Separator, secondary battery and power consuming device

Abstract

The present application provides a separator including a first porous base film and a second porous base film, wherein the melting point of the first porous base film is higher than that of the second porous base film, and the average pore area of ​​the first porous base film is larger than that of the second porous base film in a cross section along the thickness direction of the separator. By providing the separator with both breathability and mechanical strength, the reliability and cycle performance of the separator can be improved.

Description

[Technical Field]

[0001] The present application relates to the field of secondary battery technology, and more particularly to separators, secondary batteries, and power consuming devices. [Background technology]

[0002] Secondary batteries are widely used in various consumer electronic products and electric vehicles due to their excellent properties such as light weight, non-polluting nature, and no memory effect.

[0003] With the continuous development of the new energy industry, users are placing higher requirements on the use of secondary batteries.

[0004] Therefore, how to improve the cycle performance of secondary batteries is currently an issue that needs to be solved urgently. Summary of the Invention

[0005] In view of the technical problems existing in the background art, the present application provides a separator for improving the cycle performance of a secondary battery.

[0006] To achieve the above object, a first aspect of the present application provides a separator comprising a first porous base film and a second porous base film, wherein the melting point of the first porous base film is higher than the melting point of the second porous base film, and in a cross section along the thickness direction of the separator, the average pore area of ​​the first porous base film is larger than the average pore area of ​​the second porous base film.

[0007] Compared with the prior art, the present invention includes at least the following beneficial effects:

[0008] A separator having the specific structure of the present application can not only improve heat resistance, but also breathability. When the two base films adopt the specific average pore area design proposal of the present application, the pore blockage caused by physical lamination during the separator manufacturing process is effectively reduced, thereby improving the breathability of the separator and maintaining the continuity and effectiveness of ion transmission, while also providing the separator with good puncture performance, thereby achieving an optimal balance between the two and improving the cycle performance of the battery.

[0009] In any embodiment of the present application, the ratio of the average pore area of ​​the first porous base film to the average pore area of ​​the second porous base film is from 1.05 to 10, and optionally from 1.5 to 3.5.

[0010] When the ratio of the average pore area of ​​the first porous base film to the average pore area of ​​the second porous base film is 1.05 to 10, the separator has better breathability, which is conducive to the passage of lithium ions. The average pore area of ​​the second porous base film is relatively smaller than that of the first porous base film. The smaller the average pore area, the greater the amount of fiber filaments in the second porous base film occupying the spatial structure of the base film. The stronger the base film, the stronger the resistance to lithium dendrites. Therefore, by providing a separator with both breathability and mechanical strength, the reliability and cycle performance of the separator can be improved. When the ratio of the average pore area of ​​the first porous base film to the average pore area of ​​the second porous base film is 1.5 to 3.5, the breathability and mechanical strength of the separator can be further improved, which further improves the reliability and cycle performance of the separator.

[0011] In any embodiment of the present application, the first porous base film has an average pore area of ​​0.0001 μm 2 ~0.5μm 2 and selectively 0.01 μm 2 ~0.3μm 2and / or the average pore area of ​​the second porous base film is 0.0001 μm 2 ~0.4μm 2 and selectively 0.01 μm 2 ~0.25μm 2 is.

[0012] The first porous base film has an average pore area of ​​0.0001 μm 2 ~0.5μm 2 and / or the average pore area of ​​the second porous base film is 0.0001 μm 2 ~0.4μm 2 In this case, the first porous base film and the second porous base film have different average pore areas, which allows the separator to have both breathability 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 film is 0.01 μm 2 ~0.25μm 2 In this case, the reliability and cycle performance of the separator can be further improved by further improving the air permeability and mechanical strength of the separator.

[0013] In any embodiment of the present application, the average pore size of the first porous base film is larger than the average pore size of the second porous base film, and optionally the average pore size of the first porous base film is 100 nm to 2000 nm, more optionally 100 nm to 350 nm, and optionally the average pore size of the second porous base film is 100 nm to 2000 nm, more optionally 100 nm to 300 nm.

[0014] When the average pore size of the first porous base film is larger than that of the second porous base film, and the average pore size of the first porous base film is 100 nm to 2000 nm and / or the average pore size of the second porous base film is 100 nm to 2000 nm, the average pore sizes of the two films are different. Therefore, the smaller the average pore size, the smaller the space occupied by the average pore area, and the larger the space occupied by the fiber filaments of the base film, resulting in stronger mechanical strength of the base film. Conversely, the smaller the space occupied by the fiber filaments of the base film, the larger the average pore area of ​​the separator and the better its breathability. Therefore, by achieving both breathability and mechanical strength in the separator, the reliability and cycle performance of the separator can be improved. When the average pore size of the first porous base film is 100 nm to 350 nm and / or the average pore size of the second porous base film is 100 nm to 300 nm, the breathability and mechanical strength of the separator can be further improved, thereby further improving the reliability and cycle performance of the separator.

[0015] In any embodiment of the present application, the porosity of the first porous base film is greater than the porosity of the second porous base film, and optionally the porosity of the first porous base film is 30% to 80%, more optionally 35% to 60%, and / or the porosity of the second porous base film is 30% to 70%, more optionally 35% to 50%.

[0016] When the porosity of the first porous base film is larger than that of the second porous base film, and the porosity of the first porous base film is 30% to 80% and / or the porosity of the second porous base film is 30% to 70%, the difference in porosity of the two base films means that the porosity ratio of the pore structure per unit area is different, i.e., the average pore area is different. The porous base film with a larger average pore area has good breathability, while the base film with a smaller average pore area has good mechanical strength. By combining the two, the separator can achieve both breathability and mechanical strength, thereby improving the reliability and cycling performance of the separator. When the porosity of the first porous base film is 35% to 60% and / or the porosity of the second porous base film is 35% to 50%, the breathability and mechanical strength of the separator can be further improved, thereby further improving the reliability and cycling performance of the separator.

[0017] In any embodiment of the present application, the separator further includes a porous coating layer disposed between the first porous base film and the second porous base film and including an adhesive, and optionally the porous coating layer includes an adhesive and a filler. When the separator further includes a porous coating layer including an adhesive and a filler, the heat resistance of the separator can be improved, and the reliability of the secondary battery can be improved.

[0018] In some embodiments of the present application, the adhesive may include one or more of polyacrylate, polyacrylic acid, polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride-trichloroethylene copolymer, polyvinylpyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyethylene oxide, polyarylate, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, polyacrylonitrile, polyvinyl alcohol, polyethylene, polypropylene, starch, and cyanoethyl pullulan. When a porous coating layer is disposed between the first porous base film and the second porous base film and the adhesive in the porous coating layer contains any of the above components, the reliability of the secondary battery can be improved.

[0019] In any embodiment of the present application, the filler comprises at least one of inorganic particles, organic particles, and metal-organic framework materials. When a porous coating layer is disposed between the first porous base film and the second porous base film, and the filler in the porous coating layer comprises at least one of inorganic particles, organic particles, and metal-organic framework materials, 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.

[0020] In any embodiment of the present application, the separator satisfies at least one of the following (1) and (2): (1) the porosity of the separator is 30% to 70%, and optionally 35% to 55%, and (2) the air permeability of the separator is 250 s / 100 cc to 400 s / 100 cc, and optionally 250 s / 100 cc to 320 s / 100 cc.

[0021] When at least one of the above characteristics of the separator satisfies a predetermined range, the separator can simultaneously have good heat resistance, breathability, and mechanical strength, thereby improving the reliability and cycle performance of the secondary battery.

[0022] A second aspect of the present application provides a secondary battery, which includes a separator according to any one of the above embodiments. When the secondary battery employs a predetermined separator, a first porous base film having a large average pore area is disposed on the positive electrode plate side, and a second porous base film having a small average pore area is disposed on the negative electrode plate side. The second porous base film has good mechanical strength, allowing it to exhibit its excellent physical properties and not be easily pierced by lithium dendrites formed in the negative electrode, thereby improving the reliability of the secondary battery.

[0023] In any embodiment of the present application, a secondary battery includes a positive electrode plate, a negative electrode plate, and any one of the above separators, the separator being disposed between the positive electrode plate and the negative electrode plate, with the second porous base film of the separator being disposed on the negative electrode plate side. When a predetermined separator is used in a secondary battery, the second porous base film having a large average pore area is disposed on the negative electrode plate side, and the second porous base film has good mechanical strength, so it can demonstrate its excellent physical performance and is not easily pierced by lithium dendrites generated in the negative electrode, thereby improving the reliability of the secondary battery.

[0024] A third aspect of the present application provides a power consumption device, the power consumption device including the secondary battery of the second aspect of the present application. When the secondary battery of the power consumption device employs a predetermined separator, the reliability of the power consumption device can be improved. The device of the present application includes the secondary battery of the present application, and therefore has at least the same advantages as the secondary battery. [Brief explanation of the drawings]

[0025] In order to more clearly describe the technical solutions of the present application, the following briefly describes the drawings used in the present application. Obviously, the drawings described below are only some embodiments of the present application, and those skilled in the art can obtain other drawings based on the drawings without creative efforts.

[0026] [Figure 1] 1 is a structural schematic diagram of an embodiment of a separator according to the present application. [Figure 2] FIG. 2 is a structural schematic diagram of another embodiment of the separator according to the present application. [Figure 3] FIG. 1 is a schematic diagram of an embodiment of a secondary battery. [Figure 4] FIG. 4 is an exploded view of FIG. 3. [Figure 5] FIG. 1 is a schematic diagram of one embodiment of a battery module. [Figure 6] FIG. 1 is a schematic diagram of one embodiment of a battery pack. [Figure 7] FIG. 7 is an exploded view of FIG. [Figure 8] FIG. 1 is a schematic diagram of an embodiment of an apparatus that uses a secondary battery as a power source. DETAILED DESCRIPTION OF THE INVENTION

[0027] 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 do not limit the scope of the present application.

[0028] For brevity, this specification specifically discloses only a few numerical ranges. However, any lower limit can be combined with any upper limit to form an open-ended range, any lower limit can be combined with another lower limit to form an open-ended range, and any upper limit can be combined with another upper limit to form an open-ended range. Furthermore, each point or single value disclosed individually can itself be combined as a lower or upper limit with other points or single values, or with other lower or upper limits, to form an open-ended range.

[0029] In the description herein, unless otherwise stated, the term "or" is inclusive. That is, the phrase "A or B" means "A, B, or both A and B." More specifically, any one of the following conditions satisfies the condition "A or B": 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).

[0030] In the description of this specification, unless otherwise specified, it should be understood that "more than" and "less than" include the numbers themselves, and "more than one" in "one or more" means two or more.

[0031] Unless otherwise specified, the terms used herein have the meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of each parameter referred to herein can be measured by various measurement methods commonly used in the art (for example, they can be tested according to the methods described in the examples of the present application).

[0032] secondary battery A secondary battery refers to a battery that can be continuously used by activating the active material by charging the battery after discharging.

[0033] A typical secondary battery includes a positive electrode plate, a negative electrode plate, a separator, and an electrolyte. During the charge and discharge process, active ions are repeatedly 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 the active ions between the positive and negative electrodes.

[0034] [Separator] Referring to Figure 1, an embodiment of the present application provides a separator 10, which includes a first porous base film 11 and a second porous base film 12, wherein the melting point of the first porous base film 11 is higher than the melting point of the second porous base film 12, and in a cross section along the thickness direction of the separator, the average pore area of ​​the first porous base film 11 is larger than the average pore area of ​​the second porous base film 12.

[0035] In this application, the average pore area of ​​the porous base film refers to the ratio of the total pore area of ​​the porous base film to the number of pores in the porous base film in a cross section along the thickness direction of the separator.

[0036] Without wishing to be bound by any theory, the inventors have found through extensive research that a separator having the specific structure of the present application can not only improve heat resistance, but also breathability, and that when the two base films adopt the specific average pore area design proposal of the present application, the breathability of the separator can be improved by effectively reducing pore blockage caused by physical lamination in the separator manufacturing process, maintaining the continuity and effectiveness of ion transmission, while also providing the separator with good puncture performance, thereby achieving an optimal balance between the two and improving the cycle performance of the battery.

[0037] Through extensive research, the inventors have found that the performance of a secondary battery can be further improved when the separator of the present application satisfies the above conditions and, in addition, selectively satisfies one or more of the following conditions:

[0038] The materials of the first and second porous base films are not particularly limited, and any known base film having good chemical and mechanical stability can be selected. The materials of the first and second porous base films of the separator may be the same or different. In some embodiments, the first and second porous base films may be one or more selected from polyolefin, polyether, polyether ether ketone, ethylene terephthalate, polyimide, polytetrafluoroethylene, polyvinylidene tetrafluoride, polyvinyl alcohol, glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride.

[0039] The melting points of the first and second porous base films can be tested using instruments and methods known in the art. For example, they can be measured using differential scanning calorimetry. Specifically, reference can be made to standard GB / T19466.3-2004. For example, they can be measured according to the following method: a test sample weighing 4 mg to 6 mg is taken and placed in the sample chamber of a differential scanning calorimeter. The temperature is increased from 25°C to 400°C at a rate of 10°C / min to obtain a melting endothermic curve of the sample. The temperature corresponding to the peak value of the curve is the melting point of the sample.

[0040] In any embodiment of the present application, the ratio of the average pore area of ​​the first porous base film to the average pore area of ​​the second porous base film is 1.05 to 10, and may be, 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 may be 1.05 to 2.5, 1.05 to 3.5, 3 to 6, 4 to 7, 5 to 9, 1.05 to 10, 7 to 10, 8 to 10, 9 to 10, etc. In some embodiments, the ratio of the average pore area of ​​the first porous base film to the average pore area of ​​the second porous base film is 1.05 to 10. Alternatively, the ratio of the average pore area of ​​the first porous base film to the average pore area of ​​the second porous base film may be 1.5 to 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, such as 1.5 to 2.5, 1.5 to 3.3, 2 to 3, or 2.5 to 3.5.

[0041] When the ratio of the average pore area of ​​the first porous base film to the average pore area of ​​the second porous base film is 1.05 to 10, the separator has better breathability, which is conducive to the passage of lithium ions. The average pore area of ​​the second porous base film is relatively smaller than that of the first porous base film. The smaller the average pore area, the greater the amount of fiber filaments in the second porous base film occupying the spatial structure of the base film. The stronger the base film, the stronger the resistance to lithium dendrites. Therefore, by providing a separator with both breathability and mechanical strength, the reliability and cycle performance of the separator can be improved. When the ratio of the average pore area of ​​the first porous base film to the average pore area of ​​the second porous base film is 1.5 to 3.5, the breathability and mechanical strength of the separator can be further improved, which further improves the reliability and cycle performance of the separator.

[0042] In any embodiment of the present application, the first porous base film has an average pore area of ​​0.0001 μm 2 ~0.5μm 2 For example, 0.0001 μm 2 , 0.0005 μm 2 , 0.001 μm 2 , 0.005 μm 2 , 0.01 μm 2 , 0.05 μm 2 , 0.1 μm 2 , 0.2 μm 2 , 0.3 μm 2 , 0.4 μm 2 , 0.5 μm 2 Alternatively, it may be a range consisting of any two of the above values. For example, 0.0001 μm 2 ~0.01μm 2 , 0.01 μm 2 ~0.3μm 2 , 0.05 μm 2 ~0.4μm 2 , 0.1 μm 2 ~0.5μm 2 In some embodiments, the first porous base film has an average pore area of ​​0.01 μm 2 ~0.3μm 2 The average pore area of ​​the second porous base film is 0.0001 μm 2 ~0.4μm 2 For example, 0.0001 μm 2 , 0.0005 μm 2 , 0.001 μm 2 , 0.005 μm 2 , 0.01 μm 2 , 0.05 μm 2 , 0.1 μm 2 , 0.2 μm 2 , 0.25 μm 2 , 0.3 μm 2 , 0.4 μm 2 Alternatively, it may be a range consisting of any two of the above values. For example, 0.0001 μm 2 ~0.01μm 2 , 0.01 μm 2 ~0.25μm 2 , 0.05 μm 2 ~0.4μm2 , 0.1 μm 2 ~0.4μm 2 In some embodiments, the second porous base film has an average pore area of ​​0.01 μm 2 ~0.25μm 2 is.

[0043] 1 The average pore area of ​​the porous base film is 0.0001 μm 2 ~0.5μm 2 and / or the average pore area of ​​the second porous base film is 0.0001 μm 2 ~0.4μm 2 In this case, the first porous base film and the second porous base film have different average pore areas, which allows the separator to simultaneously have heat resistance, breathability, 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 film is 0.01 μm 2 ~0.25μm 2 In this case, the heat resistance, air permeability, and mechanical strength of the separator can be further improved, thereby further improving the reliability and cycle performance of the separator.

[0044] In this application, the cross-sectional image of the separator is an image taken along the thickness direction of the separator. A test separator sample of a certain size (e.g., 15 mm × 15 mm) is cut from any region of the separator and cut under frozen conditions (e.g., -80 ° C) using an ion beam polisher (e.g., Hitachi Arblade 5000) to obtain a separator cross section. The cross section is then scanned using a scanning electron microscope (e.g., ZEISS Sigma 300 scanning electron microscope, Germany) to obtain an SEM image of the separator cross section (magnification can be 1000x to 30000x). An image processing detection system (e.g., Yihong Separator Detection System 2022-0408) can be used to obtain the average pore area of ​​the porous base film by a multi-segment binarization method.

[0045] When cutting with an ion beam polishing machine, the test sample can be wrapped in copper or aluminum foil before cutting. When obtaining SEM images of the separator cross section, the test sample can be gold sprayed.

[0046] The image processing detection system can be used to obtain the pore area data of the first porous base film and the second porous base film of the separator, respectively, and then the Mintab software can be used to obtain the average pore area of ​​the first porous base film and the second porous base film of the separator, respectively, where the ratio of the total pore area of ​​the first porous base film of the separator to the number of pores in the first porous base film is the average pore area of ​​the first porous base film, and the ratio of the total pore area of ​​the second porous base film of the separator to the number of pores in the second porous base film is the average pore area of ​​the second porous base film.

[0047] In any embodiment of the present application, the average pore size of the first porous base film is larger than the average pore size of the second porous base film, and the average pore size of the first porous base film is 100 nm to 2000 nm, for example, 100 nm, 200 nm, 250 nm, 300 nm, 350 nm, 500 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 above values. For example, it may be 100 nm to 350 nm, 200 nm to 900 nm, 300 nm to 1000 nm, 500 nm to 1500 nm, 1000 nm to 1800 nm, 1250 nm to 2000 nm, etc. In some embodiments, the average pore size of the first porous base film is 100 nm to 350 nm. The average pore size of the second porous base film is 100 nm to 2000 nm, and may be, 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 above values. For example, it may 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 film is 100 nm to 300 nm.

[0048] When the average pore size of the first porous base film is larger than that of the second porous base film, and the average pore size of the first porous base film is 100 nm to 2000 nm and / or the average pore size of the second porous base film is 100 nm to 2000 nm, the average pore sizes of the two films are different. Therefore, the smaller the average pore size, the smaller the space occupied by the average pore area, and the larger the space occupied by the fiber filaments of the base film, resulting in stronger mechanical strength of the base film. Conversely, the smaller the space occupied by the fiber filaments of the base film, the larger the average pore area of ​​the separator and the better its breathability. Therefore, by achieving both breathability and mechanical strength in the separator, the reliability and cycle performance of the separator can be improved. When the average pore size of the first porous base film is 100 nm to 350 nm and / or the average pore size of the second porous base film is 100 nm to 300 nm, the breathability and mechanical strength of the separator can be further improved, thereby further improving the reliability and cycle performance of the separator.

[0049] According to some embodiments, average pore size has a meaning known in the art and can be tested using methods known in the art, for example, using a mercury porosimeter and referring to GB / T21650.1-2008.

[0050] In any embodiment of the present application, the porosity of the first porous base film is greater than the porosity of the second porous base film. Optionally, the porosity of the first porous base film is 30% to 80%, e.g., 30%, 35%, 38%, 40%, 50%, 55%, 60%, 70%, 75%, 80%, or a range consisting of any two of the above values. For example, 30% to 40%, 35% to 60%, 50% to 70%, 75% to 80%, etc. In some embodiments, the porosity of the first porous base film is 35% to 60%. The porosity of the second porous base film is 30% to 70%, e.g., 30%, 35%, 40%, 45%, 50%, 60%, 65%, 70%, or a range consisting of any two of the above values. For example, it may be 30% to 40%, 35% to 50%, 50% to 60%, 65% to 70%, etc. In some embodiments, the porosity of the second porous base film is 35% to 50%.

[0051] When the porosity of the first porous base film is 30% to 80% and / or the porosity of the second porous base film is 30% to 70%, the difference in porosity between the two base films means a difference in the pore structure's occupation ratio per unit area, i.e., a difference in the average pore area. A porous base film with a large average pore area has good breathability, while a base film with a small average pore area has good mechanical strength. By combining the two, the separator can achieve both breathability and mechanical strength, thereby improving the reliability and cycle performance of the separator. When the porosity of the first porous base film is 35% to 60% and / or the porosity of the second porous base film is 35% to 50%, the breathability and mechanical strength of the separator can be further improved, thereby further improving the reliability and cycle performance of the separator.

[0052] According to some embodiments, porosity has a meaning known in the art and can be tested using methods known in the art, for example, using a mercury porosimeter and referring to GB / T21650.1-2008.

[0053] Referring to FIG. 2 , in any embodiment of the present application, a porous coating layer 13 may be further disposed between the first porous base film 11 and the second porous base film 12, and the porous coating layer 13 is disposed between the first porous base film 11 and the second porous base film 12. The porous coating layer 13 includes an adhesive. Optionally, the porous coating layer 13 may include an adhesive and a filler. When the porous coating layer 13 is disposed between the first porous base film and the second porous base film and includes an adhesive and a filler, process defects in the hot-press composite process can be reduced, and the heat resistance and mechanical strength of the separator can be further improved, thereby improving the reliability of the secondary battery.

[0054] The first and second porous base films can be directly combined by hot pressing. In the hot pressing process, if the temperature is too high, the porosity will be small and the breathability will be low, and if the temperature is too low, the adhesion between the first and second porous base films will be weak. Therefore, it is necessary to adjust the hot pressing temperature appropriately. Optionally, the hot pressing temperature is 20°C to 50°C.

[0055] In some embodiments of the present application, the adhesive may include one or more of polyacrylate, polyacrylic acid, polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride-trichloroethylene copolymer, polyvinylpyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyethylene oxide, polyarylate, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, polyacrylonitrile, polyvinyl alcohol, polyethylene, polypropylene, starch, and cyanoethyl pullulan. When a porous coating layer 13 is disposed between the first porous base film 11 and the second porous base film 12, and the adhesive in the porous coating layer 13 contains the above components, the heat resistance and mechanical strength of the separator 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.

[0056] In any embodiment of the present application, the filler comprises at least one of inorganic particles, organic particles, and metal organic framework materials.

[0057] Optionally, the inorganic particles may include one or more of inorganic particles having a dielectric constant of 5 or greater, inorganic particles that are ionically conductive but do not store ions, and inorganic particles capable of electrochemical reactions.

[0058] Alternatively, the inorganic particles having a charge constant of 5 or more may be 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, magnesium lithium silicate, magnesium sodium 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 The inorganic particles may include at least one of PMN-PT, PO3-PbTiO3, and modified inorganic particles thereof. Optionally, each inorganic particle may be modified by chemical and / or physical modification. Chemical modification methods include coupling agent modification (e.g., the use of a silane coupling agent, a titanate ester coupling agent, etc.), surfactant modification, and polymer graft modification. Physical modification methods include mechanical dispersion, ultrasonic dispersion, and high-energy treatment. Modification treatments can reduce the aggregation of inorganic particles and make the structure of the adhesive layer more stable and uniform. Furthermore, selecting a coupling agent, surfactant, or polymer with a specific functional group to modify the inorganic particles can improve the wettability and retention of the adhesive layer with the electrolyte and the adhesion of the adhesive layer to the first and second porous base films.

[0059] Alternatively, the inorganic particles having ionic conductivity but not storing ions may be Li3PO4, lithium titanium phosphate, Li x1 Ti y1 (PO4)3, Lithium titanium aluminum phosphate Li x2 Al y2 Ti z1(PO4)3, (LiAlTiP) x3 O y3 glass, lithium lanthanum titanate Li x4 La y4 TiO3, lithium germanium thiophosphate Li x5 Ge y5 P z2 S w , lithium nitride Li x6 N y6 , Li-SiS2 glass x7 Si y7 S z3 and Li-P2S5 glass x8 P y8 S z4 may include at least one of them, and 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. Thereby, the ion conductivity of the separator can be further improved.

[0060] Optionally, the inorganic particles capable of the above 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.

[0061] Optionally, the organic particles may comprise one or more of polycarbonate, polythiophene, polypyridine, polystyrene, polyacrylic wax, polyethylene, polypropylene, cellulose, cellulose modifiers (e.g., carboxymethyl cellulose), melamine resin, phenolic resin, polyester (e.g., polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate), silicone resin, polyimide, polyamideimide, polyaramid, polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, polyaryletherketone, copolymer of butyl acrylate and ethyl methacrylate (e.g., crosslinked polymer of butyl acrylate and ethyl methacrylate).

[0062] Optionally, the metal organic framework may comprise one or more of nitrogen-containing heterocyclic ligand frameworks, organic carboxylic acid-based ligand frameworks, and nitrogen-oxygen-containing mixed ligand frameworks.

[0063] In some embodiments, the content of the adhesive may be 10% or more, and optionally 10% to 30%, by total weight of the adhesive layer.

[0064] In some embodiments, the content of the filler may be 90% or less, optionally 40%-90%, or 60%-80% by total weight of the adhesive layer.

[0065] In some embodiments, the coating layer may further include a dispersant, such as carboxymethyl cellulose, which can adjust the viscosity of the coating layer slurry and improve the mass and uniformity of the coating layer.

[0066] In some embodiments, the dispersant content may be 25% or less, and optionally 20% or less, by total weight of the adhesive layer.

[0067] When a porous coating layer is disposed between the first porous base film and the second porous base film, and the filler in the porous coating layer includes at least one of the 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 separator, thereby improving the reliability of the secondary battery.

[0068] In any embodiment of the present application, the separator satisfies at least one of the following (1) and (2): (1) the porosity of the separator is 30% to 70%, and optionally 35% to 55%, and (2) the air permeability of the separator is 250 s / 100 cc to 400 s / 100 cc, and optionally 250 s / 100 cc to 320 s / 100 cc.

[0069] When at least one of the above characteristics of the separator satisfies a predetermined range, the separator can simultaneously have good heat resistance, breathability, and mechanical strength, thereby improving the reliability and cycle performance of the secondary battery.

[0070] A second aspect of the present application provides a secondary battery, which includes a separator according to any one of the above embodiments. When the secondary battery employs a predetermined separator, a first porous base film having a large average pore area is disposed on the positive electrode plate side, and a second porous base film having a small average pore area is disposed on the negative electrode plate side. The second porous base film has good mechanical strength, allowing it to exhibit its excellent physical properties and not be easily pierced by lithium dendrites formed in the negative electrode, thereby improving the reliability of the secondary battery.

[0071] In any embodiment of the present application, a secondary battery includes a positive electrode plate, a negative electrode plate, and any one of the above separators, the separator being disposed between the positive electrode plate and the negative electrode plate, with the second porous base film of the separator being disposed on the negative electrode plate side. When a predetermined separator is used in a secondary battery, the second porous base film having a large average pore area is disposed on the negative electrode plate side, and the second porous base film has good mechanical strength, so it can demonstrate its excellent physical performance and is not easily pierced by lithium dendrites generated in the negative electrode, thereby improving the reliability of the secondary battery.

[0072] Unless otherwise specified, each of the raw materials used in the separator (for example, the first porous base film, the second porous base film, the adhesive, the filler, etc.) is commercially available.

[0073] [Positive electrode] In a secondary battery, the positive electrode plate generally includes a positive electrode current collector and a positive electrode film layer disposed on the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0074] The positive electrode current collector can be a conventional metal foil or a composite current collector (a metal material can be attached to a polymer substrate to form a composite current collector). For example, the positive electrode current collector can be aluminum foil.

[0075] The specific type of the positive electrode active material is not limited, and any positive electrode active material known in the art that can be used for secondary batteries can be used, and those skilled in the art can select it according to actual needs.

[0076] For example, the positive electrode active material may include, but is not limited to, one or more of lithium transition metal oxides, lithium-containing phosphates having an olivine structure, 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 lithium-containing phosphates having an olivine structure may include, but are not limited to, one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their modified compounds. All of these materials are commercially available.

[0077] The modifying compound for each of the above materials may be a material that has been subjected to doping modification and / or surface coating modification.

[0078] The positive electrode film layer usually further optionally contains an adhesive, a conductive agent, and other optional auxiliary agents.

[0079] By way of 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.

[0080] By way of example, the adhesive may be one or more of Polymerized 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 (Vinylalcohol Polymer (PVA)), and Polyvinyl Butyral (PVB).

[0081] [Negative electrode] 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, and the negative electrode film layer includes a negative electrode active material.

[0082] The negative electrode current collector can be a conventional metal foil or a composite current collector (e.g., a metal material can be attached to a polymer substrate to form a composite current collector). For example, the negative electrode current collector can be a copper foil.

[0083] The specific type of the negative electrode active material is not limited, and any negative electrode active material known in the art that can be used in secondary batteries can be used. Those skilled in the art can select the material according to their actual needs. For 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 one or more selected from silicon elemental, silicon oxide (e.g., silicon suboxide), silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be one or more selected from tin elemental, tin oxide, and tin alloys. All of these materials are commercially available.

[0084] In some embodiments, to further improve the energy density of the battery, the negative electrode active material may include a silicon-based material.

[0085] The negative electrode film layer usually further optionally contains an adhesive, a conductive agent, and other optional auxiliary agents.

[0086] By way of 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.

[0087] By way of example, the adhesive may be one or more of styrene butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0088] For example, other optional auxiliaries may be thickeners and dispersants (eg, Carboxymethylcellulose Sodium, CMC-Na), PTC thermistor materials.

[0089] [Electrolyte] The secondary battery may include an electrolyte that functions to conduct ions between the positive electrode and the negative electrode. The electrolyte may include an electrolyte salt and a solvent.

[0090] By way of example, the electrolyte salt may be one or more selected from lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium perchlorate (LiClO), lithium hexafluoroarsenate (LiAsF), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), difluoroboranyl lithiooxalate (LiDFOB), lithium bisoxalatoborate (LiBOB), lithium difluorophosphate (LiPOF), lithium difluorobis(oxalato)phosphate (LiDFOP), and lithium tetrafluoro(oxalato)phosphate (LiTFOP).

[0091] Examples of the solvent include ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), diisopropyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), n-propyl acetate (PA), methyl propionate (Methyl The sulfonate may be one or more selected from the group consisting of n-propyl propionate (MP), ethyl propionate (EP), n-propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (tetramethylene sulfone (SF), dimethyl sulfone (methyl sulfone (MSM), methyl ethyl sulfone (EMS)), and diethyl sulfone (diethyl sulfone (ESE)).

[0092] In some embodiments, the electrolyte solution further includes an additive. For example, the additive may include a negative electrode film-forming additive, a positive electrode film-forming additive, or an additive that can improve specific battery performance, such as an additive that improves battery overcharge performance, an additive that improves battery high-temperature performance, or an additive that improves battery low-temperature performance.

[0093] When a secondary battery uses a specified separator, a first porous base film with a large average pore area is placed on the positive electrode plate side, and a second porous base film with a small average pore area is placed on the negative electrode plate side.The second porous base film has good mechanical strength, so it can demonstrate its excellent physical performance and is not easily pierced by lithium dendrites formed in the negative electrode, thereby improving the reliability of the secondary battery.

[0094] The embodiment of the present application is not particularly limited to the shape of the secondary battery, and it may be cylindrical, rectangular, or any other shape. Figure 3 shows an example of a secondary battery 5 having a rectangular structure.

[0095] In some embodiments, the secondary battery may include an outer package for enclosing the positive electrode plate, the negative electrode plate, and the electrolyte, and the first porous base film of the separator is disposed on the positive electrode plate side.

[0096] In some embodiments, the exterior packaging of the secondary battery may be a hard casing such as a hard plastic casing, an aluminum casing, or a steel casing. The exterior packaging of the secondary battery may be a soft pack such as a bag-type soft pack. The material of the soft pack may be plastic, and may include, for example, one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0097] 4, in some embodiments, the exterior package may include a casing 51 and a cover plate 53. Here, the casing 51 may include a base plate and a side plate connected to the base plate, and the base plate and the side plate surround and form a receiving cavity. The casing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can cover the opening and seal the receiving cavity.

[0098] Methods for manufacturing the secondary battery of the present application are well known. In some embodiments, a secondary battery can be formed by assembling a positive electrode plate, a separator, a negative electrode plate, and an electrolyte. For example, the positive electrode plate, the separator, and the negative electrode plate can be wound and / or stacked to form an electrode assembly. The electrode assembly can then be placed in an outer package, dried, and then injected with an electrolyte. A battery cell can be obtained through processes such as vacuum sealing, standing, chemical formation, and shaping. A plurality of battery cells can be further connected in series, parallel, or series-parallel to form a battery module. A plurality of battery modules can be further connected in series, parallel, or series-parallel to form a battery pack. In some embodiments, a plurality of battery cells can be directly connected to form a battery pack.

[0099] Fig. 5 shows an example of a battery module 4. Referring to Fig. 5, in the battery module 4, the plurality of secondary batteries 5 may be arranged in order along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the plurality of secondary batteries 5 may be fixed by a fastening member.

[0100] The battery module 4 may further include a housing having an accommodating space, and a plurality of secondary batteries 5 are accommodated in the accommodating space.

[0101] In some embodiments, the battery modules may be further assembled into a battery pack, and the number of battery modules included in the battery pack may be selected according to the application and capacity of the battery pack.

[0102] 6 and 7 show an example battery pack 1. Referring to FIGS. 6 and 7, the battery pack 1 may include a battery box and a plurality of battery modules 4 installed in the battery box. The battery box includes an upper case 2 and a lower case 3, and the upper case 2 may be attached to the lower case 3 as a lid to form a sealed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery box in any manner.

[0103] [Device] The present application further provides a power consuming device, wherein the battery cell, battery module, or battery pack including the secondary battery of the present application may be a power source for the device or an energy storage unit for the device, and the device may be, but is not limited to, a mobile device (e.g., mobile phone, laptop), an electric vehicle (e.g., pure electric vehicle, hybrid electric vehicle, plug-in hybrid electric vehicle, electric bicycle, electric scooter, electric golf cart, electric truck), an electric train, a ship, a satellite, or an energy storage system.

[0104] The device can select battery cells, battery modules or battery packs according to its usage needs.

[0105] 8 shows an example of a power consuming device. The power consuming device may be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. A battery pack or a battery module can be used to meet the high power and high energy density needs of the secondary battery of the power consuming device.

[0106] Another example of a power consuming device may be a mobile phone, a tablet, a laptop, etc. Such a power consuming device is typically required to be thin and light, and may use a battery cell as a power source.

[0107] The device of the present application includes the secondary battery of the present application, and therefore has at least the same advantages as the secondary battery.

[0108] The beneficial effects of the present invention will be further explained below in conjunction with examples.

[0109] In order to clarify the technical problems, technical solutions, and beneficial effects achieved by the embodiments of the present application, the present application will be described in more detail below in conjunction with the embodiments and drawings. Obviously, the described embodiments are only a portion of the embodiments of the present application, and not all of the embodiments. The following description of at least one exemplary embodiment is for illustrative purposes only and does not limit the present application and its applications. Based on the embodiments of the present application, those skilled in the art will be able to derive all other embodiments without any creative effort, all of which fall within the scope of the claims of the present application.

[0110] 1. Separator manufacturing First separator: (1) A first porous base film and a second porous base film were provided.

[0111] The first porous base film is made of polypropylene (PP), has a thickness of 6 μm, and an average pore area S1 of 0.0025 μm. 2 It fulfilled the requirement.

[0112] The second porous base film is made of polyethylene (PE), has a thickness of 4 μm, and an average pore area S2 of 0.0023 μm. 2 It fulfilled the requirement.

[0113] Here, the ratio of the average pore area S1 of the first porous base film to the average pore area S2 of the second porous base film is 1.09.

[0114] (2) Preparation of coating layer slurry: Polyacrylate as an adhesive, aluminum oxide particles as a filler, and carboxymethyl cellulose were uniformly mixed in a ratio of 1:4:1 with an appropriate amount of deionized water as a solvent to prepare a coating layer slurry.

[0115] (3) The coating layer slurry of step (2) was applied to one side of the second porous base film of step (1) to form a coating layer.

[0116] (4) The first porous base film and the second porous base film coated in step (3) were hot-pressed to combine them to obtain a separator, where the coating layer was located between the first porous base film and the second porous base film.

[0117] The manufacturing methods of the second to eleventh separators were similar to that of the first separator 1, with the difference being that the average pore area of ​​the first porous base film or the second porous base film was adjusted, as detailed in Table 1. All other manufacturing methods were consistent with the manufacturing method of the separator of Example 1.

[0118] The first separator prepared by the above method was subjected to relevant performance tests, and the specific results are detailed in Table 1.

[0119] 2. Battery manufacturing Example 1

[0120] 1. Manufacturing of positive electrode plates Cathode active material LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), conductive carbon black (SuperP), and adhesive polyvinylidene fluoride (PVDF) were uniformly mixed in a mass ratio of 96.2:2.7:1.1 in an appropriate amount of solvent N-methylpyrrolidone (NMP) to obtain a positive electrode slurry. The positive electrode slurry was then applied to a positive electrode current collector aluminum foil, and a positive electrode plate was obtained through processes such as drying, cold pressing, slitting, and cutting.

[0121] 2. Manufacturing of negative electrode plates The negative electrode active material, artificial graphite, the conductive agent, carbon black (SuperP), the adhesive, styrene butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC-Na), were uniformly mixed in a mass ratio of 96.4:0.7:1.8:1.1 with an appropriate amount of deionized water as a solvent to obtain a negative electrode slurry. The negative electrode slurry was then applied to a negative electrode current collector copper foil, and the negative electrode plate was obtained through processes such as drying, cold pressing, slitting, and cutting.

[0122] 3. Separator The separator used is the first separator produced above.

[0123] 4. Electrolyte production Ethylene carbonate (EC) and methyl ethyl carbonate (EMC) were mixed in a mass ratio of 30:70 to obtain an organic solvent. Thoroughly dried electrolyte salt LiPF6 with a concentration of 1.0 mol / L was dissolved in the mixed solvent and mixed uniformly to obtain an electrolytic solution.

[0124] 5. Secondary battery manufacturing A positive electrode plate, a separator, and a negative electrode plate are stacked in this order, and a separator is interposed between the positive electrode plate and the negative electrode plate to separate them.Then, the stack is wound to obtain an electrode assembly.The electrode assembly is placed in an outer package, and the above-mentioned electrolyte solution is injected into the dried secondary battery.The secondary battery is then obtained through processes such as vacuum sealing, standing, chemical formation, and shaping.

[0125] The secondary batteries of Examples 2 to 10 and Comparative Example 1 were manufactured using methods similar to those of the secondary battery of Example 1, with the difference being the use of different separators (here, Examples 1 to 10 used separators 1 to 10, and Comparative Example 1 used separator 11), as detailed in Table 1.

[0126] 3. Battery performance test 1. Breathability test The air permeability of the separator has a meaning known in the art and can be measured using methods known in the art, for example, tests can be performed in accordance with standard GB / T36363-2018.

[0127] 2. Battery cycle performance (cycles) The secondary batteries manufactured in the examples and comparative examples were charged at 25°C at a constant current of 1C to a charge cutoff voltage V1, then charged at a constant voltage to a current of 0.05C or less, allowed to stand for 5 minutes, and then discharged at a constant current of 0.33C to a discharge cutoff voltage V2, allowed to stand for 5 minutes. This constituted one charge-discharge cycle. According to this method, the batteries were subjected to a cycle charge-discharge test until the battery capacity decreased to 80%. The number of cycles at this time was taken as the cycle life of the battery at 25°C.

[0128] [Table 1]

[0129] As can be seen from Table 1, in Examples 1 to 10, the separators used satisfied the requirements that the melting point of the first porous base film was higher than that of the second porous base film and the average pore area of ​​the first porous base film was larger than that of the second porous base film, and the batteries produced thereby had good cycle performance and higher reliability.On the other hand, the separator used in Comparative Example 1 did not satisfy the design of the present application, and therefore the cycle performance of the produced battery was relatively poor.

[0130] The above description is merely a specific embodiment of the present application, and the scope of the claims of the present application is not limited thereto. Those skilled in the art can easily think of various equivalent modifications or replacements within the technical scope disclosed in the present application, and all of these modifications or replacements should be included in the scope of the claims of the present application. Therefore, the scope of protection of the present application should be consistent with the scope of protection of the claims.

Claims

1. A separator comprising a first porous base film and a second porous base film, wherein the melting point of the first porous base film is higher than the melting point of the second porous base film, and in a cross section along the thickness direction of the separator, the average pore area of ​​the first porous base film is larger than the average pore area of ​​the second porous base film.

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

5.

3. The first porous base film has an average pore area of ​​0.0001 μm to 0.5 μm, and optionally 0.01 μm to 0.3 μm; and / or 3. The separator according to claim 1, wherein the second porous base film has an average pore area of ​​0.0001 μm 2 to 0.4 μm 2 , and optionally 0.01 μm 2 to 0.25 μm 2 .

4. the first porous base film has an average pore size larger than the average pore size of the second porous base film; Preferably, the first porous base film has an average pore size of 100 nm to 2000 nm, more preferably 100 nm to 350 nm; 4. The separator according to claim 1, wherein the second porous base film has an average pore size of 100 nm to 2000 nm, and more preferably 100 nm to 300 nm.

5. the porosity of the first porous base film is greater than the porosity of the second porous base film; Preferably, the porosity of the first porous base film is between 30% and 80%, more preferably between 35% and 60%; 5. The separator according to claim 1, wherein the porosity of the second porous base film is optionally between 30% and 70%, and more optionally between 35% and 50%.

6. The separator according to any one of claims 1 to 5, further comprising a porous coating layer disposed between the first porous base film and the second porous base film and including an adhesive, and optionally, the porous coating layer includes an adhesive and a filler.

7. 7. The separator of claim 6, wherein the adhesive comprises one or more of polyacrylate, polyacrylic acid, polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride-trichloroethylene copolymer, polyvinylpyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyethylene oxide, polyarylate, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, polyacrylonitrile, polyvinyl alcohol, polyethylene, polypropylene, starch, and cyanoethyl pullulan.

8. The separator according to claim 6 or 7, wherein the filler comprises at least one of inorganic particles, organic particles, and organic-metal framework materials.

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

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

11. 11. The secondary battery according to claim 10, comprising a positive electrode plate and a negative electrode plate, the separator being disposed between the positive electrode plate and the negative electrode plate, and the second porous base film of the separator being disposed on the side of the negative electrode plate.

12. A power consuming device comprising the secondary battery according to claim 10 or 11.

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