Electrolytic capacitor and method for manufacturing the same

Abstract

To provide an electrolytic capacitor for intermediate and high levels of voltages of at least 100 V, in which the total amount of gas to be generated in an electrolytic capacitor is suppressed.SOLUTION: A positive electrode foil of an electrolytic capacitor includes: a diffusion part including a tunnel-shaped pit formed from a foil surface to a foil-thickness direction; and a dielectric oxide coating film formed in the surface of the diffusion part. The negative electrode body of the electrolytic capacitor has a negative electrode foil formed of a valve-action metal and a carbon layer formed on the negative electrode foil.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an electrolytic capacitor.

Background Art

[0002] An electrolytic capacitor is a passive element that stores and discharges electric charges according to its capacitance. An electrolytic capacitor is configured by housing a capacitor element impregnated with an electrolytic solution in an outer case, sealing the outer case with a sealing body, and drawing out lead terminals from the sealing body. The capacitor element is configured by opposing an anode foil having a dielectric oxide film formed on a valve metal foil and a cathode foil made of a foil of the same or another metal, with a separator interposed between the anode foil and the cathode foil.

[0003] There are cases where an electrolytic capacitor is required to have a withstand voltage of 100 V or more, such as in in-vehicle applications such as electric vehicles or in power applications. An electrolytic capacitor capable of withstanding medium to high voltages of 100 V or more requires a thick dielectric oxide film. However, when the dielectric oxide film becomes thick, the capacitance decreases. Therefore, an electrolytic capacitor for medium to high voltage applications of 100 V or more is provided with an enlarged surface layer composed of a large number of tunnel-shaped pits on the anode foil. Further, the electrolytic capacitor is provided with an enlarged surface layer having tunnel-shaped pits that penetrate the foil partially or entirely on the anode foil. Thus, by means of the enlarged surface technology, an electrolytic capacitor for medium to high voltage applications of 100 V or more aims to increase the large surface area of the anode foil while ensuring the thickness of the dielectric oxide film.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Incidentally, various phenomena cause gas generation inside an electrolytic capacitor. For example, on the anode side, when the dielectric oxide film dissolves and the moisture in the electrolytic solution comes into contact with the valve-acting metal, hydrogen gas is generated along with the hydration deterioration of the valve-acting metal. Hydrogen gas is also generated at the foil interface on the cathode side. When the amount of gas generated inside the electrolytic capacitor increases, there is a risk of causing the swelling, valve opening, or liquid leakage of the outer package case.

[0006] On the other hand, in recent years, for electrolytic capacitors for medium and high voltage applications of 100 V or more, a further large capacitance has been demanded. In other words, it is also required to thin the dielectric oxide film while maintaining the withstand voltage. However, when thinning the dielectric oxide film, the contact between the valve-acting metal and the moisture in the electrolytic solution becomes easy, the reaction opportunity between the valve-acting metal and the moisture in the electrolytic solution increases, and a problem occurs in that the amount of hydrogen gas generated increases.

[0007] Therefore, it is conceivable to add a gas absorbent or a gas control agent such as a nitro compound to the electrolytic solution of the electrolytic capacitor. However, nitro compounds tend to lower the withstand voltage of the electrolytic capacitor, and it is desirable to reduce the addition amount in electrolytic capacitors that require a medium and high voltage of 100 V or more.

[0008] The present invention has been proposed to solve the above problems, and its object is to provide an electrolytic capacitor for medium and high voltage applications of 100 V or more that suppresses the total amount of gas generated inside the electrolytic capacitor.

Means for Solving the Problems

[0009] First, the capacitance appearance rate is defined. The capacitance appearance rate is the ratio of the capacitance of the electrolytic capacitor to the capacitance on the anode side. That is, the capacitance appearance rate is the percentage of the ratio obtained by dividing the combined capacitance obtained by regarding the electrolytic capacitor as a capacitor in which the anode side and the cathode side are connected in series by the anode side capacitance. The combined capacitance is obtained by dividing the multiplication result of the anode side capacitance and the cathode side capacitance by the sum of the anode side capacitance and the cathode side capacitance. Therefore, the capacitance appearance rate is expressed by the following formula 1.

[0010] (Formula 1) TIFF2025108719000001.tif16161

[0011] As shown in Formula 1, when the capacitance on the anode side is large, the influence of the cathode side on the capacitance appearance rate becomes large. On the other hand, when the capacitance on the anode side is small, the influence of the cathode side on the capacitance appearance rate becomes small.

[0012] Here, in the field of electrolytic capacitors, for anode foils for electrolytic capacitors for so-called medium and high voltage applications of 100 V or more, the capacitance per unit area is smaller than that of anode foils for electrolytic capacitors for low voltage applications. This is because in the anode foil for electrolytic capacitors for medium and high voltage applications, the dielectric oxide film on the surface of the extended surface layer becomes thick in order to ensure the withstand voltage. From the viewpoint of improving the capacitance appearance rate, in electrolytic capacitors in the low voltage region where the capacitance on the anode side is large, in order to increase the capacitance appearance rate, the effect of increasing the capacitance on the cathode side is large. However, in electrolytic capacitors for medium and high voltage applications where the capacitance on the anode side is small, even if the capacitance on the cathode side is improved, the effect on the capacitance appearance rate is small.

[0013] For example, as an electrolytic capacitor for low voltage applications, when using an anode foil with a capacitance of 10 μF per 1 cm 2 and a cathode foil with a capacitance of 100 μF per 1 cm 2 , the capacitance appearance rate is 90.9%. However, when the capacitance of the cathode foil per 1 cm 2 is changed to 1000 μF, the capacitance appearance rate becomes 99.0%, and an improvement in the capacitance appearance rate of 109% is expected. On the other hand, as an electrolytic capacitor for medium and high voltage applications, in an anode foil with a capacitance of 1 μF per 1 cm 2 , when using a cathode foil with a capacitance of 100 μF per 1 cm 2 , the capacitance appearance rate is 99.0%. However, when the capacitance of the cathode foil per 1 cm 2 is changed to 1000 μF, the capacitance appearance rate is 99.9% and the capacitance appearance rate hardly improves.

[0014] In electrolytic capacitors for medium- and high-voltage applications where improving the capacitance on the cathode side has little effect on the capacitance appearance rate, considering factors such as an increase in the number of processes due to the use of carbon materials, the capacitance of the cathode foil has not been improved. However, as a result of the intensive research by the present inventors, it has been found that in electrolytic capacitors for medium- and high-voltage applications of 100 V or more, when a carbon layer is formed on the cathode foil, the total amount of gas generated in the electrolytic capacitor is suppressed.

[0015] The present invention has been made based on the findings obtained by the present inventors. The electrolytic capacitor of the present invention is an electrolytic capacitor including an anode foil and a cathode body. The anode foil has an anode-side enlarged portion formed on the foil surface and a dielectric oxide film formed on the surface of the anode-side enlarged portion. The cathode body has a cathode foil made of a valve-acting metal and a carbon layer formed on the cathode foil.

[0016] The anode-side enlarged portion may have tunnel-shaped pits formed from the foil surface in the foil thickness direction.

[0017] 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.

[0018] The carbon layer and the cathode-side enlarged portion may be in pressure contact.

[0019] The carbon layer may penetrate into the cathode-side enlarged portion.

[0020] The cathode-side enlarged portion may be composed of sponge-like pits, and the carbon material of the carbon layer may penetrate into the sponge-like pits.

[0021] The device includes an element composed of the anode foil and the cathode body and an electrolyte filled in the element. The electrolyte may not contain nitro-based compounds.

[0022] The cathode body may include an insulating layer formed on the foil surface, and the carbon layer may be formed on the insulating layer.

[0023] The insulating layer may be a natural oxide film or a conversion film.

[0024] An element composed of the anode foil and the cathode body, a solvent containing ethylene glycol, and an electrolyte filled in the element may be provided.

[0025] Some or all of the tunnel-shaped pits may penetrate the anode foil.

[0026] It may be used for medium and high voltage applications of 100V or more.

Advantages of the Invention

[0027] According to the present invention, even in an electrolytic capacitor for medium and high voltage applications of 100V or more, the amount of gas generated in the electrolytic capacitor can be suppressed.

Brief Description of the Drawings

[0028]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0029] The electrode body according to the embodiment of the present invention and an electrolytic capacitor using this electrode body as a cathode will be described. In this embodiment, an electrolytic capacitor having an electrolytic solution will be exemplified and described, but the present invention is not limited thereto. The present invention can be applied to any electrolytic capacitor using a gel electrolyte as an electrolyte.

[0030] (Electrolytic capacitor) An electrolytic capacitor is a passive component that stores and discharges electric charges according to its capacitance. This electrolytic capacitor has a wound type or multilayer type capacitor element. The capacitor element is formed by opposing an anode foil with a dielectric oxide film formed on its surface and a cathode body via a separator and impregnating it with an electrolytic solution. The electrolytic solution adheres closely to the uneven surface of the dielectric oxide film provided on the anode foil and functions as a true cathode.

[0031] (Cathode body) The cathode body has a cathode foil formed by stretching a valve action metal as a current collector. A natural oxide film or a formed oxide film is formed on the surface of the cathode foil. A natural or intentionally formed oxide film is formed. The natural oxide film is formed by the reaction of the cathode foil with oxygen in the air, and the formed oxide film is an oxide film intentionally formed by a forming process in which a voltage is applied in a solution without halogen ions such as an aqueous solution of adipic acid, boric acid, phosphoric acid, etc. When the valve action metal is an aluminum foil, the oxide film is aluminum oxide.

[0032] A carbon layer containing a carbon material as a main material is formed on the surface of this cathode foil. That is, the cathode body has an oxide film, which is an insulating layer, on the cathode foil that is a current collector, and has a carbon layer on this oxide film. And 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 generation in the electrolytic capacitor is suppressed. In addition, it is presumed that the total amount of gas generation in the electrolytic capacitor is suppressed due to a decrease in the amount of gas generation on the cathode side.

[0033] The carbon layer is preferably in close contact with the cathode foil and is difficult to peel off from the cathode foil even by impact. When the carbon layer is difficult to peel off from the cathode foil, the total amount of gas generation in the electrolytic capacitor is further suppressed. In order to improve the adhesion between the carbon layer and the cathode foil, it is preferable to form a roughened layer on the surface of the cathode foil and form a carbon layer on the roughened layer. Also, in order to improve the adhesion between the carbon layer and the cathode foil, it is preferable to press-process the cathode body composed of the carbon layer and the cathode foil.

[0034] This cathode body will be described in detail. The valve-acting metal constituting the cathode foil is aluminum, tantalum, niobium, titanium, hafnium, zirconium, zinc, tungsten, bismuth, antimony, etc. The purity is desirably about 99% or more, but it may contain impurities such as silicon, iron, copper, magnesium, and zinc. As the cathode foil, for example, an aluminum material with a temper symbol of H as defined in JIS standard H0001, so-called H material, or an aluminum material with a temper symbol of O as defined in JIS standard H0001, so-called O material may be used.

[0035] The enlarged surface layer is formed by electrolytic etching, chemical etching, sandblasting, etc., or by vapor-depositing or sintering metal particles, etc. on the foil body. Examples of electrolytic etching include alternating current etching. In the alternating current etching process, for example, the cathode foil is immersed in an acidic aqueous solution containing halogen ions such as hydrochloric acid, and an alternating current is passed through. In chemical etching, the metal foil is immersed in an acid solution or an alkali solution. That is, the enlarged surface layer refers to a region having a porous structure formed by a region of sponge-like etching pits or voids between densely packed powders. Incidentally, the etching pits may be tunnel-shaped pits formed by direct current etching, or the tunnel-shaped pits may be formed so as to penetrate the cathode foil.

[0036] The carbon material contained in the carbon layer is graphite, carbon black, or a mixture thereof. Examples of graphite include natural graphite, artificial graphite, graphitized ketjen black, etc. Examples of carbon black include ketjen black, acetylene black, channel black, and thermal black.

[0037] The carbon material contained in the carbon layer is preferably carbon black which is spherical carbon. When the enlarged surface layer formed on the surface of the cathode foil is an etching pit, by using carbon black having a particle diameter smaller than the opening diameter of the etching pit, it is easier to enter deeper into the etching pit, and the carbon layer adheres closely to the cathode foil.

[0038] Further, the carbon material contained in the carbon layer may be flaky or scaly graphite and carbon black which is spherical carbon. The flaky or scaly graphite preferably has an aspect ratio of the minor axis to the major axis in the range of 1:5 to 1:100. The carbon black which is spherical carbon preferably has an average primary particle diameter of 100 nm or less. When a carbon layer containing this combination of carbon materials is laminated on the cathode foil, the carbon black is easily rubbed into the pores of the enlarged surface layer by the graphite. The graphite is easily deformed along the uneven surface of the enlarged surface layer and is easily stacked on the uneven surface. And the graphite serves as a pressing lid to hold the spherical carbon rubbed into the pores. Therefore, the adhesion and fixing property between the carbon layer and the cathode foil are further enhanced.

[0039] In addition, the carbon layer may contain activated carbon, carbon nanohorns, or fibrous carbon as the carbon material. The activated carbon is made from natural plant tissues such as coconut husks, synthetic resins such as phenol, and fossil fuels such as coal, coke, and pitch. Examples of the fibrous carbon include carbon nanotubes (hereinafter referred to as CNTs), carbon nanofibers (hereinafter referred to as CNFs), and the like. Activated carbon and fibrous carbon are preferable because the π electrons are delocalized and the specific surface area is large.

[0040] Examples of the method for forming the carbon layer on the cathode foil include vacuum evaporation, sputtering, ion plating, CVD method, coating, electroplating, electroless plating, and the like. In the case of the coating method, the carbon material is dispersed in a dispersion solvent to prepare a slurry, and the slurry is applied and dried on the cathode foil by a slurry casting method, a doctor blade method, a spray spraying method, or the like. In the case of the evaporation method, the carbon material is evaporated by heating it by passing an electric current in a vacuum, or the carbon material is evaporated by irradiating it with an electron beam in a vacuum, and a carbon film is formed on the cathode foil. Further, in the case of the sputtering method, a target made of the carbon material and the cathode foil are placed in a vacuum chamber, an inert gas is introduced into the vacuum chamber, and a voltage is applied to cause the plasmaized inert gas to collide with the target, and the particles of the carbon material knocked out from the target are deposited on the cathode foil.

[0041] After laminating the carbon layer and the cathode foil, it is preferably pressure-bonded by pressing. In pressing, for example, a cathode body composed of a carbon layer and a cathode foil is sandwiched between press rollers and a press line pressure is applied. The pressing pressure is desirably about 0.01 to 100 t / cm 2 degree. If the carbon layer and the cathode foil can be pressure-bonded, there is no particular limitation on the pressure-bonded structure generated at the interface of the cathode foil. However, by pressing, the carbon material can be pushed into the pores of the expanded surface layer, and the carbon material can be deformed along the uneven surface of the expanded surface layer. In this way, the adhesion and fixing property between the carbon layer and the cathode body are further improved. In particular, carbon black, which is spherical carbon, is rubbed into the pores of the expanded surface layer by graphite under pressing pressure, and the graphite is deformed along the uneven surface of the expanded surface layer and is easy to stack.

[0042] In addition, carbon materials such as graphite and carbon black may be subjected to a porous treatment such as an activation treatment or an opening treatment. As the porous treatment, conventionally known activation treatments such as a gas activation method and a chemical activation method can be used. Examples of the gas used in the gas activation method include water vapor, air, carbon monoxide, carbon dioxide, hydrogen chloride, oxygen, or a gas composed of a mixture thereof. Examples of the chemical used in the chemical activation method 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 this activation treatment, heat treatment is performed as necessary.

[0043] (Anode foil) The anode foil is a long foil made of a valve metal. The purity is desirably about 99.9% or more with respect to the anode foil. This anode foil is formed by forming an enlarged surface layer on the stretched foil and forming a dielectric oxide film on the surface of the enlarged surface layer. The enlarged surface layer is for medium and high voltage applications of 100V or more, and has a large number of tunnel-shaped pits dug from the foil surface in the thickness direction by DC etching. In order to cope with the increase in capacitance in medium and high voltage applications of 100V or more, the tunnel-shaped pits may be formed to penetrate the anode foil. Alternatively, the enlarged surface layer is formed by sintering the powder of the valve metal, or by depositing a film such as metal particles on the foil to form a film.

[0044] The dielectric oxide film formed on the anode foil is typically an oxide film formed on the surface layer of the anode foil. If the anode foil is made of aluminum, it is an aluminum oxide layer obtained by oxidizing a porous structure region. This dielectric oxide film is formed by a forming process in which a voltage is applied in a solution free of halogen ions such as an acid such as ammonium borate, ammonium phosphate, ammonium adipate, or an aqueous solution of these acids.

[0045] (Electrolyte) The solvent of the electrolyte is preferably ethylene glycol. When ethylene glycol is used as the solvent, the withstand voltage of the electrolytic capacitor is improved, making it suitable for medium and high voltage applications of 100V or more. However, as long as the withstand voltage required by the surface enlargement treatment and the forming treatment on the anode foil can be obtained, the solvent may be either a protic polar solvent or an aprotic polar solvent. Representative examples of protic polar solvents include monohydric alcohols, polyhydric alcohols, oxyalcohol compounds, and water. Representative examples of aprotic polar solvents include sulfones, amides, lactones, cyclic amides, nitriles, and oxides.

[0046] Examples of monohydric alcohols include ethanol, propanol, butanol, pentanol, hexanol, cyclobutanol, cyclopentanol, cyclohexanol, benzyl alcohol, and the like. Examples of polyhydric alcohols and oxyalcohol compounds include ethylene glycol, propylene glycol, glycerin, methyl cellosolve, ethyl cellosolve, methoxypropylene glycol, dimethoxypropanol, and the like. Examples of sulfones include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, sulfolane, 3-methyl sulfolane, 2,4-dimethyl sulfolane, and the like. Examples of amides include N-methylformamide, N,N-dimethylformamide, N-ethylformamide, N,N-diethylformamide, N-methylacetamide, N,N-dimethylacetamide, N-ethylacetamide, N,N-diethylacetamide, hexamethylphosphoric amide, and the like. Examples of lactones and cyclic amides include γ-butyrolactone, γ-valerolactone, δ-valerolactone, N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, butylene carbonate, isobutylene carbonate, and the like. Examples of nitriles include acetonitrile, 3-methoxypropionitrile, glutaronitrile, and the like. Examples of oxides include dimethyl sulfoxide and the like. These may be used alone as the solvent, or in combination of two or more kinds.

[0047] The solute contained in the electrolyte contains anionic and cationic components, and typically is an organic acid or its salt, an inorganic acid or its salt, or a composite compound of an organic acid and an inorganic acid or its ion-dissociable salt, and is used alone or in combination of two or more kinds. The acid serving as the anion and the base serving as the cation may be separately added to the electrolyte as solute components.

[0048] Examples of organic acids that become anion components in the electrolyte include carboxylic 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, enanthic acid, malonic acid, 1,6-decanedicarboxylic acid, 1,7-octanedicarboxylic acid, azelaic acid, undecanedioic acid, dodecanedioic acid, tridecanedioic acid, etc., phenols, and sulfonic acids. Examples of inorganic acids include boric acid, phosphoric acid, phosphorous acid, hypophosphorous acid, carbonic acid, silicic acid, etc. Examples of composite compounds of organic acids and inorganic acids include borodisalicylate, boromalonate, borodiglycolate, etc.

[0049] Examples of at least one kind of salt of an organic acid, an inorganic acid, and a composite compound of an organic acid and an inorganic acid include ammonium salts, quaternary ammonium salts, quaternized amidinium salts, amine salts, sodium salts, potassium salts, etc. Examples of quaternary ammonium ions of quaternary ammonium salts include tetramethylammonium, triethylmethylammonium, tetraethylammonium, etc. Examples of quaternized amidinium include ethyldimethylimidazolinium, tetramethylimidazolinium, etc. Examples of amines of amine salts include primary amines, secondary amines, and tertiary amines. Examples of primary amines include methylamine, ethylamine, propylamine, etc., examples of secondary amines include dimethylamine, diethylamine, ethylmethylamine, dibutylamine, etc., and examples of tertiary amines include trimethylamine, triethylamine, tributylamine, ethyldimethylamine, ethyldiisopropylamine, etc.

[0050] Furthermore, other additives can also be added to the electrolyte. 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 and sugar alcohols such as mannitol and sorbitol, polyoxyalkylene polyols such as polyethylene glycol, polyglycerin, and polypropylene glycol, colloidal silica, etc., and these can improve the withstand voltage of the electrolytic capacitor.

[0051] In addition, a nitro compound may be included as an additive. Examples of the nitro compound 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. The nitro compound has an action of absorbing hydrogen gas. However, the nitro compound reduces the breakdown voltage. On the other hand, in this electrolytic capacitor, by forming a carbon layer on the cathode foil, the total amount of gas generation in the electrolytic capacitor is suppressed. Therefore, in order to cope with medium and high voltage applications of 100 V or more, it is preferable to reduce the addition amount of the nitro compound as much as possible, and it is more preferable not to contain it.

[0052] (Separator) The separator is interposed between the anode foil and the cathode body to prevent a short circuit between the anode foil and the cathode body, and holds the electrolytic solution. The separator includes cellulose such as kraft, manila hemp, esparto, hemp, rayon, and mixed papers thereof, polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and their derivatives, polytetrafluoroethylene resins, polyvinylidene fluoride resins, vinylon resins, polyamide resins such as aliphatic polyamides, semi-aromatic polyamides, and wholly aromatic polyamides, polyimide resins, polyethylene resins, polypropylene resins, trimethylpentene resins, polyphenylene sulfide resins, acrylic resins, etc. These resins can be used alone or in combination, and can also be used in combination with cellulose. In addition, when the electrolyte has shape retention and the thickness of the electrolyte is maintained, the separator may be excluded.

[0053] (Examples) Hereinafter, the present invention will be described in more detail based on examples. Note that the present invention is not limited to the following examples.

[0054] (Examples 1 to 4) (Example 1) The electrolytic capacitor of Example 1 was fabricated. Aluminum foil was used as the cathode foil. The aluminum foil was subjected to AC etching treatment to form an enlarged surface layer composed of sponge-like etching pits on both sides of the foil. In the AC etching treatment, the cathode foil was immersed in an acidic aqueous solution with a liquid temperature of 25 °C and about 8 wt% hydrochloric acid as the main electrolyte, and a current of AC 10 Hz and a current density of 0.14 A / cm 2 was applied to the base material for about 5 minutes to enlarge both sides of the aluminum foil.

[0055] Next, the aluminum foil was subjected to formation treatment to form an oxide film on the surface of the enlarged surface layer. In the formation treatment, chlorine attached during the AC etching treatment was removed with an aqueous phosphoric acid solution, and then a voltage was applied in an aqueous solution of ammonium dihydrogen phosphate.

[0056] First, the carbon layer of the cathode body contained graphite and carbon black as carbon materials. Graphite (G) and carbon black (C) were contained in the carbon layer at a weight ratio of G:C = 75:25. Specifically, a slurry was prepared by mixing 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-containing aqueous solution and kneading them.

[0057] This slurry was uniformly applied to the cathode foil. Then, after heating and drying the slurry to volatilize the solvent, the cathode body was subjected to pressing. In the pressing, the cathode body was sandwiched between press rollers, and a press line pressure of 5.38 kNcm -1 was applied to fix the carbon layer on the cathode foil. The press line pressure was applied using a press machine manufactured by Takumi Giken Co., Ltd. The diameter of the press roller was 180 mm, the press treatment width was 130 mm, and the cathode body was conveyed once at 3 m / min.

[0058] Also, an aluminum foil was used as the anode foil. The aluminum foil was subjected to a direct current etching treatment to form an enlarged surface layer composed of tunnel-shaped etching pits. In the direct current etching treatment, a first step of forming pits and a second step of enlarging the pits were used. In the first step, the aluminum foil was electrochemically etched with a direct current in an aqueous solution containing chlorine ions. The etching treatment in the first step was carried out at a current density of 400 mA / cm 2 for about 1 minute. In the second step, in order to enlarge the pits formed on the aluminum foil that had undergone the first step, an electrochemical etching treatment was carried out with a direct current in an aqueous solution containing nitrate ions. The current density of the etching treatment in the second step was 300 mA / cm 2 and it was carried out for about 2 minutes.

[0059] After forming the enlarged surface layer, a forming treatment was performed on the anode foil to form a dielectric oxide film on the surface of the enlarged surface layer. Specifically, a voltage of 286 V was applied in a forming solution of 4 wt% boric acid at a liquid temperature of 85°C.

[0060] Tab-shaped lead terminals made of aluminum were ultrasonically connected to the anode foil and the cathode body, respectively. Then, a separator folded ninety times was prepared, and the cathode body and the anode foil were alternately sandwiched at each fold to oppose the cathode body and the anode foil through the separator, thereby producing a laminate of the cathode body, the anode foil, and the separator. As the separator, a kraft-based separator was used.

[0061] The laminate was impregnated with an electrolytic solution. The electrolytic solution used ethylene glycol as a solvent and azelate as a solute. No nitro compound was added to the electrolytic solution. After impregnating the electrolytic solution, the laminate was sealed with a laminate material. Thereby, an electrolytic capacitor of a laminated cell was produced. As the laminate material, an aluminum one with a thickness of 110 μm was used. After producing the laminated cell, an aging treatment was performed. The aging treatment was to apply a voltage of 230 V to the laminated cell at room temperature (25°C) for 120 minutes, and then apply a voltage of 230 V at a temperature environment of 85°C for 60 minutes.

[0062] (Example 2) An electrolytic capacitor of Example 2 was manufactured. For the electrolytic capacitor of Example 2, an alternating current etching treatment was not performed on the cathode foil, and an enlarged surface layer was not formed on the cathode foil. Other than that, including the composition of the carbon layer formed on the cathode foil, the pressing process on the cathode body, and the fact that no nitro compound was added, the electrolytic capacitor of Example 2 was manufactured by the same method and under the same conditions as Example 1.

[0063] (Example 3) An electrolytic capacitor of Example 3 was manufactured. For the electrolytic capacitor of Example 3, the pressing process was not performed in the process of forming the carbon layer on the cathode foil. Other than that, including the formation of the enlarged surface layer by the alternating current etching treatment on the cathode foil, the composition of the carbon layer formed on the cathode foil, and the fact that no nitro compound was added, the electrolytic capacitor of Example 3 was manufactured by the same method and under the same conditions as Example 1.

[0064] (Example 4) An electrolytic capacitor of Example 4 was manufactured. In the electrolytic capacitor of Example 4, a cathode body on which a carbon layer was formed by a sputtering method was used. An enlarged surface layer was formed on the cathode foil, and a natural oxide film was formed as the oxide film. In the process of forming the carbon layer, the pressing process was not performed. Other than that, including the formation of the enlarged surface layer by the alternating current etching treatment on the cathode foil and the fact that no nitro compound was added, the electrolytic capacitor of Example 4 was manufactured by the same method and under the same conditions as Example 1.

[0065] (Comparative Example 1) An electrolytic capacitor of Comparative Example 1 was manufactured. In the electrolytic capacitor of Comparative Example 1, although an enlarged surface layer was formed on the cathode foil, no carbon layer was formed. Other than that, including the fact that no nitro compound was added, the electrolytic capacitor of Comparative Example 1 was manufactured by the same method and under the same conditions as Example 1.

[0066] (Gas Generation Amount Measurement Test) The gas generation amounts of the electrolytic capacitors of Examples 1 to 4 and Comparative Example 1 were measured. A voltage of DC 219V was continuously applied to each electrolytic capacitor in a temperature environment of 105°C, and the gas generation amount after 392 hours was measured. The gas generation amount was measured by the swelling amount of the laminate cell. The swelling amount of the laminate cell was measured by the Archimedes method. That is, the volume of the liquid displaced by the laminate cell was measured by measuring the increase in weight when the laminate cell was immersed in water.

[0067] The measurement results of the gas generation amount are shown in Table 1 below. In Table 1 below, the differences in the cathode bodies of Examples 1 to 4 and Comparative Example 1 are also described. Also, based on Table 1, the graph of FIG. 1 was created. FIG. 1 is a graph showing the swelling amounts of Examples 1 to 4 and Comparative Example 1. (Table 1) TIFF2025108719000002.tif71161

[0068] As shown in Table 1 above and FIG. 1, the swelling amount of the electrolytic capacitor of Comparative Example 1 exceeded 3 cm 3 whereas the swelling amounts of the electrolytic capacitors of Examples 1 to 4 were at most 2.5 cm 3 and were within the range. As shown in Table 1, in Comparative Example 1, the carbon layer was not laminated on the cathode foil, whereas in Examples 1 to 4, the carbon layer was laminated on the cathode foil. Therefore, it was confirmed that laminating a carbon layer on the cathode foil suppresses the total amount of gas generation in the electrolytic capacitor.

[0069] Also, as shown in Table 1 above and FIG. 1, the swelling amount of the electrolytic capacitor of Example 2 was 2.5 cm 3 whereas the swelling amounts of the electrolytic capacitors of Examples 1, 3, and 4 were at most 2.1 cm 3 and were within the range. As shown in Table 1, in Example 2, the enlarged surface layer was not formed on the cathode foil, whereas in Examples 1, 3, and 4, the enlarged surface layer was formed on the cathode foil. Therefore, it was confirmed that forming an enlarged surface layer and a carbon layer on the cathode foil further suppresses the total amount of gas generation in the electrolytic capacitor.

[0070] Also, as shown in Table 1 above and FIG. 1, the swelling amount of the electrolytic capacitor of Example 1 was 2 cm 3 was interrupted. As shown in Table 1, in Examples 3 and 4, pressing was omitted when forming the carbon layer on the cathode foil, whereas in Example 1, pressing was performed when forming the carbon layer on the cathode foil. Therefore, it was confirmed that when forming the enlarged surface layer and the carbon layer on the cathode foil and adding pressing during the formation of the carbon layer, the total amount of gas generation in the electrolytic capacitor was further suppressed.

[0071] (Examples 5 to 13) (Example 5) An electrolytic capacitor of Example 5 was manufactured. The electrolytic capacitor of Example 5 was manufactured by the same method and under the same conditions as in Example 1, except for the voltage of the formation treatment and the voltage of the aging. In Example 5, compared with Example 1, the voltage during the formation treatment of the anode foil was increased, and a formation treatment was performed by applying a voltage of 534 V. Also, in Example 5, compared with Example 1, the voltage during aging was increased, and a voltage of 450 V was applied to the laminate cell at room temperature for 120 minutes, and then a voltage of 425 V was applied at a temperature environment of 85 degrees Celsius for 60 minutes.

[0072] (Example 6) An electrolytic capacitor of Example 6 was manufactured. The electrolytic capacitor of Example 6 was manufactured by the same method and under the same conditions as in Example 2, except for the voltage of the formation treatment of the anode foil and the voltage of the aging. The voltage of the formation treatment of the anode foil and the voltage of the aging are the same as in Example 5.

[0073] (Example 7) An electrolytic capacitor of Example 7 was manufactured. The electrolytic capacitor of Example 7 was manufactured by the same method and under the same conditions as in Example 3, except for the voltage of the formation treatment of the anode foil and the voltage of the aging. The voltage of the formation treatment of the anode foil and the voltage of the aging are the same as in Example 5.

[0074] (Example 8) An electrolytic capacitor of Example 8 was fabricated. For the electrolytic capacitor of Example 8, no AC etching was performed on the cathode foil, and no enlarged surface layer was formed on the cathode foil. Also, in the process of forming the carbon layer on the cathode foil, no pressing process was carried out. Other than that, including the fact that the composition of the carbon layer formed on the cathode foil and no nitro compound was added, the electrolytic capacitor of Example 8 was fabricated by the same method and under the same conditions as in Example 1. However, the voltage for the formation treatment of the anode foil and the voltage for aging were the same as in Example 5.

[0075] (Example 9) An electrolytic capacitor of Example 9 was fabricated. The carbon layer of the electrolytic capacitor of Example 9 contained only carbon black 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 carboxymethyl cellulose sodium (CMC-Na) as an aqueous solution containing a dispersant and kneading them. Other than that, including the formation of the enlarged surface layer by AC etching treatment on the cathode foil, the pressing process on the cathode body, and the fact that no nitro compound was added, the electrolytic capacitor of Example 9 was fabricated by the same method and under the same conditions as in Example 1. However, the voltage for the formation treatment of the anode foil and the voltage for aging were the same as in Example 5.

[0076] (Example 10) An electrolytic capacitor of Example 10 was fabricated. In the process of forming the carbon layer on the cathode foil of the electrolytic capacitor of Example 10, no pressing process was carried out. Other than that, including the formation of the enlarged surface layer by AC etching treatment on the cathode foil, the composition of the carbon layer formed on the cathode foil, and the fact that no nitro compound was added, the electrolytic capacitor of Example 10 was fabricated by the same method and under the same conditions as in Example 9. The voltage for the formation treatment of the anode foil and the voltage for aging were the same as in Example 5.

[0077] (Example 11) An electrolytic capacitor of Example 11 was fabricated. For the electrolytic capacitor of Example 11, AC etching was not performed on the cathode foil, and no enlarged surface layer was formed on the cathode foil. Also, pressing was not performed in the process of forming the carbon layer on the cathode foil. Other than that, including the fact that no nitro compound was added, the electrolytic capacitor of Example 11 was fabricated by the same method and under the same conditions as Example 9. However, the voltage for the formation treatment of the anode foil and the voltage for aging were the same as those of Example 5.

[0078] (Example 12) An electrolytic capacitor of Example 12 was fabricated. The electrolytic capacitor of Example 12 was fabricated by the same method and under the same conditions as Example 4, except for the voltage for the formation treatment and the voltage for aging. The voltage for the formation treatment of the anode foil and the voltage for aging were the same as those of Example 5.

[0079] (Example 13) An electrolytic capacitor of Example 13 was fabricated. For the electrolytic capacitor of Example 13, AC etching was not performed on the cathode foil, and no enlarged surface layer was formed on the cathode foil. Also, pressing was not performed in the process of forming the carbon layer on the cathode foil. Other than that, including the fact that no nitro compound was added, the electrolytic capacitor of Example 13 was fabricated by the same method and under the same conditions as Example 12. The voltage for the formation treatment of the anode foil and the voltage for aging were the same as those of Example 5.

[0080] (Comparative Example 2) An electrolytic capacitor of Comparative Example 2 was fabricated. For the electrolytic capacitor of Comparative Example 2, it was fabricated by the same method and under the same conditions as Comparative Example 1, except for the voltage for the formation treatment and the voltage for aging. The voltage for the formation treatment of the anode foil and the voltage for aging were the same as those of Example 5.

[0081] (Gas Generation Amount Measurement Test) The gas generation amounts of the electrolytic capacitors of Examples 5 to 13 and Comparative Example 2 were measured. The measurement method and conditions of the gas generation amount were the same as those for Examples 1 to 4 and Comparative Example 1, except for the applied voltage and the timing of measuring the swelling amount. That is, for the electrolytic capacitors of Examples 5 to 13 and Comparative Example 2, a voltage of DC409V was continuously applied in a temperature environment of 105°C, and the gas generation amount after 232 hours was measured.

[0082] The measurement results of the gas generation amount are shown in Table 2 below. Three samples were prepared for each example and comparative example, and the average value of the three samples was used as the measurement result. In Table 2 below, the differences in the cathode bodies of Examples 5 to 13 and Comparative Example 2 are also described. Also, based on Table 2, the graph in FIG. 2 was created. FIG. 2 is a graph showing the swelling amounts of Examples 5 to 13 and Comparative Example 2. (Table 2) TIFF2025108719000003.tif121161

[0083] As shown in Table 2 and FIG. 2 above, the swelling amount of the electrolytic capacitor of Comparative Example 2 exceeded 1.5 cm 3 whereas the swelling amounts of the electrolytic capacitors of Examples 5 to 13 were at most 1.01 cm 3 As shown in Table 2, in Comparative Example 2, the carbon layer was not laminated on the cathode foil, whereas in Examples 5 to 13, the carbon layer was laminated on the cathode foil. Therefore, also from the results of Examples 5 to 13 and Comparative Example 2, it was confirmed that laminating a carbon layer on the cathode foil suppresses the total amount of gas generation in the electrolytic capacitor.

[0084] In Table 2 and FIG. 2, the electrolytic capacitors of Examples 5 to 8 with the same carbon layer configuration are compared. Example 6 with pressing applied has a swelling amount suppressed compared to Example 8 without an enlarged surface layer and without pressing. Example 7 with an enlarged surface layer formed has a swelling amount suppressed compared to Example 8 without an enlarged surface layer and without pressing. Further, Example 5 with an enlarged surface layer formed and pressing applied has a better swelling amount compared to any of Examples 6 to 8. Also, the electrolytic capacitors of Examples 9 to 11 with a configuration in which only carbon black is contained as the carbon material in the carbon layer are compared. Example 9 with pressing applied has a swelling amount suppressed compared to Examples 10 and 11 without pressing applied.

[0085] Thus, from the results of Examples 5 to 13 and Comparative Example 2, it was confirmed that when an enlarged surface layer and a carbon layer are formed on the cathode foil, or when a carbon layer is formed on the cathode foil and then pressing is applied, the total amount of gas generation in the electrolytic capacitor tends to be further suppressed.

[0086] Also, in Table 2 and FIG. 2, when comparing Example 7 and Example 10 which differ only in the configuration of the carbon layer, Example 7 with graphite mixed in the carbon layer has a more suppressed swelling amount. That is, it was confirmed that when graphite is selected as the carbon material to be contained in the carbon layer in addition to carbon black, the total amount of gas generation in the electrolytic capacitor is further suppressed.

[0087] (Example 14) Furthermore, an electrolytic capacitor of Example 14 was fabricated. The electrolytic capacitor of Example 14 was inserted into an aluminum exterior case and sealed with a sealing body, while the capacitor element of Example 1 was sealed with a laminate material. The exterior case is a cylindrical bottomed cylinder with a side thickness of 0.4 mm. The conditions for the formation treatment of the anode foil were different from those of Example 1. In Example 14, a voltage of 650 V was applied in a formation solution of boric acid at a liquid temperature of 85°C and 4 wt%. Also, the conditions for the aging treatment were different from those of Example 1. In Example 14, a voltage of 481 V was applied at room temperature (30°C) for 95 minutes. Otherwise, the electrolytic capacitor of Example 14 was fabricated by the same method and under the same conditions as Example 1, including the composition of the carbon layer formed on the cathode foil, the pressing process for the cathode body, and the fact that no nitro compound was added.

[0088] (Example 15) 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 electrolytic solution. In the electrolytic capacitor of Example 15, p-nitrobenzyl alcohol was added as a nitro compound to the electrolytic solution. The addition amount of the nitro compound is 2 wt%. Otherwise, the electrolytic capacitor of Example 15 was fabricated by the same method and under the same conditions as Example 14, including the composition of the carbon layer formed on the cathode foil and the pressing process for the cathode body.

[0089] (Comparative Example 3) An electrolytic capacitor of Comparative Example 3 was fabricated. In the electrolytic capacitor of Comparative Example 3, no carbon layer was formed on the cathode body. Otherwise, the electrolytic capacitor of Comparative Example 3 was fabricated by the same method and under the same conditions as Example 13, including the fact that no nitro compound was added.

[0090] (Comparative Example 4) An electrolytic capacitor of Comparative Example 4 was fabricated. In the electrolytic capacitor of Comparative Example 4, no carbon layer was formed on the cathode body. However, in the electrolytic capacitor of Comparative Example 4, paranitrobenzyl alcohol was added as a nitro compound to the electrolytic solution. The addition amount of the nitro compound was 2% by weight. Otherwise, the electrolytic capacitor of Comparative Example 4 was fabricated by the same method and under the same conditions as those of Comparative Example 3.

[0091] (Gas generation amount measurement test) The gas generation amounts of the electrolytic capacitors of Examples 14 and 15 and Comparative Examples 3 and 4 were measured. A voltage of DC450V was continuously applied to each electrolytic capacitor in a temperature environment of 105°C, and the gas generation amount at each time until 3000 hours had elapsed was measured. The gas generation amount was measured visually by selecting the maximum expansion location of the outer case as the measurement location and measuring the change amount of the radius at the measurement location.

[0092] The measurement results of the gas generation amount are shown in FIG. 3. In FIG. 3, the black diamond marks represent Example 14, the black circle marks represent Example 15, the white circle marks represent Comparative Example 3, and the white diamond marks represent Comparative Example 4. FIG. 3 is a graph showing the swelling amount of the outer case with the passage of time, with the elapsed time on the horizontal axis and the swelling amounts of Examples 14 and 15 and Comparative Examples 3 and 4 on the vertical axis. 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 differences between Comparative Examples 3 and 4 with respect to Examples 14 and 15 are the presence or absence of the carbon layer, and the difference between Example 14 and Example 15 is the presence or absence of the addition of the nitro compound.

[0093] (Table 3) TIFF2025108719000004.tif61141

[0094] As shown in Table 3 and FIG. 3, in Comparative Example 4 where a nitro compound was added to the electrolytic solution, the time for the swelling amount, which is the swelling limit of the exterior case, to reach 1.5 mm was slower than that in Comparative Example 3 where no nitro compound was added. That is, it was confirmed that the nitro compound suppresses the gas generation amount. However, even in the electrolytic capacitor of Comparative Example 4, when the time exceeded 1500 hours, the swelling amount reached the swelling limit of the exterior case. On the other hand, as shown in Table 3 and FIG. 3, in Examples 14 and 15 where a carbon layer was formed on the cathode foil having an enlarged surface layer with pressing, the swelling of the exterior case was suppressed to a low level and the swelling amount did not reach the limit.

[0095] Moreover, as can be seen from the comparison with Examples 14 and 15, the degree of swelling of the exterior case did not change significantly depending on the presence or absence of the nitro compound. The electrolytic capacitor of Example 5 did not contain a nitro compound in the electrolytic solution, and the electrolytic capacitor of Example 15 contained a nitro compound in the electrolytic solution. That is, if a carbon layer is laminated on the electrode foil, the total amount of gas generation in the electrolytic capacitor can be suppressed, and it was confirmed that the nitro compound, which is a gas absorbent, can be made not to be contained. Thereby, the withstand voltage of the electrolytic capacitor can also be improved.

Claims

1. An electrolytic capacitor comprising an anode foil and a cathode body, wherein the anode foil has an anodic side extended portion formed on the foil surface, and a dielectric oxide film formed on the surface of the extended portion, and the cathode body has a cathode foil made of a valve action metal, and a carbon layer formed on the cathode foil, and is characterized by the above.

2. The electrolytic capacitor according to claim 1, wherein the anodic side extended portion has tunnel-shaped pits formed from the foil surface in the foil thickness direction.

3. The electrolytic capacitor according to claim 1 or 2, wherein the cathode body has a cathodic side extended portion on the surface of the cathode foil, and the carbon layer is formed on the cathodic side extended portion.

4. The electrolytic capacitor according to claim 3, wherein the carbon layer is in pressure contact with the cathodic side extended portion.

5. The electrolytic capacitor according to claim 3 or 4, wherein the carbon layer penetrates into the cathodic side extended portion.

6. The electrolytic capacitor according to claim 5, wherein the cathodic side extended portion is composed of sponge-like pits, and the carbon material of the carbon layer penetrates into the sponge-like pits.

7. An element composed of the anode foil and the cathode body, and an electrolyte filled in the element, and the electrolyte is free of nitro-based compounds. The electrolytic capacitor according to any one of claims 1 to 6 is characterized by the above.

8. The electrolytic capacitor according to any one of claims 1 to 7, wherein the cathode body is provided with an insulating layer formed on the foil surface, and the carbon layer is formed on the insulating layer.

9. The electrolytic capacitor according to claim 8, wherein the insulating layer is a natural oxide film or a conversion film.

10. An element composed of the anode foil and the cathode body, and an electrolyte filled in the element, the electrolyte being a solvent containing ethylene glycol. and The electrolytic capacitor according to any one of claims 1 to 9 is characterized by the above.

11. The electrolytic capacitor according to any one of claims 1 to 10, wherein part or all of the tunnel-shaped pits penetrate the anode foil.

12. The electrolytic capacitor according to any one of claims 1 to 11, characterized in that it is used for medium and high voltage applications of 100 V or more. ​

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