CN114400322A - Positive electrode active material, electrochemical device, and electronic device - Google Patents
Positive electrode active material, electrochemical device, and electronic device Download PDFInfo
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- CN114400322A CN114400322A CN202210155845.2A CN202210155845A CN114400322A CN 114400322 A CN114400322 A CN 114400322A CN 202210155845 A CN202210155845 A CN 202210155845A CN 114400322 A CN114400322 A CN 114400322A
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- 239000007774 positive electrode material Substances 0.000 title claims abstract description 39
- 239000011149 active material Substances 0.000 claims abstract description 104
- DVATZODUVBMYHN-UHFFFAOYSA-K lithium;iron(2+);manganese(2+);phosphate Chemical compound [Li+].[Mn+2].[Fe+2].[O-]P([O-])([O-])=O DVATZODUVBMYHN-UHFFFAOYSA-K 0.000 claims abstract description 42
- 239000002245 particle Substances 0.000 claims description 34
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 claims description 20
- 239000011230 binding agent Substances 0.000 claims description 8
- 239000006258 conductive agent Substances 0.000 claims description 6
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 6
- 238000012360 testing method Methods 0.000 description 16
- 238000000034 method Methods 0.000 description 13
- 230000000052 comparative effect Effects 0.000 description 11
- 238000005056 compaction Methods 0.000 description 10
- 239000002002 slurry Substances 0.000 description 8
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 7
- 238000000576 coating method Methods 0.000 description 7
- 230000000694 effects Effects 0.000 description 6
- 239000003792 electrolyte Substances 0.000 description 6
- 239000000463 material Substances 0.000 description 6
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 5
- 239000011248 coating agent Substances 0.000 description 5
- 229910052748 manganese Inorganic materials 0.000 description 5
- 239000011572 manganese Substances 0.000 description 5
- 238000002360 preparation method Methods 0.000 description 5
- 239000011164 primary particle Substances 0.000 description 5
- 239000002033 PVDF binder Substances 0.000 description 4
- 229910052799 carbon Inorganic materials 0.000 description 4
- ILXAVRFGLBYNEJ-UHFFFAOYSA-K lithium;manganese(2+);phosphate Chemical compound [Li+].[Mn+2].[O-]P([O-])([O-])=O ILXAVRFGLBYNEJ-UHFFFAOYSA-K 0.000 description 4
- 229910021382 natural graphite Inorganic materials 0.000 description 4
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 4
- 239000000843 powder Substances 0.000 description 4
- 229910052710 silicon Inorganic materials 0.000 description 4
- 239000010703 silicon Substances 0.000 description 4
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 3
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 3
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 3
- 229910052782 aluminium Inorganic materials 0.000 description 3
- 229910021383 artificial graphite Inorganic materials 0.000 description 3
- 238000005336 cracking Methods 0.000 description 3
- 230000001351 cycling effect Effects 0.000 description 3
- 238000001035 drying Methods 0.000 description 3
- 239000011267 electrode slurry Substances 0.000 description 3
- 229910021385 hard carbon Inorganic materials 0.000 description 3
- 229910001416 lithium ion Inorganic materials 0.000 description 3
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 3
- 239000002904 solvent Substances 0.000 description 3
- 238000003756 stirring Methods 0.000 description 3
- KMTRUDSVKNLOMY-UHFFFAOYSA-N Ethylene carbonate Chemical compound O=C1OCCO1 KMTRUDSVKNLOMY-UHFFFAOYSA-N 0.000 description 2
- 229910010710 LiFePO Inorganic materials 0.000 description 2
- 229910015645 LiMn Inorganic materials 0.000 description 2
- 229910019142 PO4 Inorganic materials 0.000 description 2
- 238000007599 discharging Methods 0.000 description 2
- JBTWLSYIZRCDFO-UHFFFAOYSA-N ethyl methyl carbonate Chemical compound CCOC(=O)OC JBTWLSYIZRCDFO-UHFFFAOYSA-N 0.000 description 2
- 239000011888 foil Substances 0.000 description 2
- DALUDRGQOYMVLD-UHFFFAOYSA-N iron manganese Chemical compound [Mn].[Fe] DALUDRGQOYMVLD-UHFFFAOYSA-N 0.000 description 2
- 230000014759 maintenance of location Effects 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 238000002156 mixing Methods 0.000 description 2
- 239000011163 secondary particle Substances 0.000 description 2
- 238000001694 spray drying Methods 0.000 description 2
- 230000002195 synergetic effect Effects 0.000 description 2
- 229920002134 Carboxymethyl cellulose Polymers 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 229910013872 LiPF Inorganic materials 0.000 description 1
- 101150058243 Lipf gene Proteins 0.000 description 1
- 238000005054 agglomeration Methods 0.000 description 1
- 230000002776 aggregation Effects 0.000 description 1
- 239000006183 anode active material Substances 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000001768 carboxy methyl cellulose Substances 0.000 description 1
- 235000010948 carboxy methyl cellulose Nutrition 0.000 description 1
- 239000008112 carboxymethyl-cellulose Substances 0.000 description 1
- 238000001311 chemical methods and process Methods 0.000 description 1
- 239000011889 copper foil Substances 0.000 description 1
- IEJIGPNLZYLLBP-UHFFFAOYSA-N dimethyl carbonate Chemical compound COC(=O)OC IEJIGPNLZYLLBP-UHFFFAOYSA-N 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 239000004973 liquid crystal related substance Substances 0.000 description 1
- 229910003002 lithium salt Inorganic materials 0.000 description 1
- 159000000002 lithium salts Chemical class 0.000 description 1
- 239000007773 negative electrode material Substances 0.000 description 1
- 239000010450 olivine Substances 0.000 description 1
- 229910052609 olivine Inorganic materials 0.000 description 1
- 238000004806 packaging method and process Methods 0.000 description 1
- 239000002985 plastic film Substances 0.000 description 1
- 229920006255 plastic film Polymers 0.000 description 1
- 238000005245 sintering Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—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
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/028—Positive electrodes
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Engineering & Computer Science (AREA)
- Inorganic Chemistry (AREA)
- Materials Engineering (AREA)
- Crystallography & Structural Chemistry (AREA)
- Manufacturing & Machinery (AREA)
- Battery Electrode And Active Subsutance (AREA)
- Secondary Cells (AREA)
Abstract
The invention provides a positive active material, an electrochemical device and electronic equipment, wherein the positive active material comprises a first active material and a second active material, and the first active material comprises lithium manganese iron phosphate; the first active material satisfies: dmin is 0.1 to 0.3 μm, D10 is 0.3 to 0.6 μm, D50 is 0.8 to 2.5 μm, D90 is 3.0 to 10 μm, and the ratio of D50 of the first active material and the second active material is 0.1 to 0.35; alternatively, the first active material satisfies: dmin is 0.2 to 0.4 μm, D10 is 1 to 3 μm, D50 is 7 to 11 μm, D90 is 15 to 25 μm, and the ratio of D50 of the first active material and the second active material is 3 to 14. The electrode prepared by the positive active material has higher compacted density, and the prepared electrochemical device has higher energy density and better cycle stability.
Description
Technical Field
The invention belongs to the technical field of batteries, and relates to a positive electrode active material, an electrochemical device and electronic equipment.
Background
Lithium manganese phosphate is (LiMnPO)4) Is a lithium iron phosphate (LiFePO)4) The positive electrode material of the lithium ion battery has an olivine structure. Lithium manganese phosphate has a higher plateau voltage (4.1V vs. Li/Li) than lithium iron phosphate+) Therefore, the material is a more ideal positive electrode material of the high-energy-density power battery. However, the intrinsic conductivity of lithium manganese phosphate is low (<10-10S/cm) which results in that the electrochemical properties thereof cannot be exerted. Meanwhile, manganese has a relatively serious ginger-taylor effect in the charging and discharging processes and a problem of manganese dissolution, resulting in relatively poor cycle performance.
In the prior art, partial iron doping or replacement is mainly performed on a manganese site of lithium manganese phosphate to obtain lithium manganese iron phosphate (LiMn)xFe1-xPO4) To ameliorate these problems. However, in the prior art, in order to meet the requirement of energy density, lithium manganese iron phosphate often needs a high proportion of manganese content, and the high content of manganese can cause the decrease of the conductivity of the lithium manganese iron phosphate, so the conductivity is usually improved by reducing the size of primary particles, coating the surface with carbon, preparing secondary spheres by spray drying, and the like.
Disclosure of Invention
In view of the problems in the prior art, it is an object of the present invention to provide a positive electrode active material, an electrochemical device, and an electronic apparatus. According to the invention, by reasonably designing the size of the lithium manganese iron phosphate and matching the lithium manganese iron phosphate with other active materials of specific sizes, the problem of low conductivity of the lithium manganese iron phosphate is solved, and the compaction density, the energy density and the cycling stability of an electrochemical device of the electrode plate are improved.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a positive active material, comprising a first active material and a second active material, wherein the first active material comprises lithium manganese iron phosphate;
the first active material satisfies: dmin is 0.1 μm to 0.3 μm, D10 is 0.3 μm to 0.6 μm, D50 is 0.8 μm to 2.5 μm, D90 is 3.0 μm to 10 μm, and the ratio of the particle diameter D50 of the first active material and the second active material is 0.1 to 0.35; or,
the first active material satisfies: dmin is 0.2 to 0.4 μm, D10 is 1 to 3 μm, D50 is 7 to 11 μm, D90 is 15 to 25 μm, and the ratio of the particle diameters D50 of the first active material and the second active material is 3 to 14.
In the present invention, the first active material satisfies: dmin is 0.1 μm to 0.3 μm, and may be, for example, 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm or the like; d10 is 0.3 μm to 0.6. mu.m, and may be, for example, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm, 0.55 μm or 0.6 μm; d50 is 0.8 μm to 2.5. mu.m, and may be, for example, 0.8. mu.m, 0.9. mu.m, 1. mu.m, 1.1. mu.m, 1.2. mu.m, 1.3. mu.m, 1.4. mu.m, 1.5. mu.m, 1.6. mu.m, 1.7. mu.m, 1.8. mu.m, 1.9. mu.m, 2. mu.m, 2.1. mu.m, 2.2. mu.m, 2.3. mu.m, 2.4. mu.m, 2.5. mu.m, or the like; d90 is 3.0 μm to 10 μm, and may be, for example, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm; the ratio of the particle diameter D50 of the first active material and the second active material is 0.1 to 0.35, and may be, for example, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, or the like.
In the present invention, the first active material satisfies: dmin is 0.2 μm to 0.4. mu.m, and may be, for example, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm or 0.4 μm; d10 is 1 μm to 3 μm, and may be, for example, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm or the like; d50 is 7 μm to 11 μm, and may be, for example, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, or the like; d90 is 15 μm to 25 μm, and may be, for example, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, or the like; the ratio of the particle diameter D50 of the first active material and the second active material is 3 to 14, and may be, for example, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or the like.
The compacted density of the lithium iron manganese phosphate powder widely used at present is only 1.9g/cm3To 2.2g/cm3Far below the compacted density of lithium iron phosphate (2.4 g/cm)3) Therefore, when used as a positive electrode active material, it results in a low volumetric energy density of a battery. In addition, in the prior art, the compaction density of the material is easily further reduced by reducing the size of primary particles of the lithium manganese iron phosphate or improving the conductivity of the material by surface carbon coating, and the problems that the specific surface area of the lithium manganese iron phosphate is relatively high, the pole piece is difficult to manufacture, the energy density and the cycling stability of an electrochemical device are poor and the like are caused.
According to the invention, the lithium manganese iron phosphate with a specific size is selected and matched with second active materials with other sizes for use, the materials are reasonably matched in size, and under the synergistic effect, the prepared positive active material has a relatively appropriate specific surface area and good electrochemical performance, the problem of low conductivity of the lithium manganese iron phosphate can be solved, the problems of slurry gel, diaphragm cracking, powder falling and the like in the homogenizing and coating processes can be solved, the content of a binder is reduced, the compaction density and the energy density of a pole piece are improved, and the cycle stability of an electrochemical device is improved.
Preferably, the morphology of the first active material is a nano-morphology and the morphology of the second active material is a secondary sphere morphology.
Preferably, the mass ratio of the first active material to the second active material is (1 to 5: 1), and may be, for example, 1:1, 2:1, 3:1, 4:1, or 5:1, etc.
Preferably, the ratio of the particle size D50 of the first active material and the second active material is 0.11 to 0.15, and may be, for example, 0.11, 0.12, 0.13, 0.14, 0.15, or the like.
Preferably, the morphology of the first active material is a secondary sphere morphology and the morphology of the second active material is a nano-morphology.
Preferably, the mass ratio of the first active material to the second active material is 1 (1 to 5), and may be, for example, 1:1, 2:1, 3:1, 4:1, or 5:1.
Preferably, the ratio of the particle size D50 of the first active material and the second active material is 7 to 9, and may be, for example, 7, 7.5, 8, 8.5, or 9, etc.
The nano-form in the present invention means that the average particle diameter of primary particles of the active material is in the range of one nanometer to several hundred nanometers, which has a problem that agglomeration causes a large particle diameter test result during the test process, but the preferred nano-form active material of the present invention is distributed in a nano-form during the process of preparing the positive electrode; the secondary sphere shape refers to secondary particles formed by subjecting primary particles to physical or chemical processes such as spray drying and sintering, and is distributed in a secondary sphere shape during the process of preparing the positive electrode.
The active material of primary particles in a nano form and the active material of secondary particles in a secondary ball form are preferably matched for use, the grading effect is better, the nano form particles in a specific proportion are filled among the particles in the secondary ball form, the utilization rate of space is improved, the compaction density and the volume energy density are improved, meanwhile, the specific surface area of the slurry can be reduced by introducing the active material in the secondary ball form, the proportion of the nano form particles with specific content to the particles in the secondary ball form is improved, the process performance of homogenate coating is improved, the positive active material prepared by adopting the combination and matching is more regular in form, and the cycle performance is obviously improved.
Preferably, the general formula of the lithium iron manganese phosphate in the first active material is LiMnxFe1-xPO4，0.5<x<0.9 may be, for example, 0.5, 0.6, 0.7, 0.8, 0.9, or the like.
As a preferable technical solution of the positive electrode active material of the present invention, the second active material includes lithium iron phosphate and/or lithium manganese iron phosphate.
The second active material can be selected from lithium iron phosphate and/or lithium manganese iron phosphate, when the lithium manganese iron phosphate is selected, the chemical formula of the second active material is not limited, and the second active material can be matched with the lithium manganese iron phosphate in the first active material only by proper particle size.
As a preferable embodiment of the positive electrode active material of the present invention, the lithium iron phosphate is a nano-form lithium iron phosphate, and the particle size D50 of the lithium iron phosphate is 0.8 μm to 2.5 μm, and may be, for example, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, or 2.5 μm.
Preferably, the lithium iron phosphate is lithium iron phosphate in a secondary sphere form, and the particle size D50 of the lithium iron phosphate in the secondary sphere form is 7 μm to 11 μm, and may be, for example, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, or 11 μm.
Preferably, the lithium manganese iron phosphate is a nano-form lithium manganese iron phosphate, and the particle size D50 of the lithium manganese iron phosphate is 0.8 μm to 2.5 μm, and may be, for example, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, or 2.5 μm.
Preferably, the lithium manganese iron phosphate is lithium manganese iron phosphate in a secondary sphere form, and the particle size D50 of the lithium manganese iron phosphate is 7 μm to 11 μm, and may be, for example, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, or 11 μm.
In a second aspect, the present invention provides an electrochemical device comprising the positive electrode active material according to the first aspect in a positive electrode thereof.
The electrochemical device prepared by the positive active material has higher energy density and better cycle stability.
In some embodiments, the electrochemical device comprises a lithium ion battery, but the application is not limited thereto.
Preferably, the positive electrode further comprises a positive electrode active material, a conductive agent and a binder, wherein the mass ratio of the positive electrode active material, the conductive agent and the binder in the positive electrode is (90-99): 1.5:2, such as 90:1.5:2, 91:1.5:2, 92:1.5:2, 93:1.5:2, 94:1.5:2, 95:1.5:2, 96:1.5:2, 97:1.5:2, 98:1.5:2 or 99:1.5: 2.
Preferably, the conductive agent comprises conductive carbon black (Super P) and/or conductive carbon tubes (CNT).
Preferably, the binder comprises polyvinylidene fluoride (PVDF).
Preferably, the mass ratio of the positive electrode active material, the conductive carbon black, the conductive carbon tube and the polyvinylidene fluoride in the positive electrode is (90 to 99):1:0.5:2, and may be, for example, 90:1:0.5:2, 91:1:0.5:2, 92:1:0.5:2, 93:1:0.5:2, 94:1:0.5:2, 95:1:0.5:2, 96:1:0.5:2, 97:1:0.5:2, 98:1:0.5:2, or 99:1:0.5:2, or the like.
The preparation method of the positive electrode is not limited, and for example, a positive electrode active material, a conductive agent and a binder in a certain proportion are mixed in a solvent to obtain positive electrode slurry, and then the prepared positive electrode slurry is uniformly coated on the surface of a current collector and dried to obtain the positive electrode.
Illustratively, the electrochemical device further includes a negative electrode, a separator, and an electrolyte.
Illustratively, the kind of the negative active material in the negative electrode includes, but is not limited to, any one of or a combination of at least two of artificial graphite, natural graphite, hard carbon, or silicon, and may be, for example, a combination of artificial graphite and natural graphite, a combination of hard carbon and silicon, a combination of natural graphite and silicon, or a combination of artificial graphite, natural graphite, hard carbon, and silicon, or the like.
Illustratively, the electrolyte includes a lithium salt and a nonaqueous solvent.
In the present invention, the method of assembling an electrochemical device using the positive electrode is prior art, and those skilled in the art can assemble the electrochemical device by referring to the methods disclosed in the prior art. Taking a lithium ion battery as an example, a positive electrode, a diaphragm and a negative electrode are sequentially wound or stacked to form a battery core, the battery core is placed in a battery case, electrolyte is injected, formation and packaging are performed, and the electrochemical device is obtained.
In a third aspect, the present invention provides an electronic device comprising an electrochemical device according to the second aspect.
The electronic device according to the present invention may be, for example, a mobile computer, a portable phone, a memory card, a liquid crystal television, an automobile, a motorcycle, a motor, a timepiece, a camera, or the like.
Compared with the prior art, the invention has the following beneficial effects:
according to the invention, the lithium manganese iron phosphate with a specific size is selected and matched with second active materials with other sizes for use, the materials are reasonably matched in size, and under the synergistic effect, the prepared positive active material has a relatively appropriate specific surface area and good electrochemical performance, the problem of low conductivity of the lithium manganese iron phosphate can be solved, the problems of slurry gel, diaphragm cracking, powder falling and the like in the homogenizing and coating processes can be solved, the content of a binder is reduced, the compaction density and the energy density of a pole piece are improved, and the cycle stability of an electrochemical device is improved.
Drawings
Fig. 1 is a graph comparing the compacted densities of the positive electrode sheets in example 1 of the present invention and comparative example 1.
Detailed Description
The technical solution of the present invention is further explained by the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.
Example 1
The present embodiment provides a positive electrode active material including a first active material and a second active material, where the first active material is a nano-form lithium iron manganese phosphate (LiMn)0.6Fe0.4PO4) The second active material is lithium iron phosphate (LiFePO) in a secondary sphere form4) The mass ratio of the first active material to the second active material is 4.85: 1;
particle size D of nano-form lithium iron manganese phosphate in first active materialmin0.24 μm, 0.4 μm for D10, 1.1 μm for D50, 9.6 μm for D90; the particle diameter D50 of the secondary-sphere-shaped lithium iron phosphate in the second active material was 8.6 μm, and the ratio of the particle diameter D50 of the first active material to the particle diameter D50 of the second active material was 0.13.
The invention also provides a preparation method of the positive active material, which comprises the following steps: and placing the lithium iron manganese phosphate and the lithium iron phosphate with the mass ratio of 80:16.5 into a container, and stirring and mixing at a high speed of 1500r/min to obtain the anode active material.
The present embodiment also provides an electrochemical device, in which a positive electrode of the electrochemical device includes the positive electrode active material, and a method for manufacturing the electrochemical device includes:
(1) preparation of the positive electrode: dispersing and stirring Super P, CNT, N-methyl pyrrolidone (NMP) and PVDF at a mass ratio of 1:0.5:80:2 for 2h at a rotation speed of 1500r/min to prepare conductive slurry, stirring and mixing a positive active material and the conductive slurry at a high speed to prepare positive slurry with certain viscosity, uniformly coating the prepared slurry on an aluminum foil by using a scraper, placing the aluminum foil on a blast drying box, and drying at 120 ℃ for 20min to obtain a positive electrode, wherein the surface density of the positive active material in the positive electrode is 20mg/cm2；
(2) Preparation of a negative electrode: dispersing graphite, conductive carbon black and carboxymethyl cellulose with a mass ratio of 96:2:2 in NMP to prepare negative electrode slurry with certain viscosity, then uniformly coating the prepared slurry on the surface of copper foil by using a scraper, and drying for 20min at 120 ℃ to obtain a negative electrode;
(3) assembling the electrochemical device: the electrolyte adopts LiPF with the concentration of 1M6And (3) electrolyte, wherein the solvents in the electrolyte are Ethylene Carbonate (EC), Ethyl Methyl Carbonate (EMC) and dimethyl carbonate (DMC) in a mass ratio of 1:1:1, the diaphragm adopts a PE base film with the thickness of 8 mu m, and then the positive electrode and the negative electrode are adopted, assembled and packaged by using an aluminum plastic film to obtain the electrochemical device.
In examples 2 and 3, parameters were changed in addition to the procedure of example 1, and specific changed parameters are shown in table 1.
First, compaction Density test
The positive electrodes prepared in the examples and comparative examples of the present invention were rolled at a pressure of 20MPa to obtain a positive electrode sheet, and the mass thereof was divided by (thickness × area) to obtain a compacted density.
Second, energy density test
The method comprises the steps of adopting a battery performance testing system (testing cabinet) of the electrical and gas company Limited of the Hongyong electrical apparatus, wherein the equipment model is BTS05/10C8D-HP, placing the electrochemical devices of the embodiment and the comparative example in the testing cabinet to test at 25 ℃, charging the electrochemical devices to 100% SOC at 0.33C, standing for 30min, discharging the 0.33C to 0% SOC, recording the discharge energy, and obtaining the energy density by dividing the discharge energy by the thickness of a positive pole piece.
Third, testing the stability of the cycle
A battery performance testing system (testing cabinet) of the electrical and gas company Limited of the Honghong electrical apparatus is adopted, the model number of the equipment is BTS05/10C8D-HP, the electrochemical devices of the embodiment and the comparative example are placed in the testing cabinet to be tested at 25 ℃, the discharge capacity of the testing battery is tested at 1C/1C circulation, and the 100 th discharge capacity is divided by the first discharge capacity to obtain the 100 th capacity retention rate.
The test results of examples 1 to 3 are shown in table 2.
TABLE 1
TABLE 2
| Compacted density (g/cm)3) | Energy Density (Wh/L) | Capacity retention (%) | |
| Example 1 | 2.46 | 1391 | 99.7 |
| Example 2 | 2.48 | 1450 | 99.0 |
| Example 3 | 2.62 | 1551 | 98.8 |
In example 4, parameters were changed in addition to the procedure of example 2, and specific changed parameters and test results are shown in table 3.
TABLE 3
As can be seen from comparison between the embodiment 2 and the embodiment 4 in table 3, the first active material and the second active material in two different forms have a better effect when used in combination, when the first active material and the second active material are both in a nano form, the specific surface area of the first active material and the second active material is large, the problems of cracking, gelling, powder falling and the like can occur in the preparation process of the pole piece, the grading effect of the two materials is poor, and the compaction density and the cycle stability of the prepared positive active material are both reduced, so that the technical effect of the embodiment 2 is better than that of the embodiment 4.
Examples 5 to 7 and comparative examples 1 to 2 were modified based on the procedure of example 1, and the specific modified parameters and test results are shown in tables 4 to 5.
TABLE 4
As can be seen from a comparison of example 1 with examples 5 through 6 in Table 4, the first active material and the second active material are preferably present in amounts that, when combined in the proper ratio, provide the best results; when the content of the first active material is higher, the grading effect is not significant, the increase of the compaction density is not significant, and the cycle performance of the process is poor, and when the content of the first active material is lower, the increase of the compaction density is hardly generated, so that the energy density of examples 5 to 6 is lower than that of example 1.
TABLE 5
As is clear from comparison between example 1 and example 7 in table 5, the iron-manganese ratio of the lithium manganese iron phosphate in the present invention is preferable, and a higher manganese-iron ratio is selected to achieve a higher energy density.
TABLE 6
As can be seen from comparison between example 1 and example 8 in table 6 and comparative examples 1 to 2, the first active material having an appropriate particle size D50 and the second active material having an appropriate particle size ratio are selected in the present invention, so as to improve the overall performance of the positive electrode active material; the ratio of the particle size D50 in example 8 exceeds the range of 0.11 to 0.15, the ratio of the particle size D50 of the first active material and the second active material in comparative examples 1 and 2 both exceed the range of (0.1 to 0.35) or (3 to 14) of the invention, and the particle size D50 of the nano-form lithium iron manganese phosphate in comparative example 2 is smaller, the compacted density of the prepared pole piece is lower, fig. 1 is a comparison of the compacted densities of the pole pieces prepared in example 1 of the invention and comparative example, and from fig. 1, the compacted densities of the pole pieces prepared in example 1 of the invention and comparative example can be obtained by comparing fig. 1As can be seen, the compacted density of the pole piece in example 1 was about 0.24g/cm higher than that of comparative example 13The electrochemical device is inferior in both energy density and cycle stability.
In summary, in embodiments 1 to 8, it can be seen that, by reasonably designing the size of the lithium manganese iron phosphate, and matching the lithium manganese iron phosphate with other active materials of specific sizes, the problem of low conductivity of the lithium manganese iron phosphate is solved, and the compaction density, the energy density, and the cycling stability of the electrochemical device of the electrode plate are improved.
The above description is only for the specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are within the protection scope and the disclosure of the present invention.
Claims (10)
1. A positive electrode active material, characterized in that the positive electrode active material comprises a first active material and a second active material, the first active material comprising lithium manganese iron phosphate;
the first active material satisfies: dmin is 0.1 μm to 0.3 μm, D10 is 0.3 μm to 0.6 μm, D50 is 0.8 μm to 2.5 μm, D90 is 3.0 μm to 10 μm, and the ratio of the particle diameter D50 of the first active material and the second active material is 0.1 to 0.35; or,
the first active material satisfies: dmin is 0.2 to 0.4 μm, D10 is 1 to 3 μm, D50 is 7 to 11 μm, D90 is 15 to 25 μm, and the ratio of the particle diameters D50 of the first active material and the second active material is 3 to 14.
2. The positive electrode active material according to claim 1, wherein the morphology of the first active material is a nano-morphology, the morphology of the second active material is a secondary sphere morphology, and the first active material and the second active material satisfy at least one of the following conditions (a) to (b):
(a) the mass ratio of the first active material to the second active material is (1 to 5): 1;
(b) the ratio of the particle diameter D50 of the first active material and the second active material is 0.11 to 0.15.
3. The positive electrode active material according to claim 1, wherein the morphology of the first active material is a secondary sphere morphology, the morphology of the second active material is a nano-morphology, and the first active material and the second active material satisfy at least one of the following conditions (c) to (d):
(c) the mass ratio of the first active material to the second active material is 1 (1 to 5);
(d) the ratio of the particle diameter D50 of the first active material and the second active material is 7 to 9.
4. The positive electrode active material according to claim 1, wherein the general formula of the lithium iron manganese phosphate in the first active material is LiMnxFe1-xPO4，0.5<x<0.9。
5. The positive electrode active material according to claim 1, wherein the second active material comprises lithium iron phosphate and/or lithium manganese iron phosphate.
6. The positive electrode active material according to claim 5, wherein in the second active material, the lithium iron phosphate satisfies at least one of the following conditions (e) to (f):
(e) the lithium iron phosphate is in a nano form, and the particle size D50 of the lithium iron phosphate is 0.8-2.5 μm;
(f) the lithium iron phosphate is in a secondary sphere shape, and the particle size D50 of the lithium iron phosphate in the secondary sphere shape is 7-11 μm.
7. The positive electrode active material according to claim 5, wherein in the second active material, the lithium iron manganese phosphate satisfies at least one of the following conditions (g) to (h):
(g) the lithium manganese iron phosphate is in a nano form, and the particle size D50 of the lithium manganese iron phosphate is 0.8-2.5 mu m;
(h) the lithium manganese iron phosphate is in a secondary sphere shape, and the particle size D50 of the lithium manganese iron phosphate is 7-11 μm.
8. An electrochemical device, characterized in that a positive electrode of the electrochemical device comprises the positive electrode active material according to any one of claims 1 to 7.
9. The electrochemical device according to claim 8, wherein the positive electrode further comprises a conductive agent and a binder, and the mass ratio of the positive electrode active material, the conductive agent and the binder in the positive electrode is (90-99): 1.5: 2.
10. An electronic device, characterized in that the electrochemical device according to claim 8 or 9 is included in the electronic device.
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