Isolating membrane and preparation method thereof, secondary battery and electric device

Abstract

The invention provides an isolating membrane which comprises a first base membrane and a second base membrane, and the melting point of the second base membrane is smaller than that of the first base membrane; the swelling ratio of the first base membrane is smaller than that of the second base membrane. Through mutual cooperation of the two layers of base membrane structures, even if one layer of base membrane loses insulation performance due to swelling in an application environment of the isolating membrane, the other layer of base membrane can play a role in supplementing performance, so that the risk of electrode short circuit is reduced, the strength of the isolating membrane is improved, and the reliability of a battery in a long-term service life process is further improved.

Description

Separator and preparation method thereof, secondary battery and electric device Technical Field

[0001] The present application belongs to the technical field of secondary batteries, and specifically relates to an isolation membrane and a preparation method thereof, a secondary battery, and an electrical device. Background Art

[0002] Secondary batteries are widely used in various consumer electronic products and electric vehicles due to their outstanding features of light weight, no pollution and no memory effect.

[0003] With the continuous development of the new energy industry, users have placed higher demands on secondary batteries. However, during battery use, there is a risk of electrode short circuit failure, which challenges the reliability of secondary batteries.

[0004] Summary of the Invention

[0005] In view of the technical problems existing in the background technology, the present application provides an isolation membrane and a preparation method thereof, a secondary battery and an electrical device, aiming to improve the reliability of the isolation membrane and the secondary battery.

[0006] In order to achieve the above-mentioned purpose, the first aspect of the present application provides an isolation film, which includes a first base film and a second base film, the melting point of the second base film is lower than the melting point of the first base film; the swelling rate of the first base film is lower than the swelling rate of the second base film.

[0007] Compared with the prior art, the present application has at least the following beneficial effects: through the mutual cooperation of the two-layer base film structure, the isolation membrane can be used in the application environment for a long time. Even if one layer of the base film loses its insulating properties due to swelling, the other layer of the base film can also play a role in supplementing the performance, reducing the risk of electrode short circuit, and at the same time can improve the strength of the diaphragm, thereby improving the reliability of the battery in the long life process.

[0008] In any embodiment of the present application, the ratio of the swelling rate of the first base film to the swelling rate of the second base film is less than or equal to 0.8, and can be optionally less than or equal to 0.3.

[0009] When the ratio of the swelling rate of the first base film to the swelling rate of the second base film is within the given range, the isolation membrane can be used in the application environment for a long time. Even if one base film loses its insulating properties due to swelling, the other base film can also play a role in supplementing the performance, reducing the risk of electrode short circuit. At the same time, it can increase the strength of the separator, thereby improving the reliability of the battery over the long life.

[0010] In any embodiment of the present application, the swelling rate of the first base film is less than or equal to 5%, and may be 0.2%-2%; the swelling rate of the second base film is less than or equal to 10%, and may be 1-8%.

[0011] When the swelling rate of the first base film and the swelling rate of the second base film are respectively within the given ranges, the isolation membrane can be used in the application environment for a long time. Even if one layer of the base film loses its insulating properties due to swelling, the other layer of the base film can also play a role in supplementing the performance, reducing the risk of electrode short circuit, and at the same time can increase the strength of the separator, thereby improving the reliability of the battery over the long life.

[0012] In any embodiment of the present application, the crystallinity of the first base film is lower than the crystallinity of the second base film.

[0013] 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 can be optionally 0.4-0.6.

[0014] In any embodiment of the present application, the crystallinity of the first base film is 40%-60%, and can be optionally 45%-50%; the crystallinity of the second base film is 45%-85%, and can be optionally 65%-80%.

[0015] 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.

[0016] 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; the degree of branching of the second base film is 0.01-0.4, optionally 0.01-0.2.

[0017] Crystallinity reflects, to a certain extent, the orderliness of the material structure. Higher crystallinity results in an ordered structure, making it less susceptible to swelling, meaning its swelling rate decreases. In contrast to the ordered structure of crystallinity, branching reflects the extent to which nonlinear polymeric structures are added to the material's backbone. Higher branching results in more and more complex side chains, making the material more susceptible to swelling, meaning its swelling rate increases. By regulating the crystallinity of the first base film to be lower than that of the second base film, and the branching of the first base film to be greater than that of the second base film, and keeping these values ​​within the aforementioned range, the swelling rates of the first and second base films can be balanced, and both the first and second base films can have good strength while maintaining sufficient swelling capacity, further improving the reliability of the secondary battery.

[0018] In any embodiment of the present application, the melting point of the first base film is 155°C-365°C, and can be optionally 160°C-340°C; the melting point of the second base film is 130°C-250°C, and can be optionally 135°C-220°C.

[0019] When the degrees Celsius melting point of the first base film and the degrees Celsius melting point of the second base film meet the above conditions, the first base film with a high melting point supplements the heat resistance, and the second base film with a low melting point supplements the swelling performance, so that the isolation membrane enhances the heat resistance in the battery environment and reduces the degree of swelling, thereby improving the reliability of the battery and extending its service life.

[0020] 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 fluoride and their derivatives, polyvinylidene fluoride and their derivatives, and polyethylene terephthalate and its derivatives. Using at least one of the above materials as the first and second base films can ensure that the first and second base films have good chemical stability, while also ensuring that the isolation film has low swelling and high strength.

[0021] 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 includes an adhesive; alternatively, the adhesive layer includes an adhesive and a filler. The provision of the adhesive layer not only compensates for process defects during the base film lamination process but also further improves the physical properties of the separator, thereby enhancing the reliability of the secondary battery.

[0022] In any embodiment of the present application, the adhesive includes one or more of polyacrylate, polyacrylic acid, polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride-trichloroethylene copolymer, polyvinyl pyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyethylene oxide, polyarylate, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, polyacrylonitrile, polyvinyl alcohol, polyethylene, polypropylene, starch, and cyanoethyl pullulan.

[0023] In any embodiment of the present application, the filler includes at least one of inorganic particles, organic particles, and organic-metal framework materials.

[0024] In any embodiment of the present application, the air permeability of the isolation membrane is less than or equal to 400s / 100cc, and can be optionally 250s / 100cc-320s / 100cc.

[0025] In any embodiment of the present application, the transverse tensile strength of the separator is 1500-4500 kgf / cm 2 , optional 3000-4500kgf / cm 2 .

[0026] In any embodiment of the present application, the longitudinal tensile strength of the separator is 1500-4500 kgf / cm 2 , optional 3000-4500kgf / cm 2 .

[0027] In any embodiment of the present application, the transverse heat shrinkage rate of the isolation film at 250° C. for 1 hour is less than or equal to 0.4%, and can be optionally less than or equal to 0.2%.

[0028] In any embodiment of the present application, the longitudinal thermal shrinkage rate of the isolation film at 250° C. for 1 hour is less than or equal to 0.4%, and can optionally be less than or equal to 0.2%.

[0029] When at least one of the above items of the separator satisfies the given range, the separator has good physical properties, thereby improving the reliability of the secondary battery.

[0030] A second aspect of the present application provides a method for preparing an isolation membrane. The method comprises: providing a first base membrane and a second base membrane, wherein the second base membrane has a melting point lower than that of the first base membrane, and the swelling rate of the first base membrane is lower than that of the second base membrane; and then laminating the first base membrane and the second base membrane to obtain an isolation membrane.

[0031] In any embodiment of the present application, the method further includes providing an adhesive layer slurry, wherein the adhesive layer slurry includes an adhesive and coating the adhesive layer slurry on the first base film and / or the second base film to form an adhesive layer.

[0032] In any embodiment of the present application, the bonding layer slurry further includes a filler; optionally, the filler includes at least one of inorganic particles, organic particles, and an organic-metal framework material. When the bonding layer slurry further includes a filler, and the filler includes at least one of the above materials, the physical properties of the separator can be further improved, thereby enhancing the reliability of the secondary battery.

[0033] The third aspect of the present application provides a secondary battery comprising the separator of the first aspect of the present application or the separator prepared according to the method of the second aspect of the present application. When the secondary battery uses the separator, the reliability of the secondary battery can be improved.

[0034] In any embodiment of the present application, it also includes a positive electrode sheet and a negative electrode sheet, and the isolation membrane is arranged between the positive electrode sheet and the negative electrode sheet, and the second base membrane faces the negative electrode sheet, so that the second base membrane facing the negative electrode sheet can supplement the swelling performance, and can make the physical properties of the isolation membrane more stable. In a long-term battery application environment, even if the first base membrane loses its insulating performance due to swelling, the second base membrane can also play a role in supplementing the performance to prevent electrode short circuit, while also taking into account the strength of the isolation membrane, thereby improving the reliability and cycle life of the battery in the long-term cycle life process.

[0035] The fourth aspect of the present application provides an electric device comprising the secondary battery of the third aspect of the present application. When the secondary battery of the electric device uses the given separator, the reliability of the electric device can be improved.

[0036] Since the device of the present application includes the secondary battery provided by the present application, it has at least the same advantages as the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] To more clearly illustrate the technical solution of this application, the following is a brief introduction to the drawings used in this application. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without inventive effort.

[0038] FIG1 is a schematic structural diagram of an isolation membrane according to an embodiment of the present application.

[0039] FIG2 is a schematic structural diagram of an isolation membrane according to an embodiment of the present application.

[0040] FIG3 is a schematic flow chart of an embodiment of a method for preparing an isolation membrane of the present application.

[0041] FIG. 4 is a schematic diagram of an embodiment of a secondary battery.

[0042] FIG. 5 is an exploded view of FIG. 4 .

[0043] FIG. 6 is a schematic diagram of an embodiment of a battery module.

[0044] FIG. 7 is a schematic diagram of an embodiment of a battery pack.

[0045] FIG8 is an exploded view of FIG7 .

[0046] FIG. 9 is a schematic diagram of an embodiment of a device using a secondary battery as a power source. DETAILED DESCRIPTION

[0047] The present application will be further described below in conjunction with specific embodiments. It should be understood that these specific embodiments are only used to illustrate the present application and are not used to limit the scope of the present application.

[0048] For the sake of clarity, only some numerical ranges are specifically disclosed herein. However, any lower limit may be combined with any upper limit to form an unspecified range; and any lower limit may be combined with other lower limits to form an unspecified range, and similarly, any upper limit may be combined with any other upper limit to form an unspecified range. In addition, each individually disclosed point or single value may itself serve as a lower limit or upper limit and be combined with any other point or single value, or with other lower limits or upper limits, to form an unspecified range.

[0049] In the description herein, unless otherwise indicated, the term "or" is inclusive. That is, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0050] In the description of this article, it should be noted that, unless otherwise specified, “above” and “below” include the number itself, and “several” in “one or several” means two or more.

[0051] Unless otherwise specified, the terms used in this application have the commonly understood meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the various parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

[0052] secondary batteries

[0053] A secondary battery is a battery that can be recharged to activate the active materials after discharge and continue to be used.

[0054] Typically, a secondary battery consists of a positive electrode, a negative electrode, a separator, and an electrolyte. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The separator is placed between the positive and negative electrodes to provide isolation. The electrolyte conducts ions between the positive and negative electrodes.

[0055] [Isolation film]

[0056] Referring to Figure 1 , an embodiment of the present application provides an isolation film 10 comprising a first base film 11 and a second base film 12. The second base film 12 has a lower melting point than the first base film 11, and the first base film 11 has a lower swelling rate than the second base film 12. The interaction of the two base film structures enables the isolation film to have both good heat resistance and good reliability.

[0057] Without wishing to be limited to any theory, in the specific diaphragm structure of the present application, two base membranes with different swelling rates are selected for compounding, which can make the physical properties of the isolation membrane more stable. In a long-term battery application environment, even if one layer of base membrane loses its insulating performance due to swelling, the other layer of base membrane can also play a role in supplementing the performance to prevent electrode short circuit, while also taking into account the strength of the isolation membrane, thereby improving the reliability and cycle life of the battery in the long-term cycle life process.

[0058] In any embodiment of the present application, the ratio of the swelling rate of the first base film to the swelling rate of the second base film is less than or equal to 0.8, and can be less than or equal to 0.3. For example, the ratio of the swelling rate of the first base film to the swelling rate of the second base film can be 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 rate of the first base film to the swelling rate of the second base film can be selected as 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.

[0059] When the ratio of the swelling rate of the first base film to the swelling rate of the second base film is within the given range, the isolation membrane can be used in the application environment for a long time. Even if one base film loses its insulating properties due to swelling, the other base film can also play a role in supplementing the performance, preventing electrode short circuit, and at the same time improving the strength of the separator, thereby improving the reliability and cycle life of the battery in the long life process.

[0060] In any embodiment of the present application, the swelling rate of the first base film is less than or equal to 5%, and can be selected from 0.2-2%. For example, the swelling rate of the first base film can be selected from 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 rate of the first base film can be selected as 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.

[0061] In any embodiment of the present application, the swelling rate of the second base film is less than or equal to 10%, and can be 1%-8%. For example, the swelling rate of the second base film can be 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 rate of the second base film can be selected as 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.

[0062] When the ratio of the swelling ratio of the first base film to the swelling ratio of the second base film is within the given range, the reliability of the battery over a long cycle life can be further improved.

[0063] The swelling rates of the base films have meanings well known in the art and can be measured using methods known in the art. For example, the following test method can be adopted: take 6 groups of base film parallel samples with a size of 50 mm × 100 mm. Soak the samples in the electrolyte, completely immerse the samples in the electrolyte, and place them in a 70°C environment. Monitor the mass change every 24 hours for seven consecutive days. The rate of increase in the mass of the base film is the swelling rate. Among them, the solvent used in the electrolyte includes ethylene carbonate (EC) and ethyl methyl carbonate (EMC), the mass ratio of which is 30:70, the electrolyte salt is LiPF6, and the concentration of the electrolyte salt is 1.0 mol / L.

[0064] Those skilled in the art will appreciate that the swelling rate of the base film can be adjusted by adjusting the intrinsic parameters of the base film (e.g., one or more of the crystallinity and branching degree of the base film material) and the base film preparation process parameters (e.g., one or more of the stretch ratio and stretching temperature). For example, under the condition that other conditions remain unchanged, the greater the crystallinity of the base film, the smaller the swelling rate; and the greater the branching degree of the base film, the greater the swelling rate. Those skilled in the art can adjust the swelling rate of the base film by known methods within the parameter ranges given in this application, such as adjusting the production process of the base film (controlling the crystallinity, branching degree, etc.), and obtain a base film with the desired swelling rate through a limited number of experiments.

[0065] In any embodiment of the present application, the crystallinity of the first base film is lower than the crystallinity of the second base film.

[0066] In some optional 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 can be 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 can be 0.4-0.5, 0.5-0.7, 0.7-0.85, etc.

[0067] In some optional embodiments, the crystallinity of the first base film may be 40%-60%, or 45%-50%. The crystallinity of the first base film may be specifically 40%, 42%, 46%, 49%, 51%, 52%, 54%, 57%, 59%, 60%, or the like, or a range consisting of any two of the above values. For example, the crystallinity of the first base film may be specifically 40%-42%, 42%-49%, 49%-52%, 52%-57%, 57%-60%, or the like. The crystallinity of the second base film may be 45%-85%, or 65%-80%. The crystallinity of the second base film may be specifically 45%, 46%, 49%, 54%, 61%, 66%, 74%, 77%, 81%, 84%, 85%, or the like, or a range consisting of any two of the above values. For example, the crystallinity of the second base film can be specifically selected to be 45%-46%, 46%-54%, 54%-66%, 74%-77%, 81%-85%, etc.

[0068] The crystallinity reflects the orderliness of the material structure to a certain extent. As the crystallinity increases, the material structure becomes more orderly and less prone to swelling, that is, the swelling rate becomes smaller. By adjusting the crystallinity of the first base film and the crystallinity of the second base film to be selected within the above ranges, the swelling rates of the first base film and the second base film can be adjusted to better complement the performance of the first base film and the second base film. 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 to be selected within the above ranges, the first base film and the second base film can have good strength while meeting the swelling requirements of this application, thereby improving the reliability of the secondary battery over the long life cycle.

[0069] The crystallinity of the base film has a well-known meaning in the art and can be tested using equipment 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 testing method can be adopted: 4-6 mg of the base film sample to be tested is placed in the sample chamber of a differential scanning calorimeter. The temperature is raised from 25°C to 350°C at a heating rate of 10°C / min. A melting endotherm curve is obtained. The crystallinity can be obtained by calculating the peak area of ​​the curve relative to a reference value of 100% crystalline polyolefin.

[0070] 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.

[0071] 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; the degree of branching of the second base film is 0.01-0.4, optionally 0.01-0.2. For example, the degree of branching of the first base film is 0.4, 0.5, 0.6, 0.7, 0.75, 0.78, 0.8, 0.9. Or a range consisting of any two of the above values. For example, the degree of branching of the first base film is 0.4-0.6, 0.6-0.75, 0.75-0.78, 0.78-0.9. The degree of branching of the second base film can be 0.01, 0.03, 0.09, 0.14, 0.18, 0.25, 0.33, 0.38, 0.4, etc. Or a range consisting of any two of the above values. For example, the degree of branching of the second base film can be selected to be 0.01-0.03, 0.03-0.14, 0.14-0.25, 0.25-0.4, etc.

[0072] In contrast to the ordered structure of crystallinity, the degree of branching is the degree of adding branches of nonlinear polymer structure to the main chain of the base film material, that is, the higher the degree of branching, the more and more complex the side chains formed. The higher the degree of branching, the greater the swelling rate. By selecting the ratio of the degree of branching of the first base film and the second base film within the above range, the swelling rate of the first base film and the second base film can be adjusted to make the performance of the first base film and the second base film better complementary. Furthermore, the degree of crystallinity will also affect the swelling rate of the material. By combining the regulation of the degree of branching and the degree of crystallinity within the above range, the first base film and the second base film can also have good strength while meeting the swelling requirements of this application, thereby improving the reliability of the secondary battery during its long life.

[0073] The degree of branching of the base film has a well-known meaning in the art and can be tested using equipment and methods known in the art. For example, infrared spectroscopy can be used. Specifically, the following steps can be followed: 3-5 groups of base film samples are selected and placed in an infrared spectrometer for scanning in the range of 400-4000 cm -1 After scanning, the infrared curve of the sample was processed and the 1377cm-1 The peak area at 1996-2062cm -1 The ratio of the peak areas is the degree of branching.

[0074] In some embodiments, the first base film simultaneously satisfies a crystallinity of 45%-50% and a branching degree of 0.7-0.9.

[0075] In some embodiments, the second base film simultaneously satisfies a crystallinity of 65%-80% and a branching degree of 0.01-0.2.

[0076] When the crystallinity and branching degree of the first base film and / or the second base film simultaneously meet the above-mentioned ranges, the two base films can meet the swelling degree designed in this application while also taking into account good strength performance.

[0077] 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; 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 can be 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 can be 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 can be 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, or a range consisting of any two of the above values. For example, the melting point of the second base film can be 130°C-131°C, 131°C-136°C, 145°C-151°C, 163°C-174°C, 174°C-210°C, or 210°C-250°C.

[0078] By adjusting the melting point of the first base film in degrees Celsius and the melting point of the second base film in degrees Celsius to meet the above conditions, the first base film with a high melting point supplements the heat resistance, and the second base film with a low melting point supplements the swelling performance, so that the isolation film has good heat resistance and swelling performance.

[0079] According to some embodiments, the melting points of the first and second base films have meanings generally known in the art and can be measured using methods known in the art. For example, differential scanning calorimetry can be used for measurement. For details, reference can be made to standard GB / T 19466.3-2004. As an example, the measurement can be performed as follows: 4-6 mg of a sample to be tested is placed in the sample chamber of a differential scanning calorimeter. The temperature is raised from 25°C to 400°C at a rate of 10°C / min. The melting endothermic curve of the sample is obtained, and the temperature corresponding to the peak of the curve is the melting point of the sample.

[0080] 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 alcohol and their derivatives, polytetrafluoroethylene and their derivatives, polyvinyl fluoride and their derivatives, polyvinylidene fluoride and their derivatives, polyethylene terephthalate and their derivatives. For example, the first base film can be made of polyolefins and their derivatives or halogenated polyolefins and their derivatives. The first base film can also be made of polyethers and their derivatives, polyetheretherketones and their derivatives, polyesters and their derivatives, etc. The first base film and the second base film can also be made of polyvinylidene fluoride and its derivatives or polyethylene terephthalate, etc. Among them, derivatives generally refer to products derived from the replacement of hydrogen atoms or atomic groups in a compound by other atoms or atomic groups. At least one of the above materials as the first base film and the second base film can improve the chemical stability of the first base film and the second base film, while making the isolation film have lower swelling and higher strength.

[0081] Referring to FIG. 2 , an embodiment of the present application provides a separator 10 comprising a first base film 11 and a second base film 12 . In any embodiment of the present application, an adhesive layer 13 is provided between the first base film 11 and the second base film 12 . The adhesive layer comprises an adhesive. Optionally, the adhesive layer comprises an adhesive and a filler.

[0082] When an adhesive layer is provided between the first and second base films, and the adhesive layer includes an adhesive, it not only compensates for process defects during the hot-pressing lamination of the base films, but also further improves the physical properties of the separator (e.g., tensile strength, puncture strength, heat resistance, etc.), thereby enhancing the reliability of the secondary battery. The filler is located between the first and second base films, thereby reducing the risk of powder loss.

[0083] In any embodiment of the present application, the adhesive includes one or more of polyacrylate, polyacrylic acid, polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride-trichloroethylene copolymer, polyvinyl pyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyethylene oxide, polyarylate, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, polyacrylonitrile, polyvinyl alcohol, polyethylene, polypropylene, starch, and cyanoethyl pullulan.

[0084] In any embodiment of the present application, the filler includes at least one of inorganic particles, organic particles, and organic-metal framework materials.

[0085] Optionally, the inorganic particles include one or more of inorganic particles having a dielectric constant of 5 or greater, inorganic particles having ion conductivity but not storing ions, and inorganic particles capable of undergoing electrochemical reactions.

[0086] Alternatively, the inorganic particles having a dielectric constant of 5 or more may include boehmite, aluminum oxide, zinc oxide, silicon oxide, titanium oxide, zirconium oxide, barium oxide, calcium oxide, magnesium oxide, nickel oxide, tin oxide, cerium oxide, yttrium oxide, hafnium oxide, aluminum hydroxide, magnesium hydroxide, silicon carbide, boron carbide, aluminum nitride, silicon nitride, boron nitride, magnesium fluoride, calcium fluoride, barium fluoride, barium sulfate, magnesium aluminum silicate, lithium magnesium silicate, sodium magnesium silicate, bentonite, hectorite, zirconium titanate, barium titanate, Pb(Zr,Ti)O3 (abbreviated as PZT), Pb1-mLamZr1-nTinO3 (abbreviated as PLZT, 0<m<1, 0<n<1), Pb(Mg3Nb 2 / 3 )O3-PbTiO3 (abbreviated as PMN-PT), and at least one of their respective modified inorganic particles. Optionally, the modification method of each inorganic particle may be chemical modification and / or physical modification. The chemical modification method includes coupling agent modification (for example, using silane coupling agent, titanate coupling agent, etc.), surfactant modification, polymer grafting modification, etc. The physical modification method may be mechanical force dispersion, ultrasonic dispersion, high energy treatment, etc. The modification treatment can reduce the agglomeration of inorganic particles, thereby enabling the adhesive layer to have a more stable and uniform structure; in addition, by selecting a coupling agent, surfactant or polymer with a specific functional group to modify the inorganic particles, it is also helpful to improve the wetting and retention properties of the adhesive layer to the electrolyte, and improve the adhesion of the adhesive layer to the first base film and the second base film.

[0087] Alternatively, the inorganic particles having ion conductivity but not storing ions may include Li3PO4, lithium titanium phosphate Li x1 Ti y1 (PO4)3, lithium aluminum titanium phosphate Li x2 Al y2 Tiz1 (PO4)3, (LiAlTiP) x3 O y3 Type glass, lanthanum lithium titanate Li x4 La y4 TiO3, lithium germanium thiophosphate Li x5 Ge y5 P z2 S w , lithium nitride Li x6 N y6 、SiS2 type glass Li x7 Si y7 S z3 and P2S5 glass Li x8 P y8 S z4 At least one of the following: 0<x1<2, 0<y1<3, 0<x2<2, 0<y2<1, 0<z1<3, 0<x3<4, 0<y3<13, 0<x4<2, 0<y4<3, 0<x5<4, 0<y5<1, 0<z2<1, 0<w<5, 0<x6<4, 0<y6<2, 0<x7<3, 0<y7<2, 0<z3<4, 0<x8<3, 0<y8<3, 0<z4<7. This can further improve the ion conductivity of the isolation membrane.

[0088] Alternatively, the inorganic particles capable of undergoing electrochemical reaction may include at least one of lithium-containing transition metal oxides, lithium-containing phosphates, carbon-based materials, silicon-based materials, tin-based materials, and lithium-titanium compounds.

[0089] Alternatively, the organic particles may include one or more of polycarbonate, polythiophene, polypyridine, polystyrene, polyacrylic wax, polyethylene, polypropylene, cellulose, a cellulose modifier (e.g., carboxymethyl cellulose), a melamine resin, a phenolic resin, a polyester (e.g., polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate), a silicone resin, a polyimide, a polyamideimide, a polyaromatic amide, polyphenylene sulfide, a polysulfone, a polyethersulfone, a polyetheretherketone, a polyaryletherketone, a copolymer of butyl acrylate and ethyl methacrylate (e.g., a cross-linked polymer of butyl acrylate and ethyl methacrylate).

[0090] Optionally, the organic-metal framework material may include one or more of a nitrogen-containing heterocyclic ligand building structure, an organic carboxylic acid ligand building structure, and a nitrogen-oxygen mixed ligand building structure.

[0091] In some embodiments, the content of the adhesive may be greater than or equal to 10%, optionally 10%-30%, based on the total weight of the adhesive layer.

[0092] In some embodiments, the content of the filler may be less than or equal to 90%, optionally 40%-90%, 60%-80%, based on the total weight of the adhesive layer.

[0093] In some embodiments, the adhesive layer may further include a dispersant, such as carboxymethyl cellulose, to adjust the viscosity of the adhesive layer slurry and improve the quality and uniformity of the adhesive layer.

[0094] In some embodiments, the content of the dispersant may be less than or equal to 25%, optionally less than or equal to 20%, based on the total weight of the adhesive layer.

[0095] The thickness of the adhesive layer is greater than or equal to 0.3 μm, and can be optionally 0.5-4 μm.

[0096] According to some embodiments, the adhesive layer thickness can be tested using equipment and methods known in the art. Specifically, a scanning electron microscope (SEM) image of a cross-section of the separator can be obtained using a scanning electron microscope (e.g., a ZEISS Sigma 300) in accordance with JY / T010-1996. As an example, the following method can be used to test the thickness of the coating: randomly select multiple areas on the cross-section of the separator and measure the coating thickness at least five times at a specific magnification. The measured values ​​for the different areas are then tallied and the average value is taken as the adhesive layer thickness.

[0097] In any embodiment of the present application, the air permeability of the isolation membrane is less than or equal to 400s / 100cc, and can be 250s / 100cc-320s / 100cc; the transverse tensile strength of the isolation membrane is 1500-4500kgf / cm 2 , optional 3000-4500kgf / cm 2 ; The longitudinal tensile strength of the isolation film is 1500-4500kgf / cm 2 , optional 3000-4500kgf / cm 2 The separator's transverse thermal shrinkage at 250°C for 1 hour is 0-0.4%, optionally 0%-0.2%. The separator's longitudinal thermal shrinkage at 250°C for 1 hour is 0-0.4%, optionally 0-0.2%. For example, in one embodiment, the separator's air permeability can be 260s / 100cc; the separator's transverse thermal shrinkage at 250°C for 1 hour can be 0.4%, and the separator's longitudinal thermal shrinkage at 250°C for 1 hour can be 0.15%. When at least one of the above items of the separator meets the given range, the separator has excellent heat resistance and physical properties, thereby improving the reliability of the secondary battery.

[0098] According to some embodiments, the air permeability, transverse tensile strength, longitudinal tensile strength, transverse heat shrinkage, and longitudinal heat shrinkage of the first and second base films have well-known meanings in the art and can be tested using equipment and methods known in the art. For example, the tests can be performed in accordance with standard GB / T 36363-2018.

[0099] [Method for preparing isolation film]

[0100] The present application also provides a method for preparing the isolation film provided in the embodiments of the present application, the method comprising: providing a first base film and a second base film, and compounding the first base film and the second base film to obtain the isolation film according to any of the above embodiments. The melting point of the second base film is lower than the melting point of the first base film, and the swelling rate of the first base film is lower than the swelling rate of the second base film.

[0101] Referring to FIG3 , an embodiment of the present application provides a method for preparing an isolation membrane. The method comprises the following steps:

[0102] S100: providing 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.

[0103] S200: Providing an adhesive layer slurry, the adhesive layer slurry including an adhesive. Optionally, the adhesive layer slurry includes an adhesive and a filler. Providing an adhesive layer between the first and second base films not only compensates for process defects during the overheating and pressing lamination process but also further improves the heat resistance and physical properties of the separator, thereby enhancing the reliability of the secondary battery.

[0104] S300: Applying an adhesive layer slurry 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 only to one surface of the first base film or the second base film; or the adhesive layer slurry may be applied to both the first base film and the second base film to form an adhesive layer.

[0105] S400: The first base film and the second base film are laminated to obtain the isolation film of any of the above embodiments. The first base film and the second base film can be laminated by hot pressing. During the hot pressing process, if the temperature is too high, the porosity will be small and the air permeability will be poor; if the temperature is too low, the first base film and the second base film will not be firmly bonded. Therefore, it is necessary to adjust the hot pressing temperature appropriately. Optionally, the hot pressing temperature is 20°C-50°C.

[0106] Unless otherwise specified, all raw materials used in the method for preparing the separator (eg, the first base film, the second base film, the adhesive, the filler, etc.) can be purchased commercially.

[0107] [Positive electrode]

[0108] In a secondary battery, a positive electrode sheet generally includes a positive electrode current collector and a positive electrode film layer disposed on the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0109] The positive electrode current collector may be a conventional metal foil or a composite current collector (a metal material may be disposed on a polymer substrate to form a composite current collector). As an example, the positive electrode current collector may be an aluminum foil.

[0110] There is no limitation on the specific type of the positive electrode active material. Active materials known in the art that can be used for the positive electrode of a secondary battery can be used. Those skilled in the art can select according to actual needs.

[0111] As an example, the positive electrode active material may include, but is not limited to, one or more of lithium transition metal oxides, olivine-structured lithium-containing phosphates, and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon, and their modified compounds. These materials can all be obtained through commercial channels.

[0112] The modified compounds of the above materials may be doping-modified and / or surface-coated modified materials.

[0113] The positive electrode film layer usually optionally includes a binder, a conductive agent and other optional additives.

[0114] As an example, the conductive agent may be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, conductive carbon black (Super P, SP), graphene, and carbon nanofibers.

[0115] As an example, the adhesive can be one or more of styrene butadiene rubber (SBR), water based acrylic resin, polyvinylidene difluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA) and polyvinyl butyral (PVB).

[0116] [Negative electrode]

[0117] In a secondary battery, a negative electrode sheet generally includes a negative electrode current collector and a negative electrode film layer disposed on the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0118] The negative electrode current collector may be a conventional metal foil or a composite current collector (for example, a metal material may be disposed on a polymer substrate to form a composite current collector). As an example, the negative electrode current collector may be a copper foil.

[0119] The specific type of negative electrode active material is not limited, and active materials that can be used for the negative electrode of a secondary battery known in the art can be used, and those skilled in the art can make a selection according to actual needs. As an example, the negative electrode active material may include, but is not limited to, one or more of artificial graphite, natural graphite, hard carbon, soft carbon, silicon-based materials and tin-based materials. The silicon-based material may be selected from one or more of elemental silicon, silicon oxide compounds (such as silicon monoxide), silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from one or more of elemental tin, tin oxide compounds, and tin alloys. These materials can all be obtained commercially.

[0120] In some embodiments, to further increase the energy density of the battery, the negative electrode active material may include a silicon-based material.

[0121] The negative electrode film layer usually optionally includes a binder, a conductive agent and other optional additives.

[0122] As an example, the conductive agent may be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0123] As an 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).

[0124] As an example, other optional auxiliary agents may be thickening and dispersing agents (such as carboxymethylcellulose sodium, CMC-Na), and PTC thermistor materials.

[0125] [Electrolyte]

[0126] Secondary batteries may include an electrolyte that conducts ions between a positive electrode and a negative electrode. The electrolyte may include an electrolyte salt and a solvent.

[0127] As an example, the electrolyte salt can be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalatophosphate) (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0128] As an example, the solvent may be selected from ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl darbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), n-propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), n-propyl propionate (NP), propylene glycol (PEG), propylene glycol (PP), propylene glycol (C1), propylene glycol (C2), propylene glycol (C3), propylene glycol (C4), propylene glycol (C5), propylene glycol (C6), propylene glycol (C7), propylene glycol (C8), propylene glycol (C9), propylene glycol (D1), propylene glycol (D2), propylene glycol (D3), propylene glycol (D4), propylene glycol (D5), propylene glycol (D6), propylene glycol (D7), propylene glycol (D8), propylene glycol (D9), propylene glycol (D10), propylene glycol (D11), propylene glycol (D12), propylene glycol (D13), propylene glycol (D14), propylene glycol (D15), propylene glycol (D16), propylene glycol (D17), propylene glycol (D18), propylene glycol (D19), propylene glycol (D20), propylene glycol (D21), propylene glycol (D22), propylene glycol (D23), propylene glycol (D24), propylene glycol (D25), propylene glycol (D26), propylene glycol (D27), propylene glycol (D28), propylene glycol (D29), propylene glycol (D31), propylene glycol (D32), propylene glycol (D33), propylene glycol (D34), propylene glycol (D35), propylene glycol (D36), propylene glycol (D37), propylene glycol (D38), propylene glycol (D39), propylene One or more of the group consisting of propionate (PP), methyl butyrate (Methyl Butyrate MB), ethyl butyrate (Ethyl Butyrate, EB), 1,4-butyrolactone (1,4-Butyrolactone, GBL), tetramethylene sulfone (SF), dimethyl sulfone (Methyl Sulfone, MSM), methyl ethyl sulfone (Methyl Ethyl Sulfone, EMS) and diethyl sulfone (Diethyl Sulfone, ESE).

[0129] In some embodiments, the electrolyte further includes additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives capable of improving certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature performance.

[0130] In some embodiments, the secondary battery may be a lithium-ion secondary battery.

[0131] In any embodiment of the present application, the second base film of the separator faces the negative electrode. The second base film faces the negative electrode, so that the second base film facing the negative electrode can supplement the swelling performance, making the physical properties of the separator more stable. In a long-term battery application environment, even if the first base film loses its insulating properties due to swelling, the second base film can still play a role in supplementing the performance and preventing electrode short circuits. At the same time, it also takes into account the strength of the separator, thereby improving the reliability and cycle life of the battery over the long cycle life.

[0132] Through the mutual cooperation of the two-layer base membrane structure, namely the first base membrane and the second base membrane, and the swelling rate of the first base membrane is smaller than that of the second base membrane, in the long-term application environment of the isolation membrane, even if one layer of the base membrane loses its insulating performance due to swelling, the other layer of the base membrane can also play a role in supplementing the performance, reducing the risk of electrode short circuit, and at the same time improving the strength of the separator, thereby improving the reliability of the battery in the long-term life process.

[0133] The embodiment of the present application has no particular limitation on the shape of the secondary battery, which can be cylindrical, square, or any other shape. FIG4 shows a secondary battery 5 with a square structure as an example.

[0134] In some embodiments, the secondary battery may include an outer package for encapsulating a positive electrode sheet, a negative electrode sheet, and an electrolyte, wherein the second base film of the separator faces the negative electrode sheet.

[0135] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0136] In some embodiments, referring to FIG5 , the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, which together form a receiving cavity. The housing 51 may have an opening communicating with the receiving cavity, and the cover 53 may be positioned over the opening to seal the receiving cavity.

[0137] The preparation method of the secondary battery of the present application is well known. In some embodiments, the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte can be assembled to form a secondary battery. As an example, the positive electrode sheet, the separator, and the negative electrode sheet can be formed into an electrode assembly through a winding process and / or a lamination process, and the electrode assembly is placed in an outer package, dried and injected with electrolyte, and then vacuum packaged, left to stand, formed, and shaped to obtain a battery cell. Multiple battery cells can also be further connected in series, in parallel, or mixed to form a battery module. Multiple battery modules can also be connected in series, in parallel, or mixed to form a battery pack. In some embodiments, multiple battery cells can also directly form a battery pack.

[0138] Figure 6 shows an example battery module 4. Referring to Figure 6 , within the battery module 4, multiple secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the multiple secondary batteries 5 may be secured using fasteners.

[0139] The battery module 4 may further include a housing having a housing space, and the plurality of secondary batteries 5 may be housed in the housing space.

[0140] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0141] Figures 7 and 8 illustrate an example battery pack 1. Referring to Figures 7 and 8 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be positioned over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0142] In any embodiment of the present application, the second base film of the isolation membrane faces the positive electrode sheet. The second base film has good swelling properties and faces the positive electrode, which can reduce the possibility of thermal breakdown and improve the reliability of the secondary battery.

[0143] [Installation]

[0144] The present application also provides an electrical device, which includes the secondary battery of the present application. The battery cell, battery module, or battery pack can serve as a power source for the device, or as an energy storage unit for the device. The device can be, but is not limited to, a mobile device (e.g., a mobile phone, a laptop computer), an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck), an electric train, a ship, a satellite, or an energy storage system.

[0145] The device can select a battery cell, a battery module or a battery pack according to its usage requirements.

[0146] Figure 9 shows an example of an electric device. This device can be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0147] As another example, an electric device may be a mobile phone, a tablet computer, or a laptop computer. Such an electric device is generally required to be lightweight and thin, and may use a battery cell as a power source.

[0148] The beneficial effects of the present application are further illustrated below with reference to the examples.

[0149] In order to make the technical problems, technical solutions and beneficial effects solved by the embodiments of the present application clearer, the following will be further described in detail with reference to the embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present application and its applications. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0150] 1. Preparation of batteries

[0151] Example 1

[0152] 1. Preparation of positive electrode sheet

[0153] The positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), conductive agent carbon black (SuperP), and adhesive polyvinylidene fluoride (PVDF) are mixed evenly in an appropriate amount of solvent N-methylpyrrolidone (NMP) in a mass ratio of 96.2:2.7:1.1 to obtain positive electrode slurry, which is then coated on the positive electrode current collector aluminum foil, and the positive electrode sheet is obtained through drying, cold pressing, slitting, and cutting processes.

[0154] 2. Preparation of negative electrode sheet

[0155] The negative electrode active material artificial graphite, conductive agent carbon black (SuperP), binder styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC-Na) were mixed uniformly in an appropriate amount of solvent deionized water at a mass ratio of 96.4:0.7:1.8:1.1 to obtain a negative electrode slurry. The negative electrode slurry was coated on the negative electrode current collector copper foil, and the negative electrode sheet was obtained through the processes of drying, cold pressing, slitting and cutting.

[0156] 3. Preparation of isolation membrane

[0157] (1) A first base film is provided, wherein the material includes polypropylene (PP), the melting point is 165° C., and the swelling rate is 0.01%.

[0158] (2) Providing a second base film, the material includes polyethylene (PE), the melting point is 135 ° C, and the swelling rate is 8%.

[0159] (3) Preparation of bonding layer slurry: boehmite, polyacrylate, and carboxymethyl cellulose were mixed evenly in a proper amount of deionized water as a solvent in a ratio of 4:1:1 to prepare bonding layer slurry.

[0160] (4) The adhesive layer slurry of step (3) is coated on the PE base film to form an adhesive layer, and the PP and PE base films are hot-pressed so that the adhesive layer is between the PP base film and the PE base film to prepare an isolation film.

[0161] 4. Preparation of electrolyte

[0162] Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 30:70 to obtain an organic solvent. Fully dried electrolyte salt LiPF6 is dissolved in the above mixed solvent. The concentration of the electrolyte salt is 1.0 mol / L. After mixing evenly, an electrolyte solution is obtained.

[0163] 5. Preparation of secondary batteries

[0164] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive electrode sheet and the negative electrode sheet to serve as an isolation, and then wound to obtain an electrode assembly; the electrode assembly is placed in an outer package, and the prepared electrolyte is injected into the dried shell. After vacuum packaging, standing, formation, and shaping processes, a secondary battery is obtained.

[0165] The secondary batteries of Examples 2-17 and Comparative Examples 1-6 were prepared in a similar manner to the secondary battery of Example 1, except that different separators were used. See Table 1 for details.

[0166] 3. Performance Testing

[0167] 1. Thermal shrinkage of the isolation film (250°C)

[0168] Sample preparation: Punch the prepared isolation film into samples with a width of 50 mm and a length of 100 mm using a punching machine. Place 5 parallel samples on A4 paper and fix them. Then place the A4 paper with the samples on corrugated paper with a thickness of 1 mm to 5 mm.

[0169] Sample test: Place A4 paper on corrugated paper into a blast 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 isolation film. The value is marked as a.

[0170] Transverse direction (TD) thermal shrinkage = [(50-a) / 50] × 100%, and the average value of 5 parallel samples is taken as the test result.

[0171] 2. Battery cycle life

[0172] At 25°C, the batteries of the above examples and comparative examples were charged at a constant current of 1C to a voltage of 3.65V. They were then charged at a constant voltage of 3.65V to a current of ≤0.05C. The batteries were then discharged at a constant current of 1C to a voltage of 2.5V. This constituted one charge and discharge cycle, and the discharge capacity at this point was recorded as the discharge capacity of the battery's first cycle. This charge and discharge cycle was repeated, and the number of cycles required for the capacity to drop to 80% was recorded.

[0173] As shown in Table 1, in Examples 1-17, the melting point of the first base film is greater than that of the second base film; at the same time, the swelling rate of the first base film is less than that of the second base film; and the batteries produced thereby have a long cycle life. In contrast, the separators used in Comparative Examples 1-6 do not meet the design requirements of this application, and the resulting batteries have a poor cycle life. Therefore, using the separators defined in this application results in a more reliable battery.

[0174] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present application, and such modifications or substitutions should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A separation film, comprising: First basement membrane; a second base film, wherein the melting point of the second base film is lower than the melting point of the first base film; The swelling rate of the first base film is smaller than the swelling rate of the second base film.

2. The isolation film according to claim 1, wherein The ratio of the swelling rate of the first base film to the swelling rate of the second base film is less than or equal to 0.8, and can be optionally less than or equal to 0.

3.

3. The isolation film according to claim 1 or 2, wherein: The swelling rate of the first base film is less than or equal to 5%, and can be optionally 0.2%-2%; and / or The swelling rate of the second base film is less than or equal to 10%, and can be optionally 1%-8%.

4. The isolation film according to any one of claims 1 to 3, wherein: The crystallinity of the first base film is lower than that of the second base film.

5. The isolation film according to any one of claims 1 to 4, 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 can be optionally 0.4-0.

6.

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

7. The isolation film according to any one of claims 1 to 6, wherein: The degree of branching of the first base film is greater than the degree of branching of the second base film.

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

2.

9. The isolation film according to any one of claims 1 to 8, wherein: The melting point of the first base film is 155° C.-365° C., and can be 160° C.-340° C.; and / or The melting point of the second base film is 130°C-250°C, and can be optionally 135°C-220°C.

10. The isolation film according to any one of claims 1 to 9, wherein: 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, polytetrafluoroethylene and their derivatives, polyvinyl fluoride and their derivatives, polyvinylidene fluoride and their derivatives, and polyethylene terephthalate and its derivatives.

11. The isolation film according to any one of claims 1 to 10, wherein: An adhesive layer is further provided between the first base film and the second base film, and the adhesive layer includes an adhesive; optionally, the adhesive layer includes an adhesive and a filler.

12. The isolation film according to claim 11, wherein The adhesive includes polyacrylate, polyacrylic acid, polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride-trichloroethylene copolymer, polyvinyl pyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyethylene oxide, polyarylate, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, cellulose acetate, cellulose acetate propionate One or more of cellulose, cellulose acetate butyrate, polyacrylonitrile, polyvinyl alcohol, polyethylene, polypropylene, starch, and cyanoethyl pullulan; and / or The filler includes at least one of inorganic particles, organic particles, and organic-metal framework materials.

13. The isolation film according to any one of claims 1 to 12, wherein: The air permeability of the isolation film is less than or equal to 400s / 100cc, and can be 250s / 100cc-320s / 100cc; and / or, The transverse tensile strength of the isolation film is 1500-4500 kgf / cm 2 , optional 3000-4500kgf / cm 2 ; The longitudinal tensile strength of the isolation film is 1500-4500 kgf / cm 2 , optional 3000-4500kgf / cm 2 ; The transverse heat shrinkage rate of the isolation film at 250° C. for 1 hour is less than or equal to 0.4%, and can be less than or equal to 0.2%; and / or, The longitudinal heat shrinkage rate of the isolation film at 250° C. for 1 hour is less than or equal to 0.4%, and can be optionally less than or equal to 0.2%.

14. A method for preparing an isolation film, wherein: include: 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 rate of the first base film is lower than the swelling rate of the second base film; The first base film and the second base film are compounded to obtain the isolation film.

15. The method for preparing a separator according to claim 14, wherein: The method further comprises: Providing an adhesive layer slurry, wherein the adhesive layer slurry includes an adhesive; Applying the adhesive layer slurry on the first base film and / or the second base film to form an adhesive layer; Optionally, the bonding layer slurry further includes a filler; optionally, the filler includes at least one of inorganic particles, organic particles, and organic-metal framework materials. 16 . A secondary battery comprising the separator according to claim 1 ; or the separator prepared by the method according to claim 14 or 15 .

17. The secondary battery according to claim 16, wherein The secondary battery further includes a positive electrode sheet and a negative electrode sheet, the separator is arranged between the positive electrode sheet and the negative electrode sheet, and the second base film faces the negative electrode sheet.

18. An electrical device comprising the secondary battery according to claim 16 or 17.

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