Electrolytic capacitor

Abstract

This invention provides an electrolytic capacitor for medium-high voltage applications above 100V, which suppresses the total amount of gas generated within the electrolytic capacitor. The anode foil of the electrolytic capacitor includes: an expanded portion including tunnel-shaped pits formed from the foil surface in the foil thickness direction; and a dielectric oxide film formed on the surface of the expanded portion. The cathode of the electrolytic capacitor includes: a cathode foil containing a valve-acting metal; and a carbon layer formed on the cathode foil.

Description

Technical Field

[0001] This invention relates to an electrolytic capacitor. Background Technology

[0002] An electrolytic capacitor is a passive component that stores and discharges electrical charge through electrostatic capacitance. An electrolytic capacitor is constructed by housing a capacitor element immersed in an electrolyte within an outer casing, sealing the casing with a sealing body, and extending the lead terminals from the sealing body. The capacitor element is constructed by positioning an anode foil and a cathode foil facing each other and placing a separator between the anode and cathode foils. The anode foil has a dielectric oxide film formed on a metal foil, and the cathode foil includes foils of the same or other metals.

[0003] For electrolytic capacitors, such as those used in electric vehicles or in electrical applications, a voltage withstand capability of 100 V or higher is sometimes required. Electrolytic capacitors capable of withstanding medium to high voltages above 100 V require a thick dielectric oxide film. However, as the dielectric oxide film thickens, the electrostatic capacitance decreases. Therefore, electrolytic capacitors for medium to high voltage applications above 100 V include an expanded surface layer on the anode foil consisting of multiple tunnel-like pits. Alternatively, electrolytic capacitors may include an expanded surface layer on the anode foil with tunnel-like pits penetrating the foil, either partially or entirely. Through this expanded surface technology, electrolytic capacitors for medium to high voltage applications above 100 V achieve a large anode foil surface area while ensuring the thickness of the dielectric oxide film.

[0004] [Existing technical documents]

[0005] [Patent Literature]

[0006] Patent Document 1: Japanese Patent Application Publication No. 2014-181368 Summary of the Invention

[0007] [The problem the invention aims to solve]

[0008] However, gases are generated within electrolytic capacitors due to various phenomena. For example, on the anode side, if the dielectric oxide film dissolves and the water in the electrolyte comes into contact with the valve-acting metal, hydrogen gas is generated as the valve-acting metal hydrates and deteriorates. Hydrogen gas is also generated at the foil interface on the cathode side. If the amount of gas generated within the electrolytic capacitor increases, it may cause the outer casing to expand, the valve to open, or leakage.

[0009] On the other hand, in recent years, electrolytic capacitors for medium and high voltage applications above 100 V have required larger electrostatic capacitance. In other words, it is also required to maintain the withstand voltage while making the dielectric oxide film thinner. However, if the dielectric oxide film is made thinner, the contact between the valve metal and the moisture in the electrolyte becomes easier, which increases the chance of reaction between the valve metal and the moisture in the electrolyte, resulting in an increase in the amount of hydrogen produced.

[0010] Therefore, adding gas absorbers or gas control agents such as nitro compounds to the electrolyte of electrolytic capacitors is considered. However, nitro compounds tend to reduce the voltage withstand capability of electrolytic capacitors, and in electrolytic capacitors requiring medium to high voltages above 100 V, it is desirable to reduce the amount added.

[0011] The present invention is proposed to solve the aforementioned problem, and its purpose is to provide an electrolytic capacitor for medium and high voltage applications above 100 V that suppresses the total amount of gas generated inside the electrolytic capacitor.

[0012] [Technical means to solve the problem]

[0013] First, the capacitance occurrence rate is defined. The capacitance occurrence rate is the ratio of the electrolytic capacitor's capacitance to the capacitance on the anode side. That is, the capacitance occurrence rate is the percentage obtained by dividing the combined capacitance of the electrolytic capacitor (considering it as a capacitor connected in series between the anode and cathode sides) by the capacitance on the anode side. The combined capacitance is obtained by multiplying the capacitance on the anode side and the capacitance on the cathode side, and then dividing by the sum of the capacitances on the anode side and the cathode side. Therefore, the capacitance occurrence rate is expressed by Equation 1.

[0014] (Equation 1)

[0015]

[0016] As shown in Equation 1, when the electrostatic capacitance on the anode side is large, the influence of the cathode side on the capacitance occurrence rate becomes greater. On the other hand, when the electrostatic capacitance on the anode side is small, the influence of the cathode side on the capacitance occurrence rate becomes smaller.

[0017] In the field of electrolytic capacitors, the anode foil used for electrolytic capacitors intended for medium-high voltage applications (above 100 V) has a smaller capacitance per unit area compared to the anode foil used for electrolytic capacitors intended for low-voltage applications. This is because in the anode foil used for medium-high voltage applications, the dielectric oxide film on the surface of the expanded layer is thicker to ensure withstand voltage. From the perspective of improving capacitance yield, in electrolytic capacitors in the low-voltage region where the anode-side capacitance is large, increasing the capacitance on the cathode side is very effective in increasing the capacitance yield. However, in electrolytic capacitors intended for medium-high voltage applications where the anode-side capacitance is small, even increasing the cathode-side capacitance has a small effect on improving the capacitance yield.

[0018] For example, as an electrolytic capacitor intended for low-voltage applications, when using 1 cm 2 With an anode foil having an electrostatic capacitance of 10 μF, using per 1 cm 2 The capacitance occurrence rate was 90.9% for a cathode foil with an electrostatic capacitance of 100 μF, making each 1 cm of cathode foil... 2 The capacitance occurrence rate when the electrostatic capacitance reaches 1000 μF is 99.0%, an improvement over the estimated 109% capacitance occurrence rate. On the other hand, for electrolytic capacitors intended for medium and high voltage applications, the capacitance occurrence rate per 1 cm 2 In an anode foil with an electrostatic capacitance of 1 μF, using per 1 cm 2 The capacitance occurrence rate was 99.0% for a cathode foil with an electrostatic capacitance of 100 μF, resulting in a capacitance per 1 cm of cathode foil. 2 When the electrostatic capacitance reaches 1000 μF, the capacitance occurrence rate is 99.9%, and the capacitance occurrence rate hardly increases.

[0019] In electrolytic capacitors intended for medium- to high-voltage applications, even with increased cathode-side electrostatic capacitance, the capacitance occurrence rate remains small. Considering the increased number of steps due to the use of carbon materials, the capacitance of the cathode foil has not been improved. However, the inventors' efforts have shown that in electrolytic capacitors intended for medium- to high-voltage applications above 100 V, forming a carbon layer on the cathode foil suppresses the total amount of gas generated within the electrolytic capacitor.

[0020] This invention was made by the inventors based on the aforementioned insights. The electrolytic capacitor of this invention is an electrolytic capacitor comprising an anode foil and a cathode body. The electrode capacitor of this invention is characterized in that the anode foil comprises: an anode-side expansion portion formed on the surface of the foil, and a dielectric oxide film formed on the surface of the anode-side expansion portion. The cathode body comprises: a cathode foil made of a valve-acting metal and a carbon layer formed on the cathode foil.

[0021] The anode-side expansion section may include tunnel-shaped pits formed from the foil surface toward the foil thickness direction.

[0022] The cathode body may have an enlarged portion on the surface of the cathode foil, and the carbon layer may be formed on the cathode-side enlarged portion.

[0023] The carbon layer can be press-fitted to the cathode side expansion area.

[0024] The carbon layer can penetrate into the cathode side expansion area.

[0025] The cathode-side expansion section may include sponge-like pits, into which the carbon material of the carbon layer may enter.

[0026] The electrolytic capacitor of the present invention may include: an element comprising the anode foil and the cathode; and an electrolyte filling the element, wherein the electrolyte may not contain nitro compounds.

[0027] The cathode may include an insulating layer formed on the surface of the foil, and the carbon layer may be formed on the insulating layer.

[0028] The insulating layer can be a natural oxide film or a chemically converted film.

[0029] The electrolytic capacitor of the present invention may include: an element comprising the anode foil and the cathode; and an electrolyte, which is filled in the element as a solvent containing ethylene glycol.

[0030] Part or all of the tunnel-like pit may penetrate the anode foil.

[0031] The electrolytic capacitor of the present invention can be used for medium and high voltage applications above 100 V.

[0032] [The effects of the invention]

[0033] According to the present invention, even for electrolytic capacitors used in medium and high voltage applications above 100 V, the amount of gas generated inside the electrolytic capacitor can be suppressed. Attached Figure Description

[0034] Figure 1 This is a graph showing the expansion of the lamination units of the electrolytic capacitors of Examples 1 to 4 and Comparative Example 1.

[0035] Figure 2 This is a graph showing the expansion of the lamination units of the electrolytic capacitors of Examples 5 to 13 and Comparative Example 2.

[0036] Figure 3 This is a graph showing the expansion of the outer casing of the electrolytic capacitors of Examples 14 and 15, and Comparative Examples 3 and 4. Detailed Implementation

[0037] The electrode body of an embodiment of the present invention and an electrolytic capacitor using the electrode body as a cathode will be described. In this embodiment, an electrolytic capacitor having an electrolyte is illustrated, but the invention is not limited thereto. The present invention can be applied to any electrolytic capacitor using a gel electrolyte as the electrolyte.

[0038] (Electrolytic capacitor)

[0039] An electrolytic capacitor is a passive component that stores and discharges charge, corresponding to electrostatic capacitance. The electrolytic capacitor has a wound or laminated capacitor element. The capacitor element is formed by placing an anode foil with a dielectric oxide film on its surface facing a cathode separator, and impregnating it with an electrolyte. The electrolyte is in close contact with the uneven surface of the dielectric oxide film included in the anode foil, thus functioning as a true cathode.

[0040] (Cathode)

[0041] The cathode body has a cathode foil, formed by extending the valve-acting metal, as a current collector. The surface of the cathode foil has either a natural oxide film or a chemically converted oxide film. The oxide film is formed naturally or intentionally. A natural oxide film is formed by the reaction of the cathode foil with oxygen in the air, while a chemically converted oxide film is intentionally formed by applying a voltage to a solution free of halide ions, such as an aqueous solution of adipic acid, boric acid, or phosphoric acid. When the valve-acting metal is aluminum foil, the oxide film is aluminum oxide.

[0042] A carbon layer containing carbon material as the main component is formed on the surface of the cathode foil. That is, the cathode body has an oxide film serving as an insulating layer on the cathode foil, which acts as a current collector, and a carbon layer is formed on this oxide film. Furthermore, the carbon layer is located on the outermost surface of the cathode body. When the carbon layer is located on the outermost surface of the cathode body, the total amount of gas generated within the electrolytic capacitor is suppressed. Moreover, it is presumed that the suppression of the total amount of gas generated within the electrolytic capacitor is due to a reduction in the amount of gas generated on the cathode side.

[0043] The carbon layer is preferably in close contact with the cathode foil and is not easily peeled off from the cathode foil even under impact. If the carbon layer is not easily peeled off from the cathode foil, the total amount of gas generated in the electrolytic capacitor is further suppressed. To improve the adhesion between the carbon layer and the cathode foil, it is preferable to form an expanded surface layer on the surface of the cathode foil and form the carbon layer on the expanded surface layer. In addition, to improve the adhesion between the carbon layer and the cathode foil, it is preferable to perform a pressing process on the cathode body including the carbon layer and the cathode foil.

[0044] The cathode body is described in detail. The valve-acting metals constituting the cathode foil include aluminum, tantalum, niobium, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. Ideally, the purity should be approximately 99% or higher, but it may contain impurities such as silicon, iron, copper, magnesium, and zinc. For example, aluminum with the tempering symbol H as specified in Japanese Industrial Standard (JIS) specification H0001 (so-called H-material) or aluminum with the tempering symbol O as specified in JIS specification H0001 (so-called O-material) can be used as the cathode foil.

[0045] The expanded layer is formed through electrolytic etching, chemical etching, or sandblasting, or by vapor deposition or sintering of metal particles onto a foil. For example, electrolytic etching includes alternating current etching. In alternating current etching, the cathode foil is immersed in an acidic aqueous solution containing halide ions, such as hydrochloric acid, and an alternating current is passed through it. In chemical etching, the metal foil is immersed in an acidic or alkaline solution. In short, the expanded layer refers to the area where sponge-like etch pits are formed, or a region with a porous structure formed by the voids between dense powder particles. Furthermore, etch pits can also be tunnel-shaped pits formed by direct current etching, and these tunnel-shaped pits can also be formed by penetrating the cathode foil.

[0046] The carbon material contained in the carbon layer is graphite, carbon black, or a mixture of these. Examples of graphite include natural graphite, artificial graphite, and graphitized Ketjen black. Examples of carbon black include Ketjen black, acetylene black, channel black, and thermal black.

[0047] The carbon material contained in the carbon layer is preferably carbon black, which is spherical carbon. When the extended layer formed on the surface of the cathode foil is an etching pit, by using carbon black with a particle size smaller than the opening diameter of the etching pit, it is easy to penetrate deeper into the etching pit, and the carbon layer is in close contact with the cathode foil.

[0048] Furthermore, the carbon material contained in the carbon layer can also be flake-shaped or scaly graphite or carbon black as spherical carbon. The flake-shaped or scaly graphite is preferably in the range of a minor axis to major axis ratio of 1:5 to 1:100. The carbon black as spherical carbon is preferably in the range of an average primary particle size of 100 nm or less. When a carbon layer containing the aforementioned carbon material is laminated onto a cathode foil, the carbon black is easily incorporated into the fine pores of the expanded layer by the graphite. The graphite easily deforms along the uneven surface of the expanded layer and easily accumulates on the uneven surface. Then, the graphite acts as a pressure cap, preventing the spherical carbon from being incorporated into the fine pores. Therefore, the adhesion and fixation between the carbon layer and the cathode foil are further improved.

[0049] In addition, the carbon layer may also contain activated carbon, carbon nanotubes, or fibrous carbon as carbon materials. Activated carbon is derived from natural plant tissues such as palm, synthetic resins such as phenol, and fossil fuels such as coal, coke, and asphalt. As fibrous carbon, examples include carbon nanotubes (CNTs) and carbon nanofibers (CNFs). Activated carbon or fibrous carbon is preferred because of its large specific surface area due to the delocalization of π electrons.

[0050] Methods for forming a carbon layer on a cathode foil include vacuum evaporation, sputtering, ion plating, chemical vapor deposition (CVD), coating, electrolytic plating, and electroless electroplating. In the coating method, carbon material is dispersed in a dispersion solvent to prepare a slurry, which is then applied to the cathode foil using methods such as slurry casting, doctor blade application, or spraying, and then dried. In the evaporation method, carbon material is evaporated by heating it in a vacuum with an electric current, or by irradiating it with an electron beam in a vacuum, thus forming a carbon film on the cathode foil. In the sputtering method, a target made of carbon material and a cathode foil are placed in a vacuum container, an inert gas is introduced into the container, and a voltage is applied, causing the plasma-generated inert gas to collide with the target, resulting in carbon material particles ejected from the target and deposited on the cathode foil.

[0051] After the carbon layer and cathode foil are stacked, they are preferably joined by pressing. In the pressing process, for example, a pressure roller is used to clamp the cathode body including the carbon layer and cathode foil, and a pressing line pressure is applied. The ideal pressing pressure is 0.01 t / cm. 2 ~100 t / cm 2 The bonding structure at the cathode foil interface is not particularly limited as long as the carbon layer can be pressed together with the cathode foil. If a pressing process is used to press the carbon material into the fine pores of the expanded layer, and the carbon material is deformed along the uneven surface of the expanded layer, the adhesion and fixation between the carbon layer and the cathode body are further improved. In particular, carbon black, as spherical carbon, is kneaded into the fine pores of the expanded layer by the graphite under pressure, and the graphite easily accumulates by deforming along the uneven surface of the expanded layer.

[0052] Furthermore, carbon materials such as graphite or carbon black can also undergo pore-forming treatments such as activation or opening treatments. As a pore-forming treatment, existing and known activation methods such as gas activation and chemical activation can be used. Examples of gases used in gas activation include water vapor, air, carbon monoxide, carbon dioxide, hydrogen chloride, oxygen, or mixtures thereof. Examples of reagents used in chemical activation include: 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. During the activation treatment, heating may be performed as needed.

[0053] (Anode foil)

[0054] The anode foil is a long foil made of valve-acting metal. Ideally, the purity of the anode foil should be approximately 99.9% or higher. The anode foil is formed by forming an extended layer on an extended foil, and then forming a dielectric oxide film on the surface of the extended layer. The extended layer, designed for medium-high voltage applications above 100 V, has multiple tunnel-like pits etched into the foil surface along its thickness direction using DC etching. To address the high capacitance required for medium-high voltage applications above 100 V, the tunnel-like pits can also be formed as a continuous anode foil. Alternatively, the extended layer can be formed by sintering valve-acting metal powder, or by depositing a film of metal particles onto the foil.

[0055] The dielectric oxide film formed on the anode foil is typically an oxide film formed on the surface of the anode foil. If the anode foil is made of aluminum, it is an alumina layer obtained by oxidizing the porous structural regions. The dielectric oxide film is formed by a chemical conversion treatment in a solution free of halide ions, such as ammonium borate, ammonium phosphate, ammonium adipate, or aqueous solutions of these acids, by applying a voltage.

[0056] (Electrolyte)

[0057] Ethylene glycol is the preferred solvent for the electrolyte. Using ethylene glycol as the solvent increases the voltage withstand capability of the electrolytic capacitor, making it suitable for medium to high voltage applications above 100 V. However, as long as the necessary voltage withstand capability is obtained through anode foil expansion and chemical conversion treatment, the solvent can be any of a protic polar solvent or a non-protic polar solvent. Examples of protic polar solvents include monohydric alcohols, polyhydric alcohols, oxyhydric alcohols, and water. Examples of non-protic polar solvents include sulfones, amides, lactones, cyclic amides, nitriles, and sulfoxides.

[0058] Examples of monohydric alcohols include ethanol, propanol, butanol, pentanol, hexanol, cyclobutanol, cyclopentanol, cyclohexanol, and benzyl alcohol. Examples of polyhydric alcohols and oxyhydric alcohols include ethylene glycol, propylene glycol, glycerol, methyl cellosolve, ethyl cellosolve, methoxypropylene glycol, and dimethoxypropanol. Examples of sulfone compounds include dimethyl sulfone, ethylmethyl sulfone, diethyl sulfone, sulfolane, 3-methylsulfolane, and 2,4-dimethylsulfolane. Examples of amide compounds include N-methylformamide, N,N-dimethylformamide, N-ethylformamide, N,N-diethylformamide, N-methylacetamide, N,N-dimethylacetamide, N-ethylacetamide, and hexamethylphosphoramide. Examples of lactones and cyclic amides include γ-butyrolactone, γ-valerolactone, δ-valerolactone, N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, butenyl carbonate, and isobutylene carbonate. Examples of nitrile compounds include acetonitrile, 3-methoxypropionitrile, and glutaronitrile. Examples of sulfoxide compounds include dimethyl sulfoxide. These can be used as solvents alone or in combination of two or more.

[0059] The solutes in the electrolyte contain both anionic and cationic components, typically organic acids or their salts, inorganic acids or their salts, or complex compounds of organic and inorganic acids, or salts with ionic dissociation properties. Two or more can be used alone or in combination. Alternatively, acids that become anions and bases that become cations can be added separately as solute components to the electrolyte.

[0060] Organic acids that serve as anionic components in electrolytes include: oxalic acid, succinic acid, glutaric acid, heptanoic acid, octanoic 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, undecanoic acid, dodecanoic acid, tridecanoic acid, and other carboxylic acids, phenols, and sulfonic acids. In addition, inorganic acids include: boric acid, phosphoric acid, phosphorous acid, hypophosphite, carbonic acid, and silicic acid. Compounds of organic and inorganic acids include: borodisalicylic acid, borodioxalic acid, and borodiglycolic acid.

[0061] In addition, salts of at least one of organic acids, inorganic acids, and complex compounds of organic and inorganic acids can be listed as: ammonium salts, quaternary ammonium salts, quaternary amidonium salts, amine salts, sodium salts, potassium salts, etc. Quaternary ammonium ions, as quaternary ammonium salts, can be listed as tetramethylammonium, triethylmethylammonium, tetraethylammonium, etc. Quaternary amidonium salts can be listed as ethyldimethylimidazolium, tetramethylimidazolium, etc. Amines, as amine salts, can be listed as primary amines, secondary amines, and tertiary amines. Primary amines can be listed as methylamine, ethylamine, propylamine, etc.; secondary amines can be listed as dimethylamine, diethylamine, ethylmethylamine, dibutylamine, etc.; and tertiary amines can be listed as trimethylamine, triethylamine, tributylamine, ethyldimethylamine, ethyldiisopropylamine, etc.

[0062] Furthermore, other additives can be added to the electrolyte. These additives may include: phosphoric acid compounds such as phosphoric acid and phosphate esters; boric acid compounds such as boric acid and borate esters; complex compounds of boric acid with sugar alcohols such as mannitol or sorbitol; polyoxyalkylene polyols such as polyethylene glycol, polyglycerol, and polypropylene glycol; and colloidal silica, etc. These additives improve the voltage withstand capability of the electrolytic capacitor.

[0063] In addition, nitro compounds may be included as additives. Examples of nitro compounds include: o-nitrobenzoic acid, m-nitrobenzoic acid, p-nitrobenzoic acid, o-nitrophenol, m-nitrophenol, p-nitrophenol, p-nitrobenzene, o-nitrophenol, m-nitrophenol, and p-nitrophenol. Nitro compounds have the function of absorbing hydrogen gas. However, nitro compounds reduce the withstand voltage. On the other hand, the electrolytic capacitor suppresses the total amount of gas generated inside the electrolytic capacitor by forming a carbon layer on the cathode foil. Therefore, in order to cope with medium and high voltage applications above 100 V, it is preferable to minimize the amount of nitro compounds added, and more preferably to eliminate them altogether.

[0064] (Partition)

[0065] A separator exists between the anode foil and the cathode to prevent short circuits and to retain the electrolyte. Examples of separators include: kraft paper, Manila hemp, esparto, hemp, rayon, and other cellulose-based papers and their blends; polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, and their derivatives; polytetrafluoroethylene resins; polyvinylidene fluoride resins; vinylon resins; aliphatic polyamides, semi-aromatic polyamides, and fully aromatic polyamides; polyimide resins; polyethylene resins; polypropylene resins; trimethylpentene resins; polyphenylene sulfide resins; and acrylic resins. These resins can be used alone or in combination, and can also be mixed with cellulose. Furthermore, the electrolyte has shape-retaining properties, allowing the separator to be discharged while maintaining the thickness of the electrolyte. Example

[0066] The present invention will now be described in more detail based on embodiments. However, the present invention is not limited to the embodiments described below.

[0067] (Examples 1 to 4)

[0068] (Example 1)

[0069] The electrolytic capacitor of Example 1 was fabricated. Aluminum foil was used as the cathode foil. The aluminum foil was subjected to AC etching to form an expanded surface layer consisting of sponge-like etching pits on both sides of the foil. In the AC etching process, the cathode foil was immersed in an acidic aqueous solution with approximately 8% by weight hydrochloric acid as the main electrolyte at a liquid temperature of 25°C, and an AC current of 10 Hz and a current density of 0.14 A / cm² was applied to the substrate. 2 The current is applied for about 5 minutes to expand both sides of the aluminum foil.

[0070] Next, a chemical conversion treatment is performed on the aluminum foil to form an oxide film on the surface of the expansion layer. In the chemical conversion treatment, after removing the chlorine adhering during the AC etching process with an aqueous phosphoric acid solution, a voltage is applied in an aqueous solution of ammonium dihydrogen phosphate.

[0071] First, the carbon layer of the cathode contains graphite and carbon black as carbon materials. Graphite (G) and carbon black (C) are contained in the carbon layer in a weight ratio of G:C = 75:25. Specifically, a slurry is prepared by mixing and kneading graphite powder, carbon black powder, styrene butadiene rubber (SBR) as a binder, and an aqueous solution of sodium carboxymethyl cellulose (CMC-Na) as a dispersant.

[0072] The slurry is uniformly coated onto the cathode foil. Then, the slurry is heated and dried to evaporate the solvent, followed by pressing of the cathode body. During pressing, the cathode body is clamped with pressure rollers, and a pressure of 5.38 kN / cm² is applied. -1 The carbon layer is fixed onto the cathode foil by a pressing wire. The pressing wire is applied using a pressing machine manufactured by TAKUMI Corporation. The diameter of the pressing roller is 180 mm, the pressing width is 130 mm, and the cathode body is fed at a rate of 3 m / min.

[0073] In addition, aluminum foil is used as the anode foil. The aluminum foil is subjected to DC etching to form an expanded layer consisting of tunnel-like etching pits. In the DC etching process, a first step of pit formation and a second step of pit expansion are employed. The first step involves electrochemically etching the aluminum foil using a direct current in an aqueous solution containing chloride ions. The etching process in the first step is performed at a current density of 400 mA / cm². 2 The etching process was carried out for approximately 1 minute under the specified conditions. In the second step, to expand the pits formed on the aluminum foil after the first step, an electrochemical etching process was performed using a direct current in an aqueous solution containing nitrate ions. The current density in the etching process of the second step was set to 300 mA / cm². 2 It lasted for about 2 minutes.

[0074] After the expansion layer was formed, the anode foil underwent a chemical conversion treatment to form a dielectric oxide film on the surface of the expansion layer. Specifically, a voltage of 286 V was applied in a chemical conversion solution of 4% boric acid at a liquid temperature of 85°C.

[0075] Aluminum tab-shaped leads were ultrasonically connected to the anode foil and cathode body respectively. Then, a 99-fold partition was prepared by alternately inserting the cathode body and anode foil into the folds, so that the cathode body and anode foil faced each other, thus creating a laminate of the cathode body, anode foil, and partition. Kraft paper partitions were used as the partitions.

[0076] The laminate was impregnated with an electrolyte. Ethylene glycol was used as the solvent, and azelaate was added as the solute. No nitro compounds were added to the electrolyte. After impregnation with the electrolyte, the laminate was sealed in a laminated material. This produced an electrolytic capacitor with a laminated cell. Aluminum with a thickness of 110 μm was used as the laminated material. After fabrication of the laminated cell, an aging treatment was performed. The aging treatment involved applying a voltage of 230 V to the laminated cell at room temperature (25°C) for 120 minutes, followed by applying a voltage of 230 V to the laminated cell at a temperature of 85°C for 60 minutes.

[0077] (Example 2)

[0078] The electrolytic capacitor of Example 2 was fabricated. In the electrolytic capacitor of Example 2, the cathode foil was not subjected to AC etching, and no expansion layer was formed on the cathode foil. Furthermore, including the composition of the carbon layer formed on the cathode foil, the pressing process of the cathode body, and the absence of nitro compounds, the electrolytic capacitor of Example 2 was fabricated using the same method and under the same conditions as that of Example 1.

[0079] (Example 3)

[0080] The electrolytic capacitor of Example 3 was fabricated. In the electrolytic capacitor of Example 3, pressing was not performed in the step of forming a carbon layer on the cathode foil. Furthermore, including the formation of the expanded surface layer by AC etching of the cathode foil, the composition of the carbon layer formed on the cathode foil, and the absence of added nitro compounds, the electrolytic capacitor of Example 3 was fabricated using the same method and under the same conditions as that of Example 1.

[0081] (Example 4)

[0082] An electrolytic capacitor of Example 4 was fabricated. In the electrolytic capacitor of Example 4, a cathode body with a carbon layer formed by sputtering was used. An expanded surface layer was formed on the cathode foil, and a natural oxide film was formed as the oxide film. No pressing process was performed in the carbon layer formation step. Furthermore, including the formation of the expanded surface layer by AC etching of the cathode foil and the absence of added nitro compounds, the electrolytic capacitor of Example 4 was fabricated using the same method and under the same conditions as in Example 1.

[0083] (Comparative Example 1)

[0084] An electrolytic capacitor of Comparative Example 1 was fabricated. In the electrolytic capacitor of Comparative Example 1, although an expanded surface layer was formed on the cathode foil, a carbon layer was not formed. Furthermore, including the aspect of not adding nitro compounds, the electrolytic capacitor of Comparative Example 1 was fabricated using the same method and under the same conditions as in Example 1.

[0085] (Gas production measurement test)

[0086] The amount of gas generated in the electrolytic capacitors of Examples 1 to 4 and Comparative Example 1 was measured. A direct current (DC) voltage of 219 V was continuously applied to each electrolytic capacitor at a temperature of 105°C, and the amount of gas generated was measured after 392 hours. The amount of gas generated was measured based on the expansion of the laminated unit. The expansion of the laminated unit was measured according to the Archimedes method. That is, the volume of liquid displaced from the laminated unit was measured by measuring the weight increase when the laminated unit was immersed in water.

[0087] The results of the gas generation measurement are shown in Table 1 below. Table 1 also records the differences in the cathodes of Examples 1 to 4 and Comparative Example 1. Furthermore, based on Table 1, [the following was done / was / etc.]... Figure 1 The chart. Figure 1 This is a graph showing the expansion amount of Examples 1 to 4 and Comparative Example 1.

[0088] (Table 1)

[0089]

[0090] As shown in Table 1 above and Figure 1 As shown, the expansion of the electrolytic capacitor in Comparative Example 1 exceeded 3 cm. 3 In contrast, the maximum expansion of the electrolytic capacitors in Examples 1 to 4 was controlled to be 2.5 cm. 3 As shown in Table 1, in Comparative Example 1, the carbon layer was not stacked on the cathode foil, while in Examples 1 to 4, the carbon layer was stacked on the cathode foil. Therefore, it was confirmed that when a carbon layer is stacked on the cathode foil, the total amount of gas generated in the electrolytic capacitor is suppressed.

[0091] Additionally, as shown in Table 1 above and Figure 1 As shown, the expansion of the electrolytic capacitor in Example 2 is 2.5 cm. 3 In contrast, the maximum expansion of the electrolytic capacitors in Examples 1, 3, and 4 was also controlled to be 2.1 cm. 3 As shown in Table 1, in Example 2, no expanded surface layer was formed on the cathode foil, while in Examples 1, 3, and 4, an expanded surface layer was formed on the cathode foil. Therefore, it was confirmed that forming both an expanded surface layer and a carbon layer on the cathode foil further suppressed the total amount of gas generated within the electrolytic capacitor.

[0092] Additionally, as shown in Table 1 above and Figure 1 As shown, the expansion of the electrolytic capacitor in Example 1 is less than 2 cm. 3 As shown in Table 1, in Examples 3 and 4, the pressing process was omitted when forming the carbon layer on the cathode foil. In contrast, in Example 1, the pressing process was performed when forming the carbon layer on the cathode foil. Therefore, it was confirmed that when an extended surface layer and a carbon layer are formed on the cathode foil, and a pressing process is added when forming the carbon layer, the total amount of gas generated in the electrolytic capacitor is further suppressed.

[0093] (Examples 5 to 13)

[0094] (Example 5)

[0095] The electrolytic capacitor of Example 5 was fabricated. Except for the voltage of the chemical conversion treatment and the aging voltage, the electrolytic capacitor of Example 5 was fabricated using the same method and conditions as in Example 1. In Example 5, compared to Example 1, the voltage during the chemical conversion treatment of the anode foil was increased, and a voltage of 534 V was applied for the chemical conversion treatment. Furthermore, in Example 5, compared to Example 1, the voltage during aging was increased; a voltage of 450 V was applied to the laminating unit at room temperature for 120 minutes, followed by a voltage of 425 V applied at a temperature of 85 degrees Celsius for 60 minutes.

[0096] (Example 6)

[0097] The electrolytic capacitor of Example 6 was fabricated. Except for the voltage of the chemical conversion treatment of the anode foil and the aging voltage, the electrolytic capacitor of Example 6 was fabricated using the same method and under the same conditions as in Example 2. The voltage of the chemical conversion treatment of the anode foil and the aging voltage were the same as in Example 5.

[0098] (Example 7)

[0099] The electrolytic capacitor of Example 7 was fabricated. Except for the voltage of the chemical conversion treatment of the anode foil and the aging voltage, the electrolytic capacitor of Example 7 was fabricated using the same method and under the same conditions as in Example 3. The voltage of the chemical conversion treatment of the anode foil and the aging voltage were the same as in Example 5.

[0100] (Example 8)

[0101] The electrolytic capacitor of Example 8 was fabricated. In the electrolytic capacitor of Example 8, the cathode foil was not AC etched, and no expansion layer was formed on the cathode foil. Furthermore, no pressing process was performed in the step of forming the carbon layer on the cathode foil. Apart from this, including the composition of the carbon layer formed on the cathode foil and the absence of nitro compounds, the electrolytic capacitor of Example 8 was fabricated using the same method and under the same conditions as in Example 1. However, the voltage of the chemical conversion treatment of the anode foil and the aging voltage were the same as in Example 5.

[0102] (Example 9)

[0103] An electrolytic capacitor of Example 9 was fabricated. In the carbon layer of the electrolytic capacitor of Example 9, only carbon black was contained as the carbon material. Specifically, a slurry was prepared by mixing carbon black powder, styrene-butadiene rubber (SBR) as a binder, and an aqueous solution of sodium carboxymethyl cellulose (CMC-Na) containing an aqueous dispersant. Furthermore, including the formation of the expanded surface layer by AC etching of the cathode foil, the pressing process of the cathode body, and the absence of added nitro compounds, the electrolytic capacitor of Example 9 was fabricated using the same method and under the same conditions as in Example 1. However, the voltage of the chemical conversion treatment of the anode foil and the aging voltage were the same as in Example 5.

[0104] (Example 10)

[0105] The electrolytic capacitor of Example 10 was fabricated. In the step of forming the carbon layer on the cathode foil, no pressing process was performed on the electrolytic capacitor of Example 10. Furthermore, including the formation of the expanded surface layer by AC etching of the cathode foil, the composition of the carbon layer formed on the cathode foil, and the absence of added nitro compounds, the electrolytic capacitor of Example 10 was fabricated using the same method and under the same conditions as in Example 9. The voltage of the chemical conversion treatment of the anode foil and the aging voltage were the same as in Example 5.

[0106] (Example 11)

[0107] The electrolytic capacitor of Example 11 was fabricated. In Example 11, the cathode foil was not subjected to AC etching, and no expansion layer was formed on the cathode foil. Furthermore, no pressing process was performed in the step of forming the carbon layer on the cathode foil. In addition, including the composition of the carbon layer formed on the cathode foil and the absence of added nitro compounds, the electrolytic capacitor of Example 11 was fabricated using the same method and under the same conditions as in Example 9. However, the voltage of the chemical conversion treatment of the anode foil and the aging voltage were the same as in Example 5.

[0108] (Example 12)

[0109] The electrolytic capacitor of Example 12 was fabricated. Except for the voltage of the chemical conversion treatment and the aging voltage, the electrolytic capacitor of Example 12 was fabricated using the same method and under the same conditions as in Example 4. The voltage of the chemical conversion treatment and the aging voltage of the anode foil were the same as in Example 5.

[0110] (Example 13)

[0111] The electrolytic capacitor of Example 13 was fabricated. In Example 13, the cathode foil was not subjected to AC etching, and no expansion layer was formed on the cathode foil. Furthermore, no pressing process was performed in the step of forming the carbon layer on the cathode foil. In addition, including the aspect of not adding nitro compounds, the electrolytic capacitor of Example 13 was fabricated using the same method and under the same conditions as in Example 12. The voltage for the chemical conversion treatment of the anode foil and the aging voltage were the same as in Example 5.

[0112] (Comparative Example 2)

[0113] An electrolytic capacitor of Comparative Example 2 was manufactured. The electrolytic capacitor of Comparative Example 2 was manufactured using the same method and under the same conditions as Comparative Example 1, except for the voltage of the chemical conversion treatment and the aging voltage. The voltage of the chemical conversion treatment of the anode foil and the aging voltage were the same as in Example 5.

[0114] (Gas production measurement test)

[0115] The amount of gas generated by the electrolytic capacitors of Examples 5 to 13 and Comparative Example 2 was measured. The method and conditions for measuring the amount of gas generated were the same as those of Examples 1 to 4 and Comparative Example 1, except for the applied voltage and the timing of the expansion measurement. Specifically, a DC voltage of 409 V was continuously applied to the electrolytic capacitors of Examples 5 to 13 and Comparative Example 2 at a temperature of 105°C, and the amount of gas generated was measured after 232 hours.

[0116] Table 2 below shows the measurement results of gas generation. Three samples from each of the examples and the comparative example were prepared, and the average value of the three samples was taken as the measurement result. Table 2 also records the differences in the cathodes of Examples 5 to 13 and Comparative Example 2. Furthermore, based on Table 2, [the following was done / was / etc.]. Figure 2 The chart. Figure 2 This is a graph showing the expansion amount of Examples 5 to 13 and Comparative Example 2.

[0117] (Table 2)

[0118]

[0119] As shown in Table 2 and Figure 2 As shown, the expansion of the electrolytic capacitor in Comparative Example 2 exceeded 1.5 cm. 3 In contrast, the expansion of the electrolytic capacitors in Examples 5 to 13 was also controlled to a maximum of 1.01 cm. 3 As shown in Table 2, in Comparative Example 2, the carbon layer was not stacked on the cathode foil, while in Examples 5 to 13, the carbon layer was stacked on the cathode foil. Therefore, the results of Examples 5 to 13 and Comparative Example 2 also confirmed that if a carbon layer is stacked on the cathode foil, the total amount of gas generated in the electrolytic capacitor is suppressed.

[0120] Table 2 above and Figure 2 In this comparison, electrolytic capacitors of Examples 5 to 8, which have the same carbon layer structure, were examined. Example 6, which underwent pressing, showed suppressed expansion compared to Example 8, which did not form an expanded layer or undergo pressing. Example 7, which formed an expanded layer, showed suppressed expansion compared to Example 8, which did not form an expanded layer or undergo pressing. Furthermore, Example 5, which formed an expanded layer and underwent pressing, showed good expansion compared to any of Examples 6 to 8. Additionally, electrolytic capacitors of Examples 9 to 11, which have a structure containing only carbon black as the carbon material in the carbon layer, were compared. Compared to Examples 10 and 11, which did not undergo pressing, Example 9, which underwent pressing, showed suppressed expansion.

[0121] Therefore, in the results of Examples 5 to 13 and Comparative Example 2, it was confirmed that when an expanded surface layer and a carbon layer are formed on the cathode foil, or when a pressing process is performed on the basis of forming a carbon layer on the cathode foil, there is a tendency to further suppress the total amount of gas generated in the electrolytic capacitor.

[0122] Additionally, in Table 2 above and Figure 2In comparing Example 7 and Example 10, which differ only in the structure of the carbon layer, the expansion of Example 7, which mixes graphite and the carbon layer, was suppressed. That is, it was confirmed that when graphite, in addition to carbon black, is selected as the carbon material contained in the carbon layer, the total amount of gas generated in the electrolytic capacitor is further suppressed.

[0123] (Example 14)

[0124] Furthermore, the electrolytic capacitor of Example 14 was fabricated. Unlike Example 1, where the capacitor element was sealed in a laminated material, the electrolytic capacitor of Example 14 was inserted into an aluminum outer casing and sealed with a sealing body. The outer casing was a cylindrical, bottomed tube with a side thickness of 0.4 mm. The chemical conversion treatment conditions for the anode foil differed from those of Example 1; in Example 14, a voltage of 650 V was applied in a chemical conversion solution of 4% by weight boric acid at a liquid temperature of 85°C. Additionally, the aging treatment conditions differed from those of Example 1; in Example 14, a voltage of 481 V was applied for 95 minutes at room temperature (30°C). Furthermore, including the composition of the carbon layer formed on the cathode foil, the pressing process of the cathode body, and the absence of added nitro compounds, the electrolytic capacitor of Example 14 was fabricated using the same method and under the same conditions as that of Example 1.

[0125] (Example 15)

[0126] An electrolytic capacitor of Example 15 was fabricated. The electrolytic capacitor of Example 15 differs from that of Example 14 in the presence or absence of a nitro compound in the electrolyte. In the electrolytic capacitor of Example 15, p-nitrobenzyl alcohol was added to the electrolyte as a nitro compound. The amount of nitro compound added was 2% by weight. Furthermore, including the composition of the carbon layer formed on the cathode foil and the pressing process of the cathode body, the electrolytic capacitor of Example 15 was fabricated using the same method and under the same conditions as that of Example 14.

[0127] (Comparative Example 3)

[0128] An electrolytic capacitor of Comparative Example 3 was prepared. In the electrolytic capacitor of Comparative Example 3, no carbon layer was formed on the cathode. Furthermore, including the aspect of not adding nitro compounds, the electrolytic capacitor of Comparative Example 3 was prepared by the same method and under the same conditions as that of Example 13.

[0129] (Comparative Example 4)

[0130] An electrolytic capacitor of Comparative Example 4 was prepared. In the electrolytic capacitor of Comparative Example 4, no carbon layer was formed on the cathode. However, in the electrolytic capacitor of Comparative Example 4, p-nitrobenzyl alcohol was added to the electrolyte as a nitro compound. The amount of nitro compound added was 2% by weight. In addition, the electrolytic capacitor of Comparative Example 4 was prepared by the same method and under the same conditions as Comparative Example 3.

[0131] (Gas production measurement test)

[0132] The gas generation of the electrolytic capacitors in Examples 14 and 15, and Comparative Examples 3 and 4 was measured. A DC voltage of 450 V was continuously applied to each electrolytic capacitor at a temperature of 105°C, and the gas generation was measured at various time points after 3000 hours. Regarding the gas generation, the area of ​​maximum expansion of the outer casing was selected as the measurement site, and the change in radius of the measurement site was visually measured.

[0133] Figure 3 The results of the gas production measurement are shown. Figure 3 In the examples, the black diamond-shaped mark is Example 14, the black circular mark is Example 15, the white circular mark is Comparative Example 3, and the white diamond-shaped mark is Comparative Example 4. Figure 3 This is a graph showing the expansion of the outer casing relative to the passage of time. The horizontal axis represents the elapsed time, and the vertical axis represents the expansion of Examples 14 and 15, as well as Comparative Examples 3 and 4. Furthermore, the differences in the cathode bodies of Examples 14 and 15, and Comparative Examples 3 and 4 are summarized in Table 3 below. As shown in Table 3, the difference between Comparative Examples 3 and 4 and Examples 14 and 15 is the presence or absence of a carbon layer, and the difference between Examples 14 and 15 is the presence or absence of the addition of a nitro compound.

[0134] (Table 3)

[0135]

[0136] As shown in Table 3 and Figure 3 As shown, Comparative Example 4, in which a nitro compound was added to the electrolyte, reached the expansion limit of the outer casing (1.5 mm) later than Comparative Example 3, in which no nitro compound was added. This confirms that the nitro compound suppressed gas generation. However, the electrolytic capacitor of Comparative Example 4 also reached the expansion limit of the outer casing after 1500 hours. On the other hand, as shown in Table 3 and... Figure 3 As shown, in Examples 14 and 15, in which a carbon layer is formed on a cathode foil with an expanded surface layer by pressing, the expansion of the outer casing is suppressed to a low degree and the expansion amount does not reach the limit.

[0137] Furthermore, a comparison with Examples 14 and 15 shows that the degree of expansion of the outer casing did not change significantly due to the presence or absence of the nitro compound. The electrolytic capacitor of Example 5 did not contain the nitro compound in the electrolyte, while the electrolytic capacitor of Example 15 contained the nitro compound in the electrolyte. That is, it was confirmed that if a carbon layer is stacked on the electrode foil, the total amount of gas generated inside the electrolytic capacitor is suppressed; therefore, the nitro compound, which acts as a gas absorbent, can be omitted. This also improves the voltage withstand capability of the electrolytic capacitor.

Claims

1. An electrolytic capacitor, comprising an anode foil, a cathode, and an electrolyte, characterized in that, The anode foil includes: The anode-side expansion portion is formed on the foil surface; and A dielectric oxide film is formed on the surface of the expanded portion, and The cathode body includes: Cathode foil, containing valve-acting metal; A cathode-side expansion portion is formed on the surface of the cathode foil; and A carbon layer is formed on the cathode-side expansion portion of the cathode foil, pressed against the cathode-side expansion portion and extending into the cathode-side expansion portion, and the carbon layer is scaly graphite, spherical carbon black, or a mixture thereof. The cathode body includes an insulating layer formed on the surface of the foil. The carbon layer is formed on the insulating layer. The insulating layer is a chemically converted film.

2. The electrolytic capacitor according to claim 1, characterized in that... The anode-side expansion section includes tunnel-shaped pits formed from the foil surface toward the foil thickness direction.

3. The electrolytic capacitor according to claim 1 or 2, characterized in that... The cathode-side expansion portion includes sponge-like pits. The carbon material of the carbon layer enters the sponge-like pit.

4. The electrolytic capacitor according to claim 1 or 2, characterized in that... include: The element includes the anode foil and the cathode body; as well as Electrolyte, filled in the element, and The electrolyte does not contain nitro compounds.

5. The electrolytic capacitor according to claim 1 or 2, characterized in that... include: The element includes the anode foil and the cathode body; as well as An electrolyte, which is a solvent containing ethylene glycol, is filled into the element.

6. The electrolytic capacitor according to claim 2, characterized in that... The tunnel-like pit may extend partially or entirely through the anode foil.

7. The electrolytic capacitor according to claim 1 or 2, characterized in that, It is used for medium and high voltage applications above 100 V.

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