Preparation method of blocky monocrystal iron phosphate

Abstract

The invention relates to the technical field of battery materials, in particular to a preparation method of blocky monocrystal iron phosphate. The preparation method comprises the following steps: (1) preparing a phosphoric acid solution, a hydrogen peroxide solution, ammonia water, a phosphorus salt solution and a ferrite solution; adding ammonia water into the phosphorus salt solution to obtain a phosphorus salt solution A; (2) uniformly mixing a hydrogen peroxide solution and the phosphorus salt solution A to obtain a phosphorus salt solution B; (3) feeding the ferrous salt solution and the phosphorus salt solution B together to obtain slurry A; (4) filtering to obtain a filter cake; (5) slurrying to obtain slurry B; (6) dividing the slurry B into two parts, adding one part into a reaction kettle, and adding a phosphoric acid solution; (7) adding the other part of slurry B after heating, and keeping the temperature to obtain slurry; (8) obtaining iron phosphate dihydrate; and (9) obtaining anhydrous iron phosphate. The preparation method is compatible with existing ammonium process equipment, batch production can be achieved, the prepared iron phosphate is blocky single crystals, and all specifications meet the market product requirements.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, specifically to a method for preparing bulk single-crystal iron phosphate. Background Technology

[0002] With the rapid development of the new energy industry, lithium iron phosphate (LFP) batteries, due to their high safety and long cycle life, are increasingly widely used in power batteries, energy storage batteries, and other fields, leading to continuously increasing market demands for their energy density. Improving the compaction density of LFP materials is an effective technical path to enhance the energy density of LFP batteries, and multi-level particle size distribution technology is one of the mainstream techniques for achieving high compaction density. As a precursor for synthesizing LFP, the chemical purity, particle morphology, and particle size distribution of iron phosphate directly determine the microstructure and physicochemical properties of LFP materials, thus decisively influencing the energy density and electrochemical characteristics of LFP batteries. In existing technologies, two types of iron phosphate with different morphologies and particle size distributions are typically used as composite precursors to prepare LFP materials with varying particle sizes, thereby optimizing the material's compaction density and electrochemical performance.

[0003] There are three main existing methods for preparing large-particle single-crystal iron phosphate: 1. Mixing iron salts and phosphate salts to obtain a molten iron solution, then oxidizing and aging it at a certain temperature to prepare single-crystal iron phosphate; 2. Mixing oxidized iron salts with phosphate salts and phosphoric acid separately, then reacting them at low temperature under certain pH conditions to obtain single-crystal iron phosphate; 3. First preparing ferrous phosphate as an intermediate product, then adding phosphoric acid and reacting it with hydrogen peroxide to prepare single-crystal iron phosphate. A brief description of the specific technical solutions is as follows: Patent CN119776967A describes a process of preparing a molten iron solution by mixing purified fertilizer acid with phosphoric acid, adding an iron source to the molten iron solution, oxidizing it at a certain temperature, and then aging it at a certain temperature for a period of time to obtain single-crystal iron phosphate.

[0004] Patent CN115506006B describes a method for obtaining single-crystal iron phosphate by sequentially adding an iron source, hydrogen peroxide, and 1,2-propanediol to phosphoric acid, reacting at room temperature for 10-30 minutes, then reacting at 70-100℃ for 3-6 hours, and finally allowing it to stand and age.

[0005] Patent CN118814272B describes a process where an oxidant is added to a ferrous solution to control the ferrous content at 1% to 5%, and phosphate salts and phosphoric acid are added sequentially to adjust the pH. The reaction is carried out at 50 to 60°C to obtain single-crystal ferric phosphate.

[0006] Patent CN119100346A describes a process where ferrous phosphate is first prepared as an intermediate. After filtration, washing, and pulping, a mixture of phosphoric acid and hydrogen peroxide is added and heated to convert the ferrous phosphate into single-crystal ferric phosphate.

[0007] However, the above technical solutions have two major problems: First, the phosphate salt dissolution method for preparing single-crystal iron phosphate in patents CN119776967A and CN115506006B is significantly different from the mainstream ammonium method process in the market, and is incompatible with existing equipment and cannot be directly used, which increases the production cost. The one-step method in patent CN118814272B and the ferrous phosphate intermediate method in patent CN119100346A both have impurity content that exceeds the market specifications. Summary of the Invention

[0008] To address the technical problems of existing methods for preparing monocrystalline iron phosphate, such as incompatibility with existing equipment and impurity content exceeding market specifications, this invention provides a method for preparing bulk monocrystalline iron phosphate based on the mainstream ammonium process, and the prepared products meet market requirements in all specifications.

[0009] The technical solution of this invention is as follows: This invention provides a method for preparing bulk single-crystal iron phosphate, comprising the following steps: (1) Prepare 40-85 wt% phosphoric acid solution, 10-28 wt% hydrogen peroxide solution, 15-35 wt% ammonia solution, phosphate salt solution and ferrous salt solution for later use. Add ammonia solution to phosphate salt solution to obtain phosphate salt solution A. (2) Pour hydrogen peroxide solution and phosphate salt solution A into a mixing tank and stir evenly to obtain phosphate salt solution B; (3) Add a certain amount of pure water to the reactor, and heat it to 20-60°C under the condition of stirring frequency of 30-180Hz. Add the above ferrous salt solution and phosphate salt solution B into the reactor together within 30-90min. After reacting for 30-60min, slurry A is obtained. (4) The above slurry A is subjected to solid-liquid separation, the mother liquor is removed, and a filter cake is obtained. Then, hot pure water is added to wash the filter cake until the conductivity of the wash water after washing is reduced to below 5000 μS / cm. (5) Transfer the above filter cake into a pulping tank, add hot pure water, and stir for 30~180min to pulp to obtain pulp B; (6) Divide the above slurry B into two portions, one portion for later use, and the other portion into the reaction vessel, along with the above phosphoric acid solution; take one portion for crystallization as a seed crystal; (7) Heat the temperature to 80~98℃. After the slurry turns white, add another portion of slurry B within 30~90 minutes. After adding the slurry, keep it warm for 30~180 minutes to obtain white slurry. (8) The above white slurry is subjected to solid-liquid separation, the slurry liquid is removed, and ferric phosphate dihydrate filter cake is obtained. Then, hot pure water is added to wash the filter cake until the conductivity of the wash water after washing is reduced to below 500 μS / cm. (9) After the filter cake is dried and calcined, battery-grade single-crystal anhydrous iron phosphate is obtained; the drying and calcining methods and equipment are the common methods and equipment in the existing iron phosphate preparation technology.

[0010] Furthermore, in step (1), the concentration of phosphorus in the phosphate salt solution A is 0.5~2.0 mol / L; the phosphate salt solution is at least one of ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, and sodium phosphate.

[0011] Furthermore, in step (1), the concentration of iron in the ferrous salt solution is 0.5~2.0 mol / L; the ferrous salt solution is at least one of ferrous sulfate, ferrous nitrate, ferrous chloride, iron powder, and iron sheet.

[0012] Furthermore, in step (2), the pH value of the phosphate salt solution A is 6~8.

[0013] Furthermore, in step (3), the molar ratio of iron in the ferrous salt solution to phosphorus in the phosphate salt solution B is 1:(0.9~1.2).

[0014] Furthermore, in step (3), the pH value of the reaction system is 1~4, preferably 2~3.

[0015] Furthermore, in steps (4) and (8), the solid-liquid separation method is any one of centrifugation, pressure filtration, or filtration; the equipment for solid-liquid separation is a common washing equipment in existing iron phosphate preparation technology, such as a centrifuge, filter press, or leaf filter.

[0016] Furthermore, the solid content (calculated as anhydrous ferric phosphate) of the pulp in step (5) is 8% to 20%, preferably 10% to 15%.

[0017] Furthermore, in step (6), the slurry B is divided into two parts, and the ratio of the part added to the reactor to the part reserved is (1:9) to (7:3), preferably (3:7) to (6:4); the molar ratio of phosphoric acid to iron in the reaction system is (0.1 to 0.8):1, preferably (0.3 to 0.6):1.

[0018] Furthermore, the temperature of the hot pure water mentioned in steps (4), (5) and (8) is 40~90℃.

[0019] The beneficial effects of this invention are as follows: 1. The method for preparing bulk single-crystal iron phosphate provided by the present invention is simple, has a short process flow, is compatible with existing ammonium process equipment for mass production, and reduces production energy consumption and equipment modification costs.

[0020] 2. The method for preparing bulk single-crystal iron phosphate provided by the present invention, in the preparation stage, adopts simultaneous feeding of ferrous salt solution and phosphate salt solution to keep the iron-phosphorus ratio in the reaction system stable and controllable, significantly improving the uniformity of the prepared intermediate product; in the aging stage, the pH value of the reaction system is adjusted by adding acidic substances, so that a part of the slurry preferentially transforms into crystal seed crystals, and another part of the slurry grows directly on the surface of the crystal seed crystals when fed at high temperature, effectively reducing the spontaneous nucleation process of the system. At the same time, the high temperature environment can promote the full growth of crystals, and prepare single-crystal iron phosphate with regular crystal shape that meets market requirements. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a 50,000x SEM image of the ferric phosphate dihydrate prepared in Example 1.

[0023] Figure 2 This is a 50,000x SEM image of the anhydrous ferric phosphate prepared in Example 1.

[0024] Figure 3 These are 50,000x SEM images of ferric phosphate prepared at different stages in Example 4, where (a) is an SEM image of ferric phosphate dihydrate and (b) is an SEM image of ferric phosphate anhydrous.

[0025] Figure 4 These are 50,000x SEM images of ferric phosphate prepared at different stages in Example 5, where (a) is an SEM image of ferric phosphate dihydrate and (b) is an SEM image of ferric phosphate anhydrous.

[0026] Figure 5 These are 50,000x SEM images of ferric phosphate prepared at different stages in Example 6, where (a) is an SEM image of ferric phosphate dihydrate and (b) is an SEM image of ferric phosphate anhydrous.

[0027] Figure 6 These are 50,000x SEM images of ferric phosphate prepared at different stages in Example 7, where (a) is an SEM image of ferric phosphate dihydrate and (b) is an SEM image of ferric phosphate anhydrous.

[0028] Figure 7 The images are SEM images of ferric phosphate prepared at different stages in Comparative Example 1, magnified 50,000 times. (a) is the SEM image of ferric phosphate dihydrate; (b) is the SEM image of ferric phosphate anhydrous.

[0029] Figure 8The images are SEM images of ferric phosphate prepared at different stages in Comparative Example 2, magnified 50,000 times. (a) is the SEM image of ferric phosphate dihydrate; (b) is the SEM image of ferric phosphate anhydrous.

[0030] Figure 9 The images are 50,000x SEM images of ferric phosphate prepared at different stages in Comparative Example 3, where (a) is the SEM image of ferric phosphate dihydrate and (b) is the SEM image of ferric phosphate anhydrous.

[0031] Figure 10 The images are SEM images of ferric phosphate prepared at different stages in Comparative Example 4, magnified 50,000 times. (a) is the SEM image of ferric phosphate dihydrate; (b) is the SEM image of ferric phosphate anhydrous.

[0032] Figure 11 This is a particle size distribution diagram of the anhydrous ferric phosphate prepared in Example 1.

[0033] Figure 12 This is a particle size distribution diagram of the anhydrous iron phosphate prepared in Example 4.

[0034] Figure 13 This is a particle size distribution diagram of the anhydrous ferric phosphate prepared in Example 5.

[0035] Figure 14 This is a particle size distribution diagram of the anhydrous ferric phosphate prepared in Example 6.

[0036] Figure 15 This is a particle size distribution diagram of the anhydrous ferric phosphate prepared in Example 7. Detailed Implementation

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

[0038] Example 1 This embodiment provides a method for preparing bulk single-crystal iron phosphate, including the following steps: (1) Prepare solutions of 25 wt% ammonia, 28 wt% hydrogen peroxide, and 85 wt% phosphoric acid respectively; weigh ferrous sulfate with an iron concentration of 82 g / L, and dissolve it to a volume of 0.38 m³. 3 Add water to a final volume of 0.40 ml. 3 A ferrous salt solution with an iron concentration of 1.39 mol / L was obtained; 64 kg of ammonium dihydrogen phosphate solid was weighed, dissolved in water, and diluted to a final volume of 0.30 mL. 3; (2) Add ammonia water to the above phosphate salt solution in small amounts several times to make the pH=7.5, and then add pure water to make up to 0.4m. 3 A phosphate solution A with a concentration of 1.39 mol / L was obtained. Then, 44 kg of hydrogen peroxide solution was added and stirred evenly to obtain phosphate solution B. (3) Add 0.6m to the reactor 3 Pure water was submerged to the bottom of the stirring paddle. The temperature of the pure water was raised to 40°C, and the stirring was turned on at 30 Hz. The above ferrous salt solution and phosphate salt solution B were added into the reactor together within 45 minutes. After the addition was completed, the reaction was carried out for 30 minutes to obtain a yellow slurry A with pH=2. (4) Use a filter press to separate the yellow slurry A into solid and liquid. The resulting mother liquor is discharged into the wastewater treatment system for treatment. The resulting yellow filter cake is left in the filter chamber of the filter press and rinsed with hot pure water at 60°C until the conductivity of the rinse water drops to 4200 μS / cm. (5) The obtained yellow filter cake is transferred to a slurry tank, and hot pure water at 50°C is added at a ratio of 13% based on the solid content of anhydrous ferric phosphate. Stirring is started at a frequency of 30Hz and slurrying is carried out for 40 minutes to obtain yellow slurry B. (6) Add 50% of the above yellow slurry B into the reactor and add 32.05 kg of phosphoric acid solution; (7) Heat the temperature to 90°C. After the slurry turns white, add another 50% of yellow slurry B within 40 minutes. After adding the slurry, keep it warm for 60 minutes to obtain white slurry. (8) Use a filter press to separate the white slurry after the heat preservation is completed. The resulting filtrate is discharged into the wastewater treatment system for treatment. The resulting filter cake is left in the filter chamber of the filter press and rinsed with hot pure water at 60°C until the conductivity of the rinse water drops to 470 μS / cm. (9) The filter cake is blown in the filter press and discharged to obtain iron phosphate dihydrate filter cake. It is then flash-dried and calcined to obtain battery-grade anhydrous iron phosphate material.

[0039] The microstructures of the ferric phosphate dihydrate and anhydrous ferric phosphate prepared in Example 1 are as follows: Figures 1-2 As shown in the figure, the ferric phosphate prepared in this embodiment is a blocky single-crystal ferric phosphate, according to... Figures 1-2 The size of the single-crystal primary particles obtained by manual measurement using the shooting scale is 200~300nm. Figure 11This is the particle size distribution diagram of anhydrous ferric phosphate. Its D0 is 0.36 μm, D10 is 9.76 μm, D50 is 17.84 μm, D90 is 28.14 μm, D99 is 33.03 μm, and D100 is 40.13 μm. The primary particles of anhydrous ferric phosphate are nanoscale particles, which spontaneously aggregate during the reaction to form large secondary or tertiary aggregates. Therefore, particle size measurement detects the size of these large aggregates.

[0040] Example 2 This embodiment provides a method for preparing bulk single-crystal iron phosphate, including the following steps: (1) Prepare solutions of 15 wt% ammonia, 28 wt% hydrogen peroxide, and 85 wt% phosphoric acid respectively; weigh a ferrous chloride solution with an iron concentration of 111.7 g / L, with a volume of 0.4 m³. 3 A ferrous salt solution with an iron concentration of 2.0 mol / L was obtained; 102.21 kg of sodium monohydrogen phosphate solid was weighed, dissolved in water, and diluted to a final volume of 0.3 m³. 3 ; (2) Add liquid alkali to the above phosphate solution in small amounts several times to make the pH of the phosphate solution = 8, and then add pure water to make up to 0.36m. 3 A phosphate salt solution A with a concentration of 2.0 mol / L was obtained, and then 63.3 kg of hydrogen peroxide solution was added and stirred evenly to obtain phosphate salt solution B. (3) Add 0.6m to the reactor 3 Pure water was submerged to the bottom of the stirring paddle. The temperature of the pure water was raised to 60°C, and the stirring was turned on at 180 Hz. The above ferrous salt solution and phosphate salt solution B were added into the reactor together within 90 minutes. After the addition was completed, the reaction was carried out for 30 minutes to obtain a yellow slurry A with pH=2.8. (4) Use a centrifuge to separate the yellow slurry A into solid and liquid. The resulting mother liquor is discharged into the wastewater treatment system for treatment. The resulting yellow filter cake is left in the filter chamber of the filter press and rinsed with hot pure water at 90°C until the conductivity of the rinse water drops to 4500 μS / cm. (5) The obtained yellow filter cake is transferred to a slurry tank, and hot pure water at 90°C is added at a ratio of 20% based on the solid content of anhydrous ferric phosphate. Stirring is started at a frequency of 30Hz and slurrying is carried out for 30 minutes to obtain yellow slurry B. (6) Add 50% of the above yellow slurry B into the reactor and add 73.8 kg of phosphoric acid solution; (7) Heat the temperature to 98°C. After the slurry turns white, add another 50% of yellow slurry B within 90 minutes. After the addition is completed, keep the temperature for 180 minutes to obtain white slurry. (8) Use a centrifuge to separate the white slurry after the heat preservation is completed. The resulting filtrate is discharged into the wastewater treatment system for treatment. The resulting filter cake is left in the filter chamber of the filter press and rinsed with hot pure water at 90°C until the conductivity of the rinse water drops to 430 μS / cm. (9) The filter cake is blown in a centrifuge, unloaded, and ferric phosphate dihydrate filter cake is obtained. It is then flash-dried and calcined to obtain anhydrous ferric phosphate material.

[0041] Example 3 This embodiment provides a method for preparing bulk single-crystal iron phosphate, including the following steps: (1) Prepare solutions of 35 wt% ammonia, 10 wt% hydrogen peroxide, and 40 wt% phosphoric acid respectively; weigh ferrous nitrate with an iron concentration of 37.3 g / L, and dissolve it to a volume of 0.3 m³. 3 Add water to a final volume of 0.4m. 3 A ferrous salt solution with an iron concentration of 0.5 mol / L was obtained; 35.76 kg of ammonium phosphate solid was weighed, dissolved in water, and diluted to a final volume of 0.3 m³. 3 ; (2) Add ammonia water to the above phosphate solution in small amounts several times to make the pH of the phosphate solution = 6, and then add pure water to make up to 0.48m. 3 A phosphate salt solution A with a concentration of 0.5 mol / L was obtained, and then 44 kg of hydrogen peroxide solution was added and stirred evenly to obtain phosphate salt solution B. (3) Add 0.6m to the reactor 3 Pure water was submerged to the bottom of the stirring paddle. The temperature of the pure water was raised to 20°C, and the stirring was turned on at 30 Hz. The above ferrous salt solution and phosphate salt solution B were added into the reactor together within 30 minutes. After the addition was completed, the reaction was carried out for 60 minutes to obtain a yellow slurry A with pH=1.8. (4) Use a leaf filter to separate the yellow slurry A into solid and liquid. The resulting mother liquor is discharged into the wastewater treatment system for treatment. The resulting yellow filter cake is left in the filter chamber of the filter press and rinsed with hot pure water at 40°C until the conductivity of the rinse water drops to 4200 μS / cm. (5) The obtained yellow filter cake is transferred to a pulping tank, and hot pure water at 40°C is added at a ratio of 8% based on the solid content of anhydrous ferric phosphate. Stirring is started at a frequency of 30Hz and pulping is carried out for 180 minutes to obtain yellow pulp B. (6) Add 50% of the above yellow slurry B into the reactor and add 4.9 kg of phosphoric acid solution; (7) Heat the temperature to 80°C. After the slurry turns white, add another 50% of yellow slurry B within 30 minutes. After adding the slurry, keep it warm for 30 minutes to obtain white slurry. (8) Use a leaf filter to separate the white slurry after the heat preservation is completed. The resulting filtrate is discharged into the wastewater treatment system for treatment. The resulting filter cake is left in the filter chamber of the filter press and rinsed with hot pure water at 40°C until the conductivity of the rinse water drops to 470 μS / cm. (9) The filter cake is blown in the leaf filter and discharged to obtain iron phosphate dihydrate filter cake. It is then flash-dried and calcined to obtain battery-grade anhydrous iron phosphate material.

[0042] Example 4 This embodiment provides a method for preparing bulk single-crystal iron phosphate. The reaction ratio in this embodiment is similar to that in Example 1, except that the molar ratio of phosphoric acid to iron in the reaction system is 0.7:1, while in Example 1 it is 0.5:1. The method includes the following steps: (1) Prepare solutions of 25 wt% ammonia, 28 wt% hydrogen peroxide, and 85 wt% phosphoric acid respectively; weigh ferrous sulfate with an iron concentration of 82 g / L, and dissolve it to a volume of 0.38 m³. 3 Add water to a final volume of 0.40 ml. 3 A ferrous salt solution with an iron concentration of 1.39 mol / L was obtained; 64 kg of ammonium dihydrogen phosphate solid was weighed, dissolved in water, and diluted to a final volume of 0.30 mL. 3 ; (2) Add ammonia water to the above phosphate solution in small amounts several times to make the pH of the phosphate solution 7.5, and then add pure water to make up to 0.4 m³. 3 A phosphate salt solution A with a concentration of 1.39 mol / L was obtained. Then, 44 kg of the above hydrogen peroxide solution was added and stirred evenly to obtain a phosphate salt solution B. (3) Add 0.6m to the reactor 3 Pure water was submerged to the bottom of the stirring paddle. The temperature of the pure water was raised to 40°C, and the stirring was turned on at 30 Hz. The above ferrous salt solution and phosphate salt solution B were added into the reactor together within 45 minutes. After the addition was completed, the reaction was carried out for 30 minutes to obtain a yellow slurry A with pH=2. (4) Use a filter press to separate the yellow slurry A into solid and liquid. The resulting mother liquor is discharged into the wastewater treatment system for treatment. The resulting yellow filter cake is left in the filter chamber of the filter press and rinsed with hot pure water at 60°C until the conductivity of the rinse water drops to 4200 μS / cm. (5) The obtained yellow filter cake is transferred to a slurry tank, and hot pure water at 50°C is added at a ratio of 13% based on the solid content of anhydrous ferric phosphate. Stirring is started at a frequency of 30Hz and slurrying is carried out for 40 minutes to obtain yellow slurry B. (6) Add 50% of the above yellow slurry B to the reactor and add 44.87 kg of phosphoric acid solution; (7) Heat the temperature to 90°C. After the slurry turns white, add another 50% of yellow slurry B within 40 minutes. After adding the slurry, keep it warm for 60 minutes to obtain white slurry. (8) Use a filter press to separate the white slurry after the heat preservation is completed. The resulting filtrate is discharged into the wastewater treatment system for treatment. The resulting filter cake is left in the filter chamber of the filter press and rinsed with hot pure water at 60°C until the conductivity of the rinse water drops to 470 μS / cm. (9) The filter cake is blown in the filter press and discharged to obtain iron phosphate dihydrate filter cake. It is then flash-dried and calcined to obtain battery-grade anhydrous iron phosphate material.

[0043] The microstructures of the ferric phosphate dihydrate and anhydrous ferric phosphate prepared in this embodiment are as follows: Figure 3 As shown in the figure, the ferric phosphate prepared in this experiment is a blocky single-crystal ferric phosphate. Figure 3 The single-crystal primary particle size obtained by manual measurement of the shooting scale in (a) and (b) is 400~500nm. Figure 12 This is the particle size distribution diagram of anhydrous ferric phosphate. Its D0 is 0.36 μm, D10 is 10.23 μm, D50 is 19.49 μm, D90 is 30.66 μm, D99 is 35.56 μm, and D100 is 45.42 μm. The primary particles of anhydrous ferric phosphate are nanoscale particles, which spontaneously aggregate during the reaction to form large secondary or tertiary aggregates. Therefore, particle size measurement detects the size of these large aggregates.

[0044] Example 5 This embodiment provides a method for preparing bulk single-crystal iron phosphate. The reaction ratio in this embodiment is similar to that in Example 1, except that the yellow slurry B is divided into two parts. The ratio of the part added to the reaction vessel to the part reserved is 3:7, while in Example 1 it is 5:5. The method includes the following steps: (1) Prepare solutions of 25 wt% ammonia, 28 wt% hydrogen peroxide, and 85 wt% phosphoric acid respectively; weigh ferrous sulfate with an iron concentration of 82 g / L, and dissolve it to a volume of 0.38 m³. 3 Add water to a final volume of 0.40 ml. 3 A ferrous salt solution with an iron concentration of 1.39 mol / L was obtained; 64 kg of ammonium dihydrogen phosphate solid was weighed, dissolved in water, and diluted to a final volume of 0.30 mL. 3 ; (2) Add ammonia water to the above phosphate solution in small amounts several times to make the pH of the phosphate solution 7.5, and then add pure water to make up to 0.4 m³. 3 A phosphate salt solution A with a concentration of 1.39 mol / L was obtained. Then, 44 kg of the above hydrogen peroxide solution was added and stirred evenly to obtain a phosphate salt solution B. (3) Add 0.6m to the reactor3 Pure water was submerged to the bottom of the stirring paddle. The temperature of the pure water was raised to 40°C, and the stirring was turned on at 30 Hz. The above ferrous salt solution and phosphate salt solution B were added into the reactor together within 45 minutes. After the addition was completed, the reaction was carried out for 30 minutes to obtain a yellow slurry A with pH=2. (4) Use a filter press to separate the yellow slurry A into solid and liquid. The resulting mother liquor is discharged into the wastewater treatment system for treatment. The resulting yellow filter cake is left in the filter chamber of the filter press and rinsed with hot pure water at 60°C until the conductivity of the rinse water drops to 4200 μS / cm. (5) The obtained yellow filter cake is transferred to a slurry tank, and hot pure water at 50°C is added at a ratio of 13% based on the solid content of anhydrous ferric phosphate. Stirring is started at a frequency of 30Hz and slurrying is carried out for 40 minutes to obtain yellow slurry B. (6) Add 30% of the above yellow slurry B into the reactor and add 32.05 kg of phosphoric acid solution; (7) Heat the temperature to 90°C. After the slurry turns white, add the remaining 70% of the yellow slurry B within 40 minutes. After the addition is completed, keep the temperature for 60 minutes to obtain a white slurry. (8) Use a filter press to separate the white slurry after the heat preservation is completed. The resulting filtrate is discharged into the wastewater treatment system for treatment. The resulting filter cake is left in the filter chamber of the filter press and rinsed with hot pure water at 60°C until the conductivity of the rinse water drops to 470 μS / cm. (9) The filter cake is blown in the filter press and discharged to obtain iron phosphate dihydrate filter cake. It is then flash-dried and calcined to obtain battery-grade anhydrous iron phosphate material.

[0045] The microstructures of the ferric phosphate dihydrate and anhydrous ferric phosphate prepared in this embodiment are as follows: Figure 4 As shown in the figure, the ferric phosphate prepared in this experiment is a blocky single-crystal ferric phosphate. Figure 4 The single-crystal primary particle size obtained by manual measurement of the shooting scale in (a) and (b) is 150~300nm. Figure 13 This is the particle size distribution diagram of anhydrous ferric phosphate. Its D0 is 0.36 μm, D10 is 10.60 μm, D50 is 16.13 μm, D90 is 23.41 μm, D99 is 26.66 μm, and D100 is 31.10 μm. The primary particles of anhydrous ferric phosphate are nanoscale particles, which spontaneously aggregate during the reaction to form large secondary or tertiary aggregates. Therefore, particle size measurement detects the size of these large aggregates.

[0046] Example 6 This embodiment provides a method for preparing bulk single-crystal iron phosphate. The reaction ratio in this embodiment is similar to that in Example 1, except that the yellow slurry B is divided into two parts. The ratio of the part added to the reaction vessel to the part reserved is 7:3, while in Example 1 it is 5:5. The method includes the following steps: (1) Prepare solutions of 25 wt% ammonia, 28 wt% hydrogen peroxide, and 85 wt% phosphoric acid respectively; weigh ferrous sulfate with an iron concentration of 82 g / L, and dissolve it to a volume of 0.38 m³. 3 Add water to a final volume of 0.40 ml. 3 A ferrous salt solution with an iron concentration of 1.39 mol / L was obtained; 64 kg of ammonium dihydrogen phosphate solid was weighed, dissolved in water, and diluted to a final volume of 0.30 mL. 3 ; (2) Add ammonia water to the above phosphate solution in small amounts several times to make the pH of the phosphate solution 7.5, and then add pure water to make up to 0.4 m³. 3 A phosphate salt solution A with a concentration of 1.39 mol / L was obtained. Then, 44 kg of the above hydrogen peroxide solution was added and stirred evenly to obtain a phosphate salt solution B. (3) Add 0.6m to the reactor 3 Pure water was submerged to the bottom of the stirring paddle. The temperature of the pure water was raised to 40°C, and the stirring was turned on at 30 Hz. The above ferrous salt solution and phosphate salt solution B were added into the reactor together within 45 minutes. After the addition was completed, the reaction was carried out for 30 minutes to obtain a yellow slurry A with pH=2. (4) Use a filter press to separate the yellow slurry A into solid and liquid. The resulting mother liquor is discharged into the wastewater treatment system for treatment. The resulting yellow filter cake is left in the filter chamber of the filter press and rinsed with hot pure water at 60°C until the conductivity of the rinse water drops to 4200 μS / cm. (5) The obtained yellow filter cake is transferred to a slurry tank, and hot pure water at 50°C is added at a ratio of 13% based on the solid content of anhydrous ferric phosphate. Stirring is started at a frequency of 30Hz and slurrying is carried out for 40 minutes to obtain yellow slurry B. (6) Add 70% of the above yellow slurry B into the reactor and add 32.05 kg of phosphoric acid solution; (7) Heat the temperature to 90°C. After the slurry turns white, add another 30% of yellow slurry B within 40 minutes. After the addition is completed, keep the temperature for 60 minutes to obtain white slurry. (8) Use a filter press to separate the white slurry after the heat preservation is completed. The resulting filtrate is discharged into the wastewater treatment system for treatment. The resulting filter cake is left in the filter chamber of the filter press and rinsed with hot pure water at 60°C until the conductivity of the rinse water drops to 470 μS / cm. (9) The filter cake is blown in the filter press and discharged to obtain iron phosphate dihydrate filter cake. It is then flash-dried and calcined to obtain battery-grade anhydrous iron phosphate material.

[0047] The microstructures of the ferric phosphate dihydrate and anhydrous ferric phosphate prepared in this embodiment are as follows: Figure 5 As shown in the figure, the ferric phosphate prepared in this experiment is a blocky single-crystal ferric phosphate. Figure 5 The single-crystal primary particle size obtained by manual measurement of the shooting scale in (a) and (b) is 100~200nm. Figure 14 This is the particle size distribution diagram of anhydrous ferric phosphate. Its D0 is 0.36 μm, D10 is 7.31 μm, D50 is 12.61 μm, D90 is 19.61 μm, D99 is 25.92 μm, and D100 is 34.07 μm. The primary particles of anhydrous ferric phosphate are nanoscale particles, which spontaneously aggregate during the reaction to form large secondary or tertiary aggregates. Therefore, particle size measurement detects the size of these large aggregates.

[0048] Example 7 This embodiment provides a method for preparing bulk single-crystal iron phosphate. The reaction ratio in this embodiment is similar to that in Example 1, except that the yellow slurry B is divided into two parts. The ratio of the part added to the reaction vessel to the part reserved is 1:9, while in Example 1 it is 5:5. The method includes the following steps: (1) Prepare solutions of 25 wt% ammonia, 28 wt% hydrogen peroxide, and 85 wt% phosphoric acid respectively; weigh ferrous sulfate with an iron concentration of 82 g / L, and dissolve it to a volume of 0.38 m³. 3 Add water to a final volume of 0.40 ml. 3 A ferrous salt solution with an iron concentration of 1.39 mol / L was obtained; 64 kg of ammonium dihydrogen phosphate solid was weighed, dissolved in water, and diluted to a final volume of 0.30 mL. 3 ; (2) Add ammonia water to the above phosphate solution in small amounts several times to make the pH of the phosphate solution 7.5, and then add pure water to make up to 0.4 m³. 3 A phosphate salt solution A with a concentration of 1.39 mol / L was obtained. Then, 44 kg of the above hydrogen peroxide solution was added and stirred evenly to obtain a phosphate salt solution B. (3) Add 0.6m to the reactor 3 Pure water was submerged to the bottom of the stirring paddle. The temperature of the pure water was raised to 40°C, and the stirring was turned on at 30 Hz. The above ferrous salt solution and phosphate salt solution B were added into the reactor together within 45 minutes. After the addition was completed, the reaction was carried out for 30 minutes to obtain a yellow slurry A with pH=2. (4) Use a filter press to separate the yellow slurry A into solid and liquid. The resulting mother liquor is discharged into the wastewater treatment system for treatment. The resulting yellow filter cake is left in the filter chamber of the filter press and rinsed with hot pure water at 60°C until the conductivity of the rinse water drops to 4200 μS / cm. (5) The obtained yellow filter cake is transferred to a slurry tank, and hot pure water at 50°C is added at a ratio of 13% based on the solid content of anhydrous ferric phosphate. Stirring is started at a frequency of 30Hz and slurrying is carried out for 40 minutes to obtain yellow slurry B. (6) Add 10% of the above yellow slurry B into the reactor and add 32.05 kg of phosphoric acid solution; (7) Heat the temperature to 90°C. After the slurry turns white, add the remaining 90% of the yellow slurry B within 40 minutes. After the addition is completed, keep the temperature for 60 minutes to obtain a white slurry. (8) Use a filter press to separate the white slurry after the heat preservation is completed. The resulting filtrate is discharged into the wastewater treatment system for treatment. The resulting filter cake is left in the filter chamber of the filter press and rinsed with hot pure water at 60°C until the conductivity of the rinse water drops to 470 μS / cm. (9) The filter cake is blown in the filter press and discharged to obtain iron phosphate dihydrate filter cake. It is then flash-dried and calcined to obtain battery-grade anhydrous iron phosphate material.

[0049] The microstructures of the ferric phosphate dihydrate and anhydrous ferric phosphate prepared in this embodiment are as follows: Figure 6 As shown in the figure, the ferric phosphate prepared in this experiment is a blocky single-crystal ferric phosphate. Figure 6 The single-crystal primary particle size obtained by manual measurement of the shooting scale in (a) and (b) is 50~100nm. Figure 15 This is the particle size distribution diagram of anhydrous ferric phosphate. Its D0 is 0.36 μm, D10 is 2.84 μm, D50 is 13.80 μm, D90 is 24.71 μm, D99 is 33.30 μm, and D100 is 39.99 μm. The primary particles of anhydrous ferric phosphate are nanoscale particles, which spontaneously aggregate during the reaction to form large secondary or tertiary aggregates. Therefore, particle size measurement detects the size of these large aggregates.

[0050] Comparative Example 1 This comparative example provides a method for preparing blocky single-crystal iron phosphate. The reaction ratio of this comparative example is similar to that of Example 1, except that all of the yellow slurry B is added to the reactor, while in Example 1, the yellow slurry B is divided into two portions, with the ratio of the portion added to the reactor to the portion reserved being 5:5. The method includes the following steps: (1) Prepare solutions of 25 wt% ammonia, 28 wt% hydrogen peroxide, and 85 wt% phosphoric acid respectively; weigh ferrous sulfate with an iron concentration of 82 g / L, and dissolve it to a volume of 0.38 m³.3 Add water to a final volume of 0.40 ml. 3 A ferrous salt solution with an iron concentration of 1.39 mol / L was obtained; 64 kg of ammonium dihydrogen phosphate solid was weighed, dissolved in water, and diluted to a final volume of 0.30 mL. 3 ; (2) Add ammonia water to the above phosphate solution in small amounts several times to make the pH of the phosphate solution 7.5, and then add pure water to make up to 0.4 m³. 3 A phosphate salt solution A with a concentration of 1.39 mol / L was obtained. Then, 44 kg of the above hydrogen peroxide solution was added and stirred evenly to obtain a phosphate salt solution B. (3) Add 0.6m to the reactor 3 Pure water was submerged to the bottom of the stirring paddle. The temperature of the pure water was raised to 40°C, and the stirring was turned on at 30 Hz. The above ferrous salt solution and phosphate salt solution B were added into the reactor together within 45 minutes. After the addition was completed, the reaction was carried out for 30 minutes to obtain a yellow slurry A with pH=2. (4) Use a filter press to separate the yellow slurry A into solid and liquid. The resulting mother liquor is discharged into the wastewater treatment system for treatment. The resulting yellow filter cake is left in the filter chamber of the filter press and rinsed with hot pure water at 60°C until the conductivity of the rinse water drops to 4200 μS / cm. (5) The obtained yellow filter cake is transferred to a slurry tank, and hot pure water at 50°C is added at a ratio of 13% based on the solid content of anhydrous ferric phosphate. Stirring is started at a frequency of 30Hz and slurrying is carried out for 40 minutes to obtain yellow slurry B. (6) Add the above yellow slurry B into the reactor and add 32.05 kg of phosphoric acid solution; (7) Heat to 90℃, and keep warm for 60 minutes after the slurry turns white to obtain a white slurry; (8) Use a filter press to separate the white slurry after the heat preservation is completed. The resulting filtrate is discharged into the wastewater treatment system for treatment. The resulting filter cake is left in the filter chamber of the filter press and rinsed with hot pure water at 60°C until the conductivity of the rinse water drops to 470 μS / cm. (9) The filter cake is blown in the filter press and discharged to obtain iron phosphate dihydrate filter cake. It is then flash-dried and calcined to obtain battery-grade anhydrous iron phosphate material.

[0051] The microstructures of the dihydrate ferric phosphate and anhydrous ferric phosphate prepared in this comparative example are as follows: Figure 7 As shown in the figure, the ferric phosphate prepared in this experiment is conventional flake ferric phosphate.

[0052] Comparative Example 2 This comparative example provides a method for preparing blocky single-crystal iron phosphate. The reaction ratio of this comparative example is similar to that of Example 1, except that the yellow slurry B is divided into two parts. The ratio of the part added to the reaction vessel to the part reserved is 8:2, while that in Example 1 is 5:5. The method includes the following steps: (1) Prepare solutions of 25 wt% ammonia, 28 wt% hydrogen peroxide, and 85 wt% phosphoric acid respectively; weigh ferrous sulfate with an iron concentration of 82 g / L, and dissolve it to a volume of 0.38 m³. 3 Add water to a final volume of 0.40 ml. 3 A ferrous salt solution with an iron concentration of 1.39 mol / L was obtained; 64 kg of ammonium dihydrogen phosphate solid was weighed, dissolved in water, and diluted to a final volume of 0.30 mL. 3 ; (2) Add ammonia water to the above phosphate solution in small amounts several times to make the pH of the phosphate solution 7.5, and then add pure water to make up to 0.4 m³. 3 A phosphate salt solution A with a concentration of 1.39 mol / L was obtained. Then, 44 kg of the above hydrogen peroxide solution was added and stirred evenly to obtain a phosphate salt solution B. (3) Add 0.6m to the reactor 3 Pure water was submerged to the bottom of the stirring paddle. The temperature of the pure water was raised to 40°C, and the stirring was turned on at 30 Hz. The above ferrous salt solution and phosphate salt solution B were added into the reactor together within 45 minutes. After the addition was completed, the reaction was carried out for 30 minutes to obtain a yellow slurry A with pH=2. (4) Use a filter press to separate the yellow slurry A into solid and liquid. The resulting mother liquor is discharged into the wastewater treatment system for treatment. The resulting yellow filter cake is left in the filter chamber of the filter press and rinsed with hot pure water at 60°C until the conductivity of the rinse water drops to 4200 μS / cm. (5) The obtained yellow filter cake is transferred to a slurry tank, and hot pure water at 50°C is added at a ratio of 13% based on the solid content of anhydrous ferric phosphate. Stirring is started at a frequency of 30Hz and slurrying is carried out for 40 minutes to obtain yellow slurry B. (6) Add 80% of the above yellow slurry B to the reactor and add 32.05 kg of phosphoric acid solution; (7) Heat the temperature to 90°C. After the slurry turns white, add another 20% of yellow slurry B within 40 minutes. After the addition is completed, keep the temperature for 60 minutes to obtain white slurry. (8) Use a filter press to separate the white slurry after the heat preservation is completed. The resulting filtrate is discharged into the wastewater treatment system for treatment. The resulting filter cake is left in the filter chamber of the filter press and rinsed with hot pure water at 60°C until the conductivity of the rinse water drops to 470 μS / cm. (9) The filter cake is blown in the filter press and discharged to obtain iron phosphate dihydrate filter cake. It is then flash-dried and calcined to obtain battery-grade anhydrous iron phosphate material.

[0053] The microstructures of the dihydrate ferric phosphate and anhydrous ferric phosphate prepared in this comparative example are as follows: Figure 8 As shown in the figure, the ferric phosphate prepared in this experiment is in the form of thick flakes.

[0054] Comparative Example 3 This comparative example provides a method for preparing bulk single-crystal iron phosphate. The reaction ratio of this comparative example is similar to that of Example 1, except that the molar ratio of phosphoric acid to iron in the reaction system is 1:1, while that in Example 1 is 0.5:1. The method includes the following steps: (1) Prepare solutions of 25 wt% ammonia, 28 wt% hydrogen peroxide, and 85 wt% phosphoric acid respectively; weigh ferrous sulfate with an iron concentration of 82 g / L, and dissolve it to a volume of 0.38 m³. 3 Add water to a final volume of 0.40 ml. 3 A ferrous salt solution with an iron concentration of 1.39 mol / L was obtained; 64 kg of ammonium dihydrogen phosphate solid was weighed, dissolved in water, and diluted to a final volume of 0.30 mL. 3 ; (2) Add ammonia water to the above phosphate solution in small amounts several times to make the pH of the phosphate solution 7.5, and then add pure water to make up to 0.4 m³. 3 A phosphate solution A with a concentration of 1.39 mol / L was obtained. Then, 44 kg of hydrogen peroxide solution was added and stirred evenly to obtain phosphate solution B. (3) Add 0.6m to the reactor 3 Pure water was submerged to the bottom of the stirring paddle. The temperature of the pure water was raised to 40°C, and the stirring was turned on at 30 Hz. The above ferrous salt solution and phosphate salt solution B were added into the reactor together within 45 minutes. After the addition was completed, the reaction was carried out for 30 minutes to obtain a yellow slurry A with pH=2. (4) Use a filter press to separate the yellow slurry A into solid and liquid. The resulting mother liquor is discharged into the wastewater treatment system for treatment. The resulting yellow filter cake is left in the filter chamber of the filter press and rinsed with hot pure water at 60°C until the conductivity of the rinse water drops to 4200 μS / cm. (5) The obtained yellow filter cake is transferred to a slurry tank, and hot pure water at 50°C is added at a ratio of 13% based on the solid content of anhydrous ferric phosphate. Stirring is started at a frequency of 30Hz and slurrying is carried out for 40 minutes to obtain yellow slurry B. (6) Add 50% of the above yellow slurry B to the reactor and add 64.10 kg of phosphoric acid solution; (7) Heat the temperature to 90°C. After the slurry turns white, add another 50% of yellow slurry B within 40 minutes. After adding the slurry, keep it warm for 60 minutes to obtain white slurry. (8) Use a filter press to separate the white slurry after the heat preservation is completed. The resulting filtrate is discharged into the wastewater treatment system for treatment. The resulting filter cake is left in the filter chamber of the filter press and rinsed with hot pure water at 60°C until the conductivity of the rinse water drops to 470 μS / cm. (9) The filter cake is blown in the filter press and discharged to obtain iron phosphate dihydrate filter cake. It is then flash-dried and calcined to obtain battery-grade anhydrous iron phosphate material.

[0055] The microstructures of the dihydrate ferric phosphate and anhydrous ferric phosphate prepared in this comparative example are as follows: Figure 9 As shown in the figure, the ferric phosphate prepared in this experiment is conventional flake ferric phosphate.

[0056] Comparative Example 4 This comparative example provides a method for preparing bulk single-crystal iron phosphate. The steps of this comparative example are similar to those of Example 1, and the reaction ratios are the same. The difference lies in the feeding method during the preparation stage. In this comparative example, the ferrous salt solution is added first, followed by the phosphate solution B. In Example 1, the ferrous salt solution and the phosphate solution B are added together. The method includes the following steps: (1) Prepare solutions of 25 wt% ammonia, 28 wt% hydrogen peroxide, and 85 wt% phosphoric acid respectively; weigh ferrous sulfate with an iron concentration of 82 g / L, and dissolve it to a volume of 0.38 m³. 3 Add water to a final volume of 0.40 ml. 3 A ferrous salt solution with an iron concentration of 1.39 mol / L was obtained; 64 kg of ammonium dihydrogen phosphate solid was weighed, dissolved in water, and diluted to a final volume of 0.30 mL. 3 ; (2) Add ammonia water to the above phosphate solution in small amounts several times to make the pH of the phosphate solution 7.5, and then add pure water to make up to 0.4 m³. 3 A phosphate solution A with a concentration of 1.39 mol / L was obtained. Then, 44 kg of hydrogen peroxide solution was added and stirred evenly to obtain phosphate solution B. (3) Add 0.6m to the reactor 3 Pure water was added to the bottom of the stirring paddle, and the above ferrous salt solution was added. The solution temperature was raised to 40°C, and the stirring was turned on at 30 Hz. The above phosphate salt solution B was added into the reactor within 45 minutes. After the addition was completed, the reaction was carried out for 30 minutes to obtain a yellow slurry A with pH=2. (4) Use a filter press to separate the yellow slurry A into solid and liquid. The resulting mother liquor is discharged into the wastewater treatment system for treatment. The resulting yellow filter cake is left in the filter chamber of the filter press and rinsed with hot pure water at 60°C until the conductivity of the rinse water drops to 4200 μS / cm. (5) The obtained yellow filter cake is transferred to a slurry tank, and hot pure water at 50°C is added at a ratio of 13% based on the solid content of anhydrous ferric phosphate. Stirring is started at a frequency of 30Hz and slurrying is carried out for 40 minutes to obtain yellow slurry B. (6) Add 50% of the above yellow slurry B into the reactor and add 32.05 kg of phosphoric acid solution; (7) Heat the temperature to 90°C. After the slurry turns white, add another 50% of yellow slurry B within 40 minutes. After adding the slurry, keep it warm for 60 minutes to obtain white slurry. (8) Use a filter press to separate the white slurry after the heat preservation is completed. The resulting filtrate is discharged into the wastewater treatment system for treatment. The resulting filter cake is left in the filter chamber of the filter press and rinsed with hot pure water at 60°C until the conductivity of the rinse water drops to 470 μS / cm. (9) The filter cake is blown in the filter press and discharged to obtain iron phosphate dihydrate filter cake. It is then flash-dried and calcined to obtain battery-grade anhydrous iron phosphate material.

[0057] The microstructures of the ferric phosphate dihydrate and anhydrous ferric phosphate prepared in Comparative Example 4 are as follows: Figure 10 As shown in the figure, the ferric phosphate prepared in this experiment is in the form of thick flakes.

[0058] Test Example 1 The iron phosphates prepared in Examples 1-7 and Comparative Examples 1-4 were subjected to ICP (inductively coupled plasma) for impurity content detection, and the results are shown in Table 1.

[0059] Table 1. Impurity content test results (ppm)

[0060] Although the present invention has been described in detail with reference to the accompanying drawings and preferred embodiments, the present invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should also be covered within the protection scope of the present invention.

Claims

1. A method for preparing bulk single-crystal iron phosphate, characterized in that, Includes the following steps: (1) Prepare 40-85 wt% phosphoric acid solution, 10-28 wt% hydrogen peroxide solution, 15-35 wt% ammonia solution, phosphate salt solution and ferrous salt solution for later use; Adding ammonia to a phosphate salt solution yields phosphate salt solution A. (2) Pour the above hydrogen peroxide solution and phosphate salt solution A into a mixing tank and stir evenly to obtain phosphate salt solution B; (3) Add pure water to the reactor, and heat it to 20-60°C under the condition of stirring frequency of 30-180Hz. Add the above ferrous salt solution and phosphate salt solution B into the reactor together within 30-90min. After reacting for 30-60min, slurry A is obtained. (4) The above slurry A is subjected to solid-liquid separation, the mother liquor is removed, and a filter cake is obtained. Then, hot pure water is added to wash the filter cake until the conductivity of the wash water after washing is reduced to below 5000 μS / cm. (5) Transfer the above filter cake into a pulping tank, add hot pure water, and stir for 30~180min to pulp to obtain pulp B; (6) Divide the above slurry B into two portions, one portion for later use, and the other portion into the reaction vessel, along with the above phosphoric acid solution; (7) Heat the temperature to 80~98℃. After the slurry turns white, add another portion of slurry B within 30~90 minutes. After adding the slurry, keep it warm for 30~180 minutes to obtain white slurry. (8) The above white slurry is subjected to solid-liquid separation, the slurry liquid is removed, and ferric phosphate dihydrate filter cake is obtained. Then, hot pure water is added to wash the filter cake until the conductivity of the wash water after washing is reduced to below 500 μS / cm. (9) After the filter cake is dried and calcined, battery-grade single-crystal anhydrous iron phosphate is obtained.

2. The method for preparing bulk single-crystal iron phosphate as described in claim 1, characterized in that, In step (1), the concentration of phosphorus in phosphate salt solution A is 0.5~2.0 mol / L; the phosphate salt solution is at least one of ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, or sodium phosphate.

3. The method for preparing bulk single-crystal iron phosphate as described in claim 1, characterized in that, In step (1), the concentration of iron in the ferrous salt solution is 0.5~2.0 mol / L; the ferrous salt solution is at least one of ferrous sulfate, ferrous nitrate, ferrous chloride, iron powder or iron sheet.

4. The method for preparing bulk single-crystal iron phosphate as described in claim 1, characterized in that, In step (2), the pH value of phosphate salt solution A is 6~8.

5. The method for preparing bulk single-crystal iron phosphate as described in claim 1, characterized in that, In step (3), the molar ratio of iron in the ferrous salt solution to phosphorus in the phosphate salt solution B is 1:(0.9~1.2).

6. The method for preparing bulk single-crystal iron phosphate as described in claim 1, characterized in that, In step (3), the pH value of the reaction system is 1 to 4.

7. The method for preparing bulk single-crystal iron phosphate as described in claim 1, characterized in that, In steps (4) and (8), the solid-liquid separation method is any one of centrifugation, pressure filtration, or filtration.

8. The method for preparing bulk single-crystal iron phosphate as described in claim 1, characterized in that, In step (5), the solid content of the pulp is 8%~20%.

9. The method for preparing bulk single-crystal iron phosphate as described in claim 1, characterized in that, In step (6), slurry B is divided into two parts, and the ratio of the part added to the reactor to the spare part is (1:9) to (7:3); the molar ratio of phosphoric acid to iron in the reaction system is (0.1 to 0.8):

1.

10. The method for preparing bulk single-crystal iron phosphate as described in claim 1, characterized in that, In steps (4), (5) and (8), the temperature of the hot pure water is 40~90℃.

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