Material comprising iron phosphate

Abstract

The present application discloses a process for preparing a material comprising iron phosphate, comprising reacting an iron source lepidocrocite (gamma-FeOOH) with a phosphorus source, thereby forming a material comprising iron phosphate.

Description

Background Technology

[0001] Demand for iron phosphate materials is expected to increase in the future due to global population growth and growing pressures on sustainable agriculture, steel production, and energy storage. Therefore, governments are encouraging the localization of manufacturing of critical commodity materials essential to infrastructure and the economy to reduce reliance on foreign resources.

[0002] Iron phosphate materials play a crucial role in food additives, biopesticides, steel surface coatings, and adsorbent materials. Due to the widespread use of cobalt and nickel in battery cathode materials, the recent expansion of the electric vehicle (EV) manufacturing industry is expected to lead to future shortages of these elements. Therefore, abundant alternative cathode chemistry systems on Earth, such as lithium iron phosphate (also known as LFP, lithium iron phosphate, or LiFePO4), are now being selected as suitable substitutes. LFP has an olivine-type crystal structure.

[0003] This shift towards energy storage requires not only the production of larger quantities of materials, but also higher purity and homogeneity. To achieve these goals, higher quality and more refined raw materials must be obtained. In the case of lithium iron phosphate cathode materials, iron is the largest source of impurities, as it typically originates from waste streams and / or recycled sources.

[0004] The purity of raw materials is crucial because it affects battery manufacturing processes, performance, and cycle life. For example, ferric sulfate is commonly used as a raw material in the production of lithium iron phosphate. However, when this material is calcined at high temperatures, sulfates cause environmental problems. Other impurities, such as sodium or potassium, compete with lithium, while other metals create potential inhomogeneities on the electrode surface, leading to dendrite formation and premature battery failure.

[0005] One way to remove impurities is to introduce an intermediate process that transforms (recrystallizes) the starting material into a compound that can be separated, filtered, and washed. Iron (II) or iron (III) salts can be used in the following general formulas: Where n = 2 or 3 and m = 1 or 2 and A is SO4, NO3 or Cl.

[0006] Then, iron salts typically react with alkaline substances in a two-step reaction to form iron oxide.

[0007] Step 1:

[0008] Step 2:

[0009] Where n=2 or 3; m=1 or 2; x=0–∞; when b=0, a=0 or 1; when a=0, b=0–2.

[0010] North American lithium iron phosphate suppliers have begun to favor using iron oxide as the iron source because it is one of the cheapest production intermediates and one of the easiest to convert.

[0011] US Patent No. 8,673,497 mentions the use of various iron sources for the preparation of lithium iron phosphate, including iron oxide, iron hydroxide, and iron hydroxide α-FeOOH (goethite), β-FeOOH (hematite), and γ-FeOOH (ferrihydrite). α-FeOOH is the most preferred iron source. The reaction time is long: at least 16 hours when using α-FeOOH and 60 hours when using γ-FeOOH.

[0012] Lin et al. , CrystEngComm In 2016, 18, 3174, Lin discussed the synthesis of iron phosphate via phosphorylation using β-FeOOH nanorods. Lin emphasized the importance of β-FeOOH nanorods for controlling the synthesis of FePO4·2H2O with different phases and morphologies.

[0013] There was no prior indication that γ-FeOOH exhibited significantly superior reaction kinetics compared to other forms of iron sources, such as α-FeOOH and β-FeOOH, during the conversion to iron phosphate.

[0014] This application addresses the need for iron phosphate materials with improved reaction kinetics and faster production times.

[0015] Any reference or designation to any document in this application is not an admission that it represents prior art of the present invention. Summary of the Invention

[0016] This application discloses a high-speed method for preparing iron-containing materials using ferriferrite (γ-FeOOH), which exhibits a significant improvement in reaction kinetics (reaction rate) compared to other forms of iron oxide during the conversion to iron-containing materials.

[0017] Specifically, in a first aspect, the present invention provides a method for forming a material containing iron phosphate, comprising reacting an iron source, ferrihydrite (γ-FeOOH), with a phosphorus source to form a material containing iron phosphate; wherein the material containing iron phosphate is not lithium iron phosphate or a material having an olivine-type crystal structure.

[0018] In a second aspect, the present invention provides a method for forming a material comprising iron phosphate, comprising the following steps: (a) React the iron source ferrihydrite (γ-FeOOH) with another iron source to form Fe3O4; (b) React the obtained Fe3O4 with a phosphorus source to form a material containing iron phosphate; The material containing iron phosphate is not lithium iron phosphate or a material with an olivine-type crystal structure.

[0019] As previously mentioned, the preparation of materials containing iron phosphate using various iron sources, such as α-FeOOH and β-FeOOH, is known. Surprisingly, γ-FeOOH reacts more rapidly, giving it an advantage over other forms of iron oxide or ferric hydroxide. While not wishing to be bound by theory, the applicant believes the higher reactivity of γ-FeOOH may be due to its tendency to adopt smaller particle sizes with more reactive sites. Interestingly, it was also found that the reaction rate to materials containing iron phosphate remains rapid when γ-FeOOH is converted to Fe3O4 (black iron oxide). Attached Figure Description

[0020] Figure 1A This is a scanning electron microscope (SEM) image of the sample prepared in Example 25.

[0021] Figure 1B This is an SEM image of the sample prepared in Example 26 and calcined at 650°C.

[0022] Figure 2A This is the X-ray diffraction (XRD) pattern of the sample prepared in Example 25.

[0023] Figure 2B This is the XRD pattern of the sample prepared in Example 26 and calcined at 650°C. Detailed Implementation

[0024] γ-FeOOH is available from commercial suppliers. γ-FeOOH can also be prepared using a chlorination process. US Patent No. 2939767 mentions a chlorination process for preparing α-FeOOH. Gustavo Navarro et al. (2008 J. Phys.:Conf. Ser. 134 012023) discuss the synthesis of γ-FeOOH from ferrous chloride (FeCl2).

[0025] The phosphorus source can be selected from phosphoric acid (H3PO4), phosphorous acid (H3PO3), (NH4)H2PO4, (NH4)2HPO4, (NH4)3PO4, Li3PO4, Li2HPO4, and LiH2PO4 and mixtures thereof; or selected from H3PO4, H3PO3, (NH4)H2PO4, (NH4)2HPO4, (NH4)3PO4, and mixtures thereof. H3PO4 is preferred as the phosphorus source. For example, the phosphorus source can be 75% or 85% by weight of H3PO4 in water.

[0026] The reaction is typically carried out in an aqueous solution under acidic conditions with a pH < 5. The preferred reaction pH is 0.5-4.0, more preferably 0.5-3.5, and most preferably 1.0-2.5. The preferred reaction temperature is 50℃-100℃, more preferably 60℃-90℃, and most preferably 70℃-90℃. The preferred reaction time is < 7 hours, more preferably 1-6 hours, and most preferably 1-5 hours.

[0027] Because iron exists in its 3+ oxidation state in the γ-FeOOH iron source and the desired iron-containing material product, the advantage of this invention is that iron-containing materials can be easily formed without controlling the atmosphere during the reaction, for example, without needing to conduct the reaction under an inert or reducing atmosphere. Therefore, the reaction is typically carried out under a non-inert atmosphere. A non-inert atmosphere can be defined as an atmosphere in which the oxidation state of iron in the iron source is maintained in the iron-containing material product. For example, a non-inert atmosphere may contain at least 1% by volume oxygen, preferably at least 5% by volume oxygen. Air is a preferred non-inert atmosphere. The reaction to form the iron-containing material can be carried out in the absence of a reducing agent.

[0028] It has been found that the P:Fe molar ratio affects the rate of conversion of γ-FeOOH to materials containing iron phosphate. The reaction can be carried out with a P:Fe molar ratio ≥3:1 or ≥4:1, preferably ≥6:1, or most preferably ≥7:1. The upper limit of the P:Fe ratio can be appropriately selected so as not to waste excess phosphorus source and / or to eliminate the need for recovery and reuse. Optionally, the reaction is carried out with a P:Fe molar ratio ≤100:1 or ≤50:1 or ≤20:1 or ≤12:1. Therefore, the reaction can be carried out with a P:Fe molar ratio of 3:1-100:1 or 4:1-50:1, preferably 6:1-20:1, and most preferably 7:1-12:1.

[0029] The reaction can be carried out at a P:Fe molar ratio ≤4:1, ≤3:1, or ≤1.5:1. At these lower ratios, other reaction parameters can be controlled to convert γ-FeOOH into a material containing iron phosphate within a commercially available timescale. If the reaction is carried out at a P:Fe molar ratio ≤1.5:1, ≤3:1, or ≤4:1, the reaction is preferably carried out at a temperature of at least 80°C, more preferably at least 82°C or at least 85°C, such as at about 90°C. For example, if the reaction is carried out at a P:Fe molar ratio ≤1.5:1, the reaction can be carried out at a temperature of at least 85°C. If the reaction is carried out at a P:Fe molar ratio ≤3:1, the reaction can be carried out at a temperature of at least 82°C. If the reaction is carried out at a P:Fe molar ratio ≤4:1, the reaction can be carried out at a temperature of at least 80°C. At these lower ratios, the reaction time can be increased to achieve the conversion, particularly when the reaction temperature is below 80°C. For example, if the reaction is carried out at a P:Fe molar ratio of ≤1.5:1, ≤3:1, or ≤4:1 and at a temperature below 80°C, the reaction can proceed for at least 6 hours, at least 8 hours, or at least 10 hours.

[0030] The reaction is preferably carried out with a P:Fe molar ratio of at least 1:1, which is the stoichiometric ratio in FePO4, or more preferably at least 1.05:1.

[0031] It has been found that γ-FeOOH can be used to rapidly convert materials containing iron phosphate over a wide range of water contents, defined as the mass of γ-FeOOH in the reaction vessel relative to the volume of water. The reaction is preferably carried out with a mass of γ-FeOOH relative to the volume of water ≤ 45 g dm³. -3 or ≤35 g dm -3 Perform, or optimally ≤25 g dm -3 Optionally, the reaction proceeds with a mass of γ-FeOOH relative to the volume of water ≥ 0.1 g dm³. -3 ≥0.5 g dm -3 or ≥1 g dm -3 conduct.

[0032] The reaction can produce γ-FeOOH with a mass relative to the volume of water ≥ 45 g dm. -3 The reaction can be carried out at these higher ratios of γ-FeOOH to water, allowing other reaction parameters to be controlled, enabling the conversion of γ-FeOOH to materials containing iron phosphate within a commercially available timescale. If the reaction proceeds at a mass ratio of γ-FeOOH to water ≥ 45 g dm³, the reaction can proceed. -3 If the reaction is to be carried out, it is preferably carried out at a temperature of at least 80°C, more preferably at least 82°C or at least 85°C, such as at about 90°C.

[0033] Furthermore, the reaction rate to ferric phosphate materials remains rapid when γ-FeOOH is converted to Fe3O4 (black iron oxide). This further illustrates the importance of selecting γ-FeOOH (e.g., γ-FeOOH produced by a chlorination process) as a highly reactive source of iron oxide to produce materials containing ferric phosphate. The present invention may include a step of producing γ-FeOOH by a chlorination process prior to step (a).

[0034] Other methods exist for producing iron oxide, the most common being the use of ferric sulfate, a byproduct of titanium dioxide refining from titanium ore. The ferric sulfate is then reacted with oxygen and an alkali (such as sodium hydroxide) in a hydrothermal process to bring the pH to approximately 4, during which iron oxide precipitates. Typically, this method produces Fe₂O₃, Fe₃O₄, and α-FeOOH, but not γ-FeOOH. It is known that iron oxide prepared using this method retains sulfur impurities, which is undesirable for the production of battery materials because sulfur is converted into sulfur during calcination. SOx It escapes in the form of (sulfur oxides). x Emissions of sulfur or other volatile sulfur compounds are either pollutants or have extremely low odor thresholds. Sulfur can also cause harmful side reactions during battery operation, ultimately shortening battery life. Iron oxide produced by the chlorination process contains significantly lower residual sulfur content and produces cleaner iron oxide. Furthermore, iron oxide from the chlorination process can form smaller particles of iron phosphate-containing materials, thereby contributing to further improved reactivity and potentially enhancing the processability and performance of battery materials. Therefore, an advantage of this invention is its ability to minimize the content of impurities such as sulfur in iron phosphate-containing materials. In a preferred embodiment, the method of this application produces iron phosphate-containing materials with <1000 ppm sulfur, more preferably <500 ppm sulfur. The concentrations of elements, including sulfur, in the iron phosphate-containing materials can be determined by elemental analysis (e.g., by ICP-OES).

[0035] Materials containing iron phosphate refer to any compound containing at least one iron and at least one phosphate group, and can be formed in solution in the presence of other compounds, ions, dopants, surfactants and / or chelating agents, and can exist as an intermediate generated in situ during the reaction process. If the material containing iron phosphate contains a metal other than iron, the metal may be present in a concentration of less than 10 atomic%, preferably less than 5 atomic%, and most preferably less than 1 atomic%, relative to the iron content in the material containing iron phosphate.

[0036] Materials containing iron phosphate are not lithium iron phosphate or materials with an olivine-type crystal structure. Materials with an olivine-type crystal structure typically have the general formula M. 1 M2 PO4, where M 1 and M 2 This refers to octahedral coordinated cations (e.g., M). 1 =Vacant, Na and / or Li; M 2 =Mn, Fe, Fe, Mn and / or Mg), and P corresponds to tetrahedral coordinated P. 5+ Cations. It is well known that the crystal structure of a material can be determined by X-ray diffraction.

[0037] The iron phosphate-containing material formed by the method can be selected from FePO4, FePO4·2H2O, Fe5(PO4)4(OH)2·2H2O, Fe4(P2O7)3, and Fe3(PO4)2·8H2O; preferably FePO4 and FePO4·2H2O. The material formed by the method may depend on the initial iron species, reaction conditions (such as the use of an oxidizing or reducing environment), and post-processing heat treatment for the synthesis of anhydrous variants. A simplified reaction scheme for the formation of FePO4·2H2O is shown below:

[0038] The resulting material containing iron phosphate can be separated using conventional methods, such as filtration and centrifugation. After separation, the iron phosphate-containing material can be reacted with a lithium source to form lithium iron phosphate.

[0039] Anhydrous iron phosphate-containing materials are commonly used precursors for the preparation of lithium iron phosphate. Therefore, the method may further include the step of calcining the iron phosphate-containing material to form anhydrous iron phosphate-containing material. A preferred anhydrous iron phosphate-containing material is FePO4.

[0040] Preferably, the FePO4 formed by the process adopts a trigonal phase structure, and most preferably an α-quartz structure.

[0041] The iron-containing material formed by the method is not lithium iron phosphate. Therefore, when γ-FeOOH reacts with a phosphorus source, a lithium source is typically absent. However, in a further step, the iron-containing material formed by the method (e.g., after separation and / or calcination) can react with a lithium source to form lithium iron phosphate. The lithium source can be selected from lithium carbonate (Li₂CO₃), lithium hydroxide (LiOH), lithium oxide (Li₂O), lithium sulfate (Li₂SO₄), lithium chloride (LiCl), their hydrates, and mixtures thereof; preferably lithium carbonate (Li₂CO₃), lithium hydroxide (LiOH), their hydrates, and mixtures thereof; most preferably Li₂CO₃.

[0042] There are several methods for reacting a lithium source with a material containing iron phosphate to form lithium iron phosphate. Some variations use a "one-pot" method, where the lithium source, the iron phosphate-containing material, and a reducing agent such as carbon are added together to a mixing vessel. The resulting slurry is then wet-milled, spray-dried, and calcined in an inert atmosphere at a temperature ranging from 300 to 1000°C (typically around 650°C). During calcination, the inert atmosphere means that no oxygen reacts with the carbon source. Instead, the carbon source reacts with the oxygen present in the raw materials to generate CO2 and reduce the iron. Fe ions bound to phosphate groups... 3+ The ions are reduced to Fe 2+ This allows positively charged lithium ions to combine with now negatively charged phosphate ions to form lithium iron phosphate.

[0043] Lithium iron phosphate can then be incorporated into products such as electrodes or battery cells.

[0044] Because ferric phosphate is highly insoluble, the reaction can proceed in the presence of other compounds, ions, dopants, surfactants and / or chelating agents, and ferric phosphate can be formed in solution together with such other compounds, ions, dopants, surfactants and / or chelating agents, and can exist as an intermediate generated in situ during coprecipitation.

[0045] Preferably, the material containing iron phosphate has a D50 ≤ 20 µm or ≤ 15 µm or ≤ 12 µm or ≤ 8 µm or ≤ 6 µm or ≤ 4 µm or ≤ The characteristic particle size distribution is 3 µm.

[0046] Preferably, γ-FeOOH has a D50 ≤ 50 µm or ≤ 30 µm, more preferably ≤ 20 µm or ≤ The characteristic particle size distribution is 15 µm.

[0047] Unless otherwise stated, the term "Dn" refers to the diameter of a particle population that is less than n% by volume; for example, the term "D50" refers to the median particle diameter based on volume, which is less than 50% by volume of the particle population. Dn values ​​are preferably determined by laser diffraction. For example, Dn values ​​can be determined according to ISO 13320:2009 using the Mie theory.

[0048] After the reaction, an advantageous characteristic of iron phosphate is its uniform particle size. Therefore, preferably, the material containing iron phosphate has a particle size spanning D10, D50, and D90.≤ 6 or ≤ 5 or ≤ 4 or ≤ 3 or ≤ 2 or ≤ 1.5 or ≤ 1 is the characteristic particle size distribution.

[0049] The particle size distribution span is calculated using the following formula:

[0050] The particle size distribution of γ-FeOOH can also be determined by sedimentation methods, for example using a disc centrifugal particle size analyzer. γ-FeOOH can exhibit particle size distributions determined by sedimentation methods with a density of D... w A particle size distribution characterized by 50 ≤ 5 µm, ≤ 1 µm, or ≤ 500 nm, where D w 50 means that 50% of the particle population by weight is smaller than its diameter.

[0051] The first aspect can be defined as a method for forming a material containing iron phosphate, which includes reacting an iron source, ferrihydrite (γ-FeOOH), with a phosphorus source to form a material containing iron phosphate, wherein: If the reaction is carried out with a P:Fe molar ratio of ≤3:1 or ≤4:1, the reaction is carried out at a temperature of at least 80°C, more preferably at least 82°C or at least 85°C, such as at about 90°C. If the reaction proceeds with a mass of γ-FeOOH relative to the volume of water ≥ 45 g dm -3 If the reaction is carried out, the reaction is carried out at a temperature of at least 80°C, more preferably at least 82°C or at least 85°C, such as at about 90°C.

[0052] In one variant of the first aspect: If the reaction is carried out with a P:Fe molar ratio ≤ 1.5:1, the reaction shall be carried out at a temperature of at least 85°C. If the reaction is carried out with a P:Fe molar ratio of 1.5:1 to 3:1, the reaction shall be carried out at a temperature of at least 82°C. If the reaction is carried out with a P:Fe molar ratio of 3:1 to 4:1, the reaction shall be carried out at a temperature of at least 80°C. If the reaction is carried out with a P:Fe molar ratio ≥ 4:1, the reaction shall be carried out at a temperature of at least 50°C. If the reaction proceeds with a mass of γ-FeOOH relative to the volume of water ≥ 45 g dm -3 If the reaction is carried out, the reaction is carried out at a temperature of at least 80°C, more preferably at least 82°C or at least 85°C, such as at about 90°C.

[0053] In one variant of the first aspect: If the reaction is carried out with a P:Fe molar ratio of ≤3:1 or ≤4:1, the reaction is carried out at a temperature of at least 80°C, more preferably at least 82°C or at least 85°C, such as at about 90°C. If the reaction proceeds with a mass of γ-FeOOH relative to the volume of water ≥ 45 g dm -3 If the reaction is to be carried out, the reaction is carried out at a temperature of at least 80°C, more preferably at least 82°C or at least 85°C, such as at about 90°C; The reaction is carried out at a pH of 0.5-4.0, more preferably 0.5-3.5, and most preferably 1.0-2.5. Furthermore, the iron phosphate-containing material formed by the method is selected from FePO4 and FePO4·2H2O.

[0054] In one variant of the first aspect: γ-FeOOH has a D50 value determined by laser diffraction. ≤ 30 µm, more preferably ≤ 20 µm or ≤ The characteristic particle size distribution is 15 µm; The reaction is carried out at a temperature of 50℃-100℃, more preferably 60℃-90℃, and most preferably 70℃-90℃. The reaction takes less than 7 hours, more preferably 1–6 hours, more preferably 1–5 hours, more preferably 2–4 hours, and most preferably 2.5–3 hours. If the reaction is carried out with a P:Fe molar ratio ≤ 4:1, the reaction is carried out at a temperature of at least 80°C, more preferably at least 82°C or at least 85°C, such as at about 90°C. If the reaction proceeds with a mass of γ-FeOOH relative to the volume of water ≥ 45 g dm -3 If the reaction is to be carried out, the reaction is carried out at a temperature of at least 80°C, more preferably at least 82°C or at least 85°C, such as at about 90°C; The reaction is carried out at a pH of 0.5-4.0, more preferably 0.5-3.5, and most preferably 1.0-2.5. Furthermore, the iron phosphate-containing material formed by the method is selected from FePO4 and FePO4·2H2O.

[0055] In a second aspect, γ-FeOOH first reacts to generate Fe3O4, which is then converted into iron phosphate. Therefore, the present invention provides a method for forming a material comprising iron phosphate, comprising the following steps: (a) React the iron source ferrihydrite (γ-FeOOH) with another iron source to form Fe3O4; (b) React the obtained Fe3O4 with a phosphorus source to form a material containing iron phosphate; The material containing iron phosphate is not lithium iron phosphate or a material with an olivine-type crystal structure.

[0056] It should be understood that the second aspect, including γ-FeOOH, the phosphorus source, the reaction for forming a material containing iron phosphate, and the resulting material containing iron phosphate, can be described in the same manner as the first aspect.

[0057] The simplified reaction scheme based on the second aspect is as follows:

[0058]

[0059] Another preferred iron source in step (a) is a ferrous source, i.e., one containing Fe. 2+ For example, a ferrous solution is added stoichiometrically to γ-FeOOH to achieve the correct Fe:O ratio for Fe3O4. A base is then added (usually under reducing conditions) to drive the reaction but prevent oxidation.

[0060] Step (b) of the second aspect can be implemented using a procedure equivalent to that in the first aspect, which reacts γ-FeOOH with a phosphorus source, but instead of γ-FeOOH, Fe3O4 is used.

[0061] The invention is further illustrated below by groups and combinations of embodiments resulting from the shown dependencies and reverse references. It should be particularly noted that when referring to a series of embodiments, such as in the context of terms like "the method as described in any one of embodiments 1 to 5," each embodiment within this scope is intended to clearly disclose to those skilled in the art that the wording of this term should be understood as synonymous with "the method as described in any one of embodiments 1, 2, 3, 4, and 5." Furthermore, it should be clearly noted that the following group of embodiments is not a group of claims defining the scope of protection, but rather represents a suitable structured portion of the specification relating to both general and specific aspects of the invention.

[0062] 1. A method for forming a material comprising iron phosphate, comprising the following steps: a. Reaction of the iron oxide source ferrihydrite (γ-FeOOH) with a phosphorus source; and b. Separate the obtained material containing iron phosphate.

[0063] 2. As described in paragraph 1, wherein the phosphorus source is phosphoric acid (H3PO4).

[0064] 3. The method as described in paragraph 1 or 2, wherein the iron phosphate material contains a sulfur content of <1000 ppm, more preferably <500 ppm.

[0065] 4. The method as described in any of the preceding paragraphs, wherein an additional step of converting γ-FeOOH to Fe3O4 is added between step a and step b.

[0066] 5. The method described in any of the preceding paragraphs further includes ferrihydrite derivatives.

[0067] 6. The method as described in any of the preceding paragraphs, wherein the iron phosphate has a D50 ≤ 15 micrometers or ≤ 12 or ≤ The particle size distribution is characterized by 10 or ≤6 or ≤4 or ≤3.

[0068] 7. The method as described in any of the preceding paragraphs, wherein the iron phosphate has a particle size distribution span of ≤6 or ≤5 or ≤4 or ≤3 or ≤2 or ≤1.5 or ≤1.

[0069] 8. The method as described in any of the preceding paragraphs further includes additional reactants and / or additives selected from the group consisting of an ion source, a dopant, a surfactant, and a chelating agent.

[0070] 9. The method described in any of the preceding paragraphs further includes introducing an ion source or a dopant.

[0071] 10. The method as described in any of the preceding paragraphs, wherein the phosphorus source comprises phosphoric acid.

[0072] 11. The method as described in any of the preceding paragraphs, wherein the reaction is carried out at an acidic pH, preferably 0.5-4.0, more preferably 0.5-3.5.

[0073] 12. The method as described in any of the preceding paragraphs, wherein the reaction is carried out at a temperature of 50°C-100°C, more preferably 60°C-90°C, and most preferably 70°C-90°C.

[0074] 13. The method as described in any of the preceding paragraphs, wherein the reaction takes place for <7 hours, more preferably 1-6 hours, more preferably 1-5 hours, more preferably 2-4 hours, and most preferably 2.5-3 hours.

[0075] 14. An article comprising ferric phosphate produced by any one or more of the methods described in paragraphs 1-13.

[0076] 15. The article described in paragraph 14 is a battery cell.

[0077] The present invention, including its various embodiments, has been described in detail. However, it should be understood that those skilled in the art, upon considering this disclosure, can make modifications and / or improvements to the invention that fall within the scope and spirit of the invention.

[0078] Example The invention is further described by way of the following non-limiting embodiments, which further illustrate the invention and are not intended to, nor should be construed as, limiting the scope of the invention.

[0079] The γ-FeOOH, α-FeOOH (Y5102, equivalent to ZMAG-5102), and Fe3O4 used in the following examples were provided by Sun Cosmetics, LLC, a subsidiary of Sun Chemical in Valparaiso, Indiana, USA. β-FeOOH was synthesized as described in Example 17A. Particle size distribution was determined using a Malvern 3000 particle size analyzer by laser diffraction. γ-FeOOH had D10 = 0.5 μm, D50 = 9.6 μm, and D90 = 38.4 μm. α-FeOOH had D10 = 0.33 μm, D50 = 0.61 μm, and D90 = 2.66 μm. β-FeOOH had D10 = 0.3 μm, D50 = 2.6 μm, and D90 = 33.4 μm.

[0080] The particle size distribution of these materials was also determined using a disc centrifuge. Particle sizes were measured at 24,000 RPM in a deionized water / sucrose gradient on a disc centrifuge. The weight-based particle size distribution results were taken from 0.2–10 micrometers. The fibrous ore used has a D... w 10 = 86nm, D w 50 = 163nm, D w The particle size distribution is 90=249, and the iron content is 61-62%.

[0081] It is converted into ferric phosphate, indicated by its color changing to a white powder.

[0082] Note: In all the following examples, FeOOH was sieved through a 10-mesh sieve (2000 μm screen) before the reaction to remove any abnormally large lumps of material.

[0083] For Examples 1-19, 25 and 28-33, the particle size distribution was determined by laser diffraction using a Malvern 3000 particle size analyzer.

[0084] Table 1 below records the characteristics of each embodiment after the reaction.

[0085] Example 1A (Comparative Example) and Example 1B (Inventive Example). FeOOH is converted into iron phosphate. The reaction rates between α-FeOOH and γ-FeOOH were compared using the following procedure: One gram of α-FeOOH (Comparative Example 1A) or γ-FeOOH (Inventive Example 1B) was added to a 1L Morton flask containing 200mL of 5% H3PO4 (P:Fe ratio 8.9:1), and stirred at 300rpm with a magnetic stir bar at 80°C for 3 hours. The precipitate was vacuum filtered, washed with 4 × 10mL of deionized water, and dried at 100°C for 2 hours. After 3 hours, no color change occurred in the conversion of Example 1A, indicating that almost no reaction occurred. In contrast, the conversion of Example 1B was marked by a rapid change in color from yellow-orange to a very pale grayish-white, indicating its conversion to ferric phosphate. Therefore, the reaction rate resulting from the use of γ-FeOOH was higher than that from α-FeOOH, even though the particle size of γ-FeOOH used in these examples was larger than that of α-FeOOH.

[0086] The material produced by Example 1B has a particle size distribution of D10=2.46 μm, D50=11.51 μm, and D90=21.23 μm, with a span of 1.63.

[0087] Example 2 – Conversion of γ-FeOOH to ferric phosphate The conversion of γ-FeOOH was carried out at 70°C using the procedure in Examples 1A / 1B. The result was a very light grayish-white color, indicating conversion to iron phosphate. The material had a particle size distribution of D10 = 2.167 μm, D50 = 8.47 μm, and D90 = 13.82 μm, with a span of 1.38. Example 2 was intended to demonstrate that the conversion could be carried out at a lower temperature (70°C).

[0088] Example 3 – Conversion of γ-FeOOH to ferric phosphate The conversion of γ-FeOOH was carried out at 90°C using the procedure in Examples 1A / 1B. The result was a very light grayish-white color, indicating conversion to iron phosphate. The material had a particle size distribution of D10 = 5.99 μm, D50 = 12.43 μm, and D90 = 19.62 μm, spanning 1.10. Example 2 was intended to demonstrate that the conversion could be carried out at a higher temperature (90°C).

[0089] Example 4 – Conversion of γ-FeOOH to ferric phosphate The conversion of γ-FeOOH was carried out at 60°C using the procedure in Examples 1A / 1B. Compared with Examples 1, 2, and 3, the result was a darker grayish-white color, indicating partial conversion to ferric phosphate. The material had a particle size distribution of D10 = 1.42 μm, D50 = 8.33 μm, and D90 = 15.74 μm, with a span of 1.72. The purpose of Example 4 was to demonstrate that further reducing the reaction temperature to 60°C slowed the reaction down, resulting in only partial conversion occurring after 3 hours. 1 .

[0090] 1 Note: Although not the preferred method, partial conversion is still useful because these are also iron phosphate-containing materials and can be combined with other processes to shorten the relative time required to prepare iron phosphate-containing materials. Furthermore, increasing the reaction time is expected to achieve complete conversion.

[0091] Example 5 – Conversion of γ-FeOOH to ferric phosphate The conversion of γ-FeOOH was carried out using the procedure in Examples 1A / 1B at 70°C and with a stirring time of 2 hours. Compared with Examples 1, 2, and 3, the result was a darker grayish-white color, indicating partial conversion to ferric phosphate. The material had a particle size distribution of D10 = 4.12 μm, D50 = 9.68 μm, and D90 = 16.43 μm, with a span of 1.27. The purpose of Example 5 was to demonstrate that reducing the time to 2 hours resulted in a partial conversion reaction. 1 .

[0092] 1 Note: Although not the preferred method, partial conversion is still useful because these are also iron phosphate-containing materials and can be combined with other processes to shorten the relative time required to prepare iron phosphate-containing materials. Furthermore, increasing the reaction time is expected to achieve complete conversion.

[0093] Example 6 – Conversion of γ-FeOOH to ferric phosphate The conversion of γ-FeOOH was carried out using the procedure in Examples 1A / 1B at 70°C and with a stirring time of 4 hours. The result was a very light grayish-white color, indicating conversion to ferric phosphate. The material had a particle size distribution of D10 = 1.73 μm, D50 = 8.53 μm, and D90 = 15.18 μm, with a span of 1.58. Example 6 aimed to demonstrate that increasing the reaction time to 4 hours had little effect on the reaction, implying that the reaction could potentially be completed within 3 hours. However, the increased mixing time did advantageously reduce the particle size.

[0094] Example 7 – Conversion of γ-FeOOH to ferric phosphate Using the procedure in Examples 1A / 1B, the conversion of γ-FeOOH was carried out at 70°C, with a stirring time of 3 hours and a P:Fe ratio of 12:1. The result was a very light grayish-white color, indicating conversion to ferric phosphate. The material had a particle size distribution of D10 = 2.43 μm, D50 = 12.61 μm, and D90 = 22.92 μm, with a span of 1.63. The purpose of Example 7 was to demonstrate that increasing the P:Fe ratio to 12:1 did not affect the reaction, meaning that the reaction remained fully effective at this ratio.

[0095] Example 8 – Conversion of γ-FeOOH to ferric phosphate Using the procedure in Examples 1A / 1B, the conversion of γ-FeOOH was carried out at 70°C, with a stirring time of 3 hours and a P:Fe ratio of 6:1. Compared with Examples 1, 2, and 3, the result was a darker grayish-white color, indicating partial conversion to iron phosphate. The material had a particle size distribution of D10 = 1.28 μm, D50 = 7.65 μm, and D90 = 14.79 μm, with a span of 1.76. The purpose of Example 8 was to demonstrate that reducing the P:Fe ratio to 6:1 resulted in a partial conversion reaction. 1 .

[0096] 1 Note: Although not the preferred method, partial conversion is still useful because these are also iron phosphate-containing materials and can be combined with other processes to shorten the relative time required to prepare iron phosphate-containing materials. Furthermore, increasing the reaction time is expected to achieve complete conversion.

[0097] Example 9 – Conversion of γ-FeOOH to ferric phosphate Using the procedure in Examples 1A / 1B, the conversion of γ-FeOOH was carried out at 80°C, with a stirring time of 3 hours and a P:Fe ratio of 6:1. Compared with Examples 1, 2, and 3, the result was a darker grayish-white color, but lighter than that of Example 8, indicating partial conversion to iron phosphate. The material had a particle size distribution of D10 = 2.95 μm, D50 = 11.66 μm, and D90 = 21.02 μm, with a span of 1.55. The purpose of Example 9 was to demonstrate that increasing the temperature from Example 8 to 80°C produced a partial conversion reaction. 1 Although the slightly darker color indicates that the reaction was faster than in Example 8.

[0098] 1 Note: Although not the preferred method, partial conversion is still useful because these are also iron phosphate-containing materials and can be combined with other processes to shorten the relative time required to prepare iron phosphate-containing materials. Furthermore, increasing the reaction time is expected to achieve complete conversion.

[0099] Example 10 – Conversion of γ-FeOOH to ferric phosphate Using the procedure in Examples 1A / 1B, the conversion of γ-FeOOH was carried out at 70°C, with a stirring time of 4 hours and a P:Fe ratio of 6:1. The result was a very light grayish-white color, indicating conversion to ferric phosphate. The material had a particle size distribution of D10 = 0.89 μm, D50 = 4.59 μm, and D90 = 13.29 μm, with a span of 2.71. The purpose of Example 10 was to demonstrate that increasing the reaction time of Example 8 to 4 hours was sufficient to complete the reaction.

[0100] Example 11 – Conversion of γ-FeOOH to ferric phosphate Using the procedure in Examples 1A / 1B, the conversion of γ-FeOOH was carried out at 70°C, 4 hours of stirring, and a P:Fe ratio of 3:1. The result was a yellow-orange color, indicating a very small amount of conversion to ferric phosphate. The material had a particle size distribution of D10 = 0.90 μm, D50 = 4.86 μm, and D90 = 10.61 μm, spanning 2.00. The purpose of Example 11 was to demonstrate that reducing the P:Fe ratio in Example 10 to 3:1 resulted in very little or no reaction. However, if the reaction in Example 11 allowed for a longer reaction time, it is likely that the conversion would eventually be achieved.

[0101] Example 12 – Conversion of γ-FeOOH to ferric phosphate Using the procedure in Examples 1A / 1B, the conversion of γ-FeOOH was carried out at 70°C, with a stirring time of 5 hours and a P:Fe ratio of 3:1. The result was a yellow-orange color, indicating a very small amount of conversion to ferric phosphate. The material had a particle size distribution of D10 = 0.98 μm, D50 = 5.45 μm, and D90 = 12.07 μm, with a span of 2.04. The purpose of Example 12 was to demonstrate that increasing the reaction time of Example 11 to 5 hours still resulted in very little or no reaction. However, if the reaction in Example 12 allowed for a longer reaction time, it is likely that the conversion would eventually be achieved.

[0102] Example 13 – Conversion of γ-FeOOH to ferric phosphate Using the procedure in Examples 1A / 1B, the conversion of γ-FeOOH was carried out on a double-scale basis (i.e., the amounts of reactants γ-FeOOH and H3PO4 were doubled) at 70°C, with a stirring time of 4 hours and a P:Fe ratio of 6:1. The result was a very light grayish-white color, indicating conversion to ferric phosphate. The material had a particle size distribution of D10 = 1.88 μm, D50 = 7.95 μm, and D90 = 14.78 μm, with a span of 1.62. Doubling the scale of Example 10 resulted in a slight increase in particle size and a decrease in span. The purpose of Example 13 was to demonstrate that the reaction would proceed to completion under scaled-up (double-scale) manufacturing conditions.

[0103] In Examples 14-19, 20, 21, 25, and 27-33, a top-mounted mixer (Heidolph RZR 2021, equipped with a 6cm flat paddle stirrer) was used. The purpose of these examples was to demonstrate that using a top-mounted mixer under scale-up manufacturing conditions will achieve complete conversion. Example 14 – Conversion of γ-FeOOH to ferric phosphate Using the procedure in Examples 1A / 1B, the conversion of γ-FeOOH was carried out at 2x scale, 70°C, 4 hours of stirring time, 300 rpm in a top-mounted mixer, and a P:Fe ratio of 6:1. The result was a very light grayish-white color, indicating conversion to ferric phosphate. The material had a particle size distribution of D10 = 1.02 μm, D50 = 4.48 μm, and D90 = 8.47 μm, spanning 1.67. The purpose of Example 14 was to demonstrate that using a top-mounted mixer instead of the magnetic stirrer in Example 13 resulted in a significant decrease in particle size. Therefore, the reaction is not dependent on any particular mixer or mixing method.

[0104] Example 15 – Conversion of γ-FeOOH to ferric phosphate Using the procedure in Examples 1A / 1B, the conversion of γ-FeOOH was carried out on a double-scale basis at 70°C, 4 hours of stirring time, 500 rpm in a top-mounted mixer, and a P:Fe ratio of 6:1. The result was a very light grayish-white color, indicating conversion to ferric phosphate. The material had a particle size distribution of D10 = 0.89 μm, D50 = 2.43 μm, D90 = 4.57 μm, with a span of 1.52. Increasing the mixing speed from 300 rpm in Example 14 to 500 rpm resulted in a favorable reduction in particle size and span. The purpose of Example 15 was to demonstrate that utilizing a higher mixing speed can be advantageous.

[0105] Example 16 – Conversion of γ-FeOOH to ferric phosphate Using the procedure in Examples 1A / 1B, at twice the scale with a 25% reduction in water, the conversion of γ-FeOOH was carried out at 70°C, 4 hours of stirring time, 500 rpm in a top-mounted mixer, and a P:Fe ratio of 6:1. The result was a very light grayish-white color, indicating conversion to ferric phosphate. The material had a particle size distribution of D10 = 0.91 μm, D50 = 2.62 μm, D90 = 5.00 μm, spanning 1.56. Reducing the water volume by 25% compared to Example 15 resulted in a slightly larger particle size. The purpose of Example 16 was to demonstrate that the reaction can be carried out with a 25% reduction in water.

[0106] Example 17 – Conversion of γ-FeOOH to ferric phosphate Using the procedure in Examples 1A / 1B, at a 3x scale with 50% less water, the conversion of γ-FeOOH was carried out in an overhead mixer at 70°C, 4 hours of stirring time, a P:Fe ratio of 6:1, and 500 rpm. The result was a very light grayish-white color, indicating conversion to ferric phosphate. The material had a particle size distribution of D10 = 1.17 μm, D50 = 3.67 μm, and D90 = 6.78 μm, with a span of 1.53. The purpose of Example 17 was to demonstrate that the reaction could be carried out with 50% less water and a 3x scale-up.

[0107] Example 17A - Conversion of β-FeOOH to ferric phosphate (Comparative Example) β-FeOOH was synthesized in a 5L Morton flask by dissolving 130g of FeCl3·6H2O crystals in 4000mL of DI H2O. The solution was then heated to 80°C and stirred for 2 hours. The particle sizes of β-FeOOH, determined by laser diffraction using a Malvern 3000, were D10 = 0.3 µm, D50 = 2.6 µm, and D90 = 33.4 µm. These particle sizes were too small for conventional filtration methods, so centrifugation was used for separation. Two 500 mL fractions were centrifuged at 3500 RPM for 30 min. The supernatant was discarded, and the flask was then refilled with deionized water. This cycle was repeated twice. After a final centrifugation, the β-FeOOH was collected. This centrifugation process was repeated on the remaining reaction slurry. The collected β-FeOOH was then dried at 60°C for 24 hours.

[0108] Using a procedure equivalent to that of Example 17, β-FeOOH was converted to iron phosphate. The conversion of β-FeOOH took 6 hours and produced a particle size distribution with D10=3.89 mm, D50=8.65 mm, and D90=14.42 mm, spanning 1.22; in contrast, γ-FeOOH took 4 hours and produced a particle size distribution with D10=1.17 μm, D50=3.67 μm, and D90=6.78 μm, spanning 1.53. Therefore, the reaction rate using β-FeOOH was lower than that using γ-FeOOH, even though the particle size of β-FeOOH used in these examples was smaller than that of γ-FeOOH.

[0109] Example 18 - Conversion of FeOOH to Ferric Phosphate Using the procedure in Examples 1A / 1B, at a 5-fold scale with a 75% reduction in water, the conversion of γ-FeOOH was carried out in an overhead mixer at 70°C, 4 hours of stirring time, a P:Fe ratio of 6:1, and 500 rpm. The result was a very light grayish-white color, indicating conversion to ferric phosphate. The material had a particle size distribution of D10 = 1.15 μm, D50 = 7.05 μm, and D90 = 12.17 μm, spanning 1.56. The purpose of Example 18 was to demonstrate that the reaction could be carried out with a 75% reduction in water and a 5-fold scale-up.

[0110] Example 19 - Conversion of FeOOH to Ferric Phosphate Using the procedure in Examples 1A / 1B, at a 15-fold scale, with 90% less water, the conversion of γ-FeOOH was carried out in an overhead mixer at 70°C, 4 hours of stirring time, a P:Fe ratio of 6:1, and 500 rpm. The result was a yellow-orange color, indicating a very small amount of conversion to ferric phosphate. The material had a particle size distribution of D10 = 1.14 μm, D50 = 4.70 μm, and D90 = 10.01 μm, with a span of 1.88. The purpose of Example 19 was to demonstrate that reducing the water volume by 90% resulted in almost no or no reaction. However, if the reaction in Example 19 allowed for a longer reaction time, it is likely that the conversion would eventually be achieved.

[0111] Based on the above embodiments, the following preferred reaction conditions were recorded: - The preferred pH value is acidic; more preferably 0.5-4.0; most preferably 0.5-3.5.

[0112] - The preferred reaction temperature is 50℃-100℃; more preferably 60℃-90℃; and most preferably 70℃-90℃.

[0113] - The preferred reaction time is <7 hours, more preferably 1–6 hours; more preferably 1–5 hours; more preferably 2–4 hours; and most preferably 2.5–3 hours.

[0114]

[0115] Example 20 – Reaction rate of γ-FeOOH Using the procedure in Examples 1A / 1B, the conversion of γ-FeOOH was carried out in a 5L flask at 70°C, a P:Fe ratio of 6:1, and 500 rpm using a top-mounted mixer at 50x scale with 50% less water. During the reaction, 100 mL of sample was taken every 30 minutes for filtration, washing, and drying. Color determination was performed on the initial unreacted γ-FeOOH and subsequent samples after 4.5 hours of reaction. For color determination, 6% of Example 20 was added to the nitrocellulose varnish and stirred by hand until homogeneous. The varnish was applied to a Leneta chart using a 3-mil doctor blade. Measurements were taken using a BYK-mac spectrophotometer on the white portion of the card at a 15-degree offset from the mirror. The hue data in Table 2 show the color changes during the reaction, which began to stabilize after approximately 2.5 hours.

[0116] Example 21 – Reaction rate of α-FeOOH (Comparative Example) The operation in this embodiment is the same as in Example 20, except that α-FeOOH is used instead of γ-FeOOH. Sampling is performed every 30 minutes until the reaction time is 5 hours, and then a final sampling is performed after a total reaction time of 21.5 hours. The hue data in Table 3 show that the color change is minimal within 5 hours and only a small change after 21.5 hours, indicating that although α-FeOOH has a smaller particle size, its reaction rate is slower than that of γ-FeOOH.

[0117] Table 2: Color data of Example 20: Reaction rate of γ-FeOOH

[0118] Table 3: Color data of Example 21: Reaction rate of α-FeOOH

[0119] Examples 22-24: The following experiments were conducted to determine and evaluate the feasibility of converting Fe3O4 (FeO·Fe2O3, iron oxide (II, III), black iron oxide) to ferric phosphate and γ-FeOOH (γ-Fe2O3·H2O, iron oxide-hydroxide, iron oxyhydroxide) to ferric phosphate in the presence of an alkaline environment. In all the following examples, γ-FeOOH was sieved through a 10-mesh sieve (2000 μm screen) before the reaction to remove any abnormally large lumps of material.

[0120] γ-FeOOH has D w 10 = 86nm, D w 50 = 163nm, D wThe particle size distribution is 90 = 249 nm, and Fe3O4 has D w 10 = 32nm, D w 50 = 453nm, D w The particle size distribution was 90 = 626 nm. The sample was measured using a disc centrifugal particle size analyzer. The reaction was determined by color change, more precisely by the gradual lightening of the color during the reaction. A pale yellow or white color was optimal. The reaction was considered complete when the color stopped changing. The initial pH target was approximately 2. After 8 hours, the sample was filtered and dried in a convection oven at 60°C.

[0121] Example 22: Conversion of γ-FeOOH to ferric phosphate γ-FeOOH was ground using a mortar and pestle. Then, 57.840 g of 50% H3PO4 was added to a 250-mL Erlenmeyer flask and heated to 80°C. 3.554 g of γ-FeOOH was slowly added with vigorous stirring. The volume was increased to 75 mL using reverse osmosis (RO) water. The contents of the flask were stirred every 15 to 30 minutes. After approximately 45 hours, the color began to change to a milky yellow, indicating conversion. During digestion, the reaction continued under visual observation until 5 hours. After approximately 5 hours, there was no change in appearance. Additionally, at 5 hours, 5% excess 50% H3PO4 (0.392 g) was added to attempt to complete the conversion. The total digestion time was approximately 8 hours. The initial pH was 1.51, and the final pH was 1.48. The contents were filtered and washed with 20 g of RO water. The total filtrate was 96.76 g. The total dry weight was 7.29 g. No unreacted γ-FeOOH agglomerates were found in the final mixture. There was clear evidence that γ-FeOOH was converted to ferric phosphate, and the reaction rate was significantly increased. This was quite unexpected, as the reaction time was significantly faster than that described in US Patent No. 8673497.

[0122] Example 23: Conversion of Fe3O4 (black iron oxide) to iron phosphate In this experiment, γ-FeOOH was converted to Fe3O4 as follows: ferrous solution was added stoichiometrically to achieve the correct FeO content, and then a base was added under reducing conditions to drive the reaction but prevent oxidation. 55.879 g of 50% H3PO4 was added to a 250-mL Erlenmeyer flask and heated to 80°C. 2.315 g of Fe3O4 was slowly added with vigorous stirring. The volume was increased to 75 mL using reverse osmosis (RO) water. The contents of the flask were stirred every 15 to 30 minutes. After approximately 2 hours, the color began to change to a slightly grayish hue, indicating conversion. During digestion, the reaction continued under visual observation until 5 hours. After approximately 5 hours, no change in appearance was observed. At 5 hours, 5% excess 50% H3PO4 (0.293 g) was added to attempt to complete the conversion. The total digestion time was approximately 8 hours. The initial pH was 1.47, and the final pH was 1.91. The contents were filtered and washed with 20 g of RO water. The total filtrate was 97.37 g. The total dry weight was 4.77 g. There was clear evidence that Fe3O4 was converted to ferric phosphate, although the conversion was incomplete, showing a significant increase in the reaction rate. This was quite unexpected, as the reaction time was significantly faster than that described in US Patent No. 8673497.

[0123] Example 24: Conversion of γ-FeOOH to ferric phosphate in the presence of alkali In this experiment, 57.840 g of 50% H3PO4 and 1.599 g of NaOH were added to a 250-mL Erlenmeyer flask and heated to 80°C. The pH had to be adjusted from 3.2 to the target value of 2. For this purpose, 2.4 mL of 50% HCl was added. HCl was chosen because it can catalyze the reaction. 3.554 g of γ-FeOOH was slowly added with vigorous stirring. The volume was increased to 75 mL using reverse osmosis (RO) water. The contents of the flask were stirred every 15 to 30 minutes. After about 2 hours, the color began to change to a milky yellow, indicating that conversion had occurred. During digestion, the reaction continued under visual observation until 5 hours. The initial pH was 1.94 and eventually reached 2.57. There was no change in appearance after 3 hours; however, to maintain experimental consistency, it was allowed to continue for about 5 hours. At 5 hours, 5% excess 50% H3PO4 (0.392 g) was added to attempt to complete the conversion. The total digestion time was about 8 hours. The contents were filtered and washed with 20 g of reverse osmosis water. The total filtrate was 67.69 g. The total dry weight was 5.89 g. No unreacted γ-FeOOH agglomerates were found in the final mixture. There was clear evidence that γ-FeOOH was converted to ferric phosphate, and the reaction rate was significantly increased. This was quite unexpected, as the reaction time was significantly faster than that in US Patent No. 8673497. The final color of the dried material was comparable to the control experiment in Example 22.

[0124] Example 25 - Scale-up of FeOOH conversion to ferric phosphate Using the procedure from Example 17, the conversion of γ-FeOOH was carried out on a 20-fold scale instead of a 3-fold scale. The result was a very light grayish-white color, indicating conversion to iron phosphate. The material had a particle size distribution of D10 = 2.43 μm, D50 = 5.28 μm, and D90 = 9.27 μm, spanning 1.30. This example demonstrates that the reaction can be carried out on a 20-fold scale.

[0125] Figure 1A The image provided is a SEM image of the iron phosphate material. Figure 2A The XRD pattern of the material is provided. The pattern confirms that the material is FePO4·2H2O.

[0126] Example 26 - Calcination of Ferric Phosphate Calcination experiments were conducted using the material produced in Example 25. Calcination was carried out at 200, 300, 400, 550, and 650 °C, with 6 g of sample placed in the furnace at the corresponding temperature and held for 4 hours. The color of the resulting calcined sample depended on the calcination temperature. The initially very pale grayish-white turned pale yellow at 200 °C, pale orange at both 300 and 400 °C, pale pink at 550 °C, and finally grayish-white at 650 °C.

[0127] Figure 1B The image provided is a SEM image of the iron phosphate material calcined at 650°C. Figure 2B The XRD pattern of the material is provided. The pattern confirms that the material is FePO4 with an α-quartz structure.

[0128] Example 27 - Conversion of Fe2O3 to ferric phosphate (Comparative Example) Using the procedure in Example 25, where 18 g of Fe₂O₃ replaced 20 g of γ-FeOOH, the result was only a very small color change, even after 27 hours, indicating no conversion to ferric phosphate. This example demonstrates that the reaction rate for preparing ferric phosphate using γ-FeOOH is significantly faster than that using Fe₂O₃.

[0129] Example 28: Conversion of γ-FeOOH to ferric phosphate A slurry of 25 g γ-FeOOH in 422.5 mL of deionized water and 48.6 g of 85% H3PO4 (P:Fe ratio 1.5:1) was placed in a 1 L Morton flask, stirred at 500 rpm, and heated to 90 °C. After stirring at 90 °C for 3 hours, the resulting product was pinkish-white, indicating conversion to ferric phosphate. The precipitate was vacuum filtered, washed with 4 × 500 mL of deionized water, and dried at 100 °C for 2 hours. The material had a particle size distribution of D10 = 1.28 μm, D50 = 4.4 μm, and D90 = 8.24 μm, with a span of 1.58. The purpose of Example 28 was to demonstrate that a lower P:Fe ratio and a smaller water volume can completely convert to ferric phosphate when heated to 90 °C.

[0130] Example 29: Conversion of γ-FeOOH to ferric phosphate Example 29 was performed in the same manner as Example 28, except that 50 g of γ-FeOOH was slurried in 800 mL of deionized water and 173 g of 85% H3PO4 in a 3 L Morton flask (P:Fe ratio of 2.67:1). The resulting material was pinkish-white, indicating conversion to ferric phosphate, and had a particle size distribution of D10 = 0.80 μm, D50 = 3.04 μm, D90 = 6.59 μm, with a span of 1.9. The purpose of Example 29 was to demonstrate that a P:Fe ratio of 2.4:1 can be completely converted to ferric phosphate under low water volume and heating to 90 °C.

[0131] Example 30: Conversion of γ-FeOOH to ferric phosphate Example 30 was performed in the same manner as Example 28, except that 50 g of γ-FeOOH was slurried in 825 mL of deionized water and 130.5 g of 85% H3PO4 in a 3 L Morton flask (P:Fe ratio of 2.01:1). The resulting material was pinkish-white, indicating conversion to ferric phosphate, and had a particle size distribution of D10 = 2.41 μm, D50 = 4.11 μm, D90 = 6.75 μm, with a span of 1.06. The purpose of Example 30 was to demonstrate that a P:Fe ratio of 2.1:1 can be completely converted to ferric phosphate under low water volume and heating to 90 °C.

[0132] Example 31: Conversion of γ-FeOOH to ferric phosphate Example 31 was performed in the same manner as Example 28, except that 25 g of γ-FeOOH was slurried in 427.5 mL of deionized water and 40.5 g of 85% H3PO4 in a 1 L Morton flask (P:Fe ratio of 1.25:1). The resulting material was light grayish-white in color, indicating conversion to ferric phosphate, and had a particle size distribution of D10 = 1.31 μm, D50 = 4.10 μm, D90 = 7.64 μm, with a span of 1.55. The purpose of Example 31 was to demonstrate that a P:Fe ratio of 1.25 can be completely converted to ferric phosphate under low water volume and heating to 90°C.

[0133] Example 32: Conversion of γ-FeOOH to ferric phosphate Example 32 was performed in the same manner as Example 28, except that 25 g of γ-FeOOH was slurried in 430.35 mL of deionized water and 35.7 g of 85% H3PO4 in a 1 L Morton flask (P:Fe ratio of 1.1:1). The resulting material was a dark grayish-white color, indicating partial conversion to ferric phosphate, and had a particle size distribution of D10 = 1.06 μm, D50 = 3.70 μm, D90 = 7.10 μm, with a span of 1.63. The purpose of Example 32 was to demonstrate that, with a low water volume and heating to 90°C, a P:Fe ratio of 1.1:1 can partially convert ferric phosphate.

[0134] Example 33: Conversion of γ-FeOOH to ferric phosphate Example 33 was performed in the same manner as Example 28, except that the slurry was heated to 80°C before the 3-hour stirring time, and the pH of the slurry was raised to 1.5 with 35% NaOH. The resulting material was light grayish-white in color, indicating conversion to ferric phosphate, and had a particle size distribution of D10=0.60μm, D50=1.59μm, D90=6.71μm, with a span of 3.84. The purpose of Example 33 was to demonstrate that complete conversion to ferric phosphate was achieved when the slurry pH was 1.5.

Claims

1. A method for forming a material comprising iron phosphate, comprising: The iron source ferrihydrite (γ-FeOOH) is reacted with a phosphorus source to form a material containing iron phosphate; The material containing iron phosphate is not lithium iron phosphate or a material with an olivine-type crystal structure.

2. The method of claim 1, wherein the phosphorus source is selected from phosphoric acid (H3PO4), phosphorous acid (H3PO3), (NH4)H2PO4, (NH4)2HPO4, (NH4)3PO4, Li3PO4, Li2HPO4 and LiH2PO4 and mixtures thereof; or selected from H3PO4, H3PO3, (NH4)H2PO4, (NH4)2HPO4, (NH4)3PO4 and mixtures thereof; or H3PO4.

3. The method of any of the preceding claims, wherein the material comprising iron phosphate contains a sulfur content of <1000 ppm or <500 ppm.

4. The method as described in any of the preceding claims, wherein the material comprising iron phosphate has a D50 ≤ 20 μm or ≤ 15 μm or ≤ Particle size distribution characterized by 12 μm or ≤10 μm.

5. The method as described in any of the preceding claims, wherein the particle size distribution span ((D90-D10) / D50) of the material comprising iron phosphate is ≤6 or ≤5 or ≤4 or ≤3 or ≤2.

6. The method as described in any of the preceding claims, wherein the γ-FeOOH has a D50 ≤ 50 μm or ≤ 30 μm or ≤ 20 μm or ≤ The particle size distribution is characterized by 15 μm.

7. The method of any of the preceding claims, wherein the reaction is carried out in the presence of additional reactants and / or additives selected from the group consisting of an ion source, a dopant, a surfactant, and a chelating agent; optionally, wherein the reaction is carried out in the presence of an additional ion source and / or a dopant.

8. The method as claimed in any of the preceding claims, wherein the material containing iron phosphate is selected from FePO4, FePO4·2H2O, Fe5(PO4)4(OH)2·2H2O, Fe4(P2O7)3 and Fe3(PO4)2·8H2O; optionally wherein the material containing iron phosphate is selected from FePO4 and FePO4·2H2O.

9. The method as described in any of the preceding claims, wherein the material comprising iron phosphate is FePO4 in the trigonal phase, more preferably FePO4 with an α-quartz structure.

10. The method of any of the preceding claims, wherein the reaction is carried out at an acidic pH or at pH < 5 or at pH 0.5-4.0 or at pH 0.5-3.5 or at pH 1.0-2.

5.

11. The method as described in any of the preceding claims, wherein, If the reaction is carried out with a P:Fe molar ratio of ≤1.5:1, ≤3:1, or ≤4:1, the reaction is carried out at a temperature of at least 80°C, at least 82°C, or at least 85°C, such as at about 90°C.

12. The method of any of the preceding claims, wherein the reaction is carried out at a P:Fe molar ratio of ≥3:1 or ≥4:1 or ≥6:1 or ≥7:

1.

13. The method of any of the preceding claims, wherein the reaction is carried out at a P:Fe molar ratio of ≤100:1 or ≤50:1 or ≤20:1 or ≤12:

1.

14. The method of any of the preceding claims, wherein the reaction is carried out at a temperature of 50°C-100°C, 60°C-90°C, or 70°C-90°C.

15. The method as described in any of the preceding claims, wherein the reaction takes place for a time of <7 hours or 1-6 hours or 1-5 hours or 2-4 hours or 2.5-3 hours.

16. The method as described in any of the preceding claims, wherein, If the reaction is carried out with a mass of γ-FeOOH relative to the volume of water ≥ 45 g dm -3 If the reaction is to be carried out, the reaction is carried out at a temperature of at least 80°C, at least 82°C, or at least 85°C, such as at about 90°C.

17. The method as described in any of the preceding claims, wherein the reaction is carried out with a mass of γ-FeOOH relative to the volume of water ≤ 45 g dm³. -3 or ≤35 g dm -3 or ≤25 g dm -3 And optionally ≥0.1 g dm -3 ≥0.5 g dm -3 or ≥1 g dm -3 conduct.

18. The method of any of the preceding claims, wherein the reaction is carried out in a non-inert atmosphere such as air.

19. A method for forming a material comprising iron phosphate, comprising the following steps: (a) React the iron source ferrihydrite (γ-FeOOH) with another iron source to form Fe3O4; (b) React the obtained Fe3O4 with a phosphorus source to form a material containing iron phosphate; The material containing iron phosphate is not lithium iron phosphate or a material with an olivine-type crystal structure.

20. The method of claim 19, wherein the other iron source is a ferriferrous source.

21. A method for forming a material comprising iron phosphate according to any one of the preceding claims, wherein, If the material containing ferric phosphate contains metals other than iron, then the metals are present in amounts of less than 10 atomic%, less than 5 atomic%, or less than 1 atomic% relative to the iron content in the material containing ferric phosphate.

22. A method for forming a material comprising ferric phosphate according to any one of the preceding claims, comprising separating the obtained material comprising ferric phosphate.

23. The method of forming a material containing iron phosphate according to claim 22, comprising calcining the separated material containing iron phosphate to form anhydrous material containing iron phosphate; optionally, wherein the anhydrous material containing iron phosphate is FePO4.

24. A method for forming lithium iron phosphate, comprising following the method as described in any one of the preceding claims, and reacting the material containing iron phosphate with a lithium source to form lithium iron phosphate.

25. A method of forming an article comprising forming a material comprising iron phosphate by following the method of any one of claims 1-23, or forming lithium iron phosphate by following the method of claim 24, and forming an article comprising the material comprising iron phosphate or the lithium iron phosphate.

26. The method of claim 25, wherein the article is an electrode or a battery cell.

27. A material comprising iron phosphate, formed by any one of claims 1-23.

28. Lithium iron phosphate, formed by the method of claim 24.

29. An article comprising the iron phosphate material formed by the method of any one of claims 1-23 or the lithium iron phosphate formed by the method of claim 24.

30. The article of claim 29, wherein it is an electrode or a battery cell.

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