Photoinitiated copolymer resin, crosslinked structure-containing separation membrane for lithium secondary batteries, and method for producing the same

Abstract

The present invention relates to a novel photoinitiated copolymer resin capable of penetrating an olefin polymer under aqueous dispersion conditions and crosslinking a porous olefin polymer support, a crosslinked structure-containing separation membrane for lithium secondary batteries containing the photoinitiated copolymer resin, and a method for producing the same.

Description

Technical Field

[0001] This application claims priority based on Korean Patent Application No. 10-2023-0108620 filed on August 18, 2023. The present invention relates to a photoinitiator-type copolymer resin, a crosslinked structure-containing separator for a lithium secondary battery including the same, and a method for manufacturing the same.

Background Art

[0002] Recently, interest in energy storage technology has been increasing. As the application fields expand to include mobile phones, video cameras, notebook PCs, and even the energy of electric vehicles, the demand for higher energy density of batteries used as power sources for such electronic devices has been rising. Lithium secondary batteries are the batteries that best meet such demands, and currently, research on them is actively underway. [[ID=第十三条]]

[0003] Such a lithium secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator. Among these, the separator is required to have high ion conductivity to enhance the permeability of lithium ions based on its insulation property for separating the positive electrode and the negative electrode and electrically insulating them and high porosity.

[0004] Although olefin polymer separators are widely used as such separators, in the case of ethylene polymer (PE)-based separators, which are typical olefin polymer separators, since the melting point (Tm) is low, when the battery temperature rises above the melting point of the ethylene polymer in a battery misuse environment, a melt-down phenomenon may occur, leading to the risk of ignition and explosion. Due to its material properties and manufacturing process characteristics, the separator exhibits intense heat shrinkage behavior in situations such as high temperature, resulting in safety problems such as internal short circuits.

[0005] *

[0006] ​Korean Patent Publication No. 10-2006-0021221 proposed a separation membrane that forms a coating layer containing ceramic particles, which are inorganic fillers, and a binder polymer on at least one surface of an olefin polymer separation membrane. However, when the temperature of the battery rises above the melting point of the olefin polymer, there still exists the problem of the occurrence of the melt-down phenomenon. Also, there were problems such as the coating layer being peeled off due to the shrinkage of the olefin polymer, or the inorganic filler being desorbed from the coating layer, resulting in a decrease in the heat-resistant safety of the separation membrane. Therefore, the need for a separation membrane that can ensure safety at high temperatures remains very high.

[0007] Alternatively, a measure has been proposed to directly crosslink the olefin polymer with a photoinitiator to enhance the safety of the separation membrane. However, since the conventionally used photoinitiators are substances that are easily soluble in organic solvents, they cannot ensure sufficient solubility in aqueous solvents and cannot be used in aqueous solvents that are advantageous in terms of price and environmental considerations.

[0008] Therefore, at present, it is necessary to develop a resin for the binder of the separation membrane coating layer that can be applied to the coating layer to prevent the desorption of the binder particles and the peeling of the coating layer, thereby improving the heat resistance of the separation membrane. Also, there is an increasing need for a binder resin for the coating layer that can be applied to the coating layer composition using an aqueous solvent and can crosslink the olefin polymer.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] Therefore, the problem that the present invention aims to solve is to provide a novel photoinitiated copolymer resin and a method for producing the same, which can solve the aforementioned problems and prevent peeling of the separation film coating layer and detachment of inorganic fillers.

[0011] Furthermore, another problem that the present invention aims to solve is to provide a crosslinked structure-containing separation membrane for lithium secondary batteries containing the photoinitiated copolymer resin of the novel structure, and a method for producing the same. [Means for solving the problem]

[0012] A first aspect of the present invention relates to a photoinitiated copolymer resin comprising, as a repeating unit, a first unit to which a functional group derived from an aromatic carbonyl compound is bonded, and a second unit to which a hydrophilic group containing a nitrogen-containing ring and / or an amine group at its terminal end.

[0013] A second aspect of the present invention is that, in the above-described aspect, the aromatic carbonyl compound comprises a benzophenone compound, a xanthone compound, a thioxanthone compound, or a combination of two or more thereof.

[0014] A third aspect of the present invention is that, in any one of the above-described aspects, the first unit includes a repeating unit represented by the following chemical formula 1a, a repeating unit represented by the following chemical formula 1b, or both thereof.

[0015] [ka]

[0016] Here, X1 is a single bond or a linear or branched alkylene group (-CH2-) having 1 to 5 carbon atoms, and at least one hydrogen atom of the alkylene group may be substituted with a linear or branched alkyl group having 1 to 3 carbon atoms. The aforementioned X2 is hydrogen, or a linear or branched alkyl group having 1 to 5 carbon atoms. The aforementioned X3 is R1, R2, or R1R2, where R1 is an alkylene group having 1 to 10 carbon atoms, -O-, -C(=O)-, -C(=O)-O-, -OC(=O)-O-, -OC(=O)-, -NH-, an ester group, an amide group, an alkoxy group, or a carbonyl group, and R2 is a divalent linking group comprising at least one selected from the group consisting of an ester group, an amide group, an alkoxy group, a carbonyl group, a carboxyl group, -O-, -C(=O)-, -C(=O)-O-, -OC(=O)-O-, -OC(=O)-, -S-, -S(=O)2-, -S(=O)2-O-, -NH-, -NR3 (where R3 is an alkyl group or acyl group), -NH-C(=O)-, -C(=O)NH-, and =N-. X4 is oxygen or sulfur. The dashed line indicates the linkage of X3, which is bonded to the 2nd, 3rd, or 4th position of the aromatic ring.

[0017] A fourth aspect of the present invention is that, in any one of the above-described aspects, the first unit includes the following chemical formulas 2a, 2b, 2c, 2d, or two or more combinations thereof.

[0018] [ka] [ka]

[0019] In the above chemical formula 2d, X5 is sulfur or oxygen.

[0020] A fifth aspect of the present invention is that, in at least one of the above-described aspects, the second unit has a hydrophilic group linked to the main chain by an amide bond.

[0021] A sixth aspect of the present invention is that, in at least one of the above-described aspects, the second unit includes a repeating unit represented by the following chemical formula 5.

[0022] [ka]

[0023] Here, A1 is a single bond or a linear or branched alkylene group (-CH2-) having 1 to 5 carbon atoms, and at least one hydrogen atom of the alkylene group may be substituted with a linear or branched alkyl group having 1 to 3 carbon atoms. A2 is hydrogen, or a linear or branched alkyl group having 1 to 5 carbon atoms. A3 is either null, R1, R2, or R1R2, where R1 is an alkylene group having 1 to 10 carbon atoms, -O-, -C(=O)-, -C(=O)-O-, -OC(=O)-O-, -OC(=O)-, -NH-, an ester group, an amide group, an alkoxy group, or a carbonyl group, and R2 is an ester group, an amide group, an alkoxy group, a carbonyl group, a carboxyl group, -O-, -C(=O)-, - A divalent linking group comprising at least one selected from the group consisting of C(=O)-O-, -OC(=O)-O-, -OC(=O)-, -S-, -S(=O)2-, -S(=O)2-O-, -NH-, -NR3 (where R3 is an alkyl or acyl group), -NH-C(=O)-, -C(=O)NH-, and =N-, where if A3 is absent (null), (L) means a single bond directly bonded to a carbon in the main chain. The aforementioned (L) has a hydrophilic group containing a nitrogen-containing ring and / or an amine group at its terminal end.

[0024] A seventh aspect of the present invention is that in at least one of the above-described aspects, the hydrophilic group comprises a group derived from morpholine, a group derived from piperidine, a group derived from oxazolidine, a group derived from thiooxazolidine, a group derived from ethyleneimine, a group derived from pyrrole, a group derived from imidazole, a group derived from diazetidine, a group derived from dithiazine, a group derived from azocane, a group derived from azonane, -NR4R5, or two or more of these, wherein R4 and R5 are each independently hydrogen or an alkyl group having 1 to 10 carbon atoms.

[0025] An eighth aspect of the present invention is that, in at least one of the above-described aspects, the second unit includes one or more repeating units represented by chemical formula 5a and repeating units represented by chemical formula 5b.

[0026] [ka]

[0027] In the above chemical formula 5a, A4 is oxygen (O), sulfur (S), or phosphorus (P), and A5 is an alkenylene group (-(CH2)-) having 1 to 5 carbon atoms.

[0028] A ninth aspect of the present invention is that, in at least one of the above-described aspects, the photoinitiated copolymer resin comprises a compound represented by the following chemical formula 7a and / or a compound represented by chemical formula 7b, wherein the first unit is included in an amount of 10 wt% or less with respect to 100 wt% of the photoinitiated copolymer resin.

[0029] [ka]

[0030] A tenth aspect of the present invention is, in at least one of the above-described aspects, the photo-initiated copolymer resin has a content of first repeating units of 10 wt% or less relative to 100 wt% of the total photo-initiated copolymer resin.

[0031] An eleventh aspect of the present invention is that, in at least one of the above-described aspects, the photoinitiated copolymer resin has a glass transition temperature of 130°C to 220°C.

[0032] A twelfth aspect of the present invention is that, in at least one of the above-described aspects, the photoinitiated copolymer resin has a molecular weight of 0.5 million to 100,000.

[0033] A thirteenth aspect of the present invention is that, in at least one of the above-described aspects, the photo-initiated copolymer resin has a PDI of 7 to 20.

[0034] A fourteenth aspect of the present invention is, in at least one of the above-described aspects, the separation membrane comprises a crosslinked structure-containing olefin polymer porous support having a crosslinked structure in which polymer chains are directly linked, a binder resin and an inorganic filler, The binder resin comprises a photoinitiated copolymer resin according to at least one of the embodiments described above, wherein the photoinitiated copolymer resin is present in an amount of 50 wt% or more relative to 100 wt% of the binder resin.

[0035] A 15th aspect of the present invention is, in at least one of the above-described aspects, the separation membrane comprises the crosslinked structure-containing olefin polymer porous support and an organic / inorganic composite porous coating layer located on at least one surface of the porous support. The photo-initiated copolymer resin is included in one or more of the crosslinked structure-containing olefin polymer porous support and the organic / inorganic composite porous coating layer. The organic / inorganic composite porous coating layer comprises a binder resin and an inorganic filler, wherein the inorganic filler is present in an amount of 70 wt% or more relative to 100 wt% of the organic / inorganic composite porous coating layer.

[0036] A sixteenth aspect of the present invention is that, in at least one of the above-described aspects, the photo-initiated copolymer resin is included in an amount of 0.1 to 5 parts by weight per 100 parts by weight of the inorganic filler.

[0037] A 17th aspect of the present invention relates to a lithium secondary battery, the lithium secondary battery 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 a separation membrane containing a crosslinked structure for a lithium secondary battery according to at least one of the above-described aspects.

[0038] An 18th aspect of the present invention relates to a method for producing a crosslinked structure-containing separation membrane for lithium secondary batteries, the method comprising the steps of: applying a composition comprising a photoinitiated copolymer resin, an inorganic filler, and an aqueous dispersion medium to an olefin polymer porous support, drying it, and coating it; and irradiating the olefin polymer porous support coated with the composition with ultraviolet light, wherein the photoinitiated copolymer resin is a photoinitiated copolymer resin according to at least one of the above-described aspects.

[0039] A 19th aspect of the present invention is, in at least one of the above-described aspects, in the step of irradiating with ultraviolet light, the amount of ultraviolet light irradiated is 10 mJ / cm². 2 More than 20,000mJ / cm 2 The following applies:

[0040] A 20th aspect of the present invention is, in at least one of the aspects described above, the photoinitiated copolymer resin includes, as a first repeating unit, a repeating unit represented by the following chemical formula 2a, a repeating unit represented by the following chemical formula 2b, or both thereof, and as a second repeating unit, a repeating unit represented by the chemical formula 5a, wherein the first repeating unit is included in an amount of 10 wt% or less per 100 wt% of the photoinitiated copolymer resin.

[0041] [ka] [ka]

[0042] In the above chemical formula 5a, A4 is oxygen (O), sulfur (S), or phosphorus (P), and A5 is an alkenylene group (-(CH2)-) having 1 to 5 carbon atoms. [Effects of the Invention]

[0043] The photoinitiated copolymer resin according to the present invention can penetrate olefin polymers under aqueous dispersion media conditions and crosslink the porous olefin polymer support.

[0044] Furthermore, the crosslinked structure-containing separation membrane for lithium secondary batteries containing the photoinitiated copolymer resin according to the present invention includes a crosslinked structure-containing olefin polymer porous support having a crosslinked structure in which polymer chains are directly linked, exhibiting excellent heat resistance and capable of having a high meltdown temperature. [Modes for carrying out the invention]

[0045] The present invention will now be described in detail. Prior to this, terms and words used in this specification and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may appropriately define the concepts of terms in order to best describe their invention. Therefore, it should be understood that the configurations described in the examples herein represent only one of the most preferred embodiments of the present invention and do not represent the entire technical idea of ​​the present invention, and that there may be a variety of equivalents and modifications that can substitute for them at the time of filing.

[0046] Whenever in the entirety of this specification a part "includes" or "companies" a certain component, this means, unless otherwise stated, that it may further include or possess other components rather than excluding them.

[0047] Throughout this specification, the phrase "A and / or B" means "A or B or all of these."

[0048] Throughout this specification, "approximately," "substantially," etc., are used to mean either the numerical value or a value close to the manufacturing and material tolerances inherent in the meaning referred to, and are used to prevent unscrupulous infringers from unfairly exploiting disclosures that refer to precise or absolute numerical values ​​for the understanding of this application.

[0049] Throughout this specification, unless otherwise specified, temperature refers to Celsius temperature, and the unit is °C.

[0050] In this invention, the term alkylene group refers to a group with two bonding positions to an alkyl group, i.e., a divalent group.

[0051] In this invention, the term "alkenylene group" refers to a group having two bonding positions to an alkenyl group, i.e., a divalent group.

[0052] In the present invention, the term cycloalkylene group means a divalent alicyclic hydrocarbon group, which is a divalent group derived from a monocyclic or polycyclic non-aromatic hydrocarbon.

[0053] In this invention, the term "arylene group" can mean a group in which there are two bonding positions to an aryl group, i.e., a divalent group.

[0054] Aqueous dispersion media have advantages in that they are environmentally friendly and do not require excessive heat for drying. Organic solvents, which are widely used in the manufacture of separation membranes, have many environmental problems, require solvent recovery facilities, and are subject to strict control and regulation. Therefore, many attempts are being made to utilize such aqueous dispersion media as an alternative to organic solvents.

[0055] On the other hand, a method has been proposed to photocrosslink polymer chains within an olefin polymer porous support by adding a photoinitiator to a coating layer composition, thereby crosslinking the olefin polymer chains of the porous support during the formation of the coating layer. For this to work, a sufficient amount of the photoinitiator must be introduced so that it dissolves well in the solvent and can crosslink the polymer chains on the surface of the olefin polymer porous support.

[0056] However, photoinitiators, which are primarily used to crosslink polymer chains within porous olefin polymer supports, dissolve well in organic solvents but have very low solubility in aqueous dispersions. When using aqueous dispersions, not only is it difficult to introduce a sufficient amount of photoinitiator to crosslink polymer chains on the surface of the porous olefin polymer support, but there is also the problem that the photoinitiator is not uniformly coated on the surface of the porous olefin polymer support.

[0057] Therefore, the inventors of the present invention have completed the present invention by inventing a novel photoinitiated copolymer resin that dissolves sufficiently even in an aqueous dispersion medium and can directly crosslink the polymer chains and / or heat-resistant resin of the photoinitiated copolymer resin within the porous olefin polymer support.

[0058] Photoinitiated copolymer resin The photoinitiated copolymer resin according to the present invention comprises a first unit to which a functional group derived from an aromatic carbonyl compound is bonded. The first unit may comprise one or more of the photoinitiated copolymer resins. In embodiments of the present invention, the photoinitiated copolymer resin may comprise a second unit to which a hydrophilic group is bonded. The second unit may comprise one or more of the photoinitiated copolymer resins. The photoinitiated copolymer resin may be a block copolymer or a random copolymer comprising the first and second units, but the form of copolymerization is not limited thereto. The first and second units in the photoinitiated copolymer resin may have a molar ratio of 99.9:0.1 to 0.1:99.9. In a specific embodiment of the present invention, the photoinitiated copolymer resin may contain about 0.1 wt% to about 10 wt% of the first unit per 100 wt% of total weight. Preferably, the first unit may be present in an amount of about 5 wt% or less, or about 3 wt% or less, or about 2.5 wt% or less, or 2.0 wt% or less. In one embodiment of the present invention, the first unit may be present in an amount of about 0.1 wt% or more, or 0.5 wt% or more, or 0.7 wt% or more, or 1.0 wt% or more. The first and second units may be present independently in groups of one or more within the range that satisfies the molar ratio and / or weight ratio described above. If the content is less than 0.1 wt%, it is undesirable in that crosslinking by photoreaction is not sufficiently carried out. On the other hand, if the content is excessively high, exceeding 10 wt%, it is undesirable in terms of solubility during the production of the coating layer forming composition. In one embodiment of the present invention, the second repeating unit may be present in an amount of 90 wt% to 99.1 wt% based on 100 wt% of the total weight of the photoinitiated copolymer resin.

[0059] The content of the repeating units can be confirmed by comparing the number of hydrogen peaks in the CH2 group of the polymer main chain and the aromatic group of the polymer side chain using 1H-NMR. Alternatively, in one embodiment, 1H-NMR can be based on the chemical transfer or residual solvent peak of tetramethylsilane (TMS).

[0060] In one embodiment of the present invention, the aromatic carbonyl compound may be at least one selected from benzophenone compounds, xanthone compounds, and thioxanthone compounds.

[0061] Examples of the benzophenone compounds include benzophenone, 4-phenylbenzophenone, 4-methoxybenzophenone, 4,4'-dimethoxybenzophenone, 4,4'-dimethylbenzophenone, 4,4'-dichlorobenzophenone, 4,4'-dimethylaminobenzophenone, 4,4'-diethylaminobenzophenone, 4-methylbenzophenone, 2,4,6-trimethylbenzophenone, 4-(4-methylthiophenyl)benzophenone, 3,3'-dimethyl-4-methoxybenzophenone, methyl-2-benzoylbenzoate, and 4-(2-hydroxyethylthio) It may also be benzophenone, 4-(4-trillthio)benzophenone, 4-benzoyl-N,N,N-trimethylbenzenemethaneaminium chloride, 2-hydroxy-3-(4-benzoylphenoxy)-N,N,N-trimethyl-1-propaneaminium chloride monohydrate, 4-(13-acryloyl-1,4,7,10,13-pentaoxatridecyl)benzophenone, or 4-benzoyl-N,N-dimethyl-N-[2-(1-oxo-2-propenyl)oxy]ethyl-benzenemethaneaminium chloride, or may contain one or more of these.

[0062] Non-limiting examples of the xanthone and thioxanthone compounds include thioxanthone, 2-isopropylthioxanthone, 2-chlorothioxanthone, 1-chloro-4-propoxythioxanthone, 2-dodecylthioxanthone, 2,4-diethylthioxanthone, 2,4-dimethylthioxanthone, 1-methoxycarbonylthioxanthone, 2-ethoxycarbonylthioxanthone, 3-(2-methoxyethoxycarbonyl)-thioxanthone, and 4-butoxycarbonylthioxanthone. Oxanthonone, 3-butoxycarbonyl-7-methylthioxanthone, 1-cyano-3-chlorothioxanthone, 1-ethoxycarbonyl-3-chlorothioxanthone, 1-ethoxycarbonyl-3-ethoxythioxanthone, 1-ethoxycarbonyl-3-aminothioxanthone, 1-ethoxycarbonyl-3-phenylsulfurylthioxanthone, 3,4-di-[2-(2-methoxyethoxy)ethoxycarbonyl]-thioxanthone, 1,3-dimethyl-2-hydroxy-9H-thio Xanthene-9-one 2-ethylhexyl ether, 1-ethoxycarbonyl-3-(1-methyl-1-morpholinoethyl)-thioxanthone, 2-methyl-6-dimethoxymethyl-thioxanthone, 2-methyl-6-(1,1-dimethoxybenzyl)-thioxanthone, 2-morpholinomethylthioxanthone, 2-methyl-6-morpholinomethylthioxanthone, N-allylthioxanthone-3,4-dicarboxymide, N-octylthioxanthone-3,4-dicarboxymide, N-( Examples include 1,1,3,3-tetramethylbutyl)-thioxanthone-3,4-dicarboxymide, 1-phenoxythioxanthone, 6-ethoxycarbonyl-2-methoxythioxanthone, 6-ethoxycarbonyl-2-methylthioxanthone, thioxanthone-2-carboxylic acid polyethylene glycol ester, and 2-hydroxy-3-(3,4-dimethyl-9-oxo-9H-thioxanthone-2-yloxy)-N,N,N-trimethyl-1-propaneaminium chloride. In a specific embodiment, the aromatic carbonyl compound may include one or more selected from xanthones and thioxanthones.

[0063] In one embodiment of the present invention, the first unit includes a repeating unit that can be represented by the following chemical formula 1a, chemical formula 1b, or chemical formula 1c. The first repeating unit may include one or more photoinitiated copolymer resins.

[0064] [ka]

[0065] In the above chemical formulas 1a and 1b, X1 is a single bond or a linear or branched alkylene group (-CH2-) having 1 to 5 carbon atoms, and at least one hydrogen atom of the alkylene group may be substituted with a linear or branched alkyl group having 1 to 3 carbon atoms. The aforementioned X2 is hydrogen, or a linear or branched alkyl group having 1 to 5 carbon atoms. The aforementioned X3 is R1, R2, or R1R2, where R1 is an alkylene group having 1 to 10 carbon atoms, -O-, -C(=O)-, -C(=O)-O-, -OC(=O)-O-, -OC(=O)-, -NH-, an ester group, an amide group, an alkoxy group, or a carbonyl group, and R2 is a divalent linking group comprising at least one selected from the group consisting of an ester group, an amide group, an alkoxy group, a carbonyl group, a carboxyl group, -O-, -C(=O)-, -C(=O)-O-, -OC(=O)-O-, -OC(=O)-, -S-, -S(=O)2-, -S(=O)2-O-, -NH-, -NR3 (where R3 is an alkyl group or acyl group), -NH-C(=O)-, -C(=O)NH-, and =N-, and the dashed line (dashed The line indicates the linkage of X3, which can be bonded to the 2nd, 3rd, 4th, or 5th position of the aromatic ring.

[0066] In one embodiment of the present invention, X3 may be -C(=O)O- or -C(=O)NR4-, where R4 may be hydrogen or an alkyl group having 1 to 10 carbon atoms. On the other hand, in the chemical formula 1b, X4 may be oxygen (O) or sulfur (S).

[0067] In a more specific embodiment of the present invention, the first unit may include repeating units represented by the following chemical formulas 2a, 2b, 2c, or 2d.

[0068] [ka] [ka]

[0069] In the above chemical formula 2d, X5 may be oxygen (O) or sulfur (S).

[0070] In one specific embodiment, the first unit may be derived from a first monomer which is an acrylic compound having a functional group derived from the aromatic carbonyl compound.

[0071] In one specific embodiment, the first monomer may be 4-benzoylphenyl methacrylate, or it may be represented as shown in the following chemical formula 3a. On the other hand, other specific examples of acrylic compounds having a functional group derived from the aromatic carbonyl chemical may be represented as shown in the following chemical formula 3b or chemical formula 3c.

[0072] [ka]

[0073] In one embodiment of the present invention, the first monomer may be commercially available or obtained by a nucleophilic acyl substitution reaction between a hydroxyl-containing benzophenone and a (meth)acrylic anhydride. Alternatively, it may be obtained by a nucleophilic acyl substitution reaction between a hydroxyl-containing hydroxythioxanthone and a (meth)acrylic anhydride. Furthermore, it may be obtained by reacting an aminobenzophenone with a methacryloyl chloride under an inorganic acid catalyst. To accelerate the reaction, an acid catalyst may be added and may be carried out during heating. In the nucleophilic acyl substitution reaction, it is appropriate to add an inorganic acid to prevent the anions formed after ionization from affecting the reaction, and examples of the inorganic acid include sulfuric acid, nitric acid, and phosphoric acid. The inorganic acid may include one or more selected from sulfuric acid, nitric acid, and phosphoric acid.

[0074] On the other hand, the benzophenone, thioxanthone, or xanthone containing the hydroxyl group may each have a hydroxyl group or amine group directly linked to any ring. Chemical formula 4a below represents the structure of hydroxybenzophenone. Chemical formula 4b below represents the structure of hydroxythioxanthone. Chemical formula 4c below shows that the hydroxyl group or amine group can be located in any position in the linked ring where a hydrogen atom is substituted, without limitation. For example, the hydroxyl group can be located at at least one position from 1 to 8 of the benzophenone, xanthone, or thiooxathone. For example, the thiooxathone containing the hydroxyl group may be 2-hydroxy-9H-thioxanthene-9-one.

[0075] [ka]

[0076] On the other hand, in one embodiment of the present invention, the second unit has a hydrophilic group bonded to its terminal. For example, the second unit may include one or more of those represented by the following chemical formula 5. The second unit may also include one or more of the photoinitiated copolymer resins according to the present invention.

[0077] [ka]

[0078] In the above chemical formula 5, A1 is a single bond or a linear or branched alkylene group (-CH2-) having 1 to 5 carbon atoms, and at least one hydrogen atom of the alkylene group may be substituted with a linear or branched alkyl group having 1 to 3 carbon atoms. A2 is hydrogen, or a linear or branched alkyl group having 1 to 5 carbon atoms. A3 is either null, R1, R2, or R1R2, where R1 is an alkylene group having 1 to 10 carbon atoms, -O-, -C(=O)-, -C(=O)-O-, -OC(=O)-O-, -OC(=O)-, -NH-, an ester group, an amide group, an alkoxy group, or a carbonyl group, and R2 is an ester group, an amide group, an alkoxy group, a carbonyl group, a carboxyl group, -O-, -C(=O)-, - A divalent linking group comprising at least one selected from the group consisting of C(=O)-O-, -OC(=O)-O-, -OC(=O)-, -S-, -S(=O)2-, -S(=O)2-O-, -NH-, -NR3 (where R3 is an alkyl or acyl group), -NH-C(=O)-, -C(=O)NH-, and =N-, where the absence of A3 (null) means a single bond in which (L) is directly bonded to a carbon in the main chain.

[0079] The aforementioned (L) is a terminal group containing a hydrophilic group at its terminal end, and it is preferable that it has the effect of improving the hydrophilicity of the photoinitiated copolymer resin, or that it can raise the glass transition temperature, or that it can provide both of these effects.

[0080] For example, the hydrophilic group may include -OH, -C(=O)OH, a nitrogen-containing ring, an amine group, or one or more of these. In a preferred embodiment of the present invention, the hydrophilic group may include a nitrogen-containing ring and / or an amine group, and more preferably, the hydrophilic group can be linked to the main chain by an amide bond.

[0081] In one specific embodiment, the hydrophilic group may be a group derived from morpholine, a group derived from piperidine, a group derived from oxazolidine, a group derived from thiooxazolidine, a group derived from ethyleneimine, a group derived from pyrrole, a group derived from imidazole, a group derived from diazetidine, a group derived from dithiazine, a group derived from azocane, a group derived from azonane, -NR4R5, or a combination of two or more of these, where R4 and R5 may each be independently hydrogen or an alkyl group having 1 to 10 carbon atoms.

[0082] In one specific embodiment of the present invention, the second unit may be represented more specifically by the following chemical formulas 5a and 5b.

[0083] [ka]

[0084] In the above chemical formula 5a, A4 is oxygen (O), sulfur (S), or phosphorus (P), and A5 may be an alkenylene group (-(CH2)-) having 1 to 5 carbon atoms.

[0085] [ka]

[0086] On the other hand, in yet another embodiment, the second unit may further include a second unit in which the hydrophilic group is -OH or -C(=O)OH, in addition to the nitrogen-containing ring and / or amine group described above as the hydrophilic group. For example, the second unit may further include a repeating unit represented by the following chemical formula 5c.

[0087] [ka]

[0088] In one specific embodiment of the present invention, the second unit may be derived from a second monomer which is a vinyl compound containing a morpholine group. In one specific embodiment, an unrestricted example of the second monomer is acryloylmorpholine, which may be represented as shown in the following chemical formula 6.

[0089] [ka]

[0090] In a specific embodiment of the present invention, the first unit may be derived from an acrylic monomer (first monomer) to which a functional group derived from a benzophenone compound is attached, and the second unit may be derived from an acrylic monomer (second monomer) to which a morpholine group is attached.

[0091] In one embodiment of the present invention, the copolymer resin comprising the first unit and the second unit may be represented, for example, by the following chemical formula 7a or chemical formula 7b.

[0092] [ka]

[0093] In the chemical formulas 7a and / or 7b, the first unit and the second unit may each be independently comprised of one or more units. The order of the first and second repeating units in the chemical formulas 7a and 7b is illustrative and not particularly limited thereto. Furthermore, in the chemical formulas 7a and / or 7b, the first unit and the second unit may have a ratio (molar ratio) of 99.9:0.1 to 0.1:99.9. In other embodiments of the present invention, in the chemical formulas 7a and / or 7b, at least one hydrogen atom bonded to the carbon atoms of the main chain of the copolymer resin may be substituted with a linear or branched alkyl group having 1 to 5 carbon atoms.

[0094] On the other hand, in one specific embodiment of the present invention, the photoinitiated copolymer resin may have a molecular weight (weight-average molecular weight, Mw) in the range of 0.5 million to 100,000. Alternatively, it may have a molecular weight in the range of 10,000 to 100,000. Within this range, the molecular weight may be 70,000 or less, or 50,000 or less, or 30,000 or less. Within this range, the molecular weight may be 0.5 million or more, or 0.7 million or more, or 10,000 or more. In one embodiment of the present invention, the unit of molecular weight may be g / mol.

[0095] In conjunction with or independently thereof, the photoinitiated copolymer resin may have a polydispersity index (PDI) in the range of 7 to 20. The polydispersity index may be 17 or less, or 15 or less, within the range. The polydispersity index may be 10 or more, or 11 or more, or 12 or more, within the range.

[0096] The photoinitiated copolymer resin according to the present invention can exhibit a glass transition temperature (Tg) in the range of 130°C to 220°C. Preferably, the glass transition temperature may be 150°C or higher or 170°C or higher. In one embodiment of the present invention, the glass transition temperature may be 200°C or lower or 180°C or lower.

[0097] If the molecular weight of the photoinitiated copolymer resin is excessively large, its water solubility may decrease. If the molecular weight is excessively small and falls outside the aforementioned range, the thermal shrinkage rate may increase, leading to a decrease in heat resistance. On the other hand, if the PDI is outside the aforementioned range, the thermal shrinkage rate may increase, leading to a decrease in heat resistance. The photoinitiated copolymer resin of the present invention exhibits a high glass transition temperature, so when applied to a separation membrane, it minimizes fluidity even at high temperatures, effectively preventing shrinkage of the separation membrane.

[0098] In one embodiment of the present invention, the molecular weight of the photoinitiated copolymer resin can be measured by gel permeation chromatography (GPC). The analytical instrument is not particularly limited, and for example, Agilent Technologies' PL GPC220 or JASCO's GPC-900 can be used. The measurement conditions can be set to, for example, the following conditions.

[0099] -Column(maker, model no.):2x TSKgel SupermultiporeHZ-M+TSKgel SuperHZ-2500 -Eluent:THF -Temperature: 40℃ -Flow rate: 1.0 mL / min -Injection volume, sample concentration: 30μl, 1~10mg / mL -Standard:Polystyrene -Detector:RI

[0100] On the other hand, the PDI can be measured based on the following formula (Equation 1). In Equation 1 below, the weight-average molecular weight and the number-average molecular weight can be confirmed by the molecular weight measurement method described above.

[0101] (Formula 1) Multivariance Index (PDI) PDI=weight average molecular weight (Mw) / number average molecular weight (Mn)

[0102] On the other hand, the glass transition temperature Tg can be measured using a DSC (TA Instrument) device.

[0103] Method for producing photoinitiated copolymer resins The photoinitiated copolymer resin of chemical formula 1 described above can be produced by polymerization of a first monomer and a second monomer. This polymerization can be carried out by one or more of the following methods: bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization, and is not particularly limited.

[0104] For example, the polymerization may be carried out by a solution polymerization method.

[0105] In one specific embodiment, first, the first and second monomers are mixed in a polymerization solvent in an amount such that the first monomer is present in the polymerization resin at a concentration of approximately 0.1 to 5 wt%. After that, the solvent is replaced with N2, the temperature is raised to the starting temperature, and an initiator is added. Subsequently, the precipitated solid can be washed with a solvent such as ethyl acetate and dried to obtain a polymer. If necessary, the dried sample may be prepared by diluting it with distilled water to a concentration of approximately 10 wt%.

[0106] The initiators are not limited to, but include, for example, oxygen; dialkyl peroxides and their derivatives such as di-t-butyl peroxide, t-butylcumyl peroxide and dicumyl peroxide; diacyl peroxides such as diacetyl peroxide and dioctanoyl peroxide; peroxydicarbonates such as di-isopropyl peroxydicarbonate and di-2-ethylhexyl peroxydicarbonate; peroxyesters such as t-butyl peroxyisobutyrate, t-butyl peroxypivalate and t-butyl peroxylaurate; ketone peroxides such as methyl ethyl ketone peroxide and cyclohexanone peroxide; hydroperoxides such as 2,2-bis(t-butyl-peroxy)octane and 1,1-bis(t-butyl-peroxy)cyclohexane; Potassium persulfate, Ammonium persulfate, Sodium hydrosulfite, Sodium persulfate, Sodium Sulfur oxides such as bisulfate, and azo compounds such as α,α'-azoisobutyronitrile can be used. In one specific embodiment, the initiator can be AIBN (Azobisisobutyronitrile).

[0107] On the other hand, in one embodiment of the present invention, a molecular weight modifier can be added in an amount of approximately 5000 ppm relative to the monomer introduced during the reaction. The molecular weight modifier may include, for example, mercaptopropionic acid.

[0108] As the polymerization solvent, water, aliphatic alcohols, and aliphatic esters can be used. Specific examples include aliphatic alcohols such as methanol, ethanol, and propanol, and methyl, ethyl, propyl, and butyl esters of formic acid, acetic acid, and propionic acid, as well as mixtures thereof. Methanol and ethyl acetate are particularly preferred because they not only have a small chain transfer effect but also exhibit excellent solubility with vinyl compounds. Therefore, polymers with a relatively high vinyl monomer content and high molecular weight can be easily and preferably obtained.

[0109] Cross-linked structure-containing separation membrane for lithium secondary batteries The present invention provides a crosslinked structure-containing separation membrane for lithium secondary batteries, comprising a crosslinked structure-containing olefin polymer porous support having a crosslinked structure in which polymer chains are directly linked, an inorganic filler, and a binder resin, wherein the binder resin includes the aforementioned photoinitiated copolymer resin.

[0110] In one embodiment of the present invention, the separation membrane may include the crosslinked structure-containing olefin polymer porous support and an organic / inorganic composite porous coating layer located on at least one surface of the porous support.

[0111] In this case, the photoinitiated copolymer resin may be included in one or more of the crosslinked structure-containing olefin polymer porous support and the organic / inorganic composite porous coating layer. On the other hand, components such as inorganic fillers, binder resins other than the photoinitiated copolymer resin and surfactants may be located in the organic / inorganic composite porous coating layer.

[0112] Photoinitiated copolymer resin In one embodiment of the present invention, the photoinitiated copolymer resin contained in the crosslinked structure-containing separation membrane for lithium secondary batteries includes all of the contents of the photoinitiated copolymer resin described above.

[0113] The photo-initiated copolymer resin directly photocrosslinks the polymer chains within the porous olefin polymer support. Specifically, the photo-initiated copolymer resin acts like a photoinitiator, generating radicals in the polymer chains within the porous olefin polymer support, thereby forming a crosslinked structure in which the polymer chains are directly linked. Furthermore, the photo-initiated copolymer resin can dissolve sufficiently in an aqueous dispersion medium due to the effect of the second monomer having hydrophilic groups. In one embodiment of the present invention, the photo-initiated copolymer resin may have a solubility of 0.01 g or more per 100 g of aqueous dispersion medium. Therefore, the photo-initiated copolymer resin can dissolve sufficiently in the aqueous dispersion medium to crosslink the polymer chains within the porous olefin polymer support.

[0114] The solubility can be measured using a UV-Visible Spectrophotometer. Specifically, a photoinitiated copolymer resin is dissolved in a solvent to prepare solutions of various concentrations whose mass concentrations are known in advance. After allowing the undissolved photoinitiated copolymer resin to precipitate or suspend on the solvent for one hour, the amount of light absorbed by the solution is measured at a specific wavelength (e.g., 550 nm). The starting point at which the amount of light absorbed saturates to a constant level in a graph with concentration on the x-axis and light absorbed on the y-axis can be defined as the solubility of the photoinitiated copolymer resin.

[0115] The photoinitiated copolymer resin may be present in an amount of 0.1 to 5 parts by weight, 0.3 to 3 parts by weight, or 0.5 to 1.5 parts by weight per 100 parts by weight of the inorganic filler described later. When the content of the photoinitiated copolymer resin satisfies the range described above, it is possible to crosslink the olefin polymer by generating appropriate radicals and raise the meltdown temperature of the porous support itself.

[0116] Olefin polymer porous support The aforementioned olefin polymer porous support includes a "crosslinked structure in which polymer chains are directly linked."

[0117] In this specification, "a crosslinked structure in which polymer chains are directly linked" means a state in which polymer chains substantially composed of olefin polymers, more preferably polymer chains composed solely of olefin polymers, become reactive upon the addition of the photoinitiated copolymer resin, and the polymer chains directly crosslink with each other. Therefore, crosslinking reactions that occur between crosslinking agents when additional crosslinking agents are added in addition to the photoinitiated copolymer resin do not constitute a "crosslinked structure in which polymer chains are directly linked" as defined in this invention. Furthermore, crosslinking reactions that occur between additional crosslinking agents and the polymer chains do not constitute a "crosslinked structure in which polymer chains are directly linked" as defined in this invention, even if the polymer chains are substantially composed of olefin polymers or consist solely of olefin polymers.

[0118] Furthermore, crosslinking can occur between photoinitiated copolymer resins during the process of crosslinking polyolefin polymer chains with each other, and photoinitiated copolymer resins and polyolefin polymer chains can also be crosslinked with each other.

[0119] A separation membrane containing a crosslinked structure for lithium secondary batteries according to one embodiment of the present invention can have improved heat resistance by comprising a crosslinked structure-containing olefin polymer porous support having a crosslinked structure in which polymer chains are directly linked.

[0120] In one embodiment of the present invention, the degree of crosslinking of the crosslinked structure-containing olefin polymer porous support may be 10% to 80%, 30% to 55%, 10% to 45%, 15% to 40%, or 20% to 35%. When the crosslinked structure-containing olefin polymer porous support has a degree of crosslinking within the above range, it can have the desired level of heat resistance and may be even easier to increase the modulus.

[0121] At this time, the degree of crosslinking is calculated by physically enclosing the crosslinked olefin polymer porous support in a metal mesh, immersing it in trichlorobenzene at 135°C and stirring for 20 hours, then removing it, measuring its weight after it has completely dried, and calculating it as the percentage of the weight of the remaining olefin polymer porous support relative to the initial weight.

[0122] In one embodiment of the present invention, the olefin polymer porous support may be a porous film.

[0123] The olefin polymer may include ethylene polymers; propylene polymers; butylene polymers; pentene polymers; hexene polymers; octene polymers; copolymers of two or more of ethylene, propylene, butene, pentene, 4-methylpentene, hexene, and octene; or mixtures thereof.

[0124] Non-limiting examples of the ethylene polymer include low-density ethylene polymer (LDPE), linear low-density ethylene polymer (LLDPE), and high-density ethylene polymer (HDPE). In the case of a high-density ethylene polymer with high crystallinity and a high melting point, it is possible to achieve the desired level of heat resistance and to further increase the modulus.

[0125] A separation membrane containing a crosslinked structure for lithium secondary batteries according to one embodiment of the present invention can achieve excellent heat resistance without sacrificing other physical properties of the olefin polymer porous support, by including a crosslinked structure-containing olefin polymer porous support.

[0126] Organic / inorganic composite porous coating layer The separation membrane according to the present invention may comprise an organic / inorganic composite porous coating layer containing inorganic particles and a binder resin on at least one side surface of an olefin polymer porous support. The binder resin may contain a photocrosslinkable copolymer resin according to the present invention, and the photocrosslinkable copolymer resin may be present in an amount of 30 wt% or more, 50 wt% or more, or 70 wt% or more per 100 wt% of the binder resin. On the other hand, the binder resin in the organic / inorganic composite porous coating layer may be present in an amount of 30 wt% or less, 20 wt% or less, 10 wt% or less, 5 wt% or less, 3 wt% or less, or 1 wt% or less. Furthermore, the organic / inorganic composite porous coating layer may contain an organic filler and / or an inorganic filler. The filler may be, for example, an inorganic filler, and the inorganic filler may be present in an amount of 70 wt% or more, 80 wt% or more, or 90 wt% or more, 95 wt% or more, or 97 wt% or more in 100 wt% of the coating layer. In addition, additives such as surfactants and dispersants included during the manufacture of the separation membrane may be present, and these additives may be present in an amount of 10 wt% or less, 5 wt% or less, or 3 wt% or less in 100 wt% of the organic / inorganic composite porous coating layer.

[0127] Furthermore, the inorganic filler may have the form of particles having a predetermined particle size. In this case, interstitial volumes exist between the particles, forming fine pores. That is, the binder resin adheres the inorganic filler particles to each other so that they remain bound together, and the binder resin also maintains the bond between the porous support and the coating layer. Moreover, as explained earlier, crosslinking occurs between the photoinitiated copolymer resins during the process of crosslinking between polyolefin polymer chains, and the photoinitiated copolymer resins and polyolefin polymer chains can crosslink with each other. In this way, the crosslinking of the copolymer resin prevents the desorption of the inorganic filler, and the peel strength between the coating layer and the porous support can be improved.

[0128] inorganic fillers In one embodiment of the present invention, the separation membrane includes an organic / inorganic composite porous coating layer, wherein the organic / inorganic composite porous coating layer is bonded to each other by a binder resin while filled with inorganic fillers that are in contact with each other, thereby forming interstitial volumes between the inorganic fillers, and the interstitial volumes between the inorganic fillers become empty spaces that form pores.

[0129] The inorganic filler is not particularly limited as long as it is electrochemically stable. That is, the inorganic filler usable in the present invention is not particularly limited as long as it does not undergo oxidation and / or reduction reactions within the operating voltage range of the electrochemical element to which it is applied (e.g., Li / Li+ reference 0~5V). In particular, when an inorganic filler with a high dielectric constant is used as the inorganic filler, it can contribute to increasing the degree of dissociation of the electrolyte salt in the liquid electrolyte, such as a lithium salt, thereby improving the ionic conductivity of the electrolyte.

[0130] For the reasons stated above, in one embodiment of the present invention, the inorganic filler may include a high dielectric constant inorganic filler having a dielectric constant of 5 or more, preferably 10 or more. Non-restrictive examples of inorganic fillers with a dielectric constant of 5 or more include BaTiO3, Pb(Zr,Ti)O3(PZT), and Pb 1-x La x Zr 1-y Ti y O3(PLZT, 0 <x<1、0<y<1)、Pb(Mg 1 / 3 Nb 2 / 3 Examples include O3-PbTiO3 (PMN-PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, Mg(OH)2, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, AlOOH, Al(OH)3, SiC, TiO2, or mixtures thereof.

[0131] In addition, as the inorganic filler, an inorganic filler having lithium ion conduction ability, that is, an inorganic filler containing a lithium element and having a function of moving lithium ions without storing lithium can be used. Non-limiting examples of inorganic fillers having lithium ion conduction ability include lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z (PO4)3, 0 < x < 2, 0 < y < 1, 0 < z < 3), (LiAlTiP) x O y -based glass such as 14Li2O - 9Al2O3 - 38TiO2 - 39P2O5 (0 < x < 4, 0 < y < 13), lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), lithium germanium thiophosphate such as Li 3.25 Ge 0.25 P 0.75 S4 (0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride such as Li3N (Li x ) N y , 0 < x < 4, 0 < y < 2), SiS2 - based glass such as Li3PO4 - Li2S - SiS2 (Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4), P2S5 - based glass such as LiI - Li2S - P2S5 (Li x P y S z , 0 < x < 3, 0 < y < 3, 0 < z < 7), or mixtures thereof, etc.

[0132] ​​​​​​​​On the other hand, in one embodiment of the present invention, the inorganic filler may include an inorganic filler having hydrophilic properties. Examples of the hydrophilic inorganic filler include aluminum hydroxide-based inorganic particles. In specific embodiments, examples of the aluminum hydroxide-based inorganic particles include boehmite (γ-AlO(OH)), pseudo-boehmite (Al2O3·H2O), diaspore (α-AlO(OH)), Bayerite (α-Al(OH)3), gibbsite (γ-Al(OH)3), and nordstrandite (Al(OH)3).

[0133] Furthermore, the inorganic filler may include fumed-type inorganic fillers. The "fumed-type inorganic filler" refers to an inorganic filler in which basic particles formed by hydrolysis in a flame of 1,000°C or higher are linked together by collisions to form secondary particles, and such secondary particles form three-dimensional aggregates (aggregates, agglomerates).

[0134] Examples of such fumed-type inorganic fillers include fumed alumina, fumed silica, fumed titanium dioxide, or two or more of these.

[0135] The average particle size of the inorganic filler may be 0.005 to 0.5 μm. For example, the average particle size of the inorganic filler may be 0.01 μm or more, or 0.02 μm or more, or 0.03 μm or more, or 0.05 μm or more, or 0.1 μm or more, or 0.3 μm or more and 0.3 μm or less, or 0.1 μm or less, or 0.05 μm or less, or 0.03 μm or less, or 0.02 μm or less, or 0.01 μm or less. When the average particle size of the inorganic filler satisfies the above range, dispersibility is maintained, making it easy to adjust the physical properties of the separation membrane and improve its mechanical properties. In addition, the probability of internal short circuits occurring during charging and discharging of the electrochemical element due to excessively large pore sizes can be reduced.

[0136] In this case, the average particle size of the inorganic filler is the D50 particle size, and "D50 particle size" refers to the particle size at the 50% point of the cumulative particle number distribution by particle size. The particle size can be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it can be introduced into a commercially available laser diffraction particle size analyzer (for example, Microtrac S3500), and the particle size distribution can be calculated by measuring the difference in diffraction patterns due to particle size as the particles pass through the laser beam. The D50 particle size can be measured by calculating the particle diameter at the point where the cumulative particle number distribution by particle size in the measuring device reaches 50%.

[0137] In one embodiment of the present invention, the weight ratio of the inorganic filler to the binder resin may be 80:20 to 99.9:0.1, 90:10 to 99.9:0.1, 95:5 to 99.9:0.1, 96:4 to 99.5:0.5, or 97:3 to 99:1. Alternatively, the amount of the inorganic filler may be 20 parts by weight or less, 10 parts by weight or less, or 7 parts by weight or less per 100 parts by weight of the inorganic filler. When the weight ratio of the inorganic filler to the binder resin is within the above range, the amount of inorganic filler distributed per unit area of ​​the separation membrane is high, and the thermal safety of the separation membrane can be improved at high temperatures. For example, it may be easy to achieve thermal shrinkage rates of 20% or less, or 2% to 15%, 2% to 10%, 2% to 5%, 0% to 5%, or 0% to 2% in the machine direction and transverse direction, respectively, after leaving the film at 150°C for 30 minutes. Furthermore, it may be easy to ensure sufficient adhesion between the inorganic fillers while also ensuring sufficient void space between them.

[0138] Binding binder resin The binder resin is a component that provides binding between inorganic fillers and binding force between the porous coating layer and the porous support. The binder resin may further include a binder resin having binding properties (binding binder resin) in addition to the photoinitiated polymer resin according to the present invention. The binding binder resin is soluble or dispersible in an aqueous dispersion medium, and when dispersed in an aqueous dispersion medium, the binding binder resin may be latex in particle form or emulsion form.

[0139] The binding binder resin may have a glass transition temperature (Tg) of -200 to 200°C. For example, Tg may be 130°C or less, 100°C or less, 70°C or less, 50°C or less, 30°C or less, or 0°C or less. When the glass transition temperature of the binding binder resin satisfies the above-mentioned range, the mechanical properties of the coating layer of the final separation film, such as flexibility and elasticity, can be improved. The binding binder resin may also have ion conductivity. When the binding binder resin has ion conductivity, the performance of the battery can be further improved. The binding binder resin may have a dielectric constant of 1.0 to 100 (measurement frequency = 1 kHz), or 10 to 100. When the dielectric constant of the binding binder resin satisfies the above-mentioned range, the degree of salt dissociation in the electrolyte can be improved.

[0140] In one embodiment of the present invention, the binding binder resin may include an acrylic polymer, styrene-butadiene rubber, polyvinyl alcohol, polyvinylpyrrolidone, or two or more of these.

[0141] The acrylic polymer may include an acrylic homopolymer obtained by polymerizing only acrylic monomers, or it may include a copolymer of an acrylic monomer and another monomer. For example, the acrylic polymer may include polyacrylic acid, a polymer of ethylhexyl acrylate and methyl methacrylate, poly(methylmethacrylate), poly(ethylhexyl acrylate), poly(butylacrylate), polyacrylonitrile, a polymer of butyl acrylate and methyl methacrylate, or two or more of these.

[0142] The binding binder resin may be included, for example, in an amount of 0.1 to 10 parts by weight per 100 parts by weight of inorganic filler.

[0143] surfactants In one embodiment of the present invention, the crosslinked structure-containing separation membrane for lithium secondary batteries may include a surfactant if necessary. A surfactant can be added to the composition for forming the coating layer in order to form a coating layer on the olefin polymer porous support, and as a result, the coating layer may contain a surfactant.

[0144] The surfactant can improve the dispersibility in the composition. Furthermore, as will be described later, it enhances the wettability of the separation film of the composition for forming a coating layer containing an aqueous dispersion medium, thereby preventing the dewetting phenomenon, that is, the phenomenon in which the composition cannot be uniformly coated on the surface of the olefin polymer porous support due to the difference in surface energy between the olefin polymer porous support and the aqueous dispersion medium, and adheres like water droplets, thereby ensuring that the fibril coating is performed successfully.

[0145] The aforementioned surfactant can be any type that does not degrade the performance of the battery. Non-limiting examples include fluorinated surfactants and sulfur-based surfactants. The fluorinated surfactant plays a role in lowering surface tension and improving coating properties, and any common surfactant used in the industry can be used. Preferably, specific examples of fluorinated aliphatic polymeric esters include FC4430 from 3M, 4300 from Novec, and Capstone from DuPont. The sulfur-based surfactant may include WE3475 from BASF.

[0146] The amount of the surfactant may be 0.1 to 7 parts by weight, or 0.3 to 3 parts by weight, based on 100 parts by weight of the inorganic filler. When the amount of the surfactant satisfies this range, the performance of the separation membrane can be maintained while ensuring the fibrill coating properties of the coating solution.

[0147] In one embodiment of the present invention, the separation membrane may further contain additives such as dispersants and / or thickeners. These additives may include, but are not limited to, hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), ethyl hydroxyethyl cellulose (EHEC), methylcellulose (MC), carboxymethyl cellulose (CMC), hydroxyalkyl methyl cellulose, cyanoethylene polyvinyl alcohol, ammonium polyacrylate, or two or more of these.

[0148] Method for manufacturing a cross-linked structure-containing separation membrane for lithium secondary batteries A method for producing a crosslinked structure-containing separation membrane for lithium secondary batteries according to one embodiment of the present invention includes the steps of preparing an organic / inorganic composite porous coating layer-forming composition, coating a porous support with this composition, and then irradiating the olefin polymer porous support coated with the composition with ultraviolet light. The organic / inorganic composite porous coating layer-forming composition may be prepared by adding a binder resin and an inorganic filler to an aqueous dispersion medium. The composition may further contain a surfactant and / or a dispersant. The binder may further contain a photoinitiated copolymer resin according to the present invention and may further contain an auxiliary binding binder resin.

[0149] The binder resin includes a photoinitiated copolymer resin according to the present invention.

[0150] The following describes a method for manufacturing a cross-linked structure-containing separation membrane for lithium secondary batteries according to one embodiment of the present invention, focusing on its main components.

[0151] First, a coating layer-forming composition comprising a binder resin, an inorganic filler, and an aqueous dispersion medium is prepared, and then coated onto at least one surface of an olefin polymer porous support. The composition may further contain additives such as surfactants and dispersants as needed.

[0152] The aqueous dispersion medium has advantages in that it is environmentally friendly and does not require excessive heat for drying. Depending on the type of binder resin, the aqueous dispersion medium can act as a solvent to dissolve the binder resin, or it can act as a dispersion medium to disperse the binder resin rather than dissolve it. For example, the aqueous dispersion medium may include water, methanol, ethanol, ethylene glycol, diethylene glycol, glycerol alcohol, or two or more of these. In particular, the aqueous dispersion medium may include water.

[0153] Non-limiting examples of methods for applying the composition to the olefin polymer porous support include dip coating, die coating, roll coating, comma coating, microgravure coating, doctor blade coating, reverse roll coating, and direct roll coating.

[0154] By coating the olefin polymer porous support with the composition, the photoinitiated copolymer resin can be introduced to the surface of the olefin polymer porous support, and the olefin polymer porous support can be crosslinked upon ultraviolet irradiation. Here, the "surface of the olefin polymer porous support" may include not only the surface of the outermost layer of the olefin polymer porous support, but also the surface of pores present inside the olefin polymer porous support.

[0155] Next, the process includes irradiating the porous olefin polymer support coated with the composition with ultraviolet light.

[0156] When exposed to ultraviolet light, the polymer chains within the porous olefin polymer support are crosslinked, thereby obtaining a porous olefin polymer support containing a crosslinked structure.

[0157] Ultraviolet irradiation may be performed using an ultraviolet crosslinking apparatus, with the irradiation time and irradiation intensity appropriately adjusted considering the content ratio of the photoinitiated copolymer resin. For example, the irradiation time and irradiation intensity of the ultraviolet light can be set to conditions that ensure sufficient crosslinking of the polymer chains in the porous olefin polymer support to secure the desired heat resistance, while preventing damage to the separation membrane from the heat generated by the ultraviolet lamp. Furthermore, the ultraviolet lamp used in the ultraviolet crosslinking apparatus can be appropriately selected from high-pressure mercury lamps, metal lamps, gallium lamps, etc., depending on the photoinitiated copolymer resin used, and the emission wavelength and capacity of the ultraviolet lamp can be appropriately selected according to the process.

[0158] The method for producing a crosslinked structure-containing separation membrane for lithium secondary batteries according to one embodiment of the present invention makes it possible to photocrosslink polymer chains within an olefin polymer porous support even with an irradiation amount of ultraviolet light that is significantly less than the amount of light used in general photocrosslinking, thereby increasing the applicability of the crosslinked structure-containing separation membrane for lithium secondary batteries to the mass production process.

[0159] In one embodiment of the present invention, the amount of ultraviolet light irradiation is 10 mJ / cm². 2 More than 50mJ / cm 2 More than 100mJ / cm 2 More than 500mJ / cm 2 More than 1,000mJ / cm 2 More than 2,000mJ / cm 2 Above or above 5,000 mJ / cm 2 The above, and 20,000 mJ / cm² 2 Below, 15,000mJ / cm 2 The following range may also be used. When the amount of ultraviolet light irradiation satisfies the above range, crosslinking of polymer chains within the porous olefin polymer support can occur sufficiently, thereby improving heat resistance.

[0160] The amount of ultraviolet light irradiated can be measured using Miltec's H-type UV bulb and a portable light intensity meter called a UV power puck. When measuring the light intensity using Miltec's H-type UV bulb, three different wavelength values ​​are obtained for each wavelength: UVA, UVB, and UVC. The ultraviolet light of the present invention corresponds to UVA.

[0161] In the present invention, the method for measuring the amount of ultraviolet light irradiation involves passing a UV power puck on a conveyor under the same conditions as the sample, and the numerical value of the amount of ultraviolet light displayed on the UV power puck at this time is referred to as the "amount of ultraviolet light irradiation".

[0162] The meltdown temperature of the crosslinked structure-containing separation membrane for lithium secondary batteries according to one embodiment of the present invention may be 150°C or higher. The meltdown temperature of the separation membrane can be increased compared to the meltdown temperature of a separation membrane containing a non-crosslinked porous polyolefin substrate. For example, the meltdown temperature of the separation membrane may be 150°C or higher, 160°C or higher, 170°C or higher, 180°C or higher, 190°C or higher, or 200°C or higher.

[0163] Lithium-ion battery A lithium secondary battery according to one embodiment 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 separation membrane may include the aforementioned separation membrane containing a crosslinked structure for lithium secondary batteries.

[0164] The lithium secondary battery may have various shapes, such as cylindrical, rectangular, or pouch-type.

[0165] The lithium secondary battery may include a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0166] The electrodes to which the present invention applies are not particularly limited and can be manufactured in a form in which the electrode active material is bonded to the electrode current collector by conventional methods known in the industry.

[0167] Among the electrode active materials, non-restrictive examples of positive electrode active materials include conventional positive electrode active materials used in the positive electrodes of lithium secondary batteries, and in particular, lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or lithium composite oxides combining these materials can be used.

[0168] Among the electrode active materials, non-limiting examples of negative electrode active materials include conventional negative electrode active materials used in the negative electrodes of lithium secondary batteries, and in particular, lithium adsorbent materials such as lithium metal or lithium alloy, carbon, petroleum coke, activated carbon, graphite, or other carbon compounds can be used.

[0169] Non-limiting examples of positive electrode current collectors include foils made from aluminum, nickel, or combinations thereof, and non-limiting examples of negative electrode current collectors include foils made from copper, gold, nickel, or copper alloys, or combinations thereof.

[0170] In one embodiment of the present invention, the lithium secondary battery includes an electrolyte, and the electrolyte may include a lithium salt and an organic solvent for dissolving it. Furthermore, an organic solid electrolyte or an inorganic solid electrolyte can be used as the electrolyte.

[0171] The lithium salt can be any type commonly used in electrolytes for secondary batteries, and for example, as the anion of the lithium salt, F - Cl - , I - NO3 - , N(CN)2 - BF4 - ClO4 - PF6 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - CF3SO3 - CF3CF2SO3 - (CF3SO2)2N - , (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2) 2CH - (SF5)3C -(CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - , (CF3CF2SO2)2N - , or mixtures thereof can be used.

[0172] The organic solvent contained in the electrolyte can be any commonly used one without restriction. Typical examples include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, tetrahydrofuran, or mixtures thereof.

[0173] Furthermore, the electrolyte may be further enriched with, for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, etc., for the purpose of improving charge-discharge characteristics, flame retardancy, etc. In some cases, halogen-containing solvents such as carbon tetrachloride and trifluoroethylene may be further added to impart nonflammability, and carbon dioxide may be further added to improve high-temperature storage characteristics.

[0174] Examples of the organic solid electrolytes that can be used include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyagitation lysine, polyester sulfides, polyvinyl alcohol, polyvinylidene fluoride, and polymers containing ionic dissociation groups.

[0175] Examples of the inorganic solid electrolytes that can be used include lithium nitrides, halides, and sulfates such as Li3N, LiI, Li5NI2, Li3N-LiI-LiOH, LiSiO4, LiSiO4-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, and Li3PO4-Li2S-SiS2.

[0176] The injection of the electrolyte may be carried out at an appropriate stage in the battery manufacturing process, depending on the manufacturing process and required physical properties of the final product. That is, it can be applied before battery assembly or at the final stage of battery assembly.

[0177] The embodiments described above in this invention can be realized individually. Furthermore, it is of course possible to realize two or more embodiments in combination. Hereinafter, the invention will be described in detail with reference to specific examples. However, the embodiments of the present invention can be modified into various different forms, and the scope of the invention should not be construed as being limited to the embodiments detailed below. The embodiments of the present invention are provided to give a more complete explanation of the invention to a person with average knowledge in the art. [Examples]

[0178] Manufacturing Example 1 The first repeating unit, benzophenone methacrylate, and the second repeating unit, acryloyl morpholine, were prepared and added to the reaction vessel in a weight ratio of 1:99, and then added to the polymerization solvent. In addition, mercaptopropionic acid was added as a molecular weight modifier (CTA) at a concentration of approximately 5000 ppm relative to the monomer content. The polymerization solvent was a mixture of distilled water and ethanol in a weight ratio of 9:1. Thereafter, the reaction vessel was replaced with nitrogen (N2), and the temperature was raised to the starting temperature of 70°C. Potassium persulfate was added as an initiator, and the reaction proceeded for approximately 8 hours. After polymerization, the precipitated solid was washed with ethylacetate and dried in an oven at approximately 50°C to obtain a photoinitiated copolymer resin. The obtained photoinitiated copolymer resin had a molecular weight (Mw) of 11,600 and a PDI of 13.17. Furthermore, the Tg was confirmed to be approximately 170°C. The content of the first repeating unit was approximately 1 wt%, which was consistent with the amount added.

[0179] Manufacturing Example 2 Benzophenone methacrylate and acryloyl morpholine were prepared and added to a reaction vessel in a weight ratio of 1.5:98.5, then added to the polymerization solvent. Mercaptopropionic acid was added as a molecular weight modifier (CTA) at a concentration of approximately 5000 ppm relative to the monomer content. The polymerization solvent was a mixture of distilled water and ethanol in a weight ratio of 9:1. Subsequently, the reaction vessel was purged with nitrogen (N2), and the temperature was raised to the starting temperature of 70°C. Potassium persulfate was added as an initiator, and the reaction proceeded for approximately 8 hours. After polymerization, the precipitated solid was washed with ethylacetate and dried in an oven at approximately 50°C to obtain a photoinitiated copolymer resin. The obtained photoinitiated copolymer resin had a molecular weight (Mw) of 13,000 and a PDI of 13.5. The Tg was confirmed to be approximately 171°C. The content of the first repeating unit was approximately 1.5 wt%, which was consistent with the amount added.

[0180] Manufacturing Example 3 Benzophenone methacrylate and acryloyl morpholine were prepared and added to a reaction vessel in a weight ratio of 2.0:98, then added to the polymerization solvent. Mercaptopropionic acid was added as a molecular weight modifier (CTA) at a concentration of approximately 5000 ppm relative to the monomer content. The polymerization solvent was a mixture of distilled water and ethanol in a weight ratio of 9:1. The reaction vessel was then purged with nitrogen (N2) and heated to the starting temperature of 70°C. Potassium persulfate was added as an initiator, and the reaction was allowed to proceed for approximately 8 hours. After polymerization, the precipitated solid was washed with ethylacetate and dried in an oven at approximately 50°C to obtain a photoinitiated copolymer resin. The obtained photoinitiated copolymer resin had a molecular weight (Mw) of 17,000 and a PDI of 14.1. The Tg was confirmed to be approximately 172°C. The content of the first repeating unit was approximately 2.0 wt%, which was consistent with the amount added.

[0181] [Table 1]

[0182] Comparative Manufacturing Example 1 Acrylic acid was added to a reaction vessel and then to the polymerization solvent. Mercaptopropionic acid was added as a molecular weight modifier (CTA) at a concentration of approximately 8000 ppm relative to the monomer content. Distilled water was used as the polymerization solvent. The reaction vessel was then purged with nitrogen (N2) and the temperature was raised to the starting temperature of 70°C. Potassium persulfate was added as an initiator, and the reaction was allowed to proceed for approximately 8 hours. After polymerization, the precipitated solid was washed with ethylacetate and dried in an oven at approximately 50°C to obtain polyacrylic acid. Its molecular weight (Mw) was confirmed to be approximately 110,000, and its PDI was approximately 4.08. Its Tg was confirmed to be approximately 100°C.

[0183] Example 1 A coating layer-forming composition (solids content 35%) was prepared by mixing the photo-initiated copolymer resin, inorganic filler, binding binder resin, dispersant, and surfactant from the above-mentioned Production Example 1 with water as an aqueous dispersion medium. The types and contents of the components contained in the composition are shown in Table 2 below.

[0184] The composition was applied to a porous polyethylene film (thickness approximately 14.8 μm, porosity approximately 40% to 45%) using a Meyer bar, then dried. An exposure machine (Miltec HPI UV exposure machine) and a lamp (Miltec Arc lamp) were prepared, and ultraviolet light was irradiated onto the porous film coated with the composition until the integrated light intensity reached 5800 mJ / cm². 2 The separation membrane was fabricated by irradiating it with UV-A at a UV irradiation intensity of 50% of the UV light source. The organic / inorganic composite porous coating layer formed on the surface of the separation membrane had a thickness of approximately 3.3 μm.

[0185] Example 2 The separation membrane was manufactured in the same manner as in Example 1, except that the photo-initiated copolymer resin of Manufacturing Example 2 was used.

[0186] Example 3 The separation membrane was manufactured in the same manner as in Example 1, except that the photo-initiated copolymer resin of Manufacturing Example 3 was used.

[0187] Comparative Example 1 A coating layer-forming composition (solids content 35%) was prepared using a heat-resistant binder 1 (see Table 1 below) instead of a photoinitiated copolymer resin. The composition was applied to a porous polyethylene film (thickness approximately 14.5 μm, porosity approximately 40% to 45%) using a Meyer bar and then dried. The organic / inorganic composite porous coating layer formed on the surface of the separation membrane was approximately 3.3 μm thick.

[0188] Comparative Example 2 The polyacrylic acid produced in Comparative Production Example 1 was added to an aqueous NaOH solution to prepare a dispersion solution. At this time, the amount of NaOH was approximately 1 molar equivalent (1.0 eq.) relative to the carboxyl groups of the polyacrylic acid. + The glass transition temperature of polyacrylic acid containing a carboxylate at the substituted end was measured to rise to approximately 170°C. Subsequently, an inorganic filler, a binding binder resin, a dispersant, and a surfactant were added to the dispersion solution thus prepared to create a coating layer composition (solid content 35%). The composition was applied to a porous polyethylene film (thickness approximately 14.8 μm, porosity approximately 40%~45%) using a Meyer bar and then dried. The organic / inorganic composite porous coating layer formed on the surface of the separation membrane was approximately 3.3 μm thick.

[0189] [Table 2]

[0190] [Table 3]

[0191] Evaluation Example 1: Measurement of Contraction Rate The separation membranes obtained in Examples 1 to 3, Comparative Example 1, and Comparative Example 2 were cut into 5cm x 5cm sections to prepare samples. Four points were marked on each sample at 1.5cm intervals from the center. After placing the samples in a 150°C Mathis Oven for 30 minutes, they were removed, and the distance between the points on the separation membrane was measured with a ruler to calculate and confirm the shrinkage rate, which is summarized in Table 4 below. Referring to this, it was confirmed that the separation membranes from Examples 1 to 3 showed a shrinkage rate in the range of 7% to 13%, while the separation membranes from Comparative Example 1 and Comparative Example 2 showed a shrinkage rate of approximately 20% or more. Therefore, it was confirmed that the heat resistance is improved in separation membranes into which the photoinitiated copolymer resin according to the present invention is introduced. In the present invention, the shrinkage rate is expressed as a percentage of the difference between the distance between points before and after shrinkage relative to the distance between points before shrinkage.

[0192] [Table 4]

[0193] (Measurement of molecular weight) The molecular weight (weight-average molecular weight and number-average molecular weight) of the aforementioned photoinitiated copolymer resin was measured by gel permeation chromatography (GPC). An Agilent Technologies PL GPC220 was used, and the measurement conditions were as follows.

[0194] -Column(maker, model no.):2x TSKgel SupermultiporeHZ-M+TSKgel SuperHZ-2500 -Eluent:THF -Temperature: 40℃ -Flow rate: 1.0 mL / min -Injection volume, sample concentration: 30μl, 1~10mg / mL -Standard:Polystyrene -Detector:RI

[0195] (Measurement of the content of repeating units) The content of the repeating units was measured by 1H-NMR. This was confirmed by comparing the number of hydrogen peaks in the CH2 group of the main chain and the aromatic group of the side chains in the obtained polymer. A Bbruker (300 MHz) was used as the measurement instrument, with tetramethylsilane (TMS) as the reference material and CDCl3 (deuterated chloride) as the solvent. All spectral data were processed with MestReNova (Version 6.0.2).

[0196] (Measurement of glass transition temperature) The glass transition temperature (Tg) of the photoinitiated copolymer resin was measured using a Differential Scanning Calorimetry (TA Instrument) device. For each production example, Tg was obtained for 10 mg to 15 mg of sample, cooled from ambient temperature to -30°C, and then heated to 200°C at a rate of 10°C / min. After cooling to -30°C, the Tg was measured while reheating at a rate of 10°C / min.

Claims

1. A photoinitiated copolymer resin comprising, as a repeating unit, a first unit to which a functional group derived from an aromatic carbonyl compound is bonded, and a second unit having a hydrophilic group containing a nitrogen-containing ring and / or an amine group at its terminal end.

2. The photo-initiated copolymer resin according to claim 1, wherein the aromatic carbonyl compound comprises a benzophenone compound, a xanthone compound, a thioxanthone compound, or a combination of two or more thereof.

3. The photoinitiated copolymer resin according to claim 1, wherein the first unit comprises a repeating unit of chemical formula 1a, a repeating unit of chemical formula 1b, or both of these repeating units: 【Chemistry 1】 In the aforementioned chemical formulas 1a and 1b, X １ The bonds are single bonds or linear or branched alkylene groups (-CH) having 1 to 5 carbon atoms. ２ -) and at least one hydrogen atom of the alkylene group may be substituted with a linear or branched alkyl group having 1 to 3 carbon atoms. The aforementioned X ２ is hydrogen, or a linear or branched alkyl group having 1 to 5 carbon atoms. Said X ３ is R １ or R ２ or R １ R ２ and here, R １ is an alkylene group having 1 to 10 carbon atoms, -O-, -C(=O)-, -C(=O)-O-, -O-C(=O)-O-, -O-C(=O)-, -NH-, an ester group, an amide group, an alkoxy group or a carbonyl group; R ２ is an ester group, an amide group, an alkoxy group, a carbonyl group, a carboxyl group, -O-, -C(=O)-, -C(=O)-O-, -O-C(=O)-O-, -O-C(=O)-, -S-, -S(=O) ２ -, -S(=O) ２ -O-, -NH-, -NR ３ (R ３ is an alkyl group or an acyl group), -NH-C(=O)-, -C(=O)NH- and =N-, and is a divalent linking group containing at least one selected from the group consisting of X ４ It is oxygen or sulfur, The dashed line is X ３ This indicates a linkage, where the atom is bonded to the 2nd, 3rd, or 4th position of the aromatic ring.

4. The photoinitiated copolymer resin according to claim 1, wherein the first unit comprises the following chemical formulas 2a, 2b, 2c, 2d, or two or more combinations thereof; 【Chemistry 2】 【Transformation 3】 In the chemical formula 2d, X ５ It is either sulfur or oxygen.

5. The photoinitiated copolymer resin according to claim 1, wherein the second unit has hydrophilic groups linked to the main chain by amide bonds.

6. The photoinitiated copolymer resin according to claim 1, wherein the second unit includes a repeating unit represented by the following chemical formula 5: 【Chemistry 4】 Here, A １ The bonds are single bonds or linear or branched alkylene groups (-CH) having 1 to 5 carbon atoms. ２ -) and at least one hydrogen atom of the alkylene group may be substituted with a linear or branched alkyl group having 1 to 3 carbon atoms. A ２ is hydrogen, or a linear or branched alkyl group having 1 to 5 carbon atoms. A ３ Is there no (null), R １ or R ２ or R １ R ２ And here, R １ R is an alkylene group having 1 to 10 carbon atoms, -O-, -C(=O)-, -C(=O)-O-, -O-C(=O)-O-, -O-C(=O)-, -NH-, an ester group, an amide group, an alkoxy group, or a carbonyl group, ２ These are ester groups, amide groups, alkoxy groups, carbonyl groups, carboxyl groups, -O-, -C(=O)-, -C(=O)-O-, -O-C(=O)-O-, -O-C(=O)-, -S-, -S(=O) ２ -, -S (=O) ２ -O-, -NH-, -NR ３ (R ３ A is a divalent linking group comprising at least one selected from the group consisting of an alkyl group or acyl group, -NH-C(=O)-, -C(=O)NH-, and =N-, where A ３ If there is no (null), it means that (L) is a single bond directly bonded to a carbon in the main chain. The (L) has a hydrophilic group containing a nitrogen-containing ring and / or an amine group at its terminal end.

7. The hydrophilic groups are derived from morpholine, piperidine, oxazolidine, thioxazolidine, ethyleneimine, pyrrole, imidazole, diazetidine, dithiazine, azocane, azonane, and -N Ｒ 4R ５ , or including two or more of these, the R ４ and R ５ The photo-initiated copolymer resin according to claim 1, wherein each of them is independently hydrogen or an alkyl group having 1 to 10 carbon atoms.

8. The photoinitiated copolymer resin according to claim 6, wherein the second unit comprises a repeating unit represented by chemical formula 5a, a repeating unit represented by chemical formula 5b, or both thereof: 【Transformation 5】 In the above chemical formula 5a, A ４ is oxygen (O), sulfur (S), or phosphorus (P), A ５ This is an alkenylene group having 1 to 5 carbon atoms (-(CH ２ ) - ) is.

9. The photo-initiated copolymer resin comprises a compound represented by the following chemical formula 7a and / or a compound represented by the chemical formula 7b, wherein the first unit is included in an amount of 10 wt% or less relative to 100 wt% of the photo-initiated copolymer resin, according to claim 1: 【Transformation 6】

10. The photo-initiated copolymer resin according to claim 1, wherein the content of the first repeating unit is 10 wt% or less with respect to 100 wt% of the total photo-initiated copolymer resin.

11. The photo-initiated copolymer resin according to claim 1, wherein the photo-initiated copolymer resin has a glass transition temperature of 130°C to 220°C.

12. The photo-initiated copolymer resin according to claim 1, wherein the photo-initiated copolymer resin has a molecular weight of 0.5 million to 100,000.

13. The photo-initiated copolymer resin is the photo-initiated copolymer resin according to claim 1, wherein the PDI is 7 to 20.

14. The material comprises a crosslinked olefin polymer porous support having a crosslinked structure in which polymer chains are directly linked, a binder resin, and an inorganic filler. A crosslinked structure-containing separation membrane for lithium secondary batteries, wherein the binder resin comprises the photoinitiated copolymer resin described in claim 1, and the photoinitiated copolymer resin is present in an amount of 50 wt% or more relative to 100 wt% of the binder resin.

15. The separation membrane comprises a crosslinked structure-containing olefin polymer porous support and an organic / inorganic composite porous coating layer located on at least one surface of the porous support. The photo-initiated copolymer resin is included in one or more of the crosslinked structure-containing olefin polymer porous support and the organic / inorganic composite porous coating layer. The organic / inorganic composite porous coating layer comprises a binder resin and an inorganic filler, wherein the inorganic filler is present in an amount of 70 wt% or more relative to 100 wt% of the organic / inorganic composite porous coating layer, according to claim 14, a crosslinked structure-containing separation membrane for lithium secondary batteries.

16. The separation membrane containing a crosslinked structure for a lithium secondary battery according to claim 15, characterized in that the photo-initiated copolymer resin is contained in an amount of 0.1 to 5 parts by weight per 100 parts by weight of the inorganic filler.

17. A lithium secondary battery 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 a cross-linked structure-containing separation membrane for lithium secondary batteries as described in claim 14.

18. A step of coating an olefin polymer porous support with a composition comprising a photoinitiated copolymer resin, an inorganic filler, and an aqueous dispersion medium, by applying and drying the composition, The step of irradiating an olefin polymer porous support coated with the composition with ultraviolet light, A method for producing a crosslinked structure-containing separation membrane for lithium secondary batteries, characterized in that the photo-initiated copolymer resin is the photo-initiated copolymer resin described in claim 1.

19. In the step of irradiating with ultraviolet light, the amount of ultraviolet light irradiated is 10 mJ / cm². ２ 20,000mJ / cm or more ２ A method for producing a crosslinked structure-containing separation membrane for lithium secondary batteries according to claim 18, characterized in that it is as follows.

20. The photo-initiated copolymer resin comprises, as a first repeating unit, a repeating unit represented by the following chemical formula 2a, a repeating unit represented by the following chemical formula 2b, or both thereof, and as a second repeating unit, a repeating unit represented by the chemical formula 5a, wherein the first repeating unit is included in an amount of 10 wt% or less relative to 100 wt% of the photo-initiated copolymer resin, according to claim 1: 【Transformation 7】 【Transformation 8】 In the above chemical formula 5a, A ４ is oxygen (O), sulfur (S), or phosphorus (P), A ５ This is an alkenylene group having 1 to 5 carbon atoms (-(CH ２ ) - ) is.

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