Separator for electrochemical device and electrochemical device comprising same

Abstract

The present invention relates to a separator for an electrochemical device, comprising: a porous substrate; and a coating layer formed on at least one surface of the porous substrate, wherein the coating layer includes inorganic particles, a polymer binder, and cellulose nanofibers, wherein, by incorporating lithium ions and silane, the cellulose nanofibers lower the moisture content of the separator and provide improved electrical resistance.

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. 10-2024-0141291 dated October 16, 2024 and Korean Patent Application No. 10-2025-0144910 dated October 2, 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] Meanwhile, the separator of a lithium secondary battery prevents electrical contact between the positive and negative electrodes while enabling the movement of lithium ions between the electrodes, playing a crucial role in the safety and performance of the battery.

[0007]

[0008] The present invention provides a separator for an electrochemical device having a reduced electrical resistance value due to the low moisture content of the separator, and an electrochemical device including the same.

[0009]

[0010] One aspect of the present invention provides a separator for an electrochemical device comprising a porous substrate and a coating layer formed on at least one surface of the porous substrate, wherein the coating layer comprises inorganic particles, a polymer binder, and cellulose nanofibers, and wherein the cellulose nanofibers are introduced with lithium ions and silane.

[0011] Another aspect of the present invention provides a method for manufacturing a separator for an electrochemical device, comprising the steps of: preparing a slurry for a coating layer comprising inorganic particles, a polymer binder, cellulose nanofibers (CNF), and a dispersion medium; forming a coating layer by coating at least one surface of a porous substrate with the slurry for the coating layer; and drying the coating layer and removing the dispersion medium, wherein the step of preparing the slurry for the coating layer further comprises the step of introducing lithium ions and a silane component into the cellulose nanofibers (CNF).

[0012] The above cellulose nanofibers may be in which lithium ions and silane are introduced in a molar ratio of about 5:1 to 25:1.

[0013] The coating layer may contain about 1% by weight or more and 15% by weight or less of the cellulose nanofiber.

[0014] The average diameter of the above cellulose nanofibers may be about 5 nm or more and 50 nm or less.

[0015] The aspect ratio of the above cellulose nanofibers may be about 50 to 200.

[0016] The above silanes are N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane hydrochloride, vinyltrimethoxysilane, vinyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, p-styryltrimethoxysilane, It may be one or more selected from 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, tris-(trimethoxysilylpropyl)isocyanurate, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, and 3-isocyanatepropyltriethoxysilane.

[0017] The thickness of the coating layer may be about 0.5 μm or more and 2 μm or less.

[0018] The content of the inorganic particles relative to the total weight of the coating layer may be about 80 weight% or more and 95 weight% or less.

[0019] The above-described separator for the electrochemical device may further include an adhesive layer formed on the surface of the coating layer.

[0020] One aspect of the present invention provides an electrochemical device comprising an anode, a cathode, and a separator disposed between the anode and the cathode, wherein the separator is a separator for another electrochemical device according to the one aspect.

[0021] The above electrochemical device may be a lithium secondary battery.

[0022]

[0023] The separator for an electrochemical device according to the present invention includes a hydrophobic coating layer and can provide low moisture content and reduced resistance.

[0024]

[0025] Hereinafter, each component of the present invention is described in more detail so that a person skilled in the art to which the present invention pertains can easily implement it; however, this is merely an example, and the scope of the rights of the present invention is not limited by the following.

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

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

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

[0029] As used in this specification, “aspect ratio” refers to the value obtained by dividing the length of a fiber by its diameter in a fibrous material, such as cellulose nanofiber, in which the diameter and length of the fiber can be measured. The length, diameter, and aspect ratio of the fiber can be measured using a scanning electron microscope, and the aspect ratio refers to the average of the aspect ratios measured for any 20 samples measured using the scanning electron microscope.

[0030] Although the present invention has been described below by way of examples, the present invention is not limited thereto and may include a combination of one or more configurations of specific examples and examples by those skilled in the art to which the present invention belongs, and various modifications and variations are possible within the scope of the technical spirit of the present invention and the equivalent scope of the claims described below.

[0031] A separator of a lithium secondary battery may include a coating layer comprising a polymer binder and inorganic particles on at least one surface of a porous substrate. The inorganic particles may be connected to other inorganic particles by the polymer binder to form an interstitial volume, and lithium ions may pass through the interstitial volume to move between the positive and negative electrodes. In addition to fixing the inorganic particles, the polymer binder may impart adhesion to the coating layer, and the coating layer may adhere to the porous substrate and the electrode, respectively.

[0032] The thinner the separator of a lithium secondary battery, the higher the energy density of the battery; accordingly, thinning the separator is required to increase the energy density of lithium secondary batteries. Cellulose nanofibers (CNFs) are nano-sized fibers formed by the bonding of cellulose chains, possessing excellent tensile strength while simultaneously having low density. When used for separator coatings, cellulose nanofibers not only allow for the utilization of their excellent mechanical properties but also facilitate the realization of thin films, making them a material of interest for separator coatings. Nevertheless, due to their high hydrophilicity, cellulose nanofibers present a problem where the moisture content of the separator increases when included in a coating layer. As the moisture content of the separator increases, it hinders the movement of lithium ions within the secondary battery, leading to a problem of increased electrical resistance.

[0033] Considering these points, the present invention provides a technology that secures a coating layer capable of realizing a thin film of a separation membrane by compensating for the moisture vulnerability of cellulose nanofibers.

[0034] The present invention provides a separator for an electrochemical device comprising a porous substrate and a coating layer formed on at least one surface of the porous substrate, wherein the coating layer comprises inorganic particles, a polymer binder, and cellulose nanofibers (CNF), and wherein the cellulose nanofibers (CNF) are introduced with lithium ions and silane components.

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

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

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

[0038] The thickness of the porous substrate may be approximately 1 μm or more and 100 μm or less. For example, the thickness of the porous substrate may be approximately 10 μm or more and 90 μm or less, 20 μm or more and 80 μm or less, 30 μm or more and 70 μm or less, or 40 μm or more and 60 μm or less. According to one embodiment, the thickness of the porous substrate may be approximately 1 μm or more and 30 μm or less. Alternatively, the thickness of the porous substrate may be approximately 5 μm or more and 15 μm or less, or approximately 8 μm or more and 13 μm or less. By controlling the thickness of the porous substrate within the above-described range, the volume of the electrochemical device can be minimized while electrically insulating the anode and the cathode, thereby increasing the amount of active material included in the electrochemical device.

[0039] The porous substrate may include pores with an average diameter of about 0.01 μm or more and 1 μm or less. For example, the size of the pores included in the porous substrate may be about 0.01 μm or more and 0.09 μm or less, 0.02 μm or more and 0.08 μm or less, 0.03 μm or more and 0.07 μm or less, or 0.04 μm or more and 0.06 μm or less. For example, the size of the pores may be about 0.02 μm or more and 0.06 μm or less. By controlling the pore size of the porous substrate within the above-described range, the air permeability and ion conductivity of the entire separation membrane being manufactured can be controlled.

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

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

[0042] The porous substrate may have a porosity of about 10 vol% or more and 60 vol% or less. For example, the porosity of the porous substrate may be about 15 vol% or more and 55 vol% or less, 20 vol% or more and 50 vol% or less, 25 vol% or more and 45 vol% or less, or 30 vol% or more and 40 vol% or less. According to one embodiment, the porosity of the porous substrate may be about 30 vol% or more and 50 vol% or less. When the porosity of the porous substrate is within the range described above, the ion conductivity of the manufactured separator may be provided within a range suitable for securing the output and cycle characteristics of the electrochemical device.

[0043] The above porosity refers to the ratio of the volume of pores to the total volume of the porous substrate. The above porosity can be measured by methods known in the art. For example, it can be measured by the BET (Brunauer Emmett Teller) measurement method using nitrogen gas adsorption, the capillary flow porometer, or the water or mercury infiltration method.

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

[0045] The dispersion medium may be one selected from water, ethanol, acetone, isopropyl alcohol (IPA), dimethylacetamide (DMAc), dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), acetonitrile, and combinations thereof. According to one embodiment, the dispersion medium may be a mixture of water and isopropyl alcohol or water. Using the above-described type of dispersion medium, a coating layer in which inorganic particles, a polymer binder, and cellulose nanofibers are uniformly dispersed can be formed.

[0046] The coating slurry may further include additives such as dispersants, surfactants, defoaming agents, and flame retardants to improve dispersibility and flame retardancy and to improve the uniformity of the coating layer formed. For example, the dispersant may include one or more selected from polyacrylic acid, oil-soluble polyamines, oil-soluble amine compounds, fatty acids, fatty alcohols, sorbitan fatty acid esters, tannic acid, and pyrogallic acid. By using a dispersant of the type described above, the stability of the coating slurry can be improved and the uniformity of the coating layer formed by the coating slurry can be ensured.

[0047] Based on the total weight of the coating slurry, the additive may be included in an amount of about 0% by weight or more and 5% by weight or less. For example, the content of the additive may be about 0.01% by weight or more and 4% by weight or less, about 0.1% by weight or more and 3% by weight or less, or about 1% by weight or more and 2% by weight or less. For example, the content of the additive may be about 1% by weight or more and 5% by weight or less. By controlling the content of the additive within the above-described range, uniform dispersion and stability of the inorganic particles included in the coating slurry can be achieved.

[0048] The dispersion medium included in the coating slurry may be removed by drying or heating after the formation of the coating layer. During the process of removing the dispersion medium, multiple pores may be formed on the surface and inside the coating layer. The pores may include interstitial volumes formed between inorganic particles and may have a structure that allows fluid to pass through by forming a three-dimensional network.

[0049] The polymer binder can bind inorganic particles included in the coating layer and impart adhesion to the coating layer. 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 its particle shape in the coating slurry and the 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 binder may be one or more selected from polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, and polyvinylidene fluoride-trichloroethylene.

[0050] The above inorganic particles may be electrochemically stable. The above inorganic particles may be used within the operating voltage range of the electrochemical device (e.g., Li / Li). +There are no particular limitations as long as oxidation and / or reduction reactions do not occur at a voltage of 0 to 5V. When inorganic particles with a high dielectric constant are used as inorganic particles, the ionic conductivity of the electrolyte can be improved by contributing to an increase in the degree of dissociation of electrolyte salts, such as lithium salts, within the liquid electrolyte. For the reasons stated above, the inorganic particles may include high dielectric constant inorganic particles having a dielectric constant of about 5 or more, for example, about 10 or more. Non-limiting examples of inorganic particles with a dielectric constant of about 5 or more include BaTiO3, Pb(Zr,Ti)O3 (PZT), and Pb 1-x La x Zr 1-y Ti y O3(PLZT, 0 <x<1, 0<y<1), Pb(Mg 1 / 3 Nb 2 / 3 There are O3-PbTiO3(PMN-PT), HfO2, SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, Al(OH)3, SiC, AlOOH, TiO2, or mixtures thereof.

[0051] In addition, as inorganic particles, inorganic particles having lithium ion transport capability may be used; that is, inorganic particles containing lithium elements that do not store lithium but have the function of transporting lithium ions. Non-limiting examples of inorganic particles having lithium ion transport capability include lithium phosphate (Li3PO4) and lithium titanium phosphate (Li x Ti y (PO4)3, 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z (PO4)3, 0 < x < 2, 0 < y < 1, 0 < z < 3), such as (LiAlTiP) 14Li2O-9Al2O3-38TiO2-39P2O5 x O ySeries glass (0 <x < 4, 0 < y < 13), 리튬란탄티타네이트(Li x La y TiO3, 0 < x <2, 0 <y <3), Li 3.25 Ge 0.25 P 0.75 Lithium germanium thiophosphate (Li) such as S4, etc. x Ge y P z S w Lithium nitrides such as , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), Li3N, etc. (Li x N y , 0 < x < 4, 0 < y < 2), SiS2 series glass such as Li3PO4-Li2S-SiS2 (Li x Si y S z , 0 < x < 3, 0 <y < 2, 0 < z < 4), LiI-Li2S-P2S5등과 같은 P2S5계열 glass(Li x P y S z , 0 < x < 3, 0 < y < 3, 0 < z < 7) or mixtures thereof, etc.

[0052] In addition, as inorganic particles, flame-retardant inorganic particles can be used to impart flame-retardant properties to the separator or to prevent a rapid rise in temperature inside the electrochemical device. Non-limiting examples of flame-retardant inorganic particles include Sb2O3, Sb2O4, Sb2O5, SrTiO3, SnO2, CeO2, MgO, Mg(OH)2, NiO, CaO, ZnO, Zn2SnO4, ZnSnO3, ZnSn(OH)6, ZrO2, Y2O3, SiO2, Al2O3, AlOOH, Al(OH)3, SiC, TiO2, H3BO3, HBO2, and mixtures thereof.

[0053] The average particle size (D50) of the inorganic particles may be approximately 50 nm or more and 4,000 nm or less. For example, the average particle size (D50) of the inorganic particles may be approximately 100 nm or more and 3,500 nm or less, 200 nm or more and 3,000 nm or less, 300 nm or more and 2,000 nm or less, 400 nm or more and 1,000 nm or less, or 400 nm or more and 800 nm or less. If the average particle size of the inorganic particles is less than 50 nm, as the specific surface area increases, an additional polymer binder is required for bonding between the inorganic particles, which may be disadvantageous in terms of electrical resistance. If the average particle size of the inorganic particles exceeds 4,000 nm, the uniformity of the coating layer surface is reduced, which may cause damage to the porous substrate or electrode during lamination, and the thickness of the coating layer becomes thicker, making it difficult to achieve thin film formation.

[0054] The above cellulose nanofibers (CNF) exhibit excellent physical properties, such as tensile strength and elastic modulus, relative to their low density. When the above cellulose nanofibers (CNF) are included in a coating layer, excellent mechanical strength can be imparted to the separation membrane even in small amounts. Furthermore, due to the fiber bundle form with a large surface area, the above cellulose nanofibers (CNF) can improve the dispersibility of solid components, including inorganic particles, within the coating slurry. Additionally, the above cellulose nanofibers (CNF) can evenly bind inorganic particles within the coating layer, thereby enabling the realization of a thin coating layer and achieving thin film formation of the separation membrane. Moreover, the above cellulose nanofibers (CNF) have excellent heat resistance, which can mitigate the problem of thermal shrinkage that may occur in thin coating layers.

[0055] The above cellulose nanofiber (CNF) may have metal ions introduced into it. For example, the above cellulose nanofiber (CNF) may have lithium ions introduced into it. The above cellulose nanofiber (CNF) may have lithium ions ionically bonded to at least one end functional group. The lithium ion-bonded cellulose nanofiber (CNF) can improve the ion conductivity of the separator and lower the resistance, and can improve the output and cycle characteristics of the electrochemical device.

[0056] According to one embodiment, the cellulose nanofiber (CNF) may be a modified form of at least a portion of the cellulose. The cellulose nanofiber (CNF) may have a functional group substituted at least at one end through surface modification, and metal ions can be easily introduced through the substituted functional group. The cellulose nanofiber (CNF) may be oxidized, carboxymethylated, or phosphorylated. For example, the surface of the cellulose nanofiber (CNF) may be modified by TEMPO (2,2,6,6-tetramethylpipiridine-1-oxyl radical) catalytic oxidation, carboxymethylation, or phosphorylation. For example, the cellulose nanofiber (CNF) may have one end substituted with a negatively charged carboxyl group by TEMPO catalytic oxidation. When the TEMPO catalytically oxidized cellulose nanofiber (CNF) comes into contact with lithium ions, the lithium ions combine with the carboxyl group to form lithium carboxylate (COO). - Li + It can be introduced in the form of ).

[0057] According to one embodiment, the cellulose nanofiber (CNF) may have a silane component introduced therein. The cellulose nanofiber (CNF) had a problem of increasing the moisture content of the separator due to high hydrophilicity caused by terminal hydroxyl groups or substituted carboxyl groups. The cellulose nanofiber (CNF) had a problem of impregnating moisture into the separator during the manufacture of the separator, the manufacture of the electrochemical device, or storage, thereby impairing the lifespan of the electrochemical device. The cellulose nanofiber (CNF) may have a moiety containing a silane group attached through at least one terminal functional group. The cellulose nanofiber (CNF) with the silane group introduced therein can improve the vulnerability of the separator to moisture by imparting hydrophobicity through the silane group. For example, the silane can impart hydrophobicity to the surface of the cellulose nanofiber (CNF) by coupling with one or more terminal hydroxyl groups of the cellulose nanofiber (CNF).

[0058] The above silane may be a substance in which organic functional groups including amino groups, vinyl groups, methacrylic groups, acrylic groups, isocyanate groups, mercapto groups, epoxy groups, etc. are substituted on methyltrimethoxysilane (MTMS), tetraethoxysilane (TEOS), methyltriethoxysilane (MTES), and dimethyldiethoxysilane (DMDS), which are classified according to hydrolytic groups. For example, the silane is N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane hydrochloride, vinyltrimethoxysilane, vinyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, p-styryltrimethoxysilane, It may be one or more selected from 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, tris-(trimethoxysilylpropyl)isocyanurate, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, and 3-isocyanatepropyltriethoxysilane. By appropriately using the above-mentioned types of silanes to modify the surface of the cellulose nanofibers, the moisture content of the separation membrane can be reduced and the resistance improved.

[0059] According to one embodiment, the cellulose nanofiber (CNF) may have lithium ions and silane introduced into it. The cellulose nanofiber (CNF) may have lithium ions and silane introduced in a molar ratio of about 5:1 to 25:1. For example, the cellulose nanofiber (CNF) may have lithium ions and silane in a ratio of about 6:1 to 25:1, 7:1 to 25:1, 10:1 to 25:1, 5:1 to 22:1, 6:1 to 22:1, 7:1 to 22:1, 10:1 to 22:1, 15:1 to 25:1, 15:1 to 22:1, or 20:1 to 22:1. If less silane is introduced than the above-described range, moisture vulnerability increases, which may increase the electrical resistance of the electrochemical device and degrade the cycle characteristics. If silane is introduced excessively beyond the range described above, the intrinsic tensile strength and elasticity of the cellulose nanofiber (CNF) may decrease, thereby reducing mechanical properties including the puncture strength of the separator. By introducing lithium ions and silane into the cellulose nanofiber (CNF) in the molar ratio of the range described above, excellent mechanical properties of the cellulose nanofiber (CNF) are maintained, while hydrophobicity is imparted, thereby providing a separator with low resistance resulting from reduced moisture content.

[0060] The average diameter of the cellulose nanofiber (CNF) may be approximately 5 nm or more and 50 nm or less. For example, the average diameter of the cellulose nanofiber (CNF) may be approximately 5 nm or more, 10 nm or more, 15 nm or more, 20 nm or more, 25 nm or more, 30 nm or less, 35 nm or less, 40 nm or less, 45 nm or less, or 50 nm or less. When the average diameter of the cellulose nanofiber (CNF) satisfies the above-described range, the pores of the coating layer are not shielded, resulting in excellent air permeability and reduced electrical resistance of the separator. Additionally, when the average diameter of the cellulose nanofiber (CNF) satisfies the above-described range, it may be easy to introduce lithium ions and silane components onto the surface due to the high surface area.

[0061] The average length of the cellulose nanofiber (CNF) may be approximately 1 μm or more and 10 μm or less. For example, the average length of the cellulose nanofiber (CNF) may be approximately 1 μm or more, 2 μm or more, 3 μm or more, 4 μm or more, 5 μm or more, 6 μm or less, 7 μm or less, 8 μm or less, 9 μm or less, or 10 μm or less. When the average length of the cellulose nanofiber (CNF) satisfies the above-described range, it may have excellent dispersibility together with inorganic particles and polymer binders in the coating slurry, and the air permeability of the separation membrane may be excellent as it does not block pores when forming the coating layer.

[0062] The aspect ratio of the cellulose nanofiber (CNF) may be approximately 50 to 200. For example, the aspect ratio of the cellulose nanofiber (CNF) may be approximately 50 or more, 60 or more, 70 or more, 80 or more, 90 or more, 100 or more, 110 or less, 120 or less, 140 or less, 160 or less, 180 or less, or 200 or less. When the aspect ratio of the cellulose nanofiber (CNF) satisfies the above-described range, the mechanical properties may be excellent by preventing aggregation of the cellulose nanofiber, and lithium ions and silane components can be easily introduced into the cellulose nanofiber (CNF).

[0063] The content of the inorganic particles relative to the total weight of the coating layer may be about 80 weight% or more and 95 weight% or less. For example, for 100 weight% of the coating layer, the content of the inorganic particles may be about 80 weight% or more and 95 weight% or less, 81 weight% or more and 94 weight% or less, 82 weight% or more and 93 weight% or less, 83 weight% or more and 92 weight% or less, 84 weight% or more and 91 weight% or less, 85 weight% or more and 90 weight% or less, 86 weight% or more and 89 weight% or less, or 87 weight% or more and 88 weight% or less. According to one embodiment, for 100 weight% of the coating layer, the content of the inorganic particles may be about 85 weight% or more and 95 weight% or less, or 90 weight% or more and 95 weight% or less. A coating layer satisfying the above-described range can bond with the porous substrate to minimize thermal shrinkage of the porous substrate.

[0064] The coating layer may contain the cellulose nanofiber (CNF) in an amount of about 1% by weight or more and 15% by weight or less. For example, the coating layer may contain the cellulose nanofiber (CNF) in an amount of about 1% by weight or more and 15% by weight or less, 1% by weight or more and 10% by weight or less, 1% by weight or more and 8% by weight or less, 1% by weight or more and 6% by weight or less, 1% by weight or more and 5% by weight or less, 3% by weight or more and 15% by weight or less, 3% by weight or more and 10% by weight or less, 3% by weight or more and 8% by weight or less, 3% by weight or more and 6% by weight or less, or 3% by weight or more and 5% by weight or less. A coating layer satisfying the above-described range can be formed with a thin thickness, enabling thin film formation, and at the same time, can have excellent mechanical strength. In addition, if the above-mentioned range is satisfied, the cellulose nanofibers (CNF) dispersed within the coating layer can easily bond with inorganic particles, a porous substrate, and electrodes, thereby improving the adhesion of the separator.

[0065] The thickness of the coating layer may be approximately 0.5 μm or more and 2 μm or less. For example, the thickness of the coating layer may be approximately 0.5 μm or more and 1.75 μm or less, 0.5 μm or more and 1.5 μm or less, 0.5 μm or more and 1.25 μm or less, or 0.5 μm or more and 1 μm or less. By controlling the thickness of the coating layer within the above-described range, lithium ions can easily pass through the coating layer, thereby reducing the resistance of the separator. By controlling the thickness of the coating layer within the above-described range, the mechanical strength of the porous substrate is supplemented, and a thin film of the separator is realized, thereby enabling the realization of an electrochemical device with high energy density.

[0066] The separator for the electrochemical device described above may further include an adhesive layer formed on the surface of the coating layer. The adhesive layer covers at least a portion of the surface of the coating layer and can impart adhesion to the electrode to the separator. The adhesive layer may be formed by additionally applying and drying an adhesive layer forming slurry containing a polymer binder for the adhesive layer onto the surface of the coating layer formed by drying the aforementioned coating slurry. The application may be performed using a bar coater, wire bar coater, roll coater, spray coater, spin coater, inkjet coater, screen coater, reverse coater, gravure coater, knife coater, slot die coater, hot melt coater, comma coater, direct metering coater, etc., but is not limited thereto. According to one embodiment, the adhesive layer may be formed by spraying and drying the adhesive layer forming slurry. The adhesive layer may cover approximately 20% to 80% of the surface of the coating layer.

[0067] The polymer binder for the adhesive layer may be the same as or different from the polymer binder. According to one embodiment, the polymer binder for the adhesive layer may be a fluorine-based binder, an acrylic binder, or a mixture thereof. For example, the fluorine-based binder may be a particulate polyvinylidene fluoride-based binder. Alternatively, the adhesive layer may include both a fluorine-based binder and an acrylic binder to stably maintain adhesion to the electrode of the separator in both a dry state without an electrolyte and a wet state in which the separator is impregnated with an electrolyte. For example, the adhesive layer may include a fluorine-based binder and an acrylic binder as the polymer binder for the adhesive layer in a weight ratio of approximately 2:8 to 8:2, 3:7 to 7:3, or 4:6 to 6:4. The thickness of the adhesive layer is formed to be smaller than the thickness of the coating layer, thereby providing electrode adhesion while minimizing the reduction in air permeability of the separator.

[0068]

[0069] The separator for the electrochemical device described above may have an electrical resistance of about 0.60 Ohm or less. For example, the electrical resistance of the separator for the electrochemical device described above may be about 0.40 Ohm or more, 0.45 Ohm or more, 0.49 Ohm or more, 0.60 Ohm or less, 0.65 Ohm or less, 0.70 Ohm or less, 0.75 Ohm or less, or 0.80 Ohm or less. When the electrical resistance of the separator for the electrochemical device described above is within the range described above, the output of the electrochemical device is excellent and cycle characteristics can be secured.

[0070] The separator for the electrochemical device described above may have an air permeability of approximately 80 s / 100cc or more and 105 s / 100cc or less. For example, the air permeability of the separator for the electrochemical device described above may be approximately 85 s / 100cc or more and 105 s / 100cc or less, or 85 s / 100cc or more and 100 s / 100cc or less. When the separator for the electrochemical device is within the range described above, the output, stability, and cycle characteristics of the electrochemical device can be secured.

[0071] The above-mentioned separator for an electrochemical device may have a puncture strength of approximately 400 gf or more. For example, the puncture strength of the above-mentioned separator for an electrochemical device may be approximately 420 gf or more, 450 gf or more, 460 gf or more, 470 gf or more, 500 gf or more, 700 gf or less, or 670 gf or less. The above-mentioned puncture strength refers to the resistance of the separator to penetration by an external object. The above-mentioned puncture strength can be tested, for example, by penetrating the separator vertically at a predetermined speed with a needle or pin having a predetermined diameter, and measuring the force applied when the separator is penetrated using ASTM D5748-95 and ASTM D4649.

[0072] The above-described separator for an electrochemical device may have a moisture content of about 1700 ppm or less. For example, the above-described separator for an electrochemical device may have a moisture content of about 1600 ppm or less, 1500 ppm or less, 1300 ppm or less, 1100 ppm or less, 500 ppm or more, 700 ppm or more, or 800 ppm or more. When the moisture content of the above-described separator for an electrochemical device is within the above-described range, lithium ions can easily pass through when impregnated with an electrolyte, thereby reducing the electrical resistance of the electrochemical device and improving output, stability, and cycle performance.

[0073] The above moisture content may refer to the amount of moisture impregnated into the separator during the manufacture of the separator with the coating layer formed, the manufacture of the electrochemical device, or storage. The above moisture content may be measured by the Karl Fischer method. For example, the above moisture content may be measured using a Karl Fischer moisture meter from Metrohm, etc.

[0074] The separator for the electrochemical device described above may have a water contact angle of approximately 90° or more. For example, the separator for the electrochemical device may have a water contact angle of approximately 95° or more, 100° or more, 105° or more, 110° or more, 120° or more, 130° or more, 180° or less, or 150° or less. When the water contact angle of the separator for the electrochemical device is within the range described above, hydrophobic properties are imparted to the coating layer, thereby reducing the moisture content of the separator and reducing the cell resistance value of the electrochemical device.

[0075] The above water contact angle may be measured, for example, by a static contact angle measurement method according to the Sessil Drop Method or by a dynamic contact angle measurement method according to the Tilting Drop Method, Captive Drop Method, or Whilhelmy Plate Method, but is not limited thereto. The above water contact angle may be measured by using commonly used contact angle measuring equipment to measure the contact angle of a water droplet that is maintained even after a predetermined period of time has elapsed under room temperature conditions.

[0076]

[0077] A method for manufacturing a separator for an electrochemical device according to one embodiment of the present invention comprises the steps of: preparing a slurry for a coating layer comprising inorganic particles, a polymer binder, cellulose nanofibers (CNF), and a dispersion medium; forming a coating layer by coating at least one surface of a porous substrate with the slurry for the coating layer; and manufacturing a separator by drying the coating layer and removing the dispersion medium. Any content overlapping with that described in the description of the separator for an electrochemical device is replaced by the description of the preceding embodiment.

[0078] The step of preparing the slurry for the coating layer may further include the step of introducing lithium ions and silane components into the cellulose nanofiber (CNF). For example, the step of introducing the lithium ions and silane components may involve contacting the cellulose nanofiber (CNF) with the lithium ions and silane under a dispersion medium. According to one embodiment, the step of introducing the lithium ions and silane components may involve adding a lithium compound and a silane compound to a dispersion of cellulose nanofiber (CNF) and stirring. The lithium compound may be, for example, lithium hydroxide or lithium carbonate, but other lithium compounds known in the art may also be used. By adjusting the weight ratio of the lithium compound and the silane compound, the lithium ions and silane may be introduced into the cellulose nanofiber (CNF) in a molar ratio within the range described above.

[0079] The step of coating with the above-described coating layer slurry involves coating at least one surface of a porous substrate with a coating slurry comprising a polymer binder, inorganic particles, and a dispersion medium. For example, the coating may be formed by methods such as a bar coater, wire bar coater, roll coater, spray coater, spin coater, inkjet coater, screen coater, reverse coater, gravure coater, knife coater, slot die coater, hot melt coater, comma coater, direct metering coater, etc., but is not limited thereto. According to one embodiment, the step of coating with the above-described coating layer slurry may involve coating a cross-section of the porous substrate or simultaneously coating both sides using a bar coater or a slot die coater with the coating slurry.

[0080] The step of coating with the slurry for the coating layer may further include the step of corona discharge treatment of at least one surface of the porous substrate. For example, the coating slurry may be coated onto the porous substrate after the corona discharge treatment step. The step of corona discharge treatment of at least one surface of the porous substrate prevents a decrease in the bonding strength between the surface of the porous substrate and the surface of the coating layer at high temperatures, and can prevent or suppress a decrease in the bonding strength between the surface of the porous substrate and the surface of the coating layer caused by the electrolyte.

[0081] The corona discharge treatment may involve treating at least one surface of the porous substrate with a voltage of about 0.1 kV to 10 kV in air. For example, the corona discharge treatment may involve treating with a voltage of about 0.2 kV to 9 kV, 0.3 kV to 8 kV, 0.4 kV to 7 kV, 0.5 kV to 6 kV, 0.6 kV to 5 kV, 0.7 kV to 4 kV, 0.8 kV to 3 kV, 0.9 kV to 2 kV, or 1.0 kV to 2 kV in air. According to one embodiment, the corona discharge treatment may involve treating with a voltage of about 1.8 kV in air. By adjusting the applied voltage of the corona discharge treatment within the above-described range, appropriate waterway functional groups can be formed on the surface of the porous substrate, and damage to the surface of the porous substrate can be prevented.

[0082] The step of manufacturing a separation membrane by drying the slurry for the coating layer and removing the dispersion medium may involve drying or heating the coating layer to evaporate the dispersion medium contained within the coating layer. The removal of the dispersion medium may be performed at a temperature that allows only the dispersion medium contained within the coating layer to evaporate without deforming the polymer binder contained within the coating layer. For example, the removal of the dispersion medium may involve heating the coating layer to a predetermined temperature, provided that the surface temperature of the coating layer does not exceed approximately 60°C. When heating the coating layer under these conditions, thermal energy may first be used to heat the dispersion medium to cause a phase change, and may not be used to deform the polymer binder.

[0083]

[0084] The method for manufacturing a separator for an electrochemical device may further include the step of forming an adhesive layer by applying a slurry for forming an adhesive layer to the surface of the coating layer and drying it. For example, a coating layer may be formed by drying the slurry for the coating layer and removing the dispersion medium, and then applying a slurry for forming an adhesive layer onto the surface of the coating layer and drying it to form an adhesive layer.

[0085] A cylindrical lithium secondary battery according to one embodiment of the present invention is an electrochemical device comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein the separator is a separator for an electrochemical device according to the aforementioned embodiment. The cylindrical lithium secondary battery can be manufactured by inserting an electrode assembly comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode into a battery case and sealing it. Before sealing the battery case, an electrolyte may be injected to impregnate the electrode assembly with the electrolyte. In this embodiment, a cylindrical lithium secondary battery is exemplified as the electrochemical device, but the present invention is not limited thereto and may include other types of secondary batteries; for example, the electrochemical device may be a cylindrical, prismatic, coin-type, or pouch-type lithium secondary battery.

[0086] 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.

[0087] The above-described positive electrode comprises a positive current collector and a positive active material layer comprising a positive active material, a conductive material, and a binder resin on at least one surface of the current collector. The positive active material is a layered compound such as a lithium manganese complex oxide (LiMn2O4, LiMnO2, etc.), lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2, etc.; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7, etc.; chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x = 0.01 ~ 0.3); chemical formula LiMn 1-x M xIt may include a lithium manganese complex oxide represented by O2 (where M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn); LiMn2O4 in which part of the Li of the chemical formula is substituted with alkaline earth metal ions; a disulfide compound; and one or more of Fe2(MoO4)3.

[0088] 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 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; Sn x Me 1-x Me y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Group 1, 2, and 3 elements of the periodic table, halogens; 0 <x≤1; 1≤y≤3; 1≤z≤8) 등의 금속 복합 산화물; 리튬 금속; 리튬 합금; 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.

[0089] The conductive material may be any one selected from graphite, carbon black, carbon fiber or metal fiber, metal powder, conductive whiskers, conductive metal oxide, carbon nanotubes, activated carbon, and polyphenylene derivatives, or a mixture of two or more of these conductive materials. According to one embodiment, the conductive material may be one selected from natural graphite, artificial graphite, acetylene black, channel black, furnace black, lamp black, thermal black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium oxide, or a mixture of two or more of these conductive materials.

[0090] As the above binder resin, a binder resin commonly used in the electrodes of electrochemical devices can be used. Non-limiting examples of such binder resins include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-cotrichloroethylene, polymethylmethacrylate, polyethylhexyl acrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate. Examples include acetatepropionate), cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxyl methyl cellulose, but are not limited thereto.

[0091] The above electrolyte is A + B - As a salt with a structure like that, A + is Li + , Na +, K + It includes alkali metal cations such as or ions composed of combinations thereof, and B - is PF6 - , BF4 - , Cl - , Br - , I - , ClO4 - , AsF6 - , CH3CO2 - , CF3SO3 - , N(CF3SO2)2 - , C(CF2SO2)3 - A salt comprising an anion such as or a combination thereof may be dissolved or dissociated in an organic solvent comprising propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethyl carbonate (EMC), gamma butyrolactone, or a mixture thereof, but is not limited thereto.

[0092] The electrochemical device including the above electrode assembly can be used as a unit cell, and can be used as a battery module including the unit cell, a battery pack including the battery module, or a device including the battery pack as a power source. Examples of such devices include small devices such as computers, mobile phones, and power tools; electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs) that are powered by an electric motor; electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters (E-scooters); electric golf carts; and medium-to-large devices such as power storage systems, but are not limited thereto.

[0093]

[0094] The present invention will be explained in more detail below through examples and experimental examples. The following examples and experimental examples are intended to illustrate the present invention, and the present invention is not limited by the following examples and experimental examples.

[0095]

[0096] Example 1

[0097] Preparation of Cellulose Nanofibers (CNF)

[0098] TEMPO-oxidized cellulose nanofibers (CNF) (average diameter 25 nm, average length 5 μm) were prepared. Lithium hydroxide (LiOH·H2O, Deoksan General Science) was prepared as a material for introducing lithium ions. 3-aminopropyltriethoxysilane (Sigma Aldrich) (hereinafter referred to as “APTES”) was prepared as a silane material.

[0099] The cellulose nanofibers (CNF) prepared above were dispersed in distilled water (DI water) to prepare a cellulose nanofiber dispersion. Lithium hydroxide and APTES were added to the dispersion in a molar ratio of 20:1, and lithium ions and silane were introduced into the cellulose nanofibers (CNF) by stirring at 30°C for 5 minutes (sonication). After stirring was finished, the cellulose nanofibers (CNF) were filtered, washed with ethanol, and dried at 60°C to prepare Li-CNF-APTES. XPS analysis of the Li-CNF-APTES confirmed that lithium ions and APTES were bound to the surface of the cellulose nanofibers (CNF).

[0100] Preparation of coating slurry

[0101] Al2O3 (particle size: 400 nm) was prepared as an inorganic particle, and PVdF (thermo scientific chemical) was prepared as a polymer binder. The inorganic particles, polymer binder, and Li-CNF-APTES were added to distilled water in a weight ratio of 94:3:3, and then stirred for 60 minutes to prepare a coating slurry.

[0102] Preparation of porous substrate

[0103] As a porous substrate, polyethylene resin is extruded and manufactured by a wet method, (MI: 0.2 g / 10 min, T m A polyethylene film with a thickness of 10 μm was used, having a temperature of 135°C, a porosity of 45%, and an average pore size of 45 nm.

[0104] Manufacturing of separation membranes

[0105] The coating slurry was coated on one side of a polyethylene film using a bar coating method with a doctor blade. A low-temperature airflow was applied to the film coated with the coating slurry, and the process of drying and removing the dispersion medium was repeated 5 times while controlling the surface temperature of the coating layer so as not to exceed 50℃ to form a coating layer with a thickness of 2 μm.

[0106] Example 2

[0107] A separator was prepared in the same manner as in Example 1, except that in Example 1, the polyethylene film was coated on both sides with a coating thickness of 1 μm each.

[0108] Example 3

[0109] A separator was prepared in the same manner as in Example 1, except that in Example 1, the polyethylene film was coated on both sides with a coating thickness of 0.5 μm each.

[0110] Example 4

[0111] A separation membrane was prepared in the same manner as in Example 1, except that inorganic particles, a polymer binder, and Li-CNF-APTES were added in a weight ratio of 88:2:10 when preparing the coating slurry in Example 1.

[0112] Example 5

[0113] A separator was prepared in the same manner as in Example 1, except that lithium hydroxide and APTES were added in a 10:1 molar ratio when preparing the cellulose nanofibers in Example 1.

[0114] Example 6

[0115] A separation membrane was prepared in the same manner as in Example 1, except that tetraethoxysilane (TEOS) (Sigma Aldrich) was used as the silane material in Example 1.

[0116] Example 7

[0117] A separator was prepared in the same manner as in Example 1, except that lithium hydroxide and APTES were added in a 4:1 molar ratio when preparing the cellulose nanofiber (CNF) in Example 1.

[0118] Comparative Example 1

[0119] A separation membrane was prepared in the same manner as in Example 1, except that a coating slurry containing inorganic particles and a polymer binder in a weight ratio of 95:5 was used instead of using cellulose nanofibers (CNF).

[0120] Comparative Example 2

[0121] A separation membrane was prepared in the same manner as in Example 2, except that a coating slurry containing inorganic particles and a polymer binder in a weight ratio of 95:5 was used instead of using cellulose nanofibers (CNF).

[0122] Comparative Example 3

[0123] A separation membrane was prepared in the same manner as in Example 3, except that a coating slurry containing inorganic particles and a polymer binder in a weight ratio of 95:5 was used instead of using cellulose nanofibers (CNF).

[0124] Comparative Example 4

[0125] A separator was prepared in the same manner as in Example 1, except that cellulose nanofibers (CNF) without lithium ions and silanes were used in Example 1.

[0126] Comparative Example 5

[0127] A separator was prepared in the same manner as in Example 2, except that cellulose nanofibers (CNF) without lithium ions and silanes were used in Example 2.

[0128] Comparative Example 6

[0129] A separation membrane was prepared in the same manner as in Example 1, except that Li-CNF prepared without adding APTES to the cellulose nanofiber dispersion in Example 1 was used.

[0130] Comparative Example 7

[0131] A separation membrane was prepared in the same manner as in Example 2, except that Li-CNF prepared without adding APTES to the cellulose nanofiber dispersion in Example 2 was used.

[0132]

[0133] Experimental Example. Confirmation of membrane properties

[0134] Air permeability measurement

[0135] Using a Gurley densometer (Gurley, 4110N), 100 cc of air with a diameter of 28.6 mm and an area of ​​645 mm 2 The time taken to pass through the separation membrane was measured.

[0136] Water contact angle measurement

[0137] After dropping 1 µl of water onto the surface of the membranes of the examples and comparative examples, the water contact angle at room temperature was measured using a contact angle measuring device (Biolin Scientific Attension Theta Flex).

[0138] Moisture content measurement

[0139] After sampling the membranes of the examples and comparative examples at a weight of 0.07 g, the moisture content was measured using a moisture measuring device (831 Coulometer, Metrohm) under conditions of 120°C and N2 flow rate of 60 ml / min.

[0140] Electrical resistance measurement

[0141] Coin cells were prepared by interposing the separators of the examples and comparative examples, respectively, between SUS. An electrolyte containing 1M LiPF6 and mixed with ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1:2 was injected into the coin cells. To measure the resistance of the coin cells, the resistance was measured using the results of electrochemical impedance spectroscopic analysis with a VMP3 from BioLogic Science Instrument at 25°C under conditions of Amplitude 10 mV and Scan range 0.1 Hz to 1 MHz.

[0142] Verification of electrochemical device lifespan characteristics

[0143] After weighing the lithium manganese-based composite oxide (LiMnO2):conductive material (Denka black):binder (PVdF) in a weight ratio of 95:2.5:2.5, the mixture was added to N-methylpyrrolidone (NMP) and mixed to prepare a positive electrode active material slurry, and the positive electrode active material slurry was coated to a thickness of 100 μm onto a 20 μm thick aluminum foil, followed by rolling and drying to produce a positive electrode.

[0144] A Li metal plate with a thickness of 100 μm was used as the cathode, and the anode and cathode were laminated with the separator of the example or comparative example in between, and then inserted into an aluminum pouch.

[0145] A coin cell was manufactured by injecting an electrolyte containing 1 mol of the lithium salt LiPF6 into a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a volume ratio of 1 / 1 into the above aluminum pouch.

[0146] The above coin cell was charged and discharged once at 1.0 C in a 60°C chamber in a voltage range of 3.0 V to 4.2 V, and the capacity retention rate was checked while repeating the 1.0 C charging and 1.0 C discharging three times and is shown in Table 1. The capacity retention rate in Table 1 was calculated as the ratio of the discharge capacity after three cycles to the initial discharge capacity.

[0147] Measurement of puncture strength

[0148] The maximum load value when the individual membranes of the examples and comparative examples were pierced at a speed of 120 mm / min using a needle with a diameter of 1 mm (0.5 mmR) was measured using ASTM D5748-95 and ASTM D4649. This was performed 5 times for each membrane, and the average value was calculated using an Instron testing machine.

[0149]

[0150] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Cellulose nanofibers used Li-CNF-APTESLi-CNF-APTESLi-CNF-APTESLi-CNF-APTESLi-CNF-APTESLi-CNF-TEOSLi-CNF-APTES Introduced lithium ions:silane molar ratio 20:1 20:1 20:1 20:1 10:1 10:14:1 Coating layer weight ratio (inorganic particles:polymer binder:cellulose nanofibers) 94:3:3 94:3:3 94:3:3 88:2:10 94:3:3 94:3:3 94:3:3 Single-sided / Double-sided Coating Layer Thickness (㎛) 2 1 / 10.5 / 0.5 2 2 2 Total Membrane Thickness (㎛) 12.2 1 2.3 1 1.2 1 2.0 1 2.1 1 2.3 1 2.2 Air Permeability (s / 100cc) 9 4 8 8 8 5 10 19 7 9 8 1 2 Water Contact Angle (°) 13 0 12 5 12 6 11 5 11 7 11 2 13 Moisture Content (ppm) 10 2 3 8 30 7 8 8 8 15 9 8 7 9 9 0 9 Electrical Resistance (Ohm) 0.5 10.4 9 0.5 7 0.5 8 0.4 5 0.5 10.5 Capacity Retention Rate (%) 9 4.5 9 4.8 9 5.6 9 5.4 9 3.8 9 4.2 9 3.8 Perforation Strength (gf)667479521460421453398

[0151]

[0152] Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 Cellulose nanofibers used ---CNFCNFLi-CNFLi-CNF Introduced lithium ions:silane Weight ratio-------Coating layer weight ratio (Inorganic particles:Polymer binder:Cellulose nanofibers) 95:5:0 95:5:0 95:5:0 94:3:3 94:3:3 94:3:3 94:3:3 Single-sided / Double-sided Single-sided Double-sided Single-sided Double-sided Coating layer thickness (㎛) 2 1 / 10.5 / 0.5 2 1 / 12 1 / 1 Separator total thickness (㎛) 12.3 12.5 11.5 12.1 11.9 12.4 12.0 Air permeability (s / 100cc) 837880143100138100 Water Contact Angle (°) 82788164677570 Moisture Content (ppm) 1670141313212750288017381863 Electrical Resistance (Ohm) 0.660.640.650.650.600.580.57 Capacity Retention Rate (%) 93.293.793.893.994.094.394.1 Perforation Strength (gf) 443475468470513491521

[0153]

[0154] Referring to Tables 1 and 2, it can be seen that in Examples 1-7, in which lithium and silane components were introduced into cellulose nanofibers (CNF), the moisture content of the separator is relatively lower and the resistance is reduced compared to Comparative Examples 1-7, in which lithium and silane components were not introduced. For example, in the case of Examples 1-7, the moisture content of the separator was approximately between 788 ppm and 1023 ppm, whereas in the case of Comparative Examples 1-7, the moisture content was approximately between 1321 ppm and 2880 ppm. The water contact angle was between 112° and 134° for Examples 1-7, whereas it was much smaller between 64° and 82° for Comparative Examples 1-7. Furthermore, regarding electrical resistance, some examples showed values ​​of approximately 0.5 Ω or less, whereas the electrical resistance of most of the comparative examples exceeded 0.5 Ω.

[0155] 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

1. Porous substrate; and It includes a coating layer formed on at least one surface of the above-mentioned porous substrate, and The above coating layer comprises inorganic particles, a polymer binder, and cellulose nanofibers, and The above cellulose nanofibers are those into which lithium ions and silanes have been introduced, Separator for electrochemical devices.

2. In Paragraph 1, The above cellulose nanofiber is a separator for an electrochemical device in which lithium ions and silane are introduced in a molar ratio of 5:1 to 25:

1.

3. In Paragraph 1, A separator for an electrochemical device, wherein the coating layer comprises 1% by weight or more and 15% by weight or less of the cellulose nanofiber.

4. In Paragraph 1, A separator for an electrochemical device, wherein the average diameter of the cellulose nanofibers is 5 nm or more and 50 nm or less.

5. In Paragraph 1, A separator for an electrochemical device, wherein the aspect ratio of the cellulose nanofibers is 50 to 200.

6. In Paragraph 1, The above silanes are N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane hydrochloride, vinyltrimethoxysilane, vinyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, p-styryltrimethoxysilane, A separator for an electrochemical device, one or more selected from 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, tris-(trimethoxysilylpropyl)isocyanurate, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, and 3-isocyanatepropyltriethoxysilane.

7. In Paragraph 1, A separator for an electrochemical device, wherein the thickness of the coating layer is 0.5 μm or more and 2 μm or less.

8. In Paragraph 1, A separator for an electrochemical device, wherein the content of the inorganic particles relative to the total weight of the coating layer is 80% by weight or more and 95% by weight or less.

9. In Paragraph 1, A separator for an electrochemical device, further comprising an adhesive layer formed on the surface of the coating layer.

10. An electrochemical device comprising an anode, a cathode, and a separator disposed between the anode and the cathode, wherein The above separator is an electrochemical device, which is a separator for an electrochemical device according to claim 1.