Low-pressure anhydrous iron phosphate materials prepared by stress-transformation coupling and their applications
By preparing low-pressure anhydrous iron phosphate materials through stress-transfer crystal coupling, the problem of low grinding efficiency in the co-precipitation method for preparing iron phosphate materials was solved, enabling the production of low-energy-consumption and high-efficiency lithium iron phosphate and lithium-ion batteries.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- GUANGDONG BRUNP RECYCLING TECH CO LTD
- Filing Date
- 2025-09-01
- Publication Date
- 2026-08-04
AI Technical Summary
In existing iron phosphate synthesis processes, the co-precipitation method produces iron phosphate materials with high lattice strength, resulting in low grinding efficiency and high energy consumption costs, which makes it difficult to meet the needs of industrial production.
Low-pressure anhydrous iron phosphate material was prepared by stress-crystallization coupling. Through steps such as flocculation sedimentation, crystallization, calcination and rapid cooling, the grinding strength of the material was controlled to not exceed 2.8 MPa, forming an easy-to-grind product with micropores and high brittleness.
It reduces wear and tear on grinding machines, shortens processing time, improves grinding efficiency, and lowers energy costs, making it suitable for the preparation of lithium iron phosphate and lithium-ion batteries.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of lithium battery cathode material precursor technology, and more specifically, to a low-pressure anhydrous iron phosphate material prepared by stress-transformation coupling and its application. Background Technology
[0002] Compared with ternary lithium batteries, lithium iron phosphate batteries have advantages in safety and cost. They also have advantages such as good thermal stability, long cycle life, environmental friendliness, and abundant raw material sources, making them a cathode material for power lithium-ion batteries with high application potential.
[0003] The process route for synthesizing lithium iron phosphate using iron phosphate is one of the most widely used technical routes for preparing lithium iron phosphate. Compared with processes such as preparing lithium iron phosphate using ferrous oxalate or iron oxide red, the process route for synthesizing lithium iron phosphate using iron phosphate has the advantages of high sintering rate and finer product particle size, which enables downstream battery products to have good low-temperature performance and rate performance.
[0004] Currently, the industrial preparation method for iron phosphate typically employs a co-precipitation method. This method involves reacting a mixture containing an iron source, a phosphorus source, and other auxiliary components under specific conditions to generate uniformly dispersed iron phosphate particles. To ensure the performance of subsequent lithium iron phosphate materials, the generated iron phosphate particles need to be thoroughly ground. However, the iron phosphate prepared by the co-precipitation method has a high lattice strength, resulting in high macroscopic hardness, low grinding efficiency, and significant wear and tear on grinding machines, greatly increasing time and energy costs.
[0005] In view of this, the present invention is proposed. Summary of the Invention
[0006] The purpose of this invention is to provide low-pressure anhydrous iron phosphate materials prepared by stress-transformation coupling and their applications, so as to solve or improve the above-mentioned technical problems.
[0007] This invention can be implemented as follows:
[0008] In a first aspect, the present invention provides a low-pressure anhydrous iron phosphate material, wherein the grinding strength M of the low-pressure anhydrous iron phosphate material is ≤2.8MPa;
[0009] Where M=P(α-β) / β, P is the average compressive strength of a single anhydrous iron phosphate particle in the low-pressure anhydrous iron phosphate material, in MPa; α is the maximum deformation of the low-pressure anhydrous iron phosphate material during the process of holding pressure at 200MPa for 10s; and β is the irreversible deformation of the low-pressure anhydrous iron phosphate material after holding pressure at 200MPa for 10s and then depressurizing to 0MPa and holding pressure for 10s.
[0010] In an optional embodiment, the low-pressure anhydrous iron phosphate material further includes at least one of the following features:
[0011] Feature 1: 0.9MPa≤M≤2.8MPa;
[0012] Feature 2: 10MPa≤P≤50MPa;
[0013] Feature 3: 40%≤α≤70%;
[0014] Feature 4: 35% ≤ β ≤ 65%;
[0015] Feature 5: 2% ≤ α - β ≤ 5%;
[0016] Feature 6: The iron-to-phosphorus ratio is 0.96~1.02.
[0017] Secondly, the present invention provides a method for preparing a low-pressure anhydrous iron phosphate material as described in the aforementioned embodiments, comprising the following steps: flocculating and precipitating an iron solution and a starch solution to obtain an iron hydroxide mixture containing starch particles; subsequently heating and adding a phosphorus source during the heat preservation process to induce crystallization; then performing solid-liquid separation; washing and drying the separated solid to obtain a dried material; calcining the dried material; immediately cooling the obtained calcined product in water after calcination; then performing solid-liquid separation on the cooled material; and finally drying the solid obtained from the solid-liquid separation.
[0018] In an optional embodiment, the ferric hydroxide mixture containing starch granules comprises at least one of the following characteristics:
[0019] Feature 7: The mass ratio of iron in the iron solution to starch in the starch solution is 2:1 to 20:1;
[0020] Feature 8: The mass percentage of solute in the iron solution is 5%~30%;
[0021] Feature 9: Iron solutions include polyferric sulfate solutions or polyferric chloride solutions;
[0022] Feature 10: The concentration of the starch solution is 1 g / L to 100 g / L;
[0023] Feature 11: Flocculation and sedimentation of iron solution and starch solution includes: adding iron solution to starch solution, stirring at a first rate, then adding pH adjuster to adjust pH value to 6-8, and stirring at a second rate.
[0024] In an optional embodiment, the first stirring rate is 200 rpm to 400 rpm, and / or, stirring at the first rate for 1 min to 2 min.
[0025] In an optional embodiment, the second stirring rate is 30 rpm to 50 rpm, and / or, stirring at the second rate for 10 min to 15 min.
[0026] In an optional implementation, the pH adjuster includes a sodium hydroxide solution.
[0027] In an optional embodiment, the concentration of the sodium hydroxide solution is 0.1 mol / L to 2.0 mol / L.
[0028] In an optional implementation, the temperature is raised to 88°C~95°C;
[0029] And / or, the heat preservation time is 2h~6h.
[0030] In an optional embodiment, the crystallization is carried out under conditions of pH 1.5 to 2.0;
[0031] And / or, the phosphorus source includes at least one of phosphoric acid and phosphate.
[0032] In an optional embodiment, the content of phosphorus in the mixture of ferric hydroxide mixture containing starch particles and phosphorus source is 3 g / L to 10 g / L.
[0033] In an optional embodiment, calcination includes at least one of the following characteristics:
[0034] Feature 12: Calcination temperature is 600℃~750℃;
[0035] Feature 13: Calcination time is 2h~5h;
[0036] Feature 14: The heating rate during calcination is 3℃ / min~5℃ / min;
[0037] Feature 15: Calcination is carried out in an air or oxygen atmosphere.
[0038] In an optional embodiment, during the cooling process, the solid-liquid ratio of the calcined product to water is from 1 g:1 L to 100 g:1 L.
[0039] In an optional implementation, the temperature of the water used for cooling is 0°C to 10°C.
[0040] Thirdly, the present invention provides a lithium iron phosphate cathode material, the raw materials for which the preparation of the lithium iron phosphate cathode material includes the grinding material obtained by grinding the low-pressure anhydrous iron phosphate material of the aforementioned embodiments.
[0041] In an optional implementation, the D of the abrasive 50 The range is 5μm to 20μm.
[0042] Fourthly, the present invention provides a battery comprising the lithium iron phosphate cathode material of the aforementioned embodiments.
[0043] The beneficial effects of this invention include:
[0044] This invention controls the grinding intensity of low-pressure anhydrous iron phosphate material to a range not exceeding 2.8 MPa. Within this range, the grinding intensity of low-pressure anhydrous iron phosphate material is low, the macroscopic hardness is small, the lattice strength of the anhydrous iron phosphate particles contained in the low-pressure anhydrous iron phosphate material is small, and the wear on the grinding machine is small. This is beneficial to shorten the processing time, improve the grinding efficiency and reduce energy consumption costs.
[0045] This invention provides a feasible preparation method for the low-pressure anhydrous iron phosphate material, which is simple to operate and can be industrially produced.
[0046] The low-pressure anhydrous iron phosphate material provided by this invention can be further used to prepare lithium iron phosphate and lithium-ion batteries. Detailed Implementation
[0047] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.
[0048] The following is a detailed description of the low-pressure anhydrous iron phosphate material prepared by stress-transformation coupling provided by the present invention and its applications.
[0049] This invention provides a low-pressure anhydrous iron phosphate material with a grinding strength M≤2.8MPa.
[0050] This invention controls the grinding intensity of low-pressure anhydrous iron phosphate material to a range not exceeding 2.8 MPa. Within this range, the grinding intensity of low-pressure anhydrous iron phosphate material is low, the macroscopic hardness is small, the lattice strength of the anhydrous iron phosphate particles contained in the low-pressure anhydrous iron phosphate material is small, and the wear on the grinding machine is small. This is beneficial to shorten the processing time, improve the grinding efficiency and reduce energy consumption costs.
[0051] In some optional implementations, the value of M can be 0.9MPa≤M≤2.8MPa, and can be, for example, 1.3MPa~1.8MPa.
[0052] In this invention, M = P(α-β) / β, where P is the average compressive strength of a single anhydrous iron phosphate particle in the low-pressure anhydrous iron phosphate material, in MPa; α is the maximum deformation of the low-pressure anhydrous iron phosphate material during a 10s pressurization period at 200 MPa; and β is the irreversible deformation of the low-pressure anhydrous iron phosphate material after a 10s pressurization period at 200 MPa, followed by depressurization to 0 MPa and a 10s pressurization period. The unit of M is MPa.
[0053] The average compressive strength P of the above-mentioned single anhydrous iron phosphate particles can be tested by way of example using the standard GB / T 43091-2023 "Test Method for Compressive Strength of Powder"; during the test, three particles are selected and the average value is calculated.
[0054] In some alternative implementations, 10 MPa ≤ P ≤ 50 MPa. The smaller the P value, the easier it is for the anhydrous iron phosphate particles to break during the grinding process, and the easier it is to grind them to obtain the target particle size.
[0055] In some alternative implementations, P is 18 MPa to 30 MPa.
[0056] The maximum deformation α and irreversible deformation β mentioned above can be exemplarily tested using a compaction density meter. The specific testing method is as follows: Weigh the sample, recording its mass as m; place it in a cylindrical mold with a bottom diameter of d, apply pressure to 200 MPa, and measure the sample height h1 after holding the pressure at 200 MPa for 10 seconds; then release the pressure to 0 MPa and hold the pressure for 10 seconds to measure the sample height h2. Additionally, test the loose density ρ according to GB / T 31057.1-2014 "Physical Properties Testing of Granular Materials Part 1: Measurement of Loose Density", and calculate α and β accordingly.
[0057] α=[1-(h1×0.25π×d 2 ×10 -3 [(m / ρ)]×100%;
[0058] β=[1-(h2×0.25π×d 2 ×10 -3 [(m / ρ)] ×100%;
[0059] Where h1 and h2 are in mm, d is in mm, sample mass m is in g, and ρ is in g / cm³. 3 .
[0060] In some optional embodiments, 35% ≤ β ≤ 65%. A larger β indicates poorer toughness of the anhydrous iron phosphate particles, making them more difficult to recover during grinding, thus improving grinding efficiency. In some optional embodiments, β is 39%~63.5%.
[0061] In some optional embodiments, 40% ≤ α ≤ 70%. The larger the α, the easier the anhydrous iron phosphate material is to be extruded. In some optional embodiments, α is 42%~66.5%.
[0062] "α-β" represents the difference between the maximum deformation α and the irreversible deformation β. This difference can be understood as the reversible deformation of the low-pressure anhydrous ferric phosphate material. The larger the difference between α and β, the larger the reversible deformation, and the worse the grinding effect of the corresponding low-pressure anhydrous ferric phosphate material, thus reducing grinding efficiency. In this invention, α-β is controlled within the range of 2% to 5%. In some optional embodiments, α-β is 2.8% to 3.8%.
[0063] In some optional embodiments, the iron-to-phosphorus ratio of the low-pressure anhydrous iron phosphate material is 0.96~1.02. The iron-to-phosphorus ratio can be tested according to the test methods in "HG / T 4701-2021 Iron Phosphate for Batteries".
[0064] As mentioned above, the low-pressure anhydrous iron phosphate material provided by this invention has a low P content and suitable deformation (α, β, and α-β) under high pressure (e.g., 200 MPa), which is beneficial for subsequent grinding and processing during the synthesis of lithium iron phosphate.
[0065] Accordingly, the present invention also provides a method for preparing the above-mentioned low-pressure anhydrous iron phosphate material, which may include the following steps: flocculating and precipitating an iron solution and a starch solution to obtain an iron hydroxide mixture containing starch particles; then heating, adding a phosphorus source during the heat preservation process to induce crystallization, followed by solid-liquid separation, washing and drying the separated solid to obtain a dried material; calcining the dried material, immediately cooling the obtained calcined product in water after calcination, then performing solid-liquid separation on the cooled material, and finally drying the solid obtained from the solid-liquid separation.
[0066] In some alternative embodiments, the mass ratio of iron in the iron solution to starch in the starch solution can be from 2:1 to 20:1, such as 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 12:1, 15:1, 18:1 or 20:1, or other values within the range of 2:1 to 20:1.
[0067] If too little starch is used, the micropores inside the low-pressure anhydrous ferric phosphate material will be fewer after the starch is removed by calcination, resulting in higher hardness and making it difficult to grind and process. If too much starch is used, it will waste costs.
[0068] In some alternative embodiments, the concentration of the starch solution can be from 1 g / L to 100 g / L, such as 1 g / L, 5 g / L, 10 g / L, 20 g / L, 50 g / L, 80 g / L, or 100 g / L, or other values within the range of 1 g / L to 100 g / L.
[0069] The mass percentage of solute in the iron solution can be 5% to 30%, such as 5%, 10%, 15%, 20%, 25%, or 30%, or other values within the range of 5% to 30%. The iron solution may, exemplarily, include polyferric sulfate solution or polyferric chloride solution.
[0070] In some alternative embodiments, the above-mentioned flocculation and sedimentation of iron solution and starch solution may include: adding iron solution to starch solution, stirring at a first rate, then adding pH adjuster to adjust pH value to 6-8, and stirring at a second rate.
[0071] The first stirring rate can be 200 rpm to 400 rpm, such as 200 rpm, 250 rpm, 300 rpm, 350 rpm, or 400 rpm, or other values within the range of 200 rpm to 400 rpm. The stirring time corresponding to the first rate can be 1 min to 2 min, such as 1 min, 1.5 min, or 2 min.
[0072] The second stirring rate can be 30 rpm to 50 rpm, such as 30 rpm, 35 rpm, 40 rpm, 45 rpm, or 50 rpm, or other values within the range of 30 rpm to 50 rpm. The stirring time corresponding to the second rate can be 10 min to 15 min, such as 10 min, 12 min, or 15 min.
[0073] In some alternative embodiments, the pH adjuster may exemplary include a sodium hydroxide solution. The concentration of the sodium hydroxide solution may exemplary be 0.1 mol / L to 2.0 mol / L, such as 0.1 mol / L, 0.2 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, or 2.0 mol / L, etc.
[0074] pH adjusters are used to adjust the pH value to 6-8, such as 6, 6.5, 7, 7.5, or 8, or other values within the range of 6-8. If the pH value is less than 6, it is not conducive to the flocculation and precipitation of iron.
[0075] In some alternative implementations, the temperature can be increased to 88°C to 95°C, such as 88°C, 89°C, 90°C, 91°C, 92°C, 93°C, 94°C or 95°C, or other values within the range of 88°C to 95°C.
[0076] Under the above-mentioned heating conditions, starch gelatinizes and absorbs water to expand, which can increase the porosity of the flocculated precipitate particles. Furthermore, under the above-mentioned heating conditions, the activity of ions can also be increased, accelerating the conversion of phosphate and hydroxide ions, and rapidly forming ferric phosphate dihydrate.
[0077] The heat preservation time after heating can be 2h to 6h, such as 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h or 6h, or other values within the range of 2h to 6h.
[0078] During the heat preservation process, a phosphorus source is added. In some embodiments, the phosphorus source can be added under stirring conditions, and the stirring rate can be 100 rpm to 300 rpm (such as 100 rpm, 150 rpm, 200 rpm, 250 rpm or 300 rpm, etc.).
[0079] In some alternative implementations, the crystallization can be carried out at a pH of 1.5 to 2.0 (e.g., 1.5, 1.6, 1.7, 1.8, 1.9, or 2.0).
[0080] In some alternative embodiments, the phosphorus source may include at least one of phosphoric acid and phosphate.
[0081] Through the above-described crystallization process, the ferric hydroxide mixture containing starch granules reacts with a phosphorus source, converting the ferric hydroxide into ferric phosphate dihydrate. During this process, the phosphorus source also acts as a buffer to adjust the pH value.
[0082] In some optional embodiments, the phosphorus content in the mixture of ferric hydroxide mixture containing starch particles and phosphorus source can be 3 g / L to 10 g / L, such as 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L or 10 g / L, or other values within the range of 3 g / L to 10 g / L.
[0083] In some alternative embodiments, solid-liquid separation after crystallization can be carried out by pressure filtration, washing can be done with water, drying temperature can be 120℃~150℃ (e.g., 120℃, 125℃, 130℃, 135℃, 140℃, 145℃ or 150℃, etc.), and drying time can be 2h~4h (e.g., 2h, 2.5h, 3h, 3.5h or 4h, etc.).
[0084] In some alternative embodiments, the calcination temperature can be 600℃~750℃, such as 600℃, 620℃, 650℃, 680℃, 700℃, 720℃ or 750℃, or other values within the range of 600℃~750℃.
[0085] The calcination time can be 2h to 5h, such as 2h, 2.5h, 3h, 3.5h, 4h, 4.5h or 5h, or other values within the range of 2h to 5h.
[0086] The heating rate for calcination can be 3℃ / min to 5℃ / min, such as 3℃ / min, 3.5℃ / min, 4℃ / min, 4.5℃ / min or 5℃ / min, or other values within the range of 3℃ / min to 5℃ / min.
[0087] Calcination is carried out in an air or oxygen atmosphere.
[0088] Calcination under the above conditions effectively removes starch, resulting in micropores within the low-pressure anhydrous ferric phosphate material. This reduces particle hardness, increases irreversible deformation, and facilitates subsequent grinding. It should be noted that if starch, phosphorus, and iron sources are directly mixed, and the pH is adjusted to precipitate before calcination, the resulting low-pressure anhydrous ferric phosphate material remains difficult to grind. This is because direct precipitation of ferric phosphate results in only a very small amount of starch flocculating inside the particles, and the resulting pores after calcination are limited.
[0089] If the calcination temperature is below 600℃, it is not conducive to the crystallization of anhydrous ferric phosphate.
[0090] In some alternative embodiments, during the cooling process, the solid-liquid ratio of the calcined product to water can be from 1g:1L to 100g:1L, such as 1g:1L, 2g:1L, 10g:1L, 20g:1L, 50g:1L, 80g:1L, or 100g:1L, or other values within the range of 1g:1L to 100g:1L.
[0091] In some alternative implementations, the temperature of the water used for cooling can be 0℃~10℃, such as 0℃, 1℃, 2℃, 3℃, 4℃, 5℃, 6℃, 7℃, 8℃, 9℃ or 10℃, or other values within the range of 0℃~10℃.
[0092] By cooling the material immediately after calcination, further stress deformation can be generated, thereby improving the material's brittleness and machinability.
[0093] In some alternative embodiments, the mixture of calcined product and cold water is pressure filtered and then dried at 100°C to 120°C (e.g., 100°C, 105°C, 110°C, 115°C or 120°C) for 1 h to 3 h (e.g., 1 h, 1.5 h, 2 h, 2.5 h or 3 h).
[0094] Continuing from the above, this invention first transforms the pre-precipitate into the target precipitate through ion replacement, then calcines it to form the target crystalline state and rapidly cools it at a high temperature to cause stress deformation inside and outside; through the combined effect of transformation crystallization and stress deformation, an easy-to-grind product with high brittleness and low crushing force is obtained.
[0095] It should be noted that the low-pressure anhydrous iron phosphate material provided by the present invention can be prepared using the above-mentioned preparation method provided by the present invention. However, those skilled in the art will know that the low-pressure anhydrous iron phosphate material of the present invention is not limited to the preparation method of the present invention. The preparation method of the present invention is only an example.
[0096] In addition, the present invention also provides a lithium iron phosphate cathode material, the raw materials for which include the grinding material obtained by grinding the above-mentioned low-pressure anhydrous iron phosphate material.
[0097] In some alternative implementations, the D of the abrasive 50 The value can be 5μm to 20μm, such as 5μm, 8μm, 10μm, 12μm, 15μm, 18μm or 20μm, or other values within the range of 5μm to 20μm.
[0098] In addition, the present invention also provides a battery cell, wherein the positive electrode material of the battery cell includes the above-mentioned lithium iron phosphate positive electrode material.
[0099] For example, the aforementioned battery cells can be used, but are not limited to, in electrical devices such as vehicles, ships, or aircraft.
[0100] The present invention also provides a battery comprising the above-described battery cells. This battery can exhibit both superior rate performance and low-temperature performance.
[0101] The present invention also provides an electrical device comprising the aforementioned battery cell and / or battery. As examples, the electrical device may include, but is not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys may include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., while spacecraft may include airplanes, rockets, space shuttles, and spacecraft, etc.
[0102] The features and performance of the present invention will be further described in detail below with reference to embodiments.
[0103] Example 1
[0104] This embodiment provides an easily grindable, low-pressure anhydrous iron phosphate material, the preparation method of which includes:
[0105] S1: Prepare a starch solution with a mass concentration of 1 g / L and a polyferric sulfate solution with a mass percentage of 5%.
[0106] S2: According to the mass ratio of iron in polyferric sulfate solution to starch in starch solution of 5:1, add polyferric sulfate solution to starch solution and stir at the first speed (200 rpm) for 1 min. Then add 0.1 mol / L sodium hydroxide solution to adjust the pH value to 6, stir at the second speed (30 rpm) for 10 min, and then let stand for 10 min.
[0107] S3: Heat to 88℃, start stirring, control the stirring speed at 100rpm, keep warm for 2h, and add phosphoric acid and sodium phosphate as buffers during this process to adjust the pH value to 1.5; control the P element content in the mixture of ferric hydroxide mixed with starch particles and the mixture of phosphorus source to be 3g / L.
[0108] S4: Filter by pressure and wash with pure water, then dry at 120℃ for 2 hours to obtain dried material;
[0109] S5: The dried material is calcined in air at a temperature of 600℃ for 2 hours at a heating rate of 3℃ / min to obtain the calcined product.
[0110] S6: Add the calcined product to cold water at 0℃ immediately to cool it down, according to the solid-liquid ratio of 1g:1L.
[0111] S7: Filter by pressure and dry at 100℃ for 1 hour to obtain easily grindable low-pressure anhydrous iron phosphate material.
[0112] Example 2
[0113] This embodiment provides an easily grindable, low-pressure anhydrous iron phosphate material, the preparation method of which includes:
[0114] S1: Prepare a starch solution with a mass concentration of 10 g / L and a polyferric chloride solution with a mass percentage of 10%.
[0115] S2: According to the mass ratio of iron in the polyferric chloride solution to starch in the starch solution of 8:1, add the polyferric chloride solution to the starch solution and stir at the first speed (220 rpm) for 1 min. Then add 0.5 mol / L sodium hydroxide solution to adjust the pH value to 7, stir at the second speed (35 rpm) for 12 min, and then let stand for 15 min.
[0116] S3: Heat to 90℃, start stirring, control the stirring speed at 120rpm, keep warm for 3h, and add phosphoric acid and sodium phosphate as buffers during this process to adjust the pH value to 1.8; control the P element content in the mixture of iron hydroxide mixture containing starch particles and the mixture of phosphorus source to be 6g / L.
[0117] S4: Filter by pressure and wash with pure water, then dry at 130℃ for 3 hours to obtain dried material;
[0118] S5: The dried material is calcined in air at a temperature of 650℃ for 3 hours at a heating rate of 4℃ / min to obtain the calcined product.
[0119] S6: Add the calcined product to cold water at 5°C immediately to cool it down, according to a solid-liquid ratio of 10g:1L.
[0120] S7: Filter by pressure and dry at 110℃ for 2 hours to obtain easily grindable low-pressure anhydrous iron phosphate material.
[0121] Example 3
[0122] This embodiment provides an easily grindable, low-pressure anhydrous iron phosphate material, the preparation method of which includes:
[0123] S1: Prepare a starch solution with a mass concentration of 30 g / L and a polyferric sulfate solution with a mass percentage of 15%.
[0124] S2: According to the mass ratio of iron in polyferric sulfate solution to starch in starch solution of 10:1, add polyferric sulfate solution to starch solution and stir at the first speed (300 rpm) for 2 min. Then add 1 mol / L sodium hydroxide solution to adjust the pH value to 7, stir at the second speed (40 rpm) for 15 min, and then let stand for 20 min.
[0125] S3: Heat to 92℃, start stirring, control the stirring speed at 180 rpm, keep warm for 4 hours, and add phosphoric acid and sodium phosphate as buffers during this process to adjust the pH value to 2.0; control the P element content in the mixture of iron hydroxide mixture containing starch particles and the mixture of phosphorus source to be 8 g / L.
[0126] S4: Filter by pressure and wash with pure water, then dry at 140℃ for 4 hours to obtain dried material;
[0127] S5: The dried material is calcined in air at a temperature of 680℃ for 4 hours at a heating rate of 5℃ / min to obtain the calcined product.
[0128] S6: Add the calcined product to cold water at 5°C immediately to cool it down, according to a solid-liquid ratio of 50g:1L.
[0129] S7: Filter by pressure and dry at 120℃ for 3 hours to obtain easily grindable low-pressure anhydrous iron phosphate material.
[0130] Example 4
[0131] This embodiment provides an easily grindable, low-pressure anhydrous iron phosphate material, the preparation method of which includes:
[0132] S1: Prepare a starch solution with a mass concentration of 50 g / L and a polyferric chloride solution with a mass percentage of 20%.
[0133] S2: According to the mass ratio of iron in the polyferric chloride solution to starch in the starch solution of 12:1, add the polyferric chloride solution to the starch solution and stir at the first speed (350 rpm) for 2 min. Then add 2.0 mol / L sodium hydroxide solution to adjust the pH value to 8, stir at the second speed (50 rpm) for 15 min, and then let it stand for 20 min.
[0134] S3: Heat to 95℃, start stirring, control the stirring speed at 300 rpm, keep warm for 5 hours, and add phosphoric acid and sodium phosphate as buffers during this process to adjust the pH value to 2.0; control the P element content in the mixture of ferric hydroxide mixed with starch particles and the mixture of phosphorus source to be 10 g / L.
[0135] S4: Filter by pressure and wash with pure water, then dry at 150℃ for 2 hours to obtain dried material;
[0136] S5: The dried material is calcined in air at a temperature of 600℃ for 4 hours at a heating rate of 5℃ / min to obtain the calcined product.
[0137] S6: Add the calcined product to cold water at 10°C immediately to cool it down, according to a solid-liquid ratio of 100g:1L.
[0138] S7: Filter by pressure and dry at 120℃ for 3 hours to obtain easily grindable low-pressure anhydrous iron phosphate material.
[0139] Example 5
[0140] This embodiment provides an easily grindable, low-pressure anhydrous iron phosphate material, the preparation method of which includes:
[0141] S1: Prepare a starch solution with a mass concentration of 80 g / L and a polyferric sulfate solution with a mass percentage of 25%.
[0142] S2: According to the mass ratio of iron in polyferric sulfate solution to starch in starch solution of 15:1, add polyferric sulfate solution to starch solution and stir at the first speed (400 rpm) for 2 min. Then add 2.0 mol / L sodium hydroxide solution to adjust the pH value to 8, stir at the second speed (50 rpm) for 15 min, and then let stand for 30 min.
[0143] S3: Heat to 95℃, start stirring, control the stirring speed at 300 rpm, keep warm for 6 hours, and add phosphoric acid and sodium phosphate as buffers during this process to adjust the pH value to 2.0; control the P element content in the mixture of iron hydroxide mixture containing starch particles and the mixture of phosphorus source to be 10 g / L.
[0144] S4: Filter by pressure and wash with pure water, then dry at 150℃ for 4 hours to obtain dried material;
[0145] S5: The dried material is calcined in air at a temperature of 750℃ for 5 hours at a heating rate of 5℃ / min to obtain the calcined product.
[0146] S6: Add the calcined product to cold water at 0℃ immediately to cool it down, according to a solid-liquid ratio of 100g:1L.
[0147] S7: Filter by pressure and dry at 120℃ for 3 hours to obtain easily grindable low-pressure anhydrous iron phosphate material.
[0148] Example 6
[0149] This embodiment provides an easily grindable, low-pressure anhydrous iron phosphate material, the preparation method of which includes:
[0150] S1: Prepare a starch solution with a mass concentration of 100 g / L and a polyferric chloride solution with a mass percentage of 30%.
[0151] S2: According to the mass ratio of iron in the polyferric chloride solution to starch in the starch solution of 20:1, add the polyferric chloride solution to the starch solution and stir at the first speed (400 rpm) for 2 min. Then add 2.0 mol / L sodium hydroxide solution to adjust the pH value to 8, stir at the second speed (50 rpm) for 15 min, and then let stand for 30 min.
[0152] S3: Heat to 95℃, start stirring, control the stirring speed at 300 rpm, keep warm for 6 hours, and add phosphoric acid and sodium phosphate as buffers during this process to adjust the pH value to 2.0; control the P element content in the mixture of iron hydroxide mixture containing starch particles and the mixture of phosphorus source to be 8 g / L.
[0153] S4: Filter by pressure and wash with pure water, then dry at 150℃ for 2 hours to obtain dried material;
[0154] S5: The dried material is calcined in an oxygen atmosphere at a temperature of 750℃ for 5 hours at a heating rate of 5℃ / min to obtain the calcined product.
[0155] S6: Add the calcined product to cold water at 5°C immediately to cool it down, according to a solid-liquid ratio of 80g:1L.
[0156] S7: Filter by pressure and dry at 120℃ for 2 hours to obtain easily grindable low-pressure anhydrous iron phosphate material.
[0157] Example 7
[0158] The difference between this embodiment and Embodiment 1 is that in S1, the polyferric sulfate solution is added to the starch solution according to a mass ratio of 2:1 between iron in the polyferric sulfate solution and starch in the starch solution.
[0159] Comparative Example 1
[0160] This comparative example provides a low-pressure anhydrous iron phosphate material, the preparation method of which includes:
[0161] S1: Take equal molar amounts of ferrous sulfate and NaH2PO4, dissolve them in water, and place them in a reaction vessel. The concentration of ferrous ions in the solution in the reaction vessel is 90 g / L.
[0162] S2: Add excess hydrogen peroxide to the reactor. The specific amount of hydrogen peroxide added is 1.2 times the amount of hydrogen peroxide required to completely oxidize ferrous ions to ferric ions.
[0163] S3: Heat the reactor to 90°C, add sodium hydroxide to adjust the pH to 1.8, and keep it at this temperature for 1 hour;
[0164] S4: Solid-liquid separation, washing the precipitate with pure water to obtain filter cake;
[0165] S5: Dry the filter cake at 120℃ for 2 hours to obtain ferric phosphate dihydrate;
[0166] S6: Calcination was carried out in an air atmosphere at a temperature of 600℃ for 2 hours with a heating rate of 3℃ / min to obtain low-pressure anhydrous iron phosphate material.
[0167] Comparative Example 2
[0168] The difference between this comparative example and Comparative Example 1 is:
[0169] S6 and later include:
[0170] S7: Add the calcined product obtained in S6 to cold water at 0℃ immediately according to the solid-liquid ratio of 1g:1L to cool it down;
[0171] S8: Filter under pressure and dry at 100℃ for 1 hour to obtain low-pressure anhydrous iron phosphate material.
[0172] Comparative Example 3
[0173] The difference between this comparative example and Example 1 is that steps S6 and S7 are omitted.
[0174] Comparative Example 4
[0175] The difference between this comparative example and Example 1 is that in S2, the pH value is adjusted to 5.0.
[0176] The comparative example showed poor flocculation, and the starch was not completely precipitated.
[0177] Comparative Example 5
[0178] The difference between this comparative example and Example 1 is that in S3, the pH value is adjusted to 1.0.
[0179] In this comparative example, step S3 failed to yield a precipitate because the pH value was too low during the crystallization process, causing the precipitated iron to redissolve.
[0180] Comparative Example 6
[0181] The difference between this comparative example and Example 1 is that no starch solution was used in the preparation of the low-pressure anhydrous iron phosphate material.
[0182] Comparative Example 7
[0183] The difference between this comparative example and Example 1 is that in S3, the temperature is raised to 80°C.
[0184] In this comparative example, a large amount of ferric hydroxide did not transform into ferric phosphate.
[0185] Experimental Example 1
[0186] The performance of the low-pressure anhydrous iron phosphate materials prepared in Examples 1-7, Comparative Examples 1-4, and Comparative Example 6 was tested, and the results are shown in Table 1.
[0187] (1) P is the average compressive strength of a single anhydrous iron phosphate particle in low-pressure anhydrous iron phosphate material, in MPa. Specifically, the test is conducted according to the standard GB / T 43091-2023 Test Method for Powder Compressive Strength. During the test, three particles are selected and the average value is calculated.
[0188] (2) α is the maximum deformation of the low-pressure anhydrous iron phosphate material during the holding period of 200MPa for 10s, and β is the irreversible deformation of the low-pressure anhydrous iron phosphate material after the pressure is released to 0MPa for 10s after holding at 200MPa for 10s. Both α and β are tested using a compaction density meter. The specific test method is as follows: weigh the sample and record it as m; place it in a cylindrical mold with a bottom diameter of d, apply pressure to 200MPa, test the sample height h1 when holding at 200MPa for 10s, and then release the pressure to 0MPa and hold for 10s to test the sample height h2. In addition, the loose density ρ is tested according to GB / T 31057.1-2014 Physical Properties Test of Granular Materials Part 1: Measurement of Loose Density, and α and β are calculated accordingly.
[0189] α=[1-(h1×0.25π×d 2 ×10 -3 [(m / ρ)]×100%;
[0190] β=[1-(h2×0.25π×d 2 ×10 -3 [(m / ρ)] ×100%;
[0191] Where h1 and h2 are in mm, d is in mm, sample mass m is in g, and ρ is in g / cm³. 3 .
[0192] Test sample of Example 1: m=0.763g, h1=5.583mm, h2=5.985mm, d=13mm, ρ=0.406g / cm 3 ;
[0193] Test sample of Example 2: m=0.999g, h1=6.714mm, h2=7.270mm, d=13mm, ρ=0.468g / cm 3 ;
[0194] Test sample in Example 3: m = 0.932 g, h1 = 6.863 mm, h2 = 7.333 mm, d = 13 mm, ρ = 0.523 g / cm³ 3 ;
[0195] Test sample of Example 4: m = 1.003 g, h1 = 7.014 mm, h2 = 7.495 mm, d = 13 mm, ρ = 0.588 g / cm³ 3 ;
[0196] Test sample of Example 5: m=1.112g, h1=7.131mm, h2=7.568mm, d=13mm, ρ=0.604g / cm3 ;
[0197] Test sample of Example 6: m=1.131g, h1=7.211mm, h2=7.623mm, d=13mm, ρ=0.681g / cm 3 ;
[0198] Test sample of Example 7: m=0.631g, h1=5.092mm, h2=5.617mm, d=13mm, ρ=0.313g / cm 3 ;
[0199] The test sample for Comparative Example 1: m = 1.013 g, h1 = 9.731 mm, h2 = 10.970 mm, d = 13 mm, ρ = 0.58 g / cm³ 3 ;
[0200] The test sample for Comparative Example 2 had the following dimensions: m = 0.986 g, h1 = 9.982 mm, h2 = 11.010 mm, d = 13 mm, and ρ = 0.48 g / cm³. 3 ;
[0201] The test sample for Comparative Example 3 had the following dimensions: m = 1.25 g, h1 = 9.640 mm, h2 = 11.122 mm, d = 13 mm, and ρ = 0.71 g / cm³. 3 ;
[0202] The test sample for Comparative Example 4: m = 1.15 g, h1 = 9.011 mm, h2 = 9.980 mm, d = 13 mm, ρ = 0.69 g / cm³ 3 ;
[0203] The test sample for Comparative Example 6: m = 1.02 g, h1 = 8.890 mm, h2 = 9.732 mm, d = 13 mm, ρ = 0.61 g / cm³ 3 .
[0204] The corresponding results are shown in Table 1.
[0205] (3) The grinding strength M is calculated according to M=P(α-β) / β, and the unit of M is MPa.
[0206] Table 1 Test Results
[0207]
[0208] As can be seen from Table 1, the grinding strength of the low-pressure anhydrous ferric phosphate materials provided in Examples 1-7 of the present invention is significantly lower than that of Comparative Examples 1-4 and Comparative Example 6. Compared with the anhydrous ferric phosphate materials provided in Comparative Examples 1-4 and Comparative Example 6, the low-pressure anhydrous ferric phosphate materials provided in Examples 1-7 of the present invention cause less wear and tear on the grinding machine, and are beneficial to shortening the processing time and improving the grinding efficiency.
[0209] A comparison of Example 1 and Comparative Examples 1-4 and Comparative Example 6 shows that when the preparation method or conditions for anhydrous ferric phosphate are inappropriate, the α, β, and P of the anhydrous ferric phosphate will differ, ultimately leading to different values of M. Based on the results of M, it is demonstrated that the preparation method and conditions provided by this invention can effectively prepare low-pressure anhydrous ferric phosphate materials with low grinding strength.
[0210] In summary, the low-pressure anhydrous iron phosphate material provided by this invention has low grinding strength, which is beneficial for subsequent grinding processes during lithium iron phosphate synthesis. Furthermore, it causes less wear and tear on grinding machines, shortening processing time, improving grinding efficiency, and reducing energy costs. The preparation method of this low-pressure anhydrous iron phosphate material is simple, easy to operate, and suitable for industrial production. This low-pressure anhydrous iron phosphate material can be further used in the preparation of lithium iron phosphate and lithium-ion batteries.
[0211] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A low-pressure anhydrous iron phosphate material, characterized in that, The grinding strength M of the low-pressure anhydrous iron phosphate material is ≤2.8 MPa; Where M = P(α-β) / β, P is the average compressive strength of a single anhydrous iron phosphate particle in the low-pressure anhydrous iron phosphate material, in MPa; α is the maximum deformation of the low-pressure anhydrous iron phosphate material during the process of holding pressure at 200 MPa for 10s; and β is the irreversible deformation of the low-pressure anhydrous iron phosphate material after holding pressure at 200 MPa for 10s and then depressurizing to 0 MPa and holding pressure for 10s. 10MPa≤P≤50MPa; 40%≤α≤70%; 35%≤β≤65%; 2%≤α-β≤5%.
2. The low-pressure anhydrous iron phosphate material according to claim 1, characterized in that, The low-pressure anhydrous iron phosphate material also includes at least one of the following characteristics: Feature 1: 0.9MPa≤M≤2.8MPa; Feature 2: The iron-to-phosphorus ratio is 0.96~1.
02.
3. A method for preparing a low-pressure anhydrous iron phosphate material as described in claim 1 or 2, characterized in that, The process includes the following steps: flocculating and precipitating an iron solution with a starch solution to obtain an iron hydroxide mixture containing starch particles; The temperature was then raised, and a phosphorus source was added during the heat preservation process to induce crystallization. Subsequently, solid-liquid separation was performed, and the separated solid was washed and dried to obtain a dried material. The dried material is calcined. After calcination, the calcined product is immediately cooled in water. The cooled material is then subjected to solid-liquid separation, and the solid obtained from the solid-liquid separation is dried.
4. The preparation method according to claim 3, characterized in that, The ferric hydroxide mixture used to prepare the starch-mixed granules includes at least one of the following characteristics: Feature 3: The mass ratio of iron in the iron solution to starch in the starch solution is 2:1 to 20:1; Feature 4: The mass percentage of solute in the iron solution is 5%~30%; Feature 5: The iron solution includes polyferric sulfate solution or polyferric chloride solution; Feature 6: The concentration of the starch solution is 1 g / L to 100 g / L; Feature 7: Flocculation and sedimentation of iron solution and starch solution includes: adding the iron solution to the starch solution, stirring at a first rate, then adding a pH adjuster to adjust the pH value to 6-8, and stirring at a second rate.
5. The preparation method according to claim 4, characterized in that, The first stirring rate is 200 rpm to 400 rpm, and / or, stirring at the first rate for 1 min to 2 min.
6. The preparation method according to claim 4, characterized in that, The second stirring rate is 30 rpm to 50 rpm, and / or, stirring at the second rate for 10 min to 15 min.
7. The preparation method according to claim 4, characterized in that, The pH adjuster includes a sodium hydroxide solution.
8. The preparation method according to claim 7, characterized in that, The concentration of the sodium hydroxide solution is 0.1 mol / L to 2.0 mol / L.
9. The preparation method according to claim 3, characterized in that, Heat to 88℃~95℃; And / or, the heat preservation time is 2h~6h.
10. The preparation method according to claim 3, characterized in that, Crystallization was carried out under conditions of pH 1.5–2.0; And / or, the phosphorus source includes at least one of phosphoric acid and phosphate.
11. The preparation method according to claim 3, characterized in that, The phosphorus content in the mixture of iron hydroxide containing starch granules and the phosphorus source is 3 g / L to 10 g / L.
12. The preparation method according to claim 3, characterized in that, Calcination includes at least one of the following characteristics: Feature 8: Calcination temperature is 600℃~750℃; Feature 9: Calcination time is 2h~5h; Feature 10: The heating rate during calcination is 3℃ / min~5℃ / min; Feature 11: Calcination is carried out in an air or oxygen atmosphere.
13. The preparation method according to claim 3, characterized in that, During the cooling process, the solid-liquid ratio of the calcined product to the water is from 1g:1L to 100g:1L; And / or, the temperature of the water used for cooling is 0℃~10℃.
14. A lithium iron phosphate cathode material, characterized in that, The raw materials for preparing the lithium iron phosphate cathode material include the grinding material obtained by grinding the low-pressure anhydrous iron phosphate material as described in claim 1 or 2.
15. The lithium iron phosphate cathode material according to claim 14, characterized in that, The D of the abrasive 50 The range is 5μm to 20μm.
16. A battery, characterized in that, The battery comprises the lithium iron phosphate cathode material as described in claim 14 or 15.