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 lower than that of the first base membrane; the average cellosilk diameter in the first base membrane is greater than the average cellosilk diameter of the second base membrane. And the average fiber diameter of the second base membrane is smaller, so that the second base membrane is endowed with richer pore structures, and the endurance capacity of the second base membrane to lithium dendrite physical puncture is enhanced. In addition, when the average fiber diameter of the first base membrane with the high melting point is larger than the average fiber diameter of the second base membrane with the low melting point, the continuity and effectiveness of an ion transmission channel of the final isolating membrane can be guaranteed. Therefore, the reliability of the separator is improved, and 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 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, aiming to improve the reliability performance of secondary batteries.

[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 average fiber filament diameter in the first base film is greater than the average fiber filament diameter of the second base film.

[0007] Compared with the prior art, this application has at least the following beneficial effects:

[0008] When the average fiber diameter of the first base film with a higher melting point is greater than that of the second base film with a lower melting point, and the average fiber diameter of the second base film is smaller, the second base film is endowed with a rich pore structure, thereby enhancing the second base film's resistance to physical penetration by lithium dendrites. Furthermore, when the average fiber diameter of the first base film with a higher melting point is greater than that of the second base film with a lower melting point, the continuity and effectiveness of the ion transport channels in the final separator are ensured, allowing the final separator to have both heat resistance and good strength, thereby improving the reliability of the separator.

[0009] In any embodiment of the present application, the ratio of the average fiber filament diameter in the first basement membrane to the average fiber filament diameter in the second basement membrane is greater than or equal to 1.1-9, and can be optionally 1.2-4.5.

[0010] In any embodiment of the present application, the average fiber filament diameter in the first basement membrane is 50nm-550nm, and can be optionally 80nm-350nm.

[0011] In any embodiment of the present application, the average fiber diameter of the second base membrane is 30nm-450nm, and can be optionally 50nm-260nm.

[0012] When the average fiber diameter of the first basement membrane and / or the second basement membrane is selected within the above range, the two basement membranes can have a rich pore structure while also having good strength, ensuring the continuity and effectiveness of the ion transmission channel of the final isolation membrane, thereby further improving the reliability of the isolation membrane.

[0013] In any embodiment of the present application, the ratio of the weight per unit area of ​​the first base film to the weight per unit area of ​​the second base film is greater than or equal to 1.02, and can be optionally 1.2-2.5.

[0014] In any embodiment of the present application, the weight per unit area of ​​the first base film is 2.5 g / m 2 -10g / m 2 , 3g / m2 is optional 2 -7g / m 2 and / or, the weight per unit area of ​​the second base film is 2g / m 2 -10g / m 2 , optional 2.5g / m 2 -6g / m 2 .

[0015] When the weight per unit area of ​​the first base film and the weight per unit area of ​​the second base film are within the above-given ranges, the isolation film can better combine heat resistance and strength, thereby further improving the reliability of the isolation film.

[0016] In any embodiment of the present application, the melting point of the first base film is 160°C-370°C, optionally 165°C-330°C; and / or the melting point of the second base film is 120°C-265°C, optionally 130°C-230°C.

[0017] When the melting point of the first base film is 160°C-370°C and / or the melting point of the second base film is 120°C-265°C, the combination of the two can provide the isolation film with both heat resistance and good strength, thereby improving the reliability of the isolation film. When the melting point of the first base film is 165°C-330°C and / or the melting point of the second base film is 130°C-230°C, the isolation film can further provide both heat resistance and good strength, thereby further improving the reliability of the isolation film.

[0018] In any embodiment of the present application, the thickness of the first base film is greater than or equal to the thickness of the second base film; optionally, the ratio of the thickness of the first base film to the thickness of the second base film is 1.1-5, and can be optionally 1.5-3.0.

[0019] In any embodiment of the present application, the thickness of the first base film is 2 μm-12 μm, optionally 3 μm-6 μm; and / or the thickness of the second base film is 2 μm-9 μm, optionally 3 μm-5 μm.

[0020] When the thickness of the first base film and / or the second base film is within the above-given range, the battery can have better reliability and further improve the energy density of the battery.

[0021] In any embodiment of the present application, the ratio of the porosity of the first base film to the porosity of the second base film is 1.05-3, and can be optionally 1.1-1.5.

[0022] When the porosity ratio of the first base film to the porosity of the second base film is 1.05-3, the first base film has a large porosity and good air permeability, while the second base film has a small porosity and strong strength, providing support. As a result, the composite of the first and second base films can improve the reliability and cycle performance of the secondary battery. When the porosity ratio of the first base film to the porosity of the second base film is 1.1-1.5, the air permeability and support performance of the separator can be further balanced, thereby further improving the reliability and cycle performance of the secondary battery.

[0023] In any embodiment of the present application, the porosity of the first base film is 30%-80%, optionally 50%-75%; and / or the porosity of the second base film is 30%-70%, optionally 40%-50%.

[0024] When the porosity of the first base film and / or the second base film is within the given range, the air permeability and supporting performance of the separator can be further balanced, thereby further improving the reliability and cycle performance of the secondary battery.

[0025] In any embodiment of the present application, the separator further includes an intermediate layer disposed between the first and second base films, and the intermediate layer includes a binder; optionally, the intermediate layer also includes filler particles. When the intermediate layer is disposed between the first and second base films, and the intermediate layer includes filler particles, the reliability of the secondary battery can be improved.

[0026] In any embodiment of the present application, the binder includes one or more of polyacrylate, acrylic acid, carboxymethyl cellulose, polyvinylidene fluoride-co-trichloroethylene copolymer, polymethyl methacrylate, polyvinyl pyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate copolymer, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, polyvinylidene fluoride, polyacrylonitrile, polyvinyl alcohol, starch, hydroxypropyl cellulose, regenerated cellulose, tetrafluoroethylene, polyethylene, polypropylene, and cyanoethyl pullulan. When an intermediate layer is provided between the first base film and the second base film, and the binder in the intermediate layer includes the above components, the reliability of the secondary battery can be improved.

[0027] In any embodiment of the present application, the filling particles include at least one of inorganic particles, organic particles, and organic-metal framework materials.

[0028] When an intermediate layer is provided between the first base film and the second base film, and the filling particles in the intermediate layer include at least one of the above-mentioned inorganic particles, organic particles, and organic-metal framework materials, the filling particles in the intermediate layer can further improve the heat resistance and strength of the isolation membrane, thereby improving the reliability of the secondary battery.

[0029] In any embodiment of the present application, the isolation film satisfies at least one of the following (1)-(3): (1) The weight per unit area of ​​the isolation film is 5-20 g / m 2 , optional 6-15g / m 2 ; (2) The porosity of the isolation membrane is 30%-55%, and can be optionally 35%-45%; (3) The air permeability of the isolation membrane is less than 350s / 100cc, and can be optionally 150s / 100cc-300s / 100cc.

[0030] When at least one of the above characteristics of the separator satisfies the given range, the separator can have good heat resistance and strength, thereby improving the reliability and cycle performance of the secondary battery.

[0031] 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.

[0032] In any embodiment of the present application, the secondary battery further includes a positive electrode sheet and a negative electrode sheet, with a separator disposed between the positive and negative electrode sheets, and the second base film of the separator facing the negative electrode sheet. When the secondary battery utilizes the given separator, the second base film having a smaller average fiber diameter faces the negative electrode sheet. The second base film has good strength, can exert its excellent physical properties, and is not easily punctured by lithium dendrites generated by the negative electrode, thereby improving the reliability of the secondary battery.

[0033] 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.

[0034] 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

[0035] 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.

[0036] FIG1 is a schematic structural diagram of an isolation membrane according to an embodiment of the present application.

[0037] FIG2 is a schematic structural diagram of another embodiment of the isolation membrane of the present application.

[0038] FIG3 is a schematic diagram of an embodiment of a secondary battery.

[0039] FIG. 4 is an exploded view of FIG. 3 .

[0040] FIG. 5 is a schematic diagram of an embodiment of a battery module.

[0041] FIG. 6 is a schematic diagram of a battery pack according to one embodiment.

[0042] FIG. 7 is an exploded view of FIG. 6 .

[0043] FIG. 8 is a schematic diagram of an embodiment of a device using a secondary battery as a power source. DETAILED DESCRIPTION

[0044] 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.

[0045] 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.

[0046] 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).

[0047] 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.

[0048] 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).

[0049] secondary batteries

[0050] A secondary battery is a battery that can be recharged to activate the active materials after discharge and continue to be used.

[0051] 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.

[0052] [Isolation film]

[0053] 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 average fiber filament diameter in the first base film 11 is greater than the average fiber filament diameter of the second base film 12.

[0054] Without wishing to be limited to any theory, the inventors have discovered through extensive research that in the specific isolation membrane 10 structure of the present application, laminating a first base membrane 11 having a high melting point and a large average fiber filament diameter and a second base membrane 12 having a low melting point and a small average fiber filament diameter can make the final isolation membrane 10 have both good heat resistance and high strength, thereby improving the reliability of the isolation membrane.

[0055] 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.

[0056] 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 are 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, polyethylene, polypropylene, and polyvinylidene fluoride.

[0057] When the average fiber diameter of the first base film with a higher melting point is greater than that of the second base film with a lower melting point, and the average fiber diameter of the second base film is smaller, the second base film is endowed with a rich pore structure, thereby enhancing the second base film's resistance to physical penetration by lithium dendrites. Furthermore, when the average fiber diameter of the first base film with a higher melting point is greater than that of the second base film with a lower melting point, the continuity and effectiveness of the ion transport channels in the final separator are ensured, allowing the final separator to have both heat resistance and good strength, thereby improving the reliability of the separator.

[0058] In any embodiment of the present application, the ratio of the average fiber filament diameter in the first basement membrane 11 to the average fiber filament diameter in the second basement membrane 12 is 1.1-9, and can be optionally 1.2-4.5. For example, the ratio of the average fiber filament diameter in the first base membrane 11 to the average fiber filament diameter in the second base membrane 12 can be 1.1, 1.2, 1.6, 2.0, 2.2, 2.4, 2.9, 3.0, 3.5, 4.0, 4.4, 4.5, 4.7, 5.2, 5.8, 6.3, 6.6, 7.0, 7.8, 8.0, 8.4, 9.0, etc., or a range consisting of any two of the above values, for example, it can be 1.1-1.2, 1.6-2.0, 2.2-2.9, 3.0-4.0, 3.5-4.5, 4.7-5.2, 5.8-6.3, 6.6-7.0, 7.8-8.0, 8.0-9.0, etc.

[0059] In any embodiment of the present application, the average fiber filament diameter in the first basement membrane 11 is 50nm-550nm, and can be optionally 80nm-350nm.

[0060] For example, the average fiber diameter in the first basement membrane 11 can be 50nm, 60nm, 75nm, 80nm, 93nm, 100nm, 116nm, 135nm, 160nm, 188nm, 200nm, 225nm, 293nm, 300nm, 316nm, 350nm, 460nm, 510nm, 550nm, etc., or a range consisting of any two of the above values, for example, it can be 80nm-350nm, 50nm-60nm, 75nm-80nm, 80nm-100nm, 100nm-135nm, 135nm-188nm, 200nm-225nm, 225nm-300nm, 316nm-350nm, 510nm-550nm, etc.

[0061] In any embodiment of the present application, the average fiber diameter of the second basement membrane 12 is 30nm-450nm, and can be optionally 50nm-260nm.

[0062] For example, the average fiber diameter in the first basement membrane 11 can be 30nm, 44nm, 75nm, 80nm, 93nm, 100nm, 116nm, 135nm, 160nm, 188nm, 204nm, 255nm, 288nm, 300nm, 326nm, 350nm, 397nm, 400nm, 420nm, 450nm, etc., or a range consisting of any two of the above values, for example, it can be 50nm-260nm, 30nm-44nm, 75nm-80nm, 80nm-93nm, 100nm-135nm, 160nm-188nm, 204nm-255nm, 288nm-300nm, 326nm-350nm, 400nm-450nm, etc.

[0063] When the average fiber diameter of the first basement membrane and / or the second basement membrane is selected within the above range, the two basement membranes can have a rich pore structure while also having good strength, ensuring the continuity and effectiveness of the ion transmission channel of the final isolation membrane, thereby further improving the reliability of the isolation membrane.

[0064] The average fiber filament diameter of the basement membrane has a meaning well known in the art and can be tested using known equipment and methods. For example, a scanning electron microscope (e.g., ZEISS Sigma 300) is used, with reference to JY / T010-1996, to obtain a scanning electron microscope (SEM) image of the basement membrane. Specifically, a test sample of length × width = 5 mm × 5 mm is arbitrarily selected on the basement membrane, and multiple test areas (e.g., 5) are randomly selected in the test sample, and at a certain magnification (e.g., 10K times) until the fiber diameter is clearly observed, a ruler is used to select multiple positions (e.g., at least 30) for measurement, and the average value of the multiple fiber filament diameters is obtained, which is the average fiber filament diameter of the basement membrane.

[0065] In any embodiment of the present application, the ratio of the weight per unit area of ​​the first base film 11 to the weight per unit area of ​​the second base film 12 is greater than or equal to 1.02, and can be optionally 1.2-2.5.

[0066] For example, it can be 1.1, 1.11, 1.2, 1.3, 1.35, 1.4, 1.5, 1.65, 1.7, 1.8, 1.9, 2, 2.3, 2.5, 2.55, 2.6, 3, 3.5, 3.85, 4, 4.5, 5, 6, etc., or a range greater than or equal to any of the above values, for example, it can be ≥1.1, ≥1.11, ≥1.2, ≥1.35, ≥1.5, ≥1.8, ≥2, ≥2.5, ≥3, ≥3.85, ≥4, ≥5, ≥6, etc., or a range composed of any two of the above values, for example, 1.2-2.5, 1.1-1.5, 1.65-1.9, 1.7-2.3, 2-2.55, 2.55-3, 2.6-3.5, etc.

[0067] In any embodiment of the present application, the weight per unit area of ​​the first base film 11 is 2.5 g / m 2 -10g / m 2 For example, it can be 2.5g / m 2 , 3g / m 2 , 3.5g / m 2 , 5g / m 2 , 7g / m 2 , 8.1g / m 2 , 9g / m 2 , 10g / m 2 , or a range consisting of any two of the above values, for example, it can be 2.5g / m 2 -3g / m 2 , 3g / m 2 -5g / m 2 , 3g / m 2 -7g / m 2 , 5g / m 2 -8.1g / m 2 , 7g / m 2 -10g / m 2 In some embodiments, the weight per unit area of ​​the first base film 11 is 3 g / m 2 -7g / m 2 .

[0068] In any embodiment of the present application, the weight per unit area of ​​the second base film 12 is 2 g / m 2 -10g / m 2 , for example, it can be 2g / m 2 , 2.5g / m 2 , 3g / m 2 , 5g / m 2 , 6g / m 2 , 8.1g / m 2 , 9g / m 2 , 10g / m2 , or a range consisting of any two of the above values, for example, it can be 2g / m 2 -3g / m 2 , 3g / m 2 -5g / m 2 , 2.5g / m 2 -6g / m 2 , 5g / m 2 -8.1g / m 2 , 7g / m 2 -10g / m 2 In some embodiments, the weight per unit area of ​​the second base film 12 is 2.5 g / m 2 -6g / m 2 .

[0069] When the weight per unit area of ​​the first base film and the weight per unit area of ​​the second base film are within the above-given ranges, the isolation film can better combine heat resistance and strength, thereby further improving the reliability of the isolation film.

[0070] The weight per unit area of ​​the base film has a meaning well known in the art and can be tested using known equipment and methods. For example, the weight per unit area of ​​the base film can be measured using the following method: (1) Stack the base film into 6 stacks, flatten them, press them tightly, and remove the air from the base film. Cut the stacked base film according to the cutting board, measure the length and width of the cut samples for each stack, and obtain the areas S1, S2, and S3 of the three samples. (2) Weigh the weights M1, M2, and M3 of the three samples respectively. (3) According to the formula: Weight per unit area of ​​the base film = M / S, obtain the weight per unit area of ​​the three samples respectively, and take the average of the weights per unit area of ​​the three samples as the weight per unit area of ​​the base film.

[0071] In any embodiment of the present application, the melting point of the first base film 11 is 160°C-370°C, for example, 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, etc., 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 first base film 11 can be selected from 165°C-330°C. The melting point of the second base film 12 is 120°C-265°C, for example, 120°C, 130°C, 135°C, 140°C, 145°C, 150°C, 155°C, 160°C, 165°C, 196°C, 200°C, 240°C, 265°C, etc., or a range consisting of any two of the above values, for example, 120°C-135°C, 130°C-150°C, 145°C-155°C, 155°C-165°C, 196°C-200°C, 240°C-265°C, etc. In some embodiments, the melting point of the second base film 12 may be 130°C-230°C.

[0072] When the melting point of the first base film is 160°C-370°C and / or the melting point of the second base film is 120°C-265°C, the combination of the two can provide the isolation film with both heat resistance and good strength, thereby improving the reliability of the isolation film. When the melting point of the first base film is 165°C-330°C and / or the melting point of the second base film is 130°C-230°C, the isolation film can further provide both heat resistance and good strength, thereby further improving the reliability of the isolation film.

[0073] 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.

[0074] In any embodiment of the present application, the thickness of the first base film 11 is greater than or equal to the thickness of the second base film 12; optionally, the ratio of the thickness of the first base film 11 to the thickness of the second base film 12 is 1.1-5, for example, 1.1, 1.2, 1.25, 1.3, 1.45, 1.5, 1.6, 1.75, 1.8, 1.9, 2.0, 2.15, 2.2, 2.3, 2.45, 2.5, 2.8, 3.0, 3.5, 4.0, 4.5, 5.0, or a range consisting of any two of the above values, for example, 1.1-2.0, 1.6-2.15, 2.3-2.5, 2.8-3.5, 3-5, etc. In some embodiments, the ratio of the thickness of the first base film 11 to the thickness of the second base film 12 can be more preferably 1.5-3.0. For example, the first base film and the second base film are selected from polyolefin materials.

[0075] In any embodiment of the present application, the thickness of the first base film 11 is 2 μm-12 μm, for example, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4.6 μm, 5 μm, 6 μm, 7 μm, 9 μm, 9.6 μm, 10 μm, 10.4 μm, 11 μm, 11.7 μm, 12 μm, or a range consisting of any two of the above values, for example, 2 μm-2.5 μm, 2.5 μm-3 μm, 3 μm-4.6 μm, 5 μm-9 μm, 10 μm-11 μm, 11 μm-12 μm, etc. In some embodiments, the thickness of the first base film 11 can be 3 μm-6 μm. The thickness of the second base film 12 is 2 μm-9 μm, for example, 2 μm, 3 μm, 3.5 μm, 5 μm, 6 μm, 7 μm, 9 μm, etc., and can also be 2 μm-3.5 μm, 3 μm-5 μm, 5 μm-6 μm, 7 μm-9 μm, etc. In some embodiments, the thickness of the second base film 12 can be selected to be 3 μm-5 μm.

[0076] When the thickness of the first base film and / or the second base film is within the above-given range, the battery can have better reliability and further improve the energy density of the battery.

[0077] The thickness of the base film can be measured using equipment and methods known in the art. For example, a thickness gauge can be used to measure the base film thickness. Specifically, the following method can be used: six sets of parallel samples are taken, and the thickness of each set of samples is measured at different locations using a micrometer thickness gauge. At least 20 points are measured for each set of samples, and the average thickness of the six sets of samples is taken as the base film thickness.

[0078] In any embodiment of the present application, the ratio of the porosity of the first base film 11 to the porosity of the second base film 12 is 1.05-3, for example, it can be 1.05, 1.2, 1.3, 1.4, 1.51, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.4, 2.5, 2.71, 2.8, 3, or a range consisting of any two of the above values, for example, it can be 1.05-2.2, 1.2-1.51, 1.3-1.8, 1.6-2.1, 1.7-2.2, 2.1-3, etc. In some embodiments, the ratio of the porosity of the first base film 11 to the porosity of the second base film 12 is 1.1-1.5.

[0079] When the porosity ratio of the first base film to the porosity of the second base film is 1.05-3, the first base film has a large porosity and good air permeability, while the second base film has a small porosity and strong strength, providing support. As a result, the composite of the first and second base films can improve the reliability and cycle performance of the secondary battery. When the porosity ratio of the first base film to the porosity of the second base film is 1.1-1.5, the air permeability and support performance of the separator can be further balanced, thereby further improving the reliability and cycle performance of the secondary battery.

[0080] In any embodiment of the present application, the porosity of the first base film 11 is 30%-80%, for example, 30%, 35%, 38%, 40%, 50%, 55%, 60%, 70%, 75%, 80%, or a range consisting of any two of the above values, for example, 30%-40%, 35%-50%, 50%-70%, 75%-80%, etc. In some embodiments, the porosity of the first base film 11 is 50%-75%.

[0081] In any embodiment of the present application, the porosity of the second base film 12 is 30%-70%, for example, 30%, 35%, 40%, 45%, 50%, 60%, 65%, 70%, or a range consisting of any two of the above values, for example, 30%-40%, 35%-45%, 50%-60%, 65%-70%, etc. In some embodiments, the porosity of the second base film 12 is 40%-50%.

[0082] When the porosity of the first base membrane is 30%-80%, and / or the porosity of the second base membrane is 30%-70%, the first base membrane has a large porosity, a coarser average fiber diameter, and better air permeability, while the second base membrane has a small porosity, a finer average fiber diameter, and greater strength, providing support. Thus, the composite of the first and second base membranes can further improve the reliability and cycle performance of the secondary battery. When the porosity of the first base membrane is 50%-75%, and / or the porosity of the second base membrane is 40%-50%, the air permeability and support performance of the separator can be further balanced, thereby further improving the reliability and cycle performance of the secondary battery.

[0083] The porosity of the isolation membrane or substrate has a well-known meaning in the art and can be tested using known equipment and methods. For example, it can be tested with reference to GB / T 24586-2009. The test method is as follows: punch the isolation membrane or substrate into small disc samples with a diameter of 14 mm, test the thickness, and calculate the apparent volume V1 of the isolation membrane or substrate according to the cylinder volume calculation formula; refer to GB / T24586-2009, use an inert gas such as helium or nitrogen as the medium, adopt the gas displacement method, and use a true density tester to measure the true volume V2 of the isolation membrane or substrate. Then the porosity of the isolation membrane or substrate = (V1-V2) / V1×100%. The testing instrument can be the AccuPyc II 1340 fully automatic true density tester from Micromeritics, USA.

[0084] 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 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 13 includes a binder and filler particles. When an intermediate layer 13 is provided between the first base film 11 and the second base film 12, it can not only avoid the process defects in the hot pressing compounding process, but also further improve the heat resistance and physical properties of the isolation membrane, thereby improving the reliability of the secondary battery.

[0085] In any embodiment of the present application, the binder includes one or more of polyacrylate, acrylic acid, carboxymethyl cellulose, polyvinylidene fluoride-co-trichloroethylene copolymer, polymethyl methacrylate, polyvinyl pyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate copolymer, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, polyvinylidene fluoride, polyacrylonitrile, polyvinyl alcohol, starch, hydroxypropyl cellulose, regenerated cellulose, tetrafluoroethylene, polyethylene, polypropylene, and cyanoethyl pullulan. When an intermediate layer is provided between the first base film and the second base film, and the binder in the intermediate layer includes the above components, the heat resistance and physical properties of the isolation membrane can be further improved, thereby improving the reliability of the secondary battery. In some embodiments, carboxymethyl cellulose can be used as a thickener to adjust the viscosity of the slurry.

[0086] In any embodiment of the present application, the filling particles include at least one of inorganic particles, organic particles, and organic-metal framework materials.

[0087] 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.

[0088] 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.

[0089] 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 Si y7 S z3 and P2S5 glass Li x8 P y8 S z4 At least one of the following: 0<x1<2, 0<y1<3, 0<x2<2, 0<y2<1, 0<z1<3, 0<x3<4, 0<y3<13, 0<x4<2, 0<y4<3, 0<x5<4, 0<y5<1, 0<z2<1, 0<w<5, 0<x6<4, 0<y6<2, 0<x7<3, 0<y7<2, 0<z3<4, 0<x8<3, 0<y8<3, 0<z4<7. This can further improve the ion conductivity of the isolation membrane.

[0090] 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.

[0091] 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).

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] In any embodiment of the present application, the isolation film 10 satisfies at least one of the following (1)-(3): (1) The weight per unit area of ​​the isolation film 10 is 5-20 g / m 2 , optional 6-15g / m 2 ; (2) The porosity of the isolation membrane 10 is 30%-55%, and can be optionally 35%-45%; (3) The air permeability of the isolation membrane 10 is less than 350s / 100cc-400s / 100cc, and can be optionally 150s / 100cc-300s / 100cc.

[0098] When at least one of the above characteristics of the separator satisfies the given range, the separator can have good heat resistance and strength, thereby improving the reliability and cycle performance of the secondary battery.

[0099] 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.

[0100] The present application provides a secondary battery, comprising the separator 10 of any of the above solutions. When the secondary battery adopts the separator 10, the reliability of the secondary battery can be improved.

[0101] In any embodiment of the present application, the secondary battery further includes a positive electrode sheet and a negative electrode sheet, the separator 10 is disposed between the positive electrode sheet and the negative electrode sheet, and the first base film 11 of the separator 10 faces the positive electrode sheet.

[0102] [Positive electrode]

[0103] In a secondary battery, the 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.

[0104] 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.

[0105] The specific type of the positive electrode active material is not limited, and any active material known in the art that can be used for the positive electrode of a secondary battery can be used. Those skilled in the art can select it according to actual needs.

[0106] 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.

[0107] The modified compounds of the above materials may be doping-modified and / or surface-coated modified materials.

[0108] The positive electrode film layer usually optionally includes a binder, a conductive agent and other optional additives.

[0109] 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.

[0110] 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).

[0111] [Negative electrode]

[0112] In a secondary battery, the 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.

[0113] 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.

[0114] The specific type of the 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. The silicon-based material may be selected from one or more of elemental silicon, silicon oxide compounds (such as silicon monoxide), silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from one or more of elemental tin, tin oxide compounds, and tin alloys. These materials can all be obtained commercially.

[0115] In some embodiments, to further improve the energy density of the battery, the negative electrode active material may include a silicon-based material.

[0116] The negative 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, graphene, and carbon nanofibers.

[0118] 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).

[0119] As an example, other optional auxiliary agents may be thickening and dispersing agents (e.g. sodium carboxymethyl cellulose

[0120] Carboxymethylcellulose Sodium, CMC-Na), PTC thermistor materials.

[0121] [Electrolyte]

[0122] A secondary battery 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.

[0123] 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).

[0124] As an example, the solvent may be selected from ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), n-propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), n-propyl propionate (n-propyl propionate) 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).

[0125] 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.

[0126] When a secondary battery utilizes a given separator, the average fiber diameter of the first base film (with a higher melting point) is greater than the average fiber diameter of the second base film (with a lower melting point), while the smaller average fiber diameter of the second base film gives the second base film a rich pore structure, enhancing its resistance to physical penetration by lithium dendrites. Furthermore, the larger average fiber diameter of the first base film (with a higher melting point) than the second base film (with a lower melting point) ensures the continuity and effectiveness of the ion transport channels in the final separator, resulting in a separator that combines heat resistance with good strength, thereby improving the reliability of the secondary battery.

[0127] 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.

[0128] In some embodiments, the secondary battery may include an outer package for encapsulating 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.

[0129] 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).

[0130] 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.

[0131] 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.

[0132] 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.

[0133] 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.

[0134] 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.

[0135] 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.

[0136] [Installation]

[0137] 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 serve 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 (e.g., a mobile phone, a laptop computer), an electric vehicle (e.g., 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, a satellite, or an energy storage system.

[0138] The device can select a battery cell, a battery module or a battery pack according to its usage requirements.

[0139] 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.

[0140] 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.

[0141] 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.

[0142] The beneficial effects of the present application are further illustrated below with reference to the examples.

[0143] 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.

[0144] 1. Preparation of isolation membrane

[0145] Isolation film 1:

[0146] (1) A first base film and a second base film are provided.

[0147] The first base film meets the following requirements: the material is polypropylene (PP), the average fiber diameter of the first base film is 80nm, and the melting point is 165°C.

[0148] The second base film satisfies the following requirements: the material is polyethylene (PE), the average fiber diameter of the second base film is 50 nm, and the melting point is 135° C.

[0149] Among them, the ratio D1 / D2 of the average fiber filament diameter D1 of the first base membrane to the average fiber filament diameter D2 of the second base membrane is 1.60.

[0150] (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.

[0151] (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.

[0152] (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.

[0153] The preparation methods of separators 2-13 are similar to those of separator 1, except that one or more of the melting point, material, and average fiber diameter of the first or second base film is adjusted, as detailed in Table 1. Other preparation methods are consistent with those of separator 1.

[0154] 2. Preparation of batteries

[0155] Example 1

[0156] 1. Preparation of positive electrode sheet

[0157] 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.

[0158] 2. Preparation of negative electrode sheet

[0159] 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.

[0160] 3. Isolation film

[0161] The isolation film used was the isolation film 1 prepared above.

[0162] 4. Preparation of electrolyte

[0163] 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.

[0164] 5. Preparation of secondary batteries

[0165] 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, wherein the second base film faces the negative electrode sheet, 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.

[0166] The preparation methods of the secondary batteries of Examples 2-9 and Comparative Examples 1-4 are similar to that of the secondary battery of Example 1, except that different isolation membranes are used (Examples 1-9 use isolation membranes 1-9, and Comparative Examples 1-4 use isolation membranes 10-13). See Table 1 for details.

[0167] 3. Battery performance test

[0168] 1. Transverse heat shrinkage test at 250℃

[0169] 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.

[0170] Sample test: Place A4 paper on top of 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 (e.g., 1 hour), measure the width of the separator. The value is marked as a.

[0171] Transverse direction (TD) thermal shrinkage = [(50-a) / 50] × 100%, and the average value of 5 parallel samples is taken as the test result.

[0172] 2. Hot box performance

[0173] At 25°C, the secondary batteries were charged at a constant current of 1C to 4.2V. They were then charged at a constant voltage until the current reached ≤0.05C and allowed to rest for 5 minutes. Each secondary battery was then tested in a DHG-9070A DHG series high-temperature oven with a fixture. The temperature was raised from room temperature to 80°C ± 2°C at a rate of 5°C / min and held for 30 minutes. The temperature was then increased again at a rate of 5°C / min, with each 5°C increase followed by a 30-minute hold. The surface temperature of the secondary battery was monitored during the heating process. The oven temperature corresponding to the temperature that began to rise sharply was the secondary battery's hot box failure temperature. A higher hot box failure temperature indicates better thermal reliability. For accuracy, the test result was the average of five replicate samples.

[0174] As shown in Table 1, in Examples 1-9, the melting point of the second base film is lower than that of the first base film, and the average fiber diameter of the first base film is larger than that of the second base film. The separators defined in this application exhibit excellent heat resistance and low lateral shrinkage, resulting in batteries fabricated using the separators provided herein exhibiting good hot box performance and significantly improved thermal reliability. In Comparative Examples 1-4, the separators exhibit poor heat resistance, which can easily lead to battery safety issues.

[0175] 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, the melting point of the second base film being lower than the melting point of the first base film; An average fiber filament diameter in the first base film is greater than an average fiber filament diameter in the second base film.

2. The isolation film according to claim 1, wherein: The ratio of the average fiber filament diameter in the first base membrane to the average fiber filament diameter in the second base membrane is greater than or equal to 1.1-9, and can be optionally 1.2-4.

5.

3. The isolation film according to claim 1, wherein: The average fiber filament diameter in the first base membrane is 50nm-550nm, and can be optionally 80nm-350nm.

4. The isolation film according to claim 1, wherein: The average fiber diameter of the second base membrane is 30nm-450nm, and can be optionally 50nm-260nm.

5. [Corrected 25.05.2023 as per Rule 26] A separator as claimed in claim 1, wherein: The ratio of the weight per unit area of ​​the first base film to the weight per unit area of ​​the second base film is greater than or equal to 1.02, and can be optionally 1.2-2.

5.

6. The isolation film according to any one of claims 1 to 5, wherein: The weight per unit area of ​​the first base film is 2.5 g / m2-10 g / m2, and can be 3 g / m2-7 g / m2; and / or, The weight per unit area of ​​the second base film is 2g / m2-10g / m2, and can be optionally 2.5g / m2-6g / m2.

7. The isolation film according to any one of claims 1 to 6, wherein: The melting point of the first base film is 160° C.-370° C., and can be 165° C.-330° C.; and / or, The melting point of the second base film is 120°C-265°C, and can be optionally 130°C-230°C.

8. The isolation film according to any one of claims 1 to 7, wherein: The thickness of the first base film is greater than or equal to the thickness of the second base film; Optionally, the ratio of the thickness of the first base film to the thickness of the second base film is 1.1-5, and can be optionally 1.5-3.

0.

9. The isolation film according to any one of claims 1 to 8, wherein: The thickness of the first base film is 2 μm-12 μm, and can be 3 μm-6 μm; And / or, the thickness of the second base film is 2 μm-9 μm, and can be 3 μm-5 μm.

10. [Corrected 25.05.2023 in accordance with Rule 26] A separator as claimed in any one of claims 1 to 8, wherein: The ratio of the porosity of the first base film to the porosity of the second base film is 1.05-3, and can be optionally 1.1-1.

5.

11. The isolation film according to any one of claims 1 to 10, wherein: The porosity of the first base film is 30%-80%, and can be 50%-75%; and / or, The porosity of the second base film is 30%-70%, and can be 40%-50%.

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 further includes filling particles.

13. The isolation film according to claim 12, wherein: The binder includes one or more of polyacrylate, acrylic acid, carboxymethyl cellulose, polyvinylidene fluoride-co-trichloroethylene copolymer, polymethyl methacrylate, polyvinyl pyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate copolymer, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, polyvinylidene fluoride, polyacrylonitrile, polyvinyl alcohol, starch, hydroxypropyl cellulose, regenerated cellulose, tetrafluoroethylene, polyethylene, polypropylene, and cyanoethyl pullulan.

14. The isolation film according to claim 12 or 13, wherein: The filling particles include at least one of inorganic particles, organic particles, and organic-metal framework materials.

15. The isolation film according to any one of claims 1 to 14, wherein: The isolation film satisfies at least one of the following (1) to (6): The weight per unit area of ​​the isolation film is 5-20 g / m2, and can be 6-15 g / m2; The porosity of the isolation film is 30%-55%, and can be optionally 35%-45%; The air permeability of the isolation film is less than 350s / 100cc, and can be selected to be 150s / 100cc-300s / 100cc. 16 . A secondary battery comprising the separator according to claim 1 .

17. The secondary battery according to claim 16, wherein: The secondary battery comprises 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.

18. An electrical device comprising the secondary battery according to claim 16 or 17.

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