KR20100072532A - Electrode-separator complex and method for preparing the same - Google Patents

Abstract

PURPOSE: An electrode-separator complex and a manufacturing method thereof are provided to firmly combine an electrode and a separator, to improve the affinity between an electrolyte and the complex, and to prevent thermal shrinkage. CONSTITUTION: An electrode-separator complex comprises the following: an electrode(10); and a porous polymer separator(20) formed with a super fine fiber including polymer layers(22,24) with two different properties. A manufacturing method of the electrode-separator complex comprises the following steps: forming the electrode by spreading slurry including an electrode active material to a current collector, and drying the active material; and coating the porous polymer separator by electrically radiating two different polymers on the surface the electrode.

Description

Electrode-separator complex and method for preparing the same

The present invention relates to an electrode-membrane composite and a method of manufacturing the same, and more particularly, to an electrode-membrane composite and a method of manufacturing the same that can improve the performance and safety of the electrochemical device.

Recently, as electronic devices and the like have become smaller and lighter, development of energy sources having high density and high energy has been intensively studied. Representative examples thereof include lithium ion batteries and lithium polymer batteries. The lithium ion battery is composed of a negative electrode active material, a positive electrode active material, an organic electrolyte and a separator, and the separator prevents internal short circuit caused by contact between the positive electrode and the negative electrode of the lithium ion battery, and serves to transmit ions. PE) and polypropylene (PP). Since the lithium ion battery has a risk of explosion when overheated, a method of installing a protection circuit, a method of using heat blocking by a separator, and the like have been proposed in order to prevent heat generation of the battery. However, the use of the protection circuit is limited to the miniaturization and cost reduction of the battery pack, and the heat blocking mechanism by the separator is not effective when the heat is generated rapidly.

On the other hand, electrochemical devices such as lithium ion batteries have problems not only with the above-mentioned safety problems but also with the separators currently used. For example, currently produced lithium ion batteries and lithium ion polymer batteries generally use a polyolefin-based separator in order to prevent a short circuit between the positive electrode and the negative electrode. However, polyolefin-based membranes are heat-shrinked at high temperatures due to the properties of the membrane material (e.g., typically melted below 200 ° C) and processing properties (e.g., stretching to control pore size and porosity). There is a drawback to returning to size. Therefore, when the temperature of the battery rises due to internal / external stimulation, the cathode and the cathode are shorted to each other due to shrinkage or melting of the separator, and there is a risk of explosion due to the release of electrical energy. Therefore, it is essential to develop a separator in which heat shrinkage does not occur at high temperatures.

U.S. Patent 5,460,904 discloses a polyvinylidene fluoride (PVdF) based polymer electrolyte in hybrid form. The hybrid type PVdF-based polymer electrolyte is prepared by preparing a polymer matrix having nano-sized pores of submicron size or less, and injecting an organic electrolyte into the pores, and the electrolyte has excellent compatibility with organic electrolytes and pores. Since the leakage of the organic electrolyte injected into the cell is small and safe, the organic electrolyte is injected at the end of the battery manufacturing process, which is advantageous in that the polymer matrix can be prepared in the air. However, in the preparation of the polymer electrolyte, in order to obtain a porous matrix having nano-sized pores, it is necessary to extract the plasticizer contained in the polymer matrix, so that the manufacturing process is difficult. In addition, if the plasticizer is not completely extracted, the remaining plasticizer may deteriorate the characteristics of the battery. In addition, since the PVdF-based electrolyte has excellent mechanical strength but poor adhesive strength with the electrode, there is a critical disadvantage that an additional heating lamination process is required when manufacturing the electrode and the battery.

In Korean Patent Publication No. 10-2005-0006540, a membrane is obtained by electrospinning PVdF, and then a lamination process of heat pressing on one side of an electrode is used to prepare an integrated separator / electrode assembly. A dissolved polyelectrolyte was used. In the above document, since the polymer fiber is manufactured by the electrospinning of the polymer, the diameter of the fiber is small, there is an advantage that the surface area ratio to volume and the porosity is larger than the conventional PE or PP separator, but the adhesion between the separator and the electrode The disadvantage is that an additional heating lamination process is required.

Accordingly, it is an object of the present invention to provide a method for producing an electrode-separation membrane composite using two or more kinds of polymers having different characteristics.

Another object of the present invention is to provide an electrode-separation membrane composite and a method for manufacturing the same, which are firmly bonded to the electrode and the separation membrane, have excellent affinity with the electrolyte solution, and can simultaneously suppress heat shrinkage.

In order to achieve the above object, the present invention, the electrode; And an electrode-separator membrane composite including an ultra-fine fibrous porous polymer membrane coated on the electrode and including two or more polymer layers having different characteristics. The present invention also comprises the steps of (a) applying a slurry containing the electrode active material to the current collector and dried to produce an electrode; And (b) sequentially electrospinning two or more kinds of polymers having different characteristics on the surface of the electrode, thereby coating an ultrafine fibrous porous polymer separator.

In the electrode-membrane composite according to the present invention, the ultrafine fibrous porous polymer membrane and the electrode are integrally bound to form a separator / electrode assembly having excellent bonding property between the membrane and the electrode. In general, in separators for secondary batteries, particularly lithium ion secondary batteries, the "shutdown" and "melt integrity" properties are important properties that govern the stability of the battery. Here, the "shutdown" characteristic is that when the electrolyte heats up due to an external short circuit during the use of the battery, the temperature inside the battery rapidly rises. At this time, the separator partially melts to the extent that the micropores of the porous separator inside the battery are blocked, thereby preventing the micropores. (shut down) It is the characteristic to cut off the flow of current by rapidly increasing the electrical resistance. In addition, the "melt integra" characteristic refers to a characteristic in which the membrane is partially melted and the micropores are blocked by the shutdown characteristic, but the overall shape of the separator is maintained as it is. In addition, if the separator is thermally sensitive to heat shrinkage, since the positive electrode and the negative electrode of the battery are in contact with each other and a short circuit occurs, the internal temperature of the battery increases and there is a risk of explosion. Therefore, the separator should have a shutdown characteristic to cut off current when the temperature rises inside the battery, and to prevent a short circuit by minimizing a meltdown phenomenon and a heat shrinkage phenomenon. Since the electrode-membrane composite according to the present invention has a shutdown layer and a heat shrinkage suppressing layer, the battery can be shut down when the battery is heated to a high temperature, and when the battery is further heated, the meltdown of the separator is prevented, Short circuit and explosion can be suppressed. In addition, in the composite according to the present invention, the separator is excellent in the ability to hold the electrolyte solution, has little leakage of the electrolyte solution, and is excellent in compatibility with the organic electrolyte solution. Therefore, the electrode-membrane composite according to the present invention is particularly useful for electrochemical devices such as lithium secondary batteries.

Hereinafter, with reference to the accompanying drawings, the present invention will be described in detail.

The present invention provides an integrated electrode-membrane composite in which a separator that serves to pass ions and an electrode that undergoes reversible occlusion and release of lithium ions are integrated into one, while preventing electrical contact between the anode and the cathode. to provide. 1 is a cross-sectional view of an electrode-membrane composite according to an embodiment of the present invention. As shown in FIG. 1, the electrode-separation membrane composite according to the present invention includes an electrode 10 and two or more polymer layers 22 and 24 coated on the electrode 10 and having different characteristics. To include, the ultra-fine fibrous porous polymer membrane (20).

The porous polymer separation membrane 20 is formed by sequentially electrospinning two or more kinds of polymer solutions (including a molten solution) having different characteristics, and micropores are formed therein. The matrix of the porous polymer membrane 20 has a form in which ultra-fine polymer fibers having a diameter of 1 to 3000 nm are randomly stacked three-dimensionally, and the surface area to volume ratio is higher than that of the conventional matrix due to the small diameter of the fiber. It was found to be very high and large porosity. Therefore, the impregnation amount of the electrolyte is high due to the high porosity, thereby increasing the ionic conductivity, and in spite of the high porosity, the contact area with the electrolyte may be increased due to the large surface area, thereby minimizing leakage of the electrolyte. And when the porous polymer matrix is prepared by electrospinning, there is an advantage that can be prepared directly in the form of a membrane. The polymer forming the porous polymer separation membrane 20 is not particularly limited as long as it can be formed into a fibrous form, more specifically, a microfine fiber by electrospinning, and examples thereof include polyethylene, polypropylene, cellulose, cellulose acetate, Cellulose acetate butyrate, cellulose acetate propionate, polyvinylpyrrolidone-vinylacetate, poly [bis (2- (2-methoxyethoxyethoxy)) phosphazene], polyethyleneimide, polyethylene oxide, Polyethylene succinate, polyethylene sulfide, poly (oxymethylene-oligo-oxyethylene), polypropylene oxide, polyvinylacetate, polyacrylonitrile, poly (acrylonitrile-co-methylacrylate), polymethylmethacrylate , Poly (methyl methacrylate-co-ethylacrylate), polyvinyl chloride And poly (vinylidene chloride-co-acrylonitrile), polyvinylidene difluoride, poly (vinylidene fluoride-co-hexafluoropropylene) or mixtures thereof. The thickness of the porous polymer matrix produced by the electrospinning method is not particularly limited, but is usually 1 to 300 µm, preferably 1 to 100 µm, more preferably 5 to 70 µm, most preferably 10 to 50 [Mu] m. In addition, the diameter of the fibrous polymer forming the polymer matrix is preferably controlled in the range of 1 to 3000 nm, more preferably in the range of 10 nm to 1000 nm, most preferably in the range of 50 nm to 500 nm. If the diameter of the fiber is too thin, it is difficult to form the separator 20, and if the fiber is too thick, the impregnability of the electrolyte may decrease. In addition, the porosity of the porous polymer membrane 20 coated on the electrode 10 is usually about 30 to 90%, the pore size is about 10 nm to 10μm, the content of the electrolyte is about 50% by weight of the membrane To 500%.

The porous polymer separator 20 according to the present invention includes two or more kinds of polymer layers 22 and 24 having different characteristics, and preferably, the shutdown polymer layer 22 and the heat shrink inhibiting polymer layer 24. It includes. The shutdown polymer layer 22 functions to shut down the battery when the battery is heated to a high temperature. In addition, the thermal shrinkage inhibiting polymer layer 24 may prevent the meltdown of the separator after shutdown in further heating of the battery, thereby ultimately reducing short circuit and explosion of the battery. The polymer is not particularly limited as long as it has a molecular weight such that electrospinning is possible, but it is particularly preferable to have a molecular weight of at least 10,000 or more. When the molecular weight of the polymer is at least 10,000, it is easy to obtain a fibrous phase during electrospinning, and the physical properties of the porous membrane are excellent. There is an advantage that is generated. In addition, the polymer may be used from a polymer having a molecular weight of 2,000 or more in terms of workability and physical properties of the porous membrane, and in the case of ultra high molecular weight polyethylene, a polymer having a molecular weight of 1,000,000 to 5,000,000 may be used. Do. Since the solvent in the polymer solution used in the present invention may be suitable for dissolving the polymer and dispersing the solid particles, those skilled in the art can select and use the polymer and the solid particles according to the type. In particular, the viscosity of the polymer solution is preferably 0.1 cp (10 ^-3 Pa.s) ~ 10 ³ Pa.s. If the viscosity of the polymer solution is within the above range, it is easy to control the electrospinning and morphology of the nanofiber web.

The shutdown polymer layer 22 is a polyolefin resin having a melt index of 1 to 25 g / min, such as polyethylene (PE), polypropylene (PP), polymethylpentene, and ethylene-propylene copolymer having a relatively low melting point. And so on. In addition, the heat shrink inhibiting polymer layer 24 may be a heat-resistant polymer having a melting point of 180 ° C. or higher or polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate, polybutylene naphthalate, or the like. Polyester, polyamide, polyimide, polyamideimide, poly (meth-phenylene isophthalamide), polysulfone, polyetherketone, polyetherimide and the like. The thickness of each of the two or more polymer layers 22 and 24 constituting the porous polymer separator 20 according to the present invention is usually 1 to 50 μm, preferably 1 to 20 μm, more preferably 5 to 10 μm, If the thickness of the polymer layers 22 and 24 is too thin, the effects of the respective polymer layers 22 and 24 are not sufficiently exhibited, and if the thickness of the polymer layers 22 and 24 is too thick, it is economically disadvantageous. There is no special benefit.

In addition, if necessary, the porous polymer separator 20 according to the present invention may further include an electrolyte solution-impregnated polymer layer. The electrolyte solution impregnated polymer layer is made of a swellable polymer material swelled in the electrolyte solution, polyvinylidene fluoride (PVdF); Poly (vinylidene fluoride-co-hexafluoropropylene); Perfuluropolymers; Polyvinyl chloride; Polyvinylidene chloride; Polyethylene glycol derivatives including polyethylene glycol dialkyl ether and polyethylene glycol dialkyl ester; Polyoxides including poly (oxymethylene-oligo-oxyethylene), polyethylene oxide and polypropylene oxide; Polyvinylacetate, poly (vinylpyrrolidone-vinylacetate); Polystyrene, polystyrene acrylonitrile copolymers; Polyacrylonitrile copolymers including polyacrylonitrile, polyacrylonitrile methyl methacrylate copolymer; Polymethyl methacrylate; It consists of polymers, such as a polymethylmethacrylate copolymer and the copolymer of the said components.

On the other hand, as the electrode 10 used in the electrode-membrane composite according to the present invention, a conventional conductive electrode, for example, a conventional positive or negative electrode included in a lithium secondary battery can be used without limitation. In the case of a lithium secondary battery, the electrode 10, the negative electrode or the positive electrode is prepared by mixing an appropriate amount of an active material, a conductive material, a binder, and an organic solvent to prepare a slurry, and then, a copper or aluminum thin grid, which is a current collector. It can be obtained by casting, drying and rolling the prepared slurry on both sides of. The negative electrode active material may be selected from the group consisting of graphite, coke, hard carbon, tin oxide, lithiated ones thereof, lithium, lithium alloys and mixtures thereof, and the positive electrode active material is LiCoO ₂ , LiNiO ₂ , LiNiCoO ₂ , LiMn ₂ O ₄ , V ₂ O ₅ , V ₆ O ₁₃ and mixtures thereof.

Next, referring to FIG. 2, a method of manufacturing the electrode-separation membrane composite according to the present invention will be described. 2 is a schematic diagram of an electrospinning apparatus that may be used in the preparation of the electrode-membrane composite according to the present invention. According to the present invention, a method of manufacturing an electrode-membrane composite includes: (a) applying an slurry containing an electrode active material to a current collector and drying to prepare an electrode; (b) sequentially electrospinning two or more kinds of polymers having different properties on the surface of the electrode, and coating a porous polymer separator on an ultra-fine fibrous surface on the electrode surface; And, if necessary, (c) heating and compressing the electrospun polymer to improve adhesion to the electrode. Electrospinning of the polymer may be performed by melting the polymer or dissolving it in a solvent to prepare a polymer solution. The electrospinning of the polymer melt or solution is coated with an active material, and the grounded electrode plate 5 is placed below the spinning nozzle 4 of the electrospinning apparatus and shuts down from the barrel 1 of the electrospinning apparatus. The molten polymer or the polymer solution having the same is withdrawn through the metering pump (2), and through the spinning nozzle (4) coupled to the high voltage generator (3), by electrospinning on the electrode plate (5) on the top of the charged ultra-fine fibers By forming the shutdown polymer layer, and again through the same process, the molten polymer or polymer solution having excellent heat resistance characteristics from the barrel (1) of the electrospinning apparatus is electrospun into the ultra-fine fibers charged on top of the shutdown polymer layer to heat It may comprise the step of forming a shrinkage inhibiting polymer layer. Using the electrode-separation membrane composite thus prepared, various electrochemical devices such as a lithium secondary battery may be manufactured according to a conventional method.

Hereinafter, the present invention will be described in more detail with reference to Examples. The following examples are intended to illustrate the invention, but the scope of the invention is not limited by the following examples. In the following examples, a slurry composed of PVdF (polyvinylidene fluoride) binder, super-P carbon, and LiCoO ₂ was cast on an aluminum foil as an anode, and MCMB (mesocarbon microbeads), PVdF, and super were used as an anode. A slurry composed of -P carbon was used by casting in copper foil. In the positive electrode and the negative electrode, after the slurry was cast respectively, roll pressing was performed to increase the adhesion between the particles and the metal foil.

Example 1 Formation of Porous Polymer Membrane

A polyethylene (PE) solution having a viscosity of 0.1 cp (10 ^-3 Pa.s) to 10 ³ Pa.s was prepared and added to the barrel (1) of the electrospinning apparatus, and 100 µl / min using the metering pump (2). The polymer solution was discharged at a rate. At this time, by applying charge to the spinning nozzle 4 using the high voltage generator 3, a shutdown polymer layer having a thickness of 50 µm was formed on the metal current collector plate 5 with the electrode plate attached thereto. The polyethylene terephthalate (PET) solution was electrospun on the shutdown polymer layer in the same manner to form a heat shrink inhibiting polymer layer, thereby forming an ultrafine fibrous porous polymer separator. Thus, a scanning electron microscope (SEM) photograph of the polymer layer coated on the surface of the electrode is shown in FIG. 3.

Example 2 Formation of Porous Polymer Membrane

A three-layer structure including an electrolyte-impregnated polymer layer by electrospinning a PVdF (polyvinylidene fluoride) solution having excellent compatibility with an electrolyte solution on the upper portion of the porous polymer separator formed in Example 1 in the same manner as in Example 1 The ultrafine fibrous porous polymer separator of was formed.

1 is a cross-sectional view of an electrode-membrane composite according to an embodiment of the present invention.

2 is a schematic diagram of an electrospinning apparatus that may be used in the preparation of an electrode-membrane composite according to the present invention.

3 is a scanning electron micrograph of a polymer layer formed on the surface of an electrode, according to one embodiment of the invention.

Claims (5)

electrode; And Electrode-separation membrane composite comprising an ultra-fine fibrous porous polymer membrane comprising two or more polymer layers coated on the electrode and having different characteristics. The electrode of claim 1, wherein the porous polymer separator has an ultra-fine fibrous form in which polymer fibers 1 to 3000 nm in diameter are randomly stacked in three dimensions, and the thickness of the porous polymer separator is 1 to 300 μm. Membrane complex. The method of claim 1, wherein the two or more polymer layers having different characteristics include: (a) a shutdown polymer layer made of a polyolefin resin; And (b) polyester, polyamide, polyimide, polyamideimide, poly (meth-phenylene isophthalamide), polysulfone, polyetherketone, polyetherimide and mixtures thereof Will comprise a thermal shrinkage inhibiting polymer layer, electrode- separator composite. The method of claim 3, wherein the two or more polymer layers having different characteristics are polyvinylidene fluoride, perfuluropolymer, polyvinyl chloride, polyvinylidene chloride, polyethylene glycol derivatives, polyoxide, polyvinylacetate, And an electrolyte solution-impregnated polymer layer selected from the group consisting of polystyrene, polyacrylonitrile, polymethylmethacrylate, copolymers of the above components, and mixtures thereof.  (a) applying a slurry containing an electrode active material to a current collector and drying to prepare an electrode; And (B) a method of producing an electrode-separator composite comprising a step of sequentially electrospinning two or more kinds of polymers having different characteristics on the surface of the electrode, to coat the ultra-fine fibrous porous polymer membrane.

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