WO2010018841A1 - Method for manufacturing electrode for electrochemical element and electrochemical element - Google Patents

Abstract

Provided is a method for manufacturing an electrochemical element in which an electrode layer is formed by supplying a charged electrode material onto at least one surface of a grounded collector.  The collector preferably has an adhesive layer on at least one surface thereof.

Description

Method for producing electrode for electrochemical device and electrochemical device

The present invention relates to a method for producing an electrode for an electrochemical element and an electrochemical element comprising the same.

Electrochemical elements such as lithium ion secondary batteries and electric double layer capacitors are expected to be applied as large power sources such as distributed power sources and hybrid vehicles due to environmental problems and resource problems of energy. However, in order to apply these electrochemical elements as a large-scale power source, it is desired to reduce internal resistance in order to reduce energy loss during large current discharge.

In order to reduce the internal resistance, it is generally performed to reduce the thickness of the electrode, and it is required to manufacture a thin film electrode with high productivity.

At the same time, it is necessary to reduce the cost of these electrochemical elements in order to be used as a large-scale power source, and it is desired to reduce the cost of manufacturing electrodes for electrochemical elements.

On the other hand, as a method for producing an electrode, a method in which an electrode material containing an electrode active material and a binder is made into a slurry, applied and dried; a method in which the electrode material is kneaded and extended to a target thickness with a rolling roll A method of pressure forming the electrode material as it is or in the form of composite particles. Among these, the method of pressure-molding the electrode material is preferable in terms of productivity, and various methods for supplying the electrode material have been proposed.

There is a method in which the electrode material is charged and electrostatically adhered as a method for supplying the electrode material. This method is excellent in productivity because the electrode material can be supplied thinly and evenly, and the electrode material that has not adhered can be recovered and reused.

For example, Patent Document 1 discloses a method in which a powder having water repellency on the surface is applied to a current collector by electrostatic powder coating. According to this method, it is said that a hydrogen storage alloy electrode having water repellency uniformly and sufficiently enhanced can be produced.

Patent Document 2 discloses a method for producing an electrode, wherein an active material layer made of an active material, a conductive material, and a binder is formed on the surface of a current collector by a powder coating method. ing. According to this method, it is said that an electrode that is easy to control, has good productivity, and has excellent load characteristics as compared with the wet method can be obtained.

Further, in Patent Document 3, an incombustible or flame-retardant electrolyte solution is applied to the surface of an electrode structure, and further, an electrode material is applied by electrostatic copying and heat-fixed, whereby the electrolyte solution becomes an electrode material and an electrode structure. An electrode manufacturing method is disclosed, which is characterized in that According to this method, a higher performance electrode can be provided.

Moreover, in patent document 4, the dispersion | distribution process which disperse | distributes electrode raw material powder on the conveyance path driven to a horizontal direction, the collector supply process which supplies a collector on the disperse | distributed electrode raw material powder, The said electrode There is disclosed a method for producing an electrode for an electrochemical device, comprising: a zone press-bonding step of continuously pressing raw material powder and a current collector to form an electrode. And the method of making it adhere by static electricity, such as an electrostatic spraying method, is illustrated as a method of supplying electrode raw material powder.

Moreover, in patent document 5, an electrode material is apply | coated to the electrode structure surface, and in the electrode manufacturing apparatus which manufactures the electrode formed, the electrostatic screen application | coating means which apply | coats to electrode material and an electrode structure surface, and forms an electrode is provided. An electrode manufacturing apparatus is disclosed. According to this apparatus, a higher performance electrode can be manufactured.

Furthermore, in Patent Document 6, a fuel cell electrode formed by adhering an electrostatically charged electrode catalyst powder to a polymer electrolyte membrane has a structure with an appropriate pore distribution, and gas diffusion is further improved. It is said that the battery performance will improve because it improves.

JP-A-9-213316 JP 2001-351616 A JP 2004-281152 A WO2005 / 117043 publication JP 2004-281221 A Japanese Patent Laid-Open No. 11-288728

As an issue of manufacturing thin film electrodes with high productivity, continuous and stable production can be mentioned. With respect to such problems, the methods described in Patent Documents 1 to 4 have a problem that continuous and stable production cannot be achieved.

Also, although there is a possibility of recovery and reuse, improvement of the coating efficiency when the electrode material is supplied electrostatically is also important in terms of productivity. With respect to such a problem, there is a problem that the coating efficiency cannot be sufficiently increased when the methods as in Patent Documents 5 and 6 are used.

Furthermore, considering that it is used in electrochemical devices such as lithium ion secondary batteries and electric double layer capacitors, a technique for manufacturing an electrode capable of reducing internal resistance is important for industrial use. For the technical problems, the methods described in Patent Documents 1 to 6 have not been sufficient.

Therefore, an object of the present invention is to provide a method for stably producing an electrode for an electrochemical element with high coating efficiency. Another object of the present invention is to provide a method for producing an electrode for an electrochemical element that can reduce the internal resistance of the electrochemical element.

As a result of diligent study, the present inventor can efficiently generate inductive charging of the current collector by forming the electrode layer by supplying the charged electrode material onto the grounded current collector. The inventors have found that the charged electrode material can be efficiently applied, and that it is possible to produce an electrode for an electrochemical element stably for a long time, and the following present invention has been completed based on these findings.

According to a first aspect of the present invention, there is provided a method for producing an electrode for an electrochemical device, wherein an electrode layer is formed by supplying a charged electrode material onto at least one surface of a grounded current collector. Is done.

In the electrode manufacturing method according to the first aspect of the present invention, although not particularly limited, a metal can be used as the current collector. Moreover, as the electrode material, composite particles containing the electrode active material can be used. Further, the average charge amount of the electrode material can be set to 0.5 to 10.0 μC / g. The current collector may be one having an adhesive layer on at least one surface thereof. Moreover, the manufacturing method of the electrode which concerns on the 1st viewpoint of this invention can be used suitably for manufacture of a polarizable electrode.

According to a second aspect of the present invention, there is provided an electrochemical element comprising an electrode for an electrochemical element obtained by the production method according to the first aspect of the present invention. An example of the electrochemical element is an electric double layer capacitor.

According to the present invention, a charged electrode material can be efficiently applied, and stable production can be performed for a long time. Therefore, it is possible to provide a method for producing an electrode for an electrochemical element with good productivity. Is possible. In addition, it is possible to produce an electrochemical device electrode having a low internal resistance with high productivity. The present invention can be suitably used particularly as a method for producing an electric double layer capacitor, an electrode for a hybrid capacitor, and an electrode for a lithium ion secondary battery.

The method for producing an electrode for an electrochemical device of the present invention is characterized in that an electrode layer is formed by supplying a charged electrode material onto at least one surface of a grounded current collector.

<Current collector>
As the current collector used in the production method of the present invention, specifically, a metal, carbon, a conductive polymer, or the like can be used, and a metal is preferably used. As the current collector metal, aluminum, platinum, nickel, tantalum, titanium, other alloys and the like are usually used. Among these, it is preferable to use copper, aluminum, or an aluminum alloy in terms of conductivity and voltage resistance.

The shape of the current collector is not particularly limited, but may be a film or a sheet, and the sheet current collector may have pores. The sheet-like current collector may have a shape such as an expanded metal, a punching metal, or a net. When a sheet-like current collector having pores is used, the capacity per volume of the obtained electrode can be increased. When the sheet-like current collector has holes, the ratio of the holes is preferably 10 to 79 area%, more preferably 20 to 60 area%.

The thickness of the current collector is appropriately selected according to the purpose of use, but is usually 1 to 200 μm, preferably 5 to 100 μm, more preferably 10 to 50 μm. When the thickness of the current collector is in this range, the resistance of electron movement can be reduced, and the internal resistance can be reduced.

The current collector preferably has an adhesive layer formed on at least one surface thereof. Among these, conductive materials are preferable because the interface resistance between the electrode layer and the current collector can be reduced. The adhesive layer can be formed by applying and drying an adhesive on the surface of the current collector. When a current collector with an adhesive layer formed on its surface is used, good adhesiveness can be obtained even when the electrode is housed together with the electrolyte in the electrochemical element. With this binder, the contact area with the electrode active material can be increased, and the interface resistance can be reduced.

In the case where the adhesive has conductivity, a conductive auxiliary powder, a binder, and a dispersant added as necessary are dispersed in water or an organic solvent. Examples of the conductive aid used for the adhesive include silver, nickel, gold, graphite, acetylene black, ketjen black, and the like, preferably graphite and acetylene black. As the binder used for the adhesive, any of those exemplified as the binder used in the production method of the present invention described later can be used. Moreover, water glass, an epoxy resin, a polyamide-imide resin, a urethane resin, etc. can also be used, and these can be used individually or in combination of 2 or more types, respectively. The binder used for the adhesive is preferably an acrylate polymer, an ammonium salt or alkali metal salt of carboxymethyl cellulose, water glass, or a polyamideimide resin. Moreover, as a dispersing agent used for an adhesive agent, a dispersing agent or a surfactant that may be used for the electrode layer in the production method of the present invention can be used.

The content of the binder in the adhesive layer is preferably 0.1 to 50 parts by weight, more preferably 0.5 to 20 parts by weight, and particularly preferably 1 to 10 parts by weight with respect to 100 parts by weight of the conductive assistant. Part range. When the amount of the binder in the adhesive layer is within this range, sufficient adhesion between the obtained electrode composition layer and the current collector can be secured, the capacity of the electrochemical device is increased, and the internal resistance is decreased. Can do.

The content of the dispersing agent in the adhesive layer is preferably 0.1 to 20 parts by weight, more preferably 0.5 to 15 parts by weight, particularly preferably 0.8 to 10 parts by weight based on 100 parts by weight of the conductive assistant. The range is parts by weight.

The content of the surfactant in the adhesive layer is preferably from 0.5 to 20 parts by weight, more preferably from 1.0 to 15 parts by weight, particularly preferably from 2.0 to 100 parts by weight based on 100 parts by weight of the conductive assistant. The range is 10 parts by weight. When the content of the surfactant in the adhesive layer is within this range, the adhesive layer can be formed uniformly, and the durability of the electrochemical element is excellent.

The adhesive layer is composed of a current collector and an adhesive obtained by mixing, kneading, and the like in a solvent (dispersion medium) with a conductive additive and a binder, and if necessary, a dispersing agent and a surfactant. It can be applied on top and dried. Although it does not restrict | limit especially as said solvent, Water is preferable at the point of environmental property and drying equipment.

Specific examples of the method for producing the adhesive used in the present invention include a ball mill, a sand mill, a pigment disperser, a pulverizer, an ultrasonic disperser, a homogenizer, a planetary mixer, and a Hobart mixer.

The method for forming the adhesive layer used in the present invention is not particularly limited. For example, a current collector is obtained by a doctor blade method, a dipping method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a brush coating, or the like. Formed on top.

The thickness of the adhesive layer is usually 0.01 to 20 μm, preferably 0.1 to 10 μm, particularly preferably 1 to 5 μm. When the thickness of the adhesive layer is within the above range, the internal resistance of the electrochemical element having an electrode obtained by the production method of the present invention can be reduced.

<Electrode material>
The electrode material used in the method for producing an electrode for an electrochemical element of the present invention is an electrode active material, a conductive agent, a binder, and other materials necessary for constituting an electrode, and is usually in the form of solid particles. The one that has a form.

(Electrode active material)
What is necessary is just to select the electrode active material used for the electrode obtained by the manufacturing method of this invention according to the element for which an electrode is utilized.

When the electrode for an electrochemical element obtained by the production method of the present invention is used for an electrode for an electric double layer capacitor or a positive electrode for a hybrid capacitor, a carbon allotrope is usually used as the electrode active material. 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 is activated carbon, and specific examples include activated carbon made from phenol resin, rayon, acrylonitrile resin, pitch, coconut shell, and the like.

When the electrode for an electrochemical element obtained by the production method of the present invention is used for an electrode for a negative electrode of a lithium ion secondary battery or an electrode for a hybrid capacitor negative electrode, as the electrode active material, amorphous carbon, graphite, natural graphite , Mesocarbon microbeads (MCMB), and carbonaceous materials such as pitch-based carbon fibers; conductive polymers such as polyacene; Si, Sn, Sb, Al, Zn, and W that can be alloyed with lithium.

When the electrode obtained by the production method of the present invention is used as a positive electrode for a lithium ion secondary battery, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiFePO ₄ , LiFeVO ₄ , and these elements Partially substituted lithium-containing composite metal oxide; transition metal sulfides such as TiS ₂ , TiS ₃ , amorphous MoS ₃ ; Cu ₂ V ₂ O ₃ , amorphous V ₂ O · P ₂ O ₅ , MoO ₃ , transition metal oxides such as V ₂ O ₅ and V ₆ O ₁₃ ; Further examples include conductive polymers such as polyacetylene and poly-p-phenylene.

The volume average particle diameter of the electrode active material used in the present invention is usually 0.1 to 100 μm, preferably 1 to 50 μm, more preferably 3 to 20 μm, more preferably 5 to 20 μm.

When the electrode for an electrochemical element obtained by the production method of the present invention is used for an electrode for an electric double layer capacitor or a positive electrode for a hybrid capacitor, the specific surface area of the electrode active material is preferably 30 m ² / g or more, preferably It is preferably 500 to 5,000 m ² / g, more preferably 1,000 to 3,000 m ² / g. Since the density of the obtained electrode composition layer tends to decrease as the specific surface area of the electrode active material increases, an electrode composition layer having a desired density can be obtained by appropriately selecting the electrode active material. Moreover, these electrode active materials can be used individually or in combination of 2 or more types.

(Conductive material)
The conductive material used in the present invention is composed of an allotrope of particulate carbon that has conductivity and does not have pores that can form an electric double layer. Specifically, furnace black, acetylene black, and kettle are used. Examples thereof include conductive carbon black such as chain black (registered trademark of Akzo Nobel Chemicals Besloten Fennaut Shap); graphite such as natural graphite and artificial graphite. 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 used in the present invention is preferably smaller than the volume average particle diameter of the electrode active material, and the range thereof is usually 0.001 to 10 μm, preferably 0.05 to 5 μm, more preferably. 0.01 to 1 μm. When the volume average particle diameter 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. When the amount of the conductive material is increased, the charge amount of the electrode material described later can be reduced, and when the amount is decreased, the charge amount can be increased. The amount of the conductive material is usually in the range of 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 the amount of the conductive material is within this range, the capacity of the electrochemical device of the present invention 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 capable of binding electrode active materials to each other. A suitable binder is a dispersion type binder having a property of being dispersed in a solvent. Examples of the dispersion-type binder include polymer compounds such as fluorine-based polymers, diene-based polymers, acrylate-based polymers, polyimides, polyamides, polyurethane-based polymers, and preferably fluorine-based polymers and diene-based binders. A polymer and an acrylate polymer, more preferably a diene polymer and an acrylate polymer. When the method of charging the electrode material is frictional charging with polytetrafluoroethylene, the charge amount described later can be adjusted by utilizing the relationship of the charge train. For example, since the acrylate polymer is more likely to be positively charged on the charged column than the diene polymer, the charge amount can be increased.

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 ester and / or methacrylic ester or a monomer mixture containing these. The ratio of acrylic acid ester and / or methacrylic acid ester in the monomer mixture is usually 40% by weight or more, preferably 50% by weight or more, more preferably 60% by weight or more.

The glass transition temperature (Tg) of the binder used in the production method of the present invention is preferably −80 ° C. to 50 ° C., more preferably −50 ° C. to 25 ° C. When the glass transition temperature (Tg) of the binder is in the above range, an electrode layer having an excellent balance between binding properties and flexibility can be obtained.

The shape of the binder used in the production method of the present invention is not particularly limited, but has good binding properties, and can suppress deterioration due to repeated decrease in capacity and charge / discharge of the created electrode. It is preferably in the form of particles. Examples of the particulate binder include those in which binder particles such as latex are dispersed in water, and powders obtained by drying such a dispersion.

The number average particle size of the binder used in the production method of the present invention is not particularly limited, but is usually 0.0001 to 100 μm, preferably 0.001 to 10 μm, more preferably 0.01 to 1 μm. It has a number average particle size. When the number average particle diameter of the binder is within this range, an excellent binding force can be imparted to the electrochemical device electrode even with a small amount of the binder. 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 is usually in the range of 0.1 to 50 parts by weight, preferably 0.5 to 20 parts by weight, more preferably 1 to 10 parts by weight with respect to 100 parts by weight of the electrode active material. When the amount of the binder is within this range, sufficient adhesion between the obtained electrode composition layer and the current collector can be secured, the capacity of the electrochemical device of the present invention can be increased and the internal resistance can be decreased. it can. Further, when the amount of the binder is increased, the charge amount of the electrode described later can be increased, and when the amount of the binder is decreased, the charge amount can be decreased.

In the production method of the present invention, the following materials necessary for constituting the electrode may be contained.

(Dispersant)
The dispersing material is used by being dissolved in a slurry solvent described later, and further has an action of uniformly dispersing the electrode active material, 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 dispersing agents 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.

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

Other additives include, for example, 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.

Surfactants 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.

The electrode material used in the present invention is preferably a composite particle comprising the above electrode active material and a binder. The composite particles refer to particles having an electrode active material and a binder as essential components and containing a conductive material, a dispersing material, and other additives as necessary.

The production method of the composite particles is not particularly limited, and is a spray drying granulation method, a rolling bed granulation method, a compression granulation method, a stirring granulation method, an extrusion granulation method, a crushing granulation method, a fluidized bed granulation method. It can be produced by a known granulation method such as a granulation method, a fluidized bed multifunctional granulation method, a pulse combustion type drying method, or a melt granulation method. Among these, the spray-drying granulation method is preferable because composite particles in which the binder and the conductive auxiliary agent are unevenly distributed in the vicinity of the surface can be easily obtained. When composite particles obtained by the spray drying granulation method are used, the electrode for an electrochemical element of the present invention can be obtained with high productivity. In addition, the internal resistance of the electrode can be further reduced.

In the spray-drying granulation method, first, the essential components of the electrode active material and the binder, and optional components such as a conductive material are dispersed or dissolved in a solvent, the electrode active material and the essential components of the binder, and A slurry is obtained in which optional components such as a conductive material, a dispersing material, and other additives are dispersed or dissolved.

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

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

The method or procedure for dispersing or dissolving the essential components of the electrode active material and the binder and the optional components such as the conductive material, the dispersion material, and other additives in the solvent is not particularly limited. For example, the electrode active material is dissolved in the solvent. A method of adding and mixing a conductive material, a binder, a dispersing agent, and the like; after dissolving the dispersant in a solvent, adding a binder (for example, an aqueous dispersion of polymer particles) dispersed in the solvent. A method of mixing and finally adding and mixing the electrode active material and the conductive material; adding and mixing the electrode active material and the conductive material to the binder dispersed in the solvent, and dispersing the mixture in the solvent For example, a method of adding and mixing materials may be used. 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 carried out in the range of room temperature to 80 ° C. for 10 minutes to several hours.

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

Next, the slurry obtained above is spray-dried and granulated to obtain composite particles. Spray drying is performed by spraying the slurry in hot air and drying. An atomizer is used as an apparatus used for spraying slurry. There are two types of atomizers: a rotating disk method and a pressure method. The rotating disk system is a system in which slurry is introduced almost at the center of a disk that rotates at a high speed, and the slurry is released out of the disk by the centrifugal force of the disk, and the slurry is atomized at that time. The rotational speed of the disk depends on the size of the disk, but is usually 5,000 to 40,000 rpm, preferably 15,000 to 40,000 rpm. The lower the rotational speed of the disk, the larger the spray droplets and the larger the weight average particle diameter of the resulting 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 The slurry is introduced from the center of the spray platen, adheres to the spraying roller by centrifugal force, moves outside the roller surface, and finally sprays away from the roller surface. On the other hand, the pressurization method is a method in which the slurry is pressurized and sprayed from a nozzle to be dried.

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

The composite particles are preferably spherical. Whether the composite particles are spherical or not is evaluated by (Ll−Ls) / {(Ls + Ll) / 2} where Ls is the minor axis diameter of the composite particles and Ll is the major axis diameter. (Hereinafter referred to as “sphericity”). Here, the minor axis diameter Ls and the major axis diameter Ll are average values for 100 arbitrary composite particles measured from a photographic image obtained by observing the composite particles using a reflection electron microscope. The smaller this value, the closer the spherical composite particle is to a true sphere.

For example, the particle observed as a square in the photographic image has a sphericity of 34.4%, so the composite particle showing a sphericity exceeding 34.4% is not at least spherical. The sphericity of the composite particles is preferably 20% or less, and more preferably 15% or less. When the sphericity of the composite particles is within the above range, the internal resistance of the electrochemical device including the electrode for an electrochemical device in which the electrode layer made of the composite particles is formed can be reduced, and the output characteristics can be improved.

The composite particles obtained by the above production method can be subjected to post-treatment after production of the particles, if necessary. As a specific example, the particle surface is modified by mixing the above-mentioned electrode active material, conductive material, binder, dispersing agent or other additives into the composite particle, thereby improving the fluidity of the composite particle. Alternatively, it is possible to reduce, improve the continuous pressure moldability, improve the electrical conductivity of the composite particles, and adjust the average charge amount of the composite particles.

In order to adjust the average charge amount of the composite particles, a charge control agent may be used. Specific examples include silicon dioxide particles, styrene-methacrylate copolymer particles, nigrosine dyes, triphenylmethane dyes, quaternary ammonium salts, resins containing quaternary ammonium groups and / or amino groups. It is done.

The shape of the composite particles suitably used in the present invention is preferably substantially spherical. That is, when the short axis diameter of the composite particles is Ls, the long axis diameter is Ll, La = (Ls + Ll) / 2, and the value of (1− (Ll−Ls) / La) × 100 is sphericity (%). The sphericity is preferably 80% or more, more preferably 90% or more. Here, the minor axis diameter Ls and the major axis diameter Ll are values measured from a transmission electron micrograph image.

The weight average particle size of the composite particles suitably used in the present invention is usually in the range of 0.1 to 1,000 μm, preferably 5 to 500 μm, more preferably 10 to 100 μm. When the weight average particle diameter of the composite particles is within this range, the composite particles are less likely to aggregate and electrostatic force is increased against gravity, which is preferable. The weight average particle diameter can be measured using a laser diffraction particle size distribution measuring apparatus.

In the present invention, the electrode layer is formed by supplying the charged electrode material onto at least one surface of the grounded current collector.

“Charging an electrode material” means that the electrode material is charged positively or negatively by treating the electrode material.

The method of charging the electrode material is not particularly limited, and examples thereof include a method of charging by directly applying a voltage to the electrode material, a method of charging the electrode material by friction, and the like.

As a method of charging by directly applying a voltage to the electrode material, a charging method using corona discharge can be mentioned. Charging methods using corona discharge include charging the electrode material by spraying it near the corona discharge electrode when sprayed on the current collector, or installing a corona discharge electrode in the fluidized bed of electrode material And charging method.

As a method of charging the electrode material by friction, a method of charging the electrode material by bringing the electrode material into contact with a material that is easily charged using a charging train is used. The charged column is inherent to a substance and has a relative order of easiness of charging from a material that is easily charged negatively to a material that is easily charged positively. As the two materials to be rubbed are more apart from each other on the charge train, each of them is charged more greatly. Therefore, on the charge train, the electrode material is easily brought into contact with the electrode material by contacting the material away from the electrode train from the electrode train. Can be charged. When the electrode material is positively charged, tetrafluoroethylene is the material that is most easily negatively charged on the charge train, and therefore the electrode material can be easily positively charged by contacting with polytetrafluoroethylene.

The electrode material may be charged by mixing a plurality of the above-mentioned electrode materials. However, since the difference in chargeability between different electrode materials can be eliminated, the composite of the above-mentioned electrode materials is charged. It is preferable to make it.

<Charge amount>
The amount of charge when the electrode material is charged can be measured as the average amount of charge of the electrode material by measuring the amount of current that the oppositely charged material flows to the ground when the electrode material is charged. The average charge amount of the electrode material is usually 0.5 μC / g or more, preferably 0.5 to 10.0 μC / g, more preferably 1.5 to 6.0 μC / g. When the average charge amount is within this range, the electrode material can be more efficiently applied on the current collector. As described above, the charge amount can be adjusted by changing the amount and type of the conductive material and the binder. The charge amount can also be adjusted using the above-described charge control agent.

<Grounding>
In the present invention, the current collector is required to be grounded. The ground resistance of the current collector is usually 1 MΩ or less, preferably 100Ω or less. When the ground resistance is within this range, effective induction charging is induced in the current collector when the charged electrode material approaches the vicinity of the current collector, so that a uniform electrode can be formed.

<Formation of electrode layer>
(Electrode material supply method)
In the present invention, the charged electrode material is supplied onto at least one surface of the grounded current collector. There is no particular limitation on the method for supplying the charged electrode material. For example, the charged electrode material may be sprayed and supplied as in electrostatic powder coating, or the charged electrode material may be transferred as in electrostatic screen printing.

Then, the current collector and the electrode material supplied by the supply method are pressurized with a pair of rolls to form an electrode layer. In this step, the electrode material heated as necessary may be formed into a sheet-like electrode layer with a pair of rolls. The temperature of the electrode material supplied is preferably 40 to 160 ° C., more preferably 70 to 140 ° C. When an electrode material in this temperature range is used, there is no slip of the electrode material on the surface of the press roll, and the electrode material is continuously and uniformly supplied to the press roll. An electrode sheet for an electrochemical element or a sheet for a polarizable electrode with small variations can be obtained.

In the present invention, the molding temperature 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 of the binder. preferable. In the case of using a press roll, the forming speed is usually 10 m / min or more, preferably 20 to 200 m / min, more preferably 30 to 80 m / min, in order to make the moldability higher and to make the film thinner. . Further, the press linear pressure between the press rolls is not particularly specified, but is preferably 0.2 to 30 kN / cm, more preferably 0.5 to 10 kN / cm in that the electrode strength of the obtained electrode can be increased. is there.

In the present invention, the arrangement of the pair of rolls is not particularly limited, but is preferably arranged substantially horizontally or substantially vertically. When arranged substantially horizontally, the current collector is continuously supplied between a pair of rolls, and the electrode material is supplied to at least one of the rolls, so that the electrode material is placed in the gap between the current collector and the rolls. The electrode layer can be formed by being supplied and pressurized. In the case of disposing substantially vertically, the 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 made uniform with a blade or the like as necessary, the current collector is supplied between a pair of rolls, and the electrode layer can be formed by pressurization.

¡Post-pressurization may be further performed as necessary in order to eliminate the variation in the thickness of the molded body, increase the density, and increase the capacity. 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 roll may be temperature controlled, such as heated or cooled.

The thickness of the electrode layer of the electrode for an electrochemical element obtained by the production method of the present invention varies depending on the type of the electrochemical element, but is usually 10 μm to 200 μm, preferably 30 to 100 μm. When the thickness of the electrode layer is within this range, an electrode for an electrochemical element having a balance between internal resistance and energy density is preferable.

(Polarizable electrode)
A polarizable electrode can be produced by the production method of the present invention. A polarizable electrode refers to an electrode that has a potential range in which no current flows even when a potential is applied. The polarizable electrode obtained by the production method of the present invention is suitably used as an electrode for a capacitor such as an electric double layer capacitor or a hybrid capacitor.

(Electrochemical element)
The electrochemical device of the present invention includes an electrode for an electrochemical device obtained by the production method of the present invention. Examples of the electrochemical element include a lithium ion secondary battery, an electric double layer capacitor, and a hybrid capacitor. An electric double layer capacitor is preferable. Hereinafter, the case where the electrode for an electrochemical element obtained by the production method of the present invention is used as an electrode for an electric double layer capacitor (polarizable electrode) will be described.

The electric double layer capacitor is composed of an electrode, a separator and an electrolytic solution, and an electrode for an electrochemical element obtained by the production method of the present invention is used as the electrode.

The separator is not particularly limited as long as it can insulate between the electrodes for the electric double layer capacitor and can pass cations and anions. Specifically, polyolefin such as polyethylene and polypropylene, rayon, aramid, or a microporous membrane or nonwoven fabric made of glass fiber, or a porous membrane mainly made of pulp called electrolytic capacitor paper can be used. A separator is arrange | positioned between the electrodes for electric double layer capacitors so that said pair of electrode composition layer may oppose, and an element is obtained. The thickness of the separator is appropriately selected depending on the purpose of use, but is usually 1 to 100 μm, preferably 10 to 80 μm, more preferably 20 to 60 μm.

Electrolyte is usually composed of electrolyte and solvent. As the electrolyte, (1) imidazolium, (2) quaternary ammonium, (3) quaternary phosphonium, (4) lithium and the like as shown below can be used as the cation.

(1) Imidazolium 1,3-dimethylimidazolium, 1-ethyl-3-methylimidazolium, 1,3-diethylimidazolium, 1,2,3-trimethylimidazolium, 1,2,3,4-tetramethyl Imidazolium, 1,3,4-trimethyl-ethylimidazolium, 1,3-dimethyl-2,4-diethylimidazolium, 1,2-dimethyl-3,4-diethylimidazolium, 1-methyl-2,3 , 4-triethylmethylimidazolium, 1,2,3,4-tetraethylimidazolium, 1,3-dimethyl-2-ethylimidazolium, 1-ethyl-2,3-dimethylimidazolium, 1,2,3- Triethylimidazolium, etc. (2) Quaternary ammonium tetramethylammonium, ethyltrimethylammonium, diethyl (3) Quaternary phosphonium Tetramethylphosphonium, tetraethylphosphonium, tetrabutylphosphonium, methyltriethylphosphonium, methyltributylphosphonium, dimethyldiethylphosphonium, etc. ( 4) Lithium

Similarly, the electrolyte has PF ₆ ⁻ , BF ₄ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , N (RfSO ₃ ) ²⁻ , C (RfSO ₃ ) ³⁻ , and RfSO ₃ ⁻ (Rf is respectively A fluoroalkyl group having 1 to 12 carbon atoms), F ⁻ , ClO ₄ ⁻ , AlCl ₄ ⁻ , AlF ₄ ^{− and the} like can be used. These electrolytes can be used alone or in combination of two or more.

The solvent of the electrolytic solution is not particularly limited as long as it is generally used as a solvent for the electrolytic solution. Specific examples include carbonates such as propylene carboat, ethylene carbonate, and butylene carbonate; lactones such as γ-butyrolactone; sulfolanes; nitriles such as acetonitrile. These can be used alone or as a mixed solvent of two or more. Of these, carbonates are preferred.

An electric double layer capacitor is obtained by impregnating the above capacitor element with an electrolytic solution. Specifically, the capacitor element can be manufactured by winding, stacking, or folding into a container as necessary, and pouring the electrolyte into the container and sealing it. Moreover, what impregnated the electrolytic solution beforehand in the capacitor element may be stored in the container. Any known container such as a coin shape, a cylindrical shape, or a square shape can be used as the container.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present 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>
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 core forming a core as a binder The constituent monomer units of the coalescence are n-butyl acrylate and ethyl methacrylate, the constituent monomer units of the polymer forming the shell portion are n-butyl methacrylate and methacrylic acid, and all monomer units The composition ratio of n-butyl acrylate: ethyl methacrylate: n-butyl methacrylate: methacrylic acid = 40: 40: 17: 3 (mass ratio), the glass transition temperature of the core part is −5 ° C., and the shell part 5 parts of an aqueous dispersion of a core-shell type acrylate polymer having a glass transition temperature of 25 ° C. (volume average particle diameter 0.31 μm, solid content concentration 40%), average particle as a conductive material 5 parts of 0.7 μm acetylene black (Denka Black powder; manufactured by Denki Kagaku Kogyo Co., Ltd.) and 1.5% aqueous solution of ammonium salt of carboxymethyl cellulose (“DN-800H” (manufactured by Daicel Chemical Industries, Ltd.)) as a dispersant. 93.3 parts and 348.7 parts of ion-exchanged water were added, and the mixture was stirred and mixed with a “TK homomixer” (manufactured by Primics) to obtain a slurry having a solid content concentration of 20%. The 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 Koki 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 under the conditions of a temperature of 150 ° C. and a particle recovery outlet temperature of 90 ° C. to obtain composite particles of an electrode material. The composite particles had a weight average particle size of 54 μm and a sphericity of 9%.

100 parts of carbon black having a volume average particle size of 0.7 μm, and 4 parts of a 4.0% aqueous solution of carboxymethyl cellulose (DN-10L; manufactured by Daicel Chemical Industries) as a dispersant, several parts as a binder A conductive adhesive layer is formed by mixing a 40% aqueous dispersion of an acrylate polymer having an average particle diameter of 0.25 μm with a solid content equivalent of 8 parts and ion exchange water so that the total solid content concentration is 30%. A slurry composition was prepared.

The slurry composition for forming a conductive adhesive was applied to a current collector made of an aluminum foil having a thickness of 30 μm, and dried at 120 ° C. for 10 minutes to form a conductive adhesive layer having a thickness of 4 μm. Thereafter, the current collector coated with the conductive adhesive layer on the surface was grounded and installed horizontally. The grounding resistance was 10Ω.

Next, charging and supply of the composite particles of the electrode material were carried out by using a friction charging electrostatic powder coating machine MTR-100VTmini manufactured by Asahi Sunac Co., Ltd. and a friction charging powder manual gun T-2m type L7 manufactured by Asahi Sunac Co., Ltd. The outer sleeve was made of polytetrafluoroethylene. Specifically, the composite particles of the electrode material were put into the hopper of the powder coating machine, the rotation speed of the screw feeder for quantitative supply was adjusted, and the composite particles of the electrode material were supplied at 1.5 g / second. . Moreover, the electrode material was supplied to the said collector from the upper part by making the conveyance air pressure from the said powder manual gun into 0.4 Mpa. The electrode material was charged by frictional charging generated when passing through the gap between the inner sleeve and outer sleeve of the powder manual gun. The current value at this time was 1.0 μA (C / sec). The average charge amount of the charged electrode material was 0.7 μC / g. The coating efficiency on the current collector was calculated from the weight of the supplied electrode material and the weight of the electrode material in which the electrode material layer was formed on the current collector according to the following formula, and found to be 43%. In the following formula, the weight of the electrode material attached on the current collector is obtained by subtracting the weight of the current collector before attaching the electrode material from the weight of the current collector attached with the electrode material.
Coating efficiency (%) = weight of electrode material deposited on current collector / weight of supplied electrode material × 100

When the appearance of the obtained electrode material layer was observed, it was confirmed that the electrode material was uniformly formed on the current collector. The current collector on which this electrode material layer is formed is 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.), and roll pressure is applied. A sheet-like consolidated electrode layer was formed by molding to produce an electrode for an electric double layer capacitor having an electrode layer thickness of 60 μm and an electrode layer density of 0.58 g / cm ³ .

<Example 2>
In Example 1, when producing composite particles of electrode material, the electrode layer thickness was 60 μm and the electrode layer was the same as Example 1 except that the amount of the aqueous dispersion used as the binder was 10 parts. An electrode having a density of 0.58 g / cm ³ was produced. There was no problem in the appearance of the electrode material layer, the current value at the time of supplying the electrode material was 3.0 μA (average charge amount 2.0 μC / g), and the coating efficiency was 60%. The composite particles had a weight average particle size of 54 μm and a sphericity of 9%.

<Example 3>
In Example 1, when producing composite particles of electrode material, the electrode layer thickness was 60 μm and the electrode layer density was the same as in Example 1 except that the amount of the aqueous dispersion used as the binder was 15 parts. An electrode of 0.60 g / cm ³ was produced. There was no problem in the appearance of the electrode material layer, the current value at the time of supplying the electrode material was 7.5 μA (average charge amount 5.0 μC / g), and the coating efficiency was 67%. The composite particles had a weight average particle size of 54 μm and a sphericity of 9%.

<Example 4>
In Example 1, when producing composite particles of the electrode material, the amount of the aqueous dispersion used as the binder was 15 parts, and the supply amount of the electrode material was 0.8 g / sec. Similarly, an electrode having an electrode layer thickness of 60 μm and an electrode layer density of 0.60 g / cm ³ was produced. There was no problem in the appearance of the electrode material layer, the current value at the time of supplying the electrode material was 13.5 μA (average charge amount 9.0 μC / g), and the coating efficiency was 45%. The composite particles had a weight average particle size of 54 μm and a sphericity of 9%.

<Example 5>
In Example 1, when producing composite particles of the electrode material, the amount of the water-dispersed latex used as the binder was 15 parts, and the supply amount of the electrode material was 0.5 g / sec. Similarly, an electrode having an electrode layer thickness of 60 μm and an electrode layer density of 0.60 g / cm ³ was produced. There was no problem in the appearance of the electrode material layer, the current value when supplying the electrode material amount was 18 μA (average charge amount 12.0 μC / g), and the coating efficiency was 35%. The composite particles had a weight average particle size of 54 μm and a sphericity of 9%.

<Example 6>
In Example 1, an electrode having an electrode layer thickness of 60 μm and an electrode density of 0.58 g / cm ³ was produced in the same manner as in Example 3 except that no adhesive layer was formed on the current collector. Although there was no problem in the appearance of the electrode material layer, the current value at the time of supplying the electrode material was 7.5 μA (average charge amount 5.0 μC / g), and the coating efficiency was 62%.

<Comparative Example 1>
In Example 1, the electrode layer was the same as in Example 1 except that the PTFE inner sleeve and outer sleeve of the triboelectric powder manual gun T-2m type L7 were replaced with stainless steel of the same shape. An electrode having a thickness of 60 μm and an electrode density of 0.58 g / cm ³ was produced. There was no problem in the appearance of the electrode material layer, the current value when supplying the electrode material was 0.0 μA (average charge amount was 0.0 μC / g), and the coating efficiency was 8%.

<Comparative example 2>
In Example 3, an electrode having an electrode layer thickness of 60 μm and an electrode density of 0.60 g / cm ³ was produced in the same manner as in Example 3 except that the aluminum foil was not grounded. A spark occurred during the supply of the electrode material, and the appearance of the electrode was impaired.

Table 1 shows the results of the above examples and comparative examples.

In Table 1, the internal resistance value was measured as follows. That is, the electrodes obtained in the above examples and comparative examples were impregnated with an electrolytic solution (1.0 mol / L of a propylene carbonate solution of tetraethylammonium fluoroborate) at room temperature for 1 hour, and then the two electrodes serve as a cellulose separator. Then, the electrodes are arranged so as to face each other, and the electrodes are arranged so as not to be in electrical contact with each other, thereby producing a coin cell-shaped electric double layer capacitor. And the internal resistance of the produced electric double layer capacitor was measured.

The internal resistance was measured by performing charge / discharge operation after allowing the produced coin cell to stand for 24 hours. Charging is started at a constant current of 10 mA. When the voltage reaches 2.7 V, the voltage is maintained and constant voltage charging is performed, and the charging is completed when the charging current is reduced to 0.5 mA. Next, discharging was performed at a constant current of 10 mA immediately after the end of charging, and the internal resistance was calculated from the voltage drop 0.1 seconds after the discharge and the constant current value. The internal resistance value is the relative value of the internal resistance value of the electric double layer capacitor manufactured using the other electrodes when the internal resistance value of the electric double layer capacitor manufactured using the electrode of Example 6 is 100%. It is. The smaller the internal resistance value, the better.

From the results in Table 1, the following can be understood.

According to the present invention, as shown in Examples 1 to 6, the electrode appearance is excellent and the electrode coating efficiency is excellent. Among the examples, Example 3 in which the current collector has an adhesive layer and the average charge amount of the electrode material is 5.0 μC / g has the best balance between internal resistance and coating efficiency.

On the other hand, in Comparative Example 1, since the electrode material is not charged, the coating efficiency of the electrode material is inferior. In Comparative Example 2, since the current collector is not grounded, the charged electrode material on the current collector causes a dielectric breakdown and sparks, which hinders the appearance of the electrode.

Although the present invention has been described with reference to the most practical and preferred embodiments at the present time, the invention is limited to the embodiments disclosed herein. However, it can be changed as appropriate without departing from the scope or spirit of the invention which can be read from the claims and the entire specification, and the method for producing an electrode for an electrochemical device with such a change is also within the technical scope of the present invention. Must be understood as encompassed by.

The present invention relates to the subject matter contained in Japanese Patent Application No. 2008-208754 filed on August 13, 2008 and Japanese Patent Application No. 2008-208755 filed on the same date, All are expressly incorporated herein by reference.

The method for producing an electrode for an electrochemical device according to the present invention has excellent electrode appearance, excellent internal resistance, and high electrode material coating efficiency. Therefore, the electric double layer capacitor electrode, hybrid capacitor electrode, It can use suitably for electrode manufacture, such as a secondary battery.

Claims (8)

1. A method for producing an electrode for an electrochemical element, wherein an electrode layer is formed by supplying a charged electrode material onto at least one surface of a grounded current collector.
2. The manufacturing method according to claim 1, wherein the current collector is a metal.
3. The method according to claim 1 or 2, wherein the electrode material is composite particles containing an electrode active material and a binder.
4. The method according to any one of claims 1 to 3, wherein an average charge amount of the electrode material is 0.5 to 10.0 µC / g.
5. The method for producing an electrode for an electrochemical element according to any one of claims 1 to 4, wherein the current collector has an adhesive layer on at least one surface thereof.
6. The manufacturing method according to any one of claims 1 to 5, wherein the electrode is a polarizable electrode.
7. An electrochemical element comprising an electrode for an electrochemical element obtained by the production method according to any one of claims 1 to 6.
8. The electrochemical device according to claim 7, wherein the electrochemical device is an electric double layer capacitor.