CN115072694A - Lithium iron phosphate anode material, preparation method thereof and lithium ion battery - Google Patents

Lithium iron phosphate anode material, preparation method thereof and lithium ion battery Download PDF

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CN115072694A
CN115072694A CN202210784479.7A CN202210784479A CN115072694A CN 115072694 A CN115072694 A CN 115072694A CN 202210784479 A CN202210784479 A CN 202210784479A CN 115072694 A CN115072694 A CN 115072694A
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iron phosphate
lithium iron
lithium
slurry
positive electrode
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黄尚尉
陈晓军
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Quzhou Huayou Cobalt New Material Co ltd
Zhejiang Huayou Cobalt Co Ltd
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Quzhou Huayou Cobalt New Material Co ltd
Zhejiang Huayou Cobalt Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/26—Phosphates
    • C01B25/45—Phosphates containing plural metal, or metal and ammonium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/01—Particle morphology depicted by an image
    • C01P2004/03—Particle morphology depicted by an image obtained by SEM
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/62—Submicrometer sized, i.e. from 0.1-1 micrometer
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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    • Y02E60/10—Energy storage using batteries

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Abstract

The application relates to the technical field of batteries, and relates to a lithium iron phosphate positive electrode material, a preparation method thereof and a lithium ion battery. Mixing an iron source, a lithium source, a phosphorus source, a carbon source, a solvent, a dispersing agent, a dopant and a sintering aid to form slurry; drying the slurry to form particles, and then pressing the particles into tablets; sintering the sheet body to obtain a lithium iron phosphate material; and preparing the lithium iron phosphate material into powder. And forming the slurry into particles, and pressing the particles into a sheet body to obtain a compact lithium iron phosphate precursor and ensure the uniformity of the particle size of the precursor. The sintering aid inhibits abnormal growth of crystal grains, promotes densification process, reduces sintering temperature, shortens sintering time, improves productivity and reduces cost; and the powder body is sintered in cooperation with the sheet body, so that the full contact of powder particles is promoted, the atomic diffusion in the sintering process is accelerated, and the sintering densification is promoted. And the dopant enables a bulk phase formed in the sintering process to be doped, so that the mobility of lithium ions is improved, and the electrochemical performance of the material is ensured.

Description

Lithium iron phosphate anode material, preparation method thereof and lithium ion battery
Technical Field
The application relates to the technical field of batteries, in particular to a lithium iron phosphate positive electrode material, a preparation method thereof and a lithium ion battery.
Background
In recent years, lithium iron phosphate has returned to the mainstream position due to its low cost and high safety, and the market demand is continuously expanding. In 2019, battery enterprises continuously provide battery structure optimization schemes, such as CTP batteries provided by Ningde era, blade batteries provided by Biddi and JTM batteries provided by Kongxuan Gaokou, and the effect of improving energy density is achieved by optimizing a module structure. The low energy density of lithium iron phosphate is still a problem to be broken through by the lithium iron technology. The powder compaction density of the lithium iron phosphate anode material on the current market is about 2.4g/cm 3 And the 1C discharge capacity is about 140 mAh/g. The energy density of the lithium iron phosphate battery can be improved to a certain extent from the battery structure, and a large space is still reserved for improving the energy density of the anode material.
Disclosure of Invention
The embodiment of the application aims to provide a lithium iron phosphate positive electrode material, a preparation method thereof and a lithium ion battery, which can improve the compacted density of lithium iron phosphate and solve the problem that the high gram capacity is difficult to ensure under the high powder compacted density.
In a first aspect, the present application provides a method for preparing a lithium iron phosphate positive electrode material, including:
mixing an iron source, a lithium source, a phosphorus source, a carbon source, a solvent, a dispersing agent, a dopant and a sintering aid to form slurry;
drying the slurry to form particles, and then pressing the particles into tablets;
sintering the sheet body to obtain a lithium iron phosphate material;
and preparing the lithium iron phosphate material into powder.
According to the preparation method, the slurry is granulated and then pressed into a sheet, so that a compact lithium iron phosphate precursor is obtained, and the uniformity of the granularity of the precursor is ensured. Meanwhile, the sintering aid is added to promote sintering and inhibit abnormal growth of crystal grains so as to promote densification process, and the sintering aid can also effectively reduce sintering temperature and shorten sintering time, thereby playing a role in improving productivity and reducing cost; and the powder body is sintered in cooperation with the sheet body, so that the full contact of powder particles is promoted, the atomic diffusion in the sintering process is accelerated, and the sintering densification is promoted. And the dopant enables a bulk phase formed in the sintering process to be doped, so that the mobility of lithium ions is improved, and the electrochemical performance of the material is ensured. The method improves the compaction density of the lithium iron phosphate anode material and also improves the gram capacity of the material by performing densification treatment on the lithium iron phosphate precursor, introducing a sintering aid, ion doping and sheet sintering.
In other alternative embodiments of the present application, the step of refining the particle size of the slurry comprises:
the particle size of the slurry was milled to a range of 0.1 μm to 1.0 μm, and D50 was 0.3 μm to 0.5 μm.
By grinding the slurry to the nanoscale range, the lithium iron phosphate precursor slurry with high activation energy and fine and uniform granularity can be obtained, a foundation is provided for subsequently obtaining spherical particles, and then a guarantee is provided for subsequently improving the compaction density of lithium iron phosphate and obtaining high-compaction-density powder.
In other alternative embodiments of the present application, the step of drying the milled slurry to form spherical particles comprises:
the spherical particles are obtained by atomization and drying, and the atomization temperature is 180-260 ℃.
By the atomization drying, spherical particles can be obtained, and the atomization drying effect can be ensured within the atomization temperature range. The spherical particles can obtain powder with uniform particle size after subsequent crushing, and high-compaction-density powder is ensured to be obtained.
It should be noted that in other alternative embodiments, the particles may have other shapes, such as polyhedral shapes or other irregular shapes.
In other alternative embodiments of the present application, after the slurry is dried to form granules, the granules are also broken into a powder, and the powder is then compressed into tablets.
In other alternative embodiments of the present application, the step of breaking into powder comprises:
and (4) crushing the particles into powder by adopting dry ball milling.
The particles can be crushed by dry ball milling to obtain powder (including crushed hollow particles) and ensure the uniformity of the particle size of the powder, so as to obtain a compact precursor, and further provide guarantee for subsequently improving the compaction density of the lithium iron phosphate and obtaining high-compaction-density powder.
In other alternative embodiments of the present application, the step of compressing into a tablet comprises:
pressing at 150-250 MPa to obtain tablet.
Within this range, a dense tablet can be obtained by pressing.
In other alternative embodiments of the present application, the step of sintering the tablet comprises:
placing the sheet body in a reducing atmosphere, and performing hot-pressing sintering; wherein the pressure is 100MPa-400MPa, the temperature is 500-750 ℃, and the heat preservation is carried out for 4-10 h.
Under the sintering condition, the sintering and the pressurization are carried out simultaneously, so that the accelerating and exhausting in the sintering process promote the full contact of powder particles, the atomic diffusion in the sintering process is accelerated, and the sintering densification is promoted.
In other alternative embodiments of the present application, the step of powdering the lithium iron phosphate material includes:
and (2) crushing the sintered lithium iron phosphate material, and controlling the granularity (D90-D10)/D50 to be 1.8-4.2, wherein the D50 is 0.5-1.2 mu m, and the granularity curve is controlled to be double peaks, so that the obtained particles have two sizes and round corners.
The sintered lithium iron phosphate material is crushed, the particle size curve is controlled to be double peaks, so that the obtained particles have two sizes, the shapes of the corners of the particles are smooth, the compaction density of the lithium iron phosphate is improved, the high compaction density powder is guaranteed, and the high gram capacity is guaranteed. In other alternative embodiments of the present application, the sintering aid comprises LiF, CaF 2 Boric acid, boron oxide, Y 2 O 3 One or more of; the addition amount of the sintering aid is 0.1-3% of the mass of the slurry.
The sintering aid can effectively reduce the sintering temperature and shorten the sintering time, has the functions of improving the productivity and reducing the cost, and is beneficial to obtaining high-compaction-density powder.
In other alternative embodiments of the present application, the iron source comprises one or more of iron phosphate, iron oxide, ferroferric oxide;
the lithium source comprises one or more of lithium phosphate, lithium carbonate, lithium dihydrogen phosphate and lithium hydroxide.
In other alternative embodiments of the present application, in the lithium source, the iron source, the phosphorus source, in terms of the ratio of the amounts of the substances, Li: p ═ 1.005-1.03, Li: 1.03-1.08, Fe: p is 0.94-0.98.
In other alternative embodiments of the present application, the carbon source includes one or more of sugars, olefins, carbon nanotubes, and alcohols.
In other alternative embodiments of the present application, the solvent includes one or more of water, alcohols, ketones, and the slurry solids content is 20% to 60%.
In other alternative embodiments herein, the dispersant comprises one or more of cetyltrimethylammonium bromide, PEG, N-methyl pyrrolidone, salicylic acid, CTAB, ascorbic acid, dimethyl succinate, polyvinyl alcohol, tween 20, citric acid, PVP; and the mass of the dispersing agent is 1-2% of the total mass of the lithium source, the iron source and the phosphorus source.
The dispersant is added to promote the dispersion uniformity of the slurry, and provide favorable conditions for obtaining high powder compaction density subsequently.
In other alternative embodiments of the present application, the dopant includes one or more of titanium oxide, vanadium pentoxide, molybdenum trioxide, zirconium oxide, magnesium oxide, and the concentration of the dopant in the slurry is from 300ppm to 2000 ppm.
By adding the doping elements, bulk phase doping is formed in the sintering process, the mobility of lithium ions is improved, and the electrochemical performance of the material is ensured.
In a second aspect, the present application provides a lithium iron phosphate positive electrode material prepared by the preparation method of any one of the foregoing lithium iron phosphate positive electrode materials.
The compacted density of the lithium iron phosphate anode material obtained by the preparation method of the lithium iron phosphate anode material is more than 2.5g/cm 3 。
In a third aspect, the present application provides a lithium ion battery comprising a lithium iron phosphate positive electrode material.
The charging capacitance of the lithium ion battery prepared by the lithium iron phosphate anode material reaches 160 +/-4 mAh/g, and the gram capacity of 1C is more than 142 mAh/g.
Drawings
To more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered as limiting the scope, and those skilled in the art can also obtain other related drawings based on the drawings without inventive efforts.
Fig. 1 is a process flow diagram of a preparation method of a lithium iron phosphate positive electrode material according to the present application;
fig. 2a and 2b are SEM images of lithium iron phosphate positive electrode material of example 1 at different magnifications;
fig. 3 is a particle size classification chart of the lithium iron phosphate positive electrode material of example 1;
FIG. 4 is a charge and discharge curve of example 1;
fig. 5a and 5b are SEM images of the lithium iron phosphate positive electrode material of comparative example 1 at different magnifications;
fig. 6 is a charge and discharge curve of comparative example 1.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some embodiments of the present application, but not all embodiments. The components of the embodiments of the present application, generally described and illustrated in the figures herein, can be arranged and designed in a wide variety of different configurations.
Thus, the following detailed description of the embodiments of the present application is not intended to limit the scope of the claimed application, but is merely representative of selected embodiments of the application. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments in the present application without making any creative effort belong to the protection scope of the present application.
The inventors have discovered that higher compaction density reduces internal cell resistance, reduces polarization losses, extends cell life, and increases cell energy density. However, too high a rise in the compaction density brings with it the problem of capacitance decay. For the lithium iron phosphate anode material, the compaction density is related to the particle morphology, the particle size and the particle size distribution. The preparation method of the lithium iron phosphate anode material can solve the technical problem of improvement of the compacted density of lithium iron phosphate and the problem that high gram capacity is difficult to guarantee under high powder compacted density.
The compaction density of the lithium iron phosphate is improved, so that the lithium iron phosphate material needs to be very compact, the charging and discharging capacity of the lithium iron phosphate material needs to be considered while the compaction density is improved, and the primary crystal of the lithium iron phosphate is required to be fine and uniform in particle size and free from abnormal particle growth.
Some embodiments of the present application provide a method for preparing a lithium iron phosphate positive electrode material, including:
mixing an iron source, a lithium source, a phosphorus source, a carbon source, a solvent, a dispersing agent, a dopant and a sintering aid to form slurry;
drying the slurry to form particles, and then pressing the particles into tablets;
sintering the sheet body to obtain a lithium iron phosphate material;
and preparing the lithium iron phosphate material into powder.
According to the preparation method, the slurry is formed into particles and then pressed into tablets; thereby obtaining a compact lithium iron phosphate precursor and ensuring the uniformity of the granularity of the precursor. Meanwhile, the sintering aid is added to promote sintering, inhibit abnormal growth of crystal grains to promote densification process, effectively reduce sintering temperature and shorten sintering time, and play a role in improving productivity and reducing cost; and the powder body is sintered in cooperation with the sheet body, so that the full contact of powder particles is promoted, the atomic diffusion in the sintering process is accelerated, and the sintering densification is promoted. And the dopant enables a bulk phase formed in the sintering process to be doped, so that the mobility of lithium ions is improved, and the electrochemical performance of the material is ensured. The compaction density of the lithium iron phosphate anode material is improved through the synergistic effect of densification treatment on the lithium iron phosphate precursor, introduction of a sintering aid, ion doping and sheet sintering, and the high gram capacity of the material is ensured.
Referring to fig. 1, in some embodiments of the present application, a method for preparing a lithium iron phosphate positive electrode material includes the following steps:
and step S1, preparing slurry.
Mixing an iron source, a lithium source, a phosphorus source, a carbon source, a solvent, a dispersing agent, a dopant and a sintering aid to form slurry.
Further, in some embodiments herein, the iron source comprises one or more of iron phosphate, iron oxide, ferroferric oxide.
Further, in some embodiments herein, the lithium source comprises one or more of lithium phosphate, lithium carbonate, lithium dihydrogen phosphate, and lithium hydroxide.
Further, in some embodiments of the present application, in the lithium source, the iron source, and the phosphorus source, in terms of a ratio of amounts of the substances, Li: p ═ 1.005-1.03, Li: 1.03-1.08, Fe: p is 0.94-0.98.
Further optionally, in some embodiments herein, the ratio of the amount of Li: 1.008-1.029, Li: fe ═ 1.025-1.075, Fe: p is 0.95-0.97. Illustratively, Li: p ═ 1.01 or 1.02, Li: 1.03, 1.04, 1.05, 1.06 or 1.07, Fe: p is 0.95, 0.96, or 0.97.
Further, in some embodiments of the present application, the carbon source is one or more of saccharides, olefins, carbon nanotubes, and alcohols.
Further, in some embodiments of the present application, the solvent is one or more of water, alcohols, and ketones, and the slurry solid content is 20% to 60%.
Further, in some embodiments herein, the dispersant is one or more of cetyltrimethylammonium bromide, PEG, N-methylpyrrolidone, salicylic acid, CTAB, ascorbic acid, dimethyl succinate, polyvinyl alcohol, tween 20, citric acid, PVP; and the mass of the dispersing agent is 1-2% of the total mass of the lithium source, the iron source and the phosphorus source.
Further optionally, the mass of the dispersant is 1.1% -1.9% of the total mass of the lithium source, the iron source and the phosphorus source. Further optionally, the mass of the dispersant is 1.2% -1.8% of the total mass of the lithium source, the iron source and the phosphorus source. Illustratively, the mass of the dispersant is 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8% of the total mass of the lithium source, the iron source, and the phosphorus source.
Further, in some embodiments of the present application, the dopant is one or more of titanium oxide, vanadium pentoxide, molybdenum trioxide, zirconium oxide, magnesium oxide, and the concentration of the dopant in the slurry is 300ppm to 2000 ppm.
Further optionally, the concentration of dopant in the slurry is from 400ppm to 1900 ppm. Further optionally, the concentration of dopant in the slurry is from 500ppm to 1800 ppm. Further optionally, the concentration of dopant in the slurry is from 500ppm to 1600 ppm. Further optionally, the concentration of dopant in the slurry is from 800ppm to 1200 ppm. Illustratively, the concentration of dopant in the slurry is 450ppm, 480ppm, 550ppm, 600ppm, 700ppm, 850ppm, 900 ppm.
Further, in some embodiments of the present application, the iron source, the lithium source, the phosphorus source, the carbon source, the solvent, the dispersant, the dopant, and the sintering aid are mixed in the above ratio, and the solvent is stirred and mixed into the slurry.
And step S2, grinding the slurry.
Further, the step of grinding the slurry comprises:
the particle size of the slurry was milled to a range of 0.1 μm to 1.0 μm, and D50 was 0.3 μm to 0.5 μm.
Further optionally, the step of grinding the slurry comprises:
the particle size of the slurry was milled to a range of 0.2 μm to 0.9 μm, and D50 was 0.35 μm to 0.45 μm.
Further optionally, the step of grinding the slurry comprises:
the particle size of the slurry was milled to a range of 0.3 μm to 0.8 μm, and D50 was 0.36 μm to 0.44 μm.
Illustratively, the step of grinding the slurry comprises:
grinding the particle size of the slurry to 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, or 0.7 μm; and D50 is 0.36 μm, 0.38 μm, 0.40 μm, 0.42 μm, or 0.43 μm.
Further, in some embodiments of the present application, the slurry is ground in a coarse and fine grinding cycle to provide a more uniform and finer slurry particles.
And step S3, drying the ground slurry to form spherical particles.
Further, the step of drying the milled slurry to form spherical particles comprises:
the spherical particles are obtained by atomization and drying, and the atomization temperature is 180-260 ℃.
Further optionally, the step of drying the milled slurry to form spherical particles comprises:
the spherical particles are obtained by atomization and drying, and the atomization temperature is 190-250 ℃.
Further optionally, the step of drying the milled slurry to form spherical particles comprises:
the spherical particles are obtained by atomization and drying, and the atomization temperature is 200-240 ℃.
Illustratively, the step of drying the milled slurry to form spherical particles comprises:
the spherical particles are obtained by atomization and drying, and the atomization temperature is 210 ℃, 220 ℃, 230 ℃ or 240 ℃.
Further, in some embodiments herein, after the slurry is dried to form particles, the particles are also broken into a powder.
Further, in some embodiments of the present application, the step of breaking the particles into a powder comprises:
and (3) crushing the spherical particles into powder by adopting dry ball milling.
Step S4, pressing the powder into tablets.
Further, the step of compressing the powder into a tablet comprises:
putting the powder into a die, and pressing the powder into tablets at 150-250 MPa.
Further optionally, the step of compressing the powder into a tablet comprises:
putting the powder into a mould, and pressing at 155MPa-245MPa to obtain the tablet.
Further optionally, the step of compressing the powder into a tablet comprises:
putting the powder into a mould, and pressing the powder into tablets at 160-240 MPa.
Illustratively, the step of compressing the powder into a tablet comprises:
placing the powder in a mould, and pressing into tablets at 165MPa, 170MPa, 175MPa, 180MPa, 190MPa, 200MPa, 210MPa, 220MPa, 230MPa or 240 MPa.
In other alternative embodiments of the present application, the spherical particles formed in step S3 may be directly compressed into tablets. Illustratively, the spherical particles formed in step S3 are compressed at 150MPa to 250MPa into tablets. Further alternatively, the spherical particles formed in step S3 are placed in a mold and compressed into tablets at 150MPa to 250 MPa.
And step S5, sintering the sheet body to obtain the lithium iron phosphate material.
The step of sintering the tablet body comprises:
placing the sheet body in a reducing atmosphere, and performing hot-pressing sintering; wherein the pressure is 100MPa-400MPa, the temperature is 500 ℃ to 750 ℃, and the heat preservation is carried out for 4h-10 h.
Further optionally, the step of sintering the tablet comprises:
placing the sheet body in a reducing atmosphere, and performing hot-pressing sintering; wherein the pressure is 110MPa-390MPa, the temperature is 550-700 ℃, and the heat preservation is carried out for 4.5h-9.5 h.
Further optionally, the step of sintering the tablet comprises:
placing the sheet body in a reducing atmosphere, and performing hot-pressing sintering; wherein the pressure is 120MPa-380MPa, the temperature is 600 ℃ -650 ℃, and the heat preservation is carried out for 5h-9 h.
Illustratively, the step of sintering the tablet comprises:
placing the sheet body in a reducing atmosphere, and performing hot-pressing sintering; wherein the pressure is 120MPa, 150MPa, 180MPa, 200MPa, 220MPa, 250MPa, 280MPa, 300MPa, 320MPa or 350MPa, the temperature is 610 ℃, 620 ℃, 630 ℃ or 640 ℃, and the temperature is kept for 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h or 9 h.
Step S6, the lithium iron phosphate material is powdered.
The step of preparing the lithium iron phosphate material into powder comprises the following steps:
and crushing the sintered lithium iron phosphate material, and controlling the granularity (D90-D10)/D50 to be 1.8-4.2, wherein the D50 is 0.5-1.2 mu m, and the granularity curve is controlled to be double peaks, so that the obtained particles have two sizes and the corners of the particles are rounded.
Further, the step of powdering the lithium iron phosphate material includes:
and crushing the sintered lithium iron phosphate material, and controlling the granularity (D90-D10)/D50 to be 1.9-4.1, wherein the D50 is 0.6-1.1 mu m, and the granularity curve is controlled to be double peaks, so that the obtained particles have two sizes and the corners of the particles are rounded.
Further, the step of powdering the lithium iron phosphate material includes:
and crushing the sintered lithium iron phosphate material, and controlling the granularity (D90-D10)/D50 to be 2.0-4.0, wherein the D50 is 0.7-1.0 mu m, and the granularity curve is controlled to be double peaks, so that the obtained particles have two sizes and the corners of the particles are rounded.
Further, the step of powdering the lithium iron phosphate material includes:
and crushing the sintered lithium iron phosphate material, and controlling the granularity (D90-D10)/D50 to be 2.5-3.5, wherein the D50 is 0.8-0.9 mu m, and the granularity curve is controlled to be double peaks, so that the obtained particles have two sizes and the corners of the particles are rounded.
Illustratively, the step of powdering the lithium iron phosphate material includes:
and crushing the sintered lithium iron phosphate material, and controlling the granularity (D90-D10)/D50 to be 2.6, 2.7, 2.8 or 3.0, wherein D50 is 0.81 mu m, 0.82 mu m, 0.83 mu m, 0.84 mu m, 0.85 mu m, 0.86 mu m or 0.88 mu m, and the granularity curve is controlled to be bimodal, so that the obtained particles have two sizes and the corners of the particles are rounded.
According to the method, the compaction density of the lithium iron phosphate anode material is improved and the high gram volume of the material is ensured by the synergistic effect of precursor densification treatment, introduction of a sintering aid, ion doping and hot-pressing sintering. Firstly, grinding and nanocrystallizing raw materials to obtain a precursor with high activation energy and fine and uniform granularity, atomizing and drying to obtain a spherical precursor, then dry-grinding the spherical precursor to crush hollow particles formed in the atomizing and drying process to obtain a compact precursor, and ensuring the granularity uniformity of the compact precursor; then, a sintering aid is added to promote sintering, abnormal growth of crystal grains is inhibited, so that a densification process is promoted, the sintering aid can also effectively reduce the sintering temperature and shorten the sintering time, and the effects of improving the productivity and reducing the cost are achieved; and (3) cooperating with hot-pressing sintering, and accelerating exhaust in the sintering process to promote full contact of powder particles while sintering and pressurizing, so that atomic diffusion in the sintering process is accelerated, and sintering densification is promoted. During the material preparation, a certain amount of doping elements are added, so that bulk phase doping is formed in the sintering process, the mobility of lithium ions is improved, and the electrochemical performance of the material is ensured.
By adopting the preparation method of the embodiment, the compaction density of the lithium iron phosphate positive electrode material can be obviously improved, and the capacity of the lithium iron phosphate battery is further improved. The method for preparing the lithium iron phosphate has the advantages of simple process, short sintering period, low sintering temperature and strong operability, and the prepared lithium iron phosphate anode material has high compaction performance and high capacity.
The method can also improve the process for preparing the lithium iron phosphate by the iron phosphate method in the prior general technology, thereby realizing the effects of shortening the sintering period, reducing the sintering temperature and realizing the high density and high capacity of the lithium iron phosphate.
Some embodiments of the present application provide a lithium iron phosphate positive electrode material, which is prepared by using the preparation method of the lithium iron phosphate positive electrode material provided in any one of the foregoing embodiments.
Some embodiments of the present application provide a lithium ion battery comprising the lithium iron phosphate positive electrode material of the previous embodiments.
The features and properties of the present application are described in further detail below with reference to examples.
Example 1
(1) Water according to mass ratio: lithium carbonate: iron phosphate: dextrose monohydrate 700: 74.12: 300: 31.41, mixing, adding PEG2000 with the total mass of 1.2%, N-methyl pyrrolidone with the total mass of 0.3%, titanium oxide and vanadium pentoxide with the theoretical mass of 0.1% of lithium iron phosphate, and LiF with the theoretical mass of 1 wt%, and stirring to obtain uniform slurry; (2) zirconia beads with the particle size of 0.6-0.8 mu m are adopted in a grinding machine, the material is roughly ground for about 2 hours, the material is transferred to a refiner, the zirconia beads with the particle size of 0.3-0.4 mu m are adopted, the material is finely ground for 2 hours, sampling and testing the particle size at intervals of 1 hour is started until D50 reaches 350nm, and grinding is finished; (3) two fluids are adopted for spray drying, the air inlet temperature is 240 ℃, and the air outlet temperature is 95 ℃; (4) adding the dried precursor into a planetary ball mill, dry-milling at 300Hz for 30min, and sieving to obtain a precursor; (5) tabletting: putting the precursor into a mold, and maintaining the pressure at 200MPa for 1min to prepare a sheet; (6) sintering the precursor by using hot isostatic pressing, wherein the atmosphere is 99.999% of nitrogen, the pressure is 300MPa, the temperature is 650 ℃, and the heat is preserved for 6h to obtain lithium iron phosphate by sintering; (7) the sintered lithium iron phosphate was primarily crushed by a crusher, and then pulverized and classified by a jet mill at a rotation speed of 1700rpm with D50 controlled to be 0.8 μm (D10-0.4 μm, D90-2.5 μm, (D90-D10)/D50-2.6). Fig. 2a and 2b show SEM images of the prepared lithium iron phosphate positive electrode material at different magnifications, which show that the material has two types of particles with different particle sizes, good carbon coating, no carbon layer falling, round and smooth particle corner morphology, and the particles with different particle sizes form a gradation, which is beneficial to improving the compaction density of the powder. Fig. 3 shows a particle size classification diagram of the lithium iron phosphate positive electrode material, the curve of which is a double peak, and illustrates that the prepared lithium iron phosphate positive electrode material powder has primary particles with two sizes, and the result is consistent with that of the SEM image.
Weighing the prepared lithium iron phosphate sample, the conductive agent and PVDF according to the mass ratio of 80: 10, and adding NMPa for regulationStirring for 4 hr after slurrying, coating on aluminum foil surface, and vacuum drying at 120 deg.C for 12 hr. And (3) manufacturing a button cell after punching, and performing corresponding charge and discharge performance test at room temperature by using a LAND cell test system. As shown in FIG. 4, it can be seen from FIG. 4 that the capacity of 0.1C g was 162mAh/g and the capacity of 1C g was 142 mAh/g. The compacted density of the powder is 2.60g/cm 3 。
Example 2
(1) Water according to mass ratio: lithium carbonate: iron phosphate: dextrose monohydrate (kg) 700: 80.31: 325: 45.79, mixing, adding 3.13kg PVP, 1000g titanium oxide and 1.5 wt% boric acid, and stirring to obtain uniform slurry; (2) adopting zirconia beads with the grain diameter of 0.6-0.8 mu m in a coarse grinding machine, roughly grinding the material for about 2 hours, transferring the material to a fine grinding machine, adopting the zirconia beads with the grain diameter of 0.3-0.4 mu m, finely grinding the material for 2 hours, starting sampling and testing the grain size at intervals of 1 hour until D50 reaches 300nm, and finishing grinding; (3) two fluids are adopted for spray drying, the air inlet temperature is 230 ℃, and the air outlet temperature is 100 ℃; (4) adding into planetary ball mill, dry milling at 300Hz for 30min, and sieving to obtain precursor; (5) tabletting: putting the precursor into a mold, and maintaining the pressure at 200MPa for 1min to prepare a sheet; (6) sintering the precursor by using hot isostatic pressing, wherein the atmosphere is 99.999% of nitrogen, the pressure is 200MPa, the temperature is 700 ℃, and the heat is preserved for 5 hours to obtain lithium iron phosphate by sintering; (7) primarily crushing the sintered lithium iron phosphate by using a crusher, crushing and grading by using a jet mill, controlling the rotating speed of a grading wheel to be 1700rpm, controlling the D50 to be 0.5 mu m (D10 is 0.3 mu m, D90 is 2.4 mu m, (D90-D10)/D50 is 4.2), and controlling the corresponding powder compaction density to be 2.5g/cm 3 (ii) a The D50 is controlled to be 1.2 μm (D10 is 0.4 μm, D90 is 2.5 μm, (D90-D10)/D50 is 1.8), and the corresponding powder compaction density is 2.47g/cm 3 (ii) a The D50 was controlled to 0.8 μm (D10 ═ 0.5 μm, D90 ═ 2.5 μm, (D90-D10)/D50 ═ 2.5), and the powder compacted density was controlled to 2.55g/cm 3 The capacity of 0.1 g is 165mAh/g, and the capacity of 1C is 145 mAh/g.
Comparative example 1
(1) Water according to mass ratio: lithium carbonate: iron phosphate: dextrose monohydrate 700: 74.12: 300: 31.41, mixing and stirring into uniform slurry; (2) zirconia beads with the particle size of 0.6-0.8 mu m are adopted in a grinding machine, the material is roughly ground for about 2 hours, the material is transferred to a refiner, the zirconia beads with the particle size of 0.3-0.4 mu m are adopted, the material is finely ground for 2 hours, sampling and testing the particle size at intervals of 1 hour is started until D50 reaches 350nm, and grinding is finished; (3) two fluids are adopted for spray drying, the air inlet temperature is 240 ℃, and the air outlet temperature is 95 ℃; (4) sintering the dried precursor by using hot isostatic pressing, wherein the atmosphere is 99.999% of nitrogen, the pressure is 300MPa, the temperature is 650 ℃, and the heat is preserved for 6h to obtain lithium iron phosphate by sintering; (5) and (3) primarily crushing the sintered lithium iron phosphate by using a crusher, and crushing and grading by using an air flow mill, wherein the rotating speed of a grading wheel is 1700rpm, and the D50 is controlled to be 0.8 mu m. Fig. 5a and 5b show SEM images of different magnifications of the prepared lithium iron phosphate cathode material, and it can be seen from the images that the particle size difference of the prepared lithium iron phosphate cathode material is not large, the number of small particles is large, no significant size particle grading can be formed, and it is not beneficial to increase the powder compaction density.
Weighing the prepared lithium iron phosphate sample, the conductive agent and PVDF according to the mass ratio of 80: 10, adding NMPa, stirring for 4h after mixing into a slurry, coating on the surface of an aluminum foil, and drying in vacuum at 120 ℃ for 12 h. And (3) manufacturing a button cell after punching, and performing corresponding charge and discharge performance test at room temperature by using a LAND cell test system. The results are shown in FIG. 6, from which it can be seen that the 0.1C discharge gram capacity is 154.7 mAh/g. The compacted density of the powder is 2.30g/cm 3 。
Comparative example 2
(1) Water according to mass ratio: lithium carbonate: iron phosphate: dextrose monohydrate 700: 74.12: 300: 31.41, mixing and stirring into uniform slurry; (2) using zirconia beads with the grain diameter of 0.6-0.8 mu m in a grinding machine, roughly grinding the material for about 2 hours, transferring the material to a refiner, using the zirconia beads with the grain diameter of 0.3-0.4 mu m, finely grinding the material for 2 hours, starting sampling and testing the grain size at intervals of 1 hour until D50 reaches 350nm, and finishing grinding; (3) two fluids are adopted for spray drying, the air inlet temperature is 240 ℃, and the air outlet temperature is 95 ℃; (4) adding the dried precursor into a planetary ball mill, dry-milling at 300Hz for 30min, and sieving to obtain a precursor; (5) tabletting: putting the precursor into a mold, and maintaining the pressure at 200MPa for 1min to prepare a sheet; (6) sintering the precursor by hot isostatic pressing, wherein the atmosphere is 99.999 percent of nitrogen, the pressure is 300MPa, the temperature is 650 ℃, the heat preservation is carried out for 6h, and the sintering is carried out to obtain the productTo lithium iron phosphate; (7) and (3) primarily crushing the sintered lithium iron phosphate by using a crusher, and then crushing and grading by using an air flow mill, wherein the rotating speed of a grading wheel is 1700rpm, and D50 is controlled to be 0.8 mu m. It corresponds to a 0.1C discharge with a gram capacity of 156.2 mAh/g. The compacted density of the powder is 2.38g/cm 3 。
Comparative example 3
(1) Water according to mass ratio: lithium carbonate: iron phosphate: dextrose monohydrate 700: 74.12: 300: 31.41, mixing, adding PEG2000 with the total mass of 1.2%, N-methyl pyrrolidone with the total mass of 0.3%, titanium oxide and vanadium pentoxide with the theoretical mass of 0.1% of lithium iron phosphate, and LiF with the theoretical mass of 1 wt%, and stirring to obtain uniform slurry; (2) zirconia beads with the particle size of 0.6-0.8 mu m are adopted in a grinding machine, the material is roughly ground for about 2 hours, the material is transferred to a refiner, the zirconia beads with the particle size of 0.3-0.4 mu m are adopted, the material is finely ground for 2 hours, sampling and testing the particle size at intervals of 1 hour is started until D50 reaches 350nm, and grinding is finished; (3) two fluids are adopted for spray drying, the air inlet temperature is 240 ℃, and the air outlet temperature is 95 ℃; (4) adding the dried precursor into a planetary ball mill, dry-milling at 300Hz for 30min, and sieving to obtain a precursor; (5) sintering the precursor by using hot isostatic pressing, wherein the atmosphere is 99.999% of nitrogen, the pressure is 300MPa, the temperature is 650 ℃, and the heat is preserved for 6h to obtain lithium iron phosphate by sintering; (6) and (3) primarily crushing the sintered lithium iron phosphate by using a crusher, and crushing and grading by using an air flow mill, wherein the rotating speed of a grading wheel is 1700rpm, and the D50 is controlled to be 0.8 mu m. The powder compaction density of the product is 2.53g/cm 3 The 0.1C gram capacity is 160.1mAh/g, and the 1C gram capacity is 144 mAh/g. The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims (17)

1. A preparation method of a lithium iron phosphate positive electrode material is characterized by comprising the following steps:
mixing an iron source, a lithium source, a phosphorus source, a carbon source, a solvent, a dispersing agent, a dopant and a sintering aid to form slurry;
drying the slurry to form particles, and then pressing the particles into tablets;
sintering the sheet body to obtain a lithium iron phosphate material;
and preparing the lithium iron phosphate material into powder.
2. The method for producing a lithium iron phosphate positive electrode material according to claim 1,
the step of drying the slurry to form particles comprises:
and forming the slurry into spherical particles by adopting atomization drying, wherein the atomization temperature is 180-260 ℃.
3. The method for producing a lithium iron phosphate positive electrode material according to claim 1,
after the slurry is dried to form granules, the granules are also crushed into powder, and then the powder is compressed into tablets.
4. The method for producing a lithium iron phosphate positive electrode material according to claim 3,
the step of breaking into a powder comprises:
and (3) crushing the particles into powder by adopting dry ball milling.
5. The method for producing a lithium iron phosphate positive electrode material according to claim 1,
the step of compressing into tablets comprises:
pressing at 150-250 MPa to obtain tablet.
6. The method for producing a lithium iron phosphate positive electrode material according to claim 1,
the method further comprises the step of milling the slurry prior to the step of drying the slurry to form particles;
the step of grinding the slurry comprises:
the particle size of the slurry was milled to a range of 0.1 μm to 1.0 μm, and D50 was 0.3 μm to 0.5 μm.
7. The method for producing a lithium iron phosphate positive electrode material according to claim 1,
the step of sintering the tablet includes:
placing the sheet body in a reducing atmosphere, and performing hot-pressing sintering; wherein the pressure is 100MPa-400MPa, the temperature is 500-750 ℃, and the heat preservation is carried out for 4-10 h.
8. The method for producing a lithium iron phosphate positive electrode material according to claim 1,
the step of making the lithium iron phosphate material into powder comprises:
and crushing the sintered lithium iron phosphate material, and controlling the granularity (D90-D10)/D50 to be 1.8-4.2, wherein D50 is 0.5-1.2 mu m, and the granularity curve is controlled to be double peaks, so that the obtained particles have two sizes and the corners of the particles are rounded.
9. The method for producing a lithium iron phosphate positive electrode material according to any one of claims 1 to 8,
the sintering aid comprises LiF and CaF 2 Boric acid, boron oxide, Y 2 O 3 One or more of; the addition amount of the sintering aid is 0.1-3% of the mass of the slurry.
10. The method for producing a lithium iron phosphate positive electrode material according to any one of claims 1 to 8,
the iron source comprises one or more of iron phosphate, ferric oxide and ferroferric oxide;
the lithium source comprises one or more of lithium phosphate, lithium carbonate, lithium dihydrogen phosphate and lithium hydroxide.
11. The method for producing a lithium iron phosphate positive electrode material according to claim 10,
in the lithium source, the iron source, and the phosphorus source, in terms of the ratio of the amounts of the substances, Li: p ═ 1.005-1.03, Li: 1.03-1.08, Fe: p is 0.94-0.98.
12. The method for producing a lithium iron phosphate positive electrode material according to any one of claims 1 to 8,
the carbon source comprises one or more of saccharides, olefins, carbon nanotubes and alcohols.
13. The method for producing a lithium iron phosphate positive electrode material according to any one of claims 1 to 8,
the solvent comprises one or more of water, alcohols and ketones, and the solid content of the slurry is 20-60%.
14. The method for producing a lithium iron phosphate positive electrode material according to any one of claims 1 to 8,
the dispersing agent comprises one or more of cetyl trimethyl ammonium bromide, PEG, N-methyl pyrrolidone, salicylic acid, CTAB, ascorbic acid, dimethyl succinate, polyvinyl alcohol, Tween 20, citric acid and PVP; and the mass of the dispersing agent is 1-2% of the total mass of the lithium source, the iron source and the phosphorus source.
15. The method for producing a lithium iron phosphate positive electrode material according to any one of claims 1 to 8,
the dopant comprises one or more of titanium oxide, vanadium pentoxide, molybdenum trioxide, zirconium oxide and magnesium oxide, and the concentration of the dopant in the slurry is 300ppm-2000 ppm.
16. A lithium iron phosphate positive electrode material characterized by being prepared by the method for preparing a lithium iron phosphate positive electrode material according to any one of claims 1 to 15.
17. A lithium ion battery comprising the lithium iron phosphate positive electrode material according to claim 16.
CN202210784479.7A 2022-06-28 2022-06-28 Lithium iron phosphate anode material, preparation method thereof and lithium ion battery Pending CN115072694A (en)

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