Method and application for producing lithium iron phosphate from iron hydroxyphosphate

Abstract

The present invention provides a method for producing lithium iron phosphate from iron hydroxyphosphate, comprising: purifying ferrous sulfate to form a ferrous sulfate solution; adding hydrogen peroxide solution, phosphoric acid, ammonium dihydrogen phosphate solution, and ammonia water to the ferrous sulfate solution and reacting them to form a mixed slurry; keeping the mixed slurry warm for a certain period of time, then washing with water and pressure filtering to form iron hydroxyphosphate precursors having different iron-phosphorus ratios; then flash drying and high-temperature sintering and grinding to obtain iron hydroxyphosphate precursors having different iron-phosphorus ratios and different specific surface areas; grinding and mixing the iron hydroxyphosphate precursors to obtain an iron hydroxyphosphate product; mixing iron hydroxyphosphate with a high iron-phosphorus ratio and iron hydroxyphosphate with a low iron-phosphorus ratio in a predetermined ratio; then blending with a lithium source and an iron source in a predetermined ratio; adding a carbon source and additives to form a mixed material; and finally, subjecting the mixed material to processes such as ball milling, bead milling, spray drying, sintering, grinding, sieving, batch synthesis, and packaging to obtain a lithium iron phosphate product.

Description

[Technical Field]

[0001] The present invention relates to the technical field of methods for manufacturing lithium-ion battery cathode materials, and more particularly to a method and application for producing lithium iron phosphate from iron hydroxyphosphate. [Background technology]

[0002] Lithium iron phosphate cathode material is the fastest-developing lithium battery cathode material in China. Its raw materials are readily available and inexpensive, leading to widespread application in the Chinese battery industry in fields such as automobiles, power tools, energy storage devices, emergency power supplies, and mobile power supplies. New energy electric vehicles are a major application area, where lithium iron phosphate accounts for over 45% of lithium battery cathode materials. Compared to other cathode materials, lithium iron phosphate 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, lithium iron phosphate is mainly produced using solid-phase methods, carbon thermal reduction methods, and sol-gel template methods.

[0003] For example, CN105024073A discloses iron hydroxyphosphate, a lithium-ion battery cathode material, and a method for producing the same, wherein the molecular formula of the lithium-ion battery cathode material is Fe 2.95 The compound is (PO4)2(OH)2, and its manufacturing method involves adding water to an H3PO4 solution and FeCl3 solid powder and mixing them uniformly. Then, methyltriethylammonium chloride is added to adjust the pH to 2.0-3.5, and the temperature is controlled to 150-200°C for 30 hours to carry out a hydrothermal synthesis reaction to obtain a reaction solution. The reaction solution is then centrifuged, washed, and dried to obtain Fe 2.95 The goal is to obtain (PO4)2(OH)2.

[0004] In the journal "Study on the performance of lithium iron phosphate produced from iron hydroxyphosphate as a cathode material for lithium-ion batteries," lithium iron phosphate was produced by synthesizing iron hydroxyphosphate using iron phosphate waste (a by-product of Phosphorus Chemical Industry), phosphoric acid, and hydrogen peroxide as raw materials.

[0005] However, the above method requires high reaction temperatures, long reaction times, stringent reaction conditions, demanding manufacturing equipment, and low production efficiency, thus failing to meet the current market need for cost reduction in lithium iron phosphate. Furthermore, the above method involves high raw material costs, results in many impurities in the subsequent product that are difficult to remove, and affects the product performance of subsequent iron hydroxyphosphate products, as well as the product performance of lithium iron phosphate. [Overview of the project]

[0006] In view of the above, the present invention aims to solve at least one of the technical problems present in the prior art. Therefore, the present invention provides a method and application for producing lithium iron phosphate from iron hydroxyphosphate. This method uses ferrous sulfate as a material and synthesizes iron hydroxyphosphate by adding hydrogen peroxide solution, phosphoric acid, ammonium dihydrogen phosphate, and aqueous ammonia to produce lithium iron phosphate with high press density and high volume. Furthermore, this method has high production efficiency, low production cost, and is suitable for application to large-scale industrial production.

[0007] Therefore, in the first embodiment, according to the first embodiment of the present invention, step S1 is to obtain a ferrous sulfate solution by adding ferrous sulfate, a by-product of titanium white, to a phosphorus source and a precipitant, purifying it, and then purifying it by pressure filtration; step S2 is to add an appropriate amount of phosphoric acid to the ferrous sulfate solution to lower the pH value of the ferrous sulfate solution; step S3 is to add hydrogen peroxide solution, phosphoric acid, ammonium dihydrogen phosphate solution and ammonia water to the ferrous sulfate solution, react it for a certain period of time to form a mixed slurry, keep the mixed slurry warm for a certain period of time, and then wash it with water and perform pressure filtration multiple times to form iron hydroxyphosphate precursors having different iron-phosphorus ratios; step S4 is to flash dry the iron hydroxyphosphate precursors in a flash dryer and sinter them at a high temperature for a certain period of time to obtain iron hydroxyphosphate precursor products having different iron-phosphorus ratios and different specific surface areas; and step S4 is to pulverize the sintered material with a mechano mill and ribo A method for producing lithium iron phosphate from iron hydroxyphosphate is provided, comprising: step S5, mixing in a mixer to obtain iron hydroxyphosphate products having different iron-phosphorus ratios and different specific surface areas; step S6, mixing iron hydroxyphosphate with a high iron-phosphorus ratio and iron hydroxyphosphate with a low iron-phosphorus ratio in a predetermined ratio, then blending with a lithium source and an iron source in a predetermined ratio, and adding a certain amount of carbon source and additives to form a mixed material; step S7, subjecting the mixed material to a bead mill to obtain a nano-sized bead mill-treated slurry, and spray-drying the nano-sized bead mill-treated slurry to obtain a spray material; step S8, placing the spray material in a box furnace and sintering it to obtain a sintered material, and pulverizing the sintered material with a jet mill to obtain a pulverized material; and step S9, further sieving the pulverized material, batch synthesis, packaging, and other processes to obtain a lithium iron phosphate product.

[0008] Preferably, in step S1, the mass ratio of ferrous sulfate:phosphorus source:precipitating agent is 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 1h, the phosphorus source is one or more of phosphoric acid, monoammonium phosphate, diammonium phosphate, and sodium phosphate, and the precipitating agent is one or more of sodium hydroxide, potassium hydroxide, lithium hydroxide, and aqueous ammonia.

[0009] Preferably, in step S2, the amount of phosphoric acid added is based on a molar ratio of n(Fe):n(phosphoric acid)=1:0.15. In step S3, if the supply ratio of iron phosphorus in the mixed slurry satisfies the molar ratio of iron phosphorus: Fe / P = 1.475 to 1.490, iron hydroxyphosphate with a high iron phosphorus ratio is formed, and if the supply ratio of iron phosphorus in the mixed slurry satisfies the molar ratio of iron phosphorus: Fe / P = 1.460 to 1.475, iron hydroxyphosphate with a low iron phosphorus ratio is produced.

[0010] Preferably, in step S3, the water is washed at least multiple times, the first wash mainly to remove impurities such as magnesium, manganese, and sulfur, and the final wash to adjust the pH to 6.5-7.0 by adding 1:1 diluted ammonia water. 2- The ions are washed away. The concentration of the hydrogen peroxide solution is 30% to 60%, and the incubation time of the mixed slurry at room temperature is 3 hours.

[0011] Preferably, step S3 includes the steps of: adding an excess of hydrogen peroxide to a ferrous sulfate solution and continuing the oxidation for a certain period of time; dissolving ammonium dihydrogen phosphate powder with water to prepare a 30% ammonium dihydrogen phosphate solution, setting the dissolution temperature to 30-40°C; then adding phosphoric acid solution and ammonia water to the ammonium dihydrogen phosphate solution, stirring and mixing uniformly to form an ammonium phosphate mixed solution; and adding the ammonium phosphate mixed solution to the oxidized ferrous sulfate solution, adjusting the pH of the solution to 3.00±0.02, and keeping it warm at room temperature for a certain period of time to form a mixed slurry; and performing multiple washes with water and pressure filters on the mixed slurry to form iron hydroxyphosphate precursors having different iron-phosphorus ratios.

[0012] Preferably, in step S4, the intake air temperature of the flash dryer is controlled to 220±20℃ and the exhaust air temperature to 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 so that D10≧1.0μm, D50:6~15μm, and D90≦60μm, the mixing frequency of the mixer is controlled to 35±2Hz, and the mixing time is 1~2h.

[0013] Preferably, in step S5, the iron hydroxyphosphate with a high iron-phosphorus ratio has a high specific surface area, and its iron-phosphorus molar ratio satisfies Fe / P = 1.460 to 1.480, and its specific surface area BET = 15 to 20 m² 2 Iron hydroxyphosphate that satisfies the requirement of / g and has a low iron-phosphorus ratio has a low specific surface area, and its iron-phosphorus molar ratio satisfies Fe / P = 1.440~1.460, and its specific surface area is BET = 5~10m² 2 Satisfy / g

[0014] Preferably, in step S6, 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, the lithium source is one or more of lithium phosphate, lithium carbonate, lithium iron phosphate electrode sheet material, and lithium iron phosphate low-carbon product material, the iron source is one or more of iron phosphate and iron oxide, the carbon source is one or more of sucrose, glucose, citric acid, starch, and polyethylene glycol, and the additive is one or more selected from titanium dioxide, ammonium metavanadate, and niobium pentoxide, with a doping amount of 300~3000 pp The pressure is controlled to 0.45~0.75μm in step S7, the particle size of the bead mill processed slurry is controlled to 0.45~0.75μm, the intake air temperature is set to 200~220℃, the exhaust air temperature to 80~110℃, and the blowing frequency to 80Hz, and the particle size of the sprayed material is controlled to D50=20~40μm, in step S8, the sintering atmosphere is set to nitrogen gas, the sintering temperature to 750~780℃, the heating rate to 3℃ / min, and the sintering time to 8~12h, and then natural cooling is performed to obtain the sintered material, in the grinding process the pressure is controlled to 0.2~0.4Mpa and the classification frequency to 80~200Hz, and the particle size of the ground material satisfies D10>0.35μm, D50=0.7~2.0μm, D90<10μm, and D100<30μm.

[0015] Preferably, according to the second embodiment of the present invention, step S1 is to obtain a ferrous sulfate solution by adding ferrous sulfate, a by-product of titanium white, to a phosphorus source and a precipitant, purifying it, and then purifying it by pressure filtration; step S2 is to lower the pH value of the ferrous sulfate solution by adding an appropriate amount of phosphoric acid to the ferrous sulfate solution; step S3 is to sequentially add hydrogen peroxide solution, phosphoric acid, ammonium dihydrogen phosphate solution, and ammonia water to the ferrous sulfate solution, react for a certain period of time to form a mixed slurry, heat and maintain the temperature of the mixed slurry for a certain period of time, then wash with water and pressure filtration multiple times to form iron hydroxyphosphate precursors having different iron-phosphorus ratios; step S4 is to flash dry the iron hydroxyphosphate precursors in a flash dryer and sinter them at a high temperature for a certain period of time to obtain iron hydroxyphosphate precursor products having different iron-phosphorus ratios and different specific surface areas; and step S4 is to grind the sintered material with a mechano mill and mix it with a ribbon mixer. A method for producing lithium iron phosphate from iron hydroxyphosphate is provided, comprising: step S5 to obtain iron hydroxyphosphate products having different iron-phosphorus ratios and different specific surface areas; step S6 to form a mixed material by mixing iron hydroxyphosphate with a high iron-phosphorus ratio and high specific surface area and iron hydroxyphosphate with a low iron-phosphorus ratio and low specific surface area in a predetermined ratio, then blending with iron phosphate, lithium phosphate and lithium carbonate in a predetermined ratio, and adding a certain amount of carbon source and additives; step S7 to perform bead milling on the mixed material to obtain a nano-sized bead milled slurry, and spray drying the nano-sized bead milled slurry to obtain a spray material; step S8 to obtain a sintered material by placing the spray material in a box furnace and sintering it, and grinding the sintered material with a jet mill to obtain a pulverized material; and step S9 to obtain a lithium iron phosphate product by further sieving the pulverized material, batch synthesis, packaging, and other processes.

[0016] Preferably, step S3 includes the steps of: adding an excess of hydrogen peroxide to the ferrous sulfate solution and continuing the oxidation for a certain period of time; adding a phosphoric acid solution to the oxidized ferrous sulfate solution, then adding water to ammonium dihydrogen phosphate powder to dissolve it and prepare a 30% ammonium dihydrogen phosphate solution, setting the dissolution temperature to 30-40°C, and adding it to the oxidized ferrous sulfate solution; and adding ammonia water to the ferrous sulfate solution, adjusting the pH of the solution to 3.00±0.02, reacting for a certain period of time to form a mixed slurry, heating and maintaining the temperature of the mixed slurry for a certain period of time, and then performing multiple washes with water and pressure filtration to form iron hydroxyphosphate precursors having different iron-phosphorus ratios.

[0017] Preferably, according to the third embodiment of the present invention, step S1 is to obtain a ferrous sulfate solution by adding ferrous sulfate, a by-product of titanium white, to a phosphorus source and a precipitant, purifying it, and then purifying it by pressure filtration; step S2 is to lower the pH value of the ferrous sulfate solution by adding an appropriate amount of phosphoric acid to the ferrous sulfate solution; step S3 is to sequentially add phosphoric acid, ammonium dihydrogen phosphate solution, hydrogen peroxide solution and ammonia solution to the ferrous sulfate solution, react for a certain period of time to form a mixed slurry, heat and maintain the temperature of the mixed slurry for a certain period of time, then wash with water and pressure filtration multiple times to form iron hydroxyphosphate precursors having different iron-phosphorus ratios; step S4 is to flash dry the iron hydroxyphosphate precursors in a flash dryer and sinter them at a high temperature for a certain period of time to obtain iron hydroxyphosphate precursor products having different iron-phosphorus ratios and different specific surface areas; and step S4 is to grind the sintered material with a mechano mill and mix it with a ribbon mixer. A method for producing lithium iron phosphate from iron hydroxyphosphate, comprising: step S5 to obtain iron hydroxyphosphate products having different iron-phosphorus ratios and different specific surface areas; step S6 to form a mixed material by mixing iron hydroxyphosphate with a high iron-phosphorus ratio and high specific surface area and iron hydroxyphosphate with a low iron-phosphorus ratio and low specific surface area in a predetermined ratio, then blending with iron oxide, lithium phosphate, lithium carbonate and ammonium dihydrogen phosphate in a predetermined ratio, and adding a certain amount of carbon source and additives; step S7 to perform bead milling on the mixed material to obtain a nano-sized bead milled slurry, and spray drying the nano-sized bead milled slurry to obtain a spray material; step S8 to obtain a sintered material by placing the spray material in a box furnace and sintering it, and grinding the sintered material with a jet mill to obtain a pulverized material; and step S9 to obtain a lithium iron phosphate product by further sieving the pulverized material, batch synthesis and packaging.

[0018] Preferably, step S3 includes the steps of: adding a phosphoric acid solution to a ferrous sulfate solution, then adding water to ammonium dihydrogen phosphate powder to dissolve it and prepare a 30% ammonium dihydrogen phosphate solution, setting the dissolution temperature to 30-40°C, and adding it to the ferrous sulfate solution; adding excess hydrogen peroxide to the ferrous sulfate solution and continuing the oxidation for a certain period of time; adding ammonia water to the ferrous sulfate solution, adjusting the pH of the solution to 3.00±0.02, reacting for a certain period of time to form a mixed slurry, heating and maintaining the temperature of the mixed slurry for a certain period of time, and then performing multiple washes with water and pressure filtration to form iron hydroxyphosphate precursors having different iron-phosphorus ratios.

[0019] Preferably, according to the fourth embodiment of the present invention, ferrous sulfate, which is a by-product of titanium white, is added to a phosphorus source and a precipitant for purification, and then pressure filtration is performed for purification to obtain a ferrous sulfate solution in step S1; in step S2, an appropriate amount of phosphoric acid is added to the ferrous sulfate solution to lower the pH value of the ferrous sulfate solution; after adding hydrogen peroxide solution, phosphoric acid, ammonium dihydrogen phosphate solution and ammonia water to the ferrous sulfate solution, reacting for a certain period of time to form a mixed slurry, keeping the mixed slurry at room temperature for a certain period of time, and then performing washing with water and pressure filtration multiple times to form hydroxy iron phosphate precursors having different iron-phosphorus ratios in step S3; in step S4, the hydroxy iron phosphate precursor is flash dried in a flash dryer and sintered at a high temperature for a certain period of time to obtain a hydroxy iron phosphate precursor product having different iron-phosphorus ratios and different specific surface areas; in step S5, the sintered material is ground by a mechanical mill and mixed by a ribbon mixer to obtain a hydroxy iron phosphate product having different iron-phosphorus ratios and different specific surface areas; in step S6, after mixing hydroxy iron phosphate with a high iron-phosphorus ratio and hydroxy iron phosphate with a low iron-phosphorus ratio at a predetermined ratio, they are blended with lithium phosphate and a lithium iron phosphate electrode sheet material at a predetermined ratio, and a certain amount of carbon source and additive are added to form a mixed material; in step S7, bead mill treatment is performed on the above mixed material to obtain a nanosized bead mill treated slurry, and the nanosized bead mill treated slurry is spray dried to obtain a spray material; in step S8, the above spray material is put into a box furnace for sintering to obtain a sintered material, and the sintered material is ground by a jet mill to obtain a ground material; in step S9, the above ground material is further subjected to processes such as sieving, batch synthesis, packaging, etc. to obtain a lithium iron phosphate product. A method for producing lithium iron phosphate from hydroxy iron phosphate is provided, which includes the above steps.

[0020] Preferably, the step S3 includes: adding excessive hydrogen peroxide solution to the ferrous sulfate solution and continuously oxidizing for a certain period of time; adding water to ammonium dihydrogen phosphate powder to dissolve it and preparing an ammonium dihydrogen phosphate solution with a concentration of 30%, setting the dissolution temperature at 30-40°C, then adding phosphoric acid solution and ammonia water to the ammonium dihydrogen phosphate solution, stirring and uniformly mixing to form an ammonium phosphate mixed solution; adding the ammonium phosphate mixed solution to the oxidized ferrous sulfate solution, adjusting the pH value of the solution to 3.00±0.02, reacting for a certain period of time to form a mixed slurry, keeping the mixed slurry at room temperature for a certain period of time, and then performing multiple times of water washing and pressure filtration to form iron hydroxyphosphate precursors with different iron-phosphorus ratios.

[0021] Preferably, in the step S6, the method for manufacturing the lithium iron phosphate electrode sheet material includes: crushing the waste lithium iron phosphate positive electrode sheet and sieving it to separate the raw materials of the foil material and the lithium iron phosphate electrode sheet material; sintering the raw materials of the lithium iron phosphate electrode sheet material in an inert atmosphere, setting the sintering temperature at 400-500°C and the sintering time at 1-4 hours, and then crushing until the particle size reaches 1-5μm to obtain the lithium iron phosphate electrode sheet material.

[0022] Preferably, according to the fifth embodiment of the present invention, step S1 is to obtain a ferrous sulfate solution by adding ferrous sulfate, a by-product of titanium white, to a phosphorus source and a precipitant, purifying it, and then purifying it by pressure filtration; step S2 is to add an appropriate amount of phosphoric acid to the ferrous sulfate solution to lower the pH value of the ferrous sulfate solution; step S3 is to add hydrogen peroxide solution, phosphoric acid, ammonium dihydrogen phosphate solution and ammonia water to the ferrous sulfate solution, react it for a certain period of time to form a mixed slurry, keep the mixed slurry warm at room temperature for a certain period of time, and then wash it with water and perform pressure filtration multiple times to form iron hydroxyphosphate precursors having different iron-phosphorus ratios; step S4 is to flash dry the iron hydroxyphosphate precursors in a flash dryer and sinter them at a high temperature for a certain period of time to obtain iron hydroxyphosphate precursor products having different iron-phosphorus ratios and different specific surface areas; and step S4 is to grind the sintered material with a mechano mill and mix it with a ribbon mixer. A method for producing lithium iron phosphate from iron hydroxyphosphate is provided, comprising: step S5, obtaining iron hydroxyphosphate products having different iron-phosphorus ratios and different specific surface areas; step S6, mixing iron hydroxyphosphate with a high iron-phosphorus ratio and iron hydroxyphosphate with a low iron-phosphorus ratio in a predetermined ratio, then blending with lithium phosphate and lithium iron phosphate low-carbon product material in a predetermined ratio, and adding a certain amount of carbon source and additives to form a mixed material; step S7, subjecting the mixed material to bead milling to obtain a nano-sized bead milled slurry, spray drying the nano-sized bead milled slurry to obtain a spray material; step S8, placing the spray material in a box furnace and sintering it to obtain a sintered material, pulverizing the sintered material with a jet mill to obtain a pulverized material; and step S9, further sieving the pulverized material, batch synthesis, packaging, and other processes to obtain a lithium iron phosphate product.

[0023] Preferably, step S3 includes the steps of: adding an excess of hydrogen peroxide to a ferrous sulfate solution and continuing the oxidation for a certain period of time; dissolving ammonium dihydrogen phosphate powder with water to prepare a 30% ammonium dihydrogen phosphate solution, setting the dissolution temperature to 30-40°C; then adding phosphoric acid solution and ammonia water to the ammonium dihydrogen phosphate solution, stirring and mixing uniformly to form an ammonium phosphate mixed solution; and adding the ammonium phosphate mixed solution to the oxidized ferrous sulfate solution, adjusting the pH of the solution to 3.00±0.02, reacting for a certain period of time to form a mixed slurry; keeping the mixed slurry warm at room temperature for a certain period of time, and then performing multiple washes with water and pressure filtration to form iron hydroxyphosphate precursors having different iron-phosphorus ratios.

[0024] Preferably, step S6 includes the steps of: mixing iron oxide with a phosphorus source, a lithium source, a primary carbon source and a dopant, then adding water and stirring to obtain a slurry; sequentially performing wet polishing, spray drying, sintering under a nitrogen gas atmosphere and air-jet grinding on the slurry to obtain a low-carbon lithium iron phosphate product material after grinding; and mixing iron hydroxyphosphate with a high iron-phosphorus ratio and iron hydroxyphosphate with a low iron-phosphorus ratio in a predetermined ratio, then blending with lithium phosphate and the low-carbon lithium iron phosphate product material in a predetermined ratio, and adding a certain amount of secondary carbon source and additives to form a mixed material.

[0025] Preferably, the phosphorus source is one or more of phosphoric acid, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate; the lithium source is lithium carbonate and / or lithium hydroxide; the primary carbon source is one or more of sucrose, glucose, citric acid, starch, and polyethylene glycol; the molar ratio of iron in the iron oxide to phosphorus in the phosphorus source is n(Fe):n(P)=(0.96~1):1; the molar ratio of lithium in the lithium source to iron in the iron oxide is n(Li):n(Fe)=(1.02~1.05):1; the dopant is a metal oxide, and the metal is Ti, V, Nb, and Mg The material is at least one of the following, the carbon content in the lithium iron phosphate low-carbon product material is 0.2% to 0.5%, the molar ratio of the mixed material is Li:Fe:P = [1.03 to 1.04]:1:[1.03 to 1.04], the secondary carbon source is one or more of sucrose, glucose, citric acid, starch, and polyethylene glycol, the amount of the primary and secondary carbon sources added is based on a carbon content of 1.2% to 1.6% in the final product, the additive is one or more selected from titanium dioxide, ammonium metavanadate, and niobium pentoxide, and the doping amount is controlled to 300 to 3000 ppm.

[0026] In a second embodiment, according to an embodiment of the present invention, a lithium-ion battery cathode material is provided which has been treated by a method for producing lithium iron phosphate from iron hydroxyphosphate provided in the first embodiment.

[0027] In a third embodiment, according to an embodiment of the present invention, a lithium-ion battery is provided which includes the lithium-ion battery cathode material described in the second embodiment.

[0028] In the method for producing lithium iron phosphate from iron hydroxyphosphate according to an embodiment of the present invention, iron sulfate is generated using ferrous sulfate, a by-product of titanium white, and after adding other materials and reacting them, iron hydroxyphosphates with different iron-phosphorus ratios are generated. Then, through different sintering processes, an iron hydroxyphosphate product with a high iron-phosphorus ratio and a high specific surface area, and an iron hydroxyphosphate product with a low iron-phosphorus ratio and a low specific surface area are obtained. After mixing the iron hydroxyphosphate with a high iron-phosphorus ratio and a high specific surface area with the iron hydroxyphosphate with a low iron-phosphorus ratio and a low specific surface area, a lithium source and an iron source are mixed in a predetermined ratio, a carbon source and additives are added to form a mixed material, and then the mixed material is subjected to processes such as bead milling, spray drying, sintering, sieving, batch synthesis, and packaging to obtain a lithium iron phosphate product. In this method, by mixing and combining iron hydroxyphosphate with a high iron-phosphorus ratio and iron hydroxyphosphate with a low iron-phosphorus ratio, a combination of large and small particles is formed, which helps to improve the press density of the lithium iron phosphate material and improve its electrochemical properties. Furthermore, this method requires a low reaction temperature, short reaction time, low equipment requirements, and a simple process flow, improving manufacturing efficiency and making it suitable for application to large-scale industrial manufacturing. [Brief explanation of the drawing]

[0029] [Figure 1] This is a flowchart of a method for producing lithium iron phosphate from iron hydroxyphosphate according to the first embodiment of the present invention. [Figure 2] This is a flowchart of step S3 of the method for producing lithium iron phosphate from iron hydroxyphosphate according to the first embodiment of the present invention. [Figure 3] This is a flowchart of a method for producing lithium iron phosphate from iron hydroxyphosphate according to a second embodiment of the present invention. [Figure 4] This is a flowchart of step S3 of the method for producing lithium iron phosphate from iron hydroxyphosphate according to the second embodiment of the present invention. [Figure 5]This is a flowchart of a method for producing lithium iron phosphate from iron hydroxyphosphate according to a third embodiment of the present invention. [Figure 6] This is a flowchart of step S3 of the method for producing lithium iron phosphate from iron hydroxyphosphate according to the third embodiment of the present invention. [Figure 7] This is a flowchart of a method for producing lithium iron phosphate from iron hydroxyphosphate according to a fourth embodiment of the present invention. [Figure 8] This is a flowchart of step S3 of the method for producing lithium iron phosphate from iron hydroxyphosphate according to the fourth embodiment of the present invention. [Figure 9] This is a flowchart of a method for producing lithium iron phosphate from iron hydroxyphosphate according to the fifth embodiment of the present invention. [Figure 10] This is a flowchart of step S3 of the fifth embodiment of the present invention, which describes a method for producing lithium iron phosphate from iron hydroxyphosphate. [Figure 11] This is a flowchart of step S6 of the method for producing lithium iron phosphate from iron hydroxyphosphate according to the fifth embodiment of the present invention. [Figure 12] This is an SEM image of iron hydroxyphosphate with a high iron-phosphorus ratio and high specific surface area, produced in Example 1 of the present invention. [Figure 13] This is an SEM image of the lithium iron phosphate cathode material produced in Example 1 of the present invention. [Figure 14] This is the XRD spectrum of iron hydroxyphosphate, which has a high iron-phosphorus ratio and high specific surface area, produced in Example 1 of the present invention. [Figure 15] This is the XRD spectrum of the lithium iron phosphate cathode material produced in Example 1 of the present invention. [Figure 16] This is an SEM image of iron hydroxyphosphate with a high iron-phosphorus ratio and high specific surface area, produced in Example 2 of the present invention. [Figure 17] This is an SEM image of the lithium iron phosphate cathode material produced in Example 2 of the present invention. [Figure 18]This is the XRD spectrum of iron hydroxyphosphate, which has a high iron-phosphorus ratio and high specific surface area, produced in Example 2 of the present invention. [Figure 19] This is the XRD spectrum of the lithium iron phosphate cathode material produced in Example 2 of the present invention. [Figure 20] This is an SEM image of iron hydroxyphosphate with a high iron-phosphorus ratio and high specific surface area, produced in Example 3 of the present invention. [Figure 21] This is an SEM image of the lithium iron phosphate cathode material manufactured in Example 3 of the present invention. [Figure 22] This is the XRD spectrum of iron hydroxyphosphate with a high iron-phosphorus ratio and high specific surface area, produced in Example 3 of the present invention. [Figure 23] This is the XRD spectrum of the lithium iron phosphate cathode material produced in Example 3 of the present invention. [Figure 24] This is an SEM image of iron hydroxyphosphate with a high iron-phosphorus ratio and high specific surface area, produced in Example 4 of the present invention. [Figure 25] This is an SEM image of the lithium iron phosphate cathode material produced in Example 4 of the present invention. [Figure 26] This is the XRD spectrum of iron hydroxyphosphate with a high iron-phosphorus ratio and high specific surface area, produced in Example 4 of the present invention. [Figure 27] This is the XRD spectrum of the lithium iron phosphate cathode material produced in Example 4 of the present invention. [Figure 28] This is an SEM image of iron hydroxyphosphate with a high iron-phosphorus ratio and high specific surface area, produced in Example 5 of the present invention. [Figure 29] This is an SEM image of the lithium iron phosphate cathode material manufactured in Example 5 of the present invention. [Figure 30] This is the XRD spectrum of iron hydroxyphosphate with a high iron-phosphorus ratio and high specific surface area, produced in Example 5 of the present invention. [Figure 31] This is the XRD spectrum of the lithium iron phosphate cathode material produced in Example 5 of the present invention. [Figure 32]This is the charge-discharge curve (0.1C) of a button-type half-cell assembled with the lithium iron phosphate cathode material manufactured in Example 1 of the present invention. [Figure 33] This is the charge-discharge curve (1C) of a button-type half-cell assembled with the lithium iron phosphate cathode material manufactured in Example 1 of the present invention. [Modes for carrying out the invention]

[0030] The embodiments of the present invention will be described in detail below, and the examples of the above embodiments are shown in the drawings. Throughout, the same or similar reference numerals indicate the same or similar parts or parts having the same or similar function. The embodiments described below with reference to the drawings are illustrative and interpretive of the present invention, and should not be understood as limiting the present invention.

[0031] The following disclosure provides many different embodiments or examples to realize different structures of the present invention. For the sake of simplicity in the disclosure of the present invention, the components and installations of specific examples are described below. Naturally, these are illustrative only and are not intended to limit the present invention. Furthermore, the present invention may use repeated reference numerals and / or reference letters in different examples. Such repetition is for the purpose of simplification and clarity and does not in itself indicate relationships between the various embodiments and / or installations described. Furthermore, the present invention provides examples of various specific processes and materials, but those skilled in the art will be able to recognize the applicability of other processes and / or the use of other materials.

[0032] According to a first embodiment of the present invention, a method for producing lithium iron phosphate from iron hydroxyphosphate is provided for producing high-press density, high-volume lithium iron phosphate. As shown in Figure 1, the method comprises the following steps S1 to S9.

[0033] In step S1, ferrous sulfate, a by-product of titanium white, is added to the phosphorus source and precipitant for purification, and then purified by pressure filtration to obtain a ferrous sulfate solution.

[0034] The mass ratio of ferrous sulfate:phosphorus source:precipitant is 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.

[0035] In this embodiment, the phosphorus source may be one or more of the following: phosphoric acid, monoammonium phosphate, diammonium phosphate, sodium phosphate, etc., and the precipitating agent may be one or more of the following: sodium hydroxide, potassium hydroxide, lithium hydroxide, aqueous ammonia, etc.

[0036] In step S2, an appropriate amount of phosphoric acid is added to the ferrous sulfate solution to lower its pH value.

[0037] The amount of phosphoric acid added is based on a molar ratio of n(Fe):n(phosphoric acid) = 1:0.15.

[0038] In step S3, hydrogen peroxide solution, phosphoric acid, ammonium dihydrogen phosphate solution, and aqueous ammonia are added to ferrous sulfate solution, and the mixture is allowed to react for a certain period of time to form a mixed slurry. The mixed slurry is then kept warm at room temperature for a certain period of time, and then washed with water and pressure filtered multiple times to form iron hydroxyphosphate precursors with different iron-phosphorus ratios.

[0039] When the supply ratio of iron and phosphorus in the mixed slurry satisfies the molar ratio of iron and phosphorus: Fe / P = 1.475 to 1.490, iron hydroxyphosphate with a high iron-phosphorus ratio can be formed, and when the supply ratio of iron and phosphorus in the mixed slurry satisfies the molar ratio of iron and phosphorus: Fe / P = 1.460 to 1.475, iron hydroxyphosphate with a low iron-phosphorus ratio can be produced.

[0040] In this example, the concentration of the hydrogen peroxide solution is 30% to 60%, and the incubation time of the mixed slurry at room temperature is 3 hours. The number of rinses may be multiple. In the first rinse, mainly impurities such as magnesium, manganese, and sulfur are washed away, and in the final rinse, ammonia water diluted 1:1 is added to adjust the pH value to 6.5 to 7.0, and SO4 2- Wash away the ions. Specifically, the number of rinses may be three. In the first and second rinses, mainly impurities such as manganese, magnesium, and sulfur are washed away, and in the third rinse, ammonia water diluted 1:1 is added to adjust the pH value to 6.5-7.0, and SO4 2- Wash away the ions.

[0041] Specifically, in this embodiment, as shown in Figure 2, step S3 is, Step S311 involves adding excess hydrogen peroxide to a ferrous sulfate solution and continuing the oxidation for a certain period of time. Step S312 involves adding water to ammonium dihydrogen phosphate powder to dissolve it and prepare a 30% ammonium dihydrogen phosphate solution, setting the dissolution temperature to 30-40°C, then adding phosphoric acid solution and ammonia water to the ammonium dihydrogen phosphate solution, stirring, and mixing to form a mixed ammonium phosphate solution. The method includes step S313, in which an ammonium phosphate mixed solution is added to an oxidized ferrous sulfate solution, the pH of the solution is adjusted to 3.00 ± 0.02, the mixture is reacted for a certain period of time to form a mixed slurry, the mixed slurry is kept warm at room temperature for a certain period of time, and then washed with water and pressure filtered multiple times to form iron hydroxyphosphate precursors having different iron-phosphorus ratios.

[0042] In step S4, the iron hydroxyphosphate precursor is flash-dried in a flash dryer and sintered at a high temperature for a certain period of time to obtain iron hydroxyphosphate precursor products having different iron-phosphorus ratios and different specific surface areas.

[0043] Flash drying the iron hydroxyphosphate precursor is to remove free water, and the intake air temperature of the flash dryer is controlled at 220 ± 20°C and the exhaust air temperature is controlled at 110 ± 5°C. The sintering atmosphere may be air, the sintering temperature may be 535 - 560°C, and the sintering time may be 4 - 5 h.

[0044] In step S5, by grinding the sintered material with a mechanomill and mixing it with a ribbon mixer, iron hydroxyphosphate products having different iron - phosphorus ratios and different specific surface areas can be obtained.

[0045] In the grinding process, the particle size is controlled such that D10 ≥ 1.0 μm, D50: 6 - 15 μm, and D90 ≤ 60 μm. The mixing frequency of the mixer may be controlled at 35 ± 2 Hz, and the mixing time may be 1 - 2 h.

[0046] In this example, the iron hydroxyphosphate with a high iron - phosphorus ratio has a high specific surface area, and its molar ratio of iron to phosphorus satisfies Fe / P = 1.460 - 1.480, and its specific surface area satisfies BET = 15 - 20 m 2 / g. The iron hydroxyphosphate with a low iron - phosphorus ratio has a low specific surface area, and its molar ratio of iron to phosphorus satisfies Fe / P = 1.440 - 1.460, and its specific surface area satisfies BET = 5 - 10 m 2 / g.

[0047] In step S6, after mixing the iron hydroxyphosphate with a high iron - phosphorus ratio and the iron hydroxyphosphate with a low iron - phosphorus ratio at a predetermined ratio, they are formulated with a lithium source and an iron source at a predetermined ratio, and a certain amount of a carbon source and an additive are added to form a mixed material.

[0048] In this embodiment, the ratio of iron hydroxyphosphate with a high iron-phosphorus ratio to iron hydroxyphosphate with a low iron-phosphorus ratio is between 2:8 and 8:2, preferably satisfying 3:7. In the mixed material, the molar ratio is Li:Fe:P = [1.03~1.04]:1:[1.03~1.04]. The lithium source may be one or more of lithium phosphate, lithium carbonate, lithium iron phosphate electrode sheet material, or lithium iron phosphate low-carbon product material, and the iron source may be one or more of iron phosphate or iron oxide, and the amount of carbon source added is based on a carbon content of 1.2% to 1.6% in the final product.

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

[0050] In step S7, the above mixed material is subjected to bead milling to obtain a nano-sized bead milled slurry, and the nano-sized bead milled slurry is spray-dried to obtain a spray material.

[0051] The particle size of the bead milled slurry is controlled to 0.45 to 0.75 μm. In spray drying, the intake air temperature may be 200 to 220°C, the exhaust air temperature 80 to 110°C, and the blower frequency 80 Hz, and the spray particle size of the final formed spray material is controlled to D50 = 20 to 40 μm.

[0052] In step S8, the above-mentioned spray material is placed in a box furnace and sintered to obtain a sintered material, and the sintered material is crushed with a jet mill to obtain a crushed material.

[0053] In the sintering process, the sintering atmosphere is nitrogen gas, the sintering temperature is 750-780°C, the heating rate is 3°C / min, and the sintering time is 8-12 hours, followed by natural cooling to obtain the sintered material. In the grinding process, the atmospheric pressure is controlled to 0.2-0.4 MPa and the classification frequency to 80-200 Hz, and the particle size of the final obtained grinding material satisfies the following conditions: D10 > 0.35 μm, D50 = 0.7-2.0 μm, D90 < 10 μm, and D100 < 30 μm.

[0054] In step S9, the above-mentioned pulverized material is further subjected to processes such as sieving, batch synthesis, and packaging to obtain lithium iron phosphate products.

[0055] In the method for producing lithium iron phosphate from iron hydroxyphosphate according to the first embodiment of the present invention, iron sulfate is generated using ferrous sulfate, a by-product of titanium white, and after adding other materials and reacting them, iron hydroxyphosphate precursors with different iron-phosphorus ratios are produced. Then, through different sintering processes, an iron hydroxyphosphate product with a high iron-phosphorus ratio and high specific surface area and an iron hydroxyphosphate product with a low iron-phosphorus ratio and low specific surface area are obtained. Compared to iron phosphate produced by conventional methods, the iron hydroxyphosphate produced by this method does not have a crystallization synthesis step at 80-90°C and belongs to a spherical small-particle amorphous precursor. In the water washing, separation, and purification stages, impurities are not easily adsorbed into the crystal, and after multiple water washings, mainly impurities such as Mn, Mg, and SO4 are removed. 2- Because impurities such as ions are washed away, the iron hydroxyphosphate product has a low impurity content and high product purity. Furthermore, the iron-phosphorus ratio of the iron hydroxyphosphate produced by this method is adjustable, and the specific surface area is also adjustable, allowing for the production of iron hydroxyphosphate with different iron-phosphorus ratios as needed. Iron hydroxyphosphate with a high iron-phosphorus ratio and high specific surface area has small particles and can improve the discharge capacity of the material. Iron hydroxyphosphate with a low iron-phosphorus ratio and low specific surface area has large particles and can improve the press density of the material, thereby contributing to the construction of the subsequent lithium iron phosphate crystal structure.

[0056] In this method, in subsequent steps, iron hydroxyphosphate with a high iron-phosphorus ratio and high specific surface area is mixed with iron hydroxyphosphate with a low iron-phosphorus ratio and low specific surface area. This mixture is then mixed with a lithium source and an iron source in predetermined ratios, and a carbon source and additives are added to form a mixed material. Finally, the mixed material undergoes processes such as bead milling, spray drying, sintering, sieving, batch synthesis, and packaging to obtain lithium iron phosphate product. By mixing and combining iron hydroxyphosphate with a high iron-phosphorus ratio and iron hydroxyphosphate with a low iron-phosphorus ratio, this method forms a combination of large and small particles, which helps to improve the press density of the lithium iron phosphate material and enhance its electrochemical properties. Furthermore, this method requires a low reaction temperature, short reaction time, low equipment requirements, and a simple process flow, improving manufacturing efficiency and making it suitable for large-scale industrial production.

[0057] According to a second embodiment of the present invention, a method for producing lithium iron phosphate from iron hydroxyphosphate is provided for producing high-press density, high-volume lithium iron phosphate. As shown in Figure 3, the method comprises the following steps S1 to S9.

[0058] In step S1, ferrous sulfate, a by-product of titanium white, is added to the phosphorus source and precipitant for purification, and then purified by pressure filtration to obtain a ferrous sulfate solution.

[0059] The mass ratio of ferrous sulfate:phosphorus source:precipitant is 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.

[0060] In this embodiment, the phosphorus source may be one or more of the following: phosphoric acid, monoammonium phosphate, diammonium phosphate, sodium phosphate, etc., and the precipitating agent may be one or more of the following: sodium hydroxide, potassium hydroxide, lithium hydroxide, aqueous ammonia, etc.

[0061] In step S2, an appropriate amount of phosphoric acid is added to the ferrous sulfate solution to lower its pH value.

[0062] The amount of phosphoric acid added is based on a molar ratio of n(Fe):n(phosphoric acid) = 1:0.15.

[0063] In step S3, hydrogen peroxide solution, phosphoric acid, ammonium dihydrogen phosphate solution, and ammonia water are added sequentially to ferrous sulfate solution, and the mixture is allowed to react for a certain period of time to form a mixed slurry. After heating and maintaining the temperature of the mixed slurry for a certain period of time, the mixture is washed with water and pressure filtered multiple times to form iron hydroxyphosphate precursors with different iron-phosphorus ratios.

[0064] In this embodiment, first, hydrogen peroxide solution is added to completely oxidize the divalent iron ions to trivalent iron ions, and then phosphoric acid and ammonium dihydrogen phosphate are added to adjust the solution ions to an appropriate molar ratio of iron and phosphorus. This makes the generated iron hydroxyphosphate precursor more stable, while also making the particles of the generated iron hydroxyphosphate precursor larger, allowing for easier washing by pressure filtration.

[0065] When the supply ratio of iron and phosphorus in the mixed slurry satisfies the molar ratio of iron and phosphorus: Fe / P = 1.475 to 1.490, iron hydroxyphosphate with a high iron-phosphorus ratio can be formed, and when the supply ratio of iron and phosphorus in the mixed slurry satisfies the molar ratio of iron and phosphorus: Fe / P = 1.460 to 1.475, iron hydroxyphosphate with a low iron-phosphorus ratio can be produced.

[0066] In this example, the concentration of the hydrogen peroxide solution is 30% to 60%, and the holding time after heating the mixed slurry to 60 to 80°C is 3 hours. The number of rinses may be multiple. In the first rinse, mainly impurities such as magnesium, manganese, and sulfur are washed away, and in the final rinse, ammonia water diluted 1:1 is added to adjust the pH value to 6.5 to 7.0, and SO4 2-Wash away the ions. Specifically, the number of rinses may be three. In the first and second rinses, mainly impurities such as manganese, magnesium, and sulfur are washed away, and in the third rinse, ammonia water diluted 1:1 is added to adjust the pH value to 6.5-7.0, and SO4 2- Wash away the ions.

[0067] Specifically, in this embodiment, as shown in Figure 4, step S3 is, Step S321 involves adding excess hydrogen peroxide to a ferrous sulfate solution and continuing the oxidation for a certain period of time. Step S322 involves adding a phosphoric acid solution to the oxidized ferrous sulfate solution, then adding water to dissolve ammonium dihydrogen phosphate powder to prepare a 30% ammonium dihydrogen phosphate solution, setting the dissolution temperature to 30-40°C, and adding it to the oxidized ferrous sulfate solution. The method includes step S323, in which aqueous ammonia is added to a ferrous sulfate solution, the pH of the solution is adjusted to 3.00 ± 0.02, the mixture is allowed to react for a certain period of time to form a mixed slurry, the mixed slurry is heated and kept warm for a certain period of time, and then washed with water and pressure filtered multiple times to form iron hydroxyphosphate precursors having different iron-phosphorus ratios.

[0068] The heating temperature of the mixed slurry is 60-80°C, and the holding time is 3 hours.

[0069] In step S4, the iron hydroxyphosphate precursor is flash-dried in a flash dryer and sintered at a high temperature for a certain period of time to obtain iron hydroxyphosphate precursor products having different iron-phosphorus ratios and different specific surface areas.

[0070] The iron hydroxyphosphate precursor is flash-dried to remove free water, and the intake air temperature of the flash dryer is controlled to 220±20°C and the exhaust air temperature to 110±5°C. The sintering atmosphere may be air, the sintering temperature may be 535-560°C, and the sintering time may be 4-5 hours.

[0071] In step S5, the sintered material is ground with a mechanomill and mixed with a ribbon mixer to obtain iron hydroxyphosphate products having different iron-phosphorus ratios and different specific surface areas.

[0072] During the grinding process, the particle size is controlled so that D10 ≥ 1.0 μm, D50 ≥ 6-15 μm, and D90 ≤ 60 μm. The mixing frequency of the mixer may be controlled to 35 ± 2 Hz, and the mixing time may be 1-2 hours.

[0073] In this embodiment, the iron hydroxyphosphate with a high iron-phosphorus ratio has a high specific surface area, and its iron-phosphorus molar ratio satisfies Fe / P = 1.460 to 1.480, and its specific surface area BET = 15 to 20 m² 2 Iron hydroxyphosphate that satisfies the requirement of / g and has a low iron-phosphorus ratio has a low specific surface area, and its iron-phosphorus molar ratio satisfies Fe / P = 1.440~1.460, and its specific surface area is BET = 5~10m² 2 Satisfy / g

[0074] In step S6, iron hydroxyphosphate with a high iron-phosphorus ratio and iron hydroxyphosphate with a low iron-phosphorus ratio are mixed in a predetermined ratio, and then iron phosphate, lithium phosphate, and lithium carbonate are added in a predetermined ratio, and a certain amount of carbon source and additives are added to form a mixed material.

[0075] In this embodiment, the ratio of iron hydroxyphosphate with a high iron-phosphorus ratio to iron hydroxyphosphate with a low iron-phosphorus ratio is between 2:8 and 8:2, preferably satisfying a ratio of 3:7. In addition, the molar ratio of the mixed material 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% to 1.6% in the final product.

[0076] In this embodiment, the carbon source may be one or more of sucrose, glucose, citric acid, starch, and polyethylene glycol, and the additive may be one or more selected from titanium dioxide, ammonium metavanadate, and niobium pentoxide, with the doping amount controlled to 300-3000 ppm.

[0077] In step S7, the above mixed material is subjected to bead milling to obtain a nano-sized bead milled slurry, and the nano-sized bead milled slurry is spray-dried to obtain a spray material.

[0078] The particle size of the bead milled slurry is controlled to 0.45 to 0.75 μm. In spray drying, the intake air temperature may be 200 to 220°C, the exhaust air temperature 80 to 110°C, and the blower frequency 80 Hz, and the spray particle size of the final formed spray material is controlled to D50 = 20 to 40 μm.

[0079] In step S8, the above-mentioned spray material is placed in a box furnace and sintered to obtain a sintered material, and the sintered material is crushed with a jet mill to obtain a crushed material.

[0080] In the sintering process, the sintering atmosphere is nitrogen gas, the sintering temperature is 750-780°C, the heating rate is 3°C / min, and the sintering time is 8-12 hours, followed by natural cooling to obtain the sintered material. In the grinding process, the atmospheric pressure is controlled to 0.2-0.4 MPa and the classification frequency to 80-200 Hz, and the particle size of the final obtained grinding material satisfies the following conditions: D10 > 0.35 μm, D50 = 0.7-2.0 μm, D90 < 10 μm, and D100 < 30 μm.

[0081] In step S9, the above-mentioned pulverized material is further subjected to processes such as sieving, batch synthesis, and packaging to obtain lithium iron phosphate products.

[0082] According to a second embodiment of the present invention, a method for producing lithium iron phosphate from iron hydroxyphosphate is provided. In this method, the iron hydroxyphosphate produced is first oxidized to ferric ions by adding hydrogen peroxide to completely oxidize the ferrous ions to ferric ions, and then ferric acid and ammonium dihydrogen phosphate are added to adjust the solution ions to an appropriate iron-phosphorus molar ratio, thereby further stabilizing the generated iron hydroxyphosphate precursor. Furthermore, by heating the mixed slurry and then maintaining the temperature, the particles of the generated iron hydroxyphosphate precursor are made larger, making it easier to wash by pressure filtration. Alternatively, after mixing iron hydroxyphosphate with a high iron-phosphorus ratio and iron hydroxyphosphate with a low iron-phosphorus ratio, the mixture is mixed with iron phosphate, lithium phosphate and lithium carbonate in predetermined ratios, and additives are added to form a mixed material. The mixed material is then subjected to processes such as bead milling, spray drying, sintering, sieving, batch synthesis, and packaging to obtain a lithium iron phosphate product. In this method, iron hydroxyphosphate with a high iron-phosphorus ratio and iron hydroxyphosphate with a low iron-phosphorus ratio are mixed and combined, and three types of materials, iron phosphate, lithium phosphate, and lithium carbonate, are introduced. By introducing iron phosphate and lithium carbonate, aggregation of lithium iron phosphate particles is reduced and the circularity of lithium iron phosphate particles is easily improved, thereby improving the press density and electrochemical properties of the lithium iron phosphate material.

[0083] A third embodiment of the present invention provides a method for producing lithium iron phosphate from iron hydroxyphosphate in order to produce high-press density, high-volume lithium iron phosphate. As shown in Figure 5, the method comprises the following steps S1 to S9.

[0084] In step S1, ferrous sulfate, a by-product of titanium white, is added to the phosphorus source and precipitant for purification, and then purified by pressure filtration to obtain a ferrous sulfate solution.

[0085] The mass ratio of ferrous sulfate:phosphorus source:precipitant is 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.

[0086] In this embodiment, the phosphorus source may be one or more of the following: phosphoric acid, monoammonium phosphate, diammonium phosphate, sodium phosphate, etc., and the precipitating agent may be one or more of the following: sodium hydroxide, potassium hydroxide, lithium hydroxide, aqueous ammonia, etc.

[0087] In step S2, an appropriate amount of phosphoric acid is added to the ferrous sulfate solution to lower its pH value.

[0088] The amount of phosphoric acid added is based on a molar ratio of n(Fe):n(phosphoric acid) = 1:0.15.

[0089] In step S3, phosphoric acid, ammonium dihydrogen phosphate solution, hydrogen peroxide solution, and ammonia water are added sequentially to ferrous sulfate solution, and the mixture is reacted for a certain period of time to form a mixed slurry. After heating and maintaining the temperature of the mixed slurry for a certain period of time, it is washed with water and pressure filtered multiple times to form iron hydroxyphosphate precursors having different iron-phosphorus ratios.

[0090] In this embodiment, first, phosphoric acid and ammonium dihydrogen phosphate are added to adjust the solution ions to an appropriate iron-phosphorus molar ratio. Then, hydrogen peroxide is added to completely oxidize the divalent iron ions to trivalent iron ions. This makes the generated iron hydroxyphosphate precursor more stable, while also making the particles of the generated iron hydroxyphosphate precursor larger and easier to wash by pressure filtration. When the supply ratio of iron and phosphorus in the mixed slurry satisfies the iron-phosphorus molar ratio: Fe / P = 1.475 to 1.490, iron hydroxyphosphate with a high iron-phosphorus ratio can be formed, and when the supply ratio of iron and phosphorus in the mixed slurry satisfies the iron-phosphorus molar ratio: Fe / P = 1.460 to 1.475, iron hydroxyphosphate with a low iron-phosphorus ratio can be produced.

[0091] In this example, the concentration of the hydrogen peroxide solution is 30% to 60%, and the holding time after heating the mixed slurry to 60 to 80°C is 3 hours. The number of rinses may be multiple. In the first rinse, mainly impurities such as magnesium, manganese, and sulfur are washed away, and in the final rinse, ammonia water diluted 1:1 is added to adjust the pH value to 6.5 to 7.0, and SO4 2- Wash away the ions. Specifically, the number of rinses may be three. In the first and second rinses, mainly impurities such as manganese, magnesium, and sulfur are washed away, and in the third rinse, ammonia water diluted 1:1 is added to adjust the pH value to 6.5-7.0, and SO4 2- Wash away the ions.

[0092] Specifically, in this embodiment, as shown in Figure 6, step S3 is, Step S331 involves adding a phosphoric acid solution to a ferrous sulfate solution, then adding water to dissolve ammonium dihydrogen phosphate powder to prepare a 30% ammonium dihydrogen phosphate solution, setting the dissolution temperature to 30-40°C, and adding it to the ferrous sulfate solution. Step S332 involves adding excess hydrogen peroxide to a ferrous sulfate solution and continuing the oxidation for a certain period of time. The method includes step S333, in which aqueous ammonia is added to a ferrous sulfate solution, the pH of the solution is adjusted to 3.00 ± 0.02, the mixture is allowed to react for a certain period of time to form a mixed slurry, the mixed slurry is heated and kept warm for a certain period of time, and then washed with water and pressure filtered multiple times to form iron hydroxyphosphate precursors having different iron-phosphorus ratios.

[0093] The heating temperature of the mixed slurry is 60-80°C, and the holding time is 3 hours.

[0094] In step S4, the iron hydroxyphosphate precursor is flash-dried in a flash dryer and sintered at a high temperature for a certain period of time to obtain iron hydroxyphosphate precursor products having different iron-phosphorus ratios and different specific surface areas.

[0095] The iron hydroxyphosphate precursor is flash-dried to remove free water, and the intake air temperature of the flash dryer is controlled to 220±20°C and the exhaust air temperature to 110±5°C. The sintering atmosphere may be air, the sintering temperature may be 535-560°C, and the sintering time may be 4-5 hours.

[0096] In step S5, the sintered material is ground with a mechanomill and mixed with a ribbon mixer to obtain iron hydroxyphosphate products having different iron-phosphorus ratios and different specific surface areas.

[0097] During the grinding process, the particle size is controlled so that D10 ≥ 1.0 μm, D50 ≥ 6-15 μm, and D90 ≤ 60 μm. The mixing frequency of the mixer may be controlled to 35 ± 2 Hz, and the mixing time may be 1-2 hours.

[0098] In this embodiment, the iron hydroxyphosphate with a high iron-phosphorus ratio has a high specific surface area, and its iron-phosphorus molar ratio satisfies Fe / P = 1.460 to 1.480, and its specific surface area BET = 15 to 20 m² 2 Iron hydroxyphosphate that satisfies the requirement of / g and has a low iron-phosphorus ratio has a low specific surface area, and its iron-phosphorus molar ratio satisfies Fe / P = 1.440~1.460, and its specific surface area is BET = 5~10m² 2 Satisfy / g

[0099] In step S6, iron hydroxyphosphate with a high iron-phosphorus ratio and iron hydroxyphosphate with a low iron-phosphorus ratio are mixed in a predetermined ratio, and then iron oxide, lithium phosphate, lithium carbonate, and ammonium dihydrogen phosphate are added in a predetermined ratio, and a certain amount of carbon source and additives are added to form a mixed material.

[0100] In this embodiment, the ratio of iron hydroxyphosphate with a high iron-phosphorus ratio to iron hydroxyphosphate with a low iron-phosphorus ratio is between 2:8 and 8:2, preferably satisfying a ratio of 3:7. In addition, the molar ratio of the mixed material 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% to 1.6% in the final product.

[0101] In this embodiment, the carbon source may be one or more of sucrose, glucose, citric acid, starch, and polyethylene glycol, and the additive may be one or more selected from titanium dioxide, ammonium metavanadate, and niobium pentoxide, with the doping amount controlled to 300-3000 ppm.

[0102] In step S7, the above mixed material is subjected to bead milling to obtain a nano-sized bead milled slurry, and the nano-sized bead milled slurry is spray-dried to obtain a spray material.

[0103] The particle size of the bead milled slurry is controlled to 0.45 to 0.75 μm. In spray drying, the intake air temperature may be 200 to 220°C, the exhaust air temperature 80 to 110°C, and the blower frequency 80 Hz, and the spray particle size of the final formed spray material is controlled to D50 = 20 to 40 μm.

[0104] In step S8, the above-mentioned spray material is placed in a box furnace and sintered to obtain a sintered material, and the sintered material is crushed with a jet mill to obtain a crushed material.

[0105] In the sintering process, the sintering atmosphere is nitrogen gas, the sintering temperature is 750-780°C, the heating rate is 3°C / min, and the sintering time is 8-12 hours, followed by natural cooling to obtain the sintered material. In the grinding process, the atmospheric pressure is controlled to 0.2-0.4 MPa and the classification frequency to 80-200 Hz, and the particle size of the final obtained grinding material satisfies the following conditions: D10 > 0.35 μm, D50 = 0.7-2.0 μm, D90 < 10 μm, and D100 < 30 μm.

[0106] In step S9, the above-mentioned pulverized material is further subjected to processes such as sieving, batch synthesis, and packaging to obtain lithium iron phosphate products.

[0107] In a third embodiment of the present invention, a method for producing lithium iron phosphate from iron hydroxyphosphate is used. This method involves mixing iron hydroxyphosphate with a high iron-phosphorus ratio and iron hydroxyphosphate with a low iron-phosphorus ratio, then mixing it with iron oxide, lithium phosphate, lithium carbonate, and ammonium dihydrogen phosphate in predetermined ratios. Additives are then added to form a mixed material. The mixed material is then subjected to processes such as bead milling, spray drying, sintering, sieving, batch synthesis, and packaging to obtain a lithium iron phosphate product. This method combines iron hydroxyphosphate with a high iron-phosphorus ratio and iron hydroxyphosphate with a low iron-phosphorus ratio, and introduces four types of materials: iron oxide, lithium phosphate, lithium carbonate, and ammonium dihydrogen phosphate. The addition of iron oxide and ammonium dihydrogen phosphate effectively reduces material costs, improves the viscosity of the subsequent bead milling slurry, and enhances slurry stability. Furthermore, the primary particles of the iron oxide raw material are small, resulting in small particles in the produced lithium iron phosphate product, effectively improving rate performance. Ammonium dihydrogen phosphate, as a phosphorus source, increases gas generation and reduces particle aggregation.

[0108] A fourth embodiment of the present invention provides a method for producing lithium iron phosphate from iron hydroxyphosphate in order to produce lithium iron phosphate with high press density and high volume. As shown in Figure 7, the method comprises the following steps S1 to S9.

[0109] In step S1, ferrous sulfate, a by-product of titanium white, is added to the phosphorus source and precipitant for purification, and then purified by pressure filtration to obtain a ferrous sulfate solution.

[0110] The mass ratio of ferrous sulfate:phosphorus source:precipitant is 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.

[0111] In this embodiment, the phosphorus source may be one or more of the following: phosphoric acid, monoammonium phosphate, diammonium phosphate, sodium phosphate, etc., and the precipitating agent may be one or more of the following: sodium hydroxide, potassium hydroxide, lithium hydroxide, aqueous ammonia, etc.

[0112] In step S2, an appropriate amount of phosphoric acid is added to the ferrous sulfate solution to lower its pH value.

[0113] The amount of phosphoric acid added is based on a molar ratio of n(Fe):n(phosphoric acid) = 1:0.15.

[0114] In step S3, hydrogen peroxide solution, phosphoric acid, ammonium dihydrogen phosphate solution, and aqueous ammonia are added to ferrous sulfate solution, and the mixture is allowed to react for a certain period of time to form a mixed slurry. The mixed slurry is then kept warm at room temperature for a certain period of time, and then washed with water and pressure filtered multiple times to form iron hydroxyphosphate precursors with different iron-phosphorus ratios.

[0115] When the supply ratio of iron and phosphorus in the mixed slurry satisfies the molar ratio of iron and phosphorus: Fe / P = 1.475 to 1.490, iron hydroxyphosphate with a high iron-phosphorus ratio can be formed, and when the supply ratio of iron and phosphorus in the mixed slurry satisfies the molar ratio of iron and phosphorus: Fe / P = 1.460 to 1.475, iron hydroxyphosphate with a low iron-phosphorus ratio can be produced.

[0116] In this example, the concentration of the hydrogen peroxide solution is 30% to 60%, and the incubation time of the mixed slurry at room temperature is 3 hours. The number of rinses may be multiple. In the first rinse, mainly impurities such as magnesium, manganese, and sulfur are washed away, and in the final rinse, ammonia water diluted 1:1 is added to adjust the pH value to 6.5 to 7.0, and SO4 2- Wash away the ions. Specifically, the number of rinses may be three. In the first and second rinses, mainly impurities such as manganese, magnesium, and sulfur are washed away, and in the third rinse, ammonia water diluted 1:1 is added to adjust the pH value to 6.5-7.0, and SO4 2- Wash away the ions.

[0117] Specifically, in this embodiment, as shown in Figure 8, step S3 is, Step S341 involves adding excess hydrogen peroxide to a ferrous sulfate solution and continuing the oxidation for a certain period of time. Step S342 involves adding water to ammonium dihydrogen phosphate powder to dissolve it and prepare a 30% ammonium dihydrogen phosphate solution, setting the dissolution temperature to 30-40°C, then adding phosphoric acid solution and ammonia water to the ammonium dihydrogen phosphate solution, stirring, and mixing to form a mixed ammonium phosphate solution. The method includes step S343, in which an ammonium phosphate mixed solution is added to an oxidized ferrous sulfate solution, the pH of the solution is adjusted to 3.00 ± 0.02, the mixture is reacted for a certain period of time to form a mixed slurry, the mixed slurry is kept warm at room temperature for a certain period of time, and then washed with water and pressure filtered multiple times to form iron hydroxyphosphate precursors having different iron-phosphorus ratios.

[0118] In step S4, the iron hydroxyphosphate precursor is flash-dried in a flash dryer and sintered at a high temperature for a certain period of time to obtain iron hydroxyphosphate precursor products having different iron-phosphorus ratios and different specific surface areas.

[0119] The iron hydroxyphosphate precursor is flash-dried to remove free water, and the intake air temperature of the flash dryer is controlled to 220±20°C and the exhaust air temperature to 110±5°C. The sintering atmosphere may be air, the sintering temperature may be 535-560°C, and the sintering time may be 4-5 hours.

[0120] In step S5, the sintered material is ground in a mechanomill and mixed in a ribbon mixer to obtain iron hydroxyphosphate products having different iron-phosphorus ratios and different specific surface areas.

[0121] During the grinding process, the particle size is controlled so that D10 ≥ 1.0 μm, D50 ≥ 6-15 μm, and D90 ≤ 60 μm. The mixing frequency of the mixer may be controlled to 35 ± 2 Hz, and the mixing time may be 1-2 hours.

[0122] In this embodiment, the iron hydroxyphosphate with a high iron-phosphorus ratio has a high specific surface area, and its iron-phosphorus molar ratio satisfies Fe / P = 1.460 to 1.480, and its specific surface area BET = 15 to 20 m² 2 Iron hydroxyphosphate that satisfies the requirement of / g and has a low iron-phosphorus ratio has a low specific surface area, and its iron-phosphorus molar ratio satisfies Fe / P = 1.440~1.460, and its specific surface area is BET = 5~10m² 2 Satisfy / g

[0123] In step S6, iron hydroxyphosphate with a high iron-phosphorus ratio and iron hydroxyphosphate with a low iron-phosphorus ratio are mixed in a predetermined ratio, then combined with lithium phosphate and lithium iron phosphate electrode sheet material in a predetermined ratio, and a certain amount of carbon source and additives are added to form a mixed material.

[0124] Preferably, lithium iron phosphate electrode sheet material can be manufactured using recovered waste lithium iron phosphate cathode sheets to reduce material costs. Specifically, lithium iron phosphate electrode sheet material can be manufactured by the following method: The waste lithium iron phosphate cathode sheet is crushed and sieved to separate the foil material from the raw materials for lithium iron phosphate electrode sheet material. The raw materials for lithium iron phosphate electrode sheet material are sintered in an inert atmosphere at a sintering temperature of 400-500°C and a sintering time of 1-4 hours, and then crushed until the particle size is 1-5 μm to obtain lithium iron phosphate electrode sheet material.

[0125] In this example, the ratio of iron hydroxyphosphate with a high iron-phosphorus ratio to iron hydroxyphosphate with a low iron-phosphorus ratio is between 2:8 and 8:2, preferably satisfying a ratio of 3:7. In addition, the molar ratio of the mixed material is Li:Fe:P = [1.03~1.04]:1:[1.03~1.04]. In this example, the amount of carbon source added is based on a carbon content of 1.2% to 1.6% in the final product.

[0126] In this embodiment, the carbon source may be one or more of sucrose, glucose, citric acid, starch, and polyethylene glycol, and the additive may be one or more selected from titanium dioxide, ammonium metavanadate, and niobium pentoxide, with the doping amount controlled to 300 to 3000 ppm.

[0127] In step S7, the above mixed material is subjected to bead milling to obtain a nano-sized bead milled slurry, and the nano-sized bead milled slurry is spray-dried to obtain a spray material.

[0128] The particle size of the bead milled slurry is controlled to 0.45 to 0.75 μm. In spray drying, the intake air temperature may be 200 to 220°C, the exhaust air temperature 80 to 110°C, and the blower frequency 80 Hz, and the spray particle size of the final formed spray material is controlled to D50 = 20 to 40 μm.

[0129] In step S8, the above-mentioned spray material is placed in a box furnace and sintered to obtain a sintered material, and the sintered material is crushed with a jet mill to obtain a crushed material.

[0130] In the sintering process, the sintering atmosphere is nitrogen gas, the sintering temperature is 750-780°C, the heating rate is 3°C / min, and the sintering time is 8-12 hours, followed by natural cooling to obtain the sintered material. In the grinding process, the atmospheric pressure is controlled to 0.2-0.4 MPa and the classification frequency to 80-200 Hz, and the particle size of the final obtained grinding material satisfies the following conditions: D10 > 0.35 μm, D50 = 0.7-2.0 μm, D90 < 10 μm, and D100 < 30 μm.

[0131] In step S9, the above-mentioned pulverized material is further subjected to processes such as sieving, batch synthesis, and packaging to obtain lithium iron phosphate products.

[0132] In a method for producing lithium iron phosphate from iron hydroxyphosphate according to a fourth embodiment of the present invention, a high iron-phosphorus ratio iron hydroxyphosphate and a low iron-phosphorus ratio iron hydroxyphosphate are mixed, then mixed with lithium phosphate and lithium iron phosphate electrode sheet material in a predetermined ratio, a carbon source and additives are added to form a mixed material, and then the mixed material is subjected to processes such as bead milling, spray drying, sintering, sieving, batch synthesis, and packaging to obtain a lithium iron phosphate product. In this method, a high iron-phosphorus ratio iron hydroxyphosphate and a low iron-phosphorus ratio iron hydroxyphosphate are mixed and combined, and lithium phosphate and lithium iron phosphate electrode sheet material produced from recovered waste lithium iron phosphate cathode sheets are introduced. By using the recovered lithium iron phosphate electrode sheet material, the cost of the material is significantly reduced, and the waste lithium iron phosphate electrode sheet material can be recovered and reused as a resource. During the sintering process, the lithium iron phosphate electrode sheet material provides steric hindrance, reduces aggregation of lithium iron phosphate particles, and helps improve the circularity of lithium iron phosphate particles, thereby improving the press density and electrochemical properties of the lithium iron phosphate material.

[0133] According to a fifth embodiment of the present invention, a method for producing lithium iron phosphate from iron hydroxyphosphate is provided for producing high-press density, high-volume lithium iron phosphate. As shown in Figure 9, the method comprises the following steps S1 to S9.

[0134] In step S1, ferrous sulfate, a by-product of titanium white, is added to the phosphorus source and precipitant for purification, and then purified by pressure filtration to obtain a ferrous sulfate solution.

[0135] The mass ratio of ferrous sulfate:phosphorus source:precipitant is 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.

[0136] In this embodiment, the phosphorus source may be one or more of the following: phosphoric acid, monoammonium phosphate, diammonium phosphate, sodium phosphate, etc., and the precipitating agent may be one or more of the following: sodium hydroxide, potassium hydroxide, lithium hydroxide, aqueous ammonia, etc.

[0137] In step S2, an appropriate amount of phosphoric acid is added to the ferrous sulfate solution to lower its pH value.

[0138] The amount of phosphoric acid added is based on a molar ratio of n(Fe):n(phosphoric acid) = 1:0.15.

[0139] In step S3, hydrogen peroxide solution, phosphoric acid, ammonium dihydrogen phosphate solution, and aqueous ammonia are added to ferrous sulfate solution, and the mixture is allowed to react for a certain period of time to form a mixed slurry. The mixed slurry is then kept warm at room temperature for a certain period of time, washed with water multiple times, and filtered under pressure to form iron hydroxyphosphate precursors having different iron-phosphorus ratios.

[0140] When the supply ratio of iron and phosphorus in the mixed slurry satisfies the molar ratio of iron and phosphorus: Fe / P = 1.475 to 1.490, iron hydroxyphosphate with a high iron-phosphorus ratio can be formed, and when the supply ratio of iron and phosphorus in the mixed slurry satisfies the molar ratio of iron and phosphorus: Fe / P = 1.460 to 1.475, iron hydroxyphosphate with a low iron-phosphorus ratio can be produced.

[0141] In this example, the concentration of the hydrogen peroxide solution is 30% to 60%, and the incubation time is 3 hours. The number of rinses may be multiple. In the first rinse, mainly impurities such as magnesium, manganese, and sulfur are washed away, and in the final rinse, ammonia water diluted 1:1 is added to adjust the pH value to 6.5 to 7.0, and SO4 2- Wash away the ions. Specifically, the number of rinses may be three. In the first and second rinses, mainly impurities such as manganese, magnesium, and sulfur are washed away, and in the third rinse, ammonia water diluted 1:1 is added to adjust the pH value to 6.5-7.0, and SO4 2- Wash away the ions.

[0142] Specifically, in this embodiment, as shown in Figure 10, step S3 is, Step S351 involves adding excess hydrogen peroxide to a ferrous sulfate solution and continuing the oxidation for a certain period of time. Step S352 involves adding water to ammonium dihydrogen phosphate powder to dissolve it and prepare a 30% ammonium dihydrogen phosphate solution, setting the dissolution temperature to 30-40°C, then adding phosphoric acid solution and ammonia water to the ammonium dihydrogen phosphate solution, stirring, and mixing to form a mixed ammonium phosphate solution. The method includes step S353, in which an ammonium phosphate mixed solution is added to an oxidized ferrous sulfate solution, the pH of the solution is adjusted to 3.00 ± 0.02, the mixture is reacted for a certain period of time to form a mixed slurry, the mixed slurry is kept warm at room temperature for a certain period of time, and then washed with water and pressure filtered multiple times to form iron hydroxyphosphate precursors having different iron-phosphorus ratios.

[0143] In step S4, the iron hydroxyphosphate precursor is flash-dried in a flash dryer and sintered at a high temperature for a certain period of time to obtain iron hydroxyphosphate precursor products having different iron-phosphorus ratios and different specific surface areas.

[0144] The iron hydroxyphosphate precursor is flash-dried to remove free water, and the intake air temperature of the flash dryer is controlled to 220±20°C and the exhaust air temperature to 110±5°C. The sintering atmosphere may be air, the sintering temperature may be 535-560°C, and the sintering time may be 4-5 hours.

[0145] In step S5, the sintered material is ground in a mechanomill and mixed in a ribbon mixer to obtain iron hydroxyphosphate products having different iron-phosphorus ratios and different specific surface areas.

[0146] During the grinding process, the particle size is controlled so that D10 ≥ 1.0 μm, D50 ≥ 6-15 μm, and D90 ≤ 60 μm. The mixing frequency of the mixer may be controlled to 35 ± 2 Hz, and the mixing time may be 1-2 hours.

[0147] In this embodiment, the iron hydroxyphosphate with a high iron-phosphorus ratio has a high specific surface area, and its iron-phosphorus molar ratio satisfies Fe / P = 1.460 to 1.480, and its specific surface area BET = 15 to 20 m² 2 Iron hydroxyphosphate that satisfies the requirement of / g and has a low iron-phosphorus ratio has a low specific surface area, and its iron-phosphorus molar ratio satisfies Fe / P = 1.440~1.460, and its specific surface area is BET = 5~10m² 2 Satisfy / g

[0148] In step S6, iron hydroxyphosphate with a high iron-phosphorus ratio and iron hydroxyphosphate with a low iron-phosphorus ratio are mixed in a predetermined ratio, and then lithium phosphate and lithium iron phosphate low-carbon product material are blended in a predetermined ratio, and a certain amount of carbon source and additives are added to form a mixed material.

[0149] In this embodiment, the carbon content in the lithium iron phosphate low-carbon product material is 0.2% to 0.5%. Specifically, in this embodiment, as shown in Figure 11, step S6 includes the following steps S61 to S63.

[0150] In step S61, iron oxide is mixed with a phosphorus source, a lithium source, a primary carbon source, and a dopant to obtain a mixed material, and then water is added and stirred to obtain a slurry.

[0151] The phosphorus source may be one or more of phosphoric acid, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate; the lithium source may be lithium carbonate and / or lithium hydroxide; the primary carbon source may be one or more of sucrose, glucose, citric acid, starch, and polyethylene glycol; the molar ratio of iron in the iron oxide to phosphorus in the phosphorus source is n(Fe):n(P)=(0.96~1):1; and the molar ratio of lithium in the lithium source to iron in the iron oxide is n(Li):n(Fe)=(1.02~1.05):1. The dopant is a metal oxide, and the metal is at least one of Ti, V, Nb, and Mg.

[0152] In step S62, the slurry is subjected to wet polishing, spray drying, sintering under a nitrogen gas atmosphere, and air-jet grinding in sequence to obtain a low-carbon lithium iron phosphate product material after grinding.

[0153] The sintering temperature is 500-600°C, the sintering time is 6-10 hours, and the sintering pressure is 50-200 Pa.

[0154] In step S63, iron hydroxyphosphate with a high iron-phosphorus ratio and iron hydroxyphosphate with a low iron-phosphorus ratio are mixed in a predetermined ratio, and then lithium phosphate and lithium iron phosphate low-carbon product material are blended in a predetermined ratio, and a certain amount of secondary carbon source and additives are added to form a mixed material.

[0155] Preferably, the ratio of iron hydroxyphosphate with a high iron-phosphorus ratio to iron hydroxyphosphate with a low iron-phosphorus ratio is between 2:8 and 8:2, and preferably, the ratio of iron hydroxyphosphate with a high iron-phosphorus ratio to iron hydroxyphosphate with a low iron-phosphorus ratio satisfies 3:7. In addition, in the mixed material, the molar ratio is Li:Fe:P = [1.03~1.04]:1:[1.03~1.04].

[0156] In this embodiment, the secondary carbon source may be one or more of sucrose, glucose, citric acid, starch, and polyethylene glycol, and the amounts of the primary and secondary carbon sources added are based on a carbon content of 1.2% to 1.6% in the final product. The additive may be one or more selected from titanium dioxide, ammonium metavanadate, and niobium pentoxide, and the doping amount is controlled to 300 to 3000 ppm.

[0157] In step S7, the above mixed material is subjected to bead milling to obtain a nano-sized bead milled slurry, and the nano-sized bead milled slurry is spray-dried to obtain a spray material.

[0158] The particle size of the bead milled slurry is controlled to 0.45 to 0.75 μm. In spray drying, the intake air temperature may be 200 to 220°C, the exhaust air temperature 80 to 110°C, and the blower frequency 80 Hz, and the spray particle size of the final formed spray material is controlled to D50 = 20 to 40 μm.

[0159] In step S8, the above-mentioned spray material is placed in a box furnace and sintered to obtain a sintered material, and the sintered material is crushed with a jet mill to obtain a crushed material.

[0160] In the sintering process, the sintering atmosphere is nitrogen gas, the sintering temperature is 750-780°C, the heating rate is 3°C / min, and the sintering time is 8-12 hours, followed by natural cooling to obtain the sintered material. In the grinding process, the atmospheric pressure is controlled to 0.2-0.4 MPa and the classification frequency to 80-200 Hz, and the particle size of the final obtained grinding material satisfies the following conditions: D10 > 0.35 μm, D50 = 0.7-2.0 μm, D90 < 10 μm, and D100 < 30 μm.

[0161] In step S9, the above-mentioned pulverized material is further subjected to processes such as sieving, batch synthesis, and packaging to obtain lithium iron phosphate products.

[0162] In the fifth embodiment of the present invention, a method for producing lithium iron phosphate from iron hydroxyphosphate is used. This method involves mixing iron hydroxyphosphate with a high iron-phosphorus ratio and iron hydroxyphosphate with a low iron-phosphorus ratio, then mixing it with lithium phosphate and a lithium iron phosphate low-carbon product material in a predetermined ratio, adding a carbon source and additives to form a mixed material, and finally obtaining a lithium iron phosphate product through processes such as bead milling, spray drying, sintering, sieving, batch synthesis, and packaging. In this method, by mixing and combining iron hydroxyphosphate with a high iron-phosphorus ratio and iron hydroxyphosphate with a low iron-phosphorus ratio, and introducing lithium phosphate and a lithium iron phosphate low-carbon product material, the lithium iron phosphate low-carbon product material is less prone to secondary growth during the sintering process, increasing steric hindrance, reducing aggregation of lithium iron phosphate particles, improving the circularity of lithium iron phosphate particles, and providing more and smaller particles, thereby improving the press density and electrochemical properties of the lithium iron phosphate material.

[0163] The specific process and effects of the method for producing lithium iron phosphate from iron hydroxyphosphate according to the present invention will be described in more detail below with reference to several specific examples, but this will not limit the scope of protection of the present invention.

[0164] (Example 1) This embodiment provides a method for producing lithium iron phosphate from iron hydroxyphosphate, comprising the following steps S1 to S9.

[0165] In step S1, ferrous sulfate, a by-product of titanium white, was purified by adding it to a solution of phosphoric acid at a mass fraction of 4‰ and sodium hydroxide at a mass fraction of 5‰, and then purified by pressure filtration to obtain a ferrous sulfate solution.

[0166] In step S2, phosphoric acid was added to the ferrous sulfate solution in a molar ratio of n(Fe):n(phosphoric acid) = 1:0.15 to lower the pH value of the ferrous sulfate solution.

[0167] In step S3, an excess of 40% hydrogen peroxide solution was added to the ferrous sulfate solution so that the supply ratio of iron and phosphorus in the mixed slurry sequentially satisfied the molar ratios of iron and phosphorus: Fe / P = 1.490 and Fe / P = 1.460. Then, phosphoric acid solution and 30% ammonium dihydrogen phosphate solution were added. Next, ammonia water was added to the ferrous sulfate solution to form a mixed slurry. The mixed slurry was kept warm at room temperature for 3 hours, then washed with water and pressure filtered to form iron hydroxyphosphate precursors having different iron-phosphorus ratios.

[0168] In step S4, the iron hydroxyphosphate precursor was flash-dried in a flash dryer, the intake air temperature of the flash dryer was controlled to 200°C, and it was sintered at high temperatures of 535°C and 560°C for 5 hours in an air atmosphere.

[0169] In step S5, the sintered material was pulverized with a mechanomill to control the particle size so that D10 ≥ 1.0 μm, D50 ≥ 6-15 μm, and D90 ≤ 60 μm. The mixture was then mixed for 1 hour at a frequency of 35 Hz using a ribbon mixer to obtain iron hydroxyphosphate products with a high iron-phosphorus ratio and high specific surface area, and iron hydroxyphosphate products with a low iron-phosphorus ratio and low specific surface area.

[0170] Figure 12 shows an SEM image of iron hydroxyphosphate, which has a high iron-phosphorus ratio and high specific surface area, produced by Example 1.

[0171] Figure 14 shows the XRD spectrum of iron hydroxyphosphate, which has a high iron-phosphorus ratio and high specific surface area, produced by Example 1.

[0172] In step S6, iron hydroxyphosphate with a high iron-phosphorus ratio and high specific surface area and iron hydroxyphosphate with a low iron-phosphorus ratio and low specific surface area were mixed in a ratio of 3:7. Then, lithium phosphate was added in a molar ratio of Li:Fe:P = 1.03:1:1.03, and a carbon source mixture containing sucrose and polyethylene glycol, as well as titanium dioxide with a dope content of 2500 ppm, were added to form a mixed material to achieve a carbon content of 1.3% in the product.

[0173] In step S7, the above mixed material was subjected to a bead milling process, and the particle size of the bead milling process was controlled to 0.60 μm to obtain a nano-sized bead milled slurry. The nano-sized bead milled slurry was then spray-dried, and the intake air temperature was controlled to 220°C, the exhaust air temperature to 100°C, and the blower frequency to 80 Hz to obtain a spray material with a spray particle size D50 = 20 to 40 μm.

[0174] In step S8, the above-mentioned spray material was placed in a box furnace and sintered under a nitrogen gas atmosphere with a heating rate of 3°C / min, a sintering temperature of 760°C, and a sintering time of 10 hours. Then, natural cooling was performed to obtain the sintered material. The sintered material was then pulverized with a jet mill, controlling the atmospheric pressure to 0.3 MPa and the classification frequency to 130 Hz to obtain pulverized material with particle sizes D10 > 0.35 μm, D50 = 0.8 ~ 1.8 μm, D90 < 10 μm, and D100 < 30 μm.

[0175] In step S9, the above-mentioned pulverized material was further subjected to processes such as sieving, batch synthesis, and packaging to obtain lithium iron phosphate product.

[0176] Figure 13 shows an SEM image of the lithium iron phosphate cathode material produced by Example 1.

[0177] Figure 15 shows the XRD spectrum of the lithium iron phosphate cathode material produced by Example 1.

[0178] (Example 2) This embodiment provides a method for producing lithium iron phosphate from iron hydroxyphosphate, comprising the following steps S1 to S9.

[0179] In step S1, ferrous sulfate, a by-product of titanium white, was purified by adding it to a solution of phosphoric acid at a mass fraction of 4‰ and sodium hydroxide at a mass fraction of 5‰, and then purified by pressure filtration to obtain a ferrous sulfate solution.

[0180] In step S2, phosphoric acid was added to the ferrous sulfate solution in a molar ratio of n(Fe):n(phosphoric acid) = 1:0.15 to lower the pH value of the ferrous sulfate solution.

[0181] In step S3, an excess of 40% hydrogen peroxide solution was added to the ferrous sulfate solution so that the supply ratio of iron and phosphorus in the mixed slurry sequentially satisfied the molar ratios of iron and phosphorus: Fe / P = 1.490 and Fe / P = 1.460. Then, phosphoric acid solution and 30% ammonium dihydrogen phosphate solution were added. Next, ammonia water was added to the ferrous sulfate solution to form a mixed slurry. The mixed slurry was heated to 60°C, kept warm for 3 hours, and washed with water and pressure filtered multiple times to form iron hydroxyphosphate precursors with different iron-phosphorus ratios.

[0182] In step S4, the iron hydroxyphosphate precursor was flash-dried in a flash dryer, the intake air temperature of the flash dryer was controlled to 200°C, and it was sintered at high temperatures of 535°C and 560°C for 5 hours in an air atmosphere.

[0183] In step S5, the sintered material was pulverized with a mechanomill to control the particle size so that D10 ≥ 1.0 μm, D50 ≥ 6-15 μm, and D90 ≤ 60 μm. The mixture was then mixed for 1 hour at a frequency of 35 Hz using a ribbon mixer to obtain iron hydroxyphosphate with a high iron-phosphorus ratio and high specific surface area, and iron hydroxyphosphate with a low iron-phosphorus ratio and low specific surface area.

[0184] Figure 16 shows an SEM image of iron hydroxyphosphate, which has a high iron-phosphorus ratio and high specific surface area, produced by Example 2.

[0185] Figure 18 shows the XRD spectrum of iron hydroxyphosphate, which has a high iron-phosphorus ratio and high specific surface area, produced by Example 2.

[0186] In step S6, iron hydroxyphosphate with a high iron-phosphorus ratio and high specific surface area and iron hydroxyphosphate with a low iron-phosphorus ratio and low specific surface area were mixed in a ratio of 3:7. Then, iron phosphate, lithium phosphate, and lithium carbonate were blended in a molar ratio of Li:Fe:P = 1.03:1:1.03. A carbon source mixture containing sucrose and polyethylene glycol, as well as titanium dioxide with a dope content of 2200 ppm, were added to form a mixed material to achieve a carbon content of 1.35% in the product.

[0187] In step S7, the above mixed material was subjected to a bead milling process, and the particle size of the bead milling process was controlled to 0.62 μm to obtain a nano-sized bead milled slurry. The nano-sized bead milled slurry was then spray-dried, and the intake air temperature was controlled to 220°C, the exhaust air temperature to 100°C, and the blower frequency to 80 Hz to obtain a spray material with a spray particle size D50 = 20 to 40 μm.

[0188] In step S8, the above-mentioned spray material was placed in a box furnace and sintered under a nitrogen gas atmosphere with a heating rate of 3°C / min, a sintering temperature of 765°C, and a sintering time of 10 hours. Then, natural cooling was performed to obtain the sintered material. The sintered material was then pulverized with a jet mill, controlling the atmospheric pressure to 0.3 MPa and the classification frequency to 130 Hz to obtain pulverized material with particle sizes D10 > 0.35 μm, D50 = 0.8 ~ 1.8 μm, D90 < 10 μm, and D100 < 30 μm.

[0189] In step S9, the above-mentioned pulverized material was further subjected to processes such as sieving, batch synthesis, and packaging to obtain lithium iron phosphate product.

[0190] Figure 17 shows an SEM image of the lithium iron phosphate cathode material produced by Example 2.

[0191] Figure 19 shows the XRD spectrum of the lithium iron phosphate cathode material produced by Example 2.

[0192] (Example 3) This embodiment provides a method for producing lithium iron phosphate from iron hydroxyphosphate, comprising the following steps S1 to S9.

[0193] In step S1, ferrous sulfate, a by-product of titanium white, was purified by adding it to a solution of phosphoric acid at a mass fraction of 4‰ and sodium hydroxide at a mass fraction of 5‰, and then purified by pressure filtration to obtain a ferrous sulfate solution.

[0194] In step S2, phosphoric acid was added to the ferrous sulfate solution in a molar ratio of n(Fe):n(phosphoric acid) = 1:0.15 to lower the pH value of the ferrous sulfate solution.

[0195] In step S3, phosphoric acid solution and 30% ammonium dihydrogen phosphate solution were added to ferrous sulfate solution so that the supply ratio of iron and phosphorus in the mixed slurry sequentially satisfies the molar ratios of iron and phosphorus: Fe / P = 1.485 and Fe / P = 1.465. Next, an excess of 40% hydrogen peroxide solution was added to the ferrous sulfate solution, followed by the addition of ammonia water to form a mixed slurry. The mixed slurry was heated to 60°C, held for 3 hours, and washed with water and pressure filtered multiple times to form iron hydroxyphosphate precursors with different iron-phosphorus ratios.

[0196] In step S4, the iron hydroxyphosphate precursor was flash-dried in a flash dryer, the intake air temperature of the flash dryer was controlled to 200°C, and it was sintered at high temperatures of 540°C and 560°C for 5 hours in an air atmosphere.

[0197] In step S5, the sintered material was pulverized with a mechanomill to control the particle size so that D10 ≥ 1.0 μm, D50 ≥ 6-15 μm, and D90 ≤ 60 μm. The mixture was then mixed for 1 hour at a frequency of 35 Hz using a ribbon mixer to obtain iron hydroxyphosphate with a high iron-phosphorus ratio and high specific surface area, and iron hydroxyphosphate with a low iron-phosphorus ratio and low specific surface area.

[0198] Figure 20 shows an SEM image of iron hydroxyphosphate, which has a high iron-phosphorus ratio and high specific surface area, produced by Example 3.

[0199] Figure 22 shows the XRD spectrum of iron hydroxyphosphate, which has a high iron-phosphorus ratio and high specific surface area, produced by Example 3.

[0200] In step S6, iron hydroxyphosphate with a high iron-phosphorus ratio and high specific surface area and iron hydroxyphosphate with a low iron-phosphorus ratio and low specific surface area were mixed in a ratio of 3:7. Then, iron oxide, lithium phosphate, lithium carbonate, and ammonium dihydrogen phosphate were added in a molar ratio of Li:Fe:P = 1.03:1:1.03. A carbon source mixture containing sucrose and polyethylene glycol, as well as titanium dioxide with a dope content of 2500 ppm, were added to form a mixed material to achieve a carbon content of 1.3% in the product.

[0201] In step S7, the above mixed material was subjected to a bead milling process, and the particle size of the bead milling process was controlled to 0.60 μm to obtain a nano-sized bead milled slurry. The nano-sized bead milled slurry was then spray-dried, and the intake air temperature was controlled to 220°C, the exhaust air temperature to 100°C, and the blower frequency to 80 Hz to obtain a spray material with a spray particle size D50 = 20 to 40 μm.

[0202] In step S8, the above-mentioned spray material was placed in a box furnace and sintered under a nitrogen gas atmosphere with a heating rate of 3°C / min, a sintering temperature of 760°C, and a sintering time of 10 hours. Then, natural cooling was performed to obtain the sintered material. The sintered material was then pulverized with a jet mill, controlling the atmospheric pressure to 0.3 MPa and the classification frequency to 130 Hz to obtain pulverized material with particle sizes D10 > 0.35 μm, D50 = 0.8 ~ 1.8 μm, D90 < 10 μm, and D100 < 30 μm.

[0203] In step S9, the above-mentioned pulverized material was further subjected to processes such as sieving, batch synthesis, and packaging to obtain lithium iron phosphate product.

[0204] Figure 21 shows an SEM image of the lithium iron phosphate cathode material produced by Example 3.

[0205] Figure 23 shows the XRD spectrum of the lithium iron phosphate cathode material produced by Example 3.

[0206] (Example 4) This embodiment provides a method for producing lithium iron phosphate from iron hydroxyphosphate, comprising the following steps S1 to S9.

[0207] In step S1, ferrous sulfate, a by-product of titanium white, was purified by adding it to a solution of phosphoric acid at a mass fraction of 4‰ and sodium hydroxide at a mass fraction of 5‰, and then purified by pressure filtration to obtain a ferrous sulfate solution.

[0208] In step S2, phosphoric acid is added to the ferrous sulfate solution in a molar ratio of n(Fe):n(phosphoric acid) = 1:0.15 to lower the pH value of the ferrous sulfate solution.

[0209] In step S3, an excess of 40% hydrogen peroxide solution was added to the ferrous sulfate solution so that the supply ratio of iron and phosphorus in the mixed slurry sequentially satisfied the molar ratios of iron and phosphorus: Fe / P = 1.490 and Fe / P = 1.460. Then, phosphoric acid solution and 30% ammonium dihydrogen phosphate solution were added. Next, ammonia water was added to the ferrous sulfate solution to form a mixed slurry. The mixed slurry was kept warm at room temperature for 3 hours, then washed with water and pressure filtered to form iron hydroxyphosphate precursors having different iron-phosphorus ratios.

[0210] In step S4, the iron hydroxyphosphate precursor was flash-dried in a flash dryer, the intake air temperature of the flash dryer was controlled to 200°C, and sintered at high temperatures of 535°C and 555°C for 5 hours in an air atmosphere.

[0211] In step S5, the sintered material was pulverized with a mechanomill to control the particle size so that D10 ≥ 1.0 μm, D50 ≥ 6-15 μm, and D90 ≤ 60 μm. The mixture was then mixed for 1 hour at a frequency of 35 Hz using a ribbon mixer to obtain iron hydroxyphosphate with a high iron-phosphorus ratio and high specific surface area, and iron hydroxyphosphate with a low iron-phosphorus ratio and low specific surface area.

[0212] Figure 24 shows an SEM image of iron hydroxyphosphate, which has a high iron-phosphorus ratio and high specific surface area, produced by Example 4.

[0213] Figure 26 shows the XRD spectrum of iron hydroxyphosphate, which has a high iron-phosphorus ratio and high specific surface area, produced by Example 4.

[0214] In step S6, iron hydroxyphosphate with a high iron-phosphorus ratio and high specific surface area and iron hydroxyphosphate with a low iron-phosphorus ratio and low specific surface area were mixed in a ratio of 3:7. Then, lithium phosphate and lithium iron phosphate electrode sheet material were blended in a molar ratio of Li:Fe:P = 1.03:1:1.03. A carbon source mixture containing sucrose and polyethylene glycol, and titanium dioxide with a dope content of 2800 ppm were added to form a mixed material to achieve a carbon content of 1.3% in the product. For the lithium iron phosphate electrode sheet material, a waste lithium iron phosphate cathode sheet was crushed and sieved to separate the foil material from the lithium iron phosphate electrode sheet raw material. The lithium iron phosphate electrode sheet raw material was sintered in an inert atmosphere at a sintering temperature of 400°C for 4 hours, and then crushed until the particle size was 3 μm.

[0215] In step S7, the above mixed material was subjected to a bead milling process, and the particle size of the bead milling process was controlled to 0.60 μm to obtain a nano-sized bead milled slurry. The nano-sized bead milled slurry was then spray-dried, and the intake air temperature was controlled to 220°C, the exhaust air temperature to 100°C, and the blower frequency to 80 Hz to obtain a spray material with a spray particle size D50 = 20 to 40 μm.

[0216] In step S8, the above-mentioned spray material was placed in a box furnace and sintered under a nitrogen gas atmosphere with a heating rate of 3°C / min, a sintering temperature of 760°C, and a sintering time of 10 hours. Then, natural cooling was performed to obtain the sintered material. The sintered material was then pulverized with a jet mill, controlling the atmospheric pressure to 0.3 MPa and the classification frequency to 130 Hz to obtain pulverized material with particle sizes D10 > 0.35 μm, D50 = 0.8 ~ 1.8 μm, D90 < 10 μm, and D100 < 30 μm.

[0217] In step S9, the above-mentioned pulverized material was further subjected to processes such as sieving, batch synthesis, and packaging to obtain lithium iron phosphate product.

[0218] Figure 25 shows an SEM image of the lithium iron phosphate cathode material produced according to Example 4.

[0219] Figure 27 shows the XRD spectrum of the lithium iron phosphate cathode material produced by Example 4.

[0220] (Example 5) This embodiment provides a method for producing lithium iron phosphate from iron hydroxyphosphate and lithium iron phosphate low-carbon product materials, comprising the following steps S1 to S9.

[0221] In step S1, ferrous sulfate, a by-product of titanium white, was purified by adding it to a solution of phosphoric acid at a mass fraction of 4‰ and sodium hydroxide at a mass fraction of 5‰, and then purified by pressure filtration to obtain a ferrous sulfate solution.

[0222] In step S2, phosphoric acid was added to the ferrous sulfate solution in a molar ratio of n(Fe):n(phosphoric acid) = 1:0.15 to lower the pH value of the ferrous sulfate solution.

[0223] In step S3, an excess of 40% hydrogen peroxide solution was added to the ferrous sulfate solution so that the supply ratio of iron and phosphorus in the mixed slurry sequentially satisfied the molar ratios of iron and phosphorus: Fe / P = 1.490 and Fe / P = 1.460. Then, phosphoric acid solution and 30% ammonium dihydrogen phosphate solution were added. Next, ammonia water was added to the ferrous sulfate solution to form a mixed slurry. The mixed slurry was kept warm at room temperature for 3 hours, then washed with water and pressure filtered to form iron hydroxyphosphate precursors having different iron-phosphorus ratios.

[0224] In step S4, the iron hydroxyphosphate precursor was flash-dried in a flash dryer, the intake air temperature of the flash dryer was controlled to 200°C, and it was sintered at high temperatures of 535°C and 560°C for 5 hours in an air atmosphere.

[0225] In step S5, the sintered material was pulverized with a mechanomill to control the particle size so that D10 ≥ 1.0 μm, D50 ≥ 6-15 μm, and D90 ≤ 60 μm. The mixture was then mixed for 1 hour at a frequency of 35 Hz using a ribbon mixer to obtain iron hydroxyphosphate with a high iron-phosphorus ratio and high specific surface area, and iron hydroxyphosphate with a low iron-phosphorus ratio and low specific surface area.

[0226] Figure 28 shows an SEM image of iron hydroxyphosphate, which has a high iron-phosphorus ratio and high specific surface area, produced according to Example 5.

[0227] Figure 30 shows the XRD spectrum of iron hydroxyphosphate, which has a high iron-phosphorus ratio and high specific surface area, produced by Example 5.

[0228] In step S6, iron hydroxyphosphate with a high iron-phosphorus ratio and high specific surface area and iron hydroxyphosphate with a low iron-phosphorus ratio and low specific surface area were mixed in a ratio of 3:7. Then, lithium phosphate and lithium iron phosphate low-carbon product material were blended with this mixture in a molar ratio of Li:Fe:P = 1.03:1:1.03. A carbon source mixture containing sucrose and polyethylene glycol, as well as titanium dioxide doped at a concentration of 2500 ppm, were added to achieve a carbon content of 1.3% in the product, thereby forming a mixed material. Key manufacturing parameters for the lithium iron phosphate low-carbon product material included controlling the particle size of the bead milled slurry to 0.45 μm, doping with 300 ppm titanium dioxide, a sintering temperature of 500°C, and a sintering time of 8 hours.

[0229] In step S7, the above mixed material was subjected to a bead milling process, and the particle size of the bead milling process was controlled to 0.60 μm to obtain a nano-sized bead milled slurry. The nano-sized bead milled slurry was then spray-dried, and the intake air temperature was controlled to 220°C, the exhaust air temperature to 100°C, and the blower frequency to 80 Hz to obtain a spray material with a spray particle size D50 = 20 to 40 μm.

[0230] In step S8, the above-mentioned spray material was placed in a box furnace and sintered under a nitrogen gas atmosphere with a heating rate of 3°C / min, a sintering temperature of 760°C, and a sintering time of 10 hours. Then, natural cooling was performed to obtain the sintered material. The sintered material was then pulverized with a jet mill, controlling the atmospheric pressure to 0.3 MPa and the classification frequency to 130 Hz to obtain pulverized material with particle sizes D10 > 0.35 μm, D50 = 0.8 ~ 1.8 μm, D90 < 10 μm, and D100 < 30 μm.

[0231] In step S9, the above-mentioned pulverized material was further subjected to processes such as sieving, batch synthesis, and packaging to obtain lithium iron phosphate product.

[0232] Figure 29 shows an SEM image of the lithium iron phosphate cathode material produced according to Example 5.

[0233] Figure 31 shows the XRD spectrum of the lithium iron phosphate cathode material produced according to Example 5.

[0234] (Comparative Example 1) According to this embodiment, Step S1 involves adding ferrous sulfate, a by-product of titanium white, to a solution of phosphoric acid at a mass fraction of 6‰ and sodium hydroxide at a mass fraction of 4‰, purifying it, and then purifying it by pressure filtration to obtain a ferrous sulfate solution. Step S2 involves adding phosphoric acid to a ferrous sulfate solution in a molar ratio of n(Fe):n(phosphoric acid) = 1:0.15 to lower the pH value of the ferrous sulfate solution. Step S3 involves adding an excess of 10% hydrogen peroxide solution to a ferrous sulfate solution so that the supply and mixing ratio of iron and phosphorus satisfies the molar ratio of iron and phosphorus: Fe / P = 1.440, then adding phosphoric acid solution and 30% ammonium dihydrogen phosphate solution, and then adding ammonia water to the ferrous sulfate solution to form a mixed slurry. After keeping the mixed slurry warm at room temperature for 2 hours, it is washed with water and pressure filtered to form an iron hydroxyphosphate precursor. Step S4 involves flash-drying the iron hydroxyphosphate precursor in a flash dryer, controlling the intake air temperature of the flash dryer to 200°C, and sintering it at a high temperature of 520°C for 2 hours in an air atmosphere. Step S5 involves grinding the sintered material with a mechanomill to control the particle size so that D10 ≥ 1.0 μm, D50 ≥ 6-15 μm, and D90 ≤ 60 μm, and mixing it with a ribbon mixer at 35 Hz for 1 hour to obtain an iron hydroxyphosphate product having a single iron-phosphorus ratio and a single specific surface area. Step S6 involves forming a mixed material by combining iron hydroxyphosphate and lithium phosphate in a molar ratio of Li:Fe:P = 1.03:1:1.03, adding a carbon source mixture containing sucrose and polyethylene glycol to achieve a carbon content of 1.2% in the product, and adding titanium dioxide with a doping amount of 3000 ppm. Step S7 involves performing a bead milling process on the above mixed material, controlling the bead milling particle size to 0.65 μm to obtain a nano-sized bead milled slurry, spray drying the nano-sized bead milled slurry, controlling the intake air temperature to 220°C, exhaust air temperature to 100°C, and blower frequency to 80 Hz to obtain a spray material with a spray particle size D50 = 20-40 μm. Step S8 involves placing the above spray material in a box furnace and sintering it under a nitrogen gas atmosphere, with a heating rate of 3°C / min, a sintering temperature of 765°C, and a sintering time of 10 hours, followed by natural cooling to obtain a sintered material, then grinding the sintered material with a jet mill, controlling the air pressure to 0.35 MPa and the classification frequency to 140 Hz to obtain a pulverized material with particle sizes D10 > 0.35 μm, D50 = 0.8 ~ 1.8 μm, D90 < 10 μm, and D100 < 30 μm. A method for producing lithium iron phosphate from iron hydroxyphosphate is provided, comprising step S9, which involves further sieving the above-mentioned pulverized material, batch synthesis, packaging, etc., to obtain a lithium iron phosphate product.

[0235] To verify the product quality of lithium iron phosphate cathode materials produced by the method for producing lithium iron phosphate from iron hydroxyphosphate according to the embodiments of the present invention, the lithium iron phosphate cathode materials produced in Examples 1 to 5 and Comparative Example 1, along with a conductive agent (carbon black) and a binder (polyvinylidene fluoride), were dispersed in N-methylpyrrolidone in a mass ratio of 90:5:5. After uniform dispersion by ball milling, the mixture was coated onto aluminum foil and vacuum-dried to produce a cathode sheet. The electrolyte was 1 mol / L LiPF6 with a solvent volume ratio of EC:DMC:EMC = 1:1:1. The separator was a Celgard polypropylene film, and the metallic lithium sheet was the anode. Both were assembled into a button-type half-cell. The test voltage range was 2.0V to 3.75V. The battery was charged to 3.75V using a constant current / constant voltage charging method and discharged to 2.0V using a constant current discharge method. The charge / discharge current was 0.1C for 2 cycles and 1C for 2 cycles. The test results are shown in Table 1. Figure 32 shows the charge / discharge curve (0.1C) of a button-type half-cell assembled with the lithium iron phosphate cathode material manufactured in Example 1 of the present invention, and Figure 33 shows the charge / discharge curve (1C) of a button-type half-cell assembled with the lithium iron phosphate cathode material manufactured in Example 1 of the present invention.

[0236] Table 1 Test items and test results for Examples 1-5 and Comparative Example 1 [Table 1]

[0237] Comparing the test results obtained from tests conducted based on the above examples and comparative examples, the button-type half-cells manufactured with lithium iron phosphate cathode materials in Examples 1 to 5 showed a significant improvement in both the initial charge-discharge ratio capacity at 0.1C and the discharge ratio capacity at 1C compared to Comparative Example 1.

[0238] As described above, in the method for producing lithium iron phosphate from iron hydroxyphosphate according to the embodiment of the present invention, iron sulfate is generated using ferrous sulfate, a by-product of titanium white, and after adding other materials and reacting them, iron hydroxyphosphates with different iron-phosphorus ratios are generated. Then, through different sintering processes, an iron hydroxyphosphate product with a high iron-phosphorus ratio and a high specific surface area and an iron hydroxyphosphate product with a low iron-phosphorus ratio and a low specific surface area are obtained. After mixing the iron hydroxyphosphate with a high iron-phosphorus ratio and a high specific surface area and the iron hydroxyphosphate with a low iron-phosphorus ratio and a low specific surface area, the mixture is mixed with a lithium source in a predetermined ratio, a carbon source and additives are added to form a mixed material, and then the mixed material is subjected to processes such as bead milling, spray drying, sintering, sieving, batch synthesis, and packaging to obtain a lithium iron phosphate product. In this method, by mixing and combining iron hydroxyphosphate with a high iron-phosphorus ratio and iron hydroxyphosphate with a low iron-phosphorus ratio, a combination of large and small particles is formed, which helps to improve the press density of the lithium iron phosphate material and improve its electrochemical properties. Button-type half-cells assembled using lithium iron phosphate cathode material produced by this method exhibit good stability and electrochemical properties. Furthermore, this method requires a low reaction temperature, short reaction time, low equipment requirements, and a simple process flow, improving manufacturing efficiency and making it suitable for large-scale industrial production.

[0239] In this specification, any reference to terms such as “one embodiment,” “several embodiments,” “example,” “specific example,” or “several examples” means that the specific features, structures, materials, or properties described in combination with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the exemplary expressions of the above terms are not necessarily limited to the same embodiment or example. Furthermore, the specific features, structures, materials, or properties described can be appropriately combined in any one or more embodiments or examples. In addition, a person skilled in the art can combine and combine different embodiments or examples and features of different embodiments or examples described herein, as long as they do not conflict with each other.

[0240] Although embodiments of the present invention have been described exemplifiedly, as will be understood by those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is limited by the claims and their equivalents.

Claims

1. Step S1 involves adding ferrous sulfate, a by-product of titanium white, to a phosphorus source and a precipitant, purifying it, and then purifying it by pressure filtration to obtain a ferrous sulfate solution. Step S2 involves adding an appropriate amount of phosphoric acid to the ferrous sulfate solution to lower the pH value of the ferrous sulfate solution, Step S3 involves adding hydrogen peroxide solution, phosphoric acid, ammonium dihydrogen phosphate solution, and aqueous ammonia to a ferrous sulfate solution, allowing it to react for a certain period of time to form a mixed slurry, keeping the mixed slurry warm for a certain period of time, and then performing multiple washes with water and pressure filtration to form iron hydroxyphosphate precursors having different iron-phosphorus ratios. Step S4 involves flash-drying the iron hydroxyphosphate precursor in a flash dryer and sintering it at a high temperature for a certain period of time to obtain an iron hydroxyphosphate precursor product having different iron-phosphorus ratios and different specific surface areas. Step S5 involves grinding the sintered material with a mechano mill and mixing it with a ribbon mixer to obtain iron hydroxyphosphate products having different iron-phosphorus ratios and different specific surface areas. Step S6 involves mixing iron hydroxyphosphate with a high iron-phosphorus ratio and iron hydroxyphosphate with a low iron-phosphorus ratio in a predetermined ratio, then blending them with a lithium source and an iron source in a predetermined ratio, and adding a certain amount of carbon source and additives to form a mixed material. Step S7 involves performing a bead milling process on the above mixed material to obtain a nano-sized bead milled slurry, and then spray-drying the nano-sized bead milled slurry to obtain a spray material. Step S8 involves placing the above-mentioned spray material into a box furnace and sintering it to obtain a sintered material, and then grinding the sintered material with a jet mill to obtain a pulverized material. Step S9 includes further sieving of the above-mentioned pulverized material, batch synthesis, and packaging to obtain a lithium iron phosphate product. A method for producing lithium iron phosphate from iron hydroxyphosphate, characterized by the following features.

2. In step S1, the mass ratio of ferrous sulfate:phosphorus source:precipitant is 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 aqueous ammonia. A method for producing lithium iron phosphate from iron hydroxyphosphate as described in feature 1.

3. In step S2, the amount of phosphoric acid added is based on a molar ratio of n(Fe):n(phosphoric acid) = 1:0.

15. In step S3, when the supply ratio of iron phosphorus in the mixed slurry satisfies the molar ratio of iron phosphorus: Fe / P = 1.475 to 1.490, iron hydroxyphosphate with a high iron phosphorus ratio is formed, and when the supply ratio of iron phosphorus in the mixed slurry satisfies the molar ratio of iron phosphorus: Fe / P = 1.460 to 1.475, iron hydroxyphosphate with a low iron phosphorus ratio is produced. A method for producing lithium iron phosphate from iron hydroxyphosphate as described in feature 1.

4. In step S3, the water is washed multiple times. In the first wash, mainly impurities such as magnesium, manganese, and sulfur are washed away. In the final wash, ammonia water diluted 1:1 is added to adjust the pH to 6.5-7.0, and SO ４ ２－ The ions are washed away, the concentration of the hydrogen peroxide solution is 30% to 60%, and the incubation time of the mixed slurry at room temperature is 3 hours. A method for producing lithium iron phosphate from iron hydroxyphosphate as described in feature 1.

5. Step S3 is, Step S311 involves adding an excess of hydrogen peroxide solution to a ferrous sulfate solution and continuing the oxidation for a certain period of time. Step S312 involves adding water to ammonium dihydrogen phosphate powder to dissolve it and prepare a 30% ammonium dihydrogen phosphate solution, setting the dissolution temperature to 30-40°C, then adding phosphoric acid solution and ammonia water to the ammonium dihydrogen phosphate solution, stirring, and mixing to form a mixed ammonium phosphate solution. Step S313 includes adding an ammonium phosphate mixed solution to an oxidized ferrous sulfate solution, adjusting the pH of the solution to 3.00 ± 0.02, allowing it to react for a certain period of time to form a mixed slurry, keeping the mixed slurry warm at room temperature for a certain period of time, and then performing multiple washes with water and pressure filtration to form iron hydroxyphosphate precursors having different iron-phosphorus ratios. A method for producing lithium iron phosphate from iron hydroxyphosphate as described in feature 1.

6. In step S4, the intake air temperature of the flash dryer is controlled to 220±20°C, the exhaust air temperature to 110±5°C, the sintering atmosphere is air, the sintering temperature is 535-560°C, and the sintering time is 4-5 hours. In step S5, the particle size is controlled so that D10≧1.0μm, D50:6-15μm, and D90≦60μm, the mixing frequency of the mixer is controlled to 35±2Hz, and the mixing time is 1-2 hours. A method for producing lithium iron phosphate from iron hydroxyphosphate as described in feature 1.

7. In step S5, the iron hydroxyphosphate with a high iron-phosphorus ratio has a high specific surface area, and its iron-phosphorus molar ratio satisfies Fe / P = 1.460 to 1.480, and its specific surface area BET = 15 to 20 m² ２ Iron hydroxyphosphate that satisfies the requirement of / g and has a low iron-phosphorus ratio has a low specific surface area, and its iron-phosphorus molar ratio satisfies Fe / P = 1.440 to 1.460, and its specific surface area BET = 5 to 10 m² ２ Satisfying / g, A method for producing lithium iron phosphate from iron hydroxyphosphate as described in feature 1.

8. In step S6, 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% to 1.6% in the final product, the lithium source is one or more of lithium phosphate, lithium carbonate, lithium iron phosphate electrode sheet material, and lithium iron phosphate low-carbon product material, the iron source is one or more of iron phosphate and iron oxide, the carbon source is one or more of sucrose, glucose, citric acid, starch, and polyethylene glycol, and the additive is one or more selected from titanium dioxide, ammonium metavanadate, and niobium pentoxide, and the doping amount is controlled to 300 to 3000 ppm. In step S7, the particle size of the bead mill processed slurry is controlled to 0.45 to 0.75 μm, and in spray drying, the intake air temperature is set to 200 to 220°C, the exhaust air temperature to 80 to 110°C, and the blowing frequency to 80 Hz, and the spray particle size of the spray material is controlled to D50 = 20 to 40 μm, and in step S8, the sintering atmosphere is set to nitrogen gas, the sintering temperature to 750 to 780°C, the heating rate to 3°C / min, and the sintering time to 8 to 12 h, and then natural cooling is performed to obtain the sintered material, and in the grinding process, the atmospheric pressure is controlled to 0.2 to 0.4 MPa and the classification frequency to 80 to 200 Hz, and the particle size of the grinding material satisfies D10 > 0.35 μm, D50 = 0.7 to 2.0 μm, D90 < 10 μm, and D100 < 30 μm. A method for producing lithium iron phosphate from iron hydroxyphosphate as described in feature 1.

9. Step S1 involves adding ferrous sulfate, a by-product of titanium white, to a phosphorus source and a precipitant, purifying it, and then purifying it by pressure filtration to obtain a ferrous sulfate solution. Step S2 involves adding an appropriate amount of phosphoric acid to the ferrous sulfate solution to lower the pH value of the ferrous sulfate solution, Step S3 involves sequentially adding hydrogen peroxide solution, phosphoric acid, ammonium dihydrogen phosphate solution, and ammonia water to a ferrous sulfate solution, allowing it to react for a certain period of time to form a mixed slurry, heating and maintaining the temperature of the mixed slurry for a certain period of time, and then performing multiple washes with water and pressure filtration to form iron hydroxyphosphate precursors having different iron-phosphorus ratios. Step S4 involves flash-drying the iron hydroxyphosphate precursor in a flash dryer and sintering it at a high temperature for a certain period of time to obtain an iron hydroxyphosphate precursor product having different iron-phosphorus ratios and different specific surface areas. Step S5 involves grinding the sintered material with a mechano mill and mixing it with a ribbon mixer to obtain iron hydroxyphosphate products having different iron-phosphorus ratios and different specific surface areas. Step S6 involves mixing iron hydroxyphosphate with a high iron-phosphorus ratio and high specific surface area with iron hydroxyphosphate with a low iron-phosphorus ratio and low specific surface area in a predetermined ratio, then blending it with iron phosphate, lithium phosphate, and lithium carbonate in a predetermined ratio, and adding a certain amount of carbon source and additives to form a mixed material. Step S7 involves performing a bead milling process on the above mixed material to obtain a nano-sized bead milled slurry, and then spray-drying the nano-sized bead milled slurry to obtain a spray material. Step S8 involves placing the above-mentioned spray material into a box furnace and sintering it to obtain a sintered material, and then grinding the sintered material with a jet mill to obtain a pulverized material. Step S9 includes further sieving of the above-mentioned pulverized material, batch synthesis, and packaging to obtain a lithium iron phosphate product. A method for producing lithium iron phosphate from iron hydroxyphosphate as described above.

10. Step S3 is, Step S321 involves adding an excess of hydrogen peroxide solution to a ferrous sulfate solution and continuing the oxidation for a certain period of time. Step S322 involves adding a phosphoric acid solution to the oxidized ferrous sulfate solution, then adding water to dissolve ammonium dihydrogen phosphate powder to prepare a 30% ammonium dihydrogen phosphate solution, setting the dissolution temperature to 30-40°C, and adding it to the oxidized ferrous sulfate solution. Step S323 includes adding aqueous ammonia to a ferrous sulfate solution, adjusting the pH of the solution to 3.00 ± 0.02, allowing it to react for a certain period of time to form a mixed slurry, heating and maintaining the mixed slurry for a certain period of time, and then performing multiple washes with water and pressure filtration to form iron hydroxyphosphate precursors having different iron-phosphorus ratios. A method for producing lithium iron phosphate from iron hydroxyphosphate according to feature 9.

11. Step S1 involves adding ferrous sulfate, a by-product of titanium white, to a phosphorus source and a precipitant, purifying it, and then purifying it by pressure filtration to obtain a ferrous sulfate solution. Step S2 involves adding an appropriate amount of phosphoric acid to the ferrous sulfate solution to lower the pH value of the ferrous sulfate solution, Step S3 involves sequentially adding phosphoric acid, ammonium dihydrogen phosphate solution, hydrogen peroxide solution, and ammonia solution to a ferrous sulfate solution, allowing it to react for a certain period of time to form a mixed slurry, heating and maintaining the temperature of the mixed slurry for a certain period of time, and then performing multiple washes with water and pressure filtration to form iron hydroxyphosphate precursors having different iron-phosphorus ratios. Step S4 involves flash-drying the iron hydroxyphosphate precursor in a flash dryer and sintering it at a high temperature for a certain period of time to obtain an iron hydroxyphosphate precursor product having different iron-phosphorus ratios and different specific surface areas. Step S5 involves grinding the sintered material with a mechano mill and mixing it with a ribbon mixer to obtain iron hydroxyphosphate products having different iron-phosphorus ratios and different specific surface areas. Step S6 involves mixing iron hydroxyphosphate with a high iron-phosphorus ratio and high specific surface area and iron hydroxyphosphate with a low iron-phosphorus ratio and low specific surface area in a predetermined ratio, then blending it with iron oxide, lithium phosphate, lithium carbonate, and ammonium dihydrogen phosphate in a predetermined ratio, and adding a certain amount of carbon source and additives to form a mixed material. Step S7 involves performing a bead milling process on the above mixed material to obtain a nano-sized bead milled slurry, and then spray-drying the nano-sized bead milled slurry to obtain a spray material. Step S8 involves placing the above-mentioned spray material into a box furnace and sintering it to obtain a sintered material, and then grinding the sintered material with a jet mill to obtain a pulverized material. Step S9 includes further sieving of the above-mentioned pulverized material, batch synthesis, and packaging to obtain a lithium iron phosphate product. A method for producing lithium iron phosphate from iron hydroxyphosphate, characterized by the following features.

12. Step S3 is, Step S331 involves adding a phosphoric acid solution to a ferrous sulfate solution, then adding water to dissolve ammonium dihydrogen phosphate powder to prepare a 30% ammonium dihydrogen phosphate solution, setting the dissolution temperature to 30-40°C, and adding it to the ferrous sulfate solution. Step S332 involves adding excess hydrogen peroxide to a ferrous sulfate solution and continuing the oxidation for a certain period of time. Step S333 includes adding aqueous ammonia to a ferrous sulfate solution, adjusting the pH of the solution to 3.00 ± 0.02, allowing it to react for a certain period of time to form a mixed slurry, heating and maintaining the mixed slurry for a certain period of time, and then performing multiple washes with water and pressure filtration to form iron hydroxyphosphate precursors having different iron-phosphorus ratios. A method for producing lithium iron phosphate from iron hydroxyphosphate according to feature 11.

13. Step S1 involves adding ferrous sulfate, a by-product of titanium white, to a phosphorus source and a precipitant, purifying it, and then purifying it by pressure filtration to obtain a ferrous sulfate solution. Step S2 involves adding an appropriate amount of phosphoric acid to the ferrous sulfate solution to lower the pH value of the ferrous sulfate solution, Step S3 involves adding hydrogen peroxide solution, phosphoric acid, ammonium dihydrogen phosphate solution, and aqueous ammonia to a ferrous sulfate solution, allowing it to react for a certain period of time to form a mixed slurry, keeping the mixed slurry warm at room temperature for a certain period of time, and then performing multiple washes with water and pressure filtration to form iron hydroxyphosphate precursors having different iron-phosphorus ratios. Step S4 involves flash-drying the iron hydroxyphosphate precursor in a flash dryer and sintering it at a high temperature for a certain period of time to obtain an iron hydroxyphosphate precursor product having different iron-phosphorus ratios and different specific surface areas. Step S5 involves grinding the sintered material with a mechano mill and mixing it with a ribbon mixer to obtain iron hydroxyphosphate products having different iron-phosphorus ratios and different specific surface areas. Step S6 involves mixing iron hydroxyphosphate with a high iron-phosphorus ratio and iron hydroxyphosphate with a low iron-phosphorus ratio in a predetermined ratio, then blending them with lithium phosphate and lithium iron phosphate electrode sheet material in a predetermined ratio, and adding a certain amount of carbon source and additives to form a mixed material. Step S7 involves performing a bead milling process on the above mixed material to obtain a nano-sized bead milled slurry, and then spray-drying the nano-sized bead milled slurry to obtain a spray material. Step S8 involves placing the above-mentioned spray material into a box furnace and sintering it to obtain a sintered material, and then grinding the sintered material with a jet mill to obtain a pulverized material. Step S9 includes further sieving of the above-mentioned pulverized material, batch synthesis, and packaging to obtain a lithium iron phosphate product. A method for producing lithium iron phosphate from iron hydroxyphosphate, characterized by the following features.

14. Step S3 is, Step S341 involves adding excess hydrogen peroxide to a ferrous sulfate solution and continuing the oxidation for a certain period of time. Step S342 involves adding water to ammonium dihydrogen phosphate powder to dissolve it and prepare a 30% ammonium dihydrogen phosphate solution, setting the dissolution temperature to 30-40°C, then adding phosphoric acid solution and ammonia water to the ammonium dihydrogen phosphate solution, stirring, and mixing to form a mixed ammonium phosphate solution. Step S343 includes adding an ammonium phosphate mixed solution to an oxidized ferrous sulfate solution, adjusting the pH of the solution to 3.00 ± 0.02, allowing it to react for a certain period of time to form a mixed slurry, keeping the mixed slurry warm at room temperature for a certain period of time, and then performing multiple washes with water and pressure filtration to form iron hydroxyphosphate precursors having different iron-phosphorus ratios. A method for producing lithium iron phosphate from iron hydroxyphosphate according to feature 13.

15. In step S6, the method for producing the lithium iron phosphate electrode sheet material includes the steps of: crushing and sieving a waste lithium iron phosphate positive electrode sheet to separate the foil material from the raw materials for the lithium iron phosphate electrode sheet material; and sintering the raw materials for the lithium iron phosphate electrode sheet material in an inert atmosphere, with a sintering temperature of 400 to 500°C and a sintering time of 1 to 4 hours, and then crushing the material until the particle size is 1 to 5 μm to obtain the lithium iron phosphate electrode sheet material. A method for producing lithium iron phosphate from iron hydroxyphosphate according to feature 13.

16. Step S1 involves adding ferrous sulfate, a by-product of titanium white, to a phosphorus source and a precipitant, purifying it, and then purifying it by pressure filtration to obtain a ferrous sulfate solution. Step S2 involves adding an appropriate amount of phosphoric acid to the ferrous sulfate solution to lower the pH value of the ferrous sulfate solution, Step S3 involves adding hydrogen peroxide solution, phosphoric acid, ammonium dihydrogen phosphate solution, and aqueous ammonia to a ferrous sulfate solution, allowing it to react for a certain period of time to form a mixed slurry, keeping the mixed slurry warm at room temperature for a certain period of time, and then performing multiple washes with water and pressure filtration to form iron hydroxyphosphate precursors having different iron-phosphorus ratios. Step S4 involves flash-drying the iron hydroxyphosphate precursor in a flash dryer and sintering it at a high temperature for a certain period of time to obtain an iron hydroxyphosphate precursor product having different iron-phosphorus ratios and different specific surface areas. Step S5 involves grinding the sintered material with a mechano mill and mixing it with a ribbon mixer to obtain iron hydroxyphosphate products having different iron-phosphorus ratios and different specific surface areas. Step S6 involves mixing iron hydroxyphosphate with a high iron-phosphorus ratio and iron hydroxyphosphate with a low iron-phosphorus ratio in a predetermined ratio, then blending them with lithium phosphate and lithium iron phosphate low-carbon product material in a predetermined ratio, and adding a certain amount of carbon source and additives to form a mixed material. Step S7 involves performing a bead milling process on the above mixed material to obtain a nano-sized bead milled slurry, and then spray-drying the nano-sized bead milled slurry to obtain a spray material. Step S8 involves placing the above-mentioned spray material into a box furnace and sintering it to obtain a sintered material, and then grinding the sintered material with a jet mill to obtain a pulverized material. Step S9 includes further sieving of the above-mentioned pulverized material, batch synthesis, and packaging to obtain a lithium iron phosphate product. A method for producing lithium iron phosphate from iron hydroxyphosphate, characterized by the following features.

17. Step S3 is, Step S351 involves adding an excess of hydrogen peroxide solution to a ferrous sulfate solution and continuing the oxidation for a certain period of time. Step S352 involves adding water to ammonium dihydrogen phosphate powder to dissolve it and prepare a 30% ammonium dihydrogen phosphate solution, setting the dissolution temperature to 30-40°C, then adding phosphoric acid solution and ammonia water to the ammonium dihydrogen phosphate solution, stirring, and mixing to form a mixed ammonium phosphate solution. Step S353 includes adding an ammonium phosphate mixed solution to an oxidized ferrous sulfate solution, adjusting the pH of the solution to 3.00 ± 0.02, allowing it to react for a certain period of time to form a mixed slurry, keeping the mixed slurry warm at room temperature for a certain period of time, and then performing multiple washes with water and pressure filtration to form iron hydroxyphosphate precursors having different iron-phosphorus ratios. A method for producing lithium iron phosphate from iron hydroxyphosphate according to feature 16.

18. Step S6 is, Step S61 involves mixing iron oxide with a phosphorus source, a lithium source, a primary carbon source, and a dopant, then adding water and stirring to obtain a slurry. Step S62 involves sequentially performing wet polishing, spray drying, sintering under a nitrogen gas atmosphere, and air-jet grinding on the slurry to obtain a low-carbon lithium iron phosphate product material after grinding. Step S63 includes mixing iron hydroxyphosphate with a high iron-phosphorus ratio and iron hydroxyphosphate with a low iron-phosphorus ratio in a predetermined ratio, then blending them with lithium phosphate and lithium iron phosphate low-carbon product material in a predetermined ratio, and adding a certain amount of secondary carbon source and additives to form a mixed material. A method for producing lithium iron phosphate from iron hydroxyphosphate according to feature 16.

19. In step S61, the phosphorus source is one or more of phosphoric acid, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate; the lithium source is lithium carbonate and / or lithium hydroxide; the primary carbon source is one or more of sucrose, glucose, citric acid, starch, and polyethylene glycol; the molar ratio of iron in the iron oxide to phosphorus in the phosphorus source is n(Fe):n(P) = (0.96 to 1):1; the molar ratio of lithium in the lithium source to iron in the iron oxide is n(Li):n(Fe) = (1.02 to 1.05):1; the dopant is a metal oxide, and the metal is one of Ti, V, Nb, and Mg. At least one of the following, in step S63, the carbon content in the lithium iron phosphate low-carbon product material is 0.2% to 0.5%, in the mixed material, the molar ratio is Li:Fe:P = [1.03 to 1.04]:1:[1.03 to 1.04], the secondary carbon source is one or more of sucrose, glucose, citric acid, starch, and polyethylene glycol, the amount of the primary and secondary carbon sources added is based on the carbon content of the final product being 1.2% to 1.6%, the additive is one or more selected from titanium dioxide, ammonium metavanadate, and niobium pentoxide, and the doping amount is controlled to 300 to 3000 ppm. A method for producing lithium iron phosphate from iron hydroxyphosphate according to feature 18.

20. Apply the method for producing lithium iron phosphate from iron hydroxyphosphate according to any one of claims 1 to 19. A lithium-ion battery cathode material characterized by the following features.

21. The lithium-ion battery cathode material described in claim 20 is included. A lithium-ion battery characterized by the following features.

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