WO2022122032A1 - 一种锂电池 - Google Patents

一种锂电池 Download PDF

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Publication number
WO2022122032A1
WO2022122032A1 PCT/CN2021/137222 CN2021137222W WO2022122032A1 WO 2022122032 A1 WO2022122032 A1 WO 2022122032A1 CN 2021137222 W CN2021137222 W CN 2021137222W WO 2022122032 A1 WO2022122032 A1 WO 2022122032A1
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Prior art keywords
diaphragm
section
inner layer
layer
separator
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PCT/CN2021/137222
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English (en)
French (fr)
Inventor
赵君义
邹浒
Original Assignee
珠海冠宇电池股份有限公司
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Priority to EP21902737.2A priority Critical patent/EP4160781A1/en
Publication of WO2022122032A1 publication Critical patent/WO2022122032A1/zh
Priority to US18/148,442 priority patent/US20230138917A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/04—Construction or manufacture in general
    • H01M10/0404—Machines for assembling batteries
    • H01M10/0409—Machines for assembling batteries for cells with wound electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or manufacture
    • H01M10/0587—Construction or manufacture of accumulators having only wound construction elements, i.e. wound positive electrodes, wound negative electrodes and wound separators
    • 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
    • H01M50/10—Primary casings; Jackets or wrappings
    • H01M50/102—Primary casings; Jackets or wrappings characterised by their shape or physical structure
    • H01M50/105—Pouches or flexible bags
    • 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
    • H01M50/406—Moulding; Embossing; Cutting
    • 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
    • H01M50/443—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
    • H01M50/446—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
    • 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
    • H01M50/46—Separators, membranes or diaphragms characterised by their combination with electrodes
    • H01M50/461—Separators, membranes or diaphragms characterised by their combination with electrodes with adhesive layers between electrodes and separators
    • 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
    • H01M50/463—Separators, membranes or diaphragms characterised by their shape
    • 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
    • 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 invention belongs to the technical field of lithium ion batteries, and in particular relates to a lithium battery.
  • the lithium battery includes a battery cell and a tab arranged on the battery core.
  • the battery core includes a separator, a positive electrode sheet and a negative electrode sheet.
  • the separator is one of the key materials of the lithium battery and is arranged between the positive and negative electrode sheets of the battery. Isolate the positive and negative plates to prevent short circuit of the battery.
  • the separators used in lithium batteries are generally polyolefin products with a porous structure, such as PE separators, PP separators, and PP/PE/PP three-layer separators.
  • Inorganic particles such as alumina, boehmite, magnesium oxide, etc.
  • glue can be a single PVDF or a mixture of multiple PVDFs
  • the coating method can be water-based coating or oil-based coating.
  • the water-based diaphragm is a finished product obtained by dispersing and grinding a single variety or multiple types of PVDF, dispersant and glue in water to form a suspension, and then coating after filtration.
  • the coating method of the water-based diaphragm can be microgravure roll transfer coating or Coating with high-speed nozzles; oil-based diaphragm is a finished product obtained by dissolving a single variety or multiple types of PVDF in an organic solvent (such as NMP, DMAC, etc.) according to a specific ratio, and then coating after forming a solution.
  • the coating method of oil-based diaphragm It can be microgravure roll transfer coating or dip coating.
  • Figures 1a and 1b are SEM images of both sides of the water-based separator coated by gravure transfer coating.
  • the filling density of the adhesive layer on the separator surface is 0.6g/m 2 -3.0g/m 2
  • the water-based separator Coatings can also be formed on the surface of the substrate separator and ceramic separator by spraying or the like.
  • Figures 2a and 2b are SEM images of both sides of the oil - based separator coated by gravure transfer coating.
  • the packing density of the adhesive layer on the The system separator can also use dip coating to form a coating on the surface of the base separator and ceramic separator.
  • a rolling needle is generally used to clamp the separator, and the separator drives the positive electrode sheet and the negative electrode sheet to rotate together to form a roll core. Since the surface of the separator is coated with a coating, when the separator is in contact with the winding needle, the roughness of the coating on the surface of the separator has an important influence on whether a series of actions of the cell winding process can be successfully completed. It does not match the surface material of the winding needle, and it is easy to cause core pulling or poor spacing between the tabs when winding the battery.
  • Figure 3 is a schematic diagram of core-pulling cores. During the winding process, the innermost diaphragm is in direct contact with the rolling needle.
  • the mirror surface adsorption between the diaphragm and the rolling needle (determined by the surface smoothness of the diaphragm and the Teflon The smoothness of the surface of the dragon leads to the phenomenon that the two are directly adsorbed together) or the large dynamic friction force will cause the diaphragm 100 to be pulled out of the winding core 200, causing the winding core to pull the core.
  • the length of the part other than 200, that is, a represents the core pulling distance of the core, and the unit is generally millimeters.
  • FIG. 4 is a schematic diagram of poor spacing between the tabs.
  • the inner diaphragm may move when the rolling needle is pulled out, thereby causing the position of the two tabs 300 to shift, making the gap between the two tabs 300 larger or smaller.
  • FIG. 4 shows the case where the distance between the two tabs 300 is smaller than the standard distance b (unit millimeter). Core pulling and poor tab spacing will affect the quality of the battery.
  • the purpose of the present invention is to provide a lithium battery, which can reduce the occurrence of production defects such as winding core pulling and unqualified electrode lug spacing, and improve the yield of the lithium battery.
  • a lithium battery comprising a winding core and a pole lug
  • the winding core is formed by superimposing and winding an inner layer diaphragm, a first pole piece, an outer layer diaphragm, and a second pole piece, and the first pole piece and the second pole piece are polar
  • the inner layer membrane is located at the innermost layer of the winding core, and both the inner layer membrane and the outer layer membrane have a clamping section, a first straight section connected with the clamping section and located after the clamping section, The tail fitting section beyond the tail end of the first pole piece, the first straight section is located in front of the first pole piece, the tail fitting section is the end of the diaphragm, the clamping section of the inner layer diaphragm, the first straight section
  • the first straight section of the inner layer diaphragm has a surface friction coefficient of 0.1 ⁇ 0.4.
  • the surface friction coefficient is the first friction coefficient and/or the second friction coefficient determined by the following methods:
  • the surface friction coefficient is the second friction coefficient between the diaphragm and Teflon.
  • both the inner layer diaphragm and the outer layer diaphragm include a base film, a ceramic layer and an adhesive layer, the surface of the base film is provided with the ceramic layer or the adhesive layer, and the outer surface of the ceramic layer is provided with the ceramic layer or the adhesive layer.
  • the adhesive layer is arranged; the surface of the diaphragm having both the ceramic layer and the adhesive layer is a ceramic surface, and at least one surface of the inner layer diaphragm and the outer layer diaphragm is a ceramic surface.
  • the surfaces of the inner layer diaphragm and the outer layer diaphragm opposite to the clamping section, the first straight section and the tail fitting section are ceramic surfaces.
  • the inner layer diaphragm and the outer layer diaphragm both include a base film and an adhesive layer, the surface of the base film on which the adhesive layer is arranged is an adhesive surface, and the inner layer diaphragm and the outer layer diaphragm are At least one side surface is a rubber surface.
  • the surfaces of the inner membrane and the outer membrane on the opposite surfaces of the clamping section, the first straight section and the tail fitting section are glue surfaces.
  • the length of the clamping section of the inner layer membrane and the length of the clamping section of the outer layer membrane are both 1-15% of the width of the winding core; and/or the first flat surface of the inner layer membrane
  • the length of the straight section and the length of the first straight section of the outer membrane are both 40-50% of the width of the roll core.
  • the length of the tail fitting section of the inner membrane and the length of the tail fitting section of the outer membrane are both ⁇ 5 mm; and/or the length of the inner membrane tail fitting and the The length of the tail fitting section of the outer layer membrane is all 0.1-10% of the width of the roll core.
  • the lithium battery of the present invention uses a diaphragm with a specific friction coefficient in the first straight section of the inner layer diaphragm, so that the diaphragm and the needle (Teflon) material are matched, so that the winding machine can be stable. After outputting the product, a battery structure whose core-pulling distance and tab spacing meet the quality requirements can be obtained, which is conducive to improving product yield and production efficiency.
  • the matching between different materials can also be predicted, for example, the matching between the diaphragm and the Teflon (rolling needle) material can be identified in advance, Before winding, the appropriate diaphragm material can be selected, so that the diaphragm and the winding needle can be used together to avoid production problems such as core pulling and poor spacing caused by the diaphragm material, so that the winding machine can output products stably and improve product yield. and production efficiency.
  • the dry peeling force of the first straight section of the inner layer membrane and the first straight section of the outer layer membrane is less than 8N/m, and the dry peeling force is determined by the following steps:
  • Hot-press the stacked diaphragm samples to be tested together the hot-pressing temperature is 100°C, the pressure is 0.2Mpa, and the hot-pressing time is 10 seconds;
  • the dry peeling force is preferably the dry peeling force of the ceramic surface of the separator.
  • the dry peel force is the dry peel force of the ceramic surface of the separator.
  • the inner layer diaphragm has a first inner layer bonding section
  • the first inner layer bonding section of the inner layer diaphragm is the bonding of the inner layer diaphragm and the inner layer diaphragm
  • the first inner layer of the inner layer diaphragm is bonded.
  • the wet peeling force of the adhesive surface of the layer bonding section is ⁇ 2N/m and the wet peeling force of the ceramic surface of the first inner layer bonding section of the inner layer separator is ⁇ 1N/m, and the wet peeling force is passed through
  • the following steps determine:
  • the hot-pressing temperature is 80°C
  • the pressure is 0.8Mpa
  • the hot-pressing time is 2 hours
  • the length of the first inner layer bonding section of the inner layer separator is 30-60% of the width of the roll core.
  • the overall hardness of the lithium battery is greater than or equal to 200N.
  • the appropriate separator material is selected based on the wet peeling force of the separator, so that the separator can form a good bonding effect, form a good bond with the positive and negative electrode sheets, and form a battery with better hardness, so that the cell can be used in the later cycle of the cycle.
  • the probability of cycle failure caused by excessive expansion is reduced, which is beneficial to prolong the cycle life.
  • the ceramic layer contains ceramic particles and a binding polymer
  • the ceramic particles are one or more of alumina, boehmite, and magnesium oxide
  • the binding polymer is a polymer.
  • the particle size distribution of the ceramic particles is: D10 particle size is 0.15-0.3 ⁇ m, D50 particle size is 0.35-0.45 ⁇ m, D90 particle size is 0.6-0.8 ⁇ m, D100 particle size is less than 4.5 ⁇ m.
  • the adhesive layer includes an adhesive polymer
  • the adhesive polymer is polyvinylidene fluoride, polyvinylpyrrolidone, vinylidene fluoride-hexafluoropropylene polymer, polyacrylonitrile, carboxymethyl Sodium cellulose, sodium polyacrylate, polyacrylic acid, polyacrylate, styrene-butadiene copolymer, butadiene-acrylonitrile polymer, polyvinyl alcohol, polymethyl acrylate, polymethyl methacrylate, poly At least one of ethyl acrylate and polyacrylic acid-styrene polymer.
  • the diaphragm is a water-based diaphragm
  • the adhesive layer includes an adhesive polymer, an adhesive and a dispersant, wherein the content of the adhesive polymer is 92-96%, and the content of the adhesive is 92-96%. is 2.5-5.5%, and the dispersant content is 1.5-2.5%; or the diaphragm is an oil-based mixed-coating diaphragm, and the adhesive layer includes adhesive polymer and ceramic particles, wherein the adhesive polymer The content is 30-50%, and the content of ceramic particles is 50-70%; or the diaphragm is a pure oil-based diaphragm, the adhesive layer includes an adhesive polymer, and the molecular weight of the adhesive polymer is 300,000 ⁇ 1 million.
  • Fig. 1a and Fig. 1b are respectively SEM images of both sides of a water-based diaphragm
  • Fig. 2a and Fig. 2b are respectively SEM images of both sides of an oil-based diaphragm
  • Fig. 3 is the schematic diagram of core-pulling core
  • FIG. 4 is a schematic diagram of the poor spacing between the tabs of the winding core
  • FIG. 5 is a schematic diagram of the external structure of the winding core
  • FIG. 6 is a schematic structural diagram of a lithium battery separator
  • FIG. 7 is a schematic structural diagram of a positive electrode sheet of a lithium battery
  • FIG. 8 is a schematic structural diagram of a lithium battery negative electrode sheet
  • Fig. 9a is the schematic diagram when the coil is wound on the separator and the positive and negative electrode sheets
  • Figure 9b is a schematic diagram of rolling the needle after the needle is drawn.
  • Fig. 10 is the schematic diagram of membrane sample wrapping mover
  • Figure 11 is a schematic diagram of the friction coefficient test
  • Fig. 12 is the schematic diagram that the diaphragm is carried out hot pressing compounding under the dry environment
  • Fig. 13 is the schematic diagram of carrying out 90° peeling with electronic universal testing machine
  • Fig. 14 is the SEM image of the ceramic surface of EJ oil-based diaphragm 5 before dry hot pressing and compounding;
  • Fig. 15 is the SEM image of the substrate surface before dry hot pressing of EJ oil-based diaphragm 1;
  • Fig. 16 is the SEM image of the ceramic surface after peeling off the EJ oil-based separator 5 composited by dry hot pressing;
  • Fig. 17 is the SEM image of the ceramic surface after peeling off the EJ oil-based separator 6 composited by dry hot pressing;
  • Fig. 19 is the SEM image of the substrate surface after the dry hot pressing composite EJ oil-based separator 2 is peeled off;
  • Figure 20 is a cross-sectional view of the core
  • Figure 21 is a schematic diagram of putting the diaphragm into the aluminum-plastic film for liquid injection and sealing;
  • Figure 22 is a schematic diagram of hot pressing the sealed aluminum-plastic film
  • Figure 23 is a cycle test graph.
  • the friction between objects includes kinetic friction and static friction. Static friction exists between two contact surfaces that are stationary, and kinetic friction exists between two contact surfaces that are in relative motion. between.
  • the invention uses the friction coefficient as a performance parameter of the roughness of the surface (coating) of the diaphragm, identifies the matching between different materials in advance, and selects a suitable diaphragm material based on the friction coefficient to prepare the battery cell, thereby improving the production yield of the lithium battery.
  • ⁇ represents the friction coefficient
  • F represents the friction force
  • F can correspond to the pulling force or the pushing force.
  • the coefficient of friction is only related to the test article and the surface coating form of the tested article, and has nothing to do with the positive pressure, test speed, and test tension during the test.
  • the lithium battery generally includes a winding core 10 and a tab 20.
  • the winding core 10 is formed by stacking a positive electrode piece (first pole piece), a negative electrode piece (second pole piece) and a separator, and then winding, The separator is located between the positive electrode sheet and the negative electrode sheet.
  • W represents the width of the winding core
  • H represents the length of the winding core
  • T represents the thickness of the winding core.
  • the separator of the lithium battery includes a base film 11 , a ceramic layer 12 is provided on one or both sides of the base film 11 , and the outermost layer of the separator is an adhesive layer 13 .
  • a ceramic layer 12 is provided on one side surface of the base film 11, an adhesive layer 13 is provided on the other side surface of the base film 11, and an adhesive layer 13 is also provided on the outer surface of the ceramic layer 12.
  • the diaphragm of this embodiment is the base film + Structure of single-layer ceramic layer + double-sided adhesive layer.
  • the surface of the diaphragm with both the ceramic layer and the adhesive layer is defined as the ceramic surface, and the surface of the diaphragm with only the adhesive layer is defined as the adhesive surface or the substrate surface.
  • the base film may be a single-layer PE (polyethylene) or a single-layer PP (polypropylene) or a PP-PE-PP three-layer structure, and the thickness of the base film may be 3 ⁇ m ⁇ 20 ⁇ m.
  • the thickness of the ceramic layer may be 0.5 ⁇ m to 3 ⁇ m, and when both sides of the diaphragm have ceramic layers, the thickness of the ceramic layer may be 0.5 ⁇ m to 5 ⁇ m.
  • the ceramic layer contains ceramic particles and a binding polymer, the ceramic particles can be alumina, boehmite, magnesium oxide, and the binding polymer is polyvinylidene fluoride, polyvinylpyrrolidone, vinylidene fluoride-hexafluoropropylene polymerization polyacrylonitrile, sodium carboxymethyl cellulose, sodium polyacrylate, polyacrylic acid, polyacrylate, styrene-butadiene copolymer, butadiene-acrylonitrile polymer, polyvinyl alcohol, polymethyl acrylate , at least one of polymethyl methacrylate, polyethyl acrylate and polyacrylic acid-styrene polymer.
  • the binding polymer is polyvinylidene fluoride, polyvinylpyrrolidone, vinylidene fluoride-hexafluoropropylene polymerization polyacrylonitrile, sodium carboxymethyl cellulose, sodium polyacrylate, polyacrylic acid, polyacrylate, s
  • the content (mass percentage) of ceramic particles in the ceramic layer is 85-92%, and the rest are adhesive polymers.
  • the particle size distribution of the ceramic particles is: D10 particle size is 0.15-0.3 ⁇ m, D50 particle size is 0.35-0.45 ⁇ m , D90 particle size is 0.6 ⁇ 0.8 ⁇ m, D100 particle size ⁇ 4.5 ⁇ m.
  • the thickness of the adhesive layer is 0.5 ⁇ m ⁇ 3 ⁇ m, the filling density of the adhesive layer is 0.6g/m2 ⁇ 3.0g/m2, the adhesive layer contains adhesive polymer, and the adhesive polymer is polyvinylidene fluoride, polyvinylpyrrolidone , vinylidene fluoride-hexafluoropropylene polymer, polyacrylonitrile, sodium carboxymethyl cellulose, sodium polyacrylate, polyacrylic acid, polyacrylate, styrene-butadiene copolymer, butadiene-acrylonitrile polymer , at least one of polyvinyl alcohol, polymethyl acrylate, polymethyl methacrylate, polyethyl acrylate, and polyacrylic acid-styrene polymer.
  • the adhesive polymer is polyvinylidene fluoride, polyvinylpyrrolidone , vinylidene fluoride-hexafluoropropylene polymer, polyacrylonitrile, sodium carboxymethyl
  • the adhesive layer includes an adhesive polymer, an adhesive and a dispersant, wherein the content (mass percentage) of the adhesive polymer is 92-96%, and the content of the adhesive is 2.5% ⁇ 5.5%, the content of dispersant is 1.5 ⁇ 2.5%;
  • the adhesive layer includes adhesive polymer and ceramic particles, wherein, the content of adhesive polymer (mass percentage)
  • the diaphragm is a pure oil-based diaphragm, the content of the adhesive polymer in the adhesive layer is 100%, and the molecular weight of the adhesive polymer is 300,000 to 100%. Ten thousand.
  • the positive electrode sheet of the lithium battery includes a positive electrode foil 14 and a positive electrode active material layer 15 coated on both sides of the positive electrode foil 14 .
  • the positive electrode foil 14 can be an aluminum foil with a thickness of 8 ⁇ m to 14 ⁇ m.
  • the positive electrode active material layer includes a positive electrode material, a conductive agent and a binder
  • the positive electrode material can be one of LiCoO2, LiNiO2, LiFePO4, LiMn2O4, LiNixCoyMn1-x-yO2
  • the conductive agent can be conductive carbon black, carbon nanotubes
  • the binder can be polyvinylidene fluoride, vinylidene fluoride-fluorinated olefin copolymer, polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene-butadiene rubber , one or more of polyurethane, fluorinated rubber, and polyvinyl alcohol
  • the content (mass percentage) of the positive electrode material in the positive electrode active material layer is 96 to 98.5%
  • the content of the conductive agent is 0.5 to 2.5%
  • the binder The content of 1 to 1.5%.
  • the negative electrode sheet of the lithium battery includes a negative electrode foil 16 and negative electrode active material layers 17 coated on both sides of the negative electrode foil 16 .
  • the negative electrode foil 16 may be copper foil, and the thickness is 5 ⁇ m to 10 ⁇ m.
  • the negative electrode active material layer includes a negative electrode material, a conductive agent, a binder and a dispersant.
  • the negative electrode material can be mesophase carbon microspheres, artificial graphite, natural graphite, hard carbon, soft carbon, lithium titanate, silicon-based material, tin-based material and lithium metal, and the conductive agent can be conductive carbon black, carbon nanotube, conductive One or more of graphite and graphene, the binder can be polyvinylidene fluoride, vinylidene fluoride-fluorinated olefin copolymer, polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene-butadiene rubber, One or more of polyurethane, fluorinated rubber, and polyvinyl alcohol, and the dispersing agent can be sodium carboxymethyl cellulose or potassium carboxymethyl cellulose.
  • the content (mass percentage) of the negative electrode material is 95-97%
  • the content of the conductive agent is 1-2%
  • the content of the binder is 1-1.5%
  • the content of the dispersant is 0-1.5% .
  • the rolling needle A clamps the heads of the two layers of diaphragms and drives the diaphragms to rotate.
  • the thick dotted line in Figure 9a indicates the inner layer of the two layers of diaphragms - the inner layer diaphragm B1, The inner diaphragm B1 is in contact with the rolling needle A, and the thin dotted line indicates the outer diaphragm B2 of the two layers of diaphragms.
  • the outer diaphragm B2 is stacked on the outside of the inner diaphragm B1 and does not directly contact the rolling needle A; When winding, the rolling needle A will clamp the heads of the two layers of diaphragms, and the part of the diaphragm that is clamped by the rolling needles is defined as the clamping section.
  • the part located in the wire frame of a; the part before the first bending of the diaphragm during winding is defined as the first straight section, the first straight section is located after the clamping section, and the inner layer diaphragm B1
  • the first straight section of the diaphragm B2 and the first straight section of the outer diaphragm B2 are stacked together, as shown in the part located in the wire frame b in Figure 9a.
  • Press the negative electrode piece C (the thick solid line in Fig. 9a represents the negative electrode piece), the negative electrode piece C is brought in by the diaphragm, and the negative electrode piece C is located between the inner layer diaphragm B1 and the outer layer diaphragm B2.
  • the positive and negative electrodes are simultaneously inserted to form a layer of diaphragm--a layer of positive plate--a layer of diaphragm--
  • the winding structure of a layer of negative electrode sheets After the winding needle clamps the clamping section of the diaphragm and rotates for half a circle, the positive and negative electrodes are simultaneously inserted to form a layer of diaphragm--a layer of positive plate--a layer of diaphragm-- The winding structure of a layer of negative electrode sheets.
  • the tails of the two layers of separators both exceed the tails of the positive electrode sheets, and the tails of the two layers of separators will overlap and fit together.
  • the fit segment as indicated by arrow Q in Figure 9b.
  • the part of the inner layer diaphragm B1 that is in direct contact with the rolling needle will overlap and contact together due to the drawing out of the rolling needle.
  • An inner layer bonding section as indicated by the arrow P in FIG. 9b, the length of the first inner layer bonding section of the inner layer diaphragm B1 is 30-60% of the width of the winding core.
  • the winding core shown in Figure 9b has two structures.
  • One structure is: the surface opposite the diaphragm and the winding needle is a ceramic surface, and the surface opposite between two adjacent layers of the diaphragm is a glue surface (the part in the wire frame a in Figure 9a). , the part in the wire frame b and the part pointed by the arrow Q in Figure 9b), after the rolling needle is drawn out, the clamping section of the inner layer diaphragm B1 will be opposite to the first straight section of itself, that is, the ceramic surface and the ceramic surface are opposite. ;
  • Another structure is: the opposite surface of the diaphragm and the rolling needle is a rubber surface, and the opposite surface between the two adjacent layers of diaphragms is a ceramic surface.
  • the clamping section of the inner layer diaphragm B1 and its own first A straight section is opposite, that is, the glue surface and the glue surface are opposite. That is, in the two structures, the opposite surfaces between the two adjacent layers of diaphragms are surfaces of the same material, and the surfaces of the inner layer diaphragm that overlap with itself are also surfaces of the same material. More specifically, the length of the clamping section of the diaphragm (the inner layer diaphragm and the outer layer diaphragm) is 1-15% of the width of the roll core, and the length of the first straight section of the diaphragm (the inner layer diaphragm and the outer layer diaphragm) is 1 to 15% of the roll core width.
  • the length of the tail-fitting section of the diaphragm is at least 5 mm, and its length can be 0.1-10% of the core width.
  • the tabs M are indicated by thick and short lines in FIGS. 9a and 9b.
  • the inner diaphragm Since the winding process of the core is driven by the diaphragm to drive the positive and negative electrodes into the film, that is, the inner diaphragm is in direct contact with the winding needle, so the surface roughness of the inner diaphragm is very important, and the surface of the part where the diaphragm and the winding needle are in direct contact should be There is a certain friction or adhesive force to prevent relative sliding, to avoid the spiral phenomenon of the winding core (unevenness between the diaphragm layers) and the phenomenon that the winding core is pulled out of the core and the gap between the tabs is poor when the needle is drawn.
  • the diaphragm surface based on the above composition structure has a specific friction coefficient, and the diaphragm and the rolling needle are adjusted according to the friction coefficient of the diaphragm surface.
  • Matching by selecting the diaphragm material with the appropriate friction coefficient, can reduce the production abnormalities such as core pulling or poor lug spacing caused by the mismatch between the diaphragm and the winding needle material during the winding process.
  • the friction coefficient of the diaphragm surface can be tested with a friction coefficient meter (the MXD-01 friction coefficient meter is used for testing in the description of the following examples), and the steps are as follows:
  • Teflon the material in direct contact with the diaphragm, such as Teflon, on the surface of the measurement area 3 of the friction coefficient meter; in actual production, the surface of the rolling needle is generally sprayed with Teflon material, the more commonly used Teflon
  • the specification of the material is ASF-121FR. Therefore, this type of Teflon material can be used to measure the static friction coefficient (first friction coefficient) and dynamic friction coefficient (second friction coefficient) of the diaphragm, so as to evaluate the diaphragm and rolling needle ( Teflon) matching degree to reduce production defects such as needle drawing;
  • the friction coefficient meter is turned on, and after a certain force accumulation time t, such as 15s, the pulling force is gradually increased.
  • t a certain force accumulation time
  • the first and second friction coefficients of the surfaces on both sides of the diaphragm can be obtained by testing the surfaces on both sides of the diaphragm (side A and side B) in turn.
  • the following table shows the results of two friction coefficient tests on 6 different water-based diaphragms and 6 different oil-based diaphragms.
  • the packing density of the diaphragm surface coating is 0.6g/m2 ⁇ 3.0g/m2.
  • the first friction coefficient of the diaphragm is mainly determined by the physical properties between the coating surface of the water-based diaphragm and the oil-based diaphragm and Teflon, and the second friction coefficient evaluates the sliding between the diaphragm and Teflon.
  • the friction between the two, the second friction coefficient of the oil-based diaphragm is smaller than that of the water-based diaphragm, indicating that the surface of the oil-based diaphragm is relatively smooth.
  • Diaphragms, the use of oil-based diaphragms is more prone to core pulling and poor spacing.
  • the water-based separator 2 Use the water-based separator 2, the water-based separator 4, the oil-based separator 4, and the oil-based separator 5, respectively, with the positive electrode sheet and the negative electrode sheet to wind up the battery cell.
  • the negative electrode sheets are conventional positive and negative electrode sheets.
  • the material on the surface of the rolling needle is Teflon material with the specification of ASF-121FR.
  • four kinds of diaphragms are used: the first friction coefficient and the second friction coefficient of the diaphragm surface are 0.35, 0.07, water-based spray diaphragm, 0.733, 0.53, oil-based diaphragm, 0.352, 0.051, and 0.653, 0.457 oil-based mixed coating diaphragm
  • W represents the width of the winding core
  • H represents the width of the winding core. Length (see Figure 5 for the size structure of the core).
  • the second friction coefficient of the diaphragm (relative to the Teflon surface) is less than 0.1, when the diaphragm is in contact with the Teflon surface, it is more likely to cause core-pulling or poor lug spacing due to mirror adsorption, and core-pulling will further lead to internal
  • the diaphragm is discounted, and there is a micro-short circuit inside the cell, which increases the proportion of low pressure and zero pressure (the ratio increases from 0.01% to about 2%).
  • the spacing is also prone to be too small or too large;
  • the second friction coefficient of the diaphragm is greater than 0.4, the surface contact between the diaphragm and the Teflon is relatively rough, and the core pulling or the gap between the pole lugs caused by the large friction force is prone to occur, and the core pulling will further cause the internal diaphragm to be discounted.
  • There is a micro-short circuit inside the cell which increases the proportion of low voltage and zero voltage (the ratio increases from 0.01% to about 1%).
  • the core pulling distance a>0.5mm the winding core is in a scrapped state, and the distance between the electrodes is also easy. appear too small or too large.
  • the diaphragm or needle winding (Teflon) material with a higher or lower friction coefficient can be used according to the actual situation to match the diaphragm and the needle winding material to each other and reduce the winding process.
  • the occurrence of core pulling, poor spacing, etc. improves the winding yield and product yield.
  • the present invention selects the diaphragm matching the winding needle according to the friction force of the diaphragm surface.
  • the friction coefficient of the inner ring diaphragm (the friction coefficient between the diaphragm surface and the Teflon material) is 0.1 to 0.4, further, the friction coefficient is the second friction coefficient.
  • the second friction coefficient of the inner ring diaphragm (the second friction coefficient between the diaphragm surface and the Teflon material) is 0.1 to 0.4, the process can be guaranteed. stability.
  • the adhesive force of the diaphragm surface (coating) will also have an impact on the core winding process and the quality of the finished product. , which may lead to production defects such as discounts on the pole pieces.
  • the separator based on the above composition also has a specific peeling force, which reflects the adhesive force of the coating on the surface of the separator, which can identify the bonding effect of the separator between the core layers, and determine in advance whether the separator can Meet the bonding requirements after the hot pressing of the battery cell, identify the adhesion between the main materials of the battery core in advance, and prepare the battery core by selecting the diaphragm material with a specific peeling force, and then output the battery with better hardness and better performance. Battery.
  • the peeling force on the surface of the separator of the present invention includes the dry peeling force and the wet peeling force.
  • the two peeling forces are determined by different test methods.
  • the dry peeling force will be described below.
  • suitable separator materials can also be selected in combination with the dry peeling force and/or the wet peeling force, and by controlling the dry peeling force and/or the wet peeling force of the separator, the yield of the winding core can be improved or the cell core can be controlled. The degree of softness and hardness after formation.
  • the dry peeling force is the 90° peeling after the separator is hot-pressed in an electrolyte-free environment, and the peeling force is the dry peeling force.
  • the specific steps of the dry peel force test are as follows:
  • Cut the tested diaphragm into a sample of suitable size For example, cut the tested diaphragm into a long strip with a certain width, such as a small strip with a width of 15mm, align and stack the two cut samples of the tested diaphragm, and Add paper at one end, and separate the two tested diaphragm samples with paper;
  • thermoplastic machine to heat-seal the bonding surface of the two stacked diaphragm samples (Fig. 12).
  • the model of the thermoplastic machine used in this example is SKY-325R6, and the hot-pressing temperature is 100°C , the surface pressure is 0.2Mpa, and the hot pressing time is 10 seconds;
  • the dry peeling force is used to reflect the adhesive force performance of the surface of the diaphragm. Therefore, when testing the dry peeling force of the diaphragm, the diaphragms of the same material that are pressed together are separated, and the two diaphragms have the same coating.
  • auxiliary materials with different surface materials such as quick-drying glue and double-sided tape, more accurate data on the adhesion of the membrane surface coating can be obtained.
  • the samples to be tested are pressed together by hot pressing, which is simple and quick to operate, and the 90° peel test is more convenient than the 180° peel test which requires the help of other auxiliary materials.
  • the table below shows the results of dry peel force testing on 3 different types of oil-based separators.
  • FIGS. 14 and 15 are the SEM images of the substrate surface of EJ oil-based diaphragm 5 and EJ oil-based diaphragm 1 before hot-pressing composite, respectively.
  • the SEM images of the substrate surface of EJ oil-based diaphragm 6-8 before hot-pressing composite are similar to Figure 14
  • the SEM image of the substrate surface of EJ oil-based diaphragm 2-4 before hot pressing composite is similar to Figure 15.
  • the transfer area is further used to determine the glue transfer performance of the dry peeling of the separator, as another performance parameter to select a suitable separator.
  • Transfer area transfer mass/separator area
  • transfer mass mass of separator before dry peeling (tested) - mass of separator after dry peeling (tested).
  • the mass of the separator before dry peeling is 0.18g
  • the mass of the separator after dry peeling is 0.12g
  • Separator adhesive transfer ratio mass of separator before dry peeling (tested) - mass of separator after dry peeling (tested) / before dry peeling (tested) Measure) the mass of the diaphragm ⁇ 100%).
  • the transfer ratio also increases, and the transfer area also increases; for the same diaphragm, the peeling force of the adhesive surface (substrate surface) is greater than the peeling force of the ceramic surface, so the dry peeling force of the ceramic surface can be used to react. Adhesion properties of the diaphragm surface;
  • the ceramic surface of the diaphragm and the substrate surface will show the SEM effect similar to Figure 16 to Figure 19 after dry pressing.
  • the ceramic surface of the diaphragm or the adhesive on the substrate surface The layer appears to peel off and transfer, and the proportion of the transfer area is reduced to 20% to 40%;
  • the separator with large dry peeling force such as when the dry peeling force is greater than 8N/m, cannot be used well in the winding process, and when the dry peeling force is less than 8N/m.
  • the phenomenon of pole piece discount is improved.
  • the separator with larger adhesive force shows better adhesive performance when it is hot-pressed in the subsequent process, which can realize the bonding between the separator and the positive and negative electrode sheets.
  • the contact adhesion between the diaphragm at the head and the bottom becomes better when hot-pressed.
  • the cell passes the furnace temperature test in the safety performance, it can avoid the internal short circuit caused by the contact of the positive and negative electrodes.
  • the pole piece or diaphragm appears The discount phenomenon will reduce the safety performance of the battery.
  • the separator in order to avoid the problem that the coil core is wound down and the pole pieces are discounted after packaging and baking, the separator can be further selected according to the dry peeling force on the surface of the separator.
  • the dry peeling force of the straight section and the first straight section of the outer membrane is less than 8N/m, so as to improve the folding phenomenon of the pole piece.
  • the first flat section of the separator with a small dry peeling force, the phenomenon of pole piece folding is improved, and the adhesion of other parts of the separator is not affected, so as to ensure the hardness of the battery.
  • the dry peel force is the dry peel force of the ceramic surface of the separator.
  • the wet peel force test is described below.
  • the wet peeling force is to first place the diaphragm in an electrolyte environment to perform a hot pressing, and then perform a second hot pressing compounding of the diaphragm in an electrolyte-free environment, and then perform a 90° peeling, which is reacted by the peeling force.
  • Swelling Adhesion Properties of Separator Surface Coatings The close-contact surface of the inner diaphragm will swell and bond in the electrolyte environment, resulting in a more obvious adhesive effect between the diaphragms.
  • This adhesive force is mainly represented by the van der Waals force, and the greater the peeling force between the diaphragms under the wet method , the more obvious the bonding effect between the diaphragms, the greater the tearing force.
  • Figure 20 is a cross-sectional view of the winding core.
  • the swelling adhesive force of the separator plays a role in fixing the winding core, and a suitable separator is selected based on the wet peeling force of the separator. material, so that the separator can form a good bonding effect, form a good bond with the positive and negative electrodes, form a battery with better hardness, and reduce the probability of cycle failure caused by excessive expansion of the battery in the later period of the cycle. Conducive to prolonging cycle life.
  • Cut the tested diaphragm into a sample of suitable size For example, cut the tested diaphragm into a long strip with a certain width, such as a small strip with a width of 15mm, align and stack the two cut samples of the tested diaphragm, and Add paper to one end, and separate the two tested diaphragm samples with paper. For example, when testing the diaphragm of the first inner layer bonding section, the first inner layer bonding section position is bonded together and the diaphragm is cut out. Cut into samples, align and stack;
  • the hot-pressing temperature can be 68-90°C, and the pressure is 0.7MPa-1.1Mpa.
  • the hot-pressing temperature in this embodiment is 80°C, and the pressure is 0.8MPa, and the hot pressing time is 2 hours;
  • One end of the diaphragm sample is fixed with the fixed end of the electronic universal testing machine, the preload speed and test speed are set to 100mm/min, the two tested diaphragm samples are separated, and the peeling force when the tested diaphragm samples are separated is recorded.
  • separators Six kinds of separators were selected from the above separators tested for wet peeling force, wound together with the positive and negative electrode sheets to form a cell, the cell was encapsulated and injected into the electrolyte, and formed into a battery.
  • the width of the separator used was 83.8mm
  • the width of the positive electrode sheet is 79.5mm
  • the width of the negative electrode sheet is 81.5mm.
  • Both the positive electrode sheet and the negative electrode sheet are conventional lithium battery positive and negative electrode sheets.
  • two kinds of existing separators and the same positive and negative electrode sheets were used to make batteries as comparative examples.
  • the obtained battery is tested for hardness, thickness expansion rate and capacity retention rate, and the hardness test can be tested by a three-point hardness test method.
  • the method of the three-point hardness test is as follows: the bottom surface of the battery is supported by two steel pipes, the two steel pipes are located at the two ends of the battery, and the other steel pipe is pressed in the middle of the top surface of the battery. During the test, the steel pipe applies pressure to the battery surface,
  • the test parameters are: the limit displacement of pressing down -3mm, the pressing speed -6mm/min, and the pressure when the battery is deformed is the hardness test result.
  • the adhesive force (wet peel force) between the hot-pressed composite adhesive surface and the ceramic surface after the water-based separator is swollen in the electrolyte environment is smaller than that of the gravure oil-based separator and the gravure oil-based mixed-coated separator.
  • Force (wet peel force) the hardness data after the battery is removed from the stand can also indirectly reflect the adhesion effect between the separators, and the cycle characteristics of the battery can also support the current data ( Figure 23).
  • the adhesion of the oil-based mixed-coated separator is better than that of the oil-based separator, which indirectly proves the adhesion effect of the separator gel after swelling in the electrolyte environment.
  • the wet peeling force becomes larger, the subsequent cycle performance of the battery is relatively excellent , the hardness of the battery is also relatively hard, and it has the possibility and execution of quantification.
  • the battery When the wet peeling force of the adhesive surface of the separator is less than 2N/m and the wet peeling force of the ceramic surface is less than 1N/m, the battery is soft as a whole, and the overall hardness of the battery is less than 200N;
  • the overall hardness of the battery is 200N ⁇ 400N;
  • the overall hardness of the battery is 400N ⁇ 550N;
  • the overall hardness of the battery is 550N to 800N.
  • the hardness and The battery cycle can meet 500cycles, the greater the peeling force of the separator, the harder the battery is, the better the bonding effect between the pole piece and the separator, the greater the battery hardness, the better the long-term cycle ability of the battery, the better the capacity retention rate and the The thickness expansion ratio becomes smaller. Therefore, when preparing the roll core, the separator can be further selected according to the wet peeling force on the surface of the separator. m and the wet peeling force of the ceramic surface of the first inner layer bonding section of the inner layer separator is ⁇ 1 N/m.

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Abstract

一种锂电池，包括卷芯和极耳，卷芯由内层隔膜、第一极片、外层隔膜、第二极片叠加卷绕形成，第一极片与第二极片极性相反；内层隔膜位于卷芯的最内层，内层隔膜和外层隔膜均具有夹持段、与夹持段相连并位于夹持段之后的第一平直段、超出第一极片尾端的尾部贴合段，第一平直段位于第一极片之前，尾部贴合段为隔膜的末端，内层隔膜的夹持段、第一平直段、尾部贴合段分别和外层隔膜的夹持段、第一平直段、尾部贴合段贴合在一起；内层隔膜的第一平直段的表面摩擦系数为0.1～0.4。本发明使用具有特定表面摩擦系数的隔膜，使隔膜与卷针材料相匹配，能够避免出现因隔膜材料导致的抽芯、间距不良等生产问题，有利于提高产品良率和生产效率。

Description

一种锂电池
本申请要求于2020年12月10日提交中国专利局、申请号为202011455854.0、申请名称为“一种锂电池”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本发明属于锂离子电池技术领域，具体涉及一种锂电池。
背景技术
锂电池包括电芯和设置于电芯上的极耳，电芯包括隔膜、正极片和负极片，隔膜是锂电池的关键材料之一，其设置于电池的正、负极片之间，用于隔离正、负极片，防止电池短路。目前锂电池中使用的隔膜一般为具有孔洞结构的聚烯烃产品，如PE隔膜、PP隔膜、PP/PE/PP三层隔膜等。在基材隔膜的单侧表面或者两侧表面涂覆有无机粒子，如氧化铝，勃母石，氧化镁等，在此基础上再对隔膜进行双面的纯胶涂布或者胶和陶瓷粒子混合涂布，最后得到隔膜产品，其中的胶可以是单一PVDF或者多种PVDF混合，涂布的方式可以水系涂布或油系涂布。水系隔膜是将单一品种或者多种PVDF和分散剂、胶水在水中分散、研磨，形成悬浊液，过滤后进行涂布得到的成品，水系隔膜的涂布方式可以是微凹版辊转移涂布或者使用高速喷头涂布；油系隔膜是将单一品种或者多种PVDF按特定比例溶解在有机溶剂中(例如NMP、DMAC等)，形成溶液后进行涂布得到的成品，油系隔膜的涂布方式可以是微凹版辊转移涂布或者浸涂。图1a和图1b为采用微凹辊转移涂布方式涂布的水系隔膜的两侧表面的扫描电镜图，隔膜表面胶层的填充密度为0.6g/m 2～3.0g/m 2，水系隔膜还可以使用喷涂等方式在基材隔膜、陶瓷隔膜表面形成涂层。图2a和图2b为采用微凹辊转移涂布方式涂布的油系隔膜的两侧表面的扫描电镜图，隔膜表面胶层的填充密度为0.6g/m 2～3.0g/m 2，油系隔膜还可以使用浸涂等方式在基材隔膜、陶瓷隔膜表面形成涂层。
在制备电池卷芯时，一般是卷针夹住隔膜，隔膜带动正极片和负极片一起旋转，从而形成卷芯。由于隔膜表面涂覆有涂层，隔膜与卷针接触时，隔膜表面涂层的粗糙度对于电芯卷绕工序的一系列动作是否能够顺利完成具有重要的影响，如果隔膜表面涂层的粗糙度和卷针表面材料不匹配，卷绕电芯时容易出现抽芯或极耳间距不良的情况。图3为卷芯抽芯的示意图，在卷绕过程中最内圈的隔膜与卷针直接接触，当卷针抽出时，隔膜与卷针之间的镜面吸附(由隔膜表面光滑度和特氟龙表面光滑度导致两者直接吸附在一起的现象)或动摩擦力较大会导致隔膜100被拉出于卷芯200之外，造成卷芯抽芯，图3中的a表示隔膜100露出于卷芯200之外的部分的长度，即a表示卷芯的抽芯距离，单位一般为毫米，当0≤a≤0.5mm时，认为卷芯质量合格，当a＞0.5mm时，认为卷芯质量不合格。图4为极耳间距不良的示意图，内层隔膜在卷针拔出时可能会出现移动，从而导致两个极耳300位置偏移，使得两个极耳300之间的间距偏大或偏小，图4所示为两个极耳300的间距小于标准间距b(单位毫米)的情况。卷芯抽芯和极耳间距不良都会对电池的质量带来影响。
发明内容
本发明的目的在于提供一种锂电池，可以减少卷芯抽芯及极耳间距不合格等生产不良的现象发生，提高锂电池的良品率。
为了实现上述目的，本发明采取如下的技术解决方案：
一种锂电池，包括卷芯和极耳，所述卷芯由内层隔膜、第一极片、外层隔膜、第二极片叠加卷绕形成，第一极片与第二极片极性相反；所述内层隔膜位于卷芯的最内层，所述内层隔膜和所述外层隔膜均具有夹持段、与夹持段相连并位于夹持段之后的第一平直段、超出所述第一极片尾端的尾部贴合段，第一平直段位于所述第一极片之前，尾部贴合段为隔膜的末端，所述内层隔膜的夹持段、第一平直段、尾部贴合段分别和所述外层隔膜的夹持段、第一平直段、尾部贴合段贴合在一起；所述内层隔膜的第一平直段的表面摩擦系数为0.1～0.4。
进一步的，所述表面摩擦系数为通过以下方法确定的第一摩擦系数和/或第二摩擦系数：
S1、裁剪合适尺寸的隔膜样品，将隔膜样品包裹在一移动子的表面；
S2、将和隔膜直接接触的材料铺开于测量区域；
S3、将包裹了隔膜样品的移动子放置于测量区域，隔膜样品的待测量表面与测量区域上的材料相接触；
S4、向移动子施加一个外力，外力使得移动子移动时，测得隔膜样品表面的第一摩擦系数；
S5、移动子移动后，外力使移动子以恒定的速度移动，测得隔膜样品表面的第二摩擦系数。
更具体的，所述表面摩擦系数是隔膜与特氟龙之间的第二摩擦系数。
更具体的，所述内层隔膜和所述外层隔膜均包括基膜、陶瓷层和胶层，所述基膜的表面设置所述陶瓷层或所述胶层，所述陶瓷层的外侧表面设置所述胶层；隔膜的同时具有陶瓷层和胶层的表面为陶瓷面，所述内层隔膜和所述外层隔膜至少一侧表面为陶瓷面。
更具体的，所述内层隔膜和外层隔膜在夹持段、第一平直段、尾部贴合段相对的表面为陶瓷面。
更具体的，所述内层隔膜和所述外层隔膜均包括基膜和胶层，所述基膜的设置所述胶层的表面为胶面，所述内层隔膜和所述外层隔膜至少一侧表面为胶面。
更具体的，所述内层隔膜和外层隔膜在夹持段、第一平直段、尾部贴合段相对的表面为胶面。
更具体的，所述内层隔膜的夹持段的长度和所述外层隔膜的夹持段的长度均为卷芯宽度的1～15％；和/或所述内层隔膜的第一平直段的长度和所述外层隔膜的第一平直段的长度均为卷芯宽度的40～50％。
更具体的，所述内层隔膜的尾部贴合段的长度和所述外层隔膜的尾部贴合段的长度均≥5mm；和/或所述内层隔膜尾部贴合段的长度和所述外层隔膜的尾部贴合段的长度均为卷芯宽度的0.1～10％。
由以上技术方案可知，本发明的锂电池通过使用内层隔膜的第一平直段具有特定摩擦系数的隔膜，使隔膜与卷针(特氟龙)材料的相匹配，从而卷绕机能够稳定输出产品，得到抽 芯距离、极耳间距符合质量要求的电池结构，有利于提高产品良率和生产效率。在测定摩擦系数的步骤中，如果配合特氟龙材料进行摩擦系数的测定，还能够对不同材料间的匹配性进行预判，如提前识别隔膜和特氟龙(卷针)材料的匹配性，在卷绕之前能够选择合适的隔膜材料，使隔膜与卷针之间搭配使用，避免出现因隔膜材料导致的抽芯、间距不良等生产问题，使卷绕机可以稳定输出产品，提高产品良率和生产效率。
进一步的，所述内层隔膜的第一平直段和所述外层隔膜的第一平直段的干法剥离力小于8N/m，所述干法剥离力通过以下步骤确定：
S1、将被测隔膜裁剪为尺寸合适的样品，将两片被测隔膜样品对齐叠放；
S2、将叠放好的被测隔膜样品热压在一起，热压温度为100℃，压强为0.2Mpa，热压时间为10秒；
S3、热压完成后，将压合在一起的被测隔膜样品从一端分开，进行90°剥离，记录被测隔膜样品分开时的剥离力，该剥离力即为干法剥离力。所述干法剥离力优选为隔膜的陶瓷面的干法剥离力。
基于隔膜的干法剥离力来选择合适的隔膜材料，使隔膜与卷针良好匹配，减少出现卷芯卷绕下台，封装、烘烤之后的极片打折的现象，从而提高产品良率和成品质量。更优选的，干法剥离力为隔膜的陶瓷面的干法剥离力。更进一步的，所述隔膜的转移面积占比为20～40％，转移面积＝转移质量/隔膜面积，转移质量＝干法剥离前隔膜的质量-干法剥离后隔膜的质量。
进一步的，所述内层隔膜具有第一内层贴合段，所述内层隔膜的第一内层贴合段为内层隔膜和内层隔膜贴合，所述内层隔膜的第一内层贴合段的胶面的湿法剥离力≥2N/m且所述内层隔膜的第一内层贴合段的陶瓷面的湿法剥离力≥1N/m，所述湿法剥离力通过以下步骤确定：
S1、将被测隔膜裁剪为尺寸合适的样品，将两片被测隔膜样品对齐叠放；
S2、将叠放好的两片被测隔膜样品放入铝塑膜中进行封装，注入电解液后，抽真空密封；
S3、用化成机对密封好的铝塑膜进行热压，热压温度为80℃，压强为0.8Mpa，热压时间为2小时；
S4、热压完成后，将被测隔膜样品从铝塑膜中取出，擦干电解液，将被测隔膜样品装入硬封带中，进行热压，热压温度为100℃，压强为0.2Mpa，热压时间为10秒；
S5、热压完成后，将压合在一起的两片被测隔膜样品从一端分开，进行90°剥离，记录被测隔膜样品分开时的剥离力，该剥离力即为湿法剥离力。
更具体的，所述内层隔膜的第一内层贴合段的长度为卷芯宽度的30～60％。
更进一步的，所述锂电池的整体硬度≥200N。
基于隔膜的湿法剥离力来选择合适的隔膜材料，使隔膜可以形成良好的粘结效果，与正、负极片形成很好的粘接，形成硬度较好的电池，使电芯在循环的后期发生因膨胀超标导致的循环失效几率降低，有利于延长循环寿命。
更具体的，所述陶瓷层中包含陶瓷颗粒和粘结性聚合物，所述陶瓷颗粒为氧化铝、勃母石、氧化镁中的一种或几种，所述粘结性聚合物为聚偏氟乙烯、聚乙烯吡咯烷酮、偏氟乙烯 一六氟丙烯聚合物、聚丙烯腈、羧甲基纤维素钠、聚丙烯酸钠、聚丙烯酸、聚丙烯酸酯、苯乙烯一丁二烯共聚物、丁二烯-丙烯腈聚合物、聚乙烯醇、聚丙烯酸甲酯、聚甲基丙烯酸甲酯、聚丙烯酸乙酯、聚丙烯酸一苯乙烯聚合物中的至少一种。
更具体的，所述陶瓷颗粒的粒径分布为：D10粒径为0.15～0.3μm，D50粒径为0.35～0.45μm，D90粒径为0.6～0.8μm，D100粒径＜4.5μm。
更具体的，所述胶层中包含粘接性聚合物，所述粘接性聚合物为聚偏氟乙烯、聚乙烯吡咯烷酮、偏氟乙烯一六氟丙烯聚合物、聚丙烯腈、羧甲基纤维素钠、聚丙烯酸钠、聚丙烯酸、聚丙烯酸酯、苯乙烯一丁二烯共聚物、丁二烯-丙烯腈聚合物、聚乙烯醇、聚丙烯酸甲酯、聚甲基丙烯酸甲酯、聚丙烯酸乙酯、聚丙烯酸一苯乙烯聚合物中的至少一种。
更具体的，所述隔膜为水系隔膜，所述胶层中包括粘接性聚合物、粘接剂和分散剂，其中，粘接性聚合物的含量为92～96％，粘接剂的含量为2.5～5.5％，分散剂的含量为1.5～2.5％；或者所述隔膜为油系混涂隔膜，所述胶层中包括粘接性聚合物和陶瓷颗粒，其中，粘接性聚合物的含量为30～50％，陶瓷颗粒的含量为50～70％；或者所述隔膜为纯油系隔膜，所述胶层中包括粘接性聚合物，所述粘结性聚合物的分子量30万～100万。
附图说明
为了更清楚地说明本发明实施例，下面将对实施例或现有技术描述中所需要使用的附图做简单介绍，显而易见地，下面描述中的附图仅仅是本发明的一些实施例，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的附图。
图1a和图1b分别为一种水系隔膜两侧表面的扫描电镜图；
图2a和图2b分别为一种油系隔膜两侧表面的扫描电镜图；
图3为卷芯抽芯的示意图；
图4为卷芯极耳间距不良的示意图；
图5为卷芯的外部结构示意图；
图6为锂电池隔膜的结构示意图；
图7为锂电池正极片的结构示意图；
图8为锂电池负极片的结构示意图；
图9a为卷针对隔膜以及正、负极片进行卷绕时的示意图；
图9b为抽针后卷针的示意图；
图10为隔膜样品包裹移动子的示意图；
图11为摩擦系数测试时的示意图；
图12为将隔膜进行干法环境下热压复合的示意图；
图13为用电子万能试验机进行90°剥离的示意图；
图14为EJ油系隔膜5干法热压复合前陶瓷面的SEM图；
图15为EJ油系隔膜1干法热压复合前基材面的SEM图；
图16为干法热压复合的EJ油系隔膜5剥离后陶瓷面的SEM图；
图17为干法热压复合的EJ油系隔膜6剥离后陶瓷面的SEM图；
图18为干法热压复合的EJ油系隔膜1剥离后基材面的SEM图；
图19为干法热压复合的EJ油系隔膜2剥离后基材面的SEM图；
图20为卷芯的剖视图；
图21为将隔膜放入铝塑膜中进行注液、密封的示意图；
图22为对密封后的铝塑膜进行热压的示意图；
图23为循环测试曲线图。
以下结合附图对本发明的具体实施方式作进一步详细地说明。
具体实施方式
下面结合附图对本发明进行详细描述，在详述本发明实施例时，为便于说明，表示器件结构的附图会不依一般比例做局部放大，而且所述示意图只是示例，其在此不应限制本发明保护的范围。需要说明的是，附图采用简化的形式且均使用非精准的比例，仅用以方便、清晰地辅助说明本发明实施例的目的。
相互接触的物体之间都存在着摩擦力，物体间的摩擦力包括动摩擦力和静摩擦力，静摩擦力存在于互为静止的两个接触表面之间，动摩擦力存在于相对运动的两个接触表面之间。本发明利用摩擦系数作为隔膜表面(涂层)的粗糙度的性能参数，提前识别不同材料间的匹配性，基于摩擦系数选择合适的隔膜材料制备电芯，以此提高锂电池的生产良率。
摩擦系数公式为F＝μF压，式中的μ表示摩擦系数，F表示摩擦力，F可对应于拉力或推力。利用摩擦系数公式，通过静摩擦系数和动摩擦系数来反应隔膜表面(涂层)的粗糙程度，便于操作，准确度高。摩擦系数只与测试物品、被测试物品的表面涂布形态有关，与测试过程中的正压力、测试速度、测试使用拉力无关。
如图5所示，锂电池一般包括卷芯10和极耳20，卷芯10由正极片(第一极片)、负极片(第二极片)和隔膜叠放在一起后卷绕形成，隔膜位于正极片和负极片之间，图5中的W表示卷芯的宽度，H表示卷芯的长度，T表示卷芯的厚度。如图6所示，锂电池的隔膜包括基膜11，在基膜11的单侧或两侧表面上设置有陶瓷层12，隔膜的最外层为胶层13，图6所示的隔膜只在基膜11的一侧表面上设置陶瓷层12，在基膜11的另一侧表面上设置胶层13，在陶瓷层12的外侧表面也设置胶层13，本实施例的隔膜为基膜+单层陶瓷层+双面胶层的结构。将隔膜的同时有陶瓷层和胶层的表面定义为陶瓷面，将隔膜的只有胶层的表面定义为胶面或基材面。
基膜可以是单层PE(聚乙烯)或单层PP(聚丙烯)或者PP-PE-PP三层结构，基膜的厚度可为3μm～20μm。当隔膜只有单面陶瓷层时，陶瓷层的厚度可为0.5μm～3μm，当隔膜双面都有陶瓷层时，陶瓷层的厚度可为0.5μm～5μm。陶瓷层中包含陶瓷颗粒和粘结性聚合物，陶瓷颗粒可以是氧化铝、勃母石、氧化镁，粘结性聚合物为聚偏氟乙烯、聚乙烯吡咯烷酮、偏氟乙烯一六氟丙烯聚合物、聚丙烯腈、羧甲基纤维素钠、聚丙烯酸钠、聚丙烯酸、聚丙烯酸酯、苯乙烯一丁二烯共聚物、丁二烯-丙烯腈聚合物、聚乙烯醇、聚丙烯酸甲酯、聚甲基丙烯酸甲酯、聚丙烯酸乙酯、聚丙烯酸一苯乙烯聚合物中的至少一种。陶瓷层中陶瓷颗粒的含量(质量百分比)为85～92％，其余为粘接性聚合物，陶瓷颗粒的粒径分布为：D10粒径为0.15～0.3μm，D50粒径为0.35～0.45μm，D90粒径为0.6～0.8μm，D100粒径＜4.5μm。
胶层的厚度为0.5μm～3μm，胶层的填充密度为0.6g/m2～3.0g/m2，胶层中包含粘接性聚合物，粘接性聚合物为聚偏氟乙烯、聚乙烯吡咯烷酮、偏氟乙烯一六氟丙烯聚合物、聚 丙烯腈、羧甲基纤维素钠、聚丙烯酸钠、聚丙烯酸、聚丙烯酸酯、苯乙烯一丁二烯共聚物、丁二烯-丙烯腈聚合物、聚乙烯醇、聚丙烯酸甲酯、聚甲基丙烯酸甲酯、聚丙烯酸乙酯、聚丙烯酸一苯乙烯聚合物中的至少一种。当隔膜为水系隔膜时，胶层中包括粘接性聚合物、粘接剂和分散剂，其中，粘接性聚合物的含量(质量百分比)为92～96％，粘接剂的含量为2.5～5.5％，分散剂的含量为1.5～2.5％；当隔膜为油系混涂隔膜时，胶层中包括粘接性聚合物和陶瓷颗粒，其中，粘接性聚合物的含量(质量百分比)为30～50％，陶瓷颗粒的含量为50～70％；当隔膜为纯油系隔膜时，胶层中粘接性聚合物的含量为100％，粘结性聚合物的分子量30万～100万。
如图7所示，锂电池的正极片包括正极箔材14以及涂覆在正极箔材14两侧表面上的正极活性物质层15，正极箔材14可以是铝箔，厚度为8μm～14μm。正极活性物质层中包括正极材料、导电剂和粘结剂，正极材料可为LiCoO2、LiNiO2、LiFePO4、LiMn2O4、LiNixCoyMn1-x-yO2中的一种，导电剂可以是导电炭黑、碳纳米管、导电石墨、石墨烯中的一种或多种，粘结剂可以是聚偏二氟乙烯、偏氟乙烯-氟化烯烃的共聚物、聚四氟乙烯、羧甲基纤维素钠、丁苯橡胶、聚胺酯、氟化橡胶、聚乙烯醇中的一种或多种，正极活性物质层中正极材料的含量(质量百分比)为96～98.5％，导电剂的含量为0.5～2.5％，粘结剂的含量为1～1.5％。
如图8所示，锂电池的负极片包括负极箔材16以及涂覆在负极箔材16两侧表面上的负极活性物质层17。负极箔材16可以是铜箔，厚度为5μm～10μm。负极活性物质层中包括负极材料、导电剂、粘结剂和分散剂。负极材料可为中间相碳微球、人造石墨、天然石墨、硬碳、软碳、钛酸锂、硅基材料、锡基材料和锂金属，导电剂可为导电炭黑、碳纳米管、导电石墨、石墨烯中的一种或多种，粘结剂可为聚偏二氟乙烯、偏氟乙烯-氟化烯烃的共聚物、聚四氟乙烯、羧甲基纤维素钠、丁苯橡胶、聚胺酯、氟化橡胶、聚乙烯醇中的一种或多种，分散剂可为羧甲基纤维素钠或羧甲基纤维素钾。负极活性物质层中，负极材料的含量(质量百分比)为95～97％，导电剂的含量为1～2％，粘接剂的含量为1～1.5％，分散剂的含量为0～1.5％。
如图9a所示，在制备卷芯时，卷针A夹住两层隔膜的头部，带动隔膜转动，图9a中的粗虚线表示两层隔膜中位于内侧的隔膜——内层隔膜B1，内层隔膜B1与卷针A相接触，细虚线表示两层隔膜中位于外侧的隔膜——外层隔膜B2，外层隔膜B2叠放在内层隔膜B1外侧，不直接与卷针A接触；卷绕时卷针A会夹住两层隔膜的头部，将隔膜被卷针夹住的部分定义为夹持段，内层隔膜B1的夹持段和外层隔膜B2的夹持段叠在一起，如图9a中位于a线框内的部分；将卷绕时隔膜第一次弯折前的部分定义为第一平直段，第一平直段位于夹持段之后，内层隔膜B1的第一平直段和外层隔膜B2的第一平直段叠在一起，如图9a中位于b线框内的部分，卷针A带动隔膜转动半周后，负极压轮(未图示)压紧负极片C(图9a中的粗实线表示负极片)，负极片C由隔膜带入，负极片C位于内层隔膜B1和外层隔膜B2之间，又转动半周后，正极压轮(未图示)压紧正极片D(图9a中的细实线表示正极片)，正极片D顺着隔膜进入，由此正极片D和负极片C之间被隔膜隔开，卷绕前体动作完成，正、负极压轮收回，正、负极片随着隔膜转动，卷绕成卷芯，形成一层隔膜--一层负极片--一层隔膜--一层正极片的卷绕结构。此外，也可以采用另一种卷绕工艺，卷针夹住隔膜的夹 持段转动半周后，同时入正极片和负极片，形成一层隔膜--一层正极片--一层隔膜--一层负极片的卷绕结构。
本实施例的卷芯中两层隔膜尾部均超过正极片尾端，两层隔膜的尾部会有重叠贴合在一起的部分，将两层隔膜末端超出正极片后贴合在一起的部分定义为尾部贴合段，如图9b中箭头Q指向的部分。当卷针A抽出后，内层隔膜B1直接与卷针接触的部分会因卷针的抽出而重叠接触在一起，将内层隔膜B1在卷针A抽出后重叠接触在一起的部分定义为第一内层贴合段，如图9b中箭头P指向的部分，内层隔膜B1的第一内层贴合段的长度为卷芯宽度的30～60％。
图9b所示的卷芯存在两种结构，一种结构是：隔膜和卷针相对的表面为陶瓷面，相邻两层隔膜之间相对的表面为胶面(图9a中线框a内的部分、线框b内的部分以及图9b中箭头Q指向的部分)，在卷针抽出后，内层隔膜B1的夹持段会和自身的第一平直段相对，即陶瓷面和陶瓷面相对；另一种结构是：隔膜和卷针相对的表面为胶面，相邻两层隔膜之间相对的表面为陶瓷面，在卷针抽出后，内层隔膜B1的夹持段和自身的第一平直段相对，即胶面和胶面相对。也就是，两种结构中，相邻两层隔膜之间相对表面都是材质相同的表面，内层隔膜与自身重叠相对的表面也是材质相同的表面。更具体的，隔膜(内层隔膜和外层隔膜)的夹持段的长度为卷芯宽度的1～15％，隔膜(内层隔膜和外层隔膜)的第一平直段的长度为卷芯宽度的40～50％，隔膜(内层隔膜和外层隔膜)的尾部贴合段的长度至少为5mm，其长度可为卷芯宽度的0.1～10％。图9a和图9b中的粗短线表示极耳M。
由于卷芯的卷绕过程是由隔膜带动正、负极片入片，即内层隔膜与卷针直接接触，因此内层隔膜表面的粗糙度非常重要，隔膜与卷针直接接触的部分的表面要有一定的摩擦力或粘接力来防止相对滑动，避免卷芯产生螺旋现象(隔膜层与层之间不齐)以及卷针抽针时卷芯抽芯和极耳间距不良的现象。
发明人发现，基于以上组成结构(包括隔膜材料的选择、材料组分的设定、隔膜各层结构的设置)的隔膜表面具有特定的摩擦系数，根据隔膜表面的摩擦系数来对隔膜和卷针进行匹配，通过选择摩擦系数合适的隔膜材料，可以减少卷绕过程中因隔膜和卷针材料不匹配而导致的抽芯或极耳间距不良等生产异常的情况。隔膜表面的摩擦系数可采用摩擦系数仪(以下实施例的说明中使用MXD-01摩擦系数仪进行测试)进行测试，步骤如下：
S1、裁剪合适尺寸的隔膜样品，将隔膜样品1包裹在摩擦系数仪的移动子2的表面(图10)，隔膜样品1至少覆盖移动子2的一个表面，如底面，隔膜样品1的待测面(即涂层表面)朝外，优选的，隔膜样品1将移动子2全包覆；
S2、将和隔膜直接接触的材料，如特氟龙铺开于摩擦系数仪的测量区域3的表面；在实际生产中，卷针表面一般会喷涂有特氟龙材料，比较常用的特氟龙材料的规格为ASF-121FR，因此，可用该型号的特氟龙材料来配合测量隔膜的静摩擦系数(第一摩擦系数)和动摩擦系数(第二摩擦系数)，以此可以评估隔膜与卷针(特氟龙)的匹配程度，减少抽针等生产不良现象；
S3、如图11所示，将包裹了隔膜样品1的移动子2放置于摩擦系数仪的测量区域3，本实施例的移动子2的重量为200g；
S4、摩擦系数仪开机，经过一定的蓄力时间t后，例如15s，逐步增加拉力，当拉力使得移动子被拉动时，测得隔膜表面的第一摩擦系数；
S5、移动子被拉动后，使其以恒定的速度移动，如100mm/min，测得隔膜表面的第二摩擦系数。
对隔膜的两侧表面(A面、B面)依次进行测试，即可得到隔膜两侧表面的第一、第二摩擦系数。
下表为对6种不同的水系隔膜和6种不同的油系隔膜进行两种摩擦系数测试的结果，隔膜表面涂层的填充密度为0.6g/m2～3.0g/m2。
类别 第一摩擦系数 第二摩擦系数 类别 第一摩擦系数 第二摩擦系数
水系隔膜1A面 0.235 0.184 油系隔膜1A面 0.157 0.112
水系隔膜2A面 0.220 0.176 油系隔膜2A面 0.138 0.108
水系隔膜3A面 0.215 0.173 油系隔膜3A面 0.149 0.107
水系隔膜4A面 0.216 0.152 油系隔膜4A面 0.192 0.102
水系隔膜5A面 0.195 0.150 油系隔膜5A面 0.172 0.117
水系隔膜6A面 0.227 0.130 油系隔膜6A面 0.169 0.113
水系隔膜1B面 0.236 0.224 油系隔膜1B面 0.156 0.148
水系隔膜2B面 0.246 0.232 油系隔膜2B面 0.150 0.109
水系隔膜3B面 0.238 0.211 油系隔膜3B面 0.165 0.120
水系隔膜4B面 0.243 0.170 油系隔膜4B面 0.153 0.120
水系隔膜5B面 0.194 0.156 油系隔膜5B面 0.164 0.127
水系隔膜6B面 0.253 0.162 油系隔膜6B面 0.177 0.125
由上表可以看出，隔膜的第一摩擦系数主要是由水系隔膜、油系隔膜的涂层表面跟特氟龙之间物性决定的，第二摩擦系数评估的是滑动时隔膜与特氟龙之间的摩擦力，油系隔膜的第二摩擦系数均比水系隔膜的第二摩擦系数要小，说明油系隔膜的表面比较光滑，在特氟龙材料相同的情况下，相较于使用水系隔膜，使用油系隔膜更容易出现抽芯、间距不良的现象。
分别使用水系隔膜2、水系隔膜4、油系隔膜4、油系隔膜5配合正极片和负极片卷绕制成电芯，卷针表面的材料是规格为ASF-121FR的特氟龙，正极片和负极片为常规的正负极片。在卷绕过程中，水系隔膜2的A面与卷针相接触，水系隔膜4的A面与卷针相接触，油系隔膜4的A面与卷针相接触，油系隔膜5的B面与卷针相接触，卷针表面的材料是规格为ASF-121FR的特氟龙材料。另外使用隔膜表面第一摩擦系数和第二摩擦系数分别为0.35、0.07的水系隔膜，0.733、0.53的水系喷涂隔膜，0.352、0.051的油系隔膜以及0.653、0.457油系混涂隔膜的4种隔膜作为对比例，配合相同的正极片和负极片卷绕制成电芯。然后对卷绕得到的8组电芯进行质检，看是否出现抽芯或极耳间距不良的情况，质检结果如下表所示，表中的W表示卷芯的宽度，H表示卷芯的长度(卷芯的尺寸结构参见图5)。
隔膜 W/H 第一摩擦系数 第二摩擦系数 抽芯距离 极耳间距
水系隔膜2 2/3 0.220 0.176 0.1mm 标准
水系隔膜4 1/3 0.216 0.152 0.0mm 标准
油系隔膜4 1/4 0.192 0.102 0.05mm 标准
油系隔膜5 4/3 0.164 0.127 0.0mm 标准
水系隔膜 1/3 0.350 0.070 1.0mm 偏小
水系喷涂隔膜 4/3 0.733 0.530 2.0mm 偏小
油系隔膜 2/3 0.352 0.051 1.5mm 偏小
油系混涂隔膜 1/4 0.653 0.457 1.3mm 偏小
当卷芯厚度T在1mm～10mm时，隔膜的第一摩擦系数和卷芯抽芯关系如下表：
Figure PCTCN2021137222-appb-000001
由以上的结果可以看出，当隔膜表面的第一摩擦系数和第二摩擦系数在0.1～0.4之间时，隔膜与特氟龙表面间的接触较为匹配，不易产生抽芯、间距不良等不良产品；
当隔膜(相对于特氟龙表面)的第二摩擦系数＜0.1时，隔膜与特氟龙表面接触时更易出现因镜面吸附而导致的抽芯或极耳间距不良，而抽芯会进一步导致内部隔膜打折，电芯内部出现微短路，增大了低压、零压占比(比例由0.01％增大至2％左右)，抽芯的距离a＞0.5mm时，卷芯处于报废状态，极耳间距也容易出现偏小或者偏大的状态；
当隔膜的第二摩擦系数＞0.4时，隔膜与特氟龙的表面接触较为粗糙，易发生因摩擦力较大而导致的抽芯或极耳间距不良，抽芯也会进一步导致内部隔膜打折，电芯内部出现微短路，增大了低压、零压占比(比例由0.01％增大至1％左右)，抽芯的距离a＞0.5mm时，卷芯处于报废状态，极耳间距也容易出现偏小或者偏大的状态。
在知道隔膜表面摩擦系数的情况下，就可以根据实际情况使用摩擦系数更高或更低的隔膜或卷针(特氟龙)材料，来使得隔膜和卷针材料间相互匹配，减少卷绕过程中抽芯、间距不良等现象的发生，提高卷绕良率和产品良率。
根据以上的测试结果，本发明根据隔膜表面的摩擦力来选择与卷针匹配的隔膜，锂电池的卷芯中，内圈隔膜的摩擦系数(隔膜表面与特氟龙材料间的摩擦系数)为0.1～0.4，进一步的，该摩擦系数为第二摩擦系数，当内圈隔膜的第二摩擦系数(隔膜表面与特氟龙材料间的第二摩擦系数)为0.1～0.4时，可以保证制程的稳定性。
除了隔膜表面的摩擦力会对卷芯制程及成品质量有影响外，隔膜表面(涂层)的粘接力也会对卷芯制程及成品质量带来影响，隔膜表面涂层的粘结力不合格，可能会导致极片出现打折等生产不良现象。发明人发现，基于以上组成结构的隔膜还具有特定的剥离力，剥离力反应了隔膜表面涂层的粘接力，可以对隔膜在卷芯层间的粘接效果进行鉴别，提前判断隔膜是否能够满足电芯热压化成后的粘接要求，提前识别出电芯各主材之间的粘附力，通过选择具有特定剥离力的隔膜材料制备电芯，进而输出硬度较好和性能较好的电池。
本发明的隔膜表面剥离力包括干法剥离力以及在湿法剥离力，两种剥离力用不同的测试方法确定，下面先对干法剥离力进行说明。本发明还可以结合干法剥离力和/或湿法剥离力来选择合适的隔膜材料，通过控制隔膜的干法剥离力和/或湿法剥离力，来提高卷芯的良品率或控制电芯化成之后的软硬程度。
干法剥离力就是在无电解液的环境下对隔膜进行热压复合后，进行90°剥离，该剥离力就是干法剥离力。干法剥离力测试的具体步骤如下：
S1、将被测隔膜裁剪为尺寸合适的样品，如将被测隔膜裁剪成具有一定宽度的长条，例如宽度为15mm的小条，将裁剪好的两片被测隔膜样品对齐叠放，并在其中的一端加入纸张，用纸张将两片被测隔膜样品隔开；
S2、将叠放好的两片被测隔膜样品使用热塑机进行贴合面热封处理(图12)，本实施例使用的热塑机的型号为SKY-325R6，热压温度为100℃，面压为0.2Mpa，热压时间为10秒；
S3、热压完成后，将夹在被测隔膜样品之间的纸张抽出，将压合在一起的两片被测隔膜样品从端部分开，进行90°剥离，记录两片被测隔膜样品分开时的干法剥离力；本实施例使用电子万能试验机对被测隔膜样品进行90°剥离测试，将其中一片被测隔膜样品的一端与电子万能试验机的移动端相固定，将另一片被测隔膜样品的一端与电子万能试验机的固定端相固定，预加载速度和测试速度设置为100mm/min，将两片被测隔膜样品进行分离(图13)，记录被测隔膜样品分开时的剥离力。
本发明通过干法剥离力来反映隔膜表面的粘接力性能，因此在测试隔膜的干法剥离力时，是对压合在一起的相同材质的隔膜进行分离，两片隔膜具有相同的涂层材质，而不是使用快干胶、双面胶等表面材质不同的辅助材料，这样可以得到更为准确的隔膜表面涂层粘接 力的数据。此外，通过热压复合的方式将待测样品压合在一起，操作简单快捷，而且相对于180°剥离测试需要借助其他的辅助材料，90°剥离测试更方便。
下表为对3种不同类型的油系隔膜进行干法剥离力测试的结果。
Figure PCTCN2021137222-appb-000002
在以上进行了干法剥离力测试的隔膜中选取5种隔膜，与正、负极片一起卷绕成电芯，包装好并注入电解液，所用的隔膜宽度为83.8mm，正极片宽度为79.5mm，负极片宽度为81.5mm，正极片和负极片均为常规的锂电池正、负极片。图14和图15分别为EJ油系隔膜5和EJ油系隔膜1热压复合前基材面的SEM图，EJ油系隔膜6-8热压复合前基材面的SEM图与图14类似，EJ油系隔膜2-4热压复合前基材面的SEM图与图15类似。取卷绕得到的部分电芯进行质检，检查隔膜的打折及涂层剥离转移现象，检查结果如下表所示，下表中的隔膜覆盖极片距离是指隔膜对负极片的超覆盖尺寸，用于防止电芯内部短路。本发明进一步用转移面积来确定隔膜干法剥离的胶转移性能，作为另一性能参数来选择合适的隔膜。转移面积＝转移质量/隔膜面积，转移质量＝干法剥离前(被测)隔膜的质量-干法剥离后(被测)隔膜的质量。以一个宽度为15mm、长度为150mm的隔膜为例，该隔膜在干法剥离前的质量为0.18g，进行干法剥离后该隔膜的质量为0.12g，则转移面积＝0.06/0.00225＝26.67，隔膜胶转移比例＝0.06/0.18×100％＝33％(隔膜胶转移比例＝干法剥离前(被测)隔膜的质量-干法剥离后(被测)隔膜的质量/干法剥离前(被测)隔膜的质量×100％)。转移面积占比越大，粘接性越大，则电芯极片隔膜之间的粘接力就越大，卷绕难度也越大，抽芯与间距不良比例越大，打折可能性变大，电池硬度越大。
Figure PCTCN2021137222-appb-000003
根据抽检结果可知，对于凹版油系隔膜，当隔膜陶瓷面的干法剥离力＞10N/m时，电芯卷绕过程下台时卷芯易出现极片、空箔打折，卷芯热压或者卷芯烘烤时易出现空箔打折或极片打折的现象，打折占比80％以上，剥离后隔膜的陶瓷面(陶瓷层+胶层)与基材面(胶层)的SEM图如图16至图19所示，隔膜的陶瓷面或者基材面的胶层均出现了剥离转移现象，转移面积占比达到40％～80％，而且随着干法剥离力的增大，剥离后发生胶转移的比例也增大，转移面积也增大；对于同一片隔膜来说，胶面(基材面)的剥离力都大于陶瓷面的剥离力的，因此可用陶瓷面的干法剥离力来反应隔膜表面的粘接力性能；
当陶瓷面的干法剥离力处于5N/m～8N/m之间时，电芯卷绕过程下台时卷芯出现极片、空箔打折的比例明显下降，卷芯热压或者卷芯烘烤时出现空箔、极片打折的比例明显下降到30％，干压之后隔膜的陶瓷面与基材面均会出现类似图16至图19的SEM效果，隔膜的陶瓷面或者基材面的胶层出现剥离转移现象，转移面积占比降到20％～40％；
当陶瓷面的干法剥离力＜5N/m时，电芯卷绕过程下台时卷芯不易出现极片和空箔打折，卷芯热压或者卷芯烘烤时不易出现空箔、极片打折，剥离后隔膜的陶瓷面与基材面没有出现类似图16至图19的SEM效果。
综上可知，干法剥离力(表面粘接力)较大的隔膜，如干法剥离力大于8N/m时，在卷绕工序中不能很好地运用，干法剥离力小于8N/m时，极片打折现象得到改善，小于5N/m时，隔膜在卷绕工序应用良好，卷芯制造过程稳定，且极片打折比例较低，甚至可低至0。但粘接力较大的隔膜在后工序进行热压化成时表现出更好的粘接性能，可以实现隔膜与正、负极片之间的粘接，电池的硬度较好，电芯的卷芯头部与底部的隔膜在热压化成时接触粘接性变好，在电芯过安全性能中的炉温测试时，能够避免正负极的接触导致的内部短路，但如果极片或隔膜出现打折现象，则会降低电芯的安全性能。
综上，为了避免卷芯卷绕下台，封装、烘烤之后的极片打折的问题，还可以进一步根据隔膜表面的干法剥离力来选择隔膜，锂电池卷芯中内层隔膜的第一平直段以及外层隔膜的第一平直段的干法剥离力小于8N/m，以改善极片打折现象。通过使用小的干法剥离力的隔膜第一平直段来改善极片打折现象，不影响隔膜其他部分的粘接性，以保证电池硬度。更优选的，干法剥离力为隔膜的陶瓷面的干法剥离力。
下面对湿法剥离力测试进行说明。湿法剥离力就是先将隔膜置于电解液的环境下进行一次热压，然后再在无电解液环境下对隔膜进行第二次热压复合，然后进行90°剥离，通过该剥离力来反应隔膜表面涂层的溶胀粘接力性能。内层隔膜紧贴面在电解液环境下会有溶胀粘接作用，导致隔膜之间的粘接效果更加明显，这种粘接力主要表现为范德华力，湿法下隔膜间的剥离力越大，隔膜之间的粘接效果越明显，撕扯力越大。
图20为卷芯的剖视图，当隔膜在电解液环境下的粘接性较好时，在电芯化成工序中，相邻的隔膜层能够发生因溶胀产生的粘连现象，起到隔膜粘接作用，隔膜粘接力越大时，粘接效果越好，电芯跌落时发生正、负极片内部接触短路的几率越小，从而能够增加电芯安全性能。发明人发现，隔膜的溶胀粘接力(即电解液环境下隔膜胶溶胀后隔膜表面胶涂层溶胀的粘附力)起固定卷芯的作用，基于隔膜的湿法剥离力来选择合适的隔膜材料，使隔膜可以 形成良好的粘结效果，与正、负极片形成很好的粘接，形成硬度较好的电池，使电芯在循环的后期发生因膨胀超标导致的循环失效几率降低，有利于延长循环寿命。
湿法剥离力测试的具体步骤如下：
S1、将被测隔膜裁剪为尺寸合适的样品，如将被测隔膜裁剪成具有一定宽度的长条，例如宽度为15mm的小条，将裁剪好的两片被测隔膜样品对齐叠放，并在其中的一端加入纸张，用纸张将两片被测隔膜样品隔开，如对第一内层贴合段的隔膜进行测试时，将第一内层贴合段位置的贴合在一起隔膜裁切成样品，对齐叠放；
S2、将叠放好的两片被测隔膜样品放入铝塑膜中进行封装，然后注入电解液，如注入10g电解液，然后抽真空密封(图21)；
S3、用化成机对密封好的铝塑膜进行热压(图22)，热压温度可为68～90℃，压力为0.7MPa～1.1Mpa，本实施例的热压温度为80℃，压力为0.8MPa，热压时间2小时；
S4、热压完成后，将被测隔膜样品从铝塑膜中取出，擦干电解液，将被测隔膜样品装入硬封带中，再进行一次高温热压复合，本实施例使用的热塑机的型号为SKY-325R6热压温度为100℃，面压为0.2Mpa，速度为1mm/s；
S5、热压完成后，将夹在被测隔膜样品之间的纸张抽出，将压合在一起的两片被测隔膜样品从一端分开，进行90°剥离，记录两片被测隔膜样品分开时的湿法剥离力；本实施例使用电子万能试验机对被测隔膜样品进行90°剥离测试，将其中一片被测隔膜样品的一端与电子万能试验机的移动端相固定，将另一片被测隔膜样品的一端与电子万能试验机的固定端相固定，预加载速度和测试速度设置为100mm/min，将两片被测隔膜样品进行分离，记录被测隔膜样品分开时的剥离力。
下表为对3种不同类型的隔膜进行湿法剥离力测试的结果。
Figure PCTCN2021137222-appb-000004
在以上进行了湿法剥离力测试的隔膜中选取6种隔膜，与正、负极片一起卷绕成电芯，将电芯封装并注入电解液，经化成后制成电池，所用的隔膜宽度为83.8mm，正极片宽度为79.5mm，负极片宽度为81.5mm，正极片和负极片均为常规的锂电池正、负极片。同时还选用了两种现有的隔膜与相同的正、负极片制成电池作为对比例。将制得的电池进行硬度、厚度膨胀率及容量保持率的测试，硬度测试可采用三点硬度测试法进行测试。三点硬度测试的方法如下：电池的底面由两根钢管支撑，这两根钢管位于电池的两端，另一根钢管压在电池顶面的中间位置，测试时使钢管向电池表面施加压力，测试参数为：下压变形极限位移-3mm，下压速度-6mm/min，电池发生变形时的压力即为硬度测试结果。
硬度、厚度膨胀率及容量保持率的测试结果如下表：
Figure PCTCN2021137222-appb-000005
由以上结果可以看出，水系隔膜在电解液环境下溶胀后热压复合胶面与陶瓷面的粘接力(湿法剥离力)均小于凹版油系隔膜和凹版油系混涂隔膜的粘接力(湿法剥离力)，电池下台后的硬度数据也可以间接体现隔膜之间的粘接力效果，电池的循环特性也可以支持目前的数据(图23)。油系混涂隔膜的粘接力优于油系隔膜优于水系隔膜，间接证明了电解液环境下隔膜胶溶胀后粘接力效果，湿法剥离力变大时，电池的后续循环性能比较优异，电池的硬度也比较硬，具有量化的可能性和执行性。基于以上测试电池硬度的数据可以得出以下结论：
当隔膜的胶面的湿法剥离力＜2N/m且陶瓷面的湿法剥离力＜1N/m时，电池整体发软，电池的整体硬度＜200N；
当隔膜的胶面的湿法剥离力为2N/m～10N/m且陶瓷面的湿法剥离力为1N/m～2N/m时，电池的整体硬度200N～400N；
当隔膜的胶面的湿法剥离力＞10N/m且陶瓷面的湿法剥离力为2N/m～10N/m时，电池的整体硬度400N～550N；
当隔膜的胶面的湿法剥离力＞10N/m且陶瓷面的湿法剥离力＞10N/m时，电池的整体硬度550N～800N。
综合硬度测试、厚度膨胀率及容量保持率的测试结果，当隔膜的胶面的湿法剥离力≥2N/m且陶瓷面的湿法剥离力≥1N/m时，制得的电池的硬度以及电池循环方面能够满足500cycles，隔膜剥离力越大，电池的硬度越硬，极片与隔膜之间的粘接效果越好，电池硬度变大，电池长期循环能力变好，容量保持率变好以及厚度膨胀率变小。因此，在制备卷芯时，可以进一步根据隔膜的表面的湿法剥离力来选择隔膜，锂电池卷芯的内层隔膜的第一内层贴 合段的胶面的湿法剥离力≥2N/m且内层隔膜的第一内层贴合段的陶瓷面的湿法剥离力≥1N/m。
对所公开的实施例的上述说明，使本领域专业技术人员能够实现或使用本发明。对这些实施例的多种修改对本领域的专业技术人员来说将是显而易见的，本文中所定义的一般原理可以在不脱离本发明的精神或范围的情况下，在其它实施例中实现。因此，本发明将不会被限制于本文所示的实施例，而是要符合与本文所公开的原理和新颖特点相一致的最宽范围。

Claims (10)

  1. 一种锂电池，包括卷芯和极耳，其特征在于：所述卷芯由内层隔膜、第一极片、外层隔膜、第二极片叠加卷绕形成，第一极片与第二极片极性相反；
    所述内层隔膜位于卷芯的最内层，所述内层隔膜和所述外层隔膜均具有夹持段、与夹持段相连并位于夹持段之后的第一平直段、超出所述第一极片尾端的尾部贴合段，第一平直段位于所述第一极片之前，尾部贴合段为隔膜的末端，所述内层隔膜的夹持段、第一平直段、尾部贴合段分别和所述外层隔膜的夹持段、第一平直段、尾部贴合段贴合在一起；
    所述内层隔膜的第一平直段的表面摩擦系数为0.1～0.4。
  2. 如权利要求1所述的锂电池，其特征在于：所述表面摩擦系数为通过以下方法确定的第一摩擦系数和/或第二摩擦系数：
    S1、裁剪合适尺寸的隔膜样品，将隔膜样品包裹在一移动子的表面；
    S2、将和隔膜直接接触的材料铺开于测量区域；
    S3、将包裹了隔膜样品的移动子放置于测量区域，隔膜样品的待测量表面与测量区域上的材料相接触；
    S4、向移动子施加一个外力，外力使得移动子移动时，测得隔膜样品表面的第一摩擦系数；
    S5、移动子移动后，外力使移动子以恒定的速度移动，测得隔膜样品表面的第二摩擦系数。
  3. 如权利要求1所述的锂电池，其特征在于：所述表面摩擦系数是隔膜与特氟龙之间的第二摩擦系数。
  4. 如权利要求1所述的锂电池，其特征在于：所述内层隔膜和所述外层隔膜均包括基膜、陶瓷层和胶层，所述基膜的表面设置所述陶瓷层或所述胶层，所述陶瓷层的外侧表面设置所述胶层；隔膜的同时具有陶瓷层和胶层的表面为陶瓷面，所述内层隔膜和所述外层隔膜至少一侧表面为陶瓷面。
  5. 如权利要求4所述的锂电池，其特征在于：所述内层隔膜和外层隔膜在夹持段、第一平直段、尾部贴合段相对的表面为陶瓷面。
  6. 如权利要求1所述的锂电池，其特征在于：所述内层隔膜和所述外层隔膜均包括基膜和胶层，所述基膜的设置所述胶层的表面为胶面，所述内层隔膜和所述外层隔膜至少一侧表面为胶面。
  7. 如权利要求6所述的锂电池，其特征在于：所述内层隔膜和外层隔膜在夹持段、第一平直段、尾部贴合段相对的表面为胶面。
  8. 如权利要求1所述的锂电池，其特征在于：所述内层隔膜的夹持段的长度和所述外层隔膜的夹持段的长度均为卷芯宽度的1～15％；和/或所述内层隔膜的第一平直段的长度和所述外层隔膜的第一平直段的长度均为卷芯宽度的40～50％；和/或所述内层隔膜的尾部贴合段的长度和所述外层隔膜的尾部贴合段的长度均≥5mm；和/或所述内层隔膜尾部贴合段的长度和所述外层隔膜的尾部贴合段的长度均为卷芯宽度的0.1～10％。
  9. 如权利要求1所述的锂电池，其特征在于：所述内层隔膜的第一平直段和所述外层隔膜的第一平直段的干法剥离力小于8N/m，所述干法剥离力通过以下步骤确定：
    S1、将被测隔膜裁剪为尺寸合适的样品，将两片被测隔膜样品对齐叠放；
    S2、将叠放好的被测隔膜样品热压在一起，热压温度为100℃，压强为0.2Mpa，热压时间为10秒；
    S3、热压完成后，将压合在一起的被测隔膜样品从一端分开，进行90°剥离，记录被测隔膜样品分开时的剥离力，该剥离力即为干法剥离力。
  10. 如权利要求1所述的锂电池，其特征在于：所述内层隔膜具有第一内层贴合段，所述内层隔膜的第一内层贴合段为内层隔膜和内层隔膜贴合，所述内层隔膜的第一内层贴合段的胶面的湿法剥离力≥2N/m且所述内层隔膜的第一内层贴合段的陶瓷面的湿法剥离力≥1N/m，所述湿法剥离力通过以下步骤确定：
    S1、将被测隔膜裁剪为尺寸合适的样品，将两片被测隔膜样品对齐叠放；
    S2、将叠放好的两片被测隔膜样品放入铝塑膜中进行封装，注入电解液后，抽真空密封；
    S3、用化成机对密封好的铝塑膜进行热压，热压温度为80℃，压强为0.8Mpa，热压时间为2小时；
    S4、热压完成后，将被测隔膜样品从铝塑膜中取出，擦干电解液，将被测隔膜样品装入硬封带中，进行热压，热压温度为100℃，压强为0.2Mpa，热压时间为10秒；
    S5、热压完成后，将压合在一起的两片被测隔膜样品从一端分开，进行90°剥离，记录被测隔膜样品分开时的剥离力，该剥离力即为湿法剥离力。
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