JP4929792B2 - Composite particles for electrochemical device electrodes - Google Patents

Description

  The present invention relates to an electrochemical element electrode composite particle for producing an electrode suitably used for an electrochemical element such as a lithium ion secondary battery or an electric double layer capacitor, particularly an electric double layer capacitor (in this specification, simply “ Sometimes referred to as “composite particles”). The present invention also relates to a method for producing the composite particle, and an electrochemical element electrode using the composite particle.

  The demand for electrochemical devices 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 is rapidly expanding. Lithium-ion secondary batteries are used in fields such as mobile phones and notebook personal computers because of their relatively high energy density, and electric double layer capacitors can be charged and discharged quickly, so they can be used as memory backups for personal computers. It is used as a small power source. 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 to manufacturing methods capable of high-speed molding and materials for electrochemical element electrodes suitable for the manufacturing method. Yes.

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 is an object of the present invention to provide a composite particle for an electrochemical element electrode that can be obtained at a speed, a method for producing the composite particle, and an electrochemical element electrode formed by the production method.

  The inventor paid attention to the powder characteristics of the composite particles and, as a result of intensive studies, found that the ratio of secondary aggregation of the composite particles greatly affects the moldability of the 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.

  1st this invention is the composite particle for electrochemical element electrodes containing an electrode active material, a electrically conductive material, and a binder, Comprising: The volume average particle diameter of the primary particle of composite particle is 1-500 micrometers, In the particle size distribution of the primary particles of the composite particles obtained in the above, the relative particle amount of the primary particles having a particle size in the minute range near the mode diameter R1 of the primary particles is ρ1, and the volume is obtained on a volume basis in the measurement at 23 ° C. In the particle size distribution of the secondary particles of the composite particles, ρ2 / ρ1 is 0.03 to 0.60, where ρ2 is the relative particle amount of the secondary particles having a particle size in the minute range. It is a composite particle for device electrodes.

  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%).

  Moreover, it is preferable that the composite particle for electrochemical element electrodes of the first aspect of the present invention further contains a dispersant.

  The second aspect of the present invention includes a step of dispersing the electrode active material, the conductive material and the binder in water to obtain slurry A, a step of adjusting the pH of slurry A to 8.0 to 10.0, and It is the manufacturing method of the composite particle for electrochemical element electrodes of 1st this invention which has the process of spray-drying the slurry A and granulating.

  The third aspect of the present invention is an electrochemical element electrode in which an active material layer formed by pressure-molding the first composite particle for an electrochemical element electrode is laminated on a current collector.

  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.

  In the composite particle for an electrochemical element electrode of the present invention, the volume average particle diameter of the primary particles is 1 to 500 μm, and ρ2 / ρ1 is in the range of 0.03 to 0.60. 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 element electrode having an active material layer having excellent accuracy, uniformity, and a large thickness can be obtained.

  The composite particle for an electrochemical element electrode of the present invention contains an electrode active material, a conductive material, and a binder, and the primary particles have a volume average particle diameter of 1 to 500 μm, and the primary particle of the composite particle obtained on a volume basis. In the particle size distribution of the particles, 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, and the secondary particles of the composite particles obtained on a volume basis in the measurement at 23 ° C. In the particle size distribution, ρ2 / ρ1 is 0.03 to 0.60, where ρ2 is the relative particle amount of the secondary particles having a particle diameter in the minute range.

<Electrode active material>
The electrode active material constituting the composite particle of the present invention is appropriately selected depending on the type 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. Further, when the volume average particle size of the electrode active material is reduced, it is easy to reduce the volume average particle size of the composite particles.

<Conductive material>
The conductive material constituting the composite particle of the present invention is composed of an allotrope of particulate carbon having conductivity and no pores capable of forming an electric double layer, and improves the conductivity of the electrochemical device electrode. Is. 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 composite particles is usually 0.1 to 50 parts by mass, preferably 0.5 to 15 parts by mass, more preferably 1 to 10 parts by mass with respect to 100 parts by mass of the electrode active material. is there. 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.

<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, polymer compounds such as fluorine-based polymers, diene-based polymers, acrylate-based polymers, polyimides, polyamides, polyurethanes, and the like, more preferably fluorine-based polymers, diene-based polymers, and acrylate-based polymers are used. Can be mentioned. 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 is exemplified, and polytetrafluoroethylene is preferable.

  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.

  Specific examples of the acrylate ester include methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, cyclohexyl acrylate, 2-ethylhexyl acrylate, isopentyl acrylate, acrylic Alkyl acrylates such as isooctyl acrylate, isobonyl acrylate, isodecyl acrylate, lauryl acrylate, stearyl acrylate, and tridecyl acrylate; butoxyethyl acrylate, ethoxydiethylene glycol acrylate, methoxydipropylene glycol acrylate, methoxy acrylate Ether group-containing acrylic esters such as polyethylene glycol, phenoxyethyl acrylate, and tetrahydrofurfuryl acrylate; acrylic acid Hydroxyl group-containing acrylic acid esters such as 2-hydroxyethyl, 2-hydroxypropyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, 2-acryloyloxyethyl-2-hydroxyethylphthalic acid; 2-acryloyl; Carboxylic acid-containing acrylic esters such as loxyethylphthalic acid and 2-acryloyloxyethylphthalic acid; Fluorine group-containing acrylic esters such as perfluorooctylethyl acrylate; Phosphoric group-containing acrylic acid such as ethyl acrylate phosphate Examples include esters; acrylic acid esters containing epoxy groups such as glycidyl acrylate; amino acid containing acrylic esters such as dimethylaminoethyl acrylate;

  Specific examples of the methacrylic acid ester include methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, isopentyl methacrylate, methacrylic acid. Methacrylic acid alkyl esters such as isooctyl acid, isobornyl methacrylate, isodecyl methacrylate, lauryl methacrylate, tridecyl methacrylate and stearyl methacrylate; butoxyethyl methacrylate, ethoxydiethylene glycol methacrylate, methoxydipropylene glycol methacrylate, methoxypolyethylene methacrylate Glycol, phenoxyethyl methacrylate, tetrahydrofurfuryl methacrylate, etc. Ether group-containing methacrylic acid esters such as 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2-hydroxy-3-phenoxypropyl methacrylate, 2-methacryloyloxyethyl-2-hydroxyethylphthalic acid, etc. Hydroxyl group-containing methacrylates; Carboxylic acid-containing methacrylates such as 2-methacryloyloxyethylphthalic acid; Fluorine group-containing methacrylates such as perfluorooctylethyl methacrylate; Phosphoric group-containing methacrylates such as ethyl methacrylate Acid group; epoxy group-containing methacrylic acid ester such as glycidyl methacrylate; amino group-containing methacrylic acid ester such as dimethylaminoethyl methacrylate;

  These acrylic acid (or methacrylic acid) esters can be used alone or in combination of two or more. In addition, the acrylate polymer may be a copolymer obtained by polymerizing a monomer mixture containing acrylic acid (or methacrylic acid) ester. In this monomer mixture, acrylic acid (or The content of (methacrylic acid) ester is usually 50% by mass or more, preferably 60 to 99% by mass, more preferably 70 to 97% by mass.

  Other monomers copolymerizable with acrylic acid (or methacrylic acid) ester in the monomer mixture include α, β-unsaturated nitrile compound, crotonic acid ester, unsaturated carboxylic acid, and two or more. And carboxylic acid ester having a carbon-carbon double bond. Specific examples of the α, β-unsaturated nitrile compound include acrylonitrile and methacrylonitrile. The content of the α, β-unsaturated nitrile compound in the acrylate polymer is preferably 30% by mass or less.

  Specific examples of the crotonic acid ester include methyl crotonate, ethyl crotonate, propyl crotonate, butyl crotonate, isobutyl crotonate, and 2-ethylhexyl crotonate. The content of crotonic acid ester in the acrylate copolymer is preferably 3% by mass or less.

  Specific examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, maleic acid, fumaric acid, citraconic acid, mesaconic acid, glutaconic acid, and itaconic acid. The content of the unsaturated carboxylic acid in the acrylate copolymer is preferably 0.1 to 10% by mass, more preferably 1 to 5% by mass.

  Specific examples of the carboxylic acid ester having two or more carbon-carbon double bonds include ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, and trimethylolpropane trimethacrylate. The content of the carboxylic acid ester having two or more carbon-carbon double bonds in the monomer composition is preferably 0.1 to 10% by mass, more preferably 1 to 5% by mass.

  In addition, other monomers copolymerizable with acrylic acid (or methacrylic acid) esters include aromatic vinyl compounds such as styrene; conjugated dienes such as 1,3-butadiene and isoprene; and ethylene and propylene. Of 1-olefins. The total content of these monomers in the monomer composition is preferably 20% by mass or less, more preferably 10% by mass or less.

  Among these, as the binder, it is preferable to use a diene polymer and an acrylate polymer from the viewpoint that an active material layer excellent in binding property and strength to the current collector can be obtained.

  The binder used in the present invention preferably has a glass transition temperature, and the glass transition temperature is usually −80 ° C. to + 180 ° C., preferably −80 ° C. to + 40 ° C., more preferably −60 ° C. to + 20 ° C. The lower the glass transition temperature of the binder, the easier the secondary aggregation of the composite particles occurs, and the value of ρ2 / ρ1 decreases. Therefore, the value of ρ2 / ρ1 can be adjusted depending on the type of binder used.

  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 in the composite particles is usually in the range of 1 to 20 parts by mass, preferably 3 to 15 parts by mass with respect to 100 parts by mass of the electrode active material. As the amount of the binder used is increased, the composite particles are more easily aggregated, so that ρ2 / ρ1 can be adjusted according to the amount of the binder.

<Dispersant>
In addition to the above, the composite particles of the present invention may contain a dispersant. The dispersant is a resin that dissolves in a solvent, and is preferably used by being dissolved in a solvent during the preparation of slurry A, which will be described later, and has an action of uniformly dispersing an electrode active material, a conductive material, and the like in the solvent. is there. Examples of the dispersant include cellulose polymers such as carboxymethylcellulose, methylcellulose, ethylcellulose, hydroxypropylcellulose, and hydroxypropylmethylcellulose, and ammonium salts or alkali metal salts thereof; ammonium salts or alkali metals of polyacrylic acid or polymethacrylic acid Salts: polyvinyl alcohol, modified polyvinyl alcohol, polyethylene oxide; polyvinyl pyrrolidone, polycarboxylic acid, oxidized starch, phosphate starch, casein, various modified starches, chitin, chitosan derivatives and the like. These dispersants can be used alone or in combination of two or more. Among these, as the dispersant, a cellulose-based polymer is preferable, and carboxymethyl cellulose or its ammonium salt or alkali metal salt is particularly preferable. Although the 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 in a composite particle, Preferably it is 0.5-5 mass parts, More preferably It is the range of 0.8-2.5 mass parts. By using a dispersing agent, sedimentation and aggregation of solid content in the slurry A can be suppressed. As the amount of the dispersant increases, the composite particles are less likely to agglomerate in the secondary state.

<Other additives>
The composite particles of the present invention may further contain other additives as necessary. Examples of other additives include a surfactant. Examples of the surfactant include amphoteric surfactants such as anionic, cationic, nonionic, and nonionic anions. Among them, anionic or nonionic surfactants that are easily thermally decomposed are preferable. The amount of the surfactant is not particularly limited, but in the composite particles, 0 to 50 parts by weight, preferably 0.1 to 10 parts by weight, more preferably 0.5 to 5 parts by weight with respect to 100 parts by weight of the electrode active material. It is the range of mass parts. As the amount of the surfactant added is increased, the composite particles are less likely to agglomerate. Therefore, ρ2 / ρ1 can be adjusted by the amount of the surfactant.

<Volume average particle diameter of primary particles>
The composite particles of the present invention have primary particles having a volume average particle diameter in the range 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. Note that “primary particles” refer to individual composite particles.

<Relationship between ρ1 and ρ2 in mode diameter R1>
In the composite particle of the present invention, in the particle size distribution of the primary particle of the composite particle obtained on a volume basis, the relative particle amount of the primary particle having a particle diameter in a minute range near the mode diameter R1 of the primary particle 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 0.03 to 0.60. The “secondary particle” refers to a large aggregated particle formed by aggregating 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.

Further, “a minute range in the vicinity of R1” means that the particle diameter distribution curve is drawn with the horizontal axis as the primary particle diameter (μm) and the vertical axis as the frequency, and the particle diameter indicating the maximum value of the primary particle diameter distribution curve is the mode diameter R1. When (μm) is obtained, the particle diameter is given 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 substantially 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 in the vicinity of the mode diameter R1 when the particle amount of the entire primary particles is a reference (100% by volume). . In FIG. 1, the relative particle amount ρ1 is a value represented by the ratio of the area of the minute range near R1 in the convex shape to the convex area surrounded by the particle size distribution curve 10 and the horizontal axis of the primary particles. .

  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 a ratio (%) of secondary particles having a particle diameter in the minute range when the particle amount of the entire secondary particles is set as a reference (100% by volume). In FIG. 1, the relative particle amount ρ2 is a value represented by the ratio of the area of the minute range near R1 in the convex shape to the convex area surrounded by the particle size distribution curve 20 and the horizontal axis of the secondary particles. is there. 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.

  In the composite particle for an electrochemical element electrode of the present invention, ρ2 / ρ1 is in the range of 0.03 to 0.60, preferably 0.03 to 0.30. 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 active material layer can be obtained at a high molding speed.

<Method for producing composite particle for electrochemical element electrode>
The composite particles for electrochemical device electrodes of the present invention are not particularly limited by the production method, but according to the production method (spray drying granulation method) described below, the composite particles of the present invention can be easily obtained. It is possible and preferable.

  The method for producing composite particles for an electrochemical element electrode of the present invention includes a step of obtaining a slurry A containing an electrode active material, a conductive material and a binder, and a step of granulating the slurry A by spray drying. Hereinafter, each step will be described.

(Step of obtaining slurry A)
In the step of obtaining the slurry A, the electrode active material, the conductive material, the binder, and the electrode active material, the conductive material, and the binder are dispersed or dissolved in a solvent. A slurry A is obtained in which the agent and, if necessary, the dispersant and other additives are dispersed or dissolved.

  Although it does not specifically limit as a solvent used in order to obtain the slurry A, When using said dispersing agent, the solvent which can melt | dissolve a dispersing agent is used suitably. 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 the slurry A can be adjusted, and production efficiency can be improved.

  The amount of the solvent used when preparing the slurry A is such that the solid content concentration of the slurry A is usually in the range of 1 to 50% by mass, preferably 5 to 50% by mass, more preferably 10 to 30% by mass. It is. When the solid content concentration is in this range, the binder is preferably dispersed uniformly. Further, since the primary average volume particle diameter of the composite particles increases as the solid content concentration of the slurry A increases, ρ2 / ρ1 can be adjusted by adjusting the solid content concentration of the slurry A.

  The viscosity of the slurry A 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 A is in this range, the productivity of the spray drying granulation step can be increased. The higher the viscosity of the slurry A, the larger the spray droplets and the larger the primary average volume particle diameter of the composite particles. Therefore, ρ2 / ρ1 can be adjusted by adjusting the viscosity of the slurry A.

  When the solvent of the slurry A is water, it is preferable to adjust the pH. The pH of the slurry A is preferably in the range of 8.0 to 10.0, more preferably 8.2 to 10.0, and most preferably 8.5 to 9.5. When the pH of the slurry A is in this range, it becomes easy to obtain composite particles having ρ2 / ρ1 in the above range. The pH of the slurry A is affected by the properties of the electrode active material to be used, and is usually in the range of 3-12. When adjusting the pH of the slurry A, it is preferable to use aqueous ammonia when raising the pH, and preferably using acetic acid or sulfuric acid when lowering the pH.

  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.

(Spray drying process)
Next, the slurry A is spray-dried and granulated. The spray drying method is a method of spraying and drying a slurry in hot air. 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 primary average volume particle diameter of the composite particles. Examples of the rotating disk type atomizer include a pin type and a vane type, and a pin type atomizer is preferable. A pin-type atomizer is a type of centrifugal spraying device that uses a spraying plate, and the spraying plate has a plurality of spraying rollers removably mounted on a concentric circle along its periphery between upper and lower mounting disks. It consists of Slurry A is introduced from the center of the spray disc, adheres to the spraying roller by centrifugal force, moves outward on 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 A is pressurized and sprayed from a nozzle to be dried.

  The temperature of the slurry A to be sprayed is usually room temperature, but it 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 the spray drying method, the hot air blowing method is not particularly limited, for example, a method in which the hot air and the spraying direction flow in parallel, a method in which the hot air is sprayed at the top of the drying tower and descends with the hot air, and the sprayed droplets and hot air are countercurrent Examples include a contact method, and a method in which sprayed droplets first flow in parallel with hot air, then drop by gravity and contact countercurrent.

  The electrochemical element electrode composite particles produced by the above production method or other methods can also control ρ2 / ρ1 by performing post-treatment after the particle production, if necessary. Specific examples include heat drying to remove residual solvent to increase ρ2 / ρ1, conversely adding a small amount of solvent to the composite particles, exposing the composite particles to water vapor, adding a binder, etc. Therefore, ρ2 / ρ1 can be reduced.

<Electrochemical element electrode>
The electrochemical device electrode of the present invention (hereinafter sometimes simply referred to as “electrode”) is formed by laminating an active material layer formed from the electrochemical device composite particles on a current collector.

(Current collector)
As the current collector material used for the electrode, for example, metal, carbon, conductive polymer, and the like can be used, and metal is preferably used. As the current collector metal, aluminum, platinum, nickel, tantalum, titanium, stainless steel, other alloys and the like are usually used. Among these, it is preferable to use aluminum or an aluminum alloy in terms of conductivity and voltage resistance. 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 step, two cylindrical rolls are arranged vertically in parallel at a narrow interval, and each is rotated in the opposite direction, and the electrodes are nipped and pressed between them. The temperature of the roll may be adjusted by heating or cooling.

  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.

<Example 1>
50 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 an aqueous solution containing 5% of carboxymethyl cellulose as a dispersant (Serogen 7A; Daiichi Kogyo Seiyaku Co., Ltd.) Part and 50 parts of water were mixed and dispersed using a planetary mixer to obtain a conductive material dispersion having a solid concentration of 20%. Next, 30 parts of the conductive material dispersion, 8 parts of an aqueous solution containing 5% of carboxymethyl cellulose (Serogen 7A; manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), a specific surface area of 1,800 m ² / g and a volume average particle diameter of 5 μm as an electrode active material 100 parts of high-purity activated carbon powder “Kuraray Coal YP-17D” (manufactured by Kuraray Chemical Co., Ltd.), carboxy-modified styrene / butadiene copolymer (average particle size 0.12 μm, glass transition temperature −5 ° C.) as a thermoplastic binder. 7.5 parts of a dispersion liquid (BM400B; manufactured by Nippon Zeon Co., Ltd., 40% concentration) and water are added and mixed with a planetary mixer, and diluted with water to a solid content concentration of 21%. Obtained. The pH of the slurry was 7.7. This slurry was adjusted to pH 9.5 with 25% aqueous ammonia, and using a spray dryer (OC-16; manufactured by Okawara Chemical Co., Ltd.), a rotating disk type atomizer (diameter 65 mm) with a rotation speed of 20,000 rpm and hot air Spray drying granulation was performed at a temperature of 150 ° C. and a particle recovery outlet temperature of 90 ° C. to obtain composite particles.

<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. 15 parts of an aqueous dispersion latex (volume average particle diameter 0.31 μm, concentration 40%) of a core-shell type polymer, and acetylene black (de- cene) having an average particle diameter 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 dispersing agent, and ion-exchanged water 348 7 parts were added and stirred and mixed with a “TK homomixer” (manufactured by Primex) to obtain a slurry having a solid content concentration of 20%. The pH of the slurry was 7.6 at 23 ° C. This slurry was adjusted to pH 8.5 with 25% aqueous ammonia, and using a spray dryer (OC-16; manufactured by Okawara Chemical Co., Ltd.), a rotating disk type atomizer (diameter 65 mm) with a rotation speed of 25,000 rpm and hot air Spray drying granulation was performed at a temperature of 150 ° C. and a particle recovery outlet temperature of 90 ° C. to obtain composite particles.

<Example 3>
The same as in Example 2 except that the pH of the slurry was not adjusted, the spray dryer was “OD-22G” (Okawara Chemical Co., Ltd.), and a rotating disk pin atomizer (diameter 125 mm) was used. Thus, composite particles were obtained.

<Example 4>
Composite particles were obtained in the same manner as in Example 2 except that the amount of the binder was 30 parts and the pH was not adjusted. The pH of the slurry used for spray drying was 7.5.

<Comparative Example 1>
Composite particles were obtained in the same manner as in Example 1 except that the pH of the slurry was not adjusted.

<Comparative example 2>
Composite particles were obtained in the same manner as in Example 2 except that the pH of the slurry was not adjusted.

<Comparative Example 3>
Composite particles were obtained in the same manner as in Example 2 except that the amount of the binder was 45 parts and the pH was not adjusted. The pH of the slurry used for spray drying was 7.4.

<Evaluation method>
(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 the relative particle amount of the primary particles in the range of 10 ^{{(logR1) −0.02389}} or more and less than 10 ^{{(logR1) +0.02389},} and the relative particles of the secondary particles in the particle size range Ρ2 was determined as a quantity.

(Evaluation of fluidity of composite particles)
Table 1 shows the results of measuring the angle of repose of the composite particles with an angle of repose measuring device (Powder Tester PT-R) and evaluating the fluidity by a four-step method based on the following criteria.
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)
Next, the obtained composite particles are supplied to a roll (roll temperature 120 ° C., press linear pressure 4 kN / cm) of a roll press machine (pressed rough surface heat roll, manufactured by Hirano Giken Kogyo Co., Ltd.) using a quantitative feeder. A sheet-like active material layer was formed by pressure molding. Molding was performed at roll speeds of 2 m / min and 5 m / min, and the film thickness of the sheet-like active material layer was measured. The results are shown in Table 1. In addition, 20 active material layers obtained at a molding speed of 5 m / min were randomly punched into a shape having a diameter of 12 mm, thickness and density were measured, and each variation was calculated by the following equation (1). The results are shown in Table 1.

  “Variation” = (standard deviation / average value) × 100 (1)

<Evaluation results>
In the composite particles for electrochemical element electrodes of the present invention (Examples 1 to 4), ρ2 / ρ1 is in the range of 0.03 to 0.60, which is the range of the present invention, 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.

  On the other hand, in Comparative Example 1 and Comparative Example 2, ρ2 / ρ1 was out of the scope of the present invention, and the fluidity of the composite particles was high, and the fluidity evaluation was not preferable. In forming the active material layer, an active material layer having a large thickness could not be formed. Furthermore, when the active material layer was formed at high speed, the sheet could not be formed continuously.

  Further, in Comparative Example 3, ρ2 / ρ1 was out of the scope of the present invention, and the thickness accuracy was inferior when the active material layer was molded at high speed.

  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. Rather, it can be changed as appropriate without departing from the spirit or idea of the invention that can be read from the claims and the entire specification, and the composite particles for electrochemical device electrodes accompanied by such changes, the method for producing the composite particles, and the method Electrochemical element electrodes formed using composite particles should also be understood as being within the scope of the present invention.

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 (6)

Electrochemical element electrode composite particles containing an electrode active material, a conductive material and a binder,
The volume average particle diameter of primary particles of the composite 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.   The composite particle for an electrochemical element electrode according to claim 1, further comprising a dispersant.   Dispersing or dissolving the electrode active material, conductive material and binder in water to obtain slurry A, adjusting the pH of slurry A to 8.0 to 10.0, and spray drying slurry A The method for producing composite particles for an electrochemical element electrode according to claim 1, further comprising a step of granulating.   An electrochemical element electrode having a current collector and an active material layer laminated on the current collector, wherein the active material layer pressurizes the composite particle for an electrochemical element electrode according to claim 1 or 2 An electrochemical element electrode formed by molding.   The electrochemical element electrode according to claim 4, wherein the pressure molding is roll pressure molding.   The electrochemical device electrode according to claim 4, which is used for an electric double layer capacitor.

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