Anhydrous ferric phosphate and a method for its preparation

Abstract

This application discloses anhydrous iron phosphate and its preparation method, belonging to the field of battery technology. The anhydrous iron phosphate provided in this application comprises secondary particles formed by the stacking of multiple primary nanoparticles. The average particle size of the primary particles forming the secondary particles is 100-150 nm, and the particle size variance Q ≤ 1000 nm. 2 The primary particles provided in this application have small particle size and good uniformity, which can improve the grinding efficiency of anhydrous iron phosphate. Lithium iron phosphate prepared using this as a precursor has a porous structure, increasing the contact area between the electrolyte and the cathode material, and exhibiting good wettability.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more specifically, to anhydrous iron phosphate and its preparation method. Background Technology

[0002] Lithium iron phosphate (LFP) is one of the most competitive cathode active materials for lithium-ion batteries currently on the market. Compared with lithium cobalt oxide and ternary cathode materials, it has a longer lifespan and better safety performance. Furthermore, LFP has a 170mAh / g capacity. -1 With its theoretical specific capacity and a plateau discharge voltage of 3.4V, lithium iron phosphate exhibits considerable energy density. Currently, most processes for preparing lithium iron phosphate employ a solid-state method, sintering anhydrous iron phosphate with lithium salts. Anhydrous iron phosphate requires grinding before sintering, and the grinding efficiency is related to the state of the anhydrous iron phosphate powder. Improving grinding efficiency can save energy and increase production capacity.

[0003] Therefore, anhydrous iron phosphate is provided that is easy to grind and can improve grinding efficiency. Summary of the Invention

[0004] The purpose of this application is to overcome the defects of the prior art and provide anhydrous ferric phosphate and its preparation method.

[0005] The technical problem solved by this application is achieved by the following technical solution.

[0006] This application provides anhydrous ferric phosphate, which comprises secondary particles formed by the stacking of multiple primary nanoparticles. The average particle size of the primary particles forming the secondary particles is 100-150 nm, and the particle size variance Q ≤ 1000 nm. 2 .

[0007] This application also provides a method for preparing anhydrous ferric phosphate, comprising: mixing an amorphous ferric phosphate solution with phosphoric acid and ammonium salt to obtain a mixture, then heating the mixture and keeping it at a constant temperature, and then washing, drying and calcining to obtain the product anhydrous ferric phosphate.

[0008] This application also provides a lithium iron phosphate cathode material, which is made from raw materials containing anhydrous iron phosphate, wherein the anhydrous iron phosphate is anhydrous iron phosphate prepared according to the above preparation method.

[0009] This application also provides a lithium-ion battery, which includes a positive electrode, a negative electrode, a separator, and an electrolyte made of the aforementioned lithium iron phosphate positive electrode material.

[0010] This application has the following beneficial effects:

[0011] This application provides anhydrous ferric phosphate and its preparation method. The provided anhydrous ferric phosphate comprises secondary particles formed by the stacking of multiple primary nanoparticles. The average particle size of the primary particles forming the secondary particles is 100-150 nm, and the particle size variance Q ≤ 1000 nm. 2 The anhydrous iron phosphate described above has the characteristics of small and uniform primary particle size and high uniformity of secondary particle pore distribution. Grinding anhydrous iron phosphate with the above characteristics results in high grinding efficiency, which can save energy, increase production capacity and reduce costs, and is more conducive to its use in the preparation of lithium iron phosphate. Attached Figure Description

[0012] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 This is a SEM image of the anhydrous ferric phosphate prepared in Example 1 of this application;

[0014] Figure 2 A cross-sectional electron microscope image (scale bar: 5 μm) of anhydrous ferric phosphate prepared in Example 1 of this application;

[0015] Figure 3 This is a SEM image of anhydrous ferric phosphate prepared in Example 2 of this application;

[0016] Figure 4 This is a SEM image of the anhydrous ferric phosphate prepared in Example 3 of this application;

[0017] Figure 5 The image shows an anhydrous ferric phosphate prepared in Comparative Example 1 of this application.

[0018] Figure 6 A cross-sectional electron microscope image (scale bar: 5 μm) of anhydrous ferric phosphate prepared in Comparative Example 1 of this application;

[0019] Figure 7 The image shows anhydrous ferric phosphate prepared in Comparative Example 2 of this application.

[0020] Figure 8 This is a SEM image of anhydrous ferric phosphate prepared in Comparative Example 3 of this application.

[0021] Figure 9 This is a SEM image of anhydrous ferric phosphate prepared in Comparative Example 4 of this application.

[0022] Figure 10 This is a SEM image of the anhydrous ferric phosphate prepared in Comparative Example 5 of this application. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in this application 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.

[0024] The following is a detailed description of anhydrous ferric phosphate and its preparation method provided in this application.

[0025] In a first aspect, this application provides anhydrous ferric phosphate, which comprises secondary particles formed by the stacking of multiple primary nanoparticles. The average particle size of the primary particles forming the secondary particles is 100-150 nm, and the particle size variance Q ≤ 1000 nm. 2 .

[0026] In an optional embodiment, the average particle size of the primary particles forming the secondary particles is 110-130 nm, and / or the particle size variance Q ≤ 300 nm. 2 .

[0027] In an optional embodiment, the overall porosity of the secondary particles in the cross-section is 10%-30%, and the cross-sectional porosity uniformity coefficient R≤5;

[0028] In an optional embodiment, the overall porosity of the secondary particles in the cross-section is 20%-30%, and / or the cross-sectional porosity uniformity coefficient R ≤ 2.

[0029] In an optional implementation, anhydrous ferric phosphate satisfies one or more of the following conditions A to C:

[0030] A. The Fe / P molar ratio in anhydrous ferric phosphate is 0.96-0.98;

[0031] B. The specific surface area (BET) of anhydrous ferric phosphate is 10⁻¹⁴ m². 2 / g;

[0032] C. The tap density (TD) of anhydrous ferric phosphate is 0.6-0.8 g / cm³. 3 .

[0033] The following describes the test methods and results for the primary particle size and particle size variance, cross-sectional porosity and cross-sectional porosity uniformity coefficient, Fe / P ratio, specific surface area (BET), and tap density (TD) of the anhydrous iron phosphate provided in this application.

[0034] (1) Method for measuring the particle size of primary particles: Select primary particles with clear boundaries in SEM images with x10000 or higher and a resolution of 1280x9180 or higher for particle size measurement. Randomly select n primary particles in each SEM image for particle size measurement. The average value of the particle size of 3n (3n≥50, preferably 50-200) primary particles in three SEM images is taken as the average particle size of primary particles, also known as the average particle size of primary particles.

[0035] The average particle size q = (q1 + q2 + ... + q 3n ) / 3n

[0036] q: The average particle size of 3n primary particles, in nm, where 3n ≥ 50. In optional embodiments, 3n is 50-200. q1...q 3n These represent the particle sizes of 3n randomly selected particles.

[0037] The test results of the primary particle size of anhydrous ferric phosphate obtained in this application are as follows: Anhydrous ferric phosphate includes secondary particles formed by the stacking of multiple primary nanoparticles. The average particle size of the primary particles forming the secondary particles is 100-150 nm. In an optional embodiment, the average particle size of the primary particles forming the secondary particles is 110-130 nm.

[0038] Optionally, the average particle size of the primary particles forming the secondary particles can be any value between 100 nm, 105 nm, 110 nm, 115 nm, 120 nm, 127 nm, 132 nm, 140 nm, 145 nm, 150 nm or 100-150 nm.

[0039] Method for measuring the uniformity of primary particles: The uniformity of primary particles is evaluated by the particle size variance. The variance of the particle size of 3n primary particles is calculated by comparing the particle size with the mean, and the particle size variance Q of the primary particles is obtained. The calculation formula is as follows:

[0040] Q = (|q - q1|) 2 +|q-q2| 2 +……+|qq 3n | 2 ) / 3n,(q1...q 3n The unit of q is nm, and according to the formula above, the unit of Q is nm. 2 );

[0041] The primary particle size variance Q of the anhydrous ferric phosphate prepared in this application is ≤1000 nm. 2 In an optional embodiment, the particle size variance Q of the primary particles in anhydrous ferric phosphate is ≤300 nm. 2In an optional embodiment, the particle size variance Q of the primary particles in anhydrous ferric phosphate is ≤150 nm. 2 The results show that Q ≤ 1000 nm 2 At that time, the particle uniformity was good, Q > 1000 nm 2 At that time, the consistency of particles was poor.

[0042] Optionally, the particle size variance of the primary particles forming the secondary particles can be 1000 nm. 2 950nm 2 900nm 2 800nm 2 700nm 2 600nm 2 500nm 2 400nm 2 200nm 2 100nm 2 50nm 2 Or ≤1000nm 2 Any value between.

[0043] (2) Method for measuring overall porosity of the cross-section: The total cross-sectional area is selected as the area where more than 80% of the secondary particles are located. The porosity of the total cross-sectional area is measured as the cross-sectional porosity. The selection of the total cross-sectional area is referenced below. Figure 2 Irregular or regular shapes are drawn inside the secondary particles along the boundaries of the secondary particles. The area occupied by the irregular or regular shapes is more than 80% of the cross-sectional area of ​​the secondary particles.

[0044] The overall porosity of the cross-section of the anhydrous ferric phosphate secondary particles obtained in this application is 10%-30%; in an optional embodiment, the overall porosity of the cross-section of the anhydrous ferric phosphate secondary particles is 20%-30%; in an optional embodiment, the overall porosity of the cross-section of the anhydrous ferric phosphate secondary particles is 24%-26%.

[0045] Optionally, the overall porosity of the profile of the anhydrous iron phosphate secondary particles is any value between 10%, 12%, 15%, 18%, 20%, 24%, 26%, 27%, 28%, 30%, or 10%-30%.

[0046] Method for measuring the uniformity coefficient of cross-sectional porosity: Select local areas with equal cross-sectional areas in the upper left, upper right, middle, lower left, and lower right corners. Figure 2 The location and area of ​​the local region shown are selected in one embodiment below, with the area of ​​the local region accounting for 10% of the total cross-sectional area. The area and pore area of ​​the local region are measured, and the porosity of the local region is calculated. The uniformity of the cross-sectional pores is evaluated using the following formula:

[0047] R = (|r - r1|) 2 +|r-r2| 2 +|r-r3| 2 +|r-r4| 2 +|r-r5| 2 ) / 5

[0048] r: Overall porosity on the secondary particle profile, r1, r2, r3, r4, and r5 are the porosities of local regions (upper left, upper right, middle, lower left, and lower right) on the profile, respectively.

[0049] The test results of the cross-sectional pore uniformity coefficient of the anhydrous ferric phosphate secondary particles obtained in this application are: R≤5; in an optional embodiment, the cross-sectional pore uniformity coefficient R≤2; in an optional embodiment, the cross-sectional pore uniformity coefficient ≤0.5. When R≤5, the pore distribution uniformity is good; when R>5, the pore distribution uniformity is poor.

[0050] Optionally, the uniformity coefficient R of the cross-sectional pores of anhydrous ferric phosphate secondary particles can be any value between 5, 4.5, 4, 3.5, 3, 2.5, 2, 1.5, 1, 0.5, 0.3, 0.1 or ≤5.

[0051] (3) The grinding process of secondary particles in the preparation of lithium iron phosphate is as follows: wet grinding solvent is added to anhydrous iron phosphate to form anhydrous iron phosphate slurry. The slurry is ball-milled using a Langling sand mill at a speed of 2200 rpm / min. A portion of the slurry is then taken at a temperature of 23.5±3℃ to test D10, D50, and D90. Wherein, Span=(D90-D10) / D50.

[0052] The anhydrous ferric phosphate prepared according to this application has small and uniform primary particles with high pore uniformity, which can improve the grinding efficiency of anhydrous ferric phosphate. The technical principle is as follows: the small particle size of the primary particles of anhydrous ferric phosphate is beneficial for grinding. When the particle size of the primary particles of anhydrous ferric phosphate is small and has good uniformity, the grinding efficiency of anhydrous ferric phosphate can be improved. If the cross-sectional porosity is too small, the primary particles in the secondary particles grow more densely, resulting in low grinding efficiency; if the cross-sectional porosity is too high, the tap density of anhydrous ferric phosphate is low. The smaller the cross-sectional porosity uniformity coefficient, the more uniform the pore distribution in the secondary particles; the larger the cross-sectional porosity uniformity coefficient, the more uneven the pore distribution in the secondary particles, and the grinding efficiency of anhydrous ferric phosphate with uneven pore distribution is reduced. Under the condition of ensuring a certain tap density, improving the porosity and pore distribution uniformity can improve the grinding efficiency. The grinding results are as follows: when the anhydrous ferric phosphate is ground to a D50 of 380nm, it only takes 80 minutes, which is shorter and the grinding efficiency is doubled; under the same grinding time, the anhydrous ferric phosphate has a smaller D50 and a narrower span value.

[0053] (4) The Fe / P molar ratio of anhydrous ferric phosphate is 0.96-0.98, and the specific surface area (BET) is 10-14 m². 2 / g, tap density TD is 0.6-0.8g / cm³ 3 .

[0054] Optionally, the Fe / P molar ratio of anhydrous ferric phosphate can be any value between 0.96, 0.963, 0.965, 0.968, 0.98, or 0.96-0.98, and the specific surface area BET can be 10 m². 2 / g、11m 2 / g、12m 2 / g、13m 2 / g、14m 2 / g or 10-14m 2 For any value between / g, the tap density TD is 0.6 g / cm³. 3 0.65g / cm 3 0.7g / cm 3 0.75g / cm 3 0.8g / cm 3 Or 0.6-0.8 g / cm³ 3 Any value between.

[0055] Secondly, this application also provides a method for preparing the above-mentioned anhydrous ferric phosphate, comprising: mixing an amorphous ferric phosphate solution with phosphoric acid and ammonium salt to obtain a mixture, then heating the mixture and keeping it at a constant temperature, and then washing, drying and calcining to obtain the product anhydrous ferric phosphate.

[0056] In the preparation process of anhydrous ferric phosphate described above, amorphous ferric phosphate is converted into crystalline ferric phosphate through crystal transformation. The crystalline ferric phosphate is then washed and dehydrated to obtain anhydrous ferric phosphate. Specifically, under heating conditions, the amorphous ferric phosphate solution is converted into crystalline ferric phosphate under acidic conditions. During this crystal transformation process, ammonium ions effectively prevent the agglomeration of ferric phosphate particles. After being kept at a constant temperature and allowed to stand, the crystalline ferric phosphate is washed to remove impurities and dehydrated to obtain anhydrous ferric phosphate with a narrow primary particle size distribution.

[0057] In an optional embodiment, the amount of phosphoric acid in the mixed slurry is 10%-20% of the molar amount of iron, and the amount of ammonium salt is 80%-120% of the molar amount of iron.

[0058] Optionally, the amount of phosphoric acid in the mixed slurry can be any value between 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20% or 10%-20% of the iron molar amount, and the amount of ammonium salt can be any value between 80%, 85%, 90%, 95%, 100%, 105%, 110%, 115%, 120% or 80%-120% of the iron molar amount.

[0059] The method for preparing anhydrous ferric phosphate provided in this application involves adding phosphoric acid and ammonium salt to an amorphous ferric phosphate slurry. Appropriate amounts of phosphoric acid and ammonium salt can promote the crystal transformation of amorphous ferric phosphate and control the crystal form after transformation, resulting in anhydrous ferric phosphate with good primary particle uniformity and narrow particle size distribution, and secondary particles with high porosity. However, if the phosphoric acid content is not within the range of 10%-20% or the ammonium salt content is not within the range of 80%-120%, the primary particle uniformity of the prepared anhydrous ferric phosphate is poor. Without the use of ammonium salt, the primary particle size of the prepared anhydrous ferric phosphate is large, and the primary particle uniformity is very poor.

[0060] In an optional implementation, the following steps are included:

[0061] A phosphate solution containing hydrogen peroxide is added dropwise to a ferrous salt solution to obtain an amorphous ferric phosphate slurry. The amorphous ferric phosphate slurry is then subjected to a single pressure filtration and rinsing to obtain the material after the first rinsing.

[0062] The material after the first rinse is slurried with water, and then phosphate and ammonium salts are added to obtain a mixed slurry. The mixed slurry is then heated and kept at a constant temperature and allowed to stand. After a second pressure filtration and rinsing, the material after the second rinse is obtained.

[0063] The material after the second rinse is then dried and calcined to obtain anhydrous ferric phosphate.

[0064] In optional embodiments, the ammonium salt includes one or more of ammonium sulfate, ammonium phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate. Generally, sulfuric acid solution is added to ammonium salts other than ammonium sulfate.

[0065] In an optional implementation, the holding time is 10-150 minutes. It is worth noting that after the mixed slurry is stirred evenly and heated to 95-100°C, a color change is usually observed. After the solution changes color, holding it at this temperature for a period of time can form ferric phosphate with higher crystallinity.

[0066] Optionally, after the mixed slurry is stirred evenly, the heating temperature can be any value between 95℃, 96℃, 97℃, 98℃, 99℃, 100℃ or 95-100℃, and the holding time can be any value between 10min, 20min, 30min, 40min, 50min, 60min, 70min, 80min, 90min, 100min, 110min, 120min, 130min, 140min, 150min or 10-150min.

[0067] In an optional embodiment, the material after the second rinse is dried at 100-200°C and then calcined at 550-800°C for 4-8 hours to obtain anhydrous ferric phosphate.

[0068] Optionally, the drying temperature of the material after the second rinse can be any value between 100℃, 105℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃ or 100-200℃, the calcination temperature can be any value between 550℃, 600℃, 650℃, 700℃, 750℃, 800℃ or 550-800℃, and the calcination time can be any value between 4h, 5h, 6h, 7h, 8h or 4h-8h.

[0069] In an optional embodiment of this application, the preparation of amorphous ferric phosphate slurry includes: adding a ferrous salt solution to a reaction vessel, then simultaneously adding a phosphate solution and hydrogen peroxide, and continuing aging after the addition is completed to obtain amorphous ferric phosphate slurry.

[0070] In an optional embodiment, the preparation of the ferrous salt solution includes: dissolving ferrous sulfate, a byproduct of titanium dioxide, in water, heating to 60-80°C, adding alkali to adjust the pH to 4.0-5.5, filtering to remove impurities and precipitates, collecting the filtrate and diluting it with water to obtain a ferrous salt solution with a concentration of 30-80 g / L.

[0071] Optionally, ferrous sulfate, a byproduct of titanium dioxide production, is dissolved in water. The heating temperature can be any value between 60°C, 65°C, 70°C, 75°C, 80°C, or 60-80°C. Then, alkali is added to adjust the pH value to any value between 4.0, 4.3, 4.5, 4.8, 5.0, 5.3, 5.5, or 4.0-5.5.

[0072] In an optional embodiment, the preparation of the phosphate solution includes: dissolving the phosphate in water, adjusting the pH to 6.0-8.0 with alkali, and then diluting it with water at a temperature of 30-50°C to a phosphate concentration of 60-100 g / L to obtain the phosphate solution.

[0073] Optionally, during the phosphate preparation process, the pH value can be adjusted by adding alkali to any value between 6.0, 6.5, 6.7, 7.0, 7.3, 7.5, 7.8, 8.0, or 6.0-8.0; the heating temperature can be any value between 30℃, 35℃, 40℃, 45℃, 50℃, or 30-50℃; and the phosphate concentration can be any value between 60g / L, 70g / L, 80g / L, 90g / L, 100g / L, or 60-100g / L.

[0074] The method for preparing anhydrous ferric phosphate provided in this application involves preparing an amorphous ferric phosphate slurry by adding a phosphate solution containing hydrogen peroxide dropwise to a ferrous salt solution for reaction. The ferrous salt raw material is ferrous sulfate, a byproduct of titanium dioxide production. Since the titanium dioxide byproduct contains impurities such as titanium and aluminum, dissolving the byproduct in water and adjusting the pH precipitates these impurities, followed by filtration to obtain a pure ferrous salt solution. In preparing the phosphate solution, the phosphate is dissolved in water, and then an alkali is added to adjust the pH. The alkali in the phosphate solution facilitates the subsequent binding of iron ions and phosphate ions, thereby obtaining pure amorphous ferric phosphate with a high iron-to-phosphorus ratio.

[0075] Thirdly, this application also provides a lithium iron phosphate cathode material, which is made from raw materials containing anhydrous iron phosphate, wherein the anhydrous iron phosphate is anhydrous iron phosphate prepared according to the above preparation method.

[0076] Fourthly, this application also provides a lithium-ion battery, which includes a positive electrode, a negative electrode, a separator, and an electrolyte made of the aforementioned lithium iron phosphate positive electrode material.

[0077] As can be seen from the above, the anhydrous iron phosphate prepared in this application has the advantages of small and uniform primary particle size and uniform pore distribution. When the above-mentioned anhydrous iron phosphate is sintered with lithium salt, it is more conducive to the entry of lithium ions, and the lithiation effect of lithium iron phosphate is better. The lithium iron phosphate prepared with it as a precursor has a porous structure, which increases the contact area between the electrolyte and the positive electrode material and has good wettability. Good electrolyte wetting can give full play to the performance of lithium-ion batteries and improve the performance of lithium-ion batteries.

[0078] The features and performance of this application will be further described in detail below with reference to the embodiments.

[0079] Example 1

[0080] This embodiment provides a method for preparing anhydrous ferric phosphate.

[0081] Step 1: Dissolve ferrous sulfate, a byproduct of titanium dioxide, in water, heat to 70°C, add alkali to adjust the pH to 5.0, filter to obtain solution A, and set aside.

[0082] Step 2: Dilute solution A obtained in step 1 with water to obtain a ferrous solution (reaction solution A) with a concentration of 55 g / L;

[0083] Step 3: Dissolve the phosphate in water, add alkali to adjust the pH to 6.8, and obtain solution B;

[0084] Step 4: Dilute solution B obtained in step 3 with water to a phosphorus concentration of 80 g / L and at a temperature of 35°C to obtain reaction solution B;

[0085] Step 5: Add reaction solution A to the reaction vessel, and then simultaneously add reaction solution B and hydrogen peroxide. After the addition is completed, continue aging for 50 minutes to obtain amorphous iron phosphate slurry.

[0086] Step 6: Press and filter the amorphous ferric phosphate slurry to obtain the material after the first rinse;

[0087] Step 7: In the aging kettle, add water to slurry the material after the first rinse, and add phosphoric acid with a molar amount of 15% iron and ammonium sulfate with a molar amount of 100%.

[0088] Step 8: After the material in the aging kettle is stirred evenly, the temperature is raised to 95-100℃. After the color changes, the temperature is kept for a period of time, and then the material is filtered and rinsed to obtain the second rinsed material.

[0089] Step 9: The material after the second rinse is dried to obtain ferric phosphate dihydrate, which is then calcined to obtain... Figure 1 , Figure 2 Anhydrous ferric phosphate.

[0090] Example 2

[0091] This embodiment provides a method for preparing anhydrous ferric phosphate. Unlike Example 1, the amounts of phosphoric acid and ammonium sulfate added in the aging process of Example 2 are different.

[0092] Step 1: Dissolve ferrous sulfate, a byproduct of titanium dioxide, in water, heat to 70°C, add alkali to adjust the pH to 5.0, filter to obtain solution A, and set aside.

[0093] Step 2: Dilute solution A obtained in step 1 with water to obtain a ferrous solution (reaction solution A) with a concentration of 55 g / L;

[0094] Step 3: Dissolve the phosphate in water, add alkali to adjust the pH to 6.8, and obtain reaction solution B;

[0095] Step 4: Dilute solution B obtained in step 3 with water to a phosphorus concentration of 80 g / L and at a temperature of 35°C to obtain reaction solution B;

[0096] Step 5: Add reaction solution A to the reaction vessel, and then simultaneously add reaction solution B and hydrogen peroxide. After the addition is completed, continue aging for 50 minutes to obtain amorphous iron phosphate slurry.

[0097] Step 6: Press and filter the amorphous ferric phosphate slurry to obtain the material after the first rinse;

[0098] Step 7: In the aging kettle, add water to slurry the material after the first rinse, and add 20% phosphoric acid and 120% ammonium sulfate by iron molar amount;

[0099] Step 8: After the material in the aging kettle is stirred evenly, the temperature is raised to 95-100℃. After the color changes, the temperature is kept for a period of time, and then the material is filtered and rinsed to obtain the second rinsed material.

[0100] Step 9: The material after the second rinse is dried to obtain ferric phosphate dihydrate, which is then calcined to obtain anhydrous ferric phosphate.

[0101] Example 3

[0102] This embodiment provides a method for preparing anhydrous ferric phosphate. Unlike Example 1, the amounts of phosphoric acid and ammonium sulfate added in the aging process of Example 3 are different.

[0103] Step 1: Dissolve ferrous sulfate, a byproduct of titanium dioxide, in water, heat to 70°C, add alkali to adjust the pH to 5.0, filter to obtain solution A, and set aside.

[0104] Step 2: Dilute solution A obtained in step 1 with water to obtain a ferrous solution (reaction solution A) with a concentration of 55 g / L;

[0105] Step 3: Dissolve the phosphate in water, add alkali to adjust the pH to 6.8, and obtain solution B;

[0106] Step 4: Dilute solution B obtained in step 3 with water to a phosphorus concentration of 80 g / L and at a temperature of 35°C to obtain reaction solution B;

[0107] Step 5: Add reaction solution A to the reaction vessel, and then simultaneously add reaction solution B and hydrogen peroxide. After the addition is completed, continue aging for 50 minutes to obtain amorphous iron phosphate slurry.

[0108] Step 6: Press and filter the amorphous ferric phosphate slurry to obtain the material after the first rinse;

[0109] Step 7: In the aging kettle, add water to slurry the material after the first rinse, and add 10% phosphoric acid and 80% ammonium sulfate by iron molar amount;

[0110] Step 8: After the material in the aging kettle is stirred evenly, the temperature is raised to 95-100℃. After the color changes, the temperature is kept for a period of time, and then the material is filtered and rinsed to obtain the second rinsed material.

[0111] Step 9: The material after the second rinse is dried to obtain ferric phosphate dihydrate, which is then calcined to obtain anhydrous ferric phosphate.

[0112] Comparative Example 1

[0113] This comparative example provides a method for preparing anhydrous ferric phosphate. Unlike Example 1, the aging process in Comparative Example 1 only involves the addition of phosphoric acid.

[0114] Step 1: Dissolve ferrous sulfate, a byproduct of titanium dioxide, in water, heat to 70°C, add alkali to adjust the pH to 5.0, filter to obtain solution A, and set aside.

[0115] Step 2: Dilute solution A obtained in step 1 with water to obtain a ferrous solution (reaction solution A) with a concentration of 55 g / L;

[0116] Step 3: Dissolve the phosphate in water, add alkali to adjust the pH to 6.8, and obtain solution B;

[0117] Step 4: Dilute solution B obtained in step 3 with water to a phosphorus concentration of 80 g / L and at a temperature of 35°C to obtain reaction solution B;

[0118] Step 5: Add reaction solution A to the reaction vessel, and then simultaneously add reaction solution B and hydrogen peroxide. After the addition is completed, continue aging for 50 minutes to obtain amorphous iron phosphate slurry.

[0119] Step 6: Press and filter the amorphous ferric phosphate slurry to obtain the material after the first rinse;

[0120] Step 7: Add water to the material after the first rinse in the aging kettle to slurry it, and add phosphoric acid with a molar amount of 15% iron.

[0121] Step 8: After the material in the aging kettle changes color, the temperature is raised to 95-100℃ and then kept at that temperature for a period of time. After that, it is filtered and rinsed to obtain the second rinsed material.

[0122] Step 9: The material after the second rinse is dried to obtain ferric phosphate dihydrate, which is then calcined to obtain anhydrous ferric phosphate.

[0123] Comparative Example 2

[0124] This comparative example provides a method for preparing anhydrous ferric phosphate. Unlike Example 1, in Comparative Example 2, the amount of ammonium sulfate added during the aging process is different.

[0125] Step 1: Dissolve ferrous sulfate, a byproduct of titanium dioxide, in water, heat to 70°C, add alkali to adjust the pH to 5.0, filter to obtain solution A, and set aside.

[0126] Step 2: Dilute solution A obtained in step 1 with water to obtain a ferrous solution (reaction solution A) with a concentration of 55 g / L;

[0127] Step 3: Dissolve the phosphate in water, add alkali to adjust the pH to 6.8, and obtain solution B;

[0128] Step 4: Dilute solution B obtained in step 3 with water to a phosphorus concentration of 80 g / L and at a temperature of 35°C to obtain reaction solution B;

[0129] Step 5: Add reaction solution A to the reaction vessel, and then simultaneously add reaction solution B and hydrogen peroxide. After the addition is completed, continue aging for 50 minutes to obtain amorphous iron phosphate slurry.

[0130] Step 6: Press and filter the amorphous ferric phosphate slurry to obtain the material after the first rinse;

[0131] Step 7: In the aging kettle, add water to slurry the material after the first rinse, and add 15% phosphoric acid and 60% ammonium sulfate by iron molar amount;

[0132] Step 8: After the material in the aging kettle is stirred evenly, the temperature is raised to 95-100℃. After the color changes, the temperature is kept for a period of time, and then the material is filtered and rinsed to obtain the second rinsed material.

[0133] Step 9: The material after the second rinse is dried to obtain ferric phosphate containing dihydrate, which is then calcined to obtain anhydrous ferric phosphate.

[0134] Comparative Example 3

[0135] This comparative example provides a method for preparing anhydrous ferric phosphate. Unlike Example 1, in Comparative Example 3, the amount of ammonium sulfate added during the aging process is different.

[0136] Step 1: Dissolve ferrous sulfate, a byproduct of titanium dioxide, in water, heat to 70°C, add alkali to adjust the pH to 5.0, filter to obtain solution A, and set aside.

[0137] Step 2: Dilute solution A obtained in step 1 with water to obtain a ferrous solution (reaction solution A) with a concentration of 55 g / L;

[0138] Step 3: Dissolve the phosphate in water, add alkali to adjust the pH to 6.8, and obtain solution B;

[0139] Step 4: Dilute solution B obtained in step 3 with water to a phosphorus concentration of 80 g / L and at a temperature of 35°C to obtain reaction solution B;

[0140] Step 5: Add reaction solution A to the reaction vessel, and then simultaneously add reaction solution B and hydrogen peroxide. After the addition is completed, continue aging for 50 minutes to obtain amorphous iron phosphate slurry.

[0141] Step 6: Press and filter the amorphous ferric phosphate slurry to obtain the material after the first rinse;

[0142] Step 7: In the aging kettle, add water to slurry the material after the first rinse, and add 15% phosphoric acid and 150% ammonium sulfate by iron molar amount;

[0143] Step 8: After the material in the aging kettle is stirred evenly, the temperature is raised to 95-100℃. After the color changes, the temperature is kept for a period of time, and then the material is filtered and rinsed to obtain the second rinsed material.

[0144] Step 9: The material after the second rinse is dried to obtain ferric phosphate dihydrate, which is then calcined to obtain anhydrous ferric phosphate.

[0145] Comparative Example 4

[0146] This comparative example provides a method for preparing anhydrous ferric phosphate. Unlike Example 1, the amount of phosphoric acid added in the aging process of Comparative Example 4 is different.

[0147] Step 1: Dissolve ferrous sulfate, a byproduct of titanium dioxide, in water, heat to 70°C, add alkali to adjust the pH to 5.0, filter to obtain solution A, and set aside.

[0148] Step 2: Dilute solution A obtained in step 1 with water to obtain a ferrous solution (reaction solution A) with a concentration of 55 g / L;

[0149] Step 3: Dissolve the phosphate in water, add alkali to adjust the pH to 6.8, and obtain solution B;

[0150] Step 4: Dilute solution B obtained in step 3 with water to a phosphorus concentration of 80 g / L and at a temperature of 35°C to obtain reaction solution B;

[0151] Step 5: Add reaction solution A to the reaction vessel, and then simultaneously add reaction solution B and hydrogen peroxide. After the addition is completed, continue aging for 50 minutes to obtain amorphous iron phosphate slurry.

[0152] Step 6: Press and filter the amorphous ferric phosphate slurry to obtain the material after the first rinse;

[0153] Step 7: In the aging kettle, add water to slurry the material after the first rinse, and add 5% phosphoric acid and 80% ammonium sulfate by iron molar amount;

[0154] Step 8: After the material in the aging kettle is stirred evenly, the temperature is raised to 95-100℃. After the color changes, the temperature is kept for a period of time, and then the material is filtered and rinsed to obtain the second rinsed material.

[0155] Step 9: The material after the second rinse is dried to obtain ferric phosphate dihydrate, which is then calcined to obtain anhydrous ferric phosphate.

[0156] Comparative Example 5

[0157] This comparative example provides a method for preparing anhydrous ferric phosphate. Unlike Example 1, the amount of phosphoric acid added in the aging process of Comparative Example 5 is different.

[0158] Step 1: Dissolve ferrous sulfate, a byproduct of titanium dioxide, in water, heat to 70°C, add alkali to adjust the pH to 5.0, filter to obtain solution A, and set aside.

[0159] Step 2: Dilute solution A obtained in step 1 with water to obtain a ferrous solution (reaction solution A) with a concentration of 55 g / L;

[0160] Step 3: Dissolve the phosphate in water, add alkali to adjust the pH to 6.8, and obtain solution B;

[0161] Step 4: Dilute solution B obtained in step 3 with water to a phosphorus concentration of 80 g / L and at a temperature of 35°C to obtain reaction solution B;

[0162] Step 5: Add reaction solution A to the reaction vessel, and then simultaneously add reaction solution B and hydrogen peroxide. After the addition is completed, continue aging for 50 minutes to obtain amorphous iron phosphate slurry.

[0163] Step 6: Press and filter the amorphous ferric phosphate slurry to obtain the material after the first rinse;

[0164] Step 7: In the aging kettle, add water to slurry the material after the first rinse, and add 25% phosphoric acid and 120% ammonium sulfate by iron molar amount;

[0165] Step 8: After the material in the aging kettle is stirred evenly, the temperature is raised to 95-100℃. After the color changes, the temperature is kept for a period of time, and then the material is filtered and rinsed to obtain the second rinsed material.

[0166] Step 9: The material after the second rinse is dried to obtain ferric phosphate containing dihydrate, which is then calcined to obtain anhydrous ferric phosphate.

[0167] Test Results

[0168] SEM images of the anhydrous ferric phosphate prepared in Examples 1-3 are shown below. Figure 1-4 As can be seen from the cross-sectional SEM image of the anhydrous ferric phosphate prepared in Example 1, the internal pores of the anhydrous ferric phosphate are very uniform. This means that the primary particles of the prepared anhydrous ferric phosphate have small and consistent particle sizes, and the pores within the secondary particles are uniformly distributed. Under the condition of ensuring a certain tap density, the high porosity and uniform pore distribution improve grinding efficiency. These factors are beneficial for grinding anhydrous ferric phosphate and improve grinding efficiency. For the SEM images of the anhydrous ferric phosphate prepared in Comparative Examples 1-5, please refer to [reference needed]. Figure 5-10 .Depend on Figure 5-10It can be seen that the anhydrous ferric phosphate produced has poor particle uniformity and uneven pore distribution, which will be detrimental to the grinding of anhydrous ferric phosphate and reduce grinding efficiency.

[0169] Table 1: Mean and variance of primary particle size of anhydrous ferric phosphate in the Examples and Comparative Examples

[0170]

[0171] Table 2: Cross-sectional porosity and cross-sectional porosity uniformity coefficient of anhydrous ferric phosphate in the examples and comparative examples

[0172]

[0173] As shown in Tables 1 and 2, the phosphoric acid and ammonium sulfate contents differ between the examples and the comparative examples. In Examples 1, 2, and 3, the phosphoric acid content is in the range of 10%-20%, and the ammonium sulfate content is in the range of 80%-120%. Examples 1-3 can prepare anhydrous ferric phosphate with good primary particle uniformity and a particle size in the range of 100-150 nm. See Table 1 for details. In addition, the anhydrous ferric phosphate in the examples has a small cross-sectional porosity and good pore uniformity. See Table 2 for details. Comparative Example 1 did not use ammonium sulfate, resulting in larger primary particle size and very poor primary particle uniformity. In Comparative Examples 2-5, the phosphoric acid content is not in the range of 10%-20%, or the ammonium sulfate content is not in the range of 80%-120%, resulting in poor primary particle uniformity.

[0174] Table 3. D50 values ​​of anhydrous ferric phosphate in Example 1 and Comparative Example 1 during the grinding process.

[0175] D50(μm) 0min 20min 80min 100min 120min 140min 160min Example 1 3.567 0.634 0.375 0.357 0.320 0.327 0.300 Comparative Example 1 3.357 0.835 0.451 0.431 0.412 0.392 0.387

[0176] Table 4. D50 and span values ​​of anhydrous ferric phosphate in the examples and comparative examples after grinding for 160 min.

[0177]

[0178] As shown in Tables 3 and 4, the anhydrous ferric phosphate with better primary particle uniformity and pore distribution uniformity in the examples has higher grinding efficiency. The grinding efficiency in Example 1 is twice that of Comparative Example 1, meaning the time required to grind to the same particle size is reduced by half (see Table 3 for details). Under the same grinding time, the anhydrous ferric phosphate with better primary particle uniformity and pore distribution uniformity has a smaller D50 and a narrower span value (see Table 4 for details). Anhydrous ferric phosphate with better primary particle uniformity and pore distribution uniformity can reduce energy consumption and save costs in the grinding process.

[0179] The above are merely preferred embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A process for the preparation of anhydrous ferric phosphate, characterized in that, include: An amorphous ferric phosphate solution is mixed with phosphoric acid and ammonium salt to obtain a mixture. The mixture is then heated and kept at a constant temperature. After washing, drying and calcination, anhydrous ferric phosphate is obtained. The amount of phosphoric acid in the mixture is 10%-20% of the molar amount of iron, and the amount of ammonium salt is 80%-120% of the molar amount of iron.

2. The production method according to claim 1, characterized by, Includes the following steps: A phosphate solution containing hydrogen peroxide is added dropwise to a ferrous salt solution to obtain an amorphous ferric phosphate slurry. The amorphous ferric phosphate slurry is then subjected to a single pressure filtration and rinsing to obtain the material after the first rinsing. The material after the first rinse is slurried with water, and then phosphate and ammonium salts are added to obtain a mixed slurry. The mixed slurry is then heated and kept at a constant temperature and allowed to stand. After a second pressure filtration and rinsing, the material after the second rinse is obtained. The material after the second rinse is then dried and calcined to obtain anhydrous ferric phosphate.

3. The preparation method according to claim 2, characterized in that, The ammonium salt includes one or more of ammonium sulfate, ammonium phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

4. The preparation method according to claim 2, characterized in that, After the mixed slurry is stirred evenly, it is heated to 95-100℃, and the heat preservation time is 10-150 minutes.

5. The preparation method according to claim 2, characterized in that, The material after the second rinse is dried at 100-200℃ and then calcined at 550-800℃ for 4-8 hours to obtain anhydrous ferric phosphate.

6. The preparation method according to claim 1, characterized in that, The preparation of amorphous ferric phosphate slurry includes: adding ferrous salt solution to a reaction vessel, then simultaneously adding phosphate solution and hydrogen peroxide, and continuing aging after the addition is completed to obtain amorphous ferric phosphate slurry.

7. The preparation method according to claim 6, characterized in that, The preparation of ferrous salt solution includes: dissolving ferrous sulfate, a byproduct of titanium dioxide, in water, heating to 60-80℃, adding alkali to adjust the pH to 4.0-5.5, filtering to remove impurities and precipitates, collecting the filtrate and diluting it with water to obtain a ferrous salt solution with a concentration of 30-80 g / L.

8. The preparation method according to claim 6, characterized in that, The preparation of phosphate solution includes: dissolving phosphate in water, adding alkali to adjust the pH to 6.0-8.0, and then diluting with water at 30-50℃ to a phosphate concentration of 60-100 g / L to obtain phosphate solution.

9. Anhydrous ferric phosphate prepared by the preparation method according to claim 1, characterized in that, The anhydrous iron phosphate comprises secondary particles formed by accumulation of primary nanoparticles, the average particle size of the primary particles forming the secondary particles is 100-150 nm, and the particle size variance Q is ≤1000 nm 2 .

10. The anhydrous ferric phosphate according to claim 9, characterized in that, The average particle diameter of the primary particles forming the secondary particles is 110-130 nm, and / or the particle diameter variance Q is ≤ 300 nm 2 .

11. The anhydrous ferric phosphate according to claim 9, characterized in that, The overall porosity of the secondary particles in the cross-section is 10%-30%, and the cross-sectional porosity uniformity coefficient R≤5.

12. The anhydrous ferric phosphate according to claim 11, characterized in that, The overall porosity of the cross-section of the secondary particles is 20%-30%, and / or the cross-sectional porosity uniformity coefficient R ≤ 2.

13. The anhydrous ferric phosphate according to any one of claims 9-12, characterized in that, The anhydrous ferric phosphate satisfies one or more of the following conditions A to C: A. The Fe / P molar ratio in the anhydrous ferric phosphate is 0.96-0.98; B. the anhydrous iron phosphate has a specific surface area BET of 10-14 m 2 / g; C. the tapped density TD of the anhydrous iron phosphate is 0.6-0.8 g / cm3 3 .

14. A lithium iron phosphate cathode material, characterized in that, The lithium iron phosphate cathode material is made from raw materials containing anhydrous iron phosphate, wherein the anhydrous iron phosphate is the anhydrous iron phosphate prepared by the preparation method of any one of claims 1-8 or the anhydrous iron phosphate of any one of claims 9-13.

15. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode, a negative electrode, a separator, and an electrolyte made of the lithium iron phosphate positive electrode material as described in claim 14.

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