CN113800493B - Lithium iron phosphate positive electrode material and preparation method and application thereof - Google Patents
Lithium iron phosphate positive electrode material and preparation method and application thereof Download PDFInfo
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- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 title claims abstract description 128
- 238000002360 preparation method Methods 0.000 title claims abstract description 16
- 239000007774 positive electrode material Substances 0.000 title claims description 15
- 239000002245 particle Substances 0.000 claims abstract description 116
- 238000001027 hydrothermal synthesis Methods 0.000 claims abstract description 22
- 239000013078 crystal Substances 0.000 claims abstract description 19
- 238000000034 method Methods 0.000 claims abstract description 18
- 238000002156 mixing Methods 0.000 claims abstract description 13
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 10
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims abstract description 5
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 claims abstract description 5
- 238000000227 grinding Methods 0.000 claims abstract description 5
- 229910052742 iron Inorganic materials 0.000 claims abstract description 5
- 229910052744 lithium Inorganic materials 0.000 claims abstract description 5
- 229910052698 phosphorus Inorganic materials 0.000 claims abstract description 5
- 239000011574 phosphorus Substances 0.000 claims abstract description 5
- 238000007873 sieving Methods 0.000 claims abstract description 5
- 239000002904 solvent Substances 0.000 claims abstract description 5
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 claims description 12
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 8
- WEVYAHXRMPXWCK-UHFFFAOYSA-N Acetonitrile Chemical compound CC#N WEVYAHXRMPXWCK-UHFFFAOYSA-N 0.000 claims description 6
- 239000010406 cathode material Substances 0.000 claims description 6
- 239000004254 Ammonium phosphate Substances 0.000 claims description 4
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 claims description 4
- 229910000148 ammonium phosphate Inorganic materials 0.000 claims description 4
- 235000019289 ammonium phosphates Nutrition 0.000 claims description 4
- MNNHAPBLZZVQHP-UHFFFAOYSA-N diammonium hydrogen phosphate Chemical compound [NH4+].[NH4+].OP([O-])([O-])=O MNNHAPBLZZVQHP-UHFFFAOYSA-N 0.000 claims description 4
- 229960002089 ferrous chloride Drugs 0.000 claims description 4
- NMCUIPGRVMDVDB-UHFFFAOYSA-L iron dichloride Chemical compound Cl[Fe]Cl NMCUIPGRVMDVDB-UHFFFAOYSA-L 0.000 claims description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 4
- 229910021578 Iron(III) chloride Inorganic materials 0.000 claims description 2
- 229910000147 aluminium phosphate Inorganic materials 0.000 claims description 2
- 238000000498 ball milling Methods 0.000 claims description 2
- 235000003891 ferrous sulphate Nutrition 0.000 claims description 2
- 239000011790 ferrous sulphate Substances 0.000 claims description 2
- RBTARNINKXHZNM-UHFFFAOYSA-K iron trichloride Chemical compound Cl[Fe](Cl)Cl RBTARNINKXHZNM-UHFFFAOYSA-K 0.000 claims description 2
- BAUYGSIQEAFULO-UHFFFAOYSA-L iron(2+) sulfate (anhydrous) Chemical compound [Fe+2].[O-]S([O-])(=O)=O BAUYGSIQEAFULO-UHFFFAOYSA-L 0.000 claims description 2
- RUTXIHLAWFEWGM-UHFFFAOYSA-H iron(3+) sulfate Chemical compound [Fe+3].[Fe+3].[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O RUTXIHLAWFEWGM-UHFFFAOYSA-H 0.000 claims description 2
- 229910000359 iron(II) sulfate Inorganic materials 0.000 claims description 2
- 229910000360 iron(III) sulfate Inorganic materials 0.000 claims description 2
- XGZVUEUWXADBQD-UHFFFAOYSA-L lithium carbonate Chemical compound [Li+].[Li+].[O-]C([O-])=O XGZVUEUWXADBQD-UHFFFAOYSA-L 0.000 claims description 2
- 229910052808 lithium carbonate Inorganic materials 0.000 claims description 2
- 238000003801 milling Methods 0.000 claims description 2
- 239000001488 sodium phosphate Substances 0.000 claims description 2
- 229910000162 sodium phosphate Inorganic materials 0.000 claims description 2
- RYFMWSXOAZQYPI-UHFFFAOYSA-K trisodium phosphate Chemical compound [Na+].[Na+].[Na+].[O-]P([O-])([O-])=O RYFMWSXOAZQYPI-UHFFFAOYSA-K 0.000 claims description 2
- 239000010405 anode material Substances 0.000 abstract description 9
- 238000009792 diffusion process Methods 0.000 abstract description 8
- 239000011149 active material Substances 0.000 abstract description 4
- 238000009413 insulation Methods 0.000 abstract description 4
- 230000000052 comparative effect Effects 0.000 description 18
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 10
- 239000000463 material Substances 0.000 description 9
- 229910001416 lithium ion Inorganic materials 0.000 description 7
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 6
- 229910052799 carbon Inorganic materials 0.000 description 6
- 238000005056 compaction Methods 0.000 description 6
- 239000011248 coating agent Substances 0.000 description 4
- 238000001878 scanning electron micrograph Methods 0.000 description 4
- 238000000576 coating method Methods 0.000 description 3
- 238000007599 discharging Methods 0.000 description 3
- 238000009826 distribution Methods 0.000 description 3
- 239000003792 electrolyte Substances 0.000 description 3
- 238000012360 testing method Methods 0.000 description 3
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 2
- 229910052782 aluminium Inorganic materials 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 239000003575 carbonaceous material Substances 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 238000005265 energy consumption Methods 0.000 description 2
- 229910021389 graphene Inorganic materials 0.000 description 2
- 238000011031 large-scale manufacturing process Methods 0.000 description 2
- 230000006911 nucleation Effects 0.000 description 2
- 238000010899 nucleation Methods 0.000 description 2
- 239000003960 organic solvent Substances 0.000 description 2
- 230000003647 oxidation Effects 0.000 description 2
- 238000007254 oxidation reaction Methods 0.000 description 2
- 238000004806 packaging method and process Methods 0.000 description 2
- 238000007086 side reaction Methods 0.000 description 2
- 229910018119 Li 3 PO 4 Inorganic materials 0.000 description 1
- 229910010710 LiFePO Inorganic materials 0.000 description 1
- 229910013870 LiPF 6 Inorganic materials 0.000 description 1
- NCZYUKGXRHBAHE-UHFFFAOYSA-K [Li+].P(=O)([O-])([O-])[O-].[Fe+2].[Li+] Chemical compound [Li+].P(=O)([O-])([O-])[O-].[Fe+2].[Li+] NCZYUKGXRHBAHE-UHFFFAOYSA-K 0.000 description 1
- 230000003213 activating effect Effects 0.000 description 1
- 230000032683 aging Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000006182 cathode active material Substances 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000018109 developmental process Effects 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000011267 electrode slurry Substances 0.000 description 1
- 238000005755 formation reaction Methods 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 230000008595 infiltration Effects 0.000 description 1
- 238000001764 infiltration Methods 0.000 description 1
- 238000010030 laminating Methods 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 229910021392 nanocarbon Inorganic materials 0.000 description 1
- 239000002105 nanoparticle Substances 0.000 description 1
- 238000006386 neutralization reaction Methods 0.000 description 1
- 239000002985 plastic film Substances 0.000 description 1
- 229920006255 plastic film Polymers 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 239000011163 secondary particle Substances 0.000 description 1
- 238000007493 shaping process Methods 0.000 description 1
- 239000002002 slurry Substances 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
- 238000004804 winding Methods 0.000 description 1
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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
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- 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
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
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- 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
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/139—Processes of manufacture
- H01M4/1397—Processes of manufacture of electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
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- 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
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- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
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- C01P2004/01—Particle morphology depicted by an image
- C01P2004/03—Particle morphology depicted by an image obtained by SEM
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Abstract
The invention provides a lithium iron phosphate anode material and a preparation method and application thereof, wherein the preparation method comprises the following steps: (1) Mixing a lithium source, an iron source, a phosphorus source and a solvent, and carrying out hydrothermal reaction to obtain a lithium iron phosphate crystal; (2) Grinding the lithium iron phosphate crystal obtained in the step (1), and sieving to obtain lithium iron phosphate particles with a first particle size and lithium iron phosphate particles with a second particle size; (3) The lithium iron phosphate anode material is obtained by mixing the first-particle-size lithium iron phosphate particles obtained in the step (2) with the second-particle-size lithium iron phosphate particles, the preparation of a lithium iron phosphate crystal is carried out by a hydrothermal synthesis process under an ideal high-pressure heat insulation environment, and the diffusion impedance is reduced, the electrochemical dynamics is improved and the low-temperature rate discharge performance of the lithium iron phosphate battery is improved by doping lithium iron phosphate active materials with different specific particle sizes.
Description
Technical Field
The invention belongs to the technical field of lithium ion batteries, and relates to a lithium iron phosphate positive electrode material, and a preparation method and application thereof.
Background
In recent years, with the proposal of the concept of 'carbon peak reaching and carbon neutralization', new energy automobiles have unprecedented market demand hot waves, and the poor low-temperature performance of the high-specific-energy lithium ion battery is a great defect which restricts the application of the high-specific-energy lithium ion battery in cold climates or northern areas. For a conventional high-performance lithium iron phosphate battery, under the same rate discharge condition, the discharge capacity at 0 ℃ is about 60% -70% of the normal-temperature capacity, at-10 ℃ is 40% -50%, and at-20 ℃ is 20% -40%, and such low-temperature performance obviously cannot meet the use requirements of a power supply. Therefore, improving the low-temperature performance of the LFP becomes a great research focus in various industries such as power battery enterprises, vehicle enterprises, colleges and universities.
CN108878797A discloses a high compaction density lithium iron phosphate positive electrode material and a positive electrode plate, which are prepared by processing lithium iron phosphate into a nanoparticle dispersion, adding a coating agent and a conductive nano carbon material, mixing, and drying a slurry to obtain lithium iron phosphate secondary particles. The prepared lithium iron phosphate anode material has higher compaction density but increased compaction, and the infiltration of the electrolyte is deteriorated, which can influence the cycle performance and low-temperature performance of the lithium ion battery.
CN103715452A discloses a low-temperature lithium iron phosphate lithium ion power battery, wherein a cathode active material adopted by the battery is nano lithium iron phosphate coated by a discontinuous graphene structure, a median particle size of the nano lithium iron phosphate is 5-10nm, graphene is 3-8 layers of multi-layer graphene, a coating area accounts for 40% -70% of a total surface area of a lithium iron phosphate material, and a prepared cathode plate has a low compacted density, resulting in a low energy density.
The scheme has the problems of poor low-temperature performance and cycle performance or low compaction density, so that the development of the lithium iron phosphate cathode material capable of achieving the balance of high energy density and good electrical performance is necessary.
Disclosure of Invention
The invention aims to provide a lithium iron phosphate positive electrode material and a preparation method and application thereof, wherein a lithium iron phosphate crystal is prepared by a hydrothermal synthesis process under an ideal environment of high-pressure heat insulation, and then the specific surface area of lithium iron phosphate is increased by doping lithium iron phosphate active materials with different specific particle sizes, namely the content of carbon coating is increased, so that the electronic conductivity is improved to a certain extent; on the other hand, li can be shortened + Increase Li + The diffusion rate effectively reduces the diffusion impedance, improves the electrochemical dynamics, and obviously improves the low-temperature rate discharge performance of the lithium iron phosphate battery.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the invention provides a preparation method of a lithium iron phosphate positive electrode material, which comprises the following steps:
(1) Mixing a lithium source, an iron source, a phosphorus source and a solvent, and carrying out hydrothermal reaction to obtain a lithium iron phosphate crystal;
(2) Grinding the lithium iron phosphate crystal obtained in the step (1), and sieving to obtain lithium iron phosphate particles with a first particle size and lithium iron phosphate particles with a second particle size;
(3) Mixing the lithium iron phosphate particles with the first particle size and the lithium iron phosphate particles with the second particle size obtained in the step (2) to obtain a lithium iron phosphate positive electrode material;
wherein the D50 of the lithium iron phosphate particles of the first particle size is 1.02 to 1.06 μm, for example: 1.02 μm, 1.03 μm, 1.04 μm, 1.05 μm, 1.06 μm, or the like, and the difference in D50 between the first-particle-size lithium iron phosphate particles and the second-particle-size lithium iron phosphate particles is 0.19 to 0.27 μm, for example: 0.19 μm, 0.2 μm, 0.22 μm, 0.25 μm, 0.27 μm or the like, and the difference between D90 and D10 of the lithium iron phosphate particles having the second particle diameter is 7.05 to 7.15 μm, for example: 7.05 μm, 7.08 μm, 7.1 μm, 7.12 μm, 7.15 μm, or the like.
The lithium iron phosphate particles synthesized by a hydrothermal method have the advantages of small crystal grains, uniform phase, simplicity and convenience in operation and the like, and are easy to realize large-scale production; in addition, the conductivity of the material can be effectively improved, so that the electrochemical performance is improved;
according to the invention, two lithium iron phosphate particles with different particle sizes are mixed, the lithium iron phosphate particles with a specific first particle size are taken as the main material, and the lithium iron phosphate particles with a second particle size, which is narrow in particle size distribution and slightly small in particle size, are doped, so that on one hand, the specific surface area of lithium iron phosphate is increased, if a material is subjected to carbon coating or an electrode slurry is prepared, a conductive carbon material is used, the surface carbon content of the lithium iron phosphate anode material is increased, and the electronic conductivity is improved to a certain extent; on the other hand, li can be shortened + Increase Li + The diffusion rate effectively reduces the diffusion impedance, improves the electrochemical dynamics, and obviously improves the low-temperature rate discharge performance of the lithium iron phosphate battery.
Preferably, the lithium source of step (1) comprises lithium hydroxide and/or lithium carbonate.
Preferably, the iron source comprises any one of ferrous sulfate, ferrous chloride, ferric sulfate or ferric chloride or a combination of at least two thereof.
Preferably, the phosphorus source comprises any one of, or a combination of at least two of, phosphoric acid, ammonium phosphate, or sodium phosphate.
Preferably, the solvent comprises any one of water, ethanol or acetonitrile, or a combination of at least two thereof.
Preferably, the temperature of the hydrothermal reaction in step (1) is 150 to 180 ℃, for example: 150 ℃, 155 ℃, 160 ℃, 170 ℃ or 180 ℃ and the like.
Preferably, the pressure of the hydrothermal reaction is 0.6 to 0.8Mpa, for example: 0.6MPa, 0.62MPa, 0.65MPa, 0.7MPa, 0.75MPa or 0.8MPa.
The preparation of the lithium iron phosphate crystal is carried out by a hydrothermal synthesis process, and water or an organic solvent is used as a carrier and is carried out in an ideal environment of high-pressure heat insulation. The hydrothermal method greatly reduces the reaction energy consumption, in addition, effectively avoids side reactions caused by high temperature and oxidation, and can obtain crystals with specific valence and special configuration.
Preferably, the hydrothermal reaction is carried out for a time of 1 to 3 hours, for example: 1h, 1.5h, 2h, 2.5h or 3h and the like.
Preferably, the milling treatment of step (2) comprises ball milling.
Preferably, the D50 of the lithium iron phosphate particles having the second particle size in step (2) is 0.79 to 0.83 μm, for example: 0.79 μm, 0.8 μm, 0.81 μm, 0.82 μm, 0.83 μm, or the like.
The lithium iron phosphate particles with the second particle size have a smaller particle size distribution range, and the compaction of the material can be improved by strictly controlling the particle size distribution of the lithium iron phosphate particles with the second particle size, so that the balance between high energy density and good electrical property is achieved.
Preferably, in the step (3), the mass ratio of the first-particle-size lithium iron phosphate particles to the second-particle-size lithium iron phosphate particles is (4-6) to (6-4), for example: 4.
Preferably, the mixing time in step (3) is 0.5 to 1.5h, for example: 0.5h, 0.8h, 1h, 1.2h or 1.5h and the like.
In a second aspect, the present invention provides a lithium iron phosphate positive electrode material, which is prepared by the method according to the first aspect.
In a third aspect, the present invention provides a positive electrode plate, where the positive electrode plate includes the lithium iron phosphate positive electrode material according to the second aspect.
In a fourth aspect, the invention provides a lithium iron phosphate battery comprising the positive electrode plate according to the third aspect.
Compared with the prior art, the invention has the following beneficial effects:
(1) The lithium iron phosphate particles synthesized by a hydrothermal method have the advantages of small crystal grains, uniform phase, simplicity and convenience in operation and the like, and are easy to realize large-scale production; in addition, the conductivity of the material can be effectively improved, thereby improving the electrochemical performance.
(2) According to the invention, by doping lithium iron phosphate active materials with different specific particle sizes, on one hand, the specific surface area of lithium iron phosphate is increased, namely the carbon-coated content is increased, and the electronic conductivity is improved to a certain extent; on the other hand, li can be shortened + Transmission path of (2), increasing Li + The diffusion rate effectively reduces the diffusion impedance, improves the electrochemical dynamics, and obviously improves the low-temperature rate discharge performance of the lithium iron phosphate battery.
Drawings
Fig. 1 is an SEM image of lithium iron phosphate particles having a first particle size in example 1.
Fig. 2 is an SEM image of lithium iron phosphate particles having a second particle size in example 1.
Detailed Description
The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.
Example 1
The embodiment provides a lithium iron phosphate anode material, and a preparation method of the lithium iron phosphate anode material comprises the following steps:
(1) Mixing lithium hydroxide, ferrous chloride, ammonium phosphate and ethanol, and carrying out hydrothermal reaction for 2 hours at 160 ℃ and under the pressure of 0.7Mpa to obtain a lithium iron phosphate crystal;
(2) Grinding the lithium iron phosphate crystal obtained in the step (1), and sieving to obtain lithium iron phosphate particles with a first particle size and a second particle size, wherein D50 is 1.04 μm, D50 is 0.81 μm, and D90-D10=7.11, the SEM image of the lithium iron phosphate particles with the first particle size is shown in figure 1, and the SEM image of the lithium iron phosphate particles with the second particle size is shown in figure 2;
(3) And (3) mixing the lithium iron phosphate particles with the first particle size and the lithium iron phosphate particles with the second particle size obtained in the step (2) according to a mass ratio of 1.
Example 2
The embodiment provides a lithium iron phosphate anode material, and a preparation method of the lithium iron phosphate anode material comprises the following steps:
(1) Mixing lithium hydroxide, ferrous chloride, ammonium phosphate and ethanol, and carrying out hydrothermal reaction at 165 ℃ and under the pressure of 0.75Mpa for 2.2h to obtain a lithium iron phosphate crystal;
(2) Grinding the lithium iron phosphate crystal obtained in the step (1), and sieving to obtain lithium iron phosphate particles with a first particle size and D50 of 1.05 microns and lithium iron phosphate particles with a second particle size, wherein the D50 of the lithium iron phosphate particles is 0.80 microns and D90-D10= 7.12;
(3) And (3) mixing the lithium iron phosphate particles with the first particle size and the lithium iron phosphate particles with the second particle size obtained in the step (2) according to a mass ratio of 1.
Example 3
This example is different from example 1 only in that the pressure of the hydrothermal reaction in step (1) is 0.5MPa, and other conditions and parameters are exactly the same as those in example 1.
Example 4
This example is different from example 1 only in that the pressure of the hydrothermal reaction in step (1) is 1MPa, and other conditions and parameters are exactly the same as those in example 1.
Example 5
The present example is different from example 1 only in that the mass ratio of the lithium iron phosphate particles having the first particle size to the lithium iron phosphate particles having the second particle size is 3.
Example 6
The present embodiment is different from embodiment 1 only in that the mass ratio of the first-particle-size lithium iron phosphate particles to the second-particle-size lithium iron phosphate particles is 7, and other conditions and parameters are completely the same as those in embodiment 1.
Comparative example 1
The comparative example is different from example 1 only in that only the lithium iron phosphate particles having the first particle size are used as the positive electrode active material, and the other conditions and parameters are exactly the same as those of example 1.
Comparative example 2
The comparative example is different from example 1 only in that only the lithium iron phosphate particles having the second particle size are used as the positive electrode active material, and the other conditions and parameters are exactly the same as those of example 1.
Comparative example 3
The comparative example is different from example 1 only in that the D50 of the lithium iron phosphate particles having the first particle size is 1 μm, and the other conditions and parameters are exactly the same as those of example 1.
Comparative example 4
The comparative example is different from example 1 only in that the D50 of the lithium iron phosphate particles having the first particle size is 1.08 μm, and the other conditions and parameters are exactly the same as those of example 1.
Comparative example 5
The comparative example is different from example 1 only in that the D50 of the lithium iron phosphate particles having the second particle size is 0.75 μm, and the other conditions and parameters are exactly the same as those in example 1.
Comparative example 6
The comparative example is different from example 1 only in that the D50 of the lithium iron phosphate particles having the second particle size is 0.85 μm, and the other conditions and parameters are exactly the same as those in example 1.
Comparative example 7
The comparative example is different from example 1 only in that a lithium iron phosphate material is prepared by a conventional method, and other conditions and parameters are completely the same as those of example 1.
And (3) performance testing:
the lithium iron phosphate positive active materials obtained in examples 1 to 6 and comparative examples 1 to 7 were prepared into positive electrode sheets,corresponding graphite negative pole piece, 12 mu M PP + PE diaphragm and 1.0M LiPF 6 The battery is characterized in that EC + EMC electrolyte is collocated, a diaphragm is positioned between a positive electrode and a negative electrode, then a naked battery core is obtained by winding or laminating, the naked battery core is arranged in an outer packaging aluminum plastic film or an aluminum shell to be assembled into a battery core, the electrolyte is injected into the dried battery core, and the lithium ion battery is obtained by aging, formation, shaping, packaging and other processes.
The prepared lithium ion battery is subjected to low-temperature different-rate discharge tests, and the test method comprises the following steps:
(1) Charging the battery to 3.65V at a constant current and a constant voltage of 0.5C and stopping current of 0.05C at normal temperature, then discharging to 2.5V at a constant current of 0.5C, circulating for 3 circles, calibrating the normal-temperature discharge capacity Q1 and the energy E1, and finally fully charging at a constant current and a constant voltage at normal temperature;
(2) Placing the battery at-10 ℃, standing for 2h, discharging at 0.1 ℃, and recording the discharge capacity Q2 and the energy E2 under the temperature multiplying power condition;
(3) Activating the battery according to the step (1) and finishing the full-charge process step;
(4) Standing at-10 deg.C for 2h, discharging at 0.33C, and recording discharge capacity Q3 and energy E3 under the temperature multiplying power condition;
(5) The measurement at-20 ℃ @0.1C and 0.33C can also be carried out by analogy with the above steps;
(6) Calculating the discharge capacity ratio and energy ratio at-10 ℃ and 0.1C, such as: the calculation formula of the discharge capacity ratio is Q2/Q1 x 100 and the energy ratio E2/E1 x 100 at-20 ℃ and 0.1C, and the test results are shown in Table 1:
TABLE 1
As can be seen from Table 1, the lithium iron phosphate positive electrode material of the present invention can be used in the battery of examples 1 to 6, wherein the energy ratio at 0.1C-10 ℃ of the battery can be 75.85% or more, the energy ratio at 0.33C-10 ℃ can be 59.36% or more, the energy ratio at 0.1C-20 ℃ can be 56.29% or more, the energy ratio at 0.33C 20 ℃ can be 41.56% or more, the capacity ratio at 0.1C-10 ℃ can be 80.48% or more, the capacity ratio at 0.33C-10 ℃ can be 65.91% or more, the capacity ratio at 0.1C-20 ℃ can be 64.29% or more, and the capacity ratio at 0.33C 20 ℃ can be 47.58% or more.
Compared with the embodiment 1 and the embodiment 3-4, the hydrothermal reaction pressure affects the performance of the prepared lithium iron phosphate material, the lithium iron phosphate anode material with good effect can be prepared by controlling the pressure to be 0.6-0.8 Mpa, and if the pressure is too high, part of LiFePO is generated 4 Will decompose to form hetero-phase Li 3 PO 4 (ii) a If the pressure is too low, liFePO 4 The nucleation and growth process is an uneven nucleation process, and the target grain diameter and morphology cannot be obtained.
Compared with the examples 5 to 6, the mass ratio of the first-particle-size lithium iron phosphate particles to the second-particle-size lithium iron phosphate particles affects the performance of the prepared cathode material, and the mass ratio of the first-particle-size lithium iron phosphate particles to the second-particle-size lithium iron phosphate particles is controlled to be (4-6) to (6-4), so that the prepared lithium iron phosphate cathode material has good performance, and if the proportion of the first-particle-size lithium iron phosphate particles is too high, the Li content is too high + The transmission path is lengthened, the diffusion impedance is increased, and the low-temperature discharge performance is weakened; if the proportion of the first-particle-size lithium iron phosphate particles is too small, the low-temperature performance is improved to a small extent, but the limit compaction is reduced, and the energy density of the battery cell is reduced.
Compared with the comparative examples 1 and 1-2, the low-temperature performance of the material can be obviously improved by adopting the first-particle-size lithium iron phosphate particles and the second-particle-size lithium iron phosphate particles to prepare the active material.
As can be seen from comparison between example 1 and comparative examples 3 to 6, the D50 of the lithium iron phosphate particles with the first particle size should be controlled to be 1.02 to 1.06 μm, and the D50 of the lithium iron phosphate particles with the second particle size should be controlled to be 0.79 to 0.83 μm, and if the D50 of the lithium iron phosphate particles with the second particle size exceeds this range, the performance of the obtained lithium iron phosphate cathode material is significantly reduced.
Compared with the comparative example 7, the preparation method of the lithium iron phosphate crystal utilizes a hydrothermal synthesis process to prepare the lithium iron phosphate crystal, and utilizes water or an organic solvent as a carrier to perform the preparation under an ideal environment of high pressure and heat insulation. The hydrothermal method greatly reduces the reaction energy consumption, in addition, effectively avoids side reaction caused by high temperature and oxidation, and can obtain crystals with specific valence state and special configuration.
The applicant declares that the above description is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are within the scope and disclosure of the present invention.
Claims (14)
1. The preparation method of the lithium iron phosphate cathode material is characterized by comprising the following steps of:
(1) Mixing a lithium source, an iron source, a phosphorus source and a solvent, and carrying out hydrothermal reaction to obtain a lithium iron phosphate crystal;
(2) Grinding the lithium iron phosphate crystal obtained in the step (1), and sieving to obtain lithium iron phosphate particles with a first particle size and lithium iron phosphate particles with a second particle size;
(3) Mixing the lithium iron phosphate particles with the first particle size and the lithium iron phosphate particles with the second particle size obtained in the step (2) to obtain a lithium iron phosphate positive electrode material;
the D50 of the first-particle-size lithium iron phosphate particles is 1.02-1.06 mu m, the D50 difference value of the first-particle-size lithium iron phosphate particles and the second-particle-size lithium iron phosphate particles is 0.19-0.27 mu m, the D90 difference value of the second-particle-size lithium iron phosphate particles is 7.05-7.15 mu m, and the pressure of the hydrothermal reaction is 0.6-0.8 Mpa.
2. The method of claim 1, wherein the lithium source of step (1) comprises lithium hydroxide and/or lithium carbonate.
3. The method of claim 1, wherein the iron source comprises any one of ferrous sulfate, ferrous chloride, ferric sulfate, or ferric chloride, or a combination of at least two thereof.
4. The method of claim 1, wherein the phosphorus source comprises any one of phosphoric acid, ammonium phosphate, or sodium phosphate, or a combination of at least two thereof.
5. The method of claim 1, wherein the solvent comprises any one of water, ethanol, or acetonitrile, or a combination of at least two thereof.
6. The method according to claim 1, wherein the hydrothermal reaction in the step (1) is carried out at a temperature of 150 to 180 ℃.
7. The method according to claim 1, wherein the hydrothermal reaction is carried out for 1 to 3 hours.
8. The method of claim 1, wherein the milling process of step (2) comprises ball milling.
9. The preparation method according to claim 1, wherein the D50 of the lithium iron phosphate particles having the second particle size in step (2) is 0.79 to 0.83 μm.
10. The preparation method according to claim 1, wherein the mass ratio of the first-particle-size lithium iron phosphate particles to the second-particle-size lithium iron phosphate particles in step (3) is (4-6) to (6-4).
11. The method of claim 1, wherein the mixing in step (3) is carried out for a time of 0.5 to 1.5 hours.
12. A lithium iron phosphate positive electrode material, characterized in that it is produced by the method of any one of claims 1 to 11.
13. A positive electrode tab, characterized in that it comprises the lithium iron phosphate positive electrode material according to claim 12.
14. A lithium iron phosphate battery comprising the positive electrode tab of claim 13.
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