Separator for electrochemical device and electrochemical device including 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 acid-based binder, an acrylamide-based binder, and inorganic particles, the porous coating layer comprising about 90 wt% to 96 wt% of the inorganic particles based on the total weight of the porous coating layer, and a weight ratio of the acrylic acid-based binder to the acrylamide-based binder being about 3:7 to 7:3.

Description

[Technical field]

[0001] This application claims priority based on Korean Patent Application No. 10-2023-0038631 filed with the Korean Intellectual Property Office on March 24, 2023, the contents of which are incorporated herein by reference in their entirety.

[0002] The present invention relates to a separator for an electrochemical device and an electrochemical device including the same. [Background technology]

[0003] Electrochemical devices convert chemical energy into electrical energy using electrochemical reactions. In recent years, electrochemical devices including lithium secondary batteries, which have high energy density and voltage, long cycle life, and can be used in various fields, have been widely used.

[0004] The lithium secondary battery may include an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, and may be manufactured by housing the electrode assembly in a case together with an electrolyte. The separator may include a porous coating layer including a polymer binder and inorganic particles on at least one surface of a porous substrate. The inorganic particles may be connected to other inorganic particles by the polymer binder to form an interstitial volume, and lithium ions may move through the interstitial volume. In addition to fixing the inorganic particles, the polymer binder may provide an adhesive force to the porous coating layer, and the porous coating layer may be attached to the porous substrate and the electrode, respectively. Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a separator for an electrochemical device having a reduced dimensional change rate under high temperature wet conditions, a method for manufacturing the same, and an electrochemical device including the separator. [Means for solving the problem]

[0006] The present invention relates to a separator having dimensional stability under high temperature and wet conditions while keeping the content of polymer binder in a porous coating layer relatively low.

[0007] In one aspect of the present invention, there is provided 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 acid-based binder, an acrylamide-based binder, and inorganic particles, the porous coating layer comprising about 90 wt% to 96 wt% of the inorganic particles based on a total weight of the porous coating layer, and a weight ratio of the acrylic acid-based binder to the acrylamide-based binder being about 3:7 to 7:3.

[0008] The acrylamide binder may have a weight average molecular weight of about 400,000 to 1,000,000.

[0009] The porous coating layer is formed by coating the porous polymer substrate with a coating slurry containing the acrylic acid-based binder, the acrylamide-based binder, the inorganic particles, a dispersant, and a dispersion medium, and the coating slurry may have a pH of 3 to 9.

[0010] The acrylic acid-based binder may include one or more monomers selected from the group consisting of acrylic acid and methacrylic acid as a repeating unit.

[0011] The acrylamide-based binder may include one or more monomers selected from the group consisting of acrylamide, methacrylamide, N-ethylacrylamide, ethylmethacrylamide, N-propylacrylamide, N-isopropylacrylamide, N-isopropylmethacrylamide, N-butylacrylamide, and N-butylmethacrylamide as a repeating unit.

[0012] The content of the acrylic acid-based binder in the porous coating layer may be equal to or greater than the content of the acrylamide-based binder.

[0013] Another aspect of the present invention provides an electrochemical device including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, the separator being a separator for an electrochemical device having the above-described characteristics.

[0014] The electrochemical device may be a lithium secondary battery.

[0015] The electrochemical device may further include an electrolyte solution including a solvent in which ethylene carbonate (EC) / ethyl methyl carbonate (EMC) is mixed at a weight ratio of about 3 / 7 or a solvent in which ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / dimethyl carbonate (DMC) is mixed at a weight ratio of about 20 / 5 / 75. Effect of the Invention

[0016] The separator for an electrochemical device according to the present invention can provide improved dimensional stability in a dry state and in a wet state in which the separator is immersed in an electrolyte. For example, the separator has a heat shrinkage rate of about 5% or less in a dry state at a high temperature of 200° C. or more and a heat shrinkage rate of about 10% or less in a wet state at a high temperature of 130° C. or more, so that exposure of electrodes due to heat shrinkage of the separator can be prevented. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, each component of the present invention will be described in more detail so that a person having ordinary skill in the art to which the present invention pertains can easily implement the present invention. However, this is merely an example, and the scope of the present invention is not limited to the following content.

[0018] As used herein, the term "comprising" is used in listing materials, compositions, devices, and methods useful in the present invention, without limiting the listed examples.

[0019] As used in this specification, the terms "about," "approximately," and "substantially" are used to mean a range or approximate value of a numerical value or degree, taking into account inherent manufacturing and material tolerances, and are used to prevent infringers from unfairly taking advantage of the disclosure in which precise numerical values ​​or absolute numerical values ​​are mentioned, which are provided to aid in the understanding of the present invention.

[0020] As used herein, "electrochemical device" may refer to a primary battery, a secondary battery, a supercapacitor, and the like.

[0021] As used herein, the term "wet state" refers to a state in which the separator is at least partially impregnated with the electrolyte, and the term "dry state" refers to a dry state in which the separator is not impregnated with the electrolyte.

[0022] As used herein, "durability" may refer to the property of a binder exhibiting adhesive strength and mechanical strength as inherent physical properties without swelling or deformation when the binder comes into contact with an electrolyte.

[0023] In the electrode assembly that constitutes a secondary battery, the separator is a film material that has the function of isolating the two electrodes (cathode / negative) to prevent electrical short circuit caused by physical contact, and providing a path through which ions can move between the two electrodes via the electrolyte held in the micropores, thereby providing ion conductivity.

[0024] The porous coating layer formed on one side of the separator includes a polymer binder and inorganic particles, and can prevent the thermal shrinkage of the porous polymer substrate. The separator including the porous coating layer exhibits excellent dimensional stability in a dry state without electrolyte, but in a wet state in which the separator is impregnated with electrolyte, the polymer binder may swell due to the electrolyte, or the separator may be exposed to a temperature of about 130°C or higher depending on the operating conditions of the lithium secondary battery including the separator, and the adhesive strength of the polymer binder may decrease. That is, in such a high-temperature wet state, the adhesive strength of the porous coating layer decreases and the separator tends to shrink significantly. For example, a cylindrical battery in which an electrode assembly is wound and inserted into a case while the electrode assembly is under tension is required to have a relatively small adhesive strength between the electrode and the separator compared to a pouch-type battery, so there is a problem that the content of the polymer binder is low and the dimensional stability in the wet state is further decreased.

[0025] The present invention provides a separator having improved dimensional stability under high temperature and wet conditions while keeping the content of polymer binder in the porous coating layer relatively low.

[0026] One embodiment of the present invention provides 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 acid-based binder, an acrylamide-based binder, and inorganic particles, the porous coating layer comprising about 90 wt% to 96 wt% of the inorganic particles based on the total weight of the porous coating layer, and a weight ratio of the acrylic acid-based binder to the acrylamide-based binder being about 3:7 to 7:3.

[0027] The porous polymer substrate may be a porous film having a plurality of pores formed therein, and may electrically insulate the positive and negative electrodes to prevent short circuits. For example, when the electrochemical device is a lithium secondary battery, the porous polymer substrate may be an ion-conductive 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 may form a three-dimensional network that communicates with the surface and the interior of the porous polymer substrate, and a fluid may pass through the porous polymer substrate through the pores.

[0028] The porous polymer substrate may be made of a material that is physically and chemically stable against the electrolyte, which is an organic solvent. For example, the porous polymer substrate may include, but is not limited to, polyolefins such as polyethylene, polypropylene, and polybutylene, polyvinyl chloride, polyethylene terephthalate, polycycloolefin, polyethersulfone, polyamide, polyimide, polyimideamide, nylon, polytetrafluoroethylene, and copolymers or mixtures thereof. For example, a polyolefin resin may be used. Polyolefin resins can be processed to a relatively thin thickness and are easy to apply a coating slurry, making them suitable for manufacturing electrochemical devices with higher energy density.

[0029] 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 having different melting points (Tm) and may provide a shutdown function during high temperature runaway of the battery. For example, the porous polymer substrate may include a polypropylene layer having a relatively high melting point and a polyethylene layer having a relatively low melting point. The porous polymer substrate may have a three-layer structure in which polypropylene, polyethylene, and polypropylene are laminated in this order. The polyethylene layer may shut down the pores as it melts as the temperature of the battery rises above a predetermined temperature, thereby preventing thermal runaway of the battery.

[0030] The thickness of the porous polymer substrate may be about 1 μm to 100 μm. For example, the thickness of the porous polymer substrate may be about 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 polymer substrate may be about 1 μm to 30 μm. For example, the thickness of the polymer substrate may be about 5 μm to 15 μm, or 8 μm to 13 μm. By adjusting the thickness of the porous polymer substrate within the above range, the volume of the electrochemical device can be minimized while electrically insulating the positive and negative electrodes, and the amount of active material contained in the electrochemical device can be increased.

[0031] The porous polymer substrate may include pores having an average diameter of about 0.01 μm to 1 μm. For example, the size of the pores in the porous polymer substrate may be about 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. For example, the size of the pores may be about 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 ion conductivity of the entire separation membrane to be manufactured can be adjusted.

[0032] The porous polymer substrate may have an air permeability of about 10s / 100cc to 100s / 100cc. For example, the air permeability of the porous polymer substrate may be 10s / 100cc to 90s / 100cc, 20s / 100cc to 80s / 100cc, 30s / 100cc to 70s / 100cc, or 40s / 100cc to 60s / 100cc. For example, the air permeability of the porous polymer substrate may be about 50s / 100cc to 70s / 100cc. When the air permeability of the porous polymer substrate is within the above range, the air permeability of the separator to be manufactured can be provided within a range suitable for ensuring the output and cycle characteristics of the electrochemical device.

[0033] The air permeability (s / 100cc) refers to the time (seconds) required for 100cc of air to pass through a porous polymeric substrate or a separator with a predetermined area under a certain pressure. The air permeability can be measured using a Gurley densometer in accordance with ASTM D 726-58, ASTM D726-94, or JIS-P8117. For example, a Gurley 4110N device is used to measure air at a pressure of 0.304kPa or 1.215kN / m. 2 of water pressure in 1 square inch (or 6.54 cm 2 For example, the time it takes for 100 cc of air to pass through a 1 inch square sample at room temperature under a constant pressure of 4.8 inches of water can be measured using the ASAHI SEIKO EG01-55-1MR device.

[0034] The porous polymer substrate may have a porosity of about 10 vol% to 60 vol%. For example, the porosity of the porous polymer substrate may be about 15 vol% to 55 vol%, 20 vol% to 50 vol%, 25 vol% to 45 vol%, or 30 vol% to 40 vol%. For example, the porosity of the porous polymer substrate may be about 30 vol% to 50 vol%. When the porosity of the porous polymer substrate is within the above range, the ion conductivity of the separator produced can be provided within a range suitable for ensuring the output and cycle characteristics of the electrochemical device.

[0035] The porosity means the volume ratio of the pores to the total volume of the porous polymer substrate. The porosity can be measured by a method known in the art. For example, the porosity can be measured by the Brunauer Emmett Teller (BET) measurement method using nitrogen gas adsorption, capillary flow porometer, water or mercury penetration method.

[0036] The porous coating layer is formed on at least one surface of the porous polymer substrate and includes a polymer binder and inorganic particles. The polymer particles may include an acrylic acid-based binder and an acrylamide-based binder.

[0037] The porous coating layer may be formed by coating at least one surface of a porous polymer substrate with a coating slurry including an acrylic acid-based binder, an acrylamide-based binder, inorganic particles, a dispersant, and a dispersion medium. For example, the separator may be manufactured by applying the coating slurry to at least one surface of a porous polymer substrate, and then drying the coating slurry to remove the dispersion medium. The porous coating layer includes an interstitial volume in which the inorganic particles are connected by the acrylic acid-based binder and the acrylamide-based binder, and is adhered to the porous polymer substrate while allowing lithium ions to pass therethrough, thereby preventing thermal shrinkage of the porous polymer substrate.

[0038] The coating slurry includes a dispersion medium, and can dissolve or disperse at least a part of the acrylic acid-based binder or the acrylamide-based binder to 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 can 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. A porous coating layer in which inorganic particles are uniformly dispersed can be formed by using the above-mentioned types of dispersion medium.

[0039] The coating slurry includes a dispersant, and the acrylic acid-based binder, the acrylamide-based binder, and the inorganic particles can be uniformly dispersed. For example, the dispersant may include at least one 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. For example, the dispersant may be a polyacrylic acid-based polymer dispersant. The use of the above-mentioned types of dispersants can improve the stability of the coating slurry and ensure the uniformity of the porous coating layer formed from the coating slurry.

[0040] The dispersant may be included in an amount of about 0.01 wt% to 5 wt% based on the total weight of the coating slurry. For example, the content of the dispersant may be included in an amount of about 0.1 wt% to 4 wt%, 0.5 wt% to 3 wt%, or 1 wt% to 2 wt%. For example, the content of the dispersant may be about 3 wt% to 5 wt%. By adjusting the content of the dispersant within the above range, uniform dispersion and stability of the polymer binder and inorganic particles included in the coating slurry can be achieved.

[0041] The coating slurry containing the dispersant may have a pH of about 3 to 9. For example, the pH of the coating slurry may be about 3.5 to 8.5, 4.0 to 8.0, 4.5 to 7.5, 5.0 to 7.0, or 5.5 to 6.5. For example, the pH of the coating slurry may be about 5.5 to 8.5, or about 6.0 to 8.0. The pH of the coating slurry may be adjusted by changing the type or physical properties of the dispersant. For example, the dispersant may be a polyacrylic acid-based polymer dispersant, and the pH of the coating slurry may be adjusted by adjusting the degree of substitution of the polyacrylic acid-based polymer dispersant. For example, by changing -COOH to -COOH in the polyacrylic acid-based polymer dispersant, - Na +By adjusting the pH of the coating slurry within the above range, the polymer binder, particularly the acrylic acid-based binder, contained in the coating slurry can be uniformly dispersed to improve the binding property with inorganic particles, thereby reducing the thermal shrinkage of the porous coating layer and the separator having the same.

[0042] The coating slurry containing the dispersant may have a viscosity of about 10 cps to 500 cps. For example, the viscosity of the coating slurry may be about 50 cps to 450 cps, 100 cps to 400 cps, 150 cps to 350 cps, or 200 cps to 300 cps. For example, the viscosity of the coating slurry may be about 10 cps to 100 cps, or about 10 cps to 50 cps. If the viscosity of the coating slurry exceeds 500 cps, lumps having an average particle size (D99) of about 100 μm are formed, making it difficult to manufacture a separation membrane by continuous coating on a porous polymer substrate, and productivity cannot be ensured.

[0043] The coating slurry may further include additives such as a surfactant, an antifoaming agent, a flame retardant, and a wetting agent. The additives may be included in an amount of about 0 to 10 wt % based on the total weight of the coating slurry. For example, the content of the additives may be about 0.01 to 9 wt %, 0.1 to 8 wt %, 1 to 7 wt %, 2 to 6 wt %, or 3 to 5 wt %. For example, the content of the additives may be about 1 to 5 wt %. By controlling the content of the additives within the above ranges, the dimensional stability and flame retardancy of the porous coating layer formed by the coating slurry can be ensured.

[0044] 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 5 ppm or less of the dispersion medium. For example, the porous coating layer may be composed of an acrylic acid-based binder, an acrylamide-based binder, inorganic particles, and a dispersant. In the process of removing the dispersion medium, a plurality of pores may be formed on the surface and inside of the porous coating layer. The pores may include interstitial volumes formed by adjacent inorganic particles being connected by the acrylic acid-based binder, the acrylamide-based binder, or both, and may have a structure that forms a three-dimensional network to allow fluid to pass through.

[0045] The thickness of the porous coating layer may be about 1 μm to 15 μm. For example, the thickness of the porous coating layer may be about 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. For example, the thickness of the porous coating layer may be about 1 μm to 5 μm. For example, the thickness of the porous coating layer may be about 1.5 μm to 3.5 μm. By adjusting the thickness of the porous coating layer within the above range, it is possible to minimize the shrinkage of the porous polymer substrate and realize stable adhesion to the porous polymer substrate.

[0046] The acrylic acid-based binder may bind inorganic particles contained in the porous coating layer and provide adhesion of the porous coating layer to the porous polymer substrate. The acrylic acid-based binder may include one or more monomers selected from the group consisting of acrylic acid and methacrylic acid as repeating units. For example, the acrylic acid-based binder may be polyacrylic acid (PAA).

[0047] When the acrylic acid-based binder is included in the coating slurry, the dispersibility of the acrylic acid-based binder can be determined by the pH concentration of the coating slurry. When the pH of the coating slurry is 3 to 9, the inorganic particles can be bound by the acrylic acid-based binder, and the dimensional stability of the porous coating layer can be ensured.

[0048] The weight average molecular weight (Mw) of the acrylic acid-based binder may be about 50,000 to 400,000. For example, the weight average molecular weight of the acrylic acid-based binder may be about 100,000 to 350,000, 150,000 to 300,000, or 200,000 to 250,000. For example, the weight average molecular weight of the acrylic acid-based binder may be about 100,000 to 200,000. By controlling the weight average molecular weight of the acrylic acid-based binder within the above range, dense binding of the inorganic particles can be achieved by uniformly mixing with the inorganic particles in the porous coating layer, thereby reducing the thermal shrinkage rate of the separator.

[0049] The weight average molecular weight of the polymer binder in the present invention can be measured by gel permeation chromatography (GPC, PL GPC220, Agilent Technologies). For example, the weight average molecular weight can be measured using an Agilent High Temperature RI detector under the conditions of a PL Olexis (Polymer Laboratories) column (column temperature 160° C.) with trichlorobenzene (TCB) as a solvent, a sample concentration of 1.0 mg / mL, a flow rate of 1.0 mL / min, and an injection amount of 200 μl (corrected with a cubic function, standard: polystyrene).

[0050] When the acrylamide-based binder is included in the porous coating layer, it can provide the porous coating layer with durability against an electrolyte. The acrylamide-based binder may include one or more monomers selected from the group consisting of acrylamide, methacrylamide, N-ethylacrylamide, ethylmethacrylamide, N-propylacrylamide, N-isopropylacrylamide, N-isopropylmethacrylamide, N-butylacrylamide, and N-butylmethacrylamide as repeating units. The butylacrylamide may collectively refer to sec-butylacrylamide and ter-butylacrylamide, and the butylmethacrylamide may collectively refer to sec-butylmethacrylamide and ter-butylmethacrylamide. For example, the acrylamide-based binder may be polyacrylamide (PAM).

[0051] The weight average molecular weight (Mw) of the acrylamide-based binder may be about 400,000 to 1,000,000. For example, the weight average molecular weight of the acrylamide-based binder may be about 450,000 to 950,000, 500,000 to 900,000, 550,000 to 850,000, 600,000 to 800,000, or 650,000 to 750,000. For example, the weight average molecular weight of the acrylamide-based binder may be about 400,000 to 900,000. By controlling the weight average molecular weight of the acrylamide-based binder within the above range, the viscosity of the coating slurry does not exceed 500 cps, forming a porous coating layer and reducing the thermal shrinkage of the separator.

[0052] The porous coating layer may contain the acrylic acid-based binder and the acrylamide-based binder in a weight ratio of about 3:7 to 7:3. For example, the porous coating layer may contain the acrylic acid-based binder and the acrylamide-based binder in a weight ratio of about 4:6 to 6:4, for example, about 4.5:5.5 to 5.5:4.5. For example, the porous coating layer may have a content of the acrylic acid-based binder equal to or greater than the content of the acrylamide-based binder while satisfying the above-mentioned range. For example, the porous coating layer may contain the acrylic acid-based binder and the acrylamide-based binder in a weight ratio of about 6:4 to 5:5.

[0053] The acrylic acid-based binder can contribute to the formation of the interstitial volume because it is easier to interact with inorganic particles than the acrylamide-based binder. For example, the acrylic acid-based binder can exhibit electrostatic attraction to inorganic particles through a carboxy group or form hydrogen bonds. The acrylamide-based binder exhibits a larger modulus than the acrylic acid-based binder, and can contribute to ensuring durability by maintaining the structure of the porous coating layer even in a wet state in which the separator is impregnated with an electrolyte. By controlling the content of the acrylic acid-based binder and the acrylamide-based binder within the above range, the formation of the interstitial volume by the acrylic acid-based binder and the structural stability of the porous coating layer by the acrylamide-based binder can be simultaneously ensured. A separator having a porous coating layer satisfying the above range can have a reduced thermal shrinkage in a wet state. If the content of the acrylic acid-based binder is higher than the above range, the structural stability of the porous coating layer may be reduced in a wet state, resulting in rapid thermal shrinkage. If the content of the acrylamide-based binder is higher than the above range, the inorganic particles may not be sufficiently bound in a dry state, resulting in rapid thermal shrinkage.

[0054] The porous coating layer includes an acrylic acid-based binder and an acrylamide-based binder, but does not include a copolymer of the acrylic acid-based binder and the acrylamide-based binder. The mixed use of the acrylic acid-based binder and the acrylamide-based binder makes it easier to control the weight average molecular weight and content ratio of each binder compared to the use of the copolymer, so that the advantages of the weight average molecular weight range and the content range described above can be easily achieved at the same time.

[0055] The porous coating layer may include the inorganic particles in an amount of about 90% to 96% by weight based on the total weight of the porous coating layer. For example, the content of the inorganic particles in the total weight of the porous coating layer may be about 90.5% to 95.5% by weight, 91.0% to 95.0% by weight, 91.5% to 94.5% by weight, 92.0% to 94.0% by weight, or 92.5% to 93.5% by weight. For example, the porous coating layer may include the inorganic particles in an amount of about 93% to 96% by weight. Within the above range, a separator having mechanical strength suitable for a cylindrical battery and reduced thermal shrinkage in a wet state may be manufactured. On the other hand, even if the content of the inorganic particles relative to the total weight of the porous coating layer deviates from the above-mentioned range to some extent within the error range, for example, if it is slightly below 90 wt % or slightly above 96 wt % within the error range, it still does not deviate from the spirit of the present invention.

[0056] The inorganic particles may be electrochemically stable. The inorganic particles may be within the operating voltage range of the electrochemical device (e.g., Li / Li +There are no particular limitations on the inorganic particles as long as they do not undergo oxidation and / or reduction reactions at a voltage of 0 to 5 V relative to the electrolyte. In particular, when inorganic particles having a high dielectric constant are used as the inorganic particles, they can contribute to an increase in the degree of dissociation of an electrolyte salt, for example, a lithium salt, in the liquid electrolyte, thereby improving the ionic conductivity of the electrolyte. For the reasons described above, it is preferable that the inorganic particles include inorganic particles having a high dielectric constant, with a dielectric constant of about 5 or more, for example, about 10 or more. Non-limiting examples of inorganic particles having a dielectric constant of 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.

[0057] In addition, inorganic particles having a lithium ion transfer ability, i.e., inorganic particles containing lithium element but having a function of transferring lithium ions without storing lithium, may be used as the inorganic particles. Non-limiting examples of inorganic particles having a lithium ion transfer ability include lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0 <x<2、0<y<3)、リチウムアルミニウムチタンホスフェート(Li x Al y Ti z (PO4)3, 0 <x<2、0<y<1、0<z<3)、14Li2O-9Al2O3-38TiO2-39P2O5などのような(LiAlTiP) x O y Glass (0 <x<4、0<y<13)、リチウムランタンチタネート(Li x La y TiO3, 0 <x<2、0<y<3)、Li 3.25 Ge0.25 P 0.75 Lithium germanium thiophosphate such as S4 (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 a mixture thereof, etc.

[0058] In addition, 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 the 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.

[0059] The average particle size (D50) of the inorganic particles may be about 50 nm to 5,000 nm. For example, the average particle size (D50) of the inorganic particles may be about 100 nm to 4,500 nm, 200 nm to 4,000 nm, 300 nm to 3,000 nm, 400 nm to 2,000 nm, or 500 nm to 1,000 nm. If the average particle size of the inorganic particles is less than about 50 nm, the specific surface area increases, and 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.

[0060] The aspect ratio of the inorganic particles may be about 1 to 2. For example, the aspect ratio of the inorganic particles may be about 1.1 to 1.9, 1.2 to 1.8, 1.3 to 1.7, or 1.4 to 1.6. By controlling the aspect ratio of the inorganic particles within the above ranges, the polymer binder can easily move through the voids between the inorganic particles, and ultimately a porous coating layer including interstitial volumes through which lithium ions can move can be formed.

[0061] The BET specific surface area of ​​the inorganic particles is approximately 5 m 2 / g or more 25m 2 For example, the BET specific surface area of ​​the inorganic particles may be about 6 m 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 By adjusting the BET specific surface area of ​​the inorganic particles within the above range, the movement of the polymer binder through the voids between the inorganic particles can be adjusted.

[0062] The separator for an electrochemical device may have an air permeability of about 50s / 100cc to 150s / 100cc. For example, the air permeability of the separator may be about 60s / 100cc to 140s / 100cc, 70s / 100cc to 130s / 100cc, 80s / 100cc to 120s / 100cc, or 90s / 100cc to 110s / 100cc. For example, the air permeability of the separator may be about 100s / 100cc to 120s / 100cc. When the air permeability of the separator is within the above range, the output, stability, and cycle characteristics of the electrochemical device can be ensured.

[0063] The separator for electrochemical devices may have a heat shrinkage of about 10% or less. For example, the separator may have a heat shrinkage of 5% or less in a dry state, and a heat shrinkage of 10% or less in a wet state. For example, the heat shrinkage of the separator in a dry state may be a dimensional change rate when exposed to 200° C. for 30 minutes, and the heat shrinkage of the separator in a wet state may be a dimensional change rate when exposed to 135° C. for 30 minutes while being immersed in an electrolyte. For example, the separator may have a heat shrinkage of about 5% or less in both MD and TD in a dry state, and a heat shrinkage of about 10% or less in both MD and TD in a wet state.

[0064] When a cell is manufactured using the separator for an electrochemical device, the cell may have an electrical resistance of about 0.5 Ohm to 1.5 Ohm. For example, the electrical resistance of the cell may be about 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. For example, the electrical resistance of the cell may be about 0.6 Ohm to 0.8 Ohm.

[0065] Another embodiment of the present invention provides an electrochemical device including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, the separator being the separator for an electrochemical device of the embodiment described above. The electrochemical device may be manufactured by inserting an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode into a case or pouch and sealing the case or pouch. Before sealing the case or pouch, an electrolyte may be injected to impregnate the electrode assembly with the electrolyte. The shape of the case or pouch is not limited. For example, the electrochemical device may be a cylindrical, square, coin, or pouch type lithium secondary battery.

[0066] The positive electrode and the negative electrode may be coated by applying and drying an electrode active material to at least one surface of each current collector. The current collector may be a material having electrical conductivity without causing a chemical change in the electrochemical device. For example, the positive electrode current collector may be, but is not limited to, aluminum, nickel, titanium, calcined carbon, stainless steel, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, or the like. For example, the negative electrode current collector may be, but is not limited to, copper, nickel, titanium, calcined carbon, stainless steel, or copper or stainless steel surface treated with carbon, nickel, titanium, silver, or the like. The current collector may be in various forms such as a metal sheet, a film, a foil, a net, a porous body, a foam, or the like.

[0067] 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 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 Li in the chemical formula is substituted with alkaline earth metal ions; disulfide compounds; one or more mixtures of Fe2(MoO4)3 may be included.

[0068] 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 oxides, graphitizable carbon, and graphite-based carbon; LixFe2O3 (0 ≤ x ≤ 1), LixWO2 (0 ≤ x ≤ 1), Si, SiO x (0 < x < 2), silicon-based materials such as SiC and Si alloys; 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.

[0069] 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 has an sp 2 bonding structure, and exhibits conductor or semiconductor characteristics depending on the winding angle and structure of the graphite sheet. 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 liquid. For example, it may be one or a mixture of two or more conductive materials 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.

[0070] As the binder resin, a binder resin that is usually used for electrodes of electrochemical elements can be used. Non-limiting examples of such binder resins include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-cotrichloroethylene, polymethylmethacrylate, polyethylhexyl acrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylene-vinyl acetate copolymer, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate. Examples of the cellulose acetate propionate include, but are not limited to, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, and carboxyl methyl cellulose.

[0071] The electrolyte is A + B - A salt having the structure: + Li + , Na + , K+ or a combination thereof, - PF6 - , BF4 - , Cl - , Br - , I - , ClO4 - , AsF6 - , CH3CO2 - , CF3SO3 - , N(CF3SO2)2 - , C(CF2SO2)3 - or a combination thereof may be dissolved or dissociated in an organic solvent such as 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 a mixture thereof.

[0072] For example, the electrolyte may include a solvent having a weight ratio of EC / EMC of approximately 3 / 7 or a solvent having a weight ratio of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / dimethyl carbonate (DMC) of approximately 20 / 5 / 75, which can maximize the dimensional stability of the separator according to the embodiment.

[0073] The electrochemical device including the electrode assembly may be a lithium secondary battery. The battery may be used as a unit cell, and may 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 the device include, but are not limited to, small devices such as computers, mobile phones, and power tools; electric vehicles including electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (PHEV), which are powered by electric motors; electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters; electric golf carts; and power storage systems.

[0074] According to another embodiment of the present invention, there is provided a method for preparing a separator for an electrochemical device, the method comprising the steps of forming a porous coating layer including an acrylic acid-based binder, an acrylamide-based binder, and inorganic particles on at least one surface of a porous polymer substrate. Any overlapping content with that described in the above embodiment of the separator for an electrochemical device shall be replaced with the description of the previous embodiment.

[0075] The step of forming the porous coating layer may include preparing a coating slurry including an acrylic acid-based binder and an acrylamide-based binder as a polymer binder, inorganic particles, a dispersant, and a dispersion medium, applying the coating slurry to the porous polymer substrate, and drying the coating slurry. For example, the coating slurry may be prepared by first mixing an acrylamide-based binder, inorganic particles, a dispersant, and a dispersion medium, and then adding an acrylic acid-based binder to prevent aggregation and precipitation of the acrylamide-based binder and the acrylic acid-based binder.

[0076] The step of forming the porous coating layer may further include a step of corona-discharging at least one surface of the porous polymer substrate before applying the coating slurry to the porous polymer substrate. The step of corona-discharging at least one surface of the porous polymer substrate may prevent a decrease in adhesion between the surface of the porous polymer substrate and the surface of the coating layer at high temperatures, and may prevent a decrease in adhesion between the surface of the polymer substrate and the surface of the coating layer due to an electrolyte.

[0077] The corona discharge treatment may be performed by treating at least one surface of the porous polymer substrate in air at a voltage of 0.1 kV to 10 kV. For example, the corona discharge treatment may be performed in air at a voltage of 0.2 kV to 9 kV, 0.3 kV to 8 kV, 0.4 kV to 7 kV, 0.5 kV to 6 kV, 0.6 kV to 5 kV, 0.7 kV to 4 kV, 0.8 kV to 3 kV, 0.9 kV to 2 kV, or 1.0 kV to 2 kV. For example, the corona discharge treatment may be performed in air at a voltage of 1.8 kV. By adjusting the applied voltage of the corona discharge treatment within the above range, an appropriate number of functional groups can be formed on the surface of the polymer substrate, and damage to the surface of the polymer substrate can be prevented.

[0078] The step of forming the porous coating layer may include applying the coating slurry to the porous polymer substrate to coat it. For example, the coating may be formed by a method such as, but not limited to, a bar coater, a wire bar coater, a roll coater, a spray coater, a spin coater, an inkjet coater, a screen coater, a reverse coater, a gravure coater, a knife coater, a slot die coater, a hot melt coater, a comma coater, a direct metering coater, etc. For example, the step of forming the coating layer may be simultaneously coating the coating slurry on both sides of the porous polymer substrate using a bar coater or a slot die coater.

[0079] The step of forming the porous coating layer may include applying the coating slurry to a porous polymer substrate, and then drying or heating the coating layer to evaporate the dispersion medium contained in the coating layer. The removal of the dispersion medium may be performed at a temperature at which only the dispersion medium contained in the coating layer can be evaporated without deforming the polymer binder contained in the coating layer. For example, the removal of the dispersion medium may be performed by heating the coating layer at a predetermined temperature, but the temperature of the surface of the coating layer does not exceed 60°C. When the coating layer is heated under the above conditions, the thermal energy may be used first to heat the dispersion medium to cause a phase change, and not to deform the polymer binder.

[0080] The present invention will be described in more detail below with reference to specific examples and experimental examples. The following examples and experimental examples are provided to illustrate the present invention, and the present invention is not limited to the following examples and experimental examples.

[0081] Example 1 Preparation of coating slurry Into a 250 mL wide-mouth round bottle at room temperature (25°C), 67 mL of water, 5.4 g (solid content 10%) of an acrylamide binder (polyacrylamide, Mw: 900,000), and 30 g of Al2O3 (particle size: 500 nm) as inorganic particles were added, and beads were further added, and the bottle was shaken to mix.

[0082] 2.1 g (solid content 25%) of acrylic acid-based binder (polyacrylic acid, Mw: 350,000) and 1.1 g (solid content 42%) of polyacrylic acid-based polymer dispersant were added to the bottle and stirred twice with a shaker (total of 2 hours), and then 0.2 g (solid content 100%) of wetting agent was added and stirred for another 15 minutes with a shaker to prepare a slurry.

[0083] The slurry was filtered through a filter to remove lumps, producing a coating slurry with a solid content of 30% and a pH of 7.0.

[0084] Preparation of porous polymer substrates A polyethylene film with a size of 20 cm×30 cm and a thickness of 10 μm was used as the porous polymer substrate.

[0085] Separation membrane manufacturing The coating slurry was coated on both sides of a polyethylene film using a bar coater to form a coating layer with a thickness of 1.5 μm.

[0086] The polyethylene film on which the coating layer was formed was subjected to a blowing force to remove the dispersion medium, and the process was repeated five times to prepare a separator with a total thickness of 13 μm.

[0087] Comparative Example 1 A separator was prepared in the same manner as in Example 1, except that a polyacrylic acid-based polymer dispersant (solid content: 25%) having a different substitution degree from the dispersant in Example 1 was used to prepare the coating slurry, and the pH of the coating slurry was adjusted to 2.5.

[0088] Example 2 A separator was prepared in the same manner as in Example 1, except that polyacrylamide (Mw: 400,000, solid content: 15%) was used as the acrylamide-based binder in preparing the coating slurry.

[0089] Comparative Example 2 A separator was prepared in the same manner as in Example 1, except that polyacrylamide (Mw: 1,200,000, solid content: 5%) was used as the acrylamide-based binder in preparing the coating slurry.

[0090] Example 3 A separation membrane was prepared in the same manner as in Example 1, except that 3 g of polyacrylic acid (solid content: 25%) and 3.2 g of polyacrylamide (solid content: 10%) were used in preparing the coating slurry.

[0091] Example 4 A separation membrane was prepared in the same manner as in Example 1, except that 1.3 g of polyacrylic acid (solid content: 25%) and 7.6 g of polyacrylamide (solid content: 10%) were used in preparing the coating slurry.

[0092] Comparative Example 3 A separator was prepared in the same manner as in Example 1, except that 4.3 g of polyacrylic acid (solid content: 25%) was used in preparing the coating slurry, and no acrylamide-based binder was used.

[0093] Comparative Example 4 A separator was manufactured in the same manner as in Example 1, except that 11 g of polyacrylamide (solid content: 10%) was used in preparing the coating slurry, and no acrylic acid-based binder was used.

[0094] Experimental example 1. Confirmation of separation membrane properties according to coating slurry properties The physical properties of the separation membranes prepared in Example 1 and Comparative Example 1 were confirmed and are shown in Table 1 below.

[0095] Confirmation of improvement in heat shrinkage rate in dry state

[0096] The separators of the examples and comparative examples were prepared as test pieces measuring 5 cm x 5 cm each. After storing them in a convection oven at 200°C for 30 minutes, the thermal shrinkage in the MD and TD directions was calculated according to [(initial test piece length - @ length after storing at 200°C / 0.5h) / (initial test piece length)] x 100(%).

[0097] Confirmation of improvement in heat shrinkage rate in wet state

[0098] The separators of the examples and comparative examples were prepared as test pieces measuring 5 cm x 5 cm, and inserted into aluminum pouches measuring 7 cm x 10 cm, respectively. 1 g of the following electrolyte was poured into the pouches, and the pouches were sealed.

[0099] The electrolyte 1 used was a mixture of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) in a weight ratio of 3 / 7, containing 2% by weight of vinylene carbonate (VC) as an additive, and lithium salt LiPF61M.

[0100] The electrolyte 2 used was a mixture of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / dimethyl carbonate (DMC) in a weight ratio of about 20 / 5 / 75. The sealed pouch was stored in a convection oven at 135° C. for 30 minutes, and then the separator was removed. The thermal shrinkage in the machine direction (MD) and transverse direction (TD) was calculated according to [(initial specimen length-@length after storage at 135° C. / 0.5 h) / (initial specimen length)]×100(%).

[0101] [Table 1]

[0102] Experimental Example 2. Confirmation of separation membrane properties according to the molecular weight of acrylamide binder The state of the separation membranes produced according to Examples 1 and 2 and Comparative Example 2 was confirmed, and the physical properties of each separation membrane were confirmed and are shown in the following Table 2. The method for confirming each physical property was the same as in the previous experimental examples.

[0103] [Table 2]

[0104] Experimental Example 3. Confirmation of the physical properties of separation membranes according to the weight ratio of acrylic acid-based binders and acrylamide-based binders The state of the separation membranes produced according to Examples 1, 3, 4 and Comparative Examples 3 to 4 was confirmed, and the physical properties of each separation membrane were confirmed and are shown in the following Table 3. The method for confirming each physical property was the same as in the previous experimental examples.

[0105] [Table 3]

[0106] Although the present invention has been described above with reference to the preferred embodiments, it will be understood that those skilled in the art or those having ordinary knowledge in the art can modify and change the present invention in various ways without departing from the spirit and technical scope of the present invention as described in the claims below. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be determined by the claims.

Claims

1. The present invention includes a porous polymer substrate and a porous coating layer formed on at least one surface of the porous polymer substrate, The porous coating layer includes an acrylic acid-based binder, an acrylamide-based binder, and inorganic particles, The porous coating layer includes the inorganic particles in an amount of 90 wt % to 96 wt % based on the total weight of the porous coating layer, A separator for an electrochemical device, wherein a weight ratio of the acrylic acid-based binder to the acrylamide-based binder is 3:7 to 7:

3.

2. 2. The separator for an electrochemical device according to claim 1, wherein the acrylamide-based binder has a weight average molecular weight of 400,000 to 1,000,000.

3. The porous coating layer is formed by coating the porous polymer substrate with a coating slurry including the acrylic acid-based binder, the acrylamide-based binder, the inorganic particles, a dispersant, and a dispersion medium, 2. The separator for an electrochemical device according to claim 1, wherein the coating slurry has a pH of 3 to 9.

4. 2. The separator for an electrochemical device according to claim 1, wherein the acrylic acid-based binder comprises at least one monomer selected from the group consisting of acrylic acid and methacrylic acid as a repeating unit.

5. 2. The separator for an electrochemical device according to claim 1, wherein the acrylamide-based binder comprises at least one monomer selected from the group consisting of acrylamide, methacrylamide, N-ethylacrylamide, ethylmethacrylamide, N-propylacrylamide, N-isopropylacrylamide, N-isopropylmethacrylamide, N-butylacrylamide, and N-butylmethacrylamide as a repeating unit.

6. The separator for an electrochemical device according to claim 1 , wherein the content of the acrylic acid-based binder in the porous coating layer is equal to or greater than the content of the acrylamide-based binder.

7. An electrochemical device comprising a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, The separation membrane is The present invention includes a porous polymer substrate and a porous coating layer formed on at least one surface of the porous polymer substrate, The porous coating layer includes an acrylic acid-based binder, an acrylamide-based binder, and inorganic particles, The porous coating layer includes the inorganic particles in an amount of 90 wt % to 96 wt % based on the total weight of the porous coating layer, The weight ratio of the acrylic acid-based binder to the acrylamide-based binder is 3:7 to 7:

3.

8. 8. The electrochemical element of claim 7, further comprising an electrolyte solution comprising a solvent in which ethylene carbonate (EC) / ethyl methyl carbonate (EMC) is mixed in a weight ratio of about 3 / 7 or a solvent in which ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / dimethyl carbonate (DMC) is mixed in a weight ratio of 20 / 5 / 75.

9. 8. The electrochemical device according to claim 7, wherein the acrylamide-based binder has a weight average molecular weight of 400,000 to 1,000,000.

10. The porous coating layer comprises: The porous polymer substrate is coated with a coating slurry including the acrylic acid-based binder, the acrylamide-based binder, the inorganic particles, a dispersant, and a dispersion medium, 8. The electrochemical device according to claim 7, wherein the coating slurry has a pH of 3 to 9.

11. 8. The electrochemical device according to claim 7, wherein the acrylic acid-based binder comprises at least one monomer selected from the group consisting of acrylic acid and methacrylic acid as a repeating unit.

12. 8. The electrochemical device of claim 7, wherein the acrylamide-based binder includes at least one monomer selected from the group consisting of acrylamide, methacrylamide, N-ethylacrylamide, ethylmethacrylamide, N-propylacrylamide, N-isopropylacrylamide, N-isopropylmethacrylamide, N-butylacrylamide, and N-butylmethacrylamide as a repeating unit.

13. The electrochemical device according to claim 7 , wherein the content of the acrylic acid-based binder in the porous coating layer is equal to or greater than the content of the acrylamide-based binder.

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