Composite separator and electrochemical device comprising same

Abstract

The invention relates to a composite diaphragm. The composite diaphragm comprises a porous base material; the composite separator according to the present invention comprises a base material, and a coating layer formed on at least one surface of the base material and containing organic particles, the coating layer satisfying formula 1, the composite separator being capable of ensuring excellent heat resistance, adhesive force, and fusion force with an electrode even in a thin thickness, and being capable of preventing a blocking phenomenon. [Formula 1] 4000 < = (A * D2) / T < = 5500 (In Formula 1, A, D, and T are as described in the specification).

Description

Technical Field

[0001] This invention relates to a diaphragm and an electrochemical device including the composite diaphragm. 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 for membranes, which play a crucial role in ensuring the heat resistance and safety of electrochemical devices, have also become increasingly demanding. For example, composite membranes, which incorporate inorganic coatings containing inorganic particles such as alumina (Al2O3), silicon dioxide (SiO2), and zirconium oxide (ZrO2) and binders onto porous substrates, are becoming an important technology.

[0003] However, existing composite separators have insufficient adhesion to the electrodes, leading to separator separation during battery assembly. This results in electrode component distortion and deformation, and short circuits between electrodes, posing safety concerns. To address these issues, solutions such as coatings containing a separate flux that can generate fusion force with the electrodes have been proposed. However, the fusion effect is insufficient, and even when sufficient fusion force is achieved, problems arise, such as blocking phenomena caused by the desorption of flux and substances in the coating.

[0004] [Existing Technical Documents]

[0005] [Patent Literature]

[0006] (Patent Document 1) KR 10-2573567B1 (August 29, 2023) Summary of the Invention

[0007] (a) Technical problems to be solved

[0008] One embodiment of the present invention relates to a composite membrane incorporating a coating containing organic particles that enable fusion with electrodes, and provides a composite membrane that ensures excellent heat resistance, adhesion and fusion with electrodes even at a relatively thin thickness and prevents blockage.

[0009] Another embodiment of the present invention provides an electrochemical device using the composite membrane.

[0010] (II) Technical Solution

[0011] One embodiment of the present invention provides a composite membrane comprising: a porous substrate; and a coating formed on at least one side of the substrate and comprising organic particles, the coating satisfying the following formula 1.

[0012] [Formula 1]

[0013] 4000≤(A×D 2 ) / T≤5500

[0014] (in Equation 1,

[0015] A represents the number of organic particles per unit area of ​​the coating surface ( / mm). 2 );

[0016] D represents the average particle size (μm) of the organic particles observed on the coating surface;

[0017] T represents the total thickness of the coating (μm).

[0018] The average particle size (D) of the coating surface of the organic particles can be from 1 μm to 10 μm.

[0019] The total thickness of the coating can be from 1 μm to 20 μm.

[0020] The glass transition temperature (T) of the organic particles g The temperature can range from 40℃ to 80℃.

[0021] The organic particles may be selected from one or more of acrylic polymers, urethane polymers, and fluoropolymers.

[0022] The acrylic polymer may comprise copolymers, the copolymers comprising: alkyl (meth)acrylate monomer polymerization units; and one or more polymerization units selected from styrene monomer polymerization units, butadiene monomer polymerization units, and vinyl monomer polymerization units.

[0023] The coating may further comprise inorganic particles and binders.

[0024] The content of the inorganic particles can be from 96% to 99% by weight relative to the total weight of the coating.

[0025] The weight ratio of the adhesive and organic particles contained therein can be from 5:5 to 7:3.

[0026] The content of the organic particles relative to the total weight of the coating can be greater than 1% by weight and less than 2% by weight.

[0027] The equivalent sphere diameter (Dv50) of the inorganic particles can be from 0.01 μm to 1 μm.

[0028] The inorganic particles may contain one or more selected from boehmite, pseudo-boehmite, BaSO4, CeO2, MgO, CaO, ZnO, Al2O3, SiO2, TiO2, BaTiO3, HfO2, SrTiO3, SnO2, NiO, ZrO2, Y2O3, and SiC.

[0029] The adhesive may include 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, and polyalkylene glycols.

[0030] The adhesive may include polyacrylamide, carboxymethyl cellulose, or a combination thereof.

[0031] The adhesive may contain carboxymethyl cellulose, wherein the carboxymethyl cellulose has a weight-average molecular weight of 180,000 g / mol or more and a degree of substitution of 0.6 to 1.2.

[0032] The porous substrate may be hydrophilic surface treated.

[0033] According to one embodiment, the composite diaphragm can have the following anti-clogging properties.

[0034] [Anti-blocking performance]

[0035] Two composite diaphragms are arranged so that the coatings face each other, and the temperature is 25°C and 15 kgf / cm². 2 Pressure was applied for 1 hour, followed by 180° peeling according to ASTM D903. Desorption of organic and / or inorganic particles was confirmed using a scanning electron microscope (SEM). Ten arbitrary locations were selected, and the number of desorbed organic and / or inorganic particles per unit area was counted. The average value of the ten points was less than 10. -4 per μm 2 Or, neither organic nor inorganic particles were desorbed.

[0036] In one embodiment of the composite diaphragm, 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%.

[0037] [Cardboard Test]

[0038] A black cardboard and a rubber pad measuring 2cm×10cm were placed sequentially on the coating of a composite diaphragm sample measuring 5cm×10cm. With a force of 10N applied to the rubber pad using a pressing device, the cardboard 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 cardboard.

[0039] Another embodiment of the present invention provides an electrochemical device comprising a positive electrode, a negative electrode, and a composite membrane, the composite membrane comprising: a porous substrate; and a coating formed on at least one side of the substrate and comprising organic particles, the coating satisfying the following formula 1.

[0040] [Formula 1]

[0041] 4000≤(A×D 2 ) / T≤5500

[0042] (in Equation 1,

[0043] A represents the number of organic particles per unit area of ​​the coating surface ( / mm). 2 );

[0044] D represents the average particle size (μm) of the organic particles observed on the coating surface;

[0045] T represents the total thickness of the coating (μm).

[0046] (III) Beneficial Effects

[0047] According to one embodiment, a composite separator includes a porous substrate and a coating formed on the substrate and comprising organic particles. The composite separator can achieve sufficient fusion with the electrode and can reduce internal resistance and improve electrical performance.

[0048] Furthermore, the composite diaphragm according to one embodiment exhibits excellent heat resistance and adhesion even at relatively thin thicknesses, and can effectively suppress shrinkage at high temperatures.

[0049] Furthermore, according to one embodiment, the composite diaphragm can suppress the desorption and blockage of organic and / or inorganic particles during the winding of the diaphragm.

[0050] Furthermore, the composite membrane according to one embodiment has excellent manufacturability and is conducive to practical commercial applications, and the electrochemical device using the composite membrane according to one embodiment can simultaneously meet the requirements of safety, high capacity and high power characteristics. Attached Figure Description

[0051] Figure 1 The results show the measurement of the number of organic particles per unit area on the coated surface of the composite membrane according to Example 1.

[0052] Figure 2 The results show an example of (a) organic particle desorption and (b) a combination of organic and inorganic particle desorption in the anti-blocking performance evaluation.

[0053] Figure 3 An example of a method for measuring the average particle size of an organic particle coating surface is shown.

[0054] Figure 4 It is a schematic plan view of an electrochemical device according to one implementation scheme.

[0055] Figure 5 This is a schematic cross-sectional view of an electrochemical device according to one implementation scheme.

[0056] [Explanation of reference numerals in the attached figures]

[0057] 100: Positive electrode; 105: Positive electrode current collector

[0058] 107: Positive electrode lead; 110: Positive electrode mixed layer

[0059] 120: Negative electrode mixture layer; 125: Negative electrode current collector

[0060] 127: Negative lead; 130: Negative electrode

[0061] 140: Diaphragm; 150: Electrode assembly

[0062] 160: Casing Detailed Implementation

[0063] 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 specific embodiments only and is not intended to limit the invention.

[0064] Unless otherwise specified in the context, the singular form used in this specification may include the plural form.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] In this specification, "equivalent spherical diameter (Dv50)" refers to the particle size of the sample being measured, corresponding to a cumulative fraction of 50% based on volume. The average particle size can be obtained by collecting samples of the target particles according to ISO 13320-1 standard and analyzing the particle size distribution using a Microtrac S3500 analyzer. The target sample refers to both inorganic and organic particles.

[0069] In this specification, "polymer" refers to a compound formed by the polymerization of one or more monomers, including homopolymers composed of a single monomer and copolymers composed of two or more different monomers. Furthermore, "polymer" in this specification also includes polymers with molecular structures such as linear, branched, and network structures.

[0070] 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.

[0071] In order to solve the problem of insufficient adhesion between the diaphragm and the electrode, the existing technology has proposed a solution of introducing a fusing agent that can achieve fusion force with the electrode. However, in recent years, with the thinning of the diaphragm in order to achieve high capacity and high power characteristics of electrochemical devices, when sufficient fusion force is to be achieved in a relatively thin thickness range, there will be limitations such as fusing agent desorption leading to blocking.

[0072] In this regard, the inventors have discovered a relationship between the number of organic particles per unit area observed on the coating surface, the average particle size of the organic particles observed on the coating surface, and the total thickness of the coating in a composite membrane comprising a porous substrate and a coating formed on the substrate and containing organic particles for achieving fusion with the electrode. This has led to the discovery of a composite membrane that exhibits excellent adhesion between inorganic particles and between inorganic particles and the substrate, even within a relatively thin thickness range, and ensures fusion with the electrode while possessing excellent anti-clogging properties.

[0073] Specifically, a composite membrane according to one embodiment includes: a porous substrate; and a coating formed on at least one side of the substrate and comprising organic particles, the coating satisfying Formula 1 below.

[0074] [Formula 1]

[0075] 4000≤(A×D 2 ) / T≤5500

[0076] (in Equation 1,

[0077] A represents the number of organic particles per unit area of ​​the coating surface ( / mm). 2 );

[0078] D represents the average particle size (μm) of the organic particles observed on the coating surface;

[0079] T represents the total thickness of the coating (μm).

[0080] According to one embodiment, the composite separator achieves sufficient adhesion to the electrode, reduces internal resistance, and improves electrical performance by ensuring that the value of Equation 1 regarding the number of organic particles per unit area of ​​the coating surface, the average particle size of the organic particles observed on the coating surface, and the total thickness of the coating is in the range of 4000 to 5500. Furthermore, according to one embodiment, the composite separator, by ensuring that the value of Equation 1 is in the range of 4000 to 5500, preferably achieves sufficient adhesion to the electrode, reduces internal resistance, and improves electrical performance even without a separate adhesive layer. Moreover, according to one embodiment, the composite separator exhibits excellent heat resistance and adhesion even at relatively thin thicknesses, effectively suppresses shrinkage at high temperatures, suppresses desorption and blockage of organic particles during winding, and suppresses desorption and blockage of inorganic and / or organic particles when the coating contains inorganic particles. Furthermore, electrochemical devices employing the composite separator can simultaneously meet the requirements of safety, high capacity, and high power characteristics.

[0081] When measuring the number of organic particles per unit area on the coating surface, the average particle size of the organic particles observed on the coating surface, and the coating thickness, the composite separator can be a composite separator obtained before battery assembly or after battery assembly and disassembly. For example, when using a composite separator disassembled after battery assembly for measurement, the battery can be disassembled and the separator washed and dried for measurement, regardless of the time elapsed since battery assembly. In this case, the drying can be performed in a vacuum oven at temperatures of 20°C to 50°C or 20°C to 40°C for 10 to 30 hours or 20 to 30 hours. If measurement is difficult due to electrolyte salts or the like, washing and drying can be repeated for measurement.

[0082] In one embodiment, Formula 1 can be 4000 to 5500, 4000 to 5400, or 4200 to 5400, and can include all possible combinations of the upper and lower limits of the above numerical range, which can make the effect of simultaneously improving fusion force and anti-blocking performance even better, thereby making the battery stability and capacity even better.

[0083] In one embodiment, the number of organic particles per unit area of ​​the coated surface ( / mm) 2 The coating surface can be measured by photographing and imagerizing it using an optical microscope. Specifically, an optical microscope is used to designate 10 locations on the coating surface, and a 1mm × 1mm area at each location is photographed for image conversion. Figure 1 The number of organic particles observed in the converted image area is counted, and the average value of 10 points is used for calculation.

[0084] In one embodiment, the number of organic particles per unit area of ​​the coating surface can be more than 300, more than 400, more than 500, more than 600, more than 700, more than 800, more than 1,000, or less than 5,000, less than 4,000, or less than 3,000. For example, it can be between 500 and 3,000, between 500 and 2,800, between 500 and 2,600, between 600 and 2,600, or between 700 and 2,600, and can include all possible combinations of the upper and lower limits of the above numerical range.

[0085] The number of organic particles per unit area on the surface of the coating can be achieved by adjusting the equivalent sphere diameter (Dv50) of the organic particles, the content of the organic particles, the thickness of the coating, the coating method, the drying conditions of the coating, or a combination thereof, but is not particularly limited in the method.

[0086] In one embodiment, the average particle size (D) of the organic particles observed on the coating surface can be measured by observing the coating surface of the composite separator using a scanning electron microscope (SEM). Specifically, an SEM image of the composite separator coating surface magnified at 10kx can be obtained using a Hitachi S-4800, and the diameter of the longest organic particle can be measured. Figure 3 The value was then rounded to one decimal place (unit: μm). The same measurement was performed on 20 organic particles and the average was taken as the average particle size of the coating surface of the organic particles.

[0087] In one embodiment, the average particle size (D) of the organic particles observed on the coating surface is combined with the number of organic particles per unit area observed on the coating surface and the total thickness of the coating. As long as the combination satisfies the range of Equation 1, there is no particular limitation on the average particle size (D) of the organic particles observed on the coating surface. As an example, it can be 1 μm or more, 1.5 μm or more, 2.0 μm or more, or 2.5 μm or more, or it can be less than 10 μm, less than 8 μm, less than 6 μm or less than 5 μm. It can also be from 1 μm to 10 μm, from 1 μm to 8 μm, from 1 μm to 6 μm, or from 2 μm to 6 μm. It can include all possible combinations of the upper and lower limits of the above numerical ranges, in which case better fusion strength and anti-blocking performance can be achieved.

[0088] In one embodiment, the glass transition temperature (T) of the organic particles g The temperature range can be above 40°C, above 45°C, above 50°C, or above 60°C, and can be below 100°C, below 90°C, or below 80°C, or can be between 40°C and 100°C, 40°C and 90°C, or 40°C and 80°C, and can include all possible combinations of the upper and lower limits of the above numerical ranges. When the above ranges are met, the fusion force between the composite separator and the electrode can be further improved, and the battery performance after battery assembly can be further improved. Preferably, the glass transition temperature of the organic particles can be between 40°C and 70°C, within which they will not flow during the drying process, will not deform during the coating step and shipping process, and can minimize changes in the permeability of the substrate even after fusion, thereby maintaining excellent performance, and is therefore more preferably. The glass transition temperature is determined by measuring the heat capacity of a sample heated at a rate of 10°C / min in a nitrogen atmosphere using a differential scanning calorimeter (DSC) within a range of -100°C to 250°C. The temperature at the midpoint of the range where the heat capacity of the sample changes drastically is calculated as the glass transition temperature.

[0089] The organic particles are not particularly limited as long as they are particulate organic substances that can achieve fusion force with the electrode, but may include acrylic polymers, urethane polymers, fluoropolymers, or combinations of two or more of them.

[0090] The acrylic polymer may include homopolymers or copolymers containing (meth)acrylate monomer polymerization units. Furthermore, the acrylic polymer may include homopolymers or copolymers containing alkyl (meth)acrylate monomer polymerization units. The alkyl (meth)acrylate monomers may include C1-C10 alkyl (meth)acrylate monomers, C1-C6 alkyl (meth)acrylate monomers, or C1-C4 alkyl (meth)acrylate monomers; specifically, they may include one or more selected from meth (meth)acrylates, ethyl (meth)acrylates, and n-butyl (meth)acrylates.

[0091] The copolymer comprising alkyl (meth)acrylate monomer polymerization units may include copolymers comprising: alkyl (meth)acrylate monomer polymerization units; and one or more polymerization units selected from styrene monomer polymerization units, butadiene monomer polymerization units, and vinyl monomer polymerization units.

[0092] The fluoropolymer may include polyvinylidene fluoride (PVdF)-based polymers. Examples of such polyvinylidene fluoride polymers include polyvinylidene fluoride homopolymers, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, and polyvinylidene fluoride-chlorotrifluoroethylene, and may include more than one selected from these. Alternatively, polyvinylidene fluoride polymers comprising a repeating unit (A) of polyvinylidene fluoride and other repeating units (B) that can be copolymerized with the repeating unit may also be used.

[0093] As a non-limiting example of the organic particles, they may include polyurethane beads, polyurethane acrylate beads, epoxy-acrylate beads, polyacrylate, polymethacrylate, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), polyvinylidene fluoride-trichloroethylene (PVdF-TCE), polyvinylidene fluoride-chlorotrifluoroethylene (PVdF-CTFE), polystyrene-polybutyl methacrylate-polymethyl methacrylate (PS-PBMA-PMMA), polybutyl methacrylate-polymethyl methacrylate (PBMA-PMMA), polystyrene-polydimethylsiloxane-polybutyl methacrylate (PS-PDMS-PBMA), polystyrene-polydimethylsiloxane-polymethyl methacrylate (PS-PDMS-PMMA), polydimethylsiloxane-polymethyl methacrylate (PDMS-PMMA), or combinations thereof, but are not limited thereto.

[0094] The organic particles can be prepared by emulsion polymerization or suspension polymerization, which are known preparation methods, so specific details are omitted.

[0095] Furthermore, the composite membrane according to one embodiment may further comprise inorganic particles and a binder, and the coating of the composite membrane according to one embodiment may comprise the aforementioned organic particles, inorganic particles and binder as a single coating, or the coating of the composite membrane according to one embodiment may comprise an organic particle layer comprising the aforementioned organic particles and an inorganic particle layer comprising inorganic particles and a binder.

[0096] Specifically, according to one embodiment, the composite separator may contain inorganic particles, binder and organic particles as a single coating. In this case, the internal resistance of the subsequent battery can be further reduced, and the electrical performance can be further improved while ensuring the bonding force with the electrode. Therefore, this is preferred, but not necessarily limited to.

[0097] In one embodiment, the composite membrane includes a porous substrate and a coating formed on one or both sides of the porous substrate, the coating being an inorganic particle bonded and fixed by an adhesive and having pores between the inorganic particles.

[0098] In one embodiment, the adhesive is not particularly limited as long as it is a conventional adhesive used in this art. As a non-limiting example, the adhesive may include one or more selected from (meth)acrylate polymers, fluoropolymers, styrene polymers, vinyl alcohol polymers, vinyl ester polymers, vinylpyrrolidone polymers, cellulose polymers, polyimide polymers, polyamide polymers, and polyalkylene glycols. The (meth)acrylate polymer may include, for example, one or more selected from polyalkyl(meth)acrylates, poly(meth)acrylic acid, poly(meth)acrylamide, poly(meth)acrylonitrile, polyhydroxyethyl(meth)acrylate, or copolymers thereof. The fluoropolymer may include polyvinylidene fluoride (PVdF) based polymers. Examples of such polyvinylidene fluoride polymers include, for instance, polyvinylidene fluoride homopolymers, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, and polyvinylidene fluoride-chlorotrifluoroethylene, and may include one or more selected from these. In addition, polyvinylidene fluoride polymers comprising repeating units (A) of vinylidene fluoride and other repeating units (B) that can copolymerize with said repeating units can also be used. As an example, the styrene-based polymer may include one or more selected from polystyrene, polyalphamethylstyrene, polybrominated styrene, or copolymers thereof. As an example of the vinyl alcohol-based polymer, it may include one or more selected from polyvinyl alcohol or copolymers containing polyvinyl alcohol. As an example of the vinyl ester-based polymer, it may include one or more selected from polyethylene ester or copolymers containing polyethylene ester. As an example of the cellulose-based polymer, it may include one or more selected from cellulose, carboxymethyl cellulose, hydroxypropyl methyl cellulose, cellulose acetate, cellulose acetate propionate, etc.

[0099] In one embodiment, the adhesive may include (meth)acrylic acid-based polymers, cellulose-based polymers, or combinations thereof.

[0100] Specifically, the adhesive may comprise polyacrylamide (PAAm), carboxymethyl cellulose, or a combination thereof. Furthermore, the adhesive may be a mixed adhesive comprising polyacrylamide and carboxymethyl cellulose, which is preferred but not limited to improving the desired effects of the invention.

[0101] In one embodiment, 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 200,000 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.

[0102] 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 one dehydrated glucose unit of the cellulose molecule, which can be measured by known or commonly used methods, for example, according to ASTM D1439, or by... 1 H-NMR or 13 Calculations were performed using C-NMR analysis.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] The number of millimoles (A) of CMC acid in 1g of dried sample is calculated using the following formula.

[0109]

[0110] Then, the degree of substitution (DS) is calculated from A using the following formula.

[0111]

[0112] In one embodiment, the weight-average molecular weight of the polyacrylamide can be above 100,000 g / mol, above 150,000 g / mol, or above 180,000 g / mol, and can be below 500,000 g / mol, below 400,000 g / mol, below 300,000 g / mol, or below 250,000 g / mol. Specifically, it can be from 100,000 g / mol to 300,000 g / mol or from 150,000 g / mol to 250,000 g / mol, or can 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 can refer to the weight-average molecular weight calculated based on a molecular weight calibration curve using a polystyrene standard sample measured by GPC methods. A sample is obtained by dissolving carboxymethyl cellulose in a standard substance at approximately 0.1% w / v, and the sample is injected into a GPC device for measurement.

[0113] When the adhesive comprises carboxymethyl cellulose and polyacrylamide, the weight ratio of carboxymethyl cellulose to polyacrylamide used may be 10 to 50: 90 to 50 or 10 to 40: 90 to 60.

[0114] In one embodiment, the inorganic particles can be used without restriction as long as they are of the types commonly used in this art. 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.

[0115] In one embodiment, the equivalent sphere diameter (Dv50) of the inorganic particles may be, for example, 0.01 μm or more, 0.02 μm or more, 0.05 μm or more, or 0.1 μm or more, and may be from 0.01 μm to 10 μm, 0.02 μm to 5.0 μm, 0.1 μm to 3.0 μm, 0.1 μm to 2.0 μm, 0.1 μm to 1.0 μm, or 0.1 μm to 0.5 μm, or may include all possible combinations of the upper and lower limits of the above numerical ranges, but is not limited thereto.

[0116] In one embodiment, the inorganic particle content in the coating 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 relative to the total weight of the coating. Compared with the inorganic particle content of existing coatings formed by linking inorganic particles with binders, this can contain a greater amount of inorganic particles. Nevertheless, it has excellent heat resistance and numerical stability, thereby allowing the coating to be formed at a thinner thickness.

[0117] In one embodiment, the content of the organic particles in the coating, relative to the total weight of the coating, can be 0.1% by weight or more, 0.5% by weight or more, 1.0% by weight or more, greater than 1.0% by weight, 1.1% by weight or more, or 1.2% by weight or more, and can be less than 5% by weight, less than 4% by weight, less than 3% by weight, less than 2% by weight, or less than 2% by weight. Specifically, it can be from 0.5% by weight to 5% by weight, from 1% by weight to 5% by weight, from 1% by weight to 3% by weight, greater than 1% by weight and less than 2% by weight, and can include all possible combinations of the upper and lower limits of the above numerical ranges.

[0118] In one embodiment, the weight ratio of the included adhesive to the organic particles can be 5:5 to 9:1, 5:5 to 8:2, or 5:5 to 7:3.

[0119] In one embodiment, the composite separator may have anti-clogging properties, which refer to the ability to suppress the desorption and clogging of organic and / or inorganic particles during separator winding. Specifically, two composite separators are arranged such that the coatings face each other, and the temperature is 25°C and the pressure is 15 kgf / cm². 2 The pressure was applied for 1 hour, followed by 180° peeling according to ASTM D903. Desorption of organic and / or inorganic particles was confirmed by scanning electron microscopy (SEM). Ten arbitrary locations were selected, and the number of desorbed organic and / or inorganic particles per unit area was counted. The average value of the ten points was calculated, with a desorbed number less than 10. -4 per μm 2 If none of them desorb, then it is considered to have anti-blocking properties.

[0120] 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%.

[0121] The paperboard test method is as follows: A black paperboard measuring 2cm × 10cm and a rubber pad are placed sequentially on the coating 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 out horizontally 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 coating, such as inorganic particles, adhesives, or a combination thereof.

[0122] When evaluating adhesive strength using the paperboard testing method described above, not only the adhesive strength between the substrate and the coating interface can be considered, but also the adhesive strength between inorganic particles within the coating. Furthermore, the adhesive strength test results can predict the degree of heat 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 heat shrinkage.

[0123] 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.

[0124] In one embodiment, the mechanical (MD) and transverse (TD) heat shrinkage rates measured after placing the composite diaphragm at 150°C for 60 minutes can both be below 5%, specifically below 3%, 2.5%, 2.0%, 1.5%, 1.0%, or 0.5%. The heat shrinkage rate of the composite diaphragm is measured according to ASTM D1204, using the following method: Mark grid points at 2cm intervals within a 10cm square of the composite diaphragm sample. One side of the square is designated as the transverse (TD), and the other side as the mechanical (MD) direction. Place the sample in the center, and place 5 sheets of paper above and below the sample, then secure the four sides of the paper with tape. Place the tape-secured sample in a hot air dryer at 150°C for 60 minutes. Afterward, remove the sample, observe the diaphragm at room temperature using a camera, and calculate the mechanical (MD) and transverse (TD) shrinkage rates.

[0125] 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.

[0126] 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.

[0127] In one embodiment, the porous substrate may be a substrate incorporating polar functional groups through a hydrophilic surface treatment, thereby achieving superior adhesion. Examples of polar functional groups include carboxyl groups, aldehyde groups, and hydroxyl groups. As an example, the hydrophilic surface treatment may be corona discharge treatment or plasma discharge treatment, but there are no particular limitations.

[0128] 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, 5 μm to 15 μm, 5 μm to 12 μm, 5 μm to 10 μm, or any value between the above values.

[0129] In one embodiment, the coating may be applied to one or both sides of the porous substrate, and when the coating is applied to both sides of the porous substrate, the thickness of the coating applied to one side and the other side may be the same or different.

[0130] The total thickness of the coating is a combination of the total thickness and the number of organic particles per unit area observed on the surface of the coating and the average particle size of the organic particles. The total thickness of the coating is not particularly limited as long as it satisfies the range of Formula 1, but can be, for example, 0.1 μm to 20 μm, 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, or any value between the above values. According to one embodiment, the composite diaphragm achieves excellent adhesion and heat resistance even when the coating is formed very thinly; therefore, electrochemical devices using the composite diaphragm can simultaneously meet safety, high capacity, and high power characteristics.

[0131] The thickness of the composite diaphragm according to one embodiment can 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, and can include all possible combinations of the upper and lower limits of the numerical range, and is not limited thereto.

[0132] Another embodiment of the present invention provides a method for manufacturing the composite membrane, the method comprising the steps of coating at least one side of a porous substrate with a coating-forming composition comprising organic particles and drying to form a coating, the coating satisfying the following formula 1.

[0133] [Formula 1]

[0134] 4000≤(A×D 2 ) / T≤5500

[0135] (in Equation 1,

[0136] A represents the number of organic particles per unit area of ​​the coating surface ( / mm). 2 );

[0137] D represents the average particle size (μm) of the organic particles observed on the coating surface;

[0138] T represents the total thickness of the coating (μm).

[0139] The A, D, T, porous substrate, organic particles, and coating are as described above, therefore detailed descriptions are omitted.

[0140] The coating-forming composition may also contain a solvent, which may be water, ethanol, methanol, propanol and other lower alcohols, dimethylformamide, acetone, tetrahydrofuran, diethyl ether, dichloromethane, N-methyl-2-pyrrolidone, hexane, cyclohexane and other solvents or mixtures thereof, but is not necessarily limited thereto.

[0141] The coating-forming composition may further include a binder and inorganic particles, and the aggregated inorganic particles may be dispersed using a ball mill.

[0142] In one embodiment, the solids content of the coating-forming composition is not particularly limited, but for example, the solids content of the ceramic layer-forming composition may be from 1% to 50% by weight, 5% to 30% by weight, or 10% to 30% by weight, but is not limited thereto. Furthermore, the viscosity of the coating-forming composition based on a solids content of 25% by weight may be from 800 cps to 5000 cps, 800 cps to 4000 cps, 800 cps to 3000 cps, or 1000 cps to 3000 cps, in which case the coating can be formed more easily, and the heat resistance and adhesion of the diaphragm can be further improved.

[0143] In one embodiment, there are no particular limitations on the method of coating or applying the coating composition onto the porous substrate, but, for example, roll coating, spin coating, dip coating, bar coating, die coating, slit coating or inkjet printing can be used.

[0144] In one embodiment, the drying can be carried out by methods such as drying with warm air, hot air, low-humidity air, vacuum drying, far-infrared radiation, or electron beam irradiation. The drying temperature can be appropriately adjusted according to the experimental environment or purpose, for example, it can be above 30°C, above 40°C, or above 50°C, or below 70°C or below 60°C. Specifically, it can be 30°C to 70°C, 40°C to 70°C, 40°C to 60°C, 50°C to 70°C, or 50°C to 60°C. The drying time can be 30 seconds to 500 seconds, 60 seconds to 500 seconds, 100 seconds to 500 seconds, 100 seconds to 400 seconds, 150 seconds to 400 seconds, approximately 180 seconds to 400 seconds, 200 seconds to 400 seconds, or 300 seconds. When the above drying conditions are met, the value of Equation 1 can be adjusted more appropriately, and the drying conditions are not particularly limited as long as they are within the range of Equation 1.

[0145] 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.

[0146] Specifically, an electrochemical device according to one embodiment may include a positive electrode, a negative electrode, and a composite membrane, wherein the composite membrane may include a porous substrate and a coating containing organic particles formed on at least one side of the porous substrate, the coating satisfying the following formula 1.

[0147] [Formula 1]

[0148] 4000≤(A×D 2 ) / T≤5500

[0149] (in Equation 1,

[0150] A represents the number of organic particles per unit area of ​​the coating surface ( / mm). 2 );

[0151] D represents the average particle size (μm) of the organic particles observed on the coating surface;

[0152] T represents the total thickness of the coating (μm).

[0153] In one embodiment, the electrochemical device includes a positive electrode, a negative electrode, and a composite membrane. The composite membrane may include a porous substrate and a coating formed on one or both sides of the substrate. The coating may contain inorganic particles, binders, and organic particles, and may satisfy Formula 1.

[0154] 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.

[0155] 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.

[0156] [positive electrode]

[0157] 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.

[0158] 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.

[0159] 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.

[0160] 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.

[0161] 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 nickel-cobalt-manganese (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 nickel-cobalt-manganese (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 Co 0.2 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.

[0162] 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.

[0163] 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.

[0164] 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.

[0165] [negative electrode]

[0166] The negative electrode may include a negative electrode current collector and a negative electrode mixture layer located on at least one side of the negative electrode current collector. The negative electrode can be manufactured by coating a negative electrode material slurry onto one or both sides of the negative electrode current collector and then drying and calendering 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 conductive materials, thickeners, etc. as needed.

[0167] The negative electrode current collector may include copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, 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.

[0168] 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 technical field. 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.

[0169] Examples of the amorphous carbon can include hard carbon, soft carbon, coke, mesocarbon microbead (MCMB), mesophase pitch-based carbon fiber (MPCF), etc. Examples of the crystalline carbon can include graphite-based carbons such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, graphitized MPCF, etc.

[0170] Elements included in the lithium alloy can include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium or indium, etc.

[0171] The silicon-containing substance can provide further increased capacity characteristics. The silicon-containing substance can include Si, SiO x (0 < x ≤ 2), metal-doped SiO x (0 < x ≤ 2), silicon-carbon composites, etc. The metal can include lithium and / or magnesium. Metal-doped SiO x (0 < x ≤ 2) can include metal silicates. The binder, conductive material, and thickening agent of the negative electrode can use the above substances that can be used in manufacturing the positive electrode.

[0172] The negative electrode binder has no particular limitation as long as it is a negative electrode binder commonly used in the technical field. The negative electrode binder can use rubber-based binders such as styrene-butadiene rubber (SBR)-based binders, carboxymethyl cellulose (CMC), polyacrylic acid, poly(3,4-ethylenedioxythiophene) (PEDOT)-based binders, etc.

[0173] [Electrolyte]

[0174] In one embodiment, the electrolyte may be a non-aqueous electrolyte, which may contain a lithium salt and an organic solvent as the electrolyte.

[0175] 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.

[0176] 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, tetrahydrofuran, 2-methyltetrahydrofuran, ethanol, isopropanol, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, sulfolane, γ-butyrolactone, and propylene sulfite, etc., one or more of these.

[0177] [Cell Structure]

[0178] For example, tabs (positive and negative tabs) can protrude from the positive and negative current collectors and extend to one side of the housing, respectively. The tabs can be fused to said side of the housing and connected to electrode leads (positive and negative leads) extending to or exposed outside the housing. For example, pouch-type housings, prismatic housings, cylindrical housings, coin-type housings, etc., can be used.

[0179] 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.

[0180] [Methods for measuring physical properties]

[0181] 1) Average particle size (D, unit: μm) of organic particles on the coating surface

[0182] The coating surface of the composite separator was observed using scanning electron microscopy (SEM), and the average particle size of the organic particles observed on the coating surface was measured. Specifically, SEM images of the composite separator coating surface were obtained at 10kx magnification using a Hitachi S-4800 microscope, and the longest diameter of a single organic particle was measured. Figure 3 The value was then rounded to one decimal place (unit: μm). The same measurement was performed on 20 organic particles and the average was taken as the average particle size of the coating surface of the organic particles.

[0183] 2) Thickness

[0184] Ten layers of the composite membrane were stacked and their thickness was measured using a Mitutoyo ID-C112X sensor 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 divided by 10 to obtain the thickness of the composite membrane. The thickness of the porous substrate was subtracted from the thickness of the composite membrane to obtain the total thickness of the coating (T, μm).

[0185] 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 layers was then obtained, and the average thickness of the porous substrate was taken as the thickness of the porous substrate by dividing the average thickness of the 10 layers by 10. In the case where a coating has been formed, the coating was peeled off and thoroughly dried, and then the average thickness of the porous substrate after coating removal was obtained using the method described above.

[0186] 3) The number of organic particles per unit area of ​​the coating surface (A, unit: / mm) 2 )

[0187] The coating surface of the composite membrane was imaged using an optical microscope (Leica-Microsystems, DVM 6), and the number of organic particles per unit area observed on the coating surface was measured ( / mm²). 2 Specifically, a PlanAPO FOV 3.60 objective lens was mounted on an optical microscope. Ten arbitrary locations on the coating surface were then selected. Each location was divided into 6×4 sections of 1mm × 1mm size, and images were captured and then joined together. The images were then converted using the following image conversion method. The number of organic particles observed within the converted image area was counted, and the average value of the 10 locations was obtained as the number of organic particles per unit area of ​​the coating surface, A.

[0188] Image conversion methods

[0189] 1. Open the prepared image using ImageJ S / W.

[0190] 2. Convert the image type to an 8-bit image.

[0191] 3. Use the Despeckle and Bandpass Filter functions to remove noise from the image, making the surrounding background and the shape of the organic particles easier to distinguish.

[0192] 4. Adjust the threshold to separate the shape of organic particles from the image.

[0193] 5. Perform particle analysis (Analyze Particles) on the image showing the separated organic particle shapes to count the number of organic particles present in the image. Figure 1 ).

[0194] 4) Adhesive force

[0195] [Cardboard Test]

[0196] 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 coating 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 surface of the cardboard. The foreign matter could be a component of the coating, such as inorganic particles, adhesives, or a combination thereof.

[0197] [Evaluation of the degree of foreign body adhesion]

[0198] 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.

[0199] A: <1.5%

[0200] B: 1.5% to 5%

[0201] C: >5%

[0202] 5) Electrode fusion force

[0203] The positive and negative electrodes are manufactured as follows, and the fusion force between the electrodes and the composite membrane is evaluated.

[0204] 94 wt% of LiCoO2 as the positive electrode active material, 2.5 wt% of polyvinylidene fluoride as a binder, and 3.5 wt% of carbon black as a conductive agent were added to N-methyl-2-pyrrolidone (NMP) as a solvent and stirred to obtain a uniform positive electrode slurry. The slurry was coated onto an aluminum foil with a thickness of 30 μm, dried at 120 °C, and then calendered to obtain a positive electrode plate with a thickness of 150 μm.

[0205] Artificial graphite, with a weight ratio of 95% as the negative electrode active material and 3% as the binder, was used. g A uniform negative electrode slurry was prepared by adding 2% by weight of acrylic latex (trade name: BM900B, solids content: 20% by weight) at -52℃ and 2% by weight of carboxymethyl cellulose (CMC) as a thickener to water as a solvent and stirring. The slurry was coated onto a copper foil with a thickness of 20 μm, dried at 120℃, and then calendered to obtain a negative electrode plate with a thickness of 150 μm.

[0206] The composite separator was stacked between four positive (negative) electrodes prepared as described above, and then pressed at 90°C and 1 MPa for 30 seconds using a hot press to prepare samples for evaluating the fusion strength with the positive and negative electrodes. When the samples were lifted vertically, the number of attached electrodes was counted, and the fusion strength between the composite separator and the positive electrode and the composite separator and the negative electrode was evaluated according to the following criteria, and recorded in Table 2 below.

[0207] 1 / 4: One of the four electrodes is fused together.

[0208] 2 / 4: Two of the four electrodes are fused together.

[0209] 3 / 4: 3 out of 4 electrodes are fused together

[0210] 4 / 4: All four electrodes out of the four electrodes are fused together.

[0211] 6) Anti-blocking performance

[0212] Two composite diaphragms are arranged so that the coatings face each other, and the temperature is 25°C and 15 kgf / cm². 2The pressure was applied for 1 hour, followed by 180° peeling according to ASTM D903. Desorption of organic and / or inorganic particles was confirmed by scanning electron microscopy (SEM). Ten arbitrary locations were selected, and the number of desorbed organic and / or inorganic particles per unit area was counted. The average value of the ten points was used to evaluate the anti-clogging performance according to the following criteria: Figure 2 ).

[0213] O: Neither organic nor inorganic particles were desorbed, or the number of desorbed particles was less than 10. -4 per μm 2 .

[0214] X: The number of organic or inorganic particles desorbed is 10⁻⁴. -4 per μm 2 above.

[0215] [Example 1]

[0216] 100 parts by weight of boehmite with a Dv50 of 0.3 μm and 2 parts by weight of dispersant 1,2-benzisothiazolin-3-one (DIO2) were mixed in water to prepare a slurry with a solid content of 45% by weight. Polyacrylamide (PAAm) (Mw 200000 g / mol, Sigma-Aldrich) and carboxymethyl cellulose (CMC) (degree of substitution 0.9, weight-average molecular weight 200000 g / mol) were added as binders to the prepared slurry. Polystyrene-polybutyl methacrylate-polymethyl methacrylate block copolymer (PS-PBMA-PMMA) (Dv50: 2.5 μm, T...) was added as organic particles. g The composition for coating formation is prepared by setting the weight ratio of boehmite / PAAm / CMC / PS-PBMA-PMMA to 96 / 2 / 0.8 / 1.2 at 62°C.

[0217] A 9μm thick polyethylene film substrate (porosity 35% to 45%, SKIET) was subjected to corona discharge treatment on both sides (power density 2W / m²). 2 To introduce surface polar groups, the corona surface treatment speed is set to 5 meters per minute (mpm). The coating-forming composition is applied to both sides of the corona-treated polyethylene film substrate by wire bar coating, and then dried in a drying oven at 50°C for 5 minutes under the operating conditions of 5 meters per minute, thereby preparing a composite diaphragm with a coating of the same thickness on both sides.

[0218] [Example 2]

[0219] The procedure was carried out using the same method as in Example 1, except that the weight ratio of boehmite / PAAm / CMC / PS-PBMA-PMMA used was 96 / 2 / 0.3 / 1.7.

[0220] [Example 3]

[0221] The same method as in Example 1 was used, except that the weight ratio of boehmite / PAAm / CMC / PS-PBMA-PMMA used was 96 / 1.8 / 0.3 / 1.9, and the thickness of the layer was changed as shown in Table 1 below.

[0222] [Example 4]

[0223] The procedure was performed using the same method as in Example 1, except that PS-PBMA-PMMA (Dv50: 5.0 μm, T) was used. g The organic particles were used at 62℃, and PAAm was used alone as the binder. The weight ratio of boehmite / PAAm / PS-PBMA-PMMA used was 96 / 2.8 / 1.2, and the coating thickness was changed as shown in Table 1 below.

[0224] [Example 5]

[0225] The procedure was performed using the same method as in Example 1, except that the polyethylene film substrate was not subjected to corona discharge treatment.

[0226] [Comparative Example 1]

[0227] The same method as in Example 1 was used, except that the weight ratio of boehmite / PAAm / CMC / PS-PBMA-PMMA used was 97 / 0.7 / 0.3 / 2, and the coating thickness was changed as shown in Table 1 below.

[0228] [Comparative Example 2]

[0229] The procedure was carried out using the same method as in Example 1, except that the weight ratio of boehmite / PAAm / CMC / PS-PBMA-PMMA used was 94 / 3 / 2 / 1.

[0230] [Comparative Example 3]

[0231] The procedure was performed using the same method as in Example 1, except that PS-PBMA-PMMA (Dv50: 3.0 μm, T) was used. g The weight ratio of boehmite / PAAm / CMC / PS-PBMA-PMMA used as organic particles (62℃) was 92.2 / 3 / 2.8 / 2, and the coating thickness was changed as shown in Table 1 below.

[0232] [Comparative Example 4]

[0233] The procedure was performed using the same method as in Example 1, except that PS-PBMA-PMMA (Dv50: 5.0 μm, T) was used. g The organic particles were 62℃, and PAAm was used alone as the binder. The weight ratio of boehmite / PAAm / PS-PBMA-PMMA used was 95 / 3 / 2, and the thickness of the coating was changed as shown in Table 1 below.

[0234] Using the composite separators obtained in the above embodiments and comparative examples, after assembling them into batteries, the physical properties are measured according to the method described in the above physical property measurement method, and the value of Equation 1 below is calculated, discarding the first decimal place, and recorded in Table 1 below.

[0235] [Formula 1]

[0236] (A×D 2 ) / T

[0237] (In Equation 1, A is the number of organic particles per unit area of ​​the coating surface ( / mm) 2 D is the average particle size (μm) of the organic particles on the coating surface; T is the total thickness of the coating (μm).

[0238] [Table 1]

[0239]

[0240] Referring to Table 1, it can be seen that the composite diaphragm according to one embodiment of the present invention can simultaneously achieve excellent electrode fusion strength and anti-clogging performance even with a relatively thin coating thickness. Furthermore, the composite diaphragm according to one embodiment not only has excellent adhesion between the substrate and coating interface, but also excellent adhesion between inorganic particles within the coating, and can effectively suppress thermal shrinkage. In addition, electrochemical devices using the composite diaphragm according to one embodiment can ensure heat resistance and safety, and are beneficial for high capacity and high power. Furthermore, it can be confirmed that Example 1, using a mixed adhesive of PAAm and CMC, has excellent air permeability characteristics. Specifically, when measuring air permeability according to ASTM D726, the air permeability of the diaphragm according to Example 1 was measured to be 165 seconds / 100 ml (cc), and the air permeability of the diaphragm according to Example 4, using PAAm alone, was measured to be 180 seconds / 100 ml.

[0241] Furthermore, according to the comparative example, even when the electrode fusion force is ensured, the composite diaphragm still experiences desorption of organic and / or inorganic particles during winding. Figure 2Furthermore, it was confirmed that when preventing desorption, the electrode fusion force could not be guaranteed.

[0242] 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.

[0243] 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.

[0244] 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 diaphragm, wherein, The composite membrane comprises: a porous substrate; and a coating formed on at least one side of the substrate and comprising organic particles. The coating satisfies the following formula 1. [Formula 1] 4000≤(A×D 2 ) / T≤5500 In Equation 1, A represents the number of organic particles per unit area of ​​the coating surface, expressed in mm. 2 ; D represents the average particle size of the organic particles observed on the coating surface, in μm. T represents the total thickness of the coating, measured in μm.

2. The composite diaphragm according to claim 1, wherein, The average particle size D of the organic particles on the coating surface is 1 μm to 10 μm.

3. The composite diaphragm according to claim 1, wherein, The total thickness of the coating is from 1 μm to 20 μm.

4. The composite diaphragm according to claim 1, wherein, The glass transition temperature T of the organic particles g The temperature ranges from 40°C to 80°C.

5. The composite diaphragm according to claim 1, wherein, The organic particles comprise one or more selected from acrylic polymers, urethane polymers, and fluoropolymers.

6. The composite diaphragm according to claim 5, wherein, The acrylic polymer comprises a copolymer, the copolymer comprising: alkyl (meth)acrylate monomer polymerization units; and one or more polymerization units selected from styrene monomer polymerization units, butadiene monomer polymerization units, and vinyl monomer polymerization units.

7. The composite diaphragm according to claim 1, wherein, The coating further comprises inorganic particles and a binder.

8. The composite diaphragm according to claim 7, wherein, The content of the inorganic particles is 96% to 99% by weight relative to the total weight of the coating.

9. The composite diaphragm according to claim 7, wherein, The weight ratio of the adhesive to the organic particles contained therein is 5:5 to 7:

3.

10. The composite diaphragm according to claim 7, wherein, The content of the organic particles relative to the total weight of the coating is in the range of greater than 1% by weight and less than 2% by weight.

11. The composite diaphragm according to claim 7, wherein, The equivalent sphere diameter Dv50 of the inorganic particles is 0.01 μm to 1 μm.

12. The composite diaphragm according to claim 7, wherein, The inorganic particles comprise one or more of the following: boehmite, pseudoboehmite, BaSO4, CeO2, MgO, CaO, ZnO, Al2O3, SiO2, TiO2, BaTiO3, HfO2, SrTiO3, SnO2, NiO, ZrO2, Y2O3, and SiC.

13. The composite diaphragm according to claim 7, wherein, The adhesive comprises 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, and polyalkylene glycols.

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

15. The composite diaphragm according to claim 7, wherein, The adhesive comprises carboxymethyl cellulose, wherein the carboxymethyl cellulose has a weight-average molecular weight of 180,000 g / mol or more and a degree of substitution of 0.6 to 1.

2.

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

17. The composite diaphragm according to claim 7, wherein, The composite diaphragm has the following anti-clogging properties. Anti-blocking performance Two composite diaphragms are arranged so that the coatings face each other, and the temperature is 25°C and 15 kgf / cm². 2 The pressure was applied for 1 hour, followed by 180° peeling according to ASTM D903. Desorption of organic and / or inorganic particles was confirmed by scanning electron microscopy (SEM). Ten arbitrary locations were selected, and the number of desorbed organic and / or inorganic particles per unit area was counted. The average value of the 10 points was less than 10. -4 per μm 2 Or, neither organic nor inorganic particles were desorbed.

18. 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%. Cardboard test A black cardboard and a rubber pad measuring 2cm×10cm were placed sequentially on the coating of a composite diaphragm sample measuring 5cm×10cm. With a force of 10N applied to the rubber pad using a pressing device, the cardboard 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 cardboard.

19. An electrochemical device, wherein, The electrochemical device is an electrochemical device comprising a positive electrode, a negative electrode, and a composite membrane. The composite membrane comprises: a porous substrate; and a coating formed on at least one side of the substrate and comprising organic particles. The coating satisfies the following formula 1. [Formula 1] 4000≤(A×D 2 ) / T≤5500 In Equation 1, A represents the number of organic particles per unit area of ​​the coating surface, expressed in mm. 2 ; D represents the average particle size of the organic particles observed on the coating surface, in μm. T represents the total thickness of the coating, measured in μm.

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