Separation membrane substrate for electrochemical elements, method for manufacturing the same, separation membrane containing the separation membrane substrate, and assembly.

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 phosphorus-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 per 1 m 2 is 10 or less.

Description

[Technical Field]

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

[0002] This application claims priority based on Korean Patent Application No. 2022-0140751, filed on 27 October 2022, and all content disclosed in the specification and drawings of said application is incorporated herein. [Background technology]

[0003] Rechargeable batteries, typified by lithium-ion batteries, are widely used as power sources for portable electronic devices such as notebook PCs, mobile phones, digital cameras, and camcorders. Furthermore, in recent years, these batteries have been applied to a variety of fields, including automobiles, due to their high energy density.

[0004] Lithium-ion batteries have attracted attention due to their advantages over conventional batteries such as Ni-MH, Ni-Cd, and lead-sulfate batteries, which use aqueous electrolytes, including higher operating voltage and significantly higher energy density. However, these lithium-ion batteries have disadvantages, such as safety issues like ignition and explosion associated with the use of organic electrolytes, and are not easy to manufacture. Recent lithium-ion polymer batteries are being hailed as a next-generation battery because they improve upon these shortcomings of lithium-ion batteries, but their capacity is still relatively lower than that of lithium-ion batteries, and their discharge capacity at low temperatures is particularly insufficient, requiring further improvement.

[0005] Evaluating the stability and ensuring the safety of such electrochemical elements is extremely important. In terms of the safety characteristics of electrochemical elements, there is a high risk of explosion if the electrochemical element overheats and undergoes thermal runaway, or if the separation membrane is penetrated. In particular, polyolefin-based separation membrane substrates, which are commonly used as separation membranes in electrochemical elements, exhibit severe thermal contraction behavior at temperatures above 100°C due to the material properties and manufacturing process characteristics, including stretching, which can cause a short circuit between the positive and negative electrodes.

[0006] To address the safety issues of such electrochemical elements, a separation membrane has been proposed in which a porous inorganic coating layer is formed by coating at least one surface of a separation membrane substrate having multiple pores with a mixture of excess inorganic particles and a binder polymer. However, there is a continuing demand for further enhanced stability. [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The present invention aims to provide a separation membrane substrate with enhanced thickness uniformity and heat resistance, and a separation membrane using the same with enhanced thickness uniformity and heat resistance. Through this, the present invention aims to provide an electrochemical element with improved stability and excellent resistance characteristics. [Means for solving the problem]

[0008] To achieve the above objectives, In one aspect of the present invention, a separation membrane substrate according to the following embodiment is provided.

[0009] The separation membrane substrate according to the first embodiment is A separation membrane substrate for an electrochemical element comprising a crosslinked polyolefin resin and chromium (Cr), wherein the crosslinked polyolefin resin contains phosphorus-containing organic groups grafted to the polyolefin chain, the gel fraction of the separation membrane substrate is 3% to 80%, the standard deviation Δd of the thickness measured at at least 100 arbitrary points is 0.5 μm or less, and the number of spots with a long side length of 50 μm or more is 1 m2 The number of winning items is 10 or less.

[0010] In the second embodiment, in the first embodiment, The phosphorus-containing organic group is a residue derived from a phosphorus compound containing a vinyl group. The aforementioned phosphorus-based compound containing a vinyl group may include a phosphate compound, a phosphonate compound, a phosphine compound, a phosphine oxide compound, or a mixture of two or more of these.

[0011] In the third embodiment, in the first or second embodiment, The chromium content may range from 0.1 to 20 ppm.

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

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

[0014] In the sixth embodiment, in the fifth embodiment, The thermal initiator may include peroxide compounds, persulfate compounds, azo compounds, or mixtures thereof.

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

[0016] In the eighth embodiment, in any 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] In another aspect of the present invention, a method for manufacturing a separation membrane substrate according to the following embodiment is provided.

[0018] The method for manufacturing a separation membrane substrate according to the ninth embodiment is 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 phosphorus 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] In 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] In the eleventh embodiment, in the ninth or tenth embodiment, the raw material substance may further include 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.

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

[0022] In still another aspect of the present invention, a separation membrane according to the following embodiment is provided.

[0023] The separation membrane according to the 13th example is The invention comprises a separation membrane substrate according to any of the first to eighth embodiments and an inorganic coating layer formed on at least one surface of the separation membrane substrate, wherein the inorganic coating layer comprises inorganic particles and a binder material.

[0024] In yet another aspect of the present invention, an electrode assembly of the following embodiment is provided.

[0025] The electrode assembly according to the 14th embodiment is The system includes a positive electrode, a negative electrode, and a separation membrane interposed between the positive electrode and the negative electrode, wherein the separation membrane may be the separation membrane described in the 13th embodiment. [Effects of the Invention]

[0026] The separation membrane substrate according to one embodiment of the present invention exhibits improved thickness uniformity and heat resistance due to the inclusion of a large amount of crosslinked structures in the polyolefin chain. Therefore, it effectively improves the operational stability, such as heat resistance, of electrochemical elements containing a separation membrane using such a separation membrane substrate.

[0027] In particular, a separation membrane substrate according to one embodiment of the present invention is manufactured using a polyolefin resin containing a large amount of terminal vinyl groups produced using a chromium-containing olefin polymerization catalyst, and a thermal initiator for crosslinking between these terminal vinyl groups. The separation membrane substrate can achieve improved thickness uniformity and heat resistance by forming a large amount of crosslinked structures between polyolefin chains, but the mechanism of the present invention is not limited thereto. [Modes for carrying out the invention]

[0028] The present invention will be described in detail below.

[0029] This invention relates to a separation membrane substrate for an electrochemical element, a separation membrane containing the same, and an electrochemical element containing the separation membrane. In this invention, the electrochemical element is a device that converts chemical energy into electrical energy by an electrochemical reaction, and is a concept that includes primary batteries and secondary batteries. The secondary battery is a concept that can be charged and discharged and includes lithium-ion batteries, nickel-cadmium batteries, nickel-metal hydride batteries, and the like.

[0030] First, we will explain in detail one aspect of the present invention: a separation membrane substrate for electrochemical devices.

[0031] A separation membrane substrate for an electrochemical element according to one aspect of the present invention is a separation membrane substrate for an electrochemical element comprising a crosslinked polyolefin resin and chromium (Cr), wherein the crosslinked polyolefin resin contains phosphorus-containing organic groups grafted to the polyolefin chain, the gel fraction of the separation membrane substrate is 3% to 80%, and the standard deviation Δd of the thickness measured at at least 100 arbitrary points is 0.5 μm or less, and 1 m 2 The number of spots with a longest side length of 50 μm or more is 10 or less.

[0032] According to one embodiment of the present invention, the monomer of the polyolefin resin is not particularly limited as long as it is used as a porous separation membrane substrate. For example, the polyolefin resin may be, but is not limited to, homopolymers of monomers selected from polyethylene, polypropylene, polybutylene, polypentene, polyhexene, polyoctene, ethylene, propylene, butene, pentene, 4-methylpentene, hexene, and octene; copolymers of two or more of these; or mixtures thereof.

[0033] As described in the method for producing the separation membrane substrate later in this specification, the polyolefin resin includes a polyolefin resin produced using an olefin polymerization catalyst containing chromium (Cr). Therefore, 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.

[0034] In one embodiment of the present invention, the olefin polymerization catalyst containing chromium may include, for example, chromium oxide and a support on which the chromium oxide is supported. The support may include, for example, at least one component from silica, titania, alumina, zirconia, and aluminum phosphate, but the present invention is not limited to these.

[0035] In one embodiment of the present invention, the chromium content 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 chromium content in the separation membrane substrate may be a value measured, for example, using inductively coupled plasma with mass spectrometer (ICP-MS). When the chromium content in the separation membrane substrate is within the range described above, 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 it, but the present invention is not limited thereto.

[0036] According to one embodiment of the present invention, the polyolefin resin produced using the chromium-containing olefin polymerization catalyst is characterized by containing a large amount of active terminal vinyl groups that can be crosslinked by a thermal initiator contained in the coating liquid in a subsequent step. As a result, the separation membrane substrate may contain a polyolefin resin in which numerous crosslinked structures between polyolefin chains are formed by a crosslinking reaction with a thermal initiator.

[0037] Furthermore, according to one embodiment of the present invention, the polyolefin resin produced using the chromium-containing olefin polymerization catalyst is characterized by containing a large amount of active terminal vinyl groups that provide positions for grafting vinyl group-containing phosphorus compounds contained in the coating liquid in a subsequent step. As a result, the separation membrane substrate may contain a polyolefin resin containing phosphorus-containing organic groups, to which numerous vinyl group-containing phosphorus compounds are grafted by the terminal vinyl groups.

[0038] In this specification, the term "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 for a separation membrane substrate are activated by an initiate reaction, thereby forming crosslinked structures within and / or between the chains of the polyolefin resin.

[0039] Specifically, in the crosslinked polyolefin resin, a vinyl group at one end of the polyolefin chain is activated by a thermal initiator to form a radical, and this radical undergoes a polymerization reaction with a radical formed in the polyolefin chain of another molecule and / or a radical formed at the other end of the polyolefin chain of the same molecule, resulting in C(Sp 2 )-C(Sp 2 ) May include a bonded cross-linked structure.

[0040] Furthermore, in one embodiment of the present invention, the "phosphorus-containing organic group grafted to a polyolefin chain" means a residue generated from the vinyl group-containing phosphorus compound when a vinyl group present in the chain of the polyolefin resin used as a raw material for a separation membrane substrate and a vinyl group present in the vinyl group-containing phosphorus compound are activated by an initiation reaction, and a new covalent bond is formed at the activated position.

[0041] In one embodiment of the present invention, the phosphorus-containing organic group represents an organic residue derived from the vinyl group-containing phosphorus compound, and the vinyl group-containing phosphorus compound may include a phosphate compound, a phosphonate compound, a phosphine compound, a phosphine compound, or a mixture of two or more of these.

[0042] Examples of the phosphate compounds include, but are not limited to, diphenyl vinyl phosphate, dimethyl vinyl phosphate, diethyl vinyl phosphate, ethenyl dihydrogen phosphate, isopropenyl dihydrogen phosphate, or mixtures of two or more of these.

[0043] Examples of the phosphonate compounds include, but are not limited to, dimethyl vinyl phosphonate, diethyl vinyl phosphonate, or mixtures of two or more of these.

[0044] The phosphinate compounds mentioned above may be known, but are not limited to them.

[0045] Examples of the phosphine-based compounds include, but are not limited to, diphenylvinyl phosphine oxide, diphenyl vinyl phosphine, or mixtures of two or more of these.

[0046] In one embodiment of the present invention, the crosslinked polyolefin resin may contain no terminal vinyl groups at all, or may contain a number of terminal vinyl groups that is less than the number of terminal vinyl groups present in the polyolefin resin before crosslinking.

[0047] In a similar embodiment, the crosslinked polyolefin resin contains C(Sp) contained in the polyolefin resin before crosslinking. 2 )-C(Sp 2 ) The number of C(Sp) increased by more than the number of bonds 2 )-C(Sp 2 ) May include bonds.

[0048] In one embodiment of the present invention, 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 carbon atoms, when the number of active groups is confirmed from the 1H-NMR spectrum results using a nuclear magnetic resonance spectrometer (Bruker, 500 NMR, 14.1 telsa). The upper limit of the terminal vinyl groups may be 1,500 or less or 1,000 or less within the range described above, but is not limited thereto.

[0049] Accordingly, in one embodiment of the present invention, the number of terminal vinyl groups in 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 carbon atoms.

[0050] In yet another embodiment of the present invention, when the separation membrane substrate also contains a polyolefin resin produced using a catalyst other than a chromium-containing olefin polymerization catalyst, it is desirable that the number of terminal vinyl groups of the polyolefin resin before crosslinking and the content of terminal vinyl groups of the polyolefin resin before crosslinking be measured based on the number of terminal vinyl groups and the content of terminal vinyl groups of the total polyolefin resin.

[0051] As described above, the cross-linked structure in the cross-linked polyolefin resin includes a structure derived from the result of a radical polymerization reaction between vinyl groups mediated by a thermal initiator.

[0052] In one embodiment of the present invention, the thermal initiator can be used without limitation as long as it is an initiator capable of activating vinyl groups present in the polyolefin chain to form radicals. Specifically, any initiator capable of activating 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.

[0053] 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 of these.

[0054] The persulfate-based compound has peroxymonosulfate ion (SO5 2- ) and peroxydisulfate (S2O8 2-The compound is not particularly limited as long as it contains at least one of the following. Examples of the persulfate compound include, but is 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 of these.

[0055] The azo compound may include, but is not limited to, 2,2'-azobis(2-methylpropionitrile; AIBN).

[0056] In one embodiment of the present invention, the separation membrane substrate may further include a polyolefin resin produced from another type of olefin polymerization catalyst, in addition to the polyolefin resin produced from a chromium-containing olefin polymerization catalyst as described above.

[0057] The other types of olefin polymerization catalysts mentioned above may include, for example, olefin polymerization catalysts containing at least one of titanium (Ti), aluminum (Al), magnesium (Mg), zirconium (Zr), and vanadium (V). Thus, the separation membrane substrate may further contain, for example, at least one of titanium (Ti), aluminum (Al), magnesium (Mg), zirconium (Zr), and vanadium (V).

[0058] In one embodiment of the present invention, the other type of olefin polymerization catalyst is, for example, a metallocene catalyst. The present invention may use a Ziegler-Natta catalyst or a mixture thereof, but is not limited thereto.

[0059] In this specification, polyolefin resins produced using the chromium-containing olefin polymerization catalyst may be referred to as "Cr-type polyolefins," and polyolefin resins produced using other types of olefin polymerization catalysts may be referred to as "ZT-type polyolefins."

[0060] In one embodiment of the present invention, if the separation membrane substrate includes a polyolefin resin produced using another type of olefin polymerization catalyst in addition to a polyolefin resin produced using a chromium-containing olefin polymerization catalyst, the weight ratio of the Cr-type polyolefin to the ZT-type polyolefin may 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 Cr-type polyolefin and ZT-type polyolefin, an advantageous effect can be obtained in that the molecular weight of the separation membrane substrate can be improved by the ZT-type polyolefin, which has a higher molecular weight, but the present invention is not limited thereto.

[0061] In one embodiment of the present invention, the separation membrane substrate may further contain, in addition to polyolefin, at least one of the following polymer resins: polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene. The separation membrane substrate may also be a nonwoven fabric, a porous polymer film, or a laminate of two or more of these, but is not particularly limited thereto.

[0062] In one embodiment of the present invention, as described later, the separation membrane substrate includes a polyolefin resin produced using a chromium-containing olefin polymerization catalyst, and when a polyolefin sheet derived from the polyolefin resin is heat-fixed during the manufacturing process of the separation membrane substrate, a crosslinking structure is formed in and / or between the chains of the polyolefin resin by a radical polymerization reaction mediated by the thermal initiator. This not only improves the uniformity of thickness and heat resistance of the separation membrane substrate but also improves the appearance characteristics of the separation membrane substrate. Furthermore, when a polyolefin sheet derived from the polyolefin resin is heat-fixed, the grafting of the vinyl group-containing phosphorus compound can improve the flame retardancy of the separation membrane substrate, but the mechanism of the present invention is not limited to this.

[0063] One aspect of the present invention is a separation membrane substrate exhibiting a gel fraction of 3% to 80%. This may be a characteristic that arises from the separation membrane substrate containing a polyolefin resin with a high degree of crosslinking, but the characteristics of the present invention are not limited thereto. The gel fraction of the separation membrane substrate may 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%.

[0064] As described above, one characteristic of the polyolefin resin is that it exhibits a high degree of crosslinking due to the crosslinking structure formed in and / or between the polyolefin chains. As a result, while the polyolefin resin before crosslinking dissolves in a benzene-based solvent, the crosslinked polyolefin resin does not dissolve in a benzene-based solvent and may exhibit the characteristic of being able to measure its gel fraction.

[0065] In this specification, the gel fraction can be measured by the following method. First, 0.2 g of a sample of the separation membrane substrate to be measured is placed in a 120-mesh stainless steel mesh and extracted in trichlorobenzene at 100°C for 12 hours, followed by drying in a vacuum oven at 100°C for 12 hours. Then, the weight of the sample remaining on the stainless steel mesh is measured, and the gel fraction is measured by the following formula. The gel fraction may represent the average value of measurements for three samples to improve the accuracy of the measurement. Gel fraction (%) = {(Weight of remaining sample (g) / 0.2g)} × 100 The separation membrane substrate of the present invention has a standard deviation Δd of thickness measured at at least 100 arbitrary points of 0.5 μm or less. As a result, the separation membrane substrate can achieve high thickness uniformity.

[0066] In one embodiment of the present invention, the standard deviation Δd of the thickness measured at at least 100 arbitrary points on the separation membrane substrate may 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. As the thickness uniformity increases as the standard deviation approaches 0, the lower limit of the standard deviation of the thickness may be 0.

[0067] The thickness of the separation membrane substrate can be measured by a method for measuring the thickness of the separation membrane substrate, and may be, for example, by analysis of an SEM image of the manufactured separation membrane substrate, or by a value measured with a known thickness measuring instrument. The thickness measuring instrument may be, for example, the VL-50S-B (Mitutoyo Corporation), but is not limited thereto.

[0068] Normally, when manufacturing separation membrane substrates, if polymer resins, interpreting agents, crosslinking agents, and other additives are added to the extruder all at once as raw materials and reacted, problems are observed where side reactions occur in the extruder, or where unmelted raw materials due to insufficient mixing between the raw materials cause spots on the surface of the separation membrane substrate that have a difference in brightness compared to the surrounding area.

[0069] In this specification, the term "spot" refers to an area on the surface of the separation membrane substrate having a white spot that is brighter and less transparent than the surrounding area.

[0070] In one embodiment of the present invention, the number of spots can be evaluated by visual observation or microscopic observation such as SEM.

[0071] In one embodiment of the present invention, the number of spots with a long side length of 50 μm or more can be determined by observing and evaluating the separation membrane substrate to be observed after it has been placed on an observation plate equipped with a backlight.

[0072] According to one embodiment of the present invention, the separation membrane substrate is formed from a polyolefin resin as a raw material, and after being formed into a polyolefin sheet, a thermal initiator and a phosphorus compound containing vinyl groups are added, thereby reducing the amount of spots that appear as described above and improving the appearance of defects. For example, the separation membrane substrate is 1 m 2 The number of spots with a longest side length of 50 μm or more may be 10 or less. Specifically, within the above conditions, the number of spots may be 0 to 7, 0 to 5, or 0 to 3. Forming the number of spots within the aforementioned range provides advantageous effects in terms of preventing uncoated areas due to appearance defects and preventing short circuits within the battery during subsequent ceramic coating.

[0073] In other embodiments of the present invention, the thickness of the separation membrane substrate may be, for example, 4 to 20 μm. While a thickness of the separation membrane substrate within the aforementioned range may provide advantageous effects in terms of conductive barrier function and the resistance of the separation membrane, the present invention is not limited thereto.

[0074] In one embodiment of the present invention, the weight-average molecular weight (Mw) of the polyolefin resin contained in the separation membrane substrate may be in the range of, for example, 100,000 to 5,000,000. While having the weight-average molecular weight of the polyolefin resin within the aforementioned range can provide advantageous effects in terms of ensuring the mechanical properties of the separation membrane substrate and the shutdown characteristics, the present invention is not limited thereto.

[0075] In this specification, the weight-average molecular weight (Mw) of the polyolefin resin may be measured by gel permeation chromatography (GPC; PL GPC220, Agilent Technologies) under the following conditions: - Column: PL Olexis (Polymer Laboratories) - Solvent: TCB (Trichlorobenzene) -Flow rate: 1.0ml / min -Sample concentration: 1.0 mg / ml -Injection volume: 200μl - Column temperature: 160℃ -Detector:Agilent High Temperature RI detector -Standard: Polystyrene (corrected to a cubic 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%. While having the pore diameter and porosity in the separation membrane substrate within the aforementioned range may provide advantageous effects in terms of the ion permeability and mechanical strength of the separation membrane, 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 break temperature of 155°C or higher. For example, the break 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 even 200°C or higher. Since a higher break temperature of the separation membrane substrate indicates superior heat resistance, the upper limit of the break 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 fracture temperature of the separation membrane substrate may be measured using a thermomechanical analysis (TMA) apparatus, by applying a load of 0.01 N to a specimen of the separation membrane substrate to be measured, observing the degree of deformation while raising the temperature at a rate of 5 °C / min, and determining the temperature at which the separation membrane substrate shrinks, then stretches, and breaks as the temperature rises.

[0079] In one embodiment of the present invention, the separation membrane substrate may have improved flame retardancy by containing a phosphorus-containing organic group grafted to the polyolefin chain, as described above.

[0080] In one embodiment of the present invention, the limited oxygen index (LOI) of the separation membrane may be, for example, 15 to 35, specifically 20 to 30. The separation membrane substrate according to one embodiment of the present invention can exhibit a high limited oxygen index by having the structure described above, which can provide advantageous effects in terms of improving battery stability.

[0081] In this specification, the term "critical oxygen index" is an index used to evaluate the flammability and flame retardancy of polymer materials, and is a term known in the art, meaning the minimum amount of oxygen required for any material to sustain combustion. The critical oxygen index can be evaluated, for example, by the ASTM D 2863 test method.

[0082] The separation membrane substrate for electrochemical elements according to one aspect of the present invention, as described above, is manufactured using a chromium-containing olefin polymerization catalyst, and when a polyolefin sheet stretched from the polyolefin resin is heat-fixed, a cross-linked structure is formed between polyolefin chains by using a thermal initiator and a phosphorus-based compound containing vinyl groups, and a grafted phosphorus-containing organic group is included, thereby improving appearance characteristics, thickness uniformity, heat resistance, and flame retardancy. However, the present invention is not limited thereto.

[0083] Next, a method for producing a separation membrane substrate for electrochemical elements according to another aspect of the present invention will be described.

[0084] A method for producing a separation membrane substrate for an electrochemical element according to another aspect of the present invention includes the steps of: obtaining a polymer molten extruded by melting and extruding a raw material containing a polyolefin resin; obtaining a polymer sheet by molding and stretching the obtained polymer molten extruded material; applying a coating liquid containing a thermal initiator and a phosphorus-based compound containing vinyl groups to the polymer sheet; and drying and heat-fixing the polymer sheet to which the coating liquid has been applied. In this case, the polyolefin resin includes a polyolefin resin produced using an olefin polymerization catalyst containing chromium.

[0085] First, a polymer melt extruder is obtained by melt extruding a raw material containing a polyolefin resin produced using the chromium-containing olefin polymerization catalyst.

[0086] In one embodiment of the present invention, for the melt extrusion, it is desirable that the raw material includes not only a polyolefin resin produced using the chromium-containing olefin polymerization catalyst, but also a diluent.

[0087] The diluent may be, for example, a liquid or solid paraffin oil, mineral oil, wax, or soybean oil, which are commonly used in the manufacture of wet separation membranes.

[0088] In one embodiment of the present invention, the diluent can also be a diluent that can separate the liquid-liquid phase from the polyolefin resin, such as phthalic acid esters such as dibutyl phthalate, dihexyl phthalate, and dioctyl phthalate; diphenyl ether and benzyl ether. Aromatic ethers such as ether; fatty acids with 10 to 20 carbon atoms such as palmitic acid, stearic acid, oleic acid, linoleic acid, and linolenic acid; fatty acid alcohols with 10 to 20 carbon atoms such as palmitic acid alcohol, stearic acid alcohol, and oleic acid alcohol; fatty acid esters in which one or more saturated and unsaturated fatty acids with 4 to 26 carbon atoms in the fatty acid group, or in which the double bond of an unsaturated fatty acid is replaced by epoxy, are esterified with an alcohol having 1 to 8 hydroxyl groups and 1 to 10 carbon atoms, such as palmitic acid mono-, di-, or triesters, stearic acid mono-, di-, or triesters, oleic acid mono-, di-, or triesters; or mixtures of two or more of these may be used, but are not limited to these.

[0089] In one embodiment of the present invention, the content of the diluent may be, for example, 100 to 350 parts by weight, 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 above numerical range, it is possible to prevent problems such as a decrease in porosity due to a high polyolefin content, resulting in smaller pore size, reduced interconnection between pores and a significant decrease in permeability, and increased viscosity of the polyolefin composition leading to increased extrusion load and difficulty in processing. Furthermore, when the polyolefin content is low, the kneadability between the polyolefin and the diluent decreases, preventing problems such as breakage and variations in thickness during stretching that occur when the polyolefin is not thermodynamically kneaded with the diluent and is extruded in a gel-like state. However, the present invention is not limited thereto.

[0090] In one embodiment of the present invention, the raw material may further include, in addition to a polyolefin resin and diluent produced using a chromium-containing olefin polymerization catalyst, a polyolefin resin and other polymer resin produced using another type of olefin polymerization catalyst, such as a Ziegler-Natta catalyst; or an olefin polymerization catalyst containing titanium (Ti), aluminum (Al), magnesium (Mg), zirconium (Zr), vanadium (V), or two or more of these; and the above-mentioned polyolefin resins and other polymer resins shall be used as referenced.

[0091] For example, in one embodiment of the present invention, the raw material may further include a polyolefin resin produced by an olefin polymerization reaction using a Ziegler-Natta catalyst.

[0092] According to one embodiment of the present invention, the weight ratio of polyolefin resin produced using a chromium-containing olefin polymerization catalyst (Cr-type polyolefin) and polyolefin resin produced using another type of olefin polymerization catalyst (ZT-type polyolefin) among the raw materials may be 1:9 to 9:1, specifically 2:8 to 8:2, 3:7 to 7:3, or 5:5, but the present invention is not limited thereto.

[0093] In another embodiment of the present invention, if a ZT-type polyolefin is further included in addition to the Cr-type polyolefin, the content of the polyolefin resin produced using the chromium-containing olefin polymerization catalyst may be, for example, 10% by weight or more, based on 100% by weight of the total raw materials. Specifically, the content of the polyolefin resin produced using the chromium-containing olefin polymerization catalyst 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.

[0094] In one embodiment of the present invention, the step of obtaining the polymer molten extruder may be performed using a conventional single-screw extruder or a twin-screw extruder, but is not limited thereto.

[0095] Next, the obtained polymer melt extruded material is molded and stretched to obtain a polymer sheet.

[0096] In one embodiment of the present invention, after extrusion of the polymer molten extruder, a cooled extruder can be formed using a conventional casting method or calendering method using methods such as water cooling or air cooling.

[0097] In one embodiment of the present invention, a separation membrane substrate having improved mechanical strength and perforation strength can be provided by going through the molding and stretching steps.

[0098] In one embodiment of the present invention, the stretching can be performed by sequential or simultaneous stretching using a roll method or a tender method. The stretching ratio may be, for example, 3 times or more or 5 to 12 times in the longitudinal direction or in the transverse direction, and the total stretching ratio may be 20 to 120 times. When the stretching ratio satisfies the above numerical range, advantageous effects can be obtained in terms of thickness uniformity and balance of physical properties between the longitudinal and transverse directions of the manufactured separation film substrate, but the present invention is not limited thereto.

[0099] 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.

[0100] Subsequently, a diluent is extracted from the stretched polymer sheet to obtain a porous polymer sheet.

[0101] In one embodiment of the present invention, a porous sheet can be formed by extracting the diluent from the stretched sheet using an organic solvent with high solubility for the diluent and then drying it.

[0102] The aforementioned organic solvent is not particularly limited as long as it can extract the diluent used, but methyl ethyl ketone, methylene chloride, hexane, etc. may be used in terms of extraction efficiency and drying rate.

[0103] In one embodiment of the present invention, the extraction method may be any of the conventional solvent extraction methods, such as immersion, solvent spray, or ultrasonic methods, either individually or in combination. In one embodiment of the present invention, the content of residual diluent after the extraction treatment may preferably be 1% by weight or less. When the content of residual diluent is within the aforementioned range, advantageous effects may be obtained in terms of the permeability and mechanical properties of the separation membrane substrate produced and the efficiency of the manufacturing process, but the present invention is not limited thereto.

[0104] The extraction time and extraction temperature may vary depending on the thickness of the polymer sheet and the type of polymer, but the present invention is not limited thereto.

[0105] Next, a coating solution containing a thermal initiator and a phosphorus-based compound containing vinyl groups is applied to the polymer sheet.

[0106] A coating solution containing a thermal initiator and a phosphorus-based compound containing vinyl groups is applied to a polymer porous sheet with pre-exposed pores according to the present invention. As described above, the thermal initiator can activate terminal vinyl groups in the polyolefin resin chain to form radicals. This not only forms a large amount of crosslinked structures in the polyolefin chain by the thermal initiator, but also allows the coating solution to penetrate to fibrils present on the surface of already formed pores, which can have a significant effect in improving the heat resistance of the separation membrane substrate, although the present invention is not limited thereto. Furthermore, the phosphorus-based compound containing vinyl groups can covalently graft bond to the activated terminal vinyl groups in the polyolefin resin chain through the activated vinyl groups in the molecule. This can have a significant effect in improving the flame retardancy of the separation membrane substrate due to the phosphorus-containing organic groups it contains, but the present invention is not limited thereto.

[0107] In one embodiment of the present invention, the thermal initiator and the vinyl group-containing phosphorus compound in the coating liquid may be present in a weight ratio of, for example, 2:8 to 8:2, specifically 3:7 to 7:3 or 4:6 to 6:4. When the weight ratio of the thermal initiator and the vinyl group-containing phosphorus compound is within the aforementioned range, the vinyl groups in the chain of the polyolefin resin can be sufficiently activated to induce crosslinking and grafting reactions, which can have advantageous effects in terms of improving the heat resistance 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 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 phosphorus compound. Furthermore, while it is desirable for the total solid content in the coating solution to be, for example, 5% to 60% by weight, specifically 7% to 40% by weight, in terms of radical activation of the double bond and improvement of the heat resistance of the separation membrane substrate, the present invention is not limited thereto.

[0109] In one embodiment of the present invention, the coating liquid may further contain, if necessary, conventional additives for improving specific functions, such as oxidation stabilizers, UV stabilizers, antistatic agents, and nucleating agents, but the present invention is not limited thereto.

[0110] Subsequently, the polymer sheet coated with the coating liquid is dried and heat-fixed to obtain a separation membrane substrate.

[0111] The purpose of performing the aforementioned thermal fixation is to fix the porous film and apply heat to forcibly fix the porous film, which would otherwise shrink, and to remove residual stress.

[0112] According to the method for producing a separation membrane substrate of the present invention, a coating liquid containing the thermal initiator and a phosphorus-based compound containing vinyl groups is applied before heat fixation. During heat fixation, a large amount of crosslinked structures are formed in and / or between polyolefin chains by a radical polymerization reaction mediated by the thermal initiator, and a separation membrane substrate made of polyolefin resin is obtained in which a large amount of phosphorus-containing organic groups are grafted onto the ends of the polyolefin chains.

[0113] In one embodiment of the present invention, the heat-fixing temperature and time vary depending on the vinyl group content in the polyolefin chain and the composition of the coating liquid, and the present invention is not particularly limited.

[0114] In yet another aspect of the present invention, a separation membrane for an electrochemical element is provided, comprising 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 comprises inorganic particles and a binder material.

[0115] The inorganic coating layer may have a porous structure due to pores caused by interstitial volumes between inorganic particles. The size and distribution of the pores can be adjusted to control the size and degree of porosity (percentage of pore volume). This structure enhances the safety of the electrochemical element by increasing resistance to metallic foreign matter present on the electrodes and suppressing shrinkage of the polyolefin separation membrane, which is the base material. In this respect, the inorganic coating layer may contain inorganic particles at a ratio of 70 to 99.5% by weight, preferably 80 to 99% by weight, per 100% by weight of the inorganic coating layer.

[0116] 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 they do not undergo oxidation and / or reduction reactions within the operating voltage range of the electrochemical element to which they are applied (e.g., 0 to 5V with respect to Li / Li+). In particular, when inorganic particles with a high dielectric constant are used as inorganic particles, it is possible to improve the ionic conductivity of the electrolyte by contributing to an increase in the degree of dissociation of the electrolyte salt in the liquid electrolyte, such as a lithium salt.

[0117] For the reasons mentioned 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-restrictive examples of inorganic particles with 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 Examples include 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, and may contain one or more of these.

[0118] In one embodiment of the present invention, the average particle size D of the inorganic particles 50 While not particularly limited, it is desirable that the thickness be in the range of 0.1 μm to 2.5 μm for the formation of an inorganic coating layer of uniform thickness and appropriate porosity.

[0119] In one embodiment of the present invention, the binder material may include an acrylic polymer and / or a PVDF polymer. The acrylic polymer may, for example, include a (meth)acrylic polymer. The (meth)acrylic polymer contains a (meth)acrylic acid ester as a monomer, and examples of such monomers include 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-oxyl (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 homopolymers of vinylidene fluoride (i.e., polyvinylidene fluoride), copolymers of vinylidene fluoride with copolymerizable monomers, and mixtures thereof. In one embodiment of the present invention, the monomer may be, for example, a fluorinated monomer and / or a chlorine monomer. 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 one or more of these may be included.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-chlorofluoroethylene (PVDF-CTFE), polyvinylidene fluoride-tetrafluoroethylene (PVdF-TFE), and polyvinylidene fluoride-trifluoroethylene (PVdF-TrFE).

[0120] In one embodiment of the present invention, the separation membrane may be manufactured by coating the separation membrane substrate with the inorganic coating layer described above.

[0121] First, the binder material is dispersed in a solvent, or a binder solution is prepared in a dissolved form. Next, inorganic particles dispersed in a bead mill form are added to the binder solution to prepare a slurry for forming an inorganic coating layer. Non-limiting examples of the solvent include one or more selected from the group consisting of water, acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (NMP), and cyclohexane.

[0122] The method for coating the substrate with the slurry separation membrane can be any conventional coating method known in the industry. For example, various methods such as dip coating, die coating, roll coating, comma coating, or a mixture thereof can be used. Furthermore, the drying can be any conventional drying method, such as natural drying or forced-air drying, without any particular limitations.

[0123] An electrode assembly according to yet another aspect of the present invention includes a positive electrode, a negative electrode, and a separation membrane interposed between the positive electrode and the negative electrode, wherein the aforementioned separation membrane is used.

[0124] In this specification, the specific configurations of the positive electrode, negative electrode, and electrode assembly may be those of ordinary components, so a detailed explanation of these will be omitted.

[0125] In yet another aspect of the present invention, a secondary battery can be provided by placing the electrode assembly prepared as described above into a suitable case and injecting an electrolyte.

[0126] The present invention will be described in more detail below with reference to examples, but these examples are for illustrative purposes only and do not limit the scope of the present invention.

[0127] [Manufacturing of separation membrane substrates] Example 1 A polyolefin molten extruder was obtained by melt-extruding 9 kg / hr of Cr-type polyolefin (DL Chemical, TR570) and 21 kg / hr of diluent (Kukdong Oil & Chemicals Co., Ltd., LP350F) as raw materials into an extruder (Korean EM, φ32 twin-screw extruder L / D=56) at 200°C.

[0128] The obtained molten polyolefin extruded material was passed through a T-die and then formed into a sheet using a cooling cast apparatus. Subsequently, polyolefin sheets were obtained by biaxial stretching in a tender-type sequential stretcher using MD stretching followed by TD stretching. The MD stretching ratio and TD stretching ratio were set to 7x and 6x, respectively, and the stretching temperatures were MD 115°C and TD 125°C.

[0129] A porous polyolefin sheet was obtained by extracting a diluent from the stretched polyolefin sheet using methylene chloride.

[0130] Next, a coating solution containing 10 wt% dicumyl peroxide in ethanol as a thermal initiator and 15 wt% diphenyl (vinyl) phosphine oxide as a vinyl group-containing phosphorus compound (flame retardant) was applied to one surface of the porous polyolefin sheet.

[0131] Subsequently, the polyolefin sheet coated with the coating liquid was dried and heat-fixed at 128°C to produce a separation membrane substrate. The thickness of the resulting separation membrane substrate was 9.0 μm.

[0132] Example 2 A separation membrane substrate was prepared in the same manner as in Example 1, except that vinylphosphonic acid was used as the vinyl group-containing phosphorus compound (flame retardant). In this case, the thickness of the obtained separation membrane substrate was 9.0 μm.

[0133] Example 3 A separation membrane substrate was prepared in the same manner as in Example 1, except that dimethyl vinyl phosphonate was used as the vinyl group-containing phosphorus compound (flame retardant). In this case, the thickness of the obtained separation membrane substrate was 9.0 μm.

[0134] Example 4 The separation membrane substrate was manufactured in the same manner as in Example 1, except that 0.9 kg of Cr-type polyolefin and 8.1 kg / hr of ZT-type polyolefin (Korea Petrochemical Ind. Co., LTD, VH350) were used as raw materials (weight ratio of Cr-type to ZT-type = 1:9). In this case, the thickness of the obtained separation membrane substrate was 9.0 μm.

[0135] Example 5 The separation membrane substrate was manufactured in the same manner as in Example 4, except that vinylphosphoic acid was used as the vinyl group-containing phosphorus compound (flame retardant). In this case, the thickness of the obtained separation membrane substrate was 9.0 μm.

[0136] Example 6 The separation membrane substrate was prepared in the same manner as in Example 4, except that dimethyl vinyl phosphonate was used as the vinyl group-containing phosphorus compound (flame retardant). In this case, the thickness of the obtained separation membrane substrate was 9.0 μm.

[0137] Comparative Example 1 As a raw material, ZT-type polyolefins were used instead of Cr-type polyolefins (Korea Petrochemical Ind. Co., LTD A separation membrane substrate was prepared in the same manner as in Example 2, except that VH035 was used. The thickness of the obtained separation membrane substrate was 9.1 μm.

[0138] Comparative Example 2 The release film substrate was manufactured in the same manner as in Example 2, except that the coating solution application step was omitted. In this case, the thickness of the resulting release film substrate was 9.0 μm.

[0139] Comparative Example 3 A separation membrane substrate was manufactured in the same manner as in Example 1, except that the coating solution did not contain a phosphorus-based compound (flame retardant) containing a vinyl group. In this case, the thickness of the obtained separation membrane substrate was 9.0 μm.

[0140] Comparative Example 4 The separation membrane substrate was manufactured in the same manner as in Example 2, except that 0.45 kg of Cr-type polyolefin and 8.55 kg of ZT-type polyolefin (Korea Petrochemical Ind. Co., LTD, VH350) were used as raw materials (weight ratio of Cr-type to ZT-type = 0.5:9.5). In this case, the thickness of the obtained separation membrane substrate was 9.0 μm.

[0141] Comparative Example 5 A separation membrane substrate was manufactured in the same manner as in Example 1, except that the process of applying the coating liquid to one side of the porous polyolefin sheet was omitted, and the same amount of dicumyl peroxide (thermal initiator) and the same amount of diphenyl(vinyl)phosphine oxide (a phosphorus compound containing vinyl groups, a flame retardant) used in the coating liquid were added to the extruder together with the Cr-type polyolefin and diluent at the raw material mixing stage.

[0142] In this case, the crosslinking reaction between the thermal initiator and the Cr-type polyolefin in the extruder prevented the production of a polyolefin sheet during the stretching process, resulting in breakage and the inability to obtain a separation membrane substrate.

[0143] [Component analysis and physical property evaluation of separation membrane substrates] The components of the manufactured Examples 1-6 and Comparative Examples 1-4 were analyzed as follows to evaluate their physical properties, and the results are shown in Table 1 below.

[0144] As mentioned above, in Comparative Example 5, the separation membrane substrate could not be manufactured due to breakage during the stretching process, and therefore the following physical property evaluations were not performed.

[0145] Measurement of gel fraction First, 0.2 g of the separation membrane substrate sample 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.

[0146] Subsequently, the weight of the specimens remaining on the stainless steel mesh was measured, and the gel fraction was determined using the following formula. The gel fraction is shown as the average value of the measurements for each of three specimens: Gel fraction (%) = {(Weight of remaining sample (g)) / 0.2g} × 100 Measurement of chromium (Cr) content First, a sample of the separation membrane substrate was reacted with sulfuric acid and sulfated on a hot plate, after which the sulfuric acid was removed. Then, it was ashed in an electric furnace (temperature: 600°C) for 4 hours, and subsequently decomposed with nitric acid and hydrogen peroxide. After the sample dissolved and became transparent, it was tertiarily diluted with ultrapure water to prepare the analytical sample.

[0147] The chromium (Cr) content in the separation membrane substrate was measured using an inductively coupled plasma mass spectrometer (ICP-MS) (Axiom MC model, Thermo Elemental Ltd, UK).

[0148] Measurement of aluminum (Al) content When using the Ziegler-Natta catalyst, aluminum (Al) becomes present on the separation membrane substrate, so the aluminum content was measured.

[0149] The aluminum content was measured using the same method as the chromium content.

[0150] Breaking temperature The rupture temperature of the separation membrane substrate manufactured as described above was analyzed using a thermal mechanical analysis (TMA) analyzer (TA Instruments, TMA Q400).

[0151] Specifically, a load of 0.01 N was applied to the separation membrane substrate, and the degree of deformation was observed while the temperature was increased at a rate of 5°C / min. As the temperature rose, the temperature at which the separation membrane substrate contracted, then stretched further, and broke was measured as the "breaking temperature".

[0152] Measurement of the number of spots A separation membrane substrate is placed on an observation plate equipped with a backlight, and the separation membrane substrate is 1 m². 2The number of spots with a longest side length of 50 μm or more was visually confirmed and then measured.

[0153] Measurement of thickness uniformity The thickness of the separation membrane substrate was measured at 10 cm intervals over a distance of 1 m in the width direction and at 3 m intervals over a distance of 30 m in the length direction. The standard deviation of the thickness was determined from the thickness measurements taken at a total of 100 locations.

[0154] Flame retardancy evaluation (measurement of critical oxygen index) Flame retardancy was evaluated using the ASTM D 2863 test method for measuring the critical oxygen index.

[0155] [Table 1] According to the results in Table 1, the separation membrane substrates of Examples 1 to 6, which were manufactured using Cr-type polyolefin resin as a raw material and by applying a coating solution containing a thermal initiator and a vinyl group-containing phosphorus compound after resin extrusion, were confirmed to have a gel fraction in the range of 3% to 80%, a standard deviation of thickness Δd of 0.5 μm or less in all cases, and a rupture temperature of 160°C or higher.

[0156] On the other hand, the separation membrane substrate of Comparative Example 1, which used only ZT-type polyolefin resin, was found to be inferior in terms of gel fraction, rupture temperature, thickness deviation, and flame retardancy. Furthermore, in Comparative Example 2, which used Cr-type polyolefin resin but did not apply a coating solution containing a thermal initiator and a phosphorus-based compound containing vinyl groups, problems were still found in terms of gel fraction, rupture temperature, and flame retardancy. In addition, in Comparative Example 3, which contained only a thermal initiator in the composition of the coating solution and did not contain a phosphorus-based compound containing vinyl groups (flame retardant), the flame retardancy was undesirable. Even when manufactured by applying a coating solution containing a thermal initiator and a phosphorus-based compound containing vinyl groups, in Comparative Example 4, which used a small amount of Cr-type polyolefin resin as the polyolefin resin, problems were still found in terms of gel fraction, rupture temperature, and flame retardancy, and the thickness uniformity was also found to be inferior to a predetermined level compared to the examples.

[0157] As described above with reference to embodiments and drawings of the present invention, a person with ordinary skill in the art to which the present invention belongs can make various applications and modifications within the scope of the present invention based on the above description.

Claims

1. A separation membrane substrate for an electrochemical element, comprising a crosslinked polyolefin resin and chromium (Cr), The aforementioned Cr is included as a residue of the polyolefin resin polymerization catalyst. The aforementioned crosslinked polyolefin resin contains phosphorus-containing organic groups grafted to the polyolefin chain, The gel fraction of the separation membrane substrate is 3% to 80%. The standard deviation Δd of the thickness measured at at least 100 arbitrary locations is 0.5 μm or less. The number of spots with a long side length of 50 μm or more is 1 m ２ A separation membrane substrate for electrochemical elements, characterized by having 10 or fewer particles per unit.

2. The phosphorus-containing organic group is a residue derived from a phosphorus-based compound containing a vinyl group. The separation membrane substrate for an electrochemical element according to claim 1, characterized in that the vinyl group-containing phosphorus compound comprises a phosphate compound, a phosphonate compound, a phosphine compound, a phosphine compound, or a mixture of two or more thereof.

3. The separation membrane substrate for an electrochemical element according to claim 1, characterized in that the chromium content is 0.1 to 20 ppm.

4. The separation membrane substrate for an electrochemical element according to claim 1, characterized in that the gel fraction of the separation membrane substrate is 3% to 50%.

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

6. The separation membrane substrate for an electrochemical element according to claim 5, characterized in that the thermal initiator comprises a peroxide compound, a persulfate compound, an azo compound, or a mixture thereof.

7. The separation membrane substrate for the electrochemical element 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 element according to claim 1, characterized in that the standard deviation Δd of the thickness measured at at least 100 arbitrary points on the separation membrane substrate is 0.3 μm or less.

9. A step of obtaining a polymer melt extruded product by melt extruding a raw material containing polyolefin resin, The steps include: molding and stretching the obtained polymer molten extruded material to obtain a polymer sheet, The steps include applying a coating solution containing a thermal initiator and a phosphorus-based compound containing a vinyl group to the polymer sheet, The steps include drying and heat-fixing the polymer sheet to which the coating liquid has been applied, Includes, A method for producing a separation membrane substrate for an electrochemical element, characterized in that the polyolefin resin includes a polyolefin resin produced using an olefin polymerization catalyst containing chromium.

10. A method for producing a separation membrane substrate for an electrochemical element according to claim 9, characterized in that the polyolefin resin among the raw materials includes a polyolefin resin having 100 or more terminal vinyl groups per 1 million carbon atoms.

11. The method for producing a separation membrane substrate for an electrochemical element according to claim 9, characterized in that the raw material further comprises 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.

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

13. The 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 is characterized by containing inorganic particles and a binder material, and is a separation membrane for an electrochemical element.

14. An electrode assembly comprising 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 described in claim 13.

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