Battery separator and lithium battery manufactured using the same

Abstract

To provide a battery separator with improved adhesive strength of a coating layer.SOLUTION: A battery separator 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 has a coating coefficient C. The coating coefficient C is equal to the ratio between an adhesive strength A of the adhesive layer and a permeability increase value P per unit coating layer thickness, satisfying a relational expression C=A / P. 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 permeability increase value P per unit coating layer thickness is s / 100 cc / μm.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This application relates to the technical field of secondary battery materials, and more particularly to separators for lithium-ion batteries and lithium batteries manufactured using the same. [Background technology]

[0002] Lithium-ion batteries are rechargeable batteries that not only convert electrical energy into chemical energy for energy storage, but also convert chemical energy back into electrical energy to supply electrical energy to electronic devices. Lithium-ion batteries are widely used due to their high energy density and long cycle life. Since the beginning of the 21st century, lithium-ion batteries have become widely used with the proliferation of laptop computers, smartphones, and electric vehicles.

[0003] As a crucial component of lithium-ion batteries, the separator's fundamental requirements are high ionic conductivity and low electronic conductivity. Currently, lithium battery separators commonly used are porous materials manufactured by unidirectional or bidirectional stretching of polyolene material. These materials possess good ionic conductivity, excellent mechanical properties, and electrolyte resistance.

[0004] Polyolefins have a low melting point and poor heat resistance, so generally, a ceramic coating is needed to improve their heat resistance. However, while the current use of ceramic coatings can improve the heat shrinkage resistance of separators, it results in poor adhesion between the ceramic coating layer and the separator, causing the ceramic layer to easily peel off the separator. Therefore, improving the adhesive strength of the coating layer is a crucial challenge. [Overview of the project] [Problems that the invention aims to solve]

[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] To solve the above technical problems, the object of the present application is to provide a battery separator including 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. 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, 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 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 includes 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 including an adhesive polymer material, the polymer material including 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 the 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 the 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 oil-based polyvinylidene fluoride, and the ratio of the α-phase in the crystalline region of the oil-based 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 the battery separator, wherein the battery separator is located between the positive electrode and the negative electrode.

Advantages of the Invention

[0017] The present application improves the adhesion 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 membrane breakage 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 adhesion strength of the current ceramic coating layer can be effectively solved. In addition, the present application reflects the adhesion and air permeability of the coating layer by designing the coating coefficient C value, and by limiting it to a specific better range, it is possible to evaluate and guarantee in a very convenient way whether the adhesion and air permeability of the separator meet the requirements.

Brief Description of the Drawings

[0018] [Figure 1] FIG. 1 is a schematic cross-sectional structure view of a battery separator of one embodiment of the present application. [Figure 2] FIG. 2 is a schematic cross-sectional structure view of a battery separator of another embodiment of the present application. [Figure 3] FIG. 3 is a schematic cross-sectional structure view of a battery separator of another embodiment of the present application. [Figure 4] FIG. 4 is a schematic cross-sectional structure view of a battery separator of another embodiment of the present application. [Figure 5] FIG. 5 is a flowchart of a manufacturing and processing method of a battery separator of one embodiment of the present application.

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 surface", etc. 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 shown exaggerated. In the drawings, for ease of understanding and explanation, the thicknesses of layers and regions, etc. are shown exaggerated. 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 on the 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, regarding its specific embodiments, structures, features, and its functions, in combination with the attached drawings and specific examples, the following will be described in detail as follows.

[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 from fibrous material such as nonwoven fabric or paper, or a composite porous sheet obtained by stacking one or more other porous layers on top of 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 non-solvent-induced phase separation, thermal-induced phase separation, or water vapor-induced phase separation. The polyolefin material is generally polyethylene and polypropylene. The porous substrate 11 may be a substrate manufactured from one or more types of materials, such as polyethylene terephthalate, nylon, aramid, polysulfone, polyetheretherketone, and polyimide fibers, by methods such as electrospinning. 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 placed on both sides of the composite material, and the surface density on each side of the composite material is 0.1 to 6.0 g / m². 2 The adhesive layer 12 may be located between, but is not limited thereto, and may be installed 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 comprises an adhesive polymer material 121, which is an aggregated layer formed by the aggregation of polyvinylidene fluoride (PVDF) fine particles or acrylic (acrylic) fine particles, but is not limited to this granular form. 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 resin may be a copolymer of materials such as methyl methacrylate (PMMA), acrylic acid, methacrylic acid, ethyl methacrylate, styrene, butyl methacrylate, methacrylamide, isobutylene, and acrylonitrile, or it may be formed by polymerization of multiple monomers such as methacrylate, acrylic acid, acrylate, styrene, ethylene glycol, and acrylonitrile, and 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. For this reason, in some examples, the adhesive layer 12 contains an adhesive polymer material, and the adhesive polymer material includes polyvinylidene fluoride homopolymer, polyvinylidene fluoride copolymer, methyl methacrylate homopolymer, methyl methacrylate copolymer, or mixtures thereof.

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

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

[0030] In this embodiment, the increase in air permeability 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 / 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 contains a polymer resin material or a mixture of a polymer 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 adhesive strength but poor air permeability. The better the adhesive strength, the closer the adhesion between the separator and the electrode plate, and the volume energy density of the separator can be significantly improved. Also, during the charge-discharge cycle, gas is generated, so there is gas between the separator and the electrode plate, which reduces ion 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 results in a decrease in air permeability and a reduction in ion conductivity, so it is necessary to simultaneously control the adhesive strength and air permeability of the separator to maximize its overall performance. Therefore, 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 the present 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 another embodiment of the present application, its structure is similar to that in 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 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 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 crosslinked polymer microsphere particles.

[0035] In this embodiment, the heat-resistant layer 13 is arranged in only one layer on one side of the porous substrate 11. However, it is not limited to this, and as shown in Figure 2, the heat-resistant layer 13 may be arranged on both sides of the porous substrate 11, where the heat-resistant layer 13 contains an aramid polymer and an inorganic filler, and the adhesive layer 12 contains polyvinylidene fluoride (PVDF) fine particles and / or acrylic acid fine particles formed from an adhesive polymer material 121. In some embodiments, as shown in Figure 3, the adhesive layer 12 contains not only the adhesive polymer material 121 but also ceramic material particles 122, and therefore the adhesive layer 12 is an aggregated layer of particles formed by the joint aggregation of polymer material particles 121 and ceramic material particles 122. In other embodiments, as shown in Figure 4, the polymer material 121 may be further coated onto the adhesive layer 12 on one side of the porous substrate 11 in Figure 3 so that the polymer material 121 can cover the ceramic material particles 122, thereby improving adhesion and increasing the overall thickness of the adhesive layer 12.

[0036] In some embodiments, the lithium battery of one embodiment of this application comprises a positive electrode, a negative electrode, and a battery separator 1, wherein the battery separator 1 is located between the positive electrode and the negative electrode and acquires electromotive force through the insertion and removal of lithium ions. Here, the positive electrode includes a positive electrode active material, a conductive agent, a binder, a current collector, and other materials. Examples of conductive agents include acetylene black, Ketjen black, and graphite powder materials. The negative electrode includes a material capable of receiving lithium ions, such as a carbon material, silicon, aluminum, or an alloy material of 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, or LiFSI. Examples of non-aqueous solvents 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 fluorosubstituted products; and cyclic esters such as γ-butyrolactone and γ-valerolactone. These can be used separately or in mixtures. Examples of external sealing materials include metal shells and aluminum laminate film packaging. Battery shapes include prismatic, cylindrical, and button-shaped, and the battery separator 1 of the present invention is suitable for any of these shapes. From the viewpoint of ion permeability, the air permeability value 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 preferably 200 to 800 gf.

[0037] Furthermore, 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 that comprises aggregates 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, and the coating process includes an aqueous coating process and an oil-based coating process, wherein 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, 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, a heat-resistant polymer material, in a suitable solvent to obtain a homogeneous 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 onto a base film and forming pores using one of the following methods, such as non-solvent-induced phase separation, or forming pores by steam-induced phase separation by placing the film directly into an oven; (3) removing the solvent by washing with water; and (4) drying the film in an oven.

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

[0039] The objectives of this application and the solution to its technical problems are achieved 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 excerpted 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 weighing 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 apparatus is a Wangyan type air permeability tester. A battery separator is fixed in place, and an air pressure of 0.05 MPa is applied to one side of the separator. Because micropores exist within the separator, the air pressure gradually decreases, and when 100 mL of air has completely passed through the separator, the air pressure becomes equal to atmospheric pressure. The time it takes for 100 mL of air to pass through the separator at a pressure of 0.05 MPa is recorded, in units of seconds per 100 cc. A shorter pressure drop time indicates better air permeability of the separator, while a shorter time indicates poorer air permeability.

[0043] Measurement Method 3: Test Method for the Adhesion 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 a temperature of 90°C to integrate the separator and electrode plate. The separator is then cut into 25mm x 200mm samples, and the adhesive strength is then tested using a universal tensile machine to obtain the adhesive strength between the separator and the electrode plate.

[0044] Measurement Method 4: Test Method for Volume Retention Rate The battery is based on a conventional 3Ah pouch-type battery, with an NCM523 electrode for the positive plate and a graphite negative plate for the negative plate. 25°C cycle performance test: A charge-discharge cycle test (500 cycles) is performed at a 1C current. Capacity retention rate is the ratio of the discharge capacity at cycle 500 to the discharge capacity at cycle 1.

[0045] Adhesion mechanism of the separator adhesive layer of this application: Polyvinylidene fluoride (PVDF) and acrylic polymer particles generate adhesive force under hot-press conditions and bond to the electrode plate. The adhesive layer can enhance the following performance of the cell: (1) The cell becomes harder and easier to insert into the shell. (2) The cycle life of the cell is extended. (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] JPEG0007833023000001.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 PVDF powder and binder to a certain amount of water so that the ratio of the solid dry weight of PVDF-HFP (copolymerization ratio of VDF and HFP: 95:5, Kynar powerflex LBG PWD manufactured by Arkema) to 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 9 μm thick separator from Shanghai Enjie Co., Ltd.), and the thickness of the coating layer was controlled to 2 microns to obtain a PVDF coated separator. Tests revealed that the crystallinity of the PVDF-HFP was 45%, the proportion of the α phase in the crystalline phase of the PVDF-HFP was 55%, the adhesion 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% after 500 cycles. Tests revealed that the adhesion 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. Batteries manufactured using this separator have a capacity retention rate of 88% after 500 cycles.

[0052] Example 2: (1) Slurry preparation: PVDF-HFP (copolymerization ratio of VDF to HFP: 95:5, Kynar powerflex LBG PWD from Arkema) was completely dissolved in DMAc solvent to form an 8% solution.

[0053] (2) Coating step: Using a roll-coating process, the PVDF-HFP solution prepared above was coated onto a separator (a 9 μm thick separator from Shanghai Enjie Co., Ltd.), and 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 2 microns to obtain a PVDF-HFP coated separator. Tests revealed that the crystallinity of the 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 in air permeability per unit coating layer thickness was approximately 25.8 s / 100 ml, and the C value was 0.79. In a battery manufactured using this separator, the capacity retention rate after 500 cycles was 90%.

[0054] Example 3: Except for replacing PVDF with PMMA (manufactured by Zeon Corporation), the procedure was the same as in Example 1. Tests 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. In batteries manufactured using this separator, the capacity retention rate after 500 cycles was 93%.

[0055] Example 4: (1) Preparation of mixed slurry: A slurry with a solid content of 20% was prepared using 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 from 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 revealed that the crystallinity of PVDF-HFP was 45%, the proportion of the 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. In batteries manufactured using this separator, the capacity retention rate after 500 cycles was 85%.

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

[0059] (2) Using a roll coating process, the alumina slurry prepared above was coated onto a separator (a 9 μm thick separator from 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) Using a solid-dry weight ratio of PVDF-HFP to binder of 9:1, a slurry with a solid content of 10% was prepared by adding a fixed amount of water to PVDF-HFP powder (monomers are VDF and HFP, and the copolymerization ratio of VDF to HFP is 95:5) and a binder (LA133, produced by Sichuan Meishan Yindile Co., Ltd.).

[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), and the thickness of the coating layer was controlled to 1 micron to obtain a PVDF-HFP coated separator. Tests revealed that the crystallinity of the PVDF-HFP was 45%, the proportion of the α phase in the crystalline phase was 55%, the adhesion 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. In a battery manufactured using this separator, the capacity retention rate after 500 cycles was 83%.

[0062] Example 6: Except for replacing alumina with magnesium hydroxide, the procedure was the same as in Example 5. Tests revealed that the crystallinity of the PVDF-HFP was 45%, the proportion of the 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. In batteries manufactured using this separator, the capacity retention rate after 500 cycles was 82%.

[0063] Example 7: Except for replacing alumina with barium titanate, the procedure was the same as in Example 6. Tests revealed that the crystallinity of the PVDF-HFP was 45%, the proportion of the 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. In batteries manufactured using this separator, the capacity retention rate after 500 cycles was 82%.

[0064] Example 8: (1) Slurry preparation: Aramid was dissolved in DMAc solvent to prepare an aramid solution with a fixed solid content. Barium sulfate was dispersed in DMAc to prepare a dispersion with a fixed solid content. A mixed dispersion of aramid and barium sulfate with a total solid content of 20% was prepared using a solid content ratio of aramid (from Teijin Limited, meta-aramid 1313):barium sulfate = 4:6.

[0065] (2) Using a roll coating process, the mixed slurry prepared above was coated onto a separator (a 9 μm thick separator from Shanghai Enjie Co., Ltd.), pores were formed by a solidification bath method, 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) Using a solid-dry weight ratio of PVDF-HFP to binder of 9:1, a slurry with a solid content of 10% was prepared by adding a fixed amount of water to PVDF-HFP powder (monomers are VDF and HFP, and the copolymerization ratio of VDF to HFP is 95:5) and a binder (LA133, produced by Sichuan Meishan Yindile Co., Ltd.).

[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. Tests revealed that the crystallinity of the PVDF-HFP was 25%, 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 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% after 500 cycles.

[0068] Comparative Example 1: Except for replacing PVDF with polystyrene microparticles (homemade in the laboratory, D50 particle size approximately 0.8 μm), the procedure was the same as in Example 1. Tests 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. In batteries manufactured using this separator, the capacity retention rate after 500 cycles was 60%.

[0069] Comparative Example 2: Except for replacing PVDF with copolymerized PVDF-HFP with a high HFP content (produced by Zhejiang Zhonghua Lantian Group Co., Ltd., 45% VDF), the procedure was the same as in Example 1. Tests revealed that the crystallinity of PVDF-HFP was 33%, the proportion of the 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. In batteries manufactured using this separator, the capacity retention rate after 500 cycles was 65%.

[0070] Comparative Example 3: The procedure was the same as in Example 2, except that the PVDF-HFP in Comparative Example 2 was replaced with homopolymerized HFP (produced by Zhejiang Zhonghua Lantian Group Co., Ltd., 100% VDF). Tests revealed that the degree of crystallinity of the homopolymerized PVDF was 65%, the proportion of the 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. In batteries manufactured using this separator, the capacity retention rate after 500 cycles was 63%.

[0071] Comparative Example 4: Except for replacing PVDF with polystyrene microparticles (homemade in the laboratory, D50 particle size approximately 0.8 μm), the procedure was the same as in Example 6. Tests 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. In batteries manufactured using this separator, the capacity retention rate after 500 cycles was 51%.

[0072] Comparative Example 5: Except for replacing PVDF with polystyrene microparticles (homemade in the laboratory, D50 particle size approximately 0.8 μm), the procedure was the same as in Example 9. Tests 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. In batteries manufactured using this separator, the capacity retention rate after 500 cycles was 52%.

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

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

[0075] Table 1: Structure and physical properties of separators in examples and comparative examples JPEG0007833023000002.jpg199170

[0076] Table 1 summarizes the experimental results described above. A comparison of the examples and comparative examples shows that coating the separator surface with materials such as PVDF and PMMA ensures excellent adhesive strength of the separator, thereby extending the cycle life (capacity retention rate) of the lithium battery. In the case of an oil-based coating layer, for example in Example 3, the adhesion of the separator is superior. This application uses the coating coefficient C value to show the ratio between adhesion and the increase in air permeability, and limits this to a certain range, thereby ensuring sufficient adhesion and air permeability 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 a low capacity retention rate and a short cycle life. When the coating coefficient C value is within the range of 0.3 to 1, the capacity retention rate is always greater than 80%, resulting in a longer cycle life.

[0077] In summary, this invention proposes a means of introducing polymer particles into the separator coating layer to enhance the adhesion between the separator and the electrode plate, in order to improve the adhesion and breathability of current battery separators. In addition, heat-resistant polymer materials such as aramid are introduced into the separator coating layer to increase the film rupture temperature of the separator. Furthermore, the heat shrinkage resistance of the separator is improved by introducing ceramics into the separator coating layer. The above improvements not only effectively solve the problem of delamination from the separator caused by the lack of adhesive strength of the current ceramic coating layer, but also ensure the breathability of the separator. Moreover, this application allows for the evaluation and assurance of whether the adhesion and breathability of the separator meet requirements in a very convenient way by designing a coating coefficient C value, which reflects the adhesion and breathability of the coating layer and limits it to a specific better range.

[0078] Terms such as "in some embodiments" and "in various embodiments" are used repeatedly. These terms do not usually refer to the same embodiment, but they may. Terms such as "include," "possess," and "contain" are synonymous unless the context indicates otherwise.

[0079] The foregoing are merely embodiments of the present application and do not constitute any limitation of the present application in any form. The present application is disclosed as described above through specific embodiments, but is not used to limit the present application. A person skilled in the art can utilize the above-disclosed technical content and modify it slightly or to create equivalent embodiments as equivalent variations, provided that the modifications do not deviate from the scope of the technical solutions of the present application. Any simple modifications, equivalent variations, and modifications made to the above embodiments by the technical substance of the present application, provided that they do not deviate from the technical solutions of the present application, still fall within the scope of the technical solutions of the present application.

Claims

1. It is a battery separator, A porous substrate, or a composite material consisting of a porous substrate and a heat-resistant layer located on the porous substrate, The material comprises an adhesive layer formed on the porous substrate or the composite material, wherein the adhesive layer comprises an adhesive polymer material, and the adhesive layer has 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 in air permeability per unit coating layer thickness P, satisfying the relationship 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 in air permeability per unit coating layer thickness P of the adhesive layer is s / 100cc / μm. A battery separator characterized in that the adhesive polymer material contains only one type of polymer, and the polymer is a polyvinylidene fluoride homopolymer, a polyvinylidene fluoride copolymer, a methyl methacrylate homopolymer, or a methyl methacrylate copolymer.

2. The battery separator according to claim 1, characterized in that the adhesive layer 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.

3. The battery separator according to claim 2, characterized in that the adhesive polymer material is an aqueous material and comprises polyvinylidene fluoride homopolymer, polyvinylidene fluoride copolymer, methyl methacrylate homopolymer, methyl methacrylate copolymer, or a mixture thereof.

4. The battery separator according to claim 3, characterized in that the molar ratio of vinylidene fluoride monomer in the polyvinylidene fluoride copolymer is higher than 50%, and the other comonomer is 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, characterized in that 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, characterized in that the heat-resistant layer comprises a ceramic material, a heat-resistant polymer material, or a mixture of a ceramic material and a heat-resistant polymer material.

7. It is a battery separator, A porous substrate, or a composite material consisting of a porous substrate and a heat-resistant layer located on the porous substrate, A battery separator comprising an adhesive layer formed on one side of the porous substrate or on one side of the composite material, wherein the adhesive layer comprises an adhesive polymer material, the polymer material comprises one type of 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 in air permeability per unit coating layer thickness P, satisfying the relationship 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 in air permeability per unit coating layer thickness P of the adhesive layer is s / 100cc / μm.

8. The battery separator according to claim 7, characterized in that the degree of crystallinity of the raw material for the polyvinylidene copolymer is between 10% and 50%.

9. The battery separator according to claim 7, characterized in that, when the adhesive layer is coated with aqueous polyvinylidene fluoride, the proportion of the α phase in the crystalline region of the aqueous polyvinylidene fluoride is greater than 30% and less than 70%.

10. The battery separator according to claim 7, characterized in that, when the adhesive layer is coated with oily polyvinylidene fluoride, the proportion of the α phase in the crystalline region of the oily polyvinylidene fluoride is less than 20%.

11. The battery separator according to claim 7, characterized in that the molar ratio of vinylidene fluoride monomer in the polyvinylidene fluoride copolymer is higher than 50%, and the other comonomer is one or more selected from hexafluoropropylene, tetrafluoroethylene, trifluoroethylene, trichloroethylene, acrylic acid, methacrylic acid, methacrylate, and vinyl acetate.

12. The battery separator according to claim 7, characterized in that the adhesive layer further comprises a filler, the filler comprising an organic or inorganic heat-resistant material.

13. The battery separator according to claim 7, characterized in that the heat-resistant layer comprises a ceramic material, a heat-resistant polymer material, or a mixture of a ceramic material and a heat-resistant polymer material.

14. A lithium battery comprising a positive electrode, a negative electrode, and a battery separator according to any one of claims 1 to 13, wherein the battery separator is located between the positive electrode and the negative electrode.

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