JP5141002B2 - Method for producing composite particle for electrochemical device electrode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide: a method for producing composite particles with which the electrode of an electrochemical element having an active material layer of large uniform thickness with excellent thickness precision can be obtained at a high formation speed when the active material layer is formed by continuous pressure forming such as roll pressure forming; composite particles obtained by that production process; and the electrode of an electrochemical element formed using those composite particles. <P>SOLUTION: The method for producing composite particles for the electrode of an electrochemical element includes: a step (I) of obtaining slurry by dispersing an electrode active material and a binder into solvent; a step (II) of obtaining granulation particles by spraying and drying the slurry; and a step (III) of coating the surface of the granulation particles at least partially with solid particulates (a) having a volume average particle size smaller than that of the granulation particles. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a method for producing an electrochemical element electrode composite particle for producing an electrochemical element such as a lithium ion secondary battery or an electric double layer capacitor, particularly an electrode suitably used for an electric double layer capacitor. Moreover, this invention relates to the electrochemical element electrode using the composite particle for electrochemical element electrodes obtained by this manufacturing method, and this composite particle for electrochemical element electrodes.

  Electrochemical elements such as lithium ion secondary batteries and electric double layer capacitors are rapidly expanding in demand by taking advantage of their small size, light weight, high energy density, and the ability to repeatedly charge and discharge. Lithium ion secondary batteries have a relatively high energy density and are used in the fields of mobile phones and notebook personal computers. Since the electric double layer capacitor can be rapidly charged and discharged, it is used as a memory backup compact power source for a personal computer or the like. Furthermore, the electric double layer capacitor is expected to be applied as a large power source for electric vehicles. 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 be further improved, such as lowering resistance, increasing capacity, improving mechanical properties and productivity. Under such circumstances, there is a demand for a more productive manufacturing method for electrochemical element electrodes, and various improvements have been made regarding manufacturing methods capable of high-speed molding and materials for electrochemical element electrodes suitable for the manufacturing method. It has been broken.

  Electrochemical device electrodes generally have an active material layer formed by binding an electrode active material such as activated carbon, lithium metal oxide, graphite, or metal alloy and a conductive material with a binder on a current collector. It is made. As a method of forming this active material layer, Patent Document 1 describes a method of pressure-molding composite particles in which a particulate electrode active material and a particulate conductive additive are adhered with a binder. Patent Document 2 describes a method of pressure-molding an electrode material that is a spherical particle containing an electrode active material and a thermoplastic binder.

JP 2005-78943 A WO2005 / 124801

  However, when an active material layer is formed by continuous pressure molding such as roll pressure molding using the composite particles described in Patent Document 1 or the electrode material described in Patent Document 2, the molding speed is increased. Since the supply of the composite particles and the electrode material cannot keep up with the molding speed, it is difficult to form an active material layer having excellent thickness accuracy, a uniform and large thickness with high productivity.

  Therefore, the present invention provides a method for quickly forming an electrochemical element electrode having an active material layer having a large thickness and excellent thickness accuracy when the active material layer is formed by continuous pressure forming such as roll pressure forming. It aims at providing the manufacturing method of the composite particle for electrochemical element electrodes which can be obtained at speed | rate, the composite particle obtained by this manufacturing method, and the electrochemical element electrode formed using this composite particle.

  The present inventor has paid attention to the structure of composite particles for electrochemical element electrodes (hereinafter sometimes simply referred to as “composite particles”) formed by binding an electrode active material and a binder to each other. As a result of investigation, a slurry obtained by dispersing an electrode active material and a binder in a solvent is spray-dried to obtain granulated particles, and the surface of the granulated particles is solid particles having a particle diameter smaller than that of the granulated particles. It was found that composite particles having excellent moldability can be obtained by coating with. Moreover, it discovered that the ratio of the secondary aggregation of the composite particle obtained had big influence on the moldability of an active material layer. Then, in the particle size distribution of the primary particles of the composite particles obtained on the volume basis, the relative particle amount of the primary particles having a particle diameter in a minute range near the mode diameter R1 is ρ1, and obtained on the volume basis in the measurement at 23 ° C. In the particle size distribution of the secondary particles of the composite particles, the value of ρ2 / ρ1 when the relative particle amount ρ2 of the secondary particles having a particle diameter in the minute range is appropriate as a value representing the ratio of secondary aggregation. I found out. When the active material layer is formed by continuous pressure molding such as roll pressure molding when ρ2 / ρ1 is in a certain range, the active material layer is excellent in thickness accuracy, uniform and has a large thickness. It is found that an electrochemical device electrode having a high speed can be obtained at a high molding speed (hereinafter, such a performance is sometimes referred to as “high-speed roll pressure moldability”). It came to complete.

The first aspect of the present invention is a step (I) of obtaining a slurry by dispersing an electrode active material and a binder in a solvent,
Step (II) of granulating the slurry by spray drying to obtain granulated particles, and at least a part of the surface of the granulated particles are made of solid particles a having a volume average particle size smaller than the granulated particles. Coating step (III),
It is a manufacturing method of the composite particle for electrochemical element electrodes characterized by having.
It is preferable that the binder contains polytetrafluoroethylene.
The solid particles a are preferably a conductive material.

2nd this invention is the composite particle for electrochemical element electrodes obtained by said manufacturing method,
The volume average particle diameter of the primary particles is 1 to 500 μm,
In the particle size distribution of the primary particles of the composite particles obtained on a volume basis, the relative particle amount of the primary particles having a particle diameter in a minute range near the mode diameter R1 of the primary particles is ρ1,
In the particle size distribution of the secondary particles of the composite particles obtained on a volume basis in the measurement at 23 ° C., when the relative particle amount of the secondary particles having a particle size in the minute range is ρ2,
ρ2 / ρ1 is a composite particle for an electrochemical element electrode having 0.03 to 0.60.

  Here, the “secondary particle” means a large aggregated particle formed by aggregating several composite particles (primary particles). Further, the “mode diameter” means a particle diameter having the largest abundance ratio of particles, which is a particle diameter showing the maximum value in the particle diameter distribution curve, and “mode diameter R1” means the composite particle. It refers to the mode diameter of primary particles.

  “Ρ1” refers to the ratio (%) of primary particles having a particle diameter in a minute range in the vicinity of the mode diameter R1 when the amount of particles of the entire primary particles is a reference (100%). “Ρ2” refers to the ratio (%) of secondary particles having a particle diameter in the minute range when the amount of particles of the entire secondary particles is the standard (100%).

  3rd this invention is an electrochemical element electrode which has an electrical power collector and the active material layer laminated | stacked on this electrical power collector, Comprising: The said active material layer is an electrochemical element obtained by said manufacturing method It is an electrochemical element electrode formed by pressure-molding the composite particles for electrodes.

  In the third aspect of the present invention, the pressure molding is preferably roll pressure molding. Moreover, as an application of the electrode of 3rd this invention, it is suitable for an electric double layer capacitor.

  According to the production method of the present invention, composite particles for electrochemical element electrodes that are excellent in high-speed roll pressure moldability can be obtained. As a result, when the active material layer is formed by continuous pressure molding such as roll pressure molding, the degree to which the supply amount of the composite particles depends on the rotation speed of the roll can be reduced. An electrochemical device electrode having excellent accuracy, uniformity, large thickness, and low internal resistance can be obtained.

  The method for producing composite particles for an electrochemical element electrode of the present invention includes the step (I) of obtaining a slurry by dispersing an electrode active material and a binder in a solvent.

<Electrode active material>
The electrode active material used for this invention is suitably selected according to the kind of electrochemical element. Examples of the electrode active material for the positive electrode of the lithium ion secondary battery include LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiFePO ₄ , LiFeVO ₄ , and a lithium-containing composite metal oxide partially substituted for these elements Transition metal sulfides such as TiS ₂ , TiS ₃ , and amorphous MoS ₃ ; Cu ₂ V ₂ O ₃ , amorphous V ₂ O · P ₂ O ₅ , MoO ₃ , V ₂ O ₅ , V ₆ O ₁₃ Transition metal oxides such as Furthermore, conductive polymers such as polyacetylene and poly-p-phenylene are listed.

  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; high conductivity such as polyacene Molecule: Si, Sn, Sb, Al, Zn, W, etc., which can be alloyed with lithium.

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

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

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

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

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

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

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

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

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

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

  The amount of the binder used in the step (I) is usually 1 to 20 parts by mass, preferably 3 to 15 parts by mass with respect to 100 parts by mass of the electrode active material.

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

<Conductive material>
In step (I), it is preferable to use a conductive material in addition to the above. The conductive material is made of an allotrope of particulate carbon that has conductivity and does not have pores capable of forming an electric double layer, and improves the conductivity of the electrochemical element electrode. Specifically, conductive 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; polyacrylonitrile-based carbon fiber; And carbon fibers such as pitch-based carbon fibers and vapor-grown carbon fibers. Among these, conductive carbon black is preferable, and acetylene black and ketjen black are more preferable. The volume average particle diameter of the conductive material is preferably smaller than the volume average particle diameter of the electrode active material, and is 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 material is within this range, high conductivity can be obtained with a smaller amount of use. These conductive materials can be used alone or in combination of two or more.

  The amount of the conductive material in the step (I) is usually 0.1 to 50 parts by mass, preferably 0.5 to 15 parts by mass, more preferably 1 to 10 parts by mass with respect to 100 parts by mass of the electrode active material. It is. By forming the electrode using composite particles containing an amount of the conductive material in this range, the capacity of the electrochemical element can be increased and the internal resistance can be decreased.

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

<Preparation of slurry>
In step (I), the electrode active material, the binder, and the electrode active material, the binder and, if necessary, the dispersant, conductive material and other additives are dispersed or dissolved in a solvent. Accordingly, a slurry in which the dispersant, the conductive material and other additives are dispersed or dissolved is obtained.

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

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

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

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

  The method for producing composite particles for electrochemical element electrodes of the present invention includes a step (II) in which the slurry obtained in the step (I) is spray-dried and granulated to obtain granulated particles.

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

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

  Granulated particles are obtained by spray drying. The volume average particle diameter of the granulated particles is usually 1 to 500 μm, preferably 5 to 300 μm, more preferably 10 to 100 μm, and most preferably 20 to 75 μm. Here, the volume average particle diameter of the granulated particles is the volume average particle diameter of primary particles measured by spraying the granulated particles under pressure with compressed air using a laser diffraction particle size distribution measuring device. The “primary particles” mean the smallest unit solids that can be clearly separated from other particles constituting the powder.

  In the method for producing composite particles for electrochemical element electrodes according to the present invention, at least a part of the surface of the granulated particles obtained in the step (II) is made of solid particles a having a volume average particle size smaller than that of the granulated particles. It has the process (III) to coat | cover.

<Solid particles a>
The solid particles a used in the present invention are particles that are solid at room temperature (25 ° C.) and have a volume average particle diameter smaller than that of the granulated particles. Specific examples of the solid particles a include silica, alumina, zirconia and the like. In addition, the above electrode active material and conductive material can also be used as the solid particles a. Among these, it is preferable to use a conductive material or an electrode active material. When a conductive material is used as the solid particles a, it is possible to reduce the internal resistance of an electrochemical element manufactured using the resulting composite particles. Moreover, when an electrode active material is used, the energy density of the electrochemical element manufactured using the composite particle obtained can be made high. Two or more kinds of these solid particles a can be used in combination. The volume average particle diameter of the primary particles of the solid particles a is usually 0.01 to 50 μm, preferably 0.5 to 10 μm.

  The amount of the solid particles a used in the step (III) is usually 0.1 to 20 parts by mass, preferably 0.5 to 15 parts by mass, and more preferably 1 to 10 parts by mass with respect to 100 parts by mass of the granulated particles. is there. When the amount of the solid particles a to be mixed is within this range, the capacity of the electrochemical device manufactured using the obtained composite particles can be increased. When an electrode active material or a conductive material is used as the solid particles a, the binder is usually 1 to 20% by mass with respect to the total amount of the electrode active material used in the step (I) and the step (III), Preferably it is used so that it may become the range of 3-15 mass%. The total amount of the conductive material used in the step (I) and the step (III) is 0.1 to 50% by mass, preferably 0 with respect to the total amount of the electrode active material used in the step (I) and the step (III). It is used so that it may become the range of 5-15 mass%, More preferably, 1-10 mass%.

<Coating process>
In step (III), at least a part of the surface of the granulated particles obtained in step (I) is coated with the solid particles a to obtain composite particles. In the present invention, “coating” means that the solid particles a adhere to at least a part of the surface of the granulated particles, and it is not necessary to cover the entire surface of the granulated particles. Although the method of coating is not particularly limited, it can be generally coated by mixing granulated particles and solid particles a. In particular, it is preferable to mix the granulated particles and the solid particles a by a method in which a strong shearing force is not applied to the granulated particles so that the granulated particles are not destroyed during the mixing. Since the above-mentioned granulated particles obtained by spray drying are unevenly distributed on the particle surface, the solid particles a are bound to the granulated particles and the surface is coated even if the shearing force during mixing is weak. can do. Furthermore, it can suppress that the ratio of the secondary aggregation of the composite particle obtained becomes excessive because the solid particle a binds to the granulated particle surface.

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

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

  According to the production method of the present invention, composite particles for electrochemical element electrodes in which at least a part of the surface is coated with the solid particles a can be obtained. By adjusting the type, volume average particle diameter, amount, and the like of the solid particles a, the ratio of secondary aggregation of the obtained composite particles can be adjusted.

<Volume average particle diameter of primary particles>
The composite particles obtained by the production method of the present invention have a volume average particle diameter of primary particles of 1 to 500 μm, preferably 5 to 300 μm, more preferably 10 to 100 μm, and most preferably 20 to 75 μm. When the volume average particle diameter of the primary particles is within this range, composite particles having excellent high-speed roll press moldability can be obtained. The smaller the volume average particle diameter of the primary particles of the composite particles, the easier it is for the composite particles that are the primary particles to agglomerate, and ρ2 / ρ1 described below becomes smaller. The volume average particle diameter of the primary particles of the composite particles can be measured by spraying the composite particles with compressed air using a laser diffraction particle size distribution measuring device. The “primary particles” mean the smallest unit solids that can be clearly separated from other particles constituting the powder.

<Relationship between ρ1 and ρ2 in mode diameter R1>
In the above composite particles, in the particle size distribution of the primary particles of the composite particles determined on a volume basis, the relative particle amount of the primary particles having a particle diameter in a minute range near the mode diameter R1 of the primary particles is ρ1, In the particle size distribution of the secondary particles of the composite particles obtained on a volume basis in the measurement at 23 ° C., ρ2 / ρ1 is 0 when the relative particle amount of the secondary particles having a particle diameter in the minute range is ρ2. 0.03 to 0.60 is preferable, 0.03 to 0.30 is more preferable, and 0.03 to 0.10 is particularly preferable. When the cohesiveness of the composite particles represented by ρ2 / ρ1 is in such a range, when forming the active material layer by continuous pressure molding such as roll pressure molding using the composite particles of the present invention, Even if the molding speed is increased, the powder can be sufficiently supplied, and an electrochemical element electrode having an excellent thickness accuracy, a uniform and large thickness active material layer can be obtained.

Here, “secondary particles” refer to large agglomerated particles formed by agglomerating several primary particles. Further, the “mode diameter” means a particle diameter having the highest particle existence probability, and means a particle diameter showing the maximum value in the particle diameter distribution curve. The “small range in the vicinity of R1” means a particle diameter distribution curve with the horizontal axis as the primary particle diameter and the vertical axis as the frequency, and the mode diameter R1 (μm) as the particle diameter indicating the maximum value of the primary particle diameter distribution curve. ^Is obtained as a range of 10 ^{(logR1) -α} (μm) or more and less than 10 ^{(logR1) + α} (μm). The value of α can be set according to the value of R1 or the measurement accuracy of the particle size measuring instrument, and the values of ρ1 and ρ2 also vary accordingly, but α is larger than the distribution range of the primary particle size and the secondary particle size. If it is sufficiently small, the value of ρ2 / ρ1 becomes almost constant regardless of the value of α. α is preferably 0.05 or less, more preferably 0.03 or less. In the examples of the present invention, 0.02389 was used as α.

  FIG. 1 shows ρ1 and ρ2. A curve 10 is a particle size distribution curve of the primary particles of the composite particles obtained on a volume basis. The particle diameter at the maximum value of the particle diameter distribution curve 10 of the primary particles is the mode diameter R1. Further, the relative particle amount of primary particles having a particle diameter in a minute range near the mode diameter R1 is defined as ρ1. Here, the “relative particle amount ρ1” is a ratio (%) of primary particles having a particle diameter in a minute range near the mode diameter R1 when the particle amount of the entire primary particles is a reference (100%).

  A curve 20 is a particle size distribution curve of the secondary particles of the composite particles obtained on a volume basis. Since the secondary particles are large particles formed by aggregation of the primary particles, the particle size distribution curve 20 of the secondary particles is distributed on the large particle size side as compared with the primary particles. The “relative particle amount ρ2” of the secondary particles refers to the relative particle amount of the secondary particles having a particle diameter in the minute range. That is, the “relative particle amount ρ2” is the ratio (%) of secondary particles having a particle diameter in the minute range when the particle amount of the entire secondary particles is used as a reference (100% by mass). Note that the particle size distribution curves 10 and 20 shown in FIG. 1 are for explaining the concept of ρ1 and ρ2, and do not show the actual particle size distribution of the composite particles.

  The volume average particle size distribution of the primary particles can be measured by spraying the composite particles with compressed air using a laser diffraction particle size distribution measuring device. Further, the volume average particle size distribution of the secondary particles can be measured by free-falling the composite particles using a laser diffraction type particle size distribution measuring device under a temperature condition of 23 ° C., for example.

<Electrochemical element electrode>
The electrochemical element electrode of the present invention (hereinafter sometimes simply referred to as “electrode”) has an active material layer formed by pressure-molding the composite particles obtained by the production method of the present invention. It is laminated on top.

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

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

  Moreover, you may use what applied the electrically conductive coating to the surface as a collector. The conductive paint is obtained by dispersing a conductive material, a binder, and a dispersant added as necessary in water or an organic solvent. Examples of the conductive material of the conductive paint include silver, nickel, gold, graphite, acetylene black, and ketjen black, and graphite and acetylene black are preferable. As the binder for the conductive paint, any of those exemplified as the binder used in the composite particles of the present invention can be used. Moreover, water glass, an epoxy resin, a polyamideimide resin, a urethane resin, etc. can also be used, and each can be used individually or in combination of 2 or more types. Preferred binders for the conductive paint are acrylate polymers, ammonium salts or alkali metal salts of carboxymethyl cellulose, water glass, and polyamideimide resins. Further, as the dispersant for the conductive paint, a dispersant that may be used for the composite particles or a surfactant can be used.

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

  Of these, the pressure molding method is preferably employed because it can be performed with simple equipment. Examples of the pressure molding method include a roll pressure molding method for forming an active material layer by supplying an electrode material containing composite particles to a roll-type pressure molding device using a feeder such as a screw feeder, or an electrode material. Is applied to the current collector, the thickness of the electrode material is adjusted with a blade or the like, the thickness is adjusted, and the molding is then performed with a pressurizing device, and the mold is filled with the electrode material, and the mold is pressurized and molded. Etc.

Of these pressure forming methods, the roll pressure forming method is preferred. In this method, the active material layer may be laminated directly on the current collector by feeding the current collector to the roll simultaneously with the supply of the electrode material. The molding temperature is usually 0 to 200 ° C., preferably higher than the melting point or glass transition temperature of the binder of the composite particles, and more preferably 20 ° C. higher than the melting point or glass transition temperature. In roll press molding, the molding speed is usually 0.1 to 20 m / min, preferably 4 to 10 m / min. The press linear pressure between the rolls is usually 0.2 to 30 kN / cm, preferably 1.5 to 15 kN / cm.
In order to eliminate variations in the thickness of the molded electrode and increase the density of the active material layer to increase the capacity, post-pressurization may be further performed as necessary. The post-pressing method is generally a roll press process. In the roll press process, two cylindrical rolls are arranged in parallel at a narrow interval in the vertical direction, and each is rotated in the opposite direction. The temperature of the roll may be adjusted by heating or cooling.

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

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

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

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

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

Measurement and evaluation of each characteristic in Examples and Comparative Examples were performed by the following methods.
(Measurement of volume average particle diameter of primary particles, measurement of ρ1, ρ2)
The particle size distribution of the obtained composite particles is as follows: a laser diffraction particle size distribution measuring device SALD-3100 manufactured by Shimadzu Corporation, a dedicated injection type dry measuring unit DS-21 (primary particle size distribution), and a dedicated free fall measuring unit DS-3. Measurement was performed at 23 ° C. using (secondary particle size distribution).
Then, the horizontal axis is the logarithmic value of the primary particle diameter or the secondary particle diameter, the vertical axis is the frequency, a particle diameter distribution curve is drawn, and the mode diameter R1 is obtained as the particle diameter indicating the maximum value of the primary particle diameter distribution curve. Is ρ1 as the relative particle amount of the primary particles in the range of 10 ^{(logR1) −0.02389} or more and 10 ^{(logR1) +0.02389} , and ρ2 is determined as the relative particle amount of the secondary particles in the particle size range. It was.

(Evaluation of fluidity of composite particles)
The angle of repose of the composite particles was measured with an angle of repose measuring device (Powder Tester PT-R), and the results of evaluating the fluidity by a four-stage method based on the following criteria are shown in Table 1.
Angle of repose is 60 ° or more: A
Angle of repose is 50 ° or more and less than 60 °: B
Angle of repose is 30 ° or more and less than 50 °: C
Angle of repose is less than 30 °: D

(Active material layer thickness, thickness accuracy)
A sheet-shaped active material layer molded at a roll speed of 2 m / min and 8 m / min was randomly punched into a shape having a diameter of 12 mm, and the thickness of the active material layer was calculated as an average value of the thickness. Further, the thickness variation of the active material layer molded at 8 m / min was calculated by the following formula (1).
“Variation” = (standard deviation / average value) × 100 (1)

(Electrical characteristics)
The sheet-shaped active material layer was bonded to an aluminum current collector having a thickness of 20 μm, which had been applied and dried in advance with a conductive coating material, to form an electrode for an electric double layer capacitor. This electrode was punched into a circular shape with a diameter of 12 mm to produce a CR2032 coin-type electric double layer capacitor, and the internal resistance was measured. As the electrolytic solution, a 1.4 mol / liter propylene carbonate solution of triethylmethylammonium tetrafluoroborate was used.
Using the obtained electric double layer capacitor, charging was started from 0 V at a constant current of 10 mA at 25 ° C., and after the voltage reached 2.7 V, the charging current was 0.5 mA at a constant voltage of 2.7 V. The battery was charged until it decreased. Thereafter, the battery was discharged at a constant current of 10 mA until it reached 0V. The internal resistance was calculated according to the calculation method of standard RC-2377 defined by the Japan Electronics and Information Technology Industries Association from the charge / discharge curve. The smaller the internal resistance, the better the electrical characteristics.

<Example 1>
100 parts of alkali-activated activated carbon powder having a specific surface area of 2,200 m ² / g and a volume average particle diameter of 8 μm as an electrode active material, and an aqueous dispersion of polytetrafluoroethylene (solid content: 64%) as a binder 15.6 parts, 5 parts of acetylene black (Denka black powder form; manufactured by Denki Kagaku Kogyo Co., Ltd.) having a volume average particle diameter of 0.7 μm as a conductive material, ammonium salt of carboxymethyl cellulose “DN-800H” (Daicel Chemical Industries) as a dispersant 93.3 parts of 1.5% aqueous solution (manufactured by Kogyo Co., Ltd.) and distilled water were added and stirred and mixed with a “TK homomixer” (manufactured by Primics) to prepare a slurry having a solid content concentration of 20%. The slurry was sprayed using a spray dryer (OC-16; manufactured by Okawara Chemical Co., Ltd.). The rotating disk type atomizer (65 mm in diameter) was rotated at 25,000 rpm, the hot air temperature was 150 ° C, and the particle recovery outlet temperature was 90 ° C. And spray-drying granulation was performed to obtain granulated particles.

  In a 2 L high speed mixer (Henschel mixer manufactured by Mitsui Miike Seisakusho Co., Ltd.) in which the powder contact part is made of 100 parts of the granulated particles and 2 parts of acetylene black having a volume average particle diameter of 0.7 μm as solid particles a at 2,000 rpm Were mixed for 15 minutes to obtain composite particles in which the solid particles a were uniformly attached to the surface of the composite particles. Table 1 shows the results of evaluating the properties of the composite particles.

  Next, the obtained composite particles are supplied to a roll (roll temperature 120 ° C., press linear pressure 4.0 kN / cm) of a roll press machine (pressed rough surface heat roll, manufactured by Hirano Giken Kogyo Co., Ltd.) using a quantitative feeder. Then, a sheet-like active material layer was formed by roll pressing. Molding was performed at roll speeds of 2 m / min and 8 m / min, and the thickness of the sheet-like active material layer was measured. Further, the thickness variation of the active material layer obtained at a molding speed of 8 m / min was measured. The results are shown in Table 1.

In addition, an active material layer having a thickness of 520 μm was formed in the same manner as above except that the press linear pressure was 4.5 kN / cm and the roll speed was 13.5 m / min, and then rolled with a heating roll adjusted to a gap of 500 μm. Thus, a sheet-like active material layer having a thickness of 500 μm and a density of 0.52 g / cm ³ was obtained. Table 1 shows the results of evaluation of electrical characteristics using this active material layer.

<Example 2>
Implemented except that 10 parts of alkali activated carbon powder having a specific surface area of 2,200 m ² / g and a volume average particle diameter of 3 μm was used as the solid particles a instead of 2 parts of acetylene black having a volume average particle diameter of 0.7 μm. In the same manner as in Example 1, composite particles were obtained. Subsequently, an active material layer was formed in the same manner as in Example 1 using the composite particles. However, the active material layer for evaluating electrical characteristics was molded at a press linear pressure of 4.5 kN / cm and a roll speed of 11.5 m / min. Table 1 shows the results of evaluating the properties of the obtained composite particles and active material layer.

<Example 3>
As the solid particles a, composite particles were obtained in the same manner as in Example 1 except that 10 parts of silica powder having a volume average particle diameter of 2 μm was used instead of 2 parts of acetylene black having a volume average particle diameter of 0.7 μm. . Subsequently, an active material layer was formed in the same manner as in Example 1 using the composite particles. However, the active material layer for evaluating electrical characteristics was molded at a press linear pressure of 4.0 kN / cm and a roll speed of 11 m / min. Table 1 shows the results of evaluating the properties of the obtained composite particles and active material layer.

<Comparative Example 1>
The granulated particles obtained in Example 1 were used as they were without being mixed with the solid particles a, and an active material layer was formed in the same manner as in Example 1. However, a continuous sheet-like active material layer was not obtained at a roll speed of 8 m / min. For electrical property evaluation, after forming an active material layer having a thickness of 610 μm by forming at a press linear pressure of 4.0 kN / cm and a roll speed of 5 m / min, rolling is repeated with a heated roll adjusted to a gap of 500 μm. Thus, a sheet-like active material layer having a thickness of 500 μm and a density of 0.52 g / cm ³ was obtained. Table 1 shows the results of evaluating the properties of the obtained composite particles and active material layer.

<Comparative example 2>
100 parts of high-purity activated carbon powder “Kuraray Coal YP-17D” (manufactured by Kuraray Chemical Co., Ltd.) having a specific surface area of 1,800 m ² / g and a volume average particle size of 5 μm as an electrode active material, and a single core forming a core part as a binder. The monomer units are n-butyl acrylate and ethyl methacrylate, the monomer units forming the shell portion are n-butyl methacrylate and methacrylic acid, and the composition ratio of all monomer units is n-acrylate. Butyl: ethyl methacrylate: n-butyl methacrylate: methacrylic acid = 40: 40: 17: 3 (mass ratio), the glass transition temperature of the core portion is −5 ° C., and the glass transition temperature of the shell portion is 25 ° C. 45 parts of an aqueous dispersion latex (volume average particle size 0.31 μm, concentration 40%) of a certain core-shell type polymer, and acetylene black (deoxygen) having an average particle size of 0.7 μm as a conductive material. 5 parts of cablack powder (manufactured by Denki Kagaku Kogyo Co., Ltd.), 93.3 parts of a 1.5% aqueous solution of ammonium salt “DN-800H” (manufactured by Daicel Chemical Industries, Ltd.) as a dispersant In addition, the mixture was stirred and mixed with a “TK homomixer” (manufactured by Primics) to obtain a slurry having a solid content concentration of 20%. The slurry was sprayed using a spray dryer (OC-16; manufactured by Okawara Chemical Co., Ltd.). The rotating disk type atomizer (65 mm in diameter) was rotated at 25,000 rpm, the hot air temperature was 150 ° C, and the particle recovery outlet temperature was 90 ° C. And spray-drying granulation was performed to obtain granulated particles.

  The granulated particles were used as they were without being mixed with the solid particles a, and an active material layer was formed in the same manner as in Example 1. However, the active material layer for evaluating electrical characteristics was molded at a press linear pressure of 4.0 kN / cm and a roll speed of 10.5 m / min. Table 1 shows the results of evaluating the properties of the obtained composite particles and active material layer.

  In the composite particles for electrochemical element electrodes (Examples 1 to 3) obtained by the production method of the present invention, ρ2 / ρ1 is in the range of 0.03 to 0.60, and the fluidity of the composite particles In the evaluation, favorable results could be obtained. In the formation of the active material layer, an active material layer having a large thickness could be formed. Furthermore, even when the active material layer was molded at high speed, an active material layer having a large thickness and good thickness accuracy could be formed. The internal resistance of the electric double layer capacitor obtained using the electric double layer capacitor electrode in which the active material layer thus obtained was formed on the current collector showed a low value.

  In Comparative Example 1, since the composite particles were not supplied uniformly, a continuous sheet-like active material layer was not obtained in high speed molding. In Comparative Example 2, high-speed molding was possible, but the internal resistance of the electric double layer capacitor was large.

  Although the present invention has been described with reference to the most practical and preferred embodiments at the present time, the invention is limited to the embodiments disclosed herein. However, the present invention can be changed as appropriate without departing from the spirit or concept of the invention that can be read from the claims and the entire specification, and the composite particles for electrochemical element electrodes with such changes are also within the technical scope of the present invention. It must be understood as included.

It is a figure which shows the relationship between (rho) 1 and (rho) 2.

Explanation of symbols

10 Particle size distribution curve of primary particles 20 Particle size distribution curve of secondary particles

Claims (7)

A step of obtaining a slurry by dispersing an electrode active material and a binder in a solvent (I),
Step (II) of granulating the slurry by spray drying to obtain granulated particles, and at least a part of the surface of the granulated particles are made of solid particles a having a volume average particle size smaller than the granulated particles. Coating step (III),
A method for producing composite particles for an electrochemical element electrode, comprising: The manufacturing method according to claim 1, wherein the binder contains polytetrafluoroethylene. The manufacturing method according to claim 1, wherein the solid particles a are a conductive material. Electrochemical element electrode composite particles obtained by the production method according to claim 1,
The volume average particle diameter of the primary particles is 1 to 500 μm,
In the particle size distribution of the primary particles of the composite particles obtained on a volume basis, the relative particle amount of the primary particles having a particle diameter in a minute range near the mode diameter R1 of the primary particles is ρ1,
In the particle size distribution of the secondary particles of the composite particles obtained on a volume basis in the measurement at 23 ° C., when the relative particle amount of the secondary particles having a particle size in the minute range is ρ2,
Composite particles for electrochemical element electrodes, wherein ρ2 / ρ1 is 0.03 to 0.60. An electrochemical element electrode having a current collector and an active material layer laminated on the current collector, wherein the active material layer is obtained by the production method according to claim 1. An electrochemical element electrode formed by pressure-molding the composite particle for a chemical element electrode. The electrochemical element electrode according to claim 5, wherein the pressure molding is roll pressure molding. The electrochemical device electrode according to claim 5 or 6, which is used for an electric double layer capacitor.

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