A composite sodium-ion cathode material, its preparation method and application

Abstract

This application provides a composite sodium ion cathode material, its preparation method, and its application. The preparation method includes the following steps: (1) preparing sodium ferrocyanide solution A, preparing iron source, antioxidant, and complexing agent into solution B, preparing vanadium source, phosphorus source, and reducing agent into solution C, and preparing sodium source and fluorine source into solution D; (2) adding solution A and solution B in parallel into a container to obtain a first solution, adding solution C and solution D in parallel into a container, adding sodium carbonate solution to adjust the pH to obtain a second solution, and adding the first solution and the second solution in parallel into a reaction vessel to react and obtain Prussian blue / vanadium fluorophosphate material; (3) calcining the Prussian blue / vanadium fluorophosphate material to obtain the composite sodium ion cathode material. In this application, the composite Prussian blue and vanadium fluorophosphate materials are subjected to low-temperature calcination treatment, which can not only improve the stability of the material but also improve its conductivity.

Description

Technical Field

[0001] This application pertains to the field of sodium-ion batteries, specifically a composite sodium-ion cathode material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries have been widely used in portable electronic devices, electric vehicles, and other fields, achieving great success and experiencing rapid growth. However, the low reserves of lithium resources have led to a continuous increase in the cost of lithium-ion batteries, prompting attention to sodium-ion batteries. Sodium-ion batteries offer advantages such as low raw material costs, abundant resources, high electrochemical performance potential, and environmental friendliness, making them one of the important research directions for next-generation battery technology.

[0003] Currently, the cathode materials for sodium-ion batteries mainly include transition metal oxides, phosphates, and Prussian blue materials. Among them, Prussian blue materials have advantages such as high specific capacity, high voltage plateau, and low cost, making them a primary choice for sodium-ion batteries. Furthermore, sodium vanadium fluorophosphate, as a typical sodium superionic conductor, has a high theoretical storage capacity, and its open three-dimensional framework is Na₂O₃. + The transport mechanism provides a unique pathway, allowing sodium vanadium fluorophosphate to exhibit excellent structural stability during long-term cycling. However, its poor electronic conductivity increases electrical resistance, hindering the rapid insertion and extraction of sodium.

[0004] CN114212802A discloses a method for preparing a Prussian blue-based sodium-ion battery cathode material, comprising adding a first nonionic surfactant and an antioxidant to a sodium ferrocyanide solution to obtain a first solution, adding a second nonionic surfactant to a transition metal salt solution to obtain a second solution, adding the second solution to the first solution under a protective atmosphere to carry out a precipitation reaction, aging after the reaction, collecting the precipitate, washing it, vacuum drying the washed precipitate, immersing it in an alcohol solution containing sodium alkoxide, filtering it, and evaporating it to dryness to obtain the Prussian blue-based sodium-ion battery cathode material.

[0005] CN105655565A discloses a composite cathode material for sodium-ion batteries, which is a composite multi-core core-shell structure. The core is composed of a mixture of sodium vanadium phosphate coated with multiple amorphous carbon layers and sodium fluorophosphate coated with multiple amorphous carbon layers. The gaps between the shell and the core are filled with conductive polymers. Amorphous carbon layers are coated on the outer layers of nanoscale sodium vanadium phosphate and sodium fluorophosphate respectively. The conductive polymer monomers are polymerized, and the prepared sodium vanadium phosphate coated with amorphous carbon layers and sodium fluorophosphate coated with amorphous carbon layers are added to the mixture. The mixture is mixed evenly, and the resulting mixture is spray-dried to obtain the target product.

[0006] The sodium ion cathode material described in the above scheme has problems with poor cycle stability or poor conductivity, which limits its application in practice. Summary of the Invention

[0007] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0008] This application provides a composite sodium ion cathode material, its preparation method, and its application. The present application combines Prussian blue and sodium vanadium fluorophosphate and then performs low-temperature calcination, which not only improves the stability of the material but also enhances its conductivity.

[0009] To achieve the purpose of this application, the following technical solution is adopted:

[0010] In a first aspect, embodiments of this application provide a method for preparing a composite sodium-ion cathode material, the method comprising the following steps:

[0011] (1) Sodium ferrocyanide and solvent are mixed to obtain solution A, iron source, antioxidant, complexing agent and solvent are mixed to obtain solution B, vanadium source, phosphorus source, reducing agent and solvent are mixed to obtain solution C, sodium source, fluorine source and solvent are mixed to obtain solution D;

[0012] (2) Solution A and solution B are added to the first container in parallel and stirred to obtain the first solution. Solution C and solution D are added to the second container in parallel. Sodium carbonate solution is added to the second container and the pH is controlled to obtain the second solution. The first solution and the second solution are added to the reaction vessel in parallel to carry out the reaction and obtain Prussian blue / vanadium fluorophosphate material.

[0013] (3) The Prussian blue / vanadium fluorophosphate material is calcined to obtain the composite sodium ion cathode material.

[0014] In this embodiment, two primary particles are simultaneously generated and composited using a co-precipitation method to obtain a Prussian blue / sodium vanadium fluorophosphate composite material. Then, the surface of the Prussian blue material is carbonized by short-time low-temperature calcination, which forms an interpenetrating conductive network between the primary particles, further improving the conductivity of the secondary particles. Ultimately, this improves the electronic conductivity of the composite cathode material and greatly enhances the electrochemical performance of the cathode material.

[0015] In one embodiment, the molar concentration of sodium ferrocyanide in solution A in step (1) is 0.1 to 0.5 mol / L, for example: 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L or 0.5 mol / L, etc.

[0016] In one embodiment, the iron source includes any one or a combination of at least two of ferrous chloride, ferrous acetate, or ferrous sulfate.

[0017] In one embodiment, the antioxidant comprises any one or a combination of at least two of tartaric acid, citric acid, or ascorbic acid.

[0018] In one embodiment, the complexing agent comprises any one or a combination of at least two of sodium citrate, ascorbic acid, tartaric acid, glucose, or ethylenediaminetetraacetic acid.

[0019] In one embodiment, the molar concentration of the iron source in solution B is 0.11 to 0.5 mol / L, for example: 0.11 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, or 0.5 mol / L, etc.

[0020] In one embodiment, the molar concentration of the antioxidant in solution B is 0.02 to 0.1 mol / L, for example: 0.02 mol / L, 0.04 mol / L, 0.06 mol / L, 0.08 mol / L, or 0.1 mol / L, etc.

[0021] In one embodiment, the molar concentration of the complexing agent in solution B is 1 to 2.5 mol / L, for example: 1 mol / L, 1.2 mol / L, 1.5 mol / L, 2 mol / L, or 2.5 mol / L, etc.

[0022] In one embodiment, the vanadium source in step (1) includes any one or a combination of at least two of vanadium pentoxide, ammonium metavanadate, or sodium metavanadate.

[0023] In one embodiment, the phosphorus source includes any one or a combination of at least two of phosphoric acid, sodium dihydrogen phosphate, or ammonium dihydrogen phosphate.

[0024] In one embodiment, the reducing agent comprises oxalic acid and / or ascorbic acid.

[0025] In one embodiment, the molar concentration of the vanadium source in solution C is 0.1 to 0.5 mol / L, for example: 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, or 0.5 mol / L, etc.

[0026] In one embodiment, the molar ratio of the reducing agent to the vanadium source is (1-2):1, for example: 1:1, 1.2:1, 1.5:1, 1.8:1 or 2:1, etc.

[0027] In one embodiment, the sodium source includes any one or a combination of at least two of sodium fluoride, sodium oxalate, sodium dihydrogen phosphate, sodium phosphate, or disodium hydrogen phosphate.

[0028] In one embodiment, the fluorine source includes sodium fluoride and / or ammonium fluoride.

[0029] In one embodiment, the molar ratio of sodium in the sodium source, vanadium in the vanadium source, phosphorus in the phosphorus source, and fluorine in the fluorine source is (3-4):2:(2-2.5):(3-4), for example: 3:2:2:3, 3.5:2:2.2:3.2, 3.5:2:2.4:3.5, 3.8:2:2.4:3.8, or 4:2:2.5:4, etc.

[0030] In one embodiment, the stirring time in the first and second containers in step (2) is independently 6 to 8 minutes, for example: 6 minutes, 6.5 minutes, 7 minutes, 7.5 minutes or 8 minutes, etc.

[0031] In one embodiment, the sodium carbonate solution is 2 to 4 mol / L, for example: 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, or 4 mol / L, etc.

[0032] In one embodiment, the pH is 5 to 7, for example: 5, 5.5, 6, 6.5 or 7, etc.

[0033] In one embodiment, the rate at which the first solution and the second solution are added to the reactor in parallel in step (2) is 40 to 60 mL / min, for example: 40 mL / min, 45 mL / min, 50 mL / min, 55 mL / min or 60 mL / min, etc.

[0034] In one embodiment, the reactor contains 50 mL of deionized water.

[0035] In one embodiment, the reaction temperature is 60–80°C, for example: 60°C, 65°C, 70°C, 75°C, or 80°C.

[0036] In one embodiment, the reaction time is 6 to 8 hours, for example: 6 hours, 6.5 hours, 7 hours, 7.5 hours, or 8 hours.

[0037] In one embodiment, a sodium carbonate solution is added during the reaction to control the pH.

[0038] In one embodiment, the pH is 5 to 7, for example: 5, 5.5, 6, 6.5 or 7, etc.

[0039] In one embodiment, the reaction described in step (2) is followed by solid-liquid separation, washing, and drying.

[0040] In one embodiment, the drying temperature is 90–110°C, for example: 90°C, 95°C, 100°C, 105°C, or 110°C.

[0041] In one embodiment, the calcination temperature in step (3) is 250 to 350°C, for example: 250°C, 280°C, 300°C, 320°C or 350°C.

[0042] In one embodiment, the calcination treatment time is 0.5 to 1.5 hours, for example: 0.5 hours, 0.8 hours, 1 hour, 1.2 hours, or 1.5 hours.

[0043] In this embodiment, the Prussian blue / sodium vanadium fluorophosphate material is calcined at 250–350°C for 0.5–1.5 hours. This short-term low-temperature calcination causes carbonization on the surface of the Prussian blue material, resulting in an interpenetrating conductive network between the primary particles (Prussian blue and sodium vanadium fluorophosphate). This improves the conductivity of the secondary particles and ultimately enhances the electronic conductivity of the composite cathode material. Compared to conventional methods that form a carbon coating layer on the surface to improve the conductivity of the cathode material, this preparation method further improves the conductivity and electrochemical performance of the cathode material.

[0044] Secondly, embodiments of this application provide a composite sodium ion cathode material, which is prepared by the method described in the first aspect.

[0045] Thirdly, embodiments of this application provide a positive electrode sheet, which comprises the composite sodium ion positive electrode material as described in the second aspect.

[0046] Fourthly, embodiments of this application provide a sodium-ion battery, the sodium-ion battery comprising a positive electrode as described in the third aspect.

[0047] Compared with related technologies, this application has the following advantages:

[0048] (1) This application uses a co-precipitation method to simultaneously generate two primary particles and combine them to obtain Prussian blue / sodium vanadium fluorophosphate composite material. This preparation method can efficiently combine the two primary particles, reduce the complexity of the preparation process, reduce production costs, and more importantly, improve the stability of the material.

[0049] (2) Due to the poor conductivity of Prussian blue and sodium vanadium fluorophosphate, this application subjects the Prussian blue / sodium vanadium fluorophosphate material to low-temperature calcination. After short-term low-temperature calcination, carbonization occurs on the surface of the Prussian blue material, which forms an interpenetrating conductive network between the primary particles (i.e., Prussian blue and sodium vanadium fluorophosphate), thereby improving the conductivity of the secondary particles and ultimately enhancing the electronic conductivity of the composite cathode material. Compared to the conventional method of forming a carbon coating layer on the surface to improve the conductivity of the cathode material, this preparation method can further improve the conductivity and electrochemical performance of the cathode material.

[0050] (3) The battery made of the composite sodium-ion cathode material described in this application can achieve a discharge specific capacity of more than 116 mAh / g at 0.1C, a discharge specific capacity of more than 106 mAh / g at 1C, a discharge specific capacity of more than 98 mAh / g at 5C, and a capacity retention rate of more than 97.1% after 100 cycles at 0.1C.

[0051] After reading and understanding the detailed description, other aspects can be understood. Detailed Implementation

[0052] The technical solution of this application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely to help understand this application and should not be regarded as specific limitations on this application.

[0053] Example 1

[0054] This embodiment provides a composite sodium-ion cathode material, and the preparation method of the composite sodium-ion cathode material is as follows:

[0055] (1) Dissolve sodium ferrocyanide in deionized water and stir until homogeneous to form a solution A with a concentration of 0.1 mol / L. Dissolve ferrous sulfate, ascorbic acid and sodium citrate in deionized water and stir until homogeneous to form a mixed solution B. The concentration of ferrous sulfate in mixed solution B is 0.11 mol / L, the concentration of ascorbic acid is 0.02 mol / L, and the concentration of sodium citrate is 1 mol / L. Mix sodium metavanadate, phosphoric acid, oxalic acid and deionized water to obtain a mixed solution C. The concentration of sodium metavanadate in mixed solution C is 0.1 mol / L, the concentration of phosphoric acid is 0.1 mol / L, and the concentration of oxalic acid is 0.1 mol / L. Mix sodium phosphate, sodium fluoride and deionized water to obtain a mixed solution D. The concentration of sodium phosphate in mixed solution D is 0.15 mol / L, and the concentration of sodium fluoride is 0.15 mol / L.

[0056] (2) Solution A and solution B were simultaneously injected into solution mixing stirrer I and mixed for 8 min; solution C and solution D were simultaneously injected into solution mixing stirrer II and mixed for 8 min, and 3 mol / L sodium carbonate solution was added dropwise to solution mixing stirrer II to maintain the solution pH at about 6.5; then the solutions in solution mixing stirrer I and solution mixing stirrer II were passed into a reaction vessel containing 50 mL of deionized water at a rate of 40 mL / min and reacted at 70 °C for 7 h. During the entire reaction, the solution pH was maintained at about 6.5 by adding 3 mol / L sodium carbonate solution dropwise; finally, the solid and liquid were separated, washed, and vacuum dried at 100 °C to obtain the Prussian blue / vanadium fluorophosphate composite material;

[0057] (3) The prepared Prussian blue / vanadium fluorophosphate material was calcined at 350°C for 0.5 h to obtain the composite sodium ion cathode material.

[0058] Example 2

[0059] This embodiment provides a composite sodium-ion cathode material, and the preparation method of the composite sodium-ion cathode material is as follows:

[0060] (1) Dissolve sodium ferrocyanide in deionized water and stir until homogeneous to form a solution A with a concentration of 0.5 mol / L. Dissolve ferrous chloride, tartaric acid and ethylenediaminetetraacetic acid in deionized water and stir until homogeneous to form a mixed solution B. The concentration of ferrous sulfate in mixed solution B is 0.55 mol / L, the concentration of ascorbic acid is 0.1 mol / L, and the concentration of sodium citrate is 5 mol / L. Mix ammonium metavanadate, sodium dihydrogen phosphate, ascorbic acid and deionized water to obtain mixed solution C. The concentration of sodium metavanadate in mixed solution C is 0.5 mol / L, the concentration of phosphoric acid is 0.5 mol / L, and the concentration of oxalic acid is 0.5 mol / L. Mix sodium oxalate, ammonium fluoride and deionized water to obtain mixed solution D. The concentration of sodium oxalate in mixed solution D is 0.75 mol / L, and the concentration of ammonium fluoride is 0.75 mol / L.

[0061] (2) Solution A and solution B were simultaneously injected into solution mixing stirrer I and mixed for 6 min; solution C and solution D were simultaneously injected into solution mixing stirrer II for 6 min, and 3 mol / L sodium carbonate solution was added dropwise to solution mixing stirrer II to maintain the solution pH at about 5.5; then the solutions in solution mixing stirrer I and solution mixing stirrer II were passed into a reaction vessel containing 50 mL of deionized water at a rate of 60 mL / min, and reacted at 80 °C for 6 h. During the entire reaction, the solution pH was maintained at about 5.5 by adding 3 mol / L sodium carbonate solution dropwise; finally, the solid and liquid were separated, washed, and vacuum dried at 100 °C to obtain the Prussian blue / vanadium fluorophosphate composite material;

[0062] (3) The prepared Prussian blue / vanadium fluorophosphate material was calcined at 250°C for 1.5 h to obtain the composite sodium ion cathode material.

[0063] Example 3

[0064] The only difference between this embodiment and Embodiment 1 is that the calcination temperature is 200℃, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0065] Example 4

[0066] The only difference between this embodiment and Embodiment 1 is that the calcination temperature is 400℃, while the other conditions and parameters are exactly the same as in Embodiment 1.

[0067] Comparative Example 1

[0068] The only difference between this comparative example and Example 1 is that step (3) calcination is not performed; all other conditions and parameters are exactly the same as in Example 1.

[0069] Comparative Example 2

[0070] This comparative example provides a sodium-ion cathode material, and the preparation method of the sodium-ion cathode material is as follows:

[0071] (1) Sodium metavanadate, phosphoric acid, oxalic acid and deionized water are mixed to obtain mixed solution A. The concentration of sodium metavanadate in the mixed solution is 0.1 mol / L, the concentration of phosphoric acid is 0.1 mol / L and the concentration of oxalic acid is 0.1 mol / L.

[0072] (2) Sodium phosphate, sodium fluoride and deionized water are mixed to obtain mixed solution B. The concentration of sodium phosphate in the mixed solution is 0.15 mol / L and the concentration of sodium fluoride is 0.15 mol / L.

[0073] (3) Solution A and solution B were simultaneously introduced into a reactor containing 50 mL of deionized water at a rate of 40 mL / min and reacted at 70 °C for 7 h. During the entire reaction, the pH of the solution was maintained at around 6.5 by adding 3 mol / L sodium carbonate solution dropwise. Finally, the solid and liquid were separated, washed, and vacuum dried at 100 °C to obtain sodium fluorophosphate material.

[0074] Comparative Example 3

[0075] This comparative example provides a sodium-ion cathode material, and the preparation method of the sodium-ion cathode material is as follows:

[0076] (1) Dissolve sodium ferrocyanide in deionized water and stir until homogeneous to form solution A with a concentration of 0.1 mol / L;

[0077] (2) Dissolve ferrous sulfate, ascorbic acid and sodium citrate in deionized water and stir until homogeneous to form mixed solution B. The concentration of ferrous sulfate in the mixed solution is 0.11 mol / L, the concentration of ascorbic acid is 0.02 mol / L and the concentration of sodium citrate is 1 mol / L.

[0078] (3) Solution A and solution B were introduced into a reactor containing 50 mL of deionized water at a rate of 40 mL / min. After reacting at 70 °C for 7 h, the solid and liquid were separated, washed, and dried under vacuum at 100 °C to obtain Prussian blue cathode material.

[0079] Performance testing:

[0080] The materials prepared in Examples 1-2 and Comparative Examples 1-2 were used as positive electrodes, with metallic sodium as the negative electrode, glass fiber as the separator, and a NaPF6 propylene carbonate / methyl ethyl carbonate solution as the electrolyte. 3% by weight of fluorinated ethylene carbonate was added to the electrolyte. Button batteries were assembled with a voltage range of 2–4V and a test temperature of 25–55°C. Charge-discharge tests were conducted at 0.1C–1C. The test results are shown in Table 1.

[0081] Table 1

[0082]

[0083] As can be seen from Table 1, and from Examples 1-2, the battery made of the composite sodium-ion cathode material described in this application can achieve a discharge specific capacity of over 116 mAh / g at 0.1C, a discharge specific capacity of over 106 mAh / g at 1C, a discharge specific capacity of over 98 mAh / g at 5C, and a capacity retention rate of over 97.1% after 100 cycles at 0.1C.

[0084] Comparing Examples 1 and 3-4, it can be seen that the calcination temperature in step (3) of the preparation process of the composite sodium ion cathode material described in this application affects its performance. Controlling the calcination temperature at 250-350℃ results in better performance of the composite sodium ion cathode material. If the calcination temperature is too low, the amount of Prussian blue decomposed is too small, the carbon coating content is low, and the rate performance is significantly reduced. If the calcination temperature is too high, the amount of Prussian blue decomposed is too large, the carbon coating content is high, and although the rate performance is improved, the specific capacity is reduced due to the increased proportion of inactive substances.

[0085] Comparing Example 1 and Comparative Example 1, it can be seen that in this application, the Prussian blue / sodium vanadium fluorophosphate material is calcined at 250–350°C for 0.5–1.5 h. After this short-term low-temperature calcination, carbonization occurs on the surface of the Prussian blue material. This forms an interpenetrating conductive network between the primary particles (i.e., Prussian blue and sodium vanadium fluorophosphate), thereby improving the conductivity of the secondary particles and ultimately enhancing the electronic conductivity of the composite cathode material. Compared to the conventional method of forming a carbon coating layer on the surface to improve the conductivity of the cathode material, this preparation method can further improve the conductivity and electrochemical performance of the cathode material.

[0086] As can be seen from the comparison between Example 1 and Comparative Examples 2-3, this application produces two primary particles simultaneously and they combine through co-precipitation, thereby obtaining a Prussian blue / sodium vanadium fluorophosphate composite material. The two primary particles are efficiently combined, and Prussian blue is used to form an internal carbon network. Compared with the two materials, the performance in all aspects is improved.

Claims

1. A method for preparing a composite sodium-ion cathode material, the method comprising the following steps: (1) Sodium ferrocyanide and solvent are mixed to obtain solution A, iron source, antioxidant, complexing agent and solvent are mixed to obtain solution B, vanadium source, phosphorus source, reducing agent and solvent are mixed to obtain solution C, sodium source, fluorine source and solvent are mixed to obtain solution D; (2) Add solutions A and B in parallel to the first container and stir to mix to obtain the first solution. Add solutions C and D in parallel to the second container. Add sodium carbonate solution to the second container and control the pH to obtain the second solution. Add the first solution and the second solution in parallel to the reaction vessel to carry out the reaction and obtain Prussian blue / vanadium fluorophosphate material. (3) The Prussian blue / vanadium fluorophosphate material is calcined to obtain the composite sodium ion cathode material; The reaction temperature is 60~80℃, the reaction time is 6~8h, the calcination temperature in step (3) is 250~350℃, and the calcination time is 0.5~1.5h.

2. The preparation method according to claim 1, wherein, The molar concentration of sodium ferrocyanide in solution A in step (1) is 0.1~0.5 mol / L.

3. The preparation method according to claim 1, wherein, The iron source includes any one or a combination of at least two of ferrous chloride, ferrous acetate, or ferrous sulfate.

4. The preparation method according to claim 1, wherein, The antioxidants include any one or a combination of at least two of tartaric acid, citric acid, or ascorbic acid.

5. The preparation method according to claim 1, wherein, The complexing agent includes any one or a combination of at least two of sodium citrate, ascorbic acid, tartaric acid, glucose, or ethylenediaminetetraacetic acid.

6. The preparation method according to claim 1, wherein, The molar concentration of the iron source in solution B is 0.11~0.5 mol / L.

7. The preparation method according to claim 1, wherein, The molar concentration of the antioxidant in solution B is 0.02~0.1 mol / L.

8. The preparation method according to claim 1, wherein, The molar concentration of the complexing agent in solution B is 1~2.5 mol / L.

9. The preparation method according to claim 1, wherein, The vanadium source in step (1) includes any one or a combination of at least two of vanadium pentoxide, ammonium metavanadate, or sodium metavanadate.

10. The preparation method according to claim 1, wherein, The phosphorus source includes any one or a combination of at least two of phosphoric acid, sodium dihydrogen phosphate, or ammonium dihydrogen phosphate.

11. The preparation method according to claim 1, wherein, The reducing agent includes oxalic acid and / or ascorbic acid.

12. The preparation method according to claim 1, wherein, The molar concentration of the vanadium source in solution C is 0.1~0.5 mol / L.

13. The preparation method according to claim 1, wherein, The molar ratio of the reducing agent to the vanadium source is (1~2):

1.

14. The preparation method according to claim 1, wherein, The sodium source includes any one or a combination of at least two of sodium fluoride, sodium oxalate, sodium dihydrogen phosphate, sodium phosphate, or disodium hydrogen phosphate.

15. The preparation method according to claim 1, wherein, The fluorine source includes sodium fluoride and / or ammonium fluoride.

16. The preparation method according to claim 1, wherein, The molar ratio of sodium in the sodium source, vanadium in the vanadium source, phosphorus in the phosphorus source, and fluorine in the fluorine source is (3~4):2:(2~2.5):(3~4).

17. The preparation method according to claim 1, wherein, In step (2), the stirring time in the first and second containers is 6 to 8 minutes independently.

18. The preparation method according to claim 1, wherein, The sodium carbonate solution has a concentration of 2-4 mol / L.

19. The preparation method according to claim 1, wherein, The pH value is 5-7.

20. The preparation method according to claim 1, wherein, In step (2), the first solution and the second solution are added to the reactor in parallel at a rate of 40-60 mL / min.

21. The preparation method according to claim 1, wherein, The reactor contains 50 mL of deionized water.

22. The preparation method according to claim 1, wherein, Sodium carbonate solution is added during the reaction to control the pH.

23. The preparation method according to claim 22, wherein, The pH value is 5-7.

24. The preparation method according to claim 1, wherein, After the reaction described in step (2), solid-liquid separation, washing, and drying are performed.

25. The preparation method according to claim 24, wherein, The drying process is carried out at a temperature of 90~110℃.

26. A composite sodium-ion cathode material, said composite sodium-ion cathode material being prepared by the method described in any one of claims 1-25.

27. A positive electrode, said positive electrode comprising the composite sodium ion positive electrode material as described in claim 26.

28. A sodium-ion battery, the sodium-ion battery comprising the positive electrode as described in claim 27.

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