Separator and manufacturing method thereof, secondary battery and power consumption 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 swelling rate of the first base film is lower than that of the second base film. Due to the cooperation of the two-layer base film structure, even if one layer of the base film loses its insulating performance due to swelling in an application environment, the other layer of the base film can compensate for that performance, reducing the risk of electrode short-circuiting and simultaneously improving the strength of the separator and further improving the reliability of the battery over the long term.

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, the need for secondary batteries is increasing. However, there is a risk of short circuit failure of the electrodes during battery use, and the reliability of secondary batteries has become an issue. 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 lower than the melting point of the first base film, and the swelling ratio of the first base film is lower than the swelling ratio of the second base film.

[0006] Compared to the prior art, the present application has at least the following beneficial effects: Due to the mutual cooperation of the two-layer base film structure, even if one layer of base film loses its insulating performance due to swelling when the separator is used in an environment over a long period of time, the other layer of base film can play a role in compensating for that performance, reducing the risk of electrode short-circuiting and at the same time improving the strength of the separator, further improving the reliability of the battery over the long term.

[0007] In any embodiment of the present application, the ratio of the swelling ratio of the first base film to the swelling ratio of the second base film is 0.8 or less, and optionally 0.3 or less.

[0008] When the ratio of the swelling rate of the first base film to the swelling rate of the second base film is within a given range, even if one layer of base film loses its insulating performance due to swelling when the separator is used in an environment over a long period of time, the other layer of base film can compensate for that performance, reducing the risk of electrode short-circuiting and at the same time improving the strength of the separator and further improving the reliability of the battery over the long term.

[0009] In any embodiment of the present application, the swelling ratio of the first base film is 5% or less, optionally 0.2%-2%, and the swelling ratio of the second base film is 10% or less, optionally 1-8%.

[0010] When the swelling ratios of the first base film and the second base film are each within a given range, even if one layer of base film loses its insulating performance due to swelling when the separator is used in an environment over a long period of time, the other layer of base film can compensate for that performance, reducing the risk of electrode short-circuiting and at the same time improving the strength of the separator 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 less than the crystallinity of the second base film.

[0012] In any embodiment of the present application, the ratio of the crystallinity of the first base film to the crystallinity of the second base film is 0.4-0.85, and optionally 0.4-0.6.

[0013] In any embodiment of the present application, the crystallinity of the first base film is 40%-60%, optionally 45%-50%, and the crystallinity of the second base film is 45%-85%, optionally 65%-80%.

[0014] In any embodiment of the present application, the degree of branching of the first base film is greater than the degree of branching of the second base film.

[0015] In any embodiment of the present application, the degree of branching of the first base film is 0.4-0.9, optionally 0.7-0.9, and the degree of branching of the second base film is 0.01-0.4, optionally 0.01-0.2.

[0016] The degree of crystallinity reflects the orderliness of the material structure to some extent. As the degree of crystallinity increases, the material structure becomes more ordered and less likely to swell, i.e., the swelling rate decreases. Conversely, the degree of branching reflects the degree of branching of the nonlinear polymer structure in the main chain of the material. The higher the degree of branching, the more numerous and complex the side chains formed, making the material more likely to swell, i.e., the higher the swelling rate. By controlling the crystallinity of the first base film to be smaller than that of the second base film and the branching rate of the first base film to be greater than that of the second base film, and within the above range, the swelling rates of the first base film and the second base film can be balanced, and the first base film and the second base film can have good strength while still having sufficient swelling ability, thereby further improving the reliability of the secondary battery.

[0017] In any embodiment of the present application, the melting point of the first base film is 155°C-365°C, optionally 160°C-340°C, and the melting point of the second base film is 130°C-250°C, optionally 135°C-220°C.

[0018] When the melting points in degrees Celsius of the first base film and the second base film satisfy the above conditions, the first base film with a higher melting point complements the heat resistance performance, and the second base film with a lower melting point complements the swelling performance, thereby enhancing the heat resistance in the battery environment in which the separator is located and at the same time reducing the degree of swelling, further improving the reliability and extending the life of the battery.

[0019] 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 fluoride 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, as well as relatively low swelling and relatively high strength for the separator.

[0020] 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. The provision of the adhesive layer can not only compensate for process defects in the base film compounding process, but also further improve the physical performance of the separator and further enhance the reliability of the secondary battery.

[0021] 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.

[0022] In any embodiment of the present application, the filler includes at least one of inorganic particles, organic particles, and organic-metallic framework materials.

[0023] In any embodiment of the present application, the separator has an air permeability of 400s / 100cc or less, and optionally 250s / 100cc-320s / 100cc.

[0024] In any embodiment of the present application, the separator has a transverse tensile strength of 1500-4500 kgf / cm 2 and selectively 3000-4500kgf / cm 2 is.

[0025] In any embodiment of the present application, the separator has a longitudinal tensile strength of 1500-4500 kgf / cm 2 and selectively 3000-4500kgf / cm 2 is.

[0026] In any embodiment of the present application, the separator has a transverse heat shrinkage of 0.4% or less, and optionally 0.2% or less, at 250° C. for 1 hour.

[0027] 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 0.2% or less.

[0028] 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.

[0029] 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 lower than that of the first base film and a swelling ratio lower than that of the second base film; and combining the first base film and the second base film to obtain a separator.

[0030] In some embodiments of the present application, 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 to form an adhesive layer.

[0031] In any embodiment of the present application, the adhesive layer slurry further includes a filler, and optionally, the filler includes at least one of inorganic particles, organic particles, and organic-metallic frame materials. When the adhesive layer slurry further includes a filler and the filler includes at least one of the above materials, the physical performance of the separator can be further improved, thereby improving the reliability of the secondary battery.

[0032] A third aspect of the present application provides a secondary battery including the separator of the first aspect of the present application or a separator produced by the method of the second aspect of the present application. Use of the given separator in a secondary battery can improve the reliability of the secondary battery.

[0033] In any embodiment of the present application, the battery further includes a positive electrode plate and a negative electrode plate, and a separator is disposed between the positive electrode plate and the negative electrode plate. The second base film faces the negative electrode plate. The second base film facing the negative electrode plate can supplement swelling performance and make the physical properties of the separator more stable. Even if the first base film loses its insulating performance due to swelling in a long-term battery application environment, the second base film can compensate for that performance, preventing short circuits between the electrodes while simultaneously maintaining the strength of the separator, thereby improving the reliability and cycle life of the battery over a long period of cycle life.

[0034] A fourth aspect of the present application provides a 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.

[0035] 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]

[0036] 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. [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 one embodiment of an apparatus that uses a secondary battery as a power source. DETAILED DESCRIPTION OF THE INVENTION

[0037] 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.

[0038] For clarity, this specification specifically discloses only some numerical ranges. However, any lower limit and any upper limit can be combined to form a range not expressly stated, and any lower limit and any other lower limit can be combined to form a range not expressly stated, and similarly, any upper limit and any other upper limit can be combined to form a range not expressly stated. Furthermore, each point or single numerical value disclosed alone may itself be combined as a lower limit or upper limit with any other point or single numerical value, or with other lower limits or upper limits, to form a range not expressly stated.

[0039] In the description of this specification, 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, "A or B" is satisfied when A is true (or exists) and B is false (or does not exist), when A is false (or does not exist) but B is true (or exists), or when both A and B are true (or exist).

[0040] In the description of this specification, it should be explained that unless otherwise specified, "more than" and "less than" include the number listed therewith, and "plurality" in "one or more" means two and more than two.

[0041] Unless otherwise specified, the terms used in this application have the known 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 by various measurement methods commonly used in the art (for example, can be tested by the methods described in the examples of this application).

[0042] secondary battery A secondary battery is a battery that can be used repeatedly by activating the active material by charging the battery after discharging it.

[0043] 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 separate them. The electrolyte conducts ions between the positive and negative electrodes.

[0044] [Separator] 1, an embodiment of the present application provides a separator 10 including a first base film 11 and a second base film 12, where the melting point of the second base film 12 is lower than that of the first base film 11, and the swelling ratio of the first base film 11 is lower than that of the second base film 12. The mutual cooperation of the two-layer base film structure allows the separator to simultaneously achieve good reliability while also having good heat resistance.

[0045] Without being limited by any theory, the specific separator structure of the present application is believed to be achieved by selecting and combining two types of base films with different swelling ratios, thereby making the physical properties of the separator more stable. Even if one layer of base film loses its insulating performance due to swelling during prolonged use of the battery, the other layer of base film can compensate for this performance, preventing short circuits between electrodes while maintaining the strength of the separator, thereby improving the reliability and cycle life of the battery over a long period of cycle life.

[0046] In any embodiment of the present application, the ratio of the swelling ratio of the first base film to the swelling ratio of the second base film is 0.8 or less, and optionally 0.3 or less, for example, 0.001, 0.01, 0.03, 0.05, 0.06, 0.08, 0.1, 0.15, 0.2, 0.25, 0.31, 0.35, 0.4, 0.45, 0.5, 0.6, 0.65, 0.7, 0.8, etc., or a range consisting of any two of the above values. For example, the ratio of the swelling ratio of the first base film to the swelling ratio of the second base film is optionally 0.001-0.01, 0.01-0.08, 0.02-0.06, 0.04-0.08, 0.1-0.15, 0.2-0.25, 0.25-0.35, 0.35-0.45, 0.5-0.65, 0.65-0.8, etc.

[0047] When the ratio of the swelling rate of the first base film to the swelling rate of the second base film is within a given range, even if one layer of base film loses its insulating performance due to swelling when the separator is used in an environment over a long period of time, the other layer of base film can compensate for that performance, preventing short circuits between the electrodes and at the same time improving the strength of the separator, thereby improving the reliability and cycle life of the battery over the long term.

[0048] In any embodiment of the present application, the swelling ratio of the first base film is 5% or less, optionally 0.2-2%, for example, 0.1%, 0.3%, 0.5%, 0.7%, 1.1%, 1.4%, 1.8%, 2.2%, 2.4%, 2.9%, 3.4%, 3.6%, 4.1%, 4.8%, 5%, etc., or a range consisting of any two of the above values. For example, the swelling ratio of the first base film may optionally be 0.01%-0.1%, 0.1%-5%, 0.1%-3.4%, 0.1%-2.9%, 0.1%-2.2%, 0.1%-0.5%, 0.5%-5%, 0.5%-4.1%, 0.5%-3.4%, 0.5%-2.4%, 0.5%-1.1%, 1.1%-5%, 1.1%-4.1%, 1.1%-3.6%, 1.1%-3.4%, 1.1%-1.8%, 2.2%-5%, 2.2%-4.8%, 2.2%-4.1%, 2.2%-3.6%, 2.2%-2.9%, 3.4%-5%, 3.4%-4.1%, 4.1%-5%, etc.

[0049] In any embodiment of the present application, the swelling ratio of the second base film is 10% or less, optionally 1%-8%, for example, 0.2%, 0.4%, 0.7%, 0.9%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 1.9%, 2.0%, 2.1%, 2.6%, 3.5%, 3.7%, 4.4%, 6.4%, 7.8%, 9.2%, 10%, etc., or a range consisting of any two of the above values. For example, the swelling ratio of the second base film may optionally be 0.01-0.05%, 0.05-0.2%, 0.05-1.0%, 0.05-1.5%, 0.05-2.0%, 0.05-5.0%, 0.05-8.0%, 0.3-0.5%, 1.0-1.5%, 1.0-2.0%, 1.5-5.0%, 2.0-8.0%, 5.0-8.0%, 3.0-8.0%, 7.5-9.0%, 0.2%-0.7%, 0.7%-1.0%, 1.0%-1.6%, 1.8%-2.0%, 2.1%-2.6%, 2.6%-3.7%, 4.4%-6.4%, 7.8%-10%, etc.

[0050] When the ratio of the swelling ratio of the first base film to the swelling ratio of the second base film is within a given range, the reliability of the battery over a long cycle life can be further improved.

[0051] The swelling ratio of the base film has a meaning known in the art and can be measured using methods known in the art. For example, the following test method can be used: six identical samples of the base film, each measuring 50 mm x 100 mm, are prepared. The samples are immersed in an electrolyte solution, and placed in an environment at 70°C. The mass change is monitored every 24 hours for seven consecutive days. The mass increase rate of the base film is the swelling ratio. Here, the solvent used in the electrolyte solution contains ethylene carbonate (EC) and ethyl methyl carbonate (EMC), with a mass ratio of 30:70. The electrolyte salt is LiPF6, with a concentration of 1.0 mol / L.

[0052] As will be understood by those skilled in the art, the swelling ratio of the base film can be adjusted by adjusting the intrinsic parameters of the base film (e.g., one or more of the crystallinity, branching degree, etc. of the base film material) and the manufacturing process parameters of the base film (e.g., one or more of the stretching rate, stretching temperature, etc.). For example, if other conditions remain unchanged, the higher the crystallinity of the base film, the smaller the swelling ratio, and the higher the branching degree of the base film, the larger the swelling ratio. Those skilled in the art can adjust the swelling ratio of the 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, branching degree, etc.) and obtaining a base film with the required swelling ratio through a limited number of tests.

[0053] In any embodiment of the present application, the crystallinity of the first base film is less than the crystallinity of the second base film.

[0054] In some alternative embodiments, the ratio of the crystallinity of the first base film to the crystallinity of the second base film is 0.4-0.85, preferably 0.4-0.6. For example, the ratio of the crystallinity of the first base film to the crystallinity of the second base film is optionally 0.4, 0.5, 0.6, 0.7, 0.8, 0.85, etc., 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 0.4-0.5, 0.5-0.7, 0.7-0.85, etc.

[0055] In some alternative embodiments, the crystallinity of the first base film is optionally 40%-60%, optionally 45%-50%, and specifically optionally 40%, 42%, 46%, 49%, 51%, 52%, 54%, 57%, 59%, 60%, etc., or a range consisting of any two of the above values. For example, the crystallinity of the first base film is specifically optionally 40%-42%, 42%-49%, 49%-52%, 52%-57%, 57%-60%, etc. The crystallinity of the second base film is optionally 45%-85%, optionally 65%-80%. The crystallinity of the second base film may be 45%, 46%, 49%, 54%, 61%, 66%, 74%, 77%, 81%, 84%, 85%, etc., or a range consisting of any two of the above values. For example, the crystallinity of the second base film may be 45%-46%, 46%-54%, 54%-66%, 74%-77%, 81%-85%, etc.

[0056] The crystallinity reflects the orderliness of the material structure to some extent. As the crystallinity increases, the material structure becomes more orderly and less prone to swelling, i.e., the swelling ratio decreases. By adjusting the crystallinity of the first base film and the crystallinity of the second base film so that they are each within the above ranges, the swelling ratios of the first base film and the second base film can be adjusted, and the performance of the first base film and the second base film can be better complemented. Furthermore, the orderliness of the material structure also affects the strength of the material. By adjusting the crystallinity of the first base film and the crystallinity of the second base film so that they are each within the above ranges, the first base film and the second base film can simultaneously have good strength while satisfying the swelling requirements of the present application, and can further improve the reliability of the secondary battery over the long term.

[0057] The crystallinity of the base film has a meaning known in the art and can be measured using instruments and methods known in the art. For example, the crystallinity of the base film can be measured using differential scanning calorimetry (DSC). Specifically, the following test method can be used: prepare a 4-6 mg sample of the base film to be measured, place it in the sample chamber of the differential scanning calorimeter, and heat it from 25°C to 350°C at a heating rate of 10°C / min. Obtain a melting endothermic curve, and calculate the peak area of ​​the curve and the reference value for 100% crystalline polyolefin to obtain the crystallinity.

[0058] In any embodiment of the present application, the degree of branching of the first base film is greater than the degree of branching of the second base film.

[0059] In any embodiment of the present application, the branching degree of the first base film is 0.4-0.9, optionally 0.7-0.9, and the branching degree of the second base film is 0.01-0.4, optionally 0.01-0.2. For example, the branching degree of the first base film is 0.4, 0.5, 0.6, 0.7, 0.75, 0.78, 0.8, or 0.9, or a range consisting of any two of the above values. For example, the branching degree of the first base film is 0.4-0.6, 0.6-0.75, 0.75-0.78, or 0.78-0.9. The branching degree of the second base film is optionally 0.01, 0.03, 0.09, 0.14, 0.18, 0.25, 0.33, 0.38, or 0.4, or a range consisting of any two of the above values. For example, the degree of branching of the second base film is optionally 0.01-0.03, 0.03-0.14, 0.14-0.25, 0.25-0.4, and so on.

[0060] In contrast to the ordered structure of crystallinity, the degree of branching increases the branching of the nonlinear polymer structure in the main chain of the base film material; i.e., the higher the degree of branching, the more and more complex the side chains formed. The higher the degree of branching, the higher the swelling ratio. By selecting the branching ratio ratio of the first base film and the second base film within the above range, the swelling ratio of the first base film and the second base film can be adjusted, and the performance of the first base film and the second base film can be better complemented. Furthermore, the crystallinity also affects the swelling ratio of the material. By controlling the branching and crystallinity in combination within the above range, the first base film and the second base film can simultaneously achieve good strength while meeting the swelling requirements of the present application, and further improve the reliability of the secondary battery over the long term.

[0061] The branching degree of the base film has a meaning known in the art and can be tested using instruments and methods known in the art. For example, infrared spectroscopy can be used. Specifically, 3-5 sets of base film samples can be selected and placed in an infrared spectrometer for scanning, with the scanning range being 400-4000 cm-1 After the scan was completed, the infrared curve of the sample was processed to obtain the peak at 1377 cm -1 Peak area and 1996-2062cm -1 The ratio of the peak area to the peak area of ​​the

[0062] In some embodiments, the first base film simultaneously has a crystallinity of 45%-50% and a branching index of 0.7-0.9.

[0063] In some embodiments, the second base film simultaneously has a crystallinity of 65%-80% and a branching index of 0.01-0.2.

[0064] When the crystallinity and branching degree of the first base film and / or the second base film simultaneously satisfy the above ranges, the two base films can satisfy the swelling degree designed in this application while also achieving good strength performance.

[0065] In any embodiment of the present application, the melting point of the first base film is 155°C-360°C, optionally 160°C-340°C, and the melting point of the second base film is 130°C-250°C, optionally 130°C-220°C. For example, the melting point of the first base film is optionally 155°C, 165°C, 175°C, 188°C, 191°C, 220°C, 239°C, 245°C, 271°C, 294°C, 310°C, 324°C, 347°C, 360°C, etc., or a range consisting of any two of the above values. For example, the melting point of the first base film is optionally 155°C-175°C, 175°C-220°C, 220°C-245°C, 245°C-271°C, 271°C-310°C, 310°C-360°C, etc. The melting point of the second base film is optionally 130°C, 131°C, 133°C, 136°C, 145°C, 151°C, 163°C, 172°C, 174°C, 210°C, 225°C, 236°C, 250°C, etc., or a range consisting of any two of the above values. For example, the melting point of the second base film is optionally 130°C-131°C, 131°C-136°C, 145°C-151°C, 163°C-174°C, 174°C-210°C, 210°C-250°C, etc.

[0066] By adjusting the melting points in degrees Celsius of the first base film and the second base film to satisfy the above conditions, the first base film with a higher melting point complements the heat resistance performance, and the second base film with a lower melting point complements the swelling performance, thereby providing the separator with good heat resistance and swelling performance.

[0067] According to some embodiments, the melting points of the first base film and the second base film 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 to be measured 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.

[0068] 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 give the separator relatively low swelling and relatively high strength.

[0069] 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.

[0070] 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 during the hot-press compounding process of the base films, 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.

[0071] 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.

[0072] In any embodiment of the present application, the filler includes at least one of inorganic particles, organic particles, and organic-metallic framework materials.

[0073] Optionally, the inorganic particles include one or more of inorganic particles having a dielectric constant of 5 or greater, inorganic particles that are ionic conductive but do not store ions, and inorganic particles that can undergo electrochemical reactions.

[0074] 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), Pb1-mLamZr1-nTinO3 (abbreviated as PLZT), and 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. The chemical modification may include coupling agent modification (e.g., using a silane coupling agent, a titanate coupling agent, etc.), surfactant modification, polymer graft modification, etc. The physical modification may include mechanical dispersion, ultrasonic dispersion, high-energy treatment, etc. The modification treatment can reduce the aggregation of the inorganic particles, thereby resulting in a more stable and uniform structure of the adhesive layer. Furthermore, by selecting a coupling agent, surfactant, or polymer with a specific functional group to modify the inorganic particles, the adhesive layer's wetting and retention properties with respect to the electrolyte can be improved, contributing to improved adhesion of the adhesive layer to the first and second base films.

[0075] 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 y3Type 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 It may contain 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.

[0076] Optionally, the inorganic particles capable of undergoing an electrochemical reaction may contain at least one of a lithium-containing transition metal oxide, a lithium-containing phosphate, a carbon-based material, a silicon-based material, a tin-based material, and a lithium titanium compound.

[0077] Optionally, the organic particles may contain one or more of polycarbonate, polythiophene, polypyridine, polystyrene, polyacrylic acid wax, polyethylene, polypropylene, cellulose, cellulose modifier (e.g., carboxymethyl cellulose), melamine resin, phenol resin, polyester (e.g., polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate), silicon resin, polyimide, polyamideimide, polyaramide, polyphenylene sulfide, polysulfone, polyether sulfone, polyether ether ketone, polyaryl ether ketone, and a copolymer of butyl acrylate and ethyl methacrylate (a cross-linked polymer of butyl acrylate and ethyl methacrylate).

[0078] 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.

[0079] In some embodiments, the adhesive content may be 10% or more, and optionally 10%-30%, based on the total weight of the adhesive layer.

[0080] In some embodiments, the filler content may be up to 90% based on the total weight of the adhesive layer, optionally 40%-90%, 60%-80%.

[0081] 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.

[0082] 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.

[0083] The thickness of the adhesive layer is greater than or equal to 0.3 μm, and optionally is 0.5-4 μm.

[0084] 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.

[0085] In any embodiment of the present application, the separator has an air permeability of 400 s / 100 cc or less, optionally 250 s / 100 cc-320 s / 100 cc, and a transverse tensile strength of 1500-4500 kgf / cm 2 and selectively 3000-4500kgf / cm 2 The longitudinal tensile strength of the separator is 1500-4500kgf / cm 2 and selectively 3000-4500kgf / cm 2 The separator has a transverse heat shrinkage of 0-0.4%, optionally 0-0.2%, at 250°C for 1 hour, and a longitudinal heat shrinkage of 0-0.4%, optionally 0-0.2% at 250°C for 1 hour. For example, in one embodiment, the separator has an air permeability of 260s / 100c, a transverse heat shrinkage of 0.4%, optionally 0.15%, at 250°C for 1 hour, and a longitudinal heat shrinkage of 0.15% at 250°C for 1 hour. When at least one of the above properties 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.

[0086] According to some embodiments, the air permeability, 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 tested using equipment and methods known in the art, for example, by referring to standard GB / T 36363-2018.

[0087] [Separator manufacturing method] The present application further provides a method for manufacturing a separator according to the present application, the manufacturing method including providing a first base film and a second base film, and combining the first base film and the second base film to obtain the separator according to any of the above embodiments, wherein the melting point of the second base film is lower than the melting point of the first base film, and the swelling ratio of the first base film is lower than the swelling ratio of the second base film.

[0088] Referring to Figure 3, an embodiment of the present application provides a method for manufacturing a separator, which includes the following steps: S100: Provide 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 swelling ratio of the first base film is lower than the swelling ratio of the second base film.

[0089] S200: Provide a slurry for an adhesive layer, including an adhesive. Optionally, the slurry for an adhesive layer includes an adhesive and a filler. When an adhesive layer is provided between a first base film and a second base film, it can not only compensate for process defects in the hot-press compounding process, but also further improve the heat resistance and physical properties of the separator, thereby improving the reliability of the secondary battery.

[0090] S300: The adhesive layer slurry is applied to the first base film and / or the second base film to form an adhesive layer. For example, the adhesive layer slurry may be applied to only one surface of the first base film or the second base film, or the adhesive layer slurry may be applied to the first base film and the second base film simultaneously to form an adhesive layer.

[0091] S400: The first base film and the second base film are combined to obtain a separator according to any of the above embodiments. The first base film and the second base film may be combined by hot pressing. During the hot pressing process, if the temperature is too high, the porosity will decrease and the breathability will be poor, and if the temperature is too low, the adhesion between the first base film and the second base film will be weak. Therefore, it is necessary to adjust the hot pressing temperature appropriately. Optionally, the hot pressing temperature is 20°C-50°C.

[0092] 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.

[0093] [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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] The modifying compound for each of the above materials may be one that performs doping modification and / or surface coating modification on the material.

[0098] The positive electrode membrane layer generally further optionally contains an adhesive, a conductive agent and other optional auxiliary agents.

[0099] By way of example, the conductive agent may be one or more of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, conductive carbon black (Super P, SP), graphene, and carbon nanofibers.

[0100] By way of example, the adhesive may be one or more of Polymerized Styrene Butadiene Rubber (SBR), water based acrylic resin, Polyvinylidene Difluoride (PVDF), Polytetrafluoroethylene (PTFE), Ethylene Vinyl Acetate Copolymer (EVA), Polyacrylic Acid (PAA), Carboxymethyl Cellulose (CMC), Polyvinyl Alcohol (Vinylalcohol Polymer (PVA)), and Polyvinyl Butyral (PVB).

[0101] [Negative electrode plate] In a secondary battery, the negative electrode plate generally includes a negative electrode current collector and a negative electrode film layer provided on the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material.

[0102] 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.

[0103] The specific type of negative electrode active material is not limited, and active materials known in the art for use in secondary battery negative electrodes may be used, and those skilled in the art may 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 silicon elemental, 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 tin elemental, stannic acid compounds, and tin alloys. All of these materials are commercially available.

[0104] In some embodiments, to further improve the energy density of the battery, the negative electrode active material may include a silicon-based material.

[0105] The negative electrode film layer generally further optionally contains an adhesive, a conductive agent and other optional auxiliary agents.

[0106] 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.

[0107] 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).

[0108] For example, other optional auxiliary agents may be thickening and dispersing agents (such as carboxymethylcellulose sodium, CMC-Na), PTC thermistor materials.

[0109] [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.

[0110] 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).

[0111] 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), diisopropyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), n-propyl acetate (PA), methyl propionate (Methyl The 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 (EMS), and 1,4-Butyrolactone (ESE).

[0112] 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.

[0113] In some embodiments, the secondary battery may be a lithium ion secondary battery.

[0114] In any embodiment of the present application, the second base film of the separator faces the negative electrode plate, and the second base film facing the negative electrode plate can complement the swelling performance and make the physical properties of the separator more stable. Even if the first base film loses its insulating performance due to swelling during long-term battery use, the second base film can complement that performance, preventing short circuits between electrodes while simultaneously maintaining the strength of the separator, thereby improving the reliability and cycle life of the battery over a long period of cycle life.

[0115] Due to the cooperation of the two-layer base film structure, i.e., the first base film and the second base film, and the swelling rate of the first base film is smaller than that of the second base film, even if one layer of base film loses its insulating performance due to swelling during long-term use of the separator, the other layer of base film can compensate for that performance, reducing the risk of electrode short-circuiting and at the same time improving the strength of the separator, thereby improving the reliability of the battery over the long term.

[0116] 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 with a rectangular structure.

[0117] In some embodiments, the secondary battery may include an outer casing for packaging the positive electrode plate, the negative electrode plate, and the electrolyte, with the second base film of the separator facing the negative electrode plate.

[0118] 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-shaped pouch. The material of the pouch may be plastic, and may include one or more of, for example, polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0119] 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 cover the opening to seal the storage cavity.

[0120] 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.

[0121] 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, they may be arranged in any other manner. Furthermore, the plurality of secondary batteries 5 may be fixed by fasteners.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] In any embodiment of the present application, the second base film of the separator faces the positive electrode plate, and the second base film has good swelling properties and faces the positive electrode, thereby reducing the possibility of thermal breakdown and improving the reliability of the secondary battery.

[0126] [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 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.

[0127] The device may select a battery cell, a battery module, or a battery pack based on its usage needs.

[0128] 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.

[0129] 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.

[0130] The beneficial effects of the present application will be further explained below in conjunction with examples.

[0131] In order to clarify the technical problems, technical solutions, and beneficial effects solved by the embodiments of the present application, the following will be described in more detail in conjunction with the embodiments and drawings. Obviously, the described embodiments are only some of the embodiments of the present application, and not all of the embodiments. The following 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.

[0132] 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, followed by drying, cold pressing, slitting, and cutting to obtain a positive electrode plate.

[0133] 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.

[0134] 3. Separator manufacturing (1) A first base film is prepared, the material of which contains polypropylene (PP), has a melting point of 165°C, and has a swelling rate of 0.01%.

[0135] (2) A second base film is prepared, the material of which contains polyethylene (PE), has a melting point of 135°C, and has a swelling rate of 8%.

[0136] (3) Preparation of slurry for adhesive layer: 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 a slurry for adhesive layer.

[0137] (4) The adhesive layer slurry from step (3) 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.

[0138] 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. Thoroughly dried electrolyte salt LiPF6 was dissolved in the mixed solvent, and the concentration of the electrolyte salt was 1.0 mol / L. After uniform mixing, an electrolyte solution was obtained.

[0139] 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 separate them, 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 a dried case. The secondary battery is obtained through vacuum packaging, standing, chemical formation, and shaping processes.

[0140] The secondary batteries of Examples 2-17 and Comparative Examples 1-6 were manufactured using methods similar to that of the secondary battery of Example 1, except that different separators were used. See Table 1 for details.

[0141] 2. Performance test 1. Heat shrinkage rate of separator (250℃) Sample preparation: The separator prepared above was punched into samples with a width of 50 mm and a length of 100 mm using a press, and five identical samples were placed on A4 paper and fixed in place. The A4 paper containing the samples was then placed on a cardboard box with a thickness of 1 mm to 5 mm.

[0142] Sample test: Place an A4 sheet of paper on a piece of cardboard and place it in a ventilated oven. Set the oven temperature to 250°C. After the temperature reaches the set temperature and stabilizes for 30 minutes, start timing. After the set time (1 hour in this application) is reached, measure the width of the separator and mark the value as a.

[0143] Transverse direction (TD) heat shrinkage rate = [(50-a) / 50] x 100%, and the average value of five identical samples is taken as the test result.

[0144] 2. Battery cycle life At 25°C, the batteries of the above examples and comparative examples were charged at a constant current of 1 C until the voltage reached 3.65 V, then charged at a constant voltage of 3.65 V until the current was ≦0.05 C, and then discharged at a constant current of 1 C until the voltage reached 2.5 V. This constitutes one charge / discharge process, and the discharge capacity at this stage is 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.

[0145] [Table 1] TIFF2025537247000003.tif255104

[0146] As can be seen from Table 1, in Examples 1 to 17, the melting point of the first base film is higher than that of the second base film, and at the same time, the swelling ratio of the first base film is lower than that of the second base film, and the batteries produced thereby have good cycle life. On the other hand, the separators used in Comparative Examples 1 to 6 do not meet the design requirements of this application, and the batteries produced thereby have poor cycle life. Therefore, by using the separators specified in this application, the reliability of the resulting batteries is higher.

[0147] 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 of the present application, and all such equivalent 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 equivalent to the scope of protection of the claims.

Claims

1. A separator, a first base film; a second base film having a melting point lower than that of the first base film, wherein the swelling ratio of the first base film is lower than that of the second base film.

2. 2. The separator according to claim 1, wherein the ratio of the swelling ratio of the first base film to the swelling ratio of the second base film is 0.8 or less, and optionally 0.3 or less.

3. The swelling ratio of the first base film is 5% or less, optionally 0.2%-2%, and / or The separator according to claim 1 or 2, wherein the swelling ratio of the second base film is 10% or less, and optionally 1%-8%.

4. The separator according to claim 1 , wherein the crystallinity of the first base film is lower than the crystallinity of the second base film.

5. 5. The separator according to claim 1, wherein the ratio of the crystallinity of the first base film to the crystallinity of the second base film is 0.4-0.85, and optionally 0.4-0.

6.

6. The crystallinity of the first base film is 40%-60%, optionally 45%-50%, and / or The separator according to any one of claims 1 to 5, wherein the crystallinity of the second base film is 45%-85%, and optionally 65%-80%.

7. The separator according to claim 1 , wherein the degree of branching of the first base film is greater than the degree of branching of the second base film.

8. The degree of branching of the first base film is 0.4-0.9, optionally 0.7-0.9; and / or The separator according to any one of claims 1 to 7, wherein the degree of branching of the second base film is 0.01-0.4, and optionally 0.01-0.

2.

9. the melting point of the first base film is 155°C-365°C, optionally 160°C-340°C; and / or The separator according to any one of claims 1 to 8, wherein the melting point of the second base film is 130°C-250°C, optionally 135°C-220°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. 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; and / or 12. The separator of claim 11, wherein the filler comprises at least one of inorganic particles, organic particles, and an organic-metallic frame material.

13. The separator has an air permeability of 400 s / 100 cc or less, optionally 250 s / 100 cc-320 s / 100 cc; and / or The separator has a transverse tensile strength of 1500-4500 kgf / cm ２ and optionally 3000-4500 kgf / cm ２ and The longitudinal tensile strength of the separator is 1500-4500 kgf / cm ２ and optionally 3000-4500 kgf / cm ２ and The separator has a transverse heat shrinkage of 0.4% or less, optionally 0.2% or less at 250°C for 1 hour, and / or The separator according to claim 1 , wherein the separator has a longitudinal heat shrinkage rate of 0.4% or less, and optionally 0.2% or less, at 250° C. for 1 hour.

14. 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 lower than the melting point of the first base film, and the swelling ratio of the first base film is lower than the swelling ratio of the second base film; and combining the first base film and the second base film to obtain the separator.

15. The method comprises: 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 to form an adhesive layer, Optionally, the adhesive layer slurry further comprises a filler, and optionally, the filler comprises at least one of inorganic particles, organic particles, and an organic-metallic frame material.

16. A secondary battery comprising the separator according to any one of claims 1 to 13 or a separator produced by the method of claim 14 or 15.

17. 17. The secondary battery of claim 16, wherein the secondary battery further includes a positive electrode plate and a negative electrode plate, the separator is disposed between the positive electrode plate and the negative electrode plate, and the second base film faces the negative electrode plate.

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

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