Method for calculating crystal structure of layered oxide-based sodium ion battery positive electrode material

Abstract

The invention provides a method for calculating a crystal structure of a layered oxide-based sodium ion battery positive electrode material, which comprises the following steps: constructing an initial crystal structure model, selecting functional calculation parameters according to the model, and performing iterative calculation on the initial crystal structure model through a functional calculation module to obtain a crystal structure optimization model, obtaining structure parameters and characteristic parameters of the crystal structure optimization model through property calculation; structural parameters and characteristic parameters of the crystal structure optimization model are checked and corrected through an experimental comparison method. According to the simulation model calculation method embedded with the functional calculation module, the problems of long consumed time, high cost, high requirements on sample quality and the like of a traditional experiment means in crystal structure determination are solved based on the density functional theory, and meanwhile, the defects of an existing calculation method in precision and efficiency are overcome; and more accurate and efficient theoretical support is provided for design, optimization and performance prediction of the sodium ion battery positive electrode material.

Description

Technical Field

[0001] The present invention relates to the technical field of crystal materials, and in particular to a method for calculating the crystal structure of a layered oxide-based sodium ion battery positive electrode material. Background Art

[0002] With the continuous growth of global energy demand, the development of high-performance, low-cost energy storage batteries has become a research hotspot in the fields of materials science and energy. Among the various energy storage technologies, battery energy storage systems have attracted widespread attention due to their high efficiency, flexibility, and scalability. Among them, sodium-ion batteries (SIBs), as a potential alternative technology, have become a research hotspot in recent years due to their advantages such as abundant resources, low cost, and similar operating principles to lithium-ion batteries. Sodium-ion batteries have broad application prospects in large-scale energy storage systems, such as smart grids and renewable energy storage.

[0003] Layered metal oxides, as an important class of sodium-ion battery cathode materials, have high specific capacity and specific energy, and can provide higher battery energy density. Their layered structure is conducive to the diffusion of sodium ions within the material, improving the battery's cycle stability and cycle life. In addition, some layered metal oxides have high electrical conductivity, which is beneficial to improving the battery's discharge performance and charging rate. However, during the insertion / extraction process of sodium ions, some phase transitions can lead to severe volume changes, local structural distortion, structural damage, and electrochemical performance degradation, thereby affecting the battery's cycle stability and rate performance. Therefore, it is necessary to perform computational analysis on the crystal structure of existing layered oxide cathode materials, summarize the laws, and predict and guide the synthesis of new sodium-ion battery cathode materials with high stability through high-throughput calculations.

[0004] In summary, it is also necessary to provide a method for calculating the crystal structure of layered oxide-based sodium ion battery positive electrode materials based on density functional theory to solve the problems existing in the existing technology and achieve accurate calculation and optimization of the crystal structure of the positive electrode material. Summary of the Invention

[0005] The present invention addresses the problems existing in the prior art and provides a method for quickly and accurately calculating the crystal structure of layered oxide-based sodium ion battery cathode materials.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A method for calculating the crystal structure of a layered oxide-based sodium ion battery cathode material mainly comprises the following steps:

[0008] Construct an initial crystal structure model based on the material characteristics of layered oxide-based sodium-ion battery cathode materials;

[0009] Configuring a simulation environment for functional calculation based on the initial crystal structure model;

[0010] Selecting functional calculation parameters according to the initial crystal structure model, and performing iterative calculation on the initial crystal structure model through a functional calculation module to obtain a crystal structure optimization model;

[0011] Based on the crystal structure optimization model, obtaining structural parameters and characteristic parameters of the crystal structure optimization model through property calculation;

[0012] Verifying the structural parameters and characteristic parameters of the crystal structure optimization model by experimental comparison method;

[0013] When a deviation occurs in the verification result and the deviation is greater than a threshold, the crystal structure optimization model is corrected by a parameter adjustment method.

[0014] Optionally, the functional calculation parameters include at least an exchange-correlation functional, a plane wave cutoff energy, an electron smearing parameter, and a k-point grid.

[0015] Optionally, the cutoff energy value of the plane wave cutoff energy is determined by a convergence test.

[0016] Optionally, in the k-point grid, the k-point grid density is set according to the crystal symmetry and calculation accuracy of the layered oxide-based sodium ion battery positive electrode material.

[0017] Optionally, the functional calculation module is configured with a molecular dynamics simulation algorithm and supports at least GGA, meta-GGA and hyper-GGA exchange-correlation functionals;

[0018] In the simulation environment, at least one of the PBE functional, the SCAN functional and the HSE functional is configured.

[0019] Optionally, the execution steps of the functional calculation module include:

[0020] First, the calculation parameters and crystal structure information of the initial crystal structure model are read, and the degree of freedom adjustment algorithm is used to release the crystal degrees of freedom;

[0021] Then, according to the information of the initial crystal structure model, the crystal type is set, and an electronic self-consistent iterative calculation is performed, and after convergence, the atomic force and stress tensor are calculated by a mechanical analysis method;

[0022] Afterwards, the threshold judgment algorithm is used to determine whether the balance is reached. If the balance is not reached, the cycle continues after adjustment through the data update strategy, and the equilibrium state is calculated after the balance is reached.

[0023] Optionally, the goal of the iterative calculation is to minimize the total energy of the system.

[0024] Optionally, the property calculation includes:

[0025] The magnetic properties and elastic properties of the crystal structure optimization model are calculated using the first principle algorithm in the density functional theory algorithm, and the thermodynamic properties of the crystal structure optimization model are calculated using the molecular dynamics algorithm.

[0026] Optionally, the structural parameters of the crystal structure optimization model include electronic band structure, state density and charge density;

[0027] The characteristic parameters of the crystal structure optimization model include conductivity, redox potential, magnetic moment, magnetic susceptibility, elastic modulus, material hardness, phase transition conditions and thermal stability.

[0028] Optionally, the experimental comparison method includes the following steps:

[0029] Comparing the structural parameters and characteristic parameters of the crystal structure optimization model with the corresponding experimental data;

[0030] The absolute value of the difference comparison is the deviation.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The simulation model calculation method embedded in the functional calculation module of the present invention solves the limitations of traditional experimental methods in crystal structure determination, such as long time consumption, high cost and high sample quality requirements, based on density functional theory. At the same time, it overcomes the shortcomings of existing calculation methods in accuracy and efficiency, and provides more accurate and efficient theoretical support for the design, optimization and performance prediction of sodium-ion battery positive electrode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0034] Figure 1 A flow chart of a method in a specific embodiment of the present invention;

[0035] Figure 2 This is a flowchart of the execution of the functional calculation module in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0036] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0037] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0038] In the description of the present invention, “plurality” means two or more, unless otherwise clearly defined.

[0039] It is worth noting that the methods used in the present invention are all conventional methods unless otherwise specified; the raw materials and devices used are all conventional commercially available products, and their sources are not specifically limited unless otherwise specified.

[0040] like Figure 1 As shown, the present application provides a method for calculating the crystal structure of a layered oxide-based sodium ion battery positive electrode material, which mainly includes the following steps:

[0041] It should be noted that for the convenience of description, the method steps are described in a certain order. Those skilled in the art may replace or perform some steps simultaneously as needed, and this should not be understood as a limitation of the present application.

[0042] 1. Model building: Construct an initial crystal structure model based on the material characteristics of layered oxide-based sodium-ion battery cathode materials;

[0043] First, based on the chemical composition and crystal structure characteristics of the layered oxide-based sodium-ion battery cathode material, the corresponding initial crystal structure model is constructed using crystal structure modeling software. When constructing the model, it is necessary to consider information such as the material's lattice parameters, atomic coordinates, and chemical bonding to ensure that the model can accurately reflect the structural characteristics of the actual material. For example, for P2-type and O3-type layered oxides, the corresponding models are constructed based on their specific stacking sequence and sodium content, and the arrangement of transition metal ions and oxygen ions is accurately set.

[0044] Afterwards, a simulation environment for functional calculations is configured based on the initial crystal structure model; this application uses VASP software to perform simulations based on density functional theory. The exchange-correlation functional is a key factor in density functional theory calculations, so this application can use appropriate functionals such as the PBE functional in the generalized gradient approximation (GGA), the strongly constrained appropriate normalization (SCAN) functional, and the Heyd-Scuseria-Ernzerhof (HSE) functional.

[0045] 2. Select calculation parameters: Select functional calculation parameters based on the initial crystal structure model;

[0046] Determine the parameters required for density functional theory calculations, including the exchange-correlation functional, plane wave cutoff energy, electron smearing parameters, and k-point mesh. The plane wave cutoff energy is used to control the accuracy and computational effort of the calculation, and the appropriate cutoff energy value is determined through convergence testing. The electron smearing parameters are used to manipulate the distribution of electrons in the band structure. The appropriate smearing method and parameter values are selected based on the electronic structure of the material. The k-point mesh is used to sample the Brillouin zone. The appropriate k-point mesh density is selected based on the material's crystal symmetry and the required computational accuracy.

[0047] 3. Embedded functional calculation module: The functional calculation module is equipped with a molecular dynamics simulation algorithm and supports at least GGA, meta-GGA and hyper-GGA exchange-correlation functionals;

[0048] The functional calculation module is embedded into the VASP software. The functional calculation module has a wide range of functional applicability and supports a variety of exchange-correlation functionals such as GGA, meta-GGA and hyper-GGA. It can directly deal with the lattice expansion and contraction problems of sodium ion battery cathode materials and optimize the atomic positions. Figure 2 As shown, the execution steps of the functional calculation module include:

[0049] First, the calculation parameters (INCAR file) and crystal structure information (POSCAR file) of the initial crystal structure model are read, and the degree of freedom adjustment algorithm is used to release the crystal degrees of freedom; specifically, under the software and hardware operating conditions of this embodiment, ISIF=3 (internal coordinates, shape and volume) is set; the ISIF (ion step and stress control) value in the INCAR file is 3, indicating that the lattice constant and atomic position are allowed to change freely, releasing all degrees of freedom, and having the function of automatically calculating the crystal unit to its equilibrium shape, which can simulate the equilibrium volume lattice parameters while maintaining symmetry.

[0050] Then, given the known lattice parameters and atomic positions, the crystal type is set and an iterative calculation of the electron self-consistent field (ESF) is performed. Under the hardware and software operating conditions of this embodiment, the setting object is the INCAR control parameter COTYPE. For example, if the initial condition is COTYPE = xx, then COTYPE = 3n (n = 1, 2, 3, 4, 5, 6) is set, corresponding to seven 3D crystal systems; while COTYPE = 2n (n = 1, 2, 3, 4) corresponds to four 2D crystal systems. Once the SCF converges, the atomic forces and stress tensors are calculated using mechanical analysis. Specifically, when the SCF converges, the forces on each atom and the stress tensor of each element are calculated.

[0051] A threshold-based algorithm then determines whether equilibrium has been reached. If not, the cycle continues after adjusting the data update strategy. Specifically, if the force per atom or the stress tensor per cell does not reach the convergence threshold, the selective cells are calculated and the matrix updated. This entire calculation process is automated, eliminating the need to manually switch applications to view and input calculation results. After equilibrium is reached, the equilibrium state is calculated.

[0052] By embedding the functional computing module, the entire high-throughput computing process only requires calling the VASP software, without the need for data conversion between different programs, greatly improving the convenience and efficiency of the calculation.

[0053] 4. Perform structural optimization: Perform iterative calculations on the initial crystal structure model through the functional calculation module to obtain the crystal structure optimization model;

[0054] The initial crystal structure model was geometrically optimized using VASP software embedded with a functional calculation module. During the optimization process, iterative calculations were performed to minimize the total energy of the system, resulting in an optimized crystal structure model. During the optimization process, changes in structural parameters such as lattice parameters, atomic positions, bond lengths, and bond angles were monitored to ensure that the optimized structure possessed a reasonable geometry and stable electronic structure. The functional calculation module accurately calculated the expansion and contraction of the lattice, optimized atomic positions, and provided an accurate structural model for subsequent property calculations.

[0055] 5. Calculation of crystal structure properties: Based on the crystal structure optimization model, the structural parameters and characteristic parameters of the crystal structure optimization model are obtained through property calculation;

[0056] The crystal structure optimization model is further calculated for its properties. The first-principles algorithm in the density functional theory algorithm is used to calculate the magnetic properties and elastic properties of the crystal structure optimization model, and then the molecular dynamics algorithm is used to calculate the thermodynamic properties of the crystal structure optimization model. These include electronic structure, magnetic properties, elastic properties, thermodynamic properties, etc. By analyzing information such as the electronic energy band structure, state density, and charge density distribution, key properties such as the conductivity and redox potential of the material can be understood. At the same time, magnetic parameters such as the magnetic moment and magnetic susceptibility of the material, as well as mechanical performance indicators such as elastic modulus and material hardness are calculated to evaluate the stability and reliability of the material in practical applications. In addition, the phase transition conditions of the material, that is, the phase transition behavior under different temperature and pressure conditions, and thermal stability can be predicted through thermodynamic property calculations.

[0057] 6. Result analysis and verification: The structural parameters and characteristic parameters of the crystal structure optimization model are verified through experimental comparison method; when the verification results deviate and the deviation is greater than the threshold, the crystal structure optimization model is corrected through parameter adjustment method;

[0058] The calculated crystal structure and property results are compared and analyzed with experimental data to verify the accuracy and reliability of the calculation method. The structural parameters and characteristic parameters of the crystal structure optimization model are compared with the corresponding experimental data; the absolute value of the difference comparison is the deviation. If there is a large deviation between the calculated results and the experimental results, which is greater than the preset threshold, the model and calculation parameters need to be adjusted and optimized, and the calculation needs to be repeated until the results are consistent with the experiment. Through in-depth analysis of the calculation results, the intrinsic relationship between the crystal structure and performance of layered oxide-based sodium-ion battery positive electrode materials is revealed, providing theoretical guidance for the design and optimization of materials.

[0059] Example 1;

[0060] 1) Model establishment: Based on P2 type sodium layered oxide Na 0.67 Ni 0.5 Mn 0.5 Taking O2 as an example, the Crystal Builder module in Materials Studio software is used to build an initial crystal structure model based on its crystal structure data. Set the lattice parameters The atomic coordinates are Na + (0, 0, 0.333), Ni 2+ (0, 0, 0), Mn 4+ (0, 0, 0.5) and O 2- (0, 0, 0.25), and taking into account appropriate lattice distortion and atomic displacement.

[0061] 2) Select the calculation parameters: Use the PBE exchange-correlation functional, set the plane wave cutoff to 400 eV, use the Gaussian method for electron smearing, and set the smearing width to 0.1 eV. Use the Monkhorst-Pack scheme for the k-point grid, set to 4 × 4 × 2.

[0062] 3) Embed the functional calculation module: Embed the module into the VASP software to ensure that the module can run normally and support the selected exchange-correlation functional.

[0063] 4) Structural optimization: Import the constructed crystal structure model into VASP software embedded with functional calculation module to optimize the geometric structure. Set the energy convergence standard to 10 -5 eV, the force convergence criterion is 0.01 The step size is During the optimization process, the changes in lattice parameters, atomic positions and total energy are monitored in real time. After multiple iterative calculations, the optimized crystal structure is finally obtained. The results are basically consistent with the experimental data. The functional calculation module effectively handles the expansion and contraction of the lattice during the optimization process and optimizes the atomic positions.

[0064] 5) Calculation of crystal structure properties: The electronic structure of the optimized crystal structure was calculated to obtain the electronic band structure and state density distribution. The results show that the material has a wide conduction band and valence band near the Fermi level, and has good conductivity. At the same time, the magnetic properties of the material were calculated and found to be paramagnetic, and the magnetic moment mainly comes from Ni 2+ and Mn 4+ In addition, the mechanical properties of the material, such as elastic modulus and hardness, were calculated to evaluate its stability in practical applications.

[0065] 6) Results Analysis and Verification: The calculated crystal structure and properties were compared with experimental data, demonstrating good consistency. For example, the optimized lattice parameters were within 0.1% of the experimentally measured values, and the calculated electronic structure and magnetic properties were also consistent with experimental observations. This validates the accuracy and reliability of the method used in this example and provides strong support for subsequent material design and performance optimization.

[0066] Example 2;

[0067] 1) Model establishment: O3 type sodium layered oxide Na 0.67 Ni 0.33 Mn 0.67 Taking O2 as an example, the initial crystal structure model was constructed using the Crystal Builder module using a method similar to that in Example 1. The atomic coordinates are Na + (0, 0, 0.167), Ni 2+ (0, 0, 0.333), Mn 4+ (0, 0, 0.667) and O 2- (0, 0, 0.25).

[0068] 2) Select the calculation parameters: Also use the PBE exchange-correlation functional, set the plane wave cutoff to 400 eV, use the Methfessel-Paxton method for electron smearing, and set the smearing width to 0.2 eV. Use the Monkhorst-Pack scheme for the k-point grid, set to 4 × 4 × 3.

[0069] 3) Embed the functional calculation module: Embed the module into the VASP software to ensure that the module can run normally and support the selected exchange-correlation functional.

[0070] 4) Structural optimization: Import the crystal structure model into VASP software embedded with functional calculation module to optimize the geometric structure. The optimized lattice parameters The results are in good agreement with the experimental data. The module effectively handles the expansion and contraction of the lattice during the optimization process and optimizes the atomic positions.

[0071] 5) Calculation of crystal structure properties: The electronic structure and magnetic properties of the material were calculated, and it was found that it had an electronic band structure and magnetic characteristics different from those in Example 1. The thermodynamic properties of the material were further analyzed, and its phase transition behavior and thermal stability at different temperatures were predicted.

[0072] 6) Results Analysis and Verification: Comparison of the calculated results with experimental data verified the applicability and accuracy of this method in the study of different types of layered oxide-based cathode materials for sodium-ion batteries. Through calculations and analysis of different materials, the mechanism by which crystal structure influences material properties was explored in depth, providing a theoretical basis for the development of high-performance cathode materials for sodium-ion batteries.

[0073] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A method for calculating the crystal structure of a layered oxide-based sodium ion battery cathode material, characterized by: The steps include: Construct an initial crystal structure model based on the material characteristics of layered oxide-based sodium-ion battery cathode materials; Configuring a simulation environment for functional calculation based on the initial crystal structure model; Selecting functional calculation parameters according to the initial crystal structure model, and performing iterative calculation on the initial crystal structure model through a functional calculation module to obtain a crystal structure optimization model; Based on the crystal structure optimization model, obtaining structural parameters and characteristic parameters of the crystal structure optimization model through property calculation; Verifying the structural parameters and characteristic parameters of the crystal structure optimization model by experimental comparison method; When a deviation occurs in the verification result and the deviation is greater than a threshold, the crystal structure optimization model is corrected by a parameter adjustment method.

2. The method for calculating the crystal structure of a layered oxide-based sodium ion battery cathode material according to claim 1, wherein: The functional calculation parameters include at least exchange-correlation functional, plane wave cutoff energy, electron smearing parameter and k-point grid.

3. The method for calculating the crystal structure of a layered oxide-based sodium ion battery cathode material according to claim 2, wherein: The cutoff energy value of the plane wave cutoff energy is determined by a convergence test.

4. The method for calculating the crystal structure of a layered oxide-based sodium ion battery cathode material according to claim 2, wherein: In the k-point grid, the k-point grid density is set according to the crystal symmetry and calculation accuracy of the layered oxide-based sodium ion battery positive electrode material.

5. The method for calculating the crystal structure of a layered oxide-based sodium ion battery cathode material according to claim 1, wherein: The functional calculation module is configured with a molecular dynamics simulation algorithm and supports at least GGA, meta-GGA and hyper-GGA exchange-correlation functionals; In the simulation environment, at least one of the PBE functional, the SCAN functional and the HSE functional is configured.

6. The method for calculating the crystal structure of a layered oxide-based sodium ion battery cathode material according to claim 5, characterized in that: The execution steps of the functional calculation module include: First, the calculation parameters and crystal structure information of the initial crystal structure model are read, and the degree of freedom adjustment algorithm is used to release the crystal degrees of freedom; Then, according to the information of the initial crystal structure model, the crystal type is set, and an electronic self-consistent iterative calculation is performed, and after convergence, the atomic force and stress tensor are calculated by a mechanical analysis method; Afterwards, the threshold judgment algorithm is used to determine whether the balance is reached. If the balance is not reached, the cycle continues after adjustment through the data update strategy, and the equilibrium state is calculated after the balance is reached.

7. The method for calculating the crystal structure of a layered oxide-based sodium ion battery cathode material according to claim 1, wherein: The goal of the iterative calculation is to minimize the total energy of the system.

8. The method for calculating the crystal structure of a layered oxide-based sodium ion battery cathode material according to claim 1, wherein: The property calculations include: The magnetic properties and elastic properties of the crystal structure optimization model are calculated using a first-principle algorithm in a density functional theory algorithm, and the thermodynamic properties of the crystal structure optimization model are calculated using a molecular dynamics algorithm.

9. The method for calculating the crystal structure of a layered oxide-based sodium ion battery cathode material according to claim 8, characterized in that: The structural parameters of the crystal structure optimization model include electronic band structure, state density and charge density; The characteristic parameters of the crystal structure optimization model include conductivity, redox potential, magnetic moment, magnetic susceptibility, elastic modulus, material hardness, phase transition conditions and thermal stability.

10. The method for calculating the crystal structure of a layered oxide-based sodium ion battery cathode material according to claim 9, characterized in that: The experimental comparison method comprises the following steps: Comparing the structural parameters and characteristic parameters of the crystal structure optimization model with the corresponding experimental data; The absolute value of the difference comparison is the deviation.

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