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WO2024192600A1 - 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
WO2024192600A1
WO2024192600A1 PCT/CN2023/082345 CN2023082345W WO2024192600A1 WO 2024192600 A1 WO2024192600 A1 WO 2024192600A1 CN 2023082345 W CN2023082345 W CN 2023082345W WO 2024192600 A1 WO2024192600 A1 WO 2024192600A1
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WO
WIPO (PCT)
Prior art keywords
base film
film
isolation
optionally
derivatives
Prior art date
Application number
PCT/CN2023/082345
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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
Original Assignee
宁德时代新能源科技股份有限公司
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Application filed by 宁德时代新能源科技股份有限公司 filed Critical 宁德时代新能源科技股份有限公司
Priority to PCT/CN2023/082345 priority Critical patent/WO2024192600A1/zh
Publication of WO2024192600A1 publication Critical patent/WO2024192600A1/zh

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
    • H01M50/457—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

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 higher than the melting point of the first base film, and the creep compliance of the first base film is greater than the creep compliance of the second base film.
  • the present application includes at least the following beneficial effects: by setting the creep compliance of the first base film and the second base film to be different, and by the mutual cooperation of the two-layer base film structure, the deformation capabilities of the two base films under stress are different, and at least one side of the base film can have a larger deformation capacity to buffer the damage to the isolation film caused by lithium dendrites, etc., and can also play a role in inhibiting the growth of lithium dendrites, reducing the risk of electrode short circuit due to dendrites penetrating the isolation film, thereby improving the reliability of the battery over the long life cycle.
  • the ratio of the creep compliance of the first base film to the creep compliance of the second base film is 1.1-3.0, and can be 1.3-2.0.
  • the strength of the second base film can be increased while further improving the buffering effect of the first base film in coping with deformation, so as to improve the strength of the overall isolation film, enhance the ability to resist dendrites, and thus improve the reliability of the battery in the long-term life process.
  • the creep compliance of the first base film is 0.0013MPa -1 -0.0050MPa -1 ; optionally 0.0013MPa -1 -0.0032MPa -1 ; and/or the creep compliance of the second base film is 0.0010MPa -1 -0.0023MPa -1 .
  • 0.0010MPa -1 -0.0020MPa -1 is optionally 0.0010MPa -1 -0.0020MPa -1 .
  • the buffering effect of the first base film in coping with deformation can be further improved, and the strength of the second base film can be ensured, reducing the risk of short circuit caused by dendrites penetrating the isolation film, thereby improving the reliability of the battery in the long-term life process.
  • the ratio of the relative molecular mass of the material of the first base film to the relative molecular mass of the material of the second base film is greater than or equal to 1.05, and can be 1.2-10.
  • the first base film and the second base film can be made The base film has sufficient flexibility and at the same time has sufficient strength.
  • the relative molecular mass of the material of the first base film is 300,000-2.5 million, and can be 500,000-2 million; and/or, the relative molecular mass of the material of the second base film is 10,000-2 million, and can be 10,000-1.2 million.
  • Limiting the relative molecular mass of the material of the first base film and the relative molecular mass of the material of the second base film to the above range can further improve the creep compliance of the first base film and thus improve its ability to cope with deformation, while increasing the support strength of the second base film to reduce the probability of puncture of lithium dendrites, thereby improving the reliability of the battery over the long life.
  • the crystallinity of the first base film is greater than that of the second base film; optionally, the ratio of the crystallinity of the first base film to the crystallinity of the second base film is 1.1-5.0. Optionally, it is 1.5-3.0.
  • the ratio of the crystallinity of the first base film to the crystallinity of the second base film is limiting the ratio of the crystallinity of the first base film to the crystallinity of the second base film to the above range, the first base film and the second base film can have sufficient flexibility and sufficient strength at the same time.
  • the crystallinity of the first base film is 40%-90%, and can be 75%-85%; and/or the crystallinity of the second base film is 20%-70%, and can be 30%-45%.
  • the first base film and the second base film can have sufficient flexibility and sufficient strength.
  • the melting point of the first base film is lower than the melting point of the second base film, and the ratio of the melting point of the first base film to the melting point of the second base film is 0.3-0.85, and can be 0.35-0.65. Limiting the ratio of the melting point of the first base film to the melting point of the second base film within the given range can make the first base film and the second base film have good heat resistance and sufficient flexibility, thereby improving the reliability of the battery in the long-term life process.
  • the melting point of the first base film is 120°C-280°C, optionally 130°C-265°C, and/or the melting point of the second base film is 150°C-360°C, optionally 160°C-350°C. Limiting the melting points of the first base film and the second base film to the above ranges can make the first base film and the second base film have good heat resistance and creep compliance, thereby improving the reliability of the battery in the long-term life course.
  • 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 high flexibility and 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 adhesive includes 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 One or more of olefins, starch, and cyanoethyl amylopectin.
  • the filler includes at least one of inorganic particles, organic particles, and organic-metal framework materials.
  • the thickness of the adhesive layer is less than or equal to 4 ⁇ m, and can be 0.5-2 ⁇ m.
  • the thickness of the adhesive layer is within the given range, the reliability of the battery in the long-term life cycle can be improved.
  • the transverse 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 0.25%.
  • 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 0.25%.
  • the transverse tensile strength of the separator is greater than or equal to 2500 kg/cm 2 , and may be 3000 kg/cm 2 -4000 kg/cm 2 .
  • the longitudinal tensile strength of the separator is greater than or equal to 2500 kg/cm 2 , and may be 3000 kg/cm 2 -4000 kg/cm 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.
  • the second aspect of the present application provides a method for preparing an isolation film.
  • the preparation method includes providing a first base film and a second base film, wherein the melting point of the second base film is higher than the melting point of the first base film, and the creep compliance of the first base film is greater than the creep compliance of the second base film; and compounding the first base film and the second base film to obtain the isolation film in any embodiment of the first aspect.
  • the preparation method further includes preparing an adhesive layer slurry, the adhesive layer slurry includes an adhesive, and the adhesive layer slurry is coated on the first base film and/or the second base film before being compounded; optionally, the adhesive layer slurry includes an adhesive and a filler.
  • the adhesive layer slurry also includes a filler, the physical properties of the isolation film 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.
  • the first base film faces the negative electrode sheet.
  • the first base film has good creep flexibility and faces the negative electrode. It can enhance the anti-dendrite puncture effect and improve the reliability of the battery in the long-term life process.
  • the second base film facing the positive electrode has a high melting point and can enhance the heat resistance.
  • the fourth aspect of the present application provides an electric device, which includes the secondary battery of the second 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 diagram of an embodiment of a method for preparing an isolation film 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 , including a first base film 11 and a second base film 12 , wherein the melting point of the second base film is higher than that of the first base film, and the creep compliance of the first base film is greater than that of the second base film.
  • the inventor has found through extensive research that in the specific isolation membrane structure of the present application, by setting the creep compliance of the first base membrane and the second base membrane to be different, the deformation capacity of the two base membranes under stress is different, and the deformation capacity of the base membrane on one side is larger.
  • the base membrane with large creep compliance deforms and wraps the dendrites to buffer the damage to the isolation membrane caused by the dendrites; at the same time, the base membrane with small creep compliance deforms less and can provide sufficient support.
  • the inventors of the present application have found through in-depth research that when the isolation membrane of the present application satisfies the above conditions and optionally satisfies one or more of the following conditions, the performance of the secondary battery can be further improved.
  • the ratio of the creep compliance of the first base film to the creep compliance of the second base film is 1.1-3.0, and can be 1.3-2.0. In some embodiments, the ratio of the creep compliance of the first base film to the creep compliance of the second base film can be 1.4-1.8. In other embodiments, the ratio of the creep compliance of the first base film to the creep compliance of the second base film can be 1.1, 1.2, 1.4, 1.6, 1.7, 1.9, 2.0, 2.2, 2.4, 2.6, 2.8, 3.0, etc. Or a range consisting of any two of the above values.
  • the ratio of the creep compliance of the first base film to the creep compliance of the second base film can be selected as 1.10-1.22, 1.22-1.40, 1.31-1.79, 1.40-1.70, 1.56-1.90, 1.70-2.39, 2.13-2.78, 2.35-2.78, 1.2-1.9, 1.6-2.6, 1.9-2.4, 2.6-2.8, etc.
  • the flexibility and strength of the isolation membrane can be well balanced; the flexibility of the first base film can be used to improve the ability of the isolation membrane to cope with external forces, and has a certain buffering effect on the deformation caused by the external force; the strength of the second base film can be used to improve the strength of the isolation membrane against external forces, and reduce the risk of short circuit caused by foreign matter (such as lithium dendrites) penetrating the isolation membrane, thereby improving the reliability and cycle life of the battery during the long cycle life.
  • foreign matter such as lithium dendrites
  • the creep compliance of the first base film is 0.0013MPa - 1-0.0050MPa -1. In some optional embodiments, the creep compliance of the first base film is 0.0013MPa-1-0.0032MPa-1 .
  • the creep compliance of the first base film can be 0.0013MPa -1 , 0.0015MPa -1 , 0.0017MPa -1 , 0.0019MPa -1 , 0.0022MPa -1 , 0.0025MPa- 1 , 0.0028MPa- 1 , 0.0031MPa -1 , 0.0034MPa -1 , 0.0039MPa -1 , 0.0043MPa -1 , 0.0048MPa- 1 , 0.0050MPa -1 , etc.
  • the creep compliance of the first base film is 0.0013MPa -1 -0.0015MPa -1 , 0.0013MPa -1 -0.0019MPa -1 , 0.0017MPa -1 -0.0022MPa -1 , 0.0022MPa -1 -0.0028MPa -1 , 0.0025MPa -1 -0.0032MPa -1 , 0.0028MPa -1 -0.0039MPa -1 , 0.0015MPa -1 -0.0017MPa -1 , 0.0019MPa -1 -0.0022MPa -1 , 0.0025MPa -1 -0.0028MPa -1 , 0.0031MPa -1 -0.0039MPa -1 , 0.0043MPa -1 -0.0048MPa -1 , etc.
  • the creep compliance of the second base film is 0.0010MPa - 1-0.0023MPa -1 . In some optional embodiments, the creep compliance of the second base film is 0.0010MPa - 1-0.0020MPa -1 .
  • the creep compliance of the second base film can be 0.0010MPa -1 , 0.0012MPa -1 , 0.0014MPa -1 , 0.0015MPa -1 , 0.0016MPa- 1 , 0.0017MPa-1, 0.0018MPa- 1 , 0.0019MPa -1 , 0.0020MPa -1 , 0.0021MPa- 1 , 0.0022MPa -1 , 0.0023MPa -1 , etc.
  • the creep compliance of the second base film is 0.0010 MPa -1 -0.0013MPa -1 , 0.0013MPa -1 -0.0016MPa -1 , 0.0014MPa -1 -0.0020MPa -1 , 0.0016MPa -1 -0.0018MPa -1 , 0.0020MPa -1 -0.0023MPa -1 , 0.0010MPa -1 -0.0 015MPa -1 , 0.0015MPa -1 -0.0020MPa -1 , 0.0015MPa -1 -0.0016MPa -1 , 0.0017MPa -1 -0.0019MPa -1 , 0.0018MPa -1 -0.0021MPa -1 , 0.0020MPa -1 -0.0021MPa -1, etc.
  • the flexibility and strength of the isolation membrane can be well balanced; the flexibility of the first base film can improve the ability of the isolation membrane to cope with external forces, and has a certain buffering effect on the deformation caused by external forces.
  • the strength of the second base film can improve the strength of the isolation membrane against external forces and reduce the risk of short circuit caused by foreign matter (such as lithium dendrites) penetrating the isolation membrane, thereby improving the reliability and cycle life of the battery in the long-term cycle life.
  • the creep compliance of the first base film and the second base film can be tested using equipment and methods known in the art. For example, the following steps can be referred to: the sample to be tested is cut into a rectangular spline with a length of 50 mm and a width of 4 mm, the spline is clamped on a dynamic thermal mechanical analyzer, the test mode is adjusted to the creep mode, the temperature is 25°C, the test time is 220 minutes, and the value at the stable part of the curve is the creep compliance of the sample.
  • the creep compliance 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 relative molecular mass of the base film material) and the base film preparation process parameters (such as one or more of the stretch ratio and stretching temperature). For example, when other conditions remain unchanged, the smaller the relative molecular weight of the base film material, the greater the creep compliance; the greater the crystallinity, the smaller the creep compliance.
  • the creep compliance 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 crystallinity, molecular weight, etc.), and a base film with the desired creep compliance can be obtained through a limited number of tests.
  • the ratio of the relative molecular mass of the material of the first base film to the relative molecular mass of the material of the second base film is greater than or equal to 1.05, and can be selected from 1.2 to 10. In some optional embodiments, the ratio of the relative molecular mass of the material of the first base film to the relative molecular mass of the material of the second base film is 2.2 to 8.
  • the ratio of the relative molecular mass of the material of the first base film to the relative molecular mass of the material of the second base film is 1.05, 1.1, 1.3, 1.5, 1.7, 2.0, 2.4, 2.8, 3.2, 3.6, 4.5, 4.9, 5.3, 5.6, 6.2, 6.7, 7.5, 7.9, 8.7, 9.4, 10, etc. Or a range consisting of any two of the above values.
  • the ratio of the relative molecular mass of the material of the first base film to the relative molecular mass of the material of the second base film is 1.05-1.3, 1.2-1.5, 1.1-1.7, 2.4-2.8, 2.2-2.6, 3.6-4.9, 4.5-5.3, 5.6-6.2, 6.7-7.9, 8.7-9.4, etc.
  • the relative molecular mass of the material of the first base film is 300,000-2.5 million, and can be 500,000-2 million. In some optional embodiments, the relative molecular mass of the material of the first base film is 600,000-1.8 million. In some embodiments, the relative molecular mass of the material of the first base film can be 300,000, 340,000, 420,000, 500,000, 750,000, 900,000, 1.2 million, 1.36 million, 1.5 million, 1.7 million, 1.82 million, 1.9 million, 1.95 million, 2 million, 2.2 million, 2.5 million, etc. Or a range consisting of any two of the above values.
  • the relative molecular mass of the material of the first base film is 300,000-450,000, 300,000-500,000, 500,000-750,000, 750,000-1.2 million, 350,000-500,000, 750,000-900,000, 1.2 million-1.36 million, 1.5 million-1.7 million, 1.82 million-2.1 million, 2.3 million-2.43 million, etc.
  • the relative molecular mass of the material of the second base film is 10,000-2,000,000, and can be 10,000-1,200,000. In some embodiments, the relative molecular mass of the material of the second base film is 400,000-800,000.
  • the relative molecular mass of the material can be 10,000, 25,000, 100,000, 200,000, 350,000, 190,000, 280,000, 370,000, 510,000, 650,000, 800,000, 1.05 million, 1.13 million, 1.3 million, 1.44 million, 1.63 million, 1.77 million, 1.8 million, 1.93 million, 2 million, etc. Or it can be a range consisting of any two of the above values.
  • the relative molecular mass of the material of the second base film is 10,000-25,000, 25,000-70,000, 80,000-150,000, 25,000-150,000, 130,000-180,000, 150,000-250,000, 180,000-400,000, 300,000-400,000, 500,000-650,000, 190,000-280,000, 370,000-510,000, 650,000-800,000, 1.05 million-1.13 million, 1.3 million-1.44 million, 1.67 million-1.77 million, 1.8 million-1.93 million, etc.
  • the relative molecular mass of the base film material has a well-known meaning in the art and can be tested using equipment and methods known in the art, for example, using a high temperature GPC test (differential refractive index detector) for testing.
  • GPC test differential refractive index detector
  • the larger the relative molecular weight of the base film material the longer its molecular chain is likely to be, and the tighter the entanglement between the chains is likely to be, and the less likely it is to deform, which will reduce the creep compliance.
  • the smaller the relative molecular weight of the base film material the greater the creep compliance.
  • the larger the relative molecular weight of the base film material the greater its corresponding strength. Therefore, when selecting the relative molecular weight of the base film material, it is necessary to balance the two properties of material flexibility and strength. In order to improve the strength of the base film, a larger relative molecular mass can be selected; however, this will reduce the creep compliance.
  • the crystallinity of the first base film is greater than the crystallinity of the second base film; optionally, the ratio of the crystallinity of the first base film to the crystallinity of the second base film is 1.1-5.0. In some optional embodiments, the ratio of the crystallinity of the first base film to the crystallinity of the second base film is 1.5-3.0.
  • the ratio of the crystallinity of the first base film to the crystallinity of the second base film can be 1.1, 1.3, 1.8, 2.2, 2.5, 2.9, 3.4, 3.7, 4.0, 4.5, 4.8, 5.0, 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 may be selected as 1.1-1.3, 1.3-1.5, 1.5-1.8, 1.3-1.8, 1.8-2.5, 2.2-2.9, 2.9-3.4, 3.4-3.7, 3.7-4.0, 3.9-4.4, 4.4-5.0, etc.
  • the crystallinity of the first base film is 40%-90%, and can be 75%-85%.
  • the crystallinity of the first base film can be 40%, 45%, 50%, 59%, 64%, 70%, 75%, 78%, 80%, 82%, 86%, 88%, 90%, etc. Or it is a range composed of any two of the above values.
  • the crystallinity of the first base film is 40%-45%, 45%-50%, 50%-59%, 60%-65%, 54%-62%, 62%-68%, 60%-71%, 72%-80%, 59%-80%, 64%-82%, 80%-86%, 82%-88%, etc.
  • the crystallinity of the second base film is 20%-70%, optionally 30%-45%.
  • the crystallinity of the second base film can be 20%, 24%, 29%, 38%, 44%, 59%, 67%, 69%, 70%, etc. Or it is a range composed of any two of the above values.
  • the crystallinity of the second base film is 20%-23%, 24%-29%, 29%-44%, 29%-38%, 38%-42%, 42%-47%, 48%-55%, 55%-59%, 60%-65%, 38%-59%, 59%-67%, 67%-70%, etc.
  • the crystallinity can be tested using equipment and methods known in the art. Specifically, 4-6 mg of the sample to be tested is placed in the sample chamber of a differential scanning calorimeter, and the temperature is increased from 25-350°C at a heating rate of 10°C/min to obtain a melting endothermic curve, and the crystallinity can be obtained by calculating the peak area of the curve and comparing it with the reference value of 100% crystalline polyolefin.
  • Crystallinity is used to indicate the proportion of crystalline regions in the base film material. Crystallinity is an orderly arrangement of molecular chains to form a molecular chain form. Generally, the higher the crystallinity, the more regular the molecular chain arrangement.
  • the crystallinity also has a certain influence on the creep compliance of the base film.
  • the greater the crystallinity the greater the creep compliance.
  • the increase in crystallinity can improve the strength of the basement membrane, such as improving the puncture strength. Therefore, in addition to the relative molecular mass of the basement membrane material, it is also necessary to balance the crystallinity; so that the isolation membrane has sufficient strength and flexibility. Therefore, the present application makes the relative molecular mass of the first basement membrane material greater than the relative molecular mass of the second basement membrane material, and the crystallinity of the first basement membrane is greater than the crystallinity of the second basement membrane; so as to improve the strength of the first basement membrane; and improve the creep flexibility.
  • the first basement membrane can have higher strength and higher creep flexibility.
  • the second basement membrane can select a material with more complex molecular chains, and then balance the creep flexibility by lowering the crystallinity.
  • the branching degree of the first basement membrane material can also be made less than the branching degree of the second basement membrane material; to improve the creep flexibility. That is, by balancing the relative molecular mass, branching degree and crystallinity of the first basement membrane, the first basement membrane can have higher strength and higher creep flexibility.
  • the creep compliance of the first base film can be greater than the creep compliance of the second base film; at the same time, the isolation film has a certain strength.
  • the melting point of the first base film is less than the melting point of the second base film.
  • the ratio of the melting point of the first base film to the melting point of the second base film is 0.3-0.85, which can be selected as 0.35-0.65.
  • the ratio of the melting point of the first base film to the melting point of the second base film can be selected as 0.3, 0.35, 0.4, 0.5, 0.6, 0.65, 0.7, 0.8, 0.85, etc. Or a range consisting of any two of the above values.
  • the ratio of the melting point of the first base film to the melting point of the second base film can be selected as 0.3-0.35, 0.35-0.4, 0.4-0.5, 0.5-0.6, 0.6-0.65, 0.5-0.7, 0.7-0.8, 0.8-0.85, etc.
  • the melting point of the first base film is 120°C-280°C, and can be 130°C-265°C. In some embodiments, the melting point of the first base film is 120°C, 125°C, 130°C, 146°C, 150°C, 152°C, 165°C, 180°C, 196°C, 204°C, 220°C, 246°C, 258°C, 265°C, 270°C, 280°C, etc. or a range consisting of any two of the above values.
  • the melting point of the first base film is 120°C-125°C, 125°C-130°C, 130°C-146°C, 146°C-152°C, 155°C-180°C, 180°C-206°C, 210°C-230°C, 231°C-240°C, 245°C-254°C, 255°C-265°C, and 265°C-280°C.
  • the melting point of the second base film is 150°C-360°C, optionally 160°C-350°C.
  • the melting point of the second base film is 150°C, 158°C, 165°C, 170°C, 185°C, 200°C, 210°C, 240°C, 255°C, 272°C, 296°C, 320°C, 335°C, 360°C, etc. Or a range consisting of any two of the above values.
  • the melting point of the second base film is 150°C-165°C, 165°C-170°C, 170°C-190°C, 190°C-210°C, 210°C-240°C, 240°C-272°C, 272°C-320°C, 320°C-340°C, 340°C-360°C.
  • both too high and too low melting points will affect the physical properties of the base film material. For example, after exceeding the predetermined melting point, even if the creep compliance of the material is very high, its strength is too low to play the role of inhibiting dendrite penetration.
  • the melting point of the first base film and the melting point of the second base film, as well as their ratio, are limited to the above range.
  • the second base film with a high melting point plays a role in supplementing the heat resistance
  • the first base film with a low melting point plays a role in supplementing the flexibility, so that the isolation film has good heat resistance and flexibility. It can improve the physical properties of the first base film and the second base film, thereby improving the reliability of the secondary battery.
  • the melting points of the first base film and the second base film have a meaning known in the art and can be measured by methods known in the art.
  • differential scanning calorimetry can be used for measurement. GB/T 19466.3-2004.
  • the measurement can be carried out as follows: take 4-6 mg of the sample to be tested, place it in the sample chamber of the differential scanning calorimeter, heat it from 25°C to 400°C at a heating rate of 10°C/min, and obtain the melting endothermic curve of the sample. 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 higher flexibility 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 (for example, using silane coupling agent, titanate).
  • the physical modification method may be mechanical dispersion, ultrasonic dispersion, high energy treatment, etc.
  • the modification treatment can reduce the agglomeration of inorganic particles, thereby making the adhesive layer have a more stable and uniform structure; in addition, by selecting a coupling agent, surfactant or polymer with a specific functional group to modify the inorganic particles, it is also helpful to improve the wetting and retention characteristics 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 less than or equal to 4 ⁇ m, and can be selected to be 0.5-2 ⁇ 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 transverse heat shrinkage rate of the isolation film at 250°C for 1 hour is less than or equal to 0.4%, optionally less than or equal to 0.25%; and/or the longitudinal heat shrinkage rate of the separator at 250°C, 1h is less than or equal to 0.4%, optionally less than or equal to 0.25%; and/or the transverse tensile strength of the separator is greater than or equal to 2500kg/ cm2 , optionally 3000kg/ cm2-4000kg / cm2 ; and/or the longitudinal tensile strength of the separator is greater than or equal to 2500kg/ cm2 , optionally 3000kg/ cm2-4000kg / cm2 .
  • the separator has good heat resistance and physical properties, thereby improving the reliability of the secondary battery.
  • the 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.
  • an embodiment of the present application provides a method for preparing an isolation membrane.
  • the preparation method comprises the following steps:
  • S10 providing a first base film and a second base film, wherein the melting point of the second base film is higher than the melting point of the first base film, and the creep compliance of the first base film is greater than the creep compliance of the second base film.
  • the first base film and the second base film can be directly laminated by hot pressing.
  • the hot pressing temperature is 20°C-50°C.
  • the method for preparing the isolation film further comprises:
  • An adhesive layer slurry is provided, the adhesive layer slurry includes an adhesive, and the adhesive layer slurry is coated on the first base film and/or the second base film before compounding.
  • the adhesive layer slurry includes an adhesive and a filler.
  • an adhesive layer can be provided between the first base film and the second base film to improve the physical properties of the separator, thereby improving the reliability of the secondary battery.
  • 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, lithium-containing phosphates of olivine structure and their respective modified compounds.
  • lithium transition metal oxides may include, but are 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 their modified compounds.
  • lithium-containing phosphates of 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 their modified compounds. 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, 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.
  • Silicon-based materials 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
  • auxiliary agents may be thickening and dispersing agents (such as sodium carboxymethyl cellulose CMC-Na), 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), propyl propionate (n-Propyl Propionate, PP), methyl butyrate (Methyl Butyrate MB), ethyl butyrate (Ethyl but
  • 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 secondary battery comprises a positive electrode sheet, a negative electrode sheet and a separator, the separator is disposed between the positive electrode sheet and the negative electrode sheet, and the separator may be any of the above embodiments.
  • the first base film of the separator faces the negative electrode. That is, the base film on the side with greater creep compliance faces the negative electrode.
  • the base film on the side with greater creep compliance faces the negative electrode.
  • the melting point of the second base film facing the positive electrode is higher than that of the first base film, and it can withstand higher temperatures, reducing the risk of the separator being thermally broken down and causing a short circuit between the positive and negative electrodes.
  • 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, a separator, and an electrolyte.
  • 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, the negative electrode sheet and the electrolyte can be assembled to form a secondary battery.
  • the pole piece is wound and/or laminated to form an electrode assembly, which is placed in an outer package, dried and injected with electrolyte, and then vacuum packaged, left to stand, formed, and shaped to obtain a battery cell.
  • Multiple battery cells can be further connected in series, in parallel, or in a mixed connection to form a battery module.
  • Multiple battery modules can also be connected in series, in parallel, or in a 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 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 battery cells, battery modules or battery packs 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), the binder Polyvinylidene fluoride (PVDF) is uniformly mixed with an appropriate amount of solvent N-methylpyrrolidone (NMP) at a mass ratio of 96.2:2.7:1.1 to obtain a positive electrode slurry, which is then coated on a positive electrode current collector aluminum foil, and then dried, cold pressed, slit, and cut to obtain a positive electrode sheet.
  • NMP 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.
  • the material includes polyethylene (PE), the melting point is 135°C, the creep compliance is 0.0013MPa -1 , the crystallinity is 88%, and the molecular weight is 500,000;
  • the material includes polypropylene (PP), the melting point is 165°C, the creep compliance is 0.0012MPa -1 , the crystallinity is 24%, and the molecular weight is 370,000;
  • 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 described in step (2) 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 separator.
  • 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.
  • 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.
  • Step 1 Take 6 sets of parallel samples of polymer film layers, the size of which is a rectangular sample with a width of 4 mm and a length of 50 mm;
  • Step 2 The specimen is clamped on the fixture of the dynamic thermal mechanical analyzer, wherein the test mode is the creep mode, the experimental temperature is room temperature, and the time is 0-220 min.
  • the secondary batteries prepared in the examples and comparative examples were charged and discharged for the first time at 25°C.
  • the melting point of the first base film is lower than the melting point of the second base film; at the same time, the creep flexibility of the first base film is greater than the creep flexibility of the second base film; the battery prepared therefrom has a small transverse heat shrinkage rate, a high transverse tensile strength, and a long cycle life; while in Comparative Examples 1 to 4, the isolation film does not simultaneously satisfy the conditions that the melting point of the first base film is lower than the melting point of the second base film, and the creep flexibility of the first base film is greater than the creep flexibility of the second base film; the battery prepared therefrom has a large transverse heat shrinkage rate and a short cycle life.
  • the creep flexibility is good, and, under the premise of the same cycle conditions and battery performance standards, the battery prepared by the isolation film provided in the present application has good cycle performance, that is, under the same battery performance standards, the battery prepared by the isolation film provided in the present application can cycle more charge and discharge cycles and has higher reliability.

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Abstract

隔离膜（10）包括第一基膜（11）和第二基膜（12），第二基膜（12）的熔点高于第一基膜（11）的熔点，第一基膜（11）的蠕变柔度大于第二基膜（12）的蠕变柔度。第一基膜（11）的蠕变柔度和第二基膜（12）的蠕变柔度不同，使得在应力作用下两基膜的变形能力不同，通过一层基膜的应力缓冲，以及另一层基膜的强度支撑，共同抑制枝晶对隔膜的破坏，降低枝晶穿透隔离膜而导致短路的风险，从而提升了电池的可靠性和循环寿命。

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。但是在电池使用过程中易出现析锂现象，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，第二基膜的熔点高于第一基膜的熔点，且第一基膜的蠕变柔度大于第二基膜的蠕变柔度。
相对于现有技术，本申请至少包括如下的有益效果：通过设置第一基膜和第二基膜的蠕变柔度不同，通过两层基膜结构的相互配合，使得在应力作用下两基膜的变形能力不同，至少有一侧基膜可以是变形能力较大，以缓冲锂枝晶等对隔离膜的损伤，且还能起到抑制锂枝晶生长的作用，降低因枝晶穿透隔离膜而导致电极短路的风险，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，第一基膜的蠕变柔度与第二基膜的蠕变柔度之比为1.1-3.0，可选为1.3-2.0。当第一基膜的蠕变柔度与第二基膜的蠕变柔度之比满足以上条件时，能够在进一步提高第一基膜应对形变的缓冲的作用的同时，增大第二基膜的强度，以提高整体隔离膜的强度，增强抵抗枝晶的能力，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，第一基膜的蠕变柔度为0.0013MPa-1-0.0050MPa-1；可选为0.0013MPa-1-0.0032MPa-1；和/或第二基膜的蠕变柔度为0.0010MPa-1-0.0023MPa-1。可选为0.0010MPa-1-0.0020MPa-1。当第一基膜的蠕变柔度与第二基膜的蠕变柔度之比满足上述范围时，能够进一步提高第一基膜应对形变的缓冲作用，且保证第二基膜的强度，降低因枝晶穿透隔离膜而导致短路的风险，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，第一基膜的材料的相对分子质量与第二基膜的材料的相对分子质量之比大于或等于1.05，可选为1.2-10。通过将第一基膜的材料的相对分子质量与第二基膜的材料的相对分子质量之比限定在以上范围，能够使第一基膜和第二 基膜具有足够的柔度的基础上，同时具有足够的强度。
在本申请任意实施方式中，第一基膜的材料的相对分子质量为30万-250万，可选为50万-200万；和/或，第二基膜的材料的相对分子质量为1万-200万，可选为1万-120万。将第一基膜的材料的相对分子质量与第二基膜的材料的相对分子质量限定在以上范围，能够在进一步提升第一基膜的蠕变柔度从而提升其应对形变的能力的同时，且提高第二基膜的支撑力度，以降低锂枝晶的穿刺概率，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，第一基膜的结晶度大于第二基膜的结晶度；可选地，第一基膜的结晶度和第二基膜的结晶度的比值为1.1-5.0。可选为1.5-3.0。通过将第一基膜的结晶度与第二基膜的结晶度之比限定在以上范围，能够使第一基膜和第二基膜具有足够柔度的基础上，同时具有足够的强度。
在本申请任意实施方式中，第一基膜的结晶度为40％-90％，可选为75％-85％；和/或，第二基膜的结晶度为20％-70％，可选为30％-45％。通过将第一基膜的结晶度与第二基膜的结晶度限定在以上范围，能够使第一基膜和第二基膜具有足够柔度的基础上，同时具有足够的强度。
在本申请任意实施方式中，第一基膜的熔点低于第二基膜的熔点，第一基膜的熔点与第二基膜的熔点之比为0.3-0.85，可选为0.35-0.65。将第一基膜的熔点与第二基膜的熔点之比限定在所给的范围，能够使第一基膜和第二基膜具有良好的耐热性的同时具有足够的柔度，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，第一基膜的熔点为120℃-280℃，可选为130℃-265℃，和/或，第二基膜的熔点为150℃-360℃，可选为160℃-350℃。将第一基膜的熔点与第二基膜的熔点限定在以上的范围内，能够使第一基膜和第二基膜具有良好的耐热性和蠕变柔度，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高的柔性和强度。
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。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物理性质稳定，从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，粘接层的厚度小于或等于4μm，可选为0.5-2μm。当粘接层的厚度在所给的范围时，能够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隔离膜在250℃、1h下的横向热收缩率为小于或等于0.4％，可选小于等于0.25％。
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％，可选为小于等于0.25％。
在本申请任意实施方式中，隔离膜的横向拉伸强度大于或等于2500kg/cm2，可选为3000kg/cm2-4000kg/cm2。
在本申请任意实施方式中，隔离膜的纵向拉伸强度大于或等于2500kg/cm2，可选为3000kg/cm2-4000kg/cm2。
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，第二基膜的熔点高于第一基膜的熔点，且第一基膜的蠕变柔度大于第二基膜的蠕变柔度；将第一基膜和第二基膜进行复合，得到第一方面任意实施方式中的隔离膜。
在本申请任意实施方式中，制备方法还包括制备粘接层浆料，粘接层浆料包括粘接剂，将粘接层浆料涂覆在第一基膜和/或第二基膜上之后再进行复合；可选地，粘接层浆料包括粘接剂和填充物。当粘接层浆料还包括填充物，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，第一基膜朝向负极极片，第一基膜的蠕变柔度好，朝向负极，可以增强抗枝晶刺破的效果，提升电池长期寿命历程中的可靠性，同时，朝向正极的第二基膜熔点高，能够增强耐热性。
本申请的第四方面提供一种用电装置，其包括本申请第二方面的二次电池。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是本申请隔离膜制备方法的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，第二基膜的熔点高于第一基膜的熔点，且第一基膜的蠕变柔度大于第二基膜的蠕变柔度。
不希望限于任何理论，发明人经大量研究发现，在本申请特定的隔离膜结构中，通过设置第一基膜和第二基膜的蠕变柔度不同，使得在应力作用下两基膜的变形能力不同，有一侧基膜的变形能力较大，枝晶生长冲刺隔膜时，蠕变柔度大的基膜变形包裹枝晶以缓冲枝晶等对隔离膜的损伤；与此同时，蠕变柔度小的基膜变形较小，能够提供足够的支撑作用。通过一层基膜的应力缓冲，以及另一层基膜的强度支撑，共同抑制枝晶对隔膜的破坏，降低枝晶穿透隔离膜而导致短路的风险，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。
本申请发明人经深入研究发现，当本申请的隔离膜在满足上述条件的基础上，若可选地满足下述条件中的一个或几个时，可以进一步改善二次电池的性能。
在本申请任意实施方式中，第一基膜的蠕变柔度与第二基膜的蠕变柔度之比为1.1-3.0，可选为1.3-2.0。在一些实施例中，第一基膜的蠕变柔度与第二基膜的蠕变柔度之比可选为1.4-1.8。在其他实施例中，第一基膜的蠕变柔度与第二基膜的蠕变柔度之比可选为1.1、1.2、1.4、1.6、1.7、1.9、2.0、2.2、2.4、2.6、2.8、3.0等。或是上述任意两个数值组成的范围。例如，第一基膜的蠕变柔度与第二基膜的蠕变柔度之比可选为1.10-1.22、1.22-1.40、1.31-1.79、1.40-1.70、1.56-1.90、1.70-2.39、2.13-2.78、2.35-2.78、1.2-1.9、1.6-2.6、1.9-2.4、2.6-2.8等。
该实施方式中，当第一基膜的蠕变柔度与第二基膜的蠕变柔度之比满足以上条件时，能够很好的平衡隔离膜的柔性和强度两个性能；利用第一基膜的柔度能够提高隔离膜应对外力的能力，对于外力带来的形变具有一定的缓冲作用；利用第二基膜的强度，能够提高隔离膜对抗外力的强度，降低因异物(例如锂枝晶)穿透隔离膜而导致短路的风险，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，第一基膜的蠕变柔度为0.0013MPa-1-0.0050MPa-1。在一些可选实施例中，第一基膜的蠕变柔度为0.0013MPa-1-0.0032MPa-1。第一基膜的蠕变柔度可以为0.0013MPa-1、0.0015MPa-1、0.0017MPa-1、0.0019MPa-1、0.0022MPa-1、0.0025MPa-1、0.0028MPa-1、0.0031MPa-1、0.0034MPa-1、0.0039MPa-1、0.0043MPa-1、0.0048MPa-1、0.0050MPa-1等。或是上述任意两个数值组成的范围。例如，第一基膜的蠕变柔度为0.0013MPa-1-0.0015MPa-1、0.0013MPa-1-0.0019MPa-1、0.0017MPa-1-0.0022MPa-1、0.0022MPa-1-0.0028MPa-1、0.0025MPa-1-0.0032MPa-1、0.0028MPa-1-0.0039MPa-1、0.0015MPa-1-0.0017MPa-1、0.0019MPa-1-0.0022MPa-1、0.0025MPa-1-0.0028MPa-1、0.0031MPa-1-0.0039MPa-1、0.0043MPa-1-0.0048MPa-1等。
在一些可选实施例中，第二基膜的蠕变柔度为0.0010MPa-1-0.0023MPa-1。在一些可选实施例中，第二基膜的蠕变柔度为0.0010MPa-1-0.0020MPa-1。第二基膜的蠕变柔度可以为0.0010MPa-1、0.0012MPa-1、0.0014MPa-1、0.0015MPa-1、0.0016MPa-1、0.0017MPa-1、0.0018MPa-1、0.0019MPa-1、0.0020MPa-1、0.0021MPa-1、0.0022MPa-1、0.0023MPa-1等。或是上述任意两个数值组成的范围。例如，第二基膜的蠕变柔度为0.0010 MPa-1-0.0013MPa-1、0.0013MPa-1-0.0016MPa-1、0.0014MPa-1-0.0020MPa-1、0.0016MPa-1-0.0018MPa-1、0.0020MPa-1-0.0023MPa-1、0.0010MPa-1-0.0015MPa-1、0.0015MPa-1-0.0020MPa-1、0.0015MPa-1-0.0016MPa-1、0.0017MPa-1-0.0019MPa-1、0.0018MPa-1-0.0021MPa-1、0.0020MPa-1-0.0021MPa-1等。
当第一基膜的蠕变柔度与第二基膜的蠕变柔度取值满足上述范围时，能够很好的平衡隔离膜的柔性和强度两个性能；利用第一基膜的柔度能够提高隔离膜应对外力的能力，对于外力带来的形变具有一定的缓冲作用，利用第二基膜的强度，能够提高隔离膜对抗外力的强度，降低因异物(例如锂枝晶)穿透隔离膜而导致短路的风险，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。
根据一些实施例，第一基膜和第二基膜的蠕变柔度可以采用本领域已知的设备和方法进行测试。例如，可以参考如下步骤：将待测样品裁切成长50mm，宽4mm的矩形样条，样条夹持在动态热机械分析仪上，调整测试模式为蠕变模式，温度为25℃，测试时间为220min，曲线平稳处的数值则为样品的蠕变柔度。
本领域的技术人员知晓，基膜的蠕变柔度可以通过调节基膜的本征参数(例如基膜材料的结晶度、相对分子质量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，基膜材料的相对分子量越小，则蠕变柔度就会变大；结晶度越大，蠕变柔度越小。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蠕变柔度，例如调整基膜的生产工艺(调控结晶度、分子量等)，通过有限次试验即可得到所需蠕变柔度大小的基膜。
在本申请任意实施方式中，第一基膜的材料的相对分子质量与第二基膜的材料的相对分子质量之比大于或等于1.05，可选为1.2-10。在一些可选的实施例中，第一基膜的材料的相对分子质量与第二基膜的材料的相对分子质量之比为2.2-8。在一些实施例中，第一基膜的材料的相对分子质量与第二基膜的材料的相对分子质量之比为1.05、1.1、1.3、1.5、1.7、2.0、2.4、2.8、3.2、3.6、4.5、4.9、5.3、5.6、6.2、6.7、7.5、7.9、8.7、9.4、10等。或是上述任意两个数值组成的范围。例如，第一基膜的材料的相对分子质量与第二基膜的材料的相对分子质量之比为1.05-1.3、1.2-1.5、1.1-1.7、2.4-2.8、2.2-2.6、3.6-4.9、4.5-5.3、5.6-6.2、6.7-7.9、8.7-9.4等。
在本申请任意实施方式中，第一基膜的材料的相对分子质量为30万-250万，可选为50万-200万。在一些可选的实施例中，第一基膜的材料的相对分子质量为60万-180万，在一些实施例中，第一基膜的材料的相对分子质量可选为30万、34万、42万、50万、75万、90万、120万、136万、150万、170万、182万、190万、195万、200万、220万、250万等。或是上述任意两个数值组成的范围。例如，第一基膜的材料的相对分子质量为30万-45万、30万-50万、50万-75万、75万-120万、35万-50万、75万-90万、120万-136万、150万-170万、182万-210万、230万-243万等。
在一些实施例中，第二基膜的材料的相对分子质量为1万-200万，可选为1万-120万。在一些实施例中，第二基膜的材料的相对分子质量为40万-80万。第二基膜的材 料的相对分子质量可以为1万、2.5万、10万、20万、35万、19万、28万、37万、51万、65万、80万、105万、113万、130万、144万、163万、177万、180万、193万、200万等。或是上述任意两个数值组成的范围。例如，第二基膜的材料的相对分子质量为1万-2.5万、2.5万-7万、8万-15万、2.5万-15万、13万-18万、15万-25万、18万-40万、30万-40万、50万-65万、19万-28万、37万-51万、65万-80万、105万-113万、130万-144万、167万-177万、180万-193万等。
基膜材料的相对分子质量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，采用高温GPC测试(示差折光检测器)进行测试。
其中，基膜材料的相对分子量越大，其分子链就有可能越长，那么链与链之间的缠绕就有可能越紧密，也就越不容易变形，进而会使得蠕变柔度变小。相对应地，基膜材料的相对分子量越小，则蠕变柔度就会变大。同时，基膜材料的相对分子量越大，其对应的强度也会变大。因此，在选择基膜材料的相对分子量时，需要平衡材料柔度和强度这两个性能。为提高基膜的强度，可选相对分子质量要大一些；但是这会降低蠕变柔度。
在本申请任意实施方式中，第一基膜的结晶度大于第二基膜的结晶度；可选地，第一基膜的结晶度和第二基膜的结晶度的比值为1.1-5.0。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1.5-3.0。第一基膜的结晶度和第二基膜的结晶度的比值可以为1.1、1.3、1.8、2.2、2.5、2.9、3.4、3.7、4.0、4.5、4.8、5.0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1.1-1.3、1.3-1.5、1.5-1.8、1.3-1.8、1.8-2.5、2.2-2.9、2.9-3.4、3.4-3.7、3.7-4.0、3.9-4.4、4.4-5.0等。
在本申请任意实施方式中，第一基膜的结晶度为40％-90％，可选为75％-85％。第一基膜的结晶度可以为40％、45％、50％、59％、64％、70％、75％、78％、80％、82％、86％、88％、90％等。或是上述任意两个数值组成的范围。例如，第一基膜的结晶度为40％-45％、45％-50％、50％-59％、60％-65％、54％-62％、62％-68％、60％-71％、72％-80％、59％-80％、64％-82％、80％-86％、82％-88％等。
在一些实施例中，第二基膜的结晶度为20％-70％，可选为30％-45％。第二基膜的结晶度可以为20％、24％、29％、38％、44％、59％、67％、69％、70％等。或是上述任意两个数值组成的范围。例如，第二基膜的结晶度为20％-23％、24％-29％、29％-44％、29％-38％、38％-42％、42％-47％、48％-55％、55％-59％、60％-65％、38％-59％、59％-67％、67％-70％等。
根据一些实施例，结晶度可以采用本领域已知的设备和方法进行测试。具体为：取4-6mg待测样品，置于差示扫描量热仪样品室，温度从25-350℃，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。
结晶度用来表示基膜的材料中结晶区域所占的比例。结晶是分子链的一种有序排列，形成分子链形式。一般结晶度越高，分子链排列越规则。
其中，结晶度对基膜的蠕变柔度也具有一定的影响。一般地，结晶度越大，蠕变 柔度越小。结晶度的增大，能提高基膜的强度，如可以提高穿刺强度。因此，除了基膜材料的相对分子质量以外，还需要平衡结晶度；以使隔离膜具有足够的强度和柔性。因此，本申请使第一基膜材料的相对分子质量大于第二基膜材料的相对分子质量，第一基膜的结晶度大于第二基膜的结晶度；以能够提高第一基膜的强度；提高蠕变柔度。即通过平衡第一基膜的相对分子质量和结晶度，能够使第一基膜具有较高的强度和较高的蠕变柔度。对应地，第二基膜可选分子链更为复杂的材料，然后通过调低结晶度来平衡蠕变柔度。另外，还可以使第一基膜材料的支化度小于第二基膜材料的支化度；以提高蠕变柔度。即通过平衡第一基膜的相对分子质量、支化度和结晶度，能够使第一基膜具有较高的强度和较高的蠕变柔度。因而，将第一基膜的材料的结晶度、相对分子质量与第二基膜的材料的结晶度、相对分子质量及其比值限定在以上范围，能够使第一基膜的蠕变柔度大于第二基膜的蠕变柔度；同时使隔离膜具有一定的强度。
在本申请任意实施方式中，第一基膜的熔点小于第二基膜的熔点。第一基膜的熔点与第二基膜的熔点之比0.3-0.85，可选为0.35-0.65。例如，在一些实施例中，第一基膜的熔点与第二基膜的熔点之比可选为0.3、0.35、0.4、0.5、0.6、0.65、0.7、0.8、0.85等。或是上述任意两个数值组成的范围。例如，第一基膜的熔点与第二基膜的熔点之比可选为0.3-0.35、0.35-0.4、0.4-0.5、0.5-0.6、0.6-0.65、0.5-0.7、0.7-0.8、0.8-0.85等。
在本申请任意实施方式中，第一基膜的熔点为120℃-280℃，可选为130℃-265℃。在一些实施例中，第一基膜的熔点为120℃、125℃、130℃、146℃、150℃、152℃、165℃、180℃、196℃、204℃、220℃、246℃、258℃、265℃、270℃、280℃等。或是上述任意两个数值组成的范围。例如，第一基膜的熔点为120℃-125℃、125℃-130℃、130℃-146℃、146℃-152℃、155℃-180℃、180℃-206℃、210℃-230℃、231℃-240℃、245℃-254℃、255℃-265℃、265℃-280℃。
在一些实施例中，第二基膜的熔点为150℃-360℃，可选为160℃-350℃。例如，在一些实施例中，第二基膜的熔点为150℃、158℃、165℃、170℃、185℃、200℃、210℃、240℃、255℃、272℃、296℃、320℃、335℃、360℃等。或是上述任意两个数值组成的范围。例如，例如，第二基膜的熔点为150℃-165℃、165℃-170℃、170℃-190℃、190℃-210℃、210℃-240℃、240℃-272℃、272℃-320℃、320℃-340℃、340℃-360℃。
其中，过高和过低的熔点均会影响基膜材料的物理性能，比如超过预定熔点之后，即使材料蠕变柔度很高，但其强度太低，无法发挥抑制枝晶穿透的作用。将第一基膜的熔点与第二基膜的熔点、以及其比值限定在以上的范围内，熔点高的第二基膜起到耐热性能的补充，熔点低的第一基膜起到柔性性能的补充，使得隔离膜具有良好的耐热性和柔度性能。能够提高第一基膜和第二基膜的物理性能，进而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高的柔性和较高的强度。
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。
粘接层的厚度小于或等于4μm，可选为0.5-2μm。
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0.25％；和/或隔离膜在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0.25％；和/或隔离膜的横向拉伸强度大于或等于2500kg/cm2，可选为3000kg/cm2-4000kg/cm2；和/或隔离膜的纵向拉伸强度大于或等于2500kg/cm2，可选为3000kg/cm2-4000kg/cm2。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]
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：
S10：提供第一基膜和第二基膜，第二基膜的熔点高于第一基膜的熔点，且第一基膜的蠕变柔度大于第二基膜的蠕变柔度。
S20：将第一基膜和第二基膜进行复合，得到隔离膜。
第一基膜和第二基膜可以直接通过热压方式复合，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，热压温度在20℃-50℃。
在本申请任意实施方式中，隔离膜的制备方法还包括：
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/或第二基膜上之后再进行复合。
可选地，粘接层浆料包括粘接剂和填充物。通过这种方式，能够在第一基膜与第二基膜之间设置粘接层，以提高隔离膜的物理性能，从而提高二次电池的可靠性。
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、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(SBR)、水性丙烯酸树脂(water-based acrylic resin)、聚偏二氟乙烯(PVDF)、聚四氟乙烯(PTFE)、乙烯-醋酸乙烯酯共聚物(EVA)、聚丙烯酸(PAA)、羧甲基纤维素(CMC)、聚乙烯醇(PVA)及聚乙烯醇缩丁醛(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，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，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。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-based acrylic resin)、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，二次电池包括正极极片、负极极片和隔离膜，隔离膜设置在正极极片和负极极片之间，隔离膜可以是上述任一实施方式的隔离膜。
在一些实施方式中，二次电池中，隔离膜的第一基膜朝向负极极片。即蠕变柔度较大的一侧基膜朝向负极极片。当负极侧有锂枝晶析出时，能够更大程度的耐受锂枝晶对隔离膜的刺击，降低隔离膜被刺穿，导致正负极短接的风险。同时朝向正极极片的第二基膜的熔点高于第一基膜的熔点，能耐受更高温，降低隔离膜被热击穿导致正负极短接的风险。通过这种设置，能够提高二次电池的可靠性。
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、隔离膜和电解质。
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(PP)、聚对苯二甲酸丁二醇酯(PBT)、聚丁二酸丁二醇酯(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能够盖设于开口，以封闭容纳腔。
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。
装置
本申请还提供一种用电装置，用电装置包括本申请的二次电池。电池单体、电池模块或电池包可以作为装置的电源，也可以作为装置的能量存储单元。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。
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：材质包括聚乙烯(PE)，熔点为135℃，蠕变柔度为0.0013MPa-1，结晶度为88％，分子量为50万；
提供第二基膜：材质包括聚丙烯(PP)，熔点为165℃，蠕变柔度为0.0012MPa-1，结晶度为24％，分子量为37万；
(2)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。
(3)将步骤(2)所述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2-14和对比例1-4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。
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。
二、性能测试
(1)隔离膜蠕变柔度的测试
步骤1：取6组聚合物膜层平行样，尺寸为宽4mm，长度50mm的矩形样条；
步骤2：将样条夹持在动态热机械分析仪夹具上，其中测试模式为蠕变模式，实验温度为室温，时间为0-220min。
(2)电池循环寿命(25℃)
将实施例和对比例制备得到的二次电池在25℃下进行第一次充电和放电，流程如 下：25℃下，将二次电池静置30min后，以1C恒流充电至4.35V，继续恒压充电至电流≤0.05C；然后以1C恒流放电至2.8V，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14中，第一基膜的熔点小于第二基膜的熔点；同时第一基膜的蠕变柔度大于第二基膜的蠕变柔度；其所制得的电池横向热收缩率小，横向拉伸强度高，循环寿命长；而对比例1-对比例4中，隔离膜中没有同时满足第一基膜的熔点小于第二基膜的熔点，第一基膜的蠕变柔度大于第二基膜的蠕变柔度；其所制得的电池横向热收缩率大，循环寿命短。因此通过使用本申请所限定的隔离膜的蠕变柔度良好，以及，在同等循环条件以及电池性能标准的前提下，本申请所提供的隔离膜所制备的电池循环性能好，也即在同样的电池性能标准下，本申请所提供的隔离膜所制备的电池可以循环更多的充放电圈数，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 (20)

  1. 一种隔离膜，包括第一基膜和第二基膜；所述第二基膜的熔点高于所述第一基膜的熔点，且所述第一基膜的蠕变柔度大于所述第二基膜的蠕变柔度。
  2. 根据权利要求1所述的隔离膜，其中，
    所述第一基膜的蠕变柔度与所述第二基膜的蠕变柔度之比为1.1-3.0，可选为1.3-2.0。
  3. 根据权利要求1或2所述的隔离膜，其中，
    所述第一基膜的蠕变柔度为0.0013MPa-1-0.0050MPa-1，可选为0.0013MPa-1-0.0032MPa-1；和/或
    所述第二基膜的蠕变柔度为0.0010MPa-1-0.0023MPa-1，可选为0.0010MPa-1-0.0020MPa-1。
  4. 根据权利要求1-3任一项所述的隔离膜，其中，
    所述第一基膜的结晶度和所述第二基膜的结晶度的比值为1.1-5.0；可选为1.5-3.0。
  5. 根据权利要求1-4任一项所述的隔离膜，其中，
    所述第一基膜的结晶度为40％-90％，可选为75％-85％；和/或
    所述第二基膜的结晶度为20％-70％，可选为30％-45％。
  6. 根据权利要求1-5任一项所述的隔离膜，其中，
    所述第一基膜的材料的相对分子质量与所述第二基膜的材料的相对分子质量之比大于或等于1.05，可选为1.2-10。
  7. 根据权利要求1-6任一项所述的隔离膜，其中，
    所述第一基膜的材料的相对分子质量为30万-250万，可选为50万-200万；和/或，
    所述第二基膜的材料的相对分子质量为1万-200万，可选为1万-120万。
  8. 根据权利要求1-7任一项所述的隔离膜，其中，
    所述第一基膜的熔点与所述第二基膜的熔点之比为0.3-0.85，可选为0.35-0.65。
  9. 根据权利要求1-8任一项所述的隔离膜，其中，
    所述第一基膜的熔点为120℃-280℃，可选为130℃-265℃，和/或
    所述第二基膜的熔点为150℃-360℃，可选为160℃-350℃。
  10. 根据权利要求1-9任一项所述的隔离膜，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. 根据权利要求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. 根据权利要求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。
  13. 根据权利要求11或12所述的隔离膜，其中，
    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。
  14. 根据权利要求1-13任一项所述的隔离膜，其中，
    所述粘接层的厚度小于或等于3μm，可选为0.5-2μm。
  15. 根据权利要求1-14任一项所述的隔离膜，其中，
    所述隔离膜在250℃、1h下的横向热收缩率为小于0.4％，可选为小于等于0.25％；和/或
    所述隔离膜在250℃、1h下的纵向热收缩率为小于0.4％，可选为小于等于0.25％；和/或
    所述隔离膜的横向拉伸强度大于或等于2500kg/cm2，可选为3000kg/cm2-4000kg/cm2；和/或
    所述隔离膜的纵向拉伸强度大于或等于2500kg/cm2，可选为3000kg/cm2-4000kg/cm2。
  16. 一种隔离膜的制备方法，包括：
    提供第一基膜和第二基膜，所述第二基膜的熔点高于所述第一基膜的熔点，且所述第一基膜的蠕变柔度大于所述第二基膜的蠕变柔度；
    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。
  17. 根据权利要求16所述的隔离膜的制备方法，还包括：
    制备粘接层浆料，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/或所述第二基膜上之后再进行复合；
    可选地，所述粘接层浆料包括粘接剂和填充物。
  18. 一种二次电池，包括如权利要求1-15任一项所述的隔离膜，或根据权利要求16或17的方法制备的隔离膜。
  19. 如权利要求18所述的二次电池，其中，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，所述第一基膜朝向所述负极极片。
  20. 一种用电装置，包括如权利要求18或19所述的二次电池。
PCT/CN2023/082345 2023-03-17 2023-03-17 隔离膜及其制备方法、二次电池和用电装置 WO2024192600A1 (zh)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101212034A (zh) * 2006-12-25 2008-07-02 王庆生 高分子聚合物电解质高温电池隔离膜
KR20180024101A (ko) * 2016-08-26 2018-03-08 더블유스코프코리아 주식회사 우수한 인성 및 내열수축성을 가지는 리튬이차전지용 분리막 필름 및 이의 제조방법
CN110364668A (zh) * 2018-04-11 2019-10-22 宁德新能源科技有限公司 隔离膜及储能装置

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101212034A (zh) * 2006-12-25 2008-07-02 王庆生 高分子聚合物电解质高温电池隔离膜
KR20180024101A (ko) * 2016-08-26 2018-03-08 더블유스코프코리아 주식회사 우수한 인성 및 내열수축성을 가지는 리튬이차전지용 분리막 필름 및 이의 제조방법
CN110364668A (zh) * 2018-04-11 2019-10-22 宁德新能源科技有限公司 隔离膜及储能装置

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