Lithium iron phosphate positive electrode material and preparation method thereof

Abstract

The application provides a lithium iron phosphate positive electrode material and a preparation method thereof. The preparation method of the lithium iron phosphate positive electrode material comprises the following steps: S1, mixing, grinding and treating an active material composition, a basic carbon source and a composite synergist in a solvent to obtain a slurry; S2, performing spray drying treatment on the slurry to obtain dry materials; S3, performing primary sintering treatment on the dry materials in a protective atmosphere to obtain lithium iron phosphate sintered materials; and S4, performing crushing treatment on the lithium iron phosphate sintered materials to obtain the lithium iron phosphate positive electrode material. The composite synergist is prepared from the following raw materials in mass percentage: 15-50% of an organic dispersant, 20-60% of a titanium compound and 10-50% of a compound of M. The application can reduce the energy requirement for synthesizing the lithium iron phosphate material and reduce the sintering temperature. The application adopts one-time addition and one-time sintering, has low energy consumption and cost, is simple to operate, simple to produce and controllable, and is easy to industrialize. The lithium iron phosphate material has high compaction density.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery technology, and in particular relates to a lithium iron phosphate cathode material and its preparation method. Background Technology

[0002] To improve the conductivity of lithium iron phosphate materials, common methods include ion doping, nano-sizing, surface coating, and carbon coating. Ion doping involves doping the lithium iron phosphate lattice with other metal ions (such as Mg). 2+ Al 3+ Ti 4+ (e.g., can introduce defects into the crystal lattice, reduce the lattice size, thereby improving the conductivity and lithium-ion diffusion rate of lithium iron phosphate cathode materials.)

[0003] Patent application CN118373399A discloses a method for preparing lithium iron phosphate cathode material. The method involves mixing a lithium source, iron source, phosphorus source, carbon source, and dopant in a predetermined ratio, combining this with hydrogen boride, and then performing multiple doping and sintering processes to obtain the lithium iron phosphate cathode material. The sintering is carried out at relatively high temperatures, and the process involves multiple doping and sintering stages. The multiple sintering processes lead to increased energy consumption and cost.

[0004] Patent application CN120136064A discloses a method for preparing lithium iron phosphate cathode material. The method involves mixing a lithium source, an iron source, a phosphorus source, a metal ion dopant, a non-metal ion dopant, and a carbon source to obtain a precursor slurry. The precursor slurry is pre-sintered, then a flux is added and mixed, followed by a first sintering. Finally, a metal salt solution is added and mixed, followed by a second sintering to obtain the modified lithium iron phosphate cathode material. This method requires multiple sintering processes and the addition of additives in stages. The secondary sintering steps are cumbersome, the sintering temperature varies significantly, and the sintering temperature switching frequency is high, resulting in low production efficiency and a decreased first-pass yield.

[0005] Patent application CN116986571A discloses a method for preparing lithium iron phosphate. The method involves stirring and dispersing lithium source, iron phosphate, carbon source, titanium source, and pure water, followed by grinding, drying, sintering, and airflow crushing to obtain a primary black material. This primary black material is then mixed with two or more metal salts and pure water, stirred, and reacted with sodium hydroxide solution. The mixture is then washed, filtered, and dried. The dried material is then subjected to a second sintering to obtain the lithium iron phosphate cathode material. This method requires multiple sintering stages and the addition of additives in stages. The multi-stage sintering process is complex and incurs significant energy consumption and cost. Staged doping results in uneven distribution of additives within the material system, affecting material performance, and the additives are also expensive. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by providing a lithium iron phosphate cathode material and its preparation method, which involves single sintering at a low sintering temperature, resulting in low energy consumption, low cost, and high compaction density of the lithium iron phosphate cathode material.

[0007] To achieve the above objectives, the present invention provides a method for preparing lithium iron phosphate cathode material, comprising the following steps:

[0008] S1. The active material composition, basic carbon source and composite synergist are mixed and ground in a solvent to obtain a slurry;

[0009] S2. The slurry is spray-dried to obtain a dry material;

[0010] S3. The dry material is sintered once in a protective atmosphere to obtain lithium iron phosphate sintered material;

[0011] S4. The lithium iron phosphate sintered material is crushed to obtain lithium iron phosphate cathode material.

[0012] In step S1, the active material composition includes a lithium source, an iron source, and a phosphorus source.

[0013] The composite synergist is prepared from the following raw materials by mass percentage: 15%–50% organic dispersant, 20%–60% titanium compound, and 10%–50% compound of M;

[0014] The organic dispersant contains C, H, and O; the compound M contains at least one of magnesium, vanadium, lithium, niobium, molybdenum, iron, and boron compounds.

[0015] The composite synergist of this invention can form a low-melting-point eutectic system with the active material composition. By reducing the activation energy barrier for crystal lattice formation, it reduces the energy requirement in the synthesis of lithium iron phosphate materials, promotes crystal formation during sintering, accelerates grain growth, and forms larger particles at lower temperatures, making it easier to sinter high-compact lithium iron phosphate materials, thereby achieving energy saving and cost reduction.

[0016] This invention utilizes the synergistic effect of multiple metal ions and organic components to simultaneously dope and carbon-coat lithium iron phosphate materials, shortening the lithium-ion transport distance, increasing the lithium migration rate, and improving the electrical performance of lithium iron phosphate materials. Compared to adding different additives, the composite synergist of this invention is more uniformly distributed in the active material composition, enabling better doping control and uniformity, and improving the material's electrical performance.

[0017] This invention employs a single addition and single sintering process, which is simple to operate and easy to control in production. This invention simplifies the process flow, improves production efficiency, and reduces the processing and manufacturing cost of lithium iron phosphate.

[0018] Another aspect of the present invention provides a lithium iron phosphate cathode material, which is prepared by the method for preparing the lithium iron phosphate cathode material;

[0019] The lithium iron phosphate cathode material includes a lithium iron phosphate core, a carbon layer coating the surface of the lithium iron phosphate core, and doping elements dispersed in the lithium iron phosphate core and the carbon layer.

[0020] The doping element includes titanium and M, wherein M includes at least one of magnesium, vanadium, lithium, niobium, molybdenum, iron, and boron.

[0021] The thickness of the carbon layer is 1 nm to 10 nm;

[0022] The total doping element content of the lithium iron phosphate cathode material is 2000ppm to 14500ppm, of which the titanium content is 1000ppm to 8000ppm and the M content is 1000ppm to 6500ppm.

[0023] The particle size of the lithium iron phosphate cathode material must meet at least the following conditions: D10 is greater than 0.2 μm, D50 is 0.3 μm to 1.6 μm, and D100 is 3 μm to 15 μm.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] The composite synergist of this invention can form a low-melting-point eutectic system with the active material composition. By reducing the activation energy barrier for crystal lattice formation, it reduces the energy requirement in the synthesis of lithium iron phosphate materials, promotes crystal formation during sintering, accelerates grain growth, and forms larger particles at lower temperatures, making it easier to sinter high-compact lithium iron phosphate materials, thereby achieving energy saving and cost reduction.

[0026] This invention utilizes the synergistic effect of multiple metal ions and organic components to simultaneously dope and carbon-coat lithium iron phosphate materials, shortening the lithium-ion transport distance, increasing the lithium migration rate, and improving the electrical performance of lithium iron phosphate materials. Compared to adding different additives, the composite synergist of this invention is more uniformly distributed in the active material composition, enabling better doping control and uniformity, and improving the material's electrical performance.

[0027] The preparation method provided by this invention achieves the preparation of lithium iron phosphate cathode materials through a simple process and mature equipment. This invention uses a single sintering and single addition process to obtain lithium iron phosphate cathode materials, which is simple to operate, easy to control in production, and easier to industrialize. This invention simplifies the process flow and improves production efficiency; it also reduces energy consumption and manufacturing costs. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the sintering process of the present invention;

[0029] Figure 2 The image shows a 1 μm scale scan electron microscope (SEM) image of the lithium iron phosphate cathode material prepared in Example 1 of this invention.

[0030] Figure 3 The image shows a 1 μm scale scan electron microscope (SEM) image of the lithium iron phosphate cathode material prepared in Example 2 of this invention.

[0031] Figure 4 The image shows a 1 μm scale scan electron microscope (SEM) image of the lithium iron phosphate cathode material prepared in Example 3 of this invention.

[0032] Figure 5 This is a transmission electron microscope (TEM) image of the lithium iron phosphate cathode material prepared in Example 3 of the present invention;

[0033] Figure 6 The image shows a transmission electron microscope (TEM) lattice image of the lithium iron phosphate cathode material prepared in Example 3 of this invention.

[0034] Figure 7 The image shows a 1 μm scale bar scanning electron microscope (SEM) image of the lithium iron phosphate cathode material prepared in Comparative Example 1 of this invention.

[0035] Figure 8 The image shown is a 1 μm scale scan electron microscope (SEM) image of the lithium iron phosphate cathode material prepared in Comparative Example 2 of this invention. Detailed Implementation

[0036] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0037] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0038] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0039] D50 represents the particle size value corresponding to when the cumulative volumetric particle size distribution number of the material reaches 50%; D10 and D100 have similar definitions to D50. Further details are omitted here, and those skilled in the art should not construe this as a limitation of the invention.

[0040] This invention provides a method for preparing lithium iron phosphate cathode material, comprising the following steps:

[0041] S1. The active material composition, basic carbon source and composite synergist are mixed and ground in a solvent to obtain a slurry;

[0042] S2. The slurry is spray-dried to obtain a dry material;

[0043] S3. The dry material is sintered once in a protective atmosphere to obtain lithium iron phosphate sintered material;

[0044] S4. The lithium iron phosphate sintered material is crushed to obtain lithium iron phosphate cathode material.

[0045] In step S1, the active material composition includes a lithium source, an iron source, and a phosphorus source.

[0046] The composite synergist is prepared from the following raw materials by mass percentage: 15%–50% organic dispersant, 20%–60% titanium compound, and 10%–50% compound of M;

[0047] The organic dispersant contains C, H, and O; the compound M contains at least one of magnesium, vanadium, lithium, niobium, molybdenum, iron, and boron compounds.

[0048] The composite synergist of this invention can form a low-melting-point eutectic system with the active material composition. By reducing the activation energy barrier for crystal lattice formation, it reduces the energy requirement in the synthesis of lithium iron phosphate materials, promotes crystal formation during sintering, accelerates grain growth, and forms larger particles at lower temperatures, making it easier to sinter high-compact lithium iron phosphate materials, thereby achieving energy saving and cost reduction.

[0049] This invention utilizes the synergistic effect of multiple metal ions and organic components to simultaneously dope and carbon-coat lithium iron phosphate materials, shortening the lithium-ion transport distance, increasing the lithium migration rate, and improving the electrical performance of lithium iron phosphate materials. Compared to adding different additives, the composite synergist of this invention is more uniformly distributed in the active material composition, enabling better doping control and uniformity, and improving the material's electrical performance.

[0050] The preparation method provided by this invention achieves the preparation of lithium iron phosphate cathode materials through a simple process and mature equipment. This invention uses a single sintering and single addition process to obtain lithium iron phosphate cathode materials, which is simple to operate, easy to control in production, and easier to industrialize. This invention simplifies the process flow and improves production efficiency; it also reduces energy consumption and manufacturing costs.

[0051] According to a preferred embodiment of the present invention, the organic dispersant comprises at least one selected from polyethylene glycol 1500, polyethylene glycol 2000, and polyethylene glycol 6000. The titanium compound comprises at least one selected from titanium dioxide, tetrabutyl titanate, isopropyl titanate, and tetraethyl titanate. The magnesium compound comprises at least one selected from magnesium oxide, magnesium fluoride, and magnesium carbonate. The vanadium compound comprises at least one selected from vanadium pentoxide, vanadium dioxide, and ammonium metavanadate. The lithium compound comprises at least one selected from lithium oxide, lithium fluoride, lithium metaborate, lithium borate, lithium titanate, and lithium hexafluorophosphate. The niobium compound comprises at least one selected from niobium pentoxide and niobium oxalate. The molybdenum compound is molybdenum trioxide. The iron compound comprises at least one selected from ferric oxide and magnetite. The boron compound comprises at least one selected from boron oxide, boron fluoride, and hydrogen boride.

[0052] Preferably, the composite synergist is prepared from the following raw materials by mass percentage: 30%–45% organic dispersant, 25%–45% titanium compound, and 20%–40% compound of M.

[0053] Preferably, the compound of M comprises at least one or two of magnesium compounds, lithium compounds, iron compounds, and boron compounds.

[0054] This invention conducts in-depth research on the components of the composite synergist. Based on the efficacy research of each component, it performs compounding and screening to select the optimal ratio, adds the synergist in one step, and sintersects in one step, thereby reducing the sintering temperature and obtaining lithium iron phosphate cathode materials with better performance.

[0055] According to a preferred embodiment of the present invention, in step S1, the composite synergist is prepared by the following process:

[0056] The titanium compound and the compound of M are added to a high-speed mixer in a certain proportion and mixed to obtain a mixture;

[0057] The mixture is placed in a high-temperature furnace, nitrogen is introduced into the furnace, and sintering is carried out at 300℃~800℃ for 1h~3h. Then, the sintered product is pulverized by a mechanical mill to obtain powder.

[0058] The powder is added to an organic solvent, and the organic dispersant is added and milled until the particle size meets the following conditions: D50 < 50 nm, D100 < 500 nm; then the product obtained after milling is spray-dried to obtain the composite synergist.

[0059] The composite synergist has a moisture content of less than 0.5%, a loose bulk density of 0.25 g / cm³ to 0.8 g / cm³, and a specific surface area of ​​40 m². 2 / g~160m 2 / g.

[0060] The organic solvent is at least one of methanol, ethanol, isopropanol, n-butanol, ethylene glycol, propylene glycol, acetone, and butanone.

[0061] According to a preferred embodiment of the present invention, in step S1, the amount of the composite synergist added is 0.5% to 4% based on the total mass of the active material composition. Preferably, the amount of the composite synergist added is 1% to 3% based on the total mass of the active material composition.

[0062] According to a preferred embodiment of the present invention, in step S1, the molar ratio of lithium, iron, and phosphorus in the lithium source, iron source, and phosphorus source is (0.9-1.1):1:(0.9-1.1). The phosphorus source includes at least one of ferric phosphate, monoammonium phosphate, and diammonium hydrogen phosphate, but is not limited thereto. The lithium source includes at least one of lithium dihydrogen phosphate, lithium monohydrogen phosphate, lithium nitrate, lithium carbonate, lithium oxalate, lithium chloride, lithium hydroxide, and lithium acetate, but is not limited thereto. The iron source includes at least one of ferric phosphate, ferrous oxalate, and ferric acetate, but is not limited thereto. Ferric phosphate can be used as both a phosphorus source and an iron source.

[0063] According to a preferred embodiment of the present invention, in step S1, the basic carbon source comprises at least one selected from citric acid, glucose, sucrose, ascorbic acid, polyaniline, and polypyrrolidone. The amount of the basic carbon source added is 5% to 20% based on the total mass of the active material composition. Preferably, the amount of the basic carbon source added is 7% to 15% based on the total mass of the active material composition.

[0064] According to a preferred embodiment of the present invention, in step S1, the solvent is at least one selected from water, ethanol, and acetone. The grinding process includes ball milling and sand milling. The ball milling temperature is 15℃~35℃, the ball milling time is 0.5h~4h, and the ball milling speed is 800rpm~2000rpm. The sand milling temperature is 15℃~35℃, the sand milling time is 0.5h~4h, and the sand milling speed is 1000rpm~2500rpm. The solid content of the slurry is 30%~50%.

[0065] According to a preferred embodiment of the present invention, the inlet temperature of the spray dryer is 80℃~300℃, the outlet temperature is 50℃~120℃, and the processing time is 0.5h-4h.

[0066] According to a preferred embodiment of the present invention, in step S3, the temperature of the first sintering is 500℃~900℃, and the heating rate is 2~10℃ / min. Preferably, the temperature of the first sintering is 550℃~800℃; more preferably, the temperature of the first sintering is 700℃~800℃. The holding time for the first sintering is 5h~30h. Preferably, the holding time for the first sintering is 8h~20h. The protective atmosphere is at least one of nitrogen, helium, or argon.

[0067] According to a preferred embodiment of the present invention, in step S4, the crushing method is air jet milling.

[0068] In another aspect, the present invention provides a lithium iron phosphate cathode material, which is prepared by the method for preparing the lithium iron phosphate cathode material;

[0069] The lithium iron phosphate cathode material includes a lithium iron phosphate core, a carbon layer coating the surface of the lithium iron phosphate core, and doping elements dispersed in the lithium iron phosphate core and the carbon layer.

[0070] The doping element includes titanium and M, wherein M includes at least one of magnesium, vanadium, lithium, niobium, molybdenum, iron, and boron.

[0071] The thickness of the carbon layer is 1 nm to 10 nm;

[0072] Preferably, the thickness of the carbon layer is 1 nm to 7 nm.

[0073] The total doping element content of the lithium iron phosphate cathode material is 2000ppm to 14500ppm, of which the titanium content is 1000ppm to 8000ppm and the M content is 1000ppm to 6500ppm.

[0074] Preferably, M contains at least one or two of the elements magnesium, lithium, iron, and boron.

[0075] The particle size of the lithium iron phosphate cathode material must meet at least the following conditions: D10 is greater than 0.2 μm, D50 is 0.3 μm to 1.6 μm, and D100 is 3 μm to 15 μm.

[0076] The lithium iron phosphate cathode material has a 0.1C discharge specific capacity of 155 mAh / g to 161 mAh / g and a compaction density of 2.5 g / cm³. 3~2.8g / cm 3 Specific surface area is 8m² 2 / g~18m 2 / g; The carbon content of the lithium iron phosphate cathode material is 1.15% to 1.55% of the mass of the lithium iron phosphate cathode material.

[0077] Preferably, the specific surface area of ​​the lithium iron phosphate cathode material is 10 m². 2 / g~14.5m 2 / g. Example 1

[0078] This embodiment describes a method for preparing a lithium iron phosphate cathode material, comprising the following steps:

[0079] (1) The composite synergist is prepared from the following raw materials by mass percentage: 45% polyethylene glycol (molecular weight 2000), 35% titanium dioxide, 10% magnesium oxide, and 10% ferric oxide.

[0080] Titanium dioxide, magnesium oxide, and ferric oxide were added to a high-speed mixer in a specific ratio and mixed thoroughly to obtain a mixture. The mixture was then placed in a high-temperature furnace, under nitrogen gas, and sintered at 500°C for 2 hours. The sintered product was then pulverized using a mechanical mill to obtain a powder. The powder was added to ethanol, followed by the addition of polyethylene glycol (molecular weight 2000), and milled until the particle size met the following conditions: D50 = 40 nm, D100 = 400 nm. The milled product was then spray-dried to obtain the composite synergist. The composite synergist had a bulk density of 0.3 g / cm³ and a specific surface area of ​​140 m². 2 / g.

[0081] Weigh 1000g of iron phosphate and 244.97g of lithium carbonate according to the molar ratio Li:Fe:P = 1:1:1. Based on the total mass of iron phosphate and lithium carbonate, weigh 1% of the compound synergist and 10% of glucose. The mass of the compound synergist is 12.45g and the mass of glucose is 124.50g.

[0082] Ferric phosphate, lithium carbonate, glucose, and a compound synergist were added to deionized water and stirred at room temperature and pressure until fully mixed. After mixing, the mixture was ball-milled until the particle size D50 was 1.50 μm, and then transferred to a sand mill for further grinding to obtain a slurry. The particle size of the slurry met the following conditions: D50 was 0.35 μm, D100 was 0.66 μm, and the solid content of the slurry was 40%.

[0083] (2) The slurry is spray-dried in a spray drying tower to obtain dry material. The inlet temperature of the spray drying is 230℃, the outlet temperature is 100℃, and the spray drying time is 2h.

[0084] (3) Place the dry material in an atmosphere furnace and heat it to 765°C at a rate of 6°C / min under a nitrogen atmosphere. Sinter at a constant temperature for 8 hours to obtain lithium iron phosphate sintered material.

[0085] (4) After the lithium iron phosphate sinter is naturally cooled, it is pulverized in an air jet mill to obtain lithium iron phosphate cathode material. The performance parameters of lithium iron phosphate cathode material are shown in Table 1. Example 2

[0086] This embodiment describes a method for preparing a lithium iron phosphate cathode material, comprising the following steps:

[0087] (1) The composite synergist is prepared from the following raw materials by mass percentage: polyethylene glycol (molecular weight 6000) 35%, tetraethyl titanate 45%, magnesium fluoride 5%, boron oxide 10%, and niobium pentoxide 5%.

[0088] Tetraethyl titanate, magnesium fluoride, boron oxide, and niobium pentoxide were added to a high-speed mixer in a specific ratio and mixed thoroughly to obtain a mixture. The mixture was then placed in a high-temperature furnace, under nitrogen gas, and sintered at 450°C for 2.5 hours. The sintered product was then pulverized using a mechanical mill to obtain a powder. The powder was added to ethanol, followed by the addition of polyethylene glycol (molecular weight 6000) and milling until the particle size met the following conditions: D50 = 45 nm, D100 = 450 nm. The milled product was then spray-dried to obtain the composite synergist. The composite synergist had a bulk density of 0.5 g / cm³ and a specific surface area of ​​120 m². 2 / g.

[0089] Weigh 1000g of iron phosphate and 247.42g of lithium carbonate according to the molar ratio Li:Fe:P = 1.01:1:1. Based on the total mass of iron phosphate and lithium carbonate, weigh 2.5% of the compound synergist and 5.4% of sucrose. The mass of the compound synergist is 31.19g and the mass of the sucrose is 67.36g.

[0090] Ferric phosphate, lithium carbonate, sucrose, and a compound synergist were added to deionized water and stirred at room temperature and pressure until fully mixed. After mixing, the mixture was ball-milled until the particle size D50 was 0.80 μm, and then transferred to a sand mill for further grinding to obtain a slurry. The slurry particle size met the following conditions: D50 was 0.38 μm, D100 was 0.62 μm, and the solid content of the slurry was 30%.

[0091] (2) The slurry is spray-dried in a spray drying tower to obtain dry material. The inlet temperature of the spray drying is 230℃, the outlet temperature is 100℃, and the spray drying time is 3h.

[0092] (3) Place the dry material in an atmosphere furnace and heat it to 770°C at a rate of 6°C / min under a nitrogen atmosphere. Sinter at a constant temperature for 10 hours to obtain lithium iron phosphate sintered material.

[0093] (4) After the lithium iron phosphate sinter is naturally cooled, it is pulverized in an air jet mill to obtain lithium iron phosphate cathode material. The performance parameters of lithium iron phosphate cathode material are shown in Table 1. Example 3

[0094] This embodiment describes a method for preparing a lithium iron phosphate cathode material, comprising the following steps:

[0095] (1) The composite synergist is prepared from the following raw materials by mass percentage: 30% polyethylene glycol (molecular weight 2000), 30% titanium dioxide, 15% ferric oxide, 15% lithium hexafluorophosphate, and 10% ammonium metavanadate.

[0096] Titanium dioxide, ferric oxide, lithium hexafluorophosphate, and ammonium metavanadate were added to a high-speed mixer in a specific ratio and mixed thoroughly to obtain a mixture. The mixture was then placed in a high-temperature furnace, under nitrogen gas, and sintered at 600°C for 1 hour. The sintered product was then pulverized using a mechanical mill to obtain a powder. The powder was added to ethanol, followed by the addition of polyethylene glycol (molecular weight 2000) and milling until the particle size met the following conditions: D50 of 35 nm and D100 of 350 nm. The milled product was then spray-dried to obtain the composite synergist. The loose packing density of the composite synergist was 0.25 g / cm³, and the specific surface area was 160 m². 2 / g.

[0097] Weigh out 1000g of ferric phosphate, 244.97g of lithium carbonate, and 38.14g of monoammonium phosphate according to the molar ratio Li:Fe:P = 1:1:1.05. Based on the total mass of ferric phosphate, lithium carbonate, and monoammonium phosphate, weigh out 3% of the composite synergist and 10% of polyaniline (molecular weight 5000). The mass of the composite synergist is 38.49g, and the mass of the polyaniline is 128.311g.

[0098] Ferric phosphate, lithium carbonate, monoammonium phosphate, polyaniline, and a composite synergist were added to deionized water and stirred at room temperature and pressure until fully mixed. After mixing, the mixture was ball-milled until the particle size D50 was 0.4 μm, and then transferred to a sand mill for grinding to obtain a slurry. The particle size of the slurry met the following conditions: D50 was 0.40 μm, D100 was 0.66 μm, and the solid content in the slurry was 35%.

[0099] (2) The slurry is spray-dried in a spray drying tower to obtain dry material. The inlet temperature of the spray drying is 240℃, the outlet temperature is 100℃, and the spray drying time is 2.5h.

[0100] (3) Place the dry material in an atmosphere furnace and heat it to 745°C at a rate of 5°C / min under a nitrogen atmosphere. Sinter at a constant temperature for 15 hours to obtain lithium iron phosphate sintered material.

[0101] (4) After the lithium iron phosphate sinter is naturally cooled, it is pulverized in an air jet mill to obtain lithium iron phosphate cathode material. The performance parameters of lithium iron phosphate cathode material are shown in Table 1. Example 4

[0102] This embodiment describes a method for preparing a lithium iron phosphate cathode material, comprising the following steps:

[0103] (1) The composite synergist is prepared from the following raw materials by mass percentage: 35% polyethylene glycol (molecular weight 6000), 25% titanium dioxide, 10% magnesium oxide, 20% boron fluoride, and 10% molybdenum trioxide.

[0104] Titanium dioxide, magnesium oxide, boron fluoride, and molybdenum trioxide were added to a high-speed mixer in a specific ratio and mixed thoroughly to obtain a mixture. The mixture was then placed in a high-temperature furnace, under nitrogen gas, and sintered at 350°C for 3 hours. The sintered product was then pulverized using a mechanical mill to obtain a powder. The powder was added to ethanol, followed by the addition of polyethylene glycol (molecular weight 6000) and milling until the particle size met the following conditions: D50 of 48 nm and D100 of 480 nm. The milled product was then spray-dried to obtain the composite synergist. The loose packing density of the composite synergist was 0.5 g / cm³, and its specific surface area was 110 m². 2 / g.

[0105] Weigh out 1000g of ferric phosphate, 246.2g of lithium carbonate, and 38.14g of monoammonium phosphate according to the molar ratio Li:Fe:P = 1.005:1:1.05. Based on the total mass of ferric phosphate, lithium carbonate, and monoammonium phosphate, weigh out 1.8% of the composite synergist and 8% of the polypyrrolidone (molecular weight 20000). The mass of the composite synergist is 23.12g, and the mass of the polypyrrolidone is 102.74g.

[0106] Ferric phosphate, lithium carbonate, monoammonium phosphate, polypyrrolidone, and a composite synergist were added to deionized water and stirred at room temperature and pressure until fully mixed. After mixing, the mixture was ball-milled until the particle size D50 was 1.0 μm, and then transferred to a sand mill for further grinding to obtain a slurry. The particle size of the slurry met the following conditions: D50 was 0.38 μm, D100 was 0.66 μm, and the solid content of the slurry was 45%.

[0107] (2) The slurry is spray-dried in a spray drying tower to obtain dry material. The inlet temperature of the spray drying is 210℃, the outlet temperature is 100℃, and the spray drying time is 2h.

[0108] (3) Place the dry material in an atmosphere furnace and heat it to 770°C at a rate of 3°C / min under a nitrogen atmosphere. Sinter at a constant temperature for 8 hours to obtain lithium iron phosphate sintered material.

[0109] (4) After the lithium iron phosphate sinter is naturally cooled, it is pulverized in an air jet mill to obtain lithium iron phosphate cathode material. The performance parameters of lithium iron phosphate cathode material are shown in Table 1. Example 5

[0110] The method for preparing a lithium iron phosphate cathode material in this embodiment differs from that in Example 1 in that:

[0111] In step (1), 1000g of iron phosphate and 246.93g of lithium carbonate are weighed according to the molar ratio Li:Fe:P = 1.008:1:1. Based on the total mass of iron phosphate and lithium carbonate, 1.1% of the composite synergist and 10% of glucose are weighed. The mass of the composite synergist is 13.72g and the mass of the glucose is 124.69g.

[0112] In step (3), the temperature is increased to 780°C at 6°C / min under a nitrogen atmosphere and held at that temperature for 6 hours. Example 6

[0113] The method for preparing a lithium iron phosphate cathode material in this embodiment differs from that in Example 4 in that:

[0114] In step (1), 1000g of iron phosphate and 244.97g of lithium carbonate are weighed according to the molar ratio Li:Fe:P=1:1:1. Based on the total mass of iron phosphate and lithium carbonate, 1.8% of the composite synergist and 8% of polypyrrolidone (molecular weight 20000) are weighed. The mass of the composite synergist is 22.41g and the mass of the polypyrrolidone is 99.60g.

[0115] In step (3), the temperature is increased to 755°C at 3°C / min under a nitrogen atmosphere and held at that temperature for 10 hours. Comparative Example 1

[0116] A method for preparing a lithium iron phosphate cathode material includes the following steps:

[0117] (1) Weigh 1000g of iron phosphate, 246.44g of lithium carbonate, and 4.58g of monoammonium phosphate according to the molar ratio Li:Fe:P=1.006:1:1.006. Based on the total mass of iron phosphate, lithium carbonate, and monoammonium phosphate, weigh 6.0% of glucose, 6% of polyethylene glycol (molecular weight 2000), and 0.62% of titanium dioxide. The mass of glucose is 75.06g, the mass of polyethylene glycol (molecular weight 2000) is 75.06g, and the mass of titanium dioxide is 7.76g.

[0118] Ferric phosphate, lithium carbonate, monoammonium phosphate, glucose, polyethylene glycol (molecular weight 2000), and titanium dioxide were added to deionized water and stirred at room temperature and pressure until fully mixed. After mixing, the mixture was ball-milled until the particle size D50 was 0.8 μm, and then transferred to a sand mill for further grinding to obtain a slurry. The particle size of the slurry met the following conditions: D50 was 0.35 μm, D100 was 0.66 μm, and the solid content of the slurry was 40%.

[0119] (2) The slurry is spray-dried in a spray drying tower to obtain dry material. The inlet temperature of the spray drying is 200℃, the outlet temperature is 100℃, and the spray drying time is 2h.

[0120] (3) Place the dry material in an atmosphere furnace and heat it to 780°C at a rate of 6°C / min under a nitrogen atmosphere. Sinter at a constant temperature for 10 hours to obtain lithium iron phosphate sintered material.

[0121] (4) After the lithium iron phosphate sinter is naturally cooled, it is subjected to air jet milling to obtain lithium iron phosphate cathode material. The performance parameters of lithium iron phosphate cathode material are shown in Table 1. Comparative Example 2

[0122] A method for preparing a lithium iron phosphate cathode material includes the following steps:

[0123] (1) Weigh 1000g of iron phosphate, 247.42g of lithium carbonate, and 7.63g of monoammonium phosphate according to the molar ratio Li:Fe:P=1.01:1:1.01. Based on the total mass of iron phosphate, lithium carbonate, and monoammonium phosphate, weigh 3.9% of glucose, 3.5% of polyethylene glycol (molecular weight 2000), and 0.62% of titanium dioxide. The mass of glucose is 49g, the mass of polyethylene glycol (molecular weight 2000) is 43.93g, and the mass of titanium dioxide is 7.78g.

[0124] Ferric phosphate, lithium carbonate, monoammonium phosphate, glucose, polyethylene glycol (molecular weight 2000), and titanium dioxide were added to deionized water and stirred at room temperature and pressure to ensure thorough mixing. After mixing, the mixture was ball-milled until the particle size D50 was 0.8 μm, and then transferred to a sand mill for further grinding to obtain a slurry. The particle size of the slurry met the following conditions: D50 was 0.35 μm, D100 was 0.7 μm, and the solid content in the slurry was 35%.

[0125] (2) The slurry is spray-dried in a spray drying tower to obtain dry material. The inlet temperature of the spray drying is 220℃, the outlet temperature is 100℃, and the spray drying time is 2.5h.

[0126] (3) Place the dry material in an atmosphere furnace and heat it to 740°C at a rate of 6°C / min under a nitrogen atmosphere. Sinter at a constant temperature for 12 hours to obtain the primary sintered material.

[0127] (4) Weigh 1000g of primary sintering material. Based on the mass of primary sintering material, weigh 3% glucose, 3.5% polyethylene glycol (molecular weight 2000) and 0.2% hydrogen borate. The mass of glucose is 30g, the mass of polyethylene glycol (molecular weight 2000) is 35g and the mass of hydrogen borate is 2g.

[0128] The primary sintering material, boron, glucose, and polyethylene glycol (molecular weight 2000) were added to deionized water, mixed and stirred evenly, and then ground until the particle size D50 was 0.6 μm. Then, the mixture was spray-dried and heated to 760°C at a rate of 6°C / min under a nitrogen atmosphere, and sintered at a constant temperature for 10 h to obtain lithium iron phosphate sintering material.

[0129] (5) After the lithium iron phosphate sinter is naturally cooled, it is subjected to air jet milling to obtain lithium iron phosphate cathode material. The performance parameters of lithium iron phosphate cathode material are shown in Table 1.

[0130] Battery Assembly and Performance Testing: Positive electrode sheets were prepared using the lithium iron phosphate cathode materials obtained in the various examples and comparative examples. Battery-grade lithium sheets were used as negative electrode sheets, and lithium hexafluorophosphate was used as the electrolyte to simulate battery assembly. The charge / discharge electrochemical window was set to 2.0–3.8 V. The specific capacity of the battery corresponding to the obtained lithium iron phosphate cathode material at the 0.1C rate for initial charge, the 0.1C rate for initial discharge, and the 1C rate for initial discharge were tested.

[0131] Specific surface area: The powder to be tested was degassed at 160℃ for 2 hours. Nitrogen was then flowed through the degassed sample, and adsorption occurred on the sample surface. The amount of gas adsorbed at different pressures was recorded, adsorption isotherms were plotted, and the specific surface area of ​​the sample was calculated according to the BET method and the BJH method.

[0132] The performance test results of the lithium iron phosphate cathode materials prepared in each embodiment and comparative example are shown in Table 1. The charge and discharge test results of each simulated battery assembled from the cathode materials prepared in each embodiment and comparative example as battery components are shown in Table 2. The cell parameters of the lithium iron phosphate cathode materials prepared in each embodiment are shown in Table 3.

[0133]

[0134]

[0135]

[0136] As can be seen from Table 1, compared with the lithium iron phosphate cathode material prepared in the comparative example, the compaction density and specific surface area of ​​the lithium iron phosphate cathode material prepared in the embodiment of the present invention are controllable.

[0137] Based on the standard card PDF#40-1499, the a, b, and c-axis unit cell parameters and unit cell volumes of each embodiment were obtained through fitting. Table 3 shows that the unit cell volumes of Examples 1-6, Comparative Example 1, and Comparative Example 2 decreased; the unit cell volumes of Examples 1-6 with the added composite synergist decreased by 0.25% to 0.29% compared to the standard card PDF#40-1499. Doping reduces the unit cell volume, shortens the lithium-ion transport path, and is more conducive to improving the electrochemical performance of lithium iron phosphate materials.

[0138] Figure 1 This is a schematic diagram of the sintering process of the present invention. Figure 2 This is a scanning electron microscope (SEM) image of the lithium iron phosphate cathode material prepared in Example 1 of this invention. Figure 3 This is a scanning electron microscope (SEM) image of the lithium iron phosphate cathode material prepared in Example 2 of the present invention. Figure 4 This is a scanning electron microscope (SEM) image of the lithium iron phosphate cathode material prepared in Example 3 of the present invention. Figure 5 This is a transmission electron microscope (TEM) image of the lithium iron phosphate cathode material prepared in Example 3 of the present invention. Figure 6 This is a transmission electron microscope (TEM) lattice image of the lithium iron phosphate cathode material prepared in Example 3 of the present invention. Figure 7 This is a scanning electron microscope (SEM) image of the lithium iron phosphate cathode material prepared in Comparative Example 1 of this invention. Figure 8 This is a scanning electron microscope (SEM) image of the lithium iron phosphate cathode material prepared in Comparative Example 2 of this invention. From... Figure 2 , Figure 3 , Figure 4 and Figure 5 It can be seen that the lithium iron phosphate cathode material prepared in the embodiments of the present invention has significant large and small particle "gradation" characteristics, and the particles have good sphericity; combined with Figure 5 It can be seen that the lithium iron phosphate cathode material particles are round and the surface carbon layer is uniformly coated; Figure 6 As can be seen, the lattice fringes of the lithium iron phosphate cathode material are clear, indicating good crystallinity. From Figure 7 It can be seen that the lithium iron phosphate cathode material prepared in Comparative Example 1 consists of small particles with uniform particle size. Figure 8 As shown in Comparative Example 2, the lithium iron phosphate cathode material underwent secondary grinding and secondary sintering. It can be seen that the lithium iron phosphate particles have poor sphericity, with large particles having irregular shapes and small particles being fine and fragmented, resulting in low bulk density and low powder compaction density of the lithium iron phosphate cathode material.

[0139] The above embodiments should be understood as being used only to illustrate the present invention more clearly, and not to limit the scope of the present invention. After reading the present invention, any modifications of the present invention in various equivalent forms by those skilled in the art fall within the scope defined by the appended claims.

Claims

1. A method for preparing a lithium iron phosphate cathode material, characterized in that, Includes the following steps: S1. The active material composition, basic carbon source and composite synergist are mixed and ground in a solvent to obtain a slurry; S2. The slurry is spray-dried to obtain a dry material; S3. The dry material is sintered once in a protective atmosphere to obtain lithium iron phosphate sintered material; S4. The lithium iron phosphate sintered material is crushed to obtain lithium iron phosphate cathode material. In step S1, the active material composition includes a lithium source, an iron source, and a phosphorus source. The composite synergist is prepared from the following raw materials by mass percentage: 15%–50% organic dispersant, 20%–60% titanium compound, and 10%–50% compound of M; The organic dispersant comprises C, H, and O; the compound of M comprises at least one of magnesium compound, vanadium compound, lithium compound, niobium compound, molybdenum compound, iron compound, and boron compound. The loose bulk density of the composite synergist is 0.25 g / cm³ to 0.8 g / cm³, and the specific surface area is 40 m². 2 / g~160m 2 / g; In step S1, based on the total mass of the active material composition, the amount of the composite synergist added is 0.5% to 4%; In step S1, the composite synergist is prepared through the following process: The titanium compound and the compound of M are added to a high-speed mixer in a certain proportion and mixed to obtain a mixture; The mixture is placed in a high-temperature furnace, nitrogen is introduced into the furnace, and sintering is carried out at 300℃~800℃ for 1h~3h. Then, the sintered product is pulverized by a mechanical mill to obtain powder. The powder is added to an organic solvent, and the organic dispersant is added and milled until the particle size meets the following conditions: D50 < 50 nm, D100 < 500 nm; then the product obtained after milling is spray-dried to obtain the composite synergist.

2. The method for preparing lithium iron phosphate cathode material according to claim 1, characterized in that, The composite synergist is prepared from the following raw materials by mass percentage: 30%–45% organic dispersant, 25%–45% titanium compound, and 20%–40% compound of M.

3. The method for preparing the lithium iron phosphate cathode material according to claim 1, characterized in that, The organic dispersant comprises at least one of polyethylene glycol 1500, polyethylene glycol 2000, and polyethylene glycol 6000; And / or, the basic carbon source comprises at least one of citric acid, glucose, sucrose, ascorbic acid, polyaniline, and polypyrrolidone.

4. The method for preparing the lithium iron phosphate cathode material according to claim 1, characterized in that, The titanium compound comprises at least one of titanium dioxide, tetrabutyl titanate, isopropyl titanate, and tetraethyl titanate. And / or, the magnesium compound comprises at least one of magnesium oxide, magnesium fluoride, and magnesium carbonate; And / or, the vanadium compound comprises at least one of vanadium pentoxide, vanadium dioxide, and ammonium metavanadate; And / or, the lithium compound comprises at least one of lithium oxide, lithium fluoride, lithium metaborate, lithium borate, lithium titanate, and lithium hexafluorophosphate; And / or, the niobium compound comprises at least one of niobium pentoxide and niobium oxalate; And / or, the molybdenum compound is molybdenum trioxide; And / or, the iron compound comprises at least one of ferric oxide and magnetite; And / or, the boron compound comprises at least one of boron oxide, boron fluoride, and hydrogen boride.

5. The method for preparing the lithium iron phosphate cathode material according to any one of claims 1 to 4, characterized in that, The moisture content of the compound synergist is less than 0.5%.

6. The method for preparing the lithium iron phosphate cathode material according to claim 1, characterized in that, In step S1, the amount of the basic carbon source added is 5% to 20% based on the total mass of the active material composition.

7. The method for preparing the lithium iron phosphate cathode material according to claim 1, characterized in that, In step S1, the molar ratio of lithium, iron, and phosphorus in the lithium source, iron source, and phosphorus source is (0.9-1.1):1:(0.9-1.1). And / or, in step S1, the solid content of the slurry is 30% to 45%.

8. The method for preparing lithium iron phosphate cathode material according to claim 1, characterized in that, In step S3, the temperature of the first sintering is 500℃~900℃, the heating rate is 2℃ / min~10℃ / min, and the holding time is 5h~30h.

9. A lithium iron phosphate cathode material, characterized in that, The lithium iron phosphate cathode material is prepared by the method described in any one of claims 1 to 8; The lithium iron phosphate cathode material includes a lithium iron phosphate core, a carbon layer coating the surface of the lithium iron phosphate core, and doping elements dispersed in the lithium iron phosphate core and the carbon layer. The doping element includes titanium and M, wherein M includes at least one of magnesium, vanadium, lithium, niobium, molybdenum, iron, and boron. The thickness of the carbon layer is 1 nm to 10 nm; The total doping element content of the lithium iron phosphate cathode material is 2000ppm to 14500ppm, of which the titanium content is 1000ppm to 8000ppm and the M content is 1000ppm to 6500ppm.

10. The lithium iron phosphate cathode material according to claim 9, characterized in that, The particle size of the lithium iron phosphate cathode material must meet at least the following conditions: D10 is greater than 0.2 μm, D50 is 0.3 μm to 1.6 μm, and D100 is 3 μm to 15 μm.

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