Separation membrane substrate for electrochemical element, method for producing the same, separation membrane including 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 manufacturing 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 October 27, 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 higher operating voltages and much higher energy densities than conventional batteries such as Ni-MH, Ni-Cd, and lead-sulfate batteries that use aqueous electrolytes. However, such lithium-ion batteries have disadvantages such as safety problems such as ignition and explosion associated with the use of organic electrolytes, and are not easy to manufacture. Recent lithium-ion polymer batteries have been cited as one of the next-generation batteries by improving such disadvantages of lithium-ion batteries, but the battery capacity 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, when the electrochemical device overheats and thermal runaway occurs, or when the separator membrane is penetrated, there is a high risk of explosion. In particular, polyolefin-based separator membrane substrates commonly used as separator membranes of electrochemical devices exhibit intense heat shrinkage behavior at temperatures of 100°C or higher due to the material characteristics and manufacturing process characteristics including stretching, and there is a problem of causing a short circuit between the positive electrode and the negative electrode.

[0006] To solve such safety problems of electrochemical devices, 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 demand for further enhancement of stability.

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, In 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 phosphorus-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] 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 phosphorus compound containing a vinyl group may include a phosphate compound, a phosphonate compound, a phosphinate compound, a phosphine oxide compound, or a mixture of two or more thereof.

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

[0012] In 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] In the fifth embodiment, in any one of the first to fourth embodiments, The cross-linked structure in the cross-linked polyolefin resin may include a structure derived from the result of 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 a peroxide-based compound, a persulfate-based compound, an azo-based compound, or a mixture thereof.

[0015] In 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 of titanium (Ti), aluminum (Al), magnesium (Mg), zirconium (Zr), and vanadium (V).

[0016] In 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] 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 9th embodiment is a step of obtaining a polymer melt extrudate by melt-extruding a raw material substance containing a polyolefin resin, a step of forming 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 thermally fixing the polymer sheet coated with the coating liquid, and the polyolefin resin includes a polyolefin resin produced using an olefin polymerization catalyst containing chromium.

[0019] In the 10th embodiment, in the 9th 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 11th embodiment, in the 9th embodiment or the 10th 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 12th embodiment, in any one of the 8th embodiment to the 11th embodiment, 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 embodiment is composed of the separation membrane substrate 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 substrate, and the inorganic coating layer contains inorganic particles and a binder material.

[0024] In still 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 composed of 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 separation membrane described in the 13th embodiment.

Advantages of the Invention

[0026] The separation membrane substrate according to an embodiment of the present invention has the effect of improving thickness uniformity and heat resistance by containing a large amount of crosslinked 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 substrate.

[0027] In particular, the separation membrane substrate 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 crosslinking between these terminal vinyl groups. The separation membrane substrate can have the effect of improving 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] Hereinafter, the present invention will be described in detail.

[0029] 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 can be charged and discharged, and is a concept including lithium ion batteries, nickel-cadmium batteries, nickel-metal hydride batteries, and the like.

[0030] First, the separation membrane substrate for an electrochemical element according to one aspect of the present invention will be described in detail.

[0031] 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 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.

[0032] According to an 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 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 of these, but is not limited thereto.

[0033] As shown in the method for manufacturing the separation membrane substrate described later in this specification, since the polyolefin resin includes a polyolefin resin produced using an olefin polymerization catalyst containing chromium (Cr), 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 supporting the chromium oxide. The support may include, for example, at least one or more components among silica, titania, alumina, zirconia, and aluminum phosphate, but the present invention is not limited thereto.

[0035] 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-mentioned 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.

[0036] 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.

[0037] Further, according to an embodiment of the present invention, the polyolefin resin produced using the olefin polymerization catalyst containing chromium contains a large amount of terminal vinyl groups in an active state that provide positions where vinyl group-containing phosphorus compounds contained in the coating liquid are grafted in subsequent processes. As a result, the separation membrane substrate may include a polyolefin resin containing a phosphorus-containing organic group grafted with a large number of vinyl group-containing phosphorus compounds by the terminal vinyl groups.

[0038] 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 substance of the separation membrane substrate are activated by an initiation reaction, and a crosslinked structure is formed within and / or between the chains of the polyolefin resin.

[0039] Specifically, in the crosslinked polyolefin resin, a vinyl group present at one end of the polyolefin chain is activated by a thermal initiator to form a radical, and the formed 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, thereby forming a C(Sp 2 )-C(Sp 2 )-bonded crosslinked structure.

[0040] Further, in an embodiment of the present invention, the "phosphorus-containing organic group grafted to the polyolefin chain" means a residue generated from the vinyl group-containing phosphorus compound by the activation of a vinyl group present in the chain of the polyolefin resin used as a raw material substance of the separation membrane substrate and a vinyl group present in the vinyl group-containing phosphorus compound by an initiation reaction, and the formation of a new covalent bond 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 phosphinate compound, a phosphine compound, or a mixture of two or more of these.

[0042] Examples of the phosphate compound include, but are not limited to, diphenyl vinylphosphate, dimethyl vinylphosphate, diethyl vinylphosphate, ethenyl dihydrogen phosphate, isopropenyl dihydrogen phosphate, or a mixture of two or more of these.

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

[0044] Known phosphinate compounds can be used, but are not limited thereto.

[0045] Examples of the phosphine compound include, but are not limited to, diphenylvinyl phosphine oxide, diphenyl vinyl phosphine, or a mixture of two or more of these.

[0046] In one embodiment of the present invention, the crosslinked polyolefin resin may contain no terminal vinyl groups or a reduced number of terminal vinyl groups compared to the number of terminal vinyl groups present in the polyolefin resin before crosslinking.

[0047] In a similar manner, the crosslinked polyolefin resin may contain an increased number of C(Sp 2 )-C(Sp 2 ) bonds compared to the number of C(Sp 2 )-C(Sp 2 ) bonds contained in the polyolefin resin before crosslinking.

[0048] In one embodiment of the present invention, when the number of functional groups is 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 aforementioned range, 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 carbons.

[0050] In still another embodiment of the present invention, when the separation membrane substrate contains both polyolefin resins produced using catalysts other than the chromium-containing olefin polymerization catalyst, it is desirable to measure the number and content of terminal vinyl groups in the polyolefin resin before crosslinking based on the number and content of terminal vinyl groups in 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 is not particularly limited as long as it is a compound containing at least one of peroxymonosulfate ion (SO 5 2- ) and peroxydisulfate (S 2 O 8 2- ) as an anion. Examples of the persulfate-based compound include, for example, sodium peroxymonosulfate (Na 2 SO 5 ), potassium peroxymonosulfate (KHSO 5) Sodium peroxydisulfate; Na 2 S 2 O 8 ) Ammonium peroxydisulfate; (NH 4 ) 2 S 2 O 8 ) Potassium peroxydisulfate; K 2 S 2 O 8 ) or a mixture of two or more thereof, but not limited thereto.

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

[0056] 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.

[0057] The other type of olefin polymerization catalyst may be, for example, an olefin polymerization catalyst containing at least one of titanium (Ti), aluminum (Al), magnesium (Mg), zirconium (Zr), and vanadium (V). Accordingly, 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 may be, for example, a metallocene catalyst, a Ziegler-Natta catalyst or a mixture thereof, but the present invention is not limited thereto.

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

[0060] In one embodiment of the present invention, when the separation membrane substrate contains a polyolefin resin produced using an olefin polymerization catalyst other than the 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 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 improved by the ZT-type polyolefin having a high 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 at least one of polymer resins such as polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene, in addition to polyolefin. Further, examples of the separation membrane substrate include non-woven fabric, porous polymer film, or a laminate of two or more of these, but the present invention is not particularly limited thereto.

[0062] In one embodiment of the present invention, as described below, the separation membrane substrate contains a polyolefin resin produced using an olefin polymerization catalyst containing chromium. When a polyolefin sheet derived from the polyolefin resin is thermally 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. This not only improves the thickness uniformity and heat resistance of the separation membrane substrate but also has the effect of improving the appearance characteristics of the separation membrane substrate. Further, when the polyolefin sheet derived from the polyolefin resin is thermally fixed, it is possible to achieve the effect of improving the flame retardancy of the separation membrane substrate by grafting the vinyl group-containing phosphorus-based compound, but the mechanism of the present invention is not limited thereto.

[0063] 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 having a high degree of crosslinking, 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%.

[0064] As described above, the polyolefin resin is characterized by exhibiting a high degree of crosslinking due to the crosslinked structure formed in the polyolefin chains and / or between the chains. As a result, 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 property of having its gel fraction measured.

[0065] 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 mesh, 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 mesh is measured, and the gel fraction is measured by the following formula. The gel fraction may indicate the average value of the measured values for three test pieces in order to improve the accuracy of the measured values. Gel fraction (%) = {(weight of remaining test piece (g) / 0.2 g} × 100 The separation membrane substrate according to one aspect of the present invention has 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 high thickness uniformity.

[0066] 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 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. Since the closer the standard deviation is to 0, the higher the thickness uniformity, 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 can indicate, for example, 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 use, for example, VL-50S-B (Mitutoyo), but is not limited thereto.

[0068] Usually, when manufacturing a separation membrane substrate, when a polymer resin, an interpretant, a crosslinking agent, and other additives are charged into an extruder as raw materials and reacted at once, side reactions occur in the extruder, or spots having a brightness difference compared to the peripheral part are generated on the surface of the separation membrane substrate due to insufficient kneadability between the raw materials.

[0069] In this specification, the "spot" refers to a region having a white spot with higher brightness and lower transparency than the peripheral part on the surface of the separation membrane substrate.

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

[0071] In one embodiment of the present invention, after placing the separation membrane substrate to be observed on an observation plate with a backlight attached, the number of spots having a long side length of 50 μm or more can be observed and evaluated.

[0072] According to one embodiment of the present invention, the separation membrane substrate is formed into a polyolefin sheet after polyolefin resin is introduced as a raw material substance, and then a thermal initiator and a vinyl group-containing phosphorus compound are introduced, whereby the generation amount of the above-mentioned spots is reduced and the appearance defect is improved. For example, the separation membrane substrate is 1 m 2 The number of spots having a long side length of 50 μm or more per meter can be 10 or less. Specifically, the number of spots can be 0 to 7, 0 to 5, or 0 to 3 within the above conditions. By forming the number of the spots within the above-mentioned range, it is advantageous in terms of preventing uncoating due to appearance defects and short circuit generation in the battery during subsequent ceramic coating.

[0073] In another embodiment of the present invention, the thickness of the separation membrane substrate can be, for example, 4 to 20 μm. When the thickness of the separation membrane substrate is within the above-mentioned range, it can 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.

[0074] In one embodiment of the present invention, the weight average molecular weight (Mw) of the polyolefin resin contained in the separation membrane substrate can 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-mentioned range, it can 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.

[0075] 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: - 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 by 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-mentioned 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 by using a thermal mechanical analysis (TMA) apparatus. A load of 0.01 N is applied to a test piece of the separation membrane substrate to be measured, and while raising the temperature at a rate of 5 °C / min, the degree of deformation is observed. As the temperature rises, it can be measured as the temperature at which the separation membrane substrate shrinks and then further stretches and breaks.

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

[0080] In one embodiment of the present invention, the limited oxygen index (LOI) of the separation membrane can 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 above-described structure, and thereby can have an advantageous effect in terms of improving the stability of the battery.

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

[0082] 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 phosphorus compound, and by including a grafted phosphorus-containing organic group, it can have the effect of improving appearance characteristics, thickness uniformity, heat resistance, and flame retardancy, but the present invention is not limited thereto.

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

[0084] A method for manufacturing a 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 phosphorus-based compound containing a vinyl group to the polymer sheet, and a step of drying and thermally 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.

[0085] 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.

[0086] 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.

[0087] As the diluent, for example, a liquid or solid paraffin oil, mineral oil, wax, soybean oil, etc. that are usually used in the production of wet separation membranes can be used.

[0088] 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, and dioctyl phthalate; aromatic ethers such as diphenyl ether and benzyl ether; fatty acids having 10 to 20 carbon atoms such as palmitic acid, stearic acid, oleic acid, linoleic acid, and linolenic acid; fatty acid alcohols having 10 to 20 carbon atoms such as palmitic acid alcohol, stearic acid alcohol, and 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, having 4 to 26 carbon atoms in the fatty acid group, such as mono-, di-, or triesters of palmitic acid, mono-, di-, or triesters of stearic acid, mono-, di-, or triesters of oleic acid, and mono-, di-, or triesters of linoleic acid; fatty acid esters in which an 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 the present invention is not limited thereto.

[0089] 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 above 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 is possible to prevent the problem that it becomes difficult to process due to the increase in the extrusion load caused by the increase in the viscosity of the polyolefin composition. Also, since the content of the polyolefin is small, it is possible to prevent problems such as breakage during stretching and thickness variation that occur when the polyolefin is extruded in a gel state without being thermodynamically kneaded with the diluent due to the decrease in the kneadability between the polyolefin and the diluent. However, the present invention is not limited thereto.

[0090] 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, such as 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 produced using these olefin polymerization catalysts and other polymer resins may be further included, and for these polyolefin resins and other polymer resins, the foregoing shall apply by reference.

[0091] 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.

[0092] 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 among the raw material substances to the polyolefin resin (ZT-type polyolefin) produced using other types of olefin polymerization catalysts 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] 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 material substances, 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 material substances, 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.

[0094] In one embodiment of the present invention, the step of obtaining the polymer melt extrudate may use, but is not limited to, an ordinary single-screw extruder or a twin-screw extruder.

[0095] Next, the obtained polymer melt extrudate is formed and stretched to obtain a polymer sheet.

[0096] In one embodiment of the present invention, after the extrusion of the polymer melt extrudate, a normal casting method or a calendering method may be used to form a cooled extrudate by 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 puncture strength can be provided by going through the forming and stretching steps.

[0098] In one embodiment of the present invention, the stretching can be performed by sequential or simultaneous stretching in a roll method or a tender method. The stretching ratio can be, for example, 3 times or more or 5 to 12 times in the longitudinal direction or the longitudinal direction respectively, 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 direction and the transverse direction, 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] Thereafter, the diluent is extracted from the stretched polymer sheet to obtain a porous polymer sheet.

[0101] In one embodiment of the present invention, the diluent can be extracted and dried from the stretched sheet by using an organic solvent highly soluble in the diluent to form a porous sheet.

[0102] 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 rate.

[0103] In one embodiment of the present invention, as the extraction method, all ordinary solvent extraction methods such as an immersion method, a solvent spray method, an ultrasonic method, etc. can be used individually or in combination. 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-described range, advantageous effects can be obtained 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.

[0104] 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.

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

[0106] A coating solution containing a thermal initiator and a vinyl group-containing phosphorus compound is applied to the polymer porous sheet with pores pre-exposed 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. Thereby, not only a large amount of crosslinked structures are formed in the polyolefin chain by the thermal initiator, but also the coating solution can penetrate into the fibrils present on the surface of the already formed pores, and significant effects can be obtained 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 phosphorus compound can be graft-bonded by a covalent bond to the site where the terminal vinyl groups in the chain of the polyolefin resin are activated through the activated vinyl groups in the molecule. Thereby, significant effects can be obtained in terms of improving the flame retardancy of the separation membrane substrate by the contained phosphorus-containing organic groups, 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 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 to the vinyl group-containing phosphorus compound is within the above-described range, the vinyl groups in the polyolefin resin chain can be sufficiently activated to induce crosslinking and graft reactions, and advantageous effects can be achieved in terms of improving the heat resistance of the separation membrane substrate. However, 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 thereof as a solvent for the thermal initiator and the vinyl group-containing phosphorus compound. Also, the total content of the solid components in the coating solution is, for example, 5 wt% to 60 wt%, specifically 7 wt% to 40 wt%, which is desirable in terms of radical activation of double bonds and improvement of the heat resistance of the separation membrane substrate. However, the present invention is not limited thereto.

[0109] In one embodiment of the present invention, the coating solution may further contain, as necessary, ordinary additives for improving specific functions, such as an oxidation stabilizer, a UV stabilizer, an antistatic agent, a nucleating agent, etc. However, the present invention is not limited thereto.

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

[0111] The heat fixation is carried out to fix the porous membrane, apply heat, and forcibly fix the porous membrane that tends to shrink to remove residual stress.

[0112] According to the method for manufacturing the separation membrane substrate of the present invention, by applying the coating liquid containing the thermal initiator and the phosphorus-based compound containing a vinyl group 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, and a separation membrane substrate of a polyolefin resin substrate with a large amount of phosphorus-containing organic groups grafted to the ends of the polyolefin chains is obtained.

[0113] 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 liquid, and the present invention is not particularly limited.

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

[0115] The inorganic coating layer may have a porous structure due to pores formed by the interstitial volume between the inorganic particles. The size and size distribution of the pore particles enable adjustment of the pore size and porosity (the ratio of the pore volume). Such a structure has the effect of enhancing the resistance to metallic foreign substances present in the electrode and strengthening the safety of the electrochemical element by suppressing the shrinkage of the polyolefin separation membrane as the substrate. 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.

[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 that can be used in the present invention are not particularly limited as long as oxidation and / or reduction reactions do not occur in 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 is possible to contribute to an increase in the dissociation degree of the electrolyte salt in the liquid electrolyte, for example, a lithium salt, and improve the ionic conductivity of the electrolyte solution.

[0117] 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 BaTiO 3 , Pb(Zr,Ti)O 3 (PZT), P 1-x La x Zr 1-y Ti y O 3 (PLZT, 0 < x < 1, 0 < y < 1), Pb(Mg 1 / 3 Nb 2 / 3 )O 3 -PbTiO 3 (PMN-PT), hafnia (HfO 2 ), SrTiO 3 , SnO 2 , CeO 2 , MgO, Mg(OH) 2 , NiO, CaO, ZnO, ZrO 2 , SiO 2 , Y 2 O 3 , Al 2 O 3 , AlOOH, Al(OH) 3 , SiC and TiO 2 etc., and may include one or more of these.

[0118] In one embodiment of the present invention, the average particle diameter D 50 of the inorganic particles is not particularly limited, but it is desirable to be 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.

[0119] In one embodiment of the present invention, the binder material may include an acrylic polymer and / or a PVDF-based 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, tetradecyl (meth)acrylate, and may include one or more of these. The PVdF-based 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 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-chlorotrifluoroethylene (PVDF-CTFE), polyvinylidene fluoride-tetrafluoroethylene (PVdF-TFE), and polyvinylidene fluoride-trifluoroethylene (PVdF-TrFE).

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

[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 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.

[0122] As the method for coating the slurry separation membrane on the substrate, ordinary coating methods known in the art can be used. For example, various methods such as dip coating, die coating, roll coating, comma coating, or a mixed method thereof can be used. Also, for the drying, ordinary drying methods such as natural drying and blow drying can be applied without particular limitation.

[0123] According to still another aspect of the present invention, an electrode assembly includes a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and in this case, the above-described separator is used.

[0124] In this specification, for the specific configurations of the positive electrode, negative electrode, and electrode assembly, ordinary materials may be used, and thus the description thereof is omitted.

[0125] In 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.

[0126] Hereinafter, the present invention will be described in more detail with reference to examples. However, the following examples are for illustrative purposes only, and the scope of the present invention is not limited thereto.

[0127] [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 fed 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.

[0128] 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 tender-type sequential stretching machine for TD stretching to obtain a polyolefin sheet. The MD stretching ratio and TD stretching ratio were each set to 7 times and 6 times, and the stretching temperatures were MD 115 °C and TD 125 °C.

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

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

[0131] 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 thickness of the obtained separation membrane substrate was 9.0 μm.

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

[0133] Example 3 A separation membrane substrate was produced in the same manner as in Example 1, except that dimethylvinylphosphonate was used as the vinyl group-containing phosphorus-based compound (flame retardant). At this time, the thickness of the obtained separation membrane substrate was 9.0 μm.

[0134] Example 4 A separation membrane substrate was produced 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) (weight ratio of Cr-type:ZT-type = 1:9) were used as raw materials. At this time, the thickness of the obtained separation membrane substrate was 9.0 μm.

[0135] Example 5 A separation membrane substrate was produced in the same manner as in Example 4, except that vinylphosphonic acid was used as the vinyl group-containing phosphorus-based compound (flame retardant). At this time, the thickness of the obtained separation membrane substrate was 9.0 μm.

[0136] Example 6 A separation membrane substrate was produced in the same manner as in Example 4, except that dimethylvinylphosphonate was used as the vinyl group-containing phosphorus compound (flame retardant). At this time, the thickness of the obtained separation membrane substrate was 9.0 μm.

[0137] Comparative Example 1 A separation membrane substrate was produced in the same manner as in Example 2, except that ZT type polyolefin (Korea Petrochemical Ind.Co.,LTD , VH035) was used. At this time, the thickness of the obtained separation membrane substrate was 9.1 μm.

[0138] Comparative Example 2 A separation membrane substrate was produced in the same manner as in Example 2, except that the coating liquid application step was not performed. At this time, the thickness of the obtained separation membrane substrate was 9.0 μm.

[0139] Comparative Example 3 A separation membrane substrate was produced in the same manner as in Example 1, except that the vinyl group-containing phosphorus compound (flame retardant) was not included in the coating liquid. At this time, the thickness of the obtained separation membrane substrate was 9.0 μm.

[0140] Comparative Example 4 A separation membrane substrate was produced 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 (weight ratio of Cr type:ZT type = 0.5:9.5). At this time, the thickness of the obtained separation membrane substrate was 9.0 μm.

[0141] Comparative Example 5 The separation membrane substrate was manufactured in the same manner as in Example 1, except that the same amount of dicumyl peroxide (thermal initiator) and the same amount of diphenyl(vinyl)phosphine oxide (vinyl group-containing phosphorus compound, flame retardant) used in the coating solution were put into an extruder together with Cr-type polyolefin and a diluent at the raw material mixing stage, without performing the process of applying the coating solution on one side of the porous polyolefin sheet.

[0142] At this time, due to the cross-linking reaction between the thermal initiator and the Cr-type polyolefin in the extruder, the polyolefin sheet was not manufactured during the stretching process and broke, and the separation membrane substrate could not be obtained.

[0143] [Component Analysis and Physical Property Evaluation of Separation Membrane Substrate] The components of Examples 1 to 6 and Comparative Examples 1 to 4 manufactured were analyzed and the physical properties were evaluated as follows, and the results are shown in Table 1 below.

[0144] As described above, in Comparative Example 5, since the separation membrane substrate could not be manufactured due to breakage in the stretching process, the following physical property evaluation was not performed.

[0145] Measurement of gel fraction First, 0.2 g of a test piece of the separation membrane substrate was put into 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] 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 three test pieces: Gel fraction (%) = {(weight of remaining test piece (g)) / 0.2 g} × 100 Measurement of chromium (Cr) content First, a specimen of the separation membrane substrate was reacted with sulfuric acid and sulfated 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. After the specimen was dissolved and became transparent, it was diluted three times with ultrapure water to prepare an analytical sample.

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

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

[0149] The method for measuring the aluminum content was carried out by the same method as the method for measuring the chromium content.

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

[0151] Specifically, a 0.01 N load 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 increased, the temperature at the time when the separation membrane substrate shrank and then stretched and broke was measured as the "breaking temperature".

[0152] 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 a length of the hitting long side of 50 μm or more was visually confirmed to measure the number of spots.

[0153] Measurement of thickness uniformity In the width direction of the separation membrane substrate, 1 m was measured at intervals of 10 cm, and in the longitudinal direction, 30 m was measured at intervals of 3 m. The standard deviation of the thickness was measured based on the thickness measurement values at a total of 100 positions.

[0154] Flammability evaluation (measurement of limiting oxygen index) The flame retardancy was evaluated by the measurement method of the limiting oxygen index using the ASTM D 2863 test method.

[0155]

Table 1

[0156] On the other hand, it was confirmed that the separation membrane substrate of Comparative Example 1 using only a ZT-type polyolefin resin was inferior in terms of gel fraction, breaking temperature, thickness deviation, and flame retardancy. Also, in the case of Comparative Example 2 where a Cr-type polyolefin resin was used but the coating solution containing a thermal initiator and a vinyl group-containing phosphorus compound was not applied, it was confirmed that there were still problems in terms of gel fraction, breaking temperature, and flame retardancy. Further, in the case of Comparative Example 3 where the coating solution composition contained only a thermal initiator and did not contain a vinyl group-containing phosphorus compound (flame retardant), the flame retardancy was not preferable. Even when produced by applying a coating solution containing a thermal initiator and a vinyl group-containing phosphorus compound, in the case of Comparative Example 4 where a trace amount of a Cr-type polyolefin resin was used as the polyolefin resin, there were still problems in terms of gel fraction, breaking temperature, and flame retardancy, and it was confirmed that the thickness uniformity was inferior to a predetermined level compared with the examples.

[0157] Although the embodiments of the present invention and the drawings have been described above, those having ordinary knowledge in the field to which the present invention pertains can 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 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, The number of spots with 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 with a long side length of 50 μm or more is 10 or less per 1 m

2. wherein the phosphorus-containing organic group is a residue derived from a vinyl group-containing phosphorus compound, the vinyl group-containing phosphorus compound contains a phosphate compound, a phosphonate compound, a phosphinate compound, a phosphine compound, or a mixture of two or more thereof, and 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 crosslinked structure in the crosslinked polyolefin resin contains a structure derived from the result of a radical polymerization reaction between vinyl groups mediated by a thermal initiator, and the separation membrane substrate for an electrochemical device according to claim 1.

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. A step of melt-extruding a raw material 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 solution containing a thermal initiator and a vinyl group-containing phosphorus compound to the polymer sheet, A step of drying and heat-fixing the polymer sheet coated with the coating liquid; including; The method for producing a separator base material for an electrochemical element, characterized in that the polyolefin resin includes a polyolefin resin produced using an olefin polymerization catalyst containing chromium.

10. The method for producing a separator base material for an electrochemical element according to claim 9, characterized in that the polyolefin resin among the raw material substances includes a polyolefin resin having 100 or more terminal vinyl groups per million carbon atoms.

11. The method for producing a separator base material for an electrochemical element according to claim 9, characterized in that the raw material substances 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.

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

13. Including the separator base material according to any one of claims 1 to 8 and an inorganic coating layer formed on at least one surface of the separator base material; The separator for an electrochemical element, characterized in that the inorganic coating layer includes inorganic particles and a binder material.

14. An electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, characterized in that the separator is the separator according to claim 13.

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