Separator, lithium secondary battery comprising same, and method for manufacturing same

Abstract

Proposed are: a polyolefin porous support; and a separator, a lithium secondary battery comprising same, and a method for manufacturing same, wherein the polyolefin porous support comprises a plurality of fibrils and pores formed by the plurality of fibrils entangling with each other, polyolefin chains constituting the fibrils are directly cross-linked with each other, and the polyolefin porous support comprises polyethylene glycol containing a hydrophilic photoinitiator-derived functional group.

Description

Separator, lithium secondary battery including same, and method for manufacturing same

[0001] The present invention relates to a separator, a lithium secondary battery including the same, and a method for manufacturing the same.

[0002] This application claims priority to Korean Application No. 10-2023-0119975, filed September 8, 2023, the entire disclosure of which is incorporated herein by reference.

[0003] Interest in energy storage technology has been growing steadily in recent years. As its applications expand to include cell phones, camcorders, laptops, and even electric vehicles, the demand for higher energy density batteries used as power sources for these electronic devices is increasing. Lithium secondary batteries are the batteries best suited to meet this demand, and active research is currently underway.

[0004] These lithium secondary batteries are composed of a positive electrode, a negative electrode, an electrolyte, and a separator. Among these, the separator is required to have high ionic conductivity to increase the permeability of lithium ions based on its insulating properties and high porosity to electrically insulate the positive and negative electrodes.

[0005] As such separators, polymer separators made of olefin materials are widely used. However, in the case of ethylene polymer (PE) separators, which are representative olefin polymer separators, the melting point (Tm) is low. Therefore, if the temperature of the battery rises above the melting point of the ethylene polymer in a battery misuse environment, a melt-down phenomenon may occur, which may cause ignition and explosion. In addition, due to the material properties and manufacturing process characteristics, the separator exhibits extreme heat shrinkage behavior in high-temperature situations, which causes safety issues such as internal short circuits.

[0006] Accordingly, various methods have been devised to improve the heat resistance of olefin polymer membranes.

[0007] Korean Patent Publication No. 10-2006-0021221 proposes a membrane in which a coating layer including ceramic particles as inorganic fillers and a binder polymer is formed on at least one surface of an olefin polymer membrane.

[0008] In order to form a coating layer containing ceramic particles and binder polymers as inorganic fillers, a slurry for forming a coating layer using an organic solvent as a medium was mainly applied.

[0009] Recently, due to price, environmental issues, and global ESG management, there has been a growing demand for a change from organic solvent-based slurry to aqueous slurry for forming the coating layer of the separator of secondary batteries.

[0010] Meanwhile, the olefin polymer porous support mainly used as a separator substrate is hydrophobic, which limits the impregnation of the electrolyte into the separator during the electrolyte injection process in the production of secondary batteries. Therefore, the development of a separator that can achieve this quickly and sufficiently is required.

[0011] Accordingly, the problem to be solved by the present invention is to provide a separator having improved electrolyte impregnation properties, a lithium secondary battery including the same, and a method for manufacturing the same, which solve the aforementioned problems.

[0012] In order to solve the above problem, according to one aspect of the present invention, a separation membrane of the following embodiment is provided.

[0013] According to the first implementation example,

[0014] Olefin polymer porous support; and

[0015] The above olefin polymer porous support includes a plurality of fibrils and pores formed by the plurality of fibrils crossing each other, and the polyolefin chains constituting the fibrils are directly cross-linked to each other,

[0016] A separation membrane is provided, characterized in that the above olefin polymer porous support includes polyethylene glycol containing a hydrophilic photoinitiator-derived functional group.

[0017] According to the second embodiment, in the first embodiment,

[0018] The above hydrophilic photoinitiator may include an aromatic carbonyl compound having a hydrophilic group.

[0019] According to the third embodiment, in the first embodiment or the second embodiment,

[0020] The above hydrophilic photoinitiator can be represented by the following chemical formula 1:

[0021] [Chemical Formula 1]

[0022]

[0023] In the above chemical formula 1, R1 is hydrogen, a straight-chain or branched alkyl group having 1 to 10 carbon atoms, or an aryl group having 6 to 20 carbon atoms, R2 is a single bond, a straight-chain or branched alkylene group having 1 to 10 carbon atoms, or an arylene group having 6 to 12 carbon atoms, R3 is a single bond, oxygen (O), or sulfur (S), and (L) is an aromatic carbonyl structure.

[0024] According to the fourth embodiment, in the third embodiment,

[0025] The above (L) can be derived from a compound represented by the following chemical formulas 2 and 3:

[0026] [Chemical Formula 2]

[0027]

[0028] (In the above chemical formula 2, X is oxygen (O) or sulfur (S))

[0029] [Chemical Formula 3]

[0030]

[0031] According to the fifth embodiment, in any one of the first to fourth embodiments,

[0032] The hydrophilic photoinitiator may include a compound represented by the following chemical formulae 4 to 7:

[0033] [Chemical Formula 4]

[0034]

[0035] [Chemical Formula 5]

[0036]

[0037] [Chemical Formula 6]

[0038]

[0039] [Chemical Formula 7]

[0040]

[0041] (In the above chemical formulas 4 and 5, X is each independently oxygen (O) or sulfur (S))

[0042] According to the sixth embodiment, in any one of the first to fifth embodiments,

[0043] The polyethylene glycol containing a functional group derived from the hydrophilic photoinitiator can be represented by the following chemical formula 8:

[0044] [Chemical Formula 8]

[0045]

[0046] (In the above chemical formula 8, x and y represent the mol% of each repeating unit, x is 95 to 99 mol%, y is 1 to 5 mol%,

[0047] R2 is a single bond, a straight-chain or branched alkylene group having 1 to 10 carbon atoms, or an arylene group having 6 to 12 carbon atoms, R3 is a single bond, oxygen (O), or sulfur (S), and (L) is an aromatic carbonyl structure.

[0048] According to the seventh embodiment, in any one of the first to sixth embodiments,

[0049] The polyethylene glycol containing the functional group derived from the hydrophilic photoinitiator may be represented by the following chemical formulas 9 to 12:

[0050] [Chemical Formula 9]

[0051]

[0052] (In the above chemical formula 9, x and y represent the mol% of each repeating unit, x is 95 to 99 mol%, y is 1 to 5 mol%, and X is each independently oxygen (O) or sulfur (S))

[0053] [Chemical Formula 10]

[0054]

[0055] (In the above chemical formula 10, x and y represent the mol% of each repeating unit, x is 95 to 99 mol%, y is 1 to 5 mol%, and X is each independently oxygen (O) or sulfur (S))

[0056] [Chemical Formula 11]

[0057]

[0058] (In the above chemical formula 11, x and y represent the mol% of each repeating unit, x is 95 to 99 mol%, and y is 1 to 5 mol%)

[0059] [Chemical Formula 12]

[0060]

[0061] (In the above chemical formula 12, x and y represent the mol% of each repeating unit, x is 95 to 99 mol%, and y is 1 to 5 mol%.)

[0062] According to the eighth embodiment, in any one of the first to seventh embodiments,

[0063] The polyethylene glycol containing the functional group derived from the hydrophilic photoinitiator can be represented by the following chemical formula 13:

[0064] [Chemical Formula 13]

[0065]

[0066] (In the above chemical formula 13, x and y represent the mol% of each repeating unit, x is 1 to 5 mol%, and y is 95 to 99 mol%.)

[0067] According to the ninth implementation example,

[0068] In a lithium secondary battery including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode,

[0069] A lithium secondary battery is provided in which the separator is a separator according to any one of claims 1 to 8.

[0070] According to the 10th implementation example,

[0071] A step of applying and drying a composition comprising a polyethylene glycol containing a hydrophilic photoinitiator-derived functional group and an aqueous dispersion medium on at least one surface of an olefin polymer porous support; and

[0072] A method for manufacturing a separation membrane according to any one of the first to ninth embodiments is provided, comprising the step of irradiating ultraviolet rays on an olefin polymer porous support to which the composition has been applied and dried.

[0073] According to the 11th embodiment, in the 10th embodiment,

[0074] In the step of irradiating the above ultraviolet rays, the amount of ultraviolet irradiation light is 10 mJ / cm 2 More than 20,000 mJ / cm 2 It could be as follows:

[0075] A separator according to one embodiment of the present invention is formed by applying a composition including a polyethylene glycol containing a hydrophilic photoinitiator-derived functional group on at least one surface of an olefin polymer porous support, and during the application process of the composition, the polyethylene glycol containing a hydrophilic photoinitiator-derived functional group is also incorporated into the pores of the olefin polymer porous support. At this time, since the polyethylene glycol portion of the polyethylene glycol containing a hydrophilic photoinitiator-derived functional group has a high affinity for an electrolyte, the separator according to one embodiment of the present invention can exhibit electrolyte impregnation characteristics that are significantly improved compared to the olefin polymer porous support alone.

[0076] Furthermore, since polyethylene glycol containing a hydrophilic photoinitiator-derived functional group is relatively nonpolar compared to an aqueous dispersion medium (e.g., water) and has a structure in which a hydrophilic photoinitiator-derived functional group is introduced into polyethylene glycol having a high affinity for olefin polymers, when a composition including polyethylene glycol containing a hydrophilic photoinitiator-derived functional group and an aqueous dispersion medium is coated on at least one surface of an olefin polymer porous support, the hydrophilic photoinitiator-derived functional group evenly penetrates into the pores of the olefin polymer porous support, and a dense cross-linked structure is formed between the fibrils of the olefin polymers of the porous support with a small amount of ultraviolet exposure, thereby providing a separation membrane having a high rupture temperature.

[0077] The following drawings attached to this specification illustrate preferred embodiments of the present invention, and serve to further understand the technical idea of ​​the present invention together with the contents of the invention described above, and therefore the present invention should not be interpreted as being limited to matters described in such drawings.

[0078] Figure 1 is a photograph showing the results of evaluating the electrolyte impregnation characteristics of the separators manufactured in Example 1 and Comparative Examples 1 to 3.

[0079] Hereinafter, the present invention will be described in detail. Prior to this, the terms and words used in this specification and claims should not be interpreted as limited to their conventional or dictionary meanings. Rather, they should be interpreted with meanings and concepts that conform to the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of the term to best explain his or her invention. Accordingly, the configurations described in the embodiments described in this specification are merely the most preferred embodiments of the present invention and do not represent the entire technical spirit of the present invention. Therefore, it should be understood that various equivalents and modified examples may exist as of the time of this application.

[0080] The terminology used in this specification is for the purpose of describing exemplary embodiments only and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

[0081] Throughout this specification, when it is said that a part “includes” or “contains” a component, this does not mean that other components are excluded, but rather that other components may be included or provided.

[0082] Throughout this specification, the description of “A and / or B” means “A or B or both.”

[0083] Throughout this specification, the terms "about" and "substantially" are used in the sense of or near to the numerical values ​​when manufacturing and material tolerances inherent to the meanings stated are presented, and are used to prevent unscrupulous infringers from unfairly exploiting disclosures that state exact or absolute values ​​to aid understanding of this specification.

[0084] Unless otherwise specified throughout this specification, temperature refers to Celsius temperature, and the unit is ℃.

[0085] In the present invention, the term alkylene group means a divalent group having two bonding positions to an alkyl group.

[0086] In the present invention, the term arylene group means a divalent group having two bonding positions to an aryl group.

[0087] Aqueous dispersion media have the advantage of being environmentally friendly and inexpensive. Organic solvents, widely used in membrane manufacturing, pose numerous environmental problems, requiring solvent recovery facilities and subject to strict management and regulation. Therefore, numerous attempts are being made to utilize these aqueous dispersion media as a replacement for organic solvents.

[0088] Meanwhile, a method has been proposed for crosslinking olefin polymer chains within an olefin polymer porous support by coating a composition containing a photoinitiator on at least one surface of the olefin polymer porous support to photocrosslink the polymer chains within the porous support. To this end, the photoinitiator must be sufficiently dissolved in a solvent and introduced in a sufficient amount to crosslink the polymer chains on the surface of the olefin polymer porous support.

[0089] However, the photoinitiator mainly used to crosslink polymer chains within the olefin polymer porous support is soluble in organic solvents, but has very low solubility in an aqueous dispersion medium. Therefore, when an aqueous dispersion medium is used, the photoinitiator cannot be introduced in a sufficient amount to crosslink polymer chains on the surface and inside the pores of the olefin polymer porous support, and there is a problem that the photoinitiator does not penetrate evenly into the surface and inside the pores of the olefin polymer porous support.

[0090] Accordingly, the inventors of the present invention have developed a separation membrane using a hydrophilic photoinitiator-derived functional group-containing polyethylene glycol, which is a hydrophilic photoinitiator that can be dissolved or dispersed in an aqueous dispersion medium, and has excellent affinity for an olefin polymer porous support, and has introduced a hydrophilic photoinitiator as a functional group into polyethylene glycol.

[0091] According to one aspect of the present invention,

[0092] Olefin polymer porous support; and

[0093] The above olefin polymer porous support includes a plurality of fibrils and pores formed by the plurality of fibrils crossing each other, and the polyolefin chains constituting the fibrils are directly cross-linked to each other,

[0094] A separation membrane is provided, characterized in that the above olefin polymer porous support includes polyethylene glycol containing a hydrophilic photoinitiator-derived functional group.

[0095]

[0096] Polyethylene glycol containing functional groups derived from hydrophilic photoinitiators

[0097] The separation membrane according to the present invention has a cross-linked structure in which the olefin polymer chains of the porous support are at least partially connected. Furthermore, the cross-linked structure can also be observed between olefin polymer chains. In the present invention, the cross-linked structure may refer to both those formed between different polymer chains or within the same chain.

[0098] According to one embodiment of the present invention, a separation membrane uses polyethylene glycol containing a functional group derived from a hydrophilic photoinitiator, thereby enabling radical generation in polymer chains within an olefin polymer porous support, thereby forming a cross-linked structure in which polymer chains are directly connected.

[0099] The polyethylene glycol containing a functional group derived from the hydrophilic photoinitiator means that at least one of the hydrogens in the -CH2CH2O- repeating unit of the polyethylene glycol is removed, and a hydrophilic photoinitiator portion is modified with a functional group via the functional group of the hydrophilic photoinitiator at that position.

[0100] Compared to applying a composition containing a hydrophilic photoinitiator and polyethylene glycol separately to an olefin polymer porous support, when applying a composition containing polyethylene glycol containing a hydrophilic photoinitiator-derived functional group obtained by modifying polyethylene glycol with a hydrophilic photoinitiator to an olefin polymer porous support, the introduction of the hydrophilic photoinitiator-derived functional group imparts polarity, so that a relatively polar electrolyte or electrolyte solution can penetrate better, and the electrolyte impregnation characteristics of the separator can be significantly improved.

[0101] In this specification, a hydrophilic photoinitiator refers to a photoinitiator having hydrophilicity that can be dissolved or dispersed in an aqueous dispersion medium.

[0102] The hydrophilic photoinitiator can crosslink an olefin polymer porous support by itself without any other components such as a crosslinking agent, co-initiator, or synergist. When hydrogen atoms in the hydrophilic photoinitiator are removed by hydrogen abstraction only through light absorption, the hydrophilic photoinitiator becomes a reactive compound, and the photoinitiator forms radicals in the polymer chains in the olefin polymer porous support, making the polymer chains reactive, so that the polymer chains can be directly connected to each other and photocrosslinked. For example, the hydrogen abstraction reaction by the photoinitiator is possible in a small amount of double bond structures or branch structures present in the olefin polymer, so that hydrogen atoms can be removed from the double bond structures or branch structures in the olefin polymer by hydrogen abstraction only through light absorption, forming radicals in the polymer chains.

[0103] At this time, since the hydrophilic photoinitiator-derived functional group of the polyethylene glycol containing the hydrophilic photoinitiator-derived functional group plays a role in forming a radical in the polymer chain within the olefin polymer porous support, the content of the hydrophilic photoinitiator plays a very important role in the formation of the radical.

[0104] The above hydrophilic photoinitiator may include an aromatic carbonyl compound having a hydrophilic group.

[0105] The above hydrophilic photoinitiator can be represented by the following chemical formula 1:

[0106] [Chemical Formula 1]

[0107]

[0108] In the above chemical formula 1, R1 is hydrogen, a straight-chain or branched alkyl group having 1 to 10 carbon atoms, or an aryl group having 6 to 20 carbon atoms, R2 is a single bond, a straight-chain or branched alkylene group having 1 to 10 carbon atoms, or an arylene group having 6 to 12 carbon atoms, R3 is a single bond, oxygen (O), or sulfur (S), and (L) is an aromatic carbonyl structure.

[0109] According to one embodiment of the present invention, in the chemical formula 1, R1 is hydrogen, a straight-chain or branched alkyl group having 1 to 5 carbon atoms, or an aryl group having 6 to 10 carbon atoms, R2 is a single bond, a straight-chain or branched alkylene group having 1 to 5 carbon atoms, or an arylene group having 6 to 10 carbon atoms, R3 is a single bond, oxygen (O), or sulfur (S), and (L) may be an aromatic carbonyl structure.

[0110] According to one embodiment of the present invention, in the chemical formula 1, R1 is hydrogen, a straight-chain or branched alkyl group having 1 to 3 carbon atoms, R2 is a single bond, a straight-chain or branched alkylene group having 1 to 3 carbon atoms, R3 is a single bond, oxygen (O), or sulfur (S), and (L) may be an aromatic carbonyl structure.

[0111] According to one embodiment of the present invention, in the chemical formula 1, R1 is hydrogen, R2 is a single bond, a straight-chain or branched alkylene group having 1 to 3 carbon atoms, R3 is a single bond, oxygen (O), or sulfur (S), and (L) may be an aromatic carbonyl structure.

[0112] The above (L) can be derived from a compound represented by the following chemical formulas 2 and 3:

[0113] [Chemical Formula 2]

[0114]

[0115] (In the above chemical formula 2, X is oxygen (O) or sulfur (S))

[0116] [Chemical Formula 3]

[0117]

[0118] The hydrophilic photoinitiator may include a compound represented by the following chemical formulae 4 to 7:

[0119] [Chemical Formula 4]

[0120]

[0121] [Chemical Formula 5]

[0122]

[0123] [Chemical Formula 6]

[0124]

[0125] [Chemical Formula 7]

[0126]

[0127] (In the above chemical formulas 4 and 5, X is each independently oxygen (O) or sulfur (S))

[0128] According to one embodiment of the present invention, the polyethylene glycol containing a functional group derived from the hydrophilic photoinitiator may be represented by the following chemical formula 8:

[0129] [Chemical Formula 8]

[0130]

[0131] At this time, in the chemical formula 8, x and y represent the mol% of each repeating unit, and x may be 95 to 99 mol%, or 96 to 98 mol%, and y may be 1 to 5 mol%, or 2 to 4 mol%. When x and y satisfy these ranges, when the polyethylene glycol containing the hydrophilic photoinitiator-derived functional group is applied, the electrolyte impregnation property of the separator can be further improved, and the polymer modification reaction for introducing the hydrophilic photoinitiator-derived functional group into the polyethylene glycol can proceed more efficiently.

[0132] In addition, R2 may be a single bond, a straight-chain or branched alkylene group having 1 to 10 carbon atoms, or an arylene group having 6 to 12 carbon atoms, R3 may be a single bond, oxygen (O), or sulfur (S), and (L) may be an aromatic carbonyl structure.

[0133] In addition, the polyethylene glycol containing a functional group derived from the hydrophilic photoinitiator can be represented by the following chemical formulas 9 to 12:

[0134] [Chemical Formula 9]

[0135]

[0136] (In the above chemical formula 9, x and y represent the mol% of each repeating unit, x may be 95 to 99 mol%, or 96 to 98 mol%, and y may be 1 to 5 mol%, or 2 to 4 mol%. Each X may independently be oxygen (O) or sulfur (S))

[0137] [Chemical Formula 10]

[0138]

[0139] (In the above chemical formula 10, x and y represent the mol% of each repeating unit, x may be 95 to 99 mol%, or 96 to 98 mol%, and y may be 1 to 5 mol%, or 2 to 4 mol%. Each X may independently be oxygen (O) or sulfur (S))

[0140]

[0141] [Chemical Formula 11]

[0142]

[0143] (In the above chemical formula 11, x and y represent the mol% of each repeating unit, and x may be 95 to 99 mol%, or 96 to 98 mol%, and y may be 1 to 5 mol%, or 2 to 4 mol%.)

[0144] [Chemical Formula 12]

[0145]

[0146] (In the above chemical formula 12, x and y represent the mol% of each repeating unit, and x may be 95 to 99 mol%, or 96 to 98 mol%, and y may be 1 to 5 mol%, or 2 to 4 mol%.)

[0147] In one embodiment of the present invention, the polyethylene glycol containing a functional group derived from the hydrophilic photoinitiator may be a polyethylene glycol containing a functional group derived from 2-carboxymethoxythioxanthone of the following chemical formula 13:

[0148] [Chemical Formula 13]

[0149]

[0150] (In the above chemical formula 13, x and y represent the mol% of each repeating unit, x may be 1 to 5 mol%, or 2 to 4 mol%, and y may be 95 to 99 mol%, or 96 to 98 mol%.)

[0151] According to one embodiment of the present invention, the polyethylene glycol containing a functional group derived from the hydrophilic photoinitiator may be at least one of a random copolymer in which two types of repeating units are randomly connected, an alternating copolymer in which two types of repeating units are cross-linked, and a block copolymer obtained by repeating a plurality of repeating units of one type to form a block, and then a plurality of repeating units of another type to form a block.

[0152] Accordingly, the polyethylene glycol containing a hydrophilic photoinitiator-derived functional group represented by chemical formulae 8 to 13 in the present specification may also be at least one of the random copolymer, alternating copolymer, or block copolymer described above.

[0153] The polyethylene glycol containing a functional group derived from the hydrophilic photoinitiator is included in a composition together with an aqueous solvent as described below, and after the composition is coated on at least one surface of an olefin polymer porous support, in a UV irradiation step, the functional group derived from the hydrophilic photoinitiator plays a role in initiating crosslinking. The functional group derived from the hydrophilic photoinitiator can directly photocrosslink polymer chains within the olefin polymer porous support. Specifically, the functional group derived from the hydrophilic photoinitiator can generate radicals in polymer chains within the olefin polymer porous support and form a crosslinked structure in which the polymer chains are directly connected.

[0154] The polyethylene glycol containing a functional group derived from a hydrophilic photoinitiator can be sufficiently dissolved in an aqueous dispersion medium, and the solubility can be 0.01 g or more per 100 g of the aqueous dispersion medium. Accordingly, the polyethylene glycol containing a functional group derived from a hydrophilic photoinitiator can be dissolved in the aqueous dispersion medium to a degree that it can crosslink polymer chains within the olefin polymer porous support.

[0155] The above solubility can be measured using a UV-Visible spectrophotometer. Specifically, polyethylene glycol containing a functional group derived from a hydrophilic photoinitiator is dissolved in a solvent to prepare solutions having various concentrations whose mass concentrations are known in advance, and after leaving it for 1 hour to cause the undissolved polyethylene glycol containing a functional group derived from a hydrophilic photoinitiator to precipitate or float on the solvent, the light absorption of the solution is measured at a specific wavelength (e.g., 550 nm), and in a graph where the x-axis represents concentration and the y-axis represents light absorption, the starting point where the light absorption becomes saturated at a constant level can be defined as the solubility of the hydrophilic photoinitiator.

[0156] The content of the polyethylene glycol containing a hydrophilic photoinitiator-derived functional group in the separator can be controlled by preparing an aqueous dispersion medium composition having a concentration of 0.1 wt% or more, 0.3 wt% or more, 0.5 wt% or more, 1 wt% or more, or 10 wt% or less, 7 wt% or less, 5 wt% or less, 3 wt% or less, or 1 wt% or less, and applying and drying the aqueous dispersion composition to the olefin polymer porous support. When the content of the polyethylene glycol containing a hydrophilic photoinitiator-derived functional group is controlled in this way, the breakdown temperature of the olefin polymer porous support itself can be increased by generating appropriate radicals, and the shrinkage rate of the separator can be reduced, and the impregnation property of the separator for the electrolyte can be greatly improved due to the polyethylene glycol portion having an affinity for the electrolyte.

[0157] In one embodiment of the present invention, a composition including a hydrophilic photoinitiator-derived functional group-containing polyethylene glycol and an aqueous dispersion medium is applied onto at least one surface of an olefin polymer porous support, and then the hydrophilic photoinitiator-derived functional group-containing polyethylene glycol evenly penetrates into the surface and pores of the olefin polymer porous support, which is a crosslinking target, and then ultraviolet irradiation is performed so that polyolefin chains constituting a plurality of fibrils included in the olefin polymer porous support are directly crosslinked to each other, thereby providing a separation membrane having a directly crosslinked structure.

[0158] Typically, the above olefin polymer porous support is hydrophobic, so when a composition containing a hydrophilic photoinitiator alone in an aqueous dispersion medium is applied to at least one surface of the olefin polymer porous support, it may be difficult for the hydrophilic photoinitiator to penetrate into the surface or pores of the olefin polymer porous support.

[0159] However, as a result of including a polyethylene glycol containing a hydrophilic photoinitiator-derived functional group, which is a hydrophilic photoinitiator that directly crosslinks an olefin polymer porous support, in the composition, the polyethylene glycol has an affinity for the olefin polymer porous support, and thus the polyethylene glycol containing a hydrophilic photoinitiator-derived functional group can evenly penetrate into the pores of the olefin polymer porous support.

[0160] According to one embodiment of the present invention, the weight average molecular weight of the polyethylene glycol in the polyethylene glycol containing a functional group derived from the hydrophilic photoinitiator may be 30,000 or less, or 100 to 20,000, or 200 to 15,000, or 300 to 10,000. When the weight average molecular weight of the polyethylene glycol satisfies this range, it may be more advantageous in terms of improving the solubility of the hydrophilic photoinitiator in an aqueous dispersion medium and acting as a carrier that drags the hydrophilic photoinitiator toward the surface and inside the pores of the olefin polymer porous support.

[0161] The molecular weight (weight average molecular weight and number average molecular weight) of the above polyethylene glycol can be measured through gel permeation chromatography (GPC). PL GPC220 from Agilent Technologies can be used, and the measurement conditions can be as follows.

[0162] -Column (maker, model no.): PL aquagel-OH Guard 8um 50 x 7.5 mm

[0163] -Eleunt: Water

[0164] -Temperature: 40℃

[0165] -Flow rate: 1.0 mL / min

[0166] -Injection volume, sample concentration: 30 ㎕, 1~10 mg / mL

[0167] -Standard: PEG / PEO

[0168] -Detector: RI

[0169]

[0170] membrane

[0171] The separation membrane according to the present invention comprises a porous support of an olefin polymer having a crosslinked structure in which polymer chains are directly connected, and polyethylene glycol containing a functional group derived from a hydrophilic photoinitiator. In addition to the above components, additives such as a surfactant and a dispersant may be further included.

[0172] The above olefin polymer porous support includes a plurality of fibrils and pores formed by the plurality of fibrils crossing each other, and the polyolefin chains constituting the fibrils are directly cross-linked to each other.

[0173] In addition, the olefin polymer porous support includes polyethylene glycol containing a hydrophilic photoinitiator-derived functional group. Specifically, the polyethylene glycol containing a hydrophilic photoinitiator-derived functional group may be included on the surface and inside the pores of the olefin polymer porous support. As described below, when a composition including polyethylene glycol containing a hydrophilic photoinitiator-derived functional group and an aqueous dispersion medium is applied on at least one surface of the olefin polymer porous support, the polyethylene glycol has a high affinity for the olefin polymer porous support, and thus the polyethylene glycol containing a hydrophilic photoinitiator-derived functional group evenly penetrates into the inside of the pores through the surface of the olefin polymer porous support.

[0174] At this time, the polyethylene glycol containing a hydrophilic photoinitiator-derived functional group included in the olefin polymer porous support may not only remain in the form in which it was introduced during the preparation of the composition, but may also include all derivatives of the polyethylene glycol containing a hydrophilic photoinitiator-derived functional group, such as a radicalized form of the hydrophilic photoinitiator-derived functional group, a converted form of the radicalized functional group (e.g., a form in which a radicalized carbonyl group is converted to an -OH group), and a dimerized form of the radicalized hydrophilic photoinitiator-derived functional group, depending on the ultraviolet irradiation step described later, and may remain in the form of a component or reaction product of the polyethylene glycol containing a hydrophilic photoinitiator-derived functional group.

[0175] Additionally, the olefin polymer porous support may further include additives such as surfactants or dispersants.

[0176]

[0177] Olefin polymer porous support

[0178] The above olefin polymer porous support includes a ‘cross-linked structure in which polymer chains are directly connected.’

[0179] In the present specification, the term "cross-linked structure in which polymer chains are directly connected" means a state in which polymer chains substantially composed of olefin polymers, more preferably polymer chains composed solely of olefin polymers, are directly cross-linked with each other. Specifically, the polyethylene glycol containing a hydrophilic photoinitiator-derived functional group included in the composition evenly penetrates into the surface and pores of the olefin polymer porous support, and then the hydrophilic photoinitiator-derived functional group portion of the polyethylene glycol containing the hydrophilic photoinitiator-derived functional group is radicalized by ultraviolet irradiation, and then the olefin polymer is also radicalized as hydrogen is removed from the olefin polymer chain by the radicalized hydrophilic photoinitiator-derived functional group, and the olefin polymers thus radicalized become reactive and form cross-links in a form in which they are directly connected to each other.

[0180] Therefore, in addition to the polyethylene glycol containing the functional group derived from the hydrophilic photoinitiator, the crosslinking reaction that occurs between the crosslinking agents when an additional crosslinking agent is added does not correspond to the 'crosslinking structure in which polymer chains are directly connected' referred to in the present invention. In addition, the crosslinking reaction that occurs between the additional crosslinking agent and the polymer chain does not correspond to the 'crosslinking structure in which polymer chains are directly connected' referred to in the present invention, even if the polymer chain is substantially composed of an olefin polymer or is composed solely of an olefin polymer.

[0181] A separation membrane according to one embodiment of the present invention can have improved heat resistance by having a porous support made of an olefin polymer containing a crosslinked structure in which polymer chains are directly connected.

[0182] In one embodiment of the present invention, the crosslinking degree of the crosslinked structure-containing olefin polymer porous support may be 10% to 80%, or 30% to 55%, or 10% to 45%, or 15% to 40%, or 20% to 35%. When the crosslinked structure-containing olefin polymer porous support has a crosslinking degree in the above-mentioned range, it may be easier to increase the modulus while having a desired level of heat resistance.

[0183] At this time, the degree of crosslinking can be calculated as the percentage of the weight of the remaining olefin polymer porous support compared to the initial weight by physically confining the olefin polymer porous support containing the crosslinking structure in a metal mesh, immersing it in trichlorobenzene at 135°C, stirring it for 20 hours, then taking it out and measuring the completely dried weight.

[0184] In one embodiment of the present invention, the olefin polymer porous support may be a porous film.

[0185] The above olefin polymer may include an ethylene polymer; a propylene polymer; a butylene polymer; a pentene polymer; a hexene polymer; an octene polymer; a copolymer of two or more of ethylene, propylene, butene, pentene, 4-methylpentene, hexene, and octene; or a mixture thereof.

[0186] Non-limiting examples of the above ethylene polymer include low-density ethylene polymer (LDPE), linear low-density ethylene polymer (LLDPE), high-density ethylene polymer (HDPE), etc., and when the above ethylene polymer is a high-density ethylene polymer having a high crystallinity and a high melting point of the resin, it can have a desired level of heat resistance and can more easily increase the modulus.

[0187] A separation membrane according to one embodiment of the present invention can have excellent heat resistance without sacrificing other properties of the olefin polymer porous support by including a cross-linked structure-containing olefin polymer porous support.

[0188]

[0189] surfactant

[0190] In one embodiment of the present invention, if necessary, the separator may include a surfactant. A surfactant may be added to a composition comprising a polyethylene glycol containing a hydrophilic photoinitiator-derived functional group and an aqueous dispersion medium on the olefin polymer porous support, and as a result, the separator may include the surfactant.

[0191] The above surfactant can improve the dispersibility of the solid component in the composition. In addition, as described below, it can increase the membrane wettability of the composition including the aqueous dispersion medium, thereby preventing the dewetting phenomenon, i.e., the phenomenon in which the composition is not evenly coated on the surface of the olefin polymer porous support due to the difference in surface energy between the olefin polymer porous support and the aqueous dispersion medium, and forms droplets, thereby enabling the coating of fibrils to be performed well.

[0192] The surfactant may be applied without limitation as long as it does not deteriorate battery performance. Non-limiting examples thereof include fluorinated surfactants and sulfuric surfactants. The fluorinated surfactant lowers surface tension to improve coatability, and can be used as a general surfactant used in the art, and preferably, a fluorinated aliphatic polymeric ester. Specific examples thereof include FC4430 from 3M, 4300 from Novec, and Capstone from DuPont. In addition, examples of the sulfuric surfactant include WE3475 from BASF.

[0193] In one embodiment of the present invention, the membrane may further include an additive such as a dispersant and / or a thickener. The additive may include hydroxy ethyl cellulose (HEC), hydroxy propyl cellulose (HPC), ethylhydroxy ethyl cellulose (EHEC), methyl cellulose (MC), carboxymethyl cellulose (CMC), hydroxyalkyl methyl cellulose, cyanoethylene polyvinyl alcohol, or two or more thereof.

[0194]

[0195] Method for manufacturing a membrane

[0196] A method for manufacturing a separation membrane according to one embodiment of the present invention comprises the steps of applying and drying a composition comprising a polyethylene glycol containing a hydrophilic photoinitiator-derived functional group and an aqueous dispersion medium on at least one surface of an olefin polymer porous support; and

[0197] It includes a step of irradiating ultraviolet rays to the olefin polymer porous support to which the above composition has been applied and dried.

[0198]

[0199] Below, a method for manufacturing a separation membrane according to one embodiment of the present invention will be examined with a focus on the main parts.

[0200]

[0201] First, a composition containing a polyethylene glycol containing a hydrophilic photoinitiator-derived functional group and an aqueous dispersion medium is prepared, and then coated on at least one surface of an olefin polymer porous support. The composition may further include additives such as a surfactant and a dispersant.

[0202] The above-mentioned aqueous dispersion medium has the advantage of being environmentally friendly and not requiring excessive heat for drying. Depending on the type of binder polymer, the aqueous dispersion medium may function as a solvent that dissolves the binder polymer, or as a dispersion medium that disperses the binder polymer without dissolving it. For example, the aqueous dispersion medium may include water, methanol, ethanol, ethylene glycol, diethylene glycol, glycerol alcohol, or two or more thereof. In particular, the aqueous dispersion medium may include water.

[0203] Non-limiting examples of methods for applying the above composition to the above olefin polymer porous support include dip coating, die coating, roll coating, comma coating, microgravure coating, doctor blade coating, reverse roll coating, and direct roll coating.

[0204] By coating the above composition on the above olefin polymer porous support, the polyethylene glycol containing the hydrophilic photoinitiator-derived functional group can be introduced to the surface of the olefin polymer porous support, and the olefin polymer porous support can be crosslinked upon ultraviolet irradiation. Here, the "surface of the olefin polymer porous support" may include not only the surface of the outermost layer of the olefin polymer porous support, but also the surface of the pores existing inside the olefin polymer porous support.

[0205] The content of the polyethylene glycol containing a hydrophilic photoinitiator-derived functional group in the separator can be controlled by preparing an aqueous dispersion medium composition having a concentration of 0.1 wt% or more, 0.3 wt% or more, 0.5 wt% or more, 1 wt% or more, or 10 wt% or less, 7 wt% or less, 5 wt% or less, 3 wt% or less, or 1 wt% or less, and applying and drying the aqueous dispersion composition to the olefin polymer porous support. When the content of the polyethylene glycol containing a hydrophilic photoinitiator-derived functional group is controlled in this way, the breakdown temperature of the olefin polymer porous support itself can be increased by generating appropriate radicals, and the shrinkage rate of the separator can be reduced, and the impregnation property of the separator for the electrolyte can be greatly improved due to the polyethylene glycol portion having an affinity for the electrolyte.

[0206] According to one embodiment of the present invention, the polyethylene glycol containing a functional group derived from the hydrophilic photoinitiator can be obtained by a process of preparing a composition by stirring a hydrophilic photoinitiator, polyethylene glycol, a coupling agent, and a solvent under a nitrogen atmosphere, heat-treating the composition to react, cooling after completion of the reaction, precipitating the reaction product in a pre-prepared solvent, and removing the remaining solvent after completion of the precipitation.

[0207] Specifically, as the coupling agent, 5.5 mmol of tert-butyl hydroperoxide (TBHP), tetrabutylammonium iodide (TBAI), etc. can be used, and as the solvent, any solvent that can dissolve a hydrophilic photoinitiator or polyethylene glycol can be used, for example, ethyl acetate, dimethylformamide, dimethylsulfoxide, etc. can be used, and a mixed solvent of two or more solvents can also be used, and a mixed solvent of ethyl acetate and dimethylformamide can be used.

[0208] In addition, the composition of the hydrophilic photoinitiator, polyethylene glycol, reaction catalyst, and solvent may be stirred at room temperature for 1 to 10 minutes under a nitrogen atmosphere, followed by reaction at 70°C to 90°C for 1 to 10 hours, and after the reaction is completed, the composition may be cooled to room temperature and then precipitated in the solvent. In addition, after the precipitation is complete, the remaining solvent may be removed using an evaporator or a vacuum drying oven, etc., at 30°C to 50°C for 5 to 20 hours.

[0209] Next, the method includes a step of irradiating ultraviolet rays to the olefin polymer porous support coated with the composition.

[0210] As ultraviolet rays are irradiated, the polymer chains within the olefin polymer porous support are crosslinked, thereby obtaining an olefin polymer porous support containing a crosslinked structure.

[0211] Ultraviolet irradiation can be performed by using an ultraviolet crosslinking device, and appropriately controlling the ultraviolet irradiation time and irradiation light intensity considering the content ratio of the hydrophilic photoinitiator-derived group of the polyethylene glycol containing the hydrophilic photoinitiator-derived functional group. For example, the ultraviolet irradiation time and irradiation light intensity can be set under conditions such that the polymer chains in the olefin polymer porous support are sufficiently crosslinked to secure the desired heat resistance, while preventing the separation membrane from being damaged by the heat generated from the ultraviolet lamp. In addition, the ultraviolet lamp used in the ultraviolet crosslinking device can be appropriately selected from a high-pressure mercury lamp, a metal lamp, a gallium lamp, etc. depending on the hydrophilic photoinitiator used, and the emission wavelength and capacity of the ultraviolet lamp can be appropriately selected according to the process.

[0212] A method for manufacturing a membrane according to one embodiment of the present invention can photocrosslink polymer chains within an olefin polymer porous support with only a significantly smaller amount of ultraviolet irradiation light compared to the amount of light used in general photocrosslinking, thereby increasing the applicability of the membrane to mass production processes.

[0213] In one embodiment of the present invention, the irradiation amount of the ultraviolet light is 10 mJ / cm 2 Above, 50 mJ / cm 2 Above, 100 mJ / cm 2 Above, 500 mJ / cm 2 Above, 1,000 mJ / cm 2 Above, 2,000 mJ / cm 2 or more than 5,000 mJ / cm 2 Above 20,000 mJ / cm 2 , less than 15,000 mJ / cm 2 , 11,600 mJ / cm 2 The range may be as follows. When the amount of ultraviolet irradiation satisfies the above range, cross-linking of polymer chains within the olefin polymer porous support can sufficiently occur, thereby improving heat resistance.

[0214] The above UV irradiation amount can be measured using a portable light meter called Miltec's H type UV bulb and UV power puck. When measuring the amount of light using Miltec's H type UV bulb, three wavelength values ​​are output, UVA, UVB, and UVC, depending on the wavelength, and the UV irradiation of the present invention corresponds to UVA.

[0215] In the present invention, the method for measuring the amount of ultraviolet ray irradiation is to pass a UV power puck on a conveyor under a light source under the same conditions as a sample, and the ultraviolet ray irradiation amount displayed on the UV power puck at this time is referred to as the 'ultraviolet ray irradiation amount'.

[0216] The fracture temperature of the separator according to one embodiment of the present invention may be 150°C or higher. The fracture temperature of the separator may be increased compared to the fracture temperature of a separator comprising a non-crosslinked porous polyolefin substrate. For example, the fracture temperature of the separator may be 150°C or higher, 160°C or higher, 170°C or higher, 180°C or higher, 190°C or higher, or 200°C or higher.

[0217] According to one embodiment of the present invention, the breaking temperature of the membrane is measured by mounting a membrane sample of 5.0 mm in width x 40 mm in length on a TMA device (TA Instrument, Q400) using a jig, applying a tension of 0.01 N, exposing it to a temperature-increasing condition (starting at room temperature, increasing at a rate of 5°C / min), and as the temperature increases, the length of the sample changes, and the length increases rapidly before the sample breaks.

[0218]

[0219] lithium secondary battery

[0220] A lithium secondary battery according to one embodiment of the present invention includes a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and the separator may include the separator described above.

[0221] The above lithium secondary battery may have various shapes such as cylindrical, square, or pouch shape.

[0222] The above lithium secondary battery may include a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0223] There is no particular limitation on the electrode to be applied to the present invention, and the electrode active material can be manufactured in a form in which it is bound to an electrode current collector according to a conventional method known in the art.

[0224] Non-limiting examples of the positive electrode active material among the above electrode active materials include conventional positive electrode active materials that can be used in the positive electrode of a conventional lithium secondary battery, and in particular, lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or a lithium composite oxide combining these may be used.

[0225] Non-limiting examples of the negative electrode active material among the above electrode active materials include conventional negative electrode active materials that can be used in the negative electrode of a conventional lithium secondary battery, and in particular, lithium metal or lithium alloy, carbon, petroleum coke, activated carbon, graphite, or other carbons, etc., lithium adsorbent materials, etc., can be used.

[0226] Non-limiting examples of positive current collectors include foils made of aluminum, nickel, or combinations thereof, and non-limiting examples of negative current collectors include foils made of copper, gold, nickel, or copper alloys, or combinations thereof.

[0227] In one embodiment of the present invention, the lithium secondary battery comprises an electrolyte, which may include a lithium salt and an organic solvent for dissolving the lithium salt. In addition, an organic solid electrolyte or an inorganic solid electrolyte may be used as the electrolyte.

[0228] The above lithium salt can be used without limitation as long as it is one commonly used in electrolytes for secondary batteries, and for example, the anion of the above lithium salt is F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH- , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , (CF3CF2SO2)2N - , or a mixture of two or more of these may be used.

[0229] As the organic solvent included in the above electrolyte, any commonly used one can be used without limitation, and representative examples thereof include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, tetrahydrofuran, or mixtures thereof.

[0230] In addition, for the purpose of improving the charge / discharge characteristics, flame retardancy, etc. of the electrolyte, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. may be added. In some cases, in order to provide incombustibility, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoroethylene may be further included, and carbon dioxide gas may be further included to improve high-temperature storage characteristics.

[0231] As the organic solid electrolyte, for example, polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, agitation lysine, polyester sulfides, polyvinyl alcohol, polyvinylidene fluoride, polymers containing ionic dissociation groups, etc. can be used.

[0232] As the above inorganic solid electrolyte, for example, nitrides, halides, sulfates, etc. of Li, such as Li3N, LiI, Li5NI2, Li3N-LiI-LiOH, LiSiO4, LiSiO4-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, Li3PO4-Li2S-SiS2, etc. can be used.

[0233] The above electrolyte injection can be performed at an appropriate stage during the battery manufacturing process, depending on the manufacturing process and required physical properties of the final product. That is, it can be applied before battery assembly or at the final stage of battery assembly.

[0234]

[0235] Hereinafter, the present invention will be described in detail using examples. However, the examples according to the present invention may be modified in various ways, and the scope of the present invention should not be construed as being limited to the examples described below. The examples of the present invention are provided to more fully explain the present invention to those of average skill in the art.

[0236]

[0237] Example

[0238] Example 1

[0239] (1) Synthesis of polyethylene glycol (CMTX-PEG) containing a hydrophilic photoinitiator-derived functional group

[0240] 2-Carboxymethoxythioxanthone (CMTX) 1.25 mmol, poly(ethylene glycol) 10000 (weight average molecular weight 10,000) 25 mmol, tert-butyl hydroperoxide (TBHP) 5.5 mmol, tetrabutylammonium iodide (TBAI) 0.25 mmol, and a mixed solvent of ethyl acetate / DMF=4 / 1 (volume ratio) were added, stirred for 5 minutes at room temperature under a nitrogen atmosphere, and then reacted at 80°C for 5 hours. After the reaction was completed, the mixture was cooled to room temperature, and the reactant was precipitated in 50 mL of previously prepared ether solvent. The precipitation process was repeated three times. After the precipitation was completed, the remaining solvent was removed using a vacuum drying oven at 40°C for 12 hours, thereby producing a polyethylene glycol containing a hydrophilic photoinitiator-derived functional group (CMTX-PEG) of the following chemical formula 13, i.e., a polyethylene glycol containing a 2-carboxymethoxythioxanthone-derived functional group.

[0241] [Chemical Formula 13]

[0242]

[0243] In the polyethylene glycol containing a hydrophilic photoinitiator-derived functional group of the above chemical formula 13, the content of the hydrophilic photoinitiator-derived functional group, i.e., the content x of the repeating unit containing the hydrophilic photoinitiator-derived functional group, was 2.86 mol%, and the content y of the repeating unit not containing the hydrophilic photoinitiator-derived functional group was 97.14 mol%.

[0244] At this time, the mol% of x and y was confirmed by dissolving the sample in trichloromethane solvent (CDCl3) using an analytical instrument, Bruker Avance III HD 500 MHz NMR, measuring the NMR 1H spectrum at room temperature, and scanning it more than 16 times.

[0245]

[0246] (2) Manufacturing of membrane

[0247] A composition (1 wt% aqueous solution) was prepared by mixing the polyethylene glycol (CMTX-PEG) containing a functional group derived from the hydrophilic photoinitiator manufactured above with water, which is an aqueous dispersion medium.

[0248] The above composition was applied to both sides of a polyethylene porous film (thickness 11㎛, porosity approximately 42.5%, product name: SW811G, manufacturer: SENIOR) using a Meyer bar, and then dried using a Matis oven at a temperature of 60℃. An exposure device (Miltec HPI UV exposure device) and a lamp (Miltec Arc lamp) were prepared, and ultraviolet rays were irradiated to the porous film coated with the composition, at 580 mJ / cm 2 The total irradiation dose was 11,600 mJ / cm2 by irradiating 20 times with the same amount of light. 2 And, the separation membrane was manufactured by irradiating UV-A with UV irradiation intensity set to 50% of the UV light source.

[0249]

[0250] Comparative Example 1

[0251] Polyethylene porous film (thickness 11㎛, porosity approximately 42.5%, product name: SW811G, manufacturer: SENIOR) was used as a separator.

[0252]

[0253] Comparative Example 2

[0254] A separation membrane was manufactured in the same manner as in Example 1, except that instead of the composition of Example 1, a composition (1 wt% aqueous solution) prepared by mixing polyethylene glycol 10000 (Poly (ethylene glycol) 10000) (weight average molecular weight 10,000) with water as an aqueous dispersion medium was used.

[0255]

[0256] Comparative Example 3

[0257] A separation membrane was manufactured in the same manner as in Example 1, except that instead of the composition of Example 1, a composition (1 wt% aqueous solution) prepared by mixing polyethylene glycol 10000 (weight average molecular weight 10,000) and 2-carboxymethoxythioxanthone (CMTX) in a weight ratio of 4:1 in water as an aqueous dispersion medium was used.

[0258]

[0259] Weight average molecular weight measurement

[0260] The molecular weight (weight average molecular weight and number average molecular weight) of the above polyethylene glycol was measured through gel permeation chromatography (GPC). PL GPC220 from Agilent Technologies was used, and the measurement conditions were as follows.

[0261] -Column (maker, model no.): PL aquagel-OH Guard 8um 50 x 7.5 mm

[0262] -Eleunt: Water

[0263] -Temperature: 40℃

[0264] -Flow rate: 1.0 mL / min

[0265] -Injection volume, sample concentration: 30 ㎕, 1~10 mg / mL

[0266] -Standard: PEG / PEO

[0267] -Detector: RI

[0268]

[0269] Evaluation example

[0270] (1) Evaluation of contact angle between water and propylene carbonate

[0271] The membranes manufactured in Example 1 and Comparative Example 1 were 5 X 5 cm 2 The size of the membrane was prepared, and 5 μl of water and propylene carbonate (PC) were each filled in a microsyringe, and water and PC drops were each dropped onto the surface of the membrane. Using a Drop shape analyzer (DSA100S) from Kruss, the angle between the membrane and the water droplet was measured from the images of the water and PC drops dropped onto the surface of the membrane, and the contact angle was evaluated.

[0272] In addition, the membranes manufactured in Example 1 and Comparative Example 1 were 5 X 5 cm 2 After preparing the membrane in the size of , it was immersed in acetone for 15 hours, taken out, and 5 ㎕ of water and propylene carbonate (PC) were each filled in a microsyringe, and water and PC drops were each dropped onto the surface of the membrane that had been immersed in acetone for 15 hours. Afterwards, using a Drop shape analyzer (DSA100S) from Kruss, the angle between the membrane and the water droplet was measured using images of the water and PC drops dropped onto the surface of the membrane, and the contact angle was evaluated.

[0273] The results of the evaluation are shown in Table 1.

[0274]

[0275] Water contact angle (°)Propylene carbonate contact angle (°)UntreatedAfter immersion in acetone for 15 hoursUntreatedAfter immersion in acetone for 15 hoursComparative example 1112.2111.644.345.3Comparative example 2112.3112.645.045.1Example 199.099.039.235.7

[0276] Referring to Table 1, the contact angles of water and PC on the separator (uncoated polyethylene porous film) of Comparative Example 1 were 112 degrees and 44 degrees, respectively, and on the separator of Comparative Example 2 (polyethylene porous film coated with 1 wt% aqueous solution of polyethylene glycol) were 11,600 mJ / cm 2 The contact angles of water and PC on the surface were 112 degrees (°) and 45 degrees (°), respectively. Meanwhile, the membrane of Example 1 (polyethylene glycol containing a functional group derived from a hydrophilic photoinitiator (CMTX-PEG) with 1 wt% aqueous solution was coated on a polyethylene porous film, and then irradiated at 11,600 mJ / cm 2 The contact angles of water and PC above (as much as exposure) were 99 degrees and 39 degrees, respectively, and it was confirmed that the membrane was modified compared to the membranes of Comparative Examples 1 and 2.

[0277] In addition, when the separators of Example 1, Comparative Example 1, and Comparative Example 2 were immersed in acetone for 15 hours and then the contact angles were measured, compared to the separators of Comparative Example 1 and Comparative Example 2, the separator of Example 1 showed almost no change in the contact angles of both water and PC, and from this, it can be inferred that there is a chemical bond between the polyethylene porous film and the polyethylene glycol (CMTX-PEG) containing a functional group derived from a hydrophilic photoinitiator.

[0278]

[0279] (2) Evaluation of electrolyte impregnation characteristics

[0280] The membranes manufactured in Example 1 and Comparative Examples 1 to 3 were 5 X 5 cm 2, and placed on a focused microscope, 2 μl of propylene carbonate (PC) was filled in a 10 μl micro syringe, and a PC droplet was dropped on the surface of the membrane (the surface of the porous coating layer). After waiting for 5 minutes, the surface of the membrane where the PC droplet had spread was photographed, and the distance at which the propylene carbonate had spread outward from the initially dropped PC droplet was measured. Figure 1 shows a photograph of the surface of the membrane where the PC droplet had spread in the membrane manufactured in Example 1 and Comparative Examples 1 to 3. At this time, the distance at which the PC droplet had spread in the membrane manufactured in Example 1 and Comparative Examples 1 to 3 was measured and shown before UV irradiation (UV X) and after UV irradiation (20 times), respectively.

[0281] Referring to FIG. 1, in the separator of Example 1, propylene carbonate diffused outside the PC droplet initially added before UV irradiation (UV X) and after UV irradiation (20 times) by 4.18 and 3.74 to 3.813 mm, respectively, which is a significantly increased value compared to the separators of Comparative Examples 1 to 3, and from this, it was found that the separator of Example 1 exhibited excellent impregnation properties for the electrolyte. In particular, Example 1, which applied polyethylene glycol (CMTX-PEG) containing a functional group derived from a hydrophilic photoinitiator, exhibited better electrolyte impregnation properties than Comparative Example 3, which applied a mixture of a hydrophilic photoinitiator (CMTX) and polyethylene glycol (PEG).

[0282] This is because polyethylene glycol containing a hydrophilic photoinitiator-derived functional group has a structure in which a hydrophilic photoinitiator-derived functional group is introduced into polyethylene glycol, which is relatively nonpolar compared to an aqueous dispersion medium (e.g., water) and has a high affinity for olefin polymers. Therefore, the separator of Example 1, which was manufactured by coating a composition including a hydrophilic photoinitiator-derived functional group-derived polyethylene glycol and an aqueous dispersion medium on at least one surface of an olefin polymer porous support, can be seen to exhibit excellent electrolyte impregnation properties both before and after UV irradiation, as compared to a separator simply coated with a composition including a hydrophilic initiator as in Comparative Example 3, because the hydrophilic photoinitiator-derived functional group evenly penetrates into the pores of the olefin polymer porous support.

Claims

1. Olefin polymer porous support; and The above olefin polymer porous support includes a plurality of fibrils and pores formed by the plurality of fibrils crossing each other, and the polyolefin chains constituting the fibrils are directly cross-linked to each other, A separation membrane characterized in that the above olefin polymer porous support comprises polyethylene glycol containing a hydrophilic photoinitiator-derived functional group.

2. In paragraph 1, A separation membrane characterized in that the hydrophilic photoinitiator comprises an aromatic carbonyl compound having a hydrophilic group.

3. In paragraph 1, A separation membrane characterized in that the hydrophilic photoinitiator is represented by the following chemical formula 1: [Chemical Formula 1] In the above chemical formula 1, R1 is hydrogen, a straight-chain or branched alkyl group having 1 to 10 carbon atoms, or an aryl group having 6 to 20 carbon atoms, R2 is a single bond, a straight-chain or branched alkylene group having 1 to 10 carbon atoms, or an arylene group having 6 to 12 carbon atoms, R3 is a single bond, oxygen (O), or sulfur (S), and (L) is an aromatic carbonyl structure.

4. In paragraph 3, A separation membrane characterized in that the above (L) is derived from a compound represented by the following chemical formulas 2 and 3: [Chemical Formula 2] (In the above chemical formula 2, X is oxygen (O) or sulfur (S)) [Chemical Formula 3] 5. In paragraph 1, A separation membrane characterized in that the hydrophilic photoinitiator comprises a compound represented by the following chemical formulae 4 to 7: [Chemical Formula 4] [Chemical Formula 5] [Chemical Formula 6] [Chemical Formula 7] (In the above chemical formulas 4 and 5, X is each independently oxygen (O) or sulfur (S)) 6. In paragraph 1, A separation membrane characterized in that the polyethylene glycol containing the hydrophilic photoinitiator-derived functional group is represented by the following chemical formula 8: [Chemical Formula 8] (In the above chemical formula 8, x and y represent the mol% of each repeating unit, x is 95 to 99 mol%, y is 1 to 5 mol%, R2 is a single bond, a straight-chain or branched alkylene group having 1 to 10 carbon atoms, or an arylene group having 6 to 12 carbon atoms, R3 is a single bond, oxygen (O), or sulfur (S), and (L) is an aromatic carbonyl structure.

7. In paragraph 1, A separation membrane characterized in that the polyethylene glycol containing the hydrophilic photoinitiator-derived functional group is represented by the following chemical formulas 9 to 12: [Chemical Formula 9] (In the above chemical formula 9, x and y represent the mol% of each repeating unit, x is 95 to 99 mol%, y is 1 to 5 mol%, and X is each independently oxygen (O) or sulfur (S)) [Chemical Formula 10] (In the above chemical formula 10, x and y represent the mol% of each repeating unit, x is 95 to 99 mol%, y is 1 to 5 mol%, and X is each independently oxygen (O) or sulfur (S)) [Chemical Formula 11] (In the above chemical formula 11, x and y represent the mol% of each repeating unit, and x is 95 to 99 mol%) [Chemical Formula 12] (In the above chemical formula 12, x and y represent the mol% of each repeating unit, x is 95 to 99 mol%, and y is 1 to 5 mol%.) 8. In paragraph 1, A separation membrane characterized in that the polyethylene glycol containing the hydrophilic photoinitiator-derived functional group is represented by the following chemical formula 13: [Chemical Formula 13] (In the above chemical formula 13, x and y represent the mol% of each repeating unit, x is 1 to 5 mol%, and y is 95 to 99 mol%.) 9. In a lithium secondary battery including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, A lithium secondary battery wherein the separator is a separator according to any one of claims 1 to 8.

10. A step of applying and drying a composition including a polyethylene glycol containing a hydrophilic photoinitiator-derived functional group and an aqueous dispersion medium on at least one surface of an olefin polymer porous support; and A method for manufacturing a separation membrane according to claim 1, comprising the step of irradiating ultraviolet rays onto an olefin polymer porous support to which the composition has been applied and dried.

11. In paragraph 10, In the step of irradiating the above ultraviolet rays, the amount of ultraviolet irradiation light is 10 mJ / cm 2 More than 20,000 mJ / cm 2 A method for manufacturing a separation membrane, characterized by the following:

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