WO2022122031A1 - 锂电池 - Google Patents

锂电池 Download PDF

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Publication number
WO2022122031A1
WO2022122031A1 PCT/CN2021/137219 CN2021137219W WO2022122031A1 WO 2022122031 A1 WO2022122031 A1 WO 2022122031A1 CN 2021137219 W CN2021137219 W CN 2021137219W WO 2022122031 A1 WO2022122031 A1 WO 2022122031A1
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WO
WIPO (PCT)
Prior art keywords
diaphragm
section
layer
inner layer
separator
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/CN2021/137219
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English (en)
French (fr)
Inventor
赵君义
邹浒
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Zhuhai Cosmx Battery Co Ltd
Original Assignee
Zhuhai Cosmx Battery Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Zhuhai Cosmx Battery Co Ltd filed Critical Zhuhai Cosmx Battery Co Ltd
Priority to EP21902736.4A priority Critical patent/EP4160780A4/en
Publication of WO2022122031A1 publication Critical patent/WO2022122031A1/zh
Priority to US18/148,966 priority patent/US20230223582A1/en
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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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
    • H01M10/04—Construction or manufacture in general
    • H01M10/0431—Cells with wound or folded 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
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • 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
    • H01M10/05—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
    • H01M50/40—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
    • H01M50/449—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
    • H01M50/489—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 core 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 type or multiple types of PVDF in an organic solvent (such as NMP, DMAC, etc.) according to a specific ratio, and coating the solution 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 schematic diagrams of two kinds of pole piece discounting.
  • Figure 1a shows a schematic diagram of a fold at the empty foil after the winding machine completes the winding action, because the diaphragm and the copper foil on the head are tightly bonded and the core cannot be stretched out during the compaction stage.
  • the one-sided paste-coated surface of the pole piece head will appear similar to the overlapping part indicated by the arrow in Figure 1b (the location and size of the occurrence are not limited to the situation shown in Figure 1b) , the overlapping part is observed under X-ray, and it can be seen that it is a thin line with a darker color, and its width is about 0-1mm. Discounted pole pieces can easily lead to potential safety hazards in the battery.
  • the purpose of the present invention is to provide a lithium battery, which can reduce the phenomenon of poor production such as pole piece discount, 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 have opposite polarities;
  • the inner layer diaphragm is located at the innermost layer of the winding core, and both the inner layer diaphragm and the outer layer diaphragm have a clamping section, a first straight section connected with the clamping section and located after the clamping section, extending beyond the clamping section.
  • the tail fitting section of 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 tail fitting section is respectively fitted with the clamping section, the first straight section and the tail fitting section of the outer membrane; the first straight section of the inner membrane and the first straight section of the outer membrane
  • the dry peel force of a straight section is less than 8N/m.
  • the dry peel force is determined by the following method:
  • 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 the dry peeling force of the ceramic surface of the separator.
  • 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.
  • the length of the first straight section of the inner layer membrane and the length of the first straight section of the outer layer 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.
  • the length of the tail fitting section of the inner layer membrane and the length of the tail fitting section of the outer layer membrane are both 0.1-10% of the width of the roll core.
  • 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 5 N/m.
  • the lithium battery of the present invention is prepared by using the separator with a specific dry peeling force in the first straight section to prepare the winding core, so that the separator can be matched with other materials, so that the winding machine can stably output the product and obtain extremely high performance.
  • a battery structure with a wafer discount rate that meets the quality requirements is conducive to improving product yield and production efficiency.
  • the dry peeling force of the diaphragm (the adhesive force of the diaphragm coating) can be directly used for the hot-pressing compounding of the diaphragm and the diaphragm, and then the peeling force between the adhesive layer or the ceramic layer of the diaphragm can be tested by using an electronic universal testing machine.
  • the peeling force can determine the battery hardness in the subsequent process in advance, and identify the adhesion between the main materials of the battery cell in advance, so as to select the separator material that meets the requirements of the dry peeling force, and then output the battery with better hardness and better performance.
  • the ceramic layer contains ceramic particles and a binding polymer, and the content of the ceramic particles is 85-92%.
  • the ceramic particles are one or more of alumina, boehmite, and magnesia.
  • the adhesive polymer is polyvinylidene fluoride, polyvinylpyrrolidone, vinylidene fluoride-hexafluoropropylene polymer, polyacrylonitrile, sodium carboxymethyl cellulose, sodium polyacrylate, polyacrylic acid, polyacrylic acid Acrylates, styrene-butadiene copolymers, butadiene-acrylonitrile polymers, polyvinyl alcohol, polymethyl acrylate, polymethyl methacrylate, polyethyl acrylate, polyacrylic acid-styrene polymers at least one of.
  • the D10 particle size is 0.15-0.3 ⁇ m
  • the D50 particle size is 0.35-0.45 ⁇ m
  • the D90 particle size is 0.6-0.8 ⁇ m
  • the 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 thickness of the adhesive layer is 0.5 ⁇ m to 3 ⁇ m, and the packing density of the adhesive layer is 0.6 g/m 2 to 3.0 g/m 2 .
  • 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 Figure 1b are schematic diagrams of pole piece discounting respectively
  • Figure 2 is a schematic structural diagram of a lithium battery separator
  • FIG. 3 is a schematic structural diagram of a positive electrode sheet of a lithium battery
  • FIG. 4 is a schematic structural diagram of a lithium battery negative electrode sheet
  • Fig. 5a is the schematic diagram when the coil is wound on the separator and the positive and negative electrode sheets
  • Figure 5b is a schematic diagram of the winding core after the needle is drawn
  • Fig. 6 is the schematic diagram that the diaphragm is hot-pressed and compounded
  • Fig. 7 is the schematic diagram of carrying out 90° peeling with electronic universal testing machine
  • Fig. 8 is the SEM image of the ceramic surface of EJ oil-based diaphragm 5 before hot pressing and compounding;
  • Fig. 9 is the SEM image of the substrate surface before the hot pressing of EJ oil-based diaphragm 1;
  • Fig. 10 is the SEM image of the ceramic surface after the EJ oil-based separator 5 is peeled off;
  • Fig. 11 is the SEM image of the ceramic surface after the EJ oil-based separator 6 is peeled off;
  • Fig. 12 is the SEM image of the substrate surface after the EJ oil-based separator 1 is peeled off;
  • FIG. 13 is a SEM image of the substrate surface after the EJ oil-based separator 2 is peeled off.
  • the lithium battery includes a winding core and tabs.
  • the winding core is formed by stacking a positive electrode sheet (first polar sheet), a negative electrode sheet (second polar sheet) and a separator, and then winding, and the separator is located between the positive electrode sheet and the negative electrode sheet.
  • 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 .
  • the separator shown in FIG. 2 only 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 adhesive polymer, the ceramic particles can be alumina, boehmite, magnesium oxide, and the adhesive 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 adhesive polymer is polyvinylidene fluoride, polyvinylpyrrolidone, vinylidene fluoride-hexafluoropropylene polymerization polyacrylonitrile, sodium carboxymethyl cellulose, sodium polyacrylate, polyacrylic acid, polyacrylate, sty
  • 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 5a represents 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 frame b in Figure 5a.
  • 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. (not shown) press the positive electrode sheet D (the thin solid line in Fig.
  • the positive electrode sheet D enters along the separator, so the positive electrode sheet D and the negative electrode sheet C are separated by the separator, before winding
  • the body action is completed, the positive and negative pressure rollers are retracted, the positive and negative plates rotate with the diaphragm, and are wound into a winding core to form a layer of diaphragm--a layer of negative plates--a layer of diaphragms--a layer of positive plates. structure.
  • another winding process can also be used.
  • 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 the arrow Q in Figure 5b.
  • 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 fit segment as indicated by arrow P in Figure 5b.
  • the winding core shown in Figure 5b 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 5a). , the part in the wire frame b and the part pointed by the arrow Q in Figure 5b), 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 thick and short lines in Figures 5a and 5b are the tabs M.
  • the separator based on the above composition structure has a specific dry peeling force (the adhesive force of the surface coating of the separator), which is achieved by The dry peeling force can identify the adhesive effect of the separator between the core layers, so that the adhesive force between the separator and the separator as well as the separator and the positive and negative electrodes can be identified in advance according to the dry peeling force, and whether the separator can be judged in advance.
  • the dry peeling force of the present invention is to perform 90° peeling after the separator is hot-pressed in an electrolyte-free environment, and the peeling force is the dry peeling force.
  • 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 samples of the tested diaphragm with paper; for example, when testing the diaphragm of the clamping section, fit the inner and outer diaphragms at the position of the clamping section and cut them into pieces. samples, aligned and stacked;
  • thermoplastic machine to heat seal the laminated surface of the two stacked diaphragm samples to be tested.
  • the model of the thermoplastic machine used in this example is SKY-325R6, the hot pressing temperature is 100°C, and the surface pressure is 0.2Mpa, hot pressing time is 10 seconds;
  • the present invention evaluates the adhesive force between the separator coatings by the dry peel force. Therefore, when testing the dry peel force of the separator, the separators of the same material that are pressed together are separated, and the two separators have the same coating. Instead of using auxiliary materials with different surface materials such as quick-drying adhesive and double-sided tape, more accurate data on the adhesion of the membrane surface coating can be obtained. In addition, 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 following table shows the results of peel force testing on 3 different types of oil-based diaphragms.
  • FIGS 8 and 9 are the SEM images of the substrate surface of EJ oil-based diaphragm 5 and EJ oil-based diaphragm 1 before hot-pressing compounding, respectively.
  • the SEM images of the substrate surface of EJ oil-based diaphragm 6-8 before hot-pressing compounding are similar to Figure 8
  • the SEM image of the substrate surface of EJ oil-based diaphragm 2-4 before hot pressing composite is similar to Figure 9.
  • the ratio of the adhesive surface also increases, and the transfer area also increases; for the same diaphragm, the dry peeling force of the adhesive surface (substrate surface) is greater than the dry peeling force of the ceramic surface, so the dry peeling force of the ceramic surface can be used.
  • the peeling force is used to select the diaphragm material;
  • the proportion of pole pieces and empty foil discounts on the core decreases significantly when the battery core is wound down, and the core is hot-pressed or core-baked.
  • the proportion of the empty foil and the pole piece is obviously reduced to 30%.
  • the ceramic surface of the diaphragm and the substrate surface will show the SEM effect similar to Figure 10 to Figure 13.
  • the ceramic surface of the diaphragm or the adhesive on the substrate surface will appear. The layer appears to peel off and transfer, and the proportion of the transfer area is reduced to 20% to 40%;
  • the core manufacturing process is stable, and the core is not easy to be folded when the core is turned off during the cell winding process.
  • the foil and the pole piece are discounted, and the ceramic surface and the substrate surface of the separator do not have the SEM effects shown in Figure 10 to Figure 13 after peeling.
  • 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 has been improved.
  • the diaphragm is well used in the winding process, the core manufacturing process is stable, and the pole piece discount ratio is low, even as low as 0.
  • the sticking effect will occur after the core is compacted, and the area of the diaphragm beyond the negative electrode is also prone to the phenomenon of diaphragm adhesion, which makes the adhesion effect of the diaphragm significantly improved. It shows better bonding performance, which can realize the bonding between the separator and the positive and negative electrode sheets.
  • the hardness of the battery is better, and the head of the winding core of the battery and the separator at the bottom are in contact with adhesiveness during hot pressing. It has become better.
  • the present invention selects the diaphragm according to the dry peeling force on the surface of the diaphragm, and the first straight section of the inner layer diaphragm in the lithium battery coil core And the dry peeling force of the first straight section of the outer layer diaphragm is less than 8N/m, so as to improve the phenomenon of pole piece folding.
  • the dry peel force is the dry peel force of the ceramic surface of the separator.
  • the invention selects the diaphragm material by the dry peeling force, which is convenient for the control of the diaphragm coating, can identify the bonding effect between the diaphragm layers in time, and selects the diaphragm material matching the rolling needle (Teflon) based on the dry peeling force.
  • Teflon rolling needle
  • the dry peeling force of the present invention is used to test the peeling force between the separator coatings using an electronic universal testing machine after the separator and the separator are hot-pressed.
  • It can identify the adhesion between the main materials of the battery in advance, and then output the battery with better hardness and better performance. It can also be used as an incoming material management method for the diaphragm coating to identify incoming diaphragm materials The macroscopic index and then whether it can meet the bonding performance of the cell after hot pressing.

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Abstract

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和所述外层隔膜的第一平直段的干法剥离力小于8N/m。本发明使用具有特定表面剥离力的隔膜生产卷芯，避免极片、空箔打折的问题，可以提高产品良率和质量。

Description

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202011451375.1、申请名称为“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。
锂电池中，隔膜与极片粘接在一起，隔膜表面涂层的粘接力直接影响电芯的卷绕、化成等工序以及成品的质量，隔膜表面涂层的粘接力不合格，可能会导致极片出现打折等质量缺陷。图1a和图1b为两种极片打折的示意图。图1a所示是卷绕机台完成卷绕动作后，由于隔膜与头部铜箔粘合较紧，卷芯压实阶段未能舒展开而导致空箔处出现打折的示意图。对存在此类缺陷的卷芯进行拆解后，发现极片头部首折会出现类似图1a中箭头所指的重叠部分(出现的位置以及大小不局限于图1a所示的情况)，重叠部分在X-ray下观察，可看到其为一条颜色较深的细线，宽度约在0～1mm之间。图1b所示是卷绕机台完成卷绕动作后，由于隔膜与头部铜箔粘合较紧，卷芯压实阶段因单面涂膏的两面张力释放不一致而导致极片未能及时舒展导致的打折的示意图。对存在此类缺陷的卷芯进行拆解后，发现极片头部单面涂膏面会出现类似图1b中箭头所指的重叠部分(出现的位置以及大小不局限于图1b所示的情况)，重叠部分在X-ray下观察，可看到其为一条颜色较深的细线，其宽度约在0～1mm之间。极片打折容易导致电池存在安全隐患。
发明内容
本发明的目的在于提供一种锂电池，可以减少极片打折等生产不良的现象，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：
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和所述外层隔膜的第一平直段的干法剥离力小于8N/m。
更具体的，所述干法剥离力通过以下方法确定：
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。
优选的，所述干法剥离力为隔膜的陶瓷面的干法剥离力。
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％。
更具体的，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。
更具体的，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％。
优选的，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5N/m。
更具体的，所述内层隔膜和所述外层隔膜的胶转移面积占比为20～40％，胶转移面积占比＝胶转移质量/隔膜面积，胶转移质量＝干法剥离前隔膜的质量-干法剥离后隔膜的质量。
由以上技术方案可知，本发明的锂电池通过使用第一平直段具有特定的干法剥离力的隔膜制备卷芯，使隔膜与其它材料相匹配，从而卷绕机能够稳定输出产品，得到极片打折率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。隔膜的干法剥离力(隔膜涂层的 粘接力)可以直接使用隔膜与隔膜进行热压复合后，使用电子万能试验机进行隔膜胶层或者陶瓷层之间的剥离力测试，通过测得的剥离力可以提前判别后工序的电池硬度，提前识别出电芯各主材之间的粘附力，从而选择干法剥离力符合要求的隔膜材料，进而输出硬度较好和性能较好的电池。
更具体的，所述陶瓷层中包含陶瓷颗粒和粘结性聚合物，陶瓷颗粒的含量为85～92％。
更具体的，所述陶瓷颗粒为氧化铝、勃母石、氧化镁中的一种或几种。
更具体的，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，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，所述胶层的厚度为0.5μm～3μm，胶层的填充密度为0.6g/m2～3.0g/m2。
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分别为极片打折的示意图；
图2为锂电池隔膜的结构示意图；
图3为锂电池正极片的结构示意图；
图4为锂电池负极片的结构示意图；
图5a为卷针对隔膜以及正、负极片进行卷绕时的示意图；
图5b为抽针后卷芯的示意图；
图6为将隔膜进行热压复合的示意图；
图7为用电子万能试验机进行90°剥离的示意图；
图8为EJ油系隔膜5热压复合前陶瓷面的SEM图；
图9为EJ油系隔膜1热压复合前基材面的SEM图；
图10为EJ油系隔膜5剥离后陶瓷面的SEM图；
图11为EJ油系隔膜6剥离后陶瓷面的SEM图；
图12为EJ油系隔膜1剥离后基材面的SEM图；
图13为EJ油系隔膜2剥离后基材面的SEM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。
锂电池包括卷芯和极耳，卷芯由正极片(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。如图2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2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接性聚合物，陶瓷颗粒可以是氧化铝、勃母石、氧化镁，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。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％，粘接性聚合物的分子量30万～100万。
如图3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4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5a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5a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5a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5a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5a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5a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5b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5b中箭头P指向的部分。
图5b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5a中线框a内的部分、线框b内的部分以及图5b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5a和图5b中的粗短线为极耳M。
当隔膜的粘接力较大时，隔膜在卷芯制作过程中较易与卷针发生粘连现象，导致卷芯下台就会出现空箔打折(图1a)和/或极片打折(图1b)的现象。而且由于隔膜常温收缩过大(标准＜0.3％)，隔膜也会与刚入的负极发生粘连吸附现象，导致卷芯Hi-Pot热压，而出现极片空箔打折和/或头部单面区负极片打折的现象。这些现象产生的主要原因是因为电芯在卷绕时，由于隔膜拉伸后回缩导致局部因吸附导致空箔、极片出现折痕，然后卷芯经过25℃～60℃卷芯压实，导致隔膜与极片无舒展地方导致的空箔、极片打折现象。
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)的隔膜具有特定的干法剥离力(隔膜表面涂层的粘接力)，通过干法剥离力可以对隔膜在卷芯层间的粘接效果进行鉴别，从而可以根据干法剥离力来提前识别隔膜与隔膜以及隔膜与正负极之间的粘附力，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，选择具有特定干法剥离力的隔膜制备电池卷芯，减少极片打折等生产异常的情况，进而输出硬度较好和性能较好的电池。本发明的干法剥离力是在无电解液的环境下对隔膜进行热压复合后，再进行90°剥离，该剥离力即为干法剥离力。
下面结合图6和图7，对本发明剥离力测试的过程进行说明，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；如对夹持段的隔膜进行测试时，将夹持段位置的贴合在一起内层隔膜和外层隔膜裁切成样品，对齐叠放；
S2、将叠放好的两片被测隔膜样品使用热塑机进行贴合面热封处理，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7)，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评估隔膜涂层之间的粘接力，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剥离力测试的结果。
Figure PCTCN2021137219-appb-000001
在以上进行了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，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8和图9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8类似，EJ油系隔膜2-4热压复合前基材面的SEM图与图9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 PCTCN2021137219-appb-000002
根据抽检结果可知，对于凹版油系隔膜，当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10至图13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)的干法剥离力都是大于陶瓷面的干法剥离力的，因此可用陶瓷面的干法剥离力来选择隔膜材料；
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10至图13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，卷芯制程稳定，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图10至图13的SEM效果。
综上可知，干法剥离力(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，卷芯压实后会发生粘连效应，隔膜超出负极的区域也易发生隔膜粘接现象，使得隔膜在粘接效果明显变好，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，而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。
因此，为了避免卷芯卷绕下台，封装、烘烤之后的极片打折的问题，本发明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。
本发明通过干法剥离力来选择隔膜材料，方便进行隔膜涂层进行管控，可以及时识别隔膜层间的粘接效果，并基于干法剥离力选择与卷针(特氟龙)匹配的隔膜材料，通过控制隔膜的干法剥离力，可以提前避免卷芯卷绕下台，封装、烘烤之后的极片打折的问题，有利于提高卷绕良率和产品良率。而且本发明的干法剥离力在将隔膜与隔膜进行热压复合后，使用电子万能试验机进行隔膜涂层之间的剥离力测试，通过层间的剥离力在卷绕初期就能够判别后工序的电池硬度，提前识别出电芯各主材之间的粘附力，进而输出硬度较好和性能较好的电池，也可以作为隔膜涂层的一种来料管理手段，及时识别隔膜来料的宏观指标进而是否能够满足电芯热压化成后的粘接性能。
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. 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和所述外层隔膜的第一平直段的干法剥离力小于8N/m。
  2. 如权利要求1所述的锂电池，其特征在于：所述干法剥离力通过下述方法确定：
    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。
  3. 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。
  4. 如权利要求3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。
  5. 如权利要求3所述的锂电池，其特征在于：所述干法剥离力为隔膜的陶瓷面的干法剥离力。
  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％。
  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％。
  10. 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5N/m。
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