KR101371061B1 - 2-layer seperator for secondary cell with excellent heat-resisting property and its method - Google Patents

Abstract

The present invention relates to a method for manufacturing a double-layered separation film with enhanced thermal resistance for a secondary cell and a separation film manufactured by the same and, more specifically, to a method for manufacturing a double-layered separation film with enhanced thermal resistance for a secondary cell which manufactures a separation film by dividing the nozzle block of an electrical discharge device into two discharge sections towards the progress direction and electrically discharging heat-resistant polymers continuously in each discharge section, thereby being able to manufacture a multi-layered separation film with enhanced thermal resistance and accordingly improving thermal stability and a separation film manufactured by the same. The method includes: a step of electrically discharging a solution which is produced by dissolving first heat-resistant polymers filled in a first supply device in an organic solvent onto a collector to form first heat-resistant polymer nano fiber; and a step of electrically discharging a solution which is produced by dissolving another heat-resistant polymers filled in a second supply device in an organic solvent onto the upper surface of the first heat-resistant polymer nano fiber to laminate second heat-resistant polymer nano fiber.

Description

2-layer separator for secondary battery with improved heat resistance and manufacturing method thereof {2-layer seperator for secondary cell with excellent heat-resisting property and its method}

The present invention relates to a secondary battery two-layer separator and a method for producing the secondary battery having improved heat resistance, and in detail, a polyimide or polyacrylonitrile first porous membrane and a metaaramid second porous membrane having heat resistance characteristics are prepared in two layers. The present invention relates to a two-layer separation membrane and a method for manufacturing the same, which can prevent heat generation due to local rapid ion movement of a battery or block the entire separation membrane from reaching a shutdown temperature.

As consumers' demands have changed due to digitization and high performance of electronic products, market demand is changing due to the development of batteries with high capacity due to thinness, light weight and high energy density. In addition, in order to cope with future energy and environmental problems, the development of hybrid electric vehicles and fuel cell vehicles has been actively progressed, and thus the size of batteries for automobile power sources is required.

Secondary batteries, including high energy density and large capacity lithium ion secondary cells, lithium ion polymer batteries, and super capacitors (electric double layer capacitors and similar capacitors), must have a relatively high operating temperature range and should be continuously used at high rate charge and discharge The separator used in these cells is required to have higher heat resistance and thermal stability than those required in ordinary separators. In addition, it should have excellent cell characteristics such as rapid charge / discharge and high ion conductivity capable of coping with low temperature.

The separator is disposed between the anode and the cathode of the battery to insulate the electrolyte and maintain the electrolyte to provide a path for ion conduction. When the temperature of the battery becomes excessively high, a part of the separator melts to block the current, Lt; / RTI >

When the temperature rises further and the separator melts, a large hole is formed and a short circuit occurs between the anode and the cathode. This temperature is called SHORT CIRCUIT TEMPERATURE. In general, the separator should have a lower SHUTDOWN temperature and a higher short-circuit temperature. In the case of the polyethylene separator, when the battery is overheated, it contracts at 150 ° C. or higher to expose the electrode part, which may cause a short circuit. Therefore, it is very important to have both a closing function and a heat resistance for a high energy density, large-sized secondary battery.

That is, there is a need for a separation membrane having excellent heat resistance, small heat shrinkage, and excellent cycle performance in accordance with high ion conductivity.

 The porous nanofiber can be used for various purposes because it has a wide surface area and excellent porosity. For example, it can be used for a water purification filter, an air purification filter, a composite material, and a separator for a battery. In particular, such porous nanofibers can be usefully applied to the separator of a fuel cell for automobiles.

Conventional lithium ion polymer batteries using a conventional polyolefin separator and a liquid electrolyte such as a lithium ion secondary battery or a gel polymer electrolyte membrane or a polymer electrolyte gel coated on a polyolefin separator have a high energy density and a very high Lack. Therefore, it does not satisfy the heat resistance and safety required in a high capacity, large area battery such as automobile.

In order to solve this problem, US Patent Publication No. 2006-0019154 discloses that a polyolefin-based separator is impregnated with a polyamide, polyimide, polyamideimide solution having a melting point of 180 ° C. or higher, and then immersed in a coagulation solution to extract a solvent to obtain porous heat resistance. A heat-resistant polyolefin separator in which a thin resin layer is bonded is proposed, and the heat shrinkage is small, and the heat resistance and excellent cycle performance are claimed. The heat-resistant thin layer is made porous through solvent extraction and the polyolefin separator used is limited to the use of an AIR PERMEABILITY of 200 sec / min or less.

In Japanese Patent Laid-Open No. 2005-209570, heat-resistant resins such as aromatic polyamides, polyimides, polyethersulfones, polyetherketones, and polyetherimides having a melting point of 200 ° C. or higher in order to ensure sufficient safety at high energy density and size increase The solution was applied to both sides of the polyolefin separator and immersed in a coagulating solution, washed with water and dried to give a polyolefin separator to which a heat resistant resin was adhered. In order to reduce the deterioration of ionic conductivity, a phase separator for providing porosity is contained in the heat resistant resin solution and the heat resistant resin layer is limited to 0.5-6.0 g / m 2.

However, the immersion of the heat resistant resin prevents the movement of lithium ions by blocking the pores of the polyolefin separation membrane, so that the charge and discharge characteristics are lowered, so that even if the heat resistance is secured, it is less than the capacity required for a large capacity battery such as an automobile. Even if the pore structure of the polyolefin porous membrane is not clogged due to the immersion of the heat resistant resin, the porosity of the polyolefin separator generally used is about 40%, and the pore size is also several tens of nanometers, which limits the ion conductivity for a large capacity battery .

US Patent No. 6,447,958B1 discloses a slurry obtained by dissolving and dispersing a ceramic powder and a heat-resistant nitrogen-containing aromatic polymer in an organic solvent. Although it is claimed to manufacture a heat resistant separator by coating a film or the like and removing the solvent, the heat resistant polymer layer is introduced in the process of introducing a heat resistant polymer layer, and a process of preparing a porous heat resistant resin layer including application of the heat resistant resin and immersion in a coagulating solution, washing with water, and drying. This is a very complicated and costly problem.

Japanese Patent Laid-Open Nos. 2001-222988 and 2006-59717 disclose gel electrolytes of polymers such as polyethylene oxide, polypropylene oxide, polyether and polyvinylidene in polyaramid, polyimide woven fabric, nonwoven fabric, cloth and porous film having a melting point of 150 ° C. or higher. It is impregnated or apply | coated to and manufactures a heat resistant electrolyte membrane. However, even in this case, the required heat resistance may be satisfied, but the ion transport in the support or the heat-resistant aromatic polymer layer is still limited in terms of ion conduction, similar to that of a separator or a gel electrolyte of a conventional lithium ion battery.

As a separator for a fuel cell currently in use, there is a perfluorosulfonic acid resin (Nafion, trade name) (hereinafter referred to as "Nafion resin") as a fluororesin. However, since the Nafion resin has a low mechanical strength, pinholes are generated when the Nafion resin is used for a long period of time, thereby deteriorating energy conversion efficiency. There is an attempt to increase the film thickness of the Nafion resin to reinforce the mechanical strength. However, in this case, there is a problem that the resistance loss is increased and the economical efficiency is lowered due to the use of the expensive material.

Therefore, the above-mentioned conventional patented techniques still do not satisfy the heat resistance and the ionic conductivity at the same time, and there is no mention of the shutdown function of the separator, High energy densities and large capacity batteries, such as batteries, are still unsatisfactory.

In order to solve the above problems, the present invention provides a method for preparing a membrane and a separator prepared according to the present invention, which can improve thermal stability by manufacturing nanofibers using two types of heat resistant polymers.

The present invention is a nozzle block having a nozzle of the electrospinning device is divided into two sections facing the horizontal direction, provided with a first supply device, a second supply device for supplying a polymer to each partitioned section on the collector In the method for producing a membrane for spinning a polymer, a solution prepared by dissolving a heat-resistant polymer polyacrylonitrile in an organic solvent in the first supply device of the electrospinning apparatus is electrospun onto a collector to obtain polyacrylonitrile nanofibers. Forming; Spinning a solution prepared by dissolving another heat-resistant polymer metaaramid in an organic solvent in the second supply device of the electrospinning apparatus on the polyacrylonitrile nanofibers to stack the metaaramid nanofibers; The present invention relates to a two-layer separator for secondary batteries comprising polyacrylonitrile / metharamid nanofibers produced by a method for producing a two-layer separator for batteries.

In still another aspect of the present invention, a nozzle block including a nozzle of an electrospinning apparatus is divided into two sections in a horizontal direction, and is provided as a first supply device and a second supply device for supplying a polymer to each partitioned section. In the method for producing a membrane for spinning a polymer on the phase, a solution prepared by dissolving a heat-resistant polymer polyimide precursor in an organic solvent in the first supply device of the electrospinning apparatus is electrospun onto a collector to form a polyimide precursor nanofiber Forming; Stacking meta-aramid nanofibers by spinning a solution prepared by dissolving another heat-resistant polymer meta-aramid in an organic solvent in the second supply device of the electrospinning apparatus on the polyimide precursor nanofibers; By heating the laminated electrospinning to imidize the polyimide precursor nanofibers to produce a polyimide nanofibers, a polyimide precursor using a polyamic acid as a polyimide precursor, It is to manufacture a two-layer separator for secondary batteries comprising the mid / meta aramid nanofibers.

The two-layer separator for secondary batteries having improved heat resistance according to the present invention has a battery blocking function to prevent a short circuit phenomenon, excellent stability of the battery even during thermal runaway, and improved wettability and excellent electrical resistance. Such polyimide or polyacrylonitrile / meta-aramid porous nanofibers having such excellent physical properties can be used for electrolyte membranes for fuel cells or separators for secondary batteries that require lightweight, high efficiency, and high stability.

The method for producing a second layer porous separator by electrospinning polyimide or polyacrylonitrile and metaaramid, which are heat resistant polymers of the present invention, will be described.

The electrolyte membrane for a fuel cell should contain ionic conductors to smoothly transfer ions. In order for these ions to move smoothly through the electrolyte membrane, the ion conductor must be evenly filled throughout the nanofiber. However, if the pore is too small or too large, the ion conductor may become unevenly charged, resulting in a problem that the ion conductivity is lowered. That is, the ion conductor can be impregnated smoothly in the nanofiber only if there are many pores having a specific pore size. In other words, if the pore size is too small, the ion conductor may not be impregnated smoothly, whereas if the pore size is too large, the ion conductor may be excessively impregnated.

In the present invention, a polyamic acid (Poly (amic acid), PAA) is synthesized, and dissolved in a (THF / DMAc) mixed solvent of tetrahydrofuran (Tetrahydrofuran, THF) and dimethylacetamide (DMAc) polyamic acid dope (Dope) ), A polyamic acid nanofiber separator using electrospinning, and then a polyimide (PI) nanofiber through imidization is prepared on a polyolefin substrate, followed by inorganic material on the PI nanofiber. The slurry prepared by adding the particles and the polyimide affinity polymer resin to acetone may be coated by a casting method to more firmly attach the inorganic coating layer, thereby improving heat resistance and wettability of the separator.

The PI is prepared by a two-step reaction.

In the first step, polyamic acid is prepared by adding dianhydride to a reaction solution in which diamine is dissolved. In order to increase the degree of polymerization, the reaction temperature, the water content of the solvent, And purity control. As the solvent used in this step, organic polar solvents such as dimethylacetamide (DMAc), dimethylformamide (DMF) and en-methyl-2-pyrrolidone (NMP) are mainly used. Examples of the anhydride include pyromellitic dianhydride (PMDA), benzophenonetetracarboxylic dianhydride (BTDA), 4,4'-oxydiphthalic anhydride (4,4'-oxydiphthalic anhydride) ODPA), biphenyltetracarboxylic dianhydride (BPDA), and bis (3,4'-dicarboxyphenyl) dimethylsilane dianhydride (SIDA). One can be used. Examples of the diamine include 4,4'-oxydianiline (ODA), p-penylene diamine (p-PDA) and o-penylenediamine o-PDA) may be used.

Reaction 1. Preparation of polyamic acid

The second step is the dehydration and ring-closing reaction step of producing polyimide from polyamic acid as the following four methods.

In the re-impregnation method, a polyamic acid solution is added to an excessive amount of a poor solvent to obtain a solid polyamic acid. As the re-precipitation solvent, water is mainly used, but toluene or ether is used as a co-solvent.

The chemical imidization method is a method in which a imidization reaction is chemically performed using a dehydration catalyst such as acetic anhydride / pyridine, and is useful for producing a polyimide film.

The thermal imidization method is a method of thermally imidating a polyamic acid solution by heating it to 150 to 200 ° C., which is the simplest process or has a high degree of crystallinity, and has a disadvantage in that the polymer is decomposed because an amine exchange reaction occurs when an amine solvent is used. have.

Isocyanate method uses diisocyanate as monomer instead of diamine, and when the monomer mixture is heated to a temperature above 120 ° C., CO ₂ gas is generated and PI is produced.

Reaction formula 2. Preparation of polyimide

The electrospinning device includes a spinning liquid main tank for storing a spinning solution, a metering pump for supplying a spinning solution in a fixed amount, a nozzle block for combining a plurality of tubular nozzles composed of a plurality of pins in block form and discharging the spinning solution in a fiber form, A collector for accumulating short fibers emitted at a position corresponding to the nozzle block, a voltage generating device for generating a high voltage, and a spinning solution discharging device connected to the top of the nozzle block.

The method of preparing the nanofibers by electrospinning the polyimide of the present invention is performed through the following process.

First, a spinning solution in which polyimide is dissolved in tetrahydrofuran (THF) / dimethylacetamide (DMAc) mixed solvent (THF / DMAc) is prepared, and the polyimide spinning solution in the spinning solution main tank is prepared. This is stored, weighed with a separate metering pump, and supplied to the spinning solution dropping device one by one.

Polyacrylonitrile used in another section is prepared a spinning solution dissolved in dimethylformamide (DMF), dimethylacetamide (DMAc) as a solvent mainly used.

Polyacrylonitrile resins are copolymers made from a mixture of acrylonitrile and monomers that make up the majority. Other monomers that are frequently incorporated are butadiene styrene, vinylidene chloride, or other vinyl compounds. Of course, the same acrylic fiber contains at least 85% acrylonitrile, and mode acrylic contains 35-85% acrylonitrile. If other monomers are involved, the fiber is a desired property, such as increased affinity for the dye. More specifically, in the production of acrylonitrile-based copolymers and spinning solutions, in the case of using acrylonitrile-based copolymers, there is little nozzle contamination and excellent electrospinning properties in the process of producing ultrafine fibers by electrospinning. By increasing the solubility in the solvent and at the same time can be given better mechanical properties.

The polymerization degree of the polyacrylonitrile is 1,000 to 1,000,000, preferably 2,000 to 1,000,000. If the degree of polymerization is too low, the efficiency of the battery tends to decrease due to the dissociation of the electrode from the current collector as the cycle is progressed as the electrolyte dissolves or swells in the carbonate electrolyte. If the degree of polymerization is too high, There is a disadvantage that it is difficult to handle by increasing the viscosity.

It is preferable to use it in a range that satisfies the usage amount of the acrylonitrile monomer, the hydrophobic monomer and the hydrophilic monomer. The weight percent of acrylonitrile monomer in the polymerization of polymer is 3: 4 ratio of hydrophilic monomer and hydrophobic monomer in a ratio of 4: 4, and when the total monomer is less than 60, the viscosity is too low for electrospinning. Even if the crosslinking agent is added to the nozzle, it is difficult not only to cause nozzle contamination but also to form a stable jet during electrospinning. If the ratio is more than 99, the spinning viscosity is too high to spin, and even if an additive capable of lowering the viscosity is added, the diameter of the microfine fibers becomes too large and the productivity of electrospray is too low to achieve the object of the present invention. In addition, as the amount of the comonomer in the acrylic polymer is increased, the amount of the crosslinking agent should be added to ensure the stability of electrospinning and to prevent the mechanical properties of the nanofibers from deteriorating.

The hydrophobic monomer is an ethylene compound such as methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, vinyl acetate, vinylpyrrolidone, vinylidene chloride, vinyl chloride and derivatives thereof. It is preferable to use any one or more selected.

The hydrophilic monomers are acrylic acid, allyl alcohol, metaallyl alcohol, hydroxy ethyl acrylate, hydroxy ethyl methacrylate, hydroxypropyl acrylate, butanediol monoacrylate, dimethylaminoethyl acrylate, butene tricarboxylic acid, vinyl It is preferable to use any one or more selected from ethylene-based compounds such as sulfonic acid, allylsulfonic acid, metalylsulfonic acid, parastyrenesulfonic acid, and polyhydric acids or derivatives thereof.

As an initiator used to prepare the acrylonitrile-based polymer, even if an azo compound or a sulfate compound is used, there is no big problem, but in general, a radical initiator used for a redox reaction may be used.

The specific gravity of the meta-aramid is 1.3 to 1.4, and the weight average molecular weight is preferably 300,000 to 1,000,000. Most preferred weight average molecular weight is from 3,000 to 500,000. Meta-oriented synthetic aromatic polyamides. The polymer should have a fiber-forming molecular weight and can include polyamide homopolymers, copolymers, and mixtures thereof, which are primarily aromatic, wherein at least 85% of the amide (-CONH-) bonds are attached directly to the two aromatic rings . The ring may be unsubstituted or substituted. The polymer becomes meta-aramid when two rings or radicals are meta-oriented relative to each other along the molecular chain. Preferably, the copolymer contains up to 10% other diamines substituted for the primary diamine used to form the polymer, or up to 10% other diacids substituted for the primary diacid chloride used to form the polymer It has a diacid chloride. Preferred meta-aramids are poly (meth-phenylene isophthalamide) (MPD-I) and copolymers thereof. One such meta-aramid fiber is Lee. Wilmington, Delaware, USA. children. Nomex® aramid fiber available from EI du Pont de Nemours and Company, while meta-aramid fiber is available from Teijin Ltd. of Tokyo, Japan. Possible trade names Tejinconex®; New Star (TM) meta-aramid available from Yantai Spandex Co. Ltd, Shandong, China; And Chinfunex (registered trademark) Aramid 1313, available from Guangdong Charming Chemical Co., Ltd., Shinduo, Guangdong, China.

The organic solvent is not particularly limited as long as it can dissolve the polymer sufficiently and is a solvent applicable to the charge induction spinning method, and when the porous polymer separator is prepared by the charge induction spinning method, the organic solvent is almost removed. Affecting may also be used. For example, propylene carbonate, butylene carbonate, 1,4-butyrolactone, diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane, 1,3-dimethyl-2-imidazolidinone, dimethyl sulfoxide, Ethylene carbonate, ethyl methyl carbonate, N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, polyethylene sulfolane, tetraethylene glycol dimethyl ether, acetone, alcohol or mixtures thereof Any one or more of them may be selected and used, and more preferably dimethylformamide (Dimethylformamide, DMF) or dimethylacetamide (Dimethylacetamide, DMAc) is used.

The meta-aramid is the first highly heat-resistant aramid fiber that can be used at 350 ° C for a short time and 210 ° C for continuous use. When exposed to temperatures above this temperature, it is carbonized without melting or burning like other fibers. Above all, unlike other products that are flame retarded or refractory treated, they do not emit toxic gases or harmful substances even when carbonized, and thus they have excellent properties as eco-friendly fibers.

In addition, since meta-aramid has a very strong molecular structure, the molecules constituting the fiber have not only a strong strength inherently, but also easy orientation of molecules in the fiber axial direction during the spinning step, thereby improving crystallinity and increasing the strength of the fiber. Can be.

An example of the electrospinning device used in the present invention will be described as follows.

Electrospinning apparatus is a combination of a spinning solution main tank for storing spinning solution, a metering pump for spinning solution quantitative supply, a multi-tubular nozzle consisting of a plurality of pins in a block form, the nozzle block for discharging the spinning solution in the form of fibers, A collector for integrating short fibers radiated at a position corresponding to the nozzle block, a voltage generator for generating a high voltage, and first and second supply devices for supplying spinning liquid for each section between the metering pump and the nozzle block. do.

The polyimide or polyacrylonitrile and metaaramid spinning solution are respectively stored in the first and second main tanks for storing the spinning solution of the electrospinning of the present invention, and the first and second supply devices have a cylindrical shape as a whole. It is designed to have a function to supply the spinning solution continuously injected from the spinning main tank by section. The nozzle block is divided into two sections, and each section is provided with the first and second supply devices, and the spinning solution is polyimide or polyacrylonitrile in the first supply device, and the metaaramid polymer is dissolved in the solvent, respectively. The prepared solution. The length of the section defined by the nozzle block can be adjusted according to the thickness of each layer constituting the separation membrane.

Next, a method for manufacturing a two-layer separator using the electrospinning apparatus of the present invention will be described.

First, the polyimide or polyacrylonitrile and the metaaramid polymer spinning liquid, which are heat-resistant polymers filled in the spinning main tank, are metered by a metering pump and supplied in a quantitative manner. The feed device is supplied with metaaramid polymer spinning solution. Then, the nozzle block is discharged from the nozzle block to the collector under the high voltage through the nozzle to manufacture the nanofibers, wherein the spinning nozzle is located on the upper side of the collector-type grounded collector moving at a constant speed. It is arranged in two rows at regular intervals along the direction of travel, and is provided with a plurality of spinning nozzles in each row.

The polymer spinning solution sequentially discharged from the two-row spinning nozzle will be described in detail. In the first supply device, the polyimide precursor solution is released into the nanofibers while passing through the spinning nozzle charged by the high voltage generator, and at a constant speed. The polyaramid precursor nanofibers spun on a grounded collector in the form of a moving conveyor, and the polyaramid precursor nanofibers spun on the collector are moved at a constant speed in a second section to sequentially stack the metaaramid nanofibers to produce two-layer nanofibers. The two-layer nanofibers prepared above were heated to imidize the polyimide precursor electrospinning and transformed into polyimide nanofibers to prepare a polyimide / metharamid two-layer separator.

In another two-layer separator, the polyacrylonitrile polymer spinning solution is discharged into the nanofibers while passing through the spinning nozzle charged by the high voltage generator, and moves on a conveyor-type grounded collector moving at a constant speed. The spun and the polyacrylonitrile nanofibers spun on the collector is moved at a constant speed in the second section to sequentially stack the metaaramid nanofibers to prepare a two-layer separator.

In this case, the grounded collector is controlled to be moved in one direction, thereby enabling a continuous process of forming a separator of two layers. The present invention has the effect of simplifying the manufacturing process of the separator and increasing the production speed through such a process.

The thickness of the polymer membrane, the diameter of the fiber, the shape of the fiber, and the mechanical characteristics of the separation membrane can be arbitrarily controlled by controlling the electrospinning process conditions such as the intensity of the applied voltage, the kind of the polymer solution, the viscosity of the polymer solution, Can be adjusted.

 The preferred electrospinning process conditions are that the spinning liquid transferred to the spinning liquid supply tube is discharged to the collector through the multiple tubular nozzles to form fibers, and the nanofibers electrospun from the tubular nozzle are discharged by the air injected from the air supply nozzle It spreads widely and is collected on the collector to widen the collecting area and to make the density of the particles uniform. The excess spinning solution that has not been fiberized in the multi-tubular nozzle is collected in the nozzle for removing the overflow and then moved back to the spinning solution supply plate through the temporary storage plate of the overflow solution.

When manufacturing nanofibers, it is preferable that the speed of air in the air supply nozzle is 0.05 m to 50 m / sec, more preferably 1 to 30 m / sec. When the air velocity is less than 0.05 m / sec, the nanofiber spreading property of the collector is low and the collection area is not greatly improved. When the air velocity exceeds 50 m / sec, the air velocity is too fast and the nanofibers are collected. Rather, the area focused on is reduced, so that a more serious problem is that not a nanofiber but a thick thread attached to the collector, causing a serious problem that the formation ability of the nanofiber is significantly reduced.

In addition, the spinning solution which is excessively supplied to the top of the nozzle block is forcibly transferred to the spinning liquid main tank by the spinning solution discharging device.

At this time, in order to promote the formation of the fiber by the electric force, a voltage of 1 kV or more, more preferably 20 kV or more, generated by the voltage generator is applied to the conductive plate and collector provided at the lower end of the nozzle block. It is more advantageous in terms of productivity to use an endless belt as the collector. The collector preferably reciprocates a predetermined distance in the left and right directions to uniform the density of the nanofibers.

In this way, the nanofibers formed on the collector are wound on the winding roller via the web support roller to complete the manufacturing process of the nanofibers.

The manufacturing apparatus can increase the collecting area to uniform the density of the nanofibers and effectively prevent the droplet phenomenon, thereby improving the quality of the nanofibers and enhancing the fiber-forming effect by the electric force, And nanofibers thereof can be mass-produced. In addition, by arranging the nozzles constituted by a plurality of pins in block form, the width and thickness of the nonwoven fabric and the filament can be freely changed and adjusted.

In addition, when the heat-resistant polymer is spun as described above, it is most preferable to spin the polymer under environmental conditions of a temperature range of 30 to 40 DEG C and a humidity of 40 to 70% depending on the polymer material.

In the present invention, the diameter of the nanofibers forming the two-layer separator is preferably 30 to 2000nm, more preferably 50 to 1500nm.

The porosity of the two-layer separation membrane is preferably 40 to 80%, and as the fiber diameter is smaller, the pore size becomes smaller and the pore size distribution becomes smaller. In addition, since the specific surface area of the fibers is increased as the diameter of the fibers is smaller, the ability to lyse the electrolyte increases and the possibility of leakage of the electrolyte decreases.

Hereinafter will be described in more detail through embodiments of the present invention. However, the embodiments are only examples of the present invention, and the scope of the present invention is not limited thereto.

Example 1

In the first section, a polyamic acid (Poly (amic acid), PAA) having a viscosity of 100,000 cps and a solid content of 20% by weight is a mixed solvent of tetrahydrofuran (THF) and dimethylacetamide (DMAc) (THF / DMAc). It is dissolved in to prepare a polyamic acid dope (dope), and in the second section, a dope is prepared by dissolving metaaramid (EI du Pont de Nemours and Company) having a weight average molecular weight of 50,000 in DMAc solvent. The distance between the electrode and the collector was 40Cm, applied voltage 15kV, spinning solution flow rate 0.1mL / h, temperature 22 ℃, and humidity 20%. In the second section, meta-aramid was spun to the top layer of polyamic acid nanofibers to have a thickness of 5 μm to form a two-layer electrospinning film, and then heated at 200 ° C. to imidize the polyamic acid nanofibers with polyimide nanofibers. To form.

[Example 2]

In the first section, a polyacrylonitrile (Korean Synthesis) having a weight average molecular weight of 157,000 is dissolved in dimethylformamide (DMF) to prepare a spinning solution, and in the second section, metaaramid is dissolved in a DMAc solvent to prepare a dope. . 5μm thick polyacrylonitrile nanofibers were formed under electrospinning conditions of 40Cm, applied voltage 15kV, spinning solution flow rate 0.1mL / h, temperature 22 ℃, and humidity 20%. The two-segment membrane is formed by spinning meta-aramid to have a thickness of 5 μm on the upper layer of polyacrylonitrile nanofibers in two sections.

Comparative Example 1

The polyamic acid was dissolved in a THF / DMAc 8: 2 mixed solvent to prepare a spinning solution, and the distance between the electrode and the collector was 40 cm, an applied voltage of 15 kV, a spinning solution flow rate of 0.1 mL / h, a temperature of 22 ° C., and a humidity of 20%. Under the conditions, a polyamic acid nanofiber having a thickness of 10 μm was prepared and then heated at 200 ° C. to imidize the polyamic acid nanofiber with the polyimide nanofiber to form a separator.

[Comparative Example 2]

Doping is prepared by dissolving polyacrylonitrile in DMF solvent. The dope was electrospun on a polyolefin substrate at a distance of 40 cm, an applied voltage of 15 kV, a spinning solution flow rate of 0.1 mL / h, a temperature of 22 ° C., and a humidity of 20% on a polyolefin substrate to prepare a polyacrylonitrile nanofiber having a thickness of 10 μm. do

- Evaluation of Heat Shrinkage of Membrane -

The separators of Examples 1 and 2 and Comparative Examples 1 and 2 were cut to 3 cm × 3 cm and stored at 150 ° C. for 30 minutes, and then evaluated for thermal shrinkage.

Example 1 Example 2 Comparative Example 1 Comparative Example 2 Heat shrinkage (%) 2 3 8 9 Thickness (㎛) 10 10 10 10

As described above, the two-layer separator provided through the present invention has improved heat stability compared to the one-layer separator.

Claims (8)

The nozzle block provided with the nozzle of the electrospinning apparatus is divided into two sections in the horizontal direction, and is provided with a first supply device and a second supply device for supplying the polymer to each partitioned section to radiate the polymer onto the collector. In the manufacturing method of the separation membrane,
Forming a polyacrylonitrile nanofiber by electrospinning a solution prepared by dissolving a heat-resistant polymer polyacrylonitrile in an organic solvent in a first supply device of the electrospinning apparatus on a collector;
Stacking the solution prepared by dissolving another heat-resistant polymer metaaramid in an organic solvent in the second supply device of the electrospinning apparatus on the polyacrylonitrile nanofibers to stack the metaaramid nanofibers;
Method of manufacturing a two-layer separator for a secondary battery comprising a.
The method of claim 1,
The weight average molecular weight (Mw) of the polyacrylonitrile is a manufacturing method of a secondary battery two-layer separator, characterized in that 2,000 to 1,000,000. A two-layer separator for secondary batteries made of polyacrylonitrile / metharamid nanofibers prepared by the method of claim 1. The nozzle block provided with the nozzle of the electrospinning apparatus is divided into two sections in the horizontal direction, and is provided with a first supply device and a second supply device for supplying the polymer to each partitioned section to radiate the polymer onto the collector. In the manufacturing method of the separation membrane,
Forming a polyimide precursor nanofiber by electrospinning a solution prepared by dissolving a heat resistant polymer polyimide precursor in an organic solvent in a first supply device of the electrospinning apparatus on a collector;
Stacking meta-aramid nanofibers by spinning a solution prepared by dissolving another heat-resistant polymer meta-aramid in an organic solvent in the second supply device of the electrospinning apparatus on the polyimide precursor nanofibers;
Heating the stacked nanofibers to imidize the polyimide precursor nanofibers with the polyimide nanofibers;
Method of manufacturing a two-layer separator for a secondary battery comprising a. 5. The method of claim 4,
The polyimide precursor is a polyamic acid (Poly (amic acid), PAA) manufacturing method of a secondary battery two-layer separator, characterized in that using. The method of claim 1 or 4.
Wherein the method of electrospinning a polymer on a collector is a bottom-up electrospinning method. The method of claim 1 or 4.
Method for producing a two-layer separator for secondary batteries, characterized in that the weight average molecular weight of the meta-aramid is 3,000 to 500,000. A two-layer separator for secondary batteries made of polyimide / metharamid nanofibers prepared by the manufacturing method of claim 4.