Amorphous iron phosphate and preparation method therefor, and anhydrous iron phosphate and preparation method therefor

Abstract

Provided in the present disclosure is amorphous iron phosphate. The X-ray diffraction pattern of the amorphous iron phosphate has a first diffraction peak θ1 and a second diffraction peak θ2 at 19-21° and 28-30°, respectively, and the ratio of the peak intensity I1 of the first diffraction peak to the peak intensity I2 of the second diffraction peak is 0.8-0.91. The amorphous iron phosphate is spherical or sphere-like particles. Further provided are a preparation method for the amorphous iron phosphate, and anhydrous iron phosphate prepared on the basis of the amorphous iron phosphate.

Description

Amorphous ferric phosphate and its preparation method, anhydrous ferric phosphate and its preparation method

[0001]

[0002] Priority information

[0003] This disclosure claims priority and benefits to patent application No. 2024117418225, filed with the China National Intellectual Property Administration on November 29, 2024, the entire contents of which are incorporated herein by reference.

[0004] Technical Field

[0005] This disclosure belongs to the field of lithium-ion battery material technology, specifically relating to the modification of iron phosphate intermediates and anhydrous iron phosphate.

[0006] Background Technology

[0007] Among lithium-ion battery cathode materials, lithium iron phosphate (LFP) has become a research hotspot due to its advantages such as non-toxicity, low cost, and good safety. With the development of applications such as new energy power generation and storage, and home energy storage, the cost and long-cycle performance advantages of LFP are becoming increasingly prominent, leading to its widespread use in automotive and large-scale energy storage applications. However, the compaction density and electrochemical performance of LFP still need improvement. As the backbone of lithium iron phosphate, the morphology and structure of iron phosphate play a decisive role in its compaction density and electrochemical performance. Therefore, researching LFP preparation processes with controllable particle distribution has high application value and research significance.

[0008] Public content

[0009] To address the aforementioned technical issues, this disclosure provides amorphous ferric phosphate and its preparation method, as well as anhydrous ferric phosphate and its preparation method.

[0010] To achieve the above objectives, this disclosure provides an amorphous iron phosphate, wherein the X-ray diffraction pattern of the amorphous iron phosphate has a first diffraction peak θ1 and a second diffraction peak θ2 at 19°~21° and 28°~30°, respectively, and the ratio of the peak intensity I1 of the first diffraction peak to the peak intensity I2 of the second diffraction peak is 0.8~0.91.

[0011] This application provides amorphous iron phosphate, the X-ray diffraction pattern of which has a peak intensity ratio of 0.8 to 0.91 for the first diffraction peak at 19°~21° and 28°~30° respectively. The amorphous iron phosphate contains low amounts of iron hydroxide, has a uniform primary particle size distribution, small primary particle size, and low degree of agglomeration, which is beneficial for the subsequent preparation of iron phosphate with high specific surface area, small primary particle size, and low agglomeration. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the embodiments of this disclosure or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0013] Figure 1 shows the XRD patterns of amorphous iron phosphate prepared in Example 1, Comparative Example 1, and Comparative Example 2.

[0014] Figure 2 shows the SEM image and particle distribution diagram of the amorphous iron phosphate prepared in Example 1.

[0015] Figure 3 shows the SEM image and particle distribution diagram of the anhydrous ferric phosphate prepared in Example 1.

[0016] Figure 4 shows the XRD pattern of anhydrous ferric phosphate prepared in Example 1.

[0017] Figure 5 shows the SEM image and particle distribution diagram of the amorphous iron phosphate prepared in Comparative Example 1.

[0018] Figure 6 shows the SEM image and particle distribution diagram of the anhydrous ferric phosphate prepared in Comparative Example 1.

[0019] Figure 7 shows the XRD pattern of anhydrous ferric phosphate prepared in Comparative Example 1.

[0020] Figure 8 shows the SEM image and particle distribution diagram of the amorphous iron phosphate prepared in Comparative Example 2.

[0021] Figure 9 shows the SEM image and particle distribution diagram of the anhydrous ferric phosphate prepared in Comparative Example 2.

[0022] Figure 10 shows the XRD pattern of anhydrous ferric phosphate prepared in Comparative Example 2.

[0023] Figure 11 shows the SEM image and particle distribution diagram of the anhydrous ferric phosphate prepared in Comparative Example 3.

[0024] Among them, the particle distribution maps in Figures 2, 3, 5, 6, 8, 9, and 11 were obtained by processing and statistically analyzing the SEM images using ImageJ software. Embodiments of the present invention

[0025] Currently, the main production process for ferric phosphate on the market is a two-step method. First, a neutralization reaction occurs between a phosphorus source and a ferric source to produce amorphous ferric phosphate. Amorphous ferric phosphate has low crystallinity, with particles that are nearly spherical, and contains metal ions such as sulfate, ammonium, and manganese. Then, the amorphous ferric phosphate undergoes a crystal transformation while removing excess impurities to form dihydrate ferric phosphate. Dihydrate ferric phosphate has a relatively high specific surface area, typically around 50 μm. 2The final dehydration process yields approximately [g] of anhydrous ferric phosphate, with spherical particles and secondary particles forming porous aggregates without a specific morphology. This process typically results in severe material agglomeration, large particles, low specific surface area, and significant difficulty in subsequent crushing. Furthermore, the numerous unfilled pores between particles reduce compaction density, and some particles may overcharge or over-discharge during charge-discharge processes, impacting electrochemical performance. Additionally, the ferric phosphate synthesis process is influenced by numerous factors, and current research on the products of amorphous ferric phosphate processes is limited.

[0026] During the synthesis of anhydrous ferric phosphate, the applicant discovered that synthesizing amorphous ferric phosphate with low ferric hydroxide content is beneficial for improving the particle size distribution of amorphous ferric phosphate and reducing agglomeration and primary particle size. Furthermore, this intermediate amorphous ferric phosphate is subsequently synthesized into anhydrous ferric phosphate through conventional crystallization and dewatering. During the crystallization process, inorganic acid diffuses into the interior of the intermediate amorphous ferric phosphate to react, removing ferric hydroxide and achieving crystallization. Since the intermediate amorphous ferric phosphate is amorphous ferric phosphate with low agglomeration and good dispersibility, the ferric phosphate obtained after crystallization and dewatering can maintain the morphological characteristics of amorphous ferric phosphate, enabling the synthesis of anhydrous ferric phosphate with smaller primary particle size, lower agglomeration, and higher specific surface area. Based on this, this disclosure is completed.

[0027] This disclosure provides an amorphous iron phosphate, wherein the X-ray diffraction pattern of the amorphous iron phosphate has a first diffraction peak θ1 and a second diffraction peak θ2 at 19°~21° and 28°~30° respectively, and the ratio of the peak intensity I1 of the first diffraction peak to the peak intensity I2 of the second diffraction peak is 0.8~0.91, and the amorphous iron phosphate is a spherical or near-spherical particle.

[0028] In the above technical solution, the characteristic peaks of 19°~21° belong to ferric hydroxide and ferric phosphate, and the characteristic peaks of 28°~30° belong to ferric phosphate. Therefore, the ratio of peak intensity I1 / I2 can reflect the content of ferric hydroxide in amorphous ferric phosphate.

[0029] In some embodiments, the ratio of the peak intensity I1 of the first diffraction peak to the peak intensity I2 of the second diffraction peak is 0.82 to 0.905, for example, 0.82, 0.825, 0.83, 0.835, 0.84, 0.845, 0.85, 0.855, 0.86, 0.865, 0.87, 0.875, 0.88, 0.885, 0.89, 0.895, 0.90, 0.905, etc.

[0030] In some embodiments, the particle size of 95% of the primary particles of the amorphous iron phosphate is below 80 nm. Specifically, the particle size of 95% of the primary particles of the amorphous iron phosphate is between 20 nm and 80 nm, and more specifically, the particle size of 95% of the primary particles of the amorphous iron phosphate is between 20 nm and 70 nm, such as 20 nm to 70 nm, 20 nm to 60 nm, etc. The primary particles of the amorphous iron phosphate have a small particle size and uniform particle size distribution.

[0031] This disclosure provides a method for preparing amorphous iron phosphate, including:

[0032] Solution A was prepared using a phosphorus source and a ferrous source. The pH and temperature of solution A were adjusted, and the reaction was carried out to obtain a grayish-white slurry.

[0033] The grayish-white slurry was oxidized to obtain a yellow amorphous ferric phosphate slurry. After solid-liquid separation and washing, amorphous ferric phosphate was obtained.

[0034] The X-ray diffraction pattern of the amorphous iron phosphate has a first diffraction peak θ1 and a second diffraction peak θ2 at 19°~21° and 28°~30°, respectively, and the ratio of the peak intensity I1 of the first diffraction peak to the peak intensity I2 of the second diffraction peak is 0.8~0.91.

[0035] The applicant's research revealed that by first neutralizing a divalent iron source and a phosphorus source (through pH adjustment), a grayish-white precipitate is formed through homogeneous nucleation. Further oxidation of the precipitate slurry yields amorphous iron phosphate material with low iron hydroxide content. This amorphous iron phosphate material exhibits uniform particle size distribution, low agglomeration, and small particle size. The applicant's research also found that the iron hydroxide content affects the particle uniformity, agglomeration degree, and primary particle size of the amorphous iron phosphate material. A lower iron hydroxide content in the prepared amorphous iron phosphate material is beneficial for improving the uniformity of particle size distribution, reducing agglomeration, and decreasing the primary particle size. Analysis suggests that in this preparation method, the preferential synthesis of the grayish-white precipitate, presumably ferrous hydrogen phosphate precipitate, inhibits the formation of iron hydroxide crystal nuclei. The resulting ferrous hydrogen phosphate solid can serve as a template, and oxidation yields amorphous iron phosphate with uniform particle size distribution. Conversely, if oxidation is used first, iron hydroxide crystal nuclei are easily formed preferentially, and phosphoric acid and iron ions grow rapidly on their surface, agglomerating in a small area to form iron phosphate particles. The resulting amorphous iron phosphate particles are very large and unevenly distributed.

[0036] In the above preparation method, solution A containing phosphorus source and ferrous source can be prepared in various ways, as long as the phosphorus source and ferrous source in solution A do not undergo precipitation reaction. For example, a phosphorus source solution can be prepared separately using the phosphorus source, and a solution can be prepared using the ferrous source as a raw material. The ferrous source can be a water-soluble or water-insoluble raw material. When using a water-insoluble raw material, the water-insoluble ferrous source can be dissolved in acid to obtain a ferrous-containing solution, and then the two solutions can be mixed to obtain solution A. Alternatively, phosphorus source and ferrous source can be used as raw materials, and solution A can be prepared while ensuring that the phosphorus source and ferrous source do not undergo precipitation reaction. Specifically, this can be achieved by adjusting and controlling the pH of the solution. The pH adjuster can be an acidic solution or an alkaline solution. The acidic solution can be sulfuric acid, hydrochloric acid, etc., and the alkaline solution can be ammonia, urea, sodium hydroxide, etc.

[0037] In some implementations, the pH of solution A is adjusted to 1.5 to 3.5, for example, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, etc.

[0038] In some embodiments, the reagent used to adjust the pH of solution A is one or more of ammonia, urea, and sodium hydroxide.

[0039] In some embodiments, the temperature of solution A is adjusted to 40°C. o C~60 o C, for example, 40℃, 45℃, 50℃, 55℃, 60℃, etc.

[0040] In some embodiments, the phosphorus source is one or more of ammonium dihydrogen phosphate, phosphoric acid, and diammonium hydrogen phosphate;

[0041] In some embodiments, the ferrous source is one or more of ferrous sulfate, ferrous chloride, ferrous nitrate, ferrous oxalate, iron powder, and ferrous oxide;

[0042] In some embodiments, the molar ratio of phosphorus in the phosphorus source to iron in the iron source is 0.95 to 1.2:1.

[0043] In some embodiments, the oxidant used in the oxidation is one or more of hydrogen peroxide, air, oxygen, and ozone.

[0044] Research has shown that the method for preparing amorphous iron phosphate provided in this disclosure requires a lower amount of oxidant than existing methods. Existing methods typically require more than 1.4 times the theoretically required amount of oxidant. In some embodiments, the amount of oxidant is 1.2 to 1.4 times the theoretically required amount, for example, 1.2, 1.3, or 1.4 times.

[0045] In some embodiments, the mass percentage concentration of phosphorus in solution A is 2% to 5%. For example, 2%, 3%, 4%, 5%, etc.

[0046] In some embodiments, the iron concentration in solution A is 3% to 7% by mass, for example, 3%, 4%, 5%, 6%, 7%, etc.

[0047] In some embodiments, before adjusting the pH of solution A to 1.5-3.5, an acidic solution is first added to solution A to adjust the initial pH to 0.5 < pH < 1.2. For example, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, etc. By keeping solution A within the above pH range, it is ensured that the phosphorus source and ferrous source do not undergo precipitation reactions.

[0048] In some embodiments, the washing is performed using pure water; the conductivity of the wash water at the end of the washing process is not greater than 20000 μs / cm.

[0049] In some embodiments, the water mass fraction in the amorphous ferric phosphate is 25% to 40%, for example, 25%, 28%, 30%, 32%, 35%, 38%, 40%, etc.

[0050] This disclosure also provides a method for preparing anhydrous ferric phosphate, including:

[0051] The aforementioned amorphous ferric phosphate or the amorphous ferric phosphate prepared by the aforementioned preparation method is mixed with a phosphoric acid solution, heated to crystallize, filtered, washed with water, and calcined to obtain anhydrous ferric phosphate.

[0052] In the above technical solution, since the amorphous ferric phosphate prepared above is used as a template, the amorphous ferric phosphate has a low content of ferric hydroxide, resulting in uniform particle size distribution, low agglomeration, and small particle size. Therefore, after crystallization and calcination, the grain size and agglomeration of the amorphous ferric phosphate are well maintained, thus obtaining anhydrous ferric phosphate with small particle size, low agglomeration, and high specific surface area. The particle size of 95% primary particles of the anhydrous ferric phosphate is below 90 nm. Specifically, the particle size of 95% primary particles of anhydrous ferric phosphate can be 30 nm to 90 nm, and further, the particle size of 95% primary particles of anhydrous ferric phosphate can be 40 nm to 90 nm. The specific surface area of ​​95% primary particles of anhydrous ferric phosphate is 9 g / cm³. 3 ~ 14 m 2 The tap density of 95% primary anhydrous ferric phosphate particles is 0.7 g / cm³. 3 ~ 1.0 g / cm 3 .

[0053] The secondary particle size (D100) of the anhydrous ferric phosphate is below 90 μm. Specifically, the secondary particle size (D100) of the anhydrous ferric phosphate is 35 μm to 90 μm, for example, 40 μm, 45 μm, 40 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, and 90 μm. The D99 is below 50 μm. More specifically, the secondary particle size (D100) of the anhydrous ferric phosphate is 20 μm to 50 μm, for example... The particle sizes of anhydrous ferric phosphate are 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, etc., with D90 below 7.5μm. More specifically, the secondary particle size of anhydrous ferric phosphate is 4μm~7.5μm, such as 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, etc., and D50 is 2μm~4μm, such as 2μm, 2.5μm, 3μm, 3.5μm, 4μm, etc.

[0054] In the preparation method of anhydrous ferric phosphate, the molar ratio of phosphoric acid to amorphous ferric phosphate in the phosphoric acid solution can be conventionally controlled, as long as the crystallization of amorphous ferric phosphate can be achieved. In some embodiments, this ratio can be 0.02~0.2∶1, for example 0.02∶1, 0.03∶1, 0.04∶1, 0.05∶1, 0.08∶1, 0.1∶1, 0.12∶1, 0.15∶1, 0.18∶1, 0.20∶1, etc.

[0055] In the preparation method of anhydrous ferric phosphate, the crystallization temperature corresponding to the heating crystallization is a conventional crystallization temperature in the art; in some embodiments, this temperature is 70°C. o C~100 o C, for example, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, 100℃, etc.

[0056] In the preparation method of anhydrous ferric phosphate, pure water can be used for washing; the conductivity of the wash water at the end of the washing process should not exceed 1000 μS / cm.

[0057] In the preparation method of anhydrous ferric phosphate, the purpose of calcination is dehydration, and conventional dehydration temperatures in the art can be used; in some embodiments, the calcination temperature is 500°C. o C~650 o C, for example, 500℃, 520℃, 550℃, 580℃, 600℃, 620℃, 650℃, etc.

[0058] This disclosure also provides anhydrous ferric phosphate, prepared using the aforementioned preparation method.

[0059] To facilitate understanding of this disclosure, it will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of this disclosure is not limited to the following specific embodiments.

[0060] The tap density test methods for the products in the following embodiments and comparative examples are as follows:

[0061] Take approximately 100g of the sample to be tested and place it into a 250mL graduated cylinder. Tap the cylinder 10, 500, and 1250 times, recording the corresponding volumes V10, V500, and V1250, accurate to the smallest graduation. If the difference between V500 and V1250 is less than 2mL, take V1250 as the tapped volume; otherwise, increase the number of taps until the difference between two consecutive volume records is less than 2mL. Calculate the tapped density using the formula m / V, where m is the sample mass and V is the tapped volume.

[0062] The test method for the specific surface area of ​​the product is as follows:

[0063] Referring to GB / T 13390-2008 Determination of specific surface area of ​​metal powders - Nitrogen adsorption method, the specific surface area was measured using a specific surface area analyzer.

[0064] The test method for particle size distribution of the product is as follows:

[0065] Referencing HG / T 4701, the method for determining the particle size of iron phosphate for batteries (5.11); mix the sample thoroughly, weigh 0.1g of the sample, place it in a 100mL clean beaker containing 50mL of water, sonicate for 15min, and then use a Bettersize2600 laser particle size analyzer wet method system for detection.

[0066] The method for detecting the particle size distribution of 95% of primary particles in the product is as follows:

[0067] Import the SEM image into ImageJ software to obtain particle distribution statistics. The particle statistics are then fitted with the statistical distribution using Origin software to obtain the data distribution results. a±b represents the 95% primary particle size range, where a and b are the mean and standard deviation, respectively.

[0068] Example 1

[0069] An aqueous solution containing 0.345 mol of ammonium dihydrogen phosphate was added to an aqueous solution containing 0.3 mol of ferrous sulfate. Sulfuric acid was added to adjust the pH of the mixed solution to 1.0, resulting in a phosphorus-to-iron ratio of 1.15. The mixed solution contained 6.0% iron and 3.5% phosphorus by mass. The mixed solution was heated to 50°C. o C. Add ammonia to adjust the pH to 2.66, forming a grayish-white slurry;

[0070] The above slurry was oxidized by adding hydrogen peroxide containing 0.21 mol of hydrogen peroxide, then filtered and washed until the conductivity of the wash water was no greater than 20000 μS / cm, to obtain ferric phosphate yellow. X-ray diffraction analysis was performed on the obtained ferric phosphate yellow, and the results are shown in Figure 1. Figure 1 shows that the peak intensity ratio between the characteristic peak at 19°~21° and the characteristic peak at approximately 28°~30° is 0.852. The SEM image and particle distribution diagram of the obtained amorphous ferric phosphate yellow are shown in Figure 2. The figures show that the particle distribution is uniform, and the 95% primary particle size of the obtained amorphous ferric phosphate is 32.7±4.5 nm.

[0071] The ferric phosphate slurry and phosphoric acid were mixed and reacted at 95°C for 3 hours. The molar ratio of phosphoric acid to ferric phosphate was 0.03. The mixture was filtered and washed with pure water until the conductivity of the wash water was no more than 1000 μS / cm.

[0072] The filtered and washed product was dried and then heated at 550°C. o Anhydrous ferric phosphate was obtained by sintering at C for 2 hours. The SEM image and particle size distribution of the anhydrous ferric phosphate are shown in Figure 3. As can be seen from the figure, 95% of the primary particles of the obtained anhydrous ferric phosphate have a particle size of 57.8 ± 14.9 nm, exhibiting consistent size. The specific surface area was measured to be 12.3 m². 2 / g, tap density 0.85g / cm³ 3 The particles showed minimal agglomeration. The X-ray diffraction pattern of the obtained anhydrous ferric phosphate is shown in Figure 4, and the secondary particle sizes are shown in Table 2.

[0073] Example 2

[0074] Add 0.315 mol of phosphoric acid to an aqueous solution containing 0.3 mol of ferrous sulfate, adjust the pH of the solution to 1.0 with ammonia, and the phosphorus-to-iron ratio is 1.05. The iron content is 6% by mass and the phosphorus content is 3.5% by mass.

[0075] Heat the mixture to 50°C. o C. Add ammonia to adjust the pH to 2.8, forming a grayish-white slurry;

[0076] The above slurry was oxidized by adding hydrogen peroxide containing 0.21 mol of hydrogen peroxide, then filtered and washed until the conductivity of the wash water was no greater than 20000 μS / cm, to obtain iron phosphate yellow. X-ray diffraction analysis of the obtained amorphous iron phosphate yellow showed a peak intensity ratio of 0.881 for the characteristic peaks at approximately 19°–21° and 28°–30°, and the 95% primary particle size of the amorphous iron phosphate was 40.5 ± 6.6 nm.

[0077] Mix ferric phosphate slurry and phosphoric acid, 85 o The reaction proceeds for 3 hours at C, with a molar ratio of phosphoric acid to iron phosphate of 0.03. The mixture is then filtered and washed with pure water until the conductivity of the wash water is no greater than 1000 μS / cm.

[0078] The filtered and washed product was dried and then heated at 550°C. o The iron phosphate was obtained by sintering at C for 2 hours. Analysis showed that 95% of the primary particles of the obtained iron phosphate were distributed at 64.2 ± 15.6 nm, with a specific surface area of ​​10.2 m². 2 / g, tap density is 0.81g / cm³ 3 The particles showed minimal agglomeration. The secondary particle size of the obtained anhydrous ferric phosphate is shown in Table 2.

[0079] Example 3

[0080] An aqueous solution containing 0.303 mol of ammonium dihydrogen phosphate was added to an aqueous solution containing 0.3 mol of ferrous sulfate. Sulfuric acid was added to adjust the pH of the solution to 1.1. The iron content was 5% by mass, and the phosphorus content was 2.8% by mass; the phosphorus-iron ratio was 1.01. The above solution was heated to 50°C. o C. Add sodium hydroxide to adjust the pH to 2.0, forming a grayish-white slurry;

[0081] The above slurry was oxidized by adding hydrogen peroxide containing 0.18 mol of hydrogen peroxide, followed by filtration and washing until the conductivity of the wash water was no greater than 20000 μS / cm, thus obtaining iron phosphate yellow. X-ray diffraction analysis of the obtained amorphous iron phosphate yellow showed a peak intensity ratio of 0.892 for the characteristic peaks at approximately 19°–21° and 28°–30°, and the 95% primary particle size of the amorphous iron phosphate was 52.5 ± 7.2 nm.

[0082] Mix ferric phosphate slurry and phosphoric acid, react at 85℃ for 3 hours, with a molar ratio of phosphoric acid to ferric phosphate of 0.03, filter and wash with pure water until the conductivity of the wash water is no greater than 1000 μS / cm.

[0083] The filtered and washed product was dried and then heated at 550°C. o The iron phosphate was obtained by sintering at C for 2 hours. Analysis showed that 95% of the primary particles of the obtained iron phosphate were distributed at 65.4 ± 14.5 nm, with a specific surface area of ​​9.3 m². 2 / g, tap density is 0.92g / cm³ 3 The particles showed minimal agglomeration. The secondary particle size of the obtained anhydrous ferric phosphate is shown in Table 2.

[0084] Example 4

[0085] An aqueous solution containing 0.345 mol of ammonium dihydrogen phosphate was added to an aqueous solution containing 0.3 mol of ferrous sulfate. Sulfuric acid was added to adjust the pH of the solution to 0.6. The iron mass fraction was 5.5%, the phosphorus mass fraction was 3.5%, and the phosphorus-iron ratio was 1.15. The mixed solution was heated to 50°C. o C. Add ammonia to adjust the pH to 2.66, forming a grayish-white slurry;

[0086] Oxygen was introduced into the above slurry for oxidation at a flow rate of 900 mL / h for 2 hours until complete oxidation. The slurry was then filtered and washed with pure water until the conductivity of the wash water was no greater than 20000 μS / cm, yielding ferric phosphate yellow. X-ray diffraction analysis of the obtained ferric phosphate yellow showed a peak intensity ratio of 0.871 between the characteristic peaks at 19°–21° and approximately 28°–30°. The particle distribution was uniform, with 95% of the primary particles of amorphous ferric phosphate having a particle size of 28.5 ± 5.8 nm, exhibiting minimal agglomeration.

[0087] The ferric phosphate slurry and phosphoric acid were mixed and reacted at 95°C for 3 hours. The molar ratio of phosphoric acid to ferric phosphate was 0.15. The mixture was filtered and washed with pure water until the conductivity of the wash water was no more than 1000 μS / cm.

[0088] The filtered and washed product was dried and then heated at 550°C. o Anhydrous ferric phosphate was obtained by sintering at C for 2 hours. 95% of the primary particles of the obtained ferric phosphate had a particle size distribution of 61.5 ± 13.8 nm, and the specific surface area was measured to be 10.7 m². 2 / g, tap density is 0.88g / cm³ 3 The particles showed minimal agglomeration. The secondary particle size of the obtained anhydrous ferric phosphate is shown in Table 2.

[0089] Example 5

[0090] An aqueous solution containing 0.285 mol of ammonium dihydrogen phosphate was added to an aqueous solution containing 0.3 mol of ferrous sulfate. Sulfuric acid was added to adjust the pH of the solution to 0.6. The iron content was 3.8% by mass, the phosphorus content was 2% by mass, and the phosphorus-iron ratio was 0.95. The mixed solution was heated to 40°C. o C. Add ammonia to adjust the pH to 1.6, forming a grayish-white solution;

[0091] The above slurry was oxidized by adding hydrogen peroxide containing 0.21 mol of hydrogen peroxide, followed by filtration and washing until the conductivity of the wash water was no greater than 20000 μS / cm, thus obtaining iron phosphate yellow. X-ray diffraction analysis of the obtained amorphous iron phosphate yellow showed a peak intensity ratio of 0.863 for the characteristic peaks at approximately 19°–21° and 28°–30°, and the 95% particle size of the amorphous iron phosphate was 41.8 ± 6.2 nm.

[0092] The ferric phosphate slurry and phosphoric acid were mixed and reacted at 95°C for 3 hours. The molar ratio of phosphoric acid to ferric phosphate was 0.15. The mixture was filtered and washed with pure water until the conductivity of the wash water was no more than 1000 μS / cm.

[0093] The filtered and washed product was dried and then heated at 550°C. oAnhydrous ferric phosphate was obtained by sintering at C for 2 hours. The 95% primary particle size of the obtained anhydrous ferric phosphate was 58.5 ± 14.5 nm, and the specific surface area was measured to be 10.5 m². 2 / g, tap density is 0.93g / cm³ 3 The particles showed minimal agglomeration. The secondary particle size of the obtained anhydrous ferric phosphate is shown in Table 2.

[0094] Example 6

[0095] An aqueous solution containing 0.348 mol of ammonium dihydrogen phosphate was added to an aqueous solution containing 0.3 mol of ferrous sulfate. Hydrochloric acid was added to adjust the pH of the solution to 1.1. The iron content was 7% by mass, the phosphorus content was 4.5% by mass, and the phosphorus-iron ratio was 1.16. The mixed solution was heated to 60°C. o C. Add ammonia to adjust the pH to 3.3, forming a grayish-white solution;

[0096] The above slurry was oxidized by adding hydrogen peroxide containing 0.21 mol of hydrogen peroxide, followed by filtration and washing until the conductivity of the wash water was no greater than 20000 μS / cm, thus obtaining iron phosphate yellow. X-ray diffraction analysis of the obtained amorphous iron phosphate yellow showed a peak intensity ratio of 0.876 for the characteristic peaks at approximately 19°–21° and 28°–30°, and the 95% particle size of the obtained amorphous iron phosphate yellow was 31.5 ± 5.6 nm.

[0097] The ferric phosphate slurry and phosphoric acid were mixed and reacted at 95°C for 3 hours. The molar ratio of phosphoric acid to ferric phosphate was 0.15. The mixture was filtered and washed with pure water until the conductivity of the wash water was no more than 1000 μS / cm.

[0098] The filtered and washed product was dried and then heated at 550°C. o Anhydrous ferric phosphate was obtained by sintering at C for 2 hours. The primary particle size of the obtained anhydrous ferric phosphate was 95.4 ± 12.5 nm, and the specific surface area was measured to be 10.7 m². 2 / g, tap density is 0.78g / cm³ 3 The particles showed minimal agglomeration. The secondary particle size of the obtained anhydrous ferric phosphate is shown in Table 2.

[0099] The ratio of the peak intensity I1 of the characteristic peak at 19°~21° to the peak intensity I2 of the characteristic peak at 28°~30°, the particle size of the primary particles of amorphous iron phosphate, the particle size of the primary particles of anhydrous iron phosphate, and the specific surface area of ​​anhydrous iron phosphate are shown in Table 1.

[0100] Comparative Example 1

[0101] The raw materials and amounts used in this comparative example are exactly the same as those in Example 1, the only difference being the preparation method. The preparation method specifically includes:

[0102] A solution containing 0.345 mol ammonium dihydrogen phosphate, hydrogen peroxide containing 0.21 mol hydrogen peroxide, and ammonia were added concurrently to an acidic aqueous solution containing 0.3 mol ferrous sulfate, with a phosphorus-to-iron ratio of 1.15. The pH of the reaction system was controlled at 2.2, and the reaction temperature was 50℃. A yellow precipitate was obtained, filtered, and washed until the conductivity of the wash water was no greater than 20000 μS / cm, yielding ferric phosphate yellow. X-ray diffraction analysis of the obtained ferric phosphate yellow was performed, and the results are shown in Figure 1. Figure 1 shows that the peak intensity ratio of the characteristic peaks at 19°~21° and 28°~30° is 0.917. The SEM image and particle distribution diagram of the obtained amorphous ferric phosphate yellow are shown in Figure 5. The figures show a good particle distribution; the 95% primary particle size of the obtained amorphous ferric phosphate is 133.98±27.8 nm, with a wide particle distribution and some agglomeration.

[0103] The ferric phosphate slurry and phosphoric acid were mixed and reacted at 95°C for 3 hours. The molar ratio of phosphoric acid to ferric phosphate was 0.03. The mixture was filtered and washed with pure water until the conductivity of the wash water was no more than 1000 μS / cm.

[0104] The filtered and washed product was dried and then sintered at 550℃ for 2 hours to obtain anhydrous ferric phosphate. The SEM image and particle size distribution diagram of the anhydrous ferric phosphate are shown in Figure 6. The figure shows that 95% of the primary particles of the obtained anhydrous ferric phosphate have a particle size of 84.3 ± 19.9 nm, and the specific surface area is measured to be 8.2 m². 2 / g, tap density is 0.95g / cm³ 3 Slight aggregation was observed. The X-ray diffraction pattern of the obtained anhydrous ferric phosphate is shown in Figure 7, and the secondary particle size is shown in Table 2.

[0105] In this comparative example, both the obtained ferric phosphate yellow material and anhydrous ferric phosphate exhibited slight agglomeration. Analysis suggests that the slight agglomeration may be due to the following: when ferrous phosphate, phosphorus, ammonia, and hydrogen peroxide are mixed, the formation of ferrous hydrogen phosphate and the oxidation of ferrous phosphate occur simultaneously, creating a competitive relationship. This can alleviate the formation of ferric hydroxide crystal nuclei and the growth of large yellow material particles to some extent. However, due to the oxidation of some ferrous ions to ferric ions, a certain amount of ferric hydroxide is generated. Phosphoric acid and ferric ions grow rapidly on the surface of ferric hydroxide, agglomerating in a small area to form ferric phosphate particles, thus resulting in slight agglomeration. During subsequent crystallization, the inorganic acid can diffuse into the interior of the yellow material to remove impurities such as ferric hydroxide. The morphology of the slightly agglomerated yellow material particles does not change significantly after crystallization, thus the anhydrous ferric phosphate also exhibits slight agglomeration.

[0106] Comparative Example 2

[0107] The raw materials and amounts used in this comparative example are exactly the same as those in Example 1, the only difference being the preparation method. The preparation method specifically includes:

[0108] Ferrous sulfate solution is obtained by adding hydrogen peroxide containing 0.21 mol hydrogen peroxide to an acidic aqueous solution containing 0.3 mol ferrous sulfate.

[0109] Ferric sulfate solution and an aqueous solution containing 0.345 mol ammonium dihydrogen phosphate were mixed, with an iron-to-phosphorus ratio of 1.15. No precipitate formed. Then, ammonia water was added dropwise to adjust the pH to 2.1. The reaction was carried out at 50℃. After filtration and washing, the conductivity of the wash water was no greater than 20000 μS / cm, yielding ferric phosphate yellow. The obtained ferric phosphate yellow was subjected to X-ray diffraction analysis, and the results are shown in Figure 1. As can be seen from Figure 1, the peak intensity ratio of the characteristic peaks at 19°~21° and 28~30° is 0.951. The SEM image and particle distribution map of the obtained amorphous ferric phosphate yellow are shown in Figure 8. As can be seen from the figure, the particles are severely agglomerated, and the primary particle size of 95% of the obtained amorphous ferric phosphate is greater than 165.8±51.2 nm.

[0110] The ferric phosphate slurry and phosphoric acid were mixed and reacted at 95°C for 3 hours. The molar ratio of phosphoric acid to ferric phosphate was 0.03. The mixture was filtered and washed with pure water until the conductivity of the wash water was no more than 1000 μS / cm.

[0111] The filtered and washed product was dried and then sintered at 550℃ for 2 hours to obtain the ferric phosphate. The SEM image and particle size distribution of the ferric phosphate are shown in Figure 9. As can be seen from Figure 9, the 95% primary particle size of the obtained anhydrous ferric phosphate is 166.3 ± 62.1 nm (Figure 9), and the specific surface area is measured to be 5.3 m². 2 / g, tap density is 0.98g / cm³ 3 The particles showed severe aggregation. The X-ray diffraction pattern of the obtained anhydrous ferric phosphate is shown in Figure 10, and the secondary particle size is shown in Table 2.

[0112] In this comparative example, both the obtained ferric phosphate yellow and anhydrous ferric phosphate exhibited severe agglomeration. Analysis suggests this may be because during the ammonia addition process, ferric iron precipitates to form ferric hydroxide, and ferric iron reacts with the phosphorus source to form ferric phosphate. However, due to the rapid nucleation rate of ferric hydroxide crystals, phosphate and iron ions grow rapidly on their surface, agglomerating in small areas to form ferric phosphate particles. The resulting ferric phosphate yellow has a large particle size and uneven particle distribution. During subsequent crystallization, inorganic acids can diffuse into the interior of the yellow to remove impurities such as ferric hydroxide. Therefore, the morphology of the severely agglomerated yellow does not change significantly after crystallization, resulting in severe agglomeration of the obtained anhydrous ferric phosphate.

[0113] Comparative Example 3

[0114] The only difference between this comparative example and Example 1 is the preparation method, which specifically includes:

[0115] An aqueous solution containing 0.305 mol ammonium dihydrogen phosphate was added to an aqueous solution containing 0.3 mol ferrous sulfate. Sulfuric acid was added to adjust the pH of the mixed solution to 1.4, and the phosphorus-iron ratio was 1.02, resulting in a mixed solution with an iron mass fraction of 6.0% and a phosphorus mass fraction of 3.5%. Ammonia was added to adjust the pH to 2.20, forming a slurry.

[0116] Hydrogen peroxide and ammonia were gradually added to the above slurry, with the total addition time controlled at 30 min. After the addition was completed, stirring was continued for 1 h to ensure full reaction. The pH value of the slurry during and after the reaction was controlled at 2.15. The ratio of the amount of hydrogen peroxide in the added hydrogen peroxide to the amount of iron in the slurry was 0.65:1. Then, the mixture was filtered and washed until the conductivity of the wash water was no greater than 20000 μS / cm, yielding ferric phosphate yellow. The filtered and washed product was dried and sintered at 550℃ for 2 h to obtain the ferric phosphate. The SEM image and particle distribution diagram of ferric phosphate are shown in Figure 11. As can be seen from Figure 11, the 95% primary particle size of the obtained anhydrous ferric phosphate was 176.05±49.1 nm (Figure 11), and the specific surface area was measured to be 4.9 m². 2 / g, tap density is 0.89 g / cm³ 3 The particles showed severe aggregation. The X-ray diffraction pattern of the obtained anhydrous ferric phosphate is shown in Figure 11, and the secondary particle sizes are shown in Table 2.

[0117] In this comparative example, both the obtained ferric phosphate yellow and anhydrous ferric phosphate exhibited severe agglomeration. Analysis suggests the following reason for this severe agglomeration: the slurry obtained in the first synthesis step is a dispersion formed by ferrous sulfate solution and ferrous phosphate precipitate (e.g., ferrous dihydrogen phosphate). When hydrogen peroxide and ammonia are gradually added to the slurry, due to the relatively slow oxidation rate of the solid, hydrogen peroxide preferentially oxidizes the ferrous ions in the solution to ferric ions. These ferric ions then readily react with ammonia to form ferric hydroxide precipitate. Subsequently, ferric sulfate and ammonium dihydrogen phosphate react to form agglomerated particles around the ferric hydroxide crystal nuclei. During subsequent crystallization, inorganic acids can diffuse into the yellow material to remove impurities such as ferric hydroxide, but the morphology of the severely agglomerated yellow material particles does not change significantly after crystallization. Therefore, the anhydrous ferric phosphate also exhibits severe agglomeration.

[0118] As can be seen from Table 1, compared with the amorphous iron phosphate prepared in each comparative example, the ratio of the characteristic peak intensity I1 at 19°~21° and the characteristic peak intensity I2 at 28°~30° in the X-ray diffraction patterns of the amorphous iron phosphate prepared in each example is lower (i.e., the iron hydroxide content is lower), and the primary particle size of the amorphous iron phosphate in each example is smaller and the particle size distribution is more uniform.

[0119] As can be seen from Table 1, compared with the anhydrous ferric phosphate prepared in each comparative example, the anhydrous ferric phosphate prepared in each example has a relatively higher specific surface area, a relatively narrower primary particle size distribution, a more uniform particle size distribution, and a smaller primary particle size; it can be seen that anhydrous ferric phosphate inherits the characteristics of the primary particles of amorphous ferric phosphate.

[0120]

[0121] As can be seen from Table 2, compared with the anhydrous ferric phosphate prepared in each comparative example, the secondary particle size of the anhydrous ferric phosphate prepared in each example is smaller, indicating that the anhydrous ferric phosphate agglomerates obtained in each example are relatively small.

[0122]

[0123] The above description is only a preferred embodiment of this disclosure. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principles of this disclosure, and these improvements and modifications should also be considered within the scope of protection of this disclosure.

Claims

1. An amorphous iron phosphate, wherein the X-ray diffraction pattern of the amorphous iron phosphate has a first diffraction peak θ1 and a second diffraction peak θ2 at 19°~21° and 28°~30° respectively, and the ratio of the peak intensity I1 of the first diffraction peak to the peak intensity I2 of the second diffraction peak is 0.8~0.

91.

2. The amorphous iron phosphate according to claim 1, wherein, The amorphous iron phosphate is in the form of spherical or near-spherical particles.

3. The amorphous iron phosphate according to claim 1 or 2, wherein, 95% of the primary particles of the amorphous iron phosphate have a particle size of less than 80 nm.

4. A method for preparing amorphous iron phosphate, comprising: Solution A was prepared using a phosphorus source and a ferrous source. The pH and temperature of solution A were adjusted, and the reaction was carried out to obtain a grayish-white slurry. The grayish-white slurry was oxidized to obtain a yellow amorphous ferric phosphate slurry. After solid-liquid separation and washing, amorphous ferric phosphate was obtained. The X-ray diffraction pattern of the amorphous iron phosphate has a first diffraction peak θ1 and a second diffraction peak θ2 at 19°~21° and 28°~30°, respectively, and the ratio of the peak intensity I1 of the first diffraction peak to the peak intensity I2 of the second diffraction peak is 0.8~0.

91.

5. The method for preparing amorphous iron phosphate according to claim 4, wherein, Adjust the pH of solution A to 1.5-3.5; and / or, The reagents for adjusting the pH of solution A include one or more of ammonia, urea, and sodium hydroxide; and / or, Adjust the temperature of solution A to 40℃~60℃.

6. The method for preparing amorphous iron phosphate according to any one of claims 4-5, wherein, The phosphorus source includes one or more of ammonium dihydrogen phosphate, phosphoric acid, diammonium hydrogen phosphate, and ammonium phosphate; and / or, The ferrous source includes one or more of ferrous sulfate, ferrous chloride, ferrous nitrate, iron powder, ferrous oxide, and ferrous oxalate; and / or, The molar ratio of the phosphorus source, calculated as phosphate, to the ferrous source, calculated as iron, is 0.95 to 1.2:

1.

7. The method for preparing amorphous iron phosphate according to any one of claims 4-6, wherein, The oxidant used in the oxidation process includes one or more of hydrogen peroxide, air, oxygen, and ozone; and / or, The amount of oxidant used is 1.2 to 1.4 times the theoretically required amount.

8. The method for preparing amorphous iron phosphate according to any one of claims 4-7, wherein, At least one of the following conditions must be met: In solution A, the mass percentage of phosphorus is 2% to 5%. In solution A, the mass percentage of iron is 3% to 7%. The raw materials for preparing solution A also include acidic or alkaline solutions; The acidic solution includes one or more of sulfuric acid and hydrochloric acid, and the alkaline solution includes one or more of ammonia water, urea solution, and sodium hydroxide solution. Before adjusting the pH of solution A to 1.5-3.5, first add the acidic solution to solution A to adjust the initial pH to 0.5 < pH < 1.

2.

9. The method for preparing amorphous iron phosphate according to any one of claims 4-8, wherein, The washing process uses pure water.

10. The method for preparing amorphous iron phosphate according to any one of claims 4-9, wherein, The conductivity of the wash water at the washing endpoint is no greater than 20000 μS / cm.

11. An anhydrous ferric phosphate, wherein the raw material for synthesis is the amorphous ferric phosphate as described in any one of claims 1-3 or the amorphous ferric phosphate prepared by the preparation method described in any one of claims 4-10.

12. The anhydrous ferric phosphate according to claim 11, wherein, At least one of the following conditions must be met: 95% of the primary particles of the anhydrous ferric phosphate have a particle size of less than 90 nm; The specific surface area of ​​95% primary particles of the anhydrous ferric phosphate is 9 g / cm³. 3 ~ 14m 2 / g; The tap density of 95% primary particles of the anhydrous ferric phosphate is 0.7 g / cm³. 3 ~ 1.0 g / cm 3 .

13. A method for preparing anhydrous ferric phosphate, comprising: The amorphous ferric phosphate prepared by any one of claims 1-3 or any one of claims 4-10 is mixed with a phosphoric acid solution, heated to crystallize, filtered, washed with water, and calcined to obtain anhydrous ferric phosphate.

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