JP4899354B2 - Method for producing composite particles, electrode material for electrochemical element, method for producing electrode for electrochemical element, and electrode for electrochemical element - Google Patents

Description

  The present invention can be suitably used as an electrode material for an electrochemical device such as a lithium ion secondary battery or an electric double layer capacitor. It is related with the manufacturing method of particle | grains. Moreover, this invention relates to the electrode material containing the composite particle obtained by this manufacturing method, the electrode for electrochemical elements using this electrode material, and its manufacturing method.

  Electrochemical elements such as lithium ion secondary batteries and electric double layer capacitors that are small and light, have high energy density, and can be repeatedly charged and discharged are rapidly expanding their demands by utilizing their characteristics. Lithium-ion secondary batteries have a relatively high energy density, so they are used in mobile phones and notebook personal computers. On the other hand, electric double-layer capacitors can be charged and discharged rapidly, so they can be used as a memory backup compact power supply for personal computers. It is used as. Furthermore, in recent years, electric double layer capacitors are expected to be used as large electric power sources for electric vehicles due to environmental problems and resource problems. 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 devices are required to be further improved, such as lowering resistance, increasing capacity, and improving mechanical properties.

  In order to improve the performance of the electrochemical device, various improvements have been made on the material forming the electrode for the electrochemical device. Electrodes for electrochemical devices are mainly composed of electrode active materials such as activated carbon and lithium metal oxides, and in order to give specific functions such as conductivity, adhesion and flexibility to the electrodes as necessary. And other components such as a conductive material and a binder. However, components other than these electrode active materials may cause a decrease in the performance of the electrochemical device, such as increasing the internal resistance or decreasing the capacity.

  In Patent Document 1, a powder obtained by pulverizing activated carbon fibers is dispersed in water, mixed with a chlorosulfonated polyethylene latex dispersion, and then a solid obtained by removing moisture is pulverized and granulated. A method for obtaining an electrode material and molding the electrode for a high-capacity electric double layer capacitor by pressing the electrode material is disclosed. According to the publication, a conductive material may be further added during granulation. However, with this method, it has not been easy to obtain an electrode material that is a granulated product that uniformly contains activated carbon and a conductive material having different specific gravities. Moreover, the electrode obtained by using the electrode material obtained by this method may have a non-uniform electrode density. Further, the current is concentrated due to the non-uniform electrode density, and the electrode may be deteriorated.

  Patent Document 2 discloses a method for producing an electrode for an electrochemical element by coating a current collector, a composite of an electrode active material, a conductive material, and a binder on a current collector by electrostatic coating or the like, and heating. . According to this document, the composite is produced by spraying polyvinylidene fluoride (PVDF) as a binder on a mixture of an electrode active material and a conductive material. However, in this method, it is not easy to uniformly mix the electrode active material and the conductive agent, and thus it is difficult to obtain a uniform electrode. In order to obtain a uniform electrode, it is necessary to repeat the coating process and the fusion process, and the manufacturing process is complicated.

Japanese Patent Laid-Open No. 62-179711 JP 2001-351616 A

  An object of the present invention is to provide a method for producing composite particles suitable as an electrode material that provides an electrode for an electrochemical device having a uniform electrode density. Another object of the present invention is to provide an electrode for an electrochemical element suitable for the production of an electrochemical element having a low internal resistance and a high capacity, and a method for producing the same.

  As a result of intensive studies to achieve the above object, the present inventors have used a carbon-based conductive material as a conductive material, and sprayed a dispersion liquid in which the carbon-based conductive material is dispersed in water onto the electrode active material, so that carbon It has been found that composite particles in which a conductive material adheres to the surface of an electrode active material can be produced. In addition, when an electrochemical element is manufactured using an electrode obtained by using an electrode for an electrochemical element containing the composite particles, the internal resistance of the electrochemical element is small, the capacity is large, and the electrode density is uniform. I found out. The present inventor has completed the present invention based on these findings.

Thus, according to the first aspect of the present invention, the electrode active material has a step of spraying a dispersion liquid in which a binder containing a carbon-based conductive material and a diene polymer or an acrylate polymer is dispersed in water. Provided is a method for producing composite particles for obtaining, by dry molding, an electrode material for an electrochemical element having a system conductive material attached to the surface of an electrode active material.
According to the second aspect of the present invention, there is provided an electrode material for an electrochemical element comprising the composite particles obtained by the above production method.
Further, according to the third aspect of the present invention, a method for producing an electrode for an electrochemical element including a step of forming an active material layer made of the electrode material for an electrochemical element on a current collector, and the production method are obtained. An electrode for an electrochemical element is provided.

  The composite particles obtained by the production method of the present invention have excellent conductivity because the carbon-based conductive material adheres to the surface of the electrode active material, and can be suitably used as an electrode material for electrochemical devices. Moreover, the electrode for electrochemical elements obtained by using the electrode material for electrochemical elements containing the composite particles has a uniform electrode density, and can be used for an electrochemical element capable of storing and converting energy.

The present invention is described in detail below.
The production method of the present invention is a method for producing composite particles in which a carbon-based conductive material adheres to the surface of an electrode active material, the method comprising spraying a dispersion liquid obtained by dispersing a carbon-based conductive material in water on the electrode active material. is there.

1. Electrode active material The electrode active material used by this invention changes with kinds of electrochemical element. As an electrode active material for a positive electrode of a lithium ion secondary battery, lithium-containing composite metal oxides such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiFePO ₄ , LiFeVO ₄ ; TiS ₂ , TiS ₃ , non Transition metal sulfides such as crystalline MoS ₃ ; transition metal oxides such as Cu ₂ V ₂ O ₃ , amorphous V ₂ O · P ₂ O ₅ , MoO ₃ , V ₂ O ₅ , V ₆ O ₁₃ ; Illustrated. Further, a conductive polymer such as polyacetylene or poly-p-phenylene can be used.
Examples of the electrode active material for the negative electrode of the lithium ion secondary battery include carbonaceous materials such as amorphous carbon, graphite, natural graphite, mesocarbon microbeads (MCMB), and pitch-based carbon fibers; and conductive materials such as polyacene. A functional polymer.

The particle shape of the electrode active material used for the electrode of the lithium ion secondary battery is preferably a spherically sized particle. When the shape of the particles is spherical, a higher density electrode can be formed at the time of electrode formation. Further, a mixture of fine particles having a particle size of about 1 μm and relatively large particles of 3 to 8 μm, and particles having a broad particle size distribution of 0.5 to 8 μm are preferable. It is preferable to use particles having a particle size of 50 μm or more by removing them by sieving. More preferably, the tap density of the electrode active material is 2 g / cm ³ or more for the positive electrode and 0.8 g / cm ³ or more for the negative electrode.

Since the electric double layer capacitor accumulates electric charge at the interface between the electrode and the electrolyte and forms an electric double layer, the electrode active material can form an interface with a larger area even with the same weight. Those having a large specific surface area are preferred. Specifically, the specific surface area of ^{30 m} 2 / g or more, preferably 500~5,000m ² / g, more preferably allotropes of carbon 1,000~3,000m ² / g is preferably used. Specific examples of the allotrope of carbon include activated carbon, polyacene, carbon whisker, and graphite. Among these, activated carbon is preferable. As the activated carbon, a phenol resin-based, rayon-based, acrylic resin-based, pitch-based, or coconut shell-based activated carbon can be used. These carbon allotropes are preferably powdery or fibrous. Furthermore, nanocomposites of these carbon allotropes and organic materials can also be used.

  Further, non-porous carbon having microcrystalline carbon similar to graphite and having an increased interlayer distance of the microcrystalline carbon can be used as the electrode active material. Such non-porous carbon is obtained by dry-distilling graphitized charcoal with microcrystals of a multilayer graphite structure at 700 to 850 ° C., then heat-treating with caustic at 800 to 900 ° C., and if necessary with heated steam. It is obtained by removing the residual alkali component. When the electrode active material is a powder, when the weight average particle diameter is 0.1 to 100 μm, preferably 1 to 50 μm, more preferably 5 to 20 μm, it is easy to reduce the thickness of the electrode for the electric double layer capacitor. It is preferable because the electric capacity can be increased.

  These electrode active materials are used alone or in combination of two or more. When the electrode active materials are used in combination, two or more types of electrode active materials having different particle size distributions may be used in combination.

2. Conductive Material The carbon-based conductive material used in the present invention is an allotrope of carbon that has conductivity and does not have pores that can form an electric double layer. The carbon-based conductive material improves the conductivity of the electrode for an electrochemical element, and is used by being attached to the surface of the electrode active material. Since the carbon-based conductive material uniformly adheres to the surface of the composite particles of the present invention, the carbon-based conductive material can be uniformly dispersed inside the electrode layer during electrode formation. The weight average particle diameter of the carbon-based conductive material is smaller than the weight average particle diameter of the electrode active material, and is usually 0.01 to 10 μm, preferably 0.5 to 5 μm, more preferably 0.1 to 1 μm. Range. When the particle size of the carbon-based conductive material is within this range, it can be easily attached to the surface of the electrode active material. Specifically, carbon black such as furnace black, acetylene black, and ketjen black (registered trademark of Akzo Nobel Chemicals Bethloten Fennaut Shap); graphite such as natural graphite and artificial graphite; carbon such as vapor grown carbon fiber Fiber; Among these, carbon black is preferable, and acetylene black and furnace black are more preferable.

  These conductive materials can be used alone or in combination of two or more, and the amount used is usually 0.1 to 50 parts by weight, preferably 0.5 to 100 parts by weight with respect to 100 parts by weight of the electrode active material. It is in the range of 15 parts by weight, more preferably 1 to 10 parts by weight. When the usage-amount of a electrically conductive material exists in this range, the electrostatic capacitance and internal resistance of an electrochemical element using the obtained electrode can be highly balanced.

3. Dispersion The conductive material used in the present invention is sprayed on the electrode active material in the state of a dispersion dispersed in water. By using water as the dispersion medium, it is possible to prevent the occurrence of ignition and dust explosion in the spraying process, and the safety is excellent. Moreover, since it is not necessary to use a special apparatus for preventing these dangers or to manufacture in an inert gas, the productivity of composite particles is excellent. The dispersion medium may contain an organic solvent as long as these effects are not impaired. 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 the like, and alkyl alcohols are preferable. When an organic solvent having a lower boiling point than water is used in combination, the drying rate in the spraying step can be increased. In addition, since the dispersibility of the binder and the solubility of the dispersant, which will be described later, change, the viscosity and fluidity of the dispersion can be adjusted depending on the amount or type of the organic solvent, and handling suitability and production efficiency can be improved. The amount of the organic solvent used is usually 50% by weight or less, preferably 30% by weight or less based on water.

The dispersion preferably further contains a binder and / or a dispersant. By using the binder, the electrode active materials are bound to each other, composite particles containing a plurality of electrode active material particles are formed, and the particle size can be controlled. Moreover, since the binder can be included in the obtained composite particles, the composite particles and the composite particles and the current collector can be bound at the time of electrode formation. The binder used in the present invention is not particularly limited as long as it is a compound having a binding force, but is preferably a fluorine polymer, diene polymer, acrylate polymer, polyimide, polyamide, polyurethane, polyvinyl alcohol. , Modified polyvinyl alcohol, and polymer compounds such as polyethylene oxide, more preferably thermoplastic polymer compounds such as fluorine-based polymers, diene-based polymers, and acrylate polymers.
The glass transition temperature (Tg) of the thermoplastic polymer compound is preferably −80 to 20 ° C., more preferably −60 ° C. to 0 ° C. When Tg is within this range, the binding force of the binder is reduced. It is excellent and it is possible to form the electrode for the electric double layer capacitor at a relatively low temperature. By using a thermoplastic polymer compound as a binder, strength and flexibility can be imparted to the electrode for the electric double layer capacitor.

  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); And vinyl cyanide / conjugated diene copolymers such as acrylonitrile / butadiene copolymer (NBR); and hydrogenated SBR and hydrogenated NBR.

  The acrylate polymer is a copolymer obtained by polymerizing a homopolymer of acrylic ester and / or methacrylic ester or a monomer mixture containing these. The ratio of acrylic acid ester and / or methacrylic acid ester 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 acrylate polymer include 2-ethylhexyl acrylate / methacrylic acid / acrylonitrile / ethylene glycol dimethacrylate copolymer, 2-ethylhexyl acrylate / methacrylic acid / methacrylonitrile / diethylene glycol dimethacrylate copolymer, acrylic acid Cross-linking type such as 2-ethylhexyl / styrene / methacrylic acid / ethylene glycol dimethacrylate copolymer, butyl acrylate / acrylonitrile / diethylene glycol dimethacrylate copolymer, and butyl acrylate / acrylic acid / trimethylolpropane trimethacrylate copolymer An acrylate polymer is mentioned.

  Also, as the acrylate polymer, ethylene such as ethylene / methyl acrylate copolymer, ethylene / methyl methacrylate copolymer, ethylene / ethyl acrylate copolymer, and ethylene / ethyl methacrylate copolymer (meth) Thermoplastic elastomers such as a copolymer with an acrylate ester; a graft polymer obtained by grafting a radical polymerizable monomer onto the above copolymer of ethylene and (meth) acrylate ester; and the like can also be used. Examples of the radical polymerizable monomer used in the graft polymer include methyl methacrylate, acrylonitrile, and methacrylic acid.

  Examples of the fluorine-based polymer include fluorine resins such as polytetrafluoroethylene and polyvinylidene fluoride. Further, ethylene / acrylic acid copolymer; ethylene / methacrylic acid copolymer; and the like can also be used as the thermoplastic polymer compound.

  Among these, a diene polymer and a crosslinked acrylate polymer are preferable, and a crosslinked acrylate polymer is particularly preferable. When these are used as a binder, an active material layer excellent in binding property and surface smoothness to a current collector can be obtained, and an electrode for an electrochemical device having a high capacitance and a low internal resistance can be produced. it can.

  There is no particular limitation on the shape of the binder that can be used in the present invention, but the binding property is good, and since the decrease in the capacitance of the prepared electrode and the deterioration during use can be minimized, the particles It is preferable that it is a shape. Examples of the particulate binder include latex in which the binder particles are dispersed in water or an organic solvent, such as latex produced by a known method such as emulsion polymerization, and such a dispersion is dried. The powdery thing obtained by doing is mentioned.

  The binder used in the present invention may be a particle having a core-shell structure obtained by stepwise polymerization of a mixture of two or more monomers. The binder having a core-shell structure is obtained by first polymerizing the monomer that gives the first-stage polymer, and using this polymer as seed particles in the same container or in a predetermined amount in another polymerization container. Thereafter, it is preferably produced by a method of polymerizing a monomer that gives a second-stage polymer.

  The ratio between the core and the shell of the binder having the core-shell structure is not particularly limited, but the core part: shell part is usually 20:80 to 99: 1, preferably 30:70 to 97: 3, by mass ratio. Preferably it is 40: 60-95: 5. As the polymer constituting the core portion and the shell portion, any of the above polymers can be used. When the Tg is observed at two points, the Tg on the low temperature side is preferably in the above range, the low temperature side is preferably less than 0 ° C, and the high temperature side is preferably 0 ° C or higher. Moreover, the difference of the glass transition temperature of a core part and a shell part is 20 degreeC or more normally, Preferably it is 50 degreeC or more.

The average particle diameter of the particulate binder used in the present invention 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 average particle diameter of the particulate binder is within this range, a high binding force can be imparted to the active material layer. Here, the 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, and the amount used is usually 0 to 50 parts by weight, preferably 0.01 to 20 parts per 100 parts by weight of the electrode active material. Parts by weight, more preferably in the range of 0.1 to 10 parts by weight.

The dispersant that can be used in the present invention is a water-soluble compound, and has an action of improving uniform dispersibility in a dispersion liquid of an electrode active material, a conductive material, and the like. Specific examples of the compound used as the dispersant include cellulosic polymers such as carboxymethylcellulose, methylcellulose, ethylcellulose, and hydroxypropylcellulose, and ammonium salts and alkali metal salts thereof; poly (meta) such as sodium poly (meth) acrylate. ) Acrylate salt; polyvinyl pyrrolidone, polycarboxylic acid, oxidized starch, phosphate starch, casein, various modified starches, chitin, chitosan derivatives and the like.
Among these, cellulose polymers and ammonium salts and alkali metal salts thereof are preferable.

  These dispersants can be used alone or in combination of two or more. Although the compounding quantity of a dispersing agent does not have special limitation, it is 0-500 weight part with respect to 100 weight part of electrically conductive materials, Preferably it is 1-100 weight part, More preferably, it is the range of 5-50 weight part.

  The dispersion used in the present invention may contain other additives as required. Examples of other additives include a surfactant. Examples of the surfactant that can be used include anions, cations, nonions, and nonionic anions. Among these, nonionic surfactants that are easily thermally decomposed are preferred. These additives can be used alone or in combination of two or more. The amount of each additive is not particularly limited, but is 0 to 50 parts by weight, preferably 0.1 to 10 parts by weight, and more preferably 0.5 to 5 parts by weight with respect to 100 parts by weight of the electrode active material. Range.

  The dispersion is obtained by uniformly mixing a carbon-based conductive material and a solvent and, if necessary, a dispersant, a binder, and other additives. The concentration of the dispersion is adjusted so that the solid content is usually in the range of 1 to 50% by weight, preferably 5 to 40% by weight, more preferably 10 to 30% by weight. When the solid content concentration is within this range, composite particles in which the conductive material adheres more uniformly to the active material surface are preferable. The mixing method for preparing the dispersion is not particularly limited, but for example, mixing is performed using a mixing device such as a ball mill, a sand mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, or a planetary mixer. can do. The mixing conditions are appropriately selected depending on the type of the mixture, but the mixing temperature is usually room temperature to 80 ° C., and the mixing time is 10 minutes to several hours.

4). Manufacturing method of composite particle The manufacturing method of the composite particle of this invention has the process of spraying the dispersion liquid which contains a carbon-type electrically conductive material in an electrode active material. In the present invention, spraying the dispersion means spraying the dispersion on the electrode active material in a mist form, and specifically, a spraying device (atomizer) can be used. The type of atomizer is roughly divided into a rotating disk system and a pressurizing system, and both can be preferably used. The rotating disk method is a method in which a dispersion liquid is introduced almost at the center of a disk that rotates at high speed. When the dispersion liquid leaves the disk, it is sprayed in the form of a mist. The rotational speed of the disk depends on the size of the disk, but is usually 5,000 to 30,000 rpm, preferably 15,000 to 30,000 rpm. The pressurization method is a method of spraying a pressurized dispersion liquid in a mist form from a nozzle. The temperature of the dispersion to be sprayed is usually room temperature, but may be warmed. By spraying the dispersion liquid onto the electrode active material and evaporating the dispersion medium, the carbon-based conductive material can be attached to the surface of the electrode active material, so that the conductivity of the electrode active material can be effectively improved. When spraying, it is preferable that the electrode active material is flowing in the container because the carbon-based conductive material uniformly adheres to the electrode active material. The temperature of the fluidized bed containing the electrode active material is usually room temperature (25 ° C.) to 150 ° C., preferably 50 to 120 ° C.

  Examples of such a production method include a rolling bed granulation method, a stirring type granulation method, a fluidized bed granulation method, and a fluidized bed multifunctional granulation method. In each method, the method of flowing the electrode active material is different, and in the rolling bed granulation method, the electrode active material and other components are rolled in a rotating container such as a rotating drum or a rotating plate. In the agitation type granulation method, a raw material powder is forcibly given a fluid motion by an agitating blade provided in a container. The fluidized bed granulation method is a method in which the powder is kept suspended and suspended in a fluid such as an air stream blown from below. The fluidized bed multi-functional granulation method is rolled and stirred to the fluidized bed granulation method. This is a method of combining the actions. A composite liquid can be obtained by spraying a dispersion containing a conductive material onto the electrode active material fluidized by these methods.

  The composite particles obtained by such a method include one or more electrode active material powders or fibers, and a carbon-based conductive material is attached to the surface of the electrode active material. The weight average particle diameter of the composite particles is usually in the range of 0.1 to 1000 μm, preferably 5 to 500 μm, more preferably 10 to 100 μm. According to the production method of the present invention, since composite particles having a conductive material attached to the surface of the electrode active material are obtained, the distribution of the conductive material inside the electrode is uniform, and the amount of the conductive material contained in the electrode for an electrochemical element Therefore, an electrochemical element having a high capacitance can be manufactured.

5. Electrode Element Electrode Material The electrochemical element electrode material of the present invention contains composite particles obtained by the production method of the present invention, and additionally contains other binders and other additives as necessary.
The content of the composite particles in the electrode material for electrochemical devices is usually 50% by weight or more, preferably 70% by weight or more, more preferably 90% by weight or more.

Examples of other binders that may be contained as necessary include the same binders that can be added to the dispersion. When the binder is mixed in the dispersion, it depends on the type of binder and the electrode manufacturing method, but it usually needs to be added separately because the composite particles contain the binder. However, other binders may be added when preparing the electrode material in order to increase the binding force between the composite particles. Each of the binders can be used alone or in combination of two or more, and the amount used thereof is usually the total amount of the binder mixed in the dispersion, with respect to 100 parts by weight of the electrode active material. It is 0.001-50 weight part, Preferably it is 0.01-20 weight part, More preferably, it is the range of 0.1-10 weight part. If the amount of the binder used is too small, it becomes difficult to form the electrode material for an electrochemical element into a sheet. Conversely, if the amount of binder used is too large, the internal resistance of the resulting electrochemical device may increase.
Other additives include molding aids such as water and alcohol, and can be appropriately selected in an amount that does not impair the effects of the present invention.

6). Method for Producing Electrode for Electrochemical Element The method for producing an electrode for electrochemical element of the present invention includes a step of forming an active material layer made of the electrode material for electrochemical element of the present invention on a current collector.
As the current collector material used in the present invention, for example, metal, carbon, conductive polymer and the like can be used, and metal is preferably used. As the current collector metal, aluminum, platinum, nickel, tantalum, titanium, stainless steel, 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. In addition, when high voltage resistance is required, high-purity aluminum disclosed in JP 2001-176757 A can be suitably used. The current collector is in the form of a film or a sheet, and the thickness thereof is appropriately selected according to the purpose of use, but is usually 1 to 200 μm, preferably 5 to 100 μm, more preferably 10 to 50 μm.

  In the production of electrodes, the electrode material for electrochemical devices may be formed into a sheet to form an active material layer, which may then be laminated on the current collector, but the active material layer is formed directly on the current collector. It is preferable to do. When the active material layer is directly formed on the current collector, it is preferable that the electrode material is supplied onto the current collector and then the thickness of the electrode material is leveled with a blade or the like because the electrode density can be easily uniformed during molding. . As a method of forming an active material layer from the electrode material for an electrochemical element of the present invention, there are a dry molding method such as a pressure molding method and a wet molding method such as a coating method, but a drying step is not required and productivity is increased. An excellent dry molding method is preferred. There is no particular limitation on the dry molding method, and specific examples thereof include pressure molding in which an active material layer is formed by densifying the electrode material by rearranging and deforming it by applying pressure to the electrode material for the electrochemical element. Method: An extrusion molding method in which an active material layer is continuously formed as an endless long product such as a film or sheet because the electrode material for an electrochemical element becomes a paste when extruded from a molding machine. And the like. Among these, the pressure molding method is preferable because it can be performed with simple equipment. In the pressure molding, for example, the composite particles are dispersed on the current collector with a screw feeder, the electrode material is quantitatively supplied onto the protective film or the current collector using the feeder, and the active material is pressurized with a roller or the like. The layers can be formed continuously. Alternatively, the composite particles can be supplied to a roll-type pressure forming apparatus provided with two parallel rolls by a supply device such as a screw feeder, and the active material layer can be formed by a roll press. Alternatively, the active material layer may be manufactured by batch-type pressure molding in which an electrode material is filled in a mold and pressed. When batch-type pressure molding is performed in a mold provided with a current collector, an active material layer can be formed directly on the current collector. The molding temperature is preferably 0 to 200 ° C.

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

  By using the electrochemical element electrode thus obtained, it is possible to manufacture an electrochemical element having a low internal resistance and a high capacitance. Therefore, a backup power source for a memory of a personal computer or a mobile terminal, a power source for an instantaneous power failure such as a personal computer, It can be suitably used for various applications such as an application to an electric vehicle or a hybrid vehicle, a solar power generation energy storage system combined with a solar cell, and a load leveling power source combined with a battery.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated further more concretely, this invention is not restrict | limited to the following Example. Parts and% are based on weight unless otherwise specified.

Example 1
Production of Electrode Material for Electric Double Layer Capacitor 5 parts of acetylene black (Denka black powder; manufactured by Denki Kagaku Kogyo Co., Ltd.) having an average particle size of 0.7 μm as a conductive material, and an aqueous solution containing 5% carboxymethylcellulose as a dispersing agent (cellogen 7A; Daiichi Kogyo Seiyaku Co., Ltd.) 30 parts, a carboxy-modified styrene / butadiene copolymer (particle size 0.12 μm, glass transition temperature −5 ° C.) dispersed in water as a binder (BM400B; manufactured by Nippon Zeon Co., Ltd.) , 40%) 17.5 parts and water were added and mixed with a planetary mixer to obtain 135 parts of a conductive material dispersion.

100 parts of high-purity activated carbon powder having a specific surface area of 2000 m ² / g and an average particle diameter of 5 μm is supplied as an electrode active material to a fluidized bed granulator (Agromaster manufactured by Hosokawa Micron Corporation), and the conductive material is dispersed in an air flow at 120 ° C. The liquid was sprayed under pressure for 10 minutes and mixed to obtain composite particles (A-1) having a weight average particle diameter of 70 μm. When the obtained particles were observed with an electron microscope, it was confirmed that acetylene black particles adhered to the surfaces of the activated carbon particles. The weight average particle diameter was measured using a powder measuring device (Powder Tester PT-R; manufactured by Hosokawa Micron Corporation).

  The obtained composite particles (A-1) are sprayed onto an aluminum current collector having a thickness of 40 μm with a screw feeder, and the thickness of the particles on the current collector is made uniform using a blade. An electric double layer capacitor having an active material layer thickness of 200 μm formed by pressure molding at 150 ° C. under a pressure of 0.2 MPa for 1 minute using a pressure molding machine (desktop test press 2-S type; manufactured by Tester Sangyo Co., Ltd.) An electrode was obtained. Using the obtained electrode for an electric double layer capacitor, the electrode density and the uniformity of the electrode density were measured by the following method. The results are shown in Table 1.

Electrode density and uniformity of electrode density From the obtained electrode for an electric double layer capacitor, a 40 mm × 60 mm electrode was cut out, the weight and volume were measured, and the electrode density excluding the current collector portion was calculated. Judged.
Electrode density is 0.60 g / cm ³ or more: A
0.55 g / cm ³ or more and less than 0.60 g / cm ³ :
0.50 g / cm ³ or more and less than 0.55 g / cm ³ ;
Less than 0.5 g / cm ³ : ×
Further, the cut out electrode was further divided into a uniform size of 10 mm × 10 mm, and the weight of each electrode was measured to calculate the electrode density excluding the current collector portion. The maximum value of the difference between the obtained electrode density after division and the electrode density before division was taken as the variation in electrode density, and the uniformity of the electrode density was judged according to the following criteria.
Variation is less than 0.1 g / cm ³ :
0.1 g / cm ³ or more and less than 0.15 g / cm ³ :
0.15 g / cm ³ or more and less than 0.2 g / cm ³ : Δ
0.2 g / cm ³ or more: ×

Electric double layer capacitor From the electrode for the electric double layer capacitor obtained above, two electrodes having a size of 40 mm x 60 mm are cut out with the lead terminal left, the two electrodes are opposed to each other, and a 25 μm thick polyethylene separator is sandwiched between them. It is. This was sandwiched between two polypropylene plates having a thickness of 2 mm, a width of 50 mm, and a height of 70 mm. The thickness between the two propylene plates was 0.68 mm. An electrolytic solution in which triethylene monomethyl ammonium tetrafluoroborate was dissolved in propylene carbonate at a concentration of 1.5 mol / L was impregnated under reduced pressure, and stored in a polypropylene container to produce an electric double layer capacitor.

Using the obtained electric double layer capacitor, at 25 ° C., it was charged from 0 V to 2.7 V with a constant current of 10 mA for 10 minutes, and then discharged to 0 V with a constant current of 1 mA. The capacitance was obtained from the obtained charge / discharge curve, and the capacitance per unit mass of the electrode layer was determined by dividing the mass of the electrode by the mass of the electrode layer obtained by subtracting the mass of the current collector from the mass of the electrode. The internal resistance was calculated according to the calculation method of standard RC-2377 established by the Japan Electronics and Information Technology Industries Association from the charge / discharge curve. The internal resistance and capacitance were judged according to the following criteria. The results are shown in Table 1.
Internal resistance less than 4ΩF: ◎
4ΩF or more and less than 5ΩF: ○
5ΩF or more and less than 6ΩF: △
6ΩF or more: ×
Capacitance 58 F / g or more: ◎
55 F / g or more and less than 58 F / g: ○
45 F / g or more and less than 55 F / g: Δ
Less than 45 F / g: ×

Example 2
Electrode material for electric double layer capacitor The copolymer composition is 2-ethylhexyl acrylate / styrene / methacrylic acid / ethylene instead of 17.5 parts of a dispersion of carboxy-modified styrene / butadiene copolymer dispersed in water as a binder. 17.5 parts of an aqueous dispersion (40% concentration) of a crosslinked acrylate polymer (particle diameter 0.15 μm, glass transition temperature −40 ° C.) having glycol dimethacrylate = 80/14/4/2 (weight ratio) Except having used, it carried out similarly to Example 1, and obtained composite particle (A-2). When the obtained composite particles (A-2) were measured in the same manner as in Example 1, the weight average particle diameter was 70 μm. When the obtained particles were observed with an electron microscope, it was confirmed that acetylene black particles adhered to the surfaces of the activated carbon particles. Subsequently, instead of the composite particles (A-1), an electrode for an electric double layer capacitor was prepared at room temperature in the same manner as in Example 1 except that the composite particles (A-2) were used. Density and uniformity of electrode density were measured. The results are shown in Table 1.

Electric double layer capacitor Using the obtained electrode, an electric double layer capacitor was prepared in the same manner as in Example 1, and the characteristics of the electric double layer capacitor obtained for the same items as in Example 1 were measured. The results are shown in Table 1.

Example 3
5 parts of acetylene black (denka black powder form; manufactured by Denki Kagaku Kogyo Co., Ltd.) having an average particle size of 0.7 μm as a conductive material, and 30 parts of an aqueous solution containing 5% carboxymethylcellulose as a dispersant (Serogen 7A; manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) And water were added and mixed with a planetary mixer to obtain 135 parts of a conductive material dispersion.
100 parts of high-purity activated carbon powder of the same kind as that used in Example 1 as an electrode active material was supplied to a fluidized bed granulator (Agromaster manufactured by Hosokawa Micron Corporation), and the conductive material dispersion was dispersed for 10 minutes in an air flow at 120 ° C. The mixture was sprayed and mixed to obtain composite particles (A-3) having a weight average particle diameter of 70 μm. When the obtained particles were observed with an electron microscope, it was confirmed that acetylene black particles adhered to the surfaces of the activated carbon particles.

Manufacture of binder powder In a nitrogen atmosphere, 674.9 parts of deionized water, 7.1 parts of 28% sodium lauryl sulfate aqueous solution, and 0.8 parts of sodium tripolyphosphate are supplied to a reactor equipped with a mechanical stirrer and a condenser. And heated to 75 ° C. with stirring. To this reactor was added 82 parts of a 2.44% aqueous ammonium persulfate solution, and then a monomer mixture consisting of 84 parts of 2-ethylhexyl acrylate, 14 parts of styrene, and 2 parts of ethylene glycol dimethacrylate was constant over 2 hours. The reaction was continued until the polymerization conversion reached 98%. Subsequently, a monomer mixture consisting of 37 parts of 2-ethylhexyl acrylate, 58 parts of methyl methacrylate, 3 parts of methacrylic acid and 2 parts of ethylene glycol dimethacrylate was added to the reactor at a constant rate over 2 hours. The reaction was continued for 3 hours while maintaining the reaction temperature at 80 ° C. to obtain an aqueous dispersion containing a binder. This dispersion was spray-dried to obtain a binder powder.

Electric double layer capacitor 128 parts of composite particles (A-3) and 7 parts of the binder powder were mixed using a Henschel mixer, and the resulting mixture was placed on an aluminum current collector having a thickness of 40 μm using a screw feeder. And using a blade to equalize the thickness of the particles on the current collector, and then press-molding in the same manner as in Example 1 to obtain an electrode for an electric double layer capacitor having an electrode layer thickness of 200 μm. It was. Using the obtained electrode for an electric double layer capacitor, the electrode density and the uniformity of the electrode density were measured by the following method. The results are shown in Table 1.

Comparative Example 1
100 parts of activated carbon powder and 5 parts of acetylene black of the same type as used in Example 1 are supplied to a fluidized bed granulator (Agromaster manufactured by Hosokawa Micron Corporation), and the same kind as that used in Example 1 in an air flow at 120 ° C. 135 parts of an aqueous dispersion containing 7 parts of the above binder was added by spraying over 10 minutes. When the obtained particles were observed with an electron microscope, acetylene black was not attached to the activated carbon powder, and the conductive material and the binder were each agglomerated. Using this mixture, an electrode for an electric double layer capacitor was prepared in the same manner as in Example 1, and the electrode density and the uniformity of the electrode density were measured in the same manner as in Example 1. The results are shown in Table 1.

  As is clear from the above Examples and Comparative Examples, when an electrode material for an electrochemical element containing composite particles obtained by the production method of the present invention is used, an electrode for an electric double layer capacitor having a high electrode density and a uniform density can be obtained. can get. Further, when the obtained electrode is used, an electric double layer capacitor having a small internal resistance and a large capacitance can be produced.

Claims (6)

The carbon-based conductive material adheres to the surface of the electrode active material, having a step of spraying a dispersion liquid in which a carbon-based conductive material and a binder containing a diene polymer or an acrylate polymer are dispersed in water. A method for producing composite particles for obtaining an electrode material for an electrochemical element by dry molding .   The manufacturing method according to claim 1, wherein the electrode active material flows in a container when spraying.   The production method according to claim 1, wherein the dispersion further contains a dispersant.   The electrode material for electrochemical devices containing the composite particle obtained by the manufacturing method in any one of Claims 1-3.   The manufacturing method of the electrode for electrochemical elements including the process of forming the active material layer which consists of an electrode material for electrochemical elements of Claim 4 on a collector.   The electrode for electrochemical elements obtained by the manufacturing method of Claim 5.