Separation membrane for electrochemical elements and electrochemical elements containing the same

Abstract

The present invention relates to a separator for an electrochemical device, comprising: a porous polymer substrate; and a porous coating layer formed on at least one surface of the porous polymer substrate, the porous coating layer comprising an acrylic polymer binder, a copolymer binder, and inorganic particles, the copolymer binder having a weight average molecular weight of 40,000 to 80,000, and the copolymer binder and the inorganic particles being contained in a weight ratio of 1:93 to 1:20.

Description

[Technical Field]

[0001] This application claims priority based on Korean Patent Applications No. 10-2023-0035101 and No. 10-2023-0035102, respectively, filed with the Korean Intellectual Property Office on March 17, 2023, and the contents of those applications are incorporated into this application by reference.

[0002] The present invention relates to a separation membrane for electrochemical elements and an electrochemical element containing the same. [Background technology]

[0003] Electrochemical devices convert chemical energy into electrical energy using electrochemical reactions. Recently, lithium-ion batteries, which have high energy density and voltage, long cycle life, and can be used in various fields, are widely used.

[0004] A lithium secondary battery may include an electrode assembly made of a positive electrode, a negative electrode, and a separation membrane placed between the positive and negative electrodes, and the electrode assembly may be manufactured by housing the electrode assembly together with an electrolyte in a case. The separation membrane may include a porous coating layer containing a polymer binder and inorganic particles on at least one surface of a porous substrate. The inorganic particles can be linked to other inorganic particles by the polymer binder to form an interstitial volume, through which lithium ions can move. In addition to fixing the inorganic particles, the polymer binder can provide adhesion to the porous coating layer, which can then be bonded to the porous substrate and the electrodes, respectively.

[0005] On the other hand, such a separation membrane needs to maintain stability under high temperatures and wet conditions that may occur during the operation of a lithium secondary battery. [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The present invention aims to provide a separation membrane for electrochemical elements in which the rate of dimensional change is reduced in a high-temperature wet state, a method for manufacturing the same, and an electrochemical element including the separation membrane for electrochemical elements. [Means for solving the problem]

[0007] One aspect of the present invention provides a separation membrane for an electrochemical element, comprising a porous polymer substrate and a porous coating layer formed on at least one surface of the porous polymer substrate, wherein the porous coating layer comprises an acrylic polymer binder, a copolymer binder, and inorganic particles, the weight-average molecular weight of the copolymer binder being approximately 40,000 to 80,000, and the copolymer binder and the inorganic particles being present in a weight ratio of approximately 1:93 to 1:20.

[0008] The aforementioned acrylic polymer binders include (meth)acrylic acid, (meth)acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-amyl acrylate, isoamyl acrylate, n-ethylhexyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, and n-ethylhexyl methacrylate. It may contain one or more monomers selected from the group consisting of 2-ethylhexyl methacrylate, hydroxyethyl methacrylate, (meth)acrylonitrile butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, ethyl (meth)acrylate, methyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, lauryl (meth)acrylate, and tetradecyl (meth)acrylate as repeating units.

[0009] The copolymer binder may be obtained by copolymerizing two or more substances selected from the group consisting of polyacrylic acid, polyacrylamide, and polyvinyl alcohol.

[0010] The copolymer binder may be a copolymer of polyacrylic acid and polyacrylamide in a ratio of approximately 8:2 to 5:5.

[0011] The acrylic polymer binder has a particle shape with an average particle size (D50) of approximately 100 nm to 500 nm, while the copolymer binder may have a non-particle shape.

[0012] The porous coating layer may contain the inorganic particles in an amount of about 90% to 95% by weight relative to the total weight of the porous coating layer.

[0013] Based on the weight of the porous coating layer, the content of the acrylic polymer binder may be greater than the content of the copolymer binder.

[0014] The acrylic polymer binder and the copolymer binder may be present in a weight ratio of approximately 5:1 to 1.5:1.

[0015] Another aspect of the present invention provides an electrochemical element comprising a positive electrode, a negative electrode, and a separation membrane disposed between the positive electrode and the negative electrode, wherein the separation membrane is a separation membrane for an electrochemical element having the features described above.

[0016] The electrochemical element may be a lithium secondary battery.

[0017] The aforementioned electrochemical element is EC(ethylene The electrolyte may further contain a solvent mixed in a weight ratio of approximately 3 / 7 of (carbonate) / EMC (ethylmethyl carbonate).

[0018] Another aspect of the present invention provides a method for producing a separation membrane for an electrochemical element, comprising forming a porous polymer substrate and a porous coating layer formed on at least one surface of the porous polymer substrate, wherein the porous coating layer contains an acrylic polymer binder, a copolymer binder, and inorganic particles, the weight-average molecular weight of the copolymer binder is approximately 40,000 to 80,000, and the copolymer binder and the inorganic particles are present in a weight ratio of approximately 1:93 to 1:20.

[0019] The aforementioned acrylic polymer binder is (meth)acrylic acid, (meth)acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-amyl acrylate, isoamyl acrylate, n-ethylhexyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, n-ethylhexyl methacrylate, 2- The material may contain one or more monomers selected from the group consisting of ethylhexyl methacrylate, hydroxyethyl methacrylate, (meth)acrylonitrile butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, ethyl (meth)acrylate, methyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, lauryl (meth)acrylate, and tetradecyl (meth)acrylate as repeating units.

[0020] The copolymerization binder may be obtained by copolymerizing two or more substances selected from the group consisting of polyacrylic acid, polyacrylamide, and polyvinyl alcohol.

[0021] The copolymer binder may be obtained by copolymerizing polyacrylic acid and polyacrylamide in a ratio of approximately 8:2 to 5:5.

[0022] The acrylic polymer binder has a particle shape with an average particle size (D50) of approximately 100 nm to 500 nm, while the copolymer binder may have a non-particle shape.

[0023] The porous coating layer may contain the inorganic particles in an amount of approximately 90% to 95% by weight relative to the total weight of the porous coating layer.

[0024] The content of the acrylic polymer binder may be greater than the content of the copolymer binder, based on the weight of the porous coating layer.

[0025] The acrylic polymer binder and the copolymer binder may be included in a weight ratio of approximately 5:1 to 1.5:1.

[0026] Another aspect of the present invention provides a method for manufacturing an electrochemical element, comprising a positive electrode, a negative electrode, and a separation membrane disposed between the positive electrode and the negative electrode, wherein the separation membrane is a separation membrane for an electrochemical element according to the other aspect described above.

[0027] The electrochemical element may further contain an electrolyte containing a solvent mixed in a weight ratio of approximately 3 / 7 of EC / EMC. [Effects of the Invention]

[0028] The separation membrane for electrochemical elements according to the present invention can provide improved dimensional stability in both a dry state and a wet state impregnated with an electrolyte. For example, the separation membrane exhibits a thermal shrinkage rate of 5% or less in both the dry state and the wet state at high temperatures of approximately 130°C or higher, thereby preventing electrode exposure due to thermal shrinkage of the separation membrane. [Modes for carrying out the invention]

[0029] The following describes in more detail each component of the present invention so that it can be easily implemented by a person with ordinary skill in the art to which the present invention belongs. However, this is merely an example, and the scope of the rights of the present invention is not limited to the following.

[0030] As used herein, the term "including" is used to list materials, compositions, apparatus, and methods useful for the present invention, and is not limited to such listed examples.

[0031] As used herein, “approximately,” “abstractly,” and “substantially” are used to mean a range or similar meaning of numerical or degree, taking into account inherent tolerances of manufacturing and materials, and are used to prevent infringers from unfairly exploiting disclosures that refer to precise or absolute numerical values ​​provided to aid in understanding the invention.

[0032] As used herein, "electrochemical elements" may refer to primary batteries, secondary batteries, supercapacitors, and the like.

[0033] As used herein, "wet state" may mean a state in which the separation membrane is impregnated with at least a portion of the electrolyte, while "dry state" may mean a dry state in which the separation membrane is not impregnated with the electrolyte.

[0034] As used herein, "durability" may refer to the property of a binder that does not swell or deform when in contact with an electrolyte, and that exhibits adhesive strength or mechanical strength as an inherent physical property.

[0035] The separation membrane used in lithium secondary batteries is manufactured by applying a porous coating layer containing a polymer binder and inorganic particles to at least one surface of a porous substrate. This prevents thermal shrinkage of the porous polymer substrate, and the separation membrane including the porous coating layer generally exhibits excellent dimensional stability in a dry state without electrolyte. However, in a wet state where the separation membrane is impregnated with electrolyte, the polymer binder may swell due to the electrolyte, or the separation membrane may be exposed to temperatures of, for example, about 130°C or higher due to the operation of the lithium secondary battery containing the separation membrane, which can reduce the adhesive strength of the polymer binder. In such a high-temperature wet state, the adhesive strength of the porous coating layer decreases, causing the separation membrane to shrink significantly. For example, cylindrical batteries, in which an electrode assembly is wound and inserted into a case while the electrode assembly is under tension, require relatively less adhesive strength between the electrodes and the separation membrane compared to pouch-type batteries. As a result, the polymer binder content is lower, leading to a problem of further reduced dimensional stability in a wet state.

[0036] In one embodiment of the present invention, a separation membrane is provided that exhibits excellent dimensional stability under high temperature and wet conditions while maintaining a relatively low content of polymer binder in the porous coating layer.

[0037] A separation membrane according to one specific example of the present invention comprises a porous polymer substrate and a porous coating layer formed on at least one surface of the porous polymer substrate, wherein the porous coating layer comprises an acrylic polymer binder, a copolymer binder, and inorganic particles, the weight-average molecular weight of the copolymer binder is approximately 40,000 to 80,000, and the copolymer binder and the inorganic particles are present in a weight ratio of approximately 1:93 to 1:20, thereby providing a separation membrane for electrochemical elements.

[0038] The porous polymer substrate is a porous membrane in which a plurality of pores are formed, and may electrically insulate the positive and negative electrodes of an electrochemical element to prevent short circuits. For example, if the electrochemical element is a lithium secondary battery, the separation membrane made of the porous polymer substrate may be an ion-conducting barrier that blocks electrical contact between the positive and negative electrodes while allowing lithium ions to pass through. At least a portion of the pores can form a three-dimensional network that connects the surface and interior of the porous polymer substrate, allowing fluids to pass through the porous polymer substrate through the pores.

[0039] The porous polymer substrate can be made of a material that is physically and chemically stable with respect to an electrolyte, which is an organic solvent. For example, the porous polymer substrate may include, but is not limited to, resins such as polyethylene, polypropylene, polybutylene and other polyolefins, polyvinyl chloride, polyethylene terephthalate, polycycloolefin, polyethersulfone, polyamide, polyimide, polyimidamide, nylon, polytetrafluoroethylene, and copolymers or mixtures thereof. For example, a polyolefin resin can be used as the porous polymer substrate. Polyolefin resins can be processed to a relatively thin thickness and are easy to apply coating slurry to, making them suitable for the manufacture of electrochemical elements with higher energy density.

[0040] The porous polymer substrate may have a single-layer or multi-layer structure. The porous polymer substrate may include two or more polymer resin layers with different melting points (Tm) and may provide a shutdown function in the event of a high-temperature runaway of the battery. For example, the porous polymer substrate may include a polypropylene layer with a relatively high melting point and a polyethylene layer with a relatively low melting point. For example, the porous polymer substrate may have a three-layer structure in which polypropylene, polyethylene, and polypropylene are laminated in that order. The polyethylene layer can shut down the pores by melting as the battery temperature rises above a predetermined temperature, thereby preventing thermal runaway of the battery.

[0041] The thickness of the porous polymer substrate may be approximately 1 μm to 100 μm. For example, the thickness of the porous polymer substrate may be approximately 10 μm to 90 μm, 20 μm to 80 μm, 30 μm to 70 μm, or 40 μm to 60 μm. For example, the thickness of the porous polymer substrate may be approximately 1 μm to 30 μm. Alternatively, the thickness of the porous polymer substrate may be approximately 5 μm to 15 μm, or approximately 8 μm to 13 μm. By adjusting the thickness of the porous polymer substrate within the above range, a separation membrane manufactured using the porous polymer substrate can electrically insulate the positive and negative electrodes of the electrochemical element while minimizing the volume of the electrochemical element and increasing the amount of active material contained in the electrochemical element.

[0042] The porous polymer substrate may contain pores with an average diameter of approximately 0.01 μm to 1 μm. For example, the diameter of the pores contained in the porous polymer substrate may be approximately 0.01 μm to 0.09 μm, 0.02 μm to 0.08 μm, 0.03 μm to 0.07 μm, or 0.04 μm to 0.06 μm. Alternatively, the size of the pores may be approximately 0.02 μm to 0.06 μm. By adjusting the size of the pores in the porous polymer substrate within the above range, the air permeability and ionic conductivity of the entire separation membrane produced can be adjusted.

[0043] In one embodiment, the porous polymer substrate may have an air permeability of approximately 10 s / 100 cc to 100 s / 100 cc. For example, the air permeability of the porous polymer substrate may be approximately 10 s / 100 cc to 90 s / 100 cc, 20 s / 100 cc to 80 s / 100 cc, 30 s / 100 cc to 70 s / 100 cc, or 40 s / 100 cc to 60 s / 100 cc. Alternatively, the air permeability of the porous polymer substrate may be approximately 50 s / 100 cc to 70 s / 100 cc. When the air permeability of the porous polymer substrate is within the above range, the air permeability of the manufactured separation membrane can be provided within a range suitable for ensuring the output and cycle characteristics of the electrochemical element.

[0044] On the other hand, the air permeability (s / 100cc) refers to the time (in seconds) it takes for 100cc of air to pass through a porous polymer substrate or separation membrane of a predetermined area under a constant pressure. The air permeability is defined in the ASTM The air permeability can be measured using a Gurley densometer according to D 726-58, ASTM D726-94, or JIS-P8117. For example, using a Gurley 4110N instrument, the air permeability can be measured using air at a pressure of 0.304 kPa or 1.215 kN / m³. 2 Under the pressure of water, 100cc of air will fill 1 square inch (or 6.54 cm) 2 It is possible to measure the time it takes for a sample to pass through. For example, using Asahi Seiko's EG01-55-1MR, it is possible to measure the time it takes for 100cc of air to pass through a 1 square inch sample at room temperature and under constant pressure in 4.8 inches of water.

[0045] The porous polymer substrate may have a porosity of approximately 10 vol% to 60 vol%. For example, the porosity of the porous polymer substrate may be approximately 15 vol% to 55 vol%, 20 vol% to 50 vol%, 25 vol% to 45 vol%, or 30 vol% to 40 vol%. Alternatively, the porosity of the porous polymer substrate may be approximately 30 vol% to 50 vol%. When the porosity of the porous polymer substrate is within the above range, the ionic conductivity of the manufactured separation membrane can be provided within a range suitable for ensuring the output and cycle characteristics of the electrochemical element.

[0046] The porosity refers to the volume ratio of pores to the total volume of the porous polymer substrate. The porosity can be measured by methods known in the art. For example, BET (Brunauer) using nitrogen gas adsorption. It can be measured by the Emmett-Teller method, capillary flow porometry, or water or mercury osmosis.

[0047] The porous coating layer is formed on at least one surface of the porous polymer substrate and may contain an acrylic polymer binder, a copolymer binder, and inorganic particles.

[0048] The porous coating layer can be formed by coating at least one surface of a porous polymer substrate with a coating slurry containing an acrylic polymer binder, a copolymer binder, inorganic particles, and a dispersion medium. For example, the separation membrane can be manufactured by applying the coating slurry to at least one surface of a porous polymer substrate, then drying it to remove the dispersion medium. The porous coating layer contains interstitial volumes in which the inorganic particles, etc., are linked by the acrylic polymer binder and the copolymer binder, and adheres to the porous polymer substrate while allowing lithium ions to pass through, thereby preventing thermal shrinkage of the porous polymer substrate.

[0049] The coating slurry contains a dispersion medium that can dissolve or disperse at least a portion of the acrylic polymer binder or copolymer binder, and disperse inorganic particles. The coating slurry can be used in which the polymer binder and inorganic particles are uniformly dispersed by adjusting the type and content of the dispersion medium. For example, the dispersion medium may be one selected from the group consisting of water, ethanol, acetone, isopropyl alcohol (IPA), dimethylacetamide (DMAc), dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), acetonitrile, and combinations thereof. In one embodiment, the dispersion medium may be water. Using the above-described types of dispersion medium, a porous coating layer in which inorganic particles are uniformly dispersed can be formed.

[0050] The coating slurry may have a viscosity of approximately 100 cps to 1,000 cps. For example, the viscosity of the coating slurry may be approximately 200 cps to 900 cps, 300 cps to 800 cps, 400 cps to 700 cps, or 500 cps to 600 cps. Alternatively, the viscosity of the coating slurry may be approximately 300 cps to 800 cps.

[0051] The coating slurry may further contain additives such as dispersants, surfactants, defoamers, flame retardants, and wetting agents to improve dispersibility and flame retardancy, and to improve the uniformity of the porous coating layer formed. For example, the dispersant may contain one or more selected from the group consisting of oil-soluble polyamines, oil-soluble amine compounds, fatty acids, fatty alcohols, sorbitan fatty acid esters, tannic acid, pyrogallic acid, and polyacrylic acid. By using the above-mentioned types of dispersants, the stability of the coating slurry can be improved, and the uniformity of the porous coating layer formed by the coating slurry can be ensured.

[0052] Based on the total weight of the coating slurry, the additive may be present in an amount of approximately 0% to 5% by weight. For example, the content of the additive may be approximately 0.01% to 4% by weight, 0.1% to 3% by weight, or 1% to 2% by weight. Alternatively, the content of the additive may be approximately 3% to 5% by weight. By adjusting the content of the additive within the above range, uniform dispersion and stability of the inorganic particles contained in the coating slurry can be achieved.

[0053] The dispersion medium contained in the coating slurry may be removed by drying or heating after the formation of the porous coating layer. For example, the porous coating layer may contain the dispersion medium at a concentration of approximately 5 ppm or less. In one embodiment, the porous coating layer may consist of an acrylic polymer binder, a copolymer binder, and inorganic particles. During the process of removing the dispersion medium, multiple pores may be formed on the surface and inside the porous coating layer. These pores may include interstitial volumes formed between the inorganic particles, forming a three-dimensional network through which fluids can pass.

[0054] The thickness of the porous coating layer may be approximately 1 μm to 15 μm. For example, the thickness of the porous coating layer may be approximately 2 μm to 14 μm, 3 μm to 13 μm, 4 μm to 12 μm, 5 μm to 11 μm, 6 μm to 10 μm, or 7 μm to 9 μm. Alternatively, the thickness of the porous coating layer may be approximately 1 μm to 5 μm. By adjusting the thickness of the porous coating layer within the above range, shrinkage of the porous polymer substrate can be minimized, and stable adhesion to the porous polymer substrate can be achieved.

[0055] The acrylic polymer binder can bind inorganic particles and the like contained in the porous coating layer, thereby imparting adhesive strength to the porous coating layer. The acrylic polymer binder includes (meth)acrylic acid, (meth)acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-amyl acrylate, isoamyl acrylate, n-ethylhexyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, and n-ethylhexyl methacrylate. It may contain one or more monomers selected from the group consisting of 2-ethylhexyl methacrylate, hydroxyethyl methacrylate, (meth)acrylonitrile butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, ethyl (meth)acrylate, methyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, lauryl (meth)acrylate, and tetradecyl (meth)acrylate as repeating units.

[0056] For example, the acrylic polymer binder may contain one or more selected from the group consisting of polyacrylic acid, methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, ethylhexyl acrylate, methyl methacrylate, styrene-butadiene rubber, nitrile-butadiene rubber, acrylonitrile-butadiene rubber, and acrylonitrile-butadiene-styrene rubber.

[0057] The acrylic polymer binder may be in the form of particles. For example, the acrylic polymer binder may be spherical or elliptical, but is not limited to these. The acrylic polymer binder may have an average particle size (D50) of about 100 nm to 500 nm. For example, the acrylic polymer binder may have an average particle size (D50) of about 150 nm to 450 nm, 200 nm to 400 nm, or 250 nm to 350 nm. Alternatively, the acrylic polymer binder may be spherical particles with an average particle size (D50) of about 250 nm to 400 nm. By adjusting the particle size of the acrylic polymer binder particles within the above range, it is possible to simultaneously ensure the lithium ion migration path and the adhesion of the porous coating layer to the porous polymer substrate.

[0058] The acrylic polymer binder can contribute to the dry adhesion strength, which is the adhesion strength of the porous coating layer in a dry state, and the copolymer binder can contribute to the wet adhesion strength, which is the adhesion strength of the porous coating layer in a wet state. The copolymer binder may be physically or chemically more stable in the electrolyte than the acrylic polymer binder, but its adhesion strength does not decrease even in a wet state, maintaining the adhesion of the porous coating layer to the porous polymer substrate in a wet state and reducing the thermal shrinkage of the porous polymer substrate.

[0059] The copolymer binder may be obtained by copolymerizing two or more substances selected from the group consisting of polyacrylic acid (PAA), polyacrylamide (PAM), and polyvinyl alcohol (PVA). For example, the copolymer binder may be obtained by randomly copolymerizing two or more substances selected from the group consisting of polyacrylic acid, polyacrylamide, and polyvinyl alcohol. In one embodiment, the copolymer binder may be a copolymer of polyacrylic acid and polyacrylamide. In the copolymer binder, the polyacrylic acid exhibits durability to the electrolyte while forming bonds between inorganic particles, etc. The polyacrylamide exhibits a higher modulus value than the polyacrylic acid, further improving the durability of the copolymer binder to the electrolyte and allowing the copolymer binder to maintain its shape even in the electrolyte.

[0060] When the copolymer binder is a copolymer of polyacrylic acid and polyacrylamide, the copolymer binder may be obtained by copolymerizing polyacrylic acid and polyacrylamide in a ratio of approximately 8:2 to 5:5. For example, the copolymer binder may be obtained by copolymerizing polyacrylic acid and polyacrylamide in a ratio of approximately 8:2, 7:3, 6:4, or 5:5. Alternatively, the copolymer binder may be obtained by copolymerizing polyacrylic acid and polyacrylamide in a ratio of approximately 7:3 to 5:5. By copolymerizing polyacrylic acid and polyacrylamide in the above ratios, it is possible to ensure durability against the electrolyte while securing interstitial volume due to the binding of inorganic particles, etc., contained in the porous coating layer.

[0061] On the other hand, the copolymer binder may be in a non-particulate form. The non-particulate form may encompass atypical shapes that are not spherical or elliptical. A non-particulate copolymer binder can form bonds between inorganic particles and bonds between inorganic particles and the acrylic polymer particles, thereby imparting adhesive strength to the porous coating layer.

[0062] Furthermore, the weight-average molecular weight (Mw) of the copolymer binder may be between approximately 40,000 and 80,000. For example, the weight-average molecular weight of the copolymer binder may be between approximately 45,000 and 75,000, between 50,000 and 70,000, or between 55,000 and 65,000. Alternatively, the weight-average molecular weight of the copolymer binder may be between approximately 60,000 and 70,000. By adjusting the weight-average molecular weight of the copolymer binder within the above range, structural deformation of the copolymer binder due to the electrolyte can be prevented, and the thermal shrinkage rate of the separation membrane in the wet state can be reduced, while keeping the viscosity of the coating slurry below 1000 cps.

[0063] The weight-average molecular weight of the copolymer binder is determined by gel permeation chromatography (GPC). Schematics (PL GPC220, Agilent Technologies) can be used to measure the weight-average molecular weight. For example, the weight-average molecular weight can be measured using PL Olexis (Polymer Measurements can be performed using an Agilent High Temperature RI detector with a column from Laboratories (column temperature 160°C), TCB (Trichlorobenzene) as the solvent, a sample concentration of 1.0 mg / mL, a flow rate of 1.0 mL / min, and an injection volume of 200 μL (corrected with a cubic function, reference: Polystyrene).

[0064] The copolymer binder and the inorganic particles may be present in a weight ratio of approximately 1:93 to 1:20. For example, the weight ratio of the copolymer binder to the inorganic particles may be 1:93, 1:92, 1:91, 1:90, 1:85, 1:80, 1:75, 1:70, 1:65, 1:60, 1:55, 1:50, 1:45, 1:40, 1:35, 1:30, 1:25, or 1:20. Alternatively, the weight ratio of the copolymer binder to the inorganic particles may be approximately 1:93 to 1:46. Within the range described above, a separation membrane suitable for cylindrical batteries can be manufactured, which exhibits reduced thermal shrinkage due to the maintenance of adhesive strength in a wet state.

[0065] Based on the total weight of the porous coating layer, the content of the acrylic polymer binder can be greater than the content of the copolymer binder. The acrylic polymer binder and the copolymer binder can be included in a weight ratio of about 5:1 to 1.5:1. For example, the weight ratio of the acrylic polymer binder to the copolymer binder can be about 5:1, 4.5:1, 4:1, 3.5:1, 3:1, 2.5:1, 2:1, or 1.5:1. By adjusting the content of the binder and the like within the above-mentioned range, a separator suitable for a cylindrical battery can be manufactured, in which both the thermal shrinkage rate in the dry state and the thermal shrinkage rate in the wet state are reduced.

[0066] In terms of the inorganic particles, those with electrochemical stability can be used. The inorganic particles are not particularly limited as long as no oxidation and / or reduction reactions occur within the operating voltage range of the electrochemical device (e.g., 0 to 5 V based on Li / Li + ). For example, when using inorganic particles with a high dielectric constant as the inorganic particles, it can contribute to an increase in the dissociation degree of electrolyte salts in the liquid electrolyte, such as lithium salts, and improve the ionic conductivity of the electrolyte solution. Due to the reasons described above, the inorganic particles can include high-dielectric-constant inorganic particles with a dielectric constant of about 5 or more, for example, about 10 or more. Non-limiting examples of inorganic particles with a dielectric constant of about 5 or more include BaTiO3, Pb(Zr,Ti)O3 (PZT), Pb 1-x La x Zr 1-y Ti y O3 (PLZT, 0 < x < 1, 0 < y < 1), Pb(Mg 1 / 3 Nb 2 / 3 )O3 - PbTiO3 (PMN - PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, Al(OH)3, SiC, AlOOH, TiO2, or mixtures thereof, etc.

[0067] In addition, as the inorganic particles, inorganic particles having lithium ion conduction ability, that is, those containing lithium element but not storing lithium and having a function of moving lithium ions can be used. Non-limiting examples of inorganic particles having lithium ion conduction ability include lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z (PO4)3, 0 < x < 2, 0 < y < 1, 0 < z < 3), (LiAlTiP) x O y -based glasses such as 14Li2O - 9Al2O3 - 38TiO2 - 39P2O5 (0 < x < 4, 0 < y < 13), lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), lithium germanium thiophosphate such as Li 3.25 Ge 0.25 P 0.75 S4 (Li x Ge y P z [[ID=3​​​​​​​​​​​​​​​​​​​​​Furthermore, the inorganic particles used may be flame-retardant inorganic particles that can impart flame retardancy to the separation membrane or prevent a rapid rise in temperature inside the electrochemical element. Non-limiting examples of flame-retardant inorganic particles include Sb2O3, Sb2O4, Sb2O5, SrTiO3, SnO2, CeO2, MgO, Mg(OH)2, NiO, CaO, ZnO, Zn2SnO4, ZnSnO3, ZnSn(OH)6, ZrO2, Y2O3, SiO2, Al2O3, AlOOH, Al(OH)3, SiC, TiO2, H3BO3, HBO2, and mixtures thereof.

[0069] The average particle size (D50) of the inorganic particles may be between approximately 50 nm and 5,000 nm. For example, the average particle size (D50) of the inorganic particles may be between approximately 100 nm and 4,500 nm, 200 nm and 4,000 nm, 300 nm and 3,000 nm, 400 nm and 2,000 nm, or 500 nm and 1,000 nm. If the average particle size of the inorganic particles is less than approximately 50 nm, the specific surface area increases, requiring more polymer binder for bonding between the inorganic particles, which is disadvantageous in terms of electrical resistance. If the average particle size of the inorganic particles exceeds approximately 5,000 nm, the uniformity of the coating layer surface decreases, which may induce damage to the porous polymer substrate or electrode during lamination.

[0070] Furthermore, the aspect ratio of the inorganic particles may be approximately 1 to 2. For example, the aspect ratio of the inorganic particles may be approximately 1.1 to 1.9, 1.2 to 1.8, 1.3 to 1.7, or 1.4 to 1.6. By adjusting the aspect ratio of the inorganic particles within the above range, the movement of the polymer binder through the voids between the inorganic particles is facilitated, and ultimately a porous coating layer containing interstitial volume that allows lithium ions to move can be formed.

[0071] The BET (Brunauer-Emmett-Teller) specific surface area of ​​the aforementioned inorganic particles is approximately 5 m². 2 / g or more 25m 2It may be less than / g. For example, the BET specific surface area of ​​the inorganic particles is approximately 6 m². 2 / g or more 24m 2 / g or less, 7m 2 / g or more 23m 2 / g or less, 8m 2 / g or more 22m 2 / g or less, 9m 2 / g or more 21m 2 / g or less, 10m 2 / g or more 20m 2 / g or less, 11m 2 / g or more 19m 2 / g or less, 12m 2 / g or more 18m 2 / g or less, 13m 2 / g or more 17m 2 / g or less, or 14m 2 / g or more 26m 2 It may be less than / g. By adjusting the BET specific surface area of ​​the inorganic particles within the range described above, the movement of the polymer binder due to the voids between the inorganic particles can be controlled.

[0072] The porous coating layer may contain inorganic particles in an amount of about 90% to 95% by weight relative to the total weight of the porous coating layer. For example, the porous coating layer may contain inorganic particles in an amount of about 90% to 95% by weight, 91% to 92% by weight, or 93% to 94% by weight. Alternatively, the porous coating layer may contain inorganic particles in an amount of about 92% to 94% by weight. By adjusting the content of inorganic particles within the above ranges, a separation membrane having mechanical strength and thermal properties suitable for cylindrical batteries can be manufactured.

[0073] In the aforementioned separation membrane, the loading amount of the porous coating layer relative to the area of ​​the porous polymer substrate is approximately 1.0 g / m². 2 More than 6.0g / m 2 The following is possible. For example, the loading amount of the porous coating layer is approximately 1.5 g / m². 2 More than 5.5g / m 2 Below 2.0g / m 2 More than 5.0g / m 2 Below 2.5g / m2 More than 4.5g / m 2 The following, or 3.0 g / m 2 More than 4.0g / m 2 The following is possible: In one embodiment, the loading amount of the porous coating layer is approximately 5.5 g / m². 2 More than 6.0g / m 2 The following is possible. By adjusting the loading amount of the porous coating layer within the range described above, the durability of the separation membrane against the electrolyte can be ensured.

[0074] The separation membrane for the electrochemical element may have an air permeability of approximately 50 s / 100 cc to 150 s / 100 cc. For example, the air permeability of the separation membrane may be approximately 60 s / 100 cc to 140 s / 100 cc, 70 s / 100 cc to 130 s / 100 cc, 80 s / 100 cc to 120 s / 100 cc, or 90 s / 100 cc to 110 s / 100 cc. In one embodiment, the air permeability of the separation membrane may be approximately 100 s / 100 cc to 120 s / 100 cc. When the air permeability of the separation membrane is within the above range, the output, stability, and cycle characteristics of the electrochemical element can be ensured.

[0075] On the other hand, the thermal shrinkage rate of the separation membrane for the electrochemical element may be about 10% or less. For example, the thermal shrinkage rate of the separation membrane in a dry state may be about 5% or less, and the thermal shrinkage rate in a wet state may be about 10% or less. In one embodiment, the thermal shrinkage rate of the separation membrane in a dry state may be the dimensional change rate based on exposure to 200°C for 30 minutes, and the thermal shrinkage rate in a wet state may be the dimensional change rate based on exposure to 135°C for 30 minutes while the separation membrane is impregnated in an electrolyte. In one embodiment, the thermal shrinkage rate in a dry state may be less than about 5%, and the thermal shrinkage rate in a wet state may be 5% or less.

[0076] When a secondary battery cell is manufactured using the aforementioned electrochemical element separation membrane, the secondary battery cell may have an electrical resistance of approximately 0.5 Ohm to 1.5 Ohm. For example, the electrical resistance of the secondary battery cell may be approximately 0.6 Ohm to 1.4 Ohm, 0.7 Ohm to 1.3 Ohm, 0.8 Ohm to 1.2 Ohm, or 0.9 Ohm to 1.1 Ohm. In one embodiment, the electrical resistance of the secondary battery cell may be approximately 0.6 Ohm to 0.8 Ohm.

[0077] Another specific example of the present invention provides an electrochemical element comprising a positive electrode, a negative electrode, and a separation membrane interposed between the positive electrode and the negative electrode, wherein the separation membrane is the separation membrane for the electrochemical element of the specific example described above. The electrochemical element can be manufactured by inserting an electrode assembly comprising the positive electrode, the negative electrode, and the separation membrane interposed between the positive electrode and the negative electrode into a case or pouch and sealing it. Before sealing the case or pouch, an electrolyte can be poured in to impregnate the electrode assembly with the electrolyte. The shape of the case or pouch is not limited. For example, the electrochemical element may be a cylindrical, rectangular, coin-type, or pouch-type lithium secondary battery.

[0078] The positive electrode and the negative electrode may be coated with an electrode active material applied and dried on at least one surface of their respective current collectors. The current collector may be made of a conductive material that does not induce a chemical change in the electrochemical element. For example, the positive electrode current collector may be made of aluminum, nickel, titanium, calcined carbon, stainless steel, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc., but is not limited to these. For example, the negative electrode current collector may be made of copper, nickel, titanium, calcined carbon, stainless steel, or copper or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc., but is not limited to these. The current collector may be in various forms such as a thin metal sheet, film, foil, net, porous material, or foam.

[0079] The positive electrode includes a positive electrode current collector and a positive electrode active material layer containing a positive electrode active material, a conductive material, and a binder resin on at least one surface of the current collector. The positive electrode active material includes layered compounds such as lithium manganese composite oxides (LiMn2O4, LiMnO2, etc.), lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), and compounds substituted with one or more transition metals; chemical formula Li 1+x Mn 2-x O4 (where x is 0 to 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7; chemical formula LiNi 1-x M x O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3), Ni-site type lithium nickel oxides represented by this formula; chemical formula LiMn 1-x M[[ID=1十一]] x O2 (where M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 to 0.1) or lithium manganese composite oxides represented by Li2Mn3MO8 (where M = Fe, Co, Ni, Cu, or Zn); LiMn2O4 in which a part of the chemical formula Li is substituted with an alkaline earth metal ion; disulfide compounds; one or a mixture of two or more of Fe2(MoO4)3 may be included.

[0080] <00,00357>The negative electrode includes a negative electrode current collector and a negative electrode active material layer containing a negative electrode active material, a conductive material, and a binder resin on at least one surface of the current collector. The negative electrode uses, as the negative electrode active material, carbon such as lithium metal oxide, graphitizable carbon, graphite-based carbon; LixFe2O3 (0 ≤ x ≤ 1), Li x WO2 (0 ≤ x ≤ 1), Si, SiO x (0 < x < 2), silicon-based materials such as SiC, Si alloys; Sn x Me<( 1-x Me’ y O<(000007)7>(Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8), etc. metal composite oxides; lithium metal; lithium alloy; tin-based alloy; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4 and Bi2O5; conductive polymers such as polyacetylene; Li-Co-Ni-based materials; one or more mixtures selected from titanium oxide may be included.

[0081] The conductive material may be any one selected from the group consisting of graphite, carbon black, carbon fiber or metal fiber, metal powder, conductive whisker, conductive metal oxide, carbon nanotube, activated carbon, and polyphenylene derivative, or a mixture of two or more of these conductive materials. The carbon nanotube has a cylindrical form with a nanosize diameter of a graphite sheet and has a sp bonding structure, and exhibits conductor or semiconductor characteristics depending on the angle and structure of the graphite sheet being wound. Carbon nanotubes can be classified into single-walled carbon nanotubes (SWCNT), double-walled carbon nanotubes (DWCNT), and multi-walled carbon nanotubes (MWCNT) according to the number of bonding layers forming the wall, and these carbon nanotubes can be appropriately selected according to the use of the dispersion. For example, it may be any one selected from the group consisting of natural graphite, artificial graphite, super-p, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black, denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium oxide, or a mixture of two or more of these conductive materials. sheet) has a cylindrical form with a nanosize diameter and has a sp 2 bonding structure, and represents conductor or semiconductor characteristics according to the angle and structure of the graphite sheet being wound. Carbon nanotubes can be classified into single-walled carbon nanotubes (SWCNT, single-walled carbon nanotube), double-walled carbon nanotubes (DWCNT, double-walled carbon nanotube) and multi-walled carbon nanotubes (MWCNT, multi-walled carbon nanotube) according to the number of bonding layers forming the wall, and these carbon nanotubes can be appropriately selected according to the use of the dispersion. For example, it may be any one selected from the group consisting of natural graphite, artificial graphite, super-p, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black, denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium oxide, or a mixture of two or more of these conductive materials.

[0082] As the binder resin, a binder resin commonly used for electrodes of electrochemical elements may be used. Non-limiting examples of the binder resin include polyvinylidene fluoride-hexafluoropropylene and polyvinylidene trichloroethylene. Fluoride-cotrichloroethylene, polymethyl methacrylate, polyethylhexyl acrylate Polyacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyethylene oxide, polyarylate, cellulose acetate cellulose acetate butyrate, cellulose acetate propionic acid Acetylpropionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxymethylcellulose. Examples include methyl cellulose, but are not limited to these.

[0083] The aforementioned electrolyte is A + B - A salt with a structure like this,+ is Li + , Na + , K + and contains ions consisting of alkali metal cations such as these or combinations thereof, and B - is PF6 - , BF4 - , Cl - , Br - , I - , ClO4 - , AsF6 - , CH3CO2 - , CF3SO3 - , N(CF3SO2)2 - , C(CF2SO2)3 - and salts containing ions consisting of anions such as these or combinations thereof can be dissolved or dissociated in an organic solvent consisting of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), gamma-butyrolactone (γ-butyrolactone) or mixtures thereof.

[0084] For example, the electrolyte may contain a solvent with a weight ratio of EC / EMC of about 3 / 7, and the dimensional stability of the separation membrane according to the specific example can be maximized.

[0085] The electrochemical element including the electrode assembly can be a lithium secondary battery. The battery may be used as a unit cell, and can be used as a battery module including the unit cell, a battery pack including the battery module, and a device including the battery pack as a power source. Examples of the device include small devices such as computers, mobile phones, and power tools, and electric vehicles (EVs) and hybrid electric vehicles that are powered by an electric motor. tool), and devices such as electric vehicles (Electric Vehicle, EV) and hybrid electric vehicles (Hybrid Electric Vehicle (HEV), Plug-in Hybrid Electric Vehicle Examples include, but are not limited to, electric vehicles (including PHEVs); electric two-wheeled vehicles (including e-bikes and e-scooters); electric golf carts; and medium- and large-sized devices such as power storage systems.

[0086] Another specific example of the present invention provides a method for manufacturing a separation membrane for an electrochemical element, which includes the step of forming a porous coating layer containing an acrylic polymer binder, a copolymer binder, and inorganic particles on at least one surface of a porous polymer substrate. Any content that overlaps with the description of the separation membrane for the electrochemical element described above will be replaced by the description of the aforementioned specific example.

[0087] The step of forming the porous coating layer may include preparing a coating slurry containing an acrylic polymer binder, a copolymer binder, inorganic particles, and a dispersion medium, and applying the coating slurry to a porous polymer substrate and drying it.

[0088] The step of forming the porous coating layer may further include a step of applying corona discharge treatment to at least one surface of the porous polymer substrate before applying the coating slurry to the porous polymer substrate. The step of applying corona discharge treatment to at least one surface of the porous polymer substrate prevents a decrease in the bonding strength between the surface of the porous polymer substrate and the surface of the porous coating layer at a temperature higher than a predetermined temperature, and prevents a decrease in the bonding strength between the surface of the porous polymer substrate and the surface of the porous coating layer due to electrolytes.

[0089] The corona discharge treatment may also be performed by treating at least one surface of the porous polymer substrate in air with a voltage of approximately 0.1kV to 10kV. For example, the corona discharge treatment may be performed in air with a voltage of approximately 0.2kV to 9kV, 0.3kV to 8kV, 0.4kV to 7kV, 0.5kV to 6kV, 0.6kV to 5kV, 0.7kV to 4kV, 0.8kV to 3kV, 0.9kV to 2kV, or 1.0kV to 2kV. In one embodiment, the corona discharge treatment may be performed in air with a voltage of approximately 1.8kV. By adjusting the applied voltage of the corona discharge treatment within the range described above, an appropriate number of functional groups can be formed on the surface of the polymer substrate, preventing damage to the surface of the polymer substrate.

[0090] The step of forming the porous coating layer may include applying the coating slurry to a porous polymer substrate to form a coating. For example, the coating can be formed by methods such as a bar coater, wire bar coater, roll coater, spray coater, spin coater, inkjet coater, screen coater, reverse coater, gravure coater, knife coater, slot die coater, hot melt coater, comma coater, or direct metering coater, but is not limited to these. In one embodiment, the step of forming the porous coating layer may involve simultaneously coating both sides of the porous polymer substrate with the coating slurry using a bar coater or slot die coater.

[0091] The step of forming the porous coating layer may involve applying the coating slurry to a porous polymer substrate, then drying or heating the porous coating layer to evaporate the dispersion medium contained in the porous coating layer. The removal of the dispersion medium may be carried out at a temperature that allows only the dispersion medium contained in the porous coating layer to evaporate without deforming the polymer binder contained in the porous coating layer. For example, the removal of the dispersion medium may involve heating the porous coating layer to a predetermined temperature, ensuring that the temperature of the surface of the porous coating layer does not exceed 60°C. When heating the porous coating layer under the above conditions, the thermal energy may be used first to heat the dispersion medium and cause a phase change, and not to deform the polymer binder.

[0092] The present invention will be described in more detail below with reference to examples and experimental examples. The following examples and experimental examples are for illustrative purposes only, and the present invention is not limited to the following examples and experimental examples.

[0093] Example 1 Preparation of coating slurry At room temperature (25°C), 2.77 g (solids content 11.4%) of a copolymer (weight-average molecular weight: 70,000, pH 7.2, viscosity 55 cps@RT) polymerized in a 5:5 ratio of polyacrylic acid and polyacrylamide as a copolymer binder, 30 g of Al2O3 (particle size (D50): 500 nm) as inorganic particles, and 3.1 g (solids content 25%) of a PAA-based polymer dispersant as an additive were added to 53.7 mL of distilled water. After stirring in a shaker for 120 minutes, 2.42 g (solids content 40%) of an acrylic polymer binder (particle size (D50): 150 nm, Tg: -25°C) and 0.19 g (solids content 100%) of a wetting agent as an additive were added to prepare a coating slurry in which the copolymer binder and inorganic particles were dispersed.

[0094] Preparation of porous polymer substrates As the porous polymer substrate, a polyethylene film with dimensions of 20 cm × 30 cm and a thickness of 10 μm was used, with specifications of MI: 0.2 g / 10 min, Tm: 135°C, porosity: 45%, and average pore size: 35 nm.

[0095] Manufacturing of separation membranes The coating slurry was applied to both sides of a polyethylene film using a bar coater, forming a coating layer with a thickness of 1.5 μm for each layer.

[0096] A polyethylene film with a coating layer was subjected to a low-temperature airflow, and the process of removing the dispersion medium was repeated five times to produce a separation membrane with a total thickness of 13 μm and a weight ratio of 3:1:3:93 of acrylic polymer binder, copolymer binder, additives, and inorganic particles contained in the porous coating layer.

[0097] The above describes the sequence of steps for manufacturing the separation membrane of the present invention, but the sequence is not limited thereto, and can be appropriately modified and adjusted as needed. For example, the preparation step for the porous substrate may be performed before the preparation step for the coating slurry, or both steps may be performed simultaneously.

[0098] Example 2 In the production of the coating slurry, the separation membrane was manufactured in the same manner as in Example 1, except that the copolymer binder had a weight-average molecular weight of 67,000.

[0099] Example 3 In the production of the coating slurry, a separation membrane (with a weight ratio of acrylic polymer binder, copolymer binder, additives, and inorganic particles contained in the porous coating layer of 3:2:3:92) was produced in the same manner as in Example 1, except that it contained 2.45 g of acrylic polymer binder, 5.6 g of copolymer binder, 30 g of inorganic particles, 3.13 g of dispersant, and 0.2 g of wetting agent.

[0100] Example 4 In the production of the coating slurry, the separation membrane was manufactured in the same manner as in Example 1, except that a copolymer of polyacrylic acid and polyacrylamide in a ratio of 7:3 was used as the copolymer binder.

[0101] Comparative Example 1 In the production of the coating slurry, the separation membrane was manufactured in the same manner as in Example 1, except that the copolymer binder had a weight-average molecular weight of 35,000.

[0102] Comparative Example 2 In the production of the coating slurry, the separation membrane was manufactured in the same manner as in Example 1, except that the copolymer binder had a weight-average molecular weight of 100,000.

[0103] Comparative Example 3 In the production of the coating slurry, the separation membrane was manufactured in the same manner as in Example 1, except that the copolymer binder had a weight-average molecular weight of 160,000.

[0104] Comparative Example 4 In the production of the coating slurry, a separation membrane (with a weight ratio of acrylic polymer binder, copolymer binder, additives, and inorganic particles in a porous coating layer of 3:0:3:94) was produced in the same manner as in Example 1, except that 2.39 g of acrylic polymer binder and 30 g of inorganic particles were included, and a copolymer binder was not used.

[0105] Comparative Example 5 In the production of the coating slurry, the separation membrane was manufactured in the same manner as in Example 1, except that 2.53 g of acrylic polymer binder, 14.48 g of copolymer binder, and 30 g of inorganic particles were included (the weight ratio of acrylic polymer binder, copolymer binder, additives, and inorganic particles was 3:5:3:89).

[0106] Comparative Example 6 In the production of the coating slurry, the separation membrane was manufactured in the same manner as in Example 1, except that 2.68 g of acrylic polymer binder, 30.68 g of copolymer binder, and 30 g of inorganic particles were included (the weight ratio of acrylic polymer binder, copolymer binder, additives, and inorganic particles was 3:10:3:84).

[0107] Comparative Example 7 In the production of the coating slurry, the separation membrane was manufactured in the same manner as in Example 1, except that polyacrylic acid was used instead of the copolymer binder.

[0108] Comparative Example 8 In the production of the coating slurry, the separation membrane was manufactured in the same manner as in Example 1, except that a copolymer of polyacrylic acid and polyacrylamide polymerized in a ratio of 3:7 was used as the copolymer binder.

[0109] Comparative Example 9 The separation membrane was manufactured in the same manner as in Example 1, except that polyacrylamide alone was used instead of the copolymer binder in the production of the coating slurry.

[0110] Experimental Example 1. Confirmation of separation membrane properties based on the properties of the copolymer binder. The state of the separation membranes produced in Example 1 and Comparative Examples 1 to 3 was confirmed, and the physical properties of the copolymer binders used were determined by molecular weight, as shown in Table 1 below.

[0111] In Comparative Examples 2 and 3, the viscosity of the coating slurry exceeded 1,000 cps, making it impossible to perform coating using a bar coater. Below, the physical properties of the separation films produced in Example 1 and Comparative Example 1 were confirmed.

[0112] Measurement of air permeability Air permeability was measured using a Gurley densometer (Gurley, 4110N) to determine that 100cc of air reaches a diameter of 28.6mm and an area of ​​645mm².2 The time taken for permeation through the separation membrane was measured. Dry Confirmation of improvement in thermal shrinkage rate under these conditions. As the separation membranes for the examples and comparative examples, test pieces each having a size of 5 cm × 5 cm were prepared. After storing the prepared test pieces in a 200°C convection oven for 30 minutes, the thermal shrinkage rates in the MD (Machine Direction) and TD (Transverse Direction) were calculated respectively by [(initial length of the test piece - length after storage for 0.5 h at 200°C) / (initial length of the test piece)]×100 (%).

[0113] Wet Confirmation of improvement in thermal shrinkage rate under these conditions. As the separation membranes for the examples and comparative examples, test pieces with a size of 5 cm × 5 cm were prepared and inserted into aluminum pouches each having a size of 7 cm × 10 cm respectively. 1 g of an electrolytic solution was injected into the pouches, and the pouches were sealed.

[0114] As the electrolytic solution, a solvent in which ethylene carbonate (EC) / ethyl methyl carbonate (EMC) was mixed at a weight ratio of 3 / 7 was used, which contained 3 mol of vinylene carbonate (VC), 1.5 mol of propane sulfone (PS), 1 mol of ethylene sulfate (ESa), and 1 mol of lithium salt LiPF6 as additives.

[0115] [[ID=2l]]After storing the sealed pouches in a hot box at 135°C for 30 minutes, the thermal shrinkage rates in the MD direction and TD direction were calculated respectively by [(initial length of the test piece - length after storage for 0.5 h at 135°C) / (initial length of the test piece)]×100 (%). Confirmation of electrolyte wettability. As the separation membranes for the examples and comparative examples, test pieces with a size of 5 cm × 5 cm were prepared. Immediately after dropping 2 μL of propylene carbonate (PC) as the electrolytic solution onto the surface of the separation membrane, the lengths spread in the MD direction and TD direction after 5 minutes were measured respectively based on the droplet interface.

[0116]

Table 1

[0117] In Comparative Examples 5 and 6, the viscosity of the coating slurry exceeded 1,000 cps, making it impossible to perform coating using a bar coater. The physical properties of the separation films produced according to Examples 2 and 3 and Comparative Example 4 were then confirmed. The methods for confirming each physical property were the same as in the experimental examples described above.

[0118] [Table 2] Experimental Example 3. Confirmation of the physical properties of separation membranes based on the copolymerization ratio of the copolymerization binder. The physical properties of the separation membranes prepared according to Examples 1 and 4 and Comparative Examples 7 to 9 were confirmed based on the copolymerization ratio of the copolymerization binder used, and are shown in Table 3 below. The method for confirming each physical property is the same as in the experimental examples described above.

[0119] [Table 3] As described above with reference to preferred embodiments of the present invention, a person skilled in the art or with ordinary knowledge in the art will understand that the present invention can be modified and altered in various ways without departing from the spirit and technical scope of the invention as described in the claims below. Therefore, the technical scope of the present invention should not be limited to what is described in the detailed description of the specification, but should be defined by the claims.

Claims

1. The material comprises a porous polymer substrate and a porous coating layer formed on at least one surface of the porous polymer substrate. The porous coating layer comprises an acrylic polymer binder, a copolymer binder, and inorganic particles. The copolymer binder is Polyacrylic acid and polyacrylamide are copolymerized in a ratio of 8:2 or 5:

5. The weight-average molecular weight of the copolymer binder is 40,000 to 80,000. A separation membrane for an electrochemical element, wherein the copolymer binder and the inorganic particles are contained in a weight ratio of 1:93 to 1:

20.

2. The aforementioned acrylic polymer binder is (Meth)acrylic acid, (meth)acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-amyl acrylate, isoamyl acrylate, n-ethylhexyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, n-ethylhexyl methacrylate, 2-ethylhexyl methacrylate Separation membrane for electrochemical elements according to claim 1, comprising one or more monomers selected from the group consisting of hydroxyethyl methacrylate, (meth)acrylonitrile butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, ethyl (meth)acrylate, methyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, n-oxyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, lauryl (meth)acrylate, and tetradecyl (meth)acrylate as repeating units. 。

3. The weight-average molecular weight of the copolymer binder is 60,000 to 80,000. The separation membrane for an electrochemical element according to claim 1, wherein the copolymer binder and the inorganic particles are contained in a weight ratio of 1:93 to 1:

46.

4. The aforementioned acrylic polymer binder has a particle shape with an average particle size (D50) of 100 nm to 500 nm. The copolymer binder is in a non-particulate form, as described in claim 1, for a separation membrane for an electrochemical element.

5. The porous coating layer is The separation membrane for an electrochemical element according to claim 1, wherein the inorganic particles are present in an amount of 90% to 95% by weight relative to the total weight of the porous coating layer.

6. The separation membrane for an electrochemical element according to claim 1, wherein the content of the acrylic polymer binder is greater than the content of the copolymer binder, based on the weight of the porous coating layer.

7. The separation membrane for an electrochemical element according to claim 6, wherein the acrylic polymer binder and the copolymer binder are contained in a weight ratio of 5:1 to 1.5:

1.

8. An electrochemical element comprising a positive electrode, a negative electrode, and a separation membrane disposed between the positive electrode and the negative electrode, The separation membrane is an electrochemical element according to any one of claims 1 to 7.

9. The electrochemical element according to claim 8, further comprising an electrolyte containing a solvent mixed in a weight ratio of EC (ethylene carbonate) / EMC (ethylmethyl carbonate) of 3 / 7.

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