A method for remaking defective iron phosphate

Abstract

The present invention discloses a method for remaking defective iron phosphate. The method comprises the following steps: (1) dissolving defective iron phosphate: adding a certain amount of sulfuric acid to the defective iron phosphate solution to make the iron phosphate reach a critical particle size. (2) reaction crystallization and aging of iron phosphate: adding ammonia water and a surfactant during the reaction process, controlling the dripping rate of ammonia water, the reaction temperature and the stirring rate, and adding phosphoric acid during the aging process to adjust the pH value of the system to promote the crystallization process and the release of impurities. (3) washing the crude product and washing after aging: removing soluble salts and part of the free acid after crystallization. (4) drying and calcining: removing free water and crystal water in the product. The present invention solves the problem of disposing defective iron phosphate caused by the adjustment of equipment and process parameters, and reduces the content of sulfur and other impurities while improving the specific surface area.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and in particular relates to a method for remaking defective iron phosphate products. Background Art

[0002] With the continued development of the new energy industry, the power battery industry, as a new energy source and environmentally friendly, low-carbon energy source, has experienced rapid growth. Lithium-ion batteries, with their excellent performance and reasonable manufacturing costs, have become the mainstream development direction for many power batteries. Lithium iron phosphate (LIFP) materials offer a stable charge-discharge platform, excellent safety, low self-discharge, low cost, and environmental friendliness. They are currently the ideal cathode material for high-energy, ultra-large-capacity lithium batteries for hybrid and electric vehicles, as well as for wind and solar energy storage devices. Currently, demand for LFP cathode materials in China is experiencing a spiraling upward trend. As a key precursor for LFP synthesis, the quality and performance of LFP batteries significantly impact their performance. Theoretically, the production of one ton of battery-grade LFP consumes 0.92 tons of anhydrous iron phosphate, representing 90% of the total LFP demand. The rapid expansion of LFP battery applications in energy storage and 5G base stations is driving a surge in demand for LFP, and consequently, demand for LFP as a raw material.

[0003] Currently, the preparation processes for ferric phosphate include solid-phase synthesis, hydrothermal, sol-gel, template, sonochemical, homogeneous precipitation, ion exchange delithiation, and air oxidation. The main method for preparing ferric phosphate in China is coprecipitation, which uses ferrous sulfate as the raw material and controls the product crystallization by adjusting the pH of the solution. Under existing production processes, the sulfate and other impurity indicators in ferric phosphate are becoming increasingly stringent with the upgrading and transformation of downstream products. Index control has always been a difficult problem in ferric phosphate production. Conventional washing and additives can achieve certain results, but they cannot completely remove some impurities entrained within the ferric phosphate. During the production process, unstable parameter control and equipment abnormalities lead to unstable product indicators, resulting in defective ferric phosphate. This part of the defective ferric phosphate cannot be removed by conventional washing and calcining, and re-calcining under high temperature conditions has a certain impact on the product morphology and specific surface area. The present invention redissolves and recrystallizes the defective ferric phosphate, and obtains high-quality ferric phosphate through secondary crystal structure combination and morphology control, which is of great significance for destocking and value-added application of defective ferric phosphate. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention provides a method for reprocessing defective ferric phosphate.

[0005] The preparation method for remaking defective iron phosphate of the present invention comprises the following steps:

[0006] (1) Add the inferior iron phosphate, sulfuric acid and desalted water into a reactor in a certain proportion, stir and dissolve them to obtain a dissolved slurry of the inferior iron phosphate.

[0007] (2) Adding alkali solution and surfactant to the dissolved slurry, adjusting the pH, stirring and reacting to obtain ferric phosphate dihydrate slurry.

[0008] (3) The ferric phosphate dihydrate slurry obtained in the above step is separated into solid and liquid, and the solid phase is washed twice with the supplementary washing liquid.

[0009] (4) Adding phosphoric acid solution and desalted water to the washed ferric phosphate dihydrate slurry, adjusting the pH, heating and stirring for aging, and filtering to obtain the aged ferric phosphate dihydrate.

[0010] (5) The aged ferric phosphate dihydrate slurry obtained in the above step is separated into solid and liquid, and the solid phase is washed twice with the supplementary washing liquid.

[0011] (6) The washed ferric phosphate dihydrate obtained in the above step is separated into solid and liquid, the solid phase is dried and crushed, and then calcined to obtain a reconstituted ferric phosphate product.

[0012] In the step (1), the ratio of defective ferric phosphate to desalted water is 1:2-2.5, and the amount of sulfuric acid added is 20%-50% of the theoretical amount, preferably 20%-30%.

[0013] In step (2), the alkali solution is 8% ammonia water, and the surfactant is citric acid, added in an amount of 0.03% to 0.1% by mass of the dissolved slurry, preferably 0.05% to 0.1%. The pH after the reaction is 1.7 to 2.0, preferably 1.70 to 1.85. The reaction temperature is controlled at 50°C to 70°C, and the reaction speed is controlled at 500 to 700 rpm.

[0014] In the steps (3) and (5), the washing liquid is desalted water at 50° C. to 70° C., and the volume of the desalted water is consistent with the volume of the filtrate after filtration.

[0015] In step (4), the concentration of phosphoric acid added is 70%, and the pH after adjustment is 1.7-1.9, preferably 1.8-1.85. The aging temperature is 80-95°C, preferably 93-95°C. The aging speed is 500-700 rpm. After aging and turning white, the mixture is stirred at a constant temperature for 30-60 minutes.

[0016] In step (6), the drying temperature is 150-170°C, and the drying time is 1.5-2.5 hours. The calcination temperature is 600-700°C, and the calcination time is 2-3 hours. Preferably, the calcination temperature is 650-680°C, and the calcination time is 2-2.5 hours.

[0017] The key concept of the present invention is that it cleverly utilizes the dissolution of ferric phosphate in sulfuric acid to achieve its critical particle size. At this critical particle size, the ferric phosphate has good crystal surface energy and formation energy, allowing the ferric phosphate to form stable crystal nuclei. The remaining fragmented small crystal nuclei and irregularly shaped or defective portions in the supersaturated solution are completely dissolved to reach the critical particle size range. The morphology and structure of the already formed ferric phosphate product are destroyed, and the ferric phosphate solution is precipitated by controlling the pH value of the solution to achieve a recombined state. Then, by controlling the stirring rate and the addition of a surfactant, the phenomenon of ferric phosphate particle agglomeration is reduced, and the morphology of the product, as well as the particle size of the ferric phosphate particles, is regulated, so that the ferric phosphate after the reaction reaches a high-quality grade at the microscopic level. This also reduces the sulfate ions and impurity content entrained between particles, fundamentally solving the problem of agglomeration and encapsulation. In subsequent steps, a secondary washing process after the reaction is performed to remove the sulfate ions and other soluble salt impurities remaining in the sulfate mother liquor, thereby reducing the content of impurities and sulfur indicators in the product. Furthermore, the addition of phosphoric acid during the aging process creates a micro-dissolution ion channel on the surface of the iron phosphate, further facilitating the release of metallic impurities and sulfur. A secondary washing process after aging removes impurities released during aging and the added phosphoric acid, maintaining normal iron and phosphorus levels in the product while also ensuring premium purity.

[0018] The method for reprocessing defective iron phosphate of the present invention has at least the following beneficial effects:

[0019] 1. The present invention innovatively dissolves defective iron phosphate in sulfuric acid, breaking the existing iron phosphate structure and morphology, allowing part of the iron phosphate to return to the solution ion state. By controlling the pH value and stirring rate during the reaction process, the particle size of the iron phosphate dihydrate is reduced, and the crystal agglomeration phenomenon during the reaction is reduced, so that the encapsulated sulfate ions can be better dissolved in water. Then, through a multi-stage washing method, the sulfur content and other impurity indicators in the product reach the level of high-quality products.

[0020] 2. The present invention adds a small amount of phosphoric acid during the aging process, slightly dissolving an ion channel on the surface of the iron phosphate, which is more conducive to the release of metal impurities and sulfur. The secondary washing process after aging is used to remove impurities released during the aging process and wash away the phosphoric acid added during the aging process, so that the iron and phosphorus indicators of the product are maintained normal and the purity of the product reaches the level of superior products.

[0021] 3. The process flow of the present invention is simple and the control is stable. Cheap defective iron phosphate and waste iron phosphate are recycled and reused, creating a greater economic benefit effect. At the same time, it also solves the inventory pressure and environmental protection problems of the warehouse.

[0022] Description of the drawings

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0024] Figure 1 1 is a process flow chart of an embodiment of the present invention. DETAILED DESCRIPTION

[0025] In order to explain the technical content of the present invention in detail and fully understand the purpose and effect of the present invention, the following is an explanation in conjunction with the embodiments and the accompanying drawings.

[0026] Example 1

[0027] A method for remaking defective iron phosphate, referring to Figure 1 The process flow chart is as follows:

[0028] (1) Dissolution of defective iron phosphate

[0029] The defective ferric phosphate and desalted water were fully stirred and mixed in a ratio of 1:2.1, and sulfuric acid was added in an amount of 20% of the theoretical amount. The mixture was stirred for 15 minutes to obtain a dissolved slurry of the defective ferric phosphate.

[0030] (2) Synthesis reaction and reaction washing

[0031] First, heat the defective ferric phosphate dissolution slurry to 50°C. Slowly add a 5% ammonia solution to the slurry, along with a surfactant (0.03% by weight of the slurry). Strictly control the ammonia addition rate, adjust the pH to 1.76, and maintain a stirring speed of 500 rpm for thorough reaction to obtain the reconstituted ferric phosphate dihydrate slurry. Filter the reaction slurry to obtain a first filter cake and a first filtrate. Then, disperse the first filter cake in 50°C desalted water at a volume equal to that of the first filtrate. Stir for 15 minutes, and filter. This yields a second filter cake and a second filtrate. Then, disperse the second filter cake in 50°C desalted water at a volume equal to that of the second filtrate. Stir for 15 minutes, and filter. This results in a washed, reacted ferric phosphate filter cake.

[0032] (3) Aging and aging washing

[0033] The washed ferric phosphate filter cake was dispersed in 85°C desalted water. 69% phosphoric acid solution was added and the pH was adjusted to 1.72. The reaction temperature was then heated to maintain a constant temperature of 85°C and a rotation speed of 500 rpm. When the ferric phosphate slurry turned pure white, stirring was continued for 30 minutes before filter pressing to obtain the first filter cake and first filtrate. The first filter cake was then dispersed in 50°C desalted water, with the volume of the desalted water being the same as that of the first filtrate. The mixture was stirred for 15 minutes before filtering. This yielded the second filter cake and second filtrate. The second filter cake was then dispersed in 50°C desalted water, with the volume of the desalted water being the same as that of the second filtrate. The mixture was stirred for 15 minutes before filtering. This resulted in the aged and washed ferric phosphate filter cake.

[0034] (4) Drying and calcination

[0035] The aged and washed iron phosphate filter cake was placed in a vacuum drying oven for drying at 150°C for 1.5 hours. After drying, the dried iron phosphate was removed and crushed. After crushing, the crushed iron phosphate was placed in a calcination ark and moved to a muffle furnace at 620°C for 3 hours. After calcination and cooling, the high-grade iron phosphate was reconstituted and pulverized by air flow.

[0036] Example 2

[0037] A method for remaking defective iron phosphate, referring to Figure 1 The process flow chart is as follows:

[0038] (1) Dissolution of defective iron phosphate

[0039] The defective ferric phosphate and desalted water were fully stirred and mixed in a ratio of 1:2.5, and sulfuric acid was added in an amount of 25% of the theoretical amount. The mixture was stirred for 15 minutes to obtain a dissolved slurry of the defective ferric phosphate.

[0040] (2) Synthesis reaction and reaction washing

[0041] First, heat the defective ferric phosphate dissolution slurry to 60°C. Then, slowly add 8% ammonia solution to the slurry. Simultaneously, add a surfactant (0.06% by weight of the slurry). Strictly control the ammonia addition rate, adjust the pH to 1.93, and maintain a stirring speed of 600 rpm for thorough reaction to obtain the reconstituted ferric phosphate dihydrate slurry. Filter the reaction slurry to obtain a first filter cake and a first filtrate. Then, disperse the first filter cake in 60°C desalted water at a volume equal to that of the first filtrate. Stir for 15 minutes, and filter. This yields a second filter cake and a second filtrate. Then, disperse the second filter cake in 60°C desalted water at a volume equal to that of the second filtrate. Stir for 15 minutes, and filter. This results in a washed, reacted ferric phosphate filter cake.

[0042] (3) Aging and aging washing

[0043] The washed ferric phosphate filter cake was dispersed in 95°C desalted water. 69% phosphoric acid solution was added and the pH was adjusted to 1.87. The reaction temperature was then heated to maintain a constant temperature of 95°C and a rotation speed of 600 rpm. When the ferric phosphate slurry turned pure white, stirring was continued for 1 hour before filter pressing to obtain the first filter cake and first filtrate. The first filter cake was then dispersed in 60°C desalted water, with the volume of the desalted water being the same as that of the first filtrate. The mixture was stirred for 15 minutes before filtering. This yielded the second filter cake and second filtrate. The second filter cake was then dispersed in 60°C desalted water, with the volume of the desalted water being the same as that of the second filtrate. The mixture was stirred for 15 minutes before filtering. This resulted in the aged and washed ferric phosphate filter cake.

[0044] (4) Drying and calcination

[0045] The aged and washed iron phosphate filter cake was placed in a vacuum drying oven for drying at 160°C for 2 hours. After drying, the dried iron phosphate was removed and crushed. After crushing, the crushed iron phosphate was placed in a calcination ark and moved to a muffle furnace for calcination at 700°C for 2 hours. After calcination, cooling, and crushing, the reconstituted high-grade iron phosphate was obtained.

[0046] Example 3

[0047] A method for remaking defective iron phosphate, referring to Figure 1 The process flow chart is as follows:

[0048] (1) Dissolution of defective iron phosphate

[0049] The defective ferric phosphate and desalted water were fully stirred and mixed in a ratio of 1:2.3, and sulfuric acid was added in an amount of 40% of the theoretical amount. The mixture was stirred for 15 minutes to obtain a dissolved slurry of the defective ferric phosphate.

[0050] (2) Synthesis reaction and reaction washing

[0051] First, heat the defective ferric phosphate dissolution slurry to 70°C. Slowly add a 7% ammonia solution to the slurry, along with a surfactant (0.1% by weight of the slurry). Strictly control the ammonia addition rate, adjust the pH to 2.0, and maintain a stirring speed of 700 rpm for thorough reaction to produce the reconstituted ferric phosphate dihydrate slurry. Filter the reaction slurry to obtain a first filter cake and a first filtrate. Then, disperse the first filter cake in 70°C desalted water at a volume equal to that of the first filtrate. Stir for 15 minutes, and filter. This produces a second filter cake and a second filtrate. Then, disperse the second filter cake in 70°C desalted water at a volume equal to that of the second filtrate. Stir for 15 minutes, and filter. This results in a washed, reacted ferric phosphate filter cake.

[0052] (3) Aging and aging washing

[0053] The washed ferric phosphate filter cake was dispersed in 80°C desalted water. 69% phosphoric acid solution was added and the pH was adjusted to 1.75. The reaction temperature was then heated to maintain a constant temperature of 80°C and a rotation speed of 700 rpm. When the ferric phosphate slurry turned pure white, stirring was continued for 45 minutes before filter pressing to obtain the first filter cake and first filtrate. The first filter cake was then dispersed in 70°C desalted water, with the volume of the desalted water being the same as that of the first filtrate. The mixture was stirred for 15 minutes before filtering. This yielded the second filter cake and second filtrate. The second filter cake was then dispersed in 70°C desalted water, with the volume of the desalted water being the same as that of the second filtrate. The mixture was stirred for 15 minutes before filtering. This resulted in the aged and washed ferric phosphate filter cake.

[0054] (4) Drying and calcination

[0055] The aged and washed iron phosphate filter cake was placed in a vacuum drying oven for drying at a temperature of 170°C for 2.5 hours. After drying, the dried iron phosphate was removed and crushed. After crushing, the crushed iron phosphate was placed in a calcination ark and moved to a muffle furnace for calcination at a temperature of 650°C for 2.5 hours. After calcination, cooling, and crushing, the reconstituted high-grade iron phosphate was obtained.

[0056] After testing, the various indicators of the obtained regenerated iron phosphate product far meet the standard requirements of "HG / T 4701-2021 Iron Phosphate for Batteries", and its various performance indicators are shown in Table 1.

[0057] Table 1 Performance indicators of iron phosphate

[0058]

Claims

1. A method for remaking defective iron phosphate, characterized in that: The following steps are involved: (1) adding the inferior ferric phosphate, sulfuric acid, and desalted water into a reactor in a certain proportion, stirring and dissolving, and obtaining a slurry of the inferior ferric phosphate solution; (2) adding alkali solution and surfactant to the dissolved slurry, adjusting the pH, stirring and reacting to obtain ferric phosphate dihydrate slurry; (3) separating the solid and liquid of the ferric phosphate dihydrate slurry obtained in the above step, and washing the solid phase with the washing solution twice; (4) adding phosphoric acid solution and desalted water to the washed ferric phosphate dihydrate slurry, adjusting the pH, heating and stirring for aging, and filtering to obtain aged ferric phosphate dihydrate; (5) separating the solid and liquid of the aged ferric phosphate dihydrate slurry obtained in the above step, and washing the solid phase with the supplementary washing liquid twice; (6) separating the washed ferric phosphate dihydrate obtained in the above step from solid and liquid, drying and crushing the solid phase, and then calcining it to obtain a reconstituted ferric phosphate product; The main problems of the defective ferric phosphate are excessive sulfur content and low specific surface area, S≥400ppm, specific surface area≤4m 2 / g; In step (1), the ratio of the defective ferric phosphate to the desalted water is 1:2-2.5, and the amount of sulfuric acid added is 20%-50% of the theoretical amount; In step (2), the alkali solution is 5% to 8% ammonia water, the surfactant is citric acid, and the added amount is 0.03% to 0.1% of the mass of the dissolved slurry. The pH after the reaction is 1.7 to 2.0, the reaction temperature is controlled at 50°C to 70°C, and the reaction speed is controlled at 500-700rpm.

2. The method for remaking defective iron phosphate according to claim 1, characterized in that: In step (3) and step (5), the washing liquid is desalted water at 50°C to 70°C, and the volume of the desalted water is consistent with the volume of the filtrate after filtration.

3. The method for remaking defective iron phosphate according to claim 1, characterized in that: In step (4), the phosphoric acid is added to a concentration of 70%, the pH after adjustment is 1.7-1.9, the aging temperature is 80-95°C, the aging speed is 500-700 rpm, and after aging and turning white, it is stirred at a constant temperature for 30-60 minutes.

4. The method for remaking defective iron phosphate according to claim 1, characterized in that: In step (6), the drying temperature is 150-170°C, the drying time is 1.5-2.5 hours, the calcination temperature is 600-700°C, and the calcination time is 2-3 hours.

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