Separator, preparation method, secondary battery, and electrical apparatus

Abstract

The present application provides a separator, a preparation method, a secondary battery and an electrical apparatus. The separator comprises a first porous base film, the first porous base film being polyolefin. The first porous base film has a viscosity-average molecular weight of ≥ 1.2 million g / mol, such that the separator has high puncture resistance. The first porous base film has a degree of branching of ≤ 5％. The molecular chain sequence in the first porous base film easily forms an ordered arrangement, increasing molecular chain regularity, and thereby increasing puncture resistance of the separator. Therefore, the separator provided by the present application can reduce the risk of the separator being punctured by metal dendrites, prolonging the cycle life of a secondary battery, and increasing the reliability of the secondary battery.

Description

Separator, preparation method, secondary battery and electrical device

[0001] This application claims priority to Chinese patent application No. 2023108264844, filed on July 6, 2023, entitled “Isolation membrane, preparation method, secondary battery and electrical device”, which is incorporated herein by reference in its entirety. Technical Field

[0002] The present application belongs to the technical field of secondary batteries, and specifically relates to an isolation membrane, a preparation method, a secondary battery, and an electrical device. Background Art

[0003] Secondary batteries are widely used in various consumer electronics and electric vehicles due to their lightweight, pollution-free, and memory-free features. With the continuous development of the new energy industry, users have placed higher demands on the reliability and performance of secondary batteries.

[0004] Therefore, how to make secondary batteries have better reliability performance is an urgent problem to be solved.

[0005] Summary of the Invention

[0006] In view of the technical problems existing in the background technology, the present application provides an isolation membrane, a preparation method, a secondary battery and an electrical device, aiming to improve the reliability performance of the secondary battery.

[0007] To achieve the above objectives, the first aspect of the present application provides an isolation membrane, which includes a first porous base membrane, the first porous base membrane is polyolefin, the viscosity average molecular weight of the first porous base membrane is ≥1.2 million g / mol, and the branching degree is ≤5%.

[0008] Compared with the prior art, the present application has at least the following beneficial effects: the isolation membrane provided by the present application, the first porous base membrane is polyolefin, and the viscosity-average molecular weight of the first porous base membrane is ≥1.2 million g / mol, so that the isolation membrane has a higher puncture resistance; since the branching degree of the first porous base membrane is ≤5%, the molecular chain sequence in the first porous base membrane can easily form an ordered arrangement, which increases the regularity of the molecular chain and thereby improves the puncture resistance of the isolation membrane. Therefore, the isolation membrane provided by the present application can reduce the risk of the isolation membrane being punctured by metal dendrites, increase the cycle life of the secondary battery, and improve the reliability of the secondary battery.

[0009] In any embodiment of the present application, the viscosity-average molecular weight of the first porous base membrane is ≥1.5 million g / mol, and can be optionally 2 million g / mol-3 million g / mol, so that the isolation membrane has a higher puncture resistance, which can reduce the risk of the isolation membrane being punctured by metal dendrites, increase the cycle life of the secondary battery, and improve the reliability of the secondary battery.

[0010] In any embodiment of the present application, the branching degree of the first porous base membrane is ≤2%, and can be optionally ≤1%, so that the molecular chain sequence in the first porous base membrane is easier to form an ordered arrangement, increasing the regularity of the molecular chain, thereby improving the puncture resistance of the isolation membrane, reducing the risk of the isolation membrane being punctured by metal dendrites, increasing the cycle life of the secondary battery, and improving the reliability of the secondary battery.

[0011] In any embodiment of the present application, the degree of polymerization of the first porous base membrane is ≥50,000, and can be optionally 80,000-200,000, so that the isolation membrane has a higher puncture resistance, which can reduce the risk of the isolation membrane being punctured by metal dendrites, increase the cycle life of the secondary battery, and improve the reliability of the secondary battery.

[0012] In any embodiment of the present application, the crystallinity of the first porous base membrane is 40%-90%, and can be optionally 75%-85%, so that the isolation membrane has a higher puncture resistance, which can reduce the risk of the isolation membrane being punctured by metal dendrites, increase the cycle life of the secondary battery, and improve the reliability of the secondary battery.

[0013] In any embodiment of the present application, the puncture strength of the first porous base membrane is ≥300gf, and can be optionally 350gf-450gf, which can reduce the risk of the isolation membrane being punctured by metal dendrites, increase the cycle life of the secondary battery, and improve the reliability of the secondary battery.

[0014] In any embodiment of the present application, the thickness of the first porous base membrane is 1μm-12μm, and can be optionally 3μm-6μm, which can reduce the risk of the isolation membrane being punctured by metal dendrites, increase the cycle life of the secondary battery, and improve the reliability of the secondary battery.

[0015] In any embodiment of the present application, the porosity of the first porous base membrane is 20%-50%, optionally 30%-40%, which can reduce the risk of the isolation membrane being punctured by metal dendrites, increase the cycle life of the secondary battery, and improve the reliability of the secondary battery.

[0016] In any embodiment of the present application, the air permeability of the first porous base membrane is 100 sec / 100 cc-300 sec / 100 cc, and can be optionally 200 sec / 100 cc-300 sec / 100 cc, which can enable the isolation membrane to have a better ion permeability.

[0017] In any embodiment of the present application, the number average molecular weight of the first porous base membrane is ≥1.4 million, and can be selected as 1.6 million-2.4 million, so that the isolation membrane has higher puncture resistance, increases the cycle life of the secondary battery, and improves the reliability of the secondary battery.

[0018] In any embodiment of the present application, the weight average molecular weight of the first porous base membrane is ≥1 million g / mol, and can be optionally 1.2 million g / mol-2 million g / mol, so that the isolation membrane has higher puncture resistance, increases the cycle life of the secondary battery, and improves the reliability of the secondary battery.

[0019] In any embodiment of the present application, the isolation membrane further comprises a porous coating layer, which is disposed on at least one surface of the first porous base membrane and comprises a binder; optionally, the porous coating layer comprises a binder and filler particles.

[0020] Providing a porous coating layer on the first porous base film can improve the heat resistance and puncture resistance of the separator, increase the cycle life of the secondary battery, and improve the reliability of the secondary battery.

[0021] In any embodiment of the present application, the isolation membrane further includes a porous coating layer and a second porous base membrane, and the porous coating layer is located between the first porous base membrane and the second porous base membrane; optionally, the porous coating layer includes a binder; more optionally, the porous coating layer includes a binder and filler particles.

[0022] When a porous coating is provided between the first porous base membrane and the second porous base membrane, it can not only compensate for the process defects of the base membrane during the hot pressing composite process, but also further improve the physical property stability of the isolation membrane, thereby improving the reliability of the secondary battery.

[0023] In any embodiment of the present application, the binder includes one or more of polyacrylate, polyacrylic acid, polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride-trichloroethylene copolymer, polyvinyl pyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyethylene oxide, polyarylate, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, polyacrylonitrile, polyvinyl alcohol, polyethylene, polypropylene, starch, and cyanoethyl pullulan; and / or the filling particles include at least one of inorganic particles, organic particles, and organic-metal framework materials.

[0024] When the binder and / or filler particles in the porous coating layer include the above components, the reliability performance of the secondary battery can be improved.

[0025] In any embodiment of the present application, the viscosity average molecular weight of the first porous base membrane is greater than the viscosity average molecular weight of the second porous base membrane; optionally, the viscosity average molecular weight of the second porous base membrane is 100,000 g / mol-2 million g / mol, and more optionally 300,000 g / mol-800,000 g / mol.

[0026] When the viscosity average molecular weight of the second porous base film is within the above range, the physical properties of the separator can be improved and stabilized, thereby improving the reliability of the secondary battery.

[0027] In any embodiment of the present application, the degree of branching of the first porous base membrane is less than that of the second porous base membrane; optionally, the degree of branching of the second porous base membrane is ≤90%, and more optionally 10%-40%.

[0028] When the branching degree of the second porous base membrane is within the above range, the physical properties of the separator can be improved and stabilized, thereby improving the reliability of the secondary battery.

[0029] In any embodiment of the present application, the degree of polymerization of the first porous base membrane is greater than that of the second porous base membrane; optionally, the degree of polymerization of the second porous base membrane is ≤8000, and more optionally 400-1000.

[0030] When the degree of polymerization of the second porous base film is within the above range, the physical properties of the separator can be improved and stabilized, thereby improving the reliability of the secondary battery.

[0031] In any embodiment of the present application, the melting point of the first porous base membrane is lower than the melting point of the second porous base membrane; optionally, the melting point of the second porous base membrane is 160°C-350°C, and more optionally 170°C-320°C.

[0032] When the melting points of the first porous base film and the second porous base film are within the above range, the heat resistance and puncture resistance of the separator are improved, thereby enhancing the reliability of the secondary battery.

[0033] In any embodiment of the present application, the crystallinity of the first porous base membrane is greater than that of the second porous base membrane; optionally, the crystallinity of the second porous base membrane is 20%-70%, more optionally 30%-45%.

[0034] In any embodiment of the present application, the puncture strength of the first porous basement membrane is greater than the puncture strength of the second porous basement membrane;

[0035] Optionally, the ratio of the puncture strength of the first porous base membrane to the puncture strength of the second porous base membrane is ≥2.5;

[0036] Optionally, the puncture strength of the second porous base film is ≥70 gf, and more optionally 100 gf-300 gf.

[0037] In any embodiment of the present application, the second porous base membrane includes at least one of polyolefin, polytetrafluoroethylene, polyvinyl fluoride, polyethylene terephthalate, polyimide, and polyetheretherketone.

[0038] In any embodiment of the present application, the isolation film satisfies at least one of the following (1)-(4):

[0039] (1) The transverse elongation at break of the separator is ≥80%, optionally ≥100%, and more preferably 100%-300%;

[0040] (2) The longitudinal elongation at break of the separator is ≥40%, optionally ≥60%, and more preferably 60%-200%;

[0041] (3) Transverse tensile strength of the separator ≥1500kgf / cm 2 , can be selected as ≥2000kgf / cm 2 , 2000kgf / cm2 is optional 2 -4000kgf / cm 2 ;

[0042] (4) The longitudinal tensile strength of the isolation film is ≥1500kgf / cm 2 , can be selected as ≥2000kgf / cm 2 , 2000kgf / cm2 is optional 2 -4000kgf / cm 2 .

[0043] When the separator satisfies at least one of the above (1) to (4) and falls within the above range, the separator has good puncture resistance, thereby improving the reliability of the secondary battery.

[0044] A second aspect of the present application provides a method for preparing the aforementioned isolation membrane, comprising:

[0045] Provide polymer powder;

[0046] mixing polymer powder with lubricating oil, antioxidant and cross-linking agent to obtain a mixture, and melting the mixture to obtain a melt;

[0047] Casting the melt, stretching, and extracting lubricating oil to obtain a first porous base film, wherein the separator includes the first porous base film;

[0048] The first porous base membrane is polyolefin, the viscosity average molecular weight of the first porous base membrane is ≥1.2 million g / mol, and the branching degree of the first porous base membrane is ≤5%.

[0049] When the preparation method of the isolation membrane provided in the present application is adopted, the isolation membrane provided in the present application can be prepared. The isolation membrane provided in the present application can reduce the risk of the isolation membrane being punctured by metal dendrites, increase the cycle life of the secondary battery, and improve the reliability of the secondary battery.

[0050] In any embodiment of the present application, the preparation method satisfies at least one of the following (1)-(4):

[0051] (1) The mass fraction of the polymer powder in the mixture is 5%-40%, and can be optionally 20%-35%;

[0052] (2) The mass fraction of the lubricating oil in the mixture is 50%-90%, and can be optionally 60%-75%;

[0053] (3) The mass fraction of the antioxidant in the polymer powder is 0.3%-1.0%, and can be optionally 0.5%-1.0%;

[0054] (4) The mass fraction of the cross-linking agent in the polymer powder is 3%-10%, and can be optionally 3%-5%.

[0055] When the polymer powder, lubricating oil, antioxidant and cross-linking agent are within the above ranges, the prepared isolation membrane has good puncture resistance.

[0056] In any embodiment of the present application, the preparation method satisfies at least one of the following (1)-(3):

[0057] The polymer powder includes polyolefin powder; the lubricating oil includes white oil and / or mineral oil; the antioxidant includes at least one of 4,4-thiobis(6-tert-butyl-m-cresol), dibutylhydroxytoluene, phosphite, tert-butylhydroquinone, β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 2-tert-butyl-6-methylphenol, N,N'-di-β-naphthyl-p-phenylenediamine, dilauryl thiodipropionate, tris(nonylphenyl) phosphite, and triphenyl phosphite; and the crosslinking agent includes a compound containing at least two unsaturated groups;

[0058] The viscosity average molecular weight of the polymer powder is ≥1.2 million g / mol, and the degree of branching is ≤5%;

[0059] In the step of melting the mixture to obtain a melt, the mixture is mixed and melted at a temperature ranging from 160°C to 250°C, optionally from 190°C to 230°C.

[0060] When the polymer powder, lubricating oil, antioxidant, cross-linking agent and melting temperature are within the above ranges, the prepared isolation film has good puncture resistance.

[0061] The third aspect of the present application provides a secondary battery comprising the separator of any of the above solutions. When the secondary battery uses the separator provided by the present application, the reliability of the secondary battery can be improved.

[0062] In any embodiment of the present application, the secondary battery further includes a positive electrode sheet and a negative electrode sheet, and the separator is disposed between the positive electrode sheet and the negative electrode sheet, with the first porous base film facing the negative electrode sheet. When the secondary battery utilizes the separator provided by the present application, the risk of the separator being punctured by metal dendrites can be reduced, thereby increasing the cycle life and reliability of the secondary battery.

[0063] The fourth aspect of the present application provides an electrical device comprising the secondary battery of the second aspect of the present application. When the secondary battery of the electrical device uses the separator provided by the present application, the reliability of the electrical device can be improved.

[0064] Since the device of the present application includes the secondary battery provided by the present application, it has at least the same advantages as the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0066] FIG1 is a schematic structural diagram of an isolation membrane according to an embodiment of the present application.

[0067] FIG2 is a schematic structural diagram of another embodiment of the isolation membrane of the present application.

[0068] FIG3 is a schematic structural diagram of another embodiment of the isolation membrane of the present application.

[0069] FIG. 4 is a schematic diagram of an embodiment of a secondary battery.

[0070] FIG. 5 is an exploded view of FIG. 4 .

[0071] FIG. 6 is a schematic diagram of an embodiment of a battery module.

[0072] FIG. 7 is a schematic diagram of an embodiment of a battery pack.

[0073] FIG8 is an exploded view of FIG7 .

[0074] FIG. 9 is a schematic diagram of an embodiment of a device using a secondary battery as a power source. DETAILED DESCRIPTION

[0075] The present application will be further described below in conjunction with specific embodiments. It should be understood that these specific embodiments are only used to illustrate the present application and are not used to limit the scope of the present application.

[0076] For the sake of clarity, only some numerical ranges are specifically disclosed herein. However, any lower limit may be combined with any upper limit to form an unspecified range; and any lower limit may be combined with other lower limits to form an unspecified range, and similarly, any upper limit may be combined with any other upper limit to form an unspecified range. In addition, each individually disclosed point or single value may itself serve as a lower limit or upper limit and be combined with any other point or single value, or with other lower limits or upper limits, to form an unspecified range.

[0077] In the description herein, unless otherwise indicated, the term "or" is inclusive. That is, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0078] In the description of this article, it should be noted that, unless otherwise specified, “above” and “below” include the number itself, and “several” in “one or several” means two or more.

[0079] Unless otherwise specified, the terms used in this application have the commonly understood meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the various parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

[0080] secondary batteries

[0081] A secondary battery is a battery that can be recharged to activate the active materials after discharge and continue to be used.

[0082] Typically, a secondary battery consists of a positive electrode, a negative electrode, a separator, and an electrolyte. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The separator is placed between the positive and negative electrodes to provide isolation. The electrolyte conducts ions between the positive and negative electrodes.

[0083] [Isolation film]

[0084] Referring to FIG. 1 , an embodiment of the present application provides an isolation membrane 10 , including a first porous base membrane 11 . The first porous base membrane 11 is polyolefin, and the viscosity-average molecular weight of the first porous base membrane 11 is ≥1.2 million g / mol, and the degree of branching is ≤5%.

[0085] In some embodiments, the viscosity average molecular weight of the first porous base membrane 11 can be 1.2 million g / mol, 1.5 million g / mol, 1.8 million g / mol, 2 million g / mol, 2.1 million g / mol, 2.2 million g / mol, 2.5 million g / mol, 2.7 million g / mol, 2.75 million g / mol, 2.8 million g / mol, 3 million g / mol, 3.1 million g / mol, 3.2 million g / mol, 3.5 million g / mol, etc., or a range consisting of any two of the above values, for example, 1.2 million g / mol-3.2 million g / mol, 1 500,000 g / mol-1.8 million g / mol, 2 million g / mol-3 million g / mol, 2 million g / mol-2.2 million g / mol, 2.5 million g / mol-2.8 million g / mol, 3 million g / mol-3.5 million g / mol, or a range greater than or equal to the above values, for example, ≥1.2 million g / mol, ≥1.5 million g / mol, ≥1.8 million g / mol, ≥2 million g / mol, ≥2.5 million g / mol, ≥2.8 million g / mol, ≥3 million g / mol, ≥3.5 million g / mol, etc.

[0086] The viscosity average molecular weight of the base film has a well-known meaning in the art and can be measured using equipment and methods known in the art, for example, using a viscosity method.

[0087] In some embodiments, the degree of branching of the first porous base membrane 11 is 5%, 4.8%, 4.5%, 4.3%, 4%, 3.93%, 3.55%, 3%, 2.36%, 2%, 1.675%, 1.5%, 1.35%, 1.3%, 1.2%, 1.1%, 1.05%, 1%, 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.45%, 0.4%, 0.3%, 0.2%, 0.1%, 0.05%, 0.01%, 0.001%, etc., or more. The range consisting of any two of the above values ​​can be, for example, 5%-4.5%, 4.5%-3%, 2.36%-1.675%, 1.5%-1.2%, 1.5%-1%, 0.9%-0.5%, 0.6%-0.3%, 0.2%-0.001%, or it can be a range less than or equal to the above values, for example, it can be ≤5%, ≤4.8%, ≤4.5%, ≤2%, ≤1.5%, ≤1.1%, ≤1%, ≤0.7%, ≤0.5%, ≤0.2%, ≤0.001%, etc.

[0088] The degree of branching of the base film has a well-known meaning in the art and can be tested using equipment and methods known in the art. For example, infrared spectroscopy can be used. Specifically, the following steps can be followed: 3-5 groups of base film samples are selected and placed in an infrared spectrometer for scanning in the range of 400-4000 cm -1 After scanning, the infrared curve of the sample was processed and the 1377cm -1 The peak area at 1996-2062cm -1 The ratio of the peak areas is the degree of branching.

[0089] In the specific isolation membrane of the present application, the first porous base membrane 11 is polyolefin, and the viscosity-average molecular weight of the first porous base membrane 11 is ≥1.2 million g / mol, so that the isolation membrane has a high puncture resistance; since the branching degree of the first porous base membrane 11 is ≤5%, the molecular chain sequence in the first porous base membrane 11 is easy to form an ordered arrangement, which increases the regularity of the molecular chain and thereby improves the puncture resistance of the isolation membrane. Therefore, the isolation membrane provided by the present application can reduce the risk of the isolation membrane being punctured by metal dendrites, increase the cycle life of the secondary battery, and improve the reliability of the secondary battery.

[0090] In any embodiment of the present application, the viscosity-average molecular weight of the first porous base membrane 11 is ≥1.5 million g / mol, and can be optionally 2 million g / mol-3 million g / mol, so that the isolation membrane has a higher puncture resistance, which can reduce the risk of the isolation membrane being punctured by metal dendrites, increase the cycle life of the secondary battery, and improve the reliability of the secondary battery.

[0091] In any embodiment of the present application, the branching degree of the first porous base membrane 11 is ≤2%, and can be optionally ≤1%, so that the molecular chain sequence in the first porous base membrane 11 is more likely to form an ordered arrangement, thereby increasing the regularity of the molecular chain, and thereby improving the puncture resistance of the isolation membrane, which can reduce the risk of the isolation membrane being punctured by metal dendrites, increase the cycle life of the secondary battery, and improve the reliability of the secondary battery.

[0092] In any embodiment of the present application, the polymerization degree of the first porous base membrane 11 is ≥50,000, and can be optionally 80,000-200,000.

[0093] In some embodiments, the degree of polymerization of the first porous base membrane 11 may be 50000, 60000, 75000, 80000, 90000, 100000, 110000, 120000, 150000, 180000, 200000, 210000, 250000, 280000, 300000, 400000, 500000, or a range consisting of any two of the above values, for example, 50000-75000, 60000-9 0000, 80000-120000, 180000-180000, 200000-210000, 80000-200000, 280000-300000, 80000-500000, etc., and can also be a range greater than or equal to the above numerical values, for example, it can be ≥50000, ≥80000, ≥110000, ≥120000, ≥150000, ≥200000, ≥250000, ≥300000, ≥500000, etc.

[0094] In any embodiment of the present application, by limiting the degree of polymerization of the first porous base membrane 11, the isolation membrane has a higher puncture resistance, which can reduce the risk of the isolation membrane being punctured by metal dendrites, increase the cycle life of the secondary battery, and improve the reliability of the secondary battery.

[0095] The degree of polymerization of the base film has a well-known meaning in the art and can be measured using equipment and methods known in the art. For example, the degree of polymerization can be calculated based on the molecular weight of the material, where the molecular weight of the material is denoted as m and the relative molecular mass of a single chain link is denoted as m0, and the degree of polymerization n = m / m0.

[0096] In any embodiment of the present application, the crystallinity of the first porous base membrane 11 is 40%-90%, and can be optionally 75%-85%.

[0097] In some embodiments, the crystallinity of the first porous base membrane 11 can be 40%, 45%, 48%, 50%, 55%, 60%, 68%, 70%, 75%, 77.5%, 80%, 85%, 90%, etc., or a range consisting of any two of the above values, for example, it can be 40%48%, 45%-50%, 55%-70%, 75%-85%, 60%-80%, 75%-90%, etc.

[0098] In any embodiment of the present application, by limiting the crystallinity of the first porous base membrane 11, the isolation membrane has a higher puncture resistance, which can reduce the risk of the isolation membrane being punctured by metal dendrites, increase the cycle life of the secondary battery, and improve the reliability of the secondary battery.

[0099] The crystallinity of the base film can be tested using equipment and methods known in the art. Specifically, 4-6 mg of the sample to be tested is placed in the sample chamber of a differential scanning calorimeter. The temperature is raised from 25°C to 350°C at a rate of 10°C / min. The melting endotherm curve is obtained. The crystallinity is then calculated by comparing the peak area of ​​the curve with a reference value of 100% crystalline polyolefin.

[0100] Crystallinity indicates the proportion of crystalline regions within the base film material. Crystallinity is the orderly arrangement of molecular chains, forming a molecular chain. Generally, the higher the crystallinity, the more regular the molecular chain arrangement.

[0101] In any embodiment of the present application, the puncture strength of the first porous base membrane 11 is ≥300 gf, and can be optionally 350 gf-450 gf.

[0102] In some embodiments, the puncture strength of the first porous base film 11 can be 300gf, 310gf, 320gf, 340gf, 345gf, 350gf, 380gf, 390gf, 400gf, 410gf, 430gf, 435gf, 450gf, 470gf, 480gf, 490gf, 500gf, etc., or a range consisting of any two of the above values. For example, The range may be 300gf-340gf, 310gf-435gf, 350gf-480gf, 350gf-450gf, 400gf-430gf, 470gf-500gf, etc., and may also be a range greater than or equal to the above values, for example, ≥300gf, ≥350gf, ≥400gf, ≥410gf, ≥435gf, ≥450gf, ≥500gf, etc.

[0103] In any embodiment of the present application, by limiting the puncture strength of the first porous base membrane 11, the risk of the separator being punctured by metal dendrites can be reduced, the cycle life of the secondary battery can be increased, and the reliability of the secondary battery can be improved.

[0104] The puncture strength of the basement membrane has a meaning well known in the art and can be tested using equipment and methods known in the art. For example, the puncture strength can be tested according to the standard: GB / T 10004-2008. Specifically, the sample to be tested can be cut into strips, wherein the width of the strip sample is 100 mm. A test piece with a width of 100 mm is mounted on a sample membrane fixing clamp ring, and then a steel needle with a diameter of 1.0 mm and a radius of 0.5 mm at the top is used to puncture at a speed of (50±5) mm / min, and the maximum load of the steel needle penetrating the test piece is read. Usually, 5 parallel test samples can be taken at the same time, 3 points are measured for each test sample, and the arithmetic mean is taken as the final puncture strength.

[0105] In any embodiment of the present application, the thickness of the first porous base membrane 11 is 1 μm-12 μm, and can be optionally 3 μm-6 μm.

[0106] In some embodiments, the thickness of the first porous base membrane 11 can be 1μm, 1.2μm, 1.6μm, 2μm, 2.8μm, 3μm, 4μm, 5μm, 5.6μm, 6μm, 6.345μm, 7μm, 8μm, 9μm, 9.6μm, 10μm, 10.5μm, 11μm, 11.5μm, 12μm, etc., or a range consisting of any two of the above values, for example, it can be 1μm-1.2μm, 1.6μm-4μm, 3μm-6μm, 5μm-5.6μm, 8μm-11.5μm, 6μm-9.6μm, 10μm-12μm, etc.

[0107] In any embodiment of the present application, by limiting the thickness of the first porous base membrane 11, the risk of the separator being punctured by metal dendrites can be reduced, the cycle life of the secondary battery can be increased, and the reliability of the secondary battery can be improved.

[0108] The thickness of the base film can be measured using equipment and methods known in the art. For example, a thickness gauge can be used to measure the base film thickness. Specifically, the following method can be used: six sets of parallel samples are taken, and the thickness of each set of samples is measured at different locations using a micrometer thickness gauge. At least 20 points are measured for each set of samples, and the average thickness of the six sets of samples is taken as the base film thickness.

[0109] In any embodiment of the present application, the porosity of the first porous base membrane 11 is 20%-50%, and can be optionally 30%-40%.

[0110] In some embodiments, the porosity of the first porous base membrane 11 can be 20%, 22%, 23.5%, 25%, 25.2%, 27.5%, 30%, 33%, 38.5%, 40%, 41%, 45%, 48%, 50%, etc., or a range consisting of any two of the above values, for example, it can be 20%-25%, 22%-41%, 25.2%-27.5%, 30%-40%, 30%-48%, 33%-40%, 45%-50%, etc.

[0111] In any embodiment of the present application, by limiting the porosity of the first porous base membrane 11, the risk of the separator being punctured by metal dendrites can be reduced, the cycle life of the secondary battery can be increased, and the reliability of the secondary battery can be improved.

[0112] The porosity of the base film is well known in the art and can be tested using equipment and methods known in the art. For example, the porosity of the base film can be tested using a mercury porosimeter in accordance with GB / T 21650.1-2008.

[0113] In any embodiment of the present application, the air permeability of the first porous base membrane 11 is 100 sec / 100 cc-300 sec / 100 cc, and can be optionally 200 sec / 100 cc-300 sec / 100 cc, which can make the isolation membrane have a better ion permeability.

[0114] In any embodiment of the present application, the number average molecular weight of the first porous base membrane 11 is ≥ 1.4 million, and can be selected from 1.6 million to 2.4 million.

[0115] In some embodiments, the number average molecular weight of the first porous base membrane 11 can be 1.4 million, 1.5 million, 1.6 million, 1.8 million, 2 million, 2.15 million, 2.4 million, 2.5 million, 2.8 million, 3 million, 3.4 million, 3.8 million, etc., or a range consisting of any two of the above values, for example, it can be 1.4 million-2.5 million, 1.5 million-2 million, 1.6 million-2.4 million, 2.15 million-2.8 million, 1.8 million-3 million, 3.4 million-3.8 million, etc., or it can be a range greater than or equal to the above values, for example, it can be ≥1.4 million, ≥1.8 million, ≥2.5 million, ≥3 million, ≥3.8 million, etc.

[0116] In any embodiment of the present application, by limiting the number average molecular weight of the first porous base membrane 11 , the separator has a higher puncture resistance, thereby increasing the cycle life of the secondary battery and improving the reliability of the secondary battery.

[0117] In any embodiment of the present application, the weight average molecular weight of the first porous base membrane is ≥1 million g / mol, and can be optionally 1.2 million g / mol-2 million g / mol, so that the isolation membrane has higher puncture resistance, increases the cycle life of the secondary battery, and improves the reliability of the secondary battery.

[0118] In some embodiments, the weight-average molecular weight of the first porous base membrane 11 can be 1 million g / mol, 1.2 million g / mol, 1.5 million g / mol, 1.7 million g / mol, 2 million g / mol, 2.2 million g / mol, 2.5 million g / mol, 2.75 million g / mol, 3 million g / mol, 4 million g / mol, etc., or a range consisting of any two of the above values, for example, it can be 1 million g / mol-2.2 million g / mol, 1.2 million g / mol-2 million g / mol, 1.5 million g / mol-2.5 million g / mol, 2 million g / mol-4 million g / mol, etc., or it can be a range greater than or equal to the above values, for example, it can be ≥1 million g / mol, ≥1.7 million g / mol, ≥2 million g / mol, ≥2.5 million g / mol, ≥3 million g / mol, ≥4 million g / mol, etc.

[0119] In any embodiment of the present application, by limiting the weight average molecular weight of the first porous base membrane 11 , the separator has a higher puncture resistance, thereby increasing the cycle life of the secondary battery and improving the reliability of the secondary battery.

[0120] 2 , in any embodiment of the present application, the isolation membrane further comprises a porous coating layer 13 , which is disposed on at least one surface of the first porous base membrane 11 and includes a binder; alternatively, the porous coating layer 13 includes a binder and filler particles.

[0121] Providing the porous coating layer 13 on the first porous base film 11 can improve the heat resistance and puncture resistance of the separator, increase the cycle life of the secondary battery, and improve the reliability of the secondary battery.

[0122] Referring to Figure 3, in any embodiment of the present application, the isolation membrane further includes a porous coating layer 13 and a second porous base membrane 12, and the porous coating layer 13 is located between the first porous base membrane 11 and the second porous base membrane 12; optionally, the porous coating layer 13 includes a binder; more optionally, the porous coating layer 13 includes a binder and filler particles.

[0123] The first porous base film 11 and the second porous base film 12 can be directly laminated by hot pressing. During the hot pressing process, if the temperature is too high, the porosity will be small and the air permeability will be poor; if the temperature is too low, the first porous base film 11 and the second porous base film 12 will not be firmly bonded. Therefore, it is necessary to adjust the hot pressing temperature appropriately. Optionally, the hot pressing temperature is 20°C-50°C.

[0124] When a porous coating layer 13 is provided between the first porous base membrane 11 and the second porous base membrane 12, it can not only compensate for process defects of the base membrane during the hot pressing composite process, but also further improve the physical property stability of the isolation membrane, thereby improving the reliability of the secondary battery.

[0125] In some embodiments, the filler particles include at least one of inorganic particles, organic particles, and organic-metal framework materials.

[0126] Optionally, the inorganic particles include one or more of inorganic particles having a dielectric constant of 5 or greater, inorganic particles having ion conductivity but not storing ions, and inorganic particles capable of undergoing electrochemical reactions.

[0127] Alternatively, the inorganic particles having a dielectric constant of 5 or more may 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, magnesium aluminum silicate, lithium magnesium silicate, sodium magnesium silicate, bentonite, hectorite, zirconium titanate, barium titanate, Pb(Zr,Ti)O3 (abbreviated as PZT), Pb 1-m La m Zr 1-n Ti n O3 (abbreviated as PLZT, 0<m<1, 0<n<1), Pb(Mg3Nb 2 / 3 )O3-PbTiO3 (abbreviated as PMN-PT), and at least one of their respective modified inorganic particles. Optionally, the modification method of each inorganic particle may be chemical modification and / or physical modification. Chemical modification methods include coupling agent modification (for example, using silane coupling agent, titanate coupling agent, etc.), surfactant modification, polymer grafting modification, etc. Physical modification methods may be mechanical force dispersion, ultrasonic dispersion, high energy treatment, etc. The modification treatment can reduce the agglomeration of inorganic particles, thereby enabling the bonding layer to have a more stable and uniform structure; in addition, by selecting a coupling agent, surfactant or polymer with a specific functional group to modify the inorganic particles, it is also helpful to improve the bonding layer's wetting and retention properties for the electrolyte, and improve the bonding layer's adhesion to the first porous base membrane 11 and the second porous base membrane 12.

[0128] Alternatively, inorganic particles having ion conductivity but not storing ions may include Li3PO4, lithium titanium phosphate, Li x1 Ti y1 (PO4)3, lithium aluminum titanium phosphate Li x2 Al y2 Ti z1 (PO4)3, (LiAlTiP) x3 Oy3 Type glass, lanthanum lithium titanate Li x4 La y4 TiO3, lithium germanium thiophosphate Li x5 Ge y5 P z2 S w , lithium nitride Li x6 N y6 、SiS2 type glass Li x7 Si y7 S z3 and P2S5 glass Li x8 P y8 S z4 At least one of the following: 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. This can further improve the ion conductivity of the isolation membrane.

[0129] Alternatively, the inorganic particles capable of undergoing electrochemical reaction may include at least one of lithium-containing transition metal oxides, lithium-containing phosphates, carbon-based materials, silicon-based materials, tin-based materials, and lithium-titanium compounds.

[0130] Alternatively, the organic particles may include one or more of polycarbonate, polythiophene, polypyridine, polystyrene, polyacrylic wax, polyethylene, polypropylene, cellulose, a cellulose modifier (e.g., carboxymethyl cellulose), a melamine resin, a phenolic resin, a polyester (e.g., polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate), a silicone resin, a polyimide, a polyamideimide, a polyaromatic amide, polyphenylene sulfide, a polysulfone, a polyethersulfone, a polyetheretherketone, a polyaryletherketone, a copolymer of butyl acrylate and ethyl methacrylate (e.g., a cross-linked polymer of butyl acrylate and ethyl methacrylate).

[0131] Optionally, the organic-metal framework material may include one or more of a nitrogen-containing heterocyclic ligand building structure, an organic carboxylic acid ligand building structure, and a nitrogen-oxygen mixed ligand building structure.

[0132] In any embodiment of the present application, the binder includes one or more of polyacrylate, polyacrylic acid, polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride-trichloroethylene copolymer, polyvinyl pyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyethylene oxide, polyarylate, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, polyacrylonitrile, polyvinyl alcohol, polyethylene, polypropylene, starch, and cyanoethyl pullulan; and / or the filler particles include at least one of inorganic particles, organic particles, and organic-metal framework materials. When the binder and / or filler particles in the porous coating layer 13 include the above components, the reliability of the secondary battery can be improved.

[0133] In some embodiments, the porous coating layer 13 may further include a dispersant, such as carboxymethyl cellulose, so as to adjust the viscosity of the porous coating layer 13 slurry and improve the quality and uniformity of the porous coating layer 13 .

[0134] In any embodiment of the present application, the viscosity average molecular weight of the first porous base membrane 11 is greater than the viscosity average molecular weight of the second porous base membrane 12; optionally, the viscosity average molecular weight of the second porous base membrane 12 is 100,000 g / mol-2,000,000 g / mol, and more optionally 300,000 g / mol-800,000 g / mol.

[0135] In some embodiments, the viscosity average molecular weight of the second porous base membrane 12 can be 100,000 g / mol, 200,000 g / mol, 300,000 g / mol, 360,000 g / mol, 400,000 g / mol, 500,000 g / mol, 550,000 g / mol, 600,000 g / mol, 800,000 g / mol, 850,000 g / mol, 1,000,000 g / mol, 1,200,000 g / mol, 1,400,000 g / mol, 1,500,000 g / mol, 1,600,000 g / mol, 1,750,000 g / mol, 1,800,000 g / mol, 1,900,000 g / mol. / mol, 2 million g / mol, etc., or a range consisting of any two of the above values, for example, 100,000 g / mol-300,000 g / mol, 360,000 g / mol-850,000 g / mol, 300,000 g / mol-800,000 g / mol, 550,000 g / mol-1.2 million g / mol, 1 million g / mol-1.5 million g / mol, 1.6 million g / mol-1.75 million g / mol, 1.4 million g / mol-1.8 million g / mol, 1.9 million g / mol-2 million g / mol, etc.

[0136] When the viscosity average molecular weight of the second porous base film 12 is within the above range, the physical properties of the separator can be improved and stabilized, thereby improving the reliability of the secondary battery.

[0137] In any embodiment of the present application, the degree of branching of the first porous base membrane 11 is less than that of the second porous base membrane 12 ; optionally, the degree of branching of the second porous base membrane 12 is ≤90%, more optionally ≤40%.

[0138] In some embodiments, the degree of branching of the second porous base membrane 12 can be 0.1%, 5%, 8%, 10%, 18%, 20%, 30%, 40%, 45%, 50%, 53%, 60%, 70%, 80%, 85%, 90%, etc., or a range consisting of any two of the above values, for example, it can be 0.1%-5%, 5%-50%, 10%-20%, 30%-85%, 53%-60%, 8%-70%, 80%-90%, etc., and can also be a range less than or equal to the above values, for example, it can be ≤0.1%, ≤5%, ≤8%, ≤10%, ≤20%, ≤30%, ≤40%, ≤45%, ≤50%, ≤60%, ≤70%, ≤80%, ≤90%, etc.

[0139] When the branching degree of the second porous base membrane is within the above range, the physical properties of the separator can be improved and stabilized, thereby improving the reliability of the secondary battery.

[0140] In any embodiment of the present application, the degree of polymerization of the first porous base membrane 11 is greater than that of the second porous base membrane 12 , and the degree of polymerization of the second porous base membrane 12 is ≤8000, and can be optionally 400-1000.

[0141] In some embodiments, the degree of polymerization of the second porous base membrane 12 may be 100, 150, 200, 280, 300, 400, 600, 700, 780, 800, 850, 900, 1000, 1500, 1750, 2000, 3000, 5000, 5600, 6000, 6500, 6800, 7000, 7500, 7850, 8000, etc., or a range consisting of any two of the above values, for example, 100-300, 400-900, 600-700, 780-6800, 400-1000, 850-1750, 1500-6000, 3000-5000, 5600-6500, 200-7000, 2000-7500, 7850-8000, etc., and can also be a range less than or equal to the above values, for example, it can be ≤100, ≤280, ≤300, ≤800, ≤1000, ≤1500, ≤3000, ≤5600, ≤6000, ≤7000, ≤8000, etc.

[0142] When the degree of polymerization of the second porous base film is within the above range, the physical properties of the separator can be improved and stabilized, thereby improving the reliability of the secondary battery.

[0143] In any embodiment of the present application, the melting point of the first porous base membrane 11 is lower than the melting point of the second porous base membrane 12; optionally, the melting point of the second porous base membrane 12 is 160°C-350°C, and more optionally 170°C-320°C.

[0144] In some embodiments, the melting point of the second porous base membrane 12 can be 160°C, 170°C, 175°C, 180°C, 195°C, 200°C, 215°C, 220°C, 235°C, 250°C, 265°C, 280°C, 300°C, 310°C, 315°C, 320°C, 330°C, 340°C, 350°C, etc., or a range consisting of any two of the above values, for example, it can be 160°C-180°C, 200°C-315°C, 235°C-250°C, 265°C-300°C, 175°C-330°C, 170°C-320°C, 195°C-340°C, 330°C-350°C, etc.

[0145] In any embodiment of the present application, by limiting the melting points of the first porous base membrane 11 and the second porous base membrane 12 , the heat resistance and puncture resistance of the separator are improved, thereby improving the reliability of the secondary battery.

[0146] The melting points of the first porous base membrane 11 and the second porous base membrane 12 can be tested using equipment and methods known in the art. For example, differential scanning calorimetry can be used for measurement. For details, reference can be made to the standard GB / T 19466.3-2004. As an example, the measurement can be performed as follows: 4 mg to 6 mg of the sample to be tested is placed in the sample chamber of a differential scanning calorimeter. The temperature is raised from 25°C to 400°C at a rate of 10°C / min. The melting endothermic curve of the sample is obtained, and the temperature corresponding to the peak of the curve is the melting point of the sample.

[0147] In any embodiment of the present application, the crystallinity of the first porous base membrane 11 is greater than that of the second porous base membrane 12 . Optionally, the crystallinity of the second porous base membrane 12 is 20%-70%, and more preferably 30%-45%.

[0148] In some embodiments, the crystallinity of the second porous base membrane 12 can be 20%, 28%, 30%, 32%, 35.5%, 40%, 45.2%, 57.5%, 50%, 53%, 56.5%, 60%, 61%, 65%, 68%, 70%, etc., or a range consisting of any two of the above values, for example, it can be 20%-56.5%, 30%-40%, 45.2%-68%, 50%-60%, 61%-70%, etc.

[0149] In any embodiment of the present application, the puncture strength of the first porous base membrane 11 is greater than the puncture strength of the second porous base membrane 12;

[0150] Optionally, the ratio of the puncture strength of the first porous base membrane 11 to the puncture strength of the second porous base membrane 12 is ≥2.5;

[0151] Optionally, the puncture strength of the second porous base film 12 is ≥70 gf, and more preferably 100 gf-300 gf.

[0152] In some embodiments, the ratio of the puncture strength of the first porous base membrane 11 to the puncture strength of the second porous base membrane 12 can be 2.5, 2.8, 3.0, 3.252, 3.35, 3.5, 3.85, 4.0, 4.5, 5, etc., or a range consisting of any two of the above values, for example, it can be 2.5-4.0, 3.0-3.35, 2.8-3.5, 3.85-5, etc., or it can be a range greater than or equal to the above values, for example, it can be ≥2.5, ≥3.0, ≥3.5, ≥4.0, ≥4.5, ≥5, etc.

[0153] In some embodiments, the puncture strength of the second porous base membrane 12 can be 70gf, 80gf, 100gf, 150gf, 170gf, 195gf, 200gf, 227gf, 250gf, 300gf, 332gf, 350gf, 400gf, 450gf, etc., or a range consisting of any two of the above values, for example, it can be 70gf-170gf, 80gf-227gf, 100gf-300gf, 195gf-332gf, 250gf-400gf, 300gf-450gf, etc.

[0154] In any embodiment of the present application, the second porous base membrane 12 includes at least one of polyolefin, polytetrafluoroethylene, polyvinyl fluoride, polyethylene terephthalate, polyimide, and polyetheretherketone.

[0155] In any embodiment of the present application, the isolation film satisfies at least one of the following (1)-(4):

[0156] (1) The transverse elongation at break of the separator is ≥80%, optionally ≥100%, and more preferably 100%-300%;

[0157] (2) The longitudinal elongation at break of the separator is ≥40%, optionally ≥60%, and more preferably 60%-200%;

[0158] (3) Transverse tensile strength of the separator ≥1500kgf / cm 2 , can be selected as ≥2000kgf / cm 2 , 2000kgf / cm2 is optional 2 -4000kgf / cm 2 ;

[0159] (4) The longitudinal tensile strength of the isolation film is ≥1500kgf / cm 2 , can be selected as ≥2000kgf / cm 2 , 2000kgf / cm2 is optional 2 -4000kgf / cm 2 .

[0160] When the isolation membrane satisfies at least one of the above (1)-(4) and meets the above range, the risk of the isolation membrane being punctured by metal dendrites can be reduced, the cycle life of the secondary battery can be increased, and the reliability of the secondary battery can be improved.

[0161] The air permeability, transverse tensile strength (MD), longitudinal tensile strength (TD), transverse elongation at break, and longitudinal elongation at break of the separator have well-known meanings in the art and can be measured using methods known in the art. For example, they can be tested in accordance with standard GB / T 36363-2018.

[0162] The present application provides a method for preparing the aforementioned isolation membrane, comprising:

[0163] mixing polymer powder with lubricating oil, antioxidant and cross-linking agent to obtain a mixture, and melting the mixture to obtain a melt;

[0164] Casting the melt, stretching, and extracting lubricating oil to obtain a first porous base film, wherein the separator includes the first porous base film;

[0165] The first porous base membrane is polyolefin, the viscosity average molecular weight of the first porous base membrane is ≥1.2 million g / mol, and the branching degree of the first porous base membrane is ≤5%.

[0166] When the preparation method of the isolation membrane provided in the present application is adopted, the isolation membrane provided in the present application can be prepared. The isolation membrane provided in the present application can reduce the risk of the isolation membrane being punctured by metal dendrites, increase the cycle life of the secondary battery, and improve the reliability of the secondary battery.

[0167] In any embodiment of the present application, the preparation method satisfies at least one of the following (1)-(4):

[0168] (1) The mass fraction of the polymer powder in the mixture is 5%-40%, and can be optionally 20%-35%;

[0169] (2) The mass fraction of the lubricating oil in the mixture is 50%-90%, and can be optionally 60%-75%;

[0170] (3) The mass fraction of the antioxidant in the polymer powder is 0.3%-1.0%, and can be optionally 0.5%-1.0%;

[0171] (4) The mass fraction of the cross-linking agent in the polymer powder is 3%-10%, and can be optionally 3%-5%.

[0172] When the polymer powder, lubricating oil, antioxidant and cross-linking agent are within the above ranges, the prepared isolation membrane has good puncture resistance.

[0173] In any embodiment of the present application, the preparation method satisfies at least one of the following (1)-(3):

[0174] (1) The polymer powder includes polyolefin powder; the lubricating oil includes white oil and / or mineral oil; the antioxidant includes at least one of 4,4-thiobis(6-tert-butyl-m-cresol), dibutylhydroxytoluene, phosphite, tert-butylhydroquinone, β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 2-tert-butyl-6-methylphenol, N,N'-di-β-naphthyl-p-phenylenediamine, dilauryl thiodipropionate, tris(nonylphenyl) phosphite, and triphenyl phosphite; the crosslinking agent includes a compound containing at least two unsaturated groups;

[0175] (2) The viscosity-average molecular weight of the polymer powder is ≥1.2 million g / mol, and the degree of branching is ≤5%;

[0176] (3) In the step of melting the mixture to obtain a melt, the mixture is mixed and melted at a temperature ranging from 160°C to 250°C, optionally from 190°C to 230°C.

[0177] When the polymer powder, lubricating oil, antioxidant, cross-linking agent and melting temperature are within the above ranges, the prepared isolation film has good puncture resistance.

[0178] In some embodiments, the polymer powder comprises polyolefin powder.

[0179] In some embodiments, the lubricating oil may include white oil and / or mineral oil. Alternatively, the mineral oil may include paraffin oil. Alternatively, the mineral oil may include at least one of white oil, paraffin oil, kerosene, and dioctyl phthalate.

[0180] In some embodiments, the antioxidant includes at least one of 4,4-thiobis(6-tert-butyl-m-cresol), dibutylhydroxytoluene, phosphite, tert-butylhydroquinone, β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 2-tert-butyl-6-methylphenol, N,N'-di-β-naphthyl-p-phenylenediamine, dilauryl thiodipropionate, tris(nonylphenyl) phosphite, and triphenyl phosphite.

[0181] In some embodiments, the crosslinking agent includes a compound containing at least two unsaturated groups. Alternatively, the crosslinking agent includes one or more of divinylbenzene, ethylene glycol dimethacrylate (EGDMA), divinyl ether, diethylene glycol divinyl ether, glycerol dimethacrylate, 1,6-hexanediol dimethacrylate, triallyl isocyanate, and trimethylolpropane trimethacrylate.

[0182] Optionally, the mixture may further include other components, such as a plasticizer, an extractant, and an additive for improving pore formation uniformity.

[0183] The present application provides three specific embodiments of methods for preparing isolation membranes, which are used to prepare the isolation membranes of any of the above embodiments.

[0184] The first preparation method of the isolation membrane: select polymer powder with a viscosity-average molecular weight ≥1.2 million g / mol and a degree of branching ≤5%, and add lubricating oil, antioxidant and cross-linking agent into a mixer in a certain proportion and mix evenly, wherein the polymer powder accounts for 5%-40% of the total mass, and can be optionally 20%-35%; the lubricating oil accounts for 50%-90% of the total mass, and can be optionally 60%-75%; the antioxidant is added to 0.3%-1.0% of the mass of the polymer powder, and can be optionally 0.5%-1.0%; the cross-linking agent is added to 3%-10% of the polymer powder, and can be optionally 3%-5%; the mixture is added to a twin-screw extruder in the temperature range of 160℃-250℃, and is fully mixed and melted to form a homogeneous melt. After the cast sheet is prepared through the die outlet, the cast sheet is stretched horizontally and longitudinally by roller calendering, and the mineral oil is extracted through a solvent tank to finally obtain a porous isolation membrane.

[0185] In some embodiments, the mixture is added to a twin-screw extruder at a temperature ranging from 160°C to 250°C for thorough mixing and melting, and the temperature may be 190°C to 230°C.

[0186] A second method for preparing a separator includes providing a first porous base membrane according to the first method; providing a coating slurry, the coating slurry including a binder; and coating the coating slurry on at least one surface of the first porous base membrane. Optionally, the coating slurry includes both the binder and filler particles.

[0187] A third method for preparing a separator includes providing a first porous base membrane according to the first method; providing a second porous base membrane; and laminating the first and second porous base membranes. Optionally, the method further includes providing a coating slurry comprising a binder, applying the coating slurry to a surface of the first and / or second porous base membranes, and laminating the two porous base membranes. More preferably, the coating slurry comprises a binder and filler particles.

[0188] The present application also provides a secondary battery comprising the separator of any of the above solutions. When the secondary battery uses the separator provided by the present application, the reliability of the secondary battery can be improved.

[0189] In any embodiment of the present application, the secondary battery further includes a positive electrode sheet and a negative electrode sheet, a separator is disposed between the positive electrode sheet and the negative electrode sheet, and the first porous base film 11 faces the negative electrode sheet. When the secondary battery uses the separator provided by the present application, the risk of the separator being punctured by metal dendrites can be reduced, thereby increasing the cycle life of the secondary battery and improving the reliability of the secondary battery.

[0190] [Positive electrode]

[0191] In a secondary battery, a positive electrode sheet generally includes a positive electrode current collector and a positive electrode film layer disposed on the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0192] The positive electrode current collector may be a conventional metal foil or a composite current collector (a metal material may be disposed on a polymer substrate to form a composite current collector). As an example, the positive electrode current collector may be an aluminum foil.

[0193] There is no limitation on the specific type of the positive electrode active material. Active materials known in the art that can be used for the positive electrode of a secondary battery can be used. Those skilled in the art can select according to actual needs.

[0194] As an example, the positive electrode active material may include, but is not limited to, one or more of lithium transition metal oxides, olivine-structured lithium-containing phosphates, and their respective modified compounds. 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 olivine-structured lithium-containing phosphates may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon, and their modified compounds. These materials can all be obtained through commercial channels.

[0195] The modified compounds of the above materials may be doping-modified and / or surface-coated modified materials.

[0196] The positive electrode film layer usually optionally includes a binder, a conductive agent and other optional additives.

[0197] As an example, the conductive agent may be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, conductive carbon black (Super P, SP), graphene, and carbon nanofibers.

[0198] As an example, the binder can be one or more of styrene butadiene rubber (SBR), water-based acrylic resin, polyvinylidene difluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA) and polyvinyl butyral (PVB).

[0199] [Negative electrode]

[0200] In a secondary battery, a negative electrode plate generally includes a negative electrode current collector and a negative electrode film layer disposed on the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0201] The negative electrode current collector may be a conventional metal foil or a composite current collector (for example, a metal material may be disposed on a polymer substrate to form a composite current collector). As an example, the negative electrode current collector may be a copper foil.

[0202] The specific type of negative electrode active material is not limited, and active materials that can be used for the negative electrode of a secondary battery known in the art can be used, and those skilled in the art can make a selection according to actual needs. As an example, the negative electrode active material may include, but is not limited to, one or more of artificial graphite, natural graphite, hard carbon, soft carbon, silicon-based materials and tin-based materials. Silicon-based materials can be selected from one or more of elemental silicon, silicon oxides (such as silicon monoxide), silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials can be selected from one or more of elemental tin, tin oxides, and tin alloys. These materials can all be obtained commercially.

[0203] In some embodiments, to further increase the energy density of the battery, the negative electrode active material may include a silicon-based material.

[0204] The negative electrode film layer usually optionally includes a binder, a conductive agent and other optional auxiliary agents.

[0205] As an example, the conductive agent may be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0206] As an example, the binder may be one or more of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyvinyl alcohol (PVA) and polyvinyl butyral (PVB).

[0207] As an example, other optional auxiliary agents may be thickening and dispersing agents (such as carboxymethylcellulose sodium, CMC-Na), and PTC thermistor materials.

[0208] [Electrolyte]

[0209] Secondary batteries may include an electrolyte that conducts ions between a positive electrode and a negative electrode. The electrolyte may include an electrolyte salt and a solvent.

[0210] As an example, the electrolyte salt can be selected from one or more of 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 difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalatophosphate) (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0211] As an example, the solvent may be selected from ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl darbonate (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), n-propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), n-propyl propionate (NP), propylene glycol (PEG), propylene glycol (PP), propylene glycol (C1), propylene glycol (C2), propylene glycol (C3), propylene glycol (C4), propylene glycol (C5), propylene glycol (C6), propylene glycol (C7), propylene glycol (C8), propylene glycol (C9), propylene glycol (D1), propylene glycol (D2), propylene glycol (D3), propylene glycol (D4), propylene glycol (D5), propylene glycol (D6), propylene glycol (D7), propylene glycol (D8), propylene glycol (D9), propylene glycol (D10), propylene glycol (D11), propylene glycol (D12), propylene glycol (D13), propylene glycol (D14), propylene glycol (D15), propylene glycol (D16), propylene glycol (D17), propylene glycol (D18), propylene glycol (D19), propylene glycol (D20), propylene glycol (D21), propylene glycol (D22), propylene glycol (D23), propylene glycol (D24), propylene glycol (D25), propylene glycol (D26), propylene glycol (D27), propylene glycol (D28), propylene glycol (D29), propylene glycol (D31), propylene glycol (D32), propylene glycol (D33), propylene glycol (D34), propylene glycol (D35), propylene glycol (D36), propylene glycol (D37), propylene glycol (D38), propylene glycol (D39), propylene One or more of the group consisting of propionate (PP), methyl butyrate (Methyl Butyrate MB), ethyl butyrate (Ethyl Butyrate, EB), 1,4-butyrolactone (1,4-Butyrolactone, GBL), tetramethylene sulfone (SF), dimethyl sulfone (Methyl Sulfone, MSM), methyl ethyl sulfone (Methyl Ethyl Sulfone, EMS) and diethyl sulfone (Diethyl Sulfone, ESE).

[0212] In some embodiments, the electrolyte further includes additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives capable of improving certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature performance.

[0213] The embodiment of the present application has no particular limitation on the shape of the secondary battery, which can be cylindrical, square, or any other shape. FIG4 shows a secondary battery 5 with a square structure as an example.

[0214] In some embodiments, the secondary battery may include an outer packaging for encapsulating the positive electrode sheet, the negative electrode sheet, and the electrolyte.

[0215] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0216] In some embodiments, referring to FIG5 , the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, which together form a receiving cavity. The housing 51 may have an opening communicating with the receiving cavity, and the cover 53 may be positioned over the opening to seal the receiving cavity.

[0217] The preparation method of the secondary battery of the present application is well known. In some embodiments, the positive electrode sheet, the separator 10, the negative electrode sheet and the electrolyte can be assembled to form a secondary battery. As an example, the positive electrode sheet, the separator 10, and the negative electrode sheet can be formed into an electrode assembly through a winding process and / or a lamination process, and the electrode assembly is placed in an outer package, dried and injected with electrolyte, and then vacuum packaged, allowed to stand, formed, and shaped to obtain a battery cell. Multiple battery cells can also be further connected in series, in parallel, or mixed to form a battery module. Multiple battery modules can also be connected in series, in parallel, or mixed to form a battery pack. In some embodiments, multiple battery cells can also directly form a battery pack.

[0218] Figure 6 shows an example battery module 4. Referring to Figure 6 , within the battery module 4, multiple secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the multiple secondary batteries 5 may be secured using fasteners.

[0219] The battery module 4 may further include a housing having a housing space, and the plurality of secondary batteries 5 may be housed in the housing space.

[0220] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0221] Figures 7 and 8 illustrate an example battery pack 1. Referring to Figures 7 and 8 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be positioned over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0222] [Installation]

[0223] FIG9 is an example of an electric device. The present application also provides an electric device 100, which includes the secondary battery provided in the present application. When the secondary battery of the electric device 100 uses the separator provided in the present application, the reliability of the electric device can be improved.

[0224] Battery cells, modules, or packs can serve as both a power source and an energy storage unit for a device. These devices include, but are not limited to, mobile devices (e.g., cell phones, laptops), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks), electric trains, ships, satellites, and energy storage systems.

[0225] The device can select battery cells, battery modules or battery packs according to its usage requirements.

[0226] The electric device 100 may be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or a battery module may be used.

[0227] As another example, the electric device 100 may be a mobile phone, a tablet computer, or a notebook computer. The electric device 100 is generally required to be lightweight and thin, and may use a battery cell as a power source.

[0228] The beneficial effects of the present application are further illustrated below with reference to the examples.

[0229] In order to make the technical problems, technical solutions and beneficial effects solved by the embodiments of the present application clearer, the following will be further described in detail with reference to the embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present application and its applications. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0230] Preparation of isolation membrane

[0231] The first porous base film serves as an isolation membrane:

[0232] (1) Isolation film 1:

[0233] A first porous base membrane is provided, and the first porous base membrane meets the following requirements: the material is polyethylene (PE), the viscosity-average molecular weight is 1.2 million g / mol, and the degree of branching is 1.6%. The first porous base membrane is sample 1 prepared using process 1. In process 1, the antioxidant ratio is 0.3%, the cross-linking agent ratio is 8%, and the casting processing temperature is 230°C.

[0234] Isolation membrane 2-7 is similar to isolation membrane 1, except that the viscosity-average molecular weight and degree of branching of the first porous base membrane are adjusted. The first porous base membrane of isolation membrane 2-7 is sample 2-7 prepared using process 2-7. Process 2-7 is similar to process 1, except that the antioxidant ratio, cross-linking agent ratio and / or casting processing temperature are adjusted.

[0235] Separator membranes 8-9 are similar to Example 1, except that the viscosity-average molecular weight and degree of branching of the first porous base membrane are adjusted.

[0236] The above isolation membranes 1-9 were subjected to relevant performance tests, and the specific results are shown in Table 2.

[0237] Separator with porous coating:

[0238] (1) Isolation film 10:

[0239] A first porous base membrane is provided. The first porous base membrane meets the following requirements: the material is polyethylene (PE), the viscosity-average molecular weight is 2.3 million g / mol, and the branching degree is 1%. The first porous base membrane is sample 4 prepared using process 4.

[0240] Prepare porous coating slurry: mix the binder polyacrylate and the fillers alumina particles and carboxymethyl cellulose in a ratio of 1:4:1 in an appropriate amount of solvent deionized water to make a porous coating slurry; apply the porous coating slurry on the first porous base membrane to form a porous coating.

[0241] (2) Isolation membranes 11-12 are similar to isolation membrane 10, except that the viscosity-average molecular weight and degree of branching of the first porous base membrane are adjusted. The first porous base membranes of isolation membranes 11-12 are samples 5-6 prepared using processes 5-6, respectively.

[0242] (3) Separator membranes 13-14 are similar to separator membrane 10, except that the viscosity average molecular weight and degree of branching of the first porous base membrane are adjusted.

[0243] The above Examples 10-14 were subjected to relevant performance tests, and the specific results are shown in Table 3.

[0244] An isolation membrane comprising a first porous base membrane and a second porous base membrane:

[0245] (1) Isolation film 15:

[0246] providing a first porous base membrane and a second porous base membrane;

[0247] The first porous base membrane meets the following requirements: the material is polyethylene (PE), the viscosity average molecular weight is 2.3 million g / mol, the branching degree is 1%, and the sample 4 is prepared by process 4;

[0248] The second porous base membrane meets the following requirements: the material is polypropylene (PP), the viscosity average molecular weight is 330,000 g / mol, and the branching degree is 70%.

[0249] Prepare porous coating slurry: mix the binder polyacrylate and the fillers alumina particles and carboxymethyl cellulose in a ratio of 1:4:1 in an appropriate amount of solvent deionized water to prepare a porous coating slurry.

[0250] The porous coating slurry is coated on the first porous base membrane to form a porous coating; the coated first porous base membrane and the second porous base membrane are hot-pressed to obtain an isolation membrane, wherein the porous coating is between the first porous base membrane and the second porous base membrane.

[0251] (2) Separator membranes 16-19 are similar to separator membrane 15, except that the material, viscosity-average molecular weight, and degree of branching of the second porous base membrane are adjusted.

[0252] (3) The separators 20 - 21 are similar to the separator 15 , except that the viscosity average molecular weight and / or the degree of branching of the first porous base membrane and / or the second porous base membrane are adjusted.

[0253] The above-mentioned isolation membranes 15-21 were subjected to relevant performance tests, and the specific results are shown in Table 4.

[0254] 2. Preparation of batteries

[0255] Example 1

[0256] 1. Preparation of positive electrode sheet

[0257] The positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), conductive agent carbon black (Super P), and binder polyvinylidene fluoride (PVDF) are mixed evenly in an appropriate amount of solvent N-methylpyrrolidone (NMP) in a mass ratio of 96.2:2.7:1.1 to obtain a positive electrode slurry. The positive electrode slurry is coated on the positive electrode current collector aluminum foil, and the positive electrode sheet is obtained through drying, cold pressing, slitting, and cutting processes.

[0258] 2. Preparation of negative electrode sheet

[0259] The negative electrode active material artificial graphite, conductive agent carbon black (Super P), binder styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC-Na) are mixed uniformly in a proper amount of solvent deionized water at a mass ratio of 96.4:0.7:1.8:1.1 to obtain a negative electrode slurry. The negative electrode slurry is coated on the negative electrode current collector copper foil, and the negative electrode sheet is obtained through the processes of drying, cold pressing, slitting and cutting.

[0260] 3. Isolation film

[0261] The isolation film used was the isolation film 1 prepared above.

[0262] 4. Preparation of electrolyte

[0263] Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 30:70 to obtain an organic solvent. Fully dried electrolyte salt LiPF6 is dissolved in the above mixed solvent. The concentration of the electrolyte salt is 1.0 mol / L. After mixing evenly, an electrolyte solution is obtained.

[0264] 5. Preparation of secondary batteries

[0265] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, with the separator placed between the positive electrode sheet and the negative electrode sheet to serve as an isolation, and then wound to obtain an electrode assembly; the electrode assembly is placed in an outer package, and the prepared electrolyte is injected into the dried secondary battery. After vacuum packaging, standing, formation, and shaping processes, a secondary battery is obtained.

[0266] The preparation methods of the secondary batteries of Examples 2-15 and Comparative Examples 1-6 are similar to that of the secondary battery of Example 1, except that the separators were prepared using different processes. See Table 1-4 for details.

[0267] 3. Battery performance test

[0268] 1. Puncture strength test

[0269] The puncture strength of the base film or isolation membrane has a meaning well known in the art and can be tested using equipment and methods known in the art. For example, the puncture strength can be tested according to the standard: GB / T 10004-2008. Specifically, the sample to be tested can be cut into strips, wherein the width of the strip sample is 100 mm. A test piece with a width of 100 mm is mounted on the sample film fixing clamp ring, and then a steel needle with a diameter of 1.0 mm and a radius of 0.5 mm at the top is used to puncture at a speed of (50±5) mm / min, and the maximum load of the steel needle penetrating the test piece is read. Usually, 5 parallel test samples can be taken at the same time, 3 points are measured for each test sample, and the arithmetic average is taken as the final puncture strength.

[0270] 2. Battery cycle performance (cycles)

[0271] At 25°C, the secondary batteries prepared in the Examples and Comparative Examples were charged at a constant current rate of 1C to a charge cutoff voltage V1, then charged at a constant voltage to a current ≤ 0.05C, allowed to rest for 5 minutes, and then discharged at a constant current rate of 0.33C to a discharge cutoff voltage V2, allowed to rest for 5 minutes. This constitutes one charge-discharge cycle. The batteries were subjected to cyclic charge-discharge testing using this method until the battery capacity decayed to 80%. The number of cycles at this point is the battery's cycle life at 25°C.

[0272] As can be seen from Tables 2-4, by comparing Examples 1-7 with Comparative Examples 1-2, comparing Examples 8-10 with Comparative Examples 3-4, and comparing Examples 11-15 with Comparative Examples 5-6, the puncture strength and cycle life of the battery are enhanced by forming an isolation membrane using a first porous base membrane as polyolefin, a viscosity-average molecular weight of the first porous base membrane ≥1.2 million g / mol, and a degree of branching of the first porous base membrane ≤5%, and the reliability of the battery is higher.

[0273] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present application, and such modifications or substitutions should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A separator, comprising a first porous base membrane, wherein the first porous base membrane is polyolefin, the viscosity average molecular weight of the first porous base membrane is ≥ 1.2 million g / mol, and the branching degree of the first porous base membrane is ≤ 5%.

2. The isolation film according to claim 1, wherein The viscosity average molecular weight of the first porous base membrane is ≥1.5 million g / mol, and can be optionally 2 million g / mol-3 million g / mol.

3. The isolation film according to claim 1 or 2, wherein: The branching degree of the first porous base membrane is ≤2%, and can be optionally ≤1%.

4. The isolation film according to any one of claims 1 to 3, wherein: The polymerization degree of the first porous base membrane is ≥50,000, and can be optionally 80,000-200,000.

5. The isolation film according to any one of claims 1 to 4, wherein: The crystallinity of the first porous base membrane is 40%-90%, and optionally 75%-85%.

6. The isolation film according to any one of claims 1 to 5, wherein: The puncture strength of the first porous base film is ≥300 gf, and can be selected to be 350 gf-450 gf.

7. The isolation film according to any one of claims 1 to 6, wherein: The thickness of the first porous base membrane is 1 μm-12 μm, and can be 3 μm-6 μm.

8. The isolation film according to any one of claims 1 to 7, wherein: The porosity of the first porous base film is 20%-50%, and can be 30%-40%.

9. The isolation film according to any one of claims 1 to 8, wherein: The air permeability of the first porous base film is 100sec / 100cc-300sec / 100cc, and can be optionally 200sec / 100cc-300sec / 100cc.

10. The isolation film according to any one of claims 1 to 9, wherein: The number average molecular weight of the first porous base membrane is ≥1.4 million, and can be selected to be 1.6 million to 2.4 million.

11. The isolation film according to any one of claims 1 to 10, wherein: The weight average molecular weight of the first porous base membrane is ≥ 1 million g / mol, and can be optionally 1.2 million g / mol-2 million g / mol.

12. The isolation film according to any one of claims 1 to 11, wherein: The isolation membrane further comprises a porous coating layer, which is disposed on at least one surface of the first porous base membrane and comprises a binder; optionally, the porous coating layer comprises a binder and filler particles.

13. The isolation film according to any one of claims 1 to 11, wherein: The isolation membrane further comprises a porous coating layer and a second porous base membrane, wherein the porous coating layer is located between the first porous base membrane and the second porous base membrane; Optionally, the porous coating comprises a binder; More optionally, the porous coating comprises a binder and filler particles.

14. The isolation film according to claim 12 or 13, wherein: The binder comprises at least one of polyacrylate, polyacrylic acid, polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride-trichloroethylene copolymer, polyvinyl pyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyethylene oxide, polyarylate, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, polyacrylonitrile, polyvinyl alcohol, polyethylene, polypropylene, starch, and cyanoethyl pullulan; and / or, The filling particles include at least one of inorganic particles, organic particles, and organic-metal framework materials.

15. The isolation film according to claim 13 or 14, wherein: The viscosity average molecular weight of the first porous base membrane is greater than the viscosity average molecular weight of the second porous base membrane; optionally, the viscosity average molecular weight of the second porous base membrane is 100,000 g / mol-2,000,000 g / mol, and more optionally 300,000 g / mol-800,000 g / mol.

16. The isolation film according to any one of claims 13 to 15, wherein: The degree of branching of the first porous base membrane is less than that of the second porous base membrane; optionally, the degree of branching of the second porous base membrane is ≤90%, and more optionally 10%-40%.

17. The isolation film according to any one of claims 13 to 16, wherein: The polymerization degree of the first porous base membrane is greater than that of the second porous base membrane; optionally, the polymerization degree of the second porous base membrane is ≤8000, and more optionally 400-1000.

18. The isolation film according to any one of claims 13 to 17, wherein: The melting point of the first porous base membrane is lower than that of the second porous base membrane; optionally, the melting point of the second porous base membrane is 160°C-350°C, and more optionally 170°C-320°C.

19. The isolation film according to any one of claims 13 to 18, wherein: The crystallinity of the first porous base membrane is greater than that of the second porous base membrane; optionally, the crystallinity of the second porous base membrane is 20%-70%, and more optionally 30%-45%.

20. The isolation film according to any one of claims 13 to 19, wherein: The puncture strength of the first porous base membrane is greater than the puncture strength of the second porous base membrane; Optionally, the ratio of the puncture strength of the first porous base membrane to the puncture strength of the second porous base membrane is ≥2.5; Optionally, the puncture strength of the second porous base film is ≥70 gf, and more optionally 100 gf-300 gf.

21. The isolation film according to any one of claims 14 to 20, wherein: The second porous base film includes at least one of polyolefin, polytetrafluoroethylene, polyvinyl fluoride, polyethylene terephthalate, polyimide, and polyetheretherketone.

22. The isolation film according to any one of claims 1 to 21, wherein: The isolation film satisfies at least one of the following (1) to (4): (1) The transverse elongation at break of the isolation film is ≥80%, optionally ≥100%, and more optionally 100%-300%; (2) The longitudinal elongation at break of the isolation film is ≥40%, optionally ≥60%, and more optionally 60%-200%; (3) The transverse tensile strength of the isolation film is ≥ 1500 kgf / cm 2 , can be selected as ≥2000kgf / cm 2 , 2000kgf / cm2 is optional 2 -4000kgf / cm 2 ; (4) The longitudinal tensile strength of the isolation film is ≥1500kgf / cm 2 , can be selected as ≥2000kgf / cm 2 , 2000kgf / cm2 is optional 2 -4000kgf / cm 2 .

23. A method for preparing the isolation film according to any one of claims 1 to 22, wherein: include: Providing polymer powder; Mixing the polymer powder with lubricating oil, an antioxidant and a cross-linking agent to obtain a mixture, and melting the mixture to obtain a melt; Casting, stretching, and extracting lubricating oil from the melt to obtain a first porous base film; Wherein, the first porous base membrane is polyolefin, the viscosity average molecular weight of the first porous base membrane is ≥1.2 million g / mol, and the branching degree of the first porous base membrane is ≤5%.

24. The method for preparing a separator according to claim 23, wherein: The preparation method satisfies at least one of the following (1)-(4): (1) The mass fraction of the polymer powder in the mixture is 5%-40%, and can be optionally 20%-35%; (2) The mass fraction of the lubricating oil in the mixture is 50%-90%, and can be 60%-75%; (3) The mass fraction of the antioxidant in the polymer powder is 0.3%-1.0%, and can be optionally 0.5%-1.0%; (4) The mass fraction of the cross-linking agent in the polymer powder is 3%-10%, and can be optionally 3%-5%.

25. The method for preparing a separator according to claim 23, wherein: The preparation method satisfies at least one of the following (1)-(3): (1) The polymer powder includes polyolefin powder; the lubricating oil includes white oil and / or mineral oil; the antioxidant includes at least one of 4,4-thiobis(6-tert-butyl-m-cresol), dibutylhydroxytoluene, phosphite, tert-butylhydroquinone, β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 2-tert-butyl-6-methylphenol, N,N'-di-β-naphthyl-p-phenylenediamine, dilauryl thiodipropionate, tris(nonylphenyl) phosphite, and triphenyl phosphite; the crosslinking agent includes a compound containing at least two unsaturated groups; (2) The viscosity average molecular weight of the polymer powder is ≥ 1.2 million g / mol, and the degree of branching is ≤ 5%; (3) In the step of melting the mixture to obtain a melt, the mixture is mixed and melted at a temperature ranging from 160°C to 250°C, and optionally 190°C to 230°C. 26 . A secondary battery comprising the separator according to claim 1 or the separator prepared by the method for preparing the separator according to claim 23 .

27. The secondary battery according to claim 26, wherein: The secondary battery includes a positive electrode sheet and a negative electrode sheet, the separator is arranged between the positive electrode sheet and the negative electrode sheet, and the first porous base film faces the negative electrode sheet.

28. An electrical device comprising the secondary battery according to claim 26 or 27.

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