JP2010171211A - 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 increase capacitance and also reduce internal resistance more than a conventional electrode for electric double layer capacitor. <P>SOLUTION: The electrode for electric double layer capacitor contains an electrode material containing active carbon activated with alkali metal hydroxide, active carbon activated with steam, and a binder, the binder being a polymer containing no fluorine. The binder is preferably a (meth)acrylate-based polymer or diene-based polymer. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

  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, Patent Document 1 discloses an electrode for an electric double layer capacitor using, as activated carbon, steam activated activated carbon and alkali activated activated carbon having a particle diameter smaller than that of steam activated activated carbon, conductive particles, and a binder at a specific ratio.

JP 2008-34720 A

  However, even with the electrode obtained by the method of Patent Document 1, a sufficient increase in capacitance and a reduction in internal resistance are not achieved, and a further increase in capacitance and a reduction in internal resistance are required.

  Accordingly, an object of the present invention is to provide an electrode for an electric double layer capacitor capable of increasing the capacitance and reducing the internal resistance as compared with the prior art.

  As a result of intensive investigations in view of the above problems, the present inventor has used a polymer containing fluorine as a binder in Patent Document 1, and therefore, in order to satisfy a desired electrode strength, the amount of the binder used is limited. As a result, it was discovered that the increase in capacitance and the reduction in internal resistance were not sufficient. Therefore, as a result of further investigation, by using together activated carbon activated with alkali metal hydroxide and activated carbon activated with water vapor as activated carbon, and using a polymer containing no fluorine as a binder, high capacity and low resistance. It has been found that an electrode can be produced.

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

(1) An activated carbon activated with an alkali metal hydroxide, activated carbon activated with water vapor, and an electrode material containing a binder, wherein the binder is a polymer containing no fluorine. Electric double layer capacitor electrode.

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

(3) The electrode for electric double layer capacitors whose glass transition temperature of the said binder is 20 degrees C or less.

(4) The electrode for an electric double layer capacitor, wherein the electrode material further contains a dispersant.

(5) An electrode for an electric double layer capacitor, wherein the electrode material is composite particles formed by binding activated carbon activated with an alkali metal hydroxide and activated carbon activated with water vapor with a binder.

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

  According to the present invention, an activated carbon activated with an alkali metal hydroxide and activated carbon activated with water vapor are used in combination as activated carbon, and a high-capacity and low-resistance electrode is obtained by using a fluorine-free polymer as a binder. can get.

<Electrode material>
The electrode for an electric double layer capacitor of the present invention comprises an electrode material containing activated carbon activated with an alkali metal hydroxide, activated carbon activated with water vapor, and a binder, and the binder does not contain fluorine. It is a polymer.

(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 electrode material is preferably 40% by weight or more, more preferably 40 to 50% by weight, and particularly preferably 45 to 50% by weight. By setting the content ratio of the alkali activated carbon in the electrode material 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 above activated carbon material and steam gas after heat treatment. It is.

BET specific surface area of steam activated carbon is, 50~2000m ² / g, preferably 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 electrode material is preferably 40% by weight or more, more preferably 40 to 50% by weight, and particularly preferably 40 to 45% by weight. By setting the content ratio of the water vapor activated activated carbon in the electrode material in the above range, the capacitance of the electric double layer capacitor can be further increased.

  The content ratio of the water vapor activated activated carbon and the alkali activated carbon in the electrode material is 80 to 95% by weight, preferably 80 to 90% by weight, and more preferably 83 to 86% by weight. By setting the content ratio of the alkali activated carbon and the water vapor activated activated carbon in the electrode material 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 formed of a polymer containing no fluorine. 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 that does not contain fluorine include polymer compounds such as diene polymers, (meth) acrylate polymers, polyimides, polyamides, and polyurethanes, among which diene polymers and (meth) acrylate polymers. Is preferred. 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 an acrylate polymer in which the proportion 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 internal resistance of the obtained electrode for an electric double layer capacitor is reduced. Can be small.

  As the acrylate polymer, a copolymerizable carboxylic acid group-containing monomer can be used in addition to the compound represented by the general formula (1). Specific examples include acrylic acid and methacrylic acid. Monobasic acid-containing monomers; 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 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 glass transition temperature of the binder is preferably 20 ° C. or less, more preferably 10 ° C. or less, and particularly preferably 0 ° C. or less. By setting the glass transition temperature of the binder within the above range, the electrode flexibility is good. In addition, the minimum of the glass transition temperature of a binder is -50 degreeC.

  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.

  These binders can be used alone or in combination of two or more. The amount of the binder used is usually 0.1 to 15% by weight, preferably 3 to 10% by weight, more preferably 5 to 10% by weight in the electrode material. By setting the content ratio of the binder in the electrode material in the above range, the balance between the mechanical properties of the electrode and the reduction in internal resistance can be improved.

  The electrode material used in the present invention may contain other components than the steam activated activated carbon, the alkali activated activated carbon, and the binder. Examples of other components include a conductive agent, a dispersant, and a surfactant.

(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 the electrode material having the amount of the conductive agent within this range is used, the capacitance of the electric double layer capacitor can be increased and the internal resistance can be decreased.

(Dispersant)
In the present invention, the electrode material preferably further contains a dispersant in addition to the activated carbon and the binder. By containing a dispersing agent, it becomes easy to disperse | distribute activated carbon and a electrically conductive agent uniformly.
The dispersant is used by being dissolved in a slurry solvent described later, and further has an action of uniformly dispersing 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, it is possible to suppress sedimentation and aggregation of solids in a slurry described later. 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.

(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. 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 electrode material used in the present invention is not particularly limited, and for example, (i) contains at least alkali activated carbon, water vapor activated activated carbon, and a binder, and is obtained by mixing these and other components added as necessary. (Ii) a paste-like product obtained by mixing at least an alkali-activated activated carbon, a steam-activated activated carbon and a binder, and these and other components added as necessary in a solvent; (iii) ) At least alkali-activated activated carbon, steam-activated activated carbon, and a binder, and include composite particles in which alkali-activated activated carbon and steam-activated activated carbon are bound by a binder. And a composite particle comprising an alkali-activated activated carbon and a steam-activated activated carbon bound by a binder. Rukoto is preferable. Electric double layer capacitor obtained by the electrode material containing at least alkali activated carbon, water vapor activated activated carbon and binder, and composite particles formed by binding alkali activated carbon and water vapor activated activated carbon with the binder The electrode strength of the working electrode can be increased, and the internal resistance can be reduced. In addition, composite particle | grains here refer to the particle | grains which several materials integrated, such as an alkali activated activated carbon, water vapor activated activated carbon, a binder, and the material which may be contained as needed.

(Composite particles)
In the present invention, a composite particle suitable as an electrode material is obtained by spray-drying a slurry containing an alkali-activated activated carbon, a steam-activated activated carbon, and an essential component of a binder, and other components that may be included as necessary. It can be obtained by spray granulation.
Examples of the other components include a conductive agent, a dispersant, and a surfactant.

  As the solvent used for obtaining the slurry, water is usually used, but 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- Examples include amides such as 2-pyrrolidone and dimethylimidazolidinone; sulfur solvents such as dimethyl sulfoxide and sulfolane; and alcohols are preferable. When an organic solvent having a lower boiling point than water is used in combination, the drying rate can be increased during granulation by the spray drying method. In addition, since the dispersibility of the dispersion-type binder or the solubility of the soluble resin varies depending on the type of solvent, the viscosity and fluidity of the slurry are adjusted by selecting the amount or type of organic solvent, and spray drying production Efficiency can be improved.

  The amount of the solvent used when preparing the slurry is such that the solid content concentration of the slurry is usually in the range of 1 to 50% by weight, preferably 5 to 50% by weight, more preferably 10 to 30% by weight. Amount.

The method or procedure for dispersing or dissolving the alkali-activated activated carbon, the steam-activated activated carbon, the binder, and the optional component in the solvent is not particularly limited. For example, the solvent-activated activated carbon, the alkali-activated activated carbon, the binder, A method of adding and mixing the other components; adding and mixing a binder (for example, latex) dispersed in a solvent, and adding and mixing the steam-activated activated carbon, the alkali-activated activated carbon, and the other components Method: Steam activated activated carbon, alkali activated activated carbon, and a method in which the above-mentioned other components are dispersed in a solvent are added to a binder 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, and a planetary mixer. Mixing is usually performed in the range of room temperature to 80 ° C. for 10 minutes to several hours.

  The spray drying method is a method of spraying and drying a slurry in hot air. A typical example of the apparatus used for the spray drying method is an atomizer. 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 high speed, and the slurry is released from the disk by the centrifugal force of the disk, and in that case, the slurry is dried in the form of a mist.

  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. 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. The hot air temperature at the time of spray drying is usually 80 to 250 ° C, preferably 100 to 200 ° C. In the spray drying method, the method of blowing hot air is not particularly limited. Examples include a contact method, and a method in which sprayed droplets first flow in parallel with hot air and then drop by gravity to make countercurrent contact. Furthermore, heat treatment is performed to cure the surface of the composite particles. The heat treatment temperature is usually 80 to 300 ° C.

  The shape of the composite particles suitably 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 suitably used in the present invention is generally 10 to 100 μm, preferably 20 to 80 μm, more preferably 30 to 60 μm. The volume average particle diameter can be measured using a laser diffraction particle size distribution measuring apparatus.

<Electrode for electric double layer capacitor>
The electrode for an electric double layer capacitor according to the present invention is one having an electrode layer containing the electrode material or an electrode layer on a current collector.

(Current collector)
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.

(Conductive adhesive layer)
In the present invention, it is preferable to have a conductive adhesive layer in addition to the electrode layer containing the electrode material. By having a 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, as the carbon particles used for the conductive adhesive layer, those mentioned above may be used alone or in combination of two kinds. 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. By including a binder in the conductive adhesive layer, 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 electrode material part can be used, and the preferred binder is a dispersion type binder having a property of being dispersed in a solvent. It is. 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 a dispersing agent, what was demonstrated in the part of the electrode material 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 in the electrode material section 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 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. Since the electrode for an electric double layer capacitor of the present invention has such a configuration, an electric double layer capacitor electrode with low productivity and high 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 base material, inorganic materials and organic materials can be used without limitation as long as the electrode layer can be formed on the base material. 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.

  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 used in the present invention 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. 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.

  In the present invention, when a conductive adhesive layer is provided between the current collector and the electrode layer, the material constituting the conductive adhesive layer such as a binder or carbon particles before forming the electrode layer The conductive adhesive layer may be formed by applying and drying a conductive adhesive slurry composition obtained by kneading in a dispersion medium such as water or an organic solvent on a current collector.

  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.

  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 within the above range, good adhesiveness can be obtained and the electron transfer resistance can be reduced.

  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 an Example and a comparative example is measured in accordance with 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 volume average particle diameter)
The volume average particle diameter of the composite particles contained in the electrode material for an electric double layer capacitor 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 electrode material for electric double layer capacitor)
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.), 100 parts of a dispersant (1% aqueous solution of carboxymethyl cellulose “DN-800H”: manufactured by Daicel Chemical Industries, Ltd.), and ion-exchanged water 290. Five parts 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 of 20%. 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.) to obtain an electrode material composed of spherical composite particles having a volume average particle size of 60 μm. .

(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 is prepared by mixing so that the partial concentration is 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 layer)
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 rolls for pressing, and the composite particles supplied from the quantitative feeder are adhered to both sides of the conductive adhesive layer. 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 preparing the electrode material of Example 1, an electrode for an electric double layer capacitor was prepared in the same manner as in Example 1 except that alkali-activated activated carbon having a specific surface area of 2400 m ² / g and a volume average particle size of 8 μm was used as the alkali-activated activated carbon. An electric double layer capacitor was produced. Each characteristic of the electric double layer capacitor was measured. The results are shown in Table 1.

(Example 3)
In the preparation of the electrode material of Example 1, an electric double layer capacitor electrode was obtained in the same manner as in Example 1 except that a water vapor activated activated carbon having a specific surface area of 1200 m ² / g and a volume average particle size of 8 μm was used as the water vapor activated carbon. An electric double layer capacitor was produced. Each characteristic of the electric double layer capacitor was measured. The results are shown in Table 1.

Example 4
In preparing the electrode material of Example 3, an electrode for an electric double layer capacitor was obtained in the same manner as in Example 3 except that alkali-activated activated carbon having a specific surface area of 2400 m ² / g and a volume average particle size of 8 μm was used as the alkali-activated activated carbon. An electric double layer capacitor was produced. Each characteristic of the electric double layer capacitor was measured. The results are shown in Table 1.

(Example 5)
In the preparation of the electrode material of Example 4, the electrode for the electric double layer capacitor and the electric double layer were used in the same manner as in Example 4 except that the amount of activated carbon used was 35 parts of water vapor activated activated carbon and 35 parts of alkali activated carbon. A capacitor was produced. Each characteristic of the electric double layer capacitor was measured. The results are shown in Table 1.

(Example 6)
In the preparation of the electrode material of Example 4, a diene polymer having a glass transition temperature of 20 ° C. and a number average particle diameter of 0.25 μm (50% by weight of styrene, 45% by weight of butadiene, An electrode for an electric double layer capacitor and an electric double layer capacitor were prepared in the same manner as in Example 4 except that a 40% aqueous dispersion of a copolymer obtained by emulsion polymerization of 5% by weight of acid was used. 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 electrode material of Example 5, a polytetrafluoroethylene (PTFE) dispersion (“D-210C”; a 60% aqueous dispersion of PTFE, manufactured by Daikin Industries, Ltd.) was 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 5 except that 7 parts were used. Each characteristic of the electric double layer capacitor was measured. The results are shown in Table 1.

(Comparative Example 2)
As the activated carbon, 35 parts of steam activated carbon having a specific surface area of 1200 m ² / g and a volume average particle diameter of 17 μm, 35 parts of alkali activated carbon having a specific surface area of 2400 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., polytetrafluoroethylene (PTFE) dispersion ("D-210C") as a dispersion-type binder (60% aqueous dispersion of PTFE, Daikin Industries, Ltd.) )) Was mixed with 11.6 parts of ethanol and kneaded, and then roll-rolled to obtain a polarizable sheet having a thickness of 280 μm.

  The above polarizable sheet was layered on an aluminum current collector formed on both sides with a conductive adhesive prepared in the same manner as in Example 1, and this was pressed through a compression roll to securely bond the contact interfaces together. A laminated sheet was obtained. The laminated sheet was passed through a continuous hot air dryer set at a temperature of 150 ° C., and the dispersion medium was evaporated and removed from the conductive adhesive liquid layer to obtain a polarizable electrode (electrode for electric double layer capacitor). In Example 1, an electric double layer capacitor was produced in the same manner as in Example 1 except that the polarizable electrode was used as the electrode for the electric double layer capacitor. Each characteristic of the electric double layer capacitor was measured. The results are shown in Table 1.

(Comparative Example 3)
An electrode for an electric double layer capacitor and an electric double layer capacitor were produced in the same manner as in Comparative Example 2, except that 16.7 parts of PTFE was used as a dispersion-type binder in the preparation of the polarizable sheet of Comparative Example 2. Each characteristic of the electric double layer capacitor was measured. The results are shown in Table 1.

(Comparative Example 4)
In the preparation of the polarizable sheet of Comparative Example 3, the amount of activated carbon used was 43 parts of water vapor activated activated carbon and 43 parts of alkali activated activated carbon. A multilayer capacitor was fabricated. Table 1 shows the measurement results for each characteristic of the electric double layer capacitor.

  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 (6)

Activated carbon activated with alkali metal hydroxide,
Activated carbon activated by steam,
And an electrode material containing a binder,
The electrode for an electric double layer capacitor, wherein the binder is a polymer containing no fluorine. The electrode for an electric double layer capacitor according to claim 1, wherein the binder is a (meth) acrylate polymer or a diene polymer. The electrode for electric double layer capacitors according to claim 1 or 2, wherein the binder has a glass transition temperature of 20 ° C or lower. The electrode for an electric double layer capacitor according to any one of claims 1 to 3, wherein the electrode material further contains a dispersant. 5. The electric double layer capacitor according to claim 1, wherein the electrode material is composite particles formed by binding activated carbon activated with an alkali metal hydroxide and activated carbon activated with water vapor with a binder. electrode. The electrode for electric double layer capacitors which has an electrode layer formed by press-molding the composite particle of Claim 5 on a collector.