A separator, a method of manufacturing the same, a secondary battery, and an electric device

Abstract

The application provides a diaphragm and a preparation method thereof, a secondary battery and an electric device. The diaphragm comprises a base film and a first coating layer and a second coating layer arranged on one side of the base film in sequence. The first coating layer comprises inorganic material and a first binder in a mass ratio of (60-95):(5-40). The second coating layer comprises zinc fluoride, polyacrylic acid and a second binder in a mass ratio of (40-80):(20-60):(1-5). The diaphragm has high mechanical strength and can promote uniform deposition of lithium elements. The application further provides a preparation method of the diaphragm, and realizes preparation of the diaphragm. Finally, the application further provides a secondary battery and an electric device, and the cycle performance and safety performance of the secondary battery and the electric device are significantly improved.

Description

Technical Field

[0001] This application relates to the field of secondary batteries, and more particularly to a separator and its preparation method, a secondary battery, and an electrical device. Background Technology

[0002] In rechargeable batteries, the lithium metal anode, due to inherent defects and a rough microscopic surface, exhibits uneven electric field distribution. This leads to uneven deposition and peeling during charging and discharging, repeatedly forming dendrites that pierce the solid electrolyte interphase (SEI) and generate new SEIs. This causes the SEI to continuously thicken, and some lithium dendrites melt and become inactive, resulting in dead lithium accumulation. Furthermore, the volumetric expansion and contraction of the lithium metal anode side also causes continuous SEI rupture, leading to increased impedance, difficulty in secondary electrolyte wetting, and deterioration of cycle performance. Lithium dendrites may also pierce the separator, causing safety issues. Summary of the Invention

[0003] This application aims to at least partially address one of the technical problems in the related art.

[0004] This application proposes a separator, in which a first coating and a second coating are sequentially disposed on one side of a base membrane. The first coating enhances the overall mechanical strength of the separator, while the second coating enables the separator to uniformly distribute the lithium-ion flux at the interface during application. At the same time, the zinc element generated in situ is a lithiophilic material that can uniformly distribute the electric field at the interface and reduce the overpotential of lithium deposition.

[0005] Another aspect of this application proposes a method for preparing a diaphragm, which enables the preparation of a diaphragm using a simple process.

[0006] This application also proposes a secondary battery in which a separator with high mechanical strength and the ability to promote uniform lithium deposition is applied to the secondary battery, resulting in a secondary battery with good cycle performance and safety performance.

[0007] The last aspect of this application proposes an electrical device that applies a separator with high mechanical strength and the ability to promote uniform lithium deposition to a secondary battery, and assembles the resulting secondary battery into the electrical device to improve the cycle performance and safety performance of the electrical device.

[0008] According to an embodiment of the first aspect of this application, a diaphragm is provided, comprising a base membrane and a first coating and a second coating sequentially disposed on one side of the base membrane; the first coating comprises an inorganic material and a first binder in a mass ratio of (60-95):(5-40); the second coating comprises zinc fluoride, polyacrylic acid and a second binder in a mass ratio of (40-80):(20-60):(1-5).

[0009] In some embodiments, the thickness of the first coating is L1; 2μm≤L1≤10μm;

[0010] And / or, the thickness of the second coating is L2; ​​1μm≤L2≤5μm;

[0011] And / or, the first coating has the same thickness as the second coating.

[0012] In some embodiments, the particle size of the inorganic material is 200 nm-10 μm;

[0013] And / or, the inorganic material includes at least one of alumina, silicon dioxide, titanium dioxide, zinc oxide, magnesium oxide, hafnium dioxide, tin oxide, zirconium oxide, and solid electrolyte materials;

[0014] The relative molecular weight of the first adhesive is 400,000 to 2,000,000;

[0015] And / or, the first adhesive comprises at least one of polyacrylic acid, polyacrylate, polyvinylidene fluoride, copolymer of vinylidene fluoride and hexafluoropropylene, copolymer of vinylidene fluoride and trichloroethylene, polyacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, copolymer of ethylene and vinyl acetate, polyimide, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl amylopectin, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, amylopectin, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, copolymer of acrylonitrile, styrene, and butadiene, polyvinyl alcohol, and copolymer of styrene and butadiene.

[0016] In some embodiments, the zinc fluoride has a particle size of 200 nm to 10 μm;

[0017] And / or, the relative molecular weight of the polyacrylic acid is 10,000 to 400,000;

[0018] And / or, the relative molecular weight of the second adhesive is 400,000 to 2,000,000;

[0019] And / or, the second adhesive comprises at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, a copolymer of vinylidene fluoride and trichloroethylene, polyacrylate, polyacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, a copolymer of ethylene and vinyl acetate, polyimide, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl amylopectin, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, amylopectin, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, a copolymer of acrylonitrile, styrene, and butadiene, polyvinyl alcohol, and a copolymer of styrene and butadiene.

[0020] In some embodiments, the base film includes a PP film and / or a PE film;

[0021] And / or, the thickness of the base film is 5-20 μm.

[0022] In this application, a first coating and a second coating are sequentially disposed on one side of the base film. The first coating can enhance the mechanical strength of the separator, prevent dendrite growth from piercing the separator, and increase the liquid retention on the lithium negative electrode side to reduce the impact of increased impedance caused by volume expansion. In the second coating, zinc fluoride will form an intermediate interface layer of LiF and Zn in situ with metallic lithium during charging and discharging. Polyacrylic acid and lithium elements will form a high-elasticity, high-ionic-conductivity PAA-li. This organic-inorganic mixed fast ion conductor, LiF and PAA-li, can not only uniformly distribute the lithium ion flux at the interface, but also has good mechanical strength and viscoelasticity to adapt to the volume expansion and contraction of the negative electrode. At the same time, the zinc metal generated in situ is a lithium-loving metal material, which uniformly distributes the electric field at the interface and reduces the overpotential of lithium element deposition. The two work together to promote uniform lithium element deposition and reduce the impact of interface SEI rupture caused by volume expansion.

[0023] According to an embodiment of the second aspect of this application, a method for preparing a diaphragm is provided, comprising the following steps:

[0024] Inorganic materials and a first binder are dispersed in a solvent according to a stoichiometric ratio to obtain a first slurry;

[0025] Zinc fluoride, polyacrylic acid, and a second binder are dispersed in a solvent according to stoichiometric ratios to obtain a second slurry.

[0026] The first slurry is applied to the base film and cured to obtain a first coating; the second slurry is applied to the first coating and cured to obtain a second coating;

[0027] Cut to the appropriate size to obtain the diaphragm described in any of the above embodiments.

[0028] In some embodiments, the solvents in the first slurry and the second slurry are the same, each comprising at least one of N-methylpyrrolidone, formamide, methanol, ethanol, propanol, acetone, dioxane, and tetrahydrofuran;

[0029] And / or, the first slurry and the second slurry have the same solid content, which is 10%-30%.

[0030] In some embodiments, the curing parameters of the first slurry and the second slurry are: temperature of 80-95℃, time of 4-10h, and vacuum degree ≤-90Kpa.

[0031] The preparation method in this application involves coating a first slurry onto a base film and curing it to form a first coating layer; then coating a second slurry onto the first coating layer and curing it. The process is simple and easy to promote.

[0032] According to an embodiment of the third aspect of this application, a secondary battery is provided, which includes the separator described in any of the above embodiments.

[0033] In some embodiments, the secondary battery further includes a positive electrode, a negative electrode, and a battery cell; wherein the second coating is in contact with the negative electrode; and the negative electrode is a lithium-copper composite strip.

[0034] In some embodiments, a hot pressing process is used to make the second coating adhere to the negative electrode sheet; the hot pressing process parameters are: temperature 60-100℃, pressure 600-1200KG, and holding time 30-120s.

[0035] This application utilizes a hot-pressing process to bond the second coating to the negative electrode sheet to assemble a secondary battery. By applying a separator with high mechanical strength that promotes uniform lithium deposition to the secondary battery, a secondary battery with good cycle performance and safety performance is obtained.

[0036] An electrical device comprising the secondary battery described in any of the above embodiments is provided according to an embodiment of the fourth aspect of this application.

[0037] This application applies a separator with high mechanical strength that can promote uniform lithium deposition to a secondary battery, and assembles the resulting secondary battery into an electrical device to improve the cycle performance and safety performance of the device.

[0038] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0039] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0040] Figure 1 This is a schematic diagram of the diaphragm provided in one embodiment of this application.

[0041] 1. Base film; 2. First coating; 3. Second coating. Detailed Implementation

[0042] Embodiments of this application are described in detail below. Examples of these embodiments are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application. Rather, this application includes all variations, modifications, and equivalents falling within the spirit and scope of the appended claims.

[0043] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0044] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0045] To achieve the above objectives, an embodiment of the first aspect of this application provides a diaphragm comprising a base membrane and a first coating and a second coating sequentially disposed on one side of the base membrane; the first coating comprises an inorganic material and a first binder in a mass ratio of (60-95):(5-40); the second coating comprises zinc fluoride, polyacrylic acid and a second binder in a mass ratio of (40-80):(20-60):(1-5).

[0046] The diaphragm includes a base membrane 1 and a first coating layer 2 and a second coating layer 3 sequentially disposed on one side of the base membrane 1. In other words, the base membrane 1 includes an upper surface and a lower surface, and the first coating layer 2 and the second coating layer 3 can be sequentially disposed on either the upper or lower surface. Figure 1 As shown in the figure, the description will be based on the up and down direction.

[0047] The base film 1 includes a PP film and / or a PE film. A first coating layer 2 and a second coating layer 3 are sequentially disposed on the upper surface of the base film 1. In some embodiments, the thickness of the base film is 5-20 μm. For example, the thickness of the base film is 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 18 μm, 20 μm, etc.

[0048] In some embodiments, the thickness of the first coating is L1; 2μm≤L1≤10μm; for example, the thickness of the first coating is 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, etc. The first coating includes inorganic materials and a first binder in a mass ratio of (60-95):(5-40). The mass ratio of inorganic materials to the first binder in the first coating is (60, 70, 80, 90, 95):(5, 10, 15, 20, 25, 30, 35, 40). When the proportion of the first binder in the first coating is too high, the porosity of the first coating itself will decrease, failing to achieve the desired electrolyte retention effect. During the application of the formed diaphragm, when the cell cycles, the volume expansion and contraction on the negative electrode side cannot be replenished by the electrolyte in the negative electrode side diaphragm, resulting in increased impedance. Furthermore, the first coating thickness is an inert coating. If it is too thick, it will easily increase the internal resistance of the cell. When it is 2μm, the mechanical strength of the separator can be greatly improved.

[0049] The inorganic materials include at least one of alumina, silicon dioxide, titanium dioxide, zinc oxide, magnesium oxide, hafnium dioxide, tin oxide, zirconium oxide, and solid electrolyte materials. Furthermore, the inorganic material is alumina, which is an inorganic rigid particle and has mechanical strength. Using alumina as a coating material is a more mature process and cheaper. Solid electrolyte materials include lithium titanium phosphate solid electrolyte (LATP), lithium lanthanum zirconium oxide / lithium lanthanum zirconate (LLZO), lithium lanthanum titanium oxide (LLTO), etc.

[0050] In some embodiments, the particle size of the inorganic material is 200 nm-10 μm; further, the particle size of the inorganic material is 100 nm-1 μm, for example, the particle size of the inorganic material is 100 nm, 200 nm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, etc. The particle size of the inorganic material in the example of this application is less prone to agglomeration and easier to process, and the formed first coating has high uniformity. When the particle size of the inorganic material is small, such as less than 200 nm, the inorganic material is not conducive to processing, is prone to agglomeration, and the smaller the particle size, the higher the tap density, and the lower the porosity after film formation, which is not conducive to liquid retention; and the smaller the particle size of the inorganic material, the larger the specific surface area, the larger the amount of the first binder used, and at this time, when the content of the first binder is low, it is easy to shed powder. In addition, when the particle size of the inorganic material is large, such as greater than 10 μm, it affects the smoothness and uniformity of the first coating.

[0051] In some embodiments, the first binder comprises at least one selected from polyacrylic acid, polyacrylate, polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, a copolymer of vinylidene fluoride and trichloroethylene, polyacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, a copolymer of ethylene and vinyl acetate, polyimide, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl amylopectin, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, amylopectin, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, a copolymer of acrylonitrile, styrene, and butadiene, polyvinyl alcohol, and a copolymer of styrene and butadiene. Further, the first binder is polyvinylidene fluoride.

[0052] In some embodiments, the relative molecular weight of the first binder is 400,000 to 2,000,000; further, the relative molecular weight of the first binder is 800,000 to 1,500,000, for example, the relative molecular weight of the first binder is 400,000, 500,000, 600,000, 700,000, 800,000, 900,000, 1,000, 1,200,000, 1,300,000, 1,400,000, 1,500,000, 1,600,000, 1,700,000, 1,800,000, 1,900,000, 2,000,000. When the molecular weight of the first binder is too large, for example greater than 2,000,000, its crystallinity is higher and its viscosity is stronger, which is not conducive to slurry leveling and coating processes; when the molecular weight of the first binder is too small, its adhesion decreases, leading to demolding and powdering. Within the scope of this application, the first binder can have adhesion while having lower crystallinity (reduced ion transport resistance), and is beneficial for processing.

[0053] In some embodiments, the thickness of the second coating is L2; ​​1μm≤L2≤5μm; for example, the thickness of the second coating is 1μm, 2μm, 3μm, 4μm, 5μm, etc., wherein the second coating is an in-situ reactive coating, and its excessive thickness will result in low reaction utilization and increase impedance. Further, the thickness of the first coating is the same as that of the second coating, which can be 2μm. The second coating includes zinc fluoride, polyacrylic acid, and a second binder in a mass ratio of (40-80):(20-60):(1-5), wherein the mass ratio of zinc fluoride, polyacrylic acid, and the second binder in the second coating is (40, 50, 60, 70, 80):(20, 30, 40, 50, 60, 70, 80):(1, 2, 3, 4, 5).

[0054] In some embodiments, the particle size of zinc fluoride is 200 nm-10 μm, and further, the particle size of zinc fluoride is 100 nm-200 nm. For example, the particle size of zinc fluoride is 100 nm, 200 nm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, etc. The zinc fluoride in this application has a higher specific surface area for reaction with metallic lithium at the example particle size.

[0055] In some embodiments, the relative molecular weight of polyacrylic acid is 10,000-400,000; further, the relative molecular weight of polyacrylic acid is 100,000-300,000, for example, the relative molecular weight of polyacrylic acid is 10,000, 50,000, 100,000, 150,000, 200,000, 300,000, 400,000, etc. The polyacrylic acid in this application has a lower molecular weight and crystallinity at the example particle size, making it easier to lithium-bear.

[0056] In some embodiments, the second adhesive comprises at least one selected from polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, a copolymer of polyvinylidene fluoride and trichloroethylene, polyacrylate, polyacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, a copolymer of ethylene and vinyl acetate, polyimide, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl amylopectin, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, amylopectin, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, a copolymer of acrylonitrile, styrene, and butadiene, polyvinyl alcohol, and a copolymer of styrene and butadiene. Further, the second adhesive is polyvinylidene fluoride.

[0057] In some embodiments, the relative molecular weight of the second binder is 400,000 to 2,000,000, and further, the relative molecular weight of the second binder is 800,000 to 1,500,000. For example, the relative molecular weight of the second binder is 400,000, 500,000, 600,000, 700,000, 800,000, 900,000, 1,000, 1,200,000, 1,300,000, 1,400,000, 1,500,000, 1,600,000, 1,700,000, 1,800,000, 1,900,000, 2,000,000. When the molecular weight of the second binder is too large, for example, greater than 2,000,000, its crystallinity is higher and its viscosity is stronger, which is not conducive to slurry leveling and coating processes. When the molecular weight of the second binder is too small, its adhesion decreases, which can lead to demolding and powdering. Within the scope of this application, the second binder can have adhesion and low crystallinity (reduced ion transport resistance), and is beneficial to processing.

[0058] In this embodiment, a first coating and a second coating are sequentially disposed on one side of the base membrane. While ensuring the mechanical strength of the separator, the in-situ generated organic-inorganic interface intermediate layer cleverly combines the characteristics of high viscoelasticity and high stability, and also possesses high ion conductivity, accelerating ion transport, uniformizing ion flux, reducing the negative impact of volume expansion on the negative electrode side, and promoting uniform lithium-ion deposition. The in-situ replaced zinc element grows uniformly on the lithium metal surface, uniformizing the electric field intensity on the negative electrode side. Simultaneously, zinc and its oxides, as lithiophilic materials, reduce the overpotential for lithium element deposition nucleation, promoting uniform lithium element deposition. The combined effect of the above materials and structures in this embodiment optimizes the lithium metal deposition interface, promotes high-quality deposition, directly improves the cell cycle performance, and indirectly inhibits dendrite formation, thus improving safety.

[0059] According to an embodiment of the second aspect of this application, a method for preparing a diaphragm is provided, comprising the following steps:

[0060] S1: Disperse the inorganic material and the first binder in a solvent according to the stoichiometric ratio to obtain the first slurry;

[0061] S2: Disperse zinc fluoride, polyacrylic acid, and the second binder in a solvent according to stoichiometric ratio to obtain the second slurry;

[0062] S3: Apply the first slurry onto the base film and cure it to obtain the first coating layer; apply the second slurry onto the first coating layer and cure it to obtain the second coating layer;

[0063] S4: Cut to the appropriate size to obtain the diaphragm in any of the above embodiments.

[0064] In step S1, inorganic materials and a first binder are dispersed in a solvent according to a stoichiometric ratio to form a first slurry. The solid content of the first slurry is 10%-30%, where the solid content is the percentage by mass of the remaining portion of the first slurry after drying under specified conditions; further, the solid content of the first slurry is 20%. When the solid content in the first slurry is too low, such as below 10%, the content of inorganic materials is too low, which has limited effect on increasing the overall mechanical strength of the diaphragm; when the solid content in the first slurry is too high, such as above 30%, it is not conducive to thin coating. In this embodiment, the solvent includes at least one of N-methylpyrrolidone, formamide, methanol, ethanol, propanol, acetone, dioxane, and tetrahydrofuran.

[0065] In step S2, zinc fluoride, polyacrylic acid, and a second binder are dispersed in a solvent according to a stoichiometric ratio to form a second slurry. The solid content of the second slurry is 10%-30%, and more specifically, 20%. If the solid content of the second slurry is too low, such as below 10%, the content of zinc fluoride and polyacrylic acid will be too low, which is not conducive to lithium deposition. If the solid content of the second slurry is too high, such as above 30%, it is not conducive to thin coating. In this embodiment, the solvent is the same as the solvent used to prepare the first slurry, including at least one of N-methylpyrrolidone, formamide, methanol, ethanol, propanol, acetone, dioxane, and tetrahydrofuran.

[0066] In step S3, the first slurry is applied to the base film using a 5μm doctor blade, and then baked in a vacuum oven at 80-95℃ for 4-10 hours with a vacuum degree ≤-90Kpa to obtain the first coating. Further, the curing parameters for the first slurry are 90℃ for 8 hours and a vacuum degree of -90Kpa. Then, the second slurry is applied to the first coating using a 5μm doctor blade, and then baked in a vacuum oven at 80-95℃ for 4-10 hours with a vacuum degree ≤-90Kpa to obtain the second coating. Further, the curing parameters for the second slurry are 90℃ for 8 hours and a vacuum degree of -90Kpa.

[0067] The preparation method in this application involves coating a first slurry onto a base film and curing it to form a first coating layer; then coating a second slurry onto the first coating layer and curing it. The process is simple and easy to promote. Therefore, by cleverly utilizing the convenience and quantifiable controllability of the separator coating, zinc fluoride, polyacrylic acid, and inorganic materials are introduced into the lithium metal interface to generate a highly uniform and stable multifunctional intermediate layer in situ. Compared with direct, non-situ treatment on the lithium metal surface, this method is more efficient and convenient, has high feasibility for process scale-up, and allows for adjustable treatment levels.

[0068] According to an embodiment of the third aspect of this application, a secondary battery is provided, which includes the separator in any of the above embodiments.

[0069] In some embodiments, the secondary battery further includes a positive electrode plate, a negative electrode plate, and an electrode core; wherein the second coating is in contact with the negative electrode plate; the negative electrode plate is a lithium copper composite tape.

[0070] The secondary battery further includes the separator provided in the above embodiments of the present application.

[0071] [Positive electrode plate]

[0072] The positive electrode plate includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector. The positive electrode film layer includes a positive electrode active material, and the proportion of the positive electrode active material is more than 95%. As an example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is provided on any one or both of the two opposite surfaces of the positive electrode current collector with a double-sided coating surface density of 380 g / m 2 .

[0073] The positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0074] In some embodiments, the positive electrode active material in the positive electrode plate of the present application can be a positive electrode active material known in the art for batteries. As an example, the positive electrode active material can include at least one of the following materials: As an example, the positive electrode active material can include, but is not limited to, lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), lithium cobalt phosphate (LiCoPO4), lithium iron pyrophosphate (Li2FeP2O7), lithium cobalt oxide (LiCoO2), spinel-type lithium manganese oxide (LiMn2O4), spinel-type lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O4), layered lithium manganese oxide (LiMnO2), lithium nickel oxide (LiNiO2), lithium niobate (LiNbO2), lithium ferrite (LiFeO2), lithium manganate (LiMgO2), lithium calcium oxide (LiCaO2), lithium copper oxide (LiCuO2), lithium zinc oxide (LiZnO2), lithium molybdate (LiMoO2), lithium tantalate (LiTaO2), lithium tungstate (LiWO2), lithium nickel cobalt aluminum oxide (LiNi x Co y Al 1-x-y O2, 0 < x < 1, 0 < y < 1, 0 < x + y < 1, for example LiNi 0.8Co 0.15 Al 0.05 (O2), lithium nickel cobalt manganese oxide (LiNi x Co y Mn 1-x-y O2, 0 < x < 1, 0 < y < 1, 0 < x + y < 1, for example LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, etc.), lithium-rich materials (such as lithium-rich nickel cobalt manganese oxide), manganese oxide (MnO2), vanadium oxide, sulfur oxide, silicate oxide, and at least one of their respective modified compounds. These materials can be used alone or in combination of two or more.

[0075] The modified compounds of the above positive electrode active materials can be doping modification, surface coating modification, or simultaneous doping and coating modification of the positive electrode active materials, etc.

[0076] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the 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 fluorinated acrylate resin.

[0077] In some embodiments, the positive electrode film layer may further optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0078] In some embodiments, the positive electrode plate can be prepared by the following method: dispersing the components for preparing the positive electrode plate, such as the positive electrode active material, conductive agent, binder, and any other components in the first aspect of the present application, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode plate can be obtained.

[0079] [Negative electrode plate]

[0080] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer comprising a negative electrode active material. As an example, the negative current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0081] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0082] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: lithium metal, artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0083] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0084] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0085] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0086] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0087] [Electrolytes]

[0088] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0089] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0090] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0091] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0092] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0093] In some embodiments, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process. For example, the positive electrode, negative electrode, and separator are cut to appropriate sizes, and then a 5Ah bare cell is stacked and subsequently hot-pressed, packaged, injected with electrolyte, formed, and capacity tested. The hot-pressing process parameters are: temperature 60-100℃, pressure 600-1200KG, and holding time 30-120s; further, the hot-pressing process parameters are: temperature 80℃, pressure 1000KG, and holding time 60s; wherein the electrolyte injection coefficient is 1.8gAh. This embodiment utilizes a hot-pressing process to bond the second coating to the negative electrode to assemble the secondary battery. By applying a separator with high mechanical strength and the ability to promote uniform lithium deposition to the secondary battery, a secondary battery with good cycle performance and safety performance is obtained.

[0094] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0095] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0096] This application does not impose any particular restrictions on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape.

[0097] An electrical device comprising the secondary battery of any of the above embodiments is provided according to an embodiment of the fourth aspect of this application.

[0098] This application applies a separator with high mechanical strength that can promote uniform lithium deposition to a secondary battery, and assembles the resulting secondary battery into an electrical device to improve the cycle performance and safety performance of the device.

[0099] To facilitate a further understanding of this application, the solutions described below are further described in conjunction with embodiments. Those skilled in the art will understand that the examples described in this application are only a portion of the examples, and any other suitable specific examples are within the scope of this application.

[0100] Example 1

[0101] This embodiment provides a diaphragm, the preparation method of which and specific operating parameters are as follows:

[0102] Preparation of the first slurry: Alumina with a particle size of 1 μm and PVDF with a relative molecular weight of 400,000 are dispersed in N-methylpyrrolidone at a mass ratio of 90:10 to obtain the first slurry, wherein the solid content of the first slurry is 20%.

[0103] Preparation of the second slurry: Zinc fluoride with a particle size of 50 nm, polyacrylic acid with a relative molecular weight of 10,000 and PVDF with a relative molecular weight of 400,000 are dispersed in N-methylpyrrolidone at a mass ratio of 50:45:5 to obtain the second slurry, and the solid content of the second slurry is controlled to be 20%.

[0104] A standard 7μm PE base film is used. The first slurry is coated with a 5μm doctor blade and then placed in a vacuum oven at 90℃ for 8 hours. The vacuum degree is -90Kpa, which yields a first coating thickness of 2μm. The second slurry is then coated on the first coating with a 5μm doctor blade and then placed in a vacuum oven at 90℃ for 8 hours. The vacuum degree is -90Kpa, which yields a second coating thickness of 2μm. The film is then cut into the corresponding size to obtain a separator.

[0105] Example 2

[0106] This embodiment provides a diaphragm that differs from Embodiment 1 in the following way: the mass ratio of zinc fluoride, polyacrylic acid, and PVDF in the preparation of the second slurry is 40:55:5.

[0107] Example 3

[0108] This embodiment provides a diaphragm that differs from Embodiment 1 in the following ways: the thickness of the first coating is 4 μm.

[0109] Example 4

[0110] This embodiment provides a diaphragm that differs from Embodiment 1 in the following way: the thickness of the second coating is 4 μm.

[0111] Example 5

[0112] This embodiment provides a diaphragm that differs from Embodiment 1 in the following ways: the thickness of the first coating is 4 μm; the thickness of the second coating is 4 μm.

[0113] Example 6

[0114] This embodiment provides a diaphragm that differs from Embodiment 1 in the following way: the mass ratio of alumina to PVDF is 80:20 when preparing the first slurry.

[0115] Example 7

[0116] This embodiment provides a diaphragm that differs from Embodiment 1 in the following way: the mass ratio of zinc fluoride, polyacrylic acid, and PVDF in the preparation of the second slurry is 60:35:5.

[0117] Comparative Example 1

[0118] This embodiment provides a diaphragm that differs from Embodiment 1 in the following ways: a conventional 7μm PE base film is taken, a second slurry is coated with a 5μm doctor blade, and then placed in a vacuum oven at 90 degrees for 8 hours with a vacuum degree of -90Kpa and a thickness of 2μm. The film is then cut into the corresponding size to obtain the diaphragm.

[0119] Comparative Example 2

[0120] This embodiment provides a diaphragm that differs from Embodiment 1 in the following ways: a conventional 7μm PE base film is taken, and a first slurry is coated with a 5μm doctor blade. Then, it is placed in a vacuum oven at 90 degrees for 8 hours and the vacuum degree is -90Kpa to obtain a first coating thickness of 2μm. The diaphragm is then cut into the corresponding size.

[0121] Comparative Example 3

[0122] This embodiment provides a diaphragm that differs from Embodiment 1 in the following ways: a conventional 7μm PE base film is cut to the appropriate size as the diaphragm.

[0123] Comparative Example 4

[0124] This embodiment provides a diaphragm that differs from Embodiment 1 in the following ways: the thickness of the first coating is 1 μm; the thickness of the second coating is 1 μm.

[0125] Test case

[0126] The separators prepared in the above embodiments and comparative examples were assembled into 5AH stacked batteries for cycle performance testing. The 5AH stacked batteries were prepared by dispersing the positive electrode active material, conductive agent Super P (manufacturer: Yirui Stone), and binder PVDF (manufacturer: Suwei, model: 5130) in N-methylpyrrolidone (NMP) at a mass ratio of 95:2:3, with a solid content of 70%, and ball milling to form a uniform positive electrode slurry. The positive electrode slurry was then coated onto the rough surface of a clean aluminum foil using a coater, with a coating density of 380 g / m², and then placed in a vacuum oven at 120°C for 12 hours to obtain the electrode sheet with a compaction density of 3.45 g / cm³. 3The electrode sheets were cut to 60mm*110mm, with corresponding tabs left. The negative electrode was a lithium-copper composite strip, cut to 62mm*112mm. The separator was the same as the separator obtained in the above examples and comparative examples, cut to 63mm*113mm. The positive electrode was stacked in 13 layers, the negative electrode in 14 layers, and the separator coating side was aligned with the negative electrode. The bare cell was hot-pressed. The hot-pressing process parameters were: temperature 80℃, pressure 1000KG and holding time 60s. Finally, the hot-pressed cell aluminum-plastic film was assembled and packaged to obtain a 5AH soft-pack battery. The electrolyte used was a 1mol / L LiPF6 solution obtained by dissolving LiPF6 in a mixed solvent of ethyl carbonate (EC) and diethyl carbonate (DMC) (volume ratio EC:DMC = 1:1).

[0127] Cyclic testing was conducted under a constant pressure of 100KG, a charge / discharge rate of 1C, a voltage of 2.8V-4.3V, a constant current and constant voltage charging method, and a cutoff current of 0.05C, until the capacity decayed to 80% of its initial capacity.

[0128] The charging DCR at 50% SOC during the first cycle of the battery cell is recorded as R1; the charging DCR at 50% SOC after 30 cycles is recorded as R2. The test method is as follows: the battery cell is adjusted to 50% SOC at a rate of 0.33C, left to stand for 30 minutes, and the voltage is recorded as V1. Then, it is charged at a rate of 2C for 10 seconds, and the voltage is recorded as V2. The sampling interval is 1 second. R = (V2 - V1) / 10Ah. The internal resistance growth rate is recorded as K, K = (R2 - R1) / R1; K indirectly reflects the degree of system deterioration (volume expansion leading to SEI rupture and regeneration, insufficient electrolyte on the negative electrode side, excessive electrolyte consumption, etc.).

[0129] The initial cell thickness is denoted as W, the thickness after the first full charge cycle is denoted as W1, the thickness after 30 full charge cycles is denoted as W2, and the thickness growth rate is denoted as Q, where Q = (W2 - W1) / W1. Q indirectly reflects the degree of deterioration of the negative electrode interface (continuous growth of lithium dendrites leading to SEI thickening, dead lithium accumulation, and the relative density of lithium deposition, etc.). All tests were conducted at room temperature, and the results are shown in Table 1.

[0130] Table 1 shows the test results of secondary batteries made with separators in each embodiment and comparative example.

[0131]

[0132]

[0133] Compared with Example 2, Example 2 showed increased K and Q values ​​and a shortened cycle life, indicating that performance began to deteriorate after the PAA content exceeded 45%. This is preliminarily speculated to be due to excessive organic components in the interface layer formed by the second coating, leading to decreased mechanical strength and poor stability at the interface.

[0134] Compared with Comparative Example 3, Example 1 shows relatively smaller K and R values ​​and a significantly improved cycle life, indicating that this double-layer structure achieves the desired effect.

[0135] Comparing Comparative Example 1 and Comparative Example 2, the example shows better results, indicating that the in-situ interface formation effect of the second coating is achieved, which is better than that of the first coating alone.

[0136] Comparing Comparative Example 1 with Comparative Example 3, and Comparative Example 2 with Comparative Example 3, the cycle life of both examples is improved, and K and Q are reduced. This indicates that the mechanical strength and liquid retention effect of the first coating, and the in-situ interface formation of the second coating, are beneficial to cell cycling. This further proves that the second coating has a more significant effect on uniform lithium deposition.

[0137] Compared with Comparative Example 1, Example 1 demonstrates that the enhanced mechanical strength and liquid retention capacity of the first coating further improve high-quality lithium deposition and cycle performance.

[0138] Comparing Example 3 with Example 1, it is shown that increasing the thickness of the first coating to 4 μm leads to an increase in K and initial internal resistance, without improving Q, further resulting in a decrease in cycle life. This proves that the thickness of the first coating should not be too thick.

[0139] Compared with Example 1, Q in Example 4 decreased slightly, but K increased significantly, indicating that the thickening of the second coating leads to low lithiation utilization and increases impedance, resulting in a decrease in cycle life.

[0140] Compared with Example 1, Example 5 shows a significant increase in K, no benefit in Q, and a decrease in cycle life. This indicates that the thick coating degrades the system to a greater extent.

[0141] Compared with Example 1, Comparative Example 4 shows that K is significantly increased, indicating that the thin coating results in poor lithium deposition quality, which leads to the continuous generation and consumption of electrolyte by SEI, and poor electrolyte retention. Q also doubles, indicating that the lithium deposition is not dense, and active lithium is continuously consumed to form dead lithium. At the same time, the cycle life is also shortened. All of the above indicate that the thin coating does not achieve the desired material structure effect.

[0142] Compared with Example 1, Example 6 shows a significant increase in K and Q, and a substantial decrease in cycle life. This is presumably due to the excessive adhesive content in the first coating, which clogs the pores, increases diffusion transport impedance, and thus degrades electrical performance.

[0143] Comparing Example 7 with Examples 1 and 2, it is shown that when the zinc fluoride content is greater than 50%, there is no significant benefit and the cycle life is slightly lower than that of Example 1. This is presumably due to the excessive zinc fluoride and the high proportion of unreacted and converted zinc.

[0144] The second coating offers a more direct advantage, complementing the first coating to significantly improve the cycle performance and lithium deposition quality of the electrical device.

[0145] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0146] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A diaphragm, characterized in that, It includes a base film and a first coating and a second coating sequentially disposed on one side of the base film; the first coating includes an inorganic material and a first binder in a mass ratio of (60-95):(5-40); the second coating includes zinc fluoride, polyacrylic acid and a second binder in a mass ratio of (40-80):(20-60):(1-5); the zinc fluoride reacts with lithium metal in situ to form an intermediate interface layer of LiF and Zn during charging and discharging; the polyacrylic acid and lithium element form PAA-li; the thickness of the first coating is L1; 2μm≤L1≤10μm; and the thickness of the second coating is L2; ​​1μm≤L2≤5μm; the inorganic material includes at least one of alumina, silicon dioxide, titanium oxide, zinc oxide, magnesium oxide, hafnium dioxide, tin oxide, zirconium oxide and solid electrolyte material.

2. The diaphragm according to claim 1, characterized in that, The first coating and the second coating have the same thickness.

3. The diaphragm according to claim 1 or 2, characterized in that, The particle size of the inorganic material is 200 nm-10 μm; And / or, the relative molecular weight of the first adhesive is 400,000 to 2,000,000; And / or, the first adhesive comprises at least one of polyacrylic acid, polyacrylate, polyvinylidene fluoride, copolymer of vinylidene fluoride and hexafluoropropylene, copolymer of vinylidene fluoride and trichloroethylene, polyacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, copolymer of ethylene and vinyl acetate, polyimide, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl amylopectin, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, amylopectin, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, copolymer of acrylonitrile, styrene, and butadiene, polyvinyl alcohol, and copolymer of styrene and butadiene.

4. The diaphragm according to claim 1 or 2, characterized in that, The zinc fluoride has a particle size of 200 nm to 10 μm; And / or, the relative molecular weight of the polyacrylic acid is 10,000 to 400,000; And / or, the relative molecular weight of the second adhesive is 400,000 to 2,000,000; And / or, the second adhesive comprises at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, a copolymer of vinylidene fluoride and trichloroethylene, polyacrylate, polyacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, a copolymer of ethylene and vinyl acetate, polyimide, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl amylopectin, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, amylopectin, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, a copolymer of acrylonitrile, styrene, and butadiene, polyvinyl alcohol, and a copolymer of styrene and butadiene.

5. The diaphragm according to claim 1 or 2, characterized in that, The base film includes PP film and / or PE film; And / or, the thickness of the base film is 5-20 μm.

6. A method for preparing a diaphragm, characterized in that, Includes the following steps: Inorganic materials and a first binder are dispersed in a solvent according to a stoichiometric ratio to obtain a first slurry; Zinc fluoride, polyacrylic acid, and a second binder are dispersed in a solvent according to stoichiometric ratios to obtain a second slurry. The first slurry is applied to the base film and cured to obtain a first coating; the second slurry is applied to the first coating and cured to obtain a second coating; Cut to the appropriate size to obtain the diaphragm as described in any of claims 1-5.

7. The preparation method according to claim 6, characterized in that, The solvents in the first slurry and the second slurry are the same, each including at least one of N-methylpyrrolidone, formamide, methanol, ethanol, propanol, acetone, dioxane, and tetrahydrofuran; And / or, the first slurry and the second slurry have the same solid content, which is 10%-30%.

8. The preparation method according to claim 6, characterized in that, The curing parameters for the first slurry and the second slurry are: temperature 80-95℃, time 4-10h, and vacuum degree ≤-90Kpa.

9. A secondary battery, characterized in that, The secondary battery comprises the separator according to any one of claims 1-5 or the separator obtained by the preparation method according to claim 6 or 7.

10. The secondary battery according to claim 9, characterized in that, The secondary battery also includes a positive electrode, a negative electrode, and a battery cell; wherein the second coating is bonded to the negative electrode; the negative electrode is a lithium-copper composite strip.

11. The secondary battery according to claim 10, characterized in that, The second coating is bonded to the negative electrode sheet using a hot pressing process; the hot pressing process parameters are: temperature 60-100℃, pressure 600-1200KG, and holding time 30-120s.

12. An electrical appliance, characterized in that, Includes the secondary battery described in any one of claims 9-11.

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