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

Abstract

The invention provides an isolating membrane and a preparation method thereof, a secondary battery and an electric device. The isolating membrane comprises a first base membrane, a second base membrane, a first bonding layer and a second bonding layer, the first bonding layer is located between the first base membrane and the second base membrane, and the first bonding layer comprises a first bonding agent; the second bonding layer is located on the first base film and / or the side, away from the first bonding layer, of the second base film, and the second bonding layer comprises a second bonding agent. The thickness of the first bonding layer is recorded as T1, the thickness of the second bonding layer is recorded as T2, and the isolating membrane meets the condition that T1 / T2 is greater than 1.

Description

Separator and preparation method thereof, secondary battery and electric device

[0001] The present application relates to an isolation film and a preparation method thereof, a secondary battery and an electrical device.

[0002] In recent years, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields. With the application and promotion of secondary batteries, the requirements for their use have become increasingly stringent.

[0003] Summary of the invention

[0004] The present application provides an isolation membrane and a preparation method thereof, a secondary battery and an electrical device, aiming to improve the cycle performance and energy density of the secondary battery.

[0005] In a first aspect, the present application provides an isolation film, which includes a first base film, a second base film, a first adhesive layer and a second adhesive layer, wherein the first adhesive layer is located between the first base film and the second base film, and the first adhesive layer includes a first adhesive; the second adhesive layer is located on a side of the first base film and / or the second base film away from the first adhesive layer, and the second adhesive layer includes a second adhesive. The thickness of the first adhesive layer is recorded as T1, and the thickness of the second adhesive layer is recorded as T2, then the isolation film satisfies: T1 / T2>1.

[0006] Without intending to be limited by any theory or explanation, in the isolation membrane structure provided in the present application, the first adhesive layer can firmly composite the first base membrane and the second base membrane together and improve the heat resistance of the isolation membrane; the second adhesive layer can improve the bonding effect between the isolation membrane and the electrode plate, reduce the gap between the isolation membrane and the electrode plate, thereby delaying the growth of lithium dendrites and effectively improving the cycle performance of the battery. Under the specific thickness ratio design of the present application, the first adhesive layer has a relatively large thickness, which is beneficial to improving the structural stability and heat resistance of the isolation membrane; the second adhesive layer has a relatively small thickness, which can ensure that the isolation membrane has a high bonding force with the electrode plate while making the isolation membrane have a smaller overall thickness. Therefore, the isolation membrane of the present application is applied to secondary batteries, which can enable the secondary batteries to have both good cycle performance and high energy density.

[0007] In any embodiment of the present application, 1.25≤T1 / T2≤5. Optionally, 1.5≤T1 / T2≤4. This can further improve the reliability and energy density of the secondary battery.

[0008] In any embodiment of the present application, the thickness T1 of the first adhesive layer is less than or equal to 4 μm. Optionally, the thickness T1 of the first adhesive layer is 0.5 μm-3 μm.

[0009] In any embodiment of the present application, the thickness T2 of the second adhesive layer is less than or equal to 2 μm. Optionally, the thickness T2 of the second adhesive layer is 0.4 μm-1.5 μm.

[0010] The thickness of the first adhesive layer and / or the thickness of the second adhesive layer satisfies the given range, so that the isolation membrane has both high heat resistance and small thickness, and has high bonding strength between the isolation membrane and the electrode plate, thereby further improving the reliability and energy density of the secondary battery.

[0011] In any embodiment of the present application, the total thickness T of the isolation film is less than 12 μm. Optionally, the total thickness T of the isolation film is 3 μm-10 μm. Thus, the energy density of the secondary battery can be effectively improved.

[0012] In any embodiment of the present application, the thickness of the first base film is less than or equal to 9 μm. Optionally, the thickness of the first base film is 3 μm-6 μm.

[0013] In any embodiment of the present application, the thickness of the second base film is less than or equal to 8 μm. Optionally, the thickness of the second base film is 1 μm-5 μm.

[0014] When the thickness of the first base film and / or the thickness of the second base film meets the above range, the heat resistance of the isolation film can be enhanced, and the high temperature cycle performance and reliability of the battery can be effectively improved.

[0015] In any embodiment of the present application, the melting point of the first base film is lower than the melting point of the second base film.

[0016] In any embodiment of the present application, the melting point of the first base film is 120° C.-280° C. Optionally, the melting point of the first base film is 130° C.-260° C.

[0017] In any embodiment of the present application, the melting point of the second base film is 160° C.-370° C. Optionally, the melting point of the second base film is 170° C.-350° C.

[0018] When the melting point of the first base film and / or the melting point of the second base film satisfies the above range, the secondary battery can have both good cycle performance and high reliability.

[0019] In any embodiment of the present application, the porosity of the first base film is smaller than the porosity of the second base film.

[0020] In any embodiment of the present application, the porosity of the first base film is 30%-70%. Optionally, the porosity of the first base film is 35%-55%.

[0021] In any embodiment of the present application, the porosity of the second base film is 35%-85%. Optionally, the porosity of the second base film is 40%-75%.

[0022] By adjusting the porosity of the first base film and / or the porosity of the second base film within the above range, it is helpful to improve the cycle performance, dynamic performance, etc. of the secondary battery.

[0023] In any embodiment of the present application, the puncture strength of the first basement film is greater than the puncture strength of the second basement film.

[0024] In any embodiment of the present application, the puncture strength of the first base film is 200 gf-450 gf. Optionally, the puncture strength of the first base film is 230 gf-420 gf.

[0025] In any embodiment of the present application, the puncture strength of the second base film is 100 gf-220 gf. Optionally, the puncture strength of the second base film is 120 gf-180 gf.

[0026] This helps reduce the risk of the isolation membrane being punctured by lithium dendrites or mechanical impact, thereby further improving the reliability of the secondary battery.

[0027] In any embodiment of the present application, the transverse elongation at break of the first base film is higher than the transverse elongation at break of the second base film.

[0028] In any embodiment of the present application, the longitudinal elongation at break of the first base film is lower than the longitudinal elongation at break of the second base film.

[0029] In any embodiment of the present application, the transverse elongation at break of the first base film is 50%-220%, and can be optionally 80%-170%.

[0030] In any embodiment of the present application, the longitudinal elongation at break of the first base film is 30%-100%, and can be optionally 40%-85%.

[0031] In any embodiment of the present application, the transverse elongation at break of the second base film is 40%-200%, and can be optionally 60%-160%.

[0032] In any embodiment of the present application, the longitudinal elongation at break of the second base film is 50%-700%, and can be optionally 80%-600%.

[0033] By adjusting the longitudinal elongation at break and / or the transverse elongation at break of the first base film and / or the second base film to meet the above range, it is beneficial to improve the ductility and strength of the isolation film, thereby helping to improve the production yield and reliability of the secondary battery.

[0034] In any embodiment of the present application, the first binder and / or the second binder each independently include one or more of polyacrylate, polyacrylic acid, polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride-trichloroethylene copolymer, polyvinyl pyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyethylene oxide, polyarylate, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, polyacrylonitrile, polyvinyl alcohol, polyethylene, polypropylene, starch, and cyanoethyl pullulan.

[0035] In any embodiment of the present application, the second adhesive layer includes a second adhesive made of a material different from that of the first adhesive.

[0036] In any embodiment of the present application, the first binder includes polyacrylate.

[0037] In any embodiment of the present application, the second binder includes polyvinylidene fluoride (PVDF).

[0038] In any embodiment of the present application, the second binder includes both polyvinylidene fluoride (PVDF) and polyacrylate.

[0039] In any embodiment of the present application, the content of the first adhesive is less than or equal to 30%, and can be optionally less than or equal to 20%, based on the total mass of the first adhesive layer.

[0040] In any embodiment of the present application, the content of the second binder is greater than or equal to 85%, and can be optionally greater than or equal to 90%, based on the total mass of the second adhesive layer.

[0041] In any embodiment of the present application, the first binder and / or the second binder includes an aqueous binder.

[0042] The first adhesive layer can give the isolation film good heat resistance and improve the reliability of the secondary battery on the basis of ensuring the adhesion strength and uniformity of the first base film and the second base film. The second adhesive layer can improve the bonding force between the isolation film and the electrode plate, reduce the gap between the isolation film and the electrode plate, thereby delaying the growth of lithium dendrites and further improving the cycle performance of the battery.

[0043] In any embodiment of the present application, the material of the first base film includes at least one of polyolefins and their derivatives, halogenated polyolefins and their derivatives, polyethers and their derivatives, polyetheretherketones and their derivatives, polyesters and their derivatives, polyimides and their derivatives, polyvinyl alcohols and their derivatives, polytetrafluoroethylene and their derivatives, polyvinyl fluoride and their derivatives, polyvinylidene fluoride and their derivatives, and polyethylene terephthalate and its derivatives.

[0044] In any embodiment of the present application, the material of the second base film includes at least one of polyolefins and their derivatives, halogenated polyolefins and their derivatives, polyethers and their derivatives, polyetheretherketones and their derivatives, polyesters and their derivatives, polyimides and their derivatives, polyvinyl alcohols and their derivatives, polytetrafluoroethylene and their derivatives, polyvinyl fluoride and their derivatives, polyvinylidene fluoride and their derivatives, and polyethylene terephthalate and its derivatives.

[0045] In any embodiment of the present application, the first bonding layer further includes a filler.

[0046] Optionally, the filler includes at least one of inorganic particles, organic particles, and organic-metal framework materials.

[0047] Optionally, the content of the filler is less than or equal to 90%, and optionally 30%-85%, based on the total mass of the first bonding layer.

[0048] Optionally, the volume distribution particle size Dv50 of the filler is 0.05 μm-1.2 μm, optionally 0.2 μm-0.8 μm.

[0049] Optionally, the filler has a specific surface area of ​​4 g / m 2 -12g / m 2 , optional 6g / m 2 -9g / m 2 .

[0050] The filler can further improve the heat resistance and physical properties (such as tensile strength, puncture strength, etc.) of the separator, thereby improving the reliability of the secondary battery.

[0051] In any embodiment of the present application, the transverse tensile strength of the separator is ≥ 600 kg / cm 2 , optional 800kg / cm 2 -2500kg / cm 2 .

[0052] Optionally, the longitudinal tensile strength of the isolation film is ≥800kg / cm 2 , optional 1000kg / cm 2 -3000kg / cm 2 .

[0053] Optionally, the air permeability of the isolation membrane is 150s / 100cc-500s / 100cc, and optionally 180s / 100cc-380s / 100cc.

[0054] Optionally, the transverse heat shrinkage rate of the isolation film at 250° C. for 1 hour is ≤5%, and may be 0.05%-3%.

[0055] Optionally, the longitudinal heat shrinkage rate of the isolation film at 250° C. for 1 hour is ≤5%, and may be 0.05%-3%.

[0056] When at least one of the transverse tensile strength, longitudinal tensile strength, air permeability, transverse heat shrinkage rate, and longitudinal heat shrinkage rate of the isolation membrane meets the given range, the isolation membrane can have good heat resistance and physical properties, thereby improving the reliability of the secondary battery.

[0057] The second aspect of the present application provides a method for preparing the isolation film of the first aspect, comprising the following steps: providing a first base film, a second base film, a first bonding layer slurry and a second bonding layer slurry, the first bonding layer slurry comprising a first adhesive, and the second bonding layer slurry comprising a second adhesive; coating the first bonding layer slurry on one of the first base film and the second base film, and then laminating with the other of the first base film and the second base film, thereby forming a first bonding layer between the first base film and the second base film; coating the second bonding layer slurry on the surface of the first base film facing away from the first bonding layer, and / or coating the second bonding layer slurry on the surface of the second base film facing away from the first bonding layer, thereby obtaining an isolation film; the thickness of the first bonding layer is denoted as T1, the thickness of the second bonding layer is denoted as T2, and the isolation film satisfies: T1 / T2>1.

[0058] Optionally, the first bonding layer slurry includes a first bonding agent and a filler.

[0059] A third aspect of the present application provides a secondary battery, comprising the isolation film of the first aspect.

[0060] A fourth aspect of the present application provides an electrical device, comprising the secondary battery of the third aspect of the present application.

[0061] The electric device of the present application includes the secondary battery provided by the present application, and thus has at least the same advantages as the secondary battery.

[0062] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some implementation methods of the present application, and for ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0063] FIG. 1 is a schematic diagram of an isolation membrane according to an embodiment of the present application.

[0064] FIG. 2 is a schematic diagram of another embodiment of the isolation membrane provided by the present application.

[0065] FIG. 3 is a schematic diagram of another embodiment of the isolation membrane provided in the present application.

[0066] FIG. 4 is a schematic diagram of an embodiment of a secondary battery provided in the present application.

[0067] FIG. 5 is an exploded schematic diagram of an embodiment of a secondary battery provided in the present application.

[0068] FIG. 6 is a schematic diagram of an embodiment of a battery module provided in the present application.

[0069] FIG. 7 is a schematic diagram of an embodiment of a battery pack provided in the present application.

[0070] FIG. 8 is an exploded schematic diagram of the embodiment of the battery pack shown in FIG. 7 .

[0071] FIG. 9 is a schematic diagram of an embodiment of an electric device including the secondary battery provided in the present application as a power source.

[0072] In the drawings, the drawings may not be drawn according to the actual scale. The reference numerals are as follows: 10, separator; 11, first base film; 12, second base film; 13, first adhesive layer; 14, second adhesive layer; 1, battery pack; 2, upper box; 3, lower box; 4, battery module; 5, secondary battery; 51, housing; 52, electrode assembly; 53, cover plate.

[0073] Hereinafter, the isolation membrane and its preparation method, secondary battery and electric device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0074] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0075] If not otherwise specified, all embodiments and optional embodiments of the present application may be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of the present application.

[0076] Unless otherwise specified, all technical features and optional technical features of the present application may be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of the present application.

[0077] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may 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.

[0078] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0079] If not specifically 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 satisfies 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).

[0080] If not otherwise specified, in this application, the terms "first", "second", etc. are used to distinguish different objects rather than to describe a specific order or a primary-secondary relationship.

[0081] In the present application, the terms "plurality", "multiplicity" and the like refer to two or more.

[0082] Unless otherwise specified, the terms used in this application have the commonly understood meanings that are commonly understood by those skilled in the art.

[0083] Unless otherwise specified, the values ​​of the parameters mentioned in this application can be measured by various test methods commonly used in the art, for example, they can be measured according to the test methods given in the examples of this application. Unless otherwise specified, the test temperature of each parameter is 25°C.

[0084] Unless otherwise specified, the ratio parameters involved in this application are compared in the same unit. For example, the thickness ratio of A to B is 1.2:1, and the thickness units of A and B are the same.

[0085] Isolation film

[0086] Typically, a secondary battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator. The separator is disposed between the positive electrode sheet and the negative electrode sheet and mainly serves to prevent the positive and negative electrodes from short-circuiting.

[0087] The isolation film provided in the embodiment of the present application includes a first base film, a second base film, a first adhesive layer and a second adhesive layer, wherein the first adhesive layer is located between the first base film and the second base film, and the first adhesive layer includes a first adhesive; the second adhesive layer is located on the side of the first base film and / or the second base film away from the first adhesive layer, and the second adhesive layer includes a second adhesive. The thickness of the first adhesive layer is recorded as T1, and the thickness of the second adhesive layer is recorded as T2, then the isolation film satisfies: T1 / T2>1.

[0088] Fig. 1 is a schematic diagram of an embodiment of the isolation film of the present application. As shown in Fig. 1, the exemplary isolation film 10 includes a first base film 11, a second base film 12, a first adhesive layer 13 and a second adhesive layer 14. The first adhesive layer 13 is located between the first base film 11 and the second base film 12, and the second adhesive layer 14 is arranged on the side of the first base film 11 away from the first adhesive layer 13, and the thickness T1 of the first adhesive layer 13 is greater than the thickness T2 of the second adhesive layer 14.

[0089] Fig. 2 is a schematic diagram of another embodiment of the isolation film of the present application. As shown in Fig. 2, the exemplary isolation film 10 includes a first base film 11, a second base film 12, a first adhesive layer 13 and a second adhesive layer 14. The first adhesive layer 13 is located between the first base film 11 and the second base film 12, and the second adhesive layer 14 is provided on the side of the second base film 12 facing away from the first adhesive layer 13, and the thickness T1 of the first adhesive layer 13 is greater than the thickness T2 of the second adhesive layer 14.

[0090] Fig. 3 is a schematic diagram of another embodiment of the isolation film of the present application. As shown in Fig. 3, the exemplary isolation film 10 includes a first base film 11, a second base film 12, a first adhesive layer 13 and a second adhesive layer 14. The first adhesive layer 13 is located between the first base film 11 and the second base film 12, and the second adhesive layer 14 is provided on the side of the first base film 11 facing away from the first adhesive layer 13 and the side of the second base film 12 facing away from the first adhesive layer. The thickness T1 of the first adhesive layer 13 is greater than the thickness T2 of the second adhesive layer 14.

[0091] Without intending to be limited by any theory or explanation, in the isolation membrane structure provided in the present application, the first adhesive layer can firmly composite the first base membrane and the second base membrane together and improve the heat resistance of the isolation membrane; the second adhesive layer can improve the bonding effect between the isolation membrane and the electrode plate, reduce the gap between the isolation membrane and the electrode plate, thereby delaying the growth of lithium dendrites and effectively improving the cycle performance of the battery. Under the specific thickness ratio design of the present application, the first adhesive layer has a relatively large thickness, which is beneficial to improving the structural stability and heat resistance of the isolation membrane; the second adhesive layer has a relatively small thickness, which can ensure that the isolation membrane has a high bonding force with the electrode plate while making the isolation membrane have a smaller overall thickness. Therefore, the isolation membrane of the present application is applied to secondary batteries, which can enable the secondary batteries to have both good cycle performance and high energy density.

[0092] In some embodiments, the thickness ratio of the first adhesive layer to the second adhesive layer can be 1.01, 1.05, 1.2, 1.25, 1.32, 1.46, 1.5, 1.58, 1.65, 1.67, 1.88, 1.91, 2.0, 2.05, 2.25, 2.32, 2.46, 2.56, 2.58, 2.67, 2.78, 2.91, 2.99, 3.05, 3.15, 3.25, 3.46, 3.56, 3.78, 3.88, 4.0, 4.05, 4.36, 4.98, 5.0, or a range consisting of any two of the above values. For example, the thickness ratio of the first bonding layer to the second bonding layer can be selected as 1.01≤T1 / T2≤1.11, 1.05≤T1 / T2≤1.20, 1.10≤T1 / T2≤1.50, 1.10≤T1 / T2≤1.86, 1.10≤T1 / T2≤2.51, 1.10≤T1 / T2≤3.04, 1.25≤T1 / T2≤5.00, 1.45≤T1 / T2≤3.70, 1.50≤T1 / T2≤4.00, 1.67≤T1 / T2≤2.50, 1.75≤T1 / T2≤2.33, 2.33≤T1 / T2≤2.5 0, 2.50≤T1 / T2≤3.50, 3.50≤T1 / T2≤4.00, 3.30≤T1 / T2≤3.50, 3.20≤T1 / T2≤3.60, 1.75≤T1 / T2≤2.50, 1.20≤T1 / T2≤1.46, 1.32≤T1 / T2≤1.67, 1.58≤T1 / T2≤2.05, 2.25≤T1 / T2≤2.99, 2.78≤T1 / T2≤3.15, 3.46≤T1 / T2≤4.00, 3.88≤T1 / T2≤4.36, 4.05≤T1 / T2≤5.00 and so on.

[0093] When the thickness ratio of the first adhesive layer to the second adhesive layer meets the above conditions, the overall thickness of the isolation film can be further reduced while maintaining the heat resistance of the isolation film, thereby further improving the reliability and energy density of the secondary battery.

[0094] In some embodiments, the thickness T1 of the first adhesive layer may be less than or equal to 4 μm, for example, may be 0.5 μm, 0.75 μm, 1 μm, 1.25 μm, 1.5 μm, 1.75 μm, 2 μm, 2.25 μm, 2.5 μm, 2.75 μm, 3 μm, 3.25 μm, 3.5 μm, 3.75 μm, 4 μm, or a range consisting of any two of the above values. For example, the thickness of the first bonding layer can be selected to be 0.5μm-4μm, 0.5μm-3.25μm, 0.5μm-2.75μm, 0.5μm-2.5μm, 1μm-4μm, 1μm-3.25μm, 1μm-2.75μm, 1μm-2.5μm, 1.75μm-3.75μm, 1.75μm-3.25μm, 2μm-4μm, 2μm-3.75μm, 2μm-3.5μm, 2μm-3.25μm and so on.

[0095] Optionally, in some embodiments, the thickness T1 of the first bonding layer can also be 0.5μm-3μm, 0.5μm-2.85μm, 0.5μm-2.65μm, 0.5μm-2.35μm, 0.5μm-2μm, 0.5μm-1.75μm, 0.5μm-1.5μm, 0.5μm-1μm, 1μm-3μm, 1μm-2.5μm, 1μm-2μm, 1μm-1.85μm, 1μm-1.5μm, 2μm-3μm, 2μm-2.85μm, 2μm-2.5μm and the like.

[0096] In some embodiments, the thickness T2 of the second adhesive layer may be less than or equal to 2 μm, for example, 0.3 μm, 0.75 μm, 1 μm, 1.25 μm, 1.5 μm, 1.75 μm, 2 μm, or a range consisting of any two of the above values. For example, the thickness of the second adhesive layer may be 0.3 μm-2 μm, 0.3 μm-1.75 μm, 0.3 μm-1.5 μm, 0.3 μm-1.25 μm, 0.3 μm-1 μm, 0.75 μm-2 μm, 0.75 μm-1.75 μm, 0.75 μm-1.5 μm, 0.75 μm-1.25 μm, 1 μm-2 μm, 1 μm-1.75 μm, 1 μm-1.5 μm, 1.25 μm-1.75 μm, 1.75 μm-2 μm, and the like.

[0097] Optionally, in some embodiments, the thickness T2 of the second bonding layer can also be 0.4μm-1.5μm, 0.4μm-1.35μm, 0.4μm-1.2μm, 0.4μm-1μm, 0.4μm-0.8μm, 0.7μm-1.5μm, 0.7μm-1.3μm, 0.7μm-1.1μm, 1μm-1.5μm, 1μm-1.4μm, 1μm-1.2μm, 1.2μm-1.5μm and so on.

[0098] When the thickness of the first bonding layer and / or the thickness of the second bonding layer meets the above range, the isolation membrane can have both high heat resistance and small thickness, and the isolation membrane and the electrode plate have high bonding strength, thereby further improving the reliability and energy density of the secondary battery.

[0099] The thickness of the bonding layer has a well-known meaning in the art and can be tested using equipment and methods known in the art. In some embodiments, a scanning electron microscope (e.g., ZEISS Sigma 300) can be used to obtain a cross-sectional scanning electron microscope (SEM) image of the isolation film with reference to JY / T 0584-2020. As an example, the test can be performed as follows: a plurality of regions are randomly selected on the cross section of the isolation film, and the thickness of the bonding layer is measured at least five times at a certain magnification, and the measured values ​​of different regions are counted, and the average is taken as the thickness of the bonding layer.

[0100] In some embodiments, the total thickness T of the isolation film may be less than or equal to 12 μm, for example, 12 μm, 11.5 μm, 11 μm, 10.5 μm, 10 μm, 9.5 μm, 9 μm, 8.5 μm, 8 μm, 7.5 μm, 7 μm, 6.5 μm, 6 μm, 5.5 μm, 5 μm, 4 μm, 3 μm, or a range of any two of the above values. For example, 3 μm-12 μm, 3 μm-10 μm, 3 μm-8 μm, 4 μm-12 μm, 4 μm-10 μm, 4 μm-8 μm, 5 μm-12 μm, 5 μm-10 μm, 5 μm-8 μm, 6 μm-12 μm, 6 μm-10 μm, 6 μm-9 μm, 7 μm-12 μm, 7 μm-10 μm, and the like.

[0101] Under the specific thickness ratio design of the present application, the separator can have the above-mentioned relatively low overall thickness while having good heat resistance and high bonding strength with the electrode plate, thereby effectively improving the energy density of the secondary battery.

[0102] In some embodiments, the thickness of the first base film can be less than or equal to 9μm, for example, it can be 1μm, 1.2μm, 1.7μm, 2μm, 2.3μm, 2.6μm, 2.9μm, 3.2μm, 3.5μm, 3.8μm, 4.1μm, 4.4μm, 4.7μm, 5μm, 5.3μm, 5.6μm, 5.9μm, 6.2μm, 6.5μm, 6.8μm, 7.1μm, 7.4μm, 7.7μm, 8μm, 8.3μm, 8.7μm, 9μm, or a range consisting of any two of the above values.

[0103] Optionally, in some embodiments, the thickness of the first base film can also be 3μm-6μm, for example, it can be 3μm, 3.2μm, 3.5μm, 3.7μm, 4μm, 4.2μm, 4.5μm, 4.7μm, 5μm, 5.2μm, 5.5μm, 5.7μm, 6μm, or a range consisting of any two of the above values.

[0104] In some embodiments, the thickness of the second base film can be less than or equal to 8μm, for example, it can be 1μm, 1.3μm, 1.6μm, 1.9μm, 2.2μm, 2.5μm, 2.8μm, 3.1μm, 3.4μm, 3.7μm, 4μm, 4.6μm, 5.2μm, 5.8μm, 6.4μm, 7μm, 7.2μm, 7.6μm, 8μm, or a range consisting of any two of the above values.

[0105] Optionally, in some embodiments, the thickness of the second base film can also be 1 μm-5 μm, for example, it can be 3 μm, 3.2 μm, 3.5 μm, 3.7 μm, 4 μm, 4.2 μm, 4.5 μm, 4.7 μm, 5 μm, or a range consisting of any two of the above values.

[0106] When the thickness of the first base film and / or the thickness of the second base film meets the above range, the heat resistance of the isolation film can be enhanced, and the high temperature cycle performance and reliability of the battery can be effectively improved.

[0107] The total thickness of the isolation film and the thickness of the base film have well-known meanings in the art and can be measured using equipment and methods known in the art. For example, six groups of parallel samples can be taken, and the thickness of different positions of each group of samples can be measured using a micrometer thickness gauge. At least 20 positions of each group of samples are measured, and the average thickness of the six groups of samples is taken as the thickness of the sample.

[0108] In some embodiments, the melting point of the first base film is lower than the melting point of the second base film.

[0109] In some embodiments, the melting point of the first base film can be 120°C-280°C, for example, it can be 120°C, 130°C, 135°C, 140°C, 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C, 200°C, 220°C, 240°C, 260°C, 280°C, or a range consisting of any two of the above values.

[0110] Optionally, in some embodiments, the melting point of the first base film can also be 130℃-260℃, 140℃-260℃, 150℃-260℃, 160℃-260℃, 170℃-260℃, 130℃-200℃, 140℃-200℃, 150℃-200℃, 160℃-200℃, 130℃-180℃, 140℃-180℃, 150℃-180℃, 130℃-150℃, 140℃-150℃ and the like.

[0111] In some embodiments, the melting point of the second base film can be 160℃-370℃, for example, it can be 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃, 290℃, 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, 360℃, 370℃, or a range consisting of any two of the above values.

[0112] Optionally, in some embodiments, the melting point of the second base film can also be 170℃-350℃, 190℃-350℃, 210℃-350℃, 250℃-350℃, 280℃-350℃, 300℃-350℃, 170℃-320℃, 200℃-320℃, 250℃-320℃, 280℃-320℃, 300℃-320℃, 170℃-300℃, 200℃-300℃, 250℃-300℃, 280℃-300℃ and the like.

[0113] By controlling the melting point of the first base film and / or the melting point of the second base film within the above range, the isolation film can have both good heat resistance and physical properties. In addition, if the melting point of the first base film and / or the melting point of the second base film satisfies the given range, the isolation film can also have good closed-cell properties, so that the isolation film can not only have good ion conductivity when the secondary battery is working normally, but also can close the pores in time when the secondary battery has thermal runaway to block the conduction of current. In this way, the secondary battery can have both good cycle performance and high reliability.

[0114] The melting point of the base film has a well-known meaning in the art and can be measured using equipment and methods known in the art. For example, it can be measured using differential scanning calorimetry. For details, please refer to the standard GB / T 19466.3-2004. As an example, the measurement can be carried out according to the following method: take 4mg-6mg of the sample to be tested, place it in the sample chamber of the differential scanning calorimeter, and heat it from 25°C to 400°C at a heating rate of 10°C / min to obtain the melting endothermic curve of the sample. The temperature corresponding to the peak of the curve is the melting point of the sample.

[0115] In some embodiments, the porosity of the first base film is less than the porosity of the second base film.

[0116] In some embodiments, the porosity of the first base film may be 30%-70%, for example, 30%, 35%, 45%, 55%, 65%, 70%, or a range consisting of any two of the above values.

[0117] Optionally, in some embodiments, the porosity of the first base film may also be 35%-55%, for example, 35%, 38%, 40%, 42%, 45%, 50%, 55%, or a range consisting of any two of the above values.

[0118] In some embodiments, the porosity of the second base film may be 35%-85%, for example, 35%, 45%, 55%, 65%, 70%, 75%, 80%, 85%, or a range consisting of any two of the above values.

[0119] Optionally, in some embodiments, the porosity of the second base film may also be 40%-75%, for example, it may be 40%, 42%, 45%, 50%, 55%, 60%, 62%, 65%, 70%, 75%, or a range consisting of any two of the above values.

[0120] By adjusting the porosity of the first base membrane and / or the porosity of the second base membrane within the above range, the air permeability and mechanical strength of the first base membrane, the second base membrane and the isolation membrane can be adjusted, and the isolation membrane can also have good ionic conductivity, which also helps to improve the cycle performance, kinetic performance, etc. of the secondary battery.

[0121] The porosity of the base film has a well-known meaning in the art and can be measured using equipment and methods known in the art, for example, by referring to the test standard GB / T 21650-2008 and using a mercury intrusion porosimeter for testing.

[0122] In some embodiments, the puncture strength of the first base film is greater than the puncture strength of the second base film.

[0123] In some embodiments, the puncture strength of the first base film may be 200gf-450gf, for example, 200gf, 230gf, 250gf, 280gf, 300gf, 350gf, 380gf, 400gf, 420gf, 450gf, or a range consisting of any two of the above values.

[0124] Optionally, in some embodiments, the puncture strength of the first base film may also be 230gf-420gf, for example, it may be 230gf, 250gf, 280gf, 300gf, 350gf, 380gf, 400gf, 420gf, or a range consisting of any two of the above values.

[0125] In some embodiments, the puncture strength of the second base film may be 100 gf-220 gf, for example, 100 gf, 120 gf, 150 gf, 180 gf, 200 gf, 220 gf, or a range consisting of any two of the above values.

[0126] Optionally, in some embodiments, the puncture strength of the second base film may also be 120gf-180gf, for example, it may be 120gf, 130gf, 140gf, 150gf, 160gf, 170gf, 180gf, or a range consisting of any two of the above values.

[0127] By adjusting the puncture strength of the first base film and / or the second base film to meet the above conditions, it is helpful to reduce the risk of the isolation film being punctured by lithium dendrites or being punctured under mechanical impact, thereby further improving the reliability of the secondary battery.

[0128] The puncture strength of the basement membrane has a meaning well known in the art, and can be measured using equipment and methods known in the art. For example, the test can be performed with reference to GB / T 10004-2008. Specifically, the basement membrane can be cut into strips to obtain a test piece, and the width of the test piece can be 100 mm. A test piece with a width of 100 mm is mounted on a sample membrane fixing clamp ring, and then a steel needle with a diameter of 1.0 mm and a radius of 0.5 mm at the top of the diameter is used to pierce the test piece at a speed of (50±5) mm / min, and the maximum load of the steel needle penetrating the test piece is read. More than 5 groups of parallel samples can be taken, and 3 points of each group of samples are randomly tested, and the arithmetic mean of the puncture strength of all parallel samples is taken as the puncture strength of the basement membrane.

[0129] In some embodiments, the transverse elongation at break of the first base film is higher than the transverse elongation at break of the second base film.

[0130] In some embodiments, the longitudinal elongation at break of the first base film is lower than the longitudinal elongation at break of the second base film.

[0131] In some embodiments, the transverse elongation at break of the first base film is higher than the transverse elongation at break of the second base film, and the longitudinal elongation at break of the first base film is lower than the longitudinal elongation at break of the second base film.

[0132] In some embodiments, the transverse elongation at break of the first base film may be 50%-220%, for example, 50%, 60%, 80%, 100%, 130%, 150%, 170%, 200%, 220%, or a range consisting of any two of the above values.

[0133] Optionally, in some embodiments, the transverse elongation at break of the first base film may be 80%-170%, for example, it may be 80%, 100%, 120%, 130%, 150%, 160%, 170%, or a range consisting of any two of the above values.

[0134] In some embodiments, the longitudinal elongation at break of the first base film may be 30%-100%, for example, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, or a range consisting of any two of the above values.

[0135] Optionally, in some embodiments, the longitudinal elongation at break of the first base film can also be 40%-85%, for example, it can be 40%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or a range consisting of any two of the above values.

[0136] In some embodiments, the transverse elongation at break of the second base film may be 40%-200%, for example, 40%, 50%, 60%, 80%, 100%, 120%, 140%, 160%, 180%, 200%, or a range consisting of any two of the above values.

[0137] Optionally, in some embodiments, the transverse elongation at break of the second base film can also be 60%-160%, for example, it can be 60%, 65%, 70%, 75%, 80%, 90%, 100%, 110%, 120%, 130%, 140%, 150%, 160%, or a range consisting of any two of the above values.

[0138] In some embodiments, the longitudinal elongation at break of the second base film may be 50%-700%, for example, it may be 50%, 80%, 100%, 150%, 200%, 300%, 400%, 500%, 550%, 600%, 650%, 680%, 700%, or a range consisting of any two of the above values.

[0139] Optionally, in some embodiments, the longitudinal elongation at break of the second base film can also be 80%-600%, for example, it can be 80%, 100%, 120%, 150%, 180%, 200%, 250%, 300%, 350%, 400%, 450%, 480%, 500%, 530%, 550%, 580%, 600%, or a range consisting of any two of the above values.

[0140] By adjusting the longitudinal elongation at break and / or the transverse elongation at break of the first base film and / or the second base film to meet the above range, it is beneficial to improve the ductility and strength of the separator, thereby improving the processability of the separator. As a result, it is beneficial for the separator to have both good processability and high heat resistance, thereby improving the production yield and reliability of the secondary battery.

[0141] The transverse elongation at break and the longitudinal elongation at break of the base film have well-known meanings in the art and can be measured using equipment and methods known in the art. For example, both can be tested with reference to standard GB / T 36363-2018.

[0142] In some embodiments, the material of the first base film may include at least one of polyolefins and their derivatives, halogenated polyolefins and their derivatives, polyethers and their derivatives, polyetheretherketones and their derivatives, polyesters and their derivatives, polyimides and their derivatives, polyvinyl alcohols and their derivatives, polytetrafluoroethylene and their derivatives, polyvinyl fluoride and their derivatives, polyvinylidene fluoride and their derivatives, and polyethylene terephthalate and its derivatives.

[0143] In some embodiments, the material of the second base film may include at least one of polyolefins and their derivatives, halogenated polyolefins and their derivatives, polyethers and their derivatives, polyetheretherketones and their derivatives, polyesters and their derivatives, polyimides and their derivatives, polyvinyl alcohols and their derivatives, polytetrafluoroethylene and their derivatives, polyvinyl fluoride and their derivatives, polyvinylidene fluoride and their derivatives, and polyethylene terephthalate and its derivatives.

[0144] Derivatives usually refer to products derived from the replacement of hydrogen atoms or atomic groups in a polymer by other atoms or atomic groups.

[0145] In some embodiments, the first binder may include one or more of polyacrylate, polyacrylic acid, polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride-trichloroethylene copolymer, polyvinyl pyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyethylene oxide, polyarylate, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, polyacrylonitrile, polyvinyl alcohol, polyethylene, polypropylene, starch, and cyanoethyl pullulan.

[0146] The first adhesive layer can impart good heat resistance to the isolation film on the basis of ensuring the adhesion strength and uniformity between the first base film and the second base film, thereby improving the reliability of the secondary battery.

[0147] In some embodiments, the first adhesive layer may further include a filler. The filler may further improve the heat resistance and physical properties (eg, tensile strength, puncture strength, etc.) of the separator, thereby improving the reliability of the secondary battery.

[0148] In some embodiments, the filler may include at least one of inorganic particles, organic particles, and organic-metal framework materials.

[0149] Alternatively, the inorganic particles may include one or more of inorganic particles having a dielectric constant of 5 or more, inorganic particles having ion conductivity but not storing ions, and inorganic particles capable of electrochemical reactions.

[0150] Optionally, the organic particles may include one or more of polycarbonate, polythiophene, polypyridine, polystyrene, polyacrylic wax, polyethylene, polypropylene, cellulose, cellulose modifier (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., cross-linked polymer of butyl acrylate and ethyl methacrylate).

[0151] Optionally, the organic-metal framework material may include one or more of a nitrogen-containing heterocyclic ligand building structure, an organic carboxylic acid ligand building structure, and a nitrogen-oxygen mixed ligand building structure.

[0152] In some embodiments, based on the total mass of the first bonding layer, the content of the filler may be less than or equal to 90%, and may be 30%-85%.

[0153] In some embodiments, based on the total mass of the first adhesive layer, the content of the first adhesive may be less than or equal to 30%, and optionally less than or equal to 20%.

[0154] In some embodiments, the first bonding layer may further include a dispersant, such as carboxymethyl cellulose, so as to adjust the viscosity of the first bonding layer slurry and improve the quality and uniformity of the film layer.

[0155] In some embodiments, the volume distribution particle size Dv50 of the filler may be 0.05 μm-1.2 μm, for example, 0.05 μm, 0.1 μm, 0.15 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, or a range consisting of any two of the above values.

[0156] Optionally, in some embodiments, the volume distribution particle size Dv50 of the filler can also be 0.2μm-0.8μm, for example, it can be 0.2μm, 0.25μm, 0.3μm, 0.35μm, 0.4μm, 0.5μm, 0.55μm, 0.6μm, 0.7μm, 0.75μm, 0.8μm, or a range consisting of any two of the above values.

[0157] The volume distribution particle size Dv50 of the filler particles has a well-known meaning in the art, which can represent the particle size corresponding to when the cumulative volume distribution percentage of the filler particles reaches 50%. The volume distribution particle size Dv50 can be measured using equipment and methods known in the art. For example, it can be measured with a laser particle size analyzer (e.g., Malvern Master Size 3000) with reference to GB / T 19077-2016 particle size distribution laser diffraction method.

[0158] In some embodiments, the specific surface area of ​​the filler may be 4 g / m 2 -12g / m 2 , for example, it can be 4g / m 2 , 5g / m 2 , 6g / m 2 , 7g / m 2 , 8g / m 2 , 9g / m 2 , 10g / m 2 , 11g / m 2 , 12g / m 2 , or a range consisting of any two of the above values.

[0159] Optionally, in some embodiments, the specific surface area of ​​the filler may also be 6 g / m 2 -9g / m 2 , for example, it can be 6g / m 2 , 6.5g / m 2 , 7g / m 2 , 7.5g / m 2 , 8g / m 2 , 8.5g / m 2 , 9g / m 2 , or a range consisting of any two of the above values.

[0160] The specific surface area of ​​filler particles has a well-known meaning in the art and can be measured by methods known in the art, for example, by using a specific surface area analyzer (such as TristarⅡ3020M) to measure the specific surface area of ​​filler particles by nitrogen adsorption / desorption method.

[0161] In some embodiments, the second binder includes one or more of polyacrylate, polyacrylic acid, polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride-trichloroethylene copolymer, polyvinyl pyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyethylene oxide, polyarylate, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, polyacrylonitrile, polyvinyl alcohol, polyethylene, polypropylene, starch, and cyanoethyl pullulan.

[0162] In some embodiments, the second adhesive layer includes a second adhesive made of a material different from that of the first adhesive.

[0163] In some embodiments, the first binder includes polyacrylate.

[0164] In some embodiments, the second binder includes polyvinylidene fluoride (PVDF).

[0165] In some embodiments, the second binder includes both polyvinylidene fluoride (PVDF) and polyacrylate.

[0166] The second binder can enhance the bonding force between the isolation membrane and the electrode plate, reduce the gap between the isolation membrane and the electrode plate, thereby delaying the growth of lithium dendrites and further improving the cycle performance of the battery.

[0167] In some embodiments, based on the total mass of the second adhesive layer, the content of the second adhesive may be greater than or equal to 85%, and may be greater than or equal to 90%. The second adhesive layer is mainly composed of an adhesive, which helps to improve the bonding force between the second adhesive layer and the electrode plate. This is conducive to further improving the reliability of the secondary battery.

[0168] In some embodiments, the second bonding layer further includes a dispersant, such as carboxymethyl cellulose, thereby adjusting the viscosity of the second bonding layer slurry and improving the quality and uniformity of the film layer.

[0169] In some embodiments, the first binder and / or the second binder comprises an aqueous binder. An aqueous binder generally refers to a binder that can use water as a dispersant or solvent.

[0170] In some embodiments, the first binder and the second binder both include aqueous binders. For example, in the first bonding layer and the second bonding layer, the first binder and the second binder may each independently include one or more of styrene-butadiene rubber (SBR), aqueous unsaturated resin SR-1B, aqueous acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), aqueous acrylate resin (e.g., polyacrylate), aqueous polyacrylamide (PAM), aqueous polyvinyl alcohol (PVA), aqueous sodium alginate (SA), aqueous carboxymethyl chitosan (CMCS) and aqueous polyvinylidene fluoride (PVDF).

[0171] In some embodiments, the transverse tensile strength of the isolation film may be greater than or equal to 600 kg / cm 2 , optional 800kg / cm 2 -2500kg / cm 2 .

[0172] In some embodiments, the longitudinal tensile strength of the isolation film may be greater than or equal to 800 kg / cm 2 , optional 1000kg / cm 2 -3000kg / cm 2 .

[0173] In some embodiments, the air permeability of the isolation membrane may be 150s / 100cc-500s / 100cc, and may be optionally 180s / 100cc--380s / 100cc.

[0174] In some embodiments, the transverse heat shrinkage rate of the isolation film at 250° C. for 1 hour may be less than or equal to 5%, and may be optionally 0.05%-3%.

[0175] In some embodiments, the longitudinal heat shrinkage rate of the isolation film at 250° C. for 1 hour may be less than or equal to 5%, and may be optionally 0.05%-3%.

[0176] When at least one of the transverse tensile strength, longitudinal tensile strength, air permeability, transverse heat shrinkage rate, and longitudinal heat shrinkage rate of the isolation membrane meets the given range, the isolation membrane can have good heat resistance and physical properties, thereby improving the reliability of the secondary battery.

[0177] The transverse tensile strength, longitudinal tensile strength, transverse heat shrinkage rate, and longitudinal heat shrinkage rate of the isolation film may have meanings known in the art, and may be measured using equipment and methods known in the art. For example, they may all be tested with reference to GB / T36363-2018.

[0178] The air permeability of the isolation membrane has a well-known meaning in the art and can be measured using equipment and methods known in the art. For example, the test can be performed with reference to GB / T 36363-2018. The test gas can be 100cc of air.

[0179] Preparation method

[0180] The embodiment of the present application also provides a method for preparing the isolation film provided by the embodiment of the present application. The method includes the following steps: providing a first base film, a second base film, a first bonding layer slurry and a second bonding layer slurry, the first bonding layer slurry includes a first adhesive, and the second bonding layer slurry includes a second adhesive; applying the first bonding layer slurry on one of the first base film and the second base film, and then pressing it with the other of the first base film and the second base film, so as to form a first bonding layer between the first base film and the second base film; applying the second bonding layer slurry on the surface of the first base film facing away from the first bonding layer, and / or applying the second bonding layer slurry on the surface of the second base film facing away from the first bonding layer, so as to obtain an isolation film. Wherein, the thickness of the first bonding layer is recorded as T1, and the thickness of the second bonding layer is recorded as T2, then the isolation film satisfies: T1 / T2>1.

[0181] In some embodiments, the first bonding layer slurry may include a first bonding agent and a filler.

[0182] In some embodiments, the bonding layer slurry may be coated by transfer coating, spin spray coating, dip coating, etc., which is not limited in the embodiments of the present application.

[0183] In some embodiments, the pressing temperature is 20°C-50°C, 20°C-40°C, 20°C-30°C, 30°C-50°C, 30°C-40°C, 40°C-50°C.

[0184] In some embodiments, the pressing time is 5s-60s, 5s-40s, 5s-20s, 5s-10s, 10s-60s, 10s-40s, 10s-20s.

[0185] In some embodiments, the pressing pressure is 1 MPa-10 MPa, 2 MPa-8 MPa, 3 MPa-7 MPa, 4 MPa-6 MPa.

[0186] Unless otherwise specified, all raw materials (such as the first base film, the second base film, the adhesive, the filler, etc.) used in the method for preparing the isolation film can be obtained commercially.

[0187] Secondary battery

[0188] The embodiment of the present application also provides a secondary battery.

[0189] Secondary batteries, also known as rechargeable batteries or storage batteries, refer to batteries that can be recharged to activate active materials and continue to be used after the battery is discharged. Generally, secondary batteries include electrode assemblies and electrolytes. The electrode assemblies include positive electrode sheets, negative electrode sheets, and separators. The separators are arranged between the positive electrode sheets and the negative electrode sheets. They mainly prevent the positive and negative electrodes from short-circuiting, while allowing active ions to pass through.

[0190] The present application has no particular limitation on the type of secondary battery. For example, the secondary battery may be a lithium ion battery, a sodium ion battery, a lithium metal battery, a sodium metal battery, etc. In particular, the secondary battery may be a lithium ion battery.

[0191] The secondary battery provided in the embodiment of the present application includes the isolation membrane as described above in the present application, which can improve the reliability and energy density of the battery.

[0192] [Positive electrode]

[0193] In some embodiments, the positive electrode sheet may include a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector and including a positive electrode active material. For example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0194] 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 iron manganese phosphate, a composite material of lithium iron manganese phosphate and carbon, and their respective modified compounds.

[0195] In some embodiments, in order to further improve the energy density of the secondary battery, the positive electrode active material for the lithium ion battery may include a general formula of Li a Ni b Co c M d O e A fAt least one of lithium transition metal oxides and modified compounds thereof. 0<a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 0<e≤2, 0≤f≤1, M is selected from at least one of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A is selected from at least one of N, F, S and Cl.

[0196] As an example, the positive electrode active material for lithium ion batteries may include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2(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.

[0197] 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 sodium-containing transition metal oxides, polyanion materials (such as phosphates, fluorophosphates, pyrophosphates, sulfates, etc.), and Prussian blue materials.

[0198] As an example, the positive electrode active material for sodium ion batteries may include 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 materials, general formula X p M' q (PO4) r O x Y 3-x In the general formula X p M'q (PO4) r O x Y 3-x , 0<p≤4, 0<q≤2, 1≤r≤3, 0≤x≤2, X is selected from H + , Li + 、Na + , K + and NH4 + At least one of, 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.

[0199] The modified compounds of the above-mentioned positive electrode active materials may be the ones that undergo doping modification and / or surface coating modification on the positive electrode active materials.

[0200] In some embodiments, the positive electrode film layer may further include a positive electrode conductive agent. The present application has no particular restrictions on the type of the positive electrode conductive agent. As an example, the positive electrode conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0201] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. The present application has no particular restrictions on the type of positive electrode binder. As an example, the positive electrode binder 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.

[0202] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base and a metal material layer formed on at least one surface of the polymer material base. As an example, the metal material may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. As an example, the polymer material base may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).

[0203] The positive electrode film layer is usually formed by coating the positive electrode slurry on the positive electrode current collector, drying and cold pressing. The positive electrode slurry is usually formed by dispersing the positive electrode active material, optional conductive agent, optional binder and any other components in a solvent and stirring them uniformly. The solvent can be N-methylpyrrolidone (NMP), but is not limited thereto.

[0204] [Negative electrode]

[0205] In some embodiments, the negative electrode sheet may include a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector and including a negative electrode active material. For example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0206] The negative electrode active material may adopt the negative electrode active material for secondary batteries known in the art. As an 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 tin, tin oxide and tin alloy material.

[0207] In some embodiments, the negative electrode film layer may further include a negative electrode conductive agent. The present application has no particular restrictions on the type of the negative electrode conductive agent. As an example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0208] In some embodiments, the negative electrode film layer may further include a negative electrode binder. The present application has no particular restrictions on the type of the negative electrode binder. As an example, the negative electrode binder may include at least one of styrene-butadiene rubber (SBR), water-based 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).

[0209] In some embodiments, the negative electrode film layer may further include other additives. As an example, the other additives may include a thickener, such as sodium carboxymethyl cellulose (CMC), a PTC thermistor material, and the like.

[0210] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).

[0211] The negative electrode film layer is usually formed by coating the negative electrode slurry on the negative electrode current collector, drying and cold pressing. The negative electrode slurry is usually formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional auxiliary agents in a solvent and stirring them evenly. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited thereto.

[0212] The negative electrode plate does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode plate also includes a conductive primer layer (e.g., composed of a conductive agent and a binder) 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 plate of the present application also includes a protective layer covering the surface of the negative electrode film layer.

[0213] [Electrolyte]

[0214] During the charge and discharge process of the secondary battery, active ions are embedded and released back and forth between the positive electrode and the negative electrode, and the electrolyte plays a role in conducting active ions between the positive electrode and the negative electrode. The present application has no particular restrictions on the type of electrolyte, which can be selected according to actual needs.

[0215] The electrolyte includes electrolyte salt and solvent. The types of electrolyte salt and solvent are not specifically limited and can be selected according to actual needs.

[0216] When the secondary battery is a lithium ion battery, as an example, the electrolyte salt may include but is not limited to at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobisoxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0217] When the secondary battery is a sodium ion battery, as an example, the electrolyte salt may include but is not limited to at least one of sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium perchlorate (NaClO4), sodium hexafluoroarsenate (NaAsF6), sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluorooxalatoborate (NaDFOB), sodium dioxalatoborate (NaBOB), sodium difluorophosphate (NaPO2F2), sodium difluorobis(oxalatophosphate) (NaDFOP) and sodium tetrafluorooxalatophosphate (NaTFOP).

[0218] As an 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), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE).

[0219] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high temperature performance, and additives that improve battery low temperature power performance.

[0220] In some embodiments, the positive electrode sheet, the separator and the negative electrode sheet can be made into an electrode assembly by a winding process and / or a lamination process. The negative electrode sheet can face the second bonding layer in the separator, so that there can be a smaller gap between the negative electrode sheet and the separator, thereby delaying the growth of lithium dendrites and improving the reliability of the battery. It can be understood that the separator of the present application includes both a first base film and a second base film, and the first base film or the second base film can be optionally facing the positive electrode sheet or the negative electrode sheet. For example, the first base film faces the positive electrode sheet, and the second base film faces the negative electrode sheet; or the first base film faces the negative electrode sheet, and the second base film faces the positive electrode sheet.

[0221] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0222] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT) and polybutylene succinate (PBS).

[0223] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. FIG4 is a secondary battery 5 of a square structure as an example.

[0224] In some embodiments, as shown in FIG5 , the outer package may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation film may form an electrode assembly 52 through a winding process and / or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 may be one or more, which can be adjusted according to demand.

[0225] The preparation method of the secondary battery is well known. In some embodiments, the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte can be assembled to form a secondary battery. As an example, the positive electrode sheet, the separator and the negative electrode sheet can be formed into an electrode assembly through a winding process and / or a lamination process, and the electrode assembly is placed in an outer package, dried and injected with an electrolyte, and then vacuum packaged, left to stand, formed, shaped and other processes are performed to obtain a secondary battery.

[0226] In some embodiments, the secondary batteries according to the present application may be assembled into a battery module. The battery module may contain multiple secondary batteries, and the specific number may be adjusted according to the application and capacity of the battery module.

[0227] FIG6 is a schematic diagram of a battery module 4 as an example. As shown in FIG6 , in the battery module 4, a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by fasteners.

[0228] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0229] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0230] FIG7 and FIG8 are schematic diagrams of a battery pack 1 as an example. As shown in FIG7 and FIG8, the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3, wherein the upper box body 2 is used to cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery box in any manner.

[0231] Electrical devices

[0232] The embodiments of the present application also provide an electrical device, which includes at least one of the secondary battery, battery module or battery pack provided in the embodiments of the present application. The secondary battery, battery module or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device can be, but is not limited to, a mobile device (such as a mobile phone, a laptop computer, etc.), an electric vehicle (such as 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 and a satellite, an energy storage system, etc.

[0233] The electric device can select a secondary battery, a battery module or a battery pack according to its usage requirements.

[0234] Fig. 9 is a schematic diagram of an electric device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirements of the electric device for high power and high energy density, a battery pack or a battery module may be used.

[0235] As another example, the electric device may be a mobile phone, a tablet computer, a notebook computer, etc. The electric device is usually required to be light and thin, and a secondary battery may be used as a power source.

[0236] Example

[0237] The following examples describe the disclosure of the present application in more detail, and these examples are only for illustrative purposes, as it is obvious to those skilled in the art that various modifications and variations can be made within the scope of the disclosure of the present application. Unless otherwise stated, all parts, percentages and ratios reported in the following examples are based on mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and the instruments used in the examples are commercially available.

[0238] Example 1

[0239] Preparation of isolation membrane

[0240] A first base film is provided, the material of which includes polyethylene (PE), has a thickness of 5 μm, and a melting point of 135° C.

[0241] A second base film is provided, wherein the material includes polypropylene (PP), the thickness is 6 μm, and the melting point is 165° C.

[0242] Prepare the first bonding layer slurry: mix the filler boehmite, the first bonding agent polyacrylate, and the dispersant carboxymethyl cellulose in a mass ratio of 8:1:1 in an appropriate amount of solvent deionized water to prepare the first bonding layer slurry.

[0243] Prepare the second bonding layer slurry: evenly disperse the second bonding agent polyvinylidene fluoride (PVDF) and polyacrylate (the mass ratio of the two is 8:2) and the dispersant carboxymethyl cellulose in a mass ratio of 9:1 in an appropriate amount of solvent deionized water to prepare the second bonding layer slurry.

[0244] The first adhesive layer slurry is applied to the PE base film to form the first adhesive layer, and the PP and PE base films are pressed together so that the first adhesive layer is between the PP base film and the PE base film; the second adhesive layer slurry is then applied to the surfaces of the PP base film and the PE base film away from the first adhesive layer, respectively, and the isolation film is prepared through drying and other processes. The thickness T1 of the first adhesive layer is 1.0 μm, the thickness T2 of the second adhesive layer is 0.8 μm, and T1 / T2 is 1.25.

[0245] Preparation of positive electrode

[0246] The positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), conductive agent carbon black (Super P), and binder polyvinylidene fluoride (PVDF) are mixed evenly in a proper amount of solvent N-methylpyrrolidone (NMP) in a mass ratio of 96.2:2.7:1.1 to obtain positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector aluminum foil, and the positive electrode sheet is obtained through processes such as drying, cold pressing, slitting, and cutting.

[0247] Preparation of negative electrode

[0248] The negative electrode active material artificial graphite, the conductive agent carbon black (Super P), the binder styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC) are mixed uniformly in a proper amount of solvent deionized water at a mass ratio of 96.4:0.7:1.8:1.1 to obtain a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector copper foil, and the negative electrode sheet is obtained through the processes of drying, cold pressing, slitting and cutting.

[0249] Preparation of electrolyte

[0250] Ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 30:30:40 to obtain an organic solvent, and fully dried LiPF6 is dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0251] Preparation of secondary batteries

[0252] The positive electrode sheet, the isolation film prepared as above, and the negative electrode sheet are stacked and wound in sequence to obtain an electrode assembly, wherein the first base film in the isolation film faces the negative electrode; the electrode assembly is placed in an outer package, and after drying, the electrolyte is injected, and after vacuum packaging, standing, forming, shaping and other processes, a secondary battery is obtained.

[0253] The secondary batteries of Examples 2-11 and Comparative Examples 1-2 are similar to Example 1, except that different base films are used or coating parameters are adjusted, as shown in Table 1 for details.

[0254] Test Section

[0255] The following tests were performed on the separators and secondary batteries of the above-mentioned Examples 1-11 and Comparative Examples 1-2. The test results are shown in Table 2, respectively.

[0256] (1) Thermal shrinkage test of isolation film

[0257] Sample preparation: The isolation film prepared above was punched out into samples with a width of 50 mm and a length of 100 mm using a punching machine. Five parallel samples were placed on a glass plate and fixed.

[0258] Sample test: The temperature of the forced air oven is set to 250°C. After the temperature reaches the set temperature and stabilizes for 30 minutes, the glass plate is placed in the forced air oven and the timing is 1 hour. After the time is up, the width of the isolation film is measured. The width value is marked as a in mm.

[0259] Calculation of heat shrinkage: Transverse direction (TD) heat shrinkage = [(50-a) / 50] × 100%, the average value of 5 parallel samples is taken as the test result.

[0260] (2) Battery room temperature cycle performance test

[0261] At 25°C, the batteries of the above embodiments and comparative examples were charged at 1C constant current to a voltage of 4.2V, then charged at 4.2V constant voltage to a current ≤ 0.05C, and then discharged at 1C constant current to a voltage of 2.8V. This is a charge and discharge process, and the discharge capacity at this time is recorded as the discharge capacity of the first cycle of the battery. Repeat the charge and discharge cycles in this way, and record the number of cycles when the capacity is reduced to 85%.

[0262] Table 1

[0263] Table 2

[0264] It can be seen from Table 1 and Table 2 that in Examples 1-11, the thickness T1 of the first adhesive layer and the thickness T2 of the second adhesive layer satisfy T1 / T2>1, and the isolation film produced therefrom has good heat resistance. In particular, under the specific thickness ratio design of the present application, the use of a high melting point base film can significantly improve the heat resistance of the isolation film. Based on the test results of Examples 1-8, it can be seen that by adjusting T1 / T2 within an appropriate range, the secondary battery can have better cycle performance while maintaining the heat resistance of the isolation film. Based on Examples 3 and 9-11, it can be seen that the material and thickness of the base film can affect the heat resistance of the isolation film and the cycle performance of the battery. Under the specific T1 and T2 ratio design of the present application, adjusting the material and thickness of the base film can further improve the heat resistance of the isolation film.

[0265] In contrast, Comparative Examples 1 and 2 do not satisfy the requirement that the thickness T1 of the first adhesive layer is greater than the thickness T2 of the second adhesive layer, and the heat resistance of the isolation films produced therefrom is poor, and the cycle performance of the batteries produced therefrom is poor.

[0266] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and the same effect as the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

A separation film, comprising: First basement membrane; Second basement membrane; A first adhesive layer, located between the first base film and the second base film, wherein the first adhesive layer comprises a first adhesive; And a second adhesive layer is located on the side of the first base film and / or the second base film away from the first adhesive layer, and the second adhesive layer includes a second adhesive; the thickness of the first adhesive layer is recorded as T1, the thickness of the second adhesive layer is recorded as T2, then the isolation film satisfies: T1 / T2>1. The isolation film according to claim 1, wherein 1.25≤T1 / T2≤5, optionally, 1.5≤T1 / T2≤4. The isolation film according to claim 1 or 2, wherein The thickness T1 of the first adhesive layer is less than or equal to 4 μm, and may be 0.5 μm-3 μm; and / or the thickness T2 of the second adhesive layer is less than or equal to 2 μm, and may be 0.4 μm-1.5 μm. The isolation film according to any one of claims 1 to 3, wherein The total thickness T of the isolation film is less than 12 μm, and can be selected to be 3 μm-10 μm. The isolation film according to any one of claims 1 to 4, wherein The thickness of the first base film is less than or equal to 9 μm, and may be 3 μm-6 μm; and / or the thickness of the second base film is less than or equal to 8 μm, and may be 1 μm-5 μm. The isolation film according to any one of claims 1 to 5, wherein The melting point of the first base film is lower than that of the second base film; optionally, the melting point of the first base film is 120°C-280°C, optionally 130°C-260°C; optionally, the melting point of the second base film is 160°C-370°C, optionally 170°C-350°C. The isolation film according to any one of claims 1 to 6, wherein The porosity of the first base film is less than that of the second base film; optionally, the porosity of the first base film is 30%-70%, optionally 35%-55%; optionally, the porosity of the second base film is 35%-85%, optionally 40%-75%. The isolation film according to any one of claims 1 to 7, wherein The puncture strength of the first basement film is greater than the puncture strength of the second basement film; optionally, the puncture strength of the first basement film is 200gf-450gf, optionally 230gf-420gf; optionally, the puncture strength of the second basement film is 100gf-220gf, optionally 120gf-180gf. The isolation film according to any one of claims 1 to 8, wherein The transverse elongation at break of the first base film is higher than the transverse elongation at break of the second base film; and / or the longitudinal elongation at break of the first base film is lower than the longitudinal elongation at break of the second base film. The isolation film according to any one of claims 1 to 9, wherein The isolation film satisfies at least one of the following (1)-(4): (1) the transverse elongation at break of the first base film is 50%-220%, and can be optionally 80%-170%; (2) the longitudinal elongation at break of the first base film is 30%-100%, and can be optionally 40%-85%; (3) the transverse elongation at break of the second base film is 40%-200%, and can be optionally 60%-160%; (4) the longitudinal elongation at break of the second base film is 50%-700%, and can be optionally 80%-600%. The isolation film according to any one of claims 1 to 10, wherein The first binder and / or the second binder each independently include one or more of polyacrylate, polyacrylic acid, polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride-trichloroethylene copolymer, polyvinyl pyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyethylene oxide, polyarylate, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, polyacrylonitrile, polyvinyl alcohol, polyethylene, polypropylene, starch, and cyanoethyl pullulan; optionally, the second adhesive layer includes a second adhesive of a material different from that of the first adhesive. The isolation film according to any one of claims 1 to 11, wherein The content of the first adhesive is less than or equal to 30%, optionally less than or equal to 20%, based on the total mass of the first adhesive layer; and / or the content of the second adhesive is greater than or equal to 85%, optionally greater than or equal to 90%, based on the total mass of the second adhesive layer. The isolation film according to any one of claims 1 to 12, wherein The first binder and / or the second binder includes an aqueous binder. The isolation film according to any one of claims 1 to 13, wherein The material of the first base film includes at least one of polyolefins and their derivatives, halogenated polyolefins and their derivatives, polyethers and their derivatives, polyetheretherketones and their derivatives, polyesters and their derivatives, polyimides and their derivatives, polyvinyl alcohol and their derivatives, polytetrafluoroethylene and their derivatives, polyvinyl fluoride and their derivatives, polyvinylidene fluoride and their derivatives, and polyethylene terephthalate and their derivatives; and / or the material of the second base film includes at least one of polyolefins and their derivatives, halogenated polyolefins and their derivatives, polyethers and their derivatives, polyetheretherketones and their derivatives, polyesters and their derivatives, polyimides and their derivatives, polyvinyl alcohol and their derivatives, polytetrafluoroethylene and their derivatives, polyvinyl fluoride and their derivatives, polyvinylidene fluoride and their derivatives, and polyethylene terephthalate and their derivatives. The isolation film according to any one of claims 1 to 14, wherein The first bonding layer further comprises a filler; optionally, the filler comprises at least one of inorganic particles, organic particles, and organic-metal framework materials; optionally, the content of the filler is less than or equal to 90%, optionally 30%-85%, based on the total mass of the first bonding layer; optionally, the volume distribution particle size Dv50 of the filler is 0.05μm-1.2μm, optionally 0.2μm-0.8μm; optionally, the specific surface area of ​​the filler is 4g / m 2 -12g / m 2 , optional 6g / m 2 -9g / m 2 . The isolation film according to any one of claims 1 to 15, wherein The separator meets at least one of the following conditions (1) to (5): (1) the transverse tensile strength of the separator is ≥ 600 kg / cm 2 , optional 800kg / cm 2 -2500kg / cm 2 ; (2) The longitudinal tensile strength of the isolation film is ≥800kg / cm 2 , optional 1000kg / cm 2 -3000kg / cm 2 ; (3) The air permeability of the isolation membrane is 150s / 100cc-500s / 100cc, and can be optionally 180s / 100cc-380s / 100cc; (4) The transverse heat shrinkage rate of the isolation membrane at 250°C and 1h is ≤5%, and can be optionally 0.05%-3%; (5) The longitudinal heat shrinkage rate of the isolation membrane at 250°C and 1h is ≤5%, and can be optionally 0.05%-3%. A method for preparing an isolation film according to any one of claims 1 to 16, comprising the following steps: providing a first base film, a second base film, a first bonding layer slurry and a second bonding layer slurry, the first bonding layer slurry comprising a first adhesive, and the second bonding layer slurry comprising a second adhesive; coating the first bonding layer slurry on one of the first base film and the second base film, and then pressing the first base film with the other of the first base film and the second base film to form a first bonding layer between the first base film and the second base film; coating the second bonding layer slurry on the surface of the first base film facing away from the first bonding layer, and / or coating the second bonding layer slurry on the surface of the second base film facing away from the first bonding layer, to obtain an isolation film; the thickness of the first bonding layer is denoted as T1, the thickness of the second bonding layer is denoted as T2, and the isolation film satisfies: T1 / T2>1; optionally, the first bonding layer slurry comprises the first adhesive and a filler. A secondary battery comprising the separator according to any one of claims 1 to 16. An electric device comprising the secondary battery according to claim 18.

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