WO2022227345A1 - 一种复合隔膜及其制备方法和用途 - Google Patents

一种复合隔膜及其制备方法和用途 Download PDF

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WO2022227345A1
WO2022227345A1 PCT/CN2021/113488 CN2021113488W WO2022227345A1 WO 2022227345 A1 WO2022227345 A1 WO 2022227345A1 CN 2021113488 W CN2021113488 W CN 2021113488W WO 2022227345 A1 WO2022227345 A1 WO 2022227345A1
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optionally
coating
ceramic
polymer
composite
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PCT/CN2021/113488
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English (en)
French (fr)
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谭小芳
陈星宇
何巍
刘建华
刘金成
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惠州亿纬锂能股份有限公司
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Priority to US18/014,087 priority Critical patent/US20240055724A1/en
Priority to EP21938809.7A priority patent/EP4333187A1/en
Publication of WO2022227345A1 publication Critical patent/WO2022227345A1/zh

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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
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/446—Composite material consisting of a mixture of organic and inorganic materials
    • 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
    • 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
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/403—Manufacturing processes of separators, membranes or diaphragms
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • 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
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • 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
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
    • H01M50/417—Polyolefins
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • 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
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
    • H01M50/42—Acrylic resins
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • 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
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
    • H01M50/426—Fluorocarbon polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • 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
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/431—Inorganic material
    • H01M50/434—Ceramics
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • 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
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/443—Particulate material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • 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
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • 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
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
    • H01M50/451—Separators, membranes or diaphragms characterised by the material having a layered structure comprising layers of only organic material and layers containing inorganic material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • 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
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
    • H01M50/457—Separators, membranes or diaphragms characterised by the material having a layered structure comprising three or more layers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • 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
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • 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
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
    • H01M50/491—Porosity
    • 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 belongs to the technical field of lithium ion batteries, and relates to a composite separator and a preparation method and application thereof.
  • Lithium-ion batteries have the advantages of high specific energy, no pollution, long service life and no memory effect. As the power source of new energy vehicles, they have become a research hotspot in recent years.
  • the separator as a key safety component of lithium-ion batteries, has a rich pore structure, and its function is to block the contact between the positive electrode and the negative electrode and provide a lithium ion transport channel.
  • the commonly used separators are mainly polyolefin separators such as polyethylene (PE) and polypropylene (PP). Since the melting point of polyethylene (PE) and polypropylene (PP) separators is generally lower than 200°C, the heat resistance is poor. Therefore, how to improve the heat resistance of the separator has become the focus of research.
  • PE polyethylene
  • PP polypropylene
  • CN104701478A discloses a polyethylene microporous film containing an organic/inorganic composite cross-linked coating for improving the use safety of lithium ion batteries and a preparation method thereof.
  • the patent uses aromatic heterocyclic polyester diol and aromatic isocyanate as the basic components, combined with cross-linking agent, foaming agent, catalyst and inorganic nano-filler, and prepares a coating solution according to a certain composition ratio; The liquid is coated on at least one surface of the polyethylene microporous membrane, and after curing under a specific temperature condition, an organic polymer/inorganic nanoparticle composite cross-linked coating with an open-cell foam structure is formed on the surface of the polyethylene microporous membrane. However, there is no bonding between the separator and the positive and negative electrode sheets.
  • CN106654119A discloses a hybrid coating diaphragm and its preparation method and application
  • the hybrid coating diaphragm includes a base film, a ceramic particle coating and a polymer coating
  • the ceramic particle coating is formed on one side or both sides of the base film
  • the polymer coating is formed on the base film and/or on the ceramic particle coating.
  • CN109994695A discloses a polymer slurry, a composite diaphragm and a preparation method thereof.
  • the polymerization slurry comprises that the slurry comprises 10-30 parts by weight of polymer, 0.05-1.0 parts by weight of thickener, 5.1-26.5 parts by weight of wetting agent, 1.0-5.0 parts by weight of binder, 0.1-1.0 parts by weight of dispersant and 80-120 parts by weight of water.
  • the composite membrane comprises a base film, a ceramic coating and a polymer dot coating respectively coated on both sides of the base film, wherein the polymer dot coating is obtained by coating the above polymer slurry through high pressure jet.
  • the present application provides a composite diaphragm and its preparation method and use.
  • the composite diaphragm has good thermal stability and electrolyte wettability, excellent mechanical properties, small air permeability value, and high lithium ion conductivity, effectively reducing the internal resistance of lithium ion batteries, and simultaneously improving the safety performance and hardness of lithium ion batteries. .
  • the present application provides a composite membrane comprising a porous base membrane, and a composite coating coated on at least one side of the porous base membrane, the composite coating comprising mutually dispersed ceramic and polymer thing.
  • ceramics have high temperature resistance, electrochemical stability, and good liquid absorption and liquid retention capacity, which can improve the heat resistance and oxidation resistance of the composite diaphragm, make the composite diaphragm safer, and prolong the lithium ion
  • the polymer can enhance the adhesion between the composite separator and the pole piece, and at the same time improve the hardness of the battery
  • the ceramic and the polymer are dispersed in each other, improve the heat resistance and mechanical properties of the porous base film, and improve the electrolyte
  • the wettability of the battery is improved, and the hardness of the battery is improved, so that the safety performance of the lithium-ion battery is greatly improved.
  • the mutual cooperation of the ceramic, polymer and porous base film reduces the air permeability of the composite diaphragm, increases the conductivity of lithium ions, reduces the internal resistance of lithium ion batteries, and reduces polymer coating
  • the phenomenon of blocking pores due to the swelling of the polymer improves the long-term performance of the battery.
  • the composite membrane has lower closed-cell temperature, higher membrane breaking temperature and excellent thermal safety, its performance is better than the porous base membrane and polymer-coated membrane in the prior art, and can be widely used in power ion Energy storage devices such as batteries.
  • the porous base film includes a polyolefin-based film, which can be optionally a polyethylene-based film and/or a polypropylene-based film.
  • the thickness of the porous base film is 3-40 ⁇ m, such as 4 ⁇ m, 5 ⁇ m, 7 ⁇ m, 10 ⁇ m, 12 ⁇ m, 15 ⁇ m, 20 ⁇ m, 25 ⁇ m, 30 ⁇ m, 35 ⁇ m or 40 ⁇ m, etc., and can be 4-20 ⁇ m.
  • the pore size of the porous base film is 10-400 nm, for example, it can be 10 nm, 12 nm, 15 nm, 30 nm, 50 nm, 100 nm, 120 nm, 170 nm, 200 nm, 230 nm, 260 nm, 300 nm, 320 nm, 380 nm or 400 nm, etc., Optional 20-100nm.
  • the porosity of the porous base film is 30-60%, such as 30%, 35%, 40%, 45%, 50%, or 55%.
  • the thickness of the composite coating is 0.5-10 ⁇ m, such as 0.5 ⁇ m, 1 ⁇ m, 1.5 ⁇ m, 2 ⁇ m, 2.5 ⁇ m, 3 ⁇ m, 3.5 ⁇ m, 4 ⁇ m, 5 ⁇ m, 6 ⁇ m, 7 ⁇ m, 8 ⁇ m, 9 ⁇ m or 10 ⁇ m, etc., optional 1-3 ⁇ m.
  • the thickness of the composite coating is limited in the range of 0.5-5 ⁇ m to ensure the air permeability and adhesion of the composite membrane.
  • the ceramic includes any one or a combination of at least two of boehmite, aluminum oxide, magnesium hydroxide, magnesium oxide, barium titanate, zinc oxide or barium sulfate, and can be optionally boehmite or Alumina.
  • the specific surface area of the ceramic is 1-12m 2 /g, for example, it can be 2m 2 /g, 4m 2 /g, 6m 2 /g, 8m 2 /g, 10m 2 /g or 12m 2 /g etc., optional 4-8m 2 /g.
  • the ceramic particles with smaller particle size can meet the requirements of thinner coating, the coating is more uniform, and has a higher specific surface area, so that the coated separator has good wettability and protection to the electrolyte.
  • the liquid rate can effectively improve the capacity retention rate of lithium-ion batteries, and the particle size of the ceramic particles can be selected according to the coating thickness requirements.
  • the particle size of the ceramic is 0.1-4 ⁇ m, such as 0.5 ⁇ m, 1 ⁇ m, 1.5 ⁇ m, 2 ⁇ m, 2.5 ⁇ m, 3 ⁇ m, 3.5 ⁇ m or 4 ⁇ m, etc., optionally 0.3-3 ⁇ m.
  • the mass percentage of the ceramic is 5-98%, for example, it can be 5%, 10%, 20%, 30%, 40% , 50%, 60%, 70%, 80%, 90% or 95%, etc., optional 80-98%.
  • the polymer comprises vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-octafluoroisobutylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polymethyl methacrylate or polystyrene acrylic acid Any one or a combination of at least two of the lipids, wherein typical but non-limiting combinations: vinylidene fluoride-hexafluoropropylene copolymer and vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-octafluoroisobutylene copolymer and polymethyl methacrylate, polystyrene acrylate, etc., can be selected from any one or at least two of vinylidene fluoride-hexafluoropropylene copolymer, polymethyl methacrylate, polystyrene acrylate combination.
  • the molecular weight of the polymer is 30-200W, that is, 300,000-2,000,000, for example, it can be 40W, 50W, 60W, 80W, 100W, 120W, 140W, 160W, 180W or 200W, etc., optionally 40 -150W.
  • the particle size of the polymer is 0.1-10 ⁇ m, such as 0.2 ⁇ m, 0.5 ⁇ m, 1 ⁇ m, 3 ⁇ m, 5 ⁇ m, 8 ⁇ m or 10 ⁇ m, etc., and optionally 0.15-7 ⁇ m.
  • the glass transition temperature of the polymer is -60-30°C, for example, it can be -60°C, -40°C, -20°C, -10°C, 0°C, 10°C, 20°C, 30°C, etc. , optional -50-15°C.
  • the mass percentage of the polymer is 2-95%, for example, it can be 3%, 5%, 10%, 20%, 30% %, 40%, 50%, 60%, 70%, 80% or 90%, etc., optional 2-20%.
  • one side of the porous base membrane is coated with a composite coating, and the other side is coated with a ceramic coating.
  • the ceramic coating and the composite coating cooperate with each other to further improve the thermal stability and mechanical properties of the composite separator, reduce the air permeability value, and improve the wettability of the electrolyte and the conductivity of lithium ions.
  • the ceramics in the ceramic coating and the ceramics in the composite coating can be the same or different, as long as they cooperate with each other, the thermal stability and mechanical properties of the composite separator can be improved, the air permeability value can be reduced, and the electrolyte performance can be improved. Wetting properties and lithium ion conductivity are sufficient.
  • the thickness of the ceramic coating is 0.5-5 ⁇ m, such as 0.5 ⁇ m, 0.8 ⁇ m, 1 ⁇ m, 1.5 ⁇ m, 2 ⁇ m, 2.5 ⁇ m, 3 ⁇ m, 3.5 ⁇ m, 4 ⁇ m, 4.5 ⁇ m, 4.8 ⁇ m or 5 ⁇ m, etc. , optional 1-3 ⁇ m.
  • the thickness of the ceramic coating is limited to 0.5-5 ⁇ m, which ensures better thermal shrinkage performance and improves the heat resistance and oxidation resistance of the composite separator.
  • the thickness of the composite coating is 0.5-10 ⁇ m.
  • the thickness of the composite coating is 1-5 ⁇ m.
  • the molecular weight of the polymer is 400,000-1,800,000.
  • the glass transition temperature of the polymer is -60-100°C, for example, it can be -60°C, -40°C, -20°C, -10°C, 0°C, 20°C, 40°C, 60°C, 80°C or 100°C, etc., optional -50-80°C.
  • the present application provides a method for preparing a composite diaphragm as described in the first aspect, the method comprising the following steps:
  • step (2) Coating the mixed slurry obtained in step (1) on the surface of at least one side of the porous base membrane to obtain the composite membrane.
  • the preparation method provided by the present application improves the thermal stability and mechanical properties of the porous base film, reduces the air permeability value, improves the wettability of the electrolyte and the conductivity of lithium ions, and reduces the lithium ion battery through the mutual dispersion of ceramics and polymers.
  • the internal resistance of the battery improves the hardness and safety performance of the battery.
  • the method has simple coating process and high production efficiency.
  • the ceramics described in step (1) include any one or at least two of boehmite, aluminum oxide, magnesium hydroxide, magnesium oxide, barium titanate, zinc oxide or barium sulfate. Combination, optional boehmite or alumina.
  • the specific surface area of the ceramic in step (1) is 1-12m 2 /g, for example, it can be 2m 2 /g, 4m 2 /g, 6m 2 /g, 8m 2 /g, 10m 2 /g or 12m 2 /g, etc., optional 4-8m 2 /g.
  • the particle size of the ceramic in step (1) is 0.1-4 ⁇ m, for example, it can be 0.5 ⁇ m, 1 ⁇ m, 1.5 ⁇ m, 2 ⁇ m, 2.5 ⁇ m, 3 ⁇ m, 3.5 ⁇ m or 4 ⁇ m, etc., optionally 0.3-3 ⁇ m.
  • the mass percentage of the ceramic is 5-98%, for example, it can be 5%, 10%, 20%, 30% %, 40%, 50%, 60%, 70%, 80%, 90% or 95%, etc., optional 80-98%.
  • the polymer in step (1) includes vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-octafluoroisobutylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polymethyl methacrylate or Any one or a combination of at least two of the polystyrene acrylates can be selected from any one or at least two of the vinylidene fluoride-hexafluoropropylene copolymer, polymethyl methacrylate, and polystyrene acrylates. combination of species.
  • the molecular weight of the polymer described in step (1) is 30-200W, that is, 300,000-2,000,000, such as 40W, 50W, 60W, 80W, 100W, 120W, 140W, 160W, 180W or 200W, etc., Optional 40-150W.
  • the particle size of the polymer described in step (1) is 0.1-10 ⁇ m, such as 0.2 ⁇ m, 0.5 ⁇ m, 1 ⁇ m, 3 ⁇ m, 5 ⁇ m, 8 ⁇ m or 10 ⁇ m, etc., optionally 0.15-7 ⁇ m.
  • the glass transition temperature of the polymer in step (1) is -60-30°C, for example, it can be -60°C, -40°C, -20°C, -10°C, 0°C, 10°C, 20°C Or 30°C, etc., optional -50-15°C.
  • the mass percentage of the polymer is 2-95%, for example, it can be 3%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90%, etc., optional 2-20%.
  • the solvent in step (1) includes any one or a combination of at least two of water, acetone, dichloromethane, cyclohexane or N-methylpyrrolidone, and can be optionally water or dichloromethane.
  • step (1) includes the following steps:
  • the polymer and the solvent are mixed once, the ceramic is added, and the mixed slurry is obtained for the second time.
  • the mixing method can uniformly disperse the polymer in the slurry.
  • the means of primary mixing and secondary mixing independently include stirring and/or sonication.
  • the viscosity of the mixed slurry in step (1) is 0-80CP, such as 10CP, 20CP, 30CP, 40CP, 50CP, 60CP, 70CP or 80CP, optionally 30-50CP.
  • the solid content of the mixed slurry in step (1) is 20-70%, for example, it can be 20%, 30%, 40%, 50%, 60% or 70%, optionally 30-50% .
  • the porous base film in step (2) includes a polyolefin base film, which can be optionally a polyethylene base film and/or a polypropylene base film.
  • the thickness of the porous base film in step (2) is 3-40 ⁇ m, such as 4 ⁇ m, 5 ⁇ m, 7 ⁇ m, 10 ⁇ m, 12 ⁇ m, 15 ⁇ m, 20 ⁇ m, 25 ⁇ m, 30 ⁇ m, 35 ⁇ m or 40 ⁇ m, etc. -20 ⁇ m.
  • the pore size of the porous base film in step (2) is 10-400 nm, for example, it can be 10 nm, 12 nm, 15 nm, 30 nm, 50 nm, 100 nm, 120 nm, 170 nm, 200 nm, 230 nm, 260 nm, 300 nm, 320 nm, 380 nm Or 400nm, etc., optional 20-100nm.
  • the porosity of the porous base film in step (2) is 30-60%, for example, it can be 30%, 35%, 40%, 45%, 50% or 55%.
  • the method of coating in step (2) includes any one or a combination of at least two of coating, roll coating, spray coating or dip coating, and may be roll coating and/or coating.
  • the thickness of the coating in step (2) is 0.5-5 ⁇ m, for example, it can be 0.5 ⁇ m, 1 ⁇ m, 1.5 ⁇ m, 2 ⁇ m, 2.5 ⁇ m, 3 ⁇ m, 3.5 ⁇ m, 4 ⁇ m, 4.5 ⁇ m or 5 ⁇ m, etc., optional 1-3 ⁇ m.
  • step (2) further includes: drying the mixed slurry after coating the surface of at least one side of the porous base film.
  • step (2) one side of the porous base membrane is coated with the mixed slurry, and the other side of the porous base membrane is coated with the ceramic slurry.
  • the mixed slurry and the ceramic slurry can be coated on the surface of the porous base membrane at the same time, or can be coated on the surface of the porous base membrane in steps, as long as the coating method is commonly used by those skilled in the art, both Suitable for this application, optional simultaneous coating, and simultaneous coating to improve production efficiency.
  • the preparation method of the ceramic slurry is not specifically limited, the binder and the solvent may be mixed first, and then mixed with the ceramic, or the ceramic may be directly added to the binder solution and mixed.
  • the preparation method of the ceramic slurry includes the following steps:
  • the ceramic is added into the binder solution and mixed to obtain the ceramic slurry.
  • the thickness of the ceramic slurry coating is 0.5-5 ⁇ m, such as 0.5 ⁇ m, 0.8 ⁇ m, 1 ⁇ m, 1.5 ⁇ m, 2 ⁇ m, 2.5 ⁇ m, 3 ⁇ m, 3.5 ⁇ m, 4 ⁇ m, 4.5 ⁇ m, 4.8 ⁇ m or 5 ⁇ m, etc., optional 1-3 ⁇ m.
  • the present application provides a preparation method of a composite diaphragm, and the preparation method specifically includes the following steps:
  • the binder optionally includes polyvinylidene fluoride, sodium carboxymethyl cellulose, polyacrylic acid, polyvinyl alcohol or butyl Any one or a combination of at least two of styrene rubber; ceramics include any one or a combination of at least two of boehmite, aluminum oxide, magnesium hydroxide, magnesium oxide, barium titanate, zinc oxide or barium sulfate ; Based on the total mass of the ceramic and the binder as 100%, the mass percentage of the binder is 2-8%, and the mass percentage of the ceramic is 92-98%.
  • polymers include vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-octafluoroisobutylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polymethyl methacrylate or polystyrene acrylate Any one or a combination of at least two;
  • the solvent includes any one or a combination of at least two of water, acetone, dichloromethane, cyclohexane or N-methylpyrrolidone;
  • the ceramic includes boehmite, Any one or a combination of at least two of aluminum oxide, magnesium hydroxide, magnesium oxide, barium titanate, zinc oxide or barium sulfate; based on 100% of the total mass of the ceramic and polymer, the mass of the ceramic is 100% The fractional content is 5-98%, and the mass percentage of the polymer is 2-95%;
  • step (3) coating the mixed slurry obtained in step (2) on one side or both sides of the porous base film, coating the ceramic slurry obtained in step (1) on one side of the porous base film, and drying to obtain the Composite diaphragm.
  • the molecular weight of the polymer in step (1) is 40-180W.
  • the glass transition temperature of the polymer in step (1) is -60-100°C, for example, it can be -60°C, -40°C, -20°C, -10°C, 0°C, 20°C, 30°C , 40°C, 60°C, 80°C or 100°C, etc., optional -50-80°C.
  • the thickness of the coating in step (2) is 0.5-10 ⁇ m, such as 0.5 ⁇ m, 0.8 ⁇ m, 1 ⁇ m, 1.5 ⁇ m, 2 ⁇ m, 2.5 ⁇ m, 3 ⁇ m, 3.5 ⁇ m, 4 ⁇ m, 4.5 ⁇ m, 4.8 ⁇ m , 5 ⁇ m, 7 ⁇ m or 10 ⁇ m, etc.
  • the thickness of the coating in step (2) is 1-5 ⁇ m.
  • the present application provides a lithium ion battery, the lithium ion battery comprising the composite separator according to the first aspect.
  • the lithium ion battery adopts the composite separator described in the first aspect, which has low internal resistance, excellent safety performance and hardness.
  • the present application at least has the following beneficial effects:
  • the composite separator of the present application has good thermal stability and electrolyte wettability, excellent mechanical properties, low air permeability value and high lithium ion conductivity, and effectively reduces the internal pressure of lithium ion batteries. resistance, while improving the safety performance and hardness of lithium-ion batteries;
  • This application further improves the thermal stability of the composite diaphragm, the electrolyte solution by adjusting the mass percentage of ceramics and polymers in the mixed slurry, the thickness of the composite coating, and the thickness difference between the composite coating and the ceramic coating. wettability and conductivity of lithium ions;
  • the preparation method provided by the application has simple process and high production efficiency.
  • FIG. 1 is a schematic structural diagram of a composite diaphragm provided by an embodiment of the present application.
  • FIG. 2 is a schematic structural diagram of a composite diaphragm provided by an embodiment of the present application.
  • FIG. 3 is a schematic structural diagram of a composite membrane provided by an embodiment of the present application.
  • FIG. 4 is a SEM image of the composite coating provided in the embodiment of the present application.
  • 1-porous base film 2-ceramic coating, 3-composite coating, 4-ceramic, 5-polymer.
  • the composite membrane includes a porous base membrane 1, a ceramic coating 2 coated on one side of the porous base membrane 1 and a composite coating 3 coated on the other side of the porous base membrane 1.
  • the composite coating Layer 3 includes ceramic 4 and polymer 5 .
  • the present embodiment provides a preparation method of a composite diaphragm, the method comprising the following steps:
  • the mass percentage content of the alumina is 93%, and the mass percentage content of the polystyrene acrylate is 7%;
  • step (2) Coating the mixed slurry obtained in step (1) on one side of a polyethylene-based film, the thickness of the polyethylene-based film being 9 ⁇ m and the porosity of 40%, and drying to obtain the composite diaphragm .
  • the composite separator prepared in this example is shown in FIG. 1 , the thickness of the composite coating is 3 ⁇ m, and the SEM photo of the composite coating is shown in FIG. 4 .
  • the present embodiment provides a preparation method of a composite diaphragm, the method comprising the following steps:
  • alumina and polystyrene acrylate into water, the specific surface area of the alumina is 8 m 2 /g, the particle size is 0.2 ⁇ m, the molecular weight of the polystyrene acrylate is 100W, and the glass transition temperature is 10°C, the particle size is 3-10 ⁇ m, stir until dissolved, and obtain a mixed slurry with a viscosity of 50CP and a solid content of 30%;
  • the mass percentage of the alumina is 95%, and the mass percentage of the polystyrene acrylate is 5%;
  • step (2) Coat the mixed slurry obtained in step (1) on both sides of a polyethylene base film with a thickness of 9 ⁇ m and a porosity of 45%, and drying to obtain the composite diaphragm .
  • the composite membrane prepared in this example as shown in FIG. 2 , the thickness of the composite coating is 2 ⁇ m.
  • the present embodiment provides a preparation method of a composite diaphragm, the method comprising the following steps:
  • boehmite (1) adding polystyrene acrylate into water, the molecular weight of the polystyrene acrylate is 200W, the glass transition temperature is -10°C, the particle size is 3-103-10 ⁇ m, stir until dissolved, add boehmite, The boehmite has a specific surface area of 9 m 2 /g, a particle size of 1 ⁇ m, and is uniformly stirred to obtain a mixed slurry with a viscosity of 60 CP and a solid content of 50%;
  • the mass percentage content of the boehmite is 97%, and the mass percentage content of the polystyrene acrylate is 3% ;
  • the mass percentage of the boehmite is 95%, and the mass percentage of the polyvinylidene fluoride is 5%;
  • step (3) Roll-coating the mixed slurry obtained in step (1) on one side of the polyethylene-based film, roll-coating the ceramic slurry obtained in step (2) on the other side of the polyethylene-based film, and the polyethylene-based film
  • the thickness of the membrane is 9 ⁇ m, the porosity is 43%, and it is dried to obtain the composite membrane.
  • the thickness of the composite coating is 2 ⁇ m
  • the thickness of the ceramic coating is 2 ⁇ m
  • Example 1 Compared with Example 1, the only difference is that the alumina in step (1) is replaced by boehmite.
  • the composite separator prepared in this example has a porosity of 38%, and the thickness of the composite coating is 3 ⁇ m.
  • Example 2 Compared with Example 2, the only difference is that the thickness of the polyethylene base film is replaced by 12 ⁇ m and the porosity is replaced by 48%.
  • the thickness of the composite coating is 3 ⁇ m.
  • Example 3 Compared with Example 3, the only difference is that this comparative example replaces the composite coating with a ceramic coating.
  • Example 4 Compared with Example 4, in this comparative example, a vinylidene fluoride-hexafluoropropylene copolymer was roll-coated on one side of the base film in Example 4, and the molecular weight of the vinylidene fluoride-hexafluoropropylene copolymer was 40W and the particle size was 40W. is 200nm.
  • the composite separator prepared in this comparative example includes a base film and a polymer layer coated on one side of the base film, and the thickness of the polymer coating is 1 ⁇ m.
  • the composite membranes provided by the examples and comparative examples were tested for thermal stability, liquid absorption rate, air permeability value and ionic conductivity.
  • the bare cell is placed on a shelf with a fixed height, and the deformation of the cell is tested after 24 hours.
  • the mass ratio of graphite, acetylene black, sodium carboxymethyl cellulose and styrene-butadiene rubber in the negative electrode sheet is 9.5:0.2:0.15:0.15, and the electrolyte is injected, and the electrolyte is LiPF 6 /EC+DEC+DMC (EC, The volume ratio of DEC and DMC is 1:1:1)
  • the internal resistance test is carried out.
  • the test method is as follows:
  • Thermal stability test Prepare 5 samples, cut out a square sample of 120mm ⁇ 120mm in the longitudinal direction of the film roll, and mark the sample with a length of 100mm ⁇ 100mm. Clamp it with a glass plate and bake it in a constant temperature oven at 130°C for 1 hour, measure the lengths in the MD and TD directions after baking, and calculate the shrinkage rate.
  • the size of the glass plate 220mm ⁇ 220mm ⁇ 4mm; the material of the glass plate: tempered glass.
  • Thermal shrinkage X is calculated as follows: (initial size - size after baking)/initial size
  • EC ethylene carbonate
  • PC propylene carbonate
  • Air permeability value test refer to GB/T 458-2008, take 5 samples to test with air permeability meter, and take the average value of the measurement as the air permeability.
  • Ionic conductivity test use inert stainless steel electrodes to make a symmetrical battery for testing. With the increase of the number of diaphragm layers, the battery resistance also increases accordingly, and there is a linear relationship, and the corresponding slope is the diaphragm resistance.
  • the formula for calculating the ionic conductivity of the diaphragm: ⁇ S d/(RS ⁇ A ⁇ 10); among them,
  • ⁇ S is the ionic conductivity of the diaphragm, unit: mS/cm;
  • d is the thickness of the diaphragm, unit: ⁇ m; measured by the thickness gauge;
  • RS is the diaphragm resistance, unit: ⁇ ;
  • A is the effective area of the diaphragm in the symmetrical battery, which is 6cm 2 ;
  • Test of battery internal resistance use a battery internal resistance tester to test.
  • Example 3 Comparing Example 3 and Comparative Example 1, in Example 3, a composite coating and a ceramic coating were respectively applied on both sides of the base film, while in Comparative Example 1, a ceramic coating was applied on both sides of the base film.
  • the thermal stability of Example 3 is better than that of Comparative Example 1, and the air permeability, ionic resistivity and battery internal resistance of Example 3 are all lower than those of Comparative Example 1, because the ceramic coating and the composite coating cooperate with each other to further improve
  • the thermal stability and mechanical properties of the composite separator can reduce the air permeability value, improve the wettability of the electrolyte and the conductivity of lithium ions.
  • Example 4 is coated with a composite coating composed of polymers and ceramics on the surface of the base film, while Comparative Example 2 is coated with a single polymer coating on the surface of the base film.
  • Layer it can be seen from the test data that the thermal stability of Example 4 is better than that of Comparative Example 2, and the liquid absorption, air permeability, air permeability, ionic resistivity and battery internal resistance of Example 4 are all lower than those of Comparative Example 2.
  • the mutual cooperation of ceramics, polymers and base film reduces the air permeability of the composite diaphragm, while improving the conductivity of lithium ions and reducing the internal resistance of lithium ion batteries.

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Abstract

本申请涉及一种复合隔膜及其制备方法和用途。所述复合隔膜包括基膜，以及涂覆在所述基膜至少一侧的复合涂层，所述复合涂层包括相互分散的陶瓷和聚合物。所述陶瓷和聚合物相互分散，使得所述复合隔膜具有良好的热稳定性和电解液的浸润性，优异的机械性能，同时提升电池的硬度，使锂离子电池的安全性能得到极大的改善。

Description

一种复合隔膜及其制备方法和用途 技术领域
本申请属于锂离子电池技术领域，涉及一种复合隔膜及其制备方法和用途。
背景技术
锂离子电池具有比能量高、无污染、使用寿命长和无记忆效应等优点，作为新能源汽车的动力源，成为近年来的研究热点。隔膜，作为锂离子电池的关键安全部件，具有丰富的孔道结构，其作用是阻断正极与负极的接触，提供锂离子传输通道。
目前，常用的隔膜主要是聚乙烯(PE)和聚丙烯(PP)等聚烯烃隔膜，由于聚乙烯(PE)和聚丙烯(PP)隔膜的熔点一般低于200℃，耐热性较差。因此，如何提高隔膜的耐热性成为研究的重点。
CN104701478A公开了一种用于提高锂离子电池使用安全性的含有机/无机复合交联涂层的聚乙烯微孔膜及其制备方法。该专利以含芳杂环聚酯二元醇和芳香族异氰酸酯为基本组份，结合交联剂、发泡剂、催化剂和无机纳米填料，按照一定的组成配比配制成涂覆液；将涂覆液涂布于聚乙烯微孔隔膜的至少一个表面上，在特定温度条件下固化后，在聚乙烯微孔隔膜表面形成具有开孔泡沫结构的有机聚合物/无机纳米粒子复合交联涂层。但是隔膜与正负极片间没有粘结作用。
CN106654119A公开了一种混合涂层隔膜及其制备方法和应用，所述混合涂层隔膜包括基膜、陶瓷颗粒涂层和聚合物涂层，陶瓷颗粒涂层形成在基膜一侧或者两侧，聚合物涂层形成在基膜上和/或陶瓷颗粒涂层上。通过在基膜上同时形成有陶瓷颗粒涂层和聚合物涂层，提升了隔膜的耐热性及隔膜与正负极片的 粘结强度。
CN109994695A公开了一种聚合物浆料、复合隔膜及其制备方法。所述聚合浆料包括所述浆料包括10-30重量份的聚合物、0.05-1.0重量份的增稠剂、5.1-26.5重量份的润湿剂、1.0-5.0重量份的粘结剂、0.1-1.0重量份的分散剂和80-120重量份的水。所述复合隔膜包括基膜，分别涂覆在基膜两侧的陶瓷涂层和聚合物点状涂层，其中聚合物点状涂层由上述聚合物浆料通过高压射流涂覆得到。
上述文献虽然可以提高隔膜的耐热性，但是聚合物涂层的引入，使得复合隔膜的透气度值会增大，离子电导率减小，从而增大锂离子电池的内阻；且涂覆工序复杂，产品生产效率较低。
基于现有技术的研究，如何提高隔膜热稳定性的同时，提高机械性能，减小隔膜的透气度值，改善电解液的浸润性，提升锂离子的传导率，降低锂离子电池的内阻，成为目前急需解决的技术问题。
发明内容
本申请提供了一种复合隔膜及其制备方法和用途。所述复合隔膜热稳定性和电解液的浸润性好，机械性能优异，透气度值小，锂离子的传导率高，有效降低锂离子电池的内阻，同时提升锂离子电池的安全性能和硬度。
为达此目的，本申请采用以下技术方案：
第一方面，本申请提供一种复合隔膜，所述复合隔膜包括多孔基膜，以及涂覆在所述多孔基膜至少一侧的复合涂层，所述复合涂层包括相互分散的陶瓷和聚合物。
本申请中，陶瓷具有耐高温，电化学稳定性，且具有较好的吸液保液能力，能够提升复合隔膜的耐热性和耐氧化性，使复合隔膜更具安全性，且可延长锂 离子电池的寿命；聚合物可增强复合隔膜与极片之间的粘结力，同时提升电池硬度；所述陶瓷和聚合物相互分散，提升多孔基膜的耐热性和机械性能，改善电解液的浸润性，同时提升电池的硬度，使锂离子电池的安全性能得到极大的改善。
本申请中，所述陶瓷、聚合物和多孔基膜的相互配合，减小所述复合隔膜的透气度值，同时提升锂离子的传导率，降低锂离子电池的内阻，减少聚合物涂覆隔膜中，由于聚合物溶胀产生堵孔的现象，提升电池的长期性能。所述复合隔膜具有较低的闭孔温度、较高的破膜温度和优异的热安全性，其性能优于现有技术中的多孔基膜和聚合物涂覆隔膜，可广泛应用于动力离子电池等储能器件。
作为本申请可选的技术方案，所述多孔基膜包括聚烯烃基膜，可选为聚乙烯基膜和/或聚丙烯基膜。
可选地，所述多孔基膜的厚度为3-40μm，例如可以是4μm、5μm、7μm、10μm、12μm、15μm、20μm、25μm、30μm、35μm或40μm等，可选为4-20μm。
可选地，所述多孔基膜的孔径为10-400nm，例如可以是10nm、12nm、15nm、30nm、50nm、100nm、120nm、170nm、200nm、230nm、260nm、300nm、320nm、380nm或400nm等，可选为20-100nm。
可选地，所述多孔基膜的孔隙率为30-60％，例如可以是30％、35％、40％、45％、50％或55％等。
作为本申请可选的技术方案，所述复合涂层的厚度为0.5-10μm，例如可以是0.5μm、1μm、1.5μm、2μm、2.5μm、3μm、3.5μm、4μm、5μm、6μm、7μm、8μm、9μm或10μm等，可选为1-3μm。
在本申请在，复合涂层的厚度限定在0.5-5μm范围内可保证复合隔膜的透气性和粘结力。
可选地，所述陶瓷包括勃姆石、氧化铝、氢氧化镁、氧化镁、钛酸钡、氧化锌或硫酸钡中的任意一种或至少两种的组合，可选为勃姆石或氧化铝。
可选地，所述陶瓷的比表面积为1-12m 2/g，例如可以是2m 2/g、4m 2/g、6m 2/g、8m 2/g、10m 2/g或12m 2/g等，可选为4-8m 2/g。
本申请中，粒径较小的陶瓷颗粒可以满足更薄的涂层要求，涂层更均匀，且具有较高的比表面积，使得涂覆后的隔膜对电解液具有良好的润湿性及保液率，能有效提高锂离子电池的容量保持率，可根据涂层厚度要求选择陶瓷颗粒的粒径大小。
可选地，所述陶瓷的粒径为0.1-4μm，例如可以是0.5μm、1μm、1.5μm、2μm、2.5μm、3μm、3.5μm或4μm等，可选为0.3-3μm。
可选地，以所述陶瓷和聚合物的总质量为100％计，所述陶瓷的质量百分含量为5-98％，例如可以是5％、10％、20％、30％、40％、50％、60％、70％、80％、90％或95％等，可选为80-98％。
可选地，所述聚合物包括偏氟乙烯-六氟丙烯共聚物、偏氟乙烯-八氟异丁烯共聚物、偏氟乙烯-四氟乙烯共聚物、聚甲基丙烯酸甲酯或聚苯乙烯丙烯酸脂中的任意一种或至少两种的组合，其中典型但非限制性组合：偏氟乙烯-六氟丙烯共聚物和偏氟乙烯-四氟乙烯共聚物，偏氟乙烯-八氟异丁烯共聚物和聚甲基丙烯酸甲酯，聚苯乙烯丙烯酸脂等，可选为偏氟乙烯-六氟丙烯共聚物、聚甲基丙烯酸甲酯、聚苯乙烯丙烯酸脂中的任意一种或至少两种的组合。
可选地，所述聚合物的分子量为30-200W，即30万-200万，例如可以是40W、 50W、60W、80W、100W、120W、140W、160W、180W或200W等，可选为40-150W。
可选地，所述聚合物的粒径为0.1-10μm，例如可以是0.2μm、0.5μm、1μm、3μm、5μm、8μm或10μm等，可选为0.15-7μm。
可选地，所述聚合物的玻璃化温度是-60-30℃，例如可以是-60℃、-40℃、-20℃、-10℃、0℃、10℃、20℃、30℃等，可选为-50-15℃。
可选地，以所述陶瓷和聚合物的总质量为100％计，所述聚合物的质量百分含量为2-95％，例如可以是3％、5％、10％、20％、30％、40％、50％、60％、70％、80％或90％等，可选为2-20％。
作为本申请可选的技术方案，所述多孔基膜的一侧涂覆有复合涂层，另一侧涂覆有陶瓷涂层。
在本申请中，所述陶瓷涂层和复合涂层相互配合，进一步提升所述复合隔膜的热稳定性和机械性能，降低透气度值，改善电解液的浸润性能和锂离子的传导率。
本申请中，陶瓷涂层中的陶瓷与复合涂层中的陶瓷，可以相同，也可以不同，只要是相互配合能够提升复合隔膜的热稳定性和机械性能，降低透气度值，改善电解液的浸润性能和锂离子的传导率即可。
可选地，所述陶瓷涂层的厚度为0.5-5μm，例如可以是0.5μm、0.8μm、1μm、1.5μm、2μm、2.5μm、3μm、3.5μm、4μm、4.5μm、4.8μm或5μm等，可选为1-3μm。
在本申请中，陶瓷涂层的厚度限定为0.5-5μm，保证较优的热收缩性能，提高复合隔膜的耐热性和耐氧化性。
在本申请中，可选地，所述复合涂层的厚度为0.5-10μm。
可选地，所述复合涂层的厚度为1-5μm。
可选地，所述聚合物的分子量为40万-180万。
可选地，所述聚合物的玻璃化温度为-60-100℃，例如可以是-60℃、-40℃、-20℃、-10℃、0℃、20℃、40℃、60℃、80℃或100℃等，可选为-50-80℃。
第二方面，本申请提供一种如上述第一方面所述的复合隔膜的制备方法，所述方法包括以下步骤：
(1)将陶瓷、聚合物和溶剂混合，得到混合浆料；
(2)将步骤(1)得到的混合浆料涂覆在多孔基膜至少一侧的表面，得到所述的复合隔膜。
本申请提供的制备方法，通过陶瓷和聚合物的相互分散，提高多孔基膜的热稳定性和机械性能，降低透气度值，提高电解液的浸润性和锂离子的传导率，降低锂离子电池的内阻，提升电池的硬度和安全性能。所述方法涂覆工艺简单，生产效率较高。
作为本申请可选的技术方案，步骤(1)所述陶瓷包括勃姆石、氧化铝、氢氧化镁、氧化镁、钛酸钡、氧化锌或硫酸钡中的任意一种或至少两种的组合，可选为勃姆石或氧化铝。
可选地，步骤(1)所述陶瓷的比表面积为1-12m 2/g，例如可以是2m 2/g、4m 2/g、6m 2/g、8m 2/g、10m 2/g或12m 2/g等，可选为4-8m 2/g。
可选地，步骤(1)所述陶瓷的粒径为0.1-4μm，例如可以是0.5μm、1μm、1.5μm、2μm、2.5μm、3μm、3.5μm或4μm等，可选为0.3-3μm。
可选地，步骤(1)中，以陶瓷和聚合物的总质量为100％计，所述陶瓷的 质量百分含量为5-98％，例如可以是5％、10％、20％、30％、40％、50％、60％、70％、80％、90％或95％等，可选为80-98％。
可选地，步骤(1)所述聚合物包括偏氟乙烯-六氟丙烯共聚物、偏氟乙烯-八氟异丁烯共聚物、偏氟乙烯-四氟乙烯共聚物、聚甲基丙烯酸甲酯或聚苯乙烯丙烯酸脂中的任意一种或至少两种的组合，可选为偏氟乙烯-六氟丙烯共聚物、聚甲基丙烯酸甲酯、聚苯乙烯丙烯酸脂中的任意一种或至少两种的组合。
可选地，步骤(1)所述聚合物的分子量为30-200W，即30万-200万，例如可以是40W、50W、60W、80W、100W、120W、140W、160W、180W或200W等，可选为40-150W。
可选地，步骤(1)所述聚合物的粒径为0.1-10μm，例如可以是0.2μm、0.5μm、1μm、3μm、5μm、8μm或10μm等，可选为0.15-7μm。
可选地，步骤(1)所述聚合物的玻璃化温度是-60-30℃，例如可以是-60℃、-40℃、-20℃、-10℃、0℃、10℃、20℃或30℃等，可选为-50-15℃。
可选地，步骤(1)中，以陶瓷和聚合物的总质量为100％计，所述聚合物的质量百分含量为2-95％，例如可以是3％、5％、10％、20％、30％、40％、50％、60％、70％、80％或90％等，可选为2-20％。
可选地，步骤(1)所述溶剂包括水、丙酮、二氯甲烷、环己烷或N-甲基吡咯烷酮中的任意一种或至少两种的组合，可选为水或二氯甲烷。
作为本申请可选的技术方案，步骤(1)所述混合包括以下步骤：
将聚合物和溶剂进行一次混合，加入陶瓷，进行二次混合，得到所述的混合浆料。
本申请中，所述混合方式能将聚合物均匀地分散在浆料中。
可选地，所述一次混合和二次混合的方式独立地包括搅拌和/或超声。
可选地，步骤(1)所述混合浆料的粘度为0-80CP，例如可以是10CP、20CP、30CP、40CP、50CP、60CP、70CP或80CP，可选为30-50CP。
可选地，步骤(1)所述混合浆料的固含量为20-70％，例如可以是20％、30％、40％、50％、60％或70％，可选为30-50％。
作为本申请可选的技术方案，步骤(2)所述多孔基膜包括聚烯烃基膜，可选为聚乙烯基膜和/或聚丙烯基膜。
可选地，步骤(2)所述多孔基膜的厚度为3-40μm，例如可以是4μm、5μm、7μm、10μm、12μm、15μm、20μm、25μm、30μm、35μm或40μm等，可选为4-20μm。
可选地，步骤(2)所述多孔基膜的孔径为10-400nm，例如可以是10nm、12nm、15nm、30nm、50nm、100nm、120nm、170nm、200nm、230nm、260nm、300nm、320nm、380nm或400nm等，可选为20-100nm。
可选地，步骤(2)所述多孔基膜的孔隙率为30-60％，例如可以是30％、35％、40％、45％、50％或55％等。
可选地，步骤(2)所述涂覆的方式包括涂布、辊涂、喷涂或浸涂中的任意一种或至少两种的组合，可选为辊涂和/或涂布。
可选地，步骤(2)所述涂覆的厚度为0.5-5μm，例如可以是0.5μm、1μm、1.5μm、2μm、2.5μm、3μm、3.5μm、4μm、4.5μm或5μm等，可选为1-3μm。
作为本申请可选的技术方案，步骤(2)还包括：所述混合浆料涂覆在多孔基膜至少一侧的表面之后，进行烘干。
可选地，步骤(2)中，多孔基膜的一侧涂覆混合浆料，多孔基膜的另一侧 涂覆陶瓷浆料。
本申请中，所述混合浆料和陶瓷浆料可以是同时涂覆在多孔基膜表面，也可以是分步涂覆在多孔基膜表面，只要是本领域技术人员常用的涂覆方法，均适用于本申请，可选为同时涂覆，同时涂覆提高生产效率。
本申请中，对所述陶瓷浆料的制备方法不作具体的限定，可以是粘结剂和溶剂先混合，再与陶瓷混合，也可以是将陶瓷直接加入粘结剂溶液中混合。
可选地，所述陶瓷浆料的制备方法包括以下步骤：
将陶瓷加入粘结剂溶液中混合，得到所述的陶瓷浆料。
可选地，所述陶瓷浆料涂覆的厚度为0.5-5μm，例如可以是0.5μm、0.8μm、1μm、1.5μm、2μm、2.5μm、3μm、3.5μm、4μm、4.5μm、4.8μm或5μm等，可选为1-3μm。
示例性地，本申请提供了一种复合隔膜的制备方法，所述的制备方法具体包括如下步骤：
(1)将粘结剂和溶剂混合，再加入陶瓷混合，得到陶瓷浆料；其中，粘结剂可选地包括聚偏氟乙烯、羧甲基纤维素钠、聚丙烯酸、聚乙烯醇或丁苯橡胶中的任意一种或至少两种的组合；陶瓷包括勃姆石、氧化铝、氢氧化镁、氧化镁、钛酸钡、氧化锌或硫酸钡中的任意一种或至少两种的组合；以所述陶瓷和粘结剂的总质量为100％计，所述粘结剂的质量百分含量为2-8％，所述陶瓷的质量百分含量为92-98％。
(2)将聚合物和溶剂混合，再加入陶瓷混合，陶瓷颗粒的粒径为0.1-4μm，比表面积为1-12m 2/g，得到粘度为0-80CP、固含量为20-70％的混合浆料；聚合物包括偏氟乙烯-六氟丙烯共聚物、偏氟乙烯-八氟异丁烯共聚物、偏氟乙烯-四 氟乙烯共聚物、聚甲基丙烯酸甲酯或聚苯乙烯丙烯酸脂中的任意一种或至少两种的组合；溶剂包括水、丙酮、二氯甲烷、环己烷或N-甲基吡咯烷酮中的任意一种或至少两种的组合；所述陶瓷包括勃姆石、氧化铝、氢氧化镁、氧化镁、钛酸钡、氧化锌或硫酸钡中的任意一种或至少两种的组合；以陶瓷和聚合物的总质量为100％计，所述陶瓷的质量百分含量为5-98％，所述聚合物的质量百分含量为2-95％；
(3)将步骤(2)得到的混合浆料涂覆在多孔基膜一侧或两侧，步骤(1)得到的陶瓷浆料涂覆在多孔基膜一侧，烘干，得到所述的复合隔膜。
可选地，步骤(1)所述聚合物的分子量为40-180W。
可选地，步骤(1)所述聚合物的玻璃化温度为-60-100℃，例如可以是-60℃、-40℃、-20℃、-10℃、0℃、20℃、30℃、40℃、60℃、80℃或100℃等，可选为-50-80℃。
可选地，步骤(2)所述涂覆的厚度为0.5-10μm，例如可以是0.5μm、0.8μm、1μm、1.5μm、2μm、2.5μm、3μm、3.5μm、4μm、4.5μm、4.8μm、5μm、7μm或10μm等。
可选地，步骤(2)所述涂覆的厚度为1-5μm。
第三方面，本申请提供一种锂离子电池，所述锂离子电池包含如第一方面所述的复合隔膜。
本申请中，所述锂离子电池采用上述第一方面所述的复合隔膜，具有较低内阻，优异的安全性能和硬度。
与现有技术相比，本申请至少具有以下有益效果：
(1)本申请的复合隔膜，具有良好的热稳定性和电解液的浸润性，优异的 机械性能，较低的透气度值和较高的锂离子的传导率，有效降低锂离子电池的内阻，同时提升锂离子电池的安全性能和硬度；
(2)本申请通过调控混合浆料中陶瓷和聚合物的质量百分含量、复合涂层的厚度，以及复合涂层与陶瓷涂层的厚度差，进一步提升复合隔膜的热稳定性、电解液浸润性和锂离子的传导率；
(3)本申请提供的制备方法，工艺简单，生产效率较高。
附图说明
图1是本申请实施例提供的一种复合隔膜的结构示意图。
图2是本申请实施例提供的一种复合隔膜的结构示意图。
图3是本申请实施例提供的一种复合隔膜的结构示意图。
图4是本申请实施例提供的复合涂层的SEM图。
其中，1-多孔基膜，2-陶瓷涂层，3-复合涂层，4-陶瓷，5-聚合物。
具体实施方式
下面结合具体实施方式来进一步说明本申请的技术方案。本领域技术人员应该明了，所述实施例仅仅是帮助理解本申请，不应视为对本申请的具体限制。
本申请实施例部分提供的复合隔膜，其结构示意图如图1、图2、图3所示。所述复合隔膜包括多孔基膜1，以及涂覆在所述多孔基膜1一侧的陶瓷涂层2和涂覆在所述多孔基膜1另一侧的复合涂层3，所述复合涂层3包括陶瓷4和聚合物5。
实施例1
本实施例提供一种复合隔膜的制备方法，所述方法包括以下步骤：
(1)将氧化铝、聚苯乙烯丙烯酸脂加入水中，所述氧化铝的比表面积为 6m 2/g，粒径为1.5μm，所述聚苯乙烯丙烯酸脂的分子量为150W，玻璃化温度为5℃，粒径为3-10μm，搅拌至溶解，得到粘度为55CP、固含量为45％的混合浆料；
以所述氧化铝和聚苯乙烯丙烯酸脂共聚物的总质量为100％计，所述氧化铝的质量百分含量为93％，所述聚苯乙烯丙烯酸脂的质量百分含量为7％；
(2)将步骤(1)得到的混合浆料涂布在聚乙烯基膜的一侧，所述聚乙烯基膜的厚度为9μm，孔隙率为40％，烘干，得到所述的复合隔膜。
本实施例制备得到的复合隔膜，如图1所示，所述复合涂层的厚度为3μm，复合涂层的SEM电镜照片如图4所示。
实施例2
本实施例提供一种复合隔膜的制备方法，所述方法包括以下步骤：
(1)将氧化铝、聚苯乙烯丙烯酸脂加入水中，所述氧化铝的比表面积为8m 2/g，粒径为0.2μm，所述聚苯乙烯丙烯酸脂的分子量为100W，玻璃化温度为10℃，粒径为3-10μm，搅拌至溶解，得到粘度为50CP、固含量为30％的混合浆料；
以所述氧化铝和聚苯乙烯丙烯酸脂共聚物的总质量为100％计，所述氧化铝的质量百分含量为95％，所述聚苯乙烯丙烯酸脂的质量百分含量为5％；
(2)将步骤(1)得到的混合浆料涂布在聚乙烯基膜的两侧，所述聚乙烯基膜的厚度为9μm，孔隙率为45％，烘干，得到所述的复合隔膜。
本实施例制备得到的复合隔膜，如图2所示，所述复合涂层的厚度为2μm。
实施例3
本实施例提供一种复合隔膜的制备方法，所述方法包括以下步骤：
(1)将聚苯乙烯丙烯酸脂加入水中，所述聚苯乙烯丙烯酸脂的分子量为200W，玻璃化温度为-10℃，粒径为3-103-10μm，搅拌至溶解，加入勃姆石，所述勃姆石的比表面积为9m 2/g，粒径为1μm，搅拌均匀，得到粘度为60CP、固含量为50％的混合浆料；
以所述勃姆石和聚苯乙烯丙烯酸脂共聚物的总质量为100％计，所述勃姆石的质量百分含量为97％，所述聚苯乙烯丙烯酸脂的质量百分含量为3％；
(2)将聚偏氟乙烯加入水中搅拌至溶解，加入勃姆石，所述勃姆石的比表面积为6m 2/g，粒径为2μm，搅拌均匀，得到粘度为65CP、固含量为50％的陶瓷浆料；
以所述勃姆石和聚偏氟乙烯的总质量为100％计，所述勃姆石的质量百分比为95％，所述聚偏氟乙烯的质量百分含量为5％；
(3)将步骤(1)得到的混合浆料辊涂在聚乙烯基膜的一侧，步骤(2)得到的陶瓷浆料辊涂在聚乙烯基膜的另一侧，所述聚乙烯基膜的厚度为9μm，孔隙率为43％，烘干，得到所述的复合隔膜。
本实施例制备得到的复合隔膜，如图3所示，所述复合涂层的厚度为2μm，所述陶瓷涂层的厚度为2μm。
实施例4
与实施例1相比，区别仅在于，将步骤(1)中氧化铝替换为勃姆石。
本实施例制备得到的复合隔膜，孔隙率为38％，所述复合涂层的厚度为3μm。
实施例5
与实施例2相比，区别仅在于，将聚乙烯基膜厚度替换为12μm，孔隙率替换为48％。
本实施例制备得到的复合隔膜，所述复合涂层的厚度为3μm。
对比例1
与实施例3相比，区别仅在于，本对比例将复合涂层替换为陶瓷涂层。
对比例2
与实施例4相比，本对比例在实施例4中的基膜一侧辊涂偏氟乙烯-六氟丙烯共聚物，所述偏氟乙烯-六氟丙烯共聚物的分子量为40W，粒径为200nm。
本对比例制备得到的复合隔膜包括基膜和涂覆于基膜一侧的聚合物层，所述聚合物涂层的厚度为1μm。
复合隔膜性能的评价：
将各实施例与对比例提供的复合隔膜，进行热稳定性、吸液率、透气度值和离子电导率的测试，同时与正极片、负极片组装成裸电芯热压，将热压后的裸电芯放置在固定高度的架子上，24h后测试电芯形变量，所述正极片中镍钴锰酸锂、乙炔黑和聚偏氟乙烯的质量比为9.5:0.2:0.3，所述负极片中石墨、乙炔黑、羧甲基纤维素钠和丁苯橡胶的质量比为9.5:0.2:0.15:0.15，注入电解液，所述电解液为LiPF 6/EC+DEC+DMC(EC、DEC和DMC的体积比为1:1:1)制备成锂离子电池后进行内阻测试，测试方法如下：
热稳定性测试：制备5块试样，在膜卷的纵向方向上裁取120mm×120mm的正方形试样，并在试样上标记长度100mm×100mm。使用玻璃板夹住并放入130℃恒温烘箱内烘烤1h，测量烘烤后MD、TD方向的长度，计算收缩率。玻璃板的尺寸：220mm×220mm×4mm；玻璃板的材质：钢化玻璃。热收缩率X按下式计算：(初始尺寸-烘烤后尺寸)/初始尺寸
隔膜吸液率测试：把大小10×10cm的涂覆膜称重，质量为W 0，室温下浸入 碳酸乙烯酯(EC):碳酸丙烯酯(PC)＝1:1的混合溶液中，静置2h，然后用滤纸吸净表面的电解液后称重，质量记为W 1，然后室温下继续放置10min后，再次称重，质量记为W 2，吸液率＝(W 2-W 0)/W 0。
透气度值测试：参考GB/T 458-2008进行，取5片样品采用透气仪进行测试，取测量的平均值为其透气度。
离子电导率测试：采用惰性不锈钢电极制作对称式电池进行测试，随着隔膜层数的增加，电池电阻也相应增加，并存在线性关系，对应斜率即是隔膜电阻。隔膜离子电导率计算公式：σS＝d/(RS×A×10)；其中，
σS为隔膜离子电导率，单位：mS/cm；
d为隔膜的厚度，单位：μm；由测厚仪测得；
RS为隔膜电阻，单位：Ω；
A为对称式电池中隔膜有效面积，取值6cm 2；
备注：分母“10”为量纲换算比值。
电池内阻的测试：采用电池内阻测试仪进行测试。
测试结果如表1所示。
表1
Figure PCTCN2021113488-appb-000001
Figure PCTCN2021113488-appb-000002
通过表1可以看出以下几点：
对实施例3和对比例1进行对比，实施例3在基膜两侧表面分别涂覆复合涂层和陶瓷涂层，而对比例1则是在基膜两侧表面均涂覆了陶瓷涂层，实施例3的热稳定性优于对比例1，实施例3的透气度、离子电阻率和电池内阻均低于对比例1，原因在于，陶瓷涂层和复合涂层相互配合，进一步提升所述复合隔膜的热稳定性和机械性能，降低透气度值，改善电解液的浸润性能和锂离子的传导率。
对实施例4和对比例2进行对比，实施例4在基膜表面涂覆的是由聚合物和陶瓷组成的复合涂层，而对比例2在基膜表面涂覆的是单一的聚合物涂层，由测试数据看出，实施例4的热稳定性优于对比例2，实施例4的吸液率、透气度、透气度、离子电阻率和电池内阻均低于对比例2，原因在于，通过陶瓷和聚合物的复合，二者相互分散，可以提升基膜的热稳定性，改善电解液的浸润性，同时提升电池的硬度，使锂离子电池的安全性能得到极大的改善。陶瓷、聚合物和基膜的相互配合，减小复合隔膜的透气度值，同时提升锂离子的传导率，降低锂离子电池的内阻。
申请人声明，本申请通过上述实施例来说明本申请的详细结构特征，但本申请并不局限于上述详细结构特征，即不意味着本申请必须依赖上述详细结构特征才能实施。

Claims (25)

  1. 一种复合隔膜，其包括多孔基膜，以及涂覆在所述多孔基膜至少一侧的复合涂层，所述复合涂层包括相互分散的陶瓷和聚合物。
  2. 根据权利要求1所述的复合隔膜，其中，所述多孔基膜的一侧涂覆有复合涂层，另一侧涂覆有陶瓷涂层。
  3. 根据权利要求2所述的复合隔膜，其中，所述陶瓷涂层的厚度为0.5-5μm。
  4. 根据权利要求3所述的复合隔膜，其中，所述陶瓷涂层的厚度为1-3μm。
  5. 根据权利要求1-4中任一项所述的复合隔膜，其中，所述多孔基膜包括聚烯烃基膜，可选为聚乙烯基膜和/或聚丙烯基膜；
    可选地，所述多孔基膜的厚度为3-40μm，可选为4-20μm；
    可选地，所述多孔基膜的孔径为10-400nm，可选为20-100nm；
    可选地，所述多孔基膜的孔隙率为30-60％。
  6. 根据权利要求1-5中任一项所述的复合隔膜，其中，所述陶瓷包括勃姆石、氧化铝、氢氧化镁、氧化镁、钛酸钡、氧化锌或硫酸钡中的任意一种或至少两种的组合，可选为勃姆石或氧化铝；
    可选地，所述陶瓷的比表面积为1-12m 2/g，可选为4-8m 2/g；
    可选地，所述陶瓷的粒径为0.1-4μm，可选为0.3-3μm；
    可选地，以所述陶瓷和聚合物的总质量为100％计，所述陶瓷的质量百分含量为5-98％，可选为80-98％；
    可选地，所述聚合物包括偏氟乙烯-六氟丙烯共聚物、偏氟乙烯-八氟异丁烯共聚物、偏氟乙烯-四氟乙烯共聚物、聚甲基丙烯酸甲酯或聚苯乙烯丙烯酸脂中的任意一种或至少两种的组合，可选为偏氟乙烯-六氟丙烯共聚物、聚甲基丙烯酸甲酯或聚苯乙烯丙烯酸脂；
    可选地，以所述陶瓷和聚合物的总质量为100％计，所述聚合物的质量百分含量为2-95％，可选为2-20％。
  7. 根据权利要求1-6中任一项所述的复合隔膜，其中，所述聚合物的分子量为30万-200万，可选为40万-150万；
    可选地，所述聚合物的粒径为0.1-10μm，可选为0.15-7μm；
    可选地，所述聚合物的玻璃化温度为-60-30℃，可选为-50-15℃。
  8. 根据权利要求1-7中任一项所述的复合隔膜，其中，所述复合涂层的厚度为0.5-5μm，可选为1-3μm。
  9. 根据权利要求1-7中任一项所述的复合隔膜，其中，所述复合涂层的厚度为0.5-10μm。
  10. 根据权利要求1-7中任一项所述的复合隔膜，其中，所述复合涂层的厚度为1-5μm。
  11. 根据权利要求1-6中任一项所述的复合隔膜，其中，所述聚合物的分子量为40万-180万。
  12. 根据权利要求1-6中任一项所述的复合隔膜，其中，所述聚合物的玻璃化温度为-60-100℃，可选为-50-80℃。
  13. 一种权利要求1-8任一项所述的复合隔膜的制备方法，其包括以下步骤：
    (1)将陶瓷、聚合物和溶剂混合，得到混合浆料；
    (2)将步骤(1)得到的混合浆料涂覆在多孔基膜至少一侧的表面，得到所述的复合隔膜。
  14. 根据权利要求13所述的方法，其中，步骤(1)所述陶瓷包括勃姆石、 氧化铝、氢氧化镁、氧化镁、钛酸钡、氧化锌或硫酸钡中的任意一种或至少两种的组合，可选为勃姆石或氧化铝；
    可选地，步骤(1)所述陶瓷的比表面积为1-12m 2/g，可选为4-8m 2/g；
    可选地，步骤(1)所述陶瓷的粒径为0.1-4μm，可选为0.3-3μm；
    可选地，步骤(1)中，以陶瓷和聚合物的总质量为100％计，所述陶瓷的质量百分含量为5-98％，可选为80-98％；
    可选地，步骤(1)所述聚合物包括偏氟乙烯-六氟丙烯共聚物、偏氟乙烯-八氟异丁烯共聚物、偏氟乙烯-四氟乙烯共聚物、聚甲基丙烯酸甲酯或聚苯乙烯丙烯酸脂中的任意一种或至少两种的组合，可选为偏氟乙烯-六氟丙烯共聚物、聚甲基丙烯酸甲酯、聚苯乙烯丙烯酸脂中的任意一种或至少两种的组合；
    可选地，步骤(1)中，以陶瓷和聚合物的总质量为100％计，所述聚合物的质量百分含量为2-95％，可选为2-20％；
    可选地，步骤(1)所述溶剂包括水、丙酮、二氯甲烷、环己烷或N-甲基吡咯烷酮中的任意一种或至少两种的组合，可选为水或二氯甲烷。
  15. 根据权利要求13或14所述的方法，其中，步骤(1)所述混合包括以下步骤：
    将聚合物和溶剂进行一次混合，加入陶瓷，进行二次混合，得到所述的混合浆料；
    可选地，所述一次混合和二次混合的方式独立地包括搅拌和/或超声；
    可选地，步骤(1)所述混合浆料的粘度为0-80CP，可选为30-50CP；
    可选地，步骤(1)所述混合浆料的固含量为20-70％，可选为30-50％。
  16. 根据权利要求13-15任一项所述的方法，其中，步骤(2)所述多孔基 膜包括聚烯烃基膜，可选为聚乙烯基膜和/或聚丙烯基膜；
    可选地，步骤(2)所述多孔基膜的厚度为3-40μm，可选为4-20μm；
    可选地，步骤(2)所述多孔基膜的孔径为10-400nm，可选为20-100nm；
    可选地，步骤(2)所述多孔基膜的孔隙率为30-60％；
    可选地，步骤(2)所述涂覆的方式包括涂布、辊涂、喷涂或浸涂中的任意一种或至少两种的组合，可选为辊涂和/或涂布。
  17. 根据权利要求13-16任一项所述的方法，其中，步骤(2)还包括：所述混合浆料涂覆在多孔基膜至少一侧的表面之后，进行烘干；
    可选地，步骤(2)中，多孔基膜的一侧涂覆混合浆料，多孔基膜的另一侧涂覆陶瓷浆料；
    可选地，所述陶瓷浆料的制备方法包括以下步骤：
    将陶瓷加入粘结剂溶液中混合，得到所述的陶瓷浆料；可选地，所述陶瓷浆料涂覆的厚度为0.5-5μm，可选为1-3μm。
  18. 根据权利要求13-17任一项所述的方法，其中，步骤(2)所述涂覆的厚度为0.5-5μm，可选为1-3μm。
  19. 根据权利要求13-18任一项所述的方法，其中，步骤(1)所述聚合物的分子量为30万-200万，可选为40万-150万；
    可选地，步骤(1)所述聚合物的粒径为0.1-10μm，可选为0.15-7μm；
    可选地，步骤(1)所述聚合物的玻璃化温度为-60-30℃，可选为-50-15℃。
  20. 根据权利要求13-17任一项所述的方法，其中，步骤(2)所述涂覆的厚度为0.5-10μm。
  21. 根据权利要求13-17任一项所述的方法，其中，步骤(2)所述涂覆的 厚度为1-5μm。
  22. 根据权利要求13-18任一项所述的方法，其中，步骤(1)所述聚合物的分子量为40万-180万。
  23. 根据权利要求13-18任一项所述的方法，其中，步骤(1)所述聚合物的玻璃化温度为-60-100℃，可选为-50-80℃。
  24. 一种锂离子电池，其包含权利要求1-8任一项所述的复合隔膜。
  25. 一种锂离子电池，其包含权利要求9-12任一项所述的复合隔膜。
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