WO2024008055A1 - 一种多孔隔膜、其制备方法及电化学装置 - Google Patents

一种多孔隔膜、其制备方法及电化学装置 Download PDF

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WO2024008055A1
WO2024008055A1 PCT/CN2023/105650 CN2023105650W WO2024008055A1 WO 2024008055 A1 WO2024008055 A1 WO 2024008055A1 CN 2023105650 W CN2023105650 W CN 2023105650W WO 2024008055 A1 WO2024008055 A1 WO 2024008055A1
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porous coating
organic porous
base film
coating
organic
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PCT/CN2023/105650
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English (en)
French (fr)
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马平川
白耀宗
刘杲珺
高飞飞
孙源
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中材锂膜有限公司
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Publication of WO2024008055A1 publication Critical patent/WO2024008055A1/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
    • H01M50/489—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
    • 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
    • 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
    • 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
    • H01M50/431—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
    • H01M50/449—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
    • 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
    • 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
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the present invention relates to a separator for an electrochemical device. Specifically, it relates to a porous separator, a preparation method thereof and an electrochemical device having the porous separator.
  • the separator is an electrically insulating film with a porous structure. It is an important component of the secondary battery. It is mainly used to separate the positive electrode sheet and the negative electrode sheet to prevent internal short circuit of the secondary battery.
  • Traditional separators mainly use polyolefin porous membranes, such as single-layer membranes or multi-layer composite membranes of polyethylene (PE) and polypropylene (PP).
  • PE polyethylene
  • PP polypropylene
  • the polyolefin separator has a low melting point and will undergo severe thermal shrinkage when the temperature is too high. When the internal heat accumulates during the use of the secondary battery, the polyolefin separator is easily deformed and the positive and negative electrodes are in direct contact, causing secondary An internal short circuit in the battery may cause safety hazards such as fire or explosion.
  • the current market mainly uses ceramic coating on the surface of polyolefin base films to give the separator high heat resistance and reduce the thermal shrinkage rate of the separator, thereby more effectively reducing internal short circuits in lithium-ion batteries. , to prevent battery thermal runaway caused by internal short circuit of the battery.
  • simple ceramic coating can easily lead to insufficient adhesion between the separator and the electrode. Therefore, on this basis, an organic coating is introduced to further improve the adhesion with the electrode.
  • a more mature method is to use Use PVDF-based materials as organic coatings.
  • the base film-inorganic coating-organic coating is formed for multi-layer compounding, a new problem arises: due to the limitations of the preparation method, the surface porosity of the organic coating is too low, that is, the surface of the organic coating will be partially Blocking the pores of the substrate leads to a reduction in the pore size and porosity of the overall surface of the separator.
  • this structure is beneficial to improving the adhesion between the separator and the electrode, improving the wettability and liquid retention rate of the separator to the electrolyte, it will also Reducing the overall breathability of the separator reduces the ion channels, hinders the migration of lithium ions, increases the internal resistance of the battery, and affects the battery rate and low-temperature performance.
  • the Chinese patent with Publication No. CN104508864B considers the deviation in the coating amount of the adhesive porous layer from the perspective of the deviation in the coating amount of the adhesive porous layer, and the adhesiveness to the electrode is also prone to deviation.
  • the standard deviation of the weight can be achieved within a certain range to ensure sufficient adhesion and ion permeability at the same time.
  • this method only reflects the uniformity of the coating as a whole and has a certain effect, but the actual production process has limited impact on solving the two problems.
  • the object of the present invention is to provide a porous separator, a preparation method thereof and an electrochemical device.
  • the porous separator has excellent positive electrode adhesion, liquid retention, air permeability and ion conductivity. It is helpful to improve the performance of lithium batteries.
  • the present invention is implemented as follows:
  • the invention provides a porous separator, which at least includes a base film layer and an organic porous coating located on one side of the base film layer.
  • the porosity of the organic porous coating is 20% to 80%.
  • the organic porous coating The surface pore area away from the base film layer accounts for 10% to 70%;
  • the interior of the organic porous coating refers to the part of the organic porous coating that is 10% or more of the total thickness of the organic porous coating from the surface, and its internal pores are in contact with the organic porous coating.
  • the distance between the coating surfaces is more than 10% of the total thickness of the organic porous coating.
  • the surface pores mentioned in the article refer to the planar pores on the surface
  • the surface pores of the organic porous coating refer to the planar pores on one side of the surface
  • the surface pores of the base film layer refer to the base film layer. A flat hole in the surface of one side.
  • the average pore diameter of the internal pores of the organic porous coating is 0.01 to 2.0 ⁇ m
  • the average pore diameter of the surface pores of the organic porous coating away from the base film layer is 0.01 to 2.0 ⁇ m
  • the The ratio of the average pore diameter of the surface pores of the organic porous coating away from the base film layer to the average pore diameter of the internal pores is 1:5 to 2:1.
  • the pore size distribution of the internal pores of the organic porous coating is 1.0 to 3.0, and the pore size distribution of the surface pores of the organic porous coating away from the base film layer is 1.0 to 3.0.
  • the surface pore area of the base film layer close to the organic porous coating accounts for 5% to 60%, and the surface pore area of the base film layer close to the organic porous coating accounts for 5% to 60%.
  • the ratio of the pore area of the surface of the coating away from the base film layer is 0.3 to 1.5.
  • the porosity of the base film layer is 20% to 60%, and the pore size distribution of the surface pores of the base film layer close to the organic porous coating is 1.0 to 3.0.
  • the Gurley value of the porous separator is 100-300 s/100cc.
  • the liquid retention rate of the porous separator is 50% to 95%.
  • the bonding strength of the porous separator is 3-20 N/m.
  • the organic porous coating is an organic porous coating formed from a resin selected from the group consisting of fluorine-containing ethylene polymers, including vinylidene fluoride homopolymer, ylidene fluoride homopolymer, and vinylidene fluoride homopolymer.
  • Copolymers of vinylidene fluoride and other copolymerizable monomers, or mixtures thereof, the monomers copolymerized with vinylidene fluoride include at least one selected from the following: tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, chlorofluoroethylene Ethylene, 1,2-difluoroethylene, perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, perfluoropropyl vinyl ether, difluorobenzo-1,3-dioxole , perfluoro-2,2-dimethyl-1,3-dioxole and trichlorethylene.
  • the organic porous coating is a single layer or multiple layers.
  • a single layer The thickness is 0.3-2 ⁇ m, and the thickness of the base film layer is 2-14 ⁇ m.
  • the porous separator further includes an inorganic layer containing ceramic particles located between the base film layer and the organic porous coating.
  • the inorganic layer is mainly composed of stacked ceramic particles.
  • the ceramic particles The average particle size is 0.2-1.0 ⁇ m, and the ceramic particles are alumina, boehmite, calcium carbonate, hydrotalcite, montmorillonite, titanium dioxide, silicon dioxide, zirconium dioxide, magnesium oxide, magnesium hydroxide, nitrogen One or more of boron, silicon nitride, aluminum nitride, titanium nitride, boron carbide, silicon carbide, and zirconium carbide.
  • the invention also provides a method for preparing the porous separator. The specific steps are:
  • Step 1 Preparation of organic porous coating glue: Disperse the fluorine-containing ethylene polymer resin and non-fluorine resin binder into an organic solvent to form an organic porous coating glue, wherein the organic solvent is selected from N, N' - One or more of dimethylformamide, N-methylpyrrolidone, acetone, and N,N'-dimethylacetamide, and the moisture content of the entire organic porous coating glue is less than 5wt%;
  • Step 2 Provide a base film layer, apply the organic porous coating glue prepared in step 1 on one or both sides of the base film layer, treat it for 0.2 to 15 seconds under the condition of an air humidity of 20% to 80%, and then immerse it in It is solidified in a coagulation bath at room temperature to form an organic porous coating of porous gel, which is then washed and dried to obtain a porous separator.
  • the mass proportion of the fluorine-containing ethylene polymer resin in the organic porous coating glue is 1 wt% to 10 wt%, preferably 3 wt% to 6 wt%.
  • the water content in the coagulation bath ranges from 40wt% to 70wt%.
  • the present invention also provides an electrochemical device, including a positive electrode, a negative electrode, a non-aqueous electrolyte and the above-mentioned porous separator.
  • the organic/inorganic composite layer porous separator obtained according to the present invention has excellent electrode and interlayer bonding properties, high temperature dimensional stability and good air permeability, so that the final lithium battery has high energy density and excellent cycle performance, thereby solving the problem This solves the technical problem in the prior art that the bonding strength and ion conductivity of the separator cannot be taken into consideration.
  • Figure 1 is a schematic structural diagram of the porous separator of the present invention.
  • Figure 2 is an SEM image of the surface of the organic porous coating away from the base film layer in the porous separator in Example 2;
  • Figure 3 is a cross-sectional SEM image of the organic porous coating in the porous separator of Example 2;
  • Figure 4 is a surface SEM image of the base film for coating in the porous separator in Example 2;
  • Figure 5 is a cross-sectional SEM image of the base film for coating in the porous separator in Example 2;
  • Icon 1-base film layer, 2-inorganic layer containing ceramic particles, 3-organic porous coating.
  • the present invention will be described in detail with reference to the embodiments of the present invention, and the main content of the present invention will be further elucidated with reference to specific examples.
  • the content of the present invention is not limited to the following examples. If specific techniques or conditions are not specified in the examples, the techniques or conditions described in literature in the field or product instructions will be followed. If the manufacturer of the reagents or instruments used is not indicated, they are all conventional products that can be purchased commercially.
  • the inventor has discovered through extensive research that when the surface pores of the organic porous coating away from the base film layer are smaller or similar in size to the internal pores, the positive electrode adhesion of the porous separator can be improved as well as the electrolyte wettability and liquid retention. On this basis, by controlling the ratio of the surface pore area of the organic porous coating and the ratio of the surface pore area of the base film layer, ideal positive electrode adhesion, wettability and ion conductivity can be obtained at the same time.
  • the surface pores of the organic porous coating refer to the surface exposed to the outside away from the base film layer
  • the pore area ratio of the surface pores of the organic porous coating refers to all surface pores of the organic porous coating. The ratio of the sum of its areas to the surface on which it is located.
  • the setting of the pore area ratio of the surface of the organic porous coating can be based on the pore area ratio of the surface pores on the base film layer.
  • the surface pores of the organic porous coating are close to the surface pores of the base film, it can It avoids the accumulation of electrolyte inside the separator due to the sudden reduction of the pore size of the membrane layer, thereby avoiding further deterioration in the cycle performance and dynamic performance of the local battery core.
  • the porous separator of the present invention may also include an inorganic layer containing ceramic particles located between the base film layer and the organic porous coating.
  • the inorganic layer is mainly composed of stacked ceramic particles, and the pores formed inside have larger pore diameters, so for porous The ion conductivity performance of the separator will not have a major impact.
  • the penetration depth and penetration of the organic coating into the inorganic layer can be controlled. specific gravity to obtain the desired results.
  • the base membrane it is usually a polyolefin porous base membrane. You can choose from the polyolefin porous base membranes suitable for lithium battery separators in the past, including polyethylene, polypropylene, polybutylene, and poly4-methylpentene. One or more copolymers or blends of olefins.
  • the polyolefin microporous membrane preferably contains polyethylene, and the content of polyethylene is preferably 95% by mass or more of the total content of the base film.
  • the polyolefin porous base membrane is a single-layer polyolefin microporous membrane. In another embodiment, the polyolefin porous base membrane is a polyolefin microporous membrane with a laminated structure of two or more layers.
  • the polyolefin contained in the polyolefin porous base film preferably has a weight average molecular weight (Mw) of 100,000 to 5 million, more preferably 200,000 to 2 million, and still more preferably 300,000 to 1 million.
  • Mw weight average molecular weight
  • the weight average molecular weight is 100,000 or more, sufficient mechanical properties can be ensured.
  • the weight average molecular weight is 5 million or less, the shutdown characteristics are good and film formation is easy.
  • the thickness of the polyolefin porous base membrane is not particularly limited, but is preferably 5 to 30 ⁇ m, and more preferably 8 to 20 ⁇ m.
  • the thickness of the porous base membrane affects the air permeability and mechanical strength of the separator.
  • the manufacturing method of the polyolefin porous base membrane there is no limitation on the manufacturing method of the polyolefin porous base membrane according to the exemplary embodiment of the present invention.
  • the polyolefin porous base membrane can be manufactured by a dry method or a wet method.
  • the dry method is a method of forming micropores by forming a polyolefin film and then stretching the film at low temperatures, which stretching causes microcracks between flakes that are crystalline portions of the polyolefin.
  • the wet method is to mix polyolefin-based resin and diluent at a high temperature where the polyolefin-based resin melts to form a single phase, the polyolefin and diluent undergo phase separation during cooling, and then the diluent is extracted to form pores therein Methods.
  • the wet method is a method of imparting mechanical strength and transparency through a stretching/extraction process after phase separation treatment. Compared with the dry method, the wet method has thin film thickness, uniform pore size, and excellent physical properties, so the wet method is more preferred.
  • the porosity of the porous base membrane is preferably 20% to 60%, and the average pore diameter is 15 to 100 nm. It is further preferred that the porosity is 30% to 50% and the average pore diameter is 20 to 80 nm.
  • the puncture strength of the polyolefin porous base membrane is preferably 200 gf or more.
  • the inorganic layer refers to an inorganic layer containing ceramic particles, located on at least one surface of the base film.
  • the inorganic layer containing ceramic particles is stacked by ceramic particles to form a film layer with certain gaps.
  • the ceramic particles are any ceramic particles that are stable and electrochemically stable relative to the electrolyte, specifically including but not limited to one or more of the following materials: alumina, boehmite, calcium carbonate, hydrotalcite, Montmorillonite, titanium dioxide, silicon dioxide, zirconium dioxide, magnesium oxide, magnesium hydroxide, boron nitride, silicon nitride, aluminum nitride, titanium nitride, boron carbide, silicon carbide, zirconium carbide, of which oxide is preferred Aluminum or boehmite.
  • Ceramic particles can have spherical, needle-shaped, plate-shaped, spindle-shaped particles, etc., and plate-shaped ceramic particles are preferably used. On the one hand, the ceramic particles are not easily detached from the inorganic layer as a whole, and on the other hand, the gap between the positive electrode and the negative electrode can be increased. The path between them has a good effect on inhibiting dendrite short circuit.
  • the average particle size of the ceramic particles is 0.2 to 1.0 ⁇ m, preferably 0.3 to 0.8 ⁇ m, and the particle size uniformity is ((D90-D10)/D50) is 3.0 to 10.0, preferably 4.0 to 8.0. By selecting the shape, particle size and particle size uniformity, the porosity and pore size of the inorganic layer are also determined to facilitate the penetration of the organic porous coating.
  • the thickness of the inorganic layer is 0.2 to 4 ⁇ m, preferably 0.5 to 2 ⁇ m. From the perspective of energy density and ion conductivity, the thickness of the inorganic layer is preferably as thin as possible. From the perspective of heat resistance and thermal shrinkage suppression effect, it is necessary to There is a certain thickness.
  • the inorganic layer also contains a non-fluorine resin binder.
  • the non-fluorine resin binder includes polyamide, polyacrylonitrile, acrylic resin, vinyl acetate-ethylene copolymer.
  • acrylate resin is preferred, and the amount of non-fluorine resin binder is 1 to 8 wt% of the total weight of the inorganic layer containing ceramic particles. If the amount of non-fluorine resin binder is too high, it will affect the heat resistance and heat shrinkage prevention effect of the ceramic particles in the inorganic layer. If the amount is too small, the ceramic particles in the inorganic layer will not be firmly fixed and will easily slip or slip. Disembedded.
  • a coatable ceramic particle slurry is first prepared, and sodium carboxymethylcellulose, inorganic ceramics, dispersant, wetting agent, acrylic adhesive, wetting agent and Deionized water is configured according to a certain feeding sequence to form a ceramic particle slurry.
  • the ceramic particle slurry is coated on at least one surface of the polymer base film, preferably by first using a dip coating method, an air knife coating method, a curtain coating method, a roller coating method, a wire rod coating method, or a gravure coating method. cloth method, or mold coating method, etc.
  • a gravure coating method or the die coating method is preferable as the coating method of the above-mentioned coating liquid.
  • the lithium battery separator coated with the ceramic particle slurry is dried.
  • the drying conditions as long as the base film does not shrink due to softening, the wind speed and drying temperature are not particularly limited.
  • drying methods include heat transfer drying (adhesion to high-heat objects), convective heat transfer (hot air), radiation heat transfer (infrared rays), and other methods (microwave, induction heating, etc.). Among them, on In the above-mentioned manufacturing method, since it is necessary to have a precise and uniform drying speed in the width direction, it is preferable to use convective heat transfer or radiation heat transfer.
  • a method that can reduce the total material movement coefficient during drying while maintaining a controllable wind speed in order to achieve a uniform drying speed in the width direction, when using a convective heat transfer drying method, it is preferable to use a method that can reduce the total material movement coefficient during drying while maintaining a controllable wind speed. Specifically, a method of conveying hot air in a direction parallel to the supporting base film, parallel to the conveying direction of the base film, or perpendicular to the base film may be used.
  • the drying temperature is preferably controlled at 60 to 100°C, preferably 70 to 90°C, and more preferably 75 to 85°C.
  • the organic porous coating is partially or completely coated on the other surface of the inorganic layer away from the base film layer. If the inorganic layer only coats one surface of the base film, the organic porous coating can also be partially or completely coated on the other surface of the inorganic layer. The surface of the base film that is not coated with the inorganic layer.
  • the organic porous coating is an organic porous coating formed from a resin selected from a fluorine-containing ethylene polymer.
  • the resin of the fluorine-containing ethylene polymer includes vinylidene fluoride homopolymer, vinylidene fluoride and other copolymerizable monomers.
  • the monomer copolymerized with vinylidene fluoride includes at least one selected from the following: tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, chlorofluoroethylene, 1,2-difluoroethylene Ethylene, perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, perfluoropropyl vinyl ether, difluorobenzo-1,3-dioxole, perfluoro-2,2- Dimethyl-1,3-dioxole, trichlorethylene and vinyl fluoride are preferably vinylidene fluoride homopolymers or copolymers of vinylidene fluoride and hexafluoropropylene.
  • the fluorine-containing ethylene polymer resin is present in a content of more than 90 wt%, or more than 95 wt%, or more than 99 wt%, and the weight average molecular weight is selected from 60,000 to 1,000,000, preferably from 100,000 to 700,000.
  • the present invention found that the coating surface of the organic porous coating away from the base film also plays a vital role in the adhesion to the electrode and the ionic conductivity.
  • the inventor found that the organic porous coating When the surface pore area of the porous coating away from the base film is limited to a reasonable range, ideal positive electrode adhesion, wettability and ion conductivity can be achieved simultaneously.
  • the setting of the pore area ratio on the surface of the organic porous coating it can be based on the base film The hole area ratio of the surface holes on the layer is carried out.
  • the surface pore area accounts for 10% to 70%, such as 10%, 12%, 15%, 16%, 18%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, but not limited thereto, more preferably 10% to 60%, further preferably 15% to 50%, further preferably 20% to 40%, if the surface holes If the area ratio is too small, the air permeability and ion conductivity will be poor. If the surface pore area ratio is too high, the adhesion to the electrode will decrease, and the interface will be too uneven, causing safety issues.
  • the surface pores here The definition of the area ratio on the surface refers to the ratio of the sum of the areas of all pores on the surface of the organic porous coating away from the base film and the total area of the coating.
  • the average pore size on the surface of the organic porous coating is limited to 0.01-2.0 ⁇ m, and the porosity of the organic porous coating is 20%-80%. It is further preferred that the average pore size on the surface of the organic porous coating is 0.01-2.0 ⁇ m.
  • the pore diameter is 0.03 to 1.0 ⁇ m, and the porosity of the organic porous coating is 40% to 70%.
  • the pore diameter of the organic porous coating is uniform in the range of 0.01 to 2.0 ⁇ m, and the pore size distribution is preferably less than 3.0, more preferably less than 2.0, and further preferably less than 1.5.
  • the control of the pore size of organic porous coatings, especially the surface pore structure is closely related to its raw materials and preparation process, such as the type of resin in the organic porous coating glue, the solid content, the natural volatilization time of the glue, and the type of coagulation bath. and the gelation process will have an impact on the pore structure of the organic porous coating, especially the surface pore structure.
  • the longer the glue evaporates under a single factor the higher the average pore size and surface pore area ratio of the organic porous coating surface will be.
  • those skilled in the art can control the pore size, especially the surface pore structure, of the organic porous coating by regulating these influencing factors according to the target range.
  • the organic porous coating since the organic porous coating it is close to is partially or completely coated on the other surface of the inorganic coating away from the base film layer, there are gaps in the inorganic layer containing ceramic particles. It can be penetrated by the organic porous coating.
  • the weight of the penetration is reflected by the weight increase per unit area.
  • the weight increase per unit area is calculated by the following formula:
  • ⁇ m k is the unit area weight increment of the inorganic layer of the organic/inorganic composite layer porous separator sample k
  • m 1 is the area density of the organic/inorganic composite layer porous separator sample 1
  • m k is the organic/inorganic composite layer porous separator sample k
  • Area density h 1 is the thickness of the organic porous coating of the organic/inorganic composite layer porous separator sample 1
  • h k is the thickness of the organic porous coating of the organic/inorganic composite layer porous separator sample k
  • n is the total number of samples
  • n ⁇ 2 What actually reflects is that after multiple tests of n samples, the average unit thickness surface density of the non-penetrated part of the organic porous coating above the inorganic layer. The larger n, the closer it is to the ideal value.
  • the unit area weight increment ⁇ m of the inorganic layer is 0.2 ⁇ 0.6g/ m2 , it indicates that the penetration amount of the organic porous coating in the inorganic layer is within the ideal range. Within this range, the organic porous coating has a greater impact on the inorganic
  • the layer has a good bonding effect, and at the same time does not affect the efficiency of ion conduction, and the air permeability can be taken into consideration, and it is further preferably 0.3 to 0.5g/m 2 .
  • a coatable organic porous coating glue needs to be prepared first, and a fluoroethylene polymer resin, a non-fluorine resin binder, and an organic good solvent must be prepared to form a coatable glue.
  • an organic good solvent one or more selected from N,N'-dimethylformamide, N-methylpyrrolidone, acetone, and N,N'-dimethylacetamide.
  • Water in the organic porous coating glue is not necessary as a poor solvent for phase separation. In fact, the water content in the organic porous coating glue is preferably less than 5 wt%.
  • the content of the organic good solvent in the mixed slurry is preferably 50 wt% to 95 wt%, and more preferably 65 wt% to 85 wt%.
  • the mass proportion of the resin in the organic porous coating glue is 1wt% to 10wt%, and more preferably 2wt% to 8wt%.
  • the organic porous coating glue is coated on at least one surface of the inorganic layer containing ceramic particles and/or the polymer base film, preferably by first using a dip coating method, an air knife coating method, a curtain coating method, or a roller coating method. , wire bar coating method, gravure coating method, or mold coating method, etc., the organic porous coating glue is coated on the surface of the above-mentioned inorganic layer containing ceramic particles and/or polymer base film, Method of forming coating film.
  • the gravure coating method or the die coating method is preferable as the coating method of the above-mentioned coating liquid.
  • the base film coated with the mixed slurry is treated with a coagulation liquid capable of coagulating the above-mentioned organic porous coating glue liquid.
  • a coagulation liquid capable of coagulating the above-mentioned organic porous coating glue liquid.
  • the organic porous coating glue is solidified to form a porous gel layer.
  • An example of a method of treating with a coagulation liquid is to spray the coagulation liquid onto a base film coated with an organic porous coating glue liquid, and immerse the base film in a bath (coagulation bath) containing the coagulation liquid. methods etc.
  • the coagulating liquid is not particularly limited as long as it is a liquid that can coagulate the organic porous coating glue.
  • it is a solution obtained by mixing an appropriate amount of water with water or a solvent used for the organic porous coating glue.
  • the water content in the coagulation bath is 30wt% to 70wt%, preferably 40wt% to 70wt%, or preferably 35wt% to 65wt%, further preferably 40wt% to 60wt%.
  • the coagulation bath temperature is normal temperature.
  • the lithium battery separator including the porous gel layer that has passed through the coagulation bath is dried.
  • the drying conditions as long as the base film does not shrink due to softening, and the organic porous coating and the inorganic layer can have controlled penetration and bonding, the wind speed and drying temperature are not particularly limited.
  • drying methods include heat transfer drying (adhesion to high-heat objects), convective heat transfer (hot air), radiation heat transfer (infrared rays), and other methods (microwave, induction heating, etc.).
  • heat transfer drying adheresion to high-heat objects
  • convective heat transfer hot air
  • radiation heat transfer infrared rays
  • the method of transporting hot air in a direction parallel to the supporting base film, parallel to the conveying direction of the base film, or perpendicular to the base film can be used.
  • the drying temperature is preferably controlled at 60 to 100°C, preferably 70 to 90°C, and more preferably 75 to 85°C.
  • Figure 1 is a schematic diagram of the overall stacking of one of the organic-inorganic composite layer porous separators prepared according to the method, in which both sides of the base film layer 1 are inorganic layers 2 containing ceramic particles, and on the other side of the inorganic layer 2 containing ceramic particles. One side is an organic porous coating 3, and the organic porous coating 3 is partially penetrated into the inorganic layer 2 containing ceramic particles.
  • the lithium battery of the present invention has a positive electrode, a negative electrode, an electrolyte and a separator of the present invention arranged between the positive electrode and the negative electrode. Specifically, the battery element and the electrolyte are sealed together in an external packaging material. The battery The element is obtained by making the negative electrode and the positive electrode face each other with a separator.
  • the positive electrode has a structure in which an active material layer containing a positive electrode active material and a binder resin is molded on a current collector, for example.
  • cathode active material examples include cathode active materials commonly used in this field, such as lithium-containing transition metal oxides. Specifically, LiCoO 2 , LiNiO 2 , LiMn 1/2 Ni 1/2 O 2 , LiCo 1/3 Mn 1/3 Ni 1/3 O 2 , LiMn 2 O 4 , LiFePO 4 , LiCO 1/2 Ni 1/2 O 2 , LiAl 1/4 Ni 3/4 O 2, etc.
  • the binder resin examples include polyvinylidene fluoride resin, styrene-butadiene copolymer, and the like. It may also contain a conductive additive, and examples thereof include carbon materials such as acetylene black, Ketjen black, and graphite powder.
  • the current collector examples include aluminum foil, titanium foil, stainless steel foil, etc. with a thickness of 5 ⁇ m to 20 ⁇ m.
  • An example of an embodiment of the negative electrode is a structure in which an active material layer including a negative electrode active material and a binder resin is molded on a current collector.
  • the active material layer may further include a conductive assistant.
  • the negative electrode active material include materials that can electrochemically absorb lithium. Specifically, examples include: carbon materials; alloys of silicon, tin, aluminum, etc. and lithium; Wood's alloy; and the like.
  • the binder resin, conductive additive and current collector are basically the same as the positive electrode part.
  • a metal lithium foil may be used as the negative electrode instead of the above-mentioned negative electrode.
  • the electrolyte solution is a solution obtained by dissolving a lithium salt in a non-aqueous solvent.
  • a lithium salt include LiPF 6 , LiBF 4 , LiClO 4 and the like.
  • non-aqueous solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, and vinylene carbonate; dimethyl carbonate, dicarbonate, etc.
  • Chain carbonates such as ethyl ester, ethyl methyl carbonate, ethylene carbonate and their fluorine substitutes; cyclic esters such as ⁇ -butyrolactone and ⁇ -valerolactone, etc. They can be used alone or in mixture.
  • the ceramic particle slurry used to prepare the inorganic layer containing ceramic particles in Examples 1 to 8 and Comparative Examples 1 to 4 was prepared by the following method: based on 100 parts by weight of the coatable slurry, 0.41 parts by weight of carboxymethyl Add 11.92 parts by weight of sodium cellulose to deionized water, mix and stir evenly to obtain slurry A; add 31.80 parts by weight of alumina with D50 of 0.5 ⁇ m, where (D90-D10)/D50 is 5, and 0.16 parts by weight of dispersant added to 50.87 weight parts of water, mix and stir evenly to obtain slurry B; the two slurries A and B are mixed and then dispersed at high speed or ball milled to prepare slurry C; add 4.77 parts by weight of adhesive and 0.06 parts by weight of wetting to slurry C agent, prepared into ceramic particle slurry.
  • PVDF coating glue Based on 100 parts by weight of the coatable slurry, disperse 5 parts by weight of PVDF resin (purchased from Arkema) with a weight average molecular weight of 400,000 to 800,000 to 95 parts of dimethyl Dissolve in acetamide at 50°C for about 3 hours to form PVDF coating glue.
  • PVDF resin purchased from Arkema
  • inorganic layer containing ceramic particles Use microgravure coating to coat the ceramic particle slurry on one side of the 5 ⁇ m base film, dry it to form an inorganic layer, and obtain a ceramic film, which is a traditional power lithium-ion battery separator (thickness 7 ⁇ m, puncture strength 350gf), single layer thickness of inorganic layer 2.0 ⁇ m.
  • PVDF coating glue Based on 100 parts by weight of the coatable slurry, disperse 3 parts by weight of PVDF resin with a weight average molecular weight of 400,000 to 800,000 into 97 parts of dimethylacetamide at 50°C Dissolve for about 3 hours to form PVDF coating glue.
  • inorganic layer containing ceramic particles Use microgravure coating to coat the ceramic particle slurry on one side of the 7 ⁇ m base film, dry it to form an inorganic layer, and obtain a ceramic film, which is a traditional power lithium-ion battery separator (thickness 9 ⁇ m, puncture strength 380gf), single layer thickness of inorganic layer 2.0 ⁇ m.
  • PVDF coating glue Based on 100 parts by weight of the coatable slurry, disperse 4 parts by weight of PVDF resin with a weight average molecular weight of 400,000 to 800,000 into 96 parts of dimethylacetamide at 50°C. Dissolve for about 3 hours to form PVDF coating glue.
  • inorganic layer containing ceramic particles Use microgravure coating to coat the ceramic particle slurry on one side of the 7 ⁇ m base film, dry it to form an inorganic layer, and obtain a ceramic film, which is a traditional power lithium-ion battery separator (thickness 9 ⁇ m, puncture strength 380gf), single layer thickness of inorganic layer 2.0 ⁇ m.
  • PVDF coating glue Based on 100 parts by weight of the coatable slurry, disperse 6 parts by weight of PVDF resin with a weight average molecular weight of 400,000 to 800,000 into 94 parts of dimethylacetamide at 50°C Dissolve for about 3 hours to form PVDF coating glue.
  • inorganic layer containing ceramic particles Use microgravure coating to coat the ceramic particle slurry on one side of the 7 ⁇ m base film, dry it to form an inorganic layer, and obtain a ceramic film, which is a traditional power lithium-ion battery separator (thickness 9 ⁇ m, puncture strength 380gf), single layer thickness of inorganic layer 2.0 ⁇ m.
  • PVDF coating glue Based on 100 parts by weight of the coatable slurry, disperse 7 parts by weight of PVDF resin with a weight average molecular weight of 400,000 to 800,000 into 93 parts of dimethylacetamide at 50°C Dissolve for about 3 hours to form PVDF coating glue.
  • inorganic layer containing ceramic particles Use microgravure coating to coat the ceramic particle slurry on one side of the 7 ⁇ m base film, dry it to form an inorganic layer, and obtain a ceramic film, which is a traditional power lithium-ion battery separator (thickness 9 ⁇ m, puncture strength 380gf), single layer thickness of inorganic layer 2.0 ⁇ m.
  • the thickness of the isolation base film after removal is the thickness of the porous coating.
  • Pore diameter d Use a scanning electron microscope (SEM) to observe the surface of the film, randomly take 5 photos at different positions with a magnification of 10,000 times, outline the holes with a pen, and use image processing software to calculate the area S of each surface hole, and then Calculate the aperture d (equivalent diameter, the diameter of a circle equal to the area of the hole) of each hole according to formula (1):
  • Average pore diameter dn Calculate the average pore diameter of each measured hole according to formula (2),
  • ⁇ d is the sum of the hole diameters d.
  • Pore size distribution SD First calculate the volume average pore diameter dv according to equation (3-1), and then calculate the pore size distribution SD according to equation (3-2).
  • Pore area ratio S% The area of surface pores accounts for the percentage of the total surface area. Specifically calculated according to formula (5):
  • ⁇ Sm is the sum of the above SEM observation areas.
  • Pore diameter d Calculate the pore diameter of the internal pore according to the aforementioned statistics and calculation methods of surface pore diameter.
  • Average pore diameter dn Calculate the average pore diameter of the holes according to formula (2).
  • Pore size distribution SD First calculate the volume average pore diameter dv according to equation (3-1), and then calculate the pore size distribution SD according to equation (3-2).
  • the resin was dissolved in DMF at a concentration of 1.0 mg/ml to obtain a sample liquid. Using 50 ml of this sample liquid, GPC measurement was performed under the following conditions to determine its weight average molecular weight (PMMA conversion).
  • HLC-8220GPC Tosoh Corporation
  • the Gurley value of a porous membrane is the Gurley value of a separator membrane with a porous membrane minus the Gurley value of a separator membrane without a porous membrane (ie, a pure porous substrate).
  • An adhesive tape with a width of 12 mm and a length of 15 cm (manufactured by Scotch, model 550R-12) is attached to the porous layer surface of one side of the separator, and the separator is cut so that the width and length are consistent with the width and length of the adhesive tape. Prepare measurement samples. When attaching the adhesive tape to the separator, make the length direction coincide with the MD direction of the separator. In addition, the adhesive tape is used as a support for peeling off one porous layer.
  • the measurement sample was left in an atmosphere with a temperature of 23 ⁇ 1°C and a relative humidity of 50 ⁇ 5% for more than 24 hours, and the following measurements were performed in the same atmosphere.
  • the adhesive tape is peeled off together with the porous layer immediately below it by about 10 cm, and the laminate (1) of the adhesive tape and the porous layer is separated from the laminate (2) of the porous base material and the other porous layer by about 10 cm.
  • the end of the laminated body (1) is fixed to the upper chuck of TENSILON (RTC-1210A manufactured by Orientec), and the end of the laminated body (2) is fixed to the lower chuck of TENSILON.
  • the measurement sample was suspended in the direction of gravity so that the stretching angle (the angle of the laminated body (1) with respect to the measurement sample) became 180°.
  • the laminated body (1) was stretched at a stretching speed of 20 mm/min, and the load when the laminated body (1) was peeled off from the porous base material was measured.
  • the load from 10 mm to 40 mm after the start of measurement was obtained at intervals of 0.4 mm, and the average value was used as the peel strength.
  • thermoplastic separator into a long strip with a length of 200mm and a width of 25mm.
  • the distance between the clamps is (100 ⁇ 5)mm, and the test speed is (50 ⁇ 10)mm/min.
  • the porosity of the substrate and porous separator is calculated according to the following calculation method:
  • the constituent materials of the membrane are a, b, c,..., n
  • the mass of each constituent material is W a , W b , W c , ..., W n (g/cm 2 )
  • the true density of each constituent material is
  • ⁇ a , ⁇ b , ⁇ c , ..., ⁇ n (g/cm 3 ) and the film thickness are expressed as t (cm)
  • the liquid retention performance of the obtained porous separator was tested.
  • M 0 is the dry weight of the separator
  • M is the mass of the separator after absorbing the saturated electrolyte
  • M t is the mass of the separator after absorbing the saturated electrolyte and leaving it outdoors for 15 hours.
  • Table 1-2 shows the preparation parameters and structure of the porous separators prepared in Examples 1-8 and Comparative Examples 1-4. Parameters and related performance indicators, it can be seen that although there are many influencing factors, by controlling the preparation conditions of the separator, for example, the PVDF content in the slurry is 3 to 6%, and the exposure time of the separator in the air after coating is no more than 15 seconds. , the concentration of the coagulation bath is between 30% and 60%, so that the porosity of the organic porous coating is 20% to 80%, and the surface pore area of the organic porous coating away from the base film layer accounts for 10% to 70%.
  • the average pore diameter of the internal pores of the coating is 0.01 to 2.0 ⁇ m, and the average pore diameter of the surface pores of the organic porous coating away from the base film layer is 0.01 to 2.0 ⁇ m.
  • the average pore diameter of the surface pores of the organic porous coating away from the base film layer is different from that inside
  • the composite laminated porous separator has better comprehensive performance, including good positive electrode bonding performance, high interlayer peeling strength, and good air permeability. And the ability to retain liquid, which is well reflected in the electrical performance of the corresponding lithium battery.
  • the above parameters are not within this range, at least one of the above properties cannot meet actual needs.

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Abstract

本发明公开了一种多孔隔膜、其制备方法及电化学装置。本发明的多孔隔膜，包括基膜层和位于所述基膜层一侧的有机多孔涂层，所述有机多孔涂层的孔隙率为20％～80％，所述有机多孔涂层远离基膜层的表面孔面积占比为10％～70％，所述有机多孔涂层的内部孔的平均孔径为0.01～2.0μm，所述有机多孔涂层远离基膜层的表面孔的平均孔径为0.01～2.0μm，所述有机多孔涂层远离基膜层的表面孔的平均孔径与内部孔的平均孔径的比值为1:5～2:1，该隔膜同时具有优良的正极粘合性、保液性、透气性及离子传导性，进而可有效提升电池的电化学性能。

Description

一种多孔隔膜、其制备方法及电化学装置
优先权信息
本公开请求于2022年7月4日向中国国家知识产权局提交的、专利申请号为202210776179.4、申请名称为“一种多孔隔膜、其制备方法及电化学装置”的中国专利申请的优先权，并且其全部内容通过引用结合在本公开中。
技术领域
本发明涉及电化学装置用隔膜，具体而言，涉及一种多孔隔膜、其制备方法及具有该多孔隔膜的电化学装置。
背景技术
隔膜是具有多孔结构的电绝缘性薄膜，其是二次电池的重要组成部分，主要用来隔开正极片和负极片，防止二次电池内部短路。传统的隔膜主要采用聚烯烃多孔膜，例如聚乙烯(PE)、聚丙烯(PP)的单层膜或多层复合膜。但是，聚烯烃隔膜的熔点较低，在温度过高时会发生严重热收缩，当二次电池使用过程中内部热积聚时，聚烯烃隔膜容易变形使正极片和负极片直接接触，引发二次电池内部短路，存在引起火灾或者爆炸等安全隐患。
为了提高聚烯烃隔膜的耐温性，目前市场主要使用陶瓷涂布于聚烯烃基膜表面来实现，赋予隔膜高耐热功能，降低隔膜的热收缩率，从而更有效地减少锂离子电池内部短路，防止因电池内部短路而引起的电池热失控。但是单纯的陶瓷涂覆，容易导致隔膜与电极之间的粘合性不足。因此在此基础上，引入有机涂层，进一步提升与电极之间的粘合性，较为成熟是使 用PVDF类物质作为有机涂层。
但是当形成基膜-无机涂层-有机涂层进行多层复合时，又带来了新的问题：由于制备方法的限制，有机涂层的表面孔隙率过低，即有机涂层表面会部分阻挡基材孔道，导致隔膜整体表面的孔径、孔隙率降低，虽然这种结构有利于提升隔膜与电极之间的粘合性，提高隔膜对电解液的浸润性和保液率，但同时也会降低隔膜整体透气性能，使得离子通道减少，阻碍锂离子迁移，增加电池内阻，影响电池倍率和低温性能。
公开号为CN104508864B的中国专利从粘结性多孔层涂布量偏差的角度考虑，认为粘接性多孔层的涂布量产生偏差，则与电极的粘接性也容易产生偏差，通过设置单位面积重量的标准偏差在一定的范围内，能够同时实现确保充分的粘接性和离子透过性，但是该方法只是从整体上体现涂层涂覆的均一性，有一定的效果，但实际生产过程中对于两个问题解决的影响有限。
因此，亟需一种方法能够使得隔膜的正极粘合性、保液率及透气性均得以充分发挥。鉴于此，特提出本发明。
发明内容
鉴于背景技术中存在的问题，本发明的目的在于提供一种多孔隔膜、其制备方法及电化学装置，该多孔隔膜兼具优良的正极粘合性、保液性、透气性及离子传导性，有利于提升锂电池的使用性能。
本发明是这样实现的：
本发明提供一种多孔隔膜，至少包括基膜层和位于所述基膜层一侧的有机多孔涂层，所述有机多孔涂层的孔隙率为20％～80％，所述有机多孔涂层远离基膜层的表面孔面积占比为10％～70％；
需要说明的是，所述有机多孔涂层的内部是指有机多孔涂层中与表面距离为有机多孔涂层总厚度的10％以上的部分，其内部孔与所述有机多孔 涂层表面的距离为有机多孔涂层总厚度的10％以上。而文中所提到的表面孔是指该表面上的平面孔，所述有机多孔涂层的表面孔是指其一侧表面上的平面孔，所述基膜层的表面孔是指基膜层一侧表面上的平面孔。
在其中一个具体实施方案中，所述有机多孔涂层的内部孔的平均孔径为0.01～2.0μm，所述有机多孔涂层远离基膜层的表面孔的平均孔径为0.01～2.0μm，所述有机多孔涂层远离基膜层的表面孔的平均孔径与内部孔的平均孔径的比值为1:5～2:1。
在其中一个具体实施方案中，所述有机多孔涂层内部孔的孔径分布为1.0～3.0，所述有机多孔涂层远离基膜层的表面孔的孔径分布为1.0～3.0。
在其中一个具体实施方案中，所述基膜层靠近有机多孔涂层的表面孔面积占比为5％～60％，所述基膜层靠近有机多孔涂层的表面孔面积占比与有机多孔涂层远离基膜层表面孔面积占比的比值为0.3～1.5。
在其中一个具体实施方案中，所述基膜层的孔隙率为20％～60％，所述基膜层靠近有机多孔涂层的表面孔的孔径分布为1.0～3.0。
在其中一个具体实施方案中，所述多孔隔膜的Gurley值为100～300s/100cc。
在其中一个具体实施方案中，所述多孔隔膜的保液率为50％～95％。
在其中一个具体实施方案中，所述多孔隔膜的粘结强度为3～20N/m。
在其中一个具体实施方案中，所述有机多孔涂层为选自含氟乙烯聚合物的树脂形成的有机多孔涂层，所述含氟乙烯聚合物的树脂包括偏二氟乙烯均聚物、偏二氟乙烯与其它可共聚单体的共聚物、或其混合物，与偏二氟乙烯共聚的单体包括选自如下中的至少一种：四氟乙烯、六氟丙烯、三氟乙烯、氯氟乙烯、1,2-二氟乙烯、全氟甲基乙烯基醚、全氟乙基乙烯基醚、全氟丙基乙烯基醚、二氟苯并-1,3-间二氧杂环戊烯、全氟-2,2-二甲基-1,3-二氧杂环戊烯以及三氯乙烯。
在其中一个具体实施方案中，所述有机多孔涂层为单层或多层，单层 厚度为0.3～2μm，所述基膜层的厚度为2～14μm。
在其中一个具体实施方案中，所述的多孔隔膜还包括位于基膜层与有机多孔涂层之间的含有陶瓷颗粒的无机层，所述无机层主要由陶瓷颗粒堆叠而成，所述陶瓷颗粒的平均粒径为0.2～1.0μm，所述陶瓷颗粒为氧化铝、勃姆石、碳酸钙、水滑石、蒙脱土、二氧化钛、二氧化硅、二氧化锆、氧化镁、氢氧化镁、氮化硼、氮化硅、氮化铝、氮化钛、碳化硼、碳化硅、碳化锆中的一种或几种。
本发明还提供了一种所述多孔隔膜的制备方法，具体步骤为：
步骤1、有机多孔涂层胶液的制备：将含氟乙烯聚合物的树脂、非氟树脂粘合剂分散至有机溶剂中，形成有机多孔涂层胶液，其中有机溶剂选自N,N’-二甲基甲酰胺、N-甲基吡咯烷酮、丙酮、N,N’-二甲基乙酰胺中的一种或多种，整个有机多孔涂层胶液的含水率低于5wt％；
步骤2、提供基膜层，将步骤1制备的有机多孔涂层胶液涂覆在基膜层的一面或两面上，在空气湿度为20％～80％条件下处理0.2～15s，然后浸渍在室温凝固浴中使其凝固，形成多孔凝胶的有机多孔涂层，进行清洗、烘干，得到多孔隔膜。
在其中一个具体实施方案中，含氟乙烯聚合物的树脂在有机多孔涂层胶液中的质量占比为1wt％～10wt％，优选3wt％～6wt％。
在其中一个具体实施方案中，凝固浴中水含量为40wt％～70wt％。
本发明还提供了一种电化学装置，包含正极、负极、非水电解液和以上所述的多孔隔膜。
本发明的有益效果：
根据本发明得到的有机/无机复合层多孔隔膜，具有优异的电极和层间粘结性能、高温尺寸稳定性以及良好的透气性，使得最终形成的锂电池能量密度高，循环性能优异，进而解决了现有技术中隔膜的粘接强度和离子传导性无法兼顾的技术问题。
附图说明
为了更清楚地说明本发明实施例的技术方案，下面将对实施例中所需要使用的附图作简单地介绍，应当理解，以下附图仅示出了本发明的某些实施例，因此不应被看作是对范围的限定，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其他相关的附图。
图1为本发明多孔隔膜的结构示意图；
图2为实施例2多孔隔膜中有机多孔涂层远离基膜层的表面SEM图；
图3为实施例2多孔隔膜中有机多孔涂层的断面SEM图；
图4为实施例2多孔隔膜中涂覆用基膜的表面SEM图；
图5为实施例2多孔隔膜中涂覆用基膜的断面SEM图；
图标：1-基膜层，2-含有陶瓷颗粒的无机层，3-有机多孔涂层。
具体实施方式
为了更好地解释本发明，参照本发明的实施方式详细地说明，并结合具体实施例进一步阐明本发明的主要内容，但本发明的内容不仅仅局限于以下实施例。实施例中未注明具体技术或条件的，按照本领域内的文献所描述的技术或条件或者按照产品说明书进行。所用试剂或仪器未注明生产厂商者，均为可以通过市购获得的常规产品。
发明人经大量研究发现，当有机多孔涂层远离基膜层的表面孔相比于内部孔的孔径缩小或相近时，可以提高多孔隔膜的正极粘结性以及对电解液的浸润性和保液率，在此基础上，通过控制有机多孔涂层表面孔孔面积占比及与基膜层表面孔面积占比的比例，便可以同时获得理想的正极粘结性、浸润性以及离子传导性能。
其中，所述有机多孔涂层的表面孔是指暴露在外部的远离基膜层的表面，所述有机多孔涂层表面孔的孔面积占比是指有机多孔涂层所有表面孔 的面积之和占其所在表面的比例。
进一步地，对于有机多孔涂层表面孔孔面积占比的设置，可以基于所述基膜层上表面孔的孔面积占比进行，当有机多孔涂层表面孔与基膜表面孔接近时，能够避免由于膜层孔径突然缩小而导致电解液在隔膜内部堆积，从而避免进一步引起局部电芯的循环性能和动力学性能变差。
本发明的多孔隔膜还可以包括位于基膜层与有机多孔涂层之间的含有陶瓷颗粒的无机层，该无机层主要由陶瓷颗粒堆叠而成，内部所形成孔的孔径较大，因此对于多孔隔膜的离子传导性能不会产生较大的影响，至于该无机层与有机多孔涂层之间的粘结性能和界面处的离子传导性能，可以通过控制有机涂层对无机层的渗透深度和渗透比重来获得理想的结果。
[基膜层]
作为基膜，通常为聚烯烃多孔基膜，可以从以往的适用于锂电池隔膜的聚烯烃多孔基膜中进行选择，包括选自聚乙烯、聚丙烯、聚丁烯、聚4-甲基戊烯中的一种或多种共聚物或多种共混物。
从呈现关闭功能的观点考虑，聚烯烃微多孔膜优选包含聚乙烯，优选聚乙烯的含量为基膜总含量的95质量％以上。
在其中一种实施方案中，聚烯烃多孔基膜为单层聚烯烃微多孔膜，在另一种实施方案中，聚烯烃多孔基膜为具有2层或以上层叠结构的聚烯烃微多孔膜。
聚烯烃多孔基膜中包含的聚烯烃优选重均分子量(Mw)为10万～500万，进一步优选为20万～200万，更进一步优选为30万～100万。重均分子量为10万以上时，能够确保充分的力学物性。另一方面，重均分子量为500万以下时，关闭特性良好，并且容易成膜。
对聚烯烃多孔基膜的厚度没有特别限定，优选为5～30μm，进一步优选为8～20μm。多孔基膜的厚度影响了隔膜的透气性以及机械强度。
对根据本发明的示例性实施方案的聚烯烃多孔基膜的制造方法没有限 制，只要聚烯烃多孔基膜由本领域技术人员制造即可，在示例性的实施方案中，聚烯烃多孔基膜可以通过干法或湿法来制造。干法是通过形成聚烯烃膜、然后在低温下拉伸该膜而形成微孔的方法，所述拉伸导致作为聚烯烃的结晶部分的薄片之间的微裂纹。湿法是将聚烯烃基树脂和稀释剂在聚烯烃基树脂熔融形成单相的高温下进行混炼、聚烯烃和稀释剂在冷却过程中进行相分离、然后稀释剂被提取以在其中形成孔隙的方法。湿法是在相分离处理后通过拉伸/提取工艺赋予机械强度和透明性的方法。因为与干法相比，湿法的膜厚度薄，孔径均匀，物理性能优异，所以更优选湿法。
从获得适当的膜电阻、关闭功能的观点考虑，多孔基膜的孔隙率优选为20％～60％，平均孔径为15～100nm。进一步优选孔隙率为30％～50％，平均孔径为20～80nm。
从提高制造成品率的观点考虑，聚烯烃多孔基膜的穿刺强度优选为200gf以上。
[无机层]
本发明中，无机层是指含有陶瓷颗粒的无机层，位于基膜的至少一个表面，含有陶瓷颗粒的无机层由陶瓷颗粒堆叠形成具有一定空隙的膜层，通过形成无机层，赋予复合隔膜耐热性并抑制高温热收缩。所述的陶瓷颗粒，选择相对于电解液稳定、电化学稳定的任何陶瓷颗粒，具体包括但不限于下述材料中的一种或多种：氧化铝、勃姆石、碳酸钙、水滑石、蒙脱土、二氧化钛、二氧化硅、二氧化锆、氧化镁、氢氧化镁、氮化硼、氮化硅、氮化铝、氮化钛、碳化硼、碳化硅、碳化锆，其中优选为氧化铝或勃姆石。
陶瓷颗粒可以具有球状、针状、板状、纺锤状等形态的颗粒，优选为板状陶瓷颗粒，一方面陶瓷颗粒不容易从无机层中整体脱嵌出来，另一方面可以增加正极和负极之间的路径，对起到抑制枝晶短路具有良好的效果。陶瓷颗粒的平均粒径为0.2～1.0μm，优选为0.3～0.8μm，粒度均一度 ((D90-D10)/D50)为3.0～10.0，优选为4.0～8.0。通过对形状、粒径和粒度均一度选择，无机层的孔隙率与孔径大小也得到确定，便于有机多孔涂层的渗透。
无机层的厚度为0.2～4μm，优选为0.5～2μm，从能量密度和离子传导性的角度考虑，无机层厚度希望越薄越好，而从耐热以及抑制热收缩效果的角度考虑，则需要有一定的厚度。
为了提升陶瓷颗粒堆叠的粘结性，无机层中还含有非氟树脂粘合剂，所述非氟树脂粘合剂包括选自聚酰胺、聚丙烯腈、丙烯酸类树脂、醋酸乙烯酯～乙烯共聚物、羧甲基纤维素纳、芳纶、聚乙烯基丁醛、聚乙烯呲咯烷酮、环氧树脂、硅氧烷类、改性聚烯烃、聚氨酯、聚乙烯醇、聚乙烯醚和丁苯橡胶中的一种或多种；其中优选丙烯酸酯类树脂，非氟树脂粘合剂的用量为含有陶瓷颗粒的无机层总重量的1～8wt％。如果非氟树脂粘合剂的用量过高，则会影响陶瓷颗粒在无机层中耐热以及防止热收缩的效果，如果用量过少，则无机层中陶瓷颗粒固定不牢，容易出现滑移或脱嵌。
为了得到多孔凝胶层，优选地，先配置可涂覆的陶瓷颗粒浆料，将羧甲基纤维素钠、无机陶瓷、分散剂、润湿剂、丙烯酸酯类粘接剂、润湿剂及去离子水按照一定的加料顺序配置形成的陶瓷颗粒浆料。
[制备无机层]
将陶瓷颗粒浆料涂覆在聚合物基膜至少一个表面上，优选首先利用浸涂法、气刀涂布法、幕涂法、辊式涂布法、线棒涂布法、照相凹板式涂布法、或模具涂布法等方式。在这些涂布方式中，优选凹板式涂布法或模具涂布法作为上述涂布液的涂布方法。
然后，对涂覆陶瓷颗粒浆料的锂电池隔膜进行干燥。对于干燥条件，只要基膜不因软化而产生收缩，风速及干燥温度就没有特别地限制。作为干燥方法，可以列举传热干燥(对高热物体的粘合)、对流传热(热风)、辐射传热(红外线)、及其他(微波、感应加热等)的方式。其中，在上 述制造方法中，由于需要使宽度方向具有精密而均匀的干燥速度，因此优选使用对流传热或辐射传热的方式。另外，在恒率干燥期间，为了在宽度方向实现均匀的干燥速度，在采用对流传热干燥方式的情况下，优选使用在维持可控风速的同时，可以降低干燥时的总物质移动系数的方法。具体来说，使用沿与支撑基膜平行、与基膜的输送方向平行、或垂直的方向输送热风的方式即可。烘干温度优选控制在60～100℃，优选为70～90℃，更优选75～85℃。
[有机多孔涂层]
本发明中，有机多孔涂层部分或者全部涂覆在无机层远离基膜层的另一表面上，如果无机层只涂覆了基膜一个表面，有机多孔涂层也可以部分或者全部涂覆在未被无机层涂覆的基膜表面。所述有机多孔涂层为选自含氟乙烯聚合物的树脂形成的有机多孔涂层，所述含氟乙烯聚合物的树脂包括偏二氟乙烯均聚物、偏二氟乙烯与其它可共聚单体的共聚物、或其混合物，与偏二氟乙烯共聚的单体包括选自如下中的至少一种：四氟乙烯、六氟丙烯、三氟乙烯、氯氟乙烯、1,2-二氟乙烯、全氟甲基乙烯基醚、全氟乙基乙烯基醚、全氟丙基乙烯基醚、二氟苯并-1,3-间二氧杂环戊烯、全氟-2,2-二甲基-1,3-二氧杂环戊烯、三氯乙烯和氟乙烯，优选为偏二氟乙烯均聚物，或偏二氟乙烯与六氟丙烯的共聚物。
在有机多孔涂层中，含氟乙烯聚合物的树脂以90wt％以上，或95wt％以上，或99wt％以上的含量存在，重均分子量选择为60,000～1,000,000，优选为100,000～700,000。
本发明通过对有机多孔涂层表面孔及内部孔研究，有机多孔涂层远离基膜的涂层表面对于与电极的粘合性以及离子传导性也发挥着至关重要的作用，发明人发现有机多孔涂层远离基膜的表面孔面积在表面的占比限定在合理的范围时，可以同时获得理想的正极粘结性、浸润性以及离子传导性能。而对于有机多孔涂层表面孔孔面积占比的设置，可以基于所述基膜 层上表面孔的孔面积占比进行。
具体而言，表面孔面积占比为10％～70％，如10％、12％、15％、16％、18％、20％、25％、30％、35％、40％、45％、50％、55％、60％、65％、70％，但不限于此，进一步优选为10％～60％，进一步优选为15％～50％，进一步优选为20％～40％，如果表面孔面积占比过小，则透气性差离子传导性不佳，而如果表面孔面积占比过高，则与电极的粘结性下降，并且由于界面过于不平整带来安全性的问题，这里表面孔面积在表面的占比的定义是指有机多孔涂层远离基膜的表面所有孔的面积之和与该涂层总面积的比值。
在本发明的体系下，并且在其中一个技术方案中，限定有机多孔涂层表面平均孔径为0.01～2.0μm，有机多孔涂层孔隙率为20％～80％，进一步优选有机多孔涂层表面平均孔径为0.03～1.0μm，有机多孔涂层孔隙率为40％～70％，这两个指标也是从单孔横截面积的角度，以及孔的数量的角度，对有机多孔涂层中孔结构进行限定，在所述范围内，有机多孔涂层的机械强度、对电极粘合力的影响以及离子传导性效果能够得到进一步优化。
考虑到孔径均匀有利于提高隔膜的机械性能和锂离子在隔膜中的传导。本发明中，所述有机多孔涂层的孔直径在0.01～2.0μm范围内的孔径均一，孔径分布优选小于3.0，更优选小于2.0，进一步优选小于1.5。
对于有机多孔涂层孔径尤其是表面孔结构的控制，与其原材料和制备工艺有密切的关系，例如有机多孔涂层胶液中树脂的种类，固含量，胶液自然挥发的时长以及凝固浴的种类及凝胶过程均会对有机多孔涂层孔结构尤其是表面孔结构存在影响，例如单因素下胶液挥发的时间越长，有机多孔涂层表面平均孔径以及表面孔面积占比就会越高，本领域技术人员能够根据目标范围通过对这些影响因素进行调控而实现对有机多孔涂层孔径尤其是表面孔结构的控制。
对于无机涂层，由于其所靠近的有机多孔涂层是部分或全部涂覆在该无机涂层远离基膜层的另一表面上，因此含有陶瓷颗粒的无机层存在空隙 可以被有机多孔涂层渗透，这里对于含有陶瓷颗粒的无机层，通过单位面积重量增值体现其渗透的重量，单位面积重量增值用以下公式计算得出：
其中，Δmk为有机/无机复合层多孔隔膜样品k无机层单位面积重量增值，m1为有机/无机复合层多孔隔膜样品1的面密度，mk为有机/无机复合层多孔隔膜样品k的面密度，h1为有机/无机复合层多孔隔膜样品1有机多孔涂层的厚度，hk为有机/无机复合层多孔隔膜样品k有机多孔涂层的厚度，n为样品总数，且n≥2。实际上反映的是，经n个样品多次测试后，有机多孔涂层在无机层以上未渗透部分的平均单位厚度面密度，n越大则越接近于理想值。
基于该式子，当无机层的单位面积重量增值Δm为0.2～0.6g/m2时，表明无机层中有机多孔涂层的渗透量在理想范围内，在该范围内有机多孔涂层对无机层有较好的粘结作用，同时也不影响离子传导的效率，透气性得以兼顾，进一步优选为0.3～0.5g/m2。
[有机多孔涂层胶液]
为了得到多孔凝胶层，需先配置可涂覆的有机多孔涂层胶液，将含氟乙烯聚合物的树脂、非氟树脂粘合剂、有机良溶剂配置形成可涂覆胶液。作为有机良溶剂，选自N,N’-二甲基甲酰胺、N-甲基吡咯烷酮、丙酮、N,N’-二甲基乙酰胺中的一种或多种。有机多孔涂层胶液中水作为相分离不良溶剂并非必须的，事实上在有机多孔涂层胶液中水含量优选在5wt％以下。
从形成良好的多孔结构的观点考虑，有机良溶剂在混合浆料中的含量优选为50wt％～95wt％，进一步优选为65wt％～85wt％。而含氟乙烯聚合物 的树脂在有机多孔涂层胶液中的质量占比为1wt％～10wt％，进一步优选为2wt％～8wt％。
[制备多孔凝胶层]
将有机多孔涂层胶液涂覆在含有陶瓷颗粒的无机层和/或聚合物基膜至少一个表面上，优选首先利用浸涂法、气刀涂布法、幕涂法、辊式涂布法、线棒涂布法、照相凹板式涂布法、或模具涂布法等方式，将有机多孔涂层胶液涂布在上述含有陶瓷颗粒的无机层和/或聚合物基膜的表面上，形成涂膜的方法。在这些涂布方式中，优选照相凹板式涂布法或模具涂布法作为上述涂布液的涂布方法。
用能够使上述有机多孔涂层胶液凝固的凝固液处理涂布有混合浆料的基膜。由此，使有机多孔涂层胶液凝固，形成多孔凝胶层。作为用凝固液处理的方法，可以举出对于涂布了有机多孔涂层胶液的基膜利用喷雾喷上凝固液的方法、将该基膜浸渍在加入了凝固液的浴(凝固浴)中的方法等。作为凝固液，没有特别限制，只要为能够将有机多孔涂层胶液凝固的液体即可，优选水、或有机多孔涂层胶液所使用的溶剂中混合适当量的水所得的溶液。其中在凝固浴中水含量为30wt％～70wt％，优选为40wt％～70wt％，或优选为35wt％～65wt％，进一步优选40wt％～60wt％。凝固浴温度为常温。
然后，对经过凝固浴的包含多孔凝胶层的锂电池隔膜进行干燥。对于干燥条件，只要基膜不因软化而产生收缩，有机多孔涂层和无机层之间能够进行可控渗透并且粘结，风速及干燥温度就没有特别地限制。作为干燥方法，可以列举传热干燥(对高热物体的粘合)、对流传热(热风)、辐射传热(红外线)、及其他(微波、感应加热等)的方式。其中，在上述制造方法中，由于需要使宽度方向具有精密而均匀的干燥速度，因此优选使用对流传热或辐射传热的方式。另外，在恒率干燥期间，为了在宽度方向实现均匀的干燥速度，在采用对流传热干燥方式的情况下，优选使用在维持可控风速的同时，可以降低干燥时的总物质移动系数的方法。具体来 说，使用沿与支撑基膜平行、与基膜的输送方向平行、或垂直的方向输送热风的方式即可。烘干温度优选控制在60～100℃，优选为70～90℃，更优选75～85℃。
图1为根据所述方法制备得到的其中一种有机无机复合层多孔隔膜整体层叠示意图，其中基膜层1两侧均为含有陶瓷颗粒的无机层2，在含有陶瓷颗粒的无机层2的另一侧为有机多孔涂层3，并且有机多孔涂层3部分渗透在含有陶瓷颗粒的无机层2中。
[锂电池]
本发明的锂电池具有正极、负极、电解液和配置于正极和负极之间的本发明所述的隔膜，具体将电池元件、电解液一同封入到外部封装材料内而成的结构，所述电池元件是使负极和正极隔着隔膜对置而得到。
正极例如是含有正极活性物质及粘结剂树脂的活性物质层被成型在集电体上而得到的结构。
作为正极活性物质，可举例为本领域常用的正极活性材料，如含锂的过渡金属氧化物等，具体而言，可举出LiCoO2、LiNiO2、LiMn1/2Ni1/2O2、LiCo1/3Mn1/3Ni1/3O2、LiMn2O4、LiFePO4、LiCO1/2Ni1/2O2、LiAl1/4Ni3/4O2等。作为粘结剂树脂，可举例如聚偏二氟乙烯系树脂、苯乙烯-丁二烯共聚物等。也可以含有导电助剂，可举例如乙炔黑、科琴黑、石墨粉末等碳材料。作为集电体，可列举例如厚度为5μm～20μm的铝箔、钛箔、不锈钢箔等。
作为负极的实施方式例，可列举包含负极活性物质和粘结剂树脂的活性物质层被成型于集电体上而成的结构。活性物质层可进一步包含导电助剂。作为负极活性物质，可列举能以电化学方式吸藏锂的材料，具体而言，可列举例如：碳材料；硅、锡、铝等与锂的合金；伍德合金(Wood's alloy)；等等。粘结剂树脂、导电助剂和集电体与正极部分大体相同。另外，也可以代替上述负极而使用金属锂箔作为负极。
电解液是将锂盐溶解于非水系溶剂中而得到的溶液。作为电解液的实 施方式例，可以是本领域常见的电解液体系。作为锂盐，可列举例如LiPF6、LiBF4、LiClO4等。作为非水系溶剂，可列举例如碳酸亚乙酯、碳酸亚丙酯、氟代碳酸亚乙酯、二氟代碳酸亚乙酯、碳酸亚乙烯酯等环状碳酸酯；碳酸二甲酯、碳酸二乙酯、碳酸甲乙酯、碳酸乙烯酯及它们的氟取代物等链状碳酸酯；γ-丁内酯、γ-戊内酯等环状酯等，它们可单独使用，也可混合使用。
实施例
以下，通过实施例更具体地说明本发明所述的隔膜及包含隔膜的锂二次电池。但是本发明的实施方式不限于以下的实施例。
实施例1～8及对比例1～4中制备含有陶瓷颗粒的无机层所使用的陶瓷颗粒浆料均由以下方法制得：基于100重量份可涂覆浆料，将0.41重量份羧甲基纤维素钠加入11.92重量份去离子水中，混合搅拌均匀获得浆料A；将31.80重量份D50为0.5μm的氧化铝，其中(D90-D10)/D50为5，和0.16重量份分散剂加入50.87重量份水中，混合搅拌均匀获得浆料B；A、B两种浆料混合后经高速分散或球磨配制成浆料C；在浆料C中添加4.77重量份粘合剂和0.06重量份润湿剂，配制成陶瓷颗粒浆料。
实施例1
1)PVDF涂覆胶液的制备：基于100重量份可涂覆浆料，将5重量份重均分子量为40～80万的PVDF树脂(购自阿珂玛)分散到95份的二甲基乙酰胺中，在50℃下溶解约3小时形成PVDF涂覆胶液。
2)含陶瓷颗粒的无机层制备：使用微凹版涂覆将陶瓷颗粒浆料涂布在5μm基膜一侧表面，烘干后形成无机层，获得陶瓷膜即传统的动力锂离子电池隔膜(厚度7μm，穿刺强度350gf)，无机层单层厚度2.0μm。
3)复合隔膜的制备：在23℃和20％相对湿度的条件下，通过凹版辊将步骤1)制得的PVDF涂覆胶液分别涂覆在陶瓷膜的两侧，涂覆后的胶液中溶剂在空气中自然挥发0.3s，经二甲基乙酰胺/水凝固液凝固(凝固浴中DMAC/水＝4:6)、纯水清洗，80℃烘干，形成多孔凝胶层，得到复合隔膜， 多孔凝胶层的涂层厚度为1.0μm。
实施例2
除涂覆后的PVDF涂覆胶液中溶剂在空气中自然挥发1s外，其他步骤与实施例1相同。
实施例3
除涂覆后的PVDF涂覆胶液中溶剂在空气中自然挥发5s外，其他步骤与实施例1相同。
实施例4
除涂覆后的PVDF涂覆胶液中溶剂在空气中自然挥发15s外，其他步骤与实施例1相同。
实施例5
1)PVDF涂覆胶液的制备：基于100重量份可涂覆浆料，将3重量份重均分子量为40～80万的PVDF树脂分散到97份的二甲基乙酰胺中，在50℃下溶解约3小时形成PVDF涂覆胶液。
2)含陶瓷颗粒的无机层制备：使用微凹版涂覆将陶瓷颗粒浆料涂布在7μm基膜一侧表面，烘干后形成无机层，获得陶瓷膜即传统的动力锂离子电池隔膜(厚度9μm，穿刺强度380gf)，无机层单层厚度2.0μm。
3)复合隔膜的制备：在23℃和20％相对湿度的条件下，通过凹版辊将步骤1)制得的PVDF涂覆胶液分别涂覆在陶瓷膜的两侧，涂覆后的胶液中溶剂在空气中自然挥发1s，经二甲基乙酰胺/水凝固液凝固(凝固浴中DMAC/水＝4:6)、纯水清洗，80℃烘干，形成多孔凝胶层，得到复合隔膜，多孔凝胶层的涂层厚度为1.2μm。
实施例6
1)PVDF涂覆胶液的制备：基于100重量份可涂覆浆料，将4重量份重均分子量为40～80万的PVDF树脂分散到96份的二甲基乙酰胺中，在50℃下溶解约3小时形成PVDF涂覆胶液。
2)含陶瓷颗粒的无机层制备：使用微凹版涂覆将陶瓷颗粒浆料涂布在7μm基膜一侧表面，烘干后形成无机层，获得陶瓷膜即传统的动力锂离子电池隔膜(厚度9μm，穿刺强度380gf)，无机层单层厚度2.0μm。
3)复合隔膜的制备：在23℃和20％相对湿度的条件下，通过凹版辊将步骤1)制得的PVDF涂覆胶液分别涂覆在陶瓷膜的两侧，涂覆后的胶液中溶剂在空气中自然挥发1s，经二甲基乙酰胺/水凝固液凝固(凝固浴中DMAC/水＝4:6)、纯水清洗，80℃烘干，形成多孔凝胶层，得到复合隔膜，多孔凝胶层的涂层厚度为1.2μm。
实施例7
1)PVDF涂覆胶液的制备：基于100重量份可涂覆浆料，将6重量份重均分子量为40～80万的PVDF树脂分散到94份的二甲基乙酰胺中，在50℃下溶解约3小时形成PVDF涂覆胶液。
2)含陶瓷颗粒的无机层制备：使用微凹版涂覆将陶瓷颗粒浆料涂布在7μm基膜一侧表面，烘干后形成无机层，获得陶瓷膜即传统的动力锂离子电池隔膜(厚度9μm，穿刺强度380gf)，无机层单层厚度2.0μm。
3)复合隔膜的制备：在23℃和20％相对湿度的条件下，通过凹版辊将步骤1)制得的PVDF涂覆胶液分别涂覆在陶瓷膜的两侧，涂覆后的胶液中溶剂在空气中自然挥发1s，经二甲基乙酰胺/水凝固液凝固(凝固浴中DMAC/水＝4:6)、纯水清洗，80℃烘干，形成多孔凝胶层，得到复合隔膜，多孔凝胶层的涂层厚度为1.2μm。
实施例8
除复合隔膜制备过程中所用凝固浴的组成更换为DMAC/水＝6：4外，其他步骤与实施例7相同。
对比例1
除涂覆后的PVDF涂覆胶液中溶剂在空气中自然挥发30s外，其他步骤与实施例1相同。
对比例2
1)PVDF涂覆胶液的制备：基于100重量份可涂覆浆料，将7重量份重均分子量为40～80万的PVDF树脂分散到93份的二甲基乙酰胺中，在50℃下溶解约3小时形成PVDF涂覆胶液。
2)含陶瓷颗粒的无机层制备：使用微凹版涂覆将陶瓷颗粒浆料涂布在7μm基膜一侧表面，烘干后形成无机层，获得陶瓷膜即传统的动力锂离子电池隔膜(厚度9μm，穿刺强度380gf)，无机层单层厚度2.0μm。
3)复合隔膜的制备：在23℃和20％相对湿度的条件下，通过凹版辊将步骤1)制得的PVDF涂覆胶液分别涂覆在陶瓷膜的两侧，涂覆后的胶液中溶剂在空气中自然挥发1s，经二甲基乙酰胺/水凝固液凝固(凝固浴中DMAC/水＝4:6)、纯水清洗，80℃烘干，形成多孔凝胶层，得到复合隔膜，多孔凝胶层的涂层厚度为1.2μm。
对比例3
除复合隔膜制备过程中所用凝固浴的组成更换为DMAC/水＝2：8外，其他步骤与实施例7相同。
对比例4
除复合隔膜制备过程中所用凝固浴的组成更换为DMAC/水＝8：2外，其他步骤与实施例7相同。
<评价方法>
(1)膜厚
先采用万分尺测试隔离基膜的厚度，然后再测试涂布之后的厚度，除去隔离基膜的厚度即为多孔涂层厚度。
(2)平均粒径
使用粒径测定装置(日机装株式会社制、MicrotracUPA150)来测定。作为测定条件，设为负荷指标＝0.15～0.3、测定时间300秒，将所得到的数据中的50％粒径的数值记作平均粒径。
(3)表面孔形貌评价
孔径d：用扫描电子显微镜(SEM)对薄膜表面进行观察，随机拍摄不同位置放大倍率10000倍的照片5张，用笔勾出孔洞轮廓后，用图像处理软件计算各表面孔的面积S，再按式(1)计算各孔的孔径d(等价直径，与孔面积相等的圆的直径)：
平均孔径dn：按式(2)计算所测各孔的孔径平均值，
其中，∑d为孔的孔径d的加和。
孔径分布SD：先按式(3-1)计算体积平均孔径dv，再按式(3-2)计算孔径分布SD，

其中，∑d4为孔的孔径d的4次方的加和；∑d3为孔的孔径d的3次方的加和。
孔面积占比S％：表面孔的面积占总表面积的百分比。具体按式(5)计算：
其中，∑Sm为上述SEM观测面积之和。
(4)内部孔形貌评价
使用钻石刀或离子抛光等手段制备出平整的截面，用SEM对该断面进行观察：
孔径d：按前述表面孔径的统计和计算方法，计算内部孔的孔径。
平均孔径dn：按式(2)计算孔的孔径平均值。
孔径分布SD：先按式(3-1)计算体积平均孔径dv，再按式(3-2)计算孔径分布SD。
(5)有机多孔涂层树脂重均分子量测定
将树脂以1.0mg/ml的浓度溶解在DMF中，得到试样液，使用50ml该试样液，在以下条件下进行GPC测定，求出其重均分子量(PMMA换算)。
装置：HLC-8220GPC(东曹株式会社)
柱：Shodex KF-606，KF-601
移动相：0.6ml/min DMF
检测器：示差折光检测器
(6)Gurley透气值
裁取100mm×100mm的设有多孔膜的隔离膜样品，利用美国Gurley4110N透气度测试仪，使用100cc的测试气体模式进行测试，记录测试气体全部通过设有多孔膜的隔离膜样品的时间，即为Gurley值。多孔膜的Gurley值为设有多孔膜的隔离膜的Gurley值减去未设有多孔膜的隔离膜(即纯多孔基材)的Gurley值。
(7)多孔基材与多孔涂层之间的剥离强度
在隔膜的一方的多孔层表面上贴合宽度为12mm、长度为15cm的粘合胶带(Scotch制，型号550R－12)，切割隔膜，使其宽度和长度与粘合胶带的宽度和长度一致，制成测定样品。在将粘合胶带贴合于隔膜时，使长度方向与隔膜的MD方向一致。需要说明的是，粘合胶带是作为用于将一方的多孔层剥离的支持体而使用的。
将测定样品在温度为23±1℃、相对湿度为50±5％的气氛中放置24小时以上，在相同气氛中进行以下的测定。
将粘合胶带与紧邻其下方的多孔层一同剥离10cm左右，使粘合胶带和多孔层的层叠体(1)、与多孔基材和另一方的多孔层的层叠体(2)分离10cm左右。将层叠体(1)的端部固定于TENSILON(Orientec公司制RTC-1210A)的上部夹头，将层叠体(2)的端部固定于TENSILON的下部夹头。使测定样品沿重力方向悬吊，使拉伸角度(层叠体(1)相对于测定样品的角度)成为180°。以20mm/min的拉伸速度对层叠体(1)进行拉伸，测定层叠体(1)从多孔基材剥离时的负荷。以0.4mm的间隔获取从测定开始后10mm至40mm的负荷，将其平均值作为剥离强度。
(8)粘结强度
参考GB/T 2792的要求进行测试。
1)将A4纸和隔膜按照A4纸/隔膜/隔膜/A4纸的顺序叠放在一起，其中隔膜涂层与隔膜涂层相对；
2)将叠放好的A4纸、隔膜进行热塑处理，温度为100℃；
3)将热塑后的隔膜裁切成长200mm、宽25mm的长条形，夹具间距离为(100±5)mm，试验速度为(50±10)mm/min。
(9)孔隙率
基材及多孔隔膜的孔隙率按照下述的计算方法求出：
设定膜的构成材料为a、b、c、…、n，各构成材料的质量为Wa、Wb、Wc、…、Wn(g/cm2)，各构成材料的真密度为ρa、ρb、ρc、…、ρn(g/cm3)，将膜厚记为t(cm)时，孔隙率ε(％)利用下式求出：
ε＝{1-(Wa/ρa+Wb/ρb+Wc/ρc+…+Wn/ρn)/t}×100。
(10)保液率
将得到的多孔隔膜进行保液性能的测试，保液率计算公式如下：
保液率＝(Mt-M)/(M-M0)×100％；
其中，M0为隔膜的干重；M为隔膜吸收饱和电解液后的质量；Mt为将吸收饱和电解液的隔膜在室外放置15小时后的质量。
表1实施例1-8以及对比例1-4中隔膜的制备参数及结构参数
表2实施例1-8以及对比例1-4中隔膜的相关性能参数指标
表1-2为实施例1-8以及对比例1-4所制备多孔隔膜的制备参数、结构 参数及各相关性能指标，由此可见，尽管有诸多影响因素，但通过控制隔膜的制备条件，例如浆料中PVDF含量为3～6％，涂覆后隔膜在空气中暴露时间不高于15s，凝固浴浓度在30～60％之间，使得有机多孔涂层的孔隙率为20％～80％，有机多孔涂层远离基膜层的表面孔面积占比为10％～70％，有机多孔涂层的内部孔的平均孔径为0.01～2.0μm，有机多孔涂层远离基膜层的表面孔的平均孔径为0.01～2.0μm，有机多孔涂层远离基膜层的表面孔的平均孔径与内部孔的平均孔径的比值为1:5～2:1时，复层合多孔隔膜具有更为优异的综合性能表现，兼具良好的正极粘结性能、高的层间剥离强度、良好的透气性以及保液能力，进而在相应锂电池的电性能方面有良好的体现。当以上参数不在该范围内时，至少上述性能中的一种无法满足实际需求。
以上所述仅为本发明的优选实施例而已，并不用于限制本发明，对于本领域的技术人员来说，本发明可以有各种更改和变化。凡在本发明的精神和原则之内，所作的任何修改、等同替换、改进等，均应包含在本发明的保护范围之内。

Claims (14)

  1. 一种多孔隔膜，至少包括基膜层和位于所述基膜层一侧的有机多孔涂层，其特征在于，所述有机多孔涂层的孔隙率为20％～80％，所述有机多孔涂层远离基膜层的表面孔面积占比为10％～70％；
    所述有机多孔涂层的内部孔与所述有机多孔涂层表面的距离为有机多孔涂层总厚度的10％以上；
    所述有机多孔涂层的内部孔的平均孔径为0.01～2.0μm，所述有机多孔涂层远离基膜层的表面孔的平均孔径为0.01～2.0μm，所述有机多孔涂层远离基膜层的表面孔的平均孔径与内部孔的平均孔径的比值为1:5～2:1。
  2. 根据权利要求1所述的多孔隔膜，其特征在于，所述有机多孔涂层内部孔的孔径分布为1.0～3.0，所述有机多孔涂层远离基膜层的表面孔的孔径分布为1.0～3.0；
    所述孔径分布由以下公式计算得到：
    其中，SD为所测表面的孔径分布，dn为所测表面上所获取孔的平均孔径，dv为所测表面上所获取孔的体积平均孔径，d为所测表面上所获取各孔的孔径，n为在所测表面上所获取孔的数量。
  3. 根据权利要求1所述的多孔隔膜，其特征在于，所述基膜层的孔隙率为20％～60％，所述基膜层靠近有机多孔涂层的表面孔面积占比为5％～60％，所述基膜层靠近有机多孔涂层的表面孔面积占比为有机多孔涂层远离基膜层的表面孔面积占比的0.3～1.5。
  4. 根据权利要求1所述的多孔隔膜，其特征在于，所述基膜层靠近有机多孔涂层的表面孔的孔径分布为1.0～3.0；
    所述孔径分布由以下公式计算得到：
    其中，SD为所测表面的孔径分布，dn为所测表面上所获取孔的平均孔径，dv为所测表面上所获取孔的体积平均孔径，d为所测表面上所获取各孔的孔径，n为在所测表面上所获取孔的数量。
  5. 根据权利要求1所述的多孔隔膜，其特征在于，所述多孔隔膜的Gurley值为100～300s/100cc。
  6. 根据权利要求1所述的多孔隔膜，其特征在于，所述多孔隔膜的保液率为50％～95％。
  7. 根据权利要求1所述的多孔隔膜，其特征在于，所述多孔隔膜的粘结强度为3～20N/m。
  8. 根据权利要求1所述的多孔隔膜，其特征在于，所述有机多孔涂层为选自含氟乙烯聚合物的树脂形成的有机多孔涂层，所述含氟乙烯聚合物的树脂包括偏二氟乙烯均聚物、偏二氟乙烯与其它可共聚单体的共聚物、或其混合物，与偏二氟乙烯共聚的单体包括选自如下中的至少一种：四氟乙烯、六氟丙烯、三氟乙烯、氯氟乙烯、1,2-二氟乙烯、全氟甲基乙烯基醚、全氟乙基乙烯基醚、全氟丙基乙烯基醚、二氟苯并-1,3-间二氧杂环戊烯、全氟-2,2-二甲基-1,3-二氧杂环戊烯以及三氯乙烯。
  9. 根据权利要求1所述的多孔隔膜，其特征在于，所述有机多孔涂层为单层或多层，单层厚度为0.3～2μm，所述基膜层的厚度为2～14μm。
  10. 根据权利要求1所述的多孔隔膜，其特征在于，还包括位于基膜层与有机多孔涂层之间的含有陶瓷颗粒的陶瓷层，所述陶瓷颗粒的平均粒径为0.2～1.0μm，所述陶瓷颗粒为氧化铝、勃姆石、碳酸钙、水滑石、蒙脱土、二氧化钛、二氧化硅、二氧化锆、氧化镁、氢氧化镁、氮化硼、氮化硅、氮化铝、氮化钛、碳化硼、碳化硅、碳化锆中的一种或几种。
  11. 一种权利要求1～10之一所述的多孔隔膜的制备方法，其特征在于，具体步骤为：
    步骤1、有机多孔涂层胶液的制备：将含氟乙烯聚合物的树脂、非氟树脂粘合剂分散至有机溶剂中，形成有机多孔涂层胶液，其中有机溶剂选自N,N’-二甲基甲酰胺、N-甲基吡咯烷酮、丙酮、N,N’-二甲基乙酰胺中的一种或多种，整个有机多孔涂层胶液的含水率低于5wt％；
    步骤2、提供基膜层，将步骤1制备的有机多孔涂层胶液涂覆在基膜层的一面或两面上，在空气湿度为20％～80％条件下处理0.2～15s，然后浸渍在室温凝固浴中使其凝固，形成多孔凝胶的有机多孔涂层，进行清洗、烘干，得到多孔隔膜。
  12. 根据权利要求11所述的制备方法，其特征在于，含氟乙烯聚合物的树脂在有机多孔涂层胶液中的质量占比为1wt％～10wt％。
  13. 根据权利要求11所述的制备方法，其特征在于，凝固浴中水含量为40wt％～70wt％。
  14. 一种电化学装置，其特征在于，包含正极、负极、非水电解液和权利要求1～10之一所述的多孔隔膜或根据权利要求11～13之一所述制备方法得到的多孔隔膜。
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