Battery separator and lithium battery manufactured using the same

Abstract

This application provides a battery separator, which includes a porous substrate and an adhesive layer formed on one side of the porous substrate. The adhesive layer contains a polymer material having adhesiveness, and the adhesive layer has a coating coefficient C. The coating coefficient C is equal to the ratio of the adhesive strength A of the adhesive layer to the increase value P of air permeability per unit coating layer thickness, satisfying the relational expression C = A / P. Moreover, the ratio range of the coating coefficient C is 0.3 < C < 1. Here, the unit of the adhesive strength A of the adhesive layer is N / m, and the unit of the increase value P of air permeability per unit coating layer thickness of the adhesive layer is s / 100cc / μm.

Description

[Technical Field]

[0001] The present application relates to the technical field of secondary battery materials, and in particular to a separator for a lithium ion battery and a lithium battery manufactured using the same. [Background technology]

[0002] Lithium-ion batteries are secondary batteries that not only convert electrical energy into chemical energy for energy storage, but also convert chemical energy into electrical energy to provide electrical energy to electrical appliances. Lithium-ion batteries are widely used due to their high energy density and long cycle life. In the 21st century, lithium-ion batteries have become widely used due to the popularity of laptops, smartphones, and electric vehicles.

[0003] As an important component of lithium-ion batteries, the separator must have high ionic conductivity and low electronic conductivity. Currently, the commonly used separator for lithium batteries is a porous material manufactured by unidirectional or bidirectional expansion of propylene. This material has good ionic conductivity, excellent mechanical properties, and electrolyte resistance.

[0004] Polyolefins have a low melting point and poor heat resistance, so they generally require a ceramic coating to improve heat resistance. However, while the use of current ceramic coatings can improve the heat shrinkage resistance of separators, they also have the problem of poor adhesion between the ceramic coating layer and the separator, which can lead to the ceramic layer easily peeling off from the separator. Therefore, how to improve the adhesive strength of the coating layer has become an important issue. Summary of the Invention [Problem to be solved by the invention]

[0005] Therefore, the main object of the present application is to provide a battery separator and a lithium battery manufactured using the same so as to further optimize the problems raised above. **Means for Solving the Problems**

[0006] In order to solve the above technical problems, the object of the present application is a composite material composed of a porous substrate or a porous substrate and a heat-resistant layer located on the porous substrate, and an adhesive layer formed on the porous substrate or the composite material. The adhesive layer contains a polymer material having adhesiveness, and the adhesive layer has a coating coefficient C. The coating coefficient C is equal to the ratio of the adhesive strength A of the adhesive layer to the increase value P of the air permeability per unit coating layer thickness, satisfies the relational expression C = A / P, and the ratio range of the coating coefficient C is 0.3 < C < 1. Here, the unit of the adhesive strength A of the adhesive layer is N / m, and the unit of the increase value P of the air permeability per unit coating layer thickness of the adhesive layer is s / 100cc / μm. The object is to provide a battery separator.

[0007] In the battery separator, the adhesive layer contains an adhesive polymer material or a mixture of an adhesive polymer material and a filler, and the filler contains an organic or inorganic heat-resistant material.

[0008] In the battery separator, the adhesive polymer material includes a polyvinylidene fluoride homopolymer, a polyvinylidene fluoride copolymer, a homopolymer of methyl methacrylate, a copolymer of methyl methacrylate, or a mixture thereof.

[0009] In the battery separator, the molar ratio of the vinylidene fluoride monomer in the polyvinylidene fluoride copolymer is higher than 50%, and the other comonomers may be one or more selected from hexafluoropropylene, tetrafluoroethylene, trifluoroethylene, trichloroethylene, acrylic acid, methacrylic acid, methacrylate, and vinyl acetate.

[0010] In the battery separator, the adhesive layer may be disposed on one side of the porous substrate, both sides of the porous substrate, one side of the composite material, or both sides of the composite material.

[0011] In the battery separator, the heat-resistant layer contains a ceramic material, a heat-resistant polymer material, or a mixture of a ceramic material and a heat-resistant polymer material.

[0012] Another object of the present application includes a porous substrate and an adhesive layer formed on one side of the porous substrate. The adhesive layer contains an adhesive polymer material, the polymer material includes polyvinylidene fluoride (PVDF), the adhesive layer has a coating coefficient C, the coating coefficient C is equal to the ratio of the adhesive strength A of the adhesive layer to the increase value P of air permeability per unit coating layer thickness, satisfies the relational expression C = A / P, and the ratio range of the coating coefficient C is 0.4 < C < 0.9. Here, the unit of the adhesive strength A of the adhesive layer is N / m, and the unit of the increase value P of air permeability per unit coating layer thickness of the adhesive layer is s / 100cc / μm. It is to provide a battery separator characterized by this.

[0013] In the battery separator, the crystallinity of the raw material of the polyvinylidene fluoride copolymer is between 10% and 50%.

[0014] In the battery separator, the adhesive layer is coated with aqueous polyvinylidene fluoride, and the ratio of the α-phase in the crystalline region of the aqueous polyvinylidene fluoride exceeds 30% and is less than 70%.

[0015] In the battery separator, the adhesive layer is coated with oily polyvinylidene fluoride, and the ratio of the α-phase in the crystalline region of the oily polyvinylidene fluoride used by the adhesive layer is less than 20%.

[0016] Another object of the present application is to provide a lithium battery comprising a positive electrode, a negative electrode and said battery separator, said battery separator being located between said positive electrode and said negative electrode. [Effects of the Invention]

[0017] This application improves the adhesion between the separator and the electrode plate by incorporating an adhesive polymer material into the separator coating layer. Additionally, incorporating a heat-resistant polymer material such as aramid into the separator coating layer increases the separator's film rupture temperature. Furthermore, incorporating ceramics into the separator coating layer improves the separator's thermal shrinkage resistance. These improvements effectively address the issue of peeling from the separator due to the current ceramic coating layer's insufficient adhesive strength. Additionally, this application designs the coating coefficient C value to reflect the adhesion and breathability of the coating layer and restrict it to a specific, better range, providing a very convenient way to evaluate and ensure whether the separator's adhesion and breathability meet requirements. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a schematic diagram of the cross-sectional structure of a battery separator in one embodiment of the present application. [Figure 2] FIG. 2 is a schematic diagram of the cross-sectional structure of a battery separator according to another embodiment of the present application. [Figure 3] FIG. 3 is a schematic diagram of the cross-sectional structure of a battery separator in another embodiment of the present application. [Figure 4] FIG. 4 is a schematic diagram of the cross-sectional structure of a battery separator in another embodiment of the present application. [Figure 5] FIG. 5 is a flow diagram of a battery separator manufacturing and processing method according to one embodiment of the present application. DETAILED DESCRIPTION OF THE INVENTION

[0019] The following description of each embodiment refers to additional diagrams to illustrate specific embodiments implemented in the present application. Directional terms such as "upper," "lower," "front," "rear," "left," "right," "inner," "outer," and "side" used in the present application merely refer to the directions of the additional diagrams. Therefore, the directional terms used are intended to explain and understand the present application, and are not intended to limit the present application.

[0020] The drawings and descriptions are intended to be illustrative in nature, rather than restrictive. In the drawings, structurally similar elements are represented by the same symbols. Additionally, for ease of understanding and description, the dimensions and thickness of each component shown in the drawings are arbitrary, but the present application is not limited thereto.

[0021] In the drawings, thicknesses of layers, films, regions, etc. are exaggerated for clarity. In the drawings, thicknesses of layers, regions, etc. are exaggerated for ease of understanding and explanation. When a component, such as a layer, film, region, or substrate, is referred to as being "on" another component, it is understood that the component may be directly on the other component, or intermediate components may be present.

[0022] Additionally, in this specification, unless expressly stated to the contrary, the word "comprising" is understood to mean including the component, but not excluding other components. Additionally, in this specification, "above" means above or below the target component, and does not necessarily mean at the top based on the direction of gravity.

[0023] In order to further explain the technical means and functions adopted to achieve the intended purpose of the present application in detail, the specific embodiments, structures, features and functions of the battery separator proposed by the present application and the proton exchange membrane manufactured using the same will be described in detail as follows, in conjunction with the accompanying drawings and specific examples.

[0024] As shown in FIG. 1, the battery separator 1 of the embodiment of the present application includes a porous substrate 11, a heat-resistant layer 13 located on one side of the porous substrate 11, and an adhesive layer 12 formed on the composite material. The porous substrate 11 and the heat-resistant layer 13 together constitute a composite material. As another option, as shown in FIG. The structure of the heat-resistant layer 13 is omitted, only the porous substrate 11 is left, and the adhesive layer 12 is directly formed on one side of the porous substrate 11. Whether the adhesive layer 12 is formed on the porous substrate 11 or on the composite material, the adhesive layer includes an agglomerated layer formed by the aggregation of the adhesive polymer material 121, and the adhesive layer 12 has a coating coefficient C, and the coating coefficient C is equal to the ratio of the adhesive strength A of the adhesive layer 12 to the increase value P of the air permeability per unit coating layer thickness, satisfying the relational expression C = A / P, and the ratio range of the coating coefficient C is 0.3 < C < 1. Here, the unit of the adhesive strength A of the adhesive layer 12 is N / m, and the unit of the increase value P of the air permeability per unit coating layer thickness of the adhesive layer 12 is s / 100cc / μm.

[0025] In this embodiment, the porous substrate 11 refers to a material having voids or pores within the substrate. It may be a porous sheet formed from a fibrous material such as a nonwoven fabric or a paper sheet, or a composite porous sheet obtained by laminating one or more other porous layers on these microporous membranes and porous sheets. The porous substrate may be a polyolefin material having a porous structure obtained by a dry or wet process after unidirectional or multidirectional stretching, or a porous material obtained by methods such as nonsolvent-induced phase separation, thermally-induced phase separation, or steam-induced phase separation. The polyolefin material is typically polyethylene and polypropylene. The porous substrate 11 may also be a substrate manufactured by a method such as electrospinning using one or more fibers of materials such as polyethylene terephthalate, nylon, aramid, polysulfone, polyether ether ketone, and polyimide. The thickness of the porous substrate 11 is typically between 3 and 30 μm, and the air permeability of the porous substrate 11 is between 30 and 500 s / 100 ml.

[0026] In this embodiment, the adhesive layer 12 may be applied to both sides of the composite material, and the surface density of each side of the composite material is 0.1 to 6.0 g / m 2 However, the adhesive layer 12 may be disposed between the porous substrate 11 and the porous substrate 11. The adhesive layer 12 may be disposed on only one side of the composite material, or on one or both sides of the porous substrate 11. In this embodiment, the adhesive layer 12 includes an adhesive polymer material 121, which is, for example, an agglomerated layer formed by agglomeration of polyvinylidene fluoride (PVDF) particles or acrylic acid particles, but is not limited to this granular form, and the adhesive polymer material 121 may be fibrous, network-like, or crosslinked.

[0027] The adhesive polymer material 121 may be a polyvinylidene fluoride or polyacrylic acid-based polymer material, and the polyacrylate-based resin may be a copolymer of materials such as methyl methacrylate (PMMA), acrylic acid, methacrylic acid, ethyl methacrylate, styrene, butyl methacrylate, methacrylamide, isobutylene, acrylonitrile, etc., or may be formed by polymerizing two or more monomers such as methacrylate, acrylic acid, acrylate, styrene, ethylene glycol, acrylonitrile, etc. The resin may be obtained by a cross-linking reaction, and the resin may also be a material with a core-shell structure, i.e., the core layer and the shell layer are made of different materials. Thus, in some embodiments, the adhesive layer 12 comprises an adhesive polymer material, and the adhesive polymer material may be a polyvinylidene fluoride homopolymer, a polyvinylidene fluoride copolymer, a methyl methacrylate homopolymer, a methyl methacrylate copolymer, or a mixture thereof.

[0028] In this embodiment, the polyvinylidene fluoride (PVDF) resin is a fluorine-containing polymer material mainly composed of vinylidene fluoride monomer, which may be polyvinylidene fluoride obtained by homopolymerization, or polyvinylidene fluoride obtained by copolymerization, such as copolymer of vinylidene fluoride and tetrafluoroethylene, copolymer of vinylidene fluoride and hexafluoropropylene, copolymer of vinylidene fluoride and trifluoroethylene, mixture of polyvinylidene fluoride and acrylic acid-based polymer, and polyvinylidene fluoride copolymer, where the comonomer is selected from monomers such as hexafluoropropylene, tetrafluoroethylene, trifluoroethylene, trichloroethylene, acrylic acid, methacrylic acid, methacrylate, vinyl acetate, etc.

[0029] In some embodiments, the adhesive layer 12 comprises an adhesive polymer material or a mixture of an adhesive polymer material and a filler, and the filler comprises an organic or inorganic heat-resistant material, where the inorganic heat-resistant material comprises a ceramic material such as alumina, boehmite, barium sulfate, magnesium hydroxide, barium titanate, etc., and the organic heat-resistant material comprises polyimide microspheres, cross-linked polyacrylic acid, cross-linked acrylic acid, cross-linked polymethacrylic acid (ester), cross-linked polystyrene, cross-linked polysiloxane, polysulfone, polyacrylonitrile, etc.

[0030] In this embodiment, the air permeability increase value P per unit coating layer thickness of the adhesive layer 12, i.e., the ratio of the difference between the air permeability value of the adhesive layer 12 and the air permeability value of the porous substrate 11 to the thickness of the adhesive layer, is approximately 0 to 50 s / 100 cc / μm, preferably 0 to 30 s / 100 cc / μm, and more preferably 0 to 15 s / 100 cc / μm. The "air permeability per unit coating layer thickness" is the value obtained by dividing the difference between the air permeability of the adhesive layer 12 and the air permeability of the porous substrate 11 by the thickness of the adhesive layer 12. The unit of air permeability is "s / 100 cc," and the unit of the thickness of the adhesive layer 12 is "μm." In this embodiment, the adhesive layer 12 includes a polymeric resin material or a mixture of a polymeric resin and a ceramic material, and the surface smoothness of the adhesive layer 12 is 1.30 or less.

[0031] In some embodiments, the oily adhesive coating layer has a larger coating area than the aqueous adhesive coating layer, so it has good adhesion strength, but its air permeability is poor. The better the adhesion strength, the closer the adhesion between the separator and the electrode plate becomes, and the volumetric energy density of the separator can be significantly improved. Also, during the charge-discharge cycle process, gas is generated, so there is gas between the separator and the electrode plate, and the ionic conductivity decreases, resulting in a shortened cycle life of the battery. The presence of the adhesive layer can avoid this problem. However, the presence of the adhesive layer causes a decrease in air permeability and reduces ionic conductivity. Therefore, it is necessary to simultaneously control the adhesion strength and air permeability of the separator so as to maximize its overall performance. For this reason, the ratio range of the coating coefficient C of the adhesive layer 12 is 0.3 < C < 1. With such parameter limitations, the battery separator 1 of this application can achieve the best design of adhesion strength and air permeability.

[0032] In this embodiment, the ratio range of the coating coefficient C of the adhesive layer 12 is approximately 0.3 < C < 1, but it is not limited to this. In some embodiments, the ratio range of the coating coefficient C is preferably 0.5 < C < 1, 0.3 < C < 0.8, or 0.4 < C < 0.9. For example, in the battery separator of other embodiments of this application, its structure is similar to FIG. 3 and includes a porous substrate and an adhesive layer located on one side of the porous substrate. The adhesive layer contains a polymer material with adhesiveness. The polymer material includes polyvinylidene fluoride (PVDF). The adhesive layer has a coating coefficient C, and the coating coefficient C is equal to the ratio of the adhesion strength A of the adhesive layer to the increase value P of air permeability per unit coating layer thickness, satisfying the relational expression C = A / P. And the ratio range of the coating coefficient C is 0.4 < C < 0.9. Here, the unit of the adhesion strength A of the adhesive layer is N / m, and the unit of the increase value P of air permeability per unit coating layer thickness of the adhesive layer is s / 100cc / μm.

[0033] For the copolymerized polymer of polyvinylidene fluoride (PVDF) above, the molar ratio of the PVDF monomer is higher than 50%. For the copolymerized polymer of PVDF above, the crystallinity of its raw material is between 10% and 50%. In the case of the aqueous PVDF coating separator, the proportion of the α-phase in the crystalline region of PVDF in the PVDF coating layer exceeds 30% and is less than 70%. In the case of the oil-based PVDF coating separator, the proportion of the α-phase in the crystalline region of PVDF in the PVDF coating layer is less than 20%. Such design of the molar ratio, the range of the crystallinity of the raw material, and the proportion of the α-phase in the crystalline region affect the ratio of the coating coefficient C, so the ratio range of the coating coefficient C is limited to 0.4 < C < 0.9.

[0034] As shown in FIG. 1, in this embodiment, the heat-resistant layer 13 includes a ceramic material, a heat-resistant polymer material, or a mixture of a ceramic and a heat-resistant polymer material. Here, the ceramic material is at least one selected from metal hydroxides, metal oxides, and salts containing metals. The ceramic material includes, but is not limited to, particles of inorganic materials such as alumina, boehmite, magnesium hydroxide, barium titanate, and barium sulfate. The heat-resistant polymer material includes, but is not limited to, polymer materials such as poly(m-phenylene isophthalamide), poly-p-phenylene terephthalamide, polyimide (including polypyromellitimide, soluble polyimide, polyetherimide, and polyamideimide), polyethersulfone, polyetheretherketone, and polyethylene terephthalate. The glass transition temperature of the polymer material is 200°C or higher, and the thermal decomposition temperature is 400°C or higher. Here, the heat-resistant polymer material may be any of granular, fibrous, network-shaped, or cross-linked polymer microsphere particles.

[0035] In this embodiment, the heat-resistant layer 13 is disposed in a single layer on one side of the porous substrate 11. However, without being limited thereto, the heat-resistant layer 13 may be disposed on both sides of the porous substrate 11, as shown in Fig. 2, where the heat-resistant layer 13 includes an aramid polymer and an inorganic filler, and the adhesive layer 12 includes polyvinylidene fluoride (PVDF) particles and / or acrylic particles formed by an adhesive polymer material 121. In some embodiments, as shown in Fig. 3, the adhesive layer 12 includes ceramic particles 122 in addition to the adhesive polymer material 121, so that the adhesive layer 12 is a particle aggregation layer formed by the aggregation of the polymer particles 121 and the ceramic particles 122. In another embodiment, as shown in FIG. 4, the adhesive layer 12 on one side of the porous substrate 11 in FIG. 3 may be further coated with a polymer material 121 so that the polymer material 121 can cover the particles 122 of the ceramic material, thereby enhancing adhesion and increasing the overall thickness of the adhesive layer 12.

[0036] In some embodiments, a lithium battery according to one embodiment of the present application includes a positive electrode, a negative electrode, and the battery separator 1. The battery separator 1 is positioned between the positive electrode and the negative electrode, and generates electromotive force through the insertion and desorption of lithium ions. The positive electrode includes a positive electrode active material, a conductive agent, a binder, a current collector, and other materials. Examples of the conductive agent include acetylene black, ketjen black, and graphite powder. The negative electrode includes a material capable of accepting lithium ions, such as a lithium alloy material with carbon, silicon, aluminum, or the like. The electrolyte is a solution obtained by dissolving a lithium salt in a non-aqueous solvent, and the lithium salt may be a material such as LiPF6, LiBF4, LiClO4, LiTFSI, or LiFSI. Examples of non-aqueous solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, fluoroethylene carbonate, and difluoroethylene carbonate; linear carbonates such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate and their fluoro-substituted derivatives; and cyclic esters such as γ-butyrolactone and γ-valerolactone. These can be used separately or in combination. Examples of external sealing materials include metal shells and aluminum laminate film packaging. Battery shapes include prismatic, cylindrical, and button types, and the battery separator 1 of the present invention is suitable for any of these shapes. From the standpoint of ion permeability, the air permeability of the battery separator 1 in this application is preferably within 300 s / 100 ml, the thickness of the battery separator 1 is preferably within 30 μm, and the resistance of the battery separator 1 is preferably 0.5 to 10 ohm.cm. 2 The puncture strength of the battery separator 1 is preferably in the range of 10 to 1200 gf, and more preferably in the range of 200 to 800 gf.

[0037] Furthermore, as long as the method for producing a non-aqueous secondary battery separator is a method for producing a non-aqueous secondary battery separator having an aggregate containing the above-mentioned amount of fine particles, a filler, and a heat-resistant polymer coating layer on one or both sides of a porous substrate, the coating process includes an aqueous coating process and an oil-based coating process, where the aqueous coating process includes: (1) adding a wetting agent, a dispersant, a thickener, a filler, an adhesive polymer material, a binder, etc. in a certain order, and then mixing and stirring to obtain a homogeneous slurry; (2) coating the separator with the slurry using a method such as bar coating or roll coating; and (3) drying in an oven to obtain an aqueous slurry coating layer. The oil-based coating process includes: (1) dissolving a polymer material or a heat-resistant polymer material in a suitable solvent to obtain a uniform solution, or mixing the solution with ceramic particles, heat-resistant polymer particles, heat-resistant polymer fibers, etc. to obtain a uniform dispersion; (2) coating the solution or dispersion onto a base film and forming pores using a method such as non-solvent-induced phase separation, or directly placing it in an oven to form pores by the method of water vapor-induced phase separation; (3) removing the solvent by washing with water; and (4) placing it in an oven to dry.

[0038] In some embodiments, an aqueous dispersion is prepared by dispersing, suspending, or emulsifying adhesive polymeric particles and a filler containing at least one of an organic compound and an inorganic compound in a solvent in their solid state. This may be an emulsion or a suspension. In the process of producing a coated separator, the water in the aqueous slurry must be evaporated to obtain a dry coating layer. In the case of an oil-based coating, the solvent must be removed by washing with water, and the separator must also be dried to remove the water.

[0039] The objectives of the present application and the solution to its technical problems are realized by the following technical solutions. This application provides a manufacturing and processing method 2 for a battery separator. Referring to both FIG. 1 and FIG. 5, this manufacturing and processing method 2 includes step S1 of providing a porous substrate, step S2 of coating a heat-resistant layer on one side of the porous substrate, and step S3 of coating an adhesive layer on the heat-resistant layer. The adhesive layer includes an agglomerated layer formed by the aggregation of an adhesive polymer material, and the adhesive layer has a coating coefficient C. The coating coefficient C is equal to the ratio of the adhesive strength A of the adhesive layer to the increase value P of the air permeability per unit coating layer thickness, satisfying the relational expression C = A / P, and the ratio range of the coating coefficient C is 0.3 < C < 1. Here, the unit of the adhesive strength A of the adhesive layer is N / m, and the unit of the increase value P of the air permeability per unit coating layer thickness of the adhesive layer is s / 100cc / μm. It is understood that the structure of the battery separator obtained by this manufacturing and processing method 2 of the battery separator includes a porous substrate, a heat-resistant layer formed on the porous substrate, and an adhesive layer formed on the heat-resistant layer. Without being limited thereto, when the customer does not require a heat-resistant layer, step S2 can be omitted and step S3 can be directly performed. In this case, the structure of the obtained battery separator includes a porous substrate and an adhesive layer formed on the porous substrate.

[0040] In the present invention, several parameters are designed for experiments, and the experimental process and results are summarized as follows.

[0041] Measurement method 1: Test method for separator thickness Test for uniform coating: The thickness measuring device is a Mahr Millimar thickness gauge, and the thickness gauge has a test head with a diameter of 12 mm and a measuring load of 0.75 N. A 100 mm * 100 mm sample is cut out, and the appearance of the sample is flat and uniform, without defects such as chips, pinholes, warping, oil stains, and scratches. Before measuring the thickness, it should be confirmed whether the device shows zero, and it should be confirmed that it shows zero before and after all groups of tests. When measuring the thickness, gently place the test head to avoid deformation of the sample and determine the center of 100 mm × 100 mm.

[0042] Measurement method 2: Air permeability test method The test equipment was an Oken air permeability tester. A battery separator was fixed in place, and an air pressure of 0.05 MPa was applied to one side of the separator. Due to the presence of micropores within the separator, the air pressure gradually decreased until 100 mL of air had completely passed through the separator, at which point the air pressure equalized with atmospheric pressure. The time it took for 100 mL of air to pass through the separator at 0.05 MPa was recorded, measured in seconds per 100 cc. The shorter the pressure drop time, the better the separator's air permeability; conversely, the worse the air permeability.

[0043] Measurement method 3: Test method for adhesive strength of electrode plates The separator and electrode plate are stacked and hot-pressed for 60 seconds under conditions of 3.5 tons of pressure and 90°C temperature to combine the separator and electrode plate. The separator is cut into 25mm x 200mm specimens, and then an adhesive strength test is performed using a universal tensile tester to obtain the adhesive strength between the separator and electrode plate.

[0044] Measurement method 4: Capacity retention rate test method The battery is a conventional 3Ah pouch-type battery, with an NCM523 positive electrode and a graphite negative electrode. 25°C cycle performance test: A charge / discharge cycle test (500 cycles) is performed at a current of 1C. The capacity retention rate is the ratio of the discharge capacity at the 500th cycle to the discharge capacity at the 1st cycle.

[0045] The adhesive mechanism of the adhesive layer of the separator of this application: Polyvinylidene fluoride (PVDF) and acrylic polymer particles generate adhesive force under hot pressing conditions, adhering to the electrode plates. The adhesive layer can improve the following cell performances: (1) The cell becomes harder and easier to insert into the shell; (2) The cycle life of the cell is extended; and (3) PVDF has excellent liquid absorption and retention capabilities.

[0046] Measurement method 5: Crystallinity test method The infrared spectrum of PVDF / PVDF-HFP was measured using a Thermo Fisher infrared spectrometer. -1 The peaks at 825-852 cm were integrated to obtain A1. -1 Integrate the peak to get A2. F(α) is equal to 1.26A1 / (1.26A1+A2).

[0047] Measurement method 6: Test method for α-phase crystals The crystallinity of PVDF / PVDF-HFP was measured using a TA differential scanning calorimeter DSC-Q2000. The samples were heated from room temperature to 300°C without any thermal history, and the heating rate was 5°C / min. The crystallinity percentage (Xc) of all samples was calculated using the following formula:

[0048] JPEG0007760825000001.jpg29132

[0049] ΔH f is the heat of fusion of the crystalline part, and ΔH f o is the heat of fusion of 100% crystal, and ΔH of PVDF f o is 104.7 J·g -1 is.

[0050] Example 1: (1) Preparation of slurry: PVDF powder and binder (Labo. Yindile Co., Ltd., Meishan, Sichuan) were added to a certain amount of water so that the solid dry weight ratio of PVDF-HFP (copolymerization ratio of VDF and HFP: 95:5, Kynar Powerflex LBG PWD manufactured by Arkema) to binder (LA133, manufactured by Meishan, Sichuan) was 9:1, to prepare a slurry with a solid content of 10%.

[0051] (2) Coating step: The PVDF slurry prepared above was applied to a separator (a 9 μm-thick separator manufactured by Shanghai Enjie Co., Ltd.) using a roll coating process, controlling the thickness of the coating layer to 2 μm to obtain a PVDF-coated separator. Testing revealed that the crystallinity of the PVDF-HFP was 45%, the proportion of α-phase in the PVDF-HFP crystalline phase was 55%, the adhesive strength between the separator and the positive electrode plate was approximately 6.1 N / m, the increase in air permeability per unit coating layer thickness was approximately 10.2 s / 100 ml, and the C value was 0.6. The battery manufactured using this separator had a capacity retention rate of 85% at the 500th cycle. Testing revealed that the adhesive strength between the separator and the positive electrode plate was approximately 8.2 N / m, the increase in air permeability per unit coating layer thickness was approximately 11.9 s / 100 ml, and the C value was 0.69. In a battery manufactured using this separator, the capacity retention rate at the 500th cycle is 88%.

[0052] Example 2: (1) Preparation of slurry: PVDF-HFP (copolymerization ratio of VDF and HFP: 95:5, Kynar powerflex LBG PWD manufactured by Arkema) was completely dissolved in DMAc solvent to form a solution with a concentration of 8%.

[0053] (2) Coating step: The PVDF-HFP solution prepared above was applied to a separator (9 μm thick separator manufactured by Shanghai Enjie Co., Ltd.) using a roll coating process, and pores were formed through non-solvent-induced phase separation to obtain an oil-based PVDF-HFP-coated separator. The thickness of the coating layer was controlled to 2 μm, resulting in a PVDF-HFP-coated separator. Testing revealed that the crystallinity of the PVDF-HFP was 25%, with an α-phase content of 8% in the crystalline phase. The adhesive strength between the separator and the positive electrode plate was approximately 20.5 N / m, the increase in air permeability per unit coating layer thickness was approximately 25.8 s / 100 ml, and the C value was 0.79. The battery manufactured using this separator had a capacity retention rate of 90% at the 500th cycle.

[0054] Example 3: The other conditions were the same as in Example 1, except that PVDF was replaced with PMMA (manufactured by Zeon Corporation). Testing revealed that the adhesive strength between the separator and the positive electrode plate was approximately 12.1 N / m, the increase in air permeability per unit coating layer thickness was approximately 12.5 s / 100 ml, and the C value was 0.97. The battery manufactured using this separator had a capacity retention rate of 93% at the 500th cycle.

[0055] Example 4: (1) Preparation of mixed slurry: A slurry with a solid content of 20% was prepared with a dry weight ratio of alumina:PVDF-HFP:binder=100:40:10.

[0056] (2) Coating step: Using a roll coating process, the mixed slurry of alumina and PVDF-HFP prepared above was coated onto a separator (a 9 μm thick separator manufactured by Shanghai Enjie Co., Ltd.), and the thickness of the coating layer was controlled to 2 microns to obtain a separator coated with a mixture of ceramics and PVDF-HFP.

[0057] Tests showed that the crystallinity of PVDF-HFP was 45%, the proportion of α-phase in the crystalline phase was 55%, the adhesive strength between the separator and the positive electrode plate was approximately 7.2 N / m, the increase in air permeability per unit coating layer thickness was approximately 12.3 s / 100 ml, and the C value was 0.59. The battery manufactured using this separator had a capacity retention rate of 85% at the 500th cycle.

[0058] Example 5: (1) Preparation of slurry: Alumina (SAO-035EQ, manufactured by Shandong National Porcelain Functional Materials Co., Ltd.) and binder (BM-900B, manufactured by Nippon Zeon Co., Ltd.) were mixed in a ratio of 100:5 to prepare a ceramic slurry with a solid content of approximately 30%.

[0059] (2) Using a roll coating process, the alumina slurry prepared above was coated onto a separator (a 9 μm thick separator manufactured by Shanghai Enjie Co., Ltd.), and the thickness of the coating layer was controlled to 1 micron to obtain a ceramic coated film separator.

[0060] (3) PVDF-HFP powder (the monomers are VDF and HFP, and the copolymerization ratio of VDF to HFP is 95:5) and binder (LA133, manufactured by Sichuan Meishan Yindile Co., Ltd.) were added to a certain amount of water at a solid dry weight ratio of PVDF-HFP to binder of 9:1 to prepare a slurry with a solid content of 10%.

[0061] (4) Coating step: Using a roll coating process, the PVDF-HFP slurry prepared above was coated onto the ceramic-coated separator obtained in step (2), controlling the thickness of the coating layer to 1 micron to obtain a PVDF-HFP-coated separator. Testing revealed that the crystallinity of the PVDF-HFP was 45%, the proportion of α-phase in the crystalline phase was 55%, the adhesive strength between the separator and the positive electrode plate was approximately 6.4 N / m, the increase in air permeability per unit coating layer thickness was approximately 11.4 s / 100 ml, and the C value was 0.56. The battery manufactured using this separator had a capacity retention rate of 83% at the 500th cycle.

[0062] Example 6: The other conditions were the same as in Example 5, except that alumina was replaced with magnesium hydroxide. Testing revealed that the crystallinity of PVDF-HFP was 45%, the proportion of α-phase in the crystalline phase was 55%, the adhesive strength between the separator and the positive electrode plate was approximately 6.5 N / m, the increase in air permeability per unit coating layer thickness was approximately 11.8 s / 100 ml, and the C value was 0.55. The battery manufactured using this separator had a capacity retention rate of 82% at the 500th cycle.

[0063] Example 7: The other conditions were the same as in Example 6, except that alumina was replaced with barium titanate. Testing revealed that the crystallinity of PVDF-HFP was 45%, the proportion of α-phase in the crystalline phase was 55%, the adhesive strength between the separator and the positive electrode plate was approximately 6.3 N / m, the increase in air permeability per unit coating layer thickness was approximately 11.5 s / 100 ml, and the C value was 0.55. The battery manufactured using this separator had a capacity retention rate of 82% at the 500th cycle.

[0064] Example 8: (1) Slurry preparation: Aramid was dissolved in DMAc solvent to prepare an aramid solution with a certain solid content. Barium sulfate was dispersed in DMAc to prepare a dispersion with a certain solid content. A mixed dispersion of aramid (Teijin, Japan, Meta-Aramid 1313):barium sulfate was prepared at a solids ratio of 4:6, with a total solids content of 20%.

[0065] (2) Using a roll coating process, the mixed slurry prepared above was coated onto a separator (a 9 μm thick separator manufactured by Shanghai Enjie Co., Ltd.), and pores were formed using a coagulation bath method. The thickness of the coating layer was controlled to 1 micron, resulting in a porous separator coated with a mixture of aramid and barium sulfate.

[0066] (3) PVDF-HFP powder (the monomers are VDF and HFP, and the copolymerization ratio of VDF to HFP is 95:5) and binder (LA133, manufactured by Sichuan Meishan Yindile Co., Ltd.) were added to a certain amount of water at a solid dry weight ratio of PVDF-HFP to binder of 9:1 to prepare a slurry with a solid content of 10%.

[0067] (4) Coating step: Using a roll coating process, the PVDF-HFP slurry prepared above was coated onto the ceramic-coated separator obtained in step 2, controlling the thickness of the coating layer to 1 micron to obtain a PVDF-HFP-coated separator. Testing revealed that the crystallinity of PVDF-HFP was 25%, the proportion of α-phase in the crystalline phase was 8%, the adhesive strength between the separator and the positive electrode plate was approximately 6.5 N / m, the increase in air permeability per unit coating layer thickness was approximately 11.2 s / 100 ml, and the C value was 0.58. The battery manufactured using this separator had a capacity retention rate of 84% at the 500th cycle.

[0068] Comparative Example 1: The other conditions were the same as in Example 1, except that PVDF was replaced with polystyrene microparticles (homemade in the laboratory, D50 particle size approximately 0.8 μm). Testing revealed that the adhesive strength between the separator and the positive electrode plate was approximately 2.1 N / m, the increase in air permeability per unit coating layer thickness was approximately 10.3 s / 100 ml, and the C value was 0.2. The battery manufactured using this separator had a capacity retention rate of 60% at the 500th cycle.

[0069] Comparative Example 2: The other components were the same as in Example 1, except that PVDF was replaced with a copolymer PVDF-HFP with a high HFP content (manufactured by Zhejiang Zhonghua Lantian Group Co., Ltd., VDF content 45%). Testing revealed that the crystallinity of the PVDF-HFP was 33%, the proportion of α-phase in the crystalline phase was 25%, the adhesive strength between the separator and the positive electrode plate was approximately 2.8 N / m, the increase in air permeability per unit coating layer thickness was approximately 11.2 s / 100 ml, and the C value was 0.25. The battery manufactured using this separator had a capacity retention rate of 65% at the 500th cycle.

[0070] Comparative Example 3: The PVDF-HFP in Comparative Example 2 was replaced with homopolymerized HFP (produced by Zhejiang Zhonghua Lantian Group Co., Ltd., 100% VDF), and all other conditions were the same as in Example 2. Testing revealed that the crystallinity of the homopolymerized PVDF was 65%, the proportion of α-phase in the crystalline phase was 76%, the adhesive strength between the separator and the positive electrode plate was approximately 2.5 N / m, the increase in air permeability per unit coating layer thickness was approximately 10.2 s / 100 ml, and the C value was 0.245. The battery manufactured using this separator had a capacity retention rate of 63% at the 500th cycle.

[0071] Comparative Example 4: The other conditions were the same as in Example 6, except that PVDF was replaced with polystyrene microparticles (homemade in the laboratory, D50 particle size approximately 0.8 μm). Testing revealed that the adhesive strength between the separator and the positive electrode plate was approximately 1.2 N / m, the increase in air permeability per unit coating layer thickness was approximately 10.4 s / 100 ml, and the C value was 0.12. The battery manufactured using this separator had a capacity retention rate of 51% at the 500th cycle.

[0072] Comparative Example 5: The other conditions were the same as in Example 9, except that PVDF was replaced with polystyrene microparticles (homemade in the laboratory, D50 particle size approximately 0.8 μm). Testing revealed that the adhesive strength between the separator and the positive electrode plate was approximately 1.5 N / m, the increase in air permeability per unit coating layer thickness was approximately 11.5 s / 100 ml, and the C value was 0.13. The battery manufactured using this separator had a capacity retention rate of 52% at the 500th cycle.

[0073] Comparative Example 6: The separator was the base film (a 9 μm thick separator manufactured by Shanghai Enjie Co., Ltd.) in Example 1. In the battery manufactured using this separator, the capacity retention rate at the 500th cycle was 45%.

[0074] Comparative Example 7: The separator used was the same as that used in step (1) and step (2) in Example 6, but did not include step (3) and step (4). The battery manufactured using this separator had a capacity retention rate of 46% at the 500th cycle.

[0075] Table 1: Structure and physical properties of separators in Examples and Comparative Examples JPEG0007760825000002.jpg199170

[0076] The above experimental results are summarized in Table 1. Comparing the examples and comparative examples, coating the separator surface with materials such as PVDF and PMMA ensures excellent adhesive strength, thereby extending the cycle life (capacity retention) of lithium batteries. In the case of an oil-based coating layer, for example, in Example 3, the separator exhibits superior adhesiveness. The present application uses the coating coefficient C value to indicate the ratio between adhesiveness and the increase in air permeability, and limits it to a certain range to ensure sufficient adhesiveness and breathability of the separator. When the separator does not have an adhesive layer, the capacity retention rate is less than 80% after 500 charge / discharge cycles, resulting in low capacity retention and short cycle life. When the coating coefficient C value is within the range of 0.3 to 1, the capacity retention rate is all greater than 80% and the cycle life is longer.

[0077] In summary, this invention proposes a method for improving the adhesion and breathability of current battery separators by introducing polymer particles into the separator coating layer to enhance the adhesion between the separator and the electrode plate. Additionally, a heat-resistant polymer material such as aramid is introduced into the separator coating layer to increase the separator's rupture temperature. Furthermore, ceramics are introduced into the separator coating layer to improve the separator's thermal shrinkage resistance. These improvements not only effectively solve the problem of peeling from the separator caused by the current ceramic coating layer's lack of adhesive strength, but also ensure the separator's breathability. Furthermore, this application designs the coating coefficient C value to reflect the adhesion and breathability of the coating layer and restrict it to a specific, better range, thereby providing a very convenient way to evaluate and ensure whether the separator's adhesion and breathability meet requirements.

[0078] Terms such as "in some embodiments" and "in various embodiments" are used repeatedly. The terms usually do not, but may, refer to the same embodiment. Terms such as "including," "having," and "comprising" are synonymous unless the context indicates otherwise.

[0079] The above is only an example of the present application and is not intended to limit the present application in any way. Although the present application has been disclosed above through specific examples, it is not used to limit the present application. Those skilled in the art can use the technical content disclosed above to make slight changes or modifications to equivalent examples as equivalent changes, as long as they do not deviate from the scope of the technical solutions of the present application. All simple modifications, equivalent changes and modifications made to the above examples according to the technical substance of the present application, as long as they do not deviate from the technical solutions of the present application, still belong to the scope of the technical solutions of the present application.

Claims

1. 1. A battery separator, comprising: a porous substrate; an adhesive layer formed on one side of the porous substrate, the adhesive layer including a polymeric material having adhesive properties; the polymeric material comprises polyvinylidene fluoride (PVDF), the adhesive layer has a coating coefficient C; The coating coefficient C is equal to the ratio of the adhesive strength A of the adhesive layer to the air permeability increase value P per unit coating layer thickness, and satisfies the relation C=A / P, and the ratio range of the coating coefficient C is 0.4<C<0.9; Here, the adhesive strength A of the adhesive layer is expressed in N / m, and the air permeability increase value P per unit coating layer thickness of the adhesive layer is expressed in s / 100 cc / μm. The adhesive layer is coated with aqueous polyvinylidene fluoride, and the proportion of the α phase in the crystalline region of the aqueous polyvinylidene fluoride is more than 30% and less than 70%.

2. 1. A battery separator, comprising: a porous substrate; an adhesive layer formed on one side of the porous substrate; the adhesive layer includes a polymeric material having adhesive properties, the polymeric material includes polyvinylidene fluoride (PVDF), and the adhesive layer has a coating coefficient C; The coating coefficient C is equal to the ratio of the adhesive strength A of the adhesive layer to the air permeability increase value P per unit coating layer thickness, and satisfies the relation C=A / P, and the ratio range of the coating coefficient C is 0.4<C<0.9; Here, the adhesive strength A of the adhesive layer is expressed in N / m, and the air permeability increase value P per unit coating layer thickness of the adhesive layer is expressed in s / 100 cc / μm. The adhesive layer is coated with oil-based polyvinylidene fluoride, and the proportion of α-phase in the crystalline region of the oil-based polyvinylidene fluoride is less than 20%.

3. 3. A lithium battery comprising a positive electrode, a negative electrode, and the battery separator of claim 1 or 2, wherein the battery separator is located between the positive electrode and the negative electrode.

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