A preparation method of composite sodium iron pyrophosphate material

Abstract

The present application discloses a method for preparing a composite sodium ferric pyrophosphate material, comprising 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; S2, sand-milling the dispersion at a temperature T1 and discharging the slurry, controlling the discharge temperature of the slurry to T2; wherein temperatures T1 and T2 satisfy the following conditions: 20°C ≤ T1 ≤ 40°C, 20°C ≤ T2 ≤ 40°C, and T1 > T2; S3, spray-drying the slurry obtained in step S2 and sintering it to obtain the composite sodium ferric pyrophosphate material. This preparation method can greatly improve the problem of slurry agglomeration, thereby obtaining a high-quality composite sodium ferric pyrophosphate material with excellent electrochemical performance.

Description

Technical Field

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

[0002] Sodium iron pyrophosphate (Na4Fe3(PO4)2P2O7, abbreviated as NFPP) is a polyanion type sodium ion battery cathode material with good structural stability, high reversible specific capacity (theoretical capacity of about 129mAh / g), long cycle life, and high average operating voltage (3.1 vs. Na + / Na), and also has the advantages of low cost, environmental friendliness, and abundant reserves.

[0003] At present, there are various methods for preparing NFPP, including hydrothermal synthesis, solid-phase synthesis, and secondary carbon coating process. Among them, the solid-phase synthesis method is to mix the phosphorus source, iron source, sodium source, and carbon source uniformly by mechanical mixing, and then obtain sodium iron pyrophosphate by sintering. This method has simple preparation steps and is easier to produce on a large scale. However, the solid-phase synthesis method is often accompanied by the formation of NaFePO4 impurities with no electrochemical activity. Although this problem can be circumvented 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 properties of the final sodium iron pyrophosphate. Summary of the Invention

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

[0005] In order to achieve the above objectives, this application adopts the following technical solutions:

[0006] One aspect of the present application discloses a method for preparing a composite sodium iron pyrophosphate material, comprising the following steps:

[0007] 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;

[0008] S2, sand-milling the dispersion at a temperature of T1 and discharging the slurry, and controlling 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;

[0009] S3. The slurry obtained in step S2 is spray-dried and sintered to obtain a composite sodium iron pyrophosphate material.

[0010] Another aspect of the present application discloses a sodium ion battery, characterized in that it contains a composite sodium iron phosphate pyrophosphate material, and the composite sodium iron phosphate pyrophosphate material is prepared using the preparation method described above.

[0011] Beneficial effects of this application:

[0012] The present application suppresses the surface energy of nanoparticles by adding a small amount of surfactant in combination with temperature control, thereby improving the dispersibility of the slurry and effectively improving the electrochemical performance of the composite sodium ferric phosphate pyrophosphate material. Compared with the method of improving the dispersibility of nanoparticles by only adding surfactants in the prior art, this method can more effectively suppress the agglomeration of nanoparticles and improve the electrochemical performance of the composite sodium ferric phosphate pyrophosphate material. In addition, the preparation method of the present application does not introduce other impurities, so it does not affect the quality of the material, ensuring the high quality of the composite sodium ferric phosphate pyrophosphate material.

[0013] The preparation method of the present application is simple, easy to operate, and suitable for large-scale production. The preparation method of the present application does not require complex equipment and technology. It only requires temperature control and the addition of a small amount of surfactant to effectively inhibit the agglomeration of nanoparticles and improve the electrochemical performance of the composite sodium iron pyrophosphate / carbon material.

[0014] Compared with the existing technology, the composite sodium iron phosphate pyrophosphate material of the present application has higher quality and electrochemical performance, and can be widely used in various high-performance batteries, supercapacitors, fuel cells and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is an SEM image of the composite sodium iron pyrophosphate material prepared in Example 1 of the present application.

[0016] Figure 2 These are the XRD patterns of the composite sodium iron pyrophosphate materials prepared in Example 1, Comparative Example 1, and Comparative Example 4 of the present application.

[0017] Figure 3 This is a graph showing the buckling voltage-to-capacity curve of the composite sodium iron phosphate pyrophosphate material prepared in Example 1, Comparative Example 1, and Comparative Example 4 of the present application. DETAILED DESCRIPTION

[0018] The following will clearly and completely describe the embodiments of the present application. The technical solutions in the embodiments described below 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 to obtain other embodiments without creative work, and these embodiments are also within the scope of protection of the present application.

[0019] The first aspect of the present application discloses a method for preparing a composite sodium iron phosphate pyrophosphate material. In the present application, the dispersibility of each component in the slurry is effectively improved, the agglomeration of nanoparticles is suppressed, and the electrochemical properties of the composite sodium iron phosphate pyrophosphate material are improved through a temperature control and surfactant process.

[0020] In this application, the preparation method of the composite phosphate sodium iron pyrophosphate material mainly comprises the following steps:

[0021] 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.

[0022] In this step, the sodium source, iron source, phosphorus source, carbon source and surfactant are evenly dispersed in a solvent to form a dispersion, which is a conventional process in the art. Among them, the sodium source, iron source, phosphorus source and carbon source can all be the types conventionally used for preparing NFPP in the art without special restrictions.

[0023] 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, and sodium chloride, but is not limited thereto.

[0024] In some examples, the iron source is at least one of iron powder, ferrous oxalate, ferrosoferric oxide, ferrous oxide, ferrous oxide, ferric phosphate dihydrate, and ferric pyrophosphate, but is not limited thereto. Preferably, as an example, the iron source is ferric phosphate dihydrate. By selecting the iron source, the generation of impurities in the composite sodium ferric pyrophosphate material can be significantly avoided, thereby improving the electrical properties of the material.

[0025] In some examples, the phosphorus source is at least one of phosphoric acid, a phosphate, and a pyrophosphate. The phosphate may be at least one of sodium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, sodium phosphate, and ferric phosphate dihydrate, but is not limited thereto. The pyrophosphate may be at least one of pyrophosphoric acid, ferric pyrophosphate, and sodium pyrophosphate, but is not limited thereto.

[0026] In some examples, the carbon source is at least one of petrolatum, oxalic acid, sucrose, corn starch, polyethylene glycol, glucose, ascorbic acid, citric acid, malic acid, maltose, cyclodextrin, activated carbon, carbon nanotubes, and graphene.

[0027] In the present application, by introducing a surfactant, the dispersion of particles in the slurry is promoted and the agglomeration of particles in the slurry is suppressed. The surfactant added in the present application can be selected accordingly based on actual needs. In some examples, the surfactant is stearic acid. Wherein, the amount of the surfactant can be selected based on actual needs or determined by an experimental method, and those skilled in the art have such ability. In some examples, the mass of the composite phosphate sodium iron pyrophosphate material is measured as a reference, and the mass proportion of the surfactant is 0.05~0.2%, for example, it can be any value in 0.05%, 0.08%, 0.1%, 0.12%, 0.15%, 0.17%, 0.2% or any range value between the two.

[0028] In some examples, the solvent is a conventional solvent in the art, such as water or ethanol, without any particular limitation.

[0029] S2. Sand-mill the dispersion at temperature T1 and then discharge the slurry, controlling the discharge temperature of the slurry to T2; wherein temperatures T1 and T2 satisfy the following conditions: 20°C ≤ T1 ≤ 40°C, 20°C ≤ T2 ≤ 40°C, and T1 > T2. Preferably, 25°C ≤ T1 ≤ 35°C, and 20°C ≤ T2 ≤ 30°C; more preferably, T1 is 25°C and T2 is 20°C.

[0030] In this application, the slurry is controlled during sand milling to maintain a constant temperature throughout the process. This prevents temperature fluctuations (such as increases or decreases) that could cause solvent volatilization or reduced solubility, reducing the effective dispersion medium for the particles in the slurry and increasing inter-particle forces that can lead to agglomeration. Temperature control during sand milling improves the dispersibility and uniformity of the slurry, significantly preventing agglomeration. Simultaneously, the slurry is cooled during discharge to maintain solvent stability, reduce inter-particle attraction, and maintain an appropriate viscosity, inhibiting particle agglomeration and thus ensuring the electrical properties of the subsequently prepared material.

[0031] In the present application, the discharge temperature can be achieved by an external temperature control circulation device, for example, by connecting an external circulation machine to the jacketed flask to provide circulating cooling water for circulating cooling, but it is not limited thereto.

[0032] In this application, the solid content of the slurry after sand grinding is between 20wt% and 40wt%. The solid content of the slurry must be maintained within an appropriate range. Too low a solid content will result in low material yield, while too high a solid content will clog the equipment and affect its operation.

[0033] There are no special requirements for the specific sanding method, and it can be any of the disc type, pin type, and turbine type. The speed and time of sanding can be determined by experiments. In some examples, the sanding time is 1~5h and the speed is 500~2000rpm. The particle size of the slurry after sanding is controlled at 0.1~1μm, preferably 0.5μm. By controlling the particle size of the slurry after sanding, the electrical properties of the subsequent prepared material are guaranteed. If the particle size is too small, the compaction will be too low, resulting in poor electrical properties of the material.

[0034] S3. The slurry obtained in step S2 is spray-dried and sintered to obtain a composite sodium iron pyrophosphate material.

[0035] Spray drying is a common drying process for NFPP production in the art. Spray drying can further improve the sphericity, dispersion, and uniformity of the slurry. In some examples, the inlet air temperature for spray drying is 200-300°C, and the outlet air temperature is 100-120°C.

[0036] In this application, the composite sodium iron phosphate pyrophosphate material is pre-sintered before sintering. The pre-sintering allows the composite sodium iron phosphate pyrophosphate to quickly form a phase, which not only facilitates subsequent sintering, but also avoids the formation of impurity phases, improves the purity of the material, and improves the electrical properties of the material.

[0037] In some examples, the specific sintering process is: pre-sintering at 200-300°C for 4-6 hours, followed by sintering at 400-600°C for 8-12 hours. The sintering temperature is increased at a rate of 2-4°C / min, and the sintering atmosphere is one of nitrogen, argon, and a mixture of H2 and N2, with the volume percentage of H2 in the H2 and N2 mixture being 3%-7%.

[0038] The second aspect of the present application discloses a sodium ion battery containing a composite sodium iron phosphate pyrophosphate material, wherein the composite sodium iron phosphate pyrophosphate material is prepared using the preparation method described in the first aspect of the present application.

[0039] It is understandable that the sodium ion battery further includes materials or components such as a conductive agent, a binder, a negative electrode, a separator and an electrolyte, and there are no special restrictions on them, and conventional types in the art can be used.

[0040] The following are specific embodiments of the present application. It should be noted that the following specific embodiments are only for illustrative purposes and do not limit the scope of the present application in any way.

[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0042] In addition, unless otherwise specified, methods without specific conditions or steps are conventional methods, and the reagents and materials used are all commercially available.

[0043] Example 1

[0044] This embodiment provides a method for preparing a composite phosphate sodium iron pyrophosphate material, and the specific steps are as follows:

[0045] S1. Sodium carbonate (sodium source), ferric phosphate dihydrate (iron source), sodium dihydrogen phosphate (phosphorus source), glucose (carbon source), and stearic acid (0.1%) (surfactant) were weighed in stoichiometric ratios and added to water and dispersed evenly to obtain a NFPP dispersion.

[0046] S2. The dispersion was placed in a sand mill for sand grinding. The temperature of the sand mill was controlled at 25°C, which was recorded as T1. The dispersion was sand milled at 2000 rpm for 2 hours to obtain NFPP slurry. The slurry was then discharged and the temperature was controlled at 20°C by a controllable temperature circulation machine, which was recorded as T2.

[0047] S3. The slurry obtained in step S2 is fed to a spray dryer at a uniform speed of 10 mL / min and spray-dried (inlet air temperature 260°C, outlet air temperature 105°C) to dry the slurry to obtain a powder.

[0048] S4. Under nitrogen protection, the powder material obtained in step S3 is heated to 250° C. at a heating rate of 2° C. / min and pre-sintered for 5 hours, then heated to 500° C. and sintered for 10 hours, and finally cooled naturally to room temperature to obtain the NFPP composite material.

[0049] Comparative Example 1

[0050] This comparative example discloses a method for preparing a composite sodium ferric pyrophosphate material. The method employs the same method as Example 1, differing only in that the slurry temperature is not controlled by a temperature-controlled circulator. In other words, spray drying is performed directly after sand milling (i.e., drying is performed at room temperature, which was 37°C). All other process steps and parameters are the same as those in Example 1.

[0051] Comparative Example 2

[0052] This comparative example discloses a method for preparing a composite sodium ferric pyrophosphate material, which is similar to that of Example 1, except that the amount of surfactant added is 0%. Other process steps and parameters are the same as those of Example 1.

[0053] Comparative Example 3

[0054] This comparative example discloses a method for preparing a composite sodium ferric pyrophosphate material, which is similar to that of Example 1, except that the surfactant is dodecyltrimethylammonium bromide. Other process steps and parameters are the same as those of Example 1.

[0055] Comparative Example 4

[0056] This comparative example discloses a method for preparing a composite sodium ferric pyrophosphate material, using the same method as Example 1, except that the iron source used is anhydrous ferric phosphate (free of crystal water). All other process steps and parameters are the same as those in Example 1.

[0057] Example 2

[0058] This example discloses a method for preparing a composite sodium iron pyrophosphate material, which is implemented in the same manner as in Example 1, with the only difference being that the temperature T1 is 30° C. and the temperature T2 is 25° C. The other process steps and parameter conditions are the same as in Example 1.

[0059] Example 3

[0060] This example discloses a method for preparing a composite sodium iron pyrophosphate material, which is implemented in the same manner as in Example 1, with the only difference being that the temperature T1 is 35° C. and the temperature T2 is 30° C. The other process steps and parameter conditions are the same as in Example 1.

[0061] Example 4

[0062] This example discloses a method for preparing a composite sodium ferric pyrophosphate material, which is implemented in the same manner as in Example 1, with the only difference being that sodium nitrate is used as the sodium source. Other process steps and parameter conditions are the same as in Example 1.

[0063] Example 5

[0064] This example discloses a method for preparing a composite phosphate sodium iron pyrophosphate material, which is implemented in the same manner as in Example 1, with the only difference being that phosphoric acid is used as the phosphorus source. Other process steps and parameter conditions are the same as in Example 1.

[0065] Example 6

[0066] This example discloses a method for preparing a composite sodium ferric pyrophosphate material, which is implemented in the same manner as in Example 1, with the only difference being that oxalic acid is used as the carbon source. Other process steps and parameter conditions are the same as in Example 1.

[0067] Example 7

[0068] This example discloses a method for preparing a composite sodium ferric pyrophosphate material, which uses the same method as Example 1, except that the amount of surfactant added is 0.05%. Other process steps and parameter conditions are the same as Example 1.

[0069] Example 8

[0070] This example discloses a method for preparing a composite sodium ferric pyrophosphate material, which is similar to that of Example 1, except that the amount of surfactant added is 0.2%. Other process steps and parameters are the same as those of Example 1.

[0071] Performance Testing

[0072] 1. The slurries of the examples and comparative examples (sampling time: 0.5 h in a temperature-controlled circulation machine) were subjected to particle size testing. The results are shown in Table 1.

[0073] Table 1 Comparison of slurry particle size between examples and comparative examples

[0074]

[0075] 2. Assembly and testing of CR2025 button batteries: The composite sodium iron phosphate material, acetylene black, and polyvinylidene fluoride (PVDF) prepared in the comparative example and the embodiment were dissolved in N-methylpyrrolidone (NMP) in a mass ratio of 8:1:1 to prepare a uniform slurry and coated on aluminum foil. After drying, the aluminum foil loaded with active material was cut into small discs with a diameter of 11 mm using a cutting machine as the positive electrode, a metal sodium sheet as the half-cell negative electrode, Celgard2300 as the diaphragm, and sodium perchlorate solution as the electrolyte. The CR2025 button batteries were assembled in an argon glove box.

[0076] The assembled CR2025 button cell batteries were tested using a CT2001A LAND battery tester at various current densities. A 1C current density is defined as 129 mAh / g, the charge and discharge voltage range is 2.0 V to 3.6 V, and the test temperature is 25°C. The test results are shown in Table 2.

[0077] Table 2 CR2025 button battery performance test results

[0078]

[0079] Tables 1 and 2 show the particle size comparison of composite sodium iron phosphate slurries prepared by different methods and the electrochemical performance comparison of composite sodium iron pyrophosphate sintered materials, respectively. It can be seen that by controlling the slurry temperature and adding specific surfactants, the slurry particle size can be effectively controlled while maintaining excellent electrochemical performance.

[0080] Comparative Example 1 shows that if the slurry temperature is not controlled, the particle size increases to varying degrees and the electrochemical performance also decreases. Comparative Examples 2 and 3 show that if no surfactant is added, the particle size changes and the electrochemical performance decreases. In addition, although the addition of the surfactant dodecyltrimethylammonium bromide does not significantly change the slurry particle size, the electrochemical performance decreases significantly, indicating that the introduction of quaternary ammonium salts into the system is detrimental to the electrochemical performance. Therefore, stearic acid is preferably used as a surfactant in this application.

[0081] The above results show that the present application achieves slurry agglomeration control by using specific surfactants and temperature control, and has a significant effect.

[0082] Further, Figure 1 This is an SEM image of the composite sodium iron phosphate pyrophosphate 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 approximately between 5 and 15 μm, and the carbon coating effect is good. This is due to the fact that the agglomeration of the slurry is well avoided and the particle size of the slurry is controlled during the slurry preparation stage in this application.

[0083] Figure 2 The XRD patterns of Example 1, Comparative Example 1 and Comparative Example 4 show that the sample prepared using FePO4·2H2O in Example 1 does not contain any NaFePO4 impurity phase (NaFePO4 prepared by the conventional method has no electrochemical activity), indicating that the high activity of ferric phosphate dihydrate can inhibit the formation of impurity phases, and does not contribute to the formation of NaFePO4 impurity phases after agglomeration. However, ferric phosphate dihydrate has a large specific surface area and is easily aggregated into large particles after sand grinding, which easily leads to a decrease in electrochemical performance. However, the preparation method in the present application avoids the agglomeration problem caused by ferric phosphate dihydrate, not only does no impurity phase occur, but also the agglomeration and particle size of the slurry are well controlled, thereby obtaining a material with excellent electrical properties.

[0084] Figure 3The charge and discharge curves of Example 1, Comparative Example 1 and Comparative Example 4 are compared. It can be seen that the 0.2C discharge capacity of the battery prepared from the composite sodium iron phosphate pyrophosphate material in Example 1 is 103.89 mAh / g, which is significantly improved compared with Comparative Example 1. The maximum particle size in the particle size characterization in Table 1 increases from 0.901 μm to 2.700 μm, indicating that if the temperature is not controlled, the slurry will agglomerate significantly, and it can be seen from Table 1 that the slurry agglomeration and electrochemical performance show a significant negative correlation. The 0.2C discharge capacity of the battery prepared from the composite sodium iron phosphate pyrophosphate material in Comparative Example 4 is 90.14 mAh / g, and the maximum particle size is 0.923 μm, indicating that the slurry particle size or the generation of impurities will affect the electrochemical performance of the material. The preparation method in this application can well avoid the generation of impurities and prepare a composite sodium iron phosphate pyrophosphate material with good electrochemical performance.

[0085] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the 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, wherein the iron source is ferric phosphate dihydrate and the surfactant is stearic acid; S2, sand-milling the dispersion at a temperature of T1 and discharging the slurry, and controlling 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. The slurry obtained in step S2 is spray-dried and sintered to obtain a composite sodium iron pyrophosphate material.

2. The method for preparing the composite phosphate sodium iron pyrophosphate material according to claim 1, wherein: 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 nitrate, sodium oxalate, sodium sulfate, sodium hydroxide, sodium formate, sodium pyrophosphate, sodium dihydrogen pyrophosphate, and sodium chloride; And / or, the phosphorus source is at least one of phosphoric acid, phosphate, pyrophosphate, 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 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, wherein 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%.

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

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

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

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

8. The method for preparing the composite phosphate sodium iron pyrophosphate material according to claim 1, wherein: 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 sintering heating rate 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%.

9. A sodium ion battery, characterized in that: The invention contains a composite sodium ferric phosphate pyrophosphate material, wherein the composite sodium ferric phosphate pyrophosphate material is prepared by the preparation method according to any one of claims 1 to 8.

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