Separator for electrochemical element and electrochemical element including the same

Abstract

The present invention provides a porous polymer substrate, comprising: a first organic-inorganic composite porous layer located on one surface of the porous polymer substrate and including first inorganic particles and a first binder polymer; a second organic-inorganic composite porous layer located on the other surface of the porous polymer substrate and including the first inorganic particles, the second inorganic particles, and a second binder polymer; Including, The first inorganic particles have an average particle size of 1 nm to 100 nm; The present invention relates to a separator for an electrochemical device, in which the average particle size of the second inorganic particles is larger than the average particle size of the first inorganic particles, and an electrochemical device including the separator. The separator for an electrochemical device according to the present invention can improve high temperature safety and assembly processability.

Description

[Technical Field]

[0001] The present invention relates to a separator for an electrochemical element and an electrochemical element including the separator. This application claims priority based on Korean Patent Application No. 10-2021-0069553, filed on May 28, 2021, and the entire contents disclosed in the specification and drawings of that application are incorporated herein by reference. [Background technology]

[0002] In recent years, interest in energy storage technology has been growing. As the range of applications for energy storage technology expands to include mobile phones, video cameras, laptops, and even electric vehicles, there is a growing need for higher energy density batteries used as power sources for these electronic devices. Secondary batteries are the type of battery that can best meet this need, and research into them is currently being actively conducted.

[0003] Such lithium secondary batteries are composed of a positive electrode, a negative electrode, an electrolyte, and a separator. Of these, the separator is required to have insulating properties that separate and electrically insulate the positive and negative electrodes, as well as high ionic conductivity that increases the permeability of lithium ions due to its high porosity.

[0004] Polyolefin separators, which use a polyolefin-based porous substrate, are widely used as such separators. However, due to their material properties and manufacturing process characteristics, polyolefin-based separators exhibit extreme thermal shrinkage behavior at high temperatures, posing safety issues such as internal short circuits.

[0005] In recent years, in order to solve such safety problems of polyolefin separators at high temperatures, a separator has been proposed in which a polyolefin separator is used as a porous substrate and at least one surface of the porous substrate is coated with a mixture of fine inorganic particles and a binder polymer.

[0006] However, such separators have the problem of being unable to ensure ease of assembly, such as causing problems such as meandering and wrinkles during the battery assembly process. Summary of the Invention [Problem to be solved by the invention]

[0007] Therefore, an object of the present invention is to provide a separator for an electrochemical device that can improve safety at high temperatures and ensure ease of assembly, and an electrochemical device including the separator. [Means for solving the problem]

[0008] In order to solve the above problems, according to one aspect of the present invention, there is provided a separator for an electrochemical element having the following features.

[0009] According to the first aspect, a porous polymer substrate; a first organic-inorganic composite porous layer located on one surface of the porous polymer substrate and including first inorganic particles and a first binder polymer; a second organic-inorganic composite porous layer located on the other surface of the porous polymer substrate and including the first inorganic particles, the second inorganic particles, and a second binder polymer; Including, The first inorganic particles have an average particle size of 1 nm to 100 nm, The separator for an electrochemical element is provided, wherein the average particle size of the second inorganic particles is larger than the average particle size of the first inorganic particles.

[0010] According to a second aspect, in the separator for an electrochemical element according to the first aspect, The average particle size of the second inorganic particles may be 1.01 to 50 times the average particle size of the first inorganic particles.

[0011] According to a third aspect, in the separator for an electrochemical element according to the first or second aspect, The average particle diameter of the second inorganic particles can be 150 nm to 800 nm.

[0012] According to a fourth aspect, in the separator for an electrochemical element according to any one of the first to third aspects, The weight ratio of the first inorganic particles to the second inorganic particles in the second organic-inorganic composite porous layer can be 40:60 to 92:8.

[0013] According to a fifth aspect, in the separator for an electrochemical element according to any one of the first to fourth aspects, The first inorganic particles may include fumed type inorganic particles.

[0014] According to a sixth aspect, in the separator for an electrochemical element according to the fifth aspect, The first inorganic particles may include fumed alumina, fumed silica, fumed titanium dioxide, or two or more of these.

[0015] According to a seventh aspect, in the separator for an electrochemical element according to any one of the first to sixth aspects, The second inorganic particles are BaTiO3, Pb(Zr,Ti)O3 (PZT), Pb La x Zr 1-y Ti y O3 (PLZT, 0 < x < 1, 0 < y < 1), Pb(Mg 1 / 3 Nb 2 / 3 )O3 - PbTiO3 (PMN - PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, Mg(OH)2, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, AlOOH, Al(OH)3, SiC, TiO2, lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti <T000008>(PO4)3, 0 < x < 2, 0 < y < 3), lithium aluminum phosphate (Li x Al y Tiz (PO4)3, 0 < x < 2, 0 < y < 1, 0 < z < 3), (LiAlTiP) x O y system glass (0 < x < 4, 0 < y < 13), lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), lithium germanium thiophosphate (Li x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride (Li x N y , 0 < x < 4, 0 < y < 2), SiS2 - based glass (Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4), P2S5 - based glass (Li x P y S z , 0 < x < 3, 0 < y < 3, 0 < z < 7), or may contain two or more of these.

[0016] According to the eighth aspect, in the separator for an electrochemical element according to any one of the first to seventh aspects, the arithmetic mean roughness of the surface of the second organic - inorganic composite porous layer of the separator for an electrochemical element can be 400 nm to 1000 nm.

[0017] According to the ninth aspect, in the separator for an electrochemical element according to any one of the first to eighth aspects, the thermal shrinkage rate after leaving the separator for an electrochemical element at 180 °C for 1 hour can be 10% or less in the machine direction (MD: Machine Direction) and the transverse direction (TD: Transverse Direction), respectively.[[ID=*]] [[ID=*]]

[0018] [[ID=*]] According to the tenth aspect, in the separator for an electrochemical element according to any one of the first to ninth aspects, The first binder polymer may be selected from the group consisting of poly(vinylidene fluoride-co-hexafluoropropylene), poly(vinylidene fluoride-co-chlorotrifluoroethylene), poly(vinylidene fluoride-co-tetrafluoroethylene), poly(vinylidene fluoride-co-trichloroethylene), acrylic copolymers, styrene-butadiene copolymers, poly(acrylic acid), and the like. acid), poly(methylmethacrylate), poly(butylacrylate), poly(acrylonitrile), poly(vinylpyrrolidone), poly(vinylalcohol), poly(vinylacetate), poly(ethylene-co-vinyl acetate), poly(ethylene oxide), poly(arylate), cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate propionate, cyanoethyl pullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, or two or more of these.

[0019] According to an eleventh aspect, in the separator for an electrochemical element according to any one of the first to tenth aspects, The second binder polymer may be selected from the group consisting of poly(vinylidene fluoride-co-hexafluoropropylene), poly(vinylidene fluoride-co-chlorotrifluoroethylene), poly(vinylidene fluoride-co-tetrafluoroethylene), poly(vinylidene fluoride-co-trichloroethylene), acrylic copolymers, styrene-butadiene copolymers, poly(acrylic acid), and the like. acid), poly(methylmethacrylate), poly(butylacrylate), poly(acrylonitrile), poly(vinylpyrrolidone), poly(vinylalcohol), poly(vinylacetate), poly(ethylene-co-vinyl acetate), poly(ethylene oxide), poly(arylate), cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate propionate, cyanoethyl pullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, or two or more of these.

[0020] In order to solve the above problems, according to one aspect of the present invention, there is provided an electrochemical device having the following configuration.

[0021] According to a twelfth aspect, a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; There is provided an electrochemical device, wherein the separator is the separator for an electrochemical device according to any one of the first to eleventh aspects.

[0022] According to a thirteenth aspect, in the electrochemical device according to the twelfth aspect, The electrochemical device may be a cylindrical lithium secondary battery. [Effects of the Invention]

[0023] The separator for an electrochemical element according to one embodiment of the present invention includes first inorganic particles having an average particle size of 1 nm to 100 nm on one surface of a porous polymer substrate, thereby improving high-temperature stability, and also includes an organic-inorganic composite porous layer on the other surface of the porous polymer substrate, which includes second inorganic particles having an average particle size larger than the average particle size of the first inorganic particles together with the first inorganic particles, thereby ensuring ease of assembly.

[0024] The separator for an electrochemical device according to one embodiment of the present invention may have a thermal shrinkage of 10% or less in both the machine direction (MD) and the transverse direction (TD) after being left at 180°C for 1 hour.

[0025] The arithmetic mean roughness of the surface of the second organic-inorganic composite porous layer of the separator for an electrochemical element according to one embodiment of the present invention may be 400 nm to 1000 nm.

[0026] The drawings attached to this specification illustrate preferred embodiments of the present invention and serve to further understand the technical concepts of the present invention as well as the content of the invention, and therefore the present invention should not be interpreted as being limited to only the matters depicted in the drawings. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a schematic diagram of a separator for an electrochemical element according to one embodiment of the present invention. [Figure 2] 4 is a roughness curve recorded by enlarging a cut surface of the surface of a second organic-inorganic composite porous layer of a separator according to an embodiment of the present invention. [Figure 3] 3 is a diagram showing the surface roughness of the second organic-inorganic composite porous layer of the separator for an electrochemical element produced in Example 1. FIG. [Figure 4] 1 is a diagram showing the surface roughness of the second organic-inorganic composite porous layer of the separator for an electrochemical element produced in Example 2. FIG. [Figure 5] 10 is a diagram showing the surface roughness of the second organic-inorganic composite porous layer of the separator for an electrochemical element produced in Example 3. FIG. [Figure 6] 10 is a diagram showing the surface roughness of the second organic-inorganic composite porous layer of the separator for an electrochemical element produced in Example 4. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0028] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, the terms and words used in the specification and claims should not be construed as being limited to their ordinary or dictionary meanings, but should be construed as having meanings and concepts corresponding to the technical ideas of the present invention, in accordance with the principle that the inventors themselves can appropriately define the concepts of terms in order to best explain the invention.

[0029] Therefore, it should be understood that the embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention and do not represent the entire technical idea of ​​the present invention, and that there may be various equivalents and modifications that can be substituted therefor at the time of this application.

[0030] A separator for an electrochemical element according to one aspect of the present invention comprises: a porous polymer substrate; a first organic-inorganic composite porous layer located on one surface of the porous polymer substrate and including first inorganic particles and a first binder polymer; a second organic-inorganic composite porous layer located on the other surface of the porous polymer substrate and including the first inorganic particles, the second inorganic particles, and a second binder polymer; Including, The first inorganic particles have an average particle size of 1 nm to 100 nm, The second inorganic particles have a larger average particle size than the first inorganic particles.

[0031] FIG. 1 is a schematic diagram of a separator for an electrochemical element according to one embodiment of the present invention. Referring to FIG. 1, a separator 1 for an electrochemical element includes a porous polymer substrate 10 . Referring to FIG. 1, a separator 1 for an electrochemical element is composed of a porous polymer substrate 10 .

[0032] In one embodiment of the present invention, the porous polymer substrate 10 can be any material that can be used as a separator for a secondary battery. The porous polymer substrate 10 is a thin film containing a polymer material. Non-limiting examples of the polymer material include polymer resins such as polyolefin resin, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene. The porous polymer substrate 10 can also be a nonwoven fabric or porous polymer film formed from the polymer material described above, or a laminate of two or more of these. Specifically, the porous polymer substrate 10 can be any one of the following a) to e).

[0033] a) a porous film formed by melting and extruding a polymer resin; b) a multilayer film in which two or more porous films of a) are laminated; c) a nonwoven web produced by accumulating filaments obtained by melting / spinning a polymer resin; d) a multilayer film in which two or more layers of the nonwoven fabric web of c) are laminated; e) A porous membrane having a multilayer structure containing two or more of the above a) to d).

[0034] In one embodiment of the present invention, the thickness of the porous polymer substrate 10 is not particularly limited, but may be 1 μm to 100 μm, or 1 μm to 30 μm. When the thickness of the porous polymer substrate 10 is within the above range, the problem of the separator being easily damaged during use of the battery can be prevented, and the energy density can be ensured.

[0035] Meanwhile, the average pore size and porosity of the porous polymer substrate 10 are not particularly limited as long as they can be suitably used in electrochemical devices, and the average pore size may be 0.01 μm to 50 μm, or 0.1 μm to 20 μm, and the porosity may be 5% to 95%. When the pore size and porosity are within the above ranges, the porous polymer substrate 10 can be easily prevented from acting as a resistor, and the mechanical properties of the porous polymer substrate 10 can be easily maintained.

[0036] In the present invention, the "average pore diameter" refers to the arithmetic mean value of the pore diameter. The porosity and pore diameter of the porous polymer substrate 10 can be measured by a BET 6-point method using a scanning electron microscope (SEM) image, a mercury porosimeter, a capillary flow porosimeter, or a porosimetry analyzer (Belsorp-II mini, manufactured by BEL Japan Co., Ltd.) via a nitrogen gas adsorption and flow method.

[0037] 1, the separator 1 for an electrochemical device includes a first organic-inorganic composite porous layer 20 on one surface of the porous polymer substrate 10. The first organic-inorganic composite porous layer 20 includes first inorganic particles 40 and a first binder polymer.

[0038] The first organic-inorganic composite porous layer 20 includes first inorganic particles 40 and a first binder polymer that attaches the first inorganic particles 40 to each other so that the first inorganic particles 40 can be maintained in a bonded state (i.e., the first binder polymer connects and fixes the first inorganic particles 40 to each other), and the first binder polymer can maintain the bonded state between the first inorganic particles 40 and the porous polymer substrate 10.

[0039] The first inorganic particles 40 have an average particle diameter of 1 nm to 100 nm. When the first inorganic particles 40 have an average particle diameter within the above range, the separator can be configured with a higher density of inorganic particles per unit area, thereby improving the thermal safety of the separator. The first organic-inorganic composite porous layer 20 contains first inorganic particles 40 with an average particle diameter of 1 nm to 100 nm, thereby preventing the porous polymer substrate 10 from exhibiting extreme thermal shrinkage behavior at high temperatures and improving the safety of the separator.

[0040] In one embodiment of the present invention, the average particle size of the first inorganic particles 40 may be 20 nm to 100 nm, or 20 nm to 50 nm, or 20 nm to 30 nm. When the average particle size of the first inorganic particles 40 is within the above range, the separator's heat shrinkage at high temperatures can be further improved. For example, the separator's heat shrinkage after being left at 180°C for 1 hour may be 10% or less, or 5% or less, or 0% to 5%, or 0% to 2% in the machine direction (MD) and transverse direction (TD), respectively.

[0041] Here, the term "machine direction" refers to the direction in which a separator travels when continuously produced, or the longitudinal direction of the separator in the direction in which the produced separator is wound up, and the term "transverse direction" refers to the direction across the machine direction, i.e., the direction perpendicular to the direction in which a separator travels when continuously produced, or the direction perpendicular to the longitudinal direction of the separator in the direction in which the produced separator is wound up.

[0042] Throughout this specification, the average particle size of inorganic particles is referred to as particle size D 50 This means that the particle diameter D 50" means the particle diameter at the 50% point of the cumulative distribution of particle numbers according to particle diameter. The particle diameter can be measured using the laser diffraction method. Specifically, the powder to be measured is dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500). The difference in the diffraction pattern according to particle size when the particles pass through a laser beam is measured, and the particle size distribution is calculated. The average particle diameter D 50 can be measured.

[0043] In one embodiment of the present invention, the first inorganic particles 40 may include fumed inorganic particles. In the present invention, fumed inorganic particles refer to inorganic particles in which elementary particles formed by hydrolysis in a flame at 1,000°C or higher are bonded to each other through collision to form secondary particles, and these secondary particles form three-dimensional aggregates (agglomerates). When the first inorganic particles 40 include fumed inorganic particles, the average particle diameter of the first inorganic particles 40 can more easily be 1 nm to 100 nm, 20 nm to 50 nm, 1 nm to 15 nm, 15 nm to 100 nm, 15 nm to 50 nm, or 15 nm to 20 nm.

[0044] In one embodiment of the present invention, the first inorganic particles 40 may include fumed alumina, fumed silica, fumed titanium dioxide, or two or more of these.

[0045] In particular, when the first inorganic particles 40 contain fumed alumina, the thermal shrinkage of the separator measured after leaving it at 180°C for 1 hour can more easily be 5% or less, or 0% to 5% or less, or 0% to 2% or less in the machine direction (MD) and transverse direction (TD).

[0046] The first binder polymer may be a binder polymer commonly used in forming organic-inorganic composite porous layers. The first binder polymer may have a glass transition temperature (Tg) of -200 to 200°C. When the glass transition temperature of the first binder polymer satisfies the above range, the mechanical properties, such as flexibility and elasticity, of the finally formed first organic-inorganic composite porous layer 20 may be improved.

[0047] The first binder polymer may have ion-conducting ability. When the first binder polymer has ion-conducting ability, the battery performance can be further improved. The first binder polymer may have a dielectric constant of 1.0 to 100 (measurement frequency = 1 kHz), or 10 to 100. When the dielectric constant of the first binder polymer satisfies the above range, the degree of dissociation of salt in the electrolyte can be improved.

[0048] In one embodiment of the present invention, the first binder polymer is selected from the group consisting of poly(vinylidene fluoride-co-hexafluoropropylene), poly(vinylidene fluoride-co-chlorotrifluoroethylene), poly(vinylidene fluoride-co-tetrafluoroethylene), poly(vinylidene fluoride-co-trichloroethylene), acrylic copolymers, styrene-butadiene copolymers, poly(acrylic acid), and the like. acid), poly(methylmethacrylate), poly(butylacrylate), poly(acrylonitrile), poly(vinylpyrrolidone), poly(vinylalcohol), poly(vinylacetate), poly(ethylene-co-vinyl acetate), poly(ethylene oxide), poly(arylate), cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate propionate, cyanoethyl pullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, or two or more of these.

[0049] The acrylic copolymer may include, but is not limited to, ethyl acrylate-acrylic acid-N,N-dimethylacrylamide copolymer, ethyl acrylate-acrylic acid-2-(dimethylamino)ethyl acrylate copolymer, ethyl acrylate-acrylic acid-N,N-diethylacrylamide copolymer, ethyl acrylate-acrylic acid-2-(diethylamino)ethyl acrylate copolymer, or two or more thereof.

[0050] In one embodiment of the present invention, the weight ratio of the first inorganic particles 40 to the first binder polymer is determined taking into consideration the thickness, pore size, and porosity of the first organic-inorganic composite porous layer 20, and may be 50:50 to 99.9:0.1, or 95:5 to 99.9:0.1. When the weight ratio of the first inorganic particles 40 to the first binder polymer is within the above range, sufficient voids (empty spaces) are formed between the first inorganic particles 40, thereby easily ensuring the pore size and porosity of the first organic-inorganic composite porous layer 20. In addition, the adhesive strength between the first inorganic particles 40 and the adhesive strength between the first inorganic particles 40 and the porous polymer substrate 1 can also be easily ensured.

[0051] In one embodiment of the present invention, the first organic-inorganic composite porous layer 20 may further include additives such as a dispersant and / or a thickener, such as citric acid, hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), ethylhydroxyethyl cellulose (EHEC), methyl cellulose (MC), carboxymethyl cellulose (CMC), hydroxyalkyl methyl cellulose, cyanoethylene polyvinyl alcohol, or two or more thereof.

[0052] In one embodiment of the present invention, the first organic-inorganic composite porous layer 20 may have a structure in which the first inorganic particles 40 are packed together and in contact with each other, and the first inorganic particles 40 are bound to each other by the first binder polymer, thereby forming interstitial volumes between the first inorganic particles 40, and the interstitial volumes between the first inorganic particles 40 become voids (empty spaces) to form pores.

[0053] In one embodiment of the present invention, the average pore diameter of the first organic-inorganic composite porous layer 20 may be 0.001 μm to 10 μm. The average pore diameter of the first organic-inorganic composite porous layer 20 can be measured by capillary flow porometry, which measures the diameter of the smallest pore in the thickness direction. Therefore, in order to measure the average pore diameter of only the first organic-inorganic composite porous layer 20 by capillary flow porometry, the first organic-inorganic composite porous layer 20 must be separated from the porous polymer substrate 10 and the separated first organic-inorganic composite porous layer 20 must be wrapped in a supportable nonwoven fabric before measurement. In this case, the pore diameter of the nonwoven fabric must be much larger than the pore diameter of the first organic-inorganic composite porous layer 20.

[0054] In one embodiment of the present invention, the porosity of the first organic-inorganic composite porous layer 20 may be 5% to 95%, or 10% to 95%, or 20% to 90%, or 30% to 80%. The porosity corresponds to a value obtained by subtracting the volume calculated based on the weight and density of each component of the first organic-inorganic composite porous layer 20 from the volume calculated based on the thickness, width, and length of the first organic-inorganic composite porous layer 20.

[0055] The porosity of the first organic-inorganic composite porous layer 20 can be measured by the BET 6-point method using a scanning electron microscope (SEM) image, a mercury porosimeter, a capillary flow porosimeter, or a porosimetry analyzer (Belsorp-II mini manufactured by Bell Japan Co., Ltd.) with a nitrogen gas adsorption and flow method.

[0056] In one embodiment of the present invention, the thickness of the first organic-inorganic composite porous layer 20 may be 1.5 μm to 5.0 μm on one surface of the porous polymer substrate 10. When the thickness of the first organic-inorganic composite porous layer 20 satisfies the above range, the adhesive strength with the electrode is excellent and the cell strength of the battery can be easily increased.

[0057] 1, the separator 1 for an electrochemical device includes a second organic-inorganic composite porous layer 30 on the other surface of the porous polymer substrate 10. The second organic-inorganic composite porous layer 30 includes the first inorganic particles 40, second inorganic particles 50, and a second binder polymer.

[0058] The second organic-inorganic composite porous layer 30 includes a second binder polymer that bonds the first inorganic particles 40 together, the second inorganic particles 50 together, and the first inorganic particles 40 and the second inorganic particles 50 together so that they can be maintained in a bonded state (i.e., the second binder polymer connects and fixes the first inorganic particles 40 together, the second inorganic particles 50 together, and the first inorganic particles 40 together and the second inorganic particles 50 together), and the second binder polymer can maintain the first inorganic particles 40 and the second inorganic particles 50 and the porous polymer substrate 10 in a bonded state.

[0059] For the first inorganic particles 40, please refer to the above description. Forming an organic-inorganic composite porous layer containing only inorganic particles with an average particle size of 1 nm to 100 nm on both sides of a porous polymer substrate improves the separator's safety at high temperatures, but this can cause problems such as insufficient processability during assembly due to differences in the roughness and / or friction with the core, leading to problems such as wrinkles and meandering in the separator during the battery assembly process.

[0060] The present inventors discovered that when an organic-inorganic composite porous layer containing first inorganic particles with an average particle diameter of 1 nm to 100 nm is located on one side of a porous polymer substrate, and an organic-inorganic composite porous layer containing the first inorganic particles and second inorganic particles with an average particle diameter larger than that of the first inorganic particles is located on the other side, slippage during assembly and tail-out problems during core discharge can be minimized, leading to the completion of the present invention.

[0061] The second inorganic particles 50 have a larger average particle diameter than the first inorganic particles 40. Since the second organic-inorganic composite porous layer 30 contains both the first inorganic particles 40 and the second inorganic particles 50, the assembly process can be more efficient than when the first inorganic particles 40 are used alone. Furthermore, since the second organic-inorganic composite porous layer 30 contains the first inorganic particles 40, the thermal stability of the separator can be maintained at the same level as when the separator contains only the first inorganic particles 40.

[0062] In one embodiment of the present invention, the average particle size of the second inorganic particles 50 may be 1.01 to 50 times, 1.15 to 25 times, 1.5 to 13.3 times, 13.3 to 50 times, or 13.3 to 25 times the average particle size of the first inorganic particles 40. When the average particle size of the second inorganic particles 50 satisfies the above range, ease of assembly can be more easily ensured.

[0063] In one embodiment of the present invention, the second inorganic particles 50 may have an average particle diameter of 150 nm to 800 nm, or 200 nm to 600 nm, or 300 nm to 500 nm, or 200 nm to 500 nm, or 200 nm to 300 nm, or 200 nm to 800 nm. When the average particle diameter of the second inorganic particles 50 satisfies the above range, ease of assembly can be more easily ensured.

[0064] The second inorganic particles 50 are not particularly limited as long as they are electrochemically stable. That is, the second inorganic particles 50 that can be used in the present invention are not particularly limited as long as they do not undergo an oxidation reaction and / or a reduction reaction within the operating voltage range of the applied electrochemical device (for example, 0 to 5V with respect to the Li / Li + reference). In particular, when using inorganic particles with a high dielectric constant as the second inorganic particles 50, it is possible to contribute to an increase in the dissociation degree of electrolyte salts, such as lithium salts, in the liquid electrolyte and improve the ionic conductivity of the electrolyte solution.

[0065] In one embodiment of the present invention, the second inorganic particles 50 may include high dielectric constant inorganic particles having a dielectric constant of 5 or more, preferably 10 or more. Non-limiting examples of inorganic particles having a dielectric constant of 5 or more include BaTiO3, Pb(Zr,Ti)O3 (PZT), Pb 1-x La x Zr 1-y Ti y O3 (PLZT, 0 < x < 1, 0 < y < 1), Pb(Mg 1 / 3 Nb 2 / 3 )O3-PbTiO3 (PMN-PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, Mg(OH)2, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, AlOOH, Al(OH)3, SiC, TiO2, or mixtures thereof, and the like.

[0066] Also, in another embodiment of the present invention, as the second inorganic particles 50, inorganic particles having lithium ion transfer ability, that is, inorganic particles containing a lithium element but not storing lithium and having a function of moving lithium ions can be used. Non-limiting examples of inorganic particles having lithium ion transfer ability include lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0 < x < 2, 0 < y < 3), lithium aluminum phosphate (Li x Al y Ti z(PO4)3, 0 < x < 2, 0 < y < 1, 0 < z < 3, (LiAlTiP) x O y -based glass (0 < x < 4, 0 < y < 13), lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), lithium germanium thiophosphate (Li x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride (Li x N y , 0 < x < 4, 0 < y < 2), SiS2-based glass (Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4), P2S5-based glass (Li x P y S z , 0 < x < 3, 0 < y < 3, 0 < z < 7), or may contain two or more of these.

[0067] In one embodiment of the present invention, the weight ratio of the first inorganic particles 40 to the second inorganic particles 50 in the second organic-inorganic composite porous layer may be 40:60 to 92:8, or 60:40 to 92:8, or 60:40 to 84:16, or 60:40 to 76:24, or 76:24 to 92:8, or 84:16 to 92:8, or 76:24 to 84:16.

[0068] When the weight ratio of the first inorganic particles 40 to the second inorganic particles 50 satisfies the above range, the thermal safety at high temperatures is improved, and it is possible to more easily ensure the arithmetic mean roughness value of the surface of the second organic-inorganic composite porous layer of the separator to ensure the assembly processability.

[0069] For example, the arithmetic mean roughness of the surface of the second organic-inorganic composite porous layer of the separator for the electrochemical device may be 400 nm to 1000 nm, or 500 nm to 1000 nm, or 400 nm to 970 nm, or 600 nm to 970 nm.

[0070] When the arithmetic mean roughness of the surface of the second organic-inorganic composite porous layer of the separator for electrochemical elements satisfies the above-mentioned range, the assembly process can be ensured and the occurrence of breaks (cuts) or cracks in the separator can be easily prevented.

[0071] In this specification, the arithmetic mean roughness of the surface of the second organic-inorganic composite porous layer of the separator refers to a value obtained by cutting the surface of the second organic-inorganic composite porous layer of the separator along a plane perpendicular to the surface of the second organic-inorganic composite porous layer, enlarging the cut surface, recording a roughness curve, and then drawing out a reference length L in the mean roughness direction of the roughness curve as shown in FIG. 2, and expressing the roughness curve by the following formula 1, with the mean line direction as the x-axis and the height direction as the y-axis.

[0072]

number

[0073] The arithmetic mean roughness can be measured using, for example, an optical profiler (NV-2700) manufactured by Nano System.

[0074] In particular, when the weight ratio of the first inorganic particles 40 to the second inorganic particles 50 satisfies 60:40 to 76:24, the arithmetic mean roughness of the surface of the second organic-inorganic composite porous layer can be 600 nm to 970 nm. In particular, when the arithmetic mean roughness of the surface of the second organic-inorganic composite porous layer of the separator is within the above range, this can be advantageous in ensuring ease of assembly.

[0075] The second binder polymer may be a binder polymer commonly used in forming organic-inorganic composite porous layers. In one embodiment of the present invention, the second binder polymer may be the same as or different from the first binder polymer. The second binder polymer may have a glass transition temperature (Tg) of -200 to 200°C. When the glass transition temperature of the second binder polymer satisfies the above range, the mechanical properties, such as flexibility and elasticity, of the finally formed second organic-inorganic composite porous layer 30 can be improved. The second binder polymer may have ion conductivity. When the second binder polymer has ion conductivity, the battery performance can be further improved. The second binder polymer may have a dielectric constant of 1.0 to 100 (measurement frequency = 1 kHz) or 10 to 100. When the dielectric constant of the second binder polymer satisfies the above range, the degree of salt dissociation in the electrolyte can be improved.

[0076] In one embodiment of the present invention, the second binder polymer is selected from the group consisting of poly(vinylidene fluoride-co-hexafluoropropylene), poly(vinylidene fluoride-co-chlorotrifluoroethylene), poly(vinylidene fluoride-co-tetrafluoroethylene), poly(vinylidene fluoride-co-trichloroethylene), acrylic copolymers, styrene-butadiene copolymers, poly(acrylic acid), and the like. acid), poly(methylmethacrylate), poly(butylacrylate), poly(acrylonitrile), poly(vinylpyrrolidone), poly(vinylalcohol), poly(vinylacetate), poly(ethylene-co-vinyl acetate), poly(ethylene oxide), poly(arylate), cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate propionate, cyanoethyl pullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, or two or more of these.

[0077] The acrylic copolymer may include, but is not limited to, ethyl acrylate-acrylic acid-N,N-dimethylacrylamide copolymer, ethyl acrylate-acrylic acid-2-(dimethylamino)ethyl acrylate copolymer, ethyl acrylate-acrylic acid-N,N-diethylacrylamide copolymer, ethyl acrylate-acrylic acid-2-(diethylamino)ethyl acrylate copolymer, or two or more thereof.

[0078] In one embodiment of the present invention, the weight ratio of the total inorganic particles, which is a combination of the first inorganic particles 40 and the second inorganic particles 50, to the second binder polymer may be 50:50 to 99.9:0.1, or 95:5 to 99.9:0.1, depending on the thickness, pore size, and porosity of the final second organic-inorganic composite porous layer 30. When the weight ratio of the total inorganic particles to the second binder polymer is within the above range, sufficient voids (empty spaces) are formed between the first inorganic particles 40, between the second inorganic particles 50, and between the first inorganic particles 40 and the second inorganic particles 50, thereby easily ensuring the pore size and porosity of the second organic-inorganic composite porous layer 30. In addition, adhesive strength can be easily ensured between the first inorganic particles 40, between the second inorganic particles 50, between the first inorganic particles 40 and the second inorganic particles 50, and between the inorganic particles as a whole and the porous polymer substrate 10.

[0079] For other characteristics of the second organic-inorganic composite porous layer 30, please refer to the above description of the first organic-inorganic composite porous layer 20.

[0080] The separator for an electrochemical device according to one embodiment of the present invention includes organic-inorganic composite porous layers on both sides of a porous polymer substrate, thereby improving impregnation with an electrolyte, thereby increasing the capacity of an electrochemical device including the separator for an electrochemical device.

[0081] Furthermore, by including organic-inorganic composite porous layers on both sides of the porous polymer substrate, safety can be improved when the separator is stored at high temperatures, for example, at about 80°C, and safety against internal short circuits can also be improved.

[0082] A separator for electrochemical elements according to one embodiment of the present invention comprises first inorganic particles having an average particle diameter of 1 nm to 100 nm on one surface of a porous polymer substrate, and the first inorganic particles and second inorganic particles having an average particle diameter larger than that of the first inorganic particles on the other surface of the porous polymer substrate, thereby improving safety at high temperatures and improving ease of assembly.

[0083] In one embodiment of the present invention, the separator for an electrochemical device may have a thermal shrinkage rate of 10% or less, 5% or less, 0% to 5%, or 0% to 2% in both the machine direction (MD) and the transverse direction (TD) after being left at 180°C for 1 hour.

[0084] In one embodiment of the present invention, the arithmetic mean roughness of the surface of the second organic-inorganic composite porous layer of the separator for electrochemical devices may be 400 nm to 1000 nm, or 500 nm to 1000 nm, or 400 nm to 970 nm, or 600 nm to 970 nm. When the arithmetic mean roughness of the surface of the second organic-inorganic composite porous layer of the separator satisfies the above range, the separator does not break (cut) or crack, and the assembly process is easily ensured. In particular, when the arithmetic mean roughness of the surface of the second organic-inorganic composite porous layer of the separator is 600 nm to 970 nm, the separator does not break (cut) or crack, and this can be advantageous in ensuring the assembly process.

[0085] The arithmetic mean roughness value of the surface of the second organic-inorganic composite porous layer of the separator for electrochemical elements can be determined by the content ratio of the first inorganic particles to the second inorganic particles, the average particle diameter of the first inorganic particles, the average particle diameter of the second inorganic particles, the surface condition of the first inorganic particles and / or the second inorganic particles, etc.

[0086] The separator for an electrochemical element according to the present invention can be produced by the following method, but is not limited thereto.

[0087] According to one embodiment of the present invention, a method for producing a separator for an electrochemical element includes the steps of: Providing a porous polymeric substrate; a step of coating one surface of the porous polymer substrate with a slurry for forming a first organic-inorganic composite porous layer, the slurry including first inorganic particles, a first binder polymer, and a first dispersion medium, and drying the slurry; a step of coating a slurry for forming a second organic-inorganic composite porous layer, the slurry including the first inorganic particles, the second inorganic particles, the second binder polymer, and the second dispersion medium, on the other surface of the porous polymer substrate and drying the slurry; Including, The first inorganic particles have an average particle size of 1 nm to 100 nm, The average particle size of the second inorganic particles may be larger than the average particle size of the first inorganic particles.

[0088] Hereinafter, the main steps of a method for producing a separator for an electrochemical element according to one embodiment of the present invention will be described.

[0089] First, a porous polymer substrate is prepared. For the porous polymer substrate, refer to the above description.

[0090] The porous polymer substrate can be prepared by forming pores from the above-mentioned materials using a conventional method known in the art, such as a wet method using a solvent, diluent, or pore-forming agent, or a dry method using a stretching method, in order to ensure excellent breathability and porosity.

[0091] Next, a slurry for forming a first organic-inorganic composite porous layer containing first inorganic particles, a first binder polymer, and a first dispersion medium is coated on one surface of the porous polymer substrate and dried. For the first inorganic particles and the first binder polymer, please refer to the above description.

[0092] Depending on the type of the first binder polymer, the first dispersion medium may function as a solvent that dissolves the first binder polymer, or may function as a dispersion medium that disperses the first binder polymer without dissolving it.

[0093] In one embodiment of the present invention, the first dispersion medium may be N-methyl-2-pyrrolidone, acetone, methyl ethyl ketone, dimethylformamide, dimethylacetamide, methanol, ethanol, isopropyl alcohol, or two or more organic solvents selected from these, or water.

[0094] The slurry for forming the first organic-inorganic composite porous layer may be prepared by dissolving or dispersing the first binder polymer in the first dispersion medium, and then adding and dispersing the first inorganic particles, but the method for preparing the slurry is not limited thereto.

[0095] Non-limiting examples of a method for coating one side of the porous polymer substrate with the slurry for forming the first organic-inorganic composite porous layer include a die coating method, a roll coating method, a comma coating method, a microgravure coating method, a doctor blade coating method, a reverse roll coating method, and a direct roll coating method.

[0096] In one embodiment of the present invention, after coating the slurry for forming the first organic-inorganic composite porous layer on one side of the porous polymer substrate, a phase separation step using a non-solvent for the first binder polymer may be further included, in order to form a pore structure in the first organic-inorganic composite porous layer, according to a conventional method known in the art.

[0097] In one embodiment of the present invention, the phase separation step may be humidification phase separation. The humidification phase separation may be performed at a temperature of 15°C to 70°C or 20°C to 50°C and a relative humidity of 15% to 80% or 30% to 50%. The slurry for forming the first organic-inorganic composite porous layer may have phase transition characteristics during the drying process due to a vapor-induced phase separation phenomenon known in the art.

[0098] For the humidification phase separation, a non-solvent for the first binder polymer can be introduced in a gaseous state. The non-solvent for the first binder polymer is not particularly limited as long as it does not dissolve the first binder polymer and is partially compatible with the dispersion medium. For example, a non-solvent in which the solubility of the first binder polymer is less than 5 wt % at 25°C can be used. For example, the non-solvent for the first binder polymer can be water, methanol, ethanol, isopropanol, butanol, butanediol, ethylene glycol, propylene glycol, tripropylene glycol, or two or more of these.

[0099] Next, a slurry for forming a second organic-inorganic composite porous layer containing the first inorganic particles, the second inorganic particles, the second binder polymer, and the second dispersion medium is coated on the other surface of the porous polymer substrate and dried.

[0100] For the first inorganic particles, the second inorganic particles, and the second binder polymer, please refer to the above description.

[0101] Depending on the type of the second binder polymer, the second dispersion medium may function as a solvent that dissolves the second binder polymer, or may function as a dispersion medium that disperses the second binder polymer without dissolving it.

[0102] In one embodiment of the present invention, the second dispersion medium may be N-methyl-2-pyrrolidone, acetone, methyl ethyl ketone, dimethylformamide, dimethylacetamide, methanol, ethanol, isopropyl alcohol, or two or more organic solvents selected from these, or water.

[0103] The slurry for forming the second organic-inorganic composite porous layer may be prepared by dissolving or dispersing the second binder polymer in the second dispersion medium, and then adding and dispersing the first inorganic particles and the second inorganic particles, but the method for preparing the slurry is not limited thereto.

[0104] Non-limiting examples of methods for coating the second organic-inorganic composite porous layer-forming slurry on the other side of the porous polymer substrate include die coating, roll coating, comma coating, microgravure coating, doctor blade coating, reverse roll coating, and direct roll coating.

[0105] In one embodiment of the present invention, after coating the slurry for forming the second organic-inorganic composite porous layer on the other side of the porous polymer substrate, a phase separation step using a non-solvent for the second binder polymer may be further included, in order to form a pore structure in the second organic-inorganic composite porous layer, according to a conventional method known in the art.

[0106] In one embodiment of the present invention, the phase separation step may be humidification phase separation. The humidification phase separation may be performed at a temperature of 15°C to 70°C or 20°C to 50°C and a relative humidity of 15% to 80% or 30% to 50%. The slurry for forming the second organic-inorganic composite porous layer may have phase transition characteristics during the drying process due to a vapor-induced phase separation phenomenon known in the art.

[0107] For the humidification phase separation, a non-solvent for the second binder polymer can be introduced in a gaseous state. The non-solvent for the second binder polymer is not particularly limited as long as it does not dissolve the second binder polymer and is partially compatible with the dispersion medium. For example, a non-solvent in which the solubility of the second binder polymer is less than 5 wt % at 25°C can be used. For example, the non-solvent for the second binder polymer can be water, methanol, ethanol, isopropanol, butanol, butanediol, ethylene glycol, propylene glycol, tripropylene glycol, or two or more of these.

[0108] In one embodiment of the present invention, phase separation after coating the first organic-inorganic composite porous layer-forming slurry may occur simultaneously with phase separation after coating the second organic-inorganic composite porous layer-forming slurry.

[0109] In another embodiment of the present invention, phase separation of the slurry for forming the second organic-inorganic composite porous layer may occur after phase separation of the slurry for forming the first organic-inorganic composite porous layer occurs.

[0110] An electrochemical device can be manufactured by interposing the separator for an electrochemical device between a positive electrode and a negative electrode.

[0111] The electrochemical device of the present invention includes any device that causes an electrochemical reaction, and specific examples include any type of primary or secondary battery, fuel cell, solar cell, or capacitor such as a supercapacitor device.

[0112] In particular, the electrochemical device may be a lithium secondary battery, including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0113] In one embodiment of the present invention, the electrochemical device may be a cylindrical lithium secondary battery. Since the separator for an electrochemical device according to one embodiment of the present invention ensures ease of assembly, when the separator for an electrochemical device according to one embodiment of the present invention is a separator for a cylindrical lithium secondary battery, the battery may be more easily assembled.

[0114] The electrode to be used together with the separator for an electrochemical device of the present invention is not particularly limited, and may be prepared in a form in which an electrode active material layer containing an electrode active material, a conductive material, and a binder is bound to a current collector according to a conventional method known in the art.

[0115] Among the electrode active materials, non-limiting examples of the positive electrode active material include layered compounds such as lithium cobalt composite oxide (LiCoO2) and lithium nickel oxide (LiNiO2), and compounds substituted with one or more transition metals; 1+x Mn 2-x O4 (where x = 0 to 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O5, LiV3O4, V2O5, and Cu2V2O7; and the chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by the formula LiMnO2 (where M=Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x=0.01 to 0.3); 2-x M xExamples of suitable lithium manganese composite oxides include, but are not limited to, lithium manganese composite oxides represented by the formula LiMnO2 (where M=Co, Ni, Fe, Cr, Zn, or Ta, and x=0.01 to 0.1) or Li2Mn3MO5 (where M=Fe, Co, Ni, Cu, or Zn); LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion; disulfide compounds; and Fe2(MoO4)3.

[0116] Non-limiting examples of the negative electrode active material include common negative electrode active materials that can be used in the negative electrodes of conventional electrochemical devices, particularly lithium metal or lithium alloys, and lithium adsorbent materials such as carbon, petroleum coke, activated carbon, graphite, or other carbons.

[0117] Non-limiting examples of positive electrode current collectors include foils made of aluminum, nickel, or a combination thereof, and non-limiting examples of negative electrode current collectors include foils made of copper, gold, nickel, or a copper alloy, or a combination thereof.

[0118] In one embodiment of the present invention, the conductive materials used in the negative electrode and the positive electrode may each be added independently in an amount of 1 to 30% by weight, based on the total weight of the active material layer. Such conductive materials are not particularly limited as long as they do not cause chemical changes in the battery and are conductive. Examples of such conductive materials include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; carbon fluoride; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0119] In one embodiment of the present invention, the binders used in the negative and positive electrodes are components that independently aid in bonding the active material to the conductive material and the current collector, and are typically added in an amount of 1 to 30 wt % based on the total weight of the active material layer. Examples of such binders include polyvinylidene fluoride (PVdF), polyacrylic acid (PAA), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers.

[0120] In one embodiment of the present invention, the electrochemical device includes an electrolyte solution, which may include an organic solvent and a lithium salt. The electrolyte solution may be an organic solid electrolyte or an inorganic solid electrolyte.

[0121] Examples of the organic solvent that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran (franc), 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0122] The lithium salt is a substance that is easily dissolved in the organic solvent, such as LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10, LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylates, lithium 4-phenylborate, imides, etc. can be used.

[0123] In addition, for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. may be added to the electrolyte solution to improve charge / discharge characteristics, flame retardancy, etc. In some cases, a halogen-containing solvent such as carbon tetrachloride or trifluoroethylene may be further added to impart non-flammability, and carbon dioxide gas may be further added to improve high-temperature storage properties.

[0124] Examples of the organic solid electrolyte that can be used include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyagitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, and polymers containing ionic dissociative groups.

[0125] Examples of the inorganic solid electrolyte that can be used include nitrides, halides, and sulfates of Li, such as LiN, LiI, LiNI, LiN-LiI-LiOH, LiSiO, LiSiO-LiI-LiOH, LiSiS, LiSiO, LiSiO-LiI-LiOH, and LiPO-LiS-SiS.

[0126] The electrolyte injection can be performed at an appropriate step in the battery manufacturing process depending on the manufacturing process and required properties of the final product, i.e., before the battery is assembled or as the final step of the battery assembly.

[0127] In one embodiment of the present invention, the process of applying the separator for an electrochemical device to a battery may include a lamination (stack) and folding process of the separator and electrodes in addition to a general winding process.

[0128] In one embodiment of the present invention, the separator for an electrochemical device may be sandwiched between a positive electrode and a negative electrode of an electrochemical device, or may be sandwiched between adjacent cells or electrodes when a plurality of cells or electrodes are assembled to form an electrode assembly. The electrode assembly may have various structures, such as a simple stack type, a jelly-roll type, a stack-folding type, or a lamination-stack type.

[0129] The present invention will be described in more detail below with reference to examples to aid in understanding the present invention. However, the examples according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the following examples. The examples of the present invention are provided to more completely explain the present invention to those skilled in the art.

[0130] Example 1 As a porous polymer substrate, a polyethylene porous film having a thickness of 11 μm was prepared. 98 parts by weight of fumed alumina (average particle size: 20 nm) as first inorganic particles, 1.7 parts by weight of polyacrylic acid as a first binder polymer, and 0.3 parts by weight of DS-F1 (polycarboxylic acid, manufactured by Sannovco) as a dispersant were added to acetone, and the first inorganic particles were crushed and dispersed using a ball mill method for a total of 12 hours to produce a slurry for forming a first organic-inorganic composite porous layer. The crushed first inorganic particles had an average particle size of 15 nm.

[0131] The slurry for forming the first organic-inorganic composite porous layer was coated on one side of the porous polymer substrate by roll coating, and then dried for 1 minute in a humid atmosphere at 23°C and a relative humidity of 42% to form a first organic-inorganic composite porous layer.

[0132] Fumed alumina (average particle size: 20 nm) as the first inorganic particles and alumina (average particle size: 500 nm) as the second inorganic particles were mixed in acetone at a weight ratio of 92:8. 98 parts by weight of the fumed alumina / alumina mixture, 1.7 parts by weight of polyacrylic acid as the second binder polymer, and 0.3 parts by weight of DS-F1 (manufactured by Sanofco) as the dispersant were added, and the first and second inorganic particles were crushed and dispersed using a ball mill for a total of 12 hours to produce a slurry for forming a second organic-inorganic composite porous layer. The crushed first inorganic particles had an average particle size of 15 nm, and the crushed second inorganic particles had an average particle size of 200 nm.

[0133] The slurry for forming the second organic-inorganic composite porous layer was coated by roll coating onto the other side of the porous polymer substrate on which the first organic-inorganic composite porous layer was not formed, and then dried in a moist atmosphere at 23°C and a relative humidity of 42% for 1 minute to produce a separator for electrochemical elements.

[0134] Example 2 A separator for an electrochemical element was produced in the same manner as in Example 1, except that fumed alumina as the first inorganic particles and alumina as the second inorganic particles were mixed in a weight ratio of 84:16.

[0135] Example 3 A separator for an electrochemical element was produced in the same manner as in Example 1, except that fumed alumina as the first inorganic particles and alumina as the second inorganic particles were mixed in a weight ratio of 76:24.

[0136] Example 4 A separator for an electrochemical element was produced in the same manner as in Example 1, except that fumed alumina as the first inorganic particles and alumina as the second inorganic particles were mixed in a weight ratio of 60:40.

[0137] Comparative Example 1 A polyethylene porous film having a thickness of 11 μm was used as a separator for an electrochemical element without any treatment.

[0138] Comparative Example 2 As a porous polymer substrate, a polyethylene porous film having a thickness of 11 μm was prepared. 98 parts by weight of alumina (average particle size: 500 nm) as inorganic particles, 1.7 parts by weight of polyacrylic acid as a binder polymer, and 0.3 parts by weight of DS-F1 (manufactured by Sanofco) as a dispersant were added to acetone, and the inorganic particles were then crushed and dispersed using a ball mill method for a total of 12 hours to produce a slurry for forming an organic-inorganic composite porous layer. The average particle size of the crushed inorganic particles was 200 nm.

[0139] The organic-inorganic composite porous layer-forming slurry was coated on both sides of the porous polymer substrate by dip coating, and then dried for 1 minute in a moist atmosphere at 23°C and a relative humidity of 42% to produce a separator for an electrochemical element.

[0140] Comparative Example 3 As a porous polymer substrate, a polyethylene porous film having a thickness of 11 μm was prepared. 92 parts by weight of fumed alumina (average particle size: 20 nm) as inorganic particles, 1.7 parts by weight of polyacrylic acid as a binder polymer, and 0.3 parts by weight of DS-F1 (Sannovco) as a dispersant were added to acetone, and the inorganic particles were crushed and dispersed using a ball mill for a total of 12 hours to produce a slurry for forming an organic-inorganic composite porous layer. The average particle size of the crushed inorganic particles was 15 nm.

[0141] The organic-inorganic composite porous layer-forming slurry was applied to both sides of the porous polymer substrate by dip coating, and then dried for 1 minute at 23°C and a relative humidity of 42% to prepare a separator for an electrochemical element.

[0142] Evaluation example 1: Method for measuring the average particle size of inorganic particles The first inorganic particles, second inorganic particles, and inorganic particles contained in the final organic-inorganic composite porous layer-forming slurries produced in Examples 1 to 4 and Comparative Examples 2 and 3 were each dispersed in a dispersion medium, and then introduced into a laser diffraction particle size analyzer (Microtrac S3500). The particle size distribution was calculated by measuring the difference in diffraction pattern depending on particle size when the particles passed through a laser beam. The particle size at the point where the cumulative distribution of particle numbers according to particle size in the measurement device reached 50% was calculated to obtain the average particle size D 50 was measured.

[0143] Evaluation example 2: Evaluation of separator properties The air permeability, basis weight, electrical resistance, perforation strength, arithmetic mean roughness of the surface of the second organic-inorganic composite porous layer, and heat shrinkage in the machine direction and transverse direction after leaving at 180°C for 1 hour for the separators produced in Examples 1 to 4 and Comparative Examples 1 to 3 are shown in Table 1 below.

[0144] (1) Air permeability evaluation Air permeability (Gurley) was measured according to ASTM D726-94. Gurley, as used herein, is the resistance to air flow and was measured using a Gurley densometer. The air permeability values ​​described herein are expressed as the time (in seconds) it takes for 100 cc of air to pass through a 1-inch square cross section of the separator at a pressure of 12.2 in H2O, i.e., the air permeability time.

[0145] (2) Basis weight evaluation Basis weight (g / m 2 ) was evaluated by preparing a sample with a separator that was 1 m wide and 1 m long, and measuring its weight.

[0146] (3) Evaluation of electrical resistance The electrical resistance was measured by preparing coin cells using the separators of Examples 1 to 4 and Comparative Examples 1 to 3, leaving the coin cells at room temperature for one day, and then measuring the resistance of the separators by an impedance measurement method. The coin cells were prepared as follows.

[0147] Anode manufacturing Artificial graphite as a negative electrode active material, carbon black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were mixed in a weight ratio of 75:5:20, and N-methylpyrrolidone (NMP) as a solvent was added to prepare a negative electrode slurry. The negative electrode slurry was charged to 3.8 mAh / cm 2 The mixture was coated on a copper current collector in a loading amount of 0.1g and dried to prepare a negative electrode.

[0148] Cathode manufacturing LiCoO2 as a positive electrode active material, Denka black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were mixed in a weight ratio of 85:5:10, respectively, and added to N-methylpyrrolidone (NMP) as a solvent to prepare a positive electrode active material slurry. The positive electrode active material slurry was coated on a sheet-shaped aluminum current collector and dried, resulting in a final positive electrode loading of 3.3 mAh / cm. 2 The positive electrode active material layer was formed so as to have the following structure.

[0149] Coin Cell Manufacturing Each separator of the Examples and Comparative Examples was interposed between the negative electrode and positive electrode prepared as described above, and a nonaqueous electrolyte (1M LiPF, ethylene carbonate (EC) / propylene carbonate (PC) / diethyl carbonate (DEC)) (volume ratio: 3:3:3:4) was poured into the separator to prepare a coin cell.

[0150] (4) Evaluation of drilling strength A test specimen having dimensions of 50 mm x 50 mm was prepared. The puncture strength was measured according to ASTM D2582 after setting a 1 mm round tip to operate at a speed of 120 mm / min.

[0151] (5) Evaluation of the arithmetic mean roughness of the surface The arithmetic mean roughness (Ra) of the surfaces of the separators produced in Examples 1 to 4 and Comparative Examples 1 to 3 was measured using an optical profiler (NV-2700) manufactured by Nano Systems Co., Ltd.

[0152] In the cases of Examples 1 to 4, the arithmetic mean roughness (Ra) of the surface of the second organic-inorganic composite porous layer was measured. In the case of Comparative Example 1, the arithmetic mean roughness (Ra) of the surface of the polyethylene porous film was measured, and in the cases of Comparative Examples 2 and 3, the arithmetic mean roughness (Ra) of the surface of the organic-inorganic composite porous layer was measured.

[0153] (6) Evaluation of thermal shrinkage rate after leaving at 180°C for 1 hour The separators produced in Examples 1 to 4 and Comparative Examples 1 to 3 were cut into test pieces measuring 50 mm in length and 50 mm in width, which were then placed in an oven heated to 180°C for 1 hour. The test pieces were then removed and the change in length in both the machine direction and the transverse direction was measured and calculated. Heat shrinkage rate after leaving at 180°C for 1 hour (%) = {(dimension before shrinkage - dimension after shrinkage) / dimension before shrinkage} x 100

[0154] [Table 1]

[0155] As can be seen from Table 1, it was confirmed that the arithmetic mean roughness of the surface of the second organic-inorganic composite porous layer of the separators produced in Examples 1 to 4 was greater than the arithmetic mean roughness of the surface of the organic-inorganic composite porous layer of the separator produced in Comparative Example 3.

[0156] In particular, it was confirmed that the arithmetic mean roughness of the surface of the second organic-inorganic composite porous layer of the separators prepared in Examples 3 and 4 satisfied the arithmetic mean roughness level of the surface of the organic-inorganic composite porous layer of the separator prepared in Comparative Example 2.

[0157] Furthermore, it was confirmed that the separators produced in Examples 1 to 4 had very low thermal shrinkage in the machine direction (MD) and transverse direction (TD) after being left at 180°C for 1 hour.

[0158] On the other hand, the separator produced in Comparative Example 1 broke when left at 180°C for 1 hour, making it difficult to measure the thermal shrinkage rate.

[0159] The separator produced in Comparative Example 2 used only inorganic particles with a relatively large average particle size, and it was confirmed that the heat shrinkage in the machine direction (MD) and transverse direction (TD) after leaving it at 180°C for 1 hour was much inferior to the heat shrinkage of the separators produced in Examples 1 to 4 after leaving it at 180°C for 1 hour.

[0160] The separator produced in Comparative Example 3 used only inorganic particles with an average particle size of 1 to 100 nm, and had excellent thermal shrinkage in the machine direction (MD) and transverse direction (TD) after being left at 180°C for 1 hour. However, the arithmetic mean roughness of the surface of the organic-inorganic composite porous layer of the separator was very low, making it difficult to ensure ease of assembly.

[0161] Evaluation example 3: Evaluation of arithmetic mean roughness of separator surface The arithmetic mean roughness of the surface of the second organic-inorganic composite porous layer of the separators produced in Examples 1 to 4 was measured using an optical profiler (NV-2700) manufactured by Nano Systems Co., Ltd., and the results are shown in Figures 3 to 6, respectively. [Explanation of symbols]

[0162] 1. Separators for electrochemical elements 10 Porous polymer substrate 20 First organic-inorganic composite porous layer 30 Second organic-inorganic composite porous layer 40 First inorganic particle 50 Second inorganic particle

Claims

1. a porous polymer substrate; a first organic-inorganic composite porous layer located on one surface of the porous polymer substrate and including first inorganic particles and a first binder polymer; a second organic-inorganic composite porous layer located on the other surface of the porous polymer substrate and including the first inorganic particles, the second inorganic particles, and a second binder polymer; Including, The first inorganic particles have an average particle size of 1 nm to 100 nm, the average particle size of the second inorganic particles is larger than the average particle size of the first inorganic particles; The first inorganic particles include fumed type inorganic particles, A separator for an electrochemical element, wherein the weight ratio of the first inorganic particles to the second inorganic particles in the second organic-inorganic composite porous layer is 76:24 to 92:

8.

2. 2. The separator for an electrochemical element according to claim 1, wherein the average particle size of the second inorganic particles is 1.01 to 50 times the average particle size of the first inorganic particles.

3. 2. The separator for an electrochemical element according to claim 1, wherein the second inorganic particles have an average particle size of 150 nm to 800 nm.

4. 2. The separator for an electrochemical element according to claim 1, wherein the first inorganic particles comprise fumed alumina, fumed silica, fumed titanium dioxide, or two or more of these.

5. The second inorganic particles are BaTiO ３ , Pb(Zr,Ti)O ３ (PZT), Pb １－ｘ La ｘ Zr １－ｙ Ti ｙ O ３ (PLZT, 0<x<1, 0<y<1), Pb(Mg １／３ Nb ２／３ ) O ３ -PbTiO ３ (PMN-PT), hafnia (HfO ２ ), SrTiO ３ , SnO ２ , CeO ２ , MgO, Mg(OH) ２ , NiO, CaO, ZnO, ZrO ２ , SiO ２ , Y ２ O ３ , Al ２ O ３ , AlOOH, Al(OH) ３ , SiC, TiO ２ , lithium phosphate (Li ３ P.O. ４ ), lithium titanium phosphate (Li ｘ Ti ｙ (P.O. ４ ) ３ , 0<x<2, 0<y<3), lithium aluminum phosphate (Li ｘ Al ｙ Ti ｚ (P.O. ４ ) ３ , 0<x<2, 0<y<1, 0<z<3), (LiAlTiP) ｘ O ｙ Lithium lanthanum titanate (Li ｘ La ｙ TiO ３ , 0<x<2, 0<y<3), lithium germanium thiophosphate (Li ｘ Ge ｙ P ｚ S ｗ , 0<x<4, 0<y<1, 0<z<1, 0<w<5), lithium nitride (Li ｘ N ｙ , 0<x<4, 0<y<2), SiS ２ Li-based glass ｘ Si ｙ S ｚ , 0<x<3, 0<y<2, 0<z<4), P ２ S ５ Li-based glass ｘ P ｙ S ｚ , 0<x<3, 0<y<3, 0<z<7), or two or more of them.

6. 2. The separator for an electrochemical element according to claim 1, wherein the arithmetic mean roughness of the surface of the second organic-inorganic composite porous layer of the separator for an electrochemical element is 400 nm to 1000 nm.

7. 2. The separator for an electrochemical element according to claim 1, wherein the separator for an electrochemical element has a thermal shrinkage of 10% or less in both a machine direction (MD) and a transverse direction (TD) after being left at 180°C for 1 hour.

8. The first binder polymer may be selected from the group consisting of poly(vinylidene fluoride-hexafluoropropylene), poly(vinylidene fluoride-co-hexafluoropropylene), poly(vinylidene fluoride-chlorotrifluoroethylene), poly(vinylidene fluoride-tetrafluoroethylene), and poly(vinylidene fluoride-trichloroethylene). fluoride-co-trichloroethylene), acrylic copolymers, styrene-butadiene copolymers, poly(acrylic acid), poly(methyl methacrylate), poly(butyl acrylate), poly(acrylonitrile), poly(vinylpyrrolidone), poly(vinyl alcohol), poly(vinyl acetate), ethylene-vinyl acetate copolymers acetate), poly(ethylene oxide), poly(arylate), cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate2. The separator for an electrochemical element according to claim 1, comprising: cyanoethyl propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, or two or more of these.

9. The second binder polymer may be selected from the group consisting of poly(vinylidene fluoride-hexafluoropropylene), poly(vinylidene fluoride-co-hexafluoropropylene), poly(vinylidene fluoride-chlorotrifluoroethylene), poly(vinylidene fluoride-tetrafluoroethylene), and poly(vinylidene fluoride-trichloroethylene). fluoride-co-trichloroethylene), acrylic copolymers, styrene-butadiene copolymers, poly(acrylic acid), poly(methyl methacrylate), poly(butyl acrylate), poly(acrylonitrile), poly(vinylpyrrolidone), poly(vinyl alcohol), poly(vinyl acetate), ethylene-vinyl acetate copolymers acetate), poly(ethylene oxide), poly(arylate), cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate2. The separator for an electrochemical element according to claim 1, comprising: cyanoethyl propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, or two or more of these.

10. a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; An electrochemical element, wherein the separator is the separator for an electrochemical element according to claim 1 .

11. 11. The electrochemical device according to claim 10, wherein the electrochemical device is a cylindrical lithium secondary battery.

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