JP5163216B2 - Hybrid capacitor electrode and hybrid capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode for hybrid capacitor having a low internal resistance, and to provide a hybrid capacitor. <P>SOLUTION: Collection of current in the thickness direction, and the contact area of an electrode composition layer and a current collector by protrusions are improved by extending a plurality of protrusions from the current collector to the electrode composition layer. Furthermore, adhesion of the electrode composition layer and the current collector is improved and the interface resistance of the electrode composition layer and the current collector can be reduced by forming a conductive adhesive layer on the current collector having protrusions. As compared with a plane current collector having neither a protrusion nor an aperture, the contact area of the electrode composition layer and the current collector exceeds one time that of the plane current collector, and the internal resistance is reduced sufficiently by setting the number of protrusions for the electrode composition layer at 1/mm<SP>2</SP>or more, setting the proportion of protrusions occupying the electrode composition layer at 1 vol.% or more, and setting the length (D) of the protrusion for the thickness (L) of the electrode composition layer as 0&lt;D/L&lt;1. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an electrode suitably used for a hybrid capacitor including a positive electrode made of a material capable of reversibly supporting lithium ions and / or anions and a negative electrode made of a material capable of reversibly supporting lithium ions. More specifically, the present invention relates to an electrode for a hybrid capacitor and a hybrid capacitor which can efficiently and uniformly dope lithium ions and / or anions and have a low internal resistance with excellent charge / discharge characteristics.

  In recent years, hybrid capacitors have a higher capacity than electric double layer capacitors and higher output than lithium ion batteries, so that they can be applied to electric vehicles or hybrid vehicles, solar power generation energy storage systems combined with solar cells, etc. The application of is expected. In particular, it has attracted attention in the fields that require capacity and output, such as electric vehicles or hybrid vehicles.

In hybrid capacitors, reduction of internal resistance is an important issue because it reduces heat loss caused by I ² R during large current charge / discharge and improves charge / discharge efficiency.

  Conventionally, in a hybrid capacitor, a method of doping lithium ions into a negative electrode and / or a positive electrode has been proposed, and a current collector having a through-hole is used to efficiently and uniformly dope lithium ions into an electrode in a cell. Has been. For example, in the organic electrolyte capacitor described in Patent Document 1, an expanded metal made of copper or aluminum having a thickness of 32 μm (porosity 50%) is used. However, if the current collector is provided with a through-hole as described in the above document, the area where the current collector and the electrode composition layer are in contact with each other is small even if the electrode can be doped with lithium ions. There was a problem that it could not be reduced.

In the electric double layer capacitor and the lithium ion battery, conventionally, in order to reduce the internal resistance, it has been proposed to reduce the internal resistance of the electrode by forming a plurality of protrusions on the current collector. For example, in the electric double layer capacitor described in Patent Document 2, a metal foil is punched out, and a through hole and a protrusion having a height of 300 μm and a size of 0.4 mm × 0.4 mm are formed to 4 pieces / mm ² , The internal resistance of the electric double layer capacitor is reduced. In this case, the height of the protrusion is preferably 0.5 to 0.8 when the electrode thickness is 1.0. However, with the protrusions proposed in the above-mentioned document, the number of protrusions with respect to the electrode composition layer and the area where the electrode composition layer and the current collector are in contact with each other are small, so that sufficient internal resistance cannot be reduced.

Patent No. 4015993 JP-A-9-134726

  The object of the present invention is to provide a hybrid capacitor comprising a positive electrode made of a material capable of reversibly supporting lithium ions and / or anions and a negative electrode made of a material capable of reversibly supporting lithium ions, and the method described in the above document. Therefore, an object of the present invention is to provide an electrode for a hybrid capacitor, which is a reduction in internal resistance of the hybrid capacitor, which cannot be said to be sufficiently solved, and can provide a hybrid capacitor suitable for high-speed charge / discharge with a large current.

  As a result of intensive studies to solve the above problems, the present inventors have extended a plurality of protrusions from the current collector to the electrode composition layer, and have a hole portion on the current collector. Current collection at the electrode and the contact area between the electrode composition layer and the current collector due to the protrusions can be improved, and in the pre-doping step of the lithium ion capacitor, lithium ions pass through the current collector, It was found that the electrode in the cell can be doped uniformly. As a result, the contact area between the electrode composition layer and the current collector, which could not be solved because a flat current collector has been conventionally used, can be improved, and the internal resistance of the hybrid capacitor can be reduced. We found that it can be drastically reduced.

Furthermore, it has been found that the interface resistance between the electrode composition layer and the current collector can be reduced by forming a conductive adhesive layer on the current collector having protrusions. Further, the area (A) where the electrode composition layer and the current collector are in contact with each other is larger than the area ratio A / B = 1 times compared to the plain current collector (B) having no protrusions and no openings, and the electrode composition The number of protrusions relative to the layer is 1 / mm ² or more, the ratio of protrusions in the electrode composition layer is 1% by volume or more, and the protrusion length (D) is the thickness (L) of the electrode composition layer. It was found that the internal resistance can be sufficiently reduced by setting 0 <D / L <1.

  By applying a conductive adhesive to the current collector and then providing a protrusion, it is possible to form a conductive adhesive layer on the side of the protrusion and block the opening of the protrusion. It was found that the adhesion between the current collector and the electrode composition layer can be improved.

  As a method for manufacturing a hybrid capacitor electrode, it has been found that a protrusion current collector with a conductive adhesive can be efficiently produced by providing protrusions on a current collector on which a conductive adhesive layer is formed.

  Based on these findings, the present inventors have completed the present invention.

Thus, according to the present invention, the following (1) to (3) are provided.
(1) An electrode for a hybrid capacitor in which an electrode composition layer containing an electrode active material and a binder is formed on a current collector, wherein the current collector has a plurality of protrusions extending to the electrode composition layer. Electrode for hybrid capacitor characterized by having

(2) A step of applying a conductive adhesive to the current collector, a step of providing protrusions on the current collector, a step of applying an electrode composition onto the current collector, and hot pressing the applied electrode composition The manufacturing method of the electrode for hybrid capacitors which has a process to carry out.

(3) A hybrid capacitor having the hybrid capacitor electrode according to (1).

  The electrode for a hybrid capacitor of the present invention has a current collector in the thickness direction by extending a plurality of protrusions from the current collector to the electrode composition layer, and having an aperture on the current collector. The contact area between the electrode composition layer and the current collector can be improved by the protrusion, and further, in the pre-doping process of the lithium ion capacitor, lithium ions pass through the current collector and efficiently and uniformly dope the electrodes in the cell. Can be done. As a result, since the current collector having a through hole has been used, the contact area between the electrode composition layer and the current collector, which could not be solved, can be improved. Resistance can be drastically reduced.

  In addition, the hybrid capacitor of the present invention has an aperture in the current collector, so that lithium ions pass through the current collector in the pre-doping process of the lithium ion capacitor, and dope the electrodes in the cell efficiently and uniformly. It can be carried out.

  The electrode for a hybrid capacitor according to the present invention is an electrode for a hybrid capacitor formed by forming an electrode composition layer containing an electrode active material and a binder on a current collector, wherein the current collector is the electrode composition. A hybrid capacitor electrode having a plurality of protrusions extending in a physical layer.

<Current collector with protrusion>
As the type of the current collector material used in the present invention, for example, metal, carbon, conductive polymer and the like can be used, and metal is preferably used. As the current collector metal, aluminum, platinum, nickel, tantalum, titanium, stainless steel, other alloys and the like are usually used.

  The current collector used in the present invention may be subjected to surface chemical treatment or surface roughening treatment as necessary in order to reduce contact resistance with the electrode composition layer or improve adhesion to the electrode composition layer. It may be given in advance. Examples of the surface chemical treatment include acid treatment and chromate treatment. Examples of the surface roughening treatment include electrochemical etching treatment and etching treatment with acid or alkali.

  The thickness of the current collector used in the present invention is usually 1 to 200 μm, preferably 5 to 100 μm, more preferably 10 to 60 μm.

The number of protrusions on the electrode composition layer of the current collector used in the present invention is usually larger than 1 piece / mm ² , preferably 2-30 pieces / mm ² . Here, the protrusion in the present invention is a protrusion having a height of 1 μm or more in the direction perpendicular to the current collector plane, and is a current collector having a roughened surface of etched aluminum or a plain current collector. Unevenness is not included in the protrusions.

  The current collector used in the present invention preferably has an aperture. The porosity is usually 10 to 90%, preferably 20 to 60%. The hole area ratio described in the present invention refers to the ratio (area%) per unit area of the current collector to the bottom area (area of the surface in contact with the current collector plane) of the protrusion having the opening. Say. By having the opening portion, in the pre-doping step of the lithium ion capacitor, lithium ions pass through the current collector, and the electrodes in the cell can be doped efficiently and uniformly. Further, when the hybrid capacitor is manufactured, it is possible to suppress the capacity variation between lots of capacitor cells. In an electrode for a hybrid capacitor using a current collector that does not have a normal aperture, if a non-facing surface is formed where the electrodes do not face each other when a multilayer hybrid capacitor is produced, the non-facing surface is static. If the capacitance cannot be taken out and the amount of active material per unit area of the electrode varies, the capacitance actually taken out may be smaller than the capacitance calculated from the weight of the active material amount. For this reason, capacity variation among lots of hybrid capacitor cells may occur. This is because the diffusion of electrolyte ions occurs only on the opposing surface of the positive and negative electrodes. However, by having an aperture in the current collector, the electrolyte ions can pass through the current collector, so that the capacitance can be taken out from the non-facing surface where the electrodes do not face each other. Even if electrodes with different amounts of active material are used, as long as the total weight of the electrode active material is matched, it is possible to easily balance the capacity within the capacitor cell, thereby suppressing capacity variation between lots of hybrid capacitor cells. It is done.

  The aperture diameter of the current collector used in the present invention is 0.01 to 10 μm, preferably 1 to 5 μm.

  The current collector used in the present invention has an area (A) where the electrode composition layer and the current collector are in contact with each other, and the area ratio is A / B = compared to the plain current collector (B) having no protrusions. It is more than 1 time, preferably 1.5 times or more. The contact area between the electrode composition layer and the current collector is the number of protrusions formed per unit area of the protrusion current collector, the protrusion dimensions, and the aperture dimensions measured using a scanning electron microscope (SEM). Further, the height of the protrusion is obtained from a thickness meter (the height of the protrusion = the thickness of the protrusion current collector−the thickness before the protrusion processing), and the electrode composition layer that is considered to contact per unit volume of one electrode surface; This means the contact area calculated with the current collector. By making this area ratio A / B = 1 times or more, the contact resistance between the electrode composition layer and the current collector can be reduced, and the internal resistance of the hybrid capacitor can be reduced.

  The proportion of the protrusions in the electrode composition layer of the current collector used in the present invention is 1% by volume or more, preferably 10% by volume or more. The ratio (volume%) of protrusions in the electrode composition layer is the number of protrusions formed per unit area of the current collector with protrusions, the protrusion dimensions, and the dimensions of the apertures measured with a scanning electron microscope (SEM). Furthermore, the height of the protrusion is obtained from a thickness meter (the height of the protrusion = the thickness of the protrusion current collector−the thickness before the protrusion processing), and the volume of the protrusion formed on one surface of the current collector is calculated. It is calculated and the ratio of the protrusion volume in the unit volume of the electrode composition layer on one side of the electrode is calculated. By setting the ratio of the protrusions in the electrode composition layer within this range, the current collection from the electrode composition layer can be sufficiently performed, and the internal resistance of the hybrid capacitor can be reduced.

The shape of the projection used in the present invention is preferably a triangular frustum shape or a quadrangular frustum shape whose upper base area is narrower than the lower base area.
The strength of the protrusion can be maintained.

  As a method for imparting protrusions to the current collector used in the present invention, a known method can be used. Among them, a method using a pair of upper and lower embossing rolls rotating in opposite directions from the viewpoint of productivity and cost is preferable. A protruding current collector can be manufactured by passing a current collector to which no protrusion is provided through the facing gap of the embossing roll. On the surface of each pair of upper and lower embossing rolls, a large number of convex portions and concave portions are alternately arranged in a grid pattern alternately in the vertical and horizontal directions, and the arrangement of the convex concave portions is imparted to the current collector. It is preferable that the protrusions are arranged so as to have a triangular frustum shape or a quadrangular frustum shape. Furthermore, it is more preferable that each of the convex portions and the concave portions provided on the embossing roll is a sharp blade, and an opening is provided on the upper portion of the protrusion.

<Conductive adhesive>
The current collector used in the present invention preferably has a conductive adhesive layer. By having a conductive adhesive layer, the adhesion between the electrode composition layer and the current collector is improved, and the interface resistance between the electrode composition layer and the current collector can be reduced. As the conductive adhesive, known ones can be used, and among them, a conductive adhesive obtained by dissolving or dispersing a conductive agent, a binder, and a thickener in a solvent is preferable.

  The conductive agent used in the conductive adhesive used in the present invention is not particularly limited as long as it has conductivity, and among them, conductive carbon black, graphite and the like are particularly preferable.

  The volume average particle diameter of the conductive agent used for the conductive adhesive used in the present invention is usually in the range of 0.001 to 10 μm, preferably 0.05 to 5 μm, more preferably 0.01 to 1 μm. These conductive agents can be used alone or in combination of two or more.

  The binder used in the conductive adhesive used in the present invention is not particularly limited. For example, polymer compounds such as fluorine polymers, diene polymers, acrylate polymers, polyimides, polyamides, and polyurethanes may be used. Can be mentioned. Furthermore, a cellulose derivative may be used as a thickener, and an ammonium salt of carboxymethyl cellulose is particularly preferable.

  The conductive adhesive used in the present invention may contain a solvent as necessary, and as this solvent component, toluene, acetone, water, methanol, ethanol, propanol, tetrachloroethylene, trichloroethylene, bromochloromethane, Each of diacetone, dimethylformamide, acetyl ether, cresol, xylene, chloroform, butanol and dimethyl ether can be used alone or in combination of two or more.

  The amount ratio of the conductive agent, the binder and the solvent in the conductive adhesive used in the present invention may be appropriately determined depending on the purpose. For example, the binder is added to 100 parts by weight of the conductive carbon black powder. The range of 1-10 weight part and 0-300 weight part of a solvent can be mentioned.

  The conductive adhesive used in the present invention can be produced by mixing the above-described components using a mixer. As the mixer, a ball mill, a sand mill, a pigment disperser, a pulverizer, an ultrasonic disperser, a homogenizer, a planetary mixer, a Hobart mixer, and the like can be used.

  The method for applying the conductive adhesive used in the present invention to the current collector is not particularly limited. Examples thereof include a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method.

  The thickness of the conductive adhesive layer applied to the current collector used in the present invention is usually 1 to 15 μm, preferably 2 to 10 μm, more preferably 2 to 5 μm.

  The conductive adhesive layer may be formed after the protrusion is applied to the current collector, but the conductive adhesive layer is formed on the current collector before the protrusion is applied, and then the protrusion is applied to the current collector. However, it is preferable because a protrusion current collector with a conductive adhesive can be efficiently produced. By applying a conductive adhesive to the current collector prior to the application of the protrusion, and then providing a protrusion, a conductive adhesive layer can be formed on the side of the protrusion. The adhesion between the current collector and the electrode composition layer can be improved without blocking the portion.

<Electrode active material>
The electrode composition layer used in the present invention contains an electrode active material and a binder as essential components. Electrode active materials used for hybrid capacitor electrodes include positive and negative electrodes. The positive electrode active material used in the present invention is not particularly limited as long as it can reversibly carry lithium ions and anions such as tetrafluoroborate, and carbon allotropes are usually used. Specifically, electrode active materials used in electric double layer capacitors can be widely used. In particular, those capable of forming an interface having a larger area with the same weight, that is, those having a large specific surface area are preferred. Specifically, the specific surface area of ^{30 m} 2 / g or more, preferably preferably 500~5,000m ² / g, more preferably 1,000~3,000m ² / g. Specific examples of the allotrope of carbon include activated carbon, polyacene, carbon whisker, and graphite, and these powders or fibers can be used. A preferable electrode active material is activated carbon, and specific examples thereof include phenol-based, rayon-based, acrylic-based, pitch-based, and coconut shell-based activated carbon. These allotropes of carbon can be used alone or in combination of two or more as the active material. When carbon allotropes are used in combination, two or more types of carbon allotropes having different average particle diameters or particle size distributions may be used in combination.

  Further, a polyacene organic semiconductor (PAS) which is a heat-treated product of an aromatic condensation polymer and has a polyacene skeleton structure having a hydrogen atom / carbon atom atomic ratio of 0.50 to 0.05 can also be used suitably. . In addition, nonporous carbon having microcrystalline carbon similar to graphite and having an increased interlayer distance of the microcrystalline carbon can be used as the electrode active material. Such non-porous carbon is obtained by dry-distilling graphitized charcoal with microcrystals of a multilayer graphite structure at 700 to 850 ° C., then heat-treating with caustic at 800 to 900 ° C., and if necessary with heated steam. It is obtained by removing the residual alkali component.

  As the positive electrode active material, a powder having a weight average particle diameter of 0.1 to 100 μm, preferably 1 to 50 μm, more preferably 2 to 10 μm is used.

  The negative electrode active material used in the present invention is formed from a material that can reversibly carry lithium ions. Preferred examples of the negative electrode active material include carbon materials such as graphite, non-graphitizable carbon, hard carbon, coke, and the polyacene organic semiconductor (PAS) described as the positive electrode active material. PAS is obtained by carbonizing a phenol resin or the like, activated as necessary, and then pulverized.

  As the shape of the electrode active material used in the present invention, powder or fiber can be used.

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

<Conductive aid>
The positive electrode for a hybrid capacitor of the present invention may use a conductive additive as necessary, and the type thereof is not particularly limited as long as it has conductivity, and includes a carbon allotrope or a metal. Preferably, an allotrope of carbon is used. Specifically, conductive carbon blacks such as furnace black, acetylene black, and ketjen black (registered trademark of Akzo Nobel Chemicals Bethloten Fennaut Shap); natural graphite, graphite such as artificial graphite; Particulate conductive aids that are: Moreover, the fibrous conductive support agent which consists of carbon allotropes, such as carbon fibers, such as a polyacrylonitrile type | system | group carbon fiber, a pitch type | system | group carbon fiber, and a vapor-grown carbon fiber; Examples of conductive assistants made of metal include particulate conductive assistants such as titanium oxide, ruthenium oxide, aluminum, and nickel; and fibrous conductive assistants such as metal fibers. Among these, carbon black is preferable, and acetylene black and furnace black are more preferable.

  The volume average particle diameter of the conductive additive used in the present invention is preferably smaller than the volume average particle diameter of the electrode active material, and is usually 0.001 to 10 μm, preferably 0.05 to 5 μm, more preferably 0. The range is from 0.01 to 1 μm. When the particle size of the conductive assistant is within this range, high conductivity can be obtained with a smaller amount of use. These conductive assistants can be used alone or in combination of two or more.

  The amount of the conductive aid used in the present invention 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. It is a range. By forming the electrode for a hybrid capacitor containing the amount of the conductive aid in this range, the capacity of the capacitor can be increased and the internal resistance can be decreased.

<Binder>
The binder used in the present invention is not particularly limited as long as it is a compound having a binding force. Examples of the binder include polymer compounds such as a fluorine polymer, a diene polymer, an acrylate polymer, polyimide, polyamide, and polyurethane. Among them, the binder is preferably an acrylate polymer, and has good binding properties with a current collector, improvement in electrode density by pressing, and internal resistance and flexibility of the obtained electrode. These binders can be used alone or in combination of two or more. Further, the binder may be a binder having a core-shell structure obtained by stepwise polymerization of a mixture of two or more monomers.

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

  The diene polymer is a homopolymer of a conjugated diene or a copolymer obtained by polymerizing a monomer mixture containing a conjugated diene, or a hydrogenated product thereof. The proportion of the conjugated diene in the monomer mixture is usually 40% by 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 thereof include vinyl cyanide / conjugated diene copolymers such as acrylonitrile / butadiene copolymer (NBR); hydrogenated SBR, hydrogenated NBR, and the like.

  The acrylate polymer is preferably an acrylate polymer containing a monomer unit obtained by polymerizing an acrylic ester and / or a methacrylic ester, usually 50% by weight or more, preferably 70% by weight or more, and has high heat resistance. And the internal resistance of the electrode for electric double layer capacitors obtained can be made small. Specific examples of the acrylate polymer include, for example, 2-ethylhexyl acrylate / methacrylic acid / acrylonitrile copolymer, 2-ethylhexyl acrylate / methacrylic acid / methacrylonitrile copolymer, butyl acrylate / acrylonitrile copolymer. Butyl acrylate / acrylic acid copolymer, 2-ethylhexyl acrylate / styrene / methacrylic acid copolymer, and butyl acrylate / methyl methacrylate / methacrylic acid copolymer.

  The Tg of the binder used in the present invention is 50 ° C. or lower, preferably −100 to 0 ° C. When the Tg of the binder is within this range, the binding property is excellent with a small amount of use, the electrode strength is high, the flexibility is high, and the electrode density can be easily increased by a pressing process during electrode formation.

  The shape of the binder used in the present invention is most preferably in the form of particles in order to minimize the increase in binding property, decrease in electrode capacity, and increase in internal resistance, such as latex. And the like are those in which the binder particles are dispersed in a solvent, and those obtained by drying such a dispersion.

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

  The method for producing the binder used in the present invention is not particularly limited, and a known polymerization method such as an emulsion polymerization method, a suspension polymerization method, a dispersion polymerization method or a solution polymerization method can be employed. Among them, it is preferable to produce by an emulsion polymerization method because the particle diameter of the binder is easy to control.

  The usage-amount of the binder used for this invention is the range of 1-20 weight part normally with respect to 100 weight part of electrode active materials, Preferably it is the range of 3-15 weight part.

<Electrode composition>
The electrode composition used in the present invention is composed of an electrode active material, a conductive aid, and a binder, and may further contain a cellulose derivative. When a cellulose derivative is used, the stability of the slurry containing the electrode composition is high, and solid matter precipitation and aggregation are unlikely to occur. Furthermore, the coating property and fluidity | liquidity of a slurry improve by using a cellulose derivative.

  The cellulose derivative used in the present invention is a compound obtained by etherifying or esterifying at least a part of the hydroxyl group of cellulose, and is preferably water-soluble. The cellulose derivative used in the present invention usually does not have a glass transition point. Specific examples include carboxymethyl cellulose, carboxymethyl ethyl cellulose, methyl cellulose, ethyl cellulose, ethyl hydroxyethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose. These salts can also be used. Examples of the salt include ammonium salt and alkali metal salt. Among these, a salt of carboxymethyl cellulose is preferable, and an ammonium salt of carboxymethyl cellulose is particularly preferable.

  The degree of etherification of the cellulose derivative used in the present invention is preferably 0.5 to 2, more preferably 0.5 to 1.5. Here, the degree of etherification is a value representing how many hydroxyl groups contained per 3 glucose units of cellulose are etherified on average. When the degree of etherification is within this range, the stability of the slurry containing the electrode composition is high, and solid matter sedimentation and aggregation are unlikely to occur. Furthermore, the coating property and fluidity | liquidity of a slurry improve by using a cellulose derivative.

  The amount of the cellulose derivative used in the present invention is appropriately selected depending on the type of electrode for a hybrid capacitor produced using the electrode composition of the present invention, but is usually 0.1% relative to the electrode active material. -10 parts by weight, preferably 0.5-5 parts by weight.

<Method for manufacturing electrode for hybrid capacitor>
Examples of the method for producing the electric double layer capacitor electrode of the present invention include a method of forming an electrode composition layer on a current collector having protrusions by wet molding or dry molding. Specifically, in wet molding, an electrode active material, a conductive aid, a cellulose derivative, and a binder are dispersed or dissolved in water or an organic solvent to prepare a slurry, and the slurry is applied onto a current collector having protrusions. The electrode composition layer is formed on the current collector by drying. Dry molding is a concept for the above-mentioned wet molding, and includes a step of mixing a binder and an electrode active material to obtain a mixture, and a step of molding the obtained mixture into a sheet-like electrode composition layer. . In dry molding, the mixture may contain a small amount of water or an organic solvent as a molding aid, but the solid content concentration in the molding step is usually more than 70% by weight, preferably 80% by weight or more. It is. Specific examples of the dry molding method include an extrusion molding method, a roll rolling method, a powder molding method, and a pressure molding method.

  As a manufacturing method of the slurry used for this invention, water and each said component can be mixed and manufactured using a mixer. As the mixer, a ball mill, a sand mill, a pigment disperser, a pulverizer, an ultrasonic disperser, a homogenizer, a planetary mixer, a Hobart mixer, and the like can be used. Also, the electrode active material and the conductivity imparting material are first mixed using a mixer such as a crusher, a planetary mixer, a Henschel mixer, and an omni mixer, and then the binder composition is added and mixed uniformly. Is also preferable. By adopting this method, a uniform slurry can be easily obtained.

  The viscosity of the slurry used in the present invention varies depending on the type of coating machine and the shape of the coating line, but is usually 100 to 100,000 mPa · s, preferably 1,000 to 50,000 mPa · s. Preferably, it is 5,000 to 20,000 mPa · s.

  The method for applying the slurry used in the present invention to the current collector is not particularly limited. Examples thereof include a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method.

  The amount of the slurry used in the present invention is preferably adjusted according to the ratio of the length (D) of the protrusion and the desired thickness (L) of the electrode composition layer, and 0 <D / L <1 Most preferably, the amount is By keeping the length of the protrusion within this range, it is possible to maximize the reduction in internal resistance and the improvement in electrode strength, which are the characteristics of a current collector having a plurality of protrusions. Further, by setting D / L <1, it is possible to prevent the protrusion from breaking through the separator and causing a short circuit.

  Examples of the drying method used in the present invention include drying by warm air, hot air, low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays or electron beams. Among these, a drying method by irradiation with far infrared rays is preferable.

  The drying temperature and drying time in the present invention are preferably a temperature and a time at which the solvent in the slurry applied to the current collector can be completely removed, and the drying temperature is 100 to 300 ° C, preferably 120 to 250 ° C. The drying time is usually 10 minutes to 100 hours, preferably 20 minutes to 20 hours.

  In the present invention, it is preferable to hot press the applied electrode composition. The hot press may be performed before the drying or after the drying. By performing the pressing, an electrode having a smooth surface and a uniform surface can be obtained. In addition, pressing after drying is preferable because the electrode density can be easily increased.

  The hot press method used in the present invention is preferably a die press or roll press.

  The temperature of the hot press in the present invention is preferably in the range of 50 ° C to 150 ° C, more preferably 80 ° C to 130 ° C.

<Hybrid capacitor>
The hybrid capacitor of the present invention has the hybrid capacitor electrode of the present invention. The hybrid capacitor can be manufactured according to a conventional method using the electrode of the present invention and components such as an electrolytic solution and a separator. Specifically, for example, the electrode is cut into an appropriate size, then the electrodes are overlapped via a separator, and this is wound into a capacitor shape, folded into a container, and an electrolytic solution is injected into the container. Can be manufactured by sealing.

  The type of the electrolytic solution used in the present invention is not particularly limited, but a nonaqueous electrolytic solution in which an electrolyte is dissolved in an organic solvent is preferable.

As the electrolyte used in the present invention, conventionally known electrolytes can be used. (C ₂ H ₅ ) ₄ NBF ₄ , (C ₂ H ₅ ) ₃ (CH ₃ ) NBF ₄ , (C ₂ H ₅ ) ₄ Examples of the salt include NPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiPF ₆ , LiN (C ₂ F ₅ SO ₂ ) ₂ , and LiN (CF ₃ SO ₂ ) ₂ . The concentration of the electrolyte in the electrolytic solution is preferably at least 0.1 mol / liter or more in order to reduce the internal resistance due to the electrolytic solution, and more preferably in the range of 0.5 to 1.5 mol / liter. preferable.

  The solvent (electrolytic solution solvent) used in the present invention is not particularly limited as long as it is generally used as an electrolytic solution solvent. Specifically, carbonates such as propylene car boat, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, and diethyl 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.

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

  Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto. In addition, the part and% in a present Example are a basis of weight unless there is particular notice.

The tests and evaluations in the examples and comparative examples are performed by the following methods.
(Measurement of area ratio where electrode composition layer and current collector are in contact)
The ratio of the area where the electrode composition layer and the current collector are in contact is measured by observing the current collector with protrusions with a scanning electron microscope (SEM), and the number of protrusions formed on the current collector plane 1 mm long × 1 mm wide, And the opening part (length x width) dimension of a quadrangular pyramid shaped projection is measured. The height of the quadrangular frustum-shaped protrusion is measured using a thickness meter (the height of the protrusion = the thickness of the protrusion current collector−the thickness before the protrusion processing), and the height of the quadrangular frustum-shaped protrusion is calculated. From these values, the contact area between the electrode composition layer and the current collector considered to be in contact per unit volume on one side of the electrode is calculated, and the area (A) where the electrode composition layer and the protrusion current collector contact with the protrusion The area ratio, A / B, with the unprocessed plain current collector (B) is obtained. In addition, after forming the electrode composition layer on the protrusion current collector, the fractured surface is confirmed using SEM, it is confirmed that the quadrangular frustum-shaped protrusion is not crushed, and the area ratio and A / B are correct. Check.

(Measurement of the ratio of protrusions in the electrode composition layer)
The ratio (volume%) of the protrusions in the electrode composition layer is determined by observing the current collector with protrusions with an SEM, the number of protrusions formed on the current collector plane length 1 mm × width 1 mm, and the truncated pyramid shape Measure the aperture (vertical x horizontal) dimensions. In addition, the height of the quadrangular frustum-shaped protrusions is measured using a thickness meter (the height of the protrusions = the thickness of the protrusion current collector-the thickness before the protrusion processing), and the height of the truncated pyramid-shaped protrusions is calculated. To do. From these values, the volume of the protrusion formed on the current collector is calculated, and the ratio of the protrusion volume in the unit volume of the electrode composition layer on one side of the electrode is determined. In addition, after forming the electrode composition layer on the protrusion current collector, the fractured surface is confirmed using SEM, it is confirmed that the quadrangular frustum-shaped protrusions are not crushed, and the proportion of the protrusion volume is confirmed to be correct. .
(Measurement of hole area ratio)
The current collector aperture ratio is measured by observing the protruding current collector with a SEM from the direction perpendicular to the current collector plane, and measuring the size of the holes. Find the area%.
(Measurement of electrode composition layer thickness)
The electrode composition layer thickness is measured using an eddy current displacement sensor (sensor head part EX-110V, amplifier unit part EX-V02: manufactured by Keyence Corporation) after forming the electrode composition layer on both sides of the current collector. To do. The thickness of each electrode layer is measured at intervals of 2 cm, and the average value thereof is taken as the thickness of the electrode layer.

(Electric characteristics of hybrid capacitor)
Charging is started at a constant current of 110 mA. When the charging voltage reaches 3.8 V, the voltage is maintained and constant voltage charging is performed, and charging is completed when constant voltage charging is performed for 20 minutes. Next, immediately after the end of charging, discharging is performed at a constant current of 110 mA until 2.1V is reached. This charge / discharge operation is performed for 3 cycles, and the capacity per volume and volume resistivity are obtained from the discharge curve of the third cycle.

  The capacity of the cell is calculated from the amount of power at the time of discharge using an energy conversion method, and the capacity of the cell is divided by the volume of the electrode layer, current collector, and separator (excluding protrusions) constituting the cell. Find the capacity per volume. The internal resistance is calculated from the voltage 0.1 seconds after discharge from the relationship of R = ΔV / I, and the volume resistivity is obtained.

<Example 1>
(Production of positive electrode for hybrid capacitor)
Carboxymethylcellulose ammonium salt having a degree of etherification of 0.6 and a 1% aqueous solution having a viscosity of 30 mPa · s is dissolved in 213.2 parts of ion-exchanged water, and a volume average particle diameter of 0. 50 parts of 035 μm acetylene black (Denka black powder: manufactured by Denki Kagaku Kogyo Co., Ltd.) is added and mixed and dispersed using a planetary mixer to obtain a conductive agent dispersion having a solid content concentration of 20%.

26 parts of the resulting conductive agent dispersion, 100 parts of activated carbon powder having an average particle size of 5 μm and a specific surface area of 2,000 m ² / g as an electrode active material, and 7.5 parts of an aqueous dispersion having an acrylate polymer solid content concentration of 40% A suitable amount of water is added to 1 part of a carboxymethyl cellulose ammonium salt having a degree of etherification of 0.6 and a 1% aqueous solution having a viscosity of 900 mPa · s, and is mixed and dispersed using a planetary mixer. A positive electrode slurry for a hybrid capacitor that falls between 20,000 mPa · s is obtained. As the acrylate polymer, a copolymer having a Tg of −20 ° C. obtained by emulsion polymerization of 76 parts of 2-ethylhexyl acrylate, 20 parts of acrylonitrile and 4 parts of itaconic acid is used.

  The conductive adhesive is 80 parts of graphite having a volume average particle diameter of 3.7 μm (KS-6: manufactured by Timcal) and 20 parts of carbon black having a volume average particle diameter of 0.4 μm (Super-P: manufactured by Timcal) as a conductive agent. 4 parts of carboxymethylcellulose ammonium salt having a degree of etherification of 0.6 and a viscosity of 1 m aqueous solution of 30 mPa · s as a dispersant, and 8 parts of an aqueous dispersion of 40% solid content of an acrylate polymer as a binder. Add 261 parts, and mix and disperse using a planetary mixer to obtain a slurry with a solid content of 30%. This conductive adhesive is applied to a current collector of 30 μm thick aluminum foil with a gravure coater and dried at 120 ° C. for 5 minutes to obtain a current collector with a 4 μm conductive adhesive layer.

By passing the current collector with the conductive adhesive layer through the opposing gap between the pair of upper and lower embossing rolls rotating in opposite directions, the upper part with 11 protrusions / mm ² and a protrusion length of 131 μm is opened. A projection current collector with a conductive adhesive layer having a porosity of 36% and having a square pyramidal trapezoidal projection (projection bottom bottom dimension, length 15 μm × width 21 μm) is obtained.

  After applying the slurry to both sides of the current collector using a roll coater on the current collector with protrusions with a conductive adhesive layer, drying at 60 ° C. for 20 minutes, and then heat-treating at 120 ° C. for 20 minutes Then, a roll press is performed at a roll temperature of 100 ° C. to obtain a positive electrode for a hybrid capacitor having a thickness of 320 μm (thickness of electrode composition layer on both sides, thickness of conductive adhesive layer and current collector thickness). When the thickness of one side is measured using an eddy current type displacement sensor (sensor head part EX-110V, amplifier unit part EX-V02: manufactured by Keyence Corporation), the thickness of the electrode composition layer is 141 μm.

(Preparation of negative electrode for hybrid capacitor)
A 0.5 mm thick phenolic resin molded plate is placed in a siliconite electric furnace, heated to 500 ° C. at a rate of 50 ° C./hour, and further at a rate of 10 ° C./hour to 660 ° C. in a nitrogen atmosphere, followed by heat treatment. Synthesize polyacene. The polyacene plate thus obtained is pulverized by a disk mill and sieved to obtain a PAS powder having an average particle diameter of 5 μm. To 100 parts of the resulting polyacene, 7.5 parts of an aqueous dispersion of an acrylate polymer having a solid content of 40%, and 1 part of carboxymethyl cellulose ammonium salt having a degree of etherification of 0.6 and a 1% aqueous solution having a viscosity of 900 mPa · s. An appropriate amount of water is added and mixed and dispersed using a planetary mixer to obtain a negative electrode slurry for a hybrid capacitor having a viscosity of between 5,000 and 20,000 mPa · s.

In the same manner as the positive electrode, a conductive adhesive layer was formed on a copper current collector and protrusions were processed, and a truncated pyramid-shaped protrusion (vertical) with an upper part having a protrusion number of 11 / mm ² and a protrusion length of 52 μm was formed. A projection current collector with a conductive adhesive layer having a porosity of 36% having a size of 15 μm × width 21 μm is obtained. A slurry is applied to this current collector using a roll coater, dried at 60 ° C. for 20 minutes, and then heat-treated at 120 ° C. for 20 minutes, followed by roll pressing at a roll temperature of 100 ° C. A negative electrode for a hybrid capacitor having a composition layer thickness, a conductive adhesive layer thickness and a current collector thickness) of 150 μm is obtained. When the thickness of one side is measured using an eddy current type displacement sensor (sensor head part EX-110V, amplifier unit part EX-V02: manufactured by Keyence Corporation), the thickness of the electrode composition layer is 56 μm.

(Preparation of measurement cell)
In the electrode sheet to be prepared, the uncoated portion where the conductive adhesive layer and the electrode composition layer are not formed is left 2 cm × 2 cm in length, and the portion where the electrode composition layer is formed is 5 cm × width Cut out to 5cm. A tab material made of aluminum having a length of 7 cm, a width of 1 cm, and a thickness of 0.01 cm is ultrasonically welded to the uncoated portion to produce a measurement electrode. As measurement electrodes, 10 sets of positive electrodes and 11 sets of negative electrodes were prepared and dried at 160 ° C. for 40 minutes. Using a cellulose / rayon mixed nonwoven fabric having 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 opposing surfaces of the positive electrode and the negative electrode are 20 layers. In addition, lamination is performed so that the outermost electrode of the laminated electrodes becomes a negative electrode. The uppermost part and the lowermost part are provided with separators, and four sides are taped, and the terminal welded part (10 sheets) of the positive electrode current collector and the terminal welded part (11 sheets) of the negative electrode current collector are ultrasonically welded.

  As a lithium electrode, an electrode in which a lithium metal foil (82 μm thick, 5 cm long × 5 cm wide) is pressure-bonded to a stainless steel mesh having a thickness of 80 μm, and the lithium electrode is laminated so as to be completely opposed to the outermost negative electrode One sheet is placed at the top and bottom of each. The terminal welding part (two sheets) of the lithium electrode current collector is resistance-welded to the negative electrode terminal welding part.

Laminate with the lithium foil placed at the top and bottom is placed inside the deep-drawn lower exterior film, covered with the exterior laminate film and fused on the three sides, and then ethylene carbonate, diethyl carbonate and propylene carbonate are used as the electrolyte. A solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / liter is vacuum impregnated in a mixed solvent having a weight ratio of 3: 4: 1, and then the remaining one side is fused to produce a film type capacitor. Table 1 shows the capacity density and volume resistivity per volume of the obtained hybrid capacitor.

<Example 2>
A hybrid capacitor electrode is obtained in the same manner as in Example 1 except that the protrusion length of the current collector used for the positive electrode is 93 μm and the protrusion length of the current collector used for the negative electrode is 37 μm. Table 1 shows the evaluation results of the electrical characteristics of the obtained hybrid capacitor electrode.

<Example 3>
A hybrid capacitor electrode is obtained in the same manner as in Example 1 except that the protrusion length of the current collector used for the positive electrode is 71 μm and the protrusion length of the current collector used for the negative electrode is 30 μm. Table 1 shows the evaluation results of the electrical characteristics of the obtained hybrid capacitor electrode.

<Comparative Example 1>
In the same manner as in Example 1, a current collector coated with a conductive adhesive was punched out using a mold so as to have a hole diameter of 15 μm and a hole area ratio of 36% to obtain a perforated current collector with a conductive adhesive layer. . A hybrid capacitor electrode is obtained in the same manner as in Example 1 except that this current collector is used. Table 1 shows the evaluation results of the electrical characteristics of the obtained hybrid capacitor electrode.

  In Examples 1 to 3, the volume resistivity of the hybrid capacitor was reduced as compared with Comparative Example 1. This is because the area where the electrode composition layer and the current collector are in contact (A / B) is increased by imparting protrusions to the current collector, and the ratio (volume%) of the protrusions in the electrode composition layer. This is considered to be because the protrusion portion length (D) / electrode thickness (L) is increased, so that the current can be efficiently collected from the electrode composition layer.

  By using the hybrid capacitor electrode of the present invention, the resistance of the cell can be reduced. Therefore, it can be suitably used for various applications such as an application to an electric vehicle or a hybrid vehicle, a solar power generation energy storage system combined with a solar battery, and a load leveling power source combined with a battery.

Claims (3)

Applying a conductive adhesive to the current collector (1),
Next, a step (2) of providing protrusions on the current collector coated with the conductive adhesive,
And (3) applying an electrode composition on the current collector provided with the protrusions.
The current collector is apertured, and the aperture ratio is 20 to 60%. Furthermore, the applied method of manufacturing a hybrid capacitor electrode according to claim 1 comprising the step (4) for hot pressing the electrode composition. The hybrid capacitor which has the electrode for hybrid capacitors obtained by the manufacturing method of Claim 1 or 2 .