Preparation method of composite ferric sodium pyrophosphate material

Abstract

The invention discloses a preparation method of a composite ferric sodium pyrophosphate material, which comprises the following steps: S1, uniformly dispersing a sodium source, an iron source, a phosphorus source, a carbon source and a surfactant in a solvent according to a stoichiometric ratio to form a dispersion liquid; s2, sanding the dispersion liquid at the temperature T1, discharging, and controlling the discharging temperature of the slurry to be T2; wherein the temperatures T1 and T2 meet the following conditions: 20 DEG C < = T1 < = 40 DEG C, 20 DEG C < = T2 < = 40 DEG C, and T1 > T2; and S3, carrying out spray drying on the slurry obtained in the step S2, and sintering to obtain the composite ferric sodium pyrophosphate material. According to the preparation method, the problem of slurry agglomeration can be improved to a great extent, so that the composite ferric sodium pyrophosphate material with high quality and good electrochemical performance is obtained.

Description

Technical Field

[0001] This application belongs to the technical field of phosphate material preparation, and specifically relates to a preparation method of a composite sodium iron pyrophosphate phosphate material. Background Art

[0002] Sodium iron pyrophosphate phosphate (Na4Fe3(PO4)2P2O7, abbreviated as NFPP) is a polyanionic sodium-ion battery cathode material, which has advantages such as good structural stability, high reversible specific capacity (theoretical capacity is about 129 mAh / g), long cycle life, and high average working voltage (3.1 vs. Na + / Na), etc. At the same time, it also has the advantages of low cost, environmental friendliness, and rich reserves.

[0003] At present, there are various preparation methods for NFPP, including hydrothermal synthesis method, solid-phase synthesis method, secondary carbon coating process, etc. Among them, the solid-phase synthesis method is to uniformly mix the phosphorus source, iron source, sodium source, and carbon source by mechanical mixing means, and then obtain sodium iron pyrophosphate phosphate through sintering. This method has simple preparation steps and is easier to produce on a large scale. However, in the solid-phase synthesis method, the formation of a NaFePO4 heterophase without electrochemical activity often occurs. Although this problem can be avoided by adjusting the raw materials, due to the large specific surface area and high surface energy of some raw materials, they are very easy to agglomerate into large particles after mechanical mixing, which still has an adverse effect on the electrochemical performance of the finally prepared sodium iron pyrophosphate phosphate. Summary of the Invention

[0004] In view of this, the primary object of this application is to provide a preparation method of a composite sodium iron pyrophosphate phosphate material, which can greatly improve the problem of slurry agglomeration, so as to obtain a high-quality composite sodium iron pyrophosphate phosphate material with good electrochemical performance.

[0005] To achieve the above object, this application adopts the following technical solutions: One aspect of this application discloses a preparation method of a composite sodium iron pyrophosphate phosphate material, including the following steps: S1. Disperse the sodium source, iron source, phosphorus source, carbon source, and surfactant in a solvent according to the stoichiometric ratio to form a dispersion; S2. Grind the dispersion at a temperature T1 and then discharge it, and control the discharge temperature of the slurry to be T2; wherein, the temperatures T1 and T2 satisfy: 20°C ≤ T1 ≤ 40°C, 20°C ≤ T2 ≤ 40°C, and T1 > T2; S3. Spray-dry and sinter the slurry obtained in step S2 to obtain a composite sodium iron pyrophosphate phosphate material.

[0006] Another aspect of the present application discloses a sodium-ion battery, characterized in that it contains a composite sodium iron pyrophosphate phosphate material, and the composite sodium iron pyrophosphate phosphate material is prepared by the preparation method described above.

[0007] Advantages of the present application: In the present application, the surface energy of nanoparticles is inhibited by adding a small amount of surfactant in combination with temperature control, and the slurry dispersibility is improved, thereby effectively improving the electrochemical performance of the composite sodium iron pyrophosphate phosphate material. Compared with the method of only adding surfactant to improve the dispersibility of nanoparticles in the prior art, this method can more effectively inhibit the agglomeration of nanoparticles and improve the electrochemical performance of the composite sodium iron pyrophosphate phosphate material. Moreover, the preparation method of the present application does not introduce other impurities, so it will not affect the quality of the material, ensuring the high quality of the composite sodium iron pyrophosphate phosphate material.

[0008] The preparation method of the present application is simple and easy to operate, suitable for large-scale production. The preparation method of the present application does not require complex equipment and technology. Only by controlling the temperature and adding a small amount of surfactant, the agglomeration of nanoparticles can be effectively inhibited, and the electrochemical performance of the composite sodium iron pyrophosphate / carbon material can be improved.

[0009] Compared with the prior art, the composite sodium iron pyrophosphate phosphate material of the present application has higher quality and electrochemical performance, and can be widely applied to various fields such as high-performance batteries, supercapacitors, and fuel cells. Description of the Drawings

[0010] Figure 1 It is the SEM diagram of the composite sodium iron pyrophosphate phosphate material prepared in Example 1 of the present application.

[0011] Figure 2 It is the XRD diagram of the composite sodium iron pyrophosphate phosphate material prepared in Example 1, Comparative Example 1, and Comparative Example 4 of the present application.

[0012] Figure 3 It is the voltage specific capacity curve diagram of the button battery prepared from the composite sodium iron pyrophosphate phosphate material in Example 1, Comparative Example 1, and Comparative Example 4 of the present application. Detailed Embodiments

[0013] The embodiments of the present application will be clearly and completely described below. The technical solutions in the following described embodiments are exemplary and are only possible technical implementations of the present application, not all possible implementations. Those skilled in the art can fully combine the embodiments of the present application and obtain other embodiments without creative work, and these embodiments are also within the protection scope of the present application.

[0014] The first aspect of the present application discloses a preparation method of a composite sodium iron pyrophosphate phosphate material. In the present application, by controlling the temperature in combination with a surfactant process, the dispersibility of each component in the slurry is effectively improved, the agglomeration of nanoparticles is inhibited, and the electrochemical performance of the composite sodium iron pyrophosphate phosphate material is improved.

[0015] In the present application, the preparation method of the composite sodium iron pyrophosphate phosphate material mainly comprises the following steps: S1. Dispersing a sodium source, an iron source, a phosphorus source, a carbon source and a surfactant uniformly in a solvent according to a stoichiometric ratio to form a dispersion liquid.

[0016] In this step, dispersing the sodium source, the iron source, the phosphorus source, the carbon source and the surfactant uniformly in the solvent to form a dispersion liquid is a conventional process in the art. Among them, the sodium source, the iron source, the phosphorus source and the carbon source can all adopt the types conventionally used in the art for preparing NFPP without special limitations.

[0017] In some examples, the sodium source is at least one of sodium acetate, sodium carbonate, sodium citrate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium phosphate, sodium carbonate, sodium nitrate, sodium oxalate, sodium acetate, sodium sulfate, sodium hydroxide, sodium formate, sodium citrate, sodium pyrophosphate, sodium dihydrogen pyrophosphate, sodium chloride, etc., but is not limited thereto.

[0018] In some examples, the iron source is at least one of iron powder, ferrous oxalate, magnetite, iron oxide, ferrous oxide, iron phosphate dihydrate, iron pyrophosphate, etc., but is not limited thereto. Preferably, as an example, the iron source is iron phosphate dihydrate. By selecting the iron source, the generation of impurity phases in the composite sodium iron pyrophosphate phosphate material can be significantly avoided, and the electrical properties of the material can be improved.

[0019] In some examples, the phosphorus source is at least one of phosphoric acid, phosphate, pyrophosphate. Among them, the phosphate can be at least one of sodium dihydrogen phosphate, ammonium hydrogen phosphate, ammonium dihydrogen phosphate, sodium phosphate, iron phosphate dihydrate, etc., but is not limited thereto. The pyrophosphate can be at least one of pyrophosphoric acid, iron pyrophosphate, sodium pyrophosphate, etc., but is not limited thereto.

[0020] In some examples, the carbon source is at least one of vaseline, oxalic acid, sucrose, corn starch, polyethylene glycol, glucose, ascorbic acid, citric acid, malic acid, maltose, cyclodextrin, activated carbon, carbon nanotube, graphene.

[0021] In this application, by introducing a surfactant, the dispersion of particles in the slurry is promoted and the agglomeration of particles in the slurry is inhibited. The surfactant added in this application can be selected accordingly based on actual needs. In some examples, the surfactant is stearic acid. Among them, the dosage of the surfactant can be selected based on actual needs or determined by experimental methods, and those skilled in the art have such capabilities. In some examples, based on the mass of the sodium ferric pyrophosphate composite material, the mass ratio of the surfactant is 0.05% - 0.2%, for example, it can be any value among 0.05%, 0.08%, 0.1%, 0.12%, 0.15%, 0.17%, 0.2% or the range value between any two of them.

[0022] In some examples, the solvent is of a conventional type in the art. For example, it can be water or ethanol, without any special limitations.

[0023] S2. The dispersion liquid is subjected to sand grinding at a temperature T1 and then discharged, and the discharge temperature of the slurry is controlled to be T2; wherein, the temperatures T1 and T2 satisfy: 20°C ≤ T1 ≤ 40°C, 20°C ≤ T2 ≤ 40°C, and T1 > T2. Preferably, 25°C ≤ T1 ≤ 35°C, 20°C ≤ T2 ≤ 30°C; more preferably, T1 is 25°C and T2 is 20°C.

[0024] In this application, by controlling the slurry during sand grinding, the slurry is always maintained at a constant temperature during the sand grinding process, avoiding the volatilization of the solvent or the decrease in solubility caused by temperature fluctuations (such as increase or decrease), resulting in a reduction in the effective dispersion medium of the particles in the slurry and an increase in the inter-particle force, which may cause agglomeration; by controlling the temperature during sand grinding, the dispersibility and uniformity of the slurry are improved, and the agglomeration of the slurry is greatly avoided. At the same time, when discharging, the temperature of the slurry is controlled to decrease, maintaining the stability of the solvent, reducing the inter-particle attraction, and keeping the slurry at an appropriate viscosity to inhibit the agglomeration of particles, thereby ensuring the electrical properties of the subsequent prepared material.

[0025] In this application, the discharge temperature can be achieved through an external temperature control circulation device. For example, by externally connecting an external circulation machine to a jacketed flask to provide circulating cooling water for circulating cooling, but it is not limited thereto.

[0026] In this application, the solid content of the slurry after sand grinding is 20wt% - 40wt%. The solid content of the slurry needs to be maintained within an appropriate range. Too low will result in low production of the material, while too high will clog the equipment and affect the operation of the equipment.

[0027] Among them, there are no special requirements for the specific sanding method, which can be any one of disk type, rod pin type, and turbine type. The rotation speed, time, etc. of sanding can be determined through experiments. In some examples, the sanding time is 1 - 5 h, and the rotation speed is 500 - 2000 rpm. Among them, the particle size of the slurry after sanding is controlled within 0.1 - 1 μm, preferably 0.5 μm. By controlling the particle size of the slurry after sanding, the electrical properties of the subsequent prepared material can be ensured. If the particle size is too small, the compaction will be too low, resulting in poor electrical properties of the material.

[0028] S3. Spray dry and then sinter the slurry obtained in step S2 to obtain a composite sodium iron pyrophosphate phosphate material.

[0029] Among them, spray drying is a conventional drying process for NFPP preparation in the art. Through spray drying, the sphericity, dispersibility, and uniformity of the slurry can be further improved. In some examples, the inlet air temperature of the spray drying is 200 - 300 °C, and the outlet air temperature is 100 - 120 °C.

[0030] In this application, the composite sodium iron pyrophosphate phosphate material is also pre-sintered before sintering. Through pre-sintering, the composite sodium iron pyrophosphate phosphate can quickly form a phase, which not only facilitates subsequent sintering, but also can avoid the generation of impurity phases, improve the purity of the material, and improve the electrical properties of the material.

[0031] In some examples, the specific sintering process is as follows: pre-sinter at 200 - 300 °C for 4 - 6 h, and then sinter at 400 - 600 °C for 8 - 12 h. Among them, the heating rate of the sintering is 2 - 4 °C / min; the atmosphere of the sintering is one of nitrogen, argon, a mixture of H2 and N2, and in the mixture of H2 and N2, the volume fraction of H2 is 3% - 7%.

[0032] The second aspect of this application discloses a sodium-ion battery containing a composite sodium iron pyrophosphate phosphate material, and the composite sodium iron pyrophosphate phosphate material is prepared by the preparation method described in the first aspect of this application.

[0033] It can be understood that the sodium-ion battery also includes materials or components such as a conductive agent, a binder, a negative electrode, a separator, and an electrolyte, etc., and there are no special restrictions on them, and conventional types in the art can be used.

[0034] The following are specific examples of this application. It should be noted that the following specific examples are only for illustrative purposes and do not limit the scope of this application in any way.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs. The terms used in the specification of this application herein are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0036] In addition, unless otherwise specified, the methods without specific conditions or steps recorded are all conventional methods, and the reagents and materials used can be obtained from commercial channels.

[0037] Example 1 A preparation method of a composite sodium iron pyrophosphate phosphate material is provided in this example, and the specific steps are as follows: S1. Weigh the sodium source sodium carbonate, the iron source iron phosphate dihydrate, the phosphorus source sodium dihydrogen phosphate, the carbon source glucose, and the surfactant stearic acid (0.1%) according to the stoichiometric ratio, add them to water and disperse evenly to obtain an NFPP dispersion.

[0038] S2. Place the dispersion in a sand mill for sanding. The temperature of the sand mill is controlled at 25 °C, denoted as T1, and sanded at 2000 rpm for 2 hours to obtain an NFPP slurry. Then, discharge the slurry and control the temperature of the slurry at 20 °C with a temperature-controlled circulating machine, denoted as T2.

[0039] S3. Spray-dry the slurry obtained in step S2 at a uniform feeding rate of 10 mL / min (inlet air temperature 260 °C, outlet air temperature 105 °C) to dry the moisture of the slurry and obtain a powder.

[0040] S4. Under the protection of nitrogen, heat the powder material obtained in step S3 to 250 °C at a heating rate of 2 °C / min for pre-sintering for 5 h, then heat it to 500 °C for sintering for 10 h, and finally cool it naturally to room temperature to obtain the NFPP composite material.

[0041] Comparative Example 1 A preparation method of a composite sodium iron pyrophosphate phosphate material is disclosed in this comparative example. It adopts the same implementation method as in Example 1, and the only difference is that: the temperature of the slurry is not controlled by a temperature-controlled circulating machine, that is, directly spray-dry after sanding (i.e., drying at room temperature, and the room temperature at that time was 37 °C). Other process steps and parameter conditions are the same as those in Example 1.

[0042] Comparative Example 2 A preparation method of a composite sodium iron pyrophosphate phosphate material is disclosed in this comparative example. It adopts the same implementation method as in Example 1, and the only difference is that: the addition amount of the surfactant is 0%. Other process steps and parameter conditions are the same as those in Example 1.

[0043] Comparative Example 3 This comparative example discloses a preparation method of a compound sodium iron pyrophosphate phosphate material, which adopts the same implementation manner as in Example 1, except that: the surfactant is dodecyl trimethyl ammonium bromide. Other process steps and parameter conditions are the same as those in Example 1.

[0044] Comparative Example 4 This comparative example discloses a preparation method of a compound sodium iron pyrophosphate phosphate material, which adopts the same implementation manner as in Example 1, except that: the iron source used is anhydrous iron phosphate (without crystal water). Other process steps and parameter conditions are the same as those in Example 1.

[0045] Example 2 This example discloses a preparation method of a compound sodium iron pyrophosphate phosphate material, which adopts the same implementation manner as in Example 1, except that: the temperature of T1 is 30 °C and the temperature of T2 is 25 °C. Other process steps and parameter conditions are the same as those in Example 1.

[0046] Example 3 This example discloses a preparation method of a compound sodium iron pyrophosphate phosphate material, which adopts the same implementation manner as in Example 1, except that: the temperature of T1 is 35 °C and the temperature of T2 is 30 °C. Other process steps and parameter conditions are the same as those in Example 1.

[0047] Example 4 This example discloses a preparation method of a compound sodium iron pyrophosphate phosphate material, which adopts the same implementation manner as in Example 1, except that: the sodium source used is sodium nitrate. Other process steps and parameter conditions are the same as those in Example 1.

[0048] Example 5 This example discloses a preparation method of a compound sodium iron pyrophosphate phosphate material, which adopts the same implementation manner as in Example 1, except that: the phosphorus source used is phosphoric acid. Other process steps and parameter conditions are the same as those in Example 1.

[0049] Example 6 This example discloses a preparation method of a compound sodium iron pyrophosphate phosphate material, which adopts the same implementation manner as in Example 1, except that: the carbon source used is oxalic acid. Other process steps and parameter conditions are the same as those in Example 1.

[0050] Example 7 This example discloses a preparation method of a compound sodium iron pyrophosphate phosphate material, which adopts the same implementation manner as in Example 1, except that: the addition amount of the surfactant is 0.05%. Other process steps and parameter conditions are the same as those in Example 1.

[0051] Example 8 In this embodiment, a preparation method of a complex sodium iron pyrophosphate phosphate material is disclosed. It adopts the same implementation manner as in Example 1, with the only difference being that the addition amount of the surfactant is 0.2%. All other process steps and parameter conditions are the same as those in Example 1.

[0052] Performance Test 1. Granularity tests were carried out on the slurries of the examples and comparative examples (the sampling time was when the temperature-controlled circulating machine was kept warm for 0.5 h). The results are shown in Table 1.

[0053] Table 1 Comparison of the particle sizes of the slurries of the examples and comparative examples

[0054] 2. Assembly and testing of CR2025 button cells: The complex sodium iron pyrophosphate phosphate materials, acetylene black, and polyvinylidene fluoride (PVDF) prepared in the comparative examples and examples were dissolved in N-methylpyrrolidone (NMP) in a mass ratio of 8:1:1 to prepare a uniform slurry, which was then coated on aluminum foil. After drying, the aluminum foil loaded with the active material was cut into small round pieces with a diameter of 11 mm using a cutting machine and used as the positive electrode. A sodium metal sheet was used as the negative electrode of the half-cell, Celgard 2300 was used as the separator, and a sodium perchlorate solution was used as the electrolyte. A CR2025 button cell was assembled in an argon glove box.

[0055] The assembled CR2025 button cells were subjected to constant current charge and discharge tests at different current densities using a CT2001A LAND battery tester. The 1C current density was defined as 129 mAh / g, the charge and discharge voltage range was 2.0 V to 3.6 V, and the test temperature was 25°C. The test results are shown in Table 2.

[0056] Table 2 Performance test results of CR2025 button cells

[0057] Table 1 and Table 2 respectively show the comparison of the particle sizes of the complex sodium iron phosphate slurries prepared by different methods and the comparison of the electrochemical properties of the sintered materials of complex sodium iron pyrophosphate phosphate. It can be seen that by controlling the slurry temperature and adding a specific surfactant simultaneously, the particle size of the slurry can be effectively controlled while maintaining excellent electrochemical properties.

[0058] It can be seen from Comparative Example 1 that if the slurry temperature is not controlled, the particle size increases to varying degrees, and the electrochemical performance also decreases. By comparing Comparative Example 2 and Comparative Example 3, it can be seen that if the surfactant is not added, the particle size will change and the electrochemical performance will decrease. In addition, although the change in the particle size of the slurry is not obvious when adding dodecyl trimethyl ammonium bromide as the surfactant, the electrochemical performance decreases significantly, indicating that the introduction of quaternary ammonium salts of organic matter into the system is unfavorable for the electrochemical performance. Therefore, stearic acid is preferably used as the surfactant in this application.

[0059] The above results show that the slurry agglomeration control of this application is achieved by specific surfactants and temperature control, and has significant effects.

[0060] Furthermore, Figure 1 FIG. is the SEM image of the composite sodium iron pyrophosphate phosphate material prepared in Example 1. It can be seen from the figure that the obtained sintered materials are basically spherical, the distribution of large and small particles is relatively uniform, the particle size is about between 5 and 15 μm, and the carbon coating effect is good. This is due to the good avoidance of slurry agglomeration and the control of the slurry particle size in the slurry preparation stage of this application.

[0061] Figure 2 FIG. is the XRD patterns of Example 1, Comparative Example 1 and Comparative Example 4. It can be seen that there is no impurity phase of NaFePO4 in the sample prepared with FePO4·2H2O in Example 1 (NaFePO4 prepared by the conventional method has no electrochemical activity), indicating that the high activity of iron phosphate dihydrate can inhibit the generation of impurity phases, and agglomeration will not contribute to the generation of NaFePO4 impurity phases. However, due to the large specific surface area of iron phosphate dihydrate, it is easy to polymerize into large particles after sanding, which easily leads to a decrease in electrochemical performance. However, by using the preparation method in this application, the agglomeration problem caused by iron phosphate dihydrate is well avoided, not only no impurity phase is generated, but also the agglomeration and particle size of the slurry are well controlled, and a material with excellent electrical performance is obtained.

[0062] Figure 3Charge-discharge curve comparison of Example 1, Comparative Example 1 and Comparative Example 4. It can be seen that the 0.2C discharge capacity of the battery prepared with the sodium iron pyrophosphate phosphate composite material in Example 1 is 103.89 mAh / g. Compared with Comparative Example 1, the capacity is significantly improved, and the maximum particle size in the particle size characterization in Table 1 increases from 0.901 μm to 2.700 μm, indicating that if temperature control is not carried out, obvious slurry agglomeration will occur, and it can be seen from Table 1 that slurry agglomeration and electrochemical performance show an obvious negative correlation; the 0.2C discharge capacity of the battery prepared with the sodium iron pyrophosphate phosphate composite material in Comparative Example 4 is 90.14 mAh / g, and the maximum particle size is 0.923 μm, indicating that slurry particle size or the generation of impurity phases will affect the results of the electrochemical performance of the material. The preparation method in the present application can well avoid the generation of impurity phases and prepare a sodium iron pyrophosphate phosphate composite material with good electrochemical performance.

[0063] It should be noted that the present application is not limited to the above embodiments. The above embodiments are only examples, and embodiments having the same composition and the same effect as the technical idea within the technical solution scope of the present application are included in the technical scope of the present application. In addition, within the scope not departing from the gist of the present application, various modifications that can be conceived by those skilled in the art to the embodiments and other ways constructed by combining some constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for preparing a composite phosphate sodium iron pyrophosphate material, characterized in that: The following steps are involved: S1. Dispersing a sodium source, an iron source, a phosphorus source, a carbon source and a surfactant in a solvent in a stoichiometric ratio to form a dispersion; S2, discharging the dispersion after sand grinding at a temperature of T1, and controlling the discharging temperature of the slurry to be T2; wherein the temperatures T1 and T2 satisfy: 20°C≤T1≤40°C, 20°C≤T2≤40°C, and T1>T2; S3. The slurry obtained in step S2 is spray-dried and sintered to obtain a composite sodium iron phosphate pyrophosphate material.

2. The method for preparing the composite phosphate sodium iron pyrophosphate material according to claim 1, characterized in that: In step S1, the sodium source is at least one of sodium acetate, sodium carbonate, sodium citrate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium phosphate, sodium carbonate, sodium nitrate, sodium oxalate, sodium acetate, sodium sulfate, sodium hydroxide, sodium formate, sodium citrate, sodium pyrophosphate, sodium dihydrogen pyrophosphate, and sodium chloride; And / or, the iron source is at least one of iron powder, ferrous oxalate, ferroferric oxide, ferrous oxide, ferrous oxide, ferrous phosphate dihydrate, and ferric pyrophosphate; And / or, the phosphorus source is at least one of phosphoric acid, phosphate, and pyrophosphate; the phosphate is at least one of sodium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, sodium phosphate, and ferric phosphate dihydrate; the pyrophosphate is at least one of pyrophosphoric acid, ferric pyrophosphate, and sodium pyrophosphate; And / or, the carbon source is at least one of vaseline, oxalic acid, sucrose, corn starch, polyethylene glycol, glucose, ascorbic acid, citric acid, malic acid, maltose, cyclodextrin, activated carbon, carbon nanotubes, and graphene; And / or, the solvent is water or ethanol.

3. The method for preparing the composite phosphate sodium iron pyrophosphate material according to claim 1, characterized in that: In step S1, the surfactant is stearic acid.

4. The method for preparing the composite phosphate sodium iron pyrophosphate material according to claim 1 or 3, characterized in that: In step S1, based on the mass of the sodium ferric pyrophosphate material, the mass proportion of the surfactant is 0.05% to 0.2%.

5. The method for preparing the composite phosphate sodium iron pyrophosphate material according to claim 1, characterized in that: In step S2, the discharge temperature of the slurry is achieved by an external temperature control circulation device.

6. The method for preparing the composite phosphate sodium iron pyrophosphate material according to claim 1, characterized in that: In step S2, the solid content of the slurry after sand grinding is 20wt%-40wt%.

7. The method for preparing the composite phosphate sodium iron pyrophosphate material according to claim 1, characterized in that: In step S2, the sand grinding method includes one of disc type, pin type and turbine type, the sand grinding time is 1-5 hours, the rotation speed is 500-2000 rpm; the particle size of the slurry after sand grinding is controlled to be 0.1-1 μm.

8. The method for preparing the composite phosphate sodium iron pyrophosphate material according to claim 1, characterized in that: In step S3, the inlet air temperature of the spray drying is 200-300°C, and the outlet air temperature is 100-120°C.

9. The method for preparing the composite phosphate sodium iron pyrophosphate material according to claim 1, characterized in that: In step S3, the sintering process is: pre-sintering at 200-300°C for 4-6 hours, and then sintering at 400-600°C for 8-12 hours; And / or, the heating rate of the sintering is 2-4°C / min; And / or, the sintering atmosphere is one of nitrogen, argon, H2 and N2 mixed gas, and the volume proportion of H2 in the H2 and N2 mixed gas is 3-7%.

10. A sodium ion battery, characterized in that: The invention contains a composite phosphate sodium iron pyrophosphate material, wherein the composite phosphate sodium iron pyrophosphate material is prepared by the preparation method according to any one of claims 1 to 9.

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