The crosslinked structure includes a polyolefin porous support, a crosslinked structure-containing separator for a lithium secondary battery including the same, a method for manufacturing the same, and a lithium secondary battery including the separator

Abstract

The present invention relates to a crosslinked structure-containing polyolefin porous support having a crosslinked structure in which the number of double bonds present in the polyolefin chain is 0.01 to 0.6 per 1000 carbon atoms when measured by H-NMR and the polymer chains are directly linked to each other, a crosslinked structure-containing separator for a lithium secondary battery including the same, a manufacturing method thereof, and a lithium secondary battery including the same. The crosslinked structure-containing separator for a lithium secondary battery according to one embodiment of the present invention has improved safety at high temperatures and can minimize performance degradation even when a lithium secondary battery including the separator is stored at high temperatures.

Description

Technical Field

[0001] This application claims priority based on Korean Patent Application Nos. 10-2021-0059585 and 10-2021-0059586, filed on May 7, 2021.

[0002] The present invention relates to a crosslinked structure-containing polyolefin porous support, a crosslinked structure-containing separator for a lithium secondary battery including the same, a method for manufacturing the same, and a lithium secondary battery including the separator.

Background Art

[0003] In recent years, interest in energy storage technology has been increasing. The application fields are expanding to mobile phones, camcorders, notebook computers, and even the energy of electric vehicles, and there is an increasing demand for higher energy density of batteries used as power sources for such electronic devices. Lithium secondary batteries are the batteries that can best meet such requirements, and research on them is currently being actively conducted.

[0004] Such a lithium secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator. Among them, the separator serves to separate the positive electrode and the negative electrode and electrically insulate them.

[0005] Although polyolefin separators are widely used as such separators, in the case of a polyethylene (PE) separator, which is a typical polyolefin separator, since the melting point (Tm) is low, if the temperature of the battery rises above the melting point of polyethylene in a battery misuse environment, a melt-down phenomenon may occur, leading to the risk of ignition and explosion. Due to its material properties and manufacturing process characteristics, the separator shows significant heat shrinkage behavior in situations such as high temperature, which may lead to safety problems such as internal short circuits.

[0006] Therefore, there is an urgent need for a separator that can ensure safety at high temperatures.

Summary of the Invention

Problems to be Solved by the Invention

[0007] The problem to be solved by the present invention is to provide a crosslinked structure-containing polyolefin porous support with improved high-temperature safety.

[0008] Another problem to be solved by the present invention is to provide a crosslinked structure-containing separator for a lithium secondary battery including the crosslinked structure-containing polyolefin porous support, and a lithium secondary battery equipped with the same, in which deterioration of performance during high-temperature storage is minimized.

[0009] Still another problem to be solved by the present invention is to provide a method for manufacturing a crosslinked structure-containing separator for a lithium secondary battery that can effectively crosslink a polyolefin porous support and minimize side reactions.

Means for Solving the Problems

[0010] To solve the above problems, according to one aspect of the present invention, a crosslinked structure-containing polyolefin porous support of the following embodiments is provided.

[0011] The first embodiment is Regarding a crosslinked structure-containing polyolefin porous support, when measured by H-NMR, the number of double bonds present in the polyolefin chain is 0.01 to 0.6 per 1000 carbon atoms, and it includes a crosslinked structure in which polymer chains are directly connected to each other.

[0012] According to the second embodiment, in the first embodiment, The crosslinking degree of the crosslinked structure-containing polyolefin porous support can be 10% to 45%.

[0013] To solve the above problems, according to one aspect of the present invention, a crosslinked structure-containing separator for a lithium secondary battery of the following embodiments is provided.

[0014] The third embodiment is Relates to a crosslinked structure-containing separator for a lithium secondary battery including a crosslinked structure-containing polyolefin porous support of a first embodiment or a second embodiment.

[0015] According to a fourth embodiment, in a third embodiment, the crosslinked structure-containing separator for a lithium secondary battery is located on at least one surface of the crosslinked structure-containing polyolefin porous support and may further include an inorganic composite void layer including an inorganic filler and a binder polymer.

[0016] According to a fifth embodiment, in a fourth embodiment, the inorganic filler is BaTiO3, Pb(Zr,Ti)O3 (PZT), Pb 1-x La x Zr 1-y Ti y O3 (PLZT, 0 < x < 1, 0 < y < 1), Pb(Mg 1 / 3 Nb 2 / 3 )O3-PbTiO3 (PMN-PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, Mg(OH)2, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, AlOOH, Al(OH)3, SiC, TiO2, lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z (PO4)3, 0 < x < 2, 0 < y < 1, 0 < z < 3), (LiAlTiP) x O y -based glass (0 < x < 4, 0 < y < 13), lithium germanium thiophosphate (Li x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride (Li x N y , 0 < x < 4, 0 < y < 2), SiS2-based glass (Li x Si y S z, (0 < x < 3, 0 < y < 2, 0 < z < 4), P2S5-based glass (Li x P y S z , (0 < x < 3, 0 < y < 3, 0 < z < 7), or may include two or more of these.

[0017] According to the sixth embodiment, in the fourth embodiment or the fifth embodiment, the binder polymer is polyvinylidene fluoride - hexafluoropropylene, polyvinylidene fluoride - chlorotrifluoroethylene, polyvinylidene fluoride - tetrafluoroethylene, polyvinylidene fluoride - trichloroethylene, acrylic copolymer, styrene - butadiene copolymer, polyacrylic acid, polymethyl methacrylate, polybutyl acrylate, polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl alcohol, polyvinyl acetate, ethylene vinyl acetate copolymer, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, or may include two or more of these.

[0018] According to the seventh embodiment, in the third embodiment, the crosslinked structure - containing separator for the lithium secondary battery is located on at least one surface of the crosslinked structure - containing polyolefin porous support, and an inorganic composite void layer containing an inorganic filler and a first binder polymer, and a porous adhesive layer containing a second binder polymer, which may be further included on the inorganic composite void layer.

[0019] According to the eighth embodiment, in the seventh embodiment, the inorganic filler is BaTiO3, Pb(Zr,Ti)O3 (PZT), Pb 1-x La x Zr 1-y Ti y O3 (PLZT, 0 < x < 1, 0 < y < 1), Pb(Mg 1 / 3 Nb2 / 3 ) O3-PbTiO3 (PMN-PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, Mg(OH)2, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, AlOOH, Al(OH)3, SiC, TiO2, lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z (PO4)3, 0 < x < 2, 0 < y < 1, 0 < z < 3), (LiAlTiP) x O y -based glass (0 < x < 4, 0 < y < 13), lithium germanium thiophosphate (Li x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride (Li x N y , 0 < x < 4, 0 < y < 2), SiS2-based glass (Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4), P2S5-based glass (Li x P y S z , 0 < x < 3, 0 < y < 3, 0 < z < 7), or may include two or more of these.

[0020] According to the ninth embodiment, in the seventh or eighth embodiment, the first binder polymer may include an acrylic polymer, polyacrylic acid, styrene-butadiene rubber, polyvinyl alcohol, or two or more of these.

[0021] According to the tenth embodiment, in any one of the seventh to ninth embodiments, The second binder polymer may include polyvinylidene fluoride, polyvinylidene fluoride - hexafluoropropylene, polyvinylidene fluoride - trichloroethylene, polyvinylidene fluoride - tetrafluoroethylene, polyvinylidene fluoride - trifluoroethylene, polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, ethylhexyl acrylate - methyl methacrylate copolymer, ethylene vinyl acetate copolymer, polyethylene oxide, polyarylate, or two or more of these.

[0022] According to the 11th embodiment, in any one of the 3rd to 10th embodiments, The melt - down temperature of the cross - linked structure - containing separator for the lithium secondary battery may be 160 °C or higher.

[0023] According to the 12th embodiment, in any one of the 3rd to 11th embodiments, The shut - down temperature of the cross - linked structure - containing separator for the lithium secondary battery may be 145 °C or lower.

[0024] To solve the above problems, according to one aspect of the present invention, there is provided a method for manufacturing a cross - linked structure - containing separator for a lithium secondary battery of the following embodiments.

[0025] The 13th embodiment is Preparing a polyolefin porous support containing a photoinitiator and having 0.01 to 0.5 double bonds per 1000 carbon atoms in the polyolefin chain when measured by H - NMR; Irradiating the polyolefin porous support with ultraviolet light, and includes The content of the photoinitiator is 0.015 to 0.36 parts by weight with respect to 100 parts by weight of the polyolefin porous support, and relates to a method for manufacturing a cross - linked structure - containing separator for a lithium secondary battery.

[0026] According to the 14th embodiment, in the 13th embodiment, At the stage of preparing the polyolefin porous support, an antioxidant is further added, and the content of the antioxidant can be 500 ppm to 20,000 ppm based on the content of the polyolefin porous support.

[0027] According to the 15th embodiment, in the 14th embodiment, The antioxidant may include a first antioxidant that is a radical scavenger and a second antioxidant that is a peroxide decomposer.

[0028] According to the 16th embodiment, in the 15th embodiment, The first antioxidant may include a phenolic antioxidant, an amine-based antioxidant, or a mixture thereof.

[0029] According to the 17th embodiment, in the 15th or 16th embodiment, The second antioxidant may include a phosphorus-based antioxidant, a sulfur-based antioxidant, or a mixture thereof.

[0030] According to the 18th embodiment, in any one of the 15th to 17th embodiments, The content of the first antioxidant is 500 ppm to 10,000 ppm based on the content of the polyolefin porous support, and the content of the second antioxidant can be 500 ppm to 10,000 ppm based on the content of the polyolefin porous support.

[0031] According to the 19th embodiment, in any one of the 13th to 18th embodiments, The photoinitiator may include a type II photoinitiator.

[0032] According to the 20th embodiment, in any one of the 13th to 19th embodiments, The photoinitiator may include thioxanthone (TX), a thioxanthone derivative, benzophenone (BPO), a benzophenone derivative, or two or more of these.

[0033] According to the 21st embodiment, in any one of the 13th to 20th embodiments, the step of preparing the polyolefin porous support may include coating and drying the photocrosslinking composition containing the photoinitiator and the solvent on the outside of the polyolefin porous support.

[0034] According to the 22nd embodiment, in the 21st embodiment, the photocrosslinking composition may be a photoinitiator solution containing the photoinitiator and the solvent.

[0035] According to the 23rd embodiment, in the 21st embodiment, the photocrosslinking composition may be a slurry for forming an inorganic composite void layer containing an inorganic filler, a binder polymer, the photoinitiator, and the solvent.

[0036] According to the 24th embodiment, in the 21st embodiment, the step of coating and drying the photocrosslinking composition containing the photoinitiator and the solvent on the outside of the polyolefin porous support may include coating and drying a slurry for forming an inorganic composite void layer containing an inorganic filler, a first binder polymer, and a dispersion medium on at least one surface of the polyolefin porous support to form an inorganic composite void layer, and coating and drying a coating liquid for forming a porous adhesive layer containing a second binder polymer, the photoinitiator, and the solvent on the upper surface of the inorganic composite void layer.

[0037] According to the 25th embodiment, in any one of the 13th to 24th embodiments, the irradiation light amount of the ultraviolet ray may be 10 to 2000 mJ / cm 2 and may be so.

[0038] To solve the above problems, according to one aspect of the present invention, there is provided a method for manufacturing a cross-linked structure-containing separator for a lithium secondary battery of the following embodiments.

[0039] The 26th embodiment is including a positive electrode, a negative electrode, and a separator for a lithium secondary battery interposed between the positive electrode and the negative electrode, relating to a lithium secondary battery in which the separator for a lithium secondary battery is a cross-linked structure-containing separator for a lithium secondary battery according to any one of the 3rd to 12th embodiments.

Effect of the Invention

[0040] The cross-linked structure-containing polyolefin porous support according to one aspect of the present invention has, at the time of H-NMR measurement, the number of double bonds present in the polyolefin chain being 0.01 to 0.6 per 1000 carbon atoms, and includes a cross-linked structure in which polymer chains are directly connected to each other, so that it has excellent high-temperature safety and at the same time can minimize side reactions.

[0041] The cross-linked structure-containing separator for a lithium secondary battery according to one aspect of the present invention includes the cross-linked structure-containing polyolefin porous support according to one embodiment of the present invention, so that it has excellent high-temperature safety and at the same time can minimize side reactions.

[0042] The method for manufacturing a cross-linked structure-containing separator for a lithium secondary battery according to one aspect of the present invention cross-links a polyolefin porous support in which the content of a photoinitiator is 0.015 to 0.36 parts by weight with respect to 100 parts by weight of the polyolefin porous support, and the number of double bonds present in the polyolefin chain is 0.01 to 0.5 per 1000 carbon atoms at the time of H-NMR measurement, so that not only can the polyolefin porous support be effectively cross-linked, but also side reactions can be minimized.

[0043] The lithium secondary battery according to one aspect of the present invention includes a cross-linked structure-containing separator for a lithium secondary battery according to one embodiment of the present invention, and thus can minimize performance degradation even when stored at high temperatures.

[0044] The following drawings attached to this specification illustrate desirable embodiments of the present invention and serve to further understand the technical idea of the present invention together with the detailed description of the invention. Therefore, the present invention should not be construed as being limited only to the matters described in the drawings.

Brief Description of the Drawings

[0045]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0046] Hereinafter, desirable embodiments of the present invention will be described in detail. Prior to this, the terms and words used in this specification and the claims are not to be construed as being limited to the ordinary and dictionary meanings. The inventor himself interprets them in accordance with the meaning and concept corresponding to the technical idea of the present invention in accordance with the principle that he can appropriately define the concept of the terms in order to explain the invention in the best way.

[0047] Therefore, the embodiments described in this specification and the configurations shown in the drawings are merely the most desirable embodiments of the present invention and do not represent all of the technical ideas of the present invention. It should be understood that there may be various equivalents and modifications that can replace them at the time of this application.

[0048] Terms such as "first" and "second" are used to distinguish one component from another, and each component is not limited by these terms.

[0049] In the present invention, the photoinitiator can crosslink the polyolefin porous support with only the photoinitiator, without a crosslinking agent or other components such as a co-initiator or a synergist. Only by light absorption, while the hydrogen atom in the photoinitiator is removed by hydrogen abstraction reaction, the photoinitiator becomes a reactive compound. Such a photoinitiator forms radicals on the polymer chains in the polyolefin porous support to make the polymer chains reactive, and the polymer chains are directly linked to each other for photocrosslinking. For example, in the small amount of double bond structures present in the polyolefin, since the hydrogen abstraction reaction by the photoinitiator is possible, radicals can be formed on the polymer chains while hydrogen atoms are being abstracted from the double bond structures in the polyolefin by the hydrogen abstraction reaction only by light absorption.

[0050] The radicals formed from the polyolefin chains by the hydrogen abstraction reaction of the photoinitiator crosslink the polymer chains. At the same time, such radicals additionally generate radicals in the polyolefin chains, whereby a double bond structure may remain or be additionally generated in the polyolefin chains.

[0051] As a result of photocrosslinking by the photoinitiator, the double bond structures remaining in the crosslinked structure-containing polyolefin porous support having a crosslinked structure in which the polymer chains are directly connected to each other become parts where many side reactions can occur. Therefore, the number of such double bonds can affect the performance of the crosslinked structure-containing polyolefin porous support.

[0052] The inventors of the present invention have found that, in a crosslinked structure-containing polyolefin porous support, the problem of side reactions can be minimized by adjusting the number of double bonds present in the polyolefin chains, and have thus completed the present invention.

[0053] The crosslinked structure-containing polyolefin porous support according to one embodiment of the present invention is When measured by 1H-NMR, the number of double bonds present in the polyolefin chains is from 0.01 to 0.6 per 1000 carbon atoms, and includes a crosslinked structure in which polymer chains are directly linked to each other.

[0054] In the present specification, the "crosslinked structure in which polymer chains are directly linked to each other" means a state in which polymer chains substantially composed of polyolefin, more preferably polymer chains composed only of polyolefin, become reactive by the addition of a photoinitiator, and the polymer chains are directly crosslinked to each other. Therefore, a crosslinking reaction that occurs between crosslinking agents by the addition of an additional crosslinking agent does not correspond to the "crosslinked structure in which polymer chains are directly linked to each other" referred to in the present invention. Further, a crosslinking reaction that occurs between an additional crosslinking agent and a polymer chain does not correspond to the "crosslinked structure in which polymer chains are directly linked to each other" referred to in the present invention, even if the polymer chain is substantially composed of polyolefin or composed only of polyolefin.

[0055] In one embodiment of the present invention, the crosslinked structure-containing polyolefin porous support may not include a crosslinked structure in which a photoinitiator and a polymer chain are directly linked, and may include only a crosslinked structure in which polymer chains are directly linked to each other.

[0056] In one embodiment of the present invention, the crosslinked structure-containing polyolefin porous support contains only a crosslinked structure in which polymer chains are directly linked to each other, and does not contain a crosslinked structure in which a photoinitiator and a polymer chain are directly linked. Since such a crosslinked structure has a lower reaction enthalpy than the crosslinked structure between polymer chains in the polyolefin porous support, it may be decomposed and cause side reactions. In addition, when the photoinitiator and the polymer chain are crosslinked with each other, there is a risk of lowering the melting temperature of the polyolefin chain and deteriorating the properties of the polyolefin porous support such as the shutdown temperature. The crosslinked structure-containing polyolefin porous support according to one embodiment of the present invention can prevent such problems by containing only a crosslinked structure in which polymer chains are directly linked to each other.

[0057] In one embodiment of the present invention, during H-NMR measurement, the number of double bonds present in the polyolefin chains of the crosslinked structure-containing polyolefin porous support is 0.01 to 0.6 per 1000 carbon atoms. When the crosslinked structure-containing polyolefin porous support has the double bonds in the above-mentioned number, the portion where side reactions occur can be minimized.

[0058] When the number of double bonds present in the polyolefin chain exceeds 0.6 per 1000 carbon atoms, side reactions occur and the performance of the crosslinked structure-containing polyolefin porous support deteriorates.

[0059] In one embodiment of the present invention, the number of double bonds present in the polyolefin chains of the crosslinked structure-containing polyolefin porous support may be 0.02 to 0.5, or 0.08 to 0.57 per 1000 carbon atoms. When the crosslinked structure-containing polyolefin porous support has the double bonds in the above-mentioned number, the portion where side reactions occur can be minimized.

[0060] In one embodiment of the present invention, the number of double bonds present in the polyolefin chains excluding the ends of the crosslinked structure-containing polyolefin porous support can be 0.005 to 0.59 per 1000 carbon atoms. Here, the "double bonds present in the polyolefin chains excluding the ends" refers to the double bonds present in the entire polyolefin chains excluding the ends of the polyolefin chains. Here, the "ends" mean the positions of the carbon atoms respectively connected to the terminals on both sides of the polyolefin chain.

[0061] In one embodiment of the present invention, the polyolefin porous support can be a porous film.

[0062] In one embodiment of the present invention, the polyolefin may include polyethylene; polypropylene; polybutylene; polypentene; polyhexene; polyoctene; copolymers of two or more of ethylene, propylene, butene, pentene, 4-methylpentene, hexene and octene; or mixtures thereof.

[0063] Non-limiting examples of the polyethylene include low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), and the like. When the polyethylene is high-density polyethylene with high crystallinity and a high melting point of the resin, it is easy to increase the modulus while having the desired level of heat resistance.

[0064] In one embodiment of the present invention, the weight average molecular weight of the polyolefin can be 200,000 to 1,500,000, 220,000 to 1,000,000, or 250,000 to 800,000. When the weight average molecular weight of the polyolefin is within the above-mentioned range, a separation membrane excellent in strength and heat resistance can be finally obtained while ensuring the uniformity and film-forming processability of the polyolefin porous support.

[0065] The weight average molecular weight can be measured under the following conditions using gel permeation chromatography (GPC: PL GPC220, manufactured by Agilent Technologies). - Column: PL Olexis (Polymer Laboratories) - Solvent: TCB (trichlorobenzene) - Flow rate: 1.0 ml / min - Sample concentration: 1.0 mg / ml - Injection volume: 200 μl - Column temperature: 160 °C - Detector: High-temperature RI detector manufactured by Agilent - Standard: Polystyrene (corrected with a cubic function)

[0066] In one embodiment of the present invention, the crosslinking degree of the crosslinked structure-containing polyolefin porous support can be 10% to 45%, 15% to 40%, 20% to 35%, or 32% to 42%. When the crosslinked structure-containing polyolefin porous support satisfies the above-mentioned crosslinking degree range, it is easy to increase the modulus while having the desired level of heat resistance. For example, when the crosslinking degree of the crosslinked structure-containing polyolefin porous support is 20% or more, the melt-down temperature of the separation membrane including the crosslinked structure-containing polyolefin porous support tends to be 170 °C or higher.

[0067] At this time, the crosslinking degree is calculated as the percentage of the residual weight to the initial weight after immersing the crosslinked structure-containing polyolefin porous support in a xylene solution at 135 °C according to ASTM D2765, boiling for 12 hours, and then measuring the residual weight.

[0068] In one embodiment of the present invention, the thickness of the crosslinked structure-containing polyolefin porous support can be 3 μm to 16 μm, or 5 μm to 12 μm. When the thickness of the crosslinked structure-containing polyolefin porous support is within the above-mentioned range, damage to the crosslinked structure-containing polyolefin porous support can be prevented, and the energy density can be easily ensured.

[0069] The crosslinked structure-containing polyolefin porous support according to an embodiment of the present invention can improve heat resistance by having a crosslinked structure in which polymer chains are directly connected to each other.

[0070] The crosslinked structure-containing polyolefin porous support according to an embodiment of the present invention can maintain the pore structure of the polyolefin porous support substantially as it was before crosslinking even after crosslinking.

[0071] The crosslinked structure-containing polyolefin porous support according to an embodiment of the present invention can be used as a crosslinked structure-containing separator for a lithium secondary battery.

[0072] The crosslinked structure-containing separator for a lithium secondary battery according to an embodiment of the present invention may include the crosslinked structure-containing polyolefin porous support according to an embodiment of the present invention.

[0073] In one embodiment of the present invention, when the crosslinked structure-containing separator for a lithium secondary battery includes the crosslinked structure-containing polyolefin porous support having the above-described number of double bonds, the problem of deterioration of battery performance at high temperature and / or high voltage can be easily prevented.

[0074] When the crosslinked structure-containing separator for a lithium secondary battery according to an embodiment of the present invention has the above-described number of double bonds, the problem of deterioration of battery performance even when a battery equipped with such a separator is stored at a high temperature can be minimized.

[0075] When the number of double bonds present in the polyolefin chains of the crosslinked structure-containing separator for a lithium secondary battery according to an embodiment of the present invention exceeds 0.6 per 1000 carbon atoms, the performance of the battery deteriorates when a battery equipped with such a separator is stored at a high temperature.

[0076] The crosslinked structure-containing separator for a lithium secondary battery according to an embodiment of the present invention may include a crosslinked structure-containing polyolefin porous support having a crosslinked structure in which polymer chains are directly connected to each other.

[0077] The cross-linked structure-containing separator for a lithium secondary battery according to another embodiment of the present invention may further include an inorganic composite void layer located on at least one surface of the cross-linked structure-containing polyolefin porous support and containing an inorganic filler and a binder polymer. That is, it may include a cross-linked structure-containing polyolefin porous support and an inorganic composite void layer located on at least one surface of the cross-linked structure-containing polyolefin porous support and containing an inorganic filler and a binder polymer. This is shown in FIG. 1.

[0078] Referring to FIG. 1, the cross-linked structure-containing separator 1 for a lithium secondary battery according to an embodiment of the present invention may include a cross-linked structure-containing polyolefin porous support 10 and an inorganic composite void layer 20 located on at least one surface of the cross-linked structure-containing polyolefin porous support 10 and containing an inorganic filler and a binder polymer.

[0079] The inorganic composite void layer 20 may be formed on one or both surfaces of the cross-linked structure-containing polyolefin porous support 10. The inorganic composite void layer 20 includes an inorganic filler and a binder polymer that adheres these inorganic fillers to each other (i.e., the binder polymer connects and fixes between the inorganic fillers) so as to maintain the state where the inorganic fillers are bound to each other, and the binder polymer can maintain the state where the inorganic filler and the cross-linked structure-containing polyolefin porous support 10 are bound. The inorganic composite void layer 20 can prevent the cross-linked structure-containing polyolefin porous support 10 from showing extremely large thermal shrinkage behavior at high temperatures due to the inorganic filler, and can improve the safety of the separator. For example, the thermal shrinkage rates of the separator in the machine direction (MD) and the transverse direction (TD) measured after leaving it at 120 °C for 30 minutes may be 20% or less, 2% to 15%, or 2% to 10%, respectively.

[0080] The inorganic filler is not particularly limited as long as it is electrochemically stable. That is, the inorganic filler that can be used in the present invention is within the operating voltage range of the applied electrochemical element (for example, Li / Li +As long as oxidation and / or reduction reactions do not occur at a reference of 0 to 5 V, it is not particularly limited. In particular, when using inorganic particles with a high dielectric constant as the inorganic filler, it is possible to contribute to an increase in the dissociation degree of the electrolyte salt, such as a lithium salt, in the liquid electrolyte and improve the ionic conductivity of the electrolyte solution.

[0081] 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, desirably 10 or more. Non-limiting examples of inorganic fillers having a dielectric constant of 5 or more include BaTiO3, Pb(Zr,Ti)O3 (PZT), Pb 1-x La x Zr 1-y Ti y O3 (PLZT, 0 < x < 1, 0 < y < 1), Pb(Mg 1 / 3 Nb 2 / 3 )O3 - PbTiO3 (PMN - PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, Mg(OH)2, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, AlOOH, Al(OH)3, SiC, TiO2, or a mixture thereof, and the like.

[0082] In another embodiment of the present invention, as the inorganic filler, an inorganic filler having lithium ion transfer ability, that is, an inorganic filler that contains lithium element but does not store lithium and has a function of moving lithium ions, can be used. Non-limiting examples of inorganic fillers having lithium ion transfer ability include lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z (PO4)3, 0 < x < 2, 0 < y < 1, 0 < z < 3), (LiAlTiP) x O y -based glass (0 < x < 4, 0 < y < 13), lithium lanthanum titanate (Lix La y TiO3, where 0 < x < 2, 0 < y < 3), Li 3.25 Ge 0.25 P 0.75 Lithium germanium thiophosphate such as Li x Ge y P z S w , where 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride such as Li3N x N y , where 0 < x < 4, 0 < y < 2), SiS2-based glass such as Li3PO4-Li2S-SiS2 x Si y S z , where 0 < x < 3, 0 < y < 2, 0 < z < 4), P2S5-based glass such as LiI-Li2S-P2S5 x P y S z , where 0 < x < 3, 0 < y < 3, 0 < z < 7), or mixtures thereof, etc. may be mentioned.

[0083] In one embodiment of the present invention, the average particle size of the inorganic filler can be 0.01 μm to 1.5 μm. When the average particle size of the inorganic filler satisfies the above-mentioned range, it is easy to form an inorganic composite void layer 20 having a uniform thickness and an appropriate porosity, the dispersibility of the inorganic filler is good, and a desired energy density can be achieved.

[0084] At this time, the average particle size of the inorganic filler means D 50 particle size, "D 50"Particle size" means the particle size at the 50% point of the cumulative particle number distribution according to the particle size. The particle size can be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size analyzer (for example, Microtrac S3500). When the particles pass through the laser beam, the difference in the diffraction pattern according to the particle size is measured to calculate the particle size distribution. By calculating the particle diameter at the point where the cumulative particle number distribution according to the particle size in the measuring device reaches 50%, D 50 the particle size can be measured.

[0085] The binder polymer may have a glass transition temperature (glass transition temperature, T g ) of -200 to 200 °C. When the glass transition temperature of the binder polymer satisfies the above-mentioned range, the mechanical properties such as the flexibility and elasticity of the finally formed inorganic composite void layer can be improved. The binder polymer may have ion conduction ability. When the binder polymer has ion conduction ability, the performance of the battery 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 above-mentioned range, the degree of dissociation of the salt in the electrolyte can be improved.

[0086] In one embodiment of the present invention, the binder polymer may include poly(vinylidene fluoride - hexafluoropropylene), poly(vinylidene fluoride - chlorotrifluoroethylene), poly(vinylidene fluoride - tetrafluoroethylene), poly(vinylidene fluoride - trichloroethylene), acrylic copolymers, styrene - butadiene copolymers, polyacrylic acid, polymethyl methacrylate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl acetate, ethylene - vinyl acetate copolymer, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, or two or more thereof.

[0087] The acrylic copolymer may include, but is not limited to, an ethyl acrylate - acrylic acid - N,N - dimethylacrylamide copolymer, an ethyl acrylate - acrylic acid - 2 - (dimethylamino)ethyl acrylate copolymer, an ethyl acrylate - acrylic acid - N,N - diethylacrylamide copolymer, an ethyl acrylate - acrylic acid - 2 - (diethylamino)ethyl acrylate copolymer, or two or more thereof.

[0088] 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 diameter, and porosity of the finally produced inorganic composite void layer 20, and may be 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 above - described range, sufficient empty spaces can be ensured between the inorganic fillers, and the pore diameter and porosity of the inorganic composite void layer 20 can be easily ensured. Also, the adhesive force between the inorganic fillers can be easily ensured.

[0089] In one embodiment of the present invention, the inorganic composite void layer 20 may further contain additives such as a dispersant and / or a thickener. In one embodiment of the present invention, the additives may include polyvinylpyrrolidone (PVP), hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), ethylhydroxyethyl cellulose (EHEC), methyl cellulose (MC), carboxymethyl cellulose (CMC), hydroxyalkylmethyl cellulose, cyanoethylated polyvinyl alcohol, or two or more of these.

[0090] In one embodiment of the present invention, in the inorganic composite void layer 20, the inorganic fillers are filled and in contact with each other, and are bound to each other by the binder polymer, whereby an interstitial volume is formed between the inorganic fillers, and the interstitial volume between the inorganic fillers may have a structure that becomes an empty space to form pores.

[0091] In another embodiment of the present invention, the inorganic composite void layer 20 includes a plurality of nodes including the inorganic filler and a binder polymer that coats at least a part of the surface of the inorganic filler, and one or more filaments formed in a thread shape from the binder polymer of the nodes. The filament has a node connecting portion that extends from the node and connects to another node, and the node connecting portion may have a structure in which a plurality of filaments derived from the binder polymer cross each other to form a three-dimensional network structure.

[0092] In one embodiment of the present invention, the average pore diameter of the inorganic composite void layer 20 can be from 0.001 μm to 10 μm. The average pore diameter of the inorganic composite void layer 20 can be measured by a capillary flow porometry method. Capillary flow porometry is a method of measuring the diameter of the smallest pores in the thickness direction. Therefore, in order to measure the average pore diameter of only the inorganic composite void layer 20 by capillary flow porometry, the inorganic composite void layer 20 must be separated from the crosslinked structure-containing polyolefin porous support 10 and measured in a state where the separated inorganic composite void layer 20 is wrapped with a nonwoven fabric capable of supporting it. At this time, the pore size of the nonwoven fabric must be much larger than the pore size of the inorganic composite void layer 20.

[0093] In one embodiment of the present invention, the porosity of the inorganic composite void layer 20 can be 5% to 95%, 10% to 95%, 20% to 90%, or 30% to 80%. The porosity corresponds to a value obtained by subtracting the volume converted from the weight and density of each component of the inorganic composite void layer 20 from the volume calculated from the thickness, horizontal length, and vertical length of the inorganic composite void layer 20.

[0094] The porosity of the inorganic composite void layer 20 can be measured by the BET six-point method by nitrogen gas adsorption flow using a scanning electron microscope (SEM) image, a mercury porosimeter, or a porosimetry analyzer (Bell Japan, Belsorp-II mini).

[0095] In one embodiment of the present invention, the thickness of the inorganic composite void layer 20 can be from 1.5 μm to 5.0 μm on one surface of the crosslinked structure-containing polyolefin porous support 10. When the thickness of the inorganic composite void layer 20 satisfies the above-described range, the cell strength of the battery can be easily increased while the adhesion force to the electrode is excellent.

[0096] The crosslinked structure-containing separator for a lithium secondary battery according to another embodiment of the present invention is located on at least one surface of the crosslinked structure-containing polyolefin porous support, and includes an inorganic composite void layer containing an inorganic filler and a first binder polymer, and a porous adhesive layer containing a second binder polymer located on the inorganic composite void layer. That is, it may further include a crosslinked structure-containing polyolefin porous support, an inorganic composite void layer containing an inorganic filler and a first binder polymer located on at least one surface of the crosslinked structure-containing polyolefin porous support, and a porous adhesive layer containing a second binder polymer located on the inorganic composite void layer. This is shown in FIG. 2.

[0097] Referring to FIG. 2, the crosslinked structure-containing separator 1' for a lithium secondary battery according to an embodiment of the present invention includes a crosslinked structure-containing polyolefin porous support 10' having a crosslinked structure in which polymer chains are directly connected to each other, an inorganic composite void layer 20' located on at least one surface of the crosslinked structure-containing polyolefin porous support 10' and containing an inorganic filler and a first binder polymer, and a porous adhesive layer 30' located on the inorganic composite void layer 20' and containing a second binder polymer.

[0098] The inorganic composite void layer 20' can be formed on one or both surfaces of the crosslinked structure-containing polyolefin porous support 10'. The inorganic composite void layer 20' contains an inorganic filler and a first binder polymer that attaches these inorganic fillers to each other so that they can maintain a state of being bound to each other (that is, the first binder polymer connects and fixes between the inorganic fillers), and the first binder polymer can maintain a state in which the inorganic filler and the crosslinked structure-containing polyolefin porous support 10' are bound. The inorganic composite void layer 20' can prevent the crosslinked structure-containing polyolefin porous support 10' from showing extremely large heat shrinkage behavior at high temperatures, and can improve the safety of the separator. For example, the heat shrinkage rates of the separator in the machine direction (MD) and the transverse direction (TD) measured after being left at 150 °C for 30 minutes can be 20% or less, 2% - 15%, or 2% - 10% respectively.

[0099] Please refer to the above-mentioned content for the inorganic filler.

[0100] The first binder polymer may have a glass transition temperature (T g ) of -200 to 200 °C. When the glass transition temperature of the first binder polymer satisfies the above-mentioned range, the mechanical properties such as flexibility and elasticity of the finally formed inorganic composite void layer can be improved. The first binder polymer may have ion-conducting ability. When a binder polymer having ion-conducting ability is used as the first binder polymer, the performance of the battery can be further improved. The first 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 first binder polymer satisfies the above-mentioned range, the dissociation degree of the salt in the electrolyte can be improved.

[0101] 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, the heat resistance characteristics of the inorganic composite void layer can be further improved. For example, the thermal shrinkage rates of the separator in the machine direction (MD) and the transverse direction (TD) measured after standing at 150 °C for 30 minutes may be 20% or less, 2% to 15%, 2% to 10%, 2% to 5%, 0% to 5%, or 0% to 2%, respectively.

[0102] 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 of these.

[0103] Specifically, the acrylic polymer may include an acrylic homopolymer obtained by polymerizing only acrylic monomers, and may also include a copolymer of acrylic monomers and other monomers. For example, the acrylic polymer may include an ethylhexyl acrylate-methyl methacrylate copolymer, polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, polyacrylonitrile, a butyl acrylate-methyl methacrylate copolymer, or two or more of these.

[0104] In one embodiment of the present invention, the first binder polymer may be in a particulate form.

[0105] 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, 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 content of the inorganic filler distributed per unit area of the separation membrane increases, and the thermal safety of the separation membrane at high temperatures can be improved. For example, the thermal shrinkage rates of the separation membrane in the machine direction (MD) and the transverse direction (TD) measured after leaving it at 150°C for 30 minutes may be 20% or less, 2% to 15%, 2% to 10%, 2% to 5%, 0% to 5%, or 0% to 2%, respectively. Also, while ensuring sufficient adhesion between the inorganic fillers, sufficient empty spaces formed between the inorganic fillers can be secured.

[0106] Hereinafter, the characteristics of the inorganic composite void layer 20' different from the above-described inorganic composite void layer 20 will be described.

[0107] In one embodiment of the present invention, in the inorganic composite void layer, the inorganic fillers are filled and in contact with each other, and are bound to each other by the first binder polymer, whereby an interstitial volume is formed between the inorganic fillers, and the interstitial volume between the inorganic fillers may have a structure that becomes an empty space to form pores.

[0108] By including the second binder polymer, the porous adhesive layer 30' can ensure the adhesion force between the separation membrane provided with the inorganic composite void layer 20' and the electrode. Further, pores are formed in the porous adhesive layer 30', which can prevent the resistance of the separation membrane from increasing.

[0109] In one embodiment of the present invention, since the second binder polymer does not penetrate the surface and / or inside of the cross-linked structure-containing polyolefin porous support 10', the phenomenon of the resistance of the separation membrane increasing can be minimized.

[0110] The second binder polymer can be a binder polymer commonly used for forming an adhesive layer. The second binder polymer may have a glass transition temperature (T g ) of -200 to 200°C. When the glass transition temperature of the second binder polymer satisfies the above-described range, the mechanical properties such as the flexibility and elasticity of the finally formed adhesive layer can be improved. The second binder polymer can have ion conduction ability. When a binder polymer having ion conduction ability is used as the second binder polymer, the performance of the battery can be further improved. 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 above-described range, the degree of dissociation of the salt in the electrolyte can be improved.

[0111] In one embodiment of the present invention, the second binder polymer may include polyvinylidene fluoride, polyvinylidene fluoride - hexafluoropropylene, polyvinylidene fluoride - trichloroethylene, polyvinylidene fluoride - tetrafluoroethylene, polyvinylidene fluoride - trifluoroethylene, polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, ethylhexyl acrylate - methyl methacrylate copolymer, ethylene vinyl acetate copolymer, polyethylene oxide, polyarylate, or two or more of these.

[0112] In one embodiment of the present invention, the porous adhesive layer 30' may have a pattern including one or more adhesive portions containing the second binder polymer and one or more non - coating regions where the adhesive portions are not formed. The pattern may be dot - type, stripe - type, diagonal - line type, wave - type, triangular, square, or semi - circular. When the porous adhesive layer 30' has a pattern, the resistance of the separation membrane is improved, and since the electrolyte can be impregnated through the non - coating region where the porous adhesive layer is not formed, the electrolyte impregnation property of the separation membrane can be improved.

[0113] In one embodiment of the present invention, the thickness of the porous adhesive layer 30' may be 0.5 μm to 1.5 μm, 0.6 μm to 1.2 μm, or 0.6 μm to 1.0 μm. When the thickness of the porous adhesive layer 30' is within the above - described range, it has excellent adhesion to the electrode, and as a result, the cell strength of the battery can be increased. Also, it is advantageous in terms of the cycle characteristics and resistance characteristics of the battery.

[0114] The crosslinked-structure-containing separator for a lithium secondary battery according to an embodiment of the present invention includes a crosslinked-structure-containing polyolefin porous support having a crosslinked structure in which polymer chains are directly connected to each other, and thus has excellent high-temperature safety. At the same time, since the number of double bonds present in the polyolefin chains during H-NMR measurement is 0.01 to 0.6 per 1000 carbon atoms, side reactions can be prevented. For example, it is possible to minimize the deterioration of the performance of a lithium secondary battery including the crosslinked-structure-containing separator for a lithium secondary battery after storage at a high temperature, for example, about 60°C.

[0115] The crosslinked-structure-containing separator for a lithium secondary battery according to an embodiment of the present invention can have an increased melt-down temperature compared to a separator including an uncrosslinked polyolefin porous support. For example, the melt-down temperature of the separator can be 160°C or higher, 170°C or higher, or 180°C to 230°C.

[0116] As used herein, the "separator including an uncrosslinked polyolefin porous support" refers to a separator composed of an uncrosslinked polyolefin porous support without a crosslinked structure; a separator including an uncrosslinked polyolefin porous support without a crosslinked structure and an inorganic composite void layer located on at least one surface of the uncrosslinked polyolefin porous support without a crosslinked structure and containing an inorganic filler and a binder polymer; or a separator including an uncrosslinked polyolefin porous support without a crosslinked structure, an inorganic composite void layer located on at least one surface of the uncrosslinked polyolefin porous support without a crosslinked structure and containing an inorganic filler and the first binder polymer, and a porous adhesive layer located on the inorganic composite void layer and containing a second binder polymer.

[0117] The melting temperature can be measured by a thermomechanical analysis method (TMA). For example, after samples in the machine direction and the transverse direction are respectively collected, a sample with a width of 4.8 mm and a length of 8 mm is placed in a TMA apparatus (Q400 manufactured by TA Instruments), and while changing the temperature from 30 °C to 220 °C at a heating rate of 5 °C / min under a state where a tension of 0.01 N is applied, the temperature at which the length rapidly increases and the sample breaks can be measured as the melting temperature.

[0118] The separator containing a crosslinked structure for a lithium secondary battery according to an embodiment of the present invention has a small increase in the shutdown temperature and a small change rate compared to a separator including an uncrosslinked polyolefin porous support. The separator containing a crosslinked structure for a lithium secondary battery according to an embodiment of the present invention has an increased melting temperature of the separator while the shutdown temperature does not increase much compared to a separator including an uncrosslinked polyolefin porous support. Therefore, overcharge safety due to the shutdown temperature can be ensured, and at the same time, the high-temperature safety of the separator is significantly improved.

[0119] In one embodiment of the present invention, the separator containing a crosslinked structure for a lithium secondary battery may have a shutdown temperature of 145 °C or lower, 140 °C or lower, or 133 °C to 140 °C. When the separator containing a crosslinked structure for a lithium secondary battery has the above-described shutdown temperature, overcharge safety can be ensured, and at the same time, the problem that the pores of the polyolefin porous support containing a crosslinked structure are damaged and the resistance increases during the high-temperature and pressurization processes during battery assembly can be easily prevented.

[0120] The shutdown temperature can be obtained by measuring the time (seconds) required for 100 ml of air to pass through the separator at a constant pressure of 0.05 Mpa when the temperature is increased by 5 °C per minute using a Wang's air permeability measuring device, and taking the temperature at which the air permeability of the separator rapidly increases as the shutdown temperature.

[0121] The crosslinked structure-containing separator for a lithium secondary battery according to an embodiment of the present invention has its air permeability, basis weight, tensile strength, tensile elongation, puncture strength, electrical resistance, etc., without significantly deteriorating compared to those of the separator for a lithium secondary battery before crosslinking, and the rate of change is also small.

[0122] The crosslinked structure-containing separator for a lithium secondary battery according to an embodiment of the present invention may have a rate of change in air permeability of 10% or less, 0% to 10%, 0% to 5%, or 0% to 3% compared to the separator for a lithium secondary battery before crosslinking.

[0123] The rate of change in air permeability can be calculated by the following formula. Rate of change in air permeability (%) = [(Air permeability of the crosslinked structure-containing separator for a lithium secondary battery after crosslinking) - (Air permeability of the separator for a lithium secondary battery before crosslinking)] / (Air permeability of the separator for a lithium secondary battery before crosslinking) × 100

[0124] Throughout this specification, the "crosslinked structure-containing separator for a lithium secondary battery after crosslinking" refers to a separator composed of a crosslinked structure-containing polyolefin porous support; a separator including a crosslinked structure-containing polyolefin porous support and an inorganic composite void layer located on at least one surface of the crosslinked structure-containing polyolefin porous support and containing an inorganic filler and a binder polymer; or a separator including a crosslinked structure-containing polyolefin porous support, an inorganic composite void layer located on at least one surface of the crosslinked structure-containing polyolefin porous support and containing an inorganic filler and a first binder polymer, and a porous adhesive layer located on the upper surface of the inorganic composite void layer and containing a second binder polymer.

[0125] The air permeability (Gurley) can be measured by the ASTM D726-94 method. The Gurley used here is the resistance to the flow of air and is measured by a Gurley densometer. The value of the air permeability described here is the time required for 100 ml of air to pass through a 1 in² sample porous support under a pressure of 12.2 in H2O. 2It is shown as the time (seconds) required to pass through the cross-section, that is, the ventilation time.

[0126] The crosslinked structure-containing separator for a lithium secondary battery according to an embodiment of the present invention may have a basis weight change rate of 5% or less, or 0% to 5%, compared with the separator for a lithium secondary battery before crosslinking.

[0127] The basis weight change rate can be calculated by the following formula. Basis weight change rate (%) = [(Basis weight of the crosslinked structure-containing separator for a lithium secondary battery after crosslinking) - (Basis weight of the separator for a lithium secondary battery before crosslinking)] / (Basis weight of the separator for a lithium secondary battery before crosslinking) × 100 The basis weight (g / m 2 ) is shown by preparing a sample with a length and width of 1 m each and measuring its weight.

[0128] The crosslinked structure-containing separator for a lithium secondary battery according to an embodiment of the present invention may have a change rate of tensile strength in the machine direction and the transverse direction of 20% or less, 0% to 20%, 0% to 10%, 0% to 9%, 0% to 8%, or 0% to 7.53%, compared with the separator for a lithium secondary battery before crosslinking.

[0129] 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 a lithium secondary battery before crosslinking) - (Tensile strength in the machine direction of the crosslinked structure-containing separator for a lithium secondary battery after crosslinking)] / (Tensile strength in the machine direction of the separator for a lithium secondary battery before crosslinking) × 100 Change rate of tensile strength in the transverse direction (%) = [(Tensile strength in the transverse direction of the separator for a lithium secondary battery before crosslinking) - (Tensile strength in the transverse direction of the crosslinked structure-containing separator for a lithium secondary battery after crosslinking)] / (Tensile strength in the transverse direction of the separator for a lithium secondary battery before crosslinking) × 100

[0130] The tensile strength may be the strength at the time when the test piece breaks when the test piece is pulled in the machine direction and the transverse direction at a speed of 50 mm / min using a Universal Testing Systems (Instron (registered trademark) 3345) in accordance with ASTM D882.

[0131] The crosslinked structure-containing separator for a lithium secondary battery according to an embodiment of the present invention may have a change rate of tensile elongation in the machine direction and the transverse direction of 20% or less, or 0% to 20% as compared with the separator for a lithium secondary battery before crosslinking.

[0132] 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 a lithium secondary battery before crosslinking) - (Tensile elongation in the machine direction of the crosslinked structure-containing separator for a lithium secondary battery after crosslinking)] / (Tensile elongation in the machine direction of the separator for a lithium secondary battery before crosslinking) × 100 Change rate of tensile elongation in the transverse direction (%) = [(Tensile elongation in the transverse direction of the separator for a lithium secondary battery before crosslinking) - (Tensile elongation in the transverse direction of the crosslinked structure-containing separator for a lithium secondary battery after crosslinking)] / (Tensile elongation in the transverse direction of the separator for a lithium secondary battery before crosslinking) × 100

[0133] The tensile elongation may be measured as the maximum length by which the test piece extends until it breaks when the test piece is pulled in the machine direction and the transverse direction at a speed of 50 mm / min using a Universal Testing Systems (Instron (registered trademark) 3345) in accordance with ASTM D882, and can be calculated by the following formula. Tensile elongation in the machine direction (%) = (Length in the machine direction of the test piece immediately before breakage - Length in the machine direction of the test piece before stretching) / (Length in the machine direction of the test piece before stretching) × 100 Tensile elongation in the transverse direction (%) = (Length in the transverse direction of the test piece immediately before breakage - Length in the transverse direction of the test piece before stretching) / (Length in the transverse direction of the test piece before stretching) × 100

[0134] The crosslinked structure-containing separator for a lithium secondary battery according to an embodiment of the present invention may have a change rate of puncture strength of 10% or less, 0.5% to 10%, 1% to 9%, or 1.18% to 8.71% compared to the separator for a lithium secondary battery before crosslinking.

[0135] The change rate of puncture strength can be calculated by the following formula. Change rate of puncture strength (%) = [(Puncture strength of the separator for a lithium secondary battery before crosslinking) - (Puncture strength of the crosslinked structure-containing separator for a lithium secondary battery after crosslinking)] / (Puncture strength of the separator for a lithium secondary battery before crosslinking) × 100

[0136] 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 can be measured according to ASTM D2582.

[0137] The crosslinked structure-containing separator for a lithium secondary battery according to an embodiment of the present invention may have a change rate of electrical resistance of 15% or less, 2% to 10%, or 2% to 5% compared to the separator for a lithium secondary battery before crosslinking.

[0138] The change rate of electrical resistance can be calculated by the following formula. Change rate of electrical resistance (%) = [(Electrical resistance of the crosslinked structure-containing separator for a lithium secondary battery after crosslinking) - (Electrical resistance of the separator for a lithium secondary battery before crosslinking)] / (Electrical resistance of the separator for a lithium secondary battery before crosslinking) × 100

[0139] The electrical resistance can be obtained by measuring the resistance of the separator by an impedance measurement method after leaving a coin cell fabricated including the separator sample at room temperature for 1 day.

[0140] A method for manufacturing a crosslinked structure-containing separator for a lithium secondary battery according to an embodiment of the present invention is preparing a polyolefin porous support containing a photoinitiator and having 0.01 to 0.5 double bonds per 1000 carbon atoms present in the polyolefin chain when measured by H-NMR; A step of irradiating the polyolefin porous support with ultraviolet light is included. The content of the photoinitiator is characterized in that it is 0.015 parts by weight to 0.36 parts by weight with respect to 100 parts by weight of the polyolefin porous support.

[0141] Hereinafter, a method for manufacturing a crosslinked structure-containing separator for a lithium secondary battery according to an embodiment of the present invention will be described centering on the main part.

[0142] First, a polyolefin porous support containing a photoinitiator and having 0.01 to 0.5 double bonds per 1000 carbon atoms present in the polyolefin chain during H-NMR measurement is prepared.

[0143] In the present invention, a photoinitiator is introduced onto the surface of the polyolefin porous support so that the polyolefin porous support can be crosslinked upon irradiation with ultraviolet light. Here, the "surface of the polyolefin porous support" may include not only the outermost surface of the polyolefin porous support but also the surfaces of the pores present inside the polyolefin porous support.

[0144] The photoinitiator directly photo-crosslinks the polymer chains in the polyolefin porous support. The photoinitiator can crosslink the polyolefin porous support with only the photo-crosslinking initiator without other components such as a crosslinking agent, a co-initiator, or a synergist. Only by light absorption, while the hydrogen atoms in the photoinitiator are removed by hydrogen abstraction reaction, the photoinitiator becomes a reactive compound. Such a photoinitiator forms radicals on the polymer chains in the polyolefin porous support to make the polymer chains reactive, and the polymer chains are directly connected to each other and photo-crosslinked.

[0145] The method for manufacturing a crosslinked structure-containing separator for a lithium secondary battery according to an embodiment of the present invention can generate radicals on the polymer chains in the polyolefin porous support by using the photoinitiator, so that a crosslinked structure in which the polymer chains are directly connected to each other can be formed.

[0146] Since the photoinitiator plays a role in forming radicals in the polymer chains within the polyolefin porous support, the content of the photoinitiator is very important in the formation of radicals.

[0147] When radicals are generated in excess, the photoinitiators may crosslink with each other or the photoinitiator and the polymer chain may crosslink. However, such a crosslinked structure has a lower reaction enthalpy than the crosslinked structure between the polymer chains within the polyolefin porous support. Therefore, there is a risk of decomposition during battery charge and discharge, causing side reactions. Also, when the photoinitiator and the polymer chain crosslink with each other, it is undesirable because it lowers the melting temperature of the polyolefin chain and deteriorates the properties of the separator such as the shutdown temperature.

[0148] In the present invention, an attempt was made to minimize side reactions when crosslinking the polyolefin porous support by adjusting the content of the photoinitiator. In one embodiment of the present invention, the content of the photoinitiator is 0.015 parts by weight to 0.36 parts by weight with respect to 100 parts by weight of the polyolefin porous support. When the content of the photoinitiator satisfies the above-mentioned range, the polyolefin porous support can be effectively crosslinked, and it is possible to prevent the excessive generation of radicals and the occurrence of side reactions. For example, a phenomenon in which radicals are generated in excess and the photoinitiators crosslink with each other or the photoinitiator and the polymer chain crosslink does not occur, and crosslinking occurs only between the polymer chains, thereby preventing side reactions.

[0149] Also, it is possible to prevent a phenomenon in which the separator shrinks due to an excessive generation of radicals and a rapid crosslinking reaction. Thereby, it is possible to prevent a decrease in the air permeability of the polyolefin porous support after crosslinking.

[0150] Also, it is possible to prevent the occurrence of main chain scission of excessive polyolefin and the like, which would lower the mechanical strength of the polyolefin porous support.

[0151] When the content of the photoinitiator is less than 0.015 parts by weight with respect to 100 parts by weight of the polyolefin porous support, radicals are not formed to such an extent that the polyolefin porous support can be sufficiently crosslinked, and the crosslinking of the polyolefin porous support cannot be carried out smoothly.

[0152] When the content of the photoinitiator exceeds 0.36 parts by weight with respect to 100 parts by weight of the polyolefin porous support, although the polyolefin porous support is crosslinked, radicals are generated excessively and side reactions occur. For example, the photoinitiators may be crosslinked with each other or the photoinitiator and the polyolefin chain may be crosslinked. In addition, when irradiated with ultraviolet rays, the crosslinking reaction occurs rapidly and the separation membrane shrinks, resulting in cleavage of the main chain of the polyolefin and a decrease in mechanical strength.

[0153] In one embodiment of the present invention, the content of the photoinitiator may be 0.015 to 0.3 parts by weight, 0.015 to 0.09 parts by weight, 0.015 to 0.07 parts by weight, or 0.018 to 0.0365 parts by weight with respect to 100 parts by weight of the polyolefin porous support. When the content of the photoinitiator satisfies the above-described range, the polyolefin porous support can be effectively crosslinked, and it is possible to more easily prevent radicals from being generated excessively and side reactions from occurring.

[0154] The content of the photoinitiator based on 100 parts by weight of the polyolefin porous support can be determined by measuring the content of the photoinitiator filled in the total pore volume of the polyolefin porous support. For example, assuming that the total pore volume of the polyolefin porous support is filled 100% with a solvent described later and there is no solvent for the second binder polymer present on the surface of the polyolefin porous support, the weight of the solvent contained in the total pore volume of the polyolefin porous support is determined from the density of the solvent, and the content of the photoinitiator with respect to 100 parts by weight of the polyolefin porous support can be determined from the content of the photoinitiator contained in the solvent.

[0155] In one embodiment of the present invention, the photoinitiator may include a type II photoinitiator.

[0156] In one embodiment of the present invention, the photoinitiator may include thioxanthone (TX), a thioxanthone derivative, benzophenone (BPO), a benzophenone derivative, or two or more of these.

[0157] The thioxanthone derivatives may include, for example, 2-isopropyl thioxanthone (ITX), 2-chloro thioxanthone, 2-dodecyl thioxanthone, 2,4-diethyl thioxanthone, 2,4-dimethyl thioxanthone, 1-methoxycarbonyl thioxanthone, 2-ethoxycarbonyl thioxanthone, 3-(2-methoxyethoxycarbonyl)-thioxanthone, 4-butoxycarbonyl-thioxanthone, 3-butoxycarbonyl-7-methyl thioxanthone, 1-cyano-3-chloro thioxanthone, 1-ethoxycarbonyl-3-chloro thioxanthone, 1-ethoxycarbonyl-3-ethoxy thioxanthone, 1-ethoxycarbonyl-3-amino thioxanthone, 1-ethoxycarbonyl-3-phenylsulfuryl thioxanthone, 3,4-di[2-(2-methoxyethoxy)ethoxycarbonyl]thioxanthone, 1-ethoxycarbonyl-3-(1-methyl-1-morpholino-ethyl)-thioxanthone, 2-methyl-6-dimethoxymethyl-thioxanthone, 2-methyl-6-(1,1-dimethoxy-benzyl)-thioxanthone, 2-morpholinomethyl thioxanthone, 2-methyl-6-morpholinomethyl-thioxanthone, N-allyl thioxanthone-3,4-dicarboximide, N-octyl thioxanthone-3,4-dicarboximide, N-(1,1,3,3-tetramethylbutyl)-thioxanthone-3,4-dicarboximide, 1-phenoxy thioxanthone, 6-ethoxycarbonyl-2-methoxy thioxanthone, 6-ethoxycarbonyl-2-methyl thioxanthone, thioxanthone-2-polyethylene glycol ester, 2-hydroxy-3-(3,4-dimethyl-9-oxo-9H-thioxanthone-2-yloxy)-N,N,N-trimethyl-1-propanaminium chloride, etc., but are not limited thereto.

[0158] The benzophenone derivative may include, 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-benzoylbenzoate, 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-hydroxybenzophenone, 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, etc., but is not limited thereto.

[0159] In particular, when the photoinitiator contains 2-isopropylthioxanthone, thioxanthone, or a mixture thereof, less light amount, for example, 500 mJ / cm 2 level, can crosslink the polyolefin porous support, which is more advantageous in terms of mass production.

[0160] In addition, when the photoinitiator contains 2-isopropylthioxanthone (ITX), since the melting point of ITX is as low as about 70°C to 80°C, when the photocrosslinking temperature is adjusted to 80°C to 100°C, the ITX on the surface of the polyolefin porous support melts while the mobility of ITX into the polyolefin porous support occurs, and the crosslinking efficiency can be increased, and finally, the physical property change of the produced separation membrane can be easily prevented.

[0161] The above-mentioned polyolefin porous support can be manufactured by forming pores using a conventional method known in the art, such as a wet method using a solvent, diluent, or pore-forming agent, or a dry method using a stretching method, in order to ensure excellent air permeability and porosity from the polyolefin material described above.

[0162] In one embodiment of the present invention, the polyolefin porous support can be a porous film.

[0163] In one embodiment of the present invention, the polyolefin may include polyethylene; polypropylene; polybutylene; polypentene; polyhexene; polyoctene; a copolymer of two or more of ethylene, propylene, butene, pentene, 4-methylpentene, hexene, and octene; or a mixture thereof.

[0164] Non-limiting examples of the polyethylene include low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), and the like. When the polyethylene is high-density polyethylene with high crystallinity and a high melting point of the resin, it is easy to increase the modulus while having the desired level of heat resistance.

[0165] In one embodiment of the present invention, the weight average molecular weight of the polyolefin can be 200,000 to 1,500,000, 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 polyolefin is within the above-described range, a separation membrane excellent in strength and heat resistance can be finally obtained while ensuring the uniformity and film-forming processability of the polyolefin porous support.

[0166] The weight average molecular weight can be measured under the following conditions using gel permeation chromatography (GPC: Gel Permeation Chromatography, PL GPC220, manufactured by Agilent Technologies). - Column: PL Olexis (Polymer Laboratories) - Solvent: TCB (trichlorobenzene) - Flow rate: 1.0 ml / min - Sample concentration: 1.0 mg / ml - Injection volume: 200 μl - Column temperature: 160 °C - Detector: High-temperature RI detector manufactured by Agilent - Standard: Polystyrene (corrected by a cubic function)

[0167] The photoinitiator can perform a hydrogen abstraction reaction in a small amount of double bond structures present in the polyolefin chain. While only absorbing light, hydrogen atoms are abstracted from the double bond structures of the polyolefin chain by the hydrogen abstraction reaction, and radicals are formed in the polymer chain. Therefore, the inventors have found that in addition to the content of the photoinitiator, the content of double bonds present in the polyolefin chain affects the crosslinking of the polyolefin chain, and thus have completed the present invention.

[0168] In one embodiment of the present invention, in the H-NMR measurement of the polyolefin porous support, the number of double bonds present in the polyolefin chain is 0.01 to 0.5 per 1000 carbon atoms. By having the polyolefin porous support have the above-described number of double bonds in the polyolefin chain, it becomes possible to adjust the radicals formed by the hydrogen abstraction reaction by the photoinitiator from the double bond structures present in the polyolefin chain, effectively crosslink the polyolefin porous support, and minimize the occurrence of side reactions due to excessive generation of radicals.

[0169] In the present invention, by adjusting the number of double bonds present in the polyolefin chain and then adjusting the radicals formed therefrom, such side reactions can be prevented so that crosslinking occurs only between the polymer chains without the photoinitiators being crosslinked to each other or the photoinitiator and the polymer chain being crosslinked.

[0170] In addition, it is possible to prevent the phenomenon in which radicals are excessively generated and the separation membrane shrinks due to a rapid crosslinking reaction. Thereby, it is possible to prevent the air permeability of the polyolefin porous support from decreasing after crosslinking.

[0171] In addition, it is possible to prevent the occurrence of main chain cleavage of excessive polyolefin and the like, which would reduce the mechanical strength of the polyolefin porous support.

[0172] When the number of double bonds present in the polyolefin chain is less than 0.01 per 1000 carbon atoms, radicals are not formed from the double bonds to such an extent that the polyolefin porous support can be sufficiently crosslinked, and the crosslinking of the polyolefin porous support does not proceed smoothly.

[0173] When the number of double bonds present in the polyolefin chain exceeds 0.5, although the polyolefin porous support is crosslinked, radicals are excessively generated and side reactions occur. For example, the photoinitiators may be crosslinked or the photoinitiator and the polyolefin chain may be crosslinked. In addition, during ultraviolet irradiation, the crosslinking reaction occurs rapidly, causing the separation membrane to shrink, and main chain cleavage of the polyolefin occurs, resulting in a decrease in mechanical strength.

[0174] In one embodiment of the present invention, in the H-NMR measurement, the number of double bonds present in the polyolefin chain of the polyolefin porous support may be 0.01 to 0.3 per 1000 carbon atoms. When the polyolefin porous support has the above-described number of double bonds, the polyolefin porous support can be effectively crosslinked, and the excessive generation of radicals and the occurrence of side reactions can be minimized. In addition, it is possible to more easily prevent the mechanical strength of the finally produced crosslinked structure-containing separation membrane for a lithium secondary battery from decreasing.

[0175] The double bond structure present in such a polyolefin chain can also exist at the ends of the polyolefin chain and can also exist inside the polyolefin chain, that is, throughout the entire polyolefin chain excluding the ends. In particular, the number of double bond structures present in the polyolefin chain excluding the ends can affect the crosslinking of the polyolefin chain.

[0176] In one embodiment of the present invention, the number of double bonds present in the polyolefin chain excluding the ends of the polyolefin porous support can be 0.005 to 0.49 per 1000 carbon atoms. The "double bonds present in the polyolefin chain excluding the ends" refers to the double bonds present throughout the entire polyolefin chain excluding the ends of the polyolefin chain. Here, the "ends" means the positions of the carbon atoms respectively connected to the terminals on both sides of the polyolefin chain.

[0177] In one embodiment of the present invention, the number of double bonds present in the polyolefin chain can be adjusted by adjusting the type, purity of the catalyst during polyolefin synthesis, addition of a linking agent, and the like.

[0178] In one embodiment of the present invention, the polyolefin 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 polyolefin porous support satisfies the above-mentioned range, the surface area of the polyolefin porous support increases, and the crosslinking efficiency of the polyolefin porous support can be increased even when a small amount of photoinitiator is used.

[0179] The BET specific surface area of the polyolefin 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 at liquid nitrogen temperature (77K) using Belsorp-mini II manufactured by BEL Japan.

[0180] In one embodiment of the present invention, the polyolefin porous support is supplying a polyolefin having 0.01 to 0.5 double bonds per 1000 carbon atoms present in the polyolefin chain and a diluent to an extruder during 1H-NMR measurement; extruding a polyolefin composition from the extruder; passing the extruded polyolefin composition through a die and a cooling roll to form and stretch it into a sheet; extracting the diluent from the stretched sheet to produce a preliminary porous support; and heat-fixing the preliminary porous support to produce a polyolefin porous support, and may be produced by a production method including these steps.

[0181] 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 acid alcohols having 10 to 20 carbon atoms such as palmitic acid alcohol, stearic acid alcohol, and oleic acid alcohol; saturated and unsaturated fatty acids having 4 to 26 carbon atoms in the fatty acid group, such as mono-, di-, or triesters of palmitic acid, mono-, di-, or triesters of stearic acid, mono-, di-, or triesters of oleic acid, mono-, di-, or triesters of linoleic acid, or one or more fatty acids in which the double bond of the unsaturated fatty acid is substituted with epoxy, and fatty acid esters in which the hydroxy group is 1 to 8 and the carbon number is 1 to 10 and is ester-bonded to an alcohol; or may contain two or more of these.

[0182] The weight ratio of the polyolefin to the diluent can be 50:50 to 20:80, or 40:60 to 30:70. When the weight ratio of the polyolefin to the diluent satisfies the above-mentioned range, an appropriate level of porosity and average pore diameter of the finally produced polyolefin porous support can be ensured, the pores are connected to each other to improve the permeability, an increase in the extrusion load can be prevented, and a viscosity that allows for easy processing can be ensured. Also, it is possible to prevent the polyolefin from being extruded in a gel form without being thermodynamically kneaded with the diluent, which can cause problems such as breakage and thickness variation during stretching. Furthermore, it is possible to easily prevent a decrease in the strength of the finally produced polyolefin porous support.

[0183] In addition to the polyolefin and the diluent, an antioxidant can be further added to the extruder. The antioxidant can regulate the cross-linking reaction between polymer chains by controlling the radicals formed in the polyolefin chains. The antioxidant can oxidize instead of the polymer chains to prevent the oxidation of the polymer chains, or can absorb the generated radicals to regulate the cross-linking reaction between the polymer chains.

[0184] Thereby, when the polyolefin porous support further contains an antioxidant, firstly, the number of double bonds present in the polyolefin chains except for the terminals is adjusted to prevent the excessive generation of radicals, and secondly, the problem of side reactions occurring can be more easily prevented by controlling the radicals generated by the antioxidant to terminate the reaction.

[0185] In one embodiment of the present invention, the content of the antioxidant can be 500 ppm to 20000 ppm, 1000 ppm to 15000 ppm, or 2000 ppm to 13000 ppm based on the content of the polyolefin porous support. When the content of the antioxidant satisfies the above-mentioned range, not only can the antioxidant sufficiently control the excessively generated radicals to easily prevent the problem of side reactions occurring, but also the phenomenon of the surface of the polyolefin porous support becoming non-uniform can be easily prevented.

[0186] Such antioxidants can be broadly classified into radical scavengers that react with radicals generated in polyolefins to stabilize the polyolefins and peroxide decomposers that decompose peroxides generated by radicals into molecules in a stable form. The radical scavenger extracts hydrogen to stabilize the radical and becomes a radical itself, but can remain in a stable form through resonance effects or electron rearrangement. The peroxide decomposer can exhibit a more excellent effect when used in combination with a radical scavenger.

[0187] 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 operating mechanisms of the first antioxidant and the second antioxidant are different, by including the antioxidant that is the first antioxidant which is a radical scavenger and the second antioxidant which is a peroxide decomposer at the same time, the synergistic effect of these antioxidants can more easily suppress the generation of unnecessary radicals.

[0188] The content of the first antioxidant and the content of the second antioxidant may be the same or different.

[0189] In one embodiment of the present invention, the first antioxidant may include a phenolic antioxidant, an amine-based antioxidant, or a mixture thereof.

[0190] The phenolic antioxidant may include 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], 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)-propionate], triethylene glycol-bis-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)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'-thiodipropionate, or may include two or more of these.

[0191] In one embodiment of the present invention, the content of the first antioxidant may be 500 ppm to 10,000 ppm, 1000 ppm to 12,000 ppm, or 1000 ppm to 10,000 ppm based on the content of the polyolefin porous support. When the content of the first antioxidant satisfies the above-described range, it is possible to easily prevent the problem of side reactions occurring due to the excessive generation of radicals.

[0192] In one embodiment of the present invention, the second antioxidant may include a phosphorus-based antioxidant, a sulfur-based antioxidant, or a mixture thereof.

[0193] The phosphorus-based antioxidant decomposes peroxides to generate alcohol and changes to phosphate. The phosphorus-based antioxidant may include 3,9-bis(2,6-di-t-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane, bis(2,6-dicumylphenyl)pentaerythritol diphosphite, 2,2'-methylenebis(4,6-di-t-butylphenyl) 2-ethylhexyl phosphite, bis(2,4-di-t-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-dicumylphenyl)pentaerythritol diphosphite, distearyl pentaerythritol diphosphite, tris(2,4-di-t-butylphenyl) phosphite, or two or more thereof.

[0194] The sulfur-based antioxidant may include 3,3'-thiobis-1,1'-dodecyl ester, dimethyl 3,3'-thiodipropionate, dioctadecyl 3,3'-thiodipropionate, 2,2-bis{[3-(dodecylthio)-1-oxopropoxy]methyl}propane-1,3-diyl bis[3-(dodecylthio)propionate], or two or more thereof.

[0195] In one embodiment of the present invention, the content of the second antioxidant may be 500 ppm to 10,000 ppm, 1000 ppm to 12,000 ppm, or 1000 ppm to 10,000 ppm based on the content of the polyolefin porous support. When the content of the second antioxidant satisfies the above-mentioned range, the problem of side reactions caused by excessive generation of radicals can be easily prevented.

[0196] In one embodiment of the present invention, when the antioxidant simultaneously contains a first antioxidant that is a radical scavenger and a second antioxidant that is a peroxide decomposer, the content of the first antioxidant may be 500 ppm to 10,000 ppm or 1,000 ppm to 5,000 ppm based on the content of the polyolefin porous support, and the content of the second antioxidant may be 500 ppm to 10,000 ppm or 1,000 ppm to 5,000 ppm based on the content of the polyolefin porous support.

[0197] The extrusion can be carried out for several minutes at a temperature of 160 to 240 °C using a single-screw or twin-screw extrusion device. For uniform reactive extrusion, an extruder with an L / D (length / diameter) of the screw of 30 or more can be used.

[0198] The extruded polyolefin composition is cooled while passing through a die and a cooling roll, and at this time, phase separation may occur between the polyolefin and the diluent. The time of such phase separation can affect the BET specific surface area, average pore diameter, pore pattern, etc. of the finally produced polyolefin porous support.

[0199] In one embodiment of the present invention, the stretching can be carried out by sequential or simultaneous stretching using a roll method or a tenter method. The stretching ratio is 3 times or more, or 5 to 10 times in the longitudinal and transverse directions, respectively, and the total stretching ratio can be 20 to 80 times. When the stretching ratio is within the above-mentioned range, the orientation in one direction is not sufficient, and the problem that the physical property balance between the machine direction and the transverse direction is disrupted and the tensile strength and puncture strength are reduced can be easily prevented. In addition, the problem that un-stretching occurs and pores are not formed, or breakage occurs during stretching and the shrinkage rate of the finally produced polyolefin porous support increases can be easily prevented.

[0200] As used herein, "Machine direction (MD)" refers to the direction of travel when the separation membrane is continuously produced, which is the longitudinal direction of the separation membrane, and "Transverse direction (TD)" refers to the direction transverse to the machine direction, that is, the direction perpendicular to the direction of travel when the separation membrane is continuously produced, which is the direction perpendicular to the longitudinal direction of the separation membrane.

[0201] The stretching temperature can vary depending on the melting point of the polyolefin used and the concentration and type of the diluent, and can be selected within the temperature range in which 30 to 80% by weight of the crystalline portion of the polyolefin in the sheet melts. When the stretching temperature satisfies the above-mentioned range, it is possible to easily prevent the sheet from being soft and breaking or not stretching during stretching. In addition, it is possible to easily prevent variations in thickness due to partial overstretching or a decrease in the orientation effect of the polyolefin and a decrease in physical properties. On the other hand, the degree of melting of the crystalline portion according to the temperature can be obtained from the DSC (differential scanning calorimetry) of the sheet.

[0202] In the step of manufacturing the preliminary porous support by extracting the diluent from the stretched sheet, the diluent can be extracted using an organic solvent. Specifically, after extracting the diluent from the stretched sheet using an organic solvent, it can be dried. The organic solvent is not particularly limited as long as it can extract the diluent. For example, methyl ethyl ketone, methylene chloride, hexane, etc. can be used.

[0203] As the extraction method, any common solvent extraction method such as an immersion method, a solvent spray method, or an ultrasonic method can be used alone or in combination. After the extraction treatment, the content of the remaining diluent can be 1% by weight or less relative to 100% by weight of the polyolefin porous support. In this case, it is possible to easily prevent the physical properties of the polyolefin porous support from deteriorating and the permeability from decreasing.

[0204] The content of the remaining diluent is affected by the extraction temperature and extraction time. Considering the increase in solubility between the diluent and the organic solvent and the safety issues due to the boiling of the organic solvent, the extraction temperature can be 40°C or lower.

[0205] Also, the extraction time varies depending on the thickness of the polyolefin porous support to be produced. In the case of a polyolefin porous support with a thickness of 10 - 30 μm, it can be 2 - 4 minutes.

[0206] Thermal fixation fixes the preliminary porous support and applies heat to forcibly fix the tendency of the finally produced polyolefin porous support to shrink and remove the residual stress.

[0207] In one embodiment of the present invention, the thermal fixation temperature can be 125°C - 132°C. In one embodiment of the present invention, the time of the thermal fixation temperature can be 10 seconds - 120 seconds, 20 seconds - 90 seconds, or 30 seconds - 60 seconds. When performing thermal fixation for the above-mentioned time, rearrangement of polyolefin molecules occurs, and the residual stress of the finally produced polyolefin porous support can be removed, and the problem of pore clogging of the polyolefin porous support due to partial melting can be reduced.

[0208] In one embodiment of the present invention, the step of preparing the polyolefin porous support containing the photoinitiator may include the step of adding the photoinitiator to an extruder for extruding the polyolefin composition to prepare the polyolefin porous support.

[0209] In another embodiment of the present invention, the step of preparing the polyolefin porous support may include the step of coating and drying a photocrosslinking composition containing the photoinitiator and a solvent on the outside of the polyolefin porous support.

[0210] In this specification, the "step of coating and drying on the outside" includes not only the case of coating and drying the photocrosslinking composition on the surface of the polyolefin porous support, but also the case of coating and drying the photocrosslinking composition on the surface of another layer after another layer is formed on the polyolefin porous support.

[0211] In one embodiment of the present invention, before coating the photoinitiator solution on the polyolefin porous support, the polyolefin porous support can be subjected to corona discharge treatment. The corona discharge treatment can be performed by applying a high-frequency, high-voltage output generated by a predetermined drive circuit unit between a predetermined discharge electrode provided in the corona discharge treatment machine and a treatment roll. Through the corona discharge treatment, the surface of the polyolefin porous support is modified, and the wettability of the polyolefin porous support with respect to the photocrosslinking composition can be further improved. Thereby, even with the same content of photoinitiator and / or the same number of double bonds in the polyolefin chains, the crosslinking of the polyolefin porous support can be performed more efficiently. The corona discharge treatment can be performed by an atmospheric pressure plasma method.

[0212] 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; ketones such as acetone, ethyl methyl ketone, diisopropyl ketone, cyclohexanone, 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; acyl nitriles such as acetonitrile and propionitrile; ethers such as tetrahydrofuran and ethylene glycol diethyl ether; alcohols such as methanol, ethanol, isopropanol, ethylene glycol, and ethylene glycol monomethyl ether; amides such as N-methylpyrrolidone and N,N-dimethylformamide; or may include two or more of these.

[0213] In one embodiment of the present invention, the content of the photoinitiator in the photo-crosslinking composition is 0.015 to 0.36 parts by weight based on 100 parts by weight of the polyolefin porous support, and may be 0.01 to 0.5 parts by weight, 0.02 to 0.45 parts by weight, or 0.25 to 0.4 parts by weight based on 100 parts by weight of the solvent.

[0214] When the content of the photoinitiator satisfies the above-mentioned range based on the solvent, the polyolefin porous support can be crosslinked, and at the same time, side reactions caused by excessive generation of radicals can be more easily prevented.

[0215] Also, in one embodiment of the present invention, the content of the photoinitiator in the photo-crosslinking composition is 0.015 to 0.36 parts by weight based on 100 parts by weight of the polyolefin porous support, and based on the specific surface area of the polyolefin porous support, it is 0.01 mg / m 2 ~1.0 mg / m 2 、0.03 mg / m 2 ~0.8 mg / m 2 、or 0.06 mg / m 2 ~0.7 mg / m 2 and may be. When the content of the type II photoinitiator satisfies the above-mentioned range, the polyolefin porous support can be crosslinked, and at the same time, side reactions caused by excessive generation of radicals can be more easily prevented.

[0216] The content of the photoinitiator based on the specific surface area of the polyolefin porous support can be measured through NMR analysis.

[0217] In one embodiment of the present invention, the photo-crosslinking composition may be a photoinitiator solution containing the photoinitiator and the solvent.

[0218] Non-limiting examples of the method for coating the photoinitiator solution on the polyolefin porous support include dip coating method, die coating method, roll coating method, comma coating method, microgravure coating method, doctor blade coating method, reverse roll coating method, Mayer bar coating method, direct roll coating method, and the like.

[0219] For the drying stage after coating the photoinitiator solution on the polyolefin porous support, methods known in the art can be used, and it can be carried out batchwise or continuously using an oven or a heating chamber within a temperature range considering the vapor pressure of the solvent used. The drying is to remove almost all of the solvent present in the photoinitiator solution, and it is desirable to carry it out as quickly as possible considering productivity and the like, and it can be carried out, for example, in a time of 1 minute or less or 30 seconds or less.

[0220] In still other embodiments of the present invention, the photocrosslinking composition may be a slurry for forming an inorganic composite void layer containing an inorganic filler, a binder polymer, the photoinitiator, and the solvent.

[0221] When the photocrosslinking composition is the slurry for forming the inorganic composite void layer, the photoinitiator is introduced onto the surface of the polyolefin porous support while the photocrosslinking composition is being coated on the polyolefin porous support, and when irradiated with ultraviolet light, the polyolefin porous support can be crosslinked and an inorganic composite void layer can be formed on at least one surface of the polyolefin porous support.

[0222] When using the slurry for forming the inorganic composite void layer as the photocrosslinking composition, additional equipment for directly applying the photoinitiator to the polyolefin porous support, such as equipment for directly coating and drying a solution containing the photoinitiator on the polyolefin porous support, is not required, and the polyolefin porous support can be photocrosslinked using the inorganic composite void layer forming process.

[0223] In addition, since the slurry for forming the inorganic composite void layer does not require other monomers or the like in addition to the photoinitiator in order to directly crosslink the polymer chains in the polyolefin porous support, even if the photoinitiator is included in the slurry for forming the inorganic composite void layer together with the inorganic filler and the binder polymer, monomers or the like do not prevent the photoinitiator from reaching the surface of the polyolefin porous support, and the photoinitiator can be sufficiently introduced onto the surface of the polyolefin porous support.

[0224] Generally, since the polyolefin porous support itself and the inorganic filler have a high ultraviolet blocking effect, when ultraviolet rays are irradiated after forming an inorganic composite void layer containing the inorganic filler, the amount of irradiated light of the ultraviolet rays reaching the polyolefin porous support may decrease. However, in the present invention, even when ultraviolet rays are irradiated after the inorganic composite void layer is formed, the polymer chains in the polyolefin porous support can be crosslinked and directly connected to each other.

[0225] In one embodiment of the present invention, when the photocrosslinking composition is the slurry for forming the inorganic composite void layer, the photoinitiator may include 2-isopropylthioxanthone, thioxanthone, or a mixture thereof. 2-Isopropylthioxanthone or thioxanthone enables photocrosslinking even at a long wavelength with a high transmittance. Thereby, even if the photoinitiator is included in the slurry for forming the inorganic composite void layer containing an inorganic filler, a binder polymer, etc., the polyolefin porous support can be easily crosslinked.

[0226] The solvent may serve as a solvent for dissolving the binder polymer according to the type of the binder polymer, or may serve as a dispersion medium for dispersing the binder polymer without dissolving it. In addition, the solvent can dissolve the photoinitiator. As the solvent, one having a solubility index similar to that of the binder polymer to be used and a low boiling point can be used. In this case, uniform mixing and subsequent solvent removal become easy. For non-limiting examples of such solvents, refer to the description of the solvents described above.

[0227] The inorganic filler is not particularly limited as long as it is electrochemically stable. That is, the inorganic filler that can be used in the present invention is not particularly limited as long as no oxidation and / or reduction reaction occurs within the operating voltage range of the applied electrochemical device (e.g., 0 to 5 V based on Li / Li + standard). In particular, when using inorganic particles with a high dielectric constant as the inorganic filler, it can contribute to an increase in the dissociation degree of electrolyte salts, such as lithium salts, in the liquid electrolyte, thereby improving the ionic conductivity of the electrolyte.

[0228] 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, desirably 10 or more. Non-limiting examples of inorganic fillers having a dielectric constant of 5 or more include BaTiO3, Pb(Zr,Ti)O3 (PZT), Pb 1-x La x Zr 1-y Ti y O3 (PLZT, 0 < x < 1, 0 < y < 1), Pb(Mg 1 / 3 Nb 2 / 3 )O3 - PbTiO3 (PMN - PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, Mg(OH)2, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, AlOOH, Al(OH)3, SiC, TiO2, or a mixture thereof, and the like.

[0229] Also, in another embodiment of the present invention, as the inorganic filler, an inorganic filler having lithium ion transfer ability, that is, an inorganic filler that contains lithium element but does not store lithium and has a function of moving lithium ions can be used. Non-limiting examples of inorganic fillers having lithium ion transfer ability include lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z(PO4)3, where 0 < x < 2, 0 < y < 1, 0 < z < 3, such as 14Li2O - 9Al2O3 - 38TiO2 - 39P2O5, (LiAlTiP) x O y glass systems (0 < x < 4, 0 < y < 13), lithium lanthanum titanate (Li x La y TiO3, where 0 < x < 2, 0 < y < 3), Li 3.25 Ge 0.25 P 0.75 such as lithium germanium thiophosphate (Li x Ge y P z S w , where 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride (Li x N y , where 0 < x < 4, 0 < y < 2), SiS2 - based glass (Li x Si y S z , such as Li3PO4 - Li2S - SiS2, where 0 < x < 3, 0 < y < 2, 0 < z < 4), P2S5 - based glass (Li x P y S z , where 0 < x < 3, 0 < y < 3, 0 < z < 7), or mixtures thereof, etc.

[0230] In one embodiment of the present invention, the average particle size of the inorganic filler can be 0.01 μm to 1.5 μm. When the average particle size of the inorganic filler satisfies the above - mentioned range, it is easy to form an inorganic composite void layer having a uniform thickness and appropriate porosity, the dispersibility of the inorganic filler is good, and the desired energy density can be achieved.

[0231] At this time, the average particle size of the inorganic filler means the particle size D 50 particle size, and "D 50"Particle size" means the particle size at the 50% point of the cumulative particle number distribution according to the particle size. The particle size can be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (for example, Microtrac S3500). When the particles pass through the laser beam, the difference in the diffraction pattern according to the particle size is measured to calculate the particle size distribution. By calculating the particle diameter at the point where the cumulative particle number distribution according to the particle size in the measuring device reaches 50%, D 50 the particle size can be measured.

[0232] The binder polymer may be dissolved in the solvent according to the type of the binder polymer, or may be dispersed without being dissolved in the solvent.

[0233] The binder polymer has a glass transition temperature (T g ) that can be -200 to 200 °C. When the glass transition temperature of the binder polymer satisfies the above-mentioned range, the mechanical properties such as flexibility and elasticity of the finally formed inorganic composite void layer can be improved. The binder polymer may have ion conduction ability. When the binder polymer has ion conduction ability, the performance of the battery 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 above-mentioned range, the degree of dissociation of the salt in the electrolyte can be improved.

[0234] In one embodiment of the present invention, the binder polymer may include polyvinylidene fluoride - hexafluoropropylene, polyvinylidene fluoride - chlorotrifluoroethylene, polyvinylidene fluoride - tetrafluoroethylene, polyvinylidene fluoride - trichloroethylene, an acrylic copolymer, a styrene - butadiene copolymer, polyacrylic acid, polymethyl methacrylate, polybutyl acrylate, polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl alcohol, polyvinyl acetate, an ethylene vinyl acetate copolymer, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, or two or more of these.

[0235] The acrylic copolymer may include, but is not limited to, an ethyl acrylate - acrylic acid - N,N - dimethylacrylamide copolymer, an ethyl acrylate - acrylic acid - 2 - (dimethylamino)ethyl acrylate copolymer, an ethyl acrylate - acrylic acid - N,N - diethylacrylamide copolymer, an ethyl acrylate - acrylic acid - 2 - (diethylamino)ethyl acrylate copolymer, or two or more of these.

[0236] 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 diameter, and porosity of the finally produced inorganic composite void layer, and may be 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 above - described range, sufficient empty spaces can be ensured between the inorganic fillers, and the pore diameter and porosity of the inorganic composite void layer can be easily ensured. Also, the adhesive force between the inorganic fillers can be easily ensured.

[0237] The slurry for forming the inorganic composite void layer can be produced by dissolving or dispersing the binder polymer in the solvent and then adding the inorganic filler and dispersing the same. The inorganic filler may be added in a state where it has been crushed in advance to have a predetermined average particle size, or after adding the inorganic filler to the slurry in which the binder polymer is dissolved or dispersed, the inorganic filler may be crushed and dispersed while controlling it to have a predetermined average particle size using a ball milling method or the like. At this time, the crushing can be performed for 1 to 20 hours, and the average particle size of the crushed inorganic filler is as described above. As the crushing method, a normal method can be used, and a ball milling method can be used.

[0238] In one embodiment of the present invention, the slurry for forming the inorganic composite void layer may further contain additives such as a dispersant and / or a thickener. In one embodiment of the present invention, the additives may include polyvinylpyrrolidone (PVP), hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), ethylhydroxyethyl cellulose (EHEC), methyl cellulose (MC), carboxymethyl cellulose (CMC), hydroxyalkylmethyl cellulose, cyanoethylated polyvinyl alcohol, or two or more of these.

[0239] In one embodiment of the present invention, the solid content of the slurry for forming the inorganic composite void layer can be 5 wt% to 60 wt%, or 30 wt% to 50 wt%. When the solid content of the slurry for forming the inorganic composite void layer is within the above-described range, coating uniformity can be easily ensured, and it is possible to easily prevent the slurry from flowing and causing unevenness or the need for a large amount of energy for drying the slurry.

[0240] In one embodiment of the present invention, when the composition for photocrosslinking is the slurry for forming the inorganic composite void layer, after coating the composition for photocrosslinking on the polyolefin porous support, a phase separation process can be performed. The phase separation can be performed by a humidification phase separation or an immersion phase separation method.

[0241] Next, the humidification phase separation among the phase separations will be described.

[0242] First, the humidification phase separation can be carried out under the conditions of a temperature range of 15°C to 70°C or 20°C to 50°C, and a relative humidity range of 15% to 80% or 30% to 50%. As the slurry for forming the inorganic composite void layer undergoes the drying process, it acquires phase transition characteristics by the vapor-induced phase separation phenomenon known in the art.

[0243] For the humidification phase separation, a non-solvent for the binder polymer can be introduced in a gaseous state. The non-solvent for the binder polymer is not particularly limited as long as it has partial compatibility with the solvent without dissolving the binder polymer. For example, those with a solubility of less than 5% by weight of the binder polymer under the condition of 25°C can be used. For example, the non-solvent for the binder polymer can be water, methanol, ethanol, isopropanol, butanol, butanediol, ethylene glycol, propylene glycol, tripropylene glycol, or two or more of these.

[0244] Regarding the immersion phase separation among the phase separations, it is as follows.

[0245] After coating the slurry for forming the inorganic composite void layer on the outside of the polyolefin porous support, it is immersed in a coagulating liquid containing a non-solvent for the binder polymer for a predetermined time. Thereby, the binder polymer is solidified while inducing a phase separation phenomenon in the coated inorganic composite void layer slurry. In this step, an inorganic composite void layer that is porous is formed. Then, the coagulating liquid is removed by washing with water and dried. For the drying, a method known in the art can be used, and it can be carried out batchwise or continuously using an oven or a heating chamber within a temperature range considering the vapor pressure of the solvent used. The drying is to remove almost all of the solvent present in the slurry, and it is desirable to be carried out as quickly as possible considering productivity and the like, and it can be carried out, for example, in a time of 1 minute or less or 30 seconds or less.

[0246] As the coagulating liquid, only a non-solvent for the binder polymer can be used, or a mixed solvent of a non-solvent for the binder polymer and a solvent as described above can be used. When using a mixed solvent of a non-solvent for the binder polymer and a solvent, from the viewpoint of forming a good porous structure and improving productivity, the content of the non-solvent for the binder polymer can be 50% by weight or more with respect to 100% by weight of the coagulating liquid.

[0247] In another embodiment of the present invention, the step of coating and drying the photocrosslinking composition containing the photoinitiator and the solvent on the outside of the polyolefin porous support is coating and drying a slurry for forming an inorganic composite void layer containing an inorganic filler, a first binder polymer, and a dispersion medium on at least one surface of the polyolefin porous support to form an inorganic composite void layer; coating and drying a coating liquid for forming a porous adhesive layer containing a second binder polymer, the photoinitiator, and the solvent on the upper surface of the inorganic composite void layer, may be included.

[0248] For the inorganic filler, refer to the above-described content.

[0249] 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. As the dispersion medium, one having a solubility index similar to that of the first binder polymer to be used and a low boiling point can be used. In this case, uniform mixing and subsequent removal of the dispersion medium become easier.

[0250] In one embodiment of the present invention, the dispersion medium can be an aqueous dispersion medium. When the dispersion medium is an aqueous dispersion medium, it is environmentally friendly, does not require excessive heat during the drying process after forming the inorganic composite void layer, and does not require additional explosion-proof equipment, so the inorganic composite void layer can be formed more easily.

[0251] In one embodiment of the present invention, the first binder polymer may be insoluble in the solvent and the non-solvent for the second binder polymer described below. In this case, even when the coating liquid described below is applied to form a porous adhesive layer after forming the inorganic composite void layer, since the first binder polymer is not dissolved, the phenomenon that the first binder polymer dissolved in the solvent or the non-solvent for the second binder polymer blocks the pores can be easily prevented.

[0252] In one embodiment of the present invention, the first binder polymer can be an aqueous 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 a particulate form.

[0253] In one embodiment of the present invention, the first binder polymer can be a binder polymer having excellent heat resistance. When the first binder polymer has excellent heat resistance, the heat resistance characteristics of the inorganic composite void layer can be further improved. For example, the thermal shrinkage rates of the separation membrane in the machine direction (MD) and the transverse direction (TD) measured after leaving it standing at 150 °C for 30 minutes can be 20% or less, 2% to 15%, 2% to 10%, 2% to 5%, 0% to 5%, or 0% to 2%, respectively.

[0254] In one embodiment of the present invention, the first binder polymer can include an acrylic polymer, polyacrylic acid, styrene-butadiene rubber, polyvinyl alcohol, or two or more of these.

[0255] Specifically, the acrylic polymer can include an acrylic homopolymer obtained by polymerizing only acrylic monomers, and can also include a copolymer of acrylic monomers and other monomers. For example, the acrylic polymer can include an ethylhexyl acrylate-methyl methacrylate copolymer, polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, polyacrylonitrile, a butyl acrylate-methyl methacrylate copolymer, or two or more of these.

[0256] In one embodiment of the present invention, the weight ratio of the inorganic filler to the first binder polymer can be 95:5 to 99.9:0.1, 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 content of the inorganic filler distributed per unit area of the separation membrane increases, and the thermal safety of the separation membrane at high temperatures can be improved. For example, the thermal shrinkage rates of the separation membrane in the machine direction (MD) and the transverse direction (TD) measured after leaving it standing at 150 °C for 30 minutes can be 20% or less, 2% to 15%, 2% to 10%, 2% to 5%, 0% to 5%, or 0% to 2%, respectively.

[0257] For the slurry for forming the inorganic composite void layer, refer to the above-described content.

[0258] The slurry for forming the inorganic composite void layer can be dried by a drying method during the production of a normal separation membrane. For example, the drying of the coated slurry can be performed by air for 10 seconds to 30 minutes, 30 seconds to 20 minutes, or 3 minutes to 10 minutes. When dried within the above time range, it has the effect of removing residual solvents while not inhibiting productivity.

[0259] The second binder polymer can be a binder polymer commonly used for forming an adhesive layer. The second binder polymer has a glass transition temperature (T g ) that can be -200 to 200°C. When the glass transition temperature of the second binder polymer satisfies the above range, mechanical properties such as the flexibility and elasticity of the finally formed adhesive layer can be improved. The second binder polymer can have ion conduction ability. When a binder polymer having ion conduction ability is used as the second binder polymer, the performance of the battery can be further improved. The second binder polymer can 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 above range, the dissociation degree of salts in the electrolyte can be improved.

[0260] In one embodiment of the present invention, the second binder polymer is polyvinylidene fluoride, polyvinylidene fluoride - hexafluoropropylene, polyvinylidene fluoride - trichloroethylene, polyvinylidene fluoride - tetrafluoroethylene, polyvinylidene fluoride - trifluoroethylene, polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, ethylhexyl acrylate - methyl methacrylate copolymer, ethylene vinyl acetate copolymer, polyethylene oxide, polyarylate, or can include two or more of these.

[0261] The solvent may be one that dissolves 5 wt% or more, 15 wt% or more, or 25 wt% or more of the second binder polymer at 25°C.

[0262] The solvent may be a non-solvent for the first binder polymer. For example, the solvent may be one that dissolves less than 5 wt% of the first binder polymer at 25°C.

[0263] For the types of the solvent, refer to the above-described content.

[0264] In one embodiment of the present invention, the second binder polymer may be contained in an amount of 3 wt% to 30 wt%, or 5 wt% to 25 wt% based on 100 wt% of the coating liquid for forming the porous adhesive layer.

[0265] When the coating liquid for forming the porous adhesive layer is coated on the upper surface of the inorganic composite void layer by including the photoinitiator in the coating liquid for forming the porous adhesive layer, the photoinitiator is introduced onto the surface of the polyolefin porous support, and at the same time, a porous adhesive layer can be formed.

[0266] In the process of coating the coating liquid for forming the porous adhesive layer, the polyolefin porous support is wetted by the solvent. At this time, the photoinitiator contained in the coating liquid for forming the porous adhesive layer is introduced onto the surface of the polyolefin porous support, and the polyolefin porous support can be photocrosslinked by the photoinitiator present on the surface of the polyolefin porous support upon irradiation with ultraviolet rays.

[0267] Thereby, the method for manufacturing a crosslinked structure-containing separator for a lithium secondary battery according to one embodiment of the present invention does not additionally require equipment for directly applying a photoinitiator to the polyolefin porous support in order to photocrosslink the polyolefin porous support, such as equipment for directly coating and drying a solution containing the photoinitiator on the polyolefin porous support, and the process can be simplified in that the polyolefin porous support can be photocrosslinked using the porous adhesive layer forming step.

[0268] The manufacturing method of the crosslinked structure-containing separator for a lithium secondary battery according to an embodiment of the present invention does not require other components such as monomers for forming radicals in addition to a photoinitiator in order to directly crosslink the polymer chains in the polyolefin porous support. Therefore, even when the photoinitiator is added to the coating liquid for forming the porous adhesive layer, other components do not interfere with the photoinitiator reaching the surface of the polyolefin porous support, and the photoinitiator can be sufficiently introduced onto the surface of the polyolefin porous support.

[0269] Also, generally, since the polyolefin porous support itself and the inorganic filler have a high ultraviolet blocking effect, if ultraviolet rays are irradiated after forming the inorganic composite void layer and the porous adhesive layer, the amount of irradiated light of the ultraviolet rays reaching the polyolefin porous support may decrease. However, in the present invention, since crosslinking is possible even with a small amount of irradiated light of ultraviolet rays, even if ultraviolet rays are irradiated after the inorganic composite void layer and the porous adhesive layer are formed, the polymer chains in the polyolefin porous support can be crosslinked and directly connected.

[0270] In one embodiment of the present invention, the coating liquid for forming the porous coating layer may contain 2-isopropylthioxanthone, thioxanthone, or a mixture thereof as the photoinitiator. 2-Isopropylthioxanthone or thioxanthone enables photocrosslinking even at a long wavelength with high transmittance. Thereby, even if ultraviolet rays are irradiated after the inorganic formation void layer and the porous adhesive layer are formed, the polyolefin porous support can be easily crosslinked.

[0271] 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 composite void layer, a pattern can be formed on the finally manufactured porous adhesive layer.

[0272] 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 composite void layer, a phase separation process can be performed. The phase separation can be performed by an immersion phase separation method.

[0273] After coating the upper surface of the inorganic composite void layer with the coating liquid for forming the porous adhesive layer, it is immersed in a coagulation liquid containing a non-solvent for the second binder polymer for a predetermined time. Thereby, the second binder polymer is solidified while inducing a phase separation phenomenon in the coated coating liquid for forming the porous adhesive layer. A porous adhesive layer is formed in this step. Then, the coagulation liquid is removed by washing with water and dried. For the drying, a method known in the art can be used, and it can be performed batchwise or continuously using an oven or a heating chamber within a temperature range considering the vapor pressure of the solvent used. The drying substantially removes the solvent present in the coating liquid for forming the porous adhesive layer, and it is desirable to be performed as quickly as possible in consideration of productivity and the like, and it can be performed, for example, in a time of 1 minute or less or 30 seconds or less.

[0274] As the coagulation liquid, only a non-solvent for the second binder polymer can be used, or a mixed solvent of a non-solvent for the second binder polymer and a solvent as described above can be used. When using a mixed solvent of a non-solvent for the second binder polymer and a solvent, from the viewpoint of forming a good porous structure and improving productivity, the content of the non-solvent for the second binder polymer can be 50% by weight or more with respect to 100% by weight of the coagulation liquid.

[0275] In the process of solidifying the second binder polymer, the second binder polymer condenses, whereby it is possible to prevent the second binder polymer from penetrating into the surface and / or inside of the polyolefin porous support, and it is possible to prevent the phenomenon that the resistance of the separation membrane increases. Also, the resistance of the separation membrane can be improved by making the adhesive layer containing the second binder polymer porous.

[0276] The non-solvent for the second binder polymer may have a solubility in the second binder polymer of less than 5% by weight at 25°C.

[0277] The non-solvent for the second binder polymer can 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.

[0278] 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 thereof.

[0279] In one embodiment of the present invention, the immersion can be performed for 3 seconds to 1 minute. When the immersion time satisfies the above-described range, phase separation occurs appropriately, the adhesion between the inorganic composite void layer and the porous adhesive layer is ensured, and the detachment of the adhesive layer can be prevented.

[0280] In one embodiment of the present invention, the coating liquid for forming the porous adhesive layer can be dried by a drying method during the production of a normal separation membrane. For example, it can be dried with air for 10 seconds to 30 minutes, 30 seconds to 20 minutes, or 3 minutes to 10 minutes. When dried within the above time range, it has the effect of removing residual solvents while not inhibiting productivity.

[0281] In the manufacturing method of the crosslinked structure-containing separation membrane for a lithium secondary battery according to one embodiment of the present invention, since the inorganic composite void layer and the porous adhesive layer are formed through separate steps, the porous adhesive layer can be formed in various forms. For example, the porous adhesive layer can be easily formed in a pattern form.

[0282] Thereafter, the polyolefin porous support is irradiated with ultraviolet light. By irradiating with ultraviolet light, the polymer chains in the polyolefin porous support are crosslinked to obtain a crosslinked structure-containing polyolefin porous support.

[0283] The ultraviolet irradiation can be carried out by appropriately adjusting the irradiation time and irradiation light amount of ultraviolet rays using an ultraviolet crosslinking device in consideration of conditions such as the content ratio of the photoinitiator. For example, the irradiation time and irradiation light amount of the ultraviolet rays can be set under conditions such that the polymer chains in the polyolefin porous support are sufficiently crosslinked to ensure the desired heat resistance and the separation membrane is not damaged by the heat generated by the ultraviolet lamp. Further, the ultraviolet lamp used in the ultraviolet crosslinking device can be appropriately selected and used from a high-pressure mercury lamp, a metal lamp, a gallium lamp, etc. according to the photoinitiator to be used, and the emission wavelength and capacity of the ultraviolet lamp can be appropriately selected according to the process.

[0284] According to a method for manufacturing a crosslinked structure-containing separator for a lithium secondary battery according to an embodiment of the present invention, even with an irradiation light amount of ultraviolet rays significantly smaller than the light amount used in general photocrosslinking, the polymer chains in the polyolefin porous support can be photocrosslinked, so that the applicability to the mass production process of the crosslinked structure-containing separator for a lithium secondary battery can be enhanced. For example, the irradiation light amount of the ultraviolet rays can be 10 to 2000 mJ / cm 2 , 50 to 1000 mJ / cm 2 , or 150 to 500 mJ / cm 2 .

[0285] In an embodiment of the present invention, the irradiation light amount of the ultraviolet rays can be measured using a portable light amount measuring device H type UV bulb and UV power pack manufactured by Miltec. When measuring the light amount using the H type UV bulb manufactured by Miltec, three types of wavelength values of UVA, UVB, and UVC can be obtained for each wavelength, and the ultraviolet rays of the present invention correspond to UVA.

[0286] In the present invention, the method for measuring the irradiation light amount of the ultraviolet rays is to pass the UV power pack under the light source on the conveyor under the same conditions as the sample, and at this time, the ultraviolet light amount numerical value indicated on the UV power pack is referred to as the "irradiation light amount of the ultraviolet rays".

[0287] According to a manufacturing method of a crosslinked structure-containing separator 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 with respect to 100 parts by weight of the polyolefin porous support, and when measured by H-NMR, the number of double bonds present in the polyolefin chain is 0.01 to 0.5 per 1000 carbon atoms. By crosslinking the polyolefin porous support, not only can the polyolefin porous support be effectively crosslinked, but side reactions can also be minimized.

[0288] Further, according to a manufacturing method of a crosslinked structure-containing separator for a lithium secondary battery according to an embodiment of the present invention, when an antioxidant is additionally used, the problem of side reactions occurring can be more easily prevented together with the number of double bonds present in the polyolefin chain.

[0289] A lithium secondary battery can be manufactured by interposing the crosslinked structure-containing separator for a lithium secondary battery between a positive electrode and a negative electrode.

[0290] The lithium secondary battery can have various shapes such as cylindrical, rectangular, or pouch type.

[0291] The lithium secondary battery can include a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery, etc.

[0292] The electrode applied together with the crosslinked structure-containing separator for a lithium secondary battery of the present invention is not particularly limited, and an electrode active material layer including an electrode active material, a conductive material, and a binder can be manufactured in a form adhered to a current collector by a usual method well known in the art.

[0293] Non-limiting examples of the positive electrode active material among the electrode active materials include layered compounds such as lithium cobalt composite oxide (LiCoO2), lithium nickel oxide (LiNiO2), or compounds substituted with one or more transition metals; chemical formula Li 1+x Mn 2-xLithium manganese oxides such as O4 (x = 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O5, LiV3O4, V2O5, Cu2V2O7; chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by O2 (M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, x = 0.01 to 0.3); chemical formula LiMn 1-x M x Lithium manganese composite oxides represented by O2 (M = Co, Ni, Fe, Cr, Zn or Ta, x = 0.01 to 0.1) or Li2Mn3MO5 (M = Fe, Co, Ni, Cu or Zn); LiMn2O4 in which part of the Li in the chemical formula is substituted with alkaline earth metal ions; disulfide compounds; Fe2(MoO4)3 and the like, but are not limited thereto.

[0294] Among the electrode active materials, non-limiting examples of the negative electrode active material include ordinary negative electrode active materials conventionally used for the negative electrode of a lithium secondary battery, and in particular, lithium metal or lithium alloy, carbon, petroleum coke, activated carbon, graphite or other carbonaceous materials such as lithium adsorbing substances can be used.

[0295] Non-limiting examples of the positive electrode current collector include foils made of aluminum, nickel or combinations thereof, and non-limiting examples of the negative electrode current collector include foils made of copper, gold, nickel or copper alloy, or combinations thereof.

[0296] In one embodiment of the present invention, the conductive materials used in the negative electrode and the positive electrode can each independently be added usually in an amount of 1 wt% to 30 wt% based on the total weight of the active material layer. Such conductive materials are not particularly limited as long as they have conductivity without inducing a chemical change in the battery. For example, graphite such as natural graphite and artificial graphite; carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, nickel powder; conductive whiskers such as zinc oxide, potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives can be used.

[0297] In one embodiment of the present invention, the binders used in the negative electrode and the positive electrode are each independently components that assist in binding the active material and the conductive material, etc., and binding to the current collector, and can usually be added in an amount of 1 wt% to 30 wt% based on the total weight of the active material layer. Examples of such binders include polyvinylidene fluoride (PVdF), polyacrylic acid (PAA), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, various copolymers, and the like.

[0298] In one embodiment of the present invention, the lithium secondary battery includes an electrolyte, and the electrolyte can include an organic solvent and a lithium salt. Also, as the electrolyte, an organic solid electrolyte, an inorganic solid electrolyte, or the like can be used.

[0299] Examples of the organic solvent include aprotic organic solvents such as N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, ethyl propionate, etc., which can be used.

[0300] The lithium salt is a substance that is easily soluble in the organic solvent, and examples thereof include LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium tetraphenylborate, imide, etc., which can be used.

[0301] Also, for the purpose of improving charge-discharge characteristics, flame retardancy, etc., for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinoneimine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. can be added to the electrolytic solution. In some cases, for imparting non-flammability, a halogen-containing solvent such as carbon tetrachloride, vinylidene fluoride, etc. may be further included, and for improving high-temperature storage characteristics, carbon dioxide gas may be further included.

[0302] Examples of the organic solid electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate esters polymers, polyagitation lysine, polyester sulfides, polyvinyl alcohol, polyvinylidene fluoride, polymers containing ionic dissociation groups, and the like that can be used.

[0303] Examples of the inorganic solid electrolyte include nitrides, halides, sulfates of Li such as Li3N, LiI, Li5NI2, Li3N - LiI - LiOH, LiSiO4, LiSiO4 - LiI - LiOH, Li2SiS3, Li4SiO4, Li4SiO4 - LiI - LiOH, Li3PO4 - Li2S - SiS2, and the like that can be used.

[0304] The injection of the electrolyte can be carried out at an appropriate stage in the battery manufacturing process according to the manufacturing process of the final product and the required physical properties. That is, it can be carried out before battery assembly or at the final stage of battery assembly.

[0305] In one embodiment of the present invention, as a process of applying the cross-linked structure-containing separator for the lithium secondary battery to the battery, in addition to winding which is a normal process, processes such as lamination and folding of the separator and the electrode are applicable.

[0306] In one embodiment of the present invention, the cross-linked structure-containing separator for the lithium secondary battery is interposed between the positive electrode and the negative electrode of the lithium secondary battery, and when a plurality of cells or electrodes are assembled to form an electrode assembly, it can be interposed between adjacent cells or electrodes. The electrode assembly can have various structures such as a simple stack type, jelly roll type, stack folding type, lamination stack type, and the like.

Examples

[0307] Hereinafter, for the purpose of facilitating the understanding of the present invention, examples will be given and described in detail. However, the examples according to the present invention can be deformed into many other forms, and the scope of the present invention should not be construed as being limited to the examples described hereinafter. The examples of the present invention are provided to more fully explain the present invention to those with average knowledge in the industry.

[0308] Example 1 30 parts by weight of a polyolefin (manufactured by Korea Petrochemical Co., Ltd.) in which the number of double bonds present in the polymer chain is 0.07 per 1000 carbon atoms during H-NMR measurement, 70 parts by weight of a liquid paraffin oil (manufactured by Kukdong Petrochemical Co., Ltd., LP350), 4000 ppm of pentaerythritol tetrakis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] (BASF, Irganox 1010) as the first antioxidant, and 4000 ppm of tris(2,4-di-t-butylphenyl)phosphite (BASF, Irgafos 168) as the second antioxidant were mixed to produce a polyolefin composition.

[0309] The produced polyolefin composition was put into a twin-screw extruder, kneaded, and extruded.

[0310] This was passed through a die and a cooling roll to be formed into a sheet shape, and then biaxially stretched by a tenter-type sequential stretching machine with stretching in the machine direction (MD) followed by stretching in the transverse direction (TD).

[0311] The liquid paraffin oil was extracted from the obtained stretched sheet with methylene chloride and heat-fixed at 128 °C to produce a polyolefin porous support.

[0312] Manufacture of a crosslinked structure-containing separator for a lithium secondary battery

[0313] 2-Isopropylthioxanthone (manufactured by Sigma Aldrich) was prepared as a photoinitiator.

[0314] As a UV light source, a high-pressure mercury lamp (Lichtzen high-pressure mercury lamp, LH-250 / 800-A) was prepared.

[0315] The photoinitiator was added so as to be 0.075 parts by weight based on 100 parts by weight of acetone to prepare a photocrosslinking composition.

[0316] The produced polyolefin porous support was immersed in the photocrosslinking composition for 30 seconds and then taken out. While cutting the coating liquid using a bar so that no photocrosslinking composition remained on the surface of the porous support, the content of the photoinitiator was made to be 0.054 parts by weight based on 100 parts by weight of the polyolefin porous support, and it was dried at room temperature (25°C) for 1 minute.

[0317] The polyolefin porous support coated with the photocrosslinking composition was irradiated with ultraviolet rays so that the integrated light amount, that is, the irradiation light amount of UV, became 500 mJ / cm 2 At this time, the irradiation intensity of the ultraviolet rays was 80% of the ultraviolet light source.

[0318] Thereby, a crosslinked structure-containing separator for a lithium secondary battery including a crosslinked structure-containing polyolefin porous support having a crosslinked structure in which polymer chains are directly connected to each other was obtained.

[0319] Example 2 A polyolefin porous support and a crosslinked structure-containing separator for a lithium secondary battery were obtained in the same manner as in Example 1, except that 2000 ppm of the first antioxidant and 2000 ppm of the second antioxidant were used.

[0320] Example 3 A crosslinked structure-containing separator for a lithium secondary battery was obtained in the same manner as in Example 1, except that the polyolefin porous support was subjected to corona discharge treatment at a voltage of 3 kV in the atmosphere while running at 40 m / min before immersing the polyolefin porous support in the photocrosslinking composition.

[0321] Example 4 A polyolefin porous support and a crosslinked structure-containing separator for a lithium secondary battery were obtained in the same manner as in Example 2, except that a polyolefin having 0.42 double bonds per 1000 carbon atoms in the polymer chain during 1H-NMR measurement was used.

[0322] Comparative Example 1 A polyethylene-based porous film (manufactured by Senior, SW709I) was used as a separator for a lithium secondary battery without any treatment.

[0323] Comparative Example 2 A crosslinked structure-containing separator for a lithium secondary battery was obtained in the same manner as in Example 1, except that it was irradiated with 200 kGy of E-beam (manufactured by EB tech). The 200 kGy of E-beam corresponds to the dose amount for causing crosslinking.

[0324] Evaluation Example 1: Measurement of the number of double bonds present in the polyolefin chains in the crosslinked structure-containing polyolefin porous support through 1H-NMR

[0325] In the crosslinked structure-containing separators for lithium secondary batteries manufactured in Example 1 and Example 2, the number of double bonds present in the polyolefin chains in the crosslinked structure-containing polyolefin porous support was measured by NMR and shown in FIGS. 3 and 4.

[0326] FIG. 3 is a document analyzing the number of double bonds in the polyolefin porous support manufactured in Example 1 through NMR analysis.

[0327] FIG. 4 is a document analyzing the number of double bonds in the polyolefin porous support manufactured in Example 2 through NMR analysis.

[0328] Evaluation Example 2: Evaluation of the physical properties of the separator In the crosslinked structure-containing separator for lithium secondary batteries manufactured in Examples 1 to 4, Comparative Examples 1 and 2, the number of double bonds present in the polyolefin chains in the crosslinked structure-containing polyolefin porous support, the degree of crosslinking, the melt-down temperature, and the shut-down temperature were measured and shown in Table 1 below.

[0329] Also, for the batteries equipped with the crosslinked structure-containing separators for lithium secondary batteries manufactured in Examples 1 to 4, Comparative Examples 1 and 2, the change in OCV (Open Circuit Voltage) after high-temperature storage was measured and shown in Table 1 below.

[0330] (1) Measurement of the number of double bonds present in the polyolefin chains in the crosslinked structure-containing polyolefin porous support The number of double bonds present in the polyolefin chains in the crosslinked structure-containing polyolefin porous support was measured using H-NMR.

[0331] (2) Evaluation of the degree of crosslinking The crosslinked structure-containing polyolefin porous supports manufactured in Examples 1 to 4, Comparative Examples 1 and 2 were each immersed in a xylene solution at 135°C according to ASTM D2765 and boiled for 12 hours, and then the residual weight was measured. The degree of crosslinking was calculated as the percentage of the residual weight to the initial weight.

[0332] (3) Evaluation of the melt-down temperature The melt-down temperature was measured by a thermomechanical analysis method (TMA) after sampling the samples in the machine direction and transverse direction of the separator respectively. Specifically, a sample with a width of 4.8 mm × a length of 8 mm was placed in a TMA apparatus (Q400 manufactured by TA Instruments), and while applying a tension of 0.01 N, the temperature was changed from 30°C to 220°C at a heating rate of 5°C / min. As the temperature increased, the length of the sample changed, and the temperature at which the length increased rapidly and the sample broke in each of the machine direction and transverse direction was measured and taken as the melt-down temperature.

[0333] (4) Evaluation of the shut-down temperature After fixing the separation membrane to the air permeability measuring device, the air permeability was measured while increasing the temperature by 5 °C per minute. The air permeability was measured by using a Wang Research type air permeability measuring machine (manufactured by Asahi Seiko, model: EG01-55-1MR) at a constant pressure of 0.05 Mpa to measure the time (seconds) required for 100 cc of air to pass through the separation membrane. The temperature at which the air permeability of the separation membrane increased rapidly was defined as the shutdown temperature.

[0334] (5) Evaluation of OCV change after high-temperature storage Monocells were manufactured using the separation membranes produced in Examples 1 to 4, Comparative Examples 1 and 2, and each monocell was charged to a state of SOC 100 by the CC (Constant Current)-CV (Constant Voltage) method at room temperature, 0.3C, and 4.2V (1 / 20C cut-off), and then stored at 60 °C for 3 days, after which the change in the OCV of the battery was measured.

[0335] Manufacture of negative electrode Artificial graphite as the negative electrode active material, Denka black (carbon black) as the conductive material, and polyvinylidene fluoride (PVdF) as the binder were mixed at a weight ratio of 75:5:20, and N-methylpyrrolidone (NMP) as the solvent was added to produce a negative electrode slurry. The negative electrode slurry was coated and dried on a copper current collector at a loading amount of 3.8 mAh / cm 2 to prepare a negative electrode.

[0336] Manufacture of positive electrode LiCoO2 as the positive electrode active material, Denka black as the conductive material, and polyvinylidene fluoride (PVdF) as the binder were added to N-methylpyrrolidone (NMP) as the solvent at a weight ratio of 85:5:10 to prepare a positive electrode slurry. The positive electrode slurry was coated and dried on a sheet-shaped aluminum current collector to form a positive electrode active material layer so that the final positive electrode loading amount was 3.3 mAh / cm 2

[0337] Manufacture of monocell ​Between the negative electrode and the positive electrode manufactured as described above, each of the separator membranes of the above-described Examples and Comparative Examples was interposed, and a non-aqueous electrolyte (1 M LiPF6, ethylene carbonate (EC) / propylene carbonate (PC) / diethyl carbonate (DEC)) (volume ratio = 3:3:4) was injected to fabricate a monocell.

[0338]

Table 1

[0339] From Table 1, it can be confirmed that the separator membranes manufactured in Examples 1 to 4 have a crosslinked structure in which the polymer chains are directly connected to each other. Although the shutdown temperature did not increase significantly compared to Comparative Example 1 without a crosslinked structure, the melt-down temperature increased very significantly to 160 °C or higher.

[0340] In addition, the separator membranes manufactured in Examples 1 to 4 have 0.01 to 0.6 double bonds present in the polyolefin chains in the crosslinked structure-containing polyolefin porous support, and even when stored at high temperatures, it can be confirmed that the OCV did not change significantly compared to the separator membrane manufactured in Comparative Example 2.

Claims

1. A crosslinked structure-containing polyolefin porous support in which, when measured by 1H-NMR, the number of double bonds present in the polyolefin chain is 0.01 to 0.6 per 1000 carbon atoms, wherein the crosslinked structure consists of polymer chains directly linked between polymer chains, the crosslinked structure does not include a crosslinked structure formed between a type II photoinitiator and a polyolefin chain, and the degree of crosslinking is 20% to 45%. A crosslinked structure-containing polyolefin porous support.

2. A crosslinked structure-containing separator for a lithium secondary battery, comprising the crosslinked structure-containing polyolefin porous support according to Claim 1.

3. The crosslinked structure-containing separator for a lithium secondary battery is located on at least one surface of the crosslinked structure-containing polyolefin porous support, and further includes an inorganic composite void layer containing an inorganic filler and a binder polymer. The crosslinked structure-containing separator for a lithium secondary battery according to Claim 2.

4. The inorganic filler is 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 , lithium phosphate (Li ３ PO ４ ), lithium titanophosphate (Li ｘ Ti ｙ (PO ４ ) ３ , 0 < x < 2, 0 < y < 3), lithium aluminum titanophosphate (Li ｘ Al ｙ Ti ｚ (PO ４ ) ３ , 0 < x < 2, 0 < y < 1, 0 < z < 3), (LiAlTiP) ｘ O ｙ - based glass (0 < x < 4, 0 < y < 13), lithium germanium thiophosphate (Li ｘ Ge ｙ P ｚ S ｗ , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride (Li ｘ N ｙ , 0 < x < 4, 0 < y < 2), SiS ２ - based glass (Li ｘ Si ｙ S ｚ (where 0 < x < 3, 0 < y < 2, 0 < z < 4), P ２ S ５ The system glass (Li ｘ P ｙ S ｚ (where 0 < x < 3, 0 < y < 3, 0 < z < 7), or a separator membrane containing a crosslinked structure for a lithium secondary battery according to claim 3, containing two or more of these.

5. The binder polymer is polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-chlorotrifluoroethylene, polyvinylidene fluoride-tetrafluoroethylene, polyvinylidene fluoride-trichloroethylene, an acrylic copolymer, styrene-butadiene copolymer, polyacrylic acid, polymethyl methacrylate, polybutyl acrylate, polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl alcohol, polyvinyl acetate, ethylene vinyl acetate copolymer, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, or a combination of two or more thereof. The crosslinked structure-containing separator for a lithium secondary battery according to Claim 3.

6. The crosslinked structure-containing separator for a lithium secondary battery, is located on at least one surface of the crosslinked structure-containing polyolefin porous support, and includes an inorganic composite void layer containing an inorganic filler and a first binder polymer, and a porous adhesive layer located on the inorganic composite void layer and containing a second binder polymer. The crosslinked structure-containing separator for a lithium secondary battery according to Claim 2.

7. The inorganic filler is 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 , lithium phosphate (Li ３ PO ４ ), lithium titanophosphate (Li ｘ Ti ｙ (PO ４ ) ３ , 0 < x < 2, 0 < y < 3), lithium aluminum titanophosphate (Li ｘ Al ｙ Ti ｚ (PO ４ ) ３ , 0 < x < 2, 0 < y < 1, 0 < z < 3), (LiAlTiP) ｘ O ｙ - based glass (0 < x < 4, 0 < y < 13), lithium germanium thiophosphate (Li ｘ Ge ｙ P ｚ S ｗ , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride (Li ｘ N ｙ , 0 < x < 4, 0 < y < 2), SiS ２ - based glass (Li ｘ Si ｙ S ｚ , 0 < x < 3, 0 < y < 2, 0 < z < 4), P ２ S ５ system glass (Li ｘ P ｙ S ｚ , 0 < x < 3, 0 < y < 3, 0 < z < 7), or including two or more of these, the crosslinked structure-containing separator for a lithium secondary battery according to claim 6.

8. The crosslinked structure-containing separator for a lithium secondary battery according to claim 6, wherein the first binder polymer contains an acrylic polymer, polyacrylic acid, styrene-butadiene rubber, polyvinyl alcohol, or two or more thereof.

9. The crosslinked structure-containing separator for a lithium secondary battery according to claim 6, wherein the second binder polymer contains polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, polyvinylidene fluoride-tetrafluoroethylene, polyvinylidene fluoride-trifluoroethylene, polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl acetate, ethylhexyl acrylate-methyl methacrylate copolymer, ethylene vinyl acetate copolymer, polyethylene oxide, polyarylate, or two or more thereof.

10. The crosslinked structure-containing separator for a lithium secondary battery according to claim 2, wherein the melt-down temperature of the crosslinked structure-containing separator for a lithium secondary battery is 160°C or higher.

11. The crosslinked structure-containing separator for a lithium secondary battery according to claim 2, wherein the shutdown temperature of the crosslinked structure-containing separator for a lithium secondary battery is 145°C or lower.

12. A step of preparing a polyolefin porous support in which the number of double bonds present in the polyolefin chain is 0.01 to 0.5 per 1000 carbon atoms during H-NMR measurement; A step of irradiating the polyolefin porous support with ultraviolet rays in the presence of a type II photoinitiator to obtain a crosslinked structure-containing polyolefin porous support having a crosslinking degree of 20% to 45%, including: wherein the content of the photoinitiator is 0.015 to 0.36 parts by weight with respect to 100 parts by weight of the polyolefin porous support; when the crosslinked structure-containing polyolefin porous support is measured by H-NMR, the number of double bonds present in the polyolefin chain is 0.01 to 0.6 per 1000 carbon atoms; wherein the crosslinked structure is composed of polymer chains directly connected between polymer chains; A method for manufacturing a crosslinked structure-containing separator for a lithium secondary battery, wherein the crosslinked structure does not include a crosslinked structure formed between a type II photoinitiator and a polyolefin chain.

13. The method for manufacturing a crosslinked structure-containing separator for a lithium secondary battery according to claim 12, wherein an antioxidant is further added at the stage of preparing the polyolefin porous support, and the content of the antioxidant is 500 ppm to 20,000 ppm based on the content of the polyolefin porous support.

14. The method for manufacturing a crosslinked structure-containing separator for a lithium secondary battery according to claim 13, wherein the antioxidant includes a first antioxidant that is a radical scavenger and a second antioxidant that is a peroxide decomposer.

15. The method for manufacturing a crosslinked structure-containing separator for a lithium secondary battery according to claim 14, wherein the first antioxidant includes a phenolic antioxidant, an amine-based antioxidant, or a mixture thereof.

16. The method for manufacturing a crosslinked structure-containing separator for a lithium secondary battery according to claim 14, wherein the second antioxidant includes a phosphorus-based antioxidant, a sulfur-based antioxidant, or a mixture thereof.

17. The method for manufacturing a crosslinked structure-containing separator for a lithium secondary battery according to claim 14, wherein the content of the first antioxidant is 500 ppm to 10,000 ppm based on the content of the polyolefin porous support, and the content of the second antioxidant is 500 ppm to 10,000 ppm based on the content of the polyolefin porous support.

18. The method for manufacturing a crosslinked structure-containing separator for a lithium secondary battery according to claim 12, wherein the photoinitiator includes thioxanthone, a thioxanthone derivative, benzophenone, a benzophenone derivative, or two or more of these.

19. The stage of preparing the polyolefin porous support is The method for manufacturing a crosslinked structure-containing separator for a lithium secondary battery according to claim 12, including the stage of coating and drying a photo-crosslinking composition containing the type II photoinitiator and a solvent on the outer side of the polyolefin porous support.

20. The method for manufacturing a crosslinked structure-containing separator for a lithium secondary battery according to claim 19, wherein the photo-crosslinking composition is a photoinitiator solution containing the type II photoinitiator and the solvent.

21. The method for manufacturing a crosslinked structure-containing separator for a lithium secondary battery according to claim 19, wherein the photo-crosslinking composition is a slurry for forming an inorganic composite void layer containing an inorganic filler, a binder polymer, the type II photoinitiator, and the solvent.

22. Coating and drying the photocrosslinking composition containing the photoinitiator and the solvent on the outside of the polyolefin porous support, Coating and drying a slurry for forming an inorganic composite void layer containing an inorganic filler, a first binder polymer, and a dispersion medium on at least one surface of the polyolefin porous support to form an inorganic composite void layer; Coating and drying a coating liquid for forming a porous adhesive layer containing a second binder polymer, the type II photoinitiator, and the solvent on the upper surface of the inorganic composite void layer, The manufacturing method of the crosslinked structure-containing separator for a lithium secondary battery according to claim 21.

23. The irradiation light amount of the ultraviolet ray is 10 to 2000 mJ / cm ２ The method for manufacturing a crosslinked structure-containing separator for a lithium secondary battery according to claim 12, wherein the irradiation light amount of the ultraviolet ray is 10 to 2000 mJ / cm

24. Including a positive electrode, a negative electrode, and a separator for a lithium secondary battery interposed between the positive electrode and the negative electrode, The lithium secondary battery, wherein the separator for a lithium secondary battery is the crosslinked structure-containing separator for a lithium secondary battery according to claim 2.

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