Tantalum-sodium alloying modified sodium metal negative electrode material and preparation method and application thereof

Abstract

This invention belongs to the technical field of sodium-ion battery anode materials, and discloses a tantalum-sodium alloy modified sodium metal anode material, its preparation method, and its application. S1. In an argon atmosphere, solid sodium metal is mixed with a tantalum source, heated, and held at a constant temperature to obtain a molten material; S2. The temperature is further increased, and mechanical stirring is used to ensure uniform mixing of the molten material. Then, the mixture is kept at a constant temperature and allowed to cool naturally to room temperature to obtain a tantalum-sodium composite billet; S3. The tantalum-sodium composite billet is rolled to obtain the tantalum-sodium alloy modified sodium metal anode material. The anode material prepared by this invention forms a dense tantalum-sodium alloy layer on its surface, which can effectively inhibit sodium dendrite growth. When assembled with a sodium iron pyrophosphate cathode to form a sodium-ion battery, it exhibits excellent rate performance and long-cycle stability. This preparation process has low equipment requirements, is simple to operate, and highly controllable, making it easy to achieve industrial mass production, fundamentally solving the technical problems of dendrite growth and severe interfacial side reactions in pure sodium metal anodes.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery anode material technology, and more specifically to a tantalum-sodium alloy modified sodium metal anode, its preparation method and application, and a high-performance sodium-ion battery assembled using this anode. Background Technology

[0002] Sodium-ion batteries have become a core candidate battery system for large-scale electrochemical energy storage, low-speed new energy vehicles, and portable electronic devices due to the abundant and widely distributed availability of sodium resources in the Earth's crust, low cost, and strong compatibility with lithium-ion battery production processes. Metallic sodium has a capacity of 1166 mAh g⁻¹. -1 Its ultra-high theoretical specific capacity and low electrode potential of -2.71 V (vs. standard hydrogen electrode) make it an ideal choice for anode materials in sodium-ion batteries.

[0003] However, the practical application of pure sodium metal anodes faces the core technical challenge of sodium dendrite formation: First, sodium metal is prone to forming disordered sodium dendrites during deposition / stripping. Dendrite growth can pierce the battery separator, causing internal short circuits and posing serious safety hazards. Second, sodium metal has extremely high surface chemical activity, which leads to continuous irreversible side reactions with the electrolyte, generating a loose and unstable solid electrolyte interphase (SEI) film. This results in rapid consumption of electrolyte and active sodium, a significant reduction in battery coulombic efficiency, and ultimately, rapid capacity decay.

[0004] Among existing sodium metal anode modification technologies, sodium alloying has become a research focus due to its ability to fundamentally improve the deposition behavior and structural stability of sodium. However, traditional melt alloying methods have many drawbacks: sodium has high viscosity at conventional melting temperatures, making it difficult to achieve uniform dispersion of the doped phase and leading to agglomeration; furthermore, the lack of utilization of rolling stress makes it difficult to form a stable alloying interface layer that is tightly bonded to the sodium matrix, resulting in limited modification effects. Simultaneously, existing modification systems are poorly matched with commercially available sodium iron pyrophosphate cathodes, making it difficult to achieve ultra-long cycle stability at high rates, severely limiting their industrial application.

[0005] Therefore, there is an urgent need to develop a sodium metal anode modification method that is simple in process, requires no complex auxiliary equipment, has uniform doping, and has a stable interface. Summary of the Invention

[0006] The purpose of this invention is to solve the technical problems of uneven dispersion of doped phases, poor interface stability, and high requirements for some process equipment in the existing sodium metal anode alloying modification, which are difficult to industrialize. This invention provides a tantalum sodium alloy modified sodium metal anode material, its preparation method and application, and provides a sodium-ion battery assembled using this anode, which achieves high stability and low impedance of the anode material, as well as high rate and ultra-long cycle performance of the battery, and the preparation process is simple and the equipment requirements are low.

[0007] One objective of this invention is to provide a method for preparing a sodium metal anode material modified with tantalum-sodium alloy, comprising the following steps: S1. In an ultra-low water-oxygen argon atmosphere with moisture and oxygen content ≤0.01 ppm, solid sodium metal sheets with purity ≥99.9wt% and tantalum source are placed in a high-temperature resistant boron nitride crucible, heated to 200℃, and held for 10 min to completely melt the solid material to obtain molten material. The material is then heated to 300℃.

[0008] This temperature is much higher than the melting point of sodium, resulting in a low-viscosity liquid reaction environment that provides a good medium for the uniform dispersion of the tantalum-based phase. At the same time, argon is used as a protective gas, which can effectively prevent sodium metal from oxidizing at high temperatures or reacting with the protective gas, thus ensuring the purity of the negative electrode material.

[0009] S2. Mechanically stir for 10 min to ensure uniform mixing of the molten metal. The shear force of mechanical stirring breaks up the agglomerates of the tantalum-based phase, achieving uniform dispersion of the tantalum-based phase in liquid sodium. Subsequently, the mixture is kept at a constant temperature of 300℃ in an argon atmosphere for 15 min. The constant temperature and argon atmosphere eliminates bubbles generated during stirring and prevents the formation of pores or microcracks inside the composite billet. Finally, it is naturally cooled to room temperature for 1 h to obtain a dense tantalum-sodium composite billet. S3. The tantalum-sodium composite billet is placed in a rolling mill for rolling. The strong compressive and shear stresses generated during rolling induce the tantalum-based phase to disperse uniformly in the sodium matrix and strengthen the interfacial bonding between the two. After rolling, a tantalum-sodium alloyed modified sodium metal anode material with uniform thickness is obtained.

[0010] Preferably, in step S1, the solid tantalum source is one of tantalum powder and tantalum pentoxide; the particle size of the solid tantalum source is about 100 nm.

[0011] Preferably, the amount of the solid tantalum source added is 2wt%-6wt% of the mass of the sodium metal sheet.

[0012] The second objective of this invention is to provide a tantalum-sodium alloy modified sodium metal anode material. The anode material has a tantalum-sodium alloy layer with a thickness of 15-18 μm formed on its surface through in-situ thermal reduction and melt diffusion. This alloy layer can effectively isolate the electrolyte from direct contact with the sodium metal substrate, reduce the occurrence of interfacial side reactions and loss of active sodium, ensure the rapid transport of sodium ions without affecting the ion dynamics performance of the battery, and guide the uniform deposition of sodium ions, thereby fundamentally inhibiting the growth of sodium dendrites.

[0013] The synergistic mechanism of tantalum-sodium alloying modification in this invention is as follows: in the temperature range of 200°C, gas is slowly discharged through low-viscosity molten sodium, and liquid sodium at 300°C provides a good medium for the dispersion of the tantalum-based phase; stepped heating ensures a more uniform temperature field inside the sodium matrix, reducing macroscopic cracks caused by uneven shrinkage during cooling; the shear force of mechanical stirring breaks up the tantalum-based phase aggregates, achieving uniform dispersion of them in liquid sodium; constant temperature static degassing ensures the compactness of the composite billet and avoids the formation of internal pores; the compressive stress and shear stress of rolling further compact the billet and improve its density, without the need for additional interface modification treatment, and the entire process is simple with no complex auxiliary steps.

[0014] The third objective of this invention is to provide an application of tantalum-sodium alloy modified sodium metal anode material in sodium-ion batteries.

[0015] Preferably, the sodium-ion battery is assembled with a sodium metal anode material modified by sodium tantalum alloy as the anode, a sodium iron pyrophosphate cathode, a sodium ion electrolyte, and a glass fiber separator; the anode and cathode are separated by the glass fiber separator and are both completely immersed in the sodium ion electrolyte.

[0016] The specific assembly method is as follows: In an argon glove box with moisture and oxygen content ≤0.01 ppm, sodium metal material modified by tantalum sodium alloy, glass fiber separator, and sodium iron pyrophosphate positive electrode are stacked in sequence, sodium ion special electrolyte is injected, and after encapsulation, standing for 12 h, and electrochemical activation, sodium ion battery is obtained.

[0017] The sodium-ion battery of this invention exhibits a charge transfer impedance ≤24.73 Ω and excellent ion transport kinetics performance; at 3 mA cm⁻¹ -2 Under high current density, the initial discharge specific capacity is ≥89 mAh g. -1 After 3000 cycles, the capacity is still ≥83 mAh g. -1 Capacity retention ≥94%; at 4 mA cm⁻¹ -2 At ultra-high current density, the capacity remains ≥84 mAh g after 740 cycles. -1 With a capacity retention rate of ≥100%, it demonstrates excellent rate performance and ultra-long cycle stability.

[0018] As can be seen from the above technical solution, compared with the prior art, the beneficial effects achieved by the present invention include at least the following: 1. This invention adapts to the physicochemical properties of sodium metal, preheating sodium metal to 200°C to obtain low-viscosity liquid sodium, which solves the problems of high sodium viscosity and difficulty in dispersing doped phases at conventional melting temperatures. At the same time, the 200°C transition period allows trace amounts of gas adsorbed on the surface and in the pores of tantalum powder to escape slowly and steadily. In addition, argon is used as a protective gas to avoid side reactions between sodium metal and protective gas at high temperatures, thus ensuring the purity of the negative electrode material.

[0019] 2. This invention uses mechanical stirring to achieve uniform dispersion of the tantalum-based phase, eliminating complex auxiliary equipment. It utilizes the shear force of the mechanical stirring paddle to break up the tantalum-based phase aggregates, combined with the good dispersion medium of low-viscosity liquid sodium, to achieve uniform dispersion of the tantalum-based phase without agglomeration. The process steps are simplified, the equipment requirements are low, the industrial production cost is significantly reduced, and it is more conducive to large-scale mass production.

[0020] 3. The present invention forms a tantalum-sodium alloy layer that is tightly bonded to the sodium matrix on the surface of the negative electrode, without the need for additional interface modification. The passivation layer is continuous and crack-free, not easy to fall off, and the interface stability is greatly improved.

[0021] 4. The tantalum-sodium alloy modified sodium metal anode of this invention exhibits excellent matching with the sodium iron pyrophosphate cathode, resulting in a sodium-ion battery with a charge transfer impedance as low as 12.09 Ω at 3 mA cm⁻¹. -2 After 3000 cycles at current density, the capacity retention rate still reaches 94%, fundamentally solving the core problems of dendrite growth, severe interfacial side reactions, and short cycle life of pure sodium anode.

[0022] 5. The preparation process of this invention is carried out in an argon atmosphere throughout, with no harmful byproducts generated, which is in line with the development concept of green chemical industry; the process parameters are controllable and the operation is simple; the selected tantalum-based dopant (tantalum powder, tantalum pentoxide) raw materials are readily available; and each step is highly compatible with existing battery production processes, which has important industrial application value.

[0023] The process parameters for preparing the tantalum-sodium alloy modified sodium metal anode of this invention are controllable, the steps are simple, and the equipment requirements are low. It does not require complex auxiliary equipment and is easier to achieve industrial mass production. The prepared anode material has excellent performance and good matching with the sodium iron pyrophosphate cathode. The assembled sodium-ion battery has the characteristics of low impedance, high rate capability, and ultra-long cycle life. It can be widely used in large-scale electrochemical energy storage power stations, low-speed electric vehicles, portable electronic devices and other fields. It solves the technical problems of poor stability and short cycle life of existing sodium-ion battery anodes and has important industrial application value and broad market prospects. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0025] Figure 1 This is an optical image of the sodium metal anode modified by tantalum-sodium alloying prepared in Example 1 of the present invention.

[0026] Figure 2 Figure 1 shows the surface scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) scans of the tantalum-sodium alloy modified sodium metal anode prepared in Example 1 of this invention; where a and b are surface morphology images of the anode, c is the backscattered electron image (BSE image) of the anode surface, and d and e are surface energy dispersive spectroscopy scans.

[0027] Figure 3 The images show cross-sectional scanning electron microscope (SEM) images and energy dispersive spectroscopy (EDS) images of the tantalum-sodium alloy modified sodium metal anode prepared in Example 1 of this invention; wherein Figure a is a schematic diagram of the overall morphology and height of the anode, Figure b is a backscattered electron image (BSE image) of the cross-section of the anode, and Figures c and d are cross-sectional EDS images.

[0028] Figure 4 This is a partially enlarged view and a schematic diagram of the thickness distribution of the sodium-tantalum alloy layer on the negative electrode cross section in Embodiment 1 of the present invention.

[0029] Figure 5 This is the electrochemical impedance spectroscopy of the sodium-ion battery assembled in Example 1 of the present invention.

[0030] Figure 6 The sodium-ion battery assembled for Example 1 of this invention operates at 3 mA cm⁻¹. -2 Cyclic performance at current density.

[0031] Figure 7 The sodium-ion battery assembled for Example 1 of this invention operates at 3 mA cm⁻¹. -2 Charge-discharge curves at current density.

[0032] Figure 8 The sodium-ion battery assembled for Example 1 of this invention operates at 4 mA cm⁻¹. -2 Cyclic performance at current density.

[0033] Figure 9 This is a partial enlarged view and a schematic diagram of the thickness distribution of the sodium-tantalum alloy layer on the negative electrode cross section in Embodiment 2 of the present invention.

[0034] Figure 10 This is the electrochemical impedance spectroscopy of the sodium-ion battery assembled in Example 2 of the present invention.

[0035] Figure 11 The sodium-ion battery assembled for Example 2 of this invention operates at 3 mA cm⁻¹. -2 Cyclic performance at current density.

[0036] Figure 12 The sodium-ion battery assembled for Example 2 of this invention operates at 3 mA cm⁻¹. -2 Charge-discharge curves at current density.

[0037] Figure 13 This is a partially enlarged view and a schematic diagram of the thickness distribution of the sodium-tantalum alloy layer on the negative electrode cross section in Embodiment 3 of the present invention.

[0038] Figure 14 This is the electrochemical impedance spectroscopy of the sodium-ion battery assembled in Example 3 of the present invention.

[0039] Figure 15 The sodium-ion battery assembled for Example 3 of this invention operates at 3 mA cm⁻¹. -2 Cyclic performance at current density.

[0040] Figure 16 The sodium-ion battery assembled for Example 3 of this invention operates at 3 mA cm⁻¹. -2 Charge-discharge curves at current density.

[0041] Figure 17 This is the electrochemical impedance spectroscopy of the sodium-ion battery assembled in Comparative Example 1 of this invention.

[0042] Figure 18 The sodium-ion battery assembled for Comparative Example 1 of this invention operates at 3 mA cm⁻¹ -2 Cyclic performance at current density.

[0043] Figure 19 The sodium-ion battery assembled for Comparative Example 1 of this invention operates at 3 mA cm⁻¹ -2 Charge-discharge curves at current density.

[0044] Figure 20 The sodium-ion battery assembled for Comparative Example 1 of this invention operates at 4 mA cm⁻¹. -2 Cyclic performance at current density.

[0045] Figure 21 This is an optical image of the sodium metal anode modified by tantalum-sodium alloying prepared in Comparative Example 2 of the present invention.

[0046] Figure 22 This is the electrochemical impedance spectroscopy of the sodium-ion battery assembled in Comparative Example 2 of this invention.

[0047] Figure 23The sodium-ion battery assembled for Comparative Example 2 of this invention operates at 3 mA cm⁻¹ -2 Cyclic performance at current density.

[0048] Figure 24 This is the electrochemical impedance spectroscopy of the sodium-ion battery assembled in Comparative Example 3 of this invention.

[0049] Figure 25 The sodium-ion battery assembled for Comparative Example 3 of this invention operates at 3 mA cm⁻¹ -2 Cyclic performance at current density.

[0050] Figure 26 This is the electrochemical impedance spectroscopy of the sodium-ion battery assembled in Comparative Example 4 of this invention.

[0051] Figure 27 The sodium-ion battery assembled for Comparative Example 4 of this invention operates at 3 mA cm⁻¹ -2 Cyclic performance at current density.

[0052] Figure 28 The electrochemical impedance spectroscopy comparison diagrams are shown for the sodium-ion batteries assembled in Examples 1-3 and Comparative Example 1 of this invention. Detailed Implementation

[0053] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0054] All experimental operations were conducted in an argon glove box with a moisture content ≤0.01 ppm and an oxygen content ≤0.01 ppm, and all reagents used were of analytical grade or higher purity. Example 1

[0055] 100 mg of solid sodium metal sheet with a purity of 99.9 wt% and 6 mg of tantalum oxide powder with a particle size of 100 nm were placed in a boron nitride crucible and heated to 200 °C in an argon glove box. The temperature was maintained for 10 min to completely melt the sodium metal sheet into a low-viscosity liquid sodium metal. The mixture was mechanically stirred at 300 °C for 10 min, then allowed to stand at the same temperature for 15 min, and finally allowed to cool naturally to room temperature to obtain a tantalum-sodium composite billet. The tantalum-sodium composite billet was rolled to obtain a tantalum-sodium alloyed modified sodium metal anode with a surface tantalum-sodium alloy layer thickness of 16.57 μm.

[0056] Using sodium metal material modified with sodium tantalum alloy as the negative electrode, sodium iron pyrophosphate as the positive electrode, a glass fiber membrane as the separator, and 1 M NaPF6-diethylene glycol dimethyl ether as the electrolyte for sodium ions, the cells were stacked and packaged into coin-type sodium-ion batteries in an argon glove box. Electrochemical activation was then performed after a 12-hour settling period. Electrochemical performance tests were conducted. Electrochemical impedance spectroscopy (EIS) showed that the battery exhibited excellent ion transport kinetics, with a charge transfer impedance of only 13.3 Ω. Constant current charge-discharge tests demonstrated that the charge transfer impedance was 3 mA cm⁻¹. -2 At the current density, the initial discharge specific capacity is 89.36 mAh g. -1 After 2900 cycles, the capacity is 86.84 mAh g. -1 Capacity retention rate 97.17%; 4 mA cm⁻¹ -2 At the current density, the initial discharge specific capacity is 84.2 mAh g. -1 After 740 cycles, the capacity is 84.9 mAh g. -1 The capacity retention rate was 100.8%.

[0057] Optical photographs of sodium metal anodes modified with tantalum-sodium alloys, such as... Figure 1 As shown, the surface of this negative electrode material is highly flat, with no visible exposed sodium metal areas or tantalum powder agglomerations. SEM morphology and EDS energy dispersive spectroscopy analysis of the negative electrode surface are as follows: Figure 2 As shown, a and b are surface morphology images of the negative electrode. The negative electrode surface exhibits a continuous and dense cauliflower-like structure, with no obvious macroscopic cracks or pores. Figure c is the BSE image of the corresponding region, serving as a reference morphology base image for EDS surface scanning. d and e are surface energy dispersive spectroscopy (SEDS) images. Na and Ta elements show a high degree of consistency and overlap on the negative electrode surface. The Ta component is uniformly distributed in a diffuse state throughout the scanning area, which helps to achieve a uniform current density distribution during electrochemical cycling, thereby inducing uniform sodium deposition and inhibiting dendrite growth. SEM morphology and EDS energy dispersive spectroscopy analysis of the cross section are as follows: Figure 3 As shown, Figure a is a schematic diagram of the overall morphology and height of the negative electrode; Figure b is the BSE image of the corresponding region, serving as a reference morphology base map for EDS surface scanning, used to compare the spatial correspondence between the elemental distribution and the actual microstructure in Figures c and d. Figures c and d are cross-sectional energy dispersive spectroscopy surface scans, where Na constitutes the main matrix of the negative electrode, and Ta components are highly enriched in the outermost layer of the electrode, forming a continuous and dense functional protective layer.

[0058] A magnified view and a schematic diagram of the thickness distribution of the sodium-tantalum alloy layer on the surface of the negative electrode are shown below. Figure 4 As shown, a sodium-tantalum alloy layer with a thickness of 16.57 μm was formed on the surface of the sodium substrate.

[0059] Electrochemical impedance spectroscopy as follows Figure 5 As shown; 3 mA cm -2 Cyclic performance curves at current density are as follows Figure 6 As shown; 3 mA cm -2 Charge-discharge curves as follows Figure 7 As shown; 4 mA cm -2 Cyclic performance curves at current density are as follows Figure 8 As shown. Example 2

[0060] 100 mg of solid sodium metal sheet with a purity of 99.9 wt% and 3 mg of tantalum oxide powder with a particle size of 100 nm were placed in a boron nitride crucible and heated to 200 °C for 10 min to obtain low-viscosity liquid sodium metal. The mixture was mechanically stirred at 300 °C for 10 min, then allowed to stand at that temperature for 15 min, and finally allowed to cool naturally to room temperature to obtain a tantalum-sodium composite billet. The tantalum-sodium composite billet was rolled to obtain a tantalum-sodium alloy-modified sodium metal anode. The thickness of the tantalum-sodium alloy layer on the surface of the tantalum-sodium alloy-modified sodium metal anode was 15.42 μm.

[0061] The sodium-ion battery assembly and testing were the same as in Example 1. The test results were: charge transfer impedance 19.24 Ω, 3 mA cm⁻¹. -2 The initial discharge specific capacity at the current density is 87.66 mAh g. -1 After 1800 cycles, the capacity retention rate was 95.3%.

[0062] A magnified view and a schematic diagram of the thickness distribution of the sodium-tantalum alloy layer on the surface of the negative electrode are shown below. Figure 9 As shown, the electrochemical impedance spectroscopy diagram is as follows: Figure 10 As shown, 3 mA cm -2 Cyclic performance curves at current density are as follows Figure 11 As shown, the charge-discharge curves are as follows: Figure 12 As shown. Example 3

[0063] 100 mg of solid sodium metal sheet with a purity of 99.9 wt% and 6 mg of tantalum powder with a particle size of 100 nm were placed in a boron nitride crucible and heated to 200 °C in an argon glove box. The mixture was held at this temperature for 10 min to completely melt the sodium metal sheet into a low-viscosity liquid sodium metal. The mixture was then mechanically stirred at 300 °C for 10 min, followed by a period of static temperature for 15 min, and finally allowed to cool naturally to room temperature to obtain a tantalum-sodium composite billet. The tantalum-sodium composite billet was rolled to obtain a tantalum-sodium alloy-modified sodium metal anode. The thickness of the tantalum-sodium alloy layer on the surface of the tantalum-sodium alloy-modified sodium metal anode was 15.74 μm.

[0064] The sodium-ion battery assembly and testing were the same as in Example 1. The test results were: charge transfer impedance 12.09 Ω, 3 mA cm⁻¹. -2 The initial discharge specific capacity at the current density is 89.03 mAh g. -1 After 3000 cycles, the capacity retention rate was 94.9%.

[0065] A magnified view and a schematic diagram of the thickness distribution of the sodium-tantalum alloy layer on the surface of the negative electrode are shown below. Figure 13 As shown, the electrochemical impedance spectroscopy diagram is as follows: Figure 14 As shown, 3 mA cm -2 Cyclic performance curves at current density are as follows Figure 15 As shown, the charge-discharge curves are as follows: Figure 16 As shown.

[0066] Comparative Example 1 100 mg of pure sodium was used as the negative electrode, sodium iron pyrophosphate as the positive electrode, glass fiber membrane as the separator, and 1 M NaPF6-diethylene glycol dimethyl ether as the electrolyte for sodium ions. The cells were stacked and packaged in an argon glove box to form a button cell sodium ion battery.

[0067] Performance test results: The charge transfer impedance of this comparative example is 268.2 Ω, significantly higher than that of the example, reflecting a limitation of the interfacial dynamics. Due to this high impedance, at 3 mA cm⁻¹... -2 At a current density of [value missing], its initial discharge specific capacity is only 84.43 mAh g⁻¹. -1 Furthermore, the battery exhibits poor cycle stability, failing after only 68 cycles due to an internal short circuit; at 4 mAcm -2 At a current density of [value missing], its initial discharge specific capacity is only 71.63 mAh g⁻¹. -1 It fails due to an internal short circuit after 45 cycles.

[0068] Electrochemical impedance spectroscopy as follows Figure 17 As shown, 3 mA cm -2 Cyclic performance curves at current density are as follows Figure 18 As shown, 3mA cm-2 Charge-discharge curves as follows Figure 19 As shown, 4 mA cm -2 Cyclic performance curves at current density are as follows Figure 20 As shown.

[0069] As can be seen from the test results of the examples and comparative examples, the sodium metal anode modified by tantalum-sodium alloying obtained by the present invention through in-situ thermal reduction and melt diffusion has excellent matching with sodium iron pyrophosphate cathode. The assembled sodium-ion battery has significant advantages of low impedance, high rate and ultra-long cycle, and low equipment requirements, making it suitable for industrial mass production.

[0070] Comparative Example 2 100 mg of solid sodium metal sheet with a purity of 99.9 wt% and 6 mg of tantalum oxide powder with a particle size of 100 nm were placed in a boron nitride crucible and placed on a heating stage inside an argon glove box. The crucible was directly heated to 300 °C, held at that temperature for 10 min, mechanically stirred for 10 min, and finally allowed to stand at a constant temperature for 15 min to cool naturally to room temperature, thus obtaining a tantalum-sodium composite billet. The tantalum-sodium composite billet was rolled to obtain a tantalum-sodium alloyed modified sodium metal anode.

[0071] The assembly and testing of the sodium-ion battery were the same as in Example 1. The sodium-ion battery was assembled, and the test results were: charge transfer impedance 21.45 Ω, 3 mA cm⁻¹ -2 The initial discharge specific capacity at the current density is 86.77 mAh g. -1 After 93 cycles, the battery short-circuited.

[0072] Figure 21 The image shows an optical photograph of the negative electrode fabricated using a direct heating process. The surface of the negative electrode exhibits obvious cracks. Furthermore, the tantalum powder shows significant uneven distribution on the sodium substrate surface, with localized agglomeration forming visible black granular aggregates. The electrochemical impedance spectroscopy is shown below. Figure 22 As shown; 3 mA cm -2 Cyclic performance curves at current density are as follows Figure 23 As shown.

[0073] Comparative Example 3 100 mg of solid sodium metal sheet with a purity of 99.9 wt% and 6 mg of tantalum oxide powder with a particle size of 100 nm were placed in a boron nitride crucible and heated to 150 °C for 10 min to obtain low-viscosity liquid sodium metal. The mixture was mechanically stirred at 250 °C for 10 min, then allowed to stand at the same temperature for 15 min, and finally naturally cooled to room temperature to obtain a tantalum-sodium composite billet. The tantalum-sodium composite billet was rolled to obtain a tantalum-sodium alloyed modified sodium metal anode.

[0074] The sodium-ion battery assembly and testing were the same as in Example 1. The test results were: charge transfer impedance 24.73 Ω, 3 mA cm⁻¹. -2 The initial discharge specific capacity at the current density is 87.91 mAh g. -1 After 71 cycles, the battery short-circuited.

[0075] Electrochemical impedance spectroscopy as follows Figure 24 As shown, 3 mA cm -2 Cyclic performance curves at current density are as follows Figure 25 As shown.

[0076] Comparative Example 4 100 mg of solid sodium metal sheet with a purity of 99.9 wt% and 6 mg of tantalum oxide powder with a particle size of 100 nm were placed in a boron nitride crucible and heated to 250 °C for 10 min to obtain low-viscosity liquid sodium metal. The mixture was mechanically stirred at 350 °C for 10 min, then allowed to stand at that temperature for 15 min, and finally naturally cooled to room temperature to obtain a tantalum-sodium composite billet. The tantalum-sodium composite billet was rolled to obtain a tantalum-sodium alloyed modified sodium metal anode.

[0077] The sodium-ion battery assembly and testing were the same as in Example 1. The test results were: charge transfer impedance 23.64 Ω, 3 mA cm⁻¹. -2 The initial discharge specific capacity at the current density is 86.46 mAh g. -1 After 298 cycles, the battery short-circuited.

[0078] Electrochemical impedance spectroscopy as follows Figure 26 As shown, 3 mA cm -2 Cyclic performance curves at current density are as follows Figure 27 As shown.

[0079] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a sodium metal anode material modified with tantalum-sodium alloy, characterized in that, Includes the following steps: S1. In an argon atmosphere, a solid sodium metal sheet is mixed with a tantalum source, heated and held at a certain temperature to obtain a molten material; S2. Continue heating and mechanically stir to mix the molten material evenly. Then, keep it at a constant temperature and let it cool naturally to room temperature to obtain the tantalum-sodium composite billet. S3. Tantalum-sodium composite billet is rolled to obtain tantalum-sodium alloyed modified sodium metal anode material; In step S1, the heating and holding temperature is 200℃ for 10 minutes; In step S2, the continued heating means heating to 300°C, and the constant temperature standing means standing at 300°C for 15 minutes.

2. The preparation method according to claim 1, characterized in that, In step S1, the moisture content of the argon atmosphere is ≤0.01 ppm and the oxygen content is ≤0.01 ppm.

3. The preparation method according to claim 1, characterized in that, In step S1, the purity of the sodium metal sheet is ≥99.9 wt%; the solid tantalum source is one of tantalum powder and tantalum pentoxide; the particle size of the solid tantalum source is 100 nm and the purity is ≥99.9 wt%.

4. The preparation method according to claim 1, characterized in that, In step S1, the amount of the solid tantalum source added is 2wt%-6wt% of the mass of the sodium metal sheet.

5. The tantalum-sodium alloy modified sodium metal anode material obtained by any one of the preparation methods described in claims 1-4, characterized in that, The surface of the negative electrode material includes a tantalum-sodium alloy layer with a thickness of 15~18μm.

6. The application of the tantalum-sodium alloy modified sodium metal anode material according to claim 5 in sodium-ion batteries.

7. The application according to claim 6, characterized in that, The sodium-ion battery is assembled from a sodium metal anode material modified by tantalum-sodium alloy, a sodium iron pyrophosphate cathode, a sodium-ion electrolyte, and a glass fiber separator.

8. The application according to claim 6, characterized in that, The sodium ion-specific electrolyte is a single-component ether electrolyte consisting of 1M NaPF6 dissolved in diethylene glycol dimethyl ether.

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