Separator for electrochemical device and electrochemical device comprising the same

Abstract

The present disclosure relates to a separator for an electrochemical device, the separator including a heat-resistant inorganic coating layer, and the coating layer including cubic boehmite and sheet-type boehmite as inorganic particles to achieve improved stability and low resistance of the separator.

Description

Technical Field

[0001] This disclosure relates to a separator for an electrochemical device and an electrochemical device comprising the separator.

[0002] This application is based on and claims priority to Korean Patent Application No. 2025-0006684, filed on January 16, 2025, and Korean Patent Application No. 2025-0188464, filed on December 2, 2025, the disclosures of which are incorporated herein by reference in their entirety. Background Technology

[0003] Electrochemical devices use electrochemical reactions to convert chemical energy into electrical energy, and recently lithium secondary batteries have been widely used due to their high energy density and voltage, long cycle life and applicability across different industrial sectors.

[0004] A separator (one of the components in an electrochemical device) comprises a porous polymer substrate with a porous structure between the positive and negative electrodes, and serves to isolate the positive and negative electrodes to prevent electrical short circuits between the two electrodes while allowing electrolytes and ions to pass through. Although the separator itself does not participate in the electrochemical reaction, its physical properties, such as electrolyte wettability, porosity, or thermal shrinkage, can affect the performance and safety of the electrochemical device.

[0005] Therefore, in order to enhance the physical properties of the separator, many different methods have been tried to form a coating on the porous polymer substrate and to add various materials to the coating to change its properties. For example, inorganic substances can be added to the coating to improve the mechanical strength of the separator, or inorganic substances or hydrates can be added to the coating to improve the flame retardancy and heat resistance of the porous polymer substrate.

[0006] Within the coating, inorganic particles can be linked together by a binder to form an interstitial volume, through which lithium ions can move. In other words, the coating, containing both binder and inorganic particles, serves to prevent thermal shrinkage of the separator and facilitate the movement of lithium ions through it.

[0007] Inorganic particles can improve the mechanical strength and heat resistance of separators used in electrochemical devices. However, due to their shape, the distance between inorganic particles may be excessively reduced, preventing the formation of an appropriate gap. This lack of proper spacing can slow ion movement within the electrochemical device and potentially increase the resistance of the separator. Consequently, the performance of electrochemical devices incorporating separators may deteriorate. Conversely, while the shape of the inorganic particles added to the coating can reduce separator resistance, the mechanical strength and heat resistance of the separator may become worse, leading to lower stability in the electrochemical device.

[0008] Therefore, it is necessary to develop separators with low resistance and high stability for electrochemical devices by controlling the shape and type of added inorganic particles. Summary of the Invention

[0009] Technical issues

[0010] One aspect of this disclosure relates to providing a separator for an electrochemical device having improved dry heat shrinkage and wet heat shrinkage at high temperatures, and an electrochemical device comprising the separator.

[0011] Another aspect of this disclosure relates to providing a separator for an electrochemical device having low resistance and improved mechanical strength and heat resistance, and an electrochemical device including said separator.

[0012] The problems to be solved by this disclosure are not limited to those described above, and those skilled in the art will clearly understand these and other problems from the following description.

[0013] Technical solution

[0014] According to one aspect of this disclosure, a separator for an electrochemical device is provided according to the following embodiments.

[0015] The separator for the electrochemical device according to the first embodiment includes:

[0016] Porous polymer substrates; and

[0017] A coating disposed on at least one surface of the porous polymer substrate, the coating comprising inorganic particles and a binder.

[0018] The inorganic particles mentioned therein include cubic boehmite and platy boehmite in a weight ratio of 1:1 to 4:1.

[0019] According to the second embodiment, in the first embodiment...

[0020] The average grain size (D) of the cubic boehmite 50 The diameter can be from 0.5 μm to 0.7 μm.

[0021] According to the third embodiment, in the first or second embodiment...

[0022] The aspect ratio of the platy boehmite can be from 2 to 10.

[0023] According to the fourth embodiment, in any one of the first to third embodiments,

[0024] The average long side of the platy boehmite can be from 0.7 μm to 0.9 μm.

[0025] According to the fifth embodiment, in any one of the first to fourth embodiments,

[0026] The bulk density of the coating can be 0.9 g / cm³. 3 Up to 1.3 g / cm 3 .

[0027] According to the sixth embodiment, in any one of the first to fifth embodiments,

[0028] The adhesive may include a non-crosslinked copolymer containing: i) repeating units derived from acrylic monomers having hydroxyl groups, ii) repeating units derived from (meth)acrylic monomers, (meth)acrylate monomers, or both, and iii) repeating units derived from acrylic monomers having amide groups.

[0029] According to the seventh embodiment, in any one of the first to sixth embodiments...

[0030] The adhesive may include a non-crosslinked copolymer containing: repeating units derived from hydroxyalkyl acrylate monomers, repeating units derived from (meth)acrylic acid monomers, and repeating units derived from acrylic acid monomers having amide groups.

[0031] According to the eighth embodiment, in any one of the first to seventh embodiments,

[0032] The (meth)acrylate monomer may include sodium (meth)acrylate, potassium (meth)acrylate, lithium (meth)acrylate, ammonium (meth)acrylate, or mixtures thereof.

[0033] According to the ninth embodiment, in any one of the first to eighth embodiments,

[0034] The acrylic monomer having an amide group may include acrylamide, methacrylamide, N,N-dimethyl (meth)acrylamide, N,N-diethyl (meth)acrylamide, N,N-dipropyl (meth)acrylamide, N,N-diisopropyl (meth)acrylamide, N,N-di(n-butyl) (meth)acrylamide, N,N-di(tert-butyl) (meth)acrylamide, N-ethyl (meth)acrylamide, N-isopropyl (meth)acrylamide, N-butyl (meth)acrylamide, N,N-butyl (meth)acrylamide, N-hydroxymethyl (meth)acrylamide, N-hydroxyethyl (meth)acrylamide, N-hydroxypropyl (meth)acrylamide, N-methoxymethyl (meth)acrylamide, N-methoxyethyl (meth)acrylamide, N-butoxymethyl (meth)acrylamide, or mixtures thereof.

[0035] According to the tenth embodiment, in any one of the first to ninth embodiments,

[0036] The alkyl group of the hydroxyalkyl acrylate monomer may have 2 to 4 carbon atoms.

[0037] According to the eleventh embodiment, in any one of the first to tenth embodiments,

[0038] The thickness of the coating on one surface of the porous polymer substrate can be from 0.5 μm to 4 μm.

[0039] According to the twelfth embodiment, in any one of the first to eleventh embodiments,

[0040] The coating may include:

[0041] A first coating, the first coating comprising the cubic boehmite and a first binder; and

[0042] A second coating disposed on the first coating, the second coating comprising flake boehmite and a second adhesive.

[0043] According to the thirteenth embodiment, in any one of the first to twelfth embodiments,

[0044] The thickness ratio of the first coating to the second coating can be from 1:0.5 to 1:1.5.

[0045] According to the fourteenth embodiment, in any one of the first to thirteenth embodiments,

[0046] Based on 100 parts by weight of the coating, the amount of inorganic particles can be from 80 parts by weight to 95 parts by weight.

[0047] According to another aspect of this disclosure, an electrochemical device according to the following embodiments can be provided.

[0048] The electrochemical device according to the fifteenth embodiment may include:

[0049] Positive electrode, negative electrode, and a separator for an electrochemical device according to any one of the first to fourteenth embodiments,

[0050] The separator for the electrochemical device can be positioned between the positive electrode and the negative electrode.

[0051] Beneficial effects

[0052] The separator for an electrochemical device according to embodiments of the present disclosure comprises cubic boehmite inorganic particles as a heat-resistant coating, thereby reducing the resistivity of the separator. Simultaneously, the separator comprises lamellar boehmite inorganic particles as a heat-resistant coating, thereby further improving the mechanical strength and heat resistance of the separator.

[0053] Specifically, the separator for an electrochemical device according to embodiments of the present disclosure may include inorganic particles containing boehmite (-OH) as a coating and a non-crosslinked copolymer containing repeating units derived from acrylic monomers having hydroxyl groups as a binder, thereby further improving the heat resistance of the coating. Specifically, the hydroxyl groups of the copolymer and the boehmite can form hydrogen bonds through intermolecular attraction, thereby improving the heat resistance of the coating and increasing the bonding strength between inorganic particles and / or between the porous polymer substrate and the coating and / or between the separator and the electrode. Therefore, the separator for an electrochemical device according to embodiments of the present disclosure has a coating to improve the thermal shrinkage characteristics of the separator, thereby significantly improving the thermal shrinkage rate, especially at high temperatures in both dry and wet states, but the effects of the present disclosure are not limited to this. Detailed Implementation

[0054] The present disclosure will be described in sufficient detail below to enable those skilled in the art to readily practice it, but this is provided for illustrative purposes only, and the scope of protection of the present disclosure is not limited by the following description.

[0055] Unless the context clearly indicates otherwise, the terms “comprising,” “including,” and “having” are used in this specification to specify the presence of the stated element, but do not exclude the presence or addition of one or more other elements.

[0056] In this specification, when it is referred to as being positioned on the “surface” of an element, the presence or addition of intermediate elements is not excluded unless the context clearly indicates otherwise.

[0057] In this specification, "electrochemical device" may refer to a primary battery, a secondary battery, or a supercapacitor. More specifically, an electrochemical device may include a lithium-ion secondary battery and may be pouch-shaped, cylindrical, prismatic, or coin-shaped, but is not limited to these shapes.

[0058] In this specification, "electrode" includes "positive electrode" and "negative electrode," and can be made by coating and drying an electrode active material on at least one surface of a material having a conductivity that does not cause chemical changes in the electrochemical device. The material and electrode active material are not limited to a specific type and can include any type of material used in the electrochemical device.

[0059] In this specification, "separator" generally refers to a functional separator having a porous coating comprising inorganic particles and a binder on at least one surface of a porous substrate such as a polyolefin substrate or a nonwoven fabric. Furthermore, the separator has porous properties including pores and acts as a porous ion-conducting barrier to allow ions to pass through while preventing electrical contact between the negative and positive electrodes in an electrochemical device.

[0060] In this specification, porous or having holes means including a plurality of voids or holes connected to each other, thereby allowing gaseous and / or liquid fluids to pass from one side to the other.

[0061] In this specification, "porous substrate" can refer to a porous membrane with pores, and can be a substrate that electrically insulates the positive and negative electrodes to prevent short circuits. For example, when the electrochemical device is a lithium secondary battery, the porous substrate can act as an ion conduction barrier to allow lithium ions to pass through while preventing electrical contact between the positive and negative electrodes. At least some of the pores can form a three-dimensional network connecting the surface and interior of the porous substrate, and fluid can pass through the pores through the porous substrate.

[0062] In this specification, "average particle size (D)" 50 "50%" refers to the particle size at the 50% point of the cumulative volumetric particle size distribution. Particle size can be measured using the laser diffraction method. Specifically, the particle size distribution is calculated by dispersing powder in a dispersion medium, introducing it into a commercially available laser diffraction particle size measurement device (e.g., Microtrac S3500), and measuring the difference in the diffraction pattern as a function of particle size when the particles pass through a laser beam. The average particle size (D) 50 It can be measured by calculating the particle size at the 50% point of the cumulative volumetric particle size distribution in the measuring device.

[0063] In this specification, "aspect ratio" is used to indicate the ratio of the long side to the short side of a plate-shaped inorganic particle. The aspect ratio is defined as the [length of the long side] / [length of the remaining side (short side) perpendicular to the direction of the long side] on the flat surface of the plate-shaped inorganic particle.

[0064] In this specification, "packing density" can be calculated as the weight per unit volume of the coating. The unit of packing density is g / cm³. 3 .

[0065] In this specification, "non-crosslinked copolymer" refers to a copolymer that dissolves into a clear solution after being left to stand in an oven at 100°C for 30 minutes, then having water added to a concentration of 10% and stirred for 30 minutes.

[0066] In this specification, "repeating unit derived from monomer" means a repeating unit contained in a copolymer formed by monomer polymerization.

[0067] In this specification, "(meth)acrylic acid monomer" includes acrylic acid monomer and methacrylic acid monomer. Furthermore, "(meth)acrylate monomer" includes acrylate monomer and methacrylate monomer.

[0068] In this specification, "acrylic monomer" refers to a monomer containing an acrylate structure in its molecule. For example, an acrylic monomer can be represented by the chemical formula CH2=CHCOOB, where B is hydrogen, nitrogen, oxygen, or a substituted or unsubstituted hydrocarbon group having 1 to 10 carbon atoms. In the chemical formula, B can be hydrolyzed by water or steam to have one or more hydroxyl groups. Furthermore, acrylic monomers are not limited to the above chemical formula structure (CH2=CHCOOB) and may contain additional functional groups bonded to carbon double bonds.

[0069] This disclosure will be described in more detail below.

[0070] According to one aspect of this disclosure, a separator for an electrochemical device is provided.

[0071] A separator for an electrochemical device according to one aspect of this disclosure includes:

[0072] Porous polymer substrates; and

[0073] A coating disposed on at least one surface of the porous polymer substrate, the coating comprising inorganic particles and a binder.

[0074] The inorganic particles mentioned above include cubic boehmite and plate boehmite in a weight ratio of 1:1 to 4:1.

[0075] [coating]

[0076] Inorganic particles

[0077] As described above, the separator according to one aspect of this disclosure comprises boehmite (AlO(OH)) containing hydroxyl groups (-OH) in its structure as inorganic particles of coating. Specifically, the coating comprises cubic boehmite and plate-shaped boehmite.

[0078] In embodiments of this disclosure, cubic boehmite can refer to a polyhedral boehmite having one or more faces. For example, the term "cubic" can include polyhedral shapes, such as cubic or rectangular prism shapes, and modified shapes thereof (where one face of the polyhedral shape is irregularly altered). Due to its unique three-dimensional structure, cubic boehmite ensures sufficient distance between inorganic particles. Sufficient distance between inorganic particles in the separator can drive rapid movement of lithium ions, thereby reducing the resistance of the separator. Furthermore, electrochemical devices including separators with low resistance can have improved output performance, but the mechanisms of this disclosure are not limited thereto.

[0079] In embodiments of this disclosure, plate-shaped boehmite can refer to boehmite having a shape with at least one long side and at least one short side. Plate-shaped boehmite may include irregular edges. Additionally, the thickness of the plate-shaped boehmite may be less than the length or short side. Plate-shaped boehmite has a particle morphology characterized by thin, flat flakes, resulting in a uniform distribution of thermal stress within the inorganic particles. Therefore, when plate-shaped boehmite is applied to the coating of a separator, it can effectively prevent the separator from excessively shrinking or expanding in specific areas due to heat. Furthermore, plate-shaped boehmite can be arranged in the planar direction of the coating and / or stacked in a thin and uniformly distributed structure within the coating. Thus, when plate-shaped boehmite is applied to the coating as inorganic particles, the mechanical strength of the separator can be improved, but the mechanism of this disclosure is not limited thereto.

[0080] According to embodiments of this disclosure, when the coating contains only cubic boehmite as inorganic particles, the resistance of the electrochemical device containing it can be reduced, but the unique three-dimensional structure reduces stress, resulting in poor mechanical properties of the separator.

[0081] Furthermore, when the coating contains only lamellar boehmite as inorganic particles, it is advantageous in terms of the thermal shrinkage and mechanical strength of the separator containing it. However, the close-packed structure of the lamellar boehmite cannot form sufficient space between the inorganic particles, resulting in an increase in the resistance of the separator.

[0082] Therefore, when the separator according to one aspect of this disclosure comprises cubic boehmite and plate boehmite together as inorganic particles in the coating, the cubic boehmite can prevent the plate boehmite from packing together tightly, thereby maintaining appropriate space between the inorganic particles. Thus, an electrochemical device including a separator with a coating comprising cubic boehmite and plate boehmite can maintain low electrical resistance and have improved heat resistance and mechanical strength, but the mechanism of this disclosure is not limited thereto.

[0083] According to embodiments of this disclosure, the average grain size (D) of cubic boehmite is... 50 The average grain size (D) of cubic boehmite can be, for example, 200 nm to 1 μm. 50The average grain size (D) of cubic boehmite can range from 0.5 μm to 0.7 μm. More specifically, the average grain size (D) of cubic boehmite... 50 The particle size can be 0.5 μm or higher and 0.7 μm or lower, 0.55 μm or higher and 0.6 μm or lower, 0.6 μm or higher and 0.65 μm or lower, 0.65 μm or higher and 0.7 μm or lower, 0.5 μm or higher and 0.54 μm or lower, 0.5 μm or higher and 0.58 μm or lower, 0.5 μm or higher and 0.62 μm or lower, or 0.5 μm or higher and 0.68 μm or lower. When the average particle size of the cubic boehmite falls within the above ranges, sufficient distance can exist between the cubic boehmite particles in the coating, and this can have a beneficial effect on reducing the resistance of the separator in the electrochemical device including the coating. In addition, the dispersion in the coating slurry prepared for forming the coating can be improved, but this disclosure is not limited thereto.

[0084] In embodiments of this disclosure, the aspect ratio of the lamellar boehmite can be, for example, 2 to 10. Specifically, the aspect ratio of the lamellar boehmite can be 2 or greater and 10 or less, 3 or greater and 7 or less, 3 or greater and 6 or less, 4 or greater and 7 or less, or 5 or greater and 8 or less. When the aspect ratio of the lamellar boehmite falls within the above range, the coating can be uniformly formed on a wide area of ​​the porous polymer substrate. Furthermore, the thermal shrinkage rate of the separator used in electrochemical devices at high temperatures can be effectively reduced and the air permeability can be appropriately maintained, but this disclosure is not limited thereto.

[0085] In embodiments of this disclosure, the average long side of the platy boehmite can be, for example, 0.7 μm to 0.9 μm. Specifically, the average long side of the platy boehmite can be 0.7 μm or greater and 0.9 μm or less, 0.8 μm or greater and 0.82 μm or less, 0.8 μm or greater and 0.84 μm or less, 0.8 μm or greater and 0.86 μm or less, 0.8 μm or greater and 0.88 μm or less, 0.82 μm or greater and 0.84 μm or less, 0.84 μm or greater and 0.86 μm or less, 0.86 μm or greater and 0.88 μm or less, 0.88 μm or greater and 0.9 μm or less, 0.83 μm or greater and 0.86 μm or less, or 0.83 μm or greater and 0.89 μm or less. When the average long side of the plate-shaped boehmite falls within the above-mentioned range, the packing density of the coating can be appropriately maintained, which can have beneficial effects on improving the air permeability and thermal stability of the partition, but this disclosure is not limited thereto.

[0086] According to embodiments of this disclosure, the thickness of the plate-like boehmite can be, for example, from 0.01 μm to 0.1 μm. Specifically, the thickness of the plate-like boehmite can be 0.01 μm or greater and 0.1 μm or less, 0.01 μm or greater and 0.05 μm or less, 0.01 μm or greater and 0.09 μm or less, 0.02 μm or greater and 0.06 μm or less, 0.02 μm or greater and 0.1 μm or less, 0.03 μm or greater and 0.07 μm or less, 0.04 μm or greater and 0.08 μm or less, or 0.05 μm or greater and 0.09 μm or less.

[0087] According to aspects of this disclosure, the coating comprises cubic boehmite and plate boehmite in a weight ratio of 1:1 to 4:1.

[0088] According to embodiments of this disclosure, the weight ratio of cubic boehmite to plate boehmite (cubic boehmite:plate boehmite) can be, for example, 1:1 to 4:1, 1:1 to 3:1, 1:1 to 2:1, 2:1 to 3:1, 2:1 to 4:1, 3:1 to 4:1, 1.5:1 to 4:1, 2.5:1 to 3:1, 2.5:1 to 3.5:1, 2.5:1 to 4:1, or 3.5:1 to 4:1. When the weight ratio of cubic boehmite to plate boehmite falls within the above ranges, the cubic boehmite can appropriately prevent the plate boehmite from being densely packed, thereby reducing the resistance of the separator used in the electrochemical device, and can be advantageous in terms of heat resistance and mechanical strength.

[0089] In embodiments of this disclosure, the packing density of the coating may be, for example, 0.9 g / cm³. 3 Up to 1.3 g / cm 3 Specifically, the bulk density of the coating can be 0.9 g / cm³. 3 Or larger and 1.3 g / cm 3 Or less, 1 g / cm³ or greater and 1.3 g / cm³ or less, 1.0 g / cm³ or greater and 1.3 g / cm³ or less, 1.1 g / cm³ or greater and 1.3 g / cm³ or less, 1.1 g / cm³ or greater and 1.2 g / cm³ or less, 1.1 g / cm³ or greater and 1.25 g / cm³ or less, or 1.2 g / cm³ or greater and 1.3 g / cm³ or less. When the bulk density falls within the above ranges, a separator with light weight and small thickness can be formed, and the separator exhibits suitable bulk density and high heat resistance, but this disclosure is not limited thereto.

[0090] In an embodiment of the present disclosure, the thickness of the coating on one surface of the porous polymer substrate may be, for example, 0.5 μm to 4 μm. Specifically, the thickness of the coating may be 0.5 μm or more, 0.7 μm or more, 0.9 μm or more, or 1.0 μm or more, and may also be 4 μm or less, 3.5 μm or less, 3 μm or less, 2 μm or less, 1.8 μm or less, 1.6 μm or less, or 1.5 μm or less. When the thickness of the coating falls within the above range, the small thickness of the coating can drive lithium ions to move faster through the coating, resulting in low resistance of the separator for electrochemical devices. In addition, the total thickness of the separator for electrochemical devices including the coating can be reduced, and a larger amount of electrode active material can be included in an electrochemical device including the separator for electrochemical devices, thereby increasing the energy density of the electrochemical device. However, the present disclosure is not limited thereto.

[0091] In an embodiment of the present disclosure, in addition to cubic boehmite and sheet boehmite, the coating may further include boehmite of other shapes.

[0092] In another embodiment of the present disclosure, in addition to cubic boehmite and sheet boehmite, the coating may further include other types of inorganic particles. Within the scope that does not impair the purpose of the present disclosure, the inorganic particles further included in the coating may include any type of inorganic particles that do not exhibit oxidation and / or reduction reactions within the operating voltage range of the electrochemical device (e.g., 0V to 5V vs. Li / Li + ) any type of inorganic particles that do not exhibit oxidation and / or reduction reactions, for example, BaTiO3, Pb(Zr,Ti)O3 (PZT), Pb 1-x La x Zr 1-y Ti y O3 (PLZT, 0<x<1, 0<y<1), Pb(Mg 1 / 3 Nb 2 / 3 )O3-PbTiO3 (PMN-PT), hafnium dioxide (HfO2), SrTiO3, 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), lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0<x<2, 0<y<3), lithium aluminum titanium phosphate (Li x Aly Ti z (PO4)3, 0<x<2, 0<y<1, 0<z<3), (LiAlTiP) x O y -based glass (0 < x < 4, 0 < y < 13) such as 14Li2O-9Al2O3-38TiO2-39P2O5, lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y <3), lithium germanium thiophosphate (Li x Ge y P z S w , 0 < x < 4, 0< y < 1, 0 < z < 1, 0 < w < 5) such as Li 3.25 Ge 0.25 P 0.75 S4, lithium nitride (Li x N y , 0 < x < 4, 0 < y < 2) such as Li3N, SiS2-based glass (Li x Si y S z ,0 < x < 3, 0 <y < 2, 0 < z < 4) such as Li3PO4-Li2S-SiS2, or P2S5-based glass (Li x P y S z , 0 < x< 3, 0< y < 3, 0 < z < 7) such as LiI-Li2S-P2S5.

[0093] In embodiments of this disclosure, based on 100 parts by weight of the coating, the amount of inorganic particles in the coating can be, for example, 80 parts by weight or more and 99 parts by weight or less. Specifically, based on the solid content of 100 parts by weight of the coating, the amount of inorganic particles can be 80 parts by weight or more, 85 parts by weight or more, 90 parts by weight or more, or 95 parts by weight or more, and can also be 99 parts by weight or less, 98 parts by weight or less, 97 parts by weight or less, 96 parts by weight or less, 95 parts by weight or less, 94 parts by weight or less, 93 parts by weight or less, 92 parts by weight or less, 91 parts by weight or less, or 90 parts by weight or less. When the amount of inorganic particles falls within the above ranges, a sufficient amount of inorganic particles in the coating can be used to minimize the thermal shrinkage rate of the polymer substrate in the composite separator of the electrochemical device, but this disclosure is not limited thereto. In this case, cubic boehmite and platy boehmite can be 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, or even 100% by weight of the total weight of the inorganic particles.

[0094] adhesives

[0095] In embodiments of this disclosure, the coating includes an adhesive to hold inorganic particles together and / or provide adhesion strength between the porous substrate and the coating and / or between the separator and the electrode.

[0096] In embodiments of this disclosure, the adhesive is not limited to a specific type and may include any type of adhesive used in the coating of the separator. For example, the adhesive may include commonly used adhesives for coatings of separators and may include, but is not limited to, acrylic adhesives, fluoropolymer adhesives, or mixtures thereof. For example, acrylic adhesives may include at least one 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 rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, and copolymers thereof. For example, fluoropolymer adhesives may include at least one selected from the group consisting of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, and polyvinylidene fluoride-trichloroethylene.

[0097] In embodiments of this disclosure, in order to further improve the heat resistance of the separator, the adhesive may include, for example, a non-crosslinked copolymer comprising: i) repeating units derived from acrylic monomers having hydroxyl groups, ii) repeating units derived from (meth)acrylic monomers, (meth)acrylate monomers, or both, and iii) repeating units derived from acrylic monomers having amide groups.

[0098] In embodiments of this disclosure, the copolymer included as an adhesive may be a random copolymer, graft copolymer, or block copolymer of the aforementioned monomers, and specifically, the copolymer may be a random copolymer.

[0099] In embodiments of this disclosure, if the copolymer included as an adhesive is a "crosslinked" copolymer, the density of the molecular chains increases and brittleness increases, resulting in insufficient adhesion area to the inorganic particles. Furthermore, the crosslinking reaction causes i) the loss of hydroxyl groups from repeating units of acrylic monomers having hydroxyl groups, leading to lower bond strength with the inorganic particles and higher wet heat shrinkage. Therefore, when a copolymer is included as an adhesive, it is preferable to retain a non-crosslinked copolymer that remains uncrosslinked after the separator manufacturing process and the battery assembly process, but this disclosure is not limited thereto. According to embodiments of this disclosure, when a "non-crosslinked" copolymer is included as an adhesive, the non-crosslinked copolymer may preferably include a water-soluble solution-type adhesive dissolved in an aqueous solvent (e.g., water), and the solution-type adhesive can adhere to the inorganic particles and porous substrate over a wider area within the coating, thereby effectively reducing the thermal shrinkage of the separator compared to particulate adhesives, but this disclosure is not limited thereto.

[0100] In embodiments of this disclosure, when the adhesive comprises a copolymer containing polyacrylic acid or ii) repeating units derived from (meth)acrylic acid monomers, (meth)acrylate monomers, or both, and iii) repeating units derived from acrylic monomers having amide groups, the adhesive is unlikely to change shape at high temperatures due to the high glass transition temperature of the copolymer, thereby reducing the thermal shrinkage rate of the separator in the dry state. However, copolymers containing only components ii) and iii) may have low bonding strength with inorganic particles in the wet state, making it difficult to improve the thermal shrinkage rate in the wet state. Specifically, for example, when polyacrylic acid is included as an adhesive, polyacrylic acid has hydrophilic properties and a high glass transition temperature, and therefore does not swell in electrolyte solutions. However, because polyacrylic acid has low bonding strength with inorganic particles, it is difficult to improve the thermal shrinkage of the separator in the wet state when polyacrylic acid is applied to the coating alone. On the other hand, polymers of acrylic monomers having amide groups, such as polyacrylamide, are unlikely to change shape at high temperatures due to their high rigidity and high glass transition temperature. However, similar to polyacrylic acid, due to the low bonding strength with inorganic particles, when polymers of acrylic monomers with amide groups are applied as adhesives to the coating alone or in combination with acrylic monomers, it is difficult to improve the thermal shrinkage of the separator in a wet state. Conversely, when the adhesive includes a copolymer, in addition to components ii) and iii), the copolymer also contains repeating units derived from hydroxyl-containing acrylic monomers (i) in sufficient quantity of hydroxyl groups, and can be strongly bonded to the surface of the porous substrate and / or the surface of the inorganic particles and the electrode via intermolecular attraction (e.g., hydrogen bonding with inorganic particles and the porous substrate at high temperatures in the presence of an electrolyte solution). Therefore, when the adhesive includes the aforementioned terpolymer, the coated separator exhibits improved thermal shrinkage in both dry and wet states at high temperatures, but the mechanism of this disclosure is not limited to this.

[0101] According to embodiments of this disclosure, when the adhesive comprises a copolymer, in addition to components ii) and iii), the copolymer also comprises i) repeating units derived from acrylic monomers having hydroxyl groups. Due to the presence of hydroxyl groups, i) repeating units derived from acrylic monomers having hydroxyl groups can have higher bonding strength through intermolecular attraction (such as hydrogen bonding with cubic boehmite and plate boehmite and porous polymer substrates at high temperatures in the presence of an electrolyte solution).

[0102] In embodiments of this disclosure, the hydroxyl-containing acrylic monomer may include hydroxyl-containing alkyl acrylic monomers. In this case, the alkyl group may have, for example, 2 to 4 carbon atoms, but is not limited thereto. More specifically, the hydroxyl-containing acrylic monomer may include, for example, hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, or mixtures thereof. When the copolymer contains the above-mentioned monomers as hydroxyalkyl acrylates, the number of carbon atoms in the alkyl group bonded to the hydroxyl group is small, so the monomer per unit volume may include a large number of hydroxyl groups, and the copolymer per unit volume may include a large number of hydroxyl groups. Therefore, the copolymer adhesive can have high adhesion strength to inorganic particles and porous polymer substrates in a wet state at high temperatures, and the separator for electrochemical devices containing the adhesive in the coating can exhibit low thermal shrinkage in a wet state at high temperatures, but this disclosure is not limited thereto.

[0103] In embodiments of this disclosure, the (meth)acrylate monomer may comprise, for example, at least one selected from the group consisting of: sodium (meth)acrylate, potassium (meth)acrylate, lithium (meth)acrylate, ammonium (meth)acrylate, or mixtures thereof, but this disclosure is not limited thereto.

[0104] In embodiments of this disclosure, the acrylic monomer having an amide group may include, for example, acrylamide, methacrylamide, N,N-dimethyl (meth)acrylamide, N,N-diethyl (meth)acrylamide, N,N-dipropyl (meth)acrylamide, N,N-diisopropyl (meth)acrylamide, N,N-di(n-butyl) (meth)acrylamide, N,N-di(tert-butyl) (meth)acrylamide, N-ethyl (meth)acrylamide, N-isopropyl (meth)acrylamide, N-butyl (meth)acrylamide, N,N-butyl (meth)acrylamide, N-hydroxymethyl (meth)acrylamide, N-hydroxyethyl (meth)acrylamide, N-hydroxypropyl (meth)acrylamide, N-methoxymethyl (meth)acrylamide, N-methoxyethyl (meth)acrylamide, N-butoxymethyl (meth)acrylamide, or mixtures thereof, but this disclosure is not limited thereto.

[0105] In embodiments of this disclosure, when the adhesive comprises a non-crosslinked copolymer, the non-crosslinked copolymer contains: i) repeating units derived from an acrylic monomer having hydroxyl groups, ii) repeating units derived from a (meth)acrylic monomer, a (meth)acrylate monomer, or both, and iii) repeating units derived from an acrylic monomer having amide groups. The molar ratio of the repeating units derived from the hydroxyl-containing acrylic monomer to the repeating units derived from the (meth)acrylic monomer, (meth)acrylate monomer, or both may be, for example, 1:0.1 or greater, 1:0.2 or greater, 1:0.3 or greater, or 1:0.4 or greater, and may also be 1:1 or less, 1:0.9 or less, 1:0.8 or less, 1:0.7 or less, 1:0.6 or less, or 1:0.5 or less. Specifically, the molar ratio of i) repeating units derived from hydroxyl-containing acrylic monomers to ii) repeating units derived from (meth)acrylic monomers, (meth)acrylate monomers, or both can be from 1:0.3 to 1:0.8. When the molar ratio of repeating units falls within the above range, a sufficient amount of the hydroxyl-containing component i) can be included in the copolymer, and the copolymer adhesive can exhibit high adhesion strength to the inorganic particles and porous polymer substrate in the wet state at high temperatures. Therefore, the separator containing the adhesive in the coating can exhibit a low rate of thermal shrinkage in the wet state at high temperatures. Furthermore, a sufficient amount of component ii) can be included in the copolymer to impart heat resistance and increase compatibility with inorganic particles, resulting in high adhesion strength to the inorganic particles and porous substrate in the dry state. Therefore, the separator used in the electrochemical device can exhibit a low rate of thermal shrinkage in the dry state, but this disclosure is not limited thereto.

[0106] In embodiments of this disclosure, when the adhesive comprises a non-crosslinked copolymer, the non-crosslinked copolymer comprises i) repeating units derived from hydroxyl-containing acrylic monomers, ii) repeating units derived from (meth)acrylic monomers, (meth)acrylate monomers, or both, and iii) repeating units derived from amide-containing acrylic monomers, wherein the molar ratio of the repeating units derived from hydroxyl-containing acrylic monomers to the repeating units derived from amide-containing acrylic monomers may be, for example, 1:1 to 1:2. Specifically, the molar ratio of repeating units derived from hydroxyalkyl acrylate monomers to repeating units derived from acrylamide monomers may be 1:1 or greater, 1:1.1 or greater, 1:1.2 or greater, 1:1.3 or greater, 1:1.4 or greater, or 1:1.5 or greater, and may also be 1:2 or less, 1:1.9 or less, 1:1.8 or less, 1:1.7 or less, or 1:1.6 or less, and particularly may be 1:1.2 to 1:1.6. When the monomer ratio in the copolymer falls within the aforementioned range, the copolymer may contain a sufficient amount of component iii) with high heat resistance, thus the separator for the electrochemical device exhibits a low thermal shrinkage rate in the dry state. Furthermore, a sufficient amount of component iii) with high adhesive strength in the wet state may be included in the copolymer, allowing the separator for the electrochemical device to exhibit a low thermal shrinkage rate at high temperatures in the wet state. In other words, when the coating contains an adhesive with a monomer ratio in the copolymer within the aforementioned range, the thermal shrinkage rate at high temperatures in both dry and wet states can be reduced more uniformly, but this disclosure is not limited thereto.

[0107] In embodiments of this disclosure, the adhesive may have a weight-average molecular weight (Mw) of, for example, from 100,000 g / mol to 200,000 g / mol. Specifically, the weight-average molecular weight of the adhesive may be 100,000 g / mol or greater, 110,000 g / mol or greater, 120,000 g / mol or greater, 130,000 g / mol or greater, 140,000 g / mol or greater, or 150,000 g / mol or greater, and may also be 200,000 g / mol or less, 190,000 g / mol or less, 180,000 g / mol or less, 170,000 g / mol or less, 160,000 g / mol or less, or 150,000 g / mol or less. When the weight-average molecular weight of the adhesive falls within the aforementioned range, the adhesive can have sufficient length to adhere the inorganic particles and the porous substrate together, thereby effectively preventing the inorganic particles from peeling off from the porous substrate. Therefore, a separator for an electrochemical device having an adhesive-containing coating on one surface of the porous substrate exhibits low thermal shrinkage in both dry and wet conditions, but this disclosure is not limited thereto.

[0108] In this specification, weight-average molecular weight can refer to the value measured using gel permeation chromatography (GPC: gel permeation chromatography, PL GPC220, Agilent Technologies). For example, weight-average molecular weight can be a value measured using a PLOlexis (Polymer Laboratories) column (column temperature 160°C), trichlorobenzene (TCB) solvent, and an Agilent high-temperature RI detector (third-order polynomial fitting, standard: polystyrene) at a sample concentration of 1.0 mg / mL, a flow rate of 1.0 mL / min, and an injection volume of 200 μL (third-order polynomial fitting, standard: polystyrene).

[0109] In embodiments of this disclosure, the glass transition temperature (Tg) of the adhesive can be, for example, from 100°C to 200°C. Specifically, the glass transition temperature of the adhesive can be, for example, from 120°C to 180°C, from 140°C to 160°C, from 150°C to 155°C, or from 155°C to 160°C. When the glass transition temperature of the adhesive falls within the above range, swelling in the electrolyte solution can be suppressed, thereby improving the dry heat shrinkage rate and wet heat shrinkage rate of the coating, but this disclosure is not limited thereto.

[0110] In this specification, the glass transition temperature of a polymer may refer, for example, to a value measured using differential scanning calorimetry (DSC). The method for measuring the glass transition temperature using DSC may include any of the commonly used methods, and, for example, the glass transition temperature may be measured using a TA Instrument DSC 2920 according to the user manual.

[0111] In embodiments of this disclosure, the adhesive may be included in an amount of, for example, from 1 to 20 parts by weight of 100 parts by weight of the coating. Specifically, based on the solids content of 100 parts by weight of the coating, the amount of adhesive may be 1 part by weight or more and 20 parts by weight or less, 2 parts by weight or more and 15 parts by weight or less, 3 parts by weight or more and 12 parts by weight or less, 5 parts by weight or more and 6 parts by weight or less, 5 parts by weight or more and 7 parts by weight or less, 5 parts by weight or more and 8 parts by weight or less, 5 parts by weight or more and 9 parts by weight or less, 7 parts by weight or more and 9 parts by weight or less, or 8 parts by weight or more and 10 parts by weight or less. Specifically, based on the solids content of 100 parts by weight of the coating, the amount of adhesive may be 3 parts by weight or more, 4 parts by weight or more, or 5 parts by weight or more, and may also be 10 parts by weight or less, 9 parts by weight or less, or 8 parts by weight or less. When the amount of adhesive falls within the aforementioned range, and when a sufficient amount of adhesive is present in the coating, high adhesion strength can be achieved between the porous substrate and the coating, and / or between the separator and the electrode, but this disclosure is not limited thereto. Furthermore, because the amount of adhesive is sufficient, the interstitial volume formed by the inorganic particles bonded by the adhesive can be increased, resulting in high porosity of the coating. Therefore, the resistance of the separator with the coating can be reduced, but this disclosure is not limited thereto.

[0112] In embodiments of this disclosure, the porosity of the coating may, for example, be 30% by volume or higher and 50% by volume or lower. Specifically, the porosity of the coating may be 30% by volume or higher, 35% by volume or higher, or 40% by volume or higher, and may also be 50% by volume or lower, 45% by volume or lower, or 40% by volume or lower. When the porosity of the coating falls within the above ranges, there may be sufficient pores in the coating to allow lithium ions to move rapidly through the pores, resulting in low resistance of the separator used in the electrochemical device. Furthermore, the separator for the electrochemical device according to this disclosure may have higher mechanical strength compared to when there is an excessive number of pores in the coating due to its extremely high porosity, but this disclosure is not limited thereto.

[0113] In this specification, the porosity of a coating refers to the ratio of pore volume to the total volume of the coating. Porosity can be measured by any commonly used method. For example, porosity can be measured using the BET (Brunauer Emmett Teller) method with nitrogen adsorption, a capillary flow porometer, or a water or mercury intrusion method.

[0114] In embodiments of this disclosure, the coating can be formed as a multilayer, wherein the inorganic particles in the upper layer have a different shape than the inorganic particles in the lower layer.

[0115] In embodiments of this disclosure, the coating may include: a first coating disposed on at least one surface of a porous polymer substrate, the first coating comprising cubic boehmite and a first adhesive; and a second coating disposed on the first coating, the second coating comprising sheet boehmite and a second adhesive.

[0116] In another embodiment of this disclosure, the coating may include: a first coating disposed on at least one surface of a porous polymer substrate, the first coating comprising sheet-like boehmite and a first adhesive; and a second coating disposed on the first coating, the second coating comprising cubic boehmite and a second adhesive.

[0117] In embodiments of this disclosure, when the coating is formed as a multilayer, preferably, the first coating may include cubic boehmite and the second coating may include plate boehmite to improve the adhesion strength between the porous polymer substrate and the first coating and reduce the resistance of the separator, but this disclosure is not limited thereto.

[0118] In embodiments of this disclosure, the total thickness of the first coating and the second coating can be, for example, from 0.5 μm to 4 μm. Specifically, the total thickness of the first coating and the second coating can be 0.5 μm or greater, 0.7 μm or greater, 0.9 μm or greater, 1.0 μm or greater, and can also be 4 μm or less, 3.5 μm or less, 3 μm or less, 2 μm or less, 1.8 μm or less, 1.6 μm or less, or 1.5 μm or less.

[0119] In embodiments of this disclosure, the thickness ratio of the first coating to the second coating can be, for example, 1:0.5 to 1:1.5, and specifically 1:0.8 to 1:1.2. Specifically, the thickness ratio can be 1:0.8 to 1:1.1, 1:0.8 to 1:1, 1:0.8 to 1:0.9, 1:0.9 to 1:1.2, or 1:1 to 1:1.2. When the thickness ratio falls within the above ranges, rapid ion movement in the first coating can be ensured, thereby reducing the resistance of the separator including the first coating and ensuring sufficient heat resistance of the second coating, which has a beneficial effect on thermal shrinkage. Thus, the separator can have improved heat resistance and ensure favorable rapid ion movement in terms of resistance, but this disclosure is not limited thereto.

[0120] In embodiments of this disclosure, the bulk density of the second coating may be 0.7 g / cm³. 3 Or larger and 1.3 g / cm 3 Or even smaller. Specifically, the bulk density of the second coating can be 0.7 g / cm³. 3 Or larger and 1.3 g / cm 3 or smaller, 0.8 g / cm 3Or larger and 1.2 g / cm 3 Or smaller, 0.9 g / cm³ 3 Or larger and 1.2 g / cm 3 Or smaller, 0.9 g / cm³ 3 or larger and 1.1 g / cm 3 Or smaller, 0.9 g / cm³ 3 or larger and 1 g / cm 3 Or smaller, 0.9 g / cm³ 3 Or larger and 1.0 g / cm 3 Or smaller, or 0.9 g / cm³ 3 Or larger and 0.95 g / cm 3 Or even less. The bulk density of the second coating can have the same meaning as the bulk density of the coating described above. When the bulk density of the second coating falls within the above range, the second coating is disposed on the first coating at an appropriate density. Therefore, the shrinkage of the partition can be effectively suppressed and the resistance of the partition can be reduced, but this disclosure is not limited thereto.

[0121] In embodiments of this disclosure, the first adhesive and the second adhesive may be the same as or different from the adhesives described above.

[0122] In embodiments of this disclosure, the first adhesive and the second adhesive may each independently comprise a non-crosslinked copolymer comprising i) repeating units derived from an acrylic monomer having hydroxyl groups, ii) repeating units derived from (meth)acrylic monomers, (meth)acrylate monomers, or both, and iii) repeating units derived from an acrylic monomer having amide groups.

[0123] In embodiments of this disclosure, the first adhesive and the second adhesive may each independently comprise a non-crosslinked copolymer containing: repeating units derived from hydroxyalkyl acrylate monomers, repeating units derived from (meth)acrylic acid monomers, and repeating units derived from acrylic acid monomers having amide groups.

[0124] According to embodiments of this disclosure, a slurry for forming a coating can be used to form a coating.

[0125] According to embodiments of this disclosure, the slurry for forming the coating may comprise: inorganic particles and binder as described above as solids, and a dispersion medium or dispersion solvent for dissolving or dispersing them.

[0126] In embodiments of this disclosure, the slurry used to form the coating may contain a dispersion medium to dissolve or disperse at least some of the binder and disperse the inorganic particles. Preferably, a slurry for forming the coating is used in which the binder and inorganic particles are uniformly dispersed by adjusting the type and amount of the dispersion medium. For example, the dispersion medium may contain water, ethanol, acetone, isopropanol (IPA), dimethylacetamide (DMAc), dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), acetonitrile, or mixtures thereof, but this disclosure is not limited thereto. Dispersion media of the types described above can be used to form coatings in which inorganic particles are uniformly dispersed, but this disclosure is not limited thereto.

[0127] In embodiments of this disclosure, a coating slurry comprising a binder, inorganic particles, and a dispersion medium can be applied to at least one surface of a porous substrate to form a coating. For example, the coating can be formed using a bar coater, wire bar coater, roller coater, spray coater, spin coater, inkjet coater, screen coater, reverse coater, gravure coater, doctor blade coater, slot die coater, hot melt coater, comma coater, or direct metering coater, but is not limited thereto. Preferably, the coating can be formed by applying the coating slurry to one surface of the porous substrate using a bar coater or slot die coater, or the coating slurry can be applied to both surfaces of the porous substrate simultaneously, but this disclosure is not limited thereto.

[0128] According to embodiments of this disclosure, the separator for an electrochemical device may further include an electrode adhesive layer on the topmost surface of the coating. The electrode adhesive layer may include an adhesive for use with the electrode adhesive layer. The adhesive for the electrode adhesive layer may include, for example, a fluorinated adhesive and an acrylic adhesive to improve adhesion strength relative to the electrode. Specifically, the adhesive for the electrode adhesive layer may include PVDF-HFP, where PVDF-HFP is a fluorinated adhesive. The electrode adhesive layer including the fluorinated adhesive and the acrylic adhesive can stably maintain the adhesion strength of the separator for the electrochemical device relative to the electrode in the absence of an electrolyte solution in a dry state and in the presence of an electrolyte solution in a wet state. For example, the electrode adhesive layer may include a fluorinated adhesive and an acrylic adhesive in a weight ratio of 4:6 to 6:4. The electrode adhesive layer may be formed with a thickness less than the thickness of the coating to provide adhesion strength relative to the electrode while minimizing a reduction in the permeability of the separator for the electrochemical device, but this disclosure is not limited thereto.

[0129] Porous polymer substrate

[0130] In one aspect of the separator according to this disclosure, the porous substrate can be a porous membrane having multiple pores and can be used to electrically insulate the positive and negative electrodes to prevent short circuits. For example, when the electrochemical device is a lithium secondary battery, the porous substrate can act as an ion conduction barrier to allow lithium ions to pass through while preventing electrical contact between the positive and negative electrodes. At least some of the pores can form a three-dimensional network connecting the surface and interior of the porous substrate, and fluid can pass through the pores through the porous substrate.

[0131] In embodiments of this disclosure, the porous substrate can be made of a material that is physically and chemically stable in the presence of an electrolyte solution in the form of an organic solvent. For example, the porous substrate can include, but is not limited to, resins such as polyolefins (including polyethylene, polypropylene, and polybutene), polyvinyl chloride, polyethylene terephthalate, polycyclic olefins, polyethersulfone, polyamides, polyimides, polyamide-imides, nylon, polytetrafluoroethylene, and copolymers or mixtures thereof. Preferably, the porous substrate may comprise a polyolefin-based resin. Because polyolefin-based resins can be processed to smaller thicknesses and are easily coated with a coating slurry, they are suitable for manufacturing electrochemical devices with higher energy densities.

[0132] In embodiments of this disclosure, the porous substrate may have a single-layer or multi-layer structure. The porous substrate may include two or more polymer resin layers with different melting points (Tm) to provide a shut-off function in the event of thermal runaway of the battery at high temperatures. For example, the porous substrate may include a polypropylene layer with a higher melting point and a polyethylene layer with a lower melting point. Preferably, the porous substrate may have a three-layer structure of polypropylene, polyethylene, and polypropylene stacked in this order. When the battery temperature rises above a preset temperature, the polyethylene layer can close the pores upon melting, thereby preventing thermal runaway of the battery.

[0133] In embodiments of this disclosure, the thickness of the porous substrate can be, for example, 1 μm or more and 100 μm or less. Specifically, the thickness of the porous substrate can be 10 μm or more and 90 μm or less, 20 μm or more and 80 μm or less, 30 μm or more and 70 μm or less, or 40 μm or more and 60 μm or less. Preferably, the thickness of the porous substrate can be 1 μm or more and 30 μm or less. More preferably, the thickness of the porous substrate can be 5 μm or more and 15 μm or less, or 8 μm or more and 13 μm or less. When the thickness of the porous substrate is adjusted within the above ranges, the volume of the electrochemical device can be minimized, while the positive and negative electrodes are electrically insulated, and the amount of active material included in the electrochemical device can be increased, but this disclosure is not limited thereto.

[0134] In embodiments of this disclosure, the porous substrate may have an average pore size of 0.01 μm or greater and 1 μm or less. Specifically, the pore size of the porous substrate may be 0.01 μm or greater and 0.09 μm or less, 0.02 μm or greater and 0.08 μm or less, 0.03 μm or greater and 0.07 μm or less, or 0.04 μm or greater and 0.06 μm or less. Preferably, the pore size may be 0.02 μm or greater and 0.06 μm or less. When the pore size of the porous substrate is adjusted within the above ranges, the total air permeability and ionic conductivity of the manufactured separator can be adjusted, but this disclosure is not limited thereto.

[0135] In embodiments of this disclosure, the porous substrate may have an air permeability of 10 s / 100cc or greater and 100 s / 100cc or less. Specifically, the air permeability of the porous substrate can be 10 s / 100cc or greater and 90 s / 100cc or less, 20 s / 100cc or greater and 85 s / 100cc or less, 30 s / 100cc or greater and 80 s / 100cc or less, 40 s / 100cc or greater and 80 s / 100cc or less, 50 s / 100cc or greater and 70 s / 100cc or less, 60 s / 100cc or greater and 78 s / 100cc or less, 65 s / 100cc or greater and 78 s / 100cc or less, 70 s / 100cc or greater and 78 s / 100cc or less, or 75 s / 100cc or greater and 78 s / 100cc or less. When the permeability of the porous substrate falls within the above range, the permeability of the separator can be set within a range suitable for ensuring the output and cycle characteristics of the electrochemical device, but this disclosure is not limited thereto.

[0136] In this specification, the air permeability (s / 100cc) of a partition refers to the time (in seconds) it takes for 100 cc of air to pass through a predetermined area of ​​a porous substrate or partition under constant pressure. Air permeability can be measured using a Gurley air permeability tester according to ASTM D 726-58, ASTM D726-94, or JIS-P8117. For example, the Gurley 4110 N can be used to measure 100 cc of air at an air pressure of 0.304 kPa or 1.215 kN / m³. 2 Under water pressure, passing through 1 square inch (or 6.54 cm) 2 The time taken. For example, the Asahi Seico EG01-55-1MR can be used to measure the time it takes for 100 cc of air to pass through 1 square inch at room temperature under a constant pressure of 4.8 inches of water.

[0137] In embodiments of this disclosure, the porous substrate may have a porosity of, for example, 10 vol% or more and 60 vol% or less. Specifically, the porosity of the porous 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 substrate may be 30 vol% or more and 50 vol% or less. When the porosity of the porous substrate falls within the above ranges, the ionic conductivity of the separator can be provided within a range suitable for ensuring the output and cycling characteristics of the electrochemical device, but this disclosure is not limited thereto.

[0138] In this specification, the porosity of a porous substrate refers to the ratio of pore volume to the total volume of the coating. Porosity can be measured by any commonly used method. For example, porosity can be measured using the BET (Brunauer Emmett Teller) method with nitrogen adsorption, a capillary flow porometer, or a water or mercury immersion method.

[0139] [Electrochemical device]

[0140] According to another aspect of this disclosure, an electrochemical device including the aforementioned separator is provided.

[0141] According to another aspect of this disclosure, an electrochemical device includes a positive electrode, a negative electrode, and a separator, wherein the separator is positioned between the positive electrode and the negative electrode.

[0142] In the electrochemical device according to the embodiments of the present disclosure, descriptions shared between the electrochemical device and the partition for the electrochemical device are omitted to avoid redundancy.

[0143] An electrochemical device is a device that converts chemical energy into electrical energy through an electrochemical reaction, and it encompasses both primary and secondary batteries. A secondary battery is a rechargeable battery and can include lithium-ion batteries, nickel-cadmium batteries, or nickel-metal hydride batteries. Lithium-ion batteries use lithium ions as the ion conductor and can include, for example, non-aqueous electrolyte batteries containing a liquid electrolyte, all-solid-state batteries containing a solid electrolyte, lithium polymer batteries containing a gel polymer electrolyte, or lithium metal batteries using lithium metal as the negative electrode, but are not limited to these.

[0144] An electrochemical device including the separator of the present disclosure can have high adhesion strength between the separator and the electrode, thereby minimizing the reduction in safety caused by separator peeling during long-term cycling of the electrochemical device.

[0145] According to embodiments of this disclosure, an electrochemical device can be manufactured, for example, by inserting an electrode assembly into a battery housing and sealing the battery housing. The electrode assembly includes a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes. Before sealing the battery housing, an electrolyte solution can be injected to fill the electrode assembly with the electrolyte solution. The battery housing is not limited to a specific shape and can be, for example, cylindrical, prismatic, coin-shaped, or pouch-shaped.

[0146] According to embodiments of this disclosure, the positive electrode may include a positive current collector and a positive active material layer disposed on at least one surface of the current collector. The positive active material layer includes a positive active material, a conductive material, and a binder resin. The positive active material may include a layered compound, such as lithium manganese composite oxide (LiMn2O4, LiMnO2), lithium cobalt oxide (LiCoO2), or lithium nickel oxide (LiNiO2), or a compound having one or more transition metal substitutions; lithium manganese oxide, for example, with the chemical formula Li... 1+x Mn 2-x O4 (x is 0 to 0.33), LiMnO3, LiMn2O3 or LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxide, such as LiV3O8, LiV3O4, V2O5 or Cu2V2O7; and LiNi 1-x M x Ni-site lithium nickel oxides represented by O2 (M = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x = 0.01 to 0.3); LiMn 1-x M x Lithium manganese composite oxides represented by O2 (M = Co, Ni, Fe, Cr, Zn or Ta, x = 0.01 to 0.1) or Li2Mn3MO8 (M = Fe, Co, Ni, Cu or Zn); LiMn2O4, wherein the Li portion in the chemical formula is partially substituted with an alkaline earth metal ion; disulfide compounds; Fe2(MoO4)3; or mixtures thereof.

[0147] According to embodiments of this disclosure, the negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the current collector. The negative electrode active material layer includes a negative electrode active material, a conductive material, and a binder resin. In the negative electrode, the negative electrode active material may include one selected from: lithium metal oxide; carbon, such as non-graphitizable carbon or graphitized carbon; metal composite oxide, such as Li... x Fe2O3 (0≤x≤1), Li x WO2(0≤x≤1), or Sn x Me 1-x Me′ y O z(wherein Me is Mn, Fe, Pb, Ge; Me' is Al, B, P, Si, an element of Group 1, Group 2 or Group 3 of the Periodic Table, a halogen; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8); lithium metal; lithium alloys; silicon-based alloys; tin-based alloys; metal oxides, such as SnO, SnO₂, PbO, PbO₂, Pb₂O₃, Pb₃O₄, Sb₂O₃, Sb₂O₄, Sb₂O₅, GeO, GeO₂, Bi₂O₃, Bi₂O₄ and Bi₂O₅); conductive polymers, such as polyacetylene; Li-Co-Ni based materials; and titanium oxides; or mixtures thereof.

[0148] According to the embodiments of the present disclosure, the conductive material may, for example, be any one selected from the group consisting of graphite, carbon black, carbon fibers or metal fibers, metal powder, conductive whiskers, conductive metal oxides, activated carbon, polyphenylene derivatives, or mixtures thereof. More specifically, the conductive material may be one selected from the group consisting of: natural graphite, artificial graphite, super-p, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, or mixtures thereof.

[0149] According to the embodiments of the present disclosure, the current collector is not limited to a specific type, and may be any highly conductive material that does not cause chemical changes to the corresponding battery, and may, for example, include stainless steel, copper, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium or silver.

[0150] According to embodiments of this disclosure, the adhesive resin may comprise any polymer commonly used in electrodes in the art. Non-limiting examples of adhesive resins may include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate. Acetatepropionate, cyanoethylpullulan, cyanoethylpolyvinyl alcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, or carboxyl methylcellulose, but not limited to these.

[0151] According to embodiments of this disclosure, the positive electrode slurry used to form the positive electrode active material layer may include a dispersant, and the dispersant may include a pyrrolidone-based compound. Specifically, the dispersant may include N-methylpyrrolidone (ADC-01, LG Chem).

[0152] According to embodiments of this disclosure, the electrochemical device may further include an electrolyte, and the electrolyte may contain components having A + B - The structure of salts and the organic solvent in which the salt dissolves or dissociates, wherein A + Including alkali metal cations such as Li + Na+ K + Or a combination of them, and B - Including anions such as PF6 - BF4 - Cl - ,Br - I - ClO4 - AsF6 - CH3CO2 - CF3SO3 - N(CF3SO2)2 - C(CF2SO2)3 - Organic solvents, or combinations thereof, but not limited to, include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), γ-butyrolactone, or mixtures thereof, but not limited to.

[0153] According to embodiments of this disclosure, a battery module may be provided, the battery module including a battery, the battery including an electrochemical device as a unit cell; a battery pack including the battery module; and a device including the battery pack as a power source. Specific examples of the device may include a power tool powered by an electric motor; an electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), or a plug-in hybrid electric vehicle (PHEV); an electric two-wheeled vehicle including an electric bicycle (E-bike) or an electric scooter (E-scooter); an electric golf cart; or a power storage system, but are not limited thereto.

[0154] According to embodiments of this disclosure, an electrochemical device may include a cylindrical secondary battery, wherein a separator for the electrochemical device is inserted between a positive electrode and a negative electrode. In this case, the separator, positive electrode, and negative electrode may be stacked to form an electrode assembly having a separator / positive electrode / separator / negative electrode structure or a positive electrode / separator / negative electrode / separator structure, and wound together. The positive and negative electrodes may be repositioned. After stacking, the electrode assembly may be wound around a core, inserted into a cylindrical container, and rolled to manufacture a cylindrical secondary battery.

[0155] The present disclosure will be described in more detail below with reference to specific embodiments and experimental examples. The following embodiments and experimental examples are intended to describe the present disclosure for illustrative purposes, and the present disclosure is not limited to the following embodiments and experimental examples.

[0156] Example 1

[0157] Preparation of separators for electrochemical devices

[0158] cubic boehmite (average grain size (D)) 50 (500 nm, KC kB-05S) and platy boehmite (average long side: 750 nm, aspect ratio: 2.0, density: 3.00 g / cm³). 3 The coating slurry was prepared by adding a non-crosslinked copolymer (weight average molecular weight: 150,000 g / mol, Tg: 155°C, no crosslinking after high-temperature storage at 80°C) containing repeating units derived from hydroxyethyl acrylate (HEA), acrylic acid (AA), and acrylamide (AM) in a molar ratio of 1:0.4:0.6 (HEA:AA:AM) to distilled water at room temperature (25°C) in a weight ratio of inorganic particles to binder of 93:6. The slurry was then stirred for 120 minutes using a shaker.

[0159] A 10 μm thick polyethylene film (porosity 55% by volume) was used as the porous polymer substrate.

[0160] A coating slurry is applied to both surfaces of a freshly prepared porous polymer substrate using a doctor blade and then dried with air at 50°C using a hot air gun to create a separator with a coating on each of the two surfaces of the porous substrate.

[0161] Based on a coating on a single surface, each coating has a thickness of 1.5 μm and a bulk density of 1.2 g / cm³. 3 The total thickness of the partition with coatings on both surfaces is 13 μm.

[0162] Example 2

[0163] The separator for the electrochemical device was manufactured using the same method as in Example 1, except that: plate-shaped boehmite with an aspect ratio of 5.0 was used, and cubic boehmite and plate-shaped boehmite were added in a weight ratio of 4:1.

[0164] Example 3

[0165] cubic boehmite (average grain size (D)) 50A non-crosslinked copolymer (weight average molecular weight: 150,000 g / mol, Tg: 155℃, no crosslinking after storage at 80℃) containing repeating units derived from hydroxyethyl acrylate (HEA), acrylic acid (AA), and acrylamide (AM) in a molar ratio of 1:0.4:0.6 (HEA:AA:AM) and 500nm KC kB-05S) was added to distilled water at a weight ratio of 93:6 at room temperature (25℃), and then stirred with a shaker for 120 minutes to prepare the first coating slurry.

[0166] A second coating slurry was prepared by adding flake-shaped boehmite (average long side: 750 nm, aspect ratio: 3.0) and a non-crosslinked copolymer (weight average molecular weight: 150,000 g / mol, Tg: 155 °C, no crosslinking after storage at 80 °C) containing repeating units derived from hydroxyethyl acrylate (HEA), acrylic acid (AA), and acrylamide (AM) in a molar ratio of 1:0.4:0.6 (HEA:AA:AM) to distilled water at a weight ratio of 93:6 at room temperature (25 °C), followed by stirring with a shaker for 120 minutes.

[0167] The first coating slurry was applied to both surfaces of the prepared porous polymer substrate (PE film, 10 μm, 55% by volume) using a doctor blade via a rod coating method, and then dried in air at 50°C using a hot air gun to form the first coating layer (bulk density of 1.2 g / cm³). 3 The second coating slurry was then applied to the surface of the first coating using a bar coating method, and dried in air at 50°C using a hot air gun to form the second coating (with a bulk density of 0.9 g / cm³). 3 The total thickness of the first and second coatings is 1.5 μm, and the thickness ratio of the first coating to the second coating is 1:1.

[0168] Comparative Example 1

[0169] The separator for the electrochemical device was manufactured using the same method as in Example 1, except that cubic boehmite and plate boehmite were added in a weight ratio of 5:1.

[0170] Comparative Example 2

[0171] The separator for the electrochemical device was manufactured using the same method as in Example 1, except that plate-shaped boehmite with an average long side length of 1 μm was used.

[0172] Comparative Example 3

[0173] The separator for the electrochemical device was manufactured using the same method as in Example 3, except that a plate-shaped boehmite with an aspect ratio of 11 was used to form the second coating.

[0174] Experiment Example 1: Measurement of the resistance of the separator

[0175] For each partition according to Examples 1 to 3 and Comparative Examples 1 to 3, the resistance was measured as follows.

[0176] Each separator for the electrochemical device in the examples and comparative examples was placed between SUS to manufacture a coin cell. An electrolyte solution containing 1 M LiPF6 in a 3:7 (volume ratio) solvent mixture of ethylene carbonate and methyl ethyl carbonate was injected into the coin cell. The resistance of the coin cell was measured by electrochemical impedance spectroscopy analysis at an amplitude of 10 mV and a scan range of 0.1 Hz to 1 MHz, and the measurement results are summarized in Tables 1 and 2 below.

[0177] Experimental Example 2: Measurement of Thermal Shrinkage of a Partition

[0178] For each partition according to Examples 1 to 3 and Comparative Examples 1 to 3, the dry heat shrinkage rate and wet heat shrinkage rate were measured as follows.

[0179] (1) Dry heat shrinkage rate

[0180] Each partition of the examples and comparative examples was prepared into a 5 cm × 5 cm sample, which was then stored in a convection oven at 180 °C for 30 minutes. After the partitions were removed, the thermal shrinkage rates in the MD direction and TD direction were calculated according to [(initial sample length - length after storage at 180 °C / 0.5 h) / (initial sample length)] × 100 (%).

[0181] The experimental results are summarized in Tables 1 and 2 below.

[0182] (2) Moist heat shrinkage rate

[0183] Each partition of the examples and comparative examples was prepared as a 5 cm × 5 cm sample, which was then inserted into an aluminum bag with a size of 7 cm × 10 cm and the bag was sealed.

[0184] The electrolyte solution contains 2% by weight of vinylene carbonate (VC) as an additive and 1M of LiPF6 as a lithium salt in a 3 / 7 (by weight) solvent mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC).

[0185] After storing the sealed bag in a convection oven at 140°C for 30 minutes and removing the partition, the thermal shrinkage rates in the MD and TD directions were calculated according to [(initial sample length - length after 0.5 hours of storage at 140°C) / (initial sample length)] × 100 (%).

[0186] The experimental results are summarized in Tables 1 and 2 below.

[0187] Table 1

[0188]

[0189] Table 2

[0190]

[0191] This confirms that the separator having a coating comprising cubic boehmite and plate boehmite in a weight ratio of 1:1 to 4:1 according to embodiments of the present disclosure maintains low resistance and exhibits low thermal shrinkage in both dry and wet conditions.

Claims

1. A separator for an electrochemical device, comprising: Porous polymer substrate; and A coating disposed on at least one surface of the porous polymer substrate, the coating comprising inorganic particles and a binder. The inorganic particles include cubic boehmite and platy boehmite in a weight ratio of 1:1 to 4:

1.

2. The separator for an electrochemical device according to claim 1, The average grain size (D) of the cubic boehmite therein 50 The thickness ranges from 0.5 μm to 0.7 μm.

3. The separator for an electrochemical device according to claim 1, The aspect ratio of the plate-shaped boehmite is 2 to 10.

4. The separator for an electrochemical device according to claim 1, The average long side of the plate-shaped boehmite is 0.7 μm to 0.9 μm.

5. The separator for an electrochemical device according to claim 1, The bulk density of the coating is 0.9 g / cm³. 3 Up to 1.3 g / cm 3 .

6. The separator for an electrochemical device according to claim 1, The adhesive comprises a non-crosslinked copolymer containing: i) repeating units derived from acrylic monomers having hydroxyl groups, ii) repeating units derived from (meth)acrylic monomers, (meth)acrylate monomers, or both, and iii) repeating units derived from acrylic monomers having amide groups.

7. The separator for an electrochemical device according to claim 1, The adhesive described herein comprises a non-crosslinked copolymer containing repeating units derived from hydroxyalkyl acrylate monomers, repeating units derived from (meth)acrylic acid monomers, and repeating units derived from acrylic acid monomers having amide groups.

8. The separator for an electrochemical device according to claim 6, The (meth)acrylate monomers include sodium (meth)acrylate, potassium (meth)acrylate, lithium (meth)acrylate, ammonium (meth)acrylate, or mixtures thereof.

9. The separator for an electrochemical device according to claim 6, The acrylic monomer having an amide group includes acrylamide, methacrylamide, N,N-dimethyl (meth)acrylamide, N,N-diethyl (meth)acrylamide, N,N-dipropyl (meth)acrylamide, N,N-diisopropyl (meth)acrylamide, N,N-di(n-butyl) (meth)acrylamide, N,N-di(tert-butyl) (meth)acrylamide, N-ethyl (meth)acrylamide, N-isopropyl (meth)acrylamide, N-butyl (meth)acrylamide, N,N-butyl (meth)acrylamide, N-hydroxymethyl (meth)acrylamide, N-hydroxyethyl (meth)acrylamide, N-hydroxypropyl (meth)acrylamide, N-methoxymethyl (meth)acrylamide, N-methoxyethyl (meth)acrylamide, N-butoxymethyl (meth)acrylamide, or mixtures thereof.

10. The separator for an electrochemical device according to claim 7, The alkyl group of the hydroxyalkyl acrylate monomer has 2 to 4 carbon atoms.

11. The separator for an electrochemical device according to claim 1, The coating on one surface of the porous polymer substrate has a thickness of 0.5 μm to 4 μm.

12. The separator for an electrochemical device according to claim 1, The coating comprises: A first coating, the first coating comprising the cubic boehmite and a first adhesive; and A second coating disposed on the first coating, the second coating comprising the sheet-like boehmite and a second adhesive.

13. The separator for an electrochemical device according to claim 12, The thickness ratio of the first coating to the second coating is from 1:0.5 to 1:1.

5.

14. The separator for an electrochemical device according to claim 12, in, Based on 100 parts by weight of the coating, the amount of inorganic particles is 80 to 95 parts by weight.

15. An electrochemical device, comprising: Positive electrode, negative electrode, and a separator for an electrochemical device according to any one of claims 1 to 14, The separator for the electrochemical device is positioned between the positive electrode and the negative electrode.

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