KR101915346B1 - Manufacturing method of separator and separator manufactured by the same method - Google Patents

Abstract

A method for producing a silane-grafted polyolefin solution, comprising the steps of: preparing a silane-grafted polyolefin solution, shaping the silane-grafted polyolefin solution into a sheet form, extracting a diluent from the sheet to prepare a porous membrane, Coating a porous coating layer slurry containing the porous coating layer slurry on the porous coating layer slurry to prepare a separator in which a porous membrane-porous coating layer is laminated by heat setting the porous coating layer slurry; And crosslinking the porous membrane in the presence of water.

Description

TECHNICAL FIELD [0001] The present invention relates to a separator and a separator produced by the same. BACKGROUND OF THE INVENTION 1. Field of the Invention [0001]

The present invention relates to a process for producing a separator and a separator produced thereby, and more particularly to a process for producing a separator having improved heat resistance and a separator produced thereby.

A secondary battery is a chemical battery that can be used semi-permanently by repeatedly charging and discharging by electrochemical reaction, and is classified into a lead acid battery, a nickel cadmium battery, a nickel hydrogen battery, and a lithium secondary battery. The lithium secondary battery is superior to other batteries in terms of high voltage and energy density characteristics, leading the secondary battery market. Depending on the type of electrolyte, a lithium ion battery using a liquid electrolyte and a lithium ion battery using a solid electrolyte Polymer battery.

The lithium secondary battery is composed of a cathode, a cathode, an electrolyte, and a separator. The separator of the lithium secondary battery is required to separate the anode and the cathode from each other and electrically insulate the same, while increasing the permeability of the lithium ion based on the high porosity. . Polyolefins such as polyethylene, which are advantageous for forming pores and having excellent chemical resistance, mechanical properties, electrical insulation characteristics and low cost, are mainly used as polymer materials of separators which are generally used.

However, when the melting point of polyethylene is as low as about 130 ° C, if the battery generates heat, it does not have dimensional stability at a temperature higher than the melting point, and contraction deformation occurs. In this case, the anode and the cathode meet and cause an internal short circuit and thermal runaway phenomenon, which leads to ignition.

In order to improve such low thermal properties, methods of improving thermal shrinkage at high temperature by coating an inorganic or heat-resistant polymer on the surface of polyethylene have been developed, but technical development is still required.

The present invention provides a method for manufacturing a separator capable of improving heat resistance by simultaneously including a silane-grafted crosslinked olefin and a porous coating layer, and a separator produced thereby.

Other objects and advantages of the present invention will become apparent from the following description. It is also to be easily understood that the objects and advantages of the present invention can be realized by the means or method described in the claims, and the combination thereof.

According to an aspect of the present invention, there is provided a method for producing a polyolefin solution, comprising the steps of: preparing a silane-grafted polyolefin solution; molding the silane-grafted polyolefin solution into a sheet; extracting a diluent from the sheet; Coating a slurry of a porous coating layer containing particles and a binder polymer on at least one surface of the porous membrane; preparing a separator in which a porous membrane-porous coating layer is laminated by fixing the slurry of the porous coating layer; and And crosslinking the porous membrane in the presence of water.

The step of preparing the silane-grafted polyolefin solution may include a step of putting the first polyolefin, the diluent, the vinyl silane containing an alkoxy group, and the initiator into an extruder, mixing and then performing the reactive extrusion.

The step of preparing the silane grafted polyolefin solution may comprise preparing a silane master batch powder comprising a second polyolefin, an alkoxy group-containing vinyl silane, and an initiator, mixing the first polyolefin and the diluent with the silane master batch powder And then performing reactive extrusion.

The particles may be at least one of inorganic particles and organic substances.

Wherein the inorganic particles are selected from the group consisting of BaTiO ₃ , Pb (Zr _x Ti _{1 -x} ) O ₃ (PZT, 0 <x <1), Pb _{1 -x} La _x Zr _{1 -y} Ti _y O ₃ , 0 <y <1), (1-x) Pb (Mg _1/3 Nb _2/3 ) O _3-x PbTiO ₃ (PMN-PT, 0 <x <1), hafnia (HfO ₂ ) ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO, ZrO ₂ , SiO _2, Y ₂ O ₃ , Al ₂ O ₃ , SiC and TiO ₂ .

Wherein the organic particles are selected from the group consisting of polystyrene, polyethylene, polyimide, melamine resin, phenol resin, cellulose, modified cellulose, polypropylene, polyester, polyphenylene sulfide, polyaramid, polyamideimide, and polyimide Or at least one of them.

The binder polymer may be at least one selected from the group consisting of polyvinylidene fluoride, polyvinylidene fluoride-co-trichlorethylene, polymethylmethacrylate, polybutylacrylate, But are not limited to, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, Cyanoethylacetate at least one selected from the group consisting of lanolulose, cyanoethylsucrose, pullulan, and carboxyl methyl cellulose.

The weight ratio of the particle to the binder polymer may be 50:50 to 99: 1.

The coating of the porous coating layer slurry may be performed such that the thickness of the slurry is 0.001 to 20 탆.

The hot fix may be carried out at a temperature of 50 to 200 캜.

Wherein shaping into the sheet form comprises: extruding the silane-grafted polyolefin solution through a die to form an extrudate; cooling the extrudate to form a cooled extrudate; And biaxially stretching in the transverse direction to form a stretched sheet.

The crosslinking step may be carried out at a temperature of 50 to 100 DEG C and a humidity of 50 to 100%.

The weight ratio of the first polyolefin and the diluent may be 50:50 to 20:80.

Wherein the first polyolefin is selected from the group consisting of polyethylene; Polypropylene; Polybutylene; Polypentene; Polyhexene; Polyolefin; At least one copolymer of ethylene, propylene, butene, pentene, 4-methylpentene, hexene, and octene; Or a mixture thereof.

The diluent may be paraffin oil, mineral oil, wax, soybean oil, phthalic acid esters, aromatic ethers, fatty acids having 10 to 20 carbon atoms, Fatty acid alcohols having 10 to 20 carbon atoms; And fatty acid esters.

According to another aspect of the present invention, there is provided a separator manufactured by the above-described method.

The separator may have a degree of crosslinking of 10% or more.

The separator may have a melt down temperature of 150 ° C or higher.

According to another aspect of the present invention, there is provided a lithium secondary battery including the above-described separator.

The present invention has the advantage of providing a high temperature stability of a secondary battery comprising the porous polyolefin separator by further including a porous coating layer on the grafted polyolefin separator and improving the heat resistance property by crosslinking.

Further, the production of the crosslinked polyolefin and the coating of the porous coating layer are carried out through a continuous process, which has an advantage that the process stability and efficiency can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate preferred embodiments of the invention and, together with the description of the invention, It is not interpreted.
1 is a flowchart of a separator manufacturing method according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail. The terms or words used in the present specification and claims should not be construed in a conventional or dictionary sense and the inventor shall appropriately define the concept of the term in order to explain its invention in the best way The present invention should be construed in accordance with the meaning and concept consistent with the technical idea of the present invention. Therefore, the embodiments described in the present specification and the configurations shown in the drawings are only the most preferred embodiments of the present invention, and are not intended to represent all of the technical ideas of the present invention. Accordingly, It should be understood that various equivalents and modifications are possible.

1 is a flowchart of a method of manufacturing a separator according to an embodiment of the present invention. Referring to FIG. 1, a method of manufacturing a separator according to a preferred embodiment of the present invention includes a step (S100) of forming a silane-grafted polyolefin solution, a step S200 of forming a sheet form, a step S300 of manufacturing a porous membrane, (S400) of coating a porous coating layer slurry (S500), and a crosslinking step (S600) of producing a separator in which a porous membrane-porous coating layer is laminated.

The step (S100) of preparing the silane-grafted polyolefin solution according to a preferred embodiment of the present invention includes a step of adding a first polyolefin, a diluent, an alkoxy group-containing vinyl silane, and an initiator to an extruder, &Lt; / RTI &gt;

Here, the first polyolefin may be any material that can be applied to the separation membrane of the electrochemical device, and is preferably polyethylene; Polypropylene; Polybutylene; Polypentene; Polyhexene; Polyolefin; At least one copolymer of ethylene, propylene, butene, pentene, 4-methylpentene, hexene, and octene; Or a mixture thereof may be used.

Particularly, examples of the polyethylene include low density polyethylene (LDPE), linear low density polyethylene (LLDPE) and high density polyethylene (HDPE). Of these, high density polyethylene having a high degree of crystallinity and a high melting point of the resin is the most preferable.

The molecular weight of the polyolefin is not critical if it can be formed into a sheet shape, but in the case of applications requiring strong physical properties such as separation membranes for secondary batteries, the larger the molecular weight, the better. The weight average molecular weight in this case the preferred polyolefin is 1x10 ⁵ to 3x10 ^6, more preferably 3x10 ⁵ to 1x10 ^6.

The silane may be an alkoxy-containing vinylsilane, and non-limiting examples thereof include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriacetoxysilane, and the like, or a mixture of two or more thereof. Such an alkoxy group-containing vinylsilane is grafted onto a polyolefin by a vinyl group, and the alkoxyl group causes water cross-linking to proceed, thereby crosslinking the polyolefin.

As the diluent, liquid or solid paraffin oil, mineral oil, wax, soybean oil and the like generally used for producing a wet separation membrane can be used.

As the diluent, a diluent capable of liquid-liquid phase separation with polyolefin may be used. Examples of the diluent include dibutyl phthalate, dihexyl phthalate, dioctyl phthalate, Phthalic acid esters; Aromatic ethers such as diphenyl ether and benzyl ether; Fatty acids of 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 alcohol, stearic alcohol, and oleic alcohol; Mono-, di-, or triesters of palmitic acid, mono-, di-, or triesters of stearic acid. One in which a double bond of a saturated or unsaturated fatty acid or an unsaturated fatty acid having 4 to 26 carbon atoms in a fatty acid group such as oleic acid mono-, di-, or triester, mono -, di-, or triester of linoleic acid is substituted with an epoxy Or a fatty acid ester in which two or more fatty acids are ester-bonded with an alcohol having 1 to 8 hydroxyl groups and 1 to 10 carbon atoms.

The diluent may be a mixture containing two or more of the above-mentioned components.

The initiator may be any initiator that is capable of generating latices. Non-limiting examples of the initiator include bezoyl peroxide, acetyl peroxide, dilauryl peroxide, di-tert-butyl peroxide, dicumyl peroxide, cumyl peroxide , Hydroperoxide, potassium persulfate, and the like.

The content of the initiator is 0.2 to 100 parts by weight, preferably 1 to 50 parts by weight, more preferably 2 to 10 parts by weight based on 100 parts by weight of the silane. When the content of the initiator satisfies this range, the problem that the silane graft ratio decreases as the content of the initiator decreases and the cross-linking between the polyolefins in the extruder as the content of the initiator increases can be prevented.

The weight ratio of the first polyolefin to the diluent in the silane grafted polyolefin solution may be 50:50 to 20:80, preferably 40:60 to 30:70. If the weight ratio is larger than 50:50 and the content of the second polyolefin is increased, the porosity decreases and the pore size becomes smaller, the interconnectivity between the pores decreases, and the permeability is greatly decreased. The viscosity of the first polyolefin solution increases, And if the weight ratio is less than 20:80 and the content of the second polyolefin is decreased, the kneading property of the first polyolefin and the diluent is lowered, and the second polyolefin is not thermodynamically kneaded in the diluent, So that it may cause problems such as breakage and unevenness of thickness upon stretching, and the strength of the produced separator may be lowered.

The step (S100) of preparing the silane grafted polyolefin solution according to another preferred embodiment of the present invention comprises preparing a silane master batch powder containing a second polyolefin, an alkoxy group-containing vinyl silane, and an initiator, And mixing the first polyolefin and the diluent with the silane master batch powder to perform reactive extrusion.

At this time, the alkoxy group-containing vinyl silane, the initiator and the diluent may be the same materials as the above-mentioned materials.

The second polyolefin may be the same material as the first polyolefin described above, and the first and second polyolefins together form a separation membrane.

In addition, the catalyst may further include a catalyst, and the catalyst may be used without limitation to any material capable of increasing the reaction rate without reacting with other materials.

The step S200 of forming the sheet form is a step of molding the silane-grafted polyolefin solution into a sheet form.

Specifically, the step of forming into the sheet form comprises: extruding the silane-grafted polyolefin solution through a die to form an extrudate; Cooling said extrudate to form a cooled extrudate; And biaxially stretching the cooled extrudate in the longitudinal and transverse directions to form a stretched sheet.

That is, the silane-grafted polyolefin solution obtained through the reaction extrusion is extruded by using an extruder equipped with a tire or the like, and then extruded using a water-

Casting or calendering methods can be used to form the cooled extrudate

All.

Thereafter, the sheet is stretched by using a cooled extrudate to form a sheet. As a result,

It is possible to provide the improved strength required for the separator for a battery.

Such stretching can be performed by a roll method or a tenter method, or by simultaneous stretching. It is preferable that the stretching ratio is 3 times or more, preferably 5 to 10 times in the longitudinal direction and 5 to 10 times in the transverse direction, respectively, and the total stretching ratio is 20 to 80. If the stretching ratio in one direction is less than 3 times, the orientation in one direction is not enough and the physical property balance between the longitudinal direction and the transverse direction is broken, and the tensile strength and puncture strength may be lowered. In addition, the total stretching ratio is less than 20 times, the non-stretching occurs, and the pore formation may not be performed. If the stretching ratio exceeds 80 times, breakage may occur during stretching and the shrinkage percentage of the final film may increase.

In this case, the stretching temperature may be varied depending on the melting point of the polyolefin used and the concentration and type of the diluting agent. Preferably, the stretching temperature is selected in a temperature range where 30 to 80% by weight of the crystalline portion of the polyolefin in the sheet melts It is appropriate. If the stretching temperature is selected in a temperature range lower than the temperature at which 30% by weight of the crystalline portion of the polyolefin in the sheet molding is melted, the softness of the film is poor and the stretchability is deteriorated, Occurs. On the other hand, if the stretching temperature is selected in a temperature range higher than the melting temperature of 80% by weight of the crystalline portion, stretching is easy and unstretched occurrence is small, but thickness deviation occurs due to partial over-stretching, . On the other hand, the degree of melting of the crystal part with temperature can be obtained from DSC (differential scanning calorimeter) analysis of the film molding.

The porous membrane manufacturing step (S300) is a step of preparing a porous membrane by extracting a diluent from the sheet.

Specifically, the diluent in the sheet is extracted using an organic solvent, and dried. The organic solvent is not particularly limited, and any solvent capable of extracting the diluent used for resin extrusion can be used. For example, as the organic solvent, methyl ethyl ketone, methylene chloride, hexane, etc., which have a high extraction efficiency and are quick drying, are suitable.

As the extraction method, any general solvent extraction method such as an immersion method, a solvent spray method, an ultrasonic method or the like can be used individually or in combination. The content of residual diluent in the extraction should preferably be not more than 1% by weight. When the residual diluent is more than 1% by weight, the physical properties are lowered and the permeability of the porous membrane is decreased. The amount of the residual diluent may be influenced by the extraction temperature and the extraction time. The extraction temperature is preferably a high temperature for increasing the solubility of the diluent and the organic solvent. However, considering the safety problem due to the boiling of the organic solvent, . If the extraction temperature is below the freezing point of the diluent, the extraction efficiency is greatly lowered and must be higher than the freezing point of the diluent.

Further, the extraction time depends on the thickness of the porous membrane to be produced, but in the case of the porous membrane having a thickness of 10 to 30 탆, 2 to 4 minutes are suitable.

The step S400 of coating the porous coating layer slurry is a step of coating a porous coating layer slurry containing particles and a binder polymer on one surface or both surfaces of the porous film.

At this time, the particles may not be reacted with the polyolefin, and the material capable of improving the thermal stability of the separator may be applied without limitation, preferably inorganic particles and / or organic particles.

The inorganic particles are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles usable in the present invention are not particularly limited as long as oxidation and / or reduction reaction does not occur in the operating voltage range of the applied electrochemical device (for example, 0 to 5 V based on Li / Li ⁺ ). Particularly, when inorganic particles having a high dielectric constant are used as the inorganic particles, the dissociation of the electrolyte salt, for example, the lithium salt in the liquid electrolyte, can be increased, and the ion conductivity of the electrolyte can be improved.

For the reasons stated above, the inorganic particles may include high-permittivity inorganic particles having a dielectric constant of 5 or more, preferably 10 or more, or inorganic particles having lithium ion transferring ability or a mixture thereof.

Nonlimiting examples of inorganic particles having a dielectric constant of 5 or more include BaTiO ₃ , Pb (Zr _x Ti _1-x ) O ₃ (PZT, 0 <x <1), Pb _1-x La _x Zr _1-y Ti _y O _{3 (PLZT, 0 <x <} 1, 0 <y <1), (1-x) Pb (Mg 1/3 Nb 2/3) O 3-x PbTiO 3 (PMN-PT, 0 <x <1) , Hafnia (HfO ₂ ), SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO, ZrO ₂ , SiO _2, Y ₂ O ₃ , Al ₂ O ₃ , SiC and TiO ₂ Inorganic particles such as any one or a mixture of two or more of them exhibit a high dielectric constant characteristic with a dielectric constant of 100 or more, as well as a piezoelectricity in which a charge is generated when a certain pressure is applied, piezoelectricity prevents the occurrence of an internal short circuit between the two electrodes due to an external impact, thereby improving the stability of the electrochemical device.

In addition, the inorganic particles having lithium ion transferring ability mean inorganic particles containing a lithium element and having a function of transferring lithium ions without storing lithium. Non-limiting examples of inorganic particles having lithium ion transferring ability include lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0 <x < lithium aluminum titanium phosphate _{(Li x Al y Ti z (} PO 4) 3, 0 <x <2,0 <y <1,0 <z <3), (LiAlTiP) x O y series glass (glass) (0 < x <4, 0 <y < 13), lithium lanthanum titanate _{(Li x La y TiO 3,} 0 <x <2,0 <y <3), lithium germanium thiophosphate Mani Titanium (Li _x Ge _y P _z S _{w, 0 <x <4,} 0 <y <1, 0 <z <1, 0 <w <5), lithium nitrides _{(Li x N y, 0 <} x <4, 0 <y <2), SiS ₂ (Li _x Si _y S _z , 0 <x <3, 0 <y < ₂ , 0 <z <4) series glass and P ₂ S ₅ (Li _x P _y S _z , 0 <x < y < 3, 0 < z < 7) series glass or a mixture thereof. When the above-mentioned high-permittivity inorganic particles and inorganic particles having lithium ion transferring ability are mixed, their synergistic effect can be doubled.

The size of the inorganic particles is not limited, but is preferably in the range of 0.001 to 10 nm, for the formation of a uniform thickness coating layer and proper porosity.

Examples of the organic particles include, but are not limited to, polystyrene, polyethylene, polyimide, melamine resin, phenol resin, cellulose, modified cellulose (such as carboxymethyl cellulose), polypropylene, polyester (polyethylene terephthalate, , Polybutylene terephthalate and the like), particles composed of various polymers such as polyphenylene sulfide, polyaramid, polyamideimide and polyimide. The organic particles may be composed of two or more kinds of polymers.

In addition, the binder polymer that can be used in the present invention may be any binder that can be used in forming the porous coating layer together with the particles. Preferably, the binder polymer includes polyvinylidene fluoride, polyvinylidene fluoride Polyvinylidene fluoride-co-trichlorethylene, polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate but are not limited to, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, Cellulose acetate propionate (ce lulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxymethylcellulose and carboxyl methyl cellulose.

In this case, the content ratio of the particles and the binder polymer is, for example, in the range of 50:50 to 99: 1, more preferably 70:30 to 95: 5. When the content ratio of the inorganic particles to the binder polymer is less than 50:50, the content of the polymer is increased and the improvement of the thermal stability of the separator may be degraded. In addition, the pore size and porosity due to the reduction of the void space formed between the particles may be reduced, resulting in a deterioration of the performance of the final battery. In addition, when the content of the particles exceeds 99 parts by weight, the content of the binder polymer is too small, so that the fillability of the porous coating layer may be weakened.

In addition, the porous coating layer slurry may further include a solvent. The solvent applicable to the present invention is not limited as long as it is electrochemically stable, but acetone, tetrahydrofuran, Is selected from the group consisting of methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (NMP), and cyclohexane Or at least one of them.

In addition, the porous coating layer slurry may be applied to at least one surface of the porous membrane at a thickness of 0.001 to 20 탆, and preferably at 2 to 7 탆. If the thickness of the coated slurry is less than 0.001 탆, there is a problem that the heat-resistant safety effect is insufficient. If it exceeds 20 탆, there is a problem of battery cycle performance deterioration due to coating layer resistance.

The step of forming the separator in which the porous membrane-porous coating layer is laminated (S500) is a step of opening and fixing the porous coating layer slurry on the surface of the porous membrane. The solvent removal in the porous coating layer slurry and the heat- . In addition, due to the uneven appearance caused by crosslinking during the extrusion-curing molding of the separator, the conventional problem of setting the molding conditions such as dimensional stability and the pressure inside the extruder very hard can be solved.

Specifically, the solvent of the porous coating layer slurry is removed, and the residual stress is reduced as in the case of separator for battery, so that the high-temperature shrinkage ratio of the final product can be reduced to 5% or less in each of the longitudinal and transverse directions.

The hot fix is to apply heat to force the porous membrane and porous coating layer to be shrunk to remove residual stress. The high heat setting temperature is advantageous for lowering the shrinkage rate, but if it is too high, the porous membrane is partially melted and the formed micropores are clogged to lower the permeability.

The preferred heat setting temperature is selected within a temperature range where 10 to 30% by weight of the crystalline portion of the porous film is melted. If the heat-setting temperature is lower than the temperature at which 10 wt% of the crystalline portion of the porous membrane is melted, the polyolefin molecules in the porous membrane will not be rearranged and the residual stress of the porous membrane will not be removed, and 30 wt% If it is selected in the temperature range, the micropores are clogged by partial melting and the permeability is lowered.

And may be applied at a temperature of 50 to 200 ° C, depending on the composition of the polyolefin, solvent, etc. to be more specifically applied.

The heat fixation time should be relatively short when the heat fixation temperature is high, and relatively long when the heat fixation temperature is low. Preferably 5 seconds to 1 minute.

The heat-set porous coating layer is bonded to each other by the binder polymer in a state where the particles are charged and in contact with each other, thereby forming an interstitial volume between the particles, The volume (interstitial volume) becomes empty space to form pores.

That is, the binder polymer adheres them to each other so that the particles can remain bonded to each other, for example, the binder polymer bonds and fixes the particles. In addition, the pores of the porous coating layer are pores in which the interstitial volume between the particles is an empty space. This is because the pores of the pores of the porous coating layer are formed into particles that are substantially interfaced with each other in a closed packed or densely packed structure . A path through which lithium ions necessary for operating the battery through the pores of the porous coating layer can be provided.

The crosslinking step (S600) is a step of crosslinking the porous membrane in the presence of water. Specifically, the crosslinking step is carried out at a constant temperature of 50 to 100 DEG C, more preferably 60 to 90 DEG C and a constant temperature and humidity of 50 to 100%, more preferably 70 to 100%, or immersed in hot or boiling water It can be carried out over several hours or several days.

When the temperature and humidity at the time of crosslinking satisfy the above range, the crosslinking rate can be increased, and the problem of deformation of the film due to melting of some polyethylene crystals at a high temperature can be prevented.

In order to promote the crosslinking reaction, a crosslinking catalyst may be used. As such a crosslinking catalyst, carboxylic acid salts, organic bases, inorganic acids and organic acids of metals such as tin, zinc, iron, lead and cobalt can be used. Specific examples thereof include dibutyltin dilaurate, dibutyltin diacetate, stannous acetate, stannous caprylate, manganese naphthenate, zinc caprylate, cobalt naphthenate, ethylamine, dibutylamine, hexyl Amine, pyridine, sulfuric acid and hydrochloric acid, and organic acids such as toluenesulfonic acid, acetic acid, stearic acid and maleic acid.

Examples of the method of using the crosslinking catalyst include a method of adding a crosslinking catalyst at the time of producing a silane-grafted polyethylene solution, a method of applying a solution or dispersion of a crosslinking catalyst to a porous film, and the like.

When the catalyst is added during the production of the silane grafted polyethylene solution, the content of the crosslinking catalyst is in the range of 0.0001 to 5% by weight based on the silane grafted polyethylene solution. Further, when the crosslinking catalyst is applied to the porous film, the concentration of the crosslinking catalyst may be adjusted in the range of 0.001 to 30 wt% with respect to the solution or dispersion of the crosslinking catalyst.

According to another aspect of the present invention, there is provided a separator produced by the above-described production method.

The separator according to one embodiment of the present invention has a degree of crosslinking of 10% or more, preferably 20 to 80%, more preferably 30 to 80%.

In addition, the separator has a meltdown temperature of 150 ° C or higher, preferably 160 to 220 ° C, more preferably 170 to 200 ° C.

According to another aspect of the present invention, there is provided a lithium secondary battery including the above-described separator.

The lithium secondary battery includes a cathode, an anode, and a separator according to one aspect of the present invention disposed therebetween.

The cathode and the anode may be produced by binding an electrode active material to an electrode current collector according to a conventional method known in the art. Examples of the cathode active material include, but are not limited to, lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or a combination thereof A lithium complex oxide may be used as the anode active material. [0041] As a non-limiting example of the anode active material, a conventional anode active material that can be used for an anode of a conventional electrochemical device can be used, and lithium metal or lithium alloy, carbon, petroleum coke ), Activated carbon, graphite or other carbon-based materials can be used. Non-limiting examples of the cathode current collector include aluminum, nickel, or a combination thereof, and examples of the anode current collector include copper, gold, nickel, or a copper alloy or a combination thereof The electrolytic solution which can be used in the lithium secondary battery according to one aspect of the present invention is a salt having a structure such as A ⁺ B ^- , wherein A ⁺ is an alkali such as Li ⁺ , Na ⁺ , K ⁺ Metal cation or a combination thereof and B ^- is an ion selected from the group consisting of 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 - anion, or a salt containing an ion composed of a combination of propylene carbonate (PC) such as, ethylene carbonate (EC), diethyl Carbon monoxide (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, (NMP), ethylmethyl carbonate (EMC), gamma-butyrolactone (g-butyrolactone), or mixtures thereof, in the presence of a base such as acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, , But the present invention is not limited thereto.

The electrolyte injection may be performed at an appropriate stage of the battery manufacturing process, depending on the manufacturing process and required properties of the final product. That is, it can be applied before assembling the cell or at the final stage of assembling the cell.

As a process for applying the crosslinked polyolefin separator according to one aspect of the present invention to a secondary battery, a lamination, stacking and folding process of a separator and an electrode can be performed in addition to a conventional winding process.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. Embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art.

[Example 1]

The resin used for the coating was a high density polyethylene having a weight average molecular weight of 300,000 and a melting temperature of 135 degrees. The diluent used was liquid paraffin oil and the kinematic viscosity at 40 ° C was 40 cSt. The ratio of the two components was 35 wt% and 65 wt%. The extrusion rate was 6 kg / hr. Trimethoxyvinylsilane was used as the vinylsilane, and its content was 2 phr as compared with the sum of the resin and the diluent. The initiator was 2,5-dimethyl-2,5-di (tert-butylperoxy) hexane at a ratio of 1/50 of vinylsilane. The catalyst was loaded with DBTDL (dibutyltin dilaurate) at 1/100 of vinylsilane. The above components were fed into a twin-screw extruder and kneaded to produce a polyethylene solution, which was simultaneously extruded and silane grafted onto polyethylene. A silane-grafted polyolefin solution was formed into a sheet through a die and a cooling casting roll, followed by MD stretching, followed by biaxial stretching by TD stretching type tenter type stretching stretching machine. Both the MD stretching ratio and the TD stretching ratio were 5.5 times. The stretching temperature was 10 degrees for MD and 123 degrees for TD. The stretched film was extracted with liquid paraffin with methylene chloride. The slurry liquid of alumina particles / carboxymethyl cellulose (CMC) / polyethylene wax / distilled water = 37.4 / 0.12 / 2.48 / 60 (weight ratio) Double-sided coating. After that, the porous membrane was prepared by opening and setting again at 123 deg. The resultant porous membrane was placed in a constant temperature and humidity room at 80 DEG C and 90% humidity for 24 hours to carry out crosslinking.

[Example 2]

The resin used for the coating was a high density polyethylene having a weight average molecular weight of 300,000 and a melting temperature of 135 degrees. The diluent used was liquid paraffin oil and the kinematic viscosity at 40 ° C was 40 cSt. The ratio of the two components was 35 wt% and 65 wt%. A dry silane master batch was prepared using a Henschel mixer as shown in Table 1 below. The prepared silane master batch (3.34 wt%) is mixed well with high density polyethylene (35 wt%). The above components were fed into a twin-screw extruder and kneaded to produce a polyethylene solution, which was simultaneously extruded and silane grafted onto polyethylene. The prepared silane-grafted polyolefin solution was passed through a die and a cooling casting roll to form a sheet, followed by MD (machine direction) stretching, and then biaxially stretched by a tenter type stretching machine of TD (transverse direction) stretching. Both the MD stretching ratio and the TD stretching ratio were 5.5 times. The stretching temperature was 108 degrees for MD and 123 degrees for TD. The stretched film was extracted with liquid paraffin with methylene chloride. The porous membrane was coated on both sides with a predetermined thickness (4.0 탆) of alumina particles / CMC / PE wax / distilled water = 37.4 / 0.12 / 2.48 / 60 (weight ratio). After that, the porous membrane was prepared by opening and setting again at 123 deg. The resultant porous membrane was placed in a constant temperature and humidity room at 80 DEG C and 90% humidity for 24 hours to carry out crosslinking.

Master batch powder composition weight% Silane 60 Porous polypropylene 35 peroxide 1.2 catalyst 1.2 Total weight% 100

[Example 3]

(18) / (1.5) / (0.5) (80) in which PMMA / butyl acrylate binder / CMC / ultrapure water having an average particle size of 0.5 μm was added to the porous film, Was coated on both surfaces of a water-based organic slurry having a predetermined thickness (4.0 탆). The conditions thereafter were the same as in Example 1.

[Comparative Example 1]

The resin used in the film formation was a high-density polyethylene having a weight average molecular weight of 300,000 and a melting temperature of 135 degrees. The diluent used was liquid paraffin oil and the kinematic viscosity at 40 ° C was 40 cSt. The ratio of the two components was 35 wt% and 65 wt%. The extrusion rate was 6 kg / hr. The above components were fed into a twin-screw extruder and kneaded to prepare a polyethylene solution. After the sheet was formed through a T-die and a cooling casting roll, MD stretching was followed by biaxial stretching by TD stretching tenter type stretching stretching machine. Both the MD stretching ratio and the TD stretching ratio were 5.5 times. The stretching temperature was 108 degrees for MD and 123 degrees for TD. The stretched membrane was extracted with liquid paraffin with methylene chloride and opened and fixed at 123 deg. C to prepare a porous membrane. An aqueous inorganic slurry having alumina particles / CMC / PE wax / distilled water = 37.4 / 0.12 / 2.48 / 60 (weight ratio) was coated on both surfaces of the prepared polyethylene porous film with a certain thickness (4.0 μm).

[Comparative Example 2]

(PMMA) / butyl acrylate binder / CMC / ultrapure water having an average particle diameter of 0.5 mu m in a weight ratio of 18 / 1.5 / 0.5 / 80 to a polyethylene membrane prepared in the same manner as in Comparative Example 1 Was coated on both sides with a constant thickness (4.0 탆).

Property evaluation

The aeration time, peel strength, and heat shrinkage of the separator prepared in Examples 1 to 3 and Comparative Examples 1 to 2 were measured and are shown in Table 2 below.

At this time, the air permeability was measured according to JIS P-8117 using a Gurley air permeability meter. At this time, the time when 100 ml of air passed through was measured with a diameter of 28.6 mm and an area of 645 mm 2.

Condition Comparative Example 1 Comparative Example 2 Example 1 Example 2 Example 3 Thickness (㎛) 22.7 21.8 21.9 22.4 22.1 Ventilation time (sec / 100cc) 385 345 325 335 311 Peel strength (gf / 15 mm) 35 50 55 60 150 Heat shrinkage
(150 DEG C / 30 minutes) MD (%) <50 <45 <40 <40 <40

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

Claims (19)

Producing a silane grafted polyolefin solution;
Molding the silane grafted polyolefin solution into a sheet form;
Extracting a diluent from the sheet to produce a silane-grafted polyolefin porous membrane;
Coating a porous coating layer slurry comprising particles and a binder polymer on at least one surface of the silane grafted polyolefin porous membrane;
Preparing a separator in which the porous coating layer slurry is thermally fixed at 50 ° C to 123 ° C to remove the solvent in the porous coating layer and simultaneously a silane grafted polyolefin porous membrane-porous coating layer is laminated; And
Crosslinking the porous membrane in the presence of moisture,
The step of preparing the silane grafted polyolefin solution comprises the steps of putting the first polyolefin, the diluent, the vinyl silane containing an alkoxy group, the crosslinking catalyst, and the initiator into an extruder, mixing and then performing the reactive extrusion, or
Wherein the step of preparing the silane grafted polyolefin solution comprises the steps of preparing a silane master batch powder comprising a second polyolefin, an alkoxy group-containing vinyl silane, a crosslinking catalyst, and an initiator, And a step of subjecting the mixture to reaction extrusion by mixing a diluent.
delete delete The method according to claim 1,
Wherein the particles are at least one of inorganic particles and organic particles 5. The method of claim 4,
Wherein the inorganic particles are selected from the group consisting of BaTiO ₃ , Pb (Zr _x Ti _{1 -x} ) O ₃ (PZT, 0 <x <1), Pb _{1 -x} La _x Zr _{1 -y} Ti _y O ₃ , 0 <y <1), (1-x) Pb (Mg _1/3 Nb _2/3 ) O _3-x PbTiO ₃ (PMN-PT, 0 <x <1), hafnia (HfO ₂ ) ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO, ZrO ₂ , SiO _2, Y ₂ O ₃ , Al ₂ O ₃ , SiC and TiO ₂ . &Lt; / RTI &gt; 5. The method of claim 4,
Wherein the organic particles are selected from the group consisting of polystyrene, polyethylene, polyimide, melamine resin, phenol resin, cellulose, modified cellulose, polypropylene, polyester, polyphenylene sulfide, polyaramid, polyamideimide, and polyimide Wherein the separator is at least one of the separator and the separator. The method according to claim 1,
The binder polymer may be at least one selected from the group consisting of polyvinylidene fluoride, polyvinylidene fluoride-co-trichlorethylene, polymethylmethacrylate, polybutylacrylate, But are not limited to, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, Cyanoethylacetate wherein the separator is at least one selected from the group consisting of lanolulose, cyanoethylsucrose, pullulan, and carboxyl methyl cellulose. . The method according to claim 1,
Wherein the weight ratio of the particle to the binder polymer is 50:50 to 99: 1. The method according to claim 1,
Wherein the coating of the porous coating layer slurry is performed such that the thickness of the coated slurry is 0.001 to 20 mu m. delete The method according to claim 1,
Wherein shaping into the sheet form comprises: extruding the silane-grafted polyolefin solution through a die to form an extrudate; Cooling said extrudate to form a cooled extrudate; And biaxially stretching the cooled extrudate in the longitudinal and transverse directions to form a stretched sheet. The method according to claim 1,
Wherein the crosslinking step is carried out at a temperature of 50 to 100 DEG C and a humidity of 50 to 100%. The method according to claim 1,
Wherein the weight ratio of the first polyolefin and the diluent is 50:50 to 20:80. The method according to claim 1,
Wherein the first polyolefin is selected from the group consisting of polyethylene; Polypropylene; Polybutylene; Polypentene; Polyhexene; Polyolefin; At least one copolymer of ethylene, propylene, butene, pentene, 4-methylpentene, hexene, and octene; Or mixtures thereof. &Lt; RTI ID = 0.0 &gt; 11. &lt; / RTI &gt; The method according to claim 1,
The diluent may be paraffin oil, mineral oil, wax, soybean oil, phthalic acid esters, aromatic ethers, fatty acids having 10 to 20 carbon atoms, Fatty acid alcohols having 10 to 20 carbon atoms; A fatty acid ester, and a fatty acid ester. A separator produced by the production method of any one of claims 1, 4 to 9, and 11 to 15. 17. The method of claim 16,
Wherein the separator has a degree of crosslinking of 10% or more. 17. The method of claim 16,
Wherein the separator has a meltdown temperature of 150 ° C or higher. A lithium secondary battery comprising the separator of claim 16.

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