Vanadium-doped modified sodium ferric pyrophosphate material based on spray drying, its preparation method and application

Abstract

This invention discloses a vanadium-doped modified sodium iron pyrophosphate material based on spray drying, its preparation method, and its applications. The material exhibits a spherical porous morphology with a particle size between 1 and 10 micrometers; its chemical formula is: Na. 4‑x Fe 3‑x V x (PO4)2P2O7, where 0 < x ≤ 0.1. It is prepared by spray drying, ensuring atomic-level mixing of vanadium and iron through a uniform and stable complexed ion solution; and promoting the formation of a porous spherical morphology through the volatilization of the acidic substrate during rapid drying. The combination of spray drying and trace vanadium doping technology is beneficial for activating more active sodium sites in the sodium iron pyrophosphate cathode material, improving the reversible sodium insertion / extraction capacity, while promoting sodium ion diffusion, reducing polarization voltage, and improving the cycle stability of the material.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery cathode material technology, specifically to a vanadium-doped modified sodium iron pyrophosphate material based on spray drying, its preparation method, and its application. Background Technology

[0002] Sodium-ion batteries possess high potential and competitiveness in large-scale energy storage applications due to their advantages such as abundant elemental reserves, low cost, and environmental friendliness. Among sodium-ion battery cathode materials, polyanionic compounds have attracted widespread attention due to their high electrode potential, robust structural framework, and rapid sodium-ion insertion / extraction kinetics. Sodium iron pyrophosphate (Na4Fe3(PO4)2P2O7) is one of the more promising sodium-ion battery cathode materials for industrialization. It combines the advantages of both NaFePO4 and Na2FeP2O7, exhibiting low cost, good structural stability, high theoretical specific capacity, and long cycle life. However, this material is sensitive to synthesis conditions, making it difficult to synthesize a pure phase. Furthermore, it suffers from low electronic and ionic conductivity, often resulting in problems such as low reversible specific capacity, poor rate performance, and high polarization voltage.

[0003] Doping and carbon coating can improve the above problems. Chinese patent (patent publication number: CN116750745A) discloses an iron-manganese-based composite phosphate material, which improves the reversible capacity and charge / discharge voltage plateau by adjusting the Fe / Mn ratio, effectively increasing the material's energy density. However, due to severe Gyntelle distortion of Mn during charge and discharge, the material's rate performance and cycle performance are poor. Chinese patent (patent publication number: CN115101738A) discloses a Na4Fe prepared by ultrasonic and ball milling dispersion followed by freeze-drying. 1.5-1.5x V 1+xVanadium doping of sodium iron pyrophosphate (PO4)2P2O7 is thought to provide certain lattice defects, resulting in better rate performance and cycle stability. However, the crystallinity and capacity of vanadium-doped sodium iron pyrophosphate prepared by this method are not ideal. Researchers at home and abroad have used various carbon coating methods to improve the conductivity of sodium iron pyrophosphate, such as using graphene oxide to form uniform microspheres, which greatly improves the rate performance of the material (Yuan T, Wang Y, Zhang J, et al. 3D graphene decorated Na4Fe3(PO4)2(P2O7) microspheres as low-cost and high-performance cathode materials for sodium-ion batteries[J]. Nano Energy, 2019, 56: 160-168.). However, this method can only improve the electronic conductivity of the material surface, but cannot improve the intrinsic conductivity of the material; at the same time, conductive materials such as graphene are expensive and not suitable for large-scale production. Summary of the Invention

[0004] To address the problems of low reversible capacity and poor rate performance of sodium iron pyrophosphate (SOP), this invention proposes a vanadium-doped modified SOP material based on spray drying, its preparation method, and its applications. The method promotes atomic-level mixing of vanadium and iron by preparing a uniform and stable complex ion solution. A weakly acidic aqueous solution is used as the solvent for the complex ion solution, which promotes the formation of a uniform and stable ion complex solution. Furthermore, the volatilization of the acidic substrate during rapid drying promotes the formation of a porous spherical morphology. The preparation method is simple and controllable. The vanadium-doped SOP cathode material prepared by spray drying exhibits good crystallinity and uniformity. Vanadium doping introduces corresponding sodium vacancies, broadening the sodium ion transport channels along the b-axis of the cathode material, thereby activating more active sodium sites and significantly improving the reversible sodium storage capacity. Simultaneously, the excellent crystallinity and sodium vacancies also improve the cycle life of the SOP cathode material and reduce the polarization voltage during cycling.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] A vanadium-doped modified sodium iron pyrophosphate material based on spray drying is disclosed. This material exhibits a porous spherical morphology with a particle size between 1 and 10 micrometers. Its chemical formula is: Na. 4-x Fe 3-x V x (PO4)2P2O7, where 0 < x ≤ 0.1.

[0007] Sodium iron pyrophosphate (SO4) has high requirements for the synthesis environment and sintering temperature. During sintering, impurities of sodium iron phosphate and sodium iron pyrophosphate are easily formed, making the choice of synthesis method crucial. The key to synthesizing a pure phase lies in the uniform mixing of elements in the precursor. Solid-state ball milling alone is insufficient to achieve this, while spray drying, utilizing a solution system, can achieve atomic-level mixing of elements. Therefore, the preparation of a uniform and stable complexed ionic solution is extremely important. This invention selects a weakly acidic aqueous solution as the solvent, primarily to: 1) promote the formation of a uniform and stable ionic complexed solution; and 2) utilize the volatility of weak acid molecules to obtain a porous morphology during rapid drying, thereby increasing the wetting area between the material and the electrolyte and shortening the sodium ion transport channels. Appropriate complexing agents and solution types are prerequisites for forming a uniform and stable solution. Iron ions readily form precipitates with various phosphate and pyrophosphate ions, leading to difficulties in phase formation and numerous impurities. Adding complexing agents such as oxalic acid to the system can effectively solve this problem, resulting in a uniform and stable complexed ionic solution. Furthermore, the spray drying process disperses the solution into micron-sized droplets and rapidly dries them during heating, successfully granulating the solution and avoiding stratification or even phase separation that occurs during prolonged drying in direct drying methods. The type and content of dopant ions are also crucial: vanadium and iron ions have similar ionic radii and both belong to the third-period transition metals, allowing vanadium ions to enter the bulk phase of the material relatively easily. Micro-doping with x≤0.1 reduces disturbance to the original system and does not disrupt the pure-phase structure of the original material. The vanadium-doped sodium iron pyrophosphate cathode material prepared by spray drying exhibits good crystallinity. Vanadium doping introduces sodium vacancies, broadening the sodium ion transport channels along the b-axis, thereby activating more active sodium sites and significantly improving the reversible sodium storage capacity. Simultaneously, the excellent crystallinity and sodium vacancies improve the cycle life of the sodium iron pyrophosphate cathode material and reduce the polarization voltage during cycling.

[0008] Specifically, the preparation method of vanadium-doped modified sodium iron pyrophosphate material based on spray drying in this invention includes the following steps:

[0009] S1. Weigh out sodium source, iron source, vanadium source and phosphorus source according to stoichiometric ratio and add them to a weakly acidic aqueous solution. Stir thoroughly to form a precipitate. After adding a complexing agent, a uniform and stable complexed ion solution is formed.

[0010] S2. The above solution is spray-dried into precursor powder, and the precursor powder is placed under a protective atmosphere for low-temperature pre-sintering to form pre-sintered powder.

[0011] S3. Thoroughly mix the pre-calcined powder and carbon source and dry them. Place the mixture under a protective atmosphere for sintering and cooling to obtain vanadium-doped sodium iron pyrophosphate.

[0012] Preferably, the weakly acidic aqueous solution in step S1 is a mixed solution of a weak acid and deionized water, with a concentration of 0.5–8 mol / L; the weak acid is one of acetic acid, formic acid, and propionic acid, preferably an acetic acid solution; the solid-liquid ratio in the complexed ion solution is 100–300 g / L.

[0013] Preferably, the complexing agent in step S1 is one or more of anhydrous oxalic acid, oxalate dihydrate, disodium ethylenediaminetetraacetate, citric acid, and ethylenediaminetetraacetic acid. The sodium source is at least one of sodium pyrophosphate, trisodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, disodium dihydrogen pyrophosphate, sodium carbonate, sodium bicarbonate, sodium oxalate, and sodium citrate; the iron source is at least one of ferric nitrate, ferric phosphate, ferrous oxalate, ferric oxalate, and ferrous acetate; the vanadium source is at least one of ammonium metavanadate, vanadium oxalate, and vanadium pentoxide; the phosphorus source is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium pyrophosphate, trisodium monohydrogen pyrophosphate, disodium dihydrogen pyrophosphate, and monosodium trihydrogen pyrophosphate; the relative molar ratio of sodium, iron, vanadium, and phosphorus is 4-x:3-x:x:4 (0 < x ≤ 0.1).

[0014] Preferably, the parameters for spray drying in step S2 are: injection rate of 100-400 mL / h, inlet temperature of 130-200℃, and outlet temperature of 80-150℃.

[0015] Preferably, the sintering temperature in step S2 is 200-350℃ and the sintering time is 1-4 hours; the sintering temperature in step S3 is 450-550℃ and the sintering time is 2-12 hours; the protective atmosphere in steps S2 and S3 is one of nitrogen, argon, or argon-hydrogen mixture (0.1-5% v / v hydrogen).

[0016] Preferably, the carbon source in step S3 is at least one of oleic acid, citric acid, graphite, and carbon nanotubes; the relative molar ratio of the pre-calcined powder to the carbon source is 5:1 to 20:1.

[0017] The present invention also provides a vanadium-doped modified sodium ferric phosphate material prepared by the above-mentioned spray drying method.

[0018] This invention also provides the application of the vanadium-doped modified sodium iron pyrophosphate material prepared by the above-mentioned spray drying method as a positive electrode material in sodium-ion batteries. The Na₂O₃ prepared by this invention... 4-x Fe 3-x V x (PO4)2P2O7, as a cathode material for sodium-ion batteries, has advantages such as low price, environmental friendliness, and stable cycle performance compared to existing cathode materials such as transition metal oxides, Prussian blue, and vanadium phosphate.

[0019] The present invention has the following beneficial effects:

[0020] (1) This invention achieves atomic-level full mixing of vanadium and iron by preparing a uniform and stable complexed ion solution, while the rapid drying method avoids the solution from separating into layers or even phases during the long drying process; combined with the segmented sintering process and carbon coating process, the phase formation reaction is fully carried out, and a pure phase material with good crystallinity is obtained.

[0021] (2) The present invention successfully granulates by spray drying. The weakly acidic aqueous solution is used as a solvent to make the particles obtained by spray drying have a porous structure left by the volatilization of a large number of acid molecules. The addition of vanadium changes the complex structure of the solution, so that the vanadium-doped iron pyrophosphate sodium material prepared has a uniform porous spherical structure.

[0022] (3) The vanadium-doped iron pyrophosphate sodium cathode material prepared by spray drying exhibits good crystallinity. Vanadium doping introduces certain sodium vacancies, broadening the sodium ion transport channels along the b-axis of the cathode material, thereby activating more active sodium sites and significantly improving the reversible sodium storage capacity. Simultaneously, the excellent crystallinity and sodium vacancies enhance the cycle life of the iron pyrophosphate cathode material and reduce the polarization voltage during cycling.

[0023] (4) The sodium, iron, phosphorus and carbon sources used in this invention are widely available and inexpensive. The spray drying method is simple and can quickly prepare kilogram-scale precursors. The calcination temperature is low and the energy consumption is low. At the same time, the trace vanadium doping has little impact on the cost, which is conducive to large-scale industrial promotion. Attached Figure Description

[0024] Figure 1 This is a scanning electron microscope image of Comparative Example 1.

[0025] Figure 2 This is a scanning electron microscope image of Example 2.

[0026] Figure 3 The X-ray diffraction patterns are for Example 1 and Comparative Examples 3 and 4.

[0027] Figure 4 The specific capacity-voltage curves during charging and discharging are shown for Example 1 and Comparative Example 2.

[0028] Figure 5 This is a rate performance diagram for Example 1.

[0029] Figure 6 The graph shows the cycling performance of Example 1 at 5C.

[0030] Table 1 shows the electrochemical data for Examples 1-2 and Comparative Examples 1-4. Detailed Implementation

[0031] 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. Experimental methods in the following embodiments that do not specify specific conditions are performed according to conventional methods and conditions, or according to the product instructions.

[0032] The raw materials and instruments used in the examples are not subject to any specific restrictions on their source; they can be purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0033] Example 1

[0034] This embodiment is based on the preparation of vanadium-doped modified sodium ferric pyrophosphate material by spray drying method. The chemical formula is Na. 3.9 Fe 2.9 V 0.1 (PO4)2P2O7, the specific preparation method is as follows:

[0035] S1. Weigh out 0.05 mol sodium pyrophosphate, 0.1 mol ammonium dihydrogen phosphate, 0.145 mol ferric nitrate nonahydrate, and 0.005 mol ammonium metavanadate respectively, add them to a 2 mol / L acetic acid solution, stir thoroughly to form a white suspension, add anhydrous oxalic acid to form a homogeneous and stable clear solution, and the solid-liquid ratio is 150 g / L.

[0036] S2. The above solution was spray-dried into precursor powder at an injection rate of 200 mL / h, an inlet temperature of 130℃, and an outlet temperature of 90℃. The precursor powder was then sintered at 300℃ for 1.5 h under an argon atmosphere to form pre-calcined powder.

[0037] S3. The pre-calcined powder and oleic acid (molar ratio of 10:1) are thoroughly mixed in acetone and dried. The mixture is then sintered at 500°C for 10 hours under an argon-hydrogen mixed atmosphere (5% hydrogen). After cooling, vanadium-doped modified Na is obtained. 3.9 Fe 2.9 V 0.1 (PO4)2P2O7 cathode material.

[0038] Example 2

[0039] This embodiment is based on the preparation of vanadium-doped modified sodium ferric pyrophosphate material by spray drying method. The chemical formula is Na. 3.95 Fe 2.95 V 0.05 (PO4)2P2O7 was prepared using the same method as in Example 1, except for the control of the stoichiometric ratio. The contents of the different raw materials were: 0.05 mol sodium pyrophosphate, 0.1 mol ammonium dihydrogen phosphate, 0.1475 mol ferric nitrate nonahydrate, and 0.0025 mol ammonium metavanadate.

[0040] Comparative Example 1

[0041] This embodiment is based on the preparation of vanadium-doped modified sodium ferric pyrophosphate material by spray drying method. The chemical formula is Na. 3.9 Fe 2.9 V 0.1 (PO4)2P2O7 was prepared by ball milling followed by spray drying granulation. The specific preparation method is as follows:

[0042] S1. Weigh out 0.05 mol sodium pyrophosphate, 0.1 mol ammonium dihydrogen phosphate, 0.145 mol ferric nitrate nonahydrate, 0.005 mol ammonium metavanadate and 50 mL acetone respectively, mix them, and ball mill at 400 r for 8 h to obtain the precursor mixture.

[0043] S2. The above mixture is spray-dried into precursor powder at an injection rate of 200 mL / h, an inlet temperature of 100℃, and an outlet temperature of 60℃. The precursor powder is then sintered at 300℃ for 1 h under an argon atmosphere to form pre-calcined powder.

[0044] S3. The pre-calcined powder and oleic acid (molar ratio of 10:1.5) are thoroughly mixed in acetone and dried. The mixture is then sintered at 500°C for 10 hours under an argon-hydrogen mixed atmosphere (5% hydrogen). After cooling, vanadium-doped modified Na is obtained. 3.9 Fe 2.9 V 0.1 (PO4)2P2O7 cathode material.

[0045] Comparative Example 2

[0046] In this comparative example, undoped Na4Fe3(PO4)2P2O7 was prepared by spray drying as a control material. The preparation method was the same as in Example 1, except that the stoichiometric ratio was controlled and vanadium was not included. The contents of the different raw materials were: 0.05 mol sodium pyrophosphate, 0.1 mol ammonium dihydrogen phosphate, and 0.15 mol ferric nitrate nonahydrate.

[0047] Comparative Example 3

[0048] In this comparative example, undoped vanadium-containing Na₄Fe₃(PO₄)₂P₂O₇ was prepared as a control material using a direct drying method. The specific preparation method is as follows:

[0049] S1. Weigh out 0.05 mol sodium pyrophosphate, 0.1 mol ammonium dihydrogen phosphate, 0.15 mol ferric nitrate nonahydrate and 0.075 mol citric acid respectively and add them to a 2 mol / L acetic acid solution. After stirring thoroughly, add an appropriate amount of anhydrous oxalic acid to form a clear solution with a solid-liquid ratio of 150 g / L.

[0050] S2. The above solution is dried in a 60°C forced-air oven and then ground to obtain precursor powder;

[0051] S3. The precursor powder was sintered at 300°C for 3 hours under an argon atmosphere, and then heated to 500°C for 10 hours. After cooling, Na4Fe3(PO4)2P2O7 prepared by direct drying method was obtained.

[0052] Comparative Example 4

[0053] In this comparative example, the vanadium-doped modified sodium iron pyrophosphate material prepared by solid-state ball milling has the chemical formula Na. 3.9 Fe 2.9 V 0.1 (PO4)2P2O7, the specific preparation method is as follows:

[0054] S1. Weigh 0.05 mol sodium pyrophosphate, 0.1 mol ammonium dihydrogen phosphate, 0.145 mol ferric nitrate nonahydrate, 0.005 mol ammonium metavanadate, 0.005 mol oleic acid and 50 mL acetone into a ball mill jar, ball mill at 400 r for 8 h and then dry to obtain precursor powder.

[0055] S2. The precursor powder was sintered at 300°C for 1.5 h under an argon atmosphere, then heated to 500°C and sintered for 10 h. After cooling, Na prepared by solid-state ball milling was obtained. 3.9 Fe 2.9 V 0.1 (PO4)2P2O7.

[0056] The materials prepared in the above embodiments and comparative examples were used as positive electrode materials in sodium-ion batteries. More specifically, the above materials, conductive carbon black, and PVDF were mixed in a mass ratio of 7:2:1, with an appropriate amount of N-methylpyrrolidone (NMP) added as a diluent. After thorough grinding, a uniform slurry was formed. The slurry was coated onto a carbon-coated aluminum foil current collector and dried to serve as a test electrode. A coin cell was assembled using a sodium metal sheet as the counter electrode. The electrolyte system used was 1M NaPF6 / DEGDME. It should be noted that both ether-based and carbonate-based electrolyte systems were used. Different electrolytes had little impact on the reversible capacity of this material. The electrolyte system presented in this paper showed the best relative cycle performance. A glass fiber membrane was used as the separator, and the electrochemical performance was tested using a Neway testing system.

[0057] Initial specific capacity test conditions: 0.1C, 1.7-3.9V test; Note: 1C = 128mA / g.

[0058] Rate performance testing conditions: 0.1C test for 3 weeks, 0.5C test for 3 weeks, 1C test for 3 weeks, 2C test for 3 weeks, 5C test for 3 weeks, 10C test for 3 weeks, 20C test for 3 weeks; Note: 1C = 128mA / g.

[0059] Cyclic performance test conditions: 5°C, 500 cycles at room temperature; Note: 1°C = 128 mA / g.

[0060] Figure 1 and 2 The scanning electron microscope images of Comparative Example 2 and Example 1 show that the undoped sodium iron pyrophosphate material is basically fragmented with a large number of pores caused by the evaporation and decomposition of acetic acid and oxalic acid on the surface. Vanadium doping enhances the solvation and complexation ability of the solution, and the particles have a good porous spherical structure after spray drying.

[0061] The X-ray diffraction patterns of the materials obtained in Example 1 and Comparative Examples 3 and 4 are as follows: Figure 3 As shown in the spectrum, the materials prepared by direct drying or solid-state ball milling contain a large number of impurity phases, the main component of which is non-electrochemically active NaFePO4. However, no impurity phases were observed in the vanadium-doped sodium iron pyrophosphate material prepared by spray drying, and it exhibited good crystallinity. This indicates that a small amount of vanadium doping does not change the crystal structure of the material, nor does it generate new impurity phases; instead, it shows a small peak shift, further verifying the successful incorporation of vanadium into the material. Simple lattice constant calculations revealed a slight increase in the lattice constant b of sodium iron pyrophosphate after vanadium doping. In sodium iron pyrophosphate, sodium ions have a very complete and clear transport channel along the b-axis, and the increase in the lattice constant b will facilitate the transport of sodium ions along the b-axis.

[0062] The charge-discharge curves of Example 1 and Comparative Example 2 at 0.1C are shown in the figure below. Figure 4 As shown, the reversible capacity of the material was significantly improved and the charging polarization voltage decreased after the addition of trace amounts of vanadium. The rate performance of Example 1 at 0.1-20C is shown in the figure below. Figure 5 As shown, a reversible capacity of 104.8 mAh / g can be achieved under a charge-discharge cycle at a current density of 1C; even under 20C fast charge-discharge conditions, the material with trace vanadium doping can still maintain a high reversible capacity of 87 mAh / g. The cycling performance of Example 1 at a high current density of 5C is shown in the figure. Figure 6 As shown, the material retains 98.2% of its capacity during the first 500 cycles, demonstrating excellent cycling performance.

[0063] The electrochemical data of Examples 1-2 and Comparative Examples 1-4 are summarized in Table 1. The table shows that the reversible capacity and cycle performance of vanadium-doped iron pyrophosphate sodium prepared by the complex ion solution spray drying method are effectively improved. In Comparative Example 1, the reversible capacity of the mixture prepared by ball milling followed by spray drying was slightly lower than that prepared by the complex ion solution mixing method, indicating that ball milling can achieve a certain degree of element mixing, but the mixing uniformity is not as good as that of the complex ion solution mixing method. A comparison between Comparative Examples 1 and 4 shows that spray drying is crucial for forming a pure phase. Comparative Examples 3 and 4 did not use spray drying to prepare the materials, which severely affected the phase formation of the materials and introduced a large number of non-electrochemically active impurities, leading to a sharp decrease in the reversible capacity of the materials.

[0064] Table 1: Electrochemical data for each example and control example

[0065]

[0066] The technical features of the embodiments described above can be combined arbitrarily. The description of the embodiments is only for the purpose of helping to understand the method and core idea of ​​this application; as long as the combination of these technical features does not contradict each other, it should be considered as within the scope of this specification. The scope of protection claimed by this application shall be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing vanadium-doped modified sodium iron pyrophosphate material based on spray drying, characterized in that, The material is pure-phase Na. 4-x Fe 3-x V x (PO4)2P2O7 porous spherical particulate material, wherein 0 < x ≤ 0.1; prepared by spray drying, the preparation method comprising the following steps: S1. Weigh out sodium source, iron source, vanadium source and phosphorus source according to stoichiometric ratio and add them to a weakly acidic aqueous solution. Stir thoroughly to form a precipitate. After adding a complexing agent, a uniform and stable complexed ion solution is formed. S2. The above solution is spray-dried into precursor powder, and the precursor powder is placed under a protective atmosphere for low-temperature pre-sintering to form pre-sintered powder. S3. The pre-calcined powder and carbon source are thoroughly mixed and dried. The mixture is then sintered and cooled under a protective atmosphere to obtain the vanadium-doped modified sodium iron pyrophosphate material.

2. The preparation method of vanadium-doped modified sodium iron pyrophosphate material based on spray drying according to claim 1, characterized in that, The weakly acidic aqueous solution mentioned in step S1 is a mixed solution of a weak acid and deionized water with a concentration of 0.5~8 mol / L; the weak acid is one of acetic acid, formic acid, and propionic acid; the solid-liquid ratio in the complexed ion solution is 100~300 g / L.

3. The preparation method of vanadium-doped modified sodium iron pyrophosphate material based on spray drying according to claim 1, characterized in that, In step S1, the complexing agent is one or more of anhydrous oxalic acid, oxalate dihydrate, disodium ethylenediaminetetraacetate, citric acid, and ethylenediaminetetraacetic acid; the sodium source is at least one of sodium pyrophosphate, trisodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, disodium dihydrogen pyrophosphate, sodium carbonate, sodium bicarbonate, sodium oxalate, and sodium citrate; the iron source is at least one of ferric nitrate, ferric phosphate, ferrous oxalate, ferric oxalate, and ferrous acetate; the vanadium source is at least one of ammonium metavanadate, vanadium oxalate, and vanadium pentoxide; the phosphorus source is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium pyrophosphate, trisodium monohydrogen pyrophosphate, disodium dihydrogen pyrophosphate, and monosodium trihydrogen pyrophosphate; the relative molar ratio of the corresponding elements in the sodium, iron, vanadium, and phosphorus sources is 4-x:3-x:x:4, where 0 < x ≤ 0.

1.

4. The preparation method of vanadium-doped modified sodium iron pyrophosphate material based on spray drying according to claim 1, characterized in that, The parameters for spray drying in step S2 are: injection rate of 100~400 mL / h, inlet temperature of 130~200 ℃, and outlet temperature of 80~150 ℃.

5. The preparation method of vanadium-doped modified sodium iron pyrophosphate material based on spray drying according to claim 1, characterized in that, The pre-sintering temperature in step S2 is 200~350 ℃, and the sintering time is 1-4 hours; the sintering temperature in step S3 is 450~550 ℃, and the sintering time is 2-12 hours; the protective atmosphere in steps S2 and S3 is one of nitrogen, argon, or argon-hydrogen mixture.

6. The preparation method of vanadium-doped modified sodium iron pyrophosphate material based on spray drying according to claim 1, characterized in that, In step S3, the carbon source is at least one of oleic acid, citric acid, graphite, and carbon nanotubes; the relative molar ratio of the pre-calcined powder to the carbon source is 5:1 to 20:

1.

7. A positive electrode sheet comprising vanadium-doped modified sodium iron pyrophosphate material prepared by any one of claims 1-6.

8. A sodium-ion battery, characterized in that, It contains the positive electrode sheet as described in claim 7.

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