JP2010171213A - Electrode for electric double layer capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode for electric double layer capacitor that can improve diffusivity of electrolyte ions, reduce electrode resistance, and improve electrostatic capacity more than a conventional electrode for electric double layer capacitor. <P>SOLUTION: The electrode for electric double layer capacitor contains composite particles containing active carbon activated with steam, active carbon activated with alkali metal hydroxide, and a binder, and having a surface average rate of porosity of ≥15%. The composite particles are preferably particles obtained by atomizing and drying slurry containing active carbon activated with steam, active carbon activated with alkali metal hydroxide, and a binder. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrode for an electric double layer capacitor.

  Utilizing the small size, light weight, high energy density, and the ability to repeatedly charge and discharge, electrochemical devices such as lithium ion secondary batteries, electric double layer capacitors, and lithium ion capacitors are rapidly expanding their demand. ing. Lithium ion secondary batteries have a relatively high energy density and are therefore used in fields such as mobile phones and notebook personal computers. In addition, since the electric double layer capacitor can be rapidly charged and discharged, it is used as a memory backup compact power source for personal computers and the like. Furthermore, the electric double layer capacitor is expected to be applied as a large power source for electric vehicles. Also, with the aim of achieving both high energy density and charge / discharge speed, a hybrid capacitor that uses a Faraday reaction electrode for one of the positive electrode and the negative electrode and a non-Faraday reaction electrode for the other has been developed. In addition, redox capacitors that utilize the oxidation-reduction reaction (pseudo electric double layer capacitance) on the surface of metal oxides or conductive polymers are also attracting attention due to their large capacity. With the expansion and development of applications, these electrochemical elements are required to further improve characteristics such as low resistance, high capacity, and improved mechanical characteristics. Under such circumstances, various improvements have been made on the material forming the electrode for the electric double layer capacitor in order to improve the performance of the electrochemical element.

For example, in Patent Document 1, an electrode active material, a conductive material, a dispersion-type binder, and a soluble resin are dispersed or dissolved in a solvent, and the electrode active material, the conductive material, and the dispersion-type binder are dispersed and dissolved. An electric double layer capacitor electrode having an electrode active material layer obtained by forming a slurry in which a mold resin is dissolved and sheet-forming composite particles obtained by spray drying has been introduced.

  Patent Document 2 introduces an electrode for an electric double layer capacitor that has improved capacitance by using water vapor activated activated carbon and alkali activated activated carbon having a smaller particle diameter, conductive particles, and a binder resin at a specific ratio. Has been.

JP 2006-303395 A JP 2008-34720 A

  However, the composite particles obtained by the method of Patent Document 1 have a surface coated with a conductive material or a fine electrode active material in most of the composite particles. For this reason, the electrode obtained using the particles has insufficient diffusion of electrolyte ions in the electrolytic solution, and the resistance of the electrode has not been sufficiently reduced.

  In addition, the electrode obtained by the method of Patent Document 2 is densely filled with electrode constituent particles, so that the capacity is increased, but the diffusion resistance of electrolyte ions in the electrolytic solution is increased, so that the cell resistance is sufficient. There is no reduction

  Therefore, the present invention provides an electrode for an electric double layer capacitor capable of improving the diffusibility of electrolyte ions, reducing the electrode resistance, and improving the capacitance as compared with the conventional electrode for electric double layer capacitor. It is intended to provide.

As a result of intensive studies in view of the above problems, the present inventors have found that the composite particles obtained by the method of Patent Document 1 often have a low porosity on the surface, and there are few particles with a highly porous surface. I found. For this reason, it has been found that an electrode for an electric double layer capacitor made of the composite particles has a high ion diffusion resistance of the electrolytic solution and it is difficult to reduce the resistance.
As a result of further intensive studies, activated carbon activated with water vapor and activated carbon activated with alkali metal hydroxide are used as activated carbon, and porous composite particles having a high surface porosity are included and have a porosity of a certain amount or more. It has been found that by forming an electrode for an electric double layer capacitor with composite particles, the ion diffusion resistance can be reduced, the resistance of the electrode can be lowered, and the capacitance can be improved. The present inventor has completed the present invention based on these findings.

  That is, this invention which solves the said subject contains the following matters as a summary.

(1) An electrode for an electric double layer capacitor comprising activated carbon activated with water vapor, activated carbon activated with an alkali metal hydroxide, and a composite particle comprising a binder and having a surface average porosity of 15% or more.

(2) An electrode for an electric double layer capacitor, wherein the composite particles are particles obtained by spray-drying a slurry containing activated carbon activated with water vapor, activated carbon activated with an alkali metal hydroxide, and a binder.

(3) An electrode for an electric double layer capacitor, wherein the binder is a polymer containing no fluorine.

(4) An electrode for an electric double layer capacitor, wherein the binder is a (meth) acrylate polymer or a diene polymer.

(5) An electrode for an electric double layer capacitor having an electrode layer formed by pressure-molding the composite particles on a current collector.

  The electrode for the electric double layer capacitor of the present invention uses activated carbon activated with water vapor and activated carbon activated with an alkali metal hydroxide as activated carbon, and the composite particles having a large surface porosity containing the activated carbon are formed into an electrode layer. By using it as a material, it is possible to achieve higher capacity and lower resistance than conventional electrodes.

  An electrode for an electric double layer capacitor of the present invention comprises activated carbon activated with water vapor, activated carbon activated with an alkali metal hydroxide, and a composite particle having a surface average porosity of 15% or more. Is included.

<Composite particle>
The composite particles used in the present invention include activated carbon activated with water vapor, activated carbon activated with an alkali metal hydroxide, and a binder.
The composite particles referred to in the present invention are a combination of a plurality of materials such as activated carbon activated with water vapor, activated carbon activated with alkali metal hydroxide and an essential component of a binder, and optional components such as a conductive agent described later. It refers to the particles that have become.

(Activated carbon)
Examples of the activated carbon material used for the electric double layer capacitor electrode of the present invention include phenol-based, rayon-based, acrylic-based, pitch-based, and coconut shell-based activated carbon.

  Activated carbon activated with an alkali metal hydroxide used in the present invention (hereinafter sometimes abbreviated as “alkali activated activated carbon”) is a mixture of the activated carbon material and an alkaline agent such as potassium hydroxide (KOH), After the heat treatment, it is obtained by repeating washing, filtration and drying.

BET specific surface area of the alkali activated carbon used in the present invention, 1,500~5,000m ² / g, preferably 2,000~4,000m ² / g, more preferably 2,000~3,000m ² / g It is. By making the BET specific surface area of the alkali activated carbon within the above range, it is possible to achieve a balance between low resistance and high capacity.

  The volume average particle diameter of the alkali activated carbon is 0.1 to 50 μm, preferably 0.5 to 20 μm, more preferably 2 to 10 μm.

  The content ratio of the alkali activated carbon in the composite particles is 40% by weight or more, preferably 40 to 50% by weight, more preferably 40 to 45% by weight. By setting the content ratio of the alkali activated carbon in the composite particles in the above range, the internal resistance of the electric double layer capacitor can be further reduced.

  The activated carbon activated with steam used in the present invention (hereinafter sometimes abbreviated as “steam activated activated carbon”) is obtained by repeatedly washing, filtering and drying the activated carbon material and the steam gas after the heat treatment. is there.

BET specific surface area of steam activated carbon used in the present invention, 50~2000m ² / g, preferably from 200~1,700m ² / g, more preferably 1000~1,700m ² / g. By setting the BET specific surface area of the steam activated activated carbon within the above range, a balance between low resistance and high capacity can be achieved.

  The volume average particle diameter of the steam activated activated carbon is 0.5 to 100 μm, preferably 1 to 50 μm, more preferably 12 to 20 μm.

  The content ratio of the steam activated activated carbon in the composite particles is 40% by weight or more, preferably 40 to 50% by weight, and more preferably 40 to 45% by weight. By setting the content ratio of the water vapor activated activated carbon in the composite particles in the above range, the capacitance of the electric double layer capacitor can be further increased.

  The content ratio of the water vapor activated carbon and the alkali activated carbon in the composite particles is 80 to 95% by weight, preferably 80 to 90% by weight, and more preferably 83 to 86% by weight. When the content ratio of the alkali activated carbon and the water vapor activated activated carbon in the composite particles is within the above range, the capacitance can be increased, and the electrode strength can be prevented from being lowered.

(Binder)
The binder used for the electrode for the electric double layer capacitor of the present invention is not particularly limited as long as it is a polymer capable of binding an alkali-activated activated carbon, a steam-activated activated carbon, a conductive agent described later, and the like. It is preferable that it is a polymer which does not contain. Because the binder is a polymer that does not contain fluorine, binding can be achieved with a smaller amount of use than a polymer that contains fluorine, so increasing the amount of activated carbon per volume increases the capacitance density. Also, the internal resistance can be reduced.

  Examples of the polymer not containing fluorine include polymer compounds such as diene polymers, (meth) acrylate polymers, polyimides, polyamides, polyurethanes, among which diene polymers and acrylate polymers are preferable. When a diene polymer or (meth) acrylic polymer is used as the binder, these binders have high binding strength, so the amount of the binder used can be reduced. Capacitance and low internal resistance are possible.

  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 weight or more, preferably 50% by weight or more, more preferably 60% by weight 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); Copolymers of styrene / butadiene / methacrylic acid copolymer and aromatic vinyl / conjugated diene / carboxylic acid group-containing monomers such as styrene / butadiene / itaconic acid copolymer; acrylonitrile / butadiene copolymer (NBR) And vinyl cyanide / conjugated diene copolymers such as hydrogenated SBR and hydrogenated NBR.

The (meth) acrylate-based polymer has the general formula (1): CH ₂ = CR ¹ -COOR ² (wherein R ¹ represents a hydrogen atom or a methyl group, and R ² represents an alkyl group or a cycloalkyl group). It is a polymer containing the monomer unit derived from the compound represented by these. Specific examples of the compound represented by the general formula (1) include ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, n-amyl acrylate, Acrylates such as isoamyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, hexyl acrylate, nonyl acrylate, lauryl acrylate, stearyl acrylate; ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n methacrylate -Butyl, isobutyl methacrylate, t-butyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, isodecyl methacrylate, methacrylate Le lauryl, tridecyl methacrylate include methacrylates such as such as stearyl methacrylate. Among these, acrylate is preferable, and n-butyl acrylate and 2-ethylhexyl acrylate are particularly preferable in that the strength of the obtained electrode can be improved. The ratio of the monomer unit derived from the compound represented by the general formula (1) in the acrylate polymer is usually 50% by weight or more, preferably 70% by weight or more. When a (meth) acrylate polymer in which the ratio of the monomer unit derived from the compound represented by the general formula (1) is in the above range is used, the heat resistance is high and the obtained electrode for an electric double layer capacitor The internal resistance can be reduced.

  As the (meth) acrylate polymer, in addition to the compound represented by the general formula (1), a copolymerizable carboxylic acid group-containing monomer can be used. Specific examples include acrylic acid, methacrylic acid, Monobasic acid-containing monomers such as acids; dibasic acid-containing monomers such as maleic acid, fumaric acid, and itaconic acid. Among these, a dibasic acid-containing monomer is preferable, and itaconic acid is particularly preferable in terms of enhancing the binding property with the current collector and improving the electrode strength. These monobasic acid-containing monomers and dibasic acid-containing monomers can be used alone or in combination of two or more. The amount of the carboxylic acid group-containing monomer in the copolymerization is usually 0.1 to 50 parts by weight, preferably 0.5 to 20 parts per 100 parts by weight of the compound represented by the general formula (1). Part by weight, more preferably in the range of 1 to 10 parts by weight. When the amount of the carboxylic acid group-containing monomer is within this range, the binding property with the current collector is excellent, and the obtained electrode strength is increased.

  In addition to the compound represented by the general formula (1), a copolymerizable nitrile group-containing monomer can be used for the (meth) acrylate polymer. Specific examples of the nitrile group-containing monomer include acrylonitrile, methacrylonitrile, and the like. Among them, acrylonitrile is preferable in that the binding strength with the current collector is increased and the electrode strength can be improved. The amount of acrylonitrile is usually 0.1 to 40 parts by weight, preferably 0.5 to 30 parts by weight, more preferably 1 to 20 parts by weight with respect to 100 parts by weight of the compound represented by the general formula (1). Range. When the amount of acrylonitrile is within this range, the binding property with the current collector is excellent, and the obtained electrode strength is increased.

  The binder is not particularly limited depending on its shape, but has good binding properties, and can be prevented from being deteriorated due to a decrease in the capacitance of the created electrode or repeated charge / discharge, so that it is particulate. Is preferred. Examples of the particulate binder include those in which particles of a dispersion-type binder such as latex are dispersed in water, and powders obtained by drying such a dispersion.

  The number average particle size of the particulate binder is not particularly limited, but is usually 0.0001 to 100 μm, preferably 0.001 to 10 μm, more preferably 0.01 to 1 μm. When the number average particle diameter of the binder is within this range, an excellent binding force can be imparted to the electrode layer described later even when a small amount of the binder is used. Here, the number average particle diameter is a number average particle diameter calculated as an arithmetic average value obtained by measuring the diameter of 100 binder particles randomly selected in a transmission electron micrograph. The shape of the particles can be either spherical or irregular.

  A binder can be used individually or in combination of 2 or more types. The content ratio of the binder in the composite particles is preferably 0.1 to 15% by weight, preferably 3 to 10% by weight, more preferably 5 to 10% by weight. By setting the content ratio of the binder in the composite particles in the above range, the balance between the mechanical properties of the electric double layer capacitor electrode and the reduction in internal resistance can be improved.

  The composite particles may contain components other than water vapor activated activated carbon, alkali activated activated carbon, and binder. Examples of other components include a conductive agent, a dispersant, and a surfactant.

(Conductive agent)
The composite particles used in the present invention preferably contain a conductive agent. The conductive agent is composed of an allotrope of particulate carbon that has conductivity and does not have pores that can form an electric double layer, and improves the conductivity of the electric double layer capacitor. Specific examples of the conductive material include conductive carbon black such as furnace black, acetylene black, and ketjen black (registered trademark of Akzo Nobel Chemicals Bethloten Fennot Shap); graphite such as natural graphite and artificial graphite; Can be mentioned. Among these, conductive carbon black is preferable, and acetylene black and furnace black are more preferable.

  The volume average particle size of the conductive agent is preferably smaller than the volume average particle size of the alkali-activated activated carbon, usually in the range of 0.001 to 10 μm, preferably 0.05 to 5 μm, more preferably 0.01 to 1 μm. is there. When the particle size of the conductive agent is within this range, high conductivity can be obtained with a smaller amount of use.

  These conductive agents can be used alone or in combination of two or more. The amount of the conductive agent is usually 0.1 to 20 parts by weight, preferably 0.5 to 15 parts by weight, and more preferably 1 to 10 parts by weight with respect to 100 parts by weight of activated carbon (a total of steam-activated activated carbon and alkali-activated activated carbon). The range is parts by weight. When composite particles having an amount of the conductive agent in this range are used, the capacitance of the electric double layer capacitor can be increased and the internal resistance can be decreased.

(Dispersant)
The dispersant is used by being dissolved in a solvent of a slurry described later, and further has an action of uniformly dispersing activated carbon (water vapor activated activated carbon and alkali activated activated carbon), a binder, a conductive agent, and the like in the solvent. For example, cellulosic polymers such as carboxymethyl cellulose, methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, and ammonium salts or alkali metal salts thereof; polyacrylic acid (or methacrylic acid) salts such as sodium polyacrylic acid (or methacrylic acid); polyvinyl Examples include alcohol, modified polyvinyl alcohol, polyethylene oxide; polyvinyl pyrrolidone, polycarboxylic acid, oxidized starch, phosphate starch, casein, various modified starches, chitin, and chitosan derivatives. These dispersants can be used alone or in combination of two or more. Among these, a cellulose polymer is preferable, and carboxymethyl cellulose or an ammonium salt or an alkali metal salt thereof is particularly preferable. In order to increase the surface average porosity on the surface of the composite particles, those having a weight average molecular weight of 300,000 or more are preferable.

  These dispersants can be used alone or in combination of two or more. Although the amount of the dispersant used is not particularly limited, it is usually 0.1 to 10 parts by weight, preferably 0.5 to 5 parts per 100 parts by weight of activated carbon (a total of water vapor activated carbon and alkali activated carbon). Part by weight, more preferably in the range of 0.8 to 2 parts by weight. By using a dispersing agent, sedimentation and aggregation of solid content in the slurry can be suppressed. Moreover, since the clogging of the atomizer at the time of spray drying can be prevented, spray drying can be performed stably and continuously.

  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. These additives can be used alone or in combination of two or more.

  The amount of the surfactant is not particularly limited, but is 0 to 20 parts by weight, preferably 0.1 to 10 parts by weight, more preferably 100 parts by weight of activated carbon (a total of water vapor activated carbon and alkali activated carbon). Is in the range of 0.5 to 5 parts by weight.

The composite particles used in the present invention have a surface average porosity of 15% or more, preferably 20% or more, more preferably 20% or more and 40% or less, and particularly preferably 20% or more and 30% or less. Here, the “surface average porosity” is an apparent appearance of voids of 0.1 μm ² or more on the surface of the composite particle for 5 particles or more (each with different fields of view) and 10 particles or more per composite particle. It is a value obtained as an average value of the ratio (%) of the apparent surface area of the void to the total visual field area (hereinafter sometimes referred to as “void ratio”). When the surface average porosity of the composite particles is less than 15%, the diffusion resistance of the electrolyte ions in the composite particles increases, and the resistance of the electrode obtained by using this increases.

Specifically, the surface average porosity is obtained by taking an electron micrograph of the composite particles used in the present invention, observing 5 or more fields per arbitrarily selected particle, and continuously having an area of 0.1 μm ² or more. The apparent surface area of the voids is measured, the same measurement is performed for 10 particles or more, and the average value of the obtained voids is calculated. The apparent surface area of the void is an area corresponding to the surface area of the opening of the void observed on the electron micrograph, and is not an actual area taking into consideration the area in the pores of the void. When individual composite particles are viewed, composite particles having a porosity of less than 15% may be included, but particles having a porosity of 15% or more (in the present specification, described as “porous composite particles”). As a result, the overall surface average porosity is increased as described above.

  The shape of the composite particles used in the present invention is preferably substantially spherical. That is, when the short axis diameter of the composite particles is Ls, the long axis diameter is Ll, La = (Ls + Ll) / 2, and the value of (1− (Ll−Ls) / La) × 100 is sphericity (%). The sphericity is preferably 80% or more, more preferably 90% or more. Here, the minor axis diameter Ls and the major axis diameter Ll are values measured from a transmission electron micrograph image.

  The volume average particle diameter of the composite particles used in the present invention is usually in the range of 10 to 200 μm, preferably 20 to 150 μm, more preferably 30 to 100 μm. The volume average particle diameter can be measured using a laser diffraction particle size distribution measuring apparatus.

  The granulation method of the composite particles is not particularly limited, and is spray drying granulation method, rolling bed granulation method, compression granulation method, stirring granulation method, extrusion granulation method, crushing granulation method, 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 these, the spray-drying granulation method is preferable because composite particles in which a binder and a conductive agent are unevenly distributed near the surface can be easily obtained.

  The composite particles used in the present invention are preferably particles obtained by spray drying a slurry containing water vapor activated activated carbon, alkali activated activated carbon, and a binder. The composite particles used in the present invention are particles obtained by spray-drying a slurry containing water vapor activated activated carbon, alkali activated activated carbon, and a binder, so that the electric double layer capacitor electrode of the present invention has high productivity. And the internal resistance of the electrode can be further reduced.

  The slurry can be obtained by dispersing or dissolving a steam-activated activated carbon, an alkali-activated activated carbon and an essential component of a binder and an optional component such as a conductive agent in a solvent.

  The solvent used for obtaining the slurry is not particularly limited, but when the above dispersant is used, 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; 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 water vapor activated activated carbon, the essential component of the alkali activated carbon and the binder, and the optional components such as the conductive agent and the dispersant in the solvent is not particularly limited. For example, the alkali activated carbon, A method of adding and mixing essential components of water vapor activated activated carbon and a binder, and optional components such as a conductive agent and a dispersant; a binder (for example, latex) which is dissolved in a solvent and then dispersed in the solvent Finally, a method of adding and mixing water vapor activated activated carbon and alkali activated carbon, and optional components such as a conductive agent and a dispersing agent; water vapor activated activated carbon, alkali activated to a binder dispersed in a solvent Examples include a method in which activated carbon and a conductive agent are added and mixed, and a dispersant dissolved in a solvent is added to and mixed with the mixture. 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 500 to 3000 mPa · s, preferably 750 to 2000 mPa · s, and more preferably 1000 to 1500 mPa · s at room temperature. If the slurry viscosity is too high, granulation may be difficult. On the other hand, if the slurry viscosity is too low, the surface average porosity of the resulting composite particles tends to decrease. The slurry viscosity is a value measured using a B-type viscometer under conditions of a temperature of 25 ° C. and a rotation speed of 60 rpm.

  The viscosity of the slurry can be appropriately controlled depending on the type and blending amount of the activated carbon, binder and dispersant used, and in particular when the cellulose polymer is used as the dispersant, the type of the cellulose polymer. The slurry viscosity can be easily controlled within the above range by appropriately selecting the molecular weight and the blending amount. For example, when a high molecular weight cellulose polymer is used, the slurry viscosity increases, and when a low molecular weight cellulose polymer is used, the slurry viscosity decreases.

  By spray-drying and granulating a slurry having a specific viscosity as described above, composite particles having a surface average porosity of 15% or more can be easily obtained. Although not limited theoretically, the present inventor estimates the following granulation mechanism. That is, by spray-drying the slurry, the dispersion medium in the slurry is volatilized and composite particles are obtained. At this time, the dispersion medium volatilizes from the surface of the granulated composite particles. The dispersion medium inside the composite particles moves in the composite particles toward the surface and volatilizes from the surface. Along with the dispersion medium moving inside the composite particles, the fine particles in the slurry also move to the surface. Therefore, the higher the mobility of the fine particles in the slurry, the more the fine particles gather on the surface of the composite particles, the surface becomes denser, and the surface porosity of the resulting composite particles decreases. For this reason, in order to obtain porous composite particles, the mobility of the fine particles in the slurry may be controlled to prevent the fine particles from moving to the vicinity of the surface. Based on the above estimation, the present inventor considered that porous composite particles can be easily obtained if the slurry viscosity is controlled within a specific range, and the present invention has been completed.

  Next, the slurry obtained above is spray-dried and granulated to obtain composite 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 composite 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 spraying direction flow in parallel, 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.

  The electrode for an electric double layer capacitor of the present invention preferably has an electrode layer formed by press-molding composite particles on a current collector. When the electric double layer capacitor electrode of the present invention has such a configuration, an electric double layer capacitor electrode with low productivity and low resistance can be produced.

  As a method of having an electrode layer formed by pressure-molding composite particles on a current collector, (a) pressure-molding the composite particles into a sheet shape, and using the obtained sheet-shaped electrode layer as a current collector Method of laminating; (b) A method of supplying composite particles onto a current collector and press-molding this to form an electrode layer; (c) A method of supplying composite particles onto a substrate and press-molding it And a method of forming an electrode layer on the substrate and transferring the electrode layer onto the current collector using the substrate having the electrode layer. Among these methods, (b) a method in which the composite particles are supplied onto a current collector and pressure-molded to form an electrode layer is preferable.

  As a material constituting this in the case of using a substrate, an inorganic material, an organic material or the like can be used without limitation as long as the electrode layer can be formed on the substrate. For example, aluminum foil, copper foil, ionomer film (IO film), polyethylene film (PE film), polyethylene terephthalate film (PET film), polyethylene naphthalate film (PEN film), polyvinyl chloride film (PVC film), polychlorinated Vinylidene film (PVDC film), polyvinyl alcohol film (PVA film), polypropylene film (PP film), polyester film, polycarbonate film (PC film), polystyrene film (PS film), polyacrylonitrile film (PAN film), ethylene-acetic acid Vinyl copolymer film (EVA film), ethylene-vinyl alcohol copolymer film (EVOH film), ethylene - methacrylic acid copolymer film (EMAA film), nylon film (NY film, a polyamide (PA) film), cellophane, imide films, paper and the like. Moreover, you may use the film of the multilayered structure which accumulated the said film. Among these, a thermoplastic resin film is preferable from the viewpoint of versatility and handleability, and a PET film, a PE film, a PVC film, and the like are particularly preferable. Moreover, you may give the peeling process to the base-material surface in which an electrode layer is formed.

  Although the thickness of a base material is not specifically limited, 5 micrometers-200 micrometers are suitable, and 30 micrometers-150 micrometers are more suitable. The width is not particularly limited, but is preferably about 100 mm to 1000 mm, and more preferably about 200 mm to 500 mm.

The current collector is an electrode substrate having a current collecting function. As the material, for example, metal, carbon, conductive polymer, and the like can be used, and metal is preferably used. As the metal, aluminum, platinum, nickel, tantalum, titanium, stainless steel, copper, and other alloys are usually used. Among these, it is preferable to use aluminum or an aluminum alloy in terms of conductivity and voltage resistance.
The thickness of the current collector used in the present invention is usually 5 to 100 μm, preferably 10 to 70 μm, and particularly preferably 20 to 50 μm.

  In the present invention, when producing an electrode for an electric double layer capacitor on the current collector by the method (b) above, the feeder used in the step of supplying the composite particles is not particularly limited, but the composite particles are quantitatively analyzed. It is preferable that it is a fixed quantity feeder which can be supplied to the. Here, being able to supply quantitatively means that composite particles are continuously supplied using such a feeder, the supply amount is measured a plurality of times at regular intervals, and the average value m of the measured values and the standard deviation σm are obtained. It means that the CV value (= σm / m × 100) is 4 or less. The quantitative feeder used in the present invention preferably has a CV value of 2 or less. Specific examples of the quantitative feeder include a gravity feeder such as a table feeder and a rotary feeder, and a mechanical force feeder such as a screw feeder and a belt feeder. Of these, the rotary feeder is preferred.

  Next, the current collector and the supplied composite particles are pressurized with a pair of rolls to form an electrode layer on the current collector. In this step, the composite particles heated as necessary are formed into a sheet-like electrode layer with a pair of rolls. The temperature of the supplied composite particles is preferably 40 to 160 ° C, more preferably 70 to 140 ° C. When composite particles in this temperature range are used, there is no slip of the composite particles on the surface of the press roll, and the composite particles are continuously and uniformly supplied to the press roll. An electrode layer with little variation can be obtained.

  The temperature at the time of molding is usually 0 to 200 ° C., preferably higher than the melting point or glass transition temperature of the binder, and more preferably 20 ° C. higher than the melting point or glass transition temperature. The forming speed in the case of using a roll is usually larger than 0.1 m / min, preferably 35 to 70 m / min. Moreover, the press linear pressure between the rolls for a press is 0.2-30 kN / cm normally, Preferably it is 0.5-10 kN / cm.

  In the above manufacturing method, the arrangement of the pair of rolls is not particularly limited, but is preferably arranged substantially horizontally or substantially vertically. When arranged substantially horizontally, the current collector is continuously supplied between a pair of rolls, and the composite particles are supplied to at least one of the rolls so that the composite particles are supplied to the gap between the current collector and the rolls. The electrode layer can be formed by pressurization. When arrange | positioning substantially perpendicularly, the said electrical power collector is conveyed in a horizontal direction, a composite particle is supplied on an electrical power collector, and a composite particle layer is formed. After the supplied composite particle layer is leveled with a blade or the like as necessary, the current collector is supplied between a pair of rolls, and an electrode layer can be formed by pressurization. In this case, the thickness of the composite particle layer supplied between the pair of rolls is usually a value represented by (roll gap between the pair of rolls) / (current collector thickness + electrode layer thickness). 0.01 to 1, preferably 0.1 to 0.5.

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

The density of the electrode layer is not particularly limited, but is usually 0.30 to 10 g / cm ³ , preferably 0.35 to 5.0 g / cm ³ , more preferably 0.40 to 3.0 g / cm ³ . . The thickness of the electrode layer is not particularly limited, but is usually 5 to 1000 μm, preferably 20 to 500 μm, and more preferably 30 to 300 μm.

(Conductive adhesive layer)
In the present invention, it is preferable to have a conductive adhesive layer in addition to the electrode layer containing composite particles. By having the conductive adhesive layer, the binding strength between the electrode layer and the current collector can be increased.

The conductive adhesive layer contains carbon particles as an essential component.
Carbon particles used for the conductive adhesive layer include graphite having high conductivity due to the presence of delocalized π electrons (specifically, natural graphite, artificial graphite, etc.); several layers of graphitic carbon microcrystals Carbon black (specifically, acetylene black, ketjen black, other furnace blacks, channel blacks, thermal lamp blacks, etc.), which are spherical aggregates that have gathered together to form a turbulent structure, such as carbon fibers and carbon whiskers Among these, graphite or carbon black is particularly preferable in that the carbon particles of the conductive adhesive layer can be packed at a high density, the electron transfer resistance can be reduced, and the internal resistance of the electric double layer capacitor can be reduced.

  In the present invention, it is particularly preferable that the carbon particles used in the conductive adhesive layer are those listed above alone and used in combination. Specific examples include graphite and carbon black, graphite and carbon fiber, graphite and carbon whisker, carbon black and carbon fiber, carbon black and carbon whisker, and preferably graphite and carbon black, graphite and carbon fiber, and carbon black. And carbon fiber, particularly preferably graphite and carbon black, and graphite and carbon fiber. When the carbon particles are in this combination, the carbon particles of the conductive adhesive layer are filled with high density, so that the electron transfer resistance is reduced and the internal resistance of the electric double layer capacitor is reduced.

In the present invention, the electrical resistivity of the carbon particles used for the conductive adhesive layer is preferably 0.0001 to 1 Ω · cm, more preferably 0.0005 to 0.5 Ω · cm, and particularly preferably 0.001. ~ 0.1 Ω · cm. When the electrical resistivity of the carbon particles is within this range, the electron transfer resistance of the conductive adhesive layer can be reduced, and the internal resistance of the electric double layer capacitor can be reduced. Here, the electrical resistivity is measured by using a powder resistance measurement system (MCP-PD51 type; manufactured by Dia Instruments Co., Ltd.) while measuring the resistance value while applying pressure to the carbon particles, and the resistance value converged with respect to the pressure. The electrical resistivity ρ (Ω · cm) = R × (S / d) is calculated from R (Ω), the area S (cm ² ) and the thickness d (cm) of the compressed carbon particle layer.

  In the present invention, the volume average particle diameter of the carbon particles used for the conductive adhesive layer is preferably 0.01 to 20 μm, more preferably 0.05 to 15 μm, and particularly preferably 0.1 to 10 μm. When the volume average particle diameter of the carbon particles is within this range, the carbon particles of the conductive adhesive layer are filled with high density, so that the electron transfer resistance is reduced and the internal resistance of the electric double layer capacitor is reduced. Here, the volume average particle diameter is a volume average particle diameter calculated by measuring with a laser diffraction particle size distribution analyzer (SALD-3100; manufactured by Shimadzu Corporation).

  In the present invention, the conductive adhesive layer preferably contains a binder. When the conductive adhesive layer contains a binder, the adhesion between the current collector and the electrode layer can be increased, the internal resistance of the electric double layer capacitor can be reduced, and the output density can be increased.

In the present invention, as the binder suitably used for the conductive adhesive layer, those described in the above-mentioned composite particles can be used, and the preferred binder is a dispersion-type binder having a property of being dispersed in a solvent. is there. Examples of the dispersion-type binder include polymer compounds such as fluoropolymers, diene polymers, (meth) acrylate polymers, polyimides, polyamides, polyurethane polymers, and the like. -Based polymers or (meth) acrylate-based polymers are preferable, and diene-based polymers or (meth) acrylate-based polymers can increase the withstand voltage and increase the energy density of the electric double layer capacitor. More preferred.
In the present invention, the content of the binder in the conductive adhesive layer is preferably 0.5 to 20 parts by weight, more preferably 1 to 15 parts by weight, particularly preferably 100 parts by weight of the carbon particles. 2 to 10 parts by weight.

In the present invention, examples of components other than the binder that may be contained in the conductive adhesive layer include a dispersant and a surfactant.
As the dispersant, those described for the composite particles can be used. The amount of the dispersant can be used within a range that does not impair the effects of the present invention, and is not particularly limited, but is usually 0.1 to 20 parts by weight, preferably 0.1 to 100 parts by weight of the carbon particles. It is 5-15 weight part, More preferably, it is the range of 0.8-10 weight part.

  As the surfactant, those described for the composite particles can be used. The amount of the surfactant can be used as long as the effect of the present invention is not impaired, and is in the range of 0.5 to 20 parts by weight with respect to 100 parts by weight of the carbon particles, and 1.0 to 15 parts by weight. Preferably, 2.0 to 10 parts by weight is particularly preferable. When the blending amount of the surfactant is within this range, the durability of the electric double layer capacitor is excellent.

  The thickness of the conductive adhesive layer is usually 0.01 to 20 μm, preferably 0.1 to 10 μm, particularly preferably 1 to 5 μm. When the thickness of the conductive adhesive layer is in the above range, good adhesiveness can be obtained and the electron transfer resistance can be reduced.

  As a method for forming a conductive adhesive layer, a conductive adhesive obtained by kneading a material constituting the conductive adhesive layer such as a binder or carbon particles in a dispersion medium such as water or an organic solvent. Examples of the method include forming the slurry composition by applying to a current collector and drying.

  Examples of the organic solvent when an organic solvent is used as the dispersion medium 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; And amides such as diethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone and dimethylimidazolidinone; sulfur solvents such as dimethylsulfoxide and sulfolane; and the like.

  Specifically, a ball mill, a sand mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, a planetary mixer, a Hobart mixer, and the like can be used as a method for producing the conductive adhesive slurry composition.

  The method for forming the conductive adhesive layer is not particularly limited. For example, the conductive adhesive slurry composition is formed on a current collector by a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, brushing, or the like.

  The solid content concentration of the conductive adhesive slurry composition is usually 10 to 60%, preferably 15 to 50%, and particularly preferably 20 to 40%, although it depends on the coating method. When the solid content concentration is within this range, the resulting conductive adhesive layer is highly filled, and the energy density and output density of the electric double layer capacitor are increased.

  Examples of the method for drying the conductive adhesive layer include drying by warm air, hot air, low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays or electron beams. Among these, a drying method by irradiation with far infrared rays is preferable. The drying temperature and the drying time are preferably a temperature and a time at which the solvent in the slurry applied to the current collector can be completely removed, and the drying temperature is usually 50 to 300 ° C, preferably 80 to 250 ° C. The drying time is usually 2 hours or less, preferably 5 seconds to 30 minutes.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not limited to these Examples. In the examples and comparative examples, “part” and “%” are based on weight unless otherwise specified. Each characteristic in Examples and Comparative Examples is measured according to the following method.

(Measurement of specific surface area of activated carbon)
The specific surface area of the activated carbon is measured by a BET measurement method by adsorbing nitrogen gas to the activated carbon using a specific surface area measuring device (Gemini 2310, manufactured by Shimadzu Corporation).

(Measurement of slurry viscosity)
The slurry viscosity is measured using a B-type viscometer (RB80L: manufactured by Toki Sangyo Co., Ltd.) under conditions of a temperature of 25 ° C. and a rotation speed of 60 rpm.

(Surface average porosity of composite particles)
The average surface porosity of the composite particles produced in the following examples and comparative examples is determined by the following method.

First, an electron micrograph of the composite particles was measured at a magnification of 2000 times, and arbitrary particles were read into image analysis software (analySIS: Soft Imaging System) as black and white 256-gradation image data within a field of view of 20 μm ² . The contrast is optimized so that the brightest part of the image is 255 and the darkest part is 0. Next, the threshold value is set to 77, binarization processing is performed, and the ratio of voids having an area of 0.1 μm ² or more on the composite particle surface is obtained from the obtained binarized image.

  For the same particle, the same measurement is performed 5 times in any different field of view, and the same measurement is performed for 10 particles, and the average is the surface average porosity of the composite particles.

(Measurement of volume average particle diameter)
The volume average particle diameter of the composite particles is measured using a laser diffraction particle size distribution analyzer (SALD-2000: manufactured by Shimadzu Corporation).

(Measurement of electrode layer thickness)
The thickness of the electrode layer is measured using an eddy current displacement sensor (sensor head unit EX-110V, amplifier unit unit EX-V02: manufactured by Keyence Corporation) after the electrode layers are formed on both sides of the current collector. The thickness of each electrode layer is measured at intervals of 2 cm, and the average value thereof is taken as the thickness of the electrode layer.

(Measurement of internal resistance)
The electric double layer capacitor starts to be charged with a constant current of 600 mA. When a predetermined charging voltage is reached, the voltage is maintained to be constant voltage charging, and charging is completed when constant voltage charging is performed for 5 minutes. Next, immediately after the end of charging, discharging is performed at a constant current of 15 mA until reaching 0V. This charging / discharging operation is performed for 3 cycles, and the internal resistance is calculated by the relationship of R = ΔV / I from the voltage value 0.1 seconds after the end of the third cycle discharge.

(Measurement of capacitance density)
The electric double layer capacitor starts to be charged with a constant current of 600 mA. When a predetermined charging voltage is reached, the voltage is maintained to be constant voltage charging, and charging is completed when constant voltage charging is performed for 5 minutes. Next, immediately after the end of charging, discharging is performed at a constant current of 15 mA until reaching 0V. This charge / discharge operation is performed for three cycles, and the capacitance C is obtained from the relationship of discharge energy E = 1/2 CV ^{2 in} the third cycle. The capacitance density is calculated from the capacitance C.

Example 1
(Preparation of composite particles for electrodes for electric double layer capacitors)
As the activated carbon, 43 parts of steam activated carbon having a specific surface area of 500 m ² / g and a volume average particle diameter of 17 μm, 43 parts of alkali activated carbon having a specific surface area of 1800 m ² / g and a volume average particle diameter of 8 μm, a conductive agent (acetylene black “DENKA BLACK” "Powder": 6 parts of Denki Kagaku Kogyo Co., Ltd., dispersion type binder (number average particle size 0.15 µm, glass transition temperature-40 ° C cross-linked acrylate polymer 40% aqueous dispersion: 17.5 parts of “AD211” (manufactured by Nippon Zeon Co., Ltd.), 50 parts of dispersant 1 (1% aqueous solution of carboxymethylcellulose “DN-800H”: manufactured by Daicel Chemical Industries, Ltd.), dispersant 2 (carboxy 50 parts of 1% aqueous solution of methylcellulose “BSH-12” (Daiichi Kogyo Seiyaku Co., Ltd.) and 290.5 parts of ion-exchanged water K. The mixture was stirred and mixed with a homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.) to obtain a slurry having a solid content concentration of 20% and a viscosity of 760 mPa · s. Subsequently, this slurry was spray-dried with hot air at 150 ° C. using a spray dryer (with a pin type atomizer manufactured by Okawara Chemical Industries Co., Ltd.), and spherical composite particles having a surface porosity of 15% and a volume average particle size of 72 μm were obtained. Obtained.

(Preparation of conductive adhesive layer)
100 parts of graphite (KS-6; manufactured by Timcal) having a volume average particle diameter of 3.7 μm and electric resistivity of 0.004 Ω · cm as carbon particles, and 4.0% aqueous solution of carboxymethyl cellulose (DN-10L) as a dispersant Manufactured by Daicel Chemical Industries, Ltd.) 4 parts in solid content, 8 parts of a 40% aqueous dispersion of a diene polymer having a number average particle size of 0.25 μm as a binder, and 8 parts of ion exchange water in total solids. A slurry composition for forming a conductive adhesive layer was prepared by mixing so that the partial concentration was 30%.

  A pair of dies are disposed downstream of the current direction of the current collector so as to sandwich an aluminum current collector having a thickness of 20 μm, which travels in the vertical direction (the current direction of the current collector is upward from the bottom). The slurry composition for forming the conductive adhesive layer was discharged from the die, applied to both the front and back surfaces of the current collector at a molding speed of 30 m / min, dried at 120 ° C. for 5 minutes, and one side thickness of 4 μm. An aluminum current collector having a conductive adhesive layer formed on both sides was obtained.

(Production of electrode for electric double layer capacitor)
A roll for press of a roll press machine (pressed rough surface heat roll; manufactured by Hirano Giken Co., Ltd.) using a quantitative feeder (Nikka Spray K-V, manufactured by Nikka Co., Ltd.) at a supply rate of 70 g / min. (Roll temperature 120 ° C., press linear pressure 4 kN / cm). Then, an aluminum current collector having the conductive adhesive layer formed on both sides thereof is inserted between the press rolls, and the composite particles supplied from the quantitative feeder are adhered to both sides of the conductive adhesive layer. Then, an electrode for an electric double layer capacitor having an electrode layer with an average single-side thickness of 280 μm and an average single-side density of 0.50 g / cm ³ on both surfaces was obtained.

(Preparation of measurement cell)
The electrode produced above is cut out so that the current collector sheet portion on which no electrode layer is formed remains 2 cm long × 2 cm wide and the portion where the electrode layer is formed is 5 cm wide × 5 cm wide ( The collector sheet portion in which the electrode layer is not formed is formed so as to extend one side of the 5 cm × 5 cm square in which the electrode layer is formed. 10 sets of positive electrodes and 11 sets of negative electrodes cut out in this way are prepared, and the uncoated portions are ultrasonically welded respectively. Furthermore, the current collector sheet portion in which the electrode layer is formed by laminating and welding the tab material having a length of 7 cm, a width of 1 cm and a thickness of 0.01 cm made of aluminum for the positive electrode and nickel for the negative electrode is measured by ultrasonic welding. An electrode is prepared. The measurement electrode is vacuum-dried at 200 ° C. for 24 hours. Using a cellulose / rayon mixed non-woven fabric with a thickness of 35 μm as a separator, the terminal welds of the positive electrode current collector and the negative electrode current collector are arranged on opposite sides, and the positive electrode and the negative electrode are alternated and laminated. All of the outermost electrodes of the prepared electrodes are laminated so as to be a negative electrode. Separators were placed on the top and bottom, and four sides were taped.

  After covering the above laminated electrode with an exterior laminate film and fusing three sides, a solution prepared by dissolving tetraethylammonium borofluoride at a concentration of 1.4 mol / L in propylene carbonate as an electrolytic solution was vacuum impregnated, and then the other side was melted. A film type capacitor (electric double layer capacitor) was produced. Each characteristic was measured about the obtained film type capacitor. The results are shown in Table 1.

(Example 2)
In the preparation of the composite particles of Example 1, a water vapor activated activated carbon having a specific surface area of 1200 m ² / g and a volume average particle size of 17 μm, and an alkali activated carbon having a specific surface area of 2400 m ² / g and a volume average particle size of 8 μm. An electrode for an electric double layer capacitor and an electric double layer capacitor were produced in the same manner as in Example 1 except that alkali activated carbon was used. The slurry viscosity of this formulation was 785 mPa · s, and the composite particles had a surface porosity of 15% and a volume average particle diameter of 70 μm. Each characteristic of the electric double layer capacitor was measured. The results are shown in Table 1.

(Example 3)
In the preparation of the composite particles of Example 2, the same procedure as in Example 2 was conducted, except that 100 parts of a 1% aqueous solution of carboxymethylcellulose (“BSH-12” manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was used as the dispersant. Thus, an electrode for an electric double layer capacitor and an electric double layer capacitor were produced. The slurry viscosity of this blend was 1330 mPa · s, the surface porosity of the composite particles was 21%, and the volume average particle size was 81 μm. Each characteristic of the electric double layer capacitor was measured. The results are shown in Table 1.

Example 4
In the preparation of the composite particles of Example 3, a polytetrafluoroethylene (PTFE) dispersion (“D-210C”; a 60% aqueous dispersion of PTFE, manufactured by Daikin Industries, Ltd.) is used as a dispersion-type binder. An electrode for an electric double layer capacitor and an electric double layer capacitor were produced in the same manner as in Example 3 except that 5 parts were used. The slurry viscosity of this blend was 1480 mPa · s, the surface porosity of the composite particles was 23%, and the volume average particle diameter was 85 μm. Each characteristic of the electric double layer capacitor was measured. The results are shown in Table 1.

(Comparative Example 1)
In the preparation of the composite particles of Example 3, an electrode for an electric double layer capacitor was obtained in the same manner as in Example 3 except that 86 parts of water vapor activated activated carbon having a specific surface area of 1200 m ² / g and a volume average particle size of 17 μm was used as the activated carbon. An electric double layer capacitor was produced. The slurry viscosity of this blend was 1400 mPa · s, and the composite particles had a surface porosity of 24% and a volume average particle diameter of 79 μm. Each characteristic of the electric double layer capacitor was measured. The results are shown in Table 1.

(Comparative Example 2)
In the preparation of the composite particles of Example 3, an electrode for an electric double layer capacitor was obtained in the same manner as in Example 3 except that 86 parts of alkali activated carbon having a specific surface area of 2400 m ² / g and a volume average particle size of 17 μm was used as the activated carbon. An electric double layer capacitor was produced. The slurry viscosity of this blend was 1450 mPa · s, and the composite particles had a surface porosity of 25% and a volume average particle diameter of 82 μm. Each characteristic of the electric double layer capacitor was measured. The results are shown in Table 1.

(Comparative Example 3)
In the preparation of the composite particles of Example 3, the same procedure as in Example 3 was used except that 100 parts of a 1% aqueous solution of carboxymethyl cellulose (“DN-800H” manufactured by Daicel Chemical Industries, Ltd.) was used as a dispersant. A multilayer capacitor electrode and an electric double layer capacitor were produced. The slurry viscosity of this blend was 480 mPa · s, the surface porosity of the composite particles was 11%, and the volume average particle size was 70 μm. Each characteristic of the electric double layer capacitor was measured. The results are shown in Table 1.

  From the above, when the electrode for electric double layer capacitor electrode of the present invention is used, the capacity of the obtained electric double layer capacitor can be higher than that of the conventional one and the internal resistance can be lowered.

Claims (5)

Activated carbon activated by steam,
Activated carbon activated with alkali metal hydroxide,
And comprising a binder,
An electrode for an electric double layer capacitor comprising composite particles having a surface average porosity of 15% or more. The electrode for an electric double layer capacitor according to claim 1, wherein the composite particles are particles obtained by spray-drying a slurry containing activated carbon activated with water vapor, activated carbon activated with an alkali metal hydroxide, and a binder. . The electrode for an electric double layer capacitor according to claim 1 or 2, wherein the binder is a polymer containing no fluorine. The electrode for an electric double layer capacitor according to any one of claims 1 to 3, wherein the binder is a (meth) acrylate polymer or a diene polymer. The electrode for electric double layer capacitors which has an electrode layer formed by press-molding the composite particle of Claim 1 on a collector.