Separator, preparation method thereof, and electrochemical device including same

Abstract

According to one aspect of the present invention, a thin film separator with improved insulation properties and a preparation method thereof are provided. According to one aspect of the present invention, the separator can have an advantage of implementing a dielectric breakdown voltage of 1,000 V or less while having a thickness of 8 μm or less. To this end, according to one aspect of the present invention, the separator having a controlled maximum pore size within a polymer substrate and a preparation method thereof are provided.

Description

Separator, method of manufacturing the same, and electrochemical device including the same

[0001] The present invention relates to a separator, a method for manufacturing the same, an electrode assembly, a method for manufacturing the same, and an electrochemical device comprising the same.

[0002] This application claims priority based on Korean Patent Application No. 2024-0138007 filed with the Korean Intellectual Property Office on October 10, 2024, and all contents disclosed in the specification of said application are incorporated into this application.

[0003] Lithium secondary batteries are manufactured through a process in which an electrode assembly, comprising a positive electrode, a separator, and a negative electrode as a single unit, is inserted into a battery case, and then an electrolyte is injected and sealed. The separator serves the function of preventing direct physical contact between the positive and negative electrodes. Polyolefin-based porous substrates are typically used as separators for lithium secondary batteries.

[0004] Recently, research has been ongoing to reduce the weight of battery materials in order to increase the energy density of lithium-ion batteries. Similarly, research is being conducted to realize thin-film separators for weight reduction while utilizing conventional polyolefin-based porous substrates.

[0005] However, as the separator becomes thinner, the inherent function of the separator to block physical contact between the anode and the cathode is degraded, and instead, the risk of a short circuit caused by contact between the anode and the cathode increases.

[0006] Accordingly, improving the performance of lithium-ion batteries while simultaneously enhancing their safety by addressing issues such as ignition and thermal runaway has emerged as an important task.

[0007] Accordingly, the problem that the present invention aims to solve is to provide a separator that solves the above-mentioned problem, an electrode assembly including the same, and an electrochemical device.

[0008] Specifically, the present invention aims to provide a thin film separator as a separator, which is one of the components of a battery, for the purpose of reducing the weight of an electrochemical device, such as a lithium secondary battery.

[0009] More specifically, the present invention aims to provide a separator that is thin yet has excellent insulation properties between an anode and a cathode, a method for manufacturing the same, an electrode assembly applying the same, and an electrochemical device including the same.

[0010] In order to solve the above problem,

[0011] According to one aspect of the present invention, a separation membrane of the following embodiments is provided.

[0012] The separator according to the first embodiment is,

[0013] It includes a polyolefin-based substrate having a thickness of 8 μm or less, and

[0014] The maximum pore size of the above polyolefin-based substrate is 150 nm or less.

[0015] According to the second embodiment, in the first embodiment,

[0016] The above maximum pore size may be measured by a method of measuring the pore size at a moisture saturation of 1 volume% based on a moisture saturation of 100 volume% when moisture is infiltrated into the above polyolefin-based substrate at a constant pressure.

[0017] According to the third embodiment, in the first embodiment or the second embodiment,

[0018] The thickness of the above polyolefin-based substrate may be 5 μm or more and 8 μm or less.

[0019] According to the fourth embodiment, in any one of the first to third embodiments,

[0020] The maximum pore size of the above polyolefin-based substrate may be 120 nm or more and 150 nm or less.

[0021] According to the fifth embodiment, in any one of the first to fourth embodiments,

[0022] The above polyolefin-based substrate may further include at least one layer among a heat-resistant coating layer and a binder adhesive layer on at least one surface.

[0023]

[0024] According to another aspect of the present invention, electrode assemblies of the following embodiments are provided.

[0025] The electrode assembly according to the 6th embodiment is,

[0026] It includes a separator according to any one of the first to fifth embodiments, and an anode and a cathode provided on each of the two sides of the separator.

[0027]

[0028] According to another aspect of the present invention, a method for manufacturing a separation membrane of the following embodiments is provided.

[0029] The method for manufacturing a separation membrane according to the 7th embodiment is,

[0030] A step of obtaining a polymer sheet by extruding, cooling, and molding a polyolefin resin raw material,

[0031] A step of stretching the obtained polymer sheet in MD and TD, and

[0032] The method includes the step of obtaining a polyolefin-based substrate by heat-setting a stretched polymer sheet, and

[0033] The above heat setting temperature is performed at a temperature higher than the MD stretching and TD stretching temperatures, and

[0034] The thickness of the above polyolefin-based substrate shall be 8 μm or less.

[0035] According to the eighth embodiment, in the seventh embodiment,

[0036] The above MD stretching can be performed at a temperature of 110°C to 115°C at a stretching ratio of 4 to 10 times.

[0037] According to the ninth embodiment, in the seventh embodiment or the eighth embodiment,

[0038] The above TD stretching can be performed at a temperature of 125°C to 135°C at a stretching ratio of 4 to 10 times.

[0039] According to the 10th embodiment, in any one of the 7th to 9th embodiments,

[0040] The maximum pore size of the above polyolefin-based substrate may be 150 nm or less.

[0041]

[0042] According to another aspect of the present invention, a method for manufacturing an electrode assembly of the following embodiments is provided.

[0043] The method for manufacturing an electrode assembly according to the 11th embodiment is,

[0044] A step of interposing an anode and a cathode with a separator prepared according to any one of the 7th to 10th embodiments, and

[0045] It includes the step of hot-pressing the obtained anode / separator / cathode laminate.

[0046] According to the 12th embodiment, in the 11th embodiment,

[0047] The above hot press can be performed at a temperature of 55°C to 75°C.

[0048] According to the 13th embodiment, in the 11th embodiment or the 12th embodiment,

[0049] The above hot press can be performed at a pressure of 5 MPa to 8 MPa.

[0050]

[0051] According to another aspect of the present invention, electrochemical elements of the following embodiments are provided.

[0052] The electrochemical device according to the 14th embodiment is,

[0053] Electrode assembly according to the 6th embodiment, and

[0054] It may include a case that accommodates the above electrode assembly.

[0055] A separator according to one embodiment of the present invention may include a polyolefin-based substrate having a thickness of 8 μm or less.

[0056] Specifically, a separator according to one embodiment of the present invention can achieve the advantage of being thin while having excellent insulation properties. For example, the breakdown voltage (BDV) of the separator can be 1,000 V or higher.

[0057] Furthermore, an electrode assembly having a separator according to one embodiment of the present invention can exhibit the advantage of excellent voltage resistance.

[0058] As a result, the electrochemical device using the above-mentioned separator can exhibit the advantages of high energy density due to lightweighting as well as excellent insulation.

[0059] The following drawings attached to this specification illustrate embodiments of the present invention and serve to further enhance understanding of the technical concept of the present invention together with the detailed description of the invention provided below; therefore, the present invention should not be interpreted as being limited only to the matters described in such drawings.

[0060] FIG. 1 is a flowchart illustrating a method for manufacturing a separation membrane according to one embodiment of the present invention.

[0061] FIG. 2 is a graph showing the relationship between the pore size and the cumulative pore volume of a polyolefin substrate according to one embodiment of the present invention.

[0062] The present invention will be described in detail below.

[0063] In this specification, when a part is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0064] In this specification, the description of the term "A and / or B" means "A or B, or both."

[0065] Specific terms used in the following detailed description of the invention are for convenience only and are not intended to limit the invention. For example, words indicating direction, such as up and down, are used illustratively to describe positional relationships relative to a reference point and do not limit absolute positional relationships.

[0066]

[0067] Separator

[0068] According to one aspect of the present invention, a separation membrane comprising a polyolefin-based substrate is provided.

[0069] Specifically, a separator according to one aspect of the present invention comprises a polyolefin-based substrate having a thickness of 8 μm or less.

[0070] More specifically, a separator according to one aspect of the present invention comprises a polyolefin-based substrate having a maximum pore size of 150 nm or less.

[0071] More specifically, a separator according to one aspect of the present invention comprises a polyolefin-based substrate having a thickness of 8 μm or less, and the maximum pore size of the polyolefin-based substrate is 150 nm or less.

[0072] Specifically, the polyolefin-based substrate used as a separator substrate comprises a plurality of pores on its surface and / or inside. Through the plurality of pores, even if a separator is interposed between the anode and the cathode, it has the characteristic of enabling charge transfer and lithium ion transfer between the anode and the cathode. However, if the thickness of the polyolefin-based substrate is thin, specifically 8 μm or less, when the pore size increases, a problem may arise in which pores formed on one surface of the polyolefin-based substrate and pores formed on another surface communicate with each other, causing a short circuit between the anode and the cathode.

[0073] To prevent such problems, the separation membrane substrate according to one aspect of the present invention has a maximum pore size of 150 nm or less.

[0074] In this specification, the 'maximum pore size' refers to a value measured by the water intrusion method. Specifically, when water is infiltrated into the polyolefin-based separator substrate at a constant pressure, a graph of cumulative pore volume (volume%) according to pore size (nm) can be obtained. At this time, when the point where the pore volume is 100 volume% is defined as a state of water saturation of 100 volume% and the point where the pore volume is 1 volume% is defined as a state of water saturation of 1 volume%, the maximum pore size represents the pore size (nm) value at a water saturation of 1 volume% relative to a water saturation of 100 volume%.

[0075] According to one embodiment of the present invention, when performing the water infiltration method, water may be injected at a pressure range of, for example, 150 to 1,800 psi, but the present invention is not limited thereto.

[0076] According to one embodiment of the present invention, the maximum pore size of the polyolefin-based substrate may be 150 nm or less, for example, 100 nm or more and 150 nm or less, 110 nm or more and 150 nm or less, 120 nm or more and 150 nm or less, 130 nm or more and 150 nm or less, 135 nm or more and 145 nm or less, 140 nm or more and 145 nm or less, or 140 nm or 145 nm, but the present invention is not limited thereto. When the maximum pore size of the polyolefin-based substrate is within the range described above, it may exhibit advantageous effects in terms of air permeability and insulation of the separator, but the present invention is not limited thereto.

[0077] According to one embodiment of the present invention, the thickness of the polyolefin-based substrate is not particularly limited as long as it is 8 μm or less. According to one embodiment, in terms of the mechanical strength of the separator, it may be preferable, for example, to be 3 μm or more and 8 μm or less, 4 μm or more and 8 μm or less, 5 μm or more and 8 μm or less, or 6 μm or more and 7 μm or less, 6.5 μm or more and 7.5 μm or less, or 7.0 μm, but the present invention is not limited thereto.

[0078] In this specification, the "thickness" of the polyolefin-based substrate may be measured by a known method for measuring the thickness of each component of an electrochemical device. For example, the thickness of the polyolefin-based substrate may be measured using a known thickness gauge, and may be measured using a commercially available thickness gauge (Mitutoyo, VL-50S-B, tip diameter 9.5 mm, Spherical Radium 10 mm).

[0079] In one embodiment of the present invention, the polyolefin-based substrate may be manufactured using a polyolefin-based material as a thermoplastic resin to perform the function of an ion-conducting barrier that allows ions to pass through while blocking contact between the anode and the cathode for the inherent function of the separator, and to perform a shutdown function.

[0080] In one embodiment of the present invention, the polyolefin-based substrate represents a substrate comprising a material formed through the polymerization of an olefin, and is not particularly limited as long as a conventional material used for separators is used as the olefin. For example, the olefin may include polyethylene, polypropylene, or a mixture thereof.

[0081] According to one embodiment of the present invention, the separator may include a polyolefin-based substrate manufactured by a wet method as described below. The polyolefin-based substrate may typically be manufactured by a wet method or a dry method. In this case, it is preferable to manufacture the polyolefin-based substrate by a wet method in order to realize it in the form of a thin film and to increase the uniformity of the pore size.

[0082] According to one embodiment of the present invention, the separator may further include a binder adhesive layer comprising a binder polymer on at least one surface of the polyolefin-based substrate to improve adhesion to the electrode.

[0083] In another embodiment of the present invention, the separator may further include a heat-resistant coating layer formed on at least one surface of the polyolefin-based substrate to enhance heat resistance and comprising inorganic particles and a binder polymer.

[0084] In another embodiment of the present invention, the separator may further comprise a heat-resistant coating layer and / or a binder adhesive layer on at least one surface of the polyolefin-based substrate, but the present invention is not limited thereto.

[0085] In one embodiment of the present invention, the binder polymer that can be used in the binder adhesive layer and / or heat-resistant coating layer may be used without particular limitation as long as it is a material capable of exhibiting adhesive strength when used in a separator. For example, the binder polymer may be a polyvinylidene fluoride resin (PVdF resin), an acrylic resin, a rubber resin, or a mixture of two or more of these, but the present invention is not limited thereto.

[0086] In one embodiment of the present invention, the inorganic particles that can be used in the heat-resistant coating layer may be used without particular limitation as long as they are electrochemically stable. For example, the inorganic particles may be used without particular limitation as long as they do not undergo oxidation and / or reduction reactions within the operating voltage range of the electrochemical device to which the separator is applied (e.g., 0 to 5 V based on Li / Li+). For example, the inorganic particles may be 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 Examples include O3-PbTiO3 (PMN-PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, SiC, and TiO2, and one or more of these may be included, but the present invention is not limited thereto.

[0087] In one embodiment of the present invention, when the separator further comprises a heat-resistant coating layer, the average particle size (D) of the inorganic particles is such that the pores of the separator are not clogged by inorganic particles and the porosity of the separator is not reduced. 50 ) may preferably be, for example, 100 nm or more. Specifically, the average particle size (D) of the inorganic particles. 50 ) may be 100 nm to 1 μm, or 100 nm to 500 nm, but the present invention is not limited thereto.

[0088] In this specification, the particle size of the inorganic particles may be measured by a known particle size measurement method, for example, using a Particle Size Analyzer (PSA) from Melbourne. Additionally, the average particle size (D 50) refers to the particle size at the 50% point of the volume cumulative distribution according to particle size, and may be measured through a known laser diffraction method. In this case, the laser diffraction particle size measuring device may use, for example, the Microtrac S3500 from Microtrac Corporation.

[0089] In one embodiment of the present invention, the thickness of the binder adhesive layer and / or heat-resistant coating layer is not particularly limited as long as it is within a range that does not impede the objective of the present invention of thinning the separator. For example, the thickness of the binder adhesive layer and / or heat-resistant coating layer may be 0.5 μm to 20 μm, 0.5 μm to 10 μm, 0.5 μm to 5 μm, or 1.5 μm to 3 μm, respectively, but the present invention is not limited thereto.

[0090] A separator according to one embodiment of the present invention can basically have insulating properties by including a polyolefin-based substrate. As described above, if a thin polyolefin-based substrate is not limited to a maximum pore size, a problem may arise where the insulating properties become inferior; however, the separator according to one embodiment of the present invention can have the advantage of excellent insulating properties by limiting the maximum pore size while implementing a thin polyolefin-based substrate.

[0091] A separator according to one embodiment of the present invention has a thickness of 8 μm or less and can exhibit an dielectric breakdown voltage of 1,000 V or more.

[0092] A separator according to one embodiment of the present invention may exhibit a dielectric breakdown strength of, for example, 120 V / ㎛ or more. Specifically, the dielectric breakdown strength of the separator may be 120 V / ㎛ to 200 V / ㎛, 130 V / ㎛ to 180 V / ㎛, 140 V / ㎛ to 160 V / ㎛, 140 V / ㎛ to 155 V / ㎛, 140 V / ㎛ to 150 V / ㎛, or 143 V / ㎛ to 150 V / ㎛, but the present invention is not limited thereto.

[0093] In this specification, the 'dielectric breakdown voltage' and 'dielectric breakdown strength' of the separator may be measured using known methods for measuring the dielectric breakdown voltage and dielectric breakdown strength of insulating materials, and are not particularly limited to such measurement methods.

[0094] According to one embodiment of the present invention, the dielectric breakdown voltage and dielectric breakdown strength can be measured according to the method of standard number KS C IEC60243-2. ​​Specifically, a separator sample to be measured is placed between upper and lower aluminum jigs (upper jig diameter 30 mm, lower jig diameter 50 mm), and the dielectric breakdown voltage (V) value is measured by measuring the voltage at which current flows through the sample as the voltage applied to the sample is increased stepwise, and the dielectric breakdown strength (V / d) value can be measured by dividing the measured dielectric breakdown voltage value by the thickness (d) of the separator sample. At this time, the measuring device for measuring the dielectric breakdown voltage can be used without limitation as long as it is a device capable of measuring the dielectric breakdown voltage according to the above standard method. For example, an AC / DC / IR Hi-pot tester (Chroma, Model 19052) may be used as the measuring device, but the present invention is not limited thereto.

[0095]

[0096] electrode assembly

[0097] According to another aspect of the present invention, an electrode assembly is provided comprising the above-described separator and an anode and a cathode formed on each side of the separator.

[0098] As described above, a separator according to one aspect of the present invention is characterized by improved insulation properties, thereby achieving high dielectric breakdown voltage and dielectric breakdown strength. Accordingly, when manufacturing an electrode assembly using the separator, the high insulation properties of the separator can achieve the effect of significantly improving the short circuit failure rate between the anode and the cathode.

[0099] The configuration of the electrode described above is explained exemplarily below. However, the present invention is not limited thereto.

[0100] In one embodiment of the present invention, the positive electrode and the negative electrode may each have an electrode active material coated on a current collector, and their size, shape, or type of active material is not particularly limited.

[0101] In one embodiment of the present invention, conventional anodes and cathodes may be used to verify the short-circuit failure rate of the electrode assembly using the separator, and their types are not particularly limited.

[0102] For example, the electrode assembly may comprise, as a positive electrode active material, for example, a lithium transition metal oxide; a lithium metal iron phosphate; a lithium nickel-manganese-cobalt oxide; an oxide in which a portion of the lithium nickel-manganese-cobalt oxide is substituted with another transition metal; or two or more of these, but is not limited thereto. Specifically, the positive electrode active material may be, for example, a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2, etc.; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7, etc.; chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x = 0.01 ~ 0.3); chemical formula LiMn 2-x M xLithium manganese composite oxides represented as O2 (where M = Co, Ni, Fe, Cr, Zn, or Ta, and x = 0.01 to 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu, or Zn); lithium metal phosphate LiMPO4 (where M = Fe, CO, Ni, or Mn); lithium nickel-manganese-cobalt oxide Li 1+x (Ni a Co b Mn c ) 1-x O2(x = 0 ~ 0.03, a = 0.3 ~ 0.95, b = 0.01 ~ 0.35, c = 0.01 ~ 0.5, a+b+c=1); Lithium nickel-manganese-cobalt oxide, a lithium oxide in which a portion is substituted with aluminum Li a [Ni b Co c Mn d Al e ] 1-f M1 f O2(M1 is one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and 0.8≤a≤1.2, 0.5≤b≤0.99, 0 <c<0.5, 0<d<0.5, 0.01≤e≤0.1, 0≤f≤0.1); 리튬 니켈-망간-코발트 산화물에 일부가 다른 전이금속으로 치환된 산화물 Li 1+x (Ni a Co b Mn c M d ) 1-x O2 (x = 0 ~ 0.03, a = 0.3 ~ 0.95, b = 0.01 ~ 0.35, c = 0.01 ~ 0.5, d = 0.001 ~ 0.03, a+b+c+d=1, M is any one selected from the group consisting of Fe, V, Cr, Ti, W, Ta, Mg and Mo), disulfide compounds; may include Fe2(MoO4)3, but is not limited to these.

[0103] For example, the electrode assembly comprises, as a negative electrode active material, carbon such as non-graphitizable carbon, graphite-based carbon, etc.; Li x Fe2O3(0≤x≤1), Li x WO2(0≤x≤1), Sn x Me 1-x Me y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Group 1, 2, and 3 elements of the periodic table, halogens; 0 <x≤1; 1≤y≤3; 1≤z≤8) 등의 금속 복합 산화물; 리튬 금속; 리튬 합금; 규소계 합금; 주석계 합금; SiO, SiO / C, SiO2등의 실리콘계 산화물; SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, 및 Bi2O5등의 금속 산화물; 폴리아세틸렌 등의 도전성 고분자; Li-Co-Ni 계 재료 등을 사용할 수 있으나, 이들만으로 한정되는 것은 아니다.

[0104] In one embodiment of the present invention, the anode may be prepared, for example, in the following way. First, an anode active material (LiNi 0.8 Mn 0.1 Co 0.1 O2), a conductive material (carbon black), a dispersant, and a binder resin (PVDF) are mixed with water in a weight ratio of 97.5:0.7:0.2:1.6 to prepare a slurry for an anode active material layer with a concentration of 50 wt% of the components excluding water. Next, the slurry is applied to the surface of an aluminum thin film (thickness 10 μm) and dried to manufacture an anode having an anode active material layer (thickness 60 μm). The method for manufacturing an anode as described above is merely an example and is not intended to limit the present invention.

[0105] In one embodiment of the present invention, the cathode may be prepared by the following exemplary method. First, artificial graphite, carbon black, carboxymethylcellulose (CMC), and binder resin (SBR) are mixed with water in a weight ratio of 97.5:0.7:1.1:0.7 to prepare a slurry for a cathode active material layer with a concentration of 50 wt% of the components excluding water. Next, the slurry is applied to the surface of a copper thin film (thickness 10 μm) and dried to produce a cathode having a cathode active material layer (thickness 60 μm). The method of manufacturing the cathode as described above is merely an example and is not intended to limit the present invention.

[0106] According to one embodiment of the present invention, the electrode assembly includes a structure of sequentially stacked cathode / separator / anode, and the insulation can be tested using a known Hi-pot tester to measure the defect rate of the electrode assembly. For example, the defect rate can be measured by preparing at least 20 samples of the electrode assembly and then checking whether insulation breakdown occurs when a current is applied under conditions of 50V and <0.5 mA (Charge time: 50 ms, test time: 50 ms) using a Hi-pot tester (Chroma, Model 19052).

[0107] According to one embodiment of the present invention, when measuring the defect rate of the electrode assembly using the method described above, the electrode assembly using the separator can achieve the effect of exhibiting a defect rate of 0% among 20 samples.

[0108] According to another embodiment of the present invention, when measuring the defect rate of the electrode assembly by the method described above, as the number of samples (n) of the electrode assembly increases, the effect of showing a defect rate of 1% or less, specifically 0.5% or less, can be achieved even when 100≤n, but the present invention is not limited thereto.

[0109]

[0110] Method for manufacturing a separator and an electrode assembly

[0111] Hereinafter, a method for manufacturing a separation membrane according to one aspect of the present invention is described. However, the following manufacturing method is merely an illustrative description of the method for manufacturing the separation membrane, and the method for manufacturing the separation membrane is not limited thereto.

[0112] According to another aspect of the present invention, a method for manufacturing the separation membrane is provided.

[0113] A method for manufacturing a separation membrane according to another aspect of the present invention may adopt a wet method process.

[0114] Specifically, the method for manufacturing the above-mentioned separation membrane is,

[0115] (S1) A step of obtaining a polymer sheet by extruding, cooling, and molding a polyolefin resin raw material,

[0116] (S2) A step of stretching the obtained polymer sheet in MD and TD, and

[0117] (S3) The method may include the step of heat-setting the stretched polymer sheet to obtain a polyolefin-based substrate.

[0118] In particular, the method for manufacturing a separation membrane according to one aspect of the present invention can manufacture the polyolefin-based substrate with a thickness of 8 μm or less.

[0119] In addition, a method for manufacturing a separation membrane according to one aspect of the present invention can manufacture the polyolefin-based substrate with a maximum pore size of 150 nm or less.

[0120] According to one embodiment of the present invention, the polyolefin-based substrate is formed by using a polyolefin resin as a raw material and processing the polyolefin resin into a polymer sheet through a series of high-temperature extrusion, cooling, and stretching processes. At this time, the polymer sheet has the characteristic that the pore characteristics formed on the surface change depending on the temperature and pressure applied during the manufacturing process. In order to manufacture a porous polymer substrate without damaging the polymer sheet during this series of processes, polyethylene resin may be included as the polyolefin resin, but any polyolefin-based resin other than polyethylene resin may be used without limitation.

[0121] In one embodiment of the present invention, the polyolefin resin may include, for example, a weight-average molecular weight (Mw) of 500,000 g / mol to 5,000,000 g / mol. Specifically, the weight-average molecular weight of the polyolefin resin may be 500,000 g / mol to 2,000,000 g / mol, 500,000 g / mol to 1,000,000 g / mol, 500,000 g / mol to 800,000 g / mol, 500,000 g / mol to 700,000 g / mol, or 550,000 g / mol to 650,000 g / mol. More specifically, the weight-average molecular weight of the polyolefin resin may be 600,000 g / mol, for example, but the present invention is not limited thereto.

[0122] At this time, the weight-average molecular weight of the polymer may be a value measured by a conventional measurement method, for example, a value measured using a gel permeation chromatograph (GPC). At this time, the GPC measurement conditions may be measured by referring to the following conditions, but the present invention is not limited thereto.

[0123] - Column: PL Olexis (Polymer Laboratories)

[0124] - Solvent: TCB (Trichlorobenzene)

[0125] - Flow rate: 1.0 ml / min

[0126] - Sample concentration: 1.0 mg / ml

[0127] - Injection volume: 200 µl

[0128] - Column temperature: 160℃

[0129] - Detector: Agilent High Temperature RI detector

[0130] - Standard: Polystyrene (corrected by a cubic function)

[0131]

[0132] The above step (S1) is a step of obtaining an extruder by extruding a raw material containing the polyolefin resin described above, and obtaining a polymer sheet by cooling and molding the high-temperature extruder.

[0133] In one embodiment of the present invention, the extrusion may be performed by a conventional process for extruding polymers in the field of manufacturing separation membranes. For example, a uniaxial compressor or a twin-screw compressor may be used as the extruder for the extrusion, but is not limited thereto.

[0134] In one embodiment of the present invention, the extrusion may be performed by introducing a polyolefin resin and a diluent into an extruder and melt-extruding at a temperature of, for example, 170°C to 250°C, for example, 200°C.

[0135] In one embodiment of the present invention, the diluent may be used with a conventional diluent generally used in the manufacturing process of a separation membrane for diluting raw materials. The diluent refers to a substance that can form pores by undergoing phase separation and removal upon cooling after being mixed with a polyolefin resin to form an extruded product. The diluent is not particularly limited as long as it satisfies this function. Non-limiting examples of such diluents include, but are not limited to, aliphatic hydrocarbon solvents such as paraffin oil; vegetable oils such as soybean oil; or plasticizers such as dialkyl phthalates. Among these, liquid paraffin oil having excellent compatibility with polyolefin resins, such as paraffin oil having a kinematic viscosity of 20 to 200 cSt at 40°C, may be suitably used. The diluent may be used alone or in the form of a mixture of two or more types.

[0136] In one embodiment of the present invention, the extruded melt can be drawn out through a die, and the thickness of the polyolefin-based substrate produced can be controlled by controlling the amount discharged at this time.

[0137] In one embodiment of the present invention, it may be preferable to discharge the polyolefin-based substrate manufactured so that its thickness is 8 μm or less.

[0138] Next, after obtaining the extruder, the extruder can be cooled to obtain a polymer pre-sheet.

[0139] According to one embodiment of the present invention, the extruded product obtained above can be formed into a sheet shape using a cooling casting device at a temperature of 20°C to 60°C. For example, the extruded product discharged from the extrusion section can be formed into a polymer sheet shape while cooling the extruded product by passing it between a pair of cooling casting rolls at a travel speed of 7 m / min at a temperature of 40°C.

[0140] The above step (S2) is a step of stretching the obtained polymer sheet in the machine direction (MD) and the transverse direction (TD) perpendicular thereto, respectively.

[0141] In one embodiment of the present invention, the step (S2) may include a process of sequentially stretching the polymer pre-sheet in the machine direction and the transverse direction, for example, by using a tenter-type stretcher to stretch it 3 to 9 times in the machine direction and 3 to 9 times in the transverse direction.

[0142] In one embodiment of the present invention, the pore size formed in the polymer sheet may be modified according to the MD and TD stretching ratios and / or temperature. Accordingly, the MD and TD stretching ratios and / or temperature may be performed as follows so that the maximum pore size of the obtained polyolefin-based substrate is 150 nm or less.

[0143] In one embodiment of the present invention, the MD stretching may be performed at a temperature of 125°C or lower, for example, 100°C to 125°C, 100°C to 120°C, 110°C to 115°C, or 110°C to 112°C, taking into account the melting temperature of the polyolefin resin. If the MD stretching temperature becomes too high, the maximum pore diameter of the polyolefin substrate obtained adjacent to the melting point of the polyolefin resin becomes too small, and consequently, a problem may arise in which the intrinsic porosity of the separator cannot be secured.

[0144] In one embodiment of the present invention, the MD stretching may be performed at a stretching ratio of 6 to 9 times, 6 to 8 times, 6 to 7 times, specifically 6.0 to 6.5 times, 6.0 to 6.3 times, or 6.0 to 6.1 times, but the present invention is not limited thereto.

[0145] In one embodiment of the present invention, the MD stretching may be performed at a temperature of 110°C to 115°C at a stretching ratio of 6.0 to 6.5 times, but the present invention is not limited thereto.

[0146] In one embodiment of the present invention, the TD stretching may be performed sequentially after the MD stretching. At this time, as the degree of crystallization of the polymer sheet increases through the MD stretching, the TD stretching may be performed at a temperature a predetermined range higher than that of the MD stretching. For example, the TD stretching may be performed at a temperature 5°C or higher, 10°C or higher, 15°C or higher, 20°C or higher, or 5°C to 20°C, 10°C to 20°C, or 15°C to 20°C higher than the MD stretching temperature. For example, the TD stretching may be performed at a temperature 125°C or higher, for example, 125°C to 140°C, 125°C to 135°C, 130°C to 135°C, 130°C to 132°C, or 130°C to 131.5°C, but the present invention is not limited thereto.

[0147] In one embodiment of the present invention, the TD stretching may be performed at a stretching ratio of 6 to 9 times, 7 to 9 times, 7 to 8 times, specifically 7.5 to 8 times or 7.5 to 8.0 times, but the present invention is not limited thereto.

[0148] In one embodiment of the present invention, the TD stretching may be performed at a temperature of 125°C to 135°C at a stretching ratio of 7.5 to 8.0 times, but the present invention is not limited thereto.

[0149] In one embodiment of the present invention, after stretching the polymer sheet by MD and TD, a process of removing the diluent used in the shearing process may be further performed.

[0150] In one embodiment of the present invention, a process of extracting and removing the diluent using a suitable solvent may be performed to remove the diluent. The solvent available for removing the diluent is not particularly limited, and any solvent capable of extracting the diluent used in the extrusion step may be used. For example, methyl ethyl ketone, methylene chloride, hexane, etc., which have high extraction efficiency and rapid drying, may be used, and preferably, methylene chloride may be used. The extraction method may use any general solvent extraction method, such as an immersion method, a solvent spray method, or an ultrasonic method, either individually or in combination.

[0151] In one embodiment of the present invention, it may be preferable that the amount of diluent remaining in the polymer sheet formed after extraction of the diluent be 1% by weight or less based on the total weight of the polymer sheet. If the amount of remaining diluent exceeds 1% by weight, there may be a problem of reduced physical properties and decreased permeability of the membrane, but the present invention is not limited thereto.

[0152] The above step (S3) can be performed according to a conventional method, in which the polymer sheet with pores formed by removing the diluent above is held in MD and / or TD and heat is applied to reduce the thermal shrinkage characteristics.

[0153] According to one embodiment of the present invention, in order to achieve a maximum pore size of 150 nm or less of the polyolefin-based substrate obtained, the manufacturing method is performed at a temperature higher than the MD stretching and TD stretching temperatures.

[0154] For example, the heat setting temperature may be performed at a temperature 5°C or higher, 10°C or higher, 15°C or higher, 20°C or higher than the MD stretching temperature, or at a temperature 5°C to 25°C, 10°C to 25°C, 15°C to 25°C, or 15°C to 20°C higher. Additionally, the heat setting temperature may be performed at a temperature at least 0.5°C or higher or 1°C or higher than the TD stretching temperature, for example, 0.5°C to 5°C, 0.5°C to 3°C, 1.0°C to 3.0°C, 0.5°C to 2.0°C, 0.5°C to 1.5°C, or 0.5°C to 1.0°C higher.

[0155] In one embodiment of the present invention, the heat fixation may be performed at a temperature of, for example, 125°C or higher, specifically 125°C to 140°C, 130°C to 140°C, 130°C to 135°C, 130°C to 132°C, or 131°C to 132°C, but the present invention is not limited thereto.

[0156] In one embodiment of the present invention, the heat setting may be performed by holding the MD and / or TD and applying heat, wherein the elongation ratio of the MD and / or TD may be 1.0 to 1.5 times, for example 1.0 to 1.3 times, 1.1 to 1.2 times, or 1.0 to 1.1 times, but the present invention is not limited thereto.

[0157] Thus, according to one embodiment of the present invention, the polyolefin-based substrate obtained above may consist only of pores, which are empty spaces between polyolefin fibers and polyolefins. Accordingly, according to one aspect of the present invention, a polyolefin-based substrate having a thickness of 8 μm or less and a maximum pore size of 150 nm or less can be obtained.

[0158] In one embodiment of the present invention, the polyolefin-based substrate obtained above can itself be used as a separator.

[0159] In another embodiment of the present invention, by further performing the step of forming a binder adhesive layer and / or a heat-resistant coating layer on at least one surface of the polyolefin-based substrate obtained above, a separation membrane having a binder adhesive layer and / or a heat-resistant coating layer on at least one surface of the polyolefin-based substrate can be obtained.

[0160]

[0161] According to another aspect of the present invention, a method for manufacturing an electrode assembly using the above-described separator is provided.

[0162] The method for manufacturing the above electrode assembly is,

[0163] A step of interposing an anode and a cathode with a separator manufactured according to the above-described method, and

[0164] It may include a step of laminating the obtained anode / separator / cathode laminate.

[0165] According to one embodiment of the present invention, the lamination step may utilize a hot-press process.

[0166] For example, the hot press can be performed to bond the anode / separator / cathode laminate by applying temperature and pressure to the anode / separator / cathode laminate using a hot press machine.

[0167] In one embodiment of the present invention, the hot press may be performed at a temperature of, for example, 55°C to 75°C, 55°C to 70°C, 60°C to 65°C, or 60°C, but the present invention is not limited thereto.

[0168] In one embodiment of the present invention, the hot press may be performed at a pressure of, for example, 5 MPa to 8 MPa, 5 MPa to 7 MPa, 6 MPa to 6.5 MPa, or 6.0 MPa to 6.5 MPa, but the present invention is not limited thereto.

[0169] In one embodiment of the present invention, the hot press may be performed under conditions of 60°C and 6.5 MPa, but the present invention is not limited thereto.

[0170]

[0171] electrochemical device

[0172] According to another aspect of the present invention, an electrochemical element in which the above-described electrode assembly is housed in a case may be provided.

[0173] In one embodiment of the present invention, the electrochemical element may be an example of a primary battery, a secondary battery, a supercapacitor, an electric double layer capacitor, etc. More specifically, the secondary battery may be a lithium-ion secondary battery.

[0174] In one embodiment of the present invention, the case may be one that is conventionally used as a battery case, and is not particularly limited in its external shape according to the use of the battery. For example, the case may be a cylindrical, prismatic, pouch, or coin type using a can.

[0175] Once the electrode assembly described above is completed, it can be housed in a case and sealed in a conventional manner to manufacture an electrochemical device, wherein the electrochemical device may be, for example, a lithium secondary battery.

[0176]

[0177] The present invention will be described in more detail below through examples, but the following examples are intended to illustrate the invention and the scope of the invention is not limited thereto.

[0178] [Manufacture of Polyolefin Substrates]

[0179] Example 1

[0180] 9 kg of high-density polyethylene (HDPE) (Daehan Petrochemical, VH035) was fed into an extruder (Korea EM, φ32 twin-screw extruder L / D=56) together with 21 kg of diluent (Kukdong Petrochemical LP350F) and melt-extruded at 200°C to obtain a polyethylene melt extruder. After passing the obtained melt extruder through a T-die, it was cooled and formed into a sheet using a cooling casting device at a temperature of 40°C with a travel speed of 7 m / min. Subsequently, MD stretching (112°C, stretching ratio 6.0) followed by TD stretching (130°C, stretching ratio 8.0) was performed using a tenter-type sequential stretching machine. The diluent was extracted from the stretched polyolefin using methylene chloride to form a porous membrane, and then heat-set at a temperature of 132°C (stretch ratio 1.2) to obtain a polyolefin substrate with a thickness of 7 μm.

[0181]

[0182] Example 2

[0183] A polyolefin substrate with a thickness of 7 μm was obtained using the same method as in Example 1, except that the MD stretching ratio was changed to 6.1 times and TD stretching was performed at 131.5°C.

[0184]

[0185] Comparative Example 1

[0186] A polyolefin substrate with a thickness of 7 μm was obtained in the same manner as in Example 1, except that the MD draw ratio was changed to 6.3 times, TD drawing was performed under conditions of 133.5°C and a draw ratio of 8.4 times, and heat setting was performed under conditions of 131°C and a draw ratio of 1.3 times.

[0187]

[0188] [Evaluation of Physical Properties of Polyolefin Substrates]

[0189] Measurement of maximum pore size (nm)

[0190] The maximum pore size of the polyolefin substrate prepared above was measured using a water intrusion type Aqua pore instrument (Poretech Instrument, WMI-5K). Water was infiltrated at a pressure of 150 to 1,800 psi until the pores of the polyolefin substrate reached a saturated state (100 vol%), and a graph of cumulative pore volume according to pore size (nm) was obtained. In the graph, the pore size (nm) at which the initial 1 vol% of water was infiltrated was measured as the maximum pore size.

[0191]

[0192] Measurement of dielectric breakdown voltage (V)

[0193] Measurements were taken using an AC / DC / IR Hi-pot tester (Chroma, Model 19052). Specifically, a prepared separator sample was placed between aluminum jigs (upper jig diameter 30 mm, lower jig diameter 50 mm), and the voltage at which a failure condition (> 0.5 mA, 3 sec) occurred was measured using the Hi-pot tester.

[0194] At this time, the measurement conditions were set to DC, current 0.5 mA, and voltage step-up 100 V / s (~ 3 kV). The measured value was expressed as the average of 30 samples.

[0195]

[0196] Measurement of dielectric breakdown strength (V / d)

[0197] The dielectric breakdown strength (V / ㎛) was calculated by dividing the measured dielectric breakdown voltage by the thickness (d) of the separator sample.

[0198]

[0199] Hi-pot defect rate measurement

[0200] Using the polyolefin substrate manufactured above as a separator, 20 electrode assemblies prepared as follows were prepared, and a Hi-pot test was performed. The test was conducted using a Hi-pot tester (Chroma, Model 19052) under conditions of 50V and <0.5 mA (Charge time: 50 ms, test time: 50 ms) to measure whether there were any defects.

[0201]

[0202] The electrode assemblies were prepared as follows.

[0203] 1) Manufacture of the anode

[0204] Cathode active material (LiNi 0.8 Mn 0.1 Co 0.1 O2), a conductive material (carbon black), a dispersant, and a binder resin (PVDF) were mixed with water in a weight ratio of 97.5:0.7:0.2:1.6 to prepare a slurry for an anode active material layer with a concentration of 50 wt% of the components excluding water. Next, the slurry was applied to the surface of an aluminum thin film (thickness 10 μm) and dried to produce an anode having an anode active material layer (thickness 60 μm).

[0205] 2) Preparation of the cathode

[0206] A slurry for a negative electrode active material layer was prepared by mixing artificial graphite, carbon black, carboxymethylcellulose (CMC), and binder resin (SBR) with water in a weight ratio of 97.5:0.7:1.1:0.7, with the remaining components excluding water having a concentration of 50 wt%. Next, the slurry was applied to the surface of a copper thin film (thickness 10 μm) and dried to produce a negative electrode having a negative electrode active material layer (thickness 60 μm).

[0207] 3) Lamination Process

[0208] An electrode assembly was obtained by interposing a separator between the above-manufactured cathode and anode and laminating them, and then performing a lamination process using a hot press at 60°C and 6.5 MPa for 10 seconds.

[0209] Maximum pore size (nm) Dielectric breakdown voltage (V) Dielectric breakdown strength (V / ㎛) Hi-pot defect rate (n / 20) Example 1 140 1,050 1500 Example 2 145 1,000 1430 Comparative Example 1 155 830 1197

[0210] As shown in the results of Table 1 above, it was confirmed that when the maximum pore size exceeds 150 nm, a sharp decrease in dielectric breakdown voltage occurs, and the short-circuit defect rate increases by 35% during battery manufacturing. For example, in Examples 1 and 2, no electrode assemblies were found to be defective when measuring the Hi-pot defect rate, whereas in Comparative Example 1, 7 out of 20 electrode assemblies were found to be defective.

[0211] The above detailed description is intended to illustrate and explain the present invention. Furthermore, the foregoing merely indicates and describes embodiments of the present invention, and as described above, the present invention may be used in various other combinations, modifications, and environments, and modifications or alterations may be made within the scope of the invention disclosed herein, the scope equivalent to the foregoing disclosure, and / or the scope of the art or knowledge. Accordingly, the above detailed description of the invention is not intended to limit the present invention to the disclosed embodiments. Additionally, the appended claims should be interpreted as including other embodiments.

Claims

1. Includes a polyolefin-based substrate having a thickness of 8 μm or less, and A separator having a maximum pore size of 150 nm or less of the above polyolefin-based substrate.

2. In Claim 1, The above maximum pore size is a separation membrane, wherein the pore size at a moisture saturation of 1 volume% is measured based on a moisture saturation of 100 volume% when moisture is infiltrated into the above polyolefin-based substrate at a constant pressure.

3. In Claim 1, A separator having a thickness of 5 μm or more and 8 μm or less of the above polyolefin-based substrate.

4. In Claim 1, A separator having a maximum pore size of 120 nm or more and 150 nm or less of the above polyolefin-based substrate.

5. In Claim 1, A separator further comprising at least one layer among a heat-resistant coating layer and a binder adhesive layer on at least one surface of the above-mentioned polyolefin-based substrate.

6. An electrode assembly comprising a separator according to any one of claims 1 to 5, and an anode and a cathode provided on each of the two sides of the separator.

7. A step of obtaining a polymer sheet by extruding, cooling, and molding a polyolefin resin raw material, A step of stretching the obtained polymer sheet in the MD (Machine Direction) and TD (Transverse Direction), and The method includes the step of obtaining a polyolefin-based substrate by heat-setting a stretched polymer sheet, and The above heat setting temperature is performed at a temperature higher than the MD stretching and TD stretching temperatures, and A method for manufacturing a separator, wherein the thickness of the above polyolefin-based substrate is 8 μm or less.

8. In Claim 7, A method for manufacturing a separation membrane, wherein the above MD stretching is performed at a temperature of 110°C to 115°C at a stretching ratio of 4 to 10 times.

9. In Claim 7, A method for manufacturing a separator membrane, wherein the above TD stretching is performed at a temperature of 125°C to 135°C at a stretching ratio of 4 to 10 times.

10. In Claim 7, A method for manufacturing a separator, wherein the maximum pore size of the above polyolefin-based substrate is 150 nm or less.

11. A step of interposing an anode and a cathode with a separator prepared according to any one of claims 7 to 10, and A method for manufacturing an electrode assembly comprising the step of hot-pressing a laminate of anode / separator / cathode obtained.

12. In Claim 11, A method for manufacturing an electrode assembly, wherein the above hot press is performed at a temperature of 55°C to 75°C.

13. In Claim 11, A method for manufacturing an electrode assembly, wherein the above hot press is performed at a pressure of 5 MPa to 8 MPa.

14. Electrode assembly according to claim 6, and An electrochemical device comprising a case that accommodates the electrode assembly.

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