Separator manufacturing method and separator

Abstract

One aspect of the present invention provides a method for producing a separator, comprising: (a) extruding a first composition comprising a first polyolefin and a first pore-forming agent to produce a first sheet; (b) extruding a second composition comprising a second polyolefin and a second pore-forming agent to produce a second sheet; (c) stretching the first and second sheets in the machine direction (MD) to produce first and second precursor films, respectively; (d) laminating the first and second precursor films to obtain a laminate; (e) stretching the laminate in the transverse direction (TD), and then removing the first and second pore-forming agents from the laminate to obtain a bilayer support comprising first and second layers derived from the first and second precursor films, respectively; (f) applying a coating composition comprising a binder and a solvent to both sides of the bilayer support and drying the coating composition to form a functional layer; and (g) dividing the bilayer support into two separators along the interface formed by the lamination.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a separator and a separator manufactured using the same. [Background technology]

[0002] Lithium secondary batteries are widely used as power sources for various electrical products that require compactness and light weight, such as smartphones, laptops, and tablet PCs. As their application fields expand to include smart grids and medium- to large-sized batteries for electric vehicles, there is a demand for the development of lithium secondary batteries with large capacity, long life, and high stability.

[0003] As a means to achieve this goal, research and development is being actively conducted on separators with micropores that separate the positive and negative electrodes to prevent internal shorts and facilitate the movement of lithium ions during charging and discharging. In particular, microporous separators made of polyolefins such as polyethylene are advantageous for pore formation through thermally induced phase separation, are economical, and can easily meet the physical properties required for separators.

[0004] However, separators made of polyethylene, which has a low melting point of around 135°C, can shrink and deform at temperatures above the melting point due to heat generated by the battery. If this deformation causes a short circuit, it can lead to thermal runaway in the battery, which can pose safety issues such as fire.

[0005] To improve the heat resistance of separators, so-called ceramic-coated separators, in which ceramic particles are coated on the surface of a porous support, have been proposed. However, these ceramic-coated separators have significant technical issues related to breathability. Coating the surface of the porous support with a heat-resistant layer containing ceramic particles improves the heat resistance of the separator, but the heat-resistant layer clogs the pores formed in the porous support, reducing the breathability of the separator. This reduces the ion transfer paths between the positive and negative electrodes, resulting in a significant degradation of the battery's charge and discharge performance.

[0006] In addition, attempts have been made to further form an adhesive layer having adhesive strength to the electrode on the surface of the porous support and / or the surface of the heat-resistant layer to improve the adhesive strength to the electrode and extend the life of the battery.

[0007] A separator coated with a functional layer such as a heat-resistant layer or an adhesive layer is generally manufactured by coating one or both sides of the porous support with a composition for forming the functional layer while the porous support is traveling at a constant speed, followed by drying.

[0008] Conventionally, for porous supports with a thickness of approximately 20 μm, the workability of the coating process, specifically the mechanical properties and running stability of the porous support, was adequately ensured. However, with the recent increase in demand for large-capacity batteries, the thickness of the porous support has tended to decrease to approximately 15 μm or less, or even 10 μm or less. This thinning inevitably reduces the mechanical properties and running stability of the porous support, and deformations such as wrinkles and warping occur in the porous support during the coating and drying process of the liquid composition for forming the functional layer, resulting in defects and failures in the separator. In response to this, a method for improving workability by reducing the running speed of the porous support during coating has been proposed. However, because the running speed directly affects the productivity of the separator, this method significantly reduces productivity. Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made to solve the problems of the prior art as described above, and an object of the present invention is to provide a separator manufacturing method that can achieve and improve a good balance between productivity and separator quality when manufacturing a separator including a functional layer, such as a heat-resistant layer or an adhesive layer, coated on one surface of a porous support, and a separator manufactured using the same. [Means for solving the problem]

[0010] One aspect of the present invention provides a method for producing a separator, comprising: (a) extruding a first composition comprising a first polyolefin and a first pore-forming agent to produce a first sheet; (b) extruding a second composition comprising a second polyolefin and a second pore-forming agent to produce a second sheet; (c) stretching the first and second sheets in the machine direction (MD) to produce first and second precursor films, respectively; (d) laminating the first and second precursor films to obtain a laminate; (e) stretching the laminate in the transverse direction (TD), and then removing the first and second pore-forming agents from the laminate to obtain a bilayer support comprising first and second layers derived from the first and second precursor films, respectively; (f) applying a coating composition comprising a binder and a solvent to both sides of the bilayer support and drying the coating composition to form a functional layer; and (g) dividing the bilayer support into two separators along the interface formed by the lamination.

[0011] In one embodiment, the first and second polyolefins may each comprise one selected from the group consisting of polyethylene, polypropylene, polybutylene, polymethylpentene, ethylene vinyl acetate, ethylene butyl acrylate, ethylene ethyl acrylate, and combinations or copolymers of two or more thereof.

[0012] In one embodiment, the weight average molecular weight of each of the first and second polyolefins may be 300,000 to 4,000,000.

[0013] In one embodiment, the ratio of the weight average molecular weight of the second polyolefin to the weight average molecular weight of the first polyolefin may be 0.5 to 2.

[0014] In one embodiment, at least one of the first and second compositions may further comprise a hydrophilic polymer.

[0015] In one embodiment, the content of the hydrophilic polymer in at least one of the first and second compositions may be 0.1 to 5% by weight.

[0016] In one embodiment, the hydrophilic polymer may be one selected from the group consisting of ethylene vinyl acetate, ethylene vinyl alcohol, polyvinyl alcohol, polyacrylic acid, polyoxyethylene-polyoxypropylene block copolymer, polyethylene glycol, polyethylene oxide, polyvinylpyrrolidone, polyvinyl acetal, polyvinyl butyral, cellulose derivatives, glycerol, and combinations of two or more thereof.

[0017] In one embodiment, the first and second precursor films may be pressed against each other during the lamination, so that at least a portion of the interface between the first and second precursor films may be adhered to each other.

[0018] In one embodiment, the thickness deviation of the first layer or the second layer measured by the following formula may be 10% or less.

[0019] <expression> Thickness deviation (%) = {(maximum thickness) - (minimum thickness)} / (minimum thickness) x 100 In the above formula, the thickness deviation is determined by a method including the steps of cutting the double-layer support to a size of 100 mm x 100 mm (MD x TD), then dividing it into five equal parts in the machine direction (MD) to obtain five test pieces each having a size of 20 mm x 100 mm (MD x TD); measuring the thickness of the first layer or the second layer at the center of the test piece in the machine direction (TD); and calculating the thickness deviation using the formula based on the maximum and minimum thickness values.

[0020] In one embodiment, the binder may be one selected from the group consisting of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, ethylene vinyl acetate, polyimide, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, hydroxyethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, polyvinyl alcohol, polyvinyl butyral, acrylonitrile-acrylic acid copolymer, ethylene-acrylic acid copolymer, styrene-butadiene copolymer, alkyl acrylate-acrylonitrile copolymer, polyethylene glycol, acrylic rubber, and a combination of two or more thereof.

[0021] In one embodiment, the solvent may be one selected from the group consisting of methanol, ethanol, propanol, butanol, methoxyethanol, ethoxyethanol, lactone, acetonitrile, n-methyl-2-pyrrolidone (NMP), formic acid, nitromethane, acetic acid, dimethyl sulfoxide, water, and combinations of two or more thereof.

[0022] In one embodiment, the coating composition may further comprise one inorganic particle selected from the group consisting of SiO2, AlO(OH), Mg(OH)2, Al(OH)3, TiO2, BaTiO3, Li2O, LiF, LiOH, Li3N, BaO, Na2O, Li2CO3, CaCO3, LiAlO2, Al2O3, SiO, SnO, SnO2, PbO2, ZnO, PO5, CuO, MoO, VO5, BO3, Si3N4, CeO2, Mn3O4, Sn2PO7, Sn2BO, Sn2BPO6, and combinations of two or more thereof.

[0023] Another aspect of the present invention provides a separator manufactured using the separator manufacturing method, the separator having properties measured by a method including the steps of: (i) fixing the center of a roll of the separator to a first member, unwinding one end of the separator in the machine direction (MD) horizontally, and connecting the roll to a second member that fixes the separator in the horizontal direction; and (ii) checking for deformation of the separator after one hour under conditions of a temperature of 25°C and a humidity of 40%, and measuring the vertical displacement due to the deformation; and the separator satisfies at least one of the following conditions (1) and (2):

[0024] (1) No deformation or vertical displacement of the separator; (2) No more than five vertically descending regions in the separator, and the distance between the surface to which the separator is horizontally fixed and the lowest end of the descending region is no more than 10% of the transverse (TD) width of the separator. [Effects of the Invention]

[0025] A method for producing a separator according to one embodiment of the present invention includes the steps of: (a) extruding a first composition containing a first polyolefin and a first pore-forming agent to produce a first sheet; (b) extruding a second composition containing a second polyolefin and a second pore-forming agent to produce a second sheet; (c) stretching the first and second sheets in the machine direction (MD) to produce first and second precursor films, respectively; (d) bonding the first and second precursor films together to obtain a laminate; and (e) stretching the laminate in the transverse direction (TD), and then By including the steps of: (a) removing the first and second pore-forming agents from the laminate to obtain a bilayer support comprising first and second layers derived from the first and second precursor films, respectively; (f) applying a coating composition comprising a binder and a solvent to both sides of the bilayer support and drying the coating to form a functional layer; and (g) dividing the bilayer support into two separators along the interface formed by the lamination, it is possible to achieve a good balance between productivity and quality of the separator and improve them.

[0026] The effects of the present invention are not limited to the effects described above, but should be understood to include all effects that can be inferred from the configuration of the invention described in the detailed description of the present invention or the claims. [Brief explanation of the drawings]

[0027] [Figure 1] 3 illustrates a method for manufacturing a separator according to one embodiment of the present invention. [Figure 2] 1 illustrates a method for manufacturing a dual layer support (or separator) according to the prior art. [Figure 3] 1 illustrates a method for measuring thickness deviation of a dual layer support according to one embodiment of the present invention. [Figure 4] 3 illustrates a portion of a method for manufacturing a separator according to one embodiment of the present invention. [Figure 5] 4A and 4B show cross sections of a double-layer support and two separated separators. [Figure 6] FIG. 2 is a plan view of a dual layer support according to one embodiment of the present invention. [Figure 7] 1 illustrates a method for measuring and evaluating the properties of a separator according to one embodiment of the present invention. [Figure 8] 1 illustrates a method for manufacturing a dual-layer support according to a comparative example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0028] The present invention will be described below with reference to the accompanying drawings. However, the present invention can be implemented in various different forms and is not limited to the embodiments described herein. In addition, in the drawings, parts that are not relevant to the description are omitted in order to clearly explain the present invention, and similar parts throughout the specification are designated by similar reference numerals.

[0029] Throughout this specification, when a part is "connected" to another part, this includes not only when it is "directly connected" to another part, but also when it is "indirectly connected" with another member interposed therebetween. Furthermore, when a part is described as "comprising" any component, it does not mean that it excludes other components, but that it may further comprise other components, unless otherwise specified.

[0030] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0031] FIG. 1 shows a method for manufacturing a separator according to one embodiment of the present invention. Referring to FIG. 1 , a method for producing a separator according to one embodiment of the present invention may include the steps of: (a) extruding a first composition containing a first polyolefin and a first pore-forming agent to produce a first sheet; (b) extruding a second composition containing a second polyolefin and a second pore-forming agent to produce a second sheet; (c) stretching the first and second sheets in the machine direction (MD) to produce first and second precursor films, respectively; (d) laminating the first and second precursor films to obtain a laminate; (e) stretching the laminate in the transverse direction (TD), and then removing the first and second pore-forming agents from the laminate to obtain a bilayer support comprising first and second layers derived from the first and second precursor films, respectively; (f) applying a coating composition containing a binder and a solvent to both sides of the bilayer support, followed by drying, to form a functional layer; and (g) dividing the bilayer support into two separators along the interface formed by the lamination.

[0032] In steps (a) and (b), the first and second compositions, which may be the same or different, can be independently extruded to produce the first and second sheets. The extrusion can be carried out using two independent extruders (first and second extruders) arranged in parallel to each other. The first and second extruders may have the same structure, configuration, specifications, capacity, etc., or, if necessary, the first and second extruders can be designed differently to adjust and optimize the compositions and physical properties of the first and second compositions, and thereby the physical properties of the first and second layers constituting the double-layer support. The first and second compositions can be melted and kneaded in the first and second extruders, and then extruded at a predetermined thickness using a device or equipment, such as a T-die, installed at the rear ends of the first and second extruders to produce the first and second sheets.

[0033] The first and second polyolefins may each comprise one selected from the group consisting of polyethylene, polypropylene, polybutylene, polymethylpentene, ethylene vinyl acetate, ethylene butyl acrylate, ethylene ethyl acrylate, and combinations or copolymers of two or more thereof, preferably polyethylene and / or polypropylene, more preferably polyethylene, but are not limited thereto.

[0034] The weight-average molecular weight of the first and second polyolefins may be 300,000 to 4,000,000, and the molecular weight distribution (Mw / Mn) may be 3 to 7. The first and second polyolefins may be the same and / or of the same quality, or may be different and / or of different qualities, as needed. If the molecular weight distribution of the first and second polyolefins is less than 3, dispersibility with the first and second pore-forming agents may decrease, resulting in a decrease in the uniformity of the produced bilayer substrate. If the molecular weight distribution is greater than 7, the mechanical properties of the bilayer substrate may decrease.

[0035] The terms "weight average molecular weight" and "molecular weight distribution" used in this specification may refer to values ​​measured by gel permeation chromatography (GPC) using polystyrene as a standard sample according to a method described in the literature (e.g., Macromolecules, Vol. 34, No. 19, pp. 6812-6820 (2001)).

[0036] When the first and second polyolefins are different, the first polyolefin may be a high-density polyethylene (HDPE) having a weight-average molecular weight of 300,000 to 800,000, and the second polyolefin may be an ultra-high molecular weight polyethylene (UHMWPE) having a weight-average molecular weight of 1,000,000 to 4,000,000. Generally, the high-density polyethylene contributes to the mechanical properties of the substrate, such as tensile strength, tensile elongation, and puncture resistance, and the UHMWPE contributes to the heat resistance of the substrate. Therefore, the combination of the two can achieve the mechanical properties and heat resistance of the substrate in a mutually complementary manner. However, these effects are not necessarily mutually complementary, and in some cases, the mechanical properties and / or heat resistance may be further improved.

[0037] The ratio of the weight average molecular weight of the second polyolefin to the weight average molecular weight of the first polyolefin may be 0.5 to 2, preferably 0.65 to 1.5. If the ratio is less than 0.5 or more than 2, the deviations in structural, mechanical properties, and / or heat resistance of the first and second layers derived from the first and second compositions in the bilayer support may fall outside the allowable range, resulting in reduced compatibility with batteries.

[0038] The first and second pore-forming agents may each be paraffin oil having a kinematic viscosity of 50 to 100 cSt at 40°C. The first and second pore-forming agents may be the same type and / or of the same quality, or, if necessary, different types and / or of different qualities. If the kinematic viscosity at 40°C of the first and second pore-forming agents is outside the above range, the viscosity of the first and second compositions may become excessively low or high, resulting in reduced processability and dispersibility. In addition to the paraffin oil, the first and second pore-forming agents may each be one selected from the group consisting of paraffin wax, mineral oil, solid paraffin, soybean oil, rapeseed oil, palm oil, coconut oil, di-2-ethylhexyl phthalate, dibutyl phthalate, diisononyl phthalate, diisodecyl phthalate, bis(2-propylheptyl) phthalate, naphthenic oil, and combinations of two or more thereof, but are not limited thereto. The first and second compositions may each contain 20 to 50% by weight of the first and second polyolefins and 50 to 80% by weight of the pore-forming agent.

[0039] The first and / or second compositions may further contain a hydrophilic polymer. Substrates made solely of the first and second polyolefins are inherently hydrophobic, but a predetermined amount of hydrophilic polymer can be melted and kneaded with the polyolefin during the production of the substrate to impart a desired hydrophilicity to the substrate. In this case, the molecular weight of the polyolefin and the content of the hydrophilic polymer in the substrate are derived and combined as variables that optimize the affinity of the substrate for the coating composition and the resulting coatability and impregnation properties. This allows for a balanced realization of the productivity of the process for melting and kneading the hydrophilic polymer with the polyolefin, the hydrophilicity of the substrate, and the resulting coatability and impregnation properties of the coating composition.

[0040] The layer further comprising the hydrophilic polymer in the bilayer support may have a hydrophobic region containing the polyolefin and a hydrophilic region containing the hydrophilic polymer dispersed in the hydrophobic region. The content of the hydrophilic region in the layer may be 0.1 to 7.5 wt %, which can be achieved by adjusting the content of the hydrophilic polymer in the first or second composition to the range of 0.1 to 5 wt %.

[0041] In the layer, the hydrophobic region composed of the first or second polyolefin and the hydrophilic region composed of the hydrophilic polymer can constitute a continuous phase and a discontinuous phase, respectively. In the layer, the hydrophilic region is uniformly dispersed in a matrix composed of the hydrophobic region, which can impart substantially uniform hydrophilicity to the entire region along the area and / or thickness direction of the layer, thereby improving the layer's ability to be impregnated with a coating composition. As used herein, the term "matrix" refers to the component that constitutes the continuous phase in a layer containing two or more components or a bilayer support. That is, in the layer, the hydrophobic region containing the polyolefin may exist as a continuous phase, and the hydrophobic region containing the hydrophilic polymer may exist dispersed therein as a discontinuous phase.

[0042] The content of the hydrophilic region in the layer may be 0.1 to 7.5 wt%, preferably 1 to 6 wt%, and more preferably 3 to 6 wt%. A hydrophilic region content of 0.1 wt% may result in insufficient application and impregnation of the coating composition. A content of more than 7.5 wt% may further improve application and impregnation of the coating composition, but may result in a deterioration in the mechanical properties and heat resistance of the support, which can be achieved through the polyolefin. Furthermore, a content of the hydrophilic region greater than 7.5 wt% may result in a decrease in the dispersibility of the hydrophilic polymer, leading to an increase in the number of surface defects (having a different brightness from the surrounding area and measuring 2 mm or larger) on the surface of the layer, which may result in a deterioration in appearance. Furthermore, a sudden change in resistance may occur at sites and / or regions where the hydrophilic polymer randomly aggregates on the surface and / or inside the layer, which may adversely affect the electrochemical properties of the battery.

[0043] When the first or second polyolefin to be mixed with the hydrophilic polymer is high-density polyethylene (HDPE), the weight-average molecular weight of the polyethylene may be 200,000 to 800,000, preferably 250,000 to 600,000, more preferably 300,000 to 500,000, and the ratio of the content of the hydrophilic region to the weight-average molecular weight of the high-density polyethylene is 0.1 × 10 -5 ~1.1×10 -5 , preferably 0.2 x 10 -5 ~1×10 -5 , more preferably 0.5 × 10 -5 ~1×10 -5 may be.

[0044] The ratio of the content of the hydrophilic region to the weight average molecular weight of the high-density polyethylene is 0.1 × 10 -5 If the thickness is less than 1.1 × 10, the required level of impregnation of the coating composition cannot be achieved. -5If the ratio of the content of the hydrophilic region to the weight average molecular weight of the high density polyethylene is greater than 1.1×10, the impregnation of the coating composition may be reduced, and the mechanical properties and heat resistance of the support may be reduced. -5 If the thickness is larger, the dispersibility of the hydrophilic polymer may decrease, the number of surface defects having a different brightness from the surrounding area on the surface of the support and a size of 2 mm or more may increase, and the appearance quality may decrease.In addition, the resistance may suddenly change at sites and / or regions where the hydrophilic polymer randomly aggregates on the surface and / or inside of the support, which may adversely affect the electrochemical properties of the battery.

[0045] In addition, when the first or second polyolefin mixed with the hydrophilic polymer is ultra-high molecular weight polyethylene (UHMWPE), the weight average molecular weight of the polyethylene may be 1,000,000 to 4,000,000, preferably 1,000,000 to 2,000,000, and the ratio of the content of the hydrophilic region to the weight average molecular weight of the ultra-high molecular weight polyethylene is 0.1 × 10 -5 ~0.75×10 -5 , preferably 0.15 x 10 -5 ~0.6×10 -5 , more preferably 0.3 × 10 -5 ~0.6×10 -5 may be.

[0046] The ratio of the content of the hydrophilic region to the weight average molecular weight of the ultra-high molecular weight polyethylene is 0.1 × 10 -5 If the thickness is less than 0.75 × 10, the required level of application and impregnation of the coating composition cannot be achieved. -5 If the ratio of the content of the hydrophilic region to the weight average molecular weight of the ultra-high molecular weight polyethylene is greater than 0.75×10, not only the application and impregnation properties of the coating composition may be reduced, but also the mechanical properties and heat resistance of the support that can be achieved through the ultra-high molecular weight polyethylene may be reduced. -5If the thickness is larger, the dispersibility of the hydrophilic polymer may decrease, the number of surface defects having a different brightness from the surrounding area on the surface of the layer and a size of 2 mm or more may increase, and the appearance quality may decrease.In addition, the resistance may suddenly change at sites and / or regions where the hydrophilic polymer randomly aggregates on the surface and / or inside of the layer, which may adversely affect the electrochemical properties of the battery.

[0047] The hydrophilic polymer may be one selected from the group consisting of ethylene vinyl acetate, ethylene vinyl alcohol, polyvinyl alcohol, polyacrylic acid, polyoxyethylene-polyoxypropylene block copolymer, polyethylene glycol, polyethylene oxide, polyvinylpyrrolidone, polyvinyl acetal, polyvinyl butyral, cellulose derivatives, glycerol, and combinations of two or more thereof. Preferably, it may be ethylene vinyl acetate, and more preferably, it may be ethylene vinyl acetate with a vinyl acetate content of 15 to 30 wt%, but is not limited thereto. If the vinyl acetate content in ethylene vinyl acetate is less than 15 wt%, the mechanical properties and hydrophilicity of the support may be reduced. If it is more than 30 wt%, the processability and therefore the dispersibility of the hydrophilic polymer may be reduced. In addition to the above-mentioned hydrophilic polymers, various types of polymers having hydrophilic functional groups such as amine groups, amide groups, hydroxyl groups, and carboxylic acid groups in the main chain and / or side chains may also be used as the hydrophilic polymer.

[0048] Among the hydrophilic polymers, the ethylene vinyl acetate imparts soft properties, i.e., a predetermined flexibility, to the first and second polyolefins, thereby improving the tensile elongation of the first and second layers derived from the first and second compositions and the bilayer substrate including the same. It also increases the interlayer bonding strength of the first and second layers constituting the bilayer substrate, thereby contributing to improving mechanical properties such as puncture strength.

[0049] In the step (c), the first and second sheets can be stretched in the machine direction (MD) to produce first and second precursor films. The MD stretching of the first and second sheets can be performed using first and second stretchers installed at the rear ends of the first and second extruders, respectively.

[0050] The first and second stretching machines are devices that stretch the first and second sheets discharged from the first and second extruders, respectively, along the transport direction of the first and second sheets on a process line. The stretching direction of the first and second sheets by the first and second stretching machines can be defined as the machine direction (MD, mechanical direction). The first and second stretching machines may each be a roll stretching machine. The roll stretching machine includes multiple rolls along the transport direction of the sheet, and can stretch the sheet at a predetermined stretch ratio along the machine direction (MD) by rotating the rear roll faster than the front roll. The stretching ratio of the first and second sheets may be 2 to 20 times, preferably 5 to 10 times. The stretching ratios of the first and second sheets may be the same or different. Preferably, the stretching ratios are set to be the same in consideration of the adhesive strength of the first and second precursor films produced in step (c) and the resulting interlayer bonding strength, but are not limited thereto.

[0051] Referring to FIG. 2, in the conventional method of manufacturing a multilayer support and / or separator by laminating two or more supports and / or separators that have been completely removed through extrusion, stretching, extraction, and heat setting, there is a problem that the layers easily peel off because sufficient interlayer bonding strength cannot be imparted. To solve this problem, a step can be added in which two or more supports and / or separators are laminated and then re-stretched and heat set; however, the additional equipment and steps result in a problem of reduced productivity and economic efficiency.

[0052] In this regard, in the step (d), the first and second precursor films can be bonded together to obtain a laminate. The bonding may be performed using a predetermined bonding machine. The bonding machine may be a facility or device that bonds the first and second precursor films produced by the first and second stretching machines to each other. During the bonding, the first and second precursor films can be pressed against each other so that they come into contact with each other, and at least a portion of the interface between the first and second precursor films can be adhered.

[0053] Referring to FIG. 6, during lamination, the first and second precursor films are pressed against each other and the transverse direction (TD) ends of the first and second precursor films can be bonded. The bonding can be achieved by physical means, such as selective application of heat, ultrasound, high frequency, or laser, to the transverse direction (TD) ends of the first and second precursor films. This bonding can improve the running stability and coating workability of the bilayer substrate passing through a subsequent coating line, thereby more effectively preventing the warping phenomenon that occurs in conventional coating separators. The area ratio of the transverse direction (TD) ends of the first and second precursor films to the interface area may be 0.01 to 0.1. If the area ratio of the transverse direction (TD) ends of the first and second precursor films to the interface area is less than 0.01, the running stability and coating workability cannot be adequately improved. Furthermore, the transverse direction (TD) ends of the first and second layers can be cut and removed during separation to ensure smooth separation of the bilayer substrate in a subsequent process. The removed both ends of the first and second layers in the lateral direction (TD) are generally discarded, but if the area ratio of the both ends of the first and second layers in the lateral direction (TD) to the area of ​​the interface is greater than 0.1, the amount of discarded first and second layers increases, which may reduce productivity.

[0054] Furthermore, during lamination, the first and second precursor films may be pressed against each other to adhere the entire interface of the first and second precursor films. The adhesion may be achieved by a physical means such as heat, ultrasound, high frequency, or laser applied to the entire surface of the first and second precursor films. This adhesion can improve the running stability of the laminate and the bilayer substrate as they pass through equipment or devices for subsequent transverse direction (TD) stretching, extraction, heat setting, coating, and drying. This effectively eliminates structural non-uniformities, such as excessive deviations in the thickness and porosity of the outermost layer, that occur in conventional multilayer substrates and / or separators.

[0055] In step (e), the laminate is stretched in the transverse direction (TD), and then the first and second pore-forming agents are removed from the laminate to obtain a bilayer support comprising first and second layers derived from the first and second precursor films, respectively.

[0056] The transverse direction (TD) stretching of the laminate may be performed by a third stretching machine. The third stretching machine may stretch the laminate in the transverse direction (TD). The third stretching machine may be a tenter stretching machine. The tenter stretching machine may stretch the laminate at a predetermined stretching ratio by fixing both ends of the laminate in the transverse direction with predetermined members such as chucks or clips and separating the members in the transverse direction. The transverse direction (TD) stretching ratio of the laminate by the third stretching machine may be 2 to 20 times, preferably 5 to 10 times, but is not limited thereto.

[0057] Thereafter, a predetermined extraction solvent is applied to the laminate, and the first and second pore-forming agents can be simultaneously and selectively extracted and removed from the laminate, specifically, from the first and second precursor films that constitute the laminate. The first and second pore-forming agents can be extracted and removed by immersing the laminate in an impregnation bath containing a solution containing the extraction solvent for a predetermined time.

[0058] After extraction, the content of the pore-forming agent remaining on the surface and / or inside of the laminate may be 1 wt % or less. The extraction solvent may be, for example, methyl ethyl ketone, hexane, dichloromethane, etc., but is not limited to these. The time required to extract and remove the first and second pore-forming agents can be determined depending on the thickness and porosity of the laminate, and may be 10 minutes or less, preferably 5 minutes or less, when the thickness and porosity of the laminate are 1 to 15 μm and 40 to 70 vol %, respectively.

[0059] In addition, the laminate from which the first and second pore-forming agents have been extracted can be heated to remove the extraction solvent remaining in the laminate. Some of the extraction solvent applied in step (e) may remain on the surface and / or inside the laminate. Since the remaining extraction solvent may deteriorate the properties of subsequent processes and the resulting support, the extraction solvent remaining in the laminate can be removed by appropriately heating the laminate at a temperature equal to or higher than the boiling point of the extraction solvent.

[0060] The method for producing a separator may further include a step (e') of heat-setting the laminate after step (e). Heat-setting refers to a process of applying heat to the fixed laminate to forcibly fix the laminate, which is subject to shrinkage, and remove residual stress. A high heat-setting temperature is advantageous for reducing the shrinkage rate of the separator, specifically the heat shrinkage rate. However, if the temperature is too high, the laminate may partially melt, blocking the formed pores and reducing the transmittance. The heat-setting temperature is preferably selected within a range in which 10 to 30 wt. % of the crystalline portion of the laminate melts. Selecting a heat-setting temperature within this range can prevent problems such as insufficient rearrangement of polyolefin molecules within the laminate, resulting in ineffective removal of residual stress in the film, and partial melting, resulting in blocked pores and reduced transmittance. For example, the heat-setting temperature may be 120 to 140°C, preferably 123 to 135°C, and the heat-setting time may be 5 seconds to 1 minute.

[0061] In the double-layer support, the thickness deviation of the first layer or the second layer measured by the following formula may be 10% or less, preferably 1 to 8.5%, or 3 to 6.5%.

[0062] <expression> Thickness deviation (%) = {(maximum thickness) - (minimum thickness)} / (minimum thickness) x 100 Conventional manufacturing methods for multilayer substrates and / or separators involve interlayer intercalation, i.e., lamination, by coextrusion before the formation of pore structures by stretching, which can lead to problems with non-uniform structural properties of each layer during subsequent membrane removal processes such as stretching and extraction. Specifically, as thickness deviations between regions of the outermost layer of the multilayer substrate and / or separator increase, the mechanical properties of the multilayer substrate and / or separator itself can become non-uniform, leading to problems such as the fragility of breakage and fracture in areas significantly thinner than surrounding regions during battery assembly using the multilayer substrate and / or separator. These problems are particularly pronounced in thin-film separators (thicknesses of about 15 μm or less, preferably about 10 μm or less) that address the recent trend toward greater battery integration and higher capacity.

[0063] In this regard, the double-layer support is manufactured by stretching the first and second precursor films, which have been stretched in the machine direction (MD) and have formed predetermined pore structures, to form a laminate, which is then stretched in the cross direction (TD), and then extracting and removing the first and second pore-forming agents.This makes it possible to uniformize the structural properties of the first and second layers constituting the double-layer support and ensure stable mechanical properties, while minimizing the number of stretching machines required to manufacture the double-layer support, thereby improving productivity and economy.

[0064] Figure 3 shows a method for measuring the thickness deviation of a dual-layer support according to one embodiment of the present invention. Referring to Figure 3, the thickness deviation of the outermost layer can be calculated using the thickness of each test piece measured by the following method and the above formula. In the above formula, the thickness deviation is determined by a method including the steps of: cutting the dual-layer support to a size of 100 mm x 100 mm (MD x TD), then dividing it into five equal parts in the machine direction (MD) to obtain five test pieces each measuring 20 mm x 100 mm (MD x TD); measuring the thickness of the outermost layer at the center of the test piece in the machine direction (TD); and calculating the thickness deviation using the above formula based on the maximum and minimum thickness values.

[0065] The double-layer support satisfies at least one, preferably all, of the following conditions (i) to (vi): (i) a thickness of 1 to 15 μm, preferably 5 to 12 μm, (ii) a puncture strength of 600 gf or more, preferably 650 to 1,000 gf, more preferably 700 to 900 gf, and (iii) a machine direction (MD) tensile strength of 1,300 to 2,000 kgf / cm. 2 , preferably 1,400 to 1,800 kgf / cm 2 (iv) Transverse direction (TD) tensile strength is 3,000 to 6,000 kgf / cm 2 , preferably 3,500 to 5,500 kgf / cm 2 , and more preferably 4,000 to 5,400 kgf / cm 2 (v) a machine direction (MD) tensile elongation of 150 to 450%, preferably 200 to 400%, more preferably 230 to 350%, and (vi) a transverse direction (TD) tensile elongation of 30 to 100%, preferably 40 to 90%.

[0066] FIG. 4 shows a part of a method for manufacturing a separator according to one embodiment of the present invention, and FIG. 5 shows a cross section of a double-layer support and two divided separators corresponding to areas A and B of FIG.

[0067] Referring to FIG. 4, a method for manufacturing a separator according to one embodiment of the present invention may include: (f) applying a coating composition containing a binder and a solvent to both sides of the bilayer support obtained in step (e) and drying the coating composition to form a functional layer; and (g) dividing the bilayer support into two separators along the interface formed by the lamination.

[0068] Fig. 5(a) is a cross-sectional view of the double-layer support passing through region A in Fig. 4. Referring to Fig. 5(a), the double-layer support may include the first and second layers bonded together so as to face each other with a predetermined interface as the reference.

[0069] In step (f), a coating composition (slurry) containing a binder and a solvent is applied to both sides of the dual-layer substrate, and then dried to remove the solvent and other liquid residues contained in the coating composition at once, thereby forming a functional layer. The coating compositions applied to both sides of the dual-layer substrate may have the same composition and physical properties, or at least one of them may be different.

[0070] Figure 5(b) is a cross-sectional view of the double-layer support passing through region B in Figure 4. Referring to Figures 4 and 5(b), a coating line for applying the coating composition may include a first coater facing one side of the double-layer support running therethrough, for example, disposed above the double-layer support, and a second coater facing the other side of the double-layer support, for example, disposed below the double-layer support.

[0071] The upper surface of the first layer and the lower surface of the second layer can constitute both surfaces of the bilayer support. The first coater can apply the coating composition having a predetermined composition to the upper surface of the first layer that constitutes the upper layer of the bilayer support to form a first functional layer, and the second coater can apply the coating composition having a predetermined composition to the lower surface of the second layer that constitutes the lower layer of the bilayer support to form a second functional layer.

[0072] The first and second coaters may each be one selected from the group consisting of a roll coater, a bar coater, a spray coater, a die coater, a comma coater, and a combination of two or more thereof, and may preferably be a roll coater and / or a bar coater, but are not limited to these.

[0073] The binder may be one selected from the group consisting of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, ethylene vinyl acetate, polyimide, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, hydroxyethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, polyvinyl alcohol, polyvinyl butyral, acrylonitrile-acrylic acid copolymer, ethylene-acrylic acid copolymer, styrene-butadiene copolymer, alkyl acrylate-acrylonitrile copolymer, polyethylene glycol, acrylic rubber, and a combination of two or more thereof, and preferably, but is not limited to, carboxymethyl cellulose and alkyl acrylate-acrylonitrile copolymer. For example, the carboxymethyl cellulose and alkyl acrylate-acrylonitrile copolymer may be present in the functional layer in a weight ratio of 1:0.5 to 1.5, respectively.

[0074] The coating composition may further include inorganic particles selected from the group consisting of SiO, AlO(OH), Mg(OH), Al(OH), TiO, BaTiO, LiO, LiF, LiOH, LiN, BaO, NaO, LiCO, CaCO, LiAlO, AlO, SiO, SnO, SnO, PbO, ZnO, PO, CuO, MoO, VO, BO, SiN, CeO, MnO, SnPO, SnBO, SnBPO, and combinations of two or more thereof. The inorganic particles may contribute to improving the heat resistance of the functional layer and the separator. The inorganic particles may be, but are not limited to, AlO and / or AlO(OH).

[0075] The content of the inorganic particles in the functional layer may be 50 to 99% by weight. If the content of the inorganic particles in the functional layer is less than 50% by weight, the required level of heat resistance cannot be imparted, and if it is more than 99% by weight, the dispersibility of the inorganic particles may decrease, and coating workability and processability may decrease.

[0076] The inorganic particles tend to aggregate due to electrostatic attraction. Such aggregation of inorganic particles can hinder the uniformity of physical properties on the separator surface. In this regard, the coating composition may further contain additives, such as a dispersant or surfactant, to improve the dispersibility of the inorganic particles. In particular, the coating composition may contain sodium hexametaphosphate ((NaPO3)6) as a dispersant, and the content of sodium hexametaphosphate in the functional layer may be 0.01 to 1 wt %, preferably 0.01 to 0.5 wt %. The sodium hexametaphosphate is adsorbed to the edges of the inorganic particles, particularly plate-like inorganic particles, weakening the negative charge on the edges, effectively preventing the inorganic particles from aggregating. This improves the storage stability of the coating composition for forming the functional layer and the dispersibility of the inorganic particles in the functional layer.

[0077] To prepare the water-soluble coating composition, the solvent may be one selected from the group consisting of methanol, ethanol, propanol, butanol, methoxyethanol, ethoxyethanol, lactone, acetonitrile, n-methyl-2-pyrrolidone (NMP), formic acid, nitromethane, acetic acid, dimethyl sulfoxide, water, and a combination of two or more thereof, preferably ethanol and water, more preferably ethanol and water mixed in a weight ratio of 1:10 to 50, but is not limited thereto.

[0078] The coating composition may contain 30 to 100 parts by weight of inorganic particles and 1 to 20 parts by weight of binder per 100 parts by weight of solvent, and may be preferably water-soluble (aqueous or aqueous). The solid content of the coating composition can be adjusted to 20 to 50% by weight, preferably 30 to 40% by weight, taking into consideration the balance between processability, workability, and heat resistance. The coating composition may further contain a certain amount of dispersant, for example, 0.01 to 0.5 parts by weight of sodium hexametaphosphate.

[0079] The thickness of the functional layer formed on each side of the bilayer support, i.e., on one side and the other side, may be the same or different. The thickness of the functional layer formed on one side or the other side of the bilayer support may be 1 to 10 μm. If the thickness of the functional layer is less than 1 μm, the required level of adhesiveness and heat resistance cannot be imparted, and if it is more than 10 μm, the separator becomes too thick, which can hinder the increase in capacity, miniaturization, and integration of the battery or device.

[0080] In addition, before applying the coating composition to both sides of the dual-layer substrate in step (f), the dual-layer substrate can be plasma-treated in the presence of a mixed gas containing sulfur dioxide (SO2) and oxygen (O2). The plasma treatment can hydrophilize the surfaces of the first and second layers and / or the surfaces of the internal pores of the dual-layer substrate, improving the bonding strength between the coating composition and both sides of the dual-layer substrate, thereby significantly improving the durability of the separator, particularly its long-term durability and heat resistance.

[0081] Conventionally, a wet process has been used to hydrophilize the surface of a support, in which the support is immersed in sulfuric acid or the like for a certain period of time to sulfonate it. However, this wet process is performed separately from the plasma treatment, either before or after the plasma treatment, which makes the process complicated and generates a large amount of wastewater. In this regard, the process gas used in the plasma treatment contains not only conventional air, oxygen, and / or inert gases, but also a certain amount of sulfur dioxide gas. Therefore, functional groups such as -SO3 are generated on the surface of the support and the surfaces of the internal pores through a single dry process such as the plasma treatment, without a wet process such as immersing the support in sulfuric acid, i.e., sulfonation, thereby maximizing the hydrophilicity and ionic conductivity of the porous support. This simplifies the conventional complicated process and is advantageous from an environmental perspective.

[0082] The mixed gas used as the process gas during the plasma treatment may contain 50-90% by volume of sulfur dioxide and 10-50% by volume of oxygen, preferably 60-80% by volume of sulfur dioxide and 20-40% by volume of oxygen, and more preferably 70-80% by volume of sulfur dioxide and 20-30% by volume of oxygen. If the sulfur dioxide content in the mixed gas is less than 50% by volume, the required level of hydrophilicity of the support cannot be achieved. If the sulfur dioxide content is greater than 90% by volume, the process may become unstable. The plasma treatment may be carried out for 0.5-90 minutes, preferably 0.5-20 minutes. If the plasma treatment is carried out for less than 0.5 minutes, the required level of hydrophilicity and sulfonation of the support cannot be achieved. If the plasma treatment is carried out for longer than 90 minutes, the hydrophilicity and sulfonation levels may converge to a certain level, resulting in reduced process efficiency.

[0083] In step (g), the bilayer support can be divided into two separators along the interface formed by the lamination. Figure 5(c) shows a cross section of the two separated separators. Referring to Figure 5(c), the bilayer support can be divided along the interface formed by the lamination into a first separator including a first functional layer formed on one side of the first layer by the first coater, and a second separator including a second functional layer formed on one side of the second layer by the second coater.

[0084] The steps (a) to (g) can be performed continuously, thereby simultaneously producing two cross-section coated separators through a single coating and drying line. Furthermore, it is possible to simultaneously produce 2n cross-section coated separators through n coating and drying lines. Therefore, the separator manufacturing method not only has excellent productivity, but also achieves separator properties at levels equal to or superior to those of conventional separators, based on the mechanical properties, running stability, and workability of the double-layer support ensured by the coating and drying line.

[0085] Another aspect of the present invention provides a separator manufactured using the separator manufacturing method, the separator having properties measured by a method including the steps of: (i) fixing the center of a roll of the separator to a first member, unwinding one end of the separator in the machine direction (MD) horizontally, and connecting the roll to a second member that fixes the separator in the horizontal direction; and (ii) checking deformation of the separator after one hour under conditions of a temperature of 25°C and a humidity of 40%, and measuring the vertical displacement due to the deformation; and the separator satisfies at least one of the following conditions (1) and (2):

[0086] (1) No deformation or vertical displacement of the separator; (2) Five or fewer descending regions are formed vertically in the separator, and the distance between the surface to which the separation membrane is horizontally fixed and the lowest end of the descending region is 10% or less of the transverse (TD) width of the separator.

[0087] The term "depressed region" as used herein refers to a region where the separator, which is horizontally fixed between the first and second members, is partially and / or completely released by gravity, descends vertically, and sags. The depressed region may be formed along the machine direction (MD) and / or the transverse direction (TD) of the separator, and its shape and size are not particularly limited.

[0088] 7 shows a method for measuring and evaluating the characteristics of a separator according to one embodiment of the present invention. The separator may be one of the first and second separators separated in step (g), and the composition, thickness, effects, etc. of the first and / or second layer and the first and / or second functional layer are as described above.

[0089] Recently, with the increasing demand for large-capacity batteries, the thickness of the support has tended to be thinner, to about 15 μm or less, but this thinning inevitably reduces the mechanical properties of the support, resulting in poor running stability, and also poses the problem of deformation such as wrinkles and warping occurring in the support during the application and drying of a liquid coating composition for forming the functional layer. If any wrinkles or warping occurs in the support and the separator including the functional layer, not only does this reduce assembly with the battery, but the distribution of materials such as inorganic particles and binders contained in the functional layer may become uneven during long-term storage due to the wrinkles and warping, causing local deviations in the physical properties of the separator and reducing product reliability.

[0090] In the case of a separator including the functional layer formed by coating and drying a liquid coating composition, it is very important to achieve and maintain uniform smoothness, resulting physical properties, and structural stability for a long period of time.

[0091] The double-layer substrate obtained through steps (a) to (e) can satisfy the mechanical properties, running stability, and coating workability required for step (f). Specifically, the first and second layers of the double-layer substrate complement each other in thickness and mechanical properties, so that appropriate coating workability can be ensured even when the thicknesses of the first and second layers of the double-layer substrate are controlled to be thin or the running speed of the coating line is increased to 80 m / min, preferably 100 m / min or more.

[0092] Hereinafter, embodiments of the present invention will be described in detail.

[0093] Manufacturing Example 1 A first composition prepared by mixing 28 parts by weight of high-density polyethylene (HDPE) having a weight-average molecular weight of 600,000 and 72 parts by weight of paraffin oil having a kinematic viscosity of 70 cSt at 40°C was fed into a twin-screw extruder (first extruder, inner diameter 58 mm, L / D = 56). The extrusion was discharged from the first extruder into a 400 mm wide T-die at a screw rotation speed of 120 rpm and a temperature of 210°C, and then passed through a casting roll at 70°C to produce a first sheet having a thickness of 800 μm.

[0094] A second composition identical to the first composition was fed into a twin-screw extruder (second extruder, inner diameter 58 mm, L / D = 56) having the same configuration as the first extruder and arranged in parallel. The extrusion was discharged from the second extruder into a 400 mm wide T-die at a screw rotation speed of 120 rpm and a temperature of 210°C, and then passed through a casting roll at a temperature of 70°C to produce a second sheet having a thickness of 800 μm.

[0095] The first and second sheets were fed into first and second stretching machines (roll stretching machines) arranged parallel to each other, and stretched 8 times in the machine direction (MD) at 120°C to produce first and second precursor films. Here, the first and second stretching machines refer to the stretching machines installed at the rear ends of the first and second extruders, respectively.

[0096] The first and second precursor films were fed into a laminating machine installed at the rear end of the first and second stretching machines, and a laminate was obtained in which the first and second precursor films were laminated together while facing each other.

[0097] The laminate was placed in a third stretching machine (tenter stretching machine) and stretched 9 times in the transverse direction (TD) at 126°C, then immersed in a dichloromethane leaching bath at 25°C for 1 minute to extract and remove the paraffin oil, and dried for 5 minutes at 38°C. The laminate was stretched 1.5 times in the transverse direction (TD) at 138°C, then relaxed by 10% and heat-set to produce a support (double layer) comprising first and second layers derived from the first and second precursor films, respectively.

[0098] Manufacturing Example 2 A support (double layer) was prepared in the same manner as in Preparation Example 1, except that in the second composition, high density polyethylene (HDPE) having a weight average molecular weight of 600,000 was replaced with ultra high molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 1,000,000.

[0099] Manufacturing Example 3 A support (double layer) was prepared in the same manner as in Preparation Example 1, except that the second composition further contained ethylene vinyl acetate (EVA, HTC) with a vinyl acetate content of 28 wt %, and the contents (parts by weight) of the high-density polyethylene, ethylene vinyl acetate, and paraffin oil in the second composition were changed to 30.4 parts by weight, 1.6 parts by weight, and 68.0 parts by weight, respectively.

[0100] Production Example 4 A support (double layer) was prepared in the same manner as in Preparation Example 3, except that in the second composition, high density polyethylene (HDPE) having a weight average molecular weight of 600,000 was replaced with ultra high molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 1,000,000.

[0101] Manufacturing Example 5 A support (double layer) was prepared in the same manner as in Preparation Example 1, except that ultrasonic waves of 50 kHz were applied to the entire surface of the laminate during lamination, thereby completely bonding (fusing) the interface of the laminate.

[0102] Manufacturing Example 6 A support (double layer) was prepared in the same manner as in Preparation Example 2, except that during lamination, ultrasonic waves of 50 kHz were applied to the entire surface of the laminate to completely bond (fuse) the interface of the laminate.

[0103] Manufacturing Example 7 A support (double layer) was prepared in the same manner as in Preparation Example 3, except that during lamination, ultrasonic waves of 50 kHz were applied to the entire surface of the laminate to completely bond (fuse) the interface of the laminate.

[0104] Manufacturing Example 8 A support (double layer) was prepared in the same manner as in Preparation Example 4, except that during lamination, ultrasonic waves of 50 kHz were applied to the entire surface of the laminate to completely bond (fuse) the interface of the laminate.

[0105] Manufacturing Example 9 A support (double layer) was prepared in the same manner as in Preparation Example 1, except that both ends of the laminate, which accounted for 2% of the total area (planar area) of the interface of the laminate, were heated during lamination to bond (fuse) both ends of the laminate in the transverse direction (TD). The areas (planar areas) and specifications of the bonded portions at both ends of the laminate in the transverse direction (TD) are symmetrical to each other with respect to the center line in the transverse direction (TD).

[0106] Manufacturing Example 10 A support (double layer) was prepared in the same manner as in Preparation Example 9, except that in the second composition, high density polyethylene (HDPE) having a weight average molecular weight of 600,000 was replaced with ultra high molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 1,200,000.

[0107] Manufacturing Example 11 A support (double layer) was prepared in the same manner as in Preparation Example 9, except that in the second composition, high density polyethylene (HDPE) having a weight average molecular weight of 600,000 was replaced with ultra high molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 1,500,000.

[0108] Manufacturing Example 12 A support (double layer) was prepared in the same manner as in Preparation Example 9, except that in the second composition, high density polyethylene (HDPE) having a weight average molecular weight of 600,000 was replaced with ultra high molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 2,000,000.

[0109] Manufacturing Example 13 A support (double layer) was prepared in the same manner as in Preparation Example 9, except that in the second composition, high density polyethylene (HDPE) having a weight average molecular weight of 600,000 was replaced with ultra high molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 2,500,000.

[0110] Manufacturing Example 14 A support (double layer) was prepared in the same manner as in Preparation Example 9, except that in the second composition, high density polyethylene (HDPE) having a weight average molecular weight of 600,000 was replaced with ultra high molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 3,700,000.

[0111] Manufacturing Example 15 A support (double layer) was prepared in the same manner as in Preparation Example 9, except that in the second composition, high density polyethylene (HDPE) having a weight average molecular weight of 600,000 was replaced with ultra high molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 4,000,000.

[0112] Comparative Manufacturing Example 1 25 parts by weight of a mixture containing 60% by weight of ultra-high molecular weight polyethylene with a weight average molecular weight of 2,000,000 and 40% by weight of high-density polyethylene with a weight average molecular weight of 560,000, and 75 parts by weight of paraffin oil with a kinematic viscosity of 35 cSt at 40°C were charged into a twin-screw extruder (first extruder, inner diameter 58 mm, L / D=56) and melt-kneaded at a screw rotation speed of 250 rpm and 230°C to produce a first polyolefin solution.

[0113] 30 parts by weight of a mixture containing 50% by weight of high-density polyethylene with a weight-average molecular weight of 560,000 and 50% by weight of polypropylene with a weight-average molecular weight of 1,600,000, and 70 parts by weight of paraffin oil with a kinematic viscosity of 35 cSt at 40°C were fed into a twin-screw extruder (second extruder, inner diameter 58 mm, L / D=56) having the same configuration as the first extruder and arranged in parallel, and melt-kneaded under the same conditions to produce a second polyolefin solution.

[0114] The first and second polyolefin solutions were fed from the first and second extruders to a three-layer T-die, respectively, and extruded so that the layer thickness ratio of the first / second / first polyolefin solutions was 35 / 30 / 35. The extrudate was cooled while receiving it on a cooling roll (diameter 500 mm) at 37 ° C. to produce a gel-like three-layer sheet. The gel-like three-layer sheet was simultaneously biaxially stretched 5 × 5 times (MD × TD) at 114 ° C., and then immersed in a dichloromethane leaching bath at 25 ° C. for 5 minutes to extract and remove the paraffin oil, producing a porous membrane. The porous membrane was placed in a tenter stretching machine, re-stretched 1.4 times in the transverse direction (TD) at 124 ° C., and then heat-set to produce a support (3 layers).

[0115] Comparative Manufacturing Example 2 29.5 parts by weight of high-density polyethylene with a weight-average molecular weight (Mw) of 350,000, 0.5 parts by weight of silane-modified high-density polyethylene, and 70 parts by weight of paraffin oil with a kinematic viscosity of 70 cSt at 40°C were mixed and charged into a twin-screw extruder (inner diameter 58 mm, L / D = 56). Dibutyltin dilaurate as a crosslinking catalyst was pre-dispersed in a portion of the paraffin oil and charged via the twin-screw extruder's side injector at 0.5 wt% based on the total weight of the material passing through the twin-screw extruder. The material was discharged from the twin-screw extruder through a 300 mm wide T-die at a screw rotation speed of 40 rpm and 200°C, and then passed through a casting roll at 40°C to produce a base sheet with a thickness of 800 μm.

[0116] The base sheet was stretched 6 times in the machine direction (MD) using a roll stretcher at 110 ° C., and stretched 7 times in the transverse direction (TD) using a tenter stretcher at 125 ° C. to produce a film. The film was immersed in a dichloromethane leaching bath at 25 ° C., paraffin oil was extracted and removed for 1 minute, and then dried at 50 ° C. for 5 minutes to produce a porous film. After heating to 125 ° C. using a tenter stretcher, the film was stretched 1.45 times in the transverse direction (TD), relaxed, and heat-set to 1.25 times the original stretching ratio. The film was crosslinked for 72 hours in a thermo-hygrostat at 85 ° C. and 85% humidity to produce a support (single layer).

[0117] Comparative Manufacturing Example 3 30 parts by weight of a mixture containing 64% by weight of ultra-high molecular weight polyethylene (UHMWPE) with a weight average molecular weight (Mw) of 1,000,000 and 36% by weight of ultra-high molecular weight polyethylene (UHMWPE) with a weight average molecular weight (Mw) of 1,500,000 were mixed with 70 parts by weight of paraffin oil with a kinematic viscosity of 70 cSt at 40°C, and the mixture was fed into a twin-screw extruder (inner diameter 58 mm, L / D = 56). The mixture was extruded from the twin-screw extruder at a screw rotation speed of 40 rpm and a temperature of 200°C into a 300 mm wide T-die, and then passed through a casting roll at a temperature of 40°C to produce a base sheet with a thickness of 800 μm.

[0118] The base sheet was stretched 6 times in the machine direction (MD) using a roll stretcher at 110 ° C., and stretched 7 times in the transverse direction (TD) using a tenter stretcher at 125 ° C. to produce a film. The film was immersed in a dichloromethane leaching bath at 25 ° C. for 1 minute to extract and remove the paraffin oil, and then dried at 50 ° C. for 5 minutes to produce a porous film. After that, it was heated to 125 ° C. in a tenter stretcher, stretched 1.45 times in the transverse direction (TD), relaxed, and heat-set to 1.25 times the stretched size before stretching to produce a support (single layer).

[0119] Comparative Manufacturing Example 4 A substrate (single layer) was prepared in the same manner as in Comparative Preparation Example 3, except that 30 parts by weight of a mixture containing 42% by weight of high-density polyethylene (HDPE) having a weight-average molecular weight (Mw) of 600,000 and 58% by weight of ultra-high molecular weight polyethylene (UHMWPE) having a weight-average molecular weight (Mw) of 1,500,000 was mixed with 70 parts by weight of paraffin oil having a kinematic viscosity of 70 cSt at 40°C, and the mixture was introduced into a twin-screw extruder (inner diameter 58 mm, L / D=56).

[0120] Comparative Manufacturing Example 5 100 parts by weight of a mixture containing 90% by weight of ultra-high molecular weight polyethylene (UHMWPE) with a weight-average molecular weight of 1,000,000 and 10% by weight of high-density polyethylene (HDPE) with a weight-average molecular weight of 380,000 was charged into a twin-screw extruder (first extruder, inner diameter 58 mm, L / D = 42). 250 parts by weight of paraffin oil was supplied via a side injector of the first extruder, and the mixture was melt-kneaded at 210°C and 100 rpm to produce a first polyethylene solution.

[0121] 100 parts by weight of a mixture containing 10% by weight of ultra-high molecular weight polyethylene (UHMWPE) with a weight-average molecular weight of 1,000,000 and 90% by weight of high-density polyethylene (HDPE) with a weight-average molecular weight of 380,000 was charged into a twin-screw extruder (second extruder, inner diameter 58 mm, L / D = 42). 250 parts by weight of paraffin oil was supplied via the side injector of the second extruder, and the mixture was melt-kneaded at 210°C and 100 rpm to produce a second polyethylene solution.

[0122] The first and second polyethylene solutions were passed through a multiblock (layering device) of an extruder to alternately layer the first and second polyethylene solutions, and then extruded through a T-die to form a multilayer structure consisting of 20 layers.

[0123] The multilayer structure was passed through a cooling roll adjusted to 40°C to produce a gel-like base sheet with a thickness of 1,100 μm. The base sheet was simultaneously biaxially stretched 8 × 8 times (MD × TD) at 124°C, then immersed in a dichloromethane leaching bath at 25°C for 10 minutes to extract and remove the paraffin oil, and dried at 50°C for 5 minutes to produce a porous membrane. The porous membrane was placed in a tenter stretching machine, re-stretched 1.4 times in the transverse direction (TD) at 125°C, and then heat-set to produce a support (multilayer).

[0124] Comparative Manufacturing Example 6 A support was produced as follows using the method shown in Figure 8. A first composition, prepared by mixing 28 parts by weight of high-density polyethylene (HDPE) with a weight-average molecular weight of 600,000 and 72 parts by weight of paraffin oil with a kinematic viscosity of 70 cSt at 40°C, was fed into a twin-screw extruder (first extruder, inner diameter 58 mm, L / D = 56). The extrusion was discharged from the first extruder at a screw rotation speed of 120 rpm and a temperature of 210°C into a 400 mm wide T-die, and then passed through a casting roll heated to 70°C to produce a first sheet with a thickness of 800 µm.

[0125] A second composition identical to the first composition was fed into a twin-screw extruder (second extruder, inner diameter 58 mm, L / D = 56) having the same configuration as the first extruder and arranged in parallel. The extrusion was discharged from the second extruder into a 400 mm wide T-die at a screw rotation speed of 120 rpm and a temperature of 210°C, and then passed through a casting roll at a temperature of 70°C to produce a second sheet having a thickness of 800 μm.

[0126] The first and second sheets were placed in a laminator attached to the rear end of the first and second extruders, where the first and second sheets were bonded together to form a laminate. The laminate was then placed in a stretching machine (roll stretching machine) and stretched 8 times in the machine direction (MD) at 120°C to produce a precursor film. The precursor film was then placed in a tenter stretching machine and stretched 9 times in the transverse direction (TD) at 126°C, after which it was immersed in a dichloromethane bath at 25°C for 1 minute to extract and remove the paraffin oil, and dried at 38°C for 5 minutes. The laminate was stretched 1.5 times in the transverse direction (TD) at 138°C, relaxed 10%, and heat-set to produce a support (double layer).

[0127] Experimental Example 1 Each support (single layer, double layer, triple layer, multilayer) manufactured in the above manufacturing examples and comparative manufacturing examples was cut to 100 mm x 100 mm, and then the cut support test pieces were divided into 5 equal parts in the machine direction (MD) to obtain test pieces 1 to 5 of 20 mm x 100 mm (MD x TD).

[0128] The cross section of each specimen was photographed using an SEM, and the thickness (μm) of the outermost layer was measured at the center of the transverse direction (TD) of each specimen. Based on this, the thickness deviation defined by the following formula was calculated and shown in Table 1 below.

[0129] <expression> Thickness deviation (%) = {(maximum thickness) - (minimum thickness)} / (minimum thickness) x 100 In the case of Production Examples 1 to 8 and Comparative Production Example 6, the layer derived from the first composition was selected as the outermost layer, and in the case of Comparative Production Examples 1 and 5, the layer derived from the first polyolefin solution was selected as the outermost layer. The separators according to Comparative Production Examples 2 to 4 had a single-layer structure and were therefore excluded from the measurement targets.

[0130] [Table 1]

[0131] Experimental Example 2 The thickness, punch strength, tensile strength, and tensile elongation of the substrates (single-layer, double-layer, triple-layer, and multi-layer) prepared in the Preparation Examples and Comparative Preparation Examples were measured as follows. Unless otherwise specified, measurements were performed at room temperature (25°C), and the results are shown in Table 2 below. - Thickness (μm): The thickness of the support test piece was measured using a micro thickness measuring instrument. - Puncture strength (gf): Using a puncture strength tester, force was applied with a stick to a separator test piece measuring 100 mm x 50 mm, and the force applied until the sample was punctured was measured.

[0132] -Tensile strength (kgf / cm 2 ): Using a tensile strength tester, the stress applied to a support specimen measuring 20 mm x 200 mm in the machine direction (MD) and transverse direction (TD) until fracture occurred was measured.

[0133] -Tensile elongation (%): Using a tensile strength tester, the percentage of elongation of a 20mm x 200mm support specimen in the machine direction (MD) and transverse direction (TD) until breakage occurred was measured.

[0134] [Table 2]

[0135] Reference example Carboxymethyl cellulose salt (CMC), acrylic-acrylonitrile copolymer latex, alumina (aluminum oxide, Al2O3), dispersant ((NaPO3)6), surfactant, water, and ethanol were mixed in the proportions shown in Table 3 below, and then dispersed in a ball mill to prepare a water-dispersed ceramic slurry.

[0136] [Table 3]

[0137] Example 1 The water-dispersed ceramic slurry of the Reference Example was applied to both sides of the support (double layer) of Preparation Example 1, gravure coated with a 110-mesh coating roll, and dried in a hot air oven at 80°C for 1 hour to form a functional layer (heat-resistant layer) with a thickness of 3 μm on each side. The machine direction (MD) speed of the laminate moving along the coating roll was 120 m / min. The laminate was divided along the interface formed by the bonding on the support, to produce a first separator having a first functional layer formed on one side of the first layer and a second separator having a second functional layer formed on one side of the second layer.

[0138] Example 2 First and second separators were prepared in the same manner as in Example 1, except that the support prepared in Preparation Example 9 was used instead of the support prepared in Preparation Example 1 (double layer).

[0139] Example 3 First and second separators were prepared in the same manner as in Example 1, except that the support of Preparation Example 12 was used instead of the support of Preparation Example 1 (double layer).

[0140] Example 4 First and second separators were prepared in the same manner as in Example 1, except that the support prepared in Preparation Example 13 was used instead of the support prepared in Preparation Example 1 (double layer).

[0141] Example 5 First and second separators were prepared in the same manner as in Example 1, except that the support of Preparation Example 15 was used instead of the support of Preparation Example 1 (double layer).

[0142] Comparative Example 1 30 parts by weight of high-density polyethylene (HDPE) with a weight-average molecular weight (Mw) of 350,000 and a molecular weight distribution (Mw / Mn) of 5 and 70 parts by weight of paraffin oil with a kinematic viscosity of 70 cSt at 40°C were mixed and charged into a twin-screw extruder (inner diameter 58 mm, L / D = 56). The mixture was extruded from the twin-screw extruder at a screw rotation speed of 40 rpm and a temperature of 200°C into a 300 mm wide T-die, and then passed through a casting roll at a temperature of 40°C to produce a base sheet with a thickness of 900 μm. The base sheet was stretched 6 times in the machine direction (MD) using a roll stretcher at 110 ° C., and then stretched 7 times in the transverse direction (TD) using a tenter stretcher at 125 ° C. to produce a film. The film was immersed in a dichloromethane leaching bath at 25 ° C., paraffin oil was extracted and removed for 1 minute, and then dried at 50 ° C. for 5 minutes to produce a porous film. The film was then relaxed 10% in the transverse direction (TD) at 130 ° C. and heat-set to produce a 9 μm-thick support (single layer). The water-dispersed ceramic slurry of the Reference Example was applied to one side of the substrate, gravure coated using a 110-mesh coating roll, and dried in a hot air oven at 80°C for 1 hour to produce a separator with a 3µm-thick functional layer (heat-resistant layer) formed on one side. The running speed of the substrate along the coating roll in the machine direction (MD) was 80m / min.

[0143] Comparative Example 2 A separator was manufactured in the same manner as in Comparative Example 1, except that the machine direction (MD) running speed of the substrate moving along the coating roll was changed to 100 m / min.

[0144] Comparative Example 3 A separator was manufactured in the same manner as in Comparative Example 1, except that the machine direction (MD) running speed of the substrate moving along the coating roll was changed to 120 m / min.

[0145] Comparative Example 4 30 parts by weight of high-density polyethylene (HDPE) with a weight-average molecular weight (Mw) of 350,000 and a molecular weight distribution (Mw / Mn) of 5 and 70 parts by weight of paraffin oil with a kinematic viscosity of 70 cSt at 40°C were mixed and charged into a twin-screw extruder (inner diameter 58 mm, L / D = 56). The mixture was extruded from the twin-screw extruder at a screw rotation speed of 40 rpm and a temperature of 200°C into a 300 mm wide T-die, and then passed through a casting roll at a temperature of 40°C to produce a base sheet with a thickness of 500 μm. The base sheet was stretched 6 times in the machine direction (MD) using a roll stretcher at 110 ° C., and then stretched 7 times in the transverse direction (TD) using a tenter stretcher at 125 ° C. to produce a film. The film was immersed in a dichloromethane leaching bath at 25 ° C., paraffin oil was extracted and removed for 1 minute, and then dried at 50 ° C. for 5 minutes to produce a porous film. The film was then relaxed 10% in the transverse direction (TD) at 130 ° C. and heat-set to produce a 5 μm-thick support (single layer). A separator was manufactured in the same manner as in Comparative Example 1, except that the water-dispersed ceramic slurry of the reference example was applied to one side of the support, and the thickness of the functional layer (heat-resistant layer) formed on one side of the support was changed to 2.5 μm.

[0146] Comparative Example 5 A separator was manufactured in the same manner as in Comparative Example 4, except that the running speed of the substrate moving along the coating roll in the machine direction (MD) was changed to 100 m / min.

[0147] Comparative Example 6 30 parts by weight of high-density polyethylene (HDPE) with a weight-average molecular weight (Mw) of 350,000 and a molecular weight distribution (Mw / Mn) of 5 and 70 parts by weight of paraffin oil with a kinematic viscosity of 70 cSt at 40°C were mixed and charged into a twin-screw extruder (inner diameter 58 mm, L / D = 56). The mixture was extruded from the twin-screw extruder at a screw rotation speed of 40 rpm and a temperature of 200°C into a 300 mm wide T-die, and then passed through a casting roll at a temperature of 40°C to produce a base sheet with a thickness of 400 μm. The base sheet was stretched 6 times in the machine direction (MD) using a roll stretcher at 110 ° C and 7 times in the transverse direction (TD) using a tenter stretcher at 125 ° C to produce a film. The film was immersed in a dichloromethane leaching bath at 25 ° C, paraffin oil was extracted and removed for 1 minute, and then dried at 50 ° C for 5 minutes to produce a porous film. Then, the film was relaxed 10% in the transverse direction (TD) at 130 ° C and heat-set to produce a 4 μm thick support. The separator was manufactured in the same manner as in Comparative Example 1, except that the water-dispersed ceramic slurry of the Reference Example was applied to one side of the support, and the thickness of the functional layer (heat-resistant layer) formed on one side of the support was changed to 2 μm.

[0148] Experimental Example 3 The thickness and heat shrinkage of the separators prepared in the examples and comparative examples were measured as follows. Unless otherwise specified, the measurements were performed at room temperature (25°C), and the results are shown in Table 4 below. - Thickness (μm): The thickness of the support test piece was measured using a micro thickness measuring instrument. Heat shrinkage rate (%): A separator test piece having a size of 200 x 200 mm was placed between A4 sheets of paper in an oven at 150°C for 1 hour, and then cooled to room temperature. The length of the test piece that had shrunk in the horizontal and vertical directions was measured, and the heat shrinkage rate was calculated using the following formula. Heat shrinkage rate (%) = (l3-l4) / l3 x 100 (In the above formula, l3 is the horizontal or vertical length of the test piece before shrinkage, and l4 is the horizontal or vertical length of the test piece after shrinkage.)

[0149] [Table 4]

[0150] Experimental Example 4 With the center of the roll on which the separators manufactured in the Examples and Comparative Examples were wound fixed to a dolly, one end of the separator in the machine direction (MD) was unwound horizontally and connected to a jig that fixes the separator in the horizontal direction (see FIG. 7). After 1 hour at a temperature of 25°C and a humidity of 40%, the separator was checked for deformation and the vertical displacement due to the deformation was measured. The deflection characteristics due to the deformation of the separator were evaluated as excellent (◎), good (○), or poor (X) according to the following criteria, and the results are shown in Table 5 below. -Excellent (◎): When there is no deformation or vertical displacement of the separator -Good (○): Five or fewer descending regions are formed in the vertical direction of the separator, and the distance between the surface where the separator is fixed horizontally and the bottom edge of the descending region is 10% or less of the width of the separator in the transverse direction (TD). - Poor (X): If not applicable to excellent or good

[0151] [Table 5]

[0152] The above description of the present invention is for illustrative purposes only, and those skilled in the art will understand that the present invention may be easily modified into other specific forms without changing the technical spirit or essential characteristics of the present invention. Therefore, the above-described embodiments are illustrative in all respects and should not be construed as limiting. For example, components described in a single form may be implemented in a distributed form, and similarly, components described in a distributed form may be implemented in a combined form.

[0153] The scope of the present invention is defined by the claims set forth below, and all changes and modifications that come within the meaning and scope of the claims and equivalent concepts should be construed as being within the scope of the present invention. [Explanation of symbols]

[0154] 11 1st layer 21 2nd layer 12 1st functional layer 22 2nd functional layer 30 Interface C. Center of the double-layer support E Lateral edge of double layer support S Separator 100 First member 200 Second member R1, R2 descending area r1, r2 Depth of the descending region

Claims

1. (a) extruding a first composition comprising a first polyolefin and a first pore former to form a first sheet; (b) extruding a second composition comprising a second polyolefin and a second pore former to form a second sheet; (c) stretching the first and second sheets in the machine direction (MD), respectively, to produce first and second precursor films; (d) laminating the first and second precursor films together to obtain a laminate; (e) removing the first and second pore formers from the laminate after stretching the laminate in the transverse direction (TD) to obtain a bilayer support comprising first and second layers derived from the first and second precursor films, respectively; (f) applying a coating composition comprising a binder and a solvent to both sides of the dual-layer support and drying to form a functional layer; and (g) dividing the bilayer support into two separators along the interface formed by the lamination.

2. 2. The method for producing a separator according to claim 1, wherein the first and second polyolefins each comprise one selected from the group consisting of polyethylene, polypropylene, polybutylene, polymethylpentene, ethylene vinyl acetate, ethylene butyl acrylate, ethylene ethyl acrylate, and combinations or copolymers of two or more thereof.

3. 3. The method for producing a separator according to claim 2, wherein the weight average molecular weight of each of the first and second polyolefins is 300,000 to 4,000,000.

4. 4. The method for producing a separator according to claim 3, wherein a ratio of a weight average molecular weight of the second polyolefin to a weight average molecular weight of the first polyolefin is 0.5 to 2.

5. The method for manufacturing a separator according to claim 1 , wherein at least one of the first and second compositions further contains a hydrophilic polymer.

6. 6. The method for producing a separator according to claim 5, wherein the content of the hydrophilic polymer in at least one of the first and second compositions is 0.1 to 5 wt %.

7. 6. The method for producing a separator according to claim 5, wherein the hydrophilic polymer is one selected from the group consisting of ethylene vinyl acetate, ethylene vinyl alcohol, polyvinyl alcohol, polyacrylic acid, polyoxyethylene-polyoxypropylene block copolymer, polyethylene glycol, polyethylene oxide, polyvinylpyrrolidone, polyvinyl acetal, polyvinyl butyral, cellulose derivatives, glycerol, and combinations of two or more thereof.

8. The method for producing a separator according to claim 1 , wherein the first and second precursor films are pressed against each other during the lamination process, and at least a portion of the interface between the first and second precursor films is adhered to each other.

9. 2. The method for producing a separator according to claim 1, wherein a thickness deviation of the first layer or the second layer measured by the following formula is 10% or less: <Formula> Thickness deviation (%) = {(maximum thickness) - (minimum thickness)} / (minimum thickness) x 100 In the above formula, the thickness deviation is determined by a method including the steps of cutting the double-layer support into a size of 100 mm x 100 mm (MD x TD), then dividing it into five equal parts in the machine direction (MD) to obtain five test pieces each having a size of 20 mm x 100 mm (MD x TD); measuring the thickness of the first layer or the second layer at the center of the test piece in the machine direction (TD); and calculating the thickness deviation using the above formula based on the maximum and minimum thickness values.

10. 2. The method for producing a separator according to claim 1, wherein the binder is one selected from the group consisting of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, ethylene vinyl acetate, polyimide, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, hydroxyethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, polyvinyl alcohol, polyvinyl butyral, acrylonitrile-acrylic acid copolymer, ethylene-acrylic acid copolymer, styrene-butadiene copolymer, alkyl acrylate-acrylonitrile copolymer, polyethylene glycol, acrylic rubber, and a combination of two or more thereof.

11. 2. The method for producing a separator according to claim 1, wherein the solvent is one selected from the group consisting of methanol, ethanol, propanol, butanol, methoxyethanol, ethoxyethanol, lactone, acetonitrile, n-methyl-2-pyrrolidone (NMP), formic acid, nitromethane, acetic acid, dimethyl sulfoxide, water, and a combination of two or more thereof.

12. The coating composition contains SiO ２ , AlO(OH), Mg(OH) ２ , Al(OH) ３ , TiO ２ , BaTiO ３ , Li ２ O, LiF, LiOH, Li ３ N, BaO, Na ２ O, Li ２ CO ３ , CaCO ３ , LiAlO ２ , Al ２ O ３ , SiO, SnO, SnO ２ , PbO ２ , ZnO, P ２ O ５ , CuO, MoO, V ２ O ５ , B ２ O ３ , Si ３ N ４ , CeO ２ , Mn ３ O ４ , Sn ２ P ２ O ７ , Sn ２ B ２ O ５ , Sn ２ BPO ６ The method for producing a separator according to claim 1 , further comprising one inorganic particle selected from the group consisting of: and a combination of two or more thereof.

13. A separator manufactured by the separator manufacturing method according to any one of claims 1 to 12, (i) a step of horizontally unwinding one end of the separator in the machine direction (MD) while fixing the center of the separator roll to a first member, and connecting the separator to a second member that fixes the separator in the horizontal direction; and (ii) checking the deformation of the separator after 1 hour under conditions of a temperature of 25°C and a humidity of 40%, and measuring the vertical displacement due to the deformation; and the separator properties measured by a method including the steps of: satisfying at least one of the following conditions (1) and (2): (1) No deformation or vertical displacement of the separator; (2) The separator has five or less vertically descending regions, and the distance between the surface to which the separator is horizontally fixed and the lowest end of the descending region is 10% or less of the transverse (TD) width of the separator.

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