Iron-based phosphate positive electrode material and preparation method and application thereof

Abstract

The application provides an iron-based phosphate positive electrode material and a preparation method and application thereof. The preparation method of the positive electrode material comprises the following steps: reacting a mixture containing metallic iron and a phosphorus source at normal temperature to 100 DEG C to form a solid-liquid mixture containing an iron phosphate compound; mixing the solid-liquid mixture with an acid regulator, a carbon source and a sodium source, and then performing sand milling to obtain a slurry; performing drying treatment on the slurry to obtain a precursor material; and performing sintering on the precursor material under a protective atmosphere to obtain the iron-based phosphate positive electrode material. The method provided by the application does not need to completely dissolve the mixture of the metallic iron and the phosphorus source to form a solution, nor does it need to form an anhydrous iron phosphate in advance, and is a short-process method for preparing the iron-based phosphate positive electrode material with lower requirements on reaction conditions, which is suitable for industrial production and large-scale production.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of new energy, and particularly relates to an iron-based phosphate positive electrode material and a preparation method and application thereof. BACKGROUND

[0002] Sodium-ion batteries have attracted extensive attention in recent years due to their abundant resources, low cost and wide application prospects. In the research of key positive electrode materials for sodium-ion batteries, improving the energy density, cycle stability and rate performance is the current main research direction. Common positive electrode materials include polyanion compounds, layered oxides and prussian blue compounds. Among them, although the layered oxides have a high specific capacity, their cycle stability is poor; the prussian blue analogues are easy to introduce crystal water in the synthesis process, resulting in unstable structure and affecting the cycle performance. In comparison, the polyanion compounds become an ideal choice for the positive electrode materials of sodium-ion batteries due to their stable crystal structure and efficient sodium ion transmission channel.

[0003] Among the polyanion compounds, phosphate positive electrode materials have attracted much attention due to their good balance between low cost and high capacity. Typical materials include vanadium-based compounds (Na3V2(PO4)3, Na3V2(PO4)2F3), manganese-based compounds Na3MnTi(PO4)3, and iron-based compounds (NaFePO4, Na4Fe3(PO4)2P2O7). Among them, sodium iron pyrophosphate is considered as a promising large-scale energy storage system positive electrode material due to its high theoretical specific capacity, low raw material cost, simple synthesis process and excellent cycle performance. However, the synthesis process is easy to produce electrochemically inert sodium iron phosphate, and the existence of this impurity will significantly reduce the electrochemical performance of the material. In addition, the existing preparation method usually relies on expensive grinding equipment, and needs a long time to work to reduce the crystallinity and particle size of the material, resulting in large equipment investment, high energy consumption and long process flow, which is not conducive to large-scale production.

[0004] Therefore, developing a preparation process of high-purity sodium iron pyrophosphate and exploring an efficient and low-cost synthesis method has become the focus of current research. This not only helps to improve the electrochemical performance of the material, but also promotes the commercial application of sodium-ion batteries in the field of large-scale energy storage.

[0005] Currently, the iron-based phosphate cathode material of sodium-ion battery usually uses iron salts such as ferric nitrate, ferric phosphate, etc. as raw materials. In the prior art, CN118867197A discloses a method for preparing sodium pyrophosphate ferric phosphate cathode material by using ferrous phosphate, ferric phosphate, ferric nitrate, ferrous oxalate or ferrous carbonate as iron source; CN119008875A discloses a method for preparing sodium ferric phosphate cathode material by using at least two of ferric nitrate, ferric sulfate, ferric acetate, ferric chloride, ferric citrate, ferric tartrate and ferric tribromide as iron source. However, these methods have many limitations in practical application: compared with the most common ferric phosphate route in industrialization, first of all, the iron salt needs to be reacted with phosphoric acid to obtain anhydrous ferric phosphate through steps such as precipitation, neutralization of pH value and drying, and since the ferric phosphate needs to be treated by aging and high-temperature annealing dehydration, the crystallinity is high, the energy barrier for conversion to sodium pyrophosphate ferric phosphate phase is high, and impurities are easily produced, which is not conducive to the efficient synthesis of the material. When ferric nitrate is used as the iron source, nitrogen oxides will be produced during the preparation process, which will cause harm to human health and environmental safety; in addition, the production cost of ferrous oxalate and ferrous phosphate is high, which is difficult to meet the needs of industrialization; although the cost of iron oxide is low, its purity is low and it often contains impurities, which makes it difficult to control the consistency of the product. SUMMARY

[0006] To solve all or part of the above technical problems, the present application proposes an innovative "solid-liquid integrated" preparation method. This method directly enters the next step by generating a solid-liquid mixture, without the need to pre-prepare anhydrous ferric phosphate, thereby significantly shortening the production cycle. In addition, this method has the advantages of short reaction process, small product particle size and low hardness, reducing the difficulty of subsequent processing. At the same time, since a solid-liquid mixture is formed, the crystallinity is low and the activity is high, making it easier to obtain high-performance target materials. This invention not only simplifies the process flow, but also improves the material performance, providing a new solution for the industrialization of iron-based phosphate cathode materials for sodium-ion batteries. Accordingly, the present application provides the following technical solutions:

[0007] One of the purposes of the present application is to provide a preparation method of an iron-based phosphate cathode material, comprising:

[0008] reacting a mixture containing metallic iron and a phosphorus source at a temperature of normal temperature to 100 DEG C to form a solid-liquid mixture containing ferric phosphate compound;

[0009] mixing the solid-liquid mixture with an acid regulator, a carbon source and a sodium source, and then performing sand milling to obtain a slurry;

[0010] drying the slurry to obtain a precursor material;

[0011] sintering the precursor material under a protective atmosphere to obtain an iron-based phosphate cathode material.

[0012] The composition of the ferric phosphate compound formed by the reaction of metallic iron and phosphorus source is complex, including one or more of Fe3(PO4)2, FePO4, FeHPO4, Fe3(PO4)2(OH)2 and hydrates thereof, and also including one or more of hydroxyapatite, such as eugelite Fe3(PO4)2(OH)2, huntite Fe5(PO4)4(OH)2·2H2O, rockbridgeite Fe5(PO4)3(OH)5, Fe4(PO4)3(OH)3, etc.

[0013] In some embodiments, the method specifically comprises: mixing the metallic iron and the phosphorus source in a molar ratio of 1-1.75:2-2.25, and reacting at room temperature-100°C for 6h-12h to form the ferric phosphate compound, thereby obtaining the solid-liquid mixture.

[0014] In some embodiments, the phosphorus source comprises a combination of one or more of phosphoric acid, sodium dihydrogen phosphate, ferrous dihydrogen phosphate.

[0015] In some embodiments, the metallic iron comprises a combination of one or more of iron block, iron sheet, iron powder.

[0016] In some embodiments, the acid regulator comprises a combination of one or more of oxalic acid, tartaric acid, citric acid.

[0017] In some embodiments, the carbon source comprises glucose.

[0018] In some embodiments, the molar ratio of the acid regulator to iron element is 1:5-1:7.5.

[0019] In some embodiments, the sodium source is supplemented to the solid-liquid mixture according to the chemical formula Na 3-4.5 Fe 2-3.5 (PO4) 2-2.5 P2O7.

[0020] In some embodiments, the amount of the carbon source added satisfies a molar ratio of 1:10-1:15 to iron.

[0021] In some embodiments, the method specifically comprises: mixing the solid-liquid mixture with the acid regulator, the carbon source, the sodium source and polyethylene glycol, and then performing the sand milling, and the amount of the polyethylene glycol added is 1 / 400-1 / 600 of the total mass of the slurry.

[0022] In some embodiments, the method specifically comprises: the sand milling is performed at a temperature of 20-30°C for 2h-4h, so that the particle size in the slurry is 500-600nm.

[0023] In some embodiments, the drying is spray drying, and the inlet temperature of the spray drying is 210-250 DEG C, and the outlet temperature is 100-105 DEG C.

[0024] In some embodiments, the protective atmosphere is at least one of argon and nitrogen, or the protective atmosphere is argon-hydrogen mixed gas or nitrogen-hydrogen mixed gas, and the volume ratio of hydrogen in the argon-hydrogen mixed gas or nitrogen-hydrogen mixed gas is 5-10%.

[0025] In some embodiments, the sintering specifically comprises: first increasing the temperature to 290-310 DEG C at a rate of 1.5-2.5 DEG C / min and maintaining for 2.5-3.5 h, and then increasing the temperature to 500-550 DEG C at a rate of 1.5-2.5 DEG C / min and maintaining for 8-10 h.

[0026] The second object of the present application is to provide an iron-based phosphate cathode material prepared by any of the methods.

[0027] The third object of the present application is to provide a sodium ion battery cathode comprising a current collector and a cathode active material layer formed on the current collector, wherein the cathode active material layer comprises the iron-based phosphate cathode material.

[0028] The fifth object of the present application is to provide a sodium ion battery comprising a cathode, an anode, a separator and an electrolyte, wherein the cathode is the sodium ion battery cathode.

[0029] Compared with the prior art, the present application has at least the following beneficial effects:

[0030] (1) The present application provides a method for preparing an iron-based phosphate cathode material based on a solid-liquid mixture formed by metal iron and a phosphorus source, which does not need to completely dissolve the mixture of metal iron and the phosphorus source to form a solution, nor to form anhydrous iron phosphate first, is a short-process method for preparing an iron-based phosphate cathode material, and compared with the prior art method which needs to prepare soluble Fe(H2PO4)2 and anhydrous iron phosphate first, the method provided by the present application has a short process and lower requirements for reaction conditions, and is a method suitable for industrial production and large-scale production.

[0031] (2) Since the solid-liquid mixture has low crystallinity and high activity, it is easier to obtain high-performance target materials, and the prepared iron-based phosphate cathode material has high activity, small particle size and low hardness. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced as follows. Obviously, the drawings in the following description only illustrate some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0033] Figure 1 is the charge-discharge curve diagram of the positive electrode material prepared in Example 1 of the present application.

[0034] Figure 2 is the charge-discharge curve diagram of the positive electrode material prepared in Example 2 of the present application.

[0035] Figure 3 is the charge-discharge curve diagram of the positive electrode material prepared in Example 3 of the present application.

[0036] Figure 4a 、 Figure 4b is the SEM image of the positive electrode material prepared in Example 2 of the present application.

[0037] Figure 5 is the XRD image of the positive electrode material prepared in Examples 1 and 2 of the present application. DETAILED DESCRIPTION

[0038] The technical solutions of the present application will be described in detail below in combination with specific embodiments, so that those skilled in the art can better understand and implement the technical solutions of the present application. The specific functional details disclosed herein should not be interpreted as limiting, but only as a basis for the claims and for teaching those skilled in the art to employ the representative basis of the present application in different ways in any appropriate detailed embodiment.

[0039] In addition, unless otherwise specified, the various raw materials used in the following examples can be obtained from the market or other channels, and the various production and testing equipment used is also known in the art.

[0040] Example 1

[0041] The present embodiment provides a method for preparing high-purity sodium-ion battery phosphate positive electrode material from metallic iron, comprising the following specific steps:

[0042] (1) Put 81.2 g of metallic iron powder and 230.2 g of phosphoric acid (concentration of 85 wt%) into a beaker, add 1 L of deionized water, and react under the condition of 80℃ water bath for 8 h to form a solid-liquid mixture, which contains Fe3(PO4)2(OH)3, Fe3(PO4)2, FePO4, FeHPO4 and other iron phosphate compounds;

[0043] (2) Put the solid-liquid mixture into a sand mill, and add 27 g of oxalic acid and 30 g of glucose, and then perform sand milling treatment at a temperature of 25°C and a rotation speed of 2000 rpm. After 2 h of sand milling treatment, add 106 g of sodium carbonate, and continue sand milling for 2 h to obtain a light yellow slurry.

[0044] (3) Spray dry the light yellow slurry obtained above, with an inlet temperature of 220°C and an outlet temperature of 100°C, and set the feeding speed to 2 L of slurry per hour, to obtain a precursor material;

[0045] (4) Put the precursor material into a tube furnace for sintering, under the condition of passing a hydrogen-argon mixed gas atmosphere (hydrogen accounts for 5% by volume), first increase the temperature to 300°C at a rate of 2°C / min and maintain for 3 h, and then increase the temperature to 500°C at a rate of 2°C / min and maintain for 10 h, to obtain a product with a chemical formula of Na4Fe3(PO4)2P2O7.

[0046] Example 2

[0047] The embodiment provides a method for preparing a high-purity sodium-ion battery phosphate positive electrode material from metallic iron, comprising the following specific steps:

[0048] (1) Put 82.08 g of metallic iron powder and 230.2 g of phosphoric acid (concentration of 85 wt%) into a beaker, and add 1 L of deionized water, and fully react under the condition of a water bath at 80°C for 8 h to form a solid-liquid mixture, wherein the solid-liquid mixture contains Fe3(PO4)2(OH)3, Fe3(PO4)2, FePO4, FeHPO4 and other iron phosphate compounds;

[0049] (2) Put the obtained solid-liquid mixture into a sand mill, and add 18 g of oxalic acid and 30 g of glucose, and then perform sand milling treatment at a temperature of 20°C and a rotation speed of 1800 rpm. After 2 h, add 106 g of sodium carbonate, and continue sand milling for 2 h to obtain a light yellow slurry;

[0050] (3) Spray dry the light yellow slurry obtained above, with an inlet temperature of 250°C and an outlet temperature of about 105°C, and a feeding speed of about 2 L of slurry per hour, to obtain a precursor material;

[0051] (4) Put the precursor material into a tube furnace for sintering, under the condition of passing a hydrogen-argon mixed gas atmosphere (hydrogen accounts for 10% by volume), first increase the temperature to 190°C at a rate of 1.5°C / min and maintain for 2.5 h, and then increase the temperature to 520°C at a rate of 1.5°C / min and maintain for 8 h, to obtain a product with a chemical formula of Na4Fe 2.91 (PO4)2P2O7.

[0052] Example 3

[0053] The present embodiment provides a method for preparing high-purity sodium-ion battery phosphate positive electrode material from metallic iron, comprising the following specific steps:

[0054] (1) Put 81.2 g of metallic iron sheet, 230.2 g of phosphoric acid (concentration of 85 wt%) into a beaker, and add 1 L of deionized water, and react under the condition of 100℃ water bath for 6 h to form a solid-liquid mixture, which contains Fe3(PO4)2(OH)3, Fe3(PO4)2, FePO4, FeHPO4 and other iron phosphate compounds;

[0055] (2) Put the obtained solid-liquid mixture into a sand mill, and after adding 30 g of tartaric acid and 30 g of glucose, carry out sand milling treatment, the temperature of sand milling treatment is 30℃, the rotation speed is 2200 r / min, after sand milling treatment for 2 h, add 108.5 g of sodium carbonate, and continue sand milling for 2 h to obtain a light yellow slurry.

[0056] (3) Spray dry the light yellow slurry obtained above, the inlet temperature of spray drying is 210℃, the outlet temperature is about 100-105℃, the feeding speed is about 2 L of slurry per hour, and a precursor material is prepared;

[0057] (4) Put the precursor material into a tube furnace for sintering, under the condition of passing hydrogen-argon mixed gas (hydrogen volume ratio is 8%), first increase the temperature to 310℃ at a rate of 2.5℃ / min and keep for 3.5 h, then increase the temperature to 550℃ at a rate of 2.5℃ / min and keep for 10 h, and the obtained product has the chemical formula of Na 4.1 Fe3(PO4)2P2O7.

[0058] Example 4

[0059] (1) Put 81.2 g of iron particles with a particle size of 2.5 mm, 312.02 g of NaH2PO4·2H2O into a basket sand mill, add 1 L of deionized water, and sand mill in the basket sand mill for 8 h to react, the temperature of the grinding cabin is controlled at 50℃, and the rotation speed is controlled at 1200 r / min, to form a slurry;

[0060] (2) Put the slurry prepared above into a sand mill, and after adding 38.4 g of citric acid and 30 g of glucose, carry out sand milling treatment, the temperature of sand milling treatment is 25℃, the rotation speed is 2000 r / min, after sand milling treatment for 2 h, add 53 g of sodium carbonate, and continue sand milling for 2 h to obtain a light yellow slurry;

[0061] (3) The light yellow slurry obtained above is subjected to spray drying, the spray drying inlet temperature is 220 ℃, the outlet temperature is about 100 ℃, and the feeding speed is about 2 L of slurry per hour, thereby obtaining a precursor material;

[0062] (4) The precursor material is placed in a tube furnace for sintering, under the condition of passing in a hydrogen-argon mixed atmosphere (hydrogen accounts for 5% by volume), the temperature is first increased to 300 ℃ at a rate of 2 ℃ / min and kept for 3 h, and then the temperature is increased to 500 ℃ at a rate of 2 ℃ / min and kept for 10 h, thereby obtaining an iron-based phosphate positive electrode material.

[0063] Example 5

[0064] Example 5 is different from Example 1 only in that a pure argon atmosphere is used in the sintering process of step (4), and the rest is the same as Example 1, which is not described here.

[0065] Comparative Example 1

[0066] Comparative Example 1 uses a traditional method to prepare a positive electrode material, and the specific steps are as follows:

[0067] (1) 209.5 g of ferrous oxalate is reacted with 230.2 g of phosphoric acid solution (concentration of 85 wt%) to obtain Fe(H2PO4)2, and then Fe(H2PO4)2 is reacted with 300 ml of hydrogen peroxide solution (concentration of 30 wt%) to obtain iron phosphate dihydrate precursor, which is dehydrated to obtain anhydrous iron phosphate. The anhydrous iron phosphate, 30 g of glucose, 27 g of oxalic acid and 1000 ml of deionized water are added to a sand mill for sand milling treatment, the temperature of the sand milling treatment is 30 ℃, the rotation speed is 2200 rpm, and after 2 h of sand milling treatment, 106 g of sodium carbonate is added and the sand milling treatment is continued for 2 h to obtain a light yellow slurry;

[0068] (3) The light yellow slurry obtained above is subjected to spray drying, the spray drying inlet temperature is 220 ℃, the outlet temperature is about 100 ℃, and the feeding speed is about 2 L of slurry per hour, thereby obtaining a precursor material;

[0069] (4) The precursor material is placed in a tube furnace for sintering, under the condition of passing in a hydrogen-argon mixed atmosphere (hydrogen accounts for 5% by volume), the temperature is first increased to 300 ℃ at a rate of 2 ℃ / min and kept for 3 h, and then the temperature is increased to 500 ℃ at a rate of 2 ℃ / min and kept for 10 h, thereby obtaining an iron-based phosphate positive electrode material. 4.1 Fe3(PO4)2P2O7. The product is ground into a uniform slurry, and then dried and sintered to obtain a finished product.

[0070] The phosphate positive electrode material prepared in the above examples and comparative examples is used as a raw material to prepare a positive electrode for a sodium ion battery, and the specific steps are as follows:

[0071] The positive electrode prepared above was used to assemble a sodium ion battery, with Na foil as the negative electrode, NaClO4 dissolved in DC / EC / EMC+2% FEC (DoDo Chem, Shanghai, China) as the electrolyte, and a glass fiber membrane (GF / A What-man) as the separator. The relevant performance of the obtained sodium ion battery positive electrode was detected, and the test structure is shown in Table 1.

[0072] Figure 1 is the charge-discharge curve of the positive electrode material prepared in Example 1. Figure 2 is the charge-discharge curve of the positive electrode material prepared in Example 2. Figure 3 is the charge-discharge curve of the positive electrode material prepared in Example 3. Figure 4a 、 Figure 4b is the SEM image of the positive electrode material prepared in Example 2 of the present application. Figure 5 is the XRD image of the positive electrode material prepared in Examples 1 and 2 of the present application.

[0073] Table 1 Relevant performance of sodium ion battery

[0074] Group Charge specific capacity Discharge specific capacity Initial efficiency Example 1 115.1 mAh / g 99.4 mAh / g 86.3％ Example 2 117.1 mAh / g 102.4 mAh / g 87.4％ Example 3 115.2 mAh / g 98.2 mAh / g 85.2％ Example 4 114.8 mAh / g 98.7 mAh / g 85.9％ Example 5 114.8 mAh / g 98.7 mAh / g 85.9％ Comparative Example 1 113.2 mAh / g 98.2 mAh / g 86.7％

[0075] The method provided by the present application uses metallic iron, and does not need to add oxidants, catalysts and the like during the reaction process, which is helpful to improve the production capacity and effectively reduce the introduction of impurities. The prepared sodium ion battery iron-based phosphate positive electrode material has high purity and excellent performance in terms of charge-discharge performance such as capacity performance, rate performance and cycle life. The method uses the resource-rich metallic iron as the iron source, avoids using expensive raw materials such as organic salt compounds, and has high resource utilization rate. The method can directly prepare the positive electrode material from the metallic iron without using iron phosphate and the like as the precursor, and has short process flow, low process cost, and the prepared positive electrode material has performance comparable to that of Comparative Example 1. No wastewater, waste residue and harmful gas is generated during the preparation process, which meets the requirements of green and sustainable development.

[0076] Aspects, embodiments, features, and examples of the present application are to be considered in all respects as illustrative only and not restrictive, and the scope of the present application is defined only by the claims. Other embodiments, modifications, and uses will be apparent to those skilled in the art without departing from the spirit and scope of the claimed application.

[0077] In addition, the present inventors have also carried out tests with other raw materials, process operations and process conditions described in the present specification with reference to the foregoing examples, and all have obtained relatively ideal results.

[0078] While the application has been described with reference to the illustrative embodiments, those skilled in the art will understand that various other changes, omissions, and / or additions can be made without departing from the spirit and scope of the application. Further, many modifications can be made to adapt a particular situation or material to the teachings of the application without departing from its scope. Therefore, it is intended that the application not be limited to the disclosed embodiments, but will include all embodiments falling within the scope of the appended claims. Moreover, unless specifically stated otherwise, any use of the terms first, second, etc., does not denote any ordinal, or importance, but merely distinguishes one element from another.

Claims

1. A method for producing an iron-based phosphate positive electrode material, characterized by, The method comprises the following steps: reacting a mixture containing metallic iron and phosphoric acid at room temperature to 100 DEG C for 6-12 hours, wherein the molar ratio of the metallic iron to the phosphoric acid is 1-1.75:2-2.25, to form a solid-liquid mixture containing a ferric phosphate compound; mixing the solid-liquid mixture with an acid regulator, a carbon source and a sodium source, and then performing sand milling to obtain a slurry; performing drying treatment on the slurry to obtain a precursor material; performing sintering on the precursor material under a protective atmosphere to obtain an iron-based phosphate cathode material.

2. The method of claim 1, wherein: The metallic iron comprises one or a combination of iron blocks, iron sheets and iron powder.

3. The method of claim 1, wherein: The acid regulator comprises one or a combination of oxalic acid, tartaric acid and citric acid.

4. The method of claim 1, wherein: The carbon source comprises glucose.

5. The method of claim 1, wherein: The molar ratio of the acid regulator to the iron element is 1:5-1:7.

5.

6. The method of claim 1, wherein: According to the chemical formula Na 3-4.5 Fe 2-3.5 (PO4) 2-2.5 P2O7 to the solid-liquid mixture.

7. The method of claim 1, wherein: The amount of the carbon source added satisfies the molar ratio of 1:10-1:

15.

8. The method of claim 1, wherein, The method specifically comprises the following steps: The sand milling is performed after the solid-liquid mixture is mixed with the acid regulator, the carbon source, the sodium source and polyethylene glycol, and the amount of the polyethylene glycol added is 1 / 400-1 / 600 of the total mass of the slurry.

9. The method of claim 1, wherein, The sand milling is performed at a temperature of 20-30 DEG C, and the sand milling time is 2-4 hours, so that the particle size in the slurry is 500-600 nm. The drying is spray drying, and the inlet temperature of the spray drying is 210-250 DEG C, and the outlet temperature is 100-105 DEG C.

10. The method of claim 1, wherein, The protective atmosphere is at least one of argon and nitrogen; or the protective atmosphere is argon-hydrogen mixed gas or nitrogen-hydrogen mixed gas, and the volume ratio of hydrogen in the argon-hydrogen mixed gas or the nitrogen-hydrogen mixed gas is 5%-10%.

11. The method of claim 1, wherein: The sintering specifically comprises the following steps: first increasing the temperature to 290-310 DEG C at a rate of 1.5-2.5 DEG C / min and maintaining the temperature for 2.5-3.5 hours, and then increasing the temperature to 500-550 DEG C at a rate of 1.5-2.5 DEG C / min and maintaining the temperature for 8-10 hours.

12. The method of claim 1, wherein, The iron-based phosphate cathode material is prepared by the method in any one of claims 1-12.

13. An iron-based phosphate positive electrode material, characterized by: The sodium ion battery cathode comprises a current collector and a cathode active material layer formed on the current collector, and the cathode active material layer comprises the iron-based phosphate cathode material in claim 13.

14. A sodium-ion battery cathode, characterized in that: The cathode is the sodium ion battery cathode in claim 14.

15. A sodium-ion battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, ​

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