Polyolefin-based film and its manufacturing method, separator, secondary battery and power consumption device

Abstract

The present application relates to a polyolefin base film, which has a uniform pore structure by optimizing the tortuosity of the pore structure in the polyolefin base film, thereby improving the conformity of the base film, reducing the performance deviation of the base film, and effectively guaranteeing the air permeability of the base film. At the same time, the thickness of the polyolefin base film of the present application is extremely thin, and the energy density of the battery core can be increased by about 0.7% for every 1 μm reduction in thickness, so that the energy density of the battery core can be improved by controlling the thickness to 7 μm or less. When the polyolefin base film is used as a separator in a battery, it can improve the electrical performance of the battery, including reducing the internal resistance, DC internal resistance, self-discharge rate, short circuit rate, etc. of the battery. The present application further relates to a method for producing the polyolefin base film, a separator, a secondary battery, and a power consumption device.

Description

Cross-reference to Related Applications

[0001] This application claims the priority of an international patent application with application number PCT / CN2022 / 128110, filed on October 28, 2022, the entire content of which is incorporated herein by reference.

Technical Field

[0002] This application belongs to the field of battery technology, and specifically relates to a polyolefin-based film and its manufacturing method, a separator, a secondary battery, and an electric power consumption device.

Background Art

[0003] Secondary batteries are currently widely used in fields such as pure electric vehicles, hybrid electric vehicles, and smart grids. In secondary batteries, a separator is used to separate the positive and negative electrodes to prevent the positive and negative electrodes from directly contacting and causing a short circuit. As the demand for people's use of portable products increases day by day, ultra-thin separators have begun to be widely applied. However, the polyolefin-based film for manufacturing conventional ultra-thin separators cannot achieve both low thickness and uniformity of pore structure, and the performance deviation of the base film is relatively large.

[0004] Therefore, the development of a polyolefin-based film that can achieve both low thickness and uniformity of pore structure is strongly desired.

Summary of the Invention

[0005] In view of the problems existing in the background art, this application provides a polyolefin-based film that can achieve both low thickness and uniformity of pore structure.

[0006] The polyolefin-based film according to the first aspect of this application includes a pore structure. The polyolefin-based film includes a pore structure, the thickness of the polyolefin-based film ≤ 7 μm, and the tortuosity of the pore structure is 7 - 10.

[0007] In the invention of this application, the degree of curvature of the pore structure is optimized to give the polyolefin base film a uniform pore structure, thereby improving the consistency of the base film, reducing performance deviations of the base film, enabling faster ion transport, and effectively ensuring the air permeability of the base film. At the same time, the thickness of the polyolefin base film of this application is extremely thin, and for every 1 μm reduction in thickness, the energy density of the battery core can be increased by approximately 0.7%, and therefore, by controlling the thickness to 7 μm or less, the energy density of the battery core can be improved. When this polyolefin base film is used as a separator in a battery, the electrical performance of the battery can be improved, including a reduction in the battery's internal resistance, DC internal resistance, self-discharge rate, and short-circuit rate.

[0008] In some embodiments, according to a first embodiment, a first example of the first embodiment is provided, wherein the degree of curvature of the pore structure is 7.5 to 9.5, and selectively, the degree of curvature of the pore structure is 7.5 to 9.

[0009] In some embodiments, according to a first embodiment, a first example of the first embodiment is provided, wherein the maximum pore diameter of the pore structure is ≤ 45 nm, selectively, the maximum pore diameter of the pore structure is ≤ 40 nm, and more selectively, the maximum pore diameter of the pore structure is 20 nm to 40 nm.

[0010] In some embodiments, according to the first embodiment, a first example of the first embodiment is provided, wherein the thickness of the polyolefin-based film is 2 μm to 6.2 μm, and selectively, the thickness of the polyolefin-based film is 4 μm to 6.2 μm.

[0011] This design is advantageous in further improving the consistency of the polyolefin base film, reducing performance deviations of the base film, improving the air permeability of the base film, and increasing the energy density of the battery core by optimizing the thickness of the polyolefin base film, the degree of flexibility of the pore structure, and the maximum pore diameter of the pore structure.

[0012] In some embodiments, according to the first embodiment, a second example of the first embodiment is provided, wherein the polyolefin-based film comprises a polyolefin having a weight-average molecular weight Mw of 500,000 or more, and selectively, the polyolefin-based film comprises a polyolefin having a weight-average molecular weight Mw of 500,000 to 1,500,000.

[0013] This design is advantageous in improving the uniformity of pore formation by using polyolefins with a weight-average molecular weight (Mw) of 500,000 or more as raw materials.

[0014] In some embodiments, according to the first embodiment, a third example of the first embodiment is provided, where the polydispersity index Mw / Mn of the polyolefin is ≤ 3.5, and selectively, the polydispersity index Mw / Mn of the polyolefin is 1 to 3.5.

[0015] This design is advantageous for optimizing the polydispersity index of polyolefins, reducing the distribution width of polyolefin molecular weights, and improving molecular weight consistency.

[0016] In some embodiments, according to the first aspect, a fourth example of the first aspect is provided, where the polyolefin is one or both of polyethylene and polypropylene.

[0017] This design offers advantages such as optimizing the type of polyolefin, further improving the consistency of the polyolefin base film, increasing the strength and elongation of the base film, and reducing the thermal shrinkage of the base film.

[0018] In some embodiments, according to the first embodiment, a fifth example of the first embodiment is provided, in which the air permeability of the polyolefin-based film is ≤ 180 s / 100 cc.

[0019] This design is advantageous for optimizing the air permeability of the polyolefin-based film and improving the air permeability of the separator.

[0020] In some embodiments, according to the first embodiment, a sixth example of the first embodiment is provided, wherein the longitudinal elongation of the polyolefin-based film is ≥60%, selectively, the longitudinal elongation of the polyolefin-based film is ≥100%, and more selectively, the longitudinal elongation of the polyolefin-based film is 100% to 120%. The transverse elongation of the polyolefin-based film is ≥100%, selectively, the transverse elongation of the polyolefin-based film is ≥110%, and more selectively, the transverse elongation of the polyolefin-based film is 110% to 160%.

[0021] In this design, increasing the elongation ratio can effectively improve the toughness of the separator. If metal particles (which may originate from the operating environment, positive and negative electrode plates, or separator, etc.) are generated during the winding process, the separator can effectively coat the particles, preventing damage to the battery core and improving the manufacturability of the battery core.

[0022] In some embodiments, according to the first embodiment, a seventh example of the first embodiment is provided, in which the polyolefin-based film has a longitudinal heat shrinkage rate of ≤4% and a transverse heat shrinkage rate of ≤4% at 115°C.

[0023] This design optimizes the thermal shrinkage rate of the polyolefin-based film, effectively improving the thermal stability of the separator and enhancing the safety performance of the battery core.

[0024] In some embodiments, according to the first embodiment, an eighth example of the first embodiment is provided, wherein the polyolefin-based film is subject to the following conditions (1)-(4): (1) The condition that the puncture strength of the polyolefin-based film is ≥ 270 gf, (2) Longitudinal tensile strength of polyolefin-based film ≥ 2000 kgf / cm 2 Therefore, the lateral tensile strength is ≥ 2000 kgf / cm². 2 The conditions are, (3) The void ratio of the polyolefin-based film is 25% to 40%. (4) The surface density of the polyolefin-based film is 2-5 g / m². 2 It satisfies at least one of the following conditions.

[0025] This design is advantageous in improving the resistance of the separator by optimizing the strength of the polyethylene porous base film, and effectively ensuring the yield of the separator manufacturing process. Optimizing the pore structure of the polyethylene porous base film is advantageous in ensuring pore size consistency, and thus in achieving effective ion conduction.

[0026] A second aspect of this application provides a method for producing a polyolefin-based film, the method being: Mixing polyolefin and a pore-forming agent, and manufacturing the resulting mixture into a film sheet, The aforementioned film sheet is subjected to biaxial tension, The pore-forming agent is removed from the film sheet after biaxial tensioning, and voids are formed. The process includes tensile and thermal fixing of the film sheet after forming voids to obtain the polyolefin-based film, The polyolefin-based film contains a pore structure, has a thickness of ≤7 μm, and the degree of flexibility of the pore structure is 7 to 10.

[0027] In the invention of this application, an ultrathin polyolefin-based film can be manufactured using a polyolefin having an ultra-high weight-average molecular weight as a raw material, and simultaneously combined with biaxial tensile strength, thereby having a pore structure flexibility of 7.5 to 9.5 and a maximum pore diameter of ≤ 45 nm.

[0028] In some embodiments, according to a second embodiment, a first example of the second embodiment is provided, wherein the weight-average molecular weight Mw of the polyolefin is 500,000 or more, and selectively, the polyolefin-based film comprises a polyolefin having a weight-average molecular weight Mw of 500,000 to 1,500,000.

[0029] In some embodiments, according to a second embodiment, a first example of the second embodiment is provided, in which the occupancy rate in the polyolefin mixture is 20 wt% to 30 wt%.

[0030] This design is advantageous in improving the uniformity of film thickness, the consistency of pore sizes in the base film, and meeting the high elongation requirements of the base film by optimizing the solids content of the polyolefin. If the solids content of the polyolefin is too high (>30 wt%), the pressure curve of the extruder will fluctuate greatly, resulting in poor uniformity of film thickness and poor consistency of pore sizes in the base film. If the solids content of the polyolefin is too low (<20 wt%), the content of pore-forming agents, such as white oil, will be too high, limiting the tensile strength and preventing the achievement of the high elongation requirements. By optimizing the solids content of the polyolefin, the uniformity of pore formation is improved while simultaneously achieving the high elongation requirements.

[0031] In some embodiments, according to a second aspect, a second example of the second aspect is provided, where biaxial tension includes longitudinal tension and transverse tension. Here, the longitudinal tension ratio is 5 to 15 times, and the transverse tension ratio is 5 to 15 times, and the longitudinal and transverse tension ratios are not simultaneously 5 times, but selectively, the longitudinal tension ratio is 6 to 15 times, and the transverse tension ratio is 6 to 15 times.

[0032] This design allows for further reduction of the thickness of the polyolefin-based film and improvement of pore formation uniformity by optimizing the longitudinal and transverse tensile strengths.

[0033] A third aspect of this application provides a separator comprising a polyolefin-based film obtained by the first aspect of this application or by the manufacturing method of the second aspect of this application.

[0034] In the technical invention of the embodiment of this application, a polyolefin-based film obtained by the manufacturing method of the first embodiment of this application or the second embodiment of this application is used, and therefore the separator of this application has advantages such as being ultra-thin and having a uniform pore structure.

[0035] In some embodiments, according to a third aspect, a first example of the third aspect is provided, wherein the separator further includes a coating applied to at least one surface of the polyolefin-based film.

[0036] By applying a coating to the surface of a polyolefin-based film, the electrical and safety performance of the battery core can be improved.

[0037] In some embodiments, according to a third aspect, a first example of the third aspect is provided, in which the coating includes a filler. The filler includes at least one selected from inorganic particles, organic particles, and organic-inorganic hybrid particles.

[0038] By selecting a filler with good thermal stability and resistance to decomposition, the heat resistance of the separator can be further improved.

[0039] In some embodiments, according to a third aspect, a second example of the third aspect is provided, wherein the separator further includes an adhesive layer. The adhesive layer is provided on at least a portion of the surface of the coating. The adhesive layer includes particulate adhesive, which optionally includes at least one of acrylate monomer homopolymers or copolymers, acrylic monomer homopolymers or copolymers, and fluorine-containing olefin monomer homopolymers or copolymers.

[0040] The adhesive layer not only prevents the coating from peeling off and improves the safety performance of the secondary battery, but it can also improve the interface between the separator and the electrode, thereby improving the cycle performance of the secondary battery.

[0041] A fourth aspect of this application provides a secondary battery including the separator of the third aspect of this application.

[0042] In the technical invention of the embodiment of this application, a polyolefin-based film obtained by the manufacturing method of the first embodiment of this application or the second embodiment of this application is used, and therefore the secondary battery of this application has improved energy density and electrical performance.

[0043] A fifth aspect of this application provides a power consumption device, which includes a secondary battery according to the fourth aspect of this application.

[0044] In the technical invention of the embodiment of this application, a polyolefin-based film obtained by the manufacturing method of the first embodiment of this application or the second embodiment of this application is used, and therefore the power consumption device of this application has improved energy density and electrical performance.

[0045] The above description is merely an outline of the proposed technology of this application. To better understand the technical means of this application, it can be implemented according to the specifications. Furthermore, to make the above and other objectives, features, and advantages of this application clearer and easier to understand, the following will describe specific embodiments of this application in particular. [Brief explanation of the drawing]

[0046] [Figure 1] This is a pore size distribution diagram of the polyolefin-based film manufactured in Example 1 of this application. [Figure 2] This is a pore size distribution diagram of the polyolefin-based film produced in Comparative Example 1. [Figure 3] This is a pore size distribution diagram of the polyolefin-based film produced in Comparative Example 2. [Figure 4] This is a schematic diagram of a battery cell according to one embodiment of the present application. [Figure 5] Figure 4 is an exploded view of a battery cell according to one embodiment of this application. [Figure 6]This is a schematic diagram of a battery module according to one embodiment of the present application. [Figure 7] This is a schematic diagram of a battery pack according to one embodiment of the present application. [Figure 8] Figure 7 is an exploded view of a battery pack according to one embodiment of this application. [Figure 9] This is a schematic diagram of a power consumption device powered by a secondary battery according to one embodiment of the present application. [Modes for carrying out the invention]

[0047] The exemplary embodiments of this disclosure will be described in further detail below with reference to the drawings. While the drawings illustrate exemplary embodiments of this disclosure, it should be understood that this disclosure may be implemented in various forms, not limited to the embodiments described herein. Rather, these embodiments are provided to allow for a more complete understanding of this disclosure and to fully convey the scope of this disclosure to those skilled in the art.

[0048] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art relating to the present application, and the terms used herein are solely for the purpose of describing specific embodiments and are not intended to limit this application. The terms “including” and “having” and any variations thereof in the description of the specification, claims and drawings of this application are intended to cover non-exclusive inclusion.

[0049] For convenience, only a limited number of numerical ranges are explicitly disclosed in this specification. However, any lower and upper limit can be combined to form an unspecified range, and any lower limit and other lower limits can be combined to form an unspecified range, and similarly, any upper limit and other upper limits can be combined to form an unspecified range. Notwithstanding the foregoing, each point or single number between the endpoints of a range is included in this range. Therefore, each point or single number can be combined with any other point or single number as its own lower or upper limit, or combined with other lower or upper limits, to form an unspecified range.

[0050] In the descriptions herein, unless otherwise specified, "greater than or equal to" and "less than or equal to" include the number, and "plural" in "one or more" means two or more (including two).

[0051] Rechargeable batteries are currently widely used in fields such as pure electric vehicles, hybrid electric vehicles, and smart grids. In rechargeable batteries, separators are used to separate the positive and negative electrodes to prevent short circuits caused by direct contact between the electrodes. As people's demand for portable products increases day by day, ultra-thin separators are beginning to be widely applied. However, conventional polyolefin-based films used to manufacture ultra-thin separators cannot achieve both low thickness and uniformity of the pore structure, resulting in relatively large performance deviations of the base film. Therefore, there is a strong desire for the development of polyolefin-based films that can achieve both low thickness and uniformity of the pore structure.

[0052] Through diligent research, the inventors have designed a polyolefin-based film and optimized the flexibility of the pore structure and the maximum pore diameter of the pore structure in the polyolefin-based film. This results in a uniform pore structure in the polyolefin-based film, thereby improving the consistency of the base film, reducing performance deviations, and effectively ensuring the air permeability of the base film. Simultaneously, the thickness of the polyolefin-based film of this application is extremely thin, and for every 1 μm reduction in thickness, the energy density of the battery core can be increased by approximately 0.7%. Therefore, by controlling the thickness to 7 μm or less, the energy density of the battery core can be improved. When this polyolefin-based film is used as a separator in a battery, it is possible to improve the electrical performance of the battery, including reducing the internal resistance, DC internal resistance, self-discharge rate, and short-circuit rate of the battery.

[0053] The technical solutions described in the embodiments of this application are applicable to polyolefin-based films, and further to manufacturing processes for polyolefin-based films, separators using polyolefin-based films, secondary batteries using separators, and power consumption devices using secondary batteries.

[0054] According to some embodiments of the present application in a first aspect, the present application provides a polyolefin-based film. The polyolefin-based film includes a pore structure, the thickness of the polyolefin-based film is ≤ 7 μm, and the degree of flexibility of the pore structure is 7 to 10.

[0055] In the invention of this application, the polyolefin-based film combines ultra-thinness and a uniform pore structure, effectively improving the overall performance of the base film. When this base film is wound onto an NCM811 system, the internal resistance, DC internal resistance, and self-discharge rate of the battery can be effectively reduced, and the mass production short-circuit yield level is equivalent to that of a typical 7 μm thick polyolefin-based film.

[0056] In this application, the degree of flexibility of the pore structure of the polyolefin-based film is determined jointly by the air permeability of the base film, the thickness of the base film, the porosity of the base film, and the average pore diameter of the pore structure of the base film. The degree of flexibility of the pore structure of the polyolefin-based film can be calculated by the following formula.

number

[0057] Here, τ represents the degree of curvature of the pore structure, and t gur ε represents the air permeability of the base film, ε represents the porosity of the base film, d represents the average pore size of the pore structure, in units of cm, and L represents the thickness of the base film, in units of cm.

[0058] In some embodiments, according to the first aspect, a first example of the first aspect is provided, wherein the degree of flexibility of the pore structure is 7.5 to 9.5. Furthermore, the degree of flexibility of the pore structure is 7.5 to 9.

[0059] In some embodiments, according to the first aspect, a first example of the first aspect is provided, where the maximum pore diameter of the pore structure is ≤ 45 nm. Furthermore, the maximum pore diameter of the pore structure is ≤ 40 nm. Even further, the maximum pore diameter of the pore structure is 20 nm to 40 nm.

[0060] In some embodiments, according to the first embodiment, a first example of the first embodiment is provided, wherein the thickness of the polyolefin-based film is 2 μm to 6.2 μm. Furthermore, the thickness of the polyolefin-based film is 4 μm to 6.2 μm.

[0061] This design is advantageous in further improving the consistency of the polyolefin base film, reducing performance deviations of the base film, improving the air permeability of the base film, and increasing the energy density of the battery core by optimizing the thickness, flexibility of the pore structure, and maximum pore diameter of the polyolefin base film.

[0062] In some specific examples, the thickness of the polyolefin-based film is 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, 3.0 μm, 3.1 μm, 3.2 μm, 3.3 μm, 3.4 μm, 3.5 μm, 3.6 μm, 3.7 μm, 3.8 μm, 3.9 μm, 4 μm, 4.1 μm, 4.2 μm, 4.3 μm The thickness may be 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, or 7μm. Selectively, the thickness of the polyolefin base film may be 4μm to 5.0μm, 5.0μm to 6.2μm, or 4.5μm to 5.5μm.

[0063] In some specific embodiments, the degree of curvature 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.

[0064] In some specific embodiments, the maximum pore diameter of the pore structure may be 45 nm, 44 nm, 43 nm, 42 nm, 41 nm, 40 nm, 39.9 nm, 39.8 nm, 39.7 nm, 39.6 nm, 39.5 nm, 39.4 nm, 39.3 nm, 39.2 nm, 39.1 nm, 39 nm, 38 nm, 35 nm, 30 nm, 25 nm, or 20 nm.

[0065] In some embodiments, according to the first embodiment, a second example of the first embodiment is provided, wherein the polyolefin-based film contains a polyolefin with a weight-average molecular weight Mw of 500,000 or more.

[0066] Using polyolefins with a weight-average molecular weight (Mw) of 500,000 or more as raw materials is advantageous for improving the uniformity of pore formation.

[0067] In this application, a single weight-average molecular weight should be understood to mean that the weight-average molecular weight of the polyolefin is uniquely determined.

[0068] In some specific examples, the weight-average molecular weight Mw of the polyolefin may be between 500,000 and 1,500,000. If the weight-average molecular weight is too high, it becomes difficult to process, difficult to control the extruder pressure, and the consistency of the film surface thickness is poor. If the weight-average molecular weight is too low, the molecular chains are relatively short and the crystalline region occupancy after tensile strength is relatively low, which reduces the strength of the base film. For example, 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, 1,000,000, 1,100,000, 1,200,000, 1,300,000, 1,400,000, or 1,500,000.

[0069] In some embodiments, according to the first embodiment, a third example of the first embodiment is provided, where the polydispersity index of the polyolefin Mw / Mn ≤ 3.5.

[0070] This design is advantageous for optimizing the polydispersity index of polyolefins, reducing the distribution width of polyolefin molecular weights, and improving molecular weight consistency.

[0071] In this application, Mn is the number-average molecular weight of the polyolefin, Mw is the weight-average molecular weight of the polyolefin, and 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 represent the uniformity of the molecular weight distribution.

[0072] In some specific embodiments, the polydispersity index Mw / Mn of the polyolefin may be 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, or 3.5. Selectively, the polydispersity index Mw / Mn of the polyolefin may be 1-3.5, 1-2, or 2-3.5, etc.

[0073] In some embodiments, according to the first aspect, a fourth example of the first aspect is provided, where the polyolefin is polyethylene, polypropylene, or a mixture of polyethylene and polypropylene.

[0074] This design offers advantages such as optimizing the type of polyolefin, further improving the consistency of the polyolefin base film, increasing the strength and elongation of the base film, and reducing the thermal shrinkage of the base film.

[0075] In some embodiments, according to the first embodiment, a fifth example of the first embodiment is provided, in which the air permeability of the polyolefin-based film is ≤ 180 s / 100 cc.

[0076] This design is advantageous for optimizing the air permeability of the polyolefin-based film and improving the air permeability of the separator.

[0077] In some specific embodiments, the air permeability of the polyolefin-based film may be 100-180 s / 100 cc. For example, the air permeability of the polyolefin-based film may be 100 s / 100 cc, 105 s / 100 cc, 110 s / 100 cc, 115 s / 100 cc, 120 s / 100 cc, 125 s / 100 cc, 130 s / 100 cc, 135 s / 100 cc, 140 s / 100 cc, 145 s / 100 cc, 150 s / 100 cc, 155 s / 100 cc, 160 s / 100 cc, 165 s / 100 cc, 170 s / 100 cc, 175 s / 100 cc, or 180 s / 100 cc. Selectively, the air permeability of the polyolefin-based film may be 140-170 s / 100 cc.

[0078] In some embodiments, according to the first embodiment, a sixth example of the first embodiment is provided, wherein the longitudinal (MD) elongation of the polyolefin-based film is ≥ 60%, selectively, the longitudinal elongation of the polyolefin-based film is ≥ 100%, and more selectively, the longitudinal elongation of the polyolefin-based film is 100% to 120%. The transverse (TD) elongation of the polyolefin-based film is ≥ 100%, selectively, the transverse elongation of the polyolefin-based film is ≥ 110%, and more selectively, the transverse elongation of the polyolefin-based film is 110% to 160%.

[0079] In this design, an increase in the elongation rate indicates that the separator has better toughness. If metal particles (which may originate from the operating environment, positive and negative electrode plates, or separator, etc.) are generated during the winding process, the separator can effectively coat the particles, preventing damage to the battery core and improving the manufacturability of the battery core.

[0080] In some specific embodiments, the longitudinal elongation of the polyolefin-based film may be 60% to 120%, for example, 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%, or 120%.

[0081] In some specific embodiments, the transverse elongation of the polyolefin-based film may be 100% to 160%, for example, 100%, 101%, 102%, 105%, 106%, 107%, 108%, 109%, 110%, 111%, 113%, 114%, 115%, 117%, 118%, 120%, 121%, 125%, 130%, 135%, 140%, 145%, 150%, 155%, or 160%.

[0082] In some embodiments, according to the first embodiment, a seventh example of the first embodiment is provided, in which the polyolefin-based film has a longitudinal heat shrinkage rate of ≤4% and a transverse heat shrinkage rate of ≤4% at 115°C.

[0083] In this design, the reduced thermal shrinkage rate of the polyolefin-based film indicates high thermal stability of the separator, thus improving the safety performance of the battery core.

[0084] In some specific embodiments, the longitudinal heat shrinkage rate of the polyolefin-based film at 115°C may be 0% to 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%. Selectively, the longitudinal heat shrinkage rate of the polyolefin-based film at 115°C may be 2% to 2.5%.

[0085] In some specific embodiments, the transverse heat shrinkage rate of the polyolefin-based film at 115°C may be 0% to 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%. Selectively, the transverse heat shrinkage rate of the polyolefin-based film at 115°C may be 0.5% to 2% or 0.9% to 1.6%.

[0086] In some embodiments, according to the first embodiment, an eighth example of the first embodiment is provided, wherein the polyolefin-based film is subject to the following conditions (1)-(4): (1) The condition that the puncture strength of the polyolefin-based film is ≥ 270 gf, (2) Longitudinal tensile strength of polyolefin-based film ≥ 2000 kgf / cm 2 Therefore, the lateral tensile strength is ≥ 2000 kgf / cm². 2 The conditions are, (3) The void ratio of the polyolefin-based film is 25% to 40%. (4) The surface density of the polyolefin-based film is 2-5 g / m². 2 It satisfies at least one of the following conditions.

[0087] This design demonstrates that the polyethylene porous base film, with its relatively high puncture strength, provides good separator resistance and effectively ensures the yield of the separator manufacturing process. Optimizing the porosity of the polyethylene porous base film is advantageous in ensuring pore size consistency and achieving effective ion conduction.

[0088] In some specific embodiments, the puncture strength of the polyolefin-based film may be, for example, 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. Optionally, the puncture strength of the polyolefin-based film may be 270 - 350 gf.

[0089] In some specific embodiments, the longitudinal tensile strength of the polyolefin-based film is 2000 kgf / cm 2 , 2100 kgf / cm 2 , 2200 kgf / cm 2 , 2300 kgf / cm 2 , 2400 kgf / cm 2 , 2500 kgf / cm 2 , 2600 kgf / cm 2 , 2700 kgf / cm 2 , 2800 kgf / cm 2 , 2900 kgf / cm 2 or 3000 kgf / cm 2 and may be acceptable. Optionally, the longitudinal tensile strength of the polyolefin-based film may be 2400 - 2800 kgf / cm 2 and may be acceptable.

[0090] In some specific embodiments, the transverse tensile strength of the polyolefin-based film is 2000 kgf / cm 2 , 2100 kgf / cm 2 , 2200 kgf / cm 2 , 2300 kgf / cm 2 , 2400 kgf / cm 2 , 2500 kgf / cm 2 , 2600 kgf / cm 2 , 2700 kgf / cm 2 , 2800 kgf / cm 2 , 2900 kgf / cm 2 or 3000 kgf / cm 2 and may be acceptable. Optionally, the transverse tensile strength of the polyolefin-based film may be 2100 - 2600 kgf / cm 2That's fine.

[0091] In some specific embodiments, 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%. Selectively, the porosity of the polyolefin-based film may be 30% to 35%.

[0092] In some specific examples, the surface density of the polyolefin-based film is 2 g / m². 2 , 2.1g / m 2 2.2g / m 2 2.3g / m 2 2.4g / m 2 2.5g / m 2 2.6g / m 2 2.7g / m 2 2.8g / m 2 2.9g / m 2 3.0g / m 2 3.1g / m 2 3.2g / m 2 3.3g / m 2 3.4g / m 2 3.5g / m 2 3.6g / m 2 3.7g / m 2 3.8g / m 2 3.9g / m 2 4g / m 2 4.5g / m 2 or 5g / m 2 Alternatively, the surface density of the polyolefin-based film may be 2.5-4 g / m². 2 That's fine.

[0093] A second aspect of this application provides a method for producing a polyolefin-based film, the method being: Mixing polyolefin and a pore-forming agent, and manufacturing the resulting mixture into a film sheet, The aforementioned film sheet is subjected to biaxial tension, The pore-forming agent is removed from the film sheet after biaxial tensioning, and voids are formed. The process includes tensile and thermal fixing of the film sheet after forming voids to obtain the polyolefin-based film, The polyolefin-based film contains a pore structure, has a thickness of ≤7 μm, and the degree of flexibility of the pore structure is 7 to 10.

[0094] In the invention of this application, a polyolefin-based film with a pore structure flexibility of 7 to 10 can be manufactured by using polyolefin as a raw material and combining it with biaxial tension. The film has a thickness of ≤7 μm.

[0095] Furthermore, in the technical proposal of this embodiment, the polyolefin-based film obtained by manufacturing has the same characteristics and advantages as the aforementioned polyolefin-based film, and will not be explained further here.

[0096] In some embodiments, according to a second embodiment, a first example of the second embodiment is provided, wherein the weight-average molecular weight Mw of the polyolefin is 500,000 or more. Furthermore, the polyolefin-based film contains a polyolefin having a weight-average molecular weight Mw of 500,000 to 1,500,000.

[0097] In some embodiments, according to a second embodiment, a first example of the second embodiment is provided, in which the occupancy rate in the polyolefin mixture is 20 wt% to 30 wt%.

[0098] This design is advantageous in improving the uniformity of film thickness and the consistency of pore sizes in the base film by optimizing the occupancy rate in the polyolefin mixture, and in meeting the standard requirements for high elongation of the base film. If the occupancy rate is too high (>30 wt%), the pressure curve of the extruder will fluctuate greatly, resulting in poor uniformity of film thickness and poor consistency of pore sizes in the base film. If the occupancy rate is too low (<20 wt%), the content of the pore-forming agent will be too high, limiting the tensile magnification and preventing the achievement of the standard requirements for high elongation. By optimizing the occupancy rate in the polyolefin mixture, the uniformity of pore formation will be improved while simultaneously achieving the standard requirements for high elongation.

[0099] In some specific examples, the occupancy rate of polyolefins in the mixture was 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%, 26 wt%, 27 wt%, 28 wt%, 29 wt%, or 30 wt%.

[0100] In some embodiments, according to a second aspect, a second example of the second aspect is provided, where biaxial tension includes longitudinal tension and transverse tension. Here, the longitudinal tension ratio is 5 to 15 times, the transverse tension ratio is 5 to 15 times, and the longitudinal and transverse tension ratios are not simultaneously 5 times. Furthermore, the longitudinal tension ratio is 6 to 15 times, and the transverse tension ratio is 6 to 15 times.

[0101] This design allows for further reduction of the thickness of the polyolefin-based film and improvement of pore formation uniformity by optimizing the longitudinal and transverse tensile strengths.

[0102] In some specific embodiments, the longitudinal tensile strength ratio is 5 to 12 times, for example, 5, 6, 7, 8, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9, 9, 9.1, 9.2, 9.3, 9.4, 9.5, 10, 11, or 12 times. Selectively, the longitudinal tensile strength ratio may be 8 to 9.5 times. The longitudinal tensile temperature may be 109 to 115°C.

[0103] In some specific embodiments, the transverse tensile strength ratio was 5 to 12 times, for example, 5, 6, 7, 8, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8, 8.9, 9, 9.1, 9.2, 9.3, 9.4, 9.5, 9.6, 9.7, 9.8, 9.9, 10, 11, or 12 times. Selectively, the transverse tensile strength ratio may be 8.5 to 10 times. The transverse tensile temperature may be 113 to 119°C.

[0104] This application does not particularly restrict the pore-forming agent used, as long as it can sufficiently dissolve the polyolefin. For example, the pore-forming agent may be one or more of white oil, liquid paraffin, mineral oil, soybean oil, phthalate esters, and aromatic ethers, but is not limited to these. Selectively, the pore-forming agent is white oil. In some specific examples, the pore-forming agent is white oil, and a liquid mixture can be obtained by mixing a single weight-average molecular weight polyolefin with the white oil. The occupancy rate of the polyolefin in the liquid mixture is the solid content of the polyolefin.

[0105] In some embodiments, according to the second embodiment, a third example of the second embodiment is provided, in which the thickness of the film sheet may be 1 mm or more, selectively 1 to 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.

[0106] In some embodiments, according to the second aspect, a fourth example of the second aspect is provided, in which biaxial tension includes first performing longitudinal tension and then transverse tension, or first performing transverse tension and then longitudinal tension, or performing longitudinal tension and transverse tension synchronously.

[0107] In some embodiments, according to a second aspect, a fifth example of the second aspect is provided, in which the removal of the pore-forming agent includes extracting the pore-forming agent from the film sheet using an extractant. The type of extractant can be selected according to the type of pore-forming agent and is mainly used to dissolve the pore-forming agent and form voids in the material. Selectively, the extractant is dichloromethane.

[0108] In some embodiments, according to a second aspect, a sixth example of the second aspect is provided, in which tensile fixing includes stretching the film sheet transversely at a small magnification. The tensile magnification may be 1 to 3 times. The tensile temperature may be 130 to 133°C.

[0109] In some embodiments, according to a second embodiment, a seventh example of the second embodiment is provided, wherein heat fixing includes heating and fixing the film sheet. The heating temperature is ≥ 133°C, and selectively 133–135°C. The heating time is ≥ 20 s, and selectively 20–60 s, for example 28–40 s or 30–40 s.

[0110] A third aspect of this application provides a separator comprising a polyolefin-based film obtained by the first aspect of this application or by the manufacturing method of the second aspect of this application.

[0111] In the technical invention of the embodiment of this application, a polyolefin-based film obtained by the manufacturing method of the first embodiment of this application or the second embodiment of this application is used, and therefore the separator of this application has advantages such as being ultra-thin and having a uniform pore structure. Furthermore, by applying a coating to the surface of the polyolefin-based film, the electrical performance and safety performance of the battery core can be improved.

[0112] In some embodiments, according to a third aspect, a first example of the third aspect is provided, wherein the separator further includes a coating applied to at least one surface of the polyolefin-based film.

[0113] In some embodiments, according to a third aspect, a first example of the third aspect is provided, in which the coating includes a filler. The filler includes at least one selected from inorganic particles, organic particles and organic-inorganic hybrid particles.

[0114] In some embodiments, the decomposition temperature of the filler is selectively set to 200°C or higher, thereby allowing the filler to have excellent thermal stability and resistance to decomposition, and further improving the heat resistance of the separator.

[0115] In some embodiments, the inorganic particles selectively include at least one of inorganic particles having a dielectric constant of 5 or more, inorganic particles that are ionic conductive but do not store ions, and inorganic particles that can undergo electrochemical reactions.

[0116] Selectively, 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, barium fluoride, barium sulfate, aluminum magnesium silicate, lithium magnesium silicate, sodium magnesium silicate, bentonite, hectorite, zirconium titanate, barium titanate, Pb(Zr,Ti)O3 (abbreviated as PZT), and Pb 1-m La m Zr 1-n Ti n O 33 (Abbreviated as PLZT, 0 <m<1、0<n<1)、Pb(Mg3Nb 2 / 3The material comprises O3-PbTiO3 (abbreviated as PMN-PT) and at least one of the respective modified inorganic particles. Selectively, the modification method for each inorganic particle may be chemical modification and / or physical modification. Chemical modification methods include coupling agent modification (e.g., using silane coupling agents, titanate coupling agents, etc.), surfactant modification, polymer graft modification, etc. Physical modification methods may include mechanical force dispersion, ultrasonic dispersion, high-energy treatment, etc. Modification treatment can reduce the aggregation of inorganic particles, and by selecting coupling agents, surfactants, or polymers having specific functional groups to modify the inorganic particles, it contributes to improving the penetration characteristics of the coating into the electrolyte and the adhesion of the coating.

[0117] Selectively, inorganic particles that are ion-conductive but do not store ions include Li3PO4 and lithium titanium phosphate. x1 Ti y1 (PO4)3, Lithium Aluminum Titanium Phosphate x2 Al y2 Ti z1 (PO4)3, (LiAlTiP) x3 O y3 Patterned glass, lithium lanthanum titanate Li x4 La y4 TiO3, Lithium germanium thiophosphate x5 Ge y5 P z2 S w Lithium nitride x6 N y6 SiS2 type glass Li x7 Si y7 S z3 and P2S5 type glass Li x8 P y8 S z4including at least one of them, where 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. Thereby, the ion transport characteristics of the separator can be further improved.

[0118] Optionally, 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, silicone-based materials, tin-based materials, and lithium titanium compounds.

[0119] The organic particles have the characteristics of good thermal stability and being difficult to decompose, thereby improving the heat resistance of the separator. At the same time, when the internal temperature of the secondary battery reaches the melting point of the organic particles due to overheating and thermal runaway, the organic particles can further melt and be inhaled into the pores of the porous substrate by capillary action to play the role of closing pores and blocking, which is advantageous for ensuring that the secondary battery has high safety performance.

[0120] In some embodiments, the organic particles include, but are not limited to, at least one of polyethylene particles, polypropylene particles, polystyrene particles, cellulose, cellulose modifiers (such as carboxymethyl cellulose), melamine resin particles, phenol resin particles, polyester particles (such as polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate), silicone resin particles, polyimide particles, polyamideimide particles, polyaramid particles, polyphenylene sulfide particles, polysulfone particles, polyether sulfone particles, polyether ether ketone particles, polyallyl ether ketone particles, copolymers of butyl acrylate and ethyl methacrylate (such as cross-linked polymers of butyl acrylate and ethyl methacrylate).

[0121] In some embodiments, the glass transition temperature of the organic particles may be selectively set to 130°C or higher. This prevents the organic particles from changing from a glassy state to a viscous flow state when the internal temperature of the secondary battery reaches 130°C, thus preventing the separator from shrinking violently. Furthermore, the organic particles may selectively include, but are not limited to, at least one of the following: melamine-formaldehyde resin particles, phenolic resin particles, polyester particles, silicone resin particles, polyimide particles, polyamide-imide particles, polyaramid particles, polyphenylene sulfide particles, polysulfone particles, polyethersulfone particles, polyetheretherketone particles, and polyallyletherketone particles.

[0122] Selectively, nanocellulose may be included in the coating. Nanocellulose refers to a general term for cellulose with any dimension size being nanoscale (e.g., within 100 nm), which possesses the properties of cellulose while also having the properties of nanoparticles. Nanocellulose may also be polymer nanomaterials extracted from wood, cotton, etc., in nature by one or more means from chemistry, physics, or biology, and has advantages such as a wide supply chain, low cost, biodegradability, high elastic modulus, and high specific surface area.

[0123] In some embodiments, the nanocellulose may include at least one of the following: cellulose nanofibers (also called cellulose nanofibers, CNF, nanofibrillated cellulose, or microfibrillated cellulose), cellulose nanocrystals (also called cellulose nanocrystals, CNC, or nanocrystalline cellulose), and bacterial nanocellulose (also called bacterial nanocellulose, BNC, or microbial cellulose).

[0124] In some examples, the nanocellulose may comprise at least one of unmodified nanocellulose (also called hydroxy nanocellulose) and modified nanocellulose, and is selectively modified nanocellulose. The nanocellulose may comprise a modifying group. The modifying group comprises 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, and may further selectively comprise at least one of a sulfonic acid group, a boric acid group, and a phosphate group.

[0125] In some embodiments, organic-inorganic hybrid particles may be selected from metal-organic framework materials such as MOFs.

[0126] In some embodiments, the coating may further contain other organic compounds, such as polymers that improve heat resistance, dispersants, wetting agents, and adhesives. This application is not particularly limited to the types of other organic compounds, and any known material having good improvement performance can be selected and used.

[0127] In some specific examples, the coating thickness is ≤5 μm.

[0128] In some specific embodiments, the method for producing a separator includes the steps of (1) providing a polyolefin-based film, (2) providing a coating slurry and mixing a filler and a solvent in a predetermined ratio to prepare a coating slurry, and (3) applying the coating slurry from step (2) to at least one side of the polyolefin-based film from step (1) to form a coating and dry it to obtain a separator. Here, the polyolefin-based film includes a pore structure, has a thickness of ≤7 μm, the curvature of the pore structure is 7.5 to 9.5, and the maximum pore diameter of the pore structure is ≤45 nm.

[0129] In some specific embodiments, the separator further includes an adhesive layer. The adhesive layer is provided on at least a portion of the surface of the coating. The adhesive layer comprises a particulate adhesive, which optionally comprises at least one of acrylate monomer homopolymers or copolymers, acrylic monomer homopolymers or copolymers, or fluorine-containing olefin monomer homopolymers or copolymers.

[0130] A fourth aspect of this application provides a secondary battery including the separator of the third aspect of this application.

[0131] Because a polyolefin-based film obtained by the first embodiment of this application or the manufacturing method of the second embodiment of this application is used, the secondary battery of this application has improved energy density and electrical performance.

[0132] Generally, a secondary battery may include a positive electrode plate, a negative electrode plate, a separator, and an electrolyte. During charging and discharging of the battery, active ions intermittently

[0133] [Negative electrode plate] The negative electrode plate generally includes a negative electrode current collector and a negative electrode film layer installed on the negative electrode current collector. The negative electrode film layer includes a negative electrode active material.

[0134] The negative electrode current collector may be a conventional metal foil sheet or a composite current collector (for example, a composite current collector may be formed by placing a metal material on a polymer substrate). For example, the negative electrode current collector may be made of copper foil.

[0135] The negative electrode active material can be any negative electrode active material known in the art for batteries. For example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicone-based materials, tin-based materials, and lithium titanate. The silicone-based material may be selected from at least one of elemental silicone, silicone oxide, silicone-carbon composite, silicone-nitrogen composite, and silicone alloy. The tin-based material may be at least one selected from elemental tin, tin oxide, and tin alloy. However, this application is not limited to these materials, and other conventional materials that can be used as battery negative electrode active materials may be used. These negative electrode active materials may be used individually or in combination of two or more.

[0136] The negative electrode film layer typically further selectively contains adhesives, conductive agents, and other selective additives.

[0137] For example, the conductive agent may be one or more of the following: superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, conductive carbon black (Super P), graphene, and carbon nanofibers.

[0138] For example, the adhesive may be one or more of the following: 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).

[0139] For example, other selective additives may include thickeners and dispersants (e.g., sodium carboxymethylcellulose CMC-Na) or PTC thermistor materials.

[0140] [Positive electrode plate] The positive electrode plate generally includes a positive electrode current collector and a positive electrode film layer installed on the positive electrode current collector. The positive electrode film layer includes a positive electrode active material.

[0141] The positive electrode current collector may be a conventional metal foil sheet or a composite current collector (a composite current collector may be formed by placing metal materials on a polymer substrate). For example, the positive electrode current collector may be made of aluminum foil.

[0142] The specific type of positive electrode active material is not limited, and any active material known in the art that can be used in the positive electrode of a secondary battery may be used. Those skilled in the art can select according to their actual needs.

[0143] For example, the positive electrode active material may include, but is not limited to, one or more of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their respective modified compounds. Examples of 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. Examples of lithium-containing phosphates with an olivine structure may include, but is not limited to, one or more of lithium iron phosphate, composite materials of lithium iron phosphate and carbon, lithium manganese phosphate, composite materials of lithium manganese phosphate and carbon, lithium iron manganese phosphate, lithium iron manganese phosphate and carbon, and their modified compounds. All of these materials are available by commercial means.

[0144] In some embodiments, the modifying compounds for each of the above materials may perform doping modification and / or surface coating modification on the materials.

[0145] The positive electrode film layer generally further selectively includes an adhesive, a conductive agent, and other selective additives.

[0146] For example, the conductive agent may be one or more of the following: superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, conductive carbon black (Super P), graphene, and carbon nanofibers.

[0147] For example, the adhesive may be one or more of the following: styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethylcellulose (CMC), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0148] [Electrolyte] The electrolyte plays a role in conducting ions between the positive and negative electrodes. The electrolyte may contain an electrolyte salt and a solvent.

[0149] For example, the electrolyte salt may be selected from one or more of the following: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalato)phosphate (LiDFOP), and lithium tetrafluoro(oxalato)phosphate (LiTFOP).

[0150] For example, the solvent may be selected from one or more of the following: 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), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS), and diethyl sulfone (ESE).

[0151] In some embodiments, the electrolyte further includes additives. For example, the additives may include negative electrode film forming additives, positive electrode film forming additives, and additives that can improve some of the battery's performance characteristics, such as additives that improve the battery's overcharge performance, additives that improve the battery's high-temperature performance, and additives that improve the battery's low-temperature performance.

[0152] In some embodiments, the positive electrode plate, negative electrode plate, and separator can be manufactured into an electrode assembly by a winding process or a lamination process.

[0153] In some embodiments, the battery cell may include an outer casing. This casing may be used to package the electrode assembly and electrolyte.

[0154] In some embodiments, the battery cell casing may be a rigid case, such as a rigid plastic case, an aluminum case, or a steel case. The battery cell casing may also be a pouch, such as a bag-shaped pouch. The pouch material may be plastic, and examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0155] This application does not particularly limit the shape of the battery cell, which may be cylindrical, rectangular, or any other shape. For example, Figure 4 shows a rectangular battery cell 5 as an example.

[0156] In some embodiments, referring to Figure 5, the casing may include a case 51 and a top cover assembly 53. Here, the case 51 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates enclosing and forming a housing cavity. The case 51 has an opening that communicates with the housing cavity, and the top cover assembly 53 can cover the opening to seal the housing cavity. The positive electrode plate, negative electrode plate and separator may form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is packaged within the housing cavity. The electrolyte is impregnated into the electrode assembly 52. ​​The number of electrode assemblies 52 included in the battery cell 5 may be one or more, and a person skilled in the art can select according to specific practical needs.

[0157] In some embodiments, battery cells can be assembled into a battery module, the number of battery cells included in the battery module may be one or more, and the specific number can be selected by those skilled in the art depending on the application and capacity of the battery module.

[0158] Figure 6 shows an example of a battery module 4. Referring to Figure 6, in the battery module 4, the multiple battery cells 5 may be arranged sequentially along the longitudinal direction of the battery module 4. Of course, they may be arranged in any other manner. Furthermore, these multiple battery cells 5 may be fixed in place by fasteners.

[0159] Selectively, the battery module 4 may further include a housing having a housing space, in which a plurality of battery cells 5 are housed.

[0160] In some embodiments, the battery modules may be assembled into a battery pack, and the number of battery modules included in the battery pack may be one or more, the specific number of which can be selected by those skilled in the art depending on the application and capacity of the battery pack.

[0161] Figures 7 and 8 show an example of a battery pack 1. Referring to Figures 7 and 8, the battery pack 1 may include a battery box and a plurality of battery modules 4 installed in the battery box. The battery box includes an upper housing 2 and a lower housing 3, the upper housing 2 being lidable onto the lower housing 3 and forming a sealed space for housing the battery modules 4. The plurality of battery modules 4 may be arranged in the battery box in any manner.

[0162] Furthermore, this application provides a power consumption device, the power consumption device including a secondary battery according to this application, the secondary battery including at least one of a battery cell, a battery module, and a battery pack. The secondary battery may be used as a power source for the power consumption device or as an energy storage unit for the power consumption device. The power consumption device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., 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.

[0163] As the power consumption device, a battery cell, battery module, or battery pack can be selected based on the usage needs.

[0164] Figure 9 shows an example of a power consumption device. This power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the demand for high power output and high energy density of the power supply of this power consumption device, a battery pack or battery module may be used.

[0165] Other examples of such devices may include mobile phones, tablet computers, and laptop computers. These devices generally require a thin profile and may use battery cells as a power source.

[0166] The present invention will be further described below, with reference to examples. It should be understood that these examples are merely illustrative and do not limit the scope of the present invention.

[0167] Manufacturing of polyethylene porous base film Example 1 First, the weight-average molecular weight is 8.0 × 10⁻⁶. 5 Polyethylene with Mw / Mn = 3.5 is selected and mixed with white oil. Here, the solid content of the polyethylene is 25 wt%. Then, it is heated and melted in an extruder, followed by cooling casting and cooling molding to obtain a 2 mm cast film sheet, and the cast film sheet is subjected to longitudinal and transverse tension. The longitudinal tensile strength is 8.2 times and the longitudinal tensile temperature is 110°C, and the transverse tensile strength is 8.7 times and the transverse tensile temperature is 115°C. After heat retention, a film sheet with an area increased by 71 times is obtained, and the white oil in the film sheet is extracted using dichloromethane to form voids, and after drying, the microporous film is subjected to transverse tension again at a small tensile strength of 2 times. The transverse tensile temperature at the small tensile strength is 132°C, and heat setting is performed at 133°C accordingly. The heat setting time is 25 seconds, and a polyethylene porous base film with a thickness of 5.1 μm and a crystallinity of 78.7% can be obtained. The pore size distribution diagram of the polyolefin-based film is shown in Figure 1.

[0168] Example 2 First, the weight-average molecular weight is 7.0 × 10⁻⁶. 5Polyethylene with Mw / Mn = 3.5 is selected and mixed with white oil. Here, the solid content of the polyethylene is 25 wt%. Then, it is heated and melted in an extruder, followed by cooling casting and cooling molding to obtain a 1.5 mm cast film sheet, and the cast film sheet is subjected to longitudinal and transverse tension. The longitudinal tensile strength is 9.2 times and the longitudinal tensile temperature is 110°C, and the transverse tensile strength is 9.7 times and the transverse tensile temperature is 115°C. After heat retention, a film sheet with an area increased by 71 times is obtained, and the white oil in the film sheet is extracted using dichloromethane to form voids, and after drying, the microporous film is subjected to transverse tension again at a small tensile strength of 2 times. The transverse tensile temperature at the small tensile strength is 132°C, and heat setting is performed at 133°C accordingly. The heat setting time is 25 seconds, and a polyethylene porous base film with a thickness of 4.0 μm and a crystallinity of 79.6% can be obtained.

[0169] Example 3 First, the weight-average molecular weight is 8.0 × 10⁻⁶. 5 Polyethylene with Mw / Mn = 3.0 is selected and mixed with white oil. Here, the solid content of the polyethylene is 25 wt%. Then, it is heated and melted in an extruder, followed by cooling casting and cooling molding to obtain a 2.1 mm cast film sheet, and the cast film sheet is subjected to longitudinal and transverse tension. The longitudinal tensile strength is 8.2 times and the longitudinal tensile temperature is 110°C, and the transverse tensile strength is 8.7 times and the transverse tensile temperature is 115°C. After heat retention, a film with an area increased by 71 times is obtained, and the white oil in the film is extracted using dichloromethane to form voids, and after drying, the microporous film is subjected to transverse tension again at a small tensile strength of 2 times. The transverse tensile temperature at the small tensile strength is 132°C, and heat setting is performed at 133°C accordingly. The heat setting time is 25 seconds, and a polyethylene porous base film with a thickness of 6.2 μm and a crystallinity of 79.3% is obtained.

[0170] Example 4-23 The procedure is carried out according to the method described in Example 1, with the only difference being that the parameters listed in Table 1 below are different from those in Example 1.

[0171] Comparative Example 1 First, the weight-average molecular weight is 4.0 × 10⁻⁶. 5 Polyethylene with Mw / Mn = 3.5 is selected and mixed with white oil. Here, the solid content of the polyethylene is 25 wt%. Then, it is heated and melted in an extruder, followed by cooling casting and cooling molding to obtain a 2 mm cast film sheet, and the cast film sheet is subjected to longitudinal and transverse tension. The longitudinal tensile strength is 8.2 times and the longitudinal tensile temperature is 110°C, and the transverse tensile strength is 8.7 times and the transverse tensile temperature is 115°C. After heat retention, a film sheet with an area increased by 71 times is obtained, and the white oil in the film sheet is extracted using dichloromethane to form voids, and after drying, the microporous film is subjected to transverse tension again at a small tensile strength of 2 times. The transverse tensile temperature at the small tensile strength is 132°C, and heat setting is performed at 133°C accordingly. The heat setting time is 25 seconds, and a polyethylene porous base film with a thickness of 5.2 μm and a crystallinity of 78.7% can be obtained. The pore size distribution of the polyolefin-based film was tested using the method of Example 1. The resulting pore size distribution diagram is shown in Figure 2.

[0172] Comparative Example 2 First, the weight-average molecular weight is 8.0 × 10⁻⁶. 5Polyethylene with Mw / Mn = 4.0 is selected and mixed with white oil. Here, the solid content of the polyethylene is 25 wt%. Then, it is heated and melted in an extruder, followed by cooling casting and cooling molding to obtain a 2 mm cast film sheet, and the cast film sheet is subjected to longitudinal and transverse tension. The longitudinal tensile strength is 8.2 times and the longitudinal tensile temperature is 110°C, and the transverse tensile strength is 8.7 times and the transverse tensile temperature is 115°C. After heat retention, a film sheet with an area increased by 71 times is obtained, and the white oil in the film sheet is extracted using dichloromethane to form voids, and after drying, the microporous film is subjected to transverse tension again at a small tensile strength of 2 times. The transverse tensile temperature at the small tensile strength is 132°C, and heat setting is performed at 133°C accordingly. The heat setting time is 25 seconds, and a polyethylene porous base film with a thickness of 5.2 μm and a crystallinity of 78.7% can be obtained. The pore size distribution of the polyolefin-based film was tested using the method of Example 1. The resulting pore size distribution diagram is shown in Figure 3.

[0173] Comparative Example 3 First, the weight-average molecular weight is 8.0 × 10⁻⁶. 5 Polyethylene with Mw / Mn = 3.5 is selected and mixed with white oil. Here, the solid content of the polyethylene is 25 wt%. Then, it is heated and melted in an extruder, followed by cooling casting and cooling molding to obtain a 2 mm cast film sheet, and the cast film sheet is subjected to longitudinal and transverse tension. The longitudinal tensile strength is 5.0 times and the longitudinal tensile temperature is 110°C, and the transverse tensile strength is 5.0 times and the transverse tensile temperature is 115°C. After heat retention, a film sheet with a 25-fold increase in area is obtained, and the white oil in the film sheet is extracted using dichloromethane to form voids, and after drying, the microporous film is subjected to transverse tension again at a small tensile strength of 2 times. The transverse tensile temperature at the small tensile strength is 132°C, and heat setting is performed at 133°C accordingly. The heat setting time is 25 seconds, and a polyethylene porous base film with a thickness of 5.2 μm and a crystallinity of 78.7% can be obtained.

[0174] Comparative Example 4 First, the weight-average molecular weight is 8.0 × 10⁻⁶. 5 Polyethylene with Mw / Mn = 3.5 is selected and mixed with white oil. Here, the solid content of the polyethylene is 10 wt%. Then, it is heated and melted in an extruder, followed by cooling casting and cooling molding to obtain a 2 mm cast film sheet, and the cast film sheet is subjected to longitudinal and transverse tension. The longitudinal tensile strength is 8.2 times and the longitudinal tensile temperature is 110°C, and the transverse tensile strength is 8.7 times and the transverse tensile temperature is 115°C. After heat retention, a film sheet with an area increased by 71 times is obtained, and the white oil in the film sheet is extracted using dichloromethane to form voids, and after drying, the microporous film is subjected to transverse tension again at a small tensile strength of 2 times. The transverse tensile temperature at the small tensile strength is 132°C, and heat setting is performed at 133°C accordingly. The heat setting time is 25 seconds, and a polyethylene porous base film with a thickness of 5.2 μm and a crystallinity of 78.7% can be obtained.

[0175] Comparative Example 5-6 The procedure is carried out according to the method described in Example 1, with the only difference being that the parameters listed in Table 1 below are different from those in Example 1.

[0176] [Table 1]

[0177] Polyethylene-based film related parameter testing 1. Measurement of polyolefin-based film thickness: Clean the measuring platform and measuring head. The measuring platform and measuring head must be kept clean. The test was performed using a micrometer. If the data remained stable, the data was recorded in Table 2-4.

[0178] 2. Testing the average and maximum pore diameters of polyolefin-based films: These are measured directly using instruments such as PMI's capillary flow porosimeter or mercury porosimeter. (i) The pores of the base film to be measured are completely wetted and filled with liquid, creating positive pressure in the pores due to capillary action. (ii) The base film is placed in a sealed tank and pressurized with gas pressure to push the liquid out of the capillary pores. (iii) Based on the relative relationship between the pressure applied when the liquid in a single pore is completely pushed out of the capillary pore and the diameter of the pore, the average and maximum pore diameters of the polyolefin-based film pore structure can be obtained according to the Laplace equation. The test results are shown in Table 2-4 below.

[0179] 3. Air permeability test: Cut the base film sample; the sample size must be larger 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, and ensure the film sheet covers the test platform. First, press the RESET key (at this time, "TIMER SEEKING STARTING MARK" will be displayed on the screen), then release the slide cylinder to start the test. After the measurement is complete, slowly loosen the cock until the slide cylinder descends to its lowest position. Remove the sample, slowly raise the slide cylinder, and prepare for the next measurement. The test results are as shown in Table 2-4 below.

[0180] 4. Tensile Strength Test: Spline Punching: The base film is punched into a base film sheet with a width of 15 mm and a length greater than 40 mm. The tensile machine jig is then set to an initial jig spacing of 40 mm and a speed of 50 mm / min. The spline to be tested is placed in the middle of the jig, and the upper and lower ends are clamped with the jig, and the tensile curve is recorded. Each set consists of five parallel samples. The test results are shown in Table 2-4 below.

[0181] 5. Test of stretch ratio: The base film was punched out into a base film sheet with a width of 15 mm and a length greater than 40 mm. Then, the tensile machine jig was set to an initial jig spacing of 40 mm and a speed of 50 mm / min, the spline to be tested was placed in the middle of the jig, and the length of the base film after stretching was recorded. The stretch ratio was calculated as: length after stretching / 40 mm * 100%. The test results are shown in Table 2-4 below.

[0182] 6. Heat Shrinkage Test: The base film was punched out into 100mm*50mm samples. Before firing, the numbers were identified with a marker and measured in two dimensions. The firing temperature and time were set, and after the oven reached the set temperature, the base film was placed in the oven together with a steel disc and fired. After the predetermined firing time was reached, it was removed and allowed to stand at room temperature for 10 minutes. The lateral and vertical dimensions of the same numbered base film after firing were measured, respectively. If the edge shrinkage of the sample was uneven, the position of maximum shrinkage was used as the reference. The test results are shown in Table 2-4 below.

[0183] 7. Puncture Strength Test: A 1 mm prototype needle was passed through the base film at a speed of 50 mm / min using a Gotech tensile machine. The maximum force obtained was the puncture strength, and each set consisted of 5 parallel samples. The average value obtained was the puncture strength. The test results are shown in Table 2-4 below.

[0184] 8. Porosity Test: A rectangular sample was prepared by punching out a cut base film sample with a 100mm*50mm die. The length L and width W of the rectangular sample were measured. Then, its thickness was measured with a 0.1um micrometer, and a total of 5 thickness values ​​were measured. Four points were taken at the edge and one point in the middle, and the average of the 5 thicknesses was taken as the final thickness, denoted as T. The weighed rectangular sample was weighed using an analytical balance with an accuracy of 0.0001g, and denoted as M1. Using the measured length L, width W, thickness T, and the material density ρ of the base film, the theoretical weight of the base film was calculated and denoted as M2: M2 = L * W * T * ρ. Porosity = (1 - M1 / M2) * 100%. The test results are shown in Table 2-4 below.

[0185] 9. Test of areal density: The cut base film sample was punched with a blade die of 100 mm * 50 mm to produce a rectangular sample. The length L and width W of the rectangular sample were measured, and the weight of this sheet-like base film was weighed and denoted as M. The areal density = M / (L * W). The test results are as shown in Table 2-4 below.

[0186] 10. Calculation of tortuosity of pore structure Calculate the tortuosity of the pore structure according to the following formula.

Number

[0187]

Table 2

[0188]

Table 3

[0189]

Table 4

[0190] Using the base films of Examples 1-23 and Comparative Examples 1-6, lithium-ion batteries are manufactured according to the following general manufacturing method.

[0191] Manufacturing of lithium-ion batteries (1) Manufacture of the positive electrode plate The positive electrode active material LFP, the conductive agent Super P, and the adhesive polyvinylidene fluoride (PVDF) were mixed in a mass ratio of positive electrode active material:Super P:PVDF = 8:1:1, added to the solvent N-methylpyrrolidone (NMP), and uniformly stirred under the action of a vacuum stirrer to obtain a positive electrode slurry. The solid content in the positive electrode slurry was 50 wt%. The positive electrode slurry was uniformly applied to the positive electrode current collector aluminum foil and dried at 85°C. Then, after cold pressing, trimming, cutting, and stripping, the positive electrode plate was obtained by drying for 4 hours under vacuum conditions at 85°C.

[0192] (2) Manufacturing of negative electrode plates The negative electrode active material graphite, conductive agent Super P, thickener sodium carboxymethylcellulose (CMC), and adhesive styrene-butadiene rubber emulsion (SBR) were mixed in a mass ratio of graphite:Super P:CMC:SBR = 80:15:3:2. This mixture was added to deionized water as a solvent and uniformly stirred under the action of a vacuum stirrer to obtain a negative electrode slurry. The solid content in the negative electrode slurry was 30 wt%. The negative electrode slurry was uniformly coated onto the copper foil of the negative electrode current collector and dried at 85°C. Next, it underwent cold pressing, trimming, cutting, and stripping, and finally, it was dried for 12 hours under vacuum conditions at 120°C to obtain a negative electrode plate.

[0193] (3) Manufacturing of separators A base film of Example 1 was prepared, and inorganic particles of aluminum oxide (Al2O3), organic particles of vinylidene fluoride-hexafluoropropylene copolymer (number average molecular weight 550,000), and an aqueous solution of polyacrylic acid as an adhesive were uniformly mixed in an appropriate amount of deionized water in a mass ratio of 79.1:20:0.9 to obtain a coating slurry with a solid content of 38% (calculated by weight). The coating slurry was applied to two surfaces of the base film using a coating machine, and a separator was obtained by drying, slitting, and other processes. Here, the gravure roll line count of the coating machine was 125 LPI, the coating speed was 50 m / min, the coating line speed ratio was 1.2, the drying temperature was 50°C ± 5°C, and the drying time was 30 s.

[0194] (4) Manufacturing of electrolyte Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed according to a mass ratio of 30:70 to obtain an organic solvent. A thoroughly dried electrolyte salt LiPF6 was dissolved in the mixed solvent, and the concentration of the electrolyte salt was 1.0 mol / L. After homogeneous mixing, an electrolyte solution was obtained.

[0195] (5) The positive electrode plate from step (1), the separator from step (3), and the negative electrode plate from step (2) were stacked in order, with the separator positioned between the positive and negative electrode plates to act as a separator. Next, they were wound around a square bare cell, tabs were welded on, the bare cell was placed in a packaging foil aluminum plastic film, then baked at 80°C to remove water, after which the electrolyte was injected and the cell was sealed. Subsequently, the cell underwent processes such as standing, hot pressing and cold pressing, chemical conversion (constant current charging at 0.02C up to 3.3V, then constant current charging at 0.1C up to 3.6V), shaping, and capacity testing to obtain a finished pouch lithium-ion battery. Its thickness was 4.0 mm, its width was 60 mm, and its length was 140 mm.

[0196] The secondary batteries of Examples 2-23 and Comparative Examples 1-6 are similar to the secondary battery of Example 1 in terms of manufacturing method, the only difference being the use of different base films.

[0197] Battery performance test 1. DC internal resistance test of the battery The DC internal resistance can be obtained by performing short-duration (30s) high-current charging and discharging on a lithium-ion battery at a constant temperature and calculating the ratio of the voltage difference to the current before and after charging and discharging. The test conditions and test results are shown in Table 5 below.

[0198] 2. Battery internal resistance test Specifically, the AC resistance / AC internal resistance equipment is an Itech IT5100 series battery internal resistance tester. The test method involves applying a fixed frequency of 1 kHz and a fixed current of 50 mA to the battery core under test, sampling the voltage, and calculating the resistance value using a rectifier. The test results are shown in Table 5 below.

[0199] 3. Self-discharge rate test of bare cells After aging and cooling the battery core, the test voltage was OCV1. The battery was placed in a normal temperature and humidity environment and left standing for 48 hours. The voltage was then measured again and recorded as OCVB. The self-discharge rate is (OCV1 - OCVB) / 48h, and the test results are shown in Table 5 below.

[0200] 4. Pass rate of bare cell short-circuit test After winding, the bare cell underwent a short-circuit rate test under the following conditions: 100V, 80°C, 10s, and 5MPa. The test results are shown in Table 5 below.

[0201] [Table 5]

[0202] As can be seen from Table 5, the polyethylene porous base film of this application has a relatively large degree of flexibility in its pore structure, and the base film has a uniform pore structure, thereby improving the consistency of the base film, reducing performance deviations of the base film, and effectively ensuring the air permeability of the base film. When the polyolefin base film of this application is used as a separator in a battery, it is possible to significantly improve the electrical performance of the battery, including a reduction in the DC internal resistance, internal battery resistance, self-discharge rate, and short-circuit rate.

[0203] As can be seen by comparing Example 1 and Comparative Example 1, the weight-average molecular weight of the polyethylene used in Comparative Example 1 is not within the scope of this application, the degree of flexibility of the pore structure of the polyethylene porous base film produced in Comparative Example 1 is clearly small, and the DC internal resistance, battery internal resistance, self-discharge rate, and short-circuit rate of the battery corresponding to Comparative Example 1 are clearly large.

[0204] As can be seen by comparing Example 1 and Comparative Example 2, the polydispersity index Mw / Mn of the polyethylene used in Comparative Example 2 is not within the scope of this application, the degree of porosity of the porous polyethylene base film produced in Comparative Example 2 is clearly small, and the DC internal resistance, battery internal resistance, self-discharge rate, and short-circuit rate of the battery corresponding to Comparative Example 2 are clearly large.

[0205] As can be seen by comparing Example 1, Comparative Example 3, and Comparative Example 6, the longitudinal and transverse tensile strengths of Comparative Examples 3 and 6 are both outside the scope of this application, the degree of flexibility of the pore structure of the polyethylene porous base film produced in Comparative Examples 3 and 6 is clearly small, 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 all clearly large.

[0206] As can be seen by comparing Example 1 with Comparative Examples 4-5, the solid content of the polyethylene in Comparative Examples 4-5 is not within the scope of this application, the degree of flexibility of the pore structure of the polyethylene porous base film produced in Comparative Examples 4-5 is clearly small, 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 all clearly large.

[0207] The above are merely specific embodiments of the present invention that are relatively superior, and the scope of protection of the present invention is not limited thereto. Any changes or substitutions that a person skilled in the art could easily conceive within the technical scope presented herein should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be the same as the scope of protection of the above claims. [Explanation of Symbols]

[0208] 1: Battery pack, 2: Upper casing, 3: Lower casing, 4: Battery module, 5: Battery cell, 51: Case, 52: Electrode assembly, 53: Top cover assembly.

Claims

1. A polyolefin-based film, wherein the polyolefin-based film includes a pore structure, the thickness of the polyolefin-based film is ≤ 7 μm, the degree of flexibility of the pore structure is 7 to 10, and the polyolefin-based film contains a polyolefin having a weight-average molecular weight Mw of 500,000 to 1,500,000. The polydispersity index of the aforementioned polyolefin is 1 ≤ Mw / Mn ≤ 2.

9. A polyolefin-based film characterized by the following features.

2. The polyolefin-based film according to claim 1, characterized in that the degree of flexibility of the pore structure is 7.5 to 9.

5.

3. The polyolefin-based film according to claim 1 or 2, characterized in that the maximum pore diameter of the pore structure is ≤ 45 nm.

4. The polyolefin-based film according to claim 1 or 2, characterized in that the thickness of the polyolefin-based film is 2 μm to 6.2 μm.

5. The polyolefin-based film according to claim 1, characterized in that the polyolefin is one or two of polyethylene and polypropylene.

6. The polyolefin-based film according to claim 1 or 2, characterized in that the air permeability of the polyolefin-based film is ≤ 180 s / 100 cc.

7. The longitudinal elongation of the polyolefin-based film is ≥ 60%, The polyolefin-based film according to claim 1 or 2, characterized in that the transverse elongation of the polyolefin-based film is ≥ 100%.

8. The polyolefin-based film according to claim 1 or 2, characterized in that the longitudinal heat shrinkage rate at 115°C is ≤ 4% and the transverse heat shrinkage rate is ≤ 4%.

9. The polyolefin-based film is provided under the following conditions (1)-(4): (1) The condition that the puncture strength of the polyolefin-based film is ≥ 270 gf, (2) The longitudinal tensile strength of the polyolefin-based film is ≥ 2000 kgf / cm 2 Therefore, the lateral tensile strength is ≥ 2000 kgf / cm². 2 The conditions are, (3) The porosity of the polyolefin-based film is 25% to 40%, (4) The surface density of the polyolefin-based film is 2 to 5 g / m². 2 The polyolefin-based film according to claim 1 or 2, characterized in that it satisfies at least one of the following conditions:

10. A method for producing a polyolefin-based film, The process involves mixing polyolefin and a pore-forming agent, and then manufacturing the resulting mixture into a film sheet. The aforementioned film sheet is subjected to biaxial tension, The pore-forming agent is removed from the film sheet after biaxial tensioning, and voids are formed. The process includes tensile and thermal fixing of the film sheet after forming voids to obtain the polyolefin-based film, The polyolefin-based film contains a pore structure, has a thickness of ≤ 7 μm, has a degree of flexibility of 7 to 10, and has a weight-average molecular weight Mw of 500,000 to 1,500,000. The polydispersity index of the aforementioned polyolefin is 1 ≤ Mw / Mn ≤ 2.

9. A method for producing a polyolefin-based film, characterized by the above.

11. The manufacturing method according to claim 10, characterized in that the occupancy rate of the polyolefin in the mixture is 20 wt% to 30 wt%.

12. The manufacturing method according to claim 10, characterized in that the biaxial tension includes longitudinal tension and transverse tension, wherein the longitudinal tension ratio is 5 to 15 times, the transverse tension ratio is 5 to 15 times, and the longitudinal tension ratio and the transverse tension ratio are not simultaneously 5 times.

13. A separator comprising a polyolefin-based film as described in claim 1 or 2.

14. The separator according to claim 13, further comprising a coating applied to at least one surface of the polyolefin-based film.

15. The separator according to claim 14, characterized in that the coating comprises a filler comprising at least one selected from inorganic particles, organic particles, and organic-inorganic hybrid particles.

16. The separator according to claim 14, further comprising an adhesive layer, the adhesive layer being placed on at least a portion of the surface of the coating, the adhesive layer comprising particulate adhesive, the particulate adhesive comprising at least one of acrylate monomer homopolymers or copolymers, acrylic monomer homopolymers or copolymers, and fluorine-containing olefin monomer homopolymers or copolymers.

17. A secondary battery characterized by including the separator described in claim 13.

18. A power consumption device characterized by including the secondary battery described in claim 17.

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