Composite separator and electrochemical element containing the same

Abstract

To provide a composite separator that can prevent blocking phenomena. [Solution] The present disclosure relates to a composite separator comprising a porous substrate and a coating layer formed on at least one surface of the substrate and containing organic particles, wherein the coating layer satisfies the following formula 1, and can ensure excellent heat resistance, adhesive strength, and fusion strength with electrodes even at a thin thickness, and can prevent blocking phenomena. [Formula 1]4,000≦(A×D 2 ) / T≦5,500 (In formula 1 above, A is the number of organic particles per unit area of ​​the surface of the coating layer ( / mm) 2 ) where D is the average particle size (μm) of organic particles observed on the surface of the coating layer, and T is the total thickness (μm) of the coating layer.

Description

Technical Field

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

Background Art

[0002] Recently, as electrochemical devices 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 separators, which act as very important elements for ensuring the heat resistance and safety of electrochemical devices, 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 during the cell assembly process, the separator and the electrode separate, resulting in distortion, deformation, etc. of the electrode assembly, causing a short circuit between the electrodes and posing a safety problem. To solve this, methods such as introducing a coating layer containing another fusing agent that can exhibit fusing force with the electrode have been proposed, but the fusing effect is not sufficient, and when sufficient fusing force is achieved, problems such as a blocking phenomenon in which substances in the fusing agent and the coating layer desorb occur.

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 into which a coating layer containing organic particles capable of achieving fusion force with electrodes is introduced, and provides a composite separator that can ensure excellent heat resistance, adhesive strength, and fusion force 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 coating layer formed on at least one surface of the substrate and containing organic particles, wherein the coating layer satisfies the following formula 1. [Formula 1] 4,000 ≤ (A × D 2 ) / T≦5,500 (In formula 1 above, A is the number of organic particles per unit area ( / mm²) on the surface of the coating layer. 2 ) and D is the average particle size (μm) of organic particles observed on the surface of the coating layer. T is the total thickness (μm) of the coating layer.

[0008] The surface average particle size (D) of the coating layer of the organic particles may be 1 μm to 10 μm.

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

[0010] The glass transition temperature (T) of the aforementioned organic particles g The temperature can be 40°C to 80°C.

[0011] The organic particles may include one or more selected from the group consisting of acrylic polymers, urethane polymers, and fluorine polymers.

[0012] The acrylic polymer may include a copolymer comprising alkyl (meth)acrylate monomer polymerization units and one or more polymerization units selected from styrene monomer polymerization units, butadiene monomer polymerization units, and vinyl monomer polymerization units.

[0013] The coating layer may further contain inorganic particles and a binder.

[0014] The inorganic particles may be present in an amount of 96 to 99% by weight relative to the total weight of the coating layer.

[0015] The binder and organic particles may be present in a weight ratio of 5:5 to 7:3.

[0016] The organic particles may be present in an amount of more than 1% by weight and 2% by weight or less relative to the total weight of the coating layer.

[0017] The equivalent spherical diameter (Dv50) of the inorganic particles may be 0.01 μm to 1 μm.

[0018] The inorganic particles may include one or more selected from the group consisting of boehmite, pseudo-boehmite, BaSO4, CeO2, MgO, CaO, ZnO, Al2O3, SiO2, TiO2, BaTiO3, HfO2, SrTiO3, SnO2, NiO, ZrO2, Y2O3, and SiC.

[0019] The binder may contain one or more selected from (meth)acrylic polymers, fluorine polymers, styrene polymers, vinyl alcohol polymers, vinyl ester polymers, vinylpyrrolidone polymers, cellulose polymers, polyimide polymers, polyamide polymers, and polyalkylene glycols.

[0020] The binder may include polyacrylamide, carboxymethylcellulose, or a combination thereof.

[0021] The binder may contain carboxymethylcellulose having a weight-average molecular weight of 180,000 g / mol or more and a degree of substitution of 0.6 to 1.2.

[0022] The porous substrate may be treated with a hydrophilic surface treatment.

[0023] The composite separator in one configuration may have the following antiblocking properties. [Anti-blocking performance] Two composite separators are placed with their coating layers facing each other, at a temperature of 25°C and a load of 15 kgf / cm². 2 After pressing at a certain pressure for 1 hour, the material was peeled at 180° in accordance with ASTM D903, and a scanning electron microscope (SEM) was used to confirm whether organic and / or inorganic particles had been detached. Ten arbitrary locations were selected, and the number of detached organic and / or inorganic particles per unit area was counted. The average value of these 10 points was then calculated, resulting in 10 -4 pieces / μm 2 The result was less than 1, or neither organic nor inorganic particles had been detached.

[0024] 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 coating 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.)

[0025] 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 coating layer formed on at least one surface of the substrate and containing organic particles, the coating layer satisfying the following formula 1. [Formula 1] 4,000 ≤ (A × D 2 ) / T≦5,500 (In formula 1 above, A is the number of organic particles per unit area ( / mm²) on the surface of the coating layer. 2 ) and D is the average particle size (μm) of organic particles observed on the surface of the coating layer. T is the total thickness (μm) of the coating layer. [Effects of the Invention]

[0026] A composite separator in one form comprises a porous substrate and a coating layer containing organic particles on the substrate. The composite separator can achieve sufficient fusion force with electrodes, reduce internal resistance, and improve electrical performance.

[0027] Furthermore, a composite separator made of a single material can have excellent heat resistance and adhesive strength even at a thin thickness, and can effectively suppress shrinkage at high temperatures.

[0028] Furthermore, a uniform composite separator can suppress the desorption and blocking phenomena of organic and / or inorganic particles during separator winding.

[0029] Furthermore, composite separators using a single-mode design offer excellent productivity and are advantageous for actual commercial application. Electrochemical elements employing such composite separators can simultaneously meet safety, high capacity, and high output requirements. [Brief explanation of the drawing]

[0030] [Figure 1]This figure illustrates the measurement results of the number of organic particles per unit area on the surface of the coating layer of the composite separator in Example 1. [Figure 2] This figure illustrates the results of anti-blocking performance evaluation, showing (a) an example where organic particles were detached, and (b) an example where both organic and inorganic particles were detached. [Figure 3] This diagram illustrates an example of a method for measuring the average surface particle size of an organic particle coating layer. [Figure 4] This is a schematic plan view of an electrochemical element according to one embodiment. [Figure 5] This is a schematic cross-sectional view of an electrochemical element according to one embodiment. [Modes for carrying out the invention]

[0031] 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.

[0032] As used herein, the singular form may also include the plural form unless otherwise indicated in the context.

[0033] 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.

[0034] 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.

[0035] Unless otherwise defined herein, "about" may refer to values ​​up to 30%, 25%, 20%, 15%, 10%, or 5% of the specified value.

[0036] In this specification, "equivalent spherical diameter (Dv50)" refers to the particle size of the sample 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 sampling the sample particles being measured in accordance with the ISO 13320-1 standard and analyzing them using a MICROTRAC S3500, where the sample being measured refers to inorganic and organic particles.

[0037] In this specification, "polymer" means a compound formed by the polymerization of one or more types of monomers, and includes both homopolymers (single-monomer polymers) and copolymers (polymers) composed of two or more different monomers. Furthermore, "polymer" in this specification also includes polymers with molecular structures such as linear, branched, and network structures.

[0038] 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.

[0039] In order to solve the problem of insufficient adhesion between the separator and the electrode, a method of introducing a fusing agent capable of realizing the fusing force with the electrode has been proposed in the prior art. However, recently, due to the high-capacity and high-output characteristics of electrochemical devices, as the separator becomes thinner, when attempting to achieve sufficient fusing force even in a thin thickness range, there are limitations such as the fusing agent detaching and a blocking phenomenon occurring.

[0040] Therefore, the present inventors have found a composite separator including a porous substrate and a coating layer formed on the substrate and containing organic particles for realizing the fusing force with the electrode, and discovered the relationship among the number of organic particles per unit area observed on the surface of the coating layer, the average particle diameter of the organic particles observed on the surface of the coating layer, and the total thickness of the coating layer. As a result, a composite separator has been found that has excellent adhesion between inorganic particles and between inorganic particles and the substrate even in a thin thickness range, ensures the fusing force with the electrode, and has excellent anti-blocking performance.

[0041] Specifically, the composite separator according to one aspect includes a porous substrate and a coating layer formed on at least one surface of the substrate and containing organic particles, and the coating layer may satisfy the following formula (1).

[0042] [Formula (1)] 4,000 ≦ (A × D 2 ) / T ≦ 5,500

[0043] (In the above formula (1), A is the number of organic particles per unit area on the surface of the coating layer ( / mm 2 ), D is the average particle diameter (μm) of the organic particles observed on the surface of the coating layer, T is the total thickness (μm) of the coating layer.) [[ID=​​A composite separator made of a single material satisfies the range of 4,000 to 5,500 for the number of organic particles per unit area on the surface of the coating layer, the average particle size of organic particles observed on the surface of the coating layer, and the total thickness of the coating layer in Equation 1, thereby achieving sufficient fusion force with the electrode, reducing internal resistance, and improving electrical performance. Furthermore, because a composite separator made of a single material satisfies the range of 4,000 to 5,500 for the value of Equation 1, it is preferable that sufficient fusion force with the electrode is achieved without the need for another adhesive layer, and that internal resistance is reduced, improving electrical performance. In addition, a composite separator made of a single material can have excellent heat resistance and adhesive strength even at a thin thickness, can effectively suppress shrinkage at high temperatures, can suppress desorption and blocking of organic particles during winding, and if the coating layer contains inorganic particles, can suppress desorption and blocking of inorganic and / or organic particles. Furthermore, electrochemical elements employing this technology can simultaneously meet the requirements for safety, high capacity, and high output characteristics.

[0045] In measuring the number of organic particles per unit area on the surface of the coating layer, the average particle size of the organic particles observed on the surface of the coating layer, and the thickness of the coating layer, the composite separator may be a composite separator before battery assembly, or a composite separator obtained after disassembling the battery. For example, when measuring using a composite separator disassembled after battery assembly, the battery can be disassembled, the separator cleaned and dried, and the measurement performed regardless of the elapsed time after battery assembly. Here, the drying may be performed in a vacuum oven at a temperature of 20-50°C or 20-40°C for 10-30 hours or 20-30 hours, and the cleaning and drying process may be repeated when measurement is difficult due to electrolyte salts, etc.

[0046] In one embodiment, formula 1 may be 4,000 to 5,500, or 4,000 to 5,400, or 4,200 to 5,400, and may include all possible combinations of the upper and lower limits of the numerical range, which can improve the simultaneous improvement effect of fusion strength and antiblocking performance, and can improve the stability and capacity of the battery.

[0047] In one embodiment, the number of organic particles per unit area of ​​the surface of the coating layer ( / mm 2 The surface of the coating layer can be imaged and measured using an optical microscope. Specifically, using an optical microscope, 10 arbitrary positions were selected on the surface of the coating layer, and a 1 mm × 1 mm area was imaged at each position and converted into an image (Figure 1). The number of organic particles observed within the converted image area was counted, and the average value of the 10 points was calculated.

[0048] In one embodiment, the number of organic particles per unit area on the surface of the coating layer may be 300 or more, 400 or more, 500 or more, 600 or more, 700 or more, 800 or more, 1,000 or more, or 5,000 or less, or 4,000 or less, or 3,000 or less, for example, 500 to 3,000, or 500 to 2,800, or 500 to 2,600, or 600 to 2,600, or 700 to 2,600, and may include all possible combinations of the upper and lower limits of the numerical range.

[0049] The number of organic particles per unit area on the surface of the coating layer can be adjusted by the equivalent spherical diameter (Dv50) of the organic particles, the content of the organic particles, the thickness of the coating layer, the method of applying the coating layer, the drying conditions of the coating layer, or a combination thereof, but the means for doing so are not particularly limited.

[0050] In one embodiment, the average particle size (D) of organic particles observed on the surface of the coating layer may be measured by observing the surface of the coating layer of the composite separator with a scanning electron microscope (SEM). Specifically, an image of the surface SEM of the coating layer of the composite separator was obtained using a Hitachi S-4800 at 10k magnification, the longest diameter of one organic particle was measured (Figure 3), and this was rounded to the first decimal place (unit: μm). The same measurement was performed for 20 organic particles, the average was calculated, and this was taken as the average particle size of the organic particles on the coating layer surface.

[0051] In one embodiment, the average particle size (D) of organic particles observed on the surface of the coating layer is not particularly limited as long as it satisfies the range of formula 1, based on the combination of the number of organic particles per unit area observed on the surface of the coating layer and the total thickness of the coating layer. For example, it 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, which can result in better fusion strength and antiblocking performance.

[0052] In one embodiment, the glass transition temperature (T) of the organic particles is determined. gThe glass transition temperature may be 40°C or higher, 45°C or higher, 50°C or higher, 60°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 can be better developed, and the battery performance can be better after the battery is assembled. Preferably, the glass transition temperature may be 40°C to 70°C, which is more preferable because in this range, no flow occurs during the drying process, there is no deformation during the coating step and shipping process, and even after fusion, the change in the permeability of the substrate can be minimized, and excellent performance can be maintained. Here, the glass transition temperature was determined by measuring the heat capacity of the sample using a differential scanning calorimetry (DSC) in a nitrogen atmosphere, in the range of -100°C to 250°C, at a rate of 10°C / min. The temperature at the midpoint of the interval in which the heat capacity of the sample changed rapidly was defined as the glass transition temperature.

[0053] The organic particles are not particularly limited as long as they are particulate organic materials capable of achieving fusion with the electrodes, but may include acrylic polymers, urethane polymers, fluorine polymers, or a combination of two or more of these.

[0054] The acrylic polymer may include a homopolymer containing (meth)acrylate monomer polymerization units or a copolymer containing (meth)acrylate monomer polymerization units. It may also include a homopolymer containing alkyl (meth)acrylate monomer polymerization units or a copolymer containing the alkyl (meth)acrylate monomer polymerization units. The alkyl (meth)acrylate monomer may include 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 include one or more selected from methyl (meth)acrylate, ethyl (meth)acrylate, and n-butyl (meth)acrylate.

[0055] The copolymer containing the alkyl (meth)acrylate monomer polymerization unit may also include a copolymer comprising the alkyl (meth)acrylate monomer polymerization unit and one or more polymerization units selected from styrene monomer polymerization units, butadiene monomer polymerization units, and vinyl monomer polymerization units.

[0056] The fluorine-based polymer may include polyvinylidene fluoride (PVdF) polymers. Examples of such polyvinylidene fluoride polymers include polyvinylidene fluoride homopolymers, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, and polyvinylidene fluoride-chlorotrifluoroethylene, and may include one or more selected from these. In addition, polyvinylidene fluoride polymers containing a vinylide fluoride repeating unit (A) and other repeating units (B) copolymerizable with the repeating unit can be used.

[0057] Non-limiting examples of the organic particles include, but are not limited to, polyurethane beads, polyurethane acrylic beads, epoxy-acrylic beads, polyacrylate, polymethacrylate, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), polyvinylidene fluoride-trichloroethylene (PVdF-TCE), polyvinylidene fluoride-chlorotrifluoroethylene (PVdF-CTFE), polystyrene-polybutyl methacrylate-polymethyl methacrylate (PS-PBMA-PMMA), polybutyl methacrylate-polymethyl methacrylate (PBMA-PMMA), polystyrene-polydimethylsiloxane-polybutyl methacrylate (PS-PDMS-PBMA), polystyrene-polydimethylsiloxane-polymethyl methacrylate (PS-PDMS-PMMA), polydimethylsiloxane-polymethyl methacrylate (PDMS-PMMA), or one or more combinations thereof.

[0058] Since the method for producing the aforementioned organic particles can be carried out by emulsion polymerization or suspension polymerization, as these are known production methods, a detailed explanation will be omitted.

[0059] Furthermore, the composite separator in one form may further contain inorganic particles and a binder, and the coating layer of the composite separator in one form may contain the above-mentioned organic particles, inorganic particles and binder as a single coating layer, or the coating layer of the composite separator in one form may contain all of the above-mentioned organic particle layer containing organic particles and inorganic particle layer containing inorganic particles and a binder.

[0060] Specifically, a composite separator in a uniform form may contain inorganic particles, a binder, and organic particles in a single coating layer. In this case, it is preferable to further reduce the internal resistance of the battery and improve electrical performance while ensuring fusion with the electrodes, but the invention is not necessarily limited to this.

[0061] In one embodiment, the composite separator includes a porous substrate and a coating layer formed on one or both sides of the porous substrate, wherein the coating layer may consist of inorganic particles bound and fixed by a binder, and pores may be formed between the inorganic particles.

[0062] In one embodiment, the binder is not particularly limited as long as it is a conventional binder used in the present art, and non-limiting examples include one or more selected from (meth)acrylic polymers, fluorine polymers, styrene polymers, vinyl alcohol polymers, vinyl ester polymers, vinylpyrrolidone polymers, cellulose polymers, polyimide polymers, polyamide polymers, and polyalkylene glycols. The (meth)acrylic polymer may include, for example, one or more selected from polyalkyl (meth)acrylate, poly(meth)acrylic acid, poly(meth)acrylamide, poly(meth)acrylonitrile, polyhydroxyethyl (meth)acrylate, or copolymers thereof. The fluorine polymer may include polyvinylidene fluoride (PVdF) polymers. Examples of such polyvinylidene fluoride polymers include polyvinylidene fluoride homopolymer, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, and polyvinylidene fluoride-chlorotrifluoroethylene, and may contain one or more selected from these. In addition, polyvinylidene fluoride polymers containing a repeating unit of vinylidene fluoride (A) and other repeating units (B) copolymerizable with the repeating unit can be used. The styrene polymer may, for example, contain one or more selected from polystyrene, polyalphamethylstyrene, polybromostyrene, or copolymers thereof. The vinyl alcohol polymer may, for example, contain one or more selected from polyvinyl alcohol or copolymers containing the same. The vinyl ester polymer may, for example, contain one or more selected from polyvinyl ester or copolymers containing the same. The aforementioned cellulosic polymer may include, for example, one or more selected from cellulose, carboxymethylcellulose, hydroxypropylmethylcellulose, cellulose acetate, or cellulose acetate propionate.

[0063] In one embodiment, the binder may include a (meth)acrylic polymer, a cellulosic polymer, or a combination thereof.

[0064] Specifically, the binder may include polyacrylamide (PAAm), carboxymethylcellulose, or a combination thereof. Alternatively, the binder may include a mixed binder of polyacrylamide and carboxymethylcellulose, which is preferable as it can further improve the effects targeted by the present invention, but is not limited thereto.

[0065] In one embodiment, the carboxymethylcellulose may have a weight-average molecular weight of 180,000 to 1,500,000 g / mol, or 180,000 to 1,300,000 g / mol, or 200,000 to 1,000,000 g / mol, and may include all possible combinations of the upper and lower limits of the numerical range. Furthermore, the carboxymethylcellulose may have a degree of substitution of 0.6 to 1.2, or 0.6 to 1.0, or 0.7 to 1.0, or 0.8 to 1.0, or 0.9 to 1.0, and may include all possible combinations of the upper and lower limits of the numerical range. The weight-average molecular weight may refer to the weight-average molecular weight calculated using a molecular weight calibration curve utilizing polysaccharide standard samples measured by the GPC method.

[0066] Here, the carboxymethyl cellulose (CMC) is defined as cellulose whose hydroxyl group (-OH) is -OCH2COOH and / or -OCH2COOH - M + This means a cellulose derivative that is substituted with and etherified, and the M +This is an alkali metal cation, which 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 carboxymethylcellulose means the average number of substituents contained in one anhydrous glucose unit in a cellulose molecule, and can be measured by known or tolerant methods, for example, according to ASTM D1439. 1 H-NMR or 13 It can be calculated by 13C-NMR analysis.

[0067] The degree of substitution (DS) of carboxymethylcellulose (CMC) was measured using a titration method according to ASTM D1439. The experiment used a magnetic stirrer, aspirator, dry oven, 300 mL beaker, pipette, 250 mL Erlenmeyer flask, and Petridish. 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.

[0068] Specifically, 150 mL of 80% ethanol was placed in a 300 mL beaker, followed by the addition of 10 mL of 1N nitric acid (HNO3). Approximately 1-2 g of CMC sample was added to this mixture and stirred for 1 hour to form CMC acid. After standing for approximately 10-20 minutes, the supernatant was removed (decanting).

[0069] Next, 150 mL of 80% ethanol was added again, and the mixture was stirred for 30-40 minutes, after which the supernatant was removed again. The precipitated CMC-acid was filtered using a suction filter, washed with 500 mL of 80% ethanol, and then washed once or twice more with 100% ethanol.

[0070] 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.

[0071] 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.

[0072] The number of millimoles (A) of CMC-acid per gram of dried sample was calculated using the following formula.

[0073]

number

[0074] Next, the degree of substitution (DS) was calculated from A using the following formula.

[0075]

number

[0076] In one embodiment, the polyacrylamide may have a weight-average molecular weight of 100,000 g / mol or more, or 150,000 g / mol or more, or 180,000 g / mol or more, or 500,000 g / mol or less, or 400,000 g / mol or less, or 300,000 g / mol or less, or 250,000 g / mol or less, and specifically, it may include, but is not limited to, 100,000 g / mol to 300,000 g / mol, or 150,000 to 250,000 g / mol, or 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 polystyrene standard samples measured by the GPC method. A sample in which carboxymethylcellulose was dissolved in a standard substance at approximately 0.1% w / v was injected into a GPC instrument and measured.

[0077] If the binder contains carboxymethylcellulose and polyacrylamide, the carboxymethylcellulose and polyacrylamide can be used in a weight ratio of 10-50:90-50, or 10-40:90-60.

[0078] 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 hydrates, metal carbides, metal nitrides, and metal carbides such as boehmite, BaSO4, CeO2, MgO, CaO, ZnO, Al2O3, TiO2, BaTiO3, HfO2, SrTiO3, SnO2, NiO, ZrO2, Y2O3, and SiC.

[0079] In one embodiment, the equivalent spherical diameter (Dv50) of the inorganic particles may be, for example, 0.01 μm or more, 0.02 μm or more, 0.05 μm or more, or 0.1 μm or more, and may 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.

[0080] In one embodiment, the coating layer may contain 90-99.9% by weight, 92-99.5% by weight, 92-99% by weight, 95-99% by weight, or 96-99% by weight of inorganic particles relative to the total weight of the coating layer. Compared to the inorganic particle content of conventional coating layers formed by linking inorganic particles containing a binder, it is possible to include a larger amount of inorganic particles, and despite this, it is possible to form a coating layer (coating layer) with excellent heat resistance and numerical stability and with a thinner thickness.

[0081] In one embodiment, the coating layer may contain 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 of the organic particles relative to the total weight of the coating layer, or 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 0.5% to 5% by weight, or 1% to 5% by weight, or 1% to 3% 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.

[0082] In one embodiment, the binder and organic particles may be included in a weight ratio of 5:5 to 9:1, or 5:5 to 8:2, or 5:5 to 7:3.

[0083] In one embodiment, the composite separator may have antiblocking properties, which mean the ability to suppress the desorption and blocking phenomena of organic and / or inorganic particles during separator winding. Specifically, two composite separators are arranged with their coating layers facing each other, and the temperature is 25°C and the load capacity is 15 kgf / cm². 2 After pressing at a pressure for 1 hour, the material was peeled at 180° in accordance with ASTM D903, and a scanning electron microscope (SEM) was used to confirm whether organic and / or inorganic particles had been detached. Ten arbitrary locations were selected, and the number of detached organic and / or inorganic particles per unit area was counted. The average value of the 10 points was calculated, and the number of detached particles was 10. -4 pieces / μm 2 If the number of units is less than or not all units have been detached, the system is considered to have antiblocking properties.

[0084] 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%.

[0085] The cardboard test method involves placing a 2cm x 10cm black cardboard and a rubber pad sequentially on the upper surface of the coating 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 the cardboard surface where foreign matter adheres. The foreign matter may be a component of the coating layer, such as inorganic particles, a binder, or a combination thereof.

[0086] 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 coating layer interface, but also the adhesive strength between inorganic particles within the coating 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.

[0087] For example, in conventional composite separators, methods such as peeling tests used to evaluate the adhesive strength of the inorganic particle coating layer evaluate the adhesive strength between the substrate and the inorganic particle coating layer. However, the adhesive 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.

[0088] In one embodiment, after leaving the composite separator at 150°C for 60 minutes, the measured thermal shrinkage rates in the MD and TD directions 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. 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 being the transverse direction (TD) and the other side being the mechanical direction (MD). The test specimen was positioned in the center, and five sheets of paper were placed above and below the test specimen, and then the four sides of the paper were secured with tape. The tapered test specimen was left in a hot air dryer at 150°C for 60 minutes. Next, the test specimens were removed, the separators were observed with a camera at room temperature, and the shrinkage rates in the mechanical direction (MD) and transverse direction (TD) were calculated.

[0089] 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.

[0090] 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.

[0091] In one embodiment, the porous substrate may be subjected to a hydrophilic surface treatment to introduce polar functional groups, thereby achieving superior adhesion. Examples of the polar functional groups include carboxyl groups, aldehyde groups, and hydroxyl groups, and the hydrophilic surface treatment may, for example, be corona discharge treatment or plasma discharge treatment, but is not particularly limited.

[0092] 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, 5 μm to 15 μm, 5 μm to 12 μm, 5 μm to 10 μm, or any value between these numbers.

[0093] In one embodiment, the coating layer may be coated on one or both sides of the porous substrate, and when the coating layer is coated on both sides of the porous substrate, the thickness of the coating layer coated on one side and the other side may be the same or different.

[0094] The total thickness of the coating layer is not particularly limited, as long as the combination of the number of organic particles per unit area observed on the surface of the coating layer and the average particle size of the organic particles satisfies the range of Equation 1. For example, it may be 0.1 μm to 10.0 μm, 0.5 μm to 10.0 μm, or 1 μm to 10 μm, or 1 μm to 8 μm, or 1 μm to 5 μm, or approximately 1.5 μm to 5 μm, or 2 μm to 5 μm, or 2 μm to 4 μm, and may be a value between the above values. A composite separator in one form can achieve excellent adhesion and heat resistance even when the coating layer is formed to a very thin thickness, and an electrochemical element employing this can simultaneously satisfy safety, high capacity, and high output characteristics.

[0095] The thickness of the composite separator in one form may be, but is not limited to, 1 μm to 200 μm, or 2 μm to 200 μm, or 5 μm to 200 μm, or 5 μm to 150 μm, or 5 μm to 100 μm, or 5 to 50 μm, or 5 to 30 μm, or 5 to 20 μm, or all possible combinations of the upper and lower limits of the numerical range.

[0096] A further embodiment of the present invention provides a method for manufacturing the composite separator, the method of manufacturing the composite separator may include the step of applying a coating layer-forming composition containing organic particles to at least one surface of a porous substrate, drying it, and forming a coating layer, the coating layer may satisfy the following formula 1.

[0097] [Formula 1] 4,000 ≤ (A × D 2 ) / T≦5,500

[0098] (In formula 1 above, A is the number of organic particles per unit area ( / mm²) on the surface of the coating layer. 2 ) and D is the average particle size (μm) of organic particles observed on the surface of the coating layer. T is the total thickness (μm) of the coating layer.

[0099] The aforementioned A, D, T, porous substrate, organic particles, and coating layer are as described above, and a detailed explanation is omitted.

[0100] The coating 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, DMF, N-methyl-2-pyrrolidone, hexane, cyclohexane, or mixtures thereof.

[0101] The coating layer forming composition may further contain a binder and inorganic particles, and inorganic particles aggregated using a ball mill can be dispersed in it.

[0102] In one embodiment, the solid content of the coating 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, and is not limited thereto. Furthermore, the viscosity of the coating layer forming composition may be 800 to 5,000 cps, or 800 to 4,000 cps, or 800 to 3,000 cps, or 1,000 to 3,000 cps based on a solid content of 25% by weight, which makes the formation of the coating layer easier and can improve the heat resistance and adhesive strength of the separator.

[0103] In one embodiment, the method for applying or coating the coating 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.

[0104] In one embodiment, the drying can be performed by drying with warm air, hot air, low-humidity air, vacuum drying, or irradiation by far-infrared rays or electron beams. The drying temperature may be adjusted as appropriate depending on the experimental environment and purpose, for example, it may be 30°C or higher, 40°C or higher, 50°C or higher, 70°C or lower, or 60°C or lower. Specifically, it may be 30°C to 70°C, 40°C to 70°C, 40°C to 60°C, 50°C to 70°C, or 50°C to 60°C. The drying time may be 30 seconds to 500 seconds, 60 seconds to 500 seconds, 100 seconds to 500 seconds, 100 seconds to 400 seconds, 150 seconds to 400 seconds, or approximately 180 seconds to 400 seconds, 200 seconds to 400 seconds, or 300 seconds. When the above drying conditions are met, the value of Equation 1 can be adjusted more appropriately, and the drying conditions are not particularly limited as long as they are within the range that satisfies Equation 1.

[0105] 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.

[0106] Specifically, an 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 coating layer formed on at least one surface of the substrate and containing organic particles, the coating layer may satisfy the following formula 1.

[0107] [Formula 1] 4,000 ≤ (A × D 2 ) / T≦5,500

[0108] (In formula 1 above, A is the number of organic particles per unit area ( / mm²) on the surface of the coating layer. 2 ) and D is the average particle size (μm) of organic particles observed on the surface of the coating layer. T is the total thickness (μm) of the coating layer.

[0109] In one embodiment, the electrochemical element includes a positive electrode, a negative electrode, and a composite separator, the composite separator may include a porous substrate and a coating layer formed on one or both sides of the substrate, the coating layer may include inorganic particles, a binder, and organic particles, and satisfy the formula 1.

[0110] 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.

[0111] 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.

[0112] [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.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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 Co0.15 Mn 0.15 O2, LiLiLi 0.8 Co 0.1 Mn 0.1 While O2 is one example, it is not the only option.

[0117] 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.

[0118] 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.

[0119] 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.

[0120] [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.

[0121] 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.

[0122] The negative electrode active material can be used without limitation as long as it is a material that is commonly used in the art to adsorb and desorb lithium ions. Non-limiting examples include carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, and carbon fibers; lithium metal; lithium alloys; silicon (Si)-containing materials or tin (Sn)-containing materials.

[0123] Examples of the amorphous carbon include hard carbon, soft carbon, coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fiber (MPCF), etc. Examples of the crystalline carbon include graphite-based carbons such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, and graphitized MPCF.

[0124] Examples of the elements contained in the lithium alloy include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium, etc.

[0125] The silicon-containing substance can provide more enhanced capacity characteristics. The silicon-containing substance may include Si, SiO x (0 < x ≦ 2), metal-doped SiO x (0 < x ≦ 2), a silicon-carbon composite, etc. The metal may include lithium and / or magnesium. Metal-doped SiO x (0 < x ≦ 2) may include 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.

[0126] The negative electrode binder is not particularly limited as long as it is commonly used in the technical field. 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.

[0127] [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.

[0128] The lithium salt is, for example, Li + X - The anion of the lithium salt (X) is represented as - ) 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.

[0129] 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.

[0130] [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.

[0131] 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.

[0132] [Physical property measurement method] 1) Surface average particle size D of the organic particle coating layer (unit: μm) The surface of the coating layer of the composite separator was observed using a scanning electron microscope (SEM), and the average particle size of the organic particles observed on the surface of the coating layer was measured. Specifically, an SEM image of the surface of the coating layer of the composite separator was obtained using a Hitachi S-4800 at a magnification of 10k, the longest diameter of one organic particle was measured (Figure 3), and this was rounded to the first decimal place (unit: μm). The same measurement was performed for 20 organic particles, and the average was calculated to determine the average particle size of the organic particles on the coating layer surface.

[0133] 2) Thickness After stacking 10 layers of composite separators, the thickness was measured at room temperature and pressure using a Mitutoyo (ID-C112X) to determine the average thickness of the 10 layers of composite separators. This average thickness was then divided by 10 to obtain the thickness of the composite separators. The total thickness of the coating layer (T, μm) was obtained by subtracting the thickness of the porous substrate from the thickness of the composite separators.

[0134] The thickness of the porous substrate was determined by stacking 10 layers of the porous substrate alone, measuring the thickness using Mitutoyo (ID-C112X), deriving the average thickness of the 10 layers of porous substrate, and then dividing by 10 to obtain the thickness of the porous substrate. In cases where a coating layer had been formed, the coating layer was removed, and after sufficient drying, the average thickness of the porous substrate from which the coating layer had been removed was determined using the method described above.

[0135] 3) Number of organic particles per unit area on the surface of the coating layer A (unit: / mm 2 ) The surface of the coating layer of the composite separator was imaged using an optical microscope (Leica-Microsystems, DVM 6), and the number of organic particles per unit area ( / mm²) observed on the surface of the coating layer was determined. 2The number of organic particles per unit area of ​​the coating layer surface was measured. Specifically, after attaching a PlanAPO FOV 3.60 objective lens to an optical microscope, 10 arbitrary positions on the surface of the coating layer were selected, and a 1 mm × 1 mm area per position was divided into 6 × 4 sections and photographed. These sections were then stitched together, and the image was converted using the image conversion method described below. The number of organic particles observed within the converted image area was counted, and the average value for the 10 positions was derived. This was defined as A, the number of organic particles per unit area of ​​the coating layer surface.

[0136] [Image conversion method] 1. Open the image prepared in ImageJ S / W. 2. Convert the image type to an 8-bit image. 3. Use the Despeckle and Bandpass Filter functions to remove noise from the image and make it easier to distinguish the shape of organic particles from the surrounding background. 4. Adjust the Threshold value to separate the shapes of organic particles from the image. 5. Apply the Analyze Particles function to the image in which the shapes of organic particles have been separated, and count the number of organic particles present in the image (Figure 1).

[0137] 4) Adhesive strength [Cardboard Test] A composite separator was cut into 5cm x 10cm pieces to prepare test specimens. A 2cm x 10cm piece of black cardboard and a rubber pad were placed sequentially on the coating layer of the composite separator test specimen. While applying a force of 10N to the rubber pad using a press device, the cardboard was horizontally removed at a speed of 0.1m / s to a depth of 60mm. The adhesive strength was evaluated according to the degree to which foreign matter adhered to the surface of the cardboard. This foreign matter may be a component of the coating layer, such as inorganic particles, a binder, or a combination thereof.

[0138] [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.

[0139] A: <1.5% B: 1.5%~5% C:>5%

[0140] 5) Electrode fusion force The positive and negative electrodes were manufactured as described below, and the fusion strength between the electrodes and the composite separator was evaluated.

[0141] 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.

[0142] 95% by weight of artificial graphite is used as the negative electrode active material, and T is used as the adhesive. gAcrylic latex (trade name: BM900B, solids content: 20% by weight), which has a temperature of -52°C, was added in a ratio of 3% by weight to water as a solvent, along with CMC (Carboxymethyl cellulose) in a ratio of 2% by weight. The mixture was stirred to produce a homogeneous negative electrode slurry. The slurry was coated onto a 20 μm thick copper foil, dried at a temperature of 120°C, and then pressed to produce a 150 μm thick negative electrode plate.

[0143] 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.

[0144] 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.

[0145] 6) Anti-blocking performance Two composite separators are placed with their coating layers facing each other, at a temperature of 25°C and a load of 15 kgf / cm². 2 After pressing at a pressure for 1 hour, the material was peeled at 180° in accordance with ASTM D903, and then a scanning electron microscope (SEM) was used to confirm whether organic and / or inorganic particles had been detached. Ten arbitrary locations were selected, and the number of detached organic 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 (Figure 2).

[0146] ○: Neither organic nor inorganic particles have been removed, 10 -4 pieces / μm2 It is partially detached. ×: 10 organic or inorganic particles -4 pieces / μm 2 The above points have been removed.

[0147] [Example 1] A slurry with a solid content of 45% by weight was prepared by mixing 100 parts by weight of Dv50 0.3 μm boehmite with 2 parts by weight of the dispersant 1,2-benzoisothiazolin-3-one (DIO2) in water. Polyacrylamide (PAAm) (Mw 200,000 g / mol, sigma aldrich) and carboxymethyl cellulose (CMC) (degree of substitution 0.9, weight-average molecular weight 200,000 g / mol) were added as binders to the prepared slurry, and polystyrene-polybutyl methacrylate-polymethyl methacrylate block copolymer (PS-PBMA-PMMA) (Dv50: 2.5 μm, T) was added as organic particles. g A mixture of 62°C (boehmite / PAAm / CMC / PS-PBMA-PMMA) was added to produce a coating layer-forming composition with a weight ratio of 96 / 2 / 0.8 / 1.2.

[0148] 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, and the corona surface treatment was performed at a speed of 5 mpm (meter per minute). The coating layer forming composition was applied to both sides of the corona surface treated polyethylene film substrate by wire bar coating, and dried in a 50°C drying oven for 5 minutes at a running speed of 5 mpm (meter per minute) to produce a composite separator in which a coating layer of the same thickness was formed on both sides.

[0149] [Example 2] The procedure was carried out in the same manner as in Example 1, except that the weight ratio used was Boehmite / PAAm / CMC / PS-PBMA-PMMA = 96 / 2 / 0.3 / 1.7.

[0150] [Example 3] The procedure was carried out in the same manner as in Example 1, except that the weight ratio of boehmite / PAAm / CMC / PS-PBMA-PMMA was 96 / 1.8 / 0.3 / 1.9, and the thickness of the coating layer was changed as shown in Table 1 below.

[0151] [Example 4] As organic particles, PS-PBMA-PMMA (Dv50: 5.0 μm, T g The procedure was carried out in the same manner as in Example 1, except that PAAm was used alone as the binder at 62°C, in a weight ratio of boehmite / PAAm / PS-PBMA-PMMA = 96 / 2.8 / 1.2, and the thickness of the coating layer was changed as shown in Table 1 below.

[0152] [Example 5] The same procedure was followed as in Example 1, except that corona discharge treatment was not performed on the polyethylene film substrate.

[0153] [Comparative Example 1] The procedure was carried out in the same manner as in Example 1, except that the weight ratio of boehmite / PAAm / CMC / PS-PBMA-PMMA was 97 / 0.7 / 0.3 / 2 and the thickness of the coating layer was changed as shown in Table 1 below.

[0154] [Comparative Example 2] The procedure was carried out in the same manner as in Example 1, except that the weight ratio used was Boehmite / PAAm / CMC / PS-PBMA-PMMA = 94 / 3 / 2 / 1.

[0155] [Comparative Example 3] As organic particles, PS-PBMA-PMMA (Dv50: 3.0 μm, T gUsing (temperature: 62°C), except that the thickness of the coating layer was changed as shown in Table 1 below at a weight ratio of boehmite / PAAm / CMC / PS-PBMA-PMMA = 92.2 / 3 / 2.8 / 2, the experiment was carried out in the same manner as in Example 1 above.

[0156] [Comparative Example 4] As organic particles, PS-PBMA-PMMA (Dv50: 5.0 μm, T g Using (temperature: 62°C), using PAAm alone as a binder, at a weight ratio of boehmite / PAAm / PS-PBMA-PMMA = 95 / 3 / 2, except that the thickness of the coating layer was changed as shown in Table 1 below, the experiment was carried out in the same manner as in Example 1 above.

[0157] After battery assembly using the composite separators obtained in the above Examples and Comparative Examples, the physical properties were measured by the method described in the above physical property measurement method, the value of the following formula 1 was calculated, rounding off the first decimal place, and shown in Table 1 below.

[0158] [Formula 1] (A×D 2 ) / T

[0159] (In the above formula 1, A is the number of organic particles per unit area of the surface of the coating layer ( / mm 2 ), D is the average particle size (μm) of the organic particles, and T is the total thickness (μm) of the coating layer.)

[0160]

Table 1

[0161] Referring to Table 1 above, it can be seen that the composite separator according to one embodiment of the present invention can simultaneously satisfy excellent electrode fusion strength and antiblocking performance even with a thin coating layer thickness. Furthermore, it can be seen that the composite separator according to one embodiment has excellent adhesion not only at the interface between the substrate and the coating layer, but also at the adhesion between inorganic particles within the coating layer, and can effectively suppress the thermal shrinkage phenomenon. In addition, an electrochemical element employing the composite separator according to one embodiment can ensure heat resistance and safety, and can be advantageous for increasing capacity and output. Moreover, in the case of Example 1, which uses a PAAm and CMC mixed binder, it was confirmed that the air permeability characteristics were even better. Specifically, when the air permeability was measured according to ASTM D726, the air permeability of the separator according to Example 1 was measured at 165 s / 100 cc, and the air permeability of the separator according to Example 4, which uses PAAm alone, was measured at 180 s / 100 cc.

[0162] On the other hand, in the comparative example, even if electrode fusion force was ensured, desorption of organic and / or inorganic particles occurred during winding (Figure 2), and it was confirmed that electrode fusion force could not be ensured if the desorption phenomenon was prevented.

[0163] The composite separator disclosed herein is widely applicable in green technology fields such as electric vehicles, battery charging stations, and solar and wind power generation using batteries. 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.

[0164] 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.

[0165] 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]

[0166] 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. The material comprises a porous substrate and a coating layer formed on at least one surface of the substrate and containing organic particles. The coating layer is a composite separator that satisfies the following formula 1. [Formula 1] 4,000≦(A×D ２ ) / T≦5,500 In the above formula 1, A is the number of organic particles per unit area ( / mm) on the surface of the coating layer. ２ ) and D is the average particle size (μm) of organic particles observed on the surface of the coating layer. T is the total thickness of the coating layer (μm).

2. The composite separator according to claim 1, wherein the surface average particle size (D) of the coating layer of the organic particles is 1 μm to 10 μm.

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

4. The glass transition temperature (T) of the organic particles ｇ The composite separator according to claim 1, wherein the temperature range is 40°C to 80°C.

5. The composite separator according to claim 1, wherein the organic particles include one or more selected from the group consisting of acrylic polymers, urethane polymers, and fluorine polymers.

6. The composite separator according to claim 5, wherein the acrylic polymer comprises 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.

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

8. The composite separator according to claim 7, wherein the inorganic particles are present in an amount of 96 to 99% by weight relative to the total weight of the coating layer.

9. The composite separator according to claim 7, wherein the binder and organic particles are contained in a weight ratio of 5:5 to 7:

3.

10. The composite separator according to claim 7, wherein the organic particles are contained in an amount of more than 1% by weight and 2% by weight or less with respect to the total weight of the coating layer.

11. The composite separator according to claim 7, wherein the equivalent spherical diameter (Dv50) of the inorganic particles is 0.01 μm to 1 μm.

12. The inorganic particles include one or more selected from the group consisting of boehmite, pseudoboehmite, 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 , and SiC, and the composite separator according to claim 7.

13. The composite separator according to claim 7, wherein the binder comprises one or more selected from (meth)acrylic polymers, fluorine polymers, styrene polymers, vinyl alcohol polymers, vinyl ester polymers, vinylpyrrolidone polymers, cellulose polymers, polyimide polymers, polyamide polymers, and polyalkylene glycols.

14. The composite separator according to claim 7, wherein the binder comprises polyacrylamide, carboxymethylcellulose, or a combination thereof.

15. The composite separator according to claim 7, wherein the binder comprises carboxymethylcellulose having a weight-average molecular weight of 180,000 g / mol or more and a degree of substitution of 0.6 to 1.

2.

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

17. The composite separator according to claim 7, having the following antiblocking performance. [Anti-blocking performance] Two composite separators are placed with their coating layers facing each other, at a temperature of 25°C and a load of 15 kgf / cm². ２ After pressing at a certain pressure for one hour, the material was peeled at 180° according to ASTM D903, and a scanning electron microscope (SEM) was used to confirm whether organic and / or inorganic particles had been detached. Ten arbitrary locations were selected, and the number of detached organic and / or inorganic particles per unit area was counted. The average value of these 10 points was then calculated, resulting in 10 －４ pieces / μm ２ The result was less than 1, or neither organic nor inorganic particles had been detached.

18. 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 coating 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.

19. An electrochemical element comprising a positive electrode, a negative electrode, and a composite separator, The composite separator comprises a porous substrate and a coating layer formed on at least one surface of the substrate, which contains organic particles. The coating layer is an electrochemical element that satisfies the following formula 1. [Formula 1] 4,000≦(A×D ２ ) / T≦5,500 In the above formula 1, A is the number of organic particles per unit area ( / mm) on the surface of the coating layer. ２ ) and D is the average particle size (μm) of organic particles observed on the surface of the coating layer. T is the total thickness of the coating layer (μm).

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