Separator membrane for secondary batteries

Abstract

The present invention relates to a separation membrane comprising a separation membrane substrate made of a porous material and an inorganic layer coated on at least one surface of the separation membrane substrate, wherein the separation membrane substrate and the inorganic layer have porosities that satisfy the following relationship with respect to the air permeability of the separation membrane: (10 × porosity of separation membrane substrate) - (4 × porosity of inorganic layer) ≦ air permeability of separation membrane

Description

[Technical Field]

[0001] This application claims the benefit of priority from Korean Patent Application No. 2021-0083162 dated June 25, 2021, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a separator for a secondary battery, and more particularly to a separator for a secondary battery in which the porosity of a separator substrate and an inorganic layer of the separator can be adjusted to control the impregnation of the separator. [Background technology]

[0003] A lithium secondary battery can be manufactured by placing an electrode assembly, which is manufactured by interposing a separator between a positive electrode and a negative electrode, in a battery case, injecting an electrolyte solution, and then sealing the battery case.

[0004] The separator serves to ensure insulation by blocking electrical connection between the positive and negative electrodes, and may have a structure in which a coating layer containing an inorganic material and a binder is formed on a polyolefin-based substrate made of a porous material to allow lithium ions to move. Since the polyolefin-based material is sensitive to heat, the addition of the coating layer can improve high-temperature safety and mechanical properties.

[0005] The coating layer including the inorganic material and binder has a pore structure that increases the space through which the liquid electrolyte can flow, thereby improving the electrolyte impregnation rate and lithium ion conductivity.

[0006] In lithium secondary batteries, the electrolyte serves as a path for lithium ions to move, so increasing the electrolyte impregnation rate of the separator and reducing resistance has become an important issue. In particular, as the application fields of lithium secondary batteries expand to devices requiring high voltage and high capacity, such as electric vehicles, battery cells tend to become larger. Therefore, it is necessary to develop a separator with improved electrolyte impregnation ability to be applied to battery cells with such increased volume.

[0007] In this regard, Patent Document 1 relates to an inorganic oxide powder for forming an inorganic oxide porous membrane having excellent heat resistance, insulating properties, and membrane strength despite a small apparent weight, and further having a porosity that can impart sufficient ion permeability, and the inorganic oxide powder is added to the surface of at least one of a positive electrode, a negative electrode, or a separator.

[0008] That is, in Patent Document 1, the physical properties of the separation membrane are improved by using an inorganic oxide powder that has the property of increasing ion permeability.

[0009] In Patent Document 2, in a separator including a porous polymer film and a porous coating layer formed on the porous polymer film, the surface fibrils of the porous polymer film and particles contained in the porous coating layer are entangled at the contact surface between the porous polymer film and the porous coating layer. As such, the particles contained in the porous coating layer slurry are entangled between the pre-bonded fibrils formed on the surface of the porous polymer film, which further strengthens the bonding strength between the porous polymer film and the porous coating layer.

[0010] Patent Document 2 provides a separator with reduced heat shrinkage and improved breathability by coating a porous polyolefin film with a slurry and heat-setting the film at a temperature higher than conventional heat-setting temperatures.

[0011] In general, in a separation membrane including a separation membrane substrate having a porous structure and a coating layer having a porous structure, the porosity of the separation membrane substrate and the coating layer is related to the impregnation ability of the separation membrane.

[0012] In Patent Document 1, a specific inorganic oxide powder is added to improve the physical properties of the separator, while in Patent Document 2, heat setting is performed at a high temperature.

[0013] However, no method has been proposed that can ensure the impregnation rate of a separator at a certain level or above while using a conventional separator manufacturing method without adding an additional process or substance, or that can indirectly confirm whether the impregnation rate of a separator is good or bad. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] Korean Patent Registration No. 1913990 [Patent Document 2] Korean Patent Registration No. 1666045 Summary of the Invention [Problem to be solved by the invention]

[0015] The present invention has been made to solve the above problems, and an object of the present invention is to provide a separator for a secondary battery in which the impregnation property of the separator is improved by adjusting the porosity of the separator substrate and the porosity of the inorganic layer. [Means for solving the problem]

[0016] To achieve this object, the separation membrane according to the present invention includes a separation membrane substrate made of a porous material and an inorganic layer coated on at least one surface of the separation membrane substrate, and the separation membrane substrate and the inorganic layer have porosities that satisfy the following relationship with respect to the air permeability of the separation membrane: (10 × porosity of separation membrane substrate) - (4 × porosity of inorganic layer) ≦ air permeability of separation membrane

[0017] The inorganic layer may have a porosity of 55% or more.

[0018] The separator may have an air permeability of 200 sec / 100 cc or less.

[0019] The thickness of the inorganic layer may be 30% or more of the total thickness of the separator.

[0020] The inorganic material constituting the inorganic layer has a BET value of 3.0m 2 / g or more particles.

[0021] The inorganic material may have a dielectric constant of 1 or more, may have piezoelectricity, or may have lithium ion transport ability.

[0022] The separation membrane may have a diffusion length of 2.0 mm or more in the MD and TD directions.

[0023] The present invention provides a cylindrical secondary battery in which an electrode assembly including the separator is housed in a cylindrical battery case.

[0024] The present invention also provides a battery pack including the cylindrical secondary battery as a unit cell, the battery pack being used as an energy source for an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a power storage device.

[0025] Furthermore, the present invention can also be provided in the form of various combinations of means for solving the above problems. [Effects of the Invention]

[0026] As described above, in the separator according to the present invention, the electrolyte impregnation of the separator can be controlled by adjusting the porosity of the separator substrate and the porosity of the inorganic layer.

[0027] Furthermore, by measuring the air permeability of the separator, it is possible to indirectly check whether the separator is impregnated with an electrolyte solution.

[0028] In addition, a separator with improved impregnation properties can be provided using a conventional separator manufacturing method without adding additional processes or materials. Such a separator can be applied to large-volume cylindrical secondary batteries, making it suitable for devices that require high capacity and fast charging, such as electric vehicles. [Brief explanation of the drawings]

[0029] [Figure 1] 3 is a photograph showing a dropping experiment of the separation membrane according to Example 1. [Figure 2] 10 is a photograph showing a dropping experiment of a separation membrane according to Example 2. [Figure 3] 10 is a photograph showing a dropping experiment of a separation membrane according to Example 3. [Figure 4] 10 is a photograph showing a dropping experiment of a separation membrane according to Example 4. [Figure 5] 10 is a photograph showing a dropping experiment of a separation membrane according to Example 5. [Figure 6] 10 is a photograph showing a dropping experiment of a separation membrane according to Example 6. [Figure 7] 10 is a photograph showing a dropping experiment of the separation membrane according to Example 7. [Figure 8] 1 is a photograph showing a dropping experiment of a separation membrane according to Comparative Example 1. [Figure 9] 10 is a photograph showing a dropping experiment of a separation membrane according to Comparative Example 2. [Figure 10] 10 is a photograph showing a dropping experiment of a separation membrane according to Comparative Example 3. [Figure 11] 10 is a photograph showing a dropping experiment of a separation membrane according to Comparative Example 4. [Figure 12] 10 is a photograph showing a dropping experiment of a separation membrane according to Comparative Example 5. [Figure 13] 10 is a photograph showing a dropping experiment of a separation membrane according to Comparative Example 6. [Figure 14] 10 is a photograph showing a dropping experiment of a separation membrane according to Comparative Example 7. DETAILED DESCRIPTION OF THE INVENTION

[0030] Hereinafter, with reference to the accompanying drawings, a detailed description will be given of an embodiment of the present invention that will enable a person skilled in the art to easily carry out the present invention. However, in describing the operation principle of the preferred embodiment of the present invention in detail, detailed description of related well-known functions or configurations will be omitted if it is determined that such detailed description may unnecessarily obscure the gist of the present invention.

[0031] Furthermore, the same reference numerals are used throughout the drawings for parts having similar functions and actions. Throughout the specification, when a part is said to be connected to another part, this includes not only a direct connection but also an indirect connection via another element therebetween. Furthermore, unless otherwise specified, "including a certain element" does not mean that other elements are excluded, but that other elements may also be included.

[0032] Furthermore, in this specification, limitations or additions in one embodiment are not only applicable to that particular embodiment, but are also applicable to all embodiments in this specification.

[0033] Furthermore, throughout the description of the present invention and the claims, the singular includes the plural unless otherwise stated.

[0034] Furthermore, throughout the description of the present invention and the claims, unless otherwise specified, "or" includes "and." Therefore, "including A or B" means three cases: including A, including B, or including both A and B.

[0035] Furthermore, all numerical ranges include the endpoints and all intermediate values ​​therebetween unless expressly stated to the contrary.

[0036] The separation membrane according to the present invention includes a separation membrane substrate made of a porous material and an inorganic layer coated on at least one surface of the separation membrane substrate, and the porosity of the separation membrane substrate and the porosity of the inorganic layer may satisfy the following relationship with respect to the air permeability of the separation membrane: (10 × porosity of separation membrane substrate) - (4 × porosity of inorganic layer) ≦ air permeability of separation membrane

[0037] The separator substrate may include a polyolefin polymer resin commonly used in the art, such as at least one selected from the group consisting of high-density polyethylene, low-density polyethylene, linear low-density polyethylene, ultra-high-molecular-weight polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalene, and mixtures thereof.

[0038] Generally, when a separation membrane substrate containing a polyolefin-based polymer resin is used alone as a separation membrane, the separation membrane has problems such as poor heat resistance and low mechanical strength. To address these problems, an inorganic layer containing an inorganic material and a binder is provided on one or both sides of the separation membrane substrate.

[0039] The inorganic material constituting the inorganic material layer may have a dielectric constant of 1 or more, piezoelectricity, or lithium ion transport ability.

[0040] Specifically, non-limiting examples of inorganic materials having a dielectric constant of 1 or greater include SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, SiC, boehmite, alumina trihydrate (ATH), or mixtures thereof.

[0041] The inorganic material having piezoelectricity generates a potential difference due to positive and negative charges generated between both sides of the particle when a certain pressure is applied. Non-limiting examples of the inorganic material include BaTiO3, Pb(Zr,Ti)O3 (PZT), Pb 1-x La x Zr 1-y Ti y O3(PLZT), Pb(Mg 1 / 3 Nb 2 / 3 )O3-PbTiO3 (PMN-PT), hafnia (HfO2) or a mixture thereof.

[0042] The lithium ion transfer capability inorganic matter contains lithium element but transfers lithium ions without storing lithium, and lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3,0 <x<2、0<y<3)、リチウムアルミニウムチタンホスフェート(Li x Al y Ti z (PO4)3,0 <x<2、0<y<1、0<z<3)、14Li2O-9Al2O3-38TiO2-39P2O5のような(LiAlTiP) x O y Glass (0 <x<4、0<y<13)、リチウムランタンチタネート(Li x La y TiO3, 0 <x<2、0<y<3)、Li 3.25 Ge 0.25 P 0.75 Lithium germanium thiophosphate (Li x Ge y P z S w, (0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), a lithium nitride such as Li3N (Li x N y , (0 < x < 4, 0 < y < 2), a SiS2-based glass such as Li3PO4-Li2S-SiS2 (Li x Si y S z , (0 < x < 3, 0 < y < 2, 0 < z < 4), a P2S5-based glass such as LiI-Li2S-P2S5 (Li x P y S z , (0 < x < 3, 0 < y < 3, 0 < z < 7) or one or more selected from the group consisting of mixtures thereof.

[0043] The inorganic substance constituting the inorganic layer can be composed of particles with a BET of 3.0 m 2 / g or more.

[0044] When the BET of the inorganic substance is less than 3.0 m 2 / g, the impregnation property deteriorates, which is not preferable.

[0045] The binder is not particularly limited in type as long as it does not cause a chemical change in the inorganic layer of the separation membrane, and examples thereof include polyolefins such as polyethylene and polypropylene; fluorine-containing resins such as polyvinylidene fluoride and polytetrafluoroethylene; fluorine-containing copolymers such as vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer and ethylene-tetrafluoroethylene copolymer; styrene-butadiene copolymer and its hydrogenated products; (meth)acrylic acid ester copolymers such as methacrylic acid ester copolymer, acrylonitrile acrylic acid ester copolymer, and styrene acrylic acid ester copolymer; rubbers such as ethylene propylene rubber; polyvinyl acetate; polyphenylene The resin may be a resin having a melting point or glass transition temperature of 180°C or higher, such as ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamide, polyimide, polyamideimide, polyetheramide, polyester, aromatic polyester, or polyetheretherketone; polycarbonate; polyacetal; or a water-soluble resin, such as carboxyalkyl cellulose, alkyl cellulose, hydroxyalkyl cellulose, starch, polyvinyl alcohol, sodium alginate, polyethylene glycol, cellulose ester, polyacrylic acid, polyacrylamide, or polymethacrylic acid, or a (meth)acrylic resin, or may be a polymer containing two or more of these.

[0046] The inorganic layer may further include a dispersant, such as an acrylic copolymer, cyanoethyl polyvinyl alcohol, polyvinylpyrrolidone, baicalin, luteolin, taxifolin, myricetin, quercetin, rutin, catechin, epigallocatechin gallate, butein, piceatannol, a phenolic compound including tannic acid, pyrogallolic acid, amylase, amylopectin, xanthan gum, a fatty acid compound, or a polymer compound containing two or more of these.

[0047] Generally, when comparing the impregnation properties of a separation membrane substrate and an inorganic layer, the porosity of the separation membrane substrate tends to be smaller than the porosity of the inorganic layer, since the impregnation property of the inorganic layer is superior.

[0048] Furthermore, when the porosity of the separation membrane substrate and the inorganic layer is above a certain value, the impregnation property of the separation membrane may be improved. The separation membrane according to the present invention can be determined to have excellent impregnation property when the porosity of the separation membrane substrate and the porosity of the inorganic layer satisfy the relationship shown in the above formula, and the air permeation time of the separation membrane is 200 sec / 100 cc or less.

[0049] That is, without considering the units of porosity and air permeability, when the result of calculation using the numerical values ​​of the porosity of the separation membrane substrate and the porosity of the inorganic layer according to the above-mentioned relational expression is simply compared with the numerical value of the air permeability of the separation membrane, it can be determined that the separation membrane has excellent impregnation properties if the above-mentioned relational expression is satisfied.

[0050] In one embodiment, the porosity of the inorganic layer may be 55% or more. The porosity of the separator substrate may be adjusted so that the air permeability of the separator is 200 sec / 100 cc or less within the range of the porosity of the inorganic layer.

[0051] The porosity of the inorganic layer can be controlled by the ratio of the inorganic material to the binder, and the content of the inorganic material in the inorganic layer can be 10 wt % to 90 wt % based on 100 wt % of the mixture including the inorganic material and the binder.

[0052] Meanwhile, the thickness of the inorganic layer is 30% or more of the total thickness of the separation membrane. For example, when an inorganic layer is formed on only one side of a separation membrane substrate, the thickness of the inorganic layer formed on only one side may be 30% or more of the total thickness of the separation membrane. Alternatively, when an inorganic layer is formed on both sides of a separation membrane substrate, the sum of the thicknesses of the inorganic layers formed on both sides may be 30% or more of the total thickness of the separation membrane. Specifically, the thickness of the inorganic layer formed on only one side or the sum of the thicknesses of the inorganic layers formed on both sides may be 50% or more, more specifically 70% or more of the total thickness of the separation membrane.

[0053] In a separation membrane that satisfies the above relationship, the diffusion distances in both the MD and TD may be 2.0 mm or more. Specifically, the diffusion distance in the MD may be 3.0 mm or more, and more specifically, 3.5 mm or more. A separation membrane that does not satisfy the above relationship has a diffusion distance in both the MD and TD that is shorter than 2.0 mm. In other words, the separation membrane of the present invention exhibits a significantly improved impregnation rate.

[0054] The MD direction corresponds to the traveling direction of the separation membrane sheet during the production of the separation membrane, and the TD direction is a direction perpendicular to the MD direction.

[0055] The present invention provides a cylindrical secondary battery in which an electrode assembly including the separator is housed in a cylindrical battery case.

[0056] The electrode assembly may be a jelly-roll type electrode assembly manufactured by winding up a long separator sheet between a positive electrode sheet and a negative electrode sheet and attached to an outer surface of either the positive electrode sheet or the negative electrode sheet.

[0057] Alternatively, when manufacturing an electrode assembly for a cylindrical secondary battery, since the safety standards for cylindrical secondary batteries are relatively low due to the characteristics of the battery, the capacity and energy density of the battery can be increased by using a single-coated separator in which an inorganic layer is formed on only one side of the separator substrate.

[0058] The electrode sheets, positive electrode mixtures, and negative electrode mixtures constituting the positive and negative electrode sheets may be any conventionally used materials without any limitations, and therefore, a description thereof will be omitted in this specification.

[0059] The present invention also provides a battery pack including the cylindrical secondary battery as a unit cell. The battery pack can be used as an energy source for devices such as electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, power storage devices, and power storage systems.

[0060] The structures of the battery pack and the device are well known in the art, and therefore will not be described in detail herein.

[0061] The present invention will be described below with reference to examples, but these are for easier understanding of the present invention and are not intended to limit the scope of the present invention.

[0062] Example 1 As a porous separation membrane substrate containing a polyolefin polymer material, a separation membrane substrate with a porosity of 34% measured by a porosimeter was prepared, and as inorganic particles, a BET of 3m 2 A solid content containing 100 parts by weight of alumina (Al2O3) of 1 / g, 1 part by weight of an acrylic binder, and 1 part by weight of a dispersant was prepared.

[0063] 30% by weight of the solid content was dissolved in 70% by weight of water to prepare an inorganic slurry.

[0064] The inorganic slurry was coated on one side of the porous separator substrate to a thickness of 5 μm, thereby producing a single-sided coated aqueous separator having an inorganic layer formed on one side.

[0065] The porosity of the inorganic layer was calculated using the following formula and was found to be 56%. (1-(Inorganic layer density / solid content density))×100

[0066] In the above formula, the solid density can be calculated by the sum of the densities of the individual components constituting the solid, reflecting the content ratio.

[0067] <Example 2> In Example 1, inorganic particles having a BET value of 3 m 2 Instead of alumina at 1000 kJ / g, inorganic particles with a BET of 6m 2A single-side coated aqueous separator was prepared in the same manner as in Example 1, except that the porosity of the inorganic layer prepared using an inorganic slurry containing 100 parts by weight of inorganic particles and 2 parts by weight of binder was 58%.

[0068] Example 3 In Example 1, inorganic particles having a BET value of 3 m 2 Instead of alumina at 1000 kJ / g, inorganic particles with a BET of 9m 2 A single-side coated aqueous separator was prepared in the same manner as in Example 1, except that the porosity of the inorganic layer prepared using an inorganic slurry containing 100 parts by weight of inorganic particles and 3 parts by weight of binder was 57%.

[0069] Example 4 In Example 1, inorganic particles having a BET value of 3 m 2 Instead of alumina at 1000 kJ / g, inorganic particles with a BET of 5m 2 A single-side-coated aqueous separator was prepared in the same manner as in Example 1, except that the porosity of the inorganic layer prepared from an inorganic slurry containing 100 parts by weight of inorganic particles and 2 parts by weight of a binder was 60%.

[0070] <Example 5> In Example 1, inorganic particles having a BET value of 3 m 2 Instead of alumina, inorganic particles with a BET of 15m 2 A single-side-coated aqueous separator was prepared in the same manner as in Example 1, except that the porosity of the inorganic layer prepared from an inorganic slurry containing 100 parts by weight of inorganic particles and 6 parts by weight of a binder was 58%.

[0071] Example 6 In Example 1, inorganic particles having a BET value of 3 m 2 Instead of alumina, inorganic particles with a BET of 10m 2A single-sided coated aqueous separator was prepared in the same manner as in Example 1, except that the porosity of the inorganic layer prepared using an inorganic slurry containing 100 parts by weight of inorganic particles and 5 parts by weight of binder was 56% using ATH of 100 / g.

[0072] Example 7 In Example 1, inorganic particles having a BET value of 3 m 2 Instead of alumina, inorganic particles with a BET of 15m 2 A single-sided coated aqueous separator was prepared in the same manner as in Example 1, except that the porosity of the inorganic layer prepared using an inorganic slurry containing 100 parts by weight of inorganic particles and 6 parts by weight of binder was 55%.

[0073] <Comparative Example 1> As a porous separation membrane substrate containing a polyolefin polymer material, a separation membrane substrate with a porosity of 40% measured by a porosimeter was prepared, and inorganic particles with a BET value of 3m were used. 2 A solid content containing 100 parts by weight of alumina / g, 1 part by weight of an acrylic binder, and 1 part by weight of a dispersant was prepared.

[0074] 19% by weight of the solid content was dissolved in 81% by weight of water to prepare an inorganic slurry.

[0075] The inorganic slurry was coated on one side of the porous separator substrate to a thickness of 5 μm, thereby producing a single-sided coated aqueous separator having an inorganic layer formed on one side.

[0076] The porosity of the inorganic layer was calculated using the following formula and was found to be 47%. (1-(Inorganic layer density / solid content density))×100

[0077] In the above formula, the solid density can be calculated by the sum of the densities of the individual components constituting the solid, reflecting the content ratio.

[0078] <Comparative Example 2> In Comparative Example 1, inorganic particles having a BET value of 3 m 2 Instead of alumina at 1000 kJ / g, inorganic particles with a BET of 6m 2 A single-side coated aqueous separator was prepared in the same manner as in Comparative Example 1, except that the porosity of the inorganic layer prepared using an inorganic slurry containing 100 parts by weight of inorganic particles and 2 parts by weight of binder was 47%.

[0079] <Comparative Example 3> In Comparative Example 1, inorganic particles having a BET value of 3 m 2 Instead of alumina at 1000 kJ / g, inorganic particles with a BET of 9m 2 A single-side coated aqueous separator was prepared in the same manner as in Comparative Example 1, except that the porosity of the inorganic layer prepared using an inorganic slurry containing 100 parts by weight of inorganic particles and 5 parts by weight of binder was 48%.

[0080] <Comparative Example 4> In Comparative Example 1, inorganic particles having a BET value of 3 m 2 Instead of alumina at 1000 kJ / g, inorganic particles with a BET of 5m 2 A single-side-coated aqueous separator was prepared in the same manner as in Comparative Example 1, except that the porosity of the inorganic layer prepared using an inorganic slurry containing 100 parts by weight of inorganic particles and 2 parts by weight of a binder was 51%.

[0081] <Comparative Example 5> In Comparative Example 1, inorganic particles having a BET value of 3 m 2 Instead of alumina, inorganic particles with a BET of 15m 2 A single-side-coated aqueous separator was prepared in the same manner as in Comparative Example 1, except that the porosity of the inorganic layer prepared using an inorganic slurry containing 100 parts by weight of inorganic particles and 6 parts by weight of a binder was 49%.

[0082] <Comparative Example 6> In Comparative Example 1, inorganic particles having a BET value of 3 m 2Instead of alumina, inorganic particles with a BET of 10m 2 A single-side coated aqueous separator was prepared in the same manner as in Comparative Example 1, except that the porosity of the inorganic layer prepared using an inorganic slurry containing 100 parts by weight of inorganic particles and 5 parts by weight of binder was 47% using ATH of 100 / g.

[0083] <Comparative Example 7> In Comparative Example 1, inorganic particles having a BET value of 3 m 2 Instead of alumina, inorganic particles with a BET of 15m 2 A single-sided coated aqueous separator was prepared in the same manner as in Comparative Example 1, except that the porosity of the inorganic layer prepared using an inorganic slurry containing 100 parts by weight of inorganic particles and 6 parts by weight of binder was 46% using ATH of 100 / g.

[0084] Air permeability measurement Air permeability refers to the time it takes for 100cc of air to pass through the object being measured, and is expressed in units of sec / 100cc.

[0085] The air permeability can be expressed as a Gurley value, etc. In this specification, the air permeability of the entire separator having an inorganic layer formed thereon was measured in accordance with JIS P8117.

[0086] The air permeability measuring device used was the Seiko R150-02 model manufactured by Asahi Co., Ltd.

[0087] The results of measuring the air permeability of the separation membranes of Examples 1 to 7 and Comparative Examples 1 to 7 and the values ​​calculated using the above relational equation are shown in Tables 1 and 2 below.

[0088] [Table 1]

[0089] [Table 2]

[0090] Referring to Tables 1 and 2, it can be seen that the left side value of the relational equation for the separators of the Examples is smaller than the air permeability, while the left side value of the relational equation for the separators of the Comparative Examples is larger than the air permeability.

[0091] In order to confirm the impregnation properties of the separators of the Examples which satisfy the above-mentioned relationship and the separators of the Comparative Examples which do not satisfy the above-mentioned relationship, an electrolyte dropping experiment was carried out as follows.

[0092] <Electrolyte dripping experiment> Prepare a digital optical microscope (AD7013MZT(R4) manufactured by AnMo Electronics Corporation) and a steel ruler, and adjust the height of the digital optical microscope to focus so that the scale bar on the digital optical microscope matches the measurements on the steel ruler.

[0093] The separation membranes prepared in the Examples and Comparative Examples were cut into pieces 50 mm wide and 50 mm long, placed on a glass slide, and adhesive tape was attached to each vertex to fix the separation membrane to the glass slide.

[0094] A 10 μL microsyringe is filled with 2 μL of propylene carbonate, and a droplet is formed and dropped onto the fixed separation membrane.

[0095] Immediately after dropping, press the Capture button to check the shape of the droplets, and take an additional capture after 5 minutes.

[0096] The diffusion distance of a water droplet falling on the separation membrane was measured in both the MD and TD directions.

[0097] Photographs showing the diffusion distances of the separation membranes of Examples 1 to 7 are shown in Figures 1 to 7 and Table 3 below, and photographs showing the diffusion distances of the separation membranes of Comparative Examples 1 to 7 are shown in Figures 8 to 14 and Table 4 below.

[0098] [Table 3]

[0099] [Table 4]

[0100] Referring to Tables 3 and 4, the diffusion distances of the separation membranes of the Examples were 3.5 mm or more in the MD direction and 2.0 mm or more in the TD direction, while the diffusion distances of the separation membranes of the Comparative Examples were 1.4 mm or less in the MD direction and 1.1 mm or less in the TD direction.

[0101] Therefore, it can be seen that the impregnation ability of the separation membrane according to the examples that satisfy the above relationship is significantly improved. Therefore, when the air permeability of the separation membrane is constant, if the porosity of the separation membrane substrate and the porosity of the inorganic layer are set to satisfy the above relationship, it can be indirectly seen that the impregnation ability of the separation membrane is significantly improved.

[0102] Those skilled in the art will appreciate that various applications and modifications within the scope of the present invention will be possible based on the above content.

Claims

1. a separation membrane substrate made of a porous material; an inorganic layer coated on at least one surface of the separation membrane substrate; Including, The separation membrane substrate and the inorganic layer have porosities that satisfy the following relationship with the air permeability of the separation membrane: The inorganic material constituting the inorganic layer has a BET viscosity of 3.0 m ２ / g or more, 15m ２ / g or less of particles, The porosity of the separation membrane substrate is 34% or less, A separation membrane, wherein the porosity of the inorganic layer is 55% or more: (10×porosity of separation membrane substrate)−(4×porosity of inorganic layer)≦air permeability of separation membrane.

2. The separation membrane according to claim 1, wherein the separation membrane has an air permeability of 200 sec / 100 cc or less.

3. The separation membrane according to claim 1 , wherein the thickness of the inorganic layer is 30% or more of the total thickness of the separation membrane.

4. The separator according to claim 3 , wherein the inorganic material has a dielectric constant of 1 or more, has piezoelectricity, or has lithium ion transport ability.

5. The separation membrane according to claim 1 , wherein the diffusion distance in the MD and TD directions of the separation membrane is 2.0 mm or more.

6. A cylindrical secondary battery comprising an electrode assembly including the separator according to any one of claims 1 to 5 housed in a cylindrical battery case.

7. A battery pack including the cylindrical secondary battery according to claim 6 as a unit cell, The battery pack is used as an energy source for an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a power storage device.

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