Sodium ferric fluorophosphate positive electrode material as well as preparation method and application thereof

Abstract

The invention discloses a sodium ferric fluorophosphate positive electrode material and a preparation method and application thereof.The preparation method comprises the steps that a sodium source, an iron source, a phosphorus source, a fluorine source and a carbon source are mixed to obtain a precursor, and the carbon source is cellulose acetate; and carrying out heat treatment on the precursor to obtain the sodium ferric fluorophosphate positive electrode material. Cellulose acetate is adopted as a carbon source in battery application, and compared with traditional carbon sources such as graphene and carbon nanotubes, the raw material source is wider, no pretreatment is needed, the production cost is lower, and the method is more suitable for large-scale production and application. The specific surface area of the material is enlarged by introducing cellulose acetate with a proper proportion, the conductivity and the structural stability of the battery are enhanced, and the cycling stability and the rate capability of the battery are further improved.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion battery materials, and in particular to a sodium ferric fluorophosphate positive electrode material, a preparation method thereof, and applications thereof. Background Art

[0002] Sodium-ion batteries (SIBs) are considered to be one of the ideal choices for power vehicles and large-scale energy storage due to their abundant resources, low cost and similar electrochemical mechanism to lithium-ion batteries.

[0003] Cathode materials for SIBs primarily include transition metal oxides, polyanionic compounds, Prussian blue analogs, and organic compounds. Polyanionic compounds offer significant advantages as cathode materials for sodium-ion batteries due to their stable backbone structure, low volume expansion, and minimal phase transitions during sodium ion insertion and deintercalation. Among them, the polyanionic compound sodium ferric fluorophosphate (NFPF) has attracted widespread attention as a cathode material for sodium-ion batteries due to its high theoretical specific capacity, stable crystal structure, unique two-dimensional layered transport structure, stable operating voltage platform, and excellent thermal stability. Compared with layered oxide cathode materials, the polyanionic compound NFPF has a more stable crystal structure and improved safety. Compared with Prussian blue analogs, it exhibits higher energy density and longer cycle life. Furthermore, the abundant and environmentally friendly iron content of NFPF further reduces material costs. However, the low electronic conductivity inherent in NFPF's structure and the sluggish sodium ion migration kinetics during the electrode reaction severely limit the specific capacity and rate capability of NFPF electrode materials, and the cycle life is insufficient to meet practical requirements, limiting their application in large-scale energy storage.

[0004] Currently, the electrochemical performance of sodium iron fluorophosphate positive electrode materials can be improved through methods such as carbon coating and element doping, but the costs are generally high, the effects are unsatisfactory, and it is not easy to mass-produce. Therefore, it is still necessary to seek new systems to reduce production costs while maintaining their performance. Summary of the Invention

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

[0006] In order to achieve the above object, the present invention provides a method for preparing a sodium ferric fluorophosphate positive electrode material, comprising: A sodium source, an iron source, a phosphorus source, a fluorine source, and a carbon source are mixed to obtain a precursor, wherein the carbon source is cellulose acetate; The precursor is heat-treated to obtain sodium iron fluorophosphate positive electrode material.

[0007] Furthermore, the molar ratio of sodium, iron, phosphorus and fluorine in the precursor is 1.9-2.2:1:1:1.

[0008] 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.

[0009] Furthermore, the precursor obtained by mixing a sodium source, an iron source, a phosphorus source, a fluorine source and a carbon source comprises: wet-ball-milling a sodium source, an iron source, a phosphorus source, a fluorine source, and a carbon source, and then drying the resultant to obtain a mixture; The mixture was ground after removing impurity gases, and then sieved with a 100-200 mesh sieve to obtain a precursor.

[0010] It should be noted that the present invention does not strictly limit the types of sodium source, iron source, phosphorus source, and fluorine source, and can be any conventionally selected materials in the art. For example, the sodium source can be selected from at least one of sodium carbonate, sodium bicarbonate, sodium fluoride, sodium dihydrogen phosphate, and an organic acid salt of sodium; the iron source can be selected from at least one of ferrous sulfate, ferrous nitrate, ferrous oxalate, ferric chloride, and ferric oxalate; the phosphorus source can be selected from at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and sodium dihydrogen phosphate; and the fluorine source can be selected from at least one of sodium fluoride and ammonium fluoride.

[0011] Furthermore, the mixture is kept at 250-450° C. for 4-6 hours to remove impurity gases in the mixture.

[0012] Furthermore, the heat treatment is carried out at 450-650° C. for 8-12 hours.

[0013] The present invention also provides a sodium ferric fluoride phosphate positive electrode material, which is obtained by using the above-mentioned method for preparing the sodium ferric fluoride phosphate positive electrode material.

[0014] The present invention also provides the use of the above-mentioned sodium ferric phosphate cathode material in a sodium ion battery, including: Mixing a sodium ferric fluorophosphate cathode material, a conductive material, a binder, and a solvent to form a cathode slurry; The positive electrode slurry is coated on a conductive foil to obtain a sodium ion battery positive electrode, and then assembled into a sodium ion battery.

[0015] Furthermore, the mass ratio of the sodium ferric fluoride phosphate positive electrode material, the conductive material, and the binder is 7-8:1-2:1.

[0016] The present invention also provides a sodium ion battery comprising the above-mentioned sodium ferric phosphate fluoride positive electrode material.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention uses cellulose acetate as the carbon source in battery applications. Compared with traditional carbon sources such as graphene and carbon nanotubes, the raw material source is more extensive, and no pretreatment is required, the production cost is lower, and it is more suitable for large-scale production applications.

[0018] 2. The introduction of cellulose acetate in an appropriate proportion expands 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: At 0.1C, the specific capacity can reach up to 122.9mAh·g -1 Specific capacity at 1C is 118 mAh g -1 Specific capacity at 10C is 104 mAh·g -1 ; Specific capacity at 20C is 92 mAh·g -1 After 2000 cycles at this rate, the capacity retention rate is as high as 87.1%; the specific capacity at 30C is 83 mAh·g -1 , and the capacity retention rate is as high as 89.3% after 3000 cycles at this rate; at a high rate of 40C, the specific capacity can still be as high as 74mAh·g -1 , and after 2000 cycles at this rate, the capacity retention rate can still be as high as 83.1%.

[0019] 3. The positive electrode 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 power vehicles, large-scale power grid energy storage and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0021] Figure 1 The XRD curves of the sodium fluoroferric phosphate positive electrode materials prepared in Examples 1-3 and Comparative Example 1 are shown; Figure 2a-2d The scanning electron micrographs of the sodium fluoroferric phosphate positive electrode materials prepared in Comparative Example 1 and Examples 1-3 are shown respectively; Figure 3 The AC impedance diagrams of the sodium fluoroferric phosphate positive electrode materials prepared in Comparative Example 1 and Examples 1-3 are shown; Figure 4a-4dThe cyclic voltammograms of the sodium fluoroferric phosphate positive electrode materials prepared in Comparative Example 1 and Examples 1-3 are shown respectively; Figure 5a-5f The charge and discharge curves of the sodium fluoroferric phosphate positive electrode materials prepared in Comparative Examples 1-3 and Examples 1-3 at a rate of 0.1C are shown respectively; Figure 6 The rate cycle diagrams of the sodium fluoroferric phosphate positive electrode materials prepared in Comparative Example 1 and Examples 1-3 are shown; Figure 7a The graph shows the cycle performance of the sodium ferric fluoride phosphate cathode material prepared in Example 2 at 20C and 40C rates. Figure 7b The figure shows the cycling performance of the sodium iron fluoride phosphate cathode material prepared in Example 2 at a rate of 30C. DETAILED DESCRIPTION

[0022] The endpoints of the ranges and any values ​​disclosed herein 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 endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to form one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed in the present invention.

[0023] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the specific embodiments of the present invention and the accompanying drawings. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0024] Example 1 A method for preparing a sodium ferric fluorophosphate positive electrode material comprises the following steps: S1. Weigh 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, with the molar ratio of sodium, iron, phosphorus, and fluorine being 2:1:1:1, wherein the molar weights of ferrous oxalate, ammonium dihydrogen phosphate, sodium fluoride, and sodium bicarbonate are all 5 mmol; also weigh 0.2105 g of cellulose acetate, where the cellulose acetate accounts for 10% of the total mass of the ferrous oxalate, ammonium dihydrogen phosphate, sodium fluoride, and sodium bicarbonate; S2, transferring ferrous oxalate, ammonium dihydrogen phosphate, sodium fluoride, sodium bicarbonate, and cellulose acetate into a ball mill, using ethanol as a dispersion solvent, ball milling at a speed of 600 r / min for 8 h, and then drying in a vacuum drying oven at 80° C. for 8 h, followed by grinding and sieving with a 120-mesh sieve to obtain a mixture; S3. The mixture was transferred to a 10 mL crucible and pre-calcined at 350° C. for 5 h to remove impurities such as water and carbon dioxide to obtain a white-green powder. The powder was ground and sieved with a 120-mesh sieve to obtain a precursor. S4. The precursor was calcined at 600° C. for 8 h to obtain a sodium fluoroferric phosphate cathode material, which was named NFPF / CA-10%.

[0025] Example 2 A method for preparing a sodium fluoroferric phosphate positive electrode material comprises the following steps: S1. Weigh 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, with the molar ratio of sodium, iron, phosphorus, and fluorine being 2:1:1:1, wherein the molar weights of ferrous oxalate, ammonium dihydrogen phosphate, sodium fluoride, and sodium bicarbonate are all 5 mmol; also weigh 0.3158 g of cellulose acetate, where the cellulose acetate accounts for 15% of the total mass of the ferrous oxalate, ammonium dihydrogen phosphate, sodium fluoride, and sodium bicarbonate; S2, transferring ferrous oxalate, ammonium dihydrogen phosphate, sodium fluoride, sodium bicarbonate, and cellulose acetate into a ball mill, using ethanol as a dispersion solvent, ball milling at a speed of 600 r / min for 8 h, and then drying in a vacuum drying oven at 80° C. for 8 h, followed by grinding and sieving with a 120-mesh sieve to obtain a mixture; S3. The mixture was transferred to a 10 mL crucible and pre-calcined at 350° C. for 5 h to remove impurities such as water and carbon dioxide to obtain a white-green powder, which was then ground and sieved with a 120-mesh sieve to obtain a precursor; S4. Calcine the precursor at 600° C. for 8 h to obtain a sodium fluoroferric phosphate cathode material, which is named NFPF / CA-15%.

[0026] Example 3 A method for preparing a sodium fluoroferric phosphate positive electrode material comprises the following steps: S1. Weigh 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, with the molar ratio of sodium, iron, phosphorus, and fluorine being 2:1:1:1, wherein the molar weights of ferrous oxalate, ammonium dihydrogen phosphate, sodium fluoride, and sodium bicarbonate are all 5 mmol; also weigh 0.4210 g of cellulose acetate, where the cellulose acetate accounts for 20% of the total mass of the ferrous oxalate, ammonium dihydrogen phosphate, sodium fluoride, and sodium bicarbonate; S2, transferring ferrous oxalate, ammonium dihydrogen phosphate, sodium fluoride, sodium bicarbonate, and cellulose acetate into a ball mill, using ethanol as a dispersion solvent, ball milling at a speed of 600 r / min for 8 h, and then drying in a vacuum drying oven at 80° C. for 8 h, followed by grinding and sieving with a 120-mesh sieve to obtain a mixture; S3. The mixture was transferred to a 10 mL crucible and pre-calcined at 350° C. for 5 h to remove impurities such as water and carbon dioxide to obtain a white-green powder, which was then ground and sieved with a 120-mesh sieve to obtain a precursor; S4. The precursor was calcined at 600° C. for 8 h to obtain a sodium fluoroferric phosphate cathode material, which was named NFPF / CA-20%.

[0027] Comparative Example 1 A method for preparing a sodium ferric fluorophosphate positive electrode material comprises the following steps: S1. Weigh 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, with the molar ratio of sodium, iron, phosphorus, and fluorine being 2:1:1:1, wherein the molar amounts of ferrous oxalate, ammonium dihydrogen phosphate, sodium fluoride, and sodium bicarbonate are all 5 mmol; S2, transferring ferrous oxalate, ammonium dihydrogen phosphate, sodium fluoride, and sodium bicarbonate into a ball mill, using ethanol as a dispersing solvent, ball milling at a speed of 600 r / min for 8 h, and then drying in a vacuum drying oven at 80° C. for 8 h, followed by grinding and sieving with a 120-mesh sieve to obtain a mixture; S3. The mixture was transferred to a 10 mL crucible and pre-calcined at 350° C. for 5 h to remove impurities such as water and carbon dioxide to obtain a white-green powder, which was then ground and sieved with a 120-mesh sieve to obtain a precursor; S4. Calcine the precursor at 600° C. for 8 h to obtain a sodium fluoroferric phosphate positive electrode material, which is named NFPF.

[0028] Comparative Example 2 A method for preparing a sodium ferric fluorophosphate positive electrode material comprises the following steps: S1. Weigh 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, with the molar ratio of sodium, iron, phosphorus, and fluorine being 2:1:1:1, wherein the molar weights of ferrous oxalate, ammonium dihydrogen phosphate, sodium fluoride, and sodium bicarbonate are all 5 mmol; also weigh 0.2105 g of carbon nanotubes, wherein the carbon nanotubes account for 10% of the total mass of the ferrous oxalate, ammonium dihydrogen phosphate, sodium fluoride, and sodium bicarbonate; S2, transferring ferrous oxalate, ammonium dihydrogen phosphate, sodium fluoride, sodium bicarbonate, and carbon nanotubes into a ball mill, using ethanol as a dispersion solvent, ball milling at a speed of 600 r / min for 8 h, and then drying in a vacuum drying oven at 80° C. for 8 h, followed by grinding and sieving with a 120-mesh sieve to obtain a mixture; S3. The mixture was transferred to a 10 mL crucible and pre-calcined at 350° C. for 5 h to remove impurities such as water and carbon dioxide to obtain a white-green powder, which was then ground and sieved with a 120-mesh sieve to obtain a precursor; S4. calcining the precursor at 600° C. for 8 h to obtain a sodium ferric fluorophosphate cathode material, which is named NFPF / C-carbon nanotubes.

[0029] Comparative Example 3 A method for preparing a sodium fluoroferric phosphate positive electrode material comprises the following steps: S1. Weigh 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, with the molar ratio of sodium, iron, phosphorus, and fluorine being 2:1:1:1, wherein the molar amounts of ferrous oxalate, ammonium dihydrogen phosphate, sodium fluoride, and sodium bicarbonate are all 5 mmol; also weigh 0.2105 g of graphene, where graphene accounts for 10% of the total mass of ferrous oxalate, ammonium dihydrogen phosphate, sodium fluoride, and sodium bicarbonate; S2, transferring ferrous oxalate, ammonium dihydrogen phosphate, sodium fluoride, sodium bicarbonate, and graphene into a ball mill, using ethanol as a dispersing solvent, ball milling at a speed of 600 r / min for 8 h, and then drying in a vacuum drying oven at 80° C. for 8 h, followed by grinding and sieving with a 120-mesh sieve to obtain a mixture; S3. The mixture was transferred to a 10 mL crucible and pre-calcined at 350° C. for 5 h to remove impurities such as water and carbon dioxide to obtain a white-green powder, which was then ground and sieved with a 120-mesh sieve to obtain a precursor; S4. Calcine the precursor at 600° C. for 8 h to obtain a sodium ferric fluorophosphate cathode material, which is named NFPF / C-graphene.

[0030] Test Case Figure 1 The XRD patterns of the positive electrode materials prepared in Examples 1-3 and Comparative Example 1 are shown. It can be seen that the crystal diffraction peaks of the positive electrode materials of Examples 1-3 and Comparative Example 1 are consistent with the standard PDF card of sodium fluoroferric phosphate, indicating that they have high crystallinity. Compared with Comparative Example 1, the diffraction peak intensity of some crystal planes of Examples 1-3 is significantly reduced, which indicates the formation of carbon coating. At the same time, the growth of certain crystal planes of sodium fluoroferric phosphate is inhibited during the formation of the carbon coating.

[0031] Figure 2a-2dScanning electron micrographs of the positive electrode materials of the comparative example and Examples 1-3 are shown, respectively. It can be seen that with the introduction of cellulose acetate, the average particle size of the prepared sodium ferric fluorophosphate particles decreases and the agglomeration between the particles decreases. This shows that the introduction of the carbon source cellulose acetate forms a good carbon coating on the surface of the material. In particular, the NFPF / CA-15% prepared in Example 2 has the most uniform distribution of sodium ferric fluorophosphate particles. The smaller particle size can provide more active sites for the electrochemical reaction, shorten the sodium ion diffusion path, and thus improve the electrochemical performance. The defect-rich carbon layer is evenly coated on the surface of the sodium ferrous fluorophosphate, achieving rapid migration of sodium ions and facilitating improved conductivity.

[0032] The specific surface areas of the positive electrode materials of the comparative example and Examples 1-3 were tested using the BET method. The results are shown in Table 1.

[0033] Table 1 Specific surface area of ​​positive electrode materials

[0034] The results in Table 1 show that the introduction of cellulose acetate significantly increases the specific surface area of ​​the sodium ferric fluorophosphate material, with the surface area first increasing and then decreasing as the cellulose acetate content increases from 10% to 20%. A larger specific surface area is beneficial in providing more active sites for electrochemical reactions.

[0035] The positive electrode material to be tested was mixed with Ketjen black and polyvinylidene fluoride in a mass ratio of 7:2:1, and then added to N-methylpyrrolidone and mixed evenly to obtain a positive electrode slurry. The positive electrode slurry was coated on aluminum foil and transferred to a vacuum drying oven to dry for 12 hours to obtain a sodium ion battery positive electrode. The impedance of different sodium ion battery positive electrodes was tested using the AC impedance method. The results are as follows: Figure 3 As shown in Figure 2, the diameter of the semicircle of the curve can reflect the charge transfer resistance of the electrochemical reaction. It can be seen that the NFPF / CA-15% of Example 2 has the smallest charge transfer resistance and the best electrochemical performance. Different sodium ion battery positive electrodes were tested at a potential of 1.75V-4.0V at a rate of 0.1mV·s -1 The cyclic voltammetry curve was tested at a scan rate of . Figure 4a-4d It can be seen that after the introduction of the carbon source cellulose acetate, the redox peak of the positive electrode of the sodium ion battery becomes sharp and the current increases significantly. The NFPF / CA-15% of Example 2 has the highest redox peak.

[0036] Different sodium ion battery positive electrodes were assembled into batteries in the order of negative electrode shell, counter electrode sodium sheet, diaphragm, electrolyte, positive electrode material, gasket, shrapnel, and positive electrode shell, and the electrochemical performance of different batteries was tested at 0.1C. Figure 5a-5fIt can be seen that the battery constructed in Comparative Example 1, which does not introduce any carbon source, has the lowest specific capacity; the specific capacity of the batteries constructed in Comparative Examples 2 and 3, which use carbon nanotubes and graphene as carbon sources, has improved, but not significantly. In addition, the specific capacity of the batteries in Examples 1-3, which use cellulose acetate as the carbon source, has increased significantly, especially the NFPF / CA-15% in Example 2, which has a specific capacity of up to 122.9 mAh·g at 0.1C. -1 These results indicate that using cellulose acetate as a carbon source in battery applications is not only cheaper to produce but also can build sodium-ion batteries with better performance compared to traditional carbon sources such as graphene and carbon nanotubes. Figure 1 The peak intensity of the embodiment in the XRD diagram is obviously weaker than that of the comparative example, and it can be clearly observed that the peaks at certain locations are lower than those of the comparative example, such as the (200) and (104) crystal planes. The possible reason is that CA can effectively inhibit the growth of certain crystal planes of NFPF during the formation of carbon coating. CA carbon material acts as a physical isolation layer, which can reduce the direct contact of NFPF particles during high-temperature treatment and inhibit the agglomeration and abnormal growth of grains. This spatial limitation forces the grains to grow within a limited range, thereby effectively inhibiting the preferential growth of the crystal planes of the positive electrode material, thereby improving the structural stability and electrochemical performance of NFPF, greatly improving the electrical conductivity and ion diffusion rate of the raw materials, and significantly improving the cycle stability and rate performance of the NFPF positive electrode material, making it more suitable for large-scale commercial production of sodium iron fluorophosphate.

[0037] Figure 6 The rate performance diagrams of the positive electrode materials of the comparative example and Examples 1-3 are shown. It can be seen that the NFPF / CA-15% of Example 2 has the best rate performance. At 0.1C, the specific capacity can reach up to 122.9 mAh g -1 Specific capacity at 1C is 118 mAh g -1 Specific capacity at 10C is 104 mAh g -1 Specific capacity at 20C is 92mAh·g -1 Specific capacity at 30C is 83mAh·g -1 At a high rate of 40C, the specific capacity can still reach 74mAh·g -1 .

[0038] Figure 7a and Figure 7b As can be seen from the graph, the NFPF / CA-15% of Example 2 retains 87.1% and 83.1% of its capacity after 2000 cycles at 20C and 40C, respectively; and 89.3% of its capacity after 3000 cycles at 30C. These results demonstrate that the sodium fluoroferric phosphate cathode material prepared by the present invention has excellent rate performance.

[0039] In summary, the present 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 source is more extensive, and no pretreatment is required, the production cost is lower, and it is more suitable for large-scale production applications. The introduction of cellulose acetate in an appropriate proportion expands 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. The positive electrode material of the 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 use in power vehicles, large-scale power grid energy storage and other fields.

[0040] Finally, it should be noted that the above 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 aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a sodium fluoroferric phosphate positive electrode material, characterized in that: include, A sodium source, an iron source, a phosphorus source, a fluorine source, and a carbon source are mixed to obtain a precursor, wherein the carbon source is cellulose acetate; The precursor is heat-treated to obtain sodium iron fluorophosphate positive electrode material.

2. The method for preparing the sodium ferric fluoride phosphate cathode material according to claim 1, wherein: 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 the sodium fluoroferric phosphate cathode material according to claim 1, wherein: The mass of the carbon source accounts for 10%-20% of the total mass of the sodium source, the iron source, the phosphorus source and the fluorine source.

4. The method for preparing the sodium ferric fluoride phosphate cathode material according to claim 1, wherein: The precursor obtained by mixing a sodium source, an iron source, a phosphorus source, a fluorine source and a carbon source comprises: wet-ball-milling a sodium source, an iron source, a phosphorus source, a fluorine source, and a carbon source, and then drying the resultant to obtain a mixture; The mixture was ground after removing impurity gases, and then sieved with a 100-200 mesh sieve to obtain a precursor.

5. The method for preparing the sodium fluoroferric phosphate cathode material according to claim 4, wherein: The impurity gases in the mixture are removed by keeping the mixture at 250-450℃ for 4-6 hours.

6. The method for preparing the sodium fluoroferric phosphate cathode material according to any one of claims 1 to 5, characterized in that: The heat treatment is carried out at 450-650° C. for 8-12 hours.

7. A sodium fluoroferric phosphate positive electrode material, characterized in that The sodium ferric fluorophosphate positive electrode material is obtained by the preparation method of any one of claims 1 to 6.

8. Use of the sodium fluoroferric phosphate cathode material according to claim 7 in a sodium ion battery, characterized in that: include, Mixing a sodium ferric fluorophosphate cathode material, a conductive material, a binder, and a solvent to form a cathode slurry; The positive electrode slurry is coated on a conductive foil to obtain a sodium ion battery positive electrode, and then assembled into a sodium ion battery.

9. The use according to claim 8, characterized in that The mass ratio of the sodium fluoroferric phosphate positive electrode material, the conductive material and the adhesive is 7-8:1-2:

1.

10. A sodium ion battery, characterized in that: The invention comprises the sodium fluoroferric phosphate positive electrode material according to any one of claims 1 to 6.

Images