CN116435459B - Positive plate and preparation method thereof, lithium ion battery and preparation method thereof - Google Patents
Positive plate and preparation method thereof, lithium ion battery and preparation method thereof Download PDFInfo
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- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 title claims abstract description 48
- 229910001416 lithium ion Inorganic materials 0.000 title claims abstract description 48
- 238000002360 preparation method Methods 0.000 title claims abstract description 21
- 239000011247 coating layer Substances 0.000 claims abstract description 229
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims abstract description 97
- 229910052744 lithium Inorganic materials 0.000 claims abstract description 97
- 239000003795 chemical substances by application Substances 0.000 claims abstract description 66
- 229910003002 lithium salt Inorganic materials 0.000 claims abstract description 60
- 159000000002 lithium salts Chemical class 0.000 claims abstract description 60
- 239000007774 positive electrode material Substances 0.000 claims abstract description 42
- 239000002002 slurry Substances 0.000 claims description 126
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 58
- 239000010410 layer Substances 0.000 claims description 43
- 229920002981 polyvinylidene fluoride Polymers 0.000 claims description 42
- JXGGISJJMPYXGJ-UHFFFAOYSA-N lithium;oxido(oxo)iron Chemical compound [Li+].[O-][Fe]=O JXGGISJJMPYXGJ-UHFFFAOYSA-N 0.000 claims description 26
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 claims description 25
- 238000007600 charging Methods 0.000 claims description 21
- 239000011248 coating agent Substances 0.000 claims description 21
- 238000000576 coating method Methods 0.000 claims description 21
- 238000009849 vacuum degassing Methods 0.000 claims description 21
- 238000005520 cutting process Methods 0.000 claims description 19
- 230000015572 biosynthetic process Effects 0.000 claims description 16
- 230000032683 aging Effects 0.000 claims description 13
- 238000005096 rolling process Methods 0.000 claims description 13
- 229910002804 graphite Inorganic materials 0.000 claims description 11
- 238000007872 degassing Methods 0.000 claims description 10
- 239000011267 electrode slurry Substances 0.000 claims description 9
- 239000006258 conductive agent Substances 0.000 claims description 8
- 239000011230 binding agent Substances 0.000 claims description 7
- 239000003792 electrolyte Substances 0.000 claims description 6
- 239000002033 PVDF binder Substances 0.000 claims description 5
- PFYQFCKUASLJLL-UHFFFAOYSA-N [Co].[Ni].[Li] Chemical compound [Co].[Ni].[Li] PFYQFCKUASLJLL-UHFFFAOYSA-N 0.000 claims description 4
- QHGJSLXSVXVKHZ-UHFFFAOYSA-N dilithium;dioxido(dioxo)manganese Chemical compound [Li+].[Li+].[O-][Mn]([O-])(=O)=O QHGJSLXSVXVKHZ-UHFFFAOYSA-N 0.000 claims description 4
- 229910000625 lithium cobalt oxide Inorganic materials 0.000 claims description 4
- 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 description 4
- BFZPBUKRYWOWDV-UHFFFAOYSA-N lithium;oxido(oxo)cobalt Chemical compound [Li+].[O-][Co]=O BFZPBUKRYWOWDV-UHFFFAOYSA-N 0.000 claims description 4
- 229910000572 Lithium Nickel Cobalt Manganese Oxide (NCM) Inorganic materials 0.000 claims description 3
- 239000004642 Polyimide Substances 0.000 claims description 3
- FBDMTTNVIIVBKI-UHFFFAOYSA-N [O-2].[Mn+2].[Co+2].[Ni+2].[Li+] Chemical compound [O-2].[Mn+2].[Co+2].[Ni+2].[Li+] FBDMTTNVIIVBKI-UHFFFAOYSA-N 0.000 claims description 3
- 239000006229 carbon black Substances 0.000 claims description 3
- 239000002134 carbon nanofiber Substances 0.000 claims description 3
- 239000002041 carbon nanotube Substances 0.000 claims description 3
- 229910021389 graphene Inorganic materials 0.000 claims description 3
- 239000010439 graphite Substances 0.000 claims description 3
- 229920000058 polyacrylate Polymers 0.000 claims description 3
- 229920001721 polyimide Polymers 0.000 claims description 3
- 229910021393 carbon nanotube Inorganic materials 0.000 claims description 2
- 238000004519 manufacturing process Methods 0.000 claims 1
- 238000003786 synthesis reaction Methods 0.000 claims 1
- 230000010287 polarization Effects 0.000 abstract description 12
- 230000002687 intercalation Effects 0.000 abstract description 5
- 238000009830 intercalation Methods 0.000 abstract description 5
- 230000001502 supplementing effect Effects 0.000 abstract description 5
- 239000002109 single walled nanotube Substances 0.000 description 39
- 238000010277 constant-current charging Methods 0.000 description 16
- 239000007788 liquid Substances 0.000 description 16
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 12
- 229910052782 aluminium Inorganic materials 0.000 description 12
- 229910052799 carbon Inorganic materials 0.000 description 12
- 239000011888 foil Substances 0.000 description 12
- 238000000034 method Methods 0.000 description 9
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 9
- 238000005056 compaction Methods 0.000 description 8
- 238000013461 design Methods 0.000 description 8
- 238000010586 diagram Methods 0.000 description 8
- 238000002347 injection Methods 0.000 description 8
- 239000007924 injection Substances 0.000 description 8
- 238000010280 constant potential charging Methods 0.000 description 7
- 238000007599 discharging Methods 0.000 description 7
- 238000001035 drying Methods 0.000 description 7
- 230000000694 effects Effects 0.000 description 6
- 230000002349 favourable effect Effects 0.000 description 6
- 230000014759 maintenance of location Effects 0.000 description 6
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 5
- 239000006255 coating slurry Substances 0.000 description 5
- 238000009826 distribution Methods 0.000 description 5
- 229910052760 oxygen Inorganic materials 0.000 description 5
- 239000001301 oxygen Substances 0.000 description 5
- 239000011148 porous material Substances 0.000 description 5
- 230000000052 comparative effect Effects 0.000 description 4
- 238000000643 oven drying Methods 0.000 description 4
- 238000005516 engineering process Methods 0.000 description 3
- 230000006872 improvement Effects 0.000 description 3
- 230000008569 process Effects 0.000 description 3
- HFCVPDYCRZVZDF-UHFFFAOYSA-N [Li+].[Co+2].[Ni+2].[O-][Mn]([O-])(=O)=O Chemical compound [Li+].[Co+2].[Ni+2].[O-][Mn]([O-])(=O)=O HFCVPDYCRZVZDF-UHFFFAOYSA-N 0.000 description 2
- 239000011149 active material Substances 0.000 description 2
- 239000012467 final product Substances 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- 239000002904 solvent Substances 0.000 description 2
- 230000002195 synergetic effect Effects 0.000 description 2
- ZFPGARUNNKGOBB-UHFFFAOYSA-N 1-Ethyl-2-pyrrolidinone Chemical compound CCN1CCCC1=O ZFPGARUNNKGOBB-UHFFFAOYSA-N 0.000 description 1
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical group CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 1
- 230000004913 activation Effects 0.000 description 1
- 239000013543 active substance Substances 0.000 description 1
- 239000000853 adhesive Substances 0.000 description 1
- 230000001070 adhesive effect Effects 0.000 description 1
- 239000010406 cathode material Substances 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000010281 constant-current constant-voltage charging Methods 0.000 description 1
- 230000002596 correlated effect Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 229910002102 lithium manganese oxide Inorganic materials 0.000 description 1
- VLXXBCXTUVRROQ-UHFFFAOYSA-N lithium;oxido-oxo-(oxomanganiooxy)manganese Chemical compound [Li+].[O-][Mn](=O)O[Mn]=O VLXXBCXTUVRROQ-UHFFFAOYSA-N 0.000 description 1
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000012360 testing method 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
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
-
- 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
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/058—Construction or manufacture
-
- 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
- H01M4/04—Processes of manufacture in general
- H01M4/0402—Methods of deposition of the material
- H01M4/0404—Methods of deposition of the material by coating on electrode collectors
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/139—Processes of manufacture
-
- 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
- H01M2004/021—Physical characteristics, e.g. porosity, surface area
-
- 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)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Manufacturing & Machinery (AREA)
- Materials Engineering (AREA)
- Battery Electrode And Active Subsutance (AREA)
Abstract
The application provides a positive plate and a preparation method thereof, and a lithium ion battery and a preparation method thereof. The positive electrode current collector comprises a first surface and a second surface which are opposite, wherein the coating layers of the first surface and the second surface respectively comprise a positive electrode active material and a lithium salt pre-lithium agent, and the A1 coating layer, the A2 coating layer, the A3 coating layer, the A4 coating layer and the … … An of the first surface 1 The content of the lithium salt pre-lithium agent in the coating layer is sequentially increased, and the second surface comprises a B1 coating layer, a B2 coating layer, a B3 coating layer, a B4 coating layer and … … Bn 2 The content of the lithium salt pre-lithium agent in the coating layer is sequentially increased. The lithium supplementing agents in different coating layers in the positive plate are distributed in a gradient manner from inside to outside, so that the problem of serious polarization of a thick electrode is effectively solved while the cost is not increased, the pre-intercalation of lithium is synchronously realized, and the energy density and the high cycle performance of the lithium ion battery are remarkably improved.
Description
Technical Field
The application relates to the technical field of lithium ion batteries, in particular to a positive plate and a preparation method thereof, a lithium ion battery and a preparation method thereof.
Background
The lithium ion battery is used as a high-performance secondary battery, and has the characteristics of long cycle life, environmental friendliness and the like, so that the lithium ion battery is widely applied to various aspects of life, such as mobile phones, video cameras, computers, electric bicycles and the like. In recent years, with the increasing application range, especially in vehicles with high energy consumption, such as pure electric vehicles, plug-in hybrid electric vehicles, etc., the requirement for the energy density of lithium ion batteries is increasing. The energy density of the lithium ion battery is improved, and on one hand, a positive electrode material with high capacity is developed; on the other hand, in the preparation process of the lithium ion battery, the content of active substances in unit area is increased, in other words, thicker positive and negative plates are prepared, so that the requirement of high energy density is met. In the practical use process, the high-capacity cathode material is also required to overcome a plurality of safety problems. Thus, the preparation of thick electrodes is one of the ways in which many lithium ion battery manufacturers achieve high energy densities.
However, through practical use, the thick electrode has the defect that the thickness of the electrode plate is increased to a certain extent, the energy density of lithium ions is improved (by about 5-15%), but the improvement of the energy density is not proportional to the increase of the thickness of the electrode plate, which indicates that the multi-coated active material does not fully exert the effect of the multi-coated active material, and further research shows that the thick electrode can generate serious polarization, thereby influencing the capacity of the battery core and the exertion of high cycle performance.
Disclosure of Invention
The application mainly aims to provide a positive plate and a preparation method thereof, and a lithium ion battery and a preparation method thereof, so as to solve the problem that the lithium ion battery is difficult to achieve both energy density and high cycle performance due to polarization of a thick electrode in the prior art.
In order to achieve the above object, according to one aspect of the present application, there is provided a positive electrode sheet comprising a positive electrode current collector including opposite first and second surfaces, the first surface including An A1 coating layer, an A2 coating layer, an A3 coating layer, an A4 coating layer, and a … … An sequentially stacked thereon in a direction away from the positive electrode current collector 1 A coating layer, and/or a second surface comprising a B1 coating layer, a B2 coating layer, a B3 coating layer, a B4 coating layer, a … … Bn which are sequentially stacked 2 A coating layer, wherein n 1 Is an integer greater than or equal to 2, n 2 Is an integer more than or equal to 2; each of the coating layers on the first surface and each of the coating layers on the second surface each independently include a positive electrode active material and a lithium salt pre-coatLithium agent, A1 coating layer, A2 coating layer, A3 coating layer, A4 coating layer, … … An 1 The content of the lithium salt pre-lithium agent in the coating layer is sequentially increased, and the coating layers B1, B2, B3, B4 and … … Bn are respectively arranged in the coating layers 2 The content of the lithium salt pre-lithium agent in the coating layer increases in sequence.
Further, the above n 1 And n 2 Each independently is 2 to 10, preferably n 1 And n 2 Each independently is 2 to 4, preferably n 1 =n 2 。
Further, n 1 =n 2 =4, and each of the A1 coating layer and the B1 coating layer independently includes: 93-98.5 parts by weight of positive electrode active material and 0-3 parts by weight of lithium salt pre-lithium agent; the A2 coating layer and the B2 coating layer each independently include: 88-98 parts by weight of a positive electrode active material and 0.5-8 parts by weight of a lithium salt pre-lithium agent; the A3 coating layer and the B3 coating layer each independently include: 90-98 parts by weight of positive electrode active material and 0.6-9 parts by weight of lithium salt pre-lithium agent; the A4 coating layer and the B4 coating layer each independently include: 92-98 parts by weight of a positive electrode active material and 0.8-10 parts by weight of a lithium salt pre-lithium agent.
Further, n 1 =n 2 =3, and each of the A1 coating layer and the B1 coating layer independently includes: 93-98.5 parts by weight of positive electrode active material and 0-3 parts by weight of lithium salt pre-lithium agent; the A2 coating layer and the B2 coating layer each independently include: 90-98 parts by weight of positive electrode active material and 0.6-7.5 parts by weight of lithium salt pre-lithium agent; the A3 coating layer and the B3 coating layer each independently include: 88-98 parts by weight of a positive electrode active material and 0.8-8 parts by weight of a lithium salt pre-lithium agent.
Further, n 1 =n 2 =2, and each of the A1 coating layer and the B1 coating layer independently includes: 93-98.5 parts by weight of positive electrode active material and 0-3 parts by weight of lithium salt pre-lithium agent; the A2 coating layer and the B2 coating layer each independently include: 88-98 parts by weight of a positive electrode active material and 0.5-8 parts by weight of a lithium salt pre-lithium agent.
Further, each of the coating layers on the first surface and each of the coating layers on the second surface further independently include 1 to 5 parts by weight of a conductive agent and 1 to 5 parts by weight of a binder, preferablyThe conductive agent is selected from any one or more of superconductive carbon black, carbon nano tube, graphene, VGCF and conductive graphite, and the binder is preferably selected from any one or more of polyvinylidene fluoride, polyimide and polyacrylate; preferably, each of the coating layers on the first surface and each of the coating layers on the second surface has a thickness of 30 to 250 μm, and preferably, each of the coating layers on the first surface and each of the coating layers on the second surface has an areal density of 100 to 500g/m 2 。
Further, the positive electrode active material is selected from one or more of lithium iron phosphate, lithium iron manganese phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium cobalt oxide and lithium manganate, and preferably the lithium salt pre-lithium agent is lithium-rich lithium ferrite; preferably n 1 =n 2 =4, each of the A1 coating layer and the B1 coating layer independently includes: 94-97 parts by weight of lithium iron phosphate and 1-3 parts by weight of lithium-rich lithium ferrite; the A2 coating layer and the B2 coating layer each independently include: 93-96 parts by weight of lithium iron phosphate and 2-4 parts by weight of lithium-rich lithium ferrite; the A3 coating layer and the B3 coating layer each independently include: 92-95 parts by weight of lithium iron phosphate and 3-5 parts by weight of lithium-rich lithium ferrite; the A4 coating layer and the B4 coating layer each independently include: 93-97 parts by weight of lithium iron phosphate and 4-6 parts by weight of lithium-rich lithium ferrite; alternatively, n 1 =n 2 When=3, each of the A1 coating layer and the B1 coating layer independently includes: 94-98 parts by weight of lithium iron phosphate and 1-3 parts by weight of lithium-rich lithium ferrite; the A2 coating layer and the B2 coating layer each independently include: 91-96 parts by weight of lithium iron phosphate and 2-5 parts by weight of lithium-rich lithium ferrite; the A3 coating layer and the B3 coating layer each independently include: 89-95 parts by weight of lithium iron phosphate and 3-6 parts by weight of lithium-rich lithium ferrite.
According to another aspect of the present application, there is provided a method for preparing a front positive electrode sheet, the method comprising: step S1, A1 slurry, A2 slurry, A3 slurry, A4 slurry, … … An 1 Each positive electrode slurry of the slurry is sequentially coated on the first surface of the positive electrode current collector, and a A1 coating layer, a A2 coating layer, an A3 coating layer, an A4 coating layer and a … … An which are sequentially stacked are correspondingly formed on the first surface 1 Coating a layer to obtain a coated electrode; wherein n is 1 Is not less than 2A positive integer; and/or B1 slurry, B2 slurry, B3 slurry, B4 slurry, … … Bn 2 Each positive electrode slurry of the slurry is sequentially coated on the second surface of the positive electrode current collector, and a B1 coating layer, a B2 coating layer, a B3 coating layer, a B4 coating layer and a … … Bn which are sequentially overlapped are correspondingly formed on the second surface 2 A coating layer; n is n 2 Is a positive integer more than or equal to 2; step S2, sequentially rolling, slitting and die-cutting the coated electrode to obtain a positive plate; the positive electrode slurries each independently comprise a positive electrode active material and a lithium salt pre-lithium agent, A1 slurry, A2 slurry, A3 slurry, A4 slurry, … … An 1 The content of the lithium salt pre-lithium agent in the slurry is sequentially increased; b1 slurry, B2 slurry, B3 slurry, B4 slurry, … … Bn 2 The content of the lithium salt pre-lithium agent in the slurry is sequentially increased.
According to another aspect of the application, there is provided a method for preparing a lithium ion battery, comprising assembling a positive plate, a negative plate, an electrolyte and a separator to obtain a battery cell; and (3) immersing the battery core by adopting electrolyte, sequentially carrying out formation and aging to obtain an aged battery core, and carrying out degassing and capacity division on the aged battery core to obtain the lithium ion battery, wherein the positive plate is the positive plate.
Further, the formation is carried out at 38-50 ℃, preferably for 12-48 hours, preferably the degassing process comprises: performing primary vacuum degassing on the aged battery cell to obtain a degassed battery cell; charging the deaerated battery cell to 3.65-3.8V under the first current and then charging the deaerated battery cell to 4.1-4.5V under the second current to obtain a charging battery cell; carrying out secondary vacuum degassing on the charging battery cell; preferably, the first current is 0.01C to 1C in capacity, and preferably, the second current is 0.0005C to 0.05C in capacity.
According to still another aspect of the present application, a lithium ion battery is provided, which is a lithium ion battery prepared by the above preparation method.
By applying the technical scheme of the application, the contents of the lithium-supplementing agents in different coating layers in the positive plate are distributed in a gradient manner from inside to outside, and a large amount of oxygen is generated in the formation process of the lithium ion battery comprising the positive plate, so that pores are generated, and the positive plate with gradient porosity is finally obtained.
Drawings
The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description serve to explain the application. In the drawings:
fig. 1 shows a structure of a positive electrode sheet 1110 and a schematic view from the positive electrode sheet 1110 to the positive electrode sheet 1120 to the positive electrode sheet 1130 provided in embodiment 1 of the present application;
fig. 2 shows the structure of the positive electrode sheet 1210 and schematic diagrams from the positive electrode sheet 1210 to the positive electrode sheet 1220 to the positive electrode sheet 1230 according to embodiment 5 of the present application;
fig. 3 shows a structure of a positive electrode sheet 1310 and schematic diagrams from the positive electrode sheet 1310 to the positive electrode sheet 1320 to the positive electrode sheet 1330 according to embodiment 6 of the present application; and
fig. 4 shows a schematic cross-sectional view of a positive electrode sheet 1310 provided according to embodiment 1 of the present application.
Detailed Description
It should be noted that, without conflict, the embodiments of the present application and features of the embodiments may be combined with each other. The application will be described in detail below with reference to the drawings in connection with embodiments.
As analyzed by the background art of the application, the problem that the energy density and the high cycle performance of the lithium ion battery are difficult to be simultaneously achieved due to the polarization of the thick electrode in the prior art is solved.
In one exemplary embodiment of the present application, a positive electrode sheet is provided comprising a positive electrode current collector including opposed first and second surfaces, the first surface including an A1 coating layer, an A2 coating layer, an A3 coating layer, an A4 coating layer, and a … sequentially stacked on the first surface in a direction away from the positive electrode current collector…An 1 A coating layer, and/or a second surface comprising a B1 coating layer, a B2 coating layer, a B3 coating layer, a B4 coating layer, a … … Bn which are sequentially stacked 2 A coating layer, wherein n 1 Is a positive integer greater than or equal to 2, n 2 Is an integer more than or equal to 2; each of the coating layers on the first surface and each of the coating layers on the second surface each independently include a positive electrode active material and a lithium salt pre-lithium agent, A1 coating layer, A2 coating layer, A3 coating layer, A4 coating layer, … … An 1 The content of the lithium salt pre-lithium agent in the coating layer is sequentially increased, and the coating layers B1, B2, B3, B4 and … … Bn are respectively arranged in the coating layers 2 The content of the lithium salt pre-lithium agent in the coating layer increases in sequence.
According to the application, the contents of the lithium supplementing agents in different coating layers in the coated electrode are distributed in a gradient manner from inside to outside through the multilayer coating technology, a large amount of oxygen is generated after the battery core containing the coated electrode is formed, so that pores are generated, and finally, the positive plate with gradient porosity is obtained, so that the problem of serious polarization of the thick electrode is effectively solved without increasing the cost, the pre-lithium intercalation is synchronously realized, and the energy density and the high cycle performance of the lithium ion battery are remarkably improved. The preparation method is simple and quick, and the cost is low.
In one embodiment of the application, n is preferably 1 And n 2 Each independently is 2 to 10, preferably n 1 And n 2 Each independently is 2 to 4, preferably n 1 =n 2 。
With n 1 Or n 2 The preparation difficulty of the positive plate is increased, the preparation difficulty of the positive plate and the alleviation effect of gradient distribution of the content of the lithium supplementing agent in different coating layers of the positive plate on electrode polarization from inside to outside are comprehensively considered, and n is preferably selected 1 And n 2 The values are given above.
In one embodiment of the application, n 1 =n 2 =4, and each of the A1 coating layer and the B1 coating layer independently includes: 93-98.5 parts by weight of positive electrode active material and 0-3 parts by weight of lithium salt pre-lithium agent; the A2 coating layer and the B2 coating layer each independently include: 88-98 parts by weight of positive electrode active material0.5-8 parts by weight of a lithium salt pre-lithium agent; the A3 coating layer and the B3 coating layer each independently include: 90-98 parts by weight of positive electrode active material and 0.6-9 parts by weight of lithium salt pre-lithium agent; the A4 coating layer and the B4 coating layer each independently include: 92-98 parts by weight of a positive electrode active material and 0.8-10 parts by weight of a lithium salt pre-lithium agent.
Preferably n 1 =n 2 When=4, the content of the positive electrode active material and the lithium salt prelithiation agent in each coating layer is within the above range, thereby contributing to improvement of the energy density and high cycle performance of the positive electrode sheet.
In some embodiments of the application, n is preferably 1 =n 2 =3, and each of the A1 coating layer and the B1 coating layer independently includes: 93-98.5 parts by weight of positive electrode active material and 0-3 parts by weight of lithium salt pre-lithium agent; the A2 coating layer and the B2 coating layer each independently include: 90-98 parts by weight of positive electrode active material and 0.6-7.5 parts by weight of lithium salt pre-lithium agent; the A3 coating layer and the B3 coating layer each independently include: 88-98 parts by weight of a positive electrode active material and 0.8-8 parts by weight of a lithium salt pre-lithium agent.
Preferably n 1 =n 2 When=3, it is preferable that each coating layer of the above content is more favorable to exert the synergistic compatibility of the positive electrode active material and the lithium salt pre-lithium agent, and the gradient distribution of the lithium salt pre-lithium agent in each coating layer is more favorable to alleviate polarization of the electrode.
In one embodiment of the application, n 1 =n 2 =2, and each of the A1 coating layer and the B1 coating layer independently includes: 93-98.5 parts by weight of positive electrode active material and 0-3 parts by weight of lithium salt pre-lithium agent; the A2 coating layer and the B2 coating layer each independently include: 88-98 parts by weight of a positive electrode active material and 0.5-8 parts by weight of a lithium salt pre-lithium agent.
Preferably n 1 =n 2 When=2, the number of coating layers is relatively small, and it is preferable that each coating layer with the above content is more effective to exert the effect of alleviating electrode polarization by the gradient distribution of the lithium salt pre-lithium agent between the two coating layers.
In one embodiment of the present application, each of the coating layers on the first surface and the second surface further independently includes 1 to 5 parts by weight of a conductive agent and 1 to 5 parts by weight of a conductive agentA binder, preferably a conductive agent, is selected from any one or more of superconductive carbon black (SP), carbon Nanotubes (CNTs), graphene, VGCF and conductive graphite, preferably the binder is selected from any one or more of polyvinylidene fluoride, polyimide and polyacrylate; preferably, each of the coating layers on the first surface and each of the coating layers on the second surface has a thickness of 30 to 250 μm, and preferably, each of the coating layers on the first surface and each of the coating layers on the second surface has an areal density of 100 to 500g/m 2 。
The preferable conductive agent is favorable for improving the conductivity of the positive plate, the preferable adhesive is favorable for improving the bonding effect between each coating layer and between the coating layer and the positive current collector, the thickness and the surface density of the coating layer are positively correlated, and the preferable thickness and the surface density of each coating layer are favorable for realizing gradient distribution of the content of the lithium salt pre-lithium agent in the coating layer.
In one embodiment of the present application, the positive electrode active material is selected from one or more of lithium iron phosphate, lithium iron manganese phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium cobalt oxide, and lithium manganese oxide, and preferably the lithium salt pre-lithium agent is lithium-rich lithium ferrite; preferably n 1 =n 2 =4, each of the A1 coating layer and the B1 coating layer independently includes: 94-97 parts by weight of lithium iron phosphate and 1-3 parts by weight of lithium-rich lithium ferrite; the A2 coating layer and the B2 coating layer each independently include: 93-96 parts by weight of lithium iron phosphate and 2-4 parts by weight of lithium-rich lithium ferrite; the A3 coating layer and the B3 coating layer each independently include: 92-95 parts by weight of lithium iron phosphate and 3-5 parts by weight of lithium-rich lithium ferrite; the A4 coating layer and the B4 coating layer each independently include: 93-97 parts by weight of lithium iron phosphate and 4-6 parts by weight of lithium-rich lithium ferrite; alternatively, n 1 =n 2 When=3, each of the A1 coating layer and the B1 coating layer independently includes: 94-98 parts by weight of lithium iron phosphate and 1-3 parts by weight of lithium-rich lithium ferrite; the A2 coating layer and the B2 coating layer each independently include: 91-96 parts by weight of lithium iron phosphate and 2-5 parts by weight of lithium-rich lithium ferrite; the A3 coating layer and the B3 coating layer each independently include: 89-95 parts by weight of lithium iron phosphate and 3-6 parts by weight of lithium-rich lithium ferrite.
The positive electrode active material is favorable for better synergistic cooperation with a lithium salt pre-lithium agent, and the preferable positive electrode plate better relieves electrode polarization, so that the lithium ion battery has excellent energy density and cycle performance.
In another exemplary embodiment of the present application, there is provided a method for preparing the aforementioned positive electrode sheet, the method comprising: step S1, A1 slurry, A2 slurry, A3 slurry, A4 slurry, … … An 1 Each positive electrode slurry of the slurry is sequentially coated on the first surface of the positive electrode current collector, and a A1 coating layer, a A2 coating layer, an A3 coating layer, an A4 coating layer and a … … An which are sequentially stacked are correspondingly formed on the first surface 1 Coating a layer to obtain a coated electrode; wherein n is 1 Is a positive integer more than or equal to 2; and/or B1 slurry, B2 slurry, B3 slurry, B4 slurry, … … Bn 2 Each positive electrode slurry of the slurry is sequentially coated on the second surface of the positive electrode current collector, and a B1 coating layer, a B2 coating layer, a B3 coating layer, a B4 coating layer and a … … Bn which are sequentially overlapped are correspondingly formed on the second surface 2 A coating layer; n is n 2 Is a positive integer more than or equal to 2; step S2, sequentially rolling, slitting and die-cutting the coated electrode to obtain a positive plate; the positive electrode slurries each independently comprise a positive electrode active material and a lithium salt pre-lithium agent, A1 slurry, A2 slurry, A3 slurry, A4 slurry, … … An 1 The content of the lithium salt pre-lithium agent in the slurry is sequentially increased; b1 slurry, B2 slurry, B3 slurry, B4 slurry, … … Bn 2 The content of the lithium salt pre-lithium agent in the slurry is sequentially increased.
According to the application, the contents of the lithium supplementing agents in different coating layers in the coated electrode are distributed in a gradient manner from inside to outside through the multilayer coating technology, a large amount of oxygen is generated after the battery core containing the coated electrode is formed, so that pores are generated, and finally, the positive plate with gradient porosity is obtained, so that the problem of serious polarization of the thick electrode is effectively solved without increasing the cost, the pre-lithium intercalation is synchronously realized, and the energy density and the high cycle performance of the lithium ion battery are remarkably improved. The preparation method is simple and quick, and the cost is low.
In addition, the above positive electrode pastes further each independently include a conductive agent, a binder, and a solvent, preferably the solvent is selected from N-methylpyrrolidone and/or N-ethyl-2-pyrrolidone.
In yet another exemplary embodiment of the present application, a method for preparing a lithium ion battery is provided, including assembling a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator to obtain a battery cell; and (3) immersing the battery core by adopting electrolyte, sequentially carrying out formation and aging to obtain an aged battery core, and carrying out degassing and capacity division on the aged battery core to obtain the lithium ion battery, wherein the positive plate is the positive plate.
The battery core comprising the positive plate generates a large amount of oxygen through formation, and then generates a large amount of pores through degassing, and finally the positive plate with gradient porosity is obtained, so that the problem of serious polarization of a thick electrode is effectively solved while the cost is not increased, pre-lithium intercalation is synchronously realized, and the energy density and high cycle performance of a lithium ion battery are remarkably improved.
In one embodiment of the application, the formation is carried out at 38-50 ℃, preferably at 38-50 ℃, the aging is preferably carried out for 12-48 hours, the process of degassing preferably comprises: performing primary vacuum degassing on the aged battery cell to obtain a degassed battery cell; charging the deaerated battery cell to 3.65-3.8V under the first current and then charging the deaerated battery cell to 4.1-4.5V under the second current to obtain a charging battery cell; carrying out secondary vacuum degassing on the charging battery cell; preferably, the first current is 0.01C to 1C in capacity, and preferably, the second current is 0.0005C to 0.05C in capacity.
Preferably, the battery cell is subjected to formation, aging and degassing under the above conditions, so that the positive plate with more proper gradient distribution of porosity can be obtained efficiently. Among them, the lithium salt pre-lithium agent is inferior in conductivity, preferably more conducive to activation of the lithium salt pre-lithium agent under a small current in the above range, and further, it is preferable that the first current is 0.01C, 0.02C, 0.03C, 0.04C, 0.05C, 0.1C, 0.2C, 0.33C, 0.5C or 1C of the capacity, and the second current is 0.0005C, 0.001C, 0.005C, 0.01C, 0.02C, 0.025C or 0.05C of the capacity.
In yet another exemplary embodiment of the present application, a lithium ion battery is provided, which is a lithium ion battery prepared by the aforementioned preparation method.
The advantageous effects of the present application will be further described below with reference to examples.
The following substances were subjected to simplified expression treatment:
positive electrode active material: lithium iron phosphate (LFP), lithium iron manganese phosphate (LFMP), lithium Nickel Cobalt Manganate (NCM), lithium Nickel Cobalt Aluminate (NCA), lithium cobalt oxide (NCO), lithium Manganate (LMO);
lithium salt pre-lithium agent: lithium-rich Lithium Ferrite (LFO);
conductive agent: conductive carbon black (SP), single-walled carbon nanotubes (SWCNT);
and (2) a binder: polyvinylidene fluoride (PVDF).
Example 1
According to LFP: SP: SWCNT: pvdf=96.5: 1.18:0.02:2.3 to form slurry 1. According to LFP: LFO: SP: SWCNT: pvdf=92.5: 3:1.66:0.04:2.8 to form slurry 2. Sequentially coating slurry 1 (approaching to current collector) and slurry 2 on upper and lower surfaces of carbon coated aluminum foil 1111 by using a double-layer coating die head, and oven drying to obtain positive plate 1110, wherein 1112 layer has an areal density of 200g/m 2 The 1113 layer had an areal density of 200g/m 2 . The positive electrode sheet 1120 was obtained by rolling in accordance with compaction of 2.3g/cc, wherein the 1112 layer had a thickness of 87 μm and the 1113 layer had a thickness of 87. Mu.m. Cutting and die cutting, and assembling the battery core with a matched SiO@graphite (gram capacity of 500 mAh/g) negative electrode and a diaphragm. After the water content was qualified, the solution was poured according to a pouring coefficient of 3.2g/Ah, and after standing at room temperature for 24 hours, the solution was once formed at 0.05C (45% SOC), aged at 45℃for 24h, and then vacuum deaerated (air bag was kept). Then, 0.33C constant current and constant voltage charging is performed to 3.65V, then constant current charging is performed to 4.4V according to 50mA (0.05C of LFO design capacity), secondary vacuum degassing is performed to obtain a lithium ion battery including a positive plate 1130, and then normal charging and discharging are performed, wherein the structure of the positive plate 1110 and schematic diagrams from the positive plate 1110 to the positive plate 1120 and then to the positive plate 1130 are shown in fig. 1, and a sectional view of the positive plate 1130 is shown in fig. 4.
Example 2
According to LFP: SP: SWCNT: pvdf=96.5: 1.18:0.02:2.3 to form slurry 1. According to LFP: LFO: SP: SWCNT: pvdf=94: 2:1.48:0.02:2.5 to form slurry 2. Coating slurry 1 (approaching to current collector) and slurry 2 on the upper and lower surfaces of carbon-coated aluminum foil 1111 respectively by using a double-layer coating die head, and oven drying to obtain positive plate 1110, wherein 1112 layer has an areal density of 100g/m 2 The 1113 layer had an areal density of 300g/m 2 . The positive electrode sheet 1120 was obtained by rolling in accordance with compaction of 2.3g/cc, wherein the 1112 layer had a thickness of 43 μm and the 1113 layer had a thickness of 130. Mu.m. Cutting and die cutting, and assembling the battery core with a matched SiO@graphite (gram capacity of 500 mAh/g) negative electrode and a diaphragm. After the water content is qualified, the liquid is injected according to the injection coefficient of 3.2g/Ah, and after standing for 24 hours at normal temperature, the liquid is subjected to primary formation (45% SOC) at 0.05 ℃, aging is carried out at 45 ℃ for 24 hours, and vacuum degassing (air bag retention) is carried out. Then, 0.33C constant current and constant voltage charging is performed to 3.65V, then constant current charging is performed to 4.4V according to 50mA (0.05C of LFO design capacity), secondary vacuum degassing is performed to obtain a lithium ion battery including a positive plate 1130, and then normal charging and discharging are performed, wherein the structure of the positive plate 1110 and the schematic diagram from the positive plate 1110 to the positive plate 1120 to the positive plate 1130 are shown in fig. 1.
Example 3
According to LFP: SP: SWCNT: pvdf=96.5: 1.18:0.02:2.3 to form slurry 1. According to LFP: LFO: SP: SWCNT: pvdf=89: 6:2.46:0.04:2.5 to form slurry 2. Coating slurry 1 (approaching to current collector) and slurry 2 on the upper and lower surfaces of carbon-coated aluminum foil 1111 respectively by using a double-layer coating die head, and oven drying to obtain positive plate 1110, wherein 1112 layer has an areal density of 300g/m 2 The surface density of the 1113 layer was 100g/m 2 . The positive electrode sheet 1120 was obtained by rolling in accordance with compaction of 2.3g/cc, wherein the 1112 layer had a thickness of 130 μm and the 1113 layer had a thickness of 43. Mu.m. Cutting and die cutting, and assembling the battery core with a matched SiO@graphite (gram capacity of 500 mAh/g) negative electrode and a diaphragm. After the water content is qualified, injecting liquid according to the injection coefficient of 3.2g/Ah, standing for 24 hours at normal temperature, performing primary formation (45% SOC) at 0.05C current, aging at 45 ℃ for 24 hours, and performing vacuum degassingThe air pocket is reserved). Then, 0.33C constant current and constant voltage charging is performed to 3.65V, then constant current charging is performed to 4.4V according to 50mA (0.05C of LFO design capacity), secondary vacuum degassing is performed to obtain a lithium ion battery including a positive plate 1130, and then normal charging and discharging are performed, wherein the structure of the positive plate 1110 and the schematic diagram from the positive plate 1110 to the positive plate 1120 to the positive plate 1130 are shown in fig. 1.
Example 4
According to LFMP: SP: SWCNT: pvdf=96.5: 1.18:0.02:2.3 to form slurry 1. According to LFMP: LFO: SP: SWCNT: pvdf=89: 6:2.46:0.04:2.5 to form slurry 2. Coating slurry 1 (approaching to current collector) and slurry 2 on the upper and lower surfaces of carbon-coated aluminum foil 1111 respectively by using a double-layer coating die head, and oven drying to obtain positive plate 1110, wherein 1112 layer has an areal density of 300g/m 2 The surface density of the 1113 layer was 100g/m 2 . The positive electrode sheet 1120 was obtained by rolling in accordance with compaction of 2.3g/cc, wherein the 1112 layer had a thickness of 130 μm and the 1113 layer had a thickness of 43. Mu.m. Cutting and die cutting, and assembling the battery core with a matched SiO@graphite (gram capacity of 500 mAh/g) negative electrode and a diaphragm. After the water content is qualified, the liquid is injected according to the injection coefficient of 3.2g/Ah, the liquid is subjected to primary formation (45% SOC) by 0.05C current after standing for 24 hours at normal temperature, and vacuum degassing (air bag retention) is carried out after ageing for 24 hours at 45 ℃. Then, 0.33C constant current and constant voltage charging is performed to 3.65V, then constant current charging is performed to 4.4V according to 50mA (0.05C of LFO design capacity), secondary vacuum degassing is performed to obtain a lithium ion battery including a positive plate 1130, and then normal charging and discharging are performed, wherein the structure of the positive plate 1110 and the schematic diagram from the positive plate 1110 to the positive plate 1120 to the positive plate 1130 are shown in fig. 1.
Example 5
According to LFP: SP: SWCNT: pvdf=96.5: 1.18:0.02:2.3 to form slurry 1. According to LFP: LFO: SP: SWCNT: pvdf=94.7: 1.5:1.28:0.02:2.5 to form a slurry 3. According to LFP: LFO: SP: SWCNT: pvdf=92.5: 3:1.66:0.04:2.8 to form slurry 4. According to the three-layer coating die head, slurries are respectively coated on the upper and lower surfaces of the carbon-coated aluminum foil 12111 (near the current collector), slurry 3 and slurry 4, and drying to obtain a positive plate 1210, wherein the 1212 layer has an areal density of 133g/m 2 The surface density of 1213 layer is 133g/m 2 The 1214 layer has an areal density of 133g/m 2 . The positive electrode sheet 1220 was obtained by rolling in accordance with compaction of 2.3g/cc, wherein the thickness of layer 1212 was 58 μm and the thickness of layer 1213 was 58 μm. The 1214 layer had a thickness of 58. Mu.m. Cutting and die cutting, and assembling the battery core with a matched SiO@graphite (gram capacity of 500 mAh/g) negative electrode and a diaphragm. After the water content is qualified, the liquid is injected according to the injection coefficient of 3.2g/Ah, the liquid is subjected to primary formation (45% SOC) by 0.05C current after standing for 24 hours at normal temperature, and vacuum degassing (air bag retention) is carried out after ageing for 24 hours at 45 ℃. Then, 0.33C constant current and constant voltage charging is performed to 3.65V, then constant current charging is performed to 4.4V according to 50mA (0.05C of LFO design capacity), secondary vacuum degassing is performed to obtain a lithium ion battery including a positive plate 1230, and then normal charging and discharging are performed, wherein the structure of the positive plate 1210 and the schematic diagram from the positive plate 1210 to the positive plate 1220 to the positive plate 1230 are shown in fig. 2.
Example 6
According to LFP: SP: SWCNT: pvdf=96.5: 1.18:0.02:2.3 to form slurry 1. According to LFP: LFO: SP: SWCNT: pvdf=95.2: 1:1.28:0.02:2.5 to form a slurry 5. According to LFP: LFO: SP: SWCNT: pvdf=94: 2:1.48:0.02:2.5 to form a slurry 6. According to LFP: LFO: SP: SWCNT: pvdf=92.5: 3:1.66:0.04:2.8 to form a slurry 7. Coating slurry 1 (near the current collector), slurry 5, slurry 6 and slurry 7 on the upper and lower surfaces of the carbon-coated aluminum foil 1311 respectively by adopting a four-layer coating die head, and drying to obtain a positive plate 1310, wherein the surface density of 1312 layers is 100/m 2 The surface density of the 1313 layer was 100g/m 2 The surface density of 1314 layer was 100g/m 2 The surface density of the 1315 layer was 100g/m 2 . The positive electrode sheet 1320 was obtained by rolling in accordance with compaction of 2.3g/cc, wherein the thickness of the 1312 layer was 43 μm and the thickness of the 1313 layer was 43 μm.1314 layer was 43 μm thick and 1315 layer was 43 μm thick. Cutting and die cutting, and matching with a SiO@graphite (gram capacity of 500 mAh/g) negative electrodeAnd assembling the diaphragm into the battery cell. After the water content is qualified, the liquid is injected according to the injection coefficient of 3.2g/Ah, and after standing for 24 hours at normal temperature, the liquid is subjected to primary formation (45 ℃ C., 45% SOC) by 0.05C current, and after aging at 45 ℃ for 24 hours, the liquid is subjected to vacuum degassing (air bag is reserved). Then, 0.33C constant current and constant voltage charging is performed to 3.65V, then constant current charging is performed to 4.4V according to 50mA (0.05C of LFO design capacity), secondary vacuum degassing is performed to obtain a lithium ion battery including a positive plate 1330, and then normal charging and discharging are performed, wherein the structure of the positive plate 1310 and the schematic diagram from the positive plate 1310 to the positive plate 1320 to the positive plate 1330 are shown in fig. 3.
Example 7
The difference from example 6 is that according to LFP: SP: SWCNT: pvdf=96.5: 1.18:0.02:2.3 to form slurry 1. According to LFP: LFO: SP: SWCNT: pvdf=95.2: 1:1.28:0.02:2.5 to form a slurry 5. According to LFP: LFO: SP: SWCNT: pvdf=94: 2:1.48:0.02:2.5 to form a slurry 6. According to LFP: LFO: SP: SWCNT: pvdf=92.5: 3:1.66:0.04:2.8 to form a slurry 7. According to the four-layer coating die head, slurry 1 (close to a current collector), slurry 5, slurry 6 and slurry 7 are coated on the upper surface of the carbon-coated aluminum foil 1311 respectively, and the anode sheet 1310 is obtained after drying, so that the lithium ion battery comprising the anode sheet 1330 is finally obtained.
Example 8
The difference from example 6 is that, according to LFP, according to four-layer coating die: SP: SWCNT: pvdf=96.5: 1.18:0.02:2.3 to form slurry 1. According to LFP: LFO: SP: SWCNT: pvdf=95.2: 1:1.28:0.02:2.5 to form a slurry 5. According to LFP: LFO: SP: SWCNT: pvdf=94: 2:1.48:0.02:2.5 to form a slurry 6. According to LFP: LFO: SP: SWCNT: pvdf=92.5: 3:1.66:0.04:2.8 to form a slurry 7. According to LFP: LFO: SP: SWCNT: pvdf= 95.18:1:1.3:0.02:2.5 to form a slurry 5'. According to the four-layer coating die head, slurry 1 (close to the current collector), slurry 5, slurry 6 and slurry 7 are coated on the upper surface of the carbon-coated aluminum foil 1311 respectively, slurry 1 (close to the current collector), slurry 5', slurry 6 and slurry 7 are coated on the lower surface of the carbon-coated aluminum foil 1311 respectively, and the positive plate 1310 is obtained after drying, and finally the lithium ion battery comprising the positive plate 1330 is obtained.
Example 9
The difference from example 6 is that the change was made to a temperature of 60 c, and finally a lithium ion battery including a positive electrode sheet 1330 was obtained.
Example 10
The difference from example 6 is that the aging temperature was changed to 60 c, and finally a lithium ion battery including a positive electrode sheet 1330 was obtained.
Example 11
The difference from example 6 is that the positive electrode active material is lithium nickel cobalt manganate, and a lithium ion battery including a positive electrode sheet 1330 is finally obtained.
Example 12
The difference from example 6 is that the liquid was injected at a liquid injection coefficient of 3.2g/Ah after the water was qualified, and the mixture was allowed to stand at room temperature for 24 hours, and then subjected to primary formation (45% SOC) with a small current, aged at 45℃for 24 hours, and then subjected to vacuum degassing (air bag retention). Then 0.15C constant current constant voltage charging to 3.65V, then constant current charging to 4.4V according to 25mA (0.025C of LFO design capacity), and carrying out secondary vacuum degassing to obtain the lithium ion battery comprising the positive plate 1330.
Example 13
The difference from example 6 is that according to LFP: LFO: SP: SWCNT: pvdf=95: 3:0.95:0.05:1.0 to form slurry 1. According to LFP: LFO: SP: SWCNT: pvdf=94: 4:0.95:0.05:1.0 to form slurry 5. According to LFP: LFO: SP: SWCNT: pvdf=93: 5:0.95:0.05:1.0 to form slurry 6. According to LFP: LFO: SP: SWCNT: pvdf=93: 5:0.95:0.05:1.0 to form slurry 7.
Example 14
The difference from example 5 is that according to LFP: LFO: SP: SWCNT: pvdf=95.5: 1:1.18:0.02:2.3 to form slurry 1. According to LFP: LFO: SP: SWCNT: pvdf=92.2: 4:1.28:0.02:2.5 to form a slurry 3. According to LFP: LFO: SP: SWCNT: pvdf=90.5: 5:1.66:0.04:2.8 to form slurry 4.
Comparative example 1
According to LFP: SP: SWCNT: pvdf=96.5: 1.18:0.02:2.3 to form slurry 1. Coating the carbon-coated aluminum foil according to slurry 1 by using a conventional coating die head, and drying to obtain a final product with a post-baking density of 400g/m 2 . The rolling was carried out in accordance with compaction of 2.3g/cc and the thickness after rolling was 174. Mu.m. Cutting and die cutting, and assembling the battery core with a matched SiO@graphite (gram capacity of 500 mAh/g) negative electrode and a diaphragm. After the water content is qualified, injecting liquid according to the injection coefficient of 3.2g/Ah, standing for 24 hours at normal temperature, performing primary formation (45% SOC) with small current, aging for 24 hours at 45 ℃, performing vacuum degassing, and then performing normal charge and discharge.
Comparative example 2
According to LFP: LFO: SP: SWCNT: pvdf=94.7: 1.5:1.28:0.02:2.5 to form slurry 1. Coating the carbon-coated aluminum foil according to slurry 1 by using a conventional coating die head, and drying to obtain a final product with a post-baking density of 400g/m 2 . The rolling was carried out in accordance with compaction of 2.3g/cc and the thickness after rolling was 174. Mu.m. Cutting and die cutting, and assembling the battery core with a matched SiO@graphite (gram capacity of 500 mAh/g) negative electrode and a diaphragm. After the water content is qualified, the liquid is injected according to the injection coefficient of 3.2g/Ah, the liquid is kept stand for 24 hours at normal temperature, then the liquid is subjected to primary formation (45% SOC) by small current, and is aged for 24 hours at 45 ℃, and then vacuum degassing (air bag retention) is carried out. Then, 0.33C constant current and constant voltage charging was performed to 3.65V, then 50mA (0.05C of LFO design capacity) constant current charging was performed to 4.4V, secondary vacuum degassing was performed, and then normal charging and discharging were performed.
Comparative example 3
The difference from example 6 is that according to LFP: LFO: SP: SWCNT: pvdf=92.5: 3:1.66:0.04:2.8 to form a slurry 7. According to LFP: LFO: SP: SWCNT: pvdf=94: 2:1.48:0.02:2.5 to form a slurry 6. According to LFP: LFO: SP: SWCNT: pvdf=95.2: 1:1.28:0.02:2.5, forming a slurry 5 according to LFP: SP: SWCNT: pvdf=96.5: 1.18:0.02:2.3 to form slurry 1. According to the four-layer coating die head, slurry 7 (close to the current collector), slurry 6, slurry 5 and slurry 1 are coated on the upper and lower surfaces of the carbon-coated aluminum foil 1311 respectively in the order of slurry 1, and the positive plate 1310 is obtained after drying, and finally the lithium ion battery comprising the positive plate 1330 is obtained.
Energy density and gram discharge capacity were measured at 25.+ -. 2 ℃ and 0.33 ℃ by charge and discharge; charging the 1C constant current and constant voltage to a cut-off voltage at 25+/-2 ℃ to obtain a 1C constant current charging ratio; charging at 25+/-2 ℃ and 0.33 ℃ to cut-off voltage at constant current and constant voltage, and obtaining 2℃ discharge capacity retention rate by 2℃ discharge capacity/0.33C discharge capacity; the 1C constant-current and constant-voltage charge was carried out to a cut-off voltage, the battery was disassembled in a glove box, the presence or absence of lithium precipitation on the negative electrode sheet was observed, and the respective lithium ion batteries of examples 1 to 14 and comparative examples 1 to 3 above were subjected to electrical properties, and the test results are shown in table 1.
TABLE 1
Wherein "slightly precipitated lithium" means that 10 to 15% of lithium is precipitated, and "severely precipitated lithium" means that 70 to 80% of lithium is precipitated.
From the above description, it can be seen that the above embodiments of the present application achieve the following technical effects:
according to the application, the contents of the lithium supplementing agents in different coating layers in the coated electrode are distributed in a gradient manner from inside to outside through the multilayer coating technology, a large amount of oxygen is generated after the battery core containing the coated electrode is formed, so that pores are generated, and finally, the positive plate with gradient porosity is obtained, so that the problem of serious polarization of the thick electrode is effectively solved without increasing the cost, the pre-lithium intercalation is synchronously realized, and the energy density and the high cycle performance of the lithium ion battery are remarkably improved. The preparation method is simple and quick, and the cost is low.
The above is only a preferred embodiment of the present application, and is not intended to limit the present application, but various modifications and variations can be made to the present application by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.
Claims (9)
1. A positive electrode sheet comprises a positive electrode current collector, wherein the positive electrode current collector comprises a first surface and a second surface which are opposite, and the first surface comprises An A1 coating layer, an A2 coating layer, an A3 coating layer, an A4 coating layer and a … … An which are sequentially overlapped in the direction away from the positive electrode current collector 1 A coating layer, and/or the second surface comprises a B1 coating layer, a B2 coating layer, a B3 coating layer, a B4 coating layer and a … … Bn which are sequentially stacked 2 A coating layer, wherein n 1 Is an integer of 2 to 10, n 2 Is an integer of 2 to 10;
each of the coating layers on the first surface and each of the coating layers on the second surface each independently include a positive electrode active material and a lithium salt pre-lithium agent,
the A1 coating layer, the A2 coating layer, the A3 coating layer, the A4 coating layer, … … the An 1 The content of the lithium salt pre-lithium agent in the coating layer is sequentially increased,
the B1 coating layer, the B2 coating layer, the B3 coating layer, the B4 coating layer, … … the Bn 2 The content of the lithium salt pre-lithium agent in the coating layer is sequentially increased;
the positive electrode active material is selected from one or more of lithium iron phosphate, lithium iron manganese phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium cobalt oxide and lithium manganate, and the lithium salt pre-lithium agent is lithium-rich lithium ferrite.
2. The positive electrode sheet according to claim 1, wherein n 1 =n 2 =4, and
the A1 coating layer and the B1 coating layer each independently include: 93-98.5 parts by weight of the positive electrode active material and 0-3 parts by weight of the lithium salt pre-lithium agent;
the A2 coating layer and the B2 coating layer each independently include: 88-98 parts by weight of the positive electrode active material and 0.5-8 parts by weight of the lithium salt pre-lithium agent;
the A3 coating layer and the B3 coating layer each independently include: 90-98 parts by weight of the positive electrode active material and 0.6-9 parts by weight of the lithium salt pre-lithium agent;
the A4 coating layer and the B4 coating layer each independently include: 92-98 parts by weight of the positive electrode active material and 0.8-10 parts by weight of the lithium salt pre-lithium agent.
3. The positive electrode sheet according to claim 1, wherein n 1 =n 2 =3, and
the A1 coating layer and the B1 coating layer each independently include: 93-98.5 parts by weight of the positive electrode active material and 0-3 parts by weight of the lithium salt pre-lithium agent;
the A2 coating layer and the B2 coating layer each independently include: 90-98 parts by weight of the positive electrode active material and 0.6-7.5 parts by weight of the lithium salt pre-lithium agent;
the A3 coating layer and the B3 coating layer each independently include: 88-98 parts by weight of the positive electrode active material and 0.8-8 parts by weight of the lithium salt pre-lithium agent.
4. The positive electrode sheet according to claim 1, wherein n 1 =n 2 =2, and
the A1 coating layer and the B1 coating layer each independently include: 93-98.5 parts by weight of the positive electrode active material and 0-3 parts by weight of the lithium salt pre-lithium agent;
the A2 coating layer and the B2 coating layer each independently include: 88-98 parts by weight of the positive electrode active material and 0.5-8 parts by weight of the lithium salt pre-lithium agent.
5. The positive electrode sheet according to any one of claims 1 to 4, wherein each of the coating layers on the first surface and the second surface further independently comprises 1 to 5 parts by weight of a conductive agent selected from any one of superconducting carbon black, carbon nanotubes, graphene, VGCF, and conductive graphite, and 1 to 5 parts by weight of a binderOne or more of the binders are selected from any one or more of polyvinylidene fluoride, polyimide and polyacrylate; the thickness of each coating layer on the first surface and each coating layer on the second surface is 30-250 μm independently, and the surface density of each coating layer on the first surface and each coating layer on the second surface is 100-500 g/m independently 2 。
6. The positive electrode sheet according to any one of claims 1 to 3, wherein n 1 =n 2 =4, the A1 coating layer and the B1 coating layer each independently include: 94-97 parts by weight of lithium iron phosphate and 1-3 parts by weight of lithium ferrite; the A2 coating layer and the B2 coating layer each independently include: 93-96 parts by weight of the lithium iron phosphate and 2-4 parts by weight of the lithium-rich lithium ferrite; the A3 coating layer and the B3 coating layer each independently include: 92-95 parts by weight of the lithium iron phosphate and 3-5 parts by weight of the lithium-rich lithium ferrite; the A4 coating layer and the B4 coating layer each independently include: 93-97 parts by weight of the lithium iron phosphate and 4-6 parts by weight of the lithium-rich lithium ferrite; or,
n 1 =n 2 when=3, the A1 coating layer and the B1 coating layer each independently include: 94-98 parts by weight of the lithium iron phosphate and 1-3 parts by weight of the lithium-rich lithium ferrite; the A2 coating layer and the B2 coating layer each independently include: 91-96 parts by weight of the lithium iron phosphate and 2-5 parts by weight of the lithium-rich lithium ferrite; the A3 coating layer and the B3 coating layer each independently include: 89-95 parts by weight of lithium iron phosphate and 3-6 parts by weight of lithium ferrite rich in lithium.
7. A method for producing the positive electrode sheet according to any one of claims 1 to 6, characterized by comprising:
step S1, A1 slurry, A2 slurry, A3 slurry, A4 slurry, … … An 1 Each positive electrode slurry of the slurry is sequentially coated on the first surface of the positive electrode current collector, and a sequentially stacked A1 coating layer is correspondingly formed on the first surfaceA2 coating layer, A3 coating layer, A4 coating layer, … … An 1 Coating a layer to obtain a coated electrode; wherein n is 1 Is a positive integer of 2 to 10; and/or
B1 slurry, B2 slurry, B3 slurry, B4 slurry, … … Bn 2 Sequentially coating each positive electrode slurry of the slurry on the second surface of the positive electrode current collector, and correspondingly forming a B1 coating layer, a B2 coating layer, a B3 coating layer, a B4 coating layer and a … … Bn which are sequentially stacked on the second surface 2 A coating layer; n is n 2 Is a positive integer of 2 to 10;
step S2, rolling, slitting and die-cutting the coated electrode in sequence to obtain a positive plate;
the positive electrode slurries each independently include a positive electrode active material and a lithium salt pre-lithium agent,
the A1 slurry, the A2 slurry, the A3 slurry, the A4 slurry, … … the An 1 The content of the lithium salt pre-lithium agent in the slurry is sequentially increased;
the B1 slurry, the B2 slurry, the B3 slurry, the B4 slurry, … … the Bn 2 The content of the lithium salt pre-lithium agent in the slurry is sequentially increased.
8. A preparation method of a lithium ion battery comprises the steps of assembling a positive plate, a negative plate, electrolyte and a diaphragm to obtain a battery cell; the electrolyte is adopted to infiltrate the battery core, and then the battery core is sequentially subjected to formation and aging to obtain an aged battery core, and the aged battery core is subjected to degassing and capacity division to obtain the lithium ion battery, wherein the positive plate is the positive plate of any one of claims 1 to 6;
the chemical synthesis is carried out at 38-50 ℃, the aging time is 12-48 h, and the degassing process comprises the following steps:
performing primary vacuum degassing on the aged battery cell to obtain a degassed battery cell;
charging the degassing battery cell to 3.65-3.8V under a first current and then charging the degassing battery cell to 4.1-4.5V under a second current to obtain a charging battery cell;
performing secondary vacuum degassing on the charging battery cell;
the first current is 0.01C-1C of capacity, and the second current is 0.0005C-0.05C of capacity.
9. A lithium ion battery is characterized in that the lithium ion battery is prepared by the preparation method of claim 8.
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