WO2024192602A1 - 隔离膜及其制备方法、二次电池和用电装置 - Google Patents

隔离膜及其制备方法、二次电池和用电装置 Download PDF

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Publication number
WO2024192602A1
WO2024192602A1 PCT/CN2023/082347 CN2023082347W WO2024192602A1 WO 2024192602 A1 WO2024192602 A1 WO 2024192602A1 CN 2023082347 W CN2023082347 W CN 2023082347W WO 2024192602 A1 WO2024192602 A1 WO 2024192602A1
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WO
WIPO (PCT)
Prior art keywords
base film
film
isolation
derivatives
optionally
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/CN2023/082347
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English (en)
French (fr)
Inventor
李�权
杨建瑞
孙成栋
欧阳楚英
黄思应
韩崇旺
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Contemporary Amperex Technology Co Ltd
Original Assignee
Contemporary Amperex Technology 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.)
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Publication date
Application filed by Contemporary Amperex Technology Co Ltd filed Critical Contemporary Amperex Technology Co Ltd
Priority to PCT/CN2023/082347 priority Critical patent/WO2024192602A1/zh
Priority to KR1020257015086A priority patent/KR102937079B1/ko
Priority to JP2025526556A priority patent/JP2025537247A/ja
Priority to CN202380049306.3A priority patent/CN119452516A/zh
Priority to EP23927920.1A priority patent/EP4597720A4/en
Publication of WO2024192602A1 publication Critical patent/WO2024192602A1/zh
Priority to US19/212,821 priority patent/US20250286230A1/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
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
    • H01M50/494—Tensile strength
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B7/00—Layered products characterised by the relation between layers; Layered products characterised by the relative orientation of features between layers, or by the relative values of a measurable parameter between layers, i.e. products comprising layers having different physical, chemical or physicochemical properties; Layered products characterised by the interconnection of layers
    • B32B7/04—Interconnection of layers
    • B32B7/12—Interconnection of layers using interposed adhesives or interposed materials with bonding properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/06—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material
    • B32B27/08—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/28—Layered products comprising a layer of synthetic resin comprising synthetic resins not wholly covered by any one of the sub-groups B32B27/30 - B32B27/42
    • B32B27/281—Layered products comprising a layer of synthetic resin comprising synthetic resins not wholly covered by any one of the sub-groups B32B27/30 - B32B27/42 comprising polyimides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/30—Layered products comprising a layer of synthetic resin comprising vinyl (co)polymers; comprising acrylic (co)polymers
    • B32B27/304—Layered products comprising a layer of synthetic resin comprising vinyl (co)polymers; comprising acrylic (co)polymers comprising vinyl halide (co)polymers, e.g. PVC, PVDC, PVF, PVDF
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/36—Layered products comprising a layer of synthetic resin comprising polyesters
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/403—Manufacturing processes of separators, membranes or diaphragms
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
    • H01M50/417—Polyolefins
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
    • H01M50/426—Fluorocarbon polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
    • H01M50/457—Separators, membranes or diaphragms characterised by the material having a layered structure comprising three or more layers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2457/00—Electrical equipment
    • B32B2457/10—Batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application belongs to the technical field of secondary batteries, and specifically relates to an isolation membrane and a preparation method thereof, a secondary battery and an electrical device.
  • Secondary batteries are widely used in various consumer electronic products and electric vehicles due to their outstanding characteristics of light weight, no pollution and no memory effect.
  • the present application provides an isolation membrane and a preparation method thereof, a secondary battery and an electrical device, aiming to improve the reliability of the isolation membrane and the secondary battery.
  • the first aspect of the present application provides an isolation film, which includes a first base film and a second base film, the melting point of the second base film is lower than the melting point of the first base film; the swelling rate of the first base film is lower than the swelling rate of the second base film.
  • the present application includes at least the following beneficial effects: through the mutual cooperation of the two-layer base film structure, the isolation membrane can be used in the application environment for a long time. Even if one layer of the base film loses its insulating properties due to swelling, the other layer of the base film can also play a role in supplementing the performance, thereby reducing the risk of electrode short circuit. At the same time, it can improve the strength of the diaphragm, thereby improving the reliability of the battery during its long life.
  • the ratio of the swelling rate of the first base film to the swelling rate of the second base film is less than or equal to 0.8, and can be optionally less than or equal to 0.3.
  • the isolation membrane can be used for a long time in the application environment. Even if one base film loses its insulating properties due to swelling, the other base film can also play a role in supplementing the performance and reduce the risk of electrode short circuit. At the same time, it can increase the strength of the separator, thereby improving the reliability of the battery during its long life.
  • the swelling rate of the first base film is less than or equal to 5%, and may be 0.2%-2%; the swelling rate of the second base film is less than or equal to 10%, and may be 1-8%.
  • the isolation membrane can be used for a long time in the application environment. Even if one layer of the base film loses its insulating properties due to swelling, the other layer of the base film can also play a role in supplementing the performance and reduce the risk of electrode short circuit. At the same time, it can increase the strength of the separator, thereby improving the reliability of the battery during its long life.
  • the crystallinity of the first base film is lower than the crystallinity of the second base film.
  • the ratio of the crystallinity of the first base film to the crystallinity of the second base film is 0.4-0.85, and can be optionally 0.4-0.6.
  • the crystallinity of the first base film is 40%-60%, and can be 45%-50%;
  • the crystallinity of the second base film is 45%-85%, and can be 65%-80%.
  • the degree of branching of the first base film is greater than the degree of branching of the second base film.
  • the degree of branching of the first base film is 0.4-0.9, and can be optionally 0.7-0.9; the degree of branching of the second base film is 0.01-0.4, and can be optionally 0.01-0.2.
  • the crystallinity reflects the orderliness of the material structure to a certain extent. The higher the crystallinity, the more ordered the material structure is, and it is not easy to swell, that is, the swelling rate will decrease.
  • the branching degree reflects the degree of adding nonlinear polymer structure branches to the main chain of the material. The higher the branching degree, the more and more complex the side chains formed, and the easier the material is to swell, that is, the swelling rate increases.
  • the branching degree of the first base film is greater than the branching degree of the second base film, and the value is within the above range, the swelling rate of the first base film and the second base film can be balanced, and the first base film and the second base film can have good strength under the premise of sufficient swelling capacity, further improving the reliability of the secondary battery.
  • the melting point of the first base film is 155°C-365°C, and can be optionally 160°C-340°C; the melting point of the second base film is 130°C-250°C, and can be optionally 135°C-220°C.
  • the first base film with a high melting point plays a role in supplementing the heat resistance
  • the second base film with a low melting point plays a role in supplementing the swelling performance, so that the isolation membrane can enhance the heat resistance in the battery environment and reduce the degree of swelling, thereby improving the reliability of the battery and extending its service life.
  • the first base film and the second base film are independently selected from at least one of polyolefins and their derivatives, halogenated polyolefins and their derivatives, polyethers and their derivatives, polyetheretherketones and their derivatives, polyesters and their derivatives, polyimides and their derivatives, polyvinyl alcohols and their derivatives, polytetrafluoroethylenes and their derivatives, polyvinyl fluorides and their derivatives, polyvinylidene fluoride and their derivatives, and polyethylene terephthalate and their derivatives.
  • Using at least one of the above materials as the first base film and the second base film can make the first base film and the second base film have good chemical stability, and at the same time make the isolation film have lower swelling and higher strength.
  • an adhesive layer is further provided between the first base film and the second base film, and the adhesive layer includes an adhesive; optionally, the adhesive layer includes an adhesive and a filler.
  • the provision of the adhesive layer can not only compensate for process defects in the base film composite process, but also further improve the physical properties of the isolation film, thereby improving the reliability of the secondary battery.
  • the adhesive includes one or more of polyacrylate, polyacrylic acid, polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride-trichloroethylene copolymer, polyvinyl pyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyethylene oxide, polyarylate, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, polyacrylonitrile, polyvinyl alcohol, polyethylene, polypropylene, starch, and cyanoethyl pullulan.
  • the filler includes at least one of inorganic particles, organic particles, and organic-metal framework materials.
  • the air permeability of the isolation membrane is less than or equal to 400s/100cc, and can be optionally 250s/100cc-320s/100cc.
  • the transverse tensile strength of the separator is 1500-4500 kgf/cm 2 , which can be selected as 3000-4500kgf/ cm2 .
  • the longitudinal tensile strength of the isolation film is 1500-4500 kgf/cm 2 , and can be optionally 3000-4500 kgf/cm 2 .
  • the transverse heat shrinkage rate of the isolation film at 250° C. for 1 h is less than or equal to 0.4%, and can be optionally less than or equal to 0.2%.
  • the longitudinal heat shrinkage rate of the isolation film at 250° C. for 1 hour is less than or equal to 0.4%, and can be optionally less than or equal to 0.2%.
  • the separator When at least one of the above items of the separator satisfies the given range, the separator has good physical properties, thereby improving the reliability of the secondary battery.
  • it further comprises providing an adhesive layer slurry, wherein the adhesive layer slurry comprises an adhesive, and coating the adhesive layer slurry on the first base film and/or the second base film to form an adhesive layer.
  • the adhesive layer slurry further includes a filler; optionally, the filler includes at least one of inorganic particles, organic particles, and organic-metal framework materials.
  • the adhesive layer slurry further includes a filler, and the filler includes at least one of the above materials, the physical properties of the isolation membrane can be further improved, thereby improving the reliability of the secondary battery.
  • the third aspect of the present application provides a secondary battery, which includes the separator of the first aspect of the present application or the separator prepared according to the method of the second aspect of the present application.
  • the secondary battery adopts the given separator, the reliability of the secondary battery can be improved.
  • the present application also includes a positive electrode sheet and a negative electrode sheet, and the isolation membrane is arranged between the positive electrode sheet and the negative electrode sheet, and the second base membrane faces the negative electrode sheet, so that the second base membrane facing the negative electrode sheet can supplement the swelling performance, and can make the physical properties of the isolation membrane more stable.
  • the second base membrane can also play a role in supplementing the performance to prevent electrode short circuit, while also taking into account the strength of the isolation membrane, thereby improving the reliability and cycle life of the battery in the long-term cycle life process.
  • the fourth aspect of the present application provides an electric device, which includes the secondary battery of the third aspect of the present application.
  • the secondary battery of the electric device adopts the given isolation film, the reliability of the electric device can be improved.
  • the device of the present application includes the secondary battery provided by the present application, it has at least the same advantages as the secondary battery.
  • FIG. 1 is a schematic structural diagram of an isolation membrane according to an embodiment of the present application.
  • FIG. 2 is a schematic structural diagram of an isolation membrane according to an embodiment of the present application.
  • FIG. 3 is a schematic flow chart of an embodiment of a method for preparing an isolation membrane of the present application.
  • FIG. 4 is a schematic diagram of an embodiment of a secondary battery.
  • FIG. 5 is an exploded view of FIG. 4 .
  • FIG. 6 is a schematic diagram of an embodiment of a battery module.
  • FIG. 7 is a schematic diagram of an embodiment of a battery pack.
  • FIG. 8 is an exploded view of FIG. 7 .
  • FIG. 9 is a schematic diagram of an embodiment of a device in which a secondary battery is used as a power source.
  • any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, and any upper limit can be combined with any other upper limit to form an unspecified range.
  • each separately disclosed point or single value can itself be combined as a lower limit or upper limit with any other point or single value or with other lower limits or upper limits to form an unspecified range.
  • the term "or” is inclusive. That is, the phrase “A or (or) B” means “A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B”: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).
  • a secondary battery is a battery that can be recharged to activate the active materials after being discharged and continue to be used.
  • a secondary battery includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte.
  • active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet.
  • the separator is arranged between the positive electrode sheet and the negative electrode sheet to play a role of isolation.
  • the electrolyte plays a role of conducting ions between the positive electrode sheet and the negative electrode sheet.
  • an embodiment of the present application provides an isolation film 10, comprising a first base film 11 and a second base film 12, wherein the melting point of the second base film 12 is lower than the melting point of the first base film 11, and the swelling rate of the first base film 11 is lower than the swelling rate of the second base film 12.
  • the isolation film can have good heat resistance. At the same time, it takes into account good reliability.
  • two base membranes with different swelling rates are selected for compounding, so that the physical properties of the isolation membrane can be made more stable.
  • the other layer of the base membrane can also play a role in supplementing the performance and preventing the electrode from short-circuiting.
  • the strength of the isolation membrane is also taken into account, thereby improving the reliability and cycle life of the battery during the long-term cycle life.
  • the ratio of the swelling rate of the first base film to the swelling rate of the second base film is less than or equal to 0.8, and can be less than or equal to 0.3.
  • the ratio of the swelling rate of the first base film to the swelling rate of the second base film can be 0.001, 0.01, 0.03, 0.05, 0.06, 0.08, 0.1, 0.15, 0.2, 0.25, 0.31, 0.35, 0.4, 0.45, 0.5, 0.6, 0.65, 0.7, 0.8, etc. Or a range consisting of any two of the above values.
  • the ratio of the swelling rate of the first base film to the swelling rate of the second base film can be selected as 0.001-0.01, 0.01-0.08, 0.02-0.06, 0.04-0.08, 0.1-0.15, 0.2-0.25, 0.25-0.35, 0.35-0.45, 0.5-0.65, 0.65-0.8, etc.
  • the isolation membrane can be used for a long time in the application environment. Even if one layer of the base film loses its insulating properties due to swelling, the other layer of the base film can also play a role in supplementing the performance to prevent electrode short circuit. At the same time, the strength of the separator is improved, thereby improving the reliability and cycle life of the battery in the long life course.
  • the swelling rate of the first base film is less than or equal to 5%, and can be selected as 0.2-2%.
  • the swelling rate of the first base film can be selected as 0.1%, 0.3%, 0.5%, 0.7%, 1.1%, 1.4%, 1.8%, 2.2%, 2.4%, 2.9%, 3.4%, 3.6%, 4.1%, 4.8%, 5%, etc., or a range consisting of any two of the above values.
  • the swelling rate of the first base film can be selected as 0.01%-0.1%, 0.1%-5%, 0.1%-3.4%, 0.1%-2.9%, 0.1%-2.2%, 0.1%-0.5%, 0.5%-5%, 0.5%-4.1%, 0.5%-3.4%, 0.5%-2.4%, 0.5%-1.1%, 1.1%-5%, 1.1%-4.1%, 1.1%-3.6%, 1.1%-3.4%, 1.1%-1.8%, 2.2%-5%, 2.2%-4.8%, 2.2%-4.1%, 2.2%-3.6%, 2.2%-2.9%, 3.4%-5%, 3.4%-4.1%, 4.1%-5%, etc.
  • the swelling rate of the second base film is less than or equal to 10%, and can be 1%-8%.
  • the swelling rate of the second base film can be 0.2%, 0.4%, 0.7%, 0.9%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 1.9%, 2.0%, 2.1%, 2.6%, 3.5%, 3.7%, 4.4%, 6.4%, 7.8%, 9.2%, 10%, etc. Or it is a range consisting of any two of the above values.
  • the swelling rate of the second base film can be selected as 0.01-0.05%, 0.05-0.2%, 0.05-1.0%, 0.05-1.5%, 0.05-2.0%, 0.05-5.0%, 0.05-8.0%, 0.3-0.5%, 1.0-1.5%, 1.0-2.0%, 1.5-5.0%, 2.0-8.0%, 5.0-8.0%, 3.0-8.0%, 7.5-9.0%, 0.2%-0.7%, 0.7%-1.0%, 1.0%-1.6%, 1.8%-2.0%, 2.1%-2.6%, 2.6%-3.7%, 4.4%-6.4%, 7.8%-10%, etc.
  • the ratio of the swelling rate of the first base film to the swelling rate of the second base film is within a given range, the reliability of the battery during long-term cycle life can be further improved.
  • the swelling rate of the base film has a well-known meaning in the art and can be measured by methods known in the art. For example, the following test method can be adopted: Take 6 sets of base film parallel samples with a size of 50mm ⁇ 100mm. Soak the samples in the electrolyte, and the samples are completely immersed in the electrolyte and placed in a 70°C environment. Monitor the mass change every 24 hours for seven consecutive days. The rate of increase in the mass of the base film is the swelling rate.
  • the solvent used in the electrolyte includes carbonic acid
  • the mass ratio of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) is 30:70, the electrolyte salt is LiPF 6 , and the concentration of the electrolyte salt is 1.0 mol/L.
  • the swelling rate of the base film can be adjusted by adjusting the intrinsic parameters of the base film (such as one or more of the crystallinity and branching degree of the base film material) and the base film preparation process parameters (such as one or more of the stretching ratio and stretching temperature). For example, when other conditions remain unchanged, the greater the crystallinity of the base film, the smaller the swelling rate; the greater the branching degree of the base film, the greater the swelling rate.
  • the swelling rate of the base film by known methods within the range of parameters given in this application, such as adjusting the production process of the base film (regulating the crystallinity, branching degree, etc.), and a base film with the desired swelling rate can be obtained through a limited number of tests.
  • the crystallinity of the first base film is lower than the crystallinity of the second base film.
  • the ratio of the crystallinity of the first base film to the crystallinity of the second base film is 0.4-0.85, preferably 0.4-0.6.
  • the ratio of the crystallinity of the first base film to the crystallinity of the second base film can be 0.4, 0.5, 0.6, 0.7, 0.8, 0.85, etc. Or a range consisting of any two of the above values.
  • the ratio of the crystallinity of the first base film to the crystallinity of the second base film can be 0.4-0.5, 0.5-0.7, 0.7-0.85, etc.
  • the crystallinity of the first base film can be selected as 40%-60%, or 45%-50%; the crystallinity of the first base film can be specifically selected as 40%, 42%, 46%, 49%, 51%, 52%, 54%, 57%, 59%, 60%, etc. Or it is a range consisting of any two of the above values.
  • the crystallinity of the first base film can be specifically selected as 40%-42%, 42%-49%, 49%-52%, 52%-57%, 57%-60%, etc.
  • the crystallinity of the second base film can be selected as 45%-85%, or 65%-80%.
  • the crystallinity of the second base film can be specifically selected as 45%, 46%, 49%, 54%, 61%, 66%, 74%, 77%, 81%, 84%, 85%, etc. Or it is a range consisting of any two of the above values.
  • the crystallinity of the second base film can be specifically selected to be 45%-46%, 46%-54%, 54%-66%, 74%-77%, 81%-85%, etc.
  • the crystallinity reflects the orderliness of the material structure to a certain extent. The larger the crystallinity, the more ordered the material structure is, and the less likely it is to swell, that is, the swelling rate will become smaller.
  • the crystallinity of the first base film and the crystallinity of the second base film can be respectively selected within the above range, the swelling rate of the first base film and the second base film can be adjusted to make the performance of the first base film and the second base film better complementary.
  • the orderliness of the material structure also affects the strength of the material; by adjusting the crystallinity of the first base film and the crystallinity of the second base film to be respectively selected within the above range, the first base film and the second base film can have good strength while meeting the swelling requirements of this application, thereby improving the reliability of the secondary battery during its long life.
  • the crystallinity of the base film has a well-known meaning in the art and can be tested using equipment and methods known in the art.
  • the crystallinity of the base film is measured using differential scanning calorimetry (DSC). Specifically, the following test method can be adopted: take 4-6 mg of the base film sample to be tested, place it in the sample chamber of the differential scanning calorimeter, heat it from 25°C to 350°C, and the heating rate is 10°C/min to obtain the melting endothermic curve, calculate the peak area of the curve and the reference value of 100% crystalline polyolefin to obtain the crystallinity.
  • DSC differential scanning calorimetry
  • the degree of branching of the first base film is greater than the degree of branching of the second base film.
  • the degree of branching of the first base film is 0.4-0.9, and may be 0.7-0.9; the degree of branching of the second base film is 0.01-0.4, and may be 0.01-0.2.
  • the degree of branching of the first base film is 0.4, 0.5, 0.6, 0.7, 0.75, 0.78, 0.8, 0.9. Or a range consisting of any two of the above values.
  • the degree of branching of the first base film is 0.4-0.6, 0.6-0.75, 0.75-0.78, 0.78-0.9.
  • the degree of branching of the second base film can be selected as 0.01, 0.03, 0.09, 0.14, 0.18, 0.25, 0.33, 0.38, 0.4, etc. Or a range consisting of any two of the above values.
  • the degree of branching of the second base film can be selected as 0.01-0.03, 0.03-0.14, 0.14-0.25, 0.25-0.4, etc.
  • the degree of branching is the degree of adding branches of nonlinear polymer structure to the main chain of the base film material, that is, the higher the degree of branching, the more and more complex the side chains formed.
  • the higher the degree of branching the greater the swelling rate.
  • the degree of branching of the base film has a well-known meaning in the art and can be tested using equipment and methods known in the art.
  • infrared spectroscopy can be used. Specifically, the following operation can be performed: 3-5 groups of base film samples are selected, and the samples are placed in an infrared spectrometer for scanning in the scanning range of 400-4000 cm -1 . After the scanning is completed, the infrared curve of the sample is processed, and the ratio of the peak area at 1377 cm -1 to the peak area at 1996-2062 cm -1 is calculated as the degree of branching.
  • the first base film simultaneously satisfies a crystallinity of 45%-50% and a branching degree of 0.7-0.9.
  • the second base film simultaneously satisfies a crystallinity of 65%-80% and a branching degree of 0.01-0.2.
  • the two base films can satisfy the swelling degree designed in the present application while also taking into account good strength performance.
  • the melting point of the first base film is 155°C-360°C, and can be 160°C-340°C; the melting point of the second base film is 130°C-250°C, and can be 130°C-220°C.
  • the melting point of the first base film can be 155°C, 165°C, 175°C, 188°C, 191°C, 220°C, 239°C, 245°C, 271°C, 294°C, 310°C, 324°C, 347°C, 360°C, etc. Or it is a range composed of any two of the above values.
  • the melting point of the first base film can be 155°C-175°C, 175°C-220°C, 220°C-245°C, 245°C-271°C, 271°C-310°C, 310°C-360°C, etc.
  • the melting point of the second base film may be 130°C, 131°C, 133°C, 136°C, 145°C, 151°C, 163°C, 172°C, 174°C, 210°C, 225°C, 236°C, 250°C, etc. Or a range consisting of any two of the above values.
  • the melting point of the second base film may be 130°C-131°C, 131°C-136°C, 145°C-151°C, 163°C-174°C, 174°C-210°C, 210°C-250°C, etc.
  • the first base film with a high melting point supplements the heat resistance
  • the second base film with a low melting point supplements the swelling performance, so that the isolation film has good heat resistance and swelling performance.
  • the melting points of the first base film and the second base film have a well-known meaning in the art and can be measured by methods known in the art.
  • differential scanning calorimetry can be used for measurement.
  • the measurement can be performed as follows: 4-6 mg of the sample to be tested is placed in the sample chamber of a differential scanning calorimeter, the temperature is increased from 25°C to 400°C, and the heating rate is 10°C/min, and the melting endothermic curve of the sample is obtained, and the temperature corresponding to the peak of the curve is the melting point of the sample. .
  • the first base film and the second base film are independently selected from at least one of polyolefins and their derivatives, halogenated polyolefins and their derivatives, polyethers and their derivatives, polyetheretherketones and their derivatives, polyesters and their derivatives, polyimides and their derivatives, polyvinyl alcohols and their derivatives, polytetrafluoroethylenes and their derivatives, polyvinyl fluoride and their derivatives, polyvinylidene fluoride and their derivatives, polyethylene terephthalate and their derivatives.
  • the first base film can be made of polyolefins and their derivatives or halogenated polyolefins and their derivatives.
  • the first base film can also be made of polyethers and their derivatives, polyetheretherketones and their derivatives, polyesters and their derivatives, etc.
  • the first base film and the second base film can also be made of polyvinylidene fluoride and its derivatives or polyethylene terephthalate, etc.
  • derivatives generally refer to products derived from the replacement of hydrogen atoms or atomic groups in a compound by other atoms or atomic groups.
  • At least one of the above materials as the first base film and the second base film can improve the chemical stability of the first base film and the second base film, while making the isolation film have lower swelling and higher strength.
  • an embodiment of the present application provides an isolation film 10, including a first base film 11 and a second base film 12.
  • an adhesive layer 13 is further provided between the first base film 11 and the second base film 12, and the adhesive layer includes an adhesive.
  • the adhesive layer includes an adhesive and a filler.
  • an adhesive layer is provided between the first base film and the second base film and the adhesive layer includes an adhesive
  • the adhesive layer includes an adhesive
  • it can not only compensate for process defects during the hot pressing and laminating process of the base film, but also further improve the physical properties of the separator (such as tensile strength, puncture strength, heat resistance, etc.), thereby improving the reliability of the secondary battery.
  • the filler is located between the first base film and the second base film, thereby reducing the risk of powder loss.
  • the adhesive includes one or more of polyacrylate, polyacrylic acid, polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride-trichloroethylene copolymer, polyvinyl pyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyethylene oxide, polyarylate, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, polyacrylonitrile, polyvinyl alcohol, polyethylene, polypropylene, starch, and cyanoethyl pullulan.
  • the filler includes at least one of inorganic particles, organic particles, and organic-metal framework materials.
  • the inorganic particles include one or more of inorganic particles having a dielectric constant of 5 or more, inorganic particles having ion conductivity but not storing ions, and inorganic particles capable of electrochemical reaction.
  • the inorganic particles having a dielectric constant of 5 or more may include at least one of boehmite, aluminum oxide, zinc oxide, silicon oxide, titanium oxide, zirconium oxide, barium oxide, calcium oxide, magnesium oxide, nickel oxide, tin oxide, cerium oxide, yttrium oxide, hafnium oxide, aluminum hydroxide, magnesium hydroxide, silicon carbide, boron carbide, aluminum nitride, silicon nitride, boron nitride, magnesium fluoride, calcium fluoride, barium fluoride, barium sulfate, magnesium aluminum silicate, lithium magnesium silicate, sodium magnesium silicate, bentonite, hectorite, zirconium titanate, barium titanate, Pb(Zr,Ti)O 3 (abbreviated as PZT), Pb1-mLamZr1-nTinO 3 (abbreviated as PLZT, 0 ⁇ m ⁇ 1, 0 ⁇ n ⁇ 1), Pb(Mg 3
  • the modification of each inorganic particle can be chemical modification and/or physical modification.
  • the chemical modification includes coupling agent modification (e.g., using silane coupling agent, titanate coupling agent, etc.), surfactant modification, polymer grafting modification, etc.
  • the physical modification can be mechanical force dispersion, ultrasonic dispersion, high energy treatment, etc.
  • the modification can reduce the agglomeration of inorganic particles, thereby making the adhesive layer have a more stable and uniform structure; in addition, by selecting coupling agents, surfactants, etc. with specific functional groups, the inorganic particles can be easily dispersed, and the bonding layer ...
  • Surfactants or polymers can modify inorganic particles and help improve the wetting and retention properties of the adhesive layer to the electrolyte and improve the adhesion of the adhesive layer to the first base film and the second base film.
  • the inorganic particles having ion conductivity but not storing ions may include Li3PO4 , lithium titanium phosphate Lix1Tiy1 ( PO4 ) 3 , lithium aluminum titanium phosphate Lix2Aly2Tiz1 ( PO4 ) 3 , ( LiAlTiP) x3Oy3 type glass, lithium lanthanum titanate Lix4Lay4TiO3 , lithium germanium thiophosphate Lix5Gey5Pz2Sw , lithium nitride Lix6Ny6 , SiS2 type glass Lix7Siy7Sz3 and P2S5 type glass Lix8Py8S At least one of z4 , 0 ⁇ x1 ⁇ 2, 0 ⁇ y1 ⁇ 3, 0 ⁇ x2 ⁇ 2, 0 ⁇ y2 ⁇ 1, 0 ⁇ z1 ⁇ 3, 0 ⁇ x3 ⁇ 4, 0 ⁇ y3 ⁇ 13, 0 ⁇ x4 ⁇ 2, 0 ⁇ y4 ⁇ 3, 0 ⁇ x5 ⁇ 4,
  • the inorganic particles capable of undergoing an electrochemical reaction may include at least one of lithium-containing transition metal oxides, lithium-containing phosphates, carbon-based materials, silicon-based materials, tin-based materials, and lithium-titanium compounds.
  • the organic particles may include one or more of polycarbonate, polythiophene, polypyridine, polystyrene, polyacrylic wax, polyethylene, polypropylene, cellulose, a cellulose modifier (e.g., carboxymethyl cellulose), melamine resin, phenolic resin, polyester (e.g., polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate), silicone resin, polyimide, polyamideimide, polyaramid, polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, polyaryletherketone, a copolymer of butyl acrylate and ethyl methacrylate (e.g., a cross-linked polymer of butyl acrylate and ethyl methacrylate).
  • polycarbonate polythiophene
  • polypyridine polystyrene
  • polyacrylic wax polyethylene
  • polypropylene cellulose
  • cellulose
  • the organic-metal framework material may include one or more of a nitrogen-containing heterocyclic ligand building structure, an organic carboxylic acid ligand building structure, and a nitrogen-oxygen mixed ligand building structure.
  • the content of the adhesive may be greater than or equal to 10%, optionally 10%-30%, based on the total weight of the adhesive layer.
  • the content of the filler may be less than or equal to 90%, optionally 40%-90%, 60%-80%, based on the total weight of the adhesive layer.
  • the adhesive layer may further include a dispersant, such as carboxymethyl cellulose, so as to adjust the viscosity of the adhesive layer slurry and improve the quality and uniformity of the adhesive layer.
  • a dispersant such as carboxymethyl cellulose
  • the content of the dispersant may be less than or equal to 25%, optionally less than or equal to 20%, based on the total weight of the adhesive layer.
  • the thickness of the adhesive layer is greater than or equal to 0.3 ⁇ m, and can be selected to be 0.5-4 ⁇ m.
  • the thickness of the bonding layer can be tested using equipment and methods known in the art. Specifically, a scanning electron microscope (e.g., ZEISS Sigma 300) is used to obtain a cross-sectional scanning electron microscope (SEM) image of the isolation film with reference to JY/T010-1996. As an example, the test can be performed as follows: a plurality of regions are randomly selected on the cross section of the isolation film, and the coating thickness is measured at least five times at a certain magnification. The measured values of different regions are counted, and the average is taken as the thickness of the bonding layer.
  • a scanning electron microscope e.g., ZEISS Sigma 300
  • SEM cross-sectional scanning electron microscope
  • the air permeability of the isolation film is less than or equal to 400s/100cc, and can be selected from 250s/100cc to 320s/100cc;
  • the transverse tensile strength of the isolation film is 1500-4500kgf/ cm2 , and can be selected from 3000-4500kgf/ cm2 ;
  • the longitudinal tensile strength of the isolation film is 1500-4500kgf/ cm2 , and can be selected from 3000-4500kgf/ cm2 ;
  • the transverse heat shrinkage of the isolation film at 250°C and 1h is 0-0.4%, and can be selected from 0% to 0.2%; the insulation ...
  • the longitudinal heat shrinkage rate under 1h is 0-0.4%, and can be optionally 0-0.2%.
  • the air permeability of the isolation membrane can be selected to be 260s/100cc; the transverse heat shrinkage rate of the isolation membrane under 250°C and 1h can be selected to be 0.4%; the longitudinal heat shrinkage rate of the isolation membrane under 250°C and 1h can be selected to be 0.15%.
  • the isolation membrane has good heat resistance and physical properties, thereby improving the reliability of the secondary battery.
  • the air permeability, transverse tensile strength, longitudinal tensile strength, transverse heat shrinkage rate, and longitudinal heat shrinkage rate of the first base film and the second base film have meanings known in the art and can be tested using equipment and methods known in the art.
  • the test can be performed with reference to standard GB/T 36363-2018.
  • the present application also provides a method for preparing the isolation film provided in the embodiment of the present application, the preparation method comprising: providing a first base film and a second base film, and compounding the first base film and the second base film to obtain the isolation film in any of the above embodiments.
  • the melting point of the second base film is lower than the melting point of the first base film, and the swelling rate of the first base film is lower than the swelling rate of the second base film.
  • an embodiment of the present application provides a method for preparing an isolation membrane.
  • the preparation method comprises the following steps:
  • S100 providing a first base film and a second base film, wherein the melting point of the second base film is lower than the melting point of the first base film, and the swelling rate of the first base film is lower than the swelling rate of the second base film.
  • the adhesive layer slurry includes an adhesive.
  • the adhesive layer slurry includes an adhesive and a filler.
  • S300 Applying the adhesive layer slurry on the first base film and/or the second base film to form an adhesive layer.
  • the adhesive layer slurry can be applied only on one surface of the first base film or the second base film; the adhesive layer slurry can also be applied on the first base film and the second base film at the same time to form an adhesive layer.
  • the first base film and the second base film can be compounded by hot pressing.
  • the hot pressing compounding process if the temperature is too high, it will result in small porosity and poor air permeability; if the temperature is too low, it will result in the first base film and the second base film not being firmly bonded. Therefore, it is necessary to adjust a suitable hot pressing temperature.
  • the hot pressing temperature is 20°C-50°C.
  • all raw materials (such as the first base film, the second base film, the adhesive, the filler, etc.) used in the method for preparing the isolation film can be obtained commercially.
  • a positive electrode sheet generally includes a positive electrode current collector and a positive electrode film layer disposed on the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.
  • the positive electrode current collector may be a conventional metal foil or a composite current collector (a metal material may be disposed on a polymer substrate to form a composite current collector).
  • the positive electrode current collector may be an aluminum foil.
  • the positive electrode active material There is no limitation on the specific type of the positive electrode active material. Any active material known in the art that can be used for the positive electrode of a secondary battery can be used. Those skilled in the art can select the material according to actual needs.
  • the positive electrode active material may include, but is not limited to, one or more of lithium transition metal oxides, olivine-structured lithium-containing phosphates and their respective modified compounds.
  • lithium transition metal oxides may include Including but not limited to one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide and modified compounds thereof.
  • lithium phosphates containing olivine structure may include but are not limited to one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, a composite material of lithium iron manganese phosphate and carbon and modified compounds thereof. These materials can all be obtained through commercial channels.
  • the modified compounds of the above materials may be doping-modified and/or surface-coated modified materials.
  • the positive electrode film layer usually optionally includes a binder, a conductive agent and other optional auxiliary agents.
  • the conductive agent can be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, conductive carbon black (Super P, SP), graphene and carbon nanofibers.
  • the adhesive can be one or more of styrene butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA) and polyvinyl butyral (PVB).
  • SBR styrene butadiene rubber
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • EVA ethylene vinyl acetate copolymer
  • PAA polyacrylic acid
  • CMC carboxymethyl cellulose
  • PVA polyvinyl alcohol
  • PVB polyvinyl butyral
  • a negative electrode plate generally includes a negative electrode current collector and a negative electrode film layer disposed on the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.
  • the negative electrode current collector may be a conventional metal foil or a composite current collector (for example, a metal material may be disposed on a polymer substrate to form a composite current collector).
  • the negative electrode current collector may be a copper foil.
  • the negative electrode active material may include, but is not limited to, one or more of artificial graphite, natural graphite, hard carbon, soft carbon, silicon-based materials and tin-based materials.
  • the silicon-based material can be selected from one or more of elemental silicon, silicon oxide compounds (such as silicon monoxide), silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.
  • Tin-based materials can be selected from one or more of elemental tin, tin oxide compounds, and tin alloys. These materials can all be obtained commercially.
  • the negative electrode active material may include a silicon-based material.
  • the negative electrode film layer usually optionally includes a binder, a conductive agent and other optional auxiliary agents.
  • the conductive agent may be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the adhesive can be one or more of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyvinyl alcohol (PVA) and polyvinyl butyral (PVB).
  • SBR styrene-butadiene rubber
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • EVA ethylene-vinyl acetate copolymer
  • PVA polyvinyl alcohol
  • PVB polyvinyl butyral
  • thickeners and dispersants e.g., sodium carboxymethylcellulose, CMC-Na
  • PTC thermistor materials e.g., PTC thermistor materials
  • the secondary battery may include an electrolyte that conducts ions between the positive electrode and the negative electrode.
  • the electrolyte may include an electrolyte salt and a solvent.
  • the electrolyte salt can be selected from one or more of lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium bisoxalatoborate (LiBOB), lithium difluorophosphate (LiPO 2 F 2 ), lithium difluorobisoxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).
  • LiPF 6 lithium hexafluorophosphate
  • LiBF 4 lithium perchlor
  • the solvent can be selected from ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), One or more of methyl acetate (Methyl Acetate, MA), ethyl acetate (Ethyl Acetate, EA), propyl acetate (n-Propyl Acetate, PA), methyl propionate (Methyl Propionate, MP), ethyl propionate (Ethyl Propanoate, EP), n-Propyl Propionate (n-Propyl Propionate, PP), methyl butyrate (Methyl Butyrate MB), ethyl butyrate MB
  • the electrolyte further includes additives, such as additives that may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high temperature performance, and additives that improve battery low temperature performance.
  • additives such as additives that may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high temperature performance, and additives that improve battery low temperature performance.
  • the secondary battery may be a lithium ion secondary battery.
  • the second base film of the separator faces the negative electrode sheet.
  • the second base film faces the negative electrode sheet, so that the second base film facing the negative electrode sheet can supplement the swelling performance, and can make the physical properties of the separator more stable.
  • the second base film can also play a role in supplementing the performance, preventing the electrode from short-circuiting, while also taking into account the strength of the separator, thereby improving the reliability and cycle life of the battery in the long-term cycle life process.
  • the two-layer base membrane structure namely the first base membrane and the second base membrane
  • the swelling rate of the first base membrane is smaller than that of the second base membrane
  • the other layer of the base membrane can also play a role in supplementing the performance, reducing the risk of electrode short circuit, while increasing the strength of the separator, thereby improving the reliability of the battery in the long-term life cycle.
  • FIG4 is a secondary battery 5 of a square structure as an example.
  • the secondary battery may include an outer package for packaging a positive electrode sheet, a negative electrode sheet, and an electrolyte, wherein the second base film of the separator faces the negative electrode sheet.
  • the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell.
  • the outer packaging of the secondary battery can also be a soft package, such as a bag-type soft package.
  • the material of the soft package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).
  • the outer package may include a shell 51 and a cover plate 53.
  • the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity.
  • the shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity.
  • the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte can be assembled to form a secondary battery.
  • the positive electrode sheet, the separator, and the negative electrode sheet can be formed into an electrode assembly through a winding process and/or a lamination process, and the electrode assembly is placed in an outer package, and the electrolyte is injected after drying. After vacuum packaging, standing, forming, shaping and other processes, a battery cell is obtained.
  • Multiple battery cells can also be further connected in series, in parallel or in mixed connection to form a battery module.
  • Multiple battery modules can also be connected in series, in parallel or in mixed connection to form a battery pack. In some embodiments, multiple battery cells can also directly form a battery pack.
  • FIG6 is a battery module 4 as an example.
  • a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by fasteners.
  • the battery module 4 may further include a housing having a housing space in which the plurality of secondary batteries 5 are housed.
  • the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.
  • FIG7 and FIG8 are battery packs 1 as an example.
  • the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box.
  • the battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be covered on the lower box body 3 to form a closed space for accommodating the battery modules 4.
  • the plurality of battery modules 4 can be arranged in the battery box in any manner.
  • the second base film of the isolation film faces the positive electrode plate.
  • the second base film has good swelling properties and faces the positive electrode, which can reduce the possibility of thermal breakdown and improve the reliability of the secondary battery.
  • the present application also provides an electrical device, which includes the secondary battery of the present application.
  • the battery cell, battery module or battery pack can be used as a power source for the device, or as an energy storage unit for the device.
  • the device can be, but is not limited to, a mobile device (such as a mobile phone, a laptop computer), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck), an electric train, a ship and a satellite, and an energy storage system.
  • the device can select a battery cell, a battery module or a battery pack according to its usage requirements.
  • FIG9 is an example of an electric device.
  • the electric device may be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle.
  • a battery pack or a battery module may be used.
  • the electric device may be a mobile phone, a tablet computer, or a notebook computer.
  • the electric device is usually required to be thin and light, and a battery cell may be used as a power source.
  • the positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), the conductive agent carbon black (SuperP), and the binder polyvinylidene fluoride (PVDF) are uniformly mixed in a proper amount of solvent N-methylpyrrolidone (NMP) at a mass ratio of 96.2:2.7:1.1 to obtain a positive electrode slurry, and the positive electrode slurry is coated on a positive electrode current collector aluminum foil, and the positive electrode sheet is obtained through drying, cold pressing, slitting, and cutting processes.
  • NMP solvent N-methylpyrrolidone
  • the negative electrode active material artificial graphite, the conductive agent carbon black (SuperP), the adhesive styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC-Na) are mixed uniformly in a proper amount of solvent deionized water at a mass ratio of 96.4:0.7:1.8:1.1 to obtain a negative electrode slurry, and the negative electrode slurry is coated on the negative electrode current collector copper foil, and the negative electrode sheet is obtained through the processes of drying, cold pressing, slitting and cutting.
  • a first base film is provided, wherein the material includes polypropylene (PP), the melting point is 165° C., and the swelling rate is 0.01%.
  • PP polypropylene
  • the material includes polyethylene (PE) with a melting point of 135° C. and a swelling rate of 8%.
  • bonding layer slurry boehmite, polyacrylate and carboxymethyl cellulose are uniformly mixed in a proper amount of deionized water as a solvent in a ratio of 4:1:1 to prepare bonding layer slurry.
  • step (3) The adhesive layer slurry of step (3) is coated on the PE base film to form an adhesive layer, and the PP and PE base films are hot-pressed to form an adhesive layer between the PP base film and the PE base film to prepare a separation film.
  • Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed at a mass ratio of 30:70 to obtain an organic solvent, and fully dried electrolyte salt LiPF 6 is dissolved in the mixed solvent, the concentration of the electrolyte salt is 1.0 mol/L, and the mixture is evenly mixed to obtain an electrolyte solution.
  • the positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then they are wound to obtain an electrode assembly; the electrode assembly is placed in an outer package, and the prepared electrolyte is injected into the dried shell. After vacuum packaging, standing, forming, and shaping processes, a secondary battery is obtained.
  • Sample preparation The isolation film prepared above was punched into samples with a width of 50 mm and a length of 100 mm using a punching machine. Five parallel samples were placed on A4 paper and fixed. The A4 paper containing the samples was then placed on corrugated paper with a thickness of 1 mm to 5 mm.
  • Sample test Place the A4 paper on the corrugated paper into a blast oven, set the temperature of the blast oven to 250°C, and start timing after the temperature reaches the set temperature and stabilizes for 30 minutes. After the set time (1 hour in this application) is reached, measure the width of the isolation film, and the value is marked as a.
  • Transverse direction (TD) heat shrinkage rate [(50-a)/50] ⁇ 100%, and the average value of 5 parallel samples is taken as the test result.
  • the batteries of the above embodiments and comparative examples were charged at 1C constant current to a voltage of 3.65V, then charged at 3.65V constant voltage to a current ⁇ 0.05C, and then discharged at 1C constant current to a voltage of 2.5V. This is a charge and discharge process, and the discharge capacity at this time is recorded as the discharge capacity of the first cycle of the battery. Repeat the charge and discharge cycles in this way, and record the number of cycles when the capacity is reduced to 80%.
  • the melting point of the first base film is greater than that of the second base film; at the same time, the swelling rate of the first base film is less than that of the second base film; the batteries produced therefrom have a good cycle life; while the isolation films used in Comparative Examples 1 to 6 do not meet the design of the present application, and the cycle life of the batteries produced therefrom is poor. Therefore, by using the isolation film defined in the present application, the reliability of the resulting battery is higher.

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Abstract

本申请提供一种隔离膜，其包括第一基膜和第二基膜，第二基膜的熔点小于第一基膜的熔点；第一基膜的溶胀率小于第二基膜的溶胀率。通过两层基膜结构的相互配合，使得隔离膜在应用环境中即使一层基膜由于溶胀丧失绝缘的性能，另外一层基膜也能够起到补充性能的作用，降低电极短路风险，同时提高了隔膜的强度，进而提升了电池长期寿命历程中的可靠性。

Description

隔离膜及其制备方法、二次电池和用电装置 技术领域
本申请属于二次电池技术领域，具体涉及一种隔离膜及其制备方法、二次电池和用电装置。
背景技术
二次电池因具有重量轻、无污染、无记忆效应突出特点，被广泛应用于各类消费类电子产品和电动车辆中。
随着新能源行业的不断发展，用户对二次电池提出了更高的使用需求。但在电池使用过程中，存在电极短路失效的风险。二次电池的可靠性受到挑战。
发明内容
鉴于背景技术中存在的技术问题，本申请提供一种隔离膜及其制备方法、二次电池和用电装置，旨在提高隔离膜和二次电池的可靠性。
为了实现上述目的，本申请的第一方面提供一种隔离膜，其包括第一基膜和第二基膜，第二基膜的熔点小于第一基膜的熔点；第一基膜的溶胀率小于第二基膜的溶胀率。
相对于现有技术，本申请至少包括如下的有益效果：通过两层基膜结构的相互配合，能够使隔离膜长时间的在应用环境中，即使一层基膜由于溶胀丧失绝缘的性能，另外一层基膜也能够起到补充性能的作用，降低电极短路风险，同时能够提高隔膜的强度，进而提升电池长期寿命历程中的可靠性。
在本申请任意实施方式中，第一基膜的溶胀率与第二基膜的溶胀率之比小于等于0.8，可选为小于等于0.3。
当第一基膜的溶胀率和第二基膜的溶胀率之比在所给范围内时，能够使隔离膜长时间的在应用环境中，即使一层基膜由于溶胀丧失绝缘的性能，另外一层基膜也能够起到补充性能的作用，降低电极短路风险，同时能够提高隔膜的强度，进而提升电池长期寿命历程中的可靠性。
在本申请任意实施方式中，第一基膜的溶胀率小于等于5％，可选为0.2％-2％，第二基膜的溶胀率小于等于10％，可选为1-8％。
当第一基膜的溶胀率和第二基膜的溶胀率分别在所给范围内时，能够使隔离膜长时间的在应用环境中，即使一层基膜由于溶胀丧失绝缘的性能，另外一层基膜也能够起到补充性能的作用，降低电极短路风险，同时能够提高隔膜的强度，进而提升电池长期寿命历程中的可靠性。
在本申请任意实施方式中，第一基膜的结晶度小于第二基膜的结晶度。
在本申请任意实施方式中，第一基膜的结晶度和第二基膜的结晶度的比值为0.4-0.85，可选为0.4-0.6。
在本申请任意实施方式中，第一基膜的结晶度为40％-60％，可选为45％-50％；第 二基膜的结晶度为45％-85％，可选为65％-80％。
在本申请任意实施方式中，第一基膜的支化度大于第二基膜的支化度。
在本申请任意实施方式中，第一基膜的支化度为0.4-0.9，可选0.7-0.9；第二基膜的支化度为0.01-0.4，可选0.01-0.2。
结晶度一定程度反映材料结构的有序性，结晶度变大使得材料结构有序，不易溶胀，即溶胀率会变小；与结晶度的有序结构相反，支化度反映材料主链上增加非线性高分子结构支链的程度，支化度越高其形成的侧链越多且越复杂，材料更易溶胀，即溶胀率变大。通过调控第一基膜的结晶度小于第二基膜的结晶度，第一基膜的支化度大于第二基膜的支化度，且取值在上述范围内时，能够平衡第一基膜和第二基膜的溶胀率，且能够使第一基膜和第二基膜在有足够的溶胀能力的前提下兼具较好的强度，进一步提升二次电池的可靠性。
在本申请任意实施方式中，第一基膜的熔点为155℃-365℃，可选为160℃-340℃；第二基膜的熔点为130℃-250℃，可选为135℃-220℃。
第一基膜的摄氏度熔点和第二基膜的摄氏度熔点满足上述条件时，熔点高的第一基膜起到耐热性能的补充，熔点低的第二基膜起到溶胀性能的补充，使得隔离膜在所处电池环境中，增强耐热性，同时降低溶胀程度，进而提升电池的可靠性，延长使用寿命。
在本申请任意实施方式中，第一基膜和第二基膜各自独立地选自聚烯烃及其衍生物、卤代聚烯烃及其衍生物、聚醚及其衍生物、聚醚醚酮及其衍生物、聚酯及其衍生物、聚酰亚胺及其衍生物、聚乙烯醇及其衍生物、聚四氟乙烯及其衍生物、聚氟乙烯及其衍生物、聚偏氟乙烯及其衍生物、聚对苯二甲酸乙二醇酯及其衍生物中的至少一种。采用以上至少一种作为第一基膜和第二基膜的材料，能够使第一基膜和第二基膜具有良好的化学稳定性，同时使隔离膜具有较低的溶胀性和较高的强度。
在本申请任意实施方式中，第一基膜和第二基膜之间还设置有粘接层，粘接层包括粘接剂；可选地，粘接层包括粘接剂和填充物。粘接层的设置不仅能补偿基膜复合过程中的工艺缺陷，同时，能够进一步改善隔离膜的物理性能，进而提高二次电池的可靠性。
在本申请任意实施方式中，粘接剂包括聚丙烯酸酯、聚丙烯酸、聚四氟乙烯、聚偏氟乙烯、偏氟乙烯-三氯乙烯共聚物、聚乙烯吡咯烷酮、聚乙酸乙烯酯、乙烯-乙酸乙烯酯共聚物、聚环氧乙烷、聚芳酯、羧甲基纤维素、羟丙基纤维素、再生纤维素、乙酸纤维素、乙酸丙酸纤维素、乙酸丁酸纤维素、聚丙烯腈、聚乙烯醇、聚乙烯、聚丙烯、淀粉、氰基乙基支链淀粉中的一种或几种。
在本申请任意实施方式中，填充物包括无机颗粒、有机颗粒、有机-金属框架材料中的至少一种。
在本申请任意实施方式中，隔离膜的透气度小于等于400s/100cc，可选为250s/100cc-320s/100cc。
在本申请任意实施方式中，隔离膜的横向拉伸强度为1500-4500kgf/cm2，可选为 3000-4500kgf/cm2。
在本申请任意实施方式中，隔离膜的纵向拉伸强度为1500-4500kgf/cm2，可选为3000-4500kgf/cm2。
在本申请任意实施方式中，隔离膜在250℃、1h下的横向热收缩率为小于或等于0.4％，可选为小于或等于0.2％。
在本申请任意实施方式中，隔离膜在250℃、1h下的纵向热收缩率为小于或等于0.4％，可选为小于或等于0.2％。
当隔离膜上述至少一项满足所给的范围时，使得隔离膜具有良好的物理性能，从而可以提高二次电池的可靠性。
本申请的第二方面提供一种隔离膜的制备方法。该制备方法包括：提供第一基膜和第二基膜，第二基膜的熔点小于第一基膜的熔点，且第一基膜的溶胀率小于第二基膜的溶胀率。将第一基膜和第二基膜进行复合，得到隔离膜。
在本申请任意实施方式中，还包括提供粘接层浆料，粘接层浆料包括粘接剂。将粘接层浆料涂覆在第一基膜和/或第二基膜上形成粘接层。
在本申请任意实施方式中，粘接层浆料还包括填充物；可选地，填充物包括无机颗粒、有机颗粒、有机-金属框架材料中的至少一种。当粘接层浆料还包括填充物，且填充物包括如上的材料中的至少一种时，可以使隔离膜的物理性能得到进一步的改善，从而可以提高二次电池的可靠性。
本申请的第三方面提供一种二次电池，其包括本申请第一方面的隔离膜或根据本申请第二方面的方法制备的隔离膜。当二次电池采用所给的隔离膜时，可提高二次电池的可靠性。
在本申请任意实施方式中，还包括正极极片和负极极片，隔离膜设置在正极极片和负极极片之间，第二基膜朝向负极极片，使得朝向负极极片的第二基膜能够起到溶胀性能的补充，可以使隔离膜的物理性质更稳定，在长时间的电池应用环境中即使第一基膜由于溶胀丧失绝缘的性能，第二基膜也能够起到补充性能的作用，防止电极短路，同时还兼顾了隔离膜的强度，从而提升了电池长期循环寿命历程中的可靠性和循环寿命。
本申请的第四方面提供一种用电装置，其包括本申请第三方面的二次电池。当用电装置的二次电池采用所给的隔离膜时，可提高用电装置的可靠性。
由于本申请的装置包括本申请提供的二次电池，因而至少具有与二次电池相同的优势。
附图说明
为了更清楚地说明本申请的技术方案，下面将对本申请中所使用的附图作简单介绍。显而易见地，下面所描述的附图仅仅是本申请的一些实施方式，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，还可以根据附图获得其他的附图。
图1是本申请隔离膜的一实施方式的结构示意图。
图2是本申请隔离膜的一实施方式的结构示意图。
图3是本申请隔离膜的制备方法一实施方式的流程示意图。
图4是二次电池的一实施方式的示意图。
图5是图4的分解图。
图6是电池模块的一实施方式的示意图。
图7是电池包的一实施方式的示意图。
图8是图7的分解图。
图9是二次电池用作电源的装置的一实施方式的示意图。
具体实施方式
下面结合具体实施方式，进一步阐述本申请。应理解，这些具体实施方式仅用于说明本申请而不用于限制本申请的范围。
为了简明，本文仅具体地公开了一些数值范围。然而，任意下限可以与任意上限组合形成未明确记载的范围；以及任意下限可以与其它下限组合形成未明确记载的范围，同样任意上限可以与任意其它上限组合形成未明确记载的范围。此外，每个单独公开的点或单个数值自身可以作为下限或上限与任意其它点或单个数值组合或与其它下限或上限组合形成未明确记载的范围。
在本文的描述中，除非另有说明，术语“或(or)”是包括性的。也就是说，短语“A或(or)B”表示“A，B，或A和B两者”。更具体地，以下任一条件均满足条件“A或B”：A为真(或存在)并且B为假(或不存在)；A为假(或不存在)而B为真(或存在)；或A和B都为真(或存在)。
在本文的描述中，需要说明的是，除非另有说明，“以上”、“以下”为包括本数，“一种或几种”中“几种”的含义是两种及两种以上。
除非另有说明，本申请中使用的术语具有本领域技术人员通常所理解的公知含义。除非另有说明，本申请中提到的各参数的数值可以用本领域常用的各种测量方法进行测量(例如，可以按照在本申请的实施例中给出的方法进行测试)。
二次电池
二次电池，是指在电池放电后可通过充电的方式使活性材料激活而继续使用的电池。
通常情况下，二次电池包括正极极片、负极极片、隔离膜及电解质。在电池充放电过程中，活性离子在正极极片和负极极片之间往返嵌入和脱出。隔离膜设置在正极极片和负极极片之间，起到隔离的作用。电解质在正极极片和负极极片之间起到传导离子的作用。
[隔离膜]
参阅图1，本申请实施例提供一种隔离膜10，包括第一基膜11和第二基膜12，第二基膜12的熔点小于第一基膜11的熔点，且第一基膜11的溶胀率小于第二基膜12的溶胀率。通过两层基膜结构的相互配合，能够使隔离膜在具有较好耐热性的前提 下同时兼顾了较好的可靠性。
不希望限于任何理论，在本申请特定的隔膜结构中，选择两种溶胀率不同的基膜进行复合，可以使隔离膜的物理性质更稳定，在长时间的电池应用环境中即使一层基膜由于溶胀丧失绝缘的性能，另外一层基膜也能够起到补充性能的作用，防止电极短路，同时还兼顾了隔离膜的强度，从而提升了电池长期循环寿命历程中的可靠性和循环寿命。
在本申请任意实施方式中，第一基膜的溶胀率与第二基膜的溶胀率之比小于等于0.8，可选为小于等于0.3。例如，第一基膜的溶胀率与第二基膜的溶胀率之比可选为0.001、0.01、0.03、0.05、0.06、0.08、0.1、0.15、0.2、0.25、0.31、0.35、0.4、0.45、0.5、0.6、0.65、0.7、0.8等。或是上述任意两个数值组成的范围。例如，第一基膜的溶胀率与第二基膜的溶胀率之比可选为0.001-0.01、0.01-0.08、0.02-0.06、0.04-0.08、0.1-0.15、0.2-0.25、0.25-0.35、0.35-0.45、0.5-0.65、0.65-0.8等。
当第一基膜的溶胀率和第二基膜的溶胀率之比在所给范围内时，能够使隔离膜长时间的在应用环境中，即使一层基膜由于溶胀丧失绝缘的性能，另外一层基膜也能够起到补充性能的作用，防止电极短路，同时提升了隔膜的强度，从而提升了电池长期寿命历程中的可靠性和循环寿命。
在本申请任意实施方式中，第一基膜的溶胀率小于等于5％，可选为0.2-2％。例如，第一基膜的溶胀率可选为0.1％、0.3％、0.5％、0.7％、1.1％、1.4％、1.8％、2.2％、2.4％、2.9％、3.4％、3.6％、4.1％、4.8％、5％等。或是上述任意两个数值组成的范围。例如，第一基膜的溶胀率可选为0.01％-0.1％、0.1％-5％、0.1％-3.4％、0.1％-2.9％、0.1％-2.2％、0.1％-0.5％、0.5％-5％、0.5％-4.1％、0.5％-3.4％、0.5％-2.4％、0.5％-1.1％、1.1％-5％、1.1％-4.1％、1.1％-3.6％、1.1％-3.4％、1.1％-1.8％、2.2％-5％、2.2％-4.8％、2.2％-4.1％、2.2％-3.6％、2.2％-2.9％、3.4％-5％、3.4％-4.1％、4.1％-5％等。
在本申请任意实施方式中，第二基膜的溶胀率为小于等于10％，可选1％-8％。例如，第二基膜的溶胀率可选为0.2％、0.4％、0.7％、0.9％、1.0％、1.2％、1.4％、1.6％、1.8％、1.9％、2.0％、2.1％、2.6％、3.5％、3.7％、4.4％、6.4％、7.8％、9.2％、10％等。或是上述任意两个数值组成的范围。例如，第二基膜的溶胀率可选为0.01-0.05％、0.05-0.2％、0.05-1.0％、0.05-1.5％、0.05-2.0％、0.05-5.0％、0.05-8.0％、0.3-0.5％、1.0-1.5％、1.0-2.0％、1.5-5.0％、2.0-8.0％、5.0-8.0％、3.0-8.0％、7.5-9.0％、0.2％-0.7％、0.7％-1.0％、1.0％-1.6％、1.8％-2.0％、2.1％-2.6％、2.6％-3.7％、4.4％-6.4％、7.8％-10％等。
当第一基膜的溶胀率和第二基膜的溶胀率之比在所给范围内时，可以进一步改善电池长期循环寿命历程中的可靠性。
基膜的溶胀率均具有本领域公知的含义，可以采用本领域已知的方法进行测量。例如，可以采取如下的测试方法：取6组基膜平行样，尺寸为50mm×100mm。将样品浸泡于电解液中，样品在电解液中完全浸没，放置在70℃环境中。每24小时监测质量变化，连续七天。基膜质量的增加率即为溶胀率。其中，电解液所用溶剂包括碳酸 亚乙酯(EC)和碳酸甲乙酯(EMC)，其质量比为30:70，电解质盐为LiPF6，电解质盐的浓度为1.0mol/L。
本领域的技术人员知晓，基膜的溶胀率可以通过调节基膜的本征参数(例如基膜材料的结晶度、支化度等中的一者或者多者)及基膜制备工艺参数(例如拉伸倍率、拉伸温度等中的一者或者多者)来调整大小。例如，在其它条件不变的情况下，基膜的结晶度越大，溶胀率越小；基膜的支化度越大，溶胀率越大。本领域的技术人员可以在本申请所给的各参数范围内，通过已知的方法来调节基膜的溶胀率，例如调整基膜的生产工艺(调控结晶度、支化度等)，通过有限次试验即可得到所需溶胀率大小的基膜。
在本申请任意实施方式中，第一基膜的结晶度小于第二基膜的结晶度。
在一些可选的实施例中，第一基膜的结晶度和第二基膜的结晶度的比值为0.4-0.85，优选为0.4-0.6。例如，第一基膜的结晶度和第二基膜的结晶度的比值可选为0.4、0.5、0.6、0.7、0.8、0.85等。或是上述任意两个数值组成的范围。例如，第一基膜的结晶度和第二基膜的结晶度的比值可选为0.4-0.5、0.5-0.7、0.7-0.85等。
在一些可选的实施例中，第一基膜的结晶度可选为40％-60％，可选为45％-50％；第一基膜的结晶度具体可选为40％、42％、46％、49％、51％、52％、54％、57％、59％、60％等。或是上述任意两个数值组成的范围。例如，第一基膜的结晶度具体可选为40％-42％、42％-49％、49％-52％、52％-57％、57％-60％等。第二基膜的结晶度可选为45％-85％，可选为65％-80％。第二基膜的结晶度具体可选为45％、46％、49％、54％、61％、66％、74％、77％、81％、84％、85％等。或是上述任意两个数值组成的范围。例如，第二基膜的结晶度具体可选为45％-46％、46％-54％、54％-66％、74％-77％、81％-85％等。
结晶度一定程度反映材料结构的有序性，结晶度变大使得材料结构有序，不易溶胀，即溶胀率会变小。通过调节第一基膜的结晶度和第二基膜的结晶度分别选定在上述范围，可以调节第一基膜和第二基膜的溶胀率，使第一基膜和第二基膜的性能更好的互补。进一步地，材料结构的有序性也影响材料的强度；通过调节第一基膜的结晶度和第二基膜的结晶度分别选定在上述范围，能够使第一基膜和第二基膜在满足本申请溶胀要求的前提下同时兼具较好的强度，进行而提升了二次电池长期寿命历程中的可靠性。
基膜的结晶度具有本领域公知的含义，可以采用本领域已知的设备和方法进行测试。例如，使用差示扫描量热法(DSC法)测定基膜的结晶度。具体的，可以采取如下的测试方法：取4-6mg待测基膜样品，置于差示扫描量热仪样品室，温度从25℃升温至350℃，升温速率为10℃/min，得到熔融吸热曲线，计算曲线峰面积与100％结晶聚烯烃的参比值即可得到结晶度。
在本申请任意实施方式中，第一基膜的支化度大于第二基膜的支化度。
在本申请任意实施方式中，第一基膜的支化度为0.4-0.9，可选0.7-0.9；第二基膜的支化度为0.01-0.4，可选0.01-0.2。例如，第一基膜的支化度为0.4、0.5、0.6、 0.7、0.75、0.78、0.8、0.9。或是上述任意两个数值组成的范围。例如，第一基膜的支化度为0.4-0.6、0.6-0.75、0.75-0.78、0.78-0.9。第二基膜的支化度可选为0.01、0.03、0.09、0.14、0.18、0.25、0.33、0.38、0.4等。或是上述任意两个数值组成的范围。例如，第二基膜的支化度可选为0.01-0.03、0.03-0.14、0.14-0.25、0.25-0.4等。
与结晶度的有序结构相反，支化度是在基膜材质主链上增加非线性高分子结构的支链的程度，即支化度越高其形成的侧链越多且越复杂。支化度越高，溶胀率越大。通过将第一基膜和第二基膜的支化度的比值选定在上述范围，可以调节第一基膜和第二基膜的溶胀率，使第一基膜和第二基膜的性能更好的互补。进一步地，结晶度也会影响材料的溶胀率，通过结合调控支化度和结晶度在上述范围内，还能够使第一基膜和第二基膜在满足本申请溶胀要求的前提下同时兼具较好的强度，进行而提升了二次电池长期寿命历程中的可靠性。
基膜的支化度具有本领域公知的含义，可以采用本领域已知的设备和方法进行测试。例如，可以采用红外光谱法。具体的，可以按照如下操作：选取3-5组基膜样品，将样品放置在红外光谱仪中进行扫描，扫描范围在400-4000cm-1。扫描结束后对样品的红外曲线进行处理，计算1377cm-1处峰面积与1996-2062cm-1峰面积的比值即为支化度。
在一些实施例中，第一基膜同时满足结晶度为45％-50％，且支化度为0.7-0.9。
在一些实施例中，第二基膜同时满足结晶度为65％-80％，且支化度为0.01-0.2。
当第一基膜和/或第二基膜的结晶度和支化度同时满足上述所给范围时，两个基膜在满足本申请设计的溶胀度的同时，还可以兼顾较好的强度性能。
在本申请任意实施方式中，第一基膜的熔点为155℃-360℃，可选为160℃-340℃；第二基膜的熔点为130℃-250℃，可选为130℃-220℃。例如，第一基膜的熔点可选为155℃、165℃、175℃、188℃、191℃、220℃、239℃、245℃、271℃、294℃、310℃、324℃、347℃、360℃等。或是上述任意两个数值组成的范围。例如，第一基膜的熔点可选为155℃-175℃、175℃-220℃、220℃-245℃、245℃-271℃、271℃-310℃、310℃-360℃等。第二基膜的熔点可选为130℃、131℃、133℃、136℃、145℃、151℃、163℃、172℃、174℃、210℃、225℃、236℃、250℃等。或是上述任意两个数值组成的范围。例如，第二基膜的熔点可选为130℃-131℃、131℃-136℃、145℃-151℃、163℃-174℃、174℃-210℃、210℃-250℃等。
通过调节第一基膜的摄氏度熔点和第二基膜的摄氏度熔点满足上述条件，熔点高的第一基膜起到耐热性能的补充，熔点低的第二基膜起到溶胀性能的补充，使得隔离膜具有良好的耐热性和溶胀性能。
根据一些实施例，第一基膜和第二基膜的熔点具有本领域公知的含义，可以采用本领域已知的方法进行测定。例如，可采用差示扫描量热法进行测定。具体可参考标准GB/T 19466.3-2004。作为示例，可按照如下方法进行测定：取4-6mg待测样品，置于差示扫描量热仪的样品室，温度从25℃升温至400℃，升温速率为10℃/min，得到样品的熔融吸热曲线，曲线峰值对应的温度为样品的熔点。。
在本申请任意实施方式中，第一基膜和第二基膜各自独立地选聚烯烃及其衍生物、卤代聚烯烃及其衍生物、聚醚及其衍生物、聚醚醚酮及其衍生物、聚酯及其衍生物、聚酰亚胺及其衍生物、聚乙烯醇及其衍生物、聚四氟乙烯及其衍生物、聚氟乙烯及其衍生物、聚偏氟乙烯及其衍生物、聚对苯二甲酸乙二醇酯及其衍生物中的至少一种。例如，第一基膜可以采用聚烯烃及其衍生物或卤代聚烯烃及其衍生物。第一基膜也可以采用聚醚及其衍生物、聚醚醚酮及其衍生物、聚酯及其衍生物等。第一基膜和第二基膜还可以采用聚偏氟乙烯及其衍生物或聚对苯二甲酸乙二醇酯等。其中，衍生物通常指在化合物中的氢原子或原子团被其他原子或原子团取代而衍生的产物。以上至少一种作为第一基膜和第二基膜的材料，能够提升第一基膜和第二基膜的化学稳定性，同时使隔离膜具有较低的溶胀性和较高的强度。
参阅图2，本申请实施例提供一种隔离膜10，包括第一基膜11和第二基膜12，在本申请任意实施方式中，第一基膜11和第二基膜12之间还设置有粘接层13，粘接层包括粘接剂。可选地，粘接层包括粘接剂和填充物。
当第一基膜和第二基膜之间设置有粘接层时且粘接层包括粘接剂时，不仅能补偿基膜热压复合过程中的工艺缺陷，同时，能够进一步改善隔离膜的物理性质(例如拉伸强度、穿刺强度、耐热性等)，从而提高二次电池的可靠性。填充物位于第一基膜和第二基膜之间，由此还可以降低出现掉粉问题的风险。
在本申请任意实施方式中，粘接剂包括聚丙烯酸酯、聚丙烯酸、聚四氟乙烯、聚偏氟乙烯、偏氟乙烯-三氯乙烯共聚物、聚乙烯吡咯烷酮、聚乙酸乙烯酯、乙烯-乙酸乙烯酯共聚物、聚环氧乙烷、聚芳酯、羧甲基纤维素、羟丙基纤维素、再生纤维素、乙酸纤维素、乙酸丙酸纤维素、乙酸丁酸纤维素、聚丙烯腈、聚乙烯醇、聚乙烯、聚丙烯、淀粉、氰基乙基支链淀粉中的一种或几种。
在本申请任意实施方式中，填充物包括无机颗粒、有机颗粒、有机-金属框架材料中的至少一种。
可选地，无机颗粒包括具有5以上介电常数的无机颗粒、具有离子传导性但不储存离子的无机颗粒和能够发生电化学反应的无机颗粒中的一种或多种。
可选地，具有5以上介电常数的无机颗粒可包括勃姆石、氧化铝、氧化锌、氧化硅、氧化钛、氧化锆、氧化钡、氧化钙、氧化镁、氧化镍、氧化锡、氧化铈、氧化钇、氧化铪、氢氧化铝、氢氧化镁、碳化硅、碳化硼、氮化铝、氮化硅、氮化硼、氟化镁、氟化钙、氟化钡、硫酸钡、硅酸镁铝、硅酸镁锂、硅酸镁钠、膨润土、水辉石、钛酸锆、钛酸钡、Pb(Zr,Ti)O3(简写为PZT)、Pb1-mLamZr1-nTinO3(简写为PLZT，0＜m＜1，0＜n＜1)、Pb(Mg3Nb2/3)O3-PbTiO3(简写为PMN-PT)、及其各自的改性无机颗粒中的至少一种。可选地，各无机颗粒的改性方式可为化学改性和/或物理改性。所述化学改性方式包括偶联剂改性(例如采用硅烷偶联剂、钛酸酯偶联剂等)、表面活性剂改性、聚合物接枝改性等。所述物理改性方式可为机械力分散、超声分散、高能处理等。通过改性处理能够减少无机颗粒的团聚，由此能使粘接层具有更稳定和更均一的结构；此外，通过选择具有特定官能团的偶联剂、表 面活性剂或聚合物以改性无机颗粒，还有助于提升粘接层对电解液的浸润和保持特性、提升粘接层对第一基膜、第二基膜的粘接性。
可选地，所述具有离子传导性但不储存离子的无机颗粒可包括Li3PO4、磷酸钛锂Lix1Tiy1(PO4)3、磷酸钛铝锂Lix2Aly2Tiz1(PO4)3、(LiAlTiP)x3Oy3型玻璃、钛酸镧锂Lix4Lay4TiO3、硫代磷酸锗锂Lix5Gey5Pz2Sw、氮化锂Lix6Ny6、SiS2型玻璃Lix7Siy7Sz3和P2S5型玻璃Lix8Py8Sz4中的至少一种，0＜x1＜2，0＜y1＜3，0＜x2＜2，0＜y2＜1，0＜z1＜3，0＜x3＜4，0＜y3＜13，0＜x4＜2，0＜y4＜3，0＜x5＜4，0＜y5＜1，0＜z2＜1，0＜w＜5，0＜x6＜4，0＜y6＜2，0＜x7＜3，0＜y7＜2，0＜z3＜4，0＜x8＜3，0＜y8＜3，0＜z4＜7。由此能够进一步提升隔离膜的离子导通率。
可选地，所述能够发生电化学反应的无机颗粒可包括含锂过渡金属氧化物、含锂磷酸盐、碳基材料、硅基材料、锡基材料和锂钛化合物中的至少一种。
可选地，有机颗粒可以包括聚碳酸酯、聚噻吩、聚吡啶、聚苯乙烯、聚丙烯酸蜡、聚乙烯、聚丙烯、纤维素、纤维素改性剂(例如羧基甲基纤维素)、三聚氰胺树脂、酚醛树脂、聚酯(例如聚对苯二甲酸乙二醇酯、聚萘二甲酸乙二醇酯、聚对苯二甲酸丁二醇酯)、有机硅树脂、聚酰亚胺、聚酰胺酰亚胺、聚芳酰胺、聚苯硫醚、聚砜、聚醚砜、聚醚醚酮、聚芳醚酮、丙烯酸丁酯与甲基丙烯酸乙酯的共聚物(例如丙烯酸丁酯与甲基丙烯酸乙酯的交联聚合物)中的一种或多种。
可选地，有机-金属框架材料可以包括含氮杂环类配体构筑结构、有机羧酸类配体构筑结构、含氮氧混合类配体构筑结构中的一种或多种。
在一些实施例中，粘接剂的含量可以大于等于10％，可选为10％-30％，基于粘接层的总重量计。
在一些实施例中，填充物的含量可以小于等于90％，可选为40％-90％，60％-80％，基于粘接层的总重量计。
在一些实施例中，粘接层还可以包括分散剂，例如羧甲基纤维素，由此可以调节粘接层浆料的粘度，提升粘接层的质量和均匀性。
在一些实施例中，分散剂的含量可以小于等于25％，可选为小于等于20％，基于粘接层的总重量计。
粘接层的厚度大于或等于0.3μm，可选为0.5-4μm。
根据一些实施例，粘接层厚度可以采用本领域已知的设备和方法进行测试。具体为：使用扫描电子显微镜(例如ZEISS Sigma 300)，参考JY/T010-1996，获取隔离膜的截面扫描电子显微镜(SEM)图片。作为示例，可以按照如下方法测试：在隔离膜的截面上随机选取多个区域，在一定放大倍率下对涂层厚度进行测量至少五次，统计不同区域的测量值，取均值则为粘结层厚度。
在本申请任意实施方式中，隔离膜的透气度小于等于400s/100cc，可选为250s/100cc-320s/100cc；隔离膜的横向拉伸强度为1500-4500kgf/cm2，可选为3000-4500kgf/cm2；隔离膜的纵向拉伸强度为1500-4500kgf/cm2，可选为3000-4500kgf/cm2；隔离膜在250℃、1h下的横向热收缩率为0-0.4％，可选为0％-0.2％；隔离膜在250℃、 1h下的纵向热收缩率为0-0.4％，可选为0-0.2％。例如，在一实施例中，隔离膜的透气度可选为260s/100cc；隔离膜在250℃、1h下的横向热收缩率可选为0.4％；隔离膜在250℃、1h下的纵向热收缩率可选为0.15％。当隔离膜上述至少一项满足所给的范围时，使得隔离膜具有良好的耐热性和物理性能，从而可以提高二次电池的可靠性。
根据一些实施例，第一基膜和第二基膜的透气度、横向拉伸强度、纵向拉伸强度、横向热收缩率和纵向热收缩率均具有本领域公知的含义，可以采用本领域已知的设备和方法进行测试。例如，可参照标准GB/T 36363-2018进行测试。
[隔离膜的制备方法]
本申请实施例还提供一种用于制备本申请的实施例提供的隔离膜的方法，该制备方法包括：提供第一基膜和第二基膜，将第一基膜和第二基膜进行复合，得到以上任意实施方式中的隔离膜。其中，第二基膜的熔点小于第一基膜的熔点，且第一基膜的溶胀率小于第二基膜的溶胀率。
参阅图3，本申请实施例提供一种隔离膜的制备方法。该制备方法包括如下步骤：
S100：提供第一基膜和第二基膜，第二基膜的熔点小于第一基膜的熔点，且第一基膜的溶胀率小于第二基膜的溶胀率。
S200：提供粘接层浆料，粘接层浆料包括粘接剂。可选地，粘接层浆料包括粘接剂和填充物。当第一基膜和第二基膜之间设置有粘接层时，不仅能补偿过热压复合过程中的工艺缺陷，同时，能够进一步改善隔离膜的耐热性和物理性质，从而提高二次电池的可靠性。
S300：将粘接层浆料涂覆在第一基膜和/或第二基膜上形成粘接层。例如，粘接层浆料可以仅涂覆在第一基膜或第二基膜的仅一个表面上；粘接层浆料也可以同时涂覆在第一基膜和第二基膜上形成粘接层。
S400：将第一基膜和第二基膜进行复合，得到以上任意实施方式中的隔离膜。第一基膜和第二基膜可以通过热压方式复合，在热压方式复合的过程中，如果温度过高，将导致孔隙率小、透气性差；如果温度过低，将导致第一基膜和第二基膜粘接不牢，因此，需要调节合适的热压温度。可选地，热压温度为20℃-50℃。
如果没有特别的说明，在隔离膜的制备方法中所使用的各原料(例如第一基膜、第二基膜、粘接剂、填充物等)均可以通过市购获得。
[正极极片]
在二次电池中，正极极片通常包括正极集流体及设置在正极集流体上的正极膜层，正极膜层包括正极活性材料。
正极集流体可以采用常规金属箔片或复合集流体(可以将金属材料设置在高分子基材上形成复合集流体)。作为示例，正极集流体可以采用铝箔。
正极活性材料的具体种类不做限制，可以采用本领域已知的能够用于二次电池正极的活性材料，本领域技术人员可以根据实际需求进行选择。
作为示例，正极活性材料可以包括，但不限于，锂过渡金属氧化物，橄榄石结构的含锂磷酸盐及其各自的改性化合物中的一种或几种。锂过渡金属氧化物的示例可包 括但不限于锂钴氧化物、锂镍氧化物、锂锰氧化物、锂镍钴氧化物、锂锰钴氧化物、锂镍锰氧化物、锂镍钴锰氧化物、锂镍钴铝氧化物及其改性化合物中的一种或几种。橄榄石结构的含锂磷酸盐的示例可包括但不限于磷酸铁锂、磷酸铁锂与碳的复合材料、磷酸锰锂、磷酸锰锂与碳的复合材料、磷酸锰铁锂、磷酸锰铁锂与碳的复合材料及其改性化合物中的一种或几种。这些材料均可以通过商业途径获得。
上述各材料的改性化合物可以是对材料进行掺杂改性和/或表面包覆改性。
正极膜层通常更可选地包括粘接剂、导电剂和其他可选助剂。
作为示例，导电剂可以为超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、导电炭黑(Super P，SP)、石墨烯及碳纳米纤维中一种或几种。
作为示例，粘接剂可以为丁苯橡胶(Polymerized Styrene Butadiene Rubber，SBR)、水性丙烯酸树脂(water basedacrylicresin)、聚偏二氟乙烯(Polyvinylidene Difluoride，PVDF)、聚四氟乙烯(Polytetrafluoroethylene，PTFE)、乙烯-醋酸乙烯酯共聚物(Ethylene vinyl Acetate Copolymer，EVA)、聚丙烯酸(Polyacrylic Acid，PAA)、羧甲基纤维素(Carboxymethyl Cellulose，CMC)、聚乙烯醇(Polyvinyl Alcohol,Vinylalcohol Polymer，PVA)及聚乙烯醇缩丁醛(Polyvinyl Butyral，PVB)中的一种或几种。
[负极极片]
在二次电池中，负极极片通常包括负极集流体及设置在负极集流体上的负极膜层，所述负极膜层包括负极活性材料。
负极集流体可以采用常规金属箔片或复合集流体(例如可以将金属材料设置在高分子基材上形成复合集流体)。作为示例，负极集流体可以采用铜箔。
负极活性材料的具体种类不做限制，可以采用本领域已知的能够用于二次电池负极的活性材料，本领域技术人员可以根据实际需求进行选择。作为示例，所述负极活性材料可以包括，但不限于，人造石墨、天然石墨、硬碳、软碳、硅基材料和锡基材料中的一种或几种。所述硅基材料可选自单质硅、硅氧化合物(例如氧化亚硅)、硅碳复合物、硅氮复合物、硅合金中的一种或几种。锡基材料可选自单质锡、锡氧化合物、锡合金中的一种或几种。这些材料均可以通过商业途径获得。
在一些实施方式中，为了进一步提高电池的能量密度，负极活性材料可以包括硅基材料。
负极膜层通常更可选地包括粘接剂、导电剂和其他可选助剂。
作为示例，导电剂可以为超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中一种或几种。
作为示例，粘接剂可以为丁苯橡胶(SBR)、水性丙烯酸树脂(water basedacrylicresin)、聚偏二氟乙烯(PVDF)、聚四氟乙烯(PTFE)、乙烯-醋酸乙烯酯共聚物(EVA)、聚乙烯醇(PVA)及聚乙烯醇缩丁醛(PVB)中的一种或几种。
作为示例，其他可选助剂可以是增稠及分散剂(例如羧甲基纤维素钠Carboxymethylcellulose Sodium，CMC-Na)、PTC热敏电阻材料。
[电解液]
二次电池可以包括电解液，电解液在正极和负极之间起到传导离子的作用。电解液可以包括电解质盐和溶剂。
作为示例，电解质盐可选自六氟磷酸锂(LiPF6)、四氟硼酸锂(LiBF4)、高氯酸锂(LiClO4)、六氟砷酸锂(LiAsF6)、双氟磺酰亚胺锂(LiFSI)、双三氟甲磺酰亚胺锂(LiTFSI)、三氟甲磺酸锂(LiTFS)、二氟草酸硼酸锂(LiDFOB)、二草酸硼酸锂(LiBOB)、二氟磷酸锂(LiPO2F2)、二氟二草酸磷酸锂(LiDFOP)及四氟草酸磷酸锂(LiTFOP)中的一种或几种。
作为示例，溶剂可选自碳酸亚乙酯(Ethylene Carbonate，EC)、碳酸亚丙酯(Propylene Carbonate，PC)、碳酸甲乙酯(Methyl Ethyl Carbonate，EMC)、碳酸二乙酯(Diethyl Carbonate，DEC)、碳酸二甲酯(Dimethyl Darbonate，DMC)、碳酸二丙酯(Dipropyl Carbonate，DPC)、碳酸甲丙酯(Methyl Propyl Carbonate，MPC)、碳酸乙丙酯(Diisopropyl Carbonate，EPC)、碳酸亚丁酯(Butylene Carbonate，BC)、氟代碳酸亚乙酯(Fluoroethylene Carbonate，FEC)、甲酸甲酯(Methyl Formate，MF)、乙酸甲酯(Methyl Acetate，MA)、乙酸乙酯(Ethyl Acetate，EA)、乙酸丙酯(n-Propyl Acetate，PA)、丙酸甲酯(Methyl Propionate，MP)、丙酸乙酯(Ethyl Propanoate，EP)、丙酸丙酯(n-Propyl Propionate，PP)、丁酸甲酯(Methyl ButyrateMB)、丁酸乙酯(Ethyl Butyrate，EB)、1,4-丁内酯(1,4-Butyrolactone，GBL)、环丁砜(Tetramethylene Sulfone，SF)、二甲砜(Methyl Sulfone，MSM)、甲乙砜(Methyl Ethyl Sulfone，EMS)及二乙砜(Diethyl Sulfone，ESE)中的一种或几种。
在一些实施方式中，电解液中还包括添加剂。例如添加剂可以包括负极成膜添加剂，也可以包括正极成膜添加剂，还可以包括能够改善电池某些性能的添加剂，例如改善电池过充性能的添加剂、改善电池高温性能的添加剂、改善电池低温性能的添加剂。
在一些实施方式中，二次电池可以为锂离子二次电池。
在本申请任意实施方式中，隔离膜的第二基膜朝向负极极片。第二基膜朝向负极极片，使得朝向负极极片的第二基膜能够起到溶胀性能的补充，可以使隔离膜的物理性质更稳定，在长时间的电池应用环境中即使第一基膜由于溶胀丧失绝缘的性能，第二基膜也能够起到补充性能的作用，防止电极短路，同时还兼顾了隔离膜的强度，从而提升了电池长期循环寿命历程中的可靠性和循环寿命。
通过两层基膜结构的相互配合，即第一基膜和第二基膜，且第一基膜的溶胀率小于第二基膜，在长时间的隔离膜应用环境中即使一层基膜由于溶胀丧失绝缘的性能，另外一层基膜也能够起到补充性能的作用，降低电极短路风险，同时提高了隔膜的强度，从而提升了电池长期寿命历程中的可靠性。
本申请实施例对二次电池的形状没有特别的限制，其可以是圆柱形、方形或其他任意的形状。如图4是作为一个示例的方形结构的二次电池5。
在一些实施方式中，二次电池可包括外包装。该外包装用于封装正极极片、负极极片和电解质。隔离膜的所述第二基膜朝向所述负极极片。
在一些实施方式中，二次电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳。二次电池的外包装也可以是软包，例如袋式软包。软包的材质可以是塑料，如可包括聚丙烯(Polypropylene，PP)、聚对苯二甲酸丁二醇酯(Polybutylene Terephthalate，PBT)、聚丁二酸丁二醇酯(Polybutylene Succinate，PBS)中的一种或几种。
在一些实施方式中，参照图5，外包装可包括壳体51和盖板53。其中，壳体51可包括底板和连接于底板上的侧板，底板和侧板围合形成容纳腔。壳体51具有与容纳腔连通的开口，盖板53能够盖设于所述开口，以封闭所述容纳腔。
本申请的二次电池的制备方法是公知的。在一些实施例中，可将正极极片、隔离膜、负极极片和电解液组装形成二次电池。作为示例，可将正极极片、隔离膜、负极极片经卷绕工艺和/或叠片工艺形成电极组件，将电极组件置于外包装中，烘干后注入电解液，经过真空封装、静置、化成、整形等工序，得到电池单体。多个电池单体还可以进一步经由串联或并联或混联组成电池模块。多个电池模块还可以经由串联或并联或混联形成电池包。在一些实施例中，多个电池单体还可以直接组成电池包。
图6是作为一个示例的电池模块4。参照图6，在电池模块4中，多个二次电池5可以是沿电池模块4的长度方向依次排列设置。当然，也可以按照其他任意的方式进行排布。进一步可以通过紧固件将该多个二次电池5进行固定。
电池模块4还可以包括具有容纳空间的外壳，多个二次电池5容纳于该容纳空间。
在一些实施方式中，上述电池模块还可以组装成电池包，电池包所含电池模块的数量可以根据电池包的应用和容量进行调节。
图7和图8是作为一个示例的电池包1。参照图7和图8，在电池包1中可以包括电池箱和设置于电池箱中的多个电池模块4。电池箱包括上箱体2和下箱体3，上箱体2能够盖设于下箱体3，并形成用于容纳电池模块4的封闭空间。多个电池模块4可以按照任意的方式排布于电池箱中。
在本申请任意实施方式中，隔离膜的第二基膜朝向正极极片，第二基膜的溶胀性好，朝向正极，能够降低被热击穿的可能，提高二次电池的可靠性。
[装置]
本申请还提供一种用电装置，所述用电装置包括本申请的二次电池。所述电池单体、电池模块或电池包可以作为所述装置的电源，也可以作为所述装置的能量存储单元。所述装置可以但不限于是移动设备(例如手机、笔记本电脑)、电动车辆(例如纯电动车、混合动力电动车、插电式混合动力电动车、电动自行车、电动踏板车、电动高尔夫球车、电动卡车)、电气列车、船舶及卫星、储能系统。
所述装置可以根据其使用需求来选择电池单体、电池模块或电池包。
图9是作为一个示例的用电装置。该用电装置可以为纯电动车、混合动力电动车、或插电式混合动力电动车。为了满足该用电装置对二次电池的高功率和高能量密度的需求，可以采用电池包或电池模块。
作为另一个示例的用电装置可以是手机、平板电脑、笔记本电脑。该用电装置通常要求轻薄化，可以采用电池单体作为电源。
以下结合实施例进一步说明本申请的有益效果。
为了使本申请实施例所解决的技术问题、技术方案及有益效果更加清楚，以下将结合实施例和附图进行进一步详细说明。显然，所描述的实施例仅仅是本申请一部分实施例，而不是全部的实施例。以下对至少一个示例性实施例的描述实际上仅仅是说明性的，决不作为对本申请及其应用的任何限制。基于本申请中的实施例，本领域普通技术人员在没有付出创造性劳动前提下所获得的所有其他实施例都属于本申请保护的范围。
一、电池的制备
实施例1
1、正极极片的制备
将正极活性材料LiNi0.8Co0.1Mn0.1O2(NCM811)、导电剂炭黑(SuperP)、粘接剂聚偏二氟乙烯(PVDF)按质量比96.2:2.7:1.1在适量的溶剂N-甲基吡咯烷酮(N-Methylpyrrolidone，NMP)中混合均匀，得到正极浆料，将正极浆料涂布于正极集流体铝箔上，通过烘干、冷压、分条、裁切工序，得到正极极片。
2、负极极片的制备
将负极活性材料人造石墨、导电剂炭黑(SuperP)、粘接剂丁苯橡胶(SBR)和羧甲基纤维素钠(CMC-Na)按质量比96.4:0.7:1.8:1.1在适量的溶剂去离子水中混合均匀，得到负极浆料，将负极浆料涂布于负极集流体铜箔上，通过烘干、冷压、分条、裁切工序，得到负极极片。
3、隔离膜的制备
(1)提供第一基膜，材质包括聚丙烯(PP)，熔点为165℃，溶胀率为0.01％。
(2)提供第二基膜，材质包括聚乙烯(PE)，熔点为135℃，溶胀率为8％。
(3)配制粘接层浆料：将勃姆石、聚丙烯酸酯、羧甲基纤维素按照4:1:1比例在适量溶剂去离子水中混合均匀，制成粘接层浆料。
(4)将步骤(3)的粘接层浆料涂覆到PE基膜上形成粘结层，将PP和PE基膜进行热压成型，使得粘结层在PP基膜和PE基膜之间，制备成隔离膜。
4、电解液的制备
将碳酸亚乙酯(EC)和碳酸甲乙酯(EMC)按质量比30:70进行混合，得到有机溶剂，将充分干燥的电解质盐LiPF6溶解于上述混合溶剂中，电解质盐的浓度为1.0mol/L，混合均匀后获得电解液。
5、二次电池的制备
将正极极片、隔离膜、负极极片按顺序叠好，使隔离膜处于正极极片、负极极片之间起到隔离的作用，然后卷绕得到电极组件；将电极组件置于外包装中，将上述制备好的电解液注入到干燥后的壳体中，经过真空封装、静置、化成、整形工序，获得二次电池。
实施例2-17和对比例1-6的二次电池与实施例1的二次电池的制备方法相似，不同点在于使用了不同的隔离膜，具体详见表1。
三、性能测试
1、隔离膜的热收缩率(250℃)
样品制备：将上述制备的隔离膜用冲压机冲切成宽度为50mm、长度为100mm的样品，取5个平行样品放置在A4纸上并固定，再将装有样品的A4纸放置在厚度为1mm至5mm的瓦楞纸上。
样品测试：将放置在瓦楞纸上面的A4纸放入鼓风式烘箱，鼓风式烘箱温度设置为250℃，待温度达到设定温度并稳定30分钟后，开始计时，到达设定时间(本申请为1小时)后，测量隔离膜的宽度，数值标记为a。
横向(TD)热收缩率＝[(50-a)/50]×100％，取5个平行样品的平均值作为测试结果。
2、电池的循环寿命
在25℃下，将上述各实施例和对比例的电池以1C恒流充电至电压为3.65V，之后以3.65V恒压充电至电流≤0.05C，然后将电池以1C恒流放电至电压为2.5V，此为一个充放电过程，此时的放电容量记为电池首次循环的放电容量。如此反复进行充电和放电循环，记录容量降低至80％的时候循环圈数。
由表1可见，实施例1-实施例17中，第一基膜的熔点大于第二基膜的熔点；同时第一基膜的溶胀率小于第二基膜的溶胀率；其所制得的电池具有较好的循环寿命；而对比例1-对比例6中采用的隔离膜不满足本申请的设计，其所制得的电池的循环寿命较差。因此通过使用本申请所限定的隔离膜，所得电池的可靠性更高。
以上所述，仅为本申请的具体实施方式，但本申请的保护范围并不局限于此，任何熟悉本技术领域的技术人员在本申请揭露的技术范围内，可轻易想到各种等效的修改或替换，这些修改或替换都应涵盖在本申请的保护范围之内。因此，本申请的保护范围应以权利要求的保护范围为准。

Claims (18)

  1. 一种隔离膜，包括：
    第一基膜；
    第二基膜，所述第二基膜的熔点小于所述第一基膜的熔点；所述第一基膜的溶胀率小于所述第二基膜的溶胀率。
  2. 如权利要求1所述的隔离膜，其中，所述第一基膜的溶胀率与所述第二基膜的溶胀率之比小于等于0.8，可选为小于等于0.3。
  3. 如权利要求1或2所述的隔离膜，其中，
    所述第一基膜的溶胀率小于等于5％，可选为0.2％-2％；和/或
    所述第二基膜的溶胀率小于等于10％，可选为1％-8％。
  4. 如权利要求1-3任一项所述的隔离膜，其中，所述第一基膜的结晶度小于所述第二基膜的结晶度。
  5. 如权利要求1-4任一项所述的隔离膜，其中，所述第一基膜的结晶度和所述第二基膜的结晶度的比值为0.4-0.85，可选为0.4-0.6。
  6. 如权利要求1-5任一项所述的隔离膜，其中，
    所述第一基膜的结晶度为40％-60％，可选为45％-50％；和/或，
    所述第二基膜的结晶度为45％-85％，可选为65％-80％。
  7. 如权利要求1-6任一项所述的隔离膜，其中，所述第一基膜的支化度大于所述第二基膜的支化度。
  8. 如权利要求1-7任一项所述的隔离膜，其中，
    所述第一基膜的支化度为0.4-0.9，可选为0.7-0.9；和/或，
    所述第二基膜的支化度为0.01-0.4，可选为0.01-0.2。
  9. 如权利要求1-8任一项所述隔离膜，其中，
    所述第一基膜的熔点为155℃-365℃，可选为160℃-340℃；和/或
    所述第二基膜的熔点为130℃-250℃，可选为135℃-220℃。
  10. 如权利要求1-9任一项所述隔离膜，其中，
    所述第一基膜和所述第二基膜各自独立地选自聚烯烃及其衍生物、卤代聚烯烃及其衍生物、聚醚及其衍生物、聚醚醚酮及其衍生物、聚酯及其衍生物、聚酰亚胺及其衍生物、聚乙烯醇及其衍生物、聚四氟乙烯及其衍生物、聚氟乙烯及其衍生物、聚偏氟乙烯及其衍生物、聚对苯二甲酸乙二醇酯及其衍生物中的至少一种。
  11. 如权利要求1-10任一项所述的隔离膜，其中，
    所述第一基膜和所述第二基膜之间还设置有粘接层，所述粘接层包括粘接剂；可选地，所述粘接层包括粘接剂和填充物。
  12. 如权利要求11所述的隔离膜，其中，
    所述粘接剂包括聚丙烯酸酯、聚丙烯酸、聚四氟乙烯、聚偏氟乙烯、偏氟乙烯-三氯乙烯共聚物、聚乙烯吡咯烷酮、聚乙酸乙烯酯、乙烯-乙酸乙烯酯共聚物、聚环氧乙烷、聚芳酯、羧甲基纤维素、羟丙基纤维素、再生纤维素、乙酸纤维素、乙酸丙酸纤 维素、乙酸丁酸纤维素、聚丙烯腈、聚乙烯醇、聚乙烯、聚丙烯、淀粉、氰基乙基支链淀粉中的一种或几种；和/或
    所述填充物包括无机颗粒、有机颗粒、有机-金属框架材料中的至少一种。
  13. 如权利要求1-12任一项所述的隔离膜，其中，
    所述隔离膜的透气度小于等于400s/100cc，可选为250s/100cc-320s/100cc；和/或，
    所述隔离膜的横向拉伸强度为1500-4500kgf/cm2，可选为3000-4500kgf/cm2；
    所述隔离膜的纵向拉伸强度为1500-4500kgf/cm2，可选为3000-4500kgf/cm2；
    所述隔离膜在250℃、1h下的横向热收缩率小于或等于0.4％，可选为小于或等于0.2％；和/或，
    所述隔离膜在250℃、1h下的纵向热收缩率小于或等于0.4％，可选为小于或等于0.2％。
  14. 一种隔离膜的制备方法，其中，包括：
    提供第一基膜和第二基膜，所述第二基膜的熔点小于所述第一基膜的熔点，且所述第一基膜的溶胀率小于所述第二基膜的溶胀率；
    将所述第一基膜和所述第二基膜进行复合，得到所述隔离膜。
  15. 如权利要求14所述的隔离膜的制备方法，其中，所述方法还包括：
    提供粘接层浆料，所述粘接层浆料包括粘接剂；
    将所述粘接层浆料涂覆在所述第一基膜和/或所述第二基膜上形成粘接层；
    可选地，所述粘接层浆料还包括填充物；可选地，所述填充物包括无机颗粒、有机颗粒、有机-金属框架材料中的至少一种。
  16. 一种二次电池，包括如权利要求1-13任一项所述的隔离膜；或根据权利要求14或15的方法制备的隔离膜。
  17. 如权利要求16所述的二次电池，其中，所述二次电池还包括正极极片和负极极片，所述隔离膜设置在所述正极极片和所述负极极片之间，且所述第二基膜朝向所述负极极片。
  18. 一种用电装置，包括如权利要求16或17所述的二次电池。
PCT/CN2023/082347 2023-03-17 2023-03-17 隔离膜及其制备方法、二次电池和用电装置 Ceased WO2024192602A1 (zh)

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