Separator for electrochemical device and electrochemical device including the same

Abstract

The separator for an electrochemical device according to the present invention comprises a porous substrate and a coating layer formed on at least one surface of the porous substrate, wherein the coating layer comprises a polymer binder, inorganic particles, and hexagonal boron nitride, and the inorganic particles have a dielectric constant of 150 or higher.

Description

Technology Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0150287 dated October 30, 2024, and all contents disclosed in the document of said Korean patent application are incorporated herein as part of this specification.

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

[0004] Electrochemical devices convert chemical energy into electrical energy using electrochemical reactions; recently, lithium-ion batteries, which offer high energy density and voltage, long cycle life, and applicability to various fields, are widely used.

[0005] A lithium secondary battery may include an electrode assembly manufactured with a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes, and the electrode assembly may be manufactured by housing it in a case together with an electrolyte.

[0006] Meanwhile, the separator of a lithium secondary battery prevents electrical contact between the positive and negative electrodes while enabling the movement of lithium ions between the electrodes, playing a crucial role in the safety and performance of the battery. The problem to be solved

[0008] The present invention provides a separator for an electrochemical device comprising inorganic particles with a high dielectric constant and hexagonal boron nitride, which reduces gas generation and forms a uniform coating layer, and an electrochemical device including the same. means of solving the problem

[0010] One aspect of the present invention provides a separator for an electrochemical device comprising a porous substrate and a coating layer formed on at least one surface of the porous substrate, wherein the coating layer comprises a polymer binder, inorganic particles, and hexagonal boron nitride, and the inorganic particles have a dielectric constant of about 150 or more.

[0011] The above inorganic particles are BaTiO3, Pb(Zr,Ti)O3(PZT), and 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 It may be O3-PbTiO3(PMN-PT), HfO2, SrTiO3, SnO2, CeO2, NiO, ZnO, ZrO2, Y2O3, TiO2, or a mixture thereof.

[0012] The above inorganic particles may have an average particle size (D50) of about 200 nm or more and 1,000 nm or less.

[0013] The volume ratio of the inorganic particles and the hexagonal boron nitride may be about 7:1 to 30:1.

[0014] The average diameter of the above hexagonal boron nitride may be about 100 nm or more and 300 nm or less.

[0015] The aspect ratio of the above hexagonal boron nitride may be about 5 or more and 30 or less.

[0016] The coating layer may contain about 10 volume% or less of the hexagonal boron nitride.

[0017] The coating layer may contain about 10 volume% or more and 30 volume% or less of the polymer binder.

[0018] The thickness of the coating layer may be about 0.5 μm or more and 2 μm or less.

[0019] One aspect of the present invention provides an electrochemical device comprising an anode, a cathode, and a separator disposed between the anode and the cathode, wherein the separator is a separator for another electrochemical device according to the one aspect.

[0020] The above electrochemical device may be a lithium secondary battery.

[0021] A method for manufacturing a separator for an electrochemical device may further include the step of forming an adhesive layer formed on the surface of the coating layer. Effects of the invention

[0023] The separator for an electrochemical device according to the present invention has a uniform coating layer comprising inorganic particles with a high dielectric constant and hexagonal boron nitride, and can reduce the amount of gas generated in the electrochemical device. Specific details for implementing the invention

[0025] Hereinafter, each component of the present invention is described in more detail so that a person skilled in the art 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.

[0026] The term “comprising” as used herein is used when listing materials, compositions, devices, and methods useful to the present invention, and is not limited to the examples listed.

[0027] As used herein, “about” and “substantially” are used to mean a range of numerical or degree or an approximation thereof, taking into account inherent manufacturing and material tolerances (±5%), and are used to prevent an infringer from unfairly exploiting the disclosure in which precise or absolute figures provided to aid in understanding the invention are mentioned.

[0028] As used in this specification, the term “electrochemical device” may refer to primary batteries, secondary batteries, supercapacitors, etc.

[0029] The separator may include a coating layer comprising 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 said interstitial volume. In addition to fixing the inorganic particles, the polymer binder may impart adhesion to the coating layer, and the coating layer may adhere to the porous substrate and the electrode, respectively.

[0030] Large amounts of gas that may be generated during the storage or operation of electrochemical devices increase the resistance of the devices and cause problems such as reduced output and cycle characteristics. Accordingly, there have been attempts to apply inorganic particles with high dielectric constants to the coating layer to reduce gas generation. Inorganic particles with high dielectric constants have the advantage of low moisture adsorption and inhibit the decomposition of salts within the electrolyte upon impregnation, thereby reducing gas generation caused by side reactions of salts. However, inorganic particles with high dielectric constants have a problem of reduced dispersibility due to their high density, which causes a rapid sedimentation rate within the slurry. Consequently, if a non-uniform coating layer is formed, the physical properties of the separator membrane deteriorate.

[0031] Considering these points, the present invention provides a method for forming a uniform coating layer by lowering the sedimentation rate of inorganic particles in a coating slurry, and a separation membrane and an electrochemical device utilizing the same.

[0033] Although the present invention has been described below by way of examples, the present invention is not limited thereto and may include a combination of one or more configurations of specific examples and examples by those skilled in the art to which the present invention belongs, and various modifications and variations are possible within the scope of the technical spirit of the present invention and the equivalent scope of the claims described below.

[0034] A separator for an electrochemical device according to one embodiment of the present invention comprises a porous substrate and a coating layer formed on at least one surface of the porous substrate, wherein the coating layer comprises a polymer binder, inorganic particles, and hexagonal boron nitride (e.g., h-BN), and the inorganic particles have a dielectric constant of 150 or higher.

[0035] The porous substrate may be a porous membrane having a plurality of pores formed therein, which electrically insulates the positive electrode and the negative electrode to prevent a short circuit. For example, if the electrochemical device is a lithium secondary battery, the porous substrate may be an ion-conducting barrier that blocks electrical contact between the positive electrode and the negative electrode while allowing lithium ions to pass through. At least some of the pores may form a three-dimensional network communicating the surface and the interior of the porous substrate, and a fluid may pass through the porous substrate through the pores.

[0036] The porous substrate described above may be a material that is physically and chemically stable with respect to an electrolyte, which is an organic solvent. For example, the porous substrate may include, but is not limited to, resins such as polyolefins including polyethylene, polypropylene, and polybutylene, polyvinyl chloride, polyethylene terephthalate, polycycloolefin, polyethersulfone, polyamide, polyimide, polyamideimide, nylon, polytetrafluoroethylene, and copolymers or mixtures thereof. For example, polyolefin resins may be used. Polyolefin resins are suitable for manufacturing electrochemical devices with higher energy density because they can be processed to a relatively thin thickness and facilitate the application of coating slurries.

[0037] The porous substrate may have a single-layer or multi-layer structure. The porous substrate may include two or more polymer resin layers with different melting points (Tm) to provide a shutdown function during high-temperature runaway of the battery. For example, the porous substrate may include a polypropylene layer with a relatively high melting point and a polyethylene layer with a relatively low melting point. According to one embodiment, the porous substrate may have a three-layer structure stacked in the order of polypropylene, polyethylene, and polypropylene. The polyethylene layer may prevent thermal runaway of the battery by shutting down the pores as it melts as the temperature of the battery rises above a predetermined temperature.

[0038] The thickness of the porous substrate may be approximately 1 μm or more and 100 μm or less. For example, the thickness of the porous substrate may 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. According to one embodiment, the thickness of the porous substrate may be approximately 1 μm or more and 30 μm or less. Alternatively, the thickness of the porous substrate may be approximately 5 μm or more and 15 μm or less, or 8 μm or more and 13 μm or less. By controlling the thickness of the porous substrate within the above-described range, the volume of the electrochemical device can be minimized while electrically insulating the anode and the cathode, thereby increasing the amount of active material included in the electrochemical device.

[0039] The porous substrate may include pores with an average diameter of about 0.01 μm or more and 1 μm or less. For example, the size of the pores included in the porous substrate may be about 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. According to one embodiment, the size of the pores may be about 0.02 μm or more and 0.06 μm or less. By controlling the pore size of the porous substrate within the above-described range, the air permeability and ion conductivity of the entire separation membrane being manufactured can be controlled.

[0040] The porous substrate may have an air permeability of approximately 10 s / 100cc or more and 100 s / 100cc or less. For example, the air permeability of the porous substrate may be approximately 10 s / 100cc or more and 90 s / 100cc or less, 20 s / 100cc or more and 80 s / 100cc or less, 30 s / 100cc or more and 70 s / 100cc or less, or 40 s / 100cc or more and 60 s / 100cc or less. According to one embodiment, the air permeability of the porous substrate may be approximately 50 s / 100cc or more and 70 s / 100cc or less. When the air permeability of the porous substrate is within the range described above, the air permeability of the manufactured separator may be provided within a range suitable for securing the output and cycle characteristics of the electrochemical device.

[0041] The above air permeability (s / 100cc) refers to the time (in seconds) required for 100cc of air to pass through a porous substrate or membrane of a predetermined area under constant pressure. The above air permeability may be measured using a Gurley densometer in accordance with ASTM D 726-58, ASTM D726-94, or JIS-P8117. For example, using a Gurley 4110N instrument, air at a pressure of 0.304 kPa or 1.215 kN / m 2 100cc of air under water pressure is 1 square inch (or 6.54 cm²)2 The time it takes for ) to pass through a sample can be measured. For example, using the Asahi Seico EG01-55-1MR instrument, the time it takes for 100cc of air to pass through a 1 square inch sample under a constant pressure of 4.8 inches of water at room temperature can be measured.

[0042] The porous substrate may have a porosity of about 10 vol% or more and 60 vol% or less. For example, the porosity of the porous substrate may be about 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. According to one embodiment, the porosity of the porous substrate may be about 30 vol% or more and 50 vol% or less. When the porosity of the porous substrate is within the range described above, the ion conductivity of the manufactured separator may be provided within a range suitable for securing the output and cycle characteristics of the electrochemical device.

[0043] The above porosity refers to the ratio of the volume of pores to the total volume of the porous substrate. The above 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, the capillary flow porometer, or the water or mercury infiltration method.

[0044] The coating layer is formed on at least one surface of the porous substrate and comprises a polymer binder, inorganic particles, and hexagonal boron nitride (h-BN). The coating layer may be formed by coating a coating slurry comprising a polymer binder, inorganic particles, hexagonal boron nitride, and a dispersion medium onto at least one surface of the porous substrate. The coating layer adheres to the porous substrate and prevents thermal shrinkage of the porous substrate by including an interstitial volume in which the inorganic particles and hexagonal boron nitride are connected by a polymer binder, allowing lithium ions to pass through.

[0045] The thickness of the coating layer may be approximately 0.5 μm or more and 2 μm or less. For example, the thickness of the coating layer may be approximately 0.5 μm or more and 1.75 μm or less, 0.5 μm or more and 1.5 μm or less, 0.75 μm or more and 2 μm or less, 0.75 μm or more and 1.75 μm or less, 0.75 μm or more and 1.5 μm or less, 1.0 μm or more and 2.0 μm or less, 1.0 μm or more and 1.75 μm or less, 1.0 μm or more and 1.5 μm or less, 1.5 μm or more and 2.0 μm or less, or 1.5 μm or more and 1.75 μm or less. By controlling the thickness of the coating layer within the above-described range, shrinkage of the porous substrate can be minimized and stable adhesion to the porous substrate can be achieved. In addition, by controlling the thickness of the coating layer within the aforementioned range, it is possible to realize an electrochemical device with high energy density due to the thinning of the separator.

[0046] The above coating layer has a density of approximately 3.7 g / cm³ 3 Above 6.0 g / cm³ 3 It may be less than or equal to. For example, the density of the coating layer is approximately 4.9 g / cm³. 3 Above 5.2 g / cm³ 3 ≤ or 4.9 g / cm³ 3 Above 6.0 g / cm³ 3 It may be less than or equal to the above. When the density of the coating layer is within the range described above, a uniform coating layer is formed, and the electrical resistance and dielectric breakdown voltage of the electrochemical device can be improved.

[0047] According to one embodiment, the inorganic particles may have a dielectric constant of about 150 or higher. For example, the inorganic particles may have a dielectric constant of about 150 or higher, 200 or higher, 300 or higher, 500 or higher, 700 or higher, 1,000 or higher, or 10,000 or lower. According to one embodiment, the inorganic particles may have a dielectric constant of about 300 or higher and 10,000 or lower. When the inorganic particles have a dielectric constant within the range described above, they may exhibit a spontaneous polarization state within the electrolyte and interact with polar molecules and ions. Due to this interaction, the decomposition of salts within the electrolyte is suppressed, thereby preventing side reactions and reducing the amount of gas generated during the storage or operation of the electrochemical device.

[0048] The above relative permittivity is a value representing the degree to which a dielectric undergoes polarization in an electric field, and is a unitless physical quantity representing the ratio to the dielectric constant of vacuum. For example, the term “relative permittivity” used in this specification may refer to a value measured by the ASTM D150 test method at room temperature (25 ℃).

[0049] The above inorganic particles are BaTiO3, Pb(Zr,Ti)O3(PZT), and 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 It may be )O3-PbTiO3(PMN-PT), HfO2, SrTiO3, SnO2, CeO2, NiO, ZnO, ZrO2, Y2O3, TiO2, or a mixture thereof. For example, the inorganic particles may be 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 / 3Nb 2 / 3 It may be O3-PbTiO3 (PMN-PT) or a mixture thereof. When the above-described inorganic particles are applied to a coating layer, the amount of gas generated can be reduced according to the high dielectric constant within the above-described range, and at the same time, heat resistance can be imparted to the coating layer to prevent thermal shrinkage of the porous substrate. According to one embodiment, the inorganic particles may be BaTiO3. Since the BaTiO3 has a high dielectric constant within the above-described range, the amount of gas generated by the electrochemical device can be reduced.

[0050] The average particle size (D50) of the inorganic particles may be approximately 200 nm or more and 1,000 nm or less. For example, the average particle size (D50) of the inorganic particles may be approximately 200 nm or more, 300 nm or more, 400 nm or more, 450 nm or more, 500 nm or more, 550 nm or less, 600 nm or less, 800 nm or less, or 1,000 nm or less. When the average particle size (D50) of the inorganic particles is within the range described above, an appropriate dielectric constant can be secured, the amount of gas generated can be suppressed, and the sedimentation rate within the coating slurry can be maintained at an appropriate level to form a uniform coating layer.

[0051] The above average particle size (D50) refers to the diameter of the particle at the 50% point of the cumulative distribution of the number of particles. The above particle size can be measured using a laser diffraction method. For example, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500) to measure the difference in diffraction patterns according to the particle diameter as the particles pass through the laser beam, thereby calculating the particle size distribution. The particle size (D50) can be measured by calculating the particle size at the point that is 50% of the cumulative distribution of the number of particles according to the particle diameter in the measuring device.

[0052] The hexagonal boron nitride (h-BN) described above is a compound having a planar structure in which nitrogen atoms and boron atoms are bonded in a molar ratio of approximately 1:1. Due to its large aspect ratio and low density resulting from its unique planar structure, the hexagonal boron nitride does not easily aggregate with inorganic particles within the coating slurry, and can improve the dispersibility of the coating slurry by reducing the sedimentation rate. A solid component containing a polymer binder, inorganic particles, and hexagonal boron nitride within the coating slurry may settle over time. The sedimentation rate of the solid component may be influenced by the density of the inorganic particles, the density of the hexagonal boron nitride, and its unique planar structure and aspect ratio. In one embodiment of the present invention, the dispersibility of the coating slurry can be improved and the density and uniformity of the coating layer can be determined by controlling the sedimentation rate of the coating slurry, which will be described later.

[0053] The average diameter of the hexagonal boron nitride may be approximately 100 nm or more and 300 nm or less. For example, the average diameter of the hexagonal boron nitride may be approximately 100 nm or more and 300 nm or less, 100 nm or more and 250 nm or less, 100 nm or more and 200 nm or less, 100 nm or more and 150 nm or less, 150 nm or more and 250 nm or less, or 150 nm or more and 200 nm or less. When the average diameter of the hexagonal boron nitride is within the range described above, the sedimentation speed can be maintained within an appropriate range without easily aggregating with inorganic particles in the coating slurry, and the viscosity of the coating slurry can also be maintained at an appropriate level, thereby maintaining workability for forming a coating layer. For example, if the average diameter of the hexagonal boron nitride satisfies the range described above, the sedimentation rate within the coating slurry is reduced, thereby improving the dispersibility of the coating slurry and improving the dielectric breakdown voltage and resistance when forming the coating layer.

[0054] The thickness of the hexagonal boron nitride may be approximately 5 nm or more and 100 nm or less. For example, the thickness of the hexagonal boron nitride may be approximately 5 nm or more and 75 nm or less, 5 nm or more and 50 nm or less, 5 nm or more and 30 nm or less, 10 nm or more and 100 nm or less, 10 nm or more and 75 nm or less, 10 nm or more and 50 nm or less, 10 nm or more and 30 nm or less, 20 nm or more and 100 nm or less, 20 nm or more and 75 nm or less, 20 nm or more and 50 nm or less, or 20 nm or more and 30 nm or less. When the thickness of the hexagonal boron nitride satisfies the above-described range, the sedimentation rate in the coating slurry is reduced, and the insulation properties of the separator can be improved.

[0055] The aspect ratio of the hexagonal boron nitride may be approximately 5 to 30. The aspect ratio refers to the value obtained by dividing the average diameter of the hexagonal boron nitride by its thickness. The average diameter and thickness can be measured, for example, by laser diffraction. When the aspect ratio of the hexagonal boron nitride is maintained within the range described above, the sedimentation speed can be maintained within an appropriate range without easily aggregating with inorganic particles within the coating slurry, and the dielectric breakdown voltage of the separator does not decrease as the insulating properties are not reduced. For example, when the aspect ratio of the hexagonal boron nitride satisfies the range described above, the sedimentation speed within the coating slurry is reduced, which can improve the dispersibility of the coating slurry and improve the insulating properties of the separator.

[0056] The volume ratio of the inorganic particles and the hexagonal boron nitride may be approximately 7:1 to 30:1. For example, the volume ratio of the inorganic particles and the hexagonal boron nitride may be approximately 8:1, 10:1, 15:1, 20:1, or 25:1. When the volume ratio of the inorganic particles is maintained within the above-described range, the dispersibility of the coating slurry can be improved as the total density of the solids in the coating slurry does not increase and the sedimentation velocity does not rise, and a uniform coating layer is formed as the sedimentation of the inorganic particles in the coating slurry is suppressed, so the dielectric breakdown voltage of the separator does not decrease. For example, when the volume ratio of the hexagonal boron nitride is maintained within the above-described range, the viscosity of the coating slurry does not increase, and even if the coating slurry is applied to a porous substrate and dried, the interstitial volume is properly formed, so the resistance of the separator does not increase. For example, by adjusting the volume ratio of the inorganic particles and the hexagonal boron nitride to the range described above, gas generation in the electrochemical device can be reduced, and the sedimentation rate within the coating slurry can be reduced, thereby achieving a high dielectric breakdown voltage and low resistance due to the formation of a uniform coating layer.

[0057] The polymer binder can bind inorganic particles and hexagonal boron nitride particles included in the coating layer and impart adhesion to the coating layer. The polymer binder may include an acrylic binder, a fluorine binder, or a hybrid binder thereof, but is not limited thereto. For example, the acrylic binder may be one or more selected from 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. For example, the fluorine-based binder may be one or more selected from polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, and polyvinylidene fluoride-trichloroethylene.

[0058] The coating layer may contain about 10 volume% or less of the hexagonal boron nitride. For example, the coating layer may contain about 1 volume% or more and 10 volume% or less of the hexagonal boron nitride, 2 volume% or more and 10 volume% or less, 3 volume% or more and 10 volume% or less, or 3 volume% or more and 8 volume% or less. With the hexagonal boron nitride in the above-described range, the viscosity of the coating slurry does not increase, and the coating can be evenly coated on the porous substrate. For example, by controlling the volume% of the hexagonal boron nitride within the above-described range, the sedimentation rate within the coating slurry can be improved while maintaining the viscosity at an appropriate level, thereby achieving thin film formation of the separation membrane through a thin coating layer thickness.

[0059] The coating layer may contain the polymer binder in an amount of about 10 volume% or more and 30 volume% or less. For example, the coating layer may contain the polymer binder in an amount of about 10 volume% or more and 30 volume% or less, 12 volume% or more and 25 volume% or less, 15 volume% or more and 20 volume% or less, or 10 volume% or more and 15 volume% or less. By controlling the content of the polymer binder to the range described above, the inorganic particles and the hexagonal boron nitride can be bound together, and the bond between the coating layer and the porous substrate can be maintained.

[0060] The separator for the electrochemical device described above may further include an adhesive layer formed on the surface of the coating layer. The adhesive layer covers at least a portion of the surface of the coating layer and can impart adhesion to the electrode to the separator. The adhesive layer may be formed by additionally applying and drying an adhesive layer forming slurry containing a polymer binder for the adhesive layer onto the surface of the coating layer formed by drying the aforementioned coating slurry. The application may be performed using a bar coater, wire bar coater, roll coater, spray coater, spin coater, inkjet coater, screen coater, reverse coater, gravure coater, knife coater, slot die coater, hot melt coater, comma coater, direct metering coater, etc., but is not limited thereto. According to one embodiment, the adhesive layer may be formed by spraying and drying the adhesive layer forming slurry. The adhesive layer may cover approximately 20% to 80% of the surface of the coating layer.

[0061] The polymer binder for the adhesive layer may be the same as or different from the polymer binder. According to one embodiment, the polymer binder for the adhesive layer may be a fluorine-based binder, an acrylic binder, or a mixture thereof. For example, the fluorine-based binder may be a particulate polyvinylidene fluoride-based binder. For example, the adhesive layer may include both a fluorine-based binder and an acrylic binder, thereby stably maintaining adhesion to the electrode of the separator in both a dry state without an electrolyte and a wet state in which the separator is impregnated with an electrolyte. For example, the adhesive layer may include a fluorine-based binder and an acrylic binder as the polymer binder for the adhesive layer in a weight ratio of approximately 2:8 to 8:2, 3:7 to 7:3, or 4:6 to 6:4. The thickness of the adhesive layer is formed to be smaller than the thickness of the coating layer, thereby providing electrode adhesion while minimizing the reduction in air permeability of the separator.

[0062] The separator for the electrochemical device described above may have a gas generation amount of approximately 1,000 µL or less. For example, the separator for the electrochemical device may have a gas generation amount of approximately 1,000 µL or less, 900 µL or less, 800 µL or less, 790 µL or less, or 500 µL or more. By controlling the gas generation amount of the separator for the electrochemical device to the range described above, the output and cycle characteristics of the electrochemical device can be improved. The gas generation amount may be measured by collecting the gas generated after impregnating the separator for the electrochemical device with an electrolyte, storing it at room temperature for 12 hours, and then storing it at 130°C for 1 hour.

[0063] The separator for the electrochemical device described above may have a dielectric breakdown voltage of 1.0 kV or higher. For example, the separator for the electrochemical device may have a dielectric breakdown voltage of approximately 1.0 kV or higher, 1.5 kV or higher, 1.7 kV or higher, 1.8 kV or higher, or 2.1 kV or lower. By adjusting the dielectric breakdown voltage of the separator for the electrochemical device to the above-described range, the insulation performance of the separator at high voltage is maintained, thereby preventing short circuits inside the electrochemical device and maintaining stable battery performance.

[0064] The above dielectric breakdown voltage may be the voltage measured when the voltage exceeds 0.5 mA and 3 seconds while increasing the voltage at a rate of 100 mV / s after applying a pressure of 8 MPa at 70 ℃ to the separator for the electrochemical device.

[0065] The above-mentioned separator for an electrochemical device may have a moisture content of 3,000 ppm or less. The moisture may collectively refer to water mixed in the dispersion medium remaining during the drying process of the coating slurry, water absorbed by the inorganic particles during the manufacturing, transportation, or storage process of the separator. The coating layer may include inorganic particles with a high dielectric constant to maintain the moisture content of the separator at a level of 3,000 ppm or less.

[0067] In one embodiment of the present invention, a coating slurry comprising a polymer binder, inorganic particles, hexagonal boron nitride, and a dispersion medium is provided. In one embodiment of the present invention, the high sedimentation rate in the coating slurry that may occur due to the inclusion of inorganic particles having a high density may be reduced by including hexagonal boron nitride having a low density and a large aspect ratio. Any content overlapping with that described in the above description of the separator for the electrochemical device is replaced by the description of the preceding embodiment.

[0068] The coating slurry described above may include a dispersion medium to dissolve or disperse at least a portion of the polymer binder and to disperse the inorganic particles and the hexagonal boron nitride. The coating slurry may be used in which the polymer binder, inorganic particles, and hexagonal boron nitride are uniformly dispersed by adjusting the type and content of the dispersion medium. For example, the dispersion medium may be one selected from water, ethanol, acetone, isopropyl alcohol (IPA), dimethylacetamide (DMAc), dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), acetonitrile, and combinations thereof. By using the aforementioned types of dispersion media, a coating slurry with improved sedimentation rate can be provided in which the polymer binder, inorganic particles, and hexagonal boron nitride are uniformly dispersed.

[0069] The dispersion medium included in the coating slurry may be removed by drying or heating after the formation of the coating layer. During the process of removing the dispersion medium, multiple pores may be formed on the surface and inside the coating layer. The pores may include interstitial volumes formed between inorganic particles and may have a structure that allows fluid to pass through by forming a three-dimensional network.

[0070] The coating slurry may further include additives such as dispersants, surfactants, defoaming agents, and flame retardants to improve dispersibility and flame retardancy and to improve the uniformity of the coating layer formed. For example, the dispersant may include one or more selected from polyacrylic acid, oil-soluble polyamines, oil-soluble amine compounds, fatty acids, fatty alcohols, sorbitan fatty acid esters, tannic acid, and pyrogallic acid. By using a dispersant of the type described above, the stability of the coating slurry can be improved and the uniformity of the coating layer formed by the coating slurry can be ensured.

[0071] Based on the total weight of the coating slurry, the additive may be included in an amount of about 0% by weight or more and 5% by weight or less. For example, the content of the additive may be about 0.01% by weight or more and 4% by weight or less, 0.1% by weight or more and 3% by weight or less, or 1% by weight or more and 2% by weight or less. According to one embodiment, the content of the additive may be about 1% by weight or more and 5% by weight or less. By controlling the content of the additive within the above-described range, uniform dispersion and stability of the inorganic particles and hexagonal boron nitride contained in the coating slurry can be achieved.

[0072] According to one embodiment, the coating slurry may have a sedimentation velocity of about 100 μm / s or less. For example, the coating slurry may have a sedimentation velocity of about 100 μm / s or less, 90 μm / s or less, 70 μm / s or less, 50 μm / s or less, 30 μm / s or less, or 10 μm / s or more. When the sedimentation velocity of the coating slurry is within the range described above, the solid component including the inorganic particles is uniformly dispersed within the coating slurry, and the dielectric breakdown voltage of the separator may not be lowered below an appropriate range when forming the coating layer. As a result, when the sedimentation velocity of the coating slurry satisfies the range described above, gas generation of the separator for an electrochemical device can be suppressed and the dielectric breakdown voltage can be improved.

[0073] The above sedimentation rate refers to the rate at which solids settle within the coating slurry over time while centrifugal force is applied by rotating the coating slurry at a predetermined rotational speed. The above sedimentation rate may be, for example, obtained by using a dispersion measuring device (product name: Turbiscan, manufacturer: Foulaction) to measure the sedimentation rate (TSI, Turbiscan Stability Index) for 10 hours and then using the measured value at 6 hours.

[0074] A method for manufacturing a separator for an electrochemical device according to one embodiment of the present invention comprises the steps of: preparing a coating slurry comprising a polymer binder, inorganic particles, hexagonal boron nitride, and a dispersion medium; forming a coating layer by coating at least one surface of a porous substrate with the coating slurry; and manufacturing a separator by drying the coating layer to remove the dispersion medium. Any content overlapping with that described in the description of the separator for an electrochemical device is replaced by the description of the preceding embodiment.

[0075] According to one embodiment, the step of preparing the coating slurry includes mixing BaTiO3, hexagonal boron nitride (h-BN), and a polymer binder as inorganic particles in distilled water in an appropriate volume ratio. Additionally, the coating slurry is prepared by maintaining the total solid content at an appropriate weight% and stirring the mixture, for example, with a shaker.

[0076] The step of forming the coating layer involves coating at least one surface of a porous substrate with a coating slurry comprising a polymer binder, inorganic particles, hexagonal boron nitride, and a dispersion medium. For example, the coating may be formed by methods such as a bar coater, wire bar coater, roll coater, spray coater, spin coater, inkjet coater, screen coater, reverse coater, gravure coater, knife coater, slot die coater, hot melt coater, comma coater, direct metering coater, etc., but is not limited thereto. According to one embodiment, the step of forming the coating layer may involve coating a cross-section of the porous substrate or simultaneously coating both sides using a bar coater or a slot die coater with the coating slurry.

[0077] The step of forming the coating layer may further include the step of corona discharge treatment of at least one surface of the porous substrate. For example, the coating slurry may be coated onto the porous substrate after the corona discharge treatment step. The step of corona discharge treatment of at least one surface of the porous substrate prevents a decrease in the bonding strength between the surface of the porous substrate and the surface of the coating layer at high temperatures, and can prevent or suppress a decrease in the bonding strength between the surface of the porous substrate and the surface of the coating layer caused by the electrolyte.

[0078] The corona discharge treatment may involve treating at least one surface of the porous substrate with a voltage of about 0.1 kV to 10 kV in air. For example, the corona discharge treatment may involve treating with a voltage of about 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 in air. According to one embodiment, the corona discharge treatment may involve treating with a voltage of about 1.8 kV in air. By adjusting the applied voltage of the corona discharge treatment within the above-described range, appropriate waterway functional groups can be formed on the surface of the porous substrate, and damage to the surface of the porous substrate can be prevented or suppressed.

[0079] The step of manufacturing a separation membrane by removing the dispersion medium may involve drying or heating the coating layer to evaporate the dispersion medium contained within the coating layer. The removal of the dispersion medium may be performed at a temperature that allows only the dispersion medium contained within the coating layer to evaporate without deforming the polymer binder contained within the coating layer. For example, the step of removing the dispersion medium may involve heating the coating layer to a predetermined temperature, provided that the surface temperature of the coating layer does not exceed 60°C. When heating the coating layer under these conditions, 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.

[0080] The method for manufacturing the above-described separator for an electrochemical device may further include the step of forming an adhesive layer by applying an adhesive layer forming slurry to the surface of the coating layer and drying it. For example, after forming a coating layer by drying the coating slurry and removing the dispersion medium, an adhesive layer forming slurry may be applied to the surface of the coating layer and dried to form an adhesive layer.

[0081] A cylindrical lithium secondary battery according to one embodiment of the present invention is an electrochemical device comprising 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 device according to the aforementioned embodiment. The cylindrical lithium secondary battery can be manufactured by inserting an electrode assembly comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode into a battery case and sealing it. Before sealing the battery case, an electrolyte may be injected to impregnate the electrode assembly with the electrolyte. Although a cylindrical lithium secondary battery is exemplified as the electrochemical device in this embodiment, the present invention is not limited thereto and may include other types of secondary batteries; for example, the electrochemical device may be a cylindrical, prismatic, coin-type, or pouch-type lithium secondary battery.

[0082] The anode and the cathode may each have an electrode active material applied and dried to at least one surface of a current collector. The current collector may be made of a material that is conductive without causing chemical changes in the electrochemical device. For example, the current collector for the anode may be aluminum, nickel, titanium, calcined carbon, stainless steel; or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc., but is not limited thereto. For example, the current collector for the cathode may be copper, nickel, titanium, calcined carbon, stainless steel; or copper or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc., but is not limited thereto. The current collector may be in various forms such as a metal sheet, film, foil, net, porous body, foam, etc.

[0083] The above-described positive electrode comprises a positive current collector and a positive active material layer comprising a positive active material, a conductive material, and a binder resin on at least one surface of the current collector. The positive active material is a layered compound such as a lithium manganese complex oxide (LiMn2O4, LiMnO2, etc.), lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2, etc.; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7, etc.; chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x = 0.01 ~ 0.3); chemical formula LiMn 1-x M xIt may include a lithium manganese complex oxide 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 the Li of the chemical formula is substituted with alkaline earth metal ions; a disulfide compound; and one or more of Fe2(MoO4)3.

[0084] The above-described cathode comprises a cathode current collector and a cathode active material layer comprising a cathode active material, a conductive material, and a binder resin on at least one surface of the current collector. The above-described cathode comprises, as the cathode active material, carbon such as lithium metal oxide, non-graphitizable carbon, or graphite-based carbon; LixFe2O3 (0≤x≤1), Li x WO2(0≤x≤1), Sn x Me 1-x Me y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Group 1, 2, and 3 elements of the periodic table, halogens; 0 <x≤1; 1≤y≤3; 1≤z≤8) 등의 금속 복합 산화물; 리튬 금속; 리튬 합금; 규소계 합금; 주석계 합금; SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, 및 Bi2O5등의 금속 산화물; 폴리아세틸렌 등의 도전성 고분자; Li-Co-Ni 계 재료; 티타늄 산화물 중 선택된 1종 또는 2종 이상의 혼합물을 포함할 수 있다.

[0085] The conductive material may be any one selected from graphite, carbon black, carbon fiber or metal fiber, metal powder, conductive whiskers, conductive metal oxide, carbon nanotubes, activated carbon, and polyphenylene derivatives, or a mixture of two or more of these conductive materials. According to one embodiment, the conductive material may be one selected from natural graphite, artificial graphite, acetylene black, channel black, furnace black, lamp black, thermal black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium oxide, or a mixture of two or more of these conductive materials.

[0086] As the above binder resin, a binder resin commonly used in the electrodes of electrochemical devices 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, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate. Examples include acetatepropionate), cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxyl methyl cellulose, but are not limited thereto.

[0087] The above electrolyte is A + B - As a salt with a structure like that, A + is Li + , Na +, K + It includes alkali metal cations such as or ions composed of combinations thereof, and B - is PF6 - , BF4 - , Cl - , Br - , I - , ClO4 - , AsF6 - , CH3CO2 - , CF3SO3 - , N(CF3SO2)2 - , C(CF2SO2)3 - A salt comprising an anion such as or a combination thereof may be dissolved or dissociated in an organic solvent comprising 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), ethylmethyl carbonate (EMC), gamma butyrolactone, or a mixture thereof, but is not limited thereto.

[0088] The electrochemical device including the above electrode assembly can be used as a unit cell, and can be used as a battery module including the unit cell, a battery pack including the battery module, or a device including the battery pack as a power source. Examples of such devices include small devices such as computers, mobile phones, and power tools; electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs) that are powered by an electric motor; electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters (E-scooters); electric golf carts; and medium-to-large devices such as power storage systems, but are not limited thereto.

[0090] The present invention will be explained in more detail below through examples and experimental examples. The following examples and experimental examples are intended to illustrate the present invention, and the present invention is not limited by the following examples and experimental examples.

[0091] Example 1

[0092] Preparation of coating slurry

[0093] BaTiO3 as inorganic particles in distilled water at room temperature (25℃) (average particle size: 500 nm, dielectric constant: 2,000, density 6.0 g / cm³ 3 ), hexagonal boron nitride (average diameter: 150 nm, thickness: 30 nm, density: 2.1 g / cm³ 3 ) and a particulate acrylic binder (Styrene Butyl Acylate) as a polymer binder were added in a volume ratio of 82:3:15. At this time, the total solid content was 30 wt%, and the mixture was stirred in a shaker for 60 minutes to prepare a coating slurry.

[0094] Preparation of porous substrate

[0095] As a porous substrate (MI: 0.2 g / 10 min, T m A polyethylene film with a thickness of 9 μm was used, having a temperature of 135°C, a porosity of 45%, and an average pore size of 45 nm.

[0096] Manufacturing of separation membranes

[0097] The coating slurry was coated on both sides of a polyethylene film using a bar coater. A low-temperature airflow was applied to the film coated with the coating slurry, and the film was dried while controlling the surface temperature of the coating layer so as not to exceed 60°C to remove the dispersion medium, thereby forming a coating layer with a thickness of 1.5 μm for each coating.

[0098] Example 2

[0099] A separation membrane was prepared in the same manner as in Example 1, except that the volume ratio of BaTiO3, hexagonal boron nitride, and polymer binder was 80:5:15.

[0100] Example 3

[0101] A separation membrane was prepared in the same manner as in Example 1, except that the volume ratio of BaTiO3, hexagonal boron nitride, and polymer binder was 77:8:15.

[0102] Example 4

[0103] A separation membrane was prepared in the same manner as in Example 1, except that the volume ratio of BaTiO3, hexagonal boron nitride, and polymer binder was 84:1:15.

[0104] Comparative Example 1

[0105] A separation membrane was prepared in the same manner as in Example 1, except that hexagonal boron nitride was not used and BaTiO3 and a polymer binder were added in a volume ratio of 85:15.

[0106] Comparative Example 2

[0107] A separation membrane was prepared in the same manner as in Example 1, except that the volume ratio of BaTiO3, hexagonal boron nitride, and polymer binder was 73:12:15.

[0108] Comparative Example 3

[0109] A separator was prepared in the same manner as in Example 1, except that BaTiO3 was not used and hexagonal boron nitride and a polymer binder were added in a volume ratio of 85:15.

[0110] Comparative Example 4

[0111] A separation membrane was prepared in the same manner as in Comparative Example 1, except that alumina (average particle size: 500 nm, dielectric constant: 9) was used instead of BaTiO3 in Comparative Example 1.

[0113] Experimental Example 1. Confirmation of physical properties of coating slurry

[0114] Check sedimentation rate

[0115] The coating slurries of the examples and comparative examples were tested for sedimentation rate (TSI, Turbiscan Stability Index) for 10 hours using a dispersion measuring device (Product name: Turbiscan, Manufacturer: Foulaction), and then the sedimentation rate at 6 hours was checked.

[0116] Viscosity measurement

[0117] The coating slurries of the examples and comparative examples were measured using a cone-plate type viscometer (Product name: TV-22, Manufacturer: Toki-Sangyo).

[0119] Experimental Example 2. Confirmation of Physical Properties of the Separator

[0120] Gas generation measurement

[0121] The separator of the examples and comparative examples is 560 cm 2 Samples were taken by size. An electrolyte was prepared by adding 1.2 mol of the lithium salt LiPF6 to a solvent in which ethylene carbonate and ethyl methyl carbonate were mixed in a volume ratio of 3:7. The electrolyte and the sampled separator were placed into a cylindrical can of size 21700, sealed, and stored at room temperature for 12 hours, followed by storage in a 130°C chamber for 1 hour. The amount of gas generated inside the can was measured by collecting the gas using a BGA-06 device.

[0122] Dielectric breakdown voltage measurement

[0123] For the separators of the examples and comparative examples, a Chroma AC / DC / IR HIPOT TESTER (Model 19052) was used to apply a pressure of 8 MPa at 70°C, and then the voltage was measured when the current exceeded 0.5 mA and 3 seconds while increasing the voltage at a rate of 100 mV / s.

[0124] Air permeability measurement

[0125] Air permeability was measured using a Gurley densometer (Gurley, 4110N) for 100 cc of air with a diameter of 28.6 mm and an area of ​​645 mm² 2 The time taken to pass through the separation membrane was measured.

[0126] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Coating layer thickness (㎛) 1.5 1.5 1.5 1.5 1.5 - - 1.5 Inorganic particle volume % 82 80 77 84 85 73 0 85 (Alumina) Hexagonal Boron Nitride Volume % 3 5 8 1 0 12 85 0 Polymer binder volume % 15 15 15 15 15 15 15 15 Solid content (weight%) 30 30 30 30 30 30 30 30 Coating layer density (g / cm²) 3 ) 5.2 5.1 5.0 5.2 5.3 4.8 2.0 3.6 Sedimentation velocity (㎛ / s) 40 35 28 90 140 5 - 30 Slurry viscosity (cps) 7.1 7.8 11.6 6.2 5.4 31.5 - 8.3 Gas generation amount (µl) 785 775 790 775 780 - - 4200 Dielectric breakdown voltage (kV) 1.9 1.92 2.0 1.83 1.8 - - 2.0 Air per 100cc 105 103 110 100 102 - - 98

[0128] As shown in Table 1 above, in the case of Examples 1-4, even if BaTiO3 with a relatively high dielectric constant (approx. 2,000) is included as an inorganic particle in the coating slurry, if hexagonal boron nitride is included in an appropriate ratio, the gas generation amount of the separator is maintained at 775 ml-790 ml, which is less than 1,000 ml, and the dielectric breakdown voltage is maintained at a relatively high level of 1.83 kV-2.0 kV. In addition, it can be seen that the sedimentation velocity is maintained at 28 mm / s-90 mm / s, which is less than 100 mm / s.

[0129] Meanwhile, in the case of Comparative Example 1, which did not use hexagonal boron nitride, the sedimentation speed was relatively fast at 140 mm / s, and in the case of Comparative Example 4, which contained alumina instead of BaTiO3 as an inorganic particle, the gas generation amount was 4,200 ml, showing a significantly large value.

[0130] In Table 1 above, Comparative Example 2 could not achieve a coating layer thickness of 1.5 μm because the viscosity of the coating slurry was too high. In addition, Comparative Example 3 could not achieve a coating layer thickness of 1.5 μm because the viscosity of the coating slurry was too high, reaching the level of a paste, making it impossible to coat the porous substrate.

[0131] Although the foregoing has been described with reference to the embodiments of the present disclosure, a person skilled in the art or having ordinary knowledge in the art will understand that various modifications and changes can be made to the various embodiments of the present disclosure without departing from the technical scope of the various embodiments of the present disclosure as set forth in the claims below. Accordingly, the technical scope of the various embodiments of the present disclosure should not be limited to the contents described in the detailed description of the specification, but should be determined by the claims.

Claims

Claim 1 A porous substrate; and a coating layer formed on at least one surface of the porous substrate, wherein the coating layer comprises a polymer binder, inorganic particles, and hexagonal boron nitride, wherein the inorganic particles have a dielectric constant of 150 or higher, the hexagonal boron nitride is plate-shaped, and the density of the coating layer is 4.9 g / cm³ 3 Above 6.0 g / cm³ 3 Separator for electrochemical devices. Claim 2 In claim 1, the inorganic particles are 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 A separator for an electrochemical device, which is )O3-PbTiO3(PMN-PT), HfO2, SrTiO3, SnO2, CeO2, NiO, ZnO, ZrO2, Y2O3, TiO2, or a mixture thereof. Claim 3 In claim 1, the inorganic particles are separators for electrochemical devices having an average particle size (D50) of 200 nm or more and 1,000 nm or less. Claim 4 A separator for an electrochemical device according to claim 1, wherein the volume ratio of the inorganic particles and the hexagonal boron nitride is 7:1 to 30:

1. Claim 5 A separator for an electrochemical device according to claim 1, wherein the average diameter of the hexagonal boron nitride is 100 nm or more and 300 nm or less. Claim 6 A separator for an electrochemical device according to claim 1, wherein the aspect ratio of the hexagonal boron nitride is 5 or more and 30 or less. Claim 7 A separator for an electrochemical device according to claim 1, wherein the coating layer comprises 10 volume% or less of the hexagonal boron nitride. Claim 8 A separator for an electrochemical device according to claim 1, wherein the coating layer comprises 10 volume% or more and 30 volume% or less of the polymer binder. Claim 9 A separator for an electrochemical device according to claim 1, wherein the thickness of the coating layer is 0.5 μm or more and 2 μm or less. Claim 10 An electrochemical device comprising an anode, a cathode, and a separator disposed between the anode and the cathode, wherein the separator is a separator for an electrochemical device according to claim 1.

Images