CN116924375A - Lithium iron phosphate positive electrode material, preparation method and application - Google Patents
Lithium iron phosphate positive electrode material, preparation method and application Download PDFInfo
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- CN116924375A CN116924375A CN202310934349.1A CN202310934349A CN116924375A CN 116924375 A CN116924375 A CN 116924375A CN 202310934349 A CN202310934349 A CN 202310934349A CN 116924375 A CN116924375 A CN 116924375A
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- iron phosphate
- lithium iron
- positive electrode
- electrode material
- lithium
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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 82
- 239000007774 positive electrode material Substances 0.000 title claims abstract description 41
- 238000002360 preparation method Methods 0.000 title claims abstract description 30
- 238000005245 sintering Methods 0.000 claims abstract description 69
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 40
- 239000002243 precursor Substances 0.000 claims abstract description 37
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 31
- JMANVNJQNLATNU-UHFFFAOYSA-N oxalonitrile Chemical compound N#CC#N JMANVNJQNLATNU-UHFFFAOYSA-N 0.000 claims abstract description 31
- 239000010405 anode material Substances 0.000 claims abstract description 21
- 239000000203 mixture Substances 0.000 claims abstract description 21
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 15
- 239000002245 particle Substances 0.000 claims abstract description 13
- 239000011247 coating layer Substances 0.000 claims abstract description 11
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 claims abstract description 9
- 229910052698 phosphorus Inorganic materials 0.000 claims abstract description 9
- 239000011574 phosphorus Substances 0.000 claims abstract description 9
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims abstract description 8
- 229910052744 lithium Inorganic materials 0.000 claims abstract description 8
- 229910052742 iron Inorganic materials 0.000 claims abstract description 6
- 230000001681 protective effect Effects 0.000 claims abstract description 4
- 238000009766 low-temperature sintering Methods 0.000 claims description 35
- 238000001816 cooling Methods 0.000 claims description 24
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 22
- 238000000498 ball milling Methods 0.000 claims description 22
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 claims description 16
- 238000001354 calcination Methods 0.000 claims description 16
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical group CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 15
- 238000001035 drying Methods 0.000 claims description 13
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 claims description 12
- 238000000034 method Methods 0.000 claims description 11
- 229910052757 nitrogen Inorganic materials 0.000 claims description 11
- 229920000877 Melamine resin Polymers 0.000 claims description 9
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 claims description 9
- JDSHMPZPIAZGSV-UHFFFAOYSA-N melamine Chemical compound NC1=NC(N)=NC(N)=N1 JDSHMPZPIAZGSV-UHFFFAOYSA-N 0.000 claims description 9
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Chemical compound NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 claims description 8
- 239000004202 carbamide Substances 0.000 claims description 8
- -1 methyl titanate Chemical compound 0.000 claims description 6
- 229920001223 polyethylene glycol Polymers 0.000 claims description 6
- 239000002904 solvent Substances 0.000 claims description 6
- 239000010936 titanium Substances 0.000 claims description 6
- 229910052719 titanium Inorganic materials 0.000 claims description 6
- 239000004408 titanium dioxide Substances 0.000 claims description 6
- 239000002202 Polyethylene glycol Substances 0.000 claims description 5
- YHWCPXVTRSHPNY-UHFFFAOYSA-N butan-1-olate;titanium(4+) Chemical compound [Ti+4].CCCC[O-].CCCC[O-].CCCC[O-].CCCC[O-] YHWCPXVTRSHPNY-UHFFFAOYSA-N 0.000 claims description 3
- 239000007789 gas Substances 0.000 claims description 3
- JMXKSZRRTHPKDL-UHFFFAOYSA-N titanium ethoxide Chemical compound [Ti+4].CC[O-].CC[O-].CC[O-].CC[O-] JMXKSZRRTHPKDL-UHFFFAOYSA-N 0.000 claims description 3
- 238000004519 manufacturing process Methods 0.000 claims 1
- 238000005056 compaction Methods 0.000 abstract description 4
- 238000010438 heat treatment Methods 0.000 description 33
- 238000002156 mixing Methods 0.000 description 18
- 239000000843 powder Substances 0.000 description 13
- XGZVUEUWXADBQD-UHFFFAOYSA-L lithium carbonate Chemical compound [Li+].[Li+].[O-]C([O-])=O XGZVUEUWXADBQD-UHFFFAOYSA-L 0.000 description 12
- 229910052808 lithium carbonate Inorganic materials 0.000 description 12
- LFVGISIMTYGQHF-UHFFFAOYSA-N ammonium dihydrogen phosphate Chemical compound [NH4+].OP(O)([O-])=O LFVGISIMTYGQHF-UHFFFAOYSA-N 0.000 description 11
- 229940062993 ferrous oxalate Drugs 0.000 description 11
- OWZIYWAUNZMLRT-UHFFFAOYSA-L iron(2+);oxalate Chemical compound [Fe+2].[O-]C(=O)C([O-])=O OWZIYWAUNZMLRT-UHFFFAOYSA-L 0.000 description 11
- 229910000387 ammonium dihydrogen phosphate Inorganic materials 0.000 description 10
- 229910001416 lithium ion Inorganic materials 0.000 description 10
- 235000019837 monoammonium phosphate Nutrition 0.000 description 10
- 239000012299 nitrogen atmosphere Substances 0.000 description 10
- 239000000463 material Substances 0.000 description 9
- 239000006012 monoammonium phosphate Substances 0.000 description 8
- 238000003756 stirring Methods 0.000 description 8
- 238000009210 therapy by ultrasound Methods 0.000 description 8
- 229920002565 Polyethylene Glycol 400 Polymers 0.000 description 7
- 230000000052 comparative effect Effects 0.000 description 7
- 239000010439 graphite Substances 0.000 description 7
- 229910002804 graphite Inorganic materials 0.000 description 7
- JLFNLZLINWHATN-UHFFFAOYSA-N pentaethylene glycol Chemical compound OCCOCCOCCOCCOCCO JLFNLZLINWHATN-UHFFFAOYSA-N 0.000 description 7
- 229920002593 Polyethylene Glycol 800 Polymers 0.000 description 5
- 230000009286 beneficial effect Effects 0.000 description 5
- 239000002135 nanosheet Substances 0.000 description 5
- WQZGKKKJIJFFOK-GASJEMHNSA-N Glucose Natural products OC[C@H]1OC(O)[C@H](O)[C@@H](O)[C@@H]1O WQZGKKKJIJFFOK-GASJEMHNSA-N 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 239000008103 glucose Substances 0.000 description 4
- 239000010410 layer Substances 0.000 description 4
- 239000002105 nanoparticle Substances 0.000 description 4
- 238000004321 preservation Methods 0.000 description 4
- LYCAIKOWRPUZTN-UHFFFAOYSA-N Ethylene glycol Chemical group OCCO LYCAIKOWRPUZTN-UHFFFAOYSA-N 0.000 description 3
- 229910010707 LiFePO 4 Inorganic materials 0.000 description 3
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 description 3
- 238000005054 agglomeration Methods 0.000 description 3
- 230000002776 aggregation Effects 0.000 description 3
- 239000011248 coating agent Substances 0.000 description 3
- 238000000576 coating method Methods 0.000 description 3
- 230000001965 increasing effect Effects 0.000 description 3
- 239000007787 solid Substances 0.000 description 3
- 239000005955 Ferric phosphate Substances 0.000 description 2
- 229910012851 LiCoO 2 Inorganic materials 0.000 description 2
- 229910015643 LiMn 2 O 4 Inorganic materials 0.000 description 2
- 229910013290 LiNiO 2 Inorganic materials 0.000 description 2
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 2
- WQZGKKKJIJFFOK-VFUOTHLCSA-N beta-D-glucose Chemical compound OC[C@H]1O[C@@H](O)[C@H](O)[C@@H](O)[C@@H]1O WQZGKKKJIJFFOK-VFUOTHLCSA-N 0.000 description 2
- 239000003575 carbonaceous material Substances 0.000 description 2
- 239000010406 cathode material Substances 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 229940032958 ferric phosphate Drugs 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 238000009830 intercalation Methods 0.000 description 2
- 230000002687 intercalation Effects 0.000 description 2
- WBJZTOZJJYAKHQ-UHFFFAOYSA-K iron(3+) phosphate Chemical compound [Fe+3].[O-]P([O-])([O-])=O WBJZTOZJJYAKHQ-UHFFFAOYSA-K 0.000 description 2
- VCJMYUPGQJHHFU-UHFFFAOYSA-N iron(3+);trinitrate Chemical compound [Fe+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O VCJMYUPGQJHHFU-UHFFFAOYSA-N 0.000 description 2
- 229910000399 iron(III) phosphate Inorganic materials 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 229920001030 Polyethylene Glycol 4000 Polymers 0.000 description 1
- 238000002441 X-ray diffraction Methods 0.000 description 1
- GMLCDIVXKUWJFO-UHFFFAOYSA-N [C].C1=CC=NC=C1 Chemical compound [C].C1=CC=NC=C1 GMLCDIVXKUWJFO-UHFFFAOYSA-N 0.000 description 1
- CKUAXEQHGKSLHN-UHFFFAOYSA-N [C].[N] Chemical compound [C].[N] CKUAXEQHGKSLHN-UHFFFAOYSA-N 0.000 description 1
- 229910000147 aluminium phosphate Inorganic materials 0.000 description 1
- 238000012512 characterization method Methods 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 239000003638 chemical reducing agent Substances 0.000 description 1
- 238000005253 cladding Methods 0.000 description 1
- 230000002860 competitive effect Effects 0.000 description 1
- 239000012141 concentrate Substances 0.000 description 1
- 229920001940 conductive polymer Polymers 0.000 description 1
- MNNHAPBLZZVQHP-UHFFFAOYSA-N diammonium hydrogen phosphate Chemical compound [NH4+].[NH4+].OP([O-])([O-])=O MNNHAPBLZZVQHP-UHFFFAOYSA-N 0.000 description 1
- 229910000388 diammonium phosphate Inorganic materials 0.000 description 1
- 235000019838 diammonium phosphate Nutrition 0.000 description 1
- MTHSVFCYNBDYFN-UHFFFAOYSA-N diethylene glycol Chemical compound OCCOCCO MTHSVFCYNBDYFN-UHFFFAOYSA-N 0.000 description 1
- YNQRWVCLAIUHHI-UHFFFAOYSA-L dilithium;oxalate Chemical compound [Li+].[Li+].[O-]C(=O)C([O-])=O YNQRWVCLAIUHHI-UHFFFAOYSA-L 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 235000019441 ethanol Nutrition 0.000 description 1
- 229960002413 ferric citrate Drugs 0.000 description 1
- 125000002791 glucosyl group Chemical group C1([C@H](O)[C@@H](O)[C@H](O)[C@H](O1)CO)* 0.000 description 1
- NPFOYSMITVOQOS-UHFFFAOYSA-K iron(III) citrate Chemical compound [Fe+3].[O-]C(=O)CC(O)(CC([O-])=O)C([O-])=O NPFOYSMITVOQOS-UHFFFAOYSA-K 0.000 description 1
- XIXADJRWDQXREU-UHFFFAOYSA-M lithium acetate Chemical compound [Li+].CC([O-])=O XIXADJRWDQXREU-UHFFFAOYSA-M 0.000 description 1
- 229910021645 metal ion Inorganic materials 0.000 description 1
- 229910017464 nitrogen compound Inorganic materials 0.000 description 1
- 150000002830 nitrogen compounds Chemical class 0.000 description 1
- 230000000630 rising effect Effects 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 230000002195 synergetic effect Effects 0.000 description 1
- 238000001291 vacuum drying Methods 0.000 description 1
Classifications
-
- 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
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
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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
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
- C01B32/05—Preparation or purification of carbon not covered by groups C01B32/15, C01B32/20, C01B32/25, C01B32/30
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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
- 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
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
- H01M4/625—Carbon or graphite
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- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2002/00—Crystal-structural characteristics
- C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
- C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
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- 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
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- 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
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- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/40—Electric properties
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Abstract
The invention discloses a lithium iron phosphate positive electrode material, a preparation method and application thereof, wherein the preparation method of the lithium iron phosphate positive electrode material comprises the following steps: sintering the lithium iron phosphate precursor under protective gas to obtain a lithium iron phosphate anode material; the lithium iron phosphate precursor is mainly prepared from a first mixture, wherein the first mixture comprises an iron source, a phosphorus source, a lithium source, a carbon source and flaky graphitized carbon nitride. The flaky graphitized carbon nitride is added in the precursor preparation step, so that a uniform coating layer is formed on the surface of the lithium iron phosphate, and the prepared lithium iron phosphate positive electrode material has small particle size, high compaction and higher charge-discharge specific capacity.
Description
Technical Field
The invention relates to the technical field of lithium ion battery anode materials, in particular to a lithium iron phosphate anode material, a preparation method and application.
Background
As an important component of lithium ion batteries, the positive electrode material of lithium ion batteries plays an important role in the performance of lithium batteries. Currently, the most studied positive electrode material is LiCoO 2 、LiNiO 2 、LiMn 2 O 4 、LiFePO 4 (lithium iron phosphate), and the like. Wherein the lithium iron phosphate positive electrode material concentrates LiCoO 2 、LiNiO 2 、LiMn 2 O 4 The advantages of the materials are high in structural stability, good in safety performance, moderate in working voltage, good in platform characteristic, large in theoretical capacity and the like, and the materials gradually become hot spots for competitive research of battery workers.
LiFePO 4 Has the advantages of high theoretical capacity (170 mAh/g), low cost, environmental protection, high thermal stability and the like. However, pure phase LiFePO 4 Low electron conductivity (10) -9 ～10 -10 S/cm) and lower lithium ion diffusivity significantly limit its application. In order to obtain better electrochemical performance, researchers have made a great deal of research including reducing material particles, doping metal ions, surface coating conductive polymers, carbon layer particles, and the like. In recent years, nitrogen doped (N doped) carbon cladding methods have attracted considerable interest to researchers. It has been reported that several different nitrogen carbon species can be obtained after N doping, depending on their position in the carbon backbone, such as pyridine carbon, is considered to be the most suitable form of nitrogen compound for increasing lithium storage capacity. However, uniform N-doped carbon is obtained on the surface of the material by using a solid nitrogen source and a carbon sourceThe layers are quite difficult. The invention provides a simple method for coating a uniform N-doped carbon layer on the surface of lithium iron phosphate, and has better effect.
In view of this, the present invention has been made.
Disclosure of Invention
The invention aims to provide a lithium iron phosphate positive electrode material, a preparation method and application thereof.
The invention is realized in the following way:
in a first aspect, the present invention provides a method for preparing a lithium iron phosphate positive electrode material, comprising:
sintering the lithium iron phosphate precursor under protective gas to obtain a lithium iron phosphate anode material; the lithium iron phosphate precursor is mainly prepared from a first mixture, wherein the first mixture comprises an iron source, a phosphorus source, a lithium source, a carbon source and flaky graphitized carbon nitride.
In some embodiments, the graphitized carbon nitride flakes are predominantly obtained by calcination of urea or melamine;
preferably, the temperature of the calcination is 500-580 ℃, and the time of the calcination is 4-6 h.
In some embodiments, the carbon source is polyethylene glycol;
preferably, the mass ratio of the carbon source to the graphitized carbon nitride flake is (3 to 5): 1.
in some embodiments, the preparation step of the lithium iron phosphate precursor comprises: dispersing, ball milling and drying the components of the first mixture in a solvent;
preferably, the solvent is absolute ethanol;
preferably, the rotation speed of the ball milling is 300rpm-480rpm, and the time of the ball milling is 8h-12h;
in some embodiments, the first mixture further comprises a component comprising a doping element;
preferably, the doping element-containing component includes a titanium source including at least one of titanium dioxide, methyl titanate, ethyl titanate, n-propyl titanate, and tetrabutyl titanate;
preferably, the molar ratio of the lithium element, the phosphorus element, the iron element and the titanium element in the first mixture is (0.97 to 1): 1: (1-x): x is more than 0.1 and is more than or equal to 0;
preferably, the molar ratio of the lithium element to the nitrogen element in the first mixture is (3 to 5): 1.
in some embodiments, the sintering comprises a low temperature sintering followed by a high temperature sintering.
In some embodiments, the low temperature sintering is at a temperature of 1 ℃/min to 5 ℃/min to 350 ℃ to 450 ℃ for a low temperature sintering time of 0h to 4h.
In some embodiments, the high temperature sintering is performed at a temperature of 1 ℃/min to 5 ℃/min to 700 ℃ to 740 ℃ for a high temperature sintering time of 9h to 11h; then cooling to 20-30 ℃ at the speed of 4-6 ℃ per minute.
In a second aspect, the present invention provides a lithium iron phosphate positive electrode material obtained by the preparation method according to any one of the foregoing embodiments, including a core and a coating layer, where the median particle size of the lithium iron phosphate positive electrode material is d50=1.5 to 2.5 μm, and the thickness of the coating layer is 50 to 100nm.
In a third aspect, the present invention provides a battery comprising a lithium iron phosphate positive electrode material obtained by the preparation method according to any one of the foregoing embodiments.
The invention has the following beneficial effects:
compared with the prior art that the flaky graphitized carbon nitride is mixed with the lithium iron phosphate powder, the preparation method is more beneficial to forming a uniform coating layer on the surface of the lithium iron phosphate. The coating layer can form an extrinsic and disordered carbon structure, thereby improving the intercalation performance of lithium ions; the growth and agglomeration of the lithium iron phosphate nano particles are effectively inhibited, so that smaller lithium iron phosphate nano particles are generated, and the solid diffusion path of lithium ions is shortened; in addition, nitrogen doping can improve the electrochemical activity of the carbon material, and the active sites are induced to absorb lithium ions so as to improve the material capacity.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the embodiments will be briefly described below, it being understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and other related drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a Scanning Electron Microscope (SEM) image of the finished lithium iron phosphate cathode material prepared in this example 1.
Fig. 2 is an XRD pattern of the finished lithium iron phosphate cathode material prepared in this example 1.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below. The specific conditions are not noted in the examples and are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.
One embodiment of the present invention provides a method for preparing a lithium iron phosphate positive electrode material, comprising:
sintering the lithium iron phosphate precursor under protective gas to obtain a lithium iron phosphate anode material; the lithium iron phosphate precursor is mainly prepared from a first mixture, wherein the first mixture comprises an iron source, a phosphorus source, a lithium source, a carbon source and flaky graphitized carbon nitride.
Compared with the prior art that the flaky graphitized carbon nitride is mixed with the lithium iron phosphate powder, the preparation method is more beneficial to forming a uniform coating layer on the surface of the lithium iron phosphate. The coating layer can form an extrinsic and disordered carbon structure, thereby improving the intercalation performance of lithium ions; the growth and agglomeration of the lithium iron phosphate nano particles are effectively inhibited, so that smaller lithium iron phosphate nano particles are generated, and the solid diffusion path of lithium ions is shortened; in addition, nitrogen doping can improve the electrochemical activity of the carbon material, and the active sites are induced to absorb lithium ions so as to improve the material capacity.
In some embodiments, the graphitized carbon nitride flakes are predominantly obtained by calcination of urea or melamine.
In some embodiments, the temperature of the calcination is 500 ℃ to 580 ℃, in particular, can be 500 ℃, 520 ℃, 540 ℃, 560 ℃,580 ℃, or any value between 500 ℃ and 580 ℃; the calcination time is 4h-6h, and in particular, may be any value between 4h, 4.5h, 5h, 5.5h, 6h, or 4h-6h.
The flaky graphitized carbon nitride can be obtained after urea or melamine is calcined, and compared with other structures, the stability of the positive electrode material is improved more favorably.
In some embodiments, the lithium source comprises one or more of lithium carbonate, lithium oxalate, lithium hydroxide, lithium acetate; the phosphorus source comprises one or more of phosphoric acid, diammonium hydrogen phosphate and monoammonium dihydrogen phosphate; the iron source comprises one or more of ferric phosphate, ferrous oxalate, ferric nitrate and ferric citrate.
In some embodiments, the carbon source is polyethylene glycol, including but not limited to PEG400, PEG800, PEG4000, and the like.
In some embodiments, the mass ratio of the carbon source to the graphitized carbon nitride flakes is (3-5): 1, in particular, can be 3: 1. 3.5: 1. 4: 1. 4.5: 1. 5:1 or (3 to 5): 1.
Compared with other carbon sources, the N-doped carbon coating prepared by taking polyethylene glycol as the carbon source is more beneficial to enhancing the electron conduction performance of the positive electrode material, in addition, the polyethylene glycol can effectively reduce the surface tension of particles in the LFP preparation process, and the agglomeration of the product is improved, so that the LFP with small and uniform particle size is obtained.
In some embodiments, the preparation step of the lithium iron phosphate precursor comprises: dispersing, ball milling and drying the components of the first mixture in a solvent;
in general, in order to make the material disperse more uniformly, the carbon source and the graphitized carbon nitride flakes are dispersed in absolute ethyl alcohol, specifically, the dispersion effect can be improved by adopting ultrasonic waves, and the ultrasonic time is 3-5 hours.
In some embodiments, the solvent is absolute ethanol;
in some embodiments, the ball milling speed is 300rpm-480rpm, and in particular, may be 300rpm, 350rpm, 400rpm, 450rpm, 480rpm, or any value between 300rpm-480 rpm; the ball milling time is 8h-12h, and specifically, may be 8h, 9h, 10h, 11h, 12h or any value between 8h-12h.
In some embodiments, the mixture further includes a component comprising a doping element, the doping of titanium being advantageous in obtaining a positive electrode material having a small particle size, a high compaction and a high capacity.
The component containing the doping element comprises a titanium source, wherein the titanium source comprises at least one of titanium dioxide, methyl titanate, ethyl titanate, n-propyl titanate and tetrabutyl titanate;
the molar ratio of the lithium element, the phosphorus element, the iron element and the titanium element in the first mixture is (0.97-1): 1: (1-x): x is 0.1> x is not less than 0, specifically, x can be any value between 0, 0.01, 0.04, 0.07, 0.1 or 0-0.1.
Preferably, the molar ratio of the lithium element to the nitrogen element in the first mixture is (3 to 5): 1.
the invention also provides a preparation method of the titanium-doped lithium iron phosphate anode material, which comprises the steps of performing ball milling treatment on a mixed material formed by a lithium source, an iron source, a phosphorus source, a titanium source and the prepared nitrogen-doped carbon nano sheet, then performing sintering treatment on a powdery precursor obtained by ball milling, and obtaining the titanium-doped lithium iron phosphate anode material uniformly coated with a nitrogen-doped carbon layer through the synergistic effect of the steps. The preparation method has simple steps, and the prepared lithium iron phosphate positive electrode material has high compaction density, small particle size, good conductivity and high stability.
The nitrogen doped carbon content is too low, so that the product performance is not obviously improved, but the specific surface area is increased due to the too high content, and the electrochemical performance is influenced.
In some embodiments, the sintering comprises a low temperature sintering followed by a high temperature sintering.
In some embodiments, the low temperature sintering is at a temperature of 1 ℃/min-5 ℃/min to 350 ℃ to 450 ℃ for a low temperature sintering time of 0h-4h, specifically, the temperature rise rate may be any value between 1 ℃/min, 2 ℃/min, 3 ℃/min, 4 ℃/min, 5 ℃/min, or 1 ℃/min-5 ℃/min; the low temperature sintering temperature may be 350 ℃, 370 ℃, 390 ℃, 410 ℃, 430 ℃, 450 ℃, or any value between 350 ℃ and 450 ℃; the low temperature sintering time may be any value between 0h, 1h, 2h, 3h, 4h, or 0h-4h. The temperature rising rate is low during low-temperature sintering, the low-temperature sintering time is enough to enable the anode material to form a core, the low-temperature sintering time is preferably 0h, and if the low-temperature sintering time is too long, the cost is increased.
In some embodiments, the high temperature sintering is performed at a temperature of 1 ℃/min to 5 ℃/min to 700 ℃ to 740 ℃ for a high temperature sintering time of 9h to 11h; then cooling to 20-30 ℃ at the speed of 4-6 ℃ per minute. The high temperature sintering further forms the positive electrode material into particles.
Specifically, the heating rate may be any value between 1 ℃/min, 2 ℃/min, 3 ℃/min, 4 ℃/min, 5 ℃/min, or 1 ℃/min-5 ℃/min; the high temperature sintering temperature may be 700 ℃, 710 ℃, 720 ℃, 730 ℃, 740 ℃, or any value between 700 ℃ and 740 ℃; the high-temperature sintering time can be 9h, 10h, 11h or any value between 9h and 11h; the cooling rate may be any value between 4 deg.C/min, 4.5 deg.C/min, 5 deg.C/min, 5.5 deg.C/min, 6 deg.C/min or 4 deg.C/min-6 deg.C/min.
In a second aspect, the present invention provides a lithium iron phosphate positive electrode material obtained by the preparation method according to any one of the foregoing embodiments, including a core and a coating layer, where the median particle size of the lithium iron phosphate positive electrode material is d50=1.5 to 2.5 μm, and the thickness of the coating layer is 50 to 100nm.
In a third aspect, the present invention provides a battery comprising a lithium iron phosphate positive electrode material obtained by the preparation method according to any one of the foregoing embodiments.
The features and capabilities of the present invention are described in further detail below in connection with the examples.
Example 1:
the preparation method of the nitrogen-doped carbon nano sheet coated lithium iron phosphate positive electrode material comprises the following steps:
(1) Placing 20g of urea into a crucible, and placing the crucible into a muffle furnace for calcining for 4 hours at 550 ℃ to obtain flaky graphitized carbon nitride;
(2) PEG400 and the carbon nitride of the flake graphite phase are taken according to the mass ratio of 3:1 adding absolute ethyl alcohol (100 ml), stirring and mixing, performing ultrasonic treatment for 4 hours, adding 7.39g of lithium carbonate, 35.98g of ferrous oxalate and 21.03g of monoammonium phosphate, uniformly mixing, performing ball milling for 12 hours at a rotating speed of 360rpm, and drying to obtain a powder precursor;
(3) Sintering the powdery precursor in a nitrogen atmosphere; wherein the sintering is classified into low-temperature sintering and high-temperature sintering; the low-temperature sintering is carried out by heating from room temperature to 450 ℃ at a heating rate of 1 ℃/min, and the low-temperature heat preservation time is 0h; the high-temperature sintering is carried out at a heating rate of 5 ℃/min from 450 ℃ to 700 ℃, and the high-temperature heat preservation time is 10h; then cooling from 700 ℃ to normal temperature at a cooling rate of 5 ℃/min to obtain the lithium iron phosphate positive electrode material, and preparing the lithium iron phosphate positive electrode material with high crystallinity and high purity by the method, wherein the characterization result is shown in figures 1 and 2.
Example 2:
the preparation method of the nitrogen-doped carbon nano sheet coated lithium iron phosphate positive electrode material comprises the following steps:
(1) Placing 20g of melamine in a crucible, and placing the crucible in a muffle furnace for calcining for 4 hours at 550 ℃ to obtain flaky graphitized carbon nitride;
(2) PEG800 and the carbon nitride of the flake graphite phase are taken according to the mass ratio of 4:1 adding absolute ethyl alcohol (100 ml), stirring and mixing, performing ultrasonic treatment for 4 hours, adding 7.39g of lithium carbonate, 35.98g of ferrous oxalate and 21.03g of monoammonium phosphate, uniformly mixing, performing ball milling for 12 hours at a rotating speed of 360rpm, and drying to obtain a powder precursor;
(3) Sintering the powdery precursor in a nitrogen atmosphere; wherein the sintering is classified into low-temperature sintering and high-temperature sintering; the low-temperature sintering is carried out by heating from room temperature to 450 ℃ at a heating rate of 1 ℃/min, and the low-temperature heat preservation time is 0h; the high-temperature sintering is carried out at a heating rate of 5 ℃/min from 450 ℃ to 700 ℃, and the high-temperature heat preservation time is 10h; and then cooling from 700 ℃ to normal temperature at a cooling rate of 5 ℃/min to obtain the lithium iron phosphate anode material.
Example 3:
(1) Placing 20g of urea into a crucible, and placing the crucible into a muffle furnace for calcining for 4 hours at 500 ℃ to obtain flaky graphitized carbon nitride;
(2) PEG800 and the carbon nitride of the flake graphite phase are taken according to the mass ratio of 3:1 adding absolute ethyl alcohol (100 ml), stirring and mixing, performing ultrasonic treatment for 4 hours, adding 7.39g of lithium carbonate, 35.08g of ferrous oxalate, 21.03g of monoammonium phosphate and 0.4g of titanium dioxide, uniformly mixing, performing ball milling for 12 hours at a rotating speed of 360rpm, and drying to obtain a powder precursor;
(3) Sintering the powdery precursor in a nitrogen atmosphere; wherein the sintering is classified into low-temperature sintering and high-temperature sintering; the low-temperature sintering is to heat from room temperature to 450 ℃ at a heating rate of 1 ℃/min, and sinter for 0h; high-temperature sintering, namely, heating from 450 ℃ to 700 ℃ at a heating rate of 5 ℃/min, and sintering for 10 hours; and then cooling from 700 ℃ to normal temperature at a cooling rate of 5 ℃/min to obtain the lithium iron phosphate anode material.
Example 4
(1) Placing 20g of melamine in a crucible, placing the crucible in a muffle furnace, and calcining at 500 ℃ for 4 hours to obtain flaky graphitized carbon nitride;
(2) PEG800 and the carbon nitride of the flake graphite phase are taken according to the mass ratio of 4:1 adding absolute ethyl alcohol (100 ml), stirring and mixing, performing ultrasonic treatment for 4 hours, adding 7.39g of lithium carbonate, 34.18g of ferrous oxalate, 21.03g of monoammonium phosphate and 0.8g of titanium dioxide, uniformly mixing, performing ball milling for 12 hours at a rotating speed of 360rpm, and drying to obtain a powder precursor;
(3) Sintering the powdery precursor in a nitrogen atmosphere; wherein the sintering is classified into low-temperature sintering and high-temperature sintering; the low-temperature sintering is to heat from room temperature to 450 ℃ at a heating rate of 1 ℃/min, and sinter for 0h; high-temperature sintering, namely, heating from 450 ℃ to 700 ℃ at a heating rate of 5 ℃/min, and sintering for 10 hours; and then cooling from 700 ℃ to normal temperature at a cooling rate of 5 ℃/min to obtain the lithium iron phosphate anode material.
Example 5:
(1) Placing 20g of melamine in a crucible, placing the crucible in a muffle furnace, and calcining at 500 ℃ for 4 hours to obtain flaky graphitized carbon nitride;
(2) PEG800 and the carbon nitride of the flake graphite phase are taken according to the mass ratio of 4:1 adding absolute ethyl alcohol (100 ml), stirring and mixing, performing ultrasonic treatment for 4 hours, adding 7.39g of lithium carbonate, 35.08g of ferrous oxalate, 21.03g of monoammonium phosphate and 0.4g of titanium dioxide, uniformly mixing, performing ball milling for 12 hours at a rotating speed of 360rpm, and drying to obtain a powder precursor;
(3) Sintering the powdery precursor in a nitrogen atmosphere; wherein the sintering is classified into low-temperature sintering and high-temperature sintering; the low-temperature sintering is to heat from room temperature to 360 ℃ at a heating rate of 5 ℃/min, and sintering is carried out for 4 hours; high-temperature sintering, namely, heating from 360 ℃ to 740 ℃ at a heating rate of 5 ℃/min, and sintering for 10 hours; and then cooling from 700 ℃ to normal temperature at a cooling rate of 5 ℃/min to obtain the lithium iron phosphate anode material.
Example 6
The preparation method of the nitrogen-doped carbon nano sheet coated lithium iron phosphate positive electrode material comprises the following steps:
(1) Taking 20g of urea in a crucible, putting the crucible in a muffle furnace, and calcining at 580 ℃ for 6 hours to obtain flaky graphitized carbon nitride;
(2) PEG400 and the carbon nitride of the flake graphite phase are taken according to the mass ratio of 5:1 adding absolute ethyl alcohol (100 ml), stirring and mixing, performing ultrasonic treatment for 4 hours, adding 7.39g of lithium carbonate, 35.98g of ferrous oxalate and 21.03g of monoammonium phosphate, uniformly mixing, performing ball milling for 8 hours at a rotation speed of 480rpm, and drying to obtain a powder precursor;
(3) Sintering the powdery precursor in a nitrogen atmosphere; wherein the sintering is classified into low-temperature sintering and high-temperature sintering; the low-temperature sintering is to heat from room temperature to 450 ℃ at a heating rate of 1 ℃/min, and sinter for 0h; high-temperature sintering, namely, heating the mixture from 450 ℃ to 700 ℃ at a heating rate of 1 ℃/min, and sintering for 11h; and then cooling from 700 ℃ to normal temperature at a cooling rate of 4 ℃/min to obtain the lithium iron phosphate anode material.
Example 7
The preparation method of the nitrogen-doped carbon nano sheet coated lithium iron phosphate positive electrode material comprises the following steps:
(1) Placing 20g of urea into a crucible, and placing the crucible into a muffle furnace for calcining for 4 hours at 550 ℃ to obtain flaky graphitized carbon nitride;
(2) PEG400 and the carbon nitride of the flake graphite phase are taken according to the mass ratio of 3:1 adding absolute ethyl alcohol (100 ml), stirring and mixing, performing ultrasonic treatment for 4 hours, adding 7.39g of lithium carbonate, 35.98g of ferrous oxalate and 21.03g of monoammonium phosphate, uniformly mixing, performing ball milling for 10 hours at a rotating speed of 300rpm, and drying to obtain a powder precursor;
(3) Sintering the powdery precursor in a nitrogen atmosphere; wherein the sintering is classified into low-temperature sintering and high-temperature sintering; the low-temperature sintering is to heat from room temperature to 450 ℃ at a heating rate of 1 ℃/min, and sinter for 0h; high-temperature sintering, namely, heating from 450 ℃ to 700 ℃ at a heating rate of 5 ℃/min, and sintering for 9 hours; and then cooling from 700 ℃ to normal temperature at a cooling rate of 6 ℃/min to obtain the lithium iron phosphate anode material.
Example 8:
the only difference from example 1 is that in step (2) PEG400 is replaced with glucose.
Example 9:
the only difference from example 1 is that PEG400 is replaced with ethylene glycol in step (2).
Comparative example 1:
the only difference from example 1 is that no graphitized carbon nitride flakes were added in the preparation of the lithium iron phosphate precursor;
(1) Mixing 7.39g of lithium carbonate, 35.98g of ferrous oxalate, 21.03g of ammonium dihydrogen phosphate and 3.22g of PEG, ball milling for 12 hours at a rotating speed of 360rpm, and drying to obtain a powder precursor;
(2) Sintering the powdery precursor in a nitrogen atmosphere; wherein the sintering is classified into low-temperature sintering and high-temperature sintering; the low-temperature sintering is to heat from room temperature to 450 ℃ at a heating rate of 1 ℃/min, and sinter for 0h; high-temperature sintering, namely, heating from 450 ℃ to 700 ℃ at a heating rate of 5 ℃/min, and sintering for 10 hours; and then cooling from 700 ℃ to normal temperature at a cooling rate of 5 ℃/min to obtain the lithium iron phosphate anode material.
Comparative example 2:
the only difference from example 1 is that a common carbon source was used;
(1) Taking PEG400 and glucose according to a mass ratio of 3:1 adding absolute ethyl alcohol (100 ml), stirring and mixing, performing ultrasonic treatment for 4 hours, adding 7.39g of lithium carbonate, 35.98g of ferrous oxalate and 21.03g of monoammonium phosphate, uniformly mixing, performing ball milling for 12 hours at a rotating speed of 360rpm, and drying to obtain a powder precursor;
(2) Sintering the powdery precursor in a nitrogen atmosphere; wherein the sintering is classified into low-temperature sintering and high-temperature sintering; the low-temperature sintering is to heat from room temperature to 450 ℃ at a heating rate of 1 ℃/min, and sinter for 0h; high-temperature sintering, namely, heating from 450 ℃ to 700 ℃ at a heating rate of 5 ℃/min, and sintering for 10 hours; and then cooling from 700 ℃ to normal temperature at a cooling rate of 5 ℃/min to obtain the lithium iron phosphate anode material.
Comparative example 3:
the preparation method of the lithium iron phosphate anode material comprises the following steps:
(1) Mixing 7.39g of lithium carbonate, 35.98g of ferrous oxalate, 21.03g of ammonium dihydrogen phosphate and 3.22g of glucose uniformly, ball-milling for 12 hours at a rotating speed of 360rpm, and drying to obtain a powder precursor;
(2) Sintering the powdery precursor in a nitrogen atmosphere; wherein the sintering is classified into low-temperature sintering and high-temperature sintering; the low-temperature sintering is to heat from room temperature to 450 ℃ at a heating rate of 1 ℃/min, and sinter for 0h; high-temperature sintering, namely, heating from 450 ℃ to 700 ℃ at a heating rate of 5 ℃/min, and sintering for 10 hours; and then cooling from 700 ℃ to normal temperature at a cooling rate of 5 ℃/min to obtain the lithium iron phosphate anode material.
Comparative example 4:
the preparation method of the lithium iron phosphate anode material comprises the following steps:
(1) Lithium carbonate, anhydrous ferric phosphate, glucose (as a carbon source and a reducing agent) and melamine (as a nitrogen source) are mixed and dispersed in ethanol according to stoichiometric amount;
(2) Ball milling in a planetary mill for 4h (180 rpm), and vacuum drying the obtained gel at 100 ℃ for 12h to obtain a precursor (pale yellow powder);
(3) And heating the precursor for 5 hours at 550 ℃ under nitrogen flow, and then heating to 715 ℃ to sinter for 12 hours to obtain the final N-doped carbon-coated lithium iron phosphate material. Wherein the usage amount of melamine is 10% of the theoretical lithium iron phosphate mass, and is respectively recorded as 10% -NC-LFP.
The particle size, compacted density and capacity of each of the above examples and comparative examples were tested and the results are shown in the following table.
As can be seen from the table, the lithium iron phosphate positive electrode material prepared by the preparation method provided by the invention has small particle size, high compaction and higher specific charge and discharge capacity, the first 0.1C discharge capacity can reach 162.84mAh/g (example 3), and the first 1C discharge capacity can reach 152.52mAh/g (example 4). In the comparative example 1, the flaky graphitized carbon nitride is not added in the preparation of the lithium iron phosphate precursor, and the first discharge capacity performance of the prepared lithium iron phosphate positive electrode material is poor, because the nitrogen doping can improve the conductivity, which is beneficial to the improvement of the electrochemical performance; comparative example 2 uses a common carbon source and the electrochemical performance of the lithium iron phosphate positive electrode material prepared is significantly lower than that of the example.
The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. The preparation method of the lithium iron phosphate anode material is characterized by comprising the following steps of:
sintering the lithium iron phosphate precursor under protective gas to obtain a lithium iron phosphate anode material;
the lithium iron phosphate precursor is mainly prepared from a first mixture, wherein the first mixture comprises an iron source, a phosphorus source, a lithium source, a carbon source and flaky graphitized carbon nitride.
2. The method for preparing a lithium iron phosphate positive electrode material according to claim 1, wherein the flaky graphitized carbon nitride is mainly obtained by calcining urea or melamine;
preferably, the temperature of the calcination is 500-580 ℃, and the time of the calcination is 4-6 h.
3. The method for preparing a lithium iron phosphate positive electrode material according to claim 1, wherein the carbon source is polyethylene glycol;
preferably, the mass ratio of the carbon source to the graphitized carbon nitride flake is (3 to 5): 1.
4. the method for preparing a lithium iron phosphate positive electrode material according to claim 1, wherein the step of preparing the lithium iron phosphate precursor comprises: dispersing, ball milling and drying the components of the first mixture in a solvent;
preferably, the solvent is absolute ethanol;
preferably, the rotation speed of the ball milling is 300rpm-480rpm, and the time of the ball milling is 8h-12h.
5. The method for producing a lithium iron phosphate positive electrode material according to claim 1, wherein the first mixture further comprises a component containing a doping element;
preferably, the doping element-containing component includes a titanium source including at least one of titanium dioxide, methyl titanate, ethyl titanate, n-propyl titanate, and tetrabutyl titanate;
preferably, the molar ratio of the lithium element, the phosphorus element, the iron element and the titanium element in the first mixture is (0.97 to 1): 1: (1-x): x is more than 0.1 and is more than or equal to 0;
preferably, the molar ratio of the lithium element to the nitrogen element in the first mixture is (3 to 5): 1.
6. the method for preparing a lithium iron phosphate positive electrode material according to claim 1, wherein the sintering comprises a low-temperature sintering and a high-temperature sintering which are sequentially performed.
7. The method for preparing a lithium iron phosphate positive electrode material according to claim 6, wherein the low-temperature sintering is performed at a temperature of 1 ℃/min-5 ℃/min up to 350 ℃ -450 ℃ and a low-temperature sintering time of 0h-4h.
8. The method for preparing a lithium iron phosphate positive electrode material according to claim 6, wherein the high-temperature sintering is performed at a temperature of 1 ℃/min-5 ℃/min to 700 ℃ -740 ℃ and a high-temperature sintering time of 9h-11h; then cooling to 20-30 ℃ at the speed of 4-6 ℃ per minute.
9. A lithium iron phosphate positive electrode material obtained by the preparation method according to any one of claims 1 to 8, characterized by comprising a core and a coating layer, wherein the median particle size of the lithium iron phosphate positive electrode material is d50=1.5 to 2.5 μm, and the thickness of the coating layer is 50 to 100nm.
10. A battery comprising the lithium iron phosphate positive electrode material obtained by the preparation method of any one of claims 1 to 8.
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