Isolation film, method of manufacturing, secondary battery, and electric device

Abstract

The application provides an isolation film, a preparation method, a secondary battery and a power utilization device, which comprise a first porous base film, the first porous base film is a polyolefin, the weight average molecular weight of the first porous base film is greater than or equal to 1.2 million g / mol, so that the isolation film has high puncture resistance; the branching degree of the first porous base film is less than or equal to 5%, the molecular chain sequence in the first porous base film is easy to form an ordered arrangement, the regularity of the molecular chain is increased, and then the puncture resistance of the isolation film is improved, so that the isolation film provided by the application can reduce the risk of being punctured by metal dendrites, increase the cycle life of the secondary battery, and improve the reliability of the secondary battery.

Description

Technical Field

[0001] This application belongs to the field of secondary battery technology, specifically relating to a separator, a preparation method, a secondary battery, and an electrical device. Background Technology

[0002] Rechargeable batteries are widely used in various consumer electronics and electric vehicles due to their outstanding advantages of being lightweight, pollution-free, and having no memory effect. With the continuous development of the new energy industry, users are placing higher demands on the reliability of rechargeable batteries.

[0003] Therefore, how to improve the reliability of secondary batteries is an urgent problem to be solved. Summary of the Invention

[0004] In view of the technical problems existing in the background art, this application provides a separator, a preparation method, a secondary battery, and an electrical device, aiming to improve the reliability of the secondary battery.

[0005] To achieve the above objectives, a first aspect of this application provides a separating membrane comprising a first porous base membrane, wherein the first porous base membrane is a polyolefin, the viscosity-average molecular weight of the first porous base membrane is ≥1.2 million g / mol, and the degree of branching is ≤5%.

[0006] Compared with the prior art, this application has at least the following beneficial effects: The separator provided by this application has a first porous base membrane made of polyolefin, and the viscosity-average molecular weight of the first porous base membrane is ≥1.2 million g / mol, which makes the separator have high puncture resistance. Since the branching degree of the first porous base membrane is ≤5%, the molecular chain sequence in the first porous base membrane is easy to form an ordered arrangement, which increases the regularity of the molecular chain and thus improves the puncture resistance of the separator. Therefore, the separator provided by this application can reduce the risk of the separator being punctured by metal dendrites, increase the cycle life of the secondary battery, and improve the reliability of the secondary battery.

[0007] In any embodiment of this application, the viscosity-average molecular weight of the first porous base membrane is ≥1.5 million g / mol, and can be selected as 2 million g / mol-3 million g / mol, which makes the separator membrane have high puncture resistance, reduces the risk of the separator membrane being punctured by metal dendrites, increases the cycle life of the secondary battery, and improves the reliability of the secondary battery.

[0008] In any embodiment of this application, the branching degree of the first porous base membrane is ≤2%, which can be selected as ≤1%, making it easier for the molecular chain sequence in the first porous base membrane to form an ordered arrangement, increasing the regularity of the molecular chain, thereby improving the puncture resistance of the separator, reducing the risk of the separator being punctured by metal dendrites, increasing the cycle life of the secondary battery, and improving the reliability of the secondary battery.

[0009] In any embodiment of this application, the degree of polymerization of the first porous base membrane is ≥50,000, and can be selected as 80,000-200,000, which makes the separator membrane have high puncture resistance, reduces the risk of the separator membrane being punctured by metal dendrites, increases the cycle life of the secondary battery, and improves the reliability of the secondary battery.

[0010] In any embodiment of this application, the crystallinity of the first porous base membrane is 40%-90%, optionally 75%-85%, which makes the separator membrane have high puncture resistance, reduces the risk of the separator membrane being punctured by metal dendrites, increases the cycle life of the secondary battery, and improves the reliability of the secondary battery.

[0011] In any embodiment of this application, the puncture strength of the first porous base membrane is ≥300gf, which can be selected as 350gf-450gf. This can reduce the risk of the separator 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 this application, the thickness of the first porous base film is 1μm-12μm, and can be selected as 3μm-6μm, which can reduce the risk of the separator 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 this application, the porosity of the first porous base membrane is 20%-50%, optionally 30%-40%, which can reduce the risk of the separator 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 this application, the air permeability of the first porous base membrane is 100sec / 100cc-300sec / 100cc, and can be selected as 200sec / 100cc-300sec / 100cc, which can make the separator membrane have a good ion permeability.

[0015] In any embodiment of this application, the number average molecular weight of the first porous base membrane is ≥1.4 million, and can be selected as 1.6 million to 2.4 million, which makes the separator membrane have high puncture resistance, increases the cycle life of the secondary battery, and improves the reliability of the secondary battery.

[0016] In any embodiment of this application, the weight-average molecular weight of the first porous base membrane is ≥1 million g / mol, and can be selected as 1.2 million g / mol to 2 million g / mol, which makes the separator membrane have high puncture resistance, increases the cycle life of the secondary battery, and improves the reliability of the secondary battery.

[0017] In any embodiment of this application, the separator further includes a porous coating disposed on at least one surface of the first porous base membrane, and the porous coating includes an adhesive; optionally, the porous coating includes an adhesive and filler particles.

[0018] Adding a porous coating to the first porous base membrane 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.

[0019] In any embodiment of this application, the separator further includes a porous coating and a second porous base membrane, the porous coating being located between the first porous base membrane and the second porous base membrane; optionally, the porous coating includes an adhesive; more preferably, the porous coating includes an adhesive and filler particles.

[0020] When a porous coating is provided between the first porous base film and the second porous base film, it can not only compensate for the process defects of the base film during the hot pressing composite process, but also further improve the stability of the physical properties of the separator, thereby improving the reliability of the secondary battery.

[0021] In any embodiment of this application, the binder includes one or more of the following: polyacrylate, polyacrylic acid, polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride-trichloroethylene copolymer, polyvinylpyrrolidone, 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 amylopectin; and / or, the filler particles include at least one of the following: inorganic particles, organic particles, and organometallic framework materials.

[0022] When the binder and / or filler particles in the porous coating include the above components, the reliability of the secondary battery can be improved.

[0023] In any embodiment of this application, the viscosity-average molecular weight of the first porous base membrane is greater than that of the second porous base membrane; optionally, the viscosity-average molecular weight of the second porous base membrane is 100,000 g / mol to 2,000,000 g / mol, and more preferably 300,000 g / mol to 800,000 g / mol.

[0024] When the viscosity-average molecular weight of the second porous base membrane is within the above range, it can improve the stability of the physical properties of the separator, thereby improving the reliability of the secondary battery.

[0025] In any embodiment of this application, the branching degree of the first porous base membrane is less than that of the second porous base membrane; optionally, the branching degree of the second porous base membrane is ≤90%, and more preferably 10%-40%.

[0026] When the branching degree of the second porous base membrane is within the above range, it can improve the stability of the physical properties of the separator, thereby improving the reliability of the secondary battery.

[0027] In any embodiment of this 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 preferably 400-1000.

[0028] When the degree of polymerization of the second porous base membrane is within the above range, it can improve the stability of the physical properties of the separator, thereby improving the reliability of the secondary battery.

[0029] In any embodiment of this application, the melting point of the first porous base film is lower than that of the second porous base film; optionally, the melting point of the second porous base film is 160°C-350°C, and more preferably 170°C-320°C.

[0030] When the melting points of the first and second porous base films are within the above range, the heat resistance and puncture resistance of the separator are improved, thereby enhancing the reliability of the secondary battery.

[0031] In any embodiment of this application, the crystallinity of the first porous base film is greater than that of the second porous base film; optionally, the crystallinity of the second porous base film is 20%-70%, and more preferably 30%-45%.

[0032] In any embodiment of this application, the puncture strength of the first porous base membrane is greater than that of the second porous base membrane.

[0033] 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;

[0034] Optionally, the puncture strength of the second porous base membrane is ≥70gf, and more preferably 100gf-300gf.

[0035] In any embodiment of this application, the second porous base membrane includes at least one of polyolefin, polytetrafluoroethylene, polyvinyl fluoride, polyethylene terephthalate, polyimide, and polyetheretherketone.

[0036] In any embodiment of this application, the separator membrane satisfies at least one of the following (1)-(4):

[0037] (1) The transverse breaking elongation of the separator is ≥80%, which can be ≥100%, and even more preferably 100%-300%;

[0038] (2) The longitudinal elongation at break of the separator is ≥40%, and can be ≥60%, or even 60%-200%;

[0039] (3) The transverse tensile strength of the separator is ≥1500 kgf / cm 2 ≥2000 kgf / cm 2 2000 kgf / cm² is also available as an option. 2 -4000 kgf / cm 2 ;

[0040] (4) The longitudinal tensile strength of the separator is ≥1500 kgf / cm 2 ≥2000 kgf / cm 2 2000 kgf / cm² is also available as an option. 2 -4000 kgf / cm 2 .

[0041] When the separator meets at least one of the above conditions (1)-(4), it has good puncture resistance, thereby improving the reliability of the secondary battery.

[0042] A second aspect of this application provides a method for preparing the separator membrane as described above, comprising:

[0043] Provide polymer powders;

[0044] The polymer powder is mixed with lubricating oil, antioxidant and crosslinking agent to obtain a mixture, and the mixture is melted to obtain a melt;

[0045] The melt is cast, stretched, and lubricating oil is extracted to obtain a first porous base membrane, and the isolation membrane includes the first porous base membrane;

[0046] The first porous base membrane is a 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%.

[0047] When the preparation method of the separator provided in this application is used, the separator provided in this application can be prepared. The separator provided in this application can reduce the risk of the separator being punctured by metal dendrites, increase the cycle life of the secondary battery, and improve the reliability of the secondary battery.

[0048] In any embodiment of this application, the preparation method satisfies at least one of the following (1)-(4):

[0049] (1) The mass fraction of polymer powder in the mixture is 5%-40%, and can be selected as 20%-35%;

[0050] (2) The mass fraction of lubricating oil in the mixture is 50%-90%, and can be 60%-75%;

[0051] (3) The mass fraction of antioxidant in polymer powder is 0.3%-1.0%, and can be selected as 0.5%-1.0%;

[0052] (4) The mass fraction of the crosslinking agent in the polymer powder is 3%-10%, and can be selected as 3%-5%.

[0053] When the polymer powder, lubricating oil, antioxidant, and crosslinking agent are within the above range, the prepared separator has good puncture resistance.

[0054] In any embodiment of this application, the preparation method satisfies at least one of the following (1)-(3):

[0055] (1) The polymer powder includes polyolefin powder; the lubricant 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, dilaurate thiodipropionate, tri(nonylphenyl) phosphite, and triphenyl phosphite; the crosslinking agent includes a compound containing at least two unsaturated groups.

[0056] (2) The viscosity-average molecular weight of the polymer powder is ≥1.2 million g / mol, and the degree of branching is ≤5%.

[0057] (3) In the step of obtaining a melt from the molten mixture, the mixture is mixed and melted in a temperature range of 160℃-250℃, which may be 190℃-230℃.

[0058] When the polymer powder, lubricating oil, antioxidant, crosslinking agent, and melting temperature are within the above range, the prepared separator membrane has good puncture resistance.

[0059] A third aspect of this application provides a secondary battery including a separator membrane according to any of the above-described embodiments. When the secondary battery uses the separator membrane provided in this application, the reliability of the secondary battery can be improved.

[0060] In any embodiment of this application, the secondary battery further includes a positive electrode and a negative electrode, with a separator disposed between the positive and negative electrode, and the first porous base film facing the negative electrode. When the secondary battery uses the separator provided in this application, the risk of the separator being punctured by metal dendrites can be reduced, increasing the cycle life of the secondary battery and improving its reliability.

[0061] A fourth aspect of this application provides an electrical device that includes a secondary battery as described in the second aspect of this application. When the secondary battery of the electrical device uses the separator provided in this application, the reliability of the electrical device can be improved.

[0062] Since the device of this application includes the secondary battery provided in this application, it has at least the same advantages as the secondary battery. Attached Figure Description

[0063] To more clearly illustrate the technical solution of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without any creative effort.

[0064] Figure 1 This is a schematic diagram of one embodiment of the separator membrane of this application.

[0065] Figure 2 This is a schematic diagram of another embodiment of the separator membrane of this application.

[0066] Figure 3 This is a schematic diagram of another embodiment of the separator membrane of this application.

[0067] Figure 4 This is a schematic diagram of one embodiment of a secondary battery.

[0068] Figure 5 yes Figure 4 The exploded diagram.

[0069] Figure 6 This is a schematic diagram of one embodiment of the battery module.

[0070] Figure 7 This is a schematic diagram of one embodiment of the battery pack.

[0071] Figure 8 yes Figure 7 The exploded diagram.

[0072] Figure 9 This is a schematic diagram of one embodiment of a device that uses a secondary battery as a power source. Detailed Implementation

[0073] The present application will be further described below with reference to specific embodiments. It should be understood that these specific embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0074] For the sake of brevity, this article only discloses some specific numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0075] In this description, unless otherwise stated, the term "or" is inclusive. That is, the phrase "A or (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).

[0076] In the description of this article, it should be noted that, unless otherwise stated, "above" and "below" include the number itself, and "several" in "one or more" means two or more.

[0077] Unless otherwise stated, the terms used in this application have their common meanings as commonly understood by those skilled in the art. Unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0078] Secondary batteries

[0079] A rechargeable battery is a battery that can be recharged after it has been discharged, allowing the active materials to be activated and the battery to continue to be used.

[0080] Typically, a secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The separator, positioned between the positive and negative electrodes, serves as a barrier. The electrolyte, located between the positive and negative electrodes, conducts ions.

[0081] [Isolation membrane]

[0082] See Figure 1 See Figure 1 This application provides a separator 10, which includes a first porous base membrane 11. The first porous base membrane 11 is a 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%.

[0083] 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 of any two of the above values, for example, it can be 1.2 million g / mol to 3.2 million g / mol. 500,000 g / mol - 1,800,000 g / mol, 2,000,000 g / mol - 3,000,000 g / mol, 2,000,000 g / mol - 2,200,000 g / mol, 2,500,000 g / mol - 2,800,000 g / mol, 3,000,000 g / mol - 3,500,000 g / mol, or a range greater than or equal to the above values, for example, ≥1,200,000 g / mol, ≥1,500,000 g / mol, ≥1,800,000 g / mol, ≥2,000,000 g / mol, ≥2,500,000 g / mol, ≥2,800,000 g / mol, ≥3,000,000 g / mol, ≥3,500,000 g / mol, etc.

[0084] The viscosity-average molecular weight of the base film has a meaning known in the art and can be tested using equipment and methods known in the art. For example, it can be tested using the viscosity method.

[0085] In some embodiments, the branching degree 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 above. The range consisting of any two 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 a range less than or equal to the above values, for example, ≤5%, ≤4.8%, ≤4.5%, ≤2%, ≤1.5%, ≤1.1%, ≤1%, ≤0.7%, ≤0.5%, ≤0.2%, ≤0.001%, etc.

[0086] The degree of branching of the base film has a meaning well-known in the art and can be tested using equipment and methods known in the art. For example, infrared spectroscopy can be used. Specifically, the procedure can be as follows: select 3-5 groups of base film samples, place the samples in an infrared spectrometer for scanning, and scan within the range of 400-4000 cm⁻¹. -1 After scanning, the infrared curve of the sample was processed, and the 1377 cm⁻¹ was calculated. -1 Peak area and 1996-2062 cm -1 The ratio of peak areas is the degree of branching.

[0087] In the specific separator of this application, the first porous base membrane 11 is a polyolefin with a viscosity-average molecular weight ≥ 1.2 million g / mol, which gives the separator 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 thus improves the puncture resistance of the separator. Therefore, the separator provided by this application can reduce the risk of the separator being punctured by metal dendrites, increase the cycle life of the secondary battery, and improve the reliability of the secondary battery.

[0088] In any embodiment of this application, the viscosity-average molecular weight of the first porous base membrane 11 is ≥1.5 million g / mol, and can be selected as 2 million g / mol to 3 million g / mol, which makes the separator membrane have high puncture resistance, reduces the risk of the separator membrane being punctured by metal dendrites, increases the cycle life of the secondary battery, and improves the reliability of the secondary battery.

[0089] In any embodiment of this application, the branching degree of the first porous base membrane 11 is ≤2%, which can be selected as ≤1%, making it easier for the molecular chain sequence in the first porous base membrane 11 to form an ordered arrangement, increasing the regularity of the molecular chain, thereby improving the puncture resistance of the separator, reducing the risk of the separator being punctured by metal dendrites, increasing the cycle life of the secondary battery, and improving the reliability of the secondary battery.

[0090] In any embodiment of this application, the degree of polymerization of the first porous base membrane 11 is ≥50000, and can be selected as 80000-200000.

[0091] In some embodiments, the degree of polymerization of the first porous base membrane 11 can be 50,000, 60,000, 75,000, 80,000, 90,000, 100,000, 110,000, 120,000, 150,000, 180,000, 200,000, 210,000, 250,000, 280,000, 300,000, 400,000, 500,000, etc., or a range of any two of the above values, for example, it can be 50,000-75,000, 60,000-90,000. 0000, 80000-120000, 180000-180000, 200000-210000, 80000-200000, 280000-300000, 80000-500000, etc., or a range greater than or equal to the above values, for example, ≥50000, ≥80000, ≥110000, ≥120000, ≥150000, ≥200000, ≥250000, ≥300000, ≥500000, etc.

[0092] In any embodiment of this application, by limiting the degree of polymerization of the first porous base membrane 11, the separator has a high puncture resistance, which can reduce the risk of the separator being punctured by metal dendrites, increase the cycle life of the secondary battery, and improve the reliability of the secondary battery.

[0093] The degree of polymerization of the base film has a meaning known in the art and can be tested using equipment and methods known in the art. For example, the degree of polymerization can be calculated from the molecular weight of the material, denoted as m, and the relative molecular mass of a single unit is denoted as m0, with the degree of polymerization n = m / m0.

[0094] In any embodiment of this application, the crystallinity of the first porous base film 11 is 40%-90%, and optionally 75%-85%.

[0095] In some embodiments, the crystallinity of the first porous base film 11 can be 40%, 45%, 48%, 50%, 55%, 60%, 68%, 70%, 75%, 77.5%, 80%, 85%, 90%, etc., or a range 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.

[0096] In any embodiment of this application, by limiting the crystallinity of the first porous base film 11, the separator has a high puncture resistance, which can reduce the risk of the separator being punctured by metal dendrites, increase the cycle life of the secondary battery, and improve the reliability of the secondary battery.

[0097] 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, and the temperature is increased from 25℃ to 350℃ at a rate of 10℃ / min. The melting endothermic curve is obtained, and the crystallinity is obtained by calculating the peak area of ​​the curve and the reference value of 100% crystalline polyolefin.

[0098] Crystallinity is used to indicate the proportion of crystalline regions in the base film material. Crystallization is an ordered arrangement of molecular chains, forming a molecular chain form. Generally, the higher the crystallinity, the more regular the molecular chain arrangement.

[0099] In any embodiment of this application, the puncture strength of the first porous base membrane 11 is ≥300gf, and can be selected as 350gf-450gf.

[0100] In some embodiments, the puncture strength of the first porous base membrane 11 can be 300 gf, 310 gf, 320 gf, 340 gf, 345 gf, 350 gf, 380 gf, 390 gf, 400 gf, 410 gf, 430 gf, 435 gf, 450 gf, 470 gf, 480 gf, 490 gf, 500 gf, etc., or a range of any two of the above values. For example, it can be... These can be 300gf-340gf, 310gf-435gf, 350gf-480gf, 350gf-450gf, 400gf-430gf, 470gf-500gf, etc., or ranges greater than or equal to the above values, such as ≥300gf, ≥350gf, ≥400gf, ≥410gf, ≥435gf, ≥450gf, ≥500gf, etc.

[0101] In any embodiment of this 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.

[0102] The puncture strength of the base membrane has a well-known meaning in the art and can be tested using equipment and methods known in the art. For example, puncture strength can be tested according to the standard GB / T 10004-2008. Specifically, the sample to be tested can be cut into strips, with a width of 100 mm. The 100 mm wide sample is mounted on the sample membrane fixing ring, and then a steel needle with a diameter of 1.0 mm and a tip radius of 0.5 mm is used to puncture the sample at a speed of (50±5) mm / min. The maximum load of the steel needle penetrating the sample is read. Usually, five parallel test samples can be taken simultaneously, with three points measured for each sample, and the arithmetic mean is taken as the final puncture strength.

[0103] In any embodiment of this application, the thickness of the first porous base film 11 is 1μm-12μm, and can be selected as 3μm-6μm.

[0104] In some embodiments, the thickness of the first porous base film 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 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.

[0105] In any embodiment of this application, by limiting the thickness of the first porous base film 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.

[0106] The thickness of the base film can be tested using equipment and methods known in the art. For example, a thickness gauge can be used to determine the thickness of the base film. Specifically, the following method can be used: take six sets of parallel samples, and use a micrometer thickness gauge to measure the thickness at different locations in each set of samples. At least 20 points should be measured in each set of samples, and the average thickness of the six sets of samples is taken as the base film thickness.

[0107] In any embodiment of this application, the porosity of the first porous base membrane 11 is 20%-50%, and can be selected as 30%-40%.

[0108] 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%, or a range of any two of the above values, for example, 20%-25%, 22%-41%, 25.2%-27.5%, 30%-40%, 30%-48%, 33%-40%, 45%-50%, etc.

[0109] In any embodiment of this 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.

[0110] The porosity of the base membrane has a well-known meaning in the art and can be tested using equipment and methods known in the art. For example, the porosity of the base membrane can be tested using a mercury porosimeter, referring to GB / T 21650.1-2008.

[0111] In any embodiment of this application, the air permeability of the first porous base membrane 11 is 100sec / 100cc-300sec / 100cc, and can be selected as 200sec / 100cc-300sec / 100cc, which can make the separator membrane have a better ion permeability.

[0112] In any embodiment of this application, the number average molecular weight of the first porous base membrane 11 is ≥1.4 million, and can be selected as 1.6 million to 2.4 million.

[0113] 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.

[0114] In any embodiment of this application, by limiting the number-average molecular weight of the first porous base membrane 11, the separator has a higher puncture resistance, which increases the cycle life of the secondary battery and improves the reliability of the secondary battery.

[0115] In any embodiment of this application, the weight-average molecular weight of the first porous base membrane is ≥1 million g / mol, and can be selected as 1.2 million g / mol to 2 million g / mol, which makes the separator membrane have high puncture resistance, increases the cycle life of the secondary battery, and improves the reliability of the secondary battery.

[0116] In some embodiments, the weight-average molecular weight of the first porous base membrane 11 can be 1,000,000 g / mol, 1,200,000 g / mol, 1,500,000 g / mol, 1,700,000 g / mol, 2,000,000 g / mol, 2,200,000 g / mol, 2,500,000 g / mol, 2,750,000 g / mol, 3,000,000 g / mol, 4,000,000 g / mol, etc., or a range consisting of any two of the above values, for example, 1,000,000 g / mol-2,200,000 g / mol, 1,200,000 g / mol-2,000,000 g / mol, 1,500,000 g / mol-2,500,000 g / mol, 2,000,000 g / mol-4,000,000 g / mol, etc., or a range greater than or equal to the above values, for example, ≥1,000,000 g / mol, ≥1,700,000 g / mol, ≥2,000,000 g / mol, ≥2,500,000 g / mol, ≥3,000,000 g / mol, ≥4,000,000 g / mol, etc.

[0117] In any embodiment of this application, by limiting the weight-average molecular weight of the first porous base membrane 11, the separator has a higher puncture resistance, which increases the cycle life of the secondary battery and improves the reliability of the secondary battery.

[0118] See Figure 2 In any embodiment of this application, the separator further includes a porous coating 13, which is disposed on at least one surface of the first porous base membrane 11, and the porous coating 13 includes an adhesive; optionally, the porous coating 13 includes an adhesive and filler particles.

[0119] The porous coating 13 provided on the first porous base membrane 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.

[0120] See Figure 3 In any embodiment of this application, the separator further includes a porous coating 13 and a second porous base membrane 12, wherein the porous coating 13 is located between the first porous base membrane 11 and the second porous base membrane 12; optionally, the porous coating 13 includes an adhesive; more preferably, the porous coating 13 includes an adhesive and filler particles.

[0121] The first porous base membrane 11 and the second porous base membrane 12 can be directly laminated by hot pressing. During the hot pressing process, if the temperature is too high, it will result in low porosity and poor air permeability; if the temperature is too low, the first porous base membrane 11 and the second porous base membrane 12 will not bond firmly. Therefore, it is necessary to adjust the hot pressing temperature appropriately. Optionally, the hot pressing temperature is between 20℃ and 50℃.

[0122] When a porous coating 13 is provided between the first porous base film 11 and the second porous base film 12, it can not only compensate for the process defects of the base film in the hot pressing composite process, but also further improve the stability of the physical properties of the separator, thereby improving the reliability of the secondary battery.

[0123] In some embodiments, the filler particles include at least one of inorganic particles, organic particles, and organometallic framework materials.

[0124] Optionally, the inorganic particles include one or more of the following: inorganic particles having a dielectric constant of 5 or higher, inorganic particles having ionic conductivity but not storing ions, and inorganic particles capable of undergoing electrochemical reactions.

[0125] Optionally, inorganic particles having a dielectric constant of 5 or higher may include boehmite, alumina, 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, hydropyrite, zirconium titanate, barium titanate, Pb(Zr,Ti)O3 (abbreviated as PZT), and Pb 1-m La m Zr 1-n Ti n O3 (abbreviated as PLZT, 0 < m < 1, 0 < n < 1), Pb (Mg3Nb) 2 / 3 The inorganic particles are selected from at least one of PbTiO3 (abbreviated as PMN-PT) and their respective modified inorganic particles. Optionally, the modification of each inorganic particle can be chemical modification and / or physical modification. Chemical modification methods include coupling agent modification (e.g., using silane coupling agents, titanate coupling agents, etc.), surfactant modification, polymer grafting modification, etc. Physical modification methods can include mechanical dispersion, ultrasonic dispersion, high-energy treatment, etc. Modification treatment can reduce the agglomeration of inorganic particles, thereby enabling the adhesive layer to have a more stable and uniform structure; in addition, by selecting coupling agents, surfactants or polymers with specific functional groups to modify inorganic particles, it is also helpful to improve the wetting and retention properties of the adhesive layer to the electrolyte and improve the adhesion of the adhesive layer to the first porous base film 11 and the second porous base film 12.

[0126] Optionally, inorganic particles that are ion-conductive but do not store ions may include Li3PO4, lithium titanium phosphate (Li), etc. x1 Ti y1 (PO4)3, Lithium aluminum titanium phosphate (Li) x2 Al y2 Ti z1 (PO4)3、(LiAlTiP) x3 Oy3 Type glass, lithium lanthanum 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 type 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 separator.

[0127] Optionally, the inorganic particles capable of undergoing electrochemical reactions 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.

[0128] Optionally, the organic particles may include one or more of the following: polycarbonate, polythiophene, polypyridine, polystyrene, polyacrylic wax, polyethylene, polypropylene, cellulose, cellulose modifiers (e.g., carboxymethyl cellulose), melamine resin, phenolic resin, polyester (e.g., polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate), silicone resin, polyimide, polyamide-imide, polyarylamide, polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, polyaryletherketone, and copolymers of butyl acrylate and ethyl methacrylate (e.g., cross-linked polymers of butyl acrylate and ethyl methacrylate).

[0129] Optionally, organometallic framework materials may include one or more of the following: nitrogen-containing heterocyclic ligand structures, organic carboxylic acid ligand structures, and nitrogen-oxygen mixed ligand structures.

[0130] In any embodiment of this application, the binder includes one or more of the following: polyacrylate, polyacrylic acid, polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride-trichloroethylene copolymer, polyvinylpyrrolidone, 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 amylopectin; and / or, the filler particles include at least one of inorganic particles, organic particles, and organometallic framework materials. When the binder and / or filler particles in the porous coating 13 include the above components, the reliability of the secondary battery can be improved.

[0131] In some embodiments, the porous coating 13 may also include a dispersant, such as carboxymethyl cellulose, which can adjust the viscosity of the porous coating 13 slurry and improve the quality and uniformity of the porous coating 13.

[0132] In any embodiment of this application, the viscosity-average molecular weight of the first porous base membrane 11 is greater than that 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 to 2,000,000 g / mol, and more preferably 300,000 g / mol to 800,000 g / mol.

[0133] 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, or 1,900,000 g / mol. / mol, 2 million g / mol, or any range of two of the above values, such as 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 - 1,200,000 g / mol, 1,000,000 g / mol - 1,500,000 g / mol, 1,600,000 g / mol - 1,750,000 g / mol, 1,400,000 g / mol - 1,800,000 g / mol, 1,900,000 g / mol - 2,000,000 g / mol, etc.

[0134] When the viscosity-average molecular weight of the second porous base membrane 12 is within the above range, it can improve the stability of the physical properties of the separator, thereby improving the reliability of the secondary battery.

[0135] In any embodiment of this application, the branching degree of the first porous base membrane 11 is less than that of the second porous base membrane 12; optionally, the branching degree of the second porous base membrane 12 is ≤90%, and more preferably ≤40%.

[0136] In some embodiments, the branching degree 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 of any two of the above values, for example, 0.1%-5%, 5%-50%, 10%-20%, 30%-85%, 53%-60%, 8%-70%, 80%-90%, etc., or a range less than or equal to the above values, for example, ≤0.1%, ≤5%, ≤8%, ≤10%, ≤20%, ≤30%, ≤40%, ≤45%, ≤50%, ≤60%, ≤70%, ≤80%, ≤90%, etc.

[0137] When the branching degree of the second porous base membrane is within the above range, it can improve the stability of the physical properties of the separator, thereby improving the reliability of the secondary battery.

[0138] In any embodiment of this 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 selected as 400-1000.

[0139] In some embodiments, the degree of polymerization of the second porous base membrane 12 can 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 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., 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.

[0140] When the degree of polymerization of the second porous base membrane is within the above range, it can improve the stability of the physical properties of the separator, thereby improving the reliability of the secondary battery.

[0141] In any embodiment of this application, the melting point of the first porous base film 11 is lower than that of the second porous base film 12; optionally, the melting point of the second porous base film 12 is 160°C-350°C, and more preferably 170°C-320°C.

[0142] In some embodiments, the melting point of the second porous base film 12 can be 160℃, 170℃, 175℃, 180℃, 195℃, 200℃, 215℃, 220℃, 235℃, 250℃, 265℃, 280℃, 300℃, 310℃, 315℃, 320℃, 330℃, 340℃, 350℃, etc., or a range of any two of the above values, for example, 160℃-180℃, 200℃-315℃, 235℃-250℃, 265℃-300℃, 175℃-330℃, 170℃-320℃, 195℃-340℃, 330℃-350℃, etc.

[0143] In any embodiment of this application, by limiting the melting point of the first porous base film 11 and the second porous base film 12, the heat resistance and puncture resistance of the separator are improved, thereby enhancing the reliability of the secondary battery.

[0144] 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 (DSC) can be used for determination. Specific details can be found in standard GB / T 19466.3-2004. As an example, the determination can be performed as follows: 4-6 mg of the sample to be tested is placed in the sample chamber of a differential scanning calorimeter, and the temperature is increased 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 value of the curve is the melting point of the sample.

[0145] In any embodiment of this application, the crystallinity of the first porous base film 11 is greater than that of the second porous base film 12. Optionally, the crystallinity of the second porous base film 12 is 20%-70%, and more preferably 30%-45%.

[0146] 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%, or a range of any two of the above values, for example, 20%-56.5%, 30%-40%, 45.2%-68%, 50%-60%, 61%-70%, etc.

[0147] In any embodiment of this application, the puncture strength of the first porous base membrane 11 is greater than the puncture strength of the second porous base membrane 12.

[0148] 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;

[0149] Optionally, the puncture strength of the second porous base membrane 12 is ≥70gf, and more preferably 100gf-300gf.

[0150] 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, such as 2.5-4.0, 3.0-3.35, 2.8-3.5, 3.85-5, etc., or a range greater than or equal to the above values, such as ≥2.5, ≥3.0, ≥3.5, ≥4.0, ≥4.5, ≥5, etc.

[0151] 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 of any two of the above values, for example, 70gf-170gf, 80gf-227gf, 100gf-300gf, 195gf-332gf, 250gf-400gf, 300gf-450gf, etc.

[0152] In any embodiment of this application, the second porous base membrane 12 includes at least one of polyolefin, polytetrafluoroethylene, polyvinyl fluoride, polyethylene terephthalate, polyimide, and polyetheretherketone.

[0153] In any embodiment of this application, the separator membrane satisfies at least one of the following (1)-(4):

[0154] (1) The transverse breaking elongation of the separator is ≥80%, which can be ≥100%, and even more preferably 100%-300%;

[0155] (2) The longitudinal elongation at break of the separator is ≥40%, and can be ≥60%, or even 60%-200%;

[0156] (3) The transverse tensile strength of the separator is ≥1500 kgf / cm 2 ≥2000 kgf / cm 2 2000 kgf / cm² is also available as an option. 2 -4000 kgf / cm 2 ;

[0157] (4) The longitudinal tensile strength of the separator is ≥1500 kgf / cm 2 ≥2000 kgf / cm 2 2000 kgf / cm² is also available as an option. 2 -4000 kgf / cm 2 .

[0158] When the separator meets at least one of the above conditions (1)-(4), 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.

[0159] The air permeability, tensile strength (MD), tensile strength (TD), elongation at break (TD), and elongation at break (TD) of the separator all have meanings known in the art and can be measured using methods known in the art. For example, they can all be tested according to the standard GB / T 36363-2018.

[0160] This application provides a method for preparing the aforementioned separator membrane, comprising:

[0161] The polymer powder is mixed with lubricating oil, antioxidant and crosslinking agent to obtain a mixture, and the mixture is melted to obtain a melt;

[0162] The melt is cast, stretched, and lubricating oil is extracted to obtain a first porous base membrane, and the isolation membrane includes the first porous base membrane;

[0163] The first porous base membrane is a 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%.

[0164] When the preparation method of the separator provided in this application is used, the separator provided in this application can be prepared. The separator provided in this application can reduce the risk of the separator being punctured by metal dendrites, increase the cycle life of the secondary battery, and improve the reliability of the secondary battery.

[0165] In any embodiment of this application, the preparation method satisfies at least one of the following (1)-(4):

[0166] (1) The mass fraction of polymer powder in the mixture is 5%-40%, and can be selected as 20%-35%;

[0167] (2) The mass fraction of lubricating oil in the mixture is 50%-90%, and can be 60%-75%;

[0168] (3) The mass fraction of antioxidant in polymer powder is 0.3%-1.0%, and can be selected as 0.5%-1.0%;

[0169] (4) The mass fraction of the crosslinking agent in the polymer powder is 3%-10%, and can be selected as 3%-5%.

[0170] When the polymer powder, lubricating oil, antioxidant, and crosslinking agent are within the above range, the prepared separator has good puncture resistance.

[0171] In any embodiment of this application, the preparation method satisfies at least one of the following (1)-(3):

[0172] (1) The polymer powder includes polyolefin powder; the lubricant 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, dilaurate thiodipropionate, tri(nonylphenyl) phosphite, and triphenyl phosphite; the crosslinking agent includes a compound containing at least two unsaturated groups.

[0173] (2) The viscosity-average molecular weight of the polymer powder is ≥1.2 million g / mol, and the degree of branching is ≤5%.

[0174] (3) In the step of obtaining a melt from the molten mixture, the mixture is mixed and melted in a temperature range of 160℃-250℃, which may be 190℃-230℃.

[0175] When the polymer powder, lubricating oil, antioxidant, crosslinking agent, and melting temperature are within the above range, the prepared separator membrane has good puncture resistance.

[0176] In some embodiments, the polymer powder includes polyolefin powder.

[0177] In some embodiments, the lubricating oil may include white oil and / or mineral oil. Optionally, the mineral oil may include paraffin oil. Optionally, the mineral oil may include at least one of white oil, paraffin oil, kerosene, and dioctyl phthalate.

[0178] In some embodiments, the antioxidant includes at least one of 4,4-thiobis(6-tert-butyl-m-cresol), dibutylhydroxytoluene, phosphite, tert-butylhydroquinone, octadecyl 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, tri(nonylphenyl) phosphite, and triphenyl phosphite.

[0179] In some embodiments, the crosslinking agent comprises a compound containing at least two unsaturated groups. Optionally, the crosslinking agent comprises 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.

[0180] Optionally, the mixture may also include other components, such as plasticizers, extractants, and additives that improve pore uniformity.

[0181] This application provides specific embodiments of three methods for preparing separator membranes, which are used to prepare separator membranes according to any of the above embodiments.

[0182] (1) The first method for preparing the separator membrane: Select polymer powder with a viscosity-average molecular weight ≥1.2 million g / mol and a branching degree ≤5%, lubricating oil, antioxidant, and crosslinking agent are added to a mixer in a certain proportion and mixed evenly. The polymer powder accounts for 5%-40% of the total mass, and can be selected as 20%-35%; the lubricating oil accounts for 50%-90% of the total mass, and can be selected as 60%-75%; the antioxidant is added to the polymer powder at 0.3%-1.0% of the mass, and can be selected as 0.5%-1.0%; the crosslinking agent is added to the polymer powder at 3%-10%, and can be selected as 3%-5%; the mixture is added to a twin-screw extruder at a temperature range of 160℃-250℃ and fully mixed and melted to form a homogeneous melt. After the melt is formed, a casting is prepared through the die. The casting is stretched laterally and longitudinally by calendering and then mineral oil is extracted through a solvent tank to finally obtain a porous separator membrane.

[0183] In some embodiments, the mixture is added to a twin-screw extruder for thorough mixing and melting in a temperature range of 160°C to 250°C, with the temperature optionally being 190°C to 230°C.

[0184] (2) A second method for preparing the separator membrane: providing a first porous base membrane according to the first method described above; providing a coating slurry, the coating slurry comprising a binder; and applying the coating slurry to at least one surface of the first porous base membrane. Optionally, the coating slurry also comprises a binder and filler particles.

[0185] (3) A third method for preparing the separator membrane: providing a first porous base membrane according to the first method described above; providing a second porous base membrane; and combining the first porous base membrane and the second porous base membrane. Optionally, the method further includes a step of providing a coating slurry, the coating slurry comprising a binder, applying the coating slurry to one surface of the first porous base membrane and / or the second porous base membrane, and then combining the two porous base membranes. More preferably, the coating slurry comprises a binder and filler particles.

[0186] This application also provides a secondary battery, including a separator membrane according to any of the above embodiments. When the secondary battery uses the separator membrane provided in this application, the reliability of the secondary battery can be improved.

[0187] In any embodiment of this application, the secondary battery further includes a positive electrode and a negative electrode, with a separator disposed between the positive and negative electrode, and the first porous base film 11 facing the negative electrode. When the secondary battery uses the separator provided in this application, the risk of the separator being punctured by metal dendrites can be reduced, increasing the cycle life of the secondary battery and improving its reliability.

[0188] [Positive electrode plate]

[0189] In a secondary battery, the positive electrode typically includes a positive current collector and a positive electrode film layer disposed on the positive current collector, the positive electrode film layer including a positive active material.

[0190] The positive electrode current collector can be a conventional metal foil or a composite current collector (a composite current collector can be formed by setting metal material on a polymer substrate). As an example, the positive electrode current collector can be aluminum foil.

[0191] The specific type of positive electrode active material is not limited. Any active material known in the art that can be used as the positive electrode of a secondary battery can be used. Those skilled in the art can select according to actual needs.

[0192] As examples, positive electrode active materials may include, but are 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 oxides, lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, 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, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their modified compounds. All of these materials are commercially available.

[0193] The modified compounds for the above materials can be used to modify the materials by doping and / or by surface coating.

[0194] The positive electrode film layer typically includes binders, conductive agents, and other optional additives.

[0195] As an example, the conductive agent can be one or more of the following: superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, conductive carbon black (Super P, SP), graphene, and carbon nanofibers.

[0196] As an example, the adhesive may be one or more of the following: polymerized styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0197] [Negative electrode plate]

[0198] In a secondary battery, the negative electrode typically includes a negative current collector and a negative electrode film layer disposed on the negative current collector, the negative electrode film layer including a negative electrode active material.

[0199] The negative electrode current collector can be a conventional metal foil or a composite current collector (for example, a composite current collector can be formed by setting a metal material on a polymer substrate). As an example, the negative electrode current collector can be a copper foil.

[0200] The specific type of negative electrode active material is not limited; any active material known in the art that can be used as the negative electrode of a secondary battery can be used. Those skilled in the art can select 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 may be selected from one or more of elemental silicon, silicon oxide compounds (e.g., silicon suboxide), silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from one or more of elemental tin, tin oxide compounds, and tin alloys. All of these materials are commercially available.

[0201] In some implementations, the negative electrode active material may include a silicon-based material in order to further improve the energy density of the battery.

[0202] The negative electrode film layer typically includes binders, conductive agents, and other optional additives.

[0203] As an example, the conductive agent can be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0204] As an example, the adhesive 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).

[0205] As an example, other optional additives may be thickeners and dispersants (such as sodium carboxymethylcellulose, CMC-Na) and PTC thermistor materials.

[0206] Electrolyte

[0207] A secondary battery may include an electrolyte, which acts as a conductor of ions between the positive and negative electrodes. The electrolyte may include an electrolyte salt and a solvent.

[0208] As an example, the electrolyte salt may 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 difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0209] As an example, the solvent may be selected from ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl ethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), diisopropyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (n-Propyl Acetate (PA), methyl propionate (MP), and ethyl propionate (Ethyl... One or more of the following: Propanoate (EP), n-PropylPropionate (PP), Methyl Butyrate (MB), Ethyl Butyrate (EB), 1,4-Butyrolactone (GBL), Tetramethylene Sulfone (SF), Methyl Sulfone (MSM), Methyl Ethyl Sulfone (EMS), and Diethyl Sulfone (ESE).

[0210] In some embodiments, the electrolyte also includes additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature performance.

[0211] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. Figure 4 This is an example of a square-structured secondary battery 5.

[0212] In some embodiments, the secondary battery may include an outer packaging. The outer packaging is used to encapsulate the positive electrode, the negative electrode, and the electrolyte.

[0213] In some embodiments, the outer packaging of the secondary battery can be a rigid 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 pack, such as a pouch-type soft pack. The material of the soft pack can be plastic, including one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0214] In some implementations, refer to Figure 5 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, the bottom plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed on the opening to close the receiving cavity.

[0215] The method for preparing the secondary battery described in this application is well known. In some embodiments, a positive electrode, a separator 10, a negative electrode, and an electrolyte can be assembled to form a secondary battery. As an example, the positive electrode, separator 10, and negative electrode can be formed into an electrode assembly through a winding process and / or a stacking process. The electrode assembly is placed in an outer packaging, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping processes, a battery cell is obtained. Multiple battery cells can be further connected in series, parallel, or a combination to form a battery module. Multiple battery modules can also be connected in series, parallel, or a combination to form a battery pack. In some embodiments, multiple battery cells can also be directly assembled into a battery pack.

[0216] Figure 6 This is battery module 4, used as an example. (See reference...) Figure 6 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0217] The battery module 4 may also include a housing with a receiving space in which multiple secondary batteries 5 are received.

[0218] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0219] Figure 7 and Figure 8 This is battery pack 1 as an example. (See reference...) Figure 7 and Figure 8 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0220] [Device]

[0221] Figure 9 This is an example of an electrical device. This application also provides an electrical device 100, which includes the secondary battery provided in this application. When the secondary battery of the electrical device 100 uses the separator provided in this application, the reliability of the electrical device can be improved.

[0222] Battery cells, battery modules, or battery packs can serve as a power source for a device or as an energy storage unit for the device. Devices can be, but are not limited to, mobile devices (e.g., mobile 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 and satellites, and energy storage systems.

[0223] The device can be configured with individual battery cells, battery modules, or battery packs depending on its usage requirements.

[0224] The electrical device 100 can be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this electrical device, a battery pack or battery module can be used.

[0225] As another example, the power-consuming device 100 can be a mobile phone, tablet computer, or laptop computer. This power-consuming device 100 is typically required to be thin and light, and can use a single battery cell as its power source.

[0226] The beneficial effects of this application are further illustrated below with reference to the embodiments.

[0227] To make the technical problems, technical solutions, and beneficial effects solved by the embodiments of this application clearer, the following will provide a more detailed description in conjunction with the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0228] I. Preparation of the separating membrane

[0229] The first porous base membrane serves as a separating membrane:

[0230] (1) Separator membrane 1:

[0231] A first porous base membrane is provided, which meets the following requirements: the material is polyethylene (PE), the viscosity-average molecular weight is 1.2 million g / mol, the degree of branching is 1.6%, and the first porous base membrane is sample 1 prepared by process 1. In process 1, the antioxidant ratio is 0.3%, the crosslinking agent ratio is 8%, and the casting temperature is 230℃.

[0232] (2) The isolation membrane 2-7 is similar to the isolation membrane 1, except that the viscosity-average molecular weight and branching degree of the first porous base membrane are adjusted. The first porous base membrane of the isolation membrane 2-7 is prepared by the sample 2-7 of process 2-7. Process 2-7 is similar to process 1, except that the antioxidant ratio, crosslinking agent ratio and / or casting temperature are adjusted.

[0233] (3) The isolation membrane 8-9 is similar to that in Example 1, except that the viscosity-average molecular weight and branching degree of the first porous base membrane are adjusted.

[0234] The above-mentioned separators 1-9 underwent relevant performance tests, and the specific results are detailed in Table 2.

[0235] Separating membrane with porous coating:

[0236] (1) Separator membrane 10:

[0237] A first porous base membrane is provided, which meets the following requirements: the material is polyethylene (PE), the viscosity-average molecular weight is 2.3 million g / mol, and the degree of branching is 1%. The first porous base membrane is sample 4 prepared by process 4.

[0238] Preparation of porous coating slurry: The binder polyacrylate, filler alumina particles, and carboxymethyl cellulose are mixed evenly in an appropriate amount of deionized water at a ratio of 1:4:1 to prepare a porous coating slurry; the porous coating slurry is coated on the first porous base film to form a porous coating.

[0239] (2) Separating membranes 11-12 are similar to separating membrane 10, except that the viscosity-average molecular weight and branching degree of the first porous base membrane are adjusted. The first porous base membranes of separating membranes 11-12 are respectively prepared by process 5-6, which are sample 5-6.

[0240] (3) The separator 13-14 is similar to the separator 10, except that the viscosity-average molecular weight and branching degree of the first porous base membrane are adjusted.

[0241] The above embodiments 10-14 were subjected to relevant performance tests, and the specific results are detailed in Table 3.

[0242] The separator is formed by combining a first porous base membrane and a second porous base membrane.

[0243] (1) Separator membrane 15:

[0244] Provide a first porous base membrane and a second porous base membrane;

[0245] 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 it is sample 4 prepared by process 4.

[0246] 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 degree of branching is 70%.

[0247] Preparation of porous coating slurry: The binder polyacrylate, filler alumina particles, and carboxymethyl cellulose are mixed evenly in an appropriate amount of deionized water at a ratio of 1:4:1 to prepare a porous coating slurry.

[0248] A porous coating slurry is applied to a first porous base film to form a porous coating; the coated first porous base film and a second porous base film are hot-pressed together to obtain a separator film, wherein the porous coating is located between the first porous base film and the second porous base film.

[0249] (2) Separating membranes 16-19 are similar to separating membrane 15, except that the material, viscosity-average molecular weight and branching degree of the second porous base membrane are adjusted.

[0250] (3) Separating membranes 20-21 are similar to separating membrane 15, except that the viscosity-average molecular weight and / or branching degree of the first porous base membrane and / or the second porous base membrane are adjusted.

[0251] The aforementioned separators 15-21 underwent relevant performance tests, and the specific results are detailed in Table 4.

[0252] II. Battery Preparation

[0253] Example 1

[0254] 1. Preparation of positive electrode sheet

[0255] LiNi, the positive electrode active material 0.8 Co 0.1 Mn 0.1 O2 (NCM811), conductive carbon black (SuperP), and binder polyvinylidene fluoride (PVDF) are mixed evenly in an appropriate amount of solvent N-methylpyrrolidone (NMP) at a mass ratio of 96.2:2.7:1.1 to obtain a positive electrode slurry. The positive electrode slurry is coated onto the positive electrode current collector aluminum foil, and the positive electrode sheet is obtained through drying, cold pressing, slitting, and cutting processes.

[0256] 2. Preparation of negative electrode sheet

[0257] Artificial graphite (anode active material), carbon black (SuperP) (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC-Na) (batch ratio 96.4:0.7:1.8:1.1) are mixed evenly in an appropriate amount of deionized water to obtain a cathode slurry. The cathode slurry is then coated onto a copper foil (cathode current collector), and the cathode sheet is obtained through drying, cold pressing, slitting, and cutting processes.

[0258] 3. Separating membrane

[0259] The separator used is the separator 1 prepared above.

[0260] 4. Preparation of electrolyte

[0261] Ethyl carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a mass ratio of 30:70 to obtain an organic solvent. The fully dried electrolyte salt LiPF6 was dissolved in the above mixed solvent at a concentration of 1.0 mol / L. After mixing evenly, an electrolyte solution was obtained.

[0262] 5. Preparation of secondary batteries

[0263] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The electrode assembly is then wound up. The electrode assembly is placed in an outer package, and the prepared electrolyte is injected into the dried secondary battery. After vacuum sealing, settling, formation, and shaping, the secondary battery is obtained.

[0264] The secondary batteries of Examples 2-15 and Comparative Examples 1-6 are prepared in a similar manner to the secondary battery of Example 1, except that they use different processes to prepare the separator membrane, as detailed in Tables 1-4.

[0265] III. Battery Performance Testing

[0266] 1. Puncture strength test

[0267] The puncture strength of the base membrane or separator has a meaning well-known in the art and can be tested using equipment and methods known in the art. For example, puncture strength can be tested according to the standard GB / T 10004-2008. Specifically, the sample to be tested can be cut into strips, with a width of 100 mm. The 100 mm wide sample is mounted on the sample membrane fixing ring, and then a steel needle with a diameter of 1.0 mm and a tip radius of 0.5 mm is used to puncture the sample at a speed of (50±5) mm / min. The maximum load of the steel needle penetrating the sample is read. Usually, five parallel test samples can be taken simultaneously, with three points measured for each sample, and the arithmetic mean is taken as the final puncture strength.

[0268] 2. Battery cycle performance (cycles)

[0269] At 25°C, the secondary batteries prepared in the examples and comparative examples were charged at a constant current rate of 1C to the charging cutoff voltage V1, then charged at a constant voltage until the current ≤0.05C, allowed to stand for 5 minutes, and then discharged at a constant current rate of 0.33C to the discharge cutoff voltage V2, allowed to stand for 5 minutes. This constitutes one charge-discharge cycle. The batteries were subjected to cyclic charge-discharge tests according to this method until the battery capacity decreased to 80%. The number of cycles at this point is the cycle life of the battery at 25°C.

[0270]

[0271]

[0272]

[0273] As shown in Tables 2-4, compared with Comparative Examples 1-7, Comparative Examples 1-2, Comparative Examples 8-10, Comparative Examples 3-4, and Comparative Examples 11-15, the batteries with separators formed by using polyolefin as the first porous base membrane, having a viscosity-average molecular weight ≥1.2 million g / mol, and a branching degree ≤5% of the first porous base membrane, exhibit enhanced puncture strength and cycle life, resulting in higher battery reliability.

[0274] The above description is merely a specific embodiment of this application, but the scope of protection of this 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 this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A separating membrane, comprising a first porous base membrane, wherein the first porous base membrane is a 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%. The separator further includes a porous coating and a second porous base membrane, wherein the porous coating is located between the first porous base membrane and the second porous base membrane, and the viscosity-average molecular weight of the first porous base membrane is greater than that of the second porous base membrane. The porous coating includes an adhesive; The second porous base membrane includes at least one of polyolefin, polytetrafluoroethylene, polyvinyl fluoride, polyethylene terephthalate, polyimide, and polyetheretherketone; the viscosity-average molecular weight of the second porous base membrane is 100,000 g / mol to 2,000,000 g / mol.

2. The separator membrane as described in claim 1, characterized in that, The viscosity-average molecular weight of the first porous base membrane is ≥1.5 million g / mol.

3. The separator membrane as described in claim 2, characterized in that, The viscosity-average molecular weight of the first porous base membrane is 2 million g / mol to 3 million g / mol.

4. The separator membrane as described in claim 1, characterized in that, The branching degree of the first porous base membrane is ≤2%.

5. The separator as described in claim 4, characterized in that, The branching degree of the first porous base membrane is ≤1%.

6. The separator membrane as described in claim 1, characterized in that, The degree of polymerization of the first porous base membrane is ≥50000.

7. The separator membrane as described in claim 6, characterized in that, The degree of polymerization of the first porous base membrane is 80,000-200,000.

8. The separator membrane as described in claim 1, characterized in that, The crystallinity of the first porous base membrane is 40%-90%.

9. The separator membrane as described in claim 8, characterized in that, The crystallinity of the first porous base membrane is 75%-85%.

10. The separator membrane as claimed in claim 1, characterized in that, The puncture strength of the first porous base membrane is ≥300gf.

11. The separator membrane as described in claim 10, characterized in that, The puncture strength of the first porous base membrane is 350gf-450gf.

12. The separator membrane as claimed in claim 1, characterized in that, The thickness of the first porous base film is 1μm-12μm.

13. The separator membrane as described in claim 12, characterized in that, The thickness of the first porous base film is 3μm-6μm.

14. The separator membrane as claimed in claim 1, characterized in that, The porosity of the first porous base membrane is 20%-50%.

15. The separator membrane as described in claim 14, characterized in that, The porosity of the first porous base membrane is 30%-40%.

16. The separator membrane as claimed in claim 1, characterized in that, The air permeability of the first porous base membrane is 100sec / 100cc-300sec / 100cc.

17. The separator membrane as claimed in claim 16, characterized in that, The air permeability of the first porous base membrane is 200sec / 100cc-300sec / 100cc.

18. The separator membrane as claimed in claim 1, characterized in that, The number-average molecular weight of the first porous base membrane is ≥1.4 million.

19. The separator membrane as claimed in claim 18, characterized in that, The number-average molecular weight of the first porous base membrane is 1.6 million to 2.4 million.

20. The separator membrane as claimed in claim 1, characterized in that, The weight-average molecular weight of the first porous base membrane is ≥1 million g / mol.

21. The separator membrane as claimed in claim 20, characterized in that, The weight-average molecular weight of the first porous base membrane is 1.2 million g / mol to 2 million g / mol.

22. The separator membrane as claimed in claim 1, characterized in that, The porous coating also includes filler particles.

23. The separator membrane as claimed in claim 1, characterized in that, The adhesive comprises at least one of the following: polyacrylate, polyacrylic acid, polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride-trichloroethylene copolymer, polyvinylpyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyethylene oxide, polyarylate, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, cellulose acetate, cellulose propionate acetate, cellulose acetate butyrate, polyacrylonitrile, polyvinyl alcohol, polyethylene, polypropylene, starch, and cyanoethyl amylopectin.

24. The separator membrane as claimed in claim 22, characterized in that, The filler particles include at least one of inorganic particles, organic particles, and organic-metal framework materials.

25. The separator membrane as claimed in claim 1, characterized in that, The viscosity-average molecular weight of the second porous base membrane is 300,000 g / mol to 800,000 g / mol.

26. The separator membrane as claimed in claim 1, characterized in that, The degree of branching of the first porous base membrane is less than that of the second porous base membrane.

27. The separator membrane as claimed in claim 26, characterized in that, The branching degree of the second porous base membrane is ≤90%.

28. The separator membrane as claimed in claim 27, characterized in that, The branching degree of the second porous base membrane is 10%-40%.

29. The separator membrane as claimed in claim 1, characterized in that, The degree of polymerization of the first porous base membrane is greater than that of the second porous base membrane.

30. The separator membrane as described in claim 29, characterized in that, The degree of polymerization of the second porous base membrane is ≤8000.

31. The separator membrane as described in claim 30, characterized in that, The degree of polymerization of the second porous base membrane is 400-1000.

32. The separator membrane as claimed in claim 1, characterized in that, The melting point of the first porous base film is lower than that of the second porous base film.

33. The separator membrane as described in claim 32, characterized in that, The melting point of the second porous base film is 160℃-350℃.

34. The separator membrane as described in claim 33, characterized in that, The melting point of the second porous base film is 170℃-320℃.

35. The separator membrane as claimed in claim 1, characterized in that, The crystallinity of the first porous base film is greater than that of the second porous base film.

36. The separator membrane as described in claim 35, characterized in that, The crystallinity of the second porous base membrane is 20%-70%.

37. The separator membrane as described in claim 36, characterized in that, The crystallinity of the second porous base membrane is 30%-45%.

38. The separator membrane as described in claim 1, characterized in that, The puncture strength of the first porous base membrane is greater than that of the second porous base membrane.

39. The separator membrane as described in claim 38, characterized in that, 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.

40. The separator membrane as claimed in claim 39, characterized in that, The puncture strength of the second porous base membrane is ≥70gf.

41. The separator membrane as described in claim 40, characterized in that, The puncture strength of the second porous base membrane is 100gf-300gf.

42. The separator membrane as claimed in claim 1, characterized in that, The separator membrane satisfies at least one of the following (1)-(4): (1) The transverse elongation at break of the separator membrane is ≥80%; (2) The longitudinal elongation at break of the isolation membrane is ≥40%; (3) The transverse tensile strength of the isolation membrane is ≥1500 kgf / cm; (4) The longitudinal tensile strength of the isolation membrane is ≥1500kgf / cm.

43. The separator as described in claim 42, characterized in that, The transverse elongation at break of the separator is ≥100%.

44. The separator as described in claim 43, characterized in that, The transverse elongation at break of the separator is 100%-300%.

45. The separator membrane as described in claim 42, characterized in that, The longitudinal elongation at break of the separator is ≥60%.

46. ​​The separator as described in claim 45, characterized in that, The longitudinal elongation at break of the separator is 60%-200%.

47. The separator membrane as claimed in claim 42, characterized in that, The transverse tensile strength of the isolation membrane is ≥2000 kgf / cm.

48. The separator membrane as claimed in claim 47, characterized in that, The transverse tensile strength of the isolation membrane is 2000 kgf / cm-4000 kgf / cm.

49. The separator membrane as claimed in claim 42, characterized in that, The longitudinal tensile strength of the isolation membrane is ≥2000 kgf / cm.

50. The separator membrane as described in claim 49, characterized in that, The longitudinal tensile strength of the isolation membrane is 2000 kgf / cm-4000 kgf / cm.

51. A method for preparing a separator membrane as described in any one of claims 1-50, characterized in that, include: Provide polymer powders; The polymer powder is mixed with lubricating oil, antioxidant and crosslinking agent to obtain a mixture, and the mixture is melted to obtain a melt. The melt is cast, stretched, and lubricating oil is extracted to obtain a first porous base film; The first porous base membrane is a 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%.

52. The method for preparing the separator membrane according to claim 51, characterized in that, The preparation method satisfies at least one of the following (1)-(4): (1) The polymer powder has a mass fraction of 5%-40% in the mixture; (2) The mass fraction of the lubricating oil in the mixture is 50%-90%; (3) The antioxidant in the polymer powder has a mass fraction of 0.3%-1.0%; (4) The crosslinking agent has a mass fraction of 3%-10% in the polymer powder.

53. The method for preparing the separator membrane as described in claim 52, characterized in that, The polymer powder has a mass fraction of 20%-35% in the mixture.

54. The method for preparing the separator membrane as described in claim 52, characterized in that, The lubricating oil has a mass fraction of 60%-75% in the mixture.

55. The method for preparing the separator membrane as described in claim 52, characterized in that, The antioxidant has a mass fraction of 0.5%-1.0% in the polymer powder.

56. The method for preparing the separator membrane as described in claim 52, characterized in that, The crosslinking agent has a mass fraction of 3%-5% in the polymer powder.

57. The method for preparing the separator membrane according to claim 51, characterized in that, 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 antioxidants include at least one of the following: 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, dilaurate thiodipropionate, tri(nonylphenyl) phosphite, and triphenyl phosphite. The crosslinking agent comprises a compound containing at least two unsaturated groups; (2) The polymer powder has a viscosity-average molecular weight ≥ 1.2 million g / mol and a branching degree ≤ 5%. (3) In the step of melting the mixture to obtain a melt, the mixture is mixed and melted in a temperature range of 160°C to 250°C.

58. The method for preparing the separator membrane as described in claim 57, characterized in that, In the step of melting the mixture to obtain a melt, the mixture is mixed and melted in a temperature range of 190°C to 230°C.

59. A secondary battery, comprising a separator as described in any one of claims 1-50 or a separator prepared by a method for preparing a separator as described in any one of claims 51-58.

60. The secondary battery as described in claim 59, wherein, The secondary battery includes a positive electrode and a negative electrode, and the separator is disposed between the positive electrode and the negative electrode, with the first porous base film facing the negative electrode.

61. An electrical device comprising a secondary battery as described in claim 59 or 60.

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