A two-phase sodium vanadium fluorophosphate material, a preparation method thereof and application thereof in the field of sodium ion batteries

Abstract

The application belongs to the technical field of sodium ion battery cathode materials, and particularly relates to a two-phase sodium vanadium fluorophosphate material, a preparation method thereof and application thereof in the field of sodium ion batteries. The preparation method of the two-phase sodium vanadium fluorophosphate material is as follows: a vanadium source and a reducing agent are dissolved in water, a sodium source, a phosphorus source and a fluorine source are added, and heating and stirring are performed to obtain a solution; the solution is continuously stirred at high temperature until it becomes gelatinous; the gelatinous solution is dried to obtain a block precursor; the precursor is ground into powder and sintered at high temperature under a protective atmosphere to obtain a material with a two-phase structure of Na3V2(PO4)2F3 and Na 2.4 V2(PO4)2F3. The material has high crystallinity and particle morphology that is beneficial to sodium ion diffusion. In a sodium ion battery, the material exhibits high reversible capacity (125 mAh / g at 0.5 C), excellent rate performance (72.7% capacity retention at 50 C) and cycle stability (97% retention rate after 500 cycles), and is suitable for high-power sodium ion batteries and energy storage fields.

Description

Technical Field

[0001] This invention belongs to the technical field of sodium-ion battery cathode materials, specifically relating to a biphase sodium vanadium fluorophosphate material, its preparation method, and its application in the field of sodium-ion batteries. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Among various high-efficiency electrochemical energy storage technologies, lithium-ion batteries dominate the market due to their low self-discharge rate and high energy density. However, lithium-ion batteries face serious bottlenecks such as high cost and limited resource reserves. Sodium-ion batteries (SIBs), with their abundant natural resources and low cost, have once again sparked research interest. Significant research has been invested in the development of high-performance electrode materials and the study of the mechanisms of SIBs.

[0004] Among various cathode materials, Na3V2(PO4)2F3, as a representative member of sodium superionic conductor (NASICON) structure compounds, is considered a promising candidate due to its excellent structural stability, fast ion transport, and high operating potential. However, Na3V2(PO4)2F3 material itself has some drawbacks: low electronic conductivity, resulting in poor battery rate performance, making it only suitable for low-current operation and unable to meet the high-current requirements of power batteries; and poor cycle performance, with significant capacity loss during charge and discharge, which restricts its practical application.

[0005] To address the aforementioned shortcomings of Na3V2(PO4)2F3 materials, a multiphase structure control strategy is proposed to construct Na in situ within Na3V2(PO4)2F3. 2.4 The V2(PO4)2F3 symbiotic phase was observed. The study suggests that the in-situ composite treatment introduced a sodium-deficient Na group. 2.4 The V2(PO4)2F3 phase provides sodium vacancies and mixed valence states, which can overcome the intrinsic limitations of Na3V2(PO4)2F3 materials and promote sodium ion diffusion, synergistically improving kinetic performance and thus significantly enhancing the electrochemical performance of the material, including cycling performance and rate performance. Currently, there is a lack of simple and effective methods for precisely controlling the two-phase structure. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention designs an in-situ composite treatment to improve the defects of Na3V2(PO4)2F3 material. Based on this objective, this invention provides a biphase sodium vanadium fluorophosphate cathode material for sodium-ion batteries. The preparation process of this material is simple, the resulting product has high crystallinity, and as a cathode material for sodium-ion batteries, it exhibits high reversible specific capacity, excellent rate performance, and stable cycle performance.

[0007] Based on the above-mentioned technical effects, the present invention provides the following technical solution:

[0008] In a first aspect, the present invention provides a biphase sodium vanadium fluorophosphate material, characterized in that the material is a mixture of Na3V2(PO4)2F3 phase and Na 2.4 A symbiotic two-phase structure of the V2(PO4)2F3 phase, wherein the Na3V2(PO4)2F3 phase and Na 2.4 The ratio of V2(PO4)2F3 phase is 60~90%:10~40%. w / w Furthermore, the ratio is 75-85%:15-25% ( w / w The above-mentioned biphase sodium vanadium fluorophosphate material exhibits XRD diffraction at 2... θ Characteristic peaks are observed at angles of 14.9±0.2°, 19.3±0.2°, 28.8±0.2°, 29.3±0.2°, 34.5±0.2°, 40.1±0.2°, 43.1±0.2°, 44.2±0.2°, 50.8±0.2°, 52.6±0.2°, 54.3±0.2°, 56.2±0.2°, 58.2±0.2°, 59.1±0.2°, 61.2±0.2°, 62.3±0.2°, 65.2±0.2°, 68.2±0.2°, 69.2±0.2°, 71.5±0.2°, and 74.9±0.2°.

[0009] The above Na3V2(PO4)2F3 phase reacts with Na 2.4 The proportion of the V2(PO4)2F3 phase was obtained by Rietveld refinement of the XRD pattern. The ratio of the Na3V2(PO4)2F3 phase and Na... 2.4 Using the reported crystal structure parameters of the V2(PO4)2F3 phase as the initial model, the entire diffraction pattern was fitted using Rietveld refinement software to obtain the mass fractions of the two phases in the aforementioned material. The specific steps are as follows:

[0010] (1) Grind the prepared biphase sodium vanadium fluorophosphate material sample evenly and perform XRD testing. The scanning range is generally 10°~80°. 2θ Cu Kα radiation (λ=1.5406 Å) was used.

[0011] (2) In Rietveld refinement software (such as GSAS or FullProf), import Na3V2(PO4)2F3 and Na into the following containers respectively. 2.4 The reported crystal structure parameters of the V2(PO4)2F3 phase were used as the initial model;

[0012] (3) Perform full-spectrum fitting on the XRD pattern and refine the following parameters in sequence: background function, instrument zero point, cell parameters, peak shape parameters (including full width at half maximum and asymmetry), atomic coordinates and anisotropic temperature factor;

[0013] (4) Calculate the mass fraction of each phase based on the refined model using the quantitative analysis module in the software.

[0014] The calculation formula is based on the reference intensity ratio of each phase and the refined scaling factor, ultimately outputting the mass ratio of the two phases. The convergence criterion for refinement is to minimize the difference between the calculated spectrum and the experimental spectrum, typically using the weighted residual factor (R0). wp R0 and goodness-of-fit (GoF) values ​​are used as evaluation criteria. wp When the accuracy is below 10% and the GoF value is close to 1, the refinement result is considered reliable.

[0015] In this two-phase structure, due to the introduction of sodium-deficient Na 2.4 In the V2(PO4)2F3 phase, the average valence state of vanadium is slightly higher than +3, i.e., V 3 + With V 4+ The coexistence of Na3V2(PO4)2F3 and Na significantly improves electronic conductivity and ion diffusion rate. This invention confirms that Na3V2(PO4)2F3 and Na 2.4 The V2(PO4)2F3 coexisting two-phase material can still maintain a high discharge capacity at high current density, and the capacity retention rate is still above 97% after more than 500 charging cycles. This effectively improves the shortcomings of Na3V2(PO4)2F3 material, such as poor rate performance and inability to adapt to high current.

[0016] In a second aspect, the present invention provides a method for preparing the biphase sodium vanadium fluorophosphate material described in the first aspect, comprising the following steps:

[0017] (1) Dissolve the vanadium source and reducing agent in water at a molar ratio of 1:1~1.5, heat and stir at 65~75℃ for 25~35 min, then add sodium source, phosphorus source and fluorine source, heat and stir at 65~75℃ for 0.8~1.2 h, raise the temperature to 80~85℃ and continue stirring until gel-like, and dry it to obtain the precursor solid;

[0018] (2) Place the precursor solid obtained in the step under an inert atmosphere and heat it to 550-650℃ at a rate of 4-6℃ / min for 9-11 hours to obtain the product.

[0019] In step (1) above:

[0020] The vanadium source is an inorganic acid salt or oxide of vanadium, wherein the inorganic acid salt includes sulfates, oxalates, or vanadates, and the oxide is vanadium pentoxide. In one embodiment verified by the present invention, the vanadium source is vanadium pentoxide, which has poor water solubility. In a preferred embodiment, the reducing agent can be a reducing organic acid, such as citric acid or oxalic acid. In this embodiment, the molar ratio of vanadium pentoxide to citric acid or oxalic acid is 1:1 to 1.5, and more preferably, the molar ratio is 1:1.3.

[0021] The sodium source is preferably a sodium halide salt, selected from, but not limited to, sodium fluoride (NaF), sodium chloride (NaCl), and sodium iodide (NaI); NaF is more preferably used to avoid the introduction of other elements.

[0022] The phosphorus source is preferably a phosphate or a hydrogen phosphate, such as ammonium dihydrogen phosphate (NH4H2PO4).

[0023] In one embodiment of the present invention with better effect, the sodium source is NaF, the phosphorus source is NH4H2PO4, and the fluorine source is ammonium fluoride (NH4F). The molar ratio of NH4H2PO4:NaF:NH4F is 2.5~3.5:1.5~2.5:0.5, and more specifically, it is 3:2:0.5.

[0024] The drying method can be either negative pressure drying or thermal radiation drying, specifically, vacuum drying; the drying temperature range is 60~110℃.

[0025] In step (2), the inert atmosphere includes, but is not limited to, one of helium, neon, argon, krypton, xenon, and radon. Those skilled in the art can make conventional selections based on factors such as cost and purchasing channels.

[0026] In a third aspect, the present invention provides the application of the biphase sodium vanadium fluorophosphate material described in the first aspect in the field of sodium-ion batteries.

[0027] The feasible application methods of the third aspect mentioned above include, but are not limited to:

[0028] (1) Composite cathode material for preparing sodium-ion batteries;

[0029] (2) Used in the preparation of positive electrode sheets for sodium-ion batteries;

[0030] (3) Used as cathode material for high-power sodium-ion batteries.

[0031] Preferably, the application method (1) includes the following steps: mixing the biphase sodium vanadium fluorophosphate material, conductive agent and binder in a mass ratio of (7~9):1:1, adding water to make a slurry, coating it on the current collector, and drying it to obtain a positive electrode sheet.

[0032] Compared with the prior art, the beneficial effects of the present invention are:

[0033] 1. This invention provides biphase sodium vanadium fluorophosphate (Na) 3-x The material is composed of Na₃V₂(PO₄)₂F₃. This material consists of the Na₃V₂(PO₄)₂F₃ phase and Na₂V₂(PO₄)₂F₃ phase. 2.4 The V2(PO4)2F3 phase coexistence composition provides a stable framework and rapid sodium ion diffusion, which synergistically enhances the kinetic performance.

[0034] 2. The obtained biphase sodium vanadium fluorophosphate material exhibits excellent crystallinity and demonstrates high reversible specific capacity and energy density when used as a cathode material for sodium-ion batteries. It also has industrialization potential and can meet the demand for high-performance sodium-ion battery cathode materials in the energy storage field. Attached Figure Description

[0035] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0036] Figure 1 This is the biphase sodium vanadium fluorophosphate (Na) prepared in Example 1. 3-x XRD pattern of V2(PO4)2F3.

[0037] Figure 2 This is the biphase sodium vanadium fluorophosphate (Na) prepared in Example 1. 3-x SEM image of V2(PO4)2F3).

[0038] Figure 3 This is the biphase sodium vanadium fluorophosphate (Na) prepared in Example 1. 3-x CV plot of V2(PO4)2F3).

[0039] Figure 4 This is the biphase sodium vanadium fluorophosphate (Na) prepared in Example 1. 3-x Rate performance of V2(PO4)2F3 as the positive electrode of sodium-ion battery at different current densities.

[0040] Figure 5 This is the biphase sodium vanadium fluorophosphate (Na) prepared in Example 1. 3-x Comparison of cycling performance of V2(PO4)2F3 and Na3V2(PO4)2F3 at 10C current density.

[0041] Figure 6This is the biphase sodium vanadium fluorophosphate (Na) prepared in Example 1. 3-x Cyclic performance of V2(PO4)2F3 as the positive electrode of sodium-ion battery at 50°C and 10C current density.

[0042] Figure 7 This is the biphase sodium vanadium fluorophosphate (Na) prepared in Example 1. 3-x Refined XRD pattern of V2(PO4)2F3. Detailed Implementation

[0043] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0044] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0045] In the context of this specification, the word "including" is considered to mean "particularly including". It should not be interpreted as "consisting of only".

[0046] As described in the background section, existing Na3V2(PO4)2F3 materials suffer from insufficient rate performance and poor cycle performance. To address these issues, this invention employs a composite processing approach, designing and providing a biphase sodium vanadium fluorophosphate, which effectively improves the operating capability and cycle stability of sodium-ion batteries under high current conditions. To enable those skilled in the art to more clearly understand the technical solution of this invention, the following detailed description, in conjunction with specific embodiments and comparative examples, will illustrate the technical solution of this invention.

[0047] Example 1

[0048] This example provides a biphase sodium vanadium fluorophosphate (Na₂) for use in sodium-ion batteries. 3-x V2(PO4)2F3 material. It was prepared by the following method.

[0049] 1. Preparation of biphase sodium vanadium fluorophosphate materials:

[0050] (1) Sol-gel method: 364 mg of vanadium pentoxide and 500 mg of citric acid (molar ratio 1:1.3) were dissolved in 30 mL of deionized water to obtain a solution. The solution was heated and stirred at 70 °C for 30 min, and then 252 mg of NaF, 460 mg of NH4H2PO4 and 37 mg of NH4F were added. The solution was heated and stirred at 70 °C for 1 h. The obtained solution was stirred at 80 °C until it became gel-like. The obtained gel-like solid was dried in a vacuum drying oven at 110 °C for 12 h to obtain the precursor solid.

[0051] (2) Annealing: The obtained dry solid argon atmosphere was heated at 600℃ for 10h at a heating rate of 5℃ / min to obtain the positive electrode material sodium vanadium fluorophosphate (Na). 3-x V2(PO4)2F3).

[0052] Figure 1 This is the biphase sodium vanadium fluorophosphate (Na) prepared in Example 1. 3-x The XRD pattern of Na₃V₂(PO₄)₂F₃ shows both Na₃V₂(PO₄)₂F₃ and Na₂V₂(PO₄)₂F₃. 2.4 Characteristic peak of V2(PO4)2F3. Figure 7 This is the biphase sodium vanadium fluorophosphate (Na) prepared in Example 1. 3- x The refined XRD pattern of V2(PO4)2F3 further proves that the two-phase material was successfully synthesized.

[0053] Figure 2 The biphase sodium vanadium fluorophosphate (Na) prepared in Example 1 3-x The SEM image of V2(PO4)2F3 shows that the material surface is composed of interlaced and stacked layers, which accelerates ion diffusion.

[0054] The XRD pattern of the two-phase material from Example 1 was subjected to Rietveld refinement, and the refinement fit factor R was determined. wp A good fit is indicated when the content of Na₂O₃ is 7.876% and the GoF value is close to 1. After refinement, this sample yielded Na₃V₂(PO₄)₂F₃ and Na₂O₃. 2.4 The mass fractions of the V2(PO4)2F3 phase were 80.3% and 19.7%, respectively, which is approximately 80:20. w / w ).

[0055] Electrochemical performance testing:

[0056] The obtained Na 3-xV2(PO4)2F3 material was ground in a mortar with acetylene black and binder CMC at a mass ratio of 8:1:1. Deionized water was then added until the powder formed a black, viscous slurry. The slurry was uniformly coated onto aluminum foil using a 100 μm scraper and dried at 60 °C for 6 hours to obtain the positive electrode. A sodium-ion battery was prepared using sodium metal as the negative electrode, glass fiber as the separator, and 1M NaPF6 as the electrolyte in a glove box under an argon atmosphere.

[0057] Electrochemical performance was tested within a voltage range of 2.5–4.5 V. Figure 3 The biphase sodium vanadium fluorophosphate (Na) prepared in Example 1 3-x Cyclic voltammogram of V2(PO4)2F3. Peak splitting occurs in the low voltage region of 3.7 V, further confirming Na. 2.4 The existence of the V2(PO4)2F3 phase. Figure 4 The biphase sodium vanadium fluorophosphate (Na) prepared in Example 1 3-x The rate performance of V2(PO4)2F3 as the positive electrode of a sodium-ion battery at different current densities is shown in the figure. At a rate of 0.5C, the discharge capacity is 125 mAh / g. When the current density is 50C, the discharge capacity is still 90.9 mAh / g. Compared with the low current discharge, the capacity is maintained at 72.7%, which shows good rate performance. Figure 5 The biphase sodium vanadium fluorophosphate (Na) prepared in Example 1 3-x The cycling performance of Na3V2(PO4)2F3 as the positive electrode of a sodium-ion battery at a current density of 10C is shown in the figure. After 500 charge-discharge cycles at 10C, the discharge specific capacity decreased from 118.7 mAh / g to 115.6 mAh / g, with a capacity retention of 97.3%, and the cycling performance was significantly better than that of single-phase Na3V2(PO4)2F3.

[0058] In addition, this dual-phase material also exhibits better thermal stability and safety. Figure 6 The biphase sodium vanadium fluorophosphate (Na) prepared in Example 1 3-x The cycling performance of V2(PO4)2F3 at 50℃ and 10C current density shows that after 500 charge-discharge cycles, the capacity retention rate is 95.2%, indicating that its capacity decays slowly at high temperatures and has better potential for practical applications.

[0059] Example 2

[0060] In this embodiment, another biphase sodium vanadium fluorophosphate (Na) is provided. 3-x The preparation method of V2(PO4)2F3 material includes the following steps:

[0061] (1) Sol-gel method: Same as step (1) in step 1 of Example 1;

[0062] (2) Annealing: The obtained dry solid argon atmosphere was heated at 650℃ for 9h at a heating rate of 4℃ / min to obtain the positive electrode material sodium vanadium fluorophosphate (Na). 3-x V2(PO4)2F3).

[0063] Example 3

[0064] In this embodiment, another biphase sodium vanadium fluorophosphate (Na) is provided. 3-x The preparation method of V2(PO4)2F3 material includes the following steps:

[0065] (1) Sol-gel method: 364 mg of vanadium pentoxide and 328 mg of oxalic acid dihydrate (molar ratio 1:1.3) were dissolved in 30 mL of deionized water to obtain a solution. The solution was heated and stirred at 65 °C for 35 min, and then 252 mg of NaF, 460 mg of NH4H2PO4 and 37 mg of NH4F were added. The solution was heated and stirred at 75 °C for 0.8 h. The obtained solution was stirred at 85 °C until it became gel-like. The obtained gel-like solid was dried in a vacuum drying oven at 60 °C for 12 h to obtain the precursor solid.

[0066] (2) Annealing: Same as step (2) in step 1 of Example 1.

[0067] Example 4

[0068] In this embodiment, another biphase sodium vanadium fluorophosphate (Na) is provided. 3-x The preparation method of V2(PO4)2F3 material includes the following steps:

[0069] (1) Sol-gel method: 364 mg of vanadium pentoxide and 576 mg of citric acid (molar ratio 1:1.5) were dissolved in 30 mL of deionized water to obtain a solution. The solution was heated and stirred at 65 °C for 35 min, and then 252 mg of NaF, 460 mg of NH4H2PO4 and 37 mg of NH4F were added. The solution was heated and stirred at 65 °C for 1.2 h. The obtained solution was stirred at 80 °C until it became gel-like. The obtained gel-like solid was dried in a vacuum drying oven at 110 °C for 12 h to obtain the precursor solid.

[0070] (2) Annealing: The obtained dry solid argon atmosphere was heated at 600℃ for 10h at a heating rate of 5℃ / min to obtain the positive electrode material sodium vanadium fluorophosphate (Na). 3-x V2(PO4)2F3).

[0071] Example 5

[0072] In this embodiment, another biphase sodium vanadium fluorophosphate (Na) is provided. 3-xThe preparation method of V2(PO4)2F3 material includes the following steps:

[0073] (1) Sol-gel method: 364 mg of vanadium pentoxide and 328 mg of oxalic acid dihydrate (molar ratio 1:1.3) were dissolved in 30 mL of deionized water to obtain a solution. The solution was heated and stirred at 70 °C for 30 min, and then 252 mg of NaF, 460 mg of NH4H2PO4 and 37 mg of NH4F were added. The solution was heated and stirred at 70 °C for 1 h. The obtained solution was stirred at 80 °C until it became gel-like. The obtained gel-like solid was dried in a vacuum drying oven at 110 °C for 12 h to obtain the precursor solid.

[0074] (2) Annealing: The obtained dry solid argon atmosphere was heated at 550℃ for 11h at a heating rate of 6℃ / min to obtain the positive electrode material sodium vanadium fluorophosphate (Na). 3-x V2(PO4)2F3).

[0075] Example 6

[0076] In this embodiment, another biphase sodium vanadium fluorophosphate (Na) is provided. 3-x The preparation method of V2(PO4)2F3 material includes the following steps:

[0077] (1) Sol-gel method: 364 mg of vanadium pentoxide and 378 mg of oxalic acid dihydrate (molar ratio 1:1.5) were dissolved in 30 mL of deionized water to obtain a solution. The solution was heated and stirred at 70 °C for 30 min, and then 252 mg of NaF, 460 mg of NH4H2PO4 and 37 mg of NH4F were added. The solution was heated and stirred at 70 °C for 1 h. The obtained solution was stirred at 80 °C until it became gel-like. The obtained gel-like solid was dried in a vacuum drying oven at 60 °C for 12 h to obtain the precursor solid.

[0078] (2) Annealing: The obtained dry solid argon atmosphere was heated at 550℃ for 10h at a heating rate of 5℃ / min to obtain the positive electrode material sodium vanadium fluorophosphate (Na). 3-x V2(PO4)2F3).

[0079] The biphase sodium vanadium fluorophosphate (Na) prepared in Examples 2-6 above 3-x The V2(PO4)2F3 material exhibits essentially the same electrochemical effects as the material prepared in Example 1.

[0080] Comparative Example

[0081] In this comparative example, a cathode material Na3V2(PO4)2F3 is provided, and its preparation method is as follows:

[0082] (1) Sol-gel method: 364 mg of vanadium pentoxide and 384 mg of citric acid (molar ratio 1:1) were dissolved in 30 mL of deionized water to obtain a solution. The solution was heated and stirred at 70 °C for 30 min, and then 252 mg of NaF, 460 mg of NH4H2PO4 and 37 mg of NH4F were added. The solution was heated and stirred at 70 °C for 1 h. The obtained solution was stirred at 80 °C until it became gel-like. The obtained gel-like solid was dried in a vacuum drying oven at 110 °C for 12 h to obtain the precursor solid.

[0083] (2) Annealing: Under a dry solid argon atmosphere, the material was heated at 600℃ for 10h at a heating rate of 5℃ / min to obtain the cathode material Na3V2(PO4)2F3.

[0084] The material prepared in this comparative example is a single-phase material. The main reason for this difference is that, compared with Example 1, when the amount of reducing agent is within this specific excess range, it does not simply inhibit the oxidation of vanadium as is commonly understood, but instead induces the formation of a thermodynamically metastable sodium-deficient phase, Na. 2.4 V2(PO4)2F3 forms a stable symbiotic structure with the main phase; when the ratio is lower than 1:1.2 (e.g., 1:1), it tends to generate a pure phase; when the ratio is too high, it may lead to the formation of impurity phases. Compared with Example 1 of the present invention, the discharge capacity at 50C is only 53mAh / g, and the capacity retention rate is about 46%; the cycle performance is significantly reduced, and the capacity retention rate after 500 cycles at 10C is only 85%, which is significantly worse than that of the two-phase material.

[0085] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A two-phase sodium vanadium fluorophosphate material, characterized in that, The material is associated with Na3V2(PO4)2F3 phase and Na 2.4 V2(PO4)2F3 phase, the mass ratio of the Na3V2(PO4)2F3 phase and Na 2.4 V2(PO4)2F3 phase is 60-90%:10-40%; and the XRD diffraction thereof has characteristic peaks at 2 θ 14.9±0.2°, 19.3±0.2°, 28.8±0.2°, 29.3±0.2°, 34.5±0.2°, 40.1±0.2°, 43.1±0.2°, 44.2±0.2°, 50.8±0.2°, 52.6±0.2°, 54.3±0.2°, 56.2±0.2°, 58.2±0.2°, 59.1±0.2°, 61.2±0.2°, 62.3±0.2°, 65.2±0.2°, 68.2±0.2°, 69.2±0.2°, 71.5±0.2° and 74.9±0.2°.

2. The sodium vanadium fluoride phosphorous material of claim 1, wherein, The Na3V2(PO4)2F3 phase is in a mass ratio of 75-85%: 15-25% to Na 2.4 The mass ratio of the V2(PO4)2F3 phase is 75-85%: 15-25%.

3. A process for the preparation of the sodium vanadium phosphate fluoride material according to claim 1 or 2, characterized in that, comprising the following steps: (1) precursor preparation: a vanadium source and a reducing agent are dissolved in water according to a molar ratio of 1:1.3-1.5, heated and stirred at 65-75°C for 25-35 min, then a sodium source, a phosphorus source and a fluorine source are added, heated and stirred at 65-75°C for 0.8-1.2 h, heated and stirred at 80-85°C until gelatinous, and then dried to obtain a precursor solid; the vanadium source is vanadium pentoxide, the phosphorus source is NH4H2PO4, and the fluorine source is NH4F; (2) heat treatment: the precursor solid obtained in the step is placed in an inert atmosphere, heated at a rate of 4-6°C / min to 550-650°C for 9-11 h, and then obtained.

4. The preparation method of the biphase sodium vanadium fluorophosphate material as described in claim 3, characterized in that, The reducing agent is citric acid or oxalic acid.

5. The method for preparing the biphase sodium vanadium fluorophosphate material as described in claim 4, characterized in that, The molar ratio is 1:1.

3.

6. The method for preparing the biphase sodium vanadium fluorophosphate material as described in claim 3, characterized in that, The sodium source is selected from one of NaF, NaCl, and NaI.

7. The method for preparing the biphase sodium vanadium fluorophosphate material as described in claim 6, characterized in that, The sodium source is NaF, and the molar ratio of NH4H2PO4:NaF:NH4F is 2.5-3.5:1.5-2.5:0.

5.

8. The method for preparing the biphase sodium vanadium fluorophosphate material as described in claim 3, characterized in that, The drying method is selected from negative pressure drying or heat radiation drying, and the drying temperature is 60-110°C.

9. A sodium-ion battery positive electrode sheet, characterized by, The positive electrode plate comprises the dual-phase sodium vanadium fluorophosphate material according to any one of claims 1-2, or the material prepared by the method according to any one of claims 3-8; wherein the dual-phase sodium vanadium fluorophosphate material is mixed with a conductive agent and a binder according to a mass ratio of (7-9):1:1 to form a slurry, coated on a current collector and dried to obtain.

10. A sodium-ion battery, characterized in that, The sodium-ion battery positive electrode plate according to claim 9.

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