Battery separator, manufacturing method thereof, and secondary battery

Abstract

The present invention relates to a battery separator, a manufacturing method thereof, and a secondary battery, which are related to the technical field of battery separators. The battery separator includes a base film and an inorganic coating on at least one surface of the base film, and the contact ratio k between the inorganic particles and the base film in the longitudinal cross section of the battery separator is 15 to 90%, and the relationship between the contact ratio k, the air permeability A1 of the base film, and the air permeability A2 per unit thickness of the coating satisfies A1 × k ≥ A2. The separator has improved peel strength, pin puncture strength, and air permeability to a certain extent, making it a battery separator that combines safety and high ion permeability.

Description

[Technical Field]

[0001] The present invention relates to the technical field of battery separators, and more particularly to a battery separator, a manufacturing method thereof, and a secondary battery. [Background technology]

[0002] With "carbon peaking" and "carbon neutrality" being mentioned in government work reports, China is rapidly moving toward greening and low-carbonization. The adoption rate of new energy vehicles, which are essential for reducing carbon emissions, has increased rapidly over the past two years, and research and development of materials for power batteries, a key component of new energy vehicles, is also undergoing constant innovation.

[0003] As is well known, the main components of a lithium-ion battery include a positive electrode, a negative electrode, an electrolyte, and a separator. Lithium ions travel between the positive and negative electrodes through the separator's microporous structure, forming an electric current and completing the charge-discharge cycle. The separator's microporous structure directly affects the lithium ion transport efficiency, thereby affecting the battery's cycle and rate characteristics. Furthermore, the use of polyolefin separators provides excellent insulation and prevents short circuits caused by direct contact between the positive and negative electrodes. However, heat generation is inevitable during long-term battery use. At high temperatures, the polyolefin chain segments in the polyolefin separator migrate, shrinking the pore size and reducing lithium ion permeability, shortening the battery's lifespan. To address these issues, one or more functional coatings are typically applied to the surface of the polyolefin separator. Common coatings include inorganic filler coatings, polymeric coatings, and mixed coatings of inorganic fillers and polymeric materials. Conventional inorganic coatings significantly increase air permeability, slow the shuttle speed of lithium ions, and have poor adhesion between the inorganic coating and the substrate, which causes inorganic particles to fall off during battery winding and battery charge / discharge, adversely affecting battery safety and capacity.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] A first object of the present invention is to provide a separator for a battery. A second object of the present invention is to provide a method for producing a battery separator. A third object of the present invention is to provide a secondary battery including the above battery separator.

[0006] In order to achieve the above object, a first aspect of the present invention is a battery separator, A base film; an inorganic coating provided on at least one surface of the base film; the contact rate k between the inorganic particles and the base film in the longitudinal section of the battery separator is 15% to 90%, The relationship between the contact rate k, the air permeability A1 of the base film, and the air permeability A2 per unit thickness of the coating is as follows: A battery separator is provided that satisfies A1×k≧A2, where the air permeability A1 of the base film is in s / 100 cc and the air permeability A2 per unit thickness of the coating is in s / 100 cc / μm.

[0007] According to an embodiment of the present invention, the battery separator has a peel strength of 30 N / m or more, a pin puncture strength per unit coating thickness of 6 gf / μm or more, and an air permeability per unit coating thickness of 20 s / 100 cc / μm or less.

[0008] According to an embodiment of the present invention, the contact ratio k between the inorganic particles and the base film in the longitudinal section of the battery separator is 30% to 85%.

[0009] According to an embodiment of the present invention, the battery separator has a peel strength of 50 N / m or more, preferably 100 N / m or more, particularly 170 N / m or more, and even 190 N / m or more, an increase in pin puncture strength per unit thickness of the coating of 9 gf / μm or more, preferably 12 gf / μm or more, and an increase in air permeability per unit thickness of the coating of 15 s / 100 cc / μm or less, preferably 10 s / 100 cc / μm or less.

[0010] In a second aspect of the present invention, there is provided a method for producing the battery separator according to the first aspect, (1) providing a base film; (2) applying an inorganic coating slurry onto at least one side of the base film to obtain an inorganic coating; (3) drying the base film and the inorganic coating to obtain a battery separator; The method for producing the inorganic coating slurry in step (2) includes: 90 to 99 parts by weight of solvent is charged into a stirring tank, the rotation speed of the anchor blade is set to 10 rpm to 30 rpm, the anchor blade is started, 1 to 10 parts by weight of thickener powder is added, and after the addition is completed, the dispersion disc is started, the rotation speed of the dispersion disc is set to 500 rpm to 1300 rpm, and the stirring time is set to 80 min to 120 min to obtain a thickener stock solution, Step (2-1) of sending 50 to 60 parts by weight of solvent to a double planetary stirring tank, adding 32 to 38 parts by weight of inorganic particles, maintaining the volume of the inorganic particles and solvent at 3 / 5 to 3 / 4 of the volume of the double planetary stirring tank, maintaining the distance between the upper liquid level of the inorganic particles and solvent and the dispersion disc at 1 / 4 to 1 / 2 of the height of the double planetary stirring tank, setting the rotation speed of the anchor blade in the double planetary stirring tank to 10 rpm to 30 rpm, the rotation speed of the dispersion disc to 500 rpm to 1300 rpm, and the stirring time to 10 min to 20 min to obtain an inorganic particle stock solution; Step (2-2) of adding 5 to 15 parts by weight of thickener stock solution to the inorganic particle stock solution, and setting the rotation speed of the anchor blade in the double planetary type stirring tank to 10 rpm to 30 rpm, the rotation speed of the dispersion disc to 500 rpm to 1300 rpm, and the stirring time to 10 min to 20 min to obtain a thickened slurry; the thickened slurry is put into a high-speed disperser or a grinder, and in this process, the temperature of the thickened slurry is controlled at 15 to 30°C to obtain a semi-finished slurry; after the temperature of the semi-finished slurry is returned to room temperature, 2 to 10 parts by weight of a binder and 0.03 to 0.2 parts by weight of a wetting agent are added, and the mixture is stirred at a stirring speed of 10 to 50 rpm for 20 to 40 minutes to obtain an inorganic coating slurry step (2-3); The inorganic coating slurry has a pH of 7 to 11, particularly 7.8 to 9.8, a viscosity of 5 to 200 MPa·s, particularly 10 to 130 MPa·s, and a volume average particle diameter D50 スラリー is 0.01 to 2.5 μm, particularly 0.1 to 1.2 μm, and the average absolute value of the Zeta potential is 0.025 to 0.3 V, particularly 0.035 to 0.1 V; In the coating process of step (2), the tension applied to the base film per unit thickness and per unit width is controlled to 2.5 to 5 N / m / μm, and the difference between the speed of the coating roll and the speed of the coater in the coating process is -50 to 50 m / min; In the drying process of step (3), the drying temperature per unit thickness of the coating is controlled to be 20-50°C / μm, the intake-exhaust frequency of the oven is controlled to be 20-45Hz, and the intake frequency-exhaust frequency is controlled to be 6Hz or less.

[0011] In a third aspect of the present invention, there is provided a secondary battery comprising the battery separator according to the first aspect. [Effects of the Invention]

[0012] The technical solution of the present invention has the following beneficial effects over the prior art: In the battery separator of the present invention, the contact ratio k between the inorganic particles and the base film in the longitudinal cross section of the battery separator is controlled to 15% to 90%, and the relationship between k, the air permeability A1 of the base film, and the air permeability A2 per unit thickness of the coating is controlled to satisfy A1 × k ≥ A2. This allows the resulting separator to have improved peel strength, pin puncture strength, and air permeability to a certain extent, resulting in a battery separator that is both safe and highly permeable to ions. This reduces the difficulty of assembling secondary batteries based on this separator, and improves battery capacity while maintaining high safety.

[0013] This invention controls the ratio of inorganic particles, binder, and thickener addition, controls the temperature of the thickened slurry during the slurry production process, and maintains the ratio of the gap between the liquid surface and the dispersion disk to the height of the double planetary stirred tank within a certain range. This helps the thickener form a stable steric hindrance and allows the binder to fully adsorb to the inorganic particle surface to form a potential, thereby providing a stable carrier for the inorganic particles to bond to the base film. Furthermore, controlling the tension during the coating process to suit substrate thicknesses further improves the substrate's toughness and ductility, thereby improving the adhesion between the inorganic particles and the substrate. By adjusting the oven temperature and intake / exhaust frequency to suit the coating thickness, the drying speed of each component in the coating is balanced, preventing coating cracking and excessive binder lift-off due to excessive drying speed and ensuring uniform distribution of the inorganic particles over the surface of the base film. The binder and thickener provide good control of the contact rate between the inorganic particles and the surface of the base film (15% to 90%), so that the air permeability value per unit thickness of the separator coating after application is smaller than the product of the air permeability of the base film and the contact rate. This results in a certain degree of improvement in the separator's peel strength, pin puncture strength per unit thickness of the coating, and air permeability properties per unit thickness of the coating.

[0014] The battery separator obtained by the present invention has a peel strength of 30 N / m or more, a contact rate between the inorganic particles and the base film in the longitudinal section of the battery separator of 15 to 90% due to the binder and thickener, a pin puncture strength per unit thickness of the coating of 6 gf / μm or more, and an air permeability per unit thickness of the coating of 20 s / 100 cc / μm or less.

[0015] Additional aspects and advantages of the invention will be set forth in part in the description that follows, and in part will be obvious based on the description, or may be learned through practice of the invention. [Brief explanation of the drawings]

[0016] The drawings are included to provide a further understanding of the invention, constitute a part of this specification, and together with the following specific embodiments are used to explain, but not to limit, the invention.

[0017] [Figure 1] 1 is an electron microscope image of a cross section in the thickness direction of a battery separator produced in Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018]

[0030] The following detailed description of specific embodiments of the present invention will be given with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are used to explain and interpret the present invention, and are not intended to limit the present invention.

[0019] A first aspect of the present invention is a battery separator, a base film and an inorganic coating disposed on at least one surface of the base film; The battery separator has the following characteristics: the contact rate k between the inorganic particles and the base film in the longitudinal section of the battery separator is 15% to 90%, preferably 30% to 85%, and more preferably 30% to 65%; The relationship between the contact rate k, the air permeability A1 of the base film, and the air permeability A2 per unit thickness of the coating is as follows: A1×k≧A2, where the unit of the air permeability A1 of the base film is s / 100 cc, and the unit of the air permeability A2 per unit thickness of the coating is s / 100 cc / μm; The battery separator has a peel strength of 30 N / m or more, preferably 50 N / m or more, more preferably 100 N / m or more, and even more preferably 150 N / m or more, a pin puncture strength per unit thickness of the coating of 6 gf / μm or more, preferably 9 gf / μm or more, and even more preferably 12 gf / μm or more, and an air permeability per unit thickness of the coating of 20 s / 100 cc / μm or less, preferably 15 s / 100 cc / μm or less, and even more preferably 10 s / 100 cc / μm or less.

[0020] According to the present invention, the base film may be any material known in the art that can be used as a substrate layer for a separator, including polyolefin base films, nonwoven fabric base films, and electrospun base films, with polyolefin base films being preferred. The production process for polyolefin base films is not particularly limited and may include dry uniaxial stretching, biaxial synchronous or asynchronous stretching, and wet biaxial synchronous or asynchronous stretching. However, wet biaxial synchronous or asynchronous stretching is preferred. The polyolefin porous base film may be a single layer of polyethylene (PE) or polypropylene (PP), or a multilayer of polyethylene (PE) and polypropylene (PP). From the viewpoint of film formability, polyethylene and copolymers are preferred. Polyethylene can be obtained by single-stage or multi-stage polymerization. The molecular weight (viscosity average molecular weight) of the polyethylene may be 500,000 to 4,000,000. For example, the viscosity average molecular weight of the polyethylene may be 500,000, 550,000, 600,000, 1,000,000, 2,000,000, 3,000,000, or 4,000,000. According to one specific embodiment of the present invention, the viscosity average molecular weight of the polyethylene is 600,000 to 3,000,000, and particularly preferably 800,000 to 3,000,000. The volume average particle diameter D50 of the polyethylene isポリエチレン is less than 1000 μm.

[0021] According to the present invention, the thickness of the base film may be 1 to 30 μm, for example, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm... 29 μm, 30 μm, and according to one specific embodiment of the present invention, the thickness of the base film is 3 to 20 μm.

[0022] According to the present invention, the porosity of the base film may be 10-70%, for example, 10%, 12%, 15%...69%, 70%, and according to one specific embodiment of the present invention, the porosity of the base film may be 20-60%.

[0023] According to the present invention, the air permeability of the base film may be 40-350 s / 100 cc, for example, 40 s / 100 cc, 45 s / 100 cc, 50 s / 100 cc... 240 s / 100 cc, 300 s / 100 cc, 350 s / 100 cc. According to one specific embodiment of the present invention, the air permeability of the base film is 80-200 s / 100 cc, and the air permeability can be tested in accordance with the requirements of JIS8117-2009.

[0024] According to the present invention, the type of inorganic particles is not particularly limited as long as the electrochemical properties are stable. For the above reasons, inorganic particles with a dielectric constant of 5 or higher and the ability to transfer lithium ions are preferred. Examples include oxide particles such as silicon dioxide (SiO), aluminum oxide (AlO), magnesium oxide (MgO), zirconium oxide (ZrO), titanium oxide (TiO), and calcium oxide (CaO); nitride particles such as boehmite (ALOOH), aluminum nitride (AlN), and boron nitride (BN); and sparingly soluble ionic crystalline particles such as barium sulfate (BaSO), barium titanate (BaTiO), calcium fluoride (CaF), and barium fluoride (BaF). The inorganic particles may be one type selected from the above particles, or two or more types of particles in any ratio. Among these particles, oxide particles are preferred in terms of stability and potential in the electrolyte. Furthermore, inorganic particles must have a high thermal decomposition temperature (higher than 500°C) and low water absorption, so aluminum oxide, boehmite, magnesium oxide, and silicon dioxide are preferred, with aluminum oxide and boehmite being particularly preferred. Aluminum oxide and boehmite neutralize hydrogen fluoride, a by-product produced by the reaction of the electrolyte with water, suppress voltage drop, and improve the battery's high-temperature charge storage capacity and room-temperature cycle capacity.

[0025] According to the present invention, the shape of the inorganic particles is not particularly limited, and examples thereof include plate-like, scaly, needle-like, columnar, spherical, polyhedral, block-like, and rod-like shapes, and a combination of inorganic fillers having the above shapes may be used. From the viewpoint of improving permeability, plate-like, block-like, polyhedral, and columnar shapes having multiple faces are preferred.

[0026] According to the present invention, the volume average particle diameter D50 of the inorganic particles 無機粒子 is 0.1 μm to 3 μm, for example, 0.1 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 1 μm... 1.5 μm, 2 μm, 2.5 μm, 3.0 μm, and according to one specific embodiment of the present invention, the inorganic particles have a D50 of 0.5 μm≦D50 無機粒子≦1.4μm, where D50 無機粒子 is obtained from the value measured by a Mastersizer 300 particle size distribution analyzer.

[0027] According to the present invention, the specific surface area of ​​the inorganic particles is 100 m 2 / g or less, but preferably 50m 2 / g or less, more preferably 30m 2 / g or less. When the specific surface area of ​​the inorganic particles is within the above range, the surface energy of the particles increases, improving the infiltration of the electrolyte into the separator, which can improve the cycle characteristics of the battery. Furthermore, it is possible to improve the aggregation between the slurry particles and the fluidity of the slurry. In addition, the specific surface area of ​​the inorganic particles is 0.5 m 2 / g or more, preferably 3m 2 / g or more, the water content in the separator is effectively controlled, thereby suppressing side reactions of water in the electrolyte and improving the cycle characteristics of the battery.

[0028] According to the present invention, the inorganic particles may include particles capable of transferring lithium ions, thereby improving lithium ion conductivity, and the particles capable of transferring lithium ions are any one type of inorganic particles selected from lithium phosphate, lithium titanium phosphate, lithium aluminum titanium phosphate, lithium nitride, lithium carbonate, lithium chloride, lithium sulfide, and lithium hexafluorophosphate, or a mixture of at least two types of inorganic particles.

[0029] The inorganic coating contains components such as inorganic particles, a binder, a thickener, and a wetting agent, and the inorganic particles are in contact with the base film via the binder.

[0030] According to the present invention, the thickness of the inorganic coating may be 0.5-10 μm, for example, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm... 9 μm, 10 μm, and according to one specific embodiment of the present invention, the thickness of the inorganic coating is 2-5 μm.

[0031] According to the present invention, the battery separator of the present invention satisfies the following properties.

[0032] 1. The contact rate k between the inorganic particles and the base film in the longitudinal cross section of the battery separator is 15 to 90%, and for example, the contact rate between the inorganic particles and the base film in the longitudinal cross section of the battery separator may be 15%, 16%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 95%.

[0033] The contact ratio (k) refers to the contact length between the inorganic particles and the base film in the cross section in the thickness direction / the total length of the contact surface between the base film and the coating.

[0034] The test method for the contact rate k between the inorganic particles and the base film in the longitudinal section may be as follows.

[0035] An electron microscope photograph of a 10 cm × 10 cm longitudinal section of a separator was taken, and the contact interfaces k1, k2, k3…k between the inorganic particles and the base film were identified. n Mark the contact interfaces k1, k2, k3...k on the photograph. n The lengths l1, l2, l3…l n , and measure the total length L of the contact area between the coating and the base film in the photograph. n The ratio of the total of the above to L is the contact rate between the inorganic particles and the base film in the vertical cross section.

[0036] By controlling the contact ratio k, it is possible to ensure strong adhesion between the inorganic particles and the base film, significantly improving the peel strength of the separator after application, while also effectively controlling the coating's air permeability per unit thickness after application, reducing the battery's internal resistance and improving the battery's cycle characteristics.

[0037] 2. The air permeability A1 x k of the base film is equal to or greater than the air permeability A2 per unit thickness of the coating.

[0038] "Air permeability per unit thickness of coating" refers to the difference between the air permeability of the separator and the air permeability of the base film divided by the thickness of the inorganic coating (separator thickness - base film thickness). The unit of air permeability is "s / 100cc", and the unit of inorganic coating thickness is "μm".

[0039] By controlling the relationship between k, A1, and A2, the air permeability of the separator after coating can be significantly reduced, the lithium ion transport capacity can be improved, and the battery cycle characteristics can be improved. In addition, the peel strength and needle puncture strength of the coating can be improved, thereby improving the safety of the battery.

[0040] 3. The peel strength of the battery separator is 30 N / m or more, for example, 30 N / m, 31 N / m...79 N / m, 80 N / m, 90 N / m, 100 N / m, 110 N / m, 120 N / m, 150 N / m, 160 N / m, 170 N / m, 180 N / m, 190 N / m, 200 N / m, 220 N / m, etc.

[0041] The pin puncture strength per unit thickness of the coating is 6 gf / μm or more, and may be, for example, 6 gf / μm, 7 gf / μm... 9 gf / μm, 12 gf / μm, 16 gf / μm, etc.

[0042] "Needle puncture strength per unit coating thickness" refers to the difference between the separator's needle puncture strength and the base film's needle puncture strength divided by the inorganic coating thickness (separator thickness - base film thickness). The unit of needle puncture strength is "gf," and the unit of inorganic coating thickness is "μm."

[0043] The air permeability per unit thickness of the coating is 20s / 100cc / μm or less, and may be, for example, 20s / 100cc / μm, 19s / 100cc / μm...2s / 100cc / μm, or 1s / 100cc / μm.

[0044] A second aspect of the present invention provides a method for producing the battery separator according to the first aspect, the method comprising: (1) providing a base film; (2) applying an inorganic coating slurry onto at least one side of the base film to obtain an inorganic coating; (3) drying the base film and the inorganic coating to obtain a battery separator; The method for producing the inorganic coating slurry in step (2) includes: 90 to 99 parts by weight of solvent is placed in a stirring tank, the rotation speed of the anchor blade is set to 10 rpm to 30 rpm, the anchor blade is started, and 1 to 10 parts by weight of thickener powder is slowly added. After the addition is complete, the dispersion disc is started, the rotation speed of the dispersion disc is set to 500 rpm to 1300 rpm, and the stirring time is set to 80 min to 120 min to obtain a thickener stock solution. Step (2-1) of sending 50 to 60 parts by weight of solvent to a double planetary stirring tank, slowly adding 32 to 38 parts by weight of inorganic particles, maintaining the volume of the inorganic particles and solvent at 3 / 5 to 3 / 4 of the volume of the double planetary stirring tank, maintaining the distance between the upper liquid level of the inorganic particles and solvent and the dispersion disc at 1 / 4 to 1 / 2 of the height of the double planetary stirring tank, setting the rotation speed of the anchor blade in the double planetary stirring tank to 10 rpm to 30 rpm, the rotation speed of the dispersion disc to 500 rpm to 1300 rpm, and the stirring time to 10 min to 20 min to obtain an inorganic particle stock solution; Step (2-2) of adding 5 to 15 parts by weight of thickener stock solution to the inorganic particle stock solution, and setting the rotation speed of the anchor blade in the double planetary type stirring tank to 10 rpm to 30 rpm, the rotation speed of the dispersion disc to 500 rpm to 1300 rpm, and the stirring time to 10 min to 20 min to obtain a thickened slurry; the thickened slurry is put into a high-speed disperser or pulverizer, and the temperature of the thickened slurry is strictly controlled at 15-30°C during the process to obtain a semi-finished slurry; the temperature of the semi-finished slurry is returned to room temperature, and then 2-10 parts by weight of a binder and 0.03-0.2 parts by weight of a wetting agent are added, and the mixture is stirred at a stirring speed of 10-50 rpm for 20-40 minutes to obtain an inorganic coating slurry; The inorganic coating slurry has a pH of 7 to 11, particularly pH 7.8 to 9.8, a viscosity of 5 to 200 MPa·s, particularly 10 to 130 MPa·s, for example, 60 to 80 MPa·s, and a volume average particle diameter D50 スラリー is 0.01 to 2.5 μm, particularly 0.1 to 1.2 μm, for example, 0.8 to 1 μm, and the average absolute value of the Zeta potential is 0.025 to 0.3 V, particularly 0.035 to 0.1 V, for example, 0.07 to 0.1 V; In the coating process of step (2), the tension applied to the base film per unit thickness and per unit width is controlled to 2.5 to 5 N / m / μm, and the difference between the speed of the coating roll and the speed of the coater in the coating process is -50 to 50 m / min; In the drying process of step (3), the drying temperature for each unit thickness of the coating is controlled to be 20-50°C / μm, the oven intake-exhaust frequency is controlled to be 20-45Hz, and the intake frequency-exhaust frequency is controlled to be 6Hz or less.

[0045] Inorganic Coating Slurries and Manufacturing The pH of the inorganic coating slurry is 7 to 11. When the pH of the slurry is within this range, the charge distribution within the slurry is balanced, and the spatially stable structure formed between particles is less likely to be destroyed. When the viscosity of the slurry is 5 to 200 mPa·s, the fluidity of the slurry is significantly improved, thereby reducing the difficulty of coating processing. The volume average particle diameter D50 of the slurry is 1000 μm. スラリー The volume average particle size of the slurry is 0.01 to 2.5 μm, and if the volume average particle size of the slurry is within this range, the uniformity of the applied coating can be ensured. The average absolute value of the Zeta potential of the produced slurry is 0.025 to 0.3 V. The larger the absolute value of the Zeta potential, the more balanced the charge distribution of the produced slurry will be, and the better the stability and shelf life of the slurry will be.

[0046] The pH value is tested using a pH meter. The viscosity is measured using a Brookfield viscometer at 25°C and 40 rpm. The volume average particle size is measured using a Mastersizer 3000 particle size distribution analyzer. The zeta potential is the average of the absolute values ​​measured using a Stabilo Zeta electrometer.

[0047] According to the present invention, the solvent may be water or any organic solvent. Examples of organic solvents include aliphatic hydrocarbons such as cyclopropane and cyclohexane; ethyl methyl ketone and cyclohexanones; aromatic hydrocarbons such as benzene and toluene; nitriles such as acetonitrile and propionitrile; esters such as ethyl acetate and butyl acetate; alcohols such as methanol, ethanol, isopropanol, and ethylene glycol; ethers such as tetrahydrofuran and ethylene glycol diethyl ether; and amides such as N-methylpyrrolidone and N,N-dimethylformamide. These solvents can be used alone or in combination. Of these, water is preferred as the solvent for producing a slurry.

[0048] According to the present invention, the type of the binder is not particularly limited, and any polymer that can be used as an inorganic particle binder in the art may be used, such as acrylate, polyvinylidene fluoride, styrene butadiene rubber, polyacrylonitrile, polyvinyl alcohol, and vinyl acetate.

[0049] According to the present invention, the binder may be an acrylate polymer, and may be selected from a water-soluble acrylic polymer, an emulsion-type acrylic polymer, or a mixture of the two in any proportion, but is preferably an emulsion-type acrylic polymer.

[0050] According to the present invention, the emulsion-type acrylic polymer refers to an acrylic polymer that is in an aqueous emulsion form, i.e., has a milky white or bluish appearance, and the main monomer is a monomer containing a carboxylic acid or ester functional group, such as at least one of acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, octyl acrylate, lauryl acrylate, stearyl acrylate, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, butyl methacrylate, isobutyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl acrylate, n-octyl methacrylate, n-hexyl acrylate, dodecyl methacrylate, n-decyl methacrylate, 2-ethylhexyl acrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, and trimethylolpropane triacrylate.

[0051] The thickener is preferably a polysaccharide. Examples thereof include natural polymer compounds and semi-synthetic cellulose polymer compounds. The thickener may be used alone or in combination of two or more types in any ratio. From the viewpoint of improving the dispersibility of inorganic particles, it is preferable to use semi-synthetic cellulose compounds such as carboxymethyl cellulose, sodium carboxymethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose.

[0052] The degree of etherification of the semi-synthetic cellulose polymer compound is preferably 0.5 or more, more preferably 0.7 or more, and preferably 1.2 or less, more preferably 1.0 or less. The so-called degree of etherification refers to the degree to which the hydroxyl (three) of each anhydroglucose unit in the cellulose is substituted with a substituent such as carboxymethyl. When the degree of etherification is in the range of 0 to 3, not only is the affinity between the cellulose and the solvent ensured, but also a certain spatially stable structure is formed, the dispersibility of inorganic particles in the solvent is improved, and the storage time of the slurry can be extended.

[0053] The average degree of polymerization of the semi-synthetic cellulose polymer compound is preferably 500 or more, more preferably 1000 or more, and preferably 2500 or less, more preferably 2000 or less, and particularly preferably 1500 or less. The average degree of polymerization of the thickener forms a certain steric hindrance in combination with the solvent, promoting the flow of the slurry and thereby improving the stability and coating effect of the slurry. Controlling the average degree of polymerization of the thickener within the above range improves the stability of the slurry, storage time, and coating uniformity during application.

[0054] The wetting agent is typically an alkyl surfactant, a silicone surfactant, a fluorine surfactant, or an ether surfactant. The amount of the wetting agent is preferably 0.5% or less, more preferably 0.2% or less, and preferably 0.01% or more, more preferably 0.03% or more of the coating weight. Controlling the amount of surfactant added within the above range can reduce the surface tension of the slurry on the porous membrane and improve the wetting or spreadability of the slurry. If the amount of surfactant added is 5% or more of the slurry weight, the wetting agent will penetrate the pores of the substrate, affecting the transport of lithium ions and the adhesion of inorganic particles to the substrate. As a result, powder will fall off the separator during the battery winding process, increasing the internal resistance of the battery and reducing its capacity.

[0055] According to the present invention, the rotation speed of the anchor blade may be 10 rpm to 30 rpm, for example, 10 rpm, 15 rpm, ... 30 rpm, the rotation speed of the dispersion disc may be 500 rpm to 1300 rpm, for example, 500 rpm, 600 rpm, ... 1200 rpm, 1300 rpm, and the stirring time may be 80 to 120 min, for example, 80 min, 90 min, ... 100 min, 120 min.

[0056] In this invention, the volume of inorganic particles and solvent is maintained at 3 / 5 to 3 / 4 of the volume of the double planetary stirred tank, for example, 3 / 5, 5 / 8, 29 / 40, or 3 / 4. The distance between the upper liquid level of the inorganic particles and solvent and the dispersion disk occupies 1 / 4 to 1 / 2 of the height of the double planetary stirred tank, for example, 1 / 4, 7 / 24, 11 / 24, or 1 / 2. By controlling the volume ratio and the distance between the liquid level and the dispersion disk within this range, the inorganic particles are uniformly dispersed in the solvent during the stirring process, thereby improving the stability of the slurry.

[0057] According to the present invention, the thickening slurry is passed through a high-speed disperser or grinder, and the temperature of the thickening slurry is strictly controlled between 15°C and 30°C, for example, 15°C, 16°C, 29°C, or 30°C. If the temperature is below 5°C, the colloidal particles aggregate to form micelles, which are unfavorable for dispersion in subsequent processes and can result in coating leaks on the film surface during the coating process. If the temperature is above 30°C, the steric hindrance formed by the colloidal particles is destroyed, diluting the slurry and reducing its stability. After the temperature of the semi-finished slurry is returned to room temperature, a binder and wetting agent are added, and the stirring speed of the anchor blade is controlled to 10 rpm to 50 rpm, for example, 10 rpm, 11 rpm, 49 rpm, or 50 rpm. If the stirring speed is lower than 10 rpm, the binder and wetting agent will not be uniformly dispersed in the slurry, resulting in a poor coating uniformity on the separator after application and reduced contact between the inorganic particles and the base film on the separator's longitudinal cross section, which will affect the separator's peel strength. If the stirring speed is higher than 50 rpm, the binder will be sheared into a film and a crust will form, resulting in an increase in large particles in the slurry, poor coating consistency, and reduced separator heat resistance. Furthermore, the presence of a large number of bubbles in the slurry will reduce the utilization rate of the slurry and increase costs.

[0058] The inorganic coating slurry may contain other components in addition to the above components. Examples of such components include dispersants and electrolyte dispersion inhibitors. The components are not particularly limited as long as they do not adversely affect the lithium battery. The optional components may be one or more, but the addition ratio should not exceed 5% of the slurry weight.

[0059] By controlling the formulation and process, such as the amount of each component added, the stirring speed in the slurry manufacturing process, and the material temperature in the dispersion process, the inorganic particles in the manufactured slurry are uniformly dispersed and the volume average particle diameter D50 スラリー The particle size is 0.01 to 2.5 μm, the inorganic particles in the slurry are suspended in a solvent, and the average absolute value of the Zeta potential is 0.025 to 0.3V.

[0060] Coating and drying process According to the present invention, the tension applied to the base film during the coating process can be controlled to 2.5 N / m / μm, 1.5 N / m / μm, 4.5 N / m / μm, or 5 N / m / μm. Setting the coating tension to accommodate base films of various thicknesses and widths can reduce base film elongation during high-speed coating. Controlling the difference between the coating roll speed and the coating speed during the coating process between -50 m / min and 50 m / min ensures better spreading of the slurry on the base film, preventing demulsification of the slurry under high-speed shear. Furthermore, it ensures adhesion between the inorganic particles while maintaining a high contact area between the inorganic particles and the base film surface. The drying process temperature per unit thickness of the coating is 20 to 50°C / μm, the oven intake and exhaust frequencies are 20 to 45 Hz, and the intake and exhaust frequencies are 6 Hz or less. Setting the oven temperature and intake / exhaust frequencies within this range allows for control of the drying speed of the slurry during the drying process, preventing the coating from cracking due to a drying speed that is too fast. It also allows the binder and thickener to fully harden, forming a consistent contact area and improving the separator's peel strength.

[0061] According to the present invention, the method for applying the slurry is not particularly limited, and the slurry can be applied by a coating method, a dipping method, etc. Examples of the coating method include a doctor blade method, a reverse roll method, a direct roll method, a microgravure roll method, an extrusion method, a spray method, and a spot coating method. In consideration of the uniformity of the thickness of the porous film, the microgravure roll method is preferably used for application.

[0062] According to the present invention, the drying method is not particularly limited, and drying methods such as hot air, low humidity air, vacuum drying, spray drying, and freeze drying can be selected.

[0063] A third aspect of the present invention provides a secondary battery including the battery separator according to the first aspect.

[0064] According to the present invention, the secondary battery may include a lithium ion battery and a sodium ion battery.

[0065] The separator and secondary battery manufactured by the separator manufacturing method have the same advantages as the separator described above, but detailed description thereof will be omitted here.

[0066] The present invention will be described below with reference to specific examples. Note that these examples are merely illustrative and do not limit the present invention in any way. Unless otherwise specified, all raw materials, reagents, methods, etc. used in the examples are conventional raw materials, reagents, and methods in the relevant technical field.

[0067] Peel strength test method A sample was cut using a 2.5 cm x 30 cm mold, and the sample was attached flat to a short steel ruler with double-sided tape attached. The sample was rolled back and forth three times on a press roll, and then peeled off 1 cm by hand. The sample was then fixed to a tensile tester and subjected to a 180° test at a tensile speed of 50 mm / min. The average of the three measurements was taken.

[0068] Thickness Test Method Cut a strip of coating width 20 cm x 10 cm, where n is a natural number greater than 2. Using a Mahr thickness gauge, select one point at 10 cm intervals and measure the thickness of the base film and the coating. The difference between the two is the coating thickness, and the average of all coating thicknesses is recorded as the average coating thickness.

[0069] Air permeability testing method The tests are carried out with reference to the requirements of JIS8117-2009.

[0070] The coated base film is cut along the TD direction to a width of 5cm or more. If the TD width of the coated finished sample is less than 5cm, it is detected using a small measuring head. Using an Oken air permeability tester, set the test time to 3s to test the air permeability of the base film and the coating film. The difference between the two is the coating air permeability. The average of all coating air permeabilities is recorded as the average coating air permeability. The ratio of the average coating air permeability to the average coating thickness is recorded as the air permeability per unit thickness of the coating.

[0071] Test method for needle puncture resistance The test is carried out with reference to ASTM D4833-00e1 or GB / T10004-2008.

[0072] A sample approximately 50 mm wide is cut from the film roll along the TD and placed under the sample table fixture for testing. The needle tip is a hemisphere with a diameter of 1.0 mm, and the needle tip travels at a speed of 1 mm / s. The needle puncture strength of the base film and the coating film is measured, and the difference between the two is taken as the coating needle puncture strength. The average value of all coating needle puncture strengths is recorded as the average coating needle puncture strength, and the ratio of the average coating needle puncture strength to the average coating thickness is recorded as the needle puncture strength per unit coating thickness.

[0073] Test method for contact rate between inorganic particles and base film in longitudinal section A 10 cm × 10 cm smooth inorganic coating film was prepared, and an electron microscope photograph of the longitudinal section was taken. The contact interfaces k1, k2, k3...k between the inorganic particles and the base film were identified. n Mark the contact interfaces k1, k2, k3...k on the photograph. n The lengths l1, l2, l3…l n , and measure the total length L of the contact area between the coating and the base film in the photograph. n The ratio of the total of the above to L is the contact rate between the inorganic particles and the base film in the vertical cross section. Example 1

[0074] Inorganic coating slurry manufacturing (1) Preparation of thickener stock solution: 95 kg of ultrapure water was placed in a stirring tank, the anchor blade rotation speed was set to 20 rpm, the anchor blade was started, and 5 kg of carboxymethylcellulose sodium (Dacel, 1220) powder, which serves as a thickener, was slowly added. After the addition was completed, the dispersion disk was started, and the dispersion disk rotation speed was set to 1200 rpm and the stirring time to 100 min, yielding 100 kg of thickener stock solution.

[0075] (2) Production of aluminum oxide stock solution: 52.9 kg of ultrapure water was sent to a double planetary type stirring tank, and the volume average particle diameter D50 無機粒子 35 kg of aluminum oxide with a particle size of 0.912 μm was slowly added, and the volume of the aluminum oxide and ultrapure water was maintained at 72.04% of the volume of the double planetary stirring tank, and the distance between the upper liquid level of the aluminum oxide and ultrapure water and the dispersion disc was maintained at 32.34% of the height of the double planetary stirring tank.The anchor blade rotation speed was set to 20 rpm, the dispersion disc rotation speed to 1000 rpm, and the stirring time was set to 15 minutes, yielding 87.9 kg of aluminum oxide stock solution.

[0076] (3) 7.5 kg of thickener stock solution was added to 87.9 kg of the above aluminum oxide stock solution, and a thickening slurry was obtained using the double planetary type stirring anchor blade rotation speed, dispersion disc rotation speed, and stirring time of step (2).

[0077] (4) The thickening slurry was placed in a high-speed dispersing mill, and the temperature of the thickening slurry was controlled at 17°C to obtain a semi-finished slurry. After the temperature of the semi-finished slurry was returned to room temperature, 4.3 kg of acrylate (Zeon Corporation; 900B) as a binder and 0.05 kg of wetting agent (Guangdong Guo Yuanxing Co., Ltd. TEGO202E) were added, and the mixture was stirred at 20 rpm for 30 minutes to obtain a finished slurry. The resulting finished slurry had a pH of 8.39, a viscosity of 64.1 mPa·s, and a volume average particle diameter D50 of 1.0 g. スラリー The average particle size was 0.897 μm, and the average Zeta potential of the slurry was −0.0871 V.

[0078] Separator manufacturing A 5 μm-thick polyethylene base film (manufactured by Nakazai Ricoh Co., Ltd., air permeability 126 s / 100 cc) was used. The coating tension was 5 N / m / μm. The coater speed and coating roll speed during the coating process were 120 m / min and 100 m / min, respectively. The finished slurry was applied to one side of the base film, and the coated separator was dried in an oven with an intake frequency of 27 Hz and an exhaust frequency of 30 Hz, respectively, and a drying temperature of 22 °C / μm, to obtain a coated film. Figure 1 shows an electron microscope image of the cross section in the thickness direction.

[0079] As a result of the measurement, the contact ratio k between the inorganic particles and the base film in the longitudinal section of the coated separator was 50.37%.

[0080] The peel strength was 204 N / m, the coating thickness was 2.9 μm, the needle puncture strength per unit thickness of the coating was 12.2 gf / μm, the separator air permeability was 157 s / 100 cc, and the coating air permeability per unit thickness was 10.7 s / 100 cc / μm.

[0081] Examples 2 to 6, Comparative Examples 1 to 4 The specific raw materials, manufacturing parameters, separator parameters, and characteristics of the remaining examples and comparative examples are shown in Table 1 and Table 2 below (the parts not described are the same as those in Example 1). Table 1 JPEG2026508035000002.jpg216×154Table 2 JPEG2026508035000003.jpg208×154

[0082] Analysis: From the above table, in Examples 1 to 6, by controlling the content of each component in the slurry, the percentage of the non-conductive particle stock solution in the volume of the tank, the percentage of the distance between the interface liquid level of the non-conductive particle stock solution and the dispersion disk in the tank height, the temperature of the dispersion material, and the coating process, making k always between 15% and 90% and A1×k≥A2, it was found that the separators produced had excellent peeling strength, a high increase in puncture strength, and a low increase in air permeability. On the other hand, in Comparative Examples 1 to 4, by adjusting the temperature of the dispersion material, the percentage of the distance between the interface liquid level of the non-conductive particle stock solution and the dispersion disk in the tank height, and the coating process respectively, to make k between 15% and 90% or A1×k < A2, the separators produced could not achieve all three of these characteristics simultaneously.

[0083] The above has shown and described the embodiments of the present invention. As can be understood, the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A base film; an inorganic coating provided on at least one surface of the base film, a contact rate k between the inorganic particles and the base film in a longitudinal section of the battery separator is 15% to 90%; The contact rate k, the air permeability A of the base film １ , and the air permeability A per unit thickness of the coating ２ The relationship between A １ × k ≧ A ２ where the air permeability A of the base film is １ The unit of is s / 100cc, and the air permeability A per unit thickness of the coating ２ The unit of the thickness is s / 100 cc / μm.

2. 2. The battery separator according to claim 1, wherein the battery separator has a peel strength of 30 N / m or more, a pin puncture strength per unit thickness of the coating of 6 gf / μm or more, and an air permeability per unit thickness of the coating of 20 s / 100 cc / μm or less.

3. the contact ratio k between the inorganic particles and the base film in the longitudinal section of the battery separator is 30% to 85%, and / or 2. The battery separator according to claim 1, wherein the battery separator has a peel strength of 50 N / m or more, an increase in pin puncture strength per unit coating thickness of 9 gf / μm or more, and an increase in air permeability per unit coating thickness of 15 s / 100 cc / μm or less.

4. the thickness of the base film is between 1 and 30 μm, and / or 2. The battery separator according to claim 1, wherein the air permeability of the base film is 40 to 350 s / 100 cc.

5. the inorganic particles are one or more selected from silicon dioxide, aluminum oxide, magnesium oxide, zirconium oxide, titanium oxide, calcium oxide, boehmite, aluminum nitride, boron nitride, barium sulfate, calcium fluoride, barium fluoride, and / or Volume average particle diameter D50 of the inorganic particles 無機粒子 The battery separator according to claim 1, wherein the thickness is 0.1 μm to 3 μm.

6. 2. The battery separator according to claim 1, wherein the inorganic coating has a thickness of 0.5 to 10 μm.

7. A method for producing a battery separator according to any one of claims 1 to 6, Step (1) of providing a base film; Step (2) of applying an inorganic coating slurry onto at least one side of the base film to obtain an inorganic coating; (3) drying the base film and the inorganic coating to obtain a battery separator; The method for producing the inorganic coating slurry in step (2) includes: 90 to 99 parts by weight of solvent is charged into a stirring tank, the rotation speed of the anchor blade is set to 10 to 30 rpm, the anchor blade is started, 1 to 10 parts by weight of thickener powder is added, and after the addition is completed, the dispersion disk is started, the rotation speed of the dispersion disk is set to 500 to 1300 rpm, and the stirring time is set to 80 to 120 minutes to obtain a thickener stock solution, Step (2-1) of sending 50 to 60 parts by weight of solvent to a double planetary stirring tank, adding 32 to 38 parts by weight of inorganic particles, maintaining the volume of the inorganic particles and solvent at 3 / 5 to 3 / 4 of the volume of the double planetary stirring tank, maintaining the distance between the upper liquid level of the inorganic particles and solvent and the dispersion disc at 1 / 4 to 1 / 2 of the height of the double planetary stirring tank, setting the rotation speed of the anchor blade in the double planetary stirring tank at 10 rpm to 30 rpm, the rotation speed of the dispersion disc at 500 rpm to 1300 rpm, and the stirring time at 10 min to 20 min to obtain an inorganic particle stock solution; Step (2-2) of adding 5 to 15 parts by weight of thickener stock solution to the inorganic particle stock solution, and setting the rotation speed of the anchor blade in the double planetary stirring tank to 10 to 30 rpm, the rotation speed of the dispersion disc to 500 to 1300 rpm, and the stirring time to 10 to 20 minutes to obtain a thickened slurry; the thickened slurry is put into a high-speed disperser or pulverizer, and in this process, the temperature of the thickened slurry is controlled at 15 to 30°C to obtain a semi-finished slurry; after the temperature of the semi-finished slurry is returned to room temperature, 2 to 10 parts by weight of a binder and 0.03 to 0.2 parts by weight of a wetting agent are added, and the mixture is stirred at a stirring rotation speed of 10 to 50 rpm for 20 to 40 minutes to obtain an inorganic coating slurry step (2-3); In the coating process of step (2), the tension applied to the base film per unit thickness and per unit width is controlled to be 2.5 to 5 N / m / μm, and the difference between the speed of the coating roll and the speed of the coater in the coating process is -50 to 50 m / min; In the drying process of step (3), the drying temperature per unit thickness of the coating is controlled to 20-50°C / μm, the intake and exhaust frequencies of the oven are controlled to 20-45 Hz, and the intake frequency-exhaust frequency is controlled to 6 Hz or less.

8. The parameters of the inorganic coating slurry in step (2) are pH 7 to 11, viscosity 5 to 200 mPa·s, and volume average particle diameter D50 スラリー is 0.01 to 2.5 μm, and the average absolute value of the Zeta potential is 0.025 to 0.3 V.

9. the thickener is one or more selected from carboxymethylcellulose, sodium carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, and / or the binder is one or more selected from acrylate, polyvinylidene fluoride, styrene butadiene rubber, polyacrylonitrile, polyvinyl alcohol, vinyl acetate; and / or 8. The manufacturing method according to claim 7, wherein the wetting agent is one or more selected from the group consisting of alkyl surfactants, silicon surfactants, fluorine surfactants, and ether surfactants.

10. A secondary battery, A secondary battery comprising the battery separator according to any one of claims 1 to 6.

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