Separator, secondary battery, and electric device

Abstract

The invention provides an isolating membrane which comprises a first base membrane and a second base membrane, and the melting point of the second base membrane is smaller than that of the first base membrane; the transverse elongation at break of the second base film is larger than the longitudinal elongation at break of the second base film, and the longitudinal elongation at break of the second base film is smaller than 100%. According to the isolating membrane provided by the invention, the nail penetrating performance of the isolating membrane can be effectively improved, and metal dendrites are prevented from penetrating through the isolating membrane to cause short circuit, so that the reliability of the secondary battery can be improved.

Description

Separator, secondary battery and electrical device Technical Field

[0001] The present application belongs to the technical field of secondary batteries, and specifically relates to an isolation membrane, a secondary battery, and an electrical device. Background Art

[0002] Secondary batteries are widely used in various consumer electronics and electric vehicles due to their lightweight, pollution-free, and memory-free features. With the continuous development of the new energy industry, users have placed higher demands on the reliability and performance of secondary batteries.

[0003] Therefore, how to make secondary batteries have better reliability performance is an urgent problem to be solved.

[0004] Summary of the Invention

[0005] In view of the technical problems existing in the background technology, the present application provides a separator, a secondary battery and an electrical device, aiming to improve the reliability performance of the secondary battery.

[0006] In order to achieve the above-mentioned purpose, the first aspect of the present application provides an isolation film, which includes: a first base film and a second base film, the melting point of the second base film is lower than the melting point of the first base film; the transverse elongation at break of the second base film is greater than the longitudinal elongation at break of the second base film, and the longitudinal elongation at break of the second base film is less than 100%.

[0007] Compared with the prior art, the present application includes at least the following beneficial effects: the isolation membrane provided by the present application has a first base membrane with a higher melting point than the second base membrane, which can improve the heat resistance of the isolation membrane. By setting the transverse elongation at break of the second base membrane to be greater than the longitudinal elongation at break of the second base membrane, and the longitudinal elongation at break of the second base membrane to be less than 100%, the nail penetration performance of the isolation membrane can be effectively improved, preventing metal dendrites from penetrating the isolation membrane and causing a short circuit, thereby improving the reliability of the secondary battery.

[0008] In any embodiment of the present application, the ratio of the transverse elongation at break of the second base film to the longitudinal elongation at break of the second base film is 1.05-4.5, and can be optionally 1.2-3.0, which can effectively improve the nail penetration performance of the isolation membrane, prevent metal dendrites from penetrating the isolation membrane and causing a short circuit, thereby improving the reliability of the secondary battery.

[0009] In any embodiment of the present application, the longitudinal elongation at break of the second base film is 30%-90%, which can effectively improve the nail penetration performance of the isolation membrane, prevent metal dendrites from penetrating the isolation membrane and causing a short circuit, thereby improving the reliability of the secondary battery.

[0010] In any embodiment of the present application, the transverse elongation at break of the first base film is less than the longitudinal elongation at break of the first base film, which can effectively improve the nail penetration performance of the isolation membrane and prevent metal dendrites from penetrating the isolation membrane and causing a short circuit, thereby improving the reliability of the secondary battery.

[0011] In any embodiment of the present application, the ratio of the transverse elongation at break of the first base film to the longitudinal elongation at break of the first base film is 0.05-0.5, and can be optionally 0.1-0.3, which can effectively improve the nail penetration performance of the isolation membrane, prevent metal dendrites from penetrating the isolation membrane and causing a short circuit, thereby improving the reliability of the secondary battery.

[0012] In any embodiment of the present application, the isolation film satisfies at least one of the following (1)-(3):

[0013] (1) The transverse elongation at break of the first base film is 30%-250%, and can be optionally 40%-200%;

[0014] (2) the longitudinal elongation at break of the first base film is 40%-1000%, optionally 400%-800%;

[0015] (3) The transverse elongation at break of the second base film is 50%-250%, and can be optionally 100%-180%.

[0016] When the isolation membrane satisfies at least one of the above (1)-(3) and meets the given range, the nail penetration performance of the isolation membrane can be effectively improved, preventing metal dendrites from penetrating the isolation membrane and causing a short circuit, thereby further improving the reliability of the secondary battery.

[0017] In any embodiment of the present application, the transverse tensile strength of the second base film is less than the longitudinal tensile strength of the second base film; optionally, the ratio of the transverse tensile strength of the second base film to the longitudinal tensile strength of the second base film is 0.4-0.95, and more optionally 0.6-0.9, which can effectively improve the nail penetration performance of the isolation membrane, prevent metal dendrites from penetrating the isolation membrane and causing a short circuit, thereby further improving the reliability of the secondary battery.

[0018] In any embodiment of the present application, the transverse tensile strength of the first base film is less than the longitudinal tensile strength of the first base film; the ratio of the transverse tensile strength of the first base film to the longitudinal tensile strength of the first base film is 0.2-0.9, and can be optionally 0.3-0.6, which can effectively improve the nail penetration performance of the isolation membrane, prevent metal dendrites from penetrating the isolation membrane and causing a short circuit, thereby further improving the reliability of the secondary battery.

[0019] In any embodiment of the present application, the transverse tensile strength of the first base film is less than the transverse tensile strength of the second base film; and / or the longitudinal tensile strength of the first base film is less than the longitudinal tensile strength of the second base film.

[0020] When the lateral tensile strength of the first base film is less than the lateral tensile strength of the second base film and the longitudinal tensile strength of the first base film is less than the longitudinal tensile strength of the second base film, the nail penetration performance of the isolation film can be effectively improved, preventing metal dendrites from penetrating the isolation film and causing a short circuit, thereby further improving the reliability of the secondary battery.

[0021] In any embodiment of the present application, the isolation film satisfies at least one of the following (1)-(4):

[0022] (1) The transverse tensile strength of the first base film is 100Kgf / cm 2 -1000Kgf / cm 2 , optional 200Kgf / cm 2 -750Kgf / cm 2 ;

[0023] (2) The longitudinal tensile strength of the first base film is 700Kgf / cm 2 -2500Kgf / cm 2 , optional 1000Kgf / cm 2 -1900Kgf / cm 2 ;

[0024] (3) The transverse tensile strength of the second base film is 1200Kgf / cm 2 -3800Kgf / cm 2 , optional 2000Kgf / cm 2 -3500Kgf / cm 2 ;

[0025] (4) The longitudinal tensile strength of the second base film is 1800Kgf / cm 2 -5500Kgf / cm 2 , optional 2100Kgf / cm 2 -3500Kgf / cm 2 .

[0026] When the isolation membrane satisfies at least one of the above (1)-(4) and meets the given range, the nail penetration performance of the isolation membrane can be effectively improved, preventing metal dendrites from penetrating the isolation membrane and causing a short circuit, thereby further improving the reliability of the secondary battery.

[0027] In any embodiment of the present application, the melting point of the first base film is 160°C-370°C, optionally 170°C-350°C; and / or the melting point of the second base film is 120°C-280°C, optionally 130°C-260°C. When the melting points of the first base film and the second base film meet the above conditions, the separator has good heat resistance and physical properties, thereby improving the reliability of the secondary battery.

[0028] In any embodiment of the present application, an intermediate layer is further provided between the first base film and the second base film, the intermediate layer is provided between the first base film and the second base film, and the intermediate layer includes an adhesive; optionally, the intermediate layer includes an adhesive and filler particles.

[0029] When an intermediate layer is provided between the first base film and the second base film, it can not only compensate for process defects of the base film during the hot pressing composite process, but also further improve the physical stability of the isolation film, thereby improving the reliability of the secondary battery.

[0030] In any embodiment of the present application, the binder includes one or more of polyacrylate, polyacrylic acid, polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride-trichloroethylene copolymer, polyvinyl pyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyethylene oxide, polyarylate, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, polyacrylonitrile, polyvinyl alcohol, polyethylene, polypropylene, starch, and cyanoethyl pullulan; and / or the filler particles include at least one of inorganic particles, organic particles, and organic-metal framework materials. When an intermediate layer is provided between the first base film and the second base film, and the binder and / or filler particles in the intermediate layer include the above components, the reliability of the secondary battery can be improved.

[0031] In any embodiment of the present application, the isolation film satisfies at least one of the following (1)-(6):

[0032] (1) The transverse elongation at break of the separator is 50%-220%, and can be optionally 70%-170%;

[0033] (2) The longitudinal elongation at break of the isolation film is 30%-150%, and can be optionally 40%-100%;

[0034] (3) The transverse tensile strength of the isolation film is 1200Kgf / cm 2 -4000Kgf / cm 2 , optional 2100Kgf / cm 2 -3600Kgf / cm 2 ;

[0035] (4) The longitudinal tensile strength of the isolation film is 1900Kgf / cm 2 -5500Kgf / cm 2 , optional 2200Kgf / cm 2 -3700Kgf / cm 2 ;

[0036] (5) The transverse heat shrinkage of the isolation film at 250°C for 1 hour is ≤2%, which can be optionally ≤1.0%;

[0037] (6) The longitudinal heat shrinkage of the isolation film at 250°C for 1 hour is ≤2%, and can be optionally ≤1.0%.

[0038] When the separator satisfies at least one of the above (1) to (6) and falls within the given range, the separator has good heat resistance and physical properties, thereby improving the reliability of the secondary battery.

[0039] The second aspect of the present application provides a secondary battery comprising the separator according to any one of the above solutions. When the secondary battery adopts the separator, the reliability of the secondary battery can be improved.

[0040] In any embodiment of the present application, the secondary battery further includes a positive electrode sheet and a negative electrode sheet, and a separator is disposed between the positive electrode sheet and the negative electrode sheet, with the second base film facing the negative electrode sheet. When the secondary battery utilizes the separator, it can enhance resistance to metal dendrite puncture and inhibit dendrite precipitation, thereby improving the reliability of the secondary battery.

[0041] The third aspect of the present application provides an electric device, which includes the secondary battery of the second aspect of the present application. When the secondary battery of the electric device uses the given separator, the reliability of the electric device can be improved.

[0042] Since the device of the present application includes the secondary battery provided by the present application, it has at least the same advantages as the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] To more clearly illustrate the technical solution of this application, the following is a brief introduction to the drawings used in this application. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without inventive effort.

[0044] FIG1 is a schematic structural diagram of an isolation membrane according to an embodiment of the present application.

[0045] FIG2 is a schematic structural diagram of another embodiment of the isolation membrane of the present application.

[0046] FIG3 is a schematic diagram of an embodiment of a secondary battery.

[0047] FIG. 4 is an exploded view of FIG. 3 .

[0048] FIG. 5 is a schematic diagram of an embodiment of a battery module.

[0049] FIG. 6 is a schematic diagram of a battery pack according to one embodiment.

[0050] FIG. 7 is an exploded view of FIG. 6 .

[0051] FIG. 8 is a schematic diagram of an embodiment of a device using a secondary battery as a power source. DETAILED DESCRIPTION

[0052] The present application will be further described below in conjunction with specific embodiments. It should be understood that these specific embodiments are only used to illustrate the present application and are not used to limit the scope of the present application.

[0053] For the sake of clarity, only some numerical ranges are specifically disclosed herein. However, any lower limit may be combined with any upper limit to form an unspecified range; and any lower limit may be combined with other lower limits to form an unspecified range, and similarly, any upper limit may be combined with any other upper limit to form an unspecified range. In addition, each individually disclosed point or single value may itself serve as a lower limit or upper limit and be combined with any other point or single value, or with other lower limits or upper limits, to form an unspecified range.

[0054] In the description herein, unless otherwise indicated, the term "or" is inclusive. That is, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0055] In the description of this article, it should be noted that, unless otherwise specified, “above” and “below” include the number itself, and “several” in “one or several” means two or more.

[0056] Unless otherwise specified, the terms used in this application have the commonly understood meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the various parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

[0057] secondary batteries

[0058] A secondary battery is a battery that can be recharged to activate the active materials after discharge and continue to be used.

[0059] Typically, a secondary battery consists of a positive electrode, a negative electrode, a separator, and an electrolyte. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The separator is placed between the positive and negative electrodes to provide isolation. The electrolyte conducts ions between the positive and negative electrodes.

[0060] [Isolation film]

[0061] Referring to Figure 1, an embodiment of the present application provides an isolation film 10, including: a first base film 11 and a second base film 12, the melting point of the second base film 12 is lower than the melting point of the first base film 11; the transverse elongation at break of the second base film 12 is greater than the longitudinal elongation at break of the second base film 12, and the longitudinal elongation at break of the second base film 12 is less than 100%.

[0062] Without wishing to be limited to any theory, the inventors have discovered through extensive research that in the specific isolation membrane structure of the present application, the melting point of the first base membrane is higher than that of the second base membrane, which can improve the heat resistance of the isolation membrane. By setting the transverse elongation at break of the second base membrane to be greater than the longitudinal elongation at break of the second base membrane, and the longitudinal elongation at break of the second base membrane to be less than 100%, the nail penetration performance of the isolation membrane can be effectively improved, preventing metal dendrites from penetrating the isolation membrane and causing a short circuit, thereby improving the reliability of the secondary battery.

[0063] After further research, the inventors found that if the isolation membrane can optionally meet one or more of the following designs, the performance of the battery can be further improved.

[0064] There are no particular restrictions on the materials of the first base film 11 and the second base film 12. Any known base film with good chemical stability and strength stability can be used. The materials of the first base film 11 and the second base film 12 of the isolation film 10 can be the same or different. In some embodiments, the first base film 11 and the second base film 12 can be selected from one or more of polyolefins, polyethers, polyetheretherketones, polyethylene terephthalate, polyimides, polytetrafluoroethylene, polytetrafluoroethylene, polyvinyl alcohol, glass fiber, non-woven fabrics, polyolefins, and polyvinylidene fluoride.

[0065] In any embodiment of the present application, the ratio of the transverse elongation at break of the second base film 12 to the longitudinal elongation at break of the second base film 12 is 1.05-4.5, and can be optionally 1.2-3.0, which can effectively improve the nail penetration performance of the isolation membrane and prevent metal dendrites from penetrating the isolation membrane and causing a short circuit, thereby improving the reliability of the secondary battery. For example, the ratio of the transverse elongation at break of the second base film 12 to the longitudinal elongation at break of the second base film 12 can be 1.05, 1.2, 1.5, 2.0, 2.15, 2.755, 3.0, 3.13, 3.5, 3.88, 4.0, 4.15, 4.25, 4.35, 4.5, etc., or a range consisting of any two of the above values, for example, it can be 1.05-2.0, 1.2-3.0, 2.15-2.755, 3.0-3.5, 3.88-4.25, 4.35-4.5, etc.

[0066] In any embodiment of the present application, the longitudinal elongation at break of the second base film 12 is 30%-90%, which can effectively improve the nail penetration performance of the separator, prevent metal dendrites from penetrating the separator and causing a short circuit, thereby improving the reliability of the secondary battery. For example, the longitudinal elongation at break of the second base film 12 can be 30%, 35%, 38%, 40%, 43%, 50%, 60%, 68%, 70%, 75%, 78%, 80%, 85%, 90%, etc., or a range consisting of any two of the above values, for example, 30%-40%, 40%-60%, 68%-75%, 80%-90%, etc.

[0067] In any embodiment of the present application, the transverse elongation at break of the first base film 11 is less than the longitudinal elongation at break of the first base film 11, which can effectively improve the nail penetration performance of the isolation membrane and prevent metal dendrites from penetrating the isolation membrane and causing a short circuit, thereby improving the reliability of the secondary battery.

[0068] In any embodiment of the present application, the ratio of the transverse elongation at break of the first base film 11 to the longitudinal elongation at break of the first base film 11 is 0.05-0.5, and can be optionally 0.1-0.3, which can effectively improve the nail penetration performance of the isolation membrane and prevent metal dendrites from penetrating the isolation membrane and causing a short circuit, thereby improving the reliability of the secondary battery. For example, the ratio of the transverse elongation at break of the first base film 11 to the longitudinal elongation at break of the first base film 11 can be 0.05, 0.09, 0.1, 0.13, 0.15, 0.19, 0.2, 0.25, 0.28, 0.3, 0.34, 0.36, 0.4, 0.42, 0.45, 0.5, or a range consisting of any two of the above values, for example, it can be 0.05-0.09, 0.1-0.15, 0.15-0.19, 0.1-0.3, 0.2-0.25, 0.28-0.34, 0.34-0.36, 0.4-0.42, 0.42-0.5, etc.

[0069] In any embodiment of the present application, the isolation film 10 satisfies at least one of the following (1)-(3):

[0070] (1) The transverse elongation at break of the first base film 11 is 30%-250%, and can be optionally 40%-200%;

[0071] (2) The longitudinal elongation at break of the first base film 11 is 40%-1000%, and can be optionally 400%-800%;

[0072] (3) The transverse elongation at break of the second base film 12 is 50%-250%, and can be optionally 100%-180%.

[0073] When the isolation membrane satisfies at least one of the above (1)-(3) and meets the given range, the nail penetration performance of the isolation membrane can be effectively improved, preventing metal dendrites from penetrating the isolation membrane and causing a short circuit, thereby improving the reliability of the secondary battery.

[0074] In any embodiment of the present application, the transverse tensile strength of the second base film 12 is less than the longitudinal tensile strength of the second base film 12; optionally, the ratio of the transverse tensile strength of the second base film 12 to the longitudinal tensile strength of the second base film 12 is 0.4-0.95, and more optionally 0.6-0.9, which can effectively improve the nail penetration performance of the isolation membrane, prevent metal dendrites from penetrating the isolation membrane and causing a short circuit, thereby improving the reliability of the secondary battery. For example, the ratio of the transverse tensile strength of the second base film 12 to the longitudinal tensile strength of the second base film 12 can be 0.4, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.83, 0.85, 0.9, 0.95, or a range consisting of any two of the above values, for example, it can be 0.4-0.5, 0.55-0.6, 0.6-0.9, 0.65-0.75, 0.75-0.8, 0.8-0.85, 0.85-0.9, 0.9-0.5, etc.

[0075] In any embodiment of the present application, the transverse tensile strength of the first base film 11 is less than the longitudinal tensile strength of the first base film 11; the ratio of the transverse tensile strength of the first base film 11 to the longitudinal tensile strength of the first base film 11 is 0.2-0.9, and can be optionally 0.3-0.6, which can effectively improve the nail penetration performance of the isolation membrane, prevent metal dendrites from penetrating the isolation membrane and causing a short circuit, thereby improving the reliability of the secondary battery. For example, the ratio of the transverse tensile strength of the first base film 11 to the transverse tensile strength of the second base film 12 can be 0.2, 0.25, 0.28, 0.3, 0.35, 0.4, 0.5, 0.55, 0.6, 0.65, 0.7, 0.78, 0.8, 0.82, 0.85, 0.9, etc., or a range consisting of any two of the above values, for example, it can be 0.2-0.25, 0.15-0.3, 0.25-0.4, 0.35-0.6, 0.3-0.6, 0.4-0.55, 0.55-0.7, 0.7-0.9, etc.

[0076] In any embodiment of the present application, the transverse tensile strength of the first base film 11 is less than the transverse tensile strength of the second base film 12 ; and / or, the longitudinal tensile strength of the first base film 11 is less than the longitudinal tensile strength of the second base film 12 .

[0077] When the lateral tensile strength of the first base film is less than the lateral tensile strength of the second base film, and / or the longitudinal tensile strength of the first base film is less than the longitudinal tensile strength of the second base film, the nail penetration performance of the isolation film can be effectively improved, preventing metal dendrites from penetrating the isolation film and causing a short circuit, thereby improving the reliability of the secondary battery.

[0078] In any embodiment of the present application, the isolation film 10 satisfies at least one of the following (1)-(4):

[0079] (1) The transverse tensile strength of the first base film 11 is 100 Kgf / cm 2 -1000Kgf / cm 2 , optional 200Kgf / cm 2 -750Kgf / cm 2 ;

[0080] (2) The longitudinal tensile strength of the first base film 11 is 700 Kgf / cm 2 -2500Kgf / cm 2 , optional 1000Kgf / cm 2 -1900Kgf / cm 2 ;

[0081] (3) The transverse tensile strength of the second base film 12 is 1200 Kgf / cm 2 -3800Kgf / cm 2 , optional 2000Kgf / cm 2 -3500Kgf / cm 2 ;

[0082] (4) The longitudinal tensile strength of the second base film 12 is 1800 Kgf / cm 2 -5500Kgf / cm 2 , optional 2100Kgf / cm 2 -3500Kgf / cm 2 .

[0083] When the isolation membrane satisfies at least one of the above (1)-(4) and meets the given range, the nail penetration performance of the isolation membrane can be effectively improved, preventing metal dendrites from penetrating the isolation membrane and causing a short circuit, thereby improving the reliability of the secondary battery.

[0084] The transverse tensile strength, longitudinal tensile strength, transverse heat shrinkage, and longitudinal heat shrinkage of the base film or separator have well-known meanings in the art and can be tested using equipment and methods known in the art. For example, they can be tested in accordance with standard GB / T 36363-2018.

[0085] In any embodiment of the present application, the melting point of the first base film 11 is 160°C-370°C, and may be 170°C-350°C. For example, the melting point may be 160°C, 165°C, 170°C, 180°C, 196°C, 200°C, 225°C, 235°C, 245°C, 260°C, 280°C, 290°C, 300°C, 315°C, 320°C, 330°C, 350°C, 370°C, or a range consisting of any two of the above values, for example, 160°C-170°C, 180°C-235°C, 225°C-280°C, 290°C-315°C, 350°C-370°C, etc. In some embodiments, the melting point of the second base film 12 is 120°C-280°C, and may be 130°C-160°C. For example, the temperature may be 120°C, 130°C, 135°C, 140°C, 145°C, 150°C, 155°C, 160°C, 165°C, 180°C, 185°C, 190°C, 196°C, 200°C, 215°C, 220°C, 235°C, 240°C, 245°C, 250°C, 255°C, 260°C, 265°C, 270°C, 275°C, 280°C, or a range consisting of any two of the above values, for example, 120°C-185°C, 130°C-250°C, 245°C-255°C, 130°C-160°C, etc.

[0086] The melting points of the first and second base films can be tested using equipment and methods known in the art. For example, differential scanning calorimetry can be used. For details, please refer to the standard GB / T 19466.3-2004. As an example, the following method can be used: 4-6 mg of the sample to be tested is placed in the sample chamber of a differential scanning calorimeter. The temperature is raised from 25°C to 400°C at a rate of 10°C / min. The melting endothermic curve of the sample is obtained, and the temperature corresponding to the peak of the curve is the melting point of the sample.

[0087] The first base film 11 and the second base film 12 can be directly compounded by hot pressing. During the hot pressing compounding process, if the temperature is too high, it will result in small porosity and poor air permeability; if the temperature is too low, the first base film 11 and the second base film 12 will not be firmly bonded. Therefore, it is necessary to adjust the appropriate hot pressing temperature. Optionally, the hot pressing temperature is 20°C-50°C. Referring to Figure 2, in any embodiment of the present application, an intermediate layer 13 may be further provided between the first base film 11 and the second base film 1212, and the intermediate layer 13 includes a binder. Optionally, the intermediate layer includes a binder and filler particles; more optionally, the filler particles include at least one of inorganic particles, organic particles, and organic-metal framework materials.

[0088] Optionally, the inorganic particles include one or more of inorganic particles having a dielectric constant of 5 or greater, inorganic particles having ion conductivity but not storing ions, and inorganic particles capable of undergoing electrochemical reactions.

[0089] Alternatively, the inorganic particles having a dielectric constant of 5 or more may include boehmite, aluminum oxide, zinc oxide, silicon oxide, titanium oxide, zirconium oxide, barium oxide, calcium oxide, magnesium oxide, nickel oxide, tin oxide, cerium oxide, yttrium oxide, hafnium oxide, aluminum hydroxide, magnesium hydroxide, silicon carbide, boron carbide, aluminum nitride, silicon nitride, boron nitride, magnesium fluoride, calcium fluoride, barium fluoride, barium sulfate, magnesium aluminum silicate, lithium magnesium silicate, sodium magnesium silicate, bentonite, hectorite, zirconium titanate, barium titanate, Pb(Zr,Ti)O3 (abbreviated as PZT), Pb 1-m La m Zr 1-n Ti n O3 (abbreviated as PLZT, 0<m<1, 0<n<1), Pb(Mg3Nb 2 / 3 )O3-PbTiO3 (abbreviated as PMN-PT), and at least one of their respective modified inorganic particles. Optionally, the modification method of each inorganic particle may be chemical modification and / or physical modification. The chemical modification method includes coupling agent modification (for example, using silane coupling agent, titanate coupling agent, etc.), surfactant modification, polymer grafting modification, etc. The physical modification method may be mechanical force dispersion, ultrasonic dispersion, high energy treatment, etc. The 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 a coupling agent, surfactant or polymer with a specific functional group to modify the inorganic particles, it is also helpful to improve the wetting and retention properties of the adhesive layer to the electrolyte, and improve the adhesion of the adhesive layer to the first base film and the second base film.

[0090] Alternatively, the inorganic particles having ion conductivity but not storing ions may include Li3PO4, lithium titanium phosphate Li x1 Ti y1 (PO4)3, lithium aluminum titanium phosphate Li x2 Al y2 Ti z1 (PO4)3, (LiAlTiP) x3 O y3 Type glass, lanthanum lithium titanate Li x4 La y4 TiO3, lithium germanium thiophosphate Li x5 Ge y5 P z2 S w , lithium nitride Li x6 N y6 、SiS2 type glass Li x7 Siy7 S z3 and P2S5 glass Li x8 P y8 S z4 At least one of the following: 0<x1<2, 0<y1<3, 0<x2<2, 0<y2<1, 0<z1<3, 0<x3<4, 0<y3<13, 0<x4<2, 0<y4<3, 0<x5<4, 0<y5<1, 0<z2<1, 0<w<5, 0<x6<4, 0<y6<2, 0<x7<3, 0<y7<2, 0<z3<4, 0<x8<3, 0<y8<3, 0<z4<7. This can further improve the ion conductivity of the isolation membrane.

[0091] Alternatively, the inorganic particles capable of undergoing electrochemical reaction may include at least one of lithium-containing transition metal oxides, lithium-containing phosphates, carbon-based materials, silicon-based materials, tin-based materials, and lithium-titanium compounds.

[0092] Alternatively, the organic particles may include one or more of polycarbonate, polythiophene, polypyridine, polystyrene, polyacrylic wax, polyethylene, polypropylene, cellulose, a cellulose modifier (e.g., carboxymethyl cellulose), a melamine resin, a phenolic resin, a polyester (e.g., polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate), a silicone resin, a polyimide, a polyamideimide, a polyaromatic amide, polyphenylene sulfide, a polysulfone, a polyethersulfone, a polyetheretherketone, a polyaryletherketone, a copolymer of butyl acrylate and ethyl methacrylate (e.g., a cross-linked polymer of butyl acrylate and ethyl methacrylate).

[0093] Optionally, the organic-metal framework material may include one or more of a nitrogen-containing heterocyclic ligand building structure, an organic carboxylic acid ligand building structure, and a nitrogen-oxygen mixed ligand building structure.

[0094] In some embodiments, the content of the binder may be greater than or equal to 10%, optionally 10%-30%, based on the total weight of the adhesive layer.

[0095] In some embodiments, the content of the filler may be less than or equal to 90%, optionally 40%-90%, 60%-80%, based on the total weight of the adhesive layer.

[0096] In some embodiments, the intermediate layer may further include a dispersant, such as carboxymethyl cellulose, to adjust the viscosity of the intermediate layer slurry and improve the quality and uniformity of the intermediate layer.

[0097] In some embodiments, the content of the dispersant may be less than or equal to 25%, optionally less than or equal to 20%, based on the total weight of the adhesive layer.

[0098] When an intermediate layer is provided between the first base film and the second base film, it can not only compensate for process defects of the base film during the hot pressing composite process, but also further improve the physical stability of the isolation film, thereby improving the reliability of the secondary battery.

[0099] In any embodiment of the present application, the binder includes one or more of polyacrylate, polyacrylic acid, polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride-trichloroethylene copolymer, polyvinyl pyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyethylene oxide, polyarylate, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, polyacrylonitrile, polyvinyl alcohol, polyethylene, polypropylene, starch, and cyanoethyl pullulan. When an intermediate layer is provided between the first basement membrane and the second basement membrane, and the binder in the intermediate layer includes the above components, the reliability of the secondary battery can be improved. In some embodiments, carboxymethyl cellulose can be used as a thickener to adjust the viscosity of the slurry.

[0100] In any embodiment of the present application, the isolation film satisfies at least one of the following (1)-(6):

[0101] (1) The transverse elongation at break of the isolation film 10 is 50%-220%, and can be optionally 70%-170%;

[0102] (2) The longitudinal elongation at break of the isolation film 10 is 30%-150%, and can be optionally 40%-100%;

[0103] (3) The transverse tensile strength of the isolation film 10 is 1200-4000 Kgf / cm 2 , optional 2100-3600Kgf / cm 2 ;

[0104] (4) The longitudinal tensile strength of the separator 10 is 1900-5500 Kgf / cm 2 , optional 2200-3700Kgf / cm 2 ;

[0105] (5) The transverse heat shrinkage of the isolation film 10 at 250° C. for 1 hour is ≤2%, and may be ≤1.0%;

[0106] (6) The longitudinal heat shrinkage rate of the isolation film 10 at 250° C. for 1 hour is ≤2%, and can be optionally ≤1.0%.

[0107] When the separator satisfies at least one of the above (1) to (6) and falls within the given range, the separator has good heat resistance and physical properties, thereby improving the reliability of the secondary battery.

[0108] Unless otherwise specified, all raw materials used in the separator (eg, the first base film, the second base film, the adhesive, the filler, etc.) can be purchased commercially.

[0109] The present application provides a secondary battery comprising the separator 10 of any of the above solutions. When the secondary battery adopts the separator, the reliability of the secondary battery can be improved.

[0110] [Positive electrode]

[0111] In a secondary battery, a positive electrode sheet generally includes a positive electrode current collector and a positive electrode film layer disposed on the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0112] The positive electrode current collector may be a conventional metal foil or a composite current collector (a metal material may be disposed on a polymer substrate to form a composite current collector). As an example, the positive electrode current collector may be an aluminum foil.

[0113] There is no limitation on the specific type of the positive electrode active material. Active materials known in the art that can be used for the positive electrode of a secondary battery can be used. Those skilled in the art can select according to actual needs.

[0114] As an example, the positive electrode active material may include, but is not limited to, one or more of lithium transition metal oxides, olivine-structured lithium-containing phosphates, and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon, and their modified compounds. These materials can all be obtained through commercial channels.

[0115] The modified compounds of the above materials may be doping-modified and / or surface-coated modified materials.

[0116] The positive electrode film layer usually optionally includes a binder, a conductive agent and other optional additives.

[0117] As an example, the conductive agent may be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, conductive carbon black (Super P, SP), graphene, and carbon nanofibers.

[0118] As an example, the binder can be one or more of styrene butadiene rubber (SBR), water-based acrylic resin, polyvinylidene difluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA) and polyvinyl butyral (PVB).

[0119] [Negative electrode]

[0120] In a secondary battery, a negative electrode plate generally includes a negative electrode current collector and a negative electrode film layer disposed on the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0121] The negative electrode current collector may be a conventional metal foil or a composite current collector (for example, a metal material may be disposed on a polymer substrate to form a composite current collector). As an example, the negative electrode current collector may be a copper foil.

[0122] The specific type of negative electrode active material is not limited, and active materials that can be used for the negative electrode of a secondary battery known in the art can be used, and those skilled in the art can make a selection according to actual needs. As an example, the negative electrode active material may include, but is not limited to, one or more of artificial graphite, natural graphite, hard carbon, soft carbon, silicon-based materials and tin-based materials. Silicon-based materials can be selected from one or more of elemental silicon, silicon oxides (such as silicon monoxide), silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials can be selected from one or more of elemental tin, tin oxides, and tin alloys. These materials can all be obtained commercially.

[0123] In some embodiments, to further increase the energy density of the battery, the negative electrode active material may include a silicon-based material.

[0124] The negative electrode film layer usually optionally includes a binder, a conductive agent and other optional auxiliary agents.

[0125] As an example, the conductive agent may be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0126] As an example, the binder may be one or more of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyvinyl alcohol (PVA) and polyvinyl butyral (PVB).

[0127] As an example, other optional auxiliary agents may be thickening and dispersing agents (such as carboxymethylcellulose sodium, CMC-Na), and PTC thermistor materials.

[0128] [Electrolyte]

[0129] Secondary batteries may include an electrolyte that conducts ions between a positive electrode and a negative electrode. The electrolyte may include an electrolyte salt and a solvent.

[0130] As an example, the electrolyte salt can be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalatophosphate) (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0131] As an example, the solvent may be selected from ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl darbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), n-propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), n-propyl propionate (NP), propylene glycol (PEG), propylene glycol (PP), propylene glycol (C1), propylene glycol (C2), propylene glycol (C3), propylene glycol (C4), propylene glycol (C5), propylene glycol (C6), propylene glycol (C7), propylene glycol (C8), propylene glycol (C9), propylene glycol (D1), propylene glycol (D2), propylene glycol (D3), propylene glycol (D4), propylene glycol (D5), propylene glycol (D6), propylene glycol (D7), propylene glycol (D8), propylene glycol (D9), propylene glycol (D10), propylene glycol (D11), propylene glycol (D12), propylene glycol (D13), propylene glycol (D14), propylene glycol (D15), propylene glycol (D16), propylene glycol (D17), propylene glycol (D18), propylene glycol (D19), propylene glycol (D20), propylene glycol (D21), propylene glycol (D22), propylene glycol (D23), propylene glycol (D24), propylene glycol (D25), propylene glycol (D26), propylene glycol (D27), propylene glycol (D28), propylene glycol (D29), propylene glycol (D31), propylene glycol (D32), propylene glycol (D33), propylene glycol (D34), propylene glycol (D35), propylene glycol (D36), propylene glycol (D37), propylene glycol (D38), propylene glycol (D39), propylene One or more of the group consisting of propionate (PP), methyl butyrate (Methyl Butyrate MB), ethyl butyrate (Ethyl Butyrate, EB), 1,4-butyrolactone (1,4-Butyrolactone, GBL), tetramethylene sulfone (SF), dimethyl sulfone (Methyl Sulfone, MSM), methyl ethyl sulfone (Methyl Ethyl Sulfone, EMS) and diethyl sulfone (Diethyl Sulfone, ESE).

[0132] In some embodiments, the electrolyte further includes additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives capable of improving certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature performance.

[0133] In some embodiments, the secondary battery may be a lithium-ion secondary battery. In any embodiment of the present application, the separator 10 is disposed between the positive electrode sheet and the negative electrode sheet, and the second base film 12 faces the negative electrode sheet.

[0134] The base film with low tensile strength has good heat resistance. Therefore, the first base film with low longitudinal tensile strength is positioned toward the positive electrode, leveraging its excellent heat resistance. The base film with high longitudinal tensile strength has excellent physical properties and is less susceptible to puncture by metal dendrites. Therefore, the second base film with high longitudinal tensile strength is positioned toward the negative electrode, leveraging its excellent physical properties to inhibit dendrite precipitation. Positioning the first base film with good heat resistance toward the positive electrode and the second base film with good physical properties toward the negative electrode can enhance resistance to metal dendrite puncture, thereby improving the reliability of the secondary battery.

[0135] The embodiment of the present application has no particular limitation on the shape of the secondary battery, which can be cylindrical, square, or any other shape. FIG3 shows a secondary battery 5 with a square structure as an example.

[0136] In some embodiments, the secondary battery may include an outer package for packaging the positive electrode sheet, the negative electrode sheet, and the electrolyte. The first base film 11 of the separator 10 faces the positive electrode sheet.

[0137] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0138] In some embodiments, referring to FIG4 , the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, which together form a receiving cavity. The housing 51 may have an opening communicating with the receiving cavity, and the cover 53 may be positioned over the opening to seal the receiving cavity.

[0139] The preparation method of the secondary battery of the present application is well known. In some embodiments, the positive electrode sheet, the separator 10, the negative electrode sheet and the electrolyte can be assembled to form a secondary battery. As an example, the positive electrode sheet, the separator 10, and the negative electrode sheet can be formed into an electrode assembly through a winding process and / or a lamination process, and the electrode assembly is placed in an outer package, dried and injected with electrolyte, and then vacuum packaged, allowed to stand, formed, and shaped to obtain a battery cell. Multiple battery cells can also be further connected in series, in parallel, or mixed to form a battery module. Multiple battery modules can also be connected in series, in parallel, or mixed to form a battery pack. In some embodiments, multiple battery cells can also directly form a battery pack.

[0140] Figure 5 shows an example battery module 4. Referring to Figure 5 , in the battery module 4, multiple secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple secondary batteries 5 may be secured using fasteners.

[0141] The battery module 4 may further include a housing having a housing space, and the plurality of secondary batteries 5 may be housed in the housing space.

[0142] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0143] Figures 6 and 7 illustrate an example battery pack 1. Referring to Figures 6 and 7 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be positioned over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0144] [Installation]

[0145] The present application also provides an electrical device, which includes the secondary battery of the present application. The battery cell, battery module or battery pack can be used as a power source for the device, or as an energy storage unit for the device. The device can be, but is not limited to, a mobile device (such as a mobile phone, a laptop computer), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck), an electric train, a ship and a satellite, and an energy storage system.

[0146] The device can select battery cells, battery modules or battery packs according to its usage requirements.

[0147] Figure 8 shows an example of an electric device. This device 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, a battery pack or battery module can be used.

[0148] As another example, an electric device may be a mobile phone, a tablet computer, or a laptop computer. Such an electric device is generally required to be lightweight and thin, and may use a battery cell as a power source.

[0149] The beneficial effects of the present application are further illustrated below with reference to the examples.

[0150] In order to make the technical problems, technical solutions and beneficial effects solved by the embodiments of the present application clearer, the following will be further described in detail with reference to the embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present application and its applications. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0151] 1. Preparation of isolation membrane

[0152] Isolation film 1:

[0153] (1) A first base film and a second base film are provided.

[0154] The first base film meets the following requirements: the material is polypropylene (PP), the melting point is 165 ° C, the transverse elongation at break is 40%, the longitudinal elongation at break is 400%, and the transverse tensile strength T1 is 400Kgf / cm 2 , longitudinal tensile strength L1 is 900Kgf / cm 2 .

[0155] The second base film meets the following requirements: the material is polyethylene (PE), the melting point is 135°C, the transverse elongation at break is 105%, the longitudinal elongation at break is 50%, and the transverse tensile strength T2 is 1400Kgf / cm 2 , longitudinal tensile strength L2 is 1700Kgf / cm 2 .

[0156] Among them, the ratio T1 / T2 of the transverse tensile strength T1 of the first base film to the transverse tensile strength T2 of the second base film is 0.29, and the ratio L1 / L2 of the longitudinal tensile strength L1 of the first base film to the longitudinal tensile strength L2 of the second base film is 0.53.

[0157] (2) Preparation of intermediate layer slurry: The binder polyacrylate and the filler aluminum oxide particles and carboxymethyl cellulose are mixed uniformly in a proper amount of solvent deionized water in a ratio of 1:4:1 to prepare the intermediate layer slurry.

[0158] (3) The intermediate layer slurry of step (2) is coated on one side of the second base film of step (1) to form an intermediate layer.

[0159] (4) The first base film is laminated with the second base film coated in step (3) by hot pressing to obtain an isolation film, wherein the intermediate layer is between the first base film and the second base film.

[0160] The preparation methods of isolation films 2-13 are similar to those of isolation film 1, except that the melting point, material, transverse elongation at break, longitudinal elongation at break, transverse tensile strength, or longitudinal tensile strength of the base film are adjusted. See Table 1 for details. All other preparation methods are consistent with those of the isolation film of Example 1.

[0161] The isolation membrane 1 prepared by the above method was subjected to relevant performance tests, and the specific results are shown in Table 1.

[0162] 2. Preparation of batteries

[0163] Example 1

[0164] 1. Preparation of positive electrode sheet

[0165] The positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), conductive agent carbon black (SuperP), and binder polyvinylidene fluoride (PVDF) are mixed evenly in an appropriate amount of solvent N-methylpyrrolidone (NMP) in a mass ratio of 96.2:2.7:1.1 to obtain positive electrode slurry, which is then coated on the positive electrode current collector aluminum foil, and the positive electrode sheet is obtained through drying, cold pressing, slitting, and cutting processes.

[0166] 2. Preparation of negative electrode sheet

[0167] The negative electrode active material artificial graphite, conductive agent carbon black (SuperP), binder styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC-Na) are mixed uniformly in a proper amount of solvent deionized water at a mass ratio of 96.4:0.7:1.8:1.1 to obtain a negative electrode slurry. The negative electrode slurry is coated on the negative electrode current collector copper foil, and the negative electrode sheet is obtained through the processes of drying, cold pressing, slitting and cutting.

[0168] 3. Isolation film

[0169] The isolation film used was the isolation film 1 prepared above.

[0170] 4. Preparation of electrolyte

[0171] Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 30:70 to obtain an organic solvent. Fully dried electrolyte salt LiPF6 is dissolved in the above mixed solvent. The concentration of the electrolyte salt is 1.0 mol / L. After mixing evenly, an electrolyte solution is obtained.

[0172] 5. Preparation of secondary batteries

[0173] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, with the separator placed between the positive electrode sheet and the negative electrode sheet to serve as an isolation, and then wound to obtain an electrode assembly; the electrode assembly is placed in an outer package, and the prepared electrolyte is injected into the dried secondary battery. After vacuum packaging, standing, formation, and shaping processes, a secondary battery is obtained.

[0174] The preparation methods of the secondary batteries of Examples 2-11 and Comparative Examples 1-2 are similar to those of the secondary battery of Example 1, except that different isolation membranes are used (Example 1-11 uses isolation membrane 1-11, and Comparative Example 1-2 uses isolation membrane 12-13). See Table 1 for details.

[0175] 3. Battery performance test

[0176] 1. Transverse heat shrinkage test at 250℃

[0177] Sample preparation: Punch the prepared isolation film into samples with a width of 50 mm and a length of 100 mm using a punching machine. Place 5 parallel samples on A4 paper and fix them. Then place the A4 paper with the samples on corrugated paper with a thickness of 1 mm to 5 mm.

[0178] Sample test: Place A4 paper on corrugated paper into a blast oven. Set the oven temperature to 250°C. After the temperature reaches the set temperature and stabilizes for 30 minutes, start timing. After the set time (1 hour in this application) is reached, measure the width of the isolation film. The value is marked as a.

[0179] Calculation of thermal shrinkage: Transverse direction (TD) thermal shrinkage = [(50-a) / 50] × 100%, and the average value of 5 parallel samples is taken as the test result.

[0180] 2. Nail penetration performance

[0181] The test is carried out at 25°C and the battery is at 100% SOC. The insulation pad / puncture cell / insulation pad / test cell / insulation pad are placed in this order. The high-temperature temperature-sensitive line is connected. The water circulation is started in advance. When the temperature of the large surface of the cell is stable at 25°C, the circulation is continued for more than 10 minutes. A φ3mm high-temperature resistant steel needle is used, facing the center of the heat source, and the needle is punctured at a speed of 0.01mm / s until the punctured cell fails and burns. The changes in the voltage and other values ​​of the test cell are monitored. If the failure stops (the instrument shows that the voltage fluctuates or drops sharply), the time is recorded. If there is no change in the voltage and other values, it is considered a pass. Among them, the punctured cell refers to the punctured cell, which is used as a heat source.

[0182] As can be seen from Table 1, in Examples 1-11, the melting point of the second base film is lower than the melting point of the first base film, and the transverse elongation at break of the second base film is greater than the longitudinal elongation at break of the second base film, and the longitudinal elongation at break of the second base film is less than 100%; the battery using this isolation film has enhanced nail penetration resistance and higher battery reliability.

[0183] In Comparative Examples 1-2, the transverse elongation at break of the second base film is less than or equal to the longitudinal elongation at break of the second base film, and the heat resistance and nail penetration performance are poor, which can easily cause battery safety problems.

[0184] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present application, and such modifications or substitutions should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A separation film, comprising: First basement membrane; a second base film, wherein the melting point of the second base film is lower than the melting point of the first base film; The transverse elongation at break of the second base film is greater than the longitudinal elongation at break of the second base film, and the longitudinal elongation at break of the second base film is less than 100%.

2. The isolation film according to claim 1, wherein The ratio of the transverse elongation at break of the second base film to the longitudinal elongation at break of the second base film is 1.05-4.5, and can be optionally 1.2-3.

0.

3. The isolation film according to claim 1 or 2, wherein: The longitudinal elongation at break of the second base film is 30%-90%.

4. The isolation film according to any one of claims 1 to 3, wherein: The transverse elongation at break of the first base film is smaller than the longitudinal elongation at break of the first base film.

5. The isolation film according to any one of claims 1 to 4, wherein: The ratio of the transverse elongation at break of the first base film to the longitudinal elongation at break of the first base film is 0.05-0.5, and can be optionally 0.1-0.

3.

6. The isolation film according to any one of claims 1 to 5, wherein: The isolation film satisfies at least one of the following (1)-(3): (1) The transverse elongation at break of the first base film is 30%-250%, and can be 40%-200%; (2) the longitudinal elongation at break of the first base film is 40%-1000%, and can be 400%-800%; (3) The transverse elongation at break of the second base film is 50%-250%, and can be optionally 100%-180%.

7. The isolation film according to any one of claims 1 to 6, wherein: The transverse tensile strength of the second base film is less than the longitudinal tensile strength of the second base film; optionally, the ratio of the transverse tensile strength of the second base film to the longitudinal tensile strength of the second base film is 0.4-0.95, and more optionally 0.6-0.

9.

8. The separator according to any one of claims 1 to 7, wherein: The transverse tensile strength of the first base film is less than the longitudinal tensile strength of the first base film; the ratio of the transverse tensile strength of the first base film to the longitudinal tensile strength of the first base film is 0.2-0.9, and can be optionally 0.3-0.

6.

9. The isolation film according to any one of claims 1 to 8, wherein: The transverse tensile strength of the first base film is less than the transverse tensile strength of the second base film; and / or, The longitudinal tensile strength of the first base film is smaller than the longitudinal tensile strength of the second base film.

10. The separator according to any one of claims 1 to 9, wherein: The isolation film satisfies at least one of the following (1)-(4): (1) The transverse tensile strength of the first base film is 100Kgf / cm2-1000Kgf / cm2, and can be optionally 200Kgf / cm2-750Kgf / cm2; (2) The longitudinal tensile strength of the first base film is 700Kgf / cm2-2500Kgf / cm2, and can be 1000Kgf / cm2-1900Kgf / cm2; (3) The transverse tensile strength of the second base film is 1200Kgf / cm2-3800Kgf / cm2, and can be 2000Kgf / cm2-3500Kgf / cm2; (4) The longitudinal tensile strength of the second base film is 1800Kgf / cm2-5500Kgf / cm2, and can be optionally 2100Kgf / cm2-3500Kgf / cm2.

11. The isolation film according to any one of claims 1 to 10, wherein: The melting point of the first base film is 160° C.-370° C., and can be 170° C.-350° C.; and / or, The melting point of the second base film is 120°C-280°C, and can be optionally 130°C-260°C.

12. The isolation film according to any one of claims 1 to 11, wherein: The isolation film further includes an intermediate layer, which is disposed between the first base film and the second base film and includes a binder; optionally, the intermediate layer includes a binder and filler particles.

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

14. The isolation film according to any one of claims 1 to 13, wherein: The isolation film satisfies at least one of the following (1) to (6): (1) The transverse elongation at break of the isolation film is 50%-220%, and can be 70%-170%; (2) The longitudinal elongation at break of the isolation film is 30%-150%, and can be 40%-100%; (3) The transverse tensile strength of the isolation film is 1200Kgf / cm2-4000Kgf / cm2, and can be optionally 2100Kgf / cm2-3600Kgf / cm2; (4) The longitudinal tensile strength of the isolation film is 1900Kgf / cm2-5500Kgf / cm2, and can be optionally 2200Kgf / cm2-3700Kgf / cm2; (5) The transverse heat shrinkage rate of the isolation film at 250° C. for 1 hour is ≤2%, and can be optionally ≤1.0%; (6) The longitudinal heat shrinkage rate of the isolation film at 250° C. for 1 hour is ≤2%, and can be optionally ≤1.0%. 15 . A secondary battery comprising the separator according to claim 1 .

16. The secondary battery according to claim 15, wherein: The secondary battery further includes a positive electrode sheet and a negative electrode sheet, the separator is arranged between the positive electrode sheet and the negative electrode sheet, and the second base film faces the negative electrode sheet.

17. An electric device comprising the secondary battery according to claim 15.

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