Separator and manufacturing method therefor

Abstract

One aspect of the present invention provides a separator and a manufacturing method therefor. The separator comprises: a porous substrate; an electrode adhesive layer provided on one surface of the porous substrate and including first inorganic particles and a first binder for binding at least some of the first inorganic particles to one another; and a heat-resistant layer provided on the other surface of the porous substrate and including second inorganic particles and a second binder for binding at least some of the second inorganic particles to one another, wherein the content of the first binder in the electrode adhesive layer is 3-20 wt %.

Description

Membrane and its manufacturing method

[0001] The present invention relates to a separation membrane and a method for manufacturing the same.

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

[0003] As a means of achieving the above purpose, research and development is actively being conducted on a separator having micropores that separate the positive and negative electrodes to prevent internal short circuits and facilitate the movement of lithium ions during the charge and discharge process, and among them, a microporous separator using polyolefin such as polyethylene that is advantageous in forming pores by thermally induced phase separation, is economical, and easily satisfies the properties required for the separator.

[0004] Conventionally, widely used polyolefin-based separators suffer from poor heat resistance and mechanical strength. When exposed to temperatures of 150°C for approximately one hour, thermal shrinkage can reach 50-90%, leading to loss of membrane functionality. Furthermore, external impacts can cause internal short-circuits. To address these issues, a technology has been proposed that coats the surface of the separator with a heat-resistant layer containing ceramic particles.

[0005] However, these heat-resistant layers still leave significant technical challenges in relation to air permeability and conductivity (resistance), which are factors that have a very important impact on the performance of the separator. That is, when a heat-resistant layer containing ceramic particles is formed on the surface of a porous substrate, the heat resistance of the separator is improved, but the ceramic particles contained in the heat-resistant layer close the pores formed in the porous substrate, thereby reducing the air permeability of the separator, and accordingly, the ion transport path between the positive and negative electrodes is significantly reduced, resulting in a significant drop in the charge and discharge performance of the secondary battery. In addition, as the heat-resistant layer is continuously exposed to the electrolyte inside the battery, the ceramic particles may be partially and continuously detached from the porous substrate, and in this case, the heat resistance of the separator may also gradually deteriorate.

[0006] Meanwhile, attempts have been made to improve adhesion to electrodes and the resulting lifespan characteristics of secondary batteries by additionally forming adhesive layers containing adhesive materials on polyolefin-based separators or heat-resistant layers to enhance adhesion to electrodes. However, these adhesive layers can reduce the permeability and conductivity of the separator, and forming an adhesive layer on the heat-resistant layer requires at least two coating and drying processes, which reduces productivity and economic feasibility.

[0007] In this regard, a method of imparting a certain adhesive strength to the heat-resistant layer by including a certain amount of adhesive material in the heat-resistant layer, and a method of asymmetrically coating the adhesive layer and the heat-resistant layer on both sides of the separator have been proposed. However, in the former case, there is a problem that a certain trade-off occurs between adhesive strength and heat resistance, such as a relatively decrease in the content of ceramic particles in the heat-resistant layer due to the adhesive material, thereby lowering the heat resistance. In the latter case, there is a problem that the separator curls in the longitudinal direction (MD) and / or transverse direction (TD) due to differences in weight, moisture content, drying speed, etc. between the adhesive layer and the heat-resistant layer, and this curling phenomenon causes a problem that it causes a defect in the assembly of the battery.

[0008] The present invention is intended to solve the problems of the prior art described above, and the purpose of the present invention is to provide a separator and a method for manufacturing the same that can achieve and improve electrode adhesion, heat resistance, conductivity, and productivity in a balanced manner while suppressing the curl phenomenon.

[0009] One aspect of the present invention provides a separator comprising: a porous substrate; an electrode adhesive layer provided on one surface of the porous substrate, the electrode adhesive layer including first inorganic particles and a first binder that binds at least some of the first inorganic particles to each other; and a heat-resistant layer provided on the other surface of the porous substrate, the heat-resistant layer including second inorganic particles and a second binder that binds at least some of the second inorganic particles to each other; wherein the content of the first binder in the electrode adhesive layer is 3 to 20 wt%.

[0010] In one embodiment, the porous substrate may include one selected from the group consisting of polyethylene, polypropylene, polybutylene, polymethylpentene, ethylene vinyl acetate, ethylene butylacrylate, ethylene ethyl acrylate, and combinations or copolymers of two or more thereof.

[0011] In one embodiment, the average particle diameters of the first and second inorganic particles may each be 100 to 500 nm.

[0012] In one embodiment, the first and second inorganic particles may each include one 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, P2O5, CuO, MoO, V2O5, B2O3, Si3N4, CeO2, Mn3O4, Sn2P2O7, Sn2B2O5, Sn2BPO6, and combinations of two or more thereof.

[0013] In one embodiment, the first binder may be an organic particle comprising an insoluble polymer, and the second binder may comprise a water-soluble polymer.

[0014] In one embodiment, the average particle diameter of the organic particles may be greater than or equal to the average particle diameters of the first and second inorganic particles.

[0015] In one embodiment, the average particle diameter of the organic particles may be 500 to 1,000 nm.

[0016] In one embodiment, the curl height of the separator is 1.5 cm or less, and the curl height can be measured according to a method including the steps (1) and (2) below.

[0017] (1) A step of placing a separator having a length (vertical direction, MD) and width (horizontal direction, TD) of 300 mm each on a horizontal reference plane, such that the electrode adhesive layer faces the horizontal reference plane; and (2) a step of measuring the vertical distance between the longitudinal (MD) ends and the horizontal (TD) ends of the separator from the horizontal reference plane after 2 hours under conditions of a temperature of 21°C and a humidity having a dew point of -10°C or lower, and calculating an average value.

[0018] In one embodiment, the separator may satisfy at least one of the following conditions (i) to (iv).

[0019] (i) Electrode adhesion of 5 gf / 25 mm or more; (ii) Resistance of 0.700 Ω or less; (iii) Vertical thermal shrinkage of 4.0% or less at 150°C; and (iv) Transverse thermal shrinkage of 4.0% or less at 150°C.

[0020] Another aspect of the present invention provides a method for manufacturing a separator, comprising: (a) preparing a first coating slurry comprising first inorganic particles and a first binder that binds at least some of the first inorganic particles to each other; (b) preparing a second coating slurry comprising second inorganic particles and a second binder that binds at least some of the second inorganic particles to each other; (c) applying the first coating slurry to one surface of a porous substrate and then drying it to form an electrode adhesive layer; and (d) applying the second coating slurry to the other surface of the porous substrate and then drying it to form a heat-resistant layer; wherein the content of the first binder in the solid content of the first coating slurry is 3 to 20 wt%, and steps (c) and (d) are performed simultaneously.

[0021] According to one aspect of the present invention, a separator comprises: a porous substrate; an electrode adhesive layer provided on one surface of the porous substrate, the electrode adhesive layer including first inorganic particles and a first binder that binds at least some of the first inorganic particles to each other; and a heat-resistant layer provided on the other surface of the porous substrate, the heat-resistant layer including second inorganic particles and a second binder that binds at least some of the second inorganic particles to each other; and by adjusting the content of the first binder in the electrode adhesive layer to 3 to 20 wt%, electrode adhesive strength, heat resistance, and conductivity can be implemented and improved in a balanced manner, while effectively suppressing a curl phenomenon.

[0022] A method for manufacturing a separator according to another aspect of the present invention can improve the productivity of a double-sided asymmetrically coated separator by simultaneously performing the steps of applying a first coating slurry to one surface of the porous substrate and then drying it to form an electrode adhesive layer, and the steps of applying a second coating slurry to the other surface of the porous substrate and then drying it to form a heat-resistant layer.

[0023] The effects of the present invention are not limited to the effects described above, and should be understood to include all effects that can be inferred from the detailed description of the present invention or the composition of the invention described in the claims.

[0024] Figure 1 is a diagram illustrating a curl phenomenon of a separation membrane and a method for measuring curl height according to one embodiment of the present invention.

[0025] Hereinafter, the present invention will be described with reference to the attached drawings. However, the present invention can be implemented in various different forms and is therefore not limited to the embodiments described herein. In the drawings, irrelevant parts have been omitted for clarity of description, and similar parts have been designated with similar reference numerals throughout the specification.

[0026] Throughout the specification, when a part is said to be "connected" to another part, this includes not only "directly connected" but also "indirectly connected" with other elements intervening. Furthermore, when a part is said to "include" a component, this does not exclude other components, but rather implies that the other components may be included, unless otherwise specifically stated.

[0027] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings.

[0028] One aspect of the present invention provides a separator comprising: a porous substrate; an electrode adhesive layer provided on one surface of the porous substrate, the electrode adhesive layer including first inorganic particles and a first binder that binds at least some of the first inorganic particles to each other; and a heat-resistant layer provided on the other surface of the porous substrate, the heat-resistant layer including second inorganic particles and a second binder that binds at least some of the second inorganic particles to each other; wherein the content of the first binder in the electrode adhesive layer is 3 to 20 wt%.

[0029] The porous substrate may comprise a plurality of pores with substantially uniform average sizes, which may contribute to improving the resistance characteristics and ionic conductivity of the separator. Furthermore, the high porosity and high mechanical strength of the separator allow the membrane to be thinned to a desired thickness.

[0030] The porosity of the porous substrate may be 30 to 90 vol%, preferably 40 to 80 vol%, and more preferably 40 to 70 vol%. The term "porosity" as used herein refers to the ratio of the volume occupied by pores to the total volume of any porous article. If the porosity of the porous substrate is less than 30 vol%, air permeability and ionic conductivity may be reduced, and if it exceeds 90 vol%, mechanical properties such as tensile strength and puncture strength may be reduced.

[0031] The average size of the pores included in the porous substrate may be 10 to 100 nm, preferably 20 to 80 nm, and more preferably 30 to 60 nm. If the average size of the pores is less than 10 nm, air permeability and ionic conductivity may be reduced, and if it exceeds 100 nm, mechanical properties such as tensile strength and puncture strength may be reduced.

[0032] The thickness of the porous substrate may be 5 to 20 μm, preferably 5 to 15 μm, and more preferably 5 to 12 μm, in terms of thin film formation and high energy density of the electrochemical device. If the thickness of the porous substrate is less than 5 μm, the mechanical properties may deteriorate, and if it exceeds 20 μm, the air permeability and ionic conductivity may deteriorate.

[0033] The porous substrate may include a polymer resin having electrical insulation properties, and the polymer resin may include a thermoplastic resin in consideration of shutdown characteristics. The term "shutdown characteristics" as used herein refers to the phenomenon in which, when the battery overheats and its temperature increases, the polymer resin melts and closes the pores of the porous substrate, thereby blocking the movement of ions. From this perspective, the melting point of the polymer resin or the thermoplastic resin may be 200°C or lower.

[0034] The thermoplastic resin may include, for example, one selected from the group consisting of polyethylene, polypropylene, polybutylene, polymethylpentene, ethylene vinyl acetate, ethylene butylacrylate, ethylene ethyl acrylate, and combinations or copolymers of two or more thereof, preferably, at least one of polyethylene and polypropylene, and more preferably, polyethylene, but is not limited thereto.

[0035] The above polyethylene may be one selected from the group consisting of ultra-high molecular weight polyethylene (UHMWPE, Mw: 1,000,000 to 7,000,000 g / mol), high molecular weight polyethylene (HMWPE, Mw: 100,000 to 1,000,000 g / mol), high density polyethylene (HDPE, Mw: 100,000 to 1,000,000 g / mol), low density polyethylene (LDPE, Mw: 10,000 to 100,000 g / mol), homogeneous linear and linear low density polyethylene (LLDPE), and combinations of two or more thereof. The terms “weight average molecular weight” and “molecular weight distribution” used in this specification may mean values ​​measured by gel permeation chromatography (GPC) using polystyrene as a standard sample according to the method described in the literature (Macromolecules, Vol. 34, No. 19, pp. 6812-6820 (2001), etc.).

[0036] For example, the polyethylene has a weight average molecular weight (M w ) may be high-density polyethylene having a molecular weight of 250,000 to 600,000. If the weight average molecular weight of the polyethylene exceeds 600,000, the viscosity may increase and the processability may decrease, and if it is less than 250,000, the viscosity may decrease excessively and the dispersibility with pore-forming agents, antioxidants, etc. used when manufacturing a porous substrate may be extremely reduced, and in some cases, phase separation or layer separation may occur.

[0037] The porous substrate is hydrophilicized so as to sufficiently secure wettability of the slurry when coating the slurry to form the heat-resistant layer, thereby improving the bonding strength between the porous substrate and the heat-resistant layer. The contact angle of the hydrophilicized porous substrate with respect to water (H2O) may be 15° or less, and the absolute value of the zeta potential measured as a negative value (-) on the surface of the porous substrate may be 10 mV or more, preferably 15 mV or more, and more preferably 20 mV or more.

[0038] The hydrophilized porous substrate has hydrophilic functional groups, for example, -SO3 groups, formed on the surface and the surface of the internal pores, and thus can be easily bonded to the heat-resistant layer due to high affinity with the slurry, which is inherently hydrophilic, and the bonding strength can also be strengthened, so that the durability of the separation membrane can be significantly improved, and since loss of hydrophilic groups included in the porous substrate and / or inorganic particles of the heat-resistant layer is minimized, ionic conductivity and heat resistance can be improved.

[0039] The above separator may include an electrode adhesive layer provided on one surface of the porous substrate and including first inorganic particles and a first binder that binds at least some of the first inorganic particles to each other. The electrode adhesive layer may also include a plurality of pores formed between the first inorganic particles and / or the first binder and through which fluid and / or ions can pass.

[0040] The content of the first binder in the electrode adhesive layer may be 3 to 20 wt%, preferably 3 to 15 wt%, and relatively, the content of the first inorganic particles may be 80 to 97 wt%, preferably 85 to 97 wt%. If the content of the first binder in the electrode adhesive layer is 3 wt% or less or the content of the first inorganic particles exceeds 97 wt%, the electrode adhesive strength may be reduced, and if the content of the first binder exceeds 20 wt% or the content of the first inorganic particles is less than 80 wt%, not only may the heat resistance be reduced, but curl may also occur excessively. The curling phenomenon occurs due to differences in weight, moisture content, drying speed, etc., between the electrode adhesive layer and the heat-resistant layer formed on both sides of the porous substrate, i.e., asymmetry. If the content of the first inorganic particles is less than 80 wt%, the asymmetry with respect to the content of the second inorganic particles in the heat-resistant layer formed on the opposite side of the electrode adhesive layer may be aggravated, thereby promoting and aggravating the curling phenomenon.

[0041] The average particle diameter of the first inorganic particles may be 100 to 500 nm. The average particle diameter of the first inorganic particles may be larger than the average size of the pores included in the porous substrate. If the average particle diameter of the first inorganic particles is smaller than or equal to the average size of the pores included in the porous substrate, the inorganic particles may penetrate into the pores of the porous substrate and close the pores, thereby significantly reducing the air permeability and ionic conductivity of the separation membrane. The average particle diameter of the first inorganic particles may be 100 to 500 nm, preferably 200 to 400 nm, and more preferably 300 to 400 nm, but is not limited thereto.

[0042] The first inorganic particle may be, for example, one selected from the group consisting of SiO2, AlOOH, Mg(OH)2, Al(OH)3, TiO2, BaTiO3, Li2O, LiF, LiOH, Li3N, BaO, Na2O, Li2CO3, CaCO3, LiAlO2, Al2O3, SiO, SnO, SnO2, PbO2, ZnO, P2O5, CuO, MoO, V2O5, B2O3, Si3N4, CeO2, Mn3O4, Sn2P2O7, Sn2B2O5, Sn2BPO6, and a combination of two or more thereof, and preferably, AlOOH, Mg(OH)2, Al(OH)3, or Al2O3, but is not limited thereto.

[0043] The first binder may be an organic particle containing an insoluble polymer. The term "insoluble polymer" as used herein refers to a polymer that does not dissolve in water and has the property of being dispersed and floating in the form of fine particles in water, and is referred to as latex, emulsion, etc. The insoluble polymer may have the form of the fine particles described above in the electrode adhesive layer, and may form and maintain pores together with the first inorganic particles.

[0044] The average particle diameter of the organic particles may be equal to or greater than the average particle diameter of the first inorganic particles, and preferably, may be larger than the average particle diameter of the first inorganic particles. In this case, the average particle diameter of the organic particles may be 500 to 1,000 nm. When the average particle diameter of the organic particles is smaller than the average particle diameter of the first inorganic particles, for example, less than 500 nm, the organic particles may penetrate into the pores of the porous substrate or close the pores formed between the first inorganic particles, thereby significantly reducing the air permeability and ionic conductivity of the separator. In particular, when the organic particles close the pores formed between the first inorganic particles, the moisture content remaining in the pores of the electrode adhesive layer may decrease, and accordingly, asymmetry with the heat-resistant layer in terms of weight, moisture content, drying speed, etc. may be aggravated, which may accelerate and aggravate the curling phenomenon. Conversely, if the average particle diameter of the organic particles exceeds 1,000 nm, the surface area of ​​the electrode adhesive layer may decrease, resulting in a decrease in electrode adhesive strength.

[0045] The above-mentioned water-insoluble polymer may be, for example, one selected from the group consisting of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, polymethyl methacrylate, polyacrylonitrile, ethylene vinyl acetate, polyvinyl butyral, acrylonitrile-acrylic acid copolymer, ethylene-acrylic acid copolymer, styrene-butadiene copolymer, alkyl acrylate-acrylonitrile copolymer, acrylonitrile-styrene copolymer, acrylic rubber, and a combination of two or more thereof, but is not limited thereto.

[0046] The above-mentioned separator may include a heat-resistant layer provided on the other surface of the porous substrate and including second inorganic particles and a second binder that binds at least some of the second inorganic particles to each other. The heat-resistant layer may also include a plurality of pores formed between the second inorganic particles and through which fluid and / or ions may pass.

[0047] The second inorganic particles may be of the same type and / or quality as the first inorganic particles, and their average particle diameter may also be the same as or similar to the first inorganic particles. In this case, the type, average particle diameter, etc. of the second inorganic particles may refer to the above-described first inorganic particles. Meanwhile, if necessary, the type, properties, shape, average particle diameter, etc. of the second inorganic particles may be different from the first inorganic particles.

[0048] The content of the second inorganic particles in the heat-resistant layer may be 60 to 99 wt%. If the content of the second inorganic particles is less than 60 wt%, the required level of heat resistance cannot be provided, and if it exceeds 99 wt%, the air permeability, ionic conductivity, and resistance characteristics of the separator may deteriorate, and the dispersibility of the inorganic particles may deteriorate or workability and processability may deteriorate during slurry coating.

[0049] The second binder may include a water-soluble polymer. As used herein, the term "water-soluble polymer" refers to a polymer that dissolves in water and has the property of not being observed as particles or the like. The water-soluble polymer may melt and fuse in the heat-resistant layer to bind the second inorganic particles together, as well as bind the second inorganic particles to the porous substrate.

[0050] The water-soluble polymer may be, for example, one selected from the group consisting of polyacrylic acid, polyvinylpyrrolidone, polyvinyl acetate, polyimide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, hydroxyethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, polyvinyl alcohol, polyethylene oxide, polyethylene glycol, acrylonitrile copolymer, and a combination of two or more thereof, but is not limited thereto.

[0051] FIG. 1 is a diagram illustrating a curl phenomenon of a separator and a method for measuring curl height according to an embodiment of the present invention. Referring to FIG. 1, the curl height can be measured according to a method including the following steps (1) and (2). (1) a step of placing a separator, each having a length (vertical direction, MD) and a width (horizontal direction, TD) of 300 mm, on a horizontal reference plane, such that the electrode adhesive layer faces the horizontal reference plane; and (2) a step of measuring the vertical height of both ends of the longitudinal direction (MD) and both ends of the horizontal direction (TD) of the separator from the horizontal reference plane after 2 hours under conditions of a temperature of 21°C and a humidity having a dew point of -10°C or lower, and calculating an average value.

[0052] The curl height of the above separator may be 1.5 cm or less, preferably 1.2 cm or less, more preferably 0 to 1.0 cm, and advantageously 0 to 0.8 cm. If the curl height exceeds 1.5 cm, it may cause assembly failure of the battery.

[0053] The above separation membrane can satisfy at least one of the following conditions (i) to (iv).

[0054] (i) electrode adhesion of 5 gf / 25 mm or more, preferably 10 to 30 gf / 25 mm, more preferably 15 to 25 gf / 25 mm; (ii) resistance of 0.700 Ω or less, preferably 0.680 Ω or less, more preferably 0.650 Ω or less; (iii) longitudinal heat shrinkage of 4.0% or less, preferably 2.2% or less, more preferably 2.1% or less at 150°C; and (iv) transverse heat shrinkage of 4.0% or less, preferably 1.5% or less, more preferably 1.4% or less at 150°C.

[0055] Another aspect of the present invention provides a method for manufacturing a separator, comprising: (a) preparing a first coating slurry comprising first inorganic particles and a first binder that binds at least some of the first inorganic particles to each other; (b) preparing a second coating slurry comprising second inorganic particles and a second binder that binds at least some of the second inorganic particles to each other; (c) applying the first coating slurry to one surface of a porous substrate and then drying it to form an electrode adhesive layer; and (d) applying the second coating slurry to the other surface of the porous substrate and then drying it to form a heat-resistant layer; wherein the content of the first binder in the solid content of the first coating slurry is 3 to 20 wt%, and steps (c) and (d) are performed simultaneously.

[0056] In steps (a) and (b), the types, properties, shapes, average particle diameters, etc. of the first and second inorganic particles and the first and second binders are as described above. The first and second coating slurries may be those in which a predetermined solid content is dispersed in a solvent (medium). The solvent may be an oily solvent, an aqueous solvent, or a combination thereof, and preferably, an aqueous solvent, and more preferably, water, but is not limited thereto.

[0057] The solid content of the first coating slurry may include the first inorganic particles and the first binder, and the solid content of the second coating slurry may include the second inorganic particles and the second binder. The content of the solid content in the first coating slurry may be 20 to 40 wt%, the content of the solid content in the second coating slurry may be 10 to 30 wt%, and the first coating slurry may have a higher solid content than the second coating slurry.

[0058] In steps (c) and (d), the first and second coating slurries are simultaneously applied to one side and the other side of the porous substrate, respectively, and then dried to form the electrode adhesive layer on one side of the porous substrate and the heat-resistant layer on the other side of the porous substrate. The conventional process for forming the electrode adhesive layer and the heat-resistant layer on one side and the other side of the porous substrate, respectively, involves applying and drying the slurry for forming the electrode adhesive layer, and then applying and drying the slurry for forming the heat-resistant layer, or reversing the order thereof, and thus is performed continuously and sequentially, which makes it difficult to improve productivity and economic efficiency.

[0059] In this regard, a method has been proposed in which coating and drying for forming the electrode bonding layer and the heat-resistant layer are performed simultaneously on both sides of the porous substrate. However, there are still limitations in improving productivity, such as the need to set different process conditions for both sides due to differences in the composition and properties of the slurry applied to both sides of the porous substrate, i.e., asymmetry.

[0060] The method for manufacturing the above separator can effectively alleviate any asymmetry in properties and / or processes that may occur in the electrode adhesive layer and the heat-resistant layer, and can achieve a balanced implementation of electrode adhesive strength, heat resistance, and conductivity of the manufactured separator, even when the coating and drying processes on both sides of the porous substrate are performed simultaneously under the same conditions by controlling the composition, properties, solid content, etc. of each slurry during the process of manufacturing the first and second coating slurries.

[0061] Hereinafter, embodiments of the present invention will be described in detail.

[0062] Manufacturing Example 1-1

[0063] A first coating slurry was prepared by mixing a solid component containing 85 wt% of boehmite (AlOOH) with an average particle size of 300 nm as an inorganic particle and 15 wt% of an acrylic copolymer with an average particle size of 500 nm as an adhesive binder and distilled water in a weight ratio of 30:70, and uniformly dispersing the mixture.

[0064] Manufacturing Examples 1-2 to 1-7 and Comparative Manufacturing Examples 1-1 to 1-2

[0065] A first coating slurry was prepared in the same manner as in Manufacturing Example 1-1, except that the content of boehmite (AlOOH) and acrylic copolymer in the solid content was changed as shown in Table 1 below.

[0066] Comparative Manufacturing Example 1-3

[0067] A first coating slurry was prepared by mixing a solid component containing 85 wt% of boehmite (AlOOH) with an average particle size of 500 nm as an inorganic particle and 15 wt% of an acrylic copolymer with an average particle size of 300 nm as an adhesive binder and distilled water at a weight ratio of 30:70, and uniformly dispersing the mixture.

[0068] Manufacturing Example 2-1

[0069] A second coating slurry was prepared by mixing a solid component containing 97 wt% boehmite (AlOOH) with an average particle diameter of 300 nm as an inorganic particle and 3 wt% acrylonitrile copolymer as an organic binder and distilled water at a weight ratio of 25:75, and uniformly dispersing the mixture.

[0070] Classification Inorganic particle Organic binder Adhesive binder Manufacturing example 1-185015 Manufacturing example 1-288012 Manufacturing example 1-390010 Manufacturing example 1-49307 Manufacturing example 1-59505 Manufacturing example 1-69703 Manufacturing example 1-780020 Comparative Manufacturing example 1-170030 Comparative Manufacturing example 1-29802 Comparative Manufacturing example 1-385015 Manufacturing example 2-19730

[0071] (Unit: weight%)

[0072] Example 1

[0073] The first coating slurry according to Manufacturing Example 1-1 and the second coating slurry according to Manufacturing Example 2-1 were simultaneously roll-to-roll coated to a thickness of 2 μm on one side and the other side of a 9 μm thick polyethylene porous substrate (air permeability: 90 seconds / 100 ml), and then dried to obtain a separator in which an electrode adhesive layer (derived from the first coating slurry) was formed on one side of the porous substrate and a heat-resistant layer (derived from the second coating slurry) was formed on the other side.

[0074] Examples 2 to 7 and Comparative Examples 1 to 4

[0075] A separation membrane was obtained in the same manner as in Example 1, except that the coating slurry applied to one side and the other side of the porous substrate was changed as shown in Table 2 below.

[0076] One side of the porous substrateOther side of the porous substrateExample 1 Manufacturing Example 1-1 Manufacturing Example 2-1 Example 2 Manufacturing Example 1-2 Manufacturing Example 2-1 Example 3 Manufacturing Example 1-3 Manufacturing Example 2-1 Example 4 Manufacturing Example 1-4 Manufacturing Example 2-1 Example 5 Manufacturing Example 1-5 Manufacturing Example 2-1 Example 6 Manufacturing Example 1-6 Manufacturing Example 2-1 Example 7 Manufacturing Example 1-7 Manufacturing Example 2-1 Comparative Example 1 Comparative Manufacturing Example 1-1 Manufacturing Example 2-1 Comparative Example 2 Comparative Manufacturing Example 1-2 Manufacturing Example 2-1 Comparative Example 3 Comparative Manufacturing Example 1-3 Manufacturing Example 2-1 Comparative Example 4 Manufacturing Example 1-3 Manufacturing Example 1-3

[0077]

[0078] Experimental example

[0079] The testing methods for each physical property measured in the present invention are as follows. Unless otherwise specified, measurements were made at room temperature (25°C). The physical properties of the membranes manufactured according to the above examples and comparative examples were measured, and the results are shown in Table 3 below.

[0080] - Electrode adhesion (gf / 25mm): The adhesive layer of the separator (MD direction 180mm x TD direction 25mm) and the electrode were bonded so that they faced each other, and then inserted into an aluminum pouch. The aluminum pouch was pressurized for 30 seconds at 80℃ and 1,000kgf to compress the separator and electrode. Afterwards, the adhesion was measured while peeling the separator from the electrode using Shimadzu's UTM.

[0081] - Resistance (Ω): An electrolyte was prepared by dissolving LiPF6 at a concentration of 1.15 molar in a solvent containing ethylene carbonate and ethyl methyl carbonate in a ratio (volume ratio) of 30:70. After impregnating the separator with the electrolyte, a coin cell was manufactured, and the resistance was measured using an EIS (Electrochemical impedance spectroscopy) device.

[0082] -Thermal shrinkage rate (%): After leaving the separator (200 mm in MD direction × 200 mm in TD direction) between A4 papers in an oven at 150℃ for 1 hour, the length of the specimen in the transverse (TD) and longitudinal (MD) directions was measured after cooling to room temperature, and the thermal shrinkage rate was calculated using the following formula.

[0083] Heat shrinkage (%) = (l3-l4) / l3× 100

[0084] In the above formula, l3 is the transverse or longitudinal length of the membrane specimen before shrinkage, and l4 is the transverse or longitudinal length of the membrane specimen after shrinkage.

[0085] -Curl height (cm): The separator (300 mm in MD direction × 300 mm in TD direction) was spread out on a horizontal reference plane so that the electrode adhesive layer faced the reference plane, and after 2 hours, the height at which the MD direction ends and the TD direction ends of the separator were separated from the reference plane due to curl was measured (see Fig. 1), and the average value was calculated as the curl height.

[0086] Classification Electrode Adhesion Resistance Thermal Shrinkage (MD) Thermal Shrinkage (TD) Curl Height Example 1 260.66 12.2 1.5 1.2 Example 2 230.64 52.11.5 1.1 Example 3 200.63 62.11.5 0.8 Example 4 180.62 22.01.4 0.6 Example 5 150.61 41.8 1.30.5 Example 6 50.61 11.71.30.5 Example 7 350.68 13.3 3.6 1.4 Comparative Example 1 450.72 05.8 5.0 3.1 Comparative Example 2 40.60 31.71.30.3 Comparative Example 3 240.66 82.62.8 2.5 Comparative Example 4210.79028.026.00.2

[0087]

[0088] The foregoing description of the present invention is for illustrative purposes only, and those skilled in the art will readily appreciate that the present invention can be readily modified into other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. For example, each component described as a single entity may be implemented in a distributed manner, and similarly, components described as distributed may be implemented in a combined manner.

[0089] The scope of the present invention is indicated by the claims set forth below, and all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts should be interpreted as being included in the scope of the present invention.

Claims

1. Porous substrate; An electrode adhesive layer provided on one surface of the porous substrate and including first inorganic particles and a first binder that binds at least some of the first inorganic particles to each other; and A heat-resistant layer provided on the other surface of the porous substrate and including second inorganic particles and a second binder that binds at least some of the second inorganic particles to each other; A separator, wherein the content of the first binder in the electrode adhesive layer is 3 to 20 wt%.

2. In paragraph 1, A membrane, wherein the porous substrate comprises one selected from the group consisting of polyethylene, polypropylene, polybutylene, polymethylpentene, ethylene vinyl acetate, ethylene butylacrylate, ethylene ethyl acrylate, and combinations or copolymers of two or more thereof.

3. In paragraph 1, A separation membrane, wherein the average particle diameters of the first and second inorganic particles are each 100 to 500 nm.

4. In paragraph 3, A separation membrane, wherein the first and second inorganic particles each include one 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, P2O5, CuO, MoO, V2O5, B2O3, Si3N4, CeO2, Mn3O4, Sn2P2O7, Sn2B2O5, Sn2BPO6, and combinations of two or more thereof.

5. In paragraph 3, The above first binder is an organic particle containing an insoluble polymer, A separator, wherein the second binder comprises a water-soluble polymer.

6. In paragraph 5, A separation membrane in which the average particle diameter of the organic particles is greater than or equal to the average particle diameter of the first and second inorganic particles.

7. In paragraph 6, A separation membrane in which the average particle diameter of the above organic particles is 500 to 1,000 nm.

8. In paragraph 1, The curl height of the above separator is less than 1.5 cm, The above curl height is measured according to a method including the steps (1) and (2) below, the separator: (1) A step of placing a separator having a length (vertical direction, MD) and width (horizontal direction, TD) of 300 mm each on a horizontal reference plane, such that the electrode adhesive layer faces the horizontal reference plane; and (2) A step of calculating an average value by measuring the vertical distance between the longitudinal (MD) ends and the transverse (TD) ends of the membrane from the horizontal reference plane after 2 hours under conditions of a temperature of 21°C and a humidity of a dew point of -10°C or lower.

9. In paragraph 8, A membrane satisfying at least one of the conditions (i) to (iv): (i) Electrode adhesion of 5gf / 25mm or more; (ii) Resistance 0.700Ω or less; (iii) longitudinal heat shrinkage of 4.0% or less at 150℃; and (iv) Transverse heat shrinkage rate of 4.0% or less at 150℃.

10. In a method for manufacturing a separation membrane according to any one of clauses 1 to 9, (a) a step of preparing a first coating slurry comprising first inorganic particles and a first binder that binds at least some of the first inorganic particles to each other; (b) a step of preparing a second coating slurry comprising second inorganic particles and a second binder that binds at least some of the second inorganic particles to each other; (c) a step of applying the first coating slurry to one surface of a porous substrate and then drying it to form an electrode adhesive layer; and (d) a step of forming a heat-resistant layer by applying the second coating slurry to the other surface of the porous substrate and then drying it; The content of the first binder in the solid content of the first coating slurry is 3 to 20 wt%, Steps (c) and (d) above are performed simultaneously, Method for manufacturing a membrane.

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