Anhydrous iron phosphate and preparation method therefor

Abstract

The present disclosure relates to the technical field of batteries. Disclosed are an anhydrous iron phosphate and a preparation method therefor. The anhydrous iron phosphate provided in the present disclosure comprises secondary particles formed by aggregation of a plurality of primary nanoparticles, wherein the average particle size of the primary particles forming the secondary particles is 100-150 nm, and the particle size variance Q is less than or equal to 1000 nm2. The primary particles provided in the present disclosure have a small particle size and good consistency, thereby improving the grinding efficiency of the anhydrous iron phosphate. Lithium iron phosphate prepared by using the anhydrous iron phosphate as a precursor has a pore structure, thereby increasing the area of contact between an electrolyte and a positive electrode material, and realizing good wettability.

Description

Anhydrous ferric phosphate and preparation method thereof

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This disclosure claims priority to Chinese patent application number 2023115753489, filed with the Chinese Patent Office on November 23, 2023, entitled “A kind of anhydrous ferric phosphate and its preparation method”, the entire contents of which are incorporated by reference into this disclosure. Technical Field

[0003] The present disclosure relates to the field of battery technology, and in particular to anhydrous iron phosphate and a preparation method thereof. Background Art

[0004] Lithium iron phosphate is one of the most competitive cathode active materials for lithium-ion batteries on the market. Compared with lithium cobalt oxide and ternary cathode materials, it has a long life and good safety performance. In addition, lithium iron phosphate has a 170mAh g -1 With a theoretical specific capacity of 3.4V and a plateau discharge voltage of 3.4V, it possesses considerable energy density. Currently, most lithium iron phosphate production processes utilize a solid-phase method involving sintering anhydrous iron phosphate with lithium salts. Anhydrous iron phosphate requires grinding before sintering, and grinding efficiency is dependent on factors such as the powder's state. Improving grinding efficiency can save energy and increase production capacity.

[0005] In view of this, an anhydrous ferric phosphate which is easy to grind and can improve grinding efficiency is provided. Summary of the Invention

[0006] The purpose of the present invention is to provide an anhydrous ferric phosphate and a preparation method thereof in order to overcome the defects of the above-mentioned prior art.

[0007] The present disclosure solves its technical problems by adopting the following technical solutions.

[0008] The present disclosure provides anhydrous ferric phosphate, which includes secondary particles formed by stacking a plurality of primary nanoparticles, wherein the average particle size of the primary particles in the secondary particles is 100-150 nm, and the particle size variance Q is less than 1000 nm. 2 .

[0009] The present disclosure also provides a method for preparing anhydrous ferric phosphate, comprising: mixing an amorphous ferric phosphate solution with phosphoric acid and an ammonium salt to obtain a mixture, then heating the mixture and then keeping it warm and allowing it to stand, and then washing, drying, and calcining the mixture to obtain the product anhydrous ferric phosphate.

[0010] The present disclosure also provides a lithium iron phosphate positive electrode material, which is made of a raw material containing anhydrous iron phosphate, and the anhydrous iron phosphate is anhydrous iron phosphate prepared according to the above preparation method.

[0011] The present disclosure also provides a lithium-ion battery, which includes a positive electrode made of the above-mentioned lithium iron phosphate positive electrode material, a negative electrode, a separator and an electrolyte.

[0012] The present disclosure has the following beneficial effects:

[0013] The present disclosure provides an anhydrous ferric phosphate and a preparation method thereof. The anhydrous ferric phosphate provided comprises secondary particles formed by stacking a plurality of primary nanoparticles, wherein the average particle size of the primary particles in the secondary particles is 100-150 nm, and the particle size variance Q is ≤ 1000 nm. 2 The above anhydrous ferric phosphate has the characteristics of small primary particle size and good consistency. Grinding the anhydrous ferric phosphate with the above characteristics has high grinding efficiency, can save energy, increase production capacity and reduce costs, and is more conducive to its use in the preparation of lithium iron phosphate. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the technical solution of the present disclosure, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present disclosure and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without any creative work.

[0015] FIG1 is a SEM image of anhydrous ferric phosphate prepared in Example 1 of the present disclosure;

[0016] FIG2 is a cross-sectional electron micrograph of anhydrous ferric phosphate prepared in Example 1 of the present disclosure (scale: 5 μm);

[0017] FIG3 is a SEM image of anhydrous ferric phosphate prepared in Example 2 of the present disclosure;

[0018] FIG4 is a SEM image of anhydrous ferric phosphate prepared in Example 3 of the present disclosure;

[0019] FIG5 is a SEM image of anhydrous ferric phosphate prepared in Comparative Example 1 of the present disclosure;

[0020] FIG6 is a cross-sectional electron micrograph of anhydrous ferric phosphate prepared in Comparative Example 1 of the present disclosure (scale: 5 μm);

[0021] FIG7 is a SEM image of anhydrous ferric phosphate prepared in Comparative Example 2 of the present disclosure;

[0022] FIG8 is a SEM image of anhydrous ferric phosphate prepared in Comparative Example 3 of the present disclosure;

[0023] FIG9 is a SEM image of anhydrous ferric phosphate prepared in Comparative Example 4 of the present disclosure;

[0024] FIG10 is a SEM image of anhydrous ferric phosphate prepared in Comparative Example 5 of the present disclosure. DETAILED DESCRIPTION

[0025] To make the objectives, technical solutions, and advantages of the present disclosure more clear, the technical solutions in the present disclosure are described clearly and completely below. In the examples, where specific conditions are not specified, conventional conditions or conditions recommended by the manufacturer were used. Reagents or instruments used where the manufacturer is not specified are conventional products that can be purchased commercially.

[0026] The following is a detailed description of anhydrous ferric phosphate and its preparation method provided by the present invention.

[0027] In a first aspect, the present disclosure provides an anhydrous ferric phosphate, which comprises secondary particles formed by stacking a plurality of primary nanoparticles, wherein the average particle size of the primary particles in the secondary particles is 100-150 nm, and the particle size variance Q is ≤ 1000 nm. 2 .

[0028] 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 is ≤ 300 nm. 2 .

[0029] In an optional embodiment, the overall porosity of the cross section of the secondary particles is 10%-30%, and the cross section porosity uniformity coefficient R≤5;

[0030] In an optional embodiment, the overall cross-sectional porosity of the secondary particles is 20%-30%, and / or the cross-sectional porosity uniformity coefficient R≤2.

[0031] The following is a description of the test methods and test results for the particle size and particle size variance of the primary particles of the anhydrous ferric phosphate provided by the present disclosure, and the cross-sectional overall porosity and cross-sectional pore uniformity coefficient of the secondary particles.

[0032] (1) Method for measuring primary particle size: select primary particles with clear primary particle boundary areas on SEM images of the same magnification (above x10000) and the same resolution (above 1280x9180) for particle size measurement. Randomly select n primary particles from each SEM image for particle size measurement. The average value of the primary particle sizes of 3n (3n≥50, preferably 50-200) primary particles in three SEM images is taken as the mean primary particle size, also known as the average primary particle size. The calculation formula is as follows: q=(q1+q2+……+q 3n ) / 3n

[0033] q: the average of the particle sizes of 3n primary particles, in nm, 3n≥50. In an optional embodiment, 3n is 50-200. 3n are the particle sizes of 3n randomly selected primary particles.

[0034] The test results of the particle size of the anhydrous ferric phosphate primary particles prepared in the present invention are: the anhydrous ferric phosphate includes secondary particles formed by the accumulation of multiple primary nanoparticles, and the average particle size of the primary particles in the secondary particles is 100-150nm. In an optional embodiment, the average particle size of the primary particles in the secondary particles is 110-130nm.

[0035] Alternatively, the average particle size of the primary particles forming the secondary particles may be 100 nm, 105 nm, 110 nm, 115 nm, 120 nm, 127 nm, 130 nm, 132 nm, 140 nm, 145 nm, 150 nm or any value between 100 and 150 nm.

[0036] It is worth noting that since the average particle size of primary particles is at the nanometer level, in the present disclosure, primary particles are also referred to as primary nanoparticles.

[0037] (2) Method for measuring consistency of primary particles: The particle size variance of primary particles is used to evaluate the consistency of primary particles. The particle sizes of 3n primary particles are calculated with respect to the mean to obtain the particle size variance Q of the primary particles. The calculation formula is as follows: Q = (|q-q1| 2 +|q-q2| 2 +……+|qq 3n | 2 ) / 3n

[0038] q1...q 3n The unit of and q is nm. According to the above formula, the unit of Q is nm 2 ;

[0039] The primary particle size variance Q of the anhydrous ferric phosphate prepared by the present invention is less than 1000 nm. 2 In an optional embodiment, the primary particle size variance Q of anhydrous ferric phosphate is less than 300 nm. 2 In an optional embodiment, the primary particle size variance Q in anhydrous ferric phosphate is ≤ 150 nm 2 The results show that: Q≤1000nm 2 When the primary particles are uniform, Q>1000nm 2 When the particle size is less than 100 nm, the consistency of the primary particles is poor.

[0040] Optionally, the particle size variance of the primary particles forming the secondary particles may be 1000 nm. 2 , 950nm 2 , 900nm 2 , 800nm 2 , 700nm 2 , 600nm 2, 500nm 2 , 400nm 2 , 300nm 2 , 200nm 2 , 150nm 2 , 100nm 2 , 50nm 2 or ≤1000nm 2 Any value in between.

[0041] (3) Cross-sectional integral porosity measurement method: A cross-sectional area of ​​at least 80% of the secondary particle is selected as the total cross-sectional area. The porosity of the total cross-sectional area is measured as the cross-sectional porosity, also referred to as the cross-sectional integral porosity in this disclosure. The selection of the total cross-sectional area is described in FIG2 . An irregular or regular pattern is drawn within the secondary particle along its boundary, where the area occupied by the irregular or regular pattern is at least 80% of the cross-sectional area of ​​the secondary particle.

[0042] To improve the accuracy of overall cross-sectional porosity measurement, the cross-sectional porosity of multiple secondary particles is typically measured, and the average of these porosities is used as the overall cross-sectional porosity of the secondary particles. Alternatively, the number of secondary particles used to measure the overall cross-sectional porosity is 3, 4, 5, or any integer greater than 3.

[0043] The test results of the overall porosity of the cross section of the anhydrous ferric phosphate secondary particles prepared in the present invention are 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%.

[0044] Optionally, the overall porosity of the cross section of the anhydrous ferric phosphate secondary particles is 10%, 12%, 15%, 18%, 20%, 24%, 26%, 27%, 28%, 30% or any value between 10% and 30%.

[0045] (4) Method for measuring cross-sectional pore uniformity coefficient: select local regions with equal cross-sectional areas, namely, upper left, upper right, middle, lower left, and lower right. The position and area of ​​the local regions shown in FIG2 are a selection method of the following embodiment. The area of ​​the local regions accounts for 10% of the total cross-sectional area. Measure the area and pore area of ​​the local regions, calculate the porosity of the local regions, and then evaluate the cross-sectional pore uniformity using the following formula: R = (|r - r1| 2 +|r-r2| 2 +|r-r3| 2 +|r-r4| 2 +|r-r5| 2 ) / 5

[0046] r: overall porosity on the secondary particle cross section, r1, r2, r3, r4, and r5 are the porosities of local areas on the cross section (upper left, upper right, middle, lower left, and lower right), respectively. R is the variance of the cross section porosity, which is used to evaluate the uniformity of the cross section porosity and is also called the cross section porosity uniformity coefficient.

[0047] In order to improve the accuracy of the cross-sectional pore uniformity coefficient measurement, the overall porosity and local area porosity of multiple secondary particles are usually selected to calculate the variance respectively, and the average value of the multiple variances is calculated and used as the cross-sectional pore uniformity coefficient R of the secondary particles.

[0048] In addition, another method can be used to measure R. The overall porosity of the cross section, the porosity of the upper left local area, the porosity of the upper right local area, the porosity of the middle local area, the porosity of the lower left local area and the porosity of the lower right local area of ​​multiple secondary particles are selected and the average values ​​are calculated respectively to obtain r, r1, r2, r3, r4 and r5 (the average porosity of the overall cross section, the upper left local area, the upper right local area, the middle local area, the lower left local area and the lower right local area), and the cross section porosity uniformity coefficient R is calculated by the above-mentioned variance formula.

[0049] Optionally, the number of secondary particles used to measure the porosity of the entire cross section and a local area is 3, 4, 5 or any integer greater than 3.

[0050] The test results of the cross-sectional pore uniformity coefficient of the anhydrous ferric phosphate secondary particles prepared in the present disclosure are: R≤5; in an alternative embodiment, the cross-sectional pore uniformity coefficient of the anhydrous ferric phosphate secondary particles is R≤2; in an alternative embodiment, the cross-sectional pore uniformity coefficient of the anhydrous ferric phosphate secondary particles is R≤0.5. When R≤5, the pore distribution uniformity is good, and when R>5, the pore distribution uniformity is poor.

[0051] Optionally, the cross-sectional pore uniformity coefficient R of the anhydrous ferric phosphate secondary particles may be 5, 4.5, 4, 3.5, 3, 2.5, 2, 1.5, 1, 0.5, 0.3, 0.1 or any value between R≤5.

[0052] The anhydrous ferric phosphate prepared based on the present disclosure has the characteristics of small primary particles with good consistency and high pore uniformity of secondary particles, which improve the grinding efficiency of the anhydrous ferric phosphate.

[0053] The technical principle is that the small particle size of anhydrous ferric phosphate primary particles is conducive to grinding. When the particle size of anhydrous ferric phosphate primary particles is small and the consistency is good, the grinding efficiency is improved.

[0054] If the overall cross-sectional porosity is too low, the primary particles within the secondary particles will grow more densely, resulting in low grinding efficiency. If the overall cross-sectional porosity is too high, the tap density of the anhydrous ferric phosphate will be low. The smaller the cross-sectional pore uniformity coefficient, the more uniform the pore distribution within the secondary particles. The larger the cross-sectional pore uniformity coefficient, the more uneven the pore distribution within the secondary particles. The grinding efficiency of anhydrous ferric phosphate with uneven pore distribution decreases. While maintaining a certain tap density, improving porosity and pore uniformity can improve grinding efficiency.

[0055] The grinding results are as follows: it only takes 80 minutes to grind the prepared anhydrous ferric phosphate to a D50 of 380nm, the grinding time is shorter, and the grinding efficiency is doubled; under the same grinding time, the D50 of the anhydrous ferric phosphate is smaller and the span value is narrower.

[0056] In an optional embodiment, the anhydrous ferric phosphate satisfies one or more of the following conditions A to C:

[0057] A. The Fe / P molar ratio in anhydrous ferric phosphate is 0.96-0.98;

[0058] B. The specific surface area of ​​anhydrous ferric phosphate is 10-14m 2 / g;

[0059] C. The tap density TD of anhydrous ferric phosphate is 0.6-0.8g / cm 3 .

[0060] Optionally, the Fe / P molar ratio of anhydrous ferric phosphate can be 0.96, 0.963, 0.965, 0.968, 0.98 or any value between 0.96-0.98, and the specific surface area BET can be 10m 2 / g、11m 2 / g、12m 2 / g、13m 2 / g、14m 2 / g or 10-14m 2 / g, the tap density TD is 0.6g / cm 3 , 0.65g / cm 3 , 0.7g / cm 3 , 0.75g / cm 3 , 0.8g / cm 3 or 0.6-0.8g / cm 3 Any value in between.

[0061] When the Fe / P molar ratio in anhydrous ferric phosphate is in the range of 0.96-0.98, the positive electrode material prepared with ferric phosphate has excellent specific capacity; when the Fe / P molar ratio is lower than 0.96, the specific capacity of the positive electrode material prepared with ferric phosphate is low.

[0062] The BET specific surface area of ​​anhydrous iron phosphate is too low, which is not conducive to the embedding of lithium salts during the preparation of positive electrode materials; the BET specific surface area of ​​anhydrous iron phosphate is too high, and the anhydrous iron phosphate is relatively loose as a whole, which is not conducive to the preparation of anhydrous iron phosphate with high tap density.

[0063] If the tap density TD of anhydrous ferric phosphate is too low, the anhydrous ferric phosphate is relatively loose, which is not conducive to improving the compaction density of the positive electrode material; if the tap density TD is too high, the anhydrous ferric phosphate is relatively dense, which is not conducive to grinding.

[0064] In the present disclosure, BET is measured by a nitrogen adsorption method, which is carried out in accordance with the national standard (GB / T 13390-2008 standard), and the TD test method is carried out in accordance with the national standard (GB / T 5162-2021 standard).

[0065] In a second aspect, the present disclosure also provides a method for preparing the above-mentioned anhydrous ferric phosphate, comprising: mixing an amorphous ferric phosphate solution with phosphoric acid and an ammonium salt to obtain a mixture, then heating the mixture and then keeping it warm and letting it stand, and then washing, drying, and calcining to obtain the product anhydrous ferric phosphate.

[0066] In the aforementioned preparation process of anhydrous ferric phosphate, amorphous ferric phosphate is converted into crystalline ferric phosphate through crystal transformation, and 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 the crystal transformation process, ammonium ions effectively prevent the ferric phosphate particles from agglomerating. The crystalline ferric phosphate, after being held at a temperature and allowed to stand, is then washed, cleaned of impurities, and dehydrated to obtain anhydrous ferric phosphate with a narrow primary particle size distribution.

[0067] 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.

[0068] Optionally, the amount of phosphoric acid in the mixed slurry can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20% or any value between 10% and 20% of the molar amount of iron, and the amount of ammonium salt can be 80%, 85%, 90%, 95%, 100%, 105%, 110%, 115%, 120% or any value between 80% and 120% of the molar amount of iron.

[0069] The present disclosure provides a method for preparing anhydrous ferric phosphate. Phosphoric acid and an ammonium salt are added to an amorphous ferric phosphate slurry. Appropriate amounts of phosphoric acid and ammonium salt can promote the crystal transformation of the amorphous ferric phosphate and control the crystal form and particle size after transformation. The prepared anhydrous ferric phosphate has the characteristics of good primary particle consistency and narrow particle size distribution, and secondary particles with high porosity uniformity. 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 prepared anhydrous ferric phosphate primary particles have a larger particle size and poorer consistency.

[0070] In an optional embodiment, the following steps are included:

[0071] adding a phosphate solution containing hydrogen peroxide dropwise to a ferrous salt solution to obtain an amorphous ferric phosphate slurry, and then subjecting the amorphous ferric phosphate slurry to a filter press and rinse to obtain a first rinsed material;

[0072] The material after the first rinse is slurried with water, and then phosphoric acid and ammonium salt are added to obtain a mixed slurry. The mixed slurry is then heated and kept warm and allowed to stand, and then subjected to a second filter press and rinse to obtain a second rinsed material.

[0073] The material after the second rinse is then dried and calcined to obtain anhydrous ferric phosphate.

[0074] In an optional embodiment, the ammonium salt comprises one or more of ammonium sulfate, ammonium phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate. Generally, sulfuric acid solution is added to the other ammonium salts except ammonium sulfate.

[0075] In an optional embodiment, the holding time is 10-150 minutes. It is worth noting that after the mixed slurry is stirred evenly and then heated to 95-100°C, a color change phenomenon is usually observed. After the solution changes color, it is kept warm for a period of time to form iron phosphate with higher crystallinity.

[0076] Optionally, after the mixed slurry is stirred evenly, the heating temperature can be 95°C, 96°C, 97°C, 98°C, 99°C, 100°C or any value between 95-100°C, and the insulation time can be 10min, 20min, 30min, 40min, 50min, 60min, 70min, 80min, 90min, 100min, 110min, 120min, 130min, 140min, 150min or any value between 10-150min.

[0077] 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.

[0078] Optionally, the drying temperature of the material after the second rinsing can be 100°C, 105°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C or any value between 100-200°C, the calcination temperature can be 550°C, 600°C, 650°C, 700°C, 750°C, 800°C or any value between 550-800°C, and the calcination time can be 4h, 5h, 6h, 7h, 8h or any value between 4h-8h.

[0079] In an optional embodiment of the present disclosure, the preparation of the amorphous ferric phosphate slurry includes: adding a ferrous salt solution to a reactor, then simultaneously adding a phosphate solution and hydrogen peroxide dropwise, and continuing aging after the addition is completed to obtain the amorphous ferric phosphate slurry.

[0080] In an optional embodiment, the preparation of the ferrous salt solution includes: dissolving ferrous sulfate, a by-product of titanium dioxide, in water, heating the temperature to 60-80°C, adding alkali to adjust the pH to 4.0-5.5, filtering to remove impurity precipitates, collecting the filtrate and diluting it with water to obtain a ferrous salt solution with a concentration of 30-80 g / L.

[0081] Optionally, during the preparation of the ferrous salt solution, the heating temperature can be 60°C, 65°C, 70°C, 75°C, 80°C or any value between 60-80°C, and the pH value adjusted by adding alkali can be 4.0, 4.3, 4.5, 4.8, 5.0, 5.3, 5.5 or any value between 4.0-5.5, and the concentration of the ferrous salt solution can be 30g / L, 40g / L, 50g / L, 60g / L, 70g / L, 80g / L or any value between 30-80g / L.

[0082] In an optional embodiment, the preparation of the phosphate solution includes: dissolving phosphate in water, adding alkali to adjust the pH to 6.0-8.0, and then diluting with water at a temperature of 30-50° C. to a phosphate concentration of 60-100 g / L to obtain a phosphate solution.

[0083] Optionally, during the phosphate preparation process, the pH value adjusted by adding alkali can be 6.0, 6.5, 6.7, 7.0, 7.3, 7.5, 7.8, 8.0 or any value between 6.0-8.0, the heating temperature can be 30°C, 35°C, 40°C, 45°C, 50°C or any value between 30-50°C, and the phosphate concentration can be 60 g / L, 70 g / L, 80 g / L, 90 g / L, 100 g / L or any value between 60-100 g / L.

[0084] The present disclosure provides a method for preparing anhydrous ferric phosphate. The preparation of an amorphous ferric phosphate slurry is obtained by dropwise adding a phosphate solution containing hydrogen peroxide to a ferrous salt solution for reaction, wherein: the ferrous salt raw material is ferrous sulfate, a byproduct of titanium dioxide. Since the titanium dioxide byproduct contains impurities such as titanium and aluminum, the titanium dioxide byproduct is dissolved in water and then the pH is adjusted to precipitate impurities such as titanium and aluminum, and a pure ferrous salt solution is obtained by filtration. When preparing the phosphate solution, after dissolving the phosphate in water, alkali is added to adjust the pH to obtain a phosphate solution. The alkali in the phosphate solution is conducive to the subsequent combination of iron ions and phosphate ions, thereby obtaining pure amorphous ferric phosphate with a high iron-phosphorus ratio.

[0085] In a third aspect, the present disclosure further provides a lithium iron phosphate positive electrode material, which is made of a raw material containing anhydrous iron phosphate, and the anhydrous iron phosphate is anhydrous iron phosphate prepared according to the above preparation method.

[0086] In a fourth aspect, the present disclosure further provides a lithium-ion battery, which includes a positive electrode made of the above-mentioned lithium iron phosphate positive electrode material, a negative electrode, a separator and an electrolyte.

[0087] As can be seen from the above, the anhydrous iron phosphate prepared by the present invention has the advantages of small primary particle size and good consistency, and uniform pore distribution of secondary particles. 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 infiltration can fully exert the performance of lithium-ion batteries and improve the performance of lithium-ion batteries.

[0088] The features and performance of the present disclosure are further described in detail below with reference to the embodiments.

[0089] Example 1

[0090] This embodiment provides a method for preparing anhydrous ferric phosphate.

[0091] Step 1: dissolve ferrous sulfate, a by-product of titanium dioxide, in water, heat the water to 70° C., add alkali to adjust the pH to 5.0, and filter to obtain solution A;

[0092] Step 2: diluting the solution A obtained in step 1 with water to obtain a ferrous solution (reaction solution A) with a concentration of 55 g / L;

[0093] Step 3, dissolving the phosphate in water, adding alkali to adjust the pH to 6.8, to obtain solution B;

[0094] Step 4: dilute the solution B obtained in step 3 with water to a phosphorus concentration of 80 g / L at a temperature of 35° C. to obtain a reaction solution B;

[0095] Step 5: Add reaction solution A to the reactor, then dropwise add reaction solution B and hydrogen peroxide, and continue aging for 50 minutes after the dropwise addition to obtain an amorphous ferric phosphate slurry;

[0096] Step 6: filter-pressing and rinsing the amorphous ferric phosphate slurry to obtain a first rinsed material;

[0097] Step 7: In an aging kettle, the material after the first rinse is slurried with water, and phosphoric acid with a molar weight of 15% iron and ammonium sulfate with a molar weight of 100% iron are added;

[0098] Step 8: Stir the material in the aging kettle evenly and then heat it to 95-100°C. After the color changes, keep the temperature for a period of time, and then filter press and rinse to obtain the second rinsed material;

[0099] Step 9: The material after the second rinsing is dried to obtain ferric phosphate dihydrate, which is then calcined to obtain anhydrous ferric phosphate as shown in Figures 1 and 2.

[0100] Example 2

[0101] 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;

[0102] Step 1: dissolve ferrous sulfate, a by-product of titanium dioxide, in water, heat the water to 70° C., add alkali to adjust the pH to 5.0, and filter to obtain solution A;

[0103] Step 2: diluting the solution A obtained in step 1 with water to obtain a ferrous solution (reaction solution A) with a concentration of 55 g / L;

[0104] Step 3, dissolving the phosphate in water, adding alkali to adjust the pH to 6.8, to obtain reaction solution B;

[0105] Step 4: dilute the solution B obtained in step 3 with water to a phosphorus concentration of 80 g / L at a temperature of 35° C. to obtain a reaction solution B;

[0106] Step 5: Add reaction solution A to the reactor, then dropwise add reaction solution B and hydrogen peroxide, and continue aging for 50 minutes after the dropwise addition to obtain an amorphous ferric phosphate slurry;

[0107] Step 6: filter-pressing and rinsing the amorphous ferric phosphate slurry to obtain a first rinsed material;

[0108] Step 7: In an aging kettle, the material after the first rinse is slurried with water, and 20% of phosphoric acid and 120% of ammonium sulfate are added;

[0109] Step 8: Stir the material in the aging kettle evenly and then heat it to 95-100°C. After the color changes, keep the temperature for a period of time, and then filter press and rinse to obtain the second rinsed material;

[0110] Step 9: The material after the second rinsing is dried to obtain ferric phosphate dihydrate, and then calcined to obtain anhydrous ferric phosphate.

[0111] Example 3

[0112] 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 step of Example 3 are different;

[0113] Step 1: dissolve ferrous sulfate, a by-product of titanium dioxide, in water, heat the water to 70° C., add alkali to adjust the pH to 5.0, and filter to obtain solution A;

[0114] Step 2: diluting the solution A obtained in step 1 with water to obtain a ferrous solution (reaction solution A) with a concentration of 55 g / L;

[0115] Step 3, dissolving the phosphate in water, adding alkali to adjust the pH to 6.8, to obtain solution B;

[0116] Step 4: dilute the solution B obtained in step 3 with water to a phosphorus concentration of 80 g / L at a temperature of 35° C. to obtain a reaction solution B;

[0117] Step 5: Add reaction solution A to the reactor, then dropwise add reaction solution B and hydrogen peroxide, and continue aging for 50 minutes after the dropwise addition to obtain an amorphous ferric phosphate slurry;

[0118] Step 6: filter-pressing and rinsing the amorphous ferric phosphate slurry to obtain a first rinsed material;

[0119] Step 7: In an aging kettle, the material after the first rinse is slurried with water, and phosphoric acid with a molar weight of 10% iron and ammonium sulfate with a molar weight of 80% iron are added;

[0120] Step 8: Stir the material in the aging kettle evenly and then heat it to 95-100°C. After the color changes, keep the temperature for a period of time, and then filter press and rinse to obtain the second rinsed material;

[0121] Step 9: The material after the second rinsing is dried to obtain ferric phosphate dihydrate, and then calcined to obtain anhydrous ferric phosphate.

[0122] Example 4

[0123] 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 (step 7) of Example 4 are different.

[0124] Step 7: In an aging kettle, the material after the first rinse is slurried with water, and 20% of phosphoric acid and 80% of ammonium sulfate are added;

[0125] Step 8: Stir the material in the aging kettle evenly and then heat it to 95-100°C. After the color changes, keep the temperature for 90 minutes, filter press and rinse to obtain the second rinsed material;

[0126] Step 9: The material after the second rinsing is dried at 110° C. to obtain ferric phosphate dihydrate, and then the ferric phosphate dihydrate is calcined at 660° C. for 4 hours to obtain anhydrous ferric phosphate.

[0127] Example 5

[0128] 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 (step 7) of Example 5 are different;

[0129] Step 7: In an aging kettle, the material after the first rinse is slurried with water, and phosphoric acid with a molar weight of 10% iron and ammonium sulfate with a molar weight of 120% iron are added;

[0130] Step 8: Stir the material in the aging kettle evenly and then heat it to 95-100°C. After the color changes, keep the temperature for 90 minutes, filter press and rinse to obtain the second rinsed material;

[0131] Step 9: The material after the second rinsing is dried at 110° C. to obtain ferric phosphate dihydrate, and then the ferric phosphate dihydrate is calcined at 660° C. for 4 hours to obtain anhydrous ferric phosphate.

[0132] Comparative Example 1

[0133] This comparative example provides a method for preparing anhydrous ferric phosphate. Unlike Example 1, in the aging process of Comparative Example 1, only phosphoric acid is added;

[0134] Step 1: dissolve ferrous sulfate, a by-product of titanium dioxide, in water, heat the water to 70° C., add alkali to adjust the pH to 5.0, and filter to obtain solution A;

[0135] Step 2: diluting the solution A obtained in step 1 with water to obtain a ferrous solution (reaction solution A) with a concentration of 55 g / L;

[0136] Step 3, dissolving the phosphate in water, adding alkali to adjust the pH to 6.8, to obtain solution B;

[0137] Step 4: dilute the solution B obtained in step 3 with water to a phosphorus concentration of 80 g / L at a temperature of 35° C. to obtain a reaction solution B;

[0138] Step 5: Add reaction solution A to the reactor, then dropwise add reaction solution B and hydrogen peroxide, and continue aging for 50 minutes after the dropwise addition to obtain an amorphous ferric phosphate slurry;

[0139] Step 6: filter-pressing and rinsing the amorphous ferric phosphate slurry to obtain a first rinsed material;

[0140] Step 7: In an aging kettle, the material after the first rinse is slurried with water, and phosphoric acid with a molar weight of 15% iron is added;

[0141] Step 8: After the material in the aging kettle changes color, the temperature is raised to 95-100° C., and then kept warm for a period of time, followed by filter pressing and rinsing to obtain the second rinsed material;

[0142] Step 9: The material after the second rinsing is dried to obtain ferric phosphate dihydrate, which is then calcined to obtain anhydrous ferric phosphate as shown in Figures 5 and 6.

[0143] Comparative Example 2

[0144] This comparative example provides a method for preparing anhydrous ferric phosphate. Different from Example 1, in Comparative Example 2, the amount of ammonium sulfate added in the aging process is different.

[0145] Step 1: dissolve ferrous sulfate, a by-product of titanium dioxide, in water, heat the water to 70° C., add alkali to adjust the pH to 5.0, and filter to obtain solution A;

[0146] Step 2: diluting the solution A obtained in step 1 with water to obtain a ferrous solution (reaction solution A) with a concentration of 55 g / L;

[0147] Step 3, dissolving the phosphate in water, adding alkali to adjust the pH to 6.8, to obtain solution B;

[0148] Step 4: dilute the solution B obtained in step 3 with water to a phosphorus concentration of 80 g / L at a temperature of 35° C. to obtain a reaction solution B;

[0149] Step 5: Add reaction solution A to the reactor, then dropwise add reaction solution B and hydrogen peroxide, and continue aging for 50 minutes after the dropwise addition to obtain an amorphous ferric phosphate slurry;

[0150] Step 6: filter-pressing and rinsing the amorphous ferric phosphate slurry to obtain a first rinsed material;

[0151] Step 7: In an aging kettle, the material after the first rinse is slurried with water, and phosphoric acid with a molar weight of 15% iron and ammonium sulfate with a molar weight of 60% iron are added;

[0152] Step 8: Stir the material in the aging kettle evenly and then heat it to 95-100°C. After the color changes, keep the temperature for a period of time, and then filter press and rinse to obtain the second rinsed material;

[0153] Step 9: The material after the second rinsing is dried to obtain dihydrated iron phosphate, which is then calcined to obtain anhydrous iron phosphate.

[0154] Comparative Example 3

[0155] This comparative example provides a method for preparing anhydrous ferric phosphate. Different from Example 1, in Comparative Example 3, the amount of ammonium sulfate added in the aging process is different.

[0156] Step 1: dissolve ferrous sulfate, a by-product of titanium dioxide, in water, heat the water to 70° C., add alkali to adjust the pH to 5.0, and filter to obtain solution A;

[0157] Step 2: diluting the solution A obtained in step 1 with water to obtain a ferrous solution (reaction solution A) with a concentration of 55 g / L;

[0158] Step 3, dissolving the phosphate in water, adding alkali to adjust the pH to 6.8, to obtain solution B;

[0159] Step 4: dilute the solution B obtained in step 3 with water to a phosphorus concentration of 80 g / L at a temperature of 35° C. to obtain a reaction solution B;

[0160] Step 5: Add reaction solution A to the reactor, then dropwise add reaction solution B and hydrogen peroxide, and continue aging for 50 minutes after the dropwise addition to obtain an amorphous ferric phosphate slurry;

[0161] Step 6: filter-pressing and rinsing the amorphous ferric phosphate slurry to obtain a first rinsed material;

[0162] Step 7: In an aging kettle, the material after the first rinse is slurried with water, and phosphoric acid with a molar weight of 15% iron and ammonium sulfate with a molar weight of 150% iron are added;

[0163] Step 8: Stir the material in the aging kettle evenly and then heat it to 95-100°C. After the color changes, keep the temperature for a period of time, and then filter press and rinse to obtain the second rinsed material;

[0164] Step 9: The material after the second rinsing is dried to obtain ferric phosphate dihydrate, and then calcined to obtain anhydrous ferric phosphate.

[0165] Comparative Example 4

[0166] 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;

[0167] Step 1: dissolve ferrous sulfate, a by-product of titanium dioxide, in water, heat the water to 70° C., add alkali to adjust the pH to 5.0, and filter to obtain solution A;

[0168] Step 2: diluting the solution A obtained in step 1 with water to obtain a ferrous solution (reaction solution A) with a concentration of 55 g / L;

[0169] Step 3, dissolving the phosphate in water, adding alkali to adjust the pH to 6.8, to obtain solution B;

[0170] Step 4: dilute the solution B obtained in step 3 with water to a phosphorus concentration of 80 g / L at a temperature of 35° C. to obtain a reaction solution B;

[0171] Step 5: Add reaction solution A to the reactor, then dropwise add reaction solution B and hydrogen peroxide, and continue aging for 50 minutes after the dropwise addition to obtain an amorphous ferric phosphate slurry;

[0172] Step 6: filter-pressing and rinsing the amorphous ferric phosphate slurry to obtain a first rinsed material;

[0173] Step 7: In an aging kettle, the material after the first rinse is slurried with water, and 5% phosphoric acid and 80% ammonium sulfate are added;

[0174] Step 8: Stir the material in the aging kettle evenly and then heat it to 95-100°C. After the color changes, keep the temperature for a period of time, and then filter press and rinse to obtain the second rinsed material;

[0175] Step 9: The material after the second rinsing is dried to obtain ferric phosphate dihydrate, and then calcined to obtain anhydrous ferric phosphate.

[0176] Comparative Example 5

[0177] 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;

[0178] Step 1: dissolve ferrous sulfate, a by-product of titanium dioxide, in water, heat the water to 70° C., add alkali to adjust the pH to 5.0, and filter to obtain solution A;

[0179] Step 2: diluting the solution A obtained in step 1 with water to obtain a ferrous solution (reaction solution A) with a concentration of 55 g / L;

[0180] Step 3, dissolving the phosphate in water, adding alkali to adjust the pH to 6.8, to obtain solution B;

[0181] Step 4: dilute the solution B obtained in step 3 with water to a phosphorus concentration of 80 g / L at a temperature of 35° C. to obtain a reaction solution B;

[0182] Step 5: Add reaction solution A to the reactor, then dropwise add reaction solution B and hydrogen peroxide, and continue aging for 50 minutes after the dropwise addition to obtain an amorphous ferric phosphate slurry;

[0183] Step 6: filter-pressing and rinsing the amorphous ferric phosphate slurry to obtain a first rinsed material;

[0184] Step 7: In an aging kettle, the material after the first rinse is slurried with water, and 25% of phosphoric acid and 120% of ammonium sulfate are added;

[0185] Step 8: Stir the material in the aging kettle evenly and then heat it to 95-100°C. After the color changes, keep the temperature for a period of time, and then filter press and rinse to obtain the second rinsed material;

[0186] Step 9: The material after the second rinsing is dried to obtain dihydrated iron phosphate, which is then calcined to obtain anhydrous iron phosphate.

[0187] Test results

[0188] The SEM images of the anhydrous ferric phosphate obtained in Example 1-3 are shown in Figures 1-4. It can be seen from the cross-sectional SEM images 1-4 of the anhydrous ferric phosphate obtained in Example 1 that the primary particle size of the anhydrous ferric phosphate is small and the consistency is good. These features are conducive to the grinding of anhydrous ferric phosphate and improve the grinding efficiency. It can also be seen from the figure that the pore distribution in the secondary particles is uniform. While ensuring a certain tap density, the high porosity and uniform pore distribution can improve the grinding efficiency. The above features are all conducive to the grinding of anhydrous ferric phosphate and improve the grinding efficiency. The SEM images of the anhydrous ferric phosphate obtained in Comparative Examples 1-5 are shown in Figures 5-10. It can be seen from Figures 5-10 that the primary particles of the obtained anhydrous ferric phosphate have poor consistency and uneven pore distribution, which will be detrimental to the grinding of anhydrous ferric phosphate and reduce the grinding efficiency.

[0189] Table 1 Contents of phosphoric acid and ammonium sulfate in Examples and Comparative Examples Note: The contents of phosphoric acid and ammonium sulfate are based on molar amounts of iron.

[0190] Table 2 Mean and variance of primary particle size of anhydrous ferric phosphate in Examples and Comparative Examples

[0191] Table 3 Cross-sectional porosity, cross-sectional porosity uniformity coefficient, tap density and Fe / P molar ratio of anhydrous ferric phosphate in the examples and comparative examples

[0192] As can be seen from Tables 1, 2, and 3, the phosphoric acid and ammonium sulfate contents of the Examples and Comparative Examples are different. The phosphoric acid contents of Examples 1, 2, and 3 are all within the range of 10%-20%, and the ammonium sulfate contents are within the range of 80%-120%. Examples 1-3 can all produce anhydrous ferric phosphate with good primary particle consistency and a particle size within the range of 100-150 nm. For details, see Table 2. In addition, the cross-section porosity of the anhydrous ferric phosphate in the Examples is small and the pore uniformity is good. For details, see Table 3. Comparative Example 1 does not use ammonium sulfate, and the particle size of the primary particles is larger, and the consistency of the primary particles is poor. The phosphoric acid content in Comparative Examples 2-5 is not within the range of 10%-20% or the ammonium sulfate content is not within the range of 80%-120%, and the primary particle consistency is also poor.

[0193] The grinding process for anhydrous iron phosphate in the lithium iron phosphate preparation process is as follows: a wet grinding solvent is added to the anhydrous iron phosphate to form an anhydrous iron phosphate slurry. The slurry is ball-milled at 2200 rpm / min using a Langling sand mill (NT-V1L) to form an anhydrous iron phosphate slurry. A portion of the slurry is then tested for D10, D50, and D90 at a temperature of 23.5±3°C. Where, Span = (D90-D10) / D50. The D50 values ​​at different grinding times and the span values ​​measured after 160 minutes of grinding are shown in Tables 4 and 5 below.

[0194] Table 4 D50 values ​​(μm) of anhydrous ferric phosphate in the embodiments and comparative examples at different grinding times

[0195] Table 5 Span values ​​of anhydrous ferric phosphate in the examples and comparative examples after grinding for 160 min

[0196] It can be seen from Tables 4 and 5 that the grinding efficiency of anhydrous ferric phosphate with good primary particle consistency and pore distribution uniformity in the embodiment is higher. The grinding efficiency in Example 1 is doubled compared to that in Comparative Example 1, that is, the time required to grind to the same particle size is reduced by half. Specifically, the target grinding particle size of anhydrous ferric phosphate is generally any value between 350-450 nm (D50) or any narrower range. Here, the anhydrous ferric phosphate is ground to about 380 nm. In Example 1, it takes only 80 min to grind to 375 nm, while in the comparative example, it takes 160 min to grind to 387 nm. In addition, a comparison can also be made from another perspective. After grinding the anhydrous ferric phosphate in the embodiment and the comparative example for 80 minutes, the reduction in D50 before and after grinding is compared (the reduction is equal to the D50 of grinding for 0 minutes minus the D50 of grinding for 80 minutes). The reduction in D50 of anhydrous ferric phosphate in Examples 1-5 is 3.192, 3.188, 3.191, 3.080, and 3.045, respectively. The reduction in D50 of anhydrous ferric phosphate in Comparative Examples 1-5 is 2.906, 2.768, 2.680, 2.927, and 2.710, respectively. It can be clearly seen from this data that at the same grinding time, the reduction in D50 of the anhydrous ferric phosphate in the embodiment (the primary particles have good consistency and the secondary particles have more uniform pores) is greater than that in the comparative example, thereby achieving higher grinding efficiency. Compared with Examples 1-3, the pore uniformity of the secondary particles of anhydrous ferric phosphate in Example 4 is worse, the reduction in D50 is smaller, and thus the grinding efficiency is lower; compared with Example 4, the consistency of the primary particles and the pore uniformity of the secondary particles of anhydrous ferric phosphate in Example 5 are both worse, the reduction in D50 is smaller than that of Example 4, and thus the grinding efficiency is also lower. Details are shown in Table 4.

[0197] Since the D50 of the anhydrous ferric phosphate tested after grinding for 140 minutes in Example 1 is 7 nm larger than the D50 tested after 120 minutes, the D50 tested after grinding for 140 minutes is abnormal data, is not used for result analysis, and is not used as a reference.

[0198] Under the same grinding time, the anhydrous ferric phosphate with good primary particle consistency and pore distribution uniformity has a smaller D50 and a narrower span value. See Table 5 for details.

[0199] Anhydrous ferric phosphate with better primary particle consistency and pore uniformity can also reduce energy consumption and save costs in the grinding process.

[0200] The above are merely preferred embodiments of the present disclosure and are not intended to limit the present disclosure. Those skilled in the art will readily appreciate that various modifications and variations of the present disclosure are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present disclosure shall be included within the scope of protection of the present disclosure. Industrial Applicability

[0201] In summary, the present disclosure provides an anhydrous ferric phosphate and a preparation method thereof. The provided anhydrous ferric phosphate includes secondary particles formed by stacking a plurality of primary nanoparticles, wherein the average particle size of the primary particles in the secondary particles is 100-150 nm, and the particle size variance Q is ≤ 1000 nm. 2 The above anhydrous ferric phosphate has the characteristics of small primary particle size and good consistency. Grinding the anhydrous ferric phosphate with the above characteristics has high grinding efficiency, can save energy, increase production capacity and reduce costs, and is more conducive to its use in the preparation of lithium iron phosphate.

Claims

1. Anhydrous ferric phosphate, wherein: The anhydrous ferric phosphate comprises secondary particles formed by stacking a plurality of primary nanoparticles, wherein the average particle size of the primary particles in the secondary particles is 100-150 nm, and the particle size variance Q is less than or equal to 1000 nm. 2 .

2. The anhydrous ferric phosphate according to claim 1, wherein The average particle size of the primary particles in the secondary particles is 110-130 nm, and / or the particle size variance Q is ≤ 300 nm. 2 .

3. The anhydrous ferric phosphate according to claim 1, wherein The overall porosity of the cross section of the secondary particles is 10%-30%, and the cross section porosity uniformity coefficient R≤5; Preferably, the overall cross-sectional porosity of the secondary particles is 20%-30%, and / or the cross-sectional porosity uniformity coefficient R≤2.

4. The anhydrous ferric phosphate according to claim 1, wherein 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 specific surface area of ​​the anhydrous ferric phosphate is 10-14m 2 / g; C. The tap density TD of the anhydrous ferric phosphate is 0.6-0.8 g / cm 3 .

5. A method for preparing anhydrous ferric phosphate, wherein: include: The amorphous ferric phosphate solution is mixed with phosphoric acid and ammonium salt to obtain a mixed material, and then the mixed material is heated and then kept still, and then washed, dried and calcined to obtain anhydrous ferric phosphate.

6. The preparation method according to claim 5, wherein: 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.

7. The preparation method according to claim 5, wherein: The following steps are involved: Adding a phosphate solution containing hydrogen peroxide dropwise into a ferrous salt solution to obtain an amorphous ferric phosphate slurry, and then subjecting the amorphous ferric phosphate slurry to a filter press and rinse to obtain a first rinsed material; The material after the first rinse is slurried with water, and phosphoric acid and ammonium salt are added to obtain a mixed slurry, and then the mixed slurry is heated and then kept still, and then subjected to secondary filter pressing and rinsing to obtain a material after the second rinse; The material after the second rinse is then dried and calcined to obtain anhydrous iron phosphate; Preferably, the ammonium salt includes one or more of ammonium sulfate, ammonium phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate; Preferably, the mixed slurry is stirred evenly and then heated to 95-100° C., and the insulation time is 10-150 min; Preferably, the material after the second rinsing is dried at 100-200° C., and then calcined at 550-800° C. for 4-8 hours to obtain anhydrous iron phosphate.

8. The preparation method according to claim 5, wherein: The preparation of amorphous iron phosphate slurry comprises: adding a ferrous salt solution into a reaction kettle, then simultaneously adding a phosphate solution and hydrogen peroxide dropwise, and continuing aging after the addition is completed to obtain an amorphous iron phosphate slurry; Preferably, the preparation of the ferrous salt solution comprises: 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 impurity precipitation, collecting the filtrate and diluting it with water to obtain a ferrous salt solution with a concentration of 30-80 g / L; Preferably, the preparation of the phosphate solution comprises: dissolving phosphate in water, adding alkali to adjust the pH to 6.0-8.0, and then diluting with water at a temperature of 30-50° C. to a phosphate concentration of 60-100 g / L to obtain the phosphate solution.

9. A lithium iron phosphate positive electrode material, wherein: The lithium iron phosphate positive electrode material is made of a raw material containing anhydrous iron phosphate, and the anhydrous iron phosphate is the anhydrous iron phosphate described in any one of claims 1-4 or the anhydrous iron phosphate prepared by the preparation method described in any one of claims 5-8.

10. A lithium ion battery, wherein: The lithium-ion battery comprises a positive electrode made of the lithium iron phosphate positive electrode material according to claim 9, a negative electrode, a separator and an electrolyte.

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