Method for preparing iron phosphate dihydrate with high tap density

Abstract

The invention discloses a method for preparing iron phosphate dihydrate with high tap density, which comprises the following steps: adding an iron phosphate complexing solution into a suspension containing iron phosphate dihydrate particles at the temperature of 50-130 DEG C, and separating out and forming an iron phosphate dihydrate product in the decomplexing process of the iron phosphate complexing solution, the product has a higher tap density than the raw material iron phosphate dihydrate particles. The iron phosphate dihydrate prepared by the method has irregular polyhedral morphology, and the tap density is higher than 0.9 g / cm < 3 >.

Description

Technical Field

[0001] This invention belongs to the field of inorganic materials and lithium battery material preparation technology, specifically relating to a method for preparing iron phosphate, a precursor material for lithium-ion batteries. Background Technology

[0002] The development of lithium-ion battery materials is rapid, especially lithium iron phosphate (LFP) and ternary materials. Based on the requirement to improve the energy density of LFP batteries, increasing the compaction density of LFP can be one way to improve the energy density of LFP batteries. Iron phosphate, as a raw material for preparing LFP, has a direct impact on the compaction density of LFP. Preparing high-purity, high-compaction iron phosphate can ultimately improve the energy density of LFP battery packs.

[0003] The main methods for preparing high-pressure iron phosphate products are as follows:

[0004] CN115215313A generates an amorphous ferrous phosphate octahydrate reaction precursor in situ in a first mixture system by controlling the synthesis conditions. Then, the dissolution rate of the amorphous ferrous phosphate octahydrate reaction precursor is controlled by controlling the pH of the second slurry, thereby regulating the concentration of phosphate and ferrous ions in the reaction system. Finally, the supersaturation of ferric and phosphate ions in the reaction system is precisely controlled by adding oxidizing substances.

[0005] CN116534820B provides a method for preparing high-pressure ferric phosphate from industrial monoammonium phosphate and ferrous sulfate. The method adopts a reaction route of oxidation followed by metathesis. First, hydrogen peroxide is used to completely oxidize the refined ferrous sulfate solution. Then, monoammonium phosphate is slowly added. The initial iron concentration of the reaction solution is high, which allows the small amount of added monoammonium phosphate to react rapidly with the high concentration of iron ions to form small particles of ferric phosphate. In subsequent reactions, these small particles of ferric phosphate aggregate and grow, resulting in a complete reaction.

[0006] Increasing the tap density of iron phosphate precursors is also a common method to improve the compaction density of lithium iron phosphate materials. So far, there is a lack of a simple and low-cost industrial application method for preparing iron phosphate with high tap density. Summary of the Invention

[0007] The purpose of this application is to provide a method for improving the tap density of ferric phosphate. Furthermore, this invention discloses a method for preparing ferric phosphate material with high tap density. The inventors of this application have discovered that ferric phosphate with an irregular polyhedral morphology prepared using the method of this invention has a higher tap density.

[0008] This invention discloses a method for preparing ferric phosphate dihydrate, comprising: adding an ferric phosphate complexing solution to a suspension containing ferric phosphate dihydrate particles at a temperature of 50-130°C; and precipitating and forming ferric phosphate dihydrate product during the decomplexing process of the ferric phosphate complexing solution. The inventors of this application have discovered that the ferric phosphate dihydrate product obtained by the method of this invention has a higher tap density than the raw ferric phosphate dihydrate particles in the suspension.

[0009] According to the present invention, the temperature is, for example, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, etc., preferably 70-110°C, more preferably 85-105°C.

[0010] The ferric phosphate dihydrate particles are nanoparticles, microparticles, or particles with a larger diameter than ferric phosphate dihydrate (in this invention, they are sometimes simply referred to as ferric phosphate, such as ferric phosphate suspension, ferric phosphate particles, etc. The context suggests they are ferric phosphate dihydrate). Ferric phosphate particles can be obtained through in-situ synthesis, commercial acquisition, or by grinding after purchase. Preferably, the ferric phosphate nanoparticles are ferric phosphate dihydrate particles with an average particle size of less than 950 nm, more preferably with an average particle size of less than 400 nm. Preferably, the average particle size of the microparticles is 1-3000 micrometers.

[0011] The suspension containing ferric phosphate particles contains ferric phosphate dihydrate particles, water, and may further contain phosphoric acid and / or ferric phosphate complexes. If it contains phosphoric acid and / or ferric phosphate complexes, the weight percentage of phosphoric acid and ferric phosphate complexes is 0.01-30% of the total weight of the suspension containing ferric phosphate particles. Preferably, the suspension containing ferric phosphate particles contains ferric phosphate particles and water. The phosphoric acid and / or ferric phosphate complexes contained in the suspension may be derived from the reuse of the mother liquor after separating the ferric phosphate dihydrate solid product.

[0012] The suspension containing ferric phosphate particles can be obtained by mixing ferric phosphate dihydrate particles with a particle size of nanometer, micrometer, or larger with water or an aqueous solution containing phosphoric acid. The aqueous solution containing phosphoric acid includes water, phosphoric acid, and / or an ferric phosphate complex, wherein the phosphoric acid or ferric phosphate complex is derived from the reuse of the mother liquor after separating the ferric phosphate dihydrate solid product. The suspension containing ferric phosphate particles can also be prepared in situ by diluting the ferric phosphate complex solution with water or an aqueous solution containing phosphoric acid at a temperature of room temperature to 110°C, thereby decomposing and precipitating the ferric phosphate dihydrate particles to obtain the suspension containing ferric phosphate particles.

[0013] In a preferred embodiment of the present invention, the in-situ preparation method includes reducing the concentration of the ferric phosphate complex to 10% or less of its original concentration, preferably to 10%-0.5%, using water at a temperature of room temperature to 110°C, and aging for 10 minutes to 6 hours to obtain a suspension containing ferric phosphate dihydrate particles. Studies have found that when the temperature is below 90°C, a suspension containing nano-sized ferric phosphate dihydrate particles is obtained; when the temperature is between 90-110°C, a suspension containing micron-sized ferric phosphate dihydrate particles is obtained.

[0014] In the method for preparing ferric phosphate dihydrate, the rate of addition of the ferric phosphate complex solution is preferably controlled within a certain range so that the rate of increase in the concentration of the ferric phosphate complex solution in the suspension is within the range of 0.001-0.05 mol / (L·min), for example: 0.0015 mol / (L·min), 0.002 mol / (L·min), 0.003 mol / (L·min), 0.004 mol / (L·min), 0.005 mol / (L·min), 0.006 mol / (L·min), 0.007 mol / (L·min), 0 The concentrations are 0.008 mol / (L·min), 0.009 mol / (L·min), 0.01 mol / (L·min), 0.015 mol / (L·min), 0.02 mol / (L·min), 0.025 mol / (L·min), 0.03 mol / (L·min), 0.035 mol / (L·min), 0.04 mol / (L·min), 0.045 mol / (L·min), 0.05 mol / (L·min), etc., preferably 0.005-0.04 mol / (L·min). The inventors have found that if the concentration of the ferric phosphate complex in the suspension increases too slowly, it may lead to a decrease in ferric phosphate production efficiency and an increase in energy consumption; while if the concentration of the ferric phosphate complex in the suspension increases too quickly, it may affect the tap density of the prepared ferric phosphate dihydrate. Preferably, the liquid volume of the suspension is at least not less than the total volume of the added ferric phosphate complex solution, in order to dilute the ferric phosphate complex solution and promote the precipitation of ferric phosphate. V is preferred. 悬浮液 V 络合液 The ratio is 1:1-10:1, for example, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, etc. Since dilution with the complexing solution is sufficient to precipitate ferric phosphate, to obtain a ferric phosphate product with a higher tap density, it is preferable to control the degree of dilution of the complexing solution, and the dilution ratio (V...) 悬浮液 V 络合液 Both excessively low and excessively high values ​​will affect the tap density of the final prepared iron phosphate.

[0015] Furthermore, the present invention also provides a method for preparing iron phosphate, comprising:

[0016] S1: Prepare a suspension containing ferric phosphate dihydrate particles;

[0017] S2: Add ferric phosphate complex solution to the suspension of S1 at 50-130℃, and then keep it warm and aged.

[0018] S3: Solid-liquid separation to obtain iron phosphate dihydrate solid, followed by high-temperature dehydration to obtain iron phosphate product.

[0019] In this process, the liquid volume of the suspension in S1 should be at least as large as the volume of the ferric phosphate complex solution added in S2, in order to dilute the ferric phosphate complex solution in S2 and promote the precipitation of ferric phosphate. V is preferred. 悬浮液 V 络合液 The ratio is 1:1-10:1, for example, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, etc. Diluting the complexing solution will complete the precipitation of ferric phosphate. To obtain a ferric phosphate product with a higher tap density, it is preferable to control the degree of dilution of the complexing solution, and the dilution ratio (V...) 悬浮液 V 络合液 Both excessively low and excessively high values ​​will affect the tap density of the final prepared iron phosphate.

[0020] In one embodiment of the present invention, in step S1, the method for preparing a suspension containing ferric phosphate dihydrate particles is to add ferric phosphate dihydrate solid particles to water or an aqueous solution containing phosphoric acid.

[0021] In another embodiment of the present invention, in step S1, the method for preparing the suspension containing ferric phosphate dihydrate particles is to prepare the ferric phosphate dihydrate suspension in situ. For example, at a temperature of room temperature to 110°C, the ferric phosphate complex solution is diluted with water or an aqueous solution containing phosphoric acid, and then the complex is decomplexed to precipitate ferric phosphate dihydrate particles, thereby obtaining the suspension containing the ferric phosphate particles; preferably, the concentration of the ferric phosphate complex solution is reduced with water to 10% or less of the original concentration, for example, to 10%-0.5% of the original concentration, and aged for 10 minutes to 6 hours to obtain the suspension containing ferric phosphate dihydrate particles.

[0022] In step S2, the temperature is preferably 70-110°C, more preferably 85-105°C.

[0023] After solid-liquid separation in step S3, the separated mother liquor can be reused to replace or partially replace the water or phosphoric acid-containing aqueous solution in step S1 to prepare the suspension from step S1.

[0024] The high-temperature dehydration temperature in step S3 is 400-1000℃, preferably 500-800℃.

[0025] The present invention also provides an iron phosphate material, characterized in that the iron phosphate material has an irregular polyhedral morphology, which is a stacked micron-sized secondary particle, and the material has a tap density greater than 0.9 g / cm³. 3 The preferred tap density is 0.95-1.4 g / cm³. 3 The iron phosphate material is prepared by the aforementioned method of the present invention.

[0026] Terminology Explanation:

[0027] Ferric phosphate complex: Ferric phosphate-phosphoric acid complex formed by ferric phosphate and phosphoric acid, existing in solution form. In this invention, "ferric phosphate complex," "ferric phosphate complex solution," "ferric phosphate complex liquid," and "complex liquid" have the same meaning and can be used interchangeably.

[0028] Phosphorus-to-iron ratio: In this invention, the phosphorus-to-iron ratio (P:Fe) refers to the molar ratio (molar ratio) of phosphorus to iron in a system (e.g., a solution of ferric phosphate complex). Phosphorus refers to all phosphorus elements in the system, and iron refers to all iron elements in the system. For example, in the solution or product obtained by reacting 3 mol of phosphoric acid with 1 mol of ferric hydroxide, the phosphorus-to-iron ratio is 3:1, while the phosphorus-to-iron ratio of 6 mol of phosphoric acid with 1 mol of iron(III) oxide is 2:1. In this invention, the phosphorus-to-iron ratio is described as 3:1 or 3, which have the same meaning, both indicating that phosphorus:iron = 3:1.

[0029] Iron ions: The iron ions described in this invention include free iron ions, and free iron ions include ferrous ions (Fe2+). 2+ ), trivalent iron ions (Fe 3+ ).

[0030] Decomplexation: refers to the process or reaction of decomposing a complex. In this invention, it refers to the decomposition of ferric phosphate complex to form ferric phosphate precipitate.

[0031] Room temperature: refers to indoor temperature. In this invention, the room temperature is 15-25℃, which is a temperature that does not require heating.

[0032] Dilution concentration: refers to the concentration of the solute after dilution relative to the original solution. Although the original solute may change during the dilution process, the degree of dilution is still calculated based on the original solute concentration. For example, the iron phosphate complex in this application may decompose during the dilution process; however, the degree of dilution is calculated based on the original concentration of the iron phosphate complex, iron ions, or phosphate ions.

[0033] mol / (L·min): moles per (liters per minute), also written as mol·L -1 ·min -1 .

[0034] min: indicates minutes.

[0035] H or h: indicates hours.

[0036] Beneficial effects

[0037] This invention employs a novel method to prepare high-tap-density ferric phosphate, notably utilizing a ferric phosphate complex solution in the presence of seed crystals to decomplex and form a ferric phosphate product with even higher tap density. This invention discovers that regardless of whether the seed crystals are nanoparticles or micron-sized particles, under appropriate aging temperatures and the rate of addition of the complexing solution, high-tap-density ferric phosphate dihydrate can be obtained, thereby increasing the tap density of the final product, ferric phosphate (the tap density of ferric phosphate is higher than that of ferric phosphate dihydrate). Furthermore, the reaction conditions of this invention are simple and controllable, allowing for industrialization based on existing ferric phosphate preparation processes. Attached Figure Description

[0038] Figure 1 The images shown are SEM characterization images of the product from Example 1, corresponding to products at different aging temperatures, where (a) is 60℃, (b) is...

[0039] 70℃, (c)80℃, (d)90℃, (e)100℃.

[0040] Figure 2 This is a SEM characterization image of the product in Example 3.

[0041] Figure 3 This is a SEM characterization image of the pilot product from Example 4. Detailed Implementation

[0042] The parameters and measurement methods involved in this invention are as follows.

[0043] Tap density refers to the mass per unit volume of powder in a container after compaction under specified conditions. Tap density is a commonly used quality control parameter in ultrafine powder engineering, and it is related to the powder's size, morphology, size distribution, and degree of dryness (moisture content). The measurement method for tap density mainly includes the following steps: 1. Using a precise balance, select a clean and dry glass graduated cylinder and weigh it. Evenly fill the graduated cylinder with the powder to be tested until it reaches the maximum scale value, ensuring the powder is horizontal within the cylinder. 2. Vibration stage: Place the sample graduated cylinder in the instrument's working position, turn on the instrument switch, and set the vibration frequency and number of vibrations. The drive rod moves up and down repeatedly, automatically vibrating the sample graduated cylinder. The instrument automatically stops after the test. 3. Data recording and calculation: Read the volume of the powder and input the volume and weight data into the computer. Calculate the tap density using the formula: ρ = m / V, where m is the mass of the powder and V is the volume of the powder after compaction.

[0044] Average particle size and measurement method: Particle size can be marked using a scanning electron microscope. Calibration is performed according to the magnification and scale. The test results are then verified using a Malvern laser particle size analyzer. The Malvern laser particle size analysis method is as follows: Take a small amount of sample (0.003g-0.1g each time) with a sample spoon, add it to the testing instrument in three portions, and observe the change in the system shading rate of the testing instrument. Record the data when the shading rate reaches between 9% and 10%.

[0045] Refer to Example 1

[0046] According to the preparation method in Example 8 of Chinese Invention Patent CN116924365A, 310 mL of an 85% phosphoric acid solution was placed in a 1 L flask, and 190 mL of deionized water was added to form a 9 mol / L phosphoric acid solution. 79.84 g of iron oxide powder was accurately weighed and added to the phosphoric acid solution. The entire system was heated to 90°C and stirred at 90°C for 3 hours. After the reaction was complete, the system was filtered to obtain a purple-red iron phosphate complex solution with a phosphorus-to-iron ratio of 4.5:1 and an iron concentration of 2 mol / L. 50 mL of the purple-red iron phosphate complex solution (phosphorus-to-iron ratio of 4.5:1) was taken, and two times the volume of deionized water was added to the complex solution. The mixture formed by the deionized water and the iron phosphate complex solution was then heated to 90°C. After reacting for 6 hours, the precipitate was filtered, washed, and the product, iron phosphate dihydrate, was obtained with a mass of 17.01 g and a yield of 90.9%.

[0047] The measured tap density of ferric phosphate dihydrate was 0.8124 g / cm³. 3 .

[0048] Example 1

[0049] Measure 31 mL of H3PO4 solution (wt = 85%) and 19 mL of H2O to form a mixed solution. Accurately weigh 7.9845 g of Fe2O3 powder. Mix the Fe2O3 powder with the phosphoric acid aqueous solution to form a mixed system. Transfer the mixed system to an oil bath and keep it at 90℃ for 3 h. Filter to obtain 50 mL of ferric phosphate complex solution. The iron ion concentration in the complex solution is 2 mol / L.

[0050] 100 mL of H₂O was added to a three-necked flask and placed in an oil bath. After incubation at 60 °C for 30 min, 6 mL of ferric phosphate complex solution was added to the system, and incubation continued for another 30 min, forming a suspension containing ferric phosphate dihydrate nanoparticles. The mixture was transferred to a 90 °C oil bath and incubated for another 30 min to allow further crystallization and aging of the precipitate. After incubation, the oil bath temperature was maintained at 90 °C, and the remaining 44 mL of complex solution was pumped into the system at a rate of 1 rpm (0.3 mL / min). After pumping, incubation continued for 2 h to prepare FePO₄·2H₂O with irregular polyhedral packing, designated "EX1-1". The mass of the FePO₄·2H₂O product EX1-1 was 14.4267 g, and the tap density was 1.1422 g / cm³. 3 The yield was 77.62%.

[0051] The experimental conditions were based on 6 mL of complexing solution + 100 mL of H₂O, incubation at 60℃ for 30 min, and aging at 90℃ for 30 min. The pump rate was set to 1 rpm / min (approximately 0.33 mL / min, with an iron ion concentration increase rate of approximately 0.0062 mol / (L·min)). The system temperature and aging temperature were changed to 60℃, 70℃, 80℃, and 100℃, resulting in products EX1-2, EX1-3, EX1-4, and EX1-5, respectively. SEM results showed that under the pumping and incubation conditions at 60℃ and 70℃, the product morphology consisted of layered, micron-sized secondary particles. Under the pumping and incubation conditions at 80℃, the product morphology consisted of micron-sized secondary particles composed of both layers and irregular polyhedra. The tap density of products EX1-2, EX1-3, EX1-4, and EX1-5 was measured to be 0.6730 g / cm³. 3 0.8203 g / cm 3 0.9711 g / cm 3 and 1.2393 g / cm 3 The tap density of the product combined with EX1-1 is 1.1422 g / cm³. 3 As can be seen, increasing the aging temperature can increase the tap density of ferric phosphate dihydrate, see Table 1.

[0052] Table 1 Experimental Results of Example 1

[0053]

[0054] Furthermore, the resulting material morphology also differed. As the temperature increased from 60℃ to 80℃, the product gradually transformed from lamellar stacked micron particles to randomly stacked micron particles, and then to randomly polyhedral aggregated micron secondary particles at 90℃ and 100℃. The tap density gradually increased, as shown in the following results. Figure 1 As shown.

[0055] Example 2: Testing different complexing solution addition rates

[0056] Measure 31 mL of H3PO4 solution (wt = 85%) and 19 mL of H2O to form a mixed solution. Accurately weigh 7.9845 g of Fe2O3 powder. Mix the Fe2O3 powder with the phosphoric acid aqueous solution to form a mixed system. Transfer the mixed system to an oil bath and keep it at 90℃ for 3 h. Filter to obtain 50 mL of ferric phosphate complex solution with a concentration of 2 mol / L.

[0057] 100 mL of H₂O was added to a three-necked flask and placed in an oil bath. After incubation at 60 °C for 30 min, 6 mL of ferric phosphate complex solution was added to the system. Incubation was continued for another 30 min. The mixture was then transferred to a 90 °C oil bath and incubated for another 30 min to allow further crystallization and aging of the precipitate. After this incubation period, a suspension containing ferric phosphate dihydrate nanoparticles was formed. The oil bath temperature was controlled at 90 °C. The remaining 44 mL of complex solution was pumped into the system at a rate of 2 rpm (0.6 mL / min, with a concentration increase rate of 0.0124 mol / (L·min)). After pumping, the system was incubated at 90 °C for 2 h. The mass of the EX2-2 product FePO₄·2H₂O was 15.2537 g, and the tap density was 1.1157 g / cm³. 3 The yield was 81.64%.

[0058] The remaining 44 mL of complexing solution was pumped into the above system at a rate of 3 rpm (0.9 mL / min, with a concentration increase rate of 0.0186 mol / (L·min) during the pumping process). After pumping was completed, the mixture was kept at 90 °C for 2 h. The tap density of the obtained EX2-3 product was 0.9058 g / cm³. 3 .

[0059] Table 2 Test Results of Example 2

[0060]

[0061] Based on the data from EX1-1 in Example 1, it is shown that the product tap density is highest when the pump rate is 0.3 mL / min (the concentration increase rate during the pumping process is 0.0062 mol / (L·min)). Increasing the pump rate decreases the product tap density. However, the products in EX2-2 and EX2-3 are still considered to have high tap density.

[0062] Example 3 uses complexing solutions of different concentrations

[0063] 50 mL of complex solution was prepared according to the same method as in Example 1. 6 mL of the complex solution was added to 100 mL of H2O, and the mixture was kept at 60 °C for 30 min. Centrifugation yielded a white precipitate, which was dispersed in 50 mL of H2O and heated to 90 °C for 30 min. 44 mL of the complex solution was pumped into the above system at a feed rate of 0.5 rpm (0.15 mL / min, concentration increase rate approximately 0.006 mol / (L·min)). After pumping, the mixture was kept at 90 °C for 2 h to obtain a white precipitate. The obtained product was EX3-1, with a mass of 11.4343 g, a yield of 61.20%, and a tap density of 1.2118 g / cm³. 3 SEM characterization revealed that the samples prepared under these experimental conditions consisted of irregularly packed polyhedral micron-sized secondary particles. (See also...) Figure 2 As shown.

[0064] In this experiment, V 悬浮液 V 络合液 =50:44, compared to Examples 1-2, which is equivalent to doubling the concentration of the complexing solution added, but also yielding a product with high tap density.

[0065] Example 4 Pilot-scale experiment

[0066] 25L of ferric phosphate complex solution was prepared using the same method as in Example 1.

[0067] 50 L of H₂O was added to a 100 L reactor. When the thermometer read 60 °C, 2.5 L of ferric phosphate complex solution was slowly added. After adding the complex solution, the thermometer read 63.8 °C. After maintaining this temperature for 30 min, the reactor temperature was raised to 90 °C and maintained for another 30 min, forming a suspension containing ferric phosphate dihydrate nanoparticles. The remaining 22.5 L of complex solution was pumped into the reactor at a rate of 30 r / min (approximately 150 mL / min, with a concentration increase rate slightly less than 0.006 mol / (L·min)). After pumping, the reactor was kept at this temperature for another 2 h before stopping the reaction. The tap density of the final product EX4, phosphate dihydrate, was 1.015 g / cm³. 3 The final product, ferric phosphate dihydrate, was characterized by SEM, and the results are as follows: Figure 3 As shown in the image, the SEM results indicate that the product morphology consists of irregularly aggregated polyhedral micron-sized secondary particles. This is higher than the tap density of commercially available ordinary ferric phosphate dihydrate (0.8-0.92 g / cm³). 3 Between, such as 0.8766 g / cm³ 3 ).

[0068] Example 5

[0069] The complexing solution was prepared according to the method in Example 1.

[0070] 100 mL of H₂O was added to a three-necked flask and placed in an oil bath. The mixture was kept at 90 °C for 30 min. Then, 6 mL of complexing solution was added to the system. After 30 min of incubation, a suspension containing non-nanoparticles of ferric phosphate dihydrate was formed. The remaining complexing solution was pumped into the mixture at a rate of 1 rpm. After pumping, the mixture was kept at 90 °C for 2 h to terminate the reaction. The product mass was 14.0632 g, with a yield of 75.27%. SEM results showed that the morphology consisted of randomly packed polyhedral micron-sized secondary particles. The tap density was measured to be 1.2069 g / cm³. 3 .

[0071] This experiment shows that although the reaction temperature of 90℃ yields micron-sized (non-nano) iron phosphate dihydrate suspensions instead of nano-sized iron phosphate dihydrate suspensions, it has no substantial impact on the final result.

[0072] Example 6: Micron Seed Experiment

[0073] Take 2g of ferric phosphate dihydrate, which consists of sheet-like stacked micron-sized particles obtained from EX1-2 (60℃) (tap density 0.6730g / cm³). 3 The mixture was dispersed in 100 mL of H₂O, and the mixture was heated to 90 °C. The complex solution prepared according to Example 1 was then pumped into the mixture at a rate of 0.3 mL / min. After pumping, the mixture was kept at 90 °C for 2 hours, and then the reaction was stopped. Product EX6-1 was obtained, with a mass of 14.8561 g and a yield of 79.52%. Its tap density was measured to be 0.9520 g / cm³. 3 The morphology of the product was characterized by SEM, and the product morphology consisted of micron-sized particles of randomly packed nanoparticles.

[0074] Using the same method, ferric phosphate dihydrate obtained from EX1-3 and EX1-4 in Example 1 was used as seed crystals to obtain products EX6-2 and EX6-3. Among them, EX6-2 (70℃) had a mass of 15.7881 g, a yield of 84.50%, and a tap density of 0.9863 g / cm³. 3 The product mass of EX6-3 (80℃) was 16.1982 g, the yield was 86.70%, and the tap density was 1.0466 g / cm³. 3 .

[0075]

[0076] The experimental results of Example 6 show that using micron-sized particles as seed crystals and adding the complexing liquid to the seed crystal suspension system, while controlling the appropriate temperature and the addition rate of the complexing liquid, will increase the tap density of the iron phosphate dihydrate product.

[0077] Example 7

[0078] The complexing solution was prepared according to the method in Example 1.

[0079] Take 2g of commercially available, layered, micron-sized ferric phosphate dihydrate (from the production line of Huanggang Linli New Energy Technology Co., Ltd., with a tap density of 0.9024g / cm³). 3 The mixture was dispersed in 100 mL of H₂O, and the mixture was heated to 90 °C. The complexing solution was then pumped into the system at a rate of 0.3 mL / min. After pumping, the mixture was kept at 90 °C for 2 hours, and then the reaction was stopped. The product mass was 15.6063 g, the yield was 75.45%, and the tap density was 1.3465 g / cm³. 3 The morphology of the product was characterized by SEM, and the product morphology consisted of micron-sized particles of randomly packed nanoparticles.

[0080] This experiment shows that using commercially available iron phosphate dihydrate as seed crystals directly, this method can yield products with higher tap density.

[0081] Example 8: Increasing the initial concentration of the complexing solution (iron ion concentration 2.67 mol / L)

[0082] Measure 42 mL of 85% H3PO4 solution and 8 mL of H2O to form a phosphoric acid aqueous solution. Accurately weigh 10.646 g of Fe2O3 powder and add it to the phosphoric acid aqueous solution. Heat the mixture to 90℃ and maintain the temperature for 3 h. Filter to obtain a complex solution (iron ion concentration 2.67 mol / L). Transfer 100 mL of deionized water to a three-necked flask and maintain the temperature at 60℃ for 30 min. Add 6 mL of the iron phosphate complex solution to the system and continue to maintain the temperature for 30 min to form a suspension system. Transfer the mixture to a 90℃ oil bath and continue to maintain the temperature for 30 min to allow the precipitate to further crystallize and age. After the temperature maintenance, control the oil bath temperature at 90℃ and pump the remaining 44 mL of complex solution into the above system at a rate of 1 rpm (0.3 mL / min). After the pumping is completed, continue to maintain the temperature for 2 h to prepare FePO4·2H2O. The mass of FePO4·2H2O is 8.9959 g, and the tap density is 1.4201 g / cm³. 3 The yield was 36.1%.

[0083] This experiment shows that increasing the concentration of the complexing solution can increase the tap density.

[0084] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing ferric phosphate dihydrate, the method comprising: At a temperature of 50-130℃, an iron phosphate complex solution is added to a suspension containing iron phosphate dihydrate particles. During the decomplexation process, the iron phosphate complex solution precipitates and forms iron phosphate dihydrate products.

2. The method as described in claim 1, characterized in that, The temperature is 70-110℃, preferably 85-105℃.

3. The method as described in claim 1 or 2, characterized in that, The ferric phosphate dihydrate particles are nanoparticles, microparticles, or particles with larger diameters of ferric phosphate dihydrate.

4. The method according to any one of claims 1-3, characterized in that, The suspension containing ferric phosphate dihydrate particles is obtained by mixing ferric phosphate dihydrate particles with nano, micro, or larger particle sizes with water or an aqueous solution containing phosphoric acid; or The suspension containing ferric phosphate dihydrate particles is prepared in situ. The in-situ preparation method includes diluting the ferric phosphate complex with water or an aqueous solution containing phosphoric acid at a temperature of room temperature to 110°C, thereby decomposing the complex and precipitating the ferric phosphate dihydrate particles.

5. The method as described in claim 4, characterized in that, The aqueous solution containing phosphoric acid includes water, phosphoric acid and / or ferric phosphate complex, wherein the weight percentage of phosphoric acid and ferric phosphate complex is between 0.01% and 30% of the total weight, and wherein the phosphoric acid or ferric phosphate complex is derived from the reuse of the mother liquor after separating the solid product ferric phosphate dihydrate.

6. The method according to any one of claims 1-5, characterized in that, When adding the ferric phosphate complex solution, the rate of increase in the concentration of the ferric phosphate complex solution should be controlled within 0.001 mol / (L·min) to 0.05 mol / (L·min), preferably 0.005 mol / (L·min) to 0.04 mol / (L·min).

7. A method for preparing ferric phosphate, comprising: S1: Prepare a suspension containing ferric phosphate dihydrate particles; S2: Add ferric phosphate complex solution to the suspension of S1 at 50-130℃, and then keep it warm and aged. S3: Solid-liquid separation to obtain iron phosphate dihydrate solid, followed by high-temperature dehydration to obtain iron phosphate product; Wherein, the liquid volume in the suspension in S1 is not less than the volume of the ferric phosphate complex solution added in S2, preferably V 悬浮液 V 络合液 The ratio is 1:1 to 10:

1.

8. The method as described in claim 7, characterized in that, In step S1, solid ferric phosphate dihydrate particles are added to water or an aqueous solution containing phosphoric acid to form a suspension or to prepare a ferric phosphate dihydrate suspension in situ. In step S2, the temperature is 70-110℃. After solid-liquid separation in step S3, the separated mother liquor is reused to replace or partially replace the water or aqueous solution containing phosphoric acid in step S1 to prepare the suspension in step S1. The high-temperature dehydration temperature is 400-1000℃.

9. The method as described in claim 8, characterized in that, In step S1, the method for preparing ferric phosphate dihydrate suspension in situ includes diluting the ferric phosphate complex with water or an aqueous solution containing phosphoric acid at a temperature of room temperature to 110°C, thereby decomposing the complex and precipitating ferric phosphate dihydrate particles; in step S2, the temperature is 85-105°C; and in step S3, the temperature for high-temperature dehydration is 500-800°C.

10. A ferric phosphate material, characterized in that, This iron phosphate material exhibits an irregular polyhedral morphology, consisting of stacked micron-sized secondary particles, and has a tap density greater than 0.9 g / cm³. 3 The preferred tap density is 0.95-1.4 g / cm³. 3 The iron phosphate material is prepared by the method described in any one of claims 1-9.

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