KR20210072531A - Crosslinked polyolefin film and separator for lithium secondary batteries comprising the same - Google Patents

Abstract

According to the present invention, provided is a method for manufacturing a cross-linked polyolefin film in which two kinds of predetermined cross-linking agents are used together to manufacture a cross-linked polyolefin film so that the melt-down temperature of the cross-linked polyolefin film is increased and a shutdown temperature is lowered. In addition, provided are a cross-linked polyolefin film with improved safety manufactured by the method and a separator for a lithium secondary battery including the same.

Description

Cross-linked polyolefin film and separator for lithium secondary battery comprising same {CROSSLINKED POLYOLEFIN FILM AND SEPARATOR FOR LITHIUM SECONDARY BATTERIES COMPRISING THE SAME}

The present invention relates to a cross-linked polyolefin film and a separator for a lithium secondary battery comprising the same.

Recently, interest in energy storage technology is increasing. Efforts for research and development of electrochemical devices are becoming more and more concrete as the field of application is expanded to the energy of mobile phones, camcorders and notebook PCs, and even electric vehicles. Electrochemical devices are receiving the most attention in this aspect, and among them, the development of rechargeable batteries that are capable of charging and discharging is the focus of interest. Recently, in the development of such batteries, new electrodes to improve capacity density and specific energy and battery design research and development.

Among the currently applied secondary batteries, lithium secondary batteries developed in the early 1990s have a higher operating voltage and significantly higher energy density than conventional batteries such as Ni-MH, Ni-Cd, and lead sulfate batteries using aqueous electrolyte solutions. is gaining popularity as

This lithium secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator, among which the separator has high ionic conductivity to increase lithium ion permeability based on insulation and high porosity to separate and electrically insulate the positive and negative electrodes. is required

Such a separator should also have a wide interval between a shutdown temperature and a melt down temperature, so that the safety of a lithium secondary battery including the separator can be secured. In order to widen the gap between the two, it is necessary to control the shutdown temperature in a decreasing direction and the melt-down temperature in an increasing direction.

One problem to be solved by the present invention is to provide a crosslinked polyolefin film having improved heat resistance due to a high meltdown temperature and a low shutdown temperature, which is preferable for use in a separator for a lithium secondary battery.

Another problem to be solved by the present invention is to provide a separator for a lithium secondary battery comprising the above-described crosslinked polyolefin film.

According to one aspect of the present invention, in a first aspect of the present invention,

(S1) reacting and extruding the silane-grafted polyolefin composition by adding and mixing a polyolefin, a diluent, a first cross-linking agent represented by the following Chemical Formula 1, a second cross-linking agent represented by the following Chemical Formula 2, an initiator, and a cross-linking catalyst in an extruder;

(S2) forming and stretching the reaction-extruded silane-grafted polyolefin composition in a sheet form;

(S3) preparing a silane-grafted polyolefin porous membrane by extracting a diluent from the stretched sheet;

(S4) heat-setting the silane-grafted polyolefin porous membrane; and

(S5) crosslinking the heat-set silane-grafted polyolefin porous membrane in the presence of moisture; There is provided a method for producing a crosslinked polyolefin film comprising:

[Formula 1]

YR-Si-(X) ₃

above,

Y is a vinyl group,

R represents a bond or a (C1-C30) alkylene group,

X is a group represented by -O-A-B, wherein O is an oxygen atom, A is a (C1-C30) alkylene group, and B is a (C1-C4) alkoxy group.

[Formula 2]

YR-Si-(X) ₃

above,

Y is a vinyl group,

R represents a bond or a (C1-C30) alkylene group,

X is a (C1-C30) alkyl group.

According to a second aspect of the present invention, in the first aspect, there is provided a manufacturing method, wherein the first crosslinking agent is a compound represented by the following formula:

According to a third aspect of the present invention, in the first aspect or the second aspect, there is provided a manufacturing method characterized in that the second crosslinking agent is tributyl (vinyl) silane.

According to a fourth aspect of the present invention, in any one of the first to third aspects, the first crosslinking agent and the second crosslinking agent are used in a composition ratio of 3:1 to 1:3 based on their weight. There is provided a manufacturing method characterized in that it becomes.

According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the total content of the first crosslinking agent and the second crosslinking agent is 0.5 to 4 parts by weight based on 100 parts by weight of the total of the polyolefin and the diluent. There is provided a manufacturing method, characterized in that the denial.

According to a sixth aspect of the present invention, in any one of the first to fifth aspects, there is provided a manufacturing method, wherein the polyolefin is polyethylene.

According to another aspect of the present invention, according to the seventh aspect, a crosslinked polyolefin produced by the method described in any one of the first to sixth aspects and having a shutdown temperature in the range of 128 to 145 ° C. A film is provided.

According to an eighth aspect of the present invention, there is provided a crosslinked polyolefin film according to the seventh aspect, wherein the crosslinked polyolefin film has a meltdown temperature in the range of 150 to 230°C.

According to another aspect of the present invention, in the ninth aspect of the present invention, there is provided a separator for a lithium secondary battery comprising the crosslinked polyolefin film according to the seventh or eighth aspect.

According to a tenth aspect of the present invention, a mixture of a plurality of inorganic particles and a binder is included on at least one surface of the crosslinked polyolefin film according to any one of the seventh to ninth aspects, wherein the inorganic particles are in contact with each other. There is provided a separator for a lithium secondary battery comprising a porous coating layer that forms an interstitial volume in the state.

According to another aspect of the present invention, in the eleventh aspect of the present invention, a lithium secondary battery comprising a negative electrode, a positive electrode, and a separator interposed between the negative electrode and the positive electrode, wherein the separator is the ninth or tenth aspect There is provided a lithium secondary battery, characterized in that the separator for a lithium secondary battery according to the.

The crosslinked polyolefin film according to the present invention has a high meltdown temperature and a low shutdown temperature, so that heat resistance is improved.

In addition, the separator for a lithium secondary battery prepared including the crosslinked polyolefin film according to the present invention has a high meltdown temperature and a low shutdown temperature, so that it has improved safety when an external impact is applied.

Hereinafter, the present invention will be described in detail. The terms or words used in the present specification and claims should not be construed as being limited to their ordinary or dictionary meanings, and the inventor may properly define the concept of the term in order to best describe his invention. It should be interpreted as meaning and concept consistent with the technical idea of the present invention based on the principle that there is.

Throughout this specification, when a part "includes" a certain component, it means that other components may be further included, rather than excluding other components, unless otherwise stated.

According to one aspect of the present invention,

(S1) reacting and extruding the silane-grafted polyolefin composition by adding and mixing a polyolefin, a diluent, a first cross-linking agent represented by the following Chemical Formula 1, a second cross-linking agent represented by the following Chemical Formula 2, an initiator, and a cross-linking catalyst in an extruder;

(S2) forming and stretching the reaction-extruded silane-grafted polyolefin composition in a sheet form;

(S3) preparing a silane-grafted polyolefin porous membrane by extracting a diluent from the stretched sheet;

(S4) heat-setting the silane-grafted polyolefin porous membrane; and

(S5) crosslinking the heat-set silane-grafted polyolefin porous membrane in the presence of moisture; There is provided a method for producing a crosslinked polyolefin film comprising:

[Formula 1]

YR-Si-(X) ₃

above,

Y is a vinyl group,

R represents a bond or a (C1-C30) alkylene group,

X is a group represented by -O-A-B, wherein O is an oxygen atom, A is a (C1-C30) alkylene group, and B is a (C1-C4) alkoxy group.

[Formula 2]

YR-Si-(X) ₃

above,

Y is a vinyl group,

R represents a bond or a (C1-C30) alkylene group,

X is a (C1-C30) alkyl group.

In a specific embodiment of the present invention, R in Formula 1 is a bond or (C1-C30) alkylene group, or (C1-C10) alkylene group, or (C1-C7) alkylene group, or (C1-C4) It may be an alkylene group, or a (C1-C2) alkylene group.

In a specific embodiment of the present invention, X in Formula 1 is a group represented by -OAB, wherein O is an oxygen atom, A is a (C1-C30) alkylene group, or a (C1-C10) alkylene group, or (C1-C7) alkylene group, or (C1-C4) alkylene group, or (C1-C2) alkylene group, B is (C1-C4) alkoxy group, or (C1-C3) alkoxy group, or (C1 -C2) may be an alkoxy group.

In a specific embodiment of the present invention, the first crosslinking agent represented by Formula 1 may be a vinyltris(2-methoxy-ethoxy)silane compound represented by the following:

In a specific embodiment of the present invention, R in Formula 2 is a bond or (C1-C30) alkylene group, or (C1-C10) alkylene group, or (C1-C7) alkylene group, or (C1-C4) It may be an alkylene group, or a (C1-C2) alkylene group.

In a specific embodiment of the present invention, X in Formula 2 may be a (C1-C30) alkyl group, a (C1-C10) alkyl group, or a (C1-C5) alkyl group, or a (C1-C4) alkyl group.

In one specific embodiment of the present invention, the second crosslinking agent may be tributyl(vinyl)silane.

In a specific embodiment of the present invention, the first cross-linking agent and the second cross-linking agent are used in a composition ratio of 3:1 to 1:3 or 2:1 to 1:1 based on their weight to prepare a crosslinked polyolefin film. can be used When the composition ratio of the first cross-linking agent and the second cross-linking agent satisfies the above numerical range, the shutdown temperature may be reduced.

In a specific embodiment of the present invention, the total content of the first crosslinking agent and the second crosslinking agent is 0.5 to 4 parts by weight or 1 to 3 parts by weight or 1.5 to 2 parts by weight based on 100 parts by weight of the polyolefin resin and the diluent combined. It can be in the negative range. When the total content of the first cross-linking agent and the second cross-linking agent satisfies the above-mentioned range, it is possible to have an effect of reducing a shutdown temperature and a synergistic effect of a melt-down temperature due to cross-linking.

In a specific embodiment of the present invention, the polyolefin is polyethylene; polypropylene; polybutylene; polypentene; polyhexene; polyoctene; copolymers of two or more of ethylene, propylene, butene, pentene, 4-methylpentene, hexene, heptene and octene; or a mixture thereof.

In particular, the polyethylene includes low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), and the like, and among them, high-density polyethylene having high crystallinity and a high melting point of the resin is most preferable.

In a specific embodiment of the present invention, the weight average molecular weight of the polyethylene may be in the range of 200,000 to 1,000,000 or 220,000 to 700,000 or 250,000 to 500,000. In a specific embodiment of the present invention, a high molecular weight polyolefin having a weight average molecular weight of 200,000 to 1,000,000 is used as a starting material for producing a crosslinked polyolefin film, thereby ensuring uniformity and film forming processability of the crosslinked polyolefin film, and finally strength and heat resistance This excellent separation membrane can be obtained.

In a specific embodiment of the present invention, the initiator is a compound involved in the initiation of the crosslinking reaction, benzoperoxide (BPO, benzoperoxide), dilauroyl peroxide (dilauroyl peroxide), 1,1-bis (t) -Butylperoxy)-3,3,5-trimethylcyclohexane (1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane), dicumyl peroxide (DCP, dicumyl peroxide), 2, 5-dimethyl-2,5-di-(t-butylperoxy)hexane (2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, (DHBP)), di-tert-butyl peroxide (Di-tert-butyl peroxide (DTBP)), 2,5 Dimethyl-2,5-di(t-butylperoxy)hexaine (2,5-Dimethyl-2,5-di(tert-butylperoxy)-3- hexyne) or two or more of these.

In a specific embodiment of the present invention, the total content of the initiator may be in the range of 0.0001 to 5 parts by weight, or 0.001 to 3 parts by weight, or 0.01 to 2 parts by weight, based on 100 parts by weight of the total content of the polyolefin and the diluent. . When the content of the initiator satisfies the above numerical range, the problem of crosslinking between polyethylenes in the extruder can be prevented as the silane graft rate is lowered due to the lower content of the initiator, or the polyethylene is crosslinked due to the higher content of the initiator.

In a specific embodiment of the present invention, the diluent may be liquid or solid paraffin oil, mineral oil, wax, soybean oil, etc. which are generally used for manufacturing a wet separator.

In a specific embodiment of the present invention, as the diluent, a diluent capable of liquid-liquid phase separation from polyolefin may be used, for example, dibutyl phthalate, dihexyl phthalate, phthalic acid esters such as 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; Palmitic acid mono-, di-, or triesters, stearic acid mono-, di-, or triesters. Saturated and unsaturated fatty acids having 4 to 26 carbon atoms in fatty acid groups such as oleic acid mono-, di-, or triesters, linoleic acid mono-, di-, or triesters, or one in which the double bond of the unsaturated fatty acid is substituted with an epoxy; The two or more fatty acids may be ester-bonded fatty acid esters with an alcohol having 1 to 8 hydroxyl groups and 1 to 10 carbon atoms.

The diluent may be used alone or as a mixture including at least two or more of the above-mentioned components.

In a specific embodiment of the present invention, the crosslinking catalyst is added to promote the silane crosslinking reaction.

In a specific embodiment of the present invention, as the crosslinking catalyst, carboxylate salts of metals such as tin, zinc, iron, lead, and cobalt, organic bases, inorganic acids and organic acids may be used. Non-limiting examples of the crosslinking catalyst include dibutyl tin dilaurate, dibutyl tin diacetate, stannous acetate, stannous caprylate, zinc naphthenate, zinc caprylate, and cobalt naphthenate, and the organic base includes ethylamine, dibutylamine, hexylamine, pyridine, and the like, and the inorganic acid includes sulfuric acid and hydrochloric acid, and the organic acid includes toluene, sulfonic acid, acetic acid, and stearic acid. , maleic acid, and the like. In addition, the crosslinking catalyst may be used alone or a mixture of two or more of them.

In a specific embodiment of the present invention, the content of the crosslinking catalyst is 1 x 10 ^-6 to 1 parts by weight, 1 x 10 ^-5 to 1 parts by weight, or 2 x 10 ^-5 to 1 parts by weight based on 100 parts by weight of the polyolefin. x 10 ^-1 parts by weight. When the content of the crosslinking catalyst satisfies the above numerical range, a desired level of silane crosslinking may occur, and undesired side reactions in the lithium secondary battery do not occur. There is no cost problem such as wasted cross-linking catalyst.

In a specific embodiment of the present invention, the silane-grafted polyolefin composition may further contain general additives for improving specific functions, such as antioxidants, UV stabilizers, antistatic agents, nucleating agents, etc., if necessary. .

In a specific embodiment of the present invention, the reaction extrusion step may use a single screw extruder or a twin screw compressor.

Next, the reaction-extruded silane-grafted polyolefin composition is molded and stretched in a sheet form (S2).

For example, the reaction-extruded silane-grafted polyolefin composition is extruded using an extruder equipped with a T-die, etc., and then cooled by using a general casting or calendaring method using water cooling or air cooling. can form.

In a specific embodiment of the present invention, it is possible to provide a crosslinked polyolefin film having improved tensile strength and puncture strength by performing the stretching step as described above.

In a specific embodiment of the present invention, the stretching may be performed by a roll method or a tender method sequentially or simultaneously stretching. The draw ratio may be in the range of 3 times or more or 4 times to 10 times in the longitudinal and transverse directions, respectively, and the total draw ratio may be in the range of 14 to 100 times. When the draw ratio satisfies the above numerical range, it is possible to prevent the problem that the orientation in one direction is not sufficient and the balance of physical properties between the longitudinal and transverse directions is broken at the same time, thereby reducing the tensile strength and the puncture strength, and the total draw ratio is within the numerical range As it satisfies, it is possible to prevent the problem that non-stretching or pore formation does not occur.

In a specific embodiment of the present invention, the stretching temperature may vary depending on the melting point of the polyolefin used, the concentration and type of the diluent.

In a specific embodiment of the present invention, for example, when the polyolefin used is polyethylene, the diluent is liquid paraffin, and the kinematic viscosity of the diluent is 40 to 100 cSt at 40° C., the stretching temperature is 70 to It may be 160 ℃, 90 to 140 ℃, or 100 to 130 ℃, in the case of transverse stretching may be 90 to 180 ℃, 110 to 160 ℃ or 120 to 150 ℃, in the case of proceeding in both directions at the same time stretching 90 to 180 ℃, 110 to 160 ℃ or 120 to 150 ℃ range. When the stretching temperature satisfies the numerical range, as the stretching temperature has a low temperature range, it is possible to prevent the problem of fracture or non-stretching due to lack of softness, and occurs as the stretching temperature is high Partial overstretching or differences in physical properties can be prevented.

Thereafter, a diluent is extracted from the molded and stretched sheet to prepare a silane-grafted polyolefin porous membrane (S3).

In a specific embodiment of the present invention, a diluent may be extracted from the silane-grafted polyolefin porous membrane using an organic solvent, and the silane-grafted polyolefin porous membrane may be dried.

In a specific embodiment of the present invention, the organic solvent is not particularly limited as long as it can extract the diluent, but methyl ethyl ketone, methylene chloride or hexane with high extraction efficiency and fast drying are suitable.

In a specific embodiment of the present invention, as the extraction method, all general solvent extraction methods such as an immersion method, a solvent spray method, and an ultrasonic method may be used individually or in combination. The content of residual diluent after the extraction treatment should preferably be 1% by weight or less. When the content of the residual diluent exceeds 1 wt %, physical properties deteriorate and the permeability of the porous membrane decreases. The content of the residual diluent may be affected by the extraction temperature and extraction time. In order to increase the solubility of the diluent and the organic solvent, it is preferable that the extraction temperature is high, but in consideration of the safety problem due to the boiling of the organic solvent, it is preferable to be below 40 °C. . If the extraction temperature is below the freezing point of the diluent, the extraction efficiency is greatly reduced, so it must be higher than the freezing point of the diluent.

In addition, the extraction time varies depending on the thickness of the porous membrane to be prepared, but in the case of preparing a porous membrane having a thickness of 5 to 15 μm, an extraction time of 1 to 3 minutes is appropriate.

Thereafter, the silane-grafted polyolefin porous membrane is heat-set (S4).

The heat setting is to fix the porous membrane and apply heat to forcibly hold the porous membrane to be contracted to remove residual stress.

In a specific embodiment of the present invention, when the polyolefin is polyethylene, the heat setting temperature may be 100 to 140 ℃, 105 to 135 ℃, or 110 to 130 ℃. When the polyolefin is polyethylene and the heat setting temperature satisfies the above numerical range, the polyolefin molecules are rearranged to remove the residual stress of the porous membrane, and the problem of clogging the pores of the porous membrane due to partial melting can be reduced. have. The higher the heat setting temperature, the better the thermal contraction rate of the prepared porous membrane, and the lower the heat setting temperature, the lower the resistance of the porous membrane.

In a specific embodiment of the present invention, the time of the heat setting temperature may be in the range of 10 seconds to 120 seconds, 20 seconds to 90 seconds, or 30 seconds to 60 seconds. In the case of heat setting at this time, it is possible to remove the residual stress of the porous membrane due to rearrangement of the polyolefin molecules, and it is possible to reduce the problem of clogging the pores of the porous membrane due to partial melting.

Next, the heat-set silane-grafted polyolefin porous membrane is cross-linked in the presence of moisture (S5).

In a specific embodiment of the present invention, the crosslinking may be performed at 60 to 100 °C, 65 to 95 °C, or 70 to 90 °C.

In a specific embodiment of the present invention, the crosslinking may be performed at a humidity of 60 to 95% for 6 to 50 hours.

Another aspect of the present invention provides a crosslinked polyolefin film according to the following embodiments.

In the present invention, the 'shutdown temperature' refers to the temperature at which the micropores in the crosslinked polyolefin film are closed due to a sudden large current flowing due to an internal or external short circuit.

In one specific embodiment of the present invention, the crosslinked polyolefin film is characterized in that it has a shutdown temperature in the range of 128 to 145 ℃.

In one specific embodiment of the present invention, the shutdown temperature may be in the range of 128 to 145 °C, or 128 to 140 °C, or 130 to 138 °C, alternatively in the range of 132 to 138 °C, or in the range of 135 to 138 °C. When the shutdown temperature is within the above numerical range, safety may be maintained even under a high-temperature environment such as thermal runaway due to a short circuit.

In the present invention, the shutdown temperature is measured according to the following method.

First, while measuring the air permeability of the crosslinked polyolefin film, the crosslinked polyolefin film is exposed to elevated temperature conditions (starting at 30°C and 5°C/min). At this time, the temperature at which the air permeability (Gurley value) of the crosslinked polyolefin film exceeds 100,000 seconds/100cc for the first time is defined as the shutdown temperature. The air permeability of the crosslinked polyolefin film is measured using an air permeability meter (Asahi Seiko, EGO-IT) according to JIS P8117.

In the present invention, the 'melt-down temperature' refers to the temperature at which the separator melts as the temperature of the lithium secondary battery rises and the polyolefin crystal constituting the separator melts and the tensile strength of the separator sharply decreases.

The melt-down temperature is measured by thermomechanical analysis (TMA) after taking samples in the production direction (Machine direction, MD) and the transverse direction (TD) of the cross-linked polyolefin film, respectively. . Specifically, a 10 mm-long sample is put into a TMA equipment (TA Instrument, Q400) and exposed to elevated temperature conditions (starting at 30° C. and 5° C./min) while applying a tension of 19.6 mN. As the temperature rises, the length of the sample is changed, and the temperature is measured at which the sample is cut by rapidly increasing the length. Measure the MD and TD respectively and define the higher temperature as the meltdown temperature of the sample in question.

In a specific embodiment of the present invention, the melt-down temperature of the crosslinked polyolefin film may be 150 to 230 °C, or 155 to 210 °C, or 179 to 210 °C.

In a specific embodiment of the present invention, the thickness of the crosslinked polyolefin film may be appropriately selected within the range of 1 to 50 μm, or 3 to 20 μm, or 5 to 17 μm. Although the thickness of the crosslinked polyolefin film is not particularly limited to the above-mentioned range, if the thickness is too thin than the above-mentioned lower limit, mechanical properties may be deteriorated, and the separator may be easily damaged during battery use. Meanwhile, the pore size and pore size present in the crosslinked polyolefin film are also not particularly limited, but may be in the range of 0.01 to 50 μm and 10 to 95%, respectively.

According to another aspect of the present invention, there is provided a lithium secondary battery comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein the separator includes a separator made of the aforementioned cross-linked polyolefin film; a separator formed by laminating the aforementioned crosslinked polyolefin film with a porous polymer substrate; Alternatively, it may be a separator ('composite separator') using the cross-linked polyolefin film as a substrate and including a porous coating layer formed by mixing inorganic particles and a binder on at least one surface of the substrate.

According to a specific embodiment of the present invention, in the composite separator, the porous coating layer is formed on one or both sides of the cross-linked polyolefin film in a layered manner. The porous coating layer includes a mixture of a plurality of inorganic particles and a binder, and the inorganic particles are integrated through a binder to form a layered layer. The binder of the porous coating layer may attach the inorganic particles to each other (that is, the binder connects and fix the inorganic particles) so that the inorganic particles can maintain a binding state to each other, and the inorganic particles and the cross-linked polyolefin film are bound by the binder state can be maintained. The inorganic particles of the porous coating layer may form an interstitial volume in a state in which they are substantially in contact with each other, and in this case, the interstitial volume is in a closed packed or densely packed structure by the inorganic particles. It means a space defined by the inorganic particles that are substantially in contact. The interstitial volume between the inorganic particles may become an empty space to form pores of the porous coating layer.

In the composite separator, since the porous coating layer including inorganic particles is formed on at least one surface of the crosslinked polyolefin film as described above, the heat resistance and mechanical properties of the separator for lithium secondary batteries are further improved. That is, since the inorganic particles generally have properties that do not change their physical properties even at a high temperature of 200° C. or higher, the separator for lithium secondary batteries has excellent heat resistance due to the porous coating layer.

In a specific embodiment of the present invention, the porous coating layer may have a thickness in the range of 1 μm to 50 μm, or 2 μm to 30 μm, or 2 μm to 20 μm. When the porous coating layer has a thickness in the above-mentioned range, it may have the effect of thinning the separator, low resistance, and high heat resistance.

In a specific embodiment of the present invention, the composition ratio of the inorganic particles and the binder constituting the porous coating layer may be determined in consideration of the thickness, pore size, and porosity of the finally manufactured porous coating layer. As a non-limiting example, the composition ratio of the inorganic particles to the binder may be 50 to 99.9 wt% or 60 to 99.5 wt% of the inorganic particles, and 0.1 to 50 wt% or 0.5 to 40 wt% of the binder. When the content of the inorganic particles is less than 50% by weight, the content of the binder becomes excessively large, thereby reducing the pore size and porosity due to a decrease in the void space formed between the inorganic particles, which may cause degradation of the final battery performance. On the other hand, when the content of the inorganic particles exceeds 99.9% by weight, the mechanical properties of the final porous coating layer are deteriorated due to weakening of the adhesion between the inorganic particles because the content of the binder is too small.

In a specific embodiment of the present invention, the inorganic particle size of the porous coating layer is not limited, but in order to form a coating layer having a uniform thickness and an appropriate porosity, 0.001 to 10 μm or 0.01 to 10 μm or 0.05 to 5 μm or a D50 diameter in the range of 0.1 to 2 μm. When the inorganic particle size satisfies the diameter in this range, dispersibility is maintained, so it is easy to control the physical properties of the separator for lithium secondary batteries, and the phenomenon of increasing the thickness of the porous coating layer can be avoided, so that mechanical properties can be improved. Also, due to the excessively large pore size, the probability of an internal short circuit during battery charging and discharging is low.

In the present specification, "particle diameter D50" means a particle diameter at 50% of the cumulative distribution of the number of particles according to the particle diameter. That is, D50 means a particle diameter at 50% of the cumulative distribution of the number of particles according to the particle diameter, and the particle diameter may be measured using a laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (for example, Microtrac S3500) to measure the diffraction pattern difference according to the particle size when the particles pass through the laser beam to measure the particle size distribution to calculate D50 can be measured by calculating the particle diameter at the point used as 50% of the particle number cumulative distribution according to the particle diameter in a measuring apparatus.

The inorganic particles are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles are not particularly limited as long as oxidation and/or reduction reactions do not occur in the operating voltage range of the applied electrochemical device (eg, ^{0-5V based on Li/Li+).} In particular, when inorganic particles having an ion transport ability are used, the performance can be improved by increasing the ion conductivity in the electrochemical device. In addition, when inorganic particles having a high dielectric constant are used as the inorganic particles, the ionic conductivity of the electrolyte can be improved by contributing to an increase in the degree of dissociation of an electrolyte salt, such as a lithium salt, in a liquid electrolyte.

For the reasons described above, the inorganic particles may include high dielectric constant inorganic particles having a dielectric constant of 5 or more or 10 or more, inorganic particles having lithium ion transport ability, or a mixture thereof. Non-limiting examples of inorganic particles having a dielectric constant of 5 or more include BaTiO ₃ , Pb(Zr,Ti)O ₃ (PZT), Pb _{1 - x} La _x Zr _{1 - y} Ti _y O ₃ (PLZT, where 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 , NiO, CaO, ZnO, ZrO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , γ-AlOOH, SiC, TiO ₂ and the like may be used alone or in combination of two or more. In addition, when the above-described high dielectric constant inorganic particles and the inorganic particles having lithium ion transport ability are mixed, their synergistic effect may be doubled.

Non-limiting examples of the inorganic particles having the lithium ion transport ability include lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0 < x < 2, 0 < y < 3) , lithium aluminum titanium phosphate (Li _x Al _y Ti _z (PO ₄ ) ₃ , 0 < x < 2, 0 < y < 1, 0 < z < 3), 14Li ₂ O-9Al ₂ O ₃ -38TiO ₂ -39P (LiAlTiP) _x O _{y series glass such as 2} O ₅ (0 < x < 4, 0 < y < 13), lithium lanthanide titanate (Li _x La _y TiO ₃ , 0 < x < 2, 0 < y < 3) ), Li _{3 . 25 Ge 0 .25 P 0. 75 S} 4 Lithium germanium thiophosphate such as Li _x Ge _y P _z S _w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride such as LiN _{SiS 2} based glass (Li _x Si _y S _z , 0 < x < 3, 0), such as Li _x N _y , 0 < x < 4, 0 < y < 2), Li ₃ PO ₄ -Li ₂ S-SiS _{2 , etc. P 2} S ₅ series glass, such as < y < 2, 0 < z < 4), LiILi ₂ SP ₂ S _{5, etc. (Li x} P _y S _z , 0 < x < 3, 0 < y < 3, 0 < z < 7) or a mixture thereof.

As the binder, any polymer having a solubility index difference of 1.5 to 8.3 MPa ^0.5 between the solvent and the binder may be applied without limitation. Specifically, polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene (polyvinylidene fluorideco-hexafluoropropylene, PVdF-HFP), polyvinylidene fluoride-trichlorethylene (polyvinylidene fluoride-co-trichlorethylene) ), polyvinylidene fluoride-co-trifluoroethylene, polyvinylidene fluoride-tetrafluoroethylene, polymethylmethacrylate, or two of these It may be a mixture of the above, but is not limited thereto.

The pore size and porosity of the porous coating layer mainly depend on the size of the inorganic particles. For example, when inorganic particles having a particle diameter of 1 μm or less are used, the formed pores are also 1 μm or less. Such a pore structure is filled with an electrolyte to be injected later, and the electrolyte filled in this way plays a role of ion transfer. Therefore, the size and porosity of the pores are important factors influencing the ionic conductivity of the porous coating layer.

According to a specific embodiment of the present invention, the pore size of the porous coating layer is in the range of 0.001 to 10 μm or 0.001 to 1 μm. Further, the porosity of the porous coating layer is in the range of 5 to 95%, or in the range of 10 to 95%, or in the range of 20 to 90%, or in the range of 30 to 80%. The porosity corresponds to a value obtained by subtracting a volume converted to the weight and density of each component of the coating layer from the volume calculated in the thickness, width, and length of the porous coating layer.

When the pore size and / or porosity in the above range is formed in the porous coating layer, the separator for a lithium secondary battery according to an embodiment of the present invention can prevent short circuit in an abnormal situation while providing appropriate resistance properties and air permeability at the same time can be provided

In a specific embodiment of the present invention, the porous coating layer is formed by mixing the above-mentioned inorganic particles and a binder in a solvent to prepare a composition for forming a porous coating layer, applying it on a crosslinked polyolefin film, and drying. The solvent is an organic solvent, and is not particularly limited as long as it can uniformly disperse the inorganic particles and the binder. Non-limiting examples of the organic solvent include cyclic aliphatic hydrocarbons such as cyclopentane and cyclohexane; aromatic hydrocarbons such as toluene, xylene, and ethylbenzene; acetone, ethyl methyl ketone, diisopropyl ketone, cyclohexanone, Ketones such as methylcyclohexane and ethylcyclohexane; Chlorine-based aliphatic hydrocarbons such as methylene chloride, chloroform, and carbon tetrachloride; Esters such as ethyl acetate, butyl acetate, γ-butyrolactone, ε-caprolactone; acetonitrile, propionitrile, etc. of acylnitriles; ethers such as tetrahydrofuran and ethylene glycol diethyl ether: alcohols such as methanol, ethanol, isopropanol, ethylene glycol and ethylene glycol monomethyl ether; N-methylpyrrolidone, N,N- and amides such as dimethylformamide, and acetone may be included in the organic solvent in consideration of advantages in the drying process. These solvents may be used independently and may use the mixed solvent which mixed these 2 or more types. Among these, a solvent having a low boiling point and high volatility is preferable because it can be removed in a short time and at a low temperature. Specifically, acetone, toluene, cyclohexanone, cyclopentane, tetrahydrofuran, cyclohexane, xylene, or N-methylpyrrolidone, or a mixed solvent thereof is preferable.

The content of the inorganic particles and the binder in the composition for forming the porous coating layer is preferably the same as described above for the porous coating layer.

The method for forming the porous coating layer by applying the composition for forming the porous coating layer to at least one surface of the crosslinked polyolefin film is not limited, and there is no limitation on a dip coating method, a die coating method, a roll coating method, a comma ( comma) coating method, doctor blade coating method, reverse roll coating method, direct roll coating method, micro gravure coating method, etc. are mentioned.

The coating process for forming the porous coating layer is preferably performed at a humidity within a certain range. After coating the composition for forming a porous coating layer on one or both sides of the cross-linked polyolefin film, the binder dissolved in the coating layer (composition) through a drying process is phase-separated by a phenomenon known in the art It has a phase transition characteristic. The phase separation may be performed by humidified phase separation or immersion phase separation.

According to one embodiment of the present invention, the separator for a lithium secondary battery may be dried after phase separation. Drying may be carried out using a method known in the art, and may be performed batchwise or continuously using an oven or a heated chamber in a temperature range taking into account the vapor pressure of the solvent used. The drying is to almost remove the solvent present in the composition, which is preferably as fast as possible in consideration of productivity and the like, and may be carried out for, for example, 1 minute or less or 30 seconds or less.

The formation of the porous coating layer may be selectively performed on both sides or only one side of the crosslinked polyolefin film.

The separator for a lithium secondary battery prepared in this way can also be used as a separator for an electrochemical device. The electrochemical device includes all devices that perform an electrochemical reaction, and specific examples thereof include all kinds of primary and secondary cells, fuel cells, solar cells, or capacitors. In particular, a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery among the secondary batteries is preferable.

In a specific embodiment according to the present invention, the lithium secondary battery may be manufactured according to a conventional method known in the art. According to an embodiment of the present invention, the secondary battery may be manufactured by preparing an electrode assembly by interposing the above-described separator between the positive electrode and the negative electrode, accommodating it in a battery case, and then injecting an electrolyte solution.

In one embodiment of the present invention, the electrode of the secondary battery is prepared by applying the electrode active material to the electrode current collector in the form of a composition mixed with a conductive material and a binder according to a conventional method known in the art, drying it, and then roll pressing. can

Among the electrode active materials, non-limiting examples of the positive electrode active material include conventional positive electrode active materials that can be used in positive electrodes of conventional electrochemical devices, and in particular, lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or their A lithium intercalation material such as a composite oxide formed by combination is preferable.

As a non-limiting example of the negative electrode active material, a conventional negative electrode active material that can be used for a negative electrode of a conventional electrochemical device can be used, and in particular, lithium metal or lithium alloy, carbon, petroleum coke, activated carbon, A lithium adsorbent material such as graphite or other carbons is preferable. Non-limiting examples of the positive current collector include a foil made of aluminum, nickel, or a combination thereof, and non-limiting examples of the negative current collector include copper, gold, nickel, or a copper alloy or a combination thereof. There are manufactured foils and the like.

The electrolyte that can be used in the present invention is a salt having the same structure as ^{A +} B ^{- , A +} includes an ion consisting of alkali metal cations such as ^{Li +} , Na ⁺ , K ^{+ or a combination thereof, and B -} is PF ₆ ^- , BF ₄ ^- , Cl ^- , Br ^- , I ^- , ClO ₄ ^- , AsF ₆ ^- , CH ₃ CO ₂ ^- , CF ₃ SO ₃ ^- , N(CF ₃ SO ₂ ) ₂ ^- , C(CF ₂ SO ₂ ) ₃ ^- A salt containing an anion or a combination thereof, such as propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC) , dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethylmethyl carbonate (EMC), gamma butyrolactone (γ-butyrolactone) ) or dissolved or dissociated in an organic solvent consisting of a mixture thereof, but is not limited thereto.

The electrolyte injection may be performed at an appropriate stage during the battery manufacturing process according to the manufacturing process and required physical properties of the final product. That is, it may be applied before assembling the battery or in the final stage of assembling the battery. As a process for applying the electrode assembly of the present invention to a battery, in addition to the general process of winding, lamination, stack, and folding processes of a separator and an electrode are possible.

Hereinafter, examples will be given to describe the present invention in detail. However, the embodiments according to the present invention may be modified in various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described in detail below. The embodiments of the present invention are provided to more completely explain the present invention to those of ordinary skill in the art.

Example One

(One) Preparation of crosslinked polyolefin film

First, 30 kg of high-density polyethylene (Daehan Petrochemical, VH035, melting point 137 ℃) having a weight average molecular weight of 380,000 is put into the extruder hopper, and then liquid paraffin oil as a diluent (kinematic viscosity at 40 ℃: 40 cSt) 70 kg of initiator 10 g of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 1.5 kg of vinyltris(2-methoxy-ethoxy)silane (Evonic industry, Dynasylan® VTMOEO) as a first crosslinking agent, As a second crosslinking agent, 0.5 kg of tributyl(vinyl)silane (ChemTik, Tributyl(vinyl)silane) and 10 g of dibutyltin dilaurate (Sigma Aldrich, Dibutyltin dilaurate 95%) were pre-mixed. Thereafter, a silane-grafted polyethylene composition was prepared by reaction extrusion under a temperature condition of 180°C.

The prepared silane-grafted polyethylene composition was molded into a sheet through a T-die and a cooling casting roll, and then biaxially stretched using a tenter-type sequential stretching machine of MD stretching and TD stretching. Both the MD draw ratio and the TD draw ratio were set to 6.5 times. The stretching temperature was 108°C in MD and 123°C in TD.

A diluent was extracted from the stretched sheet using methylene chloride, and the sheet from which the diluent was extracted was heat-set at 124° C. to prepare a silane-grafted porous membrane. A crosslinked polyolefin film was prepared by crosslinking the silane-grafted porous membrane while aging at 85° C. and 85% humidity for 48 hours.

(2) Formation of a porous coating layer (manufacture of a composite separator)

In 300 g of N-methyl-2-pyrrolidone (NMP) as a solvent, 35 g of PVdF-HFP as a binder (Solvay Solef 21510, Tm 132 ° C. weight average molecular weight 300,000, HFP substitution degree 15 mol%) was dissolved, and Al2O3 (Japan Light Metals) , LS235, D50 500nm) was added and dispersed in a ball mill method to prepare a composition for forming a porous coating layer. The composition for forming the porous coating layer had a solid content of 25 wt% and a viscosity of 80 cP.

Then, the composition for forming the porous coating layer was sequentially coated on both sides of the cross-linked polyolefin film by a micro-gravure method. Water as a non-solvent was sprayed on both surfaces of the coating layer to give a residence time of 5 seconds to fix the coating layer, and excess solvent and non-solvent were removed through a pressing roll. Thereafter, the surface of the coating layer was alternately contacted with a drying roll maintained at 60° C. to complete drying, thereby preparing a composite separator. The thickness of the finally fabricated composite separator was 15 μm.

A porous coating layer is formed on both sides of the composite separator, and in the porous coating layer, the binder attaches the inorganic particles to each other to maintain a binding state to each other, and also maintains the inorganic particles and the cross-linked polyolefin film in a binding state. A structure in which the inorganic particles form an interstitial volume in a state in which they are in contact with each other, and the interstitial volume between the inorganic particles becomes an empty space to form pores of the porous coating layer have

Manufacture of pouch-type secondary battery

Preparation of anode

92 wt% of lithium cobalt composite oxide as the positive active material particles, 4 wt% of carbon black as a conductive material, and 4 wt% of polyvinylidene fluoride (PVdF) as a binder, N-methyl-2-pyrrolidone as a solvent (NMP) was added to prepare a cathode active material composition. The positive electrode active material composition was coated on an aluminum (Al) thin film positive electrode current collector having a thickness of 20 μm, dried to prepare a positive electrode, and then roll press was performed.

Preparation of the cathode

Using artificial graphite as an anode active material, polyvinylidene fluoride (PVdF) as a binder, and carbon black as a conductive material in 96 wt%, 3 wt%, and 1 wt%, respectively, N-methyl-2- It was added to pyrrolidone (NMP) to prepare a negative active material composition. The negative electrode active material composition was coated on a copper (Cu) thin film negative electrode current collector having a thickness of 10 μm, dried to prepare a negative electrode, and then roll press was performed.

Manufacture of pouch-type secondary battery

By stacking the positive electrode, the negative electrode, and the composite separator prepared by the above method, the unit cells were assembled to prepare an electrode assembly having a 1C capacity of 4120 mAh, and inserted into a pouch for a lithium secondary battery. Then, an electrolyte solution (ethylene carbonate (EC)/methylethyl carbonate (EMC) = 1/2 (volume ratio)) and lithium hexafluorophosphate (LiPF ₆ 1 mol) were injected to prepare a pouch-type secondary battery.

Example 2

1.0 kg of vinyltris(2-methoxy-ethoxy)silane (Evonic industry, Dynasylan® VTMOEO) as the first crosslinking agent and 1.0 kg of tributyl(vinyl)silane (ChemTik, Tributyl(vinyl)silane) as the second crosslinking agent A crosslinked polyethylene film was prepared in the same manner as in Example 1, except that.

In addition, a composite separator was prepared in the same manner as in Example 1 except that the cross-linked polyethylene film prepared in Example 2 was used, and then a pouch-type secondary battery was prepared.

comparative example One

A crosslinked polyethylene film was prepared in the same manner as in Example 1, except that only 0.5 kg of vinyltris(2-methoxy-ethoxy)silane (Evonic industry, Dynasylan® VTMOEO) was used as a crosslinking agent.

In addition, a composite separator was prepared in the same manner as in Example 1 except that the cross-linked polyethylene film prepared in Comparative Example 1 was used, and then a pouch-type secondary battery was prepared.

comparative example 2

A crosslinked polyethylene film was prepared in the same manner as in Example 1, except that only 2 kg of vinyltris(2-methoxy-ethoxy)silane (Evonic industry, Dynasylan® VTMOEO) was used as a crosslinking agent.

In addition, a composite separator was prepared in the same manner as in Example 1 except that the cross-linked polyethylene film prepared in Comparative Example 2 was used, and then a pouch-type secondary battery was prepared.

evaluation example

(One) shutdown temperature

The shutdown temperatures of the crosslinked polyethylene films prepared in Examples 1 and 2 and Comparative Examples 1 and 2 were measured as follows, and the results are shown in Table 1 below.

First, while measuring the air permeability of the cross-linked polyethylene film, the cross-linked polyethylene film is exposed to elevated temperature conditions (starting at 30° C. and 5° C./min). At this time, the temperature at which the air permeability (Gurley value) of the crosslinked polyethylene film exceeds 100,000 sec/100cc for the first time is defined as the shutdown temperature. The air permeability of the crosslinked polyolefin film is measured using an air permeability meter (Asahi Seiko, EGO-IT) according to JIS P8117.

(2) melt down temperature

The melt-down temperatures of the crosslinked polyethylene films prepared in Examples 1 and 2 and Comparative Examples 1 and 2 were measured as follows, and the results are shown in Table 1 below.

The crosslinked polyethylene film is measured by thermomechanical analysis (TMA) after taking samples in the production direction (Machine direction, MD) and the transverse direction (TD), respectively. Specifically, a 10 mm-long sample is put into a TMA equipment (TA Instrument, Q400) and exposed to elevated temperature conditions (starting at 30° C. and 5° C./min) while applying a tension of 19.6 mN. As the temperature rises, the length of the sample is changed, and the temperature is measured at which the sample is cut by rapidly increasing the length. Measure the MD and TD respectively and define the higher temperature as the meltdown temperature of the sample in question.

(3) The tensile strength

The tensile strength of the crosslinked polyethylene films prepared in Examples 1 to 2 and Comparative Examples 1 to 2 was measured according to ASTM D 882, and the results are shown in Table 1 below.

shutdown temperature
(℃) Meltdown temperature (℃) Tensile strength (kgf/cm ² ) MD TD Example 1 137 185 1950 1720 Example 2 135 182 1930 1750 Comparative Example 1 142 188 2010 1870 Comparative Example 2 140 187 1980 1850

From the above, the cross-linked polyolefin films according to Examples 1 and 2 of the present invention have a lower shutdown temperature than the cross-linked polyolefin films according to Comparative Examples 1 and 2, whereas the melt-down temperature is generally the temperature required to secure heat resistance in the art. It was confirmed that a temperature of 170 °C or higher was secured. On the other hand, it was confirmed that the crosslinked polyolefin films according to Examples 1 and 2 of the present invention had a slight decrease in tensile strength compared to the crosslinked polyolefin films according to Comparative Examples 1 and 2 due to the crosslinking reaction.

nail penetration Test

10 pouch-type secondary batteries prepared in Examples 1 and 2 and Comparative Examples 1 and 2, respectively, were prepared as samples, respectively. After the pouch-type secondary battery sample was fully charged to 4.35 V, a nail having a diameter of 2.5 mm was passed through the sample at a speed of 5 m/min to perform safety evaluation. A case in which there was no ignition or explosion among the 10 pouch-type secondary battery samples was evaluated as a pass, and "the number of samples passed/the number of samples" is shown in Table 2 below.

impact Test

10 pouch-type secondary batteries prepared in Examples 1 and 2 and Comparative Examples 1 and 2, respectively, were prepared as samples, respectively. After the pouch-type secondary battery sample was fully charged to 4.35 V, a bar having a diameter of 15.8 mm was placed on the fully charged pouch-type secondary battery, and 9.1 kg/weight was dropped from a height of 630 mm to evaluate safety. . A case in which there was no ignition or explosion among the 10 pouch-type secondary battery samples was evaluated as a pass, and "the number of samples passed/the number of samples" is shown in Table 2 below.

hot box Test

10 pouch-type secondary batteries prepared in Examples 1 and 2 and Comparative Examples 1 and 2, respectively, were prepared as samples, respectively. A hot box test was performed on the pouch-type secondary battery sample. In the hot box test, the pouch-type secondary battery was fully charged at 4.35 V, and the fully charged pouch-type secondary battery was maintained at 130 °C for 1 hour at a temperature increase rate of 5 °C/min and then again at a rate of 5 °C/min. After being maintained at 150° C. for 1 hour, the case where there was no ignition or explosion among the 10 samples was judged as a pass, and “the number of samples passed/the number of samples” is shown in Table 2 below.

(Number of Passes/Number of Samples) Example 1 Example 2 Comparative Example 1 Comparative Example 2 nail penetration 10/10 10/10 9/10 10/10 impact 9/10 10/10 10/10 9/10 hot box 10/10 9/10 4/10 6/10

From the above, the pouch-type secondary batteries of Examples 1 and 2 according to the present invention were evaluated to be excellent in all of the nail penetration test, the impact test, and the hot box test, whereas the pouch-type secondary batteries of Comparative Examples 1 and 2 were the hot box test It was confirmed that there were a number of samples that did not pass the test, which was found to be poor in terms of safety.

Claims (11)

(S1) reacting and extruding the silane-grafted polyolefin composition by adding and mixing a polyolefin, a diluent, a first cross-linking agent represented by the following Chemical Formula 1, a second cross-linking agent represented by the following Chemical Formula 2, an initiator, and a cross-linking catalyst in an extruder;
(S2) forming and stretching the reaction-extruded silane-grafted polyolefin composition in a sheet form;
(S3) preparing a silane-grafted polyolefin porous membrane by extracting a diluent from the stretched sheet;
(S4) heat-setting the silane-grafted polyolefin porous membrane; and
(S5) crosslinking the heat-set silane-grafted polyolefin porous membrane in the presence of moisture; Method for producing a crosslinked polyolefin film comprising:
[Formula 1]
YR-Si-(X) ₃
above,
Y is a vinyl group,
R represents a bond or a (C1-C30) alkylene group,
X is a group represented by -OAB, wherein O is an oxygen atom, A is a (C1-C30) alkylene group, and B is a (C1-C4) alkoxy group.

[Formula 2]
Y'-R'-Si-(X') ₃
above,
Y' is a vinyl group,
R' represents a bond or a (C1-C30) alkylene group,
X' is a (C1-C30) alkyl group.
According to claim 1,
The manufacturing method, characterized in that the first crosslinking agent is a vinyl tris (2-methoxy-ethoxy) silane compound.
According to claim 1,
The manufacturing method, characterized in that the second crosslinking agent is tributyl (vinyl) silane.
According to claim 1,
The manufacturing method, characterized in that the first cross-linking agent and the second cross-linking agent is used in a weight ratio in the range of 3:1 to 1:3.
According to claim 1,
The total amount of the first crosslinking agent and the second crosslinking agent is 0.5 to 4 parts by weight based on 100 parts by weight of the total of the polyolefin and the diluent.
According to claim 1,
The production method, characterized in that the polyolefin is polyethylene.
A crosslinked polyolefin film produced by the method according to claim 1 and having a shutdown temperature in the range of 128 to 145 °C.
8. The method of claim 7,
Cross-linked polyolefin film, characterized in that the cross-linked polyolefin film has a melt-down temperature in the range of 150 to 230 ℃.
A separator for a lithium secondary battery comprising the cross-linked polyolefin film according to claim 7.
10. The method of claim 9,
A porous coating layer comprising a mixture of a plurality of inorganic particles and a binder on at least one surface of the crosslinked polyolefin film, wherein the inorganic particles are in contact with each other to form an interstitial volume Separator for lithium secondary batteries.
A lithium secondary battery comprising a negative electrode, a positive electrode, and a separator interposed between the negative electrode and the positive electrode,
The lithium secondary battery, characterized in that the separator is the separator for a lithium secondary battery according to claim 9 or 10.