Novel green lithium iron phosphate precursor, its preparation method and use

Abstract

The present invention discloses a novel green lithium iron phosphate precursor, and its preparation method and use. The preparation method of the lithium iron phosphate precursor includes the steps of: S1. reacting a mixture of an iron source and a phosphoric acid solution, and pulverizing the mixture to obtain product A after the reaction is completed; reacting a mixture of an organic acid solution, a lithium source, and a carbon source, and obtaining product B after the reaction is completed, and the preparation order of the product A and the product B is not limited; S2. pulverizing the mixture of the product A and the product B to obtain the lithium iron phosphate precursor. In the preparation process of the lithium iron phosphate precursor of the present invention, the solid content can be greatly improved, the energy consumption of the subsequent steps is low, the preparation method is simple, the cost is low, the particle size of the prepared lithium iron phosphate precursor is very small, and the charge and discharge c rate is fast.

Description

[Technical Field]

[0001] This application claims priority from Chinese Patent Application No. 2021110643549, filed on September 10, 2021. This application incorporates reference to the above Chinese patent application in its entirety.

[0002] The present invention provides a novel green lithium iron phosphate precursor, and methods for its preparation and use. [Background technology]

[0003] Over the past few decades, lithium-ion battery materials have been actively developed worldwide for use in transportation such as electric vehicles and electric bicycles. Research into power batteries for on-board power sources has been a major bottleneck in the development of powered vehicles. Considering cost-effectiveness, lithium ion batteries offer significant advantages. Lithium ferrous phosphate (LiFePO4), also known as lithium iron phosphate, has many advantages, including a stable structure, abundant raw material sources, environmental friendliness, low cost, a theoretical capacity of 170 mAh / g, and a stable discharge plateau at 3.5 V. In particular, its safety performance and cycle life are unmatched, making it the most attractive cathode material today.

[0004] Current LiFePO4 synthesis methods mainly focus on synthesis processes using iron phosphate as a raw material. Synthetic methods using iron phosphate as a raw material generally involve reacting iron phosphate with a lithium source and a carbon source, which results in a low solids content in the resulting product (usually 35-40%) and high costs in subsequent processes.

[0005] LiFePO4 can also be synthesized by reacting iron powder as a raw material with iron powder 6 powder, phosphoric acid, a lithium source, and a carbon source.

[0006] For example, WO2004036671A1 discloses reacting metallic iron with phosphoric acid in an aqueous solution, adding lithium carbonate or lithium hydroxide to prepare a lithium iron phosphate precursor, drying the resulting precursor, and then calcining the precursor with a carbon source and performing a secondary calcination to obtain the finished lithium iron phosphate. However, the reaction between metallic iron powder and phosphoric acid primarily produces an insoluble divalent iron compound, ferrous phosphate (Fe3(PO4)2·8H2O), which turns the solution into a highly viscous white paste. This material hinders the sufficient reaction of the metallic iron powder and subsequent mixing with the lithium source, hinders the solids concentration of the synthesized product, and is therefore unfavorable for improving productivity and reducing the cost of the drying process. While adding hydrochloric acid, oxalic acid, etc., is said to accelerate the reaction of metallic iron powder, hydrochloric acid induces oxidation of the product, and oxalic acid is prone to producing insoluble ferrous iron, making it difficult to uniformly mix the raw materials and successfully produce lithium iron phosphate.

[0007] As another example, JP2007305585A discloses the preparation of a lithium iron phosphate precursor by reacting iron powder in an aqueous solution containing phosphoric acid and citric acid, followed by the addition of lithium hydroxide. However, in this method, the surface of the iron powder first reacts with phosphoric acid to produce an insoluble divalent iron compound, ferrous phosphate (Fe3(PO4)2·8H2O). The surface product prevents further reaction between the interior of the metallic iron powder and phosphoric acid, resulting in an insufficient reaction. Furthermore, citric acid does not exhibit a sufficient chelating effect.

[0008] Another example is patent document CN102348634A, which describes controlling the amount of oxygen chemically bonded to iron powder in an oxidizing atmosphere, allowing carboxylic acid to coexist when the iron powder reacts with phosphoric acid, and promoting the reaction between the iron powder and phosphoric acid through the carboxylic acid chelate, thereby reducing the amount of unreacted iron powder remaining. However, controlling the amount of oxygen bonded to the iron powder in this method is more complicated.

[0009] Therefore, in the prior art, when lithium iron phosphate is produced using iron phosphate as a raw material, the solid content is low, resulting in high process costs. In addition, when lithium iron phosphate is produced using iron powder as a raw material, it is difficult to control the solid content, which allows the reaction to proceed smoothly and reduces energy consumption in subsequent processes. Summary of the Invention

[0010] The present invention provides a novel green lithium iron phosphate precursor, as well as a method for producing the same, and uses thereof, which overcome the drawbacks of the prior art, namely, that when lithium iron phosphate is produced using iron phosphate as a raw material, the process cost is high due to the low solid content, and that when lithium iron phosphate is produced using iron powder as a raw material, it is difficult to control the solid content so as to smoothly proceed with the reaction and reduce energy consumption in subsequent processes.

[0011] The present inventors discovered that in conventional methods for producing lithium iron phosphate, when an iron source is used as a raw material, the solids concentration inevitably becomes too low to ensure smooth reaction, resulting in the disadvantage of increased energy consumption in downstream processes. Furthermore, as the solids content increases, the viscosity becomes too high, making the mixture difficult to stir. The present inventors unexpectedly discovered that by first completely reacting the iron source with phosphoric acid to obtain Product A, then completely reacting the iron source with an organic acid, a lithium source, and a carbon source to obtain Product B, and then further mixing and reacting the two, the solids content of the lithium iron phosphate precursor can reach 50% or even 60%, significantly reducing energy consumption in the process of producing lithium iron phosphate from the lithium iron phosphate precursor, while also simplifying and reducing production costs. Furthermore, the method of the present invention can produce a lithium iron phosphate precursor with very small particle size and high charge / discharge rates. Experiments have demonstrated that this effect cannot be achieved if an organic acid is not added to the reaction of Product B.

[0012] The present invention solves the above technical problems through the following technical solutions.

[0013] The present invention provides a method for preparing a lithium iron phosphate precursor, comprising the steps of:

[0014] S1. A mixture of an iron source and a phosphoric acid solution is reacted, and after the reaction is completed, it is pulverized to obtain product A;

[0015] The organic acid solution, the lithium source, and the carbon source are reacted to obtain a product B after the reaction is completed; the order of preparing the product A and the product B is not limited.

[0016] S2. Grinding the mixture of product A and product B to obtain a lithium iron phosphate precursor.

[0017] In the present invention, it is known to those skilled in the art that the completion state of the mixing reaction of the iron source and the phosphoric acid solution in step S1 is generally when no gas is generated by the reaction.

[0018] In S1, the iron source is known to those skilled in the art, and since the present invention is a process method including the steps of preparing iron phosphate and then preparing lithium iron phosphate, it is known to those skilled in the art that the iron source does not include iron phosphate. Preferably, the iron source is a compound containing iron and oxygen, preferably one or more of iron powder, diiron trioxide, triiron tetroxide, and ferric nitrate, more preferably one or more of iron powder, diiron trioxide, and triiron tetroxide.

[0019] Here, the iron content of the iron powder is preferably 95 wt% or more, more preferably 99 wt% or more, and even more preferably 99.5 wt% or more, for example 99.7 wt%, and the iron powder is, for example, one or more of primary reduced iron powder, secondary reduced iron powder, carbonyl reduced iron powder, and electrolytic iron powder.

[0020] Here, the purity of the diiron trioxide is preferably 95 wt% or more, more preferably 99 wt% or more, and even more preferably 99.5 wt% or more.

[0021] Here, the purity of the triiron tetroxide is preferably 95 wt% or more, more preferably 99 wt% or more, and even more preferably 99.5 wt% or more.

[0022] In S1, the mesh of the iron source is preferably 200 to 1000 mesh, more preferably 200 to 500 mesh, for example, 250 mesh or 300 mesh.

[0023] In S1, the phosphoric acid solution generally refers to an aqueous phosphoric acid solution, and the mass percentage concentration of phosphoric acid in the phosphoric acid solution is preferably 20% to 85%, for example, 49%, 59%, or 62%.

[0024] In S1, the phosphoric acid in the phosphoric acid solution may be a conventional phosphoric acid in the art, such as industrial grade phosphoric acid, food grade phosphoric acid, electrical grade phosphoric acid, or electronic grade phosphoric acid, and the electrical grade phosphoric acid can be purchased from GUANGXI QINZHOU CHENGXING CHEMICAL TECHNOLOGY CO., LTD.

[0025] In S1, the reaction temperature of the mixture of the iron source and the phosphoric acid solution is preferably 20 to 95°C, more preferably 30 to 90°C, for example, 35°C, 45°C, or 55°C.

[0026] In S1, preferably, the mixture of the iron source and the phosphoric acid solution is prepared by adding the iron source to the stirred phosphoric acid solution.

[0027] In S1, preferably, in the mixture of the iron source and the phosphoric acid solution, the molar ratio of iron element to phosphoric acid is (0.94 to 1.05):1, more preferably (0.96 to 1.0):1, for example, 0.98:1.

[0028] In S1, the grinding operation and conditions may be conventional grinding operation, such as sand milling or ball milling.

[0029] Preferably, the grinding is carried out by a sand mill. The sand mill is preferably a vertical sand mill, a horizontal sand mill (e.g., a nanoscale horizontal sand mill), a basket sand mill, or a double cone rod sand mill. The particle size of the grinding beads used in the sand mill is preferably 0.1 to 3.0 mm, for example, 0.3 mm or 0.4 mm. The grinding beads used in the sand mill are preferably zirconium oxide beads.

[0030] In S1, the viscosity of the product A is preferably 8,000 to 20,000 cps, more preferably 10,000 to 20,000 cps, for example, 15,000 cps.

[0031] In S1, preferably, the organic acid solution generally refers to a solution of an organic acid, and the mass percentage concentration of the organic acid in the organic acid solution is more preferably 5% to 98%, for example, 55%, 62%, or 72%.

[0032] In S1, the organic acid in the organic acid solution is preferably a carboxylic acid compound and / or ascorbic acid, and the carboxylic acid compound is preferably one or more of formic acid, acetic acid, oxalic acid, citric acid, tartaric acid, and malic acid, and the organic acid is, for example, citric acid and / or oxalic acid, or malic acid and / or tartaric acid.

[0033] In S1, preferably, the lithium source is one or more of lithium hydroxide monohydrate, lithium carbonate, lithium dihydrogen phosphate, lithium phosphate, and lithium acetate, more preferably lithium hydroxide monohydrate and / or lithium acetate, and the lithium carbonate is preferably industrial grade lithium carbonate or battery grade lithium carbonate.

[0034] In S1, the molar ratio of lithium element in the lithium source to phosphoric acid in the phosphoric acid solution is preferably 0.98 to 1.05, for example, 1.02, 1.03, or 1.04.

[0035] In S1, preferably, the carbon source includes one or more of glucose, sucrose, starch, phenolic resin, cyclodextrin, polyethylene, polyethylene glycol, and polyvinyl alcohol, and more preferably a mixture of polyvinyl alcohol, cyclodextrin, and polyethylene glycol.

[0036] In S1, the amount of the carbon source added is preferably 1 to 60 mass % of the iron source, more preferably 5 to 50 mass %, and even more preferably 10 to 40 mass %.

[0037] In S1, the reaction temperature of the mixture of the organic acid, lithium source, and carbon source is preferably 20 to 95°C, more preferably 30 to 90°C, for example, 35°C, 40°C, or 45°C.

[0038] In S1, the mixture of the organic acid, the lithium source, and the carbon source is preferably prepared by adding the lithium source and the carbon source to a stirred organic acid solution.

[0039] In S2, the mixture of product A and product B generally means mixing product A and product B.

[0040] In S2, the grinding operation and conditions may be conventional in the art, and the preferred embodiment of the grinding may be the same as in S1.

[0041] In S2, the particle size of the lithium iron phosphate precursor is preferably 170 to 250 nm, for example, 200 nm or 220 nm.

[0042] The present invention further provides a lithium iron phosphate precursor produced by the method for producing a lithium iron phosphate precursor.

[0043] In the present invention, the particle size of the lithium iron phosphate precursor is preferably 170 to 250 nm.

[0044] The present invention further provides a method for producing lithium iron phosphate, comprising the steps of spray drying, calcining and grinding the lithium iron phosphate precursor.

[0045] Here, the operations and conditions of the spray drying, calcination and pulverization may be those conventional in the art.

[0046] Here, in the spray drying, the gas inlet temperature may be 280°C.

[0047] Here, in the spray drying, the outlet temperature may be 110°C.

[0048] Here, the firing conditions were as follows: in a nitrogen atmosphere of 99.999% purity, the temperature was gradually increased from room temperature to 650°C at a rate of 5°C / min, the material was held at 650°C for 10 hours, and then cooled to obtain a sintered product.

[0049] Here, the pulverization conditions are that the sintered product is processed in an airflow pulverizer to obtain a target final product cathode lithium iron phosphate material with a particle size D50 of 1.5-3 μm.

[0050] The present invention further provides lithium iron phosphate produced by the method for producing lithium iron phosphate.

[0051] The present invention further provides the use of the aforementioned lithium iron phosphate in the manufacture of a positive electrode material for a lithium ion battery.

[0052] Unless contrary to common knowledge in the art, each of the above-mentioned preferred conditions can be arbitrarily combined to obtain each of the preferred embodiments of the present invention.

[0053] All reagents and materials used in the present invention are commercially available.

[0054] Positive effects of this invention:

[0055] The process for producing the lithium iron phosphate precursor of the present invention significantly improves the solid content, reduces energy consumption in downstream processes, and is simple, green, and environmentally friendly, eliminating the three waste products and at low cost, making it possible to produce lithium iron phosphate as a cathode material from an iron source at low cost. Furthermore, the lithium iron phosphate precursor produced by the present invention has extremely small particle size and a high charge / discharge rate. [Brief explanation of the drawings]

[0056] [Figure 1] 1 is an XRD spectrum of the lithium iron phosphate of Example 1. [Figure 2] 1 is a scanning electron microscope photograph of the lithium iron phosphate of Example 1. [Figure 3] 1 shows charge and discharge curves of the lithium iron phosphate of Example 1 at different c-rates. DETAILED DESCRIPTION OF THE INVENTION

[0057] The present invention will be further described below with reference to examples, but the scope of the present invention is not limited to these examples. In the following examples, experimental methods for which no particular conditions are specified will be selected according to conventional methods and conditions or product instructions.

[0058] Example 1

[0059] 1. In accordance with an iron to phosphorus molar ratio of 0.96:1, 6.895 kg of 85% industrial-grade phosphoric acid was added to 5 L of deionized water and stirred to dilute to a concentration of 49%. While stirring, 3.25 kg of 200 mesh, 99% pure secondary reduced iron powder was slowly added and reacted at 45°C. During the reaction, some gas was generated and the color of the reactant gradually changed from gray-black to gray-white. When gas generation ceased, the material was placed in a sand mill and ground. The grinding beads in the sand mill were 0.3 mm zirconium oxide beads. During grinding, the viscosity of the material gradually increased to 15,000 cps and the color gradually changed to pure white, obtaining Product A.

[0060] 2. According to the lithium to phosphorus molar ratio of 1.04:1, 4 kg of citric acid was dissolved in 3.25 kg of deionized water to prepare a solution. While stirring, 2.3 kg of battery-grade lithium carbonate and 1 kg of sucrose were added dropwise to the reaction solution, and the reaction was carried out at 40°C. A large amount of gas was generated during this reaction. The reaction was continued until the gas generation ceased, forming a transparent solution, and product B was obtained.

[0061] 3. Product B was added to Product A, and after mixing and stirring, the viscosity of the system rapidly decreased to 1000 cps, followed by grinding. The material was ground until the particle size reached a D50 of approximately 200 nm, and the reaction was completed to obtain a slurry with a solid content of 50%.

[0062] 4. The reaction product slurry was spray-dried, sintered, and ground to prepare lithium iron phosphate cathode material.

[0063] Here, the spray drying conditions were: the gas inlet temperature was 280°C, and the outlet temperature was 110°C. Sintering conditions were: in a 99.999% pure nitrogen gas atmosphere, the temperature was gradually increased from room temperature to 650°C at a rate of 5°C / min, and the mixture was held at 650°C for 10 hours, after which it was cooled to obtain a sintered product. Crushing conditions were: the sintered product was processed in an airflow crusher to obtain a target finished product of positive electrode lithium iron phosphate material with a particle size D50 of 1.5 to 3 μm.

[0064] The lithium iron phosphate positive electrode material prepared in Example 1 was subjected to PXRD (powder X-ray diffraction) and scanning electron microscope (SEM) tests.

[0065] The PXRD data in Figure 1 was obtained by testing on a Bruker D8 ADVANCE, and the SEM photograph in Figure 2 was obtained by testing on a Hitachi SU8010.

[0066] Example 2

[0067] 1. In accordance with an iron to phosphorus molar ratio of 0.98:1, 13.8 kg of 85% food-grade phosphoric acid was added to 5 L of deionized water and stirred to dilute to a concentration of 62.4%. While stirring, 6.6 kg of 250 mesh, 99.5% pure secondary reduced iron powder was slowly added and reacted at 35°C. During the reaction, some gas was generated and the color of the reactant gradually changed from gray-black to gray-white. When gas generation ceased, the material was placed in a sand mill and ground. The grinding beads in the sand mill were 0.4 mm zirconium oxide beads. During grinding, the viscosity of the material gradually increased to 20,000 cps and the color gradually changed to pure white, yielding Product A.

[0068] 2. Dissolve 4 kg of citric acid and 4 kg of oxalic acid in 5 kg of deionized water in a lithium to phosphorus molar ratio of 1.03:1 to prepare a solution. While stirring, gradually add 2 kg of glucose and 5.18 kg of industrial-grade lithium hydroxide monohydrate, and react at 35°C until a large amount of gas is generated and the reaction stops, forming a transparent, viscous solution to obtain Product B.

[0069] 3. Product B was added to Product A, and after mixing and stirring, the viscosity of the system rapidly decreased to 1200 cps, followed by grinding. The material was ground to a particle size of approximately 220 nm (D50), and the reaction was completed to obtain a slurry with a solids content of 53%.

[0070] 4. The reaction product slurry was spray-dried, sintered, and ground to obtain lithium iron phosphate cathode material.

[0071] Here, the spray drying conditions were: the gas inlet temperature was 280°C, and the outlet temperature was 110°C. Sintering conditions were: in a 99.999% pure nitrogen gas atmosphere, the temperature was gradually increased from room temperature to 650°C at a rate of 5°C / min, and the mixture was held at 650°C for 10 hours, after which it was cooled to obtain a sintered product. Crushing conditions were: the sintered product was processed in an airflow crusher to obtain a target finished product of positive electrode lithium iron phosphate material with a particle size D50 of 1.5 to 3 μm.

[0072] Example 3

[0073] 1. In accordance with a 1:1 molar ratio of iron to phosphorus, 27.6 kg of 85% food-grade phosphoric acid was added to 12 L of deionized water and stirred to dilute to a concentration of 59.2%. While stirring, 13.5 kg of 300 mesh, 99.7% pure electrolytic iron powder was slowly added and reacted at 55°C. During the reaction, some gas was generated and the color of the reactant gradually changed from gray-black to gray-white. When gas generation ceased, the material was placed in a sand mill and ground. During grinding, its viscosity gradually increased to 10,000 cps and the color gradually changed to pure white, obtaining Product A.

[0074] 2. According to the lithium to phosphorus molar ratio of 1.02:1, 6 kg of malic acid and 7 kg of tartaric acid were dissolved in 5 kg of deionized water to prepare a solution. While stirring, 4 kg of polyethylene glycol and 9.03 kg of industrial grade lithium carbonate were gradually added to the reaction solution, and the reaction was carried out under the condition of 45°C, during which a large amount of gas was generated. The reaction was continued until the gas generation ceased, forming a transparent and viscous solution, and product B was obtained.

[0075] 3. Product B was added to Product A, and after mixing and stirring, the viscosity of the system rapidly decreased, followed by grinding. The material was ground to a particle size of approximately 170 nm (D50), and the reaction was completed to obtain a slurry with a solid content of 60%.

[0076] 4. The reaction product slurry was spray-dried, sintered, and ground to obtain lithium iron phosphate cathode material.

[0077] Here, the spray drying conditions were: the gas inlet temperature was 280°C, and the outlet temperature was 110°C. Sintering conditions were: in a 99.999% pure nitrogen gas atmosphere, the temperature was gradually increased from room temperature to 650°C at a rate of 5°C / min, and the mixture was held at 650°C for 10 hours, after which it was cooled to obtain a sintered product. Crushing conditions were: the sintered product was processed in an airflow crusher to obtain a target finished product of positive electrode lithium iron phosphate material with a particle size D50 of 1.5 to 3 μm.

[0078] Example 4

[0079] 1. In accordance with an iron to phosphorus molar ratio of 0.98:1, 13.8 kg of 85% food-grade phosphoric acid was added to 5 L of deionized water and stirred to dilute to a concentration of 62.4%. While stirring, 9.11 kg of 250 mesh, 99.5% pure iron tetroxide was slowly added and the reaction was carried out at 35°C. During the reaction, some gas was generated and the color of the reactant gradually changed from gray-black to gray-white. When gas generation ceased, the material was placed in a sand mill and ground. The grinding beads in the sand mill were 0.4 mm zirconium oxide beads. During grinding, the viscosity gradually increased to 20,000 cps and the color gradually changed to pure white, obtaining Product A.

[0080] 2. According to the lithium to phosphorus molar ratio of 1.03:1, 4 kg of citric acid and 4 kg of oxalic acid were dissolved in 5 kg of deionized water to prepare a solution. While stirring, 2 kg of glucose, 4 kg of industrial grade lithium hydroxide monohydrate, and 3.43 kg of lithium acetate were added dropwise, and the mixture was reacted at 35°C. During the reaction, a large amount of gas was generated. The reaction was continued until the gas generation ceased, forming a transparent, viscous solution, and product B was obtained.

[0081] 3. Product B was added to Product A, and after mixing and stirring, the viscosity of the system rapidly decreased to 1200 cps, followed by grinding. The material was ground to a particle size of approximately 220 nm (D50), and the reaction was completed to obtain a slurry with a solids content of 53%.

[0082] 4. The reaction product slurry was spray-dried, sintered, and ground to obtain lithium iron phosphate cathode material.

[0083] Here, the spray drying conditions were: the gas inlet temperature was 280°C, and the outlet temperature was 110°C. Sintering conditions were: in a 99.999% pure nitrogen gas atmosphere, the temperature was gradually increased from room temperature to 650°C at a rate of 5°C / min, and the mixture was held at 650°C for 10 hours, after which it was cooled to obtain a sintered product. Crushing conditions were: the sintered product was processed in an airflow crusher to obtain a target finished product of positive electrode lithium iron phosphate material with a particle size D50 of 1.5 to 3 μm.

[0084] Example 4

[0085] 1. In accordance with an iron to phosphorus molar ratio of 0.98:1, 13.8 kg of 85% food-grade phosphoric acid was added to 5 L of deionized water and diluted to a concentration of 62.4% by stirring. While stirring, 2.2 kg of 250 mesh, 99.5% pure secondary reduced iron powder, 3.03 kg of iron tetraoxide, and 3.14 kg of iron trioxide were slowly added and reacted at 35°C. During the reaction, some gas was generated and the color of the reactant gradually changed from gray-black to gray-white. When gas generation ceased, the material was placed in a sand mill and ground. The grinding beads in the sand mill were 0.4 mm zirconium oxide beads. During grinding, the viscosity gradually increased to 20,000 cps and the color gradually changed to pure white, yielding Product A.

[0086] 2. According to a lithium to phosphorus molar ratio of 1.03:1, 4 kg of citric acid and 4 kg of oxalic acid were dissolved in 5 kg of deionized water to prepare a solution. While stirring, 2 kg of a mixture of polyvinyl alcohol, cyclodextrin, and polyethylene glycol and 5.18 kg of technical-grade lithium hydroxide monohydrate were added dropwise to the solution, and the mixture was reacted at 35°C. During the reaction, a large amount of gas was generated. The reaction was continued until the gas generation ceased, forming a transparent and viscous solution, and product B was obtained.

[0087] 3. Product B was added to Product A, and after mixing and stirring, the viscosity of the system rapidly decreased to 1200 cps, followed by grinding. The material was ground to a particle size of approximately 220 nm (D50), and the reaction was completed to obtain a slurry with a solid content of 50%.

[0088] 4. The reaction product slurry was spray-dried, sintered, and ground to obtain lithium iron phosphate cathode material.

[0089] Here, the spray drying conditions were: the gas inlet temperature was 280°C, and the outlet temperature was 110°C. Sintering conditions were: in a 99.999% pure nitrogen gas atmosphere, the temperature was gradually increased from room temperature to 650°C at a rate of 5°C / min, and the mixture was held at 650°C for 10 hours, after which it was cooled to obtain a sintered product. Crushing conditions were: the sintered product was processed in an airflow crusher to obtain a target finished product of positive electrode lithium iron phosphate material with a particle size D50 of 1.5 to 3 μm.

[0090] Comparative Example 1

[0091] 1. In accordance with an iron to phosphorus molar ratio of 0.96:1, 6.895 kg of 85% industrial-grade phosphoric acid was added to 5 L of deionized water and stirred to dilute to a concentration of 49%. While stirring, 3.25 kg of 200 mesh, 99% pure secondary reduced iron powder was slowly added and reacted at 45°C. During the reaction, some gas was generated and the color of the reactant gradually changed from gray-black to gray-white. When gas generation ceased, the material was placed in a sand mill and ground. The grinding beads in the sand mill were 0.3 mm zirconium oxide beads. During grinding, the viscosity gradually increased to 15,000 cps and the color gradually changed to pure white, yielding Product A.

[0092] 2. In accordance with a lithium to phosphorus molar ratio of 1.04:1, 2.3 kg of battery-grade lithium carbonate and 1 kg of sucrose were added dropwise to 3.25 kg of deionized water at 40°C while stirring to prepare a slurry (lithium carbonate has low solubility in water), to obtain Product B.

[0093] 3. After adding product B to product A and mixing and stirring, the viscosity of the system increased rapidly, the slurry solidified, and grinding could not be carried out.

[0094] Comparative Example 2

[0095] 1. In accordance with an iron to phosphorus molar ratio of 0.96:1, 6.895 kg of 85% industrial-grade phosphoric acid was added to 5 L of deionized water and stirred to dilute to a concentration of 49%. While stirring, 3.25 kg of 200 mesh, 99% pure secondary reduced iron powder was slowly added and reacted at 45°C. During the reaction, some gas was generated and the color of the reactant gradually changed from gray-black to gray-white. When gas generation ceased, the material was placed in a sand mill and ground. The grinding beads in the sand mill were 0.3 mm zirconium oxide beads. During grinding, the viscosity gradually increased to 15,000 cps and the color gradually changed to pure white, yielding Product A.

[0096] 2. To avoid the problem of solidification when mixing with Product B, 25 kg of deionized water was added to Product A to dilute it.

[0097] 3. In accordance with a lithium to phosphorus molar ratio of 1.04:1, 2.3 kg of battery-grade lithium carbonate and 1 kg of sucrose were added dropwise to 3.25 kg of deionized water at 40°C while stirring to prepare a slurry (lithium carbonate has low solubility in water), to obtain Product B.

[0098] 4. Product B was added to Product A, and after mixing and stirring, the system showed no hardening problems, so it was subsequently milled. When the primary particle size of the material finally reached a D50 of approximately 800 nm, the system was stable, and subsequent milling did not show any tendency for the primary particle size to decrease. The reaction was stopped, and a slurry with a solids content of 17% was obtained upon completion of the reaction.

[0099] 5. The reaction product slurry was spray-dried, sintered, and ground to obtain lithium iron phosphate cathode material.

[0100] Here, the spray drying conditions were: the gas inlet temperature was 280°C, and the outlet temperature was 110°C. Sintering conditions were: in a 99.999% pure nitrogen gas atmosphere, the temperature was gradually increased from room temperature to 650°C at a rate of 5°C / min, and the mixture was held at 650°C for 10 hours, after which it was cooled to obtain a sintered product. Crushing conditions were: the sintered product was processed in an airflow crusher to obtain a target finished product of positive electrode lithium iron phosphate material with a particle size D50 of 1.5 to 3 μm.

[0101] Comparative Example 3

[0102] 1. In accordance with an iron to phosphorus molar ratio of 0.96:1, 6.895 kg of 85% industrial-grade phosphoric acid was added to 5 L of deionized water and diluted to 49% concentration with stirring. While stirring, 3.25 kg of 200 mesh, 99% pure secondary reduced iron powder was slowly added, followed by 4 kg of citric acid. The reaction was allowed to proceed at 45°C. During the reaction, some gas was generated and the color of the reactant gradually changed from gray-black to yellow-green. When gas generation ceased, the material was placed in a sand mill and ground. The grinding beads in the sand mill were 0.3 mm zirconium oxide beads. During grinding, the viscosity gradually increased to 15,000 cps and the color gradually changed to yellow-green, yielding Product A.

[0103] 2. In accordance with a lithium to phosphorus molar ratio of 1.04:1, 2.3 kg of battery-grade lithium carbonate and 1 kg of sucrose were added dropwise to 3.25 kg of deionized water at 40°C while stirring to prepare a slurry (lithium carbonate has low solubility in water), to obtain Product B.

[0104] 3. After adding Product B to Product A and mixing and stirring, the viscosity of the system gradually increased to over 20,000 cps. To ensure a smooth process, an additional 10 L of deionized water was added to reduce the viscosity to 1,200 cps. When the material was ground to a particle size of approximately 500 nm (D50), the reaction was completed and a slurry with a solids content of 35% was obtained.

[0105] 4. The reaction product slurry was spray-dried, sintered, and ground to obtain lithium iron phosphate cathode material.

[0106] Here, the spray drying conditions were: the gas inlet temperature was 280°C, and the outlet temperature was 110°C. Sintering conditions were: in a 99.999% pure nitrogen gas atmosphere, the temperature was gradually increased from room temperature to 650°C at a rate of 5°C / min, and the mixture was held at 650°C for 10 hours, after which it was cooled to obtain a sintered product. Crushing conditions were: the sintered product was processed in an airflow crusher to obtain a target finished product of positive electrode lithium iron phosphate material with a particle size D50 of 1.5 to 3 μm.

[0107] The lithium iron phosphate powders prepared in Examples 1-5 and Comparative Examples 2-3 were each mixed with carbon black and polyvinylidene fluoride (PVDF) in a mass ratio of 80:10:10 until uniform, then coated on aluminum foil and dried to prepare suitable cathode test specimens. These were then assembled with metallic lithium to prepare 2032 button batteries. Charge-discharge cycle experiments were performed using a charge-discharge machine (LAND CT2001A) at charge-discharge rates of C / 10, C / 5, C / 2, 1C, 2C, and 5C over a charge-discharge range of 2.0V to 4.2V. The results are shown in Figure 3 and Table 1.

[0108] [Table 1]

[0109] [Table 2]

[0110] As shown in Table 2, in Examples 1 to 5, the amount of dehydration required to prepare the precursor can be significantly reduced compared to Comparative Examples 2 and 3, and the energy consumption required for dehydration can be significantly reduced. In Comparative Example 1, the production method based on the conventional technology only increased the solid content, and there was a problem that the viscosity was too high to stir. In Comparative Examples 2 and 3, an organic acid was not added to the reaction of Product B, so the effects of the present invention were not obtained.

[0111] While specific embodiments of the present invention have been described above, it should be understood by those skilled in the art that these are merely examples and that various changes and modifications can be made to these embodiments without departing from the principles and essence of the present invention. Accordingly, the scope of the present invention is defined by the appended claims. The present invention may include the following embodiments. <1> S1. A mixture of an iron source and a phosphoric acid solution is reacted, and after the reaction is completed, it is pulverized to obtain product A. A step of reacting a mixture of an organic acid solution, a lithium source, and a carbon source to obtain a product B after the reaction is completed, and the order of producing the product A and the product B is not limited; S2. Grinding the mixture of product A and product B to obtain a lithium iron phosphate precursor; A method for preparing a lithium iron phosphate precursor, comprising: <2> (1) the lithium iron phosphate precursor has a solid content of 50% or more; (2) The iron source is a compound containing iron and oxygen, and is preferably one or more of iron powder, diiron trioxide, triiron tetroxide, and ferric nitrate, and more preferably one or more of iron powder, diiron trioxide, and triiron tetroxide; Preferably, the iron content in the iron powder is 95 wt% or more, more preferably 99 wt% or more, and even more preferably 99.5 wt% or more, for example 99.7 wt%; Preferably, the iron powder is one or more of primary reduced iron powder, secondary reduced iron powder, carbonyl reduced iron powder, and electrolytic iron powder; Preferably, the purity of the iron trioxide is 95 wt% or more, more preferably 99 wt% or more, and even more preferably 99.5 wt% or more. Preferably, the purity of the triiron tetroxide is 95 wt% or more, more preferably 99 wt% or more, and even more preferably 99.5 wt% or more; (3) The mesh of the iron source is 200 to 1000 mesh, preferably 200 to 500 mesh, for example, 250 mesh or 300 mesh; The above is characterized by satisfying one or more of the following conditions: <1> A method for producing the lithium iron phosphate precursor according to claim 1. <3> (1) The mass percentage concentration of phosphoric acid in the phosphoric acid solution is 20% to 85%, for example, 49%, 59%, or 62%; (2) the phosphoric acid in the phosphoric acid solution is industrial grade phosphoric acid, food grade phosphoric acid, electrical grade phosphoric acid, or electronic grade phosphoric acid; (3) the reaction temperature of the mixture of the iron source and the phosphoric acid solution is 20 to 95°C, preferably 30 to 90°C, for example, 35°C, 45°C, or 55°C; (4) In the mixture of the iron source and the phosphoric acid solution, the molar ratio of iron element to phosphoric acid is (0.94-1.05):1, preferably (0.96-1.0):1, for example, 0.98:1; The above is characterized by satisfying one or more of the following conditions: <1> or <2> A method for producing the lithium iron phosphate precursor according to claim 1. <4> (1) the grinding is carried out using a sand mill; The sand mill is preferably a vertical sand mill, a horizontal sand mill, a basket sand mill, or a double cone rod sand mill; The particle size of the grinding beads used in the sand mill is preferably 0.1 to 3.0 mm, for example, 0.3 mm or 0.4 mm; The grinding beads used in the sand mill are preferably zirconium oxide beads; (2) The viscosity of the product A is 8,000 to 20,000 cps, preferably 10,000 to 20,000 cps, for example, 15,000 cps; (3) The mass percentage concentration of the organic acid in the organic acid solution is 5% to 98%, for example, 55%, 62%, or 72%; (4) The organic acid in the organic acid solution is a carboxylic acid compound and / or ascorbic acid; The carboxylic acid compound is preferably one or more of formic acid, acetic acid, oxalic acid, citric acid, tartaric acid, and malic acid; The organic acid is preferably citric acid and / or oxalic acid, or malic acid and / or tartaric acid; The above is characterized by satisfying one or more of the following conditions: <1> ~ <3> 10. A method for producing the lithium iron phosphate precursor according to claim 9. <5> (1) the lithium source is one or more of lithium hydroxide monohydrate, lithium carbonate, lithium dihydrogen phosphate, lithium phosphate, and lithium acetate, preferably lithium hydroxide monohydrate and / or lithium acetate; The lithium carbonate is preferably industrial grade lithium carbonate or battery grade lithium carbonate; (2) the molar ratio of lithium element in the lithium source to phosphoric acid in the phosphoric acid solution is 0.98 to 1.05, for example, 1.02, 1.03, or 1.04; (3) the carbon source comprises one or more of glucose, sucrose, starch, phenolic resin, cyclodextrin, polyethylene, polyethylene glycol, and polyvinyl alcohol, preferably a mixture of polyvinyl alcohol, cyclodextrin, and polyethylene glycol; (4) The amount of the carbon source added is 1 to 60% by mass, preferably 5 to 50% by mass, and more preferably 10 to 40% by mass of the iron source; (5) the reaction temperature of the mixture of the organic acid, the lithium source, and the carbon source is 20 to 95°C, preferably 30 to 90°C, for example, 35°C, 40°C, or 45°C; (6) The particle size of the lithium iron phosphate precursor is 170 to 250 nm, for example, 200 nm or 220 nm; The above is characterized by satisfying one or more of the following conditions: <1> ~ <4> 10. A method for producing the lithium iron phosphate precursor according to claim 9. <6> The aforementioned <1> ~ <5> 1. A lithium iron phosphate precursor, characterized by being produced by the method for producing a lithium iron phosphate precursor according to any one of claims 1 to 9. <7> The lithium iron phosphate precursor has a particle size of 170 to 250 nm. <6> The lithium iron phosphate precursor according to claim 1. <8> The aforementioned <6> or <7> 1. A method for producing lithium iron phosphate, comprising the steps of spray-drying, calcining, and pulverizing the lithium iron phosphate precursor according to claim 1. <9> The aforementioned <8> 1. Lithium iron phosphate, characterized by being produced by the method for producing lithium iron phosphate described in 1. <10> In the production of a positive electrode material for a lithium ion battery, <9> Use of lithium iron phosphate as described in 1.

Claims

1. S1. A mixture of an iron source and a phosphoric acid solution is reacted, and after the reaction is completed, the mixture is pulverized to obtain product A. a step of reacting a mixture of an organic acid solution, a lithium source, and a carbon source to obtain a product B after the reaction is completed, and the order of producing the product A and the product B is not limited; S2. Grinding the mixture of product A and product B to obtain a lithium iron phosphate precursor; A method for producing a lithium iron phosphate precursor, comprising: The mass percentage concentration of phosphoric acid in the phosphoric acid solution is 20% to 85%, The mass percentage concentration of the organic acid in the organic acid solution is 55% to 72%; the organic acid in the organic acid solution is one of a carboxylic acid compound and / or ascorbic acid; the carboxylic acid compound is one or more of formic acid, acetic acid, oxalic acid, citric acid, tartaric acid, and malic acid; The lithium iron phosphate precursor has a solid content of 50% or more, The particle size of the lithium iron phosphate precursor is 170 to 250 nm. Method for producing lithium iron phosphate precursor.

2. (1) the iron source is one or more of iron powder, ferric oxide, ferric oxide, and ferric nitrate; (2) The mesh of the iron source is 200 to 500 mesh; 2. A method for producing a lithium iron phosphate precursor according to claim 1, characterized in that one or more of the following conditions are met:

3. The iron content of the iron powder is 95 wt % or more, and / or the iron powder is one or more of a primary reduced iron powder, a secondary reduced iron powder, a carbonyl reduced iron powder, and an electrolytic iron powder; and / or The purity of the iron trioxide is 95 wt % or more, and / or The purity of the iron trioxide is 95 wt% or more. The method for producing the lithium iron phosphate precursor according to claim 2 .

4. The iron content of the iron powder is 99.5 wt % or more, and / or The purity of the iron trioxide is 99.5 wt % or more, and / or The purity of the iron trioxide is 99.5 wt% or more. The method for producing the lithium iron phosphate precursor according to claim 2 .

5. (1) The mass percentage concentration of phosphoric acid in the phosphoric acid solution is 49%, 59%, or 62%; (2) The phosphoric acid in the phosphoric acid solution is industrial grade phosphoric acid, food grade phosphoric acid, electrical grade phosphoric acid, or electronic grade phosphoric acid; (3) the reaction temperature of the mixture of the iron source and the phosphoric acid solution is 20 to 95°C; (4) In the mixture of the iron source and the phosphoric acid solution, the molar ratio of iron element to phosphoric acid is (0.94-1.05):1; 2. A method for producing a lithium iron phosphate precursor according to claim 1, characterized in that one or more of the following conditions are met:

6. the reaction temperature of the mixture of the iron source and the phosphoric acid solution is 35°C, 45°C, or 55°C; and / or In the mixture of the iron source and the phosphoric acid solution, the molar ratio of elemental iron to phosphoric acid is 0.98:

1. The method for producing the lithium iron phosphate precursor according to claim 1 .

7. (1) the grinding is carried out using a sand mill; (2) The viscosity of the product A is 8,000 to 20,000 cps; (3) the mass percentage concentration of the organic acid in the organic acid solution is 62%; (4) The organic acid is citric acid and / or oxalic acid, or malic acid and / or tartaric acid; 2. A method for producing a lithium iron phosphate precursor according to claim 1, characterized in that one or more of the following conditions are met:

8. the sand mill is a vertical sand mill, a horizontal sand mill, a basket sand mill, or a double cone rod sand mill; and / or The particle size of the grinding beads used in the sand mill is 0.1 to 3.0 mm, and / or the grinding beads used in the sand mill are zirconium oxide beads, and / or The viscosity of the product A is 10,000 to 20,000 cps. The method for producing the lithium iron phosphate precursor according to claim 7 .

9. The particle size of the grinding beads used in the sand mill is 0.3 mm or 0.4 mm, and / or The viscosity of the product A is 15,000 cps. The method for producing the lithium iron phosphate precursor according to claim 7 .

10. (1) the lithium source is one or more of lithium hydroxide monohydrate, lithium carbonate, lithium dihydrogen phosphate, lithium phosphate, and lithium acetate; (2) the molar ratio of lithium element in the lithium source to phosphoric acid in the phosphoric acid solution is 0.98 to 1.05; (3) the carbon source comprises one or more of glucose, sucrose, starch, phenolic resin, cyclodextrin, polyethylene, polyethylene glycol, and polyvinyl alcohol; (4) The amount of the carbon source added accounts for 1 to 60% by mass of the iron source; (5) the reaction temperature of the mixture of the organic acid solution, the lithium source, and the carbon source is 20 to 95°C; (6) The particle size of the lithium iron phosphate precursor is 200 nm or 220 nm; 2. A method for producing a lithium iron phosphate precursor according to claim 1, characterized in that one or more of the following conditions are met:

11. the lithium source is lithium hydroxide monohydrate and / or lithium acetate, and / or the molar ratio of lithium element in the lithium source to phosphoric acid in the phosphoric acid solution is 1.02, 1.03 or 1.04; and / or the carbon source is a mixture of polyvinyl alcohol, cyclodextrin and polyethylene glycol; and / or The amount of the carbon source added accounts for 5 to 50% by mass of the iron source, and / or the reaction temperature of the mixture of the organic acid solution, the lithium source and the carbon source is 30 to 90°C; The method for producing the lithium iron phosphate precursor according to claim 1 .

12. The amount of the carbon source added accounts for 10 to 40% by mass of the iron source, and / or the reaction temperature of the mixture of the organic acid solution, the lithium source, and the carbon source is 35°C, 40°C, or 45°C; The method for producing the lithium iron phosphate precursor according to claim 1 .

13. A method for producing lithium iron phosphate, comprising the steps of spray-drying, calcining, and pulverizing the lithium iron phosphate precursor produced by the method of claim 1.

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