Separator for electrochemical device and electrochemical device comprising same

Abstract

The present invention provides an electrochemical device comprising: a first coating layer including first inorganic particles and a first binder; and a second coating layer disposed on the first coating layer and including second inorganic particles and a second binder, wherein the dielectric constant of the second inorganic particles is higher than the dielectric constant of the first inorganic particles, and the particle size of the second inorganic particles is larger than the particle size of the first inorganic particles.

Description

Separator for an electrochemical device and an electrochemical device including the same

[0001] The present invention claims the benefit of the filing dates of Patent Application No. 2024-0158097 filed with the Korean Intellectual Property Office on November 8, 2024, and Patent Application No. 2025-0165506 filed with the Korean Intellectual Property Office on November 5, 2025, the entire contents of which are incorporated into the present invention.

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

[0003] 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.

[0004] Among the components of an electrochemical device, the separator comprises a porous polymer substrate located between the anode and cathode. It serves to isolate the anode and cathode, prevent electrical short circuits between the two electrodes, and allow the passage of electrolytes and ions. Although the separator itself does not participate in electrochemical reactions, its physical properties, such as wettability to the electrolyte, degree of porosity, and thermal shrinkage rate, affect the performance and safety of the electrochemical device.

[0005] Accordingly, various methods are being attempted to enhance the physical properties of the separator by adding a coating layer to a porous polymer substrate and modifying the properties of the coating layer by adding various materials. For example, inorganic materials may be added to the coating layer to improve the mechanical strength of the separator, or inorganic materials or hydrates may be added to the coating layer to improve the flame retardancy and heat resistance of the porous polymer substrate. Conventional inorganic materials used to impart heat resistance, such as Al2O3 and AlOOH, have the characteristic of adsorbing moisture due to functional groups, such as hydroxyl and carboxyl groups, exposed on their surfaces. This characteristic increases the moisture content in the separator and contributes to side reactions, such as electrolyte decomposition, which generates gas during the assembly, storage, transportation, or operation of the electrochemical device, thereby causing problems that reduce the safety and lifespan of the electrochemical device.

[0006] The present invention provides a separator for an electrochemical device that can simultaneously improve lightweighting, safety, and stability by including a coating layer comprising inorganic particles with different dielectric constants and particle sizes, and an electrochemical device including the same.

[0007] However, the problems that the present invention aims to solve are not limited to those mentioned above, and other unmentioned problems will be clearly understood by those skilled in the art from the description below.

[0008] One embodiment of the present invention provides a separator for an electrochemical device comprising: a porous polymer substrate; a first coating layer disposed on at least one surface of the porous polymer substrate and comprising a first inorganic particle and a first binder; and a second coating layer disposed on the first coating layer and comprising a second inorganic particle and a second binder, wherein the dielectric constant of the second inorganic particle is higher than the dielectric constant of the first inorganic particle, and the particle size of the second inorganic particle is equal to or greater than the particle size of the first inorganic particle.

[0009] According to one embodiment of the present invention, the ratio of the dielectric constant of the first inorganic particle to the dielectric constant of the second inorganic particle may be 1:1 to 1:20,000.

[0010] According to one embodiment of the present invention, the particle size of the first inorganic particle may be 300 nm or more and 500 nm or less.

[0011] According to one embodiment of the present invention, the particle size of the second inorganic particle may be 500 nm or more and 800 nm or less.

[0012] According to one embodiment of the present invention, the thickness ratio of the first coating layer and the second coating layer may be 1:0.5 to 1:2.

[0013] According to one embodiment of the present invention, the sum of the thicknesses of the first coating layer and the second coating layer may be 1 μm or more and 3 μm or less.

[0014] According to one embodiment of the present invention, the weight ratio of the second inorganic particle to the second binder may be 2:1 to 20:1.

[0015] According to one embodiment of the present invention, the method may further include an adhesive layer formed on the upper surface of the second coating layer and comprising at least one of an acrylic or fluorine-based binder.

[0016] According to one embodiment of the present invention, the first inorganic particle may be Al2O3 and the second inorganic particle may be BaTiO3.

[0017] According to one embodiment of the present invention, the air permeability may be 105 sec / 100cc or more and 125 sec / 100cc or less.

[0018] One embodiment of the present invention provides an electrochemical device comprising an anode, a cathode, a separator disposed between the anode and the cathode, and an electrolyte, wherein the separator is according to the one embodiment.

[0019] The separator for an electrochemical device and the electrochemical device according to the present invention can improve the stability of the electrochemical device by reducing the amount of gas generated.

[0020] FIG. 1 is a schematic diagram showing a cross-section of a separator for an electrochemical device according to one embodiment of the present invention.

[0021] 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.

[0022] In this specification, the term "comprising" is used when listing materials, compositions, devices, and methods useful for the present invention, and is not limited to the examples listed.

[0023] As used in this specification, "electrochemical device" may refer to a primary battery, a secondary battery, a supercapacitor, etc.

[0024] In this specification, "size" refers to the diameter at the 50% point of the cumulative distribution of particle numbers according to particle size. The particle size can be measured using a laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it can be introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500) to calculate the particle size distribution by measuring the difference in diffraction patterns according to particle size as the particles pass through the laser beam. The particle size can be measured by calculating the particle diameter at the 50% point of the cumulative distribution of particle numbers.

[0025] In this specification, "permittivity" refers to the magnitude of polarization created by a dielectric in response to an external electric field, and the unit is F / m. The unit of permittivity will be omitted below. Specifically, in the case of ceramic particles, a binder is mixed with the ceramic particles, compression molded, and then sintered. Electrodes are coated on both sides of the sintered body, and the inductance, capacitance, and resistance are measured using an LCR meter. The permittivity can then be measured using the following Equation 1.

[0026] [Mathematical Formula 1]

[0027]

[0028] (ε=Permittivity of BaTiO3, C=Measured capacitance, d: Dielectric thickness, A=Dielectric area, ε 0 =Dielectric constant in vacuum(8.85x10⁻⁶ -12 F / m))

[0029]

[0030] One embodiment of the present invention provides a separator (100) for an electrochemical device comprising: a porous polymer substrate (110); a first coating layer (130) disposed on at least one surface of the porous polymer substrate (110) and comprising a first inorganic particle and a first binder; and a second coating layer (150) disposed on the first coating layer (130) and comprising a second inorganic particle and a second binder, wherein the dielectric constant of the second inorganic particle is higher than the dielectric constant of the first inorganic particle, and the particle size of the second inorganic particle is equal to or greater than the particle size of the first inorganic particle.

[0031] According to one embodiment of the present invention, the separator (100) for the electrochemical device comprises the porous polymer substrate (110). The porous polymer 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 polymer 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 polymer substrate, and a fluid may pass through the porous polymer substrate through the pores.

[0032] The porous polymer substrate (110) 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 polymer 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, polyimideamide, nylon, polytetrafluoroethylene, and copolymers or mixtures thereof. Preferably, a polyolefin resin 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 are easy to apply a coating slurry to.

[0033] The porous polymer substrate (110) may have a single-layer or multi-layer structure. The porous polymer substrate may include two or more polymer resin layers with different melting points (Tm) to provide a shutdown function during high-temperature runaway of the battery. For example, the porous polymer substrate may include a polypropylene layer with a relatively high melting point and a polyethylene layer with a relatively low melting point. Preferably, the porous polymer substrate may have a three-layer structure 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.

[0034] The porous polymer substrate (110) may include pores with an average diameter of 0.01 μm or more and 1 μm or less. Specifically, the size of the pores included 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 controlling the pore size of the porous polymer substrate within the above-described range, the air permeability and ion conductivity of the entire separation membrane being manufactured can be controlled.

[0035] The porous polymer substrate (110) may have an air permeability of 10 s / 100cc or more and 100 s / 100cc or less. Specifically, the air permeability of the porous polymer substrate may be 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. Preferably, the air permeability of the porous polymer substrate may be 50 s / 100cc or more and 70 s / 100cc or less. When the air permeability of the porous polymer substrate is within the range described above, the air permeability of the manufactured separator may be provided in a range suitable for securing the output and cycle characteristics of the electrochemical device.

[0036] The above air permeability (s / 100cc) refers to the time (in seconds) required for 100 cc of air to pass through a porous polymer 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 2 100 cc 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 100 cc of air to pass through a 1 square inch sample under constant pressure of 4.8 inches of water at room temperature can be measured.

[0037] The porous polymer substrate (110) may have a porosity of 10 vol% or more and 60 vol% or less. Specifically, the porosity of the porous polymer substrate may 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 may be 30 vol% or more and 50 vol% or less. When the porosity of the porous polymer substrate is within the range described above, the ion conductivity of the separator may be provided within a range suitable for securing the output and cycle characteristics of the electrochemical device.

[0038] The above porosity refers to the ratio of the volume of pores to the total volume of the porous polymer 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.

[0039] The thickness of the porous polymer substrate (110) may be 1 μm or more and 20 μm or less. Specifically, the thickness of the porous polymer substrate may be 2 μm or more and 20 μm or less, 3 μm or more and 19 μm or less, 4 μm or more and 18 μm or less, 5 μm or more and 17 μm or less, 6 μm or more and 16 μm or less, 7 μm or more and 15 μm or less, or 8 μm or more and 14 μm or less. By controlling the thickness of the porous polymer substrate within the above-described range, the energy density and ion conductivity of the battery can be improved.

[0040] According to one embodiment of the present invention, the separator (100) for an electrochemical device comprises a first coating layer (130) disposed on at least one surface of the porous polymer substrate (110). The first coating layer may be disposed on at least a portion of the porous polymer substrate. The first coating layer can improve the heat resistance of the separator for an electrochemical device and provide dimensional stability at high temperatures. The first coating layer can improve the mechanical properties of the separator for an electrochemical device and improve stability.

[0041] According to one embodiment of the present invention, the first coating layer (130) comprises a first inorganic particle and a first binder. The first coating layer may be formed by coating a first coating slurry comprising the first inorganic particle, the first binder, and a dispersion medium onto at least one surface of the porous polymer substrate. The first coating layer may include an interstitial volume in which the first inorganic particles are connected by the first binder, allowing lithium ions to pass through, and may adhere to the porous polymer substrate to prevent thermal shrinkage of the porous polymer substrate, thereby improving the stability of the separator for the electrochemical device.

[0042] Specifically, the first inorganic particle is 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 / 3Examples include O3-PbTiO3 (PMN-PT), hafnia (HfO2), SnO2, CeO2, MgO, Mg(OH)2, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, SiC, Al(OH)3, TiO2, aluminum peroxide, zinc-tin hydroxide (ZnSn(OH)6), tin-zinc oxide (Zn2SnO4, ZnSnO3), antimony trioxide (Sb2O3), antimony tetroxide (Sb2O4), antimony pentoxide (Sb2O5), etc., and may include one or more of these. When the separator for the electrochemical device includes the aforementioned inorganic materials, high-temperature stability of the separator can be provided.

[0043] According to one embodiment of the present invention, the dielectric constant of the first inorganic particle may be 1 or more and 50 or less. Specifically, the dielectric constant may be 1 or more and 45 or less, 1 or more and 40 or less, 1 or more and 35 or less, 1 or more and 30 or less, 1 or more and 25 or less, 1 or more and 20 or less, 1 or more and 15 or less, or 1 or more and 10 or less. When the dielectric constant of the first inorganic particle is within the aforementioned range, internal short circuits of the electrochemical element can be prevented, thereby improving stability.

[0044] Specifically, the particle size of the first inorganic particle may be 300 nm or larger and 500 nm or smaller. When the particle size of the first inorganic particle satisfies the aforementioned range, internal short circuits of the electrochemical element can be prevented and ion conductivity can be improved.

[0045] According to one embodiment of the present invention, the weight of the first inorganic particles in the first coating layer may be 85 parts by weight or more and 95 parts by weight or less per 100 parts by weight of the first coating layer. Specifically, it may be 90 parts by weight or more and 95 parts by weight or 93 parts by weight or more and 95 parts by weight or less. When the weight of the first inorganic particles in the first coating layer satisfies the aforementioned range, the heat resistance of the separator for the electrochemical device can be improved.

[0046] Specifically, the first binder can bind inorganic particles included in the first coating layer and impart adhesive force to the first coating layer. The first binder may be a solution type that dissolves in the dispersion medium of the first coating slurry, a particle type that does not dissolve in the dispersion medium and maintains a particle shape in the first coating slurry and the first coating layer, or a combination thereof, but is not limited thereto. The first 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 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 comprising one or more of these. For example, the fluorine binder may be one or more selected from the group consisting of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, and polyvinylidene fluoride-trichloroethylene. Preferably, the first binder may be an acrylic binder.

[0047] According to one embodiment of the present invention, the weight of the first binder for the first coating layer may be greater than 0 parts by weight and less than or equal to 10 parts by weight with respect to 100 parts by weight of the first coating layer. Specifically, it may be 1 part by weight or more and less than or equal to 10 parts by weight, or 2 parts by weight or more and less than or equal to 5 parts by weight. When the weight of the first binder of the first coating layer satisfies the aforementioned range, it may bind the inorganic particles contained in the first coating layer and impart adhesive force to the first coating layer.

[0048] The step of forming the first coating layer involves coating at least one surface of the porous polymer substrate with the first coating slurry comprising the first inorganic particles, the first binder, and the dispersion medium. For example, the coating may be formed by 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. When using the aforementioned coating method, the first coating layer can be easily formed on the porous polymer substrate.

[0049] According to one embodiment of the present invention, the separator for an electrochemical device comprises a second coating layer (150) disposed on the first coating layer (130). The second coating layer comprises a second inorganic particle and a second binder. Since the second coating layer comprises the second inorganic particle and the second binder, gas generation of the separator for an electrochemical device can be minimized, and adhesion between the electrode and the separator for an electrochemical device can be improved.

[0050] According to one embodiment of the present invention, the second coating layer (150) may be formed by coating a second coating slurry comprising second inorganic particles, a second binder, and a dispersion medium onto at least one surface of the porous polymer substrate. The second coating layer may allow lithium ions to pass through by forming an interstitial volume in which the second inorganic particles are connected by the second binder. Additionally, the second coating layer may prevent thermal shrinkage of the porous polymer substrate, thereby improving the stability of the separator for the electrochemical device.

[0051] According to one embodiment of the present invention, the second inorganic particle is a perovskite-type inorganic ferroelectric such as SrTiO3, BaTiO3, Pb(Zr,Ti)O3 (PZT), PbTiO3, PbZrO3, BiFeO, or LiNbO3, LiTaO3, ZnO, Bi2SiO5, SrBi2Ta2O9 (SBT), Bi4Ti3O. 12 , La4Ti3O 12 It may include at least one of the non-perovskite particles. The second inorganic particle may have a high dielectric constant. The second inorganic particle may interact with polar molecules and ions due to a spontaneous polarization state. Specifically, the degree of dissociation of the lithium salt inside the electrolyte may be increased due to the spontaneous polarization state of the second inorganic particle through such interaction. When the degree of dissociation of the lithium salt increases, side reactions with the electrolyte solvent are reduced, thereby reducing gas generation inside the electrochemical device.

[0052] According to one embodiment of the present invention, the dielectric constant of the second inorganic particle may be 50 or more and 20,000 or less. Specifically, the dielectric constant of the second inorganic particle may be 50 or more and 15,000 or less, 100 or more and 15,000 or less, 300 or more and 10,000 or less, 500 or more and 10,000 or less, 500 or more and 8,000 or less, 500 or more and 6,000 or less, 500 or more and 4,000 or less, 500 or more and 3,000 or less, or 1,000 or more and 3,000 or less. When the dielectric constant of the second inorganic particle is within the aforementioned range, the ion conductivity of the electrolyte is improved, and the generation of salt within the electrochemical device is suppressed, thereby improving the stability of the electrochemical device.

[0053] According to one embodiment of the present invention, the particle size of the second inorganic particle may be 500 nm or more and 800 nm or less. Specifically, it may be 500 nm or more and 700 nm or less, 500 nm or more and 600 nm or less, or 500 nm or more and 550 nm or less. If the particle size of the second inorganic particle exceeds the range described above, the dielectric constant of the second inorganic particle tends to increase, but there is a problem in that it is difficult to uniformly coat the inorganic particle on the substrate because it is difficult to achieve uniform dispersion within the coating layer slurry. On the other hand, if the particle size of the second inorganic particle falls below the range described above, the dielectric constant also decreases, resulting in a negligible effect in suppressing the side reaction of the salt, and thereby the amount of gas generated may increase. Therefore, if the particle size of the second inorganic particle is within the range described above, the heat resistance of the electrochemical device can be improved and gas generation within the electrochemical device can be reduced.

[0054] The dielectric constant of inorganic particles tends to increase with the particle size of the inorganic particles. However, as the particle size of the inorganic particles increases, the sedimentation rate within the coating slurry increases, making it difficult to achieve uniform dispersion within the slurry. Therefore, when the second inorganic particle satisfies the aforementioned particle size and dielectric constant, it is possible to satisfy a high dielectric constant while simultaneously uniformly coating the inorganic particle onto the substrate.

[0055] According to one embodiment of the present invention, the weight of the second inorganic particles in the second coating layer (150) may be 70 parts by weight or more and 95 parts by weight or less based on 100 parts by weight of the second coating layer. Specifically, it may be 75 parts by weight or more and 95 parts by weight or less, 80 parts by weight or more and 95 parts by weight or less, 85 parts by weight or more and 95 parts by weight or less, or 90 parts by weight or more and 95 parts by weight or less. When the weight of the second inorganic particles in the second coating layer satisfies the aforementioned range, the adhesion between the second coating layer and the electrode can be improved, and the heat resistance of the separator for the electrochemical device can be improved.

[0056] According to one embodiment of the present invention, the second binder may be the same as or different from the first binder. Specifically, the second binder may be an acrylic copolymer or a fluorine-based binder, and may be a particle-type or solution-type binder. When the separator for the electrochemical device comprises the aforementioned second binder, the adhesion between the electrode and the separator for the electrochemical device is improved, thereby facilitating the manufacture of a battery and enabling a stable stacking process.

[0057] According to one embodiment of the present invention, the weight of the second binder in the second coating layer may be 5 parts by weight or more and 30 parts by weight or less based on 100 parts by weight of the second coating layer. Specifically, it may be 5 parts by weight or more and 25 parts by weight or less, 5 parts by weight or more and 20 parts by weight or less, 5 parts by weight or more and 15 parts by weight or less, or 8 parts by weight or more and 12 parts by weight or less. When the weight of the second binder in the second coating layer satisfies the aforementioned range, the adhesion between the separator for the electrochemical device and the electrode may be improved.

[0058] According to one embodiment of the present invention, the weight ratio of the second inorganic particle to the second binder may be 2:1 to 20:1. Specifically, it may be 2:1 to 20:1, 4:1 to 20:1, 6:1 to 20:1, 8:1 to 20:1, 8:1 to 18:1, 8:1 to 15:1, or 8:1 to 10:1. When the second inorganic particle and the second binder satisfy the aforementioned ranges, the heat resistance of the separator for the electrochemical device can be enhanced, and at the same time, the amount of gas generated by the separator can be reduced.

[0059] The step of forming the second coating layer involves coating at least one surface of the porous polymer substrate with a second coating slurry comprising the second inorganic particles, the second binder, and a dispersion medium. For example, the coating may be formed by 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. Preferably, the step of forming the second coating layer may involve forming the second coating layer using the second coating slurry with a spray coater or a gravure coater. When the second coating layer is coated using the spray coater or gravure coater, the second coating layer can be uniformly formed on the first coating layer.

[0060] According to one embodiment of the present invention, the ratio of the dielectric constant of the first inorganic particle to the dielectric constant of the second inorganic particle may be 1:1 to 1:20,000. Specifically, the ratio of the dielectric constant of the first inorganic particle to the dielectric constant of the second inorganic particle may be 1:1 to 1:10,000, 1:10 to 1:5,000, 1:30 to 1:5,000, 1:50 to 1:5,000, 1:50 to 1:1,000, 1:50 to 1:500, 1:50 to 1:400, or 1:50 to 1:300.

[0061] According to one embodiment of the present invention, the ratio of the dielectric constant of the first inorganic particle to the dielectric constant of the second inorganic particle may be 1:1 to 1:20,000. Specifically, the ratio of the dielectric constant of the first inorganic particle to the dielectric constant of the second inorganic particle may be 9:9 to 9:20,000, 9:400 to 9:10,000, 9:400 to 9:8,000, 9:400 to 9:6,000, 9:400 to 9:4,000, or 9:400 to 9:2,000.

[0062] When the ratio of dielectric constant is within the aforementioned range, the ionic conductivity of the electrolyte is improved, and the gas generated during the assembly or operation of the electrochemical device can be reduced.

[0063] According to one embodiment of the present invention, the ratio of the dielectric constant of the second inorganic particle to the dielectric constant of the first inorganic particle may be 10 or more. Specifically, the dielectric constant ratio may be 10 or more and 20,000 or less. More specifically, the dielectric constant ratio may be 10 or more and 10,000 or less, 100 or more and 9,000 or less, 400 or more and 9,000 or less, 400 or more and 7,000 or less, 400 or more and 5,000 or less, or 400 or more and 2,000 or less. When the dielectric constant ratio is within the aforementioned range, the ion conductivity of the electrolyte is improved, and the gas generated during the assembly or operation of the electrochemical element can be reduced.

[0064] According to one embodiment of the present invention, the first inorganic particle may be Al2O3 and the second inorganic particle may be BaTiO3. Specifically, the dielectric constant of the first inorganic particle, Al2O3, may be 10 or less, and the dielectric constant of the second inorganic particle, BaTiO3, may be 400 or more. The first inorganic particle is Al2O3, When the second inorganic particle is BaTiO3, the separator for the electrochemical device can be made lighter due to Al2O3, and at the same time, due to the high dielectric constant of BaTiO3, interaction with polar molecules and ions is possible, which can reduce side reactions with lithium ions inside the electrochemical device and reduce gas generation.

[0065] According to one embodiment of the present invention, the particle size of the second inorganic particle is equal to or greater than the particle size of the first inorganic particle. If the second inorganic particle with a higher dielectric constant is equal to or greater than the particle size of the first inorganic particle, the porosity of the separator is improved to facilitate the movement of lithium ions, and at the same time, the dielectric constant of the separator is increased to reduce gas generation inside the electrochemical device.

[0066] In contrast, if the particle size of the second inorganic particle is smaller than that of the first inorganic particle, the dielectric constant of the first inorganic particle also decreases, and as a result, the effect of suppressing the side reaction of the salt is negligible, which may increase the amount of gas generated.

[0067] According to one embodiment of the present invention, the second coating layer (152) is disposed on the first coating layer (130). The second coating layer may have an excess amount of binder compared to the first coating layer. For example, the second coating layer may have a higher amount of second binder than the amount of first binder in the first coating layer, so that it can also function as an electrode adhesive layer.

[0068] According to one embodiment of the present invention, the thickness ratio of the first coating layer to the second coating layer may be 1:0.5 to 1:2. When the thickness ratio is within the aforementioned range, heat resistance or mechanical properties resulting from the use of the first inorganic material can be secured, and at the same time, a gas reduction effect can be exhibited. On the other hand, when the thickness ratio of the first coating layer to the second coating layer is 3:1 or higher, the thickness of the first coating layer becomes relatively thick, which may cause an increase in air permeability and resistance, and the effect of suppressing gas generation may be negligible as the thickness of the second coating becomes thin. Conversely, when the thickness ratio of the first coating layer to the second coating layer is 1:3 or higher, the heat resistance may be reduced as the thickness of the first coating layer becomes relatively thin.

[0069] According to one embodiment of the present invention, the sum of the thicknesses of the first coating layer and the second coating layer may be 1 μm or more and 3 μm or less. Specifically, the sum of the thicknesses of the first coating layer and the second coating layer may be 1 μm or more and 2.5 μm or less, 1 μm or more and 2 μm or less, 1.5 μm or more and 2 μm or less, or 1 μm or more and 1.5 μm or less. If the above-described range is exceeded, the thickness of the coating layer increases, which may cause an increase in air permeability and resistance; if the above-described range is not met, heat resistance may decrease, and the effect of suppressing salt side reactions may be negligible, which may lead to an increase in gas generation.

[0070] According to one embodiment of the present invention, the separator for an electrochemical device may further comprise an electrode adhesive layer formed on the upper surface of the second coating layer and comprising a third binder. The third binder may include at least one of a fluorine-based binder or an acrylic binder to improve adhesion to the electrode. For example, the fluorine-based binder may be a particulate polyvinylidene fluoride-based binder. The electrode adhesive layer may include a fluorine-based binder and an acrylic binder to stably maintain adhesion to the electrode of the separator for an electrochemical device in both a dry state without an electrolyte and a wet state impregnated with an electrolyte.

[0071] The electrode adhesive layer may cover 20% or more and 80% or less of the surface of the second coating layer. By further including the electrode adhesive layer, the adhesion to the electrode can be further improved.

[0072] The electrode adhesive side may be formed by additionally applying a third binder to the surface of the second coating layer. For example, the electrode adhesive layer may be formed using spray application, gravure coating, slot die, etc., but is not limited thereto.

[0073] One embodiment of the present invention provides an electrochemical device comprising an anode, a cathode, a separator disposed between the anode and the cathode, and an electrolyte, wherein the separator is according to the one embodiment.

[0074] 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.

[0075] 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.

[0076] 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 cathode current collector. The above-described cathode comprises, as the cathode active material, carbon such as lithium metal oxide, non-graphitizable carbon, and graphite-based carbon; Li x Fe2O3(0≤x≤1), Li x WO2(0≤x≤1), Si, SiO x (0 <x<2), SiC, Si 합금 등의 실리콘계 재료; (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, 주기율표의 1족, 2족, 3족 원소, 할로겐; 0<x≤1; 1≤y≤3; 1≤z≤8) 등의 금속 복합 산화물; 리튬 금속; 리튬 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.

[0077] The conductive material may be any one selected from the group consisting of graphite, carbon black, carbon fiber or metal fiber, metal powder, conductive whiskers, conductive metal oxides, carbon nanotubes, activated carbon, and polyphenylene derivatives, or a mixture of two or more of these conductive materials. The carbon nanotubes have a graphite sheet having a cylindrical shape with a nano-sized diameter, and sp 2 It has a bonded structure and exhibits conductive or semiconductor properties depending on the angle and structure at which the graphite plane is rolled. Carbon nanotubes can be classified into single-walled carbon nanotubes (SWCNT), double-walled carbon nanotubes (DWCNT), and multi-walled carbon nanotubes (MWCNT) depending on the number of bonds forming the walls, and these carbon nanotubes can be appropriately selected according to the application of the dispersion. More specifically, it may be one type 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.

[0078] The separator for the electrochemical device described above may have an air permeability of 105 sec / 100cc or more and 125 sec / 100cc or less. Specifically, the air permeability may be 106 sec / 100cc or more and 125 sec / 100cc or less, 106 sec / 100cc or more and 120 sec / 100cc or less, or 106 sec / 100cc or more and 119 sec / 100cc or less. The separator for the electrochemical device described above can ensure lightweighting and stability while having the above air permeability to ensure the output and cycle characteristics of the electrochemical device.

[0079] According to one embodiment of the present invention, the electrochemical device may be manufactured by inserting an electrode assembly, comprising a positive electrode, a negative electrode, and a separator for the electrochemical device interposed between the positive electrode and the negative electrode, into a case or pouch and sealing it. Before sealing the case or pouch, an electrolyte may be injected to impregnate the electrode assembly with the electrolyte. The shape of the case or pouch is not limited. For example, the electrochemical device may be a cylindrical, prismatic, coin-type, or pouch-type lithium secondary battery.

[0080] 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.

[0081] The electrochemical device comprising the above electrode assembly may be a lithium secondary battery. The battery may be used as a unit cell, a battery module comprising the unit cell, a battery pack comprising the battery module, or a device comprising 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.

[0082] The present invention will be explained in more detail below through specific embodiments and experimental examples. The following embodiments and experimental examples are intended to illustrate the present invention, and the present invention is not limited by the following embodiments and experimental examples.

[0083]

[0084] Example 1

[0085] Preparation of the first coating slurry

[0086] At room temperature (25 ℃), a first inorganic particle Al2O3 (particle size: 500 nm) (dielectric constant: 9), an acrylic binder EHA-MMA Co-polyacrylate (Tg: -40 ℃) as a first binder, a polyacrylamid-based dispersant, and an additive (Si-based wetting agent) were added in a ratio of 94:4:1:1 and stirred with a shaker for 60 minutes to prepare a first coating slurry.

[0087]

[0088] Preparation of the second coating slurry

[0089] At room temperature (25 ℃), a second inorganic particle BaTiO3 (particle size: 500 nm) (dielectric constant: 2,000) and a second binder polystyrene-butyacrylate (Tg: 40 ℃) were added in a ratio of 9:1 and stirred with a shaker for 60 minutes to prepare a second coating slurry.

[0090]

[0091] Preparation of porous polymer substrate

[0092] As a porous polymer substrate (MI: 0.2 g / 10 min, T m A polyethylene film with a diameter of 135 ℃, porosity of 45 vol%, average pore size of 45 nm, a size of 20 cm × 30 cm, and a thickness of 9 μm was used.

[0093]

[0094] Formation of the first coating layer

[0095] After coating the first coating slurry on both sides of a polyethylene film using a bar coater, a low-temperature airflow was applied to dry the film while controlling the surface temperature of the first coating layer so that it did not exceed 60°C. A first coating layer was formed with a thickness of 0.5 μm for each coating.

[0096]

[0097] Formation of the second coating layer

[0098] After coating the second coating slurry on both sides using a bar coating method on the dried first coating layer, a low-temperature airflow was applied to dry the second coating layer while controlling the surface temperature so that it did not exceed 60°C. A second coating layer was formed with a thickness of 1.0 μm for each coating.

[0099] A separation membrane with a total thickness of 12 μm was manufactured.

[0100]

[0101] Manufacturing of electrochemical devices

[0102] Two of the above-mentioned separators, one anode with a thickness of 144 μm, and one cathode with a thickness of 185.2 μm were prepared. A laminate was prepared by stacking the anode and the cathode alternately and placing a separator between the anode and the cathode.

[0103] The above laminate was placed in a press device and laminated at 60°C and a pressure of 6.5 MPa for 0.1 seconds to manufacture an electrochemical device.

[0104]

[0105] Example 2

[0106] An electrochemical device was manufactured in the same manner as in Example 1, except that the thickness of the first coating layer and the second coating layer were each set to 1.0 μm and the thickness ratio was set to 1:1.

[0107]

[0108] Example 3

[0109] An electrochemical device was manufactured in the same manner as in Example 1, except that the thickness ratio of the first coating layer (thickness: 1.0 μm) and the second coating layer (thickness: 0.5 μm) was set to 1:0.5.

[0110]

[0111] Example 4

[0112] An electrochemical device was manufactured in the same manner as in Example 1, except that the particle size of the first inorganic material, Al2O3, was set to 300 nm.

[0113]

[0114] Comparative Example 1

[0115] An electrochemical device was manufactured in the same manner as in Example 1, except that the particle size of the second inorganic material, BaTiO3, was set to 100 nm.

[0116]

[0117] Comparative Example 2

[0118] An electrochemical device was manufactured in the same manner as in Example 1, except that the first coating layer was set to 1.5 μm and only the first coating layer was formed.

[0119]

[0120] Experimental Example

[0121] Air permeability measurement

[0122] The air permeability of the separators of Examples 1 to 4 and Comparative Examples 1 to 2 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 mm. 2 The time taken to pass through the membrane was measured. The measurement results are summarized in Table 1 below.

[0123]

[0124] Measurement of gas generation amount

[0125] The amount of gas generated after storing the electrochemical elements of Examples 1 to 4 and Comparative Examples 1 to 2 in a buffered state at 72°C for 28 days was measured using gas chromatography and summarized in Table 1 below.

[0126]

[0127] Measure the rate of resistance rise

[0128] For the electrochemical elements of Examples 1 to 4 and Comparative Examples 1 to 2 above, the resistance was calculated from the voltage change occurring for 10 seconds by flowing a 2.5C CC current through the electrochemical elements at 25 ℃ with a driving voltage of 2.5 V to 4.35 V and an SOC of 50 using the following Equation 3.

[0129] In addition, an electrochemical device comprising the separator of Examples 1 to 4 and Comparative Examples 1 to 2 was charged once at 0.5 C and discharged at 1.0 C 200 times in a voltage range of 2.5 V to 4.35 V using an electrochemical charge / discharger in a 45 ℃ chamber. Afterwards, the electrochemical device, which had undergone the above cycle, was subjected to a driving voltage of 2.5 V-4.35 V and an SOC of 50, and a 2.5 C CC current was applied, and the resistance was measured from the voltage change occurring for 10 seconds using the following Equation 2.

[0130] [Mathematical Formula 2]

[0131] R=△V / I

[0132] The initial resistance value and the rate of increase of resistance after 200 cycles were calculated and summarized in Table 1 below.

[0133]

[0134] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 First inorganic particle size 500nm 500nm 500nm 300nm 500nm 500nm Second inorganic particle size 500nm 500nm 500nm 500nm 100nm - Thickness ratio of first coating layer to second coating layer 1:21:11:0.5 1:21:2 - Dielectric constant ratio of second coating layer to first coating layer 9:2,000 9:2,000 9:2,000 9:2,000 9:2,000 9:300 - Air permeability (sec / 100cc) 115 111 106 119 132 102 Gas generation amount (uL) 78 78 55 92 180 111 52 1245 Resistance increase rate (%) 2.1 2.2 3.9 2.2 6.2 6.8

[0135]

[0136] According to Table 1 above, Examples 1 to 4 can reduce the amount of gas generated and lower the rate of increase in resistance of the electrochemical element by making the dielectric constant of the second inorganic particle higher than the dielectric constant of the first inorganic particle and the particle size of the second inorganic particle equal to or greater than the particle size of the first inorganic particle.

[0137] In addition, Examples 1 to 3 confirmed an excellent effect by adjusting the thickness ratio of the first coating layer and the second coating layer, while making the total coating layer thickness 1.5 μm.

[0138] In contrast, in Comparative Example 1 above, even though the dielectric constant of the second inorganic particle is higher than the dielectric constant of the first inorganic particle, it can be seen that the gas generation amount and the resistance increase rate are increased by making the particle size of the second inorganic particle smaller than the particle size of the first inorganic particle.

[0139] Furthermore, it can be seen that although the total coating layer thickness of Comparative Example 2 is 1.5 μm, it does not include a second coating layer containing second inorganic particles, and thus the amount of gas generated and the rate of resistance increase are increased.

[0140] Accordingly, the present invention can reduce the amount of gas generated and lower the rate of increase in resistance of an electrochemical device by making the dielectric constant of the second inorganic particle higher than the dielectric constant of the first inorganic particle and the particle size of the second inorganic particle equal to or greater than the particle size of the first inorganic particle.

[0141] [Explanation of the symbol]

[0142] 100: Separator for electrochemical devices

[0143] 110: Porous polymer substrate

[0144] 130: First coating layer

[0145] 150: Second coating layer

Claims

1. Porous polymer substrate; A first coating layer disposed on at least one surface of the above-mentioned porous polymer substrate and comprising a first inorganic particle and a first binder; and A second coating layer disposed on the first coating layer and comprising a second inorganic particle and a second binder, and The dielectric constant of the second inorganic particle is higher than the dielectric constant of the first inorganic particle, and A separator for an electrochemical device, wherein the particle size of the second inorganic particle is equal to or greater than the particle size of the first inorganic particle.

2. In Paragraph 1, A separator for an electrochemical device, wherein the ratio of the dielectric constant of the first inorganic particle to the dielectric constant of the second inorganic particle is 1:1 to 1:20,000.

3. In Paragraph 1, A separator for an electrochemical device, wherein the particle size of the first inorganic particle is 300 nm or more and 500 nm or less.

4. In Paragraph 1, A separator for an electrochemical device, wherein the particle size of the second inorganic particle is 500 nm or more and 800 nm or less.

5. In Paragraph 1, A separator for an electrochemical device, wherein the thickness ratio of the first coating layer and the second coating layer is 1:0.5 to 1:

2.

6. In Paragraph 1, A separator for an electrochemical device, wherein the sum of the thicknesses of the first coating layer and the second coating layer is 1 μm or more and 3 μm or less.

7. In Paragraph 1, A separator for an electrochemical device, wherein the weight ratio of the second inorganic particle to the second binder is 2:1 to 20:

1.

8. In Paragraph 1, A separator for an electrochemical device, further comprising an adhesive layer formed on the upper surface of the second coating layer and comprising at least one of an acrylic or fluorine-based binder.

9. In Paragraph 1, A separator for an electrochemical device, wherein the first inorganic particle is Al2O3 and the second inorganic particle is BaTiO3.

10. In Paragraph 1, A separator for an electrochemical device having an air permeability of 105 sec / 100cc or more and 125 sec / 100cc or less.

11. An electrochemical device comprising an anode, a cathode, a separator disposed between the anode and the cathode, and an electrolyte, wherein the separator is in accordance with claim 1.

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