Separation membrane substrate for electrochemical element and separation membrane containing the same

Abstract

The present invention relates to a separation membrane substrate, a separation membrane, and an electrochemical device including the same. The separation membrane substrate of the present invention is a separation membrane substrate for an electrochemical device containing a crosslinked polyolefin resin and chromium (Cr), wherein the crosslinked polyolefin resin contains a silicon-containing organic group graft-bonded to a polyolefin chain, the gel fraction of the separation membrane substrate is 3% to 80%, the standard deviation Δd of the thickness measured at any at least 100 points is 0.5 μm or less, and the number of spots having a long side length of 50 μm or more is 10 or less per meter. 2 ​

Description

Technical Field

[0001] The present invention relates to a separation membrane substrate for an electrochemical element, a separation membrane including the same, and an electrochemical element including the separation membrane.

[0002] This application claims priority based on Korean Patent Application No. 2022-0144748 filed on November 2, 2022, and all of the content disclosed in the specification and drawings of the application is incorporated into this application.

Background Art

[0003] Secondary batteries represented by lithium-ion secondary batteries are widely used as power sources for portable electronic devices such as notebook PCs, mobile phones, digital cameras, and camcorders. In recent years, these batteries have been applied to various fields such as automobiles due to their high energy density characteristics.

[0004] Lithium secondary batteries have attracted attention because they have a higher operating voltage and a much higher energy density than conventional batteries such as Ni-MH, Ni-Cd, and lead-sulfuric acid batteries that use an aqueous electrolyte. However, such lithium-ion batteries have disadvantages such as safety problems such as ignition and explosion associated with the use of an organic electrolyte, and complicated manufacturing. Recently, lithium-ion polymer batteries have been cited as one of the next-generation batteries by improving such disadvantages of lithium-ion batteries, but the capacity of the battery is still relatively low compared to lithium-ion batteries, and in particular, the discharge capacity at low temperatures is insufficient, and improvement thereof is required.

[0005] The evaluation of the stability and the assurance of the safety of such an electrochemical device are very important. In the safety characteristics of an electrochemical device, there is a high risk of explosion when the electrochemical device overheats and thermal runaway occurs, or when the separator membrane is penetrated. In particular, a polyolefin-based separator membrane substrate commonly used as the separator membrane of an electrochemical device has a problem that it shows intense heat shrinkage behavior at a temperature of 100°C or higher due to the material characteristics and the manufacturing process characteristics including stretching, causing a short circuit between the positive electrode and the negative electrode.

[0006] To solve such safety problems of an electrochemical device, a separator membrane has been proposed in which a mixture of excessive inorganic particles and a binder polymer is coated on at least one surface of a separator membrane substrate having a plurality of pores to form a porous inorganic coating layer, and there is a continuing requirement for further stability enhancement.

Summary of the Invention

Problems to be Solved by the Invention

[0007] An object of the present invention is to provide a separator membrane substrate with enhanced thickness uniformity and heat resistance, and a separator membrane with enhanced thickness uniformity and heat resistance using the same. Accordingly, an object of the present invention is to provide an electrochemical device with improved stability and excellent resistance characteristics.

Means for Solving the Problems

[0008] To achieve the above problems, According to one aspect of the present invention, a separator membrane substrate of the following embodiment is provided.

[0009] The separator membrane substrate according to the first embodiment is a separator membrane substrate for an electrochemical device containing a crosslinked polyolefin resin and chromium (Cr), wherein the crosslinked polyolefin resin contains a silicon-containing organic group graft-bonded to a polyolefin chain, the gel fraction of the separator membrane substrate is 3% to 80%, the standard deviation Δd of the thickness measured at any at least 100 points is 0.5 μm or less, and the number of spots having a long side length of 50 μm or more is 1m2 It is 10 or less per hit.

[0010] According to the second embodiment, in the first embodiment, The silicon-containing organic group is a residue derived from a vinyl group-containing silane compound, The vinyl group-containing silane compound may include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriacetoxysilane, (3-methacryloxypropyl)trimethoxysilane, (3-methacryloxypropyl)triethoxysilane, vinylmethyldimethoxysilane, vinyl-tris(2-methoxyethoxy)silane, vinylmethyldiethoxysilane, or a mixture of two or more thereof.

[0011] According to the third embodiment, in the first embodiment or the second embodiment, The content of the chromium may be 0.1 to 20 ppm.

[0012] According to the fourth embodiment, in any one of the first to third embodiments, The gel fraction of the separation membrane substrate may be 3% to 50%.

[0013] According to the fifth embodiment, in any one of the first to fourth embodiments, The crosslinked structure in the crosslinked polyolefin resin may include a structure derived from the result of a radical polymerization reaction between vinyl groups mediated by a thermal initiator.

[0014] According to the sixth embodiment, in the fifth embodiment, The thermal initiator may include a peroxide-based compound, a persulfate-based compound, an azo-based compound, or a mixture thereof.

[0015] According to the seventh embodiment, in any one of the first to sixth embodiments, The separation membrane substrate for the electrochemical element may further contain at least one or more of titanium (Ti), aluminum (Al), magnesium (Mg), zirconium (Zr), and vanadium (V).

[0016] According to the eighth embodiment, in any one of the first to seventh embodiments, The standard deviation Δd of the thickness measured at any at least 100 points of the separation membrane substrate may be 0.3 μm or less.

[0017] According to another aspect of the present invention, there is provided a method for manufacturing a separation membrane substrate of the following embodiment.

[0018] The method for manufacturing a separation membrane substrate according to the ninth embodiment includes: a step of melt-extruding a raw material substance containing a polyolefin resin to obtain a polymer melt extrudate; a step of molding and stretching the obtained polymer melt extrudate to obtain a polymer sheet; a step of applying a coating liquid containing a thermal initiator and a vinyl group-containing silane compound to the polymer sheet; and a step of drying and heat-fixing the polymer sheet coated with the coating liquid, wherein the polyolefin resin includes a polyolefin resin produced using an olefin polymerization catalyst containing chromium.

[0019] According to the tenth embodiment, in the ninth embodiment, The polyolefin resin among the raw material substances may include a polyolefin resin having 100 or more terminal vinyl groups per million carbon atoms.

[0020] According to the eleventh embodiment, in the ninth or tenth embodiment, The raw material substance may not contain chromium and may further include a polyolefin resin produced using an olefin polymerization catalyst containing titanium (Ti), aluminum (Al), magnesium (Mg), zirconium (Zr), vanadium (V), or two or more of these.

[0021] According to the twelfth embodiment, in any one of the eighth to eleventh embodiments, Based on the total weight of the polyolefin resin of the raw material substance, the content of the polyolefin resin produced using an olefin polymerization catalyst containing chromium can be 10% by weight or more.

[0022] According to another aspect of the present invention, a separation membrane of the following embodiments is provided.

[0023] The separation membrane according to the 13th embodiment is It includes a separation membrane base material described in any one of the 1st to 8th embodiments and an inorganic coating layer formed on at least one surface of the separation membrane base material, and the inorganic coating layer includes inorganic particles and a binder material.

[0024] According to another aspect of the present invention, an electrode assembly of the following embodiments is provided.

[0025] The electrode assembly according to the 14th embodiment is It includes a positive electrode, a negative electrode, and a separation membrane interposed between the positive electrode and the negative electrode, and the separation membrane can be the one described in the 13th embodiment.

Advantages of the Invention

[0026] The separation membrane base material according to an embodiment of the present invention has the effect of improving thickness uniformity and heat resistance by containing a large amount of cross-linked structures in the polyolefin chain. Therefore, it has the effect of excellently improving the operating stability such as the heat resistance characteristics of an electrochemical element including a separation membrane using such a separation membrane base material.

[0027] In particular, the separation membrane base material according to an embodiment of the present invention is produced using a polyolefin resin containing a large amount of terminal vinyl groups produced using an olefin polymerization catalyst containing chromium and a thermal initiator for cross-linking between these terminal vinyl groups. The separation membrane base material has improved thickness uniformity and heat resistance due to the formation of a large amount of cross-linked structures between the polyolefin chains, and can have the effect of improving the wettability with the electrolyte by containing a silicon-containing organic group grafted onto the polyolefin chain, but the mechanism of the present invention is not limited to this.

[0028] The following drawings attached to this specification illustrate desirable embodiments of the present invention and serve to further understand the technical idea of the present invention together with the detailed description of the invention. Therefore, the present invention should not be construed as being limited only to the matters described in the drawings.

Brief Description of the Drawings

[0029]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0030] Hereinafter, the present invention will be described in detail.

[0031] The present invention relates to a separation membrane substrate for an electrochemical element, a separation membrane including the same, and an electrochemical element including the separation membrane. In the present invention, the electrochemical element is a device that converts chemical energy into electrical energy by an electrochemical reaction, and is a concept including a primary battery and a secondary battery. The secondary battery is capable of charging and discharging, and is a concept including lithium-ion batteries, nickel-cadmium batteries, nickel-metal hydride batteries, and the like.

[0032] First, the separation membrane substrate for an electrochemical element according to one aspect of the present invention will be described in detail.

[0033] The separation membrane substrate for an electrochemical element according to one aspect of the present invention is a separation membrane substrate for an electrochemical element containing a crosslinked polyolefin resin and chromium (Cr), wherein the crosslinked polyolefin resin contains a silicon-containing organic group graft-bonded to a polyolefin chain, the gel fraction of the separation membrane substrate is 3% to 80%, the standard deviation Δd of the thickness measured at any at least 100 points is 0.5 μm or less, and the number of spots having a long side length of 50 μm or more is 10 or less per 1 m 2 or less.

[0034] According to one embodiment of the present invention, the monomer of the polyolefin resin is not particularly limited as long as it can be used as a porous separation membrane substrate. For example, the polyolefin resin may be a homopolymer of a monomer selected from polyethylene, polypropylene, polybutylene, polypentene, polyhexene, polyoctene, ethylene, propylene, butene, pentene, 4-methylpentene, hexene, and octene; a copolymer of two or more of these; or a mixture thereof, but is not limited thereto.

[0035] As described later in the method for manufacturing the separation membrane substrate in the present specification, the polyolefin resin contains a polyolefin resin produced using an olefin polymerization catalyst containing chromium (Cr), so that the separation membrane substrate according to one aspect of the present invention contains chromium. Specifically, the separation membrane substrate contains chromium as a residue of the chromium catalyst used in the polymerization of the polyolefin resin.

[0036] In one embodiment of the present invention, the olefin polymerization catalyst containing chromium may include, for example, chromium oxide and a support supporting the chromium oxide. The support may include, for example, at least one component of silica, titania, alumina, zirconia, and aluminum phosphate, but the present invention is not limited thereto.

[0037] In one embodiment of the present invention, the content of chromium contained in the separation membrane substrate may be, for example, 0.1 to 20 ppm, 1 to 10 ppm, or 5 to 10 ppm, but is not limited thereto. The content of chromium in the separation membrane substrate may be, for example, a value measured using inductively coupled plasma with mass spectrometer (ICP-MS). When the content of chromium contained in the separation membrane substrate is within the above-described range, advantageous effects can be obtained in terms of the number of vinyl groups in the polyolefin resin before crosslinking and the degree of crosslinking of the crosslinked polyolefin resin produced using the same, but the present invention is not limited thereto.

[0038] According to one embodiment of the present invention, the polyolefin resin produced using the olefin polymerization catalyst containing chromium is characterized by containing a large amount of terminal vinyl groups in an active state that can be crosslinked by a thermal initiator contained in a coating solution in a subsequent process. As a result, the separation membrane substrate may include a polyolefin resin in which a large number of crosslinked structures are formed between polyolefin chains by a crosslinking reaction with a thermal initiator.

[0039] Also, according to one embodiment of the present invention, the polyolefin resin produced using the olefin polymerization catalyst containing chromium is characterized by containing a large amount of terminal vinyl groups in an active state that provide positions where a vinyl group-containing silane compound contained in a coating solution is grafted in a subsequent process. As a result, the separation membrane substrate may contain a silicon-containing organic group grafted with a large number of vinyl group-containing silane compounds by the terminal vinyl groups.

[0040] As used herein, the "crosslinked polyolefin resin" refers to a polyolefin resin in which vinyl groups present in the chain of the polyolefin resin used as a raw material of the separation membrane substrate are activated by an initiation reaction, and a crosslinked structure is formed in and / or between the chains of the polyolefin resin.

[0041] Specifically, in the crosslinked polyolefin resin, a vinyl group present at one end in the polyolefin chain is activated by a thermal initiator to form a radical, and the formed radical polymerizes with a radical formed in the polyolefin chain of another molecule and / or a radical formed at the other end in the polyolefin chain of the same molecule, thereby forming a crosslinked structure containing C(Sp 2 )-C(Sp 2 ) bonds.

[0042] Also, in one embodiment of the present invention, the "silicon-containing organic group graft-bonded to the polyolefin chain" means a residue derived from the vinyl group-containing silane compound formed by activation of a vinyl group present in the chain of the polyolefin resin used as a raw material of the separation membrane substrate and a vinyl group present in the vinyl group-containing silane compound by an initiation reaction, and formation of a new covalent bond at the activated position.

[0043] In one embodiment of the present invention, the silicon-containing organic group represents an organic residue derived from the vinyl group-containing silane compound, and the vinyl group-containing silane compound may include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriacetoxysilane, (3-methacryloxypropyl)trimethoxysilane, (3-methacryloxypropyl)triethoxysilane, vinylmethyldimethoxysilane, vinyl-tris(2-methoxyethoxy)silane, vinylmethyldiethoxysilane, or a mixture of two or more thereof, but the present invention is not limited thereto.

[0044] In one embodiment of the present invention, the crosslinked polyolefin resin may contain no terminal vinyl groups at all, or may contain a reduced number of terminal vinyl groups compared to the number of terminal vinyl groups present in the polyolefin resin before crosslinking.

[0045] In a similar aspect, the crosslinked polyolefin resin has an increased number of C(Sp 2 )-C(Sp 2 ) bonds compared to the number of C(Sp 2)-C(Sp 2 ) may include a bond.

[0046] In one embodiment of the present invention, when the number of functional groups was confirmed from the 1H-NMR spectrum results using a nuclear magnetic resonance spectrometer (Bruker, 500 NMR, 14.1 telsa), the polyolefin resin produced using the chromium-containing olefin polymerization catalyst may contain 100 or more, 200 or more, 300 or more, 400 or more, 500 or more, 600 or more, 700 or more, 800 or more, 900 or more, or 950 or more terminal vinyl groups per 1 million carbons. The upper limit of the terminal vinyl groups may be 1,500 or less or 1,000 or less within the above-described range, but is not limited thereto.

[0047] Accordingly, in one embodiment of the present invention, the number of terminal vinyl groups of the polyolefin resin before crosslinking may be, for example, 100 or more, 200 or more, 300 or more, 400 or more, 500 or more, 600 or more, 700 or more, 800 or more, 900 or more, or 950 or more per 1 million carbons.

[0048] In still another embodiment of the present invention, when the separation membrane substrate contains, together with a polyolefin resin produced using a catalyst other than the chromium-containing olefin polymerization catalyst, the number and content of the terminal vinyl groups of the polyolefin resin before crosslinking are desirably measured based on the number and content of the terminal vinyl groups of the entire polyolefin resin.

[0049] As described above, the crosslinked structure in the crosslinked polyolefin resin includes a structure derived from the result of a radical polymerization reaction between vinyl groups mediated by a thermal initiator.

[0050] In one embodiment of the present invention, the thermal initiator can be used without limitation as long as it can activate vinyl groups present in the polyolefin chain to form radicals. Specifically, any initiator that can activate the terminal vinyl groups present in the polyolefin chain to form radicals can be used without limitation. The thermal initiator may include, for example, peroxide-based compounds, persulfate-based compounds, azo-based compounds, or mixtures thereof.

[0051] Examples of the peroxide-based compounds include, but are not limited to, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (DHBP), benzoyl peroxide, acetyl peroxide, dilauryl peroxide, di-tert-butyl peroxide, dicumyl peroxide, cumyl peroxide, hydrogen peroxide, or mixtures of two or more thereof.

[0052] The persulfate-based compound is not particularly limited as long as it is a compound containing at least one of peroxymonosulfate ion (SO5 2- ) and peroxydisulfate (S2O8 2- ) as an anion. Examples of the persulfate-based compounds include, but are not limited to, sodium peroxymonosulfate (Na2SO5), potassium peroxymonosulfate (KHSO5), sodium peroxydisulfate (Na2S2O8), ammonium peroxydisulfate ((NH4)2S2O8), potassium peroxydisulfate (K2S2O8), or mixtures of two or more thereof.

[0053] The azo compound may include, for example, 2,2’-azobis(2-methylpropionitrile; AIBN), but is not limited thereto.

[0054] In one embodiment of the present invention, the separation membrane substrate may further include a polyolefin resin produced from an olefin polymerization catalyst other than the polyolefin resin produced from the chromium-containing olefin polymerization catalyst as described above.

[0055] The other type of olefin polymerization catalyst may be, for example, an olefin polymerization catalyst containing at least one or more of titanium (Ti), aluminum (Al), magnesium (Mg), zirconium (Zr), and vanadium (V). Accordingly, the separation membrane substrate may further contain at least one or more of titanium (Ti), aluminum (Al), magnesium (Mg), zirconium (Zr), and vanadium (V).

[0056] In one embodiment of the present invention, the other type of olefin polymerization catalyst may be, for example, a metallocene catalyst, a Ziegler-Natta catalyst, or a mixture thereof, but the present invention is not limited thereto.

[0057] In this specification, the polyolefin resin produced using the chromium-containing olefin polymerization catalyst may be referred to as "Cr-type polyolefin", and the polyolefin resin produced using the other type of olefin polymerization catalyst may be referred to as "ZT-type polyolefin".

[0058] In one embodiment of the present invention, when the separation membrane substrate contains a polyolefin resin produced using an olefin polymerization catalyst containing chromium in addition to other types of olefin polymerization catalysts, the weight ratio of the Cr-type polyolefin to the ZT-type polyolefin can be, for example, 1:9 to 9:1, specifically 2:8 to 8:2, 3:7 to 7:3, or 5:5, but is not limited thereto. When the separation membrane substrate contains both the Cr-type polyolefin and the ZT-type polyolefin, an advantageous effect can be obtained in that the molecular weight of the separation membrane substrate can be increased by the ZT-type polyolefin having a high molecular weight, but the present invention is not limited thereto.

[0059] In one embodiment of the present invention, in addition to polyolefin, the separation membrane substrate may further contain at least one of high molecular weight resins such as polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene. Further, examples of the separation membrane substrate include, but are not particularly limited to, non-woven fabric, porous polymer film, or a laminate of two or more of these.

[0060] In one embodiment of the present invention, as described later, when the separation membrane substrate contains a polyolefin resin produced using an olefin polymerization catalyst containing chromium, and a polyolefin sheet derived from the polyolefin resin is heat-fixed during the manufacturing process of the separation membrane substrate, a crosslinked structure is formed in the chains and / or between the chains in the polyolefin resin by a radical polymerization reaction mediated by the thermal initiator, thereby not only improving the thickness uniformity and heat resistance of the separation membrane substrate, but also improving the appearance characteristics of the separation membrane substrate. Further, when the polyolefin sheet derived from the polyolefin resin is heat-fixed, the wettability of the separation membrane substrate can be improved by grafting the vinyl group-containing silane compound, but the mechanism of the present invention is not limited thereto.

[0061] The separation membrane substrate according to one aspect of the present invention exhibits a gel fraction of 3% to 80%. This may be a characteristic manifested by the separation membrane substrate containing a polyolefin resin with excellent crosslinking degree, but the characteristics of the present invention are not limited thereto. The gel fraction of the separation membrane substrate can be, for example, 3% to 70%, 3% to 60%, 3% to 50%, 3% to 45%, 3% to 40%, 3% to 30%, 3% to 20% or 3% to 10%.

[0062] As described above, the polyolefin resin is characterized by exhibiting a high crosslinking degree due to the crosslinked structure formed in the polyolefin chain and / or between the chains. Thereby, while the polyolefin resin before crosslinking is dissolved in a benzene-based solvent, the crosslinked polyolefin resin is not dissolved in the benzene-based solvent and can exhibit the characteristics for which the gel fraction is measured.

[0063] In this specification, the gel fraction can be measured by the following method. First, 0.2 g of a test piece of the separation membrane substrate to be measured is placed in a 120-mesh stainless steel net, extracted in trichlorobenzene at 100 °C for 12 hours, and then dried in a vacuum oven at 100 °C for 12 hours. Thereafter, the weight of the test piece remaining on the stainless steel net is measured, and the gel fraction is measured by the following formula. The gel fraction can indicate the average value of the measured values for 3 test pieces for improving the accuracy of the measured value.

[0064] Gel fraction (%) = {(weight of remaining test piece (g) / 0.2 g} × 100 The separation membrane substrate according to one aspect of the present invention is made to have a standard deviation Δd of the thickness measured at any at least 100 points of 0.5 μm or less. Thereby, the separation membrane substrate can exhibit the effect of excellent thickness uniformity.

[0065] In one embodiment of the present invention, the standard deviation Δd of the thickness measured at any at least 100 points of the separation membrane substrate can be, for example, 0.5 μm or less, 0.45 μm or less, 0.40 μm or less, 0.35 μm or less, 0.3 μm or less, or 0.25 μm or less. Since the closer the standard deviation is to 0 μm, the higher the thickness uniformity, the lower limit of the standard deviation of the thickness can be 0 μm.

[0066] The thickness of the separation membrane substrate can be measured by a method for measuring the thickness of the separation membrane substrate. For example, it can indicate the value measured by analyzing the SEM image of the manufactured separation membrane substrate or by a known thickness measuring instrument. The thickness measuring instrument can be, for example, VL-50S-B (Mitutoyo), but is not limited thereto.

[0067] Usually, when manufacturing a separation membrane substrate, when a polymer resin as a raw material substance and other additives such as a diluent and a crosslinking agent are charged into an extruder at once and reacted, side reactions occur in the extruder, or due to insufficient kneadability between the raw material substances, spots having a brightness difference compared to the peripheral part are generated on the surface of the separation membrane substrate by the unmolten raw material substances.

[0068] In this specification, the "spot" refers to a white spot-like region on the surface of the separation membrane substrate that has a higher brightness and lower transparency than the peripheral part.

[0069] In one embodiment of the present invention, the number of the spots can be evaluated by visual observation or microscopic observation such as SEM.

[0070] In one embodiment of the present invention, the number of spots having a long side length of 50 μm or more can be observed and evaluated after placing the separation membrane substrate to be observed on an observation plate equipped with a backlight.

[0071] According to one embodiment of the present invention, in the separation membrane substrate, polyolefin resin is introduced as a raw material substance. After being formed into a polyolefin sheet, a thermal initiator and a vinyl group-containing silane compound are introduced, whereby the generation amount of the spots as described above is reduced, and it exhibits the characteristic that appearance defects are improved. For example, in the separation membrane substrate, the number of spots having a long side length of 50 μm or more is 1 m 2 per 10 or less. Specifically, the number of spots may be 0 to 7, 0 to 5, or 0 to 3 within the above conditions. By forming the number of spots within the above-described range, it is advantageous in terms of preventing uncoated areas due to appearance defects and short circuit generation in the battery during subsequent ceramic coating.

[0072] In another embodiment of the present invention, the thickness of the separation membrane substrate may be, for example, 4 to 20 μm. When the thickness of the separation membrane substrate is within the above-described range, it may have an advantageous effect in terms of the conductive barrier function and the resistance of the separation membrane, but the present invention is not limited thereto.

[0073] In one embodiment of the present invention, the weight average molecular weight (Mw) of the polyolefin resin contained in the separation membrane substrate may have a range of, for example, 100,000 to 5,000,000. When the weight average molecular weight of the polyolefin resin is within the above-described range, it may have an advantageous effect in terms of ensuring the mechanical properties of the separation membrane substrate and the shutdown characteristics, but the present invention is not limited thereto.

[0074] In this specification, the weight average molecular weight (Mw) of the polyolefin resin can be measured by gel permeation chromatography (GPC; PL GPC220, Agilent Technologies) under the following conditions.

[0075] - Column: PL Olexis (Polymer Laboratories) - Solvent: TCB (Trichlorobenzene) - Flow rate: 1.0 ml / min - Sample concentration: 1.0 mg / ml - Injection volume: 200 μl - Column temperature: 160 °C - Detector: Agilent High Temperature RI detector - Standard: Polystyrene (corrected with a third-order function)

[0076] In one embodiment of the present invention, the separation membrane substrate may have a porous structure. For example, the pore diameter may be 0.01 μm to 0.10 μm, and the porosity may be 30% to 70%. When the pore diameter and porosity in the separation membrane substrate are within the above-described ranges, advantageous effects can be achieved in terms of the ion permeability and mechanical strength of the separation membrane, but the present invention is not limited thereto.

[0077] In one embodiment of the present invention, the separation membrane substrate may exhibit excellent heat resistance. For example, the separation membrane substrate may exhibit a breaking temperature of 155 °C or higher. For example, the breaking temperature of the separation membrane substrate may be 160 °C or higher, 170 °C or higher, 180 °C or higher, 190 °C or higher, 195 °C or higher, and thus 200 °C or higher. Since the higher the breaking temperature of the separation membrane substrate, the better the heat resistance, the upper limit of the breaking temperature of the separation membrane substrate is not particularly limited and may be, for example, 500 °C or lower, 450 °C or lower, 350 °C or lower, or 300 °C or lower.

[0078] In this specification, the breaking temperature of the separation membrane substrate can be measured using a thermal mechanical analysis (TMA) apparatus by applying a load of 0.01 N to a test piece of the separation membrane substrate to be measured and observing the degree of deformation while increasing the temperature at a rate of 5 °C, and measuring it as the temperature at the point when the separation membrane substrate shrinks and then further stretches and breaks as the temperature rises.

[0079] In one embodiment of the present invention, the separation membrane substrate may have the characteristic of improved wettability by including a silicon-containing organic group graft-bonded to the polyolefin chain as described above.

[0080] In one embodiment of the present invention, the "wettability" of the separation membrane substrate refers to the property of allowing the electrolyte to penetrate, and can be evaluated by a conventional method for evaluating the degree of penetration of the electrolyte. For example, it can be evaluated by dropping a certain volume of electrolyte onto the separation membrane substrate and then measuring the area over which the electrolyte spreads after a certain period of time. It can be evaluated that the wider the area over which the dropped electrolyte spreads in the same period of time, the better the wettability with the electrolyte.

[0081] The separation membrane substrate for an electrochemical element according to one aspect of the present invention as described above is a polyolefin resin produced using an olefin polymerization catalyst containing chromium, and when heat-fixing a polyolefin sheet stretched from the polyolefin resin, a crosslinked structure between polyolefin chains is formed by using a thermal initiator and a vinyl group-containing silane compound, and by containing grafted silicon-containing organic groups, it can have the effect of improving appearance characteristics, thickness uniformity, heat resistance, and wettability, but the present invention is not limited thereto.

[0082] Next, a method for manufacturing a separation membrane substrate for an electrochemical element according to another aspect of the present invention will be described.

[0083] The separation membrane substrate for an electrochemical element according to another aspect of the present invention includes a step of melt-extruding a raw material substance containing a polyolefin resin to obtain a polymer melt extrudate, a step of molding and stretching the obtained polymer melt extrudate to obtain a polymer sheet, a step of applying a coating liquid containing a thermal initiator and a vinyl group-containing silane compound to the polymer sheet, and a step of drying and heat-fixing the polymer sheet coated with the coating liquid. At this time, the polyolefin resin includes a polyolefin resin produced using an olefin polymerization catalyst containing chromium.

[0084] First, a raw material substance containing a polyolefin resin produced using an olefin polymerization catalyst containing chromium is melt-extruded to obtain a polymer melt extrudate.

[0085] In one embodiment of the present invention, for the melt extrusion, it is desirable that the raw material substance contains not only the polyolefin resin produced using the olefin polymerization catalyst containing chromium but also a diluent.

[0086] As the diluent, for example, liquid or solid paraffin oil, mineral oil, wax, soybean oil, etc., which are usually used in the production of wet separation membranes, can be used.

[0087] In one embodiment of the present invention, as the diluent, a diluent capable of liquid-liquid phase separation with the polyolefin resin can also be used. For example, phthalic acid esters such as dibutyl phthalate, dihexyl phthalate, dioctyl phthalate; aromatic ethers such as diphenyl ether, benzyl ether; fatty acids having 10 to 20 carbon atoms such as palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid; fatty acid alcohols having 10 to 20 carbon atoms such as palmitic acid alcohol, stearic acid alcohol, oleic acid alcohol; saturated and unsaturated fatty acids or one or more fatty acids in which the double bond of the unsaturated fatty acid is replaced by epoxy in the fatty acid group such as palmitic acid mono-, di-, or triester, stearic acid mono-, di-, or triester, oleic acid mono-, di-, or triester, linoleic acid mono-, di-, or triester, and fatty acid esters in which the alcohol having 1 to 8 hydroxy groups and 1 to 10 carbon atoms is ester-bonded; or a mixture of two or more of these can be used, but not limited thereto.

[0088] In one embodiment of the present invention, the content of the diluent can be, for example, 100 to 350 parts by weight, or 125 to 300 parts by weight, or 150 to 250 parts by weight based on 100 parts by weight of the polyolefin. When the total content of the diluent satisfies the numerical range, due to the large content of the polyolefin, the porosity decreases, the pore size becomes small, the interconnectivity between pores decreases, the permeability significantly decreases, and it becomes difficult to process due to the increase in the extrusion load caused by the increase in the viscosity of the polyolefin composition. On the other hand, since the content of the polyolefin is small, the kneadability between the polyolefin and the diluent decreases, and problems such as breakage during stretching and thickness variation generated when the polyolefin is extruded in a gel state without being thermodynamically kneaded with the diluent can be prevented. However, the present invention is not limited thereto.

[0089] In one embodiment of the present invention, in addition to the polyolefin resin and the diluent produced using an olefin polymerization catalyst containing chromium, the raw material substance may further include other types of olefin polymerization catalysts, for example, Ziegler-Natta catalysts; or olefin polymerization catalysts containing titanium (Ti), aluminum (Al), magnesium (Mg), zirconium (Zr), vanadium (V), or two or more of these. The polyolefin resins and other polymer resins produced using these may be further included, and for these polyolefin resins and other polymer resins, those described above are incorporated by reference.

[0090] For example, in one embodiment of the present invention, the raw material substance may further include a polyolefin resin produced by an olefin polymerization reaction using a Ziegler-Natta catalyst.

[0091] According to one embodiment of the present invention, the weight ratio of the polyolefin resin (Cr-type polyolefin) produced using an olefin polymerization catalyst containing chromium and the polyolefin resin (ZT-type polyolefin) produced using other types of olefin polymerization catalysts among the raw material substances can be 1:9 to 9:1, specifically 2:8 to 8:2, 3:7 to 7:3, or 5:5. However, the present invention is not limited thereto.

[0092] According to another embodiment of the present invention, when the ZT type polyolefin is further included in addition to the Cr type polyolefin, based on 100% by weight of the total raw materials, the content of the polyolefin resin produced using the olefin polymerization catalyst containing chromium may be, for example, 10% by weight or more. Specifically, based on 100% by weight of the total raw materials, the content of the polyolefin resin produced using the olefin polymerization catalyst containing chromium may be 15% by weight or more, 20% by weight or more, 25% by weight or less, 30% by weight or more, 35% by weight or more, 40% by weight or more, 45% by weight or more, 50% by weight or more, and / or 99.9% by weight or less, 99% by weight or less, 95% by weight or less, or 90% by weight or less, but the present invention is not limited thereto.

[0093] In one embodiment of the present invention, the step of obtaining the polymer melt extrudate may use a normal single-screw extruder or twin-screw extruder, but is not limited thereto.

[0094] Next, the obtained polymer melt extrudate is formed and stretched to obtain a polymer sheet.

[0095] In one embodiment of the present invention, after the extrusion of the polymer melt extrudate, a normal casting method or calender method may be used to form a cooled extrudate using a method such as water cooling or air cooling.

[0096] In one embodiment of the present invention, a separation membrane substrate having improved mechanical strength and puncture strength can be provided by undergoing the forming and stretching steps.

[0097] In one embodiment of the present invention, the stretching can be performed by sequential or simultaneous stretching in a roll method or a tenter method. The stretching ratio can be, for example, 3 times or more or 5 to 12 times in the longitudinal or transverse direction, and the total stretching ratio can be 20 to 120 times. When the stretching ratio satisfies the above numerical range, advantageous effects can be achieved in terms of the thickness uniformity of the produced separation membrane substrate and the physical property balance between the longitudinal and transverse directions, but the present invention is not limited thereto.

[0098] In one embodiment of the present invention, the stretching temperature varies depending on the melting point of the polyolefin resin used, the concentration and type of the diluent, and the present invention is not limited thereto.

[0099] Thereafter, the diluent is extracted from the stretched polymer sheet to obtain a porous polymer sheet.

[0100] In one embodiment of the present invention, the diluent can be extracted and dried using an organic solvent having high solubility in the diluent on the stretched sheet to form a porous sheet.

[0101] The organic solvent is not particularly limited as long as it can extract the used diluent, but methyl ethyl ketone, methylene chloride, hexane, etc. can be used in terms of extraction efficiency and drying speed.

[0102] In one embodiment of the present invention, the extraction method can be each or a combination of all ordinary solvent extraction methods such as an immersion method, a solvent spray method, an ultrasonic method, etc. In one embodiment of the present invention, the content of the residual diluent after the extraction treatment can desirably be 1% by weight or less. When the content of the residual diluent is within the above-mentioned range, it can exhibit advantageous effects in terms of the permeability and mechanical properties of the produced separation membrane substrate and the efficiency of the manufacturing process, but the present invention is not limited thereto.

[0103] The extraction time and extraction temperature can vary depending on the thickness of the polymer sheet and the type of polymer, but the present invention is not limited thereto.

[0104] Next, a coating solution containing a thermal initiator and a vinyl group-containing silane compound is applied to the polymer sheet.

[0105] A coating solution containing a thermal initiator and a vinyl group-containing silane compound is applied to the polymer porous sheet with pores exposed in advance according to the present invention. As described above, the thermal initiator can activate the terminal vinyl groups in the chain of the polyolefin resin to form radicals. As a result, not only a large amount of crosslinked structures are formed in the polyolefin chain by the thermal initiator, but the coating solution can also penetrate into the fibrils existing on the surface of the already formed pores, and excellent effects can be achieved in terms of improving the heat resistance of the separation membrane substrate, but the present invention is not limited thereto. Further, the vinyl group-containing silane compound may contain a silicon-containing organic group graft-bonded by a covalent bond at the location where the terminal vinyl group in the chain of the polyolefin resin is activated. As a result, excellent effects can be achieved in terms of improving the wettability of the separation membrane substrate, but the present invention is not limited thereto.

[0106] In one embodiment of the present invention, the thermal initiator and the vinyl group-containing silane compound in the coating solution may be contained, for example, in a weight ratio of 2:8 to 8:2, specifically in a weight ratio of 3:7 to 7:3 or 4:6 to 6:4. When the weight ratio of the thermal initiator and the vinyl group-containing silane compound is within the above-described range, the vinyl groups in the chain of the polyolefin resin can be sufficiently activated to induce crosslinking and graft reactions, and advantageous effects can be achieved in terms of improving the wettability of the separation membrane substrate, but the present invention is not limited thereto.

[0107] In one embodiment of the present invention, the coating solution may contain, for example, ethanol, propanol, acetone, NMP, DMAC, DMF, water, or a mixture of two or more of these as a solvent for the thermal initiator and the vinyl group-containing silane compound. Also, the total content of the solid components in the coating solution is, for example, 5% by weight to 60% by weight, specifically 7% by weight to 40% by weight, which is desirable in terms of radical activation of double bonds and improvement of the wettability of the separation membrane substrate, but the present invention is not limited thereto.

[0108] In one embodiment of the present invention, the coating solution may further contain ordinary additives for improving specific functions, such as an antioxidant, a UV stabilizer, an antistatic agent, a nucleating agent, etc., as necessary, but the present invention is not limited thereto.

[0109] Thereafter, the polymer sheet coated with the coating solution is dried and heat-fixed to obtain a separation membrane substrate.

[0110] The heat fixation is for fixing the porous membrane, applying heat, and forcibly fixing the porous membrane that tends to shrink to remove residual stress.

[0111] According to the method for manufacturing the separation membrane substrate of the present invention, by applying a coating solution containing the thermal initiator and the vinyl group-containing silane compound before heat fixation, during the heat fixation, a large amount of cross-linked structures are formed by a radical polymerization reaction mediated by the thermal initiator and / or a cross-linking reaction between chains in the polyolefin chains, and a separation membrane substrate of a polyolefin resin substrate with a large amount of silicon-containing organic groups grafted to the ends of the polyolefin chains is obtained.

[0112] In one embodiment of the present invention, the heat fixation temperature and time vary depending on the vinyl group content in the polyolefin chains and the composition of the coating solution, and the present invention is not limited thereto.

[0113] According to another aspect of the present invention, there is provided a separation membrane for an electrochemical device including the aforementioned separation membrane substrate and an inorganic coating layer formed on at least one surface of the separation membrane substrate, wherein the inorganic coating layer contains inorganic particles and a binder material.

[0114] The inorganic coating layer may have a porous structure due to pores formed by the interstitial volume between inorganic particles. The size and size distribution of the inorganic particles enable adjustment of the pore size and porosity (ratio of pore volume). Such a structure enhances the resistance to metallic foreign substances present in the electrode and suppresses the shrinkage of the polyolefin separator as the base material, thereby strengthening the safety of the electrochemical device. In this regard, the inorganic coating layer may contain inorganic particles in a proportion of 70 to 99.5% by weight, preferably 80 to 99% by weight, based on 100% by weight of the inorganic coating layer.

[0115] In one embodiment of the present invention, the inorganic particles are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles usable in the present invention are not particularly limited as long as no oxidation and / or reduction reaction occurs within the operating voltage range of the applied electrochemical device (for example, 0 to 5 V based on Li / Li+). In particular, when using inorganic particles with a high dielectric constant as the inorganic particles, it can contribute to an increase in the dissociation degree of electrolyte salts in the liquid electrolyte, such as lithium salts, and improve the ionic conductivity of the electrolyte solution.

[0116] For the reasons described above, it is desirable that the inorganic particles 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), P 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, and TiO2, etc., and may include one or more of these.

[0117] In one embodiment of the present invention, the average particle size D of the inorganic particles 50 is not particularly limited, but it is preferably in the range of 0.1 μm to 2.5 μm for the formation of an inorganic coating layer with a uniform thickness and an appropriate porosity.

[0118] In one embodiment of the present invention, the binder material may include an acrylic polymer and / or a PVDF polymer. The acrylic polymer may include, for example, a (meth)acrylic polymer. The (meth)acrylic polymer contains (meth)acrylic acid ester as a monomer, and such monomers include monomers such as butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, ethyl (meth)acrylate, methyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, lauryl (meth)acrylate, and tetradecyl (meth)acrylate, and may include one or more of these. The PVdF polymer may include one or more of a homopolymer of vinylidene fluoride (i.e., polyvinylidene fluoride), a copolymer of vinylidene fluoride and a copolymerizable monomer, and a mixture thereof. In one embodiment of the present invention, as the monomer, for example, a fluorinated monomer and / or a chlorine-based monomer may be used. Non-limiting examples of the fluorinated monomer include vinyl fluoride; trifluoroethyl (TrFE); chlorofluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro(alkyl vinyl)ethers such as perfluoro(methyl vinyl)ether (PMVE), perfluoro(ethyl vinyl)ether (PEVE), and perfluoro(propyl vinyl)ether (PPVE); perfluoro(1,3-dioxole); and perfluoro(2,2-dimethyl-1,3-dioxole) (PDD), and may include one or more of these.In one embodiment of the present invention, the PVDF-based polymer may include one or more selected from polyvinylidene fluoride (PVDF), polyvinylidene fluoride - hexafluoropropylene (PVDF-HFP), polyvinylidene fluoride - chlorotrifluoroethylene (PVDF-CTFE), polyvinylidene fluoride - tetrafluoroethylene (PVdF-TFE), and polyvinylidene fluoride - trifluoroethylene (PVdF-TrFE).

[0119] In an embodiment of the present invention, the separation membrane may be manufactured by coating the above-described inorganic coating layer on the separation membrane substrate.

[0120] First, the binder material is dispersed in a solvent or a binder solution is prepared in a dissolved form. Next, inorganic particles dispersed in the form of a bead mill are added to the binder solution to prepare a slurry for forming an inorganic coating layer. Non-limiting examples of the solvent may be one or a mixture of two or more selected from the group consisting of water, acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (NMP), and cyclohexane.

[0121] As the method for coating the slurry on the separation membrane substrate, a conventional coating method known in the art may be used. For example, various methods such as dip coating, die coating, roll coating, comma coating, or a mixed method thereof may be used. Also, for the drying, ordinary drying methods such as natural drying and blow drying can be applied without particular limitation.

[0122] According to still another aspect of the present invention, the electrode assembly includes a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode. At this time, the above-described separator is used as the separator.

[0123] In this specification, for the specific configurations of the positive electrode, negative electrode, and electrode assembly, ordinary ones may be used, and thus the description thereof will be omitted.

[0124] According to still another aspect of the present invention, a secondary battery can be provided by enclosing the electrode assembly prepared as described above in a suitable case and injecting an electrolytic solution.

[0125] Hereinafter, the present invention will be described in more detail with reference to examples. However, the following examples are for illustrative purposes only and do not limit the scope of the present invention.

[0126] [Manufacture of Separator Substrate] Example 1 9 kg / hr of a Cr-type polyolefin (DL Chemical, TR570) and 21 kg / hr of a diluent (Kukdong Oil&Chemicals Co., Ltd., LP350F) were charged as raw materials into an extruder (EM of Korea, φ32 twin-screw extruder L / D = 56) and melt-extruded at 200 °C to obtain a polyolefin melt extrudate.

[0127] After passing the obtained polyolefin melt extrudate through a T-die, it was formed into a sheet using a cooling casting device, and then, after MD stretching, it was biaxially stretched using a tenter-type sequential stretching machine for TD stretching to obtain a polyolefin sheet. The MD stretching ratio and TD stretching ratio were 7 times and 6 times, respectively, and the stretching temperatures were 115 °C for MD and 125 °C for TD.

[0128] A porous polyolefin sheet was obtained by extracting the diluent from the stretched polyolefin sheet using methylene chloride.

[0129] Next, a coating solution containing 10 wt% of dicumyl peroxide in solvent ethanol as a thermal initiator and 20 wt% of vinyltrimethoxysilane as a vinyl group-containing silane compound (wetting agent) was applied to one surface of the porous polyolefin sheet.

[0130] Thereafter, the polyolefin sheet coated with the coating solution was dried and heat-fixed at 128 °C to produce a separation membrane substrate. At this time, the average thickness of the obtained separation membrane substrate was 9.0 μm.

[0131] Example 2 A separation membrane substrate was produced in the same manner as in Example 1, except that 0.9 kg / hr of Cr-type polyolefin and 8.1 kg / hr of ZT-type polyolefin (Korea Petrochemical Ind. Co., LTD, VH350) (weight ratio of Cr-type: ZT-type = 1:9) were used as raw materials. At this time, the average thickness of the obtained separation membrane substrate was 9.0 μm.

[0132] Comparative Example 1 A separation membrane substrate was produced in the same manner as in Example 1, except that ZT-type polyolefin (Korea Petrochemical Ind. Co., LTD, VH035) was used instead of Cr-type polyolefin as a raw material and the coating solution application step was not performed. At this time, the average thickness of the obtained separation membrane substrate was 9.1 μm.

[0133] Comparative Example 2 A separation membrane substrate was produced in the same manner as in Example 1, except that the coating solution application step was not performed. At this time, the average thickness of the obtained separation membrane substrate was 9.0 μm.

[0134] Comparative Example 3 Into an extruder (EM of Korea, twin-screw extruder with φ32, L / D = 56), 9 kg / hr of ZT-type polyolefin (Kukdong Oil&Chemicals Co.,Ltd., VH035) was charged as a raw material substance, 100 g / hr of dicumyl peroxide as a thermal initiator, 100 g / hr of vinyltrimethoxysilane as a vinyl group-containing silane compound, and 21 kg / hr of liquid paraffin oil (Kukdong Oil&Chemicals Co.,Ltd., LP350F) as a diluent were charged, and melt extrusion was carried out at 200 °C to obtain a polyolefin melt extrudate.

[0135] After passing the obtained polyolefin melt extrudate through a T-die, it was formed into a sheet using a cooling casting device, and then, after MD stretching, it was biaxially stretched with a tenter-type sequential stretcher for TD stretching to obtain a polyolefin sheet. The MD stretching ratio and TD stretching ratio were 7 times and 6 times, respectively, and the stretching temperatures were 115 °C for MD and 125 °C for TD.

[0136] After extracting the diluent from the stretched polyolefin sheet using methylene chloride to obtain a porous polyolefin sheet, it was dried and heat-fixed at 128 °C to produce a separation membrane substrate. At this time, the average thickness of the obtained separation membrane substrate was 9.0 μm.

[0137] Comparative Example 4 A separation membrane substrate was produced in the same manner as in Comparative Example 3, except that Cr-type polyolefin (DL Chemical, TR570) was used instead of ZT-type polyolefin as the raw material substance. At this time, the average thickness of the obtained separation membrane substrate was 9.0 μm.

[0138] Comparative Example 5 A separation membrane substrate was produced in the same manner as in Example 1, except that ZT-type polyolefin (Korea Petrochemical Ind.Co.,LTD, VH035) was used instead of Cr-type polyolefin as the raw material substance. At this time, the average thickness of the obtained separation membrane substrate was 9.0 μm.

[0139] Comparative Example 6 A separation membrane substrate was produced by the same method as in Example 1, except that the vinyl group-containing silane compound (wetting agent) was removed from the coating solution. At this time, the average thickness of the obtained separation membrane substrate was 9.1 μm.

[0140] Comparative Example 7 A separation membrane substrate was produced by the same method as in Example 1, except that 0.45 kg / hr of Cr-type polyolefin and 8.55 kg / hr of ZT-type polyolefin (Korea Petrochemical Ind. Co., LTD, VH035) (weight ratio of Cr-type: ZT-type = 0.5:9.5) were used as raw material substances. At this time, the thickness of the obtained separation membrane substrate was 9.0 μm.

[0141] [Component Analysis and Physical Property Evaluation of Separation Membrane Substrate] The components of the produced Example 1, Example 2, and Comparative Examples 1 to 6 were analyzed and the physical properties were evaluated as follows, and the results are shown in Table 1 and FIG. 1 below.

[0142] Measurement of gel fraction First, 0.2 g of a test piece of the separation membrane substrate was placed in a 120-mesh stainless steel mesh, extracted in trichlorobenzene at 100 °C for 12 hours, and then dried in a vacuum oven at 100 °C for 12 hours.

[0143] Thereafter, the weight of the test piece remaining on the stainless steel mesh was measured, and the gel fraction was measured by the following formula. The gel fraction was shown as the average value of the measured values for each of the three test pieces.

[0144] Gel fraction (%) = {(weight of remaining test piece (g)) / 0.2 g} × 100 Measurement of chromium (Cr) and silicon (Si) contents First, a specimen of the separation membrane substrate was reacted with sulfuric acid and carbonized on a hot plate, and then the sulfuric acid was removed. After that, it was ashed in an electric furnace (temperature: 600 °C) for 4 hours and then decomposed with nitric acid and hydrogen peroxide. Then, when the specimen was clearly dissolved, it was diluted three times with ultrapure water to prepare an analytical sample.

[0145] The contents of chromium (Cr) and silicon (Si) in the separation membrane substrate were measured using an inductively coupled plasma with mass spectrometer (ICP-MS) (Axiom MC model, Thermo Elemental Ltd, UK).

[0146] Measurement of aluminum (Al) content When using a Ziegler-Natta catalyst, aluminum (Al) exists on the separation membrane substrate, so the aluminum content was measured.

[0147] The method for measuring the aluminum content was the same as the method for measuring the chromium content.

[0148] Breaking temperature The breaking temperature of the manufactured separation membrane substrate was analyzed using a TMA (thermal mechanical analysis) analyzer (TA Instruments, TMA Q400).

[0149] Specifically, a 0.01 N load was applied to the separation membrane substrate, and the degree of deformation was observed while the temperature was raised at a rate of 5 °C / min. The temperature at the point when the separation membrane substrate shrank and then further stretched and broke as the temperature increased was measured as the "breaking temperature".

[0150] Measurement of number of spots The separation membrane substrate was placed on an observation plate with a backlight attached, and the separation membrane substrate 1 m 2The number of spots with the length of the long side of each hit being 50 μm or more was visually confirmed, and the number of spots was measured.

[0151] Measurement of thickness uniformity 1 m was measured at intervals of 10 cm in the width direction of the separation membrane substrate, and 30 m was measured at intervals of 3 m in the longitudinal direction. The standard deviation of the thickness was measured based on the thickness measurement values at a total of 100 positions.

[0152] Measurement of wettability After 4 μm of DMC (dimethyl carbonate) was dropped onto one surface of the produced separation membrane substrates of Example 1, Example 2, and Comparative Example 1, the spread area was measured, and the results are shown in FIGS. 1 to 3, respectively.

[0153] In FIGS. 1 to 3, PG0 indicates the region where the solvent (DMC) has spread, PG1 indicates the region where the solvent adheres to the surface of the separation membrane, L indicates the longest length in each of the regions of PG0 and PG1, and A indicates the area of each of the regions of PG0 and PG1. The wettability of the separation membrane substrate was evaluated from the area of the PG0 region. [Table 1] According to the results in Table 1 above, it was confirmed that the separation membrane substrates of Example 1 and Example 2, which are produced by using a Cr-type polyolefin resin as a raw material and applying a coating solution containing a thermal initiator and a vinyl group-containing silane compound after extrusion of the resin, have gel fractions of 45% and 12%, respectively, standard deviations of thickness all of 0.5 μm or less, and a breaking temperature of 160 °C or higher.

[0154] On the other hand, it was confirmed that the separation membrane substrate of Comparative Example 1, which uses only ZT-type polyolefin resin and does not apply a coating solution containing a thermal initiator and a vinyl group-containing silane compound, is inferior in terms of gel fraction, breaking temperature, and thickness uniformity. Also, even when using Cr-type polyolefin resin, in the case of Comparative Example 2 where a coating solution containing a thermal initiator and a vinyl group-containing silane compound was not applied, it was confirmed that it was still poor in terms of gel fraction and breaking temperature. Further, in the cases of Comparative Examples 3 and 4 where a thermal initiator and a vinyl group-containing silane compound were added together with the polyolefin raw material at the raw material input stage, it was confirmed that there were defects in terms of appearance characteristics or thickness uniformity.

[0155] Furthermore, even when the coating step of the coating solution containing a thermal initiator and a vinyl group-containing silane compound was carried out, in the case of Comparative Example 5 where the raw material substance used only ZT-type polyolefin resin, it was still poor in terms of thickness uniformity. In the case of Comparative Example 6 produced without including a vinyl group-containing silane compound in the coating solution, it was poor in terms of wettability. In the case of Comparative Example 7 where a small amount of Cr-type polyolefin resin was used as the polyolefin resin, it was confirmed that it was still poor in terms of breaking temperature.

[0156] As described above with reference to the embodiments and drawings of the present invention, those with ordinary knowledge in the field to which the present invention pertains will be able to make various applications and modifications within the scope of the present invention based on the above content.

Claims

1. A separation membrane substrate for an electrochemical device comprising a crosslinked polyolefin resin and chromium (Cr), wherein the crosslinked polyolefin resin contains a silicon-containing organic group graft-bonded to a polyolefin chain, the gel fraction of the separation membrane substrate is 3% to 80%, and the standard deviation Δd of the thickness measured at any at least 100 points is 0.5 μm or less, The number of spots having a long side length of 50 μm or more is 10 or less per 1 m ２ A separation membrane substrate for an electrochemical element, characterized in that the number of spots having a long side length of 50 μm or more is 10 or less per 1 m.

2. wherein the silicon-containing organic group is a residue derived from a vinyl group-containing silane compound, and the vinyl group-containing silane compound contains vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriacetoxysilane, (3-methacryloxypropyl)trimethoxysilane, (3-methacryloxypropyl)triethoxysilane, vinylmethyldimethoxysilane, vinyl-tris(2-methoxyethoxy)silane, vinylmethyldiethoxysilane, or a mixture of two or more thereof. The separation membrane substrate for an electrochemical device according to claim 1.

3. The separation membrane substrate for an electrochemical device according to claim 1, wherein the chromium content is 0.1 to 20 ppm.

4. The separation membrane substrate for an electrochemical device according to claim 1, wherein the gel fraction of the separation membrane substrate is 3% to 50%.

5. The separation membrane substrate for an electrochemical device according to claim 1, wherein the crosslinked structure in the crosslinked polyolefin resin includes a structure derived from the result of a radical polymerization reaction between vinyl groups mediated by a thermal initiator.

6. The separation membrane substrate for an electrochemical device according to claim 5, wherein the thermal initiator contains a peroxide-based compound, a persulfate-based compound, an azo-based compound, or a mixture thereof.

7. The separation membrane substrate for an electrochemical device according to claim 1, further comprising at least one of titanium (Ti), aluminum (Al), magnesium (Mg), zirconium (Zr), and vanadium (V).

8. The separation membrane substrate for an electrochemical device according to claim 1, wherein the standard deviation Δd of the thickness measured at any at least 100 points of the separation membrane substrate is 0.3 μm or less.

9. Melting and extruding a raw material containing a polyolefin resin to obtain a polymer melt extrudate, Forming and stretching the obtained polymer melt extrudate to obtain a polymer sheet; Applying a coating solution containing a thermal initiator and a vinyl group-containing silane compound to the polymer sheet; Drying and heat-fixing the polymer sheet coated with the coating solution, and including: The polyolefin resin includes a polyolefin resin produced using an olefin polymerization catalyst containing chromium, and a method for producing a separation membrane substrate for an electrochemical device.

10. Among the raw materials, the polyolefin resin includes a polyolefin resin having 100 or more terminal vinyl groups per million carbon atoms, and a method for producing a separation membrane substrate for an electrochemical device according to claim 9.

11. The raw material further includes a polyolefin resin produced using an olefin polymerization catalyst that does not contain chromium and contains titanium (Ti), aluminum (Al), magnesium (Mg), zirconium (Zr), vanadium (V), or two or more of these, and a method for producing a separation membrane substrate for an electrochemical device according to claim 9.

12. Based on the total weight of the polyolefin resin in the raw material, the content of the polyolefin resin produced using an olefin polymerization catalyst containing chromium is 10% by weight or more, and a method for producing a separation membrane substrate for an electrochemical device according to claim 9.

13. A separation membrane substrate according to any one of claims 1 to 8 and an inorganic coating layer formed on at least one surface of the separation membrane substrate, The inorganic coating layer includes inorganic particles and a binder material, and a separation membrane for an electrochemical device.

14. An electrode assembly including a positive electrode, a negative electrode, and a separation membrane interposed between the positive electrode and the negative electrode, wherein the separation membrane is the separation membrane according to claim 13.

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