KR20160129567A - A method of manufacturing separator for electrochemical device and separator for electrochemical device manufactured thereby - Google Patents

Abstract

According to an embodiment of the present invention, a method for manufacturing a separator for electrochemical device includes: a step of extruding a resin composition containing a polyolefin and a plasticizer; a step of obtaining a polyolefin film by stretching the extruded resin composition; a step of extruding the plasticizer from the obtained polyolefin film so as to obtain the porous polyolefin film; a step of coating slurry having a porous flame coating layer formed on at least one side of the porous polyolefin film; and a step of allowing the slurry to heat-fixate the coated porous polyolefin film so as to obtain a complex separator having the porous flame coating layer formed thereon.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a separator for electrochemical devices and a separator for electrochemical devices manufactured therefrom,

The present invention relates to a process for producing a separator for an electrochemical device and a separator for an electrochemical device produced therefrom, and more particularly to a process for producing a separator for an electrochemical device having a self-extinguishing function and an electrochemical device The present invention relates to a solvent separator.

In recent years, demand for high-capacity and high-output electrochemical devices is gradually increasing in the market of small polymers and mid- to large-sized electrochemical devices. Thin film type membranes suitable for such high capacity and high output electrochemical device designs should have low electrical resistance and safety.

The substrate used for the separator can be roughly classified into three types in terms of its production method. The first is a method of making a porous substrate made of a nonwoven fabric in the form of a thin fiber such as a polyolefin. The second method is a method in which a thick polyolefin film is formed and then stretched at a low temperature to form a lamella The third method is to dry the polyolefin with diluents at a high temperature to form a single phase. During the cooling process, the polyolefin and the plasticizer are phase-separated, and the plasticizer portion is extracted to form a micro- It is a wet method to make voids in polyolefin.

Since the porous substrate (porous polymer film) thus produced has a relatively low thermal and mechanical properties, a porous coating layer containing inorganic particles or organic particles and a binder polymer is coated on the porous substrate for the purpose of enhancing safety, Composite separator. The binder polymer acts to bind inorganic particles or organic particles. However, the higher the content of the binder polymer, the greater the aeration time of the separator, which is the final product, and the higher the electrical resistance, have. In addition, as electrochemical devices become larger, the possibility of ignition and explosion due to heat generation has greatly increased.

Therefore, there is a demand for a separator having enhanced thermal stability.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to provide a method of manufacturing a separator for electrochemical devices having self-extinguishing function, will be.

It is to be understood, however, that the technical scope of the present invention is not limited to the above-mentioned problems, and other technical subjects not mentioned above can be understood by those skilled in the art from the description of the invention described below.

According to an aspect of the present invention,

Extruding a resin composition containing a polyolefin and a plasticizer; Stretching the extruded resin composition to obtain a polyolefin film; Extracting the plasticizer from the obtained polyolefin film to obtain a porous polyolefin film; Coating at least one surface of the porous polyolefin film with a slurry for forming a porous flame retardant coating layer; And a step of thermally fixing the porous polyolefin film coated with the slurry to obtain a composite separator having a porous flame retardant coating layer formed thereon.

Preferably, the slurry for forming a porous flame retardant coating layer may include flame retardant particles, inorganic particles, a binder polymer, and a solvent.

The flame-retardant particles may be hydroxides containing one or more elements selected from the group consisting of aluminum, magnesium, silicon, zirconium, calcium, strontium, barium, antimony, tin, zinc and rare earth elements.

The flame-retardant particles may be at least two selected from the group consisting of aluminum hydroxide, magnesium hydroxide and boehmite.

Preferably, the binder polymer is selected from the group consisting of polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichlorethylene, polymethyl methacrylate but are not limited to, polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, But are not limited to, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, , Cyanoethyl polyvinyl alcohol or a mixture of two or more thereof selected from the group consisting of cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan and carboxyl methyl cellulose. .

Preferably, the extruded resin composition may be uniaxially stretched at least once in the MD or TD direction, or may be biaxially stretched at least once in the MD and TD directions.

Preferably, the open and defined temperature is not more than Tm - 1 DEG C, wherein Tm may be the melting point of the polyolefin.

Preferably, the heat setting may be performed using a heat source oriented in a direction perpendicular to the surface of the slurry coated on the porous polyolefin film.

Preferably, the 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.

Preferably, the plasticizer is selected from the group consisting of 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.

Preferably, the composite separator may further include a step of winding and slitting the composite separator.

Preferably, the step of coating the slurry for forming the porous coating layer may not include the step of heat setting and the step of winding and slitting.

Preferably, the method further includes packaging the composite separator having completed the winding and slitting.

According to an aspect of the present invention, there is also provided a porous polymer film; And a porous flame retardant coating layer formed on one side or both sides of the porous polymer film including flame retardant particles, inorganic particles, and a binder polymer, wherein the porous polymer film has a plurality of fibrils arranged in parallel with the surface of the film, Wherein the diameter of the fibrils located on one side of the film having the porous flame retardant coating layer formed thereon is smaller than the diameter of the fibrils located in the center of the film thickness direction.

Preferably, the diameter of the fibrils located on one side of the film on which the porous flame retardant coating layer is formed may be 2 to 4 times smaller than the diameter of the fibrils located on the center of the film thickness direction.

Preferably, the diameter of the fibrils located on one side of the film having the porous flame retardant coating layer is 0.01 to 0.04 mu m, and the diameter of fibrils located in the center of the film thickness direction is 0.04 to 0.08 mu m.

Preferably, the porous polymeric film has a porous flame retardant coating layer formed on only one side of the porous polymeric film, and the diameter of the fibril located on one side of the film having the porous flame retardant coating layer is smaller than the diameter of the film on which the porous flame retardant coating layer is not formed May be smaller than the diameter of the fibrils.

Preferably, the diameter of the fibrils located on one side of the film having the porous flame retardant coating layer is 2 to 7 times smaller than the diameter of the fibrils located on the other side of the film on which the porous flame retardant coating layer is not formed.

Preferably, the diameter of the fibrils located on one side of the film having the porous flame retardant coating layer is 0.01 to 0.07 mu m, and the diameter of the fibrils located on the other side of the film having no porous flame retardant coating layer is 0.07 to 0.14 mu m .

Preferably, the binder polymer is located on the surface of neighboring particles and connects them to each other to form a porous structure, and the size of the binder polymer may be 10 to 100 nm.

Preferably, the flame-retardant particle may be a hydroxide containing one or more elements selected from the group consisting of aluminum, magnesium, silicon, zirconium, calcium, strontium, barium, antimony, tin, zinc and rare earth elements.

Preferably, the flame-retardant particles may be at least two selected from the group consisting of aluminum hydroxide, magnesium hydroxide and boehmite.

According to an aspect of the present invention, there is provided an electrochemical device including a cathode, an anode, and a separator interposed between the cathode and the anode, wherein the separator is the separator for the electrochemical device.

The electrochemical device may be a lithium secondary battery.

According to the present invention, it is possible to provide a separation membrane capable of improving the performance and safety of an electrochemical device by having a self-extinguishing function.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms, and the inventor should appropriately interpret the concepts of the terms appropriately It should be interpreted in accordance with the meaning and concept consistent with the technical idea of the present invention based on the principle that it can be defined. Therefore, the embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention and do not represent all the technical ideas of the present invention. Therefore, It is to be understood that equivalents and modifications are possible. It is also to be understood that, in the specification, like reference numerals denote like elements.

According to an aspect of the present invention, there is provided a method of manufacturing a separation membrane for an electrochemical device,

Extruding a resin composition containing a polyolefin and a plasticizer;

Stretching the extruded resin composition to obtain a polyolefin film;

Extracting the plasticizer from the obtained polyolefin film to obtain a porous polyolefin film;

Coating at least one surface of the porous polyolefin film with a slurry for forming a porous flame retardant coating layer; And

And the porous polyolefin film coated with the slurry is heat set to obtain a composite separator having a porous flame retardant coating layer formed thereon.

Specifically, a separation membrane is manufactured in the order of an extrusion process, a drawing process, a plasticizer extraction process, a slurry coating process, and a heat fixing process. Thus, after the plasticizer extraction process as in the conventional production process, The process is not required, and the process can be performed efficiently.

Hereinafter, each step will be described in detail.

First, in the extruding step, the polyolefin is not particularly limited as long as it is commonly used in the art. Specific examples of such polyolefins include polyethylene such as high density polyethylene (HDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), ultra high molecular weight polyethylene (UHMWPE) and the like; Polypropylene; Polybutylene; Polypentene: polyhexene: polyoctene: at least one copolymer of ethylene, propylene, butene, pentene, 4-methylpentene, hexene, and octene, or a mixture thereof, but is not limited thereto.

The plasticizer is not particularly limited as long as it is commonly used in the art. Non-limiting examples of such plasticizers include phthalic acid esters such as dibutyl phthalate, dihexyl phthalate, and dioctyl phthalate; 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 fatty acid esters 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 plasticizer may be a mixture containing two or more of the above-mentioned components.

The weight ratio of the polyolefin to the plasticizer may be 80:20 to 10:90, preferably 70:30 to 20:80, and preferably 50:50 to 30:70. If the weight ratio of polyolefin is larger than 80:20, the porosity decreases and the pore size decreases. Since the interconnection between the pores is small and the permeability is greatly decreased, the viscosity of the polyolefin solution increases, If the weight ratio is less than 10:90 and the content of the polyolefin is decreased, the kneading property between the polyolefin and the plasticizer is lowered, so that the polyolefin is extruded into a gel form without thermodynamically mixing with the plasticizer, Uniformity, and the like, and the strength of the produced separation membrane may be lowered.

In order to produce the composite membrane in the present invention, first, a part or the whole of the material is mixed using a Henschel mixer, a ribbon blender, a tumbler blender, or the like. Then, it is melted and kneaded by a screw extruder such as a single screw extruder, a twin screw extruder, a kneader or a mixer, and extruded from a T-die or a ring-shaped die. The kneaded / extruded melt can be solidified by compression cooling. Examples of the cooling method include direct contact with a cooling medium such as cold wind or cooling water, contact with a roll or a press cooled with a coolant, and the like.

Subsequently, the extruded resin composition is stretched to obtain a polyolefin film. The stretching method may be carried out by a conventional method known in the art, and examples thereof include MD (longitudinal) uniaxial stretching by a roll stretcher, TD (transverse direction) uniaxial stretching by a tenter, roll stretcher and tenter, Or simultaneous biaxial stretching by combination of tenter and tenter, simultaneous biaxial stretching by simultaneous biaxial tenter or inflation molding, and the like. Specifically, the extruded resin composition may be subjected to uniaxial stretching at least once in the MD or TD direction, or by biaxial stretching at least once in the MD and TD directions.

The stretching ratio may be 3 times or more, preferably 5 to 10 times in the longitudinal direction and 20 times or more in the transverse direction, and 20 times or more, preferably 20 to 80 times in the total stretching ratio (total surface multiplication factor).

If the stretching ratio in one direction is less than 3 times, the orientation in one direction is not sufficient 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. If the total stretching ratio is less than 20 times, undrawn stretching may occur and pores may not be formed. If the total stretching ratio is more than 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 plasticizer, and preferably, the stretching temperature is selected in a range of temperatures in which 30 to 80% by weight of the crystalline portion of the polyolefin in the film is melted It is appropriate.

If the stretching temperature is selected in a temperature range lower than the temperature at which 30 wt% of the crystalline portion of the polyolefin in the sheet molding is melted, there is a possibility that the stretchability at the time of stretching is likely to occur due to poor softness of the film, 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.

Then, the plasticizer is extracted from the stretched film to obtain a porous polyolefin film. Specifically, in the stretched film, the plasticizer is extracted using an organic solvent and dried.

The extraction solvent used for the extraction of the plasticizer is preferably a poor solvent for polyolefin, a good solvent for the plasticizer, and a boiling point lower than the melting point of the polyolefin, so that drying is preferable. Nonlimiting examples of such an extraction solvent include hydrocarbons such as n-hexane and cyclohexane, halogenated hydrocarbons such as methylene chloride, 1,1,1-trichloroethane, and fluorocarbon, alcohols such as ethanol and isopropanol, And ketones such as acetone and 2-butanone.

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 the residual plasticizer in the extraction should preferably be not more than 1% by weight. When the amount of the residual plasticizer exceeds 1% by weight, the physical properties are lowered and the permeability of the porous film is decreased. The amount of residual plasticizer may be influenced by the extraction temperature and extraction time. The extraction temperature is preferably high to increase the solubility of the plasticizer and the organic solvent. However, considering the safety problem due to the boiling of the organic solvent, Do. If the extraction temperature is lower than the solidifying point of the plasticizer, the extraction efficiency is greatly lowered, and therefore, it must be higher than the solidifying point of the plasticizer.

The thickness of the porous polyolefin film obtained above is not particularly limited, but is preferably in the range of 5 to 50 占 퐉, and the pore size and porosity present in the porous substrate are also not particularly limited, but 0.001 to 50 占 퐉 and 10 to 99% desirable.

Then, at least one side of the porous polyolefin film is coated with a slurry for forming a porous flame retardant coating layer. For this purpose, a slurry for forming a porous flame retardant coating layer must first be prepared. The slurry is prepared by dispersing a binder polymer together with flame-retardant particles and inorganic particles in a solvent.

The flame-retardant particles are capable of absorbing a large amount of heat during the dehydration and decomposition reaction and can be one kind selected from the group consisting of aluminum, magnesium, silicon, zirconium, calcium, strontium, barium, antimony, tin, Or more of the elements. Preferably, the flame-retardant particles may be at least two selected from the group consisting of aluminum hydroxide, magnesium hydroxide and boehmite. More preferably, the flame-retardant particles may be a mixture of aluminum hydroxide, magnesium hydroxide and boehmite.

The size of the flame-retardant particles is not limited, but may be in the range of 0.001 to 10 mu m in terms of forming a coating layer of uniform thickness and having an appropriate porosity.

The binder polymer used in the slurry for forming the porous flame retardant coating layer is not particularly limited as long as it can function to connect and stably fix at least one of the flame retardant particles and the inorganic particles, Polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichlorethylene, polymethylmethacrylate, polybutylacrylate, But are not limited to, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, cellulose acetate ), Cellulose acetate buty But are not limited to, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethyl sucrose acrylonitrile styrene-butadiene copolymer, polyimide, and the like, which may be used alone or in combination of two or more thereof. May be used in combination.

The composition ratio of the particles in the slurry and the binder polymer for forming the porous flame retardant coating layer may be, for example, in the range of 50:50 to 99: 1 by weight or 70:30 to 95: 5. If the content of the particles relative to the binder polymer is too small, improvement of the thermal stability of the separation membrane may be deteriorated, voids formed between the particles may not be formed sufficiently, pore size and porosity may be decreased, have. On the other hand, if the amount of particles relative to the binder polymer is too large, the fillability of the porous flame retardant coating layer may be weakened.

As the solvent contained in the slurry, it is preferable that the dispersion of the particles and the binder polymer can be made uniform, and can be easily removed thereafter. Non-limiting examples of usable solvents include acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone ( N-methyl-2-pyrrolidone, NMP), cyclohexane, water or mixtures thereof.

The slurry for forming the porous flame retardant coating layer is coated on at least one surface of the porous polyolefin film. The specific coating method may be a conventional coating method known in the art. For example, a dip coating, a die coating , Roll coating, comma coating, or a combination thereof. In addition, the porous flame retardant coating layer can be selectively formed on both or only one side of the porous polyolefin film.

Then, the porous polyolefin film coated with the slurry is heat set to obtain a composite separator having a porous flame retardant coating layer.

The hot fix is a process of fixing the film and applying heat to forcefully hold the film to be shrunk to remove residual stress. If the heat fixing temperature is higher, the shrinkage rate is decreased. However, if the heat setting temperature is too high, the polyolefin film is partially melted, so that the formed micropores may be clogged and the permeability may be lowered.

In the present invention, since the plasticizer is extracted after the polyolefin film is stretched, and then the slurry for forming the porous coating layer is coated and heat-set is performed, unlike the process of extracting the plasticizer after stretching with the polyolefin film and heat- Since the coated slurry, not the polyolefin film, is thermally stable, the polyolefin film is not directly heated.

Therefore, melting of the polyolefin film can be suppressed even when heat setting is performed at a higher temperature than the conventional method. In addition, since the amount of heat directly applied to the polyolefin film is reduced, the fibril thickness of the polyethylene-based adjacent to the porous flame retardant coating layer is made thinner than that of the conventional fibrillated polyolefin film.

As a result, the fibril number density per unit area of the porous film surface adjacent to the porous flame retardant coating layer is increased, so that the interface contact area with the coating slurry is increased and the glass transition temperature (Tg) or melting point (Tm ), The wettability of the slurry to the fibrous structure of the porous polyolefin film can be improved upon heat setting treatment.

The temperature of the open and the defined temperature is preferably adjusted to Tm - 1 DEG C or less, where Tm corresponds to the melting point of the polyolefin.

According to one embodiment of the present invention, when polyethylene is used as the polyolefin, the open and defined temperature can be carried out at a temperature of from 131 to 135 DEG C, preferably from 131 to 133 DEG C, , The bonding strength (peel strength) between the porous coating layer and the porous polyolefin film is improved, so that the structural stability can be secured and the thermal mechanical properties can be improved.

The heat setting may be performed using a heat source oriented in a direction perpendicular to the surface of the slurry coated on the porous polyolefin film.

Thus, since the hot heat source is directed in a direction perpendicular to the surface of the slurry coated on the porous polyolefin film, the probability that the binder polymer in the coated slurry is biased perpendicularly to the surface of the porous polyolefin film is rearranged Thereby forming a coating layer structure in which lithium ion migration is easy within the porous coating layer, and lithium ions can communicate with the pores formed in the porous polyolefin film. Also, the binder polymer between the particles and the binder polymer which is not completely bonded to the particles can be rearranged due to the recrystallization action by the high temperature heat source, and the resistance by the binder polymer can be greatly reduced. Such a tendency that the binder polymer is arranged in the vertical direction is particularly effective in the case of a binder polymer which is not well dispersed in a solvent such as cyanoethylpolyvinyl alcohol and forms a dense film on the porous polyolefin film to be.

In the porous coating layer, the particles are charged and bound to each other by the binder polymer in a state of being in contact with each other, thereby forming an interstitial volume between the particles, and an interstitial volume The interstitial volume forms an 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 formed by interstitial volumes between particles, which are voids, and are formed in particles that are substantially interfaced with each other in a closed packed or densely packed state . Such a pore structure is filled with an electrolyte solution to be injected at a later time, and the filled electrolyte can provide a path through which lithium ions, which are essential for operating the battery through the pores of the porous coating layer, are moved.

As described above, unlike the conventional manufacturing method, the method of manufacturing a separation membrane according to an embodiment of the present invention does not require a heat fixation process, a winding and slitting process, and an unwinding process after the plasticizer extraction process.

Herein, the winding process refers to a step of winding the composite separator obtained after slurry coating and heat setting on the porous polyolefin film obtained through the extrusion / drawing / extraction steps onto a roller, and the slitting process is a process in which the composite separator And the unnecessary portions of both ends are cut at the time of winding of the wire. In the conventional method, it is necessary to wind the porous polyolefin film after the heat-setting and the slitting process, and then to unwind the film again to unwind the film to be slurry-coated. After the slurry coating and drying process, After the process, it finally reached the packaging stage.

At this time, according to one embodiment of the present invention, by reducing the winding and the slitting process from the conventional two to one, it is possible to prevent the loss of a part of the porous polyolefin film according to the winding and the slitting process, have.

In addition, since the unwinding step is omitted after the winding and slitting steps before the slurry coating step, space utilization and process cost can be reduced. In addition, since the slitting process before the slurry coating step or the winding / unwinding process is not performed, it is possible to perform a large-area coating with a large width, and the occurrence of defects such as wrinkles, pinholes and scratches between the final separators can be greatly reduced, The area also decreases. ,

Further, in place of the two separate heat treatment steps of the heat fixation step after the conventional plasticizer extraction and the drying step after the slurry coating, it is improved to a single heat treatment step of the heat fixation step after slurry coating, Without using an oven, only one heat-stable oven can be used, allowing space utilization and cost savings.

According to one aspect of the present invention, a separation membrane for an electrochemical device includes: a porous polymer film; And a porous flame retardant coating layer formed on one side or both sides of the porous polymer film including flame retardant particles, inorganic particles, and a binder polymer, wherein the porous polymer film has a plurality of fibrils arranged in parallel with the surface of the film, Wherein the diameter of the fibrils located on one side of the film on which the porous flame retardant coating layer is formed is smaller than the diameter of the fibrils located in the center of the film thickness direction.

Here, the fibril means that the chains of the polymer constituting the porous polymer film are stretched and oriented in the longitudinal direction in the course of producing the film, so that the binding force between the adjacent molecular chains is increased and formed in the longitudinal direction. As a result, the porous polymer film has a structure in which a plurality of fibrils arranged in parallel to the surface of the film are laminated in the form of a layer.

On the other hand, in order to prepare a separation membrane having a porous flame retardant coating layer formed by a conventional wet process, a resin composition is extruded / cast, drawn, extracted and then heat set to prepare a porous polymer film. Then, a coating slurry is applied to the porous polymer film . The separation membrane formed with the porous flame retardant coating layer thus formed has a fibril structure in a drawing process after solid / liquid phase or liquid / liquid phase separation, and the final structure is determined through heat fixation. That is, in the conventional method, since the slurry is not coated and the porous polymer film is kept open before the porous flame retardant coating layer is formed, the heat received by the porous polymer film during the open time is uniform as a whole, And is constant with respect to the thickness direction of the film.

First, in the case of a separation membrane in which a porous flame retardant coating layer is formed on only one surface of a porous polymer film, the effect of the direct application of the open and the indirect and indirect application is well known. When the porous flame retardant coating layer is formed only on one side of the porous polymer film, when the porous flame retardant coating layer is formed and then the heat fixing is applied, the porous polymer film is indirectly heated in the state where there is slurry for porous coating, do. On the other hand, if heat fixation is directly applied to a porous polymer film on which a porous flame retardant coating layer is not formed, since the porous polymer film is directly heated, partial crystallization is increased due to partial melting-recrystallization, . As a result, a gradient in which the fibril diameter gradually increases in the thickness direction of the film from the surface of the film having the porous flame retardant coating layer to the other surface where the porous flame retardant coating layer is not formed tends to be generated. On the contrary, when the slurry is coated after the heat-setting of the porous polymer film like the conventional method, the fibril diameter has a constant value in all of the thickness direction of the film. That is, the diameter of the fibrils located on the surface of the film on which the porous flame retardant coating layer is formed is smaller than the diameter of the fibrils located in the center of the film thickness direction.

In the case where the porous flame retardant coating layer as an embodiment of the present invention is a separation membrane formed on both surfaces of the porous polymer film, the surface on which the coating layer is formed is indirectly heated in the state where the slurry is coated on the upper and lower surfaces of the porous polymer film But the central portion of the film thickness direction receives heat directly through the left and right sides of the film without the coating layer. As a result, the diameter of the fibrils located on the surface of the film on which the porous flame retardant coating layer is formed becomes smaller than the diameter of the fibrils located in the central portion in the film thickness direction.

Of course, even when the porous flame retardant coating layer is formed only on one side of the porous polymer film, the diameter of the fibrils located on the surface of the film having the porous flame retardant coating layer is smaller than the diameter of the fibrils located in the center of the film thickness direction.

According to an embodiment of the present invention, the diameter of the fibrils located on one side of the film formed with the porous flame retardant coating layer is 2 to 4 times smaller than the diameter of the fibrils located in the center of the film thickness direction, preferably 2 to 3 It is small.

The diameter of the fibrils located on one side of the film having the porous flame retardant coating layer may be 0.01 to 0.04 mu m and the diameter of the fibrils located in the center of the film thickness direction may be 0.04 to 0.08 mu m.

As described above, when the porous flame retardant coating layer is formed on only one side of the porous polymer film, the diameter of the fibrils located on one side of the film formed with the porous flame retardant coating layer is smaller than that of the non- It is smaller than the diameter of the fibrils.

In this case, the diameter of the fibrils located on one side of the film formed with the porous flame retardant coating layer is 2 to 7 times smaller than the diameter of the fibrils located on the other side of the film on which the porous flame retardant coating layer is not formed, preferably 4 to 7 times small.

Specifically, when the porous flame retardant coating layer is formed on only one side of the porous polymer film, the diameter of the fibrils located on one side of the film having the porous flame retardant coating layer is 0.01 to 0.07 탆, The diameter of the fibrils located on the other side of the substrate may be 0.07 to 0.14 mu m.

Also, since the density of the fibrils per unit surface area of the porous polymer film formed with the porous flame retardant coating layer is increased, the interface contact area with the coating slurry is increased and the wettability of the slurry with respect to the polyolefin porous fibrous structure can be improved .

Further, the mechanical strength of the separator can be maximized by heat setting, and the air permeability and the ion conductivity can also be improved.

The binder polymer is located on the surfaces of neighboring particles and forms a porous structure while connecting them to each other. The size of the binder polymer located on the surface of the particles is 10 to 100 nm, preferably 10 to 50 nm.

According to an aspect of the present invention, there is provided an electrochemical device including a cathode, an anode, and a separator interposed between the cathode and the anode, wherein the separator is the separator for the electrochemical device.

Such an electrochemical device may be manufactured according to a conventional method known in the art, and may be manufactured, for example, by injecting an electrolytic solution after assembling the cathode and the anode with the separator interposed therebetween have.

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 above-described embodiments. Embodiments of the invention are provided to more fully describe the present invention to those skilled in the art.

Example  One

High-density polyethylene having a weight average molecular weight of 300,000 as a polyolefin and liquid paraffin having a kinematic viscosity of 40.00 cSt as a plasticizer at a weight ratio of 35:65 were extruded at a temperature of 135 ° C. The stretching temperature was 100 占 폚 in the longitudinal direction and 120 占 폚 in the transverse direction, and the stretching ratio was 5.5 times in the longitudinal direction. Subsequently, liquid paraffin, which is a plasticizer, was extracted at a rate of 2 m / min using methylene chloride as an extraction solvent to obtain a porous polyolefin film having an average pore size of 0.04 μm.

Next, as a slurry for forming the porous flame retardant coating layer, Al (OH) ₃ (APYRAL 60D, Nabaltec) / AlOOH (ACTILOX 200SM, Nabaltec) / Mg (OH) ₂ (APYMAG 100, Nabaltec) / cyanoethylpolyvinyl alcohol / PVDF-HFP5 / PVDF-HFP15 / acetone were mixed so as to have a weight ratio of 7.85 / 4.71 / 3.14 / 0.3 / 0.8 / 2.7 / 80.5.

The slurry was coated on both surfaces of the porous polyolefin film to the plasticizer extraction process to a thickness of 5.0 탆 and then heat-set at 132 캜 at 5 m / min to prepare a 25.4 탆 thick separation membrane having a porous flame retardant coating layer .

Example  2

The same polyolefin film as used in Example 1 was prepared.

Next, as a slurry for forming a porous flame retardant coating layer, Al (OH) ₃ (APYRAL 60D, Nabaltec) / Mg (OH) ₂ (APYMAG 100, Nabaltec) / cyanoethylpolyvinyl alcohol / PVDF-HFP5 / PVDF- Acetone was prepared by mixing to have a weight ratio of 7.85 / 7.85 / 0.3 / 0.8 / 2.7 / 80.5.

The slurry was coated on both surfaces of the porous polyolefin film to the plasticizer extraction process to a thickness of 5.0 탆 and then heat-set at 132 캜 at 5 m / min to prepare a 25.0 탆 thick separation membrane having a porous flame retardant coating layer .

Example  3

The same polyolefin film as used in Example 1 was prepared.

Subsequently, AlOOH (ACTILOX 200SM, manufactured by Nabaltec) / cyanoethylpolyvinyl alcohol / PVDF-HFP5 / PVDF-HFP15 / acetone was mixed at a weight ratio of 15.7 / 0.3 / 0.8 / 2.7 / 80.5 as a slurry for forming a porous flame- Respectively.

The slurry was coated on both surfaces of the porous polyolefin film to the plasticizer extraction step to a thickness of 5.0 탆 and then heat-set at 132 캜 at 5 m / min to prepare a 24.4 탆 thick separation membrane having a porous flame retardant coating layer .

Comparative Example  One

The same polyolefin film as used in Example 1 was prepared.

The porous polyolefin film was thermally fixed at 132 캜 at a rate of 5 m / min,

Subsequently, a slurry obtained by mixing Al ₂ O ₃ particles / cyanoethylpolyvinyl alcohol / PVDF-HFP 5 / PVDF-HFP 15 / acetone so as to have a weight ratio of 15.7 / 0.3 / 0.8 / 2.7 / 80.5 was applied to both surfaces of the porous polyolefin film To prepare a separation membrane having a thickness of 25.7 탆 in which a coating layer was formed.

Next, aeration time, loading, heat shrinkage, and nail penetration test of each of the separators for electrochemical devices according to Examples 1 to 3 and Comparative Examples were measured, and the results are shown in Table 1 below.

(1) Measurement of ventilation time

The time (sec) taken for 100 ml of air to pass through the separator was measured at a constant pressure (0.05 MPa) using an air flow meter (manufacturer: Asahi Seiko, product name: EG01-55-1MR). A total of 3 points were measured for each point of left / middle / right of the sample, and the average was recorded.

(2) Heat shrinkage

The membrane sample (size: 50 mm x 50 mm) was stored at 120 ° C and 60 min using a convection oven and the length of the part where the shrinkage was most severely occurred at room temperature was measured using a steel ruler. The heat shrinkage ratio Respectively. A total of 3 points were measured for each 1 point of left / middle / right of the sample, and the average was recorded.

Heat shrinkage percentage (%) = [1- (length of shrinkage most severe portion) / (initial length)] X 100

(3) Nail penetration test

Polymer batteries were fabricated and penetrated through 2.5mm diameter nails at full speed (4.4V) at a rate of 5m / min to determine the occurrence of ignition. In the nail penetration test, the 'pass' criteria means no ignition or explosion.

division Example  One Example  2 Example  3 Comparative Example Ventilation time Sec / 100cc 878 885 895 1057 Loading amount g / m ² 12.3 13.3 12.1 18.2 Heat shrinkage (%)
(150 DEG C / 30 minutes) MD <35 <30 <35 <50 TD <25 <25 <25 <35 Nail penetration
Test Pass / Fail 5/0 5/0 5/0 4/1 Maximum temperature of the passed cell (℃) 58.8 67.3 77.8 123

Referring to the results shown in Table 1, it can be seen that the separation membranes of Examples 1 to 3 having coating layers containing flame retardant particles are excellent in heat resistance of the separation membranes of Examples 1 to 3 according to the present invention, have.

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 goes without saying that various modifications and variations are possible within the scope of equivalence of the scope.

Claims (24)

Extruding a resin composition containing a polyolefin and a plasticizer;
Stretching the extruded resin composition to obtain a polyolefin film;
Extracting the plasticizer from the obtained polyolefin film to obtain a porous polyolefin film;
Coating at least one surface of the porous polyolefin film with a slurry for forming a porous flame retardant coating layer; And
Wherein the slurry-coated porous polyolefin film is heat-set to obtain a composite separator having a porous flame-retardant coating layer formed thereon. The method according to claim 1,
Wherein the slurry for forming a porous flame retardant coating layer comprises flame retardant particles, inorganic particles, a binder polymer, and a solvent. 3. The method of claim 2,
Wherein the flame-retardant particles are hydroxides containing one or more elements selected from the group consisting of aluminum, magnesium, silicon, zirconium, calcium, strontium, barium, antimony, tin, zinc, and rare earth elements. (2). 3. The method of claim 2,
Wherein the flame-retardant particles are at least two selected from the group consisting of aluminum hydroxide, magnesium hydroxide and boehmite. The method according to claim 1,
The binder polymer may be at least one selected from the group consisting of polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichlorethylene, polymethylmethacrylate, Polybutylene terephthalate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide (polyethylene) oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpyrrolidone, Polyvinyl alcohol (cyanoethylpolyviny a mixture of two or more selected from the group consisting of lanolin, lanolin, lanolin, cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxyl methyl cellulose. Wherein the separating film is formed on the substrate. The method according to claim 1,
Wherein the extruded resin composition is subjected to uniaxial stretching at least once in the MD direction or TD direction or by biaxial stretching at least once in the MD and TD directions. The method according to claim 1,
Wherein the open and the defined temperature are Tm - 1 DEG C or less, wherein Tm is the melting point of the polyolefin. The method according to claim 1,
Wherein the heat setting is performed using a heat source oriented in a direction perpendicular to the surface of the slurry coated on the porous polyolefin film. The method according to claim 1,
Wherein the polyolefin is selected from the group consisting of polyethylene; Polypropylene; Polybutylene; A process for producing a separator for electrochemical devices, which comprises: a polyphenylene: polyhexene: polyolefin: at least one copolymer selected from the group consisting of ethylene, propylene, butene, pentene, 4-methylpentene, hexene and octene; Way. The method according to claim 1,
Examples of the plasticizer include 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 at least one selected from the group consisting of aliphatic acid esters and fatty acid esters. The method according to claim 1,
Further comprising the step of winding and slitting the composite separator. &Lt; Desc / Clms Page number 19 &gt; The method according to claim 1,
Wherein the step of coating the slurry for forming a porous coating layer does not include a step of heat setting and a step of winding and slitting. 13. The method of claim 12,
The method of claim 1, further comprising packaging the composite separator after completion of the winding and slitting. Porous polymer films; And
And a porous flame retardant coating layer formed on one side or both sides of the porous polymer film including flame retardant particles, inorganic particles, and a binder polymer,
Wherein the porous polymer film has a structure in which a plurality of fibrils arranged in parallel to the surface of the film are laminated in the form of a layer, and the diameter of the fibrils located on one side of the film on which the porous flame retardant coating layer is formed, A separation membrane for electrochemical devices smaller than the diameter of the fibrils in place. 15. The method of claim 14,
Wherein the diameter of the fibrils located on one side of the film on which the porous flame retardant coating layer is formed is 2 to 4 times smaller than the diameter of the fibrils located in the center of the film thickness direction. 15. The method of claim 14,
Wherein the diameter of the fibrils located on one side of the film having the porous flame retardant coating layer is 0.01 to 0.04 mu m and the diameter of the fibrils located in the center of the film thickness direction is 0.04 to 0.08 mu m. 15. The method of claim 14,
And a porous flame retardant coating layer formed only on one side of the porous polymer film, wherein the diameter of the fibrils located on one side of the film having the porous flame retardant coating layer is smaller than the diameter of the fibrils located on the other side of the film on which the porous flame retardant coating layer is not formed Lt; RTI ID = 0.0 &gt; 1, &lt; / RTI &gt; 18. The method of claim 17,
Wherein the diameter of the fibrils located on one side of the film formed with the porous flame retardant coating layer is 2 to 7 times smaller than the diameter of the fibrils located on the other side of the film on which the porous flame retardant coating layer is not formed. 18. The method of claim 17,
Wherein the diameter of the fibrils located on one side of the film having the porous flame retardant coating layer is 0.01 to 0.07 mu m and the diameter of the fibrils located on the other side of the film having no porous flame retardant coating layer is 0.07 to 0.14 mu m. Membranes for devices. 15. The method of claim 14,
Wherein the binder polymer is located on the surface of neighboring particles and forms a porous structure by connecting the particles to each other, and the size of the binder polymer is 10 to 100 nm. 15. The method of claim 14,
Wherein the flame-retardant particles are hydroxides containing one or more elements selected from the group consisting of aluminum, magnesium, silicon, zirconium, calcium, strontium, barium, antimony, tin, zinc, and rare earth elements. Separation membrane. 15. The method of claim 14,
Wherein the flame-retardant particles are at least two kinds selected from the group consisting of aluminum hydroxide, magnesium hydroxide and boehmite. An electrochemical device comprising a cathode, an anode, and a separator interposed between the cathode and the anode,
The electrochemical device according to any one of claims 14 to 22, wherein the separation membrane is a separation membrane for an electrochemical device. 24. The method of claim 23,
Wherein the electrochemical device is a lithium secondary battery.