Separator and manufacturing method thereof, secondary battery and power consumption device

Abstract

The separator 10 includes a first base film 11 and a second base film 12, the melting point of which is higher than that of the first base film 11, and the creep flexibility of which is higher than that of the second base film 12. The difference in creep flexibility between the first base film 11 and the second base film 12 results in different deformation capacities of the two base films under stress. The stress buffering provided by one layer of base film and the strength support provided by the other layer of base film both suppress dendrite-induced damage to the separator and reduce the risk of dendrites penetrating the separator and causing a short circuit, thereby improving the reliability and cycle life of the battery.

Description

[Technical Field]

[0001] The present application relates to the field of secondary battery technology, and more particularly to a separator and its manufacturing method, a secondary battery, and a power consuming device. [Background technology]

[0002] Secondary batteries have the excellent characteristics of being light in weight, pollution-free, and having no memory effect, and are therefore widely used in various home appliances and electric vehicles.

[0003] With the continuous development of the new energy industry, users are increasingly demanding the use of secondary batteries. However, lithium deposition is likely to occur during battery use, posing a risk of electrode short circuit failure. This has led to issues with the reliability of secondary batteries. Summary of the Invention

[0004] In view of the technical problems existing in the background art, the present application provides a separator and a manufacturing method thereof, a secondary battery, and a power consumption device, which aim to improve the reliability of the separator and secondary battery.

[0005] To achieve the above object, a first aspect of the present application provides a separator including a first base film and a second base film, wherein the melting point of the second base film is higher than the melting point of the first base film, and the creep flexibility (creep compliance) of the first base film is greater than the creep flexibility of the second base film.

[0006] Compared to the prior art, the present application has at least the following beneficial effects: by setting the creep flexibility of the first base film and the second base film to be different, the mutual cooperation of the two-layer base film structure makes the deformation capacity of the two base films different under the action of stress, and at least one of the base films can have a relatively large deformation capacity, thereby buffering damage to the separator caused by lithium dendrites and suppressing the growth of lithium dendrites, reducing the risk of electrode short-circuiting caused by dendrites penetrating the separator, and further improving the reliability of the battery over the long term.

[0007] In any embodiment of the present application, the ratio of the creep flexibility of the first base film to the creep flexibility of the second base film is 1.1 to 3.0, and optionally 1.3 to 2.0. When the ratio of the creep flexibility of the first base film to the creep flexibility of the second base film satisfies the above condition, the buffering effect against deformation of the first base film is further improved, and at the same time, the strength of the second base film is increased, improving the strength of the entire separator, strengthening the ability to resist dendrites, and further improving the reliability of the battery over the long term.

[0008] In any embodiment of the present application, the creep flexibility of the first base film is 0.0013 MPa -1 ~0.0050MPa -1 and selectively 0.0013 MPa -1 ~0.0032MPa -1 and / or the creep flexibility of the second base film is 0.0010 MPa -1 ~0.0023MPa -1 Selectively 0.0010MPa -1 ~0.0020MPa -1When the ratio of the creep flexibility of the first base film to the creep flexibility of the second base film satisfies the above range, the buffering effect against deformation of the first base film can be further improved, the strength of the second base film can be ensured, the risk of dendrites penetrating the separator and causing short circuits can be reduced, and the reliability of the battery over the long term can be improved.

[0009] In any embodiment of the present application, the ratio of the relative molecular mass of the material of the first base film to the relative molecular mass of the material of the second base film is 1.05 or more, and optionally 1.2 to 10. By limiting the ratio of the relative molecular mass of the material of the first base film to the relative molecular mass of the material of the second base film within the above range, the first base film and the second base film can be provided with sufficient strength while having sufficient flexibility.

[0010] In any embodiment of the present application, the relative molecular mass of the material of the first base film is 300,000 to 2.5 million, optionally 500,000 to 2 million, and / or the relative molecular mass of the material of the second base film is 10,000 to 2 million, optionally 10,000 to 1.2 million. By limiting the relative molecular masses of the material of the first base film and the material of the second base film to the above ranges, the creep flexibility of the first base film can be further improved, improving its deformation adaptability, while at the same time improving the support strength of the second base film, reducing the probability of lithium dendrite puncture, and further improving the reliability of the battery over the long term.

[0011] In any embodiment of the present application, the crystallinity of the first base film is greater than that of the second base film, and optionally the ratio of the crystallinity of the first base film to the crystallinity of the second base film is 1.1 to 5.0, or optionally 1.5 to 3.0. By limiting the ratio of the crystallinity of the first base film to the crystallinity of the second base film within the above range, the first base film and the second base film can be provided with sufficient strength while having sufficient flexibility.

[0012] In any embodiment of the present application, the crystallinity of the first base film is 40% to 90%, optionally 75% to 85%, and / or the crystallinity of the second base film is 20% to 70%, optionally 30% to 45%. By limiting the crystallinity of the first base film and the crystallinity of the second base film to the above ranges, the first base film and the second base film can be provided with sufficient strength while having sufficient flexibility.

[0013] In any embodiment of the present application, the melting point of the first base film is lower than that of the second base film, and the ratio of the melting point of the first base film to the melting point of the second base film is 0.3 to 0.85, and optionally 0.35 to 0.65. By limiting the ratio of the melting point of the first base film to the melting point of the second base film within a given range, the first base film and the second base film can be provided with good heat resistance and sufficient flexibility, and further reliability over the long-term life of the battery can be improved.

[0014] In any embodiment of the present application, the melting point of the first base film is 120°C to 280°C, optionally 130°C to 265°C, and / or the melting point of the second base film is 150°C to 360°C, optionally 160°C to 350°C. By limiting the melting points of the first base film and the second base film to within the above ranges, the first base film and the second base film can have good heat resistance and creep flexibility, and can further improve the reliability of the battery over the long term.

[0015] In any embodiment of the present application, the first base film and the second base film are each independently selected from at least one of polyolefins and derivatives thereof, halogenated polyolefins and derivatives thereof, polyethers and derivatives thereof, polyetheretherketones and derivatives thereof, polyesters and derivatives thereof, polyimides and derivatives thereof, polyvinyl alcohols and derivatives thereof, polytetrafluoroethylenes and derivatives thereof, polyvinyl fluorides and derivatives thereof, polyvinylidene fluorides and derivatives thereof, and polyethylene terephthalate and derivatives thereof. Using at least one of the above as the material for the first base film and the second base film can provide the first base film and the second base film with good chemical stability and can provide the separator with high flexibility and strength.

[0016] In any embodiment of the present application, an adhesive layer is further provided between the first base film and the second base film, the adhesive layer including an adhesive, and optionally the adhesive layer including an adhesive and a filler. When an adhesive layer is provided between the first base film and the second base film, it can not only compensate for process defects in the hot press compounding process, but also further improve the stability of the physical properties of the separator, thereby improving the reliability of the secondary battery.

[0017] In any embodiment of the present application, 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, cyanoethyl amylopectin.

[0018] In any embodiment of the present application, the filler includes at least one of inorganic particles, organic particles, and organic-metallic framework materials.

[0019] In any embodiment of the present application, the thickness of the adhesive layer is 4 μm or less, and optionally 0.5 to 2 μm. When the thickness of the adhesive layer is within the given range, the reliability of the battery over a long period of life can be improved.

[0020] In any embodiment of the present application, the separator has a transverse heat shrinkage of 0.4% or less, and optionally 0.25% or less, at 250° C. for 1 hour.

[0021] In any embodiment of the present application, the separator has a longitudinal heat shrinkage rate at 250° C. for 1 hour of 0.4% or less, and optionally 0.25% or less.

[0022] In any embodiment of the present application, the separator has a transverse tensile strength of 2500 kg / cm 2 or more, and optionally 3000 kg / cm 2 ~4000kg / cm 2 is.

[0023] In any embodiment of the present application, the separator has a longitudinal tensile strength of 2500 kg / cm 2 or more, and optionally 3000 kg / cm 2~4000kg / cm 2 is.

[0024] When at least one of the above items of the separator satisfies a given range, the separator has good physical performance and can improve the reliability of the secondary battery.

[0025] A second aspect of the present application provides a method for manufacturing a separator, the method including providing a first base film and a second base film, the second base film having a melting point higher than that of the first base film and a creep flexibility higher than that of the second base film, and combining the first base film and the second base film to obtain the separator of any embodiment of the first aspect.

[0026] In some embodiments of the present application, the manufacturing method further includes preparing an adhesive layer slurry containing an adhesive, applying the adhesive layer slurry to the first base film and / or the second base film, and then compounding the two. Optionally, the adhesive layer slurry includes an adhesive and a filler. If the adhesive layer slurry further includes a filler, the physical performance of the separator can be further improved, thereby improving the reliability of the secondary battery.

[0027] A third aspect of the present application provides a secondary battery, the secondary battery including the separator of the first aspect of the present application or the separator produced by the method of the second aspect of the present application. Use of a given separator in a secondary battery can improve the reliability of the secondary battery.

[0028] In any embodiment of the present application, the battery further includes a positive electrode plate and a negative electrode plate, and a separator is provided between the positive electrode plate and the negative electrode plate. The first base film faces the negative electrode plate and has good creep flexibility, and faces the negative electrode plate, enhancing the dendrite puncture resistance effect and improving the reliability of the battery over the long term of its life. At the same time, the second base film faces the positive electrode plate and has a high melting point, enhancing heat resistance.

[0029] A fourth aspect of the present application provides a power consuming device, the power consuming device including the secondary battery of the third aspect of the present application. Use of a given separator in the secondary battery of the power consuming device can improve the reliability of the power consuming device.

[0030] The device of the present application includes the secondary battery of the present application, and therefore has at least the same advantages as a secondary battery. [Brief explanation of the drawings]

[0031] In order to more clearly explain the technical solution of the present application, the following briefly introduces the drawings used in the present application. It is obvious that 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 any creative efforts.

[0032] [Figure 1] 1 is a structural schematic diagram of one embodiment of the separator of the present application. FIG. [Figure 2] 1 is a structural schematic diagram of one embodiment of the separator of the present application. FIG. [Figure 3] 1 is a flowchart of one embodiment of a method for manufacturing a separator of the present application. [Figure 4] FIG. 1 is a schematic diagram of an embodiment of a secondary battery. [Figure 5] FIG. 5 is an exploded view of FIG. [Figure 6] FIG. 1 is a schematic diagram of one embodiment of a battery module. [Figure 7] FIG. 1 is a schematic diagram of one embodiment of a battery pack. [Figure 8] FIG. 8 is an exploded view of FIG. [Figure 9] 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

[0033] The present application will be further described below in conjunction with specific embodiments. It should be understood that these specific embodiments are only used to illustrate the present application and are not intended to limit the scope of the present application.

[0034] For clarity and simplicity, this specification specifically discloses only certain numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range, any lower limit can be combined with another lower limit to form an unspecified range, and similarly, any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each point or single numerical value disclosed alone can be combined with any other point or single numerical value as a lower limit or upper limit, or can be combined with other lower limits or upper limits to form an unspecified range.

[0035] In the description herein, unless otherwise specified, the term "or" is inclusive. That is, the phrase "A or B" means "A, B, or both A and B." More specifically, the following conditions satisfy "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) but B is true (or exists); and both A and B are true (or exist).

[0036] In the description of this specification, it should be explained that unless otherwise specified, "more than" and "less than" are inclusive, and "plurality" in "one or more" means two and more than two.

[0037] Unless otherwise specified, the terms used in this application have the meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of each parameter mentioned in this application can be measured using various measurement methods commonly used in the art (for example, can be tested using the methods described in the examples of this application).

[0038] secondary battery A secondary battery refers to a battery that can be continuously used by activating the active material through charging after discharging the battery.

[0039] Generally, a secondary battery includes a positive electrode plate, a negative electrode plate, a separator, and an electrolyte. During charging and discharging, active ions shuttle between the positive and negative electrodes, absorbing and desorbing. The separator is placed between the positive and negative electrodes to provide isolation. The electrolyte conducts ions between the positive and negative electrodes.

[0040] [Separator] Referring to FIG. 1, an embodiment of the present application provides a separator 10 including a first base film 11 and a second base film 12, wherein the melting point of the second base film is higher than the melting point of the first base film, and the creep flexibility of the first base film is greater than the creep flexibility of the second base film.

[0041] While not wishing to be bound by any theory, the inventors have discovered through extensive research that in the specific separator structure of the present application, the creep flexibility of the first and second base films is different, thereby differentiating the deformation capacities of the two base films under stress. When one base film has a high deformation capacity and dendrites grow and pierce the separator, the base film with high creep flexibility deforms to encapsulate the dendrites, buffering damage to the separator caused by the dendrites. Meanwhile, the base film with low creep flexibility undergoes relatively little deformation and can provide sufficient support. The stress buffering provided by one base film layer and the strength support provided by another base film layer both inhibit dendrite-induced damage to the separator and reduce the risk of dendrites penetrating the separator and causing short circuits, thereby improving the reliability and cycle life of the battery over a long period of cycle life.

[0042] As a result of intensive research, the inventors of the present application 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:

[0043] In any embodiment of the present application, the ratio of the creep flexibility of the first base film to the creep flexibility of the second base film is 1.1 to 3.0, and optionally 1.3 to 2.0. In some embodiments, the ratio of the creep flexibility of the first base film to the creep flexibility of the second base film is optionally 1.4 to 1.8. In other embodiments, the ratio of the creep flexibility of the first base film to the creep flexibility of the second base film is optionally 1.1, 1.2, 1.4, 1.6, 1.7, 1.9, 2.0, 2.2, 2.4, 2.6, 2.8, 3.0, etc., or a range consisting of any two of the above values. For example, the ratio of the creep flexibility of the first base film to the creep flexibility of the second base film is optionally 1.10 to 1.22, 1.22 to 1.40, 1.31 to 1.79, 1.40 to 1.70, 1.56 to 1.90, 1.70 to 2.39, 2.13 to 2.78, 2.35 to 2.78, 1.2 to 1.9, 1.6 to 2.6, 1.9 to 2.4, 2.6 to 2.8, etc.

[0044] In this embodiment, when the ratio of the creep flexibility of the first base film to the creep flexibility of the second base film satisfies the above conditions, the two performance properties of the separator, namely flexibility and strength, can be well balanced. The flexibility of the first base film can be used to improve the separator's ability to respond to external forces, providing a certain buffering effect against deformation due to external forces. The strength of the second base film can be used to improve the separator's strength against external forces, reducing the risk of foreign matter (e.g., lithium dendrites) penetrating the separator and causing a short circuit, thereby improving the reliability and cycle life of the battery over a long period of cycle life.

[0045] In any embodiment of the present application, the creep flexibility of the first base film is 0.0013 MPa -1 ~0.0050MPa -1 In some optional embodiments, the creep flexibility of the first base film is 0.0013 MPa. -1 ~0.0032MPa -1The creep flexibility of the first base film is 0.0013 MPa. -1 , 0.0015MPa -1 , 0.0017MPa -1 , 0.0019MPa -1 , 0.0022MPa -1 , 0.0025MPa -1 , 0.0028MPa -1 , 0.0031MPa -1 , 0.0034MPa -1 , 0.0039MPa -1 , 0.0043MPa -1 , 0.0048MPa -1 , 0.0050MPa -1 Or it may be a range consisting of any two of the above values. For example, the creep flexibility of the first base film may be 0.0013 MPa -1 ~0.0015MPa -1 , 0.0013MPa -1 ~0.0019MPa -1 , 0.0017MPa -1 ~0.0022MPa -1 , 0.0022MPa -1 ~0.0028MPa -1 , 0.0025MPa -1 ~0.0032MPa -1 , 0.0028MPa -1 ~0.0039MPa -1 , 0.0015MPa -1 ~0.0017MPa -1 , 0.0019MPa -1 ~0.0022MPa -1 , 0.0025MPa -1 ~0.0028MPa -1 , 0.0031MPa -1 ~0.0039MPa -1 , 0.0043MPa -1 ~0.0048MPa -1 And so on.

[0046] In some optional embodiments, the creep flexibility of the second base film is 0.0010 MPa or less. -1 ~0.0023MPa-1 In some optional embodiments, the creep flexibility of the second base film is 0.0010 MPa. -1 ~0.0020MPa -1 The creep flexibility of the second base film is 0.0010 MPa. -1 , 0.0012MPa -1 , 0.0014MPa -1 , 0.0015MPa -1 , 0.0016MPa -1 , 0.0017MPa -1 , 0.0018MPa -1 , 0.0019MPa -1 , 0.0020MPa -1 , 0.0021MPa -1 , 0.0022MPa -1 , 0.0023MPa -1 For example, the creep flexibility of the second base film may be 0.0010 MPa or less. -1 ~0.0013MPa -1 , 0.0013MPa -1 ~0.0016MPa -1 , 0.0014MPa -1 ~0.0020MPa -1 , 0.0016MPa -1 ~0.0018MPa -1 , 0.0020MPa -1 ~0.0023MPa -1 , 0.0010MPa -1 ~0.0015MPa -1 , 0.0015MPa -1 ~0.0020MPa -1 , 0.0015MPa -1 ~0.0016MPa -1 , 0.0017MPa -1 ~0.0019MPa -1 , 0.0018MPa -1 ~0.0021MPa -1 , 0.0020MPa -1 ~0.0021MPa -1 And so on.

[0047] When the creep flexibility of the first base film and the creep flexibility of the second base film satisfy the above range, the separator's flexibility and strength can be well balanced. The flexibility of the first base film can be used to improve the separator's ability to withstand external forces, providing a certain buffering effect against deformation due to external forces. The strength of the second base film can be used to improve the separator's strength against external forces, reducing the risk of foreign matter (e.g., lithium dendrites) penetrating the separator and causing a short circuit, thereby improving the reliability and cycle life of the battery over a long period of cycle life.

[0048] According to some embodiments, the creep flexibility of the first base film and the second base film can be tested using equipment and methods known in the art. For example, the following steps can be taken: cut the sample to be measured into a rectangular spline with a length of 50 mm and a width of 4 mm, clamp the spline into a dynamic thermal mechanical analyzer, adjust the test mode to creep mode, set the temperature to 25°C, and set the test time to 220 minutes. The value at the stable point of the curve is the creep flexibility of the sample.

[0049] As will be understood by those skilled in the art, the creep flexibility of a base film can be adjusted by adjusting the intrinsic parameters of the base film (e.g., one or more of the crystallinity, relative molecular mass, etc. of the base film material) and the base film manufacturing process parameters (e.g., one or more of the stretching rate, stretching temperature, etc.). For example, assuming that other conditions remain unchanged, the smaller the relative molecular weight of the base film material, the greater the creep flexibility, and the greater the crystallinity, the smaller the creep flexibility. Those skilled in the art can adjust the creep flexibility of a base film by known methods within each parameter range given in this application, for example, by adjusting the manufacturing process of the base film (adjusting the crystallinity, molecular weight, etc.) and obtaining a base film with the required creep flexibility through a limited number of tests.

[0050] In any embodiment of the present application, the ratio of the relative molecular mass of the material of the first base film to the relative molecular mass of the material of the second base film is 1.05 or greater, and optionally 1.2 to 10. In some optional examples, the ratio of the relative molecular mass of the material of the first base film to the relative molecular mass of the material of the second base film is 2.2 to 8. In some examples, the ratio of the relative molecular mass of the material of the first base film to the relative molecular mass of the material of the second base film is 1.05, 1.1, 1.3, 1.5, 1.7, 2.0, 2.4, 2.8, 3.2, 3.6, 4.5, 4.9, 5.3, 5.6, 6.2, 6.7, 7.5, 7.9, 8.7, 9.4, 10, etc., or a range consisting of any two of the foregoing values. For example, the ratio of the relative molecular mass of the material of the first base film to the relative molecular mass of the material of the second base film is 1.05 to 1.3, 1.2 to 1.5, 1.1 to 1.7, 2.4 to 2.8, 2.2 to 2.6, 3.6 to 4.9, 4.5 to 5.3, 5.6 to 6.2, 6.7 to 7.9, 8.7 to 9.4, etc.

[0051] In any embodiment of the present application, the relative molecular mass of the material of the first base film is 300,000 to 2.5 million, optionally 500,000 to 2 million. In some optional examples, the relative molecular mass of the material of the first base film is 600,000 to 1.8 million, and in some examples, the relative molecular mass of the material of the first base film may be 300,000, 340,000, 420,000, 500,000, 750,000, 900,000, 1.2 million, 1.36 million, 1.5 million, 1.7 million, 1.82 million, 1.9 million, 1.95 million, 2 million, 2.2 million, 2.5 million, etc., or a range consisting of any two of the above values. For example, the relative molecular mass of the material of the first base film is 300,000 to 450,000, 300,000 to 500,000, 500,000 to 750,000, 750,000 to 1,200,000, 350,000 to 500,000, 750,000 to 900,000, 1,200,000 to 1,360,000, 1,500,000 to 1,700,000, 1,820,000 to 2,100,000, 2,300,000 to 2,430,000, etc.

[0052] In some embodiments, the relative molecular mass of the material of the second base film is 10,000 to 2,000,000, optionally 10,000 to 1,200,000. In some embodiments, the relative molecular mass of the material of the second base film is 400,000 to 800,000. The relative molecular mass of the material of the second base film can be 10,000, 25,000, 100,000, 200,000, 350,000, 190,000, 280,000, 370,000, 510,000, 650,000, 800,000, 1,050,000, 1,130,000, 1,300,000, 1,440,000, 1,630,000, 1,770,000, 1,800,000, 1,930,000, 2,000,000, etc., or a range consisting of any two of the foregoing values. For example, the relative molecular mass of the material of the second base film may be 10,000 to 25,000, 25,000 to 70,000, 80,000 to 150,000, 25,000 to 150,000, 130,000 to 180,000, 150,000 to 250,000, 180,000 to 400,000, 300,000 to 400,000, 500,000 to 650,000, 190,000 to 280,000, 370,000 to 510,000, 650,000 to 800,000, 1,050,000 to 1,130,000, 1,300,000 to 1,440,000, 1,670,000 to 1,770,000, 1,800,000 to 1,930,000, etc.

[0053] The relative molecular mass of the base film material has a meaning known in the art and can be tested using equipment and methods known in the art, for example, using a high temperature GPC test (differential refractive index detector).

[0054] Here, the higher the relative molecular weight of the base film material, the longer its molecular chains may be, and the tighter the entanglement between the chains may be, making it less likely to deform and further reducing its creep flexibility. Correspondingly, the lower the relative molecular weight of the base film material, the greater its creep flexibility. At the same time, the higher the relative molecular weight of the base film material, the greater its corresponding strength. Therefore, when selecting the relative molecular weight of the base film material, it is necessary to balance the two properties of the material: flexibility and strength. To improve the strength of the base film, a higher relative molecular mass may be selected, but this will reduce its creep flexibility.

[0055] In any embodiment of the present application, the crystallinity of the first base film is greater than the crystallinity of the second base film, and optionally the ratio of the crystallinity of the first base film to the crystallinity of the second base film is 1.1 to 5.0. In some optional examples, the ratio of the crystallinity of the first base film to the crystallinity of the second base film is 1.5 to 3.0. The ratio of the crystallinity of the first base film to the crystallinity of the second base film may be 1.1, 1.3, 1.8, 2.2, 2.5, 2.9, 3.4, 3.7, 4.0, 4.5, 4.8, 5.0, or a range consisting of any two of the above values. For example, the ratio of the crystallinity of the first base film to the crystallinity of the second base film is optionally 1.1 to 1.3, 1.3 to 1.5, 1.5 to 1.8, 1.3 to 1.8, 1.8 to 2.5, 2.2 to 2.9, 2.9 to 3.4, 3.4 to 3.7, 3.7 to 4.0, 3.9 to 4.4, 4.4 to 5.0, etc.

[0056] In any embodiment of the present application, the crystallinity of the first base film is 40% to 90%, optionally 75% to 85%. The crystallinity of the first base film may be 40%, 45%, 50%, 59%, 64%, 70%, 75%, 78%, 80%, 82%, 86%, 88%, 90%, etc., or a range consisting of any two of the above values. For example, the crystallinity of the first base film may be 40% to 45%, 45% to 50%, 50% to 59%, 60% to 65%, 54% to 62%, 62% to 68%, 60% to 71%, 72% to 80%, 59% to 80%, 64% to 82%, 80% to 86%, 82% to 88%, etc.

[0057] In some embodiments, the crystallinity of the second base film is 20% to 70%, optionally 30% to 45%. The crystallinity of the second base film may be 20%, 24%, 29%, 38%, 44%, 59%, 67%, 69%, 70%, etc., or a range consisting of any two of the above values. For example, the crystallinity of the second base film may be 20% to 23%, 24% to 29%, 29% to 44%, 29% to 38%, 38% to 42%, 42% to 47%, 48% to 55%, 55% to 59%, 60% to 65%, 38% to 59%, 59% to 67%, 67% to 70%, etc.

[0058] According to some embodiments, the crystallinity can be tested using equipment and methods known in the art. Specifically, 4-6 mg of a sample to be measured is placed in the sample chamber of a differential scanning calorimeter, and the temperature is increased from 25°C to 350°C at a heating rate of 10°C / min to obtain a melting endothermic curve. The peak area of ​​the curve and the reference value of 100% crystalline polyolefin can be calculated to obtain the crystallinity.

[0059] Crystallinity is used to indicate the percentage of crystalline regions in the base film material. Crystallization is the process of forming a molecular chain morphology by the regular arrangement of molecular chains. Generally, the higher the crystallinity, the more regular the molecular chain arrangement.

[0060] Here, the crystallinity also has a certain effect on the creep flexibility of the base film. Generally, the higher the crystallinity, the lower the creep flexibility. Increasing the crystallinity can improve the strength of the base film, for example, improving its pin puncture strength. Therefore, in addition to the relative molecular mass of the base film material, it is necessary to balance the crystallinity, thereby providing the separator with sufficient strength and flexibility. Therefore, the present application proposes increasing the relative molecular mass of the first base film material compared to the relative molecular mass of the second base film material, and increasing the crystallinity of the first base film compared to the crystallinity of the second base film, thereby improving the strength of the first base film and improving its creep flexibility. In other words, by balancing the relative molecular mass and crystallinity of the first base film, the first base film can have relatively high strength and high creep flexibility. Accordingly, the second base film may be made of a material with more complex molecular chains, and then the creep flexibility can be balanced by decreasing the crystallinity. Furthermore, the branching degree of the first base film material can be made smaller than that of the second base film material, thereby improving creep flexibility. That is, by balancing the relative molecular mass, branching degree, and crystallinity of the first base film, the first base film can be endowed with relatively high strength and high creep flexibility. Therefore, by limiting the crystallinity, relative molecular mass, and crystallinity, relative molecular mass, and ratio of the first base film material and the second base film material to the above ranges, the creep flexibility of the first base film can be made greater than that of the second base film, while at the same time maintaining a certain level of strength for the separator.

[0061] In any embodiment of the present application, the melting point of the first base film is lower than the melting point of the second base film. The ratio of the melting point of the first base film to the melting point of the second base film is 0.3 to 0.85, and optionally 0.35 to 0.65. For example, in some embodiments, the ratio of the melting point of the first base film to the melting point of the second base film is optionally 0.3, 0.35, 0.4, 0.5, 0.6, 0.65, 0.7, 0.8, 0.85, etc., or a range consisting of any two of the above values. For example, the ratio of the melting point of the first base film to the melting point of the second base film is optionally 0.3 to 0.35, 0.35 to 0.4, 0.4 to 0.5, 0.5 to 0.6, 0.6 to 0.65, 0.5 to 0.7, 0.7 to 0.8, 0.8 to 0.85, etc.

[0062] In any embodiment of the present application, the melting point of the first base film is 120° C. to 280° C., optionally 130° C. to 265° C. In some examples, the melting point of the first base film is 120° C., 125° C., 130° C., 146° C., 150° C., 152° C., 165° C., 180° C., 196° C., 204° C., 220° C., 246° C., 258° C., 265° C., 270° C., 280° C., etc., or a range consisting of any two of the above values. For example, the melting point of the first base film is 120°C to 125°C, 125°C to 130°C, 130°C to 146°C, 146°C to 152°C, 155°C to 180°C, 180°C to 206°C, 210°C to 230°C, 231°C to 240°C, 245°C to 254°C, 255°C to 265°C, or 265°C to 280°C.

[0063] In some embodiments, the melting point of the second base film is 150°C to 360°C, optionally 160°C to 350°C. For example, in some embodiments, the melting point of the second base film is 150°C, 158°C, 165°C, 170°C, 185°C, 200°C, 210°C, 240°C, 255°C, 272°C, 296°C, 320°C, 335°C, 360°C, etc., or a range consisting of any two of the above values. For example, the melting point of the second base film is 150°C to 165°C, 165°C to 170°C, 170°C to 190°C, 190°C to 210°C, 210°C to 240°C, 240°C to 272°C, 272°C to 320°C, 320°C to 340°C, or 340°C to 360°C.

[0064] Here, both a melting point that is too high and a melting point that is too low affect the physical properties of the base film material. For example, even if the material has high creep flexibility after exceeding a certain melting point, its strength is too low and it cannot suppress dendrite penetration. By limiting the melting points of the first base film and the second base film, and their ratio, within the above range, the second base film with a higher melting point functions to complement heat resistance, and the first base film with a lower melting point functions to complement flexibility, thereby providing the separator with good heat resistance and flexibility. This improves the physical properties of the first base film and the second base film, further improving the reliability of the secondary battery.

[0065] According to some embodiments, the melting points of the first and second base films have meanings known in the art and can be measured using methods known in the art. For example, they can be measured using differential scanning calorimetry. For details, see standard GB / T 19466.3-2004. For example, they can be measured as follows: a 4-6 mg sample is placed in the sample chamber 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 of the curve is the melting point of the sample.

[0066] In any embodiment of the present application, the first base film and the second base film are each independently selected from at least one of polyolefins and their derivatives, halogenated polyolefins and their derivatives, polyethers and their derivatives, polyetheretherketones and their derivatives, polyesters and their derivatives, polyimides and their derivatives, polyvinyl alcohols and their derivatives, polytetrafluoroethylenes and their derivatives, polyvinyl fluorides and their derivatives, polyvinylidene fluoride and its derivatives, and polyethylene terephthalate and its derivatives. For example, the first base film may be a polyolefin and its derivatives or a halogenated polyolefin and its derivatives. The first base film may be a polyether and its derivatives, polyetheretherketones and its derivatives, polyesters and its derivatives, etc. The first base film and the second base film may further be a polyvinylidene fluoride and its derivatives, polyethylene terephthalate, etc. Here, a derivative generally refers to a product derived by replacing a hydrogen atom or atomic group in a compound with another atom or atomic group. Using at least one of the above as the material for the first base film and the second base film improves the chemical stability of the first base film and the second base film, and can also give the separator greater flexibility and strength.

[0067] 2, an example of the present application provides a separator 10 including a first base film 11 and a second base film 12. In any embodiment of the present application, an adhesive layer 13 is further provided between the first base film 11 and the second base film 12, and the adhesive layer includes an adhesive. Optionally, the adhesive layer includes an adhesive and a filler.

[0068] When an adhesive layer is provided between the first and second base films and the adhesive layer contains an adhesive, it can not only compensate for process defects in the base film hot-press compounding process, but also further improve the physical properties of the separator (e.g., tensile strength, puncture resistance, heat resistance, etc.), thereby improving the reliability of the secondary battery. By interposing a filler between the first and second base films, the risk of powder shedding can also be reduced.

[0069] In any embodiment of the present application, 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, cyanoethyl amylopectin.

[0070] In any embodiment of the present application, the filler includes at least one of inorganic particles, organic particles, and organic-metallic framework materials.

[0071] Optionally, the inorganic particles 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 that can undergo electrochemical reactions.

[0072] Optionally, the inorganic particles having a dielectric constant of 5 or more include boehmite, aluminum oxide, zinc oxide, silicon oxide, titanium oxide, zirconium oxide, barium oxide, calcium oxide, magnesium oxide, nickel oxide, tin oxide, cerium oxide, yttrium oxide, hafnium oxide, aluminum hydroxide, magnesium hydroxide, silicon carbide, boron carbide, aluminum nitride, silicon nitride, boron nitride, magnesium fluoride, calcium fluoride, barium fluoride, barium sulfate, magnesium aluminum silicate, 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 adhesive 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, polymer graft 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 structure of the adhesive layer. Furthermore, selecting a coupling agent, surfactant, or polymer with a specific functional group to modify the inorganic particles can improve the electrolyte wetting and retention properties of the adhesive layer, thereby contributing to improved adhesion of the adhesive layer to the first and second base films.

[0073] Optionally, the inorganic particles that are ionically conductive but do not store ions include 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 type 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 type glass Li x7 Si y7 S z3 and P2S5 type glass Li x8 P y8 S z4 contains at least one of them, where 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 ionic conductivity of the separator can be further improved.

[0074] Optionally, the inorganic particles capable of undergoing an electrochemical reaction 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.

[0075] 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 (crosslinked polymer of butyl acrylate and ethyl methacrylate).

[0076] Optionally, the organic-metal framework material may include one or more of a nitrogen-containing heterocyclic ligand-based structure, an organic carboxylic acid-based ligand-based structure, and a nitrogen-containing oxygen gas mixture-based ligand-based structure.

[0077] In some embodiments, the content of the adhesive may be 10% or more, and optionally 10% to 30%, based on the total weight of the adhesive layer.

[0078] In some embodiments, the content of the filler may be 90% or less, optionally 40% to 90%, or 60% to 80%, based on the total weight of the adhesive layer.

[0079] In some embodiments, the adhesive layer may further include a dispersant, such as carboxymethyl cellulose, which can adjust the viscosity of the adhesive layer slurry and improve the quality and uniformity of the adhesive layer.

[0080] 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.

[0081] The thickness of the adhesive layer is 4 μm or less, and optionally 0.5 to 2 μm.

[0082] According to some embodiments, the thickness of the adhesive layer can be tested using equipment and methods known in the art. Specifically, a scanning electron microscope (e.g., ZEISS Sigma 300) is used to obtain a cross-sectional scanning electron microscope (SEM) photograph of the separator according to JY / T010-1996. For example, the test can be performed according to the following method: randomly select multiple areas on the separator cross section, measure the coating thickness at least five times at a certain magnification, and calculate the average value of the measurements from different areas to determine the thickness of the adhesive layer.

[0083] In any embodiment of the present application, the separator has a transverse heat shrinkage of 0.4% or less, optionally 0.25% or less at 250°C for 1 hour, and / or a longitudinal heat shrinkage of 0.4% or less, optionally 0.25% or less at 250°C for 1 hour, and / or a transverse tensile strength of 2500 kg / cm 2 or more, and optionally 3000 kg / cm 2 ~4000kg / cm 2 and / or the longitudinal tensile strength of the separator is 2500 kg / cm 2 or more, and optionally 3000 kg / cm 2 ~4000kg / cm 2 When at least one of the above items of the separator satisfies a given range, the separator has good heat resistance and physical properties, and the reliability of the secondary battery can be improved.

[0084] According to some embodiments, the transverse tensile strength, longitudinal tensile strength, transverse heat shrinkage, and longitudinal heat shrinkage of the first base film and the second base film all have meanings known in the art and can be measured using instruments and methods known in the art, for example, by referring to standard GB / T 36363-2018.

[0085] [Separator manufacturing method] Referring to Figure 3, an embodiment of the present application provides a method for manufacturing a separator, which includes the following steps: S10: Provide a first base film and a second base film, wherein the melting point of the second base film is higher than the melting point of the first base film, and the creep flexibility of the first base film is greater than the creep flexibility of the second base film.

[0086] S20: The first base film and the second base film are combined to obtain a separator.

[0087] The first and second base films may be directly combined by hot pressing, but if the temperature is too high during the hot pressing process, the porosity will decrease and the breathability will be poor, and if the temperature is too low, the adhesion between the first and second base films will be weak, so it is necessary to adjust the hot pressing temperature appropriately. Optionally, the hot pressing temperature is 20°C to 50°C.

[0088] In any embodiment of the present application, a method for manufacturing a separator includes: The method further includes providing an adhesive layer slurry containing an adhesive, and applying the adhesive layer slurry to the first base film and / or the second base film followed by compounding.

[0089] Optionally, the adhesive layer slurry contains an adhesive and a filler, which allows an adhesive layer to be formed between the first base film and the second base film, improving the physical performance of the separator and the reliability of the secondary battery.

[0090] Unless otherwise specified, each of the raw materials used in the method for producing the separator (for example, the first base film, the second base film, the adhesive, the filler, etc.) is commercially available.

[0091] [Positive electrode plate] 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.

[0092] The positive electrode current collector may be a conventional metal foil sheet or a composite current collector (a metal material may be deposited on a polymer substrate to form a composite current collector). For example, the positive electrode current collector may be aluminum foil.

[0093] The specific type of the positive electrode active material is not limited, and any active material known in the art that can be used for the positive electrode of a secondary battery may be adopted, and those skilled in the art can select it according to actual needs.

[0094] 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 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 modified compounds thereof. Examples of lithium phosphates with 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 modified compounds thereof. All of these materials are commercially available.

[0095] The modifying compound for each of the above materials may be one that performs doping modification and / or surface coating modification on the material.

[0096] The positive electrode membrane layer generally further optionally contains an adhesive, a conductive agent and other optional auxiliary agents.

[0097] 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, Super P (SP), graphene, and carbon nanofibers.

[0098] 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), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0099] [Negative electrode plate] 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.

[0100] The negative electrode current collector may be a conventional metal foil sheet or a composite current collector (e.g., a metal material may be deposited on a polymer substrate to form a composite current collector). For example, the negative electrode current collector may be a copper foil.

[0101] The specific type of negative electrode active material is not limited, and any active material known in the art for use in secondary battery negative electrodes may be used. Those skilled in the art can select the material according to 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 elemental silicon, silicon oxide (e.g., silicon suboxide), silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from one or more of elemental tin, tin oxide, and tin alloys. All of these materials are commercially available.

[0102] In some embodiments, to further improve the energy density of the battery, the negative electrode active material may include a silicon-based material.

[0103] The negative electrode film layer generally further optionally contains an adhesive, a conductive agent and other optional auxiliary agents.

[0104] 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.

[0105] 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).

[0106] For example, other optional auxiliaries may be thickening and dispersing agents (such as sodium carboxymethylcellulose CMC-Na), PTC thermistor materials.

[0107] [Electrolyte] The secondary battery may include an electrolyte, which functions to conduct ions between the positive electrode and the negative electrode. The electrolyte may include an electrolyte salt and a solvent.

[0108] 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 bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium difluorophosphate (LiPOF), lithium difluorobis(oxalato)phosphate (LiDFOP), and lithium tetrafluoro(oxalato)phosphate (LiTFOP).

[0109] Examples of solvents include ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), n-propyl acetate (PA), methyl propionate (Methyl The hydroxybenzoates may be selected from one or more of the following: n-Propyl Propionate (MP), n-Ethyl Propanoate (EP), n-Propyl Propionate (PP), n-Methyl Butyrate (MB), n-Ethyl Butyrate (EB), 1,4-Butyrolactone (GBL), 1,4-Butyrolactone (SF), 1,4-Tetramethylene Sulfone (SF), 1,4-Butyrolactone (MSM), 1,4-Butyrolactone (MES), and 1,4-Butyrolactone (ESE).

[0110] 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 may further include additives that can improve some battery performance, such as an additive that improves the overcharge performance of the battery, an additive that improves the high-temperature performance of the battery, or an additive that improves the low-temperature performance of the battery.

[0111] In some embodiments, the secondary battery may be a lithium-ion secondary battery. In any embodiment of the present application, the secondary battery includes a positive electrode plate, a negative electrode plate, and a separator, and the separator is disposed between the positive electrode plate and the negative electrode plate, and the separator may be the separator of any of the above embodiments.

[0112] In some embodiments, in a secondary battery, the first base film of the separator faces the negative electrode plate. That is, the side of the base film with a relatively high creep flexibility faces the negative electrode plate. If lithium dendrites precipitate on the negative electrode side, the separator can withstand the lithium dendrites more effectively, reducing the risk of the separator being pierced and causing a short circuit between the positive and negative electrodes. At the same time, the melting point of the second base film facing the positive electrode plate is higher than that of the first base film, allowing it to withstand higher temperatures and reducing the risk of the separator being destroyed by heat and causing a short circuit between the positive and negative electrodes. This improves the reliability of the secondary battery.

[0113] The embodiments of the present application are not particularly limited to the shape of the secondary battery, which may be cylindrical, rectangular, or any other shape. Figure 4 shows an example of a secondary battery 5 having a rectangular structure.

[0114] In some embodiments, the secondary battery may include an exterior body used to package the positive electrode plate, the negative electrode plate, the separator, and the electrolyte.

[0115] In some embodiments, the exterior of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, etc. The exterior of the secondary battery may be a pouch, such as a bag-like pouch. The material of the pouch may be plastic, and may include, for example, one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0116] 5, in some embodiments, the exterior body may include a case 51 and a cover plate 53. Here, the case 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate together form a surrounding storage cavity. The case 51 has an opening communicating with the storage cavity, and the cover plate 53 can be installed to cover the opening to seal the storage cavity.

[0117] The manufacturing method of the secondary battery of the present application is 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, a positive electrode plate, a separator, and a negative electrode plate can be formed into an electrode assembly by a winding process and / or a stacking process. The electrode assembly can then be placed in an outer casing, dried, and then injected with an electrolyte. A battery cell can be obtained through processes such as vacuum packaging, 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 directly form a battery pack.

[0118] Fig. 6 shows an example of a battery module 4. Referring to Fig. 6, a plurality of secondary batteries 5 may be arranged in order along the longitudinal direction of the battery module 4. Of course, the batteries may be arranged in any other manner. Furthermore, the plurality of secondary batteries 5 may be fixed by fasteners.

[0119] The battery module 4 may further include a housing having an accommodating space, and the plurality of secondary batteries 5 are accommodated in this accommodating space.

[0120] 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 can be adjusted according to the application and capacity of the battery pack.

[0121] 7 and 8 show an example of a battery pack 1. Referring to FIGS. 7 and 8, 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 housing 2 and a lower housing 3, and the upper housing 2 may be provided with a lid on the lower housing 3 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.

[0122] Device The present application further provides a power-consuming device including the secondary battery of the present application. The battery cell, battery module, or battery pack may be a power source for the device or an energy storage unit 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), an electric train, a ship, a satellite, or an energy storage system.

[0123] A device may select a battery cell, a battery module, or a battery pack based on its usage needs.

[0124] 9 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 demand for high power output and high energy density of the secondary battery of the power consuming device, a battery pack or battery module may be employed.

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

[0126] The beneficial effects of the present application will be further explained below in conjunction with examples.

[0127] In order to make the technical problems, technical solutions, and beneficial effects solved by the embodiments of the present application clearer, the following embodiments will be described in more detail in conjunction with the drawings. Obviously, the described embodiments are only some of the embodiments of the present application, and not all of the embodiments. In the following, the description of at least one exemplary embodiment is merely illustrative in nature and does not constitute any limitation on the present application and its applications. All other embodiments obtained by those skilled in the art based on the embodiments in the present application without any creative effort are within the scope of protection of the present application.

[0128] 1. Battery manufacturing Example 1 1. Manufacturing of positive electrode plates Positive electrode 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 the resulting mixture was dried, cold-pressed, slit, and cut to obtain a positive electrode plate.

[0129] 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 carboxymethyl cellulose sodium (CMC-Na), were uniformly mixed in a mass ratio of 96.4:0.7:1.8:1.1 in an appropriate amount of deionized water 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 drying, cold pressing, slitting, and cutting processes.

[0130] 3. Separator manufacturing (1) Providing a first base film: the material includes polyethylene (PE), has a melting point of 135°C, and has a creep flexibility of 0.0013 MPa. -1 The crystallinity is 88% and the molecular weight is 500,000. A second base film is provided: the material includes polypropylene (PP), has a melting point of 165°C, and has a creep flexibility of 0.0012 MPa. -1 The crystallinity is 24% and the molecular weight is 370,000. (2) Preparation of adhesive layer slurry: Boehmite, polyacrylate, and carboxymethyl cellulose were uniformly mixed in a ratio of 4:1:1 with an appropriate amount of deionized water as a solvent to prepare an adhesive layer slurry.

[0131] (3) The adhesive layer slurry described in step (2) was applied to a PE base film to form an adhesive layer, and the PP and PE base films were hot-pressed to form a separator so that the adhesive layer was located between the PP base film and the PE base film.

[0132] 4. Electrolyte production Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a mass ratio of 30:70 to obtain an organic solvent, and thoroughly dried electrolyte salt LiPF6 was dissolved in the mixed solvent to obtain an electrolyte solution with a concentration of 1.0 mol / L.

[0133] 5. Secondary battery manufacturing A positive electrode plate, a separator, and a negative electrode plate are stacked in this order, with the separator positioned between the positive electrode plate and the negative electrode plate to serve as an insulator, and then wound to obtain an electrode assembly. The electrode assembly is placed in an outer casing, and the prepared electrolyte solution is injected into the dried case. The secondary battery is obtained through vacuum packaging, standing, chemical formation, and shaping processes.

[0134] The secondary batteries of Examples 2 to 14 and Comparative Examples 1 to 4 were produced using the same method as the secondary battery of Example 1, except that different separators were used. See Table 1 for details.

[0135] Unless otherwise specified, each of the raw materials used in the method for producing the separator (for example, the first base film, the second base film, the adhesive, the filler, etc.) is commercially available.

[0136] 2. Performance test (1) Separator creep flexibility test Step 1: Six parallel samples of the polymer film layer are obtained, each of which is a rectangular spline with a width of 4 mm and a length of 50 mm. Step 2: The spline is clamped in a jig of a dynamic thermomechanical analyzer. Here, the test mode is creep mode, the experimental temperature is room temperature, and the test time is 0 to 220 min.

[0137] (2) Battery cycle life (25°C) The secondary batteries prepared in the examples and comparative examples were subjected to a first charge and discharge at 25°C. The procedure was as follows: After allowing the secondary batteries to stand for 30 minutes at 25°C, they were charged at a constant current of 1C to 4.35V, then continuously charged at a constant voltage until the current was ≤0.05C, and then discharged at a constant current of 1C to 2.8V. This constitutes one charge / discharge process, and the discharge capacity at this time was recorded as the discharge capacity of the first cycle of the battery. The charge / discharge cycle was repeated in this manner, and the number of cycles when the capacity decreased to 80% was recorded.

[0138] [Table 1]

[0139] As can be seen from Table 1, in Examples 1 to 14, the melting point of the first base film was lower than that of the second base film, and the creep flexibility of the first base film was higher than that of the second base film. The batteries manufactured using these materials had low transverse thermal shrinkage, high transverse tensile strength, and long cycle life. In contrast, in Comparative Examples 1 to 4, the separators did not simultaneously satisfy the requirements of a lower melting point of the first base film than that of the second base film and a higher creep flexibility of the first base film than that of the second base film. The batteries manufactured using these materials had high transverse thermal shrinkage and short cycle life. Therefore, the use of the separator defined by the present application resulted in good creep flexibility. Furthermore, under comparable cycle conditions and battery performance criteria, batteries manufactured using the separators according to the present application exhibited good cycle performance. That is, under the same battery performance criteria, batteries manufactured using the separators according to the present application could be cycled more times and had higher reliability.

[0140] The above is merely a specific embodiment of the present application, and the scope of protection of the present application is not limited thereto. Those skilled in the art may easily devise various equivalent modifications or replacements within the technical scope disclosed in the present application, and all such modifications or replacements shall be included in the scope of protection of the present application. Therefore, the scope of protection of the present application shall be based on the scope of protection of the claims.

Claims

1. A separator comprising a first base film and a second base film, wherein the melting point of the second base film is higher than the melting point of the first base film, and the creep flexibility of the first base film is greater than the creep flexibility of the second base film.

2. 2. The separator according to claim 1, wherein the ratio of the creep flexibility of the first base film to the creep flexibility of the second base film is 1.1 to 3.0, and optionally 1.3 to 2.

0.

3. The creep flexibility of the first base film is 0.0013 MPa. －１ ~0.0050MPa －１ and optionally 0.0013 MPa －１ ~0.0032MPa －１ and / or The creep flexibility of the second base film is 0.0010 MPa. －１ ~0.0023MPa －１ and optionally 0.0010 MPa －１ ~0.0020MPa －１ The separator according to claim 1 or 2,

4. The separator according to any one of claims 1 to 3, wherein the ratio of the crystallinity of the first base film to the crystallinity of the second base film is 1.1 to 5.0, and optionally 1.5 to 3.

0.

5. The crystallinity of the first base film is between 40% and 90%, optionally between 75% and 85%; and / or The separator according to any one of claims 1 to 4, wherein the crystallinity of the second base film is 20% to 70%, and optionally 30% to 45%.

6. The separator according to any one of claims 1 to 5, wherein the ratio of the relative molecular mass of the material of the first base film to the relative molecular mass of the material of the second base film is 1.05 or more, and optionally 1.2 to 10.

7. The relative molecular mass of the material of the first base film is between 300,000 and 2.5 million, optionally between 500,000 and 2 million; and / or The separator according to any one of claims 1 to 6, wherein the relative molecular mass of the material of the second base film is 10,000 to 2,000,000, and optionally 10,000 to 1,200,000.

8. The separator according to any one of claims 1 to 7, wherein the ratio of the melting point of the first base film to the melting point of the second base film is 0.3 to 0.85, and optionally 0.35 to 0.

65.

9. the melting point of the first base film is between 120°C and 280°C, optionally between 130°C and 265°C; and / or The separator according to any one of claims 1 to 8, wherein the melting point of the second base film is 150°C to 360°C, and optionally 160°C to 350°C.

10. 10. The separator according to claim 1, wherein the first base film and the second base film are each independently selected from at least one of polyolefins and derivatives thereof, halogenated polyolefins and derivatives thereof, polyethers and derivatives thereof, polyether ether ketones and derivatives thereof, polyesters and derivatives thereof, polyimides and derivatives thereof, polyvinyl alcohols and derivatives thereof, polytetrafluoroethylenes and derivatives thereof, polyvinyl fluorides and derivatives thereof, polyvinylidene fluorides and derivatives thereof, and polyethylene terephthalate and derivatives thereof.

11. The separator according to any one of claims 1 to 10, further comprising an adhesive layer between the first base film and the second base film, the adhesive layer comprising an adhesive, and optionally the adhesive layer comprising an adhesive and a filler.

12. 12. The separator of claim 11, 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 amylopectin.

13. 13. The separator according to claim 11, wherein the filler comprises at least one of inorganic particles, organic particles, and an organic-metallic frame material.

14. The separator according to any one of claims 1 to 13, wherein the adhesive layer has a thickness of 3 µm or less, and optionally 0.5 to 2 µm.

15. The separator has a transverse thermal shrinkage of less than 0.4%, optionally 0.25% or less at 250°C for 1 hour; and / or The separator has a longitudinal heat shrinkage of less than 0.4%, optionally 0.25% or less at 250°C for 1 hour; and / or The separator has a transverse tensile strength of 2500 kg / cm ２ or more, and optionally 3000 kg / cm ２ ~4000kg / cm ２ and / or The longitudinal tensile strength of the separator is 2500 kg / cm ２ or more, and optionally 3000 kg / cm ２ ~4000kg / cm ２ The separator according to claim 1 , wherein

16. A method for manufacturing a separator, comprising: providing a first base film and a second base film, wherein the melting point of the second base film is higher than the melting point of the first base film, and the creep flexibility of the first base film is higher than the creep flexibility of the second base film; A method for manufacturing a separator, comprising the step of combining the first base film and the second base film to obtain the separator.

17. The method includes a step of preparing an adhesive layer slurry containing an adhesive, and applying the adhesive layer slurry to the first base film and / or the second base film, followed by compounding; Optionally, the adhesive layer slurry includes an adhesive and a filler.

18. A secondary battery comprising the separator according to any one of claims 1 to 15 or a separator produced by the method of claim 16 or 17.

19. 19. The secondary battery according to claim 18, further comprising a positive electrode plate and a negative electrode plate, wherein the separator is provided between the positive electrode plate and the negative electrode plate, and the first base film faces the negative electrode plate.

20. A power consuming device comprising the secondary battery according to claim 18 or 19.

Images