Preparation method of high-purity iron phosphate based on novel washing mode

Abstract

The invention provides a method for preparing high-purity iron phosphate by using a novel washing mode, and belongs to the field of battery materials. The preparation method comprises the following steps: by taking crude phosphoric acid as a raw material, preparing an iron phosphate precursor in ammonia water by a coprecipitation method, pulping and washing to control water washing conductivity, aging to obtain a crude iron phosphate dihydrate filter cake, introducing a magnetic impurity removal substance and pure water, pulping to selectively adsorb alkali metal impurities such as potassium, and finally, carrying out filter pressing, drying and calcining to obtain the battery-grade high-purity iron phosphate. According to the method, low-cost and low-quality crude phosphoric acid is used as a raw material, so that the production cost of high-purity iron phosphate is greatly reduced; and the obtained iron phosphate is low in impurity content and high in tap density, the compaction density reaches 2.55 g / cm < 3 > after the iron phosphate is prepared into lithium iron phosphate, the 1C discharge capacity is 137.62 mAh / g, and the lithium iron phosphate has excellent electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of battery materials, specifically to a method for preparing high-purity iron phosphate based on a novel washing method. Background Technology

[0002] Iron phosphate (FePO4) is an important precursor for the preparation of lithium iron phosphate (LiFePO4) cathode materials. As a primary material for power batteries in new energy vehicles, the demand for lithium iron phosphate is increasing daily, thus driving up the demand for its precursor, iron phosphate. Although the demand for iron phosphate is increasing year by year, its market price remains sluggish.

[0003] Currently, the main industrial production process for ferric phosphate is the co-precipitation method of ferrous sulfate and phosphate under the action of an oxidant. The phosphorus source is mostly 85% phosphoric acid or high-quality industrial monoammonium phosphate. However, these two phosphorus sources are expensive, directly increasing the manufacturing cost of ferric phosphate. Furthermore, approximately 30 mg / ton of product generates waste gas during the production process. 3 Wastewater contains large amounts of sulfates, ammonia nitrogen, and heavy metal ions, making it difficult and costly to treat. This further increases the environmental protection burden on enterprises and hinders their green and low-carbon transformation.

[0004] Although some researchers have attempted to use low-grade phosphoric acid or low-quality monoammonium phosphate as alternatives to high-purity phosphorus sources, these raw materials often contain high levels of impurities, especially potassium (K). + Alkali metal ions, such as those found in lithium iron phosphate, are difficult to remove effectively. These impurities tend to remain in the lithium iron phosphate lattice during subsequent sintering, leading to a decline in the material's electrochemical performance and severely affecting the overall performance and consistency of the battery.

[0005] Therefore, developing a new iron phosphate preparation technology that uses low-cost, low-quality phosphorus sources and can efficiently remove impurities, thereby reducing production costs and improving product quality, is of great practical significance for promoting the development of the iron phosphate industry. Summary of the Invention

[0006] The main objective of this invention is to provide a method for preparing high-purity iron phosphate based on a novel washing method, thereby solving the problems mentioned in the background art. This invention combines a multi-stage pulping and washing process with magnetic crown ether adsorption, significantly reducing washing water consumption while efficiently removing alkali metal and alkaline earth metal impurities, ensuring that the purity of the iron phosphate meets the requirements for battery-grade applications.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A method for preparing high-purity ferric phosphate based on a novel washing method includes the following steps: (1) Mix crude phosphoric acid with ammonia water, adjust the pH to 6.5-7.5, and filter after reaction to obtain a clear phosphate solution; (2) After adding ferrous sulfate solution, hydrogen peroxide and phosphate solution to the reaction vessel and keeping it at a constant temperature, the reaction solution is filtered and washed to obtain ferric phosphate precursor after the reaction is completed. (3) Add pure water to the ferric phosphate precursor for the first pulping and dispersion, then add industrial grade phosphoric acid for the second pulping; after pulping, transfer to an aging kettle for heat preservation reaction, and after the reaction is completed, filter and wash again to obtain crude dihydrate ferric phosphate filter cake. (4) Add pure water and impurity removal material to the ferric phosphate dihydrate filter cake and slurry it. After slurrying, remove the impurity removal material and filter the mixture to obtain a high-purity ferric phosphate dihydrate filter cake. (5) After drying the high-purity iron phosphate dihydrate filter cake, calcination is performed to obtain battery-grade iron phosphate.

[0008] Preferably, in step (1), the P2O5 content in the crude phosphoric acid is 20%-30%; and the concentration of ammonia water is 10-15%.

[0009] Preferably, in step (1), a peristaltic pump is used to add ammonia water to crude phosphoric acid, and the pumping speed of the peristaltic pump is 100-300 mL / min.

[0010] Preferably, in step (2), a peristaltic pump is used to add ferrous sulfate solution, phosphate solution and hydrogen peroxide into the reaction vessel respectively, and the pumping speed of each peristaltic pump is 20-300 mL / min.

[0011] Preferably, in step (2), the iron content of the ferrous sulfate solution is 4%-6%.

[0012] Preferably, in step (2), the molar ratio of ferrous sulfate, hydrogen peroxide (calculated as H2O2) and phosphate is 1:1.1-1.5:0.98-1.1.

[0013] Preferably, in step (2), the temperature of the heat preservation reaction is 70-100℃, the time is 30-90min, and the stirring speed is 500-600rpm.

[0014] Preferably, in step (3), the heat preservation temperature is 80-100℃ and the heat preservation time is 100-150min.

[0015] Preferably, in step (4), the impurity removal substance is a magnetic crown ether, with a mass ratio of 0.01-0.03:1 to pure water. It has magnetic responsiveness and selective complexing ability, and can efficiently adsorb and remove metal impurity ions.

[0016] Preferably, the magnetic crown ether is prepared from magnetic Fe3O4 particles, tetraethyl orthosilicate, and crown ether, and the preparation method is as follows: a. Magnetic Fe3O4 particles are dispersed in an ethanol aqueous solution, ammonia is added to adjust the pH to between 9 and 10, and tetraethyl orthosilicate is gradually added dropwise. After the reaction, Fe3O4@SiO2 microspheres are obtained; b. The above product is evenly dispersed in an ethanol solution, a silane coupling agent is added, and after the reaction, Fe3O4@SiO2-NH2 microspheres are obtained; c. Fe3O4@SiO2-NH2 microspheres are reacted with crown ether to obtain magnetic crown ether particles.

[0017] Preferably, the mass ratio of the magnetic Fe3O4 particles, tetraethyl orthosilicate, and crown ether is 2:1:5.

[0018] Preferably, in step (4), the pulping and washing time is 20-30 min and the stirring rate is 300-500 rpm.

[0019] Preferably, in step (5), the calcination temperature is 400-700℃ and the calcination time is 4-6h.

[0020] The second aspect of the present invention provides a lithium iron phosphate cathode material, which is prepared by mixing battery-grade iron phosphate obtained by the above preparation method with lithium carbonate, carbon source and additives in a certain proportion, followed by ball milling, drying and sintering.

[0021] The present invention discloses a method for preparing high-purity iron phosphate: a phosphate solution prepared from low-cost, low-quality crude phosphoric acid is used as the phosphorus source; multiple pulping and washing processes are employed, and the conductivity during the washing process is controlled; simultaneously, washing water containing impurity-removing substances is introduced during the aging stage; through synergistic effects, the amount of residual impurities in iron phosphate is effectively reduced, so that the purity of the final product meets the requirements of battery-grade iron phosphate.

[0022] The beneficial effects of this invention are as follows: 1. In the preparation of ferric phosphate, this invention optimizes the washing process and adopts a new washing method to replace the traditional multiple water washing. While improving the purity of ferric phosphate, the water consumption in the washing process of dihydrate ferric phosphate is reduced by about 50%, thereby reducing water consumption and wastewater treatment burden in the ferric phosphate production process.

[0023] 2. In this invention, a small amount of impurity-removing substance is added during the aging and washing stage. This substance is highly selective and can effectively complex and remove harmful impurities such as potassium. Furthermore, the impurity-removing substance can be recovered using magnetic adsorption, leaving no residue in the final product. This ensures that the impurity content in the ferric phosphate prepared from crude phosphoric acid meets the requirements for high-purity ferric phosphate, particularly in terms of potassium content, achieving the same level as ferric phosphate prepared from 85% phosphoric acid. This method is simple to operate, low in cost, and has good prospects for industrial application.

[0024] 3. The iron phosphate particles prepared by this invention are regular in shape and have a uniform particle size distribution, exhibiting a high tap density. Lithium iron phosphate materials prepared using this material demonstrate superior electrical performance, with a tap density reaching 2.55 g / cm³. 3 The maximum 1C discharge capacity is 137.62 mAh / g, which meets the material performance requirements of high-end power batteries. Attached Figure Description

[0025] The present invention will be further described below with reference to the accompanying drawings: Figure 1 This is a SEM image of the iron phosphate prepared in Example 1 of this invention; Figure 2 This is a SEM image of the iron phosphate prepared in Example 2 of the present invention at a magnification of 30.0 KX; Figure 3 This is a SEM image of the iron phosphate prepared in Example 2 of this invention at a magnification of 50.0 KX. Detailed Implementation

[0026] To better understand the present invention, the following embodiments are provided to further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0027] In the following embodiments, the magnetic crown ether was prepared by the following method: a. 100g of magnetic Fe3O4 particles were dispersed in 1000ml of ethanol aqueous solution, ammonia was added to adjust the pH to between 9 and 10, and 50g of tetraethyl orthosilicate was added dropwise. After reacting for 30min, Fe3O4@SiO2 microspheres were obtained; b. The above product was dispersed evenly in ethanol solution, 50g of aminosilane coupling agent was added, and after reacting, Fe3O4@SiO2-NH2 microspheres were obtained; c. Fe3O4@SiO2-NH2 microspheres were reacted with 250g of crown ether to obtain magnetic crown ether particles.

[0028] Example 1: (1) Ammonia water was added to 2000g of crude phosphoric acid by means of a melting pump, and the pH value was controlled to be around 7. After the reaction solution was filtered, 1800g of clear ammonium phosphate solution was obtained; wherein, the pumping speed of the melting pump was 200mL / min. (2) Weigh 2914g of ferrous sulfate solution with an iron content of 5wt% and add it to the reaction vessel. Then add 200g of hydrogen peroxide and 1248g of phosphate solution from step (1). React at a stirring speed of 550rpm and a temperature of 80℃ for 70min to obtain ferric phosphate precursor slurry. After filtration, wash with pure water until the conductivity of the washing water is less than 6mS / cm. Stop washing to obtain qualified ferric phosphate precursor. (3) The ferric phosphate precursor was put into a pulping kettle, 3000g of pure water was added for pulping, and after pulping for 10min, 80g of industrial grade phosphoric acid was added, and after pulping for another 10min, it was transferred into an aging kettle, heated to 90℃ and kept warm for 120min to obtain ferric phosphate dihydrate slurry. After filtration, it was washed with pure water until the conductivity of the washing water was less than 1.5mS / cm, then the washing was stopped to obtain qualified crude ferric phosphate dihydrate filter cake. (4) Put the crude ferric phosphate filter cake into the pulping kettle, add 2000g of pure water and 20g of magnetic crown ether, and pulp for 25min at a stirring speed of 400rpm. Then, use a magnetic rod to adsorb the impurities and transfer the mixture into a filter press. After pressing, ferric phosphate filter cake is obtained. (5) After drying the ferric phosphate filter cake, calcine it at 600℃ for 3 hours to obtain high-purity ferric phosphate.

[0029] Figure 1 This is a SEM image of the high-purity ferric phosphate prepared in Example 1. Figure 1 It can be seen that the iron phosphate particles are spherical or near-spherical, with a sphericity of 0.85, and the primary particles on the particle surface are fine millet-like; its tap density was measured to be 0.82 g / cm³. 3 about.

[0030] Lithium iron phosphate was prepared by mixing the iron phosphate prepared in Example 1 with lithium carbonate, a carbon source, and additives, followed by grinding and sintering. The compacted density was measured to be 2.55 g / cm³. 3 The 1C discharge capacity is close to 137.62 mAh / g.

[0031] Example 2: (1) Ammonia water was added to 2000g of crude phosphoric acid by means of a melting pump, and the pH value was controlled to be around 7. After the reaction solution was filtered, 1800g of clear ammonium phosphate solution was obtained; wherein, the pumping speed of the melting pump was 200mL / min. (2) Weigh 2914g of ferrous sulfate solution with an iron content of 5wt% and add it to the reaction vessel. Then add 200g of hydrogen peroxide and 1248g of phosphate solution from step (1). React at a stirring speed of 550rpm and a temperature of 80℃ for 70min to obtain ferric phosphate precursor slurry. After filtration, wash with pure water until the conductivity of the washing water is less than 6mS / cm. Stop washing to obtain qualified ferric phosphate precursor. (3) The ferric phosphate precursor was put into a pulping kettle, 3000g of pure water was added for pulping, and after pulping for 10min, 80g of industrial grade phosphoric acid was added, and after pulping for another 10min, it was transferred into an aging kettle, heated to 90℃ and kept warm for 120min to obtain ferric phosphate dihydrate slurry. After filtration, it was washed with pure water until the conductivity of the washing water was less than 1.5mS / cm, then the washing was stopped to obtain qualified crude ferric phosphate dihydrate filter cake. (4) Put the crude ferric phosphate filter cake into the pulping kettle, add 2000g of pure water and 40g of magnetic crown ether, and pulp for 25min at a stirring speed of 400rpm. Then, use a magnetic rod to adsorb the impurities and transfer the mixture into a filter press. After pressing, ferric phosphate filter cake is obtained. (5) After drying the ferric phosphate filter cake, calcine it at 600℃ for 3 hours to obtain high-purity ferric phosphate.

[0032] Figure 2-3 This is a SEM image of the ferric phosphate prepared in this example. Figure 2-3 It can be seen that iron phosphate particles are formed by the aggregation of a large number of fine primary particles into loose aggregates with a multi-level structure, and their surface is rough and exhibits a porous morphology.

[0033] Example 3: (1) Ammonia water was added to 2000g of crude phosphoric acid by means of a melting pump, and the pH value was controlled to be around 7. After the reaction solution was filtered, 1800g of clear ammonium phosphate solution was obtained; wherein, the pumping speed of the melting pump was 200mL / min. (2) Weigh 2914g of ferrous sulfate solution with an iron content of 5wt% and add it to the reaction vessel. Then add 200g of hydrogen peroxide and 1248g of phosphate solution from step (1). React at a stirring speed of 550rpm and a temperature of 80℃ for 70min to obtain ferric phosphate precursor slurry. After filtration, wash with pure water until the conductivity of the washing water is less than 6mS / cm. Stop washing to obtain qualified ferric phosphate precursor. (3) The ferric phosphate precursor was put into a pulping kettle, 3000g of pure water was added for pulping, and after pulping for 10min, 80g of industrial grade phosphoric acid was added, and after pulping for another 10min, it was transferred into an aging kettle, heated to 90℃ and kept warm for 120min to obtain ferric phosphate dihydrate slurry. After filtration, it was washed with pure water until the conductivity of the washing water was less than 1.5mS / cm, then the washing was stopped to obtain qualified crude ferric phosphate dihydrate filter cake. (4) Put the crude ferric phosphate filter cake into the pulping kettle, add 2000g of pure water and 60g of magnetic crown ether, and pulp at a stirring speed of 400rpm for 25min. Then, use a magnetic rod to adsorb the impurities and transfer the mixture into a filter press. After pressing, ferric phosphate filter cake is obtained. (5) After drying the ferric phosphate filter cake, calcine it at 600℃ for 3 hours to obtain high-purity ferric phosphate.

[0034] Example 4: (1) Ammonia water was added to 2000g of crude phosphoric acid by means of a melting pump, and the pH value was controlled to be around 7. After the reaction solution was filtered, 1800g of clear ammonium phosphate solution was obtained; wherein, the pumping speed of the melting pump was 200mL / min. (2) Weigh 2914g of ferrous sulfate solution with an iron content of 5wt% and add it to the reaction vessel. Then add 200g of hydrogen peroxide and 1248g of phosphate solution from step (1). React at a stirring speed of 550rpm and a temperature of 80℃ for 70min to obtain ferric phosphate precursor slurry. After filtration, wash with pure water until the conductivity of the washing water is less than 6mS / cm. Stop washing to obtain qualified ferric phosphate precursor. (3) The ferric phosphate precursor was put into a pulping kettle, 3000g of pure water was added for pulping, and after pulping for 10min, 80g of industrial grade phosphoric acid was added, and after pulping for another 10min, it was transferred into an aging kettle, heated to 90℃ and kept warm for 120min to obtain ferric phosphate dihydrate slurry. After filtration, it was washed with pure water until the conductivity of the washing water was less than 1mS / cm, and then the washing was stopped to obtain qualified crude ferric phosphate dihydrate filter cake. (4) Put the crude ferric phosphate filter cake into the pulping kettle, add 2000g of pure water and 40g of magnetic crown ether, and pulp at a stirring speed of 400rpm for 25min. Then, use a magnetic rod to adsorb the magnetic crown ether, and then transfer the mixture into a filter press. After pressing, ferric phosphate filter cake is obtained. (5) After drying the ferric phosphate filter cake, calcine it at 600℃ for 3 hours to obtain high-purity ferric phosphate.

[0035] Comparative Example 1: The difference between this comparative example and Example 2 is that no impurity remover is added in step (4), and the ferric phosphate is washed directly with pure water.

[0036] Comparative Example 2: The difference between this comparative example and Example 2 is that it uses a conventional washing method and does not involve starching.

[0037] Comparative Example 3: The difference between this comparative example and Example 2 is that: in step (3), no washing is performed, the conductivity is not controlled, no magnetic crown ether is added, and the pulping and washing are performed directly.

[0038] Comparative Example 4: The difference between this comparative example and Example 2 is that: in step (3), no washing is performed, the conductivity is not controlled, and magnetic crown ether is added for pulping and washing.

[0039] The quality analysis of the iron phosphate prepared in Examples 1-4 and Comparative Examples 1-4 was performed, and the results are shown in Table 1.

[0040] Table 1

[0041] As shown in Table 1, this invention employs multi-stage pulping and washing with conductivity control during the washing process, and adds a small amount of impurity-removing material during the aging washing stage, thus achieving K... + Highly efficient selective adsorption of alkali metal ions: The potassium and other impurity contents in Comparative Examples 1-4 were generally higher than those in the Examples, and the higher the amount of magnetic crown ether used, the better the impurity removal effect. This indicates that the lack of magnetic crown ether, pulping and washing, or conductivity control would lead to impurity residues, making it impossible to prepare high-purity iron phosphate. The impurity content in Comparative Examples 3-4 was significantly higher, indicating that pulping and washing and conductivity control worked synergistically to enhance impurity removal and improve product purity. The above results show that this invention, by introducing magnetic crown ether-based impurity removal substances in the washing stage and combining them with conductivity control during the washing process, significantly reduces the content of impurities such as K, Mg, Na, and Al in iron phosphate, obtaining high-purity, high-performance iron phosphate materials, thereby improving the compaction density and electrochemical performance of lithium iron phosphate cathode materials.

[0042] The above embodiments are merely preferred technical solutions of the present invention and should not be considered as limitations on the present invention. The scope of protection of the present invention should be limited to the technical solutions described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A method for preparing high-purity ferric phosphate based on a novel washing method, characterized in that, Includes the following steps: (1) Mix crude phosphoric acid with ammonia water, adjust the pH to 6.5-7.5, and filter after reaction to obtain a clear phosphate solution; (2) After adding ferrous sulfate solution, hydrogen peroxide and phosphate solution to the reaction vessel and keeping it at a constant temperature, the reaction solution is filtered and washed to obtain ferric phosphate precursor after the reaction is completed. (3) Add pure water to the iron phosphate precursor for the first pulping and dispersion, and then add industrial grade phosphoric acid for the second pulping; After pulping, the mixture is transferred to an aging reactor for heat preservation reaction. After the reaction is completed, it is filtered and washed again to obtain crude ferric phosphate dihydrate filter cake. (4) Add pure water and impurity removal material to the ferric phosphate dihydrate filter cake and slurry it. After slurrying, remove the impurity removal material and filter the mixture to obtain a high-purity ferric phosphate dihydrate filter cake. (5) After drying the high-purity iron phosphate dihydrate filter cake, calcination is performed to obtain battery-grade iron phosphate.

2. The preparation method according to claim 1, characterized in that, In step (1), the P2O5 content in the crude phosphoric acid is 20%-30%; the concentration of ammonia water is 10-15%.

3. The preparation method according to claim 1, characterized in that, In step (2), the molar ratio of ferrous sulfate, hydrogen peroxide and phosphate is 1:1.1-1.5:0.98-1.

1.

4. The preparation method according to claim 1, characterized in that, In step (2), the temperature of the heat preservation reaction is 70-100℃, the time is 30-90min, and the stirring speed is 500-600rpm.

5. The preparation method according to claim 1, characterized in that, In step (3), the heat preservation temperature is 80-100℃ and the heat preservation time is 100-150min.

6. The preparation method according to claim 1, characterized in that, In step (4), the impurity removal substance is magnetic crown ether, and the mass ratio of it to pure water is 0.01-0.03:

1.

7. The preparation method according to claim 6, characterized in that, The magnetic crown ether is prepared from magnetic Fe3O4 particles, tetraethyl orthosilicate and crown ether, with a mass ratio of 2:1:

5.

8. The preparation method according to claim 1, characterized in that, In step (5), the calcination temperature is 400-700℃ and the calcination time is 4-6h.

9. A high-purity iron phosphate, characterized in that, It is obtained by the preparation method described in any one of claims 1-8.

10. A lithium iron phosphate cathode material, characterized in that, The battery-grade iron phosphate of claim 9 is mixed with lithium carbonate, carbon source and additives in a certain proportion, and then ball-milled, dried and sintered.

Images