Iron phosphate, process for its preparation and use thereof

Abstract

The present disclosure relates to a kind of ferric phosphate and its preparation method and use, the preparation method includes the following steps: (1) mixing ammonium ferrocyanide and phosphorus source, obtain iron-phosphorus mixed solution;(2) the iron-phosphorus mixed solution obtained in step (1) is carried out spray pyrolysis, obtain solid particles;(3) the solid particles obtained in step (2) are broken, obtain ferric phosphate.The ferric phosphate provided by the present disclosure has higher purity, tap density and specific surface area, the preparation method can avoid using pH regulator and surfactant, reduce by-product production and cleaning step, greatly simplify production process, have higher industrial application value.

Description

Technical Field

[0001] This disclosure relates to the field of lithium-ion battery technology, specifically to an iron phosphate, its preparation method, and its uses. Background Technology

[0002] In the fields of energy storage and new energy, lithium iron phosphate batteries have become one of the most promising lithium-ion batteries due to their advantages such as good rate performance, long cycle life, safety, and environmental friendliness. Iron phosphate, as a precursor to lithium iron phosphate, the cathode material of lithium-ion batteries, has received widespread attention and research.

[0003] In current industrial production, the preparation process of iron phosphate mainly involves the addition of purified ferrous sulfate or ferrous phosphate (a byproduct of titanium dioxide), ammonia, ammonium dihydrogen phosphate, or diammonium hydrogen phosphate, followed by a one-step aging process for crystallization control, ultimately yielding the iron phosphate product. However, this process is prone to insufficient oxidation precipitation, resulting in excessively large primary iron phosphate particles and a small specific surface area, which is detrimental to subsequent lithium iron phosphate production. For example, CN111115606A discloses a method for preparing ultrafine spherical iron phosphate using liquid-phase precipitation combined with spray drying. This method uses ferric salt solution and phosphoric acid as raw materials, adjusting the pH value of the reaction with ammonia and phosphoric acid. While this method can yield ultrafine spherical iron phosphate products, the use of ferric salts such as ferric sulfate leads to the production of ammonium sulfate as a byproduct. Furthermore, a large amount of sulfate ions are easily adsorbed on the surface of the iron phosphate, making it difficult to wash off, resulting in excessively high sulfur content that affects the performance of lithium iron phosphate.

[0004] Therefore, it is of great significance to provide a ferric phosphate with good purity, specific surface area and tap density and its preparation method. Summary of the Invention

[0005] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0006] To address the above problems, the purpose of this disclosure is to provide ferric phosphate, its preparation method, and its uses. Compared with the prior art, the ferric phosphate provided by this disclosure has higher purity, tap density, and specific surface area. The preparation method avoids the use of pH adjusters and surfactants, reduces the generation of by-products and cleaning steps, greatly simplifies the production process, and has high industrial application value.

[0007] To achieve this objective, the present disclosure adopts the following technical solution:

[0008] In a first aspect, this disclosure provides a method for preparing ferric phosphate, the method comprising the following steps:

[0009] (1) Mix ammonium ferricyanide and phosphorus source to obtain iron-phosphorus mixture;

[0010] (2) The iron-phosphorus mixture obtained in step (1) is subjected to spray pyrolysis to obtain solid particles;

[0011] (3) The solid particles obtained in step (2) are crushed to obtain iron phosphate.

[0012] The iron-phosphorus mixture prepared by this disclosure does not require pH adjustment with acid or alkali and is less prone to agglomeration. Furthermore, the spray pyrolysis process employed in this disclosure allows for control of the product dispersion morphology, reducing agglomeration and resulting in smaller, easier-to-grind ferric phosphate particles with higher specific surface area and tap density, and more regular morphology. Additionally, under spray pyrolysis conditions, the ammonium ferricyanide and phosphorus source in this disclosure only generate hydrogen cyanide gas and ammonia gas, with no other byproducts. Therefore, the obtained ferric phosphate has high purity, avoids multiple washing steps, simplifies the process, and is beneficial for industrial application.

[0013] In one embodiment, the ammonium ferricyanide in step (1) is mixed in the form of an ammonium ferricyanide solution.

[0014] In one embodiment, the concentration of iron ions in the ammonium ferricyanide solution is 100-200 g / L, for example, it can be 100 g / L, 110 g / L, 120 g / L, 130 g / L, 140 g / L, 150 g / L, 160 g / L, 170 g / L, 180 g / L, 190 g / L or 200 g / L, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0015] In one embodiment, the phosphorus source includes any one or a combination of at least two of phosphoric acid, ammonium dihydrogen phosphate, or diammonium hydrogen phosphate.

[0016] In this disclosure, phosphoric acid, ammonium dihydrogen phosphate, or diammonium hydrogen phosphate is reacted with ammonium ferricyanide in a spray pyrolysis process to produce ferric phosphate, hydrogen cyanide, and ammonia gas, without generating other byproducts, thus improving the purity of the ferric phosphate product. Taking diammonium hydrogen phosphate as an example, the main reaction is as follows:

[0017] (NH4)2HPO4+(NH4)3[Fe(CN)6]→FePO4+6HCN+5NH3.

[0018] In one embodiment, the molar ratio of iron to phosphorus in the iron-phosphorus mixture in step (1) is (0.98-1.02):1, for example, it can be 0.98:1, 0.99:1, 1.00:1, 1.01:1 or 1.02:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0019] In one embodiment, the carrier gas used in step (2) of the spray pyrolysis includes air.

[0020] In one embodiment, the flow rate of the carrier gas is 20-30 L / min, for example, it can be 20 L / min, 22 L / min, 24 L / min, 26 L / min, 28 L / min or 30 L / min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0021] In one embodiment, the flow rate of the iron-phosphorus mixture in the spray pyrolysis is 1.5-1.8 mL / min, for example, it can be 1.5 mL / min, 1.6 mL / min, 1.7 mL / min or 1.8 mL / min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0022] In one embodiment, the average particle size of the atomized droplets of the iron-phosphorus mixture in the spray pyrolysis is 5-15 μm, for example, it can be 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm or 15 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0023] In this disclosure, by selecting and controlling the flow rate of the iron-phosphorus mixture and the particle size of the atomized droplets, the particle size of the resulting solid particles can be further adjusted.

[0024] In one embodiment, the temperature of the spray pyrolysis is 450-650°C, for example, it can be 450°C, 460°C, 470°C, 480°C, 490°C, 500°C, 520°C, 550°C, 580°C, 600°C or 650°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0025] In this disclosure, selecting and controlling the temperature of spray pyrolysis can promote the formation of ferric phosphate and the volatilization of other substances besides ferric phosphate, thereby reducing the content of impurities in ferric phosphate and obtaining high-purity ferric phosphate.

[0026] In one embodiment, the average particle size of the solid particles in step (2) is 3-10 μm, for example, it can be 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0027] In one embodiment, the flue gas after spray pyrolysis in step (2) is subjected to gas-solid separation to obtain solid powder and tail gas; the tail gas is absorbed by an absorbent to obtain an absorbent liquid, and the absorbent liquid and iron salt are mixed to obtain regenerated ammonium ferricyanide, which is reused in step (1) to prepare iron-phosphorus mixture; the solid powder and the solid particles in step (3) are mixed and then crushed.

[0028] In this disclosure, there is no particular limitation on the type of iron salt, which can be any trivalent iron salt commonly used in the art, such as any one or a combination of at least two of ferric sulfate, ferric chloride or ferric nitrate.

[0029] In one embodiment, the absorbent comprises an ammonium carbonate solution.

[0030] In one embodiment, the mass concentration of the ammonium carbonate solution is 10-40%, for example, it can be 10%, 12%, 14%, 16%, 18%, 20%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, or 40%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] In this disclosure, ammonium carbonate solution is used to absorb the tail gas, which yields regenerated ammonium ferricyanide, thereby achieving material recycling. Taking ferric sulfate as an example, the reaction formula for absorption and regeneration of ammonium ferricyanide is as follows:

[0032] (NH4)2CO3+2HCN=2NH4CN+H2O+CO2;

[0033] Fe2(SO4)3+12NH4CN=2(NH4)3[Fe(CN)6]+3(NH4)2SO4.

[0034] In one embodiment, the crushing pressure in step (3) is 0.2-0.6 MPa, for example, it can be 0.2 MPa, 0.3 MPa, 0.4 MPa, 0.5 MPa or 0.6 MPa, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0035] As an optional technical solution of the first aspect of this disclosure, the preparation method includes the following steps:

[0036] (1) A ferricyanide solution with a concentration of 100-200 g / L and a phosphorus source are mixed to obtain an iron-phosphorus mixture, wherein the molar ratio of iron to phosphorus in the iron-phosphorus mixture is (0.98-1.02):1, and the phosphorus source includes any one or a combination of at least two of phosphoric acid, ammonium dihydrogen phosphate or diammonium hydrogen phosphate.

[0037] (2) The iron-phosphorus mixture obtained in step (1) is sprayed at a flow rate of 1.5-1.8 mL / min and air with a flow rate of 20-30 L / min is used as the carrier gas. The spray pyrolysis is carried out at a temperature of 450-650℃. The average particle size of the atomized droplets of the iron-phosphorus mixture in the spray pyrolysis is 5-15 μm, and solid particles are obtained. The average particle size of the solid particles is 3-10 μm.

[0038] The smoke and dust after spray pyrolysis are subjected to gas-solid separation to obtain solid powder and tail gas. The tail gas is absorbed by ammonium carbonate solution with a mass concentration of 10-40% to obtain absorbent. The absorbent and iron salt are mixed to obtain regenerated ammonium ferricyanide. The regenerated ammonium ferricyanide is reused in step (1) to prepare iron-phosphorus mixture.

[0039] (3) The solid particles and solid powder obtained in step (2) are mixed and crushed at 0.2-0.6 MPa to obtain iron phosphate.

[0040] Secondly, this disclosure provides an iron phosphate, which is obtained by the iron phosphate preparation method described in the first aspect of this disclosure.

[0041] The iron phosphate disclosed herein has high purity, high tap density, and high specific surface area, and its regular morphology is beneficial for improving the electrical performance of lithium-ion batteries.

[0042] In one embodiment, the purity of the ferric phosphate is 99.96-99.99%, for example, it can be 99.96%, 99.97%, 99.98% or 99.99%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0043] In one embodiment, the tap density of the iron phosphate is 1.22-1.25 g / cm³. 3 For example, it could be 1.22 g / cm³. 3 1.23g / cm 3 1.24 g / cm 3 Or 1.25g / cm 3 However, this does not limit the listed values; other unlisted values ​​within the range are also applicable.

[0044] In one embodiment, the specific surface area of ​​the iron phosphate is 9.96-1.52 m². 2 / g, for example, could be 9.96m 2 / g, 9.98m 2 / g, 1.00m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g or 1.52m 2 / g, but not limited to the listed values, other unlisted values ​​within the range also apply.

[0045] Thirdly, this disclosure provides a use of iron phosphate as described in the second aspect of this disclosure, wherein the iron phosphate is used to prepare lithium iron phosphate cathode materials.

[0046] The iron phosphate disclosed herein is used to prepare lithium iron phosphate cathode materials, which can improve the specific capacity of lithium iron phosphate materials, thereby improving electrochemical performance.

[0047] Compared with the prior art, this disclosure has the following beneficial effects:

[0048] (1) The method for preparing ferric phosphate provided in this disclosure uses ammonium ferricyanide as the iron source and adopts a spray pyrolysis process. It can not only obtain ferric phosphate with uniform morphology, high specific surface area and high tap density, but also avoid the use of pH adjusters and surfactants, avoid the introduction of acid radical ions and impurity cations, and produce no by-products, thus effectively improving the purity of ferric phosphate.

[0049] (2) The preparation method provided in this disclosure can increase the purity of ferric phosphate to over 99.90% and the tap density to 1.05 g / cm³. 3 The specific surface area reaches 9.23 m². 2 / g or higher; under optimal conditions, the purity of ferric phosphate can be increased to over 99.96%, and the tap density can reach 1.22 g / cm³. 3 The specific surface area reaches 9.96 m². 2 / g or higher; the iron phosphate provided in this disclosure is used to prepare lithium iron phosphate cathode materials, which can make the compaction density of lithium iron phosphate reach 2.40 g / cm³. 3 The above-mentioned capacity per 1C reaches over 154.6 mAh / g; under optimal conditions, the compaction density of lithium iron phosphate can reach 2.55 g / cm³. 3 The above-mentioned capacity of 1C gram reaches 160.5mAh / g or more.

[0050] (3) The preparation method provided in this disclosure does not require multiple washing processes, which simplifies the process flow and enables the recycling of materials.

[0051] (4) The iron phosphate provided in this disclosure is used to prepare lithium iron phosphate cathode material, which can improve the specific capacity of lithium iron phosphate, thereby improving the electrochemical performance.

[0052] After reading and understanding the detailed description, other aspects can be understood. Detailed Implementation

[0053] The technical solutions of this disclosure will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of this disclosure and should not be construed as specific limitations thereof.

[0054] Example 1

[0055] This embodiment provides a method for preparing ferric phosphate, the method comprising the following steps:

[0056] (1) A 150 g / L ammonium ferricyanide solution and diammonium hydrogen phosphate were mixed to obtain an iron-phosphorus mixture, wherein the molar ratio of iron to phosphorus in the iron-phosphorus mixture was 1:1.

[0057] (2) The iron-phosphorus mixture obtained in step (1) is sprayed at a flow rate of 1.7 mL / min and air with a flow rate of 25 L / min is used as the carrier gas. The average particle size of the atomized droplets of the iron-phosphorus mixture in the spray pyrolysis is 10 μm, and solid particles are obtained with an average particle size of 6 μm.

[0058] The smoke and dust after spray pyrolysis are subjected to gas-solid separation to obtain solid powder and tail gas. The tail gas is absorbed by ammonium carbonate solution with a mass concentration of 20% to obtain absorbent. The absorbent and ferric sulfate are mixed according to the stoichiometric ratio to obtain regenerated ammonium ferricyanide. The regenerated ammonium ferricyanide is reused in step (1) to prepare iron-phosphorus mixture.

[0059] (3) The solid particles and solid powder obtained in step (2) are mixed and crushed at 0.4 MPa to obtain iron phosphate.

[0060] Example 2

[0061] This embodiment provides a method for preparing ferric phosphate, the method comprising the following steps:

[0062] (1) A 100 g / L ammonium ferricyanide solution and phosphoric acid (the mass concentration of the phosphoric acid is 80%) are mixed to obtain an iron-phosphorus mixture, wherein the molar ratio of iron to phosphorus in the iron-phosphorus mixture is 0.98:1.

[0063] (2) The iron-phosphorus mixture obtained in step (1) is sprayed at a flow rate of 1.8 mL / min and air with a flow rate of 20 L / min is used as the carrier gas. The average particle size of the atomized droplets of the iron-phosphorus mixture in the spray pyrolysis is 5 μm, and solid particles are obtained with an average particle size of 3 μm.

[0064] The smoke and dust after spray pyrolysis are subjected to gas-solid separation to obtain solid powder and tail gas. The tail gas is absorbed by ammonium carbonate solution with a mass concentration of 10% to obtain absorbent. The absorbent and ferric sulfate are mixed according to the stoichiometric ratio to obtain regenerated ammonium ferricyanide. The regenerated ammonium ferricyanide is reused in step (1) to prepare iron-phosphorus mixture.

[0065] (3) The solid particles and solid powder obtained in step (2) are mixed and crushed at 0.2 MPa to obtain iron phosphate.

[0066] Example 3

[0067] This embodiment provides a method for preparing ferric phosphate, the method comprising the following steps:

[0068] (1) A ferricyanide solution with a concentration of 200 g / L and ammonium dihydrogen phosphate are mixed to obtain an iron-phosphorus mixture, wherein the molar ratio of iron to phosphorus in the iron-phosphorus mixture is 1.02:1;

[0069] (2) The iron-phosphorus mixture obtained in step (1) is sprayed at a flow rate of 1.5 mL / min and air with a flow rate of 30 L / min is used as the carrier gas. The average particle size of the atomized droplets of the iron-phosphorus mixture during the spray pyrolysis is 15 μm, and solid particles are obtained with an average particle size of 10 μm.

[0070] The smoke and dust after spray pyrolysis are subjected to gas-solid separation to obtain solid powder and tail gas. The tail gas is absorbed by ammonium carbonate solution with a mass concentration of 40% to obtain absorbent. The absorbent and ferric sulfate are mixed according to the stoichiometric ratio to obtain regenerated ammonium ferricyanide. The regenerated ammonium ferricyanide is reused in step (1) to prepare iron-phosphorus mixture.

[0071] (3) The solid particles and solid powder obtained in step (2) are mixed and crushed at 0.6 MPa to obtain iron phosphate.

[0072] Example 4

[0073] This embodiment provides a method for preparing iron phosphate, which differs from Example 1 only in that the spray pyrolysis temperature is 400°C.

[0074] Example 5

[0075] This embodiment provides a method for preparing iron phosphate, which differs from Example 1 only in that the spray pyrolysis temperature is 700°C.

[0076] Comparative Example 1

[0077] This comparative example provides a method for preparing ferric phosphate, which differs from Example 1 only in that the ammonium ferricyanide solution in step (1) is replaced with a ferric sulfate solution of equal ferric ion concentration.

[0078] The purity of the ferric phosphate obtained in Examples 1-5 and Comparative Example 1 was detected by X-ray fluorescence spectrometry. The tap density and specific surface area of ​​the ferric phosphate obtained in Examples 1-5 and Comparative Example 1 were tested by BET method. The results are shown in Table 1.

[0079] Lithium iron phosphate cathode material was prepared using the iron phosphate obtained in Examples 1-5 and Comparative Example 1. The method was as follows: iron phosphate and lithium carbonate were weighed according to the molar ratio of phosphorus to lithium of 1:1. The iron phosphate, lithium carbonate and sucrose (the mass of sucrose accounted for 10% of the mass of iron phosphate) were mixed evenly and then calcined at 720°C for 6 hours under the protection of nitrogen. After cooling, lithium iron phosphate cathode material was obtained.

[0080] Electrical performance testing: The lithium iron phosphate cathode material prepared from the iron phosphate obtained in Examples 1-5 and Comparative Example 1, the conductive agent (Super P), and the binder (polyvinylidene fluoride, PVDF) were mixed at a mass ratio of 90:5:5. The mixture was then added to the solvent N-methylpyrrolidone (NMP) and stirred to obtain a slurry of lithium iron phosphate cathode material. This slurry was coated onto an aluminum foil current collector and dried to obtain the cathode electrode. Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed at a mass ratio of 1:1:1 to prepare an electrolyte with a LiPF6 concentration of 1.0 mol / L. A 2025 coin cell was assembled using a polyethylene film (PE) as the separator and a lithium metal sheet as the negative electrode, and its electrochemical performance was tested. The coin cell was charged and discharged at 0.1C at 2-3.75V and 25℃, and the capacity was recorded. The measured capacity value was divided by the mass of the lithium iron phosphate cathode material in the battery to obtain the specific capacity of the lithium iron phosphate cathode material in the lithium-ion battery. The compaction density of the lithium iron phosphate cathode material in Table 1 was tested using a PRCD compaction density meter.

[0081] Table 1

[0082]

[0083] The following points can be observed from the data in Table 1:

[0084] (1) As can be seen from the data in Examples 1-5, the preparation method provided in this disclosure can increase the purity of ferric phosphate to over 99.90% and the tap density to 1.05 g / cm³. 3 The specific surface area reaches 9.23 m². 2 / g or higher; under optimal conditions, the purity of ferric phosphate can be increased to over 99.96%, and the tap density can reach 1.22 g / cm³. 3 The specific surface area reaches 9.96 m². 2 / g or higher; the iron phosphate provided in this disclosure is used to prepare lithium iron phosphate cathode materials, which can achieve a compaction density of 2.40 g / cm³ for the lithium iron phosphate cathode materials. 3 The above-mentioned capacity per 1C reaches over 154.6 mAh / g; under optimal conditions, the compaction density of the lithium iron phosphate cathode material reaches 2.55 g / cm³. 3 The above-mentioned capacity of 1C gram reaches 160.5mAh / g or more.

[0085] (2) A comprehensive comparison of the data from Examples 1 and 4-5 shows that the only difference between Example 1 and Examples 4-5 is that the spray pyrolysis temperature is not within the range selectable by this disclosure. The purity, tap density, and specific surface area of ​​iron phosphate in Example 1 are significantly higher than those in Examples 4-5. The compaction density and 1C specific capacity of lithium iron phosphate in Example 1 are significantly higher than those in Examples 4-5. It can be seen that by controlling the spray pyrolysis temperature, this disclosure can promote the generation of iron phosphate and the volatilization of other substances in the form of gas, significantly improve the purity, tap density, and specific surface area of ​​iron phosphate, and thus improve the compaction density and 1C specific capacity of lithium iron phosphate cathode material.

[0086] (3) A comprehensive comparison of the data from Example 1 and Comparative Example 1 shows that the only difference between Comparative Example 1 and Example 1 is that the ammonium ferricyanide solution is replaced with a ferric sulfate solution with the same iron ion concentration. The purity, tap density, and specific surface area of ​​the iron phosphate in Example 1 are significantly better than those in Comparative Example 1. Consequently, the compaction density and 1C specific capacity of the lithium iron phosphate cathode material are also significantly better than those in Comparative Example 1. It can be seen that the present disclosure can prepare iron phosphate by spray pyrolysis using ammonium ferricyanide as the iron source, which can avoid the excessive impurity content of the prepared iron phosphate caused by the use of sulfur-containing iron source as in Comparative Example 1, thereby improving the purity of iron phosphate. Moreover, it can prepare iron phosphate with high specific surface area and high tap density without the use of pH adjuster and surfactant, which is beneficial to improving the compaction density and specific capacity of lithium iron phosphate cathode material.

[0087] In summary, the preparation method provided in this disclosure enables ferric phosphate to have high purity, tap density, and specific surface area, reduces the generation of by-products and cleaning steps, greatly simplifies the production process, and has high industrial application value.

Claims

1. A method for preparing iron phosphate, comprising the following steps: (1) Mix ammonium ferricyanide and phosphorus source to obtain iron-phosphorus mixture; (2) The iron-phosphorus mixture obtained in step (1) is subjected to spray pyrolysis to obtain solid particles; (3) The solid particles obtained in step (2) are crushed to obtain iron phosphate; The phosphorus source in step (1) includes any one or a combination of at least two of phosphoric acid, ammonium dihydrogen phosphate, or diammonium hydrogen phosphate.

2. The preparation method according to claim 1, wherein, In step (1), the ammonium ferricyanide is mixed in the form of an ammonium ferricyanide solution; the concentration of iron ions in the ammonium ferricyanide solution is 100-200 g / L.

3. The preparation method according to claim 1, wherein, The molar ratio of iron to phosphorus in the iron-phosphorus mixture in step (1) is (0.98-1.02):

1.

4. The preparation method according to claim 1, wherein, The carrier gas used in step (2) of spray pyrolysis includes air; the flow rate of the carrier gas is 20-30 L / min.

5. The preparation method according to claim 1, wherein, The flow rate of the iron-phosphorus mixture in the spray pyrolysis is 1.5-1.8 mL / min.

6. The preparation method according to claim 1, wherein, The average droplet size of the atomized liquid from the iron-phosphorus mixture in the spray pyrolysis is 5-15 μm.

7. The preparation method according to claim 1, wherein, The temperature of the spray pyrolysis is 450-650℃.

8. The preparation method according to claim 1, wherein, The average particle size of the solid particles in step (2) is 3-10 μm.

9. The preparation method according to claim 1, wherein, In step (2), the flue gas after spray pyrolysis is subjected to gas-solid separation to obtain solid powder and tail gas; the tail gas is absorbed by an absorbent to obtain an absorbent liquid, and the absorbent liquid and iron salt are mixed to obtain regenerated ammonium ferricyanide, which is reused in step (1) to prepare iron-phosphorus mixed solution; the solid powder and the solid particles in step (3) are mixed and then crushed; The absorbent comprises an ammonium carbonate solution; the mass concentration of the ammonium carbonate solution is 10-40%.

10. The preparation method according to claim 1, wherein, The crushing pressure in step (3) is 0.2-0.6 MPa.

11. The preparation method according to claim 1, wherein, The preparation method includes the following steps: (1) A ferricyanide solution with a concentration of 100-200 g / L and a phosphorus source are mixed to obtain an iron-phosphorus mixture, wherein the molar ratio of iron to phosphorus in the iron-phosphorus mixture is (0.98-1.02):1, and the phosphorus source includes any one or a combination of at least two of phosphoric acid, ammonium dihydrogen phosphate or diammonium hydrogen phosphate. (2) The iron-phosphorus mixture obtained in step (1) is sprayed at a flow rate of 1.5-1.8 mL / min and air with a flow rate of 20-30 L / min as the carrier gas at a temperature of 450-650℃. The average particle size of the atomized droplets of the iron-phosphorus mixture in the spray pyrolysis is 5-15 μm, and solid particles are obtained with an average particle size of 3-10 μm. The smoke and dust after spray pyrolysis are subjected to gas-solid separation to obtain solid powder and tail gas. The tail gas is absorbed by ammonium carbonate solution with a mass concentration of 10-40% to obtain absorbent. The absorbent and iron salt are mixed to obtain regenerated ammonium ferricyanide. The regenerated ammonium ferricyanide is reused in step (1) to prepare iron-phosphorus mixture. (3) The solid particles and solid powder obtained in step (2) are crushed at 0.2-0.6 MPa to obtain iron phosphate.

12. Ferric phosphate obtained by the method for preparing ferric phosphate according to any one of claims 1-11.

13. Use of the iron phosphate as described in claim 12 to prepare lithium iron phosphate cathode material.

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