Sodium-ion battery negative electrode material heterostructure and construction method and performance prediction method

Abstract

This invention discloses a heterostructure of sodium-ion battery anode material, its construction method, and its performance prediction method. It belongs to the field of electrochemical energy storage technology, and obtains Nb by substituting Nb atoms with Ge or Sn. 1‑ x A x CO2, then combined with 2D SiC to construct SiC / Nb 1‑x A x A CO2 heterostructure was developed to obtain a sodium-ion battery anode material with improved electrochemical performance. The monolayer Nb2CO2 MXene provided good electronic conductivity and structural stability for the anode material, while the introduction of SiC ensured excellent structural stability and high theoretical capacity. The combination of SiC and Nb... 1‑x A x The heterostructure interface formed by CO2 plays an important role in promoting electronic conductivity and Na ion transport. Due to the similar electronegativity of Ge and Sn to C, the A-C bond formed between the alloying elements and C is stronger than the Nb-C bond, thus enhancing the stability of the heterostructure and maintaining the integrity of the electrode structure.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage technology, specifically to the heterostructure of sodium-ion battery anode materials, its construction method, and its performance prediction method. Background Technology

[0002] In recent years, the search for clean, low-carbon, safe, and efficient energy storage methods has become a hot topic, and electrochemical energy storage has become an increasingly important research subject. Sodium is abundant in the Earth's crust, and the standard hydrogen electrode potential of a sodium electrode is -2.71V, with a redox potential 0.3V higher than that of a lithium electrode. Therefore, sodium electrodes possess a safer redox potential and stronger chemical stability, making sodium-ion batteries (SIBs) stand out among many rechargeable metal-ion batteries. Although experience with existing lithium-ion batteries (LIBs) can play an important role in the development of SIBs, compared to Li... + Na + The larger ionic radius of Na leads to + The slow diffusion reaction kinetics in electrode materials are a significant factor. Secondly, sodium has a larger mass than lithium and a higher standard electrode potential (-2.71 V vs. -3.02 V), which inevitably reduces the energy density of SIBs. Electrode materials, including the negative electrode and cathode, are the main factors determining the reversible storage capacity, high energy density, and long cycle life of a battery. Compared to the positive electrode material, the selection of the negative electrode material is the most challenging aspect of SIBs. Firstly, sodium has a relatively large atomic radius, leading to significant volume changes during charge and discharge, which can cause structural collapse after long cycles, reducing lifespan. Secondly, sodium has a low melting point, making it unsuitable as a direct negative electrode, and it readily reacts with organic solvents, forming dendrites during cycling, posing safety concerns.

[0003] Sodium ions have a larger ionic radius than lithium ions, resulting in a slower ion diffusion rate and greater volume expansion of the electrode material during charge and discharge, thus leading to poorer rate performance and cycle stability. MXenes, with their hydrophilic surface and high metallic conductivity, exhibit excellent performance in energy storage, catalysis, and many other fields. The layered structure and numerous metal surface active sites of MXenes provide abundant channels for the storage and transport of sodium ions. However, due to limitations in preparation conditions, MXenes inevitably stack, reducing their specific surface area and consequently decreasing the number of ion adsorption sites. Furthermore, the multilayered MXenes are not stacked in an ordered manner, negating the advantages inherent in two-dimensional materials.

[0004] SiC, as an advanced functional ceramic material, possesses excellent thermal shock resistance, high temperature resistance, good chemical stability, and high modulus. However, its practical applications are often limited by the brittleness of ceramic materials. Alloy-based anode materials have high sodium storage capacity and relatively suitable operating potentials. Among many novel anode materials, Group IV alloying elements, including germanium and tin, can alloy with large amounts of sodium and have attracted much attention due to their high volumetric and gravimetric capacity, low operating potential, and natural abundance. In sodium-ion batteries, Sn alloy materials can alloy with sodium and store 3.75 mol of sodium ions, exhibiting a high theoretical specific capacity of approximately 847 mAh / g. Furthermore, Sn also has advantages such as being non-toxic, highly abundant, and low-cost. Another element, Ge, has a fast lithium-ion diffusion rate, good conductivity, and a high theoretical specific capacity of 369 mAh / g for SIBs. However, in practical applications, germanium and tin alloy-based anode materials are mainly limited by excessive volume changes leading to material pulverization or even detachment from the current collector, resulting in poor cycle performance and capacity decay. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a heterostructure of sodium-ion battery anode materials, its construction method, and its performance prediction method. This effectively solves the technical defects caused by sodium's large atomic radius, which leads to significant volume changes during charging and discharging, resulting in material structure collapse and reduced lifespan after long cycles; sodium's low melting point, making it unsuitable as a direct anode; and its tendency to react with organic solvents, forming dendrites during cycling, causing safety issues. Furthermore, this invention provides a sodium-ion battery anode material structure model with suitable pore size, enabling ion storage and mitigating damage caused by ion transport.

[0006] The first objective of this invention is to provide a method for constructing a heterostructure of a sodium-ion battery anode material, comprising the following steps:

[0007] Bulk Nb2C and SiC structural models were constructed, and the bulk Nb2C and SiC structural models were optimized to obtain 2D Nb2CO2 single-cell models and SiC single-cell models. Based on the Nb2CO2 single-cell models and SiC single-cell models, monolayer Nb2CO2 supercell models and monolayer SiC supercell models were constructed.

[0008] Introducing alloying element A into the single-layer Nb₂CO₂ supercell model yields Nb 1-x A x CO2 model.

[0009] The SiC supercell was placed on top of the Nb2CO2 supercell to construct a SiC / Nb2CT. x Heterogeneous structure model; in the Nb 1-x A xA monolayer SiC supercell was placed on top of the CO2 model, and after structural optimization, SiC / Nb was obtained. 1-x A x The CO2 heterostructure model is described, where the alloying element A is Ge or Sn, and X is 0.15~0.75.

[0010] As a preferred embodiment, when the alloying element A is Ge and X is 0.25, the SiC / Nb 1-x A x The CO2 heterostructure model is SiC / Nb 0.75 Ge 0.25 CO2, with a lattice parameter of 6.31 Å; when the alloying element A is Ge and X is 0.50, the SiC / Nb 1-x A x The CO2 heterostructure model is SiC / Nb 0.50 Ge 0.50 CO2, with a lattice parameter of 6.15 Å.

[0011] As a preferred embodiment, when the alloying element A is Sn and X is 0.25, the SiC / Nb 1-x A x The CO2 heterostructure model is SiC / Nb 0.75 Sn 0.25 CO2, with a lattice parameter of 6.46 Å; when the alloying element A is Sn and X is 0.50, the SiC / Nb 1-x A x The CO2 heterostructure model is SiC / Nb 0.50 Sn 0.50 CO2, with a lattice parameter of 6.35 Å.

[0012] In a preferred embodiment, the monolayer Nb₂CO₂ supercell model is a 2×2×1 supercell model with lattice parameters and angles of a=b=3.18Å, α=β=90° and γ=120°, and an Nb-C bond length of d. Nb-C =2.16 Å; the monolayer SiC supercell model is a 2×2×1 supercell model with lattice constants a=b=3.10 Å and Si-C bond length d. Si-C =1.78Å.

[0013] In a preferred embodiment, when the alloying element A is Ge and X is 0.25, the Nb 1-x A x The CO2 model is Nb 0.75 Ge 0.25 CO2 has a lattice constant of a = b = 3.10 Å and an Nb-C bond length of d. Nb-C =2.15Å, Ge-C bond length is dGe-C =2.13Å; when the alloying element A is Ge and X is 0.50, the Nb 1-x A x The CO2 model is Nb 0.50 Ge 0.50 CO2 has a lattice constant of a = b = 3.02 Å and an Nb-C bond length of d. Nb-C =2.15Å, Ge-C bond length is d Ge-C =2.13Å.

[0014] In a preferred embodiment, when the alloying element A is Sn and X is 0.25, the Nb 1-x A x The CO2 model is Nb 0.75 Sn 0.25 CO2 has a lattice constant of a = b = 3.15 Å and an Nb-C bond length of d. Nb-C =2.15Å, Sn-C bond length is d Sn-C =2.17Å; when the alloying element A is Sn and X is 0.50, the Nb 1-x A x The CO2 model is Nb 0.50 Sn 0.50 CO2 has a lattice constant of a = b = 3.12 Å and an Nb-C bond length of d. Nb-C =2.15Å, Sn-C bond length is d Sn-C =2.17Å.

[0015] The second objective of this invention is to provide a heterostructure of sodium-ion battery anode material constructed using the above-described construction method.

[0016] The third objective of this invention is to provide a method for predicting the performance of the aforementioned sodium-ion battery anode material heterostructure, wherein the performance prediction includes energy stability prediction, thermodynamic stability prediction, sodium ion adsorption stability prediction on the heterostructure, and conductivity prediction.

[0017] The performance prediction method includes the following steps:

[0018] For the SiC / Nb 1-x A x Ab initio molecular dynamics simulations were performed using a CO2 heterostructure model to obtain energy-time curves; the SiC / Nb ratio was calculated. 1-x A x The formation energy and phonon spectrum of the CO2 heterostructure model are used to predict energy stability based on the energy-time variation curve, and thermodynamic stability is also predicted based on the formation energy and phonon spectrum.

[0019] In the SiC / Nb1-x A x SiC side and Nb in CO2 heterostructure 1-x A x CO2 side and the SiC / Nb 1-x A x Na atoms were added to different typical sites in the interlayer of the CO2 heterostructure to obtain a sodium atom adsorption model.

[0020] The adsorption energy of sodium atoms on the surface of the negative electrode material is calculated based on the sodium atom adsorption model, and the adsorption stability of sodium ions on the heterostructure is predicted.

[0021] By calculating SiC / Nb 1-x A x Electronic property data of CO2 heterostructure before and after sodium ion adsorption, and sodium ion adsorption data in SiC / Nb 1-x A x The adsorption behavior, diffusion kinetics, open-circuit voltage, and theoretical specific capacity of CO2 heterostructures are studied to predict conductivity.

[0022] As a preferred embodiment, the method for constructing the sodium atom adsorption model is as follows:

[0023] Na atoms were added to C atoms on one side of SiC, Si atoms, the top of C atoms in SiC, and at a distance of 2 Å above the Si-C bond bridge site, resulting in Na in SiC / Nb. 1-x A x Adsorption model of CO2 on one side of SiC heterostructure.

[0024] Select Nb2CO2 / Nb 1-x A x Adding Na atoms 2 Å above the C, O, and Nb / A atoms on the CO2 side, the top of the Nb-Nb-C atoms, and above the bridge site of the Nb-O / AC bond, yields Na in SiC / Nb 1-x A x CO2 heterostructure Nb2CO2 / Nb 1-x A x Adsorption model on the CO2 side.

[0025] Na atoms were added at the top of the interlayer C atoms, O atoms, Nb / A atoms, the top of the Nb-Nb-C atoms, and 2 Å above the bridge site of the Nb-O / AC bond, resulting in Na atoms in SiC / Nb 1-x A x An adsorption model of CO2 in heterostructure layers.

[0026] In a preferred embodiment, the electronic performance data includes electronic band structure, density of states, differential charge density, and electronic localization function.

[0027] In a preferred embodiment, the calculation is implemented in the first-principles CASTEP module, and the exchange-correlation functional is described using the GGA-PBE generalized gradient method.

[0028] As a preferred implementation, when calculating electronic performance data, the plane wave cutoff energy is set to 450 eV, and a 4×4×1 K-point grid is used for Brillouin zone integration; during the calculation, atoms are fully relaxed, and the force and energy convergence criteria are set to 0.01 eV Å, respectively. -1 and 1×10 -5 eV.

[0029] As a preferred implementation, the DFT-D3 method with Grimme correction is used to describe long-range van der Waals interactions during the adsorption behavior, diffusion kinetics and theoretical specific capacity calculations, and a vacuum layer greater than 15 Å is set along the z-direction to avoid interlayer interactions.

[0030] As a preferred embodiment, when performing ab initio molecular dynamics simulations, the Nosé-Hoover method is used to control the temperature and NVT ensemble. The temperature is set to 300K, the simulation duration is 3000fs, and the time step is 1fs.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] This invention provides a heterostructure of sodium-ion battery anode material, its construction method, and its performance prediction method. It utilizes first-principles density functional theory simulation and the CASTEP module to perform SiC / Nb... 1-x A x A CO2 heterostructure model was constructed, and Nb was obtained by replacing Nb atoms with Ge or Sn alloying elements. 1-x A x CO2, then combined with 2D SiC materials to construct a SiC / Nb 1-x A x A CO2 heterostructure was used to obtain a sodium-ion battery anode material with improved electrochemical performance. The selected monolayer Nb2CO2MXene's excellent mechanical properties and high metallicity provide the anode material with good electronic conductivity and structural stability. The introduction of the ceramic semiconductor material SiC, with its inherent high hardness and strength, further ensures excellent structural stability and high theoretical capacity, while simultaneously improving the performance of Nb2. 1-x A x The aggregation of CO2MXene nanosheets; the constructed heterostructure exhibits metallic behavior that improves the electronic conductivity of the anode material during battery operation; the combination of SiC and Nb 1-x Ax The heterostructure interface formed by CO2 plays an important role in promoting electronic conductivity and Na ion transport. In addition, due to the electronegativity of the alloying elements Ge and Sn being close to that of C, the AC bond chemical bond formed between the alloying elements and C is stronger than the Nb-C bond, thereby enhancing the stability of the material structure itself and thus helping to maintain the integrity of the electrode structure.

[0033] The SiC / Nb constructed in this invention 1-x A x The CO2 heterostructure exhibits significantly enhanced Na atom adsorption capacity. Furthermore, the synergistic effect of alloying element doping accelerates electronic conductivity, further improving its applicability as an electrode; in SiC / Nb 1-x A x In the interlayer of the CO2 heterostructure, Na exhibits a reduced diffusion barrier, which ensures its high ion mobility; compared with the intrinsic SiC / Nb2CO2 heterostructure, SiC / Nb 1-x A x CO2 exhibits a significantly improved theoretical capacity; Na-supported SiC / Nb 1-x A x CO2 heterostructures exhibit enhanced conductivity, while Na-adsorbed heterostructure systems demonstrate good energy stability. Furthermore, this invention, based on first-principles calculations, reveals the influence of alloying elements on the electrochemical behavior of anode materials at the microscopic level, and provides insights for rapidly and effectively predicting and designing novel electrode materials with stable structures and improved performance. Attached Figure Description

[0034] Figure 1 This is the Nb2CO2 single-layer model provided in the embodiments of the present invention.

[0035] Figure 2 This is a SiC single-layer model provided in the embodiments of the present invention.

[0036] Figure 3 The Nb provided in the embodiments of the present invention 1-x A x CO2 single-layer model.

[0037] Figure 4 This is the intrinsic SiC / Nb2CO2 heterostructure model provided in Comparative Example 1 of this invention.

[0038] Figure 5 The embodiments of this invention provide different concentrations of SiC / Nb. 1-x A x CO2 heterojunction model.

[0039] Figure 6The intrinsic SiC / Nb2CO2 and SiC / Nb provided in the embodiments of the present invention 1-x A x AIMD simulation of CO2 heterostructure, where Figure a is Comparative Example 1, Figure b is Example 1, Figure c is Example 2, Figure d is Example 3, and Figure e is Example 4.

[0040] Figure 7 These are Na adsorption models at different sites provided in the embodiments of the present invention, wherein Figure a shows Na adsorption on SiC / Nb. 1-x A x The adsorption model of CO2 on one side of the SiC heterostructure, Figure b shows the adsorption of Na on SiC / Nb. 1-x A x CO2 heterostructure Nb2CO2 / Nb 1-x A x The adsorption model on the CO2 side, Figure c shows the adsorption of Na on SiC / Nb. 1-x A x An adsorption model of CO2 in heterostructure layers.

[0041] Figure 8 The SiC / Nb provided in Embodiment 1 of this invention 0.75 Ge 0.25 The electronic band structure, density of states, and differential charge density diagrams of the CO2 heterostructure are shown, where figures a1 to a3 represent the SiC / Nb structure of Example 1. 0.75 Ge 0.25 Electron band structure, density of states, and differential charge density diagram of CO2 heterostructure.

[0042] Figure 9 The SiC / Nb provided in Embodiment 2 of the present invention 0.50 Ge 0.50 The electronic band structure, density of states, and differential charge density diagrams of the CO2 heterostructure are shown, where figures b1 to b3 represent the SiC / Nb structure from Example 2. 0.50 Ge 0.50 Electron band structure, density of states, and differential charge density diagram of CO2 heterostructure.

[0043] Figure 10 The SiC / Nb provided in Embodiment 3 of the present invention 0.75 Sn 0.25 The electronic band structure, density of states, and differential charge density diagrams of the CO2 heterostructure are shown, where diagrams c1 to c3 represent the SiC / Nb structure of Example 3. 0.75 Sn 0.25 Electron band structure, density of states, and differential charge density diagram of CO2 heterostructure.

[0044] Figure 11The SiC / Nb provided in Embodiment 4 of the present invention 0.50 Sn 0.50 Electronic band structure, density of states, and differential charge density diagrams of CO2 heterostructures, where d1 to d3 are SiC / Nb from Example 4. 0.50 Sn 0.50 Electron band structure, density of states, and differential charge density diagram of CO2 heterostructure.

[0045] Figure 12 The SiC / Nb provided in Embodiment 1 of the present invention 0.75 Ge 0.25 Electron band structure, density of states, and differential charge density diagrams of the sodium-modified CO2 heterostructure, where figures a1 to a3 represent the sodium-modified SiC / Nb structure from Example 1. 0.75 Ge 0.25 Electron band structure, density of states, and differential charge density diagram of CO2 heterostructure.

[0046] Figure 13 The SiC / Nb provided in Embodiment 2 of the present invention 0.50 Ge 0.50 The electronic band structure, density of states, and differential charge density diagrams of the CO2 heterostructure after sodium formation are shown. Figures b1 to b3 represent the sodium-formed SiC / Nb structure from Example 2. 0.50 Ge 0.50 Electron band structure, density of states, and differential charge density diagram of CO2 heterostructure.

[0047] Figure 14 The SiC / Nb provided in Embodiment 3 of the present invention 0.75 Sn 0.25 Electron band structure, density of states, and differential charge density diagrams of the sodium-modified CO2 heterostructure, where diagrams c1 to c3 represent the sodium-modified SiC / Nb structure from Example 3. 0.75 Sn 0.25 Electron band structure, density of states, and differential charge density diagram of CO2 heterostructure.

[0048] Figure 15 The SiC / Nb provided in Embodiment 4 of the present invention 0.50 Sn 0.50 Electron band structure, density of states, and differential charge density diagrams of the sodium-modified CO2 heterostructure, where d1 to d3 are the sodium-modified SiC / Nb structures from Example 4. 0.50 Sn 0.50 Electron band structure, density of states, and differential charge density diagram of CO2 heterostructure.

[0049] Figure 16The single Na atom provided in the embodiments of the present invention is intrinsically SiC / Nb2CO2 and SiC / Nb 1-x A x The diffusion barrier between CO2 heterostructure layers is shown in Figure A, which is Comparative Example 1, Figure B is Example 1, Figure C is Example 3, and Figure D is Example 4. Detailed Implementation

[0050] To enable those skilled in the art to better understand and implement the technical solutions of this invention, the invention is further described below with reference to specific embodiments. However, the embodiments are not intended to limit the invention. Unless otherwise specified, the following test methods and detection methods are conventional methods; unless otherwise specified, the reagents and raw materials are commercially available.

[0051] The following technical problems mentioned in the background of this invention are addressed: First, sodium has a relatively large atomic radius, resulting in large volume changes during charge and discharge. Long cycles can cause material structure collapse, reducing lifespan. Second, sodium has a low melting point, making it unsuitable as a direct negative electrode. Furthermore, it readily reacts with organic solvents and can form dendrites during cycling, posing safety risks. Second, because sodium ions have a larger ionic radius than lithium ions, the ion diffusion rate is slower, leading to greater volume expansion of the electrode material during charge and discharge. This results in poorer rate performance and cycle stability. While MXene possesses a hydrophilic surface, high metallic conductivity, a layered structure, and numerous metal surface active sites, providing abundant channels for sodium ion storage and transport, MXene inevitably stacks, reducing specific surface area and consequently decreasing ion adsorption sites. Moreover, multilayer MXene is not stacked in an orderly manner, thus negating the advantages of two-dimensional materials. Third, although SiC exhibits good thermal shock resistance, high temperature resistance, good chemical stability, and high modulus, it is also relatively brittle. Fourth, alloy-type anode materials possess high sodium storage capacity and relatively suitable operating potential. Among numerous novel anode materials, group IV alloying elements, including germanium and tin, can alloy with large amounts of sodium and have attracted considerable attention due to their high volumetric and mass capacity, low operating potential, and natural abundance. However, in practical applications, the excessive volume change of germanium and tin alloy-based anode materials leads to material pulverization or even detachment from the current collector, resulting in poor cycle performance and capacity decay.

[0052] The technical solution of the present invention will be described in detail below.

[0053] This invention first provides a method for constructing a heterostructure of sodium-ion battery anode material, including the following steps:

[0054] Bulk Nb2C and SiC structural models were constructed using Material Studio software. The bulk structures were optimized using the CASTEP module, and 2D Nb2CO2 and SiC single-cell models were obtained through the slicing function. Based on the single-cell models, monolayer Nb2CO2 and monolayer SiC supercell models were constructed.

[0055] Introducing alloying element A into a single-layer Nb₂CO₂ supercell yields Nb 1-x A x CO2 model.

[0056] For the intrinsic SiC / Nb2CO2 and Nb constructed above 1-x A x The CO2 heterostructure model is set with convergence parameters in the CASTEP module and fully relaxed to obtain the stable configuration with the lowest energy and the corresponding characteristic parameters, including changes in lattice parameters, bond lengths and bond angles.

[0057] The SiC supercell was placed on top of the Nb2CO2 supercell, and the SiC / Nb2CT was constructed using the Build layer function. x Heterogeneous structure model; in the Nb 1-x A x A monolayer SiC supercell was placed on top of the CO2 model, and after structural optimization using the CASTEP module, SiC / Nb was obtained. 1-x A x The CO2 heterostructure model is described, where the alloying element A is Ge or Sn, and X is 0.25 or 0.50.

[0058] It should be noted that when the alloying element A is Ge and X is 0.25, the SiC / Nb 1-x A x The CO2 heterostructure model is SiC / Nb 0.75 Ge 0.25 CO2, with a lattice parameter of 6.31 Å; when the alloying element A is Ge and X is 0.50, the SiC / Nb 1-x A x The CO2 heterostructure model is SiC / Nb 0.50 Ge 0.50 CO2, with a lattice parameter of 6.15 Å. When the alloying element A is Sn and X is 0.25, the SiC / Nb... 1-x A x The CO2 heterostructure model is SiC / Nb 0.75 Sn 0.25 CO2, with a lattice parameter of 6.46 Å; when the alloying element A is Sn and X is 0.50, the SiC / Nb 1-x Ax The CO2 heterostructure model is SiC / Nb 0.50 Sn 0.50 CO2, with a lattice parameter of 6.35 Å.

[0059] It should be noted that the monolayer Nb₂CO₂ supercell model is a 2×2×1 supercell model with lattice parameters and angles of a=b=3.18Å, α=β=90° and γ=120°, and Nb-C bond length of d. Nb-C =2.16 Å; the monolayer SiC supercell model is a 2×2×1 supercell model with lattice constants a=b=3.10 Å and Si-C bond length d. Si-C =1.78Å.

[0060] It should be emphasized that when the alloying element A is Ge and X is 0.25, the Nb 1-x A x The CO2 model is Nb 0.75 Ge 0.25 CO2 has a lattice constant of a = b = 3.10 Å and an Nb-C bond length of d. Nb-C =2.15Å, Ge-C bond length is d Ge-C =2.13Å; when the alloying element A is Ge and X is 0.50, the Nb 1-x A x The CO2 model is Nb 0.50 Ge 0.50 CO2 has a lattice constant of a = b = 3.02 Å and an Nb-C bond length of d. Nb-C =2.15Å, Ge-C bond length is d Ge-C =2.13Å.

[0061] When the alloying element A is Sn and X is 0.25, the Nb 1-x A x The CO2 model is Nb 0.75 Sn 0.25 CO2 has a lattice constant of a = b = 3.15 Å and an Nb-C bond length of d. Nb-C =2.15Å, Sn-C bond length is d Sn-C =2.17Å; when the alloying element A is Sn and X is 0.50, the Nb 1-x A x The CO2 model is Nb 0.50 Sn 0.50 CO2 has a lattice constant of a = b = 3.12 Å and an Nb-C bond length of d. Nb-C =2.15Å, Sn-C bond length is d Sn-C =2.17Å.

[0062] The second objective of this invention is to provide a heterostructure of sodium-ion battery anode material constructed using the above-described construction method.

[0063] The optimized intrinsic SiC / Nb2CO2 and SiC / Nb 1-x A x Structural stability calculations were performed on the CO2 heterostructure based on intrinsic SiC / Nb2CO2 and SiC / Nb 1-x A x The total energy after complete relaxation of the CO2 heterostructure is calculated. Intrinsic SiC / Nb2CO2 and SiC / Nb2CO2 are also calculated. 1-x A x Phonon spectra, formation energies (Ef), and ab initio molecular dynamics simulations (AIMD) of CO2 heterostructure models confirm the energy and thermodynamic stability of these heterostructure systems.

[0064] After confirming the stability of the heterostructure as described above, the intrinsic SiC / Nb2CO2 and SiC / Nb ratios were calculated. 1-x A x The electronic properties of CO2 heterostructures, including electronic band structure, density of states, differential charge density, work function, electronic localization function, and Mulliken population analysis, were studied to obtain the influence of alloying element types and concentrations on conductivity, electronic structure, and interatomic bonding.

[0065] The third objective of this invention is to provide a method for predicting the performance of the aforementioned sodium-ion battery anode material heterostructure, wherein the performance prediction includes energy stability prediction, thermodynamic stability prediction, sodium ion adsorption stability prediction on the heterostructure, and conductivity prediction.

[0066] The performance prediction method includes the following steps:

[0067] For the SiC / Nb 1-x A x Ab initio molecular dynamics simulations were performed using a CO2 heterostructure model to obtain energy-time curves; the SiC / Nb ratio was calculated. 1-x A x The formation energy and phonon spectrum of the CO2 heterostructure model are used to predict energy stability based on the energy-time variation curve, and thermodynamic stability is also predicted based on the formation energy and phonon spectrum.

[0068] In the SiC / Nb 1-x A x SiC side and Nb in CO2 heterostructure 1-x A x CO2 side and the SiC / Nb 1-x A xNa atoms were added to different typical sites in the interlayer of the CO2 heterostructure to obtain a sodium atom adsorption model.

[0069] Specifically, the method for constructing the sodium atom adsorption model is as follows:

[0070] Na atoms were added to C atoms on one side of SiC, Si atoms, the top of C atoms in SiC, and at a distance of 2 Å above the Si-C bond bridge site, resulting in Na in SiC / Nb. 1-x A x Adsorption model of CO2 on one side of SiC heterostructure.

[0071] Select Nb2CO2 / Nb 1-x A x Adding Na atoms 2 Å above the C, O, and Nb / A atoms on the CO2 side, the top of the Nb-Nb-C atoms, and above the bridge site of the Nb-O / AC bond, yields Na in SiC / Nb 1-x A x CO2 heterostructure Nb2CO2 / Nb 1-x A x Adsorption model on the CO2 side.

[0072] Na atoms were added at the top of the interlayer C atoms, O atoms, Nb / A atoms, the top of the Nb-Nb-C atoms, and 2 Å above the bridge site of the Nb-O / AC bond, resulting in Na atoms in SiC / Nb 1-x A x An adsorption model of CO2 in heterostructure layers.

[0073] The adsorption structure obtained above was fully relaxed, and the adsorption energy of the stable configuration was calculated, i.e. E ad Integrate characteristic parameters; compare the adsorption energies of various heterostructures, and select the adsorption model of the heterostructure with the most stable adsorption energy in each type of heterostructure.

[0074] Based on the most stable heterostructure adsorption model mentioned above, the obtained electronic band structure, density of states, differential charge density, work function, electronic localization function, and Mulliken population analysis were analyzed to reveal the microscopic mechanism of the changes in electronic properties of the system before and after sodium adsorption.

[0075] The adsorption energy of sodium atoms on the surface of the negative electrode material was calculated to predict the adsorption stability of sodium ions on the heterostructure. Based on the adsorption energy results, diffusion paths of Na atoms were set on both sides and between the layers of each heterostructure. The most stable adsorption configuration and the adjacent most stable adsorption configuration were selected from the stable adsorption model using Reaction Preview as the starting state and final state of migration, respectively, and used as reactants and products.

[0076] Based on the minimum energy configuration of the initial and final states, the CI-NEB method was used to calculate the transition state, analyze the obtained migration barrier and diffusion rate, obtain the optimal reaction path, and establish the influence mechanism of alloying elements on the diffusion kinetics of heterostructures.

[0077] By calculating SiC / Nb 1-x A x Electronic property data of CO2 heterostructure before and after sodium ion adsorption, and sodium ion adsorption data in SiC / Nb 1-x A x The adsorption behavior, diffusion kinetics, open-circuit voltage, and theoretical specific capacity of CO2 on heterostructures are studied to predict conductivity, power density, and cycle performance.

[0078] Based on the adsorption energy of sodium atoms on the surface of the negative electrode material, the first layer of sodium atoms is added layer by layer at the most stable site, and the corresponding sequence adsorption energy, E, is calculated. layer-n Then, a second sodium atom layer is added to the substable site, and the hierarchical adsorption energy is obtained sequentially until the value is positive or close to positive, which is the maximum number of sodium atom layers that can be accommodated.

[0079] Structural and thermal stability simulations were performed for each heterostructure with different Na atom concentrations. Phonon dispersion curve calculations were performed in the CASTEP module, and thermal stability simulations were implemented using first-principles molecular dynamics in the DMol3 module.

[0080] To accurately determine the maximum adsorption concentration of Na atoms, host atoms are added to the substrate one by one, and the corresponding order adsorption energies, E, are calculated simultaneously. sae This process continues until the value becomes positive, in order to accurately obtain the maximum Na atom storage concentration for each heterostructure.

[0081] With the insertion of sodium atoms, the formation energy of the anode material loaded with the same concentration of Na atoms under different configurations was calculated, and convex hull diagrams were plotted to further obtain the energy-stable intermediate phase during the Na loading process.

[0082] Based on the above convex hull diagram, the open-circuit voltage corresponding to the stable intermediate point is obtained, and the theoretical specific capacity at the maximum Na atom concentration is calculated. The changes in the open-circuit voltage and theoretical specific capacity of the system before and after the introduction of alloying elements are analyzed.

[0083] In a preferred embodiment, the electronic performance data includes electronic band structure, density of states, differential charge density, and electronic localization function.

[0084] In a preferred embodiment, the calculation is implemented in the first-principles CASTEP module, and the exchange-correlation functional is described using the GGA-PBE generalized gradient method.

[0085] In this invention, when calculating electronic performance data, the plane wave cutoff energy is set to 450 eV, and a 4×4×1 K-point grid is used for Brillouin zone integration; during the calculation process, atoms are fully relaxed, and the force and energy convergence criteria are set to 0.01 eV Å, respectively. -1 and 1×10 -5 eV.

[0086] It is important to emphasize that in the adsorption behavior, diffusion kinetics and theoretical specific capacity calculations, the DFT-D3 method with Grimme correction is used to describe long-range van der Waals interactions, and a vacuum layer greater than 15 Å is set along the z-direction to avoid interlayer interactions.

[0087] It should be noted that the ab initio molecular dynamics simulation was performed under the conditions of temperature and NVT ensemble controlled by the Nosé-Hoover method. The temperature was set to 300K, the simulation duration was 3000fs, and the time step was 1fs.

[0088] The invention will now be described in detail through the following embodiments and comparative examples.

[0089] Example 1

[0090] A SiC / Nb 0.75 Ge 0.25 The method for constructing CO2 heterostructures includes the following steps:

[0091] Bulk Nb2C and SiC structural models were constructed using Material Studio software. The bulk structures were optimized using the CASTEP module, and 2D Nb2CO2 and SiC single-cell models were obtained through the slicing function. Based on the single-cell models, monolayer Nb2CO2 and monolayer SiC supercell models were constructed.

[0092] Introducing the alloying element Ge into a single-layer Nb₂CO₂ supercell yields Nb 0.75 Ge 0.25 CO2 model.

[0093] For the Nb constructed above 0.75 Ge 0.25 The CO2 heterostructure model was configured with computational parameters in the CASTEP module. The plane wave cutoff energy was set to 450 eV, and a 4×4×1 K-point grid was used for Brillouin zone integration. During the calculation, atoms were fully relaxed, and the force and energy convergence criteria were set to 0.01 eV Å. -1 and 1×10 -5 At eV, complete relaxation is performed to obtain the stable configuration with the lowest energy and the corresponding characteristic parameters, including changes in lattice parameters, bond lengths and bond angles.

[0094] The SiC supercell was placed on top of the Nb2CO2 supercell, and the SiC / Nb2CT was constructed using the Build layer function. 25 Heterogeneous structure model; in the Nb 0.75 Ge 0.25 A monolayer SiC supercell was placed on top of the CO2 model, and after structural optimization using the CASTEP module, SiC / Nb was obtained. 0.75 Ge 0.25 CO2 heterostructure model.

[0095] Example 2

[0096] A SiC / Nb 0.50 Ge 0.50 The method for constructing CO2 heterostructures includes the following steps:

[0097] Bulk Nb2C and SiC structural models were constructed using Material Studio software. The bulk structures were optimized using the CASTEP module, and 2D Nb2CO2 and SiC single-cell models were obtained through the slicing function. Based on the single-cell models, monolayer Nb2CO2 and monolayer SiC supercell models were constructed.

[0098] Introducing the alloying element Ge into a single-layer Nb₂CO₂ supercell yields Nb 0.50 Ge 0.50 CO2 model.

[0099] For the Nb constructed above 0.50 Ge 0.50 The CO2 heterostructure model was configured with computational parameters in the CASTEP module. The plane wave cutoff energy was set to 450 eV, and a 4×4×1 K-point grid was used for Brillouin zone integration. During the calculation, atoms were fully relaxed, and the force and energy convergence criteria were set to 0.01 eV Å. -1 and 1×10 -5 At eV, complete relaxation is performed to obtain the stable configuration with the lowest energy and the corresponding characteristic parameters, including changes in lattice parameters, bond lengths and bond angles.

[0100] The SiC supercell was placed on top of the Nb2CO2 supercell, and the SiC / Nb2CT was constructed using the Build layer function. 50 Heterogeneous structure model; in the Nb 0.50 Ge 0.50 A monolayer SiC supercell was placed on top of the CO2 model, and after structural optimization using the CASTEP module, SiC / Nb was obtained. 0.50 Ge 0.50 CO2 heterostructure model.

[0101] Example 3

[0102] A SiC / Nb 0.75 Sn 0.25 The method for constructing CO2 heterostructures includes the following steps:

[0103] Bulk Nb2C and SiC structural models were constructed using Material Studio software. The bulk structures were optimized using the CASTEP module, and 2D Nb2CO2 and SiC single-cell models were obtained through the slicing function. Based on the single-cell models, monolayer Nb2CO2 and monolayer SiC supercell models were constructed.

[0104] Introducing the alloying element Sn into a single-layer Nb₂CO₂ supercell yields Nb 0.75 Sn 0.25 CO2 model.

[0105] For the Nb constructed above 0.75 Sn 0.25 The CO2 heterostructure model was configured with computational parameters in the CASTEP module. The plane wave cutoff energy was set to 450 eV, and a 4×4×1 K-point grid was used for Brillouin zone integration. During the calculation, atoms were fully relaxed, and the force and energy convergence criteria were set to 0.01 eV Å. -1 and 1×10 -5 At eV, complete relaxation is performed to obtain the stable configuration with the lowest energy and the corresponding characteristic parameters, including changes in lattice parameters, bond lengths and bond angles.

[0106] The SiC supercell was placed on top of the Nb2CO2 supercell, and the SiC / Nb2CT was constructed using the Build layer function. 25 Heterogeneous structure model; in the Nb 0.75 Sn 0.25 A monolayer SiC supercell was placed on top of the CO2 model, and after structural optimization using the CASTEP module, SiC / Nb was obtained. 0.75 Sn 0.25 CO2 heterostructure model.

[0107] Example 4

[0108] A SiC / Nb 0.50 Sn 0.50 The method for constructing CO2 heterostructures includes the following steps:

[0109] Bulk Nb2C and SiC structural models were constructed using Material Studio software. The bulk structures were optimized using the CASTEP module, and 2D Nb2CO2 and SiC single-cell models were obtained through the slicing function. Based on the single-cell models, monolayer Nb2CO2 and monolayer SiC supercell models were constructed.

[0110] Introducing the alloying element Sn into a single-layer Nb₂CO₂ supercell yields Nb 0.50 Sn 0.50 CO2 model.

[0111] For the Nb constructed above 0.50 Sn 0.50 The CO2 heterostructure model was configured with computational parameters in the CASTEP module. The plane wave cutoff energy was set to 450 eV, and a 4×4×1 K-point grid was used for Brillouin zone integration. During the calculation, atoms were fully relaxed, and the force and energy convergence criteria were set to 0.01 eV Å. -1 and 1×10 -5 At eV, complete relaxation is performed to obtain the stable configuration with the lowest energy and the corresponding characteristic parameters, including changes in lattice parameters, bond lengths and bond angles.

[0112] The SiC supercell was placed on top of the Nb2CO2 supercell, and the SiC / Nb2CT was constructed using the Build layer function. 50 Heterogeneous structure model; in the Nb 0.50 Sn 0.50 A monolayer SiC supercell was placed on top of the CO2 model, and after structural optimization using the CASTEP module, SiC / Nb was obtained. 0.50 Sn 0.50 CO2 heterostructure model.

[0113] To further illustrate the technical effects of the present invention, a comparative example is also provided, as follows:

[0114] Comparative Example 1

[0115] A method for constructing a SiC / Nb2CO2 heterostructure includes the following steps:

[0116] Bulk Nb2C and SiC structural models were constructed using Material Studio software. The bulk structures were optimized using the CASTEP module, and 2D Nb2CO2 and SiC single-cell models were obtained through the slicing function. Based on the single-cell models, monolayer Nb2CO2 and monolayer SiC supercell models were constructed.

[0117] For the constructed monolayer Nb₂CO₂ supercell model, the computational parameters were set in the CASTEP module. The plane wave cutoff energy was set to 450 eV, and a 4×4×1 K-point grid was used for Brillouin zone integration. During the calculation, atoms were fully relaxed, and the force and energy convergence criteria were set to 0.01 eV Å. -1 and 1×10 -5 At eV, complete relaxation is performed to obtain the stable configuration with the lowest energy and the corresponding characteristic parameters, including changes in lattice parameters, bond lengths and bond angles.

[0118] The SiC supercell was placed on top of the Nb2CO2 supercell, and the SiC / Nb2CO2 heterostructure model was constructed using the Build layer function. After structural optimization using the CASTEP module, the SiC / Nb2CO2 heterostructure model was obtained.

[0119] The parameters and performance of the heterostructure models constructed in Examples 1-4 and Comparative Example 1 were tested, and the results are as follows.

[0120] Example 5

[0121] A sodium-ion battery anode material SiC / Nb 0.75 Ge 0.25 A method for predicting the performance of CO2 heterostructures includes the following steps:

[0122] For the SiC / Nb 0.75 Ge 0.25 Ab initio molecular dynamics simulations were performed using a CO2 heterostructure model to obtain energy-time variation curves, such as... Figure 6 Figure b in the diagram; calculate the SiC / Nb ratio. 1-x A x The formation energy and phonon spectrum of the CO2 heterostructure model are used to predict energy stability based on the energy-time variation curve, and thermodynamic stability is also predicted based on the formation energy and phonon spectrum.

[0123] SiC / Nb 0.75 Ge 0.25 The formation energies of CO2 heterostructures are -2.13 eV and SiC / Nb, respectively. 0.75 Ge 0.25 The formation energy of the CO2 heterostructure is negative, indicating that the system is a spontaneously exothermic reaction.

[0124] from Figure 6 As shown in Figure b, after 3000 fs of complete relaxation at room temperature, SiC / Nb 0.75 Ge 0.25 The CO2 heterostructure undergoes only minor changes with minimal energy fluctuations, indicating that the SiC / Nb 0.75Ge 0.25 The CO2 heterostructure model is thermodynamically stable.

[0125] In the SiC / Nb 0.75 Ge 0.25 SiC side and Nb in CO2 heterostructure 0.75 Ge 0.25 CO2 side and the SiC / Nb 0.75 Ge 0.25 By adding Na atoms to different typical sites in the interlayer of a CO2 heterostructure, a sodium atom adsorption model was obtained, as follows:

[0126] Na atoms were added to C atoms on one side of SiC, Si atoms, the top of C atoms in SiC, and at a distance of 2 Å above the Si-C bond bridge site, resulting in Na in SiC / Nb. 0.75 Ge 0.25 Adsorption model of CO2 on one side of SiC heterostructure.

[0127] Select Nb 0.75 Ge 0.25 Adding Na atoms 2 Å above the C, O, and Nb / A atoms on the CO2 side, the top of the Nb-Nb-C atoms, and above the bridge site of the Nb-O / AC bond, yields Na in SiC / Nb 0.75 Ge 0.25 CO2 heterostructure Nb 0.75 Ge 0.25 Adsorption model on the CO2 side.

[0128] Na atoms were added at the top of the interlayer C atoms, O atoms, Nb / A atoms, the top of the Nb-Nb-C atoms, and 2 Å above the bridge site of the Nb-O / AC bond, resulting in Na atoms in SiC / Nb 0.75 Ge 0.25 An adsorption model of CO2 in heterostructure layers.

[0129] Based on the above adsorption model of sodium atoms at different sites, the adsorption energy E on the surface of the negative electrode material is calculated when sodium atoms are adsorbed at different sites. ad The perpendicular distance H from the Na atom to the substrate is shown in Table 2, which helps predict the adsorption stability of sodium ions on the heterostructure. Table 2 shows that the adsorption energies of all stable Na atom adsorption configurations are negative, indicating that Na atoms are stably adsorbed at all sites. Specifically, the adsorption energies of Na atoms in SiC / Nb... 0.75 Ge 0.25 The adsorption energy at the top of the C atom on one side of the CO2 heterostructure SiC is more negative than that in the pure SiC / Nb2CO2 heterostructure, indicating that Na atoms tend to occupy these sites.

[0130] By calculating SiC / Nb 0.75 Ge 0.25 Electronic property data of CO2 heterostructure before and after sodium ion adsorption, and sodium ion adsorption data in SiC / Nb 0.75 Ge 0.25 The adsorption behavior, diffusion kinetics, open-circuit voltage, and theoretical specific capacity of CO2 heterostructures are studied to predict conductivity.

[0131] SiC / Nb 0.75 Ge 0.25 The configuration with the lowest formation energy for CO2 heterostructures is calculated. The electronic band structure, density of states, differential charge density, and Mulliken population analysis related electronic properties are then performed. Figures 8-15 As shown. Based on the electronic band structure and density of states before and after Na adsorption, it can be seen that the Na-adsorbed SiC / Nb... 0.75 Ge 0.25 The metallic nature of CO2 heterostructures is beneficial for improving electrode conductivity. The differential charge density of Na-adsorbed heterostructures is as follows: Figure 16 As shown, a large number of electrons accumulate on the SiC side, while electrons are lost around Na atoms, indicating a transfer of electrons from Na atoms to the substrate. Simultaneously, the formation of electron density between Na atoms and the substrate indicates that a strong chemical interaction dominates between them. Mulliken population analysis further clarifies these results, showing that Na atoms migrate to SiC / Nb... 0.75 Ge 0.25 The CO2 heterostructure exhibits electron transfer values ​​of 0.809 e, 0.862 e, 0.839 e, and 0.867 e. Electron localization function calculations show a significant electron density accumulation between Ge and C atoms, indicating covalent bonding. Electronic band structure and density of states analysis reveal that, compared to the intrinsic SiC / Nb2CO2 heterostructure, the introduction of alloying elements significantly increases the number of electronic states at the Fermi level, resulting in a significantly improved conductivity. Furthermore, the heterostructure retains its metallic properties despite the continuous incorporation of Na atoms. The excellent theoretical conductivity and relatively small molar mass of the alloying element Ge contribute to the improved conductivity of SiC / Nb2CO2. 0.75 Ge 0.25 The CO2 heterostructure exhibits a significantly improved Na storage capacity compared to the original heterostructure.

[0132] Example 6

[0133] SiC / Nb in Example 5 0.75 Ge 0.25 The CO2 heterostructure is replaced with SiC / Nb 0.50 Ge 0.50 CO2 heterostructure.

[0134] Example 7

[0135] SiC / Nb in Example 5 0.75 Ge 0.25 The CO2 heterostructure is replaced with SiC / Nb 0.75 Sn 0.25 CO2 heterostructure.

[0136] Example 8

[0137] SiC / Nb in Example 5 0.75 Ge 0.25 The CO2 heterostructure is replaced with SiC / Nb 0.50 Sn 0.50 CO2 heterostructure.

[0138] The detection data of each heterostructure in Examples 6 to 8 are shown in Tables 1 and 2 below.

[0139] Modeling was performed using Material Studio software. Literature review confirmed that Nb₂AlC belongs to the hexagonal crystal system with space group P63 / mmc. The precursor Nb₂AlC was then obtained from the Materials Project crystal structure database. Geometric optimization of the bulk crystal structure was performed to obtain a stable configuration. A single-cell Nb₂C MXene monolayer was obtained using the Cleave Surface function, and then a 2×2×1 supercell Nb₂CO₂MXene monolayer was obtained using Supercell. Figure 1 As shown. By setting appropriate parameters on the CASTEP module, a stable structural model is obtained by performing complete structural relaxation of the supercell monolayer using the BFGS algorithm. Then, relevant characteristic parameters are calculated, including lattice parameters and angles a=b=3.18 Å, α=β=90° and γ=120°, and the Nb-C bond length is... d Nb-C =2.16 Å.

[0140] Single-layer SiC model construction and optimization:

[0141] The bulk structure of SiC was obtained from the MS structure library and its geometry was optimized. Based on a stable crystal structure model, a single-layer SiC unit cell structure was obtained by cross-sectioning, resulting in a 2×2×1 supercell model. Figure 2 As shown. Based on the characteristics of SiC, the computational parameters were reasonably set to optimize its structure, resulting in a monolayer SiC supercell model with the lowest total energy. Then, relevant characteristic parameters were calculated, with the lattice constant being a=b=3.10 Å and the Si-C bond length being... d Si-C =1.78 Å.

[0142] Single-layer Nb 1-x Ax CO2 Model Construction and Optimization:

[0143] Constructing Nb with different contents of Ge and Sn 1-x A x The 2×2×1 supercell model of CO2 Nb 0.75 Ge 0.25 CO2, Nb 0.50 Ge 0.50 CO2, Nb 0.75 Sn 0.25 CO2 and Nb 0.50 Ge 0.50 CO2, using CASTEP to set structural optimization parameters and perform geometric optimization, yields a stable monolayer constituting the heterostructure, such as... Figure 3 As shown in Table 1, the results of the lattice constants and bond lengths for each monolayer are presented.

[0144] Table 1 Nb of the present invention 1-x A x Lattice constant and bond length of CO2 monolayer

[0145]

[0146] Intrinsic SiC / Nb2CO2 and SiC / Nb 1-x A x CO2 heterostructure model construction and optimization:

[0147] Establish intrinsic SiC / Nb2CO2 and SiC / Nb with different alloying elements and contents. 1-x A x CO2 heterostructure model, SiC / Nb 0.75 Ge 0.25 CO2, SiC / Nb 0.50 Ge 0.50 CO2, SiC / Nb 0.75 Sn 0.25 CO2, SiC / Nb 0.50 Sn 0.50 CO2, such as Figure 5 and Figure 6 As shown, the stable configurations of each heterostructure were obtained based on first-principles optimization. The effects of the type and content of alloying elements on the lattice parameters of the heterostructures were analyzed. The lattice parameters of each heterostructure were 6.31 Å, 6.15 Å, 6.46 Å and 6.35 Å, respectively.

[0148] Intrinsic SiC / Nb2CO2 and SiC / Nb 1-x A x CO2 heterostructure stability:

[0149] Energy and thermodynamic stability calculations were performed on the optimized heterostructure model to obtain the formation energy of each heterostructure and the energy-time variation curves in the AIMD simulation, such as... Figure 6 As shown. The formation energies of the heterostructures with different alloying element types and concentrations are -6.26 eV, -2.13 eV, -2.06 eV, -2.91 eV, and -2.79 eV, respectively. The formation energy of each heterostructure is negative, indicating that the system undergoes a spontaneously exothermic reaction. The corresponding formation energy formula is:

[0150] ;

[0151] in, The total energy of the heterostructure. and These represent the total energy of the two monolayers that make up the heterogeneous structure.

[0152] The energy-time curves from the AIMD simulation show that after 3000 fs of complete relaxation at room temperature, each heterostructure undergoes only minor changes and energy fluctuations, indicating that the model under consideration is thermodynamically stable.

[0153] Sodium atoms are intrinsic and SiC / Nb 1-x A x Study on CO2 adsorption behavior on heterostructure

[0154] Sodium ion adsorption model construction:

[0155] Based on the optimized intrinsic SiC / Nb2CO2 and SiC / Nb 1-x A x Using a CO2 heterostructure as a substrate, adsorption structures of individual Na atoms were constructed at typical sites on both sides of the heterostructure and between layers, such as... Figure 7 As shown. Specifically, for the SiC side, the C atoms on that side... C Si atoms T Si The top T of C atoms in SiC C(SiC) and Si-C bond bridge site B Si-C Adding Na atoms at a distance of 2 Å from the top, we obtain Na in SiC / Nb 1-x A x Adsorption model of CO2 on one side of SiC heterostructure.

[0156] For Nb2CO2 / Nb 1-x A x C atom T on the CO2 side C O atoms T O Nb / A atoms T Nb / T A The top of the Nb-Nb-C atom, the top TNb-Nb-C and the bridge site B of the Nb-O / AC bond Nb-O / B A-C Adding Na atoms at a distance of 2 Å from the top, we obtain Na in SiC / Nb 1- x A x CO2 heterostructure Nb2CO2 / Nb 1-x A x Adsorption model on the CO2 side.

[0157] For interlayer C atoms T C O atoms T O Nb / A atoms T Nb / T A The top of the Nb-Nb-C atom, the top T Nb-Nb-C and the bridge site B of the Nb-O / AC bond Nb-O / B A-C Adding Na atoms at a distance of 2 Å from the top, we obtain Na in SiC / Nb 1-x A x An adsorption model of CO2 in heterostructure layers.

[0158] Adsorption energy calculation:

[0159] Structural optimization was performed on the different site adsorption configurations constructed in the above steps to obtain the adsorption configuration that minimizes energy, and the adsorption energy at different sites was calculated. E ad The results, including the perpendicular distance H from the Na atom to the substrate, are shown in Table 2. The adsorption energy formula can be expressed as:

[0160] ;

[0161] in, Sodium-modified SiC / Nb 1-x A x Total energy of CO2 heterojunction This represents the total energy of the heterostructure without adsorbed Na atoms. This represents the total energy of a single Na atom in the bulk phase.

[0162] As can be clearly seen from Table 2, the adsorption energies of all stable Na atom adsorption configurations are negative, indicating the stable adsorption of Na atoms at each site. Specifically, the adsorption energies of Na atoms in SiC / Nb... 1-x A x The adsorption energy at the top of the C atom on one side of the CO2 heterostructure SiC is more negative than that in the pure SiC / Nb2CO2 heterostructure, indicating that Na atoms tend to occupy these sites.

[0163] Table 2 Adsorption energies and perpendicular distances to the substrate for stable adsorption configurations of Na atoms

[0164]

[0165] Electronic property calculation

[0166] By comparing and selecting the configuration with the lowest formation energy for each heterostructure, the electronic band structure, density of states, differential charge density, and Mulliken population analysis were performed to determine the relevant electronic properties, such as... Figures 8-15 As shown. Based on the electronic band structure and density of states before and after Na adsorption, it can be seen that the Na-adsorbed SiC / Nb... 1-x A x The metallic nature of CO2 heterostructures is beneficial for improving electrode conductivity. The differential charge density of Na-adsorbed heterostructures is as follows: Figure 16 As shown, a large number of electrons accumulate on the SiC side, while electrons are lost around Na atoms, indicating a transfer of electrons from Na atoms to the substrate. Simultaneously, the formation of electron density between Na atoms and the substrate indicates that a strong chemical interaction dominates between them. Mulliken population analysis further clarifies these results, showing that Na atoms migrate to four SiC / Nb44444444444444444444444444444444446 ... 1-x A x The CO2 heterostructures transferred 0.809 e, 0.862 e, 0.839 e and 0.867 e, respectively.

[0167] The aforementioned geometric optimization and performance calculations are implemented in the first-principles CASTEP module, and the exchange-correlation functional is described using the GGA-PBE generalized gradient.

[0168] Structural optimization and electronic property calculations were performed with a plane wave cutoff energy set to 450 eV and Brillouin zone integration using a 4×4×1 K-point grid. Throughout the calculations, atoms were fully relaxed, and the force and energy convergence criteria were set to 0.01 eV Å. -1 and 1×10 -5 eV.

[0169] In the adsorption-diffusion and capacity calculations, the DFT-D3 method with Grimme correction was used to describe long-range van der Waals interactions. To effectively avoid interlayer interactions, a vacuum layer greater than 15 Å was set along the z-direction.

[0170] In this invention, ab initio molecular dynamics simulations are performed under the conditions of temperature control and NVT ensemble control using the Nosé-Hoover method. The temperature is set to 300K, the simulation duration is 3000 fs, and the time step is 1 fs.

[0171] Study on the diffusion dynamics of Na atoms in heterostructures

[0172] Diffusion path settings

[0173] The most stable, second most stable, and adjacent most stable adsorption configurations were used as the initial, intermediate, and final states, respectively, and possible sodium diffusion paths were set using MS software. SiC / Nb 0.75 Ge 0.25 Taking CO2 as an example, on the SiC side, the most stable site and the adjacent most stable T C The site is defined as an initial state and a final state, with T as the starting point. Si and T C(SiC) As an intermediate state, three paths are set: T C -T C T C -T Si -T C and T C -T C(SiC) -T C For Nb 75 Ge 25 On the CO2 side, set to T C -T C T C -T O -T C and T C- T Nb -T C For inter-layer paths, the three paths are T in sequence. C -T C T C -T Nb -T C and T C -T Ge -T C ,like Figure 16 As shown.

[0174] Transitional state search

[0175] The CI-NEB (Climbing Elastic Band) method was used to search for transition states to select the optimal migration path. Furthermore, the diffusion barriers and diffusion coefficients of sodium atoms along different paths were obtained, and the influence mechanism of alloying elements on diffusion kinetics was clarified.

[0176] In summary, compared with SiC / Nb2CO2, the SiC / Nb2CO2 constructed in this invention has better performance. 1-x A x The CO2 heterostructure model exhibits improved stability: due to the electronegativity of alloying elements Ge and Sn being similar to that of C, the bond strength of Sn-C / Ge-C bonds is stronger than that of Nb-C bonds, thus endowing SiC / Nb with improved stability. 1-x A xCO2 exhibits good structural stability. Electron localization function calculations show a significant electron density accumulation between the Ge-C and Sn-C bonds, indicating covalent interactions. Based on AIMD simulations, after complete relaxation at room temperature for 3000 fs, the SiC / Nb constructed in Examples 1-4 of this invention… 1-x A x The CO2 heterostructure model exhibits only minor changes and small energy fluctuations, fully demonstrating that the heterostructure model constructed in this invention is thermodynamically stable.

[0177] Through electronic band and density of states analysis, compared with the intrinsic SiC / Nb2CO2 heterostructure, the introduction of alloying elements significantly increased the electronic states at the Fermi level, and the heterostructure exhibited a significantly improved electrical conductivity. Moreover, the heterostructure still maintained its metallic properties as Na atoms were continuously embedded.

[0178] Adsorption energy calculations show that, due to the synergistic effect between the two monolayers, SiC / Nb 1-x A x Compared to the intrinsic SiC / Nb2CO2 heterostructure, the CO2 heterostructure exhibits a higher Na atom adsorption strength. Benefiting from the excellent theoretical capacities of the alloying elements Ge and Sn, and their smaller molar mass, the heterostructure demonstrates a significantly improved Na storage capacity compared to the original heterostructure. Furthermore, the SiC / Nb2CO2 heterostructure constructed in this invention… 1-x A x The CO2 interlayer exhibits a lower diffusion barrier, which is more conducive to the insertion and rapid migration rate of sodium atoms, enabling rapid charge and discharge rates.

[0179] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for constructing a heterostructure of a sodium-ion battery negative electrode material, characterized in that, Includes the following steps: Bulk Nb2C and SiC structural models were constructed, and the bulk Nb2C and SiC structural models were optimized to obtain 2DNb2CO2 single-cell models and SiC single-cell models. Based on the Nb2CO2 single-cell models and SiC single-cell models, monolayer Nb2CO2 supercell models and monolayer SiC supercell models were constructed. Introducing alloying element A into the single-layer Nb₂CO₂ supercell model yields Nb 1-x A x CO2 model; In the Nb 1-x A x A monolayer SiC supercell was placed on top of the CO2 model. After structural optimization, SiC / Nb was obtained. 1-x A x CO2 heterostructure model; The alloying element A is Ge or Sn, and X is 0.15~0.

75.

2. The construction method according to claim 1, characterized in that, When the alloying element A is Ge and X is 0.25, the SiC / Nb 1-x A x The CO2 heterostructure model is SiC / Nb 0.75 Ge 0.25 CO2, with a lattice parameter of 6.31 Å; when the alloying element A is Ge and X is 0.50, the SiC / Nb 1-x A x The CO2 heterostructure model is SiC / Nb 0.50 Ge 0.50 CO2, with a lattice parameter of 6.15 Å.

3. The construction method according to claim 1, characterized in that, When the alloying element A is Sn and X is 0.25, the SiC / Nb 1-x A x The CO2 heterostructure model is SiC / Nb 0.75 Sn 0.25 CO2, with a lattice parameter of 6.46 Å; when the alloying element A is Sn and X is 0.50, the SiC / Nb 1-x A x The CO2 heterostructure model is SiC / Nb 0.50 Sn 0.50 CO2, with a lattice parameter of 6.35 Å.

4. A method for predicting the performance of a heterostructure of sodium-ion battery anode material, wherein the heterostructure of sodium-ion battery anode material is obtained by the construction method according to any one of claims 1 to 3, characterized in that, The performance predictions include energy stability prediction, thermodynamic stability prediction, sodium ion adsorption stability prediction on heterostructures, and electrical conductivity prediction. The performance prediction method includes the following steps: For the SiC / Nb 1-x A x Ab initio molecular dynamics simulations were performed using a CO2 heterostructure model to obtain energy-time curves; the SiC / Nb ratio was calculated. 1-x A x The formation energy and phonon spectrum of the CO2 heterostructure model are used to predict energy stability based on the energy-time variation curve, and thermodynamic stability is also predicted based on the formation energy and phonon spectrum. In the SiC / Nb 1-x A x SiC side and Nb in CO2 heterostructure 1-x A x CO2 side and the SiC / Nb 1-x A x Na atoms were added to different typical sites in the interlayer of the CO2 heterostructure to obtain a sodium atom adsorption model. The adsorption energy of sodium atoms on the surface of the negative electrode material is calculated based on the sodium atom adsorption model, and the adsorption stability of sodium ions on the heterostructure is predicted. By calculating SiC / Nb 1-x A x Electronic property data of CO2 heterostructure before and after sodium ion adsorption, and sodium ion adsorption data in SiC / Nb 1-x A x The adsorption behavior, diffusion kinetics, open-circuit voltage, and theoretical specific capacity of CO2 heterostructures are studied to predict conductivity.

5. The performance prediction method for heterostructured sodium-ion battery anode materials according to claim 4, characterized in that, The specific method for constructing the sodium atom adsorption model is as follows: Na atoms were added to C atoms on one side of SiC, Si atoms, the top of C atoms in SiC, and at a distance of 2 Å above the Si-C bond bridge site, resulting in Na in SiC / Nb. 1-x A x Adsorption model of CO2 on one side of SiC heterostructure; Select Nb 1-x A x Adding Na atoms 2 Å above the C, O, and Nb / A atoms on the CO2 side, the top of the Nb-Nb-C atoms, and above the bridge site of the Nb-O / AC bond, yields Na in SiC / Nb 1-x A x CO2 heterostructure Nb 1-x A x Adsorption model on the CO2 side; Na atoms were added at the top of the interlayer C atoms, O atoms, Nb / A atoms, the top of the Nb-Nb-C atoms, and 2 Å above the bridge site of the Nb-O / AC bond, resulting in Na atoms in SiC / Nb 1-x A x An adsorption model of CO2 between heterostructure layers.

6. The performance prediction method for heterostructured sodium-ion battery anode materials according to claim 4, characterized in that, The calculations are implemented in the first-principles CASTEP module, and the exchange-correlation functional is described using the GGA-PBE generalized gradient method.

7. The performance prediction method for heterostructured sodium-ion battery anode materials according to claim 4, characterized in that, When calculating electronic performance data, the plane wave cutoff energy was set to 450 eV, and a 4×4×1 K-point grid was used for Brillouin zone integration. During the calculation, atoms were fully relaxed, and the force and energy convergence criteria were set to 0.01 eV Å. -1 and 1×10 -5 eV.

8. The method for predicting the performance of heterostructured sodium-ion battery anode materials according to claim 4, characterized in that, In the adsorption behavior, diffusion kinetics and theoretical specific capacity calculations, the DFT-D3 method with Grimme correction is used to describe long-range van der Waals interactions, and a vacuum layer greater than 15 Å is set along the z-direction to avoid interlayer interactions.

9. The method for predicting the performance of heterostructured sodium-ion battery anode materials according to claim 4, characterized in that, When performing ab initio molecular dynamics simulations, the Nosé-Hoover method was used to control the temperature and NVT ensemble. The temperature was set to 300K, the simulation duration was 3000fs, and the time step was 1fs.

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