Method for preparing lithium iron phosphate by using iron hydroxy phosphate and lithium iron phosphate pole piece material and application thereof

Abstract

This invention provides a method for preparing lithium iron phosphate from hydroxyferric phosphate and lithium iron phosphate electrode material. Ferrous sulfate is purified to form a ferrous sulfate solution. Hydrogen peroxide, phosphoric acid, ammonium dihydrogen phosphate solution, and ammonia are added to the ferrous sulfate solution to form a mixed slurry. The mixed slurry is kept at room temperature for a period of time, then washed with water and filtered to form hydroxyferric phosphate precursors with different iron-phosphorus ratios. These precursors are then flash-dried and sintered at high temperature to obtain hydroxyferric phosphate precursors with different iron-phosphorus ratios and specific surface areas. The hydroxyferric phosphate precursors are pulverized and mixed to obtain the finished hydroxyferric phosphate product. High-iron-phosphorus ratio hydroxyferric phosphate and low-iron-phosphorus ratio hydroxyferric phosphate are mixed in a certain proportion and then formulated with lithium phosphate, lithium iron phosphate, and electrode material in a specific ratio, with the addition of a carbon source and additives to form a mixture. The mixture is then subjected to ball milling, sand milling, spray drying, sintering, pulverizing, sieving, batching, and packaging processes to obtain the finished lithium iron phosphate product.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of a lithium ion battery positive electrode material preparation method, in particular to a method for preparing lithium iron phosphate from iron hydroxyphosphate and lithium iron phosphate pole piece materials and application of the method. BACKGROUND

[0002] The lithium iron phosphate positive electrode material is a lithium battery positive electrode material that is currently developing most rapidly in China, raw materials of the lithium iron phosphate positive electrode material are widely available, the lithium iron phosphate positive electrode material is low in price, and is widely applied to the domestic battery industry and is applied to the fields of automobiles, electric tools, energy storage equipment, emergency power supply equipment and mobile power sources. New energy electric vehicles are main application fields, and the proportion of lithium iron phosphate used in the new energy electric vehicles accounts for more than 45% of the total amount of lithium iron phosphate. Compared with other positive electrode materials, the lithium iron phosphate positive electrode material has the advantages of safety, environmental protection, low price, long cycle life and good high-temperature performance, and is one of the most potential lithium ion battery positive electrode materials. At present, the methods for preparing lithium iron phosphate mainly include a solid phase method, a carbon thermal reduction method and a sol-gel template method.

[0003] For example, CN105024073A discloses a lithium ion battery positive electrode material, iron hydroxyphosphate, and a preparation method thereof. The molecular formula of the lithium ion battery positive electrode material is Fe 2.95 (PO4)2(OH)2; the preparation method is as follows: H3PO4 solution, FeCl3 solid powder and water are uniformly mixed, methyl triethyl ammonium chloride is added to adjust the pH to 2.0-3.5, a hydrothermal synthesis reaction is performed at a temperature of 150-200 DEG C for 30 h to obtain a reaction liquid, and the reaction liquid is subjected to centrifugal separation, cleaning and drying to obtain Fe 2.95 (PO4)2(OH)2.

[0004] In the journal “Performance Research on Lithium Iron Phosphate Prepared from Iron Hydroxyphosphate for Lithium Ion Battery Positive Electrode Material”, iron phosphate waste slag, phosphoric acid and hydrogen peroxide are used as raw materials to synthesize iron hydroxyphosphate and then prepare lithium iron phosphate.

[0005] However, the reaction temperature required by the above method is high, the reaction time is long, the reaction conditions are harsh, high equipment is required for production, and the generation efficiency is low, which does not meet the needs of reducing the cost of lithium iron phosphate in the market. Moreover, the raw material cost price of the above method is high, there are many impurities in the finished product and it is difficult to remove the impurities, which will affect the product performance of the iron hydroxyphosphate and the product performance of the lithium iron phosphate. SUMMARY

[0006] In view of the above, the present invention aims to at least solve one of the technical problems existing in the prior art. Therefore, the present invention proposes a method for preparing lithium iron phosphate from lithium hydroxyphosphate and lithium iron phosphate electrode materials, and its application. This method uses ferrous sulfate as a material, adds hydrogen peroxide, phosphoric acid, ammonium dihydrogen phosphate, and ammonia to synthesize lithium hydroxyphosphate, and uses lithium phosphate and lithium iron phosphate electrode materials as raw materials to prepare low-cost, high-density, and high-capacity lithium iron phosphate. Furthermore, this method has high production efficiency and low production cost, making it suitable for large-scale industrial production applications.

[0007] Therefore, in a first aspect, embodiments of the present invention provide a method for preparing lithium iron phosphate from lithium hydroxyphosphate and lithium iron phosphate electrode material. The method includes: adding ferrous sulfate, a byproduct of titanium dioxide, to a phosphorus source and a precipitant for purification, and obtaining a ferrous sulfate solution after pressure filtration; adding an appropriate amount of phosphoric acid to the ferrous sulfate solution to lower its pH value; adding hydrogen peroxide, phosphoric acid, ammonium dihydrogen phosphate solution, and ammonia to the ferrous sulfate solution and reacting for a period of time to form a mixed slurry; keeping the mixed slurry at room temperature for a period of time and then washing and filtration multiple times to form hydroxyphosphate precursors with different iron-phosphorus ratios; flash drying the hydroxyphosphate precursors in a flash evaporator and sintering at high temperature for a certain time to obtain hydroxyphosphate precursors with different iron-phosphorus ratios and different specific surface areas. The process involves: 1) pulverizing the sintered material using a mechanical mill and mixing it with a ribbon mixer to obtain hydroxyferric phosphate products with different iron-to-phosphorus ratios and specific surface areas; 2) mixing high-iron-to-phosphorus ratio hydroxyferric phosphate and low-iron-to-phosphorus ratio hydroxyferric phosphate in a certain proportion, then blending it with lithium phosphate and lithium iron phosphate electrode materials in a certain proportion, and adding a certain amount of carbon source and additives to form a mixture; 3) sand milling the mixture to obtain a nano-sized sand mill slurry; 4) spray drying the nano-sized sand mill slurry to obtain a spray material; 5) sintering the spray material in a box furnace to obtain a sintered material, then pulverizing the sintered material using an air jet mill to obtain a pulverized material; and finally, further processing the pulverized material through sieving, batching, and packaging to obtain the finished lithium iron phosphate product.

[0008] Preferably, in step S1, the ferrous sulfate : phosphorus source : precipitant are in a mass ratio of 1 : [0.001-0.005] : [0.005-0.007], the purification reaction temperature is 40°C, the reaction pH is 2.2-2.5, the reaction time is 1 hour, the phosphorus source is one or more of phosphoric acid, monoammonium phosphate, diammonium phosphate, and sodium phosphate, and the precipitant is one or more of sodium hydroxide, potassium hydroxide, lithium hydroxide, and ammonia water.

[0009] Preferably, in step S2, the amount of phosphoric acid added is in a molar ratio of n(Fe):n(phosphoric acid) = 1:0.15; in step S3, when the iron-phosphorus feeding ratio in the mixed slurry meets the iron-phosphorus molar ratio: Fe / P = 1.475-1.490, high iron-phosphorus ratio hydroxyferric phosphate can be formed; when the iron-phosphorus feeding ratio in the mixed slurry meets the iron-phosphorus molar ratio: Fe / P = 1.460-1.475, low iron-phosphorus ratio hydroxyferric phosphate can be generated.

[0010] Preferably, in step S3, the water washing is performed at least multiple times. The first water wash mainly removes impurities such as magnesium, manganese, and sulfur. In the final water wash, a 1:1 diluted ammonia solution is added to adjust the pH to 6.5-7.0 to remove SO4. 2- Ions; the hydrogen peroxide concentration is 30%-60%, and the mixed slurry is kept at room temperature for 3 hours.

[0011] Preferably, step S3 includes: adding excess hydrogen peroxide to the ferrous sulfate solution and continuing oxidation for a certain period of time; dissolving ammonium dihydrogen phosphate powder in water to prepare a 30% concentration ammonium dihydrogen phosphate solution at a dissolution temperature of 30-40℃; then adding phosphoric acid solution and ammonia water to the ammonium dihydrogen phosphate solution and stirring to mix evenly to form a phosphate-ammonium mixed solution; adding the phosphate-ammonium mixed solution to the oxidized ferrous sulfate solution, adjusting the pH of the solution to 3.00±0.02, reacting for a period of time to form a mixed slurry, and then repeatedly washing and filtering the mixed slurry with water at room temperature for a period of time to form hydroxyferric phosphate precursors with different iron-phosphorus ratios.

[0012] Preferably, in step S4, the inlet air temperature of the flash evaporator is controlled at 220±20℃, the outlet air temperature at 110±5℃, the sintering atmosphere is air, the sintering temperature is 535-560℃, and the sintering time is 4-5h; in step S5, the particle size is controlled at D10≥1.0μm, D50: 6-15μm, D90≤60μm, the mixing frequency of the mixer is controlled at 35±2Hz, and the mixing time is 1-2h; the high-iron-phosphorus hydroxyferric phosphate has a high specific surface area, and its iron-phosphorus molar ratio satisfies: Fe / P=1.460-1.480, and its specific surface area satisfies: BET=15-20m². 2 / g; the low iron-to-phosphorus ratio hydroxyferric phosphate has a low specific surface area, and its iron-to-phosphorus molar ratio satisfies: Fe / P=1.440-1.460, and its specific surface area satisfies: BET=5-10m². 2 / g.

[0013] Preferably, in step S6, the method for preparing the lithium iron phosphate electrode material includes: crushing and sieving waste lithium iron phosphate positive electrode sheets to separate foil and lithium iron phosphate electrode material raw materials; sintering the lithium iron phosphate electrode material raw materials under an inert atmosphere at a sintering temperature of 400-500℃ for 1-4 hours, and then crushing them to a particle size of 1-5μm to obtain the lithium iron phosphate electrode material.

[0014] Preferably, in step S6, according to the molar ratio Li:Fe:P = [1.03-1.04]:1:[1.03-1.04], the amount of carbon source added is based on the carbon content in the final product being between 1.2% and 1.6%. The carbon source is one or more of sucrose, glucose, citric acid, starch, and polyethylene glycol. The additive is one or more of titanium dioxide, ammonium metavanadate, and niobium pentoxide, and the doping amount is controlled between 300 and 3000 ppm. In step S7, the abrasive particle size in the abrasive slurry is controlled between 0.45 and 0.75 μm, and in spray drying, the inlet air temperature is 200-220°C. The temperature is 0℃, the outlet air temperature is 80-110℃, the blowing frequency is 80Hz, and the spray particle size in the spray material is controlled between D50=20-40μm; in step S8, the sintering atmosphere is nitrogen, the sintering temperature is 750-780℃, the heating rate is 3℃ / min, the sintering time is 8-12h, and after natural cooling, the sintered material can be obtained. During the crushing process, the air pressure is controlled between 0.2-0.4Mpa, the grading frequency is 80-200Hz, and the particle size of the crushed material meets the following requirements: D10>0.35μm, D50=0.7-2.0μm, D90<10μm, D100<30μm.

[0015] Secondly, embodiments of the present invention provide a lithium-ion battery cathode material obtained by processing lithium iron phosphate prepared by the method for preparing lithium iron phosphate using hydroxy iron phosphate and lithium iron phosphate electrode material provided in the first aspect above.

[0016] Thirdly, embodiments of the present invention provide a lithium-ion battery, including the lithium-ion battery cathode material described in the second aspect above.

[0017] This invention provides a method for preparing lithium iron phosphate from ferrous hydroxyphosphate and lithium iron phosphate electrode materials. Ferrous sulfate, a byproduct of titanium dioxide production, is used to generate ferric sulfate. After adding other materials and reacting, ferrous hydroxyphosphate with different iron-to-phosphorus ratios is generated. Different sintering processes are then used to obtain ferrous hydroxyphosphate products with high iron-to-phosphorus ratio and high specific surface area, and low iron-to-phosphorus ratio and low specific surface area. The high-iron-to-phosphorus-ratio, high-specific-surface-area ferrous phosphate and low-iron-to-phosphorus-ratio, low-specific-surface-area ferrous phosphate are mixed and then mixed with lithium phosphate and lithium iron phosphate electrode materials in a certain proportion. A carbon source and additives are added to form a mixture. The mixture is then subjected to sand milling, spray drying, sintering, sieving, batching, and packaging to obtain the finished lithium iron phosphate product. This method uses a mixture of high- and low-iron-phosphorus-ratio ferrous phosphates and introduces lithium phosphate and recycled waste lithium iron phosphate positive electrode materials to prepare lithium iron phosphate electrode materials. The recycled lithium iron phosphate electrode materials can greatly reduce material costs and recycle waste lithium iron phosphate electrode materials. During the sintering process, lithium iron phosphate electrode material helps to provide steric hindrance, reduce the agglomeration of lithium iron phosphate particles, improve the roundness of lithium iron phosphate particles, and enhance the compaction density and electrochemical performance of lithium iron phosphate materials. Furthermore, this method requires low reaction temperatures and short reaction times, has low equipment requirements, and a simple process flow, thus improving production efficiency and making it suitable for large-scale industrial production. Attached Figure Description

[0018] Figure 1 This is a flowchart of a method for preparing lithium iron phosphate from lithium hydroxyphosphate and lithium iron phosphate electrode material according to an embodiment of the present invention;

[0019] Figure 2 A flowchart illustrating step S3 of the present invention for preparing lithium iron phosphate from lithium hydroxyphosphate and lithium iron phosphate electrode material;

[0020] Figure 3 This is the SEM image of the high iron-to-phosphorus ratio and high specific surface area ferric hydroxyphosphate prepared in Example 1 of the present invention;

[0021] Figure 4 The image shows the SEM spectrum of the lithium iron phosphate cathode material prepared in Example 1 of this invention.

[0022] Figure 5 The XRD pattern of the high ferric phosphorus ratio and high specific surface area hydroxyferric phosphate prepared in Example 1 of this invention;

[0023] Figure 6 The image shows the XRD pattern of the lithium iron phosphate cathode material prepared in Example 1 of this invention.

[0024] Figure 7 The charge-discharge curve (0.1C) of a coin cell assembled with the lithium iron phosphate cathode material prepared in Example 1 of this invention;

[0025] Figure 8 The charge-discharge curve (1C) of a coin cell assembled with the lithium iron phosphate cathode material prepared in Example 1 of this invention. Detailed Implementation

[0026] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0027] The following disclosure provides numerous different embodiments or examples for implementing various structures of the invention. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples. Such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. Additionally, examples of various specific processes and materials are provided in this invention; however, those skilled in the art will recognize the applicability of other processes and / or the use of other materials.

[0028] This invention provides a method for preparing lithium iron phosphate from lithium hydroxyapatite and lithium iron phosphate electrode materials, thereby producing low-cost, high-density, and high-capacity lithium iron phosphate. Figure 1 As shown, this method includes:

[0029] Step S1: Add ferrous sulfate, a byproduct of titanium dioxide, to a phosphorus source and a precipitant for purification. After pressure filtration and purification, a ferrous sulfate solution is obtained.

[0030] The reaction was carried out in the following mass ratio: ferrous sulfate: phosphorus source: precipitant = 1: [0.001-0.005]: [0.005-0.007]. The purification reaction temperature was 40℃, the reaction pH was 2.2-2.5, and the reaction time was 1h.

[0031] In this embodiment, the phosphorus source can be one or more of phosphoric acid, monoammonium phosphate, diammonium phosphate, sodium phosphate, etc., and the precipitant can be one or more of sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonia water, etc.

[0032] Step S2: Add an appropriate amount of phosphoric acid to the ferrous sulfate solution to lower the pH value of the ferrous sulfate solution;

[0033] The amount of phosphoric acid added is based on a molar ratio of n(Fe):n(phosphoric acid) = 1:0.15.

[0034] Step S3: Add hydrogen peroxide, phosphoric acid, ammonium dihydrogen phosphate solution and ammonia to ferrous sulfate solution and react for a period of time to form a mixed slurry. After keeping the mixed slurry at room temperature for a period of time, wash and filter it multiple times with water to form hydroxyferric phosphate precursors with different iron-phosphorus ratios.

[0035] When the iron-phosphorus feeding ratio in the mixed slurry meets the iron-phosphorus molar ratio of Fe / P = 1.475-1.490, high iron-phosphorus ratio hydroxyferric phosphate can be formed; when the iron-phosphorus feeding ratio in the mixed slurry meets the iron-phosphorus molar ratio of Fe / P = 1.460-1.475, low iron-phosphorus ratio hydroxyferric phosphate can be generated.

[0036] In this embodiment, the hydrogen peroxide concentration is between 30% and 60%, and the mixed slurry is kept at room temperature for 3 hours. The washing process can be repeated multiple times. The first wash primarily removes impurities such as magnesium, manganese, and sulfur. The final wash involves adding 1:1 diluted ammonia to adjust the pH to 6.5-7.0 to remove SO4. 2- Ions. Specifically, the water washing can be performed three times. The first and second water washes mainly remove impurities such as manganese, magnesium, and sulfur. In the third water wash, a 1:1 diluted ammonia solution is added to adjust the pH to 6.5-7.0 to remove SO4. 2- ion.

[0037] Specifically, in the first embodiment of the present invention, as Figure 2 As shown, step S3 includes:

[0038] Step S31: Add excess hydrogen peroxide to the ferrous sulfate solution and continue oxidation for a certain period of time;

[0039] Step S32: Dissolve ammonium dihydrogen phosphate powder in water to prepare a 30% concentration ammonium dihydrogen phosphate solution at a dissolution temperature of 30-40℃. Then add phosphoric acid solution and ammonia water to the ammonium dihydrogen phosphate solution and stir to mix evenly to form a mixed ammonium phosphate solution.

[0040] Step S33: Add the ammonium phosphate mixed solution to the oxidized ferrous sulfate solution, adjust the pH of the solution to 3.00±0.02, and after reacting for a period of time, a mixed slurry is formed. After keeping the mixed slurry at room temperature for a period of time, it is washed and filtered repeatedly with water to form hydroxyferric phosphate precursors with different iron-phosphorus ratios.

[0041] Step S4: Flash dry the hydroxyferric phosphate precursor in a flash evaporator and sinter it at high temperature for a certain time to obtain hydroxyferric phosphate precursor products with different iron-phosphorus ratios and different specific surface areas.

[0042] The flash drying of the ferric hydroxyphosphate precursor is to remove free water. The inlet air temperature of the flash evaporator is controlled at 220±20℃, and the outlet air temperature is controlled at 110±5℃. The sintering atmosphere is air, the sintering temperature can be 535-560℃, and the sintering time can be 4-5 hours.

[0043] Step S5: The sintered material is crushed by a mechanical mill and mixed by a ribbon mixer to obtain hydroxy ferric phosphate products with different iron-phosphorus ratios and different specific surface areas.

[0044] During the pulverization process, the particle size is controlled as follows: D10 ≥ 1.0 μm, D50 6-15 μm, and D90 ≤ 60 μm. The mixing frequency of the mixer is controlled at 35 ± 2 Hz, and the mixing time can be 1-2 hours.

[0045] In this embodiment of the invention, the high-iron-phosphorus ferric phosphate has a high specific surface area, and its iron-phosphorus molar ratio satisfies: Fe / P = 1.460-1.480, and its specific surface area satisfies: BET = 15-20 m². 2 / g; The low iron-to-phosphorus ratio hydroxyferric phosphate precursor has a low specific surface area, and its iron-to-phosphorus molar ratio satisfies: Fe / P=1.440-1.460, and its specific surface area satisfies: BET=5-10m². 2 / g.

[0046] Step S6: Mix high-iron-phosphorus ratio hydroxyferric phosphate and low-iron-phosphorus ratio hydroxyferric phosphate in a certain proportion, then mix them with lithium phosphate and lithium iron phosphate electrode materials in a certain proportion, and add a certain amount of carbon source and additives to form a mixture.

[0047] Preferably, the lithium iron phosphate electrode material can be prepared from recycled waste lithium iron phosphate positive electrode sheets to reduce material costs. Specifically, the lithium iron phosphate electrode material can be prepared by the following method: crushing and sieving the waste lithium iron phosphate positive electrode sheets to separate the foil material from the lithium iron phosphate electrode material raw material; sintering the lithium iron phosphate electrode material raw material under an inert atmosphere at a sintering temperature of 400-500℃ for 1-4 hours, and then crushing it to a particle size of 1-5μm to obtain the lithium iron phosphate electrode material.

[0048] In this embodiment of the invention, the ratio of high-iron-phosphorus hydroxyferric phosphate to low-iron-phosphorus hydroxyferric phosphate is between 2:8 and 8:2, preferably, the ratio of high-iron-phosphorus hydroxyferric phosphate to low-iron-phosphorus hydroxyferric phosphate is 3:7. Furthermore, in the mixture, the molar ratio is Li:Fe:P = [1.03-1.04]:1:[1.03-1.04]. In this embodiment of the invention, the amount of carbon source added is based on a carbon content of 1.2%-1.6% in the final product.

[0049] In this embodiment of the invention, the carbon source can be one or more of sucrose, glucose, citric acid, starch, and polyethylene glycol, and the additive can be one or more of titanium dioxide, ammonium metavanadate, and niobium pentoxide, with the doping amount controlled between 300-3000 ppm.

[0050] Step S7: The above mixture is milled to obtain a nano-sized milled slurry; the nano-sized milled slurry is spray-dried to obtain a spray-dried material;

[0051] Specifically, the abrasive particle size in the abrasive slurry is controlled between 0.45 and 0.75 μm. In spray drying, the inlet air temperature can be 200-220℃, the outlet air temperature can be 80-110℃, the blowing frequency can be 80Hz, and the final spray particle size in the sprayed material is controlled between D50 and 20-40 μm.

[0052] Step S8: The above sprayed material is placed in a box furnace for sintering to obtain sintered material, and the sintered material is pulverized by an air jet mill to obtain pulverized material;

[0053] During the sintering process, the sintering atmosphere is nitrogen, the sintering temperature is 750-780℃, the heating rate is 3℃ / min, and the sintering time is 8-12h. After natural cooling, the sintered material is obtained. During the pulverization process, the gas pressure is controlled between 0.2-0.4Mpa, the grading frequency is 80-200Hz, and the particle size of the final pulverized material meets the following requirements: D10>0.35μm, D50=0.7-2.0μm, D90<10μm, D100<30μm.

[0054] Step S9: After further processing the above-mentioned pulverized material through screening, batching, and packaging, the finished lithium iron phosphate product can be obtained.

[0055] The method for preparing lithium iron phosphate from ferrous hydroxyphosphate and lithium iron phosphate electrode material provided in this invention utilizes ferrous sulfate, a byproduct of titanium dioxide production, to generate ferric sulfate. After adding other materials and reacting, ferrous hydroxyphosphate precursors with different iron-to-phosphorus ratios are generated. These precursors are then subjected to different sintering processes to obtain ferrous hydroxyphosphate products with high iron-to-phosphorus ratios and high specific surface areas, and low iron-to-phosphorus ratios and low specific surface areas. Compared with iron phosphate prepared by traditional methods, the ferrous hydroxyphosphate prepared by this method does not require an 80-90℃ crystallization synthesis step and is a spherical, small-particle amorphous precursor. During the water washing and purification stage, impurities are not easily trapped inside the crystals. After multiple water washes, the main impurities removed are magnesium, manganese, sulfur, and SO4. 2-The product contains few ions and other impurities, resulting in low impurity content and high purity. Furthermore, the iron-to-phosphorus ratio and specific surface area of ​​the hydroxyferric phosphate produced by this method are adjustable, allowing for the generation of hydroxyferric phosphates with different iron-to-phosphorus ratios as needed. High iron-to-phosphorus ratio hydroxyferric phosphate particles are smaller, improving the material's discharge capacity; low iron-to-phosphorus ratio hydroxyferric phosphate particles are larger, increasing the material's compaction density, which is more conducive to the subsequent construction of the lithium iron phosphate crystal structure.

[0056] In this method, high-iron-phosphorus ratio hydroxyferric phosphate and low-iron-phosphorus ratio hydroxyferric phosphate are mixed in subsequent steps, and then mixed with lithium phosphate and lithium iron phosphate electrode materials in a certain proportion. After adding carbon sources and additives to form a mixture, the mixture undergoes sand milling, spray drying, sintering, sieving, batching, and packaging to obtain the finished lithium iron phosphate product. This method uses a mixture of high- and low-iron-phosphorus ratio hydroxyferric phosphates, and introduces lithium phosphate and recycled waste lithium iron phosphate positive electrode materials to prepare lithium iron phosphate electrode materials. The recycled lithium iron phosphate electrode materials can significantly reduce material costs, and the waste lithium iron phosphate electrode materials are recycled and reused. During the sintering process, the lithium iron phosphate electrode materials help provide steric hindrance, reduce the agglomeration of lithium iron phosphate particles, and improve the roundness of lithium iron phosphate particles, thereby improving the compaction density and electrochemical performance of the lithium iron phosphate material. In addition, this method requires low reaction temperature and short reaction time, has low equipment requirements, and a simple process flow, improving production efficiency and making it suitable for large-scale industrial production.

[0057] The following detailed description, in conjunction with some specific embodiments, further illustrates the specific process and effects of the method for preparing lithium iron phosphate using hydroxyferric phosphate and lithium iron phosphate electrode materials of the present invention, but does not limit the scope of protection of the present invention.

[0058] Example 1

[0059] This embodiment provides a method for preparing lithium iron phosphate from hydroxyapatite and lithium iron phosphate electrode material, including the following steps:

[0060] Step S1: Add ferrous sulfate, a byproduct of titanium dioxide, to a solution containing 4‰ phosphoric acid and 5‰ sodium hydroxide for purification. After pressure filtration, a ferrous sulfate solution is obtained.

[0061] Step S2: Add phosphoric acid to the ferrous sulfate solution according to the molar ratio n(Fe):n(phosphoric acid) = 1:0.15 to lower the pH value of the ferrous sulfate solution;

[0062] Step S3: Add excess 40% hydrogen peroxide to the ferrous sulfate solution, then add phosphoric acid solution and 30% ammonium dihydrogen phosphate solution to the ferrous sulfate solution so that the iron-phosphorus feeding ratio in the mixed slurry successively meets the iron-phosphorus molar ratio: Fe / P = 1.490 and Fe / P = 1.460. Then add ammonia water to the ferrous sulfate solution to form a mixed slurry. After keeping the mixed slurry at room temperature for 3 hours, wash it with water and filter it to form hydroxyferric phosphate precursors with different iron-phosphorus ratios.

[0063] Step S4: The hydroxyferric phosphate precursor is flash-dried in a flash evaporator, with the flash evaporator inlet air temperature controlled at 200°C, and sintered in air atmosphere at 535°C and 555°C for 5 hours.

[0064] Step S5: The sintered material is crushed by mechanical mill, and the particle size is controlled as follows: D10≥1.0μm, D50:6-15μm, D90≤60μm. The material is then mixed by ribbon mixer at 35Hz for 1 hour to obtain hydroxy ferric phosphate with high iron-phosphorus ratio and high specific surface area and hydroxy ferric phosphate with low iron-phosphorus ratio and low specific surface area.

[0065] The SEM image of the high ferric phosphorus ratio and high specific surface area ferric phosphate prepared according to Example 1 is shown below. Figure 3 As shown.

[0066] The XRD pattern of the high ferric phosphorus ratio and high specific surface area ferric phosphate prepared according to Example 1 is shown below. Figure 5 As shown.

[0067] Step S6: Mix hydroxyferric phosphate with a high iron-to-phosphorus ratio and high specific surface area with hydroxyferric phosphate with a low iron-to-phosphorus ratio and low specific surface area in a 3:7 ratio, and then mix it with lithium phosphate and lithium iron phosphate electrode materials in a molar ratio of Li:Fe:P = 1.03:1:1.03. Add a carbon source mixture of sucrose and polyethylene glycol to make the carbon content of the finished product 1.3%, and titanium dioxide with a doping amount of 2800ppm to form a mixture. The lithium iron phosphate electrode material can be obtained by crushing and sieving waste lithium iron phosphate positive electrode sheets to separate the foil material from the lithium iron phosphate electrode material raw material. The lithium iron phosphate electrode material raw material is sintered in an inert atmosphere at a sintering temperature of 400℃ for 4 hours, and then crushed to a particle size of 3μm.

[0068] Step S7: The above mixture is sand-milled, and the sand-milling particle size is controlled to be 0.60μm to obtain a nano-sized sand-milling slurry; the nano-sized sand-milling slurry is spray-dried, and the inlet air temperature is controlled to be 220℃, the outlet air temperature is controlled to be 100℃, and the blowing frequency is 80Hz to obtain a spray material with a spray particle size D50 = 20-40μm.

[0069] Step S8: The above sprayed material is placed in a box furnace and sintered under a nitrogen atmosphere at a heating rate of 3℃ / min, a sintering temperature of 760℃, and a sintering time of 10h. After natural cooling, the sintered material is obtained. The sintered material is then pulverized by an air jet mill, with the air pressure controlled at 0.3Mpa and the grading frequency at 130Hz, to obtain pulverized material with particle sizes of D10>0.35μm, D50=0.8-1.8μm, D90<10μm, and D100<30μm.

[0070] Step S9: After further processing the above-mentioned pulverized material through screening, batching, and packaging, the finished lithium iron phosphate product can be obtained.

[0071] The SEM spectrum of the lithium iron phosphate cathode material prepared according to Example 1 is shown below. Figure 4 As shown.

[0072] The XRD pattern of the lithium iron phosphate cathode material prepared according to Example 1 is shown below. Figure 6 As shown.

[0073] Example 2

[0074] This embodiment provides a method for preparing lithium iron phosphate from hydroxyapatite and lithium iron phosphate electrode material, including the following steps:

[0075] Step S1: Add ferrous sulfate, a byproduct of titanium dioxide, to a solution of phosphoric acid with a mass fraction of 3‰ and sodium hydroxide with a mass fraction of 5‰ for purification. After purification by pressure filtration, a ferrous sulfate solution is obtained.

[0076] Step S2: Add phosphoric acid to the ferrous sulfate solution according to the molar ratio n(Fe):n(phosphoric acid) = 1:0.15 to lower the pH value of the ferrous sulfate solution;

[0077] Step S3: Add excess 50% hydrogen peroxide to the ferrous sulfate solution, add phosphoric acid solution and 30% ammonium dihydrogen phosphate solution to the ferrous sulfate solution to make the iron-phosphorus feeding ratio in the mixed slurry meet the iron-phosphorus molar ratio: Fe / P = 1.490 and Fe / P = 1.460. Then add ammonia water to the ferrous sulfate solution to form a mixed slurry. After keeping the mixed slurry at room temperature for 3 hours, wash it with water and filter it to form hydroxyferric phosphate precursors with different iron-phosphorus ratios.

[0078] Step S4: The hydroxyferric phosphate precursor is flash-dried in a flash evaporator, with the flash evaporator inlet air temperature controlled at 200°C, and sintered in air atmosphere at high temperatures of 540°C and 560°C for 4 hours.

[0079] Step S5: The sintered material is crushed by mechanical mill, and the particle size is controlled as follows: D10≥1.0μm, D50:6-15μm, D90≤60μm. The material is then mixed by ribbon mixer at 35Hz for 1 hour to obtain hydroxy ferric phosphate with high iron-phosphorus ratio and high specific surface area and hydroxy ferric phosphate with low iron-phosphorus ratio and low specific surface area.

[0080] Step S6: Hydroxyferric phosphate with a high iron-to-phosphorus ratio and high specific surface area is mixed with hydroxyferric phosphate with a low iron-to-phosphorus ratio and low specific surface area in a 4:6 ratio. This mixture is then combined with lithium phosphate and lithium iron phosphate electrode material in a molar ratio of Li:Fe:P = 1.03:1:1.03. A carbon source mixture consisting of glucose and polyethylene glycol, which makes the carbon content of the finished product 1.4%, and ammonium metavanadate with a doping amount of 3000ppm are added to form a mixture. The lithium iron phosphate electrode material can be obtained by crushing and sieving waste lithium iron phosphate positive electrode sheets to separate the foil material from the lithium iron phosphate electrode material raw material. The lithium iron phosphate electrode material raw material is sintered in an inert atmosphere at a sintering temperature of 400℃ for 4 hours, and then crushed to a particle size of 3μm.

[0081] Step S7: The above mixture is sand-milled, and the sand-milling particle size is controlled to be 0.55μm to obtain a nano-sized sand-milling slurry; the nano-sized sand-milling slurry is spray-dried, and the inlet air temperature is controlled to be 220℃, the outlet air temperature is controlled to be 100℃, and the blowing frequency is 80Hz to obtain a spray material with a spray particle size D50 = 20-40μm.

[0082] Step S8: The above sprayed material is placed in a box furnace and sintered under a nitrogen atmosphere. The heating rate is 3℃ / min, the sintering temperature is 770℃, and the sintering time is 8h. After natural cooling, the sintered material is obtained. The sintered material is then pulverized by an air jet mill, with the air pressure controlled at 0.3Mpa and the classification frequency at 130Hz, to obtain pulverized material with particle sizes of D10>0.35μm, D50=0.8-1.8μm, D90<10μm, and D100<30μm.

[0083] Step S9: After further processing the above-mentioned pulverized material through screening, batching, and packaging, the finished lithium iron phosphate product can be obtained.

[0084] Example 3

[0085] This embodiment provides a method for preparing lithium iron phosphate from hydroxyapatite and lithium iron phosphate electrode material, including the following steps:

[0086] Step S1: Add ferrous sulfate, a byproduct of titanium dioxide, to a solution containing 2‰ phosphoric acid and 4‰ sodium hydroxide for purification. After pressure filtration, a ferrous sulfate solution is obtained.

[0087] Step S2: Add phosphoric acid to the ferrous sulfate solution according to the molar ratio n(Fe):n(phosphoric acid) = 1:0.15 to lower the pH value of the ferrous sulfate solution;

[0088] Step S3: Add excess 40% hydrogen peroxide to the ferrous sulfate solution, then add phosphoric acid solution and 30% ammonium dihydrogen phosphate solution to the ferrous sulfate solution so that the iron-phosphorus feeding ratio in the mixed slurry successively meets the iron-phosphorus molar ratio: Fe / P = 1.480 and Fe / P = 1.465. Then add ammonia water to the ferrous sulfate solution to form a mixed slurry. After keeping the mixed slurry at room temperature for 3 hours, wash it with water and filter it to form hydroxyferric phosphate precursors with different iron-phosphorus ratios.

[0089] Step S4: The hydroxyferric phosphate precursor is flash-dried in a flash evaporator, with the flash evaporator inlet air temperature controlled at 200°C, and sintered in air atmosphere at 540°C and 555°C for 4 hours.

[0090] Step S5: The sintered material is crushed by mechanical mill, and the particle size is controlled as follows: D10≥1.0μm, D50:6-15μm, D90≤60μm. The material is then mixed by ribbon mixer at 35Hz for 1 hour to obtain hydroxy ferric phosphate with high iron-phosphorus ratio and high specific surface area and hydroxy ferric phosphate with low iron-phosphorus ratio and low specific surface area.

[0091] Step S6: Hydroxyferric phosphate with a high iron-to-phosphorus ratio and high specific surface area is mixed with hydroxyferric phosphate with a low iron-to-phosphorus ratio and low specific surface area in a 5:5 ratio. This mixture is then combined with lithium phosphate and lithium iron phosphate electrode materials in a molar ratio of Li:Fe:P = 1.03:1:1.03. A carbon source mixture consisting of sucrose, polyethylene glycol, and citric acid, with a carbon content of 1.5% in the finished product, and titanium dioxide with a doping amount of 3000 ppm are added to form a mixture. The lithium iron phosphate electrode material can be obtained by pulverizing and sieving waste lithium iron phosphate positive electrode sheets to separate the foil material from the lithium iron phosphate electrode material raw material. The lithium iron phosphate electrode material raw material is sintered under an inert atmosphere at a sintering temperature of 400℃ for 4 hours, and then pulverized to a particle size of 3 μm.

[0092] Step S7: The above mixture is sand-milled, and the sand-milling particle size is controlled to be 0.65μm to obtain a nano-sized sand-milling slurry; the nano-sized sand-milling slurry is spray-dried, and the inlet air temperature is controlled to be 210℃, the outlet air temperature is controlled to be 100℃, and the blowing frequency is 80Hz to obtain a spray material with a spray particle size D50 = 20-40μm.

[0093] Step S8: The above sprayed material is placed in a box furnace and sintered under a nitrogen atmosphere at a heating rate of 3℃ / min, a sintering temperature of 765℃, and a sintering time of 10h. After natural cooling, the sintered material is obtained. The sintered material is then pulverized by an air jet mill, with the air pressure controlled at 0.35Mpa and the grading frequency at 140Hz, to obtain pulverized material with particle sizes of D10>0.35μm, D50=0.8-1.8μm, D90<10μm, and D100<30μm.

[0094] Step S9: After further processing the above-mentioned pulverized material through screening, batching, and packaging, the finished lithium iron phosphate product can be obtained.

[0095] Comparative Example 1

[0096] This embodiment provides a method for preparing lithium iron phosphate from hydroxyapatite and lithium iron phosphate electrode material, including the following steps:

[0097] Step S1: Add ferrous sulfate, a byproduct of titanium dioxide, to a solution containing 6‰ phosphoric acid and 4‰ sodium hydroxide for purification. After purification by pressure filtration, a ferrous sulfate solution is obtained.

[0098] Step S2: Add phosphoric acid to the ferrous sulfate solution according to the molar ratio n(Fe):n(phosphoric acid) = 1:0.15 to lower the pH value of the ferrous sulfate solution;

[0099] Step S3: Add excess 10% hydrogen peroxide to the ferrous sulfate solution, then add phosphoric acid solution and 30% ammonium dihydrogen phosphate solution to the ferrous sulfate solution so that the iron-phosphorus feeding ratio in the mixed slurry successively meets the iron-phosphorus molar ratio: Fe / P = 1.44. Then add ammonia water to the ferrous sulfate solution to form a mixed slurry. After keeping the mixed slurry at room temperature for 2 hours, wash it with water and filter it to form the hydroxyferric phosphate precursor.

[0100] Step S4: The hydroxyferric phosphate precursor is flash-dried in a flash evaporator, with the flash evaporator inlet air temperature controlled at 200°C, and sintered in air atmosphere at 520°C for 2 hours.

[0101] Step S5: The sintered material is crushed by mechanical mill, and the particle size is controlled as D10≥1.0μm, D50:6-15μm, D90≤60μm. The material is then mixed with a ribbon mixer at 35Hz for 1 hour to obtain hydroxyferric phosphate product with a single iron-phosphorus ratio and a single specific surface area.

[0102] Step S6: Hydroxyferric phosphate, lithium phosphate, and lithium iron phosphate electrode material are mixed in a molar ratio of Li:Fe:P = 1.03:1:1.03. A carbon source mixture consisting of sucrose and polyethylene glycol, with a carbon content of 1.2% in the finished product, and titanium dioxide with a doping amount of 2000ppm are added to form a mixture. The lithium iron phosphate electrode material can be obtained by crushing and sieving waste lithium iron phosphate positive electrode material to separate the foil material from the lithium iron phosphate electrode material raw material. The lithium iron phosphate electrode material raw material is sintered in an inert atmosphere at a sintering temperature of 400℃ for 4 hours, and then crushed to a particle size of 3μm.

[0103] Step S7: The above mixture is sand-milled, and the sand-milling particle size is controlled to be 0.65μm to obtain a nano-sized sand-milling slurry; the nano-sized sand-milling slurry is spray-dried, and the inlet air temperature is controlled to be 220℃, the outlet air temperature is 100℃, and the blowing frequency is 80Hz to obtain a spray material with a spray particle size D50 = 20-40μm.

[0104] Step S8: The above sprayed material is placed in a box furnace and sintered under a nitrogen atmosphere at a heating rate of 3℃ / min, a sintering temperature of 755℃, and a sintering time of 10h. After natural cooling, the sintered material is obtained. The sintered material is then pulverized by an air jet mill, with the air pressure controlled at 0.35Mpa and the grading frequency at 140Hz, to obtain pulverized material with particle sizes of D10>0.35μm, D50=0.8-1.8μm, D90<10μm, and D100<30μm.

[0105] Step S9: After further processing the above-mentioned pulverized material through screening, batching, and packaging, the finished lithium iron phosphate product can be obtained.

[0106] To verify the quality of the lithium iron phosphate cathode material prepared by the method of preparing lithium iron phosphate cathode material using hydroxyl iron phosphate and lithium iron phosphate electrode material provided in the embodiments of the present invention, the lithium iron phosphate cathode material prepared in Examples 1-3 and Comparative Example 1 was dispersed in N-methylpyrrolidone with conductive agent carbon black and binder polyvinylidene fluoride at a mass ratio of 90:5:5. After ball milling and uniform dispersion, the dispersion was coated on aluminum foil and vacuum dried to obtain the cathode electrode. The electrolyte was 1 mol / L LiPF6, with a solvent volume ratio of EC:DMC:EMC = 1:1:1. The separator was Celgard polypropylene membrane, and the lithium metal sheet was used as the negative electrode. Together, they were assembled into a coin cell. The test voltage range was 2.0V-3.75V. The cathode was charged to 3.75V using a constant current and constant voltage charging method and discharged to 2.0V using a constant current discharging method. The charge and discharge currents were 0.1C for two cycles and 1C for two cycles. The test results are shown in Table 1. The charge-discharge curve (0.1C) of the coin cell assembled with the lithium iron phosphate cathode material prepared in Example 1 of the present invention is shown below. Figure 7As shown, the charge-discharge curve (1C) of the coin cell assembled with the lithium iron phosphate cathode material prepared in Example 1 of the present invention is as follows. Figure 8 As shown.

[0107] Table 1. Test items and test results for Examples 1-3 and Comparative Example 1

[0108]

[0109] Based on the above examples and comparative examples, and the test results obtained from the tests, the coin cells prepared with lithium iron phosphate cathode materials in Examples 1-3 showed significant improvements in both the initial charge-discharge specific capacity at 0.1C and the discharge specific capacity at 1C compared to Comparative Example 1.

[0110] In summary, the method for preparing lithium iron phosphate from hydroxyferric phosphate and lithium iron phosphate electrode materials provided in this invention utilizes ferrous sulfate, a byproduct of titanium dioxide production, to generate ferric sulfate. After adding other materials and reacting, hydroxyferric phosphate with different iron-to-phosphorus ratios is generated. Different sintering processes are then used to obtain hydroxyferric phosphate products with high iron-to-phosphorus ratio and high specific surface area, and low iron-to-phosphorus ratio and low specific surface area. The high-iron-to-phosphorus-ratio, high-specific-surface-area hydroxyferric phosphate and the low-iron-to-phosphorus-ratio, low-specific-surface-area hydroxyferric phosphate are mixed and then mixed with lithium phosphate and lithium iron phosphate electrode materials in a certain proportion. A carbon source and additives are added to form a mixture. The mixture is then subjected to sand milling, spray drying, sintering, sieving, batching, and packaging processes to obtain the finished lithium iron phosphate product. This method uses a mixture of high- and low-iron-phosphorus-ratio hydroxyferric phosphate and introduces lithium phosphate and recycled waste lithium iron phosphate positive electrode materials to prepare lithium iron phosphate electrode materials. The recycled lithium iron phosphate electrode materials can greatly reduce material costs, and the waste lithium iron phosphate electrode materials are recycled and reused. During the sintering process, the steric hindrance provided by the lithium iron phosphate electrode material reduces the agglomeration of lithium iron phosphate particles, improves the roundness of the particles, and enhances the compaction density and electrochemical performance of the lithium iron phosphate material. The coin cells assembled from the lithium iron phosphate cathode material prepared by this method exhibit good stability and electrochemical performance. Furthermore, this method requires low reaction temperatures and short reaction times, has low equipment requirements, and a simple process flow, thus improving production efficiency and making it suitable for large-scale industrial production.

[0111] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0112] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for preparing lithium iron phosphate from lithium hydroxyapatite and lithium iron phosphate electrode material, characterized in that, The method includes: Step S1: Add ferrous sulfate, a byproduct of titanium dioxide, to a phosphorus source and a precipitant for purification. After pressure filtration and purification, a ferrous sulfate solution is obtained. Step S2: Add an appropriate amount of phosphoric acid to the ferrous sulfate solution to lower the pH value of the ferrous sulfate solution; Step S3: Add hydrogen peroxide, phosphoric acid, ammonium dihydrogen phosphate solution, and ammonia to the ferrous sulfate solution and react for a period of time to form a mixed slurry. After keeping the mixed slurry at room temperature for a period of time, wash and filter it multiple times with water to form a hydroxyferric phosphate precursor. Specifically, control the iron-phosphorus feeding ratio in the mixed slurry to meet the iron-phosphorus molar ratio of Fe / P = 1.475-1.490 to form a high iron-phosphorus ratio hydroxyferric phosphate precursor; control the iron-phosphorus feeding ratio in the mixed slurry to meet the iron-phosphorus molar ratio of Fe / P = 1.460-1.465 to form a low iron-phosphorus ratio hydroxyferric phosphate precursor. Step S4: Flash dry the high-iron-phosphorus-ratio hydroxyferric phosphate precursor and the low-iron-phosphorus-ratio hydroxyferric phosphate precursor in a flash evaporator and sinter them at high temperature for a certain time to obtain the high-iron-phosphorus-ratio hydroxyferric phosphate precursor product and the low-iron-phosphorus-ratio hydroxyferric phosphate precursor product, respectively. Step S5: The high iron-to-phosphorus ratio hydroxy ferric phosphate precursor product and the low iron-to-phosphorus ratio hydroxy ferric phosphate precursor product obtained in step S4 are pulverized by mechanical mill and mixed by ribbon mixer to obtain the high iron-to-phosphorus ratio hydroxy ferric phosphate product and the low iron-to-phosphorus ratio hydroxy ferric phosphate product. Step S6: Mix high-iron-phosphorus ratio hydroxyferric phosphate and low-iron-phosphorus ratio hydroxyferric phosphate in a certain proportion, then mix them with lithium phosphate and lithium iron phosphate electrode materials in a certain proportion, and add a certain amount of carbon source and additives to form a mixture. Step S7: The above mixture is milled to obtain a nano-sized milled slurry; the nano-sized milled slurry is spray-dried to obtain a spray-dried material; Step S8: The above sprayed material is placed in a box furnace for sintering to obtain sintered material, and the sintered material is pulverized by an air jet mill to obtain pulverized material; Step S9: After further sieving, batching and packaging of the above-mentioned pulverized material, the finished lithium iron phosphate product can be obtained.

2. The method for preparing lithium iron phosphate from hydroxyapatite and lithium iron phosphate electrode material according to claim 1, characterized in that, In step S1, the ferrous sulfate : phosphorus source : precipitant are in a mass ratio of 1 : [0.001-0.005] : [0.005-0.007]. The purification reaction temperature is 40°C, the reaction pH is 2.2-2.5, and the reaction time is 1 hour. The phosphorus source is one or more of phosphoric acid, monoammonium phosphate, diammonium phosphate, and sodium phosphate. The precipitant is one or more of sodium hydroxide, potassium hydroxide, lithium hydroxide, and ammonia water.

3. The method for preparing lithium iron phosphate from hydroxyapatite and lithium iron phosphate electrode material according to claim 1, characterized in that, In step S2, the amount of phosphoric acid added is in a molar ratio of n(Fe):n(phosphoric acid) = 1:0.

15.

4. The method for preparing lithium iron phosphate from hydroxyapatite and lithium iron phosphate electrode material according to claim 1, characterized in that, In step S3, the water washing is performed multiple times. The first water wash mainly removes impurities such as magnesium, manganese, and sulfur. In the final water wash, a 1:1 diluted ammonia solution is added to adjust the pH to 6.5-7.0 to remove SO4. 2- Ions; the hydrogen peroxide concentration is 30%-60%, and the mixed slurry is kept at room temperature for 3 hours.

5. The method for preparing lithium iron phosphate from hydroxyapatite and lithium iron phosphate electrode material according to claim 1, characterized in that, Step S3 includes: Step S31: Add excess hydrogen peroxide to the ferrous sulfate solution and continue oxidation for a certain period of time; Step S32: Dissolve ammonium dihydrogen phosphate powder in water to prepare a 30% concentration ammonium dihydrogen phosphate solution at a dissolution temperature of 30-40℃. Then add phosphoric acid solution and ammonia water to the ammonium dihydrogen phosphate solution and stir to mix evenly to form a mixed ammonium phosphate solution. Step S33: Add the ammonium phosphate mixed solution to the oxidized ferrous sulfate solution, adjust the pH of the solution to 3.00±0.02, and after reacting for a period of time, a mixed slurry is formed. After keeping the mixed slurry at room temperature for a period of time, it is washed and filtered repeatedly with water to form a high iron-to-phosphorus ratio hydroxyferric phosphate precursor and a low iron-to-phosphorus ratio hydroxyferric phosphate precursor.

6. The method for preparing lithium iron phosphate from hydroxyapatite and lithium iron phosphate electrode material according to claim 1, characterized in that, In step S6, the method for preparing the lithium iron phosphate electrode material includes: crushing and sieving waste lithium iron phosphate positive electrode sheets to separate foil and lithium iron phosphate electrode material raw materials; sintering the lithium iron phosphate electrode material raw materials under an inert atmosphere at a sintering temperature of 400-500℃ for 1-4 hours, and then crushing them to a particle size of 1-5μm to obtain the lithium iron phosphate electrode material.

7. The method for preparing lithium iron phosphate from hydroxyapatite and lithium iron phosphate electrode material according to claim 1, characterized in that, In step S6, according to the molar ratio Li:Fe:P = [1.03-1.04]:1:[1.03-1.04], the amount of carbon source added is based on the carbon content in the final product being between 1.2% and 1.6%. The carbon source is one or more of sucrose, glucose, citric acid, starch, and polyethylene glycol. The additive is one or more of titanium dioxide, ammonium metavanadate, and niobium pentoxide, and the doping amount is controlled between 300 and 3000 ppm. In step S7, the particle size of the sand-milling slurry is controlled between 0.45 and 0.75 μm, and the inlet air temperature is 200-220℃ during spray drying. The outlet air temperature is 80-110℃, the blowing frequency is 80Hz, and the spray particle size in the spray material is controlled between D50=20-40μm; in step S8, the sintering atmosphere is nitrogen, the sintering temperature is 750-780℃, the heating rate is 3℃ / min, the sintering time is 8-12h, and after natural cooling, the sintered material can be obtained. During the crushing process, the gas pressure is controlled between 0.2-0.4Mpa, the grading frequency is 80-200Hz, and the particle size of the crushed material meets the following requirements: D10>0.35μm, D50=0.7-2.0μm, D90<10μm, D100<30μm.

8. A lithium-ion battery cathode material, characterized in that, The positive electrode material of the lithium-ion battery uses lithium iron phosphate prepared by the method for preparing lithium iron phosphate from hydroxy iron phosphate and lithium iron phosphate electrode material as described in any one of claims 1-7.

9. A lithium-ion battery, characterized in that, The lithium-ion battery includes the lithium-ion battery cathode material as described in claim 8.

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