A sodium-rich sodium-iron-phosphate positive electrode material, a preparation method and application thereof

Abstract

The application discloses a sodium-rich sodium iron phosphate positive electrode material, and has a general chemical formula of Na 4+x Fe 3+x (PO4) 2+x (P2O7), and 0 < x < 1. The application further discloses a preparation method of the sodium iron phosphate positive electrode material, which comprises the following steps: taking a carbon source, an iron source, a sodium source and a phosphorus source according to the general chemical formula, and uniformly dispersing the four sources in deionized water to obtain a dispersion liquid, wherein the molar ratio of sodium in the sodium source, iron in the iron source and phosphorus in the phosphorus source satisfies Na:Fe:P=(4+x):(3+x):(4+x), and 0 < x < 1; after the dispersion liquid is stirred and dispersed, wet sand milling is performed at a rotating speed of 300-1000 rpm to obtain a slurry with a particle size of 0.2-2 microns; the slurry is subjected to spray granulation, and the particle size is controlled to be 3-15 microns to obtain a sprayed powder; and the sprayed powder is sintered in an inert atmosphere to obtain the sodium iron phosphate positive electrode material. 4+x Fe 3+x (PO4) 2+x (P2O7) positive electrode material can improve the initial charge specific capacity of Na4Fe3(PO4)2(P2O7), and can compensate for the irreversible capacity loss of the negative electrode material. Compared with the prior art Na4Fe3(PO4)2(P2O7) positive electrode material, the energy density of the full battery can be improved.

Description

Technical Field

[0001] This invention relates to the field of sodium battery technology, and in particular to a sodium-rich sodium iron phosphate (NFPP) cathode material, its preparation method, and its application. Background Technology

[0002] In recent years, lithium-ion batteries have developed rapidly and have been widely used in various industries. However, the ever-increasing demand and the scarcity of lithium resources directly restrict the development of lithium-ion batteries. Sodium atoms have similar atomic structures and chemical properties to lithium atoms, and the global reserves of sodium are extremely abundant. Sodium-ion batteries also have high specific energy and low production costs. Therefore, as the widespread application of lithium-ion batteries is limited by lithium resources and production costs, sodium-ion batteries with similar electrochemical properties have become the focus of researchers' attention.

[0003] Na4Fe3(PO4)2(P2O7) cathode material is low-cost and abundant, perfectly aligning with the initial goals of sodium-ion battery development. However, Na4Fe3(PO4)2(P2O7) cathode material has a low specific capacity, especially a small initial charge capacity. After compensating for the capacity loss at the anode, the energy density of sodium-ion batteries further decreases. To compensate for the irreversible loss of sodium in the anode material of sodium-ion batteries, researchers typically employ methods such as pre-intercalating sodium into the anode material or adding sodium-replenishing agents to the cathode material. However, these methods are cumbersome, costly, and difficult to scale up. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a sodium-rich iron sodium phosphate cathode material with a simple preparation process and high charging capacity for sodium-ion batteries, as well as its preparation method and application.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] A sodium-iron sodium phosphate cathode material rich in sodium, wherein the general chemical formula of the sodium-iron sodium phosphate cathode material is Na. 4+x Fe 3+x (PO4) 2+x (P2O7), 0 <x≤1。

[0007] The sodium iron phosphate cathode material has a particle size of 2–10 μm and a specific surface area of ​​3–15 m². 2 / g, tap density is 0.9~1.5g / cm³ 3 .

[0008] As a general inventive concept, the present invention also provides a method for preparing sodium iron phosphate cathode material, comprising the following steps:

[0009] S1, according to the general chemical formula, weigh out the carbon source, iron source, sodium source, and phosphorus source, and disperse them evenly in deionized water to obtain a dispersion, wherein the molar ratio of sodium in the sodium source, iron in the iron source, and phosphorus in the phosphorus source satisfies Na:Fe:P=(4+x):(3+x):(4+x), 0 <x≤1;

[0010] S2, after stirring and dispersing the dispersion, wet mill it at a speed of 300-1000 rpm until the particle size is between 0.2-2 μm to obtain a slurry;

[0011] S3, spray granulation of the slurry, with the particle size controlled between 3 and 15 μm, to obtain the sprayed powder;

[0012] S4. The sprayed powder is sintered under an inert atmosphere to obtain sodium iron phosphate cathode material.

[0013] As a further improvement to the above technical solution:

[0014] In step S4, the sintering temperature is 400–600°C, and the sintering time is 2–10 hours.

[0015] In step S4, the sintering atmosphere includes one of argon, nitrogen, an argon-hydrogen mixture, and a nitrogen-hydrogen mixture. In step S1, the sodium source includes one or more of inorganic sodium salts and organic sodium salts.

[0016] The inorganic sodium salt includes at least one of trisodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium pyrophosphate, trisodium monohydrogen pyrophosphate, disodium dihydrogen pyrophosphate, monosodium trihydrogen pyrophosphate, sodium carbonate, and sodium bicarbonate.

[0017] The organic sodium salt includes at least one of sodium acetate, sodium oxalate, and sodium citrate.

[0018] In step S1, the phosphorus source includes one or more of phosphoric acid, phosphate, and pyrophosphate.

[0019] The phosphate includes at least one of sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

[0020] The pyrophosphate includes at least one of sodium pyrophosphate, trisodium pyrophosphate, disodium dihydrogen pyrophosphate, and monosodium trihydrogen pyrophosphate.

[0021] In step S1, the carbon source includes one or more of graphite, activated carbon, carbon nanotubes, graphene, glucose, and sucrose.

[0022] In step S1, the dispersion specifically involves sand milling for 0.5 to 3 hours.

[0023] In step S1, the iron source is one or more of ferrous oxalate or ferric phosphate, and the particle size of the iron source is 0.5 to 7 μm.

[0024] In step S2, the grinding method includes one of disc type, pin type, and turbine type.

[0025] In step S2, the grinding medium includes one or more of the following: natural sand, glass beads, steel beads, zirconium oxide beads, zirconium silicate beads, and agate beads.

[0026] In step S2, the grinding time is 0.5 to 3 hours.

[0027] As a general inventive concept, the present invention also provides the application of the aforementioned sodium-rich sodium iron phosphate cathode material or the sodium iron phosphate cathode material prepared by the aforementioned preparation method in sodium-ion batteries.

[0028] The application includes the following steps: using the sodium iron phosphate cathode material as the cathode, assembling it with a negative electrode, a separator, and an electrolyte to form a sodium-ion battery.

[0029] Compared with the prior art, the advantages of the present invention are as follows:

[0030] This invention discloses a sodium-rich sodium iron phosphate cathode material with the general chemical formula Na. 4+x Fe 3+x (PO4) 2+x (P2O7), satisfying 0 <x≤1,Na 4+x Fe 3+x (PO4) 2+x The sodium iron phosphate (P2O7) cathode material can improve the initial charge specific capacity of Na4Fe3(PO4)2(P2O7), ensuring a high initial charge specific capacity and compensating for the irreversible loss of sodium on the negative electrode side during the first charge and discharge of sodium-ion batteries. Compared with existing Na4Fe3(PO4)2(P2O7) cathode materials, it can improve the energy density of the entire battery. The particle size of the sodium iron phosphate cathode material is 2-10 μm, and the specific surface area is 3-15 m². 2 / g, tap density is 0.9~1.5g / cm³ 3 .

[0031] The present invention discloses a method for preparing sodium-rich iron sodium phosphate cathode material, which uses inexpensive and readily available raw materials, and the preparation method is simple, pollution-free, and can be mass-produced. Attached Figure Description

[0032] Figure 1 This is a scanning electron microscope image of the cathode material Na5Fe4(PO4)3(P2O7) prepared in Example 1.

[0033] Figure 2 This is the XRD pattern of the cathode material Na5Fe4(PO4)3(P2O7) prepared in Example 1.

[0034] Figure 3 The image shows the 0.2C charge-discharge curve of the cathode material Na5Fe4(PO4)3(P2O7) prepared in Example 1.

[0035] Figure 4 The 0.2C charge-discharge curves of the cathode material Na4Fe3(PO4)2(P2O7) prepared in Comparative Example 1 are shown. Detailed Implementation

[0036] The present invention will be further described in detail below. Unless otherwise specified, the instruments or materials used in the present invention are commercially available.

[0037] Example 1

[0038] The sodium-rich iron phosphate cathode material of this embodiment has the chemical formula Na5Fe4(PO4)3(P2O7). The particle size of the sodium iron phosphate cathode material is 6.7 μm, and the specific surface area is 11.5 m². 2 / g, tap density is 1.2g / cm³ 3 .

[0039] The preparation method of the positive electrode active material in this embodiment specifically includes the following steps:

[0040] S1. Weigh out 4 mol of ferric phosphate (FePO4, iron and phosphorus source), 4 mol of sodium acetate (CH3COONa, sodium and carbon source), 1 mol of sodium dihydrogen phosphate (NaH2PO4, sodium and phosphorus source), and 0.5 mol of sucrose (carbon source) according to the stoichiometric ratio, wherein the molar ratio of Na:Fe:P is 5:4:5, and disperse them evenly in deionized water; the particle size distribution range of the FePO4 is 0.5-7 μm.

[0041] S2, after dispersing the above dispersion in a vertical mixer for 1 hour, transfer it to a sand mill and wet-mill it at 800 rpm for 2 hours, with the particle size distribution range controlled between 0.2 and 2 μm;

[0042] S3, the slurry after sand milling is spray granulated, and the particle size distribution range is controlled within 3 to 15 μm;

[0043] S4. The sprayed powder was sintered under an inert atmosphere at a temperature of 500℃ for 5 hours to obtain sodium-rich Na5Fe4(PO4)3(P2O7) powder.

[0044] Figure 1The image shows a scanning electron microscope image of the positive electrode active material Na5Fe4(PO4)3(P2O7) prepared in this embodiment. It can be seen that the powder has a spherical morphology and the particle size of the product is controllable.

[0045] Figure 2 The image shows the XRD pattern of the positive electrode active material Na5Fe4(PO4)3(P2O7) prepared in this embodiment. The * indicates that an additional diffraction peak appears at the position marked, indicating that excess NaFePO4 has been successfully doped into the final product.

[0046] A sodium-ion battery is assembled using the sodium-rich iron sodium phosphate cathode material as the cathode, along with a negative electrode, a separator, and an electrolyte. Figure 3 It can be seen that the coin cell assembled with the material prepared in this embodiment as the positive electrode material has an initial charge capacity of 118 mAh / g at 0.2C and a discharge capacity of 102 mAh / g.

[0047] Example 2

[0048] This embodiment describes a sodium-rich sodium iron phosphate cathode material with the chemical formula Na. 4.5 Fe 3.5 (PO4) 2.5 (P2O7). The sodium iron phosphate cathode material has a particle size of 2.1 μm and a specific surface area of ​​14.9 m². 2 / g, tap density is 0.95g / cm³ 3 .

[0049] The preparation method of the positive electrode active material in this embodiment specifically includes the following steps:

[0050] S1. Weigh out the raw materials according to the stoichiometric ratio: 3.5 mol ferrous oxalate (FeC2O4, iron source), 1.5 mol sodium dihydrogen phosphate (NaH2PO4, sodium and phosphorus source), 3 mol ammonium dihydrogen phosphate (NH4H2PO4, phosphorus source), 1 mol sodium citrate (C6H5Na3O7, sodium and carbon source), and 0.5 mol glucose (carbon source), wherein the molar ratio of Na:Fe:P is 4.5:3.5:4.5, and disperse them evenly in deionized water; the particle size distribution range of the ferrous oxalate is 0.5–7 μm.

[0051] S2, after dispersing the above dispersion in a vertical mixer for 1 hour, transfer it to a sand mill and wet-mill it at 300 rpm for 3 hours, with the particle size distribution range controlled between 0.2 and 2 μm;

[0052] S3, the slurry after sand milling is spray granulated, and the particle size distribution range is controlled within 3 to 15 μm;

[0053] S4. The sprayed powder is sintered under an inert atmosphere at a temperature of 600°C for 2 hours to obtain the sodium-rich Na. 4.5 Fe 3.5 (PO4) 2.5 (P2O7) powder.

[0054] The coin cell assembled using the material prepared in this embodiment as the positive electrode material has an initial charge capacity of 111 mAh / g at 0.2C and a discharge capacity of 99 mAh / g.

[0055] Example 3

[0056] This embodiment describes a sodium-rich sodium iron phosphate cathode material with the chemical formula Na. 4.1 Fe 3.1 (PO4) 2.1 (P2O7). The sodium iron phosphate cathode material has a particle size of 9.8 μm and a specific surface area of ​​3.5 m². 2 / g, tap density is 1.48g / cm³ 3 .

[0057] The preparation method of the positive electrode active material in this embodiment specifically includes the following steps:

[0058] S1, according to the stoichiometric ratio, weigh 3.1 mol FePO4 (iron source and phosphorus source), 1.05 mol sodium oxalate (Na2C2O4, sodium source and carbon source), 1 mol disodium hydrogen phosphate (Na2HPO4, sodium source and phosphorus source), and 0.5 mol glucose (carbon source), wherein the Na:Fe:P molar ratio is 4.1:3.1:4.1, and disperse them evenly in deionized water; the particle size distribution range of the FePO4 is 0.5-7 μm;

[0059] S2, after dispersing the above dispersion in a vertical mixer for 1 hour, transfer it to a sand mill and wet-mill it at 500 rpm for 2 hours, with the particle size distribution range controlled between 0.2 and 2 μm;

[0060] S3, the slurry after sand milling is spray granulated, and the particle size distribution range is controlled within 3 to 15 μm;

[0061] S4. The sprayed powder is sintered under an inert atmosphere at a temperature of 550°C for 5 hours to obtain the sodium-rich Na. 4.1 Fe 3.1 (PO4) 2.1 (P2O7) powder.

[0062] The coin cell assembled using the material prepared in this embodiment as the positive electrode material has an initial charge capacity of 105 mAh / g at 0.2C and a discharge capacity of 100 mAh / g.

[0063] Example 4

[0064] This embodiment describes a sodium-rich sodium iron phosphate cathode material with the chemical formula Na. 4.5 Fe 3.5 (PO4) 2.5 (P2O7). The sodium iron phosphate cathode material has a particle size of 5.9 μm and a specific surface area of ​​10.5 m². 2 / g, tap density is 1.1g / cm³ 3 .

[0065] The preparation method of the positive electrode active material in this embodiment specifically includes the following steps:

[0066] S1. Weigh out 3.5 mol FePO4 (iron and phosphorus source), 2.5 mol sodium acetate (CH3COONa, sodium and carbon source), 1 mol disodium hydrogen phosphate (Na2HPO4, sodium and phosphorus source), and 0.5 mol glucose (carbon source) according to stoichiometric ratio, wherein the Na:Fe:P molar ratio is 4.5:3.5:4.5, and disperse them evenly in deionized water; the particle size distribution range of the FePO4 is 0.5–7 μm.

[0067] S2, after dispersing the above dispersion in a vertical mixer for 1 hour, transfer it to a sand mill and wet-mill it at 1000 rpm for 0.5 hours, with the particle size distribution range controlled between 0.2 and 2 μm.

[0068] S3, the slurry after sand milling is spray granulated, and the particle size distribution range is controlled within 3 to 15 μm;

[0069] S4, the sprayed powder is sintered under an inert atmosphere at a temperature of 400°C for 10 hours to obtain the sodium-rich Na. 4.5 Fe 3.5 (PO4) 2.5 (P2O7) powder.

[0070] The coin cell assembled using the material prepared in this embodiment as the positive electrode material has an initial charge capacity of 112 mAh / g at 0.2C and a discharge capacity of 98.8 mAh / g.

[0071] Example 5

[0072] This embodiment describes a sodium-rich sodium iron phosphate cathode material with the chemical formula Na. 4.3 Fe 3.3 (PO4) 2.3 (P2O7). The sodium iron phosphate cathode material has a particle size of 7.8 μm and a specific surface area of ​​8.5 m². 2 / g, tap density is 1.25g / cm³ 3 .

[0073] The preparation method of the positive electrode active material in this embodiment specifically includes the following steps:

[0074] S1, according to the stoichiometric ratio, weigh out 3.3 mol ferrous oxalate (FeC2O4, iron source), 1 mol sodium acetate (CH3COONa, sodium and carbon source), 1.1 mol sodium phosphate (Na3PO4, sodium and phosphorus source), 3.2 mol ammonium dihydrogen phosphate (NH4H2PO4, phosphorus source), 0.5 mol sucrose (carbon source), and 1 wt% carbon nanotubes (carbon source, here is the mass fraction of carbon nanotubes in all raw materials), wherein the molar ratio of Na:Fe:P = 4.3:3.3:4.3, and disperse them evenly in deionized water;

[0075] S2, the particle size distribution range of the ferrous oxalate is 0.5–7 μm; after dispersing the above dispersion in a vertical mixer for 1 hour, it is transferred to a sand mill and wet-milled at 500 rpm for 1 hour, and the particle size distribution range is controlled between 0.2 and 2 μm.

[0076] S3, the slurry after sand milling is spray granulated, and the particle size distribution range is controlled within 3 to 15 μm;

[0077] S4. The sprayed powder is sintered under an inert atmosphere at a temperature of 500°C for 6 hours to obtain the sodium-rich Na. 4.3 Fe 3.3 (PO4) 2.3 (P2O7) powder.

[0078] The coin cell assembled using the material prepared in this embodiment as the positive electrode material has an initial charge capacity of 108.7 mAh / g at 0.2C and a discharge capacity of 99.5 mAh / g.

[0079] Comparative Example 1

[0080] The positive electrode active material in this comparative example is largely the same as that in Example 4, except that its chemical formula is Na4Fe3(PO4)2(P2O7).

[0081] The preparation method of the comparative positive electrode active material is largely the same as that of Example 4, and specifically includes the following steps:

[0082] S1. Weigh out 3 mol FePO4 (iron source and phosphorus source), 2 mol sodium acetate (CH3COONa, sodium source and carbon source), 1 mol disodium hydrogen phosphate (Na2HPO4, sodium source and phosphorus source), and 0.5 mol glucose (carbon source) according to the stoichiometric ratio, wherein the Na:Fe:P molar ratio is 4:3:4, and disperse them evenly in deionized water; the particle size distribution range of the FePO4 is 0.5-7 μm;

[0083] S2, after dispersing the above dispersion in a vertical mixer for 1 hour, transfer it to a sand mill and wet-mill it at 500 rpm for 1 hour, with the particle size distribution range controlled between 0.2 and 2 μm;

[0084] S3, the slurry after sand milling is spray granulated, and the particle size distribution range is controlled within 3 to 15 μm;

[0085] S4. The sprayed powder was sintered under an inert atmosphere at 500℃ for 6 hours to obtain Na4Fe3(PO4)2(P2O7) powder. The material prepared in this comparative example, used as the positive electrode material, resulted in a coin cell with an initial charge capacity of 101 mAh / g and a discharge capacity of 99 mAh / g at 0.2C. Figure 4 As shown, compared to Example 4, the initial charge capacity of this comparative example is lower, indicating that the initial charge capacity of the conventional sodium iron phosphate cathode material Na4Fe3(PO4)2(P2O7) is less than that of the sodium-rich sodium iron phosphate cathode material.

[0086] Comparative Example 2

[0087] The comparative example of the positive electrode active material has the chemical formula Na. 4.5 Fe 3.5 (PO4) 2.5 (P2O7).

[0088] The preparation method of the comparative positive electrode active material is largely the same as that of Example 4, and specifically includes the following steps:

[0089] S1. Weigh out 3.5 mol FePO4, 1.25 mol sodium carbonate (Na2CO3), 1 mol disodium hydrogen phosphate (Na2HPO4), and 0.5 mol glucose according to the stoichiometric ratio, wherein the molar ratio of Na:Fe:P is 4.5:3.5:4.5, and disperse them evenly in deionized water; the particle size distribution range of the FePO4 is 0.5-7 μm.

[0090] S2, after dispersing the above dispersion in a vertical mixer for 1 hour, transfer it to a sand mill and wet-mill it at 500 rpm for 1 hour, with the particle size distribution range controlled between 0.2 and 2 μm;

[0091] S3, the slurry after sand milling is spray granulated, and the particle size distribution range is controlled within 3 to 15 μm;

[0092] S4. The sprayed powder was sintered under an inert atmosphere at a temperature of 650℃ for 5 hours to obtain Na. 4.5 Fe 3.5 (PO4) 2.5 (P2O7) powder.

[0093] The material prepared in this comparative example, used as the positive electrode material, resulted in a coin cell with an initial charge capacity of 90.3 mAh / g at 0.2C and a discharge capacity of 88 mAh / g. This comparative example used the same sodium-iron molar ratio as Example 4, but sintered at a high temperature of 650°C. The resulting material, when assembled into a battery, did not achieve a higher charge capacity; its performance was significantly lower than that of Example 4. This indicates that excess sodium was not successfully incorporated into the sodium iron phosphate powder at this sintering temperature. When the sodium-iron molar ratio exceeds the range specified in this application (x > 1), excess sodium cannot be successfully incorporated into the sodium iron phosphate using the preparation method of this invention. In other words, sodium-rich sodium iron phosphate positive electrode material cannot be obtained simply by increasing the sodium content in the raw materials during preparation; increasing the sodium content also presents the technical problem of sodium not being successfully incorporated into the sodium iron phosphate.

[0094] Comparative Example 3

[0095] The comparative example of the positive electrode active material has the chemical formula Na4Fe3(PO4)2(P2O7).

[0096] The preparation method of the positive electrode active material in this comparative example is roughly the same as that in Comparative Example 1, and specifically includes the following steps:

[0097] S1, weigh out 3 mol FePO4, 1 mol sodium carbonate (Na2CO3), 1 mol disodium hydrogen phosphate (Na2HPO4), and 0.5 mol glucose according to the stoichiometric ratio, wherein the molar ratio of Na:Fe:P is 4:3:4, and disperse them evenly in deionized water; the particle size distribution range of the FePO4 is 0.5-7 μm;

[0098] S2, the slurry after dispersing the above dispersion in a vertical mixer for 1 hour is spray-granulated, and the particle size distribution range is controlled within 3 to 15 μm;

[0099] S3, the sprayed powder is sintered under an inert atmosphere at a temperature of 500℃ for 5 hours to obtain Na4Fe3(PO4)2(P2O7) powder.

[0100] The material prepared in this comparative example, used as the positive electrode material, resulted in a coin cell with an initial charge capacity of 95 mAh / g and a discharge capacity of 86 mAh / g at 0.2C. Compared to the preparation method using raw materials with the same sodium-iron molar ratio, this comparative example only employed stirring and dispersion before spray drying, without wet milling. The initial charge capacity of the final product was inferior to that of Comparative Example 1, indicating that wet ball milling can improve the initial charge capacity.

[0101] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, without departing from the scope of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the scope of the present invention, should fall within the protection scope of the present invention.

Claims

1. A sodium-rich sodium iron phosphate cathode material, characterized in that: The general chemical formula of the sodium iron phosphate cathode material is Na5Fe4(PO4)3(P2O7). The sodium iron phosphate cathode material is spherical with a controllable particle size; the particle size is 6.7 μm, and the specific surface area is 11.5 m². 2 / g, tap density is 1.2g / cm³ 3 ; The preparation method of the positive electrode active material specifically includes the following steps: S1, according to the stoichiometric ratio, weigh 4 mol of iron phosphate, 4 mol of sodium acetate, 1 mol of sodium dihydrogen phosphate, and 0.5 mol of sucrose, wherein the molar ratio of Na:Fe:P is 5:4:5, and disperse them evenly in deionized water; the particle size distribution range of the FePO4 is 0.5-7 μm; S2, after dispersing the above dispersion in a vertical mixer for 1 hour, transfer it to a sand mill and wet-mill it at 800 rpm for 2 hours, with the particle size distribution range controlled between 0.2 and 2 μm; S3, the slurry after sand milling is spray granulated, and the particle size distribution range is controlled within 3 to 15 μm; S4, the sprayed powder was sintered in an inert atmosphere at a temperature of 500℃ for 5 hours to obtain sodium-rich Na5Fe4(PO4)3(P2O7) powder.

2. A method for preparing the sodium iron phosphate cathode material according to claim 1, characterized in that: Includes the following steps: S1. Weigh carbon source, iron source, sodium source and phosphorus source according to the general chemical formula, and disperse them evenly in deionized water to obtain a dispersion, wherein the molar ratio of sodium in sodium source, iron in iron source and phosphorus in phosphorus source satisfies Na:Fe:P=5:4:

5. S2, after stirring and dispersing the dispersion, wet mill it at 800 rpm until the particle size is between 0.2 and 2 μm to obtain a slurry; S3, spray granulation of the slurry, with the particle size controlled between 3 and 15 μm, to obtain the sprayed powder; S4. The sprayed powder is sintered under an inert atmosphere to obtain sodium iron phosphate cathode material.

3. The preparation method according to claim 2, characterized in that: In step S4, the sintering temperature is 500°C and the sintering time is 5 hours.

4. The preparation method according to claim 2, characterized in that: In step S4, the sintering atmosphere includes one of argon, nitrogen, an argon-hydrogen mixture, or a nitrogen-hydrogen mixture.

5. The preparation method according to claim 2, characterized in that: In step S1, the sodium source is sodium acetate and sodium dihydrogen phosphate.

6. The preparation method according to claim 2, characterized in that: In step S1, the phosphorus source is iron phosphate and sodium dihydrogen phosphate.

7. The preparation method according to claim 2, characterized in that: In step S1, the carbon source is sodium acetate and sucrose.

8. The application of a sodium-rich sodium iron phosphate cathode material according to claim 1 or a sodium iron phosphate cathode material prepared by any one of claims 2 to 7 in a sodium-ion battery.

9. The application according to claim 8, characterized in that: Using the sodium iron phosphate cathode material as the cathode, a sodium-ion battery is assembled with a negative electrode, a separator, and an electrolyte.

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