Composite separator and electrochemical device comprising same

Abstract

The invention relates to a composite diaphragm. The composite diaphragm comprises a porous base material; and a ceramic layer which is formed on one surface or both surfaces of the porous substrate, and which contains inorganic particles and a binder, in which the average particle diameter (D50) of the inorganic particles is 0.20 [mu] m to 0.40 [mu] m, and in a particle size distribution diagram of the inorganic particles, the particle size distribution diagram of the inorganic particles is greater than the particle size distribution diagram of the inorganic particles, the particle size distribution diagram of the inorganic particles is greater than the particle size distribution diagram of the inorganic particles. The ratio (A / B) of the area (A) on the small particle diameter side to the area (B) on the large particle diameter side, based on the maximum peak, is 1.05 or more, and the composite separator can simultaneously satisfy excellent mechanical stability, thermal stability, and ion conductivity characteristics.

Description

Technical Field

[0001] This invention relates to a composite membrane and an electrochemical device including the composite membrane. Background Technology

[0002] In recent years, with the increasing capacity and power of electrochemical devices, the requirements for ensuring heat resistance and safety have become increasingly stringent. In particular, the performance requirements of the diaphragm, which plays a very important role, have also become increasingly demanding.

[0003] For example, as a solution to ensure the heat resistance and safety of the diaphragm, composite diaphragms, which incorporate coatings containing inorganic particles such as alumina (Al2O3), silica (SiO2), and zirconium oxide (ZrO2) and binders onto porous substrates, are becoming an important technology. However, in recent years, research has been focused on achieving thin-film diaphragms to meet the high capacity and high power requirements of electrochemical devices. Within the thickness range of thin-film inorganic particle coatings, sufficient heat resistance is difficult to achieve, and attempts to improve heat resistance are limited by decreased adhesion and / or air permeability.

[0004] [Existing Technical Documents]

[0005] [Patent Literature]

[0006] KR10-2023-0144943A (October 17, 2023) Summary of the Invention

[0007] (a) Technical problems to be solved

[0008] One embodiment of the present invention relates to a composite membrane comprising: a porous substrate; and a ceramic layer formed on one or both sides of the porous substrate, wherein inorganic particles are connected and fixed by an adhesive to form pores between the inorganic particles, and a composite membrane having both excellent heat resistance and adhesive strength is provided.

[0009] Another embodiment of the present invention provides an electrochemical device that uses the composite separator, thereby exhibiting excellent battery performance and safety.

[0010] (II) Technical Solution

[0011] One embodiment of the present invention provides a composite membrane comprising: a porous substrate; and a ceramic layer formed on one or both sides of the porous substrate, wherein the ceramic layer comprises inorganic particles and a binder, wherein the average particle size (D50) of the inorganic particles is 0.20 μm to 0.40 μm, and in the particle size distribution diagram of the inorganic particles, the ratio (A / B) of the area of ​​the smaller particle size side (A) to the area of ​​the larger particle size side (B) based on the maximum peak is 1.05 or more.

[0012] In the particle size distribution diagram of the inorganic particles, the (D95-D50) / D50 value can satisfy 1.8 to 2.5.

[0013] In the particle size distribution diagram of the inorganic particles, the ratio (A / B) of the area of ​​the small particle size side (A) to the area of ​​the large particle size side (B) based on the maximum peak can satisfy 1.05 to 1.3.

[0014] In the composite membrane according to one embodiment, the content of the binder may be from 0.1 parts by weight to 10 parts by weight relative to 100 parts by weight of the inorganic particles.

[0015] The inorganic particles may be selected from one or more of boehmite, BaSO4, CeO2, MgO, CaO, ZnO, Al2O3, TiO2, BaTiO3, HfO2, SrTiO3, SnO2, NiO, ZrO2, Y2O3 and SiC.

[0016] The adhesive may be one or more selected from (meth)acrylic polymers, fluoropolymers, styrene polymers, vinyl alcohol polymers, vinyl ester polymers, vinylpyrrolidone polymers, cellulose polymers, polyimide polymers, polyamide polymers, polyalkylene glycols and copolymers thereof.

[0017] The adhesive may contain polyacrylamide, carboxymethyl cellulose, or a combination thereof.

[0018] The adhesive may contain carboxymethyl cellulose with a weight-average molecular weight of 180,000 g / mol or more and a degree of substitution of 0.6 to 1.2.

[0019] The porous substrate may be hydrophilic surface treated.

[0020] The coating density of the ceramic layer can be 1.2 g / cm³. 3 Up to 1.8 g / cm 3 .

[0021] The total thickness of the ceramic layer can be from 0.5 μm to 10 μm.

[0022] According to one embodiment, the thickness of the composite diaphragm can be from 1 μm to 100 μm.

[0023] In the composite diaphragm according to one embodiment, when evaluating the degree of foreign matter adhesion to the paperboard surface after paperboard testing, the area occupied by the adhered foreign matter relative to the paperboard area can be less than 5%.

[0024] [Cardboard Test]

[0025] (A black cardboard and a rubber pad measuring 2cm × 10cm were placed sequentially on the ceramic layer of a composite diaphragm sample measuring 5cm × 10cm. While applying a force of 10N to the rubber pad using a pressing device, the cardboard was pulled horizontally out by 60mm at a speed of 0.1m / s to test the degree to which foreign matter adhered to the surface of the cardboard.)

[0026] The mechanical (MD) and transverse (TD) thermal shrinkage rates of the composite diaphragm measured after being placed at 150°C for 60 minutes were both below 4%.

[0027] Another embodiment of the present invention provides an electrochemical device comprising a positive electrode, a negative electrode, and a composite separator, wherein the composite separator comprises: a porous substrate; and a ceramic layer formed on one or both sides of the porous substrate, and the ceramic layer comprising inorganic particles and a binder, wherein the average particle size (D50) of the inorganic particles is 0.2 μm to 0.4 μm, and in the particle size distribution diagram of the inorganic particles, the ratio (A / B) of the area of ​​the smaller particle size side relative to the largest particle size side based on the maximum peak is 1.05 or more.

[0028] (III) Beneficial Effects

[0029] A composite membrane according to one embodiment can simultaneously satisfy excellent mechanical stability, thermal stability, and ionic conductivity. Specifically, the composite membrane according to one embodiment includes a porous substrate and a ceramic layer, in which inorganic particles are connected and fixed by an adhesive, thereby forming pores between the inorganic particles. Even if the thickness of the formed ceramic layer is very thin, excellent heat resistance can be ensured, and due to the excellent adhesion between the inorganic particles and between the inorganic particles and the substrate, the shedding of inorganic particles and shrinkage at high temperatures can be effectively suppressed. At the same time, the composite membrane according to one embodiment can achieve excellent air permeability and ionic conductivity.

[0030] Electrochemical devices using a composite membrane according to one embodiment can simultaneously meet the requirements of safety, high capacity, and high power characteristics. Attached Figure Description

[0031] Figure 1 This is a particle size distribution diagram of the inorganic particles used in Example 1. Detailed Implementation

[0032] In this specification, unless otherwise defined, all technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of effectively describing particular embodiments only and is not intended to limit the invention.

[0033] Unless otherwise specified in the context, the singular form used in this specification may include the plural form.

[0034] Throughout this specification, unless otherwise specifically stated to the contrary, "comprising / including," "having," "containing," or "having" a constituent element means that it may also include other constituent elements, rather than excluding other constituent elements, and does not exclude elements, materials, or processes not further listed.

[0035] The numerical ranges used in this specification include lower and upper limits, all values ​​within that range, increments logically derived from the form and width of the defined range, all values ​​defined therein, and all possible combinations of upper and lower limits of numerical ranges defined in different forms. Unless otherwise specifically defined, values ​​outside the defined numerical range that may occur due to experimental error or rounding are also included within the defined numerical range.

[0036] In this specification, unless otherwise specifically defined, “about” can be considered as a value within 30%, 25%, 20%, 15%, 10% or 5% of the explicitly stated value.

[0037] The present invention will now be described in detail. However, these are merely exemplary embodiments, and the present invention is not limited to the specific embodiments described herein.

[0038] To address the reduced heat resistance resulting from the thinning of composite membranes comprising porous substrates and inorganic coatings, existing technologies have proposed a method of introducing inorganic particles of a specific size. However, this method has the following limitations: even if heat resistance is improved, the adhesion between inorganic particles and between inorganic particles and the substrate decreases, resulting in poor air permeability, and the heat resistance deteriorates again when attempts are made to improve adhesion and / or air permeability.

[0039] The inventors have discovered that in a composite membrane comprising a porous substrate and a ceramic layer formed on one or both sides of the substrate and containing inorganic particles and a binder, when the inorganic particles meet a specific range of average particle size and have specific particle size distribution characteristics, heat resistance, adhesion and air permeability characteristics can be simultaneously satisfied even within the thickness range of the thin film.

[0040] This invention provides a composite membrane that can simultaneously ensure excellent mechanical stability, thermal stability, and ionic conductivity.

[0041] According to one embodiment, the composite membrane may include: a porous substrate; and a ceramic layer formed on one or both sides of the porous substrate, the ceramic layer comprising inorganic particles and a binder, wherein the average particle size (D50) of the inorganic particles may be from 0.20 μm to 0.40 μm, and in the particle size distribution diagram of the inorganic particles, the ratio (A / B) of the area of ​​the smaller particle size side relative to the maximum peak to the area of ​​the larger particle size side may be 1.05 or more.

[0042] The inorganic particles in the composite separator according to one embodiment have an average particle size of 0.20 μm to 0.40 μm and a particle size distribution characteristic with a ratio (A / B) of 1.05 or higher between the area (A) of the small-diameter side and the area (B) of the large-diameter side relative to the maximum peak in the particle size distribution diagram. Therefore, excellent adhesion can be achieved between the inorganic particles and between the inorganic particles and the substrate, and excellent heat resistance can also be obtained. Furthermore, in the composite separator according to one embodiment, even if the thickness of the formed ceramic layer is very thin, excellent adhesion and heat resistance can be achieved. Therefore, electrochemical devices using the composite separator can simultaneously meet the requirements of safety, high capacity, and high power characteristics.

[0043] In one embodiment, the average particle size (D50) of the inorganic particles may refer to the particle size of the inorganic particles corresponding to a cumulative fraction of 50% based on volume, and can be calculated by a particle size distribution map measured according to the KA A ISO 13320-1 standard.

[0044] In one embodiment, the particle size distribution map may be a graph based on the volume percentage of the particle diameter of the inorganic particles. In one embodiment, when using a particle size distribution map drawn in ascending order of particle diameter along the x-axis from left to right, the area (A) on the smaller particle diameter side may refer to the area from the starting point of the particle size distribution map to the x-axis of the maximum peak, and may refer to the area to the left of the maximum peak; the area (B) on the larger particle diameter side may refer to the area from the x-axis of the maximum peak to the ending point of the particle size distribution map, and may refer to the area to the right of the maximum peak.

[0045] In one embodiment, in the particle size distribution map of the inorganic particles, the ratio (A / B) of the area (A) of the smaller particle size side relative to the largest particle size side to the area (B) of the larger particle size side, based on the maximum peak, can be 1.05 or more, 1.06 or more, 1.07 or more, 1.5 or less, 1.4 or less, 1.3 or less, or 1.2 or less, and can be 1.05 to 1.5, 1.05 to 1.3, or 1.06 to 1.3, and can include all possible combinations of the upper and lower limits of the above numerical range.

[0046] In one embodiment, in the particle size distribution diagram of the inorganic particles, the (D95-D50) / D50 value can be greater than 1.5, greater than 1.7, or greater than 1.8, and can be less than 3.0, less than 2.8, less than 2.6, less than 2.5, less than 2.4, or less than 2.3, and can be from 1.5 to 3.0, 1.8 to 3.0, or 1.8 to 2.8, and can include all possible combinations of the upper and lower limits of the above numerical ranges. When inorganic particles that satisfy the above average particle size and A / B area ratio while also satisfying the above (D95-D50) / D50 value are used, the effect of simultaneously improving adhesion, heat resistance, and air permeability can be even better. In one embodiment, D95 refers to the particle size of the inorganic particles corresponding to a cumulative fraction of 95% based on volume.

[0047] In one embodiment, the type of inorganic particles can be used without limitation, as long as the above-mentioned average particle size and particle size distribution characteristics are met. As a non-limiting example, the inorganic particles can be one or more selected from metal oxides, metal hydrates, metal carbides, metal nitrides and metal carbonitrides such as boehmite, BaSO4, CeO2, MgO, CaO, ZnO, Al2O3, TiO2, BaTiO3, HfO2, SrTiO3, SnO2, NiO, ZrO2, Y2O3 and SiC.

[0048] In one embodiment, the coating density of the ceramic layer can be 1.0 g / cm³. 3 Above, 1.1g / cm 3 Above or 1.2g / cm 3 The above, and can be 2.0 g / cm³ 3 Below, 1.9g / cm 3 Below, 1.8g / cm 3 Below or 1.7g / cm 3 Below, and can be 1.0 g / cm 3 Up to 1.8 g / cm 3 Or 1.2g / cm 3 Up to 1.8 g / cm3 .

[0049] The thickness of the composite membrane according to one embodiment may be 1 μm to 200 μm, 2 μm to 200 μm, 5 μm to 200 μm, 5 μm to 150 μm, 5 μm to 100 μm, 5 μm to 50 μm, 5 μm to 30 μm or 5 μm to 20 μm, or may include all possible combinations of the upper and lower limits of the above numerical ranges, and is not limited thereto.

[0050] In one embodiment, the ceramic layer can be coated on one or both sides of a porous substrate. When the ceramic layer is coated on both sides of the porous substrate, the thicknesses of the ceramic layer coated on one side and the other side can be the same or different. Although not particularly limited, the total thickness of the ceramic layer according to one embodiment can be, for example, 0.1 μm to 10.0 μm, 0.5 μm to 10.0 μm, 1 μm to 10 μm, 1 μm to 8 μm, 1 μm to 5 μm, about 1.5 μm to 5 μm, 2 μm to 5 μm, or 2 μm to 4 μm, and can be values ​​between the above values. In the composite membrane according to one embodiment, excellent adhesion and heat resistance can be achieved even when the thickness of the formed ceramic layer is very thin, so the electrochemical device using the composite membrane can simultaneously meet the requirements of safety, high capacity, and high power characteristics.

[0051] In one embodiment, the content of inorganic particles in the ceramic layer, relative to the total weight of the ceramic layer, can be 90% to 99.9% by weight, 92% to 99.5% by weight, 92% to 99% by weight, 95% to 99% by weight, or 96% to 99% by weight. This content of inorganic particles can be higher than that of conventional coatings that include binders and are formed by the bonding of inorganic particles. Nevertheless, due to the excellent heat resistance and numerical stability, a coating (ceramic layer) with a thinner thickness can be formed.

[0052] In one embodiment, the content of the binder used in the ceramic layer, relative to 100 parts by weight of the inorganic particles, can be less than 10 parts by weight, less than 8 parts by weight, less than 5 parts by weight, less than 3 parts by weight, less than 2 parts by weight, or less than 1 part by weight, and can be more than 0.1 parts by weight, more than 0.5 parts by weight, more than 1 part by weight, or more than 2 parts by weight. Specifically, it can be between 0.1 parts by weight and 5 parts by weight, between 1 parts by weight and 5 parts by weight, between 1 parts by weight and 3 parts by weight, or between these ranges.

[0053] In one embodiment, the adhesive is not particularly limited as long as it is a conventional adhesive used in the existing art. As a non-limiting example, the adhesive may be one or more selected from (meth)acrylate-based polymers, fluoropolymers, styrene-based polymers, vinyl alcohol-based polymers, vinyl ester-based polymers, vinylpyrrolidone-based polymers, cellulose-based polymers, polyimide-based polymers, polyamide-based polymers, polyalkylene glycols, and copolymers thereof. As an example, the (meth)acrylate-based polymer may be selected from poly(alkyl methacrylate), poly(meth)acrylic acid, poly(meth)acrylamide, poly(meth)acrylonitrile, poly(hydroxyethyl methacrylate), or copolymers thereof. As an example, the styrene-based polymer may be selected from polystyrene, polyα-methylstyrene, polybrominated styrene, or copolymers thereof. As an example, the vinyl alcohol-based polymer may be polyvinyl alcohol or a copolymer containing polyvinyl alcohol. As an example, the vinyl ester-based polymer may be polyvinyl ester or a copolymer containing polyvinyl ester. As an example, the cellulose-based polymer may be selected from cellulose, carboxymethyl cellulose, hydroxypropyl methyl cellulose, cellulose acetate, or cellulose acetate propionate, etc.

[0054] In one embodiment, the adhesive may comprise a (meth)acrylic polymer, a cellulose polymer, or a combination thereof.

[0055] Specifically, the adhesive may contain polyacrylamide (PAAm), carboxymethyl cellulose, or a combination thereof. More specifically, it may contain a mixed adhesive of carboxymethyl cellulose and polyacrylamide, which may further improve the desired effect of the present invention and is therefore preferred, but not limited thereto.

[0056] In one embodiment, when the adhesive comprises polyacrylamide (PAAm), the weight-average molecular weight of the polyacrylamide may be from 100,000 g / mol to 300,000 g / mol, 150,000 g / mol to 250,000 g / mol, or 200,000 g / mol to 250,000 g / mol, and may include all possible combinations of the upper and lower limits of the above numerical ranges, but is not limited thereto. The weight-average molecular weight may refer to the weight-average molecular weight calculated based on a molecular weight calibration curve using polystyrene standard samples measured by GPC methods.

[0057] In one embodiment, when the adhesive comprises carboxymethyl cellulose, the weight-average molecular weight of the carboxymethyl cellulose can be from 180,000 g / mol to 1,500,000 g / mol, 180,000 g / mol to 1,300,000 g / mol, or 190,000 g / mol to 1,000,000 g / mol, and can include all possible combinations of the upper and lower limits of the above numerical ranges. Furthermore, the degree of substitution of the carboxymethyl cellulose can be from 0.6 to 1.2, 0.6 to 1.1, 0.6 to 1.0, 0.7 to 1.0, 0.8 to 1.0, or 0.9 to 1.0, and can include all possible combinations of the upper and lower limits of the above numerical ranges. The weight-average molecular weight can refer to the weight-average molecular weight calculated based on a molecular weight calibration curve using a polysaccharide standard sample measured by GPC methods.

[0058] The carboxymethyl cellulose (CMC) mentioned above refers to cellulose in which the hydroxyl groups (-OH) are surrounded by -OCH2COOH and / or -OCH2COO. - M + The substituted and etherified cellulose derivative, wherein the M + It is an alkali metal cation, and can be selected from lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr), etc. In this specification, the "degree of substitution (DS)" of carboxymethyl cellulose refers to the average number of the aforementioned substituents contained in a single dehydrated glucose unit in a cellulose molecule, which can be measured by known or commonly used methods, for example, according to ASTM D1439, and can be measured by... 1 H-NMR or 13 Calculations were performed using C-NMR analysis.

[0059] The degree of substitution (DS) of carboxymethyl cellulose (CMC) was measured using a titration method according to ASTM D1439. The experiment used a magnetic stirrer, aspirator, dry oven, 300 mL beakers, pipettes, 250 mL Erlenmeyer flasks, and Petri dishes. The reagents used were 80% ethanol, 100% ethanol, 0.1 N sodium hydroxide (NaOH) solution, phenolphthalein indicator, and 0.1 N sulfuric acid (H₂SO₄) solution.

[0060] Specifically, add 150 mL of 80% ethanol to a 300 mL beaker, followed by 10 mL of 1N nitric acid (HNO3). Add approximately 1 g to 2 g of CMC sample and stir for 1 hour to form CMC acid. Afterward, let stand for approximately 10 to 20 minutes, then remove (decant) the supernatant.

[0061] Next, add another 150 mL of 80% ethanol, stir for 30 to 40 minutes, and then remove the supernatant again. For the precipitated CMC acid, filter using a suction filter, wash with 500 mL of 80% ethanol, and then wash again with 100% ethanol once or twice.

[0062] Take the middle fraction of the purified CMC acid and transfer it to a clean weighing dish. Dry it in a drying oven for 20 to 30 minutes. After drying, accurately weigh approximately 0.2 ± 0.05 g of the sample and add 25 mL of 0.1 N NaOH solution. Transfer the sample solution to a 250 mL Erlenmeyer flask and add 100 mL of distilled water. Stir for 40 to 60 minutes until completely dissolved.

[0063] Then, add 2 to 3 drops of phenolphthalein indicator and titrate with 0.1N H2SO4 solution while stirring continuously until the solution color changes from red to colorless.

[0064] The number of millimoles (A) of CMC acid in 1g of dried sample is calculated using the following formula.

[0065]

[0066] Then, the degree of substitution (DS) is calculated from A using the following formula.

[0067]

[0068] When the adhesive comprises carboxymethyl cellulose and polyacrylamide, the carboxymethyl cellulose and the polyacrylamide may be used in a weight ratio of 10 to 50: 90 to 50 or 10 to 40: 90 to 60.

[0069] In one embodiment, the mechanical (MD) and transverse (TD) thermal shrinkage rates measured after placing the composite diaphragm at 150°C for 60 minutes can both be less than 5%, specifically, less than 4%, less than 3%, less than 2.5%, less than 2.0%, or less than 2.0%.

[0070] Furthermore, in one embodiment, when evaluating the degree of foreign matter adhesion to the paperboard surface after conducting a paperboard test on the composite diaphragm, the proportion of the area occupied by the adhered foreign matter relative to the area of ​​the paperboard can be less than 5%, specifically, it can be less than 5%, less than 4%, less than 3%, less than 2%, or less than 1.5%.

[0071] The paperboard test method is as follows: A black paperboard measuring 2cm × 10cm and a rubber pad are placed sequentially on the ceramic layer of a composite diaphragm sample measuring 5cm × 10cm. While applying a force of 10N to the rubber pad using a pressing device, the paperboard is pulled horizontally out by 60mm at a speed of 0.1m / s. The degree of foreign matter adhesion to the paperboard surface is tested by evaluating the area. The foreign matter can be a component of the ceramic layer, such as inorganic particles, adhesives, or a combination thereof.

[0072] When evaluating adhesive strength using the paperboard testing method described above, not only the adhesive strength between the substrate and the ceramic layer interface can be considered, but also the adhesive strength between inorganic particles within the ceramic layer. Furthermore, the adhesive strength test results can predict the degree of thermal shrinkage more accurately than existing peel tests. Specifically, when the area occupied by adhered foreign matter calculated through the paperboard test is less than 5%, less than 4%, less than 3%, less than 2%, or less than 1.5%, it indicates excellent adhesive strength between inorganic particles and between inorganic particles and the substrate, and effectively suppresses thermal shrinkage.

[0073] As an example, existing methods such as peel tests for evaluating the adhesion of inorganic particle coatings in composite diaphragms evaluate the adhesion between the substrate and the inorganic particle coating interface. Therefore, it is difficult to predict the adhesion between inorganic particles, and there is a drawback that the thermal shrinkage characteristics of the diaphragm cannot be accurately predicted through the evaluation value.

[0074] In one embodiment, the porous substrate is not limited to any porous substrate commonly used in this art; for example, the porous substrate can be woven fabric, nonwoven fabric, or porous membrane. Specifically, the porous substrate can be polyethylene, polypropylene, or other polyolefins; polyethylene terephthalate, polybutylene terephthalate, or other polyesters; polyacetal; polyamide; polyimide; polycarbonate; polyetheretherketone; polyaryletherketone; polyetherimide; polyamideimide; polybenzimidazole; polyethersulfone; polyphenylene ether; cyclic olefin copolymers; polyphenylene sulfide; polyethylene naphthalate; glass fiber; Teflon; and / or polytetrafluoroethylene, and any two or more of these can also be used. In the porous substrate, the porous membrane is prepared by dry and wet methods, which are well known in this art and will not be described further.

[0075] In one embodiment, the porosity of the porous substrate may be 20% to 60%, 30% to 60%, 30% to 50%, or 35% to 45%, but is not limited thereto.

[0076] In one embodiment, the porous substrate may be a substrate incorporating polar functional groups by performing a hydrophilic surface treatment, such as carboxyl, aldehyde, hydroxyl, etc. As an example, the hydrophilic surface treatment may be corona discharge treatment or plasma discharge treatment, but there are no particular limitations.

[0077] In one embodiment, the thickness of the porous substrate is not particularly limited. For example, the thickness of the porous substrate can be 1 μm to 100 μm, 1 μm to 50 μm, 1 μm to 30 μm, 5 μm to 20 μm, or any value between the above values.

[0078] Another embodiment of the present invention provides an electrochemical device comprising a composite separator according to one embodiment above. As an example, the electrochemical device may be a lithium secondary battery.

[0079] Specifically, an electrochemical device according to one embodiment may include a positive electrode, a negative electrode, and a composite separator, wherein the composite separator may include: a porous substrate; and a ceramic layer formed on one or both sides of the porous substrate, and the ceramic layer comprises inorganic particles and a binder, wherein the average particle size (D50) of the inorganic particles may be from 0.20 μm to 0.40 μm, and in the particle size distribution diagram of the inorganic particles, the ratio (A / B) of the area of ​​the small particle size side (A) to the area of ​​the large particle size side (B) based on the maximum peak may be 1.05 or higher.

[0080] The following describes an electrochemical device according to one embodiment, using a lithium secondary battery as an example. However, in addition to including the composite separator according to one embodiment, conventional manufacturing methods and materials in this art can be used to manufacture structures known in this art.

[0081] As an example, the lithium secondary battery can be manufactured using a conventional method that involves assembling the battery by sequentially setting a negative electrode, a composite separator, and a positive electrode, and then injecting an electrolyte.

[0082] [positive electrode]

[0083] The positive electrode may include a positive electrode current collector and a positive electrode mixture layer located on at least one side of the positive electrode current collector. The positive electrode can be manufactured by coating a positive electrode material slurry onto one or both sides of the positive electrode current collector and then drying and calendering to form the positive electrode mixture layer. The positive electrode material slurry may contain a positive electrode active material and a binder, and may further contain conductive materials, thickeners, etc. as needed.

[0084] The positive electrode current collector may include stainless steel, nickel, aluminum, titanium, or alloys thereof, and may also include aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver. The thickness of the positive electrode current collector may be, for example, from 10 μm to 50 μm, but is not limited thereto.

[0085] The positive electrode active material can be used without limitation as long as it is a compound that can reversibly insert and deintercalate lithium ions and is a positive electrode active material commonly used in this technical field. As a non-limiting example, the positive electrode active material can be a composite oxide of lithium with metals selected from cobalt (Co), manganese (Mn), nickel (Ni), iron (Fe), niobium (Nb), magnesium (Mg), copper (Cu), zinc (Zn), molybdenum (Mo), tantalum (Ta), tungsten (W), aluminum (Al) and combinations thereof.

[0086] In one embodiment, the positive electrode active material may be a lithium-nickel composite oxide, which may further contain one or more of cobalt, manganese and aluminum.

[0087] In one embodiment, the positive electrode active material may comprise a nickel-cobalt-manganese (NCM)-based lithium composite oxide. The composition of the metal is not particularly limited, but a high-capacity (high-Ni) composition with a high nickel content may be used. The Ni content in the NCM-based lithium composite oxide (e.g., the mole fraction of nickel in the total moles of nickel, cobalt, and manganese) may be 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, or 0.8 or more. In some embodiments, the Ni content may be 0.8 to 0.95, 0.82 to 0.95, 0.83 to 0.95, 0.84 to 0.95, 0.85 to 0.95, or 0.88 to 0.95. As an example, the NCM-based lithium composite oxide may be LiNi. 0.33 Co 0.33 Mn 0.33 O2, LiNi 0.4 Co 0.2 Mn 0.4 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co0.2 Mn 0.2 O2, LiNi 0.7 Co 0.15 Mn 0.15 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, etc., but not limited to these.

[0088] In one embodiment, the positive electrode active material may be, for example, lithium cobalt oxide-based material, lithium manganese oxide-based material, lithium nickel oxide-based material, lithium iron phosphate-based (LFP, e.g., LiFePO4) material, lithium manganese phosphate-based (e.g., LiMnPO4) material, lithium cobalt phosphate-based (e.g., LiCoPO4) material, lithium iron pyrophosphate-based (e.g., Li2FeP2O7) material, etc.

[0089] The positive electrode adhesive is not particularly limited as long as it is a positive electrode adhesive commonly used in this technical field. The positive electrode adhesive may include non-aqueous adhesives and / or water-based adhesives, or it may include rubber-based adhesives and / or fluorine-based adhesives. For example, it may be one or more of the following: acrylic polymers such as polyacrylate, polymethacrylate, polybutyl acrylate, and polyacrylonitrile; fluorine polymers such as polyvinylidene fluoride, polyhexafluoropropylene, poly(vinylidene fluoride-hexafluoropropylene), and poly(vinylidene fluoride-trichloroethylene); polyvinyl acetate; polyethylene oxide; cellulose; modified cellulose; polyamide; polyacrylamide; rubber; elastomers; etc., but is not limited thereto.

[0090] The conductive material can be added to enhance the conductivity and / or the mobility of lithium ions or electrons in the positive electrode mixture layer. For example, the conductive material can be a linear conductive material and / or a point-type conductive material. For instance, the conductive material may include carbon-based conductive materials such as graphite, carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes, vapor-grown carbon fiber (VGCF), carbon fiber, and carbon nanofibers, and / or metal-based conductive materials including perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3, but is not limited thereto. The term "point-type conductive material" as used in this specification can refer to a conventional spherical or particulate conductive material.

[0091] [negative electrode]

[0092] The negative electrode may include a negative electrode current collector and a negative electrode mixture layer located on at least one surface of the negative electrode current collector. The negative electrode can be manufactured by coating a negative electrode material slurry on one or both surfaces of the negative electrode current collector and drying and calendaring to form the negative electrode mixture layer. The negative electrode material slurry may contain a negative electrode active material and a binder, and may further contain a conductive material, a thickener, etc. as needed.

[0093] The negative electrode current collector may include a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a foam nickel, a foam copper, a polymer substrate coated with a conductive metal, etc. The thickness of the negative electrode current collector may be, for example, 10 μm to 50 μm, but is not limited thereto.

[0094] The negative electrode active material can be used without limitation as long as it is a material that can adsorb and desorb lithium ions and is a negative electrode active material commonly used in the art. As a non-limiting example, the negative electrode active material can use carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, carbon fibers, etc.; lithium metal; lithium alloys; silicon (Si)-containing substances or tin (Sn)-containing substances, etc.

[0095] As examples of the amorphous carbon, hard carbon, soft carbon, coke, mesocarbon microbead (MCMB), mesophase pitch-based carbon fiber (MPCF), etc. can be cited. As examples of the crystalline carbon, graphite-based carbons such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, graphitized MPCF, etc. can be cited.

[0096] As elements contained in the lithium alloy, aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium, etc. can be cited.

[0097] The silicon-containing substance can provide further enhanced capacity characteristics. The silicon-containing substance may include Si, SiO x (0 < x ≤ 2), metal-doped SiO x (0 < x ≤ 2), silicon-carbon composites, etc. The metal may include lithium and / or magnesium. Metal-doped SiO x (0 < x ≤ 2) may include metal silicates. The binder, conductive material, and thickener of the negative electrode can use the above substances that can be used in manufacturing the positive electrode.

[0098] The negative electrode adhesive is not particularly limited as long as it is a negative electrode adhesive commonly used in this technical field. The negative electrode adhesive can be rubber-based adhesives such as styrene-butadiene rubber (SBR) based adhesives, carboxymethyl cellulose (CMC), polyacrylic acid, poly(3,4-ethylenedioxythiophene) (PEDOT) based adhesives, etc.

[0099] Electrolyte

[0100] In one embodiment, the electrolyte may be a non-aqueous electrolyte, which may contain a lithium salt as an electrolyte and an organic solvent.

[0101] The lithium salt can be, for example, made of Li + X - This indicates that the anion (X) of the lithium salt is... - ), can be exemplified by F - Cl - ,Br - I - NO3 - N(CN)2 - BF4 - ClO4 - PF6 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - CF3SO3 - CF3CF2SO3 - (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - wait.

[0102] The organic solvent may comprise an organic compound that has sufficient solubility for the lithium salt and additives and is non-reactive in the battery. The organic solvent may comprise at least one of, for example, carbonate-based solvents, ester-based solvents, ether-based solvents, ketone-based solvents, alcohol-based solvents, and aprotic solvents. The organic solvent may be selected from, for example, propylene carbonate, ethylene carbonate, butenyl carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, vinylene carbonate, methyl acetate, ethyl acetate, n-propyl acetate, 1,1-dimethylethyl acetate, methyl propionate, ethyl propionate, ethyl fluoroacetate, ethyl difluoroacetate, ethyl trifluoroacetate, dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, ethanol, isopropanol, dimethyl sulfoxide, acetonitrile, diethoxyethane, sulfolane, γ-butyrolactone, and propylene sulfite, etc., one or more of these.

[0103] The specific implementation schemes described above will be explained in more detail below through examples. However, the following examples are for illustrative purposes only and do not limit the scope of the claims.

[0104] [Methods for measuring physical properties]

[0105] 1) Particle size of inorganic particles

[0106] Samples were collected according to the KS A ISO 13320-1 standard. Particle size distribution was analyzed using a Microtrac S3500 analyzer to obtain a particle size distribution map based on volume percentage (particle diameter). The particle diameter (Dn) corresponding to a cumulative volume percentage of n% was obtained from the particle size distribution map. The particle diameter of the measured sample particles corresponding to a cumulative volume percentage of 50% was taken as the average particle diameter (D50).

[0107] Furthermore, the area (A) of the small-diameter side and the area (B) of the large-diameter side, with the maximum peak as the reference, are obtained from the particle size distribution map obtained by the above method. Specifically, as... Figure 1 As shown, in the particle size distribution map drawn from left to right along the x-axis in order of increasing particle size, the area from the starting point of the particle size distribution map to the x-axis of the largest peak is set as A, and the area from the x-axis of the largest peak to the ending point of the particle size distribution map is set as B.

[0108] 2) Thickness

[0109] Ten layers of the composite membrane were stacked, and their thickness was measured using a Mitutoyo ID-C112X at room temperature and pressure to obtain the average thickness of the 10 composite membrane layers. The average thickness of the 10 composite membrane layers was then divided by 10 to obtain the thickness of the composite membrane. The thickness of the porous substrate was then subtracted from the thickness of the composite membrane to obtain the total thickness of the ceramic layer.

[0110] For the thickness of the porous substrate, the thickness was measured using a Mitutoyo ID-C112X after stacking 10 layers of the porous substrate. The average thickness of the 10 porous substrate layers was obtained, and the average thickness of the porous substrate was obtained by dividing the average thickness of the 10 porous substrate layers by 10. In the case where a ceramic layer has been formed, the ceramic layer was peeled off and thoroughly dried, and then the average thickness of the porous substrate after peeling off the ceramic layer was obtained using the method described above.

[0111] 3) Coating density of ceramic layer

[0112] The coating density of the ceramic layer is calculated according to the following formula. The weight of the ceramic layer is obtained by subtracting the weight of the porous substrate from the weight of the composite membrane. The composite membrane is cut into 100mm×100mm pieces and stacked in pairs. The weight is measured five times to obtain the average weight of the two composite membranes. The average weight of the two composite membranes is divided by 2 to obtain the weight of the composite membrane. The weight of the porous substrate is obtained using only porous substrates cut into 100mm×100mm pieces and the same method as the weight measurement of the composite membrane described above.

[0113] Ceramic layer coating density = (weight of ceramic layer / thickness of ceramic layer) / area

[0114] 4) Adhesive force

[0115] [Cardboard Test]

[0116] The composite diaphragm was cut into 5cm × 10cm samples for preparation. A 2cm × 10cm black cardboard and a rubber pad were placed sequentially on the ceramic layer of the composite diaphragm sample. With a force of 10N applied to the rubber pad using a pressing device, the cardboard was pulled horizontally 60mm at a speed of 0.1m / s. The adhesive force was evaluated based on the degree to which foreign matter adhered to the cardboard surface. The foreign matter could be a component of the ceramic layer, such as inorganic particles, adhesive, or a combination thereof.

[0117] [Evaluation of the degree of foreign body adhesion]

[0118] After the cardboard test, the cardboard surface was photographed and imaged using an optical camera, and the area of ​​adhered foreign matter was measured. Specifically, indirect lighting was set up by setting the LED lamps in the visible light area at a 60° angle, and a 640MP optical camera was used to photograph the cardboard at a height of 40cm from the sample (cardboard). The captured cardboard images were imported into ImageJ, and then the cropping function was used to select and crop only the area passing through the diaphragm and rubber pad. The image file of the cropped area was then converted to an 8-bit image, and a sharpening filter was applied to the image to adjust the brightness and contrast for easy differentiation between the cardboard and the white foreign matter. A threshold was applied to the image and it was converted to a binary image. The Analyze Particles function was used to calculate the ratio of the area occupied by the white foreign matter to the total area, and the adhesive strength was evaluated according to the following benchmarks.

[0119] A: <1.5%

[0120] B: 1.5% to 5%

[0121] C: >5%

[0122] 5) Thermal shrinkage rate

[0123] The heat shrinkage rate of the composite diaphragm was measured based on ASTM D1204 standard using the following method: On the composite diaphragm sample, grid points were marked at 2cm intervals on a 10cm square. One side of the square was for the transverse direction (TD), and the other side for the machine direction (MD). The sample was placed in the center, with five sheets of paper placed above and below it. The four sides of the paper were wrapped with tape. The paper-wrapped sample was then placed in a hot air drying oven at 150°C for 60 minutes. Afterward, the sample was removed, and the diaphragm was observed with a camera. The machine direction (MD) shrinkage rate and the transverse direction (TD) shrinkage rate were calculated and recorded in Table 2 below.

[0124] MD heat shrinkage rate (%) = (MD length before heating - MD length after heating) / MD length before heating × 100

[0125] TD heat shrinkage rate (%) = (TD length before heating - TD length after heating) / TD length before heating × 100

[0126] [Example 1]

[0127] Boehmite (D95: 0.61 μm, A / B: 1.07) with an average particle size (D50) of 0.21 μm and a dispersant 1,2-benzisothiazolin-3-one (DIO2) were mixed in water, wherein the dispersant was 2 parts by weight relative to 100 parts by weight of the boehmite, to obtain a slurry with a solid content of 45% by weight. The obtained slurry was mixed with carboxymethyl cellulose (CMC) with a degree of substitution of 0.9 and a weight average molecular weight of 200,000 g / mol, wherein the CMC was 3 parts by weight relative to 100 parts by weight of the boehmite, and diluted with water to a solid content of 25% by weight, to obtain a composition for ceramic layer formation.

[0128] Corona discharge treatment (power density 2 W / m²) was applied to both sides of a 9 μm thick polyethylene film (porosity 35% to 45%, SKIET). 2 To introduce surface polar groups, the corona surface treatment speed is set to 5 meters per minute (mpm). The ceramic layer forming composition is coated onto both sides of the corona-treated polyethylene film by bar coating and dried at 50°C to obtain a composite diaphragm with ceramic layers of the same thickness on both sides.

[0129] [Example 2]

[0130] The procedure was carried out using the same method as in Example 1, except that boehmite (D95: 0.99 μm, A / B: 1.17) with an average particle size (D50) of 0.30 μm was used.

[0131] [Example 3]

[0132] The procedure was carried out using the same method as in Example 1, except that boehmite (D95: 1.13 μm, A / B: 1.12) with an average particle size (D50) of 0.37 μm was used.

[0133] [Example 4]

[0134] The same method as in Example 1 was used, except that carboxymethyl cellulose (CMC) with a degree of substitution of 0.9 and a weight-average molecular weight of 200,000 g / mol and polyacrylamide (PAAm) (Mw of 200,000 g / mol, Sigma Aldrich) were mixed in a weight ratio of 10:90 and used as a binder.

[0135] [Example 5]

[0136] The procedure was carried out using the same method as in Example 4, except that boehmite (D95: 0.99 μm, A / B: 1.17) with an average particle size (D50) of 0.30 μm was used.

[0137] [Example 6]

[0138] The procedure was carried out using the same method as in Example 4, except that boehmite (D95: 1.13 μm, A / B: 1.12) with an average particle size (D50) of 0.37 μm was used.

[0139] [Example 7]

[0140] The procedure was carried out using the same method as in Example 4, except that boehmite with an average particle size (D50) of 0.32 μm (D95: 0.87 μm, A / B: 1.09) was used.

[0141] [Comparative Example 1]

[0142] The procedure was carried out using the same method as in Example 1, except that boehmite (D95: 1.50 μm, A / B: 1.09) with an average particle size (D50) of 0.50 μm was used.

[0143] [Comparative Example 2]

[0144] The procedure was carried out using the same method as in Example 1, except that boehmite with an average particle size (D50) of 0.64 μm (D95: 1.75 μm, A / B: 0.97) was used.

[0145] [Comparative Example 3]

[0146] The procedure was carried out using the same method as in Example 1, except that boehmite with an average particle size (D50) of 0.10 μm (D95: 0.31 μm, A / B: 1.15) was used.

[0147] [Comparative Example 4]

[0148] The procedure was carried out using the same method as in Example 1, except that boehmite with an average particle size (D50) of 0.27 μm (D95: 0.77 μm, A / B: 1.04) was used.

[0149] [Comparative Example 5]

[0150] The procedure was carried out using the same method as in Example 1, except that boehmite with an average particle size (D50) of 0.38 μm (D95: 0.91 μm, A / B: 1.02) was used.

[0151] [Table 1]

[0152]

[0153] [Table 2]

[0154]

[0155] Referring to Table 2, it can be seen that in the composite diaphragm according to an embodiment of the present invention, not only is there excellent adhesion between the interface between the substrate and the ceramic layer, but also excellent adhesion between the inorganic particles within the ceramic layer. Furthermore, it exhibits excellent heat resistance and effectively suppresses thermal shrinkage. Electrochemical devices using the composite diaphragm according to an embodiment can ensure heat resistance and safety, and can facilitate high capacity and high power output.

[0156] On the other hand, it was confirmed that the composite membranes of comparative examples using inorganic particles with an average particle size (D50) not in the range of 0.20 μm to 0.40 μm or with a ratio (A / B) of less than 1.05 between the area (A) of the small particle size side and the area (B) of the large particle size side based on the maximum peak in the particle size distribution diagram, showed significantly reduced adhesive strength and thermal shrinkage.

[0157] The composite separator of this invention can be widely used in green technology fields such as electric vehicles, battery charging stations, and other battery-powered solar and wind power generation. Furthermore, the separator of this invention can be used in eco-friendly electric vehicles and hybrid vehicles to prevent climate change by suppressing air pollution and greenhouse gas emissions.

[0158] As described above, the present invention has been illustrated with specific content and limited embodiments, but this is only provided to help to understand the present invention more fully. The present invention is not limited to the above embodiments, and those skilled in the art can make various modifications and variations based on these descriptions.

[0159] Therefore, the present invention should not be limited to the embodiments described above, and all contents that are equivalent to or have equivalent variations of the claims fall within the scope of the present invention.

Claims

1. A composite separator, the composite separator comprising: Porous substrate; And a ceramic layer formed on one or both sides of the porous substrate, the ceramic layer comprising inorganic particles and a binder. The inorganic particles have an average particle size D50 of 0.20 μm to 0.40 μm, and in the particle size distribution diagram of the inorganic particles, the ratio A / B of the area A of the small particle size side and the area B of the large particle size side based on the maximum peak is greater than 1.

05.

2. The composite diaphragm according to claim 1, wherein, In the particle size distribution diagram of the inorganic particles, the (D95-D50) / D50 value is 1.8 to 2.

5.

3. The composite diaphragm according to claim 1, wherein, In the particle size distribution diagram of the inorganic particles, the ratio A / B of the area A of the small particle size side and the area B of the large particle size side, with the maximum peak as the reference, is 1.05 to 1.

3.

4. The composite diaphragm according to claim 1, wherein, The content of the adhesive is from 0.1 parts by weight to 10 parts by weight relative to 100 parts by weight of the inorganic particles.

5. The composite diaphragm according to claim 1, wherein, The inorganic particles are selected from one or more of boehmite, BaSO4, CeO2, MgO, CaO, ZnO, Al2O3, TiO2, BaTiO3, HfO2, SrTiO3, SnO2, NiO, ZrO2, Y2O3 and SiC.

6. The composite diaphragm according to claim 1, wherein, The adhesive is selected from one or more of (meth)acrylic polymers, fluoropolymers, styrene polymers, vinyl alcohol polymers, vinyl ester polymers, vinylpyrrolidone polymers, cellulose polymers, polyimide polymers, polyamide polymers, polyalkylene glycols and copolymers thereof.

7. The composite diaphragm according to claim 1, wherein, The adhesive comprises polyacrylamide, carboxymethyl cellulose, or a combination thereof.

8. The composite diaphragm according to claim 1, wherein, The adhesive comprises carboxymethyl cellulose with a weight-average molecular weight of 180,000 g / mol or more and a degree of substitution of 0.6 to 1.

2.

9. The composite diaphragm according to claim 1, wherein, The porous substrate has undergone hydrophilic surface treatment.

10. The composite diaphragm according to claim 1, wherein, The coating density of the ceramic layer is 1.2 g / cm³. 3 Up to 1.8 g / cm 3 .

11. The composite diaphragm according to claim 1, wherein, The total thickness of the ceramic layer is 0.5 μm to 10 μm.

12. The composite diaphragm according to claim 1, wherein, The thickness of the composite diaphragm is from 1 μm to 100 μm.

13. The composite diaphragm according to claim 1, wherein, When evaluating the degree of foreign matter adhesion to the paperboard surface after conducting paperboard tests on the composite diaphragm, the area occupied by the adhered foreign matter relative to the paperboard area was less than 5%. In the paperboard test, a black paperboard measuring 2cm × 10cm and a rubber pad were placed sequentially on the ceramic layer of a composite diaphragm sample measuring 5cm × 10cm. With a force of 10N applied to the rubber pad using a pressing device, the paperboard was pulled out horizontally at a speed of 0.1m / s to test the degree to which foreign matter adhered to the surface of the paperboard.

14. The composite diaphragm according to claim 1, wherein, The mechanical and transverse thermal shrinkage rates of the composite diaphragm were both less than 4% after being placed at 150°C for 60 minutes.

15. An electrochemical device, said electrochemical device comprising a positive electrode, a negative electrode, and a composite separator, in, The composite membrane comprises: a porous substrate; and a ceramic layer formed on one or both sides of the porous substrate, wherein the ceramic layer comprises inorganic particles and a binder. The average particle size D50 of the inorganic particles is 0.2 μm to 0.4 μm. In the particle size distribution diagram of the inorganic particles, the ratio A / B of the area A of the small particle size side and the area B of the large particle size side, with the maximum peak as the reference, satisfies 1.05 or more.

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