Separator for electrochemical device and electrochemical device including same

Abstract

The present invention provides a separator for an electrochemical device and an electrochemical device having same applied thereto, the separator comprising: a porous polymer substrate; and a porous coating layer formed on at least one surface of the porous polymer substrate and containing inorganic particles, wherein the dielectric constant of the porous coating layer is 250 to 10,000 (both inclusive).

Description

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

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0153212 dated November 1, 2024 and Korean Patent Application No. 10-2025-0137403 dated September 23, 2025, and all contents disclosed in the documents of said Korean patent applications 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.

[0003]

[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]

[0007] The present invention provides a separator for an electrochemical device capable of improving the stability of the electrochemical device by controlling the dielectric constant of a porous coating layer, and an electrochemical device including the same.

[0008] 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.

[0009]

[0010] One embodiment of the present invention provides a separator for an electrochemical device comprising a porous polymer substrate and a porous coating layer formed on at least one surface of the porous polymer substrate and comprising inorganic particles, wherein the dielectric constant of the porous coating layer is about 250 or more and 10,000 or less.

[0011] According to one embodiment of the present invention, the inorganic particles may include BaTiO3 or SrTiO3.

[0012] According to one embodiment of the present invention, the inorganic particles may have a dielectric constant of about 250 or more and 10,000 or less.

[0013] According to one embodiment of the present invention, the inorganic particles may have a particle size of 300 nm or more and 1,000 nm or less.

[0014] According to one embodiment of the present invention, the crystal structure of the inorganic particle may be tetragonal.

[0015] According to one embodiment of the present invention, the thickness of the porous coating layer may be about 0.3 μm or more and 3.0 μm or less.

[0016] According to one embodiment of the present invention, the inorganic particles may be included in an amount of about 80 parts by weight or more and 99 parts by weight or less based on 100 parts by weight of the porous coating layer.

[0017] According to one embodiment of the present invention, the porous coating layer may further comprise an acrylic binder.

[0018] According to one embodiment of the present invention, the amount of gas generated by the separator for the electrochemical device may be 1,500 μL or less.

[0019] 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 in accordance with one embodiment of the present invention.

[0020]

[0021] The separator for an electrochemical device and the electrochemical device according to the present invention may have improved stability.

[0022]

[0023] 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.

[0024] 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.

[0025] In this specification, “electrochemical device” may refer to a primary battery, a secondary battery, a supercapacitor, etc.

[0026] In this specification, “size” refers to the diameter D50 at the point of 50% of the cumulative distribution of the number of particles according to size. The size can be measured using a laser diffraction method. Specifically, after dispersing the object to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction size measuring device (e.g., Microtrac S3500) to measure the difference in diffraction patterns according to particle size as the particles pass through a laser beam, thereby calculating the size distribution. The size can be measured by calculating the particle diameter at the point of 50% of the cumulative distribution of the number of particles according to size in the measuring device.

[0027] In this specification, “permittivity” is a unitless physical quantity representing the magnitude of polarization produced by a dielectric in response to an external electric field. The permittivity may be measured at a temperature of 25°C using the ASTM D150 standard test method. At this time, the sintering temperature for preparing the specimen may be 1100°C, and the thickness of the compressed plate may be approximately 1.55 mm.

[0028] As used herein, “about,” “approximately,” and “substantially” are used to mean a range of figures or degrees or approximations thereof, taking into account inherent manufacturing and material tolerances (e.g., ±5%).

[0029] Among the components of an electrochemical device, the separator comprises a porous polymer substrate with a porous structure 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.

[0030] 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 stability and lifespan of the electrochemical device.

[0031] The present invention provides a technology that improves the stability of an electrochemical device including a separator by controlling the dielectric constant of a porous coating layer included in the separator of the electrochemical device.

[0032] A separator according to one embodiment of the present invention comprises a porous polymer substrate; and a porous coating layer formed on at least one surface of the porous polymer substrate and comprising inorganic particles, wherein the dielectric constant of the porous coating layer is about 250 or more and 10,000 or less. A separator according to one embodiment of the present invention may further comprise an electrode adhesive layer formed on at least one surface of the porous coating layer.

[0033] According to one embodiment of the present invention, the separator for the electrochemical device comprises the porous polymer substrate. The porous polymer substrate may be a porous membrane having a plurality of pores formed therein, which electrically insulates the positive and negative electrodes of the electrochemical device 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 and negative electrodes 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.

[0034] The porous polymer 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 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. For example, a polyolefin resin may be used as the porous polymer substrate. 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 a coating slurry.

[0035] The porous polymer substrate may have a single-layer or multi-layer structure. The porous polymer substrate may include two or more polymer resin layers with different melting points (Tm) to provide a shutdown function 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. According to one embodiment, 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.

[0036] The porous polymer 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 polymer 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 polymer substrate within the above-described range, the air permeability and ion conductivity of the entire separator for the electrochemical device can be controlled.

[0037] The porous polymer substrate may have an air permeability of about 10 s / 100cc or more and 200 s / 100cc or less. For example, the air permeability of the porous polymer substrate may be about 10 s / 100cc or more and 150 s / 100cc or less, 20 s / 100cc or more and 100 s / 100cc or less, 30 s / 100cc or more and 90 s / 100cc or less, or 40 s / 100cc or more and 80 s / 100cc or less. According to one embodiment, the air permeability of the porous polymer substrate may be 50 s / 100cc or more and 80 s / 100cc or less. When the air permeability of the porous polymer substrate is within the range described above, the air permeability of the separator for the electrochemical device may be provided in a range suitable for securing the output and cycle characteristics of the electrochemical device.

[0038] The above air permeability (s / 100cc) refers to the time (in seconds) required for 100 cc of air to pass through the porous polymer substrate or the separator for the electrochemical device over a predetermined area under constant pressure. The above air permeability may be measured using a Gurley densometer in accordance with ASTM D726-58, 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.

[0039] The porous polymer substrate may have a porosity of 10 vol% or more and 70 vol% or less. For example, the porosity of the porous polymer substrate may be about 20 vol% or more and 60 vol% or less, 30 vol% or more and 60 vol% or less, 40 vol% or more and 55 vol% or less, or 40 vol% or more and 50 vol% or less. According to one embodiment, the porosity of the porous polymer substrate may be about 40 vol% or more and 60 vol% or less. When the porosity of the porous polymer substrate is within the range described above, the ion conductivity of the separator for the electrochemical device may be provided within a range suitable for securing the output and cycle characteristics of the electrochemical device.

[0040] 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.

[0041] The thickness of the porous polymer substrate may be about 1 μm or more and 20 μm or less. For example, the thickness of the porous polymer substrate may be about 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 electrochemical device can be improved.

[0042] According to one embodiment of the present invention, the separator for an electrochemical device comprises a porous coating layer formed on at least one surface of the porous polymer substrate. The porous coating layer may be disposed on one or both surfaces of the porous polymer substrate. The porous coating layer may be disposed on at least a portion of the porous polymer substrate. The porous coating layer can improve the heat resistance of the separator for an electrochemical device and provide high-temperature dimensional stability. Additionally, the porous coating layer can improve the mechanical properties of the separator for an electrochemical device and improve stability.

[0043] According to one embodiment of the present invention, the dielectric constant of the porous coating layer may be approximately 250 or more and 10,000 or less. For example, the dielectric constant of the porous coating layer may be approximately 250 or more and 5,000 or less, 250 or more and 3,000 or less, 250 or more and 1,000 or less, 300 or more and 5,000 or less, 300 or more and 3,000 or less, 300 or more and 1,000 or less, 350 or more and 1,000 or less, 350 or more and 900 or less, or 500 or more and 900 or less. When the dielectric constant of the porous coating layer satisfies the above-described range, it may exhibit a spontaneous polarization state upon impregnation in an electrolyte and interact with polar molecules and ions. Due to the above interaction, the decomposition of salts in the electrolyte is suppressed, thereby preventing or suppressing side reactions and reducing the amount of gas generated during the storage or operation of the electrochemical device.

[0044] According to one embodiment of the present invention, the porous coating layer comprises inorganic particles. For example, the inorganic particles may comprise BaTiO3 or SrTiO3. When the inorganic particles comprise BaTiO3 or SrTiO3, the dielectric constant of the porous coating layer can be controlled to a desirable range, thereby reducing the amount of gas generated by the electrochemical device.

[0045] According to one embodiment of the present invention, the inorganic particles included in the porous coating layer may have a dielectric constant of about 250 or more and 10,000 or less. For example, the dielectric constant of the inorganic particles may be about 500 or more and 10,000 or less, 600 or more and 10,000 or less, 1,000 or more and 10,000 or less, 250 or more and 3,000 or less, 500 or more and 3,000 or less, 600 or more and 3,000 or less, or 1,000 or more and 3,000 or less. By controlling the dielectric constant of the inorganic particles to the above-described range, side reactions between internal lithium ions of the electrochemical device and electrolyte salts can be suppressed. In addition, when the dielectric constant of the inorganic particles satisfies the above-described range, the ion conductivity of the separator for the electrochemical device can be improved, and gas generated during the assembly or operation of the electrochemical device can be reduced.

[0046] According to one embodiment of the present invention, the crystal structure of the inorganic particle may be tetragonal. When the inorganic particle forms a tetragonal crystal structure, it may exhibit high dielectric properties and have a dielectric constant value within the range described above, thereby reducing side reactions between lithium ions and electrolyte salts inside the electrochemical device.

[0047] For example, the above BaTiO3 tetragonal crystal structure may have a high dielectric constant. The high dielectric constant of the above BaTiO3 tetragonal structure can improve the degree of dissociation of Li ions inside the electrochemical device and suppress the generation of PF5, thereby reducing the hydrolysis reaction of PF5 and side reactions of hydrolysis products (such as the generation of HF and HPO2F2). In addition, by increasing the ion conductivity inside the electrochemical device, it is possible to prevent an increase in resistance inside the electrochemical device and reduce gas generation inside the electrochemical device caused by the decomposition of electrolyte salts.

[0048] According to one embodiment of the present invention, the particle size of the inorganic particles may be about 300 nm or more and 1,000 nm or less. For example, the particle size of the inorganic particles may be about 300 nm or more and 900 nm or less, 300 nm or more and 800 nm or less, 300 nm or more and 700 nm or less, 300 nm or more and 600 nm or less, 350 nm or more and 800 nm or less, 350 nm or more and 600 nm or less, 400 nm or more and 800 nm or less, or 400 nm or more and 600 nm or less. In the particle size of the inorganic particles within the above-described range, the problem of reduced stability caused by a decrease in the dielectric constant of the porous coating layer due to surface defects that occur as the surface area of ​​the particles increases can be prevented or suppressed. In addition, if the particle size of the inorganic particles satisfies the aforementioned range, uniform dispersion within the porous coating layer can be facilitated. When the inorganic particles satisfy the aforementioned particle size range, the dielectric constant of the porous coating layer can be formed within an excellent range, thereby reducing gas generation inside the electrochemical device while simultaneously improving the heat resistance characteristics of the separator for the electrochemical device.

[0049] According to one embodiment of the present invention, the porous coating layer may contain the inorganic particles in an amount of about 80 parts by weight or more and 99 parts by weight or less, based on 100 parts by weight of the porous coating layer. For example, based on 100 parts by weight of the porous coating layer, the porous coating layer may contain the inorganic particles in an amount of about 80 parts by weight or more and 99 parts by weight or less, 85 parts by weight or more and 99 parts by weight or less, 90 parts by weight or more and 99 parts by weight or less, 80 parts by weight or more and 97 parts by weight or less, 85 parts by weight or more and 97 parts by weight or less, 90 parts by weight or more and 97 parts by weight or less, 95 parts by weight or more and 95 parts by weight or less, or 95 parts by weight or more and 97 parts by weight or less. When the weight range of the inorganic particles satisfies the range described above, heat resistance of the electrochemical element is imparted, and at the same time, the dielectric constant of the porous coating layer is adjusted to the range described above, thereby reducing the amount of gas generated by the electrochemical element.

[0050] According to one embodiment of the present invention, the porous coating layer may include BaTiO3 as an inorganic particle. The BaTiO3 has high stability at high temperatures, which can improve the heat resistance of the electrochemical device. In addition, the BaTiO3 can have a high dielectric constant by controlling its particle size and crystal structure, so that when included in the porous coating layer, it can reduce side reactions inside the electrochemical device.

[0051] According to one embodiment of the present invention, the crystal structure of BaTiO3 may be a tetragonal structure. When the porous coating layer includes BaTiO3 having a tetragonal structure as an inorganic particle, the dielectric constant of the electrochemical device can be maintained high to reduce the amount of gas generated.

[0052] According to one embodiment of the present invention, the particle size of the BaTiO3 may be about 300 nm or more and 1,000 nm or less. For example, the particle size of the BaTiO3 may be about 300 nm or more and 900 nm or less, 300 nm or more and 800 nm or less, 300 nm or more and 700 nm or less, 300 nm or more and 600 nm or less, 350 nm or more and 800 nm or less, 350 nm or more and 600 nm or less, 400 nm or more and 800 nm or less, or 400 nm or more and 600 nm or less. When the particle size of the BaTiO3 satisfies the above-described range, the level of asymmetry of the Ti element within the BaTiO3 particles is maintained at an appropriate level, thereby preventing or suppressing the formation of a low dielectric constant of the porous coating layer. In addition, when the particle size of the above BaTiO3 satisfies the aforementioned range, uniform dispersion within the porous coating layer is possible. In this way, when the particle size of the above BaTiO3 satisfies the aforementioned range, the heat resistance of the separator for the electrochemical device can be maintained while simultaneously improving the effect of reducing gas generation.

[0053] According to one embodiment of the present invention, the dielectric constant of the BaTiO3 may be 250 or more and 10,000 or less. For example, the dielectric constant of the BaTiO3 may be approximately 500 or more and 10,000 or less, 600 or more and 10,000 or less, 1,000 or more and 10,000 or less, 250 or more and 3,000 or less, 500 or more and 3,000 or less, 600 or more and 3,000 or less, or 1,000 or more and 3,000 or less. When the above-described range is satisfied, the gas generated inside the electrochemical device can be reduced while maintaining a high ion conductivity of the separator for the electrochemical device.

[0054] According to one embodiment of the present invention, the density of the inorganic particles within the coating layer is Depending on the portion of the porous coating layer, it may be the same or different. For example, the density of inorganic particles in the portion close to the porous polymer substrate may be higher than the density of inorganic particles in the portion close to the electrode, or the density of inorganic particles in the portion close to the electrode may be higher than the density of inorganic particles in the portion close to the porous polymer substrate.

[0055] According to one embodiment of the present invention, the porous coating layer may further include other inorganic particles other than BaTiO3 or SrTiO3. For example, 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 Examples 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 further include one or more of these. When the separator for the electrochemical device described above includes the aforementioned inorganic materials, high-temperature stability can be imparted.

[0056] According to one embodiment of the present invention, the porous coating layer may comprise the inorganic particles and a polymer binder. The inorganic particles may be connected to other inorganic particles by the polymer binder to form an interstitial volume, and lithium ions may move through the interstitial volume.

[0057] The polymer binder may be a solution type that dissolves in the dispersion medium of the coating slurry, a particle type that does not dissolve in the dispersion medium and maintains a particle shape in the coating slurry and the porous coating layer, or a combination thereof, but is not limited thereto. 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 comprising 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. According to one embodiment, the polymer binder may be an acrylic binder. When the polymer binder is an acrylic binder, it can combine with inorganic particles satisfying the dielectric constant range to create an appropriate interstitial volume and improve adhesion to the electrode or the porous polymer substrate.

[0058] According to one embodiment of the present invention, the polymer binder for the porous coating layer may be included in an amount of about 3 parts by weight or more and 20 parts by weight or less per 100 parts by weight of the porous coating layer. For example, the polymer binder for the porous coating layer may be about 3 parts by weight or more and 15 parts by weight or less, 3 parts by weight or more and 10 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, 10 parts by weight or more and 20 parts by weight or less, 10 parts by weight or more and 15 parts by weight or less, 15 parts by weight or more and 20 parts by weight or less, 7 parts by weight or more and 16 parts by weight or less, and 10 parts by weight or more and 13 parts by weight or less, per 100 parts by weight of the porous coating layer. When satisfying the above ranges, ease of assembly can be improved in the process of assembling the electrode.

[0059] According to one embodiment of the present invention, the thickness of the porous coating layer may be about 0.3 μm or more and 3.0 μm or less. For example, the thickness of the porous coating layer may be about 0.6 μm or more and 1.4 μm or less, 0.7 μm or more and 1.3 μm or less, 0.8 μm or more and 1.2 μm or less, 0.9 μm or more and 1.1 μm or less, 0.5 μm or more and 0.8 μm or less, 0.5 μm or more and 1.1 μm or less, 0.5 μm or more and 2 μm or less, 0.5 μm or more and 2.5 μm or less, or 1.0 μm or more and 2.5 μm or less. When satisfying the above ranges, mechanical strength can be maintained while keeping the separator for the electrochemical device relatively thin. In addition, the thin thickness of the separator for the electrochemical device can improve the ionic conductivity of the separator and reduce the internal resistance of the electrochemical device. Therefore, the stability and efficiency of the electrochemical device can be increased.

[0060] According to one embodiment of the present invention, the gas generation amount of the separator for the electrochemical device may be about 1,500 µL or less. For example, the gas generation amount of the separator for the electrochemical device may be 1,200 µL or less, 1,000 µL or less, 800 µL or less, greater than 0 µL, 100 µL or more, 300 µL or more, 500 µL or more, or 700 µL or more. For example, the gas generation amount is such that the separator for the electrochemical device is 560 cm using BGA-06 equipment. 2 The sampled separator can be sampled by area, and the sampled separator can be placed in a cylindrical can of size 21700 together with an electrolyte. After storing it at room temperature for 12 hours and in a chamber at 130°C for 1 hour, the gas generated inside the can can be collected and measured. The electrolyte may be prepared by adding 1.2 mol of the lithium salt LiPF6 to a solvent mixed with ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3:7.

[0061] The porous coating layer may be formed by a method of coating at least one surface of the porous polymer substrate with the coating slurry comprising the inorganic particles, the polymer 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 porous coating layer can be easily formed on the porous polymer substrate.

[0062] According to one embodiment of the present invention, the separator for an electrochemical device may further include an electrode adhesive layer formed on the upper surface of the porous coating layer. The electrode adhesive layer may include a binder for the electrode adhesive layer. The binder for the electrode adhesive layer may include a fluorine-based binder and an acrylic binder to improve adhesion to the electrode. According to one embodiment, the electrode adhesive layer may include an acrylic binder. By including a fluorine-based binder and an acrylic binder, the electrode adhesive layer can stably maintain adhesion to the electrode of the separator for the electrochemical device in both a dry state without an electrolyte and a wet state impregnated with an electrolyte. For example, the electrode adhesive layer may include the fluorine-based binder and the acrylic binder in a weight ratio of about 1:9 to 9:1. The thickness of the electrode adhesive layer is formed to be smaller than the thickness of the porous coating layer, thereby providing electrode adhesion while minimizing the reduction in air permeability of the separator for the electrochemical device.

[0063] The electrode adhesive layer can be formed by additionally applying a binder for the electrode adhesive layer to the surface of the porous coating layer. For example, the electrode adhesive layer can be formed using spray application, gravure coating, slot die, etc., but is not limited thereto.

[0064] 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 can be injected to impregnate the electrode assembly with the electrolyte.

[0065] Meanwhile, although a cylindrical lithium secondary battery is exemplified as the electrochemical element in this embodiment, the present invention is not limited thereto and may use other types of secondary batteries, for example, the electrochemical element may be a prismatic, coin-type, or pouch-type lithium secondary battery.

[0066] 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.

[0067] 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 xNi-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 x It 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.

[0068] The above-mentioned 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-mentioned 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), 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.

[0069] The conductive material may be any one selected from 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. According to one embodiment, it may be one selected from 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.

[0070] 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 containing an ion composed of anions such as or a combination thereof may be dissolved or dissociated in an organic solvent composed of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethyl carbonate (EMC), gamma butyrolactone, or a mixture thereof, but is not limited thereto. According to one embodiment, the electrolyte may contain LiPF6. When the electrolyte contains LiPF6, BaTiO3 may suppress the side reaction of PF6 ions, thereby reducing the side reaction inside the electrochemical device. According to one embodiment, the solvent may include a carbonate-based solvent. When the solvent includes a carbonate-based solvent, the reaction of the carbonate-based solvent with the salt decomposition product can be prevented or inhibited, thereby reducing gas generation inside the electrochemical element.

[0071] The separator for the electrochemical device described above may have an air permeability of approximately 30 sec / 100cc or more and 300 sec / 100cc or less. For example, the air permeability may be approximately 50 sec / 100cc or more and 150 sec / 100cc or less, 40 sec / 100cc or more and 150 sec / 100cc or less, 80 sec / 100cc or more and 200 sec / 100cc or less, 100 sec / 100cc or more and 300 sec / 100cc or less, 150 sec / 100cc or more and 300 sec / 100cc or less, or 200 sec / 100cc or more and 300 sec / 100cc or less. The separator for the electrochemical device described above can ensure stability within the aforementioned air permeability range while simultaneously ensuring the output and cycle characteristics of the electrochemical device.

[0072]

[0073] According to one embodiment of the present invention, the electrochemical device can 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 and sealing it. Before inserting into the case and sealing it, an electrolyte can be injected to impregnate the electrode assembly with the electrolyte.

[0074] 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.

[0075]

[0076] The present invention will be explained in more detail below through examples, comparative examples, and experimental examples. The following examples, comparative examples, and experimental examples are intended to illustrate the present invention, and the present invention is not limited by the following examples, comparative examples, and experimental examples.

[0077]

[0078] Example 1

[0079] Preparation of coating slurry

[0080] At room temperature (25℃), BaTiO3 (particle size: 600 nm, dielectric constant: 2000) with a tetragonal crystal structure and a polyacrylic acid-based dispersant were added as inorganic particles and stirred with a shaker for 120 minutes to prepare an inorganic dispersion. An acrylic binder (Stryrene-Butyl Acrylate, Tg: -35 ℃) and a wetting agent (Si-based) were added to the dispersion and stirred for 30 minutes to prepare a coating slurry. At this time, the weight ratio of solids contained in the coating slurry was inorganic particles:binder:dispersant:wetting agent = 95:4.4:0.5:0.1.

[0081]

[0082] Preparation of porous polymer substrate

[0083] As a porous polymer substrate (MI: 0.02 g / 10 min, T m A polyethylene film with a diameter of 135 ℃, porosity of 55 vol%, average pore size of 50 nm, a size of 20 cm × 30 cm, and a thickness of 10 μm was used.

[0084]

[0085] Formation of a porous coating layer

[0086] After coating both sides of the coating slurry onto a polyethylene film using a bar coater, a low-temperature airflow was applied to dry the porous coating layer while controlling the surface temperature so that it did not exceed 60°C. A porous coating layer was formed with a thickness of 1.5 μm for each coating.

[0087]

[0088] Manufacturing of electrochemical devices

[0089] Two of the above-mentioned separators, one anode with a thickness of 158.3 μm, and two cathodes with a thickness of 225.3 μm were prepared, respectively. A laminate was prepared by stacking the anodes and cathodes alternately and placing a separator between the anodes and cathodes.

[0090] The above laminate was placed in a press device and laminated at 75°C and a pressure of 8.4 MPa for 1 second to manufacture an electrochemical device.

[0091]

[0092] Example 2

[0093] An electrochemical device was manufactured in the same manner as in Example 1, except that the inorganic particles used were BaTiO3 (particle size: 400 nm, dielectric constant: 1,300) with a tetragonal crystal structure.

[0094]

[0095] Example 3

[0096] An electrochemical device was manufactured in the same manner as in Example 1, except that the inorganic particles used were SrTiO3 (particle size: 500 nm, dielectric constant: 3,000) with a tetragonal crystal structure.

[0097]

[0098] Example 4

[0099] An electrochemical device was manufactured in the same manner as in Example 1, except that a fluorine-based polymer binder (PVDF-HFP) was used instead of an acrylic binder in Example 1.

[0100]

[0101] Comparative Example 1

[0102] Comparative Example 1 is for evaluating the gas generation amount of a lithium salt, and an electrolyte was prepared by adding 1.2 mol of the lithium salt LiPF6 to a solvent mixed with ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3:7.

[0103]

[0104] Comparative Example 2

[0105] An electrochemical device was manufactured in the same manner as in Example 1, except that the inorganic particles used were Al2O3 (particle size: 500 nm, dielectric constant: 9).

[0106]

[0107] Comparative Example 3

[0108] An electrochemical device was manufactured in the same manner as in Example 1, except that the above inorganic particles were used as AlOOH (particle size: 450 nm, dielectric constant: 5.5).

[0109]

[0110] Comparative Example 4

[0111] An electrochemical device was manufactured in the same manner as in Example 1, except that the inorganic particles used were BaTiO3 (particle size: 150 nm, dielectric constant: 150) with a cubic crystal structure.

[0112]

[0113] Comparative Example 5

[0114] An electrochemical device was manufactured in the same manner as in Example 1, except that the inorganic particles were set to BaTiO3 (particle size: 300 nm, dielectric constant: 600) with a tetragonal crystal structure.

[0115]

[0116] Experimental Example

[0117] Measurement of the dielectric constant of a porous coating layer

[0118] The porous coating layer of the separator membrane of Examples 1 to 4 and Comparative Examples 2 to 5 was obtained as a specimen, and the dielectric constant was measured at a temperature of 25°C using the ASTM D150 standard test method.

[0119]

[0120] Air permeability measurement

[0121] The air permeability of the separator membranes of the above examples and comparative examples was measured using a Gurley densometer (Gurley, 4110N) with 100 cc of air having 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.

[0122]

[0123] Gas generation measurement

[0124] The electrolyte of Comparative Example 1 was sampled into a 21700 size cylindrical can, sealed, and stored at room temperature for 12 hours. Afterward, it was stored in a chamber at 130°C for 1 hour, and then the gas generated inside the can was collected using a BGA-06 instrument to measure the amount of gas generated. The amount of gas generated in Comparative Example 1 was measured to be 730 µL.

[0125] The above Examples 1 to 4 and Comparative Examples 2 to 5 are 560 cm 2 The amount of gas generated was measured in the same way as in Comparative Example 1 above, except that sampling was performed using a separation membrane of the area.

[0126]

[0127] Measurement of thermal shrinkage rate at 180 ℃

[0128] The separator membranes of the above examples and comparative examples were cut to a size of 50 mm x 50 mm to prepare specimens, which were kept in an oven heated to 180 ℃ for 30 minutes, after which the specimens were retrieved and the lengths changed in the machine direction (MD) and perpendicular direction (TD) were measured and calculated as shown in Equation 1 below.

[0129]

[0130] [Equation 1]

[0131] Thermal shrinkage rate at 180 ℃ (%) = {(Dimension before shrinkage - Dimension after shrinkage) / Dimension before shrinkage} X 100

[0132]

[0133] Example 1 Example 2 Example 3 Example 4 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Porous coating layer dielectric constant 500 350 850 900 856 200 Thickness (㎛) 1.5 / 1.5 1.5 / 1.5 1.5 / 1.5 1.5 / 1.5 1.5 / 1.5 1.5 / 1.5 1.5 1.5 / 1.5 Inorganic particle type BaTiO3 BaTiO3 SrTiO3 BaTiO3 Al2O3 AlOOH BaTiO3 BaTiO3 Crystal structure Tetragonal Tetragonal Tetragonal Tetragonal Tetragonal-- Cubic Tetragonal Particle size (nm) 600 400 500 600 500 450 150 300 Dielectric Constants 2,000 1,300 3,000 2,000 9 5.5 1 50 600 Polymer Binder Acrylic Acrylic Acrylic Fluorocarbon Acrylic Acrylic Acrylic Acrylic Acrylic System Chart (sec / 100cc) 9 3 9 5 9 2 9 4 9 0 8 5 1 1 2 100 Gas Generation (µl) 8 00 1,500 8 00 8 3 4 7 00 7 8 00 2 3 00 1 8 50 Thermal Shrinkage (%, MD / TD) 3 / 2 2 / 2 2 / 2 2 / 2 5 1 5 / 1 0 2 / 1 2 / 1

[0134]

[0135] Referring to Table 1 above, in the case of a separator with a porous coating layer having a dielectric constant of about 250 to 10,000, including a material having a dielectric constant of about 250 to 10,000 as an inorganic particle, such as BaTiO3 or SrTiO3 as in Examples 1 to 4, the gas generation amount of the separator was 800 µL to 1,500 µL, which is a significantly reduced gas generation amount compared to Comparative Examples 1 to 4, which showed a gas generation amount of 1,850 µL to 7,800 µL.

[0136] As such, it can be seen that the stability of the electrochemical device to which it is applied can be improved by controlling the dielectric constant of the porous coating layer of the separator to an appropriate range.

[0137]

[0138] 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

porous polymer substrate; and A porous coating layer formed on at least one surface of the above-mentioned porous polymer substrate and comprising inorganic particles, and A separator for an electrochemical device, wherein the dielectric constant of the porous coating layer is 250 or more and 10,000 or less. In paragraph 1, The above inorganic particles comprise BaTiO3 or SrTiO3, and are separators for electrochemical devices. In paragraph 2, The above inorganic particles are separators for electrochemical devices having a dielectric constant of 250 or more and 10,000 or less. In paragraph 2 The above inorganic particles are separators for electrochemical devices, having a particle size of 300 nm or more and 1,000 nm or less. In paragraph 2 A separator for an electrochemical device, wherein the crystal structure of the above-mentioned inorganic particles is tetragonal. In paragraph 1, A separator for an electrochemical device, wherein the thickness of the porous coating layer is 0.3 μm or more and 3.0 μm or less. In paragraph 1 A separator for an electrochemical device comprising 80 parts by weight or more and 99 parts by weight or less of the inorganic particles based on 100 parts by weight of the porous coating layer. In paragraph 1, The above porous coating layer further comprises an acrylic binder, a separator for an electrochemical device. In paragraph 1, A separator for an electrochemical device having a gas generation amount of 1,500 μL or less. An electrochemical device comprising an anode, a cathode, a separator disposed between the anode and the cathode, and an electrolyte, wherein The above-mentioned separator is an electrochemical device according to claim 1. In Paragraph 10, The above electrochemical device is an electrochemical device that is a lithium secondary battery.