Separator and electrochemical device including the same

Abstract

One aspect of the present invention provides a separator including a porous substrate and a heat-resistant layer including inorganic particles and disposed on at least one surface of the porous substrate, wherein the ratio F2 / F1 of the air permeability F2 (sec / 100 ml) on a curved surface of the separator having a radius of curvature of 10 mm to the air permeability F1 (sec / 100 ml) on a flat surface of the separator is 1.5 or less, and an electrochemical element including the separator.

Description

Technical Field

[0001] The present invention relates to a separator and an electrochemical device including the same, and more particularly, to a separator that minimizes the variation in air permeability depending on the site inside the battery and an electrochemical device including the same.

Background Art

[0002] Lithium secondary batteries are widely used as power sources for various electrical products that require miniaturization and weight reduction, such as smartphones, notebook computers, and tablet computers. As the application fields expand to include medium and large-sized batteries for smart grids and 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 the above object, a separator having fine pores that separates the positive electrode and the negative electrode to prevent internal short circuit and smooth the movement of lithium ions during the charge and discharge process, among which, research and development on fine porous separators using polyolefins such as polyethylene, which is advantageous for the formation of pores by thermally induced phase separation, is economical, and easily satisfies the physical properties required for the separator, is active.

[0004] However, a separator using polyethylene having a low melting point of about 135°C may undergo shrinkage deformation at a high temperature above the melting point due to the heat generation of the battery. If a short circuit occurs due to such deformation, a thermal runaway phenomenon of the battery may occur, resulting in safety problems such as ignition.

[0005] In addition, polyolefin-based separators that have been widely used conventionally are brittle in terms of heat resistance and mechanical strength. When exposed to a temperature of 150°C for about one hour, a heat shrinkage rate of 50 to 90% occurs, resulting in the loss of the separator's function and a high possibility of internal short circuit during external impact. To complement such problems, a technique of coating a heat-resistant layer containing ceramic particles on the surface of the separator has been proposed.

[0006] However, such a heat-resistant layer leaves considerable technical problems in relation to air permeability and conductivity (resistance), which are elements that have a great 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. However, the ceramic particles contained in the heat-resistant layer close the pores formed in the porous substrate, reducing the air permeability of the separator. As a result, the ion migration path between the positive electrode and the negative electrode is greatly reduced, leading to a significant deterioration in the charging and discharging 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 partially and continuously detach from the porous substrate. In this case, the heat resistance of the separator may gradually decrease.

[0007] The above problems are more prominent in regions with a small radius of curvature in a separator that is formed into a layer with an electrode and wound and bent inside a cylindrical and / or pouch-type battery. Specifically, referring to FIG. 1, when heat-resistant layers 210 and 220 with symmetric composition, thickness, density, etc. are formed on both sides of the porous substrate 100, a greater load is applied to the heat-resistant layer 210 formed on the side facing the inside of the battery in the curved surface region of the separator than to the heat-resistant layer 220 formed on the other side. Therefore, the density of the heat-resistant layer 210 formed on the side facing the inside of the battery in such a curved surface region increases compared to the planar region, and the density of the heat-resistant layer 220 formed on the other side decreases compared to the planar region.

[0008] When the density of the heat-resistant layer provided on one surface of the separator in the curved surface region inside the battery, particularly, increases arbitrarily as described above, the performance of the separator realized in the curved surface region, for example, air permeability, ion conductivity, resistance, etc., is significantly reduced compared to the values measured and evaluated based on the flat surface region, and there is a problem that the particulate matter provided in the heat-resistant layer is arbitrarily detached by an unnecessary load. Summary of the Invention Problems to be Solved by the Invention

[0009] The present invention is for solving the problems of the prior art as described above, and an object of the present invention is to provide a separator capable of solving the problem that air permeability, ion conductivity, and resistance are reduced due to the load applied to the heat-resistant layer in the curved surface region of the separator inside the battery, and an electrochemical element including the same. Means for Solving the Problems

[0010] One aspect of the present invention is a separator including a porous base material and a heat-resistant layer provided on at least one surface of the porous base material and containing inorganic particles, wherein the ratio F2 / F1 of the air permeability F2 (sec / 100 ml) on the curved surface of the separator having a curvature radius of 10 mm to the air permeability F1 (sec / 100 ml) on the flat surface of the separator is 1.5 or less.

[0011] In one embodiment, the porous base material may include 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 separator includes a first heat-resistant layer provided on one surface of the porous base material and a second heat-resistant layer provided on the other surface of the porous base material, and the density of the first heat-resistant layer may be smaller than the density of the second heat-resistant layer.

[0013] In one embodiment, the first heat-resistant layer and the second heat-resistant layer may face the inside and the outside of a battery in which an electrode assembly having electrodes provided on both sides of the separator is wound and bent according to a predetermined standard, respectively.

[0014] In one embodiment, the first heat-resistant layer includes first inorganic particles and a first binder that binds at least a part of the first inorganic particles at a predetermined interval. The first binder includes a water-insoluble polymer, and the content of the water-insoluble polymer in the first binder is 40 to 90% by weight. The density of the first heat-resistant layer is 1.6 g / m 2 May be as follows.

[0015] In one embodiment, the second heat-resistant layer includes second inorganic particles and a second binder that binds at least a part of the second inorganic particles at a predetermined interval. The second binder includes a water-soluble polymer, and the content of the water-soluble polymer in the second binder is 70% by weight or more. The density of the second heat-resistant layer is 1.7 g / m 2 May be as above.

[0016] In one embodiment, each of the first inorganic particles and the second inorganic particles may be 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.

[0017] In one embodiment, the water-insoluble polymer may be 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, acrylic - styrene copolymer, acrylic rubber, and combinations of two or more thereof.

[0018] In one embodiment, the water-soluble polymer may be one selected from the group consisting of polyacrylic acid, polyvinyl pyrrolidone, 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, and combinations of two or more thereof.

[0019] Another aspect of the present invention provides an electrochemical element including the separator, preferably a secondary battery, more preferably a lithium secondary battery or a lithium ion battery.

Effects of the Invention

[0020] The separator according to one aspect of the present invention includes a porous substrate and a heat-resistant layer provided on at least one surface of the porous substrate and containing inorganic particles. Since the ratio F2 / F1 of the air permeability F2 (sec / 100ml) on the curved surface with a curvature radius of 10 mm of the separator to the air permeability F1 (sec / 100ml) on the flat surface of the separator is 1.5 or less, the problems of a decrease in air permeability, ionic conductivity, and resistance due to the load applied to the heat-resistant layer in the curved surface region of the separator inside the battery can be appropriately solved.

[0021] The effects of the present invention are not limited to the above-described effects, and it should be understood to include all effects that can be inferred from the configuration of the invention described in the detailed description or claims of the present invention.

Brief Description of the Drawings

[0022]

Figure 1

Modes for Carrying Out the Invention

[0023] Hereinafter, the present invention will be described with reference to the accompanying drawings. However, the present invention can be realized in various different forms, and thus is not limited to the embodiments described herein. And in the drawings, in order to clearly explain the present invention, parts not related to the explanation are omitted, and similar reference numerals are given to similar parts throughout the specification.

[0024] Throughout the specification, when any part is "connected" to another part, this includes not only the case where it is "directly connected", but also the case where other members are interposed therebetween and it is "indirectly connected". Also, when any part "includes" a certain component, this means that, unless otherwise stated to the contrary, it does not exclude other components and can further include other components.

[0025] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0026] One aspect of the present invention provides a separator including a porous base material and a heat-resistant layer provided on at least one surface of the porous base material and containing inorganic particles, wherein the ratio F2 / F1 of the air permeability F2 (sec / 100 ml) on the curved surface of the separator with a curvature radius of 10 mm to the air permeability F1 (sec / 100 ml) on the plane of the separator is 1.5 or less.

[0027] The porous substrate may contain a large number of pores with substantially uniform average size, and such pores can contribute to the improvement of the resistance characteristics and ionic conductivity of the separator. Also, even though the porosity is high, the mechanical strength is high, so the separator can be made into a thin film with the required thickness.

[0028] The porosity of the porous substrate may be 30 to 90% by volume, preferably 40 to 80% by volume, and more preferably 40 to 70% by volume. As used herein, the term "porosity" means the ratio of the volume occupied by pores to the total volume in any porous article. If the porosity of the porous substrate is less than 30% by volume, the air permeability and ionic conductivity may decrease, and if it exceeds 90% by volume, the mechanical properties such as tensile strength and puncture strength may decrease.

[0029] The average size of the pores contained 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, the air permeability and ionic conductivity may decrease, and if it exceeds 100 nm, the mechanical properties such as tensile strength and puncture strength may decrease.

[0030] From the viewpoints of thinning the electrochemical element and increasing the energy density, the thickness of the porous substrate may be 5 to 20 μm, preferably 5 to 15 μm, and more preferably 5 to 12 μm. If the thickness of the porous substrate is less than 5 μm, the mechanical properties may decrease, and if it exceeds 20 μm, the air permeability and ionic conductivity may decrease.

[0031] The porous substrate may contain a polymer resin having electrical insulation properties, and the polymer resin may contain a thermoplastic resin in consideration of shutdown characteristics. As used herein, the term "shutdown characteristics" means that when the battery overheats and the temperature rises, the polymer resin melts and closes the pores of the porous substrate, thereby blocking the movement of ions. From such a perspective, the melting point of the polymer resin or the thermoplastic resin may be 200°C or lower.

[0032] The thermoplastic resin may include, for example, 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 may include at least one of polyethylene and polypropylene, and more preferably may include polyethylene, but is not limited thereto.

[0033] The 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.

[0034] For example, the polyethylene has a weight average molecular weight M wIt may be high-density polyethylene with a weight average molecular weight of 250,000 to 450,000. When the weight average molecular weight of the polyethylene exceeds 450,000, the viscosity may increase and the processability may decrease. When it is less than 250,000, the viscosity may be excessively low, and the dispersibility with pore-forming agents, antioxidants, etc. used when manufacturing the porous substrate may extremely decrease, and in some cases, phase separation or layer separation may occur.

[0035] The porous substrate is subjected to a hydrophilic treatment, and sufficient wettability of the slurry can be ensured during the coating of the slurry for forming the heat-resistant layer, thereby improving the bonding strength between the porous substrate and the heat-resistant layer. The contact angle of the hydrophilic-treated 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.

[0036] The hydrophilic-treated porous substrate has hydrophilic functional groups generated on the surface and the surface of the internal pores, for example, -SO3 groups have hydrophilicity, so it can easily bond with the heat-resistant layer due to its high affinity with the essentially hydrophilic slurry, and the bonding strength can be enhanced, the durability of the separator can be significantly improved, and the loss of hydrophilic groups contained in the porous substrate and / or inorganic particles of the heat-resistant layer can be minimized, so the ionic conductivity and heat resistance can be improved.

[0037] The separator may be provided on at least one surface of the porous substrate and include a heat-resistant layer containing inorganic particles. The heat-resistant layer may also include a large number of pores through which fluids and / or ions can permeate.

[0038] The content of the inorganic particles in the heat-resistant layer may be 60 to 99% by weight. When the content of the inorganic particles is less than 60% by weight, a necessary level of heat resistance cannot be imparted. When it exceeds 99% by weight, the air permeability, ion conductivity, and resistance characteristics of the separator may decrease, the dispersibility of the inorganic particles may decrease, and the workability and processability during slurry coating may decrease.

[0039] The average particle size of the inorganic particles may be larger than the average size of the pores contained in the porous substrate. When the average particle size of the inorganic particles is less than or equal to the average size of the pores contained in the porous substrate, the inorganic particles penetrate into the pores of the porous substrate and close the pores, which can significantly reduce the air permeability and ion conductivity of the separator. The average particle size of the inorganic particles may be 100 to 1,000 nm, preferably 200 to 800 nm, more preferably 400 to 800 nm, but is not limited thereto.

[0040] The thickness of the heat-resistant layer may be 0.1 to 5 μm. When the thickness of the heat-resistant layer is less than 0.1 μm, a necessary level of heat resistance cannot be imparted. When it exceeds 5 μm, the separator becomes thick-film, which can inhibit the miniaturization and integration of the electrochemical device.

[0041] FIG. 1 is a cross-sectional view of a separator according to an embodiment of the present invention. Referring to FIG. 1, the separator according to an embodiment of the present invention includes a first heat-resistant layer 210 provided on one surface of the porous substrate 100 and a second heat-resistant layer 220 provided on the other surface of the porous substrate. The density of the first heat-resistant layer 210 may be smaller than the density of the second heat-resistant layer 220. As used herein, the term "density" means the weight per unit area along the area direction of the first or second heat-resistant layer, and is also referred to as "areal density", and the unit is g / m 2 is.

[0042] When heat-resistant layers 210 and 220 with symmetrical composition, thickness, density, etc. are formed on both sides of the porous base material 100 as in the prior art, a greater load is applied to the heat-resistant layer 210 formed on the side facing the inside of the battery in the curved surface area of the separator than to the heat-resistant layer 220 formed on the other side. Therefore, the density of the heat-resistant layer 210 formed on the side facing the inside of the battery in such a curved surface area increases compared to the flat area, and the density of the heat-resistant layer 220 formed on the other side decreases compared to the flat area.

[0043] When the density of the heat-resistant layer provided on one side of the separator in the curved surface area of the battery, particularly inside the battery, arbitrarily increases as described above, the performance of the separator realized in the curved surface area, such as air permeability, ion conductivity, resistance, etc., significantly decreases compared to the values measured and evaluated based on the flat area, and there is a problem that the particulate matter provided in the heat-resistant layer is arbitrarily detached by an unnecessary load.

[0044] In contrast, the first heat-resistant layer 210 and the second heat-resistant layer 220 provided on both sides of the porous base material 100 may face the inside and outside of the battery, respectively, in which the electrode assembly with electrodes provided on both sides of the separator is wound and bent according to a predetermined standard. That is, in the electrode assembly and / or the battery including the same, the first heat-resistant layer 210 faces the inside of the electrode assembly and / or the battery including the same, and the second heat-resistant layer 220 faces the outside of the electrode assembly and / or the battery including the same.

[0045] Also, by adjusting the density of the first heat-resistant layer 210 to be smaller than the density of the second heat-resistant layer 220, the density difference between the first heat-resistant layer 210 and the second heat-resistant layer 220 generated in the curved surface area during the assembly of the electrode assembly and / or the battery including the same can be alleviated.

[0046] When the electrode assembly is wound and / or bent for battery assembly, since the first heat-resistant layer 210 faces the inside of the battery, the radius of curvature is smaller than that of the second heat-resistant layer 220, and as the area of the interface between the first heat-resistant layer 210 and the porous base material 100 decreases, the density of the first heat-resistant layer 210 designed to be lower than that of the second heat-resistant layer 220 increases. Conversely, since the second heat-resistant layer 220 faces the outside of the battery, the radius of curvature is larger than that of the first heat-resistant layer 210, and as the area of the interface between the second heat-resistant layer 220 and the porous base material 100 increases, the density of the second heat-resistant layer 220 designed to be higher than that of the first heat-resistant layer 210 decreases.

[0047] When the density of the first heat-resistant layer 210 designed to be lower than that of the second heat-resistant layer 220 in the curved surface region increases and the density of the second heat-resistant layer 220 designed to be higher than that of the first heat-resistant layer 210 decreases, the densities of the first heat-resistant layer 210 and the second heat-resistant layer 220 converge to any intermediate value thereof, and the density difference can be alleviated. As a result, the problems of reduction in air permeability, ion conductivity, and resistance due to the load applied to the first heat-resistant layer 210 in the curved surface region of the separator inside the battery including the wound and / or bent electrode assembly can be appropriately solved.

[0048] When the density difference between the first heat-resistant layer 210 and the second heat-resistant layer 220 is alleviated, the ratio F2 / F1 of the air permeability F2 (sec / 100 ml) on the curved surface with a radius of curvature of 10 mm of the separator to the air permeability F1 (sec / 100 ml) on the plane of the separator is 1.5 or less, preferably 1.0 to 1.3, more preferably 1.0 to 1.2, and even more preferably 1.0 to 1.1. When the ratio F2 / F1 exceeds 1.5, the air permeability, ion conductivity, resistance, etc. in the curved surface region of the electrode assembly and / or the battery including the same may be significantly reduced compared to the plane region, and the electrochemical characteristics of the battery may deteriorate.

[0049] As used herein, the term "curved surface" means a surface having a predetermined radius of curvature generated by winding and / or bending an electrode assembly including an electrode-separator-electrode, a line bent at a predetermined angle, and its peripheral portion, and "plane" means the region of the separator excluding the curved surface.

[0050] The air permeability F1 (sec / 100ml) of the separator in the plane can be measured using a device such as a Gurley densometer with the test piece fixed on the plane. The air permeability F2 (sec / 100ml) of the separator on the curved surface with a radius of curvature of 10 mm can be measured using the same device with the test piece wound (wind) in the MD direction around a cylinder with a diameter of 20 mm, left standing for a certain period of time, and then immediately unwound and fixed on the plane.

[0051] The first heat-resistant layer 210 includes first inorganic particles and a first binder that binds at least a part of the first inorganic particles at a predetermined interval. The first binder includes a water-insoluble polymer, and the content of the water-insoluble polymer in the first binder is 40 to 90% by weight, preferably 60 to 90% by weight, and more preferably 80 to 90% by weight. The density of the first heat-resistant layer 210 is 1.6 g / m 2 Hereinafter, preferably, 1.0 to 1.5 g / m 2 More preferably, 1.2 to 1.4 g / m 2 It may be.

[0052] The second heat-resistant layer 220 includes second inorganic particles and a second binder that binds at least a part of the second inorganic particles at a predetermined interval. The second binder includes a water-soluble polymer, and the content of the water-soluble polymer in the second binder is 70% by weight or more, preferably 80% by weight or more, and more preferably 90% by weight or more. The density of the second heat-resistant layer 220 is 1.7 g / m 2 Or more, preferably, 1.8 to 2.0 g / m 2 More preferably, 1.85 to 1.95 g / m 2 It may be.

[0053] Also, the density difference between the first heat-resistant layer 210 and the second heat-resistant layer 220 is 0.2 g / m 2 or more, preferably 0.3 g / m 2 or more, more preferably 0.5 g / m 2 or more, still more preferably 0.6 g / m 2 or more may be acceptable.

[0054] As used herein, the term "water-insoluble polymer" means 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 water-insoluble polymer may have the form of the fine particles described above in the first heat-resistant layer 210, and can form and maintain pores together with the first inorganic particles. The average particle size of the water-insoluble polymer may be 50 to 300 nm. When the average particle size of the water-insoluble polymer is less than 50 nm, the air permeability and ionic conductivity of the separator may decrease, and when it exceeds 300 nm, the surface area of the heat-resistant layer may become small, and the adhesion and resistance characteristics may decrease.

[0055] On the other hand, as used herein, the term "water-soluble polymer" means a polymer that dissolves in water and has the property of not being observed as particles. The water-soluble polymer melts and fuses in the second heat-resistant layer 220, and can not only bind the second inorganic particles to each other, but also bind the second inorganic particles to the porous substrate 100.

[0056] The remainder of the first binder may contain a water-soluble polymer, and the remainder of the second binder may contain a water-insoluble polymer.

[0057] The 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, acrylic - styrene copolymer, acrylic rubber, and combinations of two or more thereof, but is not limited thereto.

[0058] The water-soluble polymer may be, for example, one selected from the group consisting of polyacrylic acid, polyvinyl pyrrolidone, 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, and combinations of two or more thereof.

[0059] The first inorganic particles and the second inorganic particles may each be 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. Preferably, the first inorganic particles may be rectangular parallelepiped-shaped AlO(OH), and the second inorganic particles may be spherical Al2O3, but are not limited thereto.

[0060] Hereinafter, embodiments of the present invention will be described in detail.

[0061] Production Example 1-1 92 parts by weight of alumina, 2 parts by weight of a water-soluble acrylic copolymer, 5 parts by weight of a carboxymethyl cellulose salt (CMC), 0.5 part by weight of a surfactant, and 60.5 parts by weight of a dispersant (NaPO3) were dispersed in water to obtain a high-density slurry having a solid content of 20% by weight and a density of 1.8 g / m 3 This high-density slurry was produced.

[0062] Production Example 1-2 92 parts by weight of alumina, 7 parts by weight of a carboxymethyl cellulose salt (CMC), 0.5 part by weight of a surfactant, and 60.5 parts by weight of a dispersant (NaPO3) were dispersed in water to obtain a high-density slurry having a solid content of 20% by weight and a density of 1.92 g / m 3 This high-density slurry was produced.

[0063] Production Example 1-3 92 parts by weight of alumina, 2 parts by weight of an acrylic-acrylonitrile copolymer, 5 parts by weight of a carboxymethyl cellulose salt (CMC), 0.5 part by weight of a surfactant, and 60.5 parts by weight of a dispersant (NaPO3) were dispersed in water to obtain a high-density slurry having a solid content of 20% by weight and a density of 1.74 g / m 3 This high-density slurry was produced.

[0064] Production Example 2-1 94 parts by weight of boehmite, 4.5 parts by weight of an acrylic-acrylonitrile copolymer, 0.5 part by weight of polyvinyl alcohol, 0.5 part by weight of a surfactant, and 60.5 parts by weight of a dispersant (NaPO3) were dispersed in water to obtain a low-density slurry having a solid content of 20% by weight and a density of 1.27 g / m 3 This low-density slurry was produced.

[0065] Production Example 2-2 94 parts by weight of boehmite, 4 parts by weight of an acrylic-acrylonitrile copolymer, 1 part by weight of polyvinyl alcohol, 0.5 part by weight of a surfactant, and 0.5 part by weight of a dispersant (NaPO3)6 are dispersed in water to obtain a low-density slurry having a solid content of 20% by weight and a density of 1.3 g / m 3 This is the production of a low-density slurry.

[0066] Production Example 2-3 94 parts by weight of boehmite, 3 parts by weight of an acrylic-acrylonitrile copolymer, 2 parts by weight of polyvinyl alcohol, 0.5 part by weight of a surfactant, and 0.5 part by weight of a dispersant (NaPO3)6 are dispersed in water to obtain a low-density slurry having a solid content of 20% by weight and a density of 1.36 g / m 3 This is the production of a low-density slurry.

[0067] Production Example 2-4 94 parts by weight of boehmite, 2 parts by weight of an acrylic-acrylonitrile copolymer, 3 parts by weight of polyvinyl alcohol, 0.5 part by weight of a surfactant, and 0.5 part by weight of a dispersant (NaPO3)6 are dispersed in water to obtain a low-density slurry having a solid content of 20% by weight and a density of 1.41 g / m 3 This is the production of a low-density slurry.

[0068] Production Example 2-5 94 parts by weight of boehmite, 1 part by weight of an acrylic-acrylonitrile copolymer, 4 parts by weight of polyvinyl alcohol, 0.5 part by weight of a surfactant, and 0.5 part by weight of a dispersant (NaPO3)6 are dispersed in water to obtain a low-density slurry having a solid content of 20% by weight and a density of 1.53 g / m 3 This is the production of a low-density slurry.

[0069] Examples and Comparative Examples The low-density and / or high-density slurries obtained in the above production examples were bar-coated on both sides of a polyethylene porous substrate having a thickness of 9 μm (air permeability: 110 seconds / 100 ml), and then dried to produce separator test pieces each having a heat-resistant layer with a thickness of 2 μm on both sides of the porous substrate.

[0070] The slurries used to form coating layers on both sides of the separator test piece, i.e., the outer surface and the inner surface, are shown in Table 1 below. In the following table, the "outer surface" of the separator means the surface facing the outside of the battery when the electrode structure including the separator is wound and / or bent during battery assembly, and the "inner surface" of the separator is the opposite surface of the outer surface and means the surface facing the inside of the battery.

[0071]

Table 1

[0072] Experimental Example The test methods for each physical property measured in the present invention are as follows. Unless otherwise mentioned regarding temperature, the measurement was performed at room temperature (25 °C).

[0073] The physical properties of the separator test pieces produced by the above Examples and Comparative Examples were measured, and the results are shown in Table 2 below. - Air permeability (Gurley, sec / 100ml): After measuring the air permeability through the time it takes for 100 ml of air to pass through a separator test piece with a diameter of 29.8 mm at a measurement pressure of 0.025 MPa using a Gurley type densometer EGO2-5 model manufactured by Asahi Seiko Co., Ltd. (F1), the separator test piece was wound (wind) in the MD direction around a cylinder with a diameter of 20 mm and left for 6 hours, and then immediately after unwinding (unwind), the air permeability was measured in the same manner as above (F2). - Thermal shrinkage rate (%): After placing a separator test piece with a size of 200 × 200 mm between A4 papers in an oven at 150 °C for 1 hour and leaving it, it was cooled to room temperature, and the shrunk length in the longitudinal direction (MD) of the test piece was measured, and the thermal shrinkage rate was calculated by the following formula. Thermal shrinkage rate (%) = (l3 - l4) / l3 × 100 (In the above formula, l3 is the longitudinal length of the test piece before shrinkage, and l4 is the longitudinal length of the test piece after shrinkage.)

[0074]

Table 2

[0075] The above description of the present invention is for illustrative purposes, and those with ordinary knowledge in the technical field to which the present invention pertains can understand that it can be easily modified into other specific forms without changing the technical idea and essential features of the present invention. Therefore, the embodiments and examples described above should be understood as illustrative in all aspects and not restrictive. For example, each component described as a single type can also be implemented in a distributed manner, and similarly, components described as distributed can also be implemented in a combined form.

[0076] The scope of the present invention is indicated by the claims described below, and all changes or modified forms derived from the meaning and scope of the claims and their equivalent concepts should be construed as being included within the scope of the present invention.

Description of Reference Numerals

[0077] 100 porous substrate 210 low-density heat-resistant layer (first heat-resistant layer) 220 high-density heat-resistant layer (second heat-resistant layer)

Claims

1. A separator comprising a porous substrate and a heat-resistant layer provided on at least one surface of the porous substrate and containing inorganic particles, comprising a first heat-resistant layer provided on one surface of the porous substrate and a second heat-resistant layer provided on the other surface of the porous substrate, wherein the ratio F2 / F1 of the air permeability F2 (sec / 100 ml) on the curved surface with a curvature radius of 10 mm of the separator to the air permeability F1 (sec / 100 ml) on the flat surface of the separator is 1.0 or more and 1.5 or less, and the surface density of the first heat-resistant layer is smaller than the surface density of the second heat-resistant layer.

2. The separator according to claim 1, wherein the porous substrate comprises 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. The first heat-resistant layer and the second heat-resistant layer each, face the inside and outside of a battery in which an electrode assembly having electrodes provided on both surfaces of the separator is wound and bent according to a predetermined standard.

4. The first heat-resistant layer includes first inorganic particles and a first binder that binds at least a part of the first inorganic particles at a predetermined interval, the first binder includes a water-insoluble polymer, and the content of the water-insoluble polymer in the first binder is 40 to 90% by weight. The areal density of the first heat-resistant layer is 1.6 g / m ２ The separator according to claim 3, wherein the areal density is 1.6 g / m or less.

5. The second heat-resistant layer includes second inorganic particles and a second binder that binds at least a part of the second inorganic particles at a predetermined interval, the second binder includes a water-soluble polymer, and the content of the water-soluble polymer in the second binder is 70% by weight or more. The areal density of the second heat-resistant layer is 1.7 g / m ２ or more. The separator according to claim 4.

6. The first inorganic particles and the second inorganic particles are each 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 and is one selected from the group consisting of combinations of two or more of these, the separator according to claim 5.

7. The non-water-soluble polymer is 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, acrylic - styrene copolymer, acrylic rubber, and combinations of two or more thereof. The separator according to claim 4.

8. The water-soluble polymer is 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, and combinations of two or more thereof. The separator according to claim 5.

9. An electrochemical device comprising the separator according to any one of claims 1 to 8.

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