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] This application relates to the technical field of secondary battery materials, and particularly to a separator for a lithium-ion battery and a lithium battery manufactured using the same.

Background Art

[0002] A lithium-ion battery is a secondary battery that can not only convert electrical energy into chemical energy to store energy, but also convert chemical energy into electrical energy to provide electrical energy to electrical products. Lithium-ion batteries are widely used because of their high energy density and long cycle life. Since the 21st century, with the popularization of notebook computers, smartphones, and electric vehicles, lithium-ion batteries have been widely used.

[0003] As an important component of a lithium-ion battery, the basic requirements for a separator are high ion conductivity and low electron conductivity. Currently, the commonly used separators for lithium batteries are porous materials manufactured by unidirectional or bidirectional stretching of polyolefin materials. This material has good ion conductivity, excellent mechanical properties, and electrolyte resistance.

[0004] Since polyolefin has a low melting point and poor heat resistance, generally, it is necessary to apply a ceramic coating to improve heat resistance. However, the current use of ceramic coatings can improve the heat shrinkage resistance of the separator, but there is a problem that the adhesion between the ceramic coating layer and the separator is poor, and the ceramic layer is easily peeled off from the separator. Therefore, how to improve the adhesion strength of the coating layer has become an important issue.

Summary of the Invention

Problems 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, which 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 to provide a battery separator comprising a porous substrate or a composite material composed of 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, wherein the adhesive layer contains a polymer material having adhesiveness, and the adhesive layer has a coating coefficient C, and 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, and the ratio range of the coating coefficient C is 0.3 < C < 1, where 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.

[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 is to provide a battery separator comprising a porous substrate and an adhesive layer formed on one side of the porous substrate, the adhesive layer containing an adhesive polymer material, the polymer material containing polyvinylidene fluoride (PVDF), the adhesive layer having a coating coefficient C, the coating coefficient C being 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, and the ratio range of the coating coefficient C being 0.4 < C < 0.9, where 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.

[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 in 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 the battery separator, wherein the battery separator is positioned between the positive electrode and the negative electrode.

Advantages of the Invention

[0017] The present application improves the adhesiveness between the separator and the electrode plate by introducing an adhesive polymer material into the separator coating layer. In addition, by introducing a heat-resistant polymer material such as aramid into the separator coating layer, the film-breaking temperature of the separator can be increased. Further, by introducing ceramics into the separator coating layer, the heat-resistant shrinkage property of the separator can be improved. By the above improvement means, the problem of peeling from the separator due to the insufficient adhesive strength of the current ceramic coating layer can be effectively solved. In addition, the present application designs the coating coefficient C value to reflect the adhesiveness and air permeability of the coating layer, and by limiting it within a specific better range, the adhesiveness and air permeability of the separator can be evaluated and guaranteed in a very convenient way to meet the requirements.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0019] The description of each of the following embodiments refers to additional diagrams for exemplifying specific embodiments implemented in this application. Directional terms such as "upper", "lower", "front", "rear", "left", "right", "inner", "outer", "side" mentioned in this application only refer to the directions of the additional diagrams. Therefore, the directional terms used are for the purpose of explaining and understanding this application and are not intended to limit this application.

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

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

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

[0023] To further elaborate on the technical means and functions adopted to achieve the intended objectives of this application, with respect to the battery separator proposed by this application and the proton exchange membrane manufactured using the same, their specific embodiments, structures, features, and functions will be described in detail as follows in combination 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. 3, the structure of the heat-resistant layer 13 is omitted, only the porous substrate 11 remains, 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 12 includes an agglomerated layer formed by the aggregation of the adhesive polymer material 121, and the adhesive layer 12 has a coating coefficient C. The coating coefficient C is equal to the ratio of the adhesion strength A of the adhesive layer 12 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 adhesion 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 inside the substrate, and may be a porous sheet formed by fibrous materials such as non-woven fabrics or papers, or may be a composite porous sheet obtained by stacking 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 multi-directional stretching, or a porous material obtained by methods such as non-solvent induced phase separation, thermal induced phase separation, and water vapor induced phase separation. The polyolefin materials are generally polyethylene and polypropylene. The porous substrate 11 may be a substrate manufactured from one or more of the materials of fibers such as polyethylene terephthalate, nylon, aramid, polysulfone, polyether ether ketone, and polyimide by a method such as the electrospinning method. The thickness of the porous substrate 11 is generally 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 provided on both sides of the composite material, and the areal density on each side of the composite material is between 0.1 and 6.0 g / m 2 but is not limited thereto. The adhesive layer 12 may be provided only on one side of the composite material, or may be provided on one or both sides of the porous substrate 11. In this embodiment, the adhesive layer 12 includes a polymer material 121 having adhesiveness. For example, it is an agglomerated layer formed by the agglomeration of polyvinylidene fluoride (PVDF) microparticles or acrylic microparticles, but is not limited to this granular form. The polymer material 121 having adhesiveness may be fibrous, or may be net-like or cross-linked.

[0027] The polymer material 121 having adhesiveness may be a polyvinylidene fluoride or polyacrylic acid-based polymer material. 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 polymerization of a plurality of monomers such as methacrylate, acrylic acid, acrylate, styrene, ethylene glycol, acrylonitrile, etc. The resin may be obtained by a crosslinking reaction, and the resin may also be a material having a core-shell structure, that is, the core layer and the shell layer are made of different materials. Therefore, in some embodiments, the adhesive layer 12 includes an adhesive polymer material, and 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.

[0028] In this embodiment, the polyvinylidene fluoride (PVDF)-based resin is a fluorine-containing polymer material mainly composed of vinylidene fluoride monomer. It may be polyvinylidene fluoride by homopolymerization, or may be polyvinylidene fluoride by copolymerization, such as a copolymer of vinylidene fluoride and tetrafluoroethylene, a copolymer of vinylidene fluoride and hexafluoropropylene, a copolymer of vinylidene fluoride and trifluoroethylene, a mixture of polyvinylidene fluoride and an acrylic acid-based polymer, and a polyvinylidene fluoride copolymer. Here, 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 includes an adhesive polymer material or a mixture of an adhesive polymer material and a filler, and the filler includes an organic or inorganic heat-resistant material. Here, the inorganic heat-resistant material includes ceramic materials such as alumina, boehmite, barium sulfate, magnesium hydroxide, and barium titanate, and the organic heat-resistant material includes polyimide microspheres, cross-linked polyacrylic acid, cross-linked acrylic acid, cross-linked polymethacrylic acid (ester), cross-linked polystyrene, cross-linked polysiloxane, polysulfone, polyacrylonitrile, and the like.

[0030] In this embodiment, the air permeability increase value P per unit coating layer thickness of the adhesive layer 12, that is, 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 / 100cc / μm, preferably 0 to 30 s / 100cc / μm, and more preferably 0 to 15 s / 100cc / μm. The "air permeability per unit coating layer thickness" is a 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 / 100cc", and the unit of the thickness of the adhesive layer 12 is "μm". In this embodiment, the adhesive layer 12 includes a polymer resin material or a mixture of a polymer resin and a ceramic material, and the smoothness of the surface of the adhesive layer 12 is 1.30 or less.

[0031] In some embodiments, the oil-based adhesive coating layer has a larger coating area compared to the water-based adhesive coating layer, so it has good adhesive strength, but its air permeability is poor. The better the adhesive 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, which reduces the ionic conductivity and shortens the 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 adhesive strength and air permeability of the separator 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 adhesive 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 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, 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.

[0033] For the above-mentioned copolymerized polymer of polyvinylidene fluoride (PVDF), the molar ratio of the PVDF monomer is higher than 50%. For the above-mentioned copolymerized polymer of PVDF, 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 oily 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 designs 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, reticular, or cross-linked polymer microsphere particles.

[0035] In this embodiment, the heat-resistant layer 13 is disposed only in one layer on one side of the porous substrate 11. However, it is not limited thereto. As shown in FIG. 2, the heat-resistant layer 13 may be disposed on both sides of the porous substrate 11. Here, the heat-resistant layer 13 includes an aramid polymer and an inorganic filler, and the adhesive layer 12 includes polyvinylidene fluoride (PVDF) fine particles and / or acrylic fine particles formed of an adhesive polymer material 121. In some embodiments, as shown in FIG. 3, in addition to including the adhesive polymer material 121, the adhesive layer 12 also includes particles 122 of a ceramic material. Therefore, the adhesive layer 12 is an aggregate layer of particles formed by the aggregation of the fine particles of the polymer material 121 and the particles 122 of the ceramic material. In other embodiments, 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 the polymer material 121 so that the polymer material 121 can cover the particles 122 of the ceramic material, thereby enhancing the adhesiveness and increasing the overall thickness of the adhesive layer 12.

[0036] In some embodiments, a lithium battery according to an embodiment of the present application includes a positive electrode, a negative electrode, and the battery separator 1, wherein the battery separator 1 is located between the positive electrode and the negative electrode, and obtains an electromotive force through the insertion and desorption of lithium ions. Here, the positive electrode includes substances such as a positive electrode active material, a conductive agent, a binder, and a current collector. Examples of the conductive agent include acetylene black, ketjen black, and graphite powder materials as conductive agents. The negative electrode includes a material capable of receiving lithium ions, such as an alloying material of carbon material, silicon, aluminum, etc. and lithium. The electrolyte is a solution obtained by dissolving a lithium salt in a non-aqueous solvent, and the lithium salt therein may be a material such as LiPF6, LiBF4, LiClO4, LiTFSI, LiFSI, etc. Examples of the non-aqueous solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, fluoroethylene carbonate, and difluoroethylene carbonate, chain carbonates such as dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and their fluoro-substituted products, and cyclic esters such as γ-butyrolactone and γ-valerolactone. These can be used separately or in combination. Examples of the external sealing material include a metal shell and an aluminum laminate film packaging. The shape of the battery includes square, cylindrical, button-shaped, etc., and the battery separator 1 of the present invention is suitable for any of these shapes. From the perspective of ion permeability, the air permeability value of the battery separator 1 in the present 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 - 10 ohm·cm 2 The piercing strength of the battery separator 1 is preferably in the range of 10 - 1200 gf, preferably 200 - 800 gf.

[0037] In addition, as long as the method for manufacturing a separator for a non-aqueous secondary battery is a method for manufacturing a separator for a non-aqueous secondary battery provided with an aggregate containing the aforementioned 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. Here, the aqueous coating process includes: (1) adding a wetting agent, a dispersant, a thickening agent, a filler, a polymer material having adhesiveness, a binder, etc. in a certain order, then mixing and stirring to obtain a homogeneous slurry; (2) using methods such as bar coating or roll coating to coat the slurry on the separator; (3) putting it into an oven and drying to obtain an aqueous slurry coating layer. The oil-based coating process includes: (1) dissolving a polymer material and a heat-resistant polymer material in an appropriate 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 homogeneous dispersion; (2) coating the solution or dispersion on a base film and forming pores by using any of methods such as non-solvent-induced phase separation, or directly putting it into an oven and forming pores by the method of water vapor-induced phase separation; (3) removing the solvent by washing with water; (4) putting it into an oven and drying.

[0038] In some embodiments, an aqueous dispersion is produced by dispersing, suspending, or emulsifying a polymer fine particle having adhesiveness and a filler containing at least one of an organic compound and an inorganic compound in a solvent in a solid state, respectively. It may be an emulsion or a suspension. In the manufacturing process of the coated separator, it is necessary to volatilize the water in the aqueous slurry to obtain a dry coating layer. In the case of the means of oil-based coating, since it is necessary to remove the solvent by washing with water, the separator also needs to be dried to remove moisture.

[0039] The object 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 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. 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 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 need 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 excerpted as follows.

[0041] Measurement method 1: Test method for separator thickness Test for uniform coating: The thickness measuring device is a thickness gauge of Mahr Millimar. The thickness gauge has a test head with a diameter of 12 mm and a weighing load of 0.75 N. A 100 mm * 100 mm sample is cut out. 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, place the test head gently to avoid deforming the sample, and determine the center of 100 mm × 100 mm.

[0042] Measurement Method 2: Test Method for Air Permeability The test apparatus is a Wangyan type air permeability tester. Fix the battery separator, apply an air pressure of 0.05 Mpa on one side of the separator. Since there are micropores in the separator, the air pressure gradually decreases. When 100 mL of air completely passes through the separator, the air pressure becomes equal to the atmospheric pressure. Record the time taken for 100 ml of air to pass through the separator at a pressure of 0.05 MPa. The unit is s / 100cc. The shorter the pressure drop time, the better the air permeability of the separator, and vice versa.

[0043] Measurement Method 3: Test Method for Adhesive Strength of Electrode Plate Overlay the separator and the electrode plate, and perform hot pressing for 60 s under the conditions of a pressure of 3.5 tons and a temperature of 90 °C to integrate the separator and the electrode plate by hot pressing. Cut the separator into samples of 25 mm * 200 mm, and then perform a test on the adhesive strength with a universal tensile machine to obtain the adhesive strength between the separator and the electrode plate.

[0044] Measurement Method 4: Test Method for Capacity Retention Rate The battery refers to a conventional 3 Ah pouch-type battery. The positive electrode plate is an NCM523 electrode, and the negative electrode plate is a graphite negative electrode. 25 °C cycle performance test: Perform a charge-discharge cycle test (500 cycles) 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 first cycle.

[0045] Adhesion mechanism of the adhesive layer of the separator in this application: Polyvinylidene fluoride (PVDF)-based and acrylic polymer particles generate adhesion under hot pressing conditions and adhere to the electrode plate. The adhesive layer can enhance the following performance of the cell: (1) The cell becomes harder and is easier to put into the shell. (2) Extend the cycle life of the cell. (3) PVDF has excellent liquid absorption and liquid retention capabilities.

[0046] Measurement Method 5: Crystallinity Test Method Using a Thermo Fisher infrared spectrometer, measure the infrared spectrum of PVDF / PVDF-HFP. Integrate the peak at 750 - 775 cm -1 to obtain A1, and integrate the peak at 825 - 852 cm -1 to obtain A2. F(α) is equal to 1.26A1 / (1.26A1 + A2).

[0047] Measurement method 6: Test method for the α-phase of the crystalline phase Using a TA differential scanning calorimeter DSC-Q2000, measure the crystallinity of PVDF / PVDF-HFP. Heat from room temperature to 300 °C to eliminate the thermal history, and the heating rate is 5 °C / min. The percentage of crystallinity (Xc) of all samples can be calculated by the following formula.

[0048] JPEG2025524278000002.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 the ΔH of PVDF f o is 104.7 J·g -1 .

[0050] Example 1: (1) Preparation of slurry: Add a certain amount of PVDF powder and binder to a certain amount of water so that the ratio of the solid dry weights of PVDF-HFP (copolymerization ratio of VDF and HFP: 95:5, Kynar powerflex LBG PWD manufactured by Arkema) and the binder (Sichuan Meishan Yindi Le Company, LA133) is 9:1, and prepare a slurry with a solid content of 10%.

[0051] (2) Coating Step: Using a roll coating process, the PVDF slurry prepared above was coated onto a separator (a separator with a thickness of 9 μm produced by Shanghai Enjie Co., Ltd.). The thickness of the coating layer was controlled to be 2 microns to obtain a PVDF-coated separator. Through testing, it was found that the crystallinity of PVDF-HFP was 45%, the proportion of the α-phase in the crystalline phase of PVDF-HFP was 55%, the adhesion strength between the separator and the positive electrode plate was approximately 6.1 N / m, the increase value of air permeability per unit coating layer thickness was approximately 10.2 s / 100 ml, and the C value was 0.6. The capacity retention rate of the battery manufactured using this separator at the 500th cycle was 85%. Through testing, it was found that the adhesion strength between the separator and the positive electrode plate was approximately 8.2 N / m, the increase value of air permeability per unit coating layer thickness was approximately 11.9 s / 100 ml, and the C value was 0.69. In the battery manufactured using this separator, the capacity retention rate at the 500th cycle was 88%.

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

[0053] (2) Coating Step: Using a roll coating process, the PVDF-HFP solution prepared above was coated onto a separator (a separator with a thickness of 9 μm produced by Shanghai Enjie Co., Ltd.). Pores were formed through a non-solvent induced phase separation method to obtain an oily PVDF-HFP coated separator. The thickness of the coating layer was controlled to be 2 microns to obtain a PVDF-HFP coated separator. Through testing, it was found that the crystallinity of PVDF-HFP was 25%, where the proportion of the α-phase in the crystalline phase was 8%, the adhesion strength between the separator and the positive electrode plate was approximately 20.5 N / m, the increase value of air permeability per unit coating layer thickness was approximately 25.8 s / 100 ml, and the C value was 0.79. In the battery manufactured using this separator, the capacity retention rate at the 500th cycle was 90%.

[0054] Example 3: Except for replacing PVDF with PMMA (produced by Zeon Corporation, Japan), the others were the same as in Example 1. Through testing, it was found that the adhesive strength between the separator and the positive electrode plate was about 12.1 N / m, the increase value of air permeability per unit coating layer thickness was about 12.5 s / 100 ml, and the C value was 0.97. In the battery manufactured using this separator, the capacity retention rate at the 500th cycle was 93%.

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

[0056] (2) Coating step: Using the roll coating process, the mixed slurry of alumina and PVDF-HFP prepared above was coated on a separator (a separator with a thickness of 9 μm produced 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] Through testing, it was found that the crystallinity of PVDF-HFP was 45%, the proportion of the α phase in the crystal phase was 55%, the adhesive strength between the separator and the positive electrode plate was about 7.2 N / m, the increase value of air permeability per unit coating layer thickness was about 12.3 s / 100 ml, and the C value was 0.59. In the battery manufactured using this separator, the capacity retention rate at the 500th cycle was 85%.

[0058] Example 5: (1) Preparation of the slurry: A ceramic slurry with a solid content of about 30% was prepared according to the ratio of alumina (produced by Shandong Guoci Functional Materials Co., Ltd., SAO-035EQ) to binder (produced by Zeon Corporation, Japan, BM-900B) of 100:5.

[0059] (2) Using the roll coating process, the alumina slurry prepared above was coated on a separator (a separator with a thickness of 9 μm produced 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) According to the solid dry weight ratio of 9:1 of PVDF-HFP to the binder, PVDF-HFP powder (the monomers are VDF and HFP, and the copolymerization ratio of VDF and HFP is 95:5) and the binder (produced by Sichuan Meishan Yindi Le Co., Ltd., LA133) were added to a certain amount of water to prepare a slurry with a solid content of 10%.

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

[0062] Example 6: Except for replacing alumina with magnesium hydroxide, the others were the same as in Example 5. Through testing, it was found that the crystallinity of PVDF-HFP was 45%, the proportion of the α-phase in the crystal phase was 55%, the adhesion strength between the separator and the positive electrode plate was about 6.5 N / m, the increase value of air permeability per unit coating layer thickness was about 11.8 s / 100 ml, and the C value was 0.55. In the battery manufactured using this separator, the capacity retention rate at the 500th cycle was 82%.

[0063] Example 7: Except for replacing alumina with barium titanate, the rest was the same as in Example 6. Through testing, it was found that the crystallinity of PVDF-HFP was 45%, the proportion of the α-phase in the crystal phase was 55%, the adhesion strength between the separator and the positive electrode plate was about 6.3 N / m, the increase value of air permeability per unit coating layer thickness was about 11.5 s / 100 ml, and the C value was 0.55. In the battery manufactured using this separator, the capacity retention rate at the 500th cycle was 82%.

[0064] Example 8: (1) Preparation of slurry: Aramid was dissolved in a 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 with a total solid content of 20% of aramid and barium sulfate was prepared according to the solid content ratio of aramid (produced by Teijin Limited, Japan, meta-aramid 1313): barium sulfate = 4:6.

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

[0066] (3) According to the solid dry weight ratio of PVDF-HFP to the binder of 9:1, PVDF-HFP powder (the monomers are VDF and HFP, and the copolymerization ratio of VDF and HFP is 95:5) and the binder (LA133 produced by Sichuan Meishan Yindi Le Co., Ltd.) were added to a certain amount of water 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, and the thickness of the coating layer was controlled to 1 micron to obtain a PVDF-HFP coated separator. Through testing, it was found that the crystallinity of PVDF-HFP was 25%, the proportion of the α-phase in the crystal phase was 8%, the adhesion strength between the separator and the positive electrode plate was approximately 6.5 N / m, the increase value of air permeability per unit coating layer thickness was approximately 11.2 s / 100 ml, and the C value was 0.58. For the battery manufactured using this separator, the capacity retention rate at the 500th cycle was 84%.

[0068] Comparative Example 1: Except for replacing PVDF with polystyrene microparticles (self-made in the laboratory, D50 particle size is approximately 0.8 μm), the rest was the same as in Example 1. Through testing, it was found that the adhesion strength between the separator and the positive electrode plate was approximately 2.1 N / m, the increase value of air permeability per unit coating layer thickness was approximately 10.3 s / 100 ml, and the C value was 0.2. For the battery manufactured using this separator, the capacity retention rate at the 500th cycle was 60%.

[0069] Comparative Example 2: Except for replacing PVDF with copolymerized PVDF-HFP with a high HFP content (produced by Zhejiang Zhonghua Blue Sky Group Co., Ltd., VDF ratio 45%), the rest was the same as in Example 1. Through testing, it was found that the crystallinity of PVDF-HFP was 33%, the proportion of the α-phase in the crystal phase was 25%, the adhesion strength between the separator and the positive electrode plate was approximately 2.8 N / m, the increase value of air permeability per unit coating layer thickness was approximately 11.2 s / 100 ml, and the C value was 0.25. For the battery manufactured using this separator, the capacity retention rate at the 500th cycle was 65%.

[0070] Comparative Example 3: Except for replacing PVDF-HFP in Comparative Example 2 with homopolymerized HFP (produced by Zhejiang Zhonghua Blue Sky Group Co., Ltd., VDF ratio 100%), the rest was the same as in Example 2. Through testing, it was found that the crystallinity of homopolymerized PVDF was 65%, the proportion of the α-phase in the crystal phase was 76%, the adhesion strength between the separator and the positive electrode plate was about 2.5 N / m, the increase value of air permeability per unit coating layer thickness was about 10.2 s / 100 ml, and the C value was 0.245. In the battery manufactured using this separator, the capacity retention rate at the 500th cycle was 63%.

[0071] Comparative Example 4: Except for replacing PVDF with polystyrene microparticles (self-made in the laboratory, D50 particle size is about 0.8 μm), the rest was the same as in Example 6. Through testing, it was found that the adhesion strength between the separator and the positive electrode plate was about 1.2 N / m, the increase value of air permeability per unit coating layer thickness was about 10.4 s / 100 ml, and the C value was 0.12. In the battery manufactured using this separator, the capacity retention rate at the 500th cycle was 51%.

[0072] Comparative Example 5: Except for replacing PVDF with polystyrene microparticles (self-made in the laboratory, D50 particle size is about 0.8 μm), the rest was the same as in Example 9. Through testing, it was found that the adhesion strength between the separator and the positive electrode plate was about 1.5 N / m, the increase value of air permeability per unit coating layer thickness was about 11.5 s / 100 ml, and the C value was 0.13. In the battery manufactured using this separator, the capacity retention rate at the 500th cycle was 52%.

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

[0074] Comparative Example 7: The separator is the same as that in steps (1) and (2) of Example 6 and does not include steps (3) and (4). In the battery manufactured using this separator, the capacity retention rate at the 500th cycle is 46%.

[0075] Table 1: Structure and Physical Properties of Separators in Examples and Comparative Examples JPEG2025524278000003.jpg199170

[0076] Summarizing the above experimental results in Table 1, by comparing Examples and Comparative Examples, it can be ensured that excellent adhesion strength of the separator can be achieved by coating materials such as PVDF and PMMA on the surface of the separator, thereby extending the cycle life (capacity retention rate) of the lithium battery. In the case of the oily coating layer, for example, in Example 3, it can be seen that the adhesion of the separator is more excellent. This application uses the coating coefficient C value to indicate the ratio of the adhesiveness to the increase value of air permeability, and limits it within a certain range, thereby ensuring sufficient adhesiveness and air permeability of the separator. When the separator does not have an adhesive layer, after 500 charge-discharge cycles, the capacity retention rate is less than 80%, the capacity retention rate is low, and the cycle life is short. When the coating coefficient C value is within the range of 0.3 to 1, the capacity retention rates are all greater than 80% and have a longer cycle life.

[0077] In summary, the present invention proposes a means of introducing polymer particles into the separator coating layer so as to enhance the adhesion between the separator and the electrode plate in order to improve the adhesion and air permeability of the current battery separator. In addition, a heat-resistant polymer material such as aramid is introduced into the separator coating layer so as to increase the breakdown temperature of the separator. Further, by introducing ceramics into the separator coating layer, the heat-resistant shrinkage property of the separator is improved. By the above improvement means, not only can the problem of peeling from the separator caused by the lack of adhesion strength of the current ceramic coating layer be effectively solved, but also the air permeability of the separator can be ensured. In addition, by designing the coating coefficient C value, the present application can reflect the adhesion and air permeability of the coating layer and limit it to a specific better range, so that it is possible to evaluate and guarantee in a very convenient way whether the adhesion and air permeability of the separator meet the requirements.

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

[0079] The above are only examples of the present application and not any form of limitation to the present application. Although the present application is disclosed as above through specific examples, it is not used to limit the present application. For those skilled in the art, without departing from the scope of the technical solution means of the present application, the technical content disclosed above can be used to make slight changes or modify it into equivalent embodiments as equivalent changes. As long as the content does not depart from the technical solution means of the present application, all simple modifications, equivalent changes and modifications made to the above examples according to the essence of the technology of the present application still belong to the scope of the technical solution means of the present application.

Claims

1. A battery separator, comprising: a composite material composed of a porous substrate or a composite material of a porous substrate and a heat-resistant layer located on the porous substrate; an adhesive layer formed on the porous substrate or the composite material, the adhesive layer containing a polymer material having adhesiveness, and the adhesive layer having a coating coefficient C, the coating coefficient C being 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, and the ratio range of the coating coefficient C being 0.3 < C < 1, wherein 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 / 100 cc / μm. A battery separator characterized by this.

2. The battery separator according to claim 1, wherein 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.

3. The battery separator according to claim 2, wherein the adhesive polymer material contains a polyvinylidene fluoride homopolymer, a polyvinylidene fluoride copolymer, a homopolymer of methyl methacrylate, a copolymer of methyl methacrylate, or a mixture thereof.

4. The battery separator according to claim 3, wherein the molar ratio of the vinylidene fluoride monomer in the polyvinylidene fluoride copolymer is higher than 50%, and the other comonomers are one or more selected from hexafluoropropylene, tetrafluoroethylene, trifluoroethylene, trichloroethylene, acrylic acid, methacrylic acid, methacrylate, and vinyl acetate.

5. The battery separator according to claim 1, wherein the adhesive layer is 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.

6. The battery separator according to claim 1, wherein 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.

7. A battery separator, comprising: a porous substrate; It includes an adhesive layer formed 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 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 0.4 < 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. The battery separator is characterized by this.

8. The crystallinity of the raw material of the polyvinylidene fluoride copolymer is between 10% and 50%. The battery separator according to claim 7 is characterized by this.

9. When the adhesive layer is coated with aqueous polyvinylidene fluoride, the ratio of the α-phase in the crystalline region of the aqueous polyvinylidene fluoride exceeds 30% and is less than 70%. The battery separator according to claim 7 is characterized by this.

10. When the adhesive layer is coated with oil-based polyvinylidene fluoride, the ratio of the α-phase in the crystalline region of the oil-based polyvinylidene fluoride is less than 20%. The battery separator according to claim 7 is characterized by this.

11. A lithium battery, comprising a positive electrode, a negative electrode, and the battery separator according to any one of claims 1 to 10, wherein the battery separator is located between the positive electrode and the negative electrode. The lithium battery is characterized by this.

Images