Preparation method of high-sphericity iron phosphate

Abstract

The invention provides a preparation process of spherical iron phosphate. The preparation process comprises the following steps: step 1, adding an iron source A into a phosphorus source B to obtain a solution I; step 2, adding an oxidizing agent C into the solution I for reaction to obtain a solution II; step 3, preparing a crystallization auxiliary agent D solution; step 4, adding a crystallization auxiliary agent D solution into the solution II which is being stirred to prepare a mother solution; step 5, adding the mother liquor obtained in the step 4 into a crystallizer, respectively dropwise adding the solution II and a crystallization aid D solution into the crystallizer in a two-way feeding manner through a peristaltic pump, and adjusting the dropwise adding rate of the two-way feeding to ensure that the pH value of the solution is kept stable and unchanged, so as to obtain amorphous iron phosphate dihydrate particles; step 6, washing and filtering the amorphous iron phosphate dihydrate particles obtained in the step 5, adding water to prepare a solid-liquid mixture III, adding a crystallization aid E into the solid-liquid mixture III, and stirring and aging at 60-95 DEG C; and step 7, filtering and drying the aged iron phosphate dihydrate to obtain the spherical iron phosphate.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery cathode material precursor preparation technology, specifically involving a method for precisely controlling the tap density and specific surface area of ​​iron phosphate particles by adjusting the stirring rate, which is applicable to the industrial production of lithium iron phosphate cathode materials with different performance requirements. Background Technology

[0002] Lithium-ion batteries have been widely used in power batteries, energy storage systems, and consumer electronics due to their advantages such as high energy density, long cycle life, and environmental friendliness. Among them, lithium iron phosphate (LiFePO4), as a cathode material, has become one of the core materials in the field of lithium-ion batteries due to its low cost, high safety, and good thermal stability.

[0003] Iron phosphate (FePO4) is a key precursor for the synthesis of LiFePO4. Currently, the solid-state method is widely used in industry to prepare LiFePO4 cathode materials from FePO4, offering advantages such as simple process, high reaction efficiency, and ease of large-scale production. Furthermore, the crystal structure, morphology, and properties of FePO4 directly determine the electrochemical performance of the final LiFePO4 cathode. Among the various FePO4 morphologies, spherical FePO4 particles exhibit significant advantages. Their spherical shape improves particle packing efficiency, increases the tap density of the cathode material, and thus enhances the energy density of lithium-ion batteries. Simultaneously, spherical particles possess a uniform particle size distribution and regular geometric structure, reducing stress concentration during electrode fabrication and improving electrode mechanical stability. Moreover, the suitable specific surface area of ​​spherical FePO4 provides ample ion transport channels, promoting the electrochemical reaction of LiFePO4 with FePO4. + Diffusion improves the rate performance and cycle stability of LiFePO4 cathodes. Therefore, developing a novel production process that achieves environmentally friendly production and stable yield of spherical FePO4 will help meet the growing market demand while promoting the rational use of resources and environmental protection. Achieving this goal is of great significance for promoting the development of related industries and enhancing product competitiveness.

[0004] Several patents related to the synthesis of spherical FePO4 have been published. For example, Chinese patent CN112661129A discloses a method for preparing ferric phosphate, which involves mixing ferrous sulfate solution and a phosphorus source in a certain proportion, adding them to a reaction vessel, adding a purifying agent, a complexing agent, and an oxidizing agent, and adjusting the pH to obtain spherical ferric phosphate. However, this method requires multiple pH adjustments and is carried out in a reaction vessel, making the process relatively complex and the reaction conditions quite harsh. Furthermore, it does not effectively avoid the risk of byproduct formation and lacks clear optimization methods for precise control of product particle size. Another Chinese patent, CN115784186A, discloses a method for preparing spherical ferric phosphate, which involves mixing a mixed solution of hydrogen peroxide and phosphate with a ferrous sulfate solution, reacting the mixture, and finally calcining to obtain spherical ferric phosphate. Both of the above methods share common drawbacks: the reaction of iron salts dissolved in nitric acid or sulfuric acid with phosphoric acid easily produces byproducts such as nitrates and sulfates, requiring the use of alkaline substances to adjust the pH. This not only prolongs the process time but also makes it difficult to accurately control the particle size and purity of the product. Furthermore, the emission of byproducts can cause serious environmental pollution. Chinese patents, publication numbers CN117658089A, CN117263155A, and CN116854063A, disclose a similar method for preparing high-performance spherical iron phosphate. This method involves mixing iron and phosphorus sources at room temperature, heating the mixture, adding seed crystals, maintaining the temperature, filtering, washing, drying, and calcining to produce high-performance spherical iron phosphate. However, this method suffers from problems such as deviations in the iron-to-phosphorus ratio due to heating, impurity inclusion, and poor particle uniformity. Chinese patents, publication numbers CN118183662A and CN119612468A, disclose a method in which a mixture of phosphorus source and oxidant is added to an iron salt solution to obtain an amorphous filter cake. This cake is then pulped, phosphoric acid is added, and the mixture is filtered, dried, and calcined to obtain spherical iron phosphate particles. The morphology and particle size are controlled by phosphoric acid. However, the addition of phosphoric acid lowers the pH of the system, requiring expensive corrosion-resistant equipment. Furthermore, the iron-to-phosphorus ratio fluctuates beyond the ideal range, and the energy consumption for washing and drying increases significantly. These drawbacks restrict the industrial application and performance improvement of spherical iron phosphate.

[0005] Existing technologies for preparing spherical iron phosphate generally suffer from problems such as reliance on complex additives (e.g., complexing agents, impurity removers, and excess phosphorus sources), long process flows, severe by-product pollution, low precision in controlling product performance (purity, tap density, specific surface area), and high equipment costs. Therefore, developing a method for preparing spherical iron phosphate that requires no complex additives, is simple in process, environmentally friendly, and enables targeted optimization of product performance has become a pressing technical challenge in this field. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for improving the tap density and specific surface area of ​​iron phosphate particles by adjusting the stirring rate, which is suitable for the industrial production of high-performance lithium iron phosphate cathode materials.

[0007] To achieve the above objectives, the present invention provides a process for preparing spherical iron phosphate, which uses iron source A and phosphorus source B as raw materials to prepare iron phosphate through a reaction with oxidant C. The process includes the following steps:

[0008] Step 1: Add iron source A solution to phosphorus source B solution to obtain solution I;

[0009] Step 2: Add oxidant C to solution I obtained in step 1 to react and obtain solution II;

[0010] Step 3: Prepare an aqueous solution of the crystallization aid to obtain crystallization aid D solution;

[0011] Step 4: Add the crystallization aid D solution to the stirred solution II, and control the endpoint of the addition by adjusting the pH of the mixed solution to obtain the mother liquor;

[0012] Step 5: Add the mother liquor obtained in step 4 into the crystallizer. Use a peristaltic pump to dropwise add solution II and crystallization aid D solution into the crystallizer in two separate feed streams. Adjust the dropping rate of the two feed streams to ensure that the pH of the solution remains stable, and obtain amorphous iron phosphate dihydrate particles.

[0013] Step 6: After washing and filtering the amorphous iron phosphate dihydrate particles obtained in Step 5, add water to make solid-liquid mixture III. Add crystallization aid E to solid-liquid mixture III and stir and age it at 60-95℃.

[0014] Step 7: Filter and dry the aged ferric phosphate dihydrate to obtain the spherical ferric phosphate. The spherical ferric phosphate of this invention is ferric phosphate dihydrate crystals.

[0015] Preferably, the iron source A solution contains at least one of ferrous sulfate, ferrous sulfate, ferrous chloride, and ferrous oxalate. More preferably, the iron source A solution is any one of ferrous sulfate, ferric sulfate, ferrous chloride, ferrous oxalate, and ferrous nitrate, or a mixture of any of these in any proportion. The process provided by this invention is not limited to the types of iron source A described above; any iron source that is soluble in water and forms favorable iron ions in water is applicable to this invention.

[0016] Preferably, the phosphorus source B solution contains at least one of phosphoric acid, monoammonium phosphate, diammonium phosphate, monopotassium phosphate, and dipotassium phosphate. More preferably, the phosphorus source B solution is any one of phosphoric acid, monoammonium phosphate, diammonium phosphate, monopotassium phosphate, and dipotassium phosphate, or a mixture of any number of these in any proportion.

[0017] In any of the above-mentioned preferred embodiments, in step 1, iron source A is dissolved in water at a temperature of 30-40°C to obtain an iron source A solution. More preferably, the dissolution temperature is 30, 35, or 40°C or a range thereof.

[0018] In any of the above-mentioned preferred embodiments, in step 1, the content of iron source in the iron source A solution is 5wt%-20wt%. Preferably, the content of iron source in the iron source A solution is 5, 10, 15, 20wt% or a range thereof.

[0019] In any of the above-mentioned preferred embodiments, in step 1, phosphorus source B is dissolved in deionized water at a temperature of 30-40°C to obtain a phosphorus source B solution. More preferably, the dissolution temperature is 30, 35, or 40°C or a range thereof.

[0020] Preferably, the phosphorus source B solution is concentrated phosphoric acid. Preferably, the concentrated phosphoric acid is not diluted during use. The concentrated phosphoric acid used in this invention is industrial and laboratory standard grade concentrated phosphoric acid. Preferably, the concentration of the concentrated phosphoric acid is 85 wt%. Preferably, the mass concentration of the concentrated phosphoric acid is greater than 85%. Preferably, the concentration of the concentrated phosphoric acid is 98 wt%.

[0021] Preferably, phosphorus source B is phosphate.

[0022] Preferably, the phosphate is dissolved in water at 30-40°C to obtain phosphorus source B solution.

[0023] Preferably, the phosphorus source B solution is a 5-20 wt% phosphate solution.

[0024] Preferably, in any of the above embodiments, iron source A solution and phosphorus source B solution are mixed at 30-40°C, wherein the molar ratio of iron source to phosphorus source is 1:1 to 1:1.3. More preferably, the mixing temperature is 30, 35, or 40°C or a range thereof. More preferably, the molar ratio of iron source to phosphorus source is 1:1, 1:1.1, 1:1.2, or 1:1.3 or a range thereof.

[0025] In any of the above-mentioned preferred embodiments, in step 2, the oxidant C includes at least one of oxygen, hydrogen peroxide, and ammonium persulfate.

[0026] In any of the above-mentioned preferred embodiments, the oxidant C is oxygen, and the oxygen is directly introduced into solution I obtained in step 1 to react and obtain solution II.

[0027] In any of the above-mentioned preferred embodiments, the oxidant C is oxygen, and the reaction time in step 2 is 24 hours. In any of the above-mentioned preferred embodiments, the oxidant C is a hydrogen peroxide solution and / or an ammonium persulfate solution, and the hydrogen peroxide solution and / or ammonium persulfate solution are added to solution I obtained in step 1 to react and obtain solution II.

[0028] Preferably, the concentration of the oxidant C solution is 5 wt% to 20 wt%. More preferably, the concentration of the oxidant C solution is 5, 15, or 20 wt% or a range thereof. More preferably, the oxidant C is a hydrogen peroxide solution and / or an ammonium persulfate solution with a concentration of 5, 15, or 20 wt% or a range thereof.

[0029] In any of the above-mentioned preferred embodiments, the oxidant C is a 5wt%-20wt% aqueous solution of hydrogen peroxide or ammonium persulfate, and the reaction time in step 2 is 0.5-1.5 h.

[0030] Preferably, in step 2, the reaction time is 0.5-1.5 h. More preferably, it is 0.5, 1.0, 1.5 h or a range thereof.

[0031] In any of the above-mentioned preferred embodiments, in step 3, the crystallization aid D includes at least one of ammonia, ethylenediamine, monoammonium phosphate, diammonium phosphate, and ammonium phosphate.

[0032] In any of the above-mentioned preferred embodiments, in step 3, the crystallization aid D is any one or any mixture of any proportions of ammonia, ethylenediamine, monoammonium phosphate, diammonium phosphate, and ammonium phosphate.

[0033] In any of the above-mentioned preferred embodiments, in step 3, the concentration of the crystallization aid D solution is 5 wt%-20 wt%. Preferably, the concentration of the crystallization aid D solution is 5, 10, 15, 20 wt% or a range thereof.

[0034] Preferably, in step 4, the stirring rate is 100-500 rpm. More preferably, it is 100, 200, 300, 400, 500 rpm or a range thereof.

[0035] Preferably, in step 4, the endpoint pH of the addition is 1.8-2.5. More preferably, the endpoint pH is 1.8, 2.0, 2.2, 2.4, 2.5, or a range thereof.

[0036] Preferably, the reaction time in step 4 is 1-3 hours. More preferably, it is 1, 2, or 3 hours or a range thereof.

[0037] In any of the above-mentioned preferred embodiments, the mother liquor obtained in step 4 is added to the crystallizer in a certain proportion as the reaction base liquid for step 5. Preferably, 5 wt% of the mother liquor obtained in step 4 is added to the crystallizer as the base liquid.

[0038] In this invention, the amorphous ferric phosphate dihydrate particles formed in the mother liquor obtained in step 4 are equivalent to seed crystals, which helps control the particle size of ferric phosphate dihydrate in step 5. In step 5, adding solution II and crystallization aid D in a two-stream manner helps control the supersaturation of amorphous ferric phosphate during the crystallization process, thereby controlling the particle size distribution of ferric phosphate dihydrate.

[0039] In any of the above-mentioned preferred embodiments, in step 5, the reaction is carried out in the crystallizer by stirring at a speed of 20-200 rpm. More preferably, the speed is 20, 40, 60, 80, 100, 120, 140, 160, 180, 200 rpm and the range thereof.

[0040] In any of the above-mentioned preferred embodiments, in step 6, the crystallization aid E includes at least one of the following: gel polysaccharide, soluble starch, 3-aminobenzoic acid, glycine, malonic acid, polyacrylamide, urea, L-hydroxysuccinic acid, and poloxamer 403.

[0041] In any of the above-mentioned preferred embodiments, in step 6, the crystallization aid E comprises any one or any combination of any proportions of gelatinizing polysaccharide, soluble starch, 3-aminobenzoic acid, glycine, malonic acid, polyacrylamide, urea, L-hydroxysuccinic acid, and poloxamer 403.

[0042] In any of the above-mentioned preferred embodiments, the stirring rate during step 6 is 50-150 rpm.

[0043] In this invention, stirring and aging are beneficial to the crystallization of iron phosphate. Controlling the stirring rate and / or adding crystallization aid E during aging helps to control the morphology of iron phosphate crystals to be spherical. Furthermore, by controlling the stirring rate and / or adding crystallization aid E, the tap density and specific surface area of ​​the obtained spherical iron phosphate can be adjusted to obtain a spherical iron phosphate product that is more conducive to the production of lithium-ion battery cathodes.

[0044] Preferably, in step 6, the content of crystallization aid E in the aging system is 0.1 wt%-1 wt%. More preferably, the content of crystallization aid E in the aging system is 0.1, 0.2, 0.4, 0.6, 0.8, 1.0 wt% or a range thereof.

[0045] Preferably, the method for preparing the spherical iron phosphate is as follows:

[0046] Step 1: Dissolve a certain amount of iron source A in deionized water to obtain iron source A solution. Add a certain amount of phosphorus source B to iron source A solution at a dissolution temperature of 30-40℃ to obtain solution I.

[0047] Step 2: Oxidizing agent C is added to solution I using a peristaltic pump over a certain period of time to obtain solution II;

[0048] Step 3: Prepare a crystallization aid D solution; use deionized water to prepare a crystallization aid D solution of a certain concentration.

[0049] Step 4: Add the crystallization aid D solution to the stirring solution II using a peristaltic pump within a certain time period, and use a pH meter to control the endpoint of the addition to obtain the mother liquor;

[0050] Step 5: Add a certain mass of mother liquor to the crystallizer. Use a peristaltic pump to add solution II and crystallization aid D solution dropwise into the crystallizer in two separate feed streams. Adjust the drop rate of the two feed streams to ensure that the pH of the solution remains stable.

[0051] Step 6: After washing and filtering the amorphous iron phosphate dihydrate particles obtained in Step 5, deionized water is added to form a solid-liquid mixture III. The mixture is then aged at 60-95℃ under a certain stirring rate, and crystallization aid E is added to the mixture.

[0052] Step 7: Filter the aged ferric phosphate dihydrate and dry it at 120℃ for 90 minutes.

[0053] Preferably, in step 5, the dropping rate of the two feed streams is adjusted to ensure that the pH of the solution is stably maintained within the pH range of the dropping endpoint in step 4. Preferably, the pH is stably maintained at 1.8-2.5 in step 5. More preferably, the pH at the dropping endpoint is 1.8, 2.0, 2.2, 2.4, 2.5, or a range thereof.

[0054] The beneficial technical effects of this invention are as follows:

[0055] From an industrial application perspective, the technology provided by this invention achieves synergistic control of the morphology of iron phosphate by regulating the reaction crystallization feeding method, the stirring rate after crystallization classification, the temperature, and the addition of organic additives. This allows for adjustable tap density and specific surface area, avoiding the drawbacks of traditional processes that rely on additives and have complex equipment. It can also directly empower the performance upgrade of downstream battery products, directly adapting to the needs of multiple scenarios such as high-energy-density power batteries, conventional energy storage batteries, and fast-charging batteries, and has significant industrial promotion value and market competitiveness. Attached Figure Description

[0056] Figure 1 This is a SEM image of a commercially available ferric phosphate product.

[0057] Figure 2 The images shown are SEM images of the spherical iron phosphate products in preferred embodiments 1-5 of the present invention. Detailed Implementation

[0058] To further illustrate the present invention, the technical solutions provided by the present invention are described in detail below with reference to embodiments, but the implementation of the invention is not limited thereto. Unless otherwise specified, the reagents and instruments used in the present invention are products of the prior art and can be purchased commercially by the public.

[0059] In a preferred embodiment of the present invention:

[0060] Preferably, the content of iron source in iron source A solution is 5wt%-20wt%.

[0061] Preferably, the phosphorus source B solution is concentrated phosphoric acid with a concentration of 98 wt%, or an aqueous solution of monoammonium phosphate, diammonium phosphate, monopotassium phosphate or dipotassium phosphate with a concentration of 5 wt% to 20 wt%, or a mixture thereof.

[0062] Preferably, the iron source A or iron source B further includes the water of crystallization molecule form of the above-mentioned compound.

[0063] Preferably, the oxidant C is a hydrogen peroxide solution and / or an ammonium persulfate solution with a concentration of 5wt%-20wt%.

[0064] Preferably, the oxidant C is oxygen, and the oxygen is directly introduced into solution I obtained in step 1 to react for 24 hours to obtain solution II.

[0065] Preferably, the concentration of crystallization aid D is 5wt%-20wt%.

[0066] Preferably, the reaction time in step 2 is 0.5-1.5 h.

[0067] Preferably, the stirring rate in step 4 is 100-500 rpm.

[0068] Preferably, the reaction endpoint pH in step 4 is 1.8-2.5.

[0069] Preferably, the reaction time in step 4 is 1-3 hours, that is, the time from the start of the droplet addition to the pH reaching 1.8-2.5 is 1-3 hours.

[0070] Preferably, the stirring rate in step 5 is 20-200 rpm.

[0071] Preferably, the content of crystallization aid E is 0.1wt%-1wt% of the aging system.

[0072] Figure 1 The image shown is a SEM image of the commercially available iron phosphate products from Guizhou Phosphate Group. Figure 2 The image shown is a SEM image of the spherical iron phosphate products obtained in preferred embodiments 1-5 of the present invention; Figure 2 SEM image of the iron phosphate product of this invention.

[0073] Depend on Figure 1 and Figure 2 The results show that commercially available products exhibit an irregular, flaky, granular agglomeration. The iron phosphate product of this invention exhibits a uniform, highly spherical morphology with regular particle shapes, which helps improve material consistency and application performance. Furthermore, due to the more regular geometry of the spherical particles, the friction between particles is reduced, resulting in higher fluidity and facilitating subsequent processing, such as slurry preparation and coating processes. In addition, the uniform particle size distribution is beneficial for improving the material's density and filling properties.

[0074] Table 1 shows the tap density and specific surface area of ​​commercially available iron phosphate products from Guizhou Phosphate Group; Table 2 shows the tap density and specific surface area of ​​iron phosphate products in the preferred embodiments and comparative examples of this invention.

[0075] Table 1:

[0076] Iron-to-phosphorus ratio <![CDATA[Tap density (m 2 / g)]]> <![CDATA[Specific surface area (g / cm 3 )]]> Commercially available sample 1 0.972 0.56 27.19 Commercially available sample 2 0.968 0.63 21.67 3 commercially available samples 0.967 0.64 22.99

[0077] Table 2:

[0078] Iron-to-phosphorus ratio <![CDATA[Tap density (m 2 / g)]]> <![CDATA[Specific surface area (g / cm 3 )]]> Example 1 0.964 1.02 35.51 Example 2 0.961 0.94 43.01 Example 3 0.967 0.72 37.46 Example 4 0.970 0.84 39.10 Example 5 0.969 0.71 39.39 Example 6 0.972 0.74 29.16 Example 7 0.966 0.82 39.39 Example 8 0.962 0.77 37.51 Example 9 0.970 0.86 31.56 Example 10 0.969 0.78 39.39 Comparative Example 1 0.971 0.75 20.35 Comparative Example 2 0.970 0.68 21.44 Comparative Example 3 0.974 0.77 23.15

[0079] By comparing Table 1 and Table 2, it can be seen that, compared with commercially available products, the tap density and specific surface area of ​​the spherical iron phosphate prepared in the preferred embodiment of the present invention are significantly higher than those of commercially available products.

[0080] Table 2 shows that, based on the data from the examples and comparative examples, the aging process in the preferred example 1 of this invention is carried out under stirring conditions, with a stirring rate preferably between 50 and 150 rpm, while the comparative example uses static aging. Stirring during aging is beneficial for increasing the tap density of the obtained spherical ferric phosphate and adjusting its specific surface area. However, the stirring rate can disrupt the formation of the spherical morphology. Therefore, the stirring rate during aging in this invention is strictly controlled. A stirring rate in the range of 50-150 rpm is beneficial for controlling the formation of spherical ferric phosphate and improving the specific surface area while maintaining a tap density higher than 0.7. Compared to the comparative example, in the method provided by this invention, the crystallization aid D solution is first mixed with solution II in step 4 to obtain a mother liquor, and a small amount of amorphous ferric phosphate dihydrate particles are obtained during the reaction process in step 4. In step 5, solution II and crystallization aid D are further added to the mother liquor obtained in step 4. The amorphous ferric phosphate dihydrate particles formed in the mother liquor in step 4 act as seed crystals, which helps control the particle size of the ferric phosphate dihydrate particles. Adding solution II and crystallization aid D in a two-stream manner helps control the supersaturation of amorphous ferric phosphate during the crystallization process, thereby controlling the particle size distribution of ferric phosphate dihydrate particles. Compared to the comparative example, the crystallization aid E added in step 6 is beneficial for the formation of spherical ferric phosphate dihydrate crystal morphology during the aging and crystallization process.

[0081] Example 1

[0082] (1) Dissolve 27.80 g (0.1 mol) of ferrous sulfate heptahydrate in 200 mL of deionized water, add 8.92 mL of 98 wt% phosphoric acid solution, and dissolve at 35 °C to obtain solution I; (2) Add 5 wt% hydrogen peroxide solution to solution I using a peristaltic pump within 1 h to prepare solution II; (3) Prepare a 5 wt% crystallization aid D solution by dissolving 1 g of sodium hydroxide in deionized water; (4) Add the crystallization aid D solution to solution II, which is being stirred (n = 300 rpm), using a peristaltic pump within 2 h, and control the addition dropwise to 2.0 using a pH meter to obtain a mother liquor; (5) Add the mother liquor obtained in step 4 to the solution I. 5 wt% of the total liquid mass is added to the crystallizer as the base liquid, and then solution II and crystallization aid D solution are added to the mother liquor being stirred (n = 300 rpm) within 2 hours respectively; (6) After washing and filtering the amorphous iron phosphate dihydrate particles obtained in step 5, deionized water is added to form a solid-liquid mixture III, which is then aged at 60°C at a certain stirring rate (n = 50 rpm), and 3-aminobenzoic acid is added to the mixture, with the amount added controlled at about 0.1 wt% of the total aging system; (7) The aged iron phosphate dihydrate is filtered and dried at 120°C for 90 min, and the obtained iron phosphate dihydrate crystals are the spherical iron phosphate product of the present invention.

[0083] Example 2

[0084] (1) Dissolve 27.80 g (0.1 mol) of ferrous sulfate heptahydrate in 200 mL of deionized water, add 8.92 mL of 98 wt% phosphoric acid solution, and dissolve at 30 °C to obtain solution I; (2) Add 5 wt% hydrogen peroxide solution to solution I using a peristaltic pump within 1 h to prepare solution II; (3) Prepare a 5 wt% crystallization aid D solution by dissolving 1 g of potassium hydroxide in deionized water; (4) Add the crystallization aid D solution to solution II, which is being stirred (n = 300 rpm), using a peristaltic pump within 2 h, and control the addition dropwise to 2.3 using a pH meter to obtain a mother liquor containing amorphous ferric phosphate dihydrate particles; (5) Add the solution to step 5 wt% of the total mass of the mother liquor obtained in step 4 is added to the crystallizer as the base liquid. Then, solution II and crystallization aid D solution are added to the mother liquor being stirred (n = 100 rpm) within 2 hours respectively. (6) After washing and filtering the amorphous iron phosphate dihydrate particles obtained in step 5, deionized water is added to form a solid-liquid mixture III. The mixture is then aged at 60°C at a certain stirring rate (n = 100 rpm). 3-aminobenzoic acid is added to the mixture, and the amount added is controlled to be about 0.1 wt% of the total aging system. (7) The aged iron phosphate dihydrate is filtered and dried at 120°C for 90 min. The resulting iron phosphate dihydrate crystals are the spherical iron phosphate product described in this invention.

[0085] Example 3

[0086] (1) Dissolve 37.4 g (0.1 mol) of ferrous nitrate nonahydrate in 200 mL of deionized water, add 8.92 mL of 98 wt% phosphoric acid solution, and dissolve at 30 °C to obtain solution I; (2) Add 5 wt% hydrogen peroxide solution to solution I using a peristaltic pump over 1 hour to prepare solution II; (3) Prepare a 5 wt% crystallization aid D solution by dissolving 1 g of potassium hydroxide in deionized water; (4) Add crystallization aid D solution to solution II, which is being stirred (n = 500 rpm), over 2 hours using a peristaltic pump, and add it dropwise to 2.0 using a pH meter to obtain a mother liquor containing amorphous ferric phosphate dihydrate particles; (5) Add 5 wt% of the total mass of the mother liquor obtained in step 4 to the crystallizer as the base liquid, and then add solution II and crystallization aid D solution to the mother liquor that is being stirred (n = 500 rpm) within 2 hours respectively; (6) After washing and filtering the amorphous iron phosphate dihydrate particles obtained in step 5, add deionized water to make solid-liquid mixture III, and then age it at 95°C at a certain stirring rate (n = 150 rpm), and add urea to the mixture, with the amount added controlled at about 0.1 wt% of the total aging system; (7) Filter the aged iron phosphate dihydrate and dry it at 120°C for 90 min. The obtained iron phosphate dihydrate crystals are the spherical iron phosphate product of the present invention.

[0087] Example 4

[0088] (1) Dissolve 37.4 g (0.1 mol) of ferrous nitrate nonahydrate in 200 mL of deionized water, add 8.92 mL of 98 wt% phosphoric acid solution, and dissolve at 30 °C to obtain solution I; (2) Add 5 wt% ammonium persulfate solution to solution I over 1 hour using a peristaltic pump to prepare solution II; (3) Prepare a 5 wt% crystallization aid D solution by dissolving 1 g of potassium hydroxide in deionized water; (4) Add crystallization aid D solution to solution II, which is being stirred (n = 500 rpm), over 2 hours using a peristaltic pump, and add it dropwise to 2.0 using a pH meter to obtain a mother liquor containing amorphous ferric phosphate dihydrate particles; (5) Add 5 wt% of the total mass of the mother liquor obtained in step 4 to the crystallizer as the base liquid, and then add solution II and crystallization aid D solution to the mother liquor that is being stirred (n = 500 rpm) within 2 hours respectively; (6) After washing and filtering the amorphous iron phosphate dihydrate particles obtained in step 5, add deionized water to form a solid-liquid mixture III, and then age it at 70°C at a certain stirring rate (n = 150 rpm), and add malonic acid to the mixture, with the amount added controlled at about 0.1 wt% of the total aging system; (7) Filter the aged iron phosphate dihydrate and dry it at 120°C for 90 min. The resulting iron phosphate dihydrate crystals are the spherical iron phosphate products described in this invention.

[0089] Example 5

[0090] (1) Dissolve 8.99 g (0.05 mol) of ferrous oxalate in 200 mL of deionized water, add 8.92 mL of 98 wt% phosphoric acid solution, and dissolve at 30 °C to obtain solution I; (2) Add 5 wt% ammonium persulfate solution to solution I over 1 hour using a peristaltic pump to prepare solution II; (3) Prepare 5 wt% crystallization aid D solution with 1 g of potassium hydroxide using deionized water; (4) Add crystallization aid D solution to solution II which is being stirred (n = 500 rpm) over 2 hours using a peristaltic pump, and add it dropwise to 2.0 using a pH meter to obtain a mother liquor containing amorphous ferric phosphate dihydrate particles; (5) Add the solution to step 5 wt% of the total mass of the mother liquor obtained in step 4 is added to the crystallizer as the base liquid. Then, solution II and crystallization aid D solution are added to the mother liquor being stirred (n = 500 rpm) within 2 hours. (6) After washing and filtering the amorphous iron phosphate dihydrate particles obtained in step 5, deionized water is added to form a solid-liquid mixture III. The mixture is then aged at 90°C at a certain stirring rate (n = 100 rpm). Polyacrylamide is added to the mixture, and the amount added is controlled to be about 0.1 wt% of the total aging system. (7) The aged iron phosphate dihydrate is filtered and dried at 120°C for 90 min. The resulting iron phosphate dihydrate crystals are the spherical iron phosphate product described in this invention.

[0091] Example 6

[0092] Dissolve 9.95 g (0.05 mol) of ferrous chloride tetrahydrate in 200 mL of deionized water, add 8.92 mL of 98 wt% phosphoric acid solution, and dissolve at 30 °C to obtain solution I; (2) Add 5 wt% hydrogen peroxide solution to solution I over 1 hour using a peristaltic pump to prepare solution II; (3) Prepare a 10 wt% crystallization aid solution using 25 wt% ammonia water with deionized water; (4) Add crystallization aid solution D to solution II which is being stirred (n = 500 rpm) over 2 hours using a peristaltic pump, and add it dropwise to 2.0 using a pH meter to obtain a mother liquor containing amorphous ferric phosphate dihydrate particles; (5) Add 5 wt% of the total mass of the mother liquor obtained in step 4 to the crystallizer as the base liquid, and then add solution II and crystallization aid D solution to the mother liquor that is being stirred (n = 500 rpm) within 2 hours respectively; (6) After washing and filtering the amorphous iron phosphate dihydrate particles obtained in step 5, add deionized water to form a solid-liquid mixture III, and then age it at 90°C at a certain stirring rate (n = 100 rpm), and add 3-aminobenzoic acid to the mixture, with the amount added controlled at about 0.1 wt% of the total aging system; (7) Filter the aged iron phosphate dihydrate and dry it at 120°C for 90 min. The resulting iron phosphate dihydrate crystals are the spherical iron phosphate products of the present invention.

[0093] Example 7

[0094] 27.80 g (0.1 mol) of ferrous sulfate heptahydrate was dissolved in 200 mL of deionized water, and a 5 wt% monoammonium phosphate solution was added. The dissolution temperature was 30 °C to obtain solution I. The iron-to-phosphorus ratio in the solution was controlled to be 1:1.15. (2) A 5 wt% hydrogen peroxide solution was added to solution I by peristaltic pump within 1 h to prepare solution II. (3) A 10 wt% crystallization aid solution was prepared by using 25 wt% ammonia water with deionized water. (4) The crystallization aid solution D was added to solution II, which was being stirred (n = 500 rpm), by peristaltic pump within 2 h. The addition was controlled by pH meter to reach 2.0 to obtain a mother product containing amorphous ferric phosphate dihydrate particles. (5) Add 5 wt% of the total mass of the mother liquor obtained in step 4 to the crystallizer as the base liquid, and then add solution II and crystallization aid D solution to the mother liquor being stirred (n = 500 rpm) within 2 h respectively; (6) After washing and filtering the amorphous iron phosphate dihydrate particles obtained in step 5, add deionized water to make solid-liquid mixture III, and then age it at 90°C at a certain stirring rate (n = 100 rpm), and add 3-aminobenzoic acid to the mixture, with the amount added controlled at about 0.1 wt% of the total aging system; (7) Filter the aged iron phosphate dihydrate and dry it at 120°C for 90 min. The obtained iron phosphate dihydrate crystals are the spherical iron phosphate products of the present invention.

[0095] Example 8

[0096] 27.80 g (0.1 mol) of ferrous sulfate heptahydrate was dissolved in 200 mL of deionized water, and a 5 wt% monoammonium phosphate solution was added. The dissolution temperature was 30 °C to obtain solution I. The iron-to-phosphorus ratio in the solution was controlled to be 1:1.15. (2) Oxygen was continuously introduced into solution I through a peristaltic pump for 24 h to prepare solution II. (3) A 10 wt% crystallization aid solution was prepared by using 25 wt% ammonia water with deionized water. (4) The crystallization aid solution D was added to solution II, which was being stirred (n = 500 rpm), through a peristaltic pump within 2 h. The pH was controlled by a pH meter to add the solution dropwise to 2.0 to obtain a mother liquor containing amorphous ferric phosphate dihydrate particles. (5) Add 5 wt% of the total mass of the mother liquor obtained in step 4 to the crystallizer as the base liquid, and then add solution II and crystallization aid D solution to the mother liquor that is being stirred (n = 500 rpm) within 2 hours respectively; (6) After washing and filtering the amorphous iron phosphate dihydrate particles obtained in step 5, add deionized water to form a solid-liquid mixture III, and then age it at 90°C at a certain stirring rate (n = 100 rpm), and add 3-aminobenzoic acid to the mixture, with the amount added controlled at about 0.1 wt% of the total aging system; (7) Filter the aged iron phosphate dihydrate and dry it at 120°C for 90 min. The resulting iron phosphate dihydrate crystals are the spherical iron phosphate products of the present invention.

[0097] Example 9

[0098] (1) Dissolve 27.80 g (0.1 mol) of ferrous sulfate heptahydrate in 200 mL of deionized water, add 8.92 mL of 98 wt% phosphoric acid solution, and dissolve at 35 °C to obtain solution I; (2) Add 5 wt% hydrogen peroxide solution to solution I using a peristaltic pump over 1 hour to prepare solution II; (3) Prepare a 5 wt% crystallization aid D solution by dissolving 2 g of ethylenediamine in deionized water; (4) Add the crystallization aid D solution to solution II, which is being stirred (n = 300 rpm), over 2 hours using a peristaltic pump, and add it dropwise to 2.0 using a pH meter to obtain a mother liquor; (5) Add the mother liquor obtained in step 4 to the solution. 5 wt% of the total mass is added to the crystallizer as the base liquid, and then solution II and crystallization aid D solution are added to the mother liquor being stirred (n = 300 rpm) within 2 hours respectively; (6) After washing and filtering the amorphous iron phosphate dihydrate particles obtained in step 5, deionized water is added to form a solid-liquid mixture III, which is then aged at 60°C at a certain stirring rate (n = 50 rpm), and 3-aminobenzoic acid is added to the mixture, with the amount added controlled at about 0.1 wt% of the total aging system; (7) The aged iron phosphate dihydrate is filtered and dried at 120°C for 90 min, and the obtained iron phosphate dihydrate crystals are the spherical iron phosphate product of the present invention.

[0099] Example 10

[0100] (1) Dissolve 27.80 g (0.1 mol) of ferrous sulfate heptahydrate in 200 mL of deionized water, add 8.92 mL of 98 wt% phosphoric acid solution, and dissolve at 35 °C to obtain solution I; (2) Add 5 wt% hydrogen peroxide solution to solution I over 1 hour using a peristaltic pump to prepare solution II; (3) Prepare a 5 wt% crystallization aid D solution by dissolving 2 g of ethylenediamine in deionized water; (4) Add the crystallization aid D solution to solution II, which is being stirred (n = 300 rpm), over 2 hours using a peristaltic pump, and add it dropwise to 2.0 using a pH meter to obtain a mother liquor; (5) Add 5 wt% of the total mass of the mother liquor obtained in step 4 to the solution. Add the solution to the crystallizer as the base liquid, and then add solution II and crystallization aid D solution to the mother liquor being stirred (n = 300 rpm) within 2 hours to obtain amorphous iron phosphate dihydrate particles; (6) After washing and filtering the obtained amorphous iron phosphate dihydrate particles, add deionized water to make solid-liquid mixture III and age it at 60°C at a certain stirring rate (n = 50 rpm), and add soluble starch to the mixture, with the amount added controlled at about 0.1 wt% of the total aging system; (7) Filter the aged iron phosphate dihydrate and dry it at 120°C for 90 min. The obtained iron phosphate dihydrate crystals are the spherical iron phosphate product described in this invention.

[0101] Example 11

[0102] Example 11 is similar to Example 8, except that the phosphorus source in step 1 of Example 8 is monoammonium phosphate, while the phosphorus source in Example 11 is any one of diammonium phosphate, monopotassium phosphate, or dipotassium phosphate, with a concentration of 5-20 wt%. The spherical iron phosphate dihydrate crystals obtained by the method described in Example 8 are the spherical iron phosphate. The results show that diammonium phosphate, monopotassium phosphate, or dipotassium phosphate are similar to monoammonium phosphate, and the method described in this invention can yield spherical iron phosphate products with high tap density and high specific surface area.

[0103] Example 12

[0104] Example 12 is similar to Example 10, except that the crystallization aid D in step 3 is ethylenediamine, while in Example 12, the crystallization aid D is monoammonium phosphate, diammonium phosphate, or ammonium phosphate at a concentration of 5-20 wt%. The spherical ferric phosphate dihydrate crystals obtained in Example 12 using the method described in Example 10 are the spherical ferric phosphate. The results show that monoammonium phosphate, diammonium phosphate, and ammonium phosphate are similar to ethylenediamine, and using the method described in this invention, spherical ferric phosphate products with high tap density and high specific surface area can be obtained.

[0105] Example 13

[0106] Example 13 is similar to Examples 1-10, except that the crystallization aid E is any one of gelatinized polysaccharide, glycine, L-hydroxysuccinic acid, and poloxamer 403, and the content of crystallization aid E in the aging system is 0.1wt%-1wt%. The ferric phosphate dihydrate crystals obtained in Example 13 using the method described in Examples 1-10 are the spherical ferric phosphate. The results show that gelatinized polysaccharide, glycine, L-hydroxysuccinic acid, poloxamer 403, and ethylenediamine are similar, and using the method described in this invention, spherical ferric phosphate products with high tap density and high specific surface area can be obtained. Crystallization aid E is beneficial for controlling the morphology of ferric phosphate crystals to be spherical, greatly improving the tap density and specific surface area range of the obtained spherical ferric phosphate, and the resulting spherical ferric phosphate product is beneficial for the production of lithium-ion battery cathodes.

[0107] Example 14

[0108] Example 14 is similar to Example 1, except that the ferrous sulfate heptahydrate iron source in step 1 of Example 1 is replaced with ferric sulfate at a concentration of 5-20 wt%. Using the method described in this invention, Example 14 can obtain spherical ferric phosphate products with high tap density and high specific surface area.

[0109] Comparative Example 1

[0110] (1) Dissolve 27.80 g (0.1 mol) of ferrous sulfate heptahydrate in 200 mL of deionized water, add 8.92 mL of 98 wt% phosphoric acid solution, and dissolve at 30 °C to obtain solution I; (2) Add 5 wt% hydrogen peroxide solution to solution I by peristaltic pump within 1 h to prepare solution II; (3) Prepare 5 wt% crystallization aid D solution by dissolving 1 g of ammonia water in deionized water; (4) Add crystallization aid D solution to solution II which is being stirred (n = 300 rpm) by peristaltic pump within 2 h, and add it dropwise to 2.0 using a pH meter to obtain amorphous ferric phosphate dihydrate particles; (5) Wash and filter the obtained amorphous ferric phosphate dihydrate particles, add deionized water to prepare solid-liquid mixture III, and then let it stand and age at 90 °C; (6) Filter the aged ferric phosphate dihydrate and dry it at 120 °C for 90 min.

[0111] Comparative Example 2

[0112] (1) Dissolve 27.80 g (0.1 mol) of ferrous sulfate heptahydrate in 200 mL of deionized water, add 8.92 mL of 98 wt% phosphoric acid solution, and dissolve at 30 °C to obtain solution I; (2) Add 5 g of ammonium dihydrogen phosphate to solution I over 1 hour using a peristaltic pump to prepare solution II; (3) Mix 5 g of ammonium dihydrogen phosphate and 5 wt% hydrogen peroxide to prepare solution D. The addition of ammonium dihydrogen phosphate helps to balance the pH of the solution after the introduction of hydrogen peroxide, and compares the pH of the solution with the pH of the solution. In Example 2, adjusting the order of adding the oxidant is beneficial to the formation of pores in individual particles; (4) Add solution D to solution II which is being stirred (n = 300 rpm) within 2 hours using a peristaltic pump, and use a pH meter to control the dropwise addition to 2.0 to obtain amorphous iron phosphate dihydrate particles; (5) After washing and filtering the obtained amorphous iron phosphate dihydrate particles, add deionized water to make solid-liquid mixture III and then let it stand and age at 90°C; (6) Filter the aged iron phosphate dihydrate and dry it at 120°C for 90 min.

[0113] Comparative Example 3

[0114] (1) Dissolve 27.80 g (0.1 mol) of ferrous sulfate heptahydrate in 200 mL of deionized water, add 8.92 mL of 98 wt% phosphoric acid solution, and dissolve at 30 °C to obtain solution I; (2) Add 5 wt% hydrogen peroxide solution to solution I by peristaltic pump over 1 h to prepare solution II; (3) Add 98 wt% ethylenediamine to solution II which is being stirred (n = 300 rpm) by peristaltic pump over 2 h, and add it dropwise to 2.0 using a pH meter to obtain amorphous ferric phosphate dihydrate particles; (4) Wash and filter the obtained amorphous ferric phosphate dihydrate particles, add deionized water to prepare solid-liquid mixture III, and then let it stand at 90 °C for aging; (5) Filter the aged ferric phosphate dihydrate and dry it at 120 °C for 90 min.

[0115] In Comparative Examples 1-3, the aging time was no less than 10 hours, and crystallization resulted in crystallizer wall adhesion, which was difficult to clean without the addition of acid, hindering industrial production. However, the spherical iron phosphate preparation process provided by this invention achieves a crystallization time of no more than 3 hours and avoids wall adhesion, making it more suitable for large-scale industrial production.

Claims

1. A process for preparing spherical iron phosphate, comprising using iron source A and phosphorus source B as raw materials and reacting them with oxidant C to obtain iron phosphate, characterized in that, The process includes the following steps: Step 1: Add iron source A solution to phosphorus source B solution to obtain solution I; Step 2: Add oxidant C to solution I obtained in step 1 to react and obtain solution II; Step 3: Prepare an aqueous solution of the crystallization aid to obtain crystallization aid D solution; Step 4: Add the crystallization aid D solution to the stirred solution II, and control the endpoint of the addition by adjusting the pH of the mixed solution to obtain the mother liquor; Step 5: Add the mother liquor obtained in step 4 into the crystallizer. Use a peristaltic pump to dropwise add solution II and crystallization aid D solution into the crystallizer in two separate feed streams. Adjust the dropping rate of the two feed streams to ensure that the pH of the solution remains stable, and obtain amorphous iron phosphate dihydrate particles. Step 6: After washing and filtering the amorphous iron phosphate dihydrate particles obtained in Step 5, add water to make solid-liquid mixture III. Add crystallization aid E to solid-liquid mixture III and stir and age it at 60-95℃. Step 7: Filter and dry the aged ferric phosphate dihydrate to obtain the spherical ferric phosphate.

2. The process as described in claim 1, characterized in that, The iron source A solution contains any one or more of ferrous sulfate, ferrous sulfate, ferrous chloride, ferrous oxalate, and ferrous nitrate mixed in any proportion.

3. The process as described in claim 2, characterized in that, The phosphorus source B solution contains at least one of phosphoric acid, monoammonium phosphate, diammonium phosphate, monopotassium phosphate, and dipotassium phosphate.

4. The process as described in claim 3, characterized in that, In step 1, iron source A is dissolved in deionized water at 30-40℃ to obtain iron source A solution, wherein the iron source content in iron source A solution is 5wt%-20wt%; or, phosphorus source B solution is concentrated phosphoric acid; or, phosphorus source B is phosphate, and phosphorus source B is dissolved in water at 30-40℃ to obtain phosphorus source B solution, wherein the phosphate concentration in phosphorus source B solution is 5wt%-20wt%; or, at 30-40℃, iron source A solution and phosphorus source B solution are mixed, wherein the molar ratio of iron source to phosphorus source is 1:1-1:1.

3.

5. The process as described in claim 1, characterized in that, In step 2, the oxidant C includes at least one of oxygen, hydrogen peroxide, and ammonium persulfate.

6. The process as described in claim 1, characterized in that, In step 2, the oxidant C is a 5wt%-20wt% aqueous solution of hydrogen peroxide or ammonium persulfate, and the reaction time in step 2 is 0.5-1.5 h; or, the oxidant C is oxygen, and the reaction time in step 2 is 24 h.

7. The process as described in claim 1, characterized in that, In step 3, the crystallization aid D includes at least one of ammonia, ethylenediamine, monoammonium phosphate, diammonium phosphate, and ammonium phosphate; in step 3, the concentration of the crystallization aid D solution is 5wt%-20wt%.

8. The process as described in claim 1, characterized in that, In step 4, the stirring rate is 100-500 rpm; the final pH of the drop addition is 1.8-2.

5.

9. The process as described in claim 1, characterized in that, In step 5, the reaction is carried out in the crystallizer by stirring at a speed of 20-200 rpm.

10. The process as described in claim 1, characterized in that, In step 6, the crystallization aid E includes at least one of gel polysaccharide, soluble starch, 3-aminobenzoic acid, glycine, malonic acid, polyacrylamide, urea, L-hydroxysuccinic acid, and poloxamer 403; the content of crystallization aid E in the aging system is 0.1wt%-1wt%.

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