阅读说明：本技术 电极体、具备电极体的电解电容器以及电极体的制造方法 (Electrode body, electrolytic capacitor provided with electrode body, and method for manufacturing electrode body ) 是由 小关良弥 大仓数马 长原和宏 町田健治 末松俊造 于 2019-09-11 设计创作，主要内容包括：本发明提供一种不仅在电解电容器的初期静电电容中,在高温环境负荷后也可显现稳定的静电电容的电极体、具备所述电极体的电解电容器以及所述电极体的制造方法。电极体用于电解电容器的阴极,且包括：包含阀作用金属的阴极箔、及形成于所述阴极箔的碳层。碳层含有石墨及球状碳。(The invention provides an electrode body which can show stable electrostatic capacitance not only in the initial electrostatic capacitance of an electrolytic capacitor but also after a high-temperature environment load, an electrolytic capacitor provided with the electrode body and a manufacturing method of the electrode body. The electrode body is used for a cathode of an electrolytic capacitor, and includes: the valve-acting metal-containing cathode foil comprises a valve-acting metal, and a carbon layer formed on the cathode foil. The carbon layer contains graphite and spherical carbon.)

1. An electrode body, which is an electrode body for a cathode of an electrolytic capacitor, characterized by comprising:

a cathode foil comprising a valve action metal;

a carbon layer formed on the cathode foil and

the carbon layer contains graphite and spherical carbon.

2. Electrode body according to claim 1, characterized in that

The spherical carbon has a specific Buert surface area of 200m²Carbon black in an amount of less than/g.

3. Electrode body according to claim 2, characterized in that

The average particle diameter of the graphite in the particle size distribution is more than 6 μm and less than 10 μm.

4. Electrode body according to claim 2, characterized in that

The average particle diameter of the graphite in the particle size distribution is less than 6 mu m.

5. The electrode body according to any one of claims 2 to 4, characterized in that

The mixing ratio of the graphite to the carbon black is 90: 10 to 25: 75.

6. the electrode body according to any one of claims 1 to 5, characterized in that

The cathode foil forms an enlarged surface layer, and

the carbon layer is formed on the surface expanding layer.

7. The electrode body according to claim 6, characterized in that

The surface expanding layer is in pressure joint with the carbon layer.

8. Electrode body according to claim 6 or 7, characterized in that

The surface enlarging layer includes an uneven surface and pores formed from the uneven surface toward a deep portion of the cathode foil,

the spherical carbon is introduced into the fine pores,

the graphite covers the pores into which the spherical carbon is inserted.

9. The electrode body according to claim 8, characterized in that

The spherical carbon enters the pores by pressure bonding of the carbon layer.

10. The electrode body according to claim 8 or 9, characterized in that

The graphite is deformed along the concave-convex surface of the enlarged surface layer.

11. An electrolytic capacitor, characterized in that:

the electrode body according to any one of claims 1 to 10 is included at the cathode.

12. A method for manufacturing an electrode body for a cathode of an electrolytic capacitor, comprising:

a carbon layer is formed on a cathode foil containing a valve metal, and the carbon layer contains graphite and spherical carbon.

13. The electrode body manufacturing method according to claim 12, characterized in that

The slurry containing the graphite and the spherical carbon is applied to a cathode foil, dried, and then pressure-bonded to form the carbon layer.

Technical Field

The present invention relates to an electrode body, an electrolytic capacitor provided with the electrode body, and a method for manufacturing the electrode body.

Background

The electrolytic capacitor includes a valve metal such as tantalum or aluminum as an anode foil and a cathode foil. The anode foil is formed by forming a valve metal into a sintered body, an etched foil, or the like, and has a dielectric oxide film layer on the surface of the formed surface. An electrolyte is interposed between the anode foil and the cathode foil. The electrolyte adheres to the uneven surface of the anode foil and functions as a true cathode. The electrolytic capacitor obtains capacitance on the anode side by dielectric polarization of the dielectric oxide film layer.

The electrolytic capacitor can be regarded as a series capacitor exhibiting capacitance on the anode side and the cathode side. Therefore, in order to efficiently utilize the anode-side capacitance, the cathode-side capacitance is also very important. The cathode foil is also increased in surface area by etching treatment, but the cathode foil is limited in the extent of surface expansion from the viewpoint of the thickness of the cathode foil.

Therefore, an electrolytic capacitor in which a film of a metal nitride such as titanium nitride is formed on a cathode foil has been proposed (see patent document 1). Titanium was evaporated by a vacuum arc evaporation method, which is one of ion plating (ion plating) methods, in a nitrogen atmosphere, and titanium nitride was deposited on the surface of the cathode foil. The metal nitride is inert and is difficult to form a natural oxide film. Further, the vapor deposition coating forms fine irregularities, and the surface area of the cathode is enlarged.

In addition, an electrolytic capacitor in which a porous carbon layer containing activated carbon is formed on a cathode foil is also known (see patent document 2). The capacitance of the electrolytic capacitor on the cathode side is exhibited by the charge storage effect of an electric double layer (electric double layer) formed on the boundary surface between the polarizing electrode and the electrolyte. Cations of the electrolyte are aligned at the interface with the porous carbon layer, and form a pair with electrons in the porous carbon layer at an extremely short distance, and form a potential barrier (cathode). The cathode foil on which the porous carbon layer is formed can be produced by: the water-soluble binder solution in which porous carbon is dispersed is kneaded to form a paste, and the paste is applied to the surface of a cathode foil and dried by exposure to high temperature.

[ Prior art documents ]

[ patent document ]

Patent document 1: japanese patent laid-open No. 4-61109

Patent document 2: japanese patent laid-open No. 2006-80111

Disclosure of Invention

[ problems to be solved by the invention ]

The evaporation process of the metal nitride is complicated, resulting in high cost of the electrolytic capacitor. In addition, in recent years, it is also assumed that the electrolytic capacitor is used in a wide temperature range from an extremely low temperature environment to a high temperature environment, for example, as in an in-vehicle application. However, in an electrolytic capacitor in which a film of a metal nitride is formed on a cathode foil, the electrostatic capacitance is greatly reduced by exposure to high temperatures for a long period of time. In this case, the capacitance of the electrolytic capacitor is greatly different from the capacitance assumed at first. In the electrolytic capacitor in which the porous carbon layer containing activated carbon is formed on the cathode foil by applying the paste, the electrostatic capacitance is significantly reduced in a high-temperature environment, as compared with the electrolytic capacitor in which the metal nitride film is formed on the cathode foil.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an electrode assembly that can exhibit a stable electrostatic capacitance even after a load is applied to a high-temperature environment, an electrolytic capacitor including the electrode assembly, and a method for manufacturing the electrode assembly.

[ means for solving problems ]

As a result of diligent studies, the present inventors have found that when a carbon layer containing graphite and spherical carbon is formed on a cathode foil, the difference between the initial capacitance and the capacitance after a high-temperature environmental load is reduced when an electrolytic capacitor using the electrode body is used in a low-frequency region. That is, it was found that the decrease in the electrostatic capacitance can be suppressed even when exposed to a high-temperature environment for a long time.

The present invention has been made based on the above-mentioned findings, and in order to solve the above-mentioned problems, the present invention provides an electrode body for a cathode of an electrolytic capacitor, the electrode body including: the valve-acting metal-containing cathode foil comprises a valve-acting metal, and a carbon layer formed on the cathode foil, wherein the carbon layer contains graphite and spherical carbon.

In addition, there has been a problem to be solved in terms of frequency characteristics in the electric double layer action, and when the electrolytic capacitor is intended to be used in a high frequency region, it is not considered that a carbon layer is formed on the cathode foil. In addition, in the low-frequency region, carbon having a small specific surface area of Brunauer-Emmett-Teller (BET) such as graphite or acetylene black is often inferior in capacitance to other carbon materials. However, as a result of diligent studies by the present inventors, the following findings were obtained: when graphite or spherical carbon having a small BET specific surface area, which is often inferior in capacitance to other carbon black in a low frequency range, is combined, there is an advantage in capacitance from the standpoint of torsion in a high frequency range. Based on the knowledge, the spherical carbon may be, for example, acetylene black or the like having a BET specific surface area of 200m²Carbon black in an amount of less than/g.

The graphite may have an average particle diameter in a particle size distribution of 6 to 10 μm.

The graphite may have an average particle diameter in a particle size distribution of 6 μm or less.

The mixing ratio of the graphite to the carbon black may be 90: 10 to 25: 75.

the cathode foil may form a facing layer, and the carbon layer may be formed on the facing layer.

The facing layer and the carbon layer may be crimped.

The surface-enlarging layer may include an uneven surface and pores formed from the uneven surface toward a deep portion of the cathode foil, the spherical carbon may enter the pores, and the graphite may cover the pores into which the spherical carbon has entered.

The spherical carbon may enter the pores by crimping of the carbon layer.

The graphite may be deformed along the uneven surface of the enlarged surface layer.

An electrolytic capacitor including the electrode body at the cathode is also an embodiment of the present invention.

In order to solve the above-described problems, a method for manufacturing an electrode body according to the present invention is a method for manufacturing an electrode body used for a cathode of an electrolytic capacitor, the method including: a carbon layer containing graphite and spherical carbon is formed on a cathode foil containing a valve metal.

The carbon layer may be formed by applying a slurry containing the graphite and the spherical carbon to a cathode foil, drying the applied slurry, and then pressing the dried slurry.

[ Effect of the invention ]

According to the present invention, the cathode body can exhibit a stable electrostatic capacitance even after a high-temperature environmental load.

Drawings

Fig. 1 is a photograph of an adhesive tape attached to a separator (separator).

Fig. 2 is a Scanning Electron Microscope (SEM) photograph showing a cross section of the cathode body.

Fig. 3 is an SEM photograph of a cross section of the cathode bodies of example 3 and reference example 1.

Fig. 4 is an SEM photograph of the cross section of the cathode bodies of example 5 and reference example 2.

Detailed Description

An electrode body according to an embodiment of the present invention and an electrolytic capacitor using the electrode body as a cathode will be described. In the present embodiment, an electrolytic capacitor having an electrolytic solution is exemplified, but the present invention is not limited thereto. Any of electrolytic capacitors having an electrolytic solution, a solid electrolyte layer such as a conductive polymer, a gel electrolyte, or an electrolyte using an electrolytic solution in combination with a solid electrolyte layer and a gel electrolyte can be used.

(electrolytic capacitor)

The electrolytic capacitor is a passive element that stores and discharges electric charge corresponding to the capacitance. The electrolytic capacitor has a wound or laminated capacitor element. The capacitor element is formed by facing the electrode bodies with separators (separators) interposed therebetween and impregnating the capacitor element with an electrolyte. The electrolytic capacitor generates a cathode-side capacitance by an electric double-layer action generated at an interface of an electrode body for a cathode side and an electrolytic solution, and generates an anode-side capacitance generated by a dielectric polarization action at the electrode body for the cathode side. Hereinafter, the electrode body used on the cathode side is referred to as a cathode body, and the electrode body used on the anode side is referred to as an anode foil.

A dielectric oxide coating layer for generating dielectric polarization is formed on the surface of the anode foil. A carbon layer that generates an electrical double-layer effect at the interface with the electrolyte is formed on the surface of the cathode body. The electrolyte is interposed between the anode foil and the cathode body, and is in close contact with the dielectric oxide coating layer of the anode foil and the carbon layer of the cathode body. In order to prevent short circuit between the anode foil and the cathode body, a separator is interposed between the anode foil and the cathode body and holds an electrolyte.

(cathode body)

The cathode body has a two-layer structure of a cathode foil and a carbon layer. The cathode foil serves as a current collector, and preferably has a surface-enlarging layer formed on the surface thereof. The carbon layer contains a carbon material as a main material. The carbon layer is closely attached to the diffusion layer, thereby forming a two-layer structure of the cathode foil and the carbon layer.

The cathode foil is a long foil body made of valve metal. The valve metal is aluminum, tantalum, niobium, titanium, hafnium, zirconium, zinc, tungsten, bismuth, antimony, etc. The purity is preferably about 99% or more, and may contain impurities such as silicon, iron, copper, magnesium, and zinc. As the cathode foil, for example, an aluminum material having a heat treatment symbol H defined by Japanese Industrial Standard (JIS) specification H0001, a so-called H material; an aluminum material having a heat-treated symbol of O defined by JIS H0001, a so-called O material. When a metal foil having high rigidity including an H-material is used, deformation of the cathode foil due to press working described later can be suppressed.

The cathode foil is subjected to a surface enlarging treatment of a metal foil extending the valve metal. The top-up layer is formed by electrolytic etching, chemical etching, sandblasting, or the like, or is formed by vapor deposition on a metal foil, sintering metal particles, or the like. As the electrolytic etching, a method such as dc etching or ac etching can be mentioned. In addition, in the chemical etching, the metal foil is immersed in an acid solution or an alkali solution. The formed enlarged surface layer is a layer region having a tunnel-like etching pit or a sponge-like etching pit etched from the foil surface toward the foil core. The etching pits may be formed so as to penetrate the cathode foil.

In the carbon layer, the carbon material is a mixture of graphite and spherical carbon. Examples of the graphite include natural graphite, artificial graphite, and graphitized ketjen black (ketjen black), and they have a scaly, scaly (massive), earthy, spherical, or flaky form. In order to crush the etching pits and improve the adhesion between the carbon layer and the cathode foil, graphite is also preferably used in a flake or flake form, and the aspect ratio (aspect ratio) of the short diameter to the long diameter is 1: 5-1: 100, or more. Examples of the spherical carbon include carbon black. Examples of the carbon black include ketjen black, acetylene black (acetylene black), channel black (channel black), thermal black (thermal black), etc., and the carbon black preferably has a primary particle diameter of 100nm or less on average and a specific surface area (hereinafter referred to as BET specific surface area) of 200m calculated by BET theory²The ratio of the carbon atoms to the carbon atoms is less than g. BET specific surface area of 200m²Carbon black in the amount of/g or less is, for example, acetylene black.

The carbon layer formed by mixing the graphite and the spherical carbon serves as an electric double-layer active material layer that exhibits cathode-side capacitance using the graphite and the spherical carbon as active materials. When the electrolytic capacitor is used in a low frequency range, the combination of graphite and spherical carbon reduces the difference between the initial capacitance of the electrolytic capacitor and the capacitance after a high-temperature environmental load. That is, the combination of graphite and spherical carbon suppresses a decrease in electrostatic capacitance even when the electrolytic capacitor is exposed to a high-temperature environment for a long time, and improves the thermal stability of the electrolytic capacitor. The initial capacitance is a capacitance at around a normal temperature, for example, 20 ℃ after the electrolytic capacitor is assembled and aged, and the capacitance after a high-temperature environmental load is a capacitance after a long time, for example, 260 hours of exposure to a high-temperature environment, for example, 125 ℃.

In particular graphite and BET specific surface area of 200m²Mixture of spherical carbons not more than gWhen the formed carbon layer is used in a high frequency region, the difference between the initial capacitance of the electrolytic capacitor and the capacitance after a high temperature environmental load is significantly reduced. In general, when the BET specific surface area is small, the electrostatic capacitance of the electrolytic capacitor becomes small. However, in the case of using the electrolytic capacitor in a high frequency region, the specific surface area of the graphite to BET is 200m²A carbon layer formed by mixing spherical carbons of not more than g exhibits a high electrostatic capacitance from the standpoint of twisting when mixed with a carbon material having a large BET specific surface area, such as activated carbon. Namely, the specific surface area of graphite to BET of 200m²A carbon layer formed by mixing spherical carbons of/g or less is preferable because it improves the thermal stability of the electrolytic capacitor and exhibits a high electrostatic capacitance when used in a high frequency range.

Furthermore, the specific surface area of the graphite and BET is 200m²A carbon layer formed by mixing spherical carbons of/g or less significantly reduces the difference between the initial capacitance of the electrolytic capacitor and the capacitance after a high-temperature environmental load even when used in a low-frequency range. Thus, the specific surface area of graphite to BET is 200m²A carbon layer formed by mixing spherical carbons of/g or less has high thermal stability in a wide frequency range in both use in a low frequency range and use in a high frequency range, and is used in general as an electrolytic capacitor.

From the viewpoint of stability of the electrostatic capacitance after a high-temperature environmental load, the graphite preferably has an average particle diameter of 6 μm or more and 10 μm or less in a particle size distribution based on the major axis. The average particle diameter referred to herein means a median particle diameter, so-called D50. When the average particle diameter is 6 μm or more and 10 μm or less, the capacitance equivalent to the initial capacitance is exhibited even after a load in a high-temperature environment. In other words, the initial capacitance is not different from the capacitance after the high-temperature environmental load.

In terms of the size of the capacitance, the graphite preferably has an average particle diameter (D50) of 6 μm or less in the particle size distribution. When the average particle diameter is 6 μm or less, the smaller the particle diameter of the graphite is, the more the capacitance of the electrolytic capacitor can be increased while maintaining the small difference between the initial capacitance of the electrolytic capacitor and the capacitance after the high-temperature environmental load.

First, when the average particle size is about 6 μm, the electrostatic capacitance itself is greatly improved as compared with the case where the average particle size is 10 μm, and the thermal stability of the electrolytic capacitor and the good electrostatic capacitance are both satisfied. When the average particle size is about 6 μm, the electrostatic capacitance after a high-temperature environmental load is equivalent to that of an electrolytic capacitor in which a titanium nitride film is formed on the cathode foil.

Next, when the average particle size is about 4 μm, the capacitance in both the low frequency region and the high frequency region after the high temperature environmental load exceeds that of the electrolytic capacitor in which the titanium nitride film is formed on the cathode foil. That is, if the average particle size is about 4 μm, the electrolytic capacitor assumed to be used in a high-temperature environment is more commonly used than an electrolytic capacitor in which a titanium nitride film is formed on a cathode foil.

Further, when the average particle size is reduced to 1 μm, the electrostatic capacitance in both the low frequency region and the high frequency region exceeds that of an electrolytic capacitor in which a titanium nitride film is formed on a cathode foil, and even exceeds that of an electrolytic capacitor in which activated carbon, which is an active material of a general electric double layer, is used as an active material in a cathode foil, in either the initial electrostatic capacitance or the electrostatic capacitance after a high-temperature environmental load, and is more commonly used.

Further, it is found that when the average particle size is 6 μm or less, graphite is easily retained in the carbon layer. Therefore, if the average particle size is 6 μm or less, the amount of the binder for retaining graphite in the carbon layer can be reduced, which is also preferable in terms of reduction in resistance of the cathode body and reduction in Equivalent Series Resistance (ESR) of the electrolytic capacitor.

Further, the mass ratio of graphite G to spherical carbon C is preferably G: c is 90: 10-25: 75, in the above range. When the mass ratio of graphite exceeds 90 wt%, the difference between the initial capacitance of the electrolytic capacitor and the capacitance of the electrolytic capacitor after a load of a high-temperature environment becomes large. In addition, if only the spherical carbon C is used, the electrostatic capacitance is reduced regardless of whether the carbon C is used in a low frequency region or a high frequency region.

Fig. 2 is an SEM photograph showing a cross section of the cathode body. As shown in fig. 2, the surface of the diffuser layer includes: a rough surface 21 having large undulations, and fine pores 22 formed from the rough surface 21 toward the deep part of the cathode foil. The graphite 11 is preferably deformed along the uneven surface 21 and stacked on the uneven surface 21. The spherical carbon 12 preferably enters the pores 22. In other words, the graphite particles 11 cover the pores 22 in a state where the spherical carbon particles 12 enter the pores 22. The spherical carbon 12 is preferably filled between the graphite particles 11 so as to fill the spaces between the graphite particles 11 stacked on the uneven surface 21.

In the form of such a carbon layer, the carbon layer penetrates into the surface-expanding layer to improve the adhesion and reduce the interface resistance between the carbon layer and the surface-expanding layer. That is, in the form of the carbon layer, the adhesion between the surface-enlarging layer and the carbon layer is improved on the uneven surface 21 of the surface-enlarging layer. In the form of the carbon layer, the graphite 11 serves as a stopper, and the spherical carbon 22 is inserted into the pores and pressed, so that the adhesion between the expanded surface layer and the carbon layer is improved in the pores 22 of the expanded surface layer.

The cathode body can be prepared by preparing slurry of a material containing a carbon layer, forming a surface expanding layer on a cathode foil in advance, coating the slurry on the surface expanding layer, drying and pressing. The top-up layer is typically formed by direct-current etching or alternating-current etching in which direct current or alternating current is applied in an acidic aqueous solution such as nitric acid, sulfuric acid, or hydrochloric acid.

The carbon layer is prepared by dispersing graphite and spherical carbon powder in a solvent and adding a binder to prepare a slurry. The average particle size of the graphite may be adjusted in advance by pulverizing the graphite using a pulverizing device such as a bead mill or a ball mill before the slurry is prepared. The solvent is selected from alcohols such as methanol, ethanol and 2-propanol, hydrocarbon solvents, aromatic solvents, amide solvents such as N-methyl-2-pyrrolidone (NMP) and N, N-Dimethylformamide (DMF), water and mixtures thereof. As a dispersion method, a mixer, jet mixing (jet mixing), ultracentrifuge treatment, other ultrasonic treatment, or the like is used. In the dispersion step, the graphite, the spherical carbon, and the binder in the mixed solution are refined and homogenized, and dispersed in the solution. Examples of the binder include styrene butadiene rubber, polyvinylidene fluoride, and polytetrafluoroethylene.

Next, the slurry is applied to the surface-expanding layer, dried, and then pressed at a predetermined pressure, whereby the graphite and spherical carbon of the carbon layer are arranged in a full state. Further, by pressing, the graphite of the carbon layer is deformed so as to follow the uneven surface of the enlarged surface layer. Further, by pressing, a pressure-bonding stress is applied to the graphite deformed along the uneven surface of the enlarged surface layer, and spherical carbon between the graphite and the enlarged surface layer is pressed into the pores. This ensures the adhesion between the carbon layer and the facing layer.

When the graphite and the spherical carbon are subjected to a porous treatment such as an activation treatment or an opening treatment, a conventionally known activation treatment such as a gas activation method or a chemical activation method may be used as long as the BET specific surface area of the spherical carbon is controlled to 200m²The concentration is below g. Examples of the gas used in the gas activation method include gases containing water vapor, air, carbon monoxide, carbon dioxide, hydrogen chloride, oxygen, and mixtures thereof. In addition, as the drug used in the drug activation method, there can be mentioned: hydroxides of alkali metals such as sodium hydroxide and potassium hydroxide; hydroxides of alkaline earth metals such as calcium hydroxide; inorganic acids such as boric acid, phosphoric acid, sulfuric acid, and hydrochloric acid; or inorganic salts such as zinc chloride. In the activation treatment, heat treatment is performed as necessary.

(Anode foil)

Next, the anode foil is a long foil body made of a valve metal. The purity of the anode foil is preferably about 99.9% or more. The anode foil is formed by etching an elongated foil, or by sintering powder of a valve metal, or by forming a coating by depositing a coating of metal particles or the like on the foil. The anode foil has an etching layer or a porous structure layer on the surface.

The dielectric oxide film layer formed on the anode foil is typically an oxide film formed on the surface layer of the anode foil, and if the anode foil is made of aluminum, it is an aluminum oxide layer obtained by oxidizing the porous structure region. The dielectric oxide film layer is formed by chemical conversion treatment in which a voltage is applied to a solution in which halogen ions are not present, such as an acid such as ammonium borate, ammonium phosphate, or ammonium adipate, or an aqueous solution of such an acid. Further, the cathode foil may be provided with a natural oxide film layer or may be intentionally provided with a dielectric oxide film layer.

(baffle)

Examples of the separator include: cellulose such as kraft paper (kraft), Manila hemp (Manila hemp), esparto grass (esparto), hemp (hemp), rayon (rayon), and mixed paper thereof; polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and derivatives thereof; a polytetrafluoroethylene-based resin; a polyvinylidene fluoride resin; vinylon (vinylon) resin; polyamide resins such as aliphatic polyamides, semi-aromatic polyamides, and wholly aromatic polyamides; a polyimide-based resin; a polyethylene resin; a polypropylene resin; a trimethylpentene resin; polyphenylene sulfide resin; acrylic resins, etc., and these resins may be used alone or in combination, and may be used in combination with cellulose.

(electrolyte)

The electrolyte is a mixed solution in which a solute is dissolved in a solvent and an additive is added as needed. The solvent may be either a protic polar solvent or an aprotic polar solvent. Typical examples of the protic polar solvent include monohydric alcohols, polyhydric alcohols, oxo alcohol compounds, and water. Typical examples of the aprotic polar solvent include sulfone-based, amide-based, lactone-based, cyclic amide-based, nitrile-based, and oxide-based solvents.

Examples of the monohydric alcohol include ethanol, propanol, butanol, pentanol, hexanol, cyclobutanol, cyclopentanol, cyclohexanol, and benzyl alcohol. Examples of the polyhydric alcohols and the oxylic alcohols include ethylene glycol, propylene glycol, glycerin, methyl cellosolve, ethyl cellosolve, methoxypropanol, and dimethoxypropanol. Examples of the sulfone system include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, sulfolane, 3-methyl sulfolane and 2, 4-dimethyl sulfolane. Examples of the amide system include N-methylformamide, N-dimethylformamide, N-ethylformamide, N-diethylformamide, N-methylacetamide, N-dimethylacetamide, N-ethylacetamide, N-diethylacetamide, hexamethylphosphoramide, and the like. Examples of the lactones and cyclic amides include γ -butyrolactone, γ -valerolactone, δ -valerolactone, N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, butylene carbonate, and isobutylene carbonate. Examples of the nitrile system include acetonitrile, 3-methoxypropionitrile, and glutaronitrile. Examples of the oxide include dimethyl sulfoxide. As the solvent, these may be used alone, and two or more kinds may also be combined.

The solute contained in the electrolyte solution contains a component containing an anion and a cation, and typically includes an organic acid or a salt thereof, an inorganic acid or a salt thereof, or a complex compound of an organic acid and an inorganic acid or a salt having an ion dissociability thereof, and two or more kinds thereof may be used alone or in combination. An acid that becomes an anion and a base that becomes a cation may be added to the electrolytic solution as solute components, respectively.

Examples of the organic acid which becomes an anion component in the electrolytic solution include: carboxylic acids, phenols and sulfonic acids such as oxalic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, maleic acid, adipic acid, benzoic acid, toluic acid, heptanoic acid, malonic acid, 1, 6-decanedicarboxylic acid, 1, 7-octanedicarboxylic acid, azelaic acid, undecanedioic acid, dodecanedioic acid and tridecanedioic acid. Further, as the inorganic acid, there can be mentioned: boric acid, phosphoric acid, phosphorous acid, hypophosphorous acid, carbonic acid, silicic acid, and the like. Examples of the complex compound of an organic acid and an inorganic acid include: boric disalicylic acid (borodisalicylic acid), boric disalicylic acid (borodiadic acid), boric diglycolic acid (borodiglycolic acid), and the like.

In addition, as at least one salt of an organic acid, an inorganic acid, and a complex compound of an organic acid and an inorganic acid, there can be mentioned: ammonium salts, quaternary amidinium salts, amine salts, sodium salts, potassium salts, and the like. Examples of the quaternary ammonium ion of the quaternary ammonium salt include tetramethylammonium, triethylmethylammonium, and tetraethylammonium. Examples of the tetraamidinium salt include ethyldimethylimidazolium, tetramethylimidazolium, and the like. Examples of the amine salt include primary amines, secondary amines, and tertiary amines. Examples of the primary amine include methylamine, ethylamine, and propylamine, examples of the secondary amine include dimethylamine, diethylamine, ethylmethylamine, and dibutylamine, and examples of the tertiary amine include trimethylamine, triethylamine, tributylamine, ethyldimethylamine, and ethyldiisopropylamine.

Further, other additives may be added to the electrolytic solution. Examples of additives include: polyethylene glycol, a complex compound of boric acid and a polysaccharide (mannitol, sorbitol, or the like), a complex compound of boric acid and a polyhydric alcohol, a boric acid ester, a nitro compound (o-nitrobenzoic acid, m-nitrobenzoic acid, p-nitrobenzoic acid, o-nitrophenol, m-nitrophenol, p-nitrophenol, or the like), a phosphate ester, colloidal silica, or the like. These may be used alone or in combination of two or more.

In the electrolytic capacitor using the electrolytic solution, when the solid electrolyte is used, the carbon layer in contact with the current collector conducts electricity to the solid electrolyte, and the capacitance of the electrolytic capacitor is formed by the capacitance of the anode side due to the dielectric polarization. When a solid electrolyte is used, polythiophene such as polyethylene dioxythiophene, or a conductive polymer such as polypyrrole or polyaniline can be used.

[ examples ]

The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples.

(example 1)

The electrolytic capacitor of example 1 was produced as follows. First, as for the cathode body, a slurry is prepared by mixing and kneading flake graphite powder and spherical carbon powder as carbon materials, Styrene Butadiene Rubber (SBR) as a binder, and a carboxymethyl cellulose sodium (CMC-Na) aqueous solution as a dispersant-containing aqueous solution. The mixing ratio of the carbon material, the adhesive and the dispersant-containing aqueous solution is 84: 10: 6. further, an aluminum foil from which the electrode lead plate was drawn was prepared as a cathode foil, and the slurry was uniformly applied to the cathode foil.An etching layer was formed in advance by applying a voltage to the aluminum foil in hydrochloric acid. The slurry is coated on the etching layer. And, after drying the slurry, at 150kNcm^-2The carbon layer is fixed to the cathode foil by vertical pressing.

Further, the aluminum foil was subjected to etching treatment so that the normalized formation voltage (nominal formation voltage) was 4V_fsThe dielectric oxide film was formed so as to obtain a projected area of 2.1cm²Aluminum foil having the size of (3) was used as the anode foil. The capacitance of the anode foil is 386 mu Fcm^-2. Then, the cathode and anode were opposed to each other with a separator made of rayon interposed therebetween, and impregnated with an electrolyte to prepare a laminate battery, which was subjected to a common secondary chemical conversion treatment. The electrolyte was prepared using tetramethylimidazolium phthalate as a solute and γ -butyrolactone as a solvent. At the time of chemical conversion again, all the electrolytic capacitors were applied with a voltage of 3.35V for 60 minutes under an environment of 105 ℃.

In the electrolytic capacitor of example 1, flake graphite having an average particle diameter of 10 μm was used, and Acetylene Black (AB) was used as spherical carbon. The acetylene black has an average primary particle diameter of 50nm and a BET specific surface area of 39m²(ii) in terms of/g. Further, the mixing ratio of graphite to acetylene black was set to 75: 25.

(examples 2, 3 and 10)

Electrolytic capacitors of examples 2, 3 and 10 were produced under the same conditions as those of the electrolytic capacitor of example 1. However, in the electrolytic capacitor of example 2, acetylene black was used as spherical carbon, and the mixing ratio of graphite to acetylene black was set to 75: 25, however, flake graphite having an average particle diameter of 6 μm was used. In the electrolytic capacitor of example 3, the mixing ratio of graphite to acetylene black was set to 75: 25, however, flake graphite having an average particle diameter of 4 μm was used. In the electrolytic capacitor of example 10, the mixing ratio of graphite to acetylene black was set to 75: 25, however, flake graphite having an average particle diameter of 0.5 μm was used. That is, the average particle size of the flaky graphite in examples 2, 3 and 10 was changed from that in example 1.

(examples 4 to 9)

Electrolytic capacitors of examples 4 to 9 were produced under the same conditions as those of the electrolytic capacitor of example 1. However, in the electrolytic capacitors of examples 4 to 9, flaky graphite having an average particle diameter of 1 μm was used. The electrolytic capacitors of examples 4 to 9 have different mixing ratios of graphite and acetylene black. In example 4, the mixing ratio of graphite to acetylene black was set to 95: 5, in example 5, the ratio of graphite was reduced to set the mixing ratio of graphite to acetylene black to 90: in example 6, the ratio of graphite was further decreased to set the mixing ratio of graphite to acetylene black at 85: in example 7, the ratio of graphite was further decreased to set the mixing ratio of graphite to acetylene black to 75: in example 8, the ratio of graphite was further decreased to set the mixing ratio of graphite to acetylene black at 50: 50, in example 9, the ratio of graphite was further reduced to set the mixing ratio of graphite to acetylene black to 25: 75.

comparative example 3 and reference example 1

As a comparison with the electrolytic capacitors of examples 4 to 9, electrolytic capacitors of comparative example 3 and reference example 1 were produced. However, in comparative example 3, a carbon layer was formed using only graphite having an average particle size of 1 μm as a carbon material without adding spherical carbon. In reference example 1, a carbon layer was formed using only acetylene black as a carbon material without adding flake graphite. Other conditions were the same as in examples 4 to 9.

(examples 11 and 12)

Electrolytic capacitors of examples 11 and 12 were produced under the same conditions as those of the electrolytic capacitor of example 2. However, the electrolytic capacitor of example 11 differs from example 2 in that ketjen black is used as spherical carbon, but the average particle size of the flaky graphite is 6 μm and the mixing ratio of the flaky graphite to the spherical carbon is 75: 25 are the same in this point. Ketjen black has an average primary particle diameter of 40nm and a BET specific surface area of 800m²(ii) in terms of/g. In the electrolytic capacitor of example 12, the mixing ratio of the flaky graphite was reduced as compared with example 11 to set 50: 50.

(examples 13 and 14)

Electrolytic capacitors of examples 13 and 14 were produced under the same conditions as those of the electrolytic capacitors of examples 11 and 12. However, the electrolytic capacitor of example 13 is different from that of example 11 in that the electrolytic capacitor of example 14 is different from that of example 12 in that the average particle diameter of the flaky graphite is 1 μm.

Comparative examples 1 and 2

Finally, as a comparison with the electrolytic capacitors of examples 1 to 14, electrolytic capacitors of comparative examples 1 and 2 were produced. In the electrolytic capacitor of comparative example 1, a titanium nitride layer was formed by an electron beam evaporation method using an aluminum foil that was not subjected to etching treatment as a current collector, and an aluminum foil having the titanium nitride layer formed thereon was used as a cathode body. In the electrolytic capacitor of comparative example 2, a carbon layer in which activated carbon having an average particle size of 5 μm and acetylene black were mixed was formed using an aluminum foil that was not subjected to etching treatment as a current collector, and the aluminum foil on which the carbon layer was formed was used as a cathode body. The BET specific surface area of the activated carbon was 1500m²(ii) in terms of/g. The BET specific surface area of the acetylene black used in comparative example 2 was 39m²(ii) in terms of/g. The electrolytic capacitors of comparative examples 1 and 2 were the same as those of the respective examples in terms of the composition of the anode foil, separator and electrolytic solution, the production steps and production conditions.

(product test)

The electrostatic capacitance (Cap) of the electrolytic capacitors of examples 1 to 14, comparative examples 1 to 3, and reference example 1 was measured. In the product test, the initial electrostatic capacitance was measured as the electrostatic capacitance (Cap) at 20 ℃ in the case of charging and discharging at 120Hz and 10 kHz. After exposure to a high-temperature environment of 125 ℃ for 260 hours, the capacitance (Cap) at the time of charging and discharging at 120Hz and 10kHz was measured at 20 ℃ as the capacitance after the high-temperature environmental load. The results are shown in table 1 below. Further, in table 1, the rate of change of the capacitance (Δ Cap) with respect to the initial capacitance after the high-temperature environmental load is described for each frequency.

(Table 1)

As shown in table 1, when the electrolytic capacitors were used at 120Hz, which is a low frequency range, the electrolytic capacitors of examples 1 to 14 were superior to the electrolytic capacitors of comparative examples 1 and 2 in the rate of change of the electrostatic capacitance (Δ Cap) with respect to the initial electrostatic capacitance after the high-temperature environmental load. In examples 1 to 14, the carbon layer of the cathode body was formed by mixing graphite with spherical carbon such as acetylene black or ketjen black. On the other hand, when the carbon layer of the cathode body was formed only of graphite as in the electrolytic capacitor of comparative example 3, a significant decrease in initial capacitance was observed as compared with comparative examples 1 and 2, and it was confirmed that the decrease in capacitance was also large after a high-temperature environmental load, and the capacitance was also significantly low in use at 10 kHz. The electrolytic capacitor of reference example 1 was good in the product test, but had poor interface resistance as described below.

From this, it was confirmed that when the carbon layer of the cathode body was formed by mixing graphite with spherical carbon, the electrolytic capacitor had stable capacitance not only in the initial stage but also after a high-temperature environmental load when used in a low frequency region such as 120 Hz.

Next, the electrolytic capacitors of examples 1 to 10 used acetylene black as spherical carbon, but it was confirmed that the rate of change of the electrostatic capacitance (Δ Cap) from the initial electrostatic capacitance after the high-temperature environmental load was good even when the electrolytic capacitor was used at 10kHz, which is a high-frequency region. That is, it was confirmed that an electrolytic capacitor having a cathode body formed with a carbon layer formed by mixing graphite and acetylene black has a stable electrostatic capacitance in a wide frequency range in both use in a low frequency range and use in a high frequency range, and is generally used in terms of electrostatic capacitance after a high-temperature environmental load.

It was also confirmed that the electrolytic capacitors of examples 1 and 2 were not reduced in electrostatic capacitance after a high-temperature environmental load, compared to the initial electrostatic capacitance, whether they were used in a high-frequency range or a low-frequency range. That is, it was confirmed that when the average particle size of graphite is 6 μm or more and 10 μm or less and acetylene black is selected as spherical carbon, the electrolytic capacitor is excellent in thermal stability and operates extremely stably in a wide temperature environment. Further, the electrostatic capacitance itself of the electrolytic capacitor of example 2 was greatly improved as compared with example 1, and the electrostatic capacitance after the high-temperature environmental load was comparable to that of the electrolytic capacitor of comparative example 1 in which a titanium nitride film was formed on the cathode foil. That is, it was confirmed that when the average particle size of graphite is about 6 μm (± 2 μm), the capacity is high and stable even in a high-temperature environment.

It was also confirmed that the electrolytic capacitors of examples 3 to 10 were used in both the high frequency range and the low frequency range, and not only the initial electrostatic capacitance of the electrolytic capacitors of comparative examples 1 and 2 but also the electrostatic capacitance after a high-temperature environmental load was comparable or superior. That is, it was confirmed that when the average particle size of graphite was less than 6 μm and acetylene black was selected as spherical carbon, the BET specific surface area was 39m²Acetylene black in a specific ratio of/g, but comparable to that of 1500m BET surface area²In comparative example 2 of the activated carbon per gram, when the average particle diameter is 1 μm, the electrostatic capacity of the electrolytic capacitor can be improved more than that in comparative example 2. Further, it was confirmed that the reduction of the capacitance after the high-temperature environmental load can be suppressed, and the operation is extremely stable in a wide frequency range in addition to the excellent thermal stability.

(interface resistance)

Here, in the electrolytic capacitors of example 3 and reference example 1, the cross section of the cathode body was photographed by a scanning electron microscope, and the interface resistance value of the carbon layer and the spread layer was measured. Fig. 3 is an SEM photograph of a cross section of the cathode body, fig. 3 (a) is 10,000 times according to example 3, fig. 3 (b) is 10,000 times according to reference example 1, fig. 3 (c) is 25,000 times according to example 3, and fig. 3 (d) is 25,000 times according to reference example 1. The interface resistance value was measured by an electrode resistance measuring system (model RM2610, manufactured by Nissan electric Motor Co., Ltd.). Example 3 is the same as reference example 1 except that example 3 is a carbon layer formed of graphite and carbon black, whereas reference example 1 is a carbon layer formed of carbon black without graphite.

As shown in fig. 3 (a) and (c), in the cathode body of example 3, graphite was deformed and spread along the uneven surface of the finishing layer, and the carbon layer and the finishing layer were closely adhered to each other on the uneven surface. In the cathode body of example 3, it was found that the graphite was used as a cap to press the carbon black into the pores of the expanded layer, and the carbon layer and the expanded layer were also in close contact with each other in the pores. In addition, the graphite is bent, and the bending angle is locally bent to about 90 °. By the graphite bent in the above manner, the carbon black is efficiently pressed into the side surfaces of the uneven surface and the fine pores in the deep part, which are difficult to directly transmit the pressure of pressure bonding.

As described above, in the cathode body of example 3, the carbon layer penetrated into the facing layer. In contrast, in the cathode body of reference example 1, carbon black accumulated on the uneven surface of the enlarged surface layer, but voids were generated at various positions between the carbon layer and the uneven surface. Further, in the cathode body of reference example 1, carbon black entered the pores of the facing layer relatively little, and many voids were generated in the pores.

As a result, the cathode of example 3 had an interfacial resistance of 1.78 m.OMEGA.cm²However, the cathode body of reference example 1 had an interfacial resistance of 2.49 m.OMEGA.cm². That is, it was confirmed that examples 1 to 14 in which both graphite and spherical carbon were contained in the carbon layer exhibited a stable electrostatic capacitance even after a high-temperature environmental load, and also exhibited a low interface resistance value.

(Press Effect test)

Here, the sum is 150kNcm^-2The cathode body of example 3, in which the vertical pressing was performed under the pressing pressure of (1), was compared, and the cathode body of reference example 2, in which the pressing step was omitted, was produced. The cathode body of reference example 2 was produced under the same conditions as in example 3, except for the presence or absence of pressing. Then, the cross sections of the cathode bodies of example 3 and reference example 2 were photographed by a scanning electron microscope. The imaging results are shown in fig. 4. FIG. 4 is an SEM photograph of a cross section of a cathode body, in which (a) of FIG. 4 is 10,000 times as much as that of example 3 and (b) of FIG. 4 is as much as that of referenceConsidering 10,000 times of example 2, (c) of fig. 4 is 25,000 times according to example 3, and (d) of fig. 4 is 25,000 times according to reference example 2.

As shown in fig. 4 (a) and (c), in the cathode body of example 3, graphite was deformed and spread along the uneven surface of the finishing layer, and the carbon layer and the finishing layer were closely adhered to each other on the uneven surface. In the cathode body of example 3, it was found that the graphite was used as a cap to press the carbon black into the pores of the expanded layer, and the carbon layer and the expanded layer were also in close contact with each other in the pores. As described above, in the cathode body of example 3, the carbon layer penetrated into the facing layer.

On the other hand, in the cathode body of reference example 2, the graphite was not deformed along the uneven surface of the enlarged surface layer, and voids were generated at various positions between the carbon layer and the uneven surface. Further, in the cathode body of reference example 2, carbon black entered the pores of the facing layer relatively little, and many voids were generated in the pores.

As a result, it was confirmed that when the slurry was uniformly applied to the cathode foil and dried, and then pressed at a predetermined pressure, graphite was easily deformed and spread along the uneven surface of the facing layer, the carbon layer and the facing layer were easily adhered to each other on the uneven surface, and the interface resistance value was easily lowered. Further, it was confirmed that graphite was used as a pressing cap by pressing, and it was easy to press carbon black into the pores of the expanded layer, and the carbon layer and the expanded layer were also easily adhered to each other in the pores, and the interface resistance value was easily lowered.

(examples 15 and 16)

Using a BET specific surface area of 39m²The electrolytic capacitor of example 7 using acetylene black of 133m BET specific surface area was prepared²Acetylene black/g of the electrolytic capacitor of example 15. The other conditions were the same as those of the electrolytic capacitor of example 7. In addition, the BET specific surface area is 800m²The electrolytic capacitor of example 13 using Ketjen black in terms of/g had a BET specific surface area of 377m²(ii) Ketjen black in g of the electrolytic capacitor of example 16. The other conditions were the same as those of the electrolytic capacitor of example 13.

The electrolytic capacitors of examples 15 and 16 were also subjected to product tests in combinations of the respective frequency ranges for the initial capacitance and the capacitance after the high-temperature environmental load. The results are shown in table 2. Table 2 also shows the results of the product tests of the electrolytic capacitors of examples 7 and 13 with reference.

(Table 2)

As shown in Table 2, it was confirmed that the BET specific surface area exceeded 200m²The electrolytic capacitors of examples 7 and 15 had better rate of change of electrostatic capacitance (Δ Cap) after high temperature environmental load at both 120Hz and 10kHz than the electrolytic capacitors of examples 13 and 16, and the electrolytic capacitors of examples 7 and 15 had BET specific surface area of 200m²A spherical carbon layer of not more than g. That is, it was confirmed that the catalyst composition contains not only acetylene black but also BET specific surface area of 200m²Not only the initial capacitance but also the capacitance stably appears in a wide frequency range even after a high-temperature environmental load.

(carbon fixation test)

The electrolytic capacitors of examples 1, 2, 3 and 7 in which the graphite particles had particle diameters of 10 μm, 6 μm, 4 μm and 1 μm were subjected to carbon material fixation tests. The electrolytic capacitors were disassembled at the stage of capacitor elements, and an adhesive tape (Scotch tape (model 144JP 32-978) manufactured by 3M) was attached to the cathode-side surface of the separator at one time and peeled off, and the adhesion on the adhesive tape was observed. The results are shown in fig. 1. Fig. 1 is a photograph of the peeled adhesive tapes of examples 1, 2, 3 and 7.

In general, it is estimated that graphite is more likely to be separated from the carbon layer as the particle diameter of graphite is smaller, but as shown in fig. 1, it is confirmed that the smaller the particle diameter of graphite is, the smaller the amount of graphite separated from the carbon layer is. In particular, the amount of adhesion to the adhesive tape was reduced in examples 2, 3 and 7 in which the average particle size of graphite was 6 μm or less, as compared with example 1 in which the average particle size of graphite was 10 μm. Therefore, it was confirmed that when the average particle size of graphite is 6 μm or less, the amount of binder that retains the carbon material in the carbon layer can be reduced, the resistance of the cathode body can be reduced, and the ESR of the electrolytic capacitor can be reduced.