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 formed on one surface or both surfaces of the porous base material. Specifically, the ceramic layer contains inorganic particles, a binder, and a particle-type fusing agent, the ceramic layer satisfies Formula 1 below, the binder is carboxymethyl cellulose having a weight average molecular weight of 180000 g / mol to 280000 g / mol, and the composite separator according to the present invention can ensure excellent heat resistance, adhesive force, and fusion force with an electrode. [Formula 1] (In Formula 1, T is the thickness ([mu] m) of the ceramic layer; w1 is the content (wt%) of the binder relative to the total weight of the ceramic layer; w2 is the content (wt%) of the particulate fusing agent with respect to the total weight of the ceramic layer; and D is the average particle diameter ([mu] m) of the granular fusing agent. )

Description

Technical Field

[0001] The present invention relates to a diaphragm and an electrochemical device including the 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, the existing composite separators have insufficient adhesion to the electrodes, leading to separator separation during cell assembly. This results in electrode component twisting and deformation, and can cause short circuits between electrodes, posing safety concerns. To address these issues, a solution has been proposed that involves introducing a separate adhesive layer on an inorganic coating to provide fusion with the electrodes. However, this solution faces challenges in practical commercialization due to increased processing steps and manufacturing costs. Furthermore, the additional adhesive layer may increase the battery's internal resistance, potentially degrading electrical performance.

[0004] [Existing Technical Documents]

[0005] [Patent Literature]

[0006] KR10-2573567B1 (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 particulate binder in a ceramic layer, and provides a composite membrane that ensures excellent heat resistance, adhesion and fusion with electrodes even when thin, and prevents adhesion phenomena.

[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 ceramic layer formed on one or both sides of the porous substrate, wherein the ceramic layer comprises inorganic particles, a binder, and a particulate flux, the ceramic layer satisfying Formula 1 below, and the binder being carboxymethyl cellulose having a weight-average molecular weight of 180,000 g / mol to 280,000 g / mol.

[0012] [Formula 1]

[0013]

[0014] (In Equation 1, T is the thickness of the ceramic layer (μm); W1 is the content of the binder relative to the total weight of the ceramic layer (wt%); W2 is the content of the particulate flux relative to the total weight of the ceramic layer (wt%); and D is the average particle size of the particulate flux (μm).)

[0015] The average particle size (D50) of the particulate flux can be from 1 μm to 10 μm.

[0016] The total thickness of the ceramic layer can be from 1 μm to 20 μm.

[0017] The carboxymethyl cellulose may have a degree of substitution of 0.6 to 1.2.

[0018] The average particle size (D50) of the inorganic particles can be from 0.01 μm to 1 μm.

[0019] The inorganic particles may be 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.

[0020] The content of the inorganic particles can be from 90% to 99% by weight relative to the total weight of the ceramic layer.

[0021] The content of the adhesive can be from 0.1% by weight to 10% by weight relative to the total weight of the ceramic layer.

[0022] The content of the particulate binder can be from 0.1% by weight to 10% by weight relative to the total weight of the ceramic layer.

[0023] The weight ratio of the adhesive to the granular fusion agent may be from 5:5 to 8:2.

[0024] The glass transition temperature (T) of the particulate fluxg The temperature can range from 40℃ to 80℃.

[0025] The porous substrate may be hydrophilic surface treated.

[0026] According to one embodiment, the composite diaphragm, after being placed at 150°C for 60 minutes, exhibits a thermal shrinkage rate of less than 4% in both the mechanical direction (MD) and transverse direction (TD).

[0027] 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%.

[0028] [Cardboard Test]

[0029] (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.)

[0030] Another embodiment of the present invention provides an electrochemical device comprising a positive electrode, a negative electrode, and a composite membrane, wherein the composite membrane comprises a porous substrate and a ceramic layer formed on one or both sides of the porous substrate, the ceramic layer comprising inorganic particles, a binder, and a particulate flux, the ceramic layer satisfying Formula 1 below, and the binder being carboxymethyl cellulose having a weight-average molecular weight of 180,000 g / mol to 280,000 g / mol.

[0031] [Formula 1]

[0032]

[0033] (In Equation 1, T is the thickness of the ceramic layer (μm); W1 is the content of the binder relative to the total weight of the ceramic layer (wt%); W2 is the content of the particulate flux relative to the total weight of the ceramic layer (wt%); and D is the average particle size of the particulate flux (μm).)

[0034] (III) Beneficial Effects

[0035] According to one embodiment, a composite separator includes a porous substrate and a ceramic layer, the ceramic layer being located on the porous substrate and comprising inorganic particles, a binder, and a particulate flux. The composite separator achieves sufficient fusion with the electrode without the need for a separate adhesive layer on the ceramic layer, and can reduce internal resistance and improve electrical performance.

[0036] Furthermore, in the composite membrane according to one embodiment, even if the thickness of the formed composite membrane is very thin, it can have superior heat resistance compared to a conventional ceramic layer membrane of the same thickness, and the inorganic particles have excellent adhesion between each other and between the inorganic particles and the substrate, thereby effectively suppressing the shedding of inorganic particles and shrinkage at high temperatures.

[0037] Furthermore, the composite diaphragm according to one embodiment can suppress the shedding and blocking of inorganic particles and / or particulate binders during winding.

[0038] 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

[0039] Figure 1 This is a cross-sectional view showing a composite diaphragm according to one embodiment.

[0040] Figure 2 It is a schematic plan view of an electrochemical device according to one implementation scheme.

[0041] Figure 3 This is a schematic cross-sectional view of an electrochemical device according to one implementation scheme.

[0042] Explanation of reference numerals in the attached figures:

[0043] 100: Positive electrode; 105: Positive electrode current collector

[0044] 107: Positive electrode lead; 110: Positive electrode mixed layer

[0045] 120: Negative electrode mixture layer; 125: Negative electrode current collector

[0046] 127: Negative lead; 130: Negative electrode

[0047] 140: Diaphragm; 150: Electrode assembly

[0048] 160: Casing Detailed Implementation

[0049] 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.

[0050] Unless otherwise specified in the context, the singular form used in this specification may include the plural form.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] In this specification, "average particle size" refers to "D50," which means the particle size of the sample being measured when the cumulative fraction based on volume is 50%. The average particle size can be obtained by collecting samples of the sample being measured according to the ISO 13320-1 standard and analyzing the particle size distribution using a Microtrac S3500. The sample being measured refers to inorganic particles and particulate fluxes.

[0055] In this specification, carboxymethyl cellulose (CMC) 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] The number of millimoles (A) of CMC acid in 1g of dried sample is calculated using the following formula.

[0062]

[0063] Then, the degree of substitution (DS) is calculated from A using the following formula.

[0064]

[0065] The present invention will now be described in detail. However, this is merely an exemplary embodiment, and the present invention is not limited to the specific embodiments described herein.

[0066] In existing technologies, to improve the fusion strength between the composite separator, which includes a porous substrate and an inorganic coating, and the electrode, a separate adhesive layer is introduced onto the inorganic coating. However, this approach is difficult to commercialize due to increased processing steps and manufacturing costs, and the additional adhesive layer may increase the battery's internal resistance, potentially reducing electrical performance. Another approach involves introducing a flux into the inorganic coating to achieve fusion strength with the electrode. However, in recent years, to achieve high capacity and high power characteristics in electrochemical devices, separators are being thinned. Achieving sufficient fusion strength even at thinner thicknesses presents problems such as flux detachment and adhesion. Therefore, a novel separator needs to be developed.

[0067] One embodiment of the present invention provides a composite diaphragm that can achieve all of the following effects: it can ensure sufficient fusion with the electrode even in a thin thickness range while having excellent anti-blocking properties; it can have excellent adhesion between inorganic particles in the coating and between inorganic particles and the substrate; and it can prevent thermal shrinkage at high temperatures.

[0068] Specifically, a composite membrane according to one embodiment may include a porous substrate and a ceramic layer formed on one or both sides of the porous substrate, wherein the ceramic layer may contain inorganic particles, a binder and a particulate flux, the ceramic layer may satisfy Formula 1 below, and the binder may be carboxymethyl cellulose having a weight-average molecular weight of 180,000 g / mol to 280,000 g / mol.

[0069] [Formula 1]

[0070]

[0071] (In Equation 1, T is the thickness of the ceramic layer (μm); W1 is the content of the binder relative to the total weight of the ceramic layer (wt%); W2 is the content of the particulate flux relative to the total weight of the ceramic layer (wt%); and D is the average particle size of the particulate flux (μm).)

[0072] According to one embodiment, the composite separator uses CMC within a specific molecular weight range as a binder, as described above. The thickness of the ceramic layer, the content of the binder and the particulate flux, and the average particle size of the particulate flux have a specific relationship and satisfy the range of Formula 1. Therefore, the composite separator and the electrode can have sufficient fusion force. Furthermore, compared with existing separators with ceramic layers of the same thickness, the composite separator can have superior heat resistance, and the aforementioned inorganic particles can have superior adhesion between themselves and between themselves and the substrate, thereby effectively suppressing the shedding of inorganic particles and shrinkage at high temperatures. In addition, the composite separator according to one embodiment can effectively suppress the shedding and adhesion of inorganic particles and / or particulate flux during winding.

[0073] In one embodiment, the thickness (T) of the ceramic layer is not particularly limited, as long as the combination of the thickness (T) of the ceramic layer with the content of the binder (W1), the content of the particulate flux (W2), and the average particle size (D) of the particulate flux satisfies the range of Formula 1. However, for example, the thickness (T) of the ceramic layer can be 0.1 μm to 10 μm, 0.5 μm to 10 μm, 0.5 μm to 8 μm, 0.5 μm to 5 μm, 1 μm to 5 μm, 1.2 μm to 5 μm, or 1.5 μm to 3 μm, and can include all possible combinations of the upper and lower limits of the above numerical range.

[0074] In one embodiment, the total thickness of the ceramic layer can be from 0.1 μm to 20.0 μm, 0.1 μm to 10.0 μm, 0.5 μm to 10.0 μm, 1 μm to 10 μm, 2 μm to 8 μm, 2 μm to 5 μm, or 3 μm to 5 μm, and can include all possible combinations of the upper and lower limits of the above numerical ranges. When the composite separator according to one embodiment includes a ceramic layer formed on one side of a porous substrate, the total thickness of the ceramic layer refers to the thickness of the ceramic layer formed on one side. When the composite separator according to one embodiment includes ceramic layers formed on both sides of a porous substrate, the total thickness of the ceramic layer refers to the sum of the thicknesses of the ceramic layers formed on both sides, and the thicknesses of the ceramic layers formed on both sides can be the same or different from each other.

[0075] In one embodiment, because the carboxymethyl cellulose (CMC) meets the weight-average molecular weight range of 180,000 g / mol to 280,000 g / mol, even when CMC is used alone as a binder for the ceramic layer, it can simultaneously satisfy excellent adhesion and heat resistance between inorganic particles and between inorganic particles and the substrate. The coating slurry has an appropriate viscosity when forming the ceramic layer, thus facilitating coating formation. As an example, when the weight-average molecular weight of the CMC is less than 180,000 g / mol, sufficient adhesion cannot be achieved; when the weight-average molecular weight of the CMC exceeds 280,000 g / mol, the coating (ceramic layer) may not form.

[0076] In one embodiment, the weight-average molecular weight of the carboxymethyl cellulose can be 180,000-280,000 g / mol, 180,000-260,000 g / mol, 180,000-250,000 g / mol, 190,000-250,000 g / mol, or 20,000-250,000 g / mol, 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. 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.

[0077] Furthermore, the degree of substitution of the carboxymethyl cellulose can be 0.6 or more, 0.7 or more, 0.8 or more, or 0.9 or more, and can be 1.5 or less, 1.2 or less, 1.1 or less, or 1.0 or less. Specifically, it can be 0.6 to 1.5, 0.6 to 1.2, 0.6 to 1.1, 0.7 to 1.1, 0.7 to 1.0, or 0.8 to 1.0, and can include all possible combinations of the upper and lower limits of the above numerical ranges.

[0078] By using carboxymethyl cellulose that satisfies the above-mentioned range of weight-average molecular weight and degree of substitution, when coating the ceramic layer onto the surface of the porous substrate using a coating slurry, the coatability is superior. Furthermore, in the composite membrane containing the carboxymethyl cellulose, even if the ceramic layer is thin, the effects of simultaneously improving heat resistance and adhesion can be further enhanced, such as superior heat resistance and improved adhesion between inorganic particles or between the ceramic layer and the porous substrate.

[0079] In one embodiment, the average particle size of the particulate flux can be greater than 1 μm, greater than 1.5 μm, greater than 2.0 μm, or greater than 2.5 μm, and can be less than 10 μm, less than 8 μm, less than 6 μm, or less than 5 μm, and can 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, and can include all possible combinations of the upper and lower limits of the above numerical ranges, within which the fusion force with the electrode can be further improved.

[0080] In one embodiment, the glass transition temperature (T0) of the particulate flux is... g The temperature range can be above 40°C, above 45°C, or above 50°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 particulate fusion agent can be between 40°C and 70°C. In this case, the particulate fusion agent will not flow during the drying step of the composite separator, and will not deform during the coating step and transportation. Even after fusion, it can minimize changes in the permeability of the substrate, thereby maintaining excellent performance, and is therefore more preferably preferred.

[0081] The particulate flux is not particularly limited as long as it is a substance that can achieve fusion force with the electrode. The particulate flux can be an acrylic polymer, a urethane polymer, or a copolymer containing them.

[0082] The acrylic polymer may be a homopolymer containing alkyl methacrylate monomer polymerization units or a copolymer containing said alkyl methacrylate monomer polymerization units. The copolymer containing said alkyl methacrylate monomer polymerization units may be a copolymer containing alkyl methacrylate monomer polymerization units, and one or more polymerization units selected from styrene monomer polymerization units, butadiene monomer polymerization units, and vinyl monomer polymerization units.

[0083] The alkyl methacrylate monomer can be a C1-C10 alkyl (meth)acrylate monomer, a C1-C6 alkyl (meth)acrylate monomer, or a C1-C4 alkyl (meth)acrylate monomer. Specifically, it can be one or more selected from methyl methacrylate, ethyl methacrylate, and n-butyl methacrylate.

[0084] A non-limiting example of the granular weld bead may be polyurethane beads, polyurethane acrylate beads, epoxy-acrylate beads, 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), but is not limited thereto.

[0085] The preparation method of the particulate flux is a well-known method, which can be prepared by emulsion polymerization or suspension polymerization, so specific details are omitted.

[0086] 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, pseudoboehmite, BaSO4, CeO2, MgO, CaO, ZnO, Al2O3, SiO2, TiO2, BaTiO3, HfO2, SrTiO3, SnO2, NiO, ZrO2, Y2O3, and SiC.

[0087] In one embodiment, the average particle size (D50) 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.

[0088] In one embodiment, the content of the inorganic particles in the ceramic layer may be 90% to 99.9% by weight, 92% to 99.5% by weight, 92% to 99% by weight, 90% to 99% by weight, 95% to 99% by weight, or 95% to 98% by weight, relative to the total weight of the ceramic layer.

[0089] In one embodiment, the content (W1) of the adhesive in the ceramic layer, relative to the total weight of the ceramic layer, can be more than 0.01 wt%, more than 0.1 wt%, more than 0.5 wt%, more than 1 wt%, more than 1.5 wt%, or more than 2 wt%, and can be less than 10 wt%, less than 8 wt%, or less than 5 wt%, and can be from 0.01 wt% to 10 wt%, from 0.1 wt% to 10 wt%, from 0.5 wt% to 5 wt%, or from 1 wt% to 5 wt%, and can include all possible combinations of the upper and lower limits of the above numerical ranges.

[0090] In one embodiment, the content (W2) of the particulate binder in the ceramic layer, relative to the total weight of the ceramic layer, 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 10% by weight, 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 0.5% by weight to 5% by weight, 1% by weight to 5% by weight, 1% by weight to 3% by weight, 1% by weight to 2% by weight, or 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 range.

[0091] 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 0.01 parts by weight, 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 numerical ranges.

[0092] In one embodiment, the weight ratio of the adhesive to the granular weld agent may be 5:5 to 9:1, 5:5 to 8:2, or 5:5 to 7:3.

[0093] 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%, below 2.5%, below 2.0%, below 1.5%, below 1.0%, or below 0.5%.

[0094] The thermal shrinkage rate of the composite diaphragm was measured according to ASTM D1204, specifically using the following method: Grid points were marked at 2cm intervals within a 10cm square of the composite diaphragm sample. One side of the square was designated as the transverse (TD) direction, and the other as the mechanical (MD) direction. The sample was placed in the center, with five sheets of paper placed above and below it, and the four sides of the paper were secured with tape. The sample, secured with tape, was placed in a hot air dryer at 150°C for 60 minutes. Afterward, the sample was removed, and the diaphragm was observed at room temperature using a camera. The shrinkage rates in the mechanical (MD) and transverse (TD) directions were calculated.

[0095] 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%.

[0096] 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 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 ceramic layer, such as inorganic particles, adhesives, or a combination thereof.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] Another embodiment of the present invention provides a method for manufacturing the composite membrane, the method comprising the steps of coating a ceramic layer forming composition comprising inorganic particles, a binder and a particulate fusion agent onto at least one side of a porous substrate and drying to form a ceramic layer, wherein the binder may be carboxymethyl cellulose having a weight-average molecular weight of 180,000 g / mol to 280,000 g / mol, and the ceramic layer may satisfy the following formula 1.

[0104] [Formula 1]

[0105]

[0106] (In Equation 1, T is the thickness of the ceramic layer (μm); W1 is the content of the binder relative to the total weight of the ceramic layer (wt%); W2 is the content of the particulate flux relative to the total weight of the ceramic layer (wt%); and D is the average particle size of the particulate flux (μm).)

[0107] The porous substrate, adhesive, and inorganic particles are described above, therefore detailed descriptions are omitted.

[0108] The ceramic layer forming composition can be prepared by dispersing binder and inorganic particles, and the aggregated inorganic particles can be dispersed using a ball mill.

[0109] The ceramic layer 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 to these.

[0110] In one embodiment, the solid content of the ceramic layer forming composition is not particularly limited, but for example, the solid content of the ceramic layer forming composition can 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 ceramic layer forming composition based on a solid content of 25% by weight can be from 800 mPa·s to 5000 mPa·s, 800 mPa·s to 4000 mPa·s, 800 mPa·s to 3000 mPa·s, or 1000 mPa·s to 3000 mPa·s. Within these ranges, the ceramic layer can be formed more easily, and the heat resistance and adhesion of the diaphragm can be further improved.

[0111] In one embodiment, there are no particular limitations on the method of coating or applying the ceramic layer forming 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.

[0112] 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 is not particularly limited and can therefore be appropriately adjusted according to the experimental environment or purpose; for example, the drying temperature can be 30°C to 120°C, 30°C to 100°C, 50°C to 80°C, or 50°C to 70°C. The drying time is not particularly limited, but can be 30 seconds to 300 seconds, 60 seconds to 300 seconds, 100 seconds to 300 seconds, 150 seconds to 250 seconds, or approximately 180 seconds.

[0113] 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.

[0114] 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 ceramic layer formed on one or both sides of the porous substrate, the ceramic layer may include inorganic particles, a binder, and a particulate flux, the ceramic layer may satisfy Formula 1 below, and the binder may be carboxymethyl cellulose having a weight-average molecular weight of 180,000 g / mol to 280,000 g / mol.

[0115] [Formula 1]

[0116]

[0117] (In Equation 1, T is the thickness of the ceramic layer (μm); W1 is the content of the binder relative to the total weight of the ceramic layer (wt%); W2 is the content of the particulate flux relative to the total weight of the ceramic layer (wt%); and D is the average particle size of the particulate flux (μm).)

[0118] 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.

[0119] 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.

[0120] [positive electrode]

[0121] 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.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] 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 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] [negative electrode]

[0130] 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.

[0131] The negative electrode current collector may include copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal, etc. The thickness of the negative electrode current collector may be, for example, from 10 μm to 50 μm, but is not limited thereto.

[0132] The negative electrode active material can be used without limitation as long as it is a material capable of adsorbing and desorbing 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 be a carbon-based material such as crystalline carbon, amorphous carbon, carbon composite, carbon fiber, etc.; lithium metal; lithium alloy; a silicon (Si)-containing material or a tin (Sn)-containing material, etc.

[0133] 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 carbon such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, graphitized MPCF, etc. can be cited.

[0134] As the elements contained in the lithium alloy, aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium, etc. can be cited.

[0135] The silicon-containing material can provide further increased capacity characteristics. The silicon-containing material can include Si, SiO x (0 < x ≤ 2), metal-doped SiO x (0 < x ≤ 2), silicon-carbon composite, etc. The metal can include lithium and / or magnesium. Metal-doped SiO x (0 < x ≤ 2) can include metal silicate. The binder, conductive material, and thickener of the negative electrode can use the above substances that can be used in manufacturing the positive electrode.

[0136] The negative electrode binder has no particular limitation as long as it is a negative electrode binder commonly used in the art. 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.

[0137] [Electrolyte]

[0138] In one embodiment, the electrolyte can be a non-aqueous electrolyte, and the non-aqueous electrolyte can contain a lithium salt as an electrolyte and an organic solvent.

[0139] The lithium salt can be represented, for example, by Li + X - As the anion of the lithium salt (X- ), 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.

[0140] 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.

[0141] [Cell Structure]

[0142] 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.

[0143] 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.

[0144] The physical properties of the following measurement examples are described.

[0145] [Methods for measuring physical properties]

[0146] 1) Glass transition temperature (T) g )

[0147] Using a differential scanning calorimeter (DSC), the sample was heated at a rate of 10℃ / min within the range of -100℃ to 250℃, and the heat capacity of the sample was measured. The temperature at the center of the range where the heat capacity of the sample changed rapidly was determined as the glass transition temperature.

[0148] 2) Thickness

[0149] 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.

[0150] 3) Adhesive force

[0151] [Cardboard Test]

[0152] 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.

[0153] [Evaluation of the degree of foreign body adhesion]

[0154] 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.

[0155] A: <1.5%

[0156] B: 1.5% to 5%

[0157] C: >5%

[0158] [Example 1]

[0159] Boehmite, an inorganic particle with an average particle size (D50) of 0.3 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, thereby obtaining a slurry with a solid content of 45% by weight.

[0160] Carboxymethyl cellulose (CMC) with a degree of substitution of 0.9 and a weight-average molecular weight of 200,000 g / mol was added as a binder to the prepared slurry, and polystyrene-polybutyl methacrylate-polymethyl methacrylate block copolymer (PS-PBMA-PMMA) (D50: 2.5 μm, T) was added as a particulate flux. g The composition for forming a ceramic layer is prepared by means of a process at 62°C, wherein the weight ratio of the inorganic particles / binder / particulate flux is 96 / 2.3 / 1.7.

[0161] Corona discharge treatment (power density 2W / m²) was applied to both sides of a 9μm thick polyethylene film substrate (porosity 35% to 45%, SKIET). 2To introduce surface polar groups, the corona surface treatment speed is set to 5 meters per minute (mpm). The same amount of the ceramic layer forming composition is applied to both sides of the corona-treated polyethylene film substrate by bar coating and dried at 50°C to obtain a composite diaphragm with ceramic layers of the same thickness formed on both sides.

[0162] [Example 2]

[0163] The process was carried out using the same method as in Example 1, except that the weight ratio of the inorganic particles / binder / particulate flux used was 95 / 3.3 / 1.7.

[0164] [Example 3]

[0165] The process was carried out using the same method as in Example 1, except that the weight ratio of inorganic particles / binder / particulate flux used was 95 / 3.8 / 1.2, and the thickness of the ceramic layer was varied according to Table 1 below.

[0166] [Example 4]

[0167] The process was carried out using the same method as in Example 1, except that the weight ratio of inorganic particles / binder / particulate flux used was 96 / 2 / 2, and the thickness of the ceramic layer was varied according to Table 1 below.

[0168] [Example 5]

[0169] The process was carried out using the same method as in Example 1, except that the weight ratio of inorganic particles / binder / particulate flux used was 95 / 3 / 2, and the thickness of the ceramic layer was varied according to Table 1 below.

[0170] [Example 6]

[0171] The process was carried out using the same method as in Example 1, except that the weight ratio of inorganic particles / binder / particulate flux used was 95 / 3.4 / 1.6, and the thickness of the ceramic layer was varied according to Table 1 below.

[0172] [Example 7]

[0173] The procedure was performed using the same method as in Example 1, except that PS-PBMA-PMMA (D50: 5.0 μm, T) was used. g The inorganic particles / binder / granular flux used at 62℃ were in a weight ratio of 95 / 3.3 / 1.7, and the thickness of the ceramic layer was varied according to Table 1 below.

[0174] [Example 8]

[0175] The process was carried out using the same method as in Example 7, except that the weight ratio of the inorganic particles / binder / particulate flux used was 96 / 2.8 / 1.2.

[0176] [Example 9]

[0177] The process was carried out using the same method as in Example 7, except that the weight ratio of the inorganic particles / binder / particulate flux used was 95 / 3.8 / 1.2, and the thickness of the ceramic layer was varied according to Table 1 below.

[0178] [Comparative Example 1]

[0179] The process was carried out using the same method as in Example 1, except that the weight ratio of the inorganic particles / binder / particulate flux used was 97 / 1.3 / 1.7.

[0180] [Comparative Example 2]

[0181] The process was carried out using the same method as in Example 1, except that the weight ratio of inorganic particles / binder / particulate flux used was 94 / 4.8 / 1.2, and the thickness of the ceramic layer was varied according to Table 1 below.

[0182] [Comparative Example 3]

[0183] The process was carried out using the same method as in Example 1, except that the weight ratio of inorganic particles / binder / particulate fusible compound used was 97 / 1 / 2, and the thickness of the ceramic layer was varied according to Table 1 below.

[0184] [Comparative Example 4]

[0185] The process was carried out using the same method as in Example 1, except that the weight ratio of inorganic particles / binder / particulate flux used was 94 / 4.65 / 1.35, and the thickness of the ceramic layer was varied according to Table 1 below.

[0186] [Comparative Example 5]

[0187] The procedure was carried out in the same manner as in Example 1, except that polyacrylamide (PAAm) (Mw of 200,000 g / mol, Sigma Aldrich) was used instead of CMC as the adhesive.

[0188] [Comparative Example 6]

[0189] The procedure was carried out in the same manner as in Example 7, except that polyacrylamide (PAAm) (Mw of 200,000 g / mol, Sigma-Aldrich) was used instead of CMC as the adhesive.

[0190] [Comparative Example 7]

[0191] The procedure was performed using the same method as in Example 1, except that PS-PBMA-PMMA (D50: 0.9μm, T) was used. g (62℃) as a granular flux.

[0192] The physical properties of the composite membranes obtained in the above embodiments and comparative examples were measured using the methods described in the above physical property measurement methods, and the values ​​of the following formula 1 were calculated, discarding the third decimal place, and recorded in Table 1 below.

[0193] In the case of the composite membranes obtained in the above embodiments and comparative examples, ceramic layers of the same thickness are formed on both sides of the substrate, and half of the total thickness of the ceramic layers measured by the above physical property measurement method is taken as the thickness (T) of the ceramic layer formed on one side.

[0194] [Formula 1]

[0195]

[0196] (In Equation 1, T is the thickness of the ceramic layer (μm); W1 is the content of the binder relative to the total weight of the ceramic layer (wt%); W2 is the content of the particulate flux relative to the total weight of the ceramic layer (wt%); and D is the average particle size of the particulate flux (μm).)

[0197] [Table 1]

[0198]

[0199] <Evaluation Example>

[0200] Evaluation 1. Anti-adhesion performance

[0201] The two composite membranes obtained in the embodiments and comparative examples are configured such that the ceramic surfaces face each other, at a temperature of 25°C and a pressure of 15 kgf / cm². 2The mixture was pressed under pressure for 1 hour, then peeled 180° according to ASTM D903. The detachment of granular binder and / or inorganic particles was then confirmed using a scanning electron microscope (SEM). Ten arbitrary locations were selected, and the number of detached granular binder and / or inorganic particles per unit area was counted. The average value of the ten points was obtained, and the results of evaluating the anti-adhesion performance based on the following criteria are presented in Table 2 below.

[0202] O: Neither the flux nor the inorganic particles have detached, or the detached flux or inorganic particles are less than 10. -4 pcs / µm 2 .

[0203] X: 10% of the detached flux or inorganic particles. -4 pcs / µm 2 above.

[0204] Evaluation 2. Electrode fusion force

[0205] The positive and negative electrodes were manufactured as follows, and the fusion force between the electrodes and the composite separators obtained in the above examples and comparative examples was evaluated.

[0206] 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.

[0207] 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, solid 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.

[0208] The composite separator was stacked between four positive (negative) electrodes prepared as described above, and then calendered at 1 MPa for 30 seconds at 90°C 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.

[0209] 1 / 4: One of the four electrodes is fused together.

[0210] 2 / 4: Two of the four electrodes are fused together.

[0211] 3 / 4: 3 out of 4 electrodes are fused together

[0212] 4 / 4: All four electrodes out of the four electrodes are fused together.

[0213] [Table 2]

[0214]

[0215] Referring to Tables 1 and 2 above, in the composite separator according to one embodiment of the present invention, it is evident that 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, and thermal shrinkage can be effectively suppressed. Furthermore, it has been confirmed that the composite separator according to one embodiment exhibits excellent bonding strength to both the positive and negative electrodes, and can suppress the shedding and adhesion of inorganic particles and / or particulate binders during separator winding. Moreover, the composite separator according to one embodiment demonstrates excellent manufacturability, thereby facilitating its practical commercial application, and electrochemical devices using the composite separator according to one embodiment can simultaneously meet the requirements of safety, high capacity, and high power characteristics.

[0216] On the other hand, in the composite membranes of Comparative Examples 1 to 4, which include the same configuration as one embodiment of the present invention but do not satisfy the range of Formula 1 (0.9 < Formula 1 < 2.4), the adhesion and / or heat resistance are reduced, and the thermal shrinkage rate is significantly increased. In the case of Comparative Example 7, it is known that the fusion force with the electrode is significantly reduced, and it is almost impossible to have fusion force.

[0217] Furthermore, in Comparative Examples 5 and 6, where PAAm was used as the adhesive, it was confirmed that the adhesive strength and heat resistance were significantly reduced compared to the composite diaphragm according to one embodiment, and the air permeability was worse, with an increase in the air permeability value (seconds / 100 ml (cc)).

[0218] 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.

[0219] 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.

[0220] 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: A porous substrate; and a ceramic layer formed on one or both sides of the porous substrate. The ceramic layer comprises inorganic particles, a binder, and a particulate flux, and the ceramic layer satisfies the following formula 1. The adhesive is carboxymethyl cellulose with a weight-average molecular weight of 180,000 g / mol to 280,000 g / mol. [Formula 1] In Equation 1, T represents the thickness of the ceramic layer, in μm. W1 represents the content of the binder relative to the total weight of the ceramic layer, expressed as a percentage by weight. W2 represents the content of particulate flux relative to the total weight of the ceramic layer, expressed as a percentage by weight. D represents the average particle size of the particulate flux, measured in μm.

2. The composite diaphragm according to claim 1, wherein, The average particle size D50 of the particulate flux is 1 μm to 10 μm.

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

4. The composite diaphragm according to claim 1, wherein, The carboxymethyl cellulose has a degree of substitution of 0.6 to 1.

2.

5. The composite diaphragm according to claim 1, wherein, The average particle size D50 of the inorganic particles is 0.01 μm to 1 μm.

6. The composite diaphragm according to claim 1, wherein, The inorganic particles are selected from one or more of boehmite, pseudoboehmite, BaSO4, CeO2, MgO, CaO, ZnO, Al2O3, SiO2, TiO2, BaTiO3, HfO2, SrTiO3, SnO2, NiO, ZrO2, Y2O3 and SiC.

7. The composite diaphragm according to claim 1, wherein, The content of inorganic particles is 90% to 99% by weight relative to the total weight of the ceramic layer.

8. The composite diaphragm according to claim 1, wherein, The content of the adhesive is from 0.1% to 10% by weight relative to the total weight of the ceramic layer.

9. The composite diaphragm according to claim 1, wherein, The content of the particulate binder is from 0.1% to 10% by weight relative to the total weight of the ceramic layer.

10. The composite diaphragm according to claim 1, wherein, The weight ratio of the adhesive to the granular fuse is 5:5 to 8:

2.

11. The composite diaphragm according to claim 1, wherein, The glass transition temperature T of the particulate flux g The temperature ranges from 40°C to 80°C.

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

13. 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.

14. 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.

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. The ceramic layer contains inorganic particles, a binder, and a particulate flux. The ceramic layer satisfies Formula 1 below. The binder is carboxymethyl cellulose having a weight-average molecular weight of 180,000 g / mol to 280,000 g / mol. [Formula 1] In Equation 1, T represents the thickness of the ceramic layer, in μm. W1 represents the content of the binder relative to the total weight of the ceramic layer, expressed as a percentage by weight. W2 represents the content of particulate flux relative to the total weight of the ceramic layer, expressed as a percentage by weight. D represents the average particle size of the particulate flux, measured in μm.

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