JPWO2009044856A1 - Electrode for electric double layer capacitor and method for manufacturing the same - Google Patents

Abstract

An object of the present invention is to provide an electrode for an electric double layer capacitor in which an internal resistance is sufficiently reduced and a capacitor suitable for high-speed charge / discharge with a large power can be obtained. An electrode for an electric double layer capacitor according to the present invention includes an active material layer formed by molding an electrode material containing an electrode active material, a granulated particle containing a conductive additive and a binder, and a current collector laminated. The electrode material further contains a fibrous conductive additive outside the granulated particles. Such an electrode for an electric double layer capacitor comprises a step of granulating an electrode active material, a conductive aid, and a binder to obtain granulated particles, and at least a part of the surface of the granulated particles is a fibrous conductive aid. To obtain composite particles, dry forming an electrode material containing the composite particles to form an active material layer, and laminating the active material layer and a current collector.

Description

  The present invention relates to an electrode for an electric double layer capacitor and a manufacturing method thereof. More specifically, the present invention relates to an electrochemical element electrode capable of obtaining an electrode for an electric double layer capacitor having high conductivity and low internal resistance, and a method for producing the same.

  In recent years, electric double layer capacitors (hereinafter sometimes simply referred to as “capacitors”) are attracting attention in high-power applications and regenerative energy applications because they can be charged and discharged at high speed, and their applications are expanding. In capacitors, reduction of internal resistance is an important issue for improving discharge efficiency and regenerative energy efficiency.

  In order to reduce the internal resistance of a capacitor, it has been proposed to form a conductive network structure in an electrode for an electric double layer capacitor (hereinafter sometimes simply referred to as “electrode”). For example, activated carbon particles, which are electrode active materials, and stainless fibers, which are conductive assistants, are kneaded together with a binder (binder), applied to a current collector using a blade, and dried to obtain an electrode. A method is disclosed (see Patent Document 1). In addition, a method is disclosed in which activated carbon, carbon fiber, and PTFE powder as a binder are kneaded to form a clay and pressed to obtain a sheet-like electrode (see Patent Document 2). In these methods, more conductive paths are formed in the electrode by using a fibrous material as the conductive assistant.

  It has also been proposed to use composite particles that contain an electrode active material, a conductive aid, and a binder, and that have a structure in which a conductive aid is unevenly distributed in the outer layer portion. (See Patent Document 3). Since the composite particles are difficult to be deformed at the time of pressure molding, the electrode structure obtained by using the composite particles maintains the particle structure and maintains a network of conductive assistants.

JP 2003-257797 A JP 2006-245386 A JP 2006-310628 A

  However, in the method described in the above document, the internal resistance may not be sufficiently reduced. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an electrode for an electric double layer capacitor in which the internal resistance is sufficiently reduced and a capacitor suitable for high-speed charge / discharge at high power can be obtained. There is.

  As a result of intensive studies, the present inventor used the composite particles obtained by coating at least a part of the surface of the granulated particles containing the electrode active material, the conductive assistant and the binder with a fibrous conductive assistant. The present inventors have found that the problem can be solved, and have completed the present invention based on this knowledge.

Thus, according to the present invention, the following (1) to (6) are provided.
(1) An active material layer formed by molding an electrode material containing granulated particles containing an electrode active material, a conductive additive, and a binder, and a current collector are laminated,
The electrode material for an electric double layer capacitor, wherein the electrode material further contains a fibrous conductive additive outside the granulated particles.

(2) The electrode for an electric double layer capacitor according to (1), wherein the fibrous conductive additive is at least one selected from aluminum fibers, stainless fibers, carbon nanofibers, and carbon nanotubes.

(3) a step of granulating an electrode active material, a conductive additive and a binder to obtain granulated particles;
Mixing the granulated particles and a fibrous conductive additive to obtain an electrode material containing a fibrous conductive aid outside the granulated particles;
A step of dry-molding the electrode material to form an active material layer, and a step of laminating the active material layer and a current collector,
The manufacturing method of the electrode for electric double layer capacitors as described in said (1) which has these.

(4) a step of granulating an electrode active material, a conductive additive and a binder to obtain granulated particles;
A step of coating at least a part of the surface of the granulated particles with a fibrous conductive aid to obtain composite particles;
A step of dry-molding an electrode material containing the composite particles to form an active material layer, and a step of laminating the active material layer and a current collector,
The manufacturing method of the electrode for electric double layer capacitors as described in said (1) which has these.

(5) An electric double layer capacitor having the electric double layer capacitor electrode according to (1) or (2).

  In the electrode for an electric double layer capacitor of the present invention, a conductive network structure is constructed between the granulated particles, and thus the electric resistance of the electric double layer capacitor obtained by using this is sufficiently reduced. Moreover, since this electrode can be manufactured by dry molding, it is excellent in productivity.

  The electrode for an electric double layer capacitor of the present invention is an electrode for an electric double layer capacitor formed by laminating an active material layer and a current collector. The active material layer is formed by molding granulated particles and an electrode material containing a fibrous conductive aid outside the granulated particles, and the granulated particles comprise an electrode active material, a conductive aid and Contains a binder.

<Electrode active material>
As the electrode active material used in the present invention, a carbon allotrope is usually used. The electrode active material preferably has a large specific surface area that can form an interface with a larger area even with the same mass. Specifically, a specific surface area of ^{30 m} 2 / g or more, preferably in the range of 500~5,000m ² / g, more preferably 1,000~3,000m ² / g. Specific examples of the allotrope of carbon include activated carbon, polyacene, carbon whisker, and graphite, and these powders or fibers can be used. A preferred electrode active material for the electric double layer capacitor is activated carbon, and specific examples include phenol-based, rayon-based, acrylic-based, pitch-based, and coconut shell-based activated carbon. These carbonaceous materials can be used alone or in combination of two or more as an electrode active material for an electric double layer capacitor.

  Further, as the electrode active material, non-porous carbon having a microcrystalline carbon similar to graphite and having an increased interlayer distance of the microcrystalline carbon can be used. Such non-porous carbon is obtained by dry-distilling graphitized charcoal with microcrystals of a multilayer graphite structure at 700 to 850 ° C., then heat-treating with caustic at 800 to 900 ° C., and if necessary with heated steam. It is obtained by removing the residual alkali component.

  The volume average particle diameter of the electrode active material is 0.1 to 100 μm, preferably 1 to 50 μm, and more preferably 3 to 35 μm. It is preferable that the volume average particle diameter is in this range because the electrode can be easily molded and the capacity can be increased. The electrode active materials described above can be used alone or in combination of two or more depending on the type of electrochemical element. When the electrode active materials are used in combination, two or more types of electrode active materials having different average particle diameters or particle size distributions may be used in combination.

<Binder>
The binder used in the present invention is not particularly limited as long as it is a compound having a binding force. For example, high molecular compounds, such as a fluorine-type polymer, a diene polymer, an acrylate polymer, a polyimide, polyamide, a polyurethane, are mentioned. Of these, fluorine-based polymers, diene-based polymers, and acrylate-based polymers are preferable, and a fluorine-based polymer is more preferable because of excellent balance between the binding property with the current collector and the internal resistance of the resulting electrode. . These binders can be used alone or in combination of two or more.

  The fluorine-based polymer is a polymer containing a monomer unit containing a fluorine atom. Specific examples of the fluoropolymer include polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer, ethylene / tetrafluoroethylene copolymer, ethylene / chlorotrifluoroethylene copolymer, A perfluoroethylene propene copolymer may be mentioned. Among them, it is preferable to include polytetrafluoroethylene because it is easy to fibrillate and retain the electrode active material.

  The diene polymer is a homopolymer of a conjugated diene or a copolymer obtained by polymerizing a monomer mixture containing a conjugated diene, or a hydrogenated product thereof. The proportion of the conjugated diene in the monomer mixture is usually 40% by mass or more, preferably 50% by mass or more, more preferably 60% by mass or more. Specific examples of the diene polymer include conjugated diene homopolymers such as polybutadiene and polyisoprene; aromatic vinyl / conjugated diene copolymers such as carboxy-modified styrene / butadiene copolymer (SBR); Examples thereof include vinyl cyanide / conjugated diene copolymers such as acrylonitrile / butadiene copolymer (NBR); hydrogenated SBR, hydrogenated NBR, and the like.

  The acrylate polymer is a copolymer obtained by polymerizing a homopolymer of an acrylic ester or a methacrylic ester or a monomer mixture containing these. As the acrylic ester and methacrylic ester, it is preferable to use an alkyl ester, and the alkyl group of the alkyl ester preferably has 1 to 18 carbon atoms.

  The shape of the binder used in the present invention is not particularly limited, but is preferably in the form of particles in order to minimize the increase in binding property, decrease in electrode capacity, and increase in internal resistance. . Examples of the particulate binder include those in which binder particles such as latex are dispersed in a solvent, and powders obtained by drying such a dispersion.

  When the shape of the binder is particulate, the particle diameter is not particularly limited, but usually a volume average particle diameter of 0.001 to 100 μm, preferably 0.01 to 10 μm, more preferably 0.05 to 1 μm. It is what you have. When the average particle size of the binder is within this range, an excellent binding force can be imparted to the active material layer even when a small amount of the binder is used.

  Moreover, the manufacturing method of the binder used for this invention is not specifically limited, Well-known polymerization methods, such as an emulsion polymerization method, a suspension polymerization method, a dispersion polymerization method, or a solution polymerization method, are employable. Among them, it is preferable to produce by an emulsion polymerization method because the particle diameter of the binder is easy to control. Further, the binder used in the present invention may be particles having a core-shell structure obtained by stepwise polymerization of a mixture of two or more monomers.

  The amount of the binder contained in the granulated particles is usually in the range of 1 to 20 parts by mass, preferably 3 to 15 parts by mass with respect to 100 parts by mass of the electrode active material.

<Conductive aid>
The conductive auxiliary agent contained in the granulated particles is not particularly limited as long as it has conductivity. By using granulated particles containing a conductive aid, the conductive aid can be uniformly dispersed during electrode formation, and the resulting capacitor can have a low internal resistance. Examples of the conductive assistant include carbon allotropes or metals, and carbon allotropes are preferably used. Such allotropes of carbon are those that do not have pores that can form an electric double layer. Specifically, furnace black, acetylene black, and ketjen black (registered trademark of Akzo Nobel Chemicals Bethloten Fennaut Shap) And the like, and particulate conductive assistants made of carbon allotropes such as graphite such as natural graphite and artificial graphite. Moreover, the fibrous conductive support agent which consists of carbon allotropes, such as carbon fiber; Examples of conductive assistants made of metal include particulate conductive assistants such as titanium oxide, ruthenium oxide, aluminum, and nickel; and fibrous conductive assistants such as metal fibers. Among these, carbon black is preferable, and acetylene black and furnace black are more preferable.

  The volume average particle diameter of the conductive assistant contained in the granulated particles is preferably smaller than the volume average particle diameter of the electrode active material, and is usually 0.001 to 10 μm, preferably 0.05 to 5 μm, more preferably 0. The range is from 0.01 to 1 μm. When the particle size of the conductive assistant is within this range, high conductivity can be obtained with a smaller amount of use. These conductive assistants can be used alone or in combination of two or more.

  The amount of the conductive assistant contained in the granulated particles is usually 0.1 to 50 parts by mass, preferably 0.5 to 15 parts by mass, more preferably 1 to 10 parts by mass with respect to 100 parts by mass of the electrode active material. It is a range. By forming the electrode using composite particles containing an amount of the conductive aid in this range, the capacitance of the capacitor can be increased and the internal resistance can be decreased.

<Dispersant>
In addition to the above, the granulated particles may contain a dispersant. The dispersant is a resin that dissolves in a solvent, and is preferably used by being dissolved in a solvent at the time of preparing a slurry, which will be described later, and has an action of uniformly dispersing an electrode active material, a conductive assistant, and the like in the solvent. is there. Examples of the dispersant include cellulose polymers such as carboxymethylcellulose, methylcellulose, ethylcellulose, hydroxypropylcellulose, and hydroxypropylmethylcellulose, and ammonium salts or alkali metal salts thereof; ammonium salts or alkali metals of polyacrylic acid or polymethacrylic acid Salts: polyvinyl alcohol, modified polyvinyl alcohol, polyethylene oxide; polyvinyl pyrrolidone, polycarboxylic acid, oxidized starch, phosphate starch, casein, various modified starches, chitin, chitosan derivatives and the like. These dispersants can be used alone or in combination of two or more.
Among these, as the dispersant, a cellulose-based polymer is preferable, and carboxymethyl cellulose or its ammonium salt or alkali metal salt is particularly preferable. Although the quantity of a dispersing agent is not specifically limited, Usually, 0.1-10 mass parts with respect to 100 mass parts of electrode active materials, Preferably it is 0.5-5 mass parts, More preferably, 0.8-2. The range is 5 parts by mass.

<Other additives>
The granulated particles may further contain other additives as necessary. Examples of other additives include a surfactant. Examples of the surfactant include amphoteric surfactants such as anionic, cationic, nonionic, and nonionic anions. Among them, anionic or nonionic surfactants that are easily thermally decomposed are preferable. . Although the quantity of surfactant is not specifically limited, 0-50 mass parts with respect to 100 mass parts of electrode active materials, Preferably it is 0.1-10 mass parts, More preferably, it is the range of 0.5-5 mass parts. is there.

<Method for producing granulated particles>
The granulated particles used in the present invention are particles obtained by granulating the electrode active material, the conductive additive, the binder, and a dispersant and other additives added as necessary. The production method of the granulated particles is not particularly limited, and is a spray drying granulation method, a rolling bed granulation method, a compression granulation method, a stirring granulation method, an extrusion granulation method, a crushing granulation method, a fluidized bed. It can be produced by a known granulation method such as a granulation method, a fluidized bed multifunctional granulation method, or a melt granulation method. Among them, the spray-drying granulation method is preferable because granulated particles in which the binder and the conductive assistant are unevenly distributed near the surface can be easily obtained. When the granulated particles obtained by the spray drying granulation method are used, the electrode of the present invention can be obtained with high productivity. In addition, the internal resistance of the electrode can be further reduced.

<Spray drying granulation method>
In the spray-drying granulation method, the electrode active material, the conductive auxiliary agent, the binder, and the electrode active material, the conductive auxiliary agent, the binder are dispersed or dissolved in a solvent as necessary. A slurry is obtained in which the adhering agent and, if necessary, the dispersing agent and other additives are dispersed or dissolved.

  The solvent used for obtaining the slurry is not particularly limited, but when using the above dispersant, a solvent capable of dissolving the dispersant is preferably used. Specifically, water is usually used, but an organic solvent may be used, or a mixed solvent of water and an organic solvent may be used. Examples of the organic solvent include alkyl alcohols such as methyl alcohol, ethyl alcohol and propyl alcohol; alkyl ketones such as acetone and methyl ethyl ketone; ethers such as tetrahydrofuran, dioxane and diglyme; diethylformamide, dimethylacetamide and N-methyl- Amides such as 2-pyrrolidone and dimethylimidazolidinone; sulfur solvents such as dimethyl sulfoxide and sulfolane; and the like. Among these, alcohols are preferable as the organic solvent. When water and an organic solvent having a lower boiling point than water are used in combination, the drying rate can be increased during spray drying. Further, the dispersibility of the binder or the solubility of the dispersant varies depending on the amount or type of the organic solvent used in combination with water. Thereby, the viscosity and fluidity | liquidity of a slurry can be adjusted and production efficiency can be improved.

  The amount of the solvent used when preparing the slurry is an amount such that the solid content concentration of the slurry is usually in the range of 1 to 50% by mass, preferably 5 to 50% by mass, more preferably 10 to 30% by mass. . When the solid content concentration is in this range, the binder is preferably dispersed uniformly.

  The method or procedure for dispersing or dissolving the electrode active material, conductive additive, binder, dispersant and other additives in a solvent is not particularly limited. For example, the electrode active material, conductive additive, binder in the solvent Add and mix the dispersant, dissolve the dispersant in the solvent, add the binder (for example, latex) dispersed in the solvent, mix, and finally add the electrode active material and conductive aid And a method in which an electrode active material and a conductive additive are added to a binder dispersed in a solvent and mixed, and a dispersant dissolved in a solvent is added to the mixture and mixed. . Examples of the mixing means include mixing equipment such as a ball mill, a sand mill, a bead mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, a homomixer, and a planetary mixer. Mixing is usually performed in the range of room temperature to 80 ° C. for 10 minutes to several hours.

  The viscosity of the slurry is usually in the range of 10 to 3,000 mPa · s, preferably 30 to 1,500 mPa · s, more preferably 50 to 1,000 mPa · s at room temperature. When the viscosity of the slurry is within this range, the productivity of the granulated particles can be increased. Moreover, the higher the viscosity of the slurry, the larger the spray droplets, and the larger the volume average particle diameter of the resulting granulated particles.

  Next, the slurry obtained above is spray-dried and granulated to obtain granulated particles. Spray drying is performed by spraying the slurry in hot air and drying. An atomizer is used as an apparatus used for spraying slurry. There are two types of atomizers: a rotating disk method and a pressure method. The rotating disk system is a system in which slurry is introduced almost at the center of a disk that rotates at a high speed, and the slurry is released out of the disk by the centrifugal force of the disk, and the slurry is atomized at that time. The rotational speed of the disc depends on the size of the disc, but is usually 5,000 to 30,000 rpm, preferably 15,000 to 30,000 rpm. The lower the rotational speed of the disk, the larger the spray droplets and the larger the volume average particle diameter of the resulting granulated particles. Examples of the rotating disk type atomizer include a pin type and a vane type, and a pin type atomizer is preferable. A pin-type atomizer is a type of centrifugal spraying device that uses a spraying plate, and the spraying plate has a plurality of spraying rollers removably mounted on a concentric circle along its periphery between upper and lower mounting disks. It consists of The slurry is introduced from the center of the spray platen, adheres to the spraying roller by centrifugal force, moves outside the roller surface, and finally sprays away from the roller surface. On the other hand, the pressurization method is a method in which the slurry is pressurized and sprayed from a nozzle to be dried.

  The temperature of the slurry to be sprayed is usually room temperature, but may be heated to room temperature or higher. Moreover, the hot air temperature at the time of spray-drying is 80-250 degreeC normally, Preferably it is 100-200 degreeC. In spray drying, the method of blowing hot air is not particularly limited, for example, a method in which the hot air and the spray direction flow in the horizontal direction, a method in which the hot air is sprayed at the top of the drying tower and descends with the hot air, and the sprayed droplets and hot air are in countercurrent contact. And a system in which sprayed droplets first flow in parallel with hot air and then drop by gravity to make countercurrent contact.

  Granulated particles are obtained by spray drying. The volume average particle diameter of the granulated particles is usually 1 to 500 μm, preferably 5 to 300 μm, more preferably 10 to 100 μm, and most preferably 20 to 75 μm. Here, the volume average particle size of the granulated particles is a volume average particle size measured by spraying the granulated particles with compressed air using a laser diffraction particle size distribution measuring device.

<Fibrous conductive auxiliary>
The electrode material used for manufacturing the electrode of the present invention contains a fibrous conductive additive outside the granulated particles in addition to the granulated particles. Here, “externally” means that the fibrous conductive auxiliary agent is present separately from the granulated particles or attached to the surface of the granulated particles, and is taken into the granulated particles. Not included. However, “externally” means that a large part of the fibrous conductive additive is present separately from the granulated particles or adhering to the surface of the granulated particles. It does not exclude the state of being taken inside the particles. That is, in the production of the granulated particles, a fibrous material can be used as the conductive auxiliary agent incorporated into the granulated particles, but even in this case, a fibrous conductive auxiliary agent is further added to the outside in addition to the conductive auxiliary agent. Indicates that it is contained in

  The fibrous conductive auxiliary agent is not limited as long as it is fibrous and has conductivity, but metal fibers such as stainless fiber, aluminum fiber, nickel fiber, iron fiber, copper fiber; polyacrylonitrile-based carbon fiber, pitch-based fiber Carbon fibers such as carbon fibers, vapor grown carbon fibers, carbon nanofibers, and carbon nanotubes are preferred. Two or more kinds of these fibrous conductive assistants can be used in combination. Of these, aluminum fibers, stainless steel fibers, carbon nanofibers, and carbon nanotubes are preferable, and aluminum fibers and carbon nanofibers are more preferable because they are excellent in voltage resistance and electrolyte resistance and can have high conductivity.

  The fiber diameter of the fibrous conductive additive is usually 0.4 nm to 150 μm, preferably 10 nm to 100 μm, more preferably 10 nm to 20 μm, and particularly preferably 10 nm to 200 nm. The fiber length is usually 1 μm to 2,000 μm, preferably 5 μm to 1500 μm, more preferably 10 μm to 1,000 μm, and particularly preferably 100 μm to 700 μm. Further, the aspect ratio (fiber length: fiber diameter) of the fibrous conductive assistant is usually 4: 1 to 15000: 1, and particularly preferably 7: 1 to 12000 when the fibrous conductive assistant is an aluminum fiber. 1: When the fibrous conductive additive is stainless fiber, carbon nanofiber, and carbon nanotube, it is preferably 10: 1 to 10000: 1. When the fiber length, fiber diameter, and aspect ratio are within this range, the conductive aid contained in the granulated particles is excellent in contact with the fibrous conductive aid, and a conductive path can be efficiently formed. An electrode with low internal resistance can be obtained. Here, the fiber diameter and the fiber length are average values of the fiber diameter and the fiber length for 10 arbitrarily selected fibrous conductive assistants when observed with a scanning electron microscope (SEM). .

  The amount of the fibrous conductive additive is usually 0.1 to 50 parts by mass, preferably 0.5 to 15 parts by mass, and more preferably 1 to 10 parts by mass with respect to 100 parts by mass of the granulated particles. When the amount of the fibrous conductive additive is within this range, the capacity of the electric double layer capacitor using the obtained electrode can be increased and the internal resistance can be decreased.

  The fibrous conductive additive is preferably one whose surface is coated with a conductive adhesive. The conductive adhesive is obtained by dispersing a conductive auxiliary powder, a binder, and a dispersant added as necessary in water or an organic solvent. Examples of the conductive assistant for the conductive adhesive include silver, nickel, gold, graphite, acetylene black, and ketjen black, and graphite and acetylene black are preferable. As the binder of the conductive adhesive, any of those exemplified as the binder used in the granulated particles of the present invention can be used. Moreover, water glass, an epoxy resin, a polyamideimide resin, a urethane resin, etc. can also be used, and each can be used individually or in combination of 2 or more types. The binder of the conductive adhesive is preferably an acrylate polymer, an ammonium salt or alkali metal salt of carboxymethyl cellulose, water glass, or polyamideimide resin. Further, as the dispersant for the conductive adhesive, a dispersant that may be used for the granulated particles or a surfactant can be used.

  The method for coating the surface is not particularly limited as long as the conductive adhesive can be brought into contact with the surface of the fibrous conductive additive. For example, the method of adding and mixing a fibrous conductive support agent in the liquid of a conductive adhesive, and then drying is mentioned. In addition, while stirring the conductive adhesive in a mixer such as a high-speed rotary blade mixer (for example, a Henschel mixer manufactured by Mitsui Miike) or an omni mixer, the conductive adhesive is added thereto by spraying or the like and mixed. A method is also mentioned.

<Coating process>
In the electrode material used in the present invention, the granulated particles are preferably used as composite particles obtained by coating at least a part of the surface with the fibrous conductive additive. Here, in the present invention, “coating” means that the fibrous conductive additive is attached to at least a part of the surface of the granulated particle, and it is not necessary to cover the entire surface of the granulated particle. Although the method of coating is not particularly limited, the coating can be usually performed by uniformly mixing the granulated particles and the fibrous conductive additive. In particular, it is preferable to mix the granulated particles and the fibrous conductive additive by a method that does not apply a strong shearing force to the granulated particles so that the granulated particles are not destroyed during the mixing. Since the above-mentioned granulated particles obtained by spray drying are unevenly distributed on the particle surface, even if the shearing force during mixing is weak, the fibrous conductive additive is bound to the granulated particles, Can be coated. Furthermore, it can suppress that the ratio of the secondary aggregation of the composite particle obtained becomes excessive because a fibrous conductive support agent binds to the granulated particle surface.

  As a specific mixing method, a container stirring method using a rocking mixer, a tumbler mixer or the like that is mixed by shaking, rotating, or vibrating the container itself; Horizontal cylindrical mixer, V-type mixer, ribbon-type mixer, conical-type screw mixer, high-speed flow-type mixer, rotation, which is a mixer equipped with blades, rotating disk or screw for stirring And mechanical stirring using a disk-type mixer and a high-speed rotating blade mixer; and airflow stirring using a swirling airflow by compressed gas to mix powder in a fluidized bed. These mechanisms can be used alone or in combination.

  Among these, from the viewpoint of productivity, a high-speed rotary blade mixer (Henschel mixer) that can reduce the stirring time and a slightly strong shear force, and airflow stirring that allows continuous coating treatment are preferable. When using a high-speed rotary blade mixer, the number of rotations is usually 1,000 to 2,500 rpm, preferably 1,500 to 2,000 rpm. When the rotational speed is within this range, composite particles having a surface uniformly coated with a fibrous conductive additive can be obtained without destroying the granulated particle structure in a short time. The mixing time is not particularly limited, but is preferably 5 to 20 minutes. It can be confirmed by observation with a scanning electron microscope or the like that the granulated particles are broken and the surface thereof is coated with the fibrous conductive additive.

  According to said method, the composite particle by which at least one part of the surface was coat | covered with the fibrous conductive support agent can be obtained. By adjusting the type, fiber diameter, fiber length, amount, etc. of the fibrous conductive additive, the ratio of secondary aggregation of the obtained composite particles can be adjusted.

  The electrode material used in the present invention comprises the above granulated particles and a fibrous conductive additive. The electrode material may contain other binders and other additives as necessary. Examples of the other binder contained as required include the same binders as those used for the granulated particles. Since the granulated particles already contain a binder, it is not necessary to add them separately when preparing the electrode material, but in order to increase the binding power, other binders and electrode materials are prepared. You may add when you do. The total amount of the binder contained in the electrode material is usually 0.1 to 50 parts by weight, preferably 0.5 to 20 parts by weight, more preferably 1 to 10 parts by weight with respect to 100 parts by weight of the electrode active material. Part range. Other additives include molding aids such as water and alcohol, and can be appropriately selected in an amount that does not impair the effects of the present invention.

<Electrode for electric double layer capacitor>
The electrode for an electric double layer capacitor of the present invention is formed by laminating an active material layer formed by molding the above electrode material and a current collector.

<Current collector>
As the current collector material used for the electrode, for example, metal, carbon, conductive polymer, and the like can be used, and metal is preferably used. As the current collector metal, aluminum, platinum, nickel, tantalum, titanium, stainless steel, other alloys and the like are usually used. Among these, it is preferable to use aluminum or an aluminum alloy in terms of conductivity and voltage resistance. Further, when high voltage resistance is required, high-purity aluminum disclosed in JP-A-2001-176757 can be suitably used. The current collector is in the form of a film or a sheet, and the thickness thereof is appropriately selected depending on the purpose of use, but is usually 1 to 200 μm, preferably 5 to 100 μm, more preferably 10 to 60 μm. Further, the sheet-like current collector may have a shape having holes such as expanded metal, punching metal, and net-like shape.

  The current collector may be subjected to a surface chemical treatment or a surface roughening treatment in advance to reduce contact resistance with the active material layer or improve adhesion to the active material layer, if necessary. . Examples of the surface chemical treatment include acid treatment and chromate treatment. Examples of the surface roughening treatment include electrochemical etching treatment and etching treatment with acid or alkali.

  Moreover, you may use what applied the conductive adhesive to the surface as a collector. As the conductive adhesive, any of those similar to those used for coating the surface of the fibrous conductive additive can be used.

<Active material layer>
The active material layer may be formed by forming the electrode material into a sheet shape and then laminating the electrode material on the current collector, or may directly form the electrode material on the current collector to form the active material layer. . As a method for forming the active material layer, there are a dry molding method such as a pressure molding method, and a wet molding method such as a coating method, but a dry molding method that does not require a drying step and can reduce manufacturing costs is preferable. . Examples of the dry molding method include a pressure molding method and an extrusion molding method (also referred to as paste extrusion). The pressure forming method is a method of forming an active material layer by applying pressure to the electrode material to perform densification by rearrangement and deformation of the electrode material. The extrusion molding method is a method in which an electrode material is molded into an extruded film, sheet or the like with an extruder.

  Of these, the pressure molding method is preferably employed because it can be performed with simple equipment. Examples of the pressure molding method include a roll pressure molding method in which an electrode material is supplied to a roll-type pressure molding device with a supply device such as a screw feeder, and an active material layer is molded, or an electrode material is placed on a current collector. There are a method of spraying, adjusting the thickness of the electrode material with a blade or the like, and then forming with a pressurizing device, a method of filling the electrode material with a mold and pressurizing the mold, and the like.

  Of these pressure forming methods, the roll pressure forming method is preferred. In this method, the active material layer may be laminated directly on the current collector by feeding the current collector to the roll simultaneously with the supply of the electrode material. The molding temperature is usually 0 to 200 ° C., preferably higher than the melting point or glass transition temperature of the binder of the composite particles, and more preferably 20 ° C. higher than the melting point or glass transition temperature. In roll press molding, the molding speed is usually 0.1 to 20 m / min, preferably 4 to 10 m / min. The press linear pressure between the rolls is usually 0.2 to 30 kN / cm, preferably 1.5 to 15 kN / cm.

  In order to eliminate variations in the thickness of the molded electrode and increase the density of the active material layer to increase the capacity, post-pressurization may be further performed as necessary. The post-pressing method is generally a roll press process. In the roll press process, two cylindrical rolls are arranged in parallel at a narrow interval in the vertical direction, and each is rotated in the opposite direction. The temperature of the roll may be adjusted by heating or cooling.

<Electric double layer capacitor>
The electric double layer capacitor of the present invention has the electrode for the electric double layer capacitor of the present invention. The electric double layer capacitor can be produced according to a conventional method using the electrode of the present invention and components such as an electrolytic solution and a separator. Specifically, for example, the electrode is cut into an appropriate size, then the electrodes are overlapped via a separator, and this is wound into a capacitor shape, folded into a container, and an electrolytic solution is injected into the container. Can be manufactured by sealing.

  The electrolytic solution is not particularly limited, but a nonaqueous electrolytic solution in which an electrolyte is dissolved in an organic solvent is preferable. As the electrolyte, any conventionally known electrolyte can be used, and examples thereof include tetraethylammonium tetrafluoroborate, triethylmonomethylammonium tetrafluoroborate, and tetraethylammonium hexafluorophosphate.

  The solvent for dissolving these electrolytes (electrolyte solvent) is not particularly limited as long as it is generally used as an electrolyte solvent. Specifically, carbonates such as propylene car boat, ethylene carbonate and butylene carbonate; lactones such as γ-butyrolactone; sulfolanes; nitriles such as acetonitrile; These can be used alone or as a mixed solvent of two or more. Of these, carbonates are preferred. The concentration of the electrolytic solution is usually 0.5 mol / liter or more, preferably 0.8 mol / liter or more.

  As the separator, for example, a microporous membrane or non-woven fabric made of polyolefin such as polyethylene or polypropylene, or a porous membrane mainly made of pulp called electrolytic capacitor paper can be used. Moreover, it can replace with a separator and a solid electrolyte can also be used.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not limited to these Examples. In addition, the part and% in an Example and a comparative example are mass references | standards unless there is particular notice.

Measurement and evaluation of each characteristic in Examples and Comparative Examples are performed by the following methods.
(Measurement of volume average particle diameter)
The volume average particle diameter of the activated carbon and the granulated particles is measured with a laser diffraction particle size distribution analyzer (SALD-2000: manufactured by Shimadzu Corporation).
(Measurement of fiber diameter and fiber length)
The fiber diameter and fiber length of the fibrous conductive additive are obtained by observing with a scanning electron microscope (SEM) as an average value of 10 points.

(Characteristics of electric double layer capacitor)
The electric double layer capacitor starts to be charged with a constant current of 10 mA. When the voltage reaches 2.7 V, the voltage is maintained to be constant voltage charging, and the charging is completed when the constant voltage charging is performed for 5 minutes. Next, immediately after the end of charging, discharging is performed at a constant current of 10 mA until reaching 0V. The internal resistance is calculated from the obtained charge / discharge curve according to the calculation method of standard RC-2377 defined by the Japan Electronics and Information Technology Industries Association.

<Example 1>
85 parts of high-purity activated carbon powder having a specific surface area of 2,000 m ² / g and a volume average particle diameter of 5 μm as an electrode active material, and acetylene black (DENKA black powder having a volume average particle diameter of 0.7 μm as a particulate conductive additive 5 parts, manufactured by Denki Kagaku Kogyo Co., Ltd., solid butyl acrylate / methyl methacrylate / methacrylic acid copolymer aqueous dispersion (solid content concentration 28%) as a binder. 9 parts in equivalent of a part, 1.5 parts of a 1.5% aqueous solution of ammonium salt of carboxymethyl cellulose (DN-800H: manufactured by Daicel Chemical Industries, Ltd.) as a dispersant, and 1 part in equivalent of a solid part, and distilled water were added, and “TK A slurry having a solid content concentration of 20% was prepared by stirring and mixing with "Homodisper" (manufactured by Primics). The slurry was sprayed using a spray dryer (OC-16; manufactured by Okawara Kako Co., Ltd.). The rotating disk atomizer (diameter 65 mm) was rotated at 25,000 rpm, the hot air temperature was 150 ° C, and the particle recovery outlet temperature was 90 ° C. Spray granulation was performed to obtain granulated particles having a volume average particle diameter of 50 μm.

  100 parts of the granulated particles and 10 parts of aluminum fibers (fiber diameter: 100 μm, fiber length: 700 μm, aspect ratio (fiber length: fiber diameter) = 7: 1) as a fibrous conductive assistant are used. Was mixed for 15 minutes at 2,000 rpm with a 2 L high-speed mixer (Mitsui Miike Seisakusho Henschel mixer), and composite particles having a fibrous conductive additive adhered to the surface were obtained.

  Next, the obtained composite particles are supplied to a roll (roll temperature 100 ° C., press linear pressure 1.7 kN / cm) of a roll press machine (pressed rough surface heat roll, manufactured by Hirano Giken Kogyo Co., Ltd.) using a quantitative feeder. Then, a sheet-shaped active material layer having a thickness of 480 μm was formed by roll press forming at a forming speed of 2 m / min.

  Separately, a conductive adhesive (Bunny Height # 523-3: manufactured by Nippon Graphite Co., Ltd.) was applied to a 30 μm thick aluminum foil as a current collector and dried to form a conductive adhesive layer. The sheet-like active material layer obtained above was laminated and bonded to the surface of the current collector on which the conductive adhesive layer was formed to obtain a sheet-like electrode having a thickness of 500 μm.

  This sheet electrode was punched out to obtain two circular electrodes having a diameter of 12 mm. Using this electrode, a 35 μm-thick rayon separator was sandwiched so that the active material layers faced each other. This was impregnated with an electrolytic solution to produce a coin cell CR2032-type electric double layer capacitor. As the electrolytic solution, a 1.4 mol / liter propylene carbonate solution of triethylmethylammonium tetrafluoroborate was used. The results of evaluating the characteristics of this capacitor are shown in Table 1.

<Example 2>
As a fibrous conductive aid, carbon nanofiber (VGCF: manufactured by Showa Denko KK, fiber diameter 150 nm, fiber length 20 μm, aspect ratio (fiber length: fiber diameter) = 133: 1) instead of 10 parts of aluminum fiber 5 parts Composite particles were obtained in the same manner as in Example 1 except that was used. Subsequently, an active material layer, an electrode, and a capacitor were formed using the composite particles in the same manner as in Example 1. Table 1 shows the evaluation results of the characteristics of the obtained capacitor.

<Example 3>
As a fibrous conductive assistant, instead of 10 parts of aluminum fiber, 5 parts of carbon nanotube (fiber length 10-30 nm, fiber length 1-100 μm, aspect ratio (fiber length: fiber diameter) = 100: 1-10000: 1) Composite particles are obtained in the same manner as in Example 1 except that is used. Next, an active material layer, an electrode, and a capacitor are formed using the composite particles in the same manner as in Example 1. Table 1 shows the evaluation results of the characteristics of the obtained capacitor.

<Example 4>
Example 1 except that instead of 10 parts of aluminum fiber, 10 parts of stainless steel fiber (fiber diameter 12 μm, fiber length 200 μm, aspect ratio (fiber length: fiber diameter) = 17: 1) is used as the fibrous conductive additive. Similarly, composite particles are obtained. Next, an active material layer, an electrode, and a capacitor are formed using the composite particles in the same manner as in Example 1. Table 1 shows the evaluation results of the characteristics of the obtained capacitor.

<Comparative Example 1>
Granulated particles were obtained in the same manner as in Example 1 except that the amount of high-purity activated carbon powder was 75 parts and the amount of acetylene black was 15 parts. An active material layer, an electrode and a capacitor were formed in the same manner as in Example 1 except that the granulated particles were used as they were without being mixed with the fibrous conductive additive.
Table 1 shows the evaluation results of the characteristics of the obtained capacitor.

<Comparative Example 2>
The amount of high-purity activated carbon powder is 75 parts, and in addition to 10 parts of acetylene black, which is a particulate conductive aid, as a conductive aid, carbon nanofibers, which are fibrous conductive aids (the same as those used in Example 2) Granulated particles were obtained in the same manner as in Example 1 except that 5 parts of the same product was used. The granulated particles were used as they were without being mixed with the fibrous conductive additive, and an active material layer, an electrode and a capacitor were formed in the same manner as in Comparative Example 1. Table 1 shows the evaluation results of the characteristics of the obtained capacitor.

  As apparent from the above, granulated particles and fibrous conductive assistants containing aluminum fibers and stainless fibers, the fibrous conductive assistants obtained using an electrode material present outside the granulated particles, When the electric double layer capacitor electrode of the present invention is used, an electric double layer capacitor having a low internal resistance can be obtained (Examples 1 and 4). On the other hand, when the fibrous conductive assistant is not included (Comparative Example 1) and when the fibrous conductive assistant is present only inside the granulated particles (Comparative Example 2), the total amount of the conductive assistant is Example 1. The electric double layer capacitor obtained has the same internal resistance as that of No. 4 and No. 4. On the other hand, the electric double layer of the present invention obtained by using an electrode material containing carbon nanofibers or carbon nanotubes as a fibrous conductive assistant, and the fibrous conductive assistant is present outside the granulated particles. When the capacitor electrode is used, an electric double layer capacitor having a low internal resistance can be obtained even though the total amount of the conductive additive is small (Examples 2 and 3).

Claims (5)

An active material layer formed by molding an electrode material containing granulated particles containing an electrode active material, a conductive additive, and a binder, and a current collector are laminated,
The electrode material for an electric double layer capacitor, wherein the electrode material further contains a fibrous conductive additive outside the granulated particles.   2. The electrode for an electric double layer capacitor according to claim 1, wherein the fibrous conductive additive is at least one selected from aluminum fibers, stainless fibers, carbon nanofibers, and carbon nanotubes. A step of granulating an electrode active material, a conductive aid, and a binder to obtain granulated particles;
Mixing the granulated particles and a fibrous conductive additive to obtain an electrode material containing a fibrous conductive aid outside the granulated particles;
A step of dry-molding the electrode material to form an active material layer, and a step of laminating the active material layer and a current collector,
The manufacturing method of the electrode for electric double layer capacitors of Claim 1 which has these. A step of granulating an electrode active material, a conductive aid, and a binder to obtain granulated particles;
A step of coating at least a part of the surface of the granulated particles with a fibrous conductive aid to obtain composite particles;
A step of dry-molding an electrode material containing the composite particles to form an active material layer, and a step of laminating the active material layer and a current collector,
The manufacturing method of the electrode for electric double layer capacitors of Claim 1 which has these.   The electric double layer capacitor which has an electrode for electric double layer capacitors in any one of Claim 1 or 2.