Separation membrane for electrochemical elements, method for manufacturing the same, and electrochemical elements containing the same

Abstract

The present invention relates to a separator for an electrochemical device, which comprises: a porous polymer substrate; a porous coating layer formed on at least one surface of the porous polymer substrate and including a polymer binder and inorganic particles; and a dopamine coating layer formed on the porous coating layer and including polydopamine and dextrin, and which has reduced thermal shrinkage even under a high-temperature wet state.

Description

[Technical Field]

[0001] This application claims priority based on Korean Patent Application No. 10-2023-0027540, filed with the Korean Intellectual Property Office on March 2, 2023, whose contents are entirely included in this application by reference.

[0002] This invention relates to a separation membrane for electrochemical elements, a method for producing the same, and an electrochemical element containing the same. [Background technology]

[0003] Electrochemical devices convert chemical energy into electrical energy using electrochemical reactions. In recent years, lithium-ion batteries, which have high energy density and voltage, long cycle life, and can be used in various fields, have become 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 with other inorganic particles by the polymer binder to form an interstitial volume, and lithium ions can move through the interstitial volume. In addition to fixing the inorganic particles, the polymer binder can provide adhesion to the porous coating layer, and the porous coating layer can be adhered to the porous substrate and the electrodes, respectively.

[0005] A porous coating layer containing a polymer binder and inorganic particles can prevent thermal shrinkage of the porous polymer substrate, and the separation membrane containing the porous coating layer 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 be swollen by the electrolyte, or the separation membrane may be exposed to temperatures of approximately 130°C or higher due to the operation of the lithium secondary battery containing the separation membrane, potentially reducing the adhesive strength of the polymer binder. In such a high-temperature wet state, the adhesive strength of the porous coating layer may decrease, potentially causing the separation membrane to shrink significantly. In particular, cylindrical batteries, in which the electrode assembly is wound up and inserted into a case while tension is applied to the electrode assembly, require relatively less adhesive strength between the electrode and the separation membrane compared to pouch-type batteries. This has led to the problem of a lower polymer binder content and a further reduction in dimensional stability in the wet state.

[0006] Therefore, research is being conducted on separation membranes that ensure dimensional stability under high temperature and wet conditions while maintaining a relatively low content of polymer binders in the porous coating layer. [Overview of the project] [Problems that the invention aims to solve]

[0007] 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 producing the same, and an electrochemical element including the separation membrane for electrochemical elements. [Means for solving the problem]

[0008] One aspect of the present invention provides a separation membrane for an electrochemical element, comprising a porous polymer substrate, a porous coating layer formed on at least one surface of the porous polymer substrate and containing a polymer binder and inorganic particles, and a dopamine coating layer formed on the porous coating layer and containing polydopamine and dextrin.

[0009] The porous coating layer may contain 5% by weight or less of the polymer binder, based on the total weight of the porous coating layer.

[0010] The separation membrane may contain the polydopamine and the dextrin in a weight ratio of 1:500 to 1:1000.

[0011] The polymer binder comprises an acrylic binder, and at least a portion of the acrylic binder can be crosslinked with the polydopamine.

[0012] The 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.

[0013] The thickness of the porous coating layer may be greater than the thickness of the dopamine coating layer.

[0014] 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 another electrochemical element in the aforementioned aspect.

[0015] The electrochemical element may be a lithium secondary battery.

[0016] The electrochemical element may further contain an electrolyte containing EC / EMC in a weight ratio of 3 / 7.

[0017] Another aspect of the present invention provides a method for producing a separation membrane for an electrochemical element, comprising the steps of: immersing a preliminary separation membrane, which includes a porous polymer substrate and a porous coating layer formed on at least one surface of the porous polymer substrate and comprising a polymer binder and inorganic particles, in a solution containing dopamine and dextrin for 1 to 50 hours; and adjusting the amount of dissolved oxygen in the solution to form a dopamine coating layer containing polydopamine and the dextrin on at least one surface of the porous coating layer.

[0018] In the method for producing the separation membrane, the polymer binder may further include an acrylic binder, and the method may further include a step of exposing the separation membrane to 60°C to 90°C to thermally crosslink the polymer binder and the polydopamine. [Effects of the Invention]

[0019] The separation membrane for electrochemical elements according to the present invention can provide improved dimensional stability in a wet state impregnated with an electrolyte. Specifically, the separation membrane has a thermal shrinkage rate of 5% or less in the TD direction under high temperature conditions of 130°C or higher, thereby preventing electrode exposure due to thermal shrinkage of the separation membrane. [Modes for carrying out the invention]

[0020] The following describes in more detail each component of the present invention so that a person with ordinary skill in the art to which the present invention belongs can easily implement it. However, this is merely an example, and the scope of the rights of the present invention is not limited to the following.

[0021] As used herein, the term “including” is used to enumerate materials, compositions, apparatus, and methods useful for the present invention, and is not limited to such enumerated examples.

[0022] As used herein, “about” and “substantially” are used to mean a range or similar of numerical values ​​or degrees, taking into account inherent manufacturing and material tolerances, 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.

[0023] As used herein, "electrochemical elements" may refer to primary batteries, secondary batteries, supercapacitors, and the like.

[0024] As used herein, "wet state" may mean a state in which the separation membrane is impregnated with at least a portion of the electrolyte.

[0025] One specific example of the present invention provides a separation membrane for an electrochemical element, comprising a porous polymer substrate, a porous coating layer formed on at least one surface of the porous polymer substrate and containing a polymer binder and inorganic particles, and a dopamine coating layer formed on the porous coating layer and containing polydopamine and dextrin.

[0026] The porous polymer substrate is a porous membrane with multiple pores formed therein, which can electrically insulate the positive and negative electrodes to prevent short circuits. For example, if the electrochemical element is a lithium secondary battery, the porous polymer substrate can be an ion-conducting barrier that blocks electrical contact between the positive and negative electrodes while allowing lithium ions to pass through. At least some of the pores can form a three-dimensional network connecting the surface and interior of the porous polymer substrate, allowing fluids to pass through the porous polymer substrate via the pores.

[0027] 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, polyimidoamide, nylon, polytetrafluoroethylene, and copolymers or mixtures thereof. Preferably, polyolefin resins can be used. Polyolefin resins can be processed to a relatively thin thickness and are easy to apply coating slurries to, making them suitable for the manufacture of electrochemical elements with higher energy density.

[0028] 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) to 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. Preferably, 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 melt and shut down the pores as the battery temperature rises above a predetermined temperature, thereby preventing thermal runaway of the battery.

[0029] The thickness of the porous polymer substrate may be between 1 μm and 100 μm. Specifically, the thickness of the porous polymer substrate may be between 10 μm and 90 μm, between 20 μm and 80 μm, between 30 μm and 70 μm, or between 40 μm and 60 μm. Preferably, the thickness of the polymer substrate may be between 1 μm and 30 μm. More preferably, the thickness of the polymer substrate may be between 5 μm and 15 μm, or between 8 μm and 13 μm. By adjusting the thickness of the porous polymer substrate within the above range, it is possible to minimize the volume of the electrochemical element while electrically insulating the positive and negative electrodes, thereby increasing the amount of active material contained in the electrochemical element.

[0030] The porous polymer substrate may contain pores with an average diameter of 0.01 μm or more and 1 μm or less. Specifically, the size of the pores contained in the porous polymer substrate may be 0.01 μm or more and 0.09 μm or less, 0.02 μm or more and 0.08 μm or less, 0.03 μm or more and 0.07 μm or less, or 0.04 μm or more and 0.06 μm or less. Preferably, the size of the pores may be 0.02 μm or more and 0.06 μm or less. 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.

[0031] The porous polymer substrate can have an air permeability of 10 s / 100 cc or more and 100 s / 100 cc or less. Specifically, the air permeability of the porous polymer substrate may be 10 s / 100 cc or more and 90 s / 100 cc or less, 20 s / 100 cc or more and 80 s / 100 cc or less, 30 s / 100 cc or more and 70 s / 100 cc or less, or 40 s / 100 cc or more and 60 s / 100 cc or less. Preferably, the air permeability of the porous polymer substrate may be 50 s / 100 cc or more and 70 s / 100 cc or less. 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.

[0032] The aforementioned 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 constant pressure. This air permeability can be measured using a Gurley densometer in accordance with ASTM D 726-58, ASTM D726-94, or JIS-P8117. For example, using a Gurley 4110N instrument, it can measure air at a pressure of 0.304 kPa or 1.215 kN / m³. 2 Under water pressure, 100cc of air covers 1 square inch (or 6.54cm). 2The time it takes for a sample to pass through can be measured. For example, using the EG01-55-1MR instrument from Asahi Seiko, the time it takes for 100cc of air to pass through a 1 square inch sample can be measured at room temperature and under constant pressure in 4.8 inches of water.

[0033] The porous polymer substrate may have a porosity of 10 vol% to 60 vol%. Specifically, the porosity of the porous polymer substrate may be 15 vol% to 55 vol%, 20 vol% to 50 vol%, 25 vol% to 45 vol%, or 30 vol% to 40 vol%. Preferably, the porosity of the porous polymer substrate may be 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.

[0034] The porosity refers to the ratio of the volume of pores to the total volume of the porous polymer substrate. The porosity can be measured by methods known in the art. For example, it can be measured by the Brunauer-Emmett-Teller (BET) method utilizing nitrogen gas adsorption, the capillary flow porometer, or the water or mercury osmosis method.

[0035] The porous coating layer is formed on at least one surface of the porous polymer substrate and may contain a polymer binder and inorganic particles. The dopamine coating layer is formed on the porous coating layer and may contain polydopamine and dextrin.

[0036] The separation membrane may be formed by sequentially coating at least one surface of a porous polymer substrate with a coating slurry containing a polymer binder, inorganic particles and a dispersion medium, and a solution containing dopamine and dextrin. For example, the separation membrane may be manufactured by applying the coating slurry to at least one surface of a porous polymer substrate and drying it to produce a preliminary separation membrane with a porous coating layer, and then immersing the preliminary separation membrane in the solution and drying it to form a dopamine coating layer. The porous coating layer adheres to the porous polymer substrate, preventing thermal shrinkage of the porous polymer substrate, while allowing lithium ions to pass through, by containing interstitial volume in which inorganic particles are linked by the polymer binder. The polydopamine contained in the dopamine coating layer may be formed by polymerization of dopamine contained in the solution. The dopamine coating layer also has a porous structure composed of polydopamine and dextrin, allowing lithium ions to pass through.

[0037] The coating slurry contains a dispersion medium that can dissolve or disperse at least a portion of the polymer 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. Preferably, the dispersion medium may be a mixture of water and isopropyl alcohol, or water. Using the above-described types of dispersion medium, a porous coating layer in which the polymer binder and inorganic particles are uniformly dispersed can be formed.

[0038] The coating slurry can further contain additives such as dispersants, surfactants, defoamers, and flame retardants to improve dispersibility and flame retardancy and enhance the uniformity of the porous coating layer formed. For example, the dispersant may include one or more selected from the group consisting of polyacrylic acid, oil-soluble polyamines, oil-soluble amine compounds, fatty acids, fatty alcohols, sorbitan fatty acid esters, tannic acid, and pyrogallic acid. By using the above-described types of dispersants, the stability of the coating slurry can be improved and the uniformity of the porous coating layer formed from the coating slurry can be ensured.

[0039] The additive may be present in an amount of 0% to 5% by weight relative to the total weight of the coating slurry. Specifically, the content of the additive may be 0.01% to 4% by weight, 0.1% to 3% by weight, or 1% to 2% by weight. Preferably, the content of the additive may be 1% 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.

[0040] The dispersion medium contained in the coating slurry may be removed by drying or heating after the formation of the porous coating layer. Preferably, the porous coating layer may contain the dispersion medium at a concentration of 5 ppm or less. Preferably, the porous coating layer may consist of a polymer 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 that allows fluid to pass through.

[0041] The solution may be a basic buffer solution containing a mixture of dopamine and dextrin. The dopamine can undergo a cyclization reaction via oxidation even without an initiator, followed by a polymerization reaction to form polydopamine.

[0042] The pH of the solution may be between 7 and 12. Specifically, the pH of the solution may be between 7.5 and 11.5, 8 and 11, 8.5 and 10.5, or 9 and 10. Preferably, the pH of the solution may be between 7.5 and 8.5. By adjusting the pH of the solution within the above range, the required polydopamine loading amount and uniform distribution of polydopamine for the dopamine coating layer can be achieved.

[0043] The sum of the thickness of the porous coating layer and the thickness of the dopamine coating layer may be between 1 μm and 15 μm. Specifically, the sum of the thickness of the porous coating layer and the thickness of the dopamine coating layer may be between 2 μm and 14 μm, 3 μm and 13 μm, 4 μm and 12 μm, 5 μm and 11 μm, 6 μm and 10 μm, or 7 μm and 9 μm. Preferably, the sum of the thickness of the porous coating layer and the thickness of the dopamine coating layer may be between 1 μm and 5 μm. By adjusting the thickness of the porous coating layer and the dopamine 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.

[0044] The thickness of the porous coating layer may be greater than the thickness of the dopamine coating layer. For example, the thickness of the porous coating layer may be 0.1 μm or more and 14 μm or less. Specifically, the thickness of the porous coating layer may be 1 μm or more and 13 μm or less, 2 μm or more and 12 μm or less, 3 μm or more and 11 μm or less, 4 μm or more and 10 μm or less, 5 μm or more and 9 μm or less, or 6 μm or more and 8 μm or less. Preferably, the thickness of the porous coating layer may be 0.1 μm or more and 5 μm or less. The thickness of the dopamine coating layer may be 0.001 μm or more and 5 μm or less. Specifically, the thickness of the dopamine coating layer may be 0.01 μm or more and 4 μm or less, 0.1 μm or more and 3 μm or less, or 1 μm or more and 2 μm or less. Preferably, the thickness of the dopamine coating layer may be 0.005 μm or more and 1 μm or less. By adjusting the thickness of the porous coating layer and the dopamine coating layer within the range described above, shrinkage of the porous polymer substrate can be minimized, and stable adhesion to the porous polymer substrate can be achieved. If the thickness of the dopamine coating layer becomes greater than the thickness of the porous coating layer, delamination will occur between the porous coating layer and the porous polymer substrate.

[0045] The porous coating layer may contain a polymer binder and inorganic particles. The polymer binder can bind the inorganic particles contained in the porous coating layer and impart adhesive force to the porous coating layer. The polymer binder may be spherical or elliptical, but may encompass other shapes except amorphous.

[0046] The polymer binder may be an acrylic binder. For example, the 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.

[0047] If the polymer binder is an acrylic binder, at least a portion of the acrylic binder can be crosslinked with the polydopamine contained in the dopamine coating layer. The acrylic binder can be crosslinked with the polydopamine contained in the dopamine coating layer by a condensation reaction. Since the acrylic binder can crosslink with polydopamine more effectively than a fluorine-based binder, it can form and maintain a bond between the porous coating layer and the dopamine coating layer, thereby reducing the thermal shrinkage of the separation membrane even when the separation membrane is in a wet state.

[0048] The porous coating layer may contain 5% by weight or less of the polymer binder, based on the total weight of the porous coating layer. Specifically, the polymer binder content may be 0.1% to 5% by weight, 0.5% to 4.5% by weight, 1% to 4% by weight, 1.5% to 3.5% by weight, or 2% to 3% by weight, based on the total weight of the porous coating layer. Preferably, the polymer binder content may be 3% to 5% by weight. By adjusting the polymer binder content within the above range, the thermal shrinkage of the wet state of the separation membrane can be improved by binding inorganic particles, stable adhesion to the porous polymer substrate, and crosslinking with polydopamine contained in the dopamine coating layer.

[0049] The weight-average molecular weight (Mw) of the polymer binder may be between 1,000 and 10,000,000. Specifically, the weight-average molecular weight of the polymer binder may be between 1,000 and 10,000,000, between 10,000 and 9,000,000, between 100,000 and 8,000,000, between 200,000 and 7,000,000, between 300,000 and 6,000,000, between 500,000 and 5,000,000, between 1,000,000 and 4,000,000, or between 2,000,000 and 3,000,000. By adjusting the weight-average molecular weight of the polymer binder within the range described above, the mechanical properties of the porous coating layer can be ensured, making it possible to manufacture a separation membrane with a durable porous coating layer.

[0050] The weight-average molecular weight can be measured by gel permeation chromatography (GPC, PL GPC220, Agilent Technologies). For example, the weight-average molecular weight can be measured using a PL Olexis (Polymer Laboratories) column (column temperature 160°C) with trichlorobenzene (TCB) as the solvent, under the conditions of a sample concentration of 1.0 mg / mL, a flow rate of 1.0 mL / min, and an injection volume of 200 μl, using an Agilent High Temperature Differential Refractive Index (RI) detector (reference: polystyrene).

[0051] The porous coating layer may contain the polymer binder and the inorganic particles in a weight ratio of 5:80 to 5:95. Specifically, the weight ratio of the polymer binder to the inorganic particles in the porous coating layer may be 5:80 to 5:95 or 5:85 to 5:90. By adjusting the composition of the porous coating layer within the above range, it is possible to simultaneously ensure the formation of interstitial volume through bonding between inorganic particles and the adhesion strength of the porous coating layer to the separation film.

[0052] The inorganic particles can be those that are electrochemically stable. The inorganic particles are not particularly limited as long as oxidation and / or reduction reactions do not occur within the operating voltage range of the electrochemical device (for example, 0 to 5 V based on Li / Li + reference). In particular, 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. For the reasons described above, it is preferable that the inorganic particles include high-dielectric-constant inorganic particles having a dielectric constant of 5 or more, preferably 10 or more. Non-limiting examples of inorganic particles having a dielectric constant of 5 or more include BaTiO3, Pb(Zr,Ti)O3 (PZT), b 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, and the like.

[0053] In addition, as the inorganic particles, inorganic particles having lithium ion transfer ability, that is, inorganic particles 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 transfer ability include lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, <x<2, <y<3), lithium aluminum titanium phosphate (Li x Al y Ti z (PO4)3, <x<2, <y<1, <z<3), 14Li2O-9Al2O3-38TiO2-39P2O5 and the like such as (LiAlTiP) x O ySystem glass (0 < x < 4, 0 < y < 13), lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), Li 3.25 Ge 0.25 P 0.75 S4 such as lithium germanium thiophosphate (Li x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride such as Li3N (Li x N y , 0 < x < 4, 0 < y < 2), SiS2-based glass such as Li3PO4 - Li2S - SiS2 (Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4), P2S5-based glass such as LiI - Li2S - P2S5 (Li x P y S z , 0 < x < 3, 0 < y < 3, 0 < z < 7), or mixtures thereof, etc.

[0054] Also, as the inorganic particles, inorganic particles having flame retardancy can be used, which can impart flame retardant properties to the separation membrane or prevent the temperature inside the electrochemical device from rising rapidly. Non-limiting examples of inorganic particles having flame retardancy 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, etc.

[0055] The average particle size (D50) of the inorganic particles may be between 50 nm and 5,000 nm. Specifically, the average particle size (D50) of the inorganic particles may be between 100 nm and 4,500 nm, between 200 nm and 4,000 nm, between 300 nm and 3,000 nm, between 400 nm and 2,000 nm, or between 500 nm and 1,000 nm. If the average particle size of the inorganic particles is less than 50 nm, as the specific surface area increases, more polymer binder is required for bonding between the inorganic particles, which is disadvantageous in terms of electrical resistance. If the average particle size of the inorganic particles exceeds 5,000 nm, the uniformity of the coating layer surface decreases, which may cause damage to the porous polymer substrate or electrode during lamination.

[0056] The aspect ratio of the inorganic particles may be between 1 and 2. Specifically, the aspect ratio of the inorganic particles may be between 1.1 and 1.9, 1.2 and 1.8, 1.3 and 1.7, or 1.4 and 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 a porous coating layer can be formed in which the film-formed regions are uniformly distributed after the movement of the polymer binder.

[0057] The BET specific surface area of ​​the inorganic particles is 5m². 2 / g or more 25m 2 It may be less than / g. Specifically, the BET specific surface area of ​​the inorganic particles is 6m². 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 18m2 / 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 through the voids between the inorganic particles can be controlled.

[0058] The polydopamine acts as a thermal shrinkage inhibitor for the dopamine coating layer and the porous coating layer, while simultaneously providing inherent adhesive strength to impart adhesion to the dopamine coating layer. At least a portion of the polydopamine forms crosslink bonds with the aforementioned polymer binder via amine groups, preventing the detachment of inorganic particles contained in the porous coating layer and maintaining the bond between the porous coating layer and the dopamine coating layer, thereby reducing thermal shrinkage of the porous polymer substrate even in a wet state.

[0059] The decomposition temperature of the aforementioned polydopamine (T d The decomposition temperature of polydopamine can be 280°C to 320°C. Specifically, the decomposition temperature of polydopamine can be 290°C to 310°C. The decomposition temperature of polydopamine can be analyzed by thermogravimetric analysis (TGA). When the decomposition temperature of polydopamine is within the above numerical range, the dimensional stability of the wet separation membrane can be improved under high-temperature conditions, and at the same time, the detachment of inorganic particles contained in the porous coating layer can be prevented, thereby preventing thermal shrinkage of the separation membrane without hindering lithium ion transfer.

[0060] The molecular weight of the polydopamine may be between 10,000 and 1,000,000. Specifically, the molecular weight of the polydopamine may be between 100,000 and 900,000, 200,000 and 800,000, 300,000 and 700,000, or 400,000 and 600,000. Preferably, the molecular weight of the polydopamine may be between 20,000 and 500,000. When the molecular weight of the polydopamine satisfies the above numerical range, the thermal shrinkage rate of the separation membrane can be reduced in a high-temperature wet state.

[0061] The loading amount of polydopamine contained in the dopamine coating layer is 0.0001 g / m². 2 More than 0.01g / m 2 The following may be the case. Specifically, the loading amount of polydopamine is 0.0005 g / m². 2 More than 0.009g / m 2 Below 0.001g / m 2 More than 0.008g / m 2 Below 0.002g / m 2 More than 0.007g / m 2 Below, 0.003g / m 2 More than 0.006g / m 2 The following, or 0.004 g / m² 2 More than 0.005g / m 2 The following may be the case. Preferably, the loading amount of polydopamine is 0.0005 g / m². 2 More than 0.002g / m 2 The following is possible. By adjusting the amount of polydopamine loaded within the range described above, the thermal shrinkage rate of the wet separation membrane can be reduced under high-temperature conditions.

[0062] During the manufacturing process of the separation membrane, polydopamine may be included in the porous coating layer by immersing a preliminary separation membrane in a dopamine solution. The loading amount of polydopamine contained in the dopamine coating layer may be greater than the loading amount of polydopamine contained in the porous coating layer. For example, the loading amount of polydopamine contained in the dopamine coating layer may be 0.0005 g / m². 2 More than 0.01g / m 2 The following is possible. Specifically, the loading amount of polydopamine contained in the dopamine coating layer is 0.001 g / m². 2 More than 0.009g / m 2 Below 0.002g / m 2 More than 0.008g / m 2 Below, 0.003g / m 2 More than 0.007g / m 2 The following, or 0.004 g / m² 2 More than 0.006g / m 2 The following may be true: The loading amount of polydopamine contained in the porous coating layer is 0.0001 g / m². 2 More than 0.005g / m 2 The following is possible. Specifically, the loading amount of polydopamine contained in the porous coating layer is 0.0001 g / m². 2 More than 0.004g / m 2 The following, or 0.001 g / m² 2 More than 0.003g / m 2 The following is possible: Within the range described above, by adjusting the loading amount of polydopamine contained in the porous coating layer and the dopamine coating layer, the amount of polydopamine exposed to the outermost surface of the separation membrane can be adjusted, thereby reducing the thermal shrinkage rate of the wet state of the separation membrane even under high-temperature conditions.

[0063] The dextrin can impart durability to the dopamine coating layer, thereby improving the dimensional stability of the separation membrane containing the dopamine coating layer. The dopamine coating layer containing the dextrin can maintain its dimensional stability even when external forces are applied, generated by the contraction and expansion of electrodes that are adhered to or adjacent to the separation membrane. The dextrin can improve the dispersibility of polydopamine, thereby forming a dopamine coating layer in which the polydopamine is uniformly dispersed. For example, the dextrin can maintain a state in which the dopamine is uniformly dispersed even when the dopamine is not yet completely dissolved in the solution containing the dopamine. The dextrin may be a cyclodextrin, and may be one or more selected from the group consisting of α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin.

[0064] The separation membrane may contain polydopamine and dextrin in a weight ratio of 1:500 to 1:1000. Specifically, the separation membrane may contain polydopamine and dextrin in a weight ratio of 1:600 ​​to 1:900, or 1:700 to 1:800. By adjusting the content of polydopamine and dextrin within the above ranges, it is possible to achieve a reduction in the thermal shrinkage rate of the separation membrane in the wet state at high temperatures through the uniform dispersion of polydopamine contained in the dopamine coating layer.

[0065] Specifically, the separation membrane of the present invention can be said to be in a high-temperature wet state when impregnated with an electrolyte at a high temperature of 135°C or higher. When exposed to the high-temperature wet state for 30 minutes or more, if the thermal shrinkage rate in the MD direction is less than 10% and the thermal shrinkage rate in the TD direction is less than 7%, the thermal shrinkage rate can be evaluated as having been reduced. Furthermore, the adhesion strength between the porous polymer substrate and the porous coating layer of the separation membrane can be evaluated by the peel strength when the surface of the separation membrane is peeled off at a speed of 300 mm / min in a direction 180° to the adhesion direction using a UTM after fixing the separation membrane to a slide glass or the like. If the peel strength is 50 gf / 15 mm or higher, the porous coating layer and the dopamine coating layer can be evaluated as being stably adhered to the porous polymer substrate. If polydopamine is present in excess of the above range, polydopamine may aggregate during the formation process of the dopamine coating layer, making it impossible to ensure the effect of reducing the thermal shrinkage rate of the separation membrane at high temperatures, and potentially reducing the stability of the separation membrane. If the dextrin is present in excess of the range described above, the peel strength between the separation membrane substrate and the porous coating layer may increase due to the inherent adhesive strength of dextrin, but the effect of reducing thermal shrinkage of the separation membrane at high temperatures cannot be ensured. The separation membrane for the electrochemical element may have an air permeability of 20 s / 100 cc or more and 90 s / 100 cc or less. Specifically, the air permeability of the separation membrane may be 25 s / 100 cc or more and 85 s / 100 cc or less, 30 s / 100 cc or more and 80 s / 100 cc or less, 35 s / 100 cc or more and 75 s / 100 cc or less, 40 s / 100 cc or more and 70 s / 100 cc or less, 45 s / 100 cc or more and 65 s / 100 cc or less, or 50 s / 100 cc or more and 55 s / 100 cc or less. Preferably, the air permeability of the separation membrane may be 80 s / 100 cc or more and 90 s / 100 cc or less. When the permeability of the separation membrane is within the range described above, the output, stability, and cycle characteristics of the electrochemical element can be ensured.

[0066] When a cell is manufactured using the aforementioned separation membrane for electrochemical elements, the cell may have an electrical resistance of 0.5 Ohm or more and 1.5 Ohm or less. Specifically, the electrical resistance of the cell may be 0.6 Ohm or more and 1.4 Ohm or less, 0.7 Ohm or more and 1.3 Ohm or less, 0.8 Ohm or more and 1.2 Ohm or less, or 0.9 Ohm or more and 1.1 Ohm or less. Preferably, the electrical resistance of the cell may be 0.6 Ohm or more and 0.8 Ohm or less.

[0067] Another specific example of the present invention provides a method for producing a separation membrane for an electrochemical element, comprising the steps of: immersing a preliminary separation membrane, which includes a porous polymer substrate and a porous coating layer formed on at least one surface of the porous polymer substrate, in a solution containing dopamine and dextrin for 1 to 50 hours; and adjusting the amount of dissolved oxygen in the solution to form a dopamine coating layer containing polydopamine and the dextrin on at least one surface of the 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 above specific example.

[0068] The step of immersing the preliminary separation membrane in the solution may further include the step of manufacturing the preliminary separation membrane by coating at least one surface of the porous polymer substrate with a coating slurry containing a polymer binder and inorganic particles. The preliminary separation membrane has a porous coating layer formed on at least one surface of the porous polymer substrate, the coating containing a polymer binder and inorganic particles. 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, and direct metering coater. Preferably, the step of forming the porous coating layer may involve simultaneously coating both surfaces of the porous polymer substrate with a coating slurry using a bar coater or slot die coater.

[0069] The step of producing the preliminary separation membrane may further include a step of corona-discharging at least one surface of the porous polymer substrate. After the corona-discharging step, the coating slurry may be coated onto the porous polymer substrate. The step of corona-discharging at least one surface of the porous polymer substrate can prevent a decrease in the bonding strength between the surface of the porous polymer substrate and the surface of the porous coating layer at high temperatures, and can prevent a decrease in the bonding strength between the surface of the polymer substrate and the surface of the porous coating layer due to electrolytes.

[0070] The corona discharge treatment may involve treating at least one surface of the porous polymer substrate in air with a voltage of 0.1kV to 10kV. Specifically, the corona discharge treatment may be performed in air with voltages of 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. Preferably, the corona discharge treatment may be performed in air with a voltage of 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.

[0071] The step of producing the preliminary separation membrane may further include a step of removing the dispersion medium contained in the coating slurry. Specifically, the step of removing the dispersion medium involves drying or heating the porous polymer substrate coated with the coating slurry to evaporate the dispersion medium contained in the coating layer.

[0072] The step of immersing the preliminary separation membrane involves immersing the preliminary separation membrane in a solution containing dopamine and dextrin for 1 to 50 hours to coat it with a dopamine coating layer containing polydopamine and dextrin. Specifically, the immersion time for the preliminary separation membrane may be 4 to 48 hours, 8 to 44 hours, or 12 to 40 hours. Preferably, the immersion time may be 40 to 48 hours. Within the above time range, the loading amount of polydopamine contained in the dopamine coating layer can be adjusted to the aforementioned range.

[0073] The step of forming the dopamine coating layer may involve adjusting the amount of dissolved oxygen in the solution while the preliminary separation membrane is immersed in the solution. To form a dopamine coating layer containing polydopamine from a dopamine-containing solution, the process may involve oxidizing the dopamine to form cyclic dopamine, followed by polymerization. The degree of oxidation of the dopamine can be adjusted by exposing the solution to oxygen; for example, the amount of dissolved oxygen in the solution can be adjusted by adjusting the degree of opening and closing of the reaction vessel on which the solution is supported.

[0074] Specifically, the amount of dissolved oxygen contained in the solution into which the preliminary separation membrane is immersed may be 8.0 to 12.0 ppm. More specifically, the amount of dissolved oxygen in the solution may be 8.5 ppm to 11.5 ppm, 9.0 ppm to 11.0 ppm, or 9.5 ppm to 10.5 ppm. When adjusting the amount of dissolved oxygen in the solution within the above range, polymerization of polydopamine and loading into the aforementioned range may be performed. As an analytical method for measuring the amount of dissolved oxygen, for example, the Winkler-sodium azide modification using manganese sulfate and an alkaline potassium iodide-sodium azide solution can be used.

[0075] The method for manufacturing the separation membrane according to the above specific example may further include a step of exposing the separation membrane to 60°C to 90°C after the step of forming the dopamine coating layer to thermal crosslink the polymer binder and the polydopamine. For example, the separation membrane on which the dopamine coating layer is formed can be dried or heated at 60°C to 90°C for 1 to 12 hours. Preferably, the separation membrane can be dried or heated at 70°C to 80°C for 6 to 12 hours. The polymer binder may be an acrylic binder, and the acrylic binder and the polydopamine contained in one or more of the porous coating layer and the dopamine coating layer can be thermally crosslinked to improve the dimensional stability of the separation membrane in a high-temperature wet state.

[0076] 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 and negative electrodes, wherein the separation membrane is the separation membrane for the electrochemical element described in the above-described example. The above-described electrochemical element can be manufactured by inserting an electrode assembly comprising a positive electrode, a negative electrode, and a separation membrane interposed between the positive and negative electrodes 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 cylindrical, rectangular, coin-type, or pouch-type lithium secondary battery.

[0077] The positive electrode and the negative electrode may be those in which an electrode active material is coated and dried on at least one surface of each current collector. The current collector can use a material having conductivity without causing a chemical change in the electrochemical element. For example, the current collector for the positive electrode can be aluminum, nickel, titanium, fired carbon, stainless steel; or those obtained by surface treatment with carbon, nickel, titanium, silver, etc. on the surface of aluminum or stainless steel, but is not limited thereto. For example, the current collector for the negative electrode can be copper, nickel, titanium, fired carbon, stainless steel; or those obtained by surface treatment with carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, but is not limited thereto. The current collector can be in various forms such as a thin metal plate, film, foil, net, porous body, foam, etc.

[0078] 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 [[ID=!0]]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 oxide represented by the chemical formula; chemical formula LiMn 1-x M xLithium manganese composite oxides represented by O2 (where M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 - 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn); LiMn2O4 in which part of Li in the chemical formula is substituted by alkaline earth metal ions; disulfide compounds; one or more mixtures of Fe2(MoO4)3 may be included.

[0079] 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. As the negative electrode active material, the negative electrode includes carbon such as lithium metal oxide, graphitized carbon, graphite-based carbon; LixFe2O3 (0 ≤ x ≤ 1), LixWO2 (0 ≤ x ≤ 1), Si, SiO x (0 < x < 2), silicon-based materials such as SiC, Si alloy; Sn x Me 1-x Me’ y O z (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 oxides may be included.

[0080] 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 cylinder shape with a nanosize diameter of a graphite sheet and sp 2The carbon nanotube has a bonded structure and exhibits conductive or semiconductor properties depending on the angle and structure in which the graphite surface is wound. Carbon nanotubes can be classified into single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), and multi-walled carbon nanotubes (MWCNTs) depending on the number of bonds forming the wall, and these carbon nanotubes can be appropriately selected depending on the application of the dispersion. More specifically, it may be one selected from the group consisting of natural graphite, artificial graphite, super-p, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium oxide, or a mixture of two or more conductive materials from this group.

[0081] As the binder resin, a binder resin usually used for an electrode of an electrochemical device can be used. Non-limiting examples of such a binder resin include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyethylhexyl acrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetatepropionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl cellulose, and the like, and are not limited thereto.

[0082] The electrolyte is a salt having a structure such as A + B - where A + is Li + , Na + , K+ It contains alkali metal cations such as, or ions consisting of combinations thereof, B - PF6 - BF4 - Cl - , Br - , I - ClO4 - AsF6 - CH3CO2 - CF3SO3 - , N(CF3SO2)2 - , C(CF2SO2)3 - Salts containing anions such as those listed above, or ions consisting of combinations thereof, may be dissolved or dissociated in organic solvents 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. Preferably, the electrolyte can be a solvent with a weight ratio of EC / EMC of 3 / 7, which can maximize the dimensional stability of the separation membrane according to the specific example.

[0083] The electrochemical element including the electrode assembly may be a lithium secondary battery. The battery can 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, or a device including the battery pack as a power source. Examples of such devices include, but are not limited to, small devices such as computers, mobile phones, and power tools, and electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs) that are powered by electric motors; electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters; electric golf carts; and power storage systems.

[0084] The present invention will be described in more detail below with reference to specific examples and experimental cases. The following examples and experimental cases are for illustrative purposes only and do not limit the present invention to the following examples and experimental cases.

[0085] Example 1 Preparation of coating slurry 100 mL of aqueous dispersion medium was prepared by mixing water and isopropyl alcohol in a weight ratio of 95:5 at room temperature (25°C). Styrene-acrylic (Particle size: 350 nm~400 nm) was added to the aqueous dispersion medium as an acrylic polymer binder. g 2g of (40℃) and 30g of inorganic particles (Al2O3, particle size: 400nm) were added and stirred in a shaker for 60 minutes to produce a coating slurry in which the polymer binder and inorganic particles were dispersed.

[0086] Preparation of porous substrate As a porous substrate (MI: 0.2g / 10min, T mA polyethylene film measuring 20cm x 30cm with a thickness of 9μm was used, with a temperature of 135℃, porosity of 45%, and average pore size of 45nm.

[0087] Manufacturing of spare separation membranes A porous coating layer was formed on both sides of a polyethylene film using a bar coater, with each coating having a thickness of 2 μm.

[0088] A preliminary separation membrane with a total thickness of 13 μm was produced by repeating the process of removing the dispersion medium by applying a low-temperature airflow to a polyethylene film on which a coating layer had been formed, five times.

[0089] Preparation of a solution containing dopamine and dextrin At room temperature (25°C), dopamine was added to a basic buffer solution (20 mM Tris-HCl buffer) at a concentration of 2 mg / mL and dextrin at a concentration of 50 mg / mL using a Petri dish. However, the amount of added dopamine and dextrin was adjusted to ensure a final ratio of 1:1000. The lid of the Petri dish was then partially opened to produce a dopamine and dextrin solution with a dissolved oxygen content of 9 ppm and a pH of 8. The preliminary separation membrane was immersed in the solution for 48 hours, and then dried at 60°C for 12 hours to produce a separation membrane with an overall thickness of 14 μm (porous coating layer thickness 2.0 μm, dopamine coating layer thickness 0.5 μm) containing polydopamine and dextrin in a weight ratio of 1:1000.

[0090] Example 2 The separation membrane was manufactured in the same manner as in Example 1, except that, during the manufacturing of the separation membrane, the preliminary separation membrane was immersed and then dried at 90°C for 12 hours to produce a separation membrane with an overall thickness of 14 μm (porous coating layer thickness 2.3 μm, dopamine coating layer thickness 0.2 μm).

[0091] Example 3 Dopamine was added to the aforementioned solution at a concentration of 10 mg / mL, except that the amount added was adjusted so that the final dopamine-to-dextrin content was 1:500. In addition, a separation membrane containing polydopamine and dextrin in a weight ratio of 1:500 was produced by the same method as in Example 1.

[0092] Comparative Example 1 The separation membrane was manufactured using the same method as in Example 1, except that a spare separation membrane was immersed in a solution containing dopamine but not dextrin during the manufacturing process.

[0093] Comparative Example 2 The separation membrane was manufactured using the same method as in Example 1, except that a spare separation membrane was immersed in a solution containing dextrin but not dopamine during the manufacturing process.

[0094] Comparative Example 3 Dopamine at a concentration of 20 mg / mL and dextrin at a concentration of 20 mg / mL were added to the aforementioned solution, except that the amount of addition was adjusted so that the final dopamine and dextrin content was 1:400. In addition, a separation membrane containing polydopamine and dextrin in a weight ratio of 1:400 was produced by the same method as in Example 1.

[0095] Experimental example: Confirmation of physical properties of separation membranes Measurement of air permeability Air permeability was measured using an air permeability tester (Gurley densometer) (Gurley, 4110N), with 100cc of air measuring a diameter of 28.6mm and an area of ​​645mm². 2 The time it took for the substance to pass through the separation membrane was measured.

[0096] Dimensional stability verification Separation membranes for the examples and comparative examples were prepared to a size of 5 cm x 5 cm and inserted into 7 cm x 10 cm aluminum pouches. 1 g of electrolyte was injected into each pouch, and the pouches were sealed. The electrolyte used was a solvent mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a weight ratio of 3 / 7, containing 3 mol of vinylene carbonate (VC), 1.5 mol of propane sultone (PS), 1 mol of ethylene sulfate (ESa), and 6 mol of lithium salt LiPF as additives.

[0097] After exposing the sealed pouch to an oven at 135°C for 30 minutes, the pouch was disassembled and the shrinkage rate in the TD direction was measured, as shown in Table 1 below.

[0098] Measurement of the peel strength of the separation membrane The separation membranes of the examples and comparative examples were sampled to a width of 20 mm, and the test samples were prepared by attaching them to a glass slide using 18 mm wide double-sided tape (3M).

[0099] The strength at which the porous coating layer peels off is measured using UTM while peeling the glass slide from the separation film at a speed of 300 mm / min in a direction 180° with respect to the adhesion direction, and the results are shown in Table 1 below.

[0100] [Table 1]

Claims

1. With a porous polymer substrate; A porous coating layer formed on at least one surface of the porous polymer substrate, comprising a polymer binder and inorganic particles; A separation membrane for an electrochemical element, comprising a dopamine coating layer formed on the porous coating layer and containing polydopamine and dextrin, The separation membrane contains the polydopamine and the dextrin in a weight ratio of 1:500 to 1:1000. The polymer binder includes an acrylic binder. A separation membrane for an electrochemical element, wherein at least a portion of the acrylic binder is cross-linked with the polydopamine.

2. The porous coating layer is The separation membrane for an electrochemical element according to claim 1, wherein the content of the polymer binder is 0.1% by weight or more and 5% by weight or less, based on the total weight of the porous coating layer.

3. The separation membrane for an electrochemical element according to claim 1, wherein the polymer binder comprises 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.

4. The separation membrane for an electrochemical element according to claim 1, wherein the thickness of the porous coating layer is greater than the thickness of the dopamine coating layer.

5. 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 4.

6. The aforementioned electrochemical element is The electrochemical element according to claim 5, further comprising an electrolyte containing EC / EMC in a weight ratio of 3 / 7.

7. A preliminary separation membrane comprising a porous polymer substrate and a porous coating layer formed on at least one surface of the porous polymer substrate, comprising a polymer binder and inorganic particles, is immersed in a solution containing dopamine and dextrin for 1 to 50 hours, and A method for producing a separation membrane for an electrochemical element, comprising the step of adjusting the amount of dissolved oxygen in the solution to form a dopamine coating layer containing polydopamine and the dextrin on at least one surface of the porous coating layer, The polymer binder includes an acrylic binder. The process further includes the step of exposing the separation membrane to 60°C to 90°C to thermally crosslink the polymer binder and the polydopamine, The separation membrane comprises the polydopamine and the dextrin in a weight ratio of 1:500 to 1:1000, and is a method for manufacturing a separation membrane for an electrochemical element.

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