Fluorinated sodium iron phosphate positive electrode material, preparation method and application thereof

Abstract

The application discloses a kind of sodium iron fluorophosphate positive electrode materials and its preparation method and application, the preparation method includes that sodium source, iron source, phosphorus source, fluorine source and carbon source are mixed to obtain precursor, wherein the carbon source is cellulose acetate;Fluorinated sodium iron phosphate positive electrode material is obtained by heat treatment of precursor.The application uses cellulose acetate as carbon source in battery application, compared with traditional carbon sources such as graphene and carbon nanotube, the raw material source is more extensive, and does not need to be preprocessed, the production cost is lower, is more suitable for large-scale production application.The introduction of suitable proportion of cellulose acetate expands the specific surface area of material, enhances the conductivity and structural stability of battery, further improves the cycle stability and rate performance of battery.

Description

Technical Field

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

[0002] Sodium-ion batteries (SIBs) are considered an ideal choice for electric vehicles and large-scale energy storage due to their abundant resources, low cost, and electrochemical mechanism similar to that of lithium-ion batteries.

[0003] The cathode materials for sodium-ion batteries (SIBs) mainly include transition metal oxides, polyanionic compounds, Prussian blue analogues, and organic compounds. Polyanionic compounds, due to their stable framework structure, exhibit lower volume expansion and smaller phase transitions during sodium ion insertion / extraction, making them advantageous as cathode materials for sodium-ion batteries. Among them, sodium fluorophosphate (NFPF), a polyanionic compound, has attracted widespread attention due to its high theoretical specific capacity, stable crystal structure, unique two-dimensional layered transport structure, stable operating voltage platform, and good thermal stability. Compared to layered oxide cathode materials, NFPF has a more stable crystal structure and higher safety; compared to Prussian blue analogues, it has higher energy density and longer cycle life. Furthermore, iron in NFPF is abundant and environmentally friendly, further reducing material costs. However, the low electronic conductivity inherent in the NFPF structure and the sluggish sodium ion migration kinetics during electrode reactions severely limit the specific capacity and rate performance of NFPF electrode materials, and their cycle life is insufficient to meet practical requirements, restricting their application in large-scale energy storage.

[0004] Currently, the electrochemical performance of sodium iron fluoride phosphate cathode materials can be improved by methods such as carbon coating and element doping, but these methods are generally costly, have unsatisfactory results, and are not easy to mass-produce. Therefore, it is still necessary to seek new systems that can maintain their performance while reducing production costs. Summary of the Invention

[0005] The purpose of this invention is to prepare carbon-coated NFPF composite cathode materials using a high-temperature solid-state method. By adjusting the content of the carbon source cellulose acetate, the conductivity and ion diffusion rate of the raw materials are greatly improved, significantly enhancing the cycle stability and rate performance of the NFPF cathode material, making it more suitable for large-scale commercial manufacturing of sodium fluorophosphate.

[0006] To achieve the above objectives, the present invention provides a method for preparing sodium iron fluoride phosphate cathode material, comprising,

[0007] A precursor is obtained by mixing sodium source, iron source, phosphorus source, fluorine source and carbon source, wherein the carbon source is cellulose acetate;

[0008] The precursor was heat-treated to obtain sodium iron fluoride phosphate cathode material.

[0009] Furthermore, the molar ratio of sodium, iron, phosphorus, and fluorine in the precursor is 1.9-2.2:1:1:1.

[0010] Furthermore, the mass of the carbon source accounts for 10%-20% of the total mass of the sodium source, iron source, phosphorus source, and fluorine source.

[0011] Furthermore, the process of mixing sodium source, iron source, phosphorus source, fluorine source and carbon source to obtain the precursor includes,

[0012] Sodium, iron, phosphorus, fluorine, and carbon sources were wet-milled and then dried to obtain a mixture.

[0013] After removing impurity gases from the mixture, it is ground and screened through a 100-200 mesh sieve to obtain the precursor.

[0014] It should be noted that the present invention does not strictly limit the types of sodium, iron, phosphorus, and fluorine sources, and can use materials conventionally available in the art. For example, the sodium source can be at least one of sodium carbonate, sodium bicarbonate, sodium fluoride, sodium dihydrogen phosphate, and organic acid salts of sodium; the iron source can be at least one of ferrous sulfate, ferrous nitrate, ferrous oxalate, ferric chloride, and ferric oxalate; the phosphorus source can be at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and sodium dihydrogen phosphate; and the fluorine source can be at least one of sodium fluoride and ammonium fluoride.

[0015] Furthermore, impurity gases in the mixture are removed by holding the mixture at 250-450℃ for 4-6 hours.

[0016] Furthermore, the heat treatment is carried out at 450-650℃ for 8-12 hours.

[0017] The present invention also provides a sodium fluorinated iron phosphate cathode material, which is obtained by the above-described method for preparing sodium fluorinated iron phosphate cathode material.

[0018] This invention also provides the application of the above-mentioned sodium iron fluoride phosphate cathode material in sodium-ion batteries, including,

[0019] A positive electrode slurry is formed by mixing sodium iron fluoride phosphate cathode material, conductive material, binder and solvent;

[0020] The positive electrode slurry is coated onto a conductive foil to obtain the positive electrode of a sodium-ion battery, and then assembled into a sodium-ion battery.

[0021] Furthermore, the mass ratio of the sodium iron fluoride phosphate cathode material, the conductive material, and the binder is 7-8:1-2:1.

[0022] The present invention also provides a sodium-ion battery comprising the above-mentioned sodium iron fluoride phosphate cathode material.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. This invention uses cellulose acetate as a carbon source in battery applications. Compared with traditional carbon sources such as graphene and carbon nanotubes, the raw material sources are more extensive, and no pretreatment is required, resulting in lower production costs and making it more suitable for large-scale production applications.

[0025] 2. The introduction of an appropriate proportion of cellulose acetate increases the specific surface area of ​​the material, enhances the conductivity and structural stability of the battery, and further improves the cycle stability and rate performance of the battery.

[0026] At 0.1C, the specific capacity can reach as high as 122.9 mAh·g. -1 The specific capacity at 1C is 118 mAh·g. -1 The specific capacity at 10C is 104 mAh·g. -1 The specific capacity at 20C is 92 mAh·g. -1 After 2000 cycles at this rate, the capacity retention rate reached 87.1%; the specific capacity at 30C was 83 mAh·g. -1 And after 3000 cycles at this rate, the capacity retention rate is as high as 89.3%; at a high rate of 40C, the specific capacity can still reach 74mAh·g. -1 And after 2000 cycles at this rate, the capacity retention rate can still be as high as 83.1%.

[0027] 3. The cathode material of the present invention has low production cost, high safety performance, and a narrow discharge voltage range, which reduces the cost of battery use and is suitable for fields such as electric vehicles and large-scale grid energy storage. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 The XRD curves of sodium iron fluoride cathode materials prepared in Examples 1-3 and Comparative Example 1 are shown.

[0030] Figures 2a-2d Scanning electron microscope (SEM) images of sodium fluorinated iron phosphate cathode materials prepared in Comparative Example 1 and Examples 1-3 are shown respectively.

[0031] Figure 3 The AC impedance diagrams of sodium iron fluoride cathode materials prepared in Comparative Example 1 and Examples 1-3 are shown.

[0032] Figures 4a-4d Cyclic voltammetry diagrams of sodium iron fluoride cathode materials prepared in Comparative Example 1 and Examples 1-3 are shown respectively;

[0033] Figures 5a-5f The charge-discharge curves of sodium iron fluoride cathode materials prepared in Comparative Examples 1-3 and Examples 1-3 at a rate of 0.1C are shown respectively.

[0034] Figure 6 Rate cycling diagrams of sodium fluorinated iron phosphate cathode materials prepared in Comparative Example 1 and Examples 1-3 are shown.

[0035] Figure 7a The cycling performance of the sodium iron fluoride phosphate cathode material prepared in Example 2 at 20C and 40C rates is shown in the graph. Figure 7b The cycling performance of the sodium fluorinated iron phosphate cathode material prepared in Example 2 at a rate of 30C is shown. Detailed Implementation

[0036] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0037] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] Example 1

[0039] A method for preparing sodium iron fluoride phosphate cathode material includes the following steps.

[0040] S1. With sodium, iron, phosphorus, and fluorine in a molar ratio of 2:1:1:1, weigh out 0.8995 g of ferrous oxalate, 0.575 g of ammonium dihydrogen phosphate, 0.2100 g of sodium fluoride, and 0.4201 g of sodium bicarbonate, respectively, wherein the molar amount of each of the following is 5 mmol: ferrous oxalate, ammonium dihydrogen phosphate, sodium fluoride, and sodium bicarbonate; also weigh out 0.2105 g of cellulose acetate, which accounts for 10% of the total mass of ferrous oxalate, ammonium dihydrogen phosphate, sodium fluoride, and sodium bicarbonate.

[0041] S2. Ferrous oxalate, ammonium dihydrogen phosphate, sodium fluoride, sodium bicarbonate and cellulose acetate were transferred to a ball mill jar, and ball milled at 600 r / min for 8 h with ethanol as the dispersion solvent. The mixture was then placed in a vacuum drying oven and dried at 80 °C for 8 h. After that, it was ground and screened with a 120 mesh sieve to obtain the mixture.

[0042] S3. Transfer the mixture to a 10mL crucible and pre-calcine at 350℃ for 5h to remove impurities such as water and carbon dioxide, and obtain a white-green powder. Grind the powder and sieve it through a 120-mesh sieve to obtain the precursor.

[0043] S4. The precursor was calcined at 600℃ for 8 hours to obtain sodium iron fluoride phosphate cathode material, which was named NFPF / CA-10.

[0044] Example 2

[0045] A method for preparing sodium iron fluoride phosphate cathode material includes the following steps.

[0046] S1. With sodium, iron, phosphorus, and fluorine in a molar ratio of 2:1:1:1, weigh out 0.8995 g of ferrous oxalate, 0.575 g of ammonium dihydrogen phosphate, 0.2100 g of sodium fluoride, and 0.4201 g of sodium bicarbonate, respectively, wherein the molar amount of each of the following is 5 mmol: ferrous oxalate, ammonium dihydrogen phosphate, sodium fluoride, and sodium bicarbonate; also weigh out 0.3158 g of cellulose acetate, which accounts for 15% of the total mass of ferrous oxalate, ammonium dihydrogen phosphate, sodium fluoride, and sodium bicarbonate.

[0047] S2. Ferrous oxalate, ammonium dihydrogen phosphate, sodium fluoride, sodium bicarbonate and cellulose acetate were transferred to a ball mill jar, and ball milled at 600 r / min for 8 h with ethanol as the dispersion solvent. The mixture was then placed in a vacuum drying oven and dried at 80 °C for 8 h. After that, it was ground and screened with a 120 mesh sieve to obtain the mixture.

[0048] S3. Transfer the mixture to a 10mL crucible and pre-calcine at 350℃ for 5h to remove impurities such as water and carbon dioxide, to obtain a white-green powder. Grind the powder and sieve it through a 120-mesh screen to obtain the precursor.

[0049] S4. The precursor was calcined at 600℃ for 8 hours to obtain sodium iron fluoride phosphate cathode material, which was named NFPF / CA-15.

[0050] Example 3

[0051] A method for preparing sodium iron fluoride phosphate cathode material includes the following steps.

[0052] S1. With sodium, iron, phosphorus, and fluorine in a molar ratio of 2:1:1:1, weigh out 0.8995 g of ferrous oxalate, 0.575 g of ammonium dihydrogen phosphate, 0.2100 g of sodium fluoride, and 0.4201 g of sodium bicarbonate, respectively, wherein the molar amount of each of the following is 5 mmol: ferrous oxalate, ammonium dihydrogen phosphate, sodium fluoride, and sodium bicarbonate; also weigh out 0.4210 g of cellulose acetate, which accounts for 20% of the total mass of ferrous oxalate, ammonium dihydrogen phosphate, sodium fluoride, and sodium bicarbonate.

[0053] S2. Ferrous oxalate, ammonium dihydrogen phosphate, sodium fluoride, sodium bicarbonate and cellulose acetate were transferred to a ball mill jar, and ball milled at 600 r / min for 8 h with ethanol as the dispersion solvent. The mixture was then placed in a vacuum drying oven and dried at 80 °C for 8 h. After that, it was ground and screened with a 120 mesh sieve to obtain the mixture.

[0054] S3. Transfer the mixture to a 10mL crucible and pre-calcine at 350℃ for 5h to remove impurities such as water and carbon dioxide, to obtain a white-green powder. Grind the powder and sieve it through a 120-mesh screen to obtain the precursor.

[0055] S4. The precursor was calcined at 600℃ for 8 hours to obtain sodium iron fluoride phosphate cathode material, which was named NFPF / CA-20.

[0056] Comparative Example 1

[0057] A method for preparing sodium iron fluoride phosphate cathode material includes the following steps.

[0058] S1. With the molar ratio of sodium, iron, phosphorus and fluorine being 2:1:1:1, weigh out 0.8995 g of ferrous oxalate, 0.575 g of ammonium dihydrogen phosphate, 0.2100 g of sodium fluoride and 0.4201 g of sodium bicarbonate, respectively, wherein the molar amount of ferrous oxalate, ammonium dihydrogen phosphate, sodium fluoride and sodium bicarbonate is 5 mmol.

[0059] S2. Ferrous oxalate, ammonium dihydrogen phosphate, sodium fluoride and sodium bicarbonate were transferred to a ball mill jar, and ball milled at 600 r / min for 8 h with ethanol as the dispersion solvent. The mixture was then placed in a vacuum drying oven and dried at 80 °C for 8 h. The mixture was then ground and screened through a 120 mesh sieve to obtain the final mixture.

[0060] S3. Transfer the mixture to a 10mL crucible and pre-calcine at 350℃ for 5h to remove impurities such as water and carbon dioxide, to obtain a white-green powder. Grind the powder and sieve it through a 120-mesh screen to obtain the precursor.

[0061] S4. The precursor was calcined at 600℃ for 8 hours to obtain sodium iron fluoride phosphate cathode material, which was named NFPF.

[0062] Comparative Example 2

[0063] A method for preparing sodium iron fluoride phosphate cathode material includes the following steps.

[0064] S1. With sodium, iron, phosphorus, and fluorine in a molar ratio of 2:1:1:1, weigh out 0.8995 g of ferrous oxalate, 0.575 g of ammonium dihydrogen phosphate, 0.2100 g of sodium fluoride, and 0.4201 g of sodium bicarbonate, respectively, wherein the molar amount of each of the following is 5 mmol: ferrous oxalate, ammonium dihydrogen phosphate, sodium fluoride, and sodium bicarbonate; also weigh out 0.2105 g of carbon nanotubes, which constitute 10% of the total mass of ferrous oxalate, ammonium dihydrogen phosphate, sodium fluoride, and sodium bicarbonate.

[0065] S2. Ferrous oxalate, ammonium dihydrogen phosphate, sodium fluoride, sodium bicarbonate and carbon nanotubes were transferred to a ball mill jar, and ball milled at 600 r / min for 8 h with ethanol as the dispersion solvent. After that, the mixture was placed in a vacuum drying oven and dried at 80 °C for 8 h. Then, it was ground and screened with a 120 mesh sieve to obtain the mixture.

[0066] S3. Transfer the mixture to a 10mL crucible and pre-calcine at 350℃ for 5h to remove impurities such as water and carbon dioxide, to obtain a white-green powder. Grind the powder and sieve it through a 120-mesh screen to obtain the precursor.

[0067] S4. The precursor was calcined at 600℃ for 8 hours to obtain sodium iron fluoride phosphate cathode material, which was named NFPF / C-carbon nanotube.

[0068] Comparative Example 3

[0069] A method for preparing sodium iron fluoride phosphate cathode material includes the following steps.

[0070] S1. With sodium, iron, phosphorus, and fluorine in a molar ratio of 2:1:1:1, weigh out 0.8995 g of ferrous oxalate, 0.575 g of ammonium dihydrogen phosphate, 0.2100 g of sodium fluoride, and 0.4201 g of sodium bicarbonate, respectively, wherein the molar amount of each of the following is 5 mmol: ferrous oxalate, ammonium dihydrogen phosphate, sodium fluoride, and sodium bicarbonate; also weigh out 0.2105 g of graphene, which accounts for 10% of the total mass of ferrous oxalate, ammonium dihydrogen phosphate, sodium fluoride, and sodium bicarbonate.

[0071] S2. Ferrous oxalate, ammonium dihydrogen phosphate, sodium fluoride, sodium bicarbonate and graphene were transferred to a ball mill jar, and ball milled at 600 r / min for 8 h with ethanol as the dispersion solvent. After that, the mixture was placed in a vacuum drying oven and dried at 80 °C for 8 h. Then, the mixture was ground and screened through a 120 mesh sieve to obtain the mixture.

[0072] S3. Transfer the mixture to a 10mL crucible and pre-calcine at 350℃ for 5h to remove impurities such as water and carbon dioxide, to obtain a white-green powder. Grind the powder and sieve it through a 120-mesh screen to obtain the precursor.

[0073] S4. The precursor was calcined at 600℃ for 8 hours to obtain sodium iron fluoride phosphate cathode material, which was named NFPF / C-graphene.

[0074] Test case

[0075] Figure 1 The XRD patterns of the cathode materials prepared in Examples 1-3 and Comparative Example 1 are shown. It can be seen that the diffraction peaks of the cathode materials in Examples 1-3 and Comparative Example 1 are consistent with the standard PDF card of sodium fluorophosphate, indicating that they have high crystallinity. Among them, compared with Comparative Example 1, the diffraction peak intensities of some crystal planes in Examples 1-3 are significantly reduced, which indicates the formation of carbon coating. At the same time, the formation of carbon coating inhibits the growth of some crystal planes of sodium fluorophosphate.

[0076] Figures 2a-2d Scanning electron microscope (SEM) images of the cathode materials in the comparative examples and Examples 1-3 are shown. It can be seen that with the introduction of cellulose acetate, the average particle size of the prepared sodium fluorophosphate particles decreases and the aggregation between particles is reduced. This indicates that the introduction of the carbon source cellulose acetate forms a good carbon coating on the material surface. In particular, the NFPF / CA-15% prepared in Example 2 has the most uniform distribution of sodium fluorophosphate particles. The smaller particle size provides more active sites for the electrochemical reaction, shortens the sodium ion diffusion path, and thus improves electrochemical performance. The defect-rich carbon layer uniformly coats the surface of the sodium fluorophosphate, enabling rapid sodium ion migration and improving its conductivity.

[0077] The specific surface area of ​​the cathode materials of the comparative examples and Examples 1-3 was tested using the BET method, and the results are shown in Table 1.

[0078] Table 1 Specific surface area of ​​cathode materials

[0079]

[0080] As shown in Table 1, the introduction of cellulose acetate significantly increased the specific surface area of ​​the sodium fluorophosphate material, exhibiting a trend of first increasing and then decreasing as the proportion of cellulose acetate increased from 10% to 20%. A larger specific surface area is beneficial for providing more active sites for electrochemical reactions.

[0081] The cathode material to be tested was mixed with Ketjen black and polyvinylidene fluoride at a mass ratio of 7:2:1, and then N-methylpyrrolidone was added and mixed evenly to obtain a cathode slurry. The cathode slurry was coated onto aluminum foil and dried in a vacuum drying oven for 12 hours to obtain the cathode of a sodium-ion battery. The impedance of different sodium-ion battery cathodes was tested using the AC impedance method, and the results are as follows. Figure 3 As shown, the diameter of the semicircle of the curve reflects the charge transfer resistance of the electrochemical reaction. It can be seen that the NFPF / CA-15% of Example 2 has the lowest charge transfer resistance and exhibits the best electrochemical performance. Different sodium-ion battery cathodes were tested at potentials ranging from 1.75V to 4.0V at 0.1mV·s. -1 Cyclic voltammetry curves were tested at a scan rate of [value missing]. From [data missing] Figures 4a-4d It can be seen that after the introduction of carbon source cellulose acetate, the redox peak of the sodium-ion battery cathode becomes sharper and the current increases significantly. The NFPF / CA-15% in Example 2 has the highest redox peak.

[0082] Different sodium-ion battery positive electrodes were assembled into batteries in the following order: negative electrode shell, counter electrode sodium sheet, separator, electrolyte, positive electrode material, gasket, spring sheet, and positive electrode shell. The electrochemical performance of these batteries was then tested at 0.1C. Figures 5a-5f It can be seen that the battery constructed in Comparative Example 1, which did not introduce any carbon source, had the lowest specific capacity. The batteries constructed in Comparative Examples 2 and 3, using carbon nanotubes and graphene as carbon sources, showed improved specific capacities, but not significantly. Furthermore, the batteries in Examples 1-3, using cellulose acetate as a carbon source, showed significant improvements in specific capacity, especially the NFPF / CA-15% battery in Example 2, which achieved a specific capacity as high as 122.9 mAh·g at 0.1C. -1 These results demonstrate that using cellulose acetate as a carbon source in battery applications, compared to traditional carbon sources such as graphene and carbon nanotubes, not only has lower production costs but also enables the construction of higher-performance sodium-ion batteries. Figure 1In the XRD pattern, the peak intensity of the embodiment is significantly weaker than that of the comparative example, and it can be clearly observed that the peaks at certain locations are much lower than those of the comparative example, such as the (200) and (104) crystal planes. The possible reason is that CA can effectively suppress the growth of certain crystal planes of NFPF during the carbon coating process. As a physical isolation layer, CA carbon material can reduce the direct contact of NFPF particles during high-temperature processing, suppress grain agglomeration and abnormal growth. This spatial restriction forces the grains to grow within a limited range, thereby effectively suppressing the preferential growth of the crystal planes of the cathode material, thereby improving the structural stability and electrochemical performance of NFPF, greatly improving the conductivity and ion diffusion rate of the raw materials, and significantly improving the cycle stability and rate performance of the NFPF cathode material, making it more suitable for the large-scale commercial manufacturing of sodium fluorophosphate.

[0083] Figure 6 The rate performance graphs of the cathode materials in Comparative Examples 1-3 are shown. It can be seen that the NFPF / CA-15% of Example 2 has the best rate performance, with a specific capacity as high as 122.9 mAh·g at 0.1C. -1 The specific capacity at 1C is 118 mAh·g. -1 The specific capacity at 10C is 104 mAh·g. -1 The specific capacity at 20C is 92 mAh·g. -1 The specific capacity at 30C is 83mAh·g. -1 Even at a high rate of 40C, the specific capacity can still reach as high as 74mAh·g. -1 .

[0084] Figure 7a and Figure 7b As can be seen, after 2000 cycles at 20C and 40C, the NFPF / CA-15% of Example 2 exhibited a capacity retention of 87.1% and 83.1%, respectively; after 3000 cycles at 30C, the capacity retention was as high as 89.3%. These results demonstrate that the sodium iron fluorinated phosphate cathode material prepared in this invention possesses excellent rate performance.

[0085] In summary, this invention utilizes cellulose acetate as the carbon source for battery applications. Compared to traditional carbon sources such as graphene and carbon nanotubes, the raw material source is more widely available, requires no pretreatment, has lower production costs, and is more suitable for large-scale production applications. The introduction of an appropriate proportion of cellulose acetate increases the specific surface area of ​​the material, enhancing the battery's conductivity and structural stability, further improving the battery's cycle stability and rate performance. The invented cathode material has low production costs, high safety performance, and a narrow discharge voltage range, reducing battery usage costs and making it suitable for fields such as electric vehicles and large-scale grid energy storage.

[0086] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a sodium iron fluorophosphate cathode material, characterized in that, include, Sodium, iron, phosphorus, fluorine, and carbon sources were wet-milled and then dried to obtain a mixture. The mixture is kept at 250-450℃ for 4-6 hours to remove impurity gases, and then ground to obtain a precursor, wherein the carbon source is cellulose acetate; The precursor was heat-treated to obtain sodium iron fluoride cathode material; The carbon source accounts for 10%-20% of the total mass of the sodium, iron, phosphorus, and fluorine sources. The heat treatment involves holding the temperature at 450-650℃ for 8-12 hours.

2. The method for preparing sodium iron fluoride cathode material according to claim 1, characterized in that, The molar ratio of sodium, iron, phosphorus and fluorine in the precursor is 1.9-2.2:1:1:

1.

3. The method for preparing sodium iron fluoride cathode material according to claim 1, characterized in that, The precursor was obtained by screening with a 100-200 mesh sieve.

4. A sodium iron fluorophosphate positive electrode material characterized in that, The sodium fluorinated iron phosphate cathode material was prepared using the method described in any one of claims 1-3.

5. Use of the sodium iron fluorophosphate positive electrode material according to claim 4 in a sodium-ion battery, characterized in that, include, A positive electrode slurry is formed by mixing sodium iron fluoride phosphate cathode material, conductive material, binder and solvent; The positive electrode slurry is coated onto a conductive foil to obtain the positive electrode of a sodium-ion battery, and then assembled into a sodium-ion battery.

6. Use according to claim 5, characterized in that, The mass ratio of the sodium fluorinated iron phosphate cathode material, conductive material, and binder is 7-8:1-2:

1.

7. A sodium-ion battery, characterized in that, Including the sodium fluorinated iron phosphate cathode material as described in claim 4.

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