with excellent rate performance. Summary of the Invention

[0003] The purpose of this invention is to provide a method for improving the diffusion performance of chloride ions on monolayer Ta2N using biaxial strain, making it a chloride ion battery electrode material with excellent chloride ion diffusion performance. The specific implementation method is carried out according to the following steps:

[0004] Step 1: Optimize the structure of single-layer Ta2N to obtain its stable structure;

[0005] Step 2: Perform band structure and density of states calculations on the stable Ta₂N structure and analyze its electronic structure;

[0006] Step 3: Apply biaxial strain (ε) of -6%≤ε≤6% to a single layer of Ta2N and analyze its mechanical properties;

[0007] Step 4: Calculate the adsorption energy of chloride ions on a monolayer Ta2N (after biaxial strain regulation of -6%≤ε≤6%);

[0008] Step 5: It was confirmed that chloride ions exhibited optimal diffusion performance on monolayer Ta2N after appropriate biaxial strain (ε = -4%).

[0009] Step 6: It was demonstrated that monolayer Ta2N, after undergoing appropriate biaxial strain (ε = -4%), exhibits good thermal stability at temperatures of 300K and 500K.

[0010] This invention addresses the poor chloride ion diffusion performance of monolayer Ta₂N by proposing a method using biaxial strain to enhance chloride ion diffusion performance on monolayer Ta₂N, thus obtaining a design scheme and technical route for achieving optimal chloride ion diffusion performance. First, the structure of monolayer Ta₂N is optimized to obtain a stable structure. Based on this, band structure and density of states calculations are performed to demonstrate its excellent electronic conductivity. Then, different degrees of biaxial strain (ε) (-6% ≤ ε ≤ 6%) are applied to monolayer Ta₂N to construct structural models for chloride ion adsorption, and the corresponding adsorption energies are calculated. Next, the gradient elastic band (CI-NEB) method was used to analyze and calculate the chloride ion diffusion path and diffusion barrier on monolayer Ta2N (after different degrees of biaxial strain, -6% ≤ ε ≤ 6%). It was confirmed that when a suitable biaxial strain (ε) is applied to Ta2N (ε = -4%), chloride ions have the best diffusion performance (chloride ion diffusion barrier is only 0.17 eV). Finally, ab initio molecular dynamics (AIMD) was used to prove that Ta2N (treated with biaxial strain of -4%) has good thermal stability at temperatures of 300 K and 500 K. Attached Figure Description

[0011] The embodiments illustrated in the accompanying drawings will be described in detail below. The accompanying drawings are merely some embodiments of the present invention. In the accompanying drawings:

[0012] Figure 1 This is an overall flowchart of a method for improving the diffusion performance of chloride ions on monolayer Ta2N using biaxial strain;

[0013] Figure 2 An optimized structure for a single-layer Ta2N (top view (a) and side view (b));

[0014] Figure 3 The band structure and density of states diagram of a single-layer Ta₂N;

[0015] Figure 4 (a) is a top view of a single-layer Ta2N structure after biaxial strain control. Figure 4 (b) shows the variation of Ta-Ta bond length with the degree of biaxial strain;

[0016] Figure 5 (a) shows the structure of a single chloride ion adsorbed on a monolayer of Ta₂N. Figure 5 (b) Chloride ions occupy the top positions of Ta atoms in a monolayer of Ta₂N (T Ta ), N atom top site (T N The variation of adsorption energy (Ead) with biaxial strain (ε) when ) and vacancy (H) are present;

[0017] Figure 6 (a) shows the optimal diffusion path of chloride ions in monolayer Ta₂N and monolayer Ta₂N after biaxial strain treatment (ε = -4%), where T N1 and T N2 H1 and H2 are two adjacent N atom top sites, and H1 and H2 are two adjacent vacancies; Figure 6 (b) shows the corresponding chloride ion diffusion barrier curve;

[0018] Figure 7 The structure of a single-layer Ta2N (with -4% biaxial strain control) after heat treatment at 300K (a) and 500K (b) and the corresponding total energy change curves over time. Detailed Implementation

[0019] This embodiment provides a method for improving the diffusion performance of chloride ions on monolayer Ta2N using biaxial strain, including the following steps:

[0020] First, structural optimization calculations were performed on monolayer Ta₂N to obtain its stable structure. Then, band structure and density of states calculations were performed on the monolayer Ta₂N to analyze its electronic conductivity. Next, different degrees of biaxial strain (ε is the biaxial strain, -6% ≤ ε ≤ 6%) were applied to the monolayer Ta₂N, and its mechanical properties were analyzed. Adsorption structures of chloride ions in monolayer Ta₂N after different biaxial strain modulations (-6% ≤ ε ≤ 6%) were constructed, and the corresponding adsorption energies were calculated. Based on this, the climbing elastic band (CI-NEB) method was used to find and calculate the optimal diffusion path and diffusion barrier of chloride ions in this system. Figure 1 This is an overall flowchart of a method for improving the diffusion performance of chloride ions on a monolayer Ta2N using biaxial strain.

[0021] Structural optimization calculations were performed on a single-layer Ta2N. Figure 2 The image shows the optimized structure of monolayer Ta₂N. Specific calculation parameters are as follows: the Perdew-Burke-Ernzerh (PBE) method with the generalized gradient approximation (GGA) is used to handle the exchange correlation energy between electrons; the projected plane wave (PAW) method is used to describe the interaction between electrons and ions; and the valence electrons of Ta, N, and Cl are considered to be 4f... 14 5d 3 6s 2 1s 2 2s 2 2p 3 and 3s 2 3p 5The plane wave cutoff energy was set to 500 eV. The Monkhorst-Pack (MP) method was used to set up a k-point grid; 2×2×1 and 4×4×1 k-point grids were used for structural optimization and electronic structure calculation of monolayer Ta₂N, respectively. The DFT-D² method was used to describe the van der Waals forces between monolayer Ta₂N and chloride ions. The force convergence accuracy and energy convergence criterion between atoms were set to [specific values ​​to be filled in]. and 10 -5 eV / atom. Furthermore, to avoid interlayer interactions, the vacuum layer thickness in the Z direction is set to...

[0022] Band structure and density of states of monolayer Ta₂N were calculated, and its electronic conductivity was analyzed. Figure 3 The band structure and density of states diagram of monolayer Ta₂N are shown below. Figure 3 It can be seen that the band structure and density of states of monolayer Ta₂N intersect with its Fermi level, indicating that it has metallic properties and thus excellent electronic conductivity, which is conducive to the rapid transport of electrons within it.

[0023] According to the definition of biaxial strain in equation (2-1), a biaxial strain (ε) is applied to monolayer Ta2N, with a biaxial strain range of -6% ≤ ε ≤ 6%. The mechanical properties of this material are further analyzed. First, hexagonal Ta2N is transformed into tetragonal Ta2N, and then different degrees of biaxial strain (-6% ≤ ε ≤ 6%) are applied to it (e.g., ...). Figure 4 (a) Further structural optimization of the tetragonal Ta₂N subjected to biaxial strain was performed to further elucidate the variation of Ta-Ta bond length with biaxial strain (ε). Calculation results show that the Ta-Ta bond length shortens with compressive strain and lengthens with compressive strain, exhibiting a linear variation (e.g., ...). Figure 4 (b) is shown.

[0024]

[0025] In equation (2-1), a0 and b0 are the lattice constants of monolayer Ta2N; a and b are the lattice constants of monolayer Ta2N after biaxial strain.

[0026] After monolayer Ta₂N was subjected to different degrees of biaxial strain (-6% ≤ ε ≤ 6%), three different structures with different chloride ion adsorption characteristics were constructed using Materials Studio software (e.g., Figure 5 (a) shows that the three chlorine adsorption sites are as follows: the position directly above Ta (T Ta The position directly above N (T) N The position (H) is directly above the center of the triangle formed by the three Ta atoms. The chloride ion adsorption energy (E) of a monolayer Ta₂N (after varying degrees of biaxial strain modulation) is calculated according to equation (2-2).ad The calculation results are as follows: Figure 5 As shown in (b).

[0027]

[0028] In equation (2-2), and E represents the total energy of the monolayer Ta₂N adsorption system for chloride ions and the total energy of a single Ta₂N layer, respectively. Cl That is the energy of a single chlorine atom.

[0029] The diffusion barrier is one of the key indicators for evaluating whether an electrode material has excellent rate performance, and it is also the core innovation of this invention. Therefore, based on the monolayer Ta₂N chloride ion adsorption system regulated by biaxial strain (-6% ≤ ε ≤ 6%), the optimal chloride ion diffusion path is further searched and its diffusion barrier is calculated using the climbing elastic band (CI-NEB) method. At this point, two adjacent optimal adsorption sites of chloride ions in the monolayer Ta₂N are selected as the initial and final states of the chloride ion diffusion path, and the relationship of the number of transition states (N) is obtained according to equation (2-3).

[0030] N = d / Δx (2-3)

[0031] Where d is the interatomic distance; Δx is the average distance of the transition states; here, the value of Δx is taken as... The number of transition states is 4.

[0032] Four transition state structures were inserted between the initial and final states, forming the chloride ion diffusion pathway. These four transition state structures, along with the initial and final states, were adjusted using Materials Studio software. Based on this, the chloride ion diffusion pathway was optimized, and its corresponding chloride ion diffusion energy barriers were compared.

[0033] After completing the transition state optimization calculation, the output file of the diffusion barrier was processed. Different chloride ion diffusion pathways were considered to obtain the chloride ion diffusion pathways and diffusion barriers of monolayer Ta₂N after different biaxial strains (-6% ≤ ε ≤ 6%). Since the optimal adsorption site of chloride ions on monolayer Ta₂N is closely related to the degree of biaxial strain, monolayer Ta₂N with different degrees of biaxial strain regulation exhibits different chloride ion diffusion pathways: when the biaxial strain (ε) is -6% ≤ ε ≤ -3%, chloride ions diffuse from the top site of the N atom (T... N It passes through a vacancy (H) and reaches the top position of the adjacent N atom (T). N (T) N →H→T N When the biaxial strain (ε) is -2% ≤ ε ≤ 6%, chloride ions move from vacancies (H) through T N Position, reaching the adjacent empty position (H)(T)H →T N →T H When monolayer Ta2N is subjected to a suitable biaxial strain (-4%), chloride ions exhibit the lowest diffusion barrier (0.17 eV). Therefore, it is confirmed that applying a suitable biaxial strain to monolayer Ta2N can significantly improve its chloride ion diffusion performance.

[0034] The effects of two different biaxial strain control conditions (ε = -4% and ε = 0%) on the diffusion path and diffusion barrier of chloride ions on monolayer Ta₂N were further compared. The calculation results are as follows: Figure 6 (a) and Figure 6 As shown in (b). From Figure 6 (b) It can be seen that after appropriate biaxial strain treatment (ε = -4%), the chloride ion diffusion barrier on monolayer Ta2N is much smaller than that on monolayer Ta2N (ε = 0%) (0.17 eV vs. 0.59 eV). Therefore, biaxial strain regulation is an effective method to significantly improve the chloride ion diffusion performance on monolayer Ta2N.

[0035] Furthermore, thermal stability is also an important indicator for evaluating the performance of electrode materials. Therefore, the thermal stability of monolayer Ta₂N after optimal biaxial strain (ε = -4%) treatment at temperatures of 300 K and 500 K was studied using ab initio molecular dynamics (AIMD). The structures after these heat treatments were obtained, and the variation of its total energy over time was also presented. The results are as follows: Figure 7 As shown in (a) and 7(b). From Figure 7 As can be seen from (a) and 7(b), after heat treatment of monolayer Ta2N (at temperatures of 300K and 500K respectively), its structure did not undergo significant distortion, and it always maintained a stable distribution over time. This indicates that Ta2N has good thermal stability after being subjected to optimal biaxial strain (ε = -4%).

[0036] Finally, it is necessary to state that the specific embodiments described above are merely illustrative 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 enhancing the diffusion performance of chloride ions on a monolayer of Ta2N using biaxial strain, characterized by, The method comprises the following steps: Step 1: structure optimization of single-layer Ta2N to obtain its stable structure; Step 2: band and state density calculation of single-layer Ta2N structure to analyze its electronic structure; Step 3: biaxial strain ε of-6%≤ε≤6% is applied to single-layer Ta2N to analyze its mechanical properties, in which, according to formula (1-1), biaxial strain ε is defined, biaxial strain ε is applied to Ta2N, and the mechanical properties of single-layer Ta2N are analyzed; the specific steps are as follows: In formula (1-1), a0 and b0 are the lattice constants of single-layer Ta2N; a and b are the lattice constants of single-layer Ta2N after biaxial strain; Step 3.1: according to step 1, hexagonal Ta2N is converted into tetragonal Ta2N, and then different degrees of biaxial strain are applied to the tetragonal Ta2N, at this time-6%≤ε≤6%; Step 3.2: structure optimization is performed on the tetragonal Ta2N after biaxial strain in step 3.1, and the bond length is measured; Step 4: the most stable structure of single-layer Ta2N after biaxial strain is analyzed, and the corresponding adsorption energy is calculated; Step 5: after single-layer Ta2N is treated by different biaxial strain regulation, the climbing elastic band (CI-NEB) method is used to search for the optimal diffusion path of chloride ion on single-layer Ta2N, and it is found that when single-layer Ta2N is treated by appropriate biaxial strain ε, chloride ion has the best diffusion performance on it, at this time ε=-4%; Step 6: the ab initio molecular dynamics (AIMD) method is used to study the thermal stability of Ta2N treated by biaxial strain ε at temperatures of 300K and 500K, respectively, at this time ε=-4%.

2. The method of claim 1, wherein the biaxial strain is applied to enhance the diffusion of the chloride ions in the monolayer of Ta2N. In the step 1, the single-layer Ta2N is structure optimized to obtain its most stable structure.

3. The method of claim 1, wherein the biaxial strain is applied to enhance the diffusion of the chloride ions in the monolayer of Ta2N. In the step 2, the single-layer Ta2N is subjected to band and state density calculation to analyze its electronic structure; the specific steps are as follows: Step 2.1: the stable Ta2N structure is subjected to static self-consistent calculation by using the Monkhorst-Pack (MP) type 4*4*1 Brillouin zone k-point grid; Step 2.2: the output file obtained by the static self-consistent calculation in step 2.1 is used for band and state density calculation of single-layer Ta2N.

4. The method of claim 1, wherein the biaxial strain is applied to enhance the diffusion of the chloride ions in the monolayer of Ta2N. In step 4, the single-layer Ta2N is subjected to different degrees of biaxial strain regulation, and then based on the structure of the adsorbed chloride ion system, the corresponding chloride ion adsorption energy (E ad ) of the single-layer Ta2N is calculated according to formula (1-2): In formula (1-2), and Etotalis the total energy of the single layer of Ta2N before and after the adsorption of the chloride ion, respectively Cl Eclis the energy of a single chlorine atom.

5. The method of claim 1, wherein the biaxial strain is applied to enhance the diffusion of the chloride ions in the monolayer of Ta2N. In the step 5, the climbing elastic band (CI-NEB) method is used to search for the optimal diffusion path of chloride ion on single-layer Ta2N and its biaxial strain system respectively; the specific steps are as follows: Step 5.1: the most stable adsorption site of chloride ion on single-layer Ta2N is obtained in step 4, and the adjacent equivalent chloride ion adsorption site is further searched; Step 5.2: the two adjacent equivalent chloride ion adsorption sites are set as the initial state and the final state of the chloride ion diffusion path respectively, and the distance between them is measured; then according to the relationship between the distance and the transition state, the number of inserted transition states is obtained, so as to design the diffusion path of chloride ion on single-layer Ta2N, at this time single-layer Ta2N is treated by biaxial strain ε, -6%≤ε≤6%. Step 5.3: The uphill elastic band (CI-NEB) method is used to optimize the diffusion path of chloride ions on monolayer Ta2N and obtain the corresponding chloride ion diffusion energy barrier, at this time the monolayer Ta2N is subjected to biaxial strain ε treatment, -6%≤ε≤6%.

6. The method of claim 1, wherein the biaxial strain is applied to enhance the diffusion of the chloride ions in the monolayer of Ta2N. In the step 6, the ab initio molecular dynamics (AIMD) method is used to prove that the Ta2N after biaxial strain treatment has good thermal stability at temperatures of 300K and 500K, at this time ε=-4%.

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