WO2024087536A1 - 聚烯烃基膜及其制备方法、隔离膜、二次电池及用电装置 - Google Patents

聚烯烃基膜及其制备方法、隔离膜、二次电池及用电装置 Download PDF

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WO2024087536A1
WO2024087536A1 PCT/CN2023/088836 CN2023088836W WO2024087536A1 WO 2024087536 A1 WO2024087536 A1 WO 2024087536A1 CN 2023088836 W CN2023088836 W CN 2023088836W WO 2024087536 A1 WO2024087536 A1 WO 2024087536A1
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polyolefin
based film
film
membrane
optionally
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PCT/CN2023/088836
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English (en)
French (fr)
Inventor
徐冲
杨建瑞
李成
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宁德时代新能源科技股份有限公司
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Publication of WO2024087536A1 publication Critical patent/WO2024087536A1/zh

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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/28—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof by elimination of a liquid phase from a macromolecular composition or article, e.g. drying of coagulum
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/64—Carriers or collectors
    • H01M4/70—Carriers or collectors characterised by shape or form
    • H01M4/80—Porous plates, e.g. sintered carriers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
    • H01M50/491—Porosity
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/26—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof by elimination of a solid phase from a macromolecular composition or article, e.g. leaching out
    • 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
    • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • 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

Definitions

  • the present application belongs to the field of battery technology, and specifically relates to a polyolefin-based film and a preparation method thereof, an isolation film, a secondary battery and an electrical device.
  • the present application provides a polyolefin-based membrane, which can take into account both low thickness and uniform pore structure.
  • the polyolefin-based membrane provided in the first aspect of the present application comprises a pore structure.
  • the polyolefin-based membrane comprises a pore structure, the thickness of the polyolefin-based membrane is ⁇ 7 ⁇ m, and the tortuosity of the pore structure is 7-10.
  • the polyolefin base film has a uniform pore structure, thereby improving the consistency of the base film, reducing the performance deviation of the base film, fast ion transmission, and effectively ensuring the air permeability of the base film.
  • the polyolefin base film of the present application is ultra-thin. For every 1 ⁇ m thinning of the thickness, the energy density of the battery cell can be increased by about 0.7%. Therefore, by controlling the thickness to below 7 ⁇ m, the energy density of the battery cell is improved.
  • the polyolefin base film is used as an isolation membrane for a battery, the electrical performance of the battery can be improved, including reducing the battery internal resistance, DC internal resistance, self-discharge rate, short circuit rate, etc.
  • a first example of the first aspect is proposed, and the tortuosity of the hole structure is 7.5-9.5; optionally, the tortuosity of the hole structure is 7.5-9.
  • the maximum pore diameter of the pore structure is ⁇ 45nm; optionally, the maximum pore diameter of the pore structure is ⁇ 40nm; further optionally, the maximum pore diameter of the pore structure is 20nm-40nm.
  • a first example of the first aspect wherein the thickness of the polyolefin-based film is 2 ⁇ m-6.2 ⁇ m; optionally, the thickness of the polyolefin-based film is 4 ⁇ m-6.2 ⁇ m.
  • the polyolefin base film includes a polyolefin with a weight average molecular weight Mw of more than 500,000; optionally, the polyolefin base film includes a polyolefin with a weight average molecular weight Mw of 500,000 to 1.5 million.
  • the polydispersity index Mw/Mn of the polyolefin is ⁇ 3.5; optionally, the polydispersity index Mw/Mn of the polyolefin is 1 to 3.5.
  • the polydispersity index of polyolefin is optimized, which is beneficial to reducing the distribution width of the molecular weight of polyolefin and improving the consistency of the molecular weight.
  • a fourth example of the first aspect is provided, and the polyolefin is one or both of polyethylene and polypropylene.
  • optimizing the type of polyolefin is beneficial to further improve the consistency of the polyolefin base film, increase the strength and elongation of the base film, and reduce the thermal shrinkage of the base film.
  • a fifth example of the first aspect is provided, wherein the air permeability of the polyolefin-based film is ⁇ 180s/100cc.
  • the air permeability of the polyolefin-based membrane is optimized, which is beneficial to improving the air permeability of the isolation membrane.
  • the longitudinal elongation of the polyolefin base film is ⁇ 60%, optionally, the longitudinal elongation of the polyolefin base film is ⁇ 100%; further optionally, the longitudinal elongation of the polyolefin base film is 100% to 120%.
  • the transverse elongation of the polyolefin base film is ⁇ 100%; optionally, the transverse elongation of the polyolefin base film is ⁇ 110%; further optionally, the transverse elongation of the polyolefin base film is 110% to 160%.
  • the increase in elongation can effectively improve the toughness of the separator.
  • the separator can effectively cover the particles to prevent the battery cell from being punctured, thereby improving the manufacturability of the battery cell.
  • a seventh example of the first aspect wherein the polyolefin-based film has a longitudinal heat shrinkage rate of ⁇ 4% and a transverse heat shrinkage rate of ⁇ 4% at 115°C.
  • optimizing the thermal shrinkage of the polyolefin-based film can effectively improve the thermal stability of the isolation film and enhance the safety performance of the battery cell.
  • an eighth example of the first aspect is provided, wherein the polyolefin-based film meets at least one of the following conditions (1)-(4):
  • the puncture strength of the polyolefin-based film is ⁇ 270 gf;
  • the longitudinal tensile strength of the polyolefin-based film is ⁇ 2000 kgf/ cm2
  • the transverse tensile strength is ⁇ 2000 kgf/ cm2 ;
  • the surface density of the polyolefin-based film is 2-5 g/m 2 .
  • a second aspect of the present application provides a method for preparing a polyolefin-based film, comprising:
  • the membrane sheet after the pores are formed is subjected to stretching and heat setting to obtain the polyolefin-based membrane
  • the polyolefin-based membrane comprises a pore structure, the thickness of the polyolefin-based membrane is ⁇ 7 ⁇ m, and the tortuosity of the pore structure is 7-10.
  • polyolefin with ultra-high weight average molecular weight is used as raw material, and biaxial stretching is combined to prepare an ultra-thin polyolefin-based membrane with a pore structure tortuosity of 7.5-9.5 and a maximum pore size of 45nm or less.
  • a first example of the second aspect wherein the weight average molecular weight Mw of the polyolefin is greater than 500,000; optionally, the polyolefin base film comprises a polyolefin having a weight average molecular weight Mw of 500,000 to 1.5 million.
  • a first example of the second aspect is provided, wherein the proportion of polyolefin in the mixture is 20 wt %-30 wt %.
  • biaxial stretching includes longitudinal stretching and transverse stretching, wherein the longitudinal stretching ratio is 5-15 times, the transverse stretching ratio is 5-15 times, and the longitudinal stretching ratio and the transverse stretching ratio are not 5 at the same time; optionally, the longitudinal stretching ratio is 6-15 times, and the transverse stretching ratio is 6-15 times.
  • the thickness of the polyolefin-based film can be further reduced and the pore-forming uniformity can be improved.
  • a third aspect of the present application provides a separation film, comprising the polyolefin-based film of the first aspect of the present application or the polyolefin-based film obtained by the preparation method of the second aspect of the present application.
  • the isolation membrane of the present application since the polyolefin-based membrane of the first aspect of the present application or the polyolefin-based membrane obtained by the preparation method of the second aspect of the present application is adopted, the isolation membrane of the present application has the advantages of being ultra-thin and having a uniform pore structure.
  • the isolation film further comprises a coating layer disposed on at least one surface of the polyolefin-based film.
  • the electrical performance and safety performance of the battery cell can be improved.
  • the coating includes a filler
  • the filler includes at least one selected from inorganic particles, organic particles, and organic-inorganic hybrid particles.
  • the isolation film further comprises an adhesive layer.
  • the adhesive layer is disposed on at least a portion of the surface of the coating.
  • the adhesive layer comprises a granular binder, and optionally, the granular binder comprises at least one of an acrylate monomer homopolymer or copolymer, an acrylic monomer homopolymer or copolymer, and a fluorine-containing olefin monomer homopolymer or copolymer.
  • the adhesive layer can not only prevent the coating from falling off and improve the safety performance of the secondary battery, but also improve the interface between the separator and the electrode and enhance the cycle performance of the secondary battery.
  • a fourth aspect of the present application provides a secondary battery, comprising the isolation membrane of the third aspect of the present application.
  • the secondary battery of the present application since the polyolefin-based film of the first aspect of the present application or the polyolefin-based film obtained by the preparation method of the second aspect of the present application is adopted, the secondary battery of the present application has improved energy density and electrical performance.
  • a fifth aspect of the present application provides an electrical device, comprising the secondary battery of the fourth aspect of the present application.
  • the electrical device of the present application since the polyolefin-based film of the first aspect of the present application or the polyolefin-based film obtained by the preparation method of the second aspect of the present application is adopted, the electrical device of the present application has improved energy density and electrical performance.
  • FIG. 1 is a pore size distribution diagram of the polyolefin-based membrane prepared in Example 1 of the present application.
  • FIG. 2 is a pore size distribution diagram of the polyolefin-based membrane prepared in Comparative Example 1.
  • FIG. 3 is a pore size distribution diagram of the polyolefin-based membrane prepared in Comparative Example 2.
  • FIG. 4 is a schematic diagram of a battery cell according to an embodiment of the present application.
  • FIG. 5 is an exploded view of the battery cell according to the embodiment of the present application shown in FIG. 4 .
  • FIG. 6 is a schematic diagram of a battery module according to an embodiment of the present application.
  • FIG. 7 is a schematic diagram of a battery pack according to an embodiment of the present application.
  • FIG. 8 is an exploded view of the battery pack shown in FIG. 7 according to an embodiment of the present application.
  • FIG. 9 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.
  • any lower limit can be combined with any upper limit to form an unambiguous range; and any lower limit can be combined with other lower limits to form an unambiguous range, and any upper limit can be combined with any other upper limit to form an unambiguous range.
  • each point or single value between the range endpoints is included in the range.
  • each point or single value can be combined as its own lower limit or upper limit with any other point or single value or with other lower limits or upper limits to form an unambiguous range.
  • the inventors designed a polyolefin-based membrane.
  • the polyolefin-based membrane has a uniform pore structure, thereby improving the consistency of the base membrane, reducing the performance deviation of the base membrane, and effectively ensuring the air permeability of the base membrane.
  • the polyolefin-based membrane of the present application is ultra-thin. For every 1 ⁇ m thinning of the thickness, the energy density of the battery cell can be increased by about 0.7%. Therefore, by controlling the thickness to below 7 ⁇ m, the energy density of the battery cell is improved.
  • the electrical performance of the battery can be improved, including reducing the battery internal resistance, DC internal resistance, self-discharge rate, short circuit rate, etc.
  • the present application provides a polyolefin-based membrane.
  • the polyolefin-based membrane comprises a pore structure, the thickness of the polyolefin-based membrane is ⁇ 7 ⁇ m, and the tortuosity of the pore structure is 7-10. .
  • the polyolefin base film has both ultra-thin thickness and uniform pore structure, which can effectively improve the overall performance of the base film.
  • the base film When the base film is wound in the NCM811 system, it can effectively reduce the battery internal resistance, DC internal resistance and self-discharge rate, and the mass production short circuit rate level is equivalent to that of ordinary 7 ⁇ m thick polyolefin base film.
  • the tortuosity of the pore structure of the polyolefin base film is determined by the air permeability of the base film, the thickness of the base film, the porosity of the base film and the average pore size of the pore structure of the base film.
  • the tortuosity of the pore structure of the polyolefin base film can be calculated by the following formula:
  • ⁇ represents the tortuosity of the pore structure
  • t gur represents the air permeability of the basement membrane
  • ⁇ represents the porosity of the basement membrane
  • d represents the average pore size of the pore structure, in cm
  • L represents the thickness of the basement membrane, in cm.
  • a first example of the first aspect is provided, wherein the tortuosity of the pore structure is 7.5-9.5. Further, the tortuosity of the pore structure is 7.5-9.
  • the maximum pore size of the pore structure is ⁇ 45nm. Further, the maximum pore size of the pore structure is ⁇ 40nm. Further, the maximum pore size of the pore structure is 20nm-40nm.
  • the thickness of the polyolefin-based film is 2 ⁇ m-6.2 ⁇ m. Further, the thickness of the polyolefin-based film is 4 ⁇ m-6.2 ⁇ m.
  • the thickness of the polyolefin-based film may be 2 ⁇ m, 2.1 ⁇ m, 2.2 ⁇ m, 2.3 ⁇ m, 2.4 ⁇ m, 2.5 ⁇ m, 2.6 ⁇ m, 2.7 ⁇ m, 2.8 ⁇ m, 2.9 ⁇ m, 3.0 ⁇ m, 3.1 ⁇ m, 3.2 ⁇ m, 3.3 ⁇ m, 3.4 ⁇ m, 3.5 ⁇ m, 3.6 ⁇ m, 3.7 ⁇ m, 3.8 ⁇ m, 3.9 ⁇ m, 4 ⁇ m, 4.1 ⁇ m, 4.2 ⁇ m, 4.3 ⁇ m, 4 ⁇ m, 4.5 ⁇ m, 4.6 ⁇ m, 4.7 ⁇ m, 4.8 ⁇ m, 4.9 ⁇ m, 5.0 ⁇ m, 5.1 ⁇ m, 5.2 ⁇ m, 5.3 ⁇ m, 5.4 ⁇ m, 5.5 ⁇ m, 5.6 ⁇ m, 5.7 ⁇ m, 5.8 ⁇ m, 5.9 ⁇ m, 6.0 ⁇ m, 6.1 ⁇ m, 6.2 ⁇ m,
  • the tortuosity of the pore structure may be 7.0, 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.7, 7.8, 7.9, 8.0, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9, 9.0, 9.1, 9.2, 9.3, 9.4, 9.5, 9.6, 9.7, 9.8, 9.9 or 10.0.
  • the maximum pore size of the pore structure may be 45nm, 44nm, 43nm, 42nm, 41nm, 40nm, 39.9nm, 39.8nm, 39.7nm, 39.6nm, 39.5nm, 39.4nm, 39.3nm, 39.2nm, 39.1nm, 39nm, 38nm, 35nm, 30nm, 25nm or 20nm.
  • a second example of the first aspect wherein the polyolefin-based film includes a polyolefin having a weight average molecular weight Mw of 500,000 or more.
  • Using a polyolefin having a weight average molecular weight Mw of 500,000 or more as a raw material is advantageous in improving the uniformity of pore formation.
  • a single weight average molecular weight is understood to mean that the weight average molecular weight of the polyolefin is uniquely determined.
  • the weight average molecular weight Mw of the polyolefin may be 500,000-1.5 million.
  • a weight average molecular weight that is too large will lead to processing difficulties, the pressure of the extruder is difficult to control, and the thickness consistency of the film surface is poor; a weight average molecular weight that is too small will result in a shorter molecular chain, and the proportion of the crystal region after stretching is small, resulting in a decrease in the strength of the base film.
  • the weight average molecular weight Mw of the polyolefin may be 500,000, 550,000, 600,000, 650,000, 700,000, 750,000, 800,000, 850,000, 900,000, 950,000, 1 million, 1.1 million, 1.2 million, 1.3 million, 1.4 million, or 1.5 million.
  • a third example of the first aspect is provided, and a polydispersity index Mw/Mn of the polyolefin is ⁇ 3.5.
  • the polydispersity index of polyolefin is optimized, which is beneficial to reducing the distribution width of the molecular weight of polyolefin and improving the consistency of the molecular weight.
  • Mn is the number average molecular weight of the polyolefin
  • Mw is the weight average molecular weight of the polyolefin
  • the polydispersity index is the value obtained by dividing the weight average molecular weight by the number average molecular weight, i.e., weight average molecular weight/number average molecular weight (Mw/Mn), which can indicate the uniformity of the molecular weight distribution.
  • the polyolefin may have a polydispersity index Mw/Mn of 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3,
  • the polyolefin may have a polydispersity index Mw/Mn of 1-3.5, 1-2 or 2-3.5, etc.
  • a fourth example of the first aspect wherein the polyolefin is polyethylene, polypropylene, or a mixture of polyethylene and polypropylene.
  • optimizing the type of polyolefin is beneficial to further improve the consistency of the polyolefin base film, increase the strength and elongation of the base film, and reduce the thermal shrinkage of the base film.
  • a fifth example of the first aspect is provided, wherein the air permeability of the polyolefin-based film is ⁇ 180s/100cc.
  • the air permeability of the polyolefin-based membrane is optimized, which is beneficial to improving the air permeability of the isolation membrane.
  • the air permeability of polyolefin-based membrane can be 100-180s/100cc.
  • the air permeability of polyolefin-based membrane can be 100s/100cc, 105s/100cc, 110s/100cc, 115s/100cc, 120s/100cc, 125s/100cc, 130s/100cc, 135s/100cc, 140s/100cc, 145s/100cc, 150s/100cc, 155s/100cc, 160s/100cc, 165s/100cc, 170s/100cc, 175s/100cc or 180s/100cc.
  • the air permeability of polyolefin-based membrane can be 140-170s/100cc.
  • the longitudinal (MD) elongation of the polyolefin base film is ⁇ 60%, optionally, the longitudinal elongation of the polyolefin base film is ⁇ 100%; further optionally, the longitudinal elongation of the polyolefin base film is 100% to 120%.
  • the transverse (TD) elongation of the polyolefin base film is ⁇ 100%; optionally, the transverse elongation of the polyolefin base film is ⁇ 110%; further optionally, the transverse elongation of the polyolefin base film is 110% to 160%.
  • the increase in elongation indicates that the separator has good toughness.
  • metal particles which may come from the operating environment, positive and negative pole pieces or separators, etc.
  • the separator can effectively cover the particles, prevent the battery cell from being punctured, and improve the manufacturability of the battery cell.
  • the longitudinal extension rate of the polyolefin-based film may be 60%-120%, for example, it may be 60%, 65%, 70%, 73%, 75%, 80%, 82%, 85%, 88%, 89%, 90%, 93%, 95%, 96%, 97%, 98%, 99%, 100%, 101%, 104%, 105%, 109%, 110%, 112%, 113%, 114%, 115%, 116%, 120%.
  • the lateral elongation of the polyolefin-based film may be 100%-160%, for example, it may be: 100%, 101%, 102%, 105%, 106%, 107%, 108%, 109%, 110%, 111%, 113%, 114%, 115%, 117%, 118%, 120%, 121%, 125%, 130%, 135%, 140%, 145%, 150%, 155%, 160%.
  • a seventh example of the first aspect wherein the polyolefin-based film has a longitudinal heat shrinkage rate of ⁇ 4% and a transverse heat shrinkage rate of ⁇ 4% at 115°C.
  • the reduction in the thermal shrinkage of the polyolefin-based film indicates that the thermal stability of the isolation film is good, which can improve the safety performance of the battery cell.
  • the longitudinal heat shrinkage of the polyolefin-based film at 115° C. may be 0%-3%, for example, 0%, 0.5%, 1%, 1.5%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9% or 3%.
  • the longitudinal heat shrinkage of the polyolefin-based film at 115° C. may be 2%-2.5%.
  • the transverse heat shrinkage of the polyolefin-based film at 115° C. may be 0%-3%, for example, 0%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.5% or 3%.
  • the transverse heat shrinkage of the polyolefin-based film at 115° C. may be 0.5%-2% or 0.9%-1.6%.
  • an eighth example of the first aspect is provided, wherein the polyolefin-based film meets at least one of the following conditions (1)-(4):
  • the puncture strength of the polyolefin-based film is ⁇ 270 gf;
  • the longitudinal tensile strength of the polyolefin-based film is ⁇ 2000 kgf/ cm2
  • the transverse tensile strength is ⁇ 2000 kgf/ cm2 ;
  • the surface density of the polyolefin-based film is 2-5 g/m 2 .
  • the polyethylene porous base film has a high puncture strength, indicating that the isolation membrane has good tolerance and can Effectively ensure the high efficiency of the isolation membrane process.
  • the puncture strength of the polyolefin-based film may be 270 gf, 275 gf, 280 gf, 285 gf, 290 gf, 295 gf, 300 gf, 305 gf, 310 gf, 315 gf, 320 gf, 325 gf, 330 gf, 340 gf or 350 gf, etc.
  • the puncture strength of the polyolefin-based film may be 270-350 gf.
  • the polyolefin-based film may have a longitudinal tensile strength of 2000kgf/ cm2 , 2100kgf/ cm2 , 2200kgf/ cm2 , 2300kgf/ cm2 , 2400kgf/cm2, 2500kgf/ cm2 , 2600kgf/ cm2 , 2700kgf/ cm2 , 2800kgf / cm2 , 2900kgf/ cm2 , or 3000kgf/ cm2 .
  • the polyolefin-based film may have a longitudinal tensile strength of 2400-2800kgf/ cm2 .
  • the polyolefin-based film may have a transverse tensile strength of 2000 kgf/ cm2 , 2100 kgf/ cm2 , 2200 kgf/ cm2 , 2300 kgf/ cm2 , 2400 kgf/ cm2 , 2500 kgf/ cm2 , 2600 kgf/ cm2 , 2700 kgf/ cm2 , 2800 kgf/ cm2 , 2900 kgf/ cm2 , or 3000 kgf/ cm2 .
  • the polyolefin-based film may have a transverse tensile strength of 2100-2600 kgf/ cm2 .
  • the porosity of the polyolefin-based film may be 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39% or 40%.
  • the porosity of the polyolefin-based film may be 30%-35%.
  • the polyolefin-based film can have an area density of 2 g/ m2 , 2.1 g/ m2 , 2.2 g/ m2 , 2.3 g/ m2 , 2.4 g/ m2 , 2.5 g/ m2 , 2.6 g/ m2 , 2.7 g/ m2 , 2.8 g/ m2 , 2.9 g/ m2 , 3.0 g/ m2 , 3.1 g/ m2 , 3.2 g/ m2 , 3.3 g/ m2 , 3.4 g/ m2 , 3.5 g/ m2 , 3.6 g/ m2 , 3.7 g/ m2 , 3.8 g/ m2 , 3.9 g/ m2 , 4 g/ m2 , 4.5 g/ m2 , or 5 g/ m2 .
  • the polyolefin-based film can
  • a second aspect of the present application provides a method for preparing a polyolefin-based film, comprising:
  • the membrane sheet after the pores are formed is subjected to stretching and heat setting to obtain the polyolefin-based membrane
  • the polyolefin-based membrane comprises a pore structure, the thickness of the polyolefin-based membrane is ⁇ 7 ⁇ m, and the tortuosity of the pore structure is 7-10.
  • polyolefin is used as a raw material, and biaxial stretching is performed simultaneously to prepare an ultra-thin polyolefin-based film with a pore structure tortuosity of 7-10 and a thickness of ⁇ 7 ⁇ m.
  • the prepared polyolefin-based film has the same characteristics and advantages as the aforementioned polyolefin-based film, which will not be described in detail here.
  • a first example of the second aspect wherein the weight average molecular weight Mw of the polyolefin is greater than 500,000.
  • the polyolefin base film comprises a polyolefin having a weight average molecular weight Mw of 500,000 to 1.5 million.
  • a first example of the second aspect is provided, wherein the proportion of polyolefin in the mixture is 20 wt %-30 wt %.
  • the polyolefin accounts for 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%, 26 wt%, 27 wt%, 28 wt%, 29 wt% or 30 wt% in the mixture.
  • the biaxial stretching includes longitudinal stretching and transverse stretching, wherein the longitudinal stretching ratio is 5-15 times, the transverse stretching ratio is 5-15 times, and the longitudinal stretching ratio and the transverse stretching ratio are not 5 at the same time. Further, the longitudinal stretching ratio is 6-15 times, and the transverse stretching ratio is 6-15 times. times.
  • the thickness of the polyolefin-based film can be further reduced and the pore-forming uniformity can be improved.
  • the longitudinal stretching ratio may be 5-12 times, for example, 5 times, 6 times, 7 times, 8 times, 8.1 times, 8.2 times, 8.3 times, 8.4 times, 8.5 times, 8.6 times, 8.7 times, 8.8 times, 8.9 times, 9 times, 9.1 times, 9.2 times, 9.3 times, 9.4 times, 9.5 times, 10 times, 11 times or 12 times.
  • the longitudinal stretching ratio may be 8-9.5 times.
  • the longitudinal stretching temperature may be 109-115°C.
  • the transverse stretching ratio may be 5-12 times, for example, 5 times, 6 times, 7 times, 8 times, 8.1 times, 8.2 times, 8.3 times, 8.4 times, 8.5 times, 8.6 times, 8.7 times, 8.8 times, 8.9 times, 9 times, 9.1 times, 9.2 times, 9.3 times, 9.4 times, 9.5 times, 9.6 times, 9.7 times, 9.8 times, 9.9 times, 10 times, 11 times or 12 times.
  • the transverse stretching ratio may be 8.5-10 times.
  • the transverse stretching temperature may be 113-119°C.
  • the present application has no particular restrictions on the pore-forming agent used, as long as it can fully dissolve the polyolefin.
  • the pore-forming agent can be, but is not limited to, one or more of white oil, liquid paraffin, mineral oil, soybean oil, phthalate and aromatic ether.
  • the pore-forming agent is white oil.
  • the pore-forming agent is white oil, and a single weight-average molecular weight polyolefin and white oil are mixed to obtain a liquid mixture. The proportion of polyolefin in the liquid mixture is the solid content of the polyolefin.
  • the thickness of the diaphragm may be greater than 1 mm, and may be optionally 1-5 mm, for example, 1 mm, 1.5 mm, 1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm, 2 mm, 2.1 mm, 2.2 mm, 2.3 mm, 2.4 mm, 2.5 mm, 3 mm, 4 mm or 5 mm.
  • a fourth example of the second aspect is proposed, and the biaxial stretching includes: first performing longitudinal stretching and then performing transverse stretching; or, first performing transverse stretching and then performing longitudinal stretching; or, performing longitudinal stretching and transverse stretching simultaneously.
  • removing the pore-forming agent comprises: extracting the pore-forming agent in the membrane using an extractant.
  • the type of the extractant can be selected according to the type of the pore-forming agent, and is mainly used to dissolve the pore-forming agent to form pores in the material.
  • the extractant is dichloromethane.
  • the stretching and shaping comprises: stretching the film sheet in a transverse direction at a small ratio, the stretching ratio may be 1-3 times, and the stretching temperature may be 130-133°C.
  • a seventh example of the second aspect is proposed, wherein the heat setting comprises: heating the film for setting.
  • the heating temperature is ⁇ 133° C., and can be 133-135° C.
  • the heating time is ⁇ 20s, and can be 20-60s, such as 28-40s or 30-40s.
  • a third aspect of the present application provides an isolation film, comprising the polyolefin-based film of the first aspect of the present application or the polyolefin-based film obtained by the preparation method of the second aspect of the present application.
  • the isolation film of the present application since the polyolefin-based film of the first aspect of the present application or the polyolefin-based film obtained by the preparation method of the second aspect of the present application is used, the isolation film of the present application has the advantages of ultra-thinness and uniform pore structure. In addition, by providing a coating on the surface of the polyolefin-based film, the electrical performance and safety performance of the battery cell can be improved.
  • the isolation film further comprises a coating layer disposed on at least one surface of the polyolefin-based film.
  • the coating layer includes a filler
  • the filler includes at least one selected from inorganic particles, organic particles, and organic-inorganic hybrid particles.
  • the decomposition temperature of the filler is above 200° C., so that the filler has the characteristics of good thermal stability and not easy to decompose, thereby further improving the heat resistance of the isolation membrane.
  • the inorganic particles optionally include at least one 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 undergoing electrochemical reactions.
  • the inorganic particles having a dielectric constant of 5 or more include 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, fluoride At least one of barium sulfate, barium aluminum silicate, lithium magnesium silicate, sodium magnesium silicate, bentonite, hectorite, zirconium titanate, barium titanate, Pb(Zr,Ti)O 3 (abbreviated as PZT), Pb 1 -mLa m Zr 1 -nTi n O 3 (abbreviated as PLZT, 0 ⁇ m ⁇ 1, 0 ⁇ n ⁇ 1), Pb(M
  • the modification method of each inorganic particle can be chemical modification and/or physical modification.
  • Chemical modification methods include coupling agent modification (for example, using silane coupling agent, titanate coupling agent, etc.), surfactant modification, polymer grafting modification, etc.
  • Physical modification methods can be mechanical force dispersion, ultrasonic dispersion, high energy treatment, etc.
  • the agglomeration of inorganic particles can be reduced through modification treatment; in addition, by selecting coupling agents, surfactants or polymers with specific functional groups to modify inorganic particles, it is also helpful to improve the coating's wetting properties to the electrolyte and improve the coating's adhesion.
  • inorganic particles having ion conductivity but not storing ions 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, 0 ⁇ ⁇ x
  • the inorganic particles capable of undergoing an electrochemical reaction 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 have good thermal stability and are not easy to decompose, thereby improving the heat resistance of the isolation membrane; at the same time, when the internal temperature of the secondary battery reaches the melting point of the organic particles due to overheating, the organic particles can also melt and be sucked into the micropores of the porous substrate due to capillary action to play a role in closing the holes and breaking the circuit, which is beneficial to ensure that the secondary battery has high safety performance.
  • the organic particles include, but are not limited to, at least one of polyethylene particles, polypropylene particles, polystyrene particles, cellulose, cellulose modifiers (e.g., carboxymethyl cellulose), melamine resin particles, phenolic resin particles, polyester particles (e.g., polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate), silicone resin particles, polyimide particles, polyamideimide particles, polyaramid particles, polyphenylene sulfide particles, polysulfone particles, polyethersulfone particles, polyetheretherketone particles, polyaryletherketone particles, and copolymers of butyl acrylate and ethyl methacrylate (e.g., cross-linked polymers of butyl acrylate and ethyl methacrylate).
  • polyethylene particles polypropylene particles
  • polystyrene particles e.g., carboxymethyl cellulose
  • melamine resin particles e.g., carb
  • the glass transition temperature of the organic particles may be above 130°C.
  • the organic particles include but are not limited to at least one of melamine formaldehyde resin particles, phenolic resin particles, polyester particles, silicone resin particles, polyimide particles, polyamideimide particles, polyaramid particles, polyphenylene sulfide particles, polysulfone particles, polyethersulfone particles, polyetheretherketone particles, and polyaryletherketone particles.
  • the coating may also include nanocellulose.
  • Nanocellulose is a general term for cellulose with any dimension at the nanoscale (e.g., within 100 nm), which has both the properties of cellulose and the properties of nanoparticles.
  • Nanocellulose can be a polymer nanomaterial extracted from wood, cotton, etc. in nature by one or more means of chemistry, physics, biology, etc., and has the advantages of wide sources, low cost, biodegradability, high modulus, and high specific surface area.
  • nanocellulose may include at least one of cellulose nanofibers (Cellulose nanofibrils, CNF, also known as nanofibrillated cellulose or microfibrillated cellulose), cellulose nanowhiskers (Cellulose nanocrystals, CNC, also known as cellulose nanocrystals, nanocrystalline cellulose) and bacterial nanocellulose (Bacterial nanocellulose, BNC, also known as bacterial cellulose or microbial cellulose).
  • CNF Cellulose nanofibrils
  • CNC also known as cellulose nanocrystals, nanocrystalline cellulose
  • BNC Bacterial nanocellulose
  • nanocellulose may include at least one of unmodified nanocellulose (also known as hydroxy nanocellulose) and modified nanocellulose, optionally modified nanocellulose.
  • Nanocellulose may include a modifying group.
  • the modifying group may include at least one of an amine group, a carboxylic acid group, an aldehyde group, a sulfonic acid group, a boric acid group, and a phosphate group, further optionally including at least one of a sulfonic acid group, a boric acid group, and a phosphate group.
  • the organic-inorganic hybrid particles may be selected from metal organic framework materials, such as MOFs.
  • the coating may further include other organic compounds, for example,
  • the present application has no particular limitation on the types of the above-mentioned other organic compounds, and any known material with good improved performance can be selected.
  • the coating has a thickness of ⁇ 5 ⁇ m.
  • the preparation method of the isolation membrane comprises the following steps: (1) providing a polyolefin base membrane; (2) providing a coating slurry, mixing a filler and a solvent in a predetermined ratio to prepare a coating slurry; (3) coating the coating slurry of step (2) on at least one side of the polyolefin base membrane of step (1) to form a coating and drying to obtain an isolation membrane.
  • the polyolefin base membrane comprises a pore structure, the thickness of the polyolefin base membrane is ⁇ 7 ⁇ m, the tortuosity of the pore structure is 7.5-9.5, and the maximum pore size of the pore structure is ⁇ 45 nm.
  • the isolation film further comprises an adhesive layer.
  • the adhesive layer is disposed on at least a portion of the surface of the coating.
  • the adhesive layer comprises a granular binder, and optionally, the granular binder comprises at least one of an acrylate monomer homopolymer or copolymer, an acrylic acid monomer homopolymer or copolymer, and a fluorine-containing olefin monomer homopolymer or copolymer.
  • a fourth aspect of the present application provides a secondary battery, comprising the isolation membrane of the third aspect of the present application.
  • the secondary battery of the present application has improved energy density and electrical performance.
  • a secondary battery may include 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.
  • the negative electrode sheet generally includes a negative electrode current collector and a negative electrode film layer disposed on the negative electrode current collector.
  • 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 be a negative electrode active material for a battery known in the art.
  • the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc.
  • the silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.
  • the tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys.
  • the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.
  • the negative electrode film layer may also optionally include a binder, a conductive agent and other optional additives.
  • 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), graphene and carbon nanofibers.
  • the binder 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, etc.
  • the positive electrode sheet generally includes a positive electrode current collector and a positive electrode film layer disposed on the positive electrode current collector.
  • 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, lithium transition metal oxides, olivine structured One or more of lithium phosphates 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 phosphates with an 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 commercially.
  • the modified compounds of the above materials may be doping-modified and/or surface-coated modified materials.
  • the positive electrode film layer may also optionally include a binder, a conductive agent and other optional additives.
  • 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), graphene and carbon nanofibers.
  • the binder 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
  • the electrolyte plays a role of conducting ions between the positive electrode and the negative electrode.
  • the electrolyte may include an electrolyte salt and a solvent.
  • the electrolyte salt may 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 one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl 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), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), cyclopentane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ES), methyl
  • 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 positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.
  • the battery cell may include an outer packaging, which may be used to encapsulate the electrode assembly and the electrolyte.
  • the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.
  • the outer packaging of the battery cell may also be a soft package, such as a bag-type soft package.
  • the material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.
  • FIG4 is a battery cell 5 of a square structure as an example.
  • 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 are enclosed to form 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 negative electrode sheet and the isolation film can be formed into an electrode assembly 52 by a winding process or a lamination process.
  • the electrode assembly 52 is encapsulated in the receiving cavity. Electrolyte The electrode assembly 52 is immersed in the electrode assembly 52.
  • the number of the electrode assembly 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.
  • battery cells may be assembled into a battery module.
  • the number of battery cells contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.
  • FIG6 is a battery module 4 as an example.
  • a plurality of battery cells 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 battery cells 5 may be fixed by fasteners.
  • the battery module 4 may further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.
  • the battery modules described above may also be assembled into a battery pack.
  • the battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art 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 electric device, the electric device includes the secondary battery provided in the present application, and the secondary battery includes at least one of a battery cell, a battery module and a battery pack.
  • the secondary battery can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device.
  • the electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.
  • a battery cell, a battery module or a battery pack can be selected according to its usage requirements.
  • FIG9 is an example of an electric device.
  • the electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc.
  • a battery pack or a battery module may be used.
  • a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a battery cell may be used as a power source.
  • the dried microporous film was stretched again transversely at a small ratio of 2 times, and the transverse small ratio stretching temperature was 132°C, followed by heat setting at 133°C, and the heat setting time was 25 seconds, to obtain a polyethylene porous base film with a thickness of 5.1 ⁇ m and a crystallinity of 78.7%.
  • the pore size distribution diagram of the polyolefin base film is shown in Figure 1.
  • the cast film was stretched longitudinally and transversely, with a longitudinal stretching ratio of 9.2 times and a longitudinal stretching temperature of 110°C, and a transverse stretching ratio of 9.7 times and a transverse stretching temperature of 115°C. After heat preservation, a film with an area increased by 71 times was obtained, and the white oil in the film was extracted with dichloromethane to form pores.
  • the dried microporous film was stretched again transversely at a small ratio of 2 times, and the transverse small ratio stretching temperature was 132°C, followed by heat setting at 133°C for 25 seconds.
  • a polyethylene porous base film with a thickness of 4.0 ⁇ m and a crystallinity of 79.6% can be obtained.
  • the dried microporous film was stretched again transversely with a small ratio of 2 times, and the transverse small ratio stretching temperature was 132°C, and then heat-set at 133°C for 25 seconds, and a polyethylene porous base film with a thickness of 6.2 ⁇ m and a crystallinity of 79.3% was obtained.
  • Example 1 The method described in Example 1 was followed, except that the parameters listed in Table 1 below were different from those in Example 1.
  • the dried microporous film was stretched again transversely at a small ratio of 2 times, and the transverse small ratio stretching temperature was 132°C, and then heat-set at 133°C for 25 seconds, and a polyethylene porous base film with a thickness of 5.2 ⁇ m and a crystallinity of 78.7% was obtained.
  • the pore size distribution of the polyolefin base film was tested by the method of Example 1, and the obtained pore size distribution diagram is shown in Figure 2.
  • the dried microporous film was stretched again transversely at a small ratio of 2 times, and the transverse small ratio stretching temperature was 132°C, and then heat-set at 133°C for 25 seconds, and a polyethylene porous base film with a thickness of 5.2 ⁇ m and a crystallinity of 78.7% was obtained.
  • the pore size distribution of the polyolefin base film was tested by the method of Example 1, and the obtained pore size distribution diagram is shown in Figure 3.
  • the dried microporous film was stretched again transversely with a small ratio of 2 times, and the transverse small ratio stretching temperature was 132°C, and then heat-set at 133°C for 25 seconds, and a polyethylene porous base film with a thickness of 5.2 ⁇ m and a crystallinity of 78.7% was obtained.
  • the dried microporous film was stretched again transversely with a small ratio of 2 times, and the transverse small ratio stretching temperature was 132°C, and then heat-set at 133°C for 25 seconds, and a polyethylene porous base film with a thickness of 5.2 ⁇ m and a crystallinity of 78.7% was obtained.
  • Example 1 The method described in Example 1 was followed, except that the parameters listed in Table 1 below were different from those in Example 1.
  • Test of polyolefin base film thickness Clean the measuring platform and measuring head. Ensure that the measuring platform and measuring head are clean. Use a micrometer to test. When the data remains stable, record the data in Table 2-4.
  • Test of average pore size and maximum pore size of the pore structure of polyolefin-based membrane Direct measurement by PMI's capillary flow porosimeter or mercury intrusion instrument. 1 Use liquid to completely wet and fill the pores of the tested base membrane, and form positive pressure in the pores due to capillary phenomenon. 2 Place the base membrane in a closed tank and use gas pressure to squeeze the liquid out of the capillary pores. 3 Based on the relative relationship between the pressure applied when the liquid in a single pore is completely squeezed out of the capillary pores and the pore diameter, the average pore size and maximum pore size of the pore structure of the polyolefin-based membrane can be obtained according to the Laplace equation. The test results are shown in Table 2-4 below.
  • Air permeability test Cut the base film sample, the sample size must be greater than 40*40mm. Place the sample on the sample test platform, the sample must cover the entire sample area, tighten the knob, select the measurement area to ensure that the membrane can cover the test platform. Press the RESET key first (the screen will display "TIMER SEEKING STARTING MARK"), then release the slide to start the test. After the measurement is completed, slowly loosen the plug until the slide drops to the lowest position. Take out the sample, slowly lift the slide, and prepare for the next measurement. The test results are shown in Table 2-4 below.
  • Test of tensile strength Punching specimens: Punch the base film into base film sheets with a width of 15 mm and a length greater than 40 mm. Then set the tensile machine fixture to a starting fixture spacing of 40 mm and a speed of 50 mm/min. Place the specimen to be tested in the fixture. The middle, upper and lower ends were clamped with fixtures, and the tensile curve was recorded, with 5 parallel samples in each group. The test results are shown in Table 2-4 below.
  • Test of heat shrinkage rate Punch the base film into samples of 100mm*50mm. Mark the number with a marker before baking and measure it under the second dimension. Set the baking temperature and time. After the oven reaches the set temperature, put the base film into the oven together with the steel plate for baking. Take it out after the specified baking time and let it stand at room temperature for 10 minutes. Measure the horizontal and vertical dimensions of the base film with the same number after baking. If the edge of the sample shrinks unevenly, the position with the maximum shrinkage shall prevail. The test results are shown in Table 2-4 below.
  • Puncture strength test Use a high-speed rail tensile machine to pass a 1mm prototype needle through the basement membrane at a speed of 50mm/min. The maximum force obtained is the puncture strength. For each group of 5 parallel samples, the average value obtained is the puncture strength. The test results are shown in Table 2-4 below.
  • the tortuosity of the pore structure is calculated according to the following formula
  • ⁇ represents the tortuosity of the pore structure
  • t gur represents the air permeability of the basement membrane (obtained by the above test method)
  • ⁇ represents the porosity of the basement membrane (obtained by the above test method)
  • d represents the average pore size of the pore structure (obtained by the above test method)
  • cm represents the thickness of the basement membrane (obtained by the above test method), in cm.
  • the base films of Examples 1-23 and Comparative Examples 1-6 were used to prepare lithium-ion batteries according to the following general preparation method.
  • NMP solvent N-methylpyrrolidone
  • the mixture was stirred evenly under the action of a vacuum mixer to obtain a positive electrode slurry, wherein the solid content in the positive electrode slurry was 50wt%; the positive electrode slurry was evenly coated on the positive electrode collector aluminum foil and dried at 85°C, and then cold pressed, trimmed, cut into pieces, and slit, and finally dried under vacuum conditions at 85°C for 4 hours to obtain a positive electrode sheet.
  • Example 1 Provide the base film of Example 1; mix inorganic particles of aluminum oxide (Al 2 O 3 ), organic particles of vinylidene fluoride-hexafluoropropylene copolymer (number average molecular weight of 550,000), and binder aqueous solution type polyacrylic acid in a mass ratio of 79.1:20:0.9 in an appropriate amount of solvent deionized water to obtain a coating slurry with a solid content of 38% (by weight); apply the coating slurry on two surfaces of the base film by a coating machine, and obtain a separation film through drying, slitting and other processes.
  • the line number of the gravure roller of the coating machine is 125 LPI
  • the coating speed is 50 m/min
  • the coating line speed ratio is 1.2
  • the drying temperature is 50°C ⁇ 5°C
  • the drying time is 30s.
  • 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 of step (1), the isolation film of step (3), and the negative electrode sheet of step (2) are stacked in order, so that the isolation film is located between the positive and negative electrode sheets to play an isolating role, and then wound into a square bare cell, the tabs are welded, and the bare cell is placed in a packaging foil aluminum-plastic film, and then baked at 80°C to remove water, and then the electrolyte is injected and sealed.
  • the secondary batteries of Examples 2-23 and Comparative Examples 1-6 were prepared in a similar manner to the secondary battery of Example 1, except that different base films were used.
  • the lithium-ion battery is charged/discharged with a large current for a short time (30s), and the DC internal resistance can be obtained by calculating the ratio of the voltage difference before and after charging and discharging to the current.
  • the test conditions and test results are shown in Table 5 below.
  • AC resistance, AC internal resistance equipment Itech IT5100 series battery internal resistance tester
  • test method add a fixed frequency of 1KHz and a fixed current of 50mA to the test cell, sample the voltage, and calculate the resistance value through the rectifier test instrument.
  • the test results are shown in Table 5.
  • the test results are shown in Table 5.
  • the bare cell After winding, the bare cell will be subjected to a short circuit rate test under the conditions of 100V, 80°C, 10s, 5MPa. The test results are shown in Table 5 below.
  • the pore structure of the polyethylene porous base film of the present application has a large tortuosity, and the base film has a uniform pore structure, thereby improving the consistency of the base film, reducing the performance deviation of the base film, and effectively ensuring the air permeability of the base film.
  • the electrical performance of the battery can be significantly improved, including reducing the DC internal resistance of the battery, the battery internal resistance, the self-discharge rate and the short circuit rate.
  • Example 1 By comparing Example 1 and Comparative Example 1, it can be seen that the weight average molecular weight of the polyethylene used in Comparative Example 1 is not within the scope of the present application, the tortuosity of the pore structure of the polyethylene porous base membrane prepared in Comparative Example 1 is significantly smaller, and the DC internal resistance, battery internal resistance, self-discharge rate and short circuit rate of the battery corresponding to Comparative Example 1 are significantly larger.
  • Example 1 By comparing Example 1 and Comparative Example 2, it can be seen that the polydispersity index Mw/Mn of the polyethylene used in Comparative Example 2 is not within the scope of the present application, the tortuosity of the pore structure of the polyethylene porous base membrane prepared in Comparative Example 2 is significantly smaller, and the DC internal resistance, battery internal resistance, self-discharge rate and short circuit rate of the battery corresponding to Comparative Example 2 are significantly larger.
  • Comparative Example 3 Comparative Example 6
  • the longitudinal stretching ratio and the transverse stretching ratio of Comparative Examples 3 and 6 are not within the scope of the present application, the tortuosity of the pore structure of the polyethylene porous base membrane prepared in Comparative Examples 3 and 6 is significantly smaller, and the DC internal resistance, battery internal resistance, self-discharge rate and short circuit rate of the batteries corresponding to Comparative Examples 3 and 6 are significantly larger.
  • Example 1 By comparing Example 1 and Comparative Examples 4-5, it can be seen that the solid content of polyethylene in Comparative Examples 4-5 is not within the scope of the present application, the tortuosity of the pore structure of the polyethylene porous base membrane prepared in Comparative Examples 4-5 is significantly smaller, and the DC internal resistance, battery internal resistance, self-discharge rate and short circuit rate of the battery corresponding to Comparative Examples 4-5 are significantly larger.

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Abstract

本申请涉及一种聚烯烃基膜，通过优化聚烯烃基膜中孔结构的曲折度，使聚烯烃基膜具有均匀的孔结构，从而提升了基膜一致性，降低了基膜性能偏差，并且还有效保证了基膜的透气性。同时，本申请的聚烯烃基膜厚度超薄，厚度每减薄1μm，电芯的能量密度能够增加约0.7％，因此通过将厚度控制在7μm以下，提高了电芯的能量密度。当将该聚烯烃基膜作为隔离膜用于电池时，能够提高电池的电性能，包括降低电池内阻、直流内阻、自放电率、短路率等。本申请还涉及聚烯烃基膜的制备方法、隔离膜、二次电池及用电装置。

Description

聚烯烃基膜及其制备方法、隔离膜、二次电池及用电装置
相关申请
本申请要求2022年10月28日申请的，申请号为PCT/CN2022/128110的国际专利申请的优先权，在此将其全文引入作为参考。
技术领域
本申请属于电池技术领域，具体涉及一种聚烯烃基膜及其制备方法、隔离膜、二次电池及用电装置。
背景技术
二次电池现已被广泛用于纯电动汽车、混合电动汽车、智能电网等领域。在二次电池中，隔离膜用于将正负两极分开，防止正负极直接接触产生短路。随着人们对便携式产品使用需求的日益增长，超薄隔离膜开始大范围应用。然而，现有的用于制备超薄隔离膜的聚烯烃基膜无法兼顾低厚度和孔结构均匀性，基膜性能偏差较大。
因此，亟需开发一种能够兼顾低厚度和孔结构均匀性的聚烯烃基膜。
发明内容
鉴于背景技术中存在的问题，本申请提供一种聚烯烃基膜，该聚烯烃基膜能够兼顾低厚度和孔结构均匀性。
本申请第一方面提供的聚烯烃基膜包括孔结构。所述聚烯烃基膜包括孔结构，所述聚烯烃基膜的厚度≤7μm，所述孔结构的曲折度为7-10。
本申请实施例的技术方案中，通过优化孔结构的曲折度，使聚烯烃基膜具有均匀的孔结构，从而提升了基膜一致性，降低了基膜性能偏差，离子传输快，并且还有效保证了基膜的透气性。同时，本申请的聚烯烃基膜厚度超薄，厚度每减薄1μm，电芯的能量密度能够增加约0.7％，因此通过将厚度控制在7μm以下，提高了电芯的能量密度。当将该聚烯烃基膜作为隔离膜用于电池时，能够提高电池的电性能，包括降低电池内阻、直流内阻、自放电率、短路率等。
在一些实施例中，根据第一方面，提出第一方面的第一种示例，所述孔结构的曲折度为7.5-9.5；可选地，所述孔结构的曲折度为7.5-9。
在一些实施例中，根据第一方面，提出第一方面的第一种示例，所述孔结构的最大孔径≤45nm；可选地，所述孔结构的最大孔径≤40nm；进一步可选地，所述孔结构的最大孔径为20nm-40nm。
在一些实施例中，根据第一方面，提出第一方面的第一种示例，所述聚烯烃基膜的厚度为2μm-6.2μm；可选地，所述聚烯烃基膜的厚度为4μm-6.2μm。
该设计中，通过优化聚烯烃基膜的厚度、孔结构的曲折度和孔结构的最大孔径，有利于进一步提高聚烯烃基膜的一致性，降低基膜性能偏差，提高基膜透气性，并提高电芯的能量密度。
在一些实施例中，根据第一方面，提出第一方面的第二种示例，聚烯烃基膜包括重均分子量Mw为50万以上的聚烯烃；可选地，所述聚烯烃基膜包括重均分子量Mw为50万～150万的聚烯烃。
该设计中，使用重均分子量Mw为50万以上的聚烯烃作为原料，有利于提高成孔的均匀性。
在一些实施例中，根据第一方面，提出第一方面的第三种示例，聚烯烃的多分散指数Mw/Mn≤3.5；可选地，所述聚烯烃的多分散指数Mw/Mn为1～3.5。
该设计中，优化聚烯烃的多分散指数，有利于减小聚烯烃分子量的分布宽度，提高分子量的一致性。
在一些实施例中，根据第一方面，提出第一方面的第四种示例，聚烯烃为聚乙烯和聚丙烯中的一种或两种。
该设计中，优化聚烯烃的种类，有利于进一步提高聚烯烃基膜的一致性，提高基膜强度和延伸率，降低基膜热收缩率等。
在一些实施例中，根据第一方面，提出第一方面的第五种示例，聚烯烃基膜的透气度≤180s/100cc。
该设计中，优化聚烯烃基膜的透气度，有利于改善隔离膜的透气性。
在一些实施例中，根据第一方面，提出第一方面的第六种示例，聚烯烃基膜的纵向延伸率≥60％，可选地，所述聚烯烃基膜的纵向延伸率≥100％；进一步可选地，所述聚烯烃基膜的纵向延伸率为100％～120％。聚烯烃基膜的横向延伸率≥100％；可选地，所述聚烯烃基膜的横向延伸率≥110％；进一步可选地，所述聚烯烃基膜的横向延伸率为110％～160％。
该设计中，延伸率的增加可有效提升隔离膜的韧性。当在卷绕过程中出现金属颗粒(可能来自操作环境、正负极极片或隔离膜等)时，隔离膜能够有效包覆住颗粒，防止电芯被击穿，提高电芯的可制造性。
在一些实施例中，根据第一方面，提出第一方面的第七种示例，聚烯烃基膜在115℃下的纵向热收缩率≤4％，横向热收缩率≤4％。
该设计中，优化聚烯烃基膜的热收缩率，可有效提升隔离膜的热稳定性，提升电芯的安全性能。
在一些实施例中，根据第一方面，提出第一方面的第八种示例，聚烯烃基膜符合下述(1)-(4)中的至少一个条件：
(1)聚烯烃基膜的穿刺强度≥270gf；
(2)聚烯烃基膜的纵向拉伸强度≥2000kgf/cm2，横向拉伸强度≥2000kgf/cm2；
(3)聚烯烃基膜的孔隙率为25％-40％；
(4)聚烯烃基膜的面密度为2-5g/m2。
该设计中，通过优化聚乙烯多孔基膜的强度，有利于提高隔离膜的耐受性能，有效保证隔离膜制程的优率。通过优化聚乙烯多孔基膜的孔结构，有利于保证孔径一致性，并且有利于实现有效的离子传导。
本申请第二方面提供一种聚烯烃基膜的制备方法，包括：
将聚烯烃和造孔剂混合，并将所得混合物制成膜片；
对所述膜片进行双轴拉伸；
去除双轴拉伸后的膜片中的所述造孔剂，形成孔隙；以及
对形成孔隙后的膜片进行拉伸定型和热定型，得到所述聚烯烃基膜；
所述聚烯烃基膜包括孔结构，所述聚烯烃基膜的厚度≤7μm，所述孔结构的曲折度为7-10。
本申请实施例的技术方案中，使用具有超高重均分子量的聚烯烃作为原料，同时配合双轴拉伸，可以制备出孔结构的曲折度为7.5-9.5且孔结构的最大孔径≤45nm的超薄聚烯烃基膜。
在一些实施例中，根据第二方面，提出第二方面的第一种示例，所述聚烯烃的重均分子量Mw为50万以上；可选地，所述聚烯烃基膜包括重均分子量Mw为50万～150万的聚烯烃。
在一些实施例中，根据第二方面，提出第二方面的第一种示例，聚烯烃在混合物中的占比为20wt％-30wt％。
该设计中，通过优化聚烯烃的固含量，有利于提高膜面厚度的均一性，提高基膜孔径一致性，并且有利于达到基膜高延伸率规格需求。如果聚烯烃的固含量过大(＞30wt％)，挤出机压力曲线波动大，膜面厚度均一性差，基膜孔径一致性差。如果聚烯烃的固含量过小(＜20％wt)，造孔剂如白油含量过高，可拉伸倍率有限，无法达成高延伸率规格需求，通过优化聚烯烃的固含量，在提高成孔均匀性同时达成高延伸率规格需求。
在一些实施例中，根据第二方面，提出第二方面的第二种示例，双轴拉伸包括纵向拉伸和横向拉伸，其中纵向拉伸倍率为5-15倍，横向拉伸倍率为5-15倍，且纵向拉伸倍率和横向拉伸倍率不同时为5；可选地，纵向拉伸倍率为6-15倍，横向拉伸倍率为6-15倍。
该设计中，通过优化纵向拉伸倍率和横向拉伸倍率，可以进一步减小聚烯烃基膜的厚度，提高成孔均匀性。
本申请第三方面提供一种隔离膜，包括本申请第一方面的聚烯烃基膜或通过本申请第二方面的制备方法获得的聚烯烃基膜。
本申请实施例的技术方案中，由于采用了本申请第一方面的聚烯烃基膜或通过本申请第二方面的制备方法获得的聚烯烃基膜，因此本申请的隔离膜具有超薄、孔结构均匀等优点。
在一些实施例中，根据第三方面，提出第三方面的第一种示例，所述隔离膜还包括设置在所述聚烯烃基膜的至少一个表面的涂层。
通过在聚烯烃基膜表面设置涂层，可以提高电芯的电性能和安全性能。
在一些实施例中，根据第三方面，提出第三方面的第一种示例，涂层包括填料。填料包括选自无机颗粒、有机颗粒、有机-无机杂化颗粒中的至少一种。
选择具有热稳定性好且不易分解的填料，可以进一步提升隔离膜的耐热性。
在一些实施例中，根据第三方面，提出第三方面的第二种示例，隔离膜还包括粘接层。粘接层设置在涂层的至少一部分表面上。粘接层包括颗粒状的粘结剂，可选地，颗粒状的粘结剂包括丙烯酸酯类单体均聚物或共聚物、丙烯酸类单体均聚物或共聚物和含氟烯烃单体均聚物或共聚物中的至少一种。
粘接层不仅能够防止涂层脱落，提高二次电池的安全性能，而且能够改善隔离膜与电极的界面，提升二次电池的循环性能。
本申请第四方面提供一种二次电池，包括本申请第三方面的隔离膜。
本申请实施例的技术方案中，由于采用了本申请第一方面的聚烯烃基膜或通过本申请第二方面的制备方法获得的聚烯烃基膜，因此本申请的二次电池具有提高的能量密度和电性能。
本申请第五方面提供一种用电装置，包括本申请第四方面的二次电池。
本申请实施例的技术方案中，由于采用了本申请第一方面的聚烯烃基膜或通过本申请第二方面的制备方法获得的聚烯烃基膜，因此本申请的用电装置具有提高的能量密度和电性能。
上述说明仅是本申请技术方案的概述，为了能够更清楚了解本申请的技术手段，可依照说明书的内容予以实施，并且为了让本申请的上述和其它目的、特征和优点能够更明显易懂，以下特举本申请的具体实施方式。
附图说明
图1为本申请实施例1制备的聚烯烃基膜的孔径分布图。
图2为对比例1制备的聚烯烃基膜的孔径分布图。
图3为对比例2制备的聚烯烃基膜的孔径分布图。
图4是本申请一实施方式的电池单体的示意图。
图5是图4所示的本申请一实施方式的电池单体的分解图。
图6是本申请一实施方式的电池模块的示意图。
图7是本申请一实施方式的电池包的示意图。
图8是图7所示的本申请一实施方式的电池包的分解图。
图9是本申请一实施方式的二次电池用作电源的用电装置的示意图。
附图标记说明：
1电池包；2上箱体；3下箱体；4电池模块；5电池单体；51壳体；52电极组件；53
顶盖组件。
具体实施方式
下面将参照附图更详细地描述本公开的示例性实施方式。虽然附图中显示了本公开的示例性实施方式，然而应当理解，可以以各种形式实现本公开而不应被这里阐述的实施方式所限制。相反，提供这些实施方式是为了能够更透彻地理解本公开，并且能够将本公开的范围完整的传达给本领域的技术人员。
除非另有定义，本文所使用的所有的技术和科学术语与属于本申请的技术领域的技术人员通常理解的含义相同；本文中所使用的术语只是为了描述具体的实施例的目的，不是旨在于限制本申请。本申请的说明书和权利要求书及上述附图说明中的术语“包括”和“具有”以及它们的任何变形，意图在于覆盖不排他的包含。
为了简便，本文仅明确地公开了一些数值范围。然而，任意下限可以与任何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，尽管未明确记载，但是范围端点间的每个点或单个数值都包含在该范围内。因而，每个点或单个数值可以作为自身的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，需要说明的是，除非另有说明，“以上”、“以下”为包含本数，“一种或多种”中“多种”的含义是两种以上(包括两种)。
二次电池现已被广泛用于纯电动汽车、混合电动汽车、智能电网等领域。在二次电池中，隔离膜用于将正负两极分开，防止正负极直接接触产生短路。随着人们对便携式产品使用需求的日益增长，超薄隔离膜开始大范围应用。然而，现有的用于制备超薄隔离膜的聚烯烃基膜无法兼顾低厚度和孔结构均匀性，基膜性能偏差较大。因此，亟需开发一种能够兼顾低厚度和孔结构均匀性的聚烯烃基膜。
发明人经过深入研究，设计了一种聚烯烃基膜，通过优化聚烯烃基膜的孔结构的曲折度以及聚烯烃基膜中孔结构的最大孔径，使聚烯烃基膜具有均匀的孔结构，从而提升了基膜一致性，降低了基膜性能偏差，并且还有效保证了基膜的透气性。同时，本申请的聚烯烃基膜厚度超薄，厚度每减薄1μm，电芯的能量密度能够增加约0.7％，因此通过将厚度控制在7μm以下，提高了电芯的能量密度。当将该聚烯烃基膜作为隔离膜用于电池时，能够提高电池的电性能，包括降低电池内阻、直流内阻、自放电率、短路率等。
本申请实施例描述的技术方案适用于聚烯烃基膜，还适用于聚烯烃基膜的制备工艺、使用聚烯烃基膜的隔离膜、使用隔离膜的二次电池以及使用二次电池的用电装置。
第一方面，根据本申请的一些实施例，本申请提供一种聚烯烃基膜。所述聚烯烃基膜包括孔结构，所述聚烯烃基膜的厚度≤7μm，所述孔结构的曲折度为7-10。。
本申请实施例的技术方案中，聚烯烃基膜兼具超薄厚度和均匀孔结构，可有效提升基膜的整体性能。当将该基膜卷绕在NCM811体系中时，可有效降低电池内阻、直流内阻及自放电率，且量产短路优率水平与普通7μm厚度的聚烯烃基膜相当。
在本申请中，聚烯烃基膜的孔结构的曲折度由基膜透气度、基膜厚度、基膜孔隙率和基膜的孔结构的平均孔径共同决定。聚烯烃基膜的孔结构的曲折度可通过如下公式计算得到：
其中，τ表示孔结构的曲折度，tgur表示基膜透气度，ε表示基膜孔隙率，d表示孔结构的平均孔径，单位为cm，L表示基膜厚度，单位为cm。
在一些实施例中，根据第一方面，提出第一方面的第一种示例，所述孔结构的曲折度为7.5-9.5。进一步地，所述孔结构的曲折度为7.5-9。
在一些实施例中，根据第一方面，提出第一方面的第一种示例，所述孔结构的最大孔径≤45nm。进一步地，所述孔结构的最大孔径≤40nm。更进一步地，所述孔结构的最大孔径为20nm-40nm。
在一些实施例中，根据第一方面，提出第一方面的第一种示例，所述聚烯烃基膜的厚度为2μm-6.2μm。进一步地，所述聚烯烃基膜的厚度为4μm-6.2μm。
该设计中，通过优化聚烯烃基膜的厚度、孔结构的曲折度和最大孔径，有利于进一步提高聚烯烃基膜的一致性，降低基膜性能偏差，提高基膜透气性，并提高电芯的能量密度。
在一些具体实施例中，聚烯烃基膜的厚度可为2μm、2.1μm、2.2μm、2.3μm、2.4μm、2.5μm、2.6μm、2.7μm、2.8μm、2.9μm、3.0μm、3.1μm、3.2μm、3.3μm、3.4μm、3.5μm、3.6μm、3.7μm、3.8μm、3.9μm、4μm、4.1μm、4.2μm、4.3μm、4.4μm、4.5μm、4.6μm、4.7μm、4.8μm、4.9μm、5.0μm、5.1μm、5.2μm、5.3μm、5.4μm、5.5μm、5.6μm、5.7μm、5.8μm、5.9μm、6.0μm、6.1μm、6.2μm、6.3μm、6.4μm、6.5μm、6.6μm、6.7μm、6.8μm、6.9μm或7μm。可选地，聚烯烃基膜的厚度可为4μm-5.0μm、5.0μm-6.2μm或4.5μm-5.5μm。
在一些具体实施例中，孔结构的曲折度可为7.0、7.1、7.2、7.3、7.4、7.5、7.6、7.7、7.8、7.9、8.0、8.1、8.2、8.3、8.4、8.5、8.6、8.7、8.8、8.9、9.0、9.1、9.2、9.3、9.4、9.5、9.6、9.7、9.8、9.9或10.0。
在一些具体实施例中，孔结构的最大孔径可为45nm、44nm、43nm、42nm、41nm、40nm、39.9nm、39.8nm、39.7nm、39.6nm、39.5nm、39.4nm、39.3nm、39.2nm、39.1nm、39nm、38nm、35nm、30nm、25nm或20nm。
在一些实施例中，根据第一方面，提出第一方面的第二种示例，聚烯烃基膜包括重均分子量Mw为50万以上的聚烯烃。
使用重均分子量Mw为50万以上的聚烯烃作为原料，有利于提高成孔的均匀性。
本申请中，单一重均分子量应理解为是指聚烯烃的重均分子量是唯一确定的。
在一些具体实施例中，聚烯烃的重均分子量Mw可为50万-150万。重均分子量过大会导致加工困难，挤出机的压力不易控制，膜面的厚度一致性差；重均分子量过小，分子链较短，经拉伸后晶区占比较少，导致基膜强度降低。例如，聚烯烃的重均分子量Mw可为50万、55万、60万、65万、70万、75万、80万、85万、90万、95万、100万、110万、120万、130万、140万或150万。
在一些实施例中，根据第一方面，提出第一方面的第三种示例，聚烯烃的多分散指数Mw/Mn≤3.5。
该设计中，优化聚烯烃的多分散指数，有利于减小聚烯烃分子量的分布宽度，提高分子量的一致性。
本申请中，Mn为聚烯烃的数均分子量，Mw为聚烯烃的重均分子量，多分散指数为将重均分子量除以数均分子量而获得的值，即重均分子量/数均分子量(Mw/Mn)，可表示分子量分布的均匀程度。
在一些具体实施例中，聚烯烃的多分散指数Mw/Mn可为1、1.1、1.2、1.3、1.4、1.5、1.6、1.7、1.8、1.9、2.0、2.1、2.2、2.3、2.4、2.5、2.6、2.7、2.8、2.9、3.0、3.1、3.2、3.3、 3.4或3.5。可选地，聚烯烃的多分散指数Mw/Mn可为1-3.5、1-2或2-3.5等。
在一些实施例中，根据第一方面，提出第一方面的第四种示例，聚烯烃为聚乙烯、聚丙烯或聚乙烯和聚丙烯混合物。
该设计中，优化聚烯烃的种类，有利于进一步提高聚烯烃基膜的一致性，提高基膜强度和延伸率，降低基膜热收缩率等。
在一些实施例中，根据第一方面，提出第一方面的第五种示例，聚烯烃基膜的透气度≤180s/100cc。
该设计中，优化聚烯烃基膜的透气度，有利于改善隔离膜的透气性。
在一些具体实施例中，聚烯烃基膜的透气度可为100-180s/100cc。例如，聚烯烃基膜的透气度可为100s/100cc、105s/100cc、110s/100cc、115s/100cc、120s/100cc、125s/100cc、130s/100cc、135s/100cc、140s/100cc、145s/100cc、150s/100cc、155s/100cc、160s/100cc、165s/100cc、170s/100cc、175s/100cc或180s/100cc。可选地，聚烯烃基膜的透气度可为140-170s/100cc。
在一些实施例中，根据第一方面，提出第一方面的第六种示例，聚烯烃基膜的纵向(MD)延伸率≥60％，可选地，所述聚烯烃基膜的纵向延伸率≥100％；进一步可选地，所述聚烯烃基膜的纵向延伸率为100％～120％。聚烯烃基膜的横向(TD)延伸率≥100％；可选地，所述聚烯烃基膜的横向延伸率≥110％；进一步可选地，所述聚烯烃基膜的横向延伸率为110％～160％。
该设计中，延伸率的增加说明隔离膜具有较好的韧性。当在卷绕过程中出现金属颗粒(可能来自操作环境、正负极极片或隔离膜等)时，隔离膜能够有效包覆住颗粒，防止电芯被击穿，提高电芯的可制造性。
在一些具体实施例中，聚烯烃基膜的纵向延伸率可为60％-120％，例如可为：60％、65％、70％、73％、75％、80％、82％、85％、88％、89％、90％、93％、95％、96％、97％、98％、99％、100％、101％、104％、105％、109％、110％、112％、113％、114％、115％、116％、120％。
在一些具体实施例中，聚烯烃基膜的横向延伸率可为100％-160％，例如可为：100％、101％、102％、105％、106％、107％、108％、109％、110％、111％、113％、114％、115％、117％、118％、120％、121％、125％、130％、135％、140％、145％、150％、155％、160％。
在一些实施例中，根据第一方面，提出第一方面的第七种示例，聚烯烃基膜在115℃下的纵向热收缩率≤4％，横向热收缩率≤4％。
该设计中，聚烯烃基膜的热收缩率的降低说明隔离膜的热稳定性好，如此可提升电芯的安全性能。
在一些具体实施例中，聚烯烃基膜在115℃下的纵向热收缩率可为0％-3％，例如可为0％、0.5％、1％、1.5％、2％、2.1％、2.2％、2.3％、2.4％、2.5％、2.6％、2.7％、2.8％、2.9％或3％。可选地，聚烯烃基膜在115℃下的纵向热收缩率可为2％-2.5％。
在一些具体实施例中，聚烯烃基膜在115℃下的横向热收缩率可为0％-3％，例如可为0％、0.1％、0.2％、0.3％、0.4％、0.5％、0.6％、0.7％、0.8％、0.9％、1％、1.1％、1.2％、1.3％、1.4％、1.5％、1.6％、1.7％、1.8％、1.9％、2％、2.5％或3％。可选地，聚烯烃基膜在115℃下的横向热收缩率可为0.5％-2％或0.9％-1.6％。
在一些实施例中，根据第一方面，提出第一方面的第八种示例，聚烯烃基膜符合下述(1)-(4)中的至少一个条件：
(1)聚烯烃基膜的穿刺强度≥270gf；
(2)聚烯烃基膜的纵向拉伸强度≥2000kgf/cm2，横向拉伸强度≥2000kgf/cm2；
(3)聚烯烃基膜的孔隙率为25％-40％；
(4)聚烯烃基膜的面密度为2-5g/m2。
该设计中，聚乙烯多孔基膜具有较高的穿刺强度，说明隔离膜的耐受性能好，能够有 效保证隔离膜制程的优率。通过优化聚乙烯多孔基膜的孔隙率，有利于保证孔径一致性，并且有利于实现有效的离子传导。
在一些具体实施例中，聚烯烃基膜的穿刺强度可为270gf、275gf、280gf、285gf、290gf、295gf、300gf、305gf、310gf、315gf、320gf、325gf、330gf、340gf或350gf等。可选地，聚烯烃基膜的穿刺强度可为270-350gf。
在一些具体实施例中，聚烯烃基膜的纵向拉伸强度可为2000kgf/cm2、2100kgf/cm2、2200kgf/cm2、2300kgf/cm2、2400kgf/cm2、2500kgf/cm2、2600kgf/cm2、2700kgf/cm2、2800kgf/cm2、2900kgf/cm2或3000kgf/cm2。可选地，聚烯烃基膜的纵向拉伸强度可为2400-2800kgf/cm2。
在一些具体实施例中，聚烯烃基膜的横向拉伸强度可为2000kgf/cm2、2100kgf/cm2、2200kgf/cm2、2300kgf/cm2、2400kgf/cm2、2500kgf/cm2、2600kgf/cm2、2700kgf/cm2、2800kgf/cm2、2900kgf/cm2或3000kgf/cm2。可选地，聚烯烃基膜的横向拉伸强度可为2100-2600kgf/cm2。
在一些具体实施例中，聚烯烃基膜的孔隙率可为25％、26％、27％、28％、29％、30％、31％、32％、33％、34％、35％、36％、37％、38％、39％或40％。可选地，聚烯烃基膜的孔隙率可为30％-35％。
在一些具体实施例中，聚烯烃基膜的面密度可为2g/m2、2.1g/m2、2.2g/m2、2.3g/m2、2.4g/m2、2.5g/m2、2.6g/m2、2.7g/m2、2.8g/m2、2.9g/m2、3.0g/m2、3.1g/m2、3.2g/m2、3.3g/m2、3.4g/m2、3.5g/m2、3.6g/m2、3.7g/m2、3.8g/m2、3.9g/m2、4g/m2、4.5g/m2或5g/m2。可选地，聚烯烃基膜的面密度可为2.5-4g/m2。
本申请第二方面提供一种聚烯烃基膜的制备方法，包括：
将聚烯烃和造孔剂混合，并将所得混合物制成膜片；
对所述膜片进行双轴拉伸；
去除双轴拉伸后的膜片中的所述造孔剂，形成孔隙；以及
对形成孔隙后的膜片进行拉伸定型和热定型，得到所述聚烯烃基膜；
所述聚烯烃基膜包括孔结构，所述聚烯烃基膜的厚度≤7μm，所述孔结构的曲折度为7-10。
本申请实施例的技术方案中，使用聚烯烃作为原料，同时配合双轴拉伸，可以制备出孔结构的曲折度为7-10的超薄聚烯烃基膜，且厚度≤7μm。
进一步地，本实施例的技术方案中，制备得到的聚烯烃基膜具有与前述聚烯烃基膜相同的特征和优点，在此不再赘述。
在一些实施例中，根据第二方面，提出第二方面的第一种示例，所述聚烯烃的重均分子量Mw为50万以上。进一步地，所述聚烯烃基膜包括重均分子量Mw为50万～150万的聚烯烃。
在一些实施例中，根据第二方面，提出第二方面的第一种示例，聚烯烃在混合物中的占比为20wt％-30wt％。
该设计中，通过优化聚烯烃在混合物中的占比，有利于提高膜面厚度的均一性，提高基膜孔径一致性，并且有利于达到基膜高延伸率规格需求。如果占比过大(＞30wt％)，挤出机压力曲线波动大，膜面厚度均一性差，基膜孔径一致性差。如果占比过小(＜20％wt)，造孔剂含量过高，可拉伸倍率有限，无法达成高延伸率规格需求，通过优化聚烯烃在混合物中的占比，在提高成孔均匀性同时达成高延伸率规格需求。
在一些具体实施例中，聚烯烃在混合物中的占比为20wt％、21wt％、22wt％、23wt％、24wt％、25wt％、26wt％、27wt％、28wt％、29wt％或30wt％。
在一些实施例中，根据第二方面，提出第二方面的第二种示例，双轴拉伸包括纵向拉伸和横向拉伸，其中纵向拉伸倍率为5-15倍，横向拉伸倍率为5-15倍，且纵向拉伸倍率和横向拉伸倍率不同时为5。进一步地，纵向拉伸倍率为6-15倍，横向拉伸倍率为6-15 倍。
该设计中，通过优化纵向拉伸倍率和横向拉伸倍率，可以进一步减小聚烯烃基膜的厚度，提高成孔均匀性。
在一些具体实施例中，纵向拉伸倍率可为5-12倍，例如可为5倍、6倍、7倍、8倍、8.1倍、8.2倍、8.3倍、8.4倍、8.5倍、8.6倍、8.7倍、8.8倍、8.9倍、9倍、9.1倍、9.2倍、9.3倍、9.4倍、9.5倍、10倍、11倍或12倍。可选地，纵向拉伸倍率可为8-9.5倍。纵向拉伸温度可为109-115℃。
在一些具体实施例中，横向拉伸倍率可为5-12倍，例如可为5倍、6倍、7倍、8倍、8.1倍、8.2倍、8.3倍、8.4倍、8.5倍、8.6倍、8.7倍、8.8倍、8.9倍、9倍、9.1倍、9.2倍、9.3倍、9.4倍、9.5倍、9.6倍、9.7倍、9.8倍、9.9倍、10倍、11倍或12倍。可选地，横向拉伸倍率可为8.5-10倍。横向拉伸温度可为113-119℃。
本申请对所采用的造孔剂没有特别限制，只要其能够充分地溶解聚烯烃即可。例如，造孔剂可以为但不限于白油、液体石蜡、矿物油、大豆油、邻苯二甲酸酯和芳香族醚中的一种或多种。可选地，造孔剂为白油。在一些具体实施例中，造孔剂为白油，将单一重均分子量的聚烯烃和白油混合，可得到液体混合物。聚烯烃在液体混合物中的占比即为聚烯烃的固含量。
在一些实施例中，根据第二方面，提出第二方面的第三种示例，膜片的厚度可为1mm以上，可选为1-5mm，例如可为1mm、1.5mm、1.6mm、1.7mm、1.8mm、1.9mm、2mm、2.1mm、2.2mm、2.3mm、2.4mm、2.5mm、3mm、4mm或5mm。
在一些实施例中，根据第二方面，提出第二方面的第四种示例，双轴拉伸包括：首先进行纵向拉伸，然后进行横向拉伸；或者，首先进行横向拉伸，然后进行纵向拉伸；或者，同步进行纵向拉伸和横向拉伸。
在一些实施例中，根据第二方面，提出第二方面的第五种示例，去除造孔剂包括：利用萃取剂萃取膜片中的造孔剂。萃取剂的种类可以根据造孔剂的种类进行选择，主要用于溶解造孔剂以在材料中形成孔隙。可选地，萃取剂为二氯甲烷。
在一些实施例中，根据第二方面，提出第二方面的第六种示例，拉伸定型包括：对膜片进行横向小倍率拉伸。拉伸倍率可为1-3倍。拉伸温度可为130-133℃。
在一些实施例中，根据第二方面，提出第二方面的第七种示例，热定型热包括：对膜片进行加热定型。加热温度≥133℃，可选为133-135℃。加热时间≥20s，可选为20-60s，例如28-40s或30-40s。
本申请第三方面提供一种隔离膜，包括本申请第一方面的聚烯烃基膜或通过本申请第二方面的制备方法获得的聚烯烃基膜。
本申请实施例的技术方案中，由于采用了本申请第一方面的聚烯烃基膜或通过本申请第二方面的制备方法获得的聚烯烃基膜，因此本申请的隔离膜具有超薄、孔结构均匀等优点。另外，通过在聚烯烃基膜表面设置涂层，可以提高电芯的电性能和安全性能。
在一些实施例中，根据第三方面，提出第三方面的第一种示例，所述隔离膜还包括设置在所述聚烯烃基膜的至少一个表面的涂层。
在一些实施例中，根据第三方面，提出第三方面的第一种示例，涂层包括填料。填料包括选自无机颗粒、有机颗粒和有机-无机杂化颗粒中的至少一种。
在一些实施例中，可选地，所述填料的分解温度在200℃以上，由此填料可具有热稳定性好且不易分解的特性，进而可以进一步提升隔离膜的耐热性。
在一些实施例中，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至少一种。
可选地，具有5以上介电常数的无机颗粒包括勃姆石、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。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。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；此外，通过选择具有特定官能团的偶联剂、表面活性材料或聚合物改性无机颗粒，还有助于提升涂层对电解液的浸润特性和提升涂层的粘结性。
可选地，具有离子传导性但不储存离子的无机颗粒包括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传输特性。
可选地，能够发生电化学反应的无机颗粒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。
有机颗粒具有热稳定性好且不易分解的特性，由此可以提升隔离膜的耐热性；同时，当二次电池因为过热失控使其内部温度达到有机颗粒的熔点时，有机颗粒还可以融化，并因毛细作用而被吸入多孔基材的微孔中起到闭孔和断路的作用，从而有利于保证二次电池具有高安全性能。
在一些实施例中，有机颗粒包括但不限于聚乙烯颗粒、聚丙烯颗粒、聚苯乙烯颗粒、纤维素、纤维素改性剂(例如羧基甲基纤维素)、三聚氰胺树脂颗粒、酚醛树脂颗粒、聚酯颗粒(例如聚对苯二甲酸乙二酯、聚萘二甲酸乙二酯、聚对苯二甲酸丁二酯)、有机硅树酯颗粒、聚酰亚胺颗粒、聚酰胺酰亚胺颗粒、聚芳酰胺颗粒、聚苯硫醚颗粒、聚砜颗粒、聚醚砜颗粒、聚醚醚酮颗粒、聚芳醚酮颗粒、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)中的至少一种。
在一些实施例中，可选地，有机颗粒的玻璃化转变温度可以在130℃以上。由此当二次电池内部温度达到130℃时，有机颗粒不会由玻璃态转变为粘流态，由此能够确保隔离膜不剧烈收缩。更可选地，有机颗粒包括但不限于三聚氰胺甲醛树脂颗粒、酚醛树脂颗粒、聚酯颗粒、有机硅树酯颗粒、聚酰亚胺颗粒、聚酰胺酰亚胺颗粒、聚芳酰胺颗粒、聚苯硫醚颗粒、聚砜颗粒、聚醚砜颗粒、聚醚醚酮颗粒、聚芳醚酮颗粒中的至少一种。
可选地，涂层中还可以包括纳米纤维素。纳米纤维素是指任一维尺寸在纳米级(例如100nm以内)的纤维素的总称，其既具有纤维素的特性，又具有纳米颗粒的特性。纳米纤维素可以是通过化学、物理、生物等中的一种或多种手段从自然界中的木材、棉花等提取出的高分子纳米材料，具有来源广泛、成本低、生物可降解、模量高、比表面积高等优势。
在一些实施例中，纳米纤维素可包括纤维素纳米纤维(Cellulose nanofibrils，CNF，又称为纳米纤丝纤维素或微纤化纤维素)、纤维素纳米晶须(Cellulose nanocrystals，CNC，又称为纤维素纳米晶、纳米晶体纤维素)和细菌纳米纤维素(Bacterial nanocellulose，BNC，又称为细菌纤维素或微生物纤维素)中的至少一种。
在一些实施例中，纳米纤维素可包括未改性纳米纤维素(又称羟基纳米纤维素)和改性纳米纤维素中的至少一种，可选为改性纳米纤维素。纳米纤维素可包括改性基团。改性基团可包括胺基、羧酸基、醛基、磺酸基、硼酸基和磷酸基中的至少一种，进一步可选地包括磺酸基、硼酸基和磷酸基中的至少一种。
在一些实施例中，有机-无机杂化颗粒可选自金属有机框架材料，例如MOF。
在一些实施例中，所述涂层中还可以包括其他有机化合物，例如，可以包括改善耐热 性的聚合物、分散剂、润湿剂、粘结剂等。本申请对上述其他有机化合物的种类没有特别的限制，可以选用任意公知的具有良好改善性能的材料。
在一些具体实施例中，涂层的厚度≤5μm。
在一些具体实施例中，隔离膜的制备方法包括如下步骤：(1)提供聚烯烃基膜；(2)提供涂层浆料，将填料和溶剂按照预定比例混合，配制成涂层浆料；(3)将步骤(2)的涂层浆料涂布在步骤(1)的聚烯烃基膜的至少一侧，形成涂层并干燥，得到隔离膜。其中，聚烯烃基膜包括孔结构，聚烯烃基膜的厚度≤7μm，孔结构的曲折度为7.5-9.5，且孔结构的最大孔径≤45nm。
在一些具体实施例中，隔离膜还包括粘接层。粘接层设置在涂层的至少一部分表面上。粘接层包括颗粒状的粘结剂，可选地，颗粒状的粘结剂包括丙烯酸酯类单体均聚物或共聚物、丙烯酸类单体均聚物或共聚物、含氟烯烃单体均聚物或共聚物中的至少一种。
本申请第四方面提供一种二次电池，包括本申请第三方面的隔离膜。
由于采用了本申请第一方面的聚烯烃基膜或通过本申请第二方面的制备方法获得的聚烯烃基膜，因此本申请的二次电池具有提高的能量密度和电性能。
通常情况下，二次电池可包括正极极片、负极极片、隔离膜及电解液。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。电解液在正极极片和负极极片之间起到传导离子的作用。
[负极极片]
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。
负极活性材料可采用本领域公知的用于电池的负极活性材料。作为示例，负极活性材料可包括以下材料中的至少一种：人造石墨、天然石墨、软炭、硬炭、硅基材料、锡基材料和钛酸锂等。所述硅基材料可选自单质硅、硅氧化合物、硅碳复合物、硅氮复合物以及硅合金中的至少一种。所述锡基材料可选自单质锡、锡氧化合物以及锡合金中的至少一种。但本申请并不限定于这些材料，还可以使用其他可被用作电池负极活性材料的传统材料。这些负极活性材料可以仅单独使用一种，也可以将两种以上组合使用。
负极膜层通常还可选地包括粘结剂、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、导电碳黑(Super P)、石墨烯及碳纳米纤维中一种或多种。
作为示例，粘结剂可以为丁苯橡胶(SBR)、水性丙烯酸树脂(water-based acrylic resin)、聚偏氟乙烯(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)中的一种或多种。
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热敏电阻材料等。
[正极极片]
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。
在一些实施方式中，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。
所述正极膜层通常还可选地包括粘结剂、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、导电碳黑(Super P)、石墨烯及碳纳米纤维中一种或多种。
作为示例，粘结剂可以为丁苯橡胶(SBR)、水性丙烯酸树脂(water-based acrylic resin)、聚偏氟乙烯(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)中的一种或多种。
[电解液]
电解液在正极和负极之间起到传导离子的作用。所述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)中的一种或多种。
作为示例，溶剂可选自碳酸亚乙酯(EC)、碳酸亚丙酯(PC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)、碳酸二甲酯(DMC)、碳酸二丙酯(DPC)、碳酸甲丙酯(MPC)、碳酸乙丙酯(EPC)、碳酸亚丁酯(BC)、氟代碳酸亚乙酯(FEC)、甲酸甲酯(MF)、乙酸甲酯(MA)、乙酸乙酯(EA)、乙酸丙酯(PA)、丙酸甲酯(MP)、丙酸乙酯(EP)、丙酸丙酯(PP)、丁酸甲酯(MB)、丁酸乙酯(EB)、1,4-丁内酯(GBL)、环丁砜(SF)、二甲砜(MSM)、甲乙砜(EMS)及二乙砜(ESE)中的一种或多种。
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等。
在一些实施方式中，正极极片、负极极片和隔离膜可通过卷绕工艺或叠片工艺制成电极组件。
在一些实施方式中，电池单体可包括外包装。该外包装可用于封装上述电极组件及电解质。
在一些实施方式中，电池单体的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。电池单体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，作为塑料，可列举出聚丙烯、聚对苯二甲酸丁二醇酯以及聚丁二酸丁二醇酯等。
本申请对电池单体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。例如，图4是作为一个示例的方形结构的电池单体5。
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。正极极片、负极极片和隔离膜可经卷绕工艺或叠片工艺形成电极组件52。电极组件52封装于所述容纳腔内。电解液 浸润于电极组件52中。电池单体5所含电极组件52的数量可以为一个或多个，本领域技术人员可根据具体实际需求进行选择。
在一些实施方式中，电池单体可以组装成电池模块，电池模块所含电池单体的数量可以为一个或多个，具体数量本领域技术人员可根据电池模块的应用和容量进行选择。
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，多个电池单体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电池单体5进行固定。
可选地，电池模块4还可以包括具有容纳空间的外壳，多个电池单体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为一个或多个，具体数量本领域技术人员可根据电池包的应用和容量进行选择。
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。
另外，本申请还提供一种用电装置，所述用电装置包括本申请提供的二次电池，二次电池包括电池单体、电池模块和电池包中的至少一种。所述二次电池可以用作所述用电装置的电源，也可以用作所述用电装置的能量存储单元。所述用电装置可以包括移动设备(例如手机、笔记本电脑等)、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、电动卡车等)、电气列车、船舶及卫星、储能系统等，但不限于此。
作为所述用电装置，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。该用电装置为纯电动车、混合动力电动车、或插电式混合动力电动车等。为了满足该用电装置对电源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。
作为另一个示例的装置可以是手机、平板电脑、笔记本电脑等。该装置通常要求轻薄化，可以采用电池单体作为电源。
下面结合实施例，进一步阐述本发明。应理解，这些实施例仅用于说明本发明而不用于限制本发明的范围。
制备聚乙烯多孔基膜
实施例1
首先选取重均分子量为8.0×105、Mw/Mn＝3.5的聚乙烯与白油进行共混，其中聚乙烯固含量为25wt％，之后，在挤出机中加热熔融，随后进行降温流延，冷却成型，得到2mm的流延膜片，将流延膜片进行纵向和横向拉伸，纵向拉伸倍率为8.2倍，纵向拉伸温度为110℃，横向拉伸倍率为8.7倍，横向拉伸温度为115℃。保温后得到面积增大71倍的膜片，利用二氯甲烷萃取膜片中的白油，形成孔隙，对干燥后的微孔膜再次进行横向小倍率2倍拉伸，横向小倍率拉伸温度为132℃，随之在133℃下进行热定型，热定型时间为25秒，即可得到厚度5.1μm，结晶度为78.7％的聚乙烯多孔基膜。聚烯烃基膜的孔径分布图如图1所示。
实施例2
首先选取重均分子量为7.0×105、Mw/Mn＝3.5的聚乙烯与白油进行共混，其中聚乙烯固含量为25wt％，之后，在挤出机中加热熔融，随后进行降温流延，冷却成型，得到1.5mm的流延膜片，将流延膜片进行纵向和横向拉伸，纵向拉伸倍率为9.2倍，纵向拉伸温度为110℃，横向拉伸倍率为9.7倍，横向拉伸温度为115℃。保温后得到面积增大71倍的膜片，利用二氯甲烷萃取膜片中的白油，形成孔隙，对干燥后的微孔膜再次进行横向小倍率2倍拉伸，横向小倍率拉伸温度为132℃，随之在133℃下进行热定型，热定型时间为25秒， 即可得到厚度4.0μm，结晶度为79.6％的聚乙烯多孔基膜。
实施例3
首先选取重均分子量为8.0×105、Mw/Mn＝3.0的聚乙烯与白油进行共混，其中聚乙烯固含量为25wt％，之后，在挤出机中加热熔融，随后进行降温流延，冷却成型，得到2.1mm的流延膜片，将流延膜片进行纵向和横向拉伸，纵向拉伸倍率为8.2倍，纵向拉伸温度为110℃，横向拉伸倍率为8.7倍，横向拉伸温度为115℃。保温后得到面积增大71倍的膜片，利用二氯甲烷萃取膜片中的白油，形成孔隙，对干燥后的微孔膜再次进行横向小倍率2倍拉伸，横向小倍率拉伸温度为132℃，随之在133℃下进行热定型，热定型时间为25秒，即可得到厚度6.2μm，结晶度为79.3％的聚乙烯多孔基膜。
实施例4-14
按照实施例1描述的方法进行，不同之处在于，下表1所列参数与实施例1不同。
对比例1
首先选取重均分子量为4.0×105、Mw/Mn＝3.5聚乙烯与白油进行共混，其中聚乙烯固含量为25wt％，之后，在挤出机中加热熔融，随后进行降温流延，冷却成型，得到2mm的流延膜片，将流延膜片进行纵向和横向拉伸，纵向拉伸倍率为8.2倍，纵向拉伸温度为110℃，横向拉伸倍率为8.7倍，横向拉伸温度为115℃。保温后得到面积增大71倍的的膜片，利用二氯甲烷萃取膜片中的白油，形成孔隙，对干燥后的微孔膜再次进行横向小倍率2倍拉伸，横向小倍率拉伸温度为132℃，随之在133℃下进行热定型，热定型时间为25秒，即可得到厚度5.2μm，结晶度为78.7％的聚乙烯多孔基膜。采用实施例1的方法测试聚烯烃基膜的孔径分布，所得孔径分布图如图2所示。
对比例2
首先选取重均分子量为8.0×105、Mw/Mn＝4.0的聚乙烯与白油进行共混，其中聚乙烯固含量为25wt％，之后，在挤出机中加热熔融，随后进行降温流延，冷却成型，得到2mm的流延膜片，将流延膜片进行纵向和横向拉伸，纵向拉伸倍率为8.2倍，纵向拉伸温度为110℃，横向拉伸倍率为8.7倍，横向拉伸温度为115℃。保温后得到面积增大71倍的的膜片，利用二氯甲烷萃取膜片中的白油，形成孔隙，对干燥后的微孔膜再次进行横向小倍率2倍拉伸，横向小倍率拉伸温度为132℃，随之在133℃下进行热定型，热定型时间为25秒，即可得到厚度5.2μm，结晶度为78.7％的聚乙烯多孔基膜。采用实施例1的方法测试聚烯烃基膜的孔径分布，所得孔径分布图如图3所示。
对比例3
首先选取重均分子量为8.0×105、Mw/Mn＝3.5的聚乙烯与白油进行共混，其中聚乙烯固含量为25wt％，之后，在挤出机中加热熔融，随后进行降温流延，冷却成型，得到2mm的流延膜片，将流延膜片进行纵向和横向拉伸，纵向拉伸倍率为5.0倍，纵向拉伸温度为110℃，横向拉伸倍率为5.0倍，横向拉伸温度为115℃。保温后得到面积增大25倍的的膜片，利用二氯甲烷萃取膜片中的白油，形成孔隙，对干燥后的微孔膜再次进行横向小倍率2倍拉伸，横向小倍率拉伸温度为132℃，随之在133℃下进行热定型，热定型时间为25秒，即可得到厚度5.2μm，结晶度为78.7％的聚乙烯多孔基膜。
对比例4
首先选取重均分子量为8.0×105、Mw/Mn＝3.5的聚乙烯与白油进行共混，其中聚乙烯固含量为10wt％，之后，在挤出机中加热熔融，随后进行降温流延，冷却成型，得到2mm的流延膜片，将流延膜片进行纵向和横向拉伸，纵向拉伸倍率为8.2倍，纵向拉伸温度为110℃，横向拉伸倍率为8.7倍，横向拉伸温度为115℃。保温后得到面积增大71倍的膜片，利用二氯甲烷萃取膜片中的白油，形成孔隙，对干燥后的微孔膜再次进行横向小倍率2倍拉伸，横向小倍率拉伸温度为132℃，随之在133℃下进行热定型，热定型时间为25秒，即可得到厚度5.2μm，结晶度为78.7％的聚乙烯多孔基膜。
对比例5-6
按照实施例1描述的方法进行，不同之处在于，下表1所列参数与实施例1不同。
表1
聚乙烯基膜相关参数测试
1、聚烯烃基膜厚度的测试：清洁测量平台及测量头。需保证测量平台及测量头清洁。使用万分尺进行测试。当数据保持稳定不变时，将数据记录到表2-4中。
2、聚烯烃基膜的孔结构的平均孔径和最大孔径测试：PMI公司的毛细管流动孔隙仪或压汞仪等设备直接测量。①用液体将待测基膜孔道完全润湿填满，因毛细现象使得孔内形成正压②将基膜放入密闭槽中，用气体压力加压将液体由毛细孔道内挤出③根据在单一孔道中的液体完全由毛细孔道内挤出时所施压力与孔道直径的相对关系，依照Laplace方程可得聚烯烃基膜的孔结构的平均孔径及最大孔径。测试结果如下表2-4所示。
3、透气度的测试：裁切基膜样品，样品尺寸必须大于40*40mm。将样品放置在样品测试平台，样品必须覆盖整个样品区，扭紧旋钮，选择测量区域保证膜片能覆盖住测试平台。先按RESET键(此时屏幕会显示“TIMER SEEKING STARTING MARK”)，然后放开滑筒开始测试。测量完成后，缓慢旋松旋塞至滑筒下降到最低位。取出样品，将滑筒缓慢提起，准备下次测量。测试结果如下表2-4所示。
4、拉伸强度的测试：冲切样条：将基膜冲切成15mm宽，长度大于40mm的基膜片材，随后将拉力机夹具设置成起始夹具间距40mm、速度50mm/min，将待测样条置于夹具 中间，上下端分别用夹具夹紧，记录拉伸曲线，每组5个平行样。测试结果如下表2-4所示。
5、延伸率的测试：将基膜冲切成15mm宽，长度大于40mm的基膜片材，随后将拉力机夹具设置成起始夹具间距40mm、速度50mm/min，将待测样条置于夹具中间，记录拉伸后基膜长度，延伸率＝拉伸后的长度/40mm*100％。测试结果如下表2-4所示。
6、热收缩率的测试：将基膜冲切成100mm*50mm的样本。烘烤前用记号笔标识编号并在二次元下进行测量，设定烘烤温度和时间，烘箱达到设定温度后连同钢盘将基膜入烘箱烘烤，到规定烘烤时间后取出并常温静置10min。分别量测相同编号基膜烘烤后的横向&纵向方向尺寸。若样品边缘收缩不均匀，则以收缩最大位置为准。测试结果如下表2-4所示。
7、穿刺强度的测试：使用高铁拉力机将1mm的原型针头以50mm/min速度穿过基膜，所获得的最大力为穿刺强度，每组5个平行样，所获得的平均值即为穿刺强度。测试结果如下表2-4所示。
8、孔隙率的测试：将截取好的基膜样品用100mm*50mm刀模冲切制备矩形样品。测量矩形样品的长度L和宽度W。之后，利用0.1um万分尺测量其厚度，共量测5点厚度值，边缘4个点，中间1个点，取5点厚度的平均值为最终厚度，记为T。将称好重量的矩形样品用精度0.0001g的分析天平进行称重，记为M1。用测量得出的长度L、宽度W、厚度T和基膜的材料密度ρ，计算出基膜的理论重量，记为M2：M2＝L*W*T*ρ。孔隙率＝(1-M1/M2)*100％。测试结果如下表2-4所示。
9.面密度的测试：将截取好的基膜样品用100mm*50mm刀模冲切制备矩形样品。测量矩形样品的长度L和宽度W，称取该片状基膜重量记为M，则面密度＝M/(L*W)。测试结果如下表2-4所示。
10.孔结构的曲折度的计算
按照如下公式计算孔结构的曲折度
其中，τ表示孔结构的曲折度，tgur表示基膜透气度(由上述测试方法得到)，ε表示基膜孔隙率(由上述测试方法得到)，d表示孔结构的平均孔径(由上述测试方法得到)，单位为cm，L表示基膜厚度(由上述测试方法得到)，单位为cm。所得结果如下表2-4所示。
表2：聚乙烯多孔基膜的相关参数测试结果

表3：聚乙烯多孔基膜的相关参数测试结果
表4：聚乙烯多孔基膜的相关参数测试结果
采用实施例1-23和对比例1-6的基膜，按照以下通用制备方法制备锂离子电池。
锂离子电池的制备
(1)正极极片制备
将正极活性材料LFP、导电剂Super P、粘结剂聚偏氟乙烯(PVDF)按照质量比正极活性材料:Super P:PVDF＝8:1:1进行混合，加入至溶剂N-甲基吡咯烷酮(NMP)中， 在真空搅拌机作用下搅拌均匀，获得正极浆料，其中正极浆料中固体含量为50wt％；将正极浆料均匀涂覆于正极集流体铝箔上并在85℃下烘干，然后经过冷压、切边、裁片、分条，最后继续在85℃的真空条件下烘干4h，得到正极极片。
(2)负极极片制备
将负极活性材料石墨、导电剂Super P、增稠剂羧甲基纤维素钠(CMC)、粘结剂丁苯橡胶乳液(SBR)按照质量比石墨:Super P:CMC:SBR＝80:15:3:2进行混合，加入至溶剂去离子水中，在真空搅拌机作用下搅拌均匀，获得负极浆料，其中负极浆料中固体含量为30wt％；将负极浆料均匀涂覆在负极集流体铜箔上并在85℃下烘干，然后经过冷压、切边、裁片、分条，最后继续在120℃的真空条件下烘干12h，得到负极极片。
(3)隔离膜的制备
提供实施例1的基膜；将无机颗粒三氧化二铝(Al2O3)、有机颗粒偏二氟乙烯-六氟丙烯共聚物(数均分子量为55万)、粘结剂水溶液型聚丙烯酸按照质量79.1:20:0.9在适量的溶剂去离子水中混合均匀得到固含量为38％(按重量计)的涂层浆料；将涂层浆料用涂布机涂布在基膜的2个表面上，通过干燥、分切等工序，得到隔离膜。其中，涂布机的凹版辊的线数为125LPI，涂布的速度为50m/min，涂布的线速比为1.2，干燥温度为50℃±5℃，干燥时间为30s。
(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)将步骤(1)的正极极片、步骤(3)的隔离膜、步骤(2)的负极极片按顺序叠好，使隔离膜处于正、负极极片之间起到隔离的作用，然后卷绕成方形的裸电芯，焊接极耳，将裸电芯装入包装箔铝塑膜中，然后在80℃下烘烤除水后，注入电解液并封口，之后经过静置、热冷压、化成(0.02C恒流充电到3.3V，再以0.1C恒流充电到3.6V)、整形、容量测试等工序，获得成品软包装锂离子电池，其厚度为4.0mm、宽度为60mm、长度为140mm。
实施例2-23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基膜。
电池性能测试
1、电池直流内阻测试
在一定温度下，对锂离子电池进行短时间(30s)的大电流充/放电，通过计算充放电前后的压差与电流的比值，即可得到直流内阻。测试条件和测试结果如下表5中所示。
2、电池内阻测试
即交流电阻，交流内阻设备：Itech公司IT5100系列电池内阻测试仪，测试方法：对测试电芯加固定频率1KHz，固定电流50mA,对电压采样，经整流仪器可计算出阻值测试结果如下表5中所示。测试结果如下表5中所示。
3、裸电芯的自放电率测试
电芯老化冷却后，测试电压为OCV1，放置在常温常湿的环境中，静置48h后再测一下电压，记为OCVB，则自放电率＝(OCV1-OCVB)/48h，测试结果如下表5中所示。
4、裸电芯的短路测试通过率
在卷绕后，裸电芯将进行一项短路率的测试，条件为100v，80℃，10s，5MPa。测试结果如下表5中所示。
表5


注：10％SOC是指10％的荷电状态。
通过表5可以看出，本申请的聚乙烯多孔基膜的孔结构的曲折度较大，基膜具有均匀的孔结构，从而提升了基膜一致性，降低了基膜性能偏差，并且还有效保证了基膜的透气性。将本申请的聚烯烃基膜作为隔离膜用于电池时，能够显著提高电池的电性能，包括降低电池的直流内阻、电池内阻、自放电率和短路率。
通过比较实施例1和对比例1可以看出，对比例1中使用的聚乙烯的重均分子量不在本申请范围内，对比例1制备的聚乙烯多孔基膜的孔结构的曲折度明显偏小，对比例1所对应的电池的直流内阻、电池内阻、自放电率和短路率明显偏大。
通过比较实施例1和对比例2可以看出，对比例2中使用的聚乙烯的多分散指数Mw/Mn不在本申请范围内，对比例2制备的聚乙烯多孔基膜的孔结构的曲折度明显偏小，对比例2所对应的电池的直流内阻、电池内阻、自放电率和短路率明显偏大。
通过比较实施例1、对比例3和对比例6可以看出，对比例3和6的纵向拉伸倍率和横向拉伸倍率均不在本申请范围内，对比例3和6制备的聚乙烯多孔基膜的孔结构的曲折度明显偏小，对比例3和6所对应的电池的直流内阻、电池内阻、自放电率和短路率均明显偏大。
通过比较实施例1和对比例4-5可以看出，对比例4-5中聚乙烯的固含量均不在本申请范围内，对比例4-5制备的聚乙烯多孔基膜的孔结构的曲折度明显偏小，对比例4-5所对应的电池的直流内阻、电池内阻、自放电率和短路率均明显偏大。
以上所述，仅为本发明较佳的具体实施方式，但本发明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发明揭露的技术范围内，可轻易想到的变化或替换，都应涵盖在本发明的保护范围之内。因此，本发明的保护范围应以所述权利要求的保护范围为准。

Claims (21)

  1. 一种聚烯烃基膜，其特征在于，所述聚烯烃基膜包括孔结构，所述聚烯烃基膜的厚度≤7μm，所述孔结构的曲折度为7-10。
  2. 根据权利要求1所述的聚烯烃基膜，其特征在于，所述孔结构的曲折度为7.5-9.5；可选地，所述孔结构的曲折度为7.5-9。
  3. 根据权利要求1或2所述的聚烯烃基膜，其特征在于，所述孔结构的最大孔径≤45nm；可选地，所述孔结构的最大孔径≤40nm；进一步可选地，所述孔结构的最大孔径为20nm-40nm。
  4. 根据权利要求1～3中任一项所述的聚烯烃基膜，其特征在于，所述聚烯烃基膜的厚度为2μm-6.2μm；可选地，所述聚烯烃基膜的厚度为4μm-6.2μm。
  5. 根据权利要求1～4中任一项所述的聚烯烃基膜，其特征在于，所述聚烯烃基膜包括重均分子量Mw为50万以上的聚烯烃；可选地，所述聚烯烃基膜包括重均分子量Mw为50万～150万的聚烯烃。
  6. 根据权利要求5所述的聚烯烃基膜，其特征在于，所述聚烯烃的多分散指数Mw/Mn≤3.5；可选地，所述聚烯烃的多分散指数Mw/Mn为1～3.5。
  7. 根据权利要求5所述的聚烯烃基膜，其特征在于，所述聚烯烃为聚乙烯和聚丙烯中的一种或两种。
  8. 根据权利要求1～7中任一项所述的聚烯烃基膜，其特征在于，所述聚烯烃基膜的透气度≤180s/100cc。
  9. 根据权利要求1～8中任一项所述的聚烯烃基膜，其特征在于，所述聚烯烃基膜的纵向延伸率≥60％，可选地，所述聚烯烃基膜的纵向延伸率≥100％；进一步可选地，所述聚烯烃基膜的纵向延伸率为100％～120％；
    所述聚烯烃基膜的横向延伸率≥100％；可选地，所述聚烯烃基膜的横向延伸率≥110％；进一步可选地，所述聚烯烃基膜的横向延伸率为110％～160％。
  10. 根据权利要求1～9中任一项所述的聚烯烃基膜，其特征在于，所述聚烯烃基膜在115℃下的纵向热收缩率≤4％，横向热收缩率≤4％。
  11. 根据权利要求1～10中任一项所述的聚烯烃基膜，其特征在于，所述聚烯烃基膜符合下述(1)-(4)中的至少一个条件：
    (1)所述聚烯烃基膜的穿刺强度≥270gf；
    (2)所述聚烯烃基膜的纵向拉伸强度≥2000kgf/cm2，横向拉伸强度≥2000kgf/cm2；
    (3)所述聚烯烃基膜的孔隙率为25％-40％；
    (4)所述聚烯烃基膜的面密度为2-5g/m2。
  12. 一种聚烯烃基膜的制备方法，其特征在于，包括：
    将聚烯烃和造孔剂混合，将所得混合物制成膜片；
    对所述膜片进行双轴拉伸；
    去除双轴拉伸后的膜片中的所述造孔剂，形成孔隙；以及
    对形成孔隙后的膜片进行拉伸定型和热定型，得到所述聚烯烃基膜；
    所述聚烯烃基膜包括孔结构，所述聚烯烃基膜的厚度≤7μm，所述孔结构的曲折度为7-10。
  13. 根据权利要求12所述的制备方法，其特征在于，所述聚烯烃的重均分子量Mw为50万以上；可选地，所述聚烯烃基膜包括重均分子量Mw为50万～150万的聚烯烃。
  14. 根据权利要求12或13所述的制备方法，其特征在于，所述聚烯烃在所述混合物中的占比为20wt％-30wt％。
  15. 根据权利要求12～14中任一项所述的制备方法，其特征在于，所述双轴拉伸包括纵向拉伸和横向拉伸，其中纵向拉伸倍率为5-15倍，横向拉伸倍率为5-15倍，且纵向拉 伸倍率和横向拉伸倍率不同时为5；可选地，纵向拉伸倍率为6-15倍，横向拉伸倍率为6-15倍。
  16. 一种隔离膜，其特征在于，包括权利要求1-11中任一项所述的聚烯烃基膜或通过权利要求12-15中任一项所述的制备方法获得的聚烯烃基膜。
  17. 根据权利要求16所述的隔离膜，其特征在于，所述隔离膜还包括设置在所述聚烯烃基膜的至少一个表面的涂层。
  18. 根据权利要求17所述的隔离膜，其特征在于，所述涂层包括填料，所述填料包括选自无机颗粒、有机颗粒和有机-无机杂化颗粒中的至少一种。
  19. 根据权利要求17或18所述的隔离膜，其特征在于，所述隔离膜还包括粘接层，所述粘接层设置在所述涂层的至少一部分表面上，所述粘接层包括颗粒状的粘结剂，可选地，所述颗粒状的粘结剂包括丙烯酸酯类单体均聚物或共聚物、丙烯酸类单体均聚物或共聚物和含氟烯烃单体均聚物或共聚物中的至少一种。
  20. 一种二次电池，其特征在于，包括权利要求16～19中任一项所述的隔离膜。
  21. 一种用电装置，其特征在于，包括权利要求20所述的二次电池。
PCT/CN2023/088836 2022-10-28 2023-04-18 聚烯烃基膜及其制备方法、隔离膜、二次电池及用电装置 WO2024087536A1 (zh)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2011192528A (ja) * 2010-03-15 2011-09-29 Teijin Ltd ポリオレフィン微多孔膜、非水系二次電池用セパレータ及び非水系二次電池
CN111697189A (zh) * 2020-06-28 2020-09-22 佛山市金辉高科光电材料股份有限公司 聚烯烃微孔基膜及其制备方法、隔膜和电池
CN113631643A (zh) * 2019-03-29 2021-11-09 东丽株式会社 聚烯烃微多孔膜、电池用隔板及二次电池
CN113921987A (zh) * 2021-10-20 2022-01-11 湖南农业大学 一种高韧性隔离膜、制备方法、电化学装置、终端
WO2022099905A1 (zh) * 2020-11-16 2022-05-19 青岛蓝科途膜材料有限公司 具有耐高温特性的锂离子电池隔膜、其制备方法及由其制得的锂离子电池

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2011192528A (ja) * 2010-03-15 2011-09-29 Teijin Ltd ポリオレフィン微多孔膜、非水系二次電池用セパレータ及び非水系二次電池
CN113631643A (zh) * 2019-03-29 2021-11-09 东丽株式会社 聚烯烃微多孔膜、电池用隔板及二次电池
CN111697189A (zh) * 2020-06-28 2020-09-22 佛山市金辉高科光电材料股份有限公司 聚烯烃微孔基膜及其制备方法、隔膜和电池
WO2022099905A1 (zh) * 2020-11-16 2022-05-19 青岛蓝科途膜材料有限公司 具有耐高温特性的锂离子电池隔膜、其制备方法及由其制得的锂离子电池
CN113921987A (zh) * 2021-10-20 2022-01-11 湖南农业大学 一种高韧性隔离膜、制备方法、电化学装置、终端

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