Method for preparing lithium iron phosphate from iron hydroxyphosphate and iron oxide and application thereof

Abstract

The application provides a method for preparing lithium iron phosphate from iron hydroxyphosphate and iron oxide, in which ferrous sulfate is purified to form a ferrous sulfate solution, phosphoric acid, an ammonium dihydrogen phosphate solution, hydrogen peroxide and ammonia are sequentially added to the solution to form a mixed slurry after reaction, the mixed slurry is heated and kept warm, and then washed with water and filtered under pressure to form an iron hydroxyphosphate precursor with different iron-phosphorus ratios; the iron hydroxyphosphate precursor is dried by flash evaporation and sintered at high temperature and then crushed to obtain an iron hydroxyphosphate precursor with different iron-phosphorus ratios and different specific surface areas; the iron hydroxyphosphate precursor is crushed and mixed to obtain an iron hydroxyphosphate finished product; the iron hydroxyphosphate with a high iron-phosphorus ratio and the iron hydroxyphosphate with a low iron-phosphorus ratio are mixed according to a certain proportion, and then iron oxide, lithium phosphate, lithium carbonate and ammonium dihydrogen phosphate are proportioned and added with a carbon source and an additive to form a mixture; and the mixture is subjected to processes such as ball milling, sand milling, spray drying, sintering, crushing, screening, batching and packaging to obtain a lithium iron phosphate finished product.

Description

Technical Field

[0001] This invention relates to the technical field of lithium-ion battery cathode material preparation methods, and particularly to a method for preparing lithium iron phosphate from hydroxy iron phosphate and iron oxide, and its application. Background Technology

[0002] Lithium iron phosphate (LFP) cathode material is currently the fastest-growing lithium-ion battery cathode material in China. Its raw materials are widely available and inexpensive, and it is widely used in the domestic battery industry in fields such as automobiles, power tools, energy storage devices, emergency power supplies, and mobile power supplies. New energy electric vehicles are the main application area, accounting for over 45% of the total LFP usage. Compared with other cathode materials, LFP has advantages such as safety, environmental friendliness, low cost, long cycle life, and good high-temperature performance, making it one of the most promising lithium-ion battery cathode materials. Currently, the main methods for preparing LFP include solid-state methods, carbothermal reduction methods, and sol-gel template methods.

[0003] For example, CN105024073A discloses a lithium-ion battery cathode material, hydroxyferric phosphate, and its preparation method, wherein the molecular formula of the lithium-ion battery cathode material is Fe. 2.95 (PO4)2(OH)2; its preparation method is as follows: H3PO4 solution and FeCl3 solid powder are mixed evenly with water, then methyltriethylammonium chloride is added to adjust the pH to 2.0-3.5, and a hydrothermal synthesis reaction is carried out at 150-200℃ for 30 hours to obtain a reaction solution. The reaction solution is then centrifuged, washed, and dried to obtain Fe. 2.95 (PO4)2(OH)2.

[0004] The journal article "Performance Study of Lithium Iron Phosphate Prepared from Hydroxyferric Phosphate as Cathode Material for Lithium-ion Batteries" describes the synthesis of lithium iron phosphate from ferric phosphate waste residue (a byproduct of phosphorus chemical industry), phosphoric acid, and hydrogen peroxide.

[0005] However, the above methods require high reaction temperatures, long reaction times, and harsh reaction conditions, placing high demands on production equipment and resulting in low production efficiency, which does not meet the current market demand for cost reduction in lithium iron phosphate. Furthermore, the raw material costs of these methods are high, and the finished product contains many impurities that are difficult to remove, which will subsequently affect the performance of hydroxyl iron phosphate and, consequently, lithium iron phosphate. Summary of the Invention

[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 ferrous hydroxyphosphate and iron oxide, and its application. This method uses ferrous sulfate as a material, sequentially adding phosphoric acid, ammonium dihydrogen phosphate, hydrogen peroxide, and ammonia to synthesize ferrous hydroxyphosphate. Using iron oxide, lithium phosphate, lithium carbonate, and ammonium dihydrogen phosphate as raw materials, low-cost, high-capacity, and high-rate lithium iron phosphate is prepared. Furthermore, this method has high production efficiency and low production cost, making it suitable for large-scale industrial production.

[0007] Therefore, in a first aspect, embodiments of the present invention provide a method for preparing lithium iron phosphate from ferric hydroxyphosphate and iron oxide, the method comprising: 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 the pH value of the ferrous sulfate solution; sequentially adding phosphoric acid, ammonium dihydrogen phosphate solution, hydrogen peroxide, and ammonia to the ferrous sulfate solution and reacting for a period of time to form a mixed slurry; heating and holding the mixed slurry at a certain temperature for a period of time, and then washing and filtration multiple times with water to form ferric hydroxyphosphate precursors with different iron-phosphorus ratios; flash drying the ferric hydroxyphosphate precursors in a flash evaporator and sintering at high temperature for a certain time to obtain finished ferric hydroxyphosphate precursors with different iron-phosphorus ratios and different specific surface areas; and sintering the sintered material... The raw materials are pulverized using a mechanical mill and mixed using a ribbon mixer to obtain hydroxyferric phosphate products with different iron-phosphorus ratios and specific surface areas. High-iron-phosphorus ratio, high-specific-surface-area hydroxyferric phosphate and low-iron-phosphorus ratio, low-specific-surface-area hydroxyferric phosphate are mixed in a certain proportion, and then formulated with iron oxide, lithium phosphate, lithium carbonate, and ammonium dihydrogen phosphate in a certain proportion, with the addition of a certain amount of carbon source and additives to form a mixture. This mixture is then sand-milled to obtain a nano-sized sand-milled slurry. The nano-sized sand-milled slurry is then spray-dried to obtain a spray-dried material. This spray-dried material is then sintered in a box furnace to obtain a sintered material, which is then pulverized using an air jet mill to obtain a pulverized material. Finally, the pulverized material undergoes further processes such as 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 heated to 60-80℃ and kept at that temperature for 3 hours.

[0011] Preferably, step S3 includes: adding phosphoric acid solution to ferrous sulfate solution, then dissolving ammonium dihydrogen phosphate powder in water to prepare a 30% concentration ammonium dihydrogen phosphate solution at a dissolution temperature of 30-40℃, and adding it to the ferrous sulfate solution; then adding excess hydrogen peroxide to the ferrous sulfate solution and continuing oxidation for a certain period of time; then adding ammonia to the ferrous sulfate solution to adjust the pH value of the solution to 3.00±0.02, and after reacting for a period of time, forming a mixed slurry; heating and keeping the mixed slurry at a certain temperature for a period of time, and then washing and filtering it multiple times with water 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 is controlled 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.

[0013] Preferably, in step S5, 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 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.

[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 iron oxide 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 iron oxide. Ferrous sulfate, a byproduct of titanium dioxide production, is used to generate ferric sulfate. After reacting with other materials, 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 and high-specific-surface-area ferrous phosphate and the low-iron-to-phosphorus-ratio and low-specific-surface-area ferrous phosphate are mixed, and then mixed with iron oxide, lithium phosphate, lithium carbonate, and ammonium dihydrogen phosphate in a certain proportion. Additives are added to form a mixture, which is then subjected to sand milling, spray drying, sintering, sieving, batching, and packaging to obtain the finished lithium iron phosphate. This method uses a mixture of high- and low-iron-to-phosphorus-ratio ferrous phosphate and introduces four materials: iron oxide, lithium phosphate, lithium carbonate, and ammonium dihydrogen phosphate. The addition of iron oxide and ammonium dihydrogen phosphate effectively reduces material costs, increases the viscosity of the subsequent sand milling slurry, and improves the stability of the slurry. Furthermore, the small particle size of the iron oxide raw material results in small finished lithium iron phosphate particles, effectively improving rate performance. Ammonium dihydrogen phosphate, as a phosphorus source, increases gas production and easily reduces particle agglomeration. Additionally, this method requires low reaction temperatures and short reaction times, has low equipment requirements, and a simple process flow, improving production efficiency and making it suitable for large-scale industrial production. Attached Figure Description

[0018] Figure 1 A flowchart of a method for preparing lithium iron phosphate from hydroxyferric phosphate and iron oxide provided in an embodiment of the present invention;

[0019] Figure 2 A flowchart illustrating step S3 of the preparation of lithium iron phosphate from hydroxyferric phosphate and iron oxide, as provided in an embodiment of the present invention;

[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 iron-to-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 8The 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 hydroxyl iron phosphate and iron oxide, which can be used to prepare lithium iron phosphate with high compaction density and high capacity. 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: Phosphoric acid, ammonium dihydrogen phosphate solution, hydrogen peroxide and ammonia water are added to ferrous sulfate solution in sequence and reacted for a period of time to form a mixed slurry. The mixed slurry is heated and kept at a certain temperature for a period of time, and then washed and filtered with water multiple times to form hydroxyferric phosphate precursors with different iron-phosphorus ratios.

[0035] In this embodiment, phosphoric acid and ammonium dihydrogen phosphate are first added to adjust the solution ions to a suitable iron-phosphorus molar ratio. Then, hydrogen peroxide is added to fully oxidize the ferrous ions to ferric ions. This makes the generated ferric hydroxyphosphate precursor more stable and results in larger ferric hydroxyphosphate precursor particles, making them easier to filter and wash. Specifically, when the iron-phosphorus feed ratio in the mixed slurry meets the iron-phosphorus molar ratio of Fe / P = 1.475-1.490, a high iron-phosphorus ratio ferric hydroxyphosphate can be formed; when the iron-phosphorus feed ratio in the mixed slurry meets the iron-phosphorus molar ratio of Fe / P = 1.460-1.475, a low iron-phosphorus ratio ferric hydroxyphosphate can be formed.

[0036] In this embodiment, the hydrogen peroxide concentration is between 30% and 60%, and the mixed slurry is heated to 60-80°C and held at that 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 a 1:1 diluted ammonia solution 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 the phosphoric acid solution to the ferrous sulfate solution, then dissolve the ammonium dihydrogen phosphate powder in water to prepare a 30% concentration ammonium dihydrogen phosphate solution at a dissolution temperature of 30-40℃, and add it to the ferrous sulfate solution;

[0039] Step S32: Add excess hydrogen peroxide to the ferrous sulfate solution and continue oxidation for a certain period of time;

[0040] Step S33: Add ammonia to the ferrous sulfate solution to adjust the pH of the solution to 3.00±0.02. After reacting for a period of time, a mixed slurry is formed. The mixed slurry is heated and kept warm for a period of time, and then washed and filtered with water multiple times to form hydroxyferric phosphate precursors with different iron-phosphorus ratios.

[0041] The heating temperature of the mixed slurry is 60-80℃, and the holding time is 3h.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] Step S6: Mix high-iron-phosphorus ratio hydroxyferric phosphate and low-iron-phosphorus ratio hydroxyferric phosphate in a certain proportion, then mix them with iron oxide, lithium phosphate, lithium carbonate, and ammonium dihydrogen phosphate in a certain proportion, and add a certain amount of carbon source and additives to form a mixture.

[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]. 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 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 ferric hydroxyphosphate and iron oxide provided in this invention involves purifying ferrous sulfate, a byproduct of titanium dioxide production, to obtain a ferrous sulfate solution. Phosphoric acid, ammonium dihydrogen phosphate solution, hydrogen peroxide, and ammonia are then added sequentially to the ferrous sulfate solution, and the mixture is reacted for a period of time to form a mixed slurry. After multiple water washings and pressure filtrations, ferric hydroxyphosphate precursors with different iron-to-phosphorus ratios are generated. These precursors are then subjected to different sintering processes to obtain ferric hydroxyphosphate products with high iron-to-phosphorus ratios and high specific surface areas, and low iron-to-phosphorus ratios and low specific surface areas. In this method, during the water washing and purification stage, impurities are less likely to be trapped inside the crystals. Multiple water washings primarily remove impurities such as 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 iron oxide, lithium phosphate, lithium carbonate, and ammonium dihydrogen phosphate in a certain proportion. After adding additives to form a mixture, the mixture is 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-iron-phosphorus ratio and low-iron-phosphorus ratio hydroxyferric phosphate, and introduces four materials: iron oxide, lithium phosphate, lithium carbonate, and ammonium dihydrogen phosphate. The addition of iron oxide and ammonium dihydrogen phosphate can effectively reduce material costs, increase the viscosity of the subsequent sand milling slurry, and improve the stability of the slurry. In addition, the small particle size of the iron oxide raw material results in small finished lithium iron phosphate particles, effectively improving rate performance; ammonium dihydrogen phosphate, as a phosphorus source, increases gas production and easily reduces particle agglomeration. Furthermore, this method requires low reaction temperature, short reaction time, 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 iron oxide according to 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 hydroxyferric phosphate and iron oxide, 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 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 successively meet the iron-phosphorus molar ratios: Fe / P = 1.485 and Fe / P = 1.465. Then add excess 40% hydrogen peroxide to the ferrous sulfate solution, and then add ammonia to the ferrous sulfate solution to form a mixed slurry. Heat the mixed slurry to 60°C, keep it at that temperature for 3 hours, and then wash and filter it multiple times with water 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 high temperatures of 540°C and 560°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 iron oxide, lithium phosphate, lithium carbonate, and ammonium dihydrogen phosphate in a molar ratio of Li:Fe:P = 1.03:1:1.03. Add a carbon source mixture consisting of sucrose and polyethylene glycol to make the carbon content of the finished product 1.3%, and titanium dioxide with a doping amount of 2500ppm to form a mixture.

[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 hydroxyferric phosphate and iron oxide, 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 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 successively meet the iron-phosphorus molar ratios: Fe / P = 1.490 and Fe / P = 1.460. Then add excess 50% hydrogen peroxide to the ferrous sulfate solution, and then add ammonia to the ferrous sulfate solution to form a mixed slurry. Heat the mixed slurry to 60°C, keep it at that temperature for 3 hours, and then wash and filter it multiple times with water 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 545°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: 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 4:6 ratio, and then mix it with iron oxide, lithium phosphate, lithium carbonate, and ammonium dihydrogen phosphate in a molar ratio of Li:Fe:P = 1.03:1:1.03. Add a carbon source mixture consisting of glucose and polyethylene glycol to make the carbon content of the finished product 1.38%, and ammonium metavanadate with a doping amount of 3000ppm to form a mixture.

[0081] Step S7: The above mixture is sand-milled, and the sand-milling particle size is controlled to be 0.58μm 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.

[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 765℃, and the sintering time is 9h. 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 hydroxyferric phosphate and iron oxide, 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 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 successively meet the iron-phosphorus molar ratios: Fe / P = 1.480 and Fe / P = 1.460. Then add excess 40% hydrogen peroxide to the ferrous sulfate solution, and then add ammonia to the ferrous sulfate solution to form a mixed slurry. Heat the mixed slurry to 60°C, keep it at that temperature for 3 hours, and then wash and filter it multiple times with water 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 with a 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: 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 5:5 ratio, and then mix it with iron oxide, lithium phosphate, lithium carbonate, and ammonium dihydrogen phosphate in a molar ratio of Li:Fe:P = 1.03:1:1.03. Add a carbon source mixture consisting of sucrose, polyethylene glycol, and citric acid to make the carbon content of the finished product 1.45%, and titanium dioxide with a doping amount of 3000ppm to form a mixture.

[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 770℃, 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 hydroxyferric phosphate and iron oxide, 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 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 = 1.44. Then add excess 15% hydrogen peroxide to the ferrous sulfate solution and ammonia water to form a mixed slurry. Heat the mixed slurry to 25°C and keep it at that temperature for 3 hours. Then wash and filter it multiple times with water 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: Mix hydroxyferric phosphate with iron oxide, lithium phosphate, lithium carbonate, and ammonium dihydrogen phosphate in a molar ratio of Li:Fe:P = 1.03:1:1.03, and add a carbon source mixture consisting of sucrose and polyethylene glycol to make the carbon content of the finished product 1.2%, and titanium dioxide with a doping amount of 3000ppm to form a mixture.

[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 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 0.35Mpa 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 for preparing lithium iron phosphate from hydroxyl iron phosphate and iron oxide 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 material was coated on aluminum foil and vacuum dried to obtain the cathode sheet. 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. The materials were assembled into a coin cell. The test voltage range was 2.0V-3.75V. The material 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 7 As 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 ferrous hydroxyphosphate and iron oxide 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 with different iron-to-phosphorus ratios is generated. Through different sintering processes, ferrous hydroxyphosphate products with high iron-to-phosphorus ratio and high specific surface area, and those with low iron-to-phosphorus ratio and low specific surface area, are obtained. The high-iron-to-phosphorus-ratio, high-specific-surface-area and low-iron-to-phosphorus-ratio, low-specific-surface-area ferrous phosphate are mixed, and then further mixed with iron oxide, lithium phosphate, lithium carbonate, and ammonium dihydrogen phosphate in a certain proportion. Additives are added to form a mixture, which is then subjected to sand milling, spray drying, sintering, sieving, batching, and packaging to obtain the finished lithium iron phosphate. This method uses a mixture of high- and low-iron-to-phosphorus-ratio ferrous phosphate and introduces four materials: iron oxide, lithium phosphate, lithium carbonate, and ammonium dihydrogen phosphate. The addition of iron oxide and ammonium dihydrogen phosphate effectively reduces material costs, increases the viscosity of the subsequent sand milling slurry, and improves the stability of the slurry. Furthermore, the small particle size of the iron oxide raw material results in small finished lithium iron phosphate particles, effectively improving rate performance. Ammonium dihydrogen phosphate, as a phosphorus source, increases gas production and facilitates particle agglomeration. The coin cells assembled from the lithium iron phosphate cathode material prepared by this method exhibit good stability and electrochemical performance. Additionally, this method requires low reaction temperatures and short reaction times, has low equipment requirements, and a simple process flow, 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 ferric hydroxyphosphate and iron oxide, 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: Phosphoric acid, ammonium dihydrogen phosphate solution, hydrogen peroxide, and ammonia are added sequentially to the ferrous sulfate solution, and the mixture is reacted for a period of time to form a mixed slurry. The mixed slurry is heated and kept at a certain temperature for a period of time, and then washed and filtered repeatedly with water to form a hydroxyferric phosphate precursor. Specifically, the iron-phosphorus feeding ratio in the mixed slurry is controlled to meet the iron-phosphorus molar ratio of Fe / P = 1.475-1.490 to form a high iron-phosphorus ratio hydroxyferric phosphate precursor; the iron-phosphorus feeding ratio in the mixed slurry is controlled 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 iron oxide, lithium phosphate, lithium carbonate, and ammonium dihydrogen phosphate 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 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 ferric hydroxyphosphate and iron oxide 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 ferric hydroxyphosphate and iron oxide 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 ferric hydroxyphosphate and iron oxide 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 heated to 60-80℃ and kept at that temperature for 3 hours.

5. The method for preparing lithium iron phosphate from ferric hydroxyphosphate and iron oxide according to claim 1, characterized in that, Step S3 includes: Step S31: Add the phosphoric acid solution to the ferrous sulfate solution, then dissolve the ammonium dihydrogen phosphate powder in water to prepare a 30% concentration ammonium dihydrogen phosphate solution at a dissolution temperature of 30-40℃, and add it to the ferrous sulfate solution. Step S32: Add excess hydrogen peroxide to the ferrous sulfate solution and continue oxidation for a certain period of time; Step S33: Add ammonia to the ferrous sulfate solution to adjust the pH of the solution to 3.00±0.

02. After reacting for a period of time, a mixed slurry is formed. The mixed slurry is heated and kept warm for a period of time, and then 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 ferric hydroxyphosphate and iron oxide according to claim 1, characterized in that, In step S4, the inlet air temperature of the flash evaporator is controlled at 220±20℃, the outlet air temperature is controlled 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.

7. The method for preparing lithium iron phosphate from ferric hydroxyphosphate and iron oxide 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 lithium-ion battery cathode material uses lithium iron phosphate prepared by the method for preparing lithium iron phosphate from hydroxy iron phosphate and iron oxide 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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