WO2023174152A1 - Preparation method for positive electrode material, positive electrode material, positive electrode sheet, and sodium-ion battery - Google Patents

Abstract

The present disclosure relates to the technical field of batteries, and in particular, to a preparation method for a positive electrode material, a positive electrode material, a positive electrode sheet, and a sodium-ion battery. The preparation method for a positive electrode material comprises the following steps: carrying out ball-milling treatment on a first mixture of iron phosphate, a phosphorus source, a sodium source, an organic carbon source, and water to obtain a first mixed system; sequentially carrying out ball-milling treatment and sanding treatment on a second mixture of the first mixed system and a carbon material to obtain a second mixed system; and drying and calcining the second mixed system. According to the present disclosure, two carbon sources having completely different attributes are introduced during the preparation process of a Na4Fe3(PO4)2P2O7 positive electrode material, and interface layers having different functions are constructed by using the difference between distribution intervals during a high-temperature calcination process, thereby improving the overall electrochemical performance of the material.

Description

Preparation method of positive electrode material, positive electrode material, positive electrode sheet and sodium ion battery

Cross-references to related applications

This disclosure requires the priority of the Chinese patent application with application number CN202210248265.8 and titled "Preparation method of cathode material, cathode material, cathode sheet and sodium ion battery" submitted to the China Patent Office on March 14, 2022, which The entire contents are incorporated by reference into this disclosure.

Technical field

The present disclosure relates to the field of battery technology, and specifically to a preparation method of a positive electrode material, a positive electrode material, a positive electrode sheet and a sodium ion battery.

Background technique

Secondary batteries have become an ideal choice for large-scale energy storage technology due to their comprehensive advantages such as mature technology, high flexibility, and high energy conversion rate. Secondary batteries include nickel metal hydride batteries, nickel cadmium batteries, lead-acid batteries, alkaline zinc-manganese batteries, lithium-ion batteries, sodium-ion batteries and potassium-ion batteries and other related categories. However, in terms of technology maturity, total system cost, energy/ In terms of power density and environmental adaptability, lithium/sodium-ion batteries are undoubtedly the best among them. Although lithium-ion batteries dominate the current 3C product market and the electric vehicle field, the scarcity and uneven distribution of lithium resources will inevitably fail to meet the needs of the growing electric vehicle field, let alone the cheap requirements of large-scale energy storage. . The working principle of sodium-ion batteries is similar to that of lithium-ion batteries, and sodium resources are more abundant, more widely distributed, and the cost of related electrode materials is cheaper. They are currently the focus of large-scale energy storage.

There are many kinds of sodium ion cathode materials, including oxides, Prussian blue and polyanions. However, in terms of the abundance of resources, the overall cost of materials, the electrochemical properties of materials and environmental sustainability, polyanions are Type sodium ion battery cathode material is undoubtedly the best choice. The iron-based composite sodium phosphate cathode material Na ₄ Fe ₃ (PO ₄ ) ₂ P ₂ O ₇ has a suitable theoretical capacity (129mAh g ^-1 ), a moderate voltage platform (3.1V), a stable framework structure, and excellent Electrochemical properties. However, its poor electronic conductivity severely limits its performance.

Contents of the invention

An object of the present disclosure is to provide a method for preparing a cathode material to solve the technical problem in the prior art that the poor electronic conductivity of the cathode material severely restricts its performance. This disclosure introduces in the material preparation process Two carbon sources with completely different properties are introduced, and the differences in their distribution intervals during high-temperature calcination are used to construct interface layers with different functions, thereby improving the overall electrochemical performance of the material.

Another object of the present disclosure is to provide a cathode material prepared by the method for preparing the cathode material.

Another object of the present disclosure is to provide a cathode sheet including the cathode material.

Another object of the present disclosure is to provide a sodium ion battery including the positive electrode sheet.

In order to achieve the above objects of the present disclosure, the following technical solutions are adopted:

The present disclosure provides a method for preparing a cathode material, which includes the following steps:

The first mixture of iron phosphate, phosphorus source, sodium source, organic carbon source and water is ball milled to obtain a first mixed system; the first mixed system and the second mixture of carbon materials are ball milled and sand milled in sequence Process to obtain a second mixed system; the second mixed system is dried and calcined.

Optionally, the organic carbon source includes at least one of citric acid, glucose and sucrose.

Optionally, the phosphorus source includes at least one of sodium dihydrogen phosphate, sodium phosphate and phosphoric acid.

Optionally, the sodium source includes at least one of sodium acetate, sodium nitrate and sodium oxalate.

Optionally, the carbon material includes graphite, acetylene black and/or carbon black.

Optionally, the particle size of the carbon material is 1 to 5 μm.

Optionally, the iron phosphate is crystalline and/or amorphous solid particles; in the iron phosphate, the molar ratio of Fe and P is 0.97 to 1.05.

Optionally, the particle size of the iron phosphate is 1 to 15 μm.

Alternatively, the molar ratio of the iron phosphate, phosphorus source and sodium source is (2.96~3):1:(3~3.05).

The molar ratio of the iron phosphate and the organic carbon source is 1: (1-5);

The molar ratio of the iron phosphate to the carbon material is 1: (0.02-0.05).

Optionally, the first mixture further includes a dispersant.

Optionally, the dispersant includes polyethylene glycol.

Optionally, the molar ratio of the dispersant to the organic carbon source is (1-2):3.

Optionally, the mass content of iron phosphate, phosphorus source, sodium source and organic carbon source in the first mixture is 10% to 40%.

Optionally, in the first mixed system, the particle size D100 of iron phosphate is 5 to 10 μm.

Optionally, the ball milling treatment time is 6 to 10 hours.

Optionally, in the second mixed system, the particle size D100 of iron phosphate is less than or equal to 0.2 μm.

Optionally, the drying includes spray drying.

Optionally, the drying temperature is 75-110°C and the drying time is 5-10 hours.

Optionally, the calcination includes: maintaining the temperature at 250-350°C for 3-5 hours, then raising the temperature to 500-600°C and maintaining the temperature for 10-15 hours.

Optionally, the heating rate is 2-5°C/min.

The positive electrode material is prepared by the preparation method of the positive electrode material.

The present disclosure also provides a cathode sheet, including the cathode material.

A sodium ion battery includes the positive electrode sheet.

Compared with the existing technology, the beneficial effects of the present disclosure are:

(1) This disclosure introduces two carbon sources with completely different properties in the preparation process of the iron-based composite phosphate Na ₄ Fe ₃ (PO ₄ ) ₂ P ₂ O ₇ cathode material, and utilizes the difference in their distribution intervals during the high-temperature calcination process. To construct interface layers with different functions, thereby improving the overall electrochemical performance of the material. Among them, the two carbon sources are carbon-containing organic matter that is easy to be pyrolyzed at high temperatures and high specific surface conductive carbon powder. Compared with the traditional single carbon source preparation process, the addition of high-specific surface conductive carbon powder greatly reduces the powder resistance, effectively increases surface reaction sites, is beneficial to electronic conductivity and ion transmission, and thereby reduces the internal resistance of the positive electrode side of the battery and electrochemistry. polarization.

(2) The particle size of the cathode material obtained by the present disclosure is 1 to 2 μm, and the size is uniform. The reversible specific capacity of the battery prepared from the iron-based composite phosphate cathode material of the present disclosure reaches 110.5mAh/g.

Description of the drawings

In order to more clearly explain the specific embodiments of the present disclosure or the technical solutions in the prior art, the drawings that need to be used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description The drawings illustrate some embodiments of the present disclosure. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without exerting creative efforts.

Figure 1 is a scanning electron microscope (SEM) image of the cathode material in Example 1 of the present disclosure;

Figure 2 is an SEM image of the cathode material in Comparative Example 1 of the present disclosure;

Figure 3 is a charge and discharge curve of the battery prepared from the cathode material in Comparative Example 1 of the present disclosure;

Figure 4 is a charge-discharge curve of a battery prepared from the cathode material in Example 1 of the present disclosure.

Detailed ways

The embodiments of the present disclosure will be described in detail below with reference to examples, but those skilled in the art will understand that the following examples are only used to illustrate the present disclosure and should not be regarded as limiting the scope of the present disclosure. If the specific conditions are not specified in the examples, the conditions should be carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not indicated, they are all conventional products that can be purchased commercially.

According to one aspect of the present disclosure, the present disclosure relates to a preparation method of a cathode material, including the following steps:

The first mixture of iron phosphate, phosphorus source, sodium source, organic carbon source and water is ball milled to obtain a first mixed system; the first mixed system and the second mixture of carbon materials are ball milled and sand milled in sequence Process to obtain a second mixed system; the second mixed system is dried and calcined.

The principle of this disclosure includes: introducing two carbon sources with completely different properties during the material preparation process, and utilizing the differences in their distribution intervals during high-temperature calcination to construct interface layers with different functions, thereby improving the overall electrochemical performance of the material. Among them, the two carbon sources are carbon-containing organic matter that is easy to be pyrolyzed at high temperatures and high specific surface conductive carbon powder. Compared with the traditional single carbon source preparation process, the addition of high-specific surface conductive carbon powder greatly reduces the powder resistance, effectively increases surface reaction sites, is beneficial to electronic conductivity and ion transmission, and thereby reduces the internal resistance of the positive electrode side of the battery and electrochemistry. polarization.

In one embodiment, the organic carbon source includes at least one of citric acid, glucose and sucrose.

In one embodiment, the phosphorus source includes at least one of sodium dihydrogen phosphate, sodium phosphate and phosphoric acid.

In one embodiment, the sodium source includes at least one of sodium acetate, sodium nitrate and sodium oxalate.

In one embodiment, the purity of sodium dihydrogen phosphate and sodium acetate is greater than or equal to 99.5%.

In one embodiment, the carbon material includes graphite, acetylene black and/or carbon black. Graphite in this disclosure includes natural graphite and/or artificial graphite. Carbon black is superconducting carbon black.

In one embodiment, the particle size of the carbon material is 1 to 5 μm. Specifically, it can be 2 μm, 3 μm, or 4 μm.

In one embodiment, the iron phosphate is crystalline and/or amorphous solid particles; in the iron phosphate, the molar ratio of Fe and P is 0.97 to 1.05. Specifically, it can be 0.98, 0.99, 1, 1.01, 1.02, 1.03 or 1.04.

In one embodiment, the particle size of the iron phosphate is 1 to 15 μm. Specifically, it can be 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, and 14 μm.

In one embodiment, the molar ratio of the iron phosphate, phosphorus source and sodium source is (2.96~3):1:(3~3.05).

The molar ratio of the iron phosphate to the organic carbon source is 1: (1-5); in one embodiment, the molar ratio of the iron phosphate to the organic carbon source is 1:1.2, 1:1.5 , 1:1.7, 1:2, 1:2.2, 1:2.5, 1:2.7, 1:3, 1:3.2, 1:3.5, 1:3.7, 1:4, 1:4.2, 1:4.5, 1 :4.7.

The molar ratio of the iron phosphate to the carbon material is 1: (0.02-0.05). In one embodiment, the phosphorus The molar ratios of iron acid and the carbon material are 1:0.03, 1:0.04, and 1:0.045.

In one embodiment, the first mixture further includes a dispersant.

In one embodiment, the dispersant includes polyethylene glycol.

In one embodiment, the molar ratio of the dispersant to the organic carbon source is (1-2):3. In one embodiment, the molar ratio of the dispersant to the organic carbon source includes but is not limited to 1:3, 1.2:3, 1.5:3, 1.7:3, and 2:3.

The present disclosure further improves the dispersion effect of the first mixture and improves its uniformity and stability by adding an appropriate amount of dispersant.

In one embodiment, the mass content of iron phosphate, phosphorus source, sodium source and organic carbon source in the first mixture is 10% to 40%. In one embodiment, the mass content (solid content) of iron phosphate, phosphorus source, sodium source and organic carbon source in the first mixture is 11%, 13%, 15%, 17%, 20%, 22 %, 25%, 27%, 30%, 32%, 35%, 37% or 39%.

In one embodiment, in the first mixed system, the particle size D100 of iron phosphate is 5 to 10 μm. In one embodiment, in the first mixed system, the particle size D100 of iron phosphate is 5.2 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm. That is, the termination condition for ball milling of the first mixture is until the particle size D100 is 5 to 10 μm.

In one embodiment, in the second mixed system, the particle size D100 of iron phosphate is less than or equal to 0.2 μm. That is, the sanding termination condition is until the particle size control range is D100≤0.2.

In one embodiment, the drying includes spray drying.

In one embodiment, the drying temperature is 75-110°C and the drying time is 5-10 hours. In one embodiment, the drying temperature includes but is not limited to 75°C, 80°C, 82°C, 85°C, 90°C, 95°C, 100°C, 102°C, 105°C, and 108°C. The drying time is 6h, 7h, 8h, 9h.

In one embodiment, the calcination includes: maintaining the temperature at 250-350°C for 3-5 hours, then raising the temperature to 500-600°C and maintaining the temperature for 10-15 hours. In one embodiment, the temperature is maintained at 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C or 340°C for 3.5h, 4h or 4.5h. Raise the temperature to 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, 590℃ and keep it warm for 11h, 12h, 13h or 14h.

In one embodiment, the heating rate is 2 to 5°C/min. Specifically, it can be 2.5°C/min, 3°C/min, 3.5°C/min, 4°C/min, or 4.5°C/min.

The calcinations of the present disclosure are performed under protective gas conditions. Protective gases include nitrogen.

According to another aspect of the disclosure, the disclosure also relates to the cathode material prepared by the method for preparing the cathode material.

The particle size of the cathode material of the present disclosure is 1 μm to 2 μm, the overall particle distribution is more uniform than that of a single carbon source, and it has excellent electrochemical performance.

According to another aspect of the present disclosure, the present disclosure also relates to a cathode sheet including the cathode material.

In one embodiment, a cathode material, a conductive agent and a binder with a mass ratio of 70:20:10 are mixed to obtain a mixed slurry; the mixed slurry is coated on an aluminum foil with a diameter of 19 mm, and the mixture is heated at 120°C Vacuum dry for 12 hours to obtain the positive electrode sheet. Among them, the conductive agent includes acetylene black; the binder includes PVDF.

According to another aspect of the present disclosure, the present disclosure also relates to a sodium ion battery, including the positive electrode sheet.

In one embodiment, the above-mentioned positive electrode sheet is taken, and metallic sodium is used as the counter electrode, 1mol/L NaClO ₄ ethylene carbonate/diethyl carbonate (volume ratio 1:1) is the electrolyte, and the separator is cellgard2035. A button battery is assembled in the box, and the battery model is CR2016.

The present disclosure will be further explained below with reference to specific examples and comparative examples.

Example 1

The preparation method of positive electrode material includes the following steps:

Add sodium dihydrogen phosphate, anhydrous sodium acetate, iron phosphate, citric acid monohydrate and polyethylene glycol dispersant to 6Kg of deionized water in a molar ratio of 1:3:3:6:2 into the ball mill tank. The total solid content is about 30%. The particle size of ferric phosphate is 6-15 μm. Ball-mill until the particle size is 10 μm at D100. Add 100g of graphite powder into the above-mentioned ball milling tank and continue ball-milling with the same process until the graphite powder is in the solution. until there is no obvious sedimentation; then change to sand grinding until the solid particle size in the solution is lower than D100 and is 0.2 μm; spray dry the above emulsion with the air inlet temperature being 300°C and the air outlet temperature being 100°C to obtain a powder Precursor; finally, in an N ₂ atmosphere, with a heating rate of 2°C, the temperature was maintained at 300°C for 5h and 550°C for 12h. After natural cooling, the Na ₄ Fe ₃ (PO ₄ ) ₂ P ₂ O ₇ /C composite was obtained. Electrode materials.

Example 2

The preparation method of positive electrode material includes the following steps:

Add sodium dihydrogen phosphate, anhydrous sodium acetate, iron phosphate, citric acid monohydrate and polyethylene glycol dispersant to 6Kg of deionized water in a molar ratio of 1:3:3:6:2 into the ball mill tank. The total solid content is about 10%, the particle size of iron phosphate is 3-10 μm, ball mill until the particle size is between D100 and 6 μm; add 100g acetylene black into the above ball milling tank, and continue ball milling with the same process until acetylene is in the solution until the black is evenly dispersed. Then change to sand grinding until the solid particle size in the solution is lower than D100 and is 0.1 μm. Spray dry the above emulsion with the inlet air temperature being 300°C and the outlet air temperature The temperature was 80°C to obtain a powdery precursor; finally, in an N ₂ atmosphere, at a heating rate of 2.5°C, the temperature was maintained at 250°C for 5 hours and at 600°C for 15 hours. After natural cooling, Na ₄ Fe ₃ (PO ₄ ) ₂ was obtained. P ₂ O ₇ /C composite electrode material.

Example 3

The preparation method of positive electrode material includes the following steps:

Add sodium dihydrogen phosphate, anhydrous sodium acetate, iron phosphate, citric acid monohydrate and polyethylene glycol dispersant to 6Kg of deionized water in a molar ratio of 1:3:3:6:2 into the ball mill tank. The total solid content is about 40%, the particle size of iron phosphate is 2-9.5 μm, ball-mill until the particle size is between D100 and 5 μm; add 100g of carbon powder to the above-mentioned ball milling tank, and continue to ball-mill with the same process until the solution until the carbon powder is evenly dispersed; then change to sand grinding until the solid particle size in the solution is lower than D100 and is 0.2 μm; spray dry the above emulsion with the air inlet temperature being 300°C and the air outlet temperature being 110°C to obtain the powder form precursor; finally, in an N ₂ atmosphere, the temperature was maintained at 350°C for 3 hours at a heating rate of 5°C, and at 500°C for 10 hours. After natural cooling, the Na ₄ Fe ₃ (PO ₄ ) ₂ P ₂ O ₇ /C composite was obtained. Electrode materials.

Example 4

In the preparation method of the positive electrode material, the phosphorus removal source is sodium phosphate, the sodium source is sodium oxalate, and the organic carbon source is glucose and sucrose, wherein the molar ratio of sodium phosphate, sodium oxalate, iron phosphate, glucose, and sucrose is 1:0.5:3 :1:0.5, other conditions are the same

Example 1.

Comparative example 1

The preparation method of a single carbon source Na ₄ Fe ₃ (PO ₄ ) ₂ P ₂ O ₇ cathode material includes the following steps:

Add sodium dihydrogen phosphate, anhydrous sodium acetate, iron phosphate and citric acid monohydrate to a ball mill tank with 6Kg of deionized water in a molar ratio of 1:3:3:6. The total solid content is about 30%. Until the particle size is at D100 of 10 μm. Then change to sand grinding until the solid particle size in the solution is lower than D100 and is 0.2 μm. The above emulsion was spray-dried with the air inlet temperature being 300°C and the air outlet temperature being 100°C, to obtain a powdery precursor. Finally, in an _N2 atmosphere, with a heating rate of 2°C, the electrode material was obtained by holding at 300°C for 5h and 550°C for 12h, and then cooling naturally.

Experimental example

1. Comparative analysis of SEM patterns

The morphology of the material in Example 1 was analyzed using SEM. As shown in Figure 1, due to the effective isolation of carbon powder, the material was broken during the sintering process, and finally formed small particles with particle sizes ranging from 1 μm to 2 μm. The overall distribution of particles is more uniform than that of a single carbon source. The morphology of the material in Comparative Example 1 was analyzed using SEM. As shown in Figure 2, it was found that the material presented regular spherical particles with particle sizes ranging from 1 μm to 10 μm and uneven size distribution.

2. Battery performance test

Na ₄ Fe ₃ (PO ₄ ) ₂ P ₂ O ₇ in the examples and comparative examples was mixed with acetylene black and PVDF respectively to obtain a mixed slurry, in which Na ₄ Fe ₃ (PO ₄ ) ₂ P ₂ O ₇ , The mass ratio of acetylene black and PVDF is 70:20:10. The mixed slurry is coated on an aluminum foil with a diameter of 19mm, and then the aluminum foil is vacuum dried at 120°C for 12 hours to obtain a positive electrode sheet. Use metallic sodium as the counter electrode, 1 mol/L NaClO ₄ ethylene carbonate/diethyl carbonate (volume ratio 1:1) as the electrolyte, and the separator is cellgard2035. A button battery is assembled in a glove box. The battery model is CR2016.

The batteries obtained in Example 1 and Comparative Example 1 were subjected to constant current charge and discharge tests respectively, and the current density was 26 mA/g. The test results of Comparative Example 1 are shown in Figure 3. In the voltage range of 2.0-4.3V, the reversible specific capacity is 97.3mAh/g. The test results of Example 1 are shown in Figure 4. In the voltage range of 2.0-4.3V, the reversible specific capacity is 110.5mAh/g, which is the same as the single carbon source Na ₄ Fe ₃ (PO ₄ ) ₂ P ₂ in Comparative Example 1. Compared with O ₇ , due to the introduction of carbon powder, the electronic conductivity between particles is increased, the difference in particle size distribution is effectively controlled, and the ion diffusion distance is shortened, thereby increasing the discharge capacity by 13.2mAh/g.

The test results of the battery's first efficiency and capacity retention rate are shown in Table 1.

Table 1 Battery performance test results

It can be seen from Table 1 that the battery prepared from the cathode material obtained by the present disclosure has excellent capacity retention rate, with a retention rate of more than 96% for 500 cycles, while the retention rate of the cathode material in Comparative Example 1 for 500 cycles is only 82%, which is far behind. in this application.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present disclosure, but not to limit it. Although the present disclosure has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: It is still possible to modify the technical solutions recorded in the foregoing embodiments, or to equivalently replace some or all of the technical features; and these modifications or substitutions do not deviate from the essence of the corresponding technical solutions from the technical solutions of the embodiments of the present disclosure. range.

Claims (10)

1. A preparation method of cathode material, characterized in that it includes the following steps:

   The first mixture of iron phosphate, phosphorus source, sodium source, organic carbon source and water is ball milled to obtain a first mixed system; the first mixed system and the second mixture of carbon materials are ball milled and sand milled in sequence Process to obtain a second mixed system; the second mixed system is dried and calcined.
2. The method for preparing a cathode material according to claim 1, wherein the organic carbon source includes at least one of citric acid, glucose and sucrose;

   Preferably, the phosphorus source includes at least one of sodium dihydrogen phosphate, sodium phosphate and phosphoric acid;

   Preferably, the sodium source includes at least one of sodium acetate, sodium nitrate and sodium oxalate;

   Preferably, the carbon material includes graphite, acetylene black and/or carbon black;

   Preferably, the particle size of the carbon material is 1 to 5 μm;

   Preferably, the iron phosphate is crystalline and/or amorphous solid particles; in the iron phosphate, the molar ratio of Fe and P is 0.97 to 1.05;

   Preferably, the particle size of the iron phosphate is 1 to 15 μm.
3. The method for preparing a cathode material according to claim 1 or 2, characterized in that the molar ratio of the iron phosphate, phosphorus source and sodium source is (2.96~3):1:(3~3.05);

   The molar ratio of the iron phosphate and the organic carbon source is 1: (1-5);

   The molar ratio of the iron phosphate to the carbon material is 1: (0.02-0.05).
4. The method for preparing a cathode material according to claim 1, wherein the first mixture further includes a dispersant;

   Preferably, the dispersant includes polyethylene glycol;

   Preferably, the molar ratio of the dispersant to the organic carbon source is (1-2):3.
5. The method for preparing a cathode material according to claim 1, wherein the mass content of iron phosphate, phosphorus source, sodium source and organic carbon source in the first mixture is 10% to 40%;

   Preferably, in the first mixed system, the particle size D100 of iron phosphate is 5 to 10 μm;

   Preferably, the ball milling treatment time is 6 to 10 hours;

   Preferably, in the second mixed system, the particle size D100 of iron phosphate is less than or equal to 0.2 μm.
6. The preparation method of cathode material according to claim 1, characterized in that the drying includes spray drying;

   Preferably, the drying temperature is 75-110°C and the drying time is 5-10 hours.
7. The method for preparing a cathode material according to claim 1, wherein the calcination includes: maintaining the temperature at 250-350°C for 3-5 hours, then raising the temperature to 500-600°C and maintaining the temperature for 10-15 hours;

   Preferably, the heating rate is 2 to 5°C/min.
8. The cathode material prepared according to the method for preparing the cathode material according to any one of claims 1 to 7.
9. A positive electrode sheet, characterized in that it includes the positive electrode material according to claim 8.
10. A sodium-ion battery, characterized by comprising the positive electrode sheet according to claim 9.