Novel precursors of green lithium iron phosphate, methods of preparation, and applications.

Abstract

Invention details;

Description

A new green lithium iron phosphate precursor and its preparation method and application

[0001] This application claims priority to Chinese Patent Application No. 2021110643549, filed on September 10, 2021. This application incorporates the entire text of the aforementioned Chinese Patent Application. Technical Field

[0002] The present invention provides a novel green lithium iron phosphate precursor and a preparation method and application thereof. Background Art

[0003] In recent decades, people around the world have been actively developing lithium-ion power battery materials for use in transportation vehicles, such as electric vehicles and electric bicycles. The research on power batteries as on-board power has become a major bottleneck in the development of power vehicles. Based on cost-effectiveness considerations, lithium-ion batteries have great advantages. Lithium iron phosphate (LiFePO4), also known as lithium iron phosphate, has many advantages due to factors such as cyclability, price, safety, and specific energy. LiFePO4 materials have stable structure, abundant raw material sources, are environmentally friendly and low-cost, and have a theoretical capacity of 170mAh / g and a stable discharge platform of 3.5V. In particular, its safety performance and cycle life are unmatched by other materials, making lithium iron phosphate the most attractive positive electrode material today.

[0004] Currently, LiFePO4 synthesis methods primarily focus on processes using iron phosphate as the raw material. These processes typically involve reacting iron phosphate with a lithium source and a carbon source. This results in a low solids content (typically 35% to 40%) and high subsequent process costs.

[0005] In addition, LiFePO4 can be synthesized by using iron powder as a raw material through the reaction of iron powder, phosphoric acid, a lithium source and a carbon source.

[0006] For example, WO2004036671A1 records that metallic iron and phosphoric acid are reacted in an aqueous solution, lithium carbonate or lithium hydroxide is added to prepare a lithium iron phosphate precursor and dried, a carbon source is added after a primary calcination, and a secondary calcination is performed to obtain a finished lithium iron phosphate product. However, during the reaction of metallic iron powder with phosphoric acid, an insoluble divalent iron compound, ferrous phosphate (Fe3(PO4)2·8H2O), is mainly generated. This substance makes the solution a white paste with high viscosity, which is not conducive to the full reaction of the metallic iron powder and the mixing of the lithium source in the later stage, and the solid content of the synthetic product cannot be increased, which is not conducive to capacity improvement and cost saving of the drying process. Although the article mentions that the reaction of metallic iron powder can be promoted by adding hydrochloric acid, oxalic acid and other processes, hydrochloric acid will promote the oxidation of the product, and oxalic acid will easily generate insoluble ferrous oxalate, making it difficult to achieve uniform mixing of the raw materials and difficult to successfully prepare lithium iron phosphate.

[0007] For example, in JP2007305585A, iron powder is first reacted in an aqueous solution containing phosphoric acid and citric acid, and then lithium hydroxide is added to prepare a lithium iron phosphate precursor. However, this method causes the surface of the iron powder to react with the phosphoric acid first, forming an insoluble divalent iron compound, ferrous phosphate (Fe3(PO4)2·8H2O). This surface product hinders further reaction between the iron powder and the phosphoric acid, resulting in an incomplete reaction. Furthermore, the citric acid cannot fully exert its chelating effect.

[0008] Another example is patent document CN102348634A, which controls the amount of oxygen chemically bonded to iron powder during the reaction in an oxidizing atmosphere. This allows the iron powder to coexist with carboxylic acid during the reaction with phosphoric acid. This carboxylic acid chelation promotes the reaction between the iron powder and phosphoric acid, reducing the amount of unreacted iron powder remaining. However, this solution is relatively complex to control the amount of oxygen bonded to the iron powder.

[0009] Therefore, the existing technology has the problem that when lithium iron phosphate is prepared using iron phosphate as raw material, the solid content is low, resulting in high process costs; when lithium iron phosphate is prepared using iron powder as raw material, the solid content is difficult to control to ensure that the reaction proceeds smoothly and the energy consumption of subsequent processes is low.

[0010] Summary of the Invention

[0011] The present invention aims to solve the problems in the prior art such as the low solid content when preparing lithium iron phosphate using iron phosphate as a raw material, resulting in high process costs; and the difficulty in controlling the solid content when preparing lithium iron phosphate using iron powder as a raw material to ensure that the reaction proceeds smoothly and the energy consumption of subsequent processes is low. A new green lithium iron phosphate precursor, a preparation method and an application thereof are provided.

[0012] The inventors have discovered that the preparation method of lithium iron phosphate in the prior art, when using an iron source as a raw material, inevitably leads to too low a solid content in order to ensure the smooth progress of the reaction, thereby causing the defect of high energy consumption in the subsequent process; and if the solid content is increased, the viscosity will be too high to be stirred. The inventors unexpectedly discovered that by first fully reacting the iron source with phosphoric acid to obtain product A, and then fully reacting with an organic acid, a lithium source and a carbon source to obtain product B, the solid content in the lithium iron phosphate precursor can be made to reach more than 50%, or even 60%, which greatly reduces the energy consumption in the process of preparing lithium iron phosphate from the lithium iron phosphate precursor. The preparation method is simple and low in cost. The method of the present invention can also prepare a lithium iron phosphate precursor with extremely small particle size and high charge and discharge rate. Experiments have shown that this effect cannot be achieved if the organic acid is not added to the reaction of product B.

[0013] The present invention solves the above technical problems through the following technical solutions.

[0014] The present invention provides a method for preparing a lithium iron phosphate precursor, which comprises the following steps:

[0015] S1. reacting a mixture of an iron source and a phosphoric acid solution, and grinding the mixture after the reaction to obtain a product A;

[0016] 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; the order of preparing the product A and the product B is not limited;

[0017] S2. Grinding the mixture of the product A and the product B to obtain a lithium iron phosphate precursor.

[0018] In the present invention, in step S1, the mixing reaction of the iron source and the phosphoric acid solution is completed. Those skilled in the art know that generally, the reaction is completed when no gas is generated.

[0019] In S1, the iron source is known to those skilled in the art. The present invention is a process for preparing lithium iron phosphate after preparing iron phosphate. Therefore, those skilled in the art know that the iron source here does not include iron phosphate. Preferably, the iron source is a compound containing iron and oxygen elements, more preferably one or more of iron powder, ferric oxide, ferroferric oxide, and ferric nitrate, and even more preferably one or more of iron powder, ferric oxide, and ferroferric oxide.

[0020] Among them, preferably, the iron content in the iron powder is more than 95wt%, more preferably more than 99wt%, and further more preferably more than 99.5wt%, for example, 99.7wt%. For example, it can be one or more of primary reduced iron powder, secondary reduced iron powder, carbonyl reduced iron powder and electrolytic iron powder.

[0021] Preferably, the purity of the ferric oxide is 95 wt % or more, more preferably 99 wt % or more, and even more preferably 99.5 wt % or more.

[0022] Preferably, the purity of the ferrosoferric oxide is 95 wt % or more, more preferably 99 wt % or more, and even more preferably 99.5 wt % or more.

[0023] In S1, preferably, the mesh size of the iron source is 200-1000 meshes, more preferably 200-500 meshes, for example, 250 meshes or 300 meshes.

[0024] In S1, the phosphoric acid solution generally refers to a phosphoric acid aqueous solution. The mass percentage concentration of phosphoric acid in the phosphoric acid solution is preferably 20-85%, for example, 49%, 59% or 62%.

[0025] In S1, the phosphoric acid in the phosphoric acid solution can be 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. The electrical-grade phosphoric acid can be purchased from Guangxi Qinzhou Chengxing Chemical Technology Co., Ltd.

[0026] In S1, preferably, the reaction temperature of the mixture of the iron source and the phosphoric acid solution is 20-95°C, more preferably 30-90°C, for example 35°C, 45°C or 55°C.

[0027] In S1, preferably, the mixture of the iron source and the phosphoric acid solution is prepared by adding the iron source to the phosphoric acid solution under stirring.

[0028] In S1, preferably, in the mixture of the iron source and the phosphoric acid solution, the molar ratio of the iron element to the phosphoric acid is (0.94-1.05):1, more preferably (0.96-1.0):1, for example 0.98:1.

[0029] In S1, the grinding operation and conditions can be conventional grinding operations, such as sand milling or ball milling.

[0030] Preferably, the grinding is performed using a sand mill. The sand mill is preferably a vertical sand mill, a horizontal sand mill (e.g., a nano-scale 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 zirconia beads.

[0031] In S1, preferably, the viscosity of the product A is 8,000 to 20,000 cps, more preferably 10,000 to 20,000 cps, for example, 15,000 cps.

[0032] In S1, preferably, the organic acid solution generally refers to an organic acid solution, and the mass percentage concentration of the organic acid in the organic acid solution is preferably 5-98%, for example, 55%, 62% or 72%.

[0033] In S1, preferably, the organic acid in the organic acid solution is 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; the organic acid is, for example, citric acid and / or oxalic acid, or malic acid and / or tartaric acid.

[0034] 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; the lithium carbonate is preferably industrial grade lithium carbonate or battery grade lithium carbonate.

[0035] In S1, preferably, the molar ratio of the lithium element in the lithium source to the phosphoric acid in the phosphoric acid solution is 0.98-1.05, for example, 1.02, 1.03 or 1.04.

[0036] In S1, preferably, the carbon source includes one or more of glucose, sucrose, starch, phenolic resin, cyclodextrin, polyethylene, polyethylene glycol and polyvinyl alcohol, more preferably a mixture of polyvinyl alcohol, cyclodextrin and polyethylene glycol.

[0037] In S1, preferably, the amount of the carbon source added accounts for 1% to 60% by mass of the iron source, more preferably 5% to 50% by mass, and even more preferably 10% to 40% by mass.

[0038] In S1, preferably, the reaction temperature of the mixture of the organic acid, the lithium source and the carbon source is 20-95°C, more preferably 30-90°C, for example 35°C, 40°C or 45°C.

[0039] In S1, preferably, the mixture of the organic acid, the lithium source and the carbon source is prepared by adding the lithium source and the carbon source to a stirred organic acid solution.

[0040] In S2, the mixture of the product A and the product B is generally prepared by mixing the product A and the product B.

[0041] In S2, the grinding operation and conditions can be conventional in the art. The preferred embodiment of the grinding can be the same as S1.

[0042] In S2, preferably, the particle size of the lithium iron phosphate precursor is 170-250 nm, for example, 200 nm or 220 nm.

[0043] The present invention also provides a lithium iron phosphate precursor, which is prepared by the above-mentioned preparation method of the lithium iron phosphate precursor.

[0044] In the present invention, preferably, the particle size of the lithium iron phosphate precursor is 170-250 nm.

[0045] The present invention also provides a method for preparing lithium iron phosphate, which comprises the following steps:

[0046] The lithium iron phosphate precursor as described above is spray dried, calcined and crushed.

[0047] The operations and conditions of the spray drying, calcining and crushing may be conventional in the art.

[0048] Wherein, during the spray drying, the air inlet temperature may be 280°C.

[0049] Wherein, during the spray drying, the outlet temperature may be 110°C.

[0050] The calcination conditions may be: in a 99.999% pure nitrogen atmosphere, gradually heating from room temperature to 650°C at a heating rate of 5°C / min, maintaining the temperature at 650°C for 10 hours, and then cooling to obtain a sintered product.

[0051] The crushing conditions may be as follows: the sintered product is processed by air flow crushing equipment to obtain a target finished positive electrode lithium iron phosphate material with a particle size of D50 = 1.5 to 3 μm.

[0052] The present invention also provides lithium iron phosphate, which is prepared by the above-mentioned preparation method of lithium iron phosphate.

[0053] The present invention also provides a use of the lithium iron phosphate as described above in preparing a positive electrode material for a lithium ion battery.

[0054] On the basis of conforming to the common sense in this field, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0055] The reagents and raw materials used in the present invention are commercially available.

[0056] The positive progress effect of the present invention is:

[0057] The lithium iron phosphate precursor prepared by the present invention significantly increases solid content, reduces energy consumption in subsequent processes, and is simple, environmentally friendly, and produces no "three wastes" (waste, waste, and wastes) at a low cost, enabling low-cost production of lithium iron phosphate, a cathode material, using an iron source as a raw material. Furthermore, the lithium iron phosphate precursor produced by the present invention has an extremely small particle size and a high charge-discharge rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] FIG1 is an XRD spectrum of lithium iron phosphate of Example 1.

[0059] FIG2 is a scanning electron microscope photograph of the lithium iron phosphate of Example 1.

[0060] FIG3 is a charge and discharge curve of the lithium iron phosphate of Example 1 at different rates. DETAILED DESCRIPTION

[0061] The present invention is further illustrated by way of examples below, but the present invention is not limited to the scope of the examples. Experimental methods in the following examples where specific conditions are not specified were performed according to conventional methods and conditions, or selected according to the product specifications.

[0062] Example 1

[0063] 1. 6.895 kg of 85% industrial-grade phosphoric acid was added to 5 L of deionized water with stirring, diluting the mixture to a 49% concentration, with an iron-to-phosphorus molar ratio of 0.96:1. While stirring, 3.25 kg of 200-mesh, 99% pure secondary reduced iron powder was slowly added. The reaction was allowed to proceed at 45°C. Gas was generated during the reaction, and the color of the reactant gradually changed from gray-black to gray-white. When no more gas was generated, the mixture was sand-milled using 0.3 mm zirconia beads. During the sand-milling process, the viscosity gradually increased to 15,000 cps, and the color gradually changed to pure white, yielding Product A.

[0064] 2. According to the molar ratio of lithium to phosphorus of 1.04:1, 4 kg of citric acid was dissolved in 3.25 kg of deionized water to prepare a solution. 2.3 kg of battery-grade lithium carbonate and 1 kg of sucrose were gradually added to the solution under stirring. The solution was reacted at 40°C. During the reaction, a large amount of gas was generated. The reaction was continued until no gas was generated and a transparent solution was formed to obtain product B.

[0065] 3. Add product B to product A and stir until the viscosity of the system drops rapidly to 1000 cps. Continue sand grinding. When the particle size D50 is approximately 200 nm, the reaction is complete to obtain a slurry with a solid content of 50%.

[0066] 4. The reaction product slurry is spray-dried, sintered, and crushed to obtain lithium iron phosphate positive electrode material.

[0067] The spray drying process was conducted under the following conditions: an inlet temperature of 280°C and an outlet temperature of 110°C. The calcination process was conducted under a 99.999% pure nitrogen atmosphere, with the temperature gradually increased from room temperature to 650°C at a rate of 5°C / min, maintained at 650°C for 10 hours, and then cooled to obtain a sintered product. The crushing process involved the sintered product being subjected to air flow crushing equipment to obtain the target finished positive electrode lithium iron phosphate material with a particle size D50 of 1.5 to 3 μm.

[0068] The lithium iron phosphate cathode material prepared in Example 1 was subjected to PXRD (powder X-Ray diffraction) and scanning electron microscopy (SEM) tests.

[0069] The PXRD data in Figure 1 were obtained using a Bruker D8 ADVANCE instrument, and the SEM image in Figure 2 was obtained using a Hitachi SU8010 instrument.

[0070] Example 2

[0071] 1. Add 13.8 kg of 85% food-grade phosphoric acid to 5 L of deionized water, stirring and diluting it to a concentration of 62.4% at a molar ratio of iron to phosphorus of 0.98:1. Slowly add 6.6 kg of 250-mesh, 99.5% pure secondary reduced iron powder while stirring. The reaction proceeds at 35°C. Gas will be generated during the reaction, and the color of the reactant will gradually change from gray-black to gray-white. When no more gas is generated, the material is sand-milled in a sand mill using 0.4 mm zirconia beads. During the sand-milling process, the viscosity gradually increases to 20,000 cps, and the color gradually changes to pure white, yielding Product A.

[0072] 2. According to the molar ratio of lithium to phosphorus 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. 2 kg of glucose and 5.18 kg of industrial-grade lithium hydroxide monohydrate were gradually added to the solution under stirring. The reaction was carried out at 35°C. During the reaction, a large amount of gas was generated. The reaction was continued until no gas was generated, forming a transparent viscous solution to obtain product B.

[0073] 3. Add product B to product A. After mixing, the system viscosity quickly drops to 1200 cps. Continue sand grinding. When the particle size D50 is about 220 nm, the reaction is completed to obtain a slurry with a solid content of 53%.

[0074] 4. The reaction product slurry is spray-dried, sintered, and crushed to obtain lithium iron phosphate positive electrode material.

[0075] The spray drying conditions are: an inlet temperature of 280°C and an outlet temperature of 110°C. The calcination conditions are: in a 99.999% pure nitrogen atmosphere, gradually increasing the temperature from room temperature to 650°C at a rate of 5°C / min, maintaining the temperature at 650°C for 10 hours, and then cooling to obtain a sintered product. The crushing conditions are: the sintered product is processed through a pneumatic crushing device to obtain the target finished positive electrode lithium iron phosphate material with a particle size D50 of 1.5 to 3 μm.

[0076] Example 3

[0077] 1. Add 27.6 kg of 85% food-grade phosphoric acid to 12 L of deionized water with stirring, diluting to a 59.2% concentration, with a molar ratio of iron to phosphorus of 1:1. Slowly add 13.5 kg of 300-mesh, 99.7% pure electrolytic iron powder while stirring. Incubate at 55°C. Gas will be generated during the reaction, and the color of the reactants will gradually change from gray-black to gray-white. When no more gas is generated, place the material in a ball mill for milling. During the milling process, the viscosity gradually increases to 10,000 cps, and the color gradually changes to pure white, yielding Product A.

[0078] 2. According to the molar ratio of lithium to phosphorus 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. 4 kg of polyethylene glycol and 9.03 kg of industrial-grade lithium carbonate were gradually added to the solution under stirring. The reaction was carried out at 45°C. During the reaction, a large amount of gas was generated. The reaction was continued until no gas was generated, forming a transparent viscous solution to obtain product B.

[0079] 3. Add product B to product A, mix and stir until the viscosity of the system decreases rapidly, and continue sand grinding. When the material particle size D50 is about 170nm, the reaction is completed to obtain a slurry with a solid content of 60%.

[0080] 4. The reaction product slurry is spray-dried, sintered, and crushed to obtain lithium iron phosphate positive electrode material.

[0081] The spray drying process was conducted under the following conditions: an inlet temperature of 280°C and an outlet temperature of 110°C. The calcination process was conducted under a 99.999% pure nitrogen atmosphere, with the temperature gradually increased from room temperature to 650°C at a rate of 5°C / min, maintained at 650°C for 10 hours, and then cooled to obtain a sintered product. The crushing process involved the sintered product being subjected to air flow crushing equipment to obtain the target finished positive electrode lithium iron phosphate material with a particle size D50 of 1.5 to 3 μm.

[0082] Example 4

[0083] 1. Add 13.8 kg of 85% food-grade phosphoric acid to 5 L of deionized water, stirring and diluting it to a concentration of 62.4% at a molar ratio of iron to phosphorus of 0.98:1. Slowly add 9.11 kg of 250-mesh, 99.5% pure ferrosoferric oxide while stirring. The reaction proceeds at 35°C. Gas will be generated during the reaction, and the color of the reactant will gradually change from gray-black to gray-white. When no more gas is generated, the material is sand-milled in a sand mill using 0.4 mm zirconium oxide beads. During the sand-milling process, the viscosity gradually increases to 20,000 cps, and the color gradually changes to pure white, yielding Product A.

[0084] 2. According to the molar ratio of lithium to phosphorus 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. 2 kg of glucose, 3 kg of industrial-grade lithium hydroxide monohydrate, and 3.43 kg of lithium acetate were gradually added to the solution under stirring. The reaction was carried out at 35°C. During the reaction, a large amount of gas was generated. The reaction was continued until no gas was generated, forming a transparent viscous solution to obtain product B.

[0085] 3. Add product B to product A. After mixing, the system viscosity quickly drops to 1200 cps. Continue sand grinding. When the particle size D50 is about 220 nm, the reaction is completed to obtain a slurry with a solid content of 53%.

[0086] 4. The reaction product slurry is spray-dried, sintered, and crushed to obtain lithium iron phosphate positive electrode material.

[0087] The spray drying process was conducted under the following conditions: an inlet temperature of 280°C and an outlet temperature of 110°C. The calcination process was conducted under a 99.999% pure nitrogen atmosphere, with the temperature gradually increased from room temperature to 650°C at a rate of 5°C / min, maintained at 650°C for 10 hours, and then cooled to obtain a sintered product. The crushing process involved the sintered product being subjected to air flow crushing equipment to obtain the target finished positive electrode lithium iron phosphate material with a particle size D50 of 1.5 to 3 μm.

[0088] Example 4

[0089] 1. 13.8 kg of 85% food-grade phosphoric acid was added to 5 L of deionized water with stirring, diluting the mixture to a concentration of 62.4% at a molar ratio of 0.98:1 between iron and phosphorus. While stirring, 2.2 kg of 250-mesh, 99.5% pure secondary reduced iron powder, 3.03 kg of ferrosoferric oxide, and 3.14 kg of ferric oxide were slowly added to the mixture. The mixture was allowed to react at 35°C. Gas was generated during the reaction, and the color of the reactant gradually changed from gray-black to gray-white. When no more gas was generated, the material was sand-milled using 0.4 mm zirconia beads. During the sand-milling process, the viscosity gradually increased to 20,000 cps, and the color gradually changed to pure white, yielding Product A.

[0090] 2. According to the molar ratio of lithium to phosphorus 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. Under stirring, 2 kg of a mixture of polyvinyl alcohol, cyclodextrin, and polyethylene glycol and 5.18 kg of industrial-grade lithium hydroxide monohydrate were gradually added to the solution. The reaction was carried out at 35°C. During the reaction, a large amount of gas was generated. The reaction was continued until no gas was generated to form a transparent viscous solution to obtain product B.

[0091] 3. Add product B to product A. After mixing, the system viscosity quickly drops to 1200 cps. Continue sand grinding. When the particle size D50 is about 220 nm, the reaction is completed to obtain a slurry with a solid content of 50%.

[0092] 4. The reaction product slurry is spray-dried, sintered, and crushed to obtain lithium iron phosphate positive electrode material.

[0093] The spray drying conditions are: an inlet temperature of 280°C and an outlet temperature of 110°C. The calcination conditions are: in a 99.999% pure nitrogen atmosphere, gradually increasing the temperature from room temperature to 650°C at a rate of 5°C / min, maintaining the temperature at 650°C for 10 hours, and then cooling to obtain a sintered product. The crushing conditions are: the sintered product is processed through a pneumatic crushing device to obtain the target finished positive electrode lithium iron phosphate material with a particle size D50 of 1.5 to 3 μm.

[0094] Comparative Example 1

[0095] 1. 6.895 kg of 85% industrial-grade phosphoric acid was added to 5 L of deionized water with stirring, diluting the mixture to a 49% concentration, with an iron-to-phosphorus molar ratio of 0.96:1. While stirring, 3.25 kg of 200-mesh, 99% pure secondary reduced iron powder was slowly added. The reaction was allowed to proceed at 45°C. Gas was generated during the reaction, and the color of the reactant gradually changed from gray-black to gray-white. When no more gas was generated, the mixture was sand-milled using 0.3 mm zirconia beads. During the sand-milling process, the viscosity gradually increased to 15,000 cps, and the color gradually changed to pure white, yielding Product A.

[0096] 2. According to the molar ratio of lithium to phosphorus of 1.04:1, 2.3 kg of battery-grade lithium carbonate and 1 kg of sucrose were gradually added to 3.25 kg of deionized water at 40°C under stirring to form a slurry (lithium carbonate has low solubility in water) to obtain product B.

[0097] 3. Add product B to product A. After mixing and stirring, the viscosity of the system increases rapidly, the slurry solidifies, and the sanding process cannot be carried out.

[0098] Comparative Example 2

[0099] 1. 6.895 kg of 85% industrial-grade phosphoric acid was added to 5 L of deionized water with stirring, diluting the mixture to a 49% concentration, with an iron-to-phosphorus molar ratio of 0.96:1. While stirring, 3.25 kg of 200-mesh, 99% pure secondary reduced iron powder was slowly added. The reaction was allowed to proceed at 45°C. Gas was generated during the reaction, and the color of the reactant gradually changed from gray-black to gray-white. When no more gas was generated, the mixture was sand-milled using 0.3 mm zirconia beads. During the sand-milling process, the viscosity gradually increased to 15,000 cps, and the color gradually changed to pure white, yielding Product A.

[0100] 2. To avoid solidification problems when mixing with product B, add 25 kg of deionized water to dilute product A.

[0101] 3. According to the molar ratio of lithium to phosphorus of 1.04:1, 2.3 kg of battery-grade lithium carbonate and 1 kg of sucrose were gradually added to 3.25 kg of 40°C deionized water under stirring to form a slurry (lithium carbonate has low solubility in water) to obtain product B.

[0102] 4. Product B was added to Product A. After mixing and stirring, the system showed no signs of solidification, and sand milling was continued. The primary particle size of the material finally stabilized at a D50 of approximately 800 nm. Sand milling was continued, and the primary particle size showed no trend of decreasing. The reaction was terminated, and a slurry with a solids content of 17% was obtained.

[0103] 5. The reaction product slurry is spray-dried, sintered, and crushed to obtain lithium iron phosphate positive electrode material.

[0104] The spray drying process was conducted under the following conditions: an inlet temperature of 280°C and an outlet temperature of 110°C. The calcination process was conducted under a 99.999% pure nitrogen atmosphere, with the temperature gradually increased from room temperature to 650°C at a rate of 5°C / min, maintained at 650°C for 10 hours, and then cooled to obtain a sintered product. The crushing process involved the sintered product being subjected to air flow crushing equipment to obtain the target finished positive electrode lithium iron phosphate material with a particle size D50 of 1.5 to 3 μm.

[0105] Comparative Example 3

[0106] 1. 6.895 kg of 85% industrial-grade phosphoric acid was added to 5 L of deionized water with a stirring ratio of 0.96:1, diluting the mixture to a concentration of 49%. 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. Gas was generated during the reaction, and the color of the reactant gradually changed from gray-black to yellow-green. When no more gas was generated, the mixture was sand-milled using 0.3 mm zirconia beads. During the sand-milling process, the viscosity gradually increased to 15,000 cps, and the color gradually changed to yellow-green, yielding Product A.

[0107] 2. According to the molar ratio of lithium to phosphorus of 1.04:1, 2.3 kg of battery-grade lithium carbonate and 1 kg of sucrose were gradually added to 3.25 kg of 40°C deionized water under stirring to form a slurry (lithium carbonate has low solubility in water) to obtain product B.

[0108] 3. Product B was added to product A. After mixing and stirring, the viscosity of the system gradually increased to more than 20,000 cps. To ensure the smooth progress of the process, 10 L of deionized water was added to reduce the viscosity to 1,200 cps. When the material particle size was ground to D50 of about 500 nm, the reaction was completed to obtain a slurry with a solid content of 35%.

[0109] 4. The reaction product slurry is spray-dried, sintered, and crushed to obtain lithium iron phosphate positive electrode material.

[0110] The spray drying process was conducted under the following conditions: an inlet temperature of 280°C and an outlet temperature of 110°C. The calcination process was conducted under a 99.999% pure nitrogen atmosphere, with the temperature gradually increased from room temperature to 650°C at a rate of 5°C / min, maintained at 650°C for 10 hours, and then cooled to obtain a sintered product. The crushing process involved the sintered product being subjected to air flow crushing equipment to obtain the target finished positive electrode lithium iron phosphate material with a particle size D50 of 1.5 to 3 μm.

[0111] The lithium iron phosphate powders prepared in Examples 1-5 and Comparative Examples 2-3 were mixed with carbon black and polyvinylidene fluoride (PVDF) at a mass ratio of 80:10:10, coated onto aluminum foil, and dried to form appropriate positive electrode test pieces. These were then combined with lithium metal to form 2032 button-type batteries. Charge-discharge cycling tests were conducted using a Blue Power CT2001A charger over a voltage range of 2.0 V to 4.2 V at rates of C / 10, C / 5, C / 2, 1 C, 2 C, and 5 C. The results are shown in Figure 3 and Table 1.

[0112] Table 1 Discharge specific capacity (mAH / g) at different discharge rates of Examples 1 to 5 and Comparative Examples 2 to 3

[0113] Discharge rate 0.1C 0.2C 0.5C 1C 2C 5C Example 1 157.8 157.4 153.1 146.3 137.7 123.1 Example 2 157.5 157.0 152.2 145.7 136.0 122.2 Example 3 158.1 157.9 154.2 146.8 138.3 124.2 Example 4 157.3 157.0 152.8 145.9 137.5 123.0 Example 5 157.2 156.8 152.1 145.8 137.2 122.9 Comparative Example 2 142.1 138.2 134.2 11397.3 84.2 Comparative Example 3 156.4 155.5 150.1 140.3 130.2 108.8

[0114] Table 2 Solid content of product slurry and spray drying dehydration of Examples 1 to 5 and Comparative Examples 2 to 3

[0115] Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 2 Comparative Example 3 Finished product slurry solid content / % 505360505017351kg precursor required dehydration amount / kg 1.00.880.661.01.04.881.861kg precursor required dehydration energy consumption low low low low low high high

[0116] As shown in Table 2, Examples 1-5 significantly reduced the amount of dehydration required for the prepared precursors compared to Comparative Examples 2-3, thereby significantly reducing the energy consumption required for dehydration. In Comparative Example 1, based on the prior art preparation method, only increasing the solids content resulted in excessively high viscosity, making stirring impossible. In Comparative Examples 2-3, the organic acid was not added to the reaction of Product B, preventing the effects of the present invention from being achieved.

[0117] Although the above describes specific embodiments of the present invention, it should be understood by those skilled in the art that these are merely illustrative and that various changes or modifications may be made to these embodiments without departing from the principles and essence of the present invention. Therefore, the scope of protection of the present invention is defined by the appended claims.

Claims

DEPCT671. Method for preparing lithium iron phosphate precursors, in which the preparation method comprises the following steps: S1. Reaction of a mixture of iron source and phosphoric acid solution and fine grinding after the reaction is complete to obtain product A, and reaction of a mixture of organic acid solution, lithium source, and carbon source to obtain product B after the reaction is complete, in which the order of preparation of products A and B is not restricted. S2. Fine grinding of the mixture of products A and B to obtain lithium iron phosphate precursors.Methods for preparing lithium iron phosphate precursors under claim 1 where one or more of the following conditions are met: (1) The lithium iron phosphate precursors contain 50 percent or more of the solid content; (2) The iron source is a compound containing iron and oxygen, and as is to be used, one or more of iron powders, ferric oxide, ferrous oxide, and ferric nitrate; and as is to be used in greater quantities, one or more of iron powders, ferric oxide, and ferrous oxide; as is to be used, the iron powder contains 95 percent by weight or more of the iron content; as is to be used, 99 percent by weight or more; as is to be used in greater quantities, 99.5 percent by weight or more; for example, 99.5 percent by weight or more.7 percent by weight of what should be used is one or more primary reduced iron powders, secondary reduced iron powders, carbonyl reduced iron powders, and electrolyte iron powders. Ferric oxide with a purity of 95 percent by weight or more should be used, 99 percent by weight or more, and even more should be used, 99.5 percent by weight or more. Ferriferous oxide with a purity of 95 percent by weight or more should be used, 99 percent by weight or more, and even more should be used, 99.5 percent by weight or more. (3) The iron source has a mesh size of 200 to 1000 mesh. What should be used is 200 to 500 mesh, for example, 250 mesh or 300 mesh.Methods for preparing lithium iron phosphate precursors according to claim 1 or 2 where the preparation method meets one or more of the following conditions: (1) The percentage by mass concentration of phosphoric acid in the phosphoric acid solution is 20 percent to 85 percent, for example 49 percent, 59 percent or 62 percent; (2) The phosphoric acid in the phosphoric acid solution is industrial grade phosphoric acid, food grade phosphoric acid, or phosphoric acid. (3) The reaction temperature for the mixture of the iron source and phosphoric acid solution is 20 to 95 °C, the recommended temperature is 30 to 90 °C, for example 35 °C, 45 °C or 55 °C. (4) In the mixture of the iron source and phosphoric acid solution, the molar ratio of iron to phosphoric acid is (0.94-1.05):1, the recommended ratio is (0.96-1.0):1, for example 0.98:14.The preparation method of lithium iron phosphate precursors under any of the claims 1 through 3 shall be subject to one or more of the following conditions: (1) The crushing shall be carried out using a sand mill; the sand mills that should be used are vertical sand mills, horizontal sand mills, basket mills or twin-cone sand mills; the crushed beads that are used in the sand mills that should be used shall have a particle size of 0.1 to 3.0 mm, for example 0.3 mm or 0.3 mm.(2) Product A has a viscosity of 8,000 to 20,000 centipoise; the appropriate viscosity is 10,000 to 20,000 centipoise, for example 15,000 centipoise. (3) The percentage by mass concentration of organic acid in the organic acid solution is 5 percent to 98 percent; for example 55 percent, 62 percent, or 72 percent. (4) The organic acid in the organic acid solution is a carboxylic acid compound and / or ascorbic acid. The appropriate carboxylic acid compounds are formic acid, acetic acid, oxalic acid, citric acid, tartaric acid, and malic acid. The appropriate organic acids are citric acid and / or oxalic acid or malic acid and / or tartaric acid. 5.Any one of the following conditions is met with the preparation of lithium iron phosphate precursors under claims 1 through 4: (1) The lithium source is one or more of lithium hydroxide monohydrate, lithium carbonate, lithium dihydrogen phosphate, lithium phosphate, and lithium acetate, of which lithium hydroxide monohydrate and / or lithium acetate are preferred; lithium carbonate is either industrial grade lithium carbonate or battery grade lithium carbonate. (2) The molar ratio of elemental lithium 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 1.05.04(3) The carbon source shall consist of one or more of glucose, sucrose, starch, phenol resin, cyclodextrin, polyethylene, polyethylene glycol, and polyvinyl alcohol, and as is preferred, a mixture of polyvinyl alcohol, cyclodextrin, and polyethylene glycol.(4) The amount added of the carbon source is 1 percent to 60 percent, as is preferred, 5 percent to 50 percent, and as is preferred, an additional 10 percent to 40 percent by mass of the carbon source.(5) The reaction temperature The temperature for the mixture of organic acids, lithium source and carbon source is 20 to 95 degrees Celsius, as should be 30 to 90 degrees Celsius, for example 35 degrees Celsius, 40 degrees Celsius or 45 degrees Celsius. (6) The precursor of lithium iron phosphate has a particle size of 170 to 250 nanometers, for example 200 nanometers or 220 nanometers.

6. The precursor of lithium iron phosphate is prepared by any of the lithium iron phosphate precursor preparation methods according to any of the claims 1 through 5. 7.

8. Precursors of lithium iron phosphate under claim 6, where the precursors of lithium iron phosphate have a particle size of 170 to 250 nm.

9. Methods of preparing lithium iron phosphate, where the preparation method includes the following steps: subjecting the precursors of lithium iron phosphate under claim 6 or 7 to spray drying, calcination, and coarse grinding.

10. Lithium iron phosphate, where lithium iron phosphate is prepared by the methods of preparing lithium iron phosphate under claim 8.

11. Use of lithium iron phosphate under claim 9 in the preparation of anode electrode materials for lithium-ion batteries.

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