CN114400322B - 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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- CN114400322B CN114400322B CN202210155845.2A CN202210155845A CN114400322B CN 114400322 B CN114400322 B CN 114400322B CN 202210155845 A CN202210155845 A CN 202210155845A CN 114400322 B CN114400322 B CN 114400322B
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- 239000007774 positive electrode material Substances 0.000 title claims abstract description 38
- 239000011149 active material Substances 0.000 claims abstract description 99
- 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 46
- 239000002245 particle Substances 0.000 claims description 33
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 claims description 21
- 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 5
- 229910015645 LiMn Inorganic materials 0.000 claims description 3
- 229910019142 PO4 Inorganic materials 0.000 claims description 3
- 238000005056 compaction Methods 0.000 abstract description 10
- 230000001351 cycling effect Effects 0.000 abstract description 8
- 238000012360 testing method Methods 0.000 description 14
- 238000000034 method Methods 0.000 description 12
- 230000000052 comparative effect Effects 0.000 description 10
- 239000011248 coating agent Substances 0.000 description 8
- 238000000576 coating method Methods 0.000 description 8
- 239000000463 material Substances 0.000 description 8
- 239000002002 slurry Substances 0.000 description 8
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 7
- 230000000694 effects Effects 0.000 description 7
- 238000002360 preparation method Methods 0.000 description 7
- 239000003792 electrolyte Substances 0.000 description 6
- 239000000843 powder Substances 0.000 description 6
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 5
- 239000002033 PVDF binder Substances 0.000 description 5
- 239000011267 electrode slurry Substances 0.000 description 5
- ILXAVRFGLBYNEJ-UHFFFAOYSA-K lithium;manganese(2+);phosphate Chemical compound [Li+].[Mn+2].[O-]P([O-])([O-])=O ILXAVRFGLBYNEJ-UHFFFAOYSA-K 0.000 description 5
- 229910052748 manganese Inorganic materials 0.000 description 5
- 239000011572 manganese Substances 0.000 description 5
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 5
- 239000011164 primary particle Substances 0.000 description 5
- 229910052799 carbon Inorganic materials 0.000 description 4
- 238000005336 cracking Methods 0.000 description 4
- 229910021382 natural graphite Inorganic materials 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
- 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
- 238000001035 drying Methods 0.000 description 3
- 229910021385 hard carbon Inorganic materials 0.000 description 3
- 229910001416 lithium ion Inorganic materials 0.000 description 3
- 239000012528 membrane Substances 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
- 230000002195 synergetic effect Effects 0.000 description 3
- OTYYBJNSLLBAGE-UHFFFAOYSA-N CN1C(CCC1)=O.[N] Chemical compound CN1C(CCC1)=O.[N] OTYYBJNSLLBAGE-UHFFFAOYSA-N 0.000 description 2
- KMTRUDSVKNLOMY-UHFFFAOYSA-N Ethylene carbonate Chemical group O=C1OCCO1 KMTRUDSVKNLOMY-UHFFFAOYSA-N 0.000 description 2
- 229910010707 LiFePO 4 Inorganic materials 0.000 description 2
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 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
- 238000002156 mixing Methods 0.000 description 2
- 238000004806 packaging method and process Methods 0.000 description 2
- 238000011056 performance test Methods 0.000 description 2
- 238000001694 spray drying Methods 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
- 229910015831 LiMn0.6Fe0.4PO4 Inorganic materials 0.000 description 1
- 229910013870 LiPF 6 Inorganic materials 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
- 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
- 239000010406 cathode material Substances 0.000 description 1
- 230000001413 cellular effect Effects 0.000 description 1
- 238000001311 chemical methods and process Methods 0.000 description 1
- 239000011889 copper foil Substances 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- IEJIGPNLZYLLBP-UHFFFAOYSA-N dimethyl carbonate Chemical compound COC(=O)OC IEJIGPNLZYLLBP-UHFFFAOYSA-N 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 238000011049 filling 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
- 238000004519 manufacturing process Methods 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
- 239000002985 plastic film Substances 0.000 description 1
- 229920006255 plastic film Polymers 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 239000011163 secondary particle Substances 0.000 description 1
- 238000005245 sintering Methods 0.000 description 1
- 238000013112 stability test Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 238000004804 winding Methods 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
-
- 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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- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- 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 electrode active material, an electrochemical device and an electronic apparatus, wherein the positive electrode 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 to 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 D50 of the first active material to the second active material is 3 to 14. The electrode prepared from the positive electrode active material has higher compaction density, and the prepared electrochemical device has higher energy density and better cycling 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
The lithium manganese phosphate (LiMnPO 4) is a lithium ion battery cathode material having an olivine structure like the lithium iron phosphate (LiFePO 4). Compared with lithium iron phosphate, the lithium manganese phosphate has higher platform voltage (4.1V vs. Li/Li +), so the lithium manganese phosphate is a more ideal high-energy-density power battery positive electrode material. However, the intrinsic conductivity of lithium manganese phosphate is low (< 10 -10 S/cm), which results in that its electrochemical performance cannot be exerted. Meanwhile, manganese has a serious ginger-taylor effect in the charging and discharging process, and has the problem of manganese dissolution, so that poor cycle performance is caused.
The prior art mainly ameliorates these problems by partially iron doping or substituting the manganese sites of lithium manganese phosphate to obtain lithium manganese iron phosphate (LiMn xFe1-xPO4). However, in the prior art, in order to meet the requirement of energy density, the lithium iron manganese phosphate often needs a higher proportion of manganese content, and the high content of manganese can lead to the reduction of the conductivity of the lithium iron manganese phosphate, so that the conductivity is improved in the modes of reducing the primary particle size, coating surface carbon, preparing secondary balls by spray drying and the like, however, the energy density of the lithium iron manganese phosphate can be reduced in the modes of improving the conductivity, and meanwhile, the problems of slurry gel, membrane cracking, powder falling and the like are easy to occur in the processes of homogenizing and coating of the material prepared by adopting the modes, so that the further development of the lithium iron manganese phosphate is limited.
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, the size of the lithium iron manganese phosphate is reasonably designed, and the lithium iron manganese phosphate is matched with other active materials with specific sizes to realize synergistic effect, so that the problem of low conductivity of the lithium iron manganese phosphate is solved, and meanwhile, 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 aim of the invention, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a positive electrode active material comprising a first active material comprising lithium iron manganese phosphate and a second active material;
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 diameters D50 of the first active material and the second active material is 0.1 to 0.35; or alternatively
The first active material satisfies: dmin is 0.2 μm to 0.4 μm, D10 is 1 μm to 3 μm, D50 is 7 μm to 11 μm, D90 is 15 μm 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, or 0.3 μm, etc.; d10 is 0.3 μm to 0.6 μm, 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, etc.; the D50 is 0.8 μm to 2.5. Mu.m, 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, etc.; d90 is 3.0 μm to 10. Mu.m, and may be, for example, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm, etc.; the ratio of the particle diameters 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, or 0.35, etc.
In the present invention, the first active material satisfies: dmin is 0.2 μm to 0.4 μm, and may be, for example, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, or 0.4 μm, etc.; 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 or 11 μm, etc.; d90 is 15 μm to 25. Mu.m, 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 diameters 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, or 14, etc.
The compacted density of the currently widely used lithium iron manganese phosphate powder is often only 1.9g/cm 3 to 2.2g/cm 3, which is far lower than the compacted density of lithium iron phosphate (2.4 g/cm 3), so that the use of the lithium iron manganese phosphate powder as a positive electrode active material leads to lower 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 primary particle size of the lithium iron manganese phosphate or coating the surface carbon to improve the conductivity of the material, and the problems that the specific surface area of the lithium iron manganese 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 is matched with the second active material with other sizes, the size collocation between the materials is reasonable, and the materials are synergistic, so that the prepared positive electrode active material has a proper 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, membrane cracking, powder falling and the like in the processes of homogenizing and coating can be solved, the content of a binder is reduced, the compaction density and the energy density of a pole piece are improved, and meanwhile, the cycling stability of an electrochemical device is improved.
Preferably, the first active material is in a nano-morphology and the second active material is in a secondary sphere morphology.
Preferably, the mass ratio of the first active material to the second active material is (1 to 5): 1, which may be, for example, 1:1, 2:1, 3:1, 4:1, or 5:1, etc.
Preferably, the ratio of the particle diameters 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 first active material is in a secondary spherical form, and the second active material is in a nano form.
Preferably, the mass ratio of the first active material to the second active material is 1 (1 to 5), which may be, for example, 1:1, 2:1, 3:1, 4:1, 5:1, etc.
Preferably, the ratio of the particle diameters D50 of the first active material and the second active material is 7 to 9, and may be 7, 7.5, 8, 8.5, 9, or the like, for example.
The nano-morphology refers to the problem that the average particle size of primary particles of an active material is in the range of one nanometer to hundreds of nanometers, and agglomeration exists in the testing process, so that the particle size testing result is larger, but the active material with the preferred nano-morphology is distributed in the nano-morphology in the process of preparing the anode; the secondary sphere shape refers to secondary particles formed by the primary particles through physical or chemical processes such as spray drying, sintering, etc., which are distributed in the secondary sphere shape during the preparation of the positive electrode.
The active material of the primary particles in the nanometer form and the active material in the secondary sphere form are preferably matched for use, the grading effect is better, the nanometer form particles in the specific proportion are filled among the particles in the secondary sphere 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 sphere form, the proportion of the nanometer form particles with the specific content and the secondary sphere form particles is improved, the processing performance of homogenate coating is improved, and the anode active material prepared by adopting the combination matching is more regular in form and obviously improved in cycle performance.
Preferably, the general formula of lithium iron manganese phosphate in the first active material is LiMn xFe1-xPO4, 0.5< x <0.9, for example, may be 0.5, 0.6, 0.7, 0.8, or 0.9, etc.
As a preferable embodiment of the positive electrode active material according to the present invention, the second active material includes lithium iron phosphate and/or lithium manganese iron phosphate.
In the invention, the second active material can be selected from lithium iron phosphate and/or lithium manganese iron phosphate, and 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 nano-form lithium iron phosphate, and the particle diameter 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, etc.
Preferably, the lithium iron phosphate is a secondary sphere form of lithium iron phosphate having a particle diameter D50 of 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, etc.
Preferably, the lithium manganese iron phosphate is nano-form lithium manganese iron phosphate, and the particle diameter 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, etc.
Preferably, the lithium iron manganese phosphate is a secondary sphere form lithium iron manganese phosphate, and the particle diameter D50 of the lithium iron manganese phosphate is 7 μm to 11 μm, and may be 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, for example.
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 of the electrochemical device.
The electrochemical device prepared from the positive electrode active material has higher energy density and better cycling stability.
In some embodiments, the electrochemical device includes a lithium ion battery, but the present 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 to 99) 1.5:2, for example, 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, 99:1.5:2, and the like.
Preferably, the conductive agent includes conductive carbon black (Super P) and/or conductive carbon tube (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, 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, etc.).
The preparation method of the positive electrode is not limited, for example, a certain proportion of positive electrode active material, conductive agent and binder can be 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 types of the negative electrode active material in the negative electrode include, but are not limited to, any one of artificial graphite, natural graphite, hard carbon, or silicon, or a combination of at least two thereof, 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 for assembling the electrochemical device using the positive electrode is a prior art, and a person skilled in the art can assemble the electrochemical device by referring to the method disclosed in the prior art. Taking a lithium ion battery as an example, sequentially winding or stacking a positive electrode, a diaphragm and a negative electrode to form a battery core, filling the battery core into a battery shell, injecting electrolyte, forming, and packaging to obtain the electrochemical device.
In a third aspect, the present invention provides an electronic device comprising the electrochemical apparatus according to the second aspect.
The electronic device according to the invention may be, for example, a mobile computer, a cellular phone, a memory card, a liquid crystal television, an automobile, a motorcycle, a motor, a timepiece, a camera, etc.
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 is matched with the second active material with other sizes, the size collocation between the materials is reasonable, and the materials are synergistic, so that the prepared positive electrode active material has a proper 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, membrane cracking, powder falling and the like in the processes of homogenizing and coating can be solved, the content of a binder is reduced, the compaction density and the energy density of a pole piece are improved, and meanwhile, the cycling stability of an electrochemical device is improved.
Drawings
Fig. 1 is a graph showing the comparison of the compacted densities of the positive electrode sheets in example 1 of the present invention and comparative example 1.
Detailed Description
The technical scheme of the invention is further described by the following specific embodiments. It will be apparent to those skilled in the art that the examples are merely to aid in understanding the invention and are not to be construed as a specific limitation thereof.
Example 1
The embodiment provides a positive electrode active material, which comprises a first active material and a second active material, wherein the first active material is nano-form lithium iron manganese phosphate (LiMn 0.6Fe0.4PO4), the second active material is secondary-sphere-form lithium iron phosphate (LiFePO 4), and the mass ratio of the first active material to the second active material is 4.85:1;
the particle size D min of the nano-form lithium iron manganese phosphate in the first active material is 0.24 μm, D10 is 0.4 μm, D50 is 1.1 μm, and D90 is 9.6 μm; the particle diameter D50 of the lithium iron phosphate in the secondary sphere form in the second active material is 8.6 μm, and the ratio of the particle diameters D50 of the first active material and the second active material is 0.13.
The invention also provides a preparation method of the positive electrode active material, which comprises the following steps: and (3) placing the lithium iron manganese phosphate and the lithium iron phosphate with the mass ratio of 80:16.5 into a container, stirring and mixing at a high speed, and obtaining the positive electrode active material at the rotating speed of 1500 r/min.
The embodiment also provides an electrochemical device, wherein the positive electrode of the electrochemical device comprises the positive electrode active material, and the preparation method of the electrochemical device comprises the following steps:
(1) Preparation of positive electrode: dispersing and stirring Super P, CNT, nitrogen Methyl Pyrrolidone (NMP) and PVDF at a mass ratio of 1:0.5:80:2 for 2 hours at a high speed, preparing conductive slurry at a rotating speed of 1500r/min, stirring and mixing a positive electrode active material and the conductive slurry at a high speed to prepare positive electrode slurry with a certain viscosity, wherein the mass ratio of the Super P, CNT, nitrogen methyl pyrrolidone and PVDF in the positive electrode slurry is 80:16.5:1:0.5:80:2, uniformly coating the prepared slurry on aluminum foil by using a scraper, placing the aluminum foil in a blast drying box, and drying for 20 minutes at 120 ℃ to obtain a positive electrode, wherein the surface density of the positive electrode active material in the positive electrode is 20mg/cm 2;
(2) Preparation of the negative electrode: dispersing graphite, conductive carbon black and carboxymethyl cellulose in a mass ratio of 96:2:2 in NMP to prepare negative electrode slurry with certain viscosity, uniformly coating the prepared slurry on the surface of a copper foil by using a scraper, and drying for 20min at 120 ℃ to obtain a negative electrode;
(3) Assembly of electrochemical device: the electrolyte adopts LiPF 6 electrolyte with the concentration of 1M, the solvent in the electrolyte is Ethylene Carbonate (EC), methyl ethyl carbonate (EMC) and dimethyl carbonate (DMC) with the mass ratio of 1:1:1, the diaphragm adopts PE base film with the thickness of 8 mu M, then the anode and the cathode are adopted, and the electrochemical device is obtained by assembling and packaging by using an aluminum plastic film.
Examples 2 and 3 were obtained by changing parameters based on the procedure of example 1, and the parameters of the specific changes are shown in table 1.
1. Compaction density test
The positive electrodes prepared in examples and comparative examples of the present invention were rolled at a pressure of 20MPa to obtain positive electrode sheets, and then the mass thereof was divided by (thickness x area) to obtain a compacted density.
2. Energy density testing
The electrochemical devices of the examples and the comparative examples were tested in a test cabinet at 25℃using Cheng Hong electric appliances, inc. battery performance test system (test cabinet) having a device model of BTS05/10C8D-HP, charged to 100% SOC at 0.33C, left to stand for 30 minutes, discharged to 0% SOC at 0.33C, and the discharged energy was recorded, divided by the thickness of the positive electrode sheet to obtain the energy density.
3. Cycle stability test
The electrochemical devices of the examples and the comparative examples are placed in a test cabinet at 25 ℃ for testing by adopting a Cheng Hong electric appliance Co., ltd battery performance test system (test cabinet) with the equipment model of BTS05/10C8D-HP, and the discharge capacity of the test battery is obtained when the test battery is cycled at 1C/1C, and the 100 th discharge capacity is divided by the first circle discharge capacity, so that the 100 th capacity retention rate is obtained.
The test results of examples 1 to 3 are shown in table 2.
TABLE 1
TABLE 2
| Compaction 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, the parameters were changed based on the procedure of example 2, and the specific changed parameters and test results are shown in table 3.
TABLE 3 Table 3
As can be seen from the comparison between the examples 2 and 4 in Table 3, the first and second active materials with two different forms have better matching effect, and when the first and second active materials are in nano form, the specific surface area is larger, and problems such as cracking, gel and powder falling occur in the pole piece preparation process, the grading effect of the two materials is poorer, and the compaction density and the cycle stability of the prepared positive electrode active material are reduced, so that the technical effect of the example 2 is better than that of the example 4.
Examples 5 to 7 and comparative examples 1 to 2 were obtained by modifying parameters based on the procedure of example 1, and the specifically modified parameters and test results are shown in tables 4 to 5.
TABLE 4 Table 4
As can be seen from a comparison of example 1 with examples 5 to 6 in Table 4, the first active material and the second active material are preferably present in the present invention, and the two are mixed in a proper ratio to give the best effect; when the content of the first active material is higher, the grading effect is not obvious, the improvement of the compacted density is not obvious, and the cycle performance of the process is poor, and when the content of the first active material is lower, the compacted density is hardly improved, so that the energy density of examples 5 to 6 is lower than that of example 1.
TABLE 5
As can be seen from a comparison of example 1 with example 7 in Table 5, the iron-manganese ratio of the lithium iron manganese phosphate in the present invention is preferred, and a higher manganese-iron ratio is selected for achieving a higher energy density.
TABLE 6
As can be seen from the comparison of examples 1 and 8 and comparative examples 1 to 2 in table 6, the selection of the first active material having a suitable particle size D50 and the second active material having a suitable particle size ratio in the present invention is advantageous in improving the overall performance of the positive electrode active material; in example 8, the ratio of the particle diameter D50 exceeds the range of 0.11 to 0.15, the ratio of the particle diameters D50 of the first active material and the second active material in comparative examples 1 and 2 is beyond the range of (0.1 to 0.35) or (3 to 14) of the present invention, and the particle diameter 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 and comparative example 1, and as can be seen from fig. 1, the compacted density of the pole piece in example 1 is about 0.24g/cm 3 higher than the compacted density of comparative example 1, and the energy density and the cycling stability of the electrochemical device are both poor.
In summary, examples 1 to 8 show that by reasonably designing the size of the lithium iron manganese phosphate and matching the lithium iron manganese phosphate with other active materials with specific sizes, the invention solves the problem of lower conductivity of the lithium iron manganese phosphate and improves the compaction density, the energy density and the cycling stability of the electrochemical device.
The foregoing is merely illustrative of the present invention, and the present invention is not limited thereto, and it should be apparent to those skilled in the art that any changes or substitutions that fall within the technical scope of the present invention disclosed herein are within the scope 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 iron manganese 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 diameters D50 of the first active material and the second active material is 0.1 to 0.35; or alternatively
The first active material satisfies: dmin is 0.2 μm to 0.4 μm, D10 is 1 μm to 3 μm, D50 is 7 μm to 11 μm, D90 is 15 μm 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 spherical 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 diameters 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 spherical morphology and the morphology of the second active material is a nano morphology, the first active material and the second active material satisfying 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 diameters 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 lithium iron manganese phosphate in the first active material is LiMn xFe1-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 nano-form lithium iron phosphate, and the particle size D50 of the lithium iron phosphate is 0.8-2.5 mu m;
(f) The lithium iron phosphate is lithium iron phosphate in the form of secondary spheres, and the particle size D50 of the lithium iron phosphate in the form of secondary spheres is 7-11 mu m.
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 nano-form lithium manganese iron phosphate, and the particle size D50 of the lithium manganese iron phosphate is 0.8-2.5 mu m;
(h) The lithium iron manganese phosphate is in a secondary sphere form, and the particle size D50 of the lithium iron manganese phosphate is 7-11 mu m.
8. An electrochemical device, characterized in that the positive electrode of the electrochemical device includes the positive electrode active material according to any one of claims 1 to 7 therein.
9. The electrochemical device of claim 8, wherein the positive electrode further comprises a conductive agent and a binder, and wherein the mass ratio of the positive electrode active material, the conductive agent and the binder in the positive electrode is (90 to 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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| EP2509143A2 (en) * | 2009-12-04 | 2012-10-10 | Route JJ Co., Ltd | Anode active material precursor and active material for a rechargeable lithium battery comprising hollow nanofibrous carbon, and a production method therefor |
| CN110759325A (en) * | 2018-07-25 | 2020-02-07 | 深圳市比亚迪锂电池有限公司 | Cathode material, preparation method thereof and lithium ion battery |
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| EP2509143A2 (en) * | 2009-12-04 | 2012-10-10 | Route JJ Co., Ltd | Anode active material precursor and active material for a rechargeable lithium battery comprising hollow nanofibrous carbon, and a production method therefor |
| CN110759325A (en) * | 2018-07-25 | 2020-02-07 | 深圳市比亚迪锂电池有限公司 | Cathode material, preparation method thereof and lithium ion battery |
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