KR101674988B1 - Method for manufacturing separator, the separator and battery using the separator - Google Patents

Abstract

The present invention relates to a process for producing a polyolefin-based separator, a separator capable of securing battery stability by improving the heat shrinkage rate and the air permeability in the transverse direction by using a pore nozzle in a heat fixation process during the separation membrane production process, And a battery using the same.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a separator,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a process for producing a separator, a separator thereof, and a battery using the same.

A separator for an electrochemical cell means an interlayer that keeps the ion conductivity constant while isolating the positive electrode and the negative electrode from each other in the battery to enable charging and discharging of the battery. In recent years, electrochemical cells for increasing the portability of electronic devices have become lightweight and miniaturized, and at the same time, they are required to have excellent heat stability for the production of high capacity batteries.

The thermal stability of the battery is affected by the shutdown temperature and heat shrinkage of the separator. Particularly, the heat shrinkage ratio in the transverse direction (TD) at high temperature has a great influence on the thermal stability of the battery. If the heat shrinkage ratio in the transverse direction is high, the end portion of the electrode is exposed in the transverse direction during the shrinking process when the inside of the cell becomes hot, so that short-circuiting occurs between the electrodes, do.

Therefore, various solutions such as raw material change and process condition control were suggested. For example, a method of improving the heat shrinkage ratio of a separator by incorporating meta-aramid (Korean Patent Registration No. 10-1377476) is disclosed. However, since the separator itself is limited to a specific composition, There is a limitation that it can not be applied.

Korean Registered Patent No. 10-1377476 (Bulletin of Mar. 26, 2014)

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It is an object of the present invention to provide a method of improving the heat shrinkage ratio applicable to various separators without limiting the composition of the separator to a specific component.

Specifically, it is possible to provide a separator which is excellent in battery stability by preventing a short circuit between electrodes by providing a method of manufacturing a separator having a high heat shrinkage ratio in a transverse direction (TD, Transverse Direction) at a high temperature while satisfying basic properties of the separator. ≪ / RTI >

Further, it is an object of the present invention to provide a separation membrane exhibiting low air permeability and a manufacturing method thereof, and to provide an electrochemical cell having excellent performance.

The present invention provides a separation membrane manufacturing method capable of securing a heat shrinkage ratio and a low air permeability in a transverse direction of a separation membrane by adjusting a heat fixing step.

According to one aspect of the present invention, there is provided a process for producing a sheet, comprising: forming a sheet with a composition comprising a polyolefin resin and a plasticizer; stretching the sheet longitudinally and transversely; extracting the plasticizer from the stretched sheet; Wherein the heat setting is performed using a pore nozzle having a perforated surface having a plurality of pores, wherein the perforation rate of the perforated surface is 3 to 10% And a manufacturing method thereof.

According to another aspect of the present invention, there is provided a thermoplastic resin composition comprising a polyolefin resin and having a heat shrinkage of 3% or less in a transverse direction (TD) measured after being left at 120 ° C for 1 hour and having an air permeability of 150 sec / 100 cc or less , And a polyolefin-based separation membrane.

According to still another embodiment of the present invention, there is provided a polyolefin-based substrate film comprising a polyolefin-based resin and having a heat shrinkage of 3% or less in a transverse direction (TD) measured after being left at 120 ° C for 1 hour; And a coating layer formed on one surface or both surfaces of the polyolefin-based film.

According to another aspect of the present invention, there is provided a polyolefin-based separator according to one aspect of the present invention, which comprises a positive electrode, a negative electrode and an electrolyte, and interposed between the positive electrode and the negative electrode, the coating separator according to one aspect of the present invention, The present invention also provides an electrochemical cell comprising the polyolefin-based separation membrane produced by the method according to one aspect of the present invention.

The separation membrane according to one aspect of the present invention provides a separation membrane or a coating separation membrane with improved heat shrinkage in a transverse direction at a high temperature, thereby improving the resistance to lateral thermal shrinkage occurring when the battery is overheated.

Further, by using a separation membrane or a coating separation membrane excellent in heat resistance for a battery, it is possible to provide a battery excellent in stability against heat, which can prevent a short circuit between electrodes and prevent a battery explosion due to overheating.

In addition, by using the pore nozzle in the heat fixing step of the manufacturing method of the separation membrane, the lateral heat shrinkage rate can be reduced regardless of the composition of the separation membrane, and it is more efficient to control the heat shrinkage rate than the conventional method.

Further, there is an advantage that a low air permeability separator is provided, and electrochemical electricity having sufficient output and charge capability can be provided.

1 is a schematic view of a pore nozzle 100 used in an embodiment of the present invention.
FIG. 2 shows only the perforated surface 102 formed with the perforations 104 in the perforated nozzle 100 of FIG.
3 is a schematic view showing the distance D between the separation membrane 200 and the pore nozzle in the heat fixing process in the separation membrane production method of one embodiment of the present invention.

Hereinafter, the present invention will be described in more detail. Those skilled in the art will appreciate that various modifications, additions, and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

A method of producing a polyolefin-based separator according to an embodiment of the present invention comprises: forming a sheet with a composition comprising a polyolefin-based resin and a plasticizer; stretching the sheet longitudinally and transversely; extracting the plasticizer; And the like. Further, the method may further include a step of winding afterward, and the thermal fixation may be performed using a punch nozzle having a perforated surface having a plurality of perforations.

Hereinafter, a method of manufacturing a separation membrane according to an embodiment of the present invention will be described in more detail.

Film forming process

A composition comprising a polyolefin resin and a plasticizer is melt-kneaded and extruded to form a cooled solidified sheet. The composition including the polyolefin-based resin and the plasticizer may be melt-kneaded using a method known to those skilled in the art.

Specifically, the polyolefin-based resin and plasticizer are melted and kneaded at a temperature of 100 to 250 ° C., injected into a twin-screw extruder and extruded, cooled using a casting roll at 20 to 90 ° C., The film can be forcibly cooled to crystallize the film to form a solidified sheet. The temperature of the cold air blown from the air knife may be 20 ° C to 90 ° C.

Non-limiting examples of the polyolefin resin include polyethylene (PE), polypropylene (PP), poly-4-methyl-1-pentene (PMP) . These may be used alone or in combination of two or more. That is, the polyolefin-based resin may be used alone, or a copolymer or a mixture thereof may be used.

Specifically, a polyethylene resin may be used. For example, a high density polyethylene (HDPE) having a weight average molecular weight (Mw) of 100,000 g / mol to 1,000,000 g / mol or a weight average molecular weight of 1,000,000 g / mol (Ultrahigh Molecular Weight Polyethylene, UHMWPE). Specifically, the weight average molecular weight of the ultrahigh molecular weight polyethylene may be 2,000,000 to 4,000,000 g / mol.

The polyolefin-based resin may be contained in an amount of 20 to 50% by weight, specifically 20 to 40% by weight, based on the total weight of the composition including the polyolefin-based resin and the plasticizer. When high-density polyethylene and ultra-molecular-weight polyethylene are mixed and used, 80 to 90% by weight of high-density polyethylene and 10 to 20% by weight of ultra-high-molecular-weight polyethylene can be contained relative to the total weight of polyolefin resin.

In addition, other resins other than the polyolefin-based resin may be used together with the polyolefin-based resin, and the composition comprising the polyolefin-based resin and the plasticizer may contain an inorganic material. Non-limiting examples of the inorganic substance include alumina, calcium carbonate, silica, barium sulfate and talc. These may be used alone or in combination of two or more.

The type of plasticizer used in this embodiment is not particularly limited and may be any organic compound that forms a single phase with the polyolefin resin (or a mixture of polyolefin resin and other resin) at the extrusion temperature.

Nonlimiting examples of such plasticizers include liquid paraffin (or paraffin oil) such as nonan, decane, decalin, liquid paraffin (LP), aliphatic or cyclic hydrocarbons such as paraffin wax ; Phthalic acid esters such as dibutyl phthalate and dioctyl phthalate; Fatty acids having 10 to 20 carbon atoms such as palmitic acid, stearic acid, oleic acid, linoleic acid and linolenic acid; Fatty acid alcohols having 10 to 20 carbon atoms such as palmitic alcohol, stearic acid alcohol and oleic acid alcohol. These may be used alone or in combination of two or more. For example, liquid paraffin may be used as the plasticizer. Liquid paraffin is harmless to the human body, has a high boiling point and low volatile components, so it has properties suitable for use as a plasticizer in a wet process.

The plasticizer may be contained in an amount of 50 to 90% by weight, specifically 60 to 80% by weight based on the total weight of the composition including the polyolefin resin and the plasticizer.

Stretching  fair

Then, a step of stretching the solidified sheet is performed. In the method of manufacturing a separation membrane according to an embodiment of the present invention, the stretching process is performed before the plasticizer is extracted, so that the polyolefin is softened by the plasticizer to make the stretching work easier, thereby improving the production stability. Further, as a result of thinning of the sheet due to stretching, the plasticizer can be more easily removed from the sheet during the extraction process after stretching.

Specifically, the solidified sheet can be stretched in the machine direction (MD) and the transverse direction (TD) (biaxial stretching), and the biaxial stretching can be performed by stretching the solidified sheet in the longitudinal and transverse directions (Simultaneous stretching) or stretching in the first longitudinal direction (or transverse direction), and then stretching in the transverse direction (or longitudinal direction) (stretching stretching).

Specifically, the biaxial stretching of the present embodiment can be performed by the streak stretching method. In accordance with the biaxial stretching method of the present invention, the difference in stretching ratio between the gripping region and the non-flapping region can be reduced by the sheet binding apparatus, thereby ensuring the uniformity of the quality of the final stretched product and preventing the separation of the sheet from the sheet- There is an advantage that stability can be secured.

In the stretching, the temperature condition can be suitably adjusted to various temperature ranges, and the physical properties of the separator manufactured according to the temperature condition to be performed can be varied. For example, the stretching can be performed at 90 to 140 占 폚, specifically 100 to 120 占 폚 in the MD direction and 100 to 135 占 폚 in the TD direction, and the stretching in the TD direction can be performed at a temperature higher than the MD direction. When stretched in the above-mentioned range, it can be stretched so as to have proper air permeability and mechanical strength without blocking the pores in the sheet. The stretching magnification can be 4 to 9 times in the MD direction, 4 to 9 times in the TD direction, and specifically 5 to 8 times in the MD and TD directions.

Plasticizer Extraction Process

The plasticizer can be extracted from the stretched sheet.

Specifically, the longitudinally stretched and transversely stretched sheets may be immersed in an organic solvent in a plasticizer extracting apparatus, followed by extracting the plasticizer, followed by drying.

The organic solvent used for the plasticizer extraction is not particularly limited, and any solvent capable of extracting the plasticizer can be used. Non-limiting examples of the organic solvent include halogenated hydrocarbons such as methylene chloride, 1,1,1-trichloroethane, and fluorocarbon which have high extraction efficiency and are easy to dry; hydrocarbons such as n-hexane and cyclohexane; Alcohols such as ethanol and isopropanol; Ketones such as acetone and 2-butanone; and when liquid paraffin is used as the plasticizer, methylene chloride can be used as an organic solvent. Since the organic solvent used in the step of extracting the plasticizer is highly volatile and toxic, water can be used if necessary to suppress the volatilization of the organic solvent.

Freeze heat  fair

After the plasticizer is extracted, a heat fixation step may be performed. The heat fixation process is for reducing the residual heat stress of the dried sheet to reduce the heat shrinkage rate in the transverse direction of the final sheet. By controlling the process parameters, physical properties such as air permeability and heat shrinkage ratio of the separator can be controlled.

The main process parameters of the heat setting process are temperature, hot wind, and fixed ratio. Particularly, the factors related to the heat quantity affecting the properties of the lateral shrinkage ratio are the temperature and the hot wind treatment in an open / close period (for example, a tenter), and the lateral heat shrinkage ratio of the separator can be controlled by the temperature and the hot wind treatment conditions.

In this embodiment, by controlling the temperature and the hot air using the pore nozzle in the heat fixing step, the air permeability of the separator and the heat shrinkage ratio in the transverse direction at high temperature can be improved without deteriorating the productivity of the separator. In addition, it is possible to suppress the phenomenon that the separation membrane is not melted and broken due to the long time exposure to high temperature.

Hot air can be injected through a slit, a perforation, or the like formed in the nozzle, and the heat shrinkage rate of the separation membrane can be controlled according to the difference in amount of hot air introduced by the slit or the perforated surface. Conventionally, a nozzle having a single slit shape has been used in a process of heat-setting a sheet extracted with a thermoplasticizer. In the case of using a nozzle having a single slit shape, since the shape of the nozzle is long and thin, the hot air is sprayed with a stronger pressure against the horizontal surface of the nozzle, A separation membrane having a large variation in heat shrinkage ratio was produced, and it was difficult to secure the cell stability. In the heat fixing process of this embodiment, by using the punch nozzle, hot air is more uniformly applied, thereby improving the heat shrinkage rate without changing the composition of the separator and increasing the heat fixing time. Further, Improvement can be achieved.

1 to 3, the heat fixing process during the separation membrane manufacturing process of this embodiment will be described in detail.

In performing the heat fixation process of this embodiment, a punch nozzle 100 having a plurality of perforations 102 formed in a metal plate may be used (see FIG. 1).

The perforation rate of the pore nozzle 100 used in this embodiment may be 3 to 10%, and may be 3 to 5%. The heat shrinkage rate in the transverse direction decreases and the low air permeability can be exhibited in the range of the perforation rate, and the stability of the battery with respect to heat can be secured. The term "perforation rate" as used herein means a perforation rate of a surface 102 having perforations formed with a plurality of perforations 104 on one surface of the perforated nozzle 100, and the perforation surface 102 has a plurality of (Refer to Fig. 2). The perforations 104 formed on the perforated surface 102 may be the same or different, and the perforation ratio may be a sum of the areas of the perforations with respect to the total area of the perforated surface 102 (hatched portions in FIG. 2) For example, the perforation rate of the perforated surface 102 having a plurality of perforations 104 having a diameter of n (mm) can be calculated by the following equation (1).

[Formula 1]

Percentage of perforation (%) = [(area of perforation having diameter n x number of perforations having diameter n) / total area of perforated surface] x 100

In addition, the diameter of the perforations 104 formed in the pore nozzle 100 used in the present embodiment may be 3 mm to 20 mm, and may be 4 mm to 10 mm. The hot air is uniformly dispersed within the above range, so that the heat resistance of the separator can be improved.

The perforated surface may be horizontally arranged in the plane direction of the separator, and may be located within 5 cm from one surface of the separator 200 to spray hot air 300 (see FIG. 3). Specifically, the distance D between the perforated surface 102 and the separation membrane 200 can be 2 cm to 3 cm, and the separation of the separation membrane 300 during the hot-air blowing operation 300 can be reduced within the above range, And an even heat shrinkage ratio can be exhibited, so that the cell stability can be improved.

In addition, the thermal fixation process of this embodiment can be performed in a tenter, and the transverse stretching and / or transverse relaxation can be repeatedly performed one or more times, depending on the strength, heat shrinkage rate, etc. of the desired separation membrane. As a volume, the heat fixation step may be a step of stretching and / or relaxing (shrinking) the dried sheet after extraction of the plasticizer in at least one axial direction. For example, the heat fixation may be stretching and relaxation And the order of stretching and relaxation is not particularly limited. For example, after performing the transverse stretching, the transversely stretched sheet may be further relaxed in the transverse direction. The heat shrinkage ratio of the separator can be improved through heat fixation by drawing and relaxation to enhance the heat resistance. Specifically, the heat-setting step may include stretching in a transverse direction at a draw ratio of 1 to 2 times and relaxation at 80% to 100% with respect to the transverse direction length. In this range, the pore size and thermal , Mechanical properties can be secured.

Also, the open-and-off temperature conditions can be appropriately adjusted to various temperature ranges, and the physical properties of the separator manufactured according to the temperature conditions to be performed can be varied. The temperature at the time of transverse stretching and / or transverse shrinkage may be 100 to 140 캜, for example, 110 to 140 캜, and specifically 120 to 140 캜. The shrinkage rate can be controlled by adjusting the temperature within the above range.

Thereafter, the transversely stretched sheet is wound to produce a polyolefin-based separator having an average thickness of 7 to 20 탆.

In addition, the permeability of the membrane of this embodiment may be 200 sec / 100 cc or less, specifically 150 sec / 100 cc or less, more specifically 100 to 150 sec / 100 cc. Within the above range, the pores formed in the separation membrane are sufficiently opened, so that the ion conductivity is excellent and the cell output and cell performance can be improved. The method for measuring the air permeability of the separation membrane is not particularly limited, and a non-limiting example of the method for measuring the air permeability is as follows: Ten specimens cut at 10 different points are prepared, Seiko Instruments Inc.) is used to measure the average time taken for each 100 cm diameter air to permeate through a 1 inch diameter circular membrane in each of the above specimens, five times each, and the average value is then measured to determine the air permeability.

The tensile strength of the separator of this embodiment may be not less than 1800 kgf / cm ² in longitudinal direction and more specifically not less than 1900 kgf / cm ^{2 in} longitudinal direction and not less than 2000 kgf / cm ^{2 in} transverse direction, Lt; ² > kgf / cm < ² > in longitudinal and transverse directions, respectively. The intensity can be controlled in the above range. The method for measuring the tensile strength of the separation membrane is not particularly limited, and a method commonly used in the technical field of the present invention can be used. The non-limiting examples of the method for measuring the tensile strength of the separator are as follows: The prepared separator was divided into 10 pieces of 10 pieces cut at 10 different points in a rectangular shape of 10 mm x MD (TD) 50 mm in width (MD) Each specimen is mounted on a UTM (tensile tester) to measure a length of 20 mm, and the specimen is pulled to measure the average tensile strength in the MD and TD directions.

The penetration strength of the membrane of this embodiment may be 400 gf or more, specifically 500 gf or more, or 500 to 600 gf or more. The penetration strength can be controlled within the above range, and the method of measuring the penetration strength of the separation membrane is not particularly limited. As a method of measuring the sting intensity, a method commonly used in the technical field of the present invention can be used. Non-limiting examples of the method of measuring the sting intensity of the separation membrane are as follows: ) Ten specimens cut out at 10 different points with 50 mm × 50 mm length (TD) were prepared. The specimens were placed on a 10 cm hole using a KATO Tech G5 instrument and punched with a 1 mm probe. The force is measured, and the puncture strength of each specimen is measured three times each, and then the average value is calculated.

According to still another aspect of the present invention, there is provided a polyolefin-based substrate film comprising a polyolefin-based resin and having a heat shrinkage of 3% or less in a transverse direction (TD) measured after being left at 120 ° C for 1 hour; And a coating layer formed on one or both surfaces of the polyolefin-based film. The thermal shrinkage of the coating separator in the transverse direction (TD) measured after being left at 120 ° C for 1 hour may be 3%, specifically 2% or less, more specifically 1% or less.

In addition, the air permeability of the coating separation membrane of this embodiment may be 200 sec / 100 cc or less, specifically 100 to 200 sec / 100 cc.

The tensile strength of the coating separator of this embodiment may be 1,500 kgf / cm ^{2 or} more in the longitudinal direction and 560 kgf / cm ² or more in the transverse direction, and may be 1,600 kgf / cm ² or more in the transverse direction and 1,500 kgf / cm ² or more in the longitudinal direction .

In addition, the penetration strength of the coating separation membrane of this embodiment may be 300 gf or more, specifically 400 gf or more, for example, 400 to 600 gf or so.

The method of measuring the heat shrinkage, air permeability, tensile strength and sting intensity of the polyolefin-based coating separating membrane according to the present embodiment is substantially the same as the method of measuring the physical properties of the polyolefin-based separator described above, and thus will not be described herein.

Hereinafter, a method of forming the coating layer of the present embodiment will be described in detail.

The coating layer of this embodiment may be formed of a coating composition, which may comprise an organic binder, and a solvent. The coating composition may further comprise inorganic particles.

The polyolefin-based film may be a polyolefin-based separator prepared by the method described in this specification or described herein.

Specifically, the organic binder is selected from the group consisting of polyvinylidene fluoride (PVdF) homopolymer, polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), polymethyl methacrylate polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate butyrate, , Cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, pullulan), carboxymethyl Carboxyl methyl cellulose, and acrylonitrile styrene-butadiene copolymer, or a mixture thereof.

Specifically, for example, a PVdF binder may be used, and the PVdF binder may have a weight average molecular weight (Mw) of 500,000 to 1,500,000 (g / mol) and may be used in combination of two or more different weight average molecular weights have. For example, one or more species having a weight average molecular weight of 1,000,000 g / mol or less and one or more species having a weight average molecular weight of 1,000,000 g / mol or more may be used in combination.

Use of a PVdF binder within the molecular weight range improves the adhesion between the coating layer and the polyolefin-based base film, effectively suppressing heat-shrinking of the polyolefin-based base film, which is weak to heat, and further enhancing the electrolyte- It is possible to produce a battery in which an electric output can be efficiently produced by utilizing it.

The inorganic particles used in this embodiment are not particularly limited, and inorganic particles that are conventionally used in the art can be used. Non-limiting examples of the inorganic particles usable in the present invention include Al ₂ O ₃ , SiO ₂ , B ₂ O ₃ , Ga ₂ O ₃ , TiO _2, and SnO ₂ . These may be used alone or in combination of two or more. As the inorganic particles used in the present invention, for example, Al ₂ O ₃ (alumina) can be used.

The size of the inorganic particles used in this embodiment is not particularly limited, but may be an average particle diameter of 1 to 2,000 nm, for example, 100 to 1,000 nm. In the case of using the inorganic particles having the above-mentioned size range, it is possible to prevent degradation of the dispersibility of the inorganic particles and the processability of the coating in the coating liquid, and the thickness of the coating layer can be appropriately controlled to prevent deterioration of mechanical properties and increase in electrical resistance . In addition, the size of the pores generated in the separation membrane is appropriately controlled, thereby reducing the probability of an internal short circuit occurring during charging and discharging of the battery.

In the preparation of the coating composition, the inorganic particles may be used in the form of an inorganic dispersion in which the inorganic particles are dispersed in an appropriate solvent. The suitable solvent is not particularly limited, and solvents commonly used in the art may be used. As an appropriate solvent for dispersing the inorganic particles, for example, acetone may be used.

In the coating layer, the inorganic particles may be contained in an amount of 70 to 95% by weight, specifically 75 to 90% by weight, more specifically 80 to 90% by weight, based on the total weight of the coating layer. When the inorganic particles are contained within the above range, the heat radiation characteristics of the inorganic particles can be sufficiently exhibited, and when the separator is coated using the inorganic particles, the heat shrinkage of the separator can be effectively suppressed.

Non-limiting examples of the solvent usable in this embodiment include dimethyl formamide, dimethyl sulfoxide, dimethylacetamide, dimethyl carbonate or N-methylpyrrolidone (N-methylpyrrolidone). The content of solvent based on the weight of the coating composition may be 20 to 99 wt%, specifically 50 to 95 wt%, and more specifically 70 to 95 wt%. When the solvent is contained in the above range, the coating agent is easily prepared and the drying process of the coating layer can be performed smoothly.

After the coating composition is formed, a coating layer may be formed on one side or both sides of the polyolefin-based film described in the present specification with the coating composition described above.

First, forming the coating composition may include mixing an organic binder, a solvent, and inorganic particles and stirring at 10 to 40 DEG C for 30 minutes to 5 hours. In this case, the solid content may be 10 to 20 parts by weight based on the coating composition, and the weight ratio of the binder and the inorganic particles in the solid content may be 3: 7 to 0.5: 9.5.

Alternatively, an inorganic dispersion in which the inorganic particles are dispersed in a dispersion medium may be prepared, and then mixed with a polymer solution containing an organic binder and a solvent to prepare a coating composition. When the inorganic dispersion is separately prepared as described above, the dispersibility of the inorganic particles and the binder and the stability of the liquid preparation can be improved. Thus, in another embodiment, in preparing the coating composition of the present invention, the binder component and the inorganic particles may each be prepared and mixed in a dissolved or dispersed state in a suitable solvent.

For example, a coating composition may be prepared by preparing each of a solution in which an organic binder is dissolved in an appropriate solvent and an inorganic dispersion in which inorganic particles are dispersed, and then mixing them together with an appropriate solvent. For the mixing, a ball mill, a beads mill, a screw mixer, or the like may be used.

Next, a coating layer is formed on one side or both sides of the polyolefin-based film with the above-mentioned coating composition.

The method of coating the polyolefin-based substrate film using the coating agent is not particularly limited, and a method commonly used in the technical field of the present invention can be used. Non-limiting examples of the coating method include a dip coating method, a die coating method, a roll coating method, and a comma coating method. These may be applied alone or in combination of two or more methods. The coating layer of the separator of the present invention may be formed by, for example, a dip coating method.

The thickness of the coating layer of the present invention may be 0.01 to 20 탆, specifically 1 to 10 탆, more specifically 1 to 5 탆. It is possible to obtain an excellent thermal stability and adhesion by forming a coating layer having an appropriate thickness within the above-mentioned thickness range, and prevent the thickness of the entire separation membrane from becoming excessively thick, thereby preventing the internal resistance of the battery from increasing.

In the present embodiment, drying of the coating layer can be performed by dry, vacuum drying or irradiation with far-infrared rays or electron beams by hot air, hot air or low-humidity air. The drying temperature may vary depending on the kind of the solvent, but it can be generally dried at a temperature of 60 to 120 ° C. Drying time may vary depending on the type of solvent but can be generally 1 minute to 1 hour. In embodiments, it may be dried at a temperature of 90 to 120 DEG C for 1 to 30 minutes, or for 1 to 10 minutes.

An electrochemical cell according to another embodiment of the present invention includes a polyolefin-based separator or a coating separator according to an embodiment of the present invention, and an anode and a cathode, and is filled with an electrolyte.

The polyolefin-based separation membrane or the coating separation membrane may be a separation membrane produced according to the above-described production methods of the present invention or the separation membrane of the present invention described above.

The type of the electrochemical cell is not particularly limited and may be a battery of a kind known in the technical field of the present invention.

The electrochemical cell may be a lithium secondary battery such as a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery. The method for manufacturing the electrochemical cell is not particularly limited, and a method commonly used in the technical field of the present invention can be used.

A method of manufacturing the electrochemical cell is as follows. A polyolefin-based separator according to one aspect of the present invention or a coating separator according to another aspect of the present invention is placed between a positive electrode and a negative electrode of a battery, , So that the battery can be manufactured by filling the electrolyte.

The electrode constituting the electrochemical cell may be manufactured by binding an electrode active material to an electrode current collector by a method commonly used in the technical field of the present invention. The cathode active material of the electrode active material is not particularly limited, and a cathode active material conventionally used in the technical field of the present invention may be used.

Non-limiting examples of the positive electrode active material include lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, and lithium composite oxide in combination thereof.

The negative electrode active material of the electrode active material is not particularly limited, and the negative electrode active material conventionally used in the technical field of the present invention may be used.

Non-limiting examples of the negative electrode active material include a lithium adsorbent material such as lithium metal or lithium alloy, carbon, petroleum coke, activated carbon, graphite or other carbon materials, and the like .

The electrode current collector is not particularly limited, and electrode current collectors commonly used in the technical field of the present invention can be used. Non-limiting examples of the positive electrode current collector material among the electrode current collectors include aluminum, nickel, or foil produced by a combination of these materials. As a non-limiting example of the cathode current collector material of the electrode current collector, copper, gold, nickel, a copper alloy, or a foil produced by a combination of these materials can be used.

The electrolytic solution is not particularly limited, and an electrolytic solution for an electrochemical cell commonly used in the technical field of the present invention can be used. The electrolytic solution may be a salt having a structure such as A ⁺ B ^- dissolved or dissociated in an organic solvent.

Non-limiting examples of the A ⁺ include alkali metal cations such as Li ⁺ , Na ^+, or K ⁺ , or cations made of combinations thereof.

Non-limiting examples of B ^- include PF ₆ ^- , BF ₄ ^- , Cl ^- , Br ^- , I ^- , ClO ₄ ^- , AsF ₆ ^- , CH ₃ CO ₂ ^- , CF ₃ SO ₃ ^- , N ₃ SO ₂ ) ₂ ^- or C (CF ₂ SO ₂ ) ₃ ^- , or an anion composed of a combination of these.

-Butyrolactone, GBL) 등을 들 수 있다. 이들은 단독으로 사용되거나 2 종 이상을 혼합하여 사용될 수 있다.
Nonlimiting examples of the organic solvent include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate Dipropyl carbonate (DPC), dimethyl sulfoxide (DMSO), acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran (THF), N-methyl- N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC) or gamma-butyrolactone

-Butyrolactone, GBL). These may be used alone or in combination of two or more.

Hereinafter, the present invention will be described in more detail by describing Examples, Comparative Examples and Experimental Examples. However, the following examples, comparative examples and experimental examples are merely examples of the present invention, and the present invention should not be construed as being limited thereto.

Example  One

High-density polyethylene (HDPE, manufactured by Mitsui Chemical Co., Ltd.) having a weight average molecular weight of 600,000 g / mol was fed to a twin-screw extruder in an amount of 30% by weight based on the total weight of the composition comprising a polyolefin resin and a plasticizer, Liquid paraffin (Escipi) was injected into the twin-screw extruder at 70% by weight based on the total weight of the composition including the polyolefin resin and the plasticizer and extruded.

After the extrusion, the gel phase obtained through the T-die is formed into a sheet-form separation membrane by using a cooling roll, and before the liquid paraffin is extracted from the sheet, in accordance with the biaxial stretching method of longitudinal stretching equipment and transverse stretching equipment , Longitudinal drawing at 100 占 폚 and transverse stretching at 110 占 폚 were carried out at a magnification of 7 × 7.

The biaxially stretched polyethylene-based film was washed with methylene chloride (Samsung Fine Chemicals) to extract liquid paraffin and dried.

Then, the perforations having a perforation diameter of 4 (mm) and uniformly forming the perforations and having a puncture rate of 3% were horizontally disposed at a distance of 2 cm from the surface direction of the separator, The laminate was stretched 1.3 times in the transverse direction while spraying for 30 seconds, and then heat-settled at a temperature of 135 DEG C by relaxing 1.2 times with respect to the length before stretching.

After the heat-setting step, the stretched separator was wound to produce a polyolefin-based separator having a thickness of 12 탆.

Example  2

High-density polyethylene having a weight-average molecular weight of 600,000 g / mol was prepared in the same manner as in Example 1, except that 85 wt% of a polyolefin-based resin and an ultra-high molecular weight polyethylene having a weight-average molecular weight of 2,400,000 g / mol were used in the preparation of a composition comprising a polyolefin resin and a plasticizer Polyolefin-based membranes were prepared under the same conditions except that 15 wt% of the polyolefin-based resin was used.

Example  3

In Example 1, a polyolefin-based membrane was prepared under the same conditions except that the perforation rate was adjusted to 5%.

Example  4

In Example 1, a polyolefin-based membrane was prepared under the same conditions except that the perforation rate was adjusted to 10%.

Example  5

A coating layer was formed by the following composition in the separation membrane of Example 1 to prepare a coating separation membrane.

(1) Preparation of coating liquid composition

1) Polyvinylidene fluoride-hexafluoropropylene (hereinafter referred to as "PVdF-HFP") copolymer (Solvay) having a weight average molecular weight of 700,000 g / mol was added to acetone (purified gold) in an amount of 10% And the mixture was stirred at 25 캜 for 4 hours using a stirrer to prepare a first polymer solution.

2) Polyvinylidene fluoride (hereinafter referred to as 'PVdF') homopolymer (Solvay) having a weight average molecular weight of 1,100,000 g / mol was added to DMF (purified gold) in an amount of 10% by weight and stirred at 25 ° C Followed by stirring for 4 hours to prepare a second polymer solution.

3) 25% by weight of alumina (Japanese light metal) was added to acetone (purified gold), and the mixture was milled at 25 캜 for 3 hours using a ball mill to prepare an inorganic dispersion.

The first polymer solution, the second polymer solution and the inorganic dispersion were mixed at a composition ratio of first polymer solution: second polymer solution: inorganic dispersion: solvent (acetone) = 1: 1: 3: 6, Lt; 0 > C for 2 hours to prepare a coating liquid composition.

(2) Preparation of coating separator

The coating liquid composition prepared above was coated on both sides of the polyolefin separator of Example 1 by dip coating method and then dried to prepare a coating separator having a coating layer of 5 탆 on both sides.

Comparative Example  One

A polyolefin-based membrane was prepared in the same manner as in Example 1, except that the perforation rate was adjusted to 2%.

Comparative Example  2

A polyolefin-based membrane was prepared in the same manner as in Example 1, except that the perforation rate was adjusted to 11%.

Comparative Example  3

A polyolefin-based membrane was prepared in the same manner as in Example 2, except that the perforation rate was adjusted to 2%.

The composition and process conditions used in Examples 1 to 5 and Comparative Examples 1 to 3 are shown in Table 1 below.

Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 Comparative Example 3 Raw material
(wt%) HDPE 30 25.5 30 30 30 30 30 25.5 UHMWPE - 4.5 - - - - - 4.5 Resin / LP 30/70 30/70 30/70 30/70 30/70 30/70 30/70 30/70 Membrane Thickness (㎛) 12 12 12 12 12 12 12 12 Coating layer thickness (탆) - - - - 5 - - - Stretching process MD x TD stretching magnification 7 × 7 7 × 7 7 × 7 7 × 7 7 × 7 7 × 7 7 × 7 7 × 7 MD and TD stretching temperature (占 폚) 100 ° C, 110 ° C 100 ° C, 110 ° C 100 ° C, 110 ° C 100 ° C, 110 ° C 100 ° C, 110 ° C 100 ° C, 110 ° C 100 ° C, 110 ° C 100 ° C, 110 ° C Ten
The
tablet Pore diameter (mm) 4 4 4 4 4 4 4 4 Percussion ratio (%) 3 3 5 10 3 2 11 2 Distance between perforated surface and separator (cm) 2 2 2 2 2 2 2 2 Hot air temperature (℃) 135 135 135 135 135 135 135 135 Hot air processing time (sec) 10 to 30 10 to 30 10 to 30 10 to 30 10 to 30 10 to 30 10 to 30 10 to 30

Experimental Example  One

Separator Heat shrinkage  Measure

Each of the separation membranes prepared in the above Examples and Comparative Examples was cut into 10 pieces of MD 50 mm × TD 50 mm. Ten specimens were prepared. Each of the specimens was allowed to stand in an oven at 120 ° C. for 1 hour, and the degree of shrinkage in the longitudinal direction and the transverse direction of each specimen was measured to calculate the average heat shrinkage ratio in consideration of the reduced size.

Experimental Example  2

Measurement of air permeability of membrane

Each of the separation membranes prepared in the above Examples and Comparative Examples was subjected to ten specimens cut out at ten different points in a size capable of entering a circle having a diameter of 1 inch. Thereafter, an air permeability meter (Asahi Seiko Co., The time of passage of 100 cc of air through each of the above specimens was measured using a sieve. The time was measured five times each, and the average value was calculated to measure the air permeability.

Experimental Example  3

Measurement of tensile strength of membrane

Each of the membranes prepared in the above Examples and Comparative Examples was cut into 10 rectangular pieces each having a size of 10 mm in MD and 50 mm in length (TD) in 10 different locations. UTM (tensile tester) to measure the length to 20 mm, and then the specimens were pulled to measure the average tensile strength in the longitudinal direction and the transverse direction.

Experimental Example  4

Measurement of seepage strength of membranes

Each of the membranes prepared in the above Examples and Comparative Examples was cut into 10 pieces of MD 50 mm × TD 50 mm at different 10 points, and then 10 specimens were prepared using KATO Tech G5 equipment The specimens were placed on a 10 cm hole and the force was measured while pushing with a 1 mm probe. The stiffness of each of the above specimens was measured three times, and then the average value was calculated.

The results of the measurements according to Experimental Examples 1 to 4 are summarized in Table 2 below.

Examples /
Comparative Example Heat Shrinkage (%) Ventilation
(sec / 100cc) The tensile strength
(kgf / cm ² ) Sting intensity
(gf) 120 DEG C MD TD MD TD Example 1 3 ± 1.0 0.5 ± 0.5 125 2,009 ± 50 2,110 ± 50 501 ± 30 Example 2 3 ± 1.0 0.5 ± 0.5 129 2,139 ± 50 2,254 ± 50 520 ± 30 Example 3 3 ± 1.0 0 132 2,194 ± 50 2,311 ± 50 526 ± 30 Example 4 2 ± 1.0 0 124 2,098 ± 50 2,185 ± 50 514 ± 30 Example 5 0 0 150 1,540 ± 50 1,615 ± 50 442 ± 30 Comparative Example 1 6 ± 1.0 5 ± 1.0 118 1,929 ± 50 1,906 ± 50 489 ± 30 Comparative Example 2 2 ± 1.0 0 392 2,057 ± 50 2,072 ± 50 513 ± 30 Comparative Example 3 6 ± 1.0 5 ± 1.0 131 1,944 ± 50 1,901 ± 50 499 ± 30

In the results of Table 2, the separating membrane or coating separating membranes of Examples 1 to 5 having a perforation rate of 3 to 10% had a heat shrinkage of 3% or less in the transverse direction (TD) measured after being left at 120 ° C for 1 hour Comparative Example 2 in which the air permeability was 150 sec / 100 cc or less, whereas Comparative Example 2 in which the perforation rate was 11% showed a marked decrease in air permeability and Comparative Examples 1 and 3 in which the perforation rate was 2% . Thus, it can be seen that the rate of perforation of 3 to 10% is advantageous in that it can satisfy all of the physical properties of heat shrinkage and air permeability.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that such detail is solved by the person skilled in the art without departing from the scope of the invention. will be. Accordingly, the actual scope of the present invention will be defined by the appended claims and their equivalents.

Claims (11)

A polyolefin resin,
The heat shrinkage in the transverse direction (TD) measured after standing at 120 ° C for 1 hour is 3% or less,
A polyolefin-based membrane having an air permeability of 132 sec / 100 cc or less. The polyolefin-based separator according to claim 1, wherein the polyolefin-based separator has a tensile strength of 1800 kgf / cm ² or more in longitudinal and transverse directions, respectively. The polyolefin-based separator according to claim 2, wherein the tensile strength of the polyolefin-based separator is 2000 kgf / cm ² or more in the longitudinal direction and in the transverse direction, respectively. The polyolefin-based membrane according to claim 1, wherein the polyolefin-based membrane has a penetration strength of 400 gf or more. The polyolefin-based membrane according to claim 4, wherein the polyolefin-based membrane has a penetration strength of 500 gf or more. A polyolefin resin,
A polyolefin based film having a heat shrinkage of 3% or less in a transverse direction (TD) measured after being left at 120 占 폚 for 1 hour; And
And a coating layer formed on one or both sides of the polyolefin-based film,
Wherein the polyolefin-based coating separating film has an air permeability of 100 to 150 sec / 100 cc. delete A sheet is formed from a composition comprising a polyolefin-based resin and a plasticizer,
Stretching the sheet longitudinally and transversely,
Extracting the plasticizer from the stretched sheet,
And heat-setting the sheet from which the plasticizer is extracted at 100 to 140 DEG C,
Wherein the thermal setting is performed using a piercing nozzle having a perforated surface having a plurality of perforations,
Wherein the perforation rate of the perforated surface is 3 to 10%. 9. The method according to claim 8, wherein the perforated surface is located within 5 cm from the surface direction of the separator. The polyolefin-based separator according to claim 8, wherein the diameter of the pores is 3 to 20 mm. An anode, a cathode, and an electrolyte,
A polyolefin-based separation membrane is interposed between the anode and the cathode,
The polyolefin-based separator is the polyolefin-based separator according to any one of claims 1 to 5 or the polyolefin-based separator according to claim 6 or the polyolefin-based separator prepared according to any one of claims 8 to 10, Chemical battery.

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