Preparation method and performance prediction method of heterostructure sodium-ion battery anode material

Abstract

This invention belongs to, but is not limited to, the field of electrochemical energy storage technology. It discloses a BNG / MoP2Ge2O2 heterostructure sodium-ion battery anode material and its performance prediction method, including the establishment of models for two-component monolayer structures and the BNG / MoP2Ge2O2 heterostructure; prediction of performance changes such as characteristic dimensions, adsorption energy, electronic properties, diffusion kinetics, open-circuit voltage, and theoretical capacity of the monolayer and heterostructure. Compared with the two-component model, the heterostructure exhibits better structural stability, electronic conductivity, higher adsorption capacity, diffusion rate, and storage capacity. Simultaneously, it solves the problems of MoP2Ge2O2 monolayer volume expansion and insufficient diffusion kinetics between two monolayers, making it suitable as a sodium-ion battery anode. This provides a new design approach for the development of high-performance SIB anode materials and will have theoretical guiding significance for the application of two-dimensional MA2Z4 materials in SIBs.

Description

Technical Field

[0001] This invention belongs to, but is not limited to, the field of electrochemical energy storage technology, and particularly relates to a BNG / MoP2Ge2O2 heterostructure sodium-ion battery anode material and its performance prediction method. Background Technology

[0002] With the increasing prominence of environmental pollution and energy crises, promoting and developing energy transition and large-scale energy storage technologies has become an urgent priority. Electrochemical energy storage technology, with its advantages of flexible performance control, minimal environmental limitations, and fast response speed, has become one of the most promising clean energy sources. Since its introduction, lithium-ion batteries have gradually gained dominance in the market for portable electronic devices, electric vehicles, and large-scale energy storage grid commercial applications due to their advantages such as high operating potential, long cycle life, and high energy density. However, the scarcity and uneven distribution of lithium resources have not only led to the continuous rise in the price of lithium-ion batteries, but also made their energy density increasingly unable to meet the growing demands of various fields. Therefore, exploring other new types of batteries that can replace lithium-ion batteries is crucial for the future development of the electrochemical field. Among the many alkali metal ion battery systems, sodium-ion batteries have similar electrochemical properties to lithium-ion batteries, and sodium is abundant in the Earth's crust and relatively inexpensive. Therefore, sodium-ion batteries are the most promising candidate to replace lithium-ion batteries as an energy storage technology. However, compared to lithium ions, sodium's larger atomic mass and ionic radius result in lower energy density in sodium-ion batteries and structural collapse of electrode materials. Furthermore, the larger ionic radius restricts diffusion kinetics during migration.

[0003] Anode materials are a crucial structural component of alkali metal-ion batteries, directly determining the battery's theoretical capacity, cycle life, and rate performance. They can be primarily categorized into intercalation-type, conversion-type, and alloying-type anode materials. Firstly, intercalation-type anode materials demonstrate significant potential in sodium-ion batteries due to their high structural stability, cycle stability, low cost, and relatively high safety. As a typical intercalation-type anode material, graphite, which has been successfully commercialized in lithium-ion batteries, remains the preferred choice for sodium-ion battery anodes. However, when graphite is used as an anode in sodium-ion batteries, the sodium-intercalated graphite compound is less stable and only provides a very low reversible theoretical capacity (~35 mAh / g), making it unsuitable for use as an anode material. Compared to graphite, soft carbon offers improved electrochemical performance as an anode material, but its reversible specific capacity and rate performance remain limited. With the development of sodium-ion batteries, hard carbon, due to its layered structure, disordered cross-linked pore structure, and internal defects, can provide abundant active centers for sodium-ion storage, thus becoming a promising anode material. However, when hard carbon is used as an anode, its limited specific capacity, low conductivity, and slow diffusion kinetics severely affect the electrode's energy, power density, and rate performance. Although these intercalated electrode materials can exhibit long-term cycling stability, the number of alkali metal ions intercalated is limited, resulting in a low specific capacity. Conversion-type anode materials have attracted considerable attention in the sodium-ion battery field due to their abundant resources, unique two-dimensional layered structure, high theoretical specific capacity, and large interlayer distance. Common conversion-type anode materials include transition metal oxides, sulfides, selenides, phosphides, and nitrides. Furthermore, these anode materials store sodium through redox reactions or conversion reactions with sodium. The conversion reaction involves multi-electron reactions, providing a relatively high theoretical capacity. However, when used as electrodes, these materials generate significant internal stress during cycling, generally have low initial coulombic efficiency, and exhibit poor electronic conductivity, typically resulting in poor rate and cycling performance. Alloy-based anode materials, including Group IV and Group V elements, exhibit advantages such as excellent sodium storage capacity, low operating potential, and high electronic conductivity due to the involvement of multiple electrons during alloying / dealloying, and are considered one of the promising anode materials for sodium-ion batteries. However, compared to other anode materials, the application of alloy-based anodes in sodium-ion batteries is not widespread, mainly because the huge volume expansion generated during the sodium formation reaction leads to rapid fracture and deactivation of the electrode material from the current collector surface, thus reducing cycle performance and capacity decay. Simultaneously, the large volume change causes the alloy nanomaterials to self-aggregate, resulting in deactivation of the active components and capacity degradation. Furthermore, the high production cost of this single anode material further hinders the widespread application of alloy-based sodium storage anode materials.

[0004] However, sodium-ion batteries still face challenges in overcoming poor cycle stability and relatively low energy density before transitioning from laboratory applications to practical commercial use. Therefore, there is an urgent need to develop and design novel electrode materials that offer structural stability, high capacity, high rate capability, and long lifespan to further advance the commercialization of sodium-ion batteries. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a BNG / MoP2Ge2O2 heterostructure sodium-ion battery anode material and its performance prediction method. The method uses the CASTEP module with first-principles calculations under the density functional theory framework for modeling and property calculation, and predicts the changes in the geometric structure, adsorption energy, electronic properties and electrochemical properties of BNG, MoP2Ge2O2 monolayers and their heterostructures.

[0006] This invention is achieved as follows: a method for preparing a BNG / MoP2Ge2O2 heterostructure sodium-ion battery anode material includes:

[0007] Step 1: Using bulk graphene imported from Material Studio (MS), an intrinsic graphene (G) monolayer structure model was established. B and N atoms were used to replace C atoms in different six-membered rings for doping (configuration II) to construct a B and N co-doped graphene (BNG) structure model.

[0008] Step two: Based on the MoS2 phase structure imported from MS software, the corresponding MoS2 monolayer structure is obtained through cross-sectioning. A MoP2Ge2O2 monolayer model is then established using an atomic transmutation strategy. The atomic transmutation strategy is a method for designing and constructing novel material structures by replacing or reconstructing the types and arrangements of atoms in a material. The core idea of ​​this strategy is to achieve desired physical or chemical properties by systematically altering specific atoms or atomic clusters based on the existing atomic structure of the material.

[0009] Step 3: Use the Build layer function to stack BNG and MoP2Ge2O2 to build a BNG / MoP2Ge2O2 heterostructure model.

[0010] Furthermore, in step two, the S atoms on both sides of the monolayer are first replaced with P atoms to obtain a MoP2 monolayer; Si-N layers are added to both sides of this structure to construct a monolayer MoP2Si2N2 model with seven atomic layers: N-Si-P-Mo-PN-Si; then, the Si atoms and N atoms in the above structure are replaced with Ge atoms and O atoms respectively to construct a MoP2Ge2O2 monolayer model.

[0011] Furthermore, step three employs a 4×4 supercell graphene monolayer and A heterogeneous structure model was constructed using a supercell MoP2Ge2O2 monolayer.

[0012] Another objective of this invention is to provide a method for predicting the performance of BNG / MoP2Ge2O2 heterostructure sodium-ion battery anode materials, comprising the following steps:

[0013] Step 1: Perform full relaxation on the single-layer and heterogeneous structure models to obtain the corresponding stable configurations and characteristic parameters;

[0014] Step 2: Establish adsorption models of single sodium atoms at different sites in monolayers and heterostructures;

[0015] Step 3: Perform complete relaxation on the adsorption system obtained in Step 2 to obtain the adsorption energy and characteristic parameters of the corresponding stable configuration.

[0016] Step four: Perform energy calculations on the optimized monolayer and heterostructures from steps one and three to obtain the electronic properties of the system before and after sodium adsorption.

[0017] Step 5: Based on the adsorption energy results in Step 3, diffusion paths are set on the surfaces of monolayers and heterostructures, and the optimal diffusion paths and migration barriers for sodium atoms are obtained.

[0018] Step 6: Based on the adsorption energy obtained in Step 3, the open-circuit voltage and theoretical capacity of the monolayer and heterojunction systems are obtained.

[0019] Step 7: Perform structural stability and thermal stability simulations on monolayer and heterostructures with different sodium atom concentrations.

[0020] Furthermore, the specific steps for constructing the intrinsic and defective graphene monolayer structure model in step one are as follows:

[0021] Step 1: An intrinsic graphene (G) monolayer structure model was established using bulk graphene imported into Material Studio (MS). Then, B and N were simultaneously substituted at the C atom sites of graphene to construct a B-N co-doped graphene (BNG) structure model.

[0022] Step 2: Perform full structural relaxation on the above G and BNG monolayers to obtain the optimized stable configuration, and examine the changes in the structural characteristic parameters of graphene before and after the defects.

[0023] Step 3: Perform formation energy calculation on the optimized structure to obtain a stable defect-state graphene structure.

[0024] Step 4: The structural stability of the system described in Step 1 is verified by phonon spectrum, elastic constant, Young's modulus and AIMD simulation.

[0025] Furthermore, the specific steps for constructing the model of the MoP2Ge2O2 monolayer structure in step one are as follows:

[0026] Step 1: Based on the MoS2 phase structure imported from MS software, the corresponding MoS2 monolayer structure is obtained by cross-sectioning. Subsequently, the MoP2Ge2O2 monolayer model is established using an atomic transmutation strategy;

[0027] Step 2: Fully relax the above structure to obtain a stable geometric structure, and calculate the formation energy;

[0028] Step 3: Further verify the structural stability of the optimized structure, including phonon spectrum, elastic constant, Young's modulus and AIMD simulation.

[0029] Furthermore, the construction of the heterostructure model in step one involves the following specific steps:

[0030] Step 1: Use the Build layer function to construct the heterostructure models of G / MoP2Ge2O2 and BNG / MoP2Ge2O2;

[0031] Step 2: Perform structural relaxation on the above heterostructure model to obtain the characteristic parameters (lattice parameters and interlayer distance) of the stable structure, and calculate the binding energy.

[0032] Step 3: Based on the optimized structure, repeat the operation in step 3 of the MoP2Ge2O2 monolayer model construction to obtain the phonon spectrum, elastic constant, Young's modulus and AIMD simulation of the heterostructure.

[0033] Furthermore, the geometric optimization algorithm for complete relaxation in steps one and three adopts BFGS, with the convergence parameters set as follows: plane wave cutoff energy of 400 eV, Brillouin zone K-point sampling of 4×4×1, and energy threshold of 1×10⁻⁶. -5 eV / atom, the maximum interatomic force and maximum displacement are divided into eV / atom, and

[0034] Furthermore, in step two, the adsorption sites of the monolayer graphene include T C B C-C and H C Different adsorption sites in the BNG monolayer include T B T N T C H C B B-C B N-C and B C-C Different adsorption sites in the MoP2Ge2O2 monolayer include T Mo T Ge and T O The adsorption sites of the heterostructure include T B TN T C B N-C B C-C H BC H NC T Mo T Ge and T O .

[0035] Furthermore, in step four, energy calculations are performed based on the CASTEP module, and electronic properties include electronic band structure, density of states, ELF, differential charge density, work function, and Mulliken atom population.

[0036] Furthermore, the calculation of the migration barrier in step five includes the following steps:

[0037] (1) Based on the stable adsorption system described in step three, the migration path is set;

[0038] (2) Use the Reaction Preview function to select the starting state and the final state of migration from the stable adsorption model described in step 3 as reactants and products, respectively.

[0039] (3) Use CASTEP to minimize the energy of the geometry of the initial and final states, and search for the structure that minimizes the energy of the system.

[0040] (4) Based on the minimum energy structure of the initial and final states, the CI-NEB method is used to calculate the transition state;

[0041] (5) Complete the transition state calculation and analyze the reaction path and migration barrier properties of the transition state.

[0042] Furthermore, the diffusion dynamics of the monolayer and heterostructure are as follows:

[0043] (1) Calculate the diffusion kinetics of a single sodium atom in the G monolayer;

[0044] Step 1: Calculate and compare the adsorption energies of a single sodium atom on the G monolayer to determine its most stable state on the monolayer surface; different adsorption sites include: the top of the C atom (T C ), C atom bridge site (B C-C ) and the top of the C six-membered ring (H C );

[0045] Step 2: Use the CI-NEB method to search for the transition state, find the optimal reaction pathway for sodium atom migration, analyze the energy barrier, and establish the reaction mechanism;

[0046] (2) Calculate the diffusion kinetics of a single sodium atom on the BNG monolayer, repeating the operation described in step two based on the most stable adsorption state; different adsorption sites include: the top of the B atom (T B ), N atom top (T N ), C atom top (T c ), BC bridge site (B B-C ), NC bridge (B N-C ), C atom bridge site (B C-C );

[0047] (3) Calculate the diffusion kinetics of a single sodium atom on the MoP2Ge2O2 monolayer. Based on the most stable adsorption state, repeat the CI-NEB method described above to find the optimal reaction pathway for sodium atom migration, obtain the energy barrier, and determine the reaction mechanism. Different adsorption sites include: the top of the Mo atom (T... Mo ), Ge atom top (T Ge ) and the top of the O atom (T O );

[0048] (4) Calculate the diffusion dynamics of a single sodium atom on the heterostructure, repeat the above steps of obtaining the energy barrier in the monolayer structure, find the optimal reaction path for sodium atom migration, calculate the energy barrier and establish the reaction mechanism; different adsorption sites include: the top of intrinsic and defective graphene, the interlayer and the bottom of MoP2Ge2O2.

[0049] Furthermore, obtaining the open-circuit voltage and theoretical capacity in step six specifically includes the following steps:

[0050] (1) Add a sodium atom layer to the most stable site and calculate the corresponding hierarchical adsorption energy; then add a second sodium atom layer to the substable site to obtain the corresponding hierarchical adsorption energy, until the hierarchical adsorption energy is positive.

[0051] (2) Accurately determine the maximum adsorption concentration of sodium atoms, add sodium atoms one by one, and calculate the corresponding sequential adsorption energy until the sequential adsorption energy is positive, and further accurately determine the maximum storage capacity of sodium atoms.

[0052] (3) Calculate the formation energy of different configurations of sodium atoms embedded in the negative electrode material with the same concentration, and draw the convex hull diagram to further obtain the energy-stable intermediate phase during sodium adsorption.

[0053] (4) Calculate the corresponding open-circuit voltage based on the stable intermediate phase obtained from the convex hull diagram, and calculate the corresponding theoretical capacity at the maximum sodium atom loading concentration; use it as a function of sodium atom concentration to plot the capacity curve and voltage plateau.

[0054] Furthermore, in step seven, the structural stability simulation uses the CASTEP module to calculate the phonon spectrum. The specific parameters are: cutoff energy of 500 eV, Brillouin zone K-point grid of 6×6×1, and finite displacement method. The thermal stability simulation uses molecular dynamics in the DMol3 module, selects the NVT ensemble, and sets the temperature to 300 K and 500 K respectively, with a time step of 1 fs and a total duration of 6 ps.

[0055] Based on the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solution to be protected by this invention are as follows:

[0056] First, the BNG / MoP2Ge2O2 heterostructure described in this invention, as a sodium-ion battery anode material, has the following advantages: B and N co-doping induces effective sodium adsorption in graphene; the synergistic effect of the interface between BNG and MoP2Ge2O2 significantly enhances the bonding strength between the heterostructure and sodium atoms; the heterostructure composed of BNG and MoP2Ge2O2 possesses metallic properties, improving the electronic and ionic conductivity of the electrode material, thus overcoming the semiconductor properties of both; the sodium-doped BNG / MoP2Ge2O2 retains its metallic properties, exhibiting enhanced electronic conductivity; the BNG and MoP2Ge2O2 monolayer interface plays a crucial role in promoting charge transfer and ion diffusion, while also contributing to enhanced interface stability; the heterostructure's good structural and thermal stability effectively prevents pulverization and collapse of the electrode material. This indicates that this heterostructure can serve as a promising anode material for sodium-ion batteries, solving the current problems of structural stability, high capacity, high rate capability, and cycle life in two-dimensional sodium-ion batteries.

[0057] Second, considering the technical solution as a whole or from a product perspective, the technical effects and advantages of the technical solution to be protected by this invention are specifically described as follows:

[0058] Two-dimensional materials (2D materials) exhibit broad application potential in electrochemistry due to their large specific surface area, rich electronic properties, and shortened diffusion distance. However, their energy density and long-cycle stability still cannot meet the requirements of sodium-ion batteries. Constructing heterostructures is an effective method to improve material performance. Therefore, this invention designs a BNG / MoP2Ge2O2 heterostructure sodium-ion battery anode material, which is predicted to exhibit good structural stability, electronic conductivity, higher adsorption capacity, diffusion rate, and storage capacity. Simultaneously, it solves the problems of MoP2Ge2O2 monolayer volume expansion and insufficient diffusion motive force between two monolayers. This invention provides a new design approach for the development of high-performance SIB anode materials and will have theoretical guiding significance for the application of MoP2Ge2O2 materials in SIBs.

[0059] Third, the technical solution of this invention solves a technical problem that people have long desired to solve but have never been able to achieve:

[0060] Sodium-ion batteries often suffer from capacity decay, severely limiting their lifespan and cycle stability. This invention provides a design that optimizes the structural stability and electrochemical performance of the electrode material by forming a BNG / MoP2Ge2O2 heterostructure through B and N co-doped graphene monolayer and MoP2Ge2O2. This effectively alleviates capacity decay during the sodium-doping process and improves cycle life. Sodium-ion batteries face low energy density and charge / discharge rates, further limiting their application in large-scale energy storage and high-energy-density fields. The synergistic design of the composition and structure of the heterostructure optimizes the ionic / electronic conductivity and reactivity of the electrode material, significantly improving the battery's energy density and charge / discharge efficiency. The BNG / MoP2Ge2O2 heterostructure has a high component richness, which is expected to reduce production costs and improve the sustainability of the material.

[0061] Fourth, the technical solution of this invention aims to predict the performance of a novel BNG / MoP2Ge2O2 heterostructure as a sodium-ion battery anode material through theoretical calculations and simulations. Through detailed and systematic calculations and design processes, this invention not only provides an innovative material design scheme but also verifies its feasibility and superiority through first-principles calculations.

[0062] The technical solution of this invention solves the following technical problems and achieves significant technical progress:

[0063] 1) Material Design and Selection:

[0064] By calculating the formation energies of different configurations, the most suitable B, N co-doped graphene (BNG) structure was selected. This doping method can effectively tune the electronic properties of graphene, thereby improving its interaction with sodium ions.

[0065] A novel MoP2Ge2O2 monolayer material was designed and constructed, and its stability was verified by calculating parameters such as cohesive energy.

[0066] 2) Construction and optimization of heterogeneous structures:

[0067] A novel heterostructure model was constructed by combining BNG with a MoP2Ge2O2 monolayer. This heterostructure brings unique interface effects and electronic properties, which are beneficial for improving battery performance.

[0068] Through geometric optimization, the stable configuration and interlayer distance of the heterostructure were determined, providing a reliable model basis for subsequent performance prediction.

[0069] 3) Stability verification:

[0070] Phonon spectrum calculations and AIMD simulations comprehensively verified the dynamic and thermal stability of monolayer and heterostructures. These stability verifications are a key prerequisite for the application of materials in practical battery systems.

[0071] 4) Adsorption performance analysis:

[0072] Adsorption models of single sodium atoms on monolayers and heterostructures were constructed, and the most stable adsorption sites of sodium atoms on the material surface were analyzed by calculating parameters such as adsorption energy. This is crucial for understanding the insertion and deintercalation processes of sodium ions in anode materials.

[0073] In summary, the technical solution of this invention systematically designs and predicts the performance of a novel BNG / MoP2Ge2O2 heterostructure as a negative electrode material for sodium-ion batteries through theoretical calculations and simulations. This heterostructure not only possesses excellent stability but also exhibits good sodium-ion adsorption performance, and is expected to provide new ideas and methods for the development of high-performance sodium-ion batteries. Attached Figure Description

[0074] Figure 1 This is a flowchart illustrating the design and performance prediction of the BNG / MoP2Ge2O2 heterostructure sodium-ion battery anode material provided in this embodiment of the invention.

[0075] Figure 2 This is the intrinsic and defective graphene monolayer model provided in the embodiments of the present invention;

[0076] Figure 3 This is the MoP2Ge2O2 single-layer structure model provided in the embodiments of the present invention;

[0077] Figure 4 This is the BNG / MoP2Ge2O2 heterojunction structure model provided in the embodiments of the present invention;

[0078] Figure 5 This is an intrinsic and defective graphene monolayer sodium adsorption band diagram provided in the embodiments of the present invention;

[0079] Figure 6 This is the intrinsic and defective graphene monolayer sodium adsorption differential charge density provided in the embodiments of the present invention;

[0080] Figure 7 This is a band structure diagram of MoP2Ge2O2 monolayer sodium adsorption before and after, provided in an embodiment of the present invention.

[0081] Figure 8 This is the differential charge density after sodium adsorption in a MoP2Ge2O2 monolayer provided in this embodiment of the invention;

[0082] Figure 9This is a band structure diagram of sodium before and after adsorption of BNG / MoP2Ge2O2 heterostructure provided in an embodiment of the present invention;

[0083] Figure 10 This refers to the differential charge density of sodium after adsorption in the BNG / MoP2Ge2O2 heterostructure provided in this embodiment of the invention.

[0084] Figure 11 This is the migration path of sodium on intrinsic and defective graphene monolayers provided in the embodiments of the present invention;

[0085] Figure 12 This is the migration path of sodium on the MoP2Ge2O2 monolayer provided in the embodiments of the present invention;

[0086] Figure 13 This is the migration path of sodium in the BNG / MoP2Ge2O2 heterostructure provided in the embodiments of the present invention. Detailed Implementation

[0087] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0088] The following are two specific embodiments used to further illustrate the technical solutions provided by the present invention:

[0089] Example 1: Construction and optimization of BNG / MoP2Ge2O2 heterostructure

[0090] 1) Constructing an intrinsic graphene monolayer:

[0091] Using Material Studio software, first import the graphite bulk structure and optimize its cell structure to obtain a stable configuration.

[0092] The intrinsic graphene (G) monolayer structure with a 4×4 supercell was obtained by cutting using the Cleave Surface function of the software.

[0093] 2) Construction of B, N co-doped graphene (BNG):

[0094] Based on the intrinsic graphene monolayer, two doping configurations were selected: Configuration I, in which B and N atoms replace C atoms in the same six-membered ring, and Configuration II, in which B and N atoms replace C atoms in different six-membered rings.

[0095] Both configurations were geometrically optimized, and their formation energies were calculated. Based on the calculated formation energies, configuration II, with its lower formation energy, was selected as the basis for subsequent heterostructure construction.

[0096] 3) Constructing a MoP2Ge2O2 monolayer:

[0097] Import the MoS2 unit cell into Material Studio software and replace the S atoms with P atoms to obtain a MoP2 monolayer.

[0098] By adding Si-N layers on both sides of the MoP2 monolayer, a monolayer MoP2Si2N2 model with seven atomic layers (N-Si-P-Mo-PN-Si) is constructed.

[0099] By further replacing the Si and N atoms in the above structure with Ge and O atoms, a monolayer MoP2Ge2O2 is obtained.

[0100] The geometry of the constructed monolayer MoP2Ge2O2 was optimized, and parameters such as cohesive energy were calculated to verify its stability.

[0101] 4) Constructing the BNG / MoP2Ge2O2 heterostructure:

[0102] To meet the lattice fit requirements, a 4×4 supercell BNG monolayer and A heterostructure model was constructed using a supercell MoP2Ge2O2 monolayer.

[0103] The constructed heterogeneous structure is geometrically optimized to obtain stable interlayer spacing and structural configuration.

[0104] Example 2: Study on the adsorption performance of sodium atoms on BNG / MoP2Ge2O2 heterostructure

[0105] 1) Constructing an adsorption model:

[0106] Based on the stable BNG / MoP2Ge2O2 heterostructure optimized in Example 1, an adsorption model of a single sodium atom on it was constructed.

[0107] Consider different adsorption sites, such as the BNG surface, the MoP2Ge2O2 surface, and the interlayer between the two.

[0108] 2) Geometric structure optimization and adsorption energy calculation:

[0109] The adsorption configurations at different sites are geometrically optimized to obtain the most stable adsorption configuration.

[0110] Calculate the vertical distance (H) from the sodium atom to the substrate and the adsorption energy (E) for each optimized configuration. ad ).

[0111] 3) Adsorption performance analysis:

[0112] By comparing the adsorption energies at different sites, the most stable adsorption sites for sodium atoms on the BNG / MoP2Ge2O2 heterostructure were determined.

[0113] The influence of adsorption energy on the electronic properties of heterostructures and the charge transfer mechanism at the interface were analyzed.

[0114] Based on the analysis results of adsorption energy and electronic properties, the potential performance of BNG / MoP2Ge2O2 heterostructure as a negative electrode material for sodium-ion batteries was evaluated.

[0115] like Figure 1 As shown, this invention provides a design and performance prediction of a BNG / MoP2Ge2O2 heterostructure sodium-ion battery anode material. First-principles calculations based on density functional theory are used to predict performance modification by calculating changes in characteristic parameters, adsorption performance, electronic properties, diffusion rate, and theoretical capacity of the defective graphene combined with the MoP2Ge2O2 monolayer synergistic effect. Specifically, the following steps are included:

[0116] S101, Construction of intrinsic and defective graphene monolayer model;

[0117] (1) Import the graphite bulk structure from Material Studio software, optimize the cell structure to obtain a stable configuration, and then obtain a 4×4 supercell intrinsic graphene (G) monolayer structure through the Cleave Surface function.

[0118] (2) Structural relaxation of the intrinsic graphene monolayer obtained in (1) is performed as follows: Figure 2 As shown, the lattice parameters of the obtained single-cell graphene are... Carbon-carbon bond length

[0119] (3) Replace the C atom sites in the same six-membered ring with B and N atoms (configuration I), and replace the C atom sites in different six-membered rings with B and N atoms respectively (configuration II) to construct a B and N co-doped graphene (BNG) structural model.

[0120] The model described in (3) is geometrically optimized to obtain a stable structure, and the relevant formation energy is calculated. The specific formula is as follows:

[0121] in, E represents the total energy of a defective graphene monolayer. C E N and E B y, z represent the total energy of a single C, N, and B atom, respectively, and x, y, and z represent the number of C, N, and B atoms, respectively.

[0122] Based on the above definition, the calculated formation energies of the two BNGs are 1.05 eV and 1.31 eV, respectively. Configuration II is selected for subsequent heterojunction model construction.

[0123] Based on the stable BNG configuration, the calculated BC and NC bond lengths are as follows: and

[0124] S102, MoP2Ge2O2 single-layer model construction;

[0125] Importing the MoS2 unit cell into Material Studio software, we first replaced the S atoms on both sides of the monolayer with P atoms to obtain a MoP2 monolayer. Then, we added Si-N layers to both sides of this structure to construct a monolayer MoP2Si2N2 model with seven atomic layers: N-Si-P-Mo-PN-Si. Next, we replaced the Si and N atoms in the above structure with Ge and O atoms respectively to construct a monolayer MoP2Ge2O2, belonging to the P6m1 space group. Figure 3 As shown.

[0126] Geometric optimization was performed on the above configuration, and the corresponding characteristic parameters and cohesive energy of the MoP2Ge2O2 monolayer were calculated. The formula is as follows:

[0127]

[0128] in, E represents the total energy of MoP2Ge2O2. Mo E P E Ge and E O , respectively, represent the total energy of a single Mo, P, Ge, and O atom; a, b, c, and d represent the number of the corresponding atoms.

[0129] The cohesive energy of the corresponding monolayer is -1.60 eV / atom, and the unit cell lattice constant is... And the bond lengths of each type of bond are respectively and

[0130] S103, heterojunction model construction;

[0131] To ensure the lattice fit is within a reasonable range (5%), the 4×4 supercell graphene monolayer in the structure described in S101 and the structure described in S102 are used. Supercell MoP2Ge2O2 monolayer heterostructure model as follows Figure 4 As shown, the adaptation rate was 4.14%.

[0132] Geometric optimization of the heterojunction model yields the corresponding interlayer distance for a stable system.

[0133] S104, Stability calculation of single-layer and heterojunction structures;

[0134] (1) The phonon spectrum curves were calculated to determine the dynamic stability of the optimized stable configurations in S101, S102 and S103. The phonon curves have no imaginary frequency, indicating that the monolayer and heterostructures are stable.

[0135] (2) To assess the thermal stability of the optimized stable configurations in S101, S102 and S103, AIMD simulations were performed at 300K and 500K. The energy fluctuations were small and the structure maintained a small deformation, further confirming the thermal stability of the system.

[0136] S105, construction of a single sodium atom adsorption model;

[0137] (1) Construct an adsorption model for a single sodium atom in the optimized stable configurations of S101, S102 and S103;

[0138] (2) The geometric structure of adsorption configurations at different sites was optimized to obtain the vertical distance (H) from the Na atom to the substrate and the adsorption energy (E) for each optimized configuration. ad As shown in Tables 1, 2 and 3, the most stable sites for sodium atom adsorption on the surface of the corresponding substrate materials were calculated and analyzed.

[0139] Table 1

[0140]

[0141] Table 2

[0142]

[0143] Table 3

[0144]

[0145] S106, Calculate the electronic properties of monolayer and heterostructure before and after sodium atom adsorption;

[0146] (1) Based on the most stable models of G, BNG, and heterostructures before and after sodium adsorption obtained from S101, S102, S103, and S105, the band structure and density of states were calculated, such as... Figure 5 , Figure 7 and Figure 9 As shown;

[0147] (2) The calculated differential charge density analysis examines the transfer of electrons in the monolayer, studies the charge transfer at the heterojunction interface and the direction of the built-in electric field at the interface, such as... Figure 6 , Figure 8 and Figure 10 As shown;

[0148] (3) The calculated Mulliken population value further yielded the charge transfer between atoms and sodium atoms in each stable configuration, as shown in Table 4.

[0149] Table 4

[0150]

[0151] S107, Calculate the diffusion dynamics of sodium atoms on monolayer and heterostructure surfaces;

[0152] (1) Based on the stable G, BNG and heterostructure obtained by sodium adsorption in S105, the diffusion path is set as follows: Figures 11-13 As shown;

[0153] (2) The optimal migration path is selected by using the CASTEP module with the climbing elastic band method (CI-NEB) to further obtain the diffusion barrier and diffusion coefficient of sodium atoms along different paths.

[0154] S108, Calculation of single-layer open-circuit voltage and theoretical capacity;

[0155] (1) Based on the adsorption energies of Na atoms obtained from S105 on G, BNG, and MoP2Ge2O2 monolayers, sodium atom layers were first added to the most stable sites on both sides of the monolayer, and the corresponding sequence adsorption energies (E) were calculated. layer Then, sodium atom layers are added to the substable sites on both sides of the monolayer to obtain the corresponding hierarchical adsorption energy. Sodium atom layers are added sequentially until the hierarchical adsorption energy is positive, indicating that the maximum number of sodium atom layers has been reached.

[0156] (2) Accurately determine the maximum adsorption concentration of sodium atoms. To do this, sodium atoms are added one by one, and the corresponding order adsorption energies (E) are calculated. sae (This continues until the order adsorption energy is positive.)

[0157] (3) Calculate the formation energy of different configurations of the anode material with the same concentration of sodium atoms embedded in it, and draw the convex hull diagram;

[0158] (4) The points on the convex hull diagram correspond to the stable intermediate phase structure during the sodiumization process. The open-circuit voltage and theoretical capacity of the corresponding configuration are calculated using the formula. These are used as functions of sodium atom concentration to plot the capacity curve and voltage plateau.

[0159] S109, Calculation of open-circuit voltage and theoretical capacity of heterojunction model;

[0160] (1) Based on S105, the adsorption energy of sodium atoms in the heterostructure is obtained. Sodium atom layers are inserted between the layers to perform structural relaxation and obtain hierarchical adsorption energy.

[0161] (2) Insert sodium atomic layer structure relaxation into the outer side of the two monolayers to obtain hierarchical adsorption energy until the value is positive.

[0162] (3) The open-circuit voltage is calculated using the formula until the voltage drops to zero, indicating that the sodium atom concentration has reached its maximum limit, and the corresponding theoretical capacity is obtained.

[0163] S110, Stability calculation of single-layer and heterojunction structures;

[0164] AIMD simulations were performed at room temperature to calculate the adsorption of sodium atoms at different concentrations on monolayers and heterostructures as the sodium atom concentration increased.

[0165] This invention provides the design and performance prediction of a BNG / MoP2Ge2O2 heterostructure sodium-ion battery anode material. First, the model establishment process is as follows: The cell structures of G and MoS2 are obtained using MS software and subjected to complete geometric relaxation. The corresponding monolayers are then obtained using the Cleave surface function. Based on the obtained monolayer structures, the two components of the heterostructure, BNG and MoP2Ge2O2, are designed through atomic substitution. Then, the BNG and MoP2Ge2O2 are stacked using the Build layer function to construct the BNG / MoP2Ge2O2 heterostructure model. Subsequently, the structural characteristic dimensions and electrochemical properties are predicted: Based on first-principles calculations using density functional theory, the changes in characteristic structure, electronic properties, diffusion rate, theoretical capacity, and structural stability of the obtained BNG / MoP2Ge2O2 heterostructure are predicted and evaluated, and compared with the properties of the two monolayers. Finally, the main controlling factors and influencing laws of the heterostructure's excellent electrochemical performance are revealed. The design and performance prediction of the BNG / MoP2Ge2O2 heterostructure anode material provided by this invention demonstrate its practical value in sodium-ion batteries and provide strong guidance for the future development of sodium-ion battery technology.

[0166] Two-dimensional materials, with their large specific surface area, flexibility, and mechanical properties, have been extensively studied in theoretical and experimental research in the field of energy storage. However, most monolayer anode materials (such as transition metal sulfides and phosphorene) suffer from many drawbacks due to their low intrinsic conductivity and large volume changes during charge and discharge, resulting in poor rate performance, slow charge and discharge rates, and rapid capacity decay. Firstly, this invention provides a monolayer MoP2Ge2O2 structure with a MA2Z4-like structure that can simultaneously adjust electronic properties and band gap size, significantly lower than that of MoS2 monolayers (1.62 eV), due to the co-doping of Ge and P. Compared to MoS2 monolayers, this system also exhibits significantly enhanced sodium atom adsorption capacity. The idea of ​​integrating various functional two-dimensional materials to construct heterostructures provides a unique platform for studying new physical phenomena that cannot be obtained from single two-dimensional materials. Experimental verification and theoretical predictions show that heterostructures are more ideal metal-ion battery anode materials than monolayers, not only improving the poor stability of monolayers but also achieving excellent structural stability and high mechanical strength, while overcoming the semiconductor properties of monolayers to achieve metallic properties with good electronic conductivity. Compared to two monolayers, the heterostructure exhibits improved interactions between both monolayers and metal atoms, resulting in higher specific capacity. Furthermore, the metal atoms in the heterostructure demonstrate lower diffusion barriers and faster ion transport. Therefore, this invention provides a BNG / MoP2Ge2O2 heterostructure as a sodium-ion battery anode material and predicts its performance. The weak interaction between B and N co-doped graphene and the MoP2Ge2O2 monolayer provides good cyclability by limiting the large volume change of the MoP2Ge2O2 monolayer during sodification. Compared to BNG and MoP2Ge2O2 monolayers, the designed BNG / MoP2Ge2O2 heterostructure exhibits significantly improved conductivity and retains metallic properties even after continuous Na atom embedding. Due to the synergistic effect between the two monolayers, the combination of BNG and MoP2Ge2O2 achieves higher adsorption strength during sodification, and the heterostructure has a significantly improved Na storage capacity compared to the original monolayer. BNG / MoP2Ge2O2 is more conducive to the insertion and rapid migration rate of sodium atoms, enabling rapid charge and discharge rates. Moreover, after adsorbing sodium atoms, the heterostructure maintains good structural stability, thermal stability, and high rigidity, ensuring resistance to shattering.

[0167] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for constructing a model of a BNG / MoP2Ge2O2 heterostructure sodium-ion battery anode material, characterized in that, include: Step 1: Using bulk graphene imported from Material Studio, an intrinsic graphene G monolayer structure model is established. B and N atoms are used to replace C atoms in different six-membered rings to construct a B and N co-doped graphene BNG structure model. Step 2: Based on the MoS2 phase structure imported from MS software, the corresponding MoS2 monolayer structure is obtained by cross-section, and a MoP2Ge2O2 monolayer model is established using the atomic transmutation strategy. Step 3: Use the Build layer function to stack BNG and MoP2Ge2O2 to build a BNG / MoP2Ge2O2 heterostructure model; In step two, firstly, P atoms are used to replace the S atoms on both sides of the monolayer to obtain a MoP2 monolayer; then, Si-N layers are added to both sides of this structure to construct a monolayer MoP2Si2N2 model with seven atomic layers: N-Si-P-Mo-PN-Si; then, Ge atoms and O atoms are used to replace the Si atoms and N atoms in the above structure to construct a MoP2Ge2O2 monolayer model. Step three uses a 4×4 supercell graphene monolayer and A heterogeneous structure model was constructed using a supercell MoP2Ge2O2 monolayer.

2. A method for predicting the performance of BNG / MoP2Ge2O2 heterostructure sodium-ion battery anode materials based on the method described in claim 1, characterized in that, Includes the following steps: Step 1: Perform full relaxation on the single-layer and heterogeneous structure models to obtain the corresponding stable configurations and characteristic parameters; Step 2: Establish adsorption models of single sodium atoms at different sites in monolayers and heterostructures; Step 3: Perform complete relaxation on the adsorption system obtained in Step 2 to obtain the corresponding stable system. Adsorption energy and characteristic parameters of the configuration; Step four: Perform energy calculations on the optimized monolayer and heterostructures from steps one and three to obtain the electronic properties of the system before and after sodium adsorption. Step 5: Based on the adsorption energy results in Step 3, diffusion paths are set on the surfaces of monolayers and heterostructures, and the optimal diffusion paths and migration barriers for sodium atoms are obtained. Step 6: Based on the adsorption energy obtained in Step 3, the open-circuit voltage and theoretical capacity of the monolayer and heterojunction systems are obtained. Step 7: Perform structural stability and thermal stability simulations on monolayer and heterostructures with different sodium atom concentrations.

3. The performance prediction method for the BNG / MoP2Ge2O2 heterostructure sodium-ion battery anode material as described in claim 2, characterized in that, The geometric optimization algorithm for complete relaxation in steps one and three uses BFGS, with the convergence parameters set as follows: plane wave cutoff energy of 400 eV, Brillouin zone K-point sampling of 4×4×1, and energy threshold of 1×10⁻⁶. -5 eV / atom, the maximum interatomic force and maximum displacement are divided into eV / atom, and 4. The performance prediction method for the BNG / MoP2Ge2O2 heterostructure sodium-ion battery anode material as described in claim 2, characterized in that, In step two, the adsorption sites of the monolayer graphene include T C B C-C and H C Different adsorption sites in the BNG monolayer include T B T N T C H C B B-C B N-C and B C-C Different adsorption sites in the MoP2Ge2O2 monolayer include T Mo T Ge and T O The adsorption sites of the heterostructure include T B T N T C B N-C B C-C H BC H NC T Mo T Ge and T O .

5. The performance prediction method for the BNG / MoP2Ge2O2 heterostructure sodium-ion battery anode material as described in claim 2, characterized in that, In step four, energy calculations are performed based on the CASTEP module. Electronic properties include electronic band structure, density of states, ELF, differential charge density, work function, and Mulliken atom population.

6. The performance prediction method for the BNG / MoP2Ge2O2 heterostructure sodium-ion battery anode material as described in claim 2, characterized in that, Step five, the calculation of the migration barrier, includes the following steps: (1) Based on the stable adsorption system in step three, the migration path was set; (2) The Reaction Preview function was used to select the starting state and the final state of migration from the stable adsorption model in step 3 as reactants and products, respectively. (3) Use CASTEP to minimize the energy of the geometry of the initial and final states, and search for the structure that minimizes the energy of the system. (4) Based on the minimum energy structure of the initial and final states, the CI-NEB method is used to calculate the transition state; (5) Complete the transition state calculation and analyze the reaction path and migration barrier properties of the transition state.

7. The performance prediction method for the BNG / MoP2Ge2O2 heterostructure sodium-ion battery anode material as described in claim 2, characterized in that, Step six, obtaining the open-circuit voltage and theoretical capacity, specifically includes the following steps: (1) Add a sodium atom layer to the most stable site and calculate the corresponding hierarchical adsorption energy; then add a second sodium atom layer to the substable site to obtain the corresponding hierarchical adsorption energy, until the hierarchical adsorption energy is positive. (2) Accurately determine the maximum adsorption concentration of sodium atoms, add sodium atoms one by one, and calculate the corresponding sequential adsorption energy until the sequential adsorption energy is positive, and further accurately determine the maximum storage capacity of sodium atoms. (3) Calculate the formation energy of different configurations of sodium atoms embedded in the negative electrode material with the same concentration, and draw the convex hull diagram to further obtain the energy-stable intermediate phase during sodium adsorption. (4) Calculate the corresponding open-circuit voltage based on the stable intermediate phase obtained from the convex hull diagram, and calculate the corresponding theoretical capacity at the maximum sodium atom loading concentration; use it as a function of sodium atom concentration to plot the capacity curve and voltage plateau.

8. The performance prediction method for the BNG / MoP2Ge2O2 heterostructure sodium-ion battery anode material as described in claim 2, characterized in that, In step seven, the structural stability simulation uses the CASTEP module to calculate the phonon spectrum. The specific parameters are: cutoff energy of 500 eV, Brillouin zone K-point grid of 6×6×1, and finite displacement method. The thermal stability simulation uses molecular dynamics in the DMol3 module, NVT ensemble, temperature of 300 K and 500 K, time step of 1 fs and total duration of 6 ps.

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