CN116960321A - Doped lithium iron phosphate and preparation method thereof, positive electrode material, positive electrode plate and lithium battery - Google Patents
Doped lithium iron phosphate and preparation method thereof, positive electrode material, positive electrode plate and lithium battery Download PDFInfo
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- CN116960321A CN116960321A CN202310867260.8A CN202310867260A CN116960321A CN 116960321 A CN116960321 A CN 116960321A CN 202310867260 A CN202310867260 A CN 202310867260A CN 116960321 A CN116960321 A CN 116960321A
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- lithium iron
- iron phosphate
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- 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 107
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 title claims abstract description 25
- 229910052744 lithium Inorganic materials 0.000 title claims abstract description 25
- 239000007774 positive electrode material Substances 0.000 title claims abstract description 18
- 238000002360 preparation method Methods 0.000 title claims abstract description 17
- BPQQTUXANYXVAA-UHFFFAOYSA-N Orthosilicate Chemical compound [O-][Si]([O-])([O-])[O-] BPQQTUXANYXVAA-UHFFFAOYSA-N 0.000 claims abstract description 30
- QSNQXZYQEIKDPU-UHFFFAOYSA-N [Li].[Fe] Chemical compound [Li].[Fe] QSNQXZYQEIKDPU-UHFFFAOYSA-N 0.000 claims abstract description 30
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 claims abstract description 29
- 239000011737 fluorine Substances 0.000 claims abstract description 27
- 229910052731 fluorine Inorganic materials 0.000 claims abstract description 27
- 229910052750 molybdenum Inorganic materials 0.000 claims abstract description 26
- 239000011733 molybdenum Substances 0.000 claims abstract description 26
- 238000002156 mixing Methods 0.000 claims abstract description 13
- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical compound [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 claims description 26
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims description 26
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 25
- MNNHAPBLZZVQHP-UHFFFAOYSA-N diammonium hydrogen phosphate Chemical compound [NH4+].[NH4+].OP([O-])([O-])=O MNNHAPBLZZVQHP-UHFFFAOYSA-N 0.000 claims description 25
- 239000006258 conductive agent Substances 0.000 claims description 22
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 21
- 238000005303 weighing Methods 0.000 claims description 20
- 239000002245 particle Substances 0.000 claims description 19
- 239000002243 precursor Substances 0.000 claims description 18
- 238000001354 calcination Methods 0.000 claims description 15
- 239000011883 electrode binding agent Substances 0.000 claims description 15
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 claims description 11
- 238000000498 ball milling Methods 0.000 claims description 11
- 239000002270 dispersing agent Substances 0.000 claims description 11
- 238000000227 grinding Methods 0.000 claims description 11
- 238000001816 cooling Methods 0.000 claims description 10
- 238000000034 method Methods 0.000 claims description 10
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 9
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 claims description 9
- 238000007873 sieving Methods 0.000 claims description 9
- DDFHBQSCUXNBSA-UHFFFAOYSA-N 5-(5-carboxythiophen-2-yl)thiophene-2-carboxylic acid Chemical group S1C(C(=O)O)=CC=C1C1=CC=C(C(O)=O)S1 DDFHBQSCUXNBSA-UHFFFAOYSA-N 0.000 claims description 8
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 claims description 8
- APUPEJJSWDHEBO-UHFFFAOYSA-P ammonium molybdate Chemical group [NH4+].[NH4+].[O-][Mo]([O-])(=O)=O APUPEJJSWDHEBO-UHFFFAOYSA-P 0.000 claims description 8
- 229910000388 diammonium phosphate Inorganic materials 0.000 claims description 8
- 235000019838 diammonium phosphate Nutrition 0.000 claims description 8
- XGZVUEUWXADBQD-UHFFFAOYSA-L lithium carbonate Chemical compound [Li+].[Li+].[O-]C([O-])=O XGZVUEUWXADBQD-UHFFFAOYSA-L 0.000 claims description 8
- 229910052808 lithium carbonate Inorganic materials 0.000 claims description 8
- 229910052698 phosphorus Inorganic materials 0.000 claims description 8
- 239000011574 phosphorus Substances 0.000 claims description 8
- 239000000126 substance Substances 0.000 claims description 8
- 239000011230 binding agent Substances 0.000 claims description 7
- 229940062993 ferrous oxalate Drugs 0.000 claims description 7
- OWZIYWAUNZMLRT-UHFFFAOYSA-L iron(2+);oxalate Chemical compound [Fe+2].[O-]C(=O)C([O-])=O OWZIYWAUNZMLRT-UHFFFAOYSA-L 0.000 claims description 7
- KFZMGEQAYNKOFK-UHFFFAOYSA-N Isopropanol Chemical compound CC(C)O KFZMGEQAYNKOFK-UHFFFAOYSA-N 0.000 claims description 6
- LRHPLDYGYMQRHN-UHFFFAOYSA-N N-Butanol Chemical compound CCCCO LRHPLDYGYMQRHN-UHFFFAOYSA-N 0.000 claims description 6
- 229910052742 iron Inorganic materials 0.000 claims description 6
- 239000000203 mixture Substances 0.000 claims description 6
- 239000007773 negative electrode material Substances 0.000 claims description 5
- DPXJVFZANSGRMM-UHFFFAOYSA-N acetic acid;2,3,4,5,6-pentahydroxyhexanal;sodium Chemical compound [Na].CC(O)=O.OCC(O)C(O)C(O)C(O)C=O DPXJVFZANSGRMM-UHFFFAOYSA-N 0.000 claims description 4
- 239000002041 carbon nanotube Substances 0.000 claims description 4
- 229910021393 carbon nanotube Inorganic materials 0.000 claims description 4
- 239000001768 carboxy methyl cellulose Substances 0.000 claims description 4
- 239000010439 graphite Substances 0.000 claims description 4
- 229910002804 graphite Inorganic materials 0.000 claims description 4
- 235000019812 sodium carboxymethyl cellulose Nutrition 0.000 claims description 4
- 229920001027 sodium carboxymethylcellulose Polymers 0.000 claims description 4
- 229920003048 styrene butadiene rubber Polymers 0.000 claims description 4
- 239000004254 Ammonium phosphate Substances 0.000 claims description 3
- MCDLETWIOVSGJT-UHFFFAOYSA-N acetic acid;iron Chemical compound [Fe].CC(O)=O.CC(O)=O MCDLETWIOVSGJT-UHFFFAOYSA-N 0.000 claims description 3
- 239000006230 acetylene black Substances 0.000 claims description 3
- 229910000148 ammonium phosphate Inorganic materials 0.000 claims description 3
- 235000019289 ammonium phosphates Nutrition 0.000 claims description 3
- 229910011570 LiFe 1-x Inorganic materials 0.000 claims description 2
- 229920002125 Sokalan® Polymers 0.000 claims description 2
- 229940010552 ammonium molybdate Drugs 0.000 claims description 2
- 235000018660 ammonium molybdate Nutrition 0.000 claims description 2
- 239000011609 ammonium molybdate Substances 0.000 claims description 2
- 239000004584 polyacrylic acid Substances 0.000 claims description 2
- 239000000463 material Substances 0.000 abstract description 28
- 239000010405 anode material Substances 0.000 abstract description 6
- PXGOKWXKJXAPGV-UHFFFAOYSA-N Fluorine Chemical compound FF PXGOKWXKJXAPGV-UHFFFAOYSA-N 0.000 abstract 1
- 238000013329 compounding Methods 0.000 abstract 1
- 230000000052 comparative effect Effects 0.000 description 30
- 239000003292 glue Substances 0.000 description 26
- 239000002033 PVDF binder Substances 0.000 description 22
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 22
- 239000002002 slurry Substances 0.000 description 22
- 238000003756 stirring Methods 0.000 description 22
- 239000011248 coating agent Substances 0.000 description 19
- 238000000576 coating method Methods 0.000 description 19
- 229910052799 carbon Inorganic materials 0.000 description 14
- 239000004615 ingredient Substances 0.000 description 14
- 238000001035 drying Methods 0.000 description 13
- 238000005096 rolling process Methods 0.000 description 13
- 238000005520 cutting process Methods 0.000 description 11
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 10
- 239000002904 solvent Substances 0.000 description 10
- 229910001416 lithium ion Inorganic materials 0.000 description 9
- 239000005696 Diammonium phosphate Substances 0.000 description 6
- 238000009792 diffusion process Methods 0.000 description 5
- 230000009286 beneficial effect Effects 0.000 description 4
- 230000007547 defect Effects 0.000 description 4
- 238000012360 testing method Methods 0.000 description 4
- 229910010710 LiFePO Inorganic materials 0.000 description 3
- 230000014759 maintenance of location Effects 0.000 description 3
- 229910021645 metal ion Inorganic materials 0.000 description 3
- 239000002994 raw material Substances 0.000 description 3
- 230000032683 aging Effects 0.000 description 2
- 239000011884 anode binding agent Substances 0.000 description 2
- HUGHRBCOAPEAIP-UHFFFAOYSA-L fluoro-dioxido-oxo-lambda5-phosphane iron(2+) Chemical compound P(=O)([O-])([O-])F.[Fe+2] HUGHRBCOAPEAIP-UHFFFAOYSA-L 0.000 description 2
- 238000009472 formulation Methods 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- 238000004806 packaging method and process Methods 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 238000004537 pulping Methods 0.000 description 2
- 238000005245 sintering Methods 0.000 description 2
- 244000025254 Cannabis sativa Species 0.000 description 1
- 239000005955 Ferric phosphate Substances 0.000 description 1
- 229910010707 LiFePO 4 Inorganic materials 0.000 description 1
- 229910006715 Li—O Inorganic materials 0.000 description 1
- 239000004372 Polyvinyl alcohol Substances 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 239000010406 cathode material Substances 0.000 description 1
- 239000004020 conductor Substances 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000001186 cumulative effect Effects 0.000 description 1
- 239000008367 deionised water Substances 0.000 description 1
- 229910021641 deionized water Inorganic materials 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000018109 developmental process Effects 0.000 description 1
- 238000004033 diameter control Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 229940032958 ferric phosphate Drugs 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- WBJZTOZJJYAKHQ-UHFFFAOYSA-K iron(3+) phosphate Chemical compound [Fe+3].[O-]P([O-])([O-])=O WBJZTOZJJYAKHQ-UHFFFAOYSA-K 0.000 description 1
- 229910000399 iron(III) phosphate Inorganic materials 0.000 description 1
- 238000010030 laminating Methods 0.000 description 1
- 238000003475 lamination Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000002715 modification method Methods 0.000 description 1
- 239000002105 nanoparticle Substances 0.000 description 1
- 238000011056 performance test Methods 0.000 description 1
- 239000002985 plastic film Substances 0.000 description 1
- 229920006255 plastic film Polymers 0.000 description 1
- -1 polytetrafluoroethylene Polymers 0.000 description 1
- 229920001343 polytetrafluoroethylene Polymers 0.000 description 1
- 239000004810 polytetrafluoroethylene Substances 0.000 description 1
- 229920002451 polyvinyl alcohol Polymers 0.000 description 1
- 238000004321 preservation Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000004904 shortening Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 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
-
- 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
-
- 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
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2002/00—Crystal-structural characteristics
- C01P2002/50—Solid solutions
- C01P2002/52—Solid solutions containing elements as dopants
- C01P2002/54—Solid solutions containing elements as dopants one element only
-
- 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
-
- C—CHEMISTRY; METALLURGY
- 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
Landscapes
- Chemical & Material Sciences (AREA)
- Inorganic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Organic Chemistry (AREA)
- Crystallography & Structural Chemistry (AREA)
- Materials Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Battery Electrode And Active Subsutance (AREA)
Abstract
The invention provides a doped lithium iron phosphate and a preparation method thereof, a positive electrode material, a positive electrode plate and a lithium battery, and belongs to the technical field of new energy batteries. The lithium iron phosphate material is doped with molybdenum and fluorine, so that the resistivity of the lithium iron phosphate material is greatly reduced, the internal resistance of the battery is reduced, and the rate performance, the cycle performance and the like of the battery are improved. And then, by compounding the lithium iron silicate material with high specific capacity, the mixing specific capacity of the anode material is improved, and the energy density and the cycle performance of the battery are further improved.
Description
Technical Field
The invention belongs to the technical field of new energy batteries, and particularly relates to a doped lithium iron phosphate, a preparation method thereof, a positive electrode material, a positive electrode plate and a lithium battery.
Background
Lithium iron phosphate (LiFePO) 4 ) The lithium ion battery anode material has the advantages of high safety, stable cycle performance, low price, stable discharge platform and environmental friendliness, and is widely regarded as the most promising lithium ion battery anode material, in particular to the power lithium ion battery anode material. Compared with other lithium ion battery anode materials, the lithium iron phosphate is safer, more environment-friendly and lower in cost. However, the lithium iron phosphate material has low conductivity and low lithium ion diffusion coefficient, and the theoretical specific capacity of the lithium iron phosphate material is also low, which is about 170mAh/g, so that the development of the lithium iron phosphate material in the field of high-rate batteries is restricted.
The best method for solving the problem of low conductivity is to modify the lithium iron phosphate. The modification method comprises doping conductive carbon or coating carbon, metal coating, particle diameter control and the like on the surface of lithium iron phosphate particles. Doping or coating carbon, although improving the conductivity of lithium iron phosphate to some extent, also reduces its tap density. Reducing the particle size of lithium iron phosphate is beneficial to shortening the diffusion path of lithium ions in the charge-discharge process, increasing the diffusion rate of lithium ions and improving the high-current charge-discharge performance, but too small particle size can reduce the tap density of the material, increase the specific surface area of the material and is not beneficial to electrode processing and battery energy density improvement. The patent with the application number of CN201710567636.8 discloses a preparation method of carbon-coated lithium iron phosphate and a lithium ion battery, wherein partial carbon sources are firstly mixed with ferric phosphate, after grinding and drying, presintering is carried out, presintering materials, lithium sources and partial carbon sources are mixed, after grinding and drying, the carbon-coated lithium iron phosphate is obtained through secondary sintering, and the surface of the prepared carbon-coated lithium iron phosphate realizes double-layer coating of a carbon layer through the processes of secondary carbon source coating and secondary sintering, so that a complete conductive network is formed, the conductivity of the carbon-coated lithium iron phosphate is obviously improved, but nano-scale particles exist in the carbon-coated lithium iron phosphate, the tap density of the material is reduced due to the fact that the particle size is too small, the specific surface area of the material is increased, and the electrode processing and the improvement of the battery energy density are not facilitated.
Therefore, research continues to be sought on how to simultaneously increase the conductivity and energy density of lithium iron phosphate materials.
Disclosure of Invention
Aiming at the defects and defects existing in the prior art, the invention aims to provide doped lithium iron phosphate, a preparation method thereof, a positive electrode material, a positive electrode plate and a lithium battery. According to the invention, firstly, metal ions are doped in the lithium iron phosphate, and after the doped metal ions enter the crystal, lattice defects in the material can be caused, so that the electric conductivity in the lithium iron phosphate particles is fundamentally improved. Compared with carbon doping or carbon coating, the metal ion doping can not only not reduce the tap density of the material, but also is beneficial to improving the energy density of the lithium iron phosphate battery. The lithium iron phosphate material is doped with molybdenum and fluorine elements, so that the resistivity of the lithium iron phosphate material is greatly reduced, the internal resistance of the battery is reduced, and the performances of multiplying power, circulation and the like of the battery are improved. Then by introducing lithium iron silicate material (Li) with high specific capacity, stable structure and low raw material price into the positive electrode formula 2 FeSiO 4 LFSO, theoretical specific capacity 331 mAh/g) and doped lithium iron phosphate, thereby improving the mixed specific capacity of the positive electrode material and further improving the energy density of the battery.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
in a first aspect, the present invention provides a doped lithium iron phosphate having the formula LiFe 1- x Mo x PO 4-y F y Wherein: x is more than or equal to 0.2 and less than or equal to 0.8 (specifically, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7 and 0.75) and y is more than or equal to 0.5 and less than or equal to 1.0 (specifically, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9 and 0.95).
The invention adopts a certain amount of molybdenum element to dope at Fe position, which can generate ion vacancy, reduce bond energy of Li-O bond and improve Li + To improve the diffusion capacity of LiFePO 4 Electrochemical properties of the material. A certain amount of fluorine element is adopted to dope at the O position, so thatProperly inhibit dislocation defect of material and improve Li + Diffusion kinetics of LiFePO can be improved 4 The conductivity of the material.
Further, the particle diameter D50 of the doped lithium iron phosphate is 0.5 to 4 μm (specifically, 0.7 μm, 0.9 μm, 1.1 μm, 1.3 μm, 1.5 μm, 1.7 μm, 1.9 μm, 2.1 μm, 2.3 μm, 2.5 μm, 2.7 μm, 2.9 μm, 3.1 μm, 3.3 μm, 3.5 μm, 3.7 μm, 3.9 μm, etc. may be mentioned).
In the invention, the particle diameter D50 is the particle diameter corresponding to the cumulative particle size distribution percentage of the doped lithium iron phosphate reaching 50 percent, and the particle diameter D50 of the doped lithium iron phosphate is within the range, so that the high-current discharge performance and the battery energy density of the battery are both good.
In a second aspect, the present invention provides a method for preparing the doped lithium iron phosphate, wherein the doped lithium iron phosphate is prepared by the following steps:
s1, weighing a lithium source, a molybdenum source, a fluorine source, an iron source and a phosphorus source, and uniformly mixing with a dispersing agent to obtain a mixture;
s2, ball milling the mixture obtained in the step S1 to obtain a precursor;
and S3, calcining the precursor obtained in the step S2, cooling, grinding and sieving to obtain the doped lithium iron phosphate.
Further, in step S1, the molar ratio of the lithium element in the lithium source, the molybdenum element in the molybdenum source, the fluorine element in the fluorine source, the iron element in the iron source, and the phosphorus element in the phosphorus source is 1:0.2 to 0.8:0.5 to 1:0.2 to 0.8:1, a step of;
and/or the lithium source is selected from one or more of lithium carbonate and lithium hydroxide;
and/or, the molybdenum source is selected from ammonium molybdate;
and/or, the fluorine source is selected from ammonium fluoride;
and/or, the iron source is selected from one or more of ferrous oxalate and ferrous acetate;
and/or the phosphorus source is selected from one or more of diammonium hydrogen phosphate, ammonium phosphate and ammonium hydrogen phosphate;
and/or the dispersing agent is selected from one or more of absolute ethyl alcohol, isopropyl alcohol and n-butyl alcohol.
Further, in step S2, the ball milling time is 6-14 h (specifically, 6.5h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 13.5h may be mentioned).
Further, in step S3, the calcination temperature is 400 to 900 ℃ (specifically, for example, 450 ℃, 500 ℃, 600 ℃, 700 ℃, 800 ℃, 850 ℃), and the calcination time is 5 to 15 hours (specifically, for example, 5.5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 14.5 hours). Wherein the calcination time includes a temperature rise time and a heat preservation time.
Further, in step S3, the calcination is performed in an air atmosphere, and then naturally cooled, ground and sieved to obtain an undersize, i.e., doped lithium iron phosphate, which is then stored in a dryer.
In a third aspect, the present invention provides a positive electrode material, which comprises 70-80% (specifically, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%) of the doped lithium iron phosphate, 15-25% (specifically, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%) of lithium iron silicate, 1-5% (specifically, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%) of a binder, and 1-5% (specifically, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%) of a conductive agent.
According to the invention, the lithium iron silicate is introduced on the basis of the formula of the doped lithium iron phosphate anode, and is mixed with the lithium iron phosphate for use, and the energy density of the battery can be greatly improved because the theoretical specific capacity of the lithium iron silicate is about 331 mAh/g. The lithium iron silicate used in the invention can be purchased from the existing commercial way, and can also be obtained by the existing raw materials and preparation methods.
Further, the positive electrode material comprises 76% of doped lithium iron phosphate, 19% of lithium iron silicate, 2.5% of binder and 2.5% of conductive agent by mass.
Further, the binder is an oily binder, such as one or more of polyvinylidene fluoride, polyvinyl alcohol, polytetrafluoroethylene and the like. Preferably polyvinylidene fluoride.
Further, the positive electrode conductive agent may be any known conductive material for positive electrode of lithium ion battery, such as: conductive carbon black, carbon Nanotubes (CNT), acetylene black, and the like. Conductive carbon black is preferred.
In a fourth aspect, the present invention provides a positive electrode sheet containing the positive electrode material described above.
In a fifth aspect, the present invention provides a lithium battery comprising the above positive electrode material or the above positive electrode sheet.
Further, the energy density of the lithium battery is not less than 180Wh/kg.
In a sixth aspect, the present invention provides a method for preparing the above lithium battery, comprising the steps of:
obtaining a positive plate: mixing lithium iron silicate, doped lithium iron phosphate, a binder and a conductive agent for pulping, coating, rolling and tabletting to obtain a positive plate;
obtaining a negative plate: mixing and pulping a negative electrode active material, a negative electrode conductive agent and a negative electrode binder, coating, rolling and tabletting to obtain a negative electrode plate;
obtaining a lithium battery: and laminating, packaging, baking, injecting liquid, forming, aging and separating the volume to obtain the lithium battery.
Further, in the lithium battery, the negative electrode sheet comprises 94% -97.5% by mass: 0.75% -3%:1.75% -3% of negative electrode active material, negative electrode conductive agent and negative electrode binder;
the negative active material is selected from graphite;
the negative electrode conductive agent is selected from one or more of conductive carbon black, carbon nano tube and acetylene black;
the negative electrode binder is selected from one or more of polyacrylic acid, styrene-butadiene rubber and sodium carboxymethyl cellulose.
Compared with the prior art, the invention has the following beneficial effects:
1. according to the invention, by doping molybdenum and fluorine elements into the lithium iron phosphate material, the resistivity of the lithium iron phosphate material is greatly reduced, so that the internal resistance of the battery is reduced, and the rate capability, the cycle performance and the like of the battery are improved.
2. According to the invention, the lithium iron silicate material with high specific capacity is introduced into the positive electrode formula, so that the mixed specific capacity of the positive electrode material is improved, and the energy density of the battery is further improved.
Drawings
Fig. 1 is a graph showing the positive electrode sheet resistivity contrast of example 1, example 2, example 3 and comparative example 1;
fig. 2 is a graph showing the normal temperature cycle performance of lithium batteries of example 1, example 2, example 3 and comparative example 2.
Detailed Description
The present invention will be further described with reference to the following examples in order to make the objects, technical solutions and advantages of the present invention more apparent. The embodiments of the present invention are implemented on the premise of the technical solution of the present invention, and detailed implementation manners and processes are given, and it should be apparent to those skilled in the art that the embodiments are merely for aiding in understanding the present invention and should not be taken as specific limitations of the present invention, and the scope of protection of the present invention is not limited to the following embodiments, based on which all other embodiments obtained by a person of ordinary skill in the art without making inventive efforts fall within the scope of protection of the present invention.
The process parameters for which specific conditions are not noted in the examples of the present invention are generally carried out according to conventional conditions. All numbers referring to amounts of components are "weight or mass values or ratios" throughout unless specified and/or stated otherwise. Unless otherwise specified, the raw materials used in the present invention can be obtained from commercial products.
In the present invention, endpoints of the disclosed ranges and any values are not limited to the precise range or value, and such range or value should be understood to include values close to the range or value. For numerical ranges, one or more new numerical ranges may be obtained in combination with each other between the endpoints of each range, between the endpoint of each range and the individual point value, and between the individual point values, and are to be considered as specifically disclosed in the present invention.
The present invention will be described in further detail with reference to specific examples.
Example 1
S1, preparing a positive plate: weighing 76% of molybdenum/fluorine co-doped lithium iron phosphate, 19% of lithium iron silicate, 2.5% of polyvinylidene fluoride serving as a positive electrode binder and 2.5% of conductive carbon black serving as a positive electrode conductive agent according to parts by mass, firstly adding polyvinylidene fluoride into an N-methylpyrrolidone solvent to prepare a glue solution, then adding the conductive carbon black into the glue solution, stirring until uniformity, and then adding the doped lithium iron phosphate and the doped lithium iron silicate into the slurry, and stirring until uniformity; finally, coating the slurry on a current collector, and drying to prepare a positive plate; rolling and cutting to obtain the positive and the minimum sheets.
S2, preparing a negative plate: weighing 96% of graphite anode material, 1.0% of anode binder sodium carboxymethyl cellulose, 1.5% of anode binder styrene-butadiene rubber and 1.5% of anode conductive agent conductive carbon black according to parts by mass, firstly adding sodium carboxymethyl cellulose into deionized water to prepare a glue solution, then adding the conductive carbon black and graphite into the glue solution, stirring until uniformity, then adding styrene-butadiene rubber into the slurry, and stirring until uniformity; finally, coating the slurry on a current collector, and drying to prepare a negative plate; rolling and cutting to obtain the negative pole micro-sheet.
S3, preparation of an electric core: and (3) baking the positive and negative micro-sheets in vacuum, and manufacturing the battery cell through lamination and packaging the battery cell in an aluminum plastic film.
S4, preparation of a battery: and (3) injecting liquid, forming, aging and separating the baked battery core to obtain the lithium iron phosphate battery with high energy density.
Preparation of doped lithium iron phosphate in the step S1:
lithium carbonate (Li) 2 CO 3 ) Ammonium molybdate ((NH 4) 2MoO 4), ammonium fluoride (NH) 4 F) Ferrous oxalate (Fe (C) 2 O 4 ) 2 ) And diammonium phosphate ((NH) 4 ) 2 HPO 4 ) According to 0.05:0.05:0.08:0.05: weighing ingredients according to a molar ratio of 0.1, uniformly mixing, taking absolute ethyl alcohol as a dispersing agent, and jointly placing the ingredients into a ball mill for ball milling for 10 hours to prepare the precursor. The precursor is arranged inCalcining at 700 deg.C in air atmosphere for 10 hr, naturally cooling, slightly grinding and sieving to obtain molybdenum/fluorine co-doped lithium iron phosphate with particle diameter D50 of 2.0 μm, chemical formula being LiFe 0.5 Mo 0.5 PO 3.2 F 0.8 Stored in a desiccator.
Example 2
The lithium iron phosphate battery of this example was prepared only as follows:
preparation of doped lithium iron phosphate in the step S1:
lithium carbonate (Li) 2 CO 3 ) Ammonium molybdate ((NH 4) 2MoO 4), ammonium fluoride (NH) 4 F) Ferrous oxalate (Fe (C) 2 O 4 ) 2 ) And diammonium phosphate (NH) 4 H 2 PO 4 ) According to 0.05:0.02:0.05:0.08: weighing ingredients according to a molar ratio of 0.1, uniformly mixing, taking absolute ethyl alcohol as a dispersing agent, and jointly placing the ingredients in a ball mill for ball milling for 6 hours to prepare the precursor. Calcining the precursor in air atmosphere at 400 ℃ for 5 hours, naturally cooling, slightly grinding and sieving to obtain molybdenum/fluorine co-doped lithium iron phosphate with the particle diameter D50 of 0.5 mu m, wherein the chemical formula is LiFe 0.8 Mo 0.2 PO 3.5 F 0.5 Stored in a desiccator.
The rest of the settings are the same as in example 1.
Example 3
The lithium iron phosphate battery of this example was prepared only as follows:
preparation of doped lithium iron phosphate in the step S1:
lithium carbonate (Li) 2 CO 3 ) Ammonium molybdate ((NH 4) 2MoO 4), ammonium fluoride (NH) 4 F) Ferrous oxalate (Fe (C) 2 O 4 ) 2 ) And diammonium phosphate (NH) 4 H 2 PO 4 ) According to 0.05:0.08:0.1:0.02: weighing ingredients according to a molar ratio of 0.1, uniformly mixing, taking absolute ethyl alcohol as a dispersing agent, and jointly placing the ingredients in a ball mill for ball milling for 14 hours to prepare the precursor. Calcining the precursor in air atmosphere at 900 deg.C for 15 hr, naturally cooling, slightly grinding and sieving to obtain molybdenum/fluorine co-doped lithium iron phosphate with particle diameter D50 of 4.0 μm, chemical formula being LiFe 0.2 Mo 0.8 PO 3 F, storing in a dryer.
The rest of the settings are the same as in example 1.
Example 4
The lithium iron phosphate battery of this example was prepared only as follows:
preparation of doped lithium iron phosphate in the step S1:
lithium hydroxide, ammonium molybdate ((NH 4) 2MoO 4), ammonium fluoride (NH) 4 F) Ferrous acetate and ammonium phosphate according to 0.1:0.05:0.08:0.05: weighing ingredients according to a molar ratio of 0.1, uniformly mixing, taking absolute ethyl alcohol as a dispersing agent, and jointly placing the ingredients into a ball mill for ball milling for 10 hours to prepare the precursor. Calcining the precursor in air atmosphere at 700 ℃ for 10 hours, naturally cooling, slightly grinding and sieving to obtain molybdenum/fluorine co-doped lithium iron phosphate with the particle diameter D50 of 2.0 mu m, wherein the chemical formula is LiFe 0.5 Mo 0.5 PO 3.2 F 0.8 Stored in a desiccator.
The rest of the settings are the same as in example 1.
Example 5
The lithium iron phosphate battery of this example was prepared only as follows:
s1, preparing a positive plate: weighing 70% of molybdenum/fluorine co-doped lithium iron phosphate, 25% of lithium iron silicate, 2.5% of polyvinylidene fluoride serving as a positive electrode binder and 2.5% of conductive carbon black serving as a positive electrode conductive agent according to parts by mass, firstly adding polyvinylidene fluoride into an N-methylpyrrolidone solvent to prepare a glue solution, then adding the conductive carbon black into the glue solution, stirring until uniformity, and then adding the doped lithium iron phosphate and the doped lithium iron silicate into the slurry, and stirring until uniformity; finally, coating the slurry on a current collector, and drying to prepare a positive plate; rolling and cutting to obtain the positive and the minimum sheets.
The rest of the settings are the same as in example 1.
Example 6
The lithium iron phosphate battery of this example was prepared only as follows:
s1, preparing a positive plate: weighing 80% of molybdenum/fluorine co-doped lithium iron phosphate, 15% of lithium iron silicate, 2.5% of polyvinylidene fluoride serving as a positive electrode binder and 2.5% of conductive carbon black serving as a positive electrode conductive agent according to parts by mass, firstly adding polyvinylidene fluoride into an N-methylpyrrolidone solvent to prepare a glue solution, then adding the conductive carbon black into the glue solution, stirring until uniformity, and then adding the doped lithium iron phosphate and the doped lithium iron silicate into the slurry, and stirring until uniformity; finally, coating the slurry on a current collector, and drying to prepare a positive plate; rolling and cutting to obtain the positive and the minimum sheets.
The rest of the settings are the same as in example 1.
Comparative example 1
The lithium iron phosphate battery of this comparative example was prepared only as follows:
s1, preparing a positive plate: weighing 95% of lithium iron phosphate, 2.5% of polyvinylidene fluoride serving as a positive electrode binder and 2.5% of conductive carbon black serving as a positive electrode conductive agent according to parts by mass, firstly adding polyvinylidene fluoride into an N-methyl pyrrolidone solvent to prepare a glue solution, then adding the conductive carbon black into the glue solution, stirring until the glue solution is uniform, then adding the lithium iron phosphate into the slurry, and stirring until the glue solution is uniform; finally, coating the slurry on a current collector, and drying to prepare a positive plate; rolling and cutting to obtain the positive and the minimum sheets.
The rest of the settings are the same as in example 1.
Comparative example 2
The lithium iron phosphate battery of this comparative example was prepared only as follows:
s1, preparing a positive plate: weighing 95% of molybdenum/fluorine co-doped lithium iron phosphate, 2.5% of positive electrode binder polyvinylidene fluoride and 2.5% of positive electrode conductive agent conductive carbon black according to parts by mass, firstly adding polyvinylidene fluoride into an N-methylpyrrolidone solvent to prepare a glue solution, then adding the conductive carbon black into the glue solution, stirring until uniformity, then adding the doped lithium iron phosphate into the slurry, and stirring until uniformity; finally, coating the slurry on a current collector, and drying to prepare a positive plate; rolling and cutting to obtain the positive and the minimum sheets.
The rest of the settings are the same as in example 1.
Comparative example 3
The lithium iron phosphate battery of this comparative example was prepared only as follows:
s1, preparing a positive plate: weighing 76% of lithium iron phosphate, 19% of lithium iron silicate, 2.5% of polyvinylidene fluoride serving as a positive electrode binder and 2.5% of conductive carbon black serving as a positive electrode conductive agent according to parts by mass, firstly adding polyvinylidene fluoride into an N-methylpyrrolidone solvent to prepare a glue solution, then adding the conductive carbon black into the glue solution, stirring until the glue solution is uniform, and then adding the lithium iron phosphate and the lithium iron silicate into the slurry, and stirring until the glue solution is uniform; finally, coating the slurry on a current collector, and drying to prepare a positive plate; rolling and cutting to obtain the positive and the minimum sheets.
The rest of the settings are the same as in example 1.
Comparative example 4
The lithium iron phosphate battery of this comparative example was prepared only as follows:
s1, preparing a positive plate: weighing 76% of molybdenum doped lithium iron phosphate, 19% of lithium iron silicate, 2.5% of polyvinylidene fluoride serving as a positive electrode binder and 2.5% of conductive carbon black serving as a positive electrode conductive agent according to parts by mass, firstly adding polyvinylidene fluoride into an N-methylpyrrolidone solvent to prepare a glue solution, then adding the conductive carbon black into the glue solution, stirring until uniformity, and then adding the doped lithium iron phosphate and the doped lithium iron silicate into the slurry, and stirring until uniformity; finally, coating the slurry on a current collector, and drying to prepare a positive plate; rolling and cutting to obtain the positive and the minimum sheets.
Preparation of molybdenum doped lithium iron phosphate in step S1:
lithium carbonate (Li) 2 CO 3 ) Ammonium molybdate ((NH 4) 2MoO 4), ferrous oxalate (Fe (C) 2 O 4 ) 2 ) And diammonium phosphate ((NH) 4 ) 2 HPO 4 ) According to 0.05:0.05:0.05: weighing ingredients according to a molar ratio of 0.1, uniformly mixing, taking absolute ethyl alcohol as a dispersing agent, and jointly placing the ingredients into a ball mill for ball milling for 10 hours to prepare the precursor. Calcining the precursor in air at 700 deg.C for 10 hr, naturally cooling, and slightly grindingSieving to obtain doped lithium iron phosphate with particle diameter D50 of 5.0 μm, chemical formula of LiFe 0.5 Mo 0.5 PO 4 Stored in a desiccator.
The rest of the settings are the same as in example 1.
Comparative example 5
The lithium iron phosphate battery of this comparative example was prepared only as follows:
s1, preparing a positive plate: weighing 76% of fluorine doped lithium iron phosphate, 19% of lithium iron silicate, 2.5% of polyvinylidene fluoride serving as a positive electrode binder and 2.5% of positive electrode conductive agent conductive carbon black according to parts by mass, firstly adding polyvinylidene fluoride into an N-methylpyrrolidone solvent to prepare a glue solution, then adding the conductive carbon black into the glue solution, stirring until uniformity, and then adding the doped lithium iron phosphate and lithium iron silicate into the slurry, and stirring until uniformity; finally, coating the slurry on a current collector, and drying to prepare a positive plate; rolling and cutting to obtain the positive and the minimum sheets.
Preparation of fluorine doped lithium iron phosphate in step S1:
lithium carbonate (Li) 2 CO 3 ) Ammonium fluoride (NH) 4 F) Ferrous oxalate (Fe (C) 2 O 4 ) 2 ) And diammonium phosphate ((NH) 4 ) 2 HPO 4 ) According to 0.05:0.08:0.05: weighing ingredients according to a molar ratio of 0.1, uniformly mixing, taking absolute ethyl alcohol as a dispersing agent, and jointly placing the ingredients into a ball mill for ball milling for 10 hours to prepare the precursor. Calcining the precursor in air atmosphere at 700 deg.C for 10 hr, naturally cooling, slightly grinding and sieving to obtain doped lithium iron phosphate with particle diameter D50 of 4.0 μm, and chemical formula of LiFePO 3.2 F 0.8 Stored in a desiccator.
The rest of the settings are the same as in example 1.
Comparative example 6
The lithium iron phosphate battery of this comparative example was prepared only as follows:
preparation of doped lithium iron phosphate in the step S1:
lithium carbonate (Li) 2 CO 3 ) Ammonium molybdate ((NH 4) 2MoO 4), ammonium fluoride (NH) 4 F) Grass of grassFerrous acid (Fe (C) 2 O 4 ) 2 ) And diammonium phosphate ((NH) 4 ) 2 HPO 4 ) According to 0.05:0.01:0.01:0.09: weighing ingredients according to a molar ratio of 0.1, uniformly mixing, taking absolute ethyl alcohol as a dispersing agent, and jointly placing the ingredients into a ball mill for ball milling for 10 hours to prepare the precursor. Calcining the precursor in air atmosphere at 700 ℃ for 10 hours, naturally cooling, slightly grinding and sieving to obtain molybdenum/fluorine co-doped lithium iron phosphate with the particle diameter D50 of 2.0 mu m, wherein the chemical formula is LiFe 0.9 Mo 0.1 PO 3.9 F 0.1 Stored in a desiccator.
Comparative example 7
The lithium iron phosphate battery of this comparative example was prepared only as follows:
s1, preparing a positive plate: weighing 65% of molybdenum/fluorine co-doped lithium iron phosphate, 30% of lithium iron silicate, 2.5% of polyvinylidene fluoride serving as a positive electrode binder and 2.5% of conductive carbon black serving as a positive electrode conductive agent according to parts by mass, firstly adding polyvinylidene fluoride into an N-methylpyrrolidone solvent to prepare a glue solution, then adding the conductive carbon black into the glue solution, stirring until uniformity, and then adding the doped lithium iron phosphate and the doped lithium iron silicate into the slurry, and stirring until uniformity; finally, coating the slurry on a current collector, and drying to prepare a positive plate; rolling and cutting to obtain the positive and the minimum sheets.
The rest of the settings are the same as in example 1.
Comparative example 8
The lithium iron phosphate battery of this comparative example was prepared only as follows:
s1, preparing a positive plate: weighing 82% of molybdenum/fluorine co-doped lithium iron phosphate, 13% of lithium iron silicate, 2.5% of polyvinylidene fluoride serving as a positive electrode binder and 2.5% of conductive carbon black serving as a positive electrode conductive agent according to parts by mass, firstly adding polyvinylidene fluoride into an N-methylpyrrolidone solvent to prepare a glue solution, then adding the conductive carbon black into the glue solution, stirring until uniformity, and then adding the doped lithium iron phosphate and the doped lithium iron silicate into the slurry, and stirring until uniformity; finally, coating the slurry on a current collector, and drying to prepare a positive plate; rolling and cutting to obtain the positive and the minimum sheets.
The rest of the settings are the same as in example 1.
Test case
The batteries prepared in examples 1 to 6 and comparative examples 1 to 8 were subjected to tests of positive electrode sheet resistivity and battery energy density, and normal temperature cycle performance and rate performance by:
resistivity detection: detecting by a diaphragm resistance meter;
and (3) testing normal temperature cycle performance: calculating the retention rate of the 1C/1C cycle 500 weeks capacity at 25 ℃;
and (3) multiplying power performance test: calculating the ratio of the capacity of 1C charge to 2.5C discharge to the capacity of 1C charge to 1C discharge;
energy density calculation: according to the formula: energy density (Wh/kg) =battery capacity (Wh)/battery mass (kg);
the test results are shown in Table 2.
TABLE 2
| Sequence number | Resistivity of positive plate (mΩ. Cm) | Energy Density (Wh/kg) | Capacity retention of 500 weeks | Rate capability |
| Example 1 | 62 | 185 | 97.97％ | 95％ |
| Example 2 | 75 | 182 | 92.99％ | 88.6％ |
| Example 3 | 85 | 180 | 90.28％ | 85.8％ |
| Example 4 | 66 | 183 | 96.5％ | 94.2％ |
| Example 5 | 80 | 187 | 91.23％ | 86.2％ |
| Example 6 | 70 | 180 | 93％ | 88.8％ |
| Comparative example 1 | 250 | 150 | 80.45％ | 80.1％ |
| Comparative example 2 | 82 | 145 | 83.72％ | 90.2％ |
| Comparative example 3 | 200 | 180 | 84.28％ | 81.1％ |
| Comparative example 4 | 155 | 175 | 87.6％ | 85.2％ |
| Comparative example 5 | 168 | 178 | 86.6％ | 84.3％ |
| Comparative example 6 | 90 | 180 | 88.4％ | 83.8％ |
| Comparative example 7 | 90 | 189 | 90.65％ | 84.6％ |
| Comparative example 8 | 67 | 177 | 93.5％ | 89％ |
As can be seen from the comparison of the data of examples 1-6 and comparative examples 1, 3, 4 and 5 in FIG. 1 and the table, the resistivity of the lithium iron phosphate material is greatly reduced by co-doping molybdenum and fluorine elements in the lithium iron phosphate material, so that the internal resistance of the battery is reduced, and the rate performance, the cycle performance and the like of the battery are improved.
As can be seen from fig. 2 and the comparison of the data of examples 1-6 and comparative examples 1 and 2 in the table, the embodiment of the invention improves the mixing specific capacity of the cathode material and further improves the energy density and cycle performance of the battery by introducing the lithium iron silicate material with high specific capacity based on the co-doped molybdenum/lithium iron fluorophosphate cathode formulation.
And further, as can be seen from the comparison of the data of examples 1-6 and comparative examples 1-8 in the tables, the inventive example was achieved by co-doping the lithium iron phosphate material with molybdenum and fluorine elements while introducing a high specific capacity lithium iron silicate material based on the co-doped molybdenum/lithium iron fluorophosphate positive electrode formulation, and further controlling the doped lithium iron phosphate LiFe 1-x Mo x PO 4-y F y X is more than or equal to 0.2 and less than or equal to 0.8,0.5 and y is more than or equal to 1.0, and the mass ratio of doped lithium iron phosphate in the positive electrode material is 70-80% and the mass ratio of doped lithium iron silicate is 15-25%, so that the resistivity of the positive electrode plate is not more than 85mΩ & cm, the energy density is not less than 180Wh/kg, the capacity retention rate is more than 90% after 500 weeks of circulation, and the multiplying power performance is more than 85%.
The foregoing description of the preferred embodiments of the invention is not intended to limit the invention to the particular embodiments disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
Claims (10)
1. A doped lithium iron phosphate is characterized in that the chemical formula of the doped lithium iron phosphate is LiFe 1-x Mo x PO 4-y F y Wherein: x is more than or equal to 0.2 and less than or equal to 0.8,0.5, y is more than or equal to 1.0.
2. The doped lithium iron phosphate of claim 1, wherein the doped lithium iron phosphate has a particle size D50 of 0.5-4 μm.
3. A method for preparing the doped lithium iron phosphate according to claim 1 or 2, wherein the doped lithium iron phosphate is prepared by the steps of:
s1, weighing a lithium source, a molybdenum source, a fluorine source, an iron source and a phosphorus source, and uniformly mixing with a dispersing agent to obtain a mixture;
s2, ball milling the mixture obtained in the step S1 to obtain a precursor;
and S3, calcining the precursor obtained in the step S2, cooling, grinding and sieving to obtain the doped lithium iron phosphate.
4. The process according to claim 3, wherein, in step S1,
the molar ratio of the lithium element in the lithium source, the molybdenum element in the molybdenum source, the fluorine element in the fluorine source, the iron element in the iron source and the phosphorus element in the phosphorus source is 1:0.2 to 0.8:0.5 to 1:0.2 to 0.8:1, a step of;
and/or the lithium source is selected from one or more of lithium carbonate and lithium hydroxide;
and/or, the molybdenum source is selected from ammonium molybdate;
and/or, the fluorine source is selected from ammonium fluoride;
and/or, the iron source is selected from one or more of ferrous oxalate and ferrous acetate;
and/or the phosphorus source is selected from one or more of diammonium hydrogen phosphate, ammonium phosphate and ammonium hydrogen phosphate;
and/or the dispersing agent is selected from one or more of absolute ethyl alcohol, isopropyl alcohol and n-butyl alcohol.
5. The method according to claim 3, wherein in the step S2, the time of the ball milling is 6 to 14 hours;
and/or, in step S3,
the calcining temperature is 400-900 ℃ and the calcining time is 5-15 h;
and/or calcining in an air atmosphere, naturally cooling, grinding and sieving to obtain undersize, namely doped lithium iron phosphate, and then preserving in a dryer.
6. A positive electrode material, characterized in that the positive electrode material comprises 70-80% by mass of the doped lithium iron phosphate according to claim 1 or the doped lithium iron phosphate obtained by the preparation method according to any one of claims 2-5, 15-25% of lithium iron silicate, 1-5% of a binder and 1-5% of a conductive agent.
7. The positive electrode material according to claim 6, wherein the positive electrode material comprises 76% by mass of doped lithium iron phosphate, 19% by mass of lithium iron silicate, 2.5% by mass of a binder and 2.5% by mass of a conductive agent.
8. A positive electrode sheet, characterized in that the positive electrode sheet contains the positive electrode material according to any one of claims 6 to 7.
9. A lithium battery comprising the positive electrode material according to any one of claims 6 to 7 or the positive electrode sheet according to claim 8.
10. The lithium battery of claim 9, wherein the energy density of the lithium battery is not less than 180Wh/kg;
and/or, in the lithium battery, the negative electrode sheet comprises 94% -97.5% by mass: 0.75% -3%:1.75% -3% of negative electrode active material, negative electrode conductive agent and negative electrode binder;
the negative active material is selected from graphite;
the negative electrode conductive agent is selected from one or more of conductive carbon black, carbon nano tube and acetylene black;
the negative electrode binder is selected from one or more of polyacrylic acid, styrene-butadiene rubber and sodium carboxymethyl cellulose.
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