Separation Membrane for Electrochemical Element and Electrochemical Element Containing the Same

Abstract

The present invention provides a porous polymer substrate and a porous coating layer formed on at least one surface of the porous polymer substrate, the porous coating layer including a polymer binder, inorganic particles, and an organic filler, the polymer binder being included in an amount of 1 to 10 parts by weight based on the total weight of the porous coating layer, and the inorganic particles having a packing density of 2 g / cm. 3 More than 2.5g / cm 3 The following separator for an electrochemical device is provided.

Description

Technical Field

[0001] This application claims priority based on Korean Patent Application No. 10-2023-0026219, filed with the Korean Intellectual Property Office on February 27, 2023, the content of which is incorporated herein by reference in its entirety.

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

Background Art

[0003] An electrochemical device can convert chemical energy into electrical energy by using an electrochemical reaction. In recent years, lithium secondary batteries with high energy density, high voltage, long cycle life, and usable in various fields have been widely used.

[0004] A lithium secondary battery may include an electrode assembly manufactured with a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, and the electrode assembly can be manufactured by housing it 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 can be connected to other inorganic particles by a polymer binder to form an intersticial volume, and lithium ions can move through the intersticial volume. In addition to fixing the inorganic particles, the polymer binder can impart adhesion to the porous coating layer, and the porous coating layer can be adhered to the porous substrate and the electrode, respectively.

[0005] A porous coating layer containing a polymer binder and inorganic particles can prevent the thermal shrinkage of a porous polymer substrate, and a separation membrane including the porous coating layer exhibits excellent dimensional stability in a dry state without an electrolyte. However, in a wet state where the separation membrane is impregnated with an electrolyte, the polymer binder may swell due to the electrolyte, or the separation membrane may be exposed to a temperature of about 130 °C or higher due to the operation of a lithium secondary battery including the separation membrane, which may reduce the adhesive force of the polymer binder. In such a high-temperature wet state, the adhesive force of the porous coating layer decreases and the separation membrane shrinks significantly. In particular, in a cylindrical battery in which an electrode assembly is wound and inserted into a case with tension applied to the electrode assembly, the adhesive force between the electrode and the separation membrane is relatively lower than that of a pouch-type battery. Therefore, there is a problem that when the content of the polymer binder decreases, the dimensional stability in the wet state further deteriorates.

[0006] Therefore, research has been conducted on a separation membrane for ensuring dimensional stability under high-temperature and wet-state conditions while relatively maintaining a low content of the polymer binder in the porous coating layer.

Summary of the Invention

Problems to be Solved by the Invention

[0007] An object of the present invention is to provide a separation membrane for an electrochemical device that has excellent heat resistance and an improved shrinkage rate in a state impregnated with an electrolyte by adjusting the packing density of inorganic particles contained in a porous coating layer and further including an organic filler.

Means for Solving the Problems

[0008] One aspect of 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 a polymer binder, inorganic particles, and an organic filler. The polymer binder is included in an amount of 1 to 10 parts by weight based on the total weight of the porous coating layer, and the packing density of the inorganic particles is 2 g / cm 3 or more and 2.5 g / cm 3 or less. A separation membrane for an electrochemical element is provided.

[0009] The organic filler may be one or more selected from the group consisting of polyethylene, polyacetal, polysulfone (PSF), polyethersulfone (PES), polyetherimide (PEI), polyphenylene sulfide (PPS), polyetheretherketone (PEEK), polycarbonate, polyamideimide (PAI), polyimide (PI), polyamide, polyphenylene oxide, polybutylene terephthalate, and polyethylene terephthalate.

[0010] The polymer binder and the organic filler may be included in a weight ratio of 5:1 to 1:5.

[0011] The polymer binder may be one or more selected from the group consisting of polyacrylic acid, polyacrylamide, methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, ethylhexyl acrylate, methyl methacrylate, styrene-butadiene rubber, nitrile-butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, and copolymers containing one or more of these.

[0012] The weight average molecular weight of the polymer binder may be 100,000 to 500,000.

[0013] The packing density of the inorganic particles may be 2.1 g / cm 3 or more and 2.3 g / cm 3 or less.

[0014] Another aspect of the present invention is an electrochemical device including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the separator is a separator for another electrochemical device on the one side, and provides an electrochemical device.

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

[0016] The electrochemical device may further include an electrolytic solution containing EC / EMC in a weight ratio of 3 / 7.

Effects of the Invention

[0017] The separator for an electrochemical device according to the present invention can provide improved dimensional stability in a wet state impregnated with an electrolytic solution. Specifically, since the separator has a thermal shrinkage rate in the TD direction of 10% or less under a high temperature condition of 130 °C or higher, it is possible to prevent exposure of the electrodes due to thermal shrinkage of the separator.

Embodiments for Carrying Out the Invention

[0018] Hereinafter, each configuration of the present invention will be described in more detail so that those having ordinary knowledge in the technical field to which the present invention pertains can easily implement it. However, this is merely an example, and the scope of the rights of the present invention is not limited by the following content.

[0019] The term "including" used in this specification is used when listing materials, compositions, devices, and methods useful for the present invention, and is not limited to the listed examples.

[0020] The terms "about" and "substantially" used in this specification are used in a sense close to or within the range of that numerical value or degree, taking into account inherent manufacturing and material tolerances, and are used to prevent an infringer from improperly using the disclosed content in which an exact numerical value or absolute numerical value is mentioned to assist in understanding the present invention.

[0021] As used herein, the "electrochemical element" may mean a primary battery, a secondary battery, a supercapacitor, etc.

[0022] As used herein, the "Wet state" may mean a state in which the separator is impregnated with at least a part of the electrolyte.

[0023] One specific example of 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 a polymer binder, inorganic particles, and an organic filler. The polymer binder is included in an amount of 1 to 10 parts by weight based on the total weight of the porous coating layer, and the packing density of the inorganic particles is 2 g / cm 3 or more and 2.5 g / cm 3 or less. A separator for an electrochemical element is provided.

[0024] The porous polymer substrate is a porous membrane having a plurality of pores, and may electrically insulate the positive electrode and the negative electrode to prevent short circuit. For example, when the electrochemical element is a lithium secondary battery, the porous polymer substrate may be an ion conductive barrier that allows lithium ions to pass through while blocking electrical contact between the positive electrode and the negative electrode. At least a part of the pores can form a three-dimensional network that connects the surface and the inside of the porous polymer substrate, and fluid can pass through the porous polymer substrate through the pores.

[0025] For the porous polymer substrate, a material that is physically and chemically stable against the electrolytic solution which is an organic solvent can be used. For example, the porous polymer substrate may include, but is not limited to, resins such as polyolefins such as polyethylene, polypropylene, and polybutylene, polyvinyl chloride, polyethylene terephthalate, polycycloolefin, polyethersulfone, polyamide, polyimide, polyimide amide, nylon, polytetrafluoroethylene, and copolymers or mixtures thereof. Preferably, polyolefin resins can be used. Polyolefin resins can be processed into a relatively thin thickness, and since it is easy to apply the coating slurry, it is suitable for manufacturing electrochemical elements having a higher energy density.

[0026] The porous polymer substrate can have a single-layer or multi-layer structure. The porous polymer substrate can provide a shutdown function during high-temperature thermal runaway of the battery by including two or more polymer resin layers having different melting points (Tm). 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 can have a three-layer structure laminated in the order of polypropylene, polyethylene, and polypropylene. The polyethylene layer can melt as the temperature of the battery rises above a predetermined temperature, thereby shutting down the pores and preventing thermal runaway of the battery.

[0027] The thickness of the porous polymer substrate can be 1 μm or more and 100 μm or less. Specifically, the thickness of the porous polymer substrate can be 10 μm or more and 90 μm or less, 20 μm or more and 80 μm or less, 30 μm or more and 70 μm or less, or 40 μm or more and 60 μm or less. Preferably, the thickness of the polymer substrate can be 1 μm or more and 30 μm or less. More preferably, the thickness of the polymer substrate can be 5 μm or more and 15 μm or less, or 8 μm or more and 13 μm or less. By adjusting the thickness of the porous polymer substrate within the above-described range, while electrically insulating the positive electrode and the negative electrode, the volume of the electrochemical element can be minimized, and the amount of the active material contained in the electrochemical element can be increased.

[0028] The porous polymer substrate may include pores having 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 pore size of the porous polymer substrate within the above-described range, the air permeability and ion conductivity of the entire produced separation membrane can be adjusted.

[0029] 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-described range, the air permeability of the produced separation membrane can be provided within a range suitable for ensuring the output and cycle characteristics of the electrochemical device.

[0030] The air permeability (s / 100 cc) means the time (seconds) required for 100 cc of air to pass through a porous polymer substrate or separation membrane of a predetermined area under a constant 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, using a 4110N device from Gurley, under a pressure of air at 0.304 kPa or water at 1.215 kN / m 2 of the pressure, the time for 100 cc of air to pass through 1 square inch (or 6.54 cm 2) The time it takes for a sample to pass through can be measured. For example, using the EG01-55-1MR device from Asahi Seiko, at room temperature under a constant pressure of 4.8 inches of water, the time it takes for 100 cc of air to pass through a 1 square inch sample can be measured.

[0031] The porous polymer substrate can have a porosity of 10 vol% or more and 60 vol% or less. Specifically, the porosity of the porous polymer substrate can be 15 vol% or more and 55 vol% or less, 20 vol% or more and 50 vol% or less, 25 vol% or more and 45 vol% or less, or 30 vol% or more and 40 vol% or less. Preferably, the porosity of the porous polymer substrate can be 30 vol% or more and 50 vol% or less. When the porosity of the porous polymer substrate is within the above-mentioned range, the ionic conductivity of the produced separation membrane can be provided within a range suitable for ensuring the output and cycle characteristics of the electrochemical device.

[0032] The porosity means the volume ratio of pores to the total volume of the porous polymer substrate. The porosity can be measured by methods known in the art. For example, it can be measured by the BET (Brunauer Emmett Teller) measurement method using nitrogen gas adsorption, capillary flow porometer, or water or mercury penetration method.

[0033] The porous coating layer is formed on at least one surface of the porous polymer substrate and contains a polymer binder, inorganic particles, and an organic filler. The porous coating layer can be formed by coating at least one surface of the porous polymer substrate with a coating slurry containing a polymer binder, inorganic particles, an organic filler, and a dispersion medium. The porous coating layer contains an interstitial volume in which the inorganic particles are connected by the polymer binder, allows lithium ions to pass through, adheres to the porous polymer substrate, and prevents thermal shrinkage of the porous polymer substrate.

[0034] The coating slurry contains a dispersion medium and can dissolve or disperse at least a part of a polymer binder and an organic filler and disperse inorganic particles. The coating slurry can be one in which the types and contents of the dispersion medium are adjusted so that the polymer binder, inorganic particles, and organic filler are uniformly dispersed. 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. Preferably, the dispersion medium can be NMP. Using the above-described types of dispersion media, a porous coating layer in which the polymer binder and inorganic particles are uniformly dispersed can be formed.

[0035] The coating slurry further contains additives such as a dispersant, a surfactant, an antifoaming agent, and a flame retardant, and can improve dispersibility and flame retardancy and improve the uniformity of the formed porous coating layer. For example, the dispersant can contain one or more selected from the group consisting of polyacrylic acid, oil-soluble polyamine, oil-soluble amine compounds, fatty acids, fatty alcohols, sorbitan fatty acid esters, tannic acid, and pyrogallic acid. 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.

[0036] Based on the total weight of the coating slurry, the additive can be contained in an amount of 0 wt% or more and 5 wt% or less. Specifically, the content of the additive can be contained in an amount of 0.01 wt% or more and 4 wt% or less, 0.1 wt% or more and 3 wt% or less, or 1 wt% or more and 2 wt% or less. Preferably, the content of the additive can be 1 wt% or more and 5 wt% or less. By adjusting the content of the additive within the above-described range, uniform dispersion and stability of the inorganic particles contained in the coating slurry can be achieved.

[0037] The dispersion medium contained in the coating slurry can be removed by drying or heating after the formation of the porous coating layer. For example, the porous coating layer can contain the dispersion medium at 5 ppm or less. Preferably, the porous coating layer can be composed of a polymer binder and inorganic particles. In the process of removing the dispersion medium, a plurality of pores can be formed on the surface and inside of the porous coating layer. The pores can include the interstitial volume formed between the inorganic particles and can have a structure that forms a three-dimensional network through which fluids can pass.

[0038] The thickness of the porous coating layer can be 1 μm or more and 15 μm or less. Specifically, the thickness of the porous coating layer can be 2 μm or more and 14 μm or less, 3 μm or more and 13 μm or less, 4 μm or more and 12 μm or less, 5 μm or more and 11 μm or less, 6 μm or more and 10 μm or less, or 7 μm or more and 9 μm or less. Preferably, the thickness of the porous coating layer can be 1 μm or more and 5 μm or less, more preferably 1 μm or more and 3 μm or less. By adjusting the thickness of the porous coating layer within the above-described range, shrinkage of the porous polymer substrate can be minimized, and stable adhesion to the porous polymer substrate can be realized.

[0039] The polymer binder can bind the inorganic particles contained in the porous coating layer and impart adhesive strength to the porous coating layer. The polymer binder can be spherical or elliptical, but can include other shapes excluding amorphous shapes.

[0040] The polymer binder may include an acrylic binder. For example, the acrylic binder may be one or more selected from the group consisting of polyacrylic acid, polyacrylamide, methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, ethylhexyl acrylate, methyl methacrylate, styrene-butadiene rubber, nitrile-butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, and copolymers containing one or more of these. The acrylic binder can bind inorganic particles to form a network structure and exhibit an adhesive force to the porous polymer substrate and the electrode. Preferably, the polymer binder may include a copolymer of polyacrylic acid and polyacrylamide. Although the polymer binder may be swollen by the electrolyte and the adhesive force may decrease, the copolymer of polyacrylic acid and polyacrylamide has less swelling by the electrolyte and is heat-resistant. Therefore, the separation membrane containing the copolymer can improve the thermal shrinkage rate in the wet state.

[0041] The weight average molecular weight of the polymer binder can be 100,000 to 500,000. Specifically, the weight average molecular weight of the polymer binder can be 150,000 or more and 450,000 or less, 200,000 or more and 400,000 or less, or 250,000 or more and 350,000 or less. Preferably, the weight average molecular weight of the polymer binder can be 100,000 to 300,000. By adjusting the weight average molecular weight of the polymer binder within the above-described range, the swelling of the polymer binder by the electrolyte can be reduced, and the thermal shrinkage rate of the separation membrane containing the same can be improved.

[0042] 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 TCB (Trichlorobenzene) as a solvent in a PL Olexis (Polymer Laboratories) column (column temperature: 160°C), with a sample concentration of 1.0 mg / mL, a flow rate of 1.0 mL / min, an injection volume of 200 μL, and an Agilent High Temperature differential refractive index detector (RI detector) (reference: Polystyrene).

[0043] The porous coating layer may contain 1 to 10 parts by weight of the polymer binder based on the total weight of the porous coating layer. Specifically, the porous coating layer may contain the polymer binder in an amount of 1 to 9 parts by weight, 2 to 8 parts by weight, 3 to 7 parts by weight, or 4 to 6 parts by weight. Preferably, the porous coating layer may contain 1 to 5 parts by weight of the polymer binder. If the content of the polymer binder is less than 1 part by weight, an interstitial volume due to binding between inorganic particles is not formed, making it difficult for lithium ions to be transmitted and increasing the electrical resistance of the separation membrane. If the content of the polymer binder exceeds 10 parts by weight, the amount of the polymer binder swollen by the electrolyte increases, and the porous coating layer may peel off from the porous polymer substrate.

[0044] The organic filler is a polymer resin with a melting point (Tm) or glass transition temperature (Tg) of 100 °C or higher, which imparts heat resistance to the porous coating layer and can prevent the separation membrane from shrinking when in a high-temperature wet state. For example, the organic filler can be one or more selected from the group consisting of polyethylene, polyacetal, polysulfone, polyethersulfone, polyetherimide, polyphenylene sulfide, polyetheretherketone, polycarbonate, polyamideimide, polyimide, polyamide, polyphenylene oxide, polybutylene terephthalate, and polyethylene terephthalate. Preferably, the organic filler can be one or more selected from the group consisting of polyethylene, polysulfone, polyethersulfone, polyimide, and polyamideimide.

[0045] Among the porous coating layer, the polymer binder and the organic filler can be contained in a weight ratio of 5:1 to 1:5. Specifically, the weight ratio of the polymer binder to the organic filler can be 4:1 to 1:4, 3:1 to 1:3, 2:1 to 1:2, or 1:1. Preferably, the weight ratio of the polymer binder to the organic filler can be 2:1 to 1:2. When the contents of the polymer binder and the organic filler are adjusted within the above-mentioned range, the adhesion and heat resistance of the porous coating layer can be ensured simultaneously, and a separation membrane with reduced thermal shrinkage even in a high-temperature wet state can be obtained.

[0046] The porous coating layer can contain the polymer binder and the inorganic particles in a weight ratio of 5:95 to 80:20. Specifically, the weight ratio of the polymer binder to the inorganic particles in the porous coating layer can be 10:90 to 80:20, 20:80 to 80:20, 30:70 to 70:30, 40:60 to 60:40, or 50:50. Preferably, the weight ratio of the polymer binder to the inorganic particles can be 60:40 to 80:20. By adjusting the composition of the porous coating layer within the above-mentioned range, the adhesion of the separation membrane and the dimensional stability in a high-temperature wet state can be ensured simultaneously.

[0047] The inorganic particles can be used as long as they 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 + standard). 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 inorganic particles with a high dielectric constant 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, etc.

[0048] In addition, as the inorganic particles, inorganic particles having lithium ion transfer ability, that is, inorganic particles containing lithium element but having a function of moving lithium ions without storing lithium 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, 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z (PO4)3, 0 < x < 2, 0 < y < 1, 0 < z < 3), (LiAlTiP) such as 14Li2O-9Al2O3-38TiO2-39P2O5 x Oy System 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.

[0049] Also, as the inorganic particles, those having flame retardancy and capable of imparting flame retardant properties to the separation membrane or preventing the temperature inside the electrochemical device from rising rapidly can be used. 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.

[0050] The average particle size (D50) of the inorganic particles can be 50 nm or more and 5,000 nm or less. Specifically, the average particle size (D50) of the inorganic particles can be 100 nm or more and 4,500 nm or less, 200 nm or more and 4,000 nm or less, 300 nm or more and 3,000 nm or less, 400 nm or more and 2,000 nm or less, or 500 nm or more and 1,000 nm or less. When the average particle size of the inorganic particles is less than 50 nm, as the specific surface area increases, a polymer binder for bonding between the inorganic particles is further required, which is disadvantageous in terms of electrical resistance. When the average particle size of the inorganic particles exceeds 5,000 nm, the uniformity of the coating layer surface decreases, and there is a possibility of causing damage to the porous polymer substrate or the electrode during lamination.

[0051] The aspect ratio of the inorganic particles can be 1 or more and 2 or less. Specifically, the aspect ratio of the inorganic particles can be 1.1 or more and 1.9 or less, 1.2 or more and 1.8 or less, 1.3 or more and 1.7 or less, or 1.4 or more and 1.6 or less. Preferably, the aspect ratio of the inorganic particles can be 1.5 or more and 1.8 or less. By adjusting the aspect ratio of the inorganic particles within the above-mentioned range, the movement of the polymer binder through the voids between the inorganic particles is facilitated, and by forming a film-formed region after the movement of the polymer binder, a porous coating layer in which the film-formed regions are uniformly distributed can be formed.

[0052] The BET specific surface area of the inorganic particles is 5 m 2 / g or more and 25 m 2 / g or less. Specifically, the BET specific surface area of the inorganic particles can be 6 m 2 / g or more and 24 m 2 / g or less, 7 m 2 / g or more and 23 m 2 / g or less, 8 m 2 / g or more and 22 m 2 / g or less, 9 m 2 / g or more and 21 m 2 / g or less, 10 m 2 / g or more and 20 m 2 / g or less, 11 m 2 / g or more and 19 m 212 m or less, per g 2 18 m or more, per g 2 13 m or less, per g 2 17 m or more, per g 2 14 m or less, or 2 26 m or more, per g 2 It may be 12 m or less, per g. By adjusting the BET specific surface area of the inorganic particles within the above-described range, the movement of the polymer binder through the voids between the inorganic particles can be adjusted.

[0053] The packing density of the inorganic particles may be 2 g / cm 3 or more and 2.5 g / cm 3 or less. The packing density is a value based on the porous coating layer formed after coating and drying the coating slurry. Specifically, the packing density of the inorganic particles may be 2.1 g / cm 3 or more and 2.4 g / cm 3 or less, or 2.2 g / cm 3 or more and 2.3 g / cm 3 or less. Preferably, the packing density of the inorganic particles may be 2.1 g / cm 3 or more and 2.3 g / cm 3 or less. If the packing density of the inorganic particles is less than 2 g / cm 3 , the separation membrane will shrink in the high-temperature wet state to expose the electrodes. If the packing density of the inorganic particles exceeds 2.5 g / cm 3 , the air permeability and resistance of the separation membrane will increase, and stable cycle characteristics cannot be ensured.

[0054] The separation membrane for the electrochemical element can 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 can 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 can be 80 s / 100 cc or more and 90 s / 100 cc or less. When the air permeability of the separation membrane is within the above-described range, the output, stability, and cycle characteristics of the electrochemical element can be ensured.

[0055] When a cell is manufactured using the separation membrane for the electrochemical element, the cell can have an electrical resistance of 0.5 Ohm or more and 1.5 Ohm or less. Specifically, the electrical resistance of the cell can 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 can be 0.6 Ohm or more and 0.8 Ohm or less.

[0056] Another specific example of the present invention provides a method for manufacturing a separation membrane for an electrochemical element, including a step of coating at least one surface of a porous polymer substrate with a coating slurry containing a polymer binder, inorganic particles, an organic filler, and a dispersion medium to form a coating layer, and a step of drying the coating layer to remove the dispersion medium. The content overlapping with that described for the separation membrane for the electrochemical element shall be replaced with the description of the previous specific example.

[0057] In the step of forming the coating layer, at least one surface of the porous polymer substrate is coated with a coating slurry containing a polymer binder, inorganic particles, an organic filler, and a dispersion medium. For example, the coating can be formed by methods such as 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., but is not limited thereto. Preferably, in the step of forming the coating layer, the coating slurry can be simultaneously coated on both surfaces of the porous polymer substrate using a bar coater or a slot die coater.

[0058] The step of forming the coating layer may further include a step of subjecting at least one surface of the porous polymer substrate to a corona discharge treatment. After the corona discharge treatment step, the coating slurry can be coated on the porous polymer substrate. In the step of subjecting at least one surface of the porous polymer substrate to a corona discharge treatment, it is possible to prevent a decrease in the adhesion between the surface of the porous polymer substrate and the surface of the coating layer at a high temperature, and to prevent a decrease in the adhesion between the surface of the polymer substrate and the surface of the coating layer due to an electrolyte.

[0059] The corona discharge treatment can be to treat at least one surface of the porous polymer substrate in air with a voltage of 0.1 kV or more and 10 kV or less. Specifically, the corona discharge treatment can be performed in air with a voltage of 0.2 kV or more and 9 kV or less, 0.3 kV or more and 8 kV or less, 0.4 kV or more and 7 kV or less, 0.5 kV or more and 6 kV or less, 0.6 kV or more and 5 kV or less, 0.7 kV or more and 4 kV or less, 0.8 kV or more and 3 kV or less, 0.9 kV or more and 2 kV or less, or 1.0 kV or more and 2 kV or less. Preferably, the corona discharge treatment can be performed in air with a voltage of 1.8 kV. By adjusting the applied voltage of the corona discharge treatment within the above-described 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.

[0060] The step of removing the dispersion medium may be to dry or heat the coating layer to evaporate the dispersion medium contained in the coating layer. The step of removing the dispersion medium can be carried out 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 step of removing the dispersion medium can be to heat the coating layer at a predetermined temperature, provided that the temperature on 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 first be used to heat the dispersion medium to cause a phase change and may not be used to deform the polymer binder.

[0061] Another specific example of the present invention provides an electrochemical element including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein the separator is a separator for an electrochemical element having the above-described characteristics. The electrochemical element can be manufactured by inserting and sealing 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 a pouch. Before sealing the case or the pouch, an electrolytic solution can be injected to impregnate the electrode assembly with the electrolytic solution. The shape of the case or the pouch is not limited. For example, the electrochemical element can be a cylindrical, rectangular, coin-type, or pouch-type lithium secondary battery.

[0062] The positive electrode and the negative electrode may be configured by applying and drying an electrode active material on at least one surface of each current collector to form a coating. The current collector can be made of 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 a material obtained by surface-treating the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc., but is not limited thereto. For example, the current collector for the negative electrode can be copper, nickel, titanium, fired carbon, stainless steel; or a material obtained by surface-treating the surface of copper or stainless steel with carbon, nickel, titanium, silver, etc., 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.

[0063] 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) represented by Ni-site type lithium nickel oxide; 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 to 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 a mixture of two or more of Fe2(MoO4)3 may be included.

[0064] 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), Li x WO2 (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 a mixture of two or more selected from titanium oxides may be included.

[0065] 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 2It has a bonding structure and exhibits the characteristics of a conductor or a semiconductor according to the angle and structure around which the graphite plane is wound. Carbon nanotubes can be classified into single-walled carbon nanotubes (SWCNT), double-walled carbon nanotubes (DWCNT), and multi-walled carbon nanotubes (MWCNT) according to the number of walls, and these carbon nanotubes can be appropriately selected according to the use 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 of these conductive materials.

[0066] As the binder resin, a binder resin commonly used for the electrodes of an electrochemical device can be used. Non-limiting examples of such binder resins 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 acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxyl methyl cellulose, etc., but are not limited thereto.

[0067] The electrolyte is salt having a structure such as A + B - wherein A + is Li + , Na + , K+ ions containing alkali metal cations such as, or combinations thereof, and B - is PF6 - 、BF4 - 、Cl - 、Br - 、I - 、ClO4 - 、AsF6 - 、CH3CO2 - 、CF3SO3 - 、N(CF3SO2)2 - 、C(CF2SO2)3 - salts containing anions such as, or combinations thereof, may be dissolved or dissociated in an organic solvent consisting of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), gamma-butyrolactone (γ-butyrolactone), or mixtures thereof, but are not limited thereto.

[0068] The electrochemical element including the electrode assembly can 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, and a device including the battery pack as a power source. Examples of the device include small devices such as computers, mobile phones, and power tools, and electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), etc. that are powered by an electric motor; electric two-wheel vehicles including electric bicycles (E-bikes) and electric scooters (E-scooters); electric golf carts; and medium to large-sized devices such as power storage systems, but are not limited thereto.

[0069] Hereinafter, the present invention will be described in more detail with specific examples and experimental examples. The following examples and experimental examples are for illustrative purposes of the present invention, and the present invention is not limited by the following examples and experimental examples.

[0070] Example 1 Preparation of coating slurry

[0071] At room temperature (25 °C), an acrylic polymer binder (a copolymer obtained by copolymerizing polyacrylic acid and polyacrylamide at a weight ratio of 50:50, Mw: 300,000) and an organic filler (polyethylene particles) were mixed with 100 mL of distilled water at a weight ratio of 2:1, and 20 g of inorganic particles (Al2O3, aspect ratio: 1.5:1, particle size: 500 nm) was added, and the mixture was stirred with a shaker for 60 minutes to produce a coating slurry in which the polymer binder, inorganic particles, and organic filler were dispersed.

[0072] Preparation of porous substrate As the porous substrate, (MI: 0.2 g / 10 min, T m: 135 °C, porosity: 45%, average pore size: 45 nm), and a polyethylene film with a size of 20 cm × 30 cm and a thickness of 9 μm was used.

[0073] Manufacture of separation membrane The coating slurry was coated on both sides of the polyethylene film using a bar coater to form a porous coating layer with a thickness of 2 μm for each coating.

[0074] Low-temperature air volume was applied to the polyethylene film with the porous coating layer formed, and the process of drying to remove the dispersion medium was repeated 5 times while adjusting the surface temperature of the porous coating layer not to exceed 60 °C, so that the packing density of the inorganic particles contained in the porous coating layer was 2.0 g / cm 3 A separation membrane with an overall thickness of 13 μm was manufactured.

[0075] Example 2 During the production of the coating slurry, the solid content was adjusted so that the packing density of the inorganic particles was 2.5 g / cm 3 A separation membrane was manufactured in the same manner as in Example 1 except for the above.

[0076] Example 3 A separation membrane was manufactured in the same manner as in Example 1 except that during the production of the coating slurry, the polymer binder and the organic filler were mixed at a weight ratio of 1:2.

[0077] Example 4 A separation membrane was manufactured in the same manner as in Example 1 except that during the production of the coating slurry, the polymer binder and the organic filler were mixed at a weight ratio of 5:1.

[0078] Comparative Example 1 A separation membrane was manufactured in the same manner as in Example 1 except that no organic filler was used during the production of the coating slurry.

[0079] Comparative Example 2 A separation membrane was produced in the same manner as in Example 1, except that a polymer binder and an organic filler were mixed at a weight ratio of 6:1 during the production of the coating slurry.

[0080] Comparative Example 3 A separation membrane was produced in the same manner as in Example 1, except that a polymer binder and an organic filler were mixed at a weight ratio of 1:6 during the production of the coating slurry.

[0081] Comparative Example 4 A separation membrane was produced in the same manner as in Example 1, except that the solid content was adjusted during the production of the coating slurry so that the packing density of the inorganic particles was 1.5 g / cm 3 3.

[0082] Comparative Example 5 A separation membrane was produced in the same manner as in Example 1, except that the solid content was adjusted during the production of the coating slurry so that the packing density of the inorganic particles was 3.0 g / cm 3 3.

[0083] Experimental Example. Physical Property Confirmation of Separation Membrane Measurement of air permeability The air permeability was measured using an air permeability tester (Gurley densometer) (manufactured by Gurley, model 4110N) to measure the time required for 100 cc of air to permeate through a separation membrane with a diameter of 28.6 mm and an area of 645 mm 2 2.

[0084] Confirmation of dimensional stability Separation membranes of the examples and comparative examples were prepared in a size of 5 cm × 5 cm and inserted into aluminum pouches of 7 cm × 10 cm size, respectively. 1 g of electrolyte was injected into the pouch and the pouch was sealed. As the electrolyte, a solvent in which ethylene carbonate (EC) / ethyl methyl carbonate (EMC) were mixed at a weight ratio of 3 / 7 was used, which contained 3 mol of vinylene carbonate (VC), 1.5 mol of propane sultone (PS), 1 mol of ethylene sulfate (ESa), and 1 mol of lithium salt LiPF6 as additives.

[0085] The sealed pouch was held in an oven at 135 °C for 30 minutes, and then the pouch was disassembled to measure the shrinkage rate in the TD direction. The results are shown in Tables 1 and 2 below.

[0086]

Table 1

[0087]

Table 2

Claims

1. A porous polymer substrate and a porous coating layer formed on at least one surface of the porous polymer substrate, wherein the porous coating layer contains a polymer binder, inorganic particles, and an organic filler, the polymer binder being contained in an amount of 1 to 10 parts by weight based on the total weight of the porous coating layer. The packing density of the inorganic particles is 2 g / cm ３ or more and 2.5 g / cm ３ or less. A separation membrane for an electrochemical device.

2. The organic filler is one or more selected from the group consisting of polyethylene, polyacetal, polysulfone (PSF), polyethersulfone (PES), polyetherimide (PEI), polyphenylene sulfide (PPS), polyetheretherketone (PEEK), polycarbonate, polyamideimide (PAI), polyimide (PI), polyamide, polyphenylene oxide, polybutylene terephthalate, and polyethylene terephthalate. The separation membrane for an electrochemical element according to Claim 1.

3. The polymer binder and the organic filler are contained in a weight ratio of 5:1 to 1:

5. The separation membrane for an electrochemical element according to Claim 1.

4. The polymer binder is one or more selected from the group consisting of polyacrylic acid, polyacrylamide, methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, ethylhexyl acrylate, methyl methacrylate, styrene-butadiene rubber, nitrile-butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, and copolymers containing one or more of these. The separation membrane for an electrochemical element according to Claim 1.

5. The weight average molecular weight of the polymer binder is 100,000 to 500,000. The separation membrane for an electrochemical element according to Claim 4.

6. The packing density of the inorganic particles is 2.1 g / cm ３ or more and 2.3 g / cm ３ or less. The separation membrane for an electrochemical element according to claim 1.

7. An electrochemical element including a positive electrode, a negative electrode, and a separation membrane disposed between the positive electrode and the negative electrode, wherein the separation membrane is the separation membrane for an electrochemical element according to any one of Claims 1 to 7. An electrochemical element.

8. The electrochemical element further includes an electrolytic solution containing EC / EMC in a weight ratio of 3 / 7. The electrochemical element according to Claim 8.

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