Separator, secondary battery and power consuming device

Abstract

The present application provides a separator, comprising a first base film and a second base film, wherein the melting point of the second base film is lower than that of the first base film, and the average fiber diameter of the first base film is larger than that of the second base film. The second base film has a smaller average fiber diameter, which provides the second base film with a rich channel structure and improves the second base film's resistance to physical puncture by lithium dendrites. Furthermore, when the average fiber diameter of the first base film with a higher melting point is larger than that of the second base film with a lower melting point, the continuity and effectiveness of the ion transmission channels of the separator can be ultimately ensured, thereby improving the reliability of the separator and the reliability of secondary batteries.

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 have the distinctive features of being lightweight, non-polluting, and having no memory effect, and are widely used in various consumer electronic products and electric vehicles. With the continuous development of the new energy industry, users are putting forward higher requirements for the reliability of secondary batteries.

[0003] Therefore, how to make secondary batteries have good reliability is an urgent problem to be solved. Summary of the Invention

[0004] In view of the technical problems existing in the background art, the present application provides a separator that aims to improve the reliability of secondary batteries.

[0005] To achieve the above object, according to a first aspect of the present application, a separator is provided, comprising a first base film and a second base film, wherein the melting point of the second base film is lower than the melting point of the first base film, and the average fiber diameter in the first base film is larger than the average fiber diameter in the second base film.

[0006] Compared with the prior art, the present invention includes at least the following beneficial effects:

[0007] The first base film with a higher melting point has a larger average fiber diameter than the second base film with a lower melting point, while the second base film has a smaller average fiber diameter, which imparts a rich channel structure to the second base film and improves its resistance to physical puncture by lithium dendrites. Furthermore, when the first base film with a higher melting point has a larger average fiber diameter than the second base film with a lower melting point, the continuity and effectiveness of the ion transmission channels in the separator can be further ensured, which ultimately allows the separator to achieve both heat resistance and good strength, improving the reliability of the separator.

[0008] In any embodiment of the present application, the ratio of the average fiber diameter in the first base film to the average fiber diameter in the second base film is 1.1 to 9 or more, and optionally 1.2 to 4.5.

[0009] In any embodiment of the present application, the average fiber diameter in the first base film is 50 nm to 550 nm, and optionally 80 nm to 350 nm.

[0010] In any embodiment of the present application, the average fiber diameter of the second base film is from 30 nm to 450 nm, and optionally from 50 nm to 260 nm.

[0011] When the average fiber diameter of the first base film and / or the second base film is selected within the above range, the two base films have a rich channel structure and good strength at the same time, which ultimately ensures the continuity and effectiveness of the ion transmission channels of the separator and further improves the reliability of the separator.

[0012] In any embodiment of the present application, the ratio of the weight per unit area of ​​the first base film to the weight per unit area of ​​the second base film is 1.02 or more, and optionally 1.2 to 2.5.

[0013] In any embodiment of the present application, the weight per unit area of ​​the first base film is 2.5 g / m2 ~10g / m 2 and selectively 3 g / m 2 ~7g / m 2 and / or the weight of the second base film per unit area is 2 g / m 2 ~10g / m 2 and optionally 2.5 g / m 2 ~6g / m 2 is.

[0014] When the weight per unit area of ​​the first base film and the weight per unit area of ​​the second base film are within the ranges specified above, the separator can have good heat resistance and strength, further improving the reliability of the separator.

[0015] In any embodiment of the present application, the melting point of the first base film is 160°C to 370°C, optionally 165°C to 330°C, and / or the melting point of the second base film is 120°C to 265°C, optionally 130°C to 230°C.

[0016] When the melting point of the first base film is 160°C to 370°C and / or the melting point of the second base film is 120°C to 265°C, the combination of the two allows the separator to have both heat resistance and good strength, improving the reliability of the separator.When the melting point of the first base film is 165°C to 330°C and / or the melting point of the second base film is 130°C to 230°C, the separator can further have both heat resistance and good strength, further improving the reliability of the separator.

[0017] In any embodiment of the present application, the thickness of the first base film is equal to or greater than the thickness of the second base film, and optionally the ratio of the thickness of the first base film to the thickness of the second base film is 1.1 to 5, and optionally 1.5 to 3.0.

[0018] In any embodiment of the present application, the thickness of the first base film is 2 μm to 12 μm, optionally 3 μm to 6 μm, and / or the thickness of the second base film is 2 μm to 9 μm, optionally 3 μm to 5 μm.

[0019] When the thickness of the first base film and / or the second base film is within the ranges indicated above, the battery has good reliability and can further improve the energy density of the battery.

[0020] In any embodiment of the present application, the ratio of the porosity of the first base film to the porosity of the second base film is 1.05 to 3, and optionally 1.1 to 1.5.

[0021] When the ratio of the porosity of the first base film to the porosity of the second base film is 1.05 to 3, the first base film has a high porosity and good breathability, and the second base film has a low porosity and high strength, providing support, thereby improving the reliability and cycle characteristics of the secondary battery by combining the first and second base films.When the ratio of the porosity of the first base film to the porosity of the second base film is 1.1 to 1.5, the balance between the breathability and support performance of the separator is even better, further improving the reliability and cycle characteristics of the secondary battery.

[0022] In any embodiment of the present application, the porosity of the first base film is 30% to 80%, optionally 50% to 75%, and / or the porosity of the second base film is 30% to 70%, optionally 40% to 50%.

[0023] When the porosity of the first base film and / or the second base film is within the specified range, the balance between the breathability and support performance of the separator is further improved, further improving the reliability and cycle characteristics of the secondary battery.

[0024] In any embodiment of the present application, the separator further includes an intermediate layer disposed between the first base film and the second base film, the intermediate layer including a binder, and optionally, the intermediate layer further including filler particles. When the intermediate layer is disposed between the first base film and the second base film and the intermediate layer includes filler particles, the reliability of the secondary battery can be improved.

[0025] In some embodiments of the present application, the binder may include one or more of polyacrylic acid ester, acrylic acid, carboxymethyl cellulose, polyvinylidene fluoride-co-trichloroethylene copolymer, polymethyl methacrylate, polyvinylpyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate copolymer, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, polyvinylidene fluoride, polyacrylonitrile, polyvinyl alcohol, starch, hydroxypropyl cellulose, regenerated cellulose, tetrafluoroethylene, polyethylene, polypropylene, and cyanoethyl amylopectin. When an intermediate layer is disposed between the first base film and the second base film and the binder in the intermediate layer includes the above components, the reliability of the secondary battery can be improved.

[0026] In any embodiment of the present application, the filler particles include at least one of inorganic particles, organic particles, and metal-organic frameworks.

[0027] When an intermediate layer is disposed between the first base film and the second base film, and the filler particles in the intermediate layer include at least one of the inorganic particles, organic particles, and organic-metallic structures, the filler particles in the intermediate layer can further improve the heat resistance and strength of the separator, thereby improving the reliability of the secondary battery.

[0028] In any embodiment of the present application, the separator satisfies at least one of the following conditions (1) to (3): (1) The weight of the separator per unit area is 5 to 20 g / m 2and selectively 6 to 15 g / m 2 (2) The porosity of the separator is 30% to 55%, and optionally 35% to 45%. (3) The air permeability of the separator is less than 350s / 100cc, and optionally 150s / 100cc to 300s / 100cc.

[0029] When the separator satisfies the ranges shown in at least one of the above characteristics, the separator can have good heat resistance and strength, and the reliability and cycle characteristics of the secondary battery can be improved.

[0030] According to a second aspect of the present invention, there is provided a secondary battery including the separator of any of the above embodiments. When the secondary battery employs the separator shown in the above, the reliability of the secondary battery can be improved.

[0031] In one embodiment of the present application, the secondary battery further includes a positive electrode sheet and a negative electrode sheet, and a separator is disposed between the positive electrode sheet and the negative electrode sheet, with the second base film of the separator facing the negative electrode sheet. When the secondary battery employs the separator described above, the second base film with a small average fiber diameter faces the negative electrode sheet, and the second base film has good strength and can exhibit its excellent physical performance, and the negative electrode is less likely to be penetrated by lithium dendrites, thereby improving the reliability of the secondary battery.

[0032] According to a third aspect of the present application, there is provided a power consuming device including the secondary battery of the second aspect of the present application. When the secondary battery of the power consuming device uses the separator shown, the reliability of the power consuming device can be improved.

[0033] The device of the present application includes the secondary battery provided by the present application, and therefore has at least the same advantages as a secondary battery.

[0034] In order to more clearly describe the technical solutions of the present application, the following briefly describes the drawings used in the present application. It should be understood that the drawings shown below are only some embodiments of the present application, and those skilled in the art can further obtain other drawings based on the drawings without creative efforts. [Brief explanation of the drawings]

[0035] [Figure 1] 1 is a structural schematic diagram of an embodiment of the separator of the present application. [Figure 2] FIG. 2 is a structural schematic diagram of another embodiment of the separator of 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

[0036] The present application will be further described below with reference to specific embodiments, which are merely for the purpose of illustrating the present application and are not intended to limit the scope of the present application.

[0037] For the sake of brevity, only a few numerical ranges are specifically disclosed herein. However, any lower limit may be combined with any upper limit to form an unstated range, and any lower limit may be combined with any other lower limit to form an unstated range, and similarly, any upper limit may be combined with any other upper limit to form an unstated range. Furthermore, each point or individual numerical value disclosed alone can serve as a lower or upper limit, and can be combined with any other point or individual numerical value, or with other lower or upper limits, to form an unstated range.

[0038] In this description, 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, the condition "A or B" is satisfied by either A being true (or existing) and B being false (or not existing), or A being false (or not existing) and B being true (or existing), or both A and B being true (or existing).

[0039] In the description of this specification, it should be noted that unless otherwise stated, "more than or equal to" and "less than or equal to" are inclusive, and the meaning of "plurality" in "one or more" is two and more than two.

[0040] Unless otherwise specified, the terms used herein have the same meaning as commonly understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of each parameter described herein can be measured using various measurement methods commonly used in the art (for example, they can be measured according to the methods shown in the examples of the present application).

[0041] secondary battery A secondary battery is a battery that can be continuously used by activating the active material through charging after discharging.

[0042] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. During the charge and discharge process, active ions are inserted and removed between the positive and negative electrode sheets. The separator is placed between the positive and negative electrode sheets to separate them. The electrolyte conducts ions between the positive and negative electrode sheets.

[0043] [Separator] Referring to FIG. 1 , an embodiment of the present application provides a separator 10, which includes a first base film 11 and a second base film 12, wherein the melting point of the second base film 12 is lower than the melting point of the first base film 11, and the average fiber diameter in the first base film 11 is larger than the average fiber diameter in the second base film 12.

[0044] While not wishing to be limited by any theory, the inventors have discovered, as a result of extensive research, that in the structure of the specific separator 10 of the present application, by laminating and combining a first base film 11 having a high melting point and a large average fiber diameter with a second base film 12 having a low melting point and a small average fiber diameter, the separator 10 can ultimately achieve both good heat resistance and high strength, thereby improving the reliability of the separator.

[0045] As a result of further research, the inventors have discovered that the performance of the battery can be further improved if the separator further selectively satisfies one or more of the following design requirements.

[0046] The materials of the first base film 11 and the second base film 12 are not particularly limited, and any known base film having good chemical stability and strength stability can be selected. The materials of the first base film 11 and the second base film 12 of the separator 10 may be the same or different. In some embodiments, the first base film 11 and the second base film 12 may be selected from one or more of polyolefin, polyether, polyether ether ketone, ethylene terephthalate, polyimide, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl alcohol, glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride.

[0047] The first base film with a higher melting point has a larger average fiber diameter than the second base film with a lower melting point, while the second base film has a smaller average fiber diameter, which imparts a rich channel structure to the second base film and improves its resistance to physical puncture by lithium dendrites. Furthermore, when the first base film with a higher melting point has a larger average fiber diameter than the second base film with a lower melting point, the continuity and effectiveness of the ion transmission channels in the separator can be further ensured, which ultimately allows the separator to achieve both heat resistance and good strength, improving the reliability of the separator.

[0048] In any embodiment of the present application, the ratio of the average fiber diameter in the first base film 11 to the average fiber diameter in the second base film 12 is 1.1 to 9, and optionally 1.2 to 4.5. For example, the ratio of the average fiber diameter in the first base film 11 to the average fiber diameter in the second base film 12 may be 1.1, 1.2, 1.6, 2.0, 2.2, 2.4, 2.9, 3.0, 3.5, 4.0, 4.4, 4.5, 4.7, 5.2, 5.8, 6.3, 6.6, 7.0, 7.8, 8.0, 8.4, 9.0, or the like, or may be a range consisting of any two of the above numerical values, for example, 1.1 to 1.2, 1.6 to 2.0, 2.2 to 2.9, 3.0 to 4.0, 3.5 to 4.5, 4.7 to 5.2, 5.8 to 6.3, 6.6 to 7.0, 7.8 to 8.0, 8.0 to 9.0, or the like.

[0049] In any embodiment of the present application, the average fiber diameter in the first base film 11 is 50 nm to 550 nm, and optionally 80 nm to 350 nm.

[0050] For example, the average fiber diameter in the first base film 11 may be 50 nm, 60 nm, 75 nm, 80 nm, 93 nm, 100 nm, 116 nm, 135 nm, 160 nm, 188 nm, 200 nm, 225 nm, 293 nm, 300 nm, 316 nm, 350 nm, 460 nm, 510 nm, 550 nm, or the like, or may be a range consisting of any two of the above numerical values, for example, 80 nm to 350 nm, 50 nm to 60 nm, 75 nm to 80 nm, 80 nm to 100 nm, 100 nm to 135 nm, 135 nm to 188 nm, 200 nm to 225 nm, 225 nm to 300 nm, 316 nm to 350 nm, 510 nm to 550 nm, or the like.

[0051] In any embodiment of the present application, the average fiber diameter of the second base film 12 is 30 nm to 450 nm, and optionally 50 nm to 260 nm.

[0052] For example, the average fiber diameter of the first base film 11 may be 30 nm, 44 nm, 75 nm, 80 nm, 93 nm, 100 nm, 116 nm, 135 nm, 160 nm, 188 nm, 204 nm, 255 nm, 288 nm, 300 nm, 326 nm, 350 nm, 397 nm, 400 nm, 420 nm, 450 nm, or the like, or may be a range consisting of any two of the above numerical values, for example, 50 nm to 260 nm, 30 nm to 44 nm, 75 nm to 80 nm, 80 nm to 93 nm, 100 nm to 135 nm, 160 nm to 188 nm, 204 nm to 255 nm, 288 nm to 300 nm, 326 nm to 350 nm, 400 nm to 450 nm, or the like.

[0053] When the average fiber diameter of the first base film and / or the second base film is selected within the above range, the two base films have a rich channel structure and good strength at the same time, which ultimately ensures the continuity and effectiveness of the ion transmission channels of the separator and further improves the reliability of the separator.

[0054] The average fiber diameter of the base film has a meaning known in the art and can be measured using known devices and methods. For example, a scanning electron microscope (e.g., a ZEISS Sigma 300) can be used to obtain a scanning electron microscope (SEM) image of the base film by referring to JY / T010-1996. Specifically, a measurement sample having a length x width of 5 mm x 5 mm is taken from the base film. Several test areas (e.g., five) are randomly selected from the measurement sample, and the fiber diameters are clearly observed at a certain magnification (e.g., 10K times). Several locations (e.g., at least 30 locations) are selected and measured on a scale. The average of the multiple fiber diameters is calculated, which is the average fiber diameter of the base film.

[0055] In any embodiment of the present application, the ratio of the weight per unit area of ​​the first base film 11 to the weight per unit area of ​​the second base film 12 is 1.02 or more, and optionally 1.2 to 2.5.

[0056] For example, it may be 1.1, 1.11, 1.2, 1.3, 1.35, 1.4, 1.5, 1.65, 1.7, 1.8, 1.9, 2, 2.3, 2.5, 2.55, 2.6, 3, 3.5, 3.85, 4, 4.5, 5, 6, or a range equal to or greater than any of the above numerical values, for example, ≧1.1, ≧1.11, ≧1.2, ≧1.35, ≧1.5, ≧1.8, ≧2, ≧2.5, ≧3, ≧3.85, ≧4, ≧5, ≧6, or a range consisting of any two of the above numerical values, for example, 1.2 to 2.5, 1.1 to 1.5, 1.65 to 1.9, 1.7 to 2.3, 2 to 2.55, 2.55 to 3, 2.6 to 3.5, etc.

[0057] In any embodiment of the present application, the weight per unit area of ​​the first base film 11 is 2.5 g / m 2 ~10g / m 2 For example, 2.5g / m 2 , 3g / m 2 , 3.5g / m 2 , 5g / m 2 , 7g / m 2 , 8.1g / m 2 , 9g / m 2 , 10g / m 2 or a range consisting of any two of the above values, for example, 2.5 g / m 2 ~3g / m 2 , 3g / m 2 ~5g / m 2 , 3g / m 2 ~7g / m 2 , 5g / m 2 ~8.1g / m 2 , 7g / m 2 ~10g / m 2 In some embodiments, the weight per unit area of ​​the first base film 11 is 3 g / m 2 ~7g / m 2 is.

[0058] In any embodiment of the present application, the weight per unit area of ​​the second base film 12 is 2 g / m 2 ~10g / m 2 For example, 2 g / m 2 , 2.5g / m 2 , 3g / m2 , 5g / m 2 , 6g / m 2 , 8.1g / m 2 , 9g / m 2 , 10g / m 2 , or a range consisting of any two of the above values, for example, 2 g / m 2 ~3g / m 2 , 3g / m 2 ~5g / m 2 , 2.5g / m 2 ~6g / m 2 , 5g / m 2 ~8.1g / m 2 , 7g / m 2 ~10g / m 2 In some embodiments, the weight per unit area of ​​the second base film 12 is 2.5 g / m 2 ~6g / m 2 is.

[0059] When the weight per unit area of ​​the first base film and the weight per unit area of ​​the second base film are within the ranges specified above, the separator can have good heat resistance and strength, further improving the reliability of the separator.

[0060] The weight per unit area of ​​the base film has a meaning known in the art and can be measured using known devices and methods. For example, the weight per unit area of ​​the base film can be measured as follows: (1) six layers of base film are stacked, flattened, and compressed to remove the air inside the base film. The stacked base film is cut according to a sample cutting plate, and the length and width of each cut sample are measured to obtain the areas S1, S2, and S3 of three samples. (2) The weights M1, M2, and M3 of these three samples are weighed, respectively. (3) The weight per unit area of ​​the three samples is obtained based on the formula: weight per unit area of ​​the base film = M / S. The average weight of the three samples is the weight per unit area of ​​the base film.

[0061] In any embodiment of the present application, the melting point of the first base film 11 is 160°C to 370°C, and may be, for example, 160°C, 165°C, 170°C, 180°C, 196°C, 200°C, 225°C, 235°C, 245°C, 260°C, 280°C, 290°C, 300°C, 315°C, 320°C, 330°C, 350°C, 370°C, etc., or may be a range consisting of any two of the above values, for example, 160°C to 170°C, 180°C to 235°C, 225°C to 280°C, 290°C to 315°C, 350°C to 370°C, etc. In some examples, the melting point of the first base film 11 is optionally 165°C to 330°C. The melting point of the second base film 12 is 120°C to 265°C, and may be, for example, 120°C, 130°C, 135°C, 140°C, 145°C, 150°C, 155°C, 160°C, 165°C, 196°C, 200°C, 240°C, 265°C, etc., or may be a range consisting of any two of the above values, for example, 120°C to 135°C, 130°C to 150°C, 145°C to 155°C, 155°C to 165°C, 196°C to 200°C, 240°C to 265°C, etc. In some embodiments, the melting point of the second base film 12 is optionally 130°C to 230°C.

[0062] When the melting point of the first base film is 160°C to 370°C and / or the melting point of the second base film is 120°C to 265°C, the combination of the two allows the separator to have both heat resistance and good strength, improving the reliability of the separator.When the melting point of the first base film is 165°C to 330°C and / or the melting point of the second base film is 130°C to 230°C, the separator can further have both heat resistance and good strength, further improving the reliability of the separator.

[0063] The melting points of the first and second base films can be measured using devices and methods known in the art. For example, they can be measured using differential scanning calorimetry. For specific details, see standard GB / T 19466.3-2004. For example, they can be measured according to the following method: 4 to 6 mg of a sample to be measured is placed in the sample box of a differential scanning calorimeter, and the temperature is increased from 25°C to 400°C at a heating rate of 10°C / min. A melting endothermic curve of the sample is obtained, and the temperature corresponding to the peak value of the curve is the melting point of the sample.

[0064] In any embodiment of the present application, the thickness of the first base film 11 is equal to or greater than the thickness of the second base film 12, and optionally the ratio of the thickness of the first base film 11 to the thickness of the second base film 12 is 1.1 to 5, e.g., 1.1, 1.2, 1.25, 1.3, 1.45, 1.5, 1.6, 1.75, 1.8, 1.9, 2.0, 2.15, 2.2, 2.3, 2.45, 2.5, 2.8, 3.0, 3.5, 4.0, 4.5, 5.0, or may be a range consisting of any two of the above numerical values, e.g., 1.1 to 2.0, 1.6 to 2.15, 2.3 to 2.5, 2.8 to 3.5, 3 to 5, etc. In some embodiments, the ratio of the thickness of the first base film 11 to the thickness of the second base film 12 is further optionally 1.5 to 3.0. For example, the first base film and the second base film are selected from polyolefin materials.

[0065] In any embodiment of the present application, the thickness of the first base film 11 is 2 μm to 12 μm, and may be, for example, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4.6 μm, 5 μm, 6 μm, 7 μm, 9 μm, 9.6 μm, 10 μm, 10.4 μm, 11 μm, 11.7 μm, or 12 μm, or may be a range consisting of any two of the above values, for example, 2 μm to 2.5 μm, 2.5 μm to 3 μm, 3 μm to 4.6 μm, 5 μm to 9 μm, 10 μm to 11 μm, or 11 μm to 12 μm, etc. In some examples, the thickness of the first base film 11 is optionally 3 μm to 6 μm. The thickness of the second base film 12 is 2 μm to 9 μm, and may be, for example, 2 μm, 3 μm, 3.5 μm, 5 μm, 6 μm, 7 μm, 9 μm, etc., or may be 2 μm to 3.5 μm, 3 μm to 5 μm, 5 μm to 6 μm, 7 μm to 9 μm, etc. In some embodiments, the thickness of the second base film 12 is optionally 3 μm to 5 μm.

[0066] When the thickness of the first base film and / or the second base film is within the ranges indicated above, the battery has good reliability and can further improve the energy density of the battery.

[0067] The thickness of the base film can be measured using devices and methods known in the art. For example, the thickness of the base film can be measured using a thickness measuring device. Specifically, the following method can be adopted: six sets of parallel samples are taken, and the thickness of each set of samples is measured at different positions using a thickness measuring micrometer. At least 20 positions are measured for each set of samples, and the average thickness of the six sets of samples is the thickness of the base film.

[0068] In any embodiment of the present application, the ratio of the porosity of the first base film 11 to the porosity of the second base film 12 is 1.05 to 3, and may be, for example, 1.05, 1.2, 1.3, 1.4, 1.51, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.4, 2.5, 2.71, 2.8, or 3, or may be a range consisting of any two of the above values, for example, 1.05 to 2.2, 1.2 to 1.51, 1.3 to 1.8, 1.6 to 2.1, 1.7 to 2.2, or 2.1 to 3. In some examples, the ratio of the porosity of the first base film 11 to the porosity of the second base film 12 is 1.1 to 1.5.

[0069] When the ratio of the porosity of the first base film to the porosity of the second base film is 1.05 to 3, the first base film has a high porosity and good breathability, and the second base film has a low porosity and high strength, providing support, thereby improving the reliability and cycle characteristics of the secondary battery by combining the first and second base films.When the ratio of the porosity of the first base film to the porosity of the second base film is 1.1 to 1.5, the balance between the breathability and support performance of the separator is even better, further improving the reliability and cycle characteristics of the secondary battery.

[0070] In any embodiment of the present application, the porosity of the first base film 11 is 30% to 80%, and may be, for example, 30%, 35%, 38%, 40%, 50%, 55%, 60%, 70%, 75%, or 80%, or may be a range consisting of any two of the above values, for example, 30% to 40%, 35% to 50%, 50% to 70%, 75% to 80%, etc. In some examples, the porosity of the first base film 11 is 50% to 75%.

[0071] In any embodiment of the present application, the porosity of the second base film 12 is 30% to 70%, and may be, for example, 30%, 35%, 40%, 45%, 50%, 60%, 65%, 70%, or a range consisting of any two of the above values, for example, 30% to 40%, 35% to 45%, 50% to 60%, 65% to 70%, etc. In some examples, the porosity of the second base film 12 is 40% to 50%.

[0072] When the porosity of the first base film is 30% to 80% and / or the porosity of the second base film is 30% to 70%, the first base film has a high porosity, a wide average fiber diameter, and good breathability, while the second base film has a low porosity, a narrow average fiber diameter, and high strength, providing support, thereby further improving the reliability and cycle characteristics of the secondary battery by combining the first and second base films.When the porosity of the first base film is 50% to 75% and / or the porosity of the second base film is 40% to 50%, the balance between the breathability and support performance of the separator is even better, further improving the reliability and cycle characteristics of the secondary battery.

[0073] The porosity of a separator or substrate has a meaning known in the art and can be measured using known devices and methods. For example, it can be measured with reference to GB / T 24586-2009. The measurement method is as follows: The separator or substrate is punched into a small circular sheet sample with a diameter of 14 mm, the thickness is measured, and the apparent volume V1 of the separator or substrate is measured according to the cylinder volume calculation formula. Then, with reference to GB / T 24586-2009, an inert gas such as helium or nitrogen is used as the medium and a true density measurement device is used to measure the actual volume V2 of the separator or substrate by the gas displacement method. The porosity of the separator or substrate = (V1 - V2) / V1 × 100%. The measurement device may be a fully automatic true density measurement device, such as an AccuPyc II 1340 model, manufactured by Micromeritics, USA.

[0074] The first base film 11 and the second base film 12 can be directly composited by hot pressing. During the hot pressing composite process, the hot pressing temperature must be adjusted appropriately because too high a temperature results in low porosity and poor breathability, while too low a temperature results in poor adhesion between the first base film 11 and the second base film 12. Optionally, the hot pressing temperature is 20°C to 50°C. Referring to FIG. 2 , in any embodiment of the present application, an intermediate layer 13 containing a binder can be disposed between the first base film 11 and the second base film 12. Optionally, the intermediate layer 13 contains a binder and filler particles. The provision of the intermediate layer 13 between the first base film 11 and the second base film 12 not only avoids process drawbacks in the hot pressing composite process, but also further improves the heat resistance and physical properties of the separator, thereby improving the reliability of the secondary battery.

[0075] In some embodiments of the present application, the binder may include one or more of polyacrylic acid ester, acrylic acid, carboxymethyl cellulose, polyvinylidene fluoride-co-trichloroethylene copolymer, polymethyl methacrylate, polyvinylpyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate copolymer, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, polyvinylidene fluoride, polyacrylonitrile, polyvinyl alcohol, starch, hydroxypropyl cellulose, regenerated cellulose, tetrafluoroethylene, polyethylene, polypropylene, and cyanoethyl amylopectin. When an intermediate layer is disposed between the first base film and the second base film and the binder in the intermediate layer includes the above-mentioned components, the heat resistance and physical properties 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 paste.

[0076] In any embodiment of the present application, the filler particles include at least one of inorganic particles, organic particles, and metal-organic frameworks.

[0077] Optionally, the inorganic particles include one or more of inorganic particles having a dielectric constant of 5 or more, inorganic particles having ionic conductivity but not storing ions, and inorganic particles capable of generating electrical and chemical reactions.

[0078] Alternatively, the inorganic particles having a dielectric 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 )O3-PbTiO3 (abbreviated as PMN-PT) and modified inorganic particles. Optionally, the inorganic particles may be modified chemically and / or physically. Chemical modification methods include coupling agent modification (e.g., using a silane coupling agent, titanate coupling agent, etc.), surfactant modification, graft polymer modification, etc. Physical modification methods may include mechanical dispersion, ultrasonic dispersion, high-energy treatment, etc. The modification treatment can reduce the aggregation of inorganic particles, thereby resulting in a more stable and uniform adhesive layer (i.e., intermediate layer). Furthermore, modifying the inorganic particles by selecting a coupling agent, surfactant, or polymer with a specific functional group can improve the electrolyte wetting and retention properties of the adhesive layer and further improve the adhesion of the adhesive layer to the first and second base films.

[0079] Optionally, the inorganic particles having the ion conductivity but not storing ions include at least one of 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 -based 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 , SiS2-based glass Li x7 Si y7 S z3 and P2S5-based glass Li x8 P y8 S z4 where at least one of them may be included, 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.

[0080] Optionally, the inorganic particles capable of generating the electrical and chemical reactions 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.

[0081] Optionally, the organic particles may include 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).

[0082] Optionally, the metal-organic framework may include one or more of a nitrogen-containing heterocyclic ligand framework, an organic carboxylic acid-based ligand framework, and a nitrogen-oxygen mixed ligand framework.

[0083] In some embodiments, the content of the binder may be 10% or more, and optionally 10% to 30%, based on the total weight of the adhesive layer.

[0084] In some embodiments, the content of the filler particles may be 90% or less, optionally 40% to 90%, or 60% to 80%, based on the total weight of the adhesive layer.

[0085] In some embodiments, the intermediate layer may further include a dispersant, such as carboxymethyl cellulose, which can adjust the viscosity of the intermediate layer paste and improve the quality and uniformity of the intermediate layer.

[0086] In some embodiments, the dispersant content may be 25% or less, and optionally 20% or less, based on the total weight of the adhesive layer.

[0087] In any embodiment of the present application, the separator 10 satisfies at least one of the following conditions (1) to (3): (1) The weight of the separator 10 per unit area is 5 to 20 g / m 2 and selectively 6 to 15 g / m 2 (2) The porosity of the separator 10 is 30% to 55%, and optionally 35% to 45%. (3) The air permeability of the separator 10 is 350s / 100cc to 400s / 100cc, and optionally 150s / 100cc to 300s / 100cc.

[0088] When the separator satisfies the ranges shown in at least one of the above characteristics, the separator can have good heat resistance and strength, and the reliability and cycle characteristics of the secondary battery can be improved.

[0089] Unless otherwise specified, each of the raw materials used in the separator (for example, the first base film, the second base film, the binder, the filler, etc.) can be obtained commercially.

[0090] The present application provides a secondary battery including the separator 10 of any of the above embodiments. When the secondary battery employs the separator 10 shown, the reliability of the secondary battery can be improved.

[0091] In any embodiment of the present application, the secondary battery further includes a positive electrode sheet and a negative electrode sheet, the separator 10 is disposed between the positive electrode sheet and the negative electrode sheet, and the first base film 11 of the separator 10 faces the positive electrode sheet.

[0092] [Positive electrode sheet] In a secondary battery, the positive electrode sheet generally includes a positive electrode current collector and a positive electrode film layer provided on the positive electrode current collector and including a positive electrode active material.

[0093] The positive electrode current collector can be a conventional metal foil or a composite current collector (which may be a composite current collector formed by placing a metal material on a polymer substrate). For example, the positive electrode current collector can be aluminum foil.

[0094] The specific type of the positive electrode active material is not particularly limited, and active materials known in the art for use in positive electrodes of secondary batteries may be used, and those skilled in the art may select the material according to their actual needs.

[0095] 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 with an olivine structure, and modified compounds thereof. Examples of lithium transition metal oxides include, but are not limited to, 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 modified compounds thereof. Examples of lithium-containing phosphates with an olivine structure include, but are not limited to, lithium iron phosphate, a composite of lithium iron phosphate and carbon, lithium manganese phosphate, a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite of lithium manganese iron phosphate and carbon, and modified compounds thereof. All of these materials are commercially available.

[0096] The modifying compounds for each of the above materials can perform doping modification and / or surface coating modification on the material.

[0097] The positive electrode film layer generally further optionally contains a binder, a conductive agent, and other optional auxiliary agents.

[0098] By way of example, the conductive agent may include 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.

[0099] By way of example, the binder 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).

[0100] [Negative electrode sheet] In a secondary battery, the negative electrode sheet generally includes a negative electrode current collector and a negative electrode film layer disposed on the negative electrode current collector and containing a negative electrode active material.

[0101] The negative electrode current collector may be a conventional metal foil or a composite current collector (e.g., a composite current collector formed by placing a metal material on a polymer substrate). For example, the negative electrode current collector may be a copper foil.

[0102] The specific type of the negative electrode active material is not particularly limited, and active materials known in the art for use in negative electrodes of secondary batteries can be used, and 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 selected from one or more of silicon elemental, silicon oxide (e.g., silicon oxide), silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material may be selected from one or more of tin elemental, tin oxide, and tin alloy. All of these materials are commercially available.

[0103] In some embodiments, the negative electrode active material may include a silicon-based material to further improve the energy density of the battery.

[0104] The negative electrode film layer generally further optionally contains a binder, a conductive agent, and other optional auxiliary agents.

[0105] By way of example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0106] By way of example, the binder may include 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).

[0107] By way of example, other optional auxiliary agents may be thickening and dispersing agents (such as carboxymethylcellulose sodium (CMC-Na)), PTC thermistor materials.

[0108] [Electrolyte] The secondary battery may include an electrolyte, which serves to conduct ions between the positive electrode and the negative electrode, and may include an electrolyte salt and a solvent.

[0109] By way of example, the electrolyte salt may be selected from one or more of lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium perchlorate (LiClO), lithium hexafluoroarsenate (LiAsF), lithium bisfluorosulfonylimide (LiFSI), lithium bistrifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium bisoxalatoborate (LiBOB), lithium difluorophosphate (LiPOF), lithium difluorobisoxalatophosphate (LiDFOP), and lithium tetrafluorooxalatophosphate (LiTFOP).

[0110] 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 Propionate (MP), Ethyl Propanoate (EP), n-Propyl Propionate (PP), Methyl Butyrate (MB), Ethyl Butyrate (EB), 1,4-Butyrolactone (GBL), Sulfolane (Tetramethylene Sulfone (SF), Methyl Sulfone (MSM), Methyl Ethyl Sulfone (EMS), and Diethyl Sulfone (ESE).

[0111] In some embodiments, the electrolyte solution further includes additives. For example, the additives may include a negative electrode film-forming additive, a positive electrode film-forming additive, and / or an additive that can improve specific battery performance, such as an additive that improves the overcharge characteristics of the battery, an additive that improves the high-temperature characteristics of the battery, or an additive that improves the low-temperature characteristics of the battery.

[0112] When a secondary battery employs the separator shown, the first base film with a higher melting point has a larger average fiber diameter than the second base film with a lower melting point, while the second base film has a smaller average fiber diameter, imparting a rich channel structure to the second base film and improving its resistance to physical puncture by lithium dendrites. Furthermore, when the average fiber diameter of the first base film with a higher melting point is larger than that of the second base film with a lower melting point, the continuity and effectiveness of the ion transmission channels in the separator can be further ensured, ultimately resulting in a separator with both heat resistance and good strength, improving the reliability of the secondary battery.

[0113] The embodiment of the present application does not particularly limit the shape of the secondary battery, and it may be cylindrical, rectangular, or any other shape. Figure 3 shows a secondary battery 5 having a rectangular structure as an example.

[0114] In some embodiments, the secondary battery may include a housing material, which is used to encapsulate the positive electrode sheet, the negative electrode sheet, and the electrolyte, with the first base film 11 of the separator 10 facing the positive electrode sheet.

[0115] In some embodiments, the exterior material of the secondary battery may be a hard case such as a hard plastic case, an aluminum case, or a steel case. The exterior material of the secondary battery may be a soft pack such as a pouch-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).

[0116] 4, in some embodiments, the exterior material may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and a side plate connected to the bottom plate, and a storage cavity surrounded by the bottom plate and the side plate is formed. The housing 51 has an opening communicating with the storage cavity, and the cover plate 53 may cover the opening to seal the storage cavity.

[0117] The method for manufacturing the secondary battery of the present application is well known. In some embodiments, a secondary battery can be formed by assembling a positive electrode sheet, a separator 10, a negative electrode sheet, and an electrolyte. For example, an electrode assembly can be formed from a positive electrode sheet, a separator 10, and a negative electrode sheet through a winding process and / or a lamination process. The electrode assembly can then be placed in a housing, dried, and then an electrolyte can be injected. A battery cell can then be obtained through processes such as vacuum sealing, standing, chemical formation, and shaping. Multiple battery cells can be further connected in series, parallel, or series-parallel to form a battery module. Multiple battery modules can be further connected in series, parallel, or series-parallel to form a battery pack. In some embodiments, multiple battery cells can be further connected directly to form a battery pack.

[0118] FIG. 5 shows an example of a battery module 4. Referring to FIG. 5, in the battery module 4, a plurality of secondary batteries 5 can be arranged in order along the length of the battery module 4. Of course, any other arrangement method may be used. The plurality of secondary batteries 5 can also be fixed by fasteners.

[0119] The battery module 4 may further include an outer case having a storage space for storing a plurality of secondary batteries 5.

[0120] In some embodiments, the battery modules can be further assembled into a battery pack, and the number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0121] 6 and 7 show an example of a battery pack 1. Referring to FIGS. 6 and 7, the battery pack 1 may include a battery case and a plurality of battery modules 4 installed in the battery case. The battery case includes an upper housing 2 and a lower housing 3, and the upper housing 2 can be fitted over the lower housing 3 to form a sealed space for accommodating the plurality of battery modules 4. The plurality of battery modules 4 may be arranged in the battery case in any manner.

[0122] [Device] The present application further provides a power consumption device including the secondary battery of the present application. The battery cell, battery module, or battery pack may be used as a power source for the device or as an energy storage element for the device. The device may be, but is not limited to, a mobile device (e.g., a mobile phone, a laptop), 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), a train, a ship, a satellite, or an energy storage system.

[0123] The device can select a battery cell, a battery module, or a battery pack depending on its usage conditions.

[0124] 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. To meet the high power and high energy density requirements for the secondary battery of the power consuming device, a battery pack or a battery module may be used.

[0125] Another example of a power consuming device may be a mobile phone, a tablet computer, or a laptop computer, which generally require a light and thin design and may use a battery cell as a power source.

[0126] The device of the present application includes the secondary battery provided by the present application, and therefore has at least the same advantages as a secondary battery. [Example]

[0127] The beneficial effects of the present invention will be further explained below with reference to examples.

[0128] In order to clarify the technical problems, technical solutions, and beneficial effects solved by the embodiments of the present application, the present application will be described in more detail below with reference to the embodiments and drawings. It should be noted that the described embodiments are only some of the embodiments of the present application, and are not all of the embodiments. The following description of at least one exemplary embodiment is merely illustrative and does not limit the present application and its applications in any way. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without requiring creative efforts fall within the scope of protection of the present application.

[0129] 1. Separator manufacturing Separator 1: (1) Provide a first base film and a second base film.

[0130] The first base film satisfies the following: it is made of polypropylene (PP), the average fiber diameter of the first base film is 80 nm, and the melting point is 165°C.

[0131] The second base film satisfies the following: it is made of polyethylene (PE), the average fiber diameter of the second base film is 50 nm, and the melting point is 135°C.

[0132] The ratio D1 / D2 of the average fiber diameter D1 of the first base film to the average fiber diameter D2 of the second base film is 1.60.

[0133] (2) Preparation of intermediate layer paste: Polyacrylic ester as a binder, aluminum oxide particles as filler particles, and carboxymethyl cellulose are uniformly mixed in a mass ratio of 1:4:1 in an appropriate amount of deionized water as a solvent to prepare an intermediate layer paste.

[0134] (3) The intermediate layer paste of step (2) is applied to one side of the second base film of step (1) to form an intermediate layer.

[0135] (4) The first base film and the second base film coated in step (3) are hot-pressed together to obtain a separator, with the intermediate layer between the first base film and the second base film.

[0136] The manufacturing methods of separators 2 to 13 are the same as those of separator 1, except that one or more of the melting point, material, and average fiber diameter of the first base film or second base film are adjusted, as shown in Table 1. All other manufacturing methods are the same as those of separator 1.

[0137] 2. Battery manufacturing Example 1 1. Manufacturing of positive electrode sheets Positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1O2 (NCM811), conductive carbon black (SuperP), and binder polyvinylidene fluoride (PVDF) are mixed uniformly 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 paste. This positive electrode paste is then applied to a positive electrode current collector aluminum foil, and the positive electrode sheet is obtained through the processes of drying, cold pressing, slitting, and cutting.

[0138] 2. Manufacturing of negative electrode sheets The negative electrode active material, artificial graphite, the conductive agent, carbon black (SuperP), the binder, styrene butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC-Na) are uniformly mixed in a mass ratio of 96.4:0.7:1.8:1.1 in an appropriate amount of deionized water as a solvent to obtain a negative electrode paste, which is then dried, cold pressed, slit, and cut to obtain a negative electrode sheet.

[0139] 3. Separator The separator used is the separator 1 manufactured as described above.

[0140] 4. Electrolyte production Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 30:70 to obtain an organic solvent, and the thoroughly dried electrolyte salt LiPF6 is dissolved in the mixed solvent to obtain an electrolyte solution with a concentration of 1.0 mol / L.

[0141] 5. Secondary battery manufacturing The positive electrode sheet, separator, and negative electrode sheet are stacked in this order, with the separator between the positive and negative electrode sheets to isolate them, and the second base film is placed facing the negative electrode sheet and then wound up to obtain an electrode assembly. The electrode assembly is placed in a housing, and the above-prepared electrolyte is injected into the secondary battery after drying, followed by vacuum sealing, standing, chemical formation, and shaping to obtain the secondary battery.

[0142] The secondary batteries of Examples 2 to 9 and Comparative Examples 1 to 4 were manufactured using the same method as the secondary battery of Example 1, with the difference being that different separators were used (Separators 1 to 9 were used in Examples 1 to 9, and Separators 10 to 13 were used in Comparative Examples 1 to 4), as specifically shown in Table 1.

[0143] 3. Battery performance test 1. 250℃ transverse heat shrinkage test Sample preparation: The separator manufactured above is punched out into samples 50 mm wide and 100 mm long using a press, and five parallel samples are placed on A4 paper and fixed in place. The A4 paper with the samples attached is then placed on a piece of cardboard with a thickness of 1 mm to 5 mm.

[0144] Sample test: Place an A4 sheet of paper on top of the cardboard box and place it in a ventilated oven. Set the temperature of the ventilated oven to 250°C. After the temperature reaches the set temperature and stabilizes for 30 minutes, start timing. After the set time (for example, 1 hour) has elapsed, record the width of the separator and record the value as a.

[0145] The transverse direction (TD) heat shrinkage rate is calculated as [(50-a) / 50] x 100%, and the average value of five parallel samples is used as the test result.

[0146] 2. High-temperature test chamber performance At 25°C, the rechargeable batteries were charged to 4.2V at a constant current of 1C, followed by constant voltage charging at a current of ≤0.05C and then allowed to rest for 5 minutes. Each rechargeable battery was then tested in a DHG-9070A DHG series high-temperature oven using a jig. The temperature was increased from room temperature to 80°C ±2°C at a rate of 5°C / min, held for 30 minutes, and then increased at a rate of 5°C / min, with each 5°C increase held for 30 minutes. The change in the surface temperature of the rechargeable battery during the heating process was monitored; the corresponding oven temperature when the temperature began to rise rapidly was the high-temperature test chamber expiration temperature of the rechargeable battery. A higher high-temperature test chamber expiration temperature indicates better thermal reliability of the rechargeable battery. For accuracy, the test results were averaged over five parallel samples.

[0147] [Table 1]

[0148] As can be seen from Table 1, in Examples 1 to 9, the melting point of the second base film was lower than that of the first base film, and the average fiber diameter in the first base film was larger than that of the second base film. By using the separator defined in the present application, the separator's heat resistance was good, the separator's lateral shrinkage rate was small, and batteries manufactured using the separator provided in the present application had good high-temperature test chamber performance and significantly improved the thermal reliability of the battery. In Comparative Examples 1 to 4, the separator's heat resistance was poor, making the battery prone to safety issues.

[0149] The above are only specific embodiments of the present application, and the scope of protection 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 such modifications or replacements 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 separator, A first base film; a second base film, wherein the melting point of the second base film is lower than the melting point of the first base film; A separator, wherein the average fiber diameter in the first base film is greater than the average fiber diameter in the second base film.

2. 2. The separator according to claim 1, wherein the ratio of the average fiber diameter in the first base film to the average fiber diameter in the second base film is 1.1 to 9 or more, and optionally 1.2 to 4.

5.

3. 2. The separator of claim 1, wherein the average fiber diameter in the first base film is 50 nm to 550 nm, and optionally 80 nm to 350 nm.

4. The separator of claim 1, wherein the second base film has an average fiber diameter of 30 nm to 450 nm, and optionally 50 nm to 260 nm.

5. 2. The separator according to claim 1, wherein the ratio of the weight per unit area of ​​the first base film to the weight per unit area of ​​the second base film is 1.02 or more, and optionally 1.2 to 2.

5.

6. The weight of the first base film per unit area is 2.5 g / m ２ ~10g / m ２ and optionally 3 g / m ２ ~7g / m ２ and / or The weight of the second base film per unit area is 2 g / m ２ ~10g / m ２ and optionally 2.5 g / m ２ ~6g / m ２ The separator according to any one of claims 1 to 5,

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

8. The thickness of the first base film is equal to or greater than the thickness of the second base film, Optionally, the ratio of the thickness of the first base film to the thickness of the second base film is 1.1 to 5, and optionally 1.5 to 3.

0. The separator according to any one of claims 1 to 7.

9. The thickness of the first base film is 2 μm to 12 μm, optionally 3 μm to 6 μm; and / or The separator according to any one of claims 1 to 8, wherein the thickness of the second base film is 2µm to 9µm, and optionally 3µm to 5µm.

10. The separator according to any one of claims 1 to 8, wherein the ratio of the porosity of the first base film to the porosity of the second base film is 1.05 to 3, and optionally 1.1 to 1.

5.

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

12. The separator according to any one of claims 1 to 11, further comprising an intermediate layer disposed between the first base film and the second base film, the intermediate layer comprising a binder, and optionally, the intermediate layer further comprising filler particles.

13. 13. The separator of claim 12, wherein the binder comprises one or more of polyacrylic ester, acrylic acid, carboxymethyl cellulose, polyvinylidene fluoride-co-trichloroethylene copolymer, polymethyl methacrylate, polyvinylpyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate copolymer, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, polyvinylidene fluoride, polyacrylonitrile, polyvinyl alcohol, starch, hydroxypropyl cellulose, regenerated cellulose, tetrafluoroethylene, polyethylene, polypropylene, and cyanoethyl amylopectin.

14. The separator according to claim 12 or 13, wherein the filler particles comprise at least one of inorganic particles, organic particles, and organic-metallic frameworks.

15. At least one of the following (1) to (6) is satisfied: The weight of the separator per unit area is 5 to 20 g / m ２ and optionally 6 to 15 g / m ２ and The porosity of the separator is 30% to 55%, and optionally 35% to 45%; The separator according to any one of claims 1 to 14, wherein the separator has an air permeability of less than 350s / 100cc, optionally between 150s / 100cc and 300s / 100cc.

16. A secondary battery comprising the separator according to any one of claims 1 to 15.

17. The secondary battery according to claim 16 , comprising a positive electrode sheet and a negative electrode sheet, the separator being disposed between the positive electrode sheet and the negative electrode sheet, and the second base film being oriented toward the negative electrode sheet.

18. A power consuming device comprising the secondary battery according to claim 16 or 17.

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