Separator, secondary battery, and electric device

Abstract

The invention provides an isolating membrane which comprises a first porous base membrane and a second porous base membrane, and the melting point of the first porous base membrane is higher than that of the second porous base membrane; the average pore area of the first porous base membrane is larger than the average pore area of the second porous base membrane in a cross section along the thickness direction of the separation membrane. The isolating membrane has air permeability and mechanical strength, so that the reliability and the cycle performance of the isolating membrane are 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 electronic products and electric vehicles due to their outstanding features of light weight, no pollution and no memory effect.

[0003] With the continuous development of the new energy industry, users have put forward higher demands on the use of secondary batteries.

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

[0005] Summary of the Invention

[0006] In view of the technical problems existing in the background technology, the present application provides a separator, which aims to improve the cyclability of secondary batteries.

[0007] In order to achieve the above-mentioned objectives, the first aspect of the present application provides an isolation membrane, which includes: a first porous base membrane and a second porous base membrane; the melting point of the first porous base membrane is higher than the melting point of the second porous base membrane; in the cross-section along the thickness direction of the isolation membrane, the average pore area of ​​the first porous base membrane is greater than the average pore area of ​​the second porous base membrane.

[0008] Compared with the prior art, this application has at least the following beneficial effects:

[0009] The isolation membrane with a specific structure in the present application can not only improve the heat resistance, but also improve the air permeability. When the two base membranes adopt the specific average pore area design scheme of the present application, the pore blockage caused by the physical lamination in the isolation membrane preparation process is effectively reduced, thereby improving the air permeability of the isolation membrane and maintaining the continuity and effectiveness of ion transmission. At the same time, the isolation membrane can also take into account good puncture performance, so that the two can achieve an optimal balance, thereby improving the cycle performance of the battery.

[0010] In any embodiment of the present application, the ratio of the average pore area of ​​the first porous base membrane to the average pore area of ​​the second porous base membrane is 1.05-10, and can be optionally 1.5-3.5.

[0011] When the ratio of the average pore area of ​​the first porous base membrane to the average pore area of ​​the second porous base membrane is 1.05-10, the separator can have better air permeability, which is conducive to the permeation of lithium ions. The average pore area of ​​the second porous base membrane is relatively smaller than the average pore area of ​​the first porous base membrane. The smaller the average pore area, the more the fiber filaments of the second porous base membrane occupy the spatial structure of the base membrane, the greater the strength of the base membrane, and the more resistant it is to lithium dendrites. Therefore, the separator can have both air permeability and mechanical strength, thereby improving the reliability and cycle performance of the separator. When the ratio of the average pore area of ​​the first porous base membrane to the average pore area of ​​the second porous base membrane is 1.5-3.5, the air permeability and mechanical strength of the separator can be further improved, thereby further improving the reliability and cycle performance of the separator.

[0012] In any embodiment of the present application, the average pore area of ​​the first porous base membrane is 0.0001 μm 2 -0.5μm 2 , 0.01μm is optional 2 -0.3μm 2 and / or, the average pore area of ​​the second porous base membrane is 0.0001 μm 2 -0.4μm 2 , 0.01μm is optional 2 -0.25μm 2 .

[0013] When the average pore area of ​​the first porous base membrane is 0.0001 μm 2 -0.5μm 2 , and / or, the average pore area of ​​the second porous base membrane is 0.0001 μm 2 -0.4μm 2 When the average pore area of ​​the first porous base membrane is different from that of the second porous base membrane, the separator can have both air permeability and mechanical strength, thereby improving the reliability and cycle performance of the separator. 2 -0.3μm 2 , and / or, the average pore area of ​​the second porous base membrane is 0.01 μm 2 -0.25μm 2 When the separator is filled with a plurality of layers of carbon monoxide, the air permeability and mechanical strength of the separator can be further improved, thereby further improving the reliability and cycle performance of the separator.

[0014] In any embodiment of the present application, the average pore size of the first porous base membrane is greater than the average pore size of the second porous base membrane; optionally, the average pore size of the first porous base membrane is 100nm-2000nm, more optionally 100nm-350nm; optionally, the average pore size of the second porous base membrane is 100nm-2000nm, more optionally 100nm-300nm.

[0015] When the average pore size of the first porous base membrane is greater than the average pore size of the second porous base membrane, the average pore size of the first porous base membrane is 100nm-2000nm, and / or the average pore size of the second porous base membrane is 100nm-2000nm, because the average pore size of the two is different, the smaller the average pore size, the smaller the space occupied by the average pore area, the larger the space occupied by the fiber filaments of the base membrane, and the stronger the mechanical strength of the base membrane; on the contrary, the smaller the space occupied by the fiber filaments of the base membrane, the larger the average pore area of ​​the base membrane, and the better the air permeability. Therefore, the base membrane can be made to have both air permeability and mechanical strength, thereby improving the reliability and cycle performance of the base membrane. When the average pore size of the first porous base membrane is 100nm-350nm, and / or the average pore size of the second porous base membrane is 100nm-300nm, the air permeability and mechanical strength of the base membrane can be further improved, thereby further improving the reliability and cycle performance of the base membrane.

[0016] In any embodiment of the present application, the porosity of the first porous base membrane is greater than the porosity of the second porous base membrane; optionally, the porosity of the first porous base membrane is 30%-80%, more optionally 35%-60%; and / or, the porosity of the second porous base membrane is 30%-70%, more optionally 35%-50%.

[0017] When the porosity of the first porous base membrane is greater than that of the second porous base membrane, and the porosity of the first porous base membrane is 30%-80%, and / or the porosity of the second porous base membrane is 30%-70%, the porosities of the two base membranes are different, indicating that the proportion of the pore structure per unit area is different, that is, the average pore area is different. The porous base membrane with a large average pore area has good air permeability, and the base membrane with a small average pore area has good mechanical strength. The combination of the two can make the separator have both air permeability and mechanical strength, thereby improving the reliability and cycle performance of the separator. When the porosity of the first porous base membrane is 35%-60%, and / or the porosity of the second porous base membrane is 35%-50%, the air permeability and mechanical strength of the separator can be further improved, thereby further improving the reliability and cycle performance of the separator.

[0018] In any embodiment of the present application, the separator further includes a porous coating layer, the porous coating layer being disposed between the first porous base membrane and the second porous base membrane, and the porous coating layer including a binder; optionally, the porous coating layer includes a binder and a filler. When the separator further includes a porous coating layer, and the porous coating layer includes a binder and a filler, the heat resistance of the separator can be improved, thereby enhancing the reliability of the secondary battery.

[0019] 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 a porous coating is provided between the first porous base membrane and the second porous base membrane, and the binder in the porous coating includes the above components, the reliability of the secondary battery can be improved.

[0020] In any embodiment of the present application, the filler includes at least one of inorganic particles, organic particles, and an organic-metal framework material. When a porous coating layer is provided between the first porous base membrane and the second porous base membrane, and the filler in the porous coating layer includes at least one of the aforementioned inorganic particles, organic particles, and an organic-metal framework material, the filler in the porous coating layer can further improve the heat resistance and mechanical strength of the separator, thereby improving the reliability of the secondary battery.

[0021] In any embodiment of the present application, the isolation membrane satisfies at least one of the following (1)-(2): (1) the porosity of the isolation membrane is 30%-70%, optionally 35%-55%; (2) the air permeability of the isolation membrane is 250s / 100cc-400s / 100cc, optionally 250s / 100cc-320s / 100cc.

[0022] When at least one of the above characteristics of the separator satisfies the given range, the separator can have good heat resistance, air permeability and mechanical strength, thereby improving the reliability and cycle performance of the secondary battery.

[0023] A second aspect of the present application provides a secondary battery comprising a separator according to any of the above embodiments. When the secondary battery employs the separator, the first porous base membrane having a large average pore area faces the positive electrode, while the second porous base membrane having a small average pore area faces the negative electrode. Because the second porous base membrane has good mechanical strength and can exert its excellent physical properties, it is not easily punctured by lithium dendrites generated by the negative electrode, thereby improving the reliability of the secondary battery.

[0024] In any embodiment of the present application, a secondary battery includes a positive electrode sheet, a negative electrode sheet, and a separator according to any of the above embodiments, wherein the separator is disposed between the positive electrode sheet and the negative electrode sheet, with the second porous base membrane of the separator facing the negative electrode sheet. When the secondary battery utilizes the given separator, the second porous base membrane having a large average pore area faces the negative electrode sheet. Because the second porous base membrane has good mechanical strength and can exert its excellent physical properties, it is not easily punctured by lithium dendrites generated by the negative electrode, thereby improving the reliability of the secondary battery.

[0025] 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.

[0026] 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

[0027] 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.

[0028] FIG1 is a schematic structural diagram of an isolation membrane according to an embodiment of the present application.

[0029] FIG2 is a schematic structural diagram of another embodiment of the isolation membrane of the present application.

[0030] FIG3 is a schematic diagram of an embodiment of a secondary battery.

[0031] FIG. 4 is an exploded view of FIG. 3 .

[0032] FIG. 5 is a schematic diagram of an embodiment of a battery module.

[0033] FIG. 6 is a schematic diagram of a battery pack according to one embodiment.

[0034] FIG. 7 is an exploded view of FIG. 6 .

[0035] FIG. 8 is a schematic diagram of an embodiment of a device using a secondary battery as a power source. DETAILED DESCRIPTION

[0036] 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.

[0037] 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.

[0038] 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).

[0039] 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.

[0040] 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).

[0041] secondary batteries

[0042] A secondary battery is a battery that can be recharged to activate the active materials after discharge and continue to be used.

[0043] 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.

[0044] [Isolation film]

[0045] Referring to Figure 1, an embodiment of the present application provides an isolation membrane 10, including: a first porous base membrane 11 and a second porous base membrane 12, the melting point of the first porous base membrane 11 is higher than the melting point of the second porous base membrane 12, and in a cross-section along the thickness direction of the isolation membrane, the average pore area of ​​the first porous base membrane 11 is greater than the average pore area of ​​the second porous base membrane 12.

[0046] In the present application, the average pore area of ​​the porous base membrane refers to the ratio of the total pore area of ​​the porous base membrane to the number of pores in the porous base membrane in a cross section along the thickness direction of the separator.

[0047] Without wishing to be limited to any theory, the inventors have discovered through extensive research that the isolation membrane with a specific structure of the present application can not only improve heat resistance, but also improve air permeability. When the two base membranes adopt the specific average pore area design scheme of the present application, the pore blockage caused by physical lamination in the isolation membrane preparation process is effectively reduced, thereby improving the air permeability of the isolation membrane and maintaining the continuity and effectiveness of ion transmission. At the same time, the isolation membrane can also have good puncture performance, so that the two can achieve an optimal balance, thereby improving the cycle performance of the battery.

[0048] After in-depth research, the present inventors have found that when the separator of the present application satisfies the above conditions and optionally satisfies one or more of the following conditions, the performance of the secondary battery can be further improved.

[0049] There is no particular restriction on the material of the first porous base membrane and the second porous base membrane, and any known base membrane with good chemical stability and mechanical stability can be selected. The materials of the first porous base membrane and the second porous base membrane of the isolation membrane are the same or different. In some embodiments, the first porous base membrane and the second porous base membrane can be selected from one or more of polyolefin, polyether, polyetheretherketone, polyethylene terephthalate, polyimide, polytetrafluoroethylene, polytetrafluoroethylene, polyvinyl alcohol, glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.

[0050] The melting points of the first and second porous base membranes can be tested using equipment and methods known in the art. For example, differential scanning calorimetry can be used for measurement. For details, reference can be made to standard GB / T 19466.3-2004. As an example, the measurement can be performed as follows: 4-6 mg of the sample to be tested is placed in the sample chamber of a differential scanning calorimeter. 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.

[0051] In any embodiment of the present application, the ratio of the average pore area of ​​the first porous base membrane to the average pore area of ​​the second porous base membrane is 1.05-10, for example, 1.05, 1.2, 1.3, 1.4, 1.5, 2, 2.3, 2.55, 3, 3.1, 3.3, 3.5, 3.7, 4, 4.5, 5, 5.3, 6, 7, 8, 8.5, 9, 9.5, 10 or a range consisting of any two of the above values. For example, it can be 1.05-2.5, 1.05-3.5, 3-6, 4-7, 5-9, 1.05-10, 7-10, 8-10, 9-10, etc. In some embodiments, the ratio of the average pore area of ​​the first porous base membrane to the average pore area of ​​the second porous base membrane is 1.05-10. Optionally, the ratio of the average pore area of ​​the first porous base membrane to the average pore area of ​​the second porous base membrane is 1.5-3.5, for example, 1.5, 1.7, 1.9, 2, 2.1, 2.3, 2.5, 2.7, 3, 3.1, 3.3, 3.5, or a range consisting of any two of the above values. For example, the ratio can be 1.5-2.5, 1.5-3.3, 2-3, 2.5-3.5, etc.

[0052] When the ratio of the average pore area of ​​the first porous base membrane to the average pore area of ​​the second porous base membrane is 1.05-10, the separator can have better air permeability, which is conducive to the permeation of lithium ions. The average pore area of ​​the second porous base membrane is relatively smaller than the average pore area of ​​the first porous base membrane. The smaller the average pore area, the more the fiber filaments of the second porous base membrane occupy the spatial structure of the base membrane, the greater the strength of the base membrane, and the more resistant it is to lithium dendrites. Therefore, the separator can have both air permeability and mechanical strength, thereby improving the reliability and cycle performance of the separator. When the ratio of the average pore area of ​​the first porous base membrane to the average pore area of ​​the second porous base membrane is 1.5-3.5, the air permeability and mechanical strength of the separator can be further improved, thereby further improving the reliability and cycle performance of the separator.

[0053] In any embodiment of the present application, the average pore area of ​​the first porous base membrane is 0.0001 μm 2 -0.5μm 2 , for example, can be 0.0001 μm 2 , 0.0005μm 2 , 0.001μm 2 , 0.005μm 2 , 0.01μm 2 , 0.05μm 2 , 0.1μm 2 , 0.2μm 2 , 0.3μm 2 , 0.4μm 2 , 0.5μm 2Or a range consisting of any two of the above values. For example, it can be 0.0001 μm 2 -0.01μm 2 , 0.01μm 2 -0.3μm 2 , 0.05μm 2 -0.4μm 2 , 0.1μm 2 -0.5μm 2 In some embodiments, the average pore area of ​​the first porous base membrane is 0.01 μm 2 -0.3μm 2 The average pore area of ​​the second porous base membrane is 0.0001 μm 2 -0.4μm 2 , for example, can be 0.0001 μm 2 , 0.0005μm 2 , 0.001μm 2 , 0.005μm 2 , 0.01μm 2 , 0.05μm 2 , 0.1μm 2 , 0.2μm 2 , 0.25μm 2 , 0.3μm 2 , 0.4μm 2 Or a range consisting of any two of the above values. For example, it can be 0.0001 μm 2 -0.01μm 2 , 0.01μm 2 -0.25μm 2 , 0.05μm 2 -0.4μm 2 , 0.1μm 2 -0.4μm 2 In some embodiments, the average pore area of ​​the second porous base membrane is 0.01 μm 2 -0.25μm 2 .

[0054] When the average pore area of ​​the first porous base membrane is 0.0001 μm 2 -0.5μm 2 , and / or, the average pore area of ​​the second porous base membrane is 0.0001 μm 2 -0.4μm 2 When the average pore area of ​​the first porous base membrane is different from that of the second porous base membrane, the separator can have heat resistance, air permeability and mechanical strength, thereby improving the reliability and cycle performance of the separator. 2-0.3μm 2 , and / or, the average pore area of ​​the second porous base membrane is 0.01 μm 2 -0.25μm 2 , the heat resistance, air permeability and mechanical strength of the isolation membrane can be further improved, thereby further improving the reliability and cycle performance of the isolation membrane.

[0055] In this application, the cross-sectional image of the separator is an image taken along the thickness direction of the separator. A sample of the separator to be tested of a certain size (e.g., 15 mm x 15 mm) can be cut from any area of ​​the separator and cut using an ion beam polisher (e.g., Hitachi Arblade 5000) under freezing conditions (e.g., -80°C) to obtain a cross-sectional view of the separator. Referring to JY / T010-1996, a scanning electron microscope (e.g., a Sigma 300 scanning electron microscope from ZEISS, Germany) can be used to obtain an SEM image of the separator cross-section (with a magnification of 1,000x to 30,000x). An image processing detection system (e.g., Yihong Separator Membrane Detection System 2022-0408) can be used to obtain the average pore area of ​​the porous base membrane using a multi-segment binarization method.

[0056] When using an ion beam polisher for cutting, the test sample can be wrapped with copper foil or aluminum foil before cutting. When obtaining an SEM image of the isolation film cross section, the test sample can be sprayed with gold.

[0057] Using an image processing detection system, the pore area data of the first porous base membrane and the second porous base membrane of the separator can be obtained respectively. Then, the average pore area of ​​the first porous base membrane and the second porous base membrane of the separator can be obtained respectively using Mintab software. Among them, the ratio of the total pore area of ​​the first porous base membrane of the separator to the number of pores in the first porous base membrane is the average pore area of ​​the first porous base membrane, and the ratio of the total pore area of ​​the second porous base membrane of the separator to the number of pores in the second porous base membrane is the average pore area of ​​the second porous base membrane.

[0058] In any embodiment of the present application, the average pore size of the first porous base membrane is greater than the average pore size of the second porous base membrane, and the average pore size of the first porous base membrane is 100nm-2000nm, for example, 100nm, 200nm, 250nm, 300nm, 350nm, 500nm, 700nm, 900nm, 1000nm, 1250nm, 1500nm, 1700nm, 1800nm, 1900nm, 2000nm or a range consisting of any two of the above values. For example, it can be 100nm-350nm, 200nm-900nm, 300nm-1000nm, 500nm-1500nm, 1000nm-1800nm, 1250nm-2000nm, etc. In some embodiments, the average pore size of the first porous base membrane is 100nm-350nm. The average pore size of the second porous base membrane is 100 nm to 2000 nm, for example, 100 nm, 200 nm, 220 nm, 250 nm, 300 nm, 350 nm, 500 nm, 550 nm, 700 nm, 900 nm, 1000 nm, 1250 nm, 1500 nm, 1700 nm, 1800 nm, 1900 nm, 2000 nm, or a range consisting of any two of the foregoing values. For example, the average pore size can be 100 nm to 350 nm, 250 nm to 700 nm, 300 nm to 1000 nm, 500 nm to 1000 nm, 1000 nm to 1800 nm, 1250 nm to 2000 nm, etc. In some embodiments, the average pore size of the first porous base membrane is 100 nm to 300 nm.

[0059] When the average pore size of the first porous base membrane is greater than the average pore size of the second porous base membrane, the average pore size of the first porous base membrane is 100nm-2000nm, and / or the average pore size of the second porous base membrane is 100nm-2000nm, because the average pore size of the two is different, the smaller the average pore size, the smaller the space occupied by the average pore area, the larger the space occupied by the fiber filaments of the base membrane, and the stronger the mechanical strength of the base membrane; on the contrary, the smaller the space occupied by the fiber filaments of the base membrane, the larger the average pore area of ​​the separator, and the better the air permeability. Therefore, the separator can have both air permeability and mechanical strength, thereby improving the reliability and cycle performance of the separator. When the average pore size of the first porous base membrane is 100nm-350nm, and / or the average pore size of the second porous base membrane is 100nm-300nm, the air permeability and mechanical strength of the separator can be further improved, thereby further improving the reliability and cycle performance of the separator.

[0060] According to some embodiments, the average pore size has a well-known meaning in the art and can be measured using methods known in the art, for example, using a mercury porosimeter with reference to GB / T 21650.1-2008.

[0061] In any embodiment of the present application, the porosity of the first porous base membrane is greater than the porosity of the second porous base membrane. Optionally, the porosity of the first porous base membrane 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, it can be 30%-40%, 35%-60%, 50%-70%, 75%-80%, etc. In some embodiments, the porosity of the first porous base membrane is 35%-60%. The porosity of the second porous base membrane 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, it can be 30%-40%, 35%-50%, 50%-60%, 65%-70%, etc. In some embodiments, the porosity of the second porous base membrane is 35%-50%.

[0062] When the porosity of the first porous base membrane is 30%-80%, and / or the porosity of the second porous base membrane is 30%-70%, the porosities of the two base membranes are different, indicating that the proportion of the pore structure per unit area is different, that is, the average pore area is different. The porous base membrane with a large average pore area has good air permeability, while the base membrane with a small average pore area has good mechanical strength. The combination of the two can make the separator have both air permeability and mechanical strength, thereby improving the reliability and cycle performance of the separator. When the porosity of the first porous base membrane is 35%-60%, and / or the porosity of the second porous base membrane is 35%-50%, the air permeability and mechanical strength of the separator can be further improved, thereby further improving the reliability and cycle performance of the separator.

[0063] According to some embodiments, porosity is well known in the art and can be measured using methods known in the art, for example, using a mercury porosimeter, with reference to GB / T 21650.1-2008.

[0064] Referring to Figure 2, in any embodiment of the present application, a porous coating layer 13 may be further provided between the first porous base membrane 11 and the second porous base membrane 12, and the porous coating layer 13 is provided between the first porous base membrane 11 and the second porous base membrane 12. The porous coating layer 13 includes a binder. Optionally, the porous coating layer 13 may include a binder and a filler. When a porous coating layer 13 is provided between the first porous base membrane and the second porous base membrane, and the porous coating layer 13 includes a binder and a filler, it can not only weaken the process defects in the overheating and pressing composite process, but also further improve the heat resistance and mechanical strength of the separator, thereby improving the reliability of the secondary battery.

[0065] The first porous base membrane and the second porous base membrane can be directly laminated by hot pressing. During the hot pressing process, if the temperature is too high, the porosity will be small and the air permeability will be poor; if the temperature is too low, the first porous base membrane and the second porous base membrane will not be firmly bonded. Therefore, it is necessary to adjust the hot pressing temperature appropriately. Optionally, the hot pressing temperature is 20°C-50°C.

[0066] 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 a porous coating layer 13 is provided between the first porous base film 11 and the second porous base film 12, and the binder in the porous coating layer 13 includes the above components, the heat resistance and mechanical strength 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.

[0067] In any embodiment of the present application, the filler includes at least one of inorganic particles, organic particles, and organic-metal framework materials.

[0068] 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.

[0069] 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 more 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 adhesive layer's wetting and retention properties for the electrolyte, and improve the adhesiveness of the adhesive layer to the first porous base membrane and the second porous base membrane.

[0070] 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.

[0071] 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.

[0072] 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).

[0073] 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.

[0074] 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.

[0075] 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.

[0076] In some embodiments, the coating may further include a dispersant, such as carboxymethyl cellulose, to adjust the viscosity of the coating slurry and improve the quality and uniformity of the coating.

[0077] 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.

[0078] When a porous coating layer is provided between the first porous base membrane and the second porous base membrane, and the filler in the porous coating layer includes at least one of the above-mentioned inorganic particles, organic particles, and organic-metal framework materials, the filler in the porous coating layer can further improve the heat resistance and mechanical strength of the isolation membrane, thereby improving the reliability of the secondary battery.

[0079] In any embodiment of the present application, the isolation membrane satisfies at least one of the following (1)-(2): (1) the porosity of the isolation membrane is 30%-70%, optionally 35%-55%; (2) the air permeability of the isolation membrane is 250s / 100cc-400s / 100cc, optionally 250s / 100cc-320s / 100cc.

[0080] When at least one of the above characteristics of the separator satisfies the given range, the separator can have good heat resistance, air permeability and mechanical strength, thereby improving the reliability and cycle performance of the secondary battery.

[0081] A second aspect of the present application provides a secondary battery comprising a separator according to any of the above embodiments. When the secondary battery employs the separator, the first porous base membrane having a large average pore area faces the positive electrode, while the second porous base membrane having a small average pore area faces the negative electrode. Because the second porous base membrane has good mechanical strength and can exert its excellent physical properties, it is not easily punctured by lithium dendrites generated by the negative electrode, thereby improving the reliability of the secondary battery.

[0082] In any embodiment of the present application, a secondary battery includes a positive electrode sheet, a negative electrode sheet, and a separator according to any of the above embodiments, wherein the separator is disposed between the positive electrode sheet and the negative electrode sheet, with the second porous base membrane of the separator facing the negative electrode sheet. When the secondary battery utilizes the given separator, the second porous base membrane having a large average pore area faces the negative electrode sheet. Because the second porous base membrane has good mechanical strength and can exert its excellent physical properties, it is not easily punctured by lithium dendrites generated by the negative electrode, thereby improving the reliability of the secondary battery.

[0083] Unless otherwise specified, all raw materials used in the separator (eg, the first porous base membrane, the second porous base membrane, the binder, the filler, etc.) can be purchased commercially.

[0084] [Positive electrode]

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] The modified compounds of the above materials may be doping-modified and / or surface-coated modified materials.

[0090] The positive electrode film layer usually optionally includes a binder, a conductive agent and other optional additives.

[0091] 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.

[0092] 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).

[0093] [Negative electrode]

[0094] 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.

[0095] 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.

[0096] 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.

[0097] In some embodiments, to further improve the energy density of the battery, the negative electrode active material may include a silicon-based material.

[0098] The negative electrode film layer usually optionally includes a binder, a conductive agent and other optional additives.

[0099] 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.

[0100] 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).

[0101] As an example, other optional auxiliary agents may be thickening and dispersing agents (such as carboxymethylcellulose sodium, CMC-Na), and PTC thermistor materials.

[0102] [Electrolyte]

[0103] 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.

[0104] 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).

[0105] 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).

[0106] 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.

[0107] When the secondary battery uses the given isolation membrane, the first porous base membrane with a large average pore area faces the positive electrode plate, and the second porous base membrane with a small average pore area faces the negative electrode plate. Because the second porous base membrane has good mechanical strength, it can exert its excellent physical properties and is not easily punctured by lithium dendrites generated by the negative electrode, which can improve the reliability of the secondary battery.

[0108] 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.

[0109] In some embodiments, the secondary battery may include an outer package for encapsulating a positive electrode sheet, a negative electrode sheet, and an electrolyte, wherein the first porous base film of the separator faces the positive electrode sheet.

[0110] 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).

[0111] 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.

[0112] The preparation method of the secondary battery of the present application is well known. In some embodiments, the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte can be assembled to form a secondary battery. As an example, the positive electrode sheet, the separator, 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, left 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.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] [Installation]

[0118] 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.

[0119] The device can select a battery cell, a battery module or a battery pack according to its usage requirements.

[0120] 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.

[0121] 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.

[0122] 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.

[0123] The beneficial effects of the present application are further illustrated below with reference to the examples.

[0124] 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.

[0125] 1. Preparation of isolation membrane

[0126] Isolation film 1:

[0127] (1) A first porous base membrane and a second porous base membrane are provided.

[0128] The first porous base membrane meets the following requirements: the material is polypropylene (PP), the thickness is 6 μm, and the average pore area S1 is 0.0025 μm 2 .

[0129] The second porous base membrane meets the following requirements: the material is polyethylene (PE), the thickness is 4 μm, and the average pore area S2 is 0.0023 μm 2 .

[0130] The ratio of the average pore area S1 of the first porous base membrane to the average pore area S2 of the second porous base membrane is 1.09.

[0131] (2) Preparation of coating slurry: Prepare coating slurry: Mix the binder polyacrylate and the filler aluminum oxide particles and carboxymethyl cellulose in a ratio of 1:4:1 in an appropriate amount of solvent deionized water to prepare a coating slurry.

[0132] (3) The coating slurry of step (2) is applied on one side of the second porous base membrane of step (1) to form a coating layer.

[0133] (4) hot-pressing the first porous base membrane and the second porous base membrane coated in step (3) to obtain a separator, wherein the coating layer is between the first porous base membrane and the second porous base membrane.

[0134] The preparation method of separator 2-11 is similar to that of separator 1, except that the average pore area of ​​the first porous base membrane or the second porous base membrane is adjusted, as shown in Table 1. Other preparation methods are consistent with the preparation method of the separator of Example 1.

[0135] The isolation membrane 1 prepared by the above method was subjected to relevant performance tests, and the specific results are shown in Table 1.

[0136] 2. Preparation of batteries

[0137] Example 1

[0138] 1. Preparation of positive electrode sheet

[0139] 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.

[0140] 2. Preparation of negative electrode sheet

[0141] 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.

[0142] 3. Isolation film

[0143] The isolation film used was the isolation film 1 prepared above.

[0144] 4. Preparation of electrolyte

[0145] 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.

[0146] 5. Preparation of secondary batteries

[0147] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, with the separator placed between the positive electrode sheet and the negative electrode sheet to serve as an isolation, and then wound to obtain an electrode assembly; the electrode assembly is placed in an outer package, and the prepared electrolyte is injected into the dried secondary battery. After vacuum packaging, standing, formation, and shaping processes, a secondary battery is obtained.

[0148] The preparation methods of the secondary batteries of Examples 2-10 and Comparative Example 1 are similar to that of the secondary battery of Example 1, except that different isolation membranes are used (Examples 1-10 use isolation membranes 1-10, and Comparative Example 1 uses isolation membrane 11). See Table 1 for details.

[0149] 3. Battery performance test

[0150] 1. Air permeability test

[0151] The air permeability of a separator has a well-known meaning in the art and can be measured using methods known in the art. For example, the test can be performed in accordance with the standard GB / T 36363-2018.

[0152] 2. Battery cycle performance (cycles)

[0153] 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 constituted one charge-discharge cycle. The batteries were cyclically charged and discharged according to 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.

[0154] As can be seen from Table 1, in Examples 1-10, the separators used satisfy the requirements that the melting point of the first porous base membrane is higher than that of the second porous base membrane, and the average pore area of ​​the first porous base membrane is larger than that of the second porous base membrane. This results in the prepared batteries having good cycle performance and higher reliability. However, the separator used in Comparative Example 1 does not meet the design requirements of this application, resulting in poor cycle performance of the prepared battery.

[0155] 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: a first porous base membrane and a second porous base membrane; The melting point of the first porous base membrane is higher than the melting point of the second porous base membrane; In a cross section along a thickness direction of the separator, an average pore area of ​​the first porous base membrane is larger than an average pore area of ​​the second porous base membrane.

2. The isolation film according to claim 1, wherein The ratio of the average pore area of ​​the first porous base membrane to the average pore area of ​​the second porous base membrane is 1.05-10, and can be optionally 1.5-3.

5.

3. The isolation film according to claim 1 or 2, wherein: The average pore area of ​​the first porous base membrane is 0.0001 μm2-0.5 μm2, and can be 0.01 μm2-0.3 μm2; and / or, The average pore area of ​​the second porous base membrane is 0.0001 μm2-0.4 μm2, and can be optionally 0.01 μm2-0.25 μm2.

4. The isolation film according to any one of claims 1 to 3, wherein: The average pore size of the first porous base membrane is greater than the average pore size of the second porous base membrane; Optionally, the average pore size of the first porous base membrane is 100nm-2000nm, and more preferably 100nm-350nm; Optionally, the average pore size of the second porous base membrane is 100nm-2000nm, and more preferably 100nm-300nm.

5. The isolation film according to any one of claims 1 to 4, wherein: The porosity of the first porous base membrane is greater than the porosity of the second porous base membrane; Optionally, the porosity of the first porous base membrane is 30%-80%, more preferably 35%-60%; Optionally, the porosity of the second porous base membrane is 30%-70%, and more preferably 35%-50%.

6. The isolation film according to any one of claims 1 to 5, wherein: The isolation membrane further includes a porous coating layer, wherein the porous coating layer is disposed between the first porous base membrane and the second porous base membrane, and the porous coating layer includes a binder; optionally, the porous coating layer includes a binder and a filler.

7. The isolation film according to claim 6, wherein: The binder includes one or more of polyacrylate, polyacrylic acid, polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride-trichloroethylene copolymer, polyvinyl pyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyethylene oxide, polyarylate, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, polyacrylonitrile, polyvinyl alcohol, polyethylene, polypropylene, starch, and cyanoethyl pullulan.

8. The isolation film according to any one of claims 6 or 7, wherein: The filler includes at least one of inorganic particles, organic particles, and organic-metal framework materials.

9. The isolation film according to any one of claims 1 to 8, wherein: The isolation film satisfies at least one of the following (1)-(2): The porosity of the isolation membrane is 30%-70%, and can be optionally 35%-55%; The air permeability of the isolation membrane is 250s / 100cc-400s / 100cc, and can be optionally 250s / 100cc-320s / 100cc.

10. A secondary battery comprising the separator according to any one of claims 1 to 9.

11. The secondary battery according to claim 10, wherein: 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 porous base film of the isolation film faces the negative electrode sheet.

12. An electrical device comprising the secondary battery according to claim 10 or 11.

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