Composite separator and electrochemical element containing the same

Abstract

This invention provides a composite separator that, even with a thin thickness, can ensure excellent heat resistance, adhesive strength, and fusion strength with electrodes, thereby preventing blocking phenomena. [Solution] The composite separator comprises a porous substrate and a ceramic layer formed on one or both sides of the substrate. The ceramic layer comprises inorganic particles, a binder, and a particulate adhesive, satisfying the following formula 1, wherein the binder is carboxymethylcellulose having a weight-average molecular weight of 180,000 g / mol to 280,000 g / mol. TIFF2026082769000014.tif21170 (In formula 1 above, T is the thickness of the ceramic layer (μm), W1 is the binder content (wt%) relative to the total weight of the ceramic layer, W2 is the particulate adhesive content (wt%) relative to the total weight of the ceramic layer, and D is the average particle size (μm) of the particulate adhesive.)

Description

Technical Field

[0001] The present disclosure relates to a separator and an electrochemical element including the same.

Background Art

[0002] Recently, as electrochemical elements are gradually becoming higher in capacity and higher in output, the need for ensuring heat resistance and safety has been increasing. In particular, the required performance for a separator, which acts as a very important element in ensuring the heat resistance and safety of an electrochemical element, has been heightened. For example, a composite separator in which an inorganic coating layer containing inorganic particles such as alumina (Al2O3), silica (SiO2), zirconia (ZrO2), etc. and a binder is introduced on a porous substrate has become an important technology.

[0003] However, conventional composite separators have insufficient adhesion to electrodes, and the separator and electrodes separate during the cell assembly process, resulting in distortion, deformation, etc., of the electrode assembly, causing a short circuit between the electrodes, and there have been safety problems. To solve this, a method has been proposed in which an adhesive layer capable of exerting adhesion to an electrode is separately introduced on the inorganic coating layer. However, this has the problem that the process steps are increased, the manufacturing cost rises, and it is difficult to apply to actual commercialization, and the added adhesive layer may increase the internal resistance of the battery and reduce the electrical performance.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] One aspect of the present invention relates to a composite separator in which a particulate adhesive is introduced into a ceramic layer, and provides a composite separator that can ensure excellent heat resistance, adhesive strength, and fusion strength with electrodes even at a thin thickness, and can prevent blocking phenomena.

[0006] A further embodiment of the present invention provides an electrochemical element employing the composite separator. [Means for solving the problem]

[0007] One embodiment of the present invention provides a composite separator comprising a porous substrate and a ceramic layer formed on one or both sides of the substrate, wherein the ceramic layer comprises inorganic particles, a binder, and a particulate adhesive, satisfying the following formula 1, and the binder is carboxymethylcellulose having a weight-average molecular weight of 180,000 g / mol to 280,000 g / mol.

number

[0008] The average particle size (D) of the aforementioned particle-type fuser 50 The size of the ) may be between 1 μm and 10 μm.

[0009] The total thickness of the ceramic layer may be 1 μm to 20 μm.

[0010] The carboxymethylcellulose may have a degree of substitution of 0.6 to 1.2.

[0011] The average particle size (D) of the inorganic particles 50 ) may be 0.01 μm to 1 μm.

[0012] 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.

[0013] The inorganic particles may be present in an amount of 90 to 99% by weight relative to the total weight of the ceramic layer.

[0014] The binder may be present in an amount of 0.1% to 10% by weight relative to the total weight of the ceramic layer.

[0015] The aforementioned particulate adhesive may be present in an amount of 0.1% to 10% by weight relative to the total weight of the ceramic layer.

[0016] The binder and the particulate adhesive may be present in a weight ratio of 5:5 to 8:2.

[0017] The glass transition temperature (T) of the aforementioned particulate fuser. g The temperature can be 40°C to 80°C.

[0018] The porous substrate may be treated with a hydrophilic surface treatment.

[0019] The thermal shrinkage rates in the MD direction and TD direction, measured after leaving the composite separator in one state at 150°C for 60 minutes, may both be 4% or less.

[0020] In the case of the composite separator made in one form, when the degree of foreign matter adhesion to the surface of the cardboard is evaluated after the cardboard test, the ratio of the area occupied by the attached foreign matter to the area of ​​the cardboard may be 5% or less. [Cardboard Test] (A 2cm x 10cm black cardboard and a rubber pad are placed sequentially on the ceramic layer of a 5cm x 10cm composite separator test piece. A force of 10N is applied to the rubber pad using a press device, and the cardboard is horizontally removed at a speed of 0.1m / s to a length of 60mm. The degree to which foreign matter adheres to the surface of the cardboard is then tested.)

[0021] A further embodiment of the present invention provides an electrochemical element comprising a positive electrode, a negative electrode, and a composite separator, wherein the composite separator comprises a porous substrate and a ceramic layer formed on one or both sides of the substrate, the ceramic layer comprising inorganic particles, a binder, and a particulate adhesive, satisfying the following formula 1, and the binder being carboxymethylcellulose having a weight-average molecular weight of 180,000 g / mol to 280,000 g / mol.

number

[0022] A composite separator in one form comprises a porous substrate and a ceramic layer on the substrate containing inorganic particles, a binder, and a particulate adhesive. This allows for sufficient bonding force with electrodes without the need for another adhesive layer on the ceramic layer, thereby reducing internal resistance and improving electrical performance.

[0023] Furthermore, even when formed with a very thin thickness, the uniform composite separator can have superior heat resistance compared to a conventional separator with a ceramic layer of the same thickness. The adhesion between the inorganic particles and between the inorganic particles and the substrate is excellent, and the desorption phenomenon of the inorganic particles and the shrinkage phenomenon at high temperatures can be effectively suppressed.

[0024] Furthermore, a composite separator made of a single material can suppress the detachment and blocking phenomena of inorganic particles and / or particulate adhesives during winding.

[0025] Furthermore, composite separators using a single-mode design offer excellent productivity and are advantageous for commercial application. Electrochemical elements employing such composite separators can simultaneously meet safety, high capacity, and high output requirements. [Brief explanation of the drawing]

[0026] [Figure 1] This is a diagram illustrating a cross-section of a composite separator according to one embodiment. [Figure 2] This is a schematic plan view of an electrochemical element according to one embodiment. [Figure 3] This is a schematic cross-sectional view of an electrochemical element according to one embodiment. [Modes for carrying out the invention]

[0027] Unless otherwise defined herein, all technical and scientific terms have the same meanings as those generally understood by those skilled in the art in which the present invention pertains. Terms used in this description are solely for the purpose of effectively describing specific examples and are not intended to limit the present invention.

[0028] As used herein, the singular form may also include the plural form unless otherwise indicated in the context.

[0029] Throughout this specification, the terms "includes," "companies," "contains," or "has" a component mean, unless otherwise specified, that it may include other components rather than excluding them, and do not exclude any other elements, materials, or processes not listed.

[0030] The numerical ranges used herein include lower and upper limits, all values ​​within those limits, increments logically derived from the form and width of the defined range, all double-limited values, and all possible combinations of upper and lower limits of numerical ranges limited to different forms. Unless otherwise specifically defined herein, values ​​outside the numerical range that may arise due to experimental error or rounding of values ​​are also included in the defined numerical range.

[0031] Unless otherwise defined herein, "about" may refer to values ​​up to 30%, 25%, 20%, 15%, 10%, or 5% of the specified value.

[0032] In this specification, "average particle size" is defined as "D 50 This means "D 50 " " refers to the particle size of the sample particles being measured that corresponds to 50% of the cumulative fraction based on volume. The average particle size can be derived from the particle size distribution results obtained by taking a sample of the sample particles being measured in accordance with the ISO 13320-1 standard and analyzing it using a MICROTRAC S3500, where the sample being measured refers to inorganic particles and particulate fuses.

[0033] In this specification, carboxymethyl cellulose (CMC) is defined as cellulose in which the hydroxyl group (-OH) is -OCH2COOH and / or -OCH2COOH - M + This means a cellulose derivative that is substituted with and etherified, and the M +is an alkali metal cation and may be selected from lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). In this specification, the "degree of substitution (DS)" of carboxymethyl cellulose means the number of the average substituents contained in one anhydroglucose unit of a cellulose molecule and can be measured by a known or tolerated method. For example, it can be measured according to ASTM D1439, or 1 H-NMR or 13 can be calculated by 13C-NMR analysis.

[0034] The degree of substitution (DS, Degree of Substitution) of carboxymethyl cellulose (CMC) was measured using a titration method according to ASTM D1439. In the experiment, a magnetic stirrer, an aspirator, a dry oven, a 300 mL beaker, a pipette, a 250 mL Erlenmeyer flask, and a Petri dish were used. 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.

[0035] Specifically, 150 mL of 80% ethanol was placed in a 300 mL beaker, and then 10 mL of 1 N nitric acid (HNO3) was added. To this, about 1 - 2 g of a CMC sample was added and stirred for 1 hour to form CMC-acid. Then, after standing for about 10 - 20 minutes, the supernatant was removed by decanting.

[0036] Next, 150 mL of 80% ethanol was added again, and after stirring for 30 - 40 minutes, the supernatant was removed again. The precipitated CMC-acid was filtered using an aspirator, washed with 500 mL of 80% ethanol, and then further washed 1 - 2 times with 100% ethanol.

[0037] The central portion of the purified CMC acid was taken and transferred to a clean weighing dish, and dried in a drying oven for 20-30 minutes. After drying, approximately 0.2 ± 0.05 g of the sample was accurately weighed, and 25 mL of 0.1 N NaOH solution was added. This sample solution was transferred to a 250 mL Erlenmeyer flask, 100 mL of distilled water was added, and the mixture was stirred for 40-60 minutes until completely dissolved.

[0038] Next, 2-3 drops of phenolphthalein indicator were added, and the 0.1N H2SO4 solution was titrated while continuously stirring until the solution changed color from red to colorless.

[0039] The number of millimoles (A) of CMC-acid per gram of dried sample was calculated using the following formula.

[0040]

number

[0041] Next, the degree of substitution (DS) was calculated from A using the following formula.

[0042]

number

[0043] The following provides a detailed description of this disclosure. However, this is illustrative only, and the disclosure is not limited to the specific embodiments described herein.

[0044] Conventional techniques have used a method of introducing another adhesive layer on top of the inorganic coating layer to improve the fusion strength of composite separators, which include a porous substrate and an inorganic coating layer, to the electrodes. However, this adds an extra process step, increases manufacturing costs, and is difficult to apply to actual commercialization. Furthermore, the added adhesive layer could increase the internal resistance of the battery and degrade its electrical performance. On the other hand, a method has been proposed to introduce a fusion agent into the inorganic coating layer that can achieve fusion strength with the electrodes. However, recently, due to the high capacity and high power characteristics of electrochemical elements, separators are being made thinner. In an attempt to achieve sufficient fusion strength even in a thin thickness range, problems such as detachment of the fusion agent and blocking occur, so the development of new separators is needed.

[0045] One aspect of the present invention provides a composite separator that can ensure sufficient fusion force with electrodes even in a thin thickness range, exhibit excellent anti-blocking performance, have outstanding adhesion between inorganic particles and between inorganic particles and the substrate within the coating layer, and can prevent thermal shrinkage at high temperatures.

[0046] Specifically, a uniform composite separator comprises a porous substrate and a ceramic layer formed on one or both sides of the substrate, wherein the ceramic layer comprises inorganic particles, a binder, and a particulate adhesive, satisfying the following formula 1, and the binder may be carboxymethylcellulose having a weight-average molecular weight of 180,000 g / mol to 280,000 g / mol.

[0047]

number

[0048] (In formula 1 above, T is the thickness of the ceramic layer (μm), W1 is the binder content (wt%) relative to the total weight of the ceramic layer. W2 is the content (wt%) of particulate adhesive relative to the total weight of the ceramic layer. D is the average particle size (μm) of the particulate adhesive.

[0049] A uniform composite separator, as described above, uses CMC within a specific molecular weight range as a binder, and the thickness of the ceramic layer, the content of the binder and particulate adhesive, and the average particle size of the particulate adhesive have a specific relationship, satisfying the range of Equation 1. This allows for sufficient fusion force with the electrode, and provides superior heat resistance compared to a separator with a conventional ceramic layer of the same thickness. The adhesion between the inorganic particles and between the inorganic particles and the substrate is excellent, and the desorption phenomenon of inorganic particles and shrinkage at high temperatures can be effectively suppressed. Furthermore, a uniform composite separator can effectively suppress the desorption phenomenon and blocking phenomenon of inorganic particles and / or particulate adhesive during winding.

[0050] In one embodiment, the thickness T of the ceramic layer is not particularly limited as long as it satisfies the range of formula 1 as a combination of the binder content W1, the particulate adhesive content W2, and the average particle size D of the particulate adhesive. For example, it may be 0.1 μm to 10 μm, 0.5 μm to 10 μm, or 0.5 μm to 8 μm, or 0.5 μm to 5 μm, or 1 μm to 5 μm, or 1.2 μm to 5 μm, or 1.5 μm to 3 μm, and may include all possible combinations of the upper and lower limits of the numerical range.

[0051] In one embodiment, the total thickness of the ceramic layer may be 0.1 μm to 20.0 μm, 0.1 μm to 10.0 μm, 0.5 μm to 10.0 μm, or 1 μm to 10 μm, or 2 μm to 8 μm, or 2 μm to 5 μm, or 3 μm to 5 μm, and may include all possible combinations of the upper and lower limits of the numerical range. The total thickness of the ceramic layer means the thickness of the ceramic layer formed on one surface when the composite separator in a uniform manner includes a ceramic layer formed on one surface of a porous substrate, or the sum of the thicknesses of the ceramic layers formed on both surfaces when the composite separator in a uniform manner includes ceramic layers formed on both surfaces of a porous substrate, and the thicknesses of the ceramic layers formed on both surfaces may be the same or different from each other.

[0052] In one embodiment, by satisfying the weight-average molecular weight range of 180,000 g / mol to 280,000 g / mol for the carboxymethyl cellulose (CMC), even when CMC is used alone as a binder for the ceramic layer, excellent adhesion between inorganic particles and between inorganic particles and the substrate, as well as heat resistance, can be simultaneously achieved. During the formation of the ceramic layer, the coating slurry has an appropriate viscosity, making the formation of the coating layer easy. For example, if the weight-average molecular weight of the CMC is less than 180,000 g / mol, sufficient adhesion cannot be achieved, and if it exceeds 280,000 g / mol, the formation of the coating layer (ceramic layer) may be impossible. A sample of carboxymethyl cellulose dissolved in a standard substance at approximately 0.1% w / v was injected into a GPC instrument and measured.

[0053] In one embodiment, the carboxymethylcellulose may have a weight-average molecular weight of 180,000 to 280,000 g / mol, 180,000 to 260,000 g / mol, or 180,000 to 250,000 g / mol, or 190,000 to 250,000 g / mol, or 20,000 to 250,000 g / mol, and may include all possible combinations of the upper and lower limits of the above numerical range. The weight-average molecular weight may mean the weight-average molecular weight converted using a molecular weight calibration curve utilizing polysaccharide standard samples measured by the GPC method.

[0054] Furthermore, the carboxymethylcellulose may have a degree of substitution of 0.6 or more, 0.7 or more, 0.8 or more, 0.9 or more, 1.5 or less, 1.2 or less, 1.1 or less, or 1.0 or less. Specifically, it may 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 may include all possible combinations of the upper and lower limits of the aforementioned numerical range.

[0055] By using carboxymethylcellulose that satisfies the aforementioned combination of weight-average molecular weight and degree of substitution, when applying the ceramic layer to the surface of the porous substrate using a coating slurry during its formation, the coating properties are improved. Furthermore, in the composite separator containing this carboxymethylcellulose, even with a thin ceramic layer, the heat resistance is excellent, and the adhesion between inorganic particles or between the ceramic layer and the porous substrate is improved, thus enhancing the effect of simultaneously improving both heat resistance and adhesion.

[0056] In one embodiment, the average particle size of the particulate adhesive may be 1 μm or more, or 1.5 μm or more, or 2.0 μm or more, or 2.5 μm or more, or 10 μm or less, or 8 μm or less, or 6 μm or less, or 5 μm or less, or 1 μm to 10 μm, or 1 μm to 8 μm, or 1 μm to 6 μm, or 2 μm to 6 μm, and may include all possible combinations of the upper and lower limits of the numerical range, thereby improving the fusion strength with the electrode.

[0057] In one embodiment, the glass transition temperature (T) of the particle-type fuser is determined to be g The glass transition temperature may be 40°C or higher, 45°C or higher, 50°C or higher, 100°C or lower, 90°C or lower, or 80°C or lower, and may be 40°C to 100°C, 40°C to 90°C, or 40°C to 80°C, and may include all possible combinations of the upper and lower limits of the numerical range. When the range is met, the fusion force between the composite separator and the electrode is more excellent, and the battery performance after battery assembly may be better. Preferably, the glass transition temperature may be 40°C to 70°C, which is more preferable because it does not flow during the drying step of the composite separator, does not deform during the coating step and shipping process, minimizes changes in the permeability of the substrate after fusion, and maintains excellent performance.

[0058] The particulate adhesive is not particularly limited as long as it is a substance that can achieve fusion force with the electrode, but it may be an acrylic polymer, a urethane polymer, or a copolymer containing these.

[0059] The acrylic polymer may be a homopolymer containing alkyl (meth)acrylate monomer polymerization units, or a copolymer containing the alkyl (meth)acrylate monomer polymerization units. The copolymer containing alkyl (meth)acrylate monomer polymerization units may be a copolymer containing 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.

[0060] The alkyl (meth)acrylate monomer may be a C1-C10 alkyl (meth)acrylate monomer, a C1-C6 alkyl (meth)acrylate monomer, or a C1-C4 alkyl (meth)acrylate monomer, and specifically, it may be one or more selected from methyl (meth)acrylate, ethyl (meth)acrylate, and n-butyl (meth)acrylate.

[0061] Non-limiting examples of the aforementioned particulate adhesives include, but are not limited to, polyurethane beads, polyurethane acrylic beads, epoxy-acrylic 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), and polydimethylsiloxane-polymethyl methacrylate (PDMS-PMMA).

[0062] Since the method for producing the aforementioned particle-type fuse can be carried out by emulsion polymerization or suspension polymerization, as these are known manufacturing methods, a detailed explanation will be omitted.

[0063] In one embodiment, the type of inorganic particle can be any type commonly used in the art, and as a non-limiting example, it may be one or more selected from metal oxides, metal hydroxides, metal carbides, metal nitrides, and metal carbonitrides such as boehmite, pseudo-boehmite, BaSO4, CeO2, MgO, CaO, ZnO, Al2O3, SiO2, TiO2, BaTiO3, HfO2, SrTiO3, SnO2, NiO, ZrO2, Y2O3, and SiC.

[0064] In one embodiment, the average particle size (D) of the inorganic particles 50 ) may be, for example, 0.01 μm or more, 0.02 μm or more, 0.05 μm or more, 0.1 μm or more, and may include, but is not limited to, 0.01 μm to 10 μm, or 0.02 μm to 5.0 μm, or 0.1 μm to 3.0 μm, or 0.1 μm to 2.0 μm, or 0.1 μm to 1.0 μm, or 0.1 μm to 0.5 μm, or all possible combinations of the upper and lower limits of these numerical ranges.

[0065] In one embodiment, the ceramic layer may contain inorganic particles in an amount of 90-99.9% by weight, 92-99.5% by weight, 92-99% by weight, 90-99% by weight, 95-99% by weight, or 95-98% by weight, relative to the total weight of the ceramic layer.

[0066] In one embodiment, the binder content W1 may be 0.01% by weight or more, or 0.1% by weight or more, or 0.5% by weight or more, or 1% by weight or more, 1.5% by weight or more, or 2% by weight or more, or 10% by weight or less, or 8% by weight or less, or 5% by weight or less, relative to the total weight of the ceramic layer, and may be between 0.01% by weight and 10% by weight, or between 0.1% by weight and 10% by weight, or between 0.5% by weight and 5% by weight, or between 1% by weight and 5% by weight, and may include all possible combinations of the upper and lower limits of the numerical range.

[0067] In one embodiment, the content W2 of the particulate adhesive may be 0.1% by weight or more, or 0.5% by weight or more, or 1.0% by weight or more, more than 1.0% by weight, or 1.1% by weight or more, or 1.2% by weight or more, relative to the total weight of the ceramic layer, and may be 10% by weight or less, 5% by weight or less, or 4% by weight or less, or 3% by weight or less, or 2% by weight or less, or less than 2% by weight, specifically, it may be 0.5% to 5% by weight, or 1% to 5% by weight, or 1% to 3% by weight, or 1% to 2% by weight, or more than 1% by weight and less than 2% by weight, and may include all possible combinations of the upper and lower limits of the numerical range.

[0068] In one embodiment, the ceramic layer may contain 10 parts by weight or less, 8 parts by weight or less, 5 parts by weight or less, 3 parts by weight or less, 2 parts by weight or less, or 1 part by weight or less of the binder per 100 parts by weight of the inorganic particles, or it may contain 0.01 parts by weight or more, 0.1 parts by weight or more, 0.5 parts by weight or more, 1 part by weight or more, or 2 parts by weight or more, specifically 0.1 to 5 parts by weight, or 1 to 5 parts by weight, or 1 to 3 parts by weight, or an amount between these numerical ranges.

[0069] In one embodiment, the binder and the particulate adhesive may be present in a weight ratio of 5:5 to 9:1, or 5:5 to 8:2, or 5:5 to 7:3.

[0070] In one embodiment, after leaving the composite separator at 150°C for 60 minutes, the measured thermal shrinkage rates in the MD direction and TD direction may all be 5% or less, specifically 3% or less, or 2.5% or less, or 2.0% or less, or 1.5% or less, or 1.0% or less, or 0.5% or less.

[0071] The thermal shrinkage rate of the composite separator was measured in accordance with the ASTM D1204 standard, specifically using the following method. Grid points were marked at 2cm intervals within a square of the composite separator test specimen with sides of 10cm, with one side of the square designated as the transverse direction (TD) and the other as the mechanical direction (MD). The test specimen was positioned in the center, and five sheets of paper were placed above and below it, and then the four sides of the paper were secured with tape. The tapered test specimen was left in a 150°C hot air dryer for 60 minutes. Next, the test specimen was removed, and the separator was observed with a camera at room temperature, and the shrinkage rates in the mechanical direction (MD) and transverse direction (TD) were calculated.

[0072] Furthermore, in one embodiment, when the degree of foreign matter adhesion to the surface of the cardboard is evaluated after the composite separator has undergone a cardboard test, the ratio of the area occupied by the adhered foreign matter to the area of ​​the cardboard may be 5% or less, specifically less than 5%, less than 4%, less than 3%, less than 2%, or less than 1.5%.

[0073] The cardboard test method involves placing a 2cm x 10cm black cardboard and a rubber pad sequentially on the upper surface of the ceramic layer of a 5cm x 10cm composite separator test piece, applying a force of 10N to the rubber pad using a press device, horizontally removing the cardboard at a speed of 0.1m / s, and evaluating the area on which foreign matter adheres to the surface of the cardboard. The foreign matter may be a component of the ceramic layer, such as inorganic particles, a binder, or a combination thereof.

[0074] When evaluating adhesive strength using the cardboard test method described above, it is possible to measure not only the adhesive strength between the substrate and the ceramic layer interface, but also the adhesive strength between inorganic particles within the ceramic layer. Based on the results of the adhesive strength test, the degree of thermal shrinkage can be predicted more accurately than with the conventional peel test. In other words, if the ratio of the area occupied by the attached foreign matter calculated by the cardboard test is less than 5%, less than 4%, less than 3%, less than 2%, or less than 1.5%, it may mean that the adhesive strength between inorganic particles and between inorganic particles and the substrate is excellent, and that the thermal shrinkage phenomenon can be effectively suppressed.

[0075] For example, in conventional composite separators, methods such as the peel test used to evaluate the adhesion strength of the inorganic particle coating layer evaluate the adhesion strength between the substrate and the inorganic particle coating layer. However, the adhesion strength between inorganic particles is difficult to predict, and there is a disadvantage in that it is not possible to accurately predict the thermal shrinkage characteristics of the separator as an evaluation value.

[0076] In one embodiment, the porous substrate is not limited as long as it is commonly used in the art, and may be, for example, a woven fabric, a nonwoven fabric, or a porous film. Specifically, the porous substrate may be a polyolefin such as polyethylene or polypropylene, a polyester such as polyethylene terephthalate or polybutylene terephthalate, a polyacetal, a polyamide, a polyimide, a polycarbonate, a polyetheretherketone, a polyaryletherketone, a polyetherimide, a polyamideimide, a polybenzimidazole, a polyethersulfone, a polyphenylene oxide, a cyclic olefin copolymer, a polyphenylene sulfide, a polyethylene naphthalate, a glass fiber, Teflon®, and / or polytetrafluoroethylene, and two or more of these may be used. Among the porous substrates, the porous film is manufactured by dry and wet methods and is known in the art, so it will not be described further.

[0077] In one embodiment, the porous substrate may have a porosity of 20-60%, 30-60%, 30-50%, or 35-45%, but is not limited thereto.

[0078] In one embodiment, the porous substrate may be subjected to a hydrophilic surface treatment to introduce polar functional groups, such as carboxyl groups, aldehyde groups, and hydroxyl groups. The hydrophilic surface treatment may, for example, be corona discharge treatment or plasma discharge treatment, but is not particularly limited.

[0079] In one embodiment, the thickness of the porous substrate is not particularly limited and may be, for example, 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 numbers.

[0080] A further embodiment of the present invention provides a method for manufacturing the composite separator, the method comprising the steps of applying a ceramic layer-forming composition comprising inorganic particles, a binder, and a particulate adhesive to at least one surface of a porous substrate, drying, and forming a ceramic layer, wherein the binder is carboxymethylcellulose 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.

[0081]

number

[0082] (In formula 1 above, T is the thickness of the ceramic layer (μm), W1 is the binder content (wt%) relative to the total weight of the ceramic layer. W2 is the content (wt%) of particulate adhesive relative to the total weight of the ceramic layer. D is the average particle size (μm) of the particulate adhesive.

[0083] The porous substrate, binder, and inorganic particles are as described above, and a detailed explanation is omitted.

[0084] The ceramic layer forming composition may be manufactured by dispersing a binder and inorganic particles, or by dispersing aggregated inorganic particles using a ball mill.

[0085] The ceramic layer forming composition further comprises a solvent, which may be, but is not limited to, water, lower alcohols such as ethanol, methanol, and propanol, solvents such as dimethylformamide, acetone, tetrahydrofuran, diethyl ether, methylene chloride, N-methyl-2-pyrrolidone, hexane, and cyclohexane, or mixtures thereof.

[0086] In one embodiment, the solid content of the ceramic layer-forming composition is not particularly limited, but may be, for example, 1 to 50% by weight, 5 to 30% by weight, or 10 to 30% by weight, but is not limited thereto. Furthermore, the ceramic layer-forming composition may have a viscosity of 800 to 5,000 mPa·s, or 800 to 4,000 mPa·s, or 800 to 3,000 mPa·s, or 1,000 to 3,000 mPa·s, based on a solid content of 25% by weight, which can facilitate the formation of the ceramic layer and improve the heat resistance and adhesive strength of the separator.

[0087] In one embodiment, the method for applying or coating the ceramic layer-forming composition onto a porous substrate is not particularly limited, but examples include roll coating, spin coating, dip coating, bar coating, die coating, slit coating, or inkjet printing.

[0088] In one embodiment, the drying can be carried out by drying with warm air, hot air, low-humidity air, vacuum drying, or irradiation by far-infrared rays or electron beams. The drying temperature is not particularly limited and may be adjusted as appropriate depending on the experimental environment and purpose, for example, it may 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 may be 30 seconds to 300 seconds, 60 seconds to 300 seconds, 100 seconds to 300 seconds, 150 seconds to 250 seconds, or about 180 seconds.

[0089] A further embodiment of the present invention provides an electrochemical element comprising a composite separator according to the above embodiment, wherein the electrochemical element may, for example, be a lithium secondary battery.

[0090] Specifically, the electrochemical element in one state includes a positive electrode, a negative electrode, and a composite separator, the composite separator includes a porous substrate and a ceramic layer formed on one or both sides of the substrate, the ceramic layer includes inorganic particles, a binder, and a particulate adhesive, satisfying the following formula 1, and the binder may be carboxymethylcellulose having a weight-average molecular weight of 180,000 g / mol to 280,000 g / mol.

[0091]

number

[0092] (In formula 1 above, T is the thickness of the ceramic layer (μm), W1 is the binder content (wt%) relative to the total weight of the ceramic layer. W2 is the content (wt%) of particulate adhesive relative to the total weight of the ceramic layer. D is the average particle size (μm) of the particulate adhesive.

[0093] The following explanation will describe electrochemical elements in a single state, using lithium secondary batteries as an example. It goes without saying that, except for composite separators in a single state, these can be manufactured using conventional manufacturing methods and materials in the art, and with structures well known in the art.

[0094] As an example, the lithium secondary battery can be manufactured by a common method in which the negative electrode, composite separator, and positive electrode are arranged in order and assembled, and then the electrolyte is injected to complete the battery.

[0095] [Positive electrode] The positive electrode may include a positive electrode current collector and a positive electrode mixture layer on at least one surface of the positive electrode current collector. The positive electrode may be manufactured by applying a positive electrode material slurry to one or both surfaces of the positive electrode current collector, drying and rolling it to form a 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.

[0096] 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, 10 μm to 50 μm, but is not limited thereto.

[0097] The positive electrode active material can be used without limitation as long as it is a compound that is commonly used in the art as a compound capable of reversibly intercalating and deintercalating lithium ions. Non-limiting examples include composite oxides 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.

[0098] In one embodiment, the positive electrode active material may be a lithium-nickel composite oxide, and the lithium-nickel composite oxide may further contain one or more selected from cobalt, manganese, and aluminum.

[0099] In one embodiment, the positive electrode active material may include a lithium nickel-cobalt-manganese (NCM) composite oxide, and the composition of the metal is not particularly limited, but a high-Ni composition with a high nickel content may be used, and the Ni content of the NCM lithium oxide (for example, the mole fraction of nickel in the total number of 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 0.8~0.95, 0.82~0.95, 0.83~0.95, 0.84~0.95, 0.85~0.95, or 0.88~0.95. The NCM composite oxide is, as an example, LiNi 0.33 Co 0.33 Mn 0.33 O2, LiLiLi 0.4 Co 0.2 Mn 0.4 O2, LiLiLi 0.5 Co 0.2 Mn 0.3 O2, LiLiLi 0.6 Co 0.2 Mn 0.2 O2, LiLiLi 0.7 Co 0.15 Mn 0.15 O2, LiLiLi 0.8 Co 0.1 Mn 0.1 While O2 is one example, it is not the only option.

[0100] In one embodiment, the positive electrode active material may be, for example, a lithium cobalt oxide system, a lithium manganese oxide system, a lithium nickel oxide system, a lithium iron phosphate system (LFP, e.g., LiFePO4), a lithium manganese phosphate system (e.g., LiMnPO4), a lithium cobalt phosphate system (e.g., LiCoPO4), a lithium iron pyrophosphate system (e.g., Li2FeP2O7), or the like.

[0101] The positive electrode binder is not particularly limited as long as it is commonly used in the art, and may include a non-aqueous binder and / or an aqueous binder, or a rubber binder and / or a fluorine-based binder. For example, it may be one or more selected from acrylic polymers such as polyacrylate, polymethacrylate, polybutyl acrylate, and polyacrylonitrile; fluorine-based polymers such as polyvinylidene fluoride, polyhexafluoropropylene, polyvinylidene fluoride-hexafluoropropylene, and polyvinylidene fluoride-trichloroethylene; polyvinyl acetate, polyethylene oxide, cellulose, modified cellulose, polyamide, polyacrylamide, rubber, elastomer, etc., but is not limited thereto.

[0102] The conductive material may 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 may be a linear conductive material and / or a point conductive material, and may include, but is not limited to, carbon-based conductive materials such as graphite, carbon black, acetylene black, Ketjenblack, graphene, carbon nanotubes, VGCF (vapor-grown carbon fiber), carbon fiber, and / or metallic conductive materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3, which are perovskite materials. As used herein, the term "point conductive material" may mean a conductive material in a general spherical or particulate form.

[0103] [Negative electrode] The negative electrode may include a negative electrode current collector and a negative electrode mixture layer on at least one surface of the negative electrode current collector. The negative electrode may be manufactured by applying a negative electrode material slurry to one or both surfaces of the negative electrode current collector, drying and rolling it to form a 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.

[0104] 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.

[0105] The negative electrode active material can be any material commonly used in the art that is capable of adsorbing and desorbing lithium ions, and non-limiting examples include carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, and carbon fibers, as well as lithium metal, lithium alloys, silicon (Si)-containing materials, or tin (Sn)-containing materials.

[0106] Examples of amorphous carbon include hard carbon, soft carbon, coke, mesocarbon microbeads (MCMB), and mesophase pitch-based carbon fiber (MPCF). Examples of crystalline carbon include graphite-based carbon such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, and graphitized MPCF.

[0107] Examples of elements contained in the aforementioned lithium alloy include aluminum, zinc, vizmus, cadmium, antimony, silicon, lead, tin, gallium, or indium.

[0108] The silicon-containing material can provide increased capacity characteristics. The silicon-containing material is Si, SiO x(0 < x ≤ 2), metal-doped SiO x (0 < x ≤ 2) may include a silicon-carbon composite, etc., and the metal may include lithium and / or magnesium, and the metal-doped SiO x (0 < x ≤ 2) may include a metal silicate. The binder, conductive material, and thickener of the negative electrode may be the above-mentioned substances that can be used during the manufacture of the positive electrode.

[0109] The negative electrode binder is not particularly limited as long as it is commonly used in the art, and rubber-based binders such as styrene-butadiene rubber (SBR)-based binders, carboxymethyl cellulose (CMC), polyacrylic acid, poly(3,4-ethylenedioxythiophene), PEDOT)-based binders, etc. can be used.

[0110] [Electrolyte] In one embodiment, the electrolyte may be a non-aqueous electrolyte, and the non-aqueous electrolyte may include a lithium salt as the electrolyte and an organic solvent.

[0111] The lithium salt is represented by, for example, Li + X - and is the anion (X - ) of the lithium salt, and 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 - These are some examples.

[0112] The organic solvent may contain organic compounds that have sufficient solubility in the lithium salt and additives and that do not react within the battery. The organic solvent may include, for example, at least one of carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, and aprotic solvents. The organic solvent may be one or more selected from, for example, propylene carbonate, ethylene carbonate, butylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl 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, fluoroethyl acetate, difluoroethyl acetate, trifluoroethyl acetate, dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, ethanol, isopropyl alcohol, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, sulfolane, γ-butyrolactone, and propylene sulfide.

[0113] [Cell structure] For example, electrode tabs (positive and negative electrode tabs) can protrude from the positive and negative electrode current collectors, respectively, and extend to one side of the case. These electrode tabs can be fused together with the aforementioned side of the case and connected to electrode leads (positive and negative electrode leads) that extend or are exposed outside the case. For example, pouch-type cases, rectangular cases, cylindrical cases, and coin-type cases can be used.

[0114] The embodiments described above will be explained in more detail below with reference to the examples. However, the following examples are for illustrative purposes only and do not limit the scope of the rights.

[0115] The physical properties of the examples were measured as follows.

[0116] [Physical property measurement method] 1) Glass transition temperature (T g ) Using a differential scanning calorimetry (DSC), the heat capacity of a sample was measured by heating it at a rate of 10°C / min in the range of -100°C to 250°C. The temperature at the midpoint of the interval in which the heat capacity of the sample changed rapidly was determined as the glass transition temperature.

[0117] 2) Thickness After stacking 10 layers of composite separators, the thickness was measured at room temperature and pressure using a Mitutoyo (ID-C112X) to derive the average thickness of the 10 layers of composite separators, and this average was then divided by 10 to obtain the thickness of the composite separators. The total thickness of the ceramic layer was obtained by subtracting the thickness of the porous substrate from the thickness of the composite separators.

[0118] 3) Adhesive strength [Cardboard Test] A composite separator was cut to a size of 5 cm x 10 cm to prepare a test specimen. A 2 cm x 10 cm black cardboard and a rubber pad were placed sequentially on the ceramic layer of the composite separator test specimen. While applying a force of 10 N to the rubber pad using a press device, the cardboard was horizontally removed at a speed of 0.1 m / s to a length of 60 mm. The adhesive strength was evaluated according to the degree to which foreign matter adhered to the surface of the cardboard. The foreign matter may be a component of the ceramic layer, such as inorganic particles, a binder, or a combination thereof.

[0119] [Evaluation of the degree of foreign matter adhesion] After the cardboard test, the surface of the cardboard was photographed with an optical camera to create an image, and the area of ​​the attached foreign matter was measured. Specifically, indirect lighting was set up with an LED lamp in the visible light range at a 60° gradient, and the cardboard was photographed with a 640M pixel optical camera at a height of 40 cm above the sample (cardboard). After loading the captured cardboard image into the ImageJ program, the crop function was used to select and cut out only the area that passed through the separator and rubber pad. The image file format of the cut-out area was then converted to an 8-bit image, and the brightness and contrast of the image were adjusted by applying a Sharpen filter to facilitate the distinction between the cardboard and the white foreign matter. A threshold was applied to the image to convert it to a binary image, and the Analyze Particles function was executed 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 criteria.

[0120] A: <1.5% B: 1.5%~5% C:>5%

[0121] [Example 1] Inorganic particles in water with average particle size (D 50 A slurry with a solid content of 45% by weight was prepared by mixing 100 parts by weight of 0.3 μm boehmite with 2 parts by weight of the dispersant 1,2-benzoisothiazolin-3-one (DIO2).

[0122] To the slurry prepared above, a 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, and polystyrene-polybutyl methacrylate-polymethyl methacrylate block copolymer (PS-PBMA-PMMA) (D) was added as a particulate fuser. 50 A ceramic layer-forming composition was prepared by adding inorganic particles (2.5 μm, Tg: 62°C) and adjusting the weight ratio of inorganic particles / binder / particle-type adhesive to 96 / 2.3 / 1.7.

[0123] Both sides of a 9μm thick polyethylene film substrate (porosity 35%~45%, SKIET) were subjected to corona discharge treatment (power density 2W / m²). 2 Surface polar groups were introduced by corona surface treatment, which was performed at a speed of 5 mpm (meters per minute). The ceramic was similarly applied to both sides of the corona-treated polyethylene film substrate, then bar-coated and dried at 50°C to produce a composite separator in which ceramic layers of the same thickness were formed on both sides.

[0124] [Example 2] The procedure was carried out in the same manner as in Example 1, except that inorganic particles / binder / particulate fuser were used in a weight ratio of 95 / 3.3 / 1.7.

[0125] [Example 3] The procedure was carried out in the same manner as in Example 1, except that inorganic particles / binder / particulate adhesive were used in a weight ratio of 95 / 3.8 / 1.2 and the thickness of the ceramic layer was changed as shown in Table 1 below.

[0126] [Example 4] The procedure was carried out in the same manner as in Example 1, except that inorganic particles / binder / particulate adhesive were used in a weight ratio of 96 / 2 / 2 and the thickness of the ceramic layer was changed as shown in Table 1 below.

[0127] [Example 5] The procedure was carried out in the same manner as in Example 1, except that inorganic particles / binder / particulate adhesive were used in a weight ratio of 95 / 3 / 2, and the thickness of the ceramic layer was changed as shown in Table 1 below.

[0128] [Example 6] The procedure was carried out in the same manner as in Example 1, except that inorganic particles / binder / particulate adhesive were used in a weight ratio of 95 / 3.4 / 1.6 and the thickness of the ceramic layer was changed as shown in Table 1 below.

[0129] [Example 7] As a particulate fusion agent, PS-PBMA-PMMA(D 50 The procedure was carried out in the same manner as in Example 1, except that the thickness of the ceramic layer was changed as shown in Table 1 below, using inorganic particles / binder / particulate adhesive in a weight ratio of 95 / 3.3 / 1.7 (5.0 μm, Tg: 62℃).

[0130] [Example 8] The procedure was carried out in the same manner as in Example 7, except that the inorganic particles / binder / particulate adhesive were used in a weight ratio of 96 / 2.8 / 1.2.

[0131] [Example 9] The procedure was carried out in the same manner as in Example 7, except that inorganic particles / binder / particulate adhesive were used in a weight ratio of 95 / 3.8 / 1.2, and the thickness of the ceramic layer was changed as shown in Table 1 below.

[0132] [Comparative Example 1] The procedure was carried out in the same manner as in Example 1, except that inorganic particles / binder / particulate adhesive were used in a weight ratio of 97 / 1.3 / 1.7.

[0133] [Comparative Example 2] The procedure was carried out in the same manner as in Example 1, except that inorganic particles / binder / particulate adhesive were used in a weight ratio of 94 / 4.8 / 1.2 and the thickness of the ceramic layer was changed as shown in Table 1 below.

[0134] [Comparative Example 3] The procedure was carried out in the same manner as in Example 1, except that inorganic particles / binder / particulate adhesive were used in a weight ratio of 97 / 1 / 2 and the thickness of the ceramic layer was changed as shown in Table 1 below.

[0135] [Comparative Example 4] The procedure was carried out in the same manner as in Example 1, except that inorganic particles / binder / particulate adhesive were used in a weight ratio of 94 / 4.65 / 1.35, and the thickness of the ceramic layer was changed as shown in Table 1 below.

[0136] [Comparative Example 5] The procedure was carried out in the same manner as in Example 1, except that polyacrylamide (PAAm) (Mw 200,000 g / mol, Sigma Aldrich) was used as the binder instead of CMC.

[0137] [Comparative Example 6] The procedure was carried out in the same manner as in Example 7, except that polyacrylamide (PAAm) (Mw 200,000 g / mol, Sigma Aldrich) was used as the binder instead of CMC.

[0138] [Comparative Example 7] As a particulate fusion agent, PS-PBMA-PMMA(D 50 The procedure was carried out in the same manner as in Example 1, except that a 0.9 μm (Tg: 62°C) was used.

[0139] The composite separators obtained in the above examples and comparative examples were subjected to physical property measurement using the method described above, and the values ​​of the following formula 1 were calculated, rounded down to three decimal places, and listed in Table 1 below.

[0140] In the composite separators obtained in the above examples and comparative examples, ceramic layers of the same thickness were formed on both sides of the substrate, and the thickness T of the ceramic layer formed on one side was set to half the total thickness of the ceramic layer measured by the above physical property measurement method.

[0141]

number

[0142] (In formula 1 above, T is the thickness of the ceramic layer (μm), W1 is the binder content (wt%) relative to the total weight of the ceramic layer, W2 is the particulate adhesive content (wt%) relative to the total weight of the ceramic layer, and D is the average particle size (μm) of the particulate adhesive.)

[0143] [Table 1]

[0144] <Example of evaluation> Evaluation 1. Anti-blocking performance Two composite separators obtained in the above examples and comparative examples are placed with their ceramic layers facing each other, and the temperature is 25°C and the humidity is 15 kgf / cm². 2 After pressing at a pressure for 1 hour, the material was peeled at 180° in accordance with ASTM D903. A scanning electron microscope (SEM) was then used to confirm whether or not the particulate adhesive and / or inorganic particles had detached. Ten arbitrary locations were selected, and the number of detached particulate adhesive and / or inorganic particles per unit area was counted. The average value of these 10 points was calculated, and the antiblocking performance was evaluated according to the following criteria. The results are shown in Table 2 below.

[0145] ○: Neither the adhesive nor the inorganic particles have detached, 10 -4 pieces / μm 2 It is partially detached. ×: 10 fusion agent or inorganic particles -4 pieces / μm 2 The above points have been removed.

[0146] Evaluation 2. Electrode fusion strength The positive and negative electrodes were manufactured as described below, and the fusion force between the electrodes and the composite separator obtained in the above example was evaluated.

[0147] A homogeneous cathode slurry was prepared by adding 94% by weight of LiCoO2 as the cathode active material, 2.5% by weight of polyvinylidene fluoride as an adhesive, and 3.5% by weight of carbon black as a conductive agent to NMP (N-methyl-2-pyrrolidone) as a solvent, and stirring. The slurry was coated onto a 30 μm thick aluminum foil, dried at 120°C, and then pressed to produce a 150 μm thick cathode plate.

[0148] A homogeneous negative electrode slurry was prepared by adding 95% by weight of artificial graphite as the negative electrode active material, 3% by weight of acrylic latex (trade name: BM900B, solids content: 20% by weight) with a Tg of -52°C as an adhesive, and 2% by weight of CMC (Carboxymethyl cellulose) as a thickener to water as a solvent, stirring, and coating the slurry onto a 20 μm thick copper foil, drying at 120°C, and then pressing to produce a 150 μm thick negative electrode plate.

[0149] After laminating a composite separator between each of the four manufactured positive (negative) electrodes, the electrodes were pressed together using a heat press at 90°C and 1 MPa for 30 seconds to prepare samples for evaluating the fusion strength to the positive and negative electrodes. When the samples were lifted vertically, the number of electrodes attached was measured, and the fusion strength between the composite separator and the positive and negative electrodes was evaluated according to the following criteria, and the results are shown in Table 2 below.

[0150] 1 / 4: One of the four electrodes is fused. 2 / 4: Two out of four electrodes are fused together. 3 / 4: Three out of four electrodes are fused together. 4 / 4: All four electrodes are fused together.

[0151] [Table 2]

[0152] Referring to Tables 1 and 2, it can be seen that the composite separator according to one embodiment of the present invention exhibits excellent adhesion not only between the interface between the substrate and the ceramic layer, but also between inorganic particles within the ceramic layer, and can effectively suppress thermal shrinkage. Furthermore, it has been confirmed that the composite separator according to one embodiment has excellent fusion force to both the positive and negative electrodes, and can suppress desorption and blocking phenomena of inorganic particles and / or particulate adhesives during the winding of the separator. Moreover, the composite separator according to one embodiment is advantageous for commercial application due to its excellent productivity, and an electrochemical element employing a composite separator of one embodiment can simultaneously satisfy safety, high capacity, and high output characteristics.

[0153] On the other hand, the composite separators 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 Equation 1 (0.9 < Equation 1 < 2.4), show reduced adhesion and / or heat resistance, a significant increase in thermal shrinkage, and in the case of Comparative Example 7, a drastic decrease in fusion strength with the electrode, resulting in almost no fusion strength at all.

[0154] Furthermore, in Comparative Examples 5 and 6, which use PAAm as a binder, it was confirmed that the adhesive strength and heat resistance were significantly reduced, the air permeability deteriorated, and the air permeability value (sec / 100cc) increased compared to the composite separator according to one embodiment.

[0155] The composite separator disclosed herein is widely applicable in green technology fields such as electric vehicles, battery charging stands, and other battery-powered solar and wind power generation. Furthermore, the separator disclosed herein can be used in eco-friendly electric vehicles, hybrid vehicles, and other applications that reduce air pollution and greenhouse gas emissions to prevent climate change.

[0156] Although this disclosure has been described through specific matters and limited embodiments, these are provided to facilitate a more general understanding of the disclosure, and the disclosure is not limited to the embodiments described above. Various modifications and variations can be made from such descriptions by a person with ordinary skill in the art to which the disclosure pertains.

[0157] Therefore, this disclosure should not be limited to the embodiments described above, and it can be said that not only the claims described later, but also all variations that are equivalent or comparable to the claims described herein, fall within the scope of this disclosure. [Explanation of Symbols]

[0158] 100 positive electrode 105 Positive electrode current collector 107 Positive lead 110 Positive electrode mixture layer 120 Negative electrode mixture layer 125 Negative electrode current collector 127 Negative lead 130 negative electrode 140 Separator 150 Electrode assembly 160 cases

Claims

1. A composite separator comprising a porous substrate and a ceramic layer formed on one or both sides of the substrate, The ceramic layer comprises inorganic particles, a binder, and a particulate adhesive, and satisfies the following formula 1. The binder is a composite separator having a weight-average molecular weight of carboxymethylcellulose ranging from 180,000 g / mol to 280,000 g / mol. [Math 1] In the above formula 1, T is the thickness of the ceramic layer (μm), W1 is the binder content (wt%) relative to the total weight of the ceramic layer. W2 is the content (wt%) of particulate adhesive relative to the total weight of the ceramic layer. D is the average particle size (μm) of the particulate adhesive.

2. The average particle size (D) of the aforementioned particulate fuser ５０ The composite separator according to claim 1, wherein the particle size is 1 μm to 10 μm.

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

4. The composite separator according to claim 1, wherein the carboxymethylcellulose has a degree of substitution of 0.6 to 1.

2.

5. The average particle size (D) of the inorganic particles ５０ The composite separator according to claim 1, wherein the particle size is 0.01 μm to 1 μm.

6. The inorganic particles are boehmite, pseudo-boehmite, BaSO ４ , CeO ２ , MgO, CaO, ZnO, Al ２ O ３ , SiO ２ , TiO ２ , BaTiO ３ , HfO ２ , SrTiO ３ , SnO ２ , NiO, ZrO ２ , Y ２ O ３ The composite separator according to claim 1, which is one or more selected from SiC.

7. The composite separator according to claim 1, wherein the inorganic particles are present in an amount of 90 to 99% by weight relative to the total weight of the ceramic layer.

8. The composite separator according to claim 1, wherein the binder is contained in an amount of 0.1% to 10% by weight relative to the total weight of the ceramic layer.

9. The composite separator according to claim 1, wherein the particulate adhesive is contained in an amount of 0.1% to 10% by weight relative to the total weight of the ceramic layer.

10. The composite separator according to claim 1, wherein the binder and the particulate fuser are contained in a weight ratio of 5:5 to 8:

2.

11. The glass transition temperature (T) of the aforementioned particulate fuser. ｇ The composite separator according to claim 1, wherein the temperature range is 40°C to 80°C.

12. The composite separator according to claim 1, wherein the porous substrate is subjected to a hydrophilic surface treatment.

13. The composite separator according to claim 1, wherein the thermal shrinkage rates in the MD direction and the TD direction, measured after leaving the composite separator at 150°C for 60 minutes, are both 4% or less.

14. The composite separator according to claim 1, wherein, after a cardboard test, when the degree of foreign matter adhesion to the surface of the cardboard is evaluated, the ratio of the area occupied by the adhered foreign matter to the area of ​​the cardboard is 5% or less. [Cardboard Test] A 2cm x 10cm black cardboard and a rubber pad are placed sequentially on the ceramic layer of a 5cm x 10cm composite separator test piece. A force of 10N is applied to the rubber pad using a press device, and the cardboard is horizontally removed at a speed of 0.1m / s. The degree to which foreign matter adheres to the surface of the cardboard is then tested.

15. An electrochemical element comprising a positive electrode, a negative electrode, and a composite separator, The composite separator comprises a porous substrate and a ceramic layer formed on one or both sides of the substrate, wherein the ceramic layer comprises inorganic particles, a binder, and a particulate adhesive, satisfying the following formula 1, and the binder is carboxymethylcellulose having a weight-average molecular weight of 180,000 g / mol to 280,000 g / mol, an electrochemical element. [Math 2] In the above formula 1, T is the thickness of the ceramic layer (μm), W1 is the binder content (wt%) relative to the total weight of the ceramic layer. W2 is the content (wt%) of particulate adhesive relative to the total weight of the ceramic layer. D is the average particle size (μm) of the particulate adhesive.

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