WO2022062890A1 - 一种正极极片及包括该正极极片的锂离子电池 - Google Patents

一种正极极片及包括该正极极片的锂离子电池 Download PDF

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WO2022062890A1
WO2022062890A1 PCT/CN2021/116799 CN2021116799W WO2022062890A1 WO 2022062890 A1 WO2022062890 A1 WO 2022062890A1 CN 2021116799 W CN2021116799 W CN 2021116799W WO 2022062890 A1 WO2022062890 A1 WO 2022062890A1
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positive electrode
active material
conductive
binder
positive
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French (fr)
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唐伟超
李素丽
赵伟
刘春洋
陈若凡
李俊义
徐延铭
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Zhuhai Cosmx Battery Co Ltd
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Zhuhai Cosmx Battery Co Ltd
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    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/50—Current conducting connections for cells or batteries
    • H01M50/572—Means for preventing undesired use or discharge
    • H01M50/574—Devices or arrangements for the interruption of current
    • H01M50/581—Devices or arrangements for the interruption of current in response to temperature
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
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    • H01M10/052—Li-accumulators
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    • 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
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    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
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    • 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
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    • H01M4/00—Electrodes
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    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
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    • 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
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    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
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    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • H—ELECTRICITY
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    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H—ELECTRICITY
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    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
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    • 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
    • H01M4/665—Composites
    • H01M4/667—Composites in the form of layers, e.g. coatings
    • H—ELECTRICITY
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    • 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
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2200/00—Safety devices for primary or secondary batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2200/00—Safety devices for primary or secondary batteries
    • H01M2200/10—Temperature sensitive devices
    • H01M2200/106—PTC
    • 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 high-safety secondary batteries, and in particular, to a positive electrode piece and a lithium ion battery including the positive electrode piece.
  • Secondary batteries mainly include secondary batteries such as lithium-ion batteries, lead-acid batteries, sodium-ion batteries, fluoride-ion batteries, zinc-ion batteries, and nickel-metal hydride batteries.
  • lithium-ion batteries have the advantages of high energy density, long life, environmental protection, etc., and are currently mainly used in energy storage, digital electronics, power vehicles and other fields. In recent years, the market has put forward higher energy density requirements for lithium-ion batteries.
  • Conventional lithium-ion batteries are mainly composed of positive electrodes, negative electrodes, electrolytes, and separators. Since the electrolyte in lithium-ion batteries is mainly composed of organic solvents, there are safety problems such as liquid leakage, fire and explosion during use.
  • the current key improvement direction is to develop a high-safety PTC coating inside the lithium-ion battery.
  • the PTC coating has problems such as high resistance, poor thermal barrier properties, poor compatibility with solvents, and poor PTC effect in the actual application process. .
  • the application provides a positive electrode piece and a lithium ion battery including the positive electrode piece; the positive electrode piece is coated with a safety coating, the safety coating is coated on the surface of the positive electrode current collector, and the safety coating has
  • the conductivity and high temperature blocking properties not only do not affect the electronic conductivity of lithium-ion batteries in normal environments, but also improve the safety performance of lithium-ion batteries.
  • a positive pole piece the positive pole piece comprises a positive electrode current collector, a safety coating, a composite fusion layer and a positive electrode active material layer, wherein the surface of the positive electrode current collector is sequentially provided with a safety coating, a composite fusion layer and a positive electrode active material layer Floor;
  • the safety coating includes functional microspheres, a first positive electrode active material, a first conductive agent, a first binder and an auxiliary agent;
  • the positive electrode active material layer includes a second positive electrode active material, a second conductive agent and a second binder;
  • the safety coating comprises the following components by weight: 20-70wt% of functional microspheres, 5-40wt% of the first positive active material, 2.9-25wt% of the first conductive agent, 2 ⁇ 30 wt% of the first binder and 0.1 to 5 wt% of the auxiliary.
  • the safety coating comprises the following components by weight: 30-60wt% of functional microspheres, 10-30wt% of the first positive active material, 5-20wt% of the first conductive agent, 5-20wt% of the first binder and 0.1-4wt% of the auxiliary agent.
  • the weight percentage of the functional microspheres is 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, 80wt% %, 85wt%, 90wt%.
  • the weight percentage of the first positive active material is 5wt%, 9wt%, 16wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt% .
  • the weight percentage of the first conductive agent is 2.9wt%, 3wt%, 4wt%, 5wt%, 8wt%, 10wt%, 12wt%, 15wt%, 18wt%, 20wt%, 22wt%, 25wt% , 28wt%, 30wt%.
  • the weight percentage of the first binder is 2wt%, 4wt%, 5wt%, 8wt%, 10wt%, 12wt%, 15wt%, 18wt%, 20wt%, 22wt%, 25wt%, 28wt% , 30wt%, 32wt%, 35wt%, 38wt%, 40wt%.
  • the weight percentage of the auxiliary agent is 0.1wt%, 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%.
  • the positive electrode active material layer includes the following components in weight percentages: 80-99 wt % of the second positive active material, 0.5-10 wt % of the second conductive agent, and 0.5-10 wt % of the second adhesive binding agent.
  • the positive electrode active material layer comprises the following components by weight: 84-99 wt% of the second positive electrode active material, 0.5-8 wt% of the second conductive agent and 0.5-8 wt% of the second binder agent.
  • the positive electrode active material layer comprises the following components by weight: 90-98 wt% of the second positive electrode active material, 1-5 wt% of the second conductive agent and 1-5 wt% of the second adhesive. binding agent.
  • the composite fusion layer is formed by mutual penetration of the safety coating and the positive electrode active material layer during the preparation process.
  • the mass relationship among the functional microspheres, the first positive electrode active material, the first conductive agent, the first binder and the auxiliary agent in the composite fusion layer is: 20-90wt% functional microspheres, 5-60wt% % of the first positive active material, 2.9 to 30 wt % of the first conductive agent, 2 to 40 wt % of the first binder, and 0.1 to 10 wt % of the auxiliary agent;
  • the mass relationship between the second conductive agent and the second binder is: 80-99 wt % of the positive electrode active material, 0.5-10 wt % of the second conductive agent and 0.5-10 wt % of the second binder.
  • the mass ratio of the first positive electrode active material and the second positive electrode active material is not particularly defined, and they may be contained simultaneously.
  • the thickness of the cathode current collector is 0.1 ⁇ m ⁇ 20 ⁇ m, preferably 2 ⁇ m ⁇ 15 ⁇ m, such as 0.5 ⁇ m, 1 ⁇ m, 3 ⁇ m, 4 ⁇ m, 5 ⁇ m, 8 ⁇ m, 10 ⁇ m, 12 ⁇ m or 15 ⁇ m.
  • the thickness of the safety coating is 0.1 ⁇ m ⁇ 8 ⁇ m, preferably 0.2 ⁇ m ⁇ 6 ⁇ m, such as 0.3 ⁇ m, 0.5 ⁇ m, 0.8 ⁇ m, 1 ⁇ m, 1.5 ⁇ m, 2 ⁇ m, 2.5 ⁇ m, 3 ⁇ m, 5 ⁇ m, 5.5 ⁇ m or 6 ⁇ m.
  • the thickness of the composite fusion layer is 0.001-0.5 ⁇ m, such as 0.001 ⁇ m, 0.005 ⁇ m, 0.01 ⁇ m, 0.02 ⁇ m, 0.05 ⁇ m, 0.08 ⁇ m, 0.1 ⁇ m, 0.2 ⁇ m, 0.3 ⁇ m, 0.4 ⁇ m or 0.5 ⁇ m .
  • the thickness of the positive electrode active material layer is 5-200 ⁇ m, preferably 5 ⁇ m-100 ⁇ m, such as 5 ⁇ m, 10 ⁇ m, 15 ⁇ m, 20 ⁇ m, 25 ⁇ m, 30 ⁇ m, 35 ⁇ m, 40 ⁇ m, 45 ⁇ m, 50 ⁇ m, 55 ⁇ m, 60 ⁇ m, 65 ⁇ m, 70 ⁇ m , 80 ⁇ m, 90 ⁇ m, 100 ⁇ m.
  • the particle size of the functional microspheres is 50 nm ⁇ 6.5 ⁇ m, preferably 500 nm ⁇ 5 ⁇ m.
  • the first conductive agent and the second conductive agent are the same or different, and are independently selected from conductive carbon black, ketjen black, conductive fibers, conductive polymers, acetylene black, carbon nanotubes, graphene, flakes One or more of graphite, conductive oxide and metal particles.
  • the first binder is selected from water-based binders or oil-based binders, wherein the water-based binders are acrylate, poly(meth)acrylic acid, styrene-butadiene rubber (SBR), polyvinyl alcohol , polyvinyl acetate, carboxymethyl cellulose (CMC), sodium carboxymethyl cellulose (CMC-Li), carboxyethyl cellulose, water-based polyurethane, ethylene-vinyl acetate copolymer, polyacrylic copolymer, poly Lithium styrene sulfonate, water-based silicone resin, nitrile-polyvinyl chloride blend, styrene-acrylic latex, pure styrene latex, etc.
  • the water-based binders are acrylate, poly(meth)acrylic acid, styrene-butadiene rubber (SBR), polyvinyl alcohol , polyvinyl acetate, carboxymethyl
  • oil-based binder is one or more combinations of polytetrafluoroethylene, polyvinylidene fluoride, and polyvinylidene fluoride-hexafluoropropylene.
  • the auxiliary agent is selected from dispersant and/or filler;
  • the dispersant is branched chain alcohol, triethyl phosphate, polyethylene glycol, fluorinated polyethylene oxide, polyethylene oxide, stearic acid, At least one of sodium dodecyl benzene sulfonate, sodium cetyl sulfonate, fatty acid glycerides, sorbitan fatty acid esters and polysorbates;
  • the filler is nano-filler (nano silicon dioxide, triglyceride) aluminum oxide, zirconium dioxide, boron nitride, aluminum nitride, etc.), nano-oxide electrolyte, etc.
  • the second binder is selected from one or more combinations of polytetrafluoroethylene, polyvinylidene fluoride, and polyvinylidene fluoride-hexafluoropropylene.
  • the present application also provides a method for preparing the above-mentioned positive electrode, the method comprising the following steps:
  • the positive electrode sheet is obtained after being placed on the surface of the current collector containing the oil-based safety coating or the current collector containing the water-based safety coating in step 1) and dried at 80-110° C. for 12-72 hours.
  • step 1) preferably adopt the following method to carry out:
  • the oil-based binder in 200-1000 parts by mass of the oil-based solvent, 5-60 parts by mass of the first positive electrode active material, 2.9-30 parts by mass of the first conductive agent, and 2-40 parts by mass of the first binder and 0.1-10 parts by mass of additives, uniformly mixed and filtered with a 100-mesh screen, then added with 20-90 parts by mass of functional microspheres, uniformly mixed and filtered with a 100-mesh screen again, and coated on the surface of the positive electrode current collector , and after drying at 80-110°C for 12-72 hours, a current collector with an oil-based safety coating on the surface is obtained;
  • the oily solvent is selected from at least one of N-methylpyrrolidone, hydrofluoroether, acetone, tetrahydrofuran, dichloromethane, and pyridine.
  • the present application provides a positive electrode piece and a lithium ion battery containing the positive electrode piece.
  • the safety coating includes the first positive electrode active material, the first conductive agent, the first binder, the functional microspheres and the auxiliary agent; the functional microspheres can be stacked disorderly and the functional microspheres have conductivity, so that the The safety coating has electrical conductivity at room temperature, can effectively reduce the internal resistance of the battery, and at the same time has the advantages of increasing the contact area between the positive electrode active material and the positive electrode current collector, improving the electrical conductivity, and effectively reducing the polarization of the battery; when the positive electrode When the operating temperature of the pole piece reaches the temperature sensitive temperature or above, the functional microspheres will melt to form multiple continuous electronic barrier layers, the morphology and structure of the functional microspheres will change, and the coating will block the current and form inside the battery.
  • the first positive active material is introduced into the safety coating, which not only maintains the high safety of the positive pole piece, but also increases the overall active material content in the positive pole piece, and improves the overall energy density of the battery.
  • FIG. 2 is a schematic structural diagram of the functional microspheres of the application; reference numerals: 8 are conductive materials; 9 are heat-sensitive polymers.
  • FIG. 3 is a curve showing the resistance value of the positive electrode pieces prepared in Example 12, Comparative Example 1, and Comparative Example 2 as the temperature increases.
  • FIG. 4 shows the ARC test results of the batteries prepared in Example 12, Comparative Example 1, and Comparative Example 2.
  • FIG. 4 shows the ARC test results of the batteries prepared in Example 12, Comparative Example 1, and Comparative Example 2.
  • the present application provides a functional microsphere
  • the functional microsphere has a core-shell structure, that is, it includes a shell layer and a core core, the material forming the shell layer includes a heat-sensitive polymer, and the core-core is formed.
  • the materials include conductive materials.
  • thermosensitive polymer is selected from thermoplastic polymers that can form a relatively stable system with the electrolyte and have phase change properties.
  • the thermosensitive temperature range of the thermosensitive polymer is, for example, 110°C to 160°C, for example, 115°C to 160°C.
  • the heat sensitive polymer is selected from polyethylene, polypropylene, polyamide, polyesteramide, polystyrene, polyvinyl chloride, polyester, polyurethane, ethylene vinyl acetate polymer, ethylene acrylate polymer, At least one of olefin copolymers, propylene copolymers, ethylene copolymers, etc., or polymers modified by monomers thereof.
  • the particle size of the conductive material is 0.1 nm ⁇ 4.5 ⁇ m.
  • the conductive material is selected from at least one of conductive polymers, conductive oxides, metal particles, carbon materials, and conductive ceramics, such as polypyrrole, polythiophene, conductive carbon black, ketjen black, conductive fiber , at least one of acetylene black, carbon nanotubes, graphene, flake graphite, silicon carbide, molybdenum disilicide, and lanthanum cobaltate.
  • conductive polymers such as polypyrrole, polythiophene, conductive carbon black, ketjen black, conductive fiber , at least one of acetylene black, carbon nanotubes, graphene, flake graphite, silicon carbide, molybdenum disilicide, and lanthanum cobaltate.
  • the surface thermosensitive polymer melts and the inner conductive material is released.
  • the inner conductive material has good conductivity and part of the conductive material can be dissolved in the electrolyte. , forming a chain-shaped conductive channel, and electrons can continue to be turned on, that is, a micro-short circuit is formed inside the lithium-ion battery, which slows down the degree of thermal runaway of the lithium-ion battery.
  • the present application also provides a method for preparing the above-mentioned functional microspheres, the method comprising the following steps:
  • the surface of the core-forming material including the heat-sensitive polymer is coated on the surface of the core-forming material including the conductive material to prepare the microspheres; wherein, the microspheres are prepared;
  • the microsphere has a core-shell structure, ie, includes a shell layer and a core, the material forming the shell layer includes a heat-sensitive polymer, and the material forming the core includes a conductive material.
  • the liquid phase coating method includes the following steps:
  • the microspheres Dissolve the shell-forming material in a solvent by stirring to form a solution containing the shell-forming material; add the core-forming material to the aforementioned solution, stir and mix evenly; remove the mixed system by vacuum heating drying or spray drying, etc. to obtain the microspheres, wherein the microspheres have a core-shell structure, that is, they include a shell layer and a core core, the material forming the shell layer includes a heat-sensitive polymer, and the material forming the core core includes a conductive Material.
  • the solvent is selected from cresol, benzene, methyl ethyl ketone, nitrobenzene, trichloroacetic acid, chlorophenol, toluene, xylene, tetrachloroethane, styrene, isopropane, chloroform and carbon tetrachloride. at least one.
  • the solid phase coating method includes the following steps:
  • the material forming the shell layer and the material forming the core are solid-phase coated by stirring, ball milling, and mechanical fusion, and then heated to the temperature of the heat-sensitive range of the heat-sensitive polymer. A coating is formed on the surface.
  • 70g of ethylene-propylene copolymer and 1.5g of silicon carbide conductive ceramics (average particle diameter of 1 micron) were solid-phase coated by ball milling, heated to 130°C, and the molten heat-sensitive polymer and silicon carbide conductive ceramic particles were ball-milled.
  • the preparation process is the same as that of Preparation Example 1, except that different heat-sensitive polymers and conductive ceramics are selected, as shown in Table 1, and the structural parameters of the prepared functional microspheres are shown in Table 1.
  • S1 Prepare safety coating slurry: mix 200 grams of water, 10 grams of acetylene black, 15 grams of CNT, 30 grams of styrene-butadiene rubber, 10 grams of carboxymethyl cellulose and 10 grams of polyethylene glycol, and filter them with 100 mesh After sieving, add 5 grams of nickel-cobalt-manganese ternary material and 20 grams of ethylene-propylene copolymer functional microspheres with a particle size of 2.5 ⁇ m (functional microspheres prepared in Preparation Example 1) after uniform mixing, and filter 100 meshes again. After screening, the safety coating slurry is obtained;
  • Preparation process Refer to Example 1 to prepare an oil-based safety coating or Reference Example 2 to prepare a water-based safety coating.
  • the distinguishing features are shown in Table 2-Table 4, and the functional microspheres added in Example 1 are prepared in Preparation Example 1. Yes, the functional microspheres added in Example 2 were prepared in Preparation Example 2, and by analogy, the functional microspheres added in Example 12 were prepared in Preparation Example 12.
  • Pole piece resistance test The ACCFILM diaphragm resistance test instrument is used, which uses a controllable voltage double probe resistance to directly test the overall resistance of the pole piece, and the output measurement value is the pole piece resistance.
  • the test process is as follows: the probe is tested by applying a suitable surface flatness and pressing 10N. The test device was placed in an oven, the initial temperature of the oven was 20°C, the temperature was increased to 150°C at a heating rate of 2°C/min, and the data was recorded in real time.
  • Figure 3 shows the change curve of the resistance value of the positive pole piece of Example 12, Comparative Example 1 and Comparative Example 2 as the temperature increases; it can be seen from Figure 3 that the positive pole piece of Example 12 is at 20 ° C.
  • the resistance of the positive electrode sheet changes little with temperature.
  • multiple continuous electronic barrier layers are formed as the heat-sensitive polymer on the surface of the functional microspheres in the positive electrode sheet melts. It forms a current block, blocks the passage of ions and electrons, and improves the safety performance of the battery.
  • the thickness of the positive electrode plates in the batteries prepared in each example increases, resulting in increased lithium ion and electron transport barriers, and increased battery impedance, resulting in a decrease in the number of effective battery cycles.
  • the difference lies in the thickness of the positive electrode sheet, wherein the thickness of the positive electrode layer in Example 10 is 70 ⁇ m, and the thickness of the positive electrode layer in Example 11 is 60 ⁇ m.
  • the positive electrode layer in the positive electrode plate increases, the lithium ion and electron transmission paths inside the electrode plate increase, and the battery impedance increases, which leads to a decrease in battery performance;
  • Comparative Example 1 Comparative Example 1 ⁇ Comparative Example 2 ⁇ Example 12, the main reason is that there is no positive primer coating in Comparative Example 1, resulting in a small internal resistance of the battery. In general, the internal resistance of the battery is not much different;
  • Example 12 ⁇ Comparative example 2>Comparative example 1 the main reason is that there is no positive primer in Comparative Example 1, although the internal resistance of the battery is slightly smaller in the early stage, but with the cycle of the battery, the polarization and dynamic internal resistance of the battery will increase. The increase results in poor battery cycling.
  • the test results of the battery cycle performance by comparing Examples 1-12 and 1-2 show that the lithium-ion battery prepared in the present application can suppress the battery polarization and reduce the dynamic internal resistance increase during the battery cycle process; at the same time, The lithium ion battery positive electrode prepared in the present application has better uniformity and can effectively improve the battery cycle life.
  • the experimental results show that the lithium ion battery prepared by the patented technology of the present application has good safety.

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Abstract

本申请提供一种正极极片及包括该正极极片的锂离子电池。所述正极极片包括正极集流体、安全涂层、复合融合层和正极活性物质层；所述安全涂层包括第一导电剂、第一粘结剂、功能微球和助剂，所述安全涂层在常温下具有导电性能，同时具有增大活性物质与集流体间的接触面积、提高电导率、有效降低电池极化等优点；当所述正极极片的使用温度达到120℃及其以上温度时，功能微球会熔融形成多个连续电子阻隔层，涂层形成电流阻断，在电池内部形成内部阻断，防止锂离子电池进一步热失控的发生。

Description

一种正极极片及包括该正极极片的锂离子电池
本申请要求于2020年09月25日提交中国专利局、申请号为202011025808.7、申请名称为“一种正极极片及包括该正极极片的锂离子电池”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请涉及高安全性二次电池领域，尤其涉及一种正极极片及包括该正极极片的锂离子电池。
背景技术
二次电池中主要有锂离子电池、铅酸电池、钠离子电池、氟离子电池、锌离子电池、镍氢电池等二次电池。其中锂离子电池具有能量密度高、寿命长、环保等优点，目前主要应用于能量存储、数码电子、动力汽车等领域。近年来，市场对锂离子电池提出更高能量密度需求，常规锂离子电池主要由正极、负极、电解液、隔膜构成。由于锂离子电池中电解液主要由有机溶剂构成，在使用过程中存在漏液、起火爆炸等安全性问题。
为改善锂离子电池安全性，目前主要方案有PTC涂层、高安全性隔膜、高安全性电解液、PTC极耳等方案。其中高安全性隔膜主要改善方向有安全基材、安全涂胶层等方向；高安全性电解液主要开发高安全性添加剂、高安全性阻燃剂等方向。PTC涂层具有良好的安全性，目前主要有二次电池外部PTC器件和二次电池内部PTC器件；其中，二次电池外部PTC器件的主要代表是PTC极耳，二次电池内部PTC器件的主要代表为PTC涂层。目前已经在高安全性隔膜、高安全性电解液和PTC极耳方向取得一定进展，但是改善效果有限。
当前重点改善方向为在锂离子电池内部开发一种高安全性的PTC涂层，目前PTC涂层在实际应用过程中存在电阻较高、热阻隔性 差、与溶剂相容性差、PTC效应差等问题。
发明内容
本申请提供一种正极极片及包括该正极极片的锂离子电池；所述正极极片中涂布安全涂层，所述安全涂层涂布在正极集流体表面，所述安全涂层具有导电性和高温阻断性，不仅不会影响锂离子电池在正常环境下的电子导通性，还能改善锂离子电池的安全性能。
本申请目的是通过如下技术方案实现的：
一种正极极片，所述正极极片包括正极集流体、安全涂层、复合融合层和正极活性物质层，其中，所述正极集流体表面依次设置安全涂层、复合融合层和正极活性物质层；
所述安全涂层包括功能微球、第一正极活性物质、第一导电剂、第一粘结剂以及助剂；
所述正极活性物质层包括第二正极活性物质、第二导电剂和第二粘结剂；
所述复合融合层包括功能微球、第一正极活性物质、第一导电剂、第一粘结剂、第二正极活性物质、第二导电剂、第二粘结剂以及助剂。
根据本申请，所述安全涂层包括如下重量百分含量的各组分：20～90wt％的功能微球、5～60wt％的第一正极活性物质、2.9～30wt％的第一导电剂、2～40wt％的第一粘结剂以及0.1～10wt％的助剂。
优选地，所述安全涂层包括如下重量百分含量的各组分：20～70wt％的功能微球、5～40wt％的第一正极活性物质、2.9～25wt％的第一导电剂、2～30wt％的第一粘结剂以及0.1～5wt％的助剂。
还优选地，所述安全涂层包括如下重量百分含量的各组分：30～60wt％的功能微球、10～30wt％的第一正极活性物质、5～20wt％的第一导电剂、5～20wt％的第一粘结剂以及0.1～4wt％的助剂。
其中，所述功能微球的重量百分含量为20wt％、25wt％、30wt％、35wt％、40wt％、45wt％、50wt％、55wt％、60wt％、65wt％、70wt％、75wt％、80wt％、85wt％、90wt％。
其中，所述第一正极活性物质的重量百分含量为5wt％、9wt％、 16wt％、20wt％、25wt％、30wt％、35wt％、40wt％、45wt％、50wt％、55wt％、60wt％。
其中，所述第一导电剂的重量百分含量为2.9wt％、3wt％、4wt％、5wt％、8wt％、10wt％、12wt％、15wt％、18wt％、20wt％、22wt％、25wt％、28wt％、30wt％。
其中，所述第一粘结剂的重量百分含量为2wt％、4wt％、5wt％、8wt％、10wt％、12wt％、15wt％、18wt％、20wt％、22wt％、25wt％、28wt％、30wt％、32wt％、35wt％、38wt％、40wt％。
其中，所述助剂的重量百分含量为0.1wt％、0.5wt％、1wt％、2wt％、3wt％、4wt％、5wt％、6wt％、7wt％、8wt％、9wt％、10wt％。
根据本申请，所述正极活性物质层包括如下重量百分含量的各组分：80～99wt％的第二正极活性物质、0.5～10wt％的第二导电剂和0.5～10wt％的第二粘结剂。
优选地，所述正极活性物质层包括如下重量百分含量的各组分：84～99wt％的第二正极活性物质、0.5～8wt％的第二导电剂和0.5～8wt％的第二粘结剂。
还优选地，所述正极活性物质层包括如下重量百分含量的各组分：90～98wt％的第二正极活性物质、1～5wt％的第二导电剂和1～5wt％的第二粘结剂。
根据本申请，所述复合融合层是所述安全涂层和所述正极活性物质层在制备过程中互相渗透形成的。其中，所述复合融合层中功能微球、第一正极活性物质、第一导电剂、第一粘结剂以及助剂之间的质量关系为：20～90wt％的功能微球、5～60wt％的第一正极活性物质、2.9～30wt％的第一导电剂、2～40wt％的第一粘结剂以及0.1～10wt％的助剂；所述复合融合层中第二正极活性物质、第二导电剂和第二粘结剂之间的质量关系为：80～99wt％的正极活性物质、0.5～10wt％的第二导电剂和0.5～10wt％的第二粘结剂。进一步地，所述第一正极活性物质和第二正极活性物质的质量比没有特别的定义，同时含有即可。
根据本申请，所述正极集流体的厚度为0.1μm～20μm，优选2μm～15μm，如0.5μm、1μm、3μm、4μm、5μm、8μm、10μm、12μm 或15μm。
根据本申请，所述安全涂层的厚度为0.1μm～8μm，优选0.2μm～6μm，如0.3μm、0.5μm、0.8μm、1μm、1.5μm、2μm、2.5μm、3μm、5μm、5.5μm或6μm。
根据本申请，所述复合融合层的厚度为0.001～0.5μm，如0.001μm、0.005μm、0.01μm、0.02μm、0.05μm、0.08μm、0.1μm、0.2μm、0.3μm、0.4μm或0.5μm。
根据本申请，所述正极活性物质层的厚度为5～200μm，优选5μm～100μm，如5μm、10μm、15μm、20μm、25μm、30μm、35μm、40μm、45μm、50μm、55μm、60μm、65μm、70μm、80μm、90μm、100μm。
根据本申请，所述功能微球的颗粒大小为50nm～6.5μm，优选为500nm～5μm。
根据本申请，所述第一导电剂和第二导电剂相同或不同，彼此独立地选自导电炭黑、科琴黑、导电纤维、导电聚合物、乙炔黑、碳纳米管、石墨烯、鳞片石墨、导电氧化物、金属颗粒中的一种或几种。
根据本申请，所述第一粘结剂选自水系粘结剂或油系粘结剂，其中水系粘结剂为丙烯酸酯、聚(甲基)丙烯酸、丁苯橡胶(SBR)、聚乙烯醇、聚醋酸乙烯酯、羧甲基纤维素(CMC)、羧甲基纤维素钠(CMC-Li)、羧乙基纤维素、水性聚氨酯、乙烯-醋酸乙烯共聚物、多元丙烯酸类共聚物、聚苯乙烯磺酸锂、水性有机硅树脂、丁腈-聚氯乙烯共混物、苯丙乳胶、纯苯乳胶等及由前述聚合物改性衍生的共混、共聚聚合物中的一种或多种组合；其中油系粘结剂为聚四氟乙烯、聚偏氟乙烯、聚偏氟乙烯-六氟丙烯中的一种或多种组合。
根据本申请，所述助剂选自分散剂和/或填充剂；所述分散剂为支链醇、磷酸三乙酯、聚乙二醇、氟化聚氧化乙烯、聚氧化乙烯、硬脂酸、十二烷基苯磺酸钠、十六烷基磺酸钠、脂肪酸甘油酯、山梨坦脂肪酸酯和聚山梨酯中的至少一种；所述填充剂为纳米填料(纳米二氧化硅、三氧化二铝、二氧化锆、氮化硼、氮化铝等)、纳米氧化物电解质等。
根据本申请，所述第一正极活性物质和第二正极活性物质选自磷酸铁锂(LiFePO 4)、钴酸锂(LiCoO 2)、镍钴锰酸锂(Li zNi xCo yMn 1-x-yO 2，其中0.95≤z≤1.05，x>0，y>0，0<x+y<1)、锰酸锂(LiMnO 2)、镍钴铝酸锂(Li zNi xCo yAl 1-x-yO 2，其中0.95≤z≤1.05，x>0，y>0，0.8≤x+y<1)、镍钴锰铝酸锂(Li zNi xCo yMn wAl 1-x-y-wO 2，其中0.95≤z≤1.05，x>0，y>0，w>0，0.8≤x+y+w<1)、镍钴铝钨材料、富锂锰基固溶体正极材料(xLi 2MnO 3·(1-x)LiMO 2，其中M＝Ni/Co/Mn)、镍钴酸锂(LiNi xCo yO 2，其中x>0，y>0，x+y＝1)、镍钛镁酸锂(LiNi xTi yMg zO 2，其中，x>0，y>0，z>0，x+y+z＝1)、镍酸锂(Li 2NiO 2)、尖晶石锰酸锂(LiMn 2O 4)、镍钴钨材料中的一种或几种的组合。
根据本申请，所述第二粘结剂选自聚四氟乙烯、聚偏氟乙烯、聚偏氟乙烯-六氟丙烯中的一种或多种组合。
本申请还提供一种二次电池，所述二次电池包括上述的正极极片。
本申请还提供一种上述正极极片的制备方法，所述方法包括如下步骤：
1)制备油系安全涂层或水系安全涂层：
a.油系安全涂层
将200～1000质量份油性溶剂、20～90质量份的功能微球、5～60质量份的第一正极活性物质、2.9～30质量份的第一导电剂、2～40质量份的第一粘结剂中的油系粘结剂以及0.1～10质量份的助剂均匀混合后，涂布在正极集流体表面，经过80～110℃干燥12～72小时后，得到表面含有油系安全涂层的集流体；
b.水系安全涂层
将200～1000质量份水、20～90质量份的功能微球、5～60质量份的第一正极活性物质、2.9～30质量份的第一导电剂、2～40质量份的第一粘结剂中的水系粘结剂以及0.1～10质量份的助剂均匀混合后，涂布在集流体表面，经过80～110℃干燥12～72小时后，得到表面含有水系安全涂层的集流体；
2)将200～1000质量份油性溶剂、80～99质量份的第二正极活性物质、0.5～1质量份的第二导电剂和0.5～10质量份的第二粘结剂均匀 混合后，涂布在步骤1)的含有油系安全涂层的集流体或含有水系安全涂层的集流体表面，经过80～110℃干燥12～72小时后，得到所述正极极片。
根据本申请，步骤1)中，优选采用如下方法进行：
a.油系安全涂层
将200～1000质量份油性溶剂、5～60质量份的第一正极活性物质、2.9～30质量份的第一导电剂、2～40质量份的第一粘结剂中的油系粘结剂以及0.1～10质量份的助剂，均匀混合且过滤100目筛网后，加入20～90质量份的功能微球，均匀混合后且再次过滤100目筛网后，涂布在正极集流体表面，经过80～110℃干燥12～72小时后，得到表面含有油系安全涂层的集流体；
b.水系安全涂层
将200～1000质量份水、5～60质量份的第一正极活性物质、2.9～30质量份的第一导电剂、2～40质量份的第一粘结剂中的水系粘结剂以及0.1～10质量份的助剂，均匀混合且过滤100目筛网后，加入20～90质量份的功能微球，均匀混合后且再次过滤100目筛网后，涂布在集流体表面，经过80～110℃干燥12～72小时后，得到表面含有水系安全涂层的集流体。
根据本申请，所述油性溶剂选自N-甲基吡咯烷酮、氢氟醚、丙酮、四氢呋喃、二氯甲烷、吡啶中的至少一种。
有益效果
本申请提供一种正极极片及含该正极极片的锂离子电池。所述安全涂层包括第一正极活性物质、第一导电剂、第一粘结剂、功能微球和助剂；所述功能微球可以进行无序堆积且功能微球具有导电性，使得所述安全涂层在常温下具有导电性能，能够有效减少电池内阻，同时具有增大正极活性物质与正极集流体间的接触面积、提高电导率、有效降低电池极化等优点；当所述正极极片的使用温度达到热敏温度及其以上温度时，功能微球会熔融形成多个连续电子阻隔层，功能微球的形貌结构会发生变化，涂层形成电流阻断，在电池内部形成内部阻断，防止锂离子电池进一步热失控的发生，提高二次电池在穿刺实 验、热失控实验、跌落实验、高温实验的通过率，提高二次电池安全性能。所述安全涂层中引入了第一正极活性物质，既保持了正极极片的高安全性，又提高了正极极片中的整体活性物质含量，提升电池整体能量密度。
附图说明
图1为本申请的正极极片的结构示意图；附图标记：1是功能微球；2是导电剂；3是粘结剂；4是正极集流体；5是安全涂层；6是复合融合层；7是正极活性物质层。
图2为本申请的功能微球的结构示意图；附图标记：8是导电材料；9是热敏聚合物。
图3为实施例12、对比例1、对比例2制备的正极极片的电阻随着温度升高，电阻数值的变化曲线。
图4为实施例12、对比例1、对比例2制备的电池的ARC测试结果。
具体实施方式
下文将结合具体实施例对本申请做更进一步的详细说明。应当理解，下列实施例仅为示例性地说明和解释本申请，而不应被解释为对本申请保护范围的限制。凡基于本申请上述内容所实现的技术均涵盖在本申请旨在保护的范围内。
<功能微球>
如前所述，本申请提供一种功能微球，所述功能微球具有核壳结构，即包括壳层和核芯，形成所述壳层的材料包括热敏聚合物，形成所述核芯的材料包括导电材料。
根据本申请，所述功能微球中，壳层的厚度为1nm～2000nm。例如为1nm、10nm、50nm、100nm、200nm、500nm、1000nm或2000nm。
根据本申请，所述热敏聚合物选自可以与电解液形成相对稳定的体系，且具有相变性能的热塑性聚合物。所述热敏聚合物的热敏温度区间例如为110℃～160℃，例如为115～160℃。
示例性地，所述热敏聚合物选自聚乙烯、聚丙烯、聚酰胺、聚酯酰胺、聚苯乙烯、聚氯乙烯、聚酯、聚氨酯、乙烯醋酸乙烯聚合物、乙烯丙烯酸酯聚合物、烯烃共聚物、丙烯共聚物、乙烯共聚物等或其单体改性共聚的聚合物的至少一种。
根据本申请，所述导电材料的粒径为0.1nm～4.5μm。例如为1nm、5nm、10nm、0.1μm、0.5μm、1μm、2μm、3μm或4.5μm。
根据本申请，所述导电材料选自导电聚合物、导电氧化物、金属颗粒、碳材料、导电陶瓷中的至少一种，例如为聚吡咯、聚噻吩、导电炭黑、科琴黑、导电纤维、乙炔黑、碳纳米管、石墨烯、鳞片石墨、碳化硅、二硅化钼、钴酸镧中的至少一种。
根据本申请，所述功能微球在温度达到热敏区间时，表面热敏聚合物熔化，释放出内部的导电材料，内部的导电材料具有良好的导电性且部分导电材料能在电解液中溶解，形成链状导电通道，电子可以继续被导通，即在锂离子电池内部形成微短路，减缓锂离子电池热失控程度。
本申请还提供上述功能微球的制备方法，所述方法包括如下步骤：
采用液相包覆法或固相包覆法，将包括热敏聚合物的形成壳层的材料包覆在包括导电材料的形成核芯的材料表面，制备得到所述微球；其中，所述微球具有核壳结构，即包括壳层和核芯，形成所述壳层的材料包括热敏聚合物，形成所述核芯的材料包括导电材料。
示例性地，采用液相包覆法的情况下，所述液相包覆法包括如下步骤：
将形成壳层的材料通过搅拌方式溶解于溶剂中形成含有形成壳层的材料的溶液；在前述溶液中加入形成核芯的材料，搅拌混合均匀；通过真空加热干燥或喷雾干燥等除去混合体系中的溶剂，得到所述微球，其中，所述微球具有核壳结构，即包括壳层和核芯，形成所述壳层的材料包括热敏聚合物，形成所述核芯的材料包括导电材料。
其中，所述溶剂选自甲酚、苯、丁酮、硝基苯、三氯醋酸、氯苯酚、甲苯、二甲苯、四氯乙烷、苯乙烯、异丙烷、氯仿和四氯化碳中的至少一种。
示例性地，采用固相包覆法的情况下，所述固相包覆法包括如下步骤：
将形成壳层的材料和形成核芯的材料用搅拌、球磨、机械融合方式进行固相包覆，然后加热到热敏聚合物的热敏区间温度，形成壳层的材料在形成核芯的材料表面形成包覆层。
下述实施例中所使用的实验方法如无特殊说明，均为常规方法；下述实施例中所用的试剂、材料等，如无特殊说明，均可从商业途径得到。
在本申请的描述中，需要说明的是，术语“第一”、“第二”等仅用于描述目的，而并非指示或暗示相对重要性。
制备例1
将240g聚乙烯和4g碳化硅导电陶瓷(颗粒平均直径1微米)，用球磨方式进行固相包覆，加热到130℃将熔融热敏聚合物与碳化硅导电陶瓷颗粒进行球磨处理36h，球磨后热敏聚合物在导电陶瓷表面形成热敏聚合物包覆层，得到热敏聚合物包覆导电陶瓷的微球(颗粒平均直径5.5微米)。
制备例2
将70g乙烯-丙烯共聚物和1.5g碳化硅导电陶瓷(颗粒平均直径1微米)，用球磨方式进行固相包覆，加热到130℃将熔融热敏聚合物与碳化硅导电陶瓷颗粒进行球磨处理72h，球磨后热敏聚合物在导电陶瓷表面形成热敏聚合物包覆层，得到热敏聚合物包覆导电陶瓷的微球(颗粒平均直径2.5微米)。
制备例3-12
其制备过程与制备例1相同，区别在于选择不同的热敏聚合物和导电陶瓷，具体如表1所示，且制备得到的功能微球的结构参数如表1所示。
表1制备例1-12制备得到的功能微球的组成
Figure PCTCN2021116799-appb-000001
实施例1
S1：配制安全涂层浆料：将1000克氢氟醚、2.9克CNT、2克聚偏氟乙烯以及0.1克磷酸三乙酯，均匀混合且过滤100目筛网后，加入90克粒径为5.5μm的聚乙烯功能微球(制备例1制备得到的功能微球)、5.0克钴酸锂，均匀混合后且再次过滤100目筛网后，得到安全涂层浆料；
S2：配制正极浆料：将500克NMP、98克钴酸锂、1克导电剂导电炭黑、1克粘结剂聚偏氟乙烯均匀混合后，得到正极涂层浆料；
S3：制备正极极片：将S1中安全涂层浆料涂布在铝箔集流体表面，经过110℃干燥12小时后，得到表面含有安全涂层的集流体；将S2中正极涂层浆料涂覆在表面含有安全涂层的集流体表面，经过烘干、压片、剪裁处理后得到正极极片，其中，安全涂层和正极活性物质层在烘干、压片过程中互相渗透形成了复合融合层，通过扫描电镜和EDS能谱分析可以观察到复合融合层的厚度；
S4：制备负极极片：将400克去离子水、97克石墨、0.5克导电炭黑、1.0克CMC、1.5克丁苯橡胶，均匀混合后，涂布在负极集流体上，并经过干燥，干燥工艺属于业内常规工艺；
S5：制备锂离子电池：将正极、负极、隔膜采用叠片或卷绕等方法，制备锂离子电池电芯，经烘烤、注液、化成、封装后得到高安全锂离子电池。
实施例2
S1：配制安全涂层浆料：将200克水、10克乙炔黑、15克CNT、30克丁苯橡胶、10克羧甲基纤维素以及10克聚乙二醇，均匀混合且过滤100目筛网后，加入5克镍钴锰三元材料、20克粒径为2.5μm的乙烯-丙烯共聚物功能微球(制备例1制备得到的功能微球)均匀混合后，且再次过滤100目筛网后，得到安全涂层浆料；
S2：配制正极浆料：将500克NMP、96克钴酸锂、2克导电剂导电炭黑、2克粘结剂聚偏氟乙烯均匀混合后，得到正极涂层浆料；
S3：制备正极极片：将S1中安全涂层浆料涂布在铝箔集流体表面，经过90℃干燥72小时后，得到表面含有安全涂层的集流体；将S2中正极涂层浆料涂覆在表面含有安全涂层的集流体表面，经过烘干、压片、剪裁处理后得到正极极片；
S4：制备负极极片：将350克去离子水、90克石墨、7克氧化亚硅、0.5克导电炭黑、1克CMC、1.5克丁苯橡胶，均匀混合后，涂布在负极集流体上，并经过干燥，干燥工艺属于业内常规工艺；
S5：制备锂离子电池：将正极、负极、隔膜采用叠片或卷绕等方法，制备锂离子电池电芯，经烘烤、注液、化成、封装后得到高安全锂离子电池。
实施例3-12和对比例1-2
制备过程参考实施例1制备油系安全涂层或参考实施例2制备水系安全涂层，区别特征如表2-表4所示，且其中实施例1加入的功能微球是制备例1制备得到的，实施例2加入的功能微球是制备例2制备得到的，以此类推，实施例12加入的功能微球是制备例12制备得到的。
表2实施例1-12和对比例1-2中安全涂层浆料的加入量及烘干条件
Figure PCTCN2021116799-appb-000002
表3实施例1-12和对比例1-2中安全涂层浆料的组成
Figure PCTCN2021116799-appb-000003
Figure PCTCN2021116799-appb-000004
表4实施例1-12和对比例1-2中正极极片的结构
Figure PCTCN2021116799-appb-000005
二、实验数据
(1)极片电阻测试：采用ACCFILM膜片电阻测试仪器，该仪器采用可控压双探头电阻直接测试极片的整体电阻，输出的测量值为极片电阻。测试过程为：通过对探头进行合适的表面平整度，加压10N，进行测试。将该测试装置置于烘箱中，烘箱初始温度20℃，以2℃/min的升温速率，升温至150℃，并实时记录数据。
图3为实施例12、对比例1、对比例2的正极极片的电阻随着温度升高，电阻数值的变化曲线；从图3中可以看出，实施例12的正极极片在20℃～115℃内，正极极片电阻随温度的变化较小，在115℃～140℃内，随着正极极片中的功能微球表面热敏聚合物熔融形成多个 连续电子阻隔层，涂层形成电流阻断，阻断离子和电子通过，改善电池安全性能。
(2)电池热测试方法：采用英国HEL品牌-PhiTEC I(ARC)型号绝热加速量热仪对实施例12、对比例1、对比例2中制备的电池在不同温度中的状态进行检测。仪器内部以0.15℃/min速率进升温，并对电池的温度进行测试，测试结果如图4。通过对比实施例12和对比例1、对比例2制备的电池ARC测试结果，发现对比例1-2的电池在180℃左右发生热失控，电池发生剧烈燃烧；实施例12的电池在195℃左右，发生热失控。主要原因：电池从100℃升温至180℃期间，存在SEI膜破解、正极和电解液剧烈反应，尤其是在160℃～180℃区间内，对比例1、对比例2电池会发生剧烈的热失控、起火等现象。本申请专利电池在100℃升温至180℃期间，在达到热敏温度时，电池内部形成阻隔层，该阻隔层有效提升电池失效温度，延长电池安全时间，提高电池热失控温度。
(3)交流阻抗测试电池内阻方法：采用Metrohm瑞士万通PGSTAT302N化学工作站在100KHz-0.1mHz范围，25℃条件下，对锂离子电池进行交流阻抗测试。
(4)电池循环性能测试方法：锂离子电池在蓝电电池充放电测试柜上进行充放电循环测试，测试条件为25℃、50％湿度、1C/1C充放电。
表5实施例1-12和对比例1-2制备的电池的EIS测试和电池循环性能测试结果
Figure PCTCN2021116799-appb-000006
通过对比实施例1-12和对比例1-2制备的电池EIS测试结果，发现：
1)实施例1-12制备的电池中，各个实施例制备的电池中正极极片厚度增加，导致锂离子、电子传输阻碍增加，电池阻抗增加，导致电池有效循环次数下降。
2)实施例10-12制备的电池中：区别在于正极极片厚度不同，其中实施例10正极层厚度70μm、实施例11正极层厚度60μm。正层极极片中的正极层增加，极片内部锂离子、电子传输路径增加，电池阻抗增加从而导致电池性能有所下降；
3)实施例12、对比例1、对比例2实验结果：
电池内阻：对比例1<对比例2<实施例12，主要原因是对比例1中无正极底涂层，导致电池内阻较小。总体来说，电池内阻相差不大；
电池循环次数：实施例12≈对比例2>对比例1，主要原因是对比例1中无正极底涂，虽然前期电池内阻稍小，但是随着电池的循环，电池极化、动态内阻增加导致电池循环变差。
综上，通过对比实施例1-12和对比例1-2制备的电池循环性能测试结果表明，本申请制备的锂离子电池能够抑制电池极化，降低电池循环过程的动态内阻增幅；同时，本申请制备的锂离子电池正极具有更好的均一性，能够有效改善电池循环寿命。实验结果说明，本申请专利技术制备的锂离子电池具有良好的安全性。
以上，对本申请的实施方式进行了说明。但是，本申请不限定于上述实施方式。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，均应包含在本申请的保护范围之内。

Claims (17)

  1. 一种正极极片，所述正极极片包括正极集流体、安全涂层、复合融合层和正极活性物质层，其中，所述正极集流体表面依次设置安全涂层、复合融合层和正极活性物质层；
    所述安全涂层包括功能微球、第一正极活性物质、第一导电剂、第一粘结剂以及助剂；
    所述正极活性物质层包括第二正极活性物质、第二导电剂和第二粘结剂；
    所述复合融合层包括功能微球、第一正极活性物质、第一导电剂、第一粘结剂、第二正极活性物质、第二导电剂、第二粘结剂以及助剂。
  2. 根据权利要求1所述的正极极片，其中，所述安全涂层包括如下重量百分含量的各组分：20～90wt％的功能微球、5～60wt％的第一正极活性物质、2.9～30wt％的第一导电剂、2～40wt％的第一粘结剂以及0.1～10wt％的助剂。
  3. 根据权利要求1或2所述的正极极片，其中，所述安全涂层包括如下重量百分含量的各组分：20～70wt％的功能微球、5～40wt％的第一正极活性物质、2.9～25wt％的第一导电剂、2～30wt％的第一粘结剂以及0.1～5wt％的助剂。
  4. 根据权利要求1-3任一项所述的正极极片，其中，所述安全涂层包括如下重量百分含量的各组分：30～60wt％的功能微球、10～30wt％的第一正极活性物质、5～20wt％的第一导电剂、5～20wt％的第一粘结剂以及0.1～4wt％的助剂。
  5. 根据权利要求1-4任一项所述的正极极片，其中，所述正极活性物质层包括如下重量百分含量的各组分：80～99wt％的第二正极活性物质、0.5～10wt％的第二导电剂和0.5～10wt％的第二粘结剂。
  6. 根据权利要求1-5任一项所述的正极极片，其中，所述正极活性物质层包括如下重量百分含量的各组分：84～99wt％的第二正极活性物质、0.5～8wt％的第二导电剂和0.5～8wt％的第二粘结剂。
  7. 根据权利要求1-6任一项所述的正极极片，其中，所述正极 活性物质层包括如下重量百分含量的各组分：90～98wt％的第二正极活性物质、1～5wt％的第二导电剂和1～5wt％的第二粘结剂。
  8. 根据权利要求1-7任一项所述的正极极片，其中，所述正极集流体的厚度为0.1μm～20μm；和/或，所述安全涂层的厚度为0.1μm～8μm；和/或，所述复合融合层的厚度为0.001～0.5μm；和/或，所述正极活性物质层的厚度为5～200μm。
  9. 根据权利要求1-8任一项所述的正极极片，其中，所述正极集流体的厚度为2μm～15μm；和/或，所述安全涂层的厚度为0.2μm～6μm；和/或，所述正极活性物质层的厚度为5～200μm。
  10. 根据权利要求1-9任一项所述的正极极片，其中，所述功能微球具有核壳结构，即包括壳层和核芯，形成所述壳层的材料包括热敏聚合物，形成所述核芯的材料包括导电材料。
  11. 根据权利要求1-10任一项所述的正极极片，其中，所述功能微球的颗粒大小为50nm～6.5μm；所述导电材料的粒径为0.1nm～4.5μm。
  12. 根据权利要求1-11任一项所述的正极极片，其中，所述功能微球的颗粒大小为500nm～5μm。
  13. 根据权利要求1-12任一项所述的正极极片，其中，所述功能微球中，壳层的厚度为1nm～2000nm。
  14. 根据权利要求10所述的正极极片，其中，所述热敏聚合物选自聚乙烯、聚丙烯、聚酰胺、聚酯酰胺、聚苯乙烯、聚氯乙烯、聚酯、聚氨酯、乙烯醋酸乙烯聚合物、乙烯丙烯酸酯聚合物、烯烃共聚物、丙烯共聚物、乙烯共聚物等或其单体改性共聚的聚合物的至少一种。
  15. 根据权利要求1-14任一项所述的正极极片，其中，所述导电材料选自导电聚合物、导电氧化物、金属颗粒、碳材料、导电陶瓷中的至少一种。
  16. 根据权利要求15所述的正极极片，其中，所述导电材料选自聚吡咯、聚噻吩、导电炭黑、科琴黑、导电纤维、乙炔黑、碳纳米管、石墨烯、鳞片石墨、碳化硅、二硅化钼、钴酸镧中的至少一种。
  17. 一种二次电池，其中，所述二次电池包括权利要求1-16任一项所述的正极极片。
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