JP2015043342A - Material for forming electrochemical element electrode, method for manufacturing the same, and electrochemical element electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide composite particles for forming an electrode active material layer of an electrochemical element electrode capable of improving diffusion property of electrolytic ions, and lowering resistance of the electrodes.SOLUTION: Material for forming an electrochemical element electrode comprises electrode active material and composite particles including a binder, with a mean surface void of the composite particles of 15% or more.

Description

  The present invention relates to a composite used for forming an electrode used for an electrochemical element such as a lithium ion secondary battery or an electric double layer capacitor (hereinafter sometimes collectively referred to as “electrochemical element electrode”). The present invention relates to an electrode-forming material comprising particles and a method for producing the same, and also relates to an electrochemical element electrode using the electrode-forming material.

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

For example, in Patent Document 1, an electrode active material, a conductive material, a dispersion-type binder, and a soluble resin are dispersed or dissolved in a solvent, and the electrode active material, the conductive material, and the dispersion-type binder are dispersed and dissolved. An electrochemical element electrode having an electrode active material layer obtained by forming a slurry in which a mold resin is dissolved and sheet-forming composite particles obtained by spray drying has been introduced.
JP 2006-303395 A

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

  Therefore, an object of the present invention is to improve the diffusibility of electrolyte ions and reduce the resistance of the electrode in the composite particles forming the electrode active material layer of the electrode for an electrochemical element.

  As a result of intensive studies in view of the above problems, the present inventors have found that the composite particles obtained by the method disclosed in Patent Document 1 often have a low porosity on the surface, and few particles with a highly porous surface. I found out. For this reason, it has been found that an electrochemical element electrode composed of the composite particles has a high ion diffusion resistance of the electrolytic solution and it is difficult to reduce the resistance. In addition, by forming the electrochemical element electrode with a material composed of composite particles having a high porosity on the surface and having a porosity of a certain amount or more as a whole, the ion diffusion resistance is reduced, and the electrode is reduced. It was found that resistance can be achieved. The present inventor has completed the present invention based on these findings.

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

(1) An electrochemical element electrode forming material comprising composite particles containing an electrode active material and a binder,
A material for forming an electrochemical element electrode, wherein the composite particles have an average surface porosity of 15% or more.

(2) The method for producing an electrochemical element electrode forming material according to (1), comprising a step of spray-drying a slurry having a viscosity of 500 to 3000 mPa · s containing an electrode active material, a binder and a dispersant.

(3) An electrochemical element electrode having an electrode active material layer formed on a current collector by press-molding the electrochemical element electrode forming material according to (1) above.

  The electrode for an electrochemical element of the present invention is derived from the porous composite particle because the electrode for an electrochemical element of the present invention contains the porous composite particle and is obtained by using the electrode forming material for an electrochemical element composed of composite particles having a certain amount or more of porosity as a whole. The diffusibility of the electrolyte ions is improved by the voids, and the resistance of the electrode is reduced.

  Hereinafter, an electrochemical element electrode forming material according to the present invention, a method for producing the same, and an electrochemical element electrode obtained using the electrochemical element electrode forming material will be described.

(Electrochemical element electrode forming material)
The electrochemical element electrode forming material according to the present invention is composed of composite particles containing an electrode active material and a binder, and the surface average porosity of the composite particles is 15% or more. The electrode active material and binder contained in the composite particles will be described later.

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

Specifically, the surface average porosity is obtained by taking an electron micrograph of the material for forming an electrochemical element electrode of the present invention (particle state before electrode molding), and at least 5 fields of view per arbitrarily selected particle. Observe and measure the apparent surface area of continuous voids with an area of 0.1 μm ² or more, perform the same measurement for 10 particles or more, and calculate the average value of the obtained voids. The apparent surface area of the void is the area of the void observed on the electron micrograph, and does not include the area in the pores of the void. When individual composite particles are viewed, composite particles having a porosity of less than 15% may be included, but particles having a porosity of 15% or more (in the present specification, described as “porous composite particles”). As a result, the overall surface average porosity is increased as described above.

  The volume average particle size of the composite particles is usually in the range of 0.1 to 1,000 μm, preferably 5 to 500 μm, more preferably 10 to 100 μm. The volume average particle diameter can be measured using a laser diffraction particle size distribution measuring apparatus.

  The material for forming an electrochemical element electrode suitable for the present invention usually has a particle size displacement rate of 5 to 70% when compressed to a maximum load of 9.8 mN at a load speed of 0.9 mN / sec by a micro compression tester, preferably 20 to 50%. The particle size displacement rate is the ratio (= ΔD / D0 × 100) of the amount of particle size reduction (ΔD = D0−D1) due to compression to the particle size D0 before compression of the composite particles. In addition, D1 is a value which changes according to a load amount with a particle size when applying a load.

  In addition, the electrochemical element electrode forming material preferably used in the present invention is a particle size displacement rate per unit second when compressed to a maximum load of 9.8 mN at a load speed of 0.9 mN / sec by a micro compression tester. The amount of change is preferably 25% or less, more preferably 10% or less, and particularly preferably 7% or less. The change amount of the particle size displacement rate per unit second is the change amount per unit second of the particle size change rate when the load increases at a load speed of 0.9 mN / sec. The particle size displacement rate when compressed to a maximum load of 9.8 mN measured by a micro-compression tester is a numerical value necessary to show the shape maintenance force of the composite particles. If the particle size displacement rate is too small, the composite particles are hardly deformed even by pressurization, so that the contact area between the particles is small and the conductivity is not increased. On the other hand, when the particle size displacement rate is too large, the composite particles are crushed, the network formed by the electrode active material and the conductive material formed in the composite particles is broken, and the conductivity is lowered. Further, the change amount of the particle size displacement rate per unit second is an index for determining the presence or absence of crushing. When crushing occurs, the particle size decreases rapidly, so the amount of change in particle size displacement rate per unit second exceeds 25%. Since the composite particle having a particle size displacement rate of 5 to 70% when compressed to a maximum load of 9.8 mN has appropriate softness, the contact area between the particles is large. And since it is not crushed, the network of an electrode active material and a electrically conductive material is maintained.

(Method of manufacturing electrochemical element electrode forming material)
The method for producing the electrochemical element electrode forming material is not particularly limited. However, since the production is easy, the viscosity is particularly 500 to 3000 mPa · s, preferably 750, containing an electrode active material, a binder and a dispersant. A spray-drying method in which a slurry of ˜2000 mPa · s, more preferably 1000 to 1500 mPa · s is spray-dried and granulated is preferred. If the slurry viscosity is too high, granulation may be difficult. On the other hand, if the slurry viscosity is too low, the surface average porosity of the resulting composite particles tends to decrease. The slurry viscosity is a value measured using a B-type viscometer under conditions of a temperature of 25 ° C. and a rotation speed of 60 rpm.

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

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

  The slurry used in the present invention contains an electrode active material, a binder and a dispersing agent, and may optionally contain a conductive material, a surfactant and the like.

  The electrode active material is a material that transfers electrons within the electrode, and specifically includes an active material for a lithium ion secondary battery and an active material for an electric double layer capacitor.

Examples of the active material for a lithium ion secondary battery include a positive electrode and a negative electrode. As an electrode active material for a positive electrode of a lithium ion secondary battery, lithium-containing composite metal oxides such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiFePO ₄ , LiFeVO ₄ ; TiS ₂ , TiS ₃ , non Transition metal sulfides such as crystalline MoS ₃ ; transition metal oxides such as Cu ₂ V ₂ O ₃ , amorphous V ₂ O · P ₂ O ₅ , MoO ₃ , V ₂ O ₅ , V ₆ O ₁₃ ; Illustrated. 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 Examples include molecules.

The electrode active material used for the electrode of the lithium ion secondary battery is preferably sized into spherical particles. When the shape of the particles is spherical, a higher density electrode can be formed during electrode molding. The volume average particle size distribution is preferably a mixture of fine particles of about 1 μm and relatively large particles of 3 to 8 μm, or particles having a broad particle size distribution of 0.5 to 8 μm. Particles having a particle size of 50 μm or more are preferably used after being removed by sieving or the like. The tap density defined by ASTM D4164 of the electrode active material is not particularly limited, and those having a positive electrode of 2 g / cm ³ or more and those of a negative electrode of 0.6 g / cm ³ or more are preferably used.

  As an electrode active material for an electric double layer capacitor, an allotrope of carbon is usually used. Specific examples of the allotrope of carbon include activated carbon, polyacene, carbon whisker, and graphite, and these powders or fibers can be used. A preferable 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.

The specific surface area of the electrode active material for an electric double layer capacitor, ^{30 m} 2 / g or more, preferably preferably 500~5,000m ² / g, more preferably 1,000~3,000m ² / g.

  The electrode active material for an electric double layer capacitor has a volume average particle size of 0.1 to 100 μm, preferably 1 to 50 μm, more preferably 5 to 20 μm. When an active material having a weight average particle diameter in this range is used, the electric double layer capacitor electrode can be easily thinned and the capacitance can be increased.

  These electrode active materials can be used individually or in combination of 2 or more types according to the kind of electrochemical element.

  The binder is a compound that can bind an electrode active material, a conductive material, and the like. For example, polymer compounds such as fluorine-based polymers, diene-based polymers, acrylate-based polymers, polyimides, polyamides, and polyurethanes are preferable, and fluorine-based polymers, diene-based polymers, and acrylate-based polymers are preferable. It is done.

  The fluorine-based polymer is a polymer containing a monomer unit containing a fluorine atom. The ratio of the monomer unit containing fluorine in the fluoropolymer is usually 50% by weight or more. Specific examples of the fluorine-based polymer include fluorine resins such as polytetrafluoroethylene and polyvinylidene fluoride, 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 weight or more, preferably 50% by weight or more, more preferably 60% by weight or more. Specific examples of the diene polymer include conjugated diene homopolymers such as polybutadiene and polyisoprene; aromatic vinyl / conjugated diene copolymers such as carboxy-modified styrene / butadiene copolymer (SBR); Examples 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 acrylic acid ester and / or methacrylic acid ester or a monomer mixture containing them. The ratio of acrylic acid ester and / or methacrylic acid ester in the monomer mixture is usually 40% by weight or more, preferably 50% by weight or more, more preferably 60% by weight or more. Specific examples of the acrylate polymer include 2-ethylhexyl acrylate / methacrylic acid / acrylonitrile / ethylene glycol dimethacrylate copolymer, 2-ethylhexyl acrylate / methacrylic acid / methacrylonitrile / diethylene glycol dimethacrylate copolymer, acrylic Crosslinking of 2-ethylhexyl acid / styrene / methacrylic acid / ethylene glycol dimethacrylate copolymer, butyl acrylate / acrylonitrile / diethylene glycol dimethacrylate copolymer, and butyl acrylate / acrylic acid / trimethylolpropane trimethacrylate copolymer Type acrylate polymer; ethylene / methyl acrylate copolymer, ethylene / methyl methacrylate copolymer, ethylene / ethyl acrylate copolymer, and A copolymer of ethylene and acrylic acid (or methacrylic acid) such as an ethylene / ethyl methacrylate copolymer; a radical polymerizable monomer in the copolymer of ethylene and acrylic acid (or methacrylic acid) Grafted graft polymers; and the like. In addition, as a radically polymerizable monomer used for the said graft polymer, methyl methacrylate, acrylonitrile, methacrylic acid etc. are mentioned, for example. In addition, a copolymer of ethylene and acrylic acid (or methacrylic acid) such as an ethylene / acrylic acid copolymer and an ethylene / methacrylic acid copolymer can be used as a binder.

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

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

  These binders can be used alone or in combination of two or more. The amount of the binder used is usually 0.1 to 50 parts by weight, preferably 0.5 to 20 parts by weight, and more preferably 1 to 10 parts by weight with respect to 100 parts by weight of the electrode active material. is there.

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

  These dispersants can be used alone or in combination of two or more. The amount of the dispersant used is not particularly limited, but is usually 0.1 to 10 parts by weight, preferably 0.5 to 5 parts by weight, and more preferably 0.8 parts per 100 parts by weight of the electrode active material. The range is ˜2 parts by weight. By using a dispersing agent, sedimentation and aggregation of solid content in the slurry can be suppressed. Moreover, since the clogging of the atomizer at the time of spray drying can be prevented, spray drying can be performed stably and continuously.

  The slurry used for the production of the positive electrode of the lithium ion secondary battery or the electrode active material of the electric double layer capacitor preferably contains a conductive material. The conductive material is made of an allotrope of particulate carbon that has conductivity and does not have pores that can form an electric double layer, and improves the conductivity of the electrochemical element electrode. Specific examples of the conductive material include conductive carbon black such as furnace black, acetylene black, and ketjen black (registered trademark of Akzo Nobel Chemicals Bethloten Fennot Shap); graphite such as natural graphite and artificial graphite; Can be mentioned. Among these, conductive carbon black is preferable, and acetylene black and furnace black are more preferable.

  The volume average particle size of the conductive material is preferably smaller than the volume average particle size 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 is usually 0.1 to 50 parts by weight, preferably 0.5 to 15 parts by weight, more preferably 1 to 10 parts by weight with respect to 100 parts by weight of the electrode active material. When an electrode having an amount of the conductive material within this range is used, the capacity of the electrochemical element can be increased and the internal resistance can be decreased.

  Examples of other additives added to the slurry include surfactants. Examples of the surfactant include amphoteric surfactants such as anionic, cationic, nonionic, and nonionic anions. Among them, anionic or nonionic surfactants that are easily thermally decomposed are preferable. These additives can be used alone or in combination of two or more.

  The amount of the surfactant is not particularly limited, but is 0 to 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 a range.

  As the solvent used for obtaining the slurry, water is usually used, but an organic solvent may be used. Examples of the organic solvent include alkyl alcohols such as methyl alcohol, ethyl alcohol and propyl alcohol; alkyl ketones such as acetone and methyl ethyl ketone; ethers such as tetrahydrofuran, dioxane and diglyme; diethylformamide, dimethylacetamide and N-methyl- Examples include amides such as 2-pyrrolidone and dimethylimidazolidinone; sulfur solvents such as dimethyl sulfoxide and sulfolane; and alcohols are preferable. When an organic solvent having a lower boiling point than water is used in combination, the drying rate can be increased during granulation by the spray drying method. Also, since the dispersibility of the dispersible binder or the dissolvability of the dissolvable resin varies depending on the type of solvent, the viscosity and fluidity of the slurry are adjusted by selecting the amount or type of organic solvent to produce spray drying Efficiency can be improved.

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

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

  The electrochemical element electrode forming material of the present invention is obtained by granulating the slurry by spray drying. The spray drying method is a method of spraying and drying a slurry in hot air. A typical example of the apparatus used for the spray drying method is an atomizer. There are two types of atomizers: a rotating disk method and a pressure method. The rotating disk system is a system in which slurry is introduced almost at the center of a disk that rotates at high speed, and the slurry is released from the disk by the centrifugal force of the disk, and in that case, the slurry is dried in the form of a mist.

  The rotational speed of the disc depends on the size of the disc, but is usually 5,000 to 30,000 rpm, preferably 15,000 to 30,000 rpm. On the other hand, the pressurization method is a method in which the slurry is pressurized and sprayed from a nozzle to be dried.

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

(Electrodes for electrochemical devices)
The electrode for an electrochemical element according to the present invention has an electrode active material layer on a current collector formed by pressure-molding an electrochemical element electrode forming material containing the porous composite particles.

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

  In the present invention, a material for forming an electrochemical element electrode is supplied onto the surface of the current collector, and this is pressure-molded. The feeder used in the step of supplying the electrode forming material is not particularly limited, but is preferably a quantitative feeder capable of supplying composite particles quantitatively. Here, the quantitative supply means that the electrode forming material is continuously supplied using such a feeder, the supply amount is measured a plurality of times at regular intervals, and the average value m and the standard deviation σm of the measurement values are measured. This means that the CV value (= σm / m × 100) obtained from the above is 4 or less. The quantitative feeder used in the present invention preferably has a CV value of 2 or less. Specific examples of the quantitative feeder include a gravity feeder such as a table feeder and a rotary feeder, and a mechanical force feeder such as a screw feeder and a belt feeder. Of these, the rotary feeder is preferred.

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

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

  In the above manufacturing method, the arrangement of the pair of rolls is not particularly limited, but is preferably arranged substantially horizontally or substantially vertically. When arranged almost horizontally, the current collector is continuously supplied between a pair of rolls, and the electrode material is supplied to at least one of the rolls, so that the electrode material is supplied to the gap between the current collector and the roll. The electrode active material layer can be formed by pressurization. In the case of disposing substantially vertically, the porous current collector is conveyed in the horizontal direction, an electrode material is supplied onto the current collector, and an electrode material layer is formed. After the supplied electrode material layer is leveled with a blade or the like as necessary, the current collector is supplied between a pair of rolls, and an electrode active material layer can be formed by pressurization. In this case, the thickness of the electrode material layer supplied between the pair of rolls is a value represented by (roll gap between the pair of rolls) / (current collector thickness + electrode active material layer thickness). Usually, it is 0.01 to 1, preferably 0.1 to 0.5.

  In order to eliminate variations in the thickness of the molded electrode active material layer, increase the density, and increase the capacity, post-pressurization may be further performed as necessary. The post-pressing method is generally a press process using a roll. In the 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.

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

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

(Surface average porosity of composite particles)
The surface average porosity of the composite particles contained in the electrochemical element electrode forming material produced in the following examples and comparative examples is determined by the following method.

First, an electron micrograph of the electrode forming material for an electrochemical element (particle state before electrode formation) was measured at a magnification of 2000 times, and an arbitrary particle was imaged as black and white 256-gradation image data in a field of view of 20 μm ^2. The image is read into analysis software (analySIS: manufactured by Soft Imaging System), and the contrast is optimized so that the brightest part of the image is 255 and the darkest part is zero. Next, the threshold value is set to 77, binarization processing is performed, and the ratio of voids having an area of 0.1 μm ² or more on the composite particle surface is obtained from the obtained binarized image.

  For the same particle, the same measurement is performed 5 times in an arbitrary field of view, and further, the same measurement is performed for 10 particles, and the averaged value is defined as the surface average porosity of the particles contained in the electrode forming material.

(Measurement of volume average particle diameter)
The volume average particle size of the composite particles contained in the electrode forming material for electrochemical devices is measured with a laser diffraction particle size distribution measuring device (SALD-2000: manufactured by Shimadzu Corporation).

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

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

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

<Example 1>
(Preparation of electrode forming material for electrochemical devices)
100 parts of an electrode active material (activated carbon with a specific surface area of 2000 m ² / g and a weight average particle size of 5 μm), 5 parts of a conductive material (acetylene black “Denka Black Powder” manufactured by Denki Kagaku Kogyo Co., Ltd.), a dispersion-type binder (Number average particle size 0.15 μm, 40% aqueous dispersion of a cross-linked acrylate polymer having a glass transition temperature of −40 ° C .: “AD211”; manufactured by Nippon Zeon Co., Ltd.) 25 parts, dispersant (carboxymethylcellulose 1 0.5% aqueous solution “Serogen BSH-12” (Daiichi Kogyo Seiyaku Co., Ltd.) 93.3 parts and ion-exchanged water 348.7 parts. K. The mixture is stirred and mixed with a homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.) to obtain a slurry having a solid content concentration of 20% and a viscosity of 1020 mPa · s. Next, the slurry is spray-dried with hot air at 150 ° C. using a spray dryer (with a pin type atomizer manufactured by Okawara Chemical Industries Co., Ltd.) to form an electrode for an electrochemical device comprising spherical composite particles having a volume average particle size of 60 μm. Material A was obtained. The surface average porosity was measured for 10 composite particles contained in the electrode forming material A for electrochemical devices.

(Production of electrodes)
The electrode forming material A for electrochemical elements is dry-mixed using a 2 L Henschel mixer (manufactured by Mitsui Miike Chemical Co., Ltd.). Thereafter, a roll for press (roll temperature 120) of a roll press machine (pressed rough surface heat roll; manufactured by Hirano Giken Kogyo Co., Ltd.) using a quantitative feeder (Nikka Corporation, Nikka Spray K-V) at a supply rate of 70 g / min. ℃, press linear pressure 4kN / cm). An etched aluminum foil with a thickness of 50 μm and Ra = 2.5 μm is inserted between the press rolls, and the composite particles supplied from the quantitative feeder are adhered to both sides of the etched aluminum foil as a current collector, and a forming speed of 15 m To obtain an electrochemical element electrode having an electrode active material layer with an average single-side thickness of 280 μm and an average single-side density of 0.50 g / cm ³ .

(Preparation of measurement cell)
In the electrode produced above, the current collector sheet portion on which the electrode active material layer is not formed remains 2 cm long × 2 cm wide, and the portion where the electrode active material layer is formed is 5 cm long × 5 cm wide. (The current collector sheet portion where the electrode active material layer is not formed is formed so as to extend one side of a 5 cm × 5 cm square where the electrode active material layer is formed). 10 sets of positive electrodes and 11 sets of negative electrodes cut out in this way are prepared, and the uncoated portions are ultrasonically welded respectively. Furthermore, the positive electrode is made of aluminum, and the negative electrode is made of nickel, and a tab material having a length of 7 cm, a width of 1 cm, and a thickness of 0.01 cm is ultrasonically welded to the current collector sheet portion on which the electrode active material layer is not formed. To prepare a measurement electrode. The measurement electrode is vacuum-dried at 200 ° C. for 24 hours. Using a cellulose / rayon mixed non-woven fabric with a thickness of 35 μm as a separator, the terminal welds of the positive electrode current collector and the negative electrode current collector are arranged on opposite sides, and the positive electrode and the negative electrode are alternated and laminated. All of the outermost electrodes of the prepared electrodes are laminated so as to be a negative electrode. Separators were placed on the top and bottom, and four sides were taped.

  After covering the laminated electrode with an exterior laminate film and fusing three sides, a solution of propylene carbonate dissolved in tetraethylammonium borofluoride at a concentration of 1.4 mol / L was vacuum impregnated as an electrolyte, and then the remaining side was melted. A film type capacitor was produced. Each characteristic was measured about the obtained film type capacitor. The results are shown in Table 1.

<Example 2>
(Preparation of electrode forming material for electrochemical devices)
In Example 1, 46.7 parts of a 1.5% aqueous solution of carboxymethylcellulose (“Serogen BSH-12” manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as a dispersant and a 1.5% aqueous solution (“DN-800H”: Daicel) A slurry having a solid content concentration of 20% and a viscosity of 620 mPa · s is obtained in the same manner except that 46.7 parts of Chemical Industry Co., Ltd. are used. Next, in Example 1, an electrode forming material B for an electrochemical element comprising spherical composite particles having a volume average particle size of 60 μm was obtained in the same manner except that the slurry was used as the slurry. The surface average porosity was measured for 10 composite particles contained in the electrochemical element electrode forming material B. The results are shown in Table 1.

  Further, in Example 1, the electrochemical element electrode (positive electrode, negative electrode) and film were similarly used except that the electrochemical element electrode forming material B obtained above was used as the electrochemical element electrode forming material. Type capacitor was fabricated and each characteristic was measured. The results are shown in Table 1.

<Comparative Example 1>
(Preparation of electrode forming material for electrochemical devices)
100 parts of an electrode active material (activated carbon with a specific surface area of 2000 m ² / g and a weight average particle size of 5 μm), 5 parts of a conductive material (acetylene black “Denka Black Powder” manufactured by Denki Kagaku Kogyo Co., Ltd.), a dispersion-type binder (Number average particle size 0.15 μm, 40% aqueous dispersion of a cross-linked acrylate polymer having a glass transition temperature of −40 ° C .: “AD211”; manufactured by Nippon Zeon Co., Ltd.) 25 parts, dispersant (carboxymethylcellulose 1 .5% aqueous solution “DN-800H” (manufactured by Daicel Chemical Industries, Ltd.) 93.3 parts and ion-exchanged water 348.7 parts. K. The mixture is stirred and mixed with a homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.) to obtain a slurry having a solid content concentration of 20% and a viscosity of 450 mPa · s. Next, the slurry was spray-dried with hot air at 150 ° C. using a spray dryer (with a pin type atomizer manufactured by Okawahara Chemical Industries Co., Ltd.) to form an electrode for an electrochemical device comprising spherical composite particles having a weight average particle size of 60 μm. Material C was obtained. The surface average porosity was measured for 10 composite particles contained in the electrode forming material C for electrochemical devices. The results are shown in Table 1.

  Further, in Example 1, the electrochemical element electrode (positive electrode, negative electrode) and film were similarly used except that the electrochemical element electrode forming material C obtained above was used as the electrochemical element electrode forming material. Type capacitor was fabricated and each characteristic was measured. The results are shown in Table 1.

  From the above, when the electrochemical element electrode forming material of the present invention is used, the internal resistance of the obtained electrode can be made lower than that of the conventional one.

Claims (3)

An electrochemical element electrode forming material comprising composite particles containing an electrode active material, a binder and a dispersant,
On the surface of the composite particle, the apparent surface area of the voids of 0.1 μm ² or more is measured, and the surface average porosity indicating the ratio of the surface area of the voids to the total visual field area is 15% or more,
An electrochemical element electrode forming material, wherein the dispersant has a weight average molecular weight of 300,000 or more.   The manufacturing method of the electrochemical element electrode forming material of Claim 1 including the process of spray-drying the slurry of a viscosity of 500-3000 mPa * s containing an electrode active material, a binder, and a dispersing agent.   The electrochemical element electrode which has an electrode active material layer formed by pressure-molding the electrochemical element electrode forming material of Claim 1 on a collector.