Composite separator and electrochemical element containing the same

Abstract

This disclosure relates to a composite separator and an electrochemical element including the same. [Solution] This disclosure includes a porous substrate and a ceramic layer formed on one or both sides of the substrate, comprising inorganic particles and a binder, wherein the average particle size (D 50 Regarding a composite separator in which the particle size is 0.20 μm to 0.40 μm, and the ratio (A / B) of the area on the smaller particle size side (A) to the area on the larger particle size side (B), based on the maximum peak in the particle size distribution of inorganic particles, is 1.05 or greater, it is possible to satisfy all of the following requirements: excellent mechanical and thermal stability and ionic conductivity.

Description

[Technical Field]

[0001] This disclosure relates to a composite separator and an electrochemical element including the same. [Background technology]

[0002] Recently, as electrochemical elements have become increasingly high-capacity and high-power, the need for heat resistance and safety has grown, and in particular, the performance requirements for separators, which play a crucial role in this regard, have become more sophisticated.

[0003] For example, composite separators, in which a coating layer containing inorganic particles such as alumina (Al2O3), silica (SiO2), and zirconia (ZrO2) and a binder is introduced on a porous substrate, have become an important technology for ensuring the heat resistance and safety of separators. However, recently, research has been conducted in the direction of thinning separators to achieve high capacitance and high power characteristics in electrochemical elements. It is difficult to achieve sufficient heat resistance within the thickness range of the thinned inorganic particle coating layer, and there is a limit to how much the adhesive strength and / or air permeability can be improved when attempting to improve heat resistance. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] KR10-2023-0144943 A (October 17, 2023) [Overview of the project] [Problems that the invention aims to solve]

[0005] One embodiment of the present invention relates to a composite separator comprising a porous substrate and a ceramic layer formed on one or both sides of the porous substrate, wherein inorganic particles are bound and fixed by a binder and pores are formed between the inorganic particles, and the present invention provides a composite separator that simultaneously possesses excellent heat resistance and adhesive strength.

[0006] Another aspect of the present invention provides an electrochemical element with excellent battery performance and safety by employing the composite separator. [Means for solving the problem]

[0007] One embodiment of the present invention is a composite separator comprising a porous substrate and a ceramic layer formed on one or both sides of the substrate, the ceramic layer comprising inorganic particles and a binder, wherein the average particle size (D 50 The present invention provides a composite separator in which the particle size is 0.20 μm to 0.40 μm, and the ratio (A / B) of the area on the smaller particle size side (A) to the area on the larger particle size side (B), based on the maximum peak in the particle size distribution of inorganic particles, is 1.05 or more.

[0008] The inorganic particles have a particle size distribution of (D 95 -D 50 ) / D 50 The value can satisfy a range of 1.8 to 2.5.

[0009] Based on the particle size distribution of the inorganic particles, the ratio (A / B) of the area on the smaller particle size side (A) to the area on the larger particle size side (B), relative to the maximum peak, can satisfy a range of 1.05 to 1.3.

[0010] The composite separator in one form may contain 0.1 to 10 parts by weight of binder per 100 parts by weight of the inorganic particles.

[0011] The inorganic particles may be one or more selected from boehmite, BaSO4, CeO2, MgO, CaO, ZnO, Al2O3, TiO2, BaTiO3, HfO2, SrTiO3, SnO2, NiO, ZrO2, Y2O3, and SiC.

[0012] The binder may be 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, polyalkylene glycols, and copolymers thereof.

[0013] The binder may include polyacrylamide, carboxymethylcellulose, or a combination thereof.

[0014] 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.

[0015] The porous substrate may be treated with a hydrophilic surface treatment.

[0016] The coating density of the ceramic layer is 1.2 to 1.8 g / cm³. 3 That's fine.

[0017] The total thickness of the ceramic layer may be 0.5 μm to 10 μm.

[0018] The thickness of the composite separator in one state may be 1 to 100 μm.

[0019] 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 depth of 60mm. The degree to which foreign matter adheres to the surface of the cardboard is then tested.

[0020] The composite separator may have a thermal shrinkage rate of 4% or less in both the MD direction and the TD direction, measured after being left at 150°C for 60 minutes.

[0021] A further embodiment of the present invention is 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, comprising inorganic particles and a binder, the average particle size (D 50 The present invention provides an electrochemical element in which the particle size is 0.2 μm to 0.4 μm, and the ratio (A / B) of the area on the smaller particle size side (A) to the area on the larger particle size side (B), based on the maximum peak in the particle size distribution of inorganic particles, is 1.05 or greater. [Effects of the Invention]

[0022] A uniform composite separator can satisfy all requirements for outstanding mechanical and thermal stability and ionic conductivity. Specifically, a uniform composite separator includes a ceramic layer in which a porous substrate and inorganic particles are bound and fixed by a binder, and pores are formed between the inorganic particles. Even if the ceramic layer is formed to a very thin thickness, outstanding heat resistance can be ensured, 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 achieve excellent air permeability and ionic conductivity.

[0023] Electrochemical elements employing a composite separator with a single configuration can simultaneously satisfy safety, high capacitance, and high output characteristics. [Brief explanation of the drawing]

[0024] [Figure 1] This is the particle size distribution of the inorganic particles used in Example 1. [Modes for carrying out the invention]

[0025] 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.

[0026] As used herein, the singular form may also include the plural form unless otherwise indicated in the context.

[0027] 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.

[0028] 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.

[0029] Unless otherwise defined herein, "about" may refer to values ​​up to 30%, 25%, 20%, 15%, 10%, or 5% of the specified value.

[0030] 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.

[0031] Conventional technologies have proposed methods to introduce inorganic particles below a certain size to solve the problem of reduced heat resistance due to the thinning of composite separators, which include porous substrates and inorganic coating layers. However, even if heat resistance is improved to some extent, this method has limitations: the adhesion between inorganic particles and between inorganic particles and the substrate decreases, air permeability deteriorates, and attempts to improve adhesion and / or air permeability also degrade heat resistance.

[0032] The present inventors have found that in a composite separator comprising a porous substrate and a ceramic layer formed on one or both sides of the substrate, which contains inorganic particles and a binder, if the inorganic particles satisfy a specific average particle size range while having specific particle size distribution characteristics, heat resistance, adhesive strength, and air permeability characteristics can be simultaneously satisfied even within a range of thin film thickness.

[0033] This disclosure provides a composite separator that can simultaneously ensure excellent mechanical and thermal stability and ionic conductivity.

[0034] A composite separator in one form comprises a porous substrate and a ceramic layer formed on one or both sides of the substrate, which contains inorganic particles and a binder, wherein the average particle size (D 50 The particle size is 0.20 μm to 0.40 μm, and the ratio (A / B) of the area on the smaller particle size side (A) to the area on the larger particle size side (B), based on the maximum peak in the particle size distribution of inorganic particles, may be 1.05 or greater.

[0035] A uniform composite separator has inorganic particles with an average particle size of 0.20 μm to 0.40 μm, and a particle size distribution characteristic in which the ratio (A / B) of the area on the smaller particle side (A) to the area on the larger particle side (B), based on the maximum peak, is 1.05 or more. As a result, it exhibits excellent adhesion between inorganic particles and between inorganic particles and the substrate, as well as superior heat resistance. Furthermore, even when the ceramic layer of the uniform composite separator is formed with a very thin thickness, it can achieve outstanding adhesion and heat resistance, and electrochemical elements employing it can simultaneously satisfy safety, high capacity, and high output characteristics.

[0036] In one embodiment, the average particle size (D) of the inorganic particles 50 This can mean the particle size of inorganic particles corresponding to 50% of the cumulative fraction by volume, and can be calculated from the particle size distribution measured in accordance with the KA A ISO 13320-1 standard.

[0037] In one embodiment, the particle size distribution may be a graph of volume % based on the particle diameter of inorganic particles. In one embodiment, when the particle size distribution is shown from smallest to largest particle size from left to right along the x-axis, the area on the small particle size side (A) may represent the area to the left of the largest peak, from the starting point of the particle size distribution to the x-axis of the maximum peak, and the area on the large particle size side (B) may represent the area to the right of the largest peak, from the x-axis of the maximum peak to the end point of the particle size distribution.

[0038] In one embodiment, the ratio (A / B) of the area on the smaller particle size side (A) to the area on the larger particle size side (B), based on the maximum peak in the particle size distribution of the inorganic particles, may be 1.05 or more, or 1.06 or more, or 1.07 or more, or 1.5 or less, or 1.4 or less, or 1.3 or less, or 1.2 or less, or 1.05 to 1.5, or 1.05 to 1.3, or 1.06 to 1.3, and may include all possible combinations of the upper and lower limits of the numerical range.

[0039] In one embodiment, the inorganic particles have a particle size distribution degree (D 95 -D 50 ) / D 50 value that may be 1.5 or more, or 1.7 or more, or 1.8 or more, and may be 3.0 or less, or 2.8 or less, or 2.6 or less, 2.5 or less, or 2.4 or less, or 2.3 or less, and may be 1.5 to 3.0, or 1.8 to 3.0, or 1.8 to 2.8, and may include all possible combinations of the upper and lower limits of the numerical range. When using inorganic particles that satisfy the above average particle size and the A / B area ratio while satisfying the (D 95 -D 50 ) / D 50 value, the simultaneous improvement effect of adhesive strength, heat resistance, and air permeability can be more excellent. In one embodiment, the D 95 means the particle size of inorganic particles corresponding to 95% in terms of volume-based integrated fraction.

[0040] In one embodiment, the type of the inorganic particles can be used without limitation as long as it satisfies the above average particle size and particle size distribution characteristics. As a non-limiting example, it may be one or more selected from metal oxides such as boehmite, BaSO4, CeO2, MgO, CaO, ZnO, Al2O3, TiO2, BaTiO3, HfO2, SrTiO3, SnO2, NiO, ZrO2, Y2O3, and SiC, metal hydrates, metal carbides, metal nitrides, and metal carbonitrides.

[0041] In one embodiment, the coating density of the ceramic layer may be 1.0 g / cm 3 or more, 1.1 g / cm 3 or more, 1.2 g / cm 3 or more, and may be 2.0 g / cm 3 or less, 1.9 g / cm 3 or less, or 1.8 g / cm 3 or less, or 1.7 g / cm 3 or less, and may be 1.0 to 1.8 g / cm 3 , or 1.2 to 1.8 g / cm 3 .

[0042] The thickness of the composite separator in one form may include, 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.

[0043] In one embodiment, the ceramic layer may be coated on one or both sides of the porous substrate. When the ceramic layer is coated on both sides of the porous substrate, the thicknesses of the ceramic layers coated on one side and the other side may be the same or different. Although not particularly limited, the total thickness of the ceramic layer in one embodiment may be, for example, 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 about 1.5 μm to 5 μm, or 2 μm to 5 μm, or 2 μm to 4 μm, or any value between these numbers. In one embodiment, the composite separator can achieve excellent adhesion and heat resistance even when the ceramic layer is formed to a very thin thickness, and the electrochemical element employing it can simultaneously satisfy safety, high capacity, and high output characteristics.

[0044] 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, 95-99% by weight, or 96-99% by weight relative to the total weight of the ceramic layer. This amount may be higher than the inorganic particle content of conventional coating layers formed by linking inorganic particles containing a binder. Nevertheless, it exhibits excellent heat resistance and numerical stability, and allows for the formation of a coating layer (ceramic layer) with a thinner thickness.

[0045] In one embodiment, the ceramic layer can use a binder of 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 per 100 parts by weight of the inorganic particles, and can be used in amounts of 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 any amount between these numerical ranges.

[0046] In one embodiment, the binder is not particularly limited as long as it is a conventional binder used in the art, and may be one or more selected from, for example, (meth)acrylic polymers, fluorine polymers, styrene polymers, vinyl alcohol polymers, vinyl ester polymers, vinylpyrrolidone polymers, cellulose polymers, polyimide polymers, polyamide polymers, polyalkylene glycols, and copolymers thereof. The (meth)acrylic polymer may be selected from, for example, polyalkyl (meth)acrylate, poly(meth)acrylic acid, poly(meth)acrylamide, poly(meth)acrylonitrile, polyhydroxyethyl (meth)acrylate, or copolymers thereof. The styrene polymer may be selected from, for example, polystyrene, poly-α-methylstyrene, polybromostyrene, or copolymers thereof. The vinyl alcohol polymer may be, for example, polyvinyl alcohol or a copolymer containing the same. The vinyl ester polymer may be, for example, polyvinyl ester or a copolymer containing the same. The aforementioned cellulosic polymer may be selected from, for example, cellulose, carboxymethylcellulose, hydroxypropylmethylcellulose, cellulose acetate, or cellulose acetate propionate.

[0047] In one embodiment, the binder may include a (meth)acrylic polymer, a cellulosic polymer, or a combination thereof.

[0048] Specifically, the binder may include polyacrylamide (PAAm), carboxymethylcellulose, or a combination thereof. More specifically, it may include a mixed binder of carboxymethylcellulose and polyacrylamide, which is preferable in the present invention as it can better improve the desired effect, but is not limited thereto.

[0049] In one embodiment, if the binder contains polyacrylamide (PAAm), the weight-average molecular weight of the polyacrylamide may include, but is not limited to, 100,000 g / mol to 300,000 g / mol, or 150,000 to 250,000 g / mol, 200,000 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.

[0050] In one embodiment, if the binder contains carboxymethylcellulose, the weight-average molecular weight of the carboxymethylcellulose may be 180,000 to 1,500,000 g / mol, or 180,000 to 1,300,000 g / mol, or 190,000 to 1,000,000 g / mol, and may include all possible combinations of the upper and lower limits of the numerical range. Furthermore, the degree of substitution of the carboxymethylcellulose may be 0.6 to 1.2, or 0.6 to 1.1, 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.

[0051] Here, carboxymethyl cellulose (CMC) is defined as cellulose with hydroxyl groups (-OH) being -OCH2COOH and / or -OCH2COOH - M + This refers to a cellulose derivative that is substituted and etherified with the aforementioned M. + is an alkali metal cation, which may 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 of the cellulose molecule, and can be measured by known or tolerant methods, for example, according to ASTM D1439, or 1 H-NMR or 13 This can be calculated using 1C-NMR analysis.

[0052] 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.

[0053] 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).

[0054] 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.

[0055] 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.

[0056] 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.

[0057] The number of millimoles (A) of CMC-acid per gram of dried sample was calculated using the following formula.

[0058]

number

[0059] Next, the degree of substitution (DS) was calculated from A using the following formula.

[0060]

number

[0061] If the binder contains carboxymethylcellulose and polyacrylamide, the carboxymethylcellulose and polyacrylamide may be used in a weight ratio of 10-50:90-50 or 10-40:90-60.

[0062] 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 both be 5% or less, specifically 4% or less, or 3% or less, or 2.5% or less, or 2.0% or less, or less than 2.0%.

[0063] 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%.

[0064] 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, and horizontally removing the cardboard at a speed of 0.1m / s to a depth of 60mm. The test then evaluates the extent to which foreign matter adheres to the surface of the cardboard by assessing the area. The foreign matter may be a component of the ceramic layer, such as inorganic particles, a binder, or a combination thereof.

[0065] 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.

[0066] 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 the thermal shrinkage characteristics of the separator cannot be accurately predicted from the evaluation value.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] Specifically, the electrochemical element in one state includes a positive electrode, a negative electrode, and a composite separator, the composite separator comprising a porous substrate and a ceramic layer formed on one or both sides of the substrate and containing inorganic particles and a binder, wherein the average particle size (D 50 The particle size is 0.20 μm to 0.40 μm, and the ratio (A / B) of the area on the smaller particle size side (A) to the area on the larger particle size side (B), based on the maximum peak in the particle size distribution of inorganic particles, may be 1.05 or greater.

[0073] 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, resulting in structures well known in the art.

[0074] As an example, the lithium secondary battery can be manufactured using 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.

[0075] [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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] [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.

[0084] The negative electrode current collector may include a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a 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.

[0085] The negative electrode active material can be used without limitation as long as it is a substance that can adsorb and desorb lithium ions and is commonly used in the relevant technical field. As a non-limiting example, carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, and carbon fibers; lithium metal; lithium alloys; silicon (Si)-containing substances or tin (Sn)-containing substances can be used.

[0086] [[ID=⑧]] [[ID=⑨]]Examples of the amorphous carbon include hard carbon, soft carbon, coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers (MPCF), etc. Examples of the crystalline carbon include graphite-based carbons such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, and graphitized MPCF.

[0087] Examples of the elements contained in the lithium alloy include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.

[0088] The silicon-containing substance can provide improved capacity characteristics. The silicon-containing substance may include Si, SiO x (0 < x ≤ 2), metal-doped SiO[[ID=①]] x (0 < x ≤ 2), silicon-carbon composites, etc. The metal may include lithium and / or magnesium. Metal-doped SiO x (0 < x ≤ 2) may include metal silicates. The binder, conductive material, and thickening agent of the negative electrode may be the above-mentioned substances that can be used during the manufacture of the positive electrode.

[0089] The negative electrode binder is not particularly limited as long as it is commonly used in the art, and can be rubber binders such as styrene-butadiene rubber (SBR) binders, carboxymethylcellulose (CMC), polyacrylic acid, polyethylene dioxythiophene (poly(3,4-ethylenedioxythiophene), or PEDOT) binders.

[0090] [Electrolytes] In one embodiment, the electrolyte may be a non-aqueous electrolyte, and the non-aqueous electrolyte may contain a lithium salt, which is the electrolyte, and an organic solvent.

[0091] The lithium salt is, for example, Li + X - The anion of the lithium salt is represented by (X - ) 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.

[0092] The organic solvent may contain organic compounds that sufficiently dissolve the lithium salt and additives and are not reactive 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, dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, ethanol, isopropyl alcohol, dimethyl sulfoxide, acetonitrile, diethoxyethane, sulfolane, γ-butyrolactone, and propylene sulfide.

[0093] 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.

[0094] [Physical property measurement method] 1) Particle size of inorganic particles Samples were collected in accordance with the KS A ISO 13320-1 standard, and the particle size distribution was analyzed using a MICROTRAC S3500 to obtain the particle size distribution in volume % based on particle diameter. The particle size (D) corresponding to n% of the volume-based cumulative fraction in the aforementioned particle size distribution was determined. n) is derived, and the particle size of the sample particles to be measured that corresponds to 50% of the cumulative fraction based on volume is the average particle size (D 50 I made it that way.

[0095] Furthermore, using the particle size distribution obtained by the above method, the area on the smaller particle size side (A) and the area on the larger particle size side (B) were obtained with respect to the maximum peak. Specifically, as shown in Figure 1, the particle size distribution is illustrated from smallest to largest particle size from left to right along the x-axis. Area A was defined as the area from the starting point of the particle size distribution to the x-axis of the maximum peak, and area B was defined as the area from the x-axis of the maximum peak to the ending point of the particle size distribution.

[0096] 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 (9 μm) from the thickness of the composite separators.

[0097] The thickness of the porous substrate was determined by stacking 10 layers of the porous substrate, measuring the thickness with 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 the case where a ceramic layer had been formed, the ceramic layer was removed, and after sufficient drying, the average thickness of the porous substrate from which the ceramic layer had been removed was derived using the method described above.

[0098] 3) Coating density of the ceramic layer The coating density of the ceramic layer was calculated using the following formula, and the weight of the ceramic layer was determined by subtracting the weight of the porous substrate from the weight of the composite separator. The composite separator was cut to a size of 100 mm x 100 mm, two pieces were stacked, and the weight was measured five times to find the average weight of the two composite separators. This average weight was then divided by 2 to determine the weight of the composite separator. The weight of the porous substrate was determined using only the porous substrate cut to a size of 100 mm x 100 mm, using the same method as for measuring the weight of the composite separator.

[0099] Ceramic layer coating density = (weight of ceramic layer / thickness of ceramic layer) / area

[0100] 4) 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.

[0101] [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.

[0102] A: <1.5% B: 1.5%~5% C:>5%

[0103] 5) Thermal shrinkage rate The thermal shrinkage rate of the composite separator was measured according to the ASTM D1204 standard, using the following method. A grid of 10 cm squares with 2 cm intervals was marked on the composite separator test specimen. One side of this square represented the transverse direction (TD), and the other side represented the machine direction (MD). The test specimen was positioned in the center, and five sheets of paper were placed above and below it. The four sides of the paper were wrapped with tape, and the paper-wrapped test specimen was placed in a 150°C hot air drying oven for 60 minutes. After that, the test specimen was removed, the separator was observed with a camera, and the shrinkage rates in the machine direction (MD) and the transverse direction (TD) were calculated and recorded in Table 2 below.

[0104] MD heat shrinkage rate (%) = (length of MD before heating - length of MD after heating) / length of MD before heating × 100 TD thermal shrinkage rate (%) = (TD length before heating - TD length after heating) / TD length before heating × 100

[0105] [Example 1] Average particle size in water (D 50 ) 0.21 μm boehmite (D 95 A slurry with a solid content of 45% by weight was prepared by mixing 100 parts by weight of a boehmite (0.61 μm, A / B: 1.07) with 2 parts by weight of the dispersant 1,2-benzoisothiazolin-3-one (DIO2). The prepared slurry was mixed with carboxymethyl cellulose (CMC) with a degree of substitution of 0.9 and a weight-average molecular weight of 200,000 g / mol in an amount of 3 parts by weight of CMC per 100 parts by weight of boehmite, and diluted with water to a solid content of 25% by weight to prepare a ceramic layer forming composition.

[0106] Both sides of a 9μm thick polyethylene film (porosity 35%~45%, SKIET) were treated with corona discharge (power density 2W / m²). 2) The surface polar groups were introduced, and at this time, the corona surface treatment was carried out at a speed of 5 mpm (meter per minute). The composition for forming the ceramic layer was applied to both sides of the corona surface-treated polyethylene film by bar coating, and dried at 50 °C to produce a composite separator in which ceramic layers of the same thickness were formed on both sides.

[0107] [Example 2] Average particle size (D 50 ) 0.30 μm boehmite (D 95 : 0.99 μm, A / B: 1.17) was used, and the procedure was the same as in Example 1.

[0108] [Example 3] Average particle size (D 50 ) 0.37 μm boehmite (D 95 : 1.13 μm, A / B: 1.12) was used, and the procedure was the same as in Example 1.

[0109] [Example 4] As the binder, carboxymethyl cellulose (CMC) with a degree of substitution of 0.9 and a weight average molecular weight of 200,000 g / mol and polyacrylamide (PAAm) (Mw 200,000 g / mol, sigma aldrich) were mixed and used at a weight ratio of 10:90, and the procedure was the same as in Example 1.

[0110] [Example 5] Average particle size (D 50 ) 0.30 μm boehmite (D 95 : 0.99 μm, A / B: 1.17) was used, and the procedure was the same as in Example 4.

[0111] [Example 6] Average particle size (D 50 ) 0.37 μm boehmite (D 95 : 1.13 μm, A / B: 1.12) was used, and the procedure was the same as in Example 4.

[0112] [Example 7] The boehmite with an average particle size (D 50 ) of 0.32 μm (D 95 : 0.87 μm, A / B: 1.09) was used, and the procedure was the same as in Example 4 above.

[0113] [Comparative Example 1] The boehmite with an average particle size (D 50 ) of 0.50 μm (D 95 : 1.50 μm, A / B: 1.09) was used, and the procedure was the same as in Example 1 above.

[0114] [Comparative Example 2] The boehmite with an average particle size (D 50 ) of 0.64 μm (D 95 : 1.75 μm, A / B: 0.97) was used, and the procedure was the same as in Example 1 above.

[0115] [Comparative Example 3] The boehmite with an average particle size (D 50 ) of 0.10 μm (D 95 : 0.31 μm, A / B: 1.15) was used, and the procedure was the same as in Example 1 above.

[0116] [Comparative Example 4] The boehmite with an average particle size (D 50 ) of 0.27 μm (D 95 : 0.77 μm, A / B: 1.04) was used, and the procedure was the same as in Example 1 above.

[0117] [Comparative Example 5] The boehmite with an average particle size (D 50 ) of 0.38 μm (D 95 : 0.91 μm, A / B: 1.02) was used, and the procedure was the same as in Example 1 above.

[0118]

Table 1

[0119] [Table 2]

[0120] Referring to Table 2 above, 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 the inorganic particles within the ceramic layer, has excellent heat resistance, and can effectively suppress thermal shrinkage. 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.

[0121] On the other hand, the average particle size (D 50 In comparative examples, composite separators using inorganic particles whose particle size range deviates from the 0.20 μm to 0.40 μm range, or whose particle size distribution ratio (A / B) of the area on the smaller particle size side (A) to the area on the larger particle size side (B) is less than 1.05 relative to the maximum peak, showed a significant decrease in adhesive strength and thermal shrinkage rate.

[0122] 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.

[0123] 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.

[0124] 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.

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 containing inorganic particles and a binder, The average particle size (D) of the inorganic particles ５０ A composite separator in which the particle size is 0.20 μm to 0.40 μm, and the ratio (A / B) of the area on the smaller particle size side (A) to the area on the larger particle size side (B), based on the maximum peak in the particle size distribution of inorganic particles, is 1.05 or more.

2. The inorganic particles have a particle size distribution of (D ９５ -D ５０ ) / D ５０ A composite separator according to claim 1, wherein the value is 1.8 to 2.

5.

3. The composite separator according to claim 1, wherein the ratio (A / B) of the area on the smaller particle size side (A) to the area on the larger particle size side (B), based on the maximum peak in the particle size distribution of the inorganic particles, is 1.05 to 1.

3.

4. The composite separator according to claim 1, comprising 0.1 to 10 parts by weight of a binder per 100 parts by weight of the inorganic particles.

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

6. The composite separator according to claim 1, wherein the binder is 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, polyalkylene glycols, and copolymers thereof.

7. The composite separator according to claim 1, wherein the binder comprises polyacrylamide, carboxymethylcellulose, or a combination thereof.

8. The composite separator according to claim 1, 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.

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

10. The coating density of the ceramic layer is 1.2 to 1.8 g / cm³. ３ The composite separator according to claim 1.

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

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

13. 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 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.

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

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, which includes inorganic particles and a binder. The average particle size (D) of the inorganic particles ５０ An electrochemical element in which the particle size is 0.2 μm to 0.4 μm, and the ratio (A / B) of the area on the smaller particle size side (A) to the area on the larger particle size side (B), based on the maximum peak in the particle size distribution of inorganic particles, is 1.05 or greater.

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