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 puncture strength of the second base membrane is 220 gf-460 gf, and the puncture strength of the isolating membrane is 330 gf-620 gf. When the puncture strength of the first base membrane and the separator is within the selected range, 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 outstanding features of being lightweight, pollution-free, and having no memory effect. With the continuous development of the new energy industry, users have put forward higher requirements for 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 an isolation membrane, a secondary battery and an electrical device, aiming to improve the reliability 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 puncture strength of the second base film is 220gf-460gf, and the puncture strength of the isolation film is 330gf-620gf.

[0007] Compared with the prior art, the present application includes at least the following beneficial effects: the isolation membrane provided by the present application, by setting the melting point of the second base membrane to be lower than the melting point of the first base membrane, and the puncture strength of the second base membrane and the puncture strength of the isolation membrane are selected within the above-mentioned range, so that the isolation membrane has different degrees of puncture resistance, that is, the puncture resistance of one side is different from that of the other side. When dealing with uneven dendrites in the battery, it can prevent 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 puncture strength of the first base film to the puncture strength of the second base film is 0.2-0.95, and optionally 0.3-0.75. When the ratio of the puncture strength of the first base film to the puncture strength of the second base film meets the above conditions, the separator has good puncture resistance while also balancing other properties, thereby further improving the reliability of the secondary battery.

[0009] In any embodiment of the present application, the puncture strength of the first base film is 100 gf-220 gf; the puncture strength of the second base film is 260 gf-400 gf. When the puncture strength of the first base film and / or the puncture strength of the second base film meet the above conditions, the separator has good puncture resistance, which can further improve the reliability of the secondary battery.

[0010] In any embodiment of the present application, the isolation film satisfies at least one of the following (1)-(4):

[0011] (1) The transverse elongation at break of the first base film is 50%-200%, and can be optionally 60%-160%;

[0012] (2) the longitudinal elongation at break of the first base film is 40%-700%, optionally 80%-600%;

[0013] (3) The transverse elongation at break of the second base film is 40%-220%, and can be optionally 80%-170%;

[0014] (4) The longitudinal elongation at break of the second base film is 30%-100%, and can be optionally 40%-85%.

[0015] When at least one of the above (1) to (4) of the separator satisfies the given range, the puncture resistance of the separator is improved, thereby further improving the reliability of the secondary battery.

[0016] In any embodiment of the present application, the average fiber filament diameter of the first base membrane is 60nm-300nm, optionally 80nm-200nm; and / or the average fiber filament diameter of the second base membrane is 40nm-350nm, optionally 70nm-180nm. When the average fiber filament diameter of the first base membrane and / or the average fiber filament diameter of the second base membrane meet the above ranges, the puncture strength of the base membrane and the separator is within the range of the present application, and the separator also has good tensile properties, thereby further improving the reliability of the secondary battery.

[0017] In any embodiment of the present application, the melting point of the first base film is 155°C-360°C, optionally 160°C-335°C; the melting point of the second base film is 125°C-260°C, optionally 130°C-220°C. Limiting the melting points of the first base film and the second base film to the above ranges can ensure that the first and second base films have good puncture resistance while also achieving good heat resistance.

[0018] In any embodiment of the present application, the relative molecular weight of the material of the first base film is 400,000-1.8 million, optionally 500,000-1.3 million; and / or the relative molecular weight of the material of the second base film is 300,000-1.5 million, optionally 400,000-1.1 million. When the relative molecular weights of the first base film and the second base film meet the above conditions, the separator has excellent puncture resistance, which can further improve the reliability of the secondary battery.

[0019] 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 1.02-5, preferably 1.1-3.0.

[0020] In any embodiment of the present application, the thickness of the first base film is 2 μm-14 μm, and can be optionally 3 μm-9 μm; the thickness of the second base film is 2 μm-12 μm, and can be optionally 3 μm-7 μm.

[0021] When the thickness of the first base film and / or the thickness of the second base film meets the above conditions, the separator has better puncture resistance, thereby further improving the reliability of the secondary battery and, at the same time, increasing the energy density of the battery.

[0022] In any embodiment of the present application, an intermediate layer is further disposed between the first base film and the second base film. The intermediate layer is disposed between the first base film and the second base film and includes a binder. Optionally, the intermediate layer also includes filler particles. Optionally, the filler particles include at least one of inorganic particles, organic particles, and an organic-metal framework material. The intermediate layer between the first base film and the second base film not only compensates for process defects during the hot-pressing lamination process but also further improves the physical stability of the separator, thereby further enhancing the reliability of the secondary battery.

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

[0024] In any embodiment of the present application, the isolation film satisfies at least one of the following (1)-(5):

[0025] (1) The puncture strength of the isolation film is 330gf-630gf, and can be selected as 400gf-600gf;

[0026] (2) Transverse tensile strength of the separator ≥700kg / cm 2 , optional 1000kg / cm 2 -1900kg / cm 2 ;

[0027] (3) The longitudinal tensile strength of the isolation film is ≥1000kg / cm 2 , optional 1200kg / cm 2 -2200kg / cm 2 ;

[0028] (4) The transverse heat shrinkage of the isolation film at 250°C for 1 hour is ≤3%, which can be optionally ≤2.0%;

[0029] (5) The longitudinal heat shrinkage rate of the isolation film at 250°C for 1 hour is ≤3%, and can be optionally ≤2.0%.

[0030] When at least one of the above (1) to (5) of the separator satisfies the given range, the separator has good puncture resistance, thereby improving the reliability of the secondary battery.

[0031] A second aspect of the present application provides a secondary battery, which includes the separator according to the first aspect of the present application. 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, the separator is arranged between the positive electrode sheet and the negative electrode sheet, and the second base film of the separator faces the negative electrode sheet.

[0033] The second base film of the isolation film faces the negative electrode sheet. The second base film has high puncture strength, which can increase the effect of resisting lithium dendrite puncture and further improve the reliability of the secondary battery.

[0034] 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.

[0035] 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

[0036] 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.

[0037] FIG1 is a schematic structural diagram of an isolation membrane according to an embodiment of the present application.

[0038] FIG2 is a schematic structural diagram of another embodiment of the isolation membrane of the present application.

[0039] FIG3 is a schematic diagram of an embodiment of a secondary battery.

[0040] FIG. 4 is an exploded view of FIG. 3 .

[0041] FIG. 5 is a schematic diagram of an embodiment of a battery module.

[0042] FIG. 6 is a schematic diagram of a battery pack according to one embodiment.

[0043] FIG. 7 is an exploded view of FIG. 6 .

[0044] FIG. 8 is a schematic diagram of an embodiment of a device using a secondary battery as a power source. DETAILED DESCRIPTION

[0045] 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.

[0046] 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.

[0047] 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).

[0048] 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.

[0049] 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).

[0050] secondary batteries

[0051] A secondary battery is a battery that can be recharged to activate the active materials after discharge and continue to be used.

[0052] 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.

[0053] [Isolation film]

[0054] 1 , an embodiment of the present application provides an isolation film 10 , comprising a first base film 11 and a second base film 12 , wherein the melting point of the second base film 12 is lower than that of the first base film 11 ; the puncture strength of the second base film 12 is 220 gf-460 gf, and the puncture strength of the isolation film 10 is 330 gf-620 gf.

[0055] Without wishing to be limited to any theory, the inventors have found through extensive research that in the isolation membrane of the specific structure of the present application, when the puncture strength of the second base film with a low melting point and the puncture strength of the isolation membrane are both within the above-mentioned specific ranges, the specific base film in the isolation membrane can be used to enhance the puncture resistance of the isolation membrane and improve the ability to resist dendrite penetration. Generally, dendrite precipitation occurs on the negative electrode side, and the requirements for the puncture resistance of the isolation membrane are higher, while the requirements for puncture resistance toward the positive electrode side are relatively weak. However, the positive electrode side may have higher requirements for other properties, such as heat resistance, to prevent thermal breakdown. Therefore, the second base film can be used to exert its excellent performance to enhance the puncture resistance of the isolation membrane, and the first base film can be used to balance and regulate other properties of the isolation membrane, such as heat resistance, air permeability, antioxidant properties, etc., so that the overall performance of the isolation membrane is improved, thereby improving the reliability of the secondary battery.

[0056] 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.

[0057] In any embodiment of the present application, the ratio of the puncture strength of the first base film 11 to the puncture strength of the second base film 12 is 0.2-0.95, and can be 0.3-0.75. For example, the ratio of the puncture strength of the first base film 11 to the puncture strength of the second base film 12 can be 0.2, 0.3, 0.32, 0.41, 0.48, 0.52, 0.54, 0.66, 0.71, 0.75, 0.85, 0.89, 0.92, 0.95, etc., or a range consisting of any two of the above values, for example, 0.2-0.32, 0.3-0.75, 0.41-0.54, 0.48-0.66, 0.71-0.89, 0.92-0.95, etc. When the ratio of the puncture strength of the first base film to the puncture strength of the second base film meets the above conditions, the puncture resistance and heat resistance of the first base film and the second base film can be taken into account, thereby further improving the reliability of the secondary battery.

[0058] In any embodiment of the present application, the puncture strength of the first base film 11 is 100 gf-220 gf; and / or the puncture strength of the second base film 12 is 260 gf-400 gf. For example, the puncture strength of the first base film 11 can be 100 gf, 102 gf, 114 gf, 120 gf, 126 gf, 133 gf, 139 gf, 140 gf, 164 gf, 190 gf, 220 gf, etc., or a range consisting of any two of the above values, for example, 100 gf-133 gf, 90 gf-114 gf, 120 gf-126 gf, 133 gf-164 gf, 190 gf-220 gf, etc. The puncture strength of the second base film 12 can be selected to be 260gf, 267gf, 277gf, 300gf, 323gf, 339gf, 361gf, 370gf, 400gf, etc., or a range consisting of any two of the above values, for example, 260gf-300gf, 323gf-361gf, 361gf-400gf, etc. When the puncture strength of the first base film and / or the puncture strength of the second base film meet the above conditions, the puncture resistance and heat resistance of the first and second base films can be balanced. While having good puncture resistance, it is also possible to balance other performance properties, thereby improving the reliability of the secondary battery.

[0059] The puncture strength of the base film or isolation membrane has a meaning well known in the art and can be tested using equipment and methods known in the art. For example, the puncture strength can be tested according to the standard: GB / T 10004-2008. Specifically, the sample to be tested can be cut into strips, wherein the width of the strip sample is 100 mm. A test piece with a width of 100 mm is mounted on the sample film fixing clamp ring, and then a steel needle with a diameter of 1.0 mm and a radius of 0.5 mm at the top is used to puncture at a speed of (50±5) mm / min, and the maximum load of the steel needle penetrating the test piece is read. Usually, 5 parallel test samples can be taken at the same time, 3 points are measured for each test sample, and the arithmetic average is taken as the final puncture strength.

[0060] In any embodiment of the present application, the isolation film 10 satisfies at least one of the following (1)-(4):

[0061] (1) The transverse elongation at break of the first base film 11 is 50%-200%, and can be 60%-160%; (2) The longitudinal elongation at break of the first base film 11 is 40%-700%, and can be 80%-600%;

[0062] (3) The transverse elongation at break of the second base film 12 is 40%-220%, and can be optionally 80%-170%;

[0063] (4) The longitudinal elongation at break of the second base film 12 is 30%-100%, and can be optionally 40%-85%.

[0064] When at least one of the above (1) to (4) of the separator satisfies the given range, the puncture resistance of the separator is improved, thereby further improving the reliability of the secondary battery.

[0065] Those skilled in the art will appreciate that the puncture strength of a basement membrane can be adjusted by adjusting one or more of the intrinsic parameters of the basement membrane (e.g., the average fiber diameter of the basement membrane, the relative molecular weight of the basement membrane material, etc.). Within the parameter ranges provided in this application, those skilled in the art can adjust the swelling rate of the basement membrane using known methods, such as adjusting the production process of the basement membrane (controlling the average fiber diameter of the basement membrane, the relative molecular weight of the basement membrane material, etc.), and through a limited number of experiments, obtain a basement membrane with the desired puncture strength.

[0066] In any embodiment of the present application, the average fiber filament diameter of the first basement membrane 11 is 60nm-300nm, optionally 80nm-200nm; and / or, the average fiber filament diameter of the second basement membrane 12 is 40nm-350nm, optionally 70nm-180nm.

[0067] The average fiber filament diameter of the first basement membrane 11 may be 60 nm, 70 nm, 75 nm, 80 nm, 96 nm, 100 nm, 124 nm, 140 nm, 172 nm, 189 nm, 200 nm, 216 nm, 238 nm, 250 nm, 264 nm, 270 nm, 283 nm, 300 nm, or a range consisting of any two of the above values, for example, 60 nm-75 nm, 70 nm-100 nm, 124 nm-189 nm, 172 nm-238 nm, 264 nm-270 nm, 283 nm-300 nm, etc. In some embodiments, the average fiber filament diameter of the first basement membrane 11 may be 80 nm-200 nm.

[0068] The average fiber filament diameter of the second basement membrane 12 may be 40 nm, 64 nm, 70 nm, 89 nm, 100 nm, 119 nm, 142 nm, 157 nm, 180 nm, 196 nm, 224 nm, 265 nm, 274 nm, 290 nm, 300 nm, 315 nm, 324 nm, 330 nm, 339 nm, 341 nm, 350 nm, or a range formed by any two of the above values, for example, 119 nm-157 nm, 157 nm-196 nm, 224 nm-265 nm, 274 nm-315 nm, 300 nm-330 nm, 330 nm-341 nm, 341 nm-350 nm, etc. In some embodiments, the average fiber filament diameter of the second basement membrane 12 may be 70 nm-100 nm.

[0069] When the average fiber diameter of the first base membrane and / or the average fiber diameter of the second base membrane meets the above range, it helps to make the puncture strength of the base membrane and the isolation membrane within the range of this application, and also enables the isolation membrane to have good tensile properties, thereby further improving the reliability of the secondary battery.

[0070] 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.

[0071] In any embodiment of the present application, the melting point of the first base film 11 is 155°C-360°C, and can be optionally 160°C-335°C; the melting point of the second base film 12 is 125°C-260°C, and can be optionally 130°C-220°C.

[0072] The melting point of the first base film 11 can be 155°C, 159°C, 160°C, 170°C, 186°C, 190°C, 212°C, 235°C, 246°C, 264°C, 279°C, 281°C, 312°C, 345°C, 355°C, 360°C, etc., or a range consisting of any two of the above values, for example, 155°C-170°C, 186°C-212°C, 235°C-279°C, 160°C-335°C, 281°C-312°C, 345°C-360°C, etc.

[0073] The melting point of the second base film 12 is 125°C, 135°C, 153°C, 171°C, 196°C, 200°C, 224°C, 235°C, 260°C, etc., or a range consisting of any two of the above values, for example, 125°C-135°C, 153°C-196°C, 130°C-220°C, 196°C-200°C, 224°C-260°C, etc.

[0074] By limiting the melting points of the first base film and the second base film to the above ranges, it is possible to ensure that the first base film and the second base film have good puncture resistance while also having good heat resistance.

[0075] 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.

[0076] In any embodiment of the present application, the relative molecular mass of the material of the first base film 11 is 400,000-1.8 million, optionally 500,000-1.3 million; and / or, the relative molecular mass of the material of the second base film 12 is 300,000-1.5 million, optionally 400,000-1.1 million.

[0077] The relative molecular weight of the material of the first base film 11 can be 400,000, 450,000, 460,000, 550,000, 640,000, 750,000, 960,000, 1.2 million, 1.37 million, 1.45 million, 1.54 million, 1.62 million, 1.71 million, 1.74 million, 1.78 million, 1.80 million, etc., or a range consisting of any two of the above values, for example, 400,000-450,000, 450,000-750,000, 750,000-960,000, 1.2 million-1.37 million, 1.45 million-1.74 million, 1.74 million-1.78 million, 1.78 million-1.80 million, etc. In some embodiments, the relative molecular weight of the material of the first base film 11 can be 500,000-1.3 million.

[0078] The relative molecular weight of the material of the second base film 12 can be 300,000, 390,000, 490,000, 570,000, 640,000, 660,000, 800,000, 970,000, 1.03 million, 1.14 million, 1.24 million, 1.38 million, 1.41 million, 1.44 million, 1.48 million, 1.50 million, etc., or a range consisting of any two of the above values, for example, 300,000-390,000, 570,000-660,000, 800,000-1.14 million, 1.14 million-1.44 million, 1.44 million-1.50 million, etc. In some embodiments, the relative molecular weight of the material of the second base film 12 can be 400,000-1.10 million.

[0079] Among them, the relative molecular mass of the base film material will affect the final film-forming state of the base film, and thus affect the puncture strength of the base film. In addition to affecting the puncture strength of the base film, the relative molecular mass of the material will also affect other properties of the material such as tensile strength. By limiting the relative molecular mass of the material of the first base film and the relative molecular mass of the material of the second base film to the above range, the puncture strength of the first base film can be further improved, thereby reducing the probability of puncture of lithium dendrites, and can increase the support strength of the first base film on the second base film, thereby improving the reliability of the secondary battery.

[0080] The relative molecular mass of the basement membrane has a well-known meaning in the art and can be measured using equipment and methods known in the art, for example, using a high-temperature GPC test (differential refractive index detector).

[0081] 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 1.02-5, preferably 1.1-3.0. 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 1.02, 1.1, 1.2, 1.4, 1.6, 2.2, 2.8, 3.0, 3.5, 3.9, 4.1, 4.4, 4.6, 4.8, 5, etc., or a range consisting of any two of the above values, for example, 1.02-1.2, 1.4-2.2, 2.8-3.5, 1.1-3.0, 3.9-4.4, 4.6-5, etc.

[0082] In any embodiment of the present application, the thickness of the first base film 11 is 2 μm-14 μm, and can be 3 μm-9 μm; the thickness of the second base film 12 is 2 μm-12 μm, and can be 3 μm-7 μm.

[0083] The thickness of the first base film 11 may be 2 μm, 3.5 μm, 4 μm, 5 μm, 7 μm, 9 μm, 10 μm, 11 μm, 11.5 μm, 12 μm, 13.5 μm, 14 μm, etc., or a range formed by any two of the above values, for example, 2 μm-4 μm, 5 μm-10 μm, 10 μm-12 μm, 12 μm-14 μm, etc. In some embodiments, the thickness of the first base film 11 may be 3 μm-9 μm.

[0084] The thickness of the second base film 12 can be 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, etc., or a range consisting of any two of the above values, for example, 2 μm-4 μm, 5 μm-7 μm, 8 μm-9 μm, 10 μm-12 μm, etc. In some embodiments, the thickness of the second base film 12 can be 3 μm-7 μm.

[0085] When the thickness of the first base film and / or the thickness of the second base film meets the above conditions, the separator has better puncture resistance, thereby improving the reliability of the secondary battery and, at the same time, increasing the energy density of the battery.

[0086] The thickness of the base film can be tested using equipment and methods known in the art. For example, a lithium battery separator thickness gauge can be used to qualitatively measure the base film thickness. The test is performed with reference to GB / T 6672, "Plastic film and sheeting - Determination of thickness - Mechanical measurement method." Specifically, the following steps can be used: Six sets of parallel samples are taken. Using a micrometer thickness gauge, the thickness of each set of samples is measured at different locations. At least 20 points are measured for each set of samples. The average thickness of the six sets of samples is taken as the base film thickness.

[0087] The first base film 11 and the second base film 12 can be directly laminated by hot pressing. During the hot pressing process, if the temperature is too high, the porosity will be small and the air permeability will be poor; if the temperature is too low, the first 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.

[0088] In any embodiment of the present application, referring to FIG2 , an intermediate layer 13 is further provided between the first base film 11 and the second base film 12. The intermediate layer 13 is provided between the first base film 11 and the second base film 12, and the intermediate layer 13 includes a binder. Optionally, the intermediate layer 13 also includes filler particles. Optionally, 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, it can not only compensate for process defects during the hot pressing composite process, but also further improve the physical property stability of the isolation membrane, thereby improving the reliability of the secondary battery.

[0089] 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 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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).

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] In any embodiment of the present application, the isolation film 10 satisfies at least one of the following (1) to (5):

[0101] (1) The puncture strength of the isolation film is 330gf-630gf, and can be selected as 400gf-600gf;

[0102] (2) Transverse tensile strength of the separator ≥700kg / cm 2 , optional 1000kg / cm 2 -1900kg / cm 2 ;

[0103] (3) The longitudinal tensile strength of the isolation film is ≥1000kg / cm 2 , optional 1200kg / cm 2 -2200kg / cm 2 ;

[0104] (4) The transverse heat shrinkage of the isolation film 10 at 250° C. for 1 hour is ≤3%, and may be ≤2.0%;

[0105] (5) The longitudinal heat shrinkage rate of the isolation film 10 at 250° C. for 1 hour is ≤3%, and can be optionally ≤2.0%.

[0106] When at least one of the above (1) to (5) of the separator satisfies the given range, the separator has good puncture resistance, thereby improving the reliability of the secondary battery.

[0107] 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, the test can be performed in accordance with standard GB / T36363-2018.

[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] [Positive electrode]

[0110] 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.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] The modified compounds of the above materials may be doping-modified and / or surface-coated modified materials.

[0115] The positive electrode film layer usually optionally includes a binder, a conductive agent and other optional additives.

[0116] 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.

[0117] 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).

[0118] [Negative electrode]

[0119] 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.

[0120] 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.

[0121] 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.

[0122] In some embodiments, to further increase the energy density of the battery, the negative electrode active material may include a silicon-based material.

[0123] The negative electrode film layer usually optionally includes a binder, a conductive agent and other optional auxiliary agents.

[0124] 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.

[0125] 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).

[0126] As an example, other optional auxiliary agents may be thickening and dispersing agents (e.g. sodium carboxymethyl cellulose

[0127] Carboxymethylcellulose Sodium, CMC-Na), 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 second base film 12 of the separator 10 faces the negative electrode.

[0134] The second base film 12 of the separator 10 faces the negative electrode. The second base film 12 has high puncture strength, which can increase the effect of resisting lithium dendrite puncture and improve 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 packaging for encapsulating the positive electrode sheet, the negative electrode sheet, and the electrolyte.

[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 , within the battery module 4, multiple secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the multiple secondary batteries 5 may be secured together 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) Providing a first base film and a second base film: the first base film is polypropylene (PP), and the second base film is polyethylene (PE), wherein the melting point of the first base film is 165°C, and the melting point of the second base film is 135°C. The transverse elongation at break of the first base film is 60%, and the longitudinal elongation at break is 80%. The transverse elongation at break of the second base film is 130%, and the longitudinal elongation at break is 75%. The puncture strength P1 of the first base film is 120 gf, and the puncture strength P2 of the second base film is 300 gf; wherein the ratio P1 / P2 of the puncture strength P1 of the first base film to the puncture strength P2 of the second base film is 0.40.

[0154] (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.

[0155] (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.

[0156] (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.

[0157] The preparation method of separators 2-11 is similar to that of separator 1, except that one or more of the melting point, material, transverse elongation at break, longitudinal elongation at break, and puncture strength of the first or second base film is adjusted, as detailed in Table 1. All other preparation methods are consistent with those of the separator of Example 1.

[0158] 2. Preparation of batteries

[0159] Example 1

[0160] 1. Preparation of positive electrode sheet

[0161] 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.

[0162] 2. Preparation of negative electrode sheet

[0163] 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.

[0164] 3. Isolation film

[0165] The isolation film used was the isolation film 1 prepared above.

[0166] 4. Preparation of electrolyte

[0167] 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.

[0168] 5. Preparation of secondary batteries

[0169] 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.

[0170] The preparation methods of the secondary batteries of Examples 2-9 and Comparative Examples 1-2 are similar to those of the secondary battery of Example 1, except that different isolation membranes are used (Example 1-9 uses isolation membrane 1-9, and Comparative Example 1-2 uses isolation membrane 10-11). See Table 1 for details.

[0171] 3. Battery performance test

[0172] 1. Shallow puncture test (60 minutes)

[0173] The battery was tested at 25°C and 100% SOC, with the temperature-sensing wires arranged in the order of positive pole / negative pole / large surface center (5mm above the puncture port) / large surface center back / cell explosion-proof valve, and the voltage wires arranged in the order of V positive and negative / V positive needle / V negative needle, with a multi-channel acquisition frequency ≤0.1S; a φ1mm high-temperature resistant steel needle (the cone angle of the needle tip is 30°) was used, aimed at the center of the large surface of the cell, with a puncture speed of 0.01mm / s; the needle was punctured into the positive pole until the voltage reached 0.5V, and the puncture depth was continued to 3mm for 1h. The value displayed on the instrument was observed. If the voltage was normal and there was no fluctuation, it was normal and not out of control, and it was recorded as PASS; if the voltage fluctuation was abnormal and the cell failed, it was recorded as NP.

[0174] 2. Battery cycle performance (cycles)

[0175] At 25°C, the secondary batteries prepared in the Examples and Comparative Examples were charged at a constant current rate of 1C to a charge cutoff voltage V1, then charged at a constant voltage to a current ≤ 0.05C, allowed to rest for 5 minutes, and then discharged at a constant current rate of 0.33C to a discharge cutoff voltage V2, allowed to rest for 5 minutes. This constitutes one charge-discharge cycle. The batteries were subjected to cyclic charge-discharge testing using this method until the battery capacity decayed to 80%. The number of cycles at this point is the battery's cycle life at 25°C.

[0176] As can be seen from Table 1, a comparison analysis of Examples 1-9 and Comparative Examples 1-2 shows that in Examples 1-9, the melting point of the second base film is lower than the melting point of the first base film, and the puncture strength of the second base film is 220gf-460gf, and the puncture strength of the isolation membrane is 330gf-620gf. The battery using the isolation membrane of the present application can not only pass the shallow puncture test, but also increase the number of cycles. That is, under the same battery performance standard, the battery prepared using the isolation membrane provided by the present application has higher reliability.

[0177] 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, include: 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; The puncture strength of the second base film is 220 gf-460 gf, and the puncture strength of the isolation film is 330 gf-620 gf.

2. The isolation film according to claim 1, in, The ratio of the puncture strength of the first base film to the puncture strength of the second base film is 0.2-0.95, and can be optionally 0.3-0.

75.

3. The isolation film according to claim 1 or 2, in, The puncture strength of the first basement membrane is 100 gf-220 gf; and / or, The puncture strength of the second base film is 260 gf-400 gf.

4. The isolation film according to any one of claims 1 to 3, in, The isolation film satisfies at least one of the following (1)-(4): (1) The transverse elongation at break of the first base film is 50%-200%, and can be 60%-160%; (2) the longitudinal elongation at break of the first base film is 40%-700%, and can be 80%-600%; (3) The transverse elongation at break of the second base film is 40%-220%, and can be 80%-170%; (4) The longitudinal elongation at break of the second base film is 30%-100%, and can be optionally 40%-85%.

5. The isolation film according to any one of claims 1 to 4, in, The average fiber diameter of the first base film is 60nm-300nm, and can be 80nm-200nm; and / or, The average fiber diameter of the second base membrane is 40nm-350nm, and can be optionally 70nm-180nm.

6. The isolation film according to any one of claims 1 to 5, in, The melting point of the first base film is 155°C-360°C, and can be 160°C-335°C; and / or, The melting point of the second base film is 125°C-260°C, and can be optionally 130°C-220°C.

7. The isolation film according to any one of claims 1 to 6, in, The relative molecular weight of the material of the first base film is 400,000-1.8 million, and can be 500,000-1.3 million; and / or, The relative molecular weight of the material of the second base film is 300,000-1.5 million, and can be optionally 400,000-1.1 million.

8. The isolation film according to any one of claims 1 to 7, in, 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 1.02-5, preferably 1.1-3.

0.

9. The isolation film according to any one of claims 1 to 8, in, The thickness of the first base film is 2 μm-14 μm, and can be 3 μm-9 μm; and / or, The thickness of the second base film is 2 μm-12 μm, and can be 3 μm-7 μm.

10. The isolation film according to any one of claims 1 to 9, in, 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.

11. The isolation film according to claim 10, in, 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.

12. The isolation film according to any one of claims 1 to 11, in, The isolation film satisfies at least one of the following (1) to (5): (1) The puncture strength of the isolation film is 330gf-630gf, and can be 400gf-600gf; (2) The transverse tensile strength of the separator is ≥700kg / cm 2 , optional 1000kg / cm 2 -1900kg / cm 2 ; (3) The longitudinal tensile strength of the isolation film is ≥ 1000 kg / cm 2 , optional 1200kg / cm 2 -2200kg / cm 2 ; (4) The transverse heat shrinkage rate of the isolation film at 250° C. for 1 hour is ≤3%, and can be optionally ≤2.0%; (5) The longitudinal heat shrinkage rate of the isolation film at 250° C. for 1 hour is ≤3%, and can be optionally ≤2.0%.

13. A secondary battery comprising the separator according to any one of claims 1 to 12.

14. The isolation film according to claim 13, in, It comprises a positive electrode sheet and a negative electrode sheet, the isolation film is arranged between the positive electrode sheet and the negative electrode sheet, and the second base film faces the negative electrode sheet.

15. An electrical device comprising the secondary battery according to claim 13 or 14.

Images