KR20220152084A - Method for manufacturing a separator containing cross-linked structure for a lithium secondary battery, a separator containing cross-linked structure for a lithium secondary battery manufactured by the method, and a lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a preparation method of a crosslinked structure-containing separator for a lithium secondary battery, a crosslinked structure-container separator for a lithium secondary battery produced thereby, and a lithium secondary battery including the same, wherein an optical initiator is included, and the method includes a step of radiating UV rays to a porous olefin polymer support having, per 1000 carbon atoms, 0.01 to 0.5 double bonds present in olefin polymer chains as measured by H-NMR, wherein the content of the optical initiator is 0.015 to 0.36 parts by weight compared to 100 parts by weight of the porous olefin polymer support. By controlling the number of double bonds present in the olefin polymer chains, the porous olefin polymer support can be effectively crosslinked while side reactions can be minimized.

Description

A method for manufacturing a separator containing a cross-linked structure for lithium secondary batteries, a separator containing a cross-linked structure for lithium secondary batteries manufactured thereby, and a lithium secondary battery including the same CROSS-LINKED STRUCTURE FOR A LITHIUM SECONDARY BATTERY MANUFACTURED BY THE METHOD, AND A LITHIUM SECONDARY BATTERY COMPRISING THE SAME}

The present invention relates to a method for manufacturing a separator containing a crosslinked structure for a lithium secondary battery, a separator containing a crosslinked structure for a lithium secondary battery manufactured according to the method, and a lithium secondary battery including the same.

Recently, interest in energy storage technology is increasing. As the field of application expands to cell phones, camcorders, notebook PCs, and even electric vehicles, the demand for high energy density of batteries used as power sources for these electronic devices is increasing. A lithium secondary battery is a battery that can best satisfy these demands, and research on this is being actively conducted.

These lithium secondary batteries are composed of a positive electrode, a negative electrode, an electrolyte solution, and a separator. Among them, the separator has high ionic conductivity to increase the permeability of lithium ions based on insulation and high porosity to electrically insulate the positive electrode and the negative electrode. is required

As such a separator, an olefin polymer separator is widely used. In the case of an ethylene polymer (PE) separator, which is a representative olefin polymer separator, the melting point (Tm) is low, so when the battery temperature rises above the melting point of the ethylene polymer in an environment where the battery is misused A melt-down phenomenon may occur, which may cause ignition and explosion, and due to its material characteristics and manufacturing process characteristics, the separator exhibits extreme thermal contraction behavior in situations such as high temperatures, resulting in internal short circuits, etc. It has safety issues.

Therefore, there is a very high need for a separation membrane capable of ensuring safety at high temperatures.

The problem to be solved by the present invention is to provide a method for producing a separator containing a crosslinked structure for a lithium secondary battery capable of effectively crosslinking an olefin polymer porous support while minimizing side reactions.

Another problem to be solved by the present invention is to provide a separator containing a cross-linked structure for a lithium secondary battery having improved high-temperature safety and a lithium secondary battery having the same.

In order to solve the above problems, according to an aspect of the present invention, a method for manufacturing a separator containing a cross-linked structure for a lithium secondary battery according to the following embodiments is provided.

In the first embodiment,

Preparing an olefin polymer porous support comprising a photoinitiator and having 0.01 to 0.5 double bonds per 1000 carbon atoms in an olefin polymer chain as measured by H-NMR;

Including; irradiating ultraviolet rays to the olefin polymer porous support,

The content of the photoinitiator relates to a method for producing a separator containing a crosslinked structure for a lithium secondary battery, characterized in that 0.015 parts by weight to 0.36 parts by weight based on 100 parts by weight of the olefin polymer porous support.

The second embodiment, in the first embodiment,

An antioxidant may be further added in the step of preparing the olefin polymer porous support, and the content of the antioxidant may be 500 ppm to 20000 ppm based on the content of the olefin polymer porous support.

In the third embodiment, in the second embodiment,

The antioxidant may include a first antioxidant that is a radical scavenger and a second antioxidant that is a peroxide decomposer.

In the fourth embodiment, in the third embodiment,

The first antioxidant may include a phenol-based antioxidant, an amine-based antioxidant, or a mixture thereof.

In the fifth embodiment, in the third embodiment or the fourth embodiment,

The second antioxidant may include a phosphorus-based antioxidant, a sulfur-based antioxidant, or a mixture thereof.

In the sixth embodiment, in any one of the third to fifth embodiments,

The content of the first antioxidant is 500 ppm to 10000 ppm based on the content of the olefin polymer porous support, and the content of the second antioxidant is 500 ppm to 10000 ppm based on the content of the olefin polymer porous support have.

In the seventh embodiment, in any one of the first to sixth embodiments,

The photoinitiator may include a Type 2 photoinitiator.

In the eighth embodiment, in any one of the first to seventh embodiments,

The photoinitiator may include thioxanthone (TX), a thioxanthone derivative, benzophenone (BPO), a benzophenone derivative, or two or more thereof.

In the ninth embodiment, in any one of the first to eighth embodiments,

The step of preparing the olefin polymer porous support,

A step of coating and drying the photocrosslinking composition containing the photoinitiator and the solvent on the outside of the olefin polymer porous support may be included.

In the tenth embodiment, in the ninth embodiment,

The composition for photocrosslinking may be a photoinitiator solution composed of the photoinitiator and the solvent.

In the eleventh embodiment, in the ninth embodiment,

The photocrosslinking composition may be a slurry for forming an inorganic hybrid void layer including an inorganic filler, a binder polymer, the photoinitiator, and the solvent.

In the twelfth embodiment, in the ninth embodiment,

The step of coating and drying the photocrosslinking composition containing the photoinitiator and the solvent on the outside of the olefin polymer porous support,

Forming an inorganic hybrid void layer by coating and drying at least one surface of the olefin polymer porous support with a slurry for forming an inorganic hybrid void layer containing an inorganic filler, a first binder polymer, and a dispersion medium; and

It may include coating and drying a coating solution for forming a porous adhesive layer containing a second binder polymer, the photoinitiator, and the solvent on the upper surface of the inorganic hybrid porous layer.

In the thirteenth embodiment, in any one of the first to twelfth embodiments,

The irradiation amount of the ultraviolet light may be 10 to 2000 mJ/cm ² .

In order to solve the above problems, according to an aspect of the present invention, cross-linked structure-containing separators for lithium secondary batteries of the following embodiments are provided.

The fourteenth embodiment,

It relates to a separator containing a crosslinked structure for a lithium secondary battery, characterized in that it includes the crosslinked structure-containing olefin polymer porous support prepared according to any one of the first to thirteenth embodiments.

The fifteenth embodiment is the fourteenth embodiment,

The crosslinked structure-containing separator for a lithium secondary battery may be located on at least one surface of the crosslinked structure-containing olefin polymer porous support and include an inorganic hybrid porous layer including an inorganic filler and a binder polymer.

In the 16th embodiment, in the 14th embodiment,

an inorganic hybrid porous layer in which the crosslinked structure-containing separator for lithium secondary battery is located on at least one surface of the crosslinked structure-containing olefin polymer porous support and includes an inorganic filler and a first binder polymer; and

It may include; a porous adhesive layer located on the inorganic hybrid void layer and containing a second binder polymer.

In the 17th embodiment, in any one of the 14th to 16th embodiments,

The meltdown temperature of the crosslinked structure-containing separator for a lithium secondary battery may be 160° C. or higher.

In the eighteenth embodiment, in any one of the fourteenth to seventeenth embodiments,

A shutdown temperature of the separator containing a cross-linked structure for a lithium secondary battery may be 145° C. or less.

In order to solve the above problems, according to an aspect of the present invention, a lithium secondary battery of the following embodiment is provided.

The 19th embodiment,

Including a positive electrode, a negative electrode, and a separator for a lithium secondary battery interposed between the positive electrode and the negative electrode,

It relates to a lithium secondary battery, characterized in that the separator for a lithium secondary battery is a crosslinked structure-containing separator for a lithium secondary battery according to any one of the 14th to 18th embodiments.

In the method for producing a separator containing a crosslinked structure for a lithium secondary battery according to an embodiment of the present invention, the content of the photoinitiator is 0.015 parts by weight to 0.36 parts by weight based on 100 parts by weight of the olefin polymer porous support, and when measured by H-NMR, the olefin polymer chain By crosslinking the olefin polymer porous support having 0.01 to 0.5 double bonds per 1000 carbon atoms, the olefin polymer porous support can be effectively crosslinked and side reactions can be minimized.

The cross-linked structure-containing separator for lithium secondary batteries prepared according to the method for manufacturing a cross-linked structure-containing separator for lithium secondary batteries according to an embodiment of the present invention comprises a cross-linked structure-containing olefin polymer porous support having a cross-linked structure in which polymer chains are directly connected. Including can have excellent high temperature safety.

Hereinafter, preferred embodiments of the present invention will be described in detail. Prior to this, the terms or words used in this specification and claims should not be construed as being limited to the usual or dictionary meaning, and the inventor appropriately uses the concept of the term in order to explain his/her invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of the present invention based on the principle that it can be defined.

Therefore, since the configurations described in the embodiments of this specification are only one of the most preferred embodiments of the present invention and do not represent all of the technical ideas of the present invention, various equivalents and modifications that can replace them at the time of this application It should be understood that there may be examples.

Terms such as "first" and "second" are used to distinguish one component from another, and each component is not limited by the terms.

A method for manufacturing a separator containing a cross-linked structure for a lithium secondary battery according to an aspect of the present invention,

Preparing an olefin polymer porous support comprising a photoinitiator and having 0.01 to 0.5 double bonds per 1000 carbon atoms in an olefin polymer chain as measured by H-NMR;

Including; irradiating ultraviolet rays to the olefin polymer porous support,

The content of the photoinitiator is characterized in that 0.015 parts by weight to 0.36 parts by weight relative to 100 parts by weight of the olefin polymer porous support.

Hereinafter, a method for manufacturing a separator containing a cross-linked structure for a lithium secondary battery according to an embodiment of the present invention will be mainly reviewed.

First, an olefin polymer porous support containing a photoinitiator and having 0.01 to 0.5 double bonds present in the olefin polymer chain as measured by H-NMR is prepared per 1000 carbon atoms.

In the present invention, a photoinitiator is introduced to the surface of the porous olefin polymer support so that the porous olefin polymer support can be cross-linked when irradiated with ultraviolet light. 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 existing inside the olefin polymer porous support.

The photoinitiator directly photocrosslinks polymer chains in the olefin polymer porous support. The photoinitiator can crosslink the olefin polymer porous support with only the photocrosslinking initiator without other components such as a crosslinking agent or a co-initiator or a synergist. As hydrogen atoms in the photoinitiator are removed by hydrogen abstraction only through light absorption, the photoinitiator becomes a reactive compound, and this photoinitiator forms radicals in the polymer chain in the olefin polymer porous support to make the polymer chain reactive, These are directly connected to each other to enable photocrosslinking.

In the method for manufacturing a separator having a crosslinked structure for a lithium secondary battery according to an embodiment of the present invention, by using the photoinitiator, radicals can be generated in the polymer chains in the olefin polymer porous support to form a crosslinked structure in which polymer chains are directly connected. can do.

Since the photoinitiator serves to form radicals in the polymer chain in the olefin polymer porous support, the content of the photoinitiator plays a very important role in radical formation.

When radicals are excessively generated, crosslinking between photoinitiators or photoinitiator and polymer chains may crosslink each other. Such a crosslinked structure has a lower reaction enthalpy than a crosslinked structure between polymer chains in an olefin polymer porous support, so that the battery is charged and discharged. It may decompose and cause a side reaction. In addition, when the photoinitiator and the polymer chain are cross-linked, the melting temperature of the olefin polymer chain is lowered and properties of the separator such as shutdown temperature are deteriorated, which is not preferable.

In the present invention, by adjusting the content of the photoinitiator to minimize the side reaction when crosslinking the olefin polymer porous support. In the present invention, the content of the photoinitiator is 0.015 parts by weight to 0.36 parts by weight relative to 100 parts by weight of the olefin polymer porous support. When the content of the photoinitiator satisfies the aforementioned range, the olefin polymer porous support can be effectively cross-linked while preventing side reactions caused by excessive generation of radicals. For example, crosslinking between photoinitiators due to excessive generation of radicals or crosslinking between the photoinitiator and polymer chains does not occur, and side reactions can be prevented by allowing crosslinking to occur only between polymer chains.

In addition, it is possible to prevent a phenomenon in which the separator shrinks due to rapid cross-linking reaction due to excessive generation of radicals. Accordingly, it is possible to prevent a decrease in air permeability of the olefin polymer porous support after crosslinking.

In addition, it is possible to prevent sacrificing the mechanical strength of the olefin polymer porous support due to excessive main chain scission of the olefin polymer.

If the content of the photoinitiator is less than 0.015 parts by weight relative to 100 parts by weight of the olefin polymer porous support, it is difficult to form radicals enough to sufficiently crosslink the olefin polymer porous support, so that the crosslinking of the olefin polymer porous support does not proceed smoothly. .

When the content of the photoinitiator exceeds 0.36 parts by weight based on 100 parts by weight of the olefin polymer porous support, the olefin polymer porous support can be crosslinked, but excessive radicals are generated and side reactions occur. For example, crosslinking between photoinitiators or crosslinking between photoinitiators and olefin polymer chains may occur. In addition, when irradiated with ultraviolet rays, a crosslinking reaction occurs rapidly, resulting in shrinkage of the separator and main chain scission of the olefin polymer, resulting in a decrease in mechanical strength.

In one embodiment of the present invention, the content of the photoinitiator is 0.015 parts by weight to 0.3 parts by weight, or 0.015 parts by weight to 0.09 parts by weight, or 0.015 parts by weight to 0.07 parts by weight based on 100 parts by weight of the olefin polymer porous support, or It may be 0.018 parts by weight to 0.0365 parts by weight. When the content of the photoinitiator satisfies the aforementioned range, it is possible to effectively cross-link the porous olefin polymer support and prevent side reactions from occurring due to excessive generation of radicals.

The content of the photoinitiator based on 100 parts by weight of the porous olefin polymer support can be obtained by measuring the content of the photo initiator filling the entire pore volume of the porous olefin polymer support. For example, assuming that the solvent described below fills 100% of the total pore volume of the olefin polymer porous support and there is no solvent for the second binder polymer present on the surface of the olefin polymer porous support, the olefin polymer from the density of the solvent The weight of the solvent contained in the total pore volume of the porous support can be obtained, and the content of the photoinitiator relative to 100 parts by weight of the olefin polymer porous support can be obtained from the content of the photoinitiator contained in the solvent.

In one embodiment of the present invention, the photoinitiator may include a Type 2 photoinitiator.

In one embodiment of the present invention, the photoinitiator may include thioxanthone (TX: Thioxanthone), a thioxanthone derivative, benzophenone (BPO: benzophenone), a benzophenone derivative, or two or more thereof.

The thioxanthone derivatives are, for example, 2-isopropylthioxanthone, 2-chlorothioxanthone, 2-dodecylthioxanthone, 2,4-diethylthioxanthone, 2,4-dimethylthioxanthone, 1- Methoxycarbonylthioxanthone, 2-ethoxycarbonylthioxanthone, 3-(2-methoxyethoxycarbonyl)-thioxanthone, 4-butoxycarbonyl-thioxanthone, 3-butoxycarbonyl -7-methylthioxanthone, 1-cyano-3-chlorothioxanthone, 1-ethoxycarbonyl-3-chlorothioxanthone, 1-ethoxycarbonyl-3-ethoxythioxanthone, 1- Ethoxy-carbonyl-3-aminothioxanthone, 1-ethoxycarbonyl-3-phenylsulfurylthioxanthone, 3,4-di[2-(2-methoxyethoxy)ethoxycarbonyl]thio Oxanthone, 1-ethoxycarbonyl-3-(1-methyl-1-morpholino-ethyl)-thioxanthone, 2-methyl-6-dimethoxymethyl-thioxanthone, 2-methyl-6- (1,1-dimethoxy-benzyl)-thioxanthone, 2-morpholinomethylthioxanthone, 2-methyl-6-morpholinomethyl-thioxanthone, N-allylthioxanthone-3,4 -Dicarboximide, N-octylthioxanthone-3,4-dicarboximide, N-(1,1,3,3-tetramethylbutyl)-thioxanthone-3,4-dicarboximide, 1- Phenoxythioxanthone, 6-ethoxycarbonyl-2-methoxythioxanthone, 6-ethoxycarbonyl-2-methylthioxanthone, thioxanthone-2-polyethylene glycol ester, 2-hydroxy-3- (3,4-dimethyl-9-oxo-9H-thioxanthon-2-yloxy)-N,N,N-trimethyl-1-propanaminium chloride, and the like, but is not limited thereto.

The benzophenone derivatives are, for example, 4-phenylbenzophenone, 4-methoxybenzophenone, 4,4'-dimethoxy-benzophenone, 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-methoxy-benzophenone, methyl-2-benzoyl benzoate, 4-(2-hydroxyethylthio)-benzophenone, 4-(4-tolylthio)benzophenone, 4-benzoyl -N,N,N-trimethylbenzenemethanaminium chloride, 2-hydroxy-3-(4-benzoylphenoxy)-N,N,N-trimethyl-propanaminium chloride monohydrate, 4-hydroxy benzophenone , 4-(13-acryloyl-1,4,7,10,13-pentaoxatridecyl)-benzophenone, 4-benzoyl-N,N-dimethyl-N-[2-(1-oxo-2 -propenyl)oxy]ethyl-benzenemethanaminium chloride and the like, but are not limited thereto.

In particular, when the photoinitiator includes 2-isopropyl thioxanthone, thioxanthone, or a mixture thereof, a smaller amount of light than when using a photoinitiator such as benzophenone, such as 500 mJ/cm ² , olefins Photocrosslinking of the polymeric porous support is possible, which can be more advantageous in terms of mass production.

In addition, when the photoinitiator includes 2-isopropyl thioxanthone (ITX), the melting point of ITX is as low as about 70 ° C to 80 ° C, and the photocrosslinking temperature condition is adjusted to 80 ° C to 100 ° C In the case of melting the ITX on the surface of the olefin polymer porous support, the mobility of ITX into the olefin polymer porous support occurs, so that the crosslinking efficiency can be increased, and it is easy to prevent the change in physical properties of the final separation membrane. can

The olefin polymer porous support is a conventional method known in the art to secure excellent air permeability and porosity from the above-mentioned olefin polymer material, such as a wet method using a solvent, diluent or pore former, or a dry method using a stretching method It can be prepared by forming pores through.

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

In one embodiment of the present invention, the olefin polymer is an ethylene polymer; propylene polymer; butylene polymer; pentene polymer; hexene polymer; octene polymer; copolymers of two or more of ethylene, propylene, butene, pentene, 4-methylpentene, hexene, and octene; or mixtures thereof.

Non-limiting examples of the ethylene polymer include low-density ethylene polymer (LDPE), linear low-density ethylene polymer (LLDPE), high-density ethylene polymer (HDPE), etc., wherein the ethylene polymer has a high crystallinity and a high melting point of the resin. In this case, it may be easier to increase the modulus while having a desired level of heat resistance.

In one embodiment of the present invention, the weight average molecular weight of the olefin polymer may be 200,000 to 1,500,000, or 220,000 to 1,000,000, or 250,000 to 800,000, or 250,000 to 600,000. When the weight average molecular weight of the olefin polymer is within the above range, a separator having excellent strength and heat resistance can be finally obtained while securing uniformity and membrane formation processability of the porous olefin polymer support.

The weight average molecular weight may be measured by gel permeation chromatography (GPC, PL GPC220, Agilent Technologies) under the following conditions.

- Column: PL Olexis (Polymer Laboratories)

- Solvent: TCB (Trichlorobenzene)

- Flow rate: 1.0 ml/min

- Sample concentration: 1.0 mg/ml

- Injection amount: 200 μl

- Column temperature: 160 ℃

- Detector: Agilent High Temperature RI detector

- Standard: Polystyrene (correction with cubic function)

The photoinitiator is capable of separating hydrogen from a small amount of double bond structure present in the olefin polymer chain, and radicals are formed in the polymer chain as hydrogen atoms are removed from the double bond structure of the olefin polymer chain by hydrogen separation reaction only by light absorption. Therefore, the inventors of the present invention completed the present invention by finding that the amount of double bonds present in the olefin polymer chain affects the crosslinking of the olefin polymer chain in addition to the amount of the photoinitiator.

In the present invention, in the olefin polymer porous support, the number of double bonds present in the olefin polymer chain is 0.01 per 1000 carbon atoms as measured by H-NMR. to 0.5 pieces. Since the olefin polymer porous support has the number of double bonds in the above-mentioned range in the olefin polymer chain, it is possible to control the radical formed by the hydrogen separation reaction by the photoinitiator from the double bond structure present in the olefin polymer chain. It is possible to effectively cross-link the porous support while minimizing the occurrence of side reactions due to excessive generation of radicals.

In the present invention, by adjusting the number of double bonds present in the olefin polymer chain to control the radicals formed therefrom, photoinitiators crosslink each other or the photoinitiator and the polymer chain are not crosslinked, but crosslinking occurs only between the polymer chains, thereby preventing such a side reaction. It can be prevented.

In addition, it is possible to prevent a phenomenon in which the separator shrinks due to rapid cross-linking reaction due to excessive generation of radicals. Accordingly, it is possible to prevent a decrease in air permeability of the olefin polymer porous support after crosslinking.

In addition, it is possible to prevent sacrificing the mechanical strength of the olefin polymer porous support due to excessive main chain scission of the olefin polymer.

If the number of double bonds present in the olefin polymer chain is less than 0.01 per 1000 carbon atoms, it is difficult to form radicals from the double bonds to the extent that the olefin polymer porous support can be sufficiently crosslinked, resulting in crosslinking of the olefin polymer porous support. is difficult to proceed smoothly.

If the number of double bonds present in the olefin polymer chain exceeds 0.5, the olefin polymer porous support can be crosslinked, but excessive radicals are generated and side reactions occur. For example, crosslinking between photoinitiators or crosslinking between photoinitiators and olefin polymer chains may occur. In addition, when irradiated with ultraviolet rays, a crosslinking reaction occurs rapidly, resulting in shrinkage of the separator and main chain scission of the olefin polymer, resulting in a decrease in mechanical strength.

In one embodiment of the present invention, the number of double bonds present in the olefin polymer chain of the olefin polymer porous support may be 0.01 to 0.3 per 1000 carbon atoms as measured by H-NMR. When the olefin polymer porous support has the number of double bonds in the above-mentioned range, it is possible to effectively cross-link the olefin polymer porous support, and it is easier to minimize the occurrence of side reactions due to excessive generation of radicals. In addition, it may be easier to prevent a decrease in mechanical strength of a finally manufactured separator containing a cross-linked structure for a lithium secondary battery.

The double bond structure present in the olefin polymer chain may be present at the terminal of the olefin polymer chain or inside the olefin polymer chain, that is, throughout the olefin polymer chain except for the terminal. In particular, the number of double bond structures present in the olefin polymer chain excluding terminals may affect the crosslinking of the olefin polymer chain.

In one embodiment of the present invention, the number of double bonds present in the olefin polymer chain excluding terminals of the olefin polymer porous support may be 0.005 to 0.49 per 1000 carbon atoms. The above "double bonds present in the olefin polymer chain excluding terminals" refers to double bonds present throughout the olefin polymer chain except for the ends of the olefin polymer chain. Here, "terminus" means the position of a carbon atom connected to both extreme ends of the olefin polymer chain, respectively.

In one embodiment of the present invention, the number of double bonds present in the olefin polymer chain can be controlled by adjusting the type of catalyst, purity, addition of a linking agent, etc. during synthesis of the olefin polymer.

In one embodiment of the present invention, the olefin polymer porous support has a BET specific surface area of 10 m ² /g to 27 m ² /g, 13 m ² /g to 25 m ² /g, or 15 m ² /g to 23 m ² /g. When the BET specific surface area of the olefin polymer porous support satisfies the above range, the surface area of the olefin polymer porous support increases, making it easier to increase the crosslinking efficiency of the olefin polymer porous support even when a small amount of photoinitiator is used can do.

The BET specific surface area of the olefin polymer porous support can be measured by the BET method. Specifically, the BET specific surface area of the inorganic particles can be calculated from the nitrogen gas adsorption amount under liquid nitrogen temperature (77K) using BELSORP-mino II manufactured by BEL Japan.

In one embodiment of the present invention, the olefin polymer porous support,

supplying an olefin polymer having 0.01 to 0.5 double bonds per 1000 carbon atoms as measured by H-NMR and a diluent to an extruder;

Extruding the olefin polymer composition from the extruder;

molding and stretching the extruded olefin polymer composition into a sheet form by passing it through a die and a cooling roll;

preparing a preliminary porous support by extracting the diluent from the stretched sheet; and

It may be prepared from a manufacturing method comprising the step of preparing an olefin polymer porous support by heat-setting the preliminary porous support.

In one embodiment of the present invention, the diluent is paraffin; wax; soybean oil; 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 alcohols having 10 to 20 carbon atoms, such as palmitic acid alcohol, stearic acid alcohol, and oleic acid alcohol; Palmitic acid mono-, di-, or triesters, stearic acid mono-, di-, or triesters. Saturated or unsaturated fatty acids having 4 to 26 carbon atoms in the fatty acid group, such as oleic acid mono-, di-, or triesters, linoleic acid mono-, di-, or triesters, or one unsaturated fatty acid whose double bond is substituted with an epoxy. or two or more fatty acids, fatty acid esters having 1 to 8 hydroxyl groups and ester-bonded alcohols having 1 to 10 carbon atoms; or two or more of these.

The weight ratio of the olefin polymer to the diluent may be 50:50 to 20:80, or 40:60 to 30:70. When the weight ratio of the olefin polymer to the diluent satisfies the above range, it is possible to secure an appropriate level of porosity and average pore size of the finally prepared olefin polymer porous support, and the pores are interconnected to improve permeability It can be, it is possible to secure a level of viscosity that is easy to process by preventing an increase in the extrusion load, and the olefin polymer is extruded in a gel form without being thermodynamically mixed with the diluent, causing problems such as breakage and uneven thickness during stretching can prevent doing so. In addition, it can be easily prevented from lowering the strength of the finally prepared olefin polymer porous support.

In addition to the olefin polymer and the diluent, an antioxidant may be further added to the extruder. Antioxidants can control the crosslinking reaction between polymer chains by controlling radicals formed in olefin polymer chains. The antioxidant may be oxidized instead of the polymer chain to prevent oxidation of the polymer chain or absorb the generated radical to control the crosslinking reaction between the polymer chains.

Accordingly, when the olefin polymer porous support further includes an antioxidant, the number of double bonds present in the olefin polymer chain, excluding the terminal, is primarily controlled to prevent excessive generation of radicals, and secondarily, oxidation By controlling the radicals generated by the inhibitor to terminate the reaction, it may be easier to prevent side reactions.

In one embodiment of the present invention, the content of the antioxidant may be 500 ppm to 20000 ppm, or 1000 ppm to 15000 ppm, or 2000 ppm to 13000 ppm based on the content of the olefin polymer porous support. When the content of the antioxidant satisfies the above-mentioned range, it is possible to sufficiently control the radicals that are excessively generated by the antioxidant, making it easy to prevent the problem of side reactions, but the surface of the olefin polymer porous support is non-uniform. can be easily prevented.

These antioxidants are largely divided into a radical scavenger that reacts with radicals generated in olefin polymers to stabilize olefin polymers, and a peroxide decomposer that decomposes peroxides generated by radicals into stable molecules. can be classified. The radical scavenger releases hydrogen to stabilize the radical and itself becomes a radical, but may remain in a stable form through a resonance effect or rearrangement of electrons. When the peroxide decomposer is used in combination with the radical scavenger, a more excellent effect can be exhibited.

In one embodiment of the present invention, the antioxidant may include a first antioxidant that is a radical scavenger and a second antioxidant that is a peroxide decomposer. Since the first antioxidant and the second antioxidant have different mechanisms of action, the antioxidant simultaneously includes the first antioxidant, which is a radical scavenger, and the second antioxidant, which is a peroxide decomposer, thereby eliminating unnecessary radicals due to the synergistic effect of the antioxidants. Production inhibition may be easier.

The content of the first antioxidant and the second antioxidant may be the same or different.

In one embodiment of the present invention, the first antioxidant may include a phenol-based antioxidant, an amine-based antioxidant, or a mixture thereof.

The phenolic antioxidants are 2,6-di-t-butyl-4-methylphenol, 4,4'-thiobis (2-t-butyl-5-methylphenol), 2,2'-thiodiethyl Bis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate], pentaerythritol-tetrakis-[3-(3,5-di-t-butyl-4 -hydroxyphenyl)-propionate] (Pentaerythritol tetrakis (3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate), 4,4'-thiobis (2-methyl-6-t- butylphenol), 2,2'-thiobis(6-t-butyl-4-methylphenol), octadecyl-[3-(3,5-di-t-butyl-4-hydroxyphenyl)-propio nate], triethylene glycol-bis-[3-(3-t-butyl-4-hydroxy-5-methylphenol)propionate], thiodiethylene bis[3-(3,5-di-t- Butyl-4-hydroxyphenyl) propionate], 6,6'-di-t-butyl-2,2'-thiodi-p-cresol, 1,3,5-tris(4-t-butyl- 3-hydroxy-2,6-xylyl)methyl-1,3,5-triazine-2,4,6-(1H,3H,5H)-trione, dioctadecyl 3,3'-thiodi propionate, or two or more of these.

In one embodiment of the present invention, the content of the first antioxidant is 500 ppm to 10000 ppm, or 1000 ppm based on the content of the olefin polymer porous support to 12000 ppm, or 1000 ppm to 10000 ppm. When the content of the first antioxidant satisfies the aforementioned range, it may be easier to prevent side reactions caused by excessive generation of radicals.

In one embodiment of the present invention, the second antioxidant may include a phosphorus-based antioxidant, a sulfur-based antioxidant, or a mixture thereof.

The phosphorus-based antioxidant decomposes peroxide to form alcohol and changes to phosphate. The phosphorus antioxidant is 3,9-bis (2,6-di-t-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphaspiro [5,5 ]Undecane (3,9-Bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane), bis(2, 6-dicumylphenyl) pentaerythritol diphosphite (Bis (2,4-dicumylphenyl) pentaerythritol diphosphate), 2,2'-methylenebis (4,6-di-t-butylphenyl) 2-ethylhexyl phosphite (2 ,2'-Methylenebis(4,6-di-tert-butylphenyl) 2-ethylhexyl phosphite), bis(2,4-di-t-butyl-6-methylphenyl)-ethyl-phosphite (bis(2,4- di-tert-butyl-6-methylphenyl)-ethyl-phosphite), bis(2,6-di-t-butyl-4-methylphenyl) pentaerythritol diphosphite, bis(2,4-di-t-butylphenyl) Pentaerythritol Diphosphite (bis(2,4-di-t-butylphenyl)Pentaerythritol Diphosphite), Bis(2,4-Dicumylphenyl)pentaerythritol Diphosphite, Distearyl Pentaerythritol Diphosphite, Tris(2,4- di-t-butylphenyl) phosphite or two or more of these.

The sulfur-based antioxidant is 3,3'-thiobis-1,1'-didodecyl ester (3,3'-thiobis-1,1'-didodecyl ester), dimethyl 3, 3'-thiodipropionate ( Dimethyl 3,3'-Thiodipropionate), Dioctadecyl 3,3'-thiodipropionate, 2,2-bis{[3-(dodecylthio)-1- oxopropoxy]methyl}propane-1,3diyl-bis[3-(dodecylthio)propionate](2,2-Bis{[3-(dodecylthio)-1-oxopropoxy]methyl}propane- 1,3-diyl bis[3-(dodecylthio)propionate]), or two or more of them.

In one embodiment of the present invention, the content of the second antioxidant is 500 ppm to 10000 ppm, or 1000 ppm based on the content of the olefin polymer porous support to 12000 ppm, or 1000 ppm to 10000. When the content of the second antioxidant satisfies the aforementioned range, it may be easier to prevent side reactions caused by excessive generation of radicals.

In one embodiment of the present invention, when the antioxidant includes a first antioxidant that is a radical scavenger and a second antioxidant that is a peroxide decomposer at the same time, the content of the first antioxidant This may be 500 ppm to 10000 ppm, or 1000 ppm to 5000 ppm based on the content of the olefin polymer porous support, and the content of the second antioxidant is 500 ppm to 10000 ppm based on the content of the olefin polymer porous support , or 1000 ppm to 5000 ppm.

The extrusion may be performed for several minutes at a temperature of 160 to 240 ° C using a single screw or twin screw extruder device. For uniform reaction extrusion, an extruder with a screw L/D (length/diameter) of 30 or more may be used.

The extruded olefin polymer composition is cooled while passing through a die and a cooling roll, and at this time, phase separation between the olefin polymer and the diluent may occur. This phase separation time may affect the BET specific surface area, average pore size, and pore shape of the olefin polymer porous support to be finally prepared.

In one embodiment of the present invention, the stretching may be performed by sequential or simultaneous stretching using a roll method or a tenter method. The stretching ratio may be 3 times or more, or 5 to 10 times in the machine direction and the transverse direction, respectively, and the total stretching ratio may be 20 to 80 times. When the above stretching ratio range is satisfied, it is easy to prevent problems in which orientation in one direction is not sufficient and the balance of physical properties between the machine direction and the transverse direction is broken, resulting in a decrease in tensile strength and puncture strength. have. In addition, it may be easy to prevent problems in which pores are not formed due to non-stretching or breakage occurs during stretching, resulting in an increase in shrinkage of the finally prepared porous olefin polymer support.

Throughout the present specification, 'Machine Direction' refers to the direction in which the separator is continuously produced, and refers to the long length direction of the separator, and 'Transverse Direction' refers to the transverse direction of the machine direction, that is, , It refers to the direction perpendicular to the direction in which the separation membrane is continuously produced, and the direction perpendicular to the long length direction of the separation membrane.

The stretching temperature may vary depending on the melting point of the olefin polymer used and the concentration and type of the diluent, and may be selected from a temperature range at which 30 to 80% by weight of the crystalline portion of the olefin polymer in the sheet melts. When the stretching temperature satisfies the above range, it may be easy to prevent breakage or non-stretching during stretching due to lack of softness of the sheet. In addition, it may be easy to prevent thickness variation due to partial overstretching or deterioration in physical properties due to a small orientation effect of olefin polymers. On the other hand, the degree of melting of the crystal part according to the temperature can be obtained from DSC (differential scanning calorimeter) analysis of the sheet.

The step of preparing a preliminary porous support by extracting the diluent from the stretched sheet may include extracting the diluent using an organic solvent. Specifically, the diluent may be extracted from the stretched sheet using an organic solvent, and then dried. The organic solvent is not particularly limited as long as it can extract the diluent. For example, methyl ethyl ketone, methylene chloride, hexane and the like can be used.

As the extraction method, all general solvent extraction methods such as an immersion method, a solvent spray method, and an ultrasonic method may be used individually or in combination. The content of the diluent remaining after the extraction treatment may be 1% by weight or less relative to 100% by weight of the olefin polymer porous support. In this case, it may be easy to prevent deterioration of physical properties and decrease in permeability of the porous olefin polymer support.

The content of the remaining diluent may be affected by the extraction temperature and extraction time, and the extraction temperature may be 40 ° C. or less considering the safety problem caused by the increase in the solubility of the diluent and the organic solvent and the boiling of the organic solvent.

In addition, the extraction time varies depending on the thickness of the porous olefin polymer support to be produced, and may be 2 to 4 minutes in the case of a porous olefin polymer support having a thickness of 10 to 30 μm.

Heat setting is to remove residual stress by fixing the preliminary porous support and applying heat to forcibly catch the shrinkage of the finally prepared olefin polymer porous support.

In one embodiment of the present invention, the heat setting temperature may be 125 ℃ to 132 ℃. In one embodiment of the present invention, the time of the heat setting temperature may be 10 seconds to 120 seconds, or 20 seconds to 90 seconds, or 30 seconds to 60 seconds. When the heat setting occurs for the above-mentioned time period, rearrangement of the olefin polymer molecules occurs to remove the residual stress of the olefin polymer porous support to be finally produced, and to reduce the problem of clogging of the pores of the olefin polymer porous support due to partial melting. can make it

In one embodiment of the present invention, the step of preparing an olefin polymer porous support containing the photoinitiator includes the step of preparing an olefin polymer porous support by adding the photoinitiator to an extruder for extruding the olefin polymer composition can do.

In another embodiment of the present invention, the step of preparing the olefin polymer porous support may include coating and drying a composition for photocrosslinking including the photoinitiator and a solvent on the outside of the olefin polymer porous support. have.

In the present specification, "coating and drying the outside" means not only the case of coating and drying the composition for photocrosslinking on the surface of the olefin polymer porous support, but also the other layer after the other layer is formed on the olefin polymer porous support. It includes the case where the composition for photocrosslinking is coated and dried on the surface of.

In one embodiment of the present invention, the olefin polymer porous support may be subjected to corona discharge treatment before coating the photocrosslinking initiator solution on the olefin polymer porous support. The corona discharge treatment may be performed by applying a high-frequency, high-voltage output generated by a predetermined driving circuit between a predetermined discharge electrode provided in the corona discharge processor and a treatment roll. Through the corona discharge treatment, the surface of the olefin polymer porous support is modified so that the wettability of the olefin polymer porous support for the photocrosslinking composition can be further improved. Accordingly, crosslinking of the olefin polymer porous support can be performed more efficiently even if the photoinitiator has the same content and/or the same number of double bonds in the olefin polymer chains. The corona discharge treatment may be performed by a normal pressure plasma method.

In one embodiment of the present invention, the solvent is cyclic aliphatic hydrocarbons such as cyclopentane and cyclohexane; aromatic hydrocarbons such as toluene, xylene and ethylbenzene; acetone, ethylmethyl ketone, diisopropyl ketone, and cyclohexane; Ketones such as rice paddy, methylcyclohexane, and ethylcyclohexane; Chlorine-based aliphatic hydrocarbons such as methylene chloride, chloroform and carbon tetrachloride; Esters such as ethyl acetate, butyl acetate, γ-butyrolactone and ε-caprolactone; Acetonitrile and propio Acylonitriles such as nitrile; Ethers such as tetrahydrofuran and ethylene glycol diethyl ether: Alcohols such as methanol, ethanol, isopropanol, ethylene glycol and ethylene glycol monomethyl ether; N-methylpyrrolidone, N, amides such as N-dimethylformamide; or two or more of these.

In one embodiment of the present invention, the content of the photoinitiator in the photocrosslinking composition is 0.015 to 0.36 parts by weight based on 100 parts by weight of the olefin polymer porous support, and at the same time 0.01 to 0.5 parts by weight based on 100 parts by weight of the solvent. , or 0.02 parts by weight to 0.45 parts by weight, or 0.25 parts by weight to 0.4 parts by weight.

When the content of the photoinitiator satisfies the above range based on the solvent, it is possible to crosslink the porous olefin polymer support and prevent side reactions from occurring due to excessive radical generation more easily.

In addition, in one embodiment of the present invention, the content of the photoinitiator in the photocrosslinking composition is 0.015 parts by weight to 0.36 parts by weight relative to 100 parts by weight of the olefin polymer porous support, and at the same time based on the specific surface area of the olefin polymer porous support to 0.01 mg/m ² to 1.0 mg/m ² , or 0.03 mg/m ² to 0.8 mg/m ² , or 0.06 mg/m ² to 0.7 mg/m ² . When the content of the Type 2 photoinitiator satisfies the aforementioned range, it may be easier to prevent side reactions from occurring due to excessive radical generation while crosslinking the olefin polymer porous support.

The content of the photoinitiator based on the specific surface area of the porous olefin polymer support can be measured through NMR analysis.

In one embodiment of the present invention, the composition for photocrosslinking may be a photoinitiator solution composed of the photoinitiator and the solvent.

Non-limiting examples of the method of coating the photoinitiator solution on the olefin polymer porous support include a dip coating method, a die coating method, a roll coating method, a comma coating method, and a microcoating method. There are microgravure coating method, doctor blade coating method, reverse roll coating method, Mayer Bar coating method, direct roll coating method, and the like.

The drying step after coating the photoinitiator solution on the olefin polymer porous support may use a method known in the art, and batchwise or continuously using an oven or heated chamber in a temperature range considering the vapor pressure of the solvent used. possible in this way The drying is to remove most of the solvent present in the photoinitiator solution, which is preferably as fast as possible in consideration of productivity and the like, and may be carried out for, for example, 1 minute or less or 30 seconds or less.

In another embodiment of the present invention, the composition for photocrosslinking may be a slurry for forming an inorganic hybrid void layer including an inorganic filler, a binder polymer, the photoinitiator, and the solvent.

When the photocrosslinking composition is the slurry for forming the inorganic mixed void layer, the photoinitiator is introduced to the surface of the olefin polymer porous support while the photocrosslinking composition is coated on the olefin polymer porous support, and when irradiated with ultraviolet rays, the olefin polymer porous paper While crosslinking the support, it is possible to form an inorganic hybrid void layer on at least one surface of the olefin polymer porous support.

When using a slurry for forming an inorganic hybrid porous layer as the photocrosslinking composition, equipment for directly applying the photoinitiator to the olefin polymer porous support, for example, directly coating a solution containing the photoinitiator on the olefin polymer porous support and The olefin polymer porous support can be photo-crosslinked using the inorganic hybrid void layer formation process without additionally requiring equipment for drying.

In addition, the slurry for forming the inorganic hybrid void layer does not require other monomers other than the photoinitiator to directly crosslink the polymer chains in the olefin polymer porous support, so the photoinitiator forms an inorganic hybrid void layer together with the inorganic filler and binder polymer Even when included in the slurry, the photoinitiator does not prevent the photoinitiator from reaching the surface of the porous olefin polymer support, so that the photoinitiator can be sufficiently introduced to the surface of the porous olefin polymer support.

In general, since the olefin polymer porous support itself and the inorganic filler have a high UV blocking effect, when an inorganic hybrid porous layer containing the inorganic filler is formed and then ultraviolet rays are irradiated, the amount of UV irradiation light reaching the olefin polymer porous support can be reduced. However, in the present invention, even when ultraviolet rays are irradiated after the inorganic hybrid void layer is formed, polymer chains in the olefin polymer porous support can be cross-linked and directly connected.

In one embodiment of the present invention, when the composition for photocrosslinking is the slurry for forming the inorganic hybrid void layer, 2-isopropyl thioxanthone, thioxanthone, or a mixture thereof may be included as the photoinitiator. 2-isopropyl thioxanthone or thioxanthone can be photocrosslinked even at long wavelengths with high transmittance. Accordingly, even if the photoinitiator is included in the slurry for forming the inorganic hybrid porous layer including the inorganic filler and the binder polymer, crosslinking of the olefin polymer porous support may be facilitated.

The solvent may serve as a solvent for dissolving the binder polymer or a dispersion medium for dispersing the binder polymer without dissolving it, depending on the type of the binder polymer. At the same time, the solvent may dissolve the photoinitiator. The solvent may have a solubility index similar to that of the binder polymer to be used and a low boiling point. In this case, uniform mixing and subsequent removal of the solvent may be facilitated. For non-limiting examples of such solvents, see the above discussion of solvents.

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 oxidation and/or reduction reactions do not occur in the operating voltage range (eg, 0 to 5V based on Li/Li ⁺ ) of the applied electrochemical device. In particular, when an inorganic filler having a high permittivity is used as the inorganic filler, the ionic conductivity of the electrolyte may be improved by contributing to an increase in the degree of dissociation of an electrolyte salt, for example, a lithium salt in the liquid electrolyte.

For the reasons described 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-limiting examples of inorganic fillers having a dielectric constant of 5 or more include BaTiO ₃ , Pb(Zr,Ti)O ₃ (PZT), Pb _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, TiO ₂ or mixtures thereof.

Further, in another embodiment of the present invention, an inorganic filler having a lithium ion transport ability, that is, an inorganic filler containing a lithium element but not storing lithium and having a function of moving lithium ions may be used as the inorganic filler. Non-limiting examples of the inorganic filler having lithium ion transport ability include lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0<x<2, 0<y<3), Lithium aluminum titanium phosphate (Li _x Al _y Ti _z (PO ₄ ) ₃ , 0<x<2, 0<y<1, 0<z<3), 14Li ₂ O-9Al ₂ O ₃ -38TiO ₂ -39P ₂ (LiAlTiP) _x O _y series glass (0<x<4, 0<y<13), lithium lanthanum titanate (Li _x La _y TiO ₃ , 0<x<2, 0<y<3), such as O ₅ , Li _3.25 Ge _0.25 P _0.75 S ₄ and the like (Li _x Ge _y P _z S _w , 0<x<4, 0<y<1, 0<z<1, 0<w<5 ), lithium nitride such as Li ₃ N (Li _x N _y , 0<x<4, 0<y<2), SiS ₂ series glass such as Li ₃ PO ₄ -Li ₂ S-SiS ₂ (Li _x Si _y S _z , 0<x<3, 0<y< _{2, 0<z<4), P 2 S 5 series} glass ₍ Li _x P _y S _z , 0<x < 3, 0<y<3, 0<z<7), or mixtures thereof.

In one embodiment of the present invention, the average particle diameter of the inorganic filler may be 0.01 μm to 1.5 μm. When the average particle diameter of the inorganic filler satisfies the aforementioned range, it is possible to easily form an inorganic hybrid pore layer having a uniform thickness and appropriate porosity, the dispersibility of the inorganic filler is good, and the desired energy density can be obtained. can provide

At this time, the average particle diameter of the inorganic filler means the D ₅₀ particle diameter, and “D ₅₀ particle diameter” means the particle diameter at the 50% point of the cumulative distribution of the number of particles according to the particle diameter. The particle size can be measured using a laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g. Microtrac S3500) to measure the difference in diffraction pattern according to the particle size when the particles pass through the laser beam to distribute the particle size. yields The D50 particle size can be measured by calculating the particle size at the point where it becomes 50% of the cumulative distribution of the number of particles according to the particle size in the measuring device.

The binder polymer may be dissolved in the solvent or may be dispersed without being dissolved in the solvent, depending on the type of the binder polymer.

The binder polymer may have a glass transition temperature (Tg) of -200 to 200 °C. When the glass transition temperature of the binder polymer satisfies the aforementioned range, mechanical properties such as flexibility and elasticity of the finally formed inorganic hybrid porous layer may be improved. The binder polymer may have ion conduction ability. When the binder polymer has ion conductivity, battery performance can be further improved. The binder polymer may have a dielectric constant of 1.0 to 100 (measurement frequency = 1 kHz) or 10 to 100. When the dielectric constant of the binder polymer satisfies the aforementioned range, the degree of salt dissociation in the electrolyte may be improved.

In one embodiment of the present invention, the binder polymer is poly(vinylidene fluoride-hexafluoropropylene) (poly(vinylidene fluoride-co-hexafluoropropylene)), poly(vinylidene fluoride-chlorotrifluoroethylene) ( poly(vinylidene fluoride-co-chlorotrifluoroethylene)), poly(vinylidene fluoride-co-tetrafluoroethylene)), poly(vinylidene fluoride-trichloroethylene) (poly(vinylidene fluoride-co-trichloroethylene)), acrylic copolymer, styrene-butadiene copolymer, poly(acrylic acid), poly(methylmethacrylate), poly(butylacrylate) (poly(butylacrylate)), poly(acrylonitrile), poly(vinylpyrrolidone), poly(vinylalcohol), poly(vinyl acetate) ) (poly(vinylacetate)), ethylene vinyl acetate copolymer (poly(ethylene-co-vinyl acetate)), poly(ethylene oxide) (poly(ethylene oxide)), poly(arylate) (poly(arylate)), Cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose (cyanoethylcellulose), cyanoethylsucrose ), pullulan, carboxyl methyl cellulose, or two or more of them.

The acrylic copolymer is ethyl acrylate-acrylic acid-N,N-dimethylacrylamide copolymer, ethyl acrylate-acrylic acid-2-(dimethylamino)ethyl acrylate copolymer, ethyl acrylate-acrylic acid-N,N-di ethyl acrylamide copolymer, ethyl acrylate-acrylic acid-2-(diethylamino)ethyl acrylate copolymer, or two or more thereof, but is not limited thereto.

In one embodiment of the present invention, the weight ratio of the inorganic filler to the binder polymer is determined in consideration of the thickness, pore size, and porosity of the inorganic hybrid porous layer to be finally prepared, but is 50:50 to 99.9:0.1, or 60:40 to 99.5:0.5. When the weight ratio of the inorganic filler to the binder polymer is within the aforementioned range, it may be easy to secure the pore size and porosity of the inorganic hybrid porous layer by sufficiently securing an empty space formed between the inorganic fillers. In addition, it may be easy to secure adhesive strength between inorganic fillers.

The slurry for forming the inorganic hybrid void layer may be prepared by dissolving or dispersing the binder polymer in the solvent, adding the inorganic filler, and dispersing the same. The inorganic fillers may be added in a state of being crushed to have a predetermined average particle diameter in advance, or after adding the inorganic filler to a slurry in which the binder polymer is dissolved or dispersed, the inorganic filler is prepared by a ball mill method or the like. It can also be crushed and dispersed while controlling to have an average particle diameter. At this time, crushing may be performed for 1 to 20 hours, and the average particle diameter of the crushed inorganic filler may be as described above. As a crushing method, a conventional method may be used, and a ball mill method may be used.

In one embodiment of the present invention, the slurry for forming the inorganic hybrid void layer may further include an additive such as a dispersant and/or a thickener. In one embodiment of the present invention, the additive is poly(vinylpyrrolidone) (PVP), hydroxy ethyl cellulose (HEC), hydroxy propyl cellulose (hydroxy propyl cellulose, HPC), ethylhydroxy ethyl cellulose (EHEC), methyl cellulose (MC), carboxymethyl cellulose (CMC), hydroxyalkyl methyl cellulose ), cyanoethylene polyvinyl alcohol, or two or more of them.

In one embodiment of the present invention, the solid content of the slurry for forming the inorganic hybrid void layer may be 5 wt% to 60 wt%, or 30 wt% to 50 wt%. When the solid content of the slurry for forming the inorganic mixed void layer is in the above range, it is easy to secure coating uniformity, and it is easy to prevent non-uniformity from flowing the slurry or requiring a lot of energy to dry the slurry. can

In one embodiment of the present invention, when the composition for photocrosslinking is the slurry for forming the inorganic mixed void layer, a phase separation process may be performed after coating the composition for photocrosslinking on the porous olefin polymer support. The phase separation may be performed by humidification phase separation or immersion phase separation.

The humidification phase separation of the phase separation is described as follows.

First, the humidified phase separation may be carried out under conditions of a temperature in the range of 15 ° C to 70 ° C or a temperature in the range of 20 ° C to 50 ° C and a relative humidity in the range of 15% to 80% or 30% to 50%. While the slurry for forming the inorganic mixed void layer undergoes a drying process, it may have phase change characteristics due to a vapor-induced phase separation phenomenon known in the art.

For the humidified phase separation, a non-solvent for the binder polymer may be introduced in a gaseous state. The non-solvent for the binder polymer is not particularly limited as long as it does not dissolve the binder polymer and has partial compatibility with the solvent. For example, one having a solubility of less than 5% by weight of the binder polymer at 25 ° C may be used. . For example, the non-solvent for the binder polymer may be water, methanol, ethanol, isopropanol, butanol, butanediol, ethylene glycol, propylene glycol, tripropylene glycol, or two or more of these.

The immersion phase separation among the phase separations will be described as follows.

After the slurry for forming the inorganic hybrid porous layer is coated on the outside of the olefin polymer porous support, it is immersed in a coagulating solution containing a non-solvent for the binder polymer for a predetermined time. Accordingly, the binder polymer is solidified while a phase separation phenomenon is induced in the coated inorganic mixed porous layer slurry. In this process, a porous inorganic hybrid void layer is formed. After that, by washing with water, the coagulation liquid is removed and dried. The drying may use a method known in the art, and may be batchwise or continuously using an oven or a heating chamber at a temperature range considering the vapor pressure of the solvent used. The drying is to remove most of the solvent present in the slurry, and it is preferable to be as fast as possible in consideration of productivity and the like, and may be performed for, for example, 1 minute or less or 30 seconds or less.

As the coagulant solution, only a non-solvent for the binder polymer or a mixed solvent of a non-solvent for the binder polymer and a solvent as described above may be used. In the case of using a mixed solvent of a solvent and a non-solvent for the binder polymer, from the viewpoint of forming a good porous structure and improving productivity, the content of the non-solvent for the binder polymer is 50% by weight relative to 100% by weight of the coagulating solution. may be ideal

In another embodiment of the present invention, the step of coating and drying the photo-crosslinking composition containing the photoinitiator and the solvent on the outside of the olefin polymer porous support,

Forming an inorganic hybrid void layer by coating and drying at least one surface of the olefin polymer porous support with a slurry for forming an inorganic hybrid void layer containing an inorganic filler, a first binder polymer, and a dispersion medium; and

It may include coating and drying a coating solution for forming a porous adhesive layer containing a second binder polymer, the photoinitiator, and the solvent on the upper surface of the inorganic hybrid porous layer.

For the inorganic filler, refer to the above description.

The dispersion medium may serve as a solvent for dissolving the first binder polymer according to the type of the first binder polymer, or may serve as a dispersion medium for dispersing the first binder polymer without dissolving it. The dispersion medium may have a solubility index similar to that of the first binder polymer to be used and a low boiling point. In this case, uniform mixing and subsequent removal of the dispersion medium may be facilitated.

In one embodiment of the present invention, the dispersion medium may be an aqueous dispersion medium. When the dispersion medium is an aqueous dispersion medium, it is environmentally friendly and does not require an excessive amount of heat to form and dry the inorganic hybrid void layer, and it may be easier to form the inorganic hybrid void layer because additional explosion-proof facilities are not required.

In one embodiment of the present invention, the first binder polymer may be insoluble in the solvent and a non-solvent for the second binder polymer to be described later. In this case, even if the coating solution described below is applied to form the porous adhesive layer after forming the inorganic hybrid porous layer, the first binder polymer is not dissolved, and the first binder polymer dissolved in the solvent or the non-solvent for the second binder polymer is dissolved in the pores. It may be easy to prevent the blocking phenomenon.

In one embodiment of the present invention, the first binder polymer may be a water-based binder polymer. At this time, the first binder polymer may be dissolved in an aqueous solvent or dispersed by an aqueous dispersion medium. When the first binder polymer is dispersed by an aqueous dispersion medium, the first binder polymer may be in the form of particles.

In one embodiment of the present invention, the first binder polymer may be a binder polymer having excellent heat resistance. When the first binder polymer has excellent heat resistance, heat resistance of the inorganic hybrid porous layer may be further improved. For example, after leaving it at 150 ° C. for 30 minutes, the thermal contraction rate of the separator in the machine direction and the transverse direction, respectively, is 20% or less, or 2% to 15%, or 2% to 10%, or 2% to 5%, or 0% to 5%, or 0% to 2%.

In one embodiment of the present invention, the first binder polymer may include an acrylic polymer, polyacrylic acid, styrene butadiene rubber, polyvinyl alcohol, or two or more thereof.

Specifically, the acrylic polymer may include an acrylic homopolymer obtained by polymerizing only an acrylic monomer, or may include a copolymer of an acrylic monomer and another monomer. For example, the acrylic polymer is a copolymer of ethylhexyl acrylate and methyl methacrylate, poly(methylmethacrylate), poly(ethylexyl acrylate) ), poly(butylacrylate), poly(acrylonitrile), a copolymer of butyl acrylate and methyl methacrylate, or two or more of these.

In one embodiment of the present invention, the weight ratio of the inorganic filler to the first binder polymer may be 95:5 to 99.9:0.1, or 96:4 to 99.5:0.5, or 97:3 to 99:1. When the weight ratio of the inorganic filler to the first binder polymer is within the above-described range, the thermal stability of the separator at high temperatures may be improved due to the high content of the inorganic filler distributed per unit area of the separator. For example, after leaving it at 150 ° C. for 30 minutes, the thermal contraction rate of the separator in the machine direction and the transverse direction, respectively, is 20% or less, or 2% to 15%, or 2% to 10%, or 2% to 5%, or 0% to 5%, or 0% to 2%.

For the slurry for forming the inorganic hybrid void layer, refer to the above description.

The drying of the slurry for forming the inorganic hybrid void layer may be performed by a conventional drying method in the manufacture of a separator. For example, drying of the coated slurry may be performed by air for 10 seconds to 30 minutes, or 30 seconds to 20 minutes, or 3 minutes to 10 minutes. When the drying time is performed within the above range, residual solvent may be removed without impairing productivity.

The second binder polymer may be a binder polymer commonly used in forming an adhesive layer. The second binder polymer may have a glass transition temperature (glass transition temperature, Tg) of -200 to 200 °C. When the glass transition temperature of the second binder polymer satisfies the aforementioned range, mechanical properties such as flexibility and elasticity of the finally formed adhesive layer may be improved. The second binder polymer may have ion conduction ability. Battery performance can be further improved when a binder polymer having ion conductivity is used as the second binder polymer. The second binder polymer may have a dielectric constant of 1.0 to 100 (measurement frequency = 1 kHz), or 10 to 100. When the dielectric constant of the second binder polymer satisfies the aforementioned range, the degree of salt dissociation in the electrolyte may be improved.

In one embodiment of the present invention, the second binder polymer is polyvinylidene fluoride (poly (vinylidene fluoride)), poly (vinylidene fluoride-hexafluoropropylene) (poly (vinylidene fluoride-co-hexafluoropropylene)) , poly(vinylidene fluoride-co-trichloroethylene), poly(vinylidene fluoride-co-tetrafluoroethylene)), poly( Vinylidene fluoride-trifluoroethylene) (poly(vinylidene fluoride-co-trifluoroethylene)), polymethylmethacrylate, polyetylexyl acrylate, polybutylacrylate, poly Polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, copolymer of ethylhexyl acrylate and methyl methacrylate, ethylene vinyl acetate copolymer ( polyethylene-co-vinyl acetate), polyethylene oxide, polyarylate, or two or more of them.

The solvent may dissolve the second binder polymer in an amount of 5 wt % or more, or 15 wt % or more, or 25 wt % or more at 25° C.

The solvent may be a non-solvent for the first binder polymer. For example, the solvent may dissolve less than 5% by weight of the first binder polymer at 25°C.

For the type of the solvent, refer to the above description.

In one embodiment of the present invention, the second binder polymer is 3 based on 100% by weight of the coating solution for forming the porous adhesive layer It may be included in weight % to 30 weight %, or 5 weight % to 25 weight %.

As the photoinitiator is included in the coating solution for forming the porous adhesive layer, when the coating solution for forming the porous adhesive layer is coated on the upper surface of the inorganic hybrid porous layer, the photoinitiator can be introduced to the surface of the olefin polymer porous support and at the same time, the porous adhesive layer can be formed. have.

In the process of coating the coating liquid for forming the porous adhesive layer, the solvent wets the olefin polymer porous support, and at this time, the photoinitiator included in the coating liquid for forming the porous adhesive layer is introduced to the surface of the olefin polymer porous support, and when irradiated with ultraviolet rays, the olefin polymer The olefin polymer porous support may be photocrosslinked by the photoinitiator present on the surface of the porous support.

Accordingly, the method for manufacturing a separator having a cross-linked structure for a lithium secondary battery according to an embodiment of the present invention includes equipment for directly applying a photoinitiator to an olefin polymer porous support in order to photocrosslink the olefin polymer porous support, such as a photoinitiator The process can be simplified in that the olefin polymer porous support can be photocrosslinked using the porous adhesive layer forming process without additional equipment for directly coating and drying the solution on the olefin polymer porous support. can

The method of manufacturing a separator containing a crosslinked structure for a lithium secondary battery according to an embodiment of the present invention does not require other components such as a monomer for forming radicals in addition to a photoinitiator in order to directly crosslink polymer chains in an olefin polymer porous support. , Even if the photoinitiator is added to the coating solution for forming the porous adhesive layer, other components do not prevent the photoinitiator from reaching the surface of the porous olefin polymer support, so that the photo initiator can be sufficiently introduced to the surface of the porous olefin polymer support.

In addition, in general, since the olefin polymer porous support itself and the inorganic filler have a high UV blocking effect, when ultraviolet rays are irradiated after forming the inorganic hybrid void layer and the porous adhesive layer, the amount of UV irradiation light reaching the olefin polymer porous support can be reduced. However, in the present invention, crosslinking is possible even with a small amount of ultraviolet light irradiation, and even when ultraviolet rays are irradiated after the inorganic hybrid void layer and the porous adhesive layer are formed, the polymer chains in the olefin polymer porous support can be crosslinked and directly connected.

In one embodiment of the present invention, the coating solution for forming the porous coating layer may include 2-isopropyl thioxanthone, thioxanthone, or a mixture thereof as the photoinitiator. 2-isopropyl thioxanthone or thioxanthone can be photocrosslinked even at long wavelengths with high transmittance. Accordingly, crosslinking of the olefin polymer porous support may be facilitated even when ultraviolet rays are irradiated after the inorganic material-forming void layer and the porous adhesive layer are formed.

In one embodiment of the present invention, by pattern-coating the coating liquid for forming the porous adhesive layer on the upper surface of the inorganic hybrid porous layer, the finally prepared porous adhesive layer may form a pattern.

In one embodiment of the present invention, after the coating liquid for forming the porous adhesive layer is coated on the upper surface of the inorganic hybrid porous layer, a phase separation process may be performed. The phase separation may be performed by an immersion phase separation method.

After the coating liquid for forming the porous adhesive layer is coated on the upper surface of the inorganic hybrid porous layer, it is immersed in a coagulating liquid containing a non-solvent for the second binder polymer for a predetermined time. Accordingly, the second binder polymer is solidified while a phase separation phenomenon is induced in the coating solution for forming the coated porous adhesive layer. In this process, a porous adhesive layer is formed. After that, by washing with water, the coagulation liquid is removed and dried. The drying may use a method known in the art, and may be batchwise or continuously using an oven or a heating chamber at a temperature range considering the vapor pressure of the solvent used. The drying is to remove most of the solvent present in the coating liquid for forming the porous adhesive layer, and it is preferable to be as fast as possible in consideration of productivity, etc., and may be performed for, for example, 1 minute or less or 30 seconds or less.

As the coagulation solution, only a non-solvent for the second binder polymer or a mixed solvent of a non-solvent for the second binder polymer and a solvent as described above may be used. In the case of using a mixed solvent of a non-solvent and a solvent for the second binder polymer, from the viewpoint of forming a good porous structure and improving productivity, the content of the non-solvent for the second binder polymer relative to 100% by weight of the coagulating solution It may be 50% by weight or more.

In the process of solidifying the second binder polymer, the second binder polymer is condensed, and as a result, the second binder polymer can be prevented from penetrating into the surface and/or inside of the olefin polymer porous support, thereby increasing the resistance of the separator. can prevent In addition, resistance of the separator may be improved by making the adhesive layer including the second binder polymer porous.

The non-solvent for the second binder polymer may have a solubility of less than 5% by weight for the second binder polymer at 25 °C.

The non-solvent for the second binder polymer may also be a non-solvent for the first binder polymer. For example, the non-solvent for the second binder polymer may have a solubility of less than 5% by weight in the first binder polymer at 25 °C.

In one embodiment of the present invention, the non-solvent for the second binder polymer may include water, methanol, ethanol, propyl alcohol, butyl alcohol, butanediol, ethylene glycol, propylene glycol, tripropylene glycol, or two or more of these have.

In one embodiment of the present invention, the immersion may be made for 3 seconds to 1 minute. When the immersion time satisfies the above-described range, phase separation occurs appropriately, thereby securing the adhesive strength between the inorganic hybrid void layer and the porous adhesive layer, thereby making it easy to prevent detachment of the adhesive layer.

In one embodiment of the present invention, the drying of the coating solution for forming the porous adhesive layer may be performed by drying by a conventional drying method when preparing a separator. For example, it may be performed by air for 10 seconds to 30 minutes, or 30 seconds to 20 minutes, or 3 minutes to 10 minutes. When the drying time is performed within the above range, residual solvent may be removed without impairing productivity.

In the method for manufacturing a separator containing a crosslinked structure for a lithium secondary battery according to an embodiment of the present invention, the porous adhesive layer can be formed in various forms as the inorganic hybrid void layer and the porous adhesive layer are formed through separate steps. For example, it may be easier to form the porous adhesive layer in the form of a pattern.

Then, ultraviolet rays are irradiated to the olefin polymer porous support. As the ultraviolet rays are irradiated, the polymer chains in the olefin polymer porous support are crosslinked to obtain a crosslinked structure-containing olefin polymer porous support.

The UV irradiation may be performed by using a UV crosslinking device and appropriately adjusting the UV irradiation time and the amount of irradiated light in consideration of conditions such as the content ratio of the photoinitiator. For example, the UV irradiation time and the amount of irradiation light are set under conditions such that the polymer chain in the olefin polymer porous support is sufficiently cross-linked to secure the desired heat resistance and the separator is not damaged by the heat generated by the UV lamp. can In addition, the ultraviolet lamp used in the ultraviolet crosslinking device may be appropriately selected from high-pressure mercury lamps, metal lamps, gallium lamps, etc. according to the photoinitiator used, and the emission wavelength and capacity of the ultraviolet lamp may be appropriately selected according to the process. .

The method for manufacturing a separator containing a crosslinked structure for a lithium secondary battery according to an embodiment of the present invention can photocrosslink polymer chains in an olefin polymer porous support with only a significantly lower amount of UV irradiation than the amount of light used for general photocrosslinking. Applicability to the mass production process of a separator containing a cross-linked structure for secondary batteries can be improved. For example, the irradiation light amount of the ultraviolet rays is 10 to 2000 mJ/cm ² , or 50 to 1000 mJ/cm ² , or 150 to 500 mJ/cm ² .

In one embodiment of the present invention, the irradiation light amount of the ultraviolet light can be measured using a portable photometer called Miltec's H type UV bulb and UV power puck. When the amount of light is measured using Miltec's H type UV bulb, three wavelength values of UVA, UVB, and UVC are obtained for each wavelength, and the ultraviolet rays of the present invention correspond to UVA.

In the method of measuring the amount of irradiation light of ultraviolet rays in the present invention, the UV power puck is passed on a conveyor under the same conditions as the sample, and at this time, the value of the amount of ultraviolet light displayed on the UV power puck is referred to as 'irradiation amount of ultraviolet rays'.

In the method for manufacturing a separator containing a crosslinked structure for a lithium secondary battery according to an embodiment of the present invention, the content of the photoinitiator is 0.015 to 0.36 parts by weight relative to 100 parts by weight of the olefin polymer porous support, and the olefin polymer chain when measured by H-NMR By crosslinking the olefin polymer porous support having 0.01 to 0.5 double bonds per 1000 carbon atoms, the olefin polymer porous support can be effectively crosslinked and side reactions can be minimized.

In addition, the method of manufacturing a separator containing a cross-linked structure for a lithium secondary battery according to an embodiment of the present invention is further used to prevent side reactions with the number of double bonds present in the olefin polymer chain when an antioxidant is additionally used. It can be easy.

As described above, a separator containing a crosslinked structure for a lithium secondary battery may be manufactured according to the method of manufacturing a separator containing a crosslinked structure for a lithium secondary battery according to an embodiment of the present invention.

The crosslinked structure-containing separator for a lithium secondary battery includes a crosslinked structure-containing olefin polymer porous support having a crosslinked structure in which polymer chains are directly connected. A crosslinked structure-containing separator for a lithium secondary battery according to an embodiment of the present invention may have improved heat resistance as it is provided with a crosslinked structure-containing olefin polymer porous support having a crosslinked structure in which polymer chains are directly connected.

In the present specification, 'a crosslinked structure in which polymer chains are directly connected' means that a polymer chain substantially composed of olefin polymers, more preferably, a polymer chain composed only of olefin polymers has reactivity by the addition of a photoinitiator, so that the polymer chains It means a state in which they are directly cross-linked with each other. Therefore, the cross-linking reaction between the cross-linking agents by adding an additional cross-linking agent does not correspond to the 'cross-linking structure in which polymer chains are directly connected' referred to in the present invention. In addition, the crosslinking reaction between the additional crosslinking agent and the polymer chains, even if the polymer chains are substantially composed of olefin polymers or only olefin polymers, is referred to in the present invention as a 'crosslinked structure in which polymer chains are directly connected' Not applicable.

In one embodiment of the present invention, the cross-linked structure-containing olefin polymer porous support may include only a cross-linked structure in which polymer chains are directly connected, and may not include a cross-linked structure in which a photoinitiator and polymer chains are directly connected. .

In one embodiment of the present invention, the crosslinked structure-containing olefin polymer porous support includes only a crosslinked structure in which polymer chains are directly connected, and does not include a crosslinked structure in which a photoinitiator and polymer chains are directly connected.

In one embodiment of the present invention, the degree of crosslinking of the crosslinked structure-containing olefin polymer porous support is 10% to 45%, or 15% to 40%, or 20% to 35% can When the crosslinked structure-containing porous olefin polymer support has a degree of crosslinking within the above-mentioned range, it may be easier to increase modulus while having a desired level of heat resistance. For example, when the degree of crosslinking of the crosslinked structure-containing olefin polymer porous support is 20% or more, the meltdown temperature of the crosslinked structure-containing olefin polymer porous support may be more easily attained to 170°C or higher.

At this time, the degree of crosslinking is measured by immersing the crosslinked structure-containing olefin polymer porous support in a xylene solution at 135 ° C and boiling for 12 hours in accordance with ASTM D 2765, and then measuring the remaining weight. Calculated as a percentage of the remaining weight compared to the initial weight do.

In one embodiment of the present invention, the cross-linked structure-containing olefin polymer porous support has a number of double bonds present in the olefin polymer chain when measured by H-NMR of 0.01 to 0.6, or 0.02 to 0.5 per 1000 carbon atoms. can be a dog When the crosslinked structure-containing porous olefin polymer support has the above-mentioned number of double bonds, it may be easy to prevent the problem of battery performance deterioration at high temperatures and/or high voltages.

In one embodiment of the present invention, the number of double bonds present in the olefin polymer chain excluding the ends of the crosslinked structure-containing olefin polymer porous support may be 0.005 to 0.59 per 1000 carbon atoms.

In one embodiment of the present invention, the thickness of the cross-linked structure-containing olefin polymer porous support may be 3 μm to 16 μm, or 5 μm to 12 μm. When the thickness of the porous olefin polymer support having a cross-linked structure is within the aforementioned range, it is possible to easily secure energy density while preventing a problem in which the separator may be easily damaged during use of the battery.

A crosslinked structure-containing separator for a lithium secondary battery according to an embodiment of the present invention may be formed of a crosslinked structure-containing olefin polymer porous support having a crosslinked structure in which polymer chains are directly connected. When the composition for photocrosslinking is a photoinitiator solution composed of the photoinitiator and the solvent, the crosslinked structure-containing separator for a lithium secondary battery may be made of a crosslinked structure-containing olefin polymer porous support having a crosslinked structure in which polymer chains are directly connected.

A cross-linked structure-containing separator for a lithium secondary battery according to another embodiment of the present invention includes the cross-linked structure-containing olefin polymer porous support; and an inorganic hybrid void layer located on at least one side of the cross-linked structure-containing olefin polymer porous support and containing an inorganic filler and a binder polymer.

The inorganic hybrid void layer may be formed on one side or both sides of the cross-linked structure-containing olefin polymer porous support. The inorganic hybrid void layer includes an inorganic filler and a binder polymer that attaches the inorganic fillers to each other (ie, the binder polymer connects and fixes the inorganic fillers) so that the inorganic fillers can remain bound to each other, and the binder polymer As a result, the state in which the inorganic filler and the crosslinked structure-containing olefin polymer porous support are bound can be maintained. The inorganic hybrid void layer can improve the safety of the separator by preventing the crosslinked structure-containing olefin polymer porous support from exhibiting extreme heat shrinkage behavior at high temperatures by the inorganic filler. For example, the thermal contraction rate of the separator in the machine direction and the transverse direction measured after being left at 120 ° C. for 30 minutes is 20% or less, or 2% to 15%, or 2% to 10%, respectively. can be

When the composition for photocrosslinking is the above-described slurry for forming an inorganic mixed void layer, the crosslinked structure-containing separator for a lithium secondary battery according to an embodiment of the present invention includes a crosslinked structure-containing olefin polymer porous support; and an inorganic hybrid void layer located on at least one side of the cross-linked structure-containing olefin polymer porous support and containing an inorganic filler and a binder polymer.

In one embodiment of the present invention, the inorganic hybrid void layer is bound to each other by the binder polymer in a state in which the inorganic fillers are filled and in contact with each other, thereby forming interstitial volumes between the inorganic fillers. formed, and the interstitial volume between the inorganic fillers may be an empty space to form pores.

In another embodiment of the present invention, the inorganic hybrid void layer includes a plurality of nodes including the inorganic filler and a binder polymer covering at least a portion of a surface of the inorganic filler; and a yarn in the binder polymer of the node. It includes one or more filaments formed in a thread shape, and the filaments extend from the node to connect other nodes, and a node connection portion, wherein the node connection portion includes a plurality of fibers derived from the binder polymer. A structure in which filaments cross each other to form a three-dimensional network structure may be provided.

In one embodiment of the present invention, the average pore size of the inorganic hybrid porous layer may be 0.001 μm to 10 μm. The average pore size of the inorganic hybrid porous layer may be measured according to a capillary flow porometry method. The capillary flow pore diameter measurement method is a method in which the diameter of the smallest pore in the thickness direction is measured. Therefore, in order to measure the average pore size of only the inorganic hybrid void layer by the capillary flow pore size measurement method, the inorganic hybrid void layer can be separated from the crosslinked structure-containing olefin polymer porous support to support the separated inorganic hybrid void layer. In this case, the pore size of the nonwoven fabric should be much larger than the pore size of the inorganic hybrid porous layer.

In one embodiment of the present invention, the porosity of the inorganic hybrid porous layer may be 5% to 95%, or 10% to 95%, or 20% to 90%, or 30% to 80%. The porosity corresponds to a value obtained by subtracting the volume converted into the weight and density of each component of the inorganic hybrid void layer from the volume calculated in the thickness, width, and length of the inorganic hybrid void layer.

The porosity of the inorganic hybrid porous layer was measured by nitrogen gas adsorption distribution using a scanning electron microscope (SEM) image, a Mercury porosimeter, or a Porosimetry analyzer (Bell Japan Inc, Belsorp-II mini). It can be measured using the BET 6-point method by law.

In one embodiment of the present invention, the inorganic hybrid porous layer may have a thickness of 1.5 μm to 5.0 μm on one side of the crosslinked structure-containing olefin polymer porous support. When the thickness of the inorganic hybrid void layer satisfies the aforementioned range, the cell strength of the battery may be easily increased while having excellent adhesion to the electrode.

A cross-linked structure-containing separator for a lithium secondary battery according to another embodiment of the present invention includes the cross-linked structure-containing olefin polymer porous support; an inorganic hybrid void layer located on at least one side of the crosslinked structure-containing olefin polymer porous support and containing an inorganic filler and a first binder polymer; and a porous adhesive layer positioned on the inorganic hybrid void layer and containing a second binder polymer.

The step of coating and drying the photocrosslinking composition containing the photoinitiator and the solvent on the outside of the olefin polymer porous support,

Forming an inorganic hybrid void layer by coating and drying at least one surface of the olefin polymer porous support with a slurry for forming an inorganic hybrid void layer containing an inorganic filler, a first binder polymer, and a dispersion medium; and

coating and drying a coating solution for forming a porous adhesive layer containing a second binder polymer, the photoinitiator, and the solvent on the upper surface of the inorganic hybrid porous layer;

A cross-linked structure-containing separator for a lithium secondary battery according to an embodiment of the present invention includes the cross-linked structure-containing olefin polymer porous support; an inorganic hybrid void layer located on at least one side of the crosslinked structure-containing olefin polymer porous support and containing an inorganic filler and a first binder polymer; and a porous adhesive layer positioned on the inorganic hybrid void layer and containing a second binder polymer.

The inorganic hybrid void layer may be formed on one side or both sides of the cross-linked structure-containing olefin polymer porous support. The inorganic hybrid void layer includes an inorganic filler and a first binder polymer that attaches the inorganic fillers to each other (ie, the first binder polymer connects and fixes between the inorganic fillers) so that the inorganic fillers can remain bound to each other, It is possible to maintain a binding state between the inorganic filler and the porous olefin polymer support having a crosslinked structure by the first binder polymer. The inorganic hybrid void layer can improve the safety of the separator by preventing the crosslinked structure-containing olefin polymer porous support from exhibiting extreme heat shrinkage behavior at high temperatures by the inorganic filler. For example, the thermal contraction rate of the separator in the machine direction and the transverse direction measured after being left at 150 ° C. for 30 minutes is 20% or less, or 2% to 15%, or 2% to 10%, respectively. can be

In one embodiment of the present invention, the inorganic hybrid void layer is bound to each other by the first binder polymer in a state in which the inorganic fillers are filled and in contact with each other, thereby interstitial volumes between the inorganic fillers ) is formed, and the interstitial volume between the inorganic fillers becomes an empty space to form pores.

The porous adhesive layer includes a second binder polymer so that the separator having the inorganic hybrid porous layer can secure adhesion to the electrode. In addition, since pores are formed in the porous adhesive layer, it is possible to prevent the resistance of the separator from increasing.

In one embodiment of the present invention, the porous adhesive layer may prevent the second binder polymer from penetrating into the surface and/or inside of the crosslinked structure-containing olefin polymer porous support, thereby minimizing an increase in resistance of the separator.

In one embodiment of the present invention, the porous adhesive layer may have a pattern including at least one adhesive portion including the second binder polymer and at least one uncoated portion on which the adhesive portion is not formed. The pattern may be dotted, striped, diagonal, wavy, triangular, square, or semicircular. When the porous adhesive layer has a pattern, the resistance of the separator can be improved, and the electrolyte can be impregnated through the non-coating region where the porous adhesive layer is not formed, so that the electrolyte impregnability of the separator can be improved. have.

In one embodiment of the present invention, the porous adhesive layer may have a thickness of 0.5 μm to 1.5 μm, or 0.6 μm to 1.2 μm, or 0.6 μm to 1.0 μm. When the thickness of the porous adhesive layer is within the aforementioned range, adhesion to the electrode is excellent, and as a result, cell strength of the battery may be increased. In addition, it may be advantageous in terms of cycle characteristics and resistance characteristics of the battery.

A crosslinked structure-containing separator for a lithium secondary battery according to an embodiment of the present invention includes a crosslinked structure-containing olefin polymer porous support having a crosslinked structure in which polymer chains are directly connected, and thus may have excellent high-temperature stability. For example, the meltdown temperature of the crosslinked separator for a lithium secondary battery may be increased compared to the conventional meltdown temperature of a separator for a lithium secondary battery before crosslinking. For example, the melt down temperature of the separator may be 160 °C or higher, 170 °C or higher, or 180 to 230 °C.

In the present specification, "separator for a lithium secondary battery before crosslinking" refers to a separator made of a porous olefin polymer support that is not crosslinked and does not contain a crosslinked structure; Or a separator comprising an olefin polymer porous support that is not crosslinked and does not contain a crosslinked structure, and an inorganic hybrid porous layer located on at least one surface of the olefin polymer porous support that does not contain a crosslinked structure and containing an inorganic filler and a binder polymer; Or, an olefin polymer porous support that is not crosslinked and does not contain a crosslinked structure, an inorganic hybrid porous layer located on at least one surface of the crosslinked structure, non-crosslinked olefin polymer porous support and containing an inorganic filler and a first binder polymer, and the inorganic hybrid porous layer Located on the top, refers to a separator including a porous adhesive layer containing a second binder polymer.

The meltdown temperature can be measured by thermomechanical analysis (TMA). For example, after taking samples in the machine direction and the transverse direction, respectively, a sample of 4.8 mm in width x 8 mm in length was put into the TMA equipment (TA Instrument, Q400) and a tension of 0.01 N was applied. While changing the temperature from 30 ° C to 220 ° C at a heating rate of 5 ° C / min in the state, the temperature at which the length is rapidly increased and the sample breaks can be measured as the meltdown temperature.

Compared to conventional separators for lithium secondary batteries before cross-linking, the separator having a cross-linked structure for lithium secondary batteries according to an embodiment of the present invention may not significantly increase the shutdown temperature, and the rate of change may also be small. In the crosslinked structure-containing separator for lithium secondary batteries according to an embodiment of the present invention, the meltdown temperature of the separator increases compared to before crosslinking, but the shutdown temperature does not increase significantly, so that the safety of overcharging by the shutdown temperature can be secured while the separator high temperature stability can be greatly increased.

In one embodiment of the present invention, the crosslinked structure-containing separator for a lithium secondary battery may have a shutdown temperature of 145°C or less, or 140°C or less, or 133°C to 140°C. When the crosslinked structure-containing separator for lithium secondary batteries has the above shutdown temperature, safety due to overcharging can be ensured, and the pores of the crosslinked structure-containing olefin polymer porous support are damaged in the high temperature and pressurization process during battery assembly, resulting in low resistance It may be easy to prevent the rising problem.

The shutdown temperature is measured by measuring the time (sec) required for 100 ml of air to pass through the separator at a constant pressure of 0.05 Mpa when the temperature is raised by 5 ° C per minute using a royal aeration device, so that the aeration of the separator rapidly increases It can be measured by measuring the temperature.

A crosslinked structure-containing separator for a lithium secondary battery according to an embodiment of the present invention is provided with a crosslinked structure-containing olefin polymer porous support having a crosslinked structure in which polymer chains in the olefin polymer porous support are directly connected, so that even after crosslinking, the olefin polymer porous support The pore structure of may be substantially maintained as it was prior to crosslinking.

A crosslinked structure-containing separator for a lithium secondary battery according to an embodiment of the present invention has air permeability, basis weight, tensile strength, tensile elongation, puncture strength, electrical resistance, etc. of a lithium secondary battery prior to crosslinking. Compared to air permeability, basis weight, tensile strength, tensile elongation, puncture strength, electrical resistance, etc. of the battery separator, it may not deteriorate significantly, and the change rate may also be small.

Compared to a separator for a lithium secondary battery before crosslinking, the crosslinked structure-containing separator for a lithium secondary battery according to an embodiment of the present invention has a rate of change in air permeability of 10% or less, 0% to 10%, 0% to 5%, or 0%. to 3%.

The change rate of air permeability can be calculated by the following formula.

Change rate of air permeability (%) = [(air permeability of separator containing crosslinked structure for lithium secondary battery after crosslinking) - (air permeability of separator for lithium secondary battery before crosslinking)]/(air permeability of separator for lithium secondary battery before crosslinking) X 100

Throughout this specification, the "separator containing a cross-linked structure for a lithium secondary battery after cross-linking" refers to a separator made of a porous olefin polymer support containing a cross-linked structure; Or a separator comprising a porous olefin polymer support having a cross-linked structure, and an inorganic hybrid porous layer including an inorganic filler and a binder polymer located on at least one side of the porous olefin polymer support having a cross-link structure; Or a crosslinked structure-containing olefin polymer porous support, an inorganic hybrid porous layer containing an inorganic filler and a first binder polymer, located on at least one surface of the crosslinked structure-containing olefin polymer porous support, and located on the upper surface of the inorganic hybrid porous layer It refers to a separator including a porous adhesive layer including a second binder polymer.

The air permeability (Gurley) can be measured by the ASTM D726-94 method. Gurley, as used herein, is the resistance to the flow of air, measured by a Gurley densometer. The air permeability value described here is expressed as the time (seconds) required for 100 cc of air to pass through the cross section of the sample porous support 1 in ² under a pressure of 12.2 inH ₂ O, that is, the air permeability time.

Compared to a separator for a lithium secondary battery before crosslinking, a separator having a crosslinked structure for a lithium secondary battery according to an embodiment of the present invention may have a rate of change in basis weight of 5% or less or 0% to 5%.

The change rate of basis weight can be calculated by the following formula.

Change rate of basis weight (%) = [(Basic weight of separator containing crosslinked structure for lithium secondary battery after crosslinking) - (Basic weight of separator for lithium secondary battery before crosslinking)]/(Basic weight of separator for lithium secondary battery before crosslinking) X 100

The basis weight (g / m ² ) is expressed by preparing a sample having a width and length of 1 m, respectively, and measuring its weight.

Compared to a separator for a lithium secondary battery before crosslinking, the separator having a crosslinked structure for a lithium secondary battery according to an embodiment of the present invention has a change rate of 20% or less in tensile strength in the machine direction and the perpendicular direction, or 0% to 20%, or 0% to 10%, or 0% to 9%, or 0% to 8%, or 0% to 7.53%.

The change rate of tensile strength can be calculated by the following formula.

Change rate (%) of tensile strength in the machine direction = [(tensile strength in the machine direction of the separator for lithium secondary batteries before crosslinking) - (tensile strength in the machine direction of the separator containing a crosslinked structure for lithium secondary batteries after crosslinking)] / (tensile strength in the machine direction of the separator for lithium secondary batteries before crosslinking) X 100

Change rate (%) of tensile strength in the orthogonal direction = [(tensile strength in the orthogonal direction of the separator for lithium secondary batteries before crosslinking) - (tensile strength in the orthogonal direction of the separator containing a crosslinked structure for lithium secondary batteries after crosslinking)] / (tensile strength in the right angle direction of the lithium secondary battery separator before crosslinking) X 100

The tensile strength is obtained when the specimen is pulled in the machine direction and the transverse direction at a rate of 50 mm/min using Universal Testing Systems (Instron® 3345) in accordance with ASTM D882. This may mean the strength at the time of breaking.

Compared to a separator for a lithium secondary battery before crosslinking, the separator having a crosslinked structure for a lithium secondary battery according to an embodiment of the present invention has a rate of change in tensile elongation of 20% or less, or 0% to 20% in the machine direction and the perpendicular direction. can

The change rate of tensile elongation can be calculated by the following formula.

Change rate (%) of tensile elongation in the machine direction = [(tensile elongation in the machine direction of the separator for lithium secondary batteries before crosslinking) - (tensile elongation in the machine direction of the separator containing a crosslinked structure for lithium secondary batteries after crosslinking)] / (tensile elongation in the machine direction of the lithium secondary battery separator before crosslinking) X 100

Change rate (%) of tensile elongation in the orthogonal direction = [(tensile elongation in the orthogonal direction of the separator for lithium secondary batteries before crosslinking) - (tensile elongation in the orthogonal direction of the crosslinked structure-containing separator for lithium secondary batteries after crosslinking)] / (tensile elongation in the orthogonal direction of the lithium secondary battery separator before crosslinking) X 100

The tensile elongation was obtained when the specimen was pulled in the machine direction and the transverse direction at a rate of 50 mm/min using Universal Testing Systems (Instron® 3345) in accordance with ASTM D882, respectively. The maximum length extended until it breaks can be measured and calculated using the following formula.

Tensile elongation in machine direction (%) = (machine direction length of specimen immediately before fracture-machine direction length of specimen before stretching)/(machine direction length of specimen before stretching) X 100

Tensile elongation in the transverse direction (%) = (Length in the transverse direction of the specimen immediately before fracture-Length in the transverse direction of the specimen before elongation)/(Length in the transverse direction of the specimen before elongation) X 100

Compared to a separator for a lithium secondary battery before crosslinking, the crosslinked structure-containing separator for a lithium secondary battery according to an embodiment of the present invention has a rate of change in puncture strength of 10% or less, or 0.5% to 10%, or 1% to 9%, or 1.18% to 8.71%.

The change rate of the puncture strength can be calculated by the following formula.

Change rate of puncture strength (%) = [(puncture strength of lithium secondary battery separator before crosslinking) - (puncture strength of crosslinked structure-containing separator for lithium secondary battery after crosslinking)]/(puncture strength of lithium secondary battery separator before crosslinking) ) X 100

The puncture strength can be measured according to ASTM D2582. Specifically, after setting a 1 mm round tip to operate at a speed of 120 mm/min, the puncture strength may be measured according to ASTM D2582.

Compared to a separator for a lithium secondary battery before crosslinking, a separator having a crosslinked structure for a lithium secondary battery according to an embodiment of the present invention may have a rate of change in electrical resistance of 15% or less, or 2% to 10%, or 2% to 5%. have.

The change rate of electrical resistance can be calculated by the following formula.

Change rate of electrical resistance (%) = [(electrical resistance of the separator containing a crosslinked structure for lithium secondary batteries after crosslinking) - (electrical resistance of the separator for lithium secondary batteries before crosslinking)]/(electrical resistance of the separator for lithium secondary batteries before crosslinking) ) X 100

The electrical resistance can be obtained by measuring the resistance of the separator by an impedance measurement method after the coin cell manufactured including the separator sample is left at room temperature for 1 day.

A lithium secondary battery may be manufactured by interposing the cross-linked structure-containing separator for lithium secondary batteries between the positive electrode and the negative electrode.

The lithium secondary battery may have various shapes such as a cylindrical shape, a prismatic shape, or a pouch shape.

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.

The electrode to be applied together with the crosslinked structure-containing separator for lithium secondary battery of the present invention is not particularly limited, and the electrode active material layer including the electrode active material, the conductive material, and the binder is bound to the current collector according to a conventional method known in the art. It can be manufactured in the form of

Among the electrode active materials, non-limiting examples of the cathode active material include layered compounds such as lithium cobalt composite oxide (LiCoO ₂ ) and lithium nickel oxide (LiNiO ₂ ), or compounds substituted with one or more transition metals; lithium manganese oxides such as Li _1+x Mn _2-x O ₄ (where x = 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , and LiMnO ₂ ; lithium copper oxide (Li ₂ CuO ₂ ); vanadium oxides such as LiV ₃ O ₅ , LiV ₃ O ₄ , V ₂ O ₅ , and Cu ₂ V ₂ O ₇ ; Ni site type lithium nickel oxide represented by the formula LiNi _1-x M _x O ₂ (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3); Formula LiMn _2-x M _x O ₂ (Where M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01-0.1) or Li ₂ Mn ₃ MO ₅ (Where M = Fe, Co, Ni , Cu or Zn); LiMn ₂ O ₄ in which a part of the chemical formula Li is replaced with an alkaline earth metal ion; disulfide compounds; Fe ₂ (MoO ₄ ) ₃ and the like can be mentioned, but are not limited only to these.

Non-limiting examples of the negative electrode active material include conventional negative electrode active materials that can be used for negative electrodes of conventional lithium secondary batteries, and in particular, lithium metal or lithium alloy, carbon, petroleum coke, activated carbon, A lithium adsorption material such as graphite or other carbons may be used.

Non-limiting examples of the anode current collector include a foil made of aluminum, nickel or a combination thereof, and non-limiting examples of the cathode current collector include copper, gold, nickel or a copper alloy or a combination thereof. There are manufactured foils and the like.

In one embodiment of the present invention, the conductive material used in the negative electrode and the positive electrode may be each independently added in an amount of 1% to 30% by weight based on the total weight of the active material layer. Such a conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and server black; conductive fibers such as carbon fibers and metal fibers; fluorinated carbon; metal powders such as aluminum and nickel powder; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

In one embodiment of the present invention, the binder used in the negative electrode and the positive electrode is a component that independently assists in the bonding of the active material and the conductive material and the bonding to the current collector, typically 1% by weight based on the total weight of the active material layer. to 30% by weight. Examples of such binders include polyvinylidene fluoride (PVdF), polyacrylic acid (PAA), polyvinyl alcohol, carboxyl methyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluorocarbon, roethylene, polyethylene, polypropylene, ethylene-propylene-dienter polymer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluororubber, various copolymers and the like.

In one embodiment of the present invention, the lithium secondary battery includes an electrolyte solution, and the electrolyte solution may include an organic solvent and a lithium salt. In addition, an organic solid electrolyte or an inorganic solid electrolyte may be used as the electrolyte solution.

Examples of the organic solvent include N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane , tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid Triester, trimethoxy methane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-ibidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, ethyl propionate An aprotic organic solvent such as may be used.

The lithium salt is a material that is easily soluble in the organic solvent, and is, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, lithium chloroborane, lithium lower aliphatic carbonate, lithium 4-phenyl borate, imide, and the like can be used. have.

In addition, for the purpose of improving charge and discharge characteristics, flame retardancy, etc. in the electrolyte solution, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, Nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxy ethanol, aluminum trichloride, etc. may be added. have. In some cases, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further included to impart incombustibility, and carbon dioxide gas may be further included to improve storage properties at high temperatures.

Examples of the organic solid electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphoric acid ester polymers, polyagitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, A polymer containing an ionic dissociation group or the like can be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitride, halide, sulfate, and the like of Li such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ , etc. may be used.

The injection of the electrolyte may be performed at an appropriate stage in the battery manufacturing process according to the manufacturing process and required physical properties of the final product. That is, it may be applied before battery assembly or at the final stage of battery assembly.

In one embodiment of the present invention, as a process of applying the separator containing a crosslinked structure for lithium secondary battery to a battery, in addition to winding, which is a general process, lamination, stack, and folding processes of a separator and an electrode can be performed. do.

In one embodiment of the present invention, the crosslinked structure-containing separator for a lithium secondary battery may be interposed between a positive electrode and a negative electrode of a lithium secondary battery, and when a plurality of cells or electrodes are assembled to form an electrode assembly, adjacent cells or electrodes may be interposed between them. The electrode assembly may have various structures such as a simple stack type, a jelly-roll type, a stack-folding type, and a lamination-stack type.

Hereinafter, examples will be described in detail to aid understanding of the present invention. However, the embodiments according to the present invention can be modified in many different forms, and the scope of the present invention should not be construed as being limited to the following examples. Embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

Example 1

Preparation of olefin polymer porous support

Ethylene polymer (Korea Petrochemical VH035, weight average molecular weight: 600,000) 70 parts by weight, liquid paraffin oil (Kukdong Petrochemical Co., Ltd., LP350) 30 parts by weight, pentaerythritol-tetrakis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] as the first antioxidant (Pentaerythritol tetrakis[3-(3,5 -di-tert-butyl-4-hydroxyphenyl)propionate] (BASF , Irganox 1010) 5000 ppm, and tris(2,4-di-t-butylphenyl)phosphite (BASF, Irgafos 168) 5000 as a secondary antioxidant An olefin polymer composition was prepared by mixing ppm.

The prepared olefin polymer composition was put into a twin screw extruder and kneaded to react and extrude.

It was molded into a sheet form by passing through a die and a cooling roll, and then biaxially stretched with a tender-type sequential stretcher in the machine direction (MD) direction and then perpendicular direction (TD) direction.

From the thus obtained stretched sheet, liquid paraffin oil was extracted with methylene chloride and heat-set at 130° C. to prepare a porous olefin polymer support.

Preparation of Separator Containing Crosslinked Structure for Lithium Secondary Battery

As a photoinitiator, 2-isopropyl thioxanthone (Sigma Aldrich Co.) was prepared.

A high-pressure mercury lamp (Ritzen high-pressure mercury lamp, LH-250 / 800-A) was prepared as a UV light source.

A composition for photocrosslinking was prepared by adding the photoinitiator in an amount of 0.05 parts by weight based on 100 parts by weight of acetone.

After immersing the prepared olefin polymer porous support in the photocrosslinking composition, take it out, and cut the coating solution using a bar so that the photocrosslinking composition does not remain on the surface of the porous support. 0.0365 parts by weight relative to 100 parts by weight of the known support was present, and dried at room temperature (25 ° C) for 1 minute.

The olefin polymer porous support coated with the photocrosslinking composition was irradiated with ultraviolet light so that the integrated light amount, that is, the irradiated light amount of UV was 500 mJ / cm ² . At this time, the ultraviolet light irradiation intensity was 80% of the ultraviolet light source did

Thus, a crosslinked structure-containing separator for a lithium secondary battery including a crosslinked structure-containing olefin polymer porous support having a crosslinked structure in which polymer chains are directly connected was obtained.

Example 2

Preparation of olefin polymer porous support

An olefin polymer porous support was prepared in the same manner as in Example 1, except that an antioxidant was not added.

Preparation of Separator Containing Crosslinked Structure for Lithium Secondary Battery

After preparing a composition for photocrosslinking by adding the photoinitiator to 0.025 parts by weight based on 100 parts by weight of acetone, the olefin polymer porous support prepared above is immersed in the composition for photocrosslinking, and then taken out for photocrosslinking on the surface of the porous support Crosslinked structure-containing separator for lithium secondary battery in the same manner as in Example 1, except that the content of the photoinitiator was 0.018 parts by weight relative to 100 parts by weight of the olefin polymer porous support while cutting the coating solution using a bar so that no composition remained. was obtained.

Comparative Example 1

In the H-NMR measurement, the number of double bonds present in the olefin polymer chain is 0.10 per 1000 carbon atoms, and as the first antioxidant, pentaerythritol-tetrakis-[3-(3,5-di-t-butyl- 4-hydroxyphenyl)propionate] (Pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (BASF® , Irganox 1010) 5000 ppm, and tris ( 2,4-di-t-butylphenyl) phosphite (BASF, Irgafos 168) 5000 ppm ethylene polymer porous film (Senior Company, Weight average molecular weight: 600,000) was used as a separator for a lithium secondary battery without any treatment.

Comparative Example 2

Preparation of olefin polymer porous support

Olefin polymer porous support in the same manner as in Example 1, except that an ethylene polymer having 8.0 double bonds per 1000 carbon atoms was used in the H-NMR measurement and no antioxidant was added. was manufactured.

Preparation of Separator Containing Crosslinked Structure for Lithium Secondary Battery

After preparing a composition for photocrosslinking by adding 0.5 parts by weight of the photoinitiator based on 100 parts by weight of acetone, the olefin polymer porous support prepared above is immersed in the composition for photocrosslinking, and then taken out for photocrosslinking on the surface of the porous support While cutting the coating solution using a bar so that no composition remains, the content of the photoinitiator is 0.365 parts by weight relative to 100 parts by weight of the olefin polymer porous support. In the same manner as in Example 1, containing a crosslinked structure for a lithium secondary battery A separation membrane was obtained.

Comparative Example 3

Preparation of olefin polymer porous support

An olefin polymer porous support was prepared in the same manner as in Example 1, except that an ethylene polymer having 8.0 double bonds per 1000 carbon atoms was used in the H-NMR measurement.

Preparation of Separator Containing Crosslinked Structure for Lithium Secondary Battery

After preparing a composition for photocrosslinking by adding the photoinitiator to 0.025 parts by weight based on 100 parts by weight of acetone, the olefin polymer porous support prepared above is immersed in the composition for photocrosslinking, and then taken out for photocrosslinking on the surface of the porous support Crosslinked structure for lithium secondary batteries in the same manner as in Example 1, except that the content of the photoinitiator was 0.018 parts by weight relative to 100 parts by weight of the olefin polymer porous support while cutting the coating solution using a bar so that no composition remained. A containing separation membrane was prepared.

Comparative Example 4

After preparing the composition for photocrosslinking by adding the photoinitiator to 1.0 parts by weight based on 100 parts by weight of acetone, the olefin polymer porous support prepared in Example 1 was immersed in the composition for photocrosslinking, and then taken out, and the surface of the porous support Lithium secondary in the same manner as in Example 1, except that the content of the photoinitiator was 0.73 parts by weight relative to 100 parts by weight of the olefin polymer porous support while cutting the coating solution using a bar so that the composition for photocrosslinking did not remain in the A separator containing a cross-linked structure for batteries was obtained.

Evaluation Example 1: Evaluation of physical properties of separation membrane

The thickness, crosslinking degree, air permeability, basis weight, meltdown temperature, shutdown temperature, and puncture strength of the separators prepared in Examples 1 to 2 and Comparative Examples 1 to 4 are shown in Table 1 below.

Evaluation of degree of crosslinking

The separator was immersed in a xylene solution at 135° C. according to ASTM D 2765 and boiled for 12 hours, and then the remaining weight was measured and the degree of crosslinking was calculated as a percentage of the remaining weight compared to the initial weight.

Air permeability evaluation

Air permeability (Gurley) was measured by the ASTM D726-94 method. Gurley, as used herein, is the resistance to the flow of air, measured by a Gurley densometer. The air permeability value described here is expressed as the time (seconds) required for 100 cc of air to pass through the cross section of the separator 1 in ² under a pressure of 12.2 inH ₂ O, that is, the aeration time.

basis weight evaluation

Basis weight (g/m ² ) was evaluated by preparing a sample so that each of the width and length of the separator was 1 m, and measuring its weight.

Meltdown temperature evaluation

The meltdown temperature was measured by thermomechanical analysis (TMA) after taking samples in the machine direction (MD) and transverse direction of the separator, respectively. Specifically, a sample having a width of 4.8 mm x a length of 8 mm was placed in a TMA device (TA Instrument, Q400), and the temperature was changed from 30 °C to 220 °C at a heating rate of 5 °C/min while a tension of 0.01 N was applied. As the temperature increased, the length of the sample was changed, and the length was rapidly increased to measure the temperature at which the sample broke in each of the machine direction (MD) and the transverse direction, and this was set as the meltdown temperature.

Shutdown temperature evaluation

After fixing the separator to an air permeability measuring device, the air permeability was measured while the temperature was raised by 5°C per minute. Air permeability was measured by using a royal air permeability meter (Asahi Seiko, model name: EG01-55-1MR) to measure the time (sec) required for 100 ml of air to pass through the membrane at a constant pressure of 0.05 Mpa. The temperature at which the air permeability of the separation membrane rapidly increased was set as the shutdown temperature.

Puncture strength evaluation

A specimen having a size of 50 mm X 50 mm was prepared.

After setting a round tip of 1 mm to operate at a speed of 120 mm/min according to ASTM D2582, the puncture strength was measured.

As can be seen in Table 1, the separators prepared in Examples 1 to 3 have a photoinitiator content of 0.36 parts by weight or less based on 100 parts by weight of the olefin polymer porous support, and the number of double bonds in the olefin polymer chain is 0.5 Since the meltdown temperature was 160 ° C. or higher, the puncture strength did not significantly decrease compared to before crosslinking.

On the other hand, in the separator prepared in Comparative Example 1, photocrosslinking of the olefin polymer porous support did not occur, so it was confirmed that the meltdown temperature of the separator was very low compared to that of the separator prepared in Example.

In the separators prepared in Comparative Examples 2 to 3, the number of double bonds in the olefin polymer chain exceeded 0.5, and the meltdown temperature was 160 ° C or higher, but excessive radical formation caused shrinkage of the separator compared to before crosslinking. The thickness decreased slightly, and the puncture strength greatly decreased compared to before crosslinking.

The separator prepared in Comparative Example 4 had a meltdown temperature of 160 ° C or more because the content of the photoinitiator exceeded 0.36 parts by weight based on 100 parts by weight of the olefin polymer porous support, but excessive radicals were formed, resulting in shrinkage of the separator compared to before crosslinking The thickness was slightly reduced, and the puncture strength was greatly reduced compared to before crosslinking.

Claims (19)

Preparing an olefin polymer porous support comprising a photoinitiator and having 0.01 to 0.5 double bonds per 1000 carbon atoms in an olefin polymer chain as measured by H-NMR;
Including; irradiating ultraviolet rays to the olefin polymer porous support,
The content of the photoinitiator is a method for producing a separator containing a crosslinked structure for a lithium secondary battery, characterized in that 0.015 parts by weight to 0.36 parts by weight relative to 100 parts by weight of the olefin polymer porous support. According to claim 1,
In the step of preparing the olefin polymer porous support, an antioxidant is further added, and the content of the antioxidant is 500 ppm to 20000 ppm based on the content of the olefin polymer porous support. Contains a crosslinked structure for a lithium secondary battery A method for manufacturing a separator. According to claim 2,
A method for producing a separator containing a crosslinked structure for a lithium secondary battery, characterized in that the antioxidant comprises a first antioxidant that is a radical scavenger and a second antioxidant that is a peroxide decomposer. According to claim 3,
The method of manufacturing a separator containing a crosslinked structure for a lithium secondary battery, characterized in that the first antioxidant comprises a phenol-based antioxidant, an amine-based antioxidant, or a mixture thereof. According to claim 3,
The method of manufacturing a separator containing a crosslinked structure for a lithium secondary battery, characterized in that the second antioxidant comprises a phosphorus-based antioxidant, a sulfur-based antioxidant, or a mixture thereof. According to claim 3,
The content of the first antioxidant is 500 ppm to 10000 ppm based on the content of the olefin polymer porous support, and the content of the second antioxidant is 500 ppm to 10000 ppm based on the content of the olefin polymer porous support Method for producing a separator containing a cross-linked structure for a lithium secondary battery. According to claim 1,
Method for producing a crosslinked structure-containing separator for a lithium secondary battery, characterized in that the photoinitiator includes a Type 2 photoinitiator. According to claim 1,
The photoinitiator is thioxanthone (TX: Thioxanthone), a thioxanthone derivative, a benzophenone (BPO: benzophenone), a benzophenone derivative, or two or more of them. Preparation of a separator containing a crosslinked structure for a lithium secondary battery, characterized in that Way. According to claim 1,
The step of preparing the olefin polymer porous support,
A method for producing a separator containing a crosslinked structure for a lithium secondary battery, comprising the steps of coating and drying the photocrosslinking composition containing the photoinitiator and the solvent on the outside of the olefin polymer porous support. According to claim 9,
The method for producing a separator containing a crosslinked structure for a lithium secondary battery, characterized in that the composition for photocrosslinking is a photoinitiator solution composed of the photoinitiator and the solvent. According to claim 9,
The method of manufacturing a separator containing a crosslinked structure for a lithium secondary battery, characterized in that the composition for photocrosslinking is a slurry for forming an inorganic hybrid void layer containing an inorganic filler, a binder polymer, the photoinitiator, and the solvent. According to claim 9,
The step of coating and drying the photocrosslinking composition containing the photoinitiator and the solvent on the outside of the olefin polymer porous support,
Forming an inorganic hybrid void layer by coating and drying at least one surface of the olefin polymer porous support with a slurry for forming an inorganic hybrid void layer containing an inorganic filler, a first binder polymer, and a dispersion medium; and
Coating and drying a coating solution for forming a porous adhesive layer containing a second binder polymer, the photoinitiator, and the solvent on the upper surface of the inorganic hybrid porous layer and drying it; manufacturing a separator containing a crosslinked structure for a lithium secondary battery, comprising: Way. According to claim 1,
Method for producing a separator containing a crosslinked structure for a lithium secondary battery, characterized in that the amount of irradiation of the ultraviolet rays is 10 to 2000 mJ / cm ² . A crosslinked structure-containing separator for a lithium secondary battery, comprising the crosslinked structure-containing olefin polymer porous support prepared according to any one of claims 1 to 13. According to claim 14,
The cross-linked structure-containing separator for lithium secondary batteries is located on at least one surface of the cross-linked structure-containing olefin polymer porous support and includes an inorganic hybrid void layer containing an inorganic filler and a binder polymer Separator containing a cross-linked structure for lithium secondary batteries, characterized in that . According to claim 14,
an inorganic hybrid void layer in which the cross-linked structure-containing separator for lithium secondary battery is located on at least one surface of the cross-linked structure-containing olefin polymer porous support and includes an inorganic filler and a first binder polymer; and
A separator containing a crosslinked structure for a lithium secondary battery, comprising: a porous adhesive layer located on the inorganic hybrid void layer and containing a second binder polymer. According to claim 14,
A crosslinked structure-containing separator for lithium secondary batteries, characterized in that the meltdown temperature of the crosslinked structure-containing separator for lithium secondary batteries is 160 ° C or higher. According to claim 14,
A cross-linked structure-containing separator for lithium secondary batteries, characterized in that the shutdown temperature of the cross-linked structure-containing separator for lithium secondary batteries is 145 ° C or less. Including a positive electrode, a negative electrode, and a separator for a lithium secondary battery interposed between the positive electrode and the negative electrode,
A lithium secondary battery, characterized in that the separator for a lithium secondary battery is a separator containing a cross-linked structure for a lithium secondary battery according to claim 14.