WO2024197875A1 - 一种二次电池及用电装置 - Google Patents

一种二次电池及用电装置 Download PDF

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Publication number
WO2024197875A1
WO2024197875A1 PCT/CN2023/085644 CN2023085644W WO2024197875A1 WO 2024197875 A1 WO2024197875 A1 WO 2024197875A1 CN 2023085644 W CN2023085644 W CN 2023085644W WO 2024197875 A1 WO2024197875 A1 WO 2024197875A1
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Prior art keywords
positive electrode
active material
region
secondary battery
electrode active
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PCT/CN2023/085644
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English (en)
French (fr)
Inventor
程文强
韩冬冬
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Ningde Amperex Technology Ltd
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Ningde Amperex Technology Ltd
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Priority to CN202380019957.8A priority Critical patent/CN118696445A/zh
Priority to PCT/CN2023/085644 priority patent/WO2024197875A1/zh
Publication of WO2024197875A1 publication Critical patent/WO2024197875A1/zh
Anticipated expiration legal-status Critical
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—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
    • 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
    • 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
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • 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
    • H01M4/64—Carriers or 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
    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials
    • 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
    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials
    • H01M4/661—Metal or alloys, e.g. alloy coatings
    • 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
    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials
    • H01M4/661—Metal or alloys, e.g. alloy coatings
    • H01M4/662—Alloys
    • 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

Definitions

  • the present application relates to the field of electrochemistry, and in particular to a secondary battery and an electrical device.
  • Secondary batteries such as lithium-ion batteries, have the advantages of high energy density, low self-discharge, no memory effect and long cycle life. Therefore, they are widely used in portable electronic devices, electric vehicles, drones, large energy storage equipment and other fields.
  • lithium-ion batteries are exposed to high temperatures for a long time during use, it is easy for the positive electrode active materials to undergo irreversible structural phase changes, leading to gas production problems, causing the thickness of the lithium-ion batteries to expand and affecting the high-temperature storage performance of the lithium-ion batteries.
  • the purpose of the present application is to provide a secondary battery and an electrical device to improve the high-temperature storage performance of the secondary battery.
  • lithium-ion batteries are used as an example of secondary batteries to explain the present application, but the secondary batteries of the present application are not limited to lithium-ion batteries.
  • the specific technical solution is as follows:
  • the present application provides a secondary battery, which includes an electrode assembly, the electrode assembly includes a positive electrode plate, the positive electrode plate includes a positive current collector and a positive active material layer, the positive active material layer includes a positive active material, the positive current collector includes a first region, a second region and a third region, the positive active material layer is disposed on both sides of the first region, the positive active material layer is disposed on one side of the second region, and the positive active material layer is not disposed on both sides of the third region.
  • the present application defines the unit area mass of the first region as Mag/ m2 , the unit area mass of the second region as Mb g/ m2 , and the unit area mass of the third region as Mc g/ m2 , satisfying: Ma ⁇ Mb ⁇ Mc, and Ma/Mc ⁇ 99%, preferably, Ma/Mc ⁇ 98.5%.
  • the present application improves the degree of crushing of the positive electrode active material particles and the structural stability of the positive electrode plate by regulating the unit area mass of the first region, the second region and the third region of the positive electrode current collector within the above-mentioned range, thereby improving the high-temperature storage performance of the secondary battery.
  • the single-sided thickness of the positive electrode active material layer located in the first region is Hc ⁇ m
  • the single-sided unit area mass of the positive electrode active material layer located in the first region is Md g/m 2 , satisfying: Ma/Mc ⁇ -0.0892 ⁇ Md/Hc+1.3652.
  • the porosity of the positive electrode sheet is P
  • the positive electrode active material located in the first region is The mass per unit area of the single surface of the layer is Md g/m 2 , satisfying: P ⁇ [Md/Hc ⁇ (-0.2429)+1.2007] ⁇ 100%.
  • the electrode assembly further includes a negative electrode sheet, the negative electrode sheet includes a negative electrode active material layer, the single-sided thickness of the negative electrode active material layer is Ha ⁇ m, and satisfies: 0.2 ⁇ Hc/Ha ⁇ 4. Preferably, 0.5 ⁇ Hc/Ha ⁇ 1.5.
  • the bonding force between the wet film of the positive electrode active material layer and the positive electrode current collector is F N/m, F ⁇ 1, preferably, F ⁇ 2.
  • the positive electrode current collector includes at least one of aluminum foil, nickel foil or aluminum-nickel alloy foil. Selecting the above materials as the positive electrode current collector can make the positive electrode current collector have good conductivity, meet the performance requirements of conductive electrons, and provide certain strength and weldability, so that the positive electrode current collector can have sufficient strength during processing and facilitate welding of the pole ear on the positive electrode current collector.
  • the positive electrode active material includes at least one of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate or lithium-rich manganese-based materials. Selecting the above materials as the positive electrode active material can improve the high-temperature storage performance of the secondary battery while taking into account the energy density and cycle performance of the secondary battery.
  • the positive electrode active material layer also includes a binder
  • the binder includes at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyamide, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, polypropylene, polyethylene, polyetherimide or a copolymer of propylene derivatives. Selecting the above materials as binders is conducive to improving the bonding strength between the positive electrode active material layer and the positive electrode current collector, thereby improving the high temperature storage performance of the secondary battery.
  • the positive electrode active material layer also includes a conductive agent
  • the conductive agent includes at least one of conductive carbon black, single-walled carbon nanotubes, multi-walled carbon nanotubes, nanocarbon fibers or graphene.
  • the present application provides an electrical device, which includes the secondary battery described in any of the above embodiments. Therefore, the electrical device has good high temperature storage performance.
  • the present application provides a secondary battery and an electrical device, wherein the secondary battery comprises an electrode assembly, the electrode assembly comprises a positive electrode sheet, the positive electrode sheet comprises a positive current collector and a positive active material layer, wherein the unit area mass of the first region of the positive current collector, i.e., the region coated with the positive active material on both sides, is Mag/ m2 , the second region, i.e., the region coated with the positive active material on one side, is Mb g/ m2 , and the unit area mass of the third region, i.e., the region not coated with the positive active material, is Mc g/ m2 , satisfying Ma ⁇ Mb ⁇ Mc, and Ma/Mc ⁇ 99%.
  • the present application improves the degree of crushing of the positive active material particles, improves the structural stability of the positive electrode sheet, and improves the high temperature storage performance of the secondary battery by regulating the unit area mass of the first region, the second region, and the third region of the positive current collector within the above range.
  • it is not necessary to achieve all the advantages described above at the same time for implementing any product or method of the present application.
  • FIG1 is a schematic diagram of the structure of an electrode assembly in some embodiments of the present application.
  • FIG2 is a schematic diagram of a cross-sectional structure of an electrode assembly along its thickness direction in some embodiments of the present application
  • FIG3 is a top view of the positive electrode current collector along its thickness direction in some embodiments of the present application.
  • FIG4 is a schematic diagram of the cross-sectional structure of a positive electrode sheet along its thickness direction in some embodiments of the present application.
  • FIG. 5 is a schematic diagram showing the relationship between bonding force and travel in a bonding force test.
  • Reference numerals 10 - electrode assembly, 20 - positive electrode sheet, 21 - positive electrode current collector, 22 - positive electrode active material layer, 30 - negative electrode sheet, 40 - separator, 211 - first region, 212 - second region, 213 - third region.
  • the lithium-ion battery is used as an example of a secondary battery to explain the present application, but the secondary battery of the present application is not limited to the lithium-ion battery.
  • the specific technical solution is as follows:
  • the present application provides a secondary battery, which includes an electrode assembly 10.
  • an electrode assembly 10 As shown in FIG1, for ease of understanding, a three-dimensional rectangular coordinate system is established with the width direction of the electrode assembly 10 as the X direction, the length direction of the electrode assembly 10 as the Y direction, and the thickness direction of the electrode assembly 10 as the Z direction.
  • the electrode assembly 10 includes a positive A positive electrode sheet 20, a negative electrode sheet 30, and a separator 40 disposed between the positive electrode sheet 20 and the negative electrode sheet 30, wherein the positive electrode sheet 20 includes a positive electrode collector 21 and a positive electrode active material layer 22, and the positive electrode active material layer 22 includes a positive electrode active material.
  • the positive electrode collector 21 includes a first region 211, a second region 212, and a third region 213. As shown in FIG4, along the X direction, the first region 211 is located in the middle of the positive electrode collector, the third region 213 is located at the head and tail ends of the positive electrode collector, and the second region 212 is located between the first region 211 and the third region 213. As shown in FIG4, the positive electrode active material layer 22 is disposed on both sides of the first region 211, the positive electrode active material layer 22 is disposed on one side of the second region 212, and the positive electrode active material layer 22 is not disposed on both sides of the third region 213.
  • the present application defines the mass per unit area of the first region 211 as Mag/m 2 , the mass per unit area of the second region 212 as Mb g/m 2 , and the mass per unit area of the third region 213 as Mc g/m 2 , satisfying: Ma ⁇ Mb ⁇ Mc, and Ma/Mc ⁇ 99%, preferably, Ma/Mc ⁇ 98.5%.
  • the first region of the positive electrode collector is a structure in which positive electrode active material layers are arranged on both sides
  • the second region is a structure in which positive electrode active material layers are arranged on one side
  • the third region is an empty foil region.
  • the first region and the second region of the positive electrode collector are more likely to be extended after being compressed than the third region, releasing a portion of the extrusion stress on the positive electrode active material particles during the cold pressing of the electrode sheet.
  • the present application improves the degree of crushing of the positive electrode active material particles and improves the structural stability of the positive electrode sheet by regulating the mass per unit area of the first region, the second region and the third region of the positive electrode collector within the above range, thereby improving the high temperature storage performance of the secondary battery.
  • the single-sided thickness of the positive electrode active material layer 22 located in the first region 211 is Hc ⁇ m
  • the single-sided unit area mass of the positive electrode active material layer 22 located in the first region 211 is Md g/m 2 , satisfying: Ma/Mc ⁇ -0.0892 ⁇ Md/Hc+1.3652.
  • the porosity of the positive electrode sheet is P
  • the mass per unit area of the positive electrode active material layer located in the first region is Md g/m 2
  • the electrode assembly further includes a negative electrode sheet, the negative electrode sheet includes a negative electrode active material layer, the single-sided thickness of the negative electrode active material layer is Ha ⁇ m, and satisfies: 0.2 ⁇ Hc/Ha ⁇ 4, preferably, 0.5 ⁇ Hc/Ha ⁇ 1.5.
  • the bonding force between the wet film of the positive electrode active material layer and the positive electrode current collector is F N/m, F ⁇ 1, preferably, F ⁇ 2.
  • the positive electrode active material layer and the positive electrode current collector can maintain appropriate bonding strength under high temperature conditions, thereby improving the high temperature storage performance of the secondary battery.
  • the present application does not particularly limit the method for adjusting the bonding force between the wet film of the positive electrode active material layer and the positive electrode current collector, as long as the purpose of the present application can be achieved.
  • the bonding force between the wet film of the positive electrode active material layer and the positive electrode current collector can be adjusted by adjusting the binder content.
  • the positive electrode current collector includes at least one of aluminum foil, nickel foil or aluminum-nickel alloy foil. Selecting the above materials as the positive electrode current collector can make the positive electrode current collector have good conductivity, meet the performance requirements of conductive electrons, and provide certain strength and weldability, so that the positive electrode current collector can have sufficient strength during processing and facilitate welding of the pole ear on the positive electrode current collector.
  • the positive electrode active material includes at least one of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate or lithium-rich manganese-based materials.
  • the positive electrode active material may also include non-metallic elements, such as fluorine, phosphorus, boron, chlorine, silicon, sulfur and other elements, which can further improve the stability of the positive electrode active material.
  • the above materials are selected as positive electrode active materials, which can take into account the energy density and cycle performance of the secondary battery on the basis of improving the high temperature storage performance of the secondary battery.
  • the positive electrode active material layer also includes a binder
  • the binder includes at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyamide, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, polypropylene, polyethylene, polyetherimide or a copolymer of propylene derivatives. Selecting the above materials as binders is conducive to improving the bonding strength between the positive electrode active material layer and the positive electrode current collector, thereby improving the high temperature storage performance of the secondary battery.
  • the positive electrode active material layer also includes a conductive agent
  • the conductive agent includes at least one of conductive carbon black, single-walled carbon nanotubes, multi-walled carbon nanotubes, nanocarbon fibers or graphene.
  • the present application does not have any particular restrictions on the mass ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode active material layer. Those skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved.
  • the mass ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode active material layer is (97.5-97.9): (0.9-1.7): (1.0-2.0).
  • the present application has no particular limitation on the preparation method of the positive electrode current collector, and any preparation method known in the art may be used as long as the purpose of the present application can be achieved.
  • the negative electrode sheet of the present application includes a negative electrode current collector and a negative electrode active material disposed on at least one surface of the negative electrode current collector.
  • the above-mentioned "negative electrode active material layer disposed on at least one surface of the negative electrode current collector” means that the negative electrode active material layer can be disposed on one surface of the negative electrode current collector along its own thickness direction, or it can be disposed on two surfaces of the negative electrode current collector along its own thickness direction.
  • the "surface” here can be the entire area of the negative electrode current collector or a partial area of the negative electrode current collector. This application has no special restrictions, as long as the purpose of this application can be achieved. This application has no special restrictions on the negative electrode current collector, as long as the purpose of this application can be achieved.
  • the negative electrode current collector may include copper foil, copper alloy foil, nickel foil, titanium foil, foamed nickel or foamed copper, etc.
  • the negative electrode active material layer includes negative electrode active materials. This application has no special restrictions on the type of negative electrode active materials, as long as the purpose of this application can be achieved.
  • the negative electrode active material may include at least one of natural graphite, artificial graphite, soft carbon, hard carbon, mesophase carbon microspheres, tin-based materials, silicon-based materials, lithium titanate, transition metal nitrides or natural flake graphite.
  • the negative electrode active material layer also includes at least one of a conductive agent, a thickener, and a binder.
  • the negative electrode binder may include, but is not limited to, at least one of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoride, polyethylene, polypropylene, polyacrylic acid, styrene-butadiene rubber, acrylic (ester) styrene-butadiene rubber, epoxy resin, or nylon.
  • the negative electrode sheet may further include a conductive layer, which is located between the negative electrode current collector and the negative electrode material layer.
  • a conductive layer which is located between the negative electrode current collector and the negative electrode material layer.
  • the present application has no particular restrictions on the composition of the conductive layer, which may be a conductive layer commonly used in the art, and may include but is not limited to the above-mentioned negative electrode conductive agent and the above-mentioned negative electrode binder.
  • the secondary battery of the present application also includes a diaphragm.
  • the present application does not particularly limit the diaphragm.
  • the material of the diaphragm may include but is not limited to polyethylene (PE), polypropylene (PP)-based polyolefin (PO), polyester, (such as polyethylene terephthalate (PET)), cellulose, polyimide (PI), polyamide, (PA), spandex or aramid at least one
  • the type of diaphragm may include but is not limited to woven membrane, non-woven membrane (non-woven fabric), microporous membrane, composite membrane, diaphragm paper, rolled membrane or spinning membrane at least one.
  • the diaphragm may include a substrate layer and a surface treatment layer.
  • the substrate layer may be a non-woven fabric, a membrane or a composite membrane with a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate or polyimide.
  • a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite membrane may be used.
  • a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic material.
  • the inorganic layer includes inorganic particles and a binder, and the inorganic particles are not particularly limited, for example It can be selected from at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate.
  • the binder is not particularly limited, for example, it can be selected from at least one of polyvinylidene fluoride, copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene.
  • the polymer layer contains a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene) etc.
  • the secondary battery of the present application also includes an electrolyte.
  • the present application has no special restrictions on the electrolyte. Those skilled in the art can choose according to actual needs, as long as the purpose of the present application can be achieved.
  • ethylene carbonate also known as ethylene carbonate, abbreviated as EC
  • PC propylene carbonate
  • DEC diethyl carbonate
  • EP ethyl propionate
  • PP propyl propionate
  • EMC ethyl methyl carbonate
  • DMC dimethyl carbonate
  • VMC vinylene carbonate
  • FEC fluoroethylene carbonate
  • the present application has no special restrictions on the above-mentioned "mass ratio", as long as the purpose of the present application can be achieved.
  • the present application has no restrictions on the type of lithium salt, as long as the purpose of the present application can be achieved.
  • the lithium salt may include at least one of LiPF 6 , LiBF 4 , LiAsF 6 , LiClO 4 , LiB(C 6 H 5 ) 4 , LiCH 3 SO 3 , LiCF 3 SO 3 , LiN(SO 2 CF 3 ) 2 , LiC(SO 2 CF 3 ) 3 , LiSiF 6 , lithium bis(oxalatoborate) (LiBOB) or lithium difluoroborate.
  • the present application has no particular limitation on the concentration of the lithium salt in the electrolyte, as long as the purpose of the present application can be achieved.
  • the concentration of the lithium salt is 1.0 mol/L to 2.0 mol/L.
  • the secondary battery of the present application also includes a shell, and the present application has no particular limitation on the shell, and those skilled in the art can select it according to actual needs, as long as the purpose of the present application can be achieved.
  • the shell may include an aluminum-plastic film.
  • the secondary battery of the present application is not particularly limited, and may include a device that generates an electrochemical reaction.
  • the secondary battery may include, but is not limited to: a lithium metal secondary battery, a lithium ion secondary battery (lithium ion battery), a sodium ion secondary battery, a lithium polymer secondary battery, and a lithium ion polymer secondary battery.
  • the preparation method of the positive electrode sheet includes but is not limited to the following steps: dispersing the active material, the conductive agent and the binder in N-methylpyrrolidone (NMP) solvent to form a uniform positive electrode slurry, coating the positive electrode slurry on the positive electrode collector, drying, cold pressing, cutting, slitting and re-drying to obtain a positive electrode sheet.
  • NMP N-methylpyrrolidone
  • the present application has no particular restrictions on the method of regulating Ma, Mb, and Mc, as long as the purpose of the present invention can be achieved.
  • the cold pressing process, the surface roughness of the active material, the elongation of the current collector, or the tensile strength of the current collector can be adjusted.
  • At least one of the following methods can be used to adjust Ma, Mb, and Mc.
  • an aluminum foil with higher extensibility is selected, or a small pressure multiple step-by-step cold pressing method is used to press the positive electrode sheet to the target thickness, thereby reducing the degree of crushing of the positive electrode active material particles and improving the structural stability of the positive electrode sheet.
  • the positive electrode sheet can be cold pressed in the following manner: in the first step, the cold pressing pressure is 20 tons, in the second step, the cold pressing pressure is 30 tons, and in the third step, the cold pressing pressure is 30 tons.
  • the elongation of the aluminum foil of the present application along the rolling line direction is 2%-5%.
  • the present application has no particular restrictions on the method for adjusting the porosity P of the positive electrode sheet, as long as the purpose of the present invention can be achieved.
  • the porosity of the positive electrode sheet usually decreases with the increase of the cold pressing pressure, and its porosity can be adjusted by adjusting the cold pressing pressure of the positive electrode sheet.
  • the present application has no particular restrictions on the method for adjusting the single-sided unit area mass Md of the positive active material layer in the first region, as long as the purpose of the present invention can be achieved. For example, it can be adjusted by a cold pressing process.
  • the preparation method of the secondary battery includes but is not limited to the following steps: stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and winding, folding and other operations as needed to obtain an electrode assembly with a winding structure, placing the electrode assembly in a packaging bag, injecting an electrolyte into the packaging bag and sealing it to obtain an electrochemical device.
  • a second aspect of the present application provides an electrical device, which includes the secondary battery described in any of the aforementioned embodiments.
  • the electrical device of the present application is not particularly limited, and it can be an electrical device known in the prior art.
  • the electrical device can include, but is not limited to: a laptop computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.
  • the single-side unit area mass of the positive electrode active material layer located in the first region is Md test:
  • Mass per unit area of a single surface Md [(M 0-1 -M 1-1 )+...+(M 0-n -M 1-n )]/2n.
  • the head is clamped, and when the tension at the clamp is greater than 0kgf and less than 0.02kgf, the high-speed rail tensile machine can be used for testing, and the average tension in the stable area is finally measured, which is recorded as the bonding force F between the wet film of the positive electrode active material layer and the positive electrode current collector.
  • the ratio of the standard deviation of the bonding force data in this stable is recorded as the bonding force F between
  • the thickness expansion rate of the secondary battery is ( after H- before H)/ after H ⁇ 100%.
  • the 3C charge capacity retention rate of the secondary battery is C 1 /C 0 ⁇ 100%.
  • Lithium cobalt oxide, polyvinylidene fluoride, and conductive carbon black (SP) are mixed in a mass ratio of 97:1.5:1.5, and N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 70wt%, and stirred evenly.
  • NMP N-methylpyrrolidone
  • the slurry is evenly coated on one surface of a positive electrode current collector aluminum foil (elongation 3.0%) with a thickness of 10 ⁇ m, and the slurry is not coated on the ends of the positive electrode current collector. Drying at 90°C obtains a positive electrode sheet with a positive electrode active material layer thickness of 40 ⁇ m. Afterwards, the slurry is also coated on the other surface of the positive electrode sheet.
  • the slurry coating length of the surface is controlled to be less than the slurry coating length of the other surface, so that the positive electrode sheet includes an empty foil area, a single-sided coating area, and a double-sided coating area.
  • the double-sided coating area of the positive electrode sheet is located in the first area, the single-sided coating area is located in the second area, and the empty foil area is located in the third area, and then the positive electrode sheet is obtained after cold pressing, cutting and other processes.
  • the parameters of the cold pressing process are three times of low pressure cold pressing: the first cold pressing pressure is 20t, the roll gap is -100 ⁇ m; the second cold pressing pressure is 30t, the roll gap is -100 ⁇ m; the third cold pressing pressure is 30t, the roll gap is -100 ⁇ m.
  • a positive electrode sheet with a porosity of 15% is obtained.
  • the slurry was evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 8 ⁇ m, and dried at 85°C to obtain a negative electrode sheet with a negative electrode active material layer thickness of 40 ⁇ m; then, the above steps were repeated on the other surface of the negative electrode sheet to obtain a negative electrode sheet with negative electrode material coated on both sides; then, the negative electrode sheet obtained above was cold pressed, striped, and cut to obtain a negative electrode sheet.
  • EC, DEC, PC, PP and VC are mixed in a mass ratio of 20:30:20:28:2 to obtain a non-aqueous organic solvent. Then, lithium salt LiPF 6 and the non-aqueous organic solvent are prepared in a mass ratio of 8:92 to obtain an electrolyte.
  • a porous polyethylene film with a thickness of 7 ⁇ m was used.
  • the positive electrode sheet, separator, and negative electrode sheet prepared above are stacked in order, with the separator placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then wound to obtain an electrode assembly.
  • the electrode assembly is placed in an aluminum-plastic film packaging bag, and after drying, the electrolyte is injected, and a lithium-ion battery is obtained through vacuum packaging, standing, formation, degassing, trimming, and other processes.
  • Hc is adjusted as shown in Table 2
  • Ma is adjusted by adjusting the cold pressing process, the elongation of the current collector, and the tensile strength of the current collector, the rest is the same as Example 1-1.
  • Hc is adjusted as shown in Table 2
  • Ma is adjusted by adjusting the cold pressing process, the elongation of the current collector, and the tensile strength of the current collector, the rest is the same as Example 1-1.
  • Examples 1-1 to 1-5 and Comparative Example 1 in Table 1 that by regulating the unit area masses Ma, Mb, and Mc of the first region, the second region, and the third region of the positive electrode current collector to satisfy: Ma ⁇ Mb ⁇ Mc, and Ma/Mc ⁇ 99%, the thickness expansion rate of the secondary battery after storage at 85°C for 24 hours is significantly reduced, indicating that the present application scheme can effectively improve the structural stability of the positive electrode sheet, thereby improving the high temperature storage performance of the secondary battery.
  • Example 1-1 Example 2-1 to Example 2-3 and Comparative Example 2 that, on the basis of satisfying Ma ⁇ Mb ⁇ Mc and Ma/Mc ⁇ 99%, by adjusting Ma/Mc ⁇ -0.0892 ⁇ Md/Hc+1.3652, the thickness expansion rate of the secondary battery after storage at 85°C for 24 hours is further reduced, indicating that the present application scheme can effectively improve the structural stability of the positive electrode sheet, thereby improving the high temperature storage performance of the secondary battery.
  • Example 1-1 Example 3-1 to Example 3-4 and Comparative Example 3 in Table 3 that, on the basis of satisfying Ma ⁇ Mb ⁇ Mc and Ma/Mc ⁇ 99%, by adjusting P ⁇ [Md/Hc ⁇ (-0.2429)+1.2007] ⁇ 100%, the 3C charging capacity retention rate of the secondary battery is significantly improved, and the thickness expansion rate of the secondary battery after being stored at 85°C for 24 hours is low.
  • the present application scheme can improve the high-temperature storage performance of the secondary battery while improving the rate performance of the lithium-ion battery, which is conducive to obtaining a lithium-ion battery with excellent rate performance and high-temperature storage performance.
  • the thickness of the positive electrode active material layer, the thickness of the negative electrode active material layer, and the bonding force F between the wet film of the positive electrode active material layer and the positive electrode current collector usually also have an impact on the performance of the secondary battery.
  • the thickness of the positive electrode active material layer, the thickness of the negative electrode active material layer, and the bonding force F between the wet film of the positive electrode active material layer and the positive electrode current collector usually also have an impact on the performance of the secondary battery.

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Abstract

本申请提供了一种二次电池及用电装置，二次电池包括电极组件，电极组件包括正极极片，正极极片包括正极集流体以及正极活性材料层，其中，正极集流体的第一区域即双面涂覆正极活性材料的区域的单位面积质量为Ma g/m2，第二区域即单面涂覆正极活性材料的区域为Mb g/m2，第三区域即未涂覆正极活性材料的区域的单位面积质量为Mc g/m2，满足Ma≤Mb＜Mc，且Ma/Mc≤99％。通过上述二次电池整体结构的设置，提高了二次电池的高温存储性能。

Description

一种二次电池及用电装置 技术领域
本申请涉及电化学领域，具体涉及一种二次电池及用电装置。
背景技术
二次电池，例如锂离子电池具有能量密度大、自放电小、无记忆效应及循环寿命长等优点，因此被广泛应用于便携式电子设备、电动汽车、无人机、大型储能设备等领域中。
锂离子电池在使用过程中，如果长期处于高温环境，易导致其中的正极活性材料发生不可逆的结构相变，进而出现产气问题，造成锂离子电池厚度膨胀，影响锂离子电池的高温存储性能。
发明内容
本申请的目的在于提供一种二次电池及用电装置，以提高二次电池的高温存储性能。
需要说明的是，在申请内容中，以锂离子电池作为二次电池的例子来解释本申请，但是本申请的二次电池并不仅限于锂离子电池。具体技术方案如下：
本申请第一方面提供了一种二次电池，其包括电极组件，电极组件包括正极极片，正极极片包括正极集流体以及正极活性材料层，正极活性材料层中包括正极活性材料，正极集流体包括第一区域、第二区域和第三区域，第一区域的两侧设置有正极活性材料层，第二区域的单侧设置有正极活性材料层，第三区域的两侧未设置正极活性材料层。本申请定义第一区域的单位面积质量为Ma g/m2，第二区域的单位面积质量为Mb g/m2，第三区域的单位面积质量为Mc g/m2，满足：Ma≤Mb<Mc，且Ma/Mc≤99％，优选地，Ma/Mc≤98.5％。
本申请实施例有益效果：本申请通过调控正极集流体的第一区域、第二区域和第三区域的单位面积质量在上述范围内，改善了正极活性材料颗粒的破碎程度，提高了正极极片的结构稳定性，进而提高二次电池的高温存储性能。
在本申请的一些实施方案中，位于第一区域的正极活性材料层的单面厚度为Hcμm，位于第一区域的正极活性材料层的单面单位面积质量为Md g/m2，满足：Ma/Mc≤-0.0892×Md/Hc+1.3652。不限于任何理论，通过调控Ma、Mc、Md、Hc之间满足上述关系，有利于得到具有良好结构稳定性的正极极片，提高二次电池的高温存储性能。
在本申请的一些实施方案中，正极极片的孔隙率为P，位于第一区域的正极活性材料 层的单面单位面积质量为Md g/m2，满足：P≥[Md/Hc×(-0.2429)+1.2007]×100％。不限于任何理论，通过调控P、Md、Hc之间满足上述关系，能够提高锂离子电池的倍率性能，有利于得到具有优异倍率性能和高温存储性能的锂离子电池。
在本申请的一些实施方案中，电极组件还包括负极极片，负极极片包括负极活性材料层，负极活性材料层的单面厚度为Haμm，满足：0.2≤Hc/Ha≤4。优选地，0.5≤Hc/Ha≤1.5。通过调控Ha和Hc之间满足上述关系，能够使锂离子电池获得良好的动力学性能。
在本申请的一些实施方案中，正极活性材料层的湿膜与正极集流体之间的粘结力为F N/m，F≥1，优选地，F≥2。通过调控正极活性材料层的湿膜与正极集流体之间的粘结力在上述范围，正极活性材料层与正极集流体之间能够在高温条件下保持适当的粘结强度，从而提高二次电池的高温存储性能。
在本申请的一些实施方案中，正极集流体包括铝箔、镍箔或铝镍合金箔中的至少一种。选用上述材质作为正极集流体，可以使正极集流体具有良好的导电性，满足传导电子的性能要求，同时提供一定的强度和焊接性，使得正极集流体够在加工过程中具有足够的强度同时方便在正极集流体上焊接极耳。
在本申请的一些实施方案中，正极活性材料包括钴酸锂、锰酸锂、镍酸锂、镍钴锰酸锂、镍钴铝酸锂、磷酸铁锂、磷酸锰铁锂、磷酸钒锂或富锂锰基材料中的至少一种。选用上述材料作为正极活性材料，可以在提高二次电池的高温存储性能的基础上，兼顾二次电池的能量密度和循环性能。
在本申请的一些实施方案中，正极活性材料层中还包括粘结剂，粘结剂包括聚偏氟乙烯、偏氟乙烯-六氟丙烯共聚物、聚丙烯腈、聚丙烯酸酯、聚丙烯酸、聚丙烯酸盐、聚乙烯吡咯烷酮、聚酰胺、聚乙烯醚、聚甲基丙烯酸甲酯、聚四氟乙烯、聚六氟丙烯、聚丙烯、聚乙烯、聚醚酰亚胺或丙烯烃类衍生物的共聚物中的至少一种。选用上述材料作为粘结剂，有利于提高正极活性材料层与正极集流体之间的粘结强度，从而提高二次电池的高温存储性能。
在本申请的一些实施方案中，正极活性材料层中还包括导电剂，导电剂包括导电炭黑、单壁碳纳米管、多壁碳纳米管、纳米碳纤维或石墨烯中的至少一种。通过选用上述材料作为正极活性材料层中的导电剂，可以提高正极活性材料层与正极集流体间的导电性，有利于二次电池倍率性能的提高。
本申请第二方面提供了一种用电装置，其包括前述任一实施方案所述的二次电池。由 此，用电装置具有良好的高温存储性能。
本申请提供了一种二次电池及用电装置，二次电池包括电极组件，电极组件包括正极极片，正极极片包括正极集流体以及正极活性材料层，其中，正极集流体的第一区域即双面涂覆正极活性材料的区域的单位面积质量为Ma g/m2，第二区域即单面涂覆正极活性材料的区域为Mb g/m2，第三区域即未涂覆正极活性材料的区域的单位面积质量为Mc g/m2，满足Ma≤Mb<Mc，且Ma/Mc≤99％。本申请通过调控正极集流体的第一区域、第二区域和第三区域的单位面积质量在上述范围内，改善了正极活性材料颗粒的破碎程度，提高了正极极片的结构稳定性，提高了二次电池的高温存储性能。当然，实施本申请的任一产品或方法并不一定需要同时达到以上所述的所有优点。
附图说明
为了更清楚地说明本申请实施例和现有技术的技术方案，下面对实施例和现有技术中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本申请的一些实施例，对于本领域普通技术人员来讲，还可以根据这些附图获得其他的附图。
图1为本申请一些实施方案中电极组件的结构示意图；
图2为本申请一些实施方案中电极组件沿自身厚度方向的剖面结构示意图；
图3为本申请一些实施方案中正极集流体沿自身厚度方向的俯视图；
图4为本申请一些实施方案中正极极片沿自身厚度方向的剖面结构示意图；
图5为在粘结力测试中粘结力与行程之间的关系示意图。
附图标记：10-电极组件，20-正极极片，21-正极集流体，22-正极活性材料层，30-负极极片，40-隔膜，211-第一区域，212-第二区域，213-第三区域。
具体实施方式
为使本申请的目的、技术方案、及优点更加清楚明白，以下参照附图并举实施例，对本申请进一步详细说明。显然，所描述的实施例仅仅是本申请一部分实施例，而不是全部的实施例。基于本申请中的实施例，本领域普通技术人员所获得的所有其他实施例，都属于本申请保护的范围。
需要说明的是，在具体实施方式中，以锂离子电池作为二次电池的例子来解释本申请，但是本申请的二次电池并不仅限于锂离子电池。具体技术方案如下：
本申请第一方面提供了一种二次电池，其包括电极组件10，如图1所示，为了方便理解，以电极组件10自身宽度方向为X方向、以电极组件10自身长度方向为Y方向、以电极组件10自身厚度方向为Z方向建立三维直角坐标系。如图2所示，电极组件10包括正 极极片20、负极极片30以及设置于正极极片20和负极极片30之间的隔膜40，其中，正极极片20包括正极集流体21以及正极活性材料层22，正极活性材料层22中包括正极活性材料。如图3所示，正极集流体21包括第一区域211、第二区域212和第三区域213。如图4所示，沿X方向，第一区域211位于正极集流体的中部，第三区域213位于正极集流体的首端和尾端，第二区域212位于第一区域211和第三区域213之间。如图4所示，第一区域211的两侧设置有正极活性材料层22，第二区域212的单侧设置有正极活性材料层22，第三区域213的两侧未设置正极活性材料层22。本申请定义第一区域211的单位面积质量为Ma g/m2，第二区域212的单位面积质量为Mb g/m2，第三区域213的单位面积质量为Mc g/m2，满足：Ma≤Mb<Mc，且Ma/Mc≤99％，优选地，Ma/Mc≤98.5％。发明人研究发现，锂离子电池例如卷绕结构电池中，正极集流体的第一区域为两侧均设置正极活性材料层的结构，第二区域为单侧设置正极活性材料层的结构，第三区域为空箔区，正极集流体的第一区域和第二区域相较于第三区域在受压后更易发生延展，释放一部分极片冷压过程中正极活性材料颗粒受到的挤压应力。本申请通过调控正极集流体的第一区域、第二区域和第三区域的单位面积质量在上述范围内，改善了正极活性材料颗粒的破碎程度，提高了正极极片的结构稳定性，进而提高二次电池的高温存储性能。
在本申请的一些实施方案中，如图4所示，位于第一区域211的正极活性材料层22的单面厚度为Hcμm，位于第一区域211的正极活性材料层22的单面单位面积质量为Md g/m2，满足：Ma/Mc≤-0.0892×Md/Hc+1.3652。不限于任何理论，通过调控Ma、Mc、Md、Hc之间满足上述关系，有利于得到具有良好结构稳定性的正极极片，提高二次电池的高温存储性能。
在本申请的一些实施方案中，正极极片的孔隙率为P，位于第一区域的正极活性材料层的单面单位面积质量为Md g/m2，满足：P≥[Md/Hc×(-0.2429)+1.2007]×100％。不限于任何理论，通过调控P、Md、Hc之间满足上述关系，能够提高锂离子电池的倍率性能，有利于得到具有优异倍率性能和高温存储性能的锂离子电池。
在本申请的一些实施方案中，电极组件还包括负极极片，负极极片包括负极活性材料层，负极活性材料层的单面厚度为Haμm，满足：0.2≤Hc/Ha≤4，优选地，0.5≤Hc/Ha≤1.5。通过调控Ha和Hc之间满足上述关系，能够使锂离子电池获得良好的动力学性能。
在本申请的一些实施方案中，正极活性材料层的湿膜与正极集流体之间的粘结力为F N/m，F≥1，优选地，F≥2。通过调控正极活性材料层的湿膜与正极集流体之间的粘结力在 上述范围，正极活性材料层与正极集流体之间能够在高温条件下保持适当的粘结强度，从而提高二次电池的高温存储性能。本申请对调整正极活性材料层的湿膜与正极集流体之间的粘结力的方法没有特别限制，只要能实现本申请发明目的即可。例如，可以通过调整粘结剂含量来调整正极活性材料层的湿膜与正极集流体之间的粘结力。
在本申请的一些实施方案中，正极集流体包括铝箔、镍箔或铝镍合金箔中的至少一种。选用上述材质作为正极集流体，可以使正极集流体具有良好的导电性，满足传导电子的性能要求，同时提供一定的强度和焊接性，使得正极集流体够在加工过程中具有足够的强度同时方便在正极集流体上焊接极耳。
在本申请的一些实施方案中，正极活性材料包括钴酸锂、锰酸锂、镍酸锂、镍钴锰酸锂、镍钴铝酸锂、磷酸铁锂、磷酸锰铁锂、磷酸钒锂或富锂锰基材料中的至少一种。在本申请中，正极活性材料还可以包含非金属元素，例如氟、磷、硼、氯、硅、硫等元素，这些元素能进一步提高正极活性材料的稳定性。选用上述材料作为正极活性材料，可以在提高二次电池的高温存储性能的基础上，兼顾二次电池的能量密度和循环性能。
在本申请的一些实施方案中，正极活性材料层中还包括粘结剂，粘结剂包括聚偏氟乙烯、偏氟乙烯-六氟丙烯共聚物、聚丙烯腈、聚丙烯酸酯、聚丙烯酸、聚丙烯酸盐、聚乙烯吡咯烷酮、聚酰胺、聚乙烯醚、聚甲基丙烯酸甲酯、聚四氟乙烯、聚六氟丙烯、聚丙烯、聚乙烯、聚醚酰亚胺或丙烯烃类衍生物的共聚物中的至少一种。选用上述材料作为粘结剂，有利于提高正极活性材料层与正极集流体之间的粘结强度，从而提高二次电池的高温存储性能。
在本申请的一些实施方案中，正极活性材料层中还包括导电剂，导电剂包括导电炭黑、单壁碳纳米管、多壁碳纳米管、纳米碳纤维或石墨烯中的至少一种。通过选用上述材料作为正极活性材料层中的导电剂，可以提高正极活性材料层与正极集流体间的导电性，有利于二次电池倍率性能的提高。
本申请对正极活性材料层中正极活性材料、导电剂、粘结剂的质量比没有特别限制，本领域技术人员可以根据实际需要选择，只要能够实现本申请目的即可。例如，正极活性材料层中正极活性材料、导电剂和粘结剂的质量比为(97.5～97.9)∶(0.9～1.7)∶(1.0～2.0)。
本申请对正极集流体的制备方法没有特别限制，可以采用本领域公知的制备方法，只要能够实现本申请目的即可。
本申请的负极极片包括负极集流体以及设置于负极集流体至少一个表面上的负极活 性材料层。上述“设置于负极集流体至少一个表面上的负极活性材料层”是指，负极活性材料层可以设置于负极集流体沿自身厚度方向上的一个表面上，也可以设置于负极集流体沿自身厚度方向上的两个表面上。需要说明，这里的“表面”可以是负极集流体的全部区域，也可以是负极集流体的部分区域，本申请没有特别限制，只要能实现本申请目的即可。本申请对负极集流体没有特别限制，只要能够实现本申请目的即可。例如，负极集流体可以包含铜箔、铜合金箔、镍箔、钛箔、泡沫镍或泡沫铜等。负极活性材料层包括负极活性材料。本申请对负极活性材料的种类没有特别限制，只要能够实现本申请目的即可。例如，负极活性材料可以包含天然石墨、人造石墨、软碳、硬碳、中间相炭微球、锡基材料、硅基材料、钛酸锂、过渡金属氮化物或天然鳞片石墨等中的至少一种。任选地，负极活性材料层还包括导电剂、增稠剂、粘结剂中的至少一种。本申请对负极活性材料层中的导电剂、增稠剂和粘结剂的种类没有特别限制，只要能够实现本申请目的即可。例如，负极粘结剂可以包括但不限于聚乙烯醇、羧甲基纤维素、羟丙基纤维素、二乙酰基纤维素、聚氯乙烯、羧化的聚氯乙烯、聚氟乙烯、含亚乙基氧的聚合物、聚乙烯吡咯烷酮、聚氨酯、聚四氟乙烯、聚偏1,1-二氟乙烯、聚乙烯、聚丙烯、聚丙烯酸、丁苯橡胶、丙烯酸(酯)化的丁苯橡胶、环氧树脂或尼龙中的至少一种。
任选地，负极极片还可以包括导电层，导电层位于负极集流体和负极材料层之间。本申请对导电层的组成没有特别限制，可以是本领域常用的导电层，导电层可以包括但不限于上述负极导电剂和上述负极粘结剂。
本申请的二次电池还包括隔膜，本申请对隔膜没有特别限制，本领域技术人员可以根据实际需要选择，只要能够实现本申请目的即可。例如，隔膜的材料可以包括但不限于聚乙烯(PE)、聚丙烯(PP)为主的聚烯烃(PO)、聚酯、(例如聚对苯二甲酸二乙酯(PET))、纤维素、聚酰亚胺(PI)、聚酰胺、(PA)、氨纶或芳纶中的至少一种；隔膜的类型可以包括但不限于织造膜、非织造膜(无纺布)、微孔膜、复合膜、隔膜纸、碾压膜或纺丝膜中的至少一种。例如，隔膜可以包括基材层和表面处理层。基材层可以为具有多孔结构的无纺布、膜或复合膜，基材层的材料可以包括聚乙烯、聚丙烯、聚对苯二甲酸乙二醇酯或聚酰亚胺等中的至少一种。任选地，可以使用聚丙烯多孔膜、聚乙烯多孔膜、聚丙烯无纺布、聚乙烯无纺布或聚丙烯-聚乙烯-聚丙烯多孔复合膜。任选地，基材层的至少一个表面上设置有表面处理层，表面处理层可以是聚合物层或无机物层，也可以是混合聚合物与无机物所形成的层。例如，无机物层包括无机颗粒和粘结剂，所述无机颗粒没有特别限制，例如 可以选自氧化铝、氧化硅、氧化镁、氧化钛、二氧化铪、氧化锡、二氧化铈、氧化镍、氧化锌、氧化钙、氧化锆、氧化钇、碳化硅、勃姆石、氢氧化铝、氢氧化镁、氢氧化钙或硫酸钡等中的至少一种。所述粘结剂没有特别限制，例如可以选自聚偏氟乙烯、偏氟乙烯-六氟丙烯的共聚物、聚酰胺、聚丙烯腈、聚丙烯酸酯、聚丙烯酸、聚丙烯酸盐、聚乙烯呲咯烷酮、聚乙烯醚、聚甲基丙烯酸甲酯、聚四氟乙烯或聚六氟丙烯中的至少一种。聚合物层中包含聚合物，聚合物的材料包括聚酰胺、聚丙烯腈、丙烯酸酯聚合物、聚丙烯酸、聚丙烯酸盐、聚乙烯呲咯烷酮、聚乙烯醚、聚偏氟乙烯或聚(偏氟乙烯-六氟丙烯)等中的至少一种。
本申请的二次电池还包括电解液，本申请对电解液没有特别限制，本领域技术人员可以根据实际需要选择，只要能够实现本申请目的即可。例如，将碳酸亚乙酯(也称碳酸乙烯酯，简写EC)、碳酸亚丙酯(PC)、碳酸二乙酯(DEC)、丙酸乙酯(EP)、丙酸丙酯(PP)碳酸甲乙酯(EMC)、碳酸二甲酯(DMC)、碳酸亚乙烯酯(VC)或碳酸氟代亚乙酯(FEC)等中的至少一种按照一定质量比例混合得到非水有机溶剂后，加入锂盐溶解并混合均匀即可。本申请对上述“质量比例”没有特别限制，只要能够实现本申请目的即可。本申请对锂盐的种类没有限制，只要能够实现本申请目的即可。例如，锂盐可以包括LiPF6、LiBF4、LiAsF6、LiClO4、LiB(C6H5)4、LiCH3SO3、LiCF3SO3、LiN(SO2CF3)2、LiC(SO2CF3)3、LiSiF6、二草酸硼酸锂(LiBOB)或二氟硼酸锂中的至少一种。本申请对锂盐在电解液中的浓度没有特别限制，只要能够实现本申请目的即可。例如，锂盐的浓度为1.0mol/L至2.0mol/L。
本申请的二次电池还包括壳体，本申请对壳体没有特别限制，本领域技术人员可以根据实际需要选择，只要能够实现本申请目的即可。例如，壳体可以包括铝塑膜。
本申请的二次电池没有特别限制，其可以包括发生电化学反应的装置。例如，二次电池可以包括但不限于：锂金属二次电池、锂离子二次电池(锂离子电池)、钠离子二次电池、锂聚合物二次电池、锂离子聚合物二次电池。
本申请对正极极片的制备方法没有特别限制，可以选用本领域公知的制备方法，只要能够实现本申请目的即可。例如，正极极片的制备方法包括但不限于如下步骤：将活性材料、导电剂和粘合剂分散于N甲基吡咯烷酮(NMP)溶剂中混合，形成均匀的正极浆料，将正极浆料涂覆在正极集流体上，经烘干、冷压、裁片、分切和再干燥后，得到正极极片。
本申请对调控Ma、Mb、Mc的方法没有特别限制，只要能实现本申请发明目的即可。例如，可以通过调整冷压工艺、活性材料的表面粗糙度、集流体延伸率或集流体抗拉强度 中的至少一种方式，实现对Ma、Mb、Mc的调整。在制备正极极片过程中，选用延伸性较高的铝箔，或采用小压力多次分步冷压方式，将正极极片压到目标厚度，从而降低正极活性材料颗粒破碎程度，提高正极极片的结构稳定性。示例性地，可以按照下述方式对正极极片进行冷压：第一步，冷压压力为20吨，第二步冷压压力为30吨，第三步冷压压力为30吨。本申请的铝箔的沿轧制线方向上的延伸率为2％-5％。
本申请对调整正极极片的孔隙率P的方法没有特别限制，只要能实现本申请发明目的即可。例如，正极极片的孔隙率通常随冷压压力增大而降低，可以通过调整正极极片冷压压力来调整其孔隙率。本申请对调整第一区域的正极活性材料层的单面单位面积质量Md的方法没有特别限制，只要能实现本申请发明目的即可。例如，可以通过冷压工艺调整。
本申请对二次电池的制备方法没有特别限制，可以选用本领域公知的制备方法，只要能够实现本申请目的即可。例如，二次电池的制备方法包括但不限于如下步骤：将正极极片、隔膜和负极极片按顺序堆叠，并根据需要将其卷绕、折叠等操作得到卷绕结构的电极组件，将电极组件放入包装袋内，将电解液注入包装袋并封口，得到电化学装置。
本申请第二方面提供了一种用电装置，其包括前述任一实施方案所述的二次电池。
本申请的用电装置没有特别限定，其可以是用于现有技术中公知的用电装置。例如，用电装置可以包括但不限于：笔记本电脑、笔输入型计算机、移动电脑、电子书播放器、便携式电话、便携式传真机、便携式复印机、便携式打印机、头戴式立体声耳机、录像机、液晶电视、手提式清洁器、便携CD机、迷你光盘、收发机、电子记事本、计算器、存储卡、便携式录音机、收音机、备用电源、电机、汽车、摩托车、助力自行车、自行车、照明器具、玩具、游戏机、钟表、电动工具、闪光灯、照相机、家庭用大型蓄电池、锂离子电容器。
实施例
以下，举出实施例及对比例来对本申请的实施方式进行更具体地说明。各种的试验及评价按照下述的方法进行。
测试方法和设备：
正极集流体单位面积重量测试：
a)在(25±3)℃的环境下，将正极极片从二次电池中拆出，并在NMP溶剂中浸泡至正极活性材料层从正极集流体上脱落；
b)在正极集流体的两侧设置有正极活性材料层的第一区域a、单侧设置有正极活性材 料层的第二区域b、两侧未设置正极活性材料层的第三区域c取样，三个区域所取的正极集流体样品的面积≥1cm2，且记为sa、sb、sc；
c)在精度为0.1mg的电子天平上称量各区域集流体样品重量为ma、mb、mc；
d)a、b、c三个区域正极集流体单位面积重量Ma＝ma/sa g/m2、Mb＝mb/sb g/m2、Mc＝mc/sc g/m2。
位于第一区域的正极活性材料层的单面厚度Hc、负极活性材料层的单面厚度Ha测试：
a)在(25±3)℃的环境下，将正、负极极片从二次电池中拆出；
b)用无尘纸拭去a)中极片表面的电解液，采用等离子切割极片，在扫描电镜下测试极片第一个目标位置的上层涂层厚度为H1-上，下层厚度H1-下，此点的厚度为H1＝(H1-上+H1-下)/2，用同样的方式测试n(n≥15)个点的厚度H1、H2……Hn，则(H1+H2+……+Hn)/n记为正极极片厚度Hc或负极极片厚度Ha。
位于第一区域的正极活性材料层的单面单位面积质量为Md测试：
a)在(25±3)℃的环境下，将正极极片从二次电池中拆出；
b)取a)中极片在60℃下烘烤60min；
c)取b)中极片，裁切出至少n(n≥5)片面积≥8cm2的双面涂层极片，编号为1～n，在精度为0.1mg的电子天平上依次测试其重量，记为M0-1～M0-n；
d)取c)中称重后的极片，在NMP中浸泡至正极活性材料层脱落，取空集流体，在60℃下烘烤60min，在精度为0.1mg的电子天平上依次测试其重量，记为M1-1～M1-n；
e)单面单位面积质量Md＝[(M0-1-M1-1)+……+(M0-n-M1-n)]/2n。
正极极片的孔隙率P：
a)将涂敷双面正极活性材料层的正极极片从二次电池中拆出；
b)在(25±3)℃条件下，将a)中所得极片在DMC中浸泡30min后取出，在通风橱中晾干；
c)使用压汞法测试b)中所得极片的孔隙率，记为正极极片的孔隙率P。
粘结力F的测试：
在(25±3)℃的环境下，将从二次电池中拆出的正极极片，将正极极片在湿度为(10±5)％的环境中静置60min后，制成宽度×长度＝30mm×120mm的条状。沿长度方向从极片的一端将极片的一部分通过宽度×长度＝20mm×100mm的双面胶粘附在钢板上；然后将钢板固定在高铁拉力机相应位置，拉起未被粘在钢板上的极片，通过连接物或直接将极片放入夹 头内夹紧，待夹口拉力在大于0kgf且小于0.02kgf时，即可开始用高铁拉力机测试，最终测得平稳区域的拉力平均值，记为正极活性材料层的湿膜与正极集流体的粘结力F。如图5所示，要求此平稳区域的粘结力数据的标准差与平均值的比值不超过10％。
二次电池85℃存储24h厚度膨胀率测试：
a)将二次电池置于25℃环境中2h，用万分尺测试其Al-Tab(铝极耳)三个不同位置的厚度，并取其平均值为H前；
b)将a)中二次电池置于85℃环境中24h，用万分尺测试其Al-Tab三个不同位置的厚度，并取其平均值为H后；
c)二次电池厚度膨胀率为(H后-H前)/H后×100％。
二次电池3C充电容量保持率：
a)取二次电池在25℃，0.5C倍率放电至3V；
b)将a)中二次电池在0.2C倍率满充至设计电压，然后以设计电压恒压充电至截止电流为0.05C，静置5min，再以1.0C电流放电至3.0V，记放电容量为C0；
c)将b)中二次电池在3C倍率满充至设计电压，然后以设计电压恒压充电至截止电流为0.05C，静置5min，再以1.0C电流放电至3.0V，记放电容量为C1；
d)二次电池的3C充电容量保持率为C1/C0×100％。
实施例1-1
<正极极片的制备>
将钴酸锂、聚偏氟乙烯、导电炭黑(SP)按质量比97︰1.5︰1.5混合，加入N-甲基吡咯烷酮(NMP)作为溶剂，调配成为固含量为70wt％的浆料，并搅拌均匀。将浆料均匀涂覆在厚度为10μm的正极集流体铝箔(延伸率3.0％)的一个表面上，正极集流体首尾两端不涂覆浆料，90℃条件下烘干，得到正极活性材料层厚度为40μm的正极极片。之后，在该正极极片的另一个表面上也涂覆浆料，沿集流体长度方向，控制该表面的浆料涂覆长度小于另一表面的浆料涂覆长度，使得正极极片包含空箔区、单面涂覆区域和双面涂覆区域。该正极极片的双面涂覆区域位于第一区域，单面涂覆区域位于第二区域，空箔区位于第三区域，然后经过冷压、裁切等工序后得到正极极片。其中，冷压工序的参数为，三次小压力冷压：第1次冷压压力为20t，辊缝为-100μm；第2次冷压压力为30t，辊缝为-100μm；第3次冷压压力为30t，辊缝为-100μm。制得孔隙率为15％的正极极片。
<负极极片的制备>
将人造石墨、丁苯橡胶(SBR)、羧甲基纤维素钠(CMC)按照质量比97.4∶1.9∶0.7混合，加入去离子水，调配成为固含量为70wt％的浆料，并搅拌均匀。将浆料均匀涂覆在厚度为8μm的负极集流体铜箔的一个表面上，在85℃条件下烘干，得到负极活性材料层厚度为40μm的负极极片；之后，在该负极极片的另一个表面上重复以上步骤，即得到双面涂布负极材料的负极极片；然后将上述得到的负极极片进行冷压、分条、裁切得到负极极片。
<电解液的制备>
将EC、DEC、PC、PP和VC按照质量比为20∶30∶20∶28∶2混合得到非水有机溶剂。然后将锂盐LiPF6与非水有机溶剂按照质量比8∶92配制得到电解液。
<隔膜的制备>
采用厚度为7μm的多孔聚乙烯薄膜。
<锂离子电池的制备>
将上述制备得到的正极极片、隔膜、负极极片按顺序叠好，使隔膜处于正极极片和负极极片中间起到隔离的作用，卷绕得到电极组件。将电极组件置于铝塑膜包装袋中，干燥后注入电解液，经过真空封装、静置、化成、脱气、切边等工序得到锂离子电池。
实施例1-2至实施例1-6
除了在<正极极片的制备中>，通过调整冷压工艺、集流体延伸率和集流体抗拉强度从而如表1调整Ma、Mb以外，其余与实施例1-1相同。
实施例2-1至实施例2-3
除了在<正极极片的制备>中，如表2调整Hc、通过调整冷压工艺、集流体延伸率和集流体抗拉强度来调整Ma以外，其余与实施例1-1相同。
实施例3-1至实施例3-4
除了在<正极极片的制备>中，通过调整冷压工艺、集流体延伸率和集流体抗拉强度从而如表3调整Ma、通过调整冷压压力从而如表3调整正极极片的孔隙率P以外，其余与实施例1-1相同。
实施例4-1至实施例4-4
除了在<正极极片的制备>中，通过调整粘结剂含量从而如表4调整F以外，其余与实施例1-6相同。
对比例1
除了在<正极极片的制备中>，通过调整冷压工艺、集流体延伸率和集流体抗拉强度从而如表1调整Ma以外，其余与实施例1-1相同。
对比例2
除了在<正极极片的制备>中，如表2调整Hc以及通过调整冷压工艺、集流体延伸率和集流体抗拉强度来调整Ma以外，其余与实施例1-1相同。
对比例3
除了在<正极极片的制备>中，通过调整冷压工艺、集流体延伸率和集流体抗拉强度从而如表3调整Ma、通过调整冷压压力从而如表3调整正极极片的孔隙率P以外，其余与实施例1-1相同。
表1
从表1实施例1-1至实施例1-5和对比例1可以看出，通过调控正极集流体的第一区域、第二区域和第三区域的单位面积质量Ma、Mb、Mc满足：Ma≤Mb<Mc，且Ma/Mc≤99％，二次电池85℃存储24h后的厚度膨胀率显著降低，表明本申请方案能够有效提高正极极片的结构稳定性，从而提高二次电池的高温存储性能。
表2

从表2实施例1-1、实施例2-1至实施例2-3和对比例2可以看出，在满足Ma≤Mb<Mc，且Ma/Mc≤99％的基础上，通过调控Ma/Mc≤-0.0892×Md/Hc+1.3652，二次电池85℃存储24h后的厚度膨胀率进一步降低，表明本申请方案能够有效提高正极极片的结构稳定性，从而提高二次电池的高温存储性能。
表3
从表3实施例1-1、实施例3-1至实施例3-4和对比例3可以看出，在满足Ma≤Mb<Mc，且Ma/Mc≤99％的基础上，通过调控P≥[Md/Hc×(-0.2429)+1.2007]×100％，二次电池3C充电容量保持率显著提高，二次电池85℃存储24h后的厚度膨胀率较低。表明本申请方案能够在提高二次电池的高温存储性能的同时提高锂离子电池的倍率性能，有利于得到具有优异倍率性能和高温存储性能的锂离子电池。
表4
从表4实施例1-6、实施例4-1至实施例4-4可以看出，正极活性材料层的厚度、负极活性材料层的厚度、正极活性材料层的湿膜与正极集流体之间的粘结力F通常也会对二次电池的性能产生影响，在满足Ma≤Mb<Mc，且Ma/Mc≤99％的基础上，通过调控上述参数在本申请范围内，有利于得到具有优异高温存储性能的二次电池。
以上所述仅为本申请的较佳实施例，并不用以限制本申请，凡在本申请的精神和原则之内，所做的任何修改、等同替换、改进等，均应包含在本申请保护的范围之内。

Claims (11)

  1. 一种二次电池，其包括电极组件，所述电极组件包括正极极片，所述正极极片包括正极集流体以及正极活性材料层，所述正极活性材料层中包括正极活性材料，所述正极集流体包括第一区域、第二区域和第三区域，所述第一区域的两侧设置有正极活性材料层，所述第二区域的单侧设置有正极活性材料层，所述第三区域的两侧未设置正极活性材料层，
    其中，所述第一区域的单位面积质量为Ma g/m2，所述第二区域的单位面积质量为Mb g/m2，所述第三区域的单位面积质量为Mc g/m2，满足：Ma≤Mb＜Mc，且Ma/Mc≤99％。
  2. 根据权利要求1所述的二次电池，其中，位于所述第一区域的正极活性材料层的单面厚度为Hcμm，位于所述第一区域的正极活性材料层的单面单位面积质量为Md g/m2，满足：Ma/Mc≤-0.0892×Md/Hc+1.3652。
  3. 根据权利要求1所述的二次电池，其中，所述正极极片的孔隙率为P，位于所述第一区域的正极活性材料层的单面单位面积质量为Md g/m2，满足：P≥[Md/Hc×(-0.2429)+1.2007]×100％。
  4. 根据权利要求2所述的二次电池，其中，所述电极组件还包括负极极片，所述负极极片包括负极活性材料层，所述负极活性材料层的单面厚度为Haμm，满足：0.2≤Hc/Ha≤4。
  5. 根据权利要求1所述的二次电池，其中，所述正极活性材料层的湿膜与所述正极集流体之间的粘结力为F N/m，F≥1。
  6. 根据权利要求1或2所述的二次电池，其中，所述二次电池满足以下特征中的至少一者：
    1)Ma/Mc≤98.5％；
    2)0.5≤Hc/Ha≤1.5。
  7. 根据权利要求1所述的二次电池，其中，所述正极集流体包括铝箔、镍箔或铝镍合金箔中的至少一种。
  8. 根据权利要求1所述的二次电池，其中，所述正极活性材料包括钴酸锂、锰酸锂、镍酸锂、镍钴锰酸锂、镍钴铝酸锂、磷酸铁锂、磷酸锰铁锂、磷酸钒锂或富锂锰基材料中的至少一种。
  9. 根据权利要求1所述的二次电池，其中，所述正极活性材料层中还包括粘结剂， 所述粘结剂包括聚偏氟乙烯、偏氟乙烯-六氟丙烯共聚物、聚丙烯腈、聚丙烯酸酯、聚丙烯酸、聚丙烯酸盐、聚乙烯吡咯烷酮、聚酰胺、聚乙烯醚、聚甲基丙烯酸甲酯、聚四氟乙烯、聚六氟丙烯、聚丙烯、聚乙烯、聚醚酰亚胺或丙烯烃类衍生物的共聚物中的至少一种。
  10. 根据权利要求1所述的二次电池，其中，所述正极活性材料层中还包括导电剂，所述导电剂包括导电炭黑、单壁碳纳米管、多壁碳纳米管、纳米碳纤维或石墨烯中的至少一种。
  11. 一种用电装置，其包括权利要求1至10任一项所述的二次电池。
PCT/CN2023/085644 2023-03-31 2023-03-31 一种二次电池及用电装置 Ceased WO2024197875A1 (zh)

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