Microporous multilayer separator for secondary battery
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- HANWHA TOTALENERGIES PETROCHEMICAL CO LTD
- Filing Date
- 2025-06-18
- Publication Date
- 2026-06-04
Abstract
Description
Microporous multilayer separator for secondary batteries
[0001] Cross-citation with related applications
[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0172368 filed November 27, 2024, and all contents disclosed in the document of said Korean Patent Application are incorporated herein as part of this specification.
[0003] Technology field
[0004] The present invention relates to a microporous multilayer separator and a secondary battery including the same.
[0005] Lithium-ion batteries are one of the most common energy storage devices, driven by the daily use of various portable IT devices (smartphones, laptops, tablet PCs) and the popularization of electric vehicles, which are representative examples of the electrification of transportation. As these devices using lithium-ion batteries as power sources evolve, there is a demand for smaller and lighter lithium-ion batteries. Furthermore, as application fields expand to electric vehicles, smart grids, and energy storage systems (ESS), there is also a demand for high capacity, long lifespan, and high stability.
[0006] To achieve the above objective, research and development of a separator having micropores is essential to ensure that lithium ions move smoothly between the two electrodes during the charging and discharging process while preventing physical contact (short circuit) between the anode and cathode.
[0007] Conventional microporous separators are formed by extruding and stretching polyolefin-based raw materials together with a plasticizer, and then removing the plasticizer with a solvent. However, due to the limitations of polyolefin raw materials, they shrink when exposed to high temperatures and lose their original dimensions, which can cause a short circuit between the anode and cathode.
[0008] To overcome this, a technique has been proposed to coat a heat-resistant layer containing ceramic particles on the surface of a separator. While a thicker coating of the heat-resistant layer can prevent thermal shrinkage of the separator, it may act as a resistance that hinders lithium ion movement, thereby reducing the performance of the secondary battery. Furthermore, since thinning and lightweighting of the separator are required to improve the energy density of the secondary battery, a separator with a low thermal shrinkage rate and a thin heat-resistant layer with a low weight per unit area can be usefully employed.
[0009] Korean Patent No. 10-1541473 discloses a method for manufacturing a separator that adsorbs excess metal ions by coating different inorganic particles in multiple layers; however, no improvement in thermal shrinkage rate has been confirmed, and there is a disadvantage that manufacturing costs increase because different inorganic particles must be coated twice. Korean Patent No. 10-2385925 also discloses a method for manufacturing a separator that can improve battery stability by increasing dielectric breakdown voltage by coating different inorganic particles in multiple layers; however, no improvement in thermal shrinkage rate or air permeability has been confirmed, and there is a disadvantage that the manufacturing process increases because different inorganic particles must be coated twice. Korean Patent No. 10-1358761 discloses a method for manufacturing a separator that can suppress the generation of by-products that may occur during the dispersion process of inorganic particles or suppress side reactions during the electrochemical reaction of a lithium secondary battery by coating two types of inorganic particles of different sizes together and coating the surface of the inorganic particles; however, similarly, no improvement in thermal shrinkage rate has been confirmed, and there is a disadvantage that an additional process of coating inorganic particles is required.
[0010]
[0011] Prior art literature
[0012] (Patent Document 1) Republic of Korea Patent No. 10-1541473
[0013] (Patent Document 2) Republic of Korea Patent No. 10-2385925
[0014] (Patent Document 3) Republic of Korea Patent No. 10-1358761
[0015]
[0016] The present invention aims to provide a microporous multilayer separator suitable for use in lithium-ion secondary batteries, which has improved energy density and safety by having a low coating weight per unit area, a thin coating layer thickness, and a low thermal shrinkage rate, in order to solve the problems described above.
[0017] In addition, the present invention aims to provide a secondary battery comprising the microporous multilayer separator.
[0018] To achieve the above objective, the present invention comprises a polyolefin-based microporous membrane; and a microporous multilayer separation membrane coated on one or both sides of the microporous membrane, wherein an inorganic coating layer is formed by binding two or more types of inorganic particles with an organic binder, wherein the inorganic particles include a first inorganic particle and a second inorganic particle, and the average diameter (D) of the first inorganic particle 50 ) is 0.1 to 10.0 μm, and the average diameter (D) of the second inorganic particle 50 ) is the average diameter (D) of the first inorganic particle 50 A microporous multilayer separation membrane is provided, characterized by having a value of 50% or less of ).
[0019] Another aspect of the present invention for achieving the above objective is to provide a secondary battery comprising the microporous multilayer separator.
[0020] The present invention forms a thin film inorganic coating layer by thinly coating one or both sides of a polyolefin-based microporous membrane with a slurry comprising two or more types of inorganic particles of different sizes, an organic binder, and a dispersant. This minimizes the reduction in air permeability caused by the introduction of the inorganic coating layer, thereby minimizing the inhibition of lithium ion movement. Furthermore, by using a mixture of relatively small inorganic particles, the coating weight is reduced, and better binding strength is exhibited between the inorganic particles and between the inorganic particles and the polyolefin-based microporous membrane, thereby preventing thermal shrinkage of the polyolefin-based microporous membrane at high temperatures. Accordingly, the microporous multilayer separator is very useful as a separator for high-capacity / high-output lithium-ion secondary batteries.
[0021] The advantages and features of the present invention and the methods for achieving them will become clear by referring to the embodiments described in detail below. However, the present invention is not limited to the embodiments disclosed below but can be implemented in various different forms. These embodiments are provided merely to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the present invention, and the present invention is defined only by the scope of the claims.
[0022] Prior to the explanation, the meanings of the terms used in this specification are briefly explained. However, since the explanation of terms is intended to aid in understanding this specification, it should be noted that they are not used to limit the technical scope of the invention unless explicitly stated to be a limiting factor.
[0023] The terms used herein are for describing the embodiments and are not intended to limit the invention. In this specification, the singular form includes the plural form unless specifically stated otherwise in the text. As used herein, "comprises" and / or "comprising" do not exclude the presence or addition of one or more other components in addition to the components mentioned.
[0024] Unless otherwise defined, all terms used herein (including technical and scientific terms) may be used in a meaning commonly understood by those skilled in the art to which the present invention pertains. Additionally, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless explicitly and specifically defined otherwise.
[0025] The present invention relates to a polyolefin-based microporous membrane; and a microporous multilayer separation membrane coated on one or both sides of the microporous membrane, wherein an inorganic coating layer is formed by binding two or more types of inorganic particles with an organic binder, wherein the inorganic particles include a first inorganic particle and a second inorganic particle, and the average diameter (D) of the first inorganic particle 50 ) is 0.1 to 10.0 μm, and the average diameter (D) of the second inorganic particle 50 ) is the average diameter (D) of the first inorganic particle 50 A microporous multilayer separation membrane is provided, characterized by having a value of 50% or less of ).
[0026] The average particle size (D) of at least one type of inorganic particle among those constituting the inorganic coating layer. 50The particle size is 0.1 to 10 μm, preferably 0.2 to 1.0 μm, and more preferably 0.25 to 0.8 μm. If at least one of the inorganic particles is less than 0.1 μm, it may block the pores of the polyolefin-based microporous membrane and inhibit lithium ion movement; if it exceeds 10 μm, it may not be able to be located in the space between the inorganic particles or at the interface between the inorganic particles and the microporous membrane, thus failing to provide sufficient binding sites and making it difficult to suppress thermal shrinkage of the microporous membrane. The average particle size of the inorganic particles refers to the cumulative 50% volume% diameter of the particle size distribution measured by the laser scattering method.
[0027] In the microporous multilayer separation membrane of the present invention, the content of the first inorganic particle among the inorganic particle content may be 50 to 95 weight%, preferably 55 to 95 weight%. When the above range is satisfied, it is advantageous for securing appropriate air permeability and has the effect of suppressing the thermal shrinkage rate of the separation membrane.
[0028] In the microporous multilayer separator of the present invention, the organic binder may be included in an amount of 1 to 20 parts by weight per 100 parts by weight of the inorganic particles, preferably in an amount of 2 to 15 parts by weight, and most preferably in an amount of 3 to 12 parts by weight. If the content of the organic binder is less than 1 part by weight, the adhesion between the inorganic particles and the polyolefin-based microporous membrane may be insufficient, which may result in reduced heat resistance, and if it exceeds 20 parts by weight, it may block the pores of the polyolefin-based microporous membrane, thereby inhibiting lithium ion movement and reducing the performance of the secondary battery.
[0029] In the microporous multilayer separator of the present invention, 0.1 to 3 parts by weight of a dispersant may be included per 100 parts by weight of the inorganic particles, preferably 0.3 to 2.5 parts by weight, and most preferably 0.5 to 1.5 parts by weight. If the amount of the dispersant is less than 0.1 parts by weight, the inorganic particles may not be evenly dispersed and may not be uniformly coated, and if the amount exceeds 3 parts by weight, it may act as a resistor in the lithium-ion secondary battery and degrade battery performance.
[0030] In the present invention, an anionic polymeric dispersant (polycarboxylic acid type) may be used as the dispersant, but is not limited thereto.
[0031] The above-mentioned inorganic coating layer can form an interstitial volume as inorganic particles, uniformly dispersed by a dispersant, come into contact with each other and are bound together by an organic binder. This interstitial volume of the inorganic coating layer can serve as a pore through which lithium ions can move.
[0032] In the present invention, the inorganic coating layer satisfies [Equation 2] with an A value calculated from the following [Equation 1], and preferably, the A value can satisfy 0.52 to 0.60:
[0033] [Equation 1] A = T / S
[0034] [Equation 2] 0.50 < A < 0.61
[0035] However, here T is the coating thickness and S is 1m 2 This is the coating weight.
[0036] If the above range is satisfied, 1m 2 A microporous multilayer separator for secondary batteries can be obtained with improved energy density and high-temperature safety, as the coating weight is low and the coating thickness is thin, resulting in a low increase in air permeability and a low MD / TD thermal shrinkage rate.
[0037] With the recent trend toward higher power and capacity in batteries, a thinner overall thickness of the microporous multilayer separator is advantageous for the inorganic coating layer, and 1m 2 The coating weight (S) per unit is 1.5 to 3.5 g / m² 2 It may be, preferably 1.8 to 3.0 g / m² 2 It could be. 1m 2 The weight of the coating layer per unit is 1.5 g / m² 2 If it is less than, the coating layer is too thin to ensure sufficient heat resistance, and 1m 2 The weight of the coating layer is 3.5 g / m² 2 If it exceeds the limit, the coating layer thickness becomes too thick, making it difficult to form a thin film.
[0038] The microporous multilayer separator of the present invention preferably has a thermal shrinkage rate of 5% or less in both the machine direction (MD) and the transverse direction (TD) after heat treatment in a convection oven at 130°C for 1 hour. If the MD / TD thermal shrinkage rate exceeds 5%, when the microporous multilayer separator is exposed to high temperatures during operation of a secondary battery, it loses dimensional stability, causing a short circuit between the positive and negative electrodes, which may lead to thermal runaway.
[0039] The microporous multilayer separator of the present invention may have an increase in air permeability of 25 sec / 100cc or less before and after coating of the inorganic coating layer. If the increase in air permeability exceeds 25 sec / 100cc, the movement of lithium ions may be inhibited, thereby degrading the performance of the secondary battery.
[0040] In the present invention, the inorganic particles may be any type of inorganic particles used in the manufacture of conventional microporous multilayer separators for lithium-ion secondary batteries without limitation.
[0041] These inorganic particles may be one or more selected from metal oxides, metal nitrides, metal carbides, metal carbonates, metal hydrates, and metal carbonitrides; more specifically, the inorganic particles may be one or more selected from Al2O3, Al(OH)3, AlOOH, CaCO3, CaO, SiO2, SnO2, BaTiO3, NiO, TiO2, ZnO, MgO, Mg(OH)2, ZrO2, Y2O3, and talc. These inorganic particles may be inorganic particles having a dielectric constant of 5 or higher, piezoelectricity, and lithium ion transfer ability. One or more of the above inorganic particles may be used in a mixture, but are not limited thereto. The shape of the above inorganic particles may be plate-shaped, spherical, or angular.
[0042] The above organic binder serves to prevent dimensional deformation and degradation of physical properties of the polyolefin-based microporous membrane at high temperatures by binding and fixing the inorganic particles and the surface of the polyolefin-based microporous membrane. The above organic binder includes one or more of an organic binder in the form of a non-water-soluble emulsion and a water-soluble binder.
[0043] The above-mentioned organic binder in the form of an emulsion may be used without limitation as long as it is an emulsion that is insoluble in water and dispersed. Specific examples include a copolymer of methyl methacrylate and ethylhexyl acrylate; or one or more types of homopolymers or copolymers thereof, such as polyacrylonitrile, polyolefin-based, nitrile-butadiene rubber (NBR), styrene-butadiene rubber (SBR), acetate-based, polyvinylidene fluoride-based, or polyvinyl alcohol-based, may be used.
[0044] The above-mentioned water-soluble organic binder may be used without limitation as long as it is a polymer compound that dissolves in water, and may include modified acrylate copolymers, modified acrylic acid copolymers, amide copolymers, carboxylic acid copolymers, cellulose acetate, cellulose acetate butyrate, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, or carboxymethyl cellulose, and may be used in combination of one or more of these.
[0045] In the microporous multilayer separation membrane of the present invention, the inorganic coating layer can be formed by applying a slurry containing the inorganic particles, the organic binder, and the dispersant to one or both sides of a polyolefin-based microporous membrane using any one of the methods of gravure coating, die coating, wire bar coating, and spray coating, and the dispersant in the aqueous slurry can be removed through a drying aid such as a hot air or drying oven by adjusting conditions such as appropriate temperature and time.
[0046] For the substrate to form the above-mentioned inorganic coating layer, it is preferable to use a thin polyolefin-based microporous membrane to increase the power output / capacity of the battery. The pore size present in the polyolefin-based microporous membrane may be 0.01 to 60 μm, and the porosity may be formed to be 10 to 90%. However, these numerical ranges may be appropriately modified depending on the embodiment or as needed.
[0047] The above polyolefin-based microporous membrane can be selected from the group consisting of polyethylene single membrane, polypropylene single membrane, polyethylene / polypropylene double membrane, polypropylene / polyethylene / polypropylene triple membrane, and polyethylene / polypropylene / polyethylene triple membrane, which are typically used in electrochemical devices.
[0048] The above-mentioned polyolefin-based microporous membrane may be manufactured by a method (dry method) in which a polyolefin polymer is melt-extruded to produce a sheet and then stretched in the machine direction (MD) to form micropores. In addition, the above-mentioned porous membrane may be manufactured by a method (wet method) in which a polyolefin polymer is kneaded with a plasticizer (diluent) at a high temperature and extruded into a single-phase sheet, and then sufficient crystal orientation is achieved through a stable biaxial stretching process in the machine direction (MD) and width direction (TD) on the extruded sheet via a first tenter frame process, followed by a step of dissolving and removing oil present in the polyolefin-based microporous membrane in an organic solvent, and then stretching the stretched sheet in the width direction (TD) during a second stretching step.
[0049] The thickness of the above polyolefin-based microporous film may be 1 to 100 μm, and preferably 5 to 20 μm. If it is less than 1 μm, it may easily deteriorate during operation of the secondary battery, leading to a loss of insulation properties or causing a short circuit between electrodes, and if it is 100 μm or more, it is difficult to increase the capacity of the secondary battery due to the thick film.
[0050] The above-mentioned polyolefin-based porous substrate may be coated with surface treatment technologies such as corona and plasma to effectively and uniformly coat a slurry containing inorganic particles.
[0051] A monomer for preparing a polyolefin resin constituting a polyolefin microporous membrane of the present invention may include one or more alpha-olefins. The alpha-olefin may have 2 to 8 carbon atoms and, preferably, may include at least one selected from the group consisting of ethylene, propylene, 1-butene, 1-hexene, and 1-octene. The polyolefin may be a monopolymer, a mixture of two or more different polyolefins, or another olefin copolymer.
[0052] Another aspect of the present invention is that the microporous multilayer separator can be used as a separator for a secondary battery, more specifically, a lithium-ion secondary battery.
[0053] The above secondary battery may be of various forms, such as electrolytic, stacked, and wound types, and as a specific example, a separator comprising the above polyolefin-based microporous membrane may be used as a separator for a wound secondary battery.
[0054] The aforementioned secondary battery is a term commonly used in the industry and refers to a power storage system that provides excellent energy density capable of converting electrical energy into the form of chemical energy for storage. Unlike primary batteries, which are non-rechargeable, secondary batteries are rechargeable and are widely used in IT devices such as smartphones, cellular phones, laptops, and tablet PCs. Recently, interest in electric vehicles has increased due to the need to prevent environmental pollution, and consequently, high-capacity secondary batteries are being adopted in electric vehicles.
[0055] In the above secondary battery, components other than the separator may include those commonly used in the industry.
[0056] The four major materials that are key components of the above lithium-ion secondary battery are the positive electrode, the negative electrode, the separator, and the electrolyte. Among these, the separator contains micropores, which allows lithium ions to move smoothly between the positive and negative electrodes during the charging and discharging process of the lithium-ion secondary battery, while preventing physical contact (short circuit) between the positive and negative electrodes to prevent thermal runaway.
[0057] Lithium-ion secondary battery separators are closely related to battery productivity and stability, and therefore require various characteristics such as mechanical properties, ion permeability, dimensional stability, and shutdown characteristics. In particular, while there is an attempt to secure higher capacity by using thinner separators in response to the demand for higher battery capacity, if the thickness of the inorganic coating layer becomes too thin, it becomes difficult to prevent deformation of the separator at high temperatures, causing the separator to shrink and resulting in a short circuit between the two electrodes, thereby reducing safety. Therefore, there is a need for a thin-film coated separator with high heat resistance that can form an inorganic coating layer as thin as possible while minimizing thermal shrinkage of the separator in high-temperature environments.
[0058] In this regard, the present invention can improve the performance of a secondary battery by using the aforementioned microporous multilayer separator with excellent properties as a separator for the secondary battery to increase the capacity of the secondary battery.
[0059]
[0060] Specific embodiments of the present invention are presented below. However, the embodiments described below are merely for the purpose of specifically illustrating or explaining the present invention and should not be limited thereby. Furthermore, details not described herein can be sufficiently technically inferred by a person skilled in the art, so such description is omitted.
[0061]
[0062] [Examples and Comparative Examples]
[0063] Examples 1 to 14 and Comparative Examples 1 to 7: Preparation of Microporous Multilayer Separator
[0064] As a substrate for coating inorganic particles, a polyethylene membrane with a thickness of 11 μm manufactured by the wet process mentioned above was used. The porosity of the polyethylene membrane was 42%, the gurley value was 120 sec / 100 cc, and the puncture strength was 590 gf.
[0065] Meanwhile, the slurry to be coated on the above polyethylene separator has an average diameter (D 50 ) 4 different types of alumina (Al2O3) (D 50 : 0.67μm, D 50 : 0.43μm, D 50 : 0.26μm, D 50 At least one of the following (0.10 μm) and a polymer-based dispersant (Korea Sannopco, CERASPERSE 5468CF, poly carboxylate ammonium salts) were added to water, an aqueous solvent, and a pre-dispersed slurry was prepared by primary stirring with an overhead stirrer for 1 hour. Inorganic particles were dispersed by circulating this pre-dispersed slurry twice at a speed of 1 L / min through a bead mill facility (Nanointec, VBM-1L) filled with zirconia beads. Subsequently, an organic binder was added to the slurry after bead milling according to content, and a final aqueous slurry was prepared by secondary stirring with a stirrer for 1 hour.
[0066] After removing foreign substances by passing the final aqueous slurry prepared above through a filter with a pore size of 10 μm, the slurry was coated on one side of a polyethylene wet separation membrane substrate using a micro gravure coating method. Subsequently, the solvent was evaporated by passing it through a hot air dryer, and an inorganic coating layer was formed.
[0067]
[0068] Evaluation: Measurement of microporous multilayer membrane properties
[0069] For the microporous multilayer separation membranes prepared in Examples 1 to 14 and Comparative Examples 1 to 7 above, the following physical properties were measured, and the results are shown in Tables 1 to 3 below.
[0070]
[0071] thickness
[0072] For the polyolefin-based microporous membranes of each example and comparative example, a VL-50 instrument from Mitutoyo, Japan was used, and the thickness was measured according to ASTM D374.
[0073]
[0074] 1m 2 Coating weight per unit (gsm, g / m²) 2 )
[0075] For each example and comparative example with a size of 50 x 50 mm, the weight of the membrane before coating and the membrane after coating were measured, respectively, and the coating amount was calculated using the following Equation 3.
[0076] [Equation 3]
[0077] Coating volume (g / m²) 2 ) = (C2-C1) Х 400
[0078] In the above Equation 3, C2 is the weight of the separator after coating, and C1 is the weight of the separator before coating.
[0079]
[0080] Increase in gurley airflow
[0081] Using a film air permeability tester (densometer, Toyoseiki Co., Ltd.), the time required for 100cc of air to pass through the membrane before coating and the membrane after coating was measured (ISO 5635 / 5), and then the increase in air permeability was calculated using the following Equation 4.
[0082] [Equation 4]
[0083] Increase in air permeability (sec / 100cc) = G3-G4
[0084] In the above Equation 4, G3 is the air permeability of the separator after coating, and G4 is the air permeability of the separator before coating.
[0085]
[0086] Thermal shrinkage rate
[0087] After marking four points at 30 mm intervals in the MD / TD directions on the center of each example and comparative example's microporous multilayer separator with a size of 50 x 50 mm, the specimens were placed between A4 papers and left in an oven at 130°C for 1 hour. Afterward, the specimens were cooled at room temperature to measure the shrinkage length in the mechanical direction (MD) and width direction (TD), and the thermal shrinkage rate was calculated using Equation 5 below.
[0088] [Equation 5]
[0089] Thermal shrinkage rate (%) = (L5-L6) / L5 × 100
[0090] In the above Equation 5, L5 is the length of the specimen before being placed in the oven, and L6 is the length of the specimen after being left in the oven and cooled to room temperature.
[0091]
[0092] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Coating liquid solid content composition (weight%) Inorganic particles 94959594949594 Dispersant 0.50.50.50.50.50.50.5 Organic binder 5.54.54.55.55.54.55.5 Inorganic particles (weight%) Al2O3(D 50 :0.67μm)95857565857565Al2O3(D 50 :0.43μm)0000000Al2O3(D 50 :0.26μm)0000152535Al2O3(D 50 :0.10μm)5152535000 Cross-sectional coating thickness (T) 1.22 1.19 1.20 1.15 1.20 1.18 1.181 m 2 Coating Weight (S) 2.29 2.17 2.16 2.03 2.30 2.23 2.19 T / S=A 0.53 30.54 80.55 50.56 70.52 10.52 90.53 Air Permeability Increase (sec / 100cc) 24 21 21 20 23 21 21 MD Thermal Shrinkage Rate (%) 4.4 4.13 83.5 4.6 4.3 4.3 TD Thermal Shrinkage Rate (%) 4.2 4.03.73.6 4.4 4.3 4.1
[0093] Examples 8, 9, 10, 11, 12, 13, 14 Coating liquid solid content composition (weight%) Inorganic particles 949594959494 Dispersant 0.50.50.50.50.50.50.5 Organic binder 5.54.55.55.54.55.55.5 Inorganic particles (weight%) Al2O3(D 50 :0.67μm)00090807060Al2O3(D 50 :0.43μm)9590850000Al2O3(D 50 :0.26μm)0005101520Al2O3(D 50 :0.10μm)510155101520 Cross-sectional coating thickness (T) 1.09 1.04 1.05 1.17 1.16 1.12 1.09 1m 2 Coating Weight (S) 2.0 1 1.8 5 1.8 0 2.2 2 2.1 3 1.9 9 1.8 8 T / S = A 0.5 4 2 0.5 6 1 0.5 8 2 0.5 2 6 0.5 4 5 0.5 6 3 0.5 7 9 Air Permeability Increase (sec / 100cc) 20 15 13 23 20 17 19 MD Thermal Shrinkage Rate (%) 2.9 2.5 1.9 4.0 3.7 3.4 3.3 T D Thermal Shrinkage Rate (%) 2.8 2.4 1.8 3.8 3.7 3.5 3.2
[0094] Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 Coating Solution Solid Content Composition (Weight%) Inorganic Particles 9494949494.59495 Dispersant 0.50.50.50.50.50.50.50.5 Organic Binder 5.55.55.55.55.05.54.5 Inorganic Particles (Weight%) Al2O3(D 50 :0.67μm)100002020500Al2O3(D 50 :0.43μm)01000005020Al2O3(D 50 :0.26μm)00100040080Al2O3(D 50 :0.10μm)000804000Sectional coating thickness(T)1.33 1.25 1.19 1.08 1.11 1.16 1.011m 2Coating Weight (S) 3.2 1 2.0 4 1.9 0 5 1.6 2 1.7 1 2.5 8 1.6 2 T / S=A 0.4 1 4 0.5 0 0.6 3 2 0.6 5 0.6 4 8 0.4 5 0 0.6 2 2 Air Permeability Increase (sec / 100cc) 4 4 3 2 3 8 3 4 3 5 4 0 4 1 MD Thermal Shrinkage Rate (%) 6.8 5.5 5.9 4.8 5.3 6.5 6.3 TD Thermal Shrinkage Rate (%) 6.5 6.0 6.1 4.7 5.1 6.2 5.8
[0095]
[0096] As can be seen from Tables 1 to 3 above, according to Examples 1 to 14, it was possible to provide a separator membrane that is advantageous for lightweighting, having excellent heat resistance with low increase in air permeability and low MD / TD thermal shrinkage rate, and a light coating weight. On the other hand, according to Comparative Examples 1 to 7, one or more characteristics of the increase in air permeability or thermal shrinkage rate were inferior. In particular, Comparative Examples 4 and 5 showed inferior characteristics of one or more characteristics of the air permeability or thermal shrinkage rate, as the relationship between coating thickness and coating weight per unit area fell outside the scope of the invention even when using inorganic particles satisfying the inorganic particle size conditions proposed in the present invention.
[0097] Although embodiments of the present invention have been described above, those skilled in the art will understand that the present invention may be implemented in other specific forms without altering its technical concept or essential features. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.
Claims
1. Polyolefin-based microporous membrane; and A microporous multilayer separation membrane having an inorganic coating layer, in which two or more types of inorganic particles are bound by an organic binder, coated on one or both sides of the above microporous membrane, The above-mentioned inorganic particles include a first inorganic particle and a second inorganic particle, and Average diameter of the first inorganic particle (D 50 ) is 0.1 to 10.0 μm, and the average diameter (D) of the second inorganic particle 50 ) is the average diameter (D) of the first inorganic particle 50 A microporous multilayer separation membrane characterized by having 50% or less of ).
2. A microporous multilayer separation membrane according to claim 1, characterized in that the content of the first inorganic particle among the inorganic particle contents is 50 to 95 weight%.
3. A microporous multilayer separation membrane according to claim 1, characterized in that it contains 1 to 20 parts by weight of an organic binder per 100 parts by weight of the inorganic particles.
4. A microporous multilayer separation membrane according to claim 1, characterized in that it contains 0.1 to 3 parts by weight of a dispersant per 100 parts by weight of the inorganic particles.
5. A microporous multilayer separation membrane according to claim 1, characterized in that the value of A calculated from the following [Equation 1] of the inorganic coating layer satisfies [Equation 2]. [Equation 1] A = T / S [Equation 2] 0.50 < A < 0.61 However, here T is the coating thickness and S is 1m 2 This is the coating weight.
6. In paragraph 5, S is 1.5 to 3.5 g / m² 2 A microporous multilayer separation membrane characterized by being.
7. A microporous multilayer separation membrane according to claim 1, characterized in that the thermal shrinkage rate (130℃, 1hr) in both the machine direction (MD) and the transverse direction (TD) is 5% or less.
8. A microporous multilayer separator according to claim 1, characterized in that the increase in air permeability before and after coating of the inorganic coating layer is 25 sec / 100cc or less.
9. A microporous multilayer separation membrane according to claim 1, characterized in that the inorganic particles are one or more selected from metal oxides, metal nitrides, metal carbides, metal carbonates, metal hydrates, and metal carbonitrides.
10. A microporous multilayer separation membrane according to claim 9, characterized in that the inorganic particles are one or more selected from Al2O3, Al(OH)3, AlOOH, CaCO3, CaO, SiO2, SnO2, BaTiO3, NiO, TiO2, ZnO, MgO, Mg(OH)2, ZrO2, Y2O3, and talc.
11. In claim 1, the organic binder comprises one or more of an organic binder in the form of a non-aqueous emulsion and a water-soluble binder, and The above-mentioned organic binder in the form of an emulsion is a copolymer of methyl methacrylate and ethylhexyl acrylate; or a homopolymer or copolymer thereof of polyacrylonitrile, polyolefin-based, nitrile-butadiene rubber (NBR), styrene-butadiene rubber (SBR), acetate-based, polyvinylidene fluoride-based, or polyvinyl alcohol-based polymers, dispersed in a manner insoluble in water. A microporous multilayer separation membrane characterized in that the above-mentioned water-soluble binder is a modified acrylate copolymer, a modified acrylic acid copolymer, an amide copolymer, a carboxylic acid copolymer, cellulose acetate, cellulose acetate butyrate, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, or carboxymethyl cellulose.
12. A microporous multilayer separation membrane according to claim 1, wherein the inorganic coating layer is formed by applying a slurry comprising the inorganic particles, the organic binder, and a dispersant to the microporous membrane using any one of gravure coating, die coating, wire bar coating, and spray coating methods.
13. A microporous multilayer separation membrane according to claim 1, characterized in that the polyolefin-based microporous membrane is selected from the group consisting of a polyethylene single membrane, a polypropylene single membrane, a polyethylene / polypropylene double membrane, a polypropylene / polyethylene / polypropylene triple membrane, and a polyethylene / polypropylene / polyethylene triple membrane.
14. A microporous multilayer separation membrane according to claim 13, characterized in that the thickness of the polyolefin-based microporous membrane is 1 to 100 μm.
15. A microporous multilayer separation membrane according to claim 13, characterized in that the monomer for producing the polyolefin comprises one or more alpha-olefins.
16. A microporous multilayer separation membrane according to claim 15, characterized in that the alpha-olefin has 2 to 8 carbon atoms.
17. A secondary battery comprising a microporous multilayer separator according to any one of claims 1 to 16.