Separator film and manufacturing method thereof, secondary battery and electric device

Abstract

This application provides a separator film, a manufacturing method thereof, a secondary battery, and an electric device. The separator film includes a first substrate film, a second substrate film, and an intermediate layer positioned between the first substrate film and the second substrate film. The first substrate film has a melting point of 175°C or higher and an average pore size of 0.22 μm or higher. The intermediate layer includes filler particles, at least a portion of which is inserted into the first substrate film.

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims priority from International Application PCT / CN2023 / 085617, filed on March 31, 2023, entitled "Separator film and manufacturing method thereof, secondary battery and electrical device," the entire contents of which are incorporated herein by reference.

[0002] The present application relates to a separator film and a method for producing the same, a secondary battery, and an electric device. [Background technology]

[0003] In recent years, secondary batteries have been widely applied in energy storage power supply systems such as hydroelectric power plants, thermal power plants, wind power plants and solar power plants, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. With the application and widespread use of secondary batteries, the requirements for their reliability are also becoming more stringent. Summary of the Invention

[0004] The present application provides a separator film and a manufacturing method thereof, a secondary battery, and an electric device, in order to improve the safety performance, energy density, and cycle performance of the secondary battery.

[0005] In a first aspect of the present application, there is provided a separator film comprising a first substrate film, a second substrate film, and an intermediate layer positioned between the first substrate film and the second substrate film. The first substrate film has a melting point of 175°C or higher and an average pore size of 0.22 μm or higher. The intermediate layer contains filler particles, at least a portion of which is inserted into the first substrate film.

[0006] Without intending to be bound by any theory or interpretation, when a separator film includes a first base film, a second base film, and an intermediate layer located between the first base film and the second base film, the separator film can have good heat resistance, relatively high mechanical strength, and self-supporting properties. Specifically, by setting the melting point of the first base film to 175°C or higher, the separator film can be provided with good heat resistance. Furthermore, by setting the average pore size of the first substrate film within the above-mentioned appropriate range, an appropriate amount of filler particles can be inserted into the first substrate film to form a composite structure between the first substrate film and the filler particles, thereby effectively improving the mechanical strength, self-supporting ability, and heat resistance of the separator film. In addition, after the filler particles are inserted into the substrate film, the overall thickness of the separator film can be reduced, thereby further improving the energy density of the battery. In addition, a specific pore size range allows the filler particles to be better inserted into the first substrate film, reducing the probability of filler particles falling off in the intermediate layer, thereby further improving the reliability of the separator film and improving the cycle performance of the battery.

[0007] Therefore, the separator film provided by the present application can simultaneously achieve relatively good safety performance, relatively high energy density, and good cycle performance of the secondary battery.

[0008] In any embodiment of the present application, the average pore size of the first substrate film is 0.22 μm to 4.0 μm, and optionally 1.0 μm to 2.7 μm.

[0009] By adjusting the average pore size of the first substrate film to satisfy the above range, it is advantageous for the filler particles to be inserted into the first substrate film to form a suitable composite structure separator film, which has a relatively thin thickness while also having excellent breathability and relatively high strength. In this way, applying the separator film to a secondary battery is advantageous for improving the energy density and cycle performance of the secondary battery.

[0010] In any embodiment of the present application, the average pore size of the second substrate film is smaller than the average pore size of the first substrate film.

[0011] Preferably, the average pore size of the second substrate film is 0.01 μm to 0.5 μm, more preferably 0.02 μm to 0.1 μm.

[0012] By adjusting the average pore size of the second substrate film to satisfy the above range, the second substrate film can have high mechanical strength, high puncture strength, and appropriate permeability, thereby further improving the reliability of the secondary battery.

[0013] In any embodiment of the present application, the insertion depth of the filler particles into the first substrate film is 0.2 μm or more, and optionally 0.5 μm to 1.0 μm.

[0014] When the insertion depth of the filler particles into the first base film satisfies the above range, the mechanical strength and self-supporting ability of the composite structure formed by the filler particles and the first base film can be effectively improved, and the overall thickness of the separator film can be reduced, which is advantageous for improving the reliability and energy density of the secondary battery.

[0015] In any embodiment of the present application, the insertion depth of the filler particles into the second substrate film is 0.1 μm or more, and optionally 0.1 μm to 0.5 μm.

[0016] When the insertion depth of the filler particles into the second substrate film satisfies the above range, the structural stability of the separator film can be improved, and the separator film can be provided with good breathability and strength, which is advantageous for further improving the safety and electrochemical performance of the secondary battery.

[0017] In any embodiment of the present application, the insertion depth of the filler particles into the first substrate film is greater than the insertion depth of the filler particles into the second substrate film, thereby providing a separator film with high structural stability and good breathability, thereby improving the reliability and electrochemical performance of the secondary battery.

[0018] In any embodiment of the present application, the melting point of the first substrate film is equal to or greater than the melting point of the second substrate film.

[0019] Preferably, the melting point of the first base film is 175°C to 350°C, more preferably 220°C to 350°C.

[0020] Preferably, the melting point of the second substrate film is 130°C to 200°C, more preferably 135°C to 180°C.

[0021] By adjusting the melting point of the first substrate film and / or the second substrate film within the above-mentioned appropriate range, the separator film can have not only good heat resistance but also good closed-cell properties, thereby allowing the secondary battery to have both good cycle performance and high reliability.

[0022] In any embodiment of the present application, the longitudinal elongation at break of the first base film is 20% to 105%, and optionally 40% to 90%.

[0023] In any embodiment of the present application, the transverse elongation at break of the first substrate film is 20% to 105%, and optionally 40% to 90%.

[0024] By adjusting the longitudinal and / or transverse elongation at break of the first substrate film to satisfy the above range, the first substrate film has an appropriate average pore size, which is advantageous for the filler particles to be inserted into the first substrate film to form an appropriate composite structure, which is advantageous for improving the heat resistance and mechanical strength of the separator film, and thus for improving the reliability of the secondary battery.

[0025] In any embodiment of the present application, the elongation at break in the machine direction of the second base film is smaller than the elongation at break in the cross direction of the second base film.

[0026] In any embodiment of the present application, the longitudinal elongation at break of the second substrate film is ≧40%, and optionally 60% to 150%.

[0027] In any embodiment of the present application, the transverse elongation at break of the second substrate film is ≧60%, and optionally 80% to 160%.

[0028] By adjusting the longitudinal and / or transverse breaking elongation of the second base film to satisfy the above ranges, it is advantageous to improve the stretchability of the separator film due to the second base film, thereby improving the processability of the separator film, which is advantageous in that the separator film has both good processability and high heat resistance, thereby improving the production yield and reliability of secondary batteries.

[0029] In any embodiment of the present application, the porosity of the first substrate film is greater than the porosity of the second substrate film.

[0030] Optionally, the porosity of the first substrate film is 50% to 98%.

[0031] Optionally, the porosity of the second substrate film is 20% to 60%.

[0032] When the porosity of the first substrate film and / or the second substrate film satisfies certain conditions, the separator film can have good permeability and electrolyte infiltration performance, further improving the electrochemical performance and rate performance of the secondary battery.

[0033] In any embodiment of the present application, the relative molecular mass of the first substrate film is greater than the relative molecular mass of the second substrate film.

[0034] Preferably, the relative molecular mass of the first substrate film is between 300,000 and 6,000,000, more preferably between 1,000,000 and 3,000,000.

[0035] Preferably, the relative molecular mass of the second substrate film is 100,000 to 3,000,000, more preferably 400,000 to 1,500,000.

[0036] By adjusting the relative molecular mass of the first substrate film and / or the second substrate film to satisfy the above range, the melting point of the first substrate film and / or the second substrate film can be adjusted to satisfy the range of the examples of the present application, which is advantageous for improving the heat resistance performance of the separator film and further improving the reliability of the secondary battery.

[0037] In any embodiment of the present application, the ratio of the thickness of the first base film to the thickness of the second base film is 0.15 to 2.0, and optionally 0.3 to 0.6.

[0038] Preferably, the thickness of the first substrate film is from 1 μm to 10 μm, more preferably from 1 μm to 3 μm.

[0039] Preferably, the thickness of the second substrate film is 2 μm to 10 μm, more preferably 3 μm to 6 μm.

[0040] When the thickness of the first substrate film and / or the second substrate film satisfies the above conditions, the separator film can have a relatively small thickness while having a relatively high mechanical strength, which is advantageous for the secondary battery to have both high reliability and high energy density.

[0041] In any embodiment of the present application, the air permeability of the first base film is less than the air permeability of the second base film.

[0042] Preferably, the ratio of the air permeability of the first base film to the air permeability of the second base film is 0.1 to 0.5, more preferably 0.2 to 0.4.

[0043] Preferably, the breathability of the first base film is 20 sec / 100 cc to 100 sec / 100 cc, more preferably 30 sec / 100 cc to 40 sec / 100 cc.

[0044] Alternatively, the breathability of the second base film is 100 sec / 100 cc to 300 sec / 100 cc, more preferably 100 sec / 100 cc to 150 sec / 100 cc.

[0045] By adjusting the air permeability of the first substrate film and / or the second substrate film to satisfy the above range, the air permeability of the first substrate film and the second substrate film can be made complementary, and the separator film has an appropriate air permeability, thereby providing the separator film with good ion conduction capability, thereby improving the electrochemical performance and rate performance of the secondary battery.

[0046] In any embodiment of the present application, the puncture strength of the first base film is lower than the puncture strength of the second base film.

[0047] Preferably, the puncture strength of the first base film is 20 gf to 150 gf, more preferably 20 gf to 80 gf.

[0048] Preferably, the puncture strength of the second base film is 60 gf to 400 gf, more preferably 80 gf to 270 gf.

[0049] Adjusting the puncture strength of the first base film and / or the second base film to satisfy the above conditions is advantageous in reducing the risk of the separator film being pierced by lithium dendrites or mechanical impact, thereby further improving the reliability of the secondary battery.

[0050] In any embodiment of the present application, the material of the first substrate film includes at least one of polytetrafluoroethylene and derivatives thereof, polyethylene terephthalate and derivatives thereof, polyimide and derivatives thereof, polyether ether ketone and derivatives thereof, polyphenylene sulfide and derivatives thereof, polybenzimidazole and derivatives thereof, polysulfone and derivatives thereof, and polylactic acid and derivatives thereof.

[0051] By selecting the material of the first substrate film from the above-mentioned appropriate substances, it is advantageous for the first substrate film to have a high melting point, which is advantageous for improving the heat resistance performance of the separator film and further advantageous for improving the reliability of the secondary battery.

[0052] In any embodiment of the present application, the material of the second substrate film includes at least one of polyolefin, halogenated polyolefin, polyether, polyester, polyvinyl alcohol, polytetrafluoroethylene and derivatives thereof, polyethylene terephthalate and derivatives thereof, polyimide and derivatives thereof, polyether ether ketone and derivatives thereof, polyphenylene sulfide and derivatives thereof, polybenzimidazole and derivatives thereof, and polysulfone and derivatives thereof.

[0053] The second substrate film can be made of a material selected from the above-mentioned suitable materials, which can be advantageous in that the second substrate film is more complementary to the first substrate film, thereby providing the separator film with good heat resistance and high structural stability, thereby further improving the reliability of the secondary battery and reducing the probability of safety issues such as fires and explosions.

[0054] In any embodiment of the present application, the volume distribution particle diameter Dv50 of the filler particles is 0.01 μm to 0.8 μm, and optionally 0.2 μm to 0.8 μm, which is advantageous for improving the mechanical strength, self-supporting performance, and heat resistance of the separator film, and thus for improving the reliability of the secondary battery.

[0055] In any embodiment of the present application, the content of the filler particles is 90% or less, and optionally 20% to 80%, based on the total mass of the intermediate layer.

[0056] In any embodiment of the present application, the specific surface area of ​​the filler particles is 2 g / m 2 ~20g / m 2 and selectively 6 g / m 2 ~9g / m 2 This is advantageous for improving the electrolyte infiltration performance of the separator film, which is therefore advantageous for reducing the internal resistance of the secondary battery, improving the cycle performance of the secondary battery, and extending the cycle life of the secondary battery.

[0057] In any embodiment of the present application, the filler particles include at least one of inorganic particles, organic particles, and organic-metallic framework materials.

[0058] Optionally, the inorganic particles include one or more of inorganic particles having a dielectric constant of 5 or greater, inorganic particles that are ionically conductive but do not store ions, and inorganic particles capable of electrochemical reactions.

[0059] Optionally, the organic particles comprise one or more of polycarbonate, polythiophene, polypyridine, polystyrene, polyacrylate, polyethylene, polypropylene, cellulose, cellulose modifiers, melamine resin, phenolic resin, polyester, silicone resin, polyimide, polyamideimide, polyaramid, polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, polyaryletherketone, copolymer of butyl acrylate and ethyl methacrylate.

[0060] Optionally, the organic-metal framework material comprises one or more of a nitrogen-containing heterocyclic ligand-based framework, an organic carboxylic acid-based ligand-based framework, and a nitrogen-oxygen-containing mixed ligand-based framework.

[0061] In any embodiment of the present application, the intermediate layer further comprises an adhesive comprising one or more of polyacrylate, polyacrylic acid, polyimide, 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, thermoplastic polyurethane, maleic anhydride, ethylene-acrylic acid copolymer.

[0062] Preferably, the adhesive content is 35% or less, more preferably 10% to 30%, based on the total mass of the intermediate layer.

[0063] In any embodiment of the present application, the thickness of the separator film is 7 μm or less, and optionally 3 μm to 6 μm. Setting the thickness of the separator film within a predetermined range is advantageous for further improving the energy density of the secondary battery.

[0064] Preferably, the separator film has an air permeability of 100 sec / 100 cc to 300 sec / 100 cc, and more preferably 120 sec / 100 cc to 200 sec / 100 cc. When the air permeability of the separator film satisfies the predetermined range, the separator film can have good ion conduction ability, and thus the secondary battery has good electrochemical performance and rate performance.

[0065] Optionally, the separator film has a transverse heat shrinkage at 250° C. for 1 hour of ≦1.0%, and optionally ≦0.4%.

[0066] Optionally, the separator film has a longitudinal heat shrinkage of ≦1.0% at 250° C. for 1 hour, and optionally ≦0.3%.

[0067] Optionally, the separator film has a transverse tensile strength of ≧0.5N, and optionally 1.2N to 3.5N.

[0068] Optionally, the longitudinal tensile strength of the separator film is ≧0.5N, and optionally 1.2N to 3.5N.

[0069] When at least one of the transverse tensile strength, longitudinal tensile strength, transverse thermal shrinkage rate, and longitudinal thermal shrinkage rate of the separator film satisfies a predetermined range, the separator film can have good heat resistance and physical properties, thereby improving the reliability of the secondary battery.

[0070] In a second aspect of the present application, there is provided a method for producing the separator film of the first aspect, comprising the steps of:

[0071] An intermediate layer slurry is provided, which includes a first substrate film having a melting point of 175° C. or higher and an average pore size of 0.22 μm or greater, a second substrate film, and filler particles.

[0072] The intermediate layer slurry is applied to one of the first and second base films and dried, and then the slurry is laminated to the other of the first and second base films and hot-pressed so that at least some of the filler particles are inserted into the first base film, thereby obtaining a separator film.

[0073] Optionally, the slurry further comprises an adhesive.

[0074] In any embodiment of the present application, the drying temperature is between 35°C and 80°C, and optionally between 40°C and 60°C.

[0075] Alternatively, the drying time is between 5 s and 60 s, and optionally between 5 s and 15 s.

[0076] Optionally, the hot welding temperature is between 40°C and 100°C, and optionally between 40°C and 70°C.

[0077] Optionally, the hot welding time is 5s to 60s, and optionally 5s to 10s.

[0078] Optionally, the hot welding pressure is between 1 MPa and 10 MPa, and optionally between 3 MPa and 7 MPa.

[0079] In a third aspect of the present application, there is provided a secondary battery including a positive electrode piece, a negative electrode piece, and the separator film of the first aspect disposed between the positive electrode piece and the negative electrode piece.

[0080] A secondary battery provided by an embodiment of the present application includes the separator film of the first aspect of the present application, which can improve the reliability of the secondary battery and further extend the cycle life of the secondary battery.

[0081] In any embodiment of the present application, the first substrate film of the separator film faces the negative electrode piece, which is advantageous for the rapid passage of active ions (e.g., lithium ions), ensuring the speed of lithium intercalation, and promoting the uniformity of lithium intercalation, which is advantageous for reducing the formation and growth of lithium dendrites, thereby further improving the safety performance of the battery.

[0082] In a fourth aspect of the present application, there is provided an electrical device including the secondary battery of the third aspect.

[0083] The electrical device of the present application includes the secondary battery provided by the present application, and therefore has at least the same advantages as the secondary battery. [Brief explanation of the drawings]

[0084] In order to more clearly explain the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings used in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application, and those skilled in the art can further derive other drawings based on these drawings without any creative work. In the drawings, the drawings are not necessarily drawn to actual scale. The symbols are as follows: 1, battery pack; 2, upper case; 3, lower case; 4, battery module; 5, secondary battery; 51, casing; 52, electrode assembly; 53, cover plate. [Figure 1] 1 is a schematic diagram of one embodiment of a secondary battery provided by the present application. [Figure 2] 1 is an exploded schematic view of one embodiment of a secondary battery provided by the present application. [Figure 3] 1 is a schematic diagram of one embodiment of a battery module provided by the present application. [Figure 4] 1 is a schematic diagram of one embodiment of a battery pack provided by the present application. [Figure 5] FIG. 5 is an exploded schematic view of the embodiment of the battery pack shown in FIG. 4. [Figure 6] 1 is a schematic diagram of one embodiment of an electrical device including a secondary battery provided by the present application as a power source. DETAILED DESCRIPTION OF THE INVENTION

[0085] Hereinafter, embodiments specifically disclosing the separator film and its manufacturing method, secondary battery, and electrical device of the present application will be described in detail with reference to the accompanying drawings. However, unnecessary detailed description may be omitted. For example, detailed description of well-known matters and repeated description of substantially identical configurations may be omitted. This is to avoid unnecessarily lengthening the following description and to facilitate understanding by those skilled in the art. Furthermore, the drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the scope of the claims.

[0086] The "ranges" disclosed herein are defined by lower and upper limits, and a given range is defined by selecting one lower limit and one upper limit, with the selected lower and upper limits defining the boundaries of that particular range. Such defined ranges may be inclusive or exclusive of their endpoints and may be arbitrarily combined; i.e., any lower limit can be combined with any upper limit to form a single range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also contemplated. Furthermore, if the minimum range values ​​listed are 1 and 2, and the maximum range values ​​are 3, 4, and 5, then the ranges 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5 are all contemplated. Unless otherwise specified, the numerical range "a to b" herein represents a shorthand notation for any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "0 to 5" indicates that all real numbers between "0 and 5" have already been listed in this specification, and "0 to 5" is simply an abbreviation for a combination of those numerical values. Note that when a parameter is described as an integer ≧2, this is equivalent to disclosing that the parameter is an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0087] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure content of the present application.

[0088] Unless otherwise specified, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure content of the present application.

[0089] Unless otherwise specified, all steps in the present application may be performed sequentially or randomly, but are preferably performed sequentially. For example, when the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, when the method described above may further include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0090] Unless otherwise specified, the terms "comprise" and "comprises" used in this application may be open or closed. For example, the terms "comprise" and "comprises" may further include or include other components not listed, or may include or include only the listed components.

[0091] Unless otherwise stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following conditions satisfy the condition "A or B": A is true (or exists) and B is false (or does not exist), A is false (or does not exist) and B is true (or exists), or both A and B are true (or exist).

[0092] Unless otherwise stated, in this application, terms such as "first," "second," etc. are used to distinguish between different objects and are not used to describe a particular order or hierarchical relationship.

[0093] As used herein, the terms "plurality," "plurality," and the like mean two or more than two.

[0094] Unless otherwise specified, terms used herein have the known meanings commonly understood by those skilled in the art.

[0095] Unless otherwise specified, the values ​​of each parameter referred to in this application can be measured using various test methods commonly used in the art, for example, according to the test methods shown in the examples of this application. Unless otherwise specified, the test temperature for each parameter is 25°C.

[0096] Unless otherwise stated, ratio parameters herein are compared in the same units. For example, if the ratio of thicknesses A to B is 1.2:1, then the thicknesses of A and B have the same units. Separator Film

[0097] Typically, a secondary battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode piece, a negative electrode piece, and a separator film disposed between the positive electrode piece and the negative electrode piece, which mainly serves to prevent short-circuiting between the positive electrode and the negative electrode.

[0098] The separator film provided by the present invention includes a first substrate film, a second substrate film, and an intermediate layer located between the first substrate film and the second substrate film. The first substrate film has a melting point of 175°C or higher and an average pore size of 0.22 μm or higher. The intermediate layer includes filler particles, at least a portion of which is inserted into the first substrate film.

[0099] Currently, the separator films used in commercially available secondary batteries are generally porous polyolefin films, which have relatively low heat resistance and undergo significant thermal shrinkage upon heating, resulting in direct contact between the positive and negative electrodes inside the battery, causing internal short circuits and further increasing the safety risks of the secondary battery. Compared to porous polyolefin films, the use of a first substrate film with a melting point of 175°C or higher can effectively improve the heat resistance of the separator film. However, first substrate films with high melting points generally have relatively low mechanical strength and self-supporting properties, making it difficult to meet the processing, transportation, and use requirements of secondary batteries, which may reduce the production yield and reliability of secondary batteries.

[0100] Without intending to be bound by any theory or interpretation, when a separator film includes a first base film, a second base film, and an intermediate layer located between the first base film and the second base film, the separator film can have good heat resistance, relatively high mechanical strength, and self-supporting properties. Specifically, by setting the melting point of the first base film to 175°C or higher, the separator film can be provided with good heat resistance. Furthermore, by setting the average pore size of the first substrate film within the above-mentioned appropriate range, an appropriate amount of filler particles can be inserted into the first substrate film to form a composite structure between the first substrate film and the filler particles, thereby effectively improving the mechanical strength, self-supporting ability, and heat resistance of the separator film. In addition, after the filler particles are inserted into the substrate film, the overall thickness of the separator film can be reduced, thereby further improving the energy density of the battery. In addition, a specific pore size range allows the filler particles to be better inserted into the first substrate film, reducing the probability of filler particles falling off in the intermediate layer, thereby further improving the reliability of the separator film and improving the cycle performance of the battery.

[0101] Therefore, the separator film provided by the present application can simultaneously achieve relatively good safety performance, relatively high energy density, and good cycle performance of the secondary battery.

[0102] In some embodiments, the average pore size of the first substrate film may be 0.22 μm to 4.0 μm, for example, 0.22 μm, 0.3 μm, 0.5 μm, 0.8 μm, 1.0 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2.0 μm, 2.5 μm, 2.7 μm, 3.0 μm, 3.5 μm, 4.0 μm, or a range consisting of any two of the above values. For example, the average pore size of the first base film is 0.22 μm to 3.5 μm, 0.22 μm to 2.7 μm, 0.22 μm to 2.5 μm, 0.22 μm to 2.0 μm, 0.22 μm to 1.8 μm, 0.22 μm to 1.5 μm, 0.22 μm to 1.0 μm, 0.22 μm to 0.5 μm, 0.3 μm to 4.0 μm, 0.3 μm to 3.5 μm, 0.3 μm to 2.7 ... .3μm~2.5μm, 0.3μm~2.0μm, 0.3μm~1.8μm, 0.3μm~1.5μm, 0.3μm~1.0μm, 0.3μm~0.5μm, 0.5μm~4.0μ m, 0.5μm~3.5μm, 0.5μm~2.7μm, 0.5μm~2.5μm, 0.5μm~2.0μm, 0.5μm~1.8μm, 0.5μm~1.5μm, 0.5μm~1 .0μm, 0.8μm~4.0μm, 0.8μm~3.5μm, 0.8μm~2.7μm, 0.8μm~2.5μm, 0.8μm~2.0μm, 0.8μm~1.8μm, 0.8μm m~1.5μm, 1.0μm~4.0μm, 1.0μm~3.5μm, 1.0μm~2.7μm, 1.0μm~2.5μm, 1.0μm~2.0μm, 1.0μm~1.8μm, 1 The thickness may be 0.0 μm to 1.5 μm, 1.2 μm to 4.0 μm, 1.2 μm to 3.5 μm, 1.2 μm to 2.7 μm, 1.2 μm to 2.5 μm, 1.2 μm to 2.0 μm, 1.2 μm to 1.8 μm, 1.2 μm to 1.5 μm, 1.5 μm to 4.0 μm, 1.5 μm to 3.5 μm, 1.5 μm to 2.7 μm, 1.5 μm to 2.5 μm, or 1.5 μm to 2.0 μm.

[0103] Without intending to be bound by any theory or interpretation, it is believed that adjusting the average pore size of the first substrate film to satisfy the above range is advantageous for the filler particles to be inserted into the first substrate film to form a suitable composite structure separator film, which has a relatively thin thickness while also having excellent breathability and relatively high strength. In this way, applying the separator film to a secondary battery is advantageous for improving the energy density and cycle performance of the secondary battery.

[0104] In some embodiments, the average pore size of the second substrate film is smaller than the average pore size of the first substrate film.

[0105] Optionally, in some embodiments, the average pore size of the second substrate film may be 0.01 μm to 0.5 μm, 0.01 μm to 0.4 μm, 0.01 μm to 0.3 μm, 0.01 μm to 0.2 μm, 0.01 μm to 0.1 μm, 0.02 μm to 0.5 μm, 0.02 μm to 0.4 μm, 0.02 μm to 0.3 μm, 0.02 μm to 0.2 μm, 0.02 μm to 0.1 μm, 0.03 μm to 0.1 μm, 0.04 μm to 0.1 μm, or 0.05 μm to 0.1 μm.

[0106] Without intending to be bound by any theory or interpretation, by adjusting the average pore size of the second substrate film to satisfy the above range, the second substrate film can have high mechanical strength, high puncture resistance, and appropriate permeability. In this way, on the one hand, improving the mechanical strength of the separator film with the second substrate film improves the structural stability of the separator film and reduces the risk of the separator film being pierced by lithium dendrites, causing contact between the positive electrode and the negative electrode and resulting in a short circuit. On the other hand, adjusting the permeability of the separator film with the second substrate film allows the separator film to have good interruption performance and reduces the risk of a short circuit due to direct contact between the positive electrode and the negative electrode. Therefore, by applying the separator film of the above example to a secondary battery, the reliability of the secondary battery can be further improved.

[0107] The average pore size of the substrate film has a meaning known in the art and can be measured using instruments and methods known in the art, for example, by referring to the test standard GB / T21650-2008 and using a mercury porosimeter.

[0108] In some embodiments, the insertion depth of the filler particles into the first substrate film may be 0.2 μm or greater, such as 0.2 μm, 0.3 μm, 0.5 μm, 0.8 μm, 1.0 μm, 1.1 μm, 1.3 μm, 1.5 μm, 1.8 μm, 2.0 μm, or a range consisting of any two of the foregoing values.

[0109] Optionally, in some embodiments, the insertion depth of the filler particles into the first substrate film may further be 0.5 μm to 1.0 μm, such as 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, or a range consisting of any two of the above values.

[0110] Without intending to be bound by any theory or interpretation, when the insertion depth of the filler particles into the first substrate film satisfies the above range, the mechanical strength and self-supporting performance of the composite structure formed by the filler particles and the first substrate film can be effectively improved. This is advantageous for further improving the structural stability of the separator film and further improving the reliability of secondary batteries. Furthermore, when the insertion depth of the filler particles into the first substrate film satisfies the above range, it is advantageous for further reducing the overall thickness of the separator film, thereby further improving the energy density of the battery.

[0111] In some embodiments, the insertion depth of the filler particles into the second substrate film may be 0.1 μm or greater, such as 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, or a range consisting of any two of the foregoing values.

[0112] Optionally, in some embodiments, the insertion depth of the filler particles into the second substrate film may be 0.1 μm to 0.5 μm, such as 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm, or a range consisting of any two of the foregoing values.

[0113] Without intending to be bound by any theory or interpretation, when the insertion depth of the filler particles into the second substrate film satisfies the above range, on the one hand, an appropriate bonding strength is provided between the intermediate layer and the second substrate film, thereby improving the structural stability of the separator film, and on the other hand, the second substrate film ensures appropriate breathability and support performance, thereby enabling the separator film to have good breathability and strength, which is advantageous for further improving the safety performance and electrochemical performance of the secondary battery.

[0114] In some embodiments, the insertion depth of the filler particles into the first substrate film may be greater than the insertion depth of the filler particles into the second substrate film.

[0115] Without intending to be bound by any theory or interpretation, by making the insertion depth of the filler particles into the first substrate film greater than the insertion depth of the filler particles into the second substrate film, the separator film can have high structural stability and good breathability, thereby improving the reliability and electrochemical performance of the secondary battery.

[0116] The penetration depth of the filler particles into the substrate film has a meaning known in the art and can be measured using equipment and methods known in the art. For example, a scanning electron microscope (e.g., ZEISS Sigma 300) can be used to perform the test. For example, the procedure can be performed according to the following steps: First, the separator film is cut into a sample to be measured (e.g., 6 mm x 6 mm) with a certain dimension, the sample to be measured is sandwiched between two electrically and thermally conductive sheets (e.g., copper foil), the sample to be measured and the sheets are adhesively fixed with tape (e.g., double-sided tape), and pressed with a flat iron block having a certain mass (e.g., about 400 g) for a certain time (e.g., 1 h) to minimize the slit between the sample to be measured and the copper foil. Next, the edges are trimmed with scissors and the sample is attached to a sample holder with a conductive adhesive, so that the sample may protrude slightly beyond the edge of the sample holder. Next, the sample stage is placed in the sample holder and locked into place. The argon ion cross-section polishing machine (e.g., IB-19500CP) is turned on and vacuumed (e.g., 10 Pa to 4 Pa). The argon gas flow rate (e.g., 0.15 MPa), voltage (e.g., 8 KV), and polishing time (e.g., 2 hours) are set. The sample stage is then adjusted to swing mode and polishing begins. After polishing is complete, a scanning electron microscope (e.g., a ZEISS Sigma 300) is used to obtain a CP image of the sample awaiting measurement. The thickness data for the substrate film and interlayer are measured, and EDS Mapping mode is selected. The distribution depth of the element (e.g., aluminum) contained in the filler particles in the substrate film is used as the insertion depth. For example, the midpoint of the element distribution curve is used as the boundary, and the thickness values ​​of the interlayer on both sides of the midpoint are removed, setting this as the initial value. The curve is then extended until the content of the element (e.g., aluminum) contained in the filler particles reaches 0, at which point the value is read and used as the insertion depth.

[0117] In some embodiments, the melting point of the first substrate film may be equal to or greater than the melting point of the second substrate film.

[0118] In some embodiments, the melting point of the first substrate film may be 175°C to 350°C, for example, 175°C, 200°C, 225°C, 250°C, 275°C, 300°C, 325°C, 350°C, or a range consisting of any two of the above values.

[0119] Optionally, in some embodiments, the melting point of the first substrate film may also be 220°C to 350°C, for example, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, or a range consisting of any two of the above values.

[0120] In some embodiments, the melting point of the second substrate film may be 130°C to 200°C, for example, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, or a range consisting of any two of the above values.

[0121] Optionally, in some embodiments, the melting point of the second substrate film may be 135°C to 180°C, for example, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, or a range consisting of any two of the above values.

[0122] Without intending to be bound by any theory or interpretation, adjusting the melting points of the first substrate film and / or the second substrate film within the above appropriate range not only allows the separator film to have good heat resistance, but also allows the separator film to have good closed-cell characteristics. In this way, the separator film not only has good ion conductivity when the secondary battery is operating normally, but also closes its pores in a timely manner to block current conduction when the secondary battery experiences thermal runaway. In this way, the secondary battery can have both good cycle performance and high reliability.

[0123] The melting point of the substrate film has a meaning known in the art and can be measured using instruments and methods known in the art. For example, it can be measured using differential scanning calorimetry. Specifically, reference can be made to standard GB / T19466.3-2004. For example, it can be measured according to the following method: A sample of 4 mg to 6 mg to be measured is taken and placed in the sample chamber of a differential scanning calorimeter. The temperature is increased from 25°C to 400°C at a heating rate of 10°C / min to obtain a melting endothermic curve of the sample. The temperature corresponding to the peak value of the curve is taken as the melting point of the sample.

[0124] In some embodiments, the longitudinal elongation at break of the first base film may be 20% to 105%, for example, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, 105%, or a range consisting of any two of the above values.

[0125] Optionally, in some embodiments, the longitudinal elongation at break of the first substrate film may also be 40% to 90%, for example, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or a range consisting of any two of the above values.

[0126] In some embodiments, the transverse elongation at break of the first substrate film may be 20% to 105%, for example, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, 105%, or a range consisting of any two of the above values.

[0127] Optionally, in some embodiments, the transverse elongation at break of the first substrate film may also be 40% to 90%, for example, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or a range consisting of any two of the above values.

[0128] Without intending to be bound by any theory or interpretation, it is believed that, when other intrinsic parameters of the first substrate film are essentially the same, the larger the average pore size of the first substrate film, the smaller its longitudinal and / or transverse breaking elongation percentages. Adjusting the longitudinal and / or transverse breaking elongation percentages of the first substrate film to satisfy the above ranges is advantageous for the first substrate film to have an appropriate average pore size, which in turn is advantageous for the filler particles to be inserted into the first substrate film to form an appropriate composite structure. This is advantageous for improving the heat resistance and mechanical strength of the separator film, which in turn is advantageous for improving the reliability of secondary batteries.

[0129] The transverse direction elongation at break and the longitudinal direction elongation at break of the first substrate film both have meanings known in the art and can be measured using instruments and methods known in the art, for example, by referring to the standard GB / T36363-2018.

[0130] In some embodiments, the elongation at break of the second substrate film in the machine direction is less than the elongation at break of the second substrate film in the cross direction.

[0131] The longitudinal breaking elongation of the second base film may be 40% or more, for example, 40%, 50%, 60%, 70%, 80%, 90%, 100%, 110%, 120%, 130%, 140%, 150%, 160%, 170%, 180%, or a range consisting of any two of the above values.

[0132] Optionally, in some embodiments, the longitudinal elongation at break of the second substrate film may be 60% to 150%, for example, 60%, 70%, 80%, 90%, 100%, 110%, 120%, 130%, 140%, 150%, or a range consisting of any two of the above values.

[0133] The transverse breaking elongation of the second base film may be 60% or more, for example, 60%, 70%, 80%, 90%, 100%, 110%, 120%, 130%, 140%, 150%, 160%, 170%, 180%, 190%, 200%, or a range consisting of any two of the above values.

[0134] Optionally, in some embodiments, the transverse elongation at break of the second substrate film may be 80% to 160%, for example, 80%, 90%, 100%, 110%, 120%, 130%, 140%, 150%, 160%, or a range consisting of any two of the above values.

[0135] Without intending to be bound by any theory or interpretation, adjusting the longitudinal breaking elongation rate and / or transverse breaking elongation rate of the second substrate film to satisfy the above ranges is advantageous in improving the stretchability of the separator film due to the second substrate film, thereby improving the processability of the separator film, and is thus advantageous in providing the separator film with both good processability and high heat resistance, thereby improving the production yield and reliability of secondary batteries.

[0136] The test method for measuring the longitudinal and / or transverse breaking elongation percentage of the second base film can refer to the test method for measuring the longitudinal and / or transverse breaking elongation percentage of the first base film.

[0137] In some embodiments, the porosity of the first substrate film may be greater than the porosity of the second substrate film.

[0138] Optionally, in some embodiments, the porosity of the first substrate film may be 30% to 98%, for example, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 98%, or a range consisting of any two of the above values.

[0139] Optionally, in some embodiments, the porosity of the second substrate film may be 20% to 60%, for example, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or a range consisting of any two of the above values.

[0140] Without intending to be bound by any theory or interpretation, when the porosity of the first substrate film is greater than that of the second substrate film, the porosities of the first substrate film and the second substrate film can be complementary, and the porosity of the separator film can be within an appropriate range, thereby providing the separator film with good permeability and electrolyte infiltration performance, and further improving the electrochemical performance and rate performance of the secondary battery. Furthermore, by adjusting the porosity of the first substrate film within the above appropriate range, the amount of filler particles inserted into the first substrate film can be adjusted appropriately, which is advantageous not only for adjusting the mechanical strength of the separator film but also for providing the separator film with good breathability. In this way, the separator film of the present embodiment not only has high reliability but also good ion conduction ability, and when applied to a secondary battery, it can improve the reliability, electrochemical performance, and rate performance of the secondary battery. By adjusting the porosity of the second substrate film to satisfy a predetermined range, the porosity of the separator film can be adjusted to an appropriate range, which is advantageous in that the separator film has good permeability and electrolyte infiltration performance, and further improves the electrochemical performance and rate performance of the secondary battery.

[0141] The porosity of the substrate film has a meaning known in the art and can be measured using instruments and methods known in the art, for example, by referring to the test standard GB / T21650-2008 and using a mercury porosimeter.

[0142] In some embodiments, the relative molecular mass of the first substrate film may be greater than the relative molecular mass of the second substrate film.

[0143] Optionally, in some embodiments, the relative molecular mass of the first substrate film may be 300,000 to 6,000,000, for example, 300,000, 500,000, 800,000, 1,000,000, 2,000,000, 3,000,000, 4,000,000, 5,000,000, 6,000,000, or a range consisting of any two of the above values.

[0144] Further optionally, in some embodiments, the relative molecular mass of the first substrate film may also be 1 million to 3 million, for example, 1 million, 1.2 million, 1.5 million, 1.8 million, 2 million, 2.2 million, 2.5 million, 2.8 million, 3 million, or a range consisting of any two of the above numerical values.

[0145] Optionally, in some embodiments, the relative molecular mass of the second substrate film may be 100,000 to 3,000,000, for example, 100,000, 500,000, 800,000, 1,000,000, 1,500,000, 2,000,000, 2,500,000, 3,000,000, or a range consisting of any two of the above values.

[0146] Further optionally, in some embodiments, the relative molecular mass of the second substrate film may also be 400,000 to 1.5 million, for example, 400,000, 600,000, 800,000, 1,000,000, 1.2 million, 1.4 million, 1.5 million, or a range consisting of any two of the above numerical values.

[0147] Without intending to be bound by any theory or interpretation, by adjusting the relative molecular mass of the first substrate film and / or the second substrate film to satisfy the above range, the melting point of the first substrate film and / or the second substrate film can be adjusted to satisfy the range of the examples of the present application, which is advantageous in improving the heat resistance performance of the separator film and further improves the reliability of the secondary battery.

[0148] The relative molecular mass of the substrate film has a meaning known in the art and can be tested using equipment and methods known in the art, for example, using a high temperature GPC test (refractive index detector).

[0149] In some embodiments, the ratio of the thickness of the first base film to the thickness of the second base film may be 0.15 to 2.0, for example, 0.15, 0.3, 0.5, 1.0, 1.2, 1.5, 1.8, 2.0, or a range consisting of any two of the above values.

[0150] Optionally, in some embodiments, the ratio of the thickness of the first substrate film to the thickness of the second substrate film may also be 0.3 to 0.6, such as 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, or a range consisting of any two of the above values.

[0151] In some embodiments, the thickness of the first substrate film may be 1 μm to 10 μm, for example, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or a range consisting of any two of the above values.

[0152] Optionally, in some embodiments, the thickness of the first substrate film may also be 1 μm to 3 μm, for example, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, or a range consisting of any two of the above values.

[0153] In some embodiments, the thickness of the second substrate film may be 2 μm to 10 μm, for example, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or a range consisting of any two of the above values.

[0154] Optionally, in some embodiments, the thickness of the second substrate film may also be 3 μm to 6 μm, for example, 3 μm, 4 μm, 5 μm, 6 μm, or a range consisting of any two of the above values.

[0155] Without intending to be bound by any theory or interpretation, when the thickness of the first substrate film and / or the second substrate film satisfies the above conditions, the separator film can have a relatively small thickness while having a relatively high mechanical strength, which is advantageous for the secondary battery to have both high reliability and high energy density.

[0156] The thickness of the substrate film has a meaning known in the art and can be measured using equipment and methods known in the art. For example, six sets of parallel samples are taken, and the thickness of each set of samples is measured at different positions using a multi-gauge thickness meter, and the thickness of each set of samples is measured at at least 20 positions, and the average value of the thickness of the six sets of samples can be used as the thickness of the sample.

[0157] In some embodiments, the air permeability of the first substrate film may be less than the air permeability of the second substrate film.

[0158] Optionally, in some embodiments, the ratio of the breathability of the first base film to the breathability of the second base film may be 0.1 to 0.5, 0.1 to 0.4, 0.1 to 0.3, 0.1 to 0.2, 0.2 to 0.5, 0.2 to 0.4, 0.2 to 0.3, 0.3 to 0.5, 0.3 to 0.4, or 0.4 to 0.5.

[0159] In some embodiments, the breathability of the first base film may be 20 sec / 100cc to 100 sec / 100cc, for example, 20 sec / 100cc, 30 sec / 100cc, 40 sec / 100cc, 50 sec / 100cc, 60 sec / 100cc, 70 sec / 100cc, 80 sec / 100cc, 90 sec / 100cc, 100 sec / 100cc, or a range consisting of any two of the above values.

[0160] Optionally, in some embodiments, the breathability of the first substrate film may also be 30 sec / 100cc to 40 sec / 100cc, for example, 30 sec / 100cc, 32 sec / 100cc, 34 sec / 100cc, 36 sec / 100cc, 38 sec / 100cc, 40 sec / 100cc, or a range consisting of any two of the above values.

[0161] In some embodiments, the breathability of the second base film may be 100 sec / 100 cc to 300 sec / 100 cc, for example, 100 sec / 100 cc, 150 sec / 100 cc, 200 sec / 100 cc, 250 sec / 100 cc, 300 sec / 100 cc, or a range consisting of any two of the above values.

[0162] Optionally, in some embodiments, the breathability of the second substrate film may also be 100 sec / 100 cc to 150 sec / 100 cc, for example, 100 sec / 100 cc, 110 sec / 100 cc, 120 sec / 100 cc, 130 sec / 100 cc, 140 sec / 100 cc, 150 sec / 100 cc, or a range consisting of any two of the above values.

[0163] Without intending to be bound by any theory or interpretation, when the average pore size of the first substrate film satisfies the range of the examples of the present application, the first substrate film generally has a relatively low air permeability. By adjusting the air permeability of the first substrate film and / or the second substrate film to satisfy the above range, the air permeabilities of the first substrate film and the second substrate film can be made complementary, and the separator film has an appropriate air permeability, thereby providing the separator film with good ion conduction ability, thereby improving the electrochemical performance and rate performance of the secondary battery.

[0164] The breathability of the substrate film has a meaning known in the art and can be measured using instruments and methods known in the art, for example, by referring to GB / T36363-2018.

[0165] In some embodiments, the puncture strength of the first base film may be less than the puncture strength of the second base film, for example, the ratio of the puncture strength of the first base film to the puncture strength of the second base film may be 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, 0.98, 0.99, or a range consisting of any two of the above values.

[0166] In some embodiments, the puncture strength of the first base film may be 20 gf to 150 gf, for example, 20 gf, 40 gf, 60 gf, 80 gf, 100 gf, 120 gf, 150 gf, or a range consisting of any two of the above values.

[0167] Optionally, in some embodiments, the puncture strength of the first substrate film may also be 20 gf to 80 gf, for example, 20 gf, 30 gf, 40 gf, 50 gf, 60 gf, 70 gf, 80 gf, or a range consisting of any two of the above values.

[0168] In some embodiments, the puncture strength of the second base film may be 60 gf to 400 gf, for example, 60 gf, 100 gf, 150 gf, 200 gf, 250 gf, 300 gf, 350 gf, 400 gf, or a range consisting of any two of the above values.

[0169] Optionally, in some embodiments, the puncture strength of the second substrate film may also be 80 gf to 270 gf, for example, 80 gf, 100 gf, 120 gf, 150 gf, 180 gf, 200 gf, 220 gf, 250 gf, 270 gf, or a range consisting of any two of the above numerical values.

[0170] Adjusting the puncture strength of the first base film and / or the second base film to satisfy the above conditions is advantageous in reducing the risk of the separator film being pierced by lithium dendrites or mechanical impact, thereby further improving the reliability of the secondary battery.

[0171] The puncture strength of a substrate film has a meaning known in the art and can be measured using instruments and methods known in the art. For example, the test can be performed with reference to GB / T 10004-2008. Specifically, the substrate film can be cut into strips to obtain test specimens, which may be 100 mm wide. The 100 mm wide test specimen is attached to a clamp ring for fixing the sample film, and then a steel needle with a diameter of 1.0 mm and a tip radius of 0.5 mm is used to pierce the test specimen at a speed of (50±5) mm / min. The maximum load at which the steel needle penetrates the test specimen is read. Five or more sets of parallel samples are taken, and three points are measured randomly for each set of samples. The arithmetic mean value of the puncture strength of all parallel samples can be used as the puncture strength of the substrate film.

[0172] In some embodiments, the material of the first substrate film includes at least one of polytetrafluoroethylene (PTFE) and derivatives thereof, polyethylene terephthalate (PET) and derivatives thereof, polyimide (PI) and derivatives thereof, polyether ether ketone (PEEK) and derivatives thereof, polyphenylene sulfide (PPS) and derivatives thereof, polybenzimidazole (PBI) and derivatives thereof, polysulfone (PSF) and derivatives thereof, and polylactic acid (PLA) and derivatives thereof.

[0173] Optionally, in some embodiments, the first substrate film comprises polytetrafluoroethylene or a polytetrafluoroethylene derivative.

[0174] Derivatives generally refer to products derived from polymers by replacing hydrogen atoms or atomic groups with other atoms or atomic groups.

[0175] Without intending to be bound by any theory or interpretation, selecting the material of the first substrate film from the above-mentioned suitable substances advantageously allows the first substrate film to have a high melting point, which is advantageous for improving the heat resistance of the separator film and further advantageous for improving the reliability of the secondary battery. In particular, if the first substrate film is a polytetrafluoroethylene substrate film, in the event of thermal runaway of the secondary battery, even if the internal temperature of the battery is higher than the melting point of the polytetrafluoroethylene substrate film and melts the polytetrafluoroethylene substrate film, the polytetrafluoroethylene substrate film will not melt off or significantly shrink, thereby allowing the separator film to have high structural stability. In this way, the separator film can effectively block contact between the positive electrode and the negative electrode during thermal runaway of the secondary battery, thereby further improving the reliability of the secondary battery and reducing the probability of safety events such as secondary battery fires and explosions.

[0176] In some embodiments, the material of the second substrate film may include at least one of polyolefin, halogenated polyolefin, polyether, polyester, polyvinyl alcohol, polytetrafluoroethylene and its derivatives, polyethylene terephthalate and its derivatives, polyimide and its derivatives, polyether ether ketone and its derivatives, polyphenylene sulfide and its derivatives, polybenzimidazole and its derivatives, and polysulfone and its derivatives.

[0177] The second substrate film can be made of a material selected from the above-mentioned suitable materials, which can be advantageous in that the second substrate film is more complementary to the first substrate film, thereby providing the separator film with good heat resistance and high structural stability, thereby further improving the reliability of the secondary battery and reducing the probability of safety issues such as fires and explosions.

[0178] In some embodiments, the volume distribution particle diameter Dv50 of the filler particles may be 0.01 μm to 0.8 μm, such as 0.01 μm, 0.05 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, or a range consisting of any two of the above values.

[0179] Optionally, in some embodiments, the volume distribution particle diameter Dv50 of the filler particles may also be 0.2 μm to 0.8 μm, such as 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm, 0.55 μm, 0.6 μm, 0.65 μm, 0.7 μm, 0.75 μm, 0.8 μm, or a range consisting of any two of the foregoing values.

[0180] Without intending to be bound by any theory or interpretation, when the volume distribution particle diameter Dv50 of the filler particles satisfies the above range, they are more compatible with the pore structure of the surface of the first substrate film, thereby forming an appropriate composite structure with the first substrate film, which is advantageous in improving the mechanical strength, self-supporting ability, and heat resistance of the separator film, and thereby in improving the reliability of the secondary battery.

[0181] The volume distribution particle diameter Dv50 of the filler particles has a meaning known in the art, and can represent the particle diameter corresponding to the cumulative particle size distribution percentage of the filler particles when the cumulative particle size distribution percentage reaches 50% in the volume-based particle size distribution. The volume distribution particle diameter Dv50 can be measured using instruments and methods known in the art. For example, it can be measured using a laser particle size analyzer (e.g., Malvern Mastersizer 2000E, UK) in accordance with GB / T19077-2016 Particle Size Distribution Laser Diffraction Method.

[0182] In some embodiments, the specific surface area of ​​the filler particles is 2 g / m 2 ~20g / m 2 For example, 2 g / m 2 , 5g / m 2 , 8g / m2 , 10g / m 2 , 12g / m 2 , 15g / m 2 , 18g / m 2 , 20g / m 2 , or a range consisting of any two of the above values.

[0183] Optionally, in some embodiments, the specific surface area of ​​the filler particles is also 6 g / m 2 ~9g / m 2 For example, 6 g / m 2 , 7g / m 2 , 8g / m 2 , 9g / m 2 , or a range consisting of any two of the above values.

[0184] Without intending to be bound by any theory or interpretation, adjusting the specific surface area of ​​the filler particles to fall within the above-mentioned appropriate range allows the filler particles to form an appropriate composite structure with the first substrate film, thereby improving the mechanical strength, self-supporting ability, and heat resistance of the separator film, as well as being advantageous in improving the electrolyte infiltration ability of the separator film, which in turn is advantageous in reducing the internal resistance of the secondary battery, improving the cycle performance of the secondary battery, and extending the cycle life of the secondary battery.

[0185] The specific surface area of ​​the packing particles has a meaning known in the art and can be measured using a method known in the art. For example, the specific surface area of ​​the packing particles can be measured by a nitrogen adsorption / desorption method using a specific surface area analyzer (e.g., Tristar II 3020M).

[0186] In some embodiments, the filler may include at least one of inorganic particles, organic particles, and organic-metallic framework materials.

[0187] Optionally, the inorganic particles may include one or more of inorganic particles having a dielectric constant of 5 or greater, inorganic particles that are ionically conductive but do not store ions, and inorganic particles capable of electrochemical reactions.

[0188] Optionally, the organic particles may comprise one or more of polycarbonate, polythiophene, polypyridine, polystyrene, polyacrylate, polyethylene, polypropylene, cellulose, cellulose modifiers (e.g., carboxymethyl cellulose), melamine resin, phenolic resin, polyester (e.g., polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate), silicone resin, polyimide, polyamideimide, polyaramid, polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, polyaryletherketone, copolymer of butyl acrylate and ethyl methacrylate (e.g., crosslinked polymer of butyl acrylate and ethyl methacrylate).

[0189] Optionally, the organic-metal framework material may include one or more of a nitrogen-containing heterocyclic ligand-based framework, an organic carboxylic acid-based framework, and a nitrogen-oxygen-containing mixed ligand-based framework.

[0190] In some embodiments, the intermediate layer may further include an adhesive, which can provide the separator film with good heat resistance by ensuring the adhesive strength and uniformity between the first and second substrate films, thereby improving the reliability of the secondary battery.

[0191] In some embodiments, the adhesive may include one or more of polyacrylate, polyacrylic acid, polyimide, 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, thermoplastic polyurethane, maleic anhydride, ethylene-acrylic acid copolymer.

[0192] In some embodiments, based on the total mass of the intermediate layer, the content of the filler particles may be 90% or less, and optionally 20% to 80%.

[0193] In some embodiments, the adhesive content may be 35% or less, and optionally 10% to 30%, based on the total weight of the intermediate layer.

[0194] In some embodiments, the intermediate layer may further include a dispersing agent, such as carboxymethyl cellulose, to adjust the viscosity of the adhesive intermediate layer slurry and improve the mass and uniformity of the film layer.

[0195] In some embodiments, the thickness of the separator film may be 7 μm or less. Optionally, in some embodiments, the thickness of the separator film may be 3 μm to 6 μm. Setting the thickness of the separator film within a predetermined range is advantageous for further improving the energy density of the secondary battery.

[0196] For the test method of the thickness of the separator film, reference can be made to the test method of the thickness of the substrate film.

[0197] In some embodiments, the separator film has an air permeability of 100 sec / 100 cc to 300 sec / 100 cc, and optionally 120 sec / 100 cc to 200 sec / 100 cc. When the air permeability of the separator film satisfies the predetermined range, the separator film can have good ion conduction ability, and thus the secondary battery has good electrochemical performance and rate performance.

[0198] The test method for the air permeability of the separator film can be referred to the test method for the air permeability of the base film.

[0199] In some embodiments, the separator film may have a transverse heat shrinkage of 1.0% or less, and optionally 0.4% or less, at 250° C. for 1 hour.

[0200] In some embodiments, the separator film may have a longitudinal heat shrinkage of 1.0% or less at 250° C. for 1 hour, and optionally 0.3% or less.

[0201] In some embodiments, the separator film has a transverse tensile strength of 0.5N or more, and optionally 1.2N to 3.5N.

[0202] In some embodiments, the separator film has a longitudinal tensile strength of 0.5N or more, and optionally 1.2N to 3.5N.

[0203] When at least one of the transverse tensile strength, longitudinal tensile strength, transverse thermal shrinkage rate, and longitudinal thermal shrinkage rate of the separator film satisfies a predetermined range, the separator film can have good heat resistance and physical properties, thereby improving the reliability of the secondary battery.

[0204] The transverse heat shrinkage, longitudinal heat shrinkage, transverse tensile strength, and longitudinal tensile strength of the separator film all have meanings known in the art and can be measured using methods known in the art, for example, by testing them in accordance with GB / T36363-2018. Manufacturing method

[0205] The present examples further provide methods for manufacturing the separator films provided by the present examples.

[0206] The method includes the steps of: providing an intermediate layer slurry containing a first substrate film having a melting point of 175°C or higher and an average pore size of 0.22 μm or greater, a second substrate film, and filler particles; applying the intermediate layer slurry to one of the first substrate film and the second substrate film, drying the intermediate layer slurry, and then laminating the other of the first substrate film and the second substrate film by hot pressing the first substrate film so that at least some of the filler particles are inserted into the first substrate film, thereby obtaining a separator film. Optionally, the slurry further includes an adhesive.

[0207] In some embodiments, the drying temperature may be 35°C to 80°C, 35°C to 70°C, 35°C to 60°C, 35°C to 50°C, 40°C to 70°C, 40°C to 60°C, 40°C to 50°C, 50°C to 80°C, 50°C to 70°C, 50°C to 60°C, or 60°C to 80°C.

[0208] In some embodiments, the drying time may be 5 to 60 seconds, 5 to 45 seconds, 5 to 30 seconds, 5 to 15 seconds, 15 to 60 seconds, 15 to 45 seconds, or 15 to 30 seconds.

[0209] In some embodiments, the hot welding temperature may be 40°C to 100°C, 40°C to 85°C, 40°C to 70°C, 40°C to 60°C, 50°C to 100°C, 50°C to 85°C, or 50°C to 70°C.

[0210] In some embodiments, the hot welding time may be 5 to 60 seconds, 5 to 40 seconds, 5 to 20 seconds, 5 to 10 seconds, 10 to 60 seconds, 10 to 40 seconds, or 10 to 20 seconds.

[0211] In some embodiments, the hot welding pressure may be between 1 MPa and 10 MPa, between 2 MPa and 8 MPa, between 3 MPa and 7 MPa, or between 4 MPa and 6 MPa.

[0212] By adjusting the separator film manufacturing parameters, such as drying parameters and hot-welding parameters, the separator film obtained by combining the first substrate film, intermediate layer, and second substrate film can have good mechanical strength, self-supporting properties, and heat resistance. Furthermore, by adjusting the hot-welding parameters of the separator film within the above ranges, the insertion depth of the filler particles into the substrate film can be adjusted, reducing the overall thickness of the separator film and thereby further improving the energy density of the battery.

[0213] In some embodiments, the method of applying the intermediate layer slurry may be transfer coating, spin spray coating, dip coating, or the like, but the embodiments of the present application are not limited thereto.

[0214] Unless otherwise specified, all of the raw materials used in the method for producing the separator film (for example, the first base film, the second base film, the filler particles, the adhesive, etc.) can be commercially available products. secondary battery

[0215] Embodiments of the present application further provide a secondary battery.

[0216] A secondary battery, also known as a rechargeable battery or storage battery, refers to a battery that can be used continuously by recharging after discharging to activate the active material. Typically, a secondary battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode piece, a negative electrode piece, and a separator film disposed between the positive and negative electrodes, which mainly serves to prevent short circuits between the positive and negative electrodes and also allows active ions to pass through.

[0217] The present application is not particularly limited by the type of secondary battery, and for example, the secondary battery may be a lithium ion battery, a sodium ion battery, a lithium metal battery, a sodium metal battery, etc., and in particular, the secondary battery may be a lithium ion battery.

[0218] A secondary battery provided by an embodiment of the present application includes the separator film of the present application or a separator film produced by the method of the present application, and the separator film can improve the reliability of the secondary battery and extend the cycle life of the secondary battery.

[0219] [Positive electrode piece] In some embodiments, the positive electrode piece may include a positive electrode current collector and a positive electrode film layer including a positive electrode active material disposed on at least one surface of the positive electrode current collector. For example, the positive electrode current collector has two opposing surfaces in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0220] When the secondary battery is a lithium ion battery, the positive electrode active material may include, but is not limited to, at least one of lithium transition metal oxides, lithium-containing phosphates, and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, at least one 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 respective modified compounds. Examples of lithium-containing phosphates may include, but are not limited to, at least one 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 respective modified compounds.

[0221] In some embodiments, in order to further improve the energy density of the secondary battery, the positive electrode active material used in the lithium ion battery may include at least one of lithium transition metal oxides having the general formula Li a Ni b Co c M d O e A f and their modified compounds. 0.8 ≦ a ≦ 1.2, 0.5 ≦ b < 1, 0 < c < 1, 0 < d < 1, 1 ≦ e ≦ 2, 0 ≦ f ≦ 1, M is at least one selected from Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A is at least one selected from N, F, S, and Cl.

[0222] As an example, the positive electrode active material used in the lithium ion battery is LiCoO₂, LiNiO₂, LiMnO₂, LiMn₂O₄, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O₂ (NCM333), LiNi 0.5 Co 0.2 Mn 0.3O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.85 Co 0.15 Al 0.05 At least one of O2, LiFePO4, and LiMnPO4 may be included.

[0223] When the secondary battery is a sodium-ion battery, the positive electrode active material may include, but is not limited to, at least one of a sodium-containing transition metal oxide, a polyanion material (e.g., phosphate, fluorophosphate, pyrophosphate, sulfate, etc.), and a Prussian blue-based material.

[0224] For example, the positive electrode active materials used in sodium-ion batteries are NaFeO2, NaCoO2, NaCrO2, NaMnO2, NaNiO2, NaNi 1 / 2 Ti 1 / 2 O2, NaNi 1 / 2 Mn 1 / 2 O2, Na 2 / 3 Fe 1 / 3 Mn 2 / 3 O2, NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, NaFePO4, NaMnPO4, NaCoPO4, Prussian blue-based materials, general formula X p M' q (PO4) r O x Y 3-x The compound may include at least one material having the general formula X p M' q (PO4) r O x Y 3-x In, 0 <p≦4、0<q≦2、1≦r≦3、0≦x≦2であり、Xは、H + , Li + , Na + , K. + and NH4 +M' is a transition metal cation, optionally at least one of V, Ti, Mn, Fe, Co, Ni, Cu, and Zn; and Y is a halogen anion, optionally at least one of F, Cl, and Br.

[0225] The modifying compound for each of the positive electrode active materials may be modified by doping the positive electrode active material and / or by coating the surface thereof.

[0226] In some embodiments, the positive electrode film layer further optionally includes a positive electrode conductive agent. The present application is not particularly limited by the type of the positive electrode conductive agent, and examples of the positive electrode conductive agent include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0227] In some embodiments, the positive electrode film layer may further include a positive electrode adhesive. The present application is not particularly limited by the type of the positive electrode adhesive, and the positive electrode adhesive may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic resin.

[0228] In some embodiments, the positive electrode current collector may be a metal foil piece or a composite current collector. An example of the metal foil piece is aluminum foil. The composite current collector may include a polymeric material base layer and a metal material layer formed on at least one surface of the polymeric material base layer. For example, the metal material may include at least one of aluminum, an aluminum alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, and a silver alloy. For example, the polymeric material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0229] The positive electrode film layer is typically formed by applying a positive electrode slurry to a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, optional conductive agent, optional adhesive, and any other components in a solvent and stirring the mixture uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP).

[0230] [Negative electrode piece] In some embodiments, the negative electrode piece may include a negative electrode current collector and a negative electrode film layer including a negative electrode active material disposed on at least one surface of the negative electrode current collector. For example, the negative electrode current collector has two opposing surfaces in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposing surfaces of the negative electrode current collector.

[0231] The negative electrode active material may be any negative electrode active material known in the art for use in secondary batteries. For example, the negative electrode active material may include, but is not limited to, at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy material. The tin-based material may include at least one of elemental silicon, tin oxide, and tin alloy material.

[0232] In some embodiments, the negative electrode film layer may further include a negative electrode conductive agent. The present application is not particularly limited by the type of the negative electrode conductive agent, and the negative electrode conductive agent may include, for example, at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0233] In some embodiments, the negative electrode film layer further optionally includes a negative electrode adhesive. The present application is not particularly limited by the type of negative electrode adhesive, and the negative electrode adhesive may include, for example, at least one of styrene butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0234] In some embodiments, the negative electrode film layer may further optionally include other additives, such as thickeners such as sodium carboxymethyl cellulose (CMC) and PTC thermistor materials.

[0235] In some embodiments, the negative electrode current collector may be a metal foil piece or a composite current collector. An example of the metal foil piece is copper foil. The composite current collector may include a polymeric material base layer and a metal material layer formed on at least one surface of the polymeric material base layer. For example, the metal material may include at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. For example, the polymeric material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0236] The negative electrode film layer is typically formed by applying a negative electrode slurry to a negative electrode current collector, drying, and cold pressing. The negative electrode slurry is typically formed by dispersing the negative electrode active material, optional conductive agent, optional adhesive, and other optional auxiliary agents in a solvent and stirring the mixture uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0237] The negative electrode piece does not exclude additional functional layers other than the negative electrode film layer. For example, in some embodiments, the negative electrode piece further includes a conductive primer layer (e.g., composed of a conductive agent and an adhesive) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector. In some embodiments, the negative electrode piece of the present application further includes a protective layer coated on the surface of the negative electrode film layer.

[0238] [Electrolyte] During the charge and discharge process of the secondary battery, active ions are repeatedly inserted and removed between the positive and negative electrode pieces, and the electrolyte serves to conduct the active ions between the positive and negative electrode pieces. The present application is not particularly limited to the type of electrolyte, and can be selected according to actual needs.

[0239] The electrolyte solution includes an electrolyte salt and a solvent, and the types of the electrolyte salt and the solvent are not specifically limited and can be selected according to actual needs.

[0240] When the secondary battery is a lithium-ion battery, by way of example, the electrolyte salt may include at least one 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 difluorooxalatoborate (LiDFOB), lithium bisoxalatoborate (LiBOB), lithium difluorophosphate (LiPOF), lithium difluorobisoxalatophosphate (LiDFOP), and lithium tetrafluorooxalatophosphate (LiTFOP), but is not limited thereto.

[0241] When the secondary battery is a sodium-ion battery, by way of example, the electrolyte salt may include at least one of sodium hexafluorophosphate (NaPF), sodium tetrafluoroborate (NaBF), sodium perchlorate (NaClO), sodium hexafluoroarsenate (NaAsF), sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluoro(oxalato)borate (NaDFOB), sodium bisoxalatoborate (NaBOB), sodium difluorophosphate (NaPOF), sodium difluorobisoxalatophosphate (NaDFOP), and sodium tetrafluorooxalatophosphate (NaTFOP), but is not limited thereto.

[0242] By way of example, the solvent may include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0243] In some embodiments, the electrolyte solution further optionally includes additives. For example, the additives may include a negative electrode film-forming additive, a positive electrode film-forming additive, or an additive that can improve specific battery performance, such as an additive that can improve the overcharge performance of the battery, an additive that can improve the high-temperature performance of the battery, or an additive that can improve the low-temperature power performance of the battery.

[0244] In some embodiments, the positive electrode pieces, separator film, and negative electrode pieces can be wound and / or stacked to form an electrode assembly. The separator film of the present application simultaneously includes a first substrate film and a second substrate film, and it is understood that the first substrate film or the second substrate film can optionally face the positive electrode piece or the negative electrode piece. For example, the first substrate film faces the positive electrode piece and the second substrate film faces the negative electrode piece, or the first substrate film faces the negative electrode piece and the second substrate film faces the positive electrode piece. To further improve the safety performance of the battery, the first substrate film of the separator film in the secondary battery of the present application can face the negative electrode piece and the second substrate film faces the positive electrode piece. According to the research of the present inventors, the pore size of the first substrate film of the separator film of the present application is within a specific range, which is more advantageous for the rapid passage of active ions (e.g., lithium ions) toward the negative electrode, ensuring the speed of lithium insertion and favoring the uniformity of lithium insertion, which is advantageous for reducing the generation and growth of lithium dendrites, thereby further improving the safety performance of the battery.

[0245] In some embodiments, the secondary battery may include an outer package, which may be used to enclose the electrode assembly and the electrolyte.

[0246] In some embodiments, the exterior packaging of the secondary battery may be a hard casing, such as a hard plastic casing, an aluminum case, a steel case, etc. The exterior packaging of the secondary battery may also be a pouch, such as a bag-type pouch. The pouch may be made of plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0247] The present application does not particularly limit the shape of the secondary battery, which may be cylindrical, rectangular, or any other shape. For example, Fig. 1 shows a secondary battery 5 having a rectangular structure as an example.

[0248] In some embodiments, as shown in FIG. 2 , the exterior package may include a casing 51 and a cover plate 53. The casing 51 may include a base plate and a side plate connected to the base plate, and the base plate and the side plate together form a surrounding accommodating cavity. The casing 51 has an opening communicating with the accommodating cavity, and the cover plate 53 is used to cover the opening and seal the accommodating cavity. The positive electrode piece, the negative electrode piece, and the separator film may be formed into an electrode assembly 52 through a winding process and / or a stacking process. The electrode assembly 52 is sealed in the accommodating cavity. An electrolyte is impregnated into the electrode assembly 52. ​​The number of electrode assemblies 52 included in the secondary battery 5 may be one or more and can be adjusted according to needs.

[0249] Methods for manufacturing secondary batteries are well known. In some embodiments, a secondary battery may be formed by assembling a positive electrode piece, a separator film, a negative electrode piece, and an electrolyte. For example, the positive electrode piece, the separator film, and the negative electrode piece may be wound and / or stacked to form an electrode assembly, which may then be placed in an outer package, dried, and then injected with an electrolyte. The secondary battery may then be obtained through processes such as vacuum sealing, standing, chemical formation, and shaping.

[0250] In some embodiments, the secondary battery according to the present application may be assembled into a battery module, and the battery module may include multiple secondary batteries, the specific number of which may be adjusted according to the application and capacity of the battery module.

[0251] Fig. 3 is a schematic diagram of an example battery module 4. As shown in Fig. 3, in the battery module 4, the multiple secondary batteries 5 may be arranged in order along the length of the battery module 4. Of course, they may be arranged in any other manner. Furthermore, the multiple secondary batteries 5 may be fixed by fastening members.

[0252] Optionally, the battery module 4 may further include an exterior casing having an accommodating space, and the plurality of secondary batteries 5 are accommodated in the accommodating space.

[0253] In some embodiments, the battery modules may be assembled into a battery pack, and the number of battery modules included in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0254] 4 and 5 are schematic diagrams of an example battery pack 1. As shown in FIGS. 4 and 5, the battery pack 1 may include a battery box and a plurality of battery modules 4 installed in the battery box. The battery box includes an upper case 2 and a lower case 3, and the upper case 2 is attached as a lid to the lower case 3 and is used to form an enclosed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in any desired position in the battery box.

[0255] Electrical equipment The present invention also provides an electric device including at least one of the secondary batteries, battery modules, or battery packs provided by the present invention. The secondary batteries, battery modules, or battery packs can be used as a power source for the electric device or as an energy storage unit for the electric device. The electric device may be, but is not limited to, a mobile device (e.g., a mobile phone, a laptop, etc.), 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, etc.), an electric train, a ship, a satellite, an energy storage system, etc.

[0256] An electric device can select a secondary battery, a battery module, or a battery pack according to its usage needs.

[0257] 6 is a schematic diagram of an example electric device, such as a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, in which a battery pack or battery module can be used to meet the high power and high energy density needs of the electric device.

[0258] Another example of the electrical device may be a mobile phone, a tablet, a laptop, etc. Typically, the electrical device is required to be thin and lightweight, and can use a secondary battery as a power source.

[0259] Example The following examples further illustrate the presently disclosed subject matter, but are for illustrative purposes only, as various modifications and variations within the scope of the presently disclosed subject matter will be apparent to those skilled in the art. Unless otherwise specified, all parts, percentages, and ratios reported in the following examples are by weight, all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and all equipment used in the examples is commercially available.

[0260] Example 1 Separator film manufacturing A first substrate film and a second substrate film were provided. The first substrate film was made of PTFE, with a melting point of 327°C, an average pore size of 0.22 μm, a porosity of 87%, and a thickness of 2.8 μm. The second substrate film was made of PE, with a melting point of 142°C, an average pore size of 0.03 μm, a porosity of 33%, and a thickness of 5 μm.

[0261] Preparation of intermediate layer slurry: Filler particles boehmite, adhesive polyacrylate, and carboxymethyl cellulose were uniformly mixed in a mass ratio of 4:1:1 with an appropriate amount of solvent deionized water to prepare the intermediate layer slurry. The volume distribution particle diameter Dv50 of the filler particles boehmite was 0.2 μm.

[0262] The intermediate layer slurry was applied to a PTFE substrate film and dried. The PE substrate film and the PTFE substrate film were then hot-pressed together so that the intermediate layer was interposed between the PTFE substrate film and the PE substrate film, to produce a separator film. The drying temperature was 37°C, the drying time was 5 seconds, the hot-pressing temperature was 40°C, the hot-pressing time was 5 seconds, and the hot-pressing pressure was 5 MPa.

[0263] Manufacture of cathode pieces Positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), conductive agent carbon black (Super P), and adhesive polyvinylidene fluoride (PVDF) were uniformly mixed in a mass ratio of 96.2:2.7:1.1 with an appropriate amount of solvent N-methylpyrrolidone (NMP) to obtain a positive electrode slurry. The positive electrode slurry was then applied to a positive electrode current collector aluminum foil, and after processes such as drying, cold pressing, slitting, and cutting, positive electrode pieces were obtained.

[0264] Manufacture of negative electrode pieces The negative electrode active material artificial graphite, conductive agent carbon black (Super P), adhesive styrene butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC) were uniformly mixed with an appropriate amount of solvent deionized water in a mass ratio of 96.4:0.7:1.8:1.1 to obtain a negative electrode slurry. The negative electrode slurry was then applied to a negative electrode current collector copper foil, and after drying, cold pressing, slitting and cutting processes, negative electrode pieces were obtained.

[0265] Electrolyte production Ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of 30:30:40 to obtain an organic solvent, and thoroughly dried LiPF6 was dissolved in the organic solvent to prepare an electrolyte solution with a concentration of 1 mol / L.

[0266] Secondary battery manufacturing The positive electrode piece, the separator film prepared above, and the negative electrode piece were stacked in order and wound up to obtain an electrode assembly, in which the first substrate film in the separator film faces the negative electrode. The electrode assembly was placed in an outer package, dried, and then an electrolyte was injected. After vacuum sealing, standing, chemical conversion, shaping, and other processes, a secondary battery was obtained.

[0267] The secondary batteries of Examples 2 to 18 and Comparative Example 1 were similar to Example 1, with the difference being the use of different substrate films or the adjustment of intermediate layer parameters, as specifically shown in Table 1.

[0268] In the above examples and comparative examples, the melting points of the first and second base films were measured by the following method: 4 mg to 6 mg of a sample to be measured was taken and placed in the sample chamber of a differential scanning calorimeter. The temperature was raised from 25°C to 400°C at a heating rate of 10°C / min to obtain a melting endothermic curve of the sample. The temperature corresponding to the peak value of the curve was determined as the melting point of the sample.

[0269] In the above examples and comparative examples, the average pore diameters of the first and second substrate films were measured using a mercury porosimeter with reference to GB / T21650-2008.

[0270] The volume distribution particle diameter Dv50 of the filler particles was measured using a laser particle size analyzer (Malvern Mastersizer 2000E, UK) in accordance with GB / T19077-2016 particle size distribution laser diffraction method.

[0271] Testing part The separator films and secondary batteries of Examples 1 to 18 and Comparative Example 1 were subjected to the following tests, and the test results are shown in Table 2.

[0272] (1) Heat shrinkage test of separator film Sample preparation: The separator film prepared above was punched into samples with a width of 50 mm and a length of 100 mm using a press, and five parallel samples were taken and placed and fixed on a glass plate.

[0273] Sample test: The temperature of the blower oven was set to 250°C, and after the temperature reached the set temperature and stabilized for 30 minutes, the glass plate was placed in the blower oven, and the test was completed after 1 hour. The length of the separator film was measured, and the length value was recorded in a, with the unit being mm.

[0274] Calculation of heat shrinkage: Machine direction (MD) heat shrinkage = [(100-a) / 100] x 100%, and the average value of five parallel samples was used as the test result.

[0275] (2) Separator film puncture strength test The test was conducted in accordance with GB / T 10004-2008. Specifically, the separator film was cut into strips to obtain 100 mm wide test pieces. The test pieces were then attached to a clamp ring for holding the sample film. A steel needle with a diameter of 1.0 mm and a tip radius of 0.5 mm was then pierced at a speed of (50±5) mm / min. The maximum load at which the steel needle penetrated the test piece was recorded. Five parallel samples were taken, and measurements were taken at three random points on each set. The arithmetic mean of the puncture strengths of all parallel samples was used as the separator film puncture strength.

[0276] (3) Separator film breathability test The air permeability of the separator film was tested according to GB / T36363-2018.

[0277] (4) Room temperature cycle performance test of secondary batteries The secondary batteries manufactured in the examples and comparative examples were subjected to a first charge and discharge at 25°C. After allowing the secondary batteries to stand for 30 minutes at 25°C, they were charged to 4.35 V at a constant current of 1 C, continued to be charged at a constant voltage until the current was ≦0.05 C, and then discharged to 2.8 V at a constant current of 1 C. This process was considered one charge and discharge process, and the discharge capacity at this time was recorded as the discharge capacity of the first cycle of the battery. The charge and discharge cycle was repeated in this manner, and the number of cycles when the capacity decreased to 80% was recorded.

[0278] (5) Secondary battery energy density test At room temperature, the secondary battery is first charged at a 1C rate current, the charging is constant current and constant voltage charging, the end voltage is 4.2V, the cut-off current is 0.05C, and the discharge is performed at a 1C rate current, the discharge end voltage is 2.8V, and the discharge capacity C of the secondary battery at the first cycle is b and the discharge platform voltage U were recorded.

[0279] The mass m of the battery was measured using an electronic balance, and the energy density of the secondary battery was calculated using the following formula.

[0280] Energy density = C b ×U / m.

[0281] [Table 1] [Table 2]

[0282] As can be seen from the test results in Table 2, when the separator film includes a first substrate film with a high melting point, a second substrate film, and an intermediate layer located between the first substrate film and the second substrate film, and the average pore size of the first substrate film is within the range of the examples of the present application, the energy density and cycle performance of the battery can be significantly improved.

[0283] As can be seen from the test results of Examples 1 to 6, when other conditions were unchanged, the heat resistance and breathability of the separator film gradually improved as the average pore size of the first substrate film increased. Furthermore, the energy density of the secondary battery gradually improved as the average pore size of the first substrate film increased. This is thought to be because a relatively large average pore size of the first substrate film is advantageous for increasing the insertion depth of the filler particles and the number of filler particles inserted into the first substrate film. This provides support through the composite structure of the first substrate film and the filler particles, while reducing the overall thickness of the separator film, thereby improving the cycle performance and energy density of the secondary battery. As can be seen from the test results of Examples 3 and 7 to 10, when other conditions were unchanged, the heat resistance and strength of the separator film decreased as the average pore size of the second substrate film increased, but the breathability of the separator film and the energy density of the secondary battery improved. Therefore, by adjusting the average pore size of the second substrate film according to actual needs, secondary batteries could be made to have both good cycle performance and high energy density. As can be seen from the test results of Examples 3 and 15 to 18, when other conditions are unchanged, increasing the porosity of the first substrate film improves the heat resistance, puncture strength, and breathability of the separator film, thereby improving the cycle performance and extending the cycle life of the secondary battery. Furthermore, increasing the porosity of the first substrate film increases the number of filler particles inserted into the first substrate film, which is advantageous for reducing the overall thickness of the separator film and further improving the energy density of the secondary battery.

[0284] In contrast, in the separator film of Comparative Example 1, the average pore size of the first substrate film was smaller than the range of the examples of the present application, making it difficult for the filler particles to be inserted into the first substrate film, and thus making it difficult to form a composite structure with high mechanical strength. It was also difficult to reduce the overall thickness of the separator film. Therefore, the heat resistance and puncture strength of the separator film of Comparative Example 1 were much lower than those of Examples 1 to 18, and the energy density and cycle performance of the secondary battery of Comparative Example 1 were also not ideal.

[0285] It should be understood that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments that have substantially the same configuration as the technical idea and achieve the same functions and effects within the scope of the technical solution of the present application are also included in the technical scope of the present application. Furthermore, various modifications conceivable by those skilled in the art may be made to the embodiments, or parts of the components of the embodiments may be combined to form other forms, without departing from the gist of the present application, and these embodiments are also included in the scope of the present application.

Claims

1. A separator film, a first base film having a melting point of 175°C or higher and an average pore size of 0.22 µm or greater; a second substrate film; an intermediate layer located between the first base film and the second base film, the intermediate layer including filler particles at least a portion of which is inserted into the first base film; Separator film.

2. The average pore size of the first substrate film is 0.22 μm to 4.0 μm, and optionally 1.0 μm to 2.7 μm; The separator film of claim 1 .

3. the average pore size of the second base film is smaller than the average pore size of the first base film; Alternatively, the average pore size of the second substrate film is 0.01 μm to 0.5 μm, more preferably 0.02 μm to 0.1 μm. The separator film according to claim 1 or 2.

4. The insertion depth of the filler particles into the first base film is 0.2 μm or more, and optionally 0.5 μm to 1.0 μm. The separator film according to any one of claims 1 to 3.

5. The insertion depth of the filler particles into the second substrate film is 0.1 μm or more, and optionally 0.1 μm to 0.5 μm. The separator film according to any one of claims 1 to 4.

6. an insertion depth of the filler particles into the first base film that is greater than an insertion depth of the filler particles into the second base film; The separator film according to any one of claims 1 to 5.

7. the melting point of the first base film is equal to or higher than the melting point of the second base film; Preferably, the melting point of the first substrate film is 175°C to 350°C, more preferably 220°C to 350°C; Preferably, the melting point of the second substrate film is 130°C to 200°C, more preferably 135°C to 180°C. The separator film according to any one of claims 1 to 6.

8. The longitudinal elongation at break of the first substrate film is 20% to 105%, and optionally 40% to 90%; and / or The transverse breaking elongation of the first base film is 20% to 105%, and optionally 40% to 90%; The separator film according to any one of claims 1 to 7.

9. the longitudinal breaking elongation of the second base film is smaller than the transverse breaking elongation of the second base film; The longitudinal elongation at break of the second substrate film is ≧40%, and optionally 60% to 150%; and / or The transverse elongation at break of the second substrate film is ≧60%, and optionally 80% to 160%; The separator film according to any one of claims 1 to 8.

10. the porosity of the first substrate film is greater than the porosity of the second substrate film; Optionally, the porosity of the first substrate film is 50% to 98%; Optionally, the porosity of the second substrate film is 20% to 60%. The separator film according to any one of claims 1 to 9.

11. the relative molecular mass of the first substrate film is greater than the relative molecular mass of the second substrate film; Preferably, the relative molecular mass of the first substrate film is 300,000 to 6,000,000, more preferably 1,000,000 to 3,000,000; Preferably, the relative molecular mass of the second substrate film is 100,000 to 3,000,000, more preferably 400,000 to 1,500,000; The separator film according to any one of claims 1 to 10.

12. the ratio of the thickness of the first substrate film to the thickness of the second substrate film is 0.15 to 2.0, and optionally 0.3 to 0.6; Preferably, the thickness of the first substrate film is 1 μm to 10 μm, more preferably 1 μm to 3 μm; Preferably, the thickness of the second substrate film is 2 μm to 10 μm, more preferably 3 μm to 6 μm. The separator film according to any one of claims 1 to 11.

13. the first base film has a lower air permeability than the second base film; Preferably, the ratio of the air permeability of the first base film to the air permeability of the second base film is 0.1 to 0.5, more preferably 0.2 to 0.4; Alternatively, the first base film has an air permeability of 20 sec / 100 cc to 100 sec / 100 cc, more preferably 30 sec / 100 cc to 40 sec / 100 cc; Alternatively, the breathability of the second substrate film is 100 sec / 100 cc to 300 sec / 100 cc, more preferably 100 sec / 100 cc to 150 sec / 100 cc; The separator film according to any one of claims 1 to 12.

14. the puncture strength of the first base film is lower than the puncture strength of the second base film; Preferably, the puncture strength of the first base film is 20 gf to 150 gf, more preferably 20 gf to 80 gf; Alternatively, the puncture strength of the second base film is 60 gf to 400 gf, more preferably 80 gf to 270 gf. The separator film according to any one of claims 1 to 13.

15. the material of the first base film includes at least one of polytetrafluoroethylene and derivatives thereof, polyethylene terephthalate and derivatives thereof, polyimide and derivatives thereof, polyether ether ketone and derivatives thereof, polyphenylene sulfide and derivatives thereof, polybenzimidazole and derivatives thereof, polysulfone and derivatives thereof, and polylactic acid and derivatives thereof; The separator film according to any one of claims 1 to 14.

16. the material of the second base film includes at least one of polyolefin, halogenated polyolefin, polyether, polyester, polyvinyl alcohol, polytetrafluoroethylene and derivatives thereof, polyethylene terephthalate and derivatives thereof, polyimide and derivatives thereof, polyether ether ketone and derivatives thereof, polyphenylene sulfide and derivatives thereof, polybenzimidazole and derivatives thereof, and polysulfone and derivatives thereof; The separator film according to any one of claims 1 to 15.

17. The volume distribution particle diameter Dv50 of the filler particles is 0.01 μm to 0.8 μm, and optionally 0.2 μm to 0.8 μm; and / or The content of the filler particles is 90% or less, optionally 20% to 80%, based on the total mass of the intermediate layer; and / or The specific surface area of ​​the filler particles is 2 g / m ２ ~20g / m ２ and optionally 6 g / m ２ ~9g / m ２ That is, The separator film according to any one of claims 1 to 16.

18. the filler particles include at least one of inorganic particles, organic particles, and organic-metallic framework materials; Optionally, the inorganic particles include one or more of inorganic particles having a dielectric constant of 5 or more, inorganic particles having ionic conductivity but not storing ions, and inorganic particles capable of electrochemical reactions; Optionally, the organic particles comprise one or more of polycarbonate, polythiophene, polypyridine, polystyrene, polyacrylate, polyethylene, polypropylene, cellulose, cellulose modifier, melamine resin, phenolic resin, polyester, silicone resin, polyimide, polyamideimide, polyaramid, polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, polyaryletherketone, copolymer of butyl acrylate and ethyl methacrylate; Optionally, the organic-metal framework material comprises one or more of nitrogen-containing heterocyclic ligand framework structures, organic carboxylic acid-based ligand framework structures, and nitrogen-oxygen-containing mixed ligand framework structures; The separator film according to any one of claims 1 to 17.

19. the intermediate layer further comprises an adhesive comprising one or more of polyacrylate, polyacrylic acid, polyimide, 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, thermoplastic polyurethane, maleic anhydride, ethylene-acrylic acid copolymer; Preferably, the adhesive content is 35% or less, more preferably 10% to 30%, based on the total mass of the intermediate layer. The separator film according to any one of claims 1 to 18.

20. The separator film is (1) The thickness of the separator film is 7 μm or less, and optionally 3 μm to 6 μm; (2) The separator film has an air permeability of 100 sec / 100 cc to 300 sec / 100 cc, and optionally 120 sec / 100 cc to 200 sec / 100 cc; (3) The separator film has a transverse heat shrinkage rate of ≦1.0% at 250° C. for 1 hour, and optionally ≦0.4%; (4) The longitudinal heat shrinkage rate of the separator film at 250°C for 1 hour is ≦1.0%, and optionally ≦0.3%; (5) The separator film has a transverse tensile strength of ≧0.5N, and optionally 1.2N to 3.5N; (6) The separator film has a longitudinal tensile strength of ≧0.5 N, and optionally 1.2 N to 3.5 N. The separator film according to any one of claims 1 to 19.

21. A method for producing the separator film of any one of claims 1 to 20, comprising: Providing an intermediate layer slurry including a first substrate film, a second substrate film, and filler particles, the first substrate film having a melting point of 175°C or higher and an average pore size of 0.22 μm or more; and applying the intermediate layer slurry to one of the first base film and the second base film, drying the applied intermediate layer slurry, and then laminating the applied intermediate layer slurry to the other of the first base film and the second base film, and hot-pressing the applied intermediate layer slurry to the first base film so that at least some of the filler particles are inserted into the first base film, thereby obtaining a separator film. Optionally, the slurry further comprises an adhesive. method.

22. The method comprises: (1) the drying temperature is 35°C to 80°C, and optionally 40°C to 60°C; (2) the drying time is 5 seconds to 60 seconds, and optionally 5 seconds to 15 seconds; (3) the hot welding temperature is 40°C to 100°C, and optionally 40°C to 70°C; (4) The hot welding time is 5 seconds to 60 seconds, and optionally 5 seconds to 10 seconds; (5) The hot welding pressure is 1 MPa to 10 MPa, and optionally 3 MPa to 7 MPa.

22. The method of claim 21.

23. A secondary battery comprising a positive electrode piece, a negative electrode piece, and the separator film according to any one of claims 1 to 20, wherein the separator film is disposed between the positive electrode piece and the negative electrode piece; Optionally, the first substrate film of the separator film faces the negative electrode piece. Secondary battery.

24. The secondary battery according to claim 23, Electrical equipment.

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