Electrolytic capacitor and manufacturing method

Abstract

Provided are an electrolytic capacitor and a manufacturing method capable of achieving both low specific resistance electrolyte and low leakage current. An anode body comprises an anode body of a valve metal, and a powder layer which is made of a valve metal powder and is formed on the anode body. A capacitor element includes the anode body, a cathode body, a separator, and an electrolyte containing moisture. The moisture content of the capacitor element is 4 wt% to 20 wt% inclusive relative to the electrolyte. This manufacturing method comprises: an element formation step for forming a capacitor element by stacking an anode body and a cathode body with a separator interposed therebetween; an impregnation step for impregnating the capacitor element with an electrolyte containing moisture; and an adjustment step for adjusting the moisture content of the capacitor element. In the element formation step, the anode body, which is formed by forming a powder layer of valve metal powder on an anode body of a valve metal, is overlaid on the cathode body with the separator interposed therebetween. In the adjustment step, the moisture content of the capacitor element is adjusted to 4-20 wt% relative to the electrolyte.

Description

Electrolytic capacitor and manufacturing method

[0001] The present invention relates to an electrolytic capacitor that obtains capacitance by the dielectric polarization of a dielectric film and stores and discharges electric charge, and to a method for manufacturing the same.

[0002] Electrolytic capacitors have valve metals such as tantalum or aluminum as anode and cathode bodies. The anode body is enlarged by forming the valve metal into a sintered body or etched foil, and a dielectric film is applied to the enlarged surface. This enlarged surface allows electrolytic capacitors to achieve a large capacitance despite their small size. In this electrolytic capacitor, the gap between the dielectric film on the anode body and the counter electrode is filled with electrolyte to ensure close contact. The electrolyte is in direct contact with the dielectric film and acts as a true cathode.

[0003] Electrolytic capacitors are required to have low impedance. One factor that affects the impedance of an electrolytic capacitor is the specific resistance of the electrolyte. To lower the specific resistance of the electrolyte, a method of adding water to the electrolyte is known (see, for example, Patent Document 1).

[0004] Specifically, the main solvent of the electrolyte is ethylene glycol, and water and electrolyte components are mixed into this electrolyte. However, water deteriorates the electrodes and increases leakage current when the electrolytic capacitor is placed in a high-temperature environment, making it difficult to incorporate a large amount of water into the electrolytic capacitor. Therefore, Patent Document 1 blends anserine into the electrolyte. However, while anserine suppresses leakage current, it also increases the resistivity of the electrolyte, unlike water.

[0005] Japanese Patent Application Laid-Open No. 2006-186213

[0006] Therefore, it is necessary to study electrolytic capacitors that can reduce the specific resistance of the electrolyte and suppress leakage current.

[0007] The present invention has been proposed to solve the above problems, and its object is to provide an electrolytic capacitor that can achieve both a low resistivity electrolyte and a low leakage current, and a manufacturing method thereof.

[0008] In order to solve the above-described problems, the electrolytic capacitor of the present embodiment includes an anode body having a dielectric coating, a cathode body facing the anode body, a separator interposed between the anode body and the cathode body, an electrolytic solution containing moisture interposed between the anode body and the cathode body, and a capacitor element including the anode body, the cathode body, the separator, and the electrolytic solution, wherein the anode body includes an anode foil of a valve metal and a powder layer made of valve metal powder and laminated on the anode foil, and the moisture content of the capacitor element is 4 wt % or more and 20 wt % or less based on the electrolytic solution.

[0009] The electrolytic solution may contain cationic components, and 50 mol % or more of the cationic components may be amines.

[0010] The amine may be methylamine, dimethylamine, diethylamine, triethylamine, ethyldimethylamine, or a combination thereof.

[0011] The electrolytic solution may contain a carboxylic acid having a total carbon number of 12 or less in the molecule.

[0012] The electrolyte may contain a glycol compound.

[0013] The capacitor element may be a wound body formed by winding the strip-shaped anode body and the cathode body, and the anode body may have a plurality of dividing portions extending in the width direction of the strip and dividing the powder layer.

[0014] The moisture content of the capacitor element may be the percentage of moisture extracted from the capacitor element based on the electrolyte.

[0015] The electrolyte solution may contain a polyol compound having a branched chain in the main skeleton.

[0016] The polyol compound may be contained in an amount of 40 wt % or less based on the total amount of the electrolyte solution.

[0017] The electrolytic solution may contain a solute, and the amount of the solute may be 45 mmol or more and 100 mmol or less per 100 g of the electrolytic solution.

[0018] In order to solve the above-described problems, the method for manufacturing an electrolytic capacitor according to the present embodiment includes an element-forming step of forming a capacitor element by stacking an anode body having a dielectric coating and a cathode body opposing the anode body with a separator interposed therebetween; an impregnation step of impregnating the capacitor element with an electrolytic solution containing moisture; and an adjustment step of adjusting the moisture content of the capacitor element, wherein in the element-forming step, the anode body formed by stacking a powder layer of valve action metal powder on an anode foil made of a valve action metal is stacked on the cathode body with the separator interposed therebetween; and in the adjustment step, the moisture content of the capacitor element is adjusted to between 4 wt % and 20 wt % based on the electrolytic solution.

[0019] The adjusting step may be included in the impregnation step, and may include adding water to the electrolytic solution in consideration of water contained during production or water volatilized from the electrolytic solution.

[0020] According to the present invention, both a low resistance electrolyte and a low leakage current are achieved.

[0021] 1 is a scatter diagram showing the relationship between moisture content in an element and leakage current for each of a powder laminate foil and an etched foil; FIG. 2 is a scatter diagram showing the relationship between the diethylamine ratio and leakage current; FIG. 3 is a scatter diagram showing the relationship between an amine series and leakage current; and FIG. 4 is a scatter diagram showing the relationship between the number of carbon atoms in the molecule of a solute acid component of an electrolyte and leakage current.

[0022] DETAILED DESCRIPTION OF THE INVENTION An electrolytic capacitor and a manufacturing method thereof according to an embodiment of the present invention will be described below. However, the present invention is not limited to the following embodiment.

[0023] (Overall Structure) An electrolytic capacitor is a passive device that obtains capacitance through the dielectric polarization of a dielectric film and stores and discharges electric charge. This electrolytic capacitor has a capacitor element. The capacitor element includes an anode body, a cathode body, a separator, and an electrolyte. The anode body has a dielectric film on its surface. The separator is interposed between the anode body and the cathode body and insulates them from each other. The anode body and the cathode body face each other via the separator. The electrolyte is impregnated in the gaps within the capacitor element, particularly between the anode body and the cathode body. The electrolyte is in close contact with the dielectric film and acts as a true cathode.

[0024] The capacitor element is housed in a case. The case is made of aluminum, an aluminum alloy containing aluminum or manganese, or stainless steel, and is, for example, a cylindrical body with a bottom and an open end. A pressure release valve may be formed at the bottom of the case so that it opens when the internal pressure of the case exceeds a set pressure.

[0025] This electrolytic capacitor is fabricated through an element formation process, an impregnation process, and a packaging process. The element formation process includes an anode formation process for forming an anode body, a cathode formation process for forming a cathode body, and a winding process for overlapping the anode body and the cathode body with a separator interposed therebetween and winding them. The impregnation process is a process for impregnating the capacitor element with an electrolyte. The packaging process is a process for housing and sealing the capacitor element in a case.

[0026] The impregnation process also serves as an adjustment process to adjust the moisture content within the capacitor element. During the manufacturing process of electrolytic capacitors, moisture from the air is mixed in. Moisture is added to the electrolyte, and the moisture content of the capacitor element is adjusted by adding the moisture mixed in during the manufacturing process and the moisture in the electrolyte so that the combined moisture content of the electrolyte is 4 wt% or more.

[0027] Here, the moisture content of the capacitor element is the amount of moisture contained in the liquid component when the capacitor element is removed from the case and the liquid component is extracted from the capacitor element. The entire amount of the liquid component extracted from the capacitor element is considered to be the electrolyte. The percentage of the moisture content contained in the liquid component relative to the total amount of the liquid component is then calculated, and this result is considered to be the moisture content in the capacitor.

[0028] The resistivity of the electrolyte decreases as the moisture content of the capacitor element increases, and when the moisture content of the capacitor element is 4 wt% or more, the resistivity of the electrolyte falls within a favorable range. Furthermore, the moisture content of the capacitor element is set to 4 wt% or more, and a powder laminate foil is used as the anode body. The powder laminate foil comprises an anode foil and a powder layer. The powder laminate foil is formed by laminating a powder layer made of agglomerated valve action metal powder on an anode foil as a base material.

[0029] Increasing the moisture content of a capacitor element generally increases the leakage current of an electrolytic capacitor. However, if the anode body is a powder laminate foil and the moisture content of the capacitor element is increased to 4 wt% or more, the leakage current of the electrolytic capacitor decreases sharply. Therefore, if the anode body is a powder laminate foil and the moisture content of the capacitor element is increased to 4 wt% or more, the resistivity decreases and the leakage current of the electrolytic capacitor decreases.

[0030] However, the moisture content of the capacitor element should be 20 wt% or less based on the electrolyte. When the moisture content of the capacitor element is 20 wt% or less, low leakage current continues, but if the moisture content of the capacitor element is too high, the leakage current will rise again. Furthermore, when the moisture content of the capacitor element is 20 wt% or less, the internal pressure of the electrolytic capacitor is kept low even when the electrolytic capacitor is exposed to a high-temperature environment for a long period of time, making the pressure relief valve at the bottom of the case less likely to open, resulting in a long life. On the other hand, if the moisture content of the capacitor element is too high, some electrolytic capacitors will be prone to opening when exposed to a high-temperature environment.

[0031] (Anode Body) In such an electrolytic capacitor, the anode foil is a long, strip-shaped foil made by stretching a valve metal. The valve metal may be aluminum, tantalum, niobium, niobium oxide, titanium, hafnium, zirconium, zinc, tungsten, bismuth, or antimony. The purity of the valve metal in the anode foil is preferably 99.9% or higher, and other elements such as silicon, iron, copper, manganese, magnesium, chromium, zinc, titanium, vanadium, gallium, nickel, boron, or zirconium may also be included.

[0032] The powder layer is formed on one or both sides of the anode foil. The powder layer is formed by laminating valve action metal particles. The valve action metal particles in the powder layer may be the same type as or different from the anode foil. This powder layer has a porous structure formed by voids between the agglomerated valve action metal particles. This powder layer expands the surface area of ​​the anode body, resulting in a surface area that exceeds one time the projected area. In other words, this powder layer serves as a surface expansion layer for the anode body.

[0033] The powder layer is a sintered layer formed by sintering valve action metal particles, or a vapor-deposited layer formed by vapor-depositing valve action metal particles onto a foil. The sintered layer is produced by attaching valve action metal particles to a foil and then heating and sintering the particles in a vacuum or reducing atmosphere. The vapor-deposited layer is produced, for example, by a resistance heating vapor deposition method or an electron beam heating vapor deposition method. This vapor-deposited layer is formed by heating and evaporating the valve action metal using resistance heat or electron beam energy, and then depositing the vapor of the valve action metal particles on the surface of the foil.

[0034] The dielectric film is formed on one or both sides of the anode body. The dielectric film is typically an oxide film formed on the surface layer of the anode body, and is an aluminum layer if the anode body is made of aluminum. In the chemical conversion treatment to form the dielectric film, a voltage is applied to the anode body in a chemical conversion solution so as to achieve a desired withstand voltage. In the chemical conversion treatment, it is preferable to form a dielectric film with a thickness of 1.1 to 1.5 nm to achieve a withstand voltage of 1 V. The chemical conversion solution is a solution free of halogen ions, and is, for example, a phosphoric acid-based chemical conversion solution such as ammonium dihydrogen phosphate, a boric acid-based chemical conversion solution such as ammonium borate, or an adipic acid-based chemical conversion solution such as ammonium adipate.

[0035] This anode body preferably has a plurality of dividing portions that divide the powder layer. The dividing portions are formed by cracking, splitting, slitting, notching, or digging into the surface layer of the powder layer. That is, examples of the actual dividing portions are cracks, fissures, slits, notches, or digging. The dividing portions are deep in the direction from the surface of the powder layer toward the core, and may be deep enough to reach the deepest part of the powder layer, deep enough not to reach the deepest part of the powder layer, or deep enough to penetrate into the anode foil. It is not necessary for all dividing portions to have the same depth.

[0036] The dividing portions generally extend in the width direction of the ribbon, in other words, in the direction along the winding axis. The dividing portions may extend completely or partially across the powder layer. That is, some dividing portions extend from one long side of the powder layer to the other long side. Other dividing portions may extend from one long side of the powder layer to a point less than or beyond the foil centerline, but not to the other long side. Other dividing portions may extend from the other long side of the powder layer to a point less than or beyond the foil centerline, but not to the other long side. It is not necessary for all dividing portions to extend in the same direction or for the same length.

[0037] The divided portions in the powder layer disperse bending stress. This allows for smooth, well-wound anode body during winding to form a capacitor element, making it less likely for numerous fine cracks to form in the anode body. Numerous fine cracks increase leakage current, counteracting the increased moisture content of the capacitor element and the leakage current suppression effect of using powder laminate foil for the anode body. However, the formation of divided portions in the powder layer suppresses the occurrence of fine cracks, further suppressing the leakage current of electrolytic capacitors.

[0038] Incidentally, after the powder layer is formed, the dividing portion may be formed before the chemical conversion treatment of the dielectric coating. The dividing portion may be formed after the chemical conversion treatment. Alternatively, the chemical conversion treatment may be performed before the dividing portion is formed, and then the chemical conversion treatment may be performed again after the dividing portion is formed. However, since the anode body is wound while the dividing portion is open in the element formation step, the chemical conversion treatment is not performed to close the dividing portion before the element formation step, and repair chemical conversion is not performed to close the dividing portion. However, preferably, a dielectric coating is also formed on the inner surface of the dividing portion.

[0039] The groove width of the dividing portion is preferably 50 μm or less (including 0) when the anode body is flattened without bending. The groove width of the dividing portion is the length along the longitudinal direction of the anode body. When the dividing portion is formed by splitting, tearing, or notching, the groove width of the dividing portion is substantially 0. "Substantially 0" refers to a state in which the interfaces of the dividing portion are at least partially in contact when the anode body is flattened without bending. If the groove width of the dividing portion is 50 μm or less, a decrease in the capacitance of the electrolytic capacitor due to a decrease in the surface area of ​​the dielectric film can be suppressed.

[0040] (Cathode body) The cathode body is a long strip-shaped cathode foil made by stretching a valve metal. The purity of the valve metal for the cathode body is preferably 99% or more. A surface-expanding layer is formed on the cathode foil as needed. The surface-expanding layer can be a sintered layer, a vapor-deposited layer, or an etched layer obtained by etching the cathode foil. That is, the surface-expanding layer has a porous structure and is composed of tunnel-shaped pits, spongy pits, or voids between densely packed powder or particles.

[0041] The tunnel-shaped etching pits are holes dug in the foil thickness direction. These tunnel-shaped etching pits are typically formed by passing a direct current in an acidic aqueous solution containing halogen ions, such as hydrochloric acid. The tunnel-shaped etching pits are further expanded by passing a direct current in an acidic aqueous solution, such as nitric acid. The spongy etching pits turn the surface-expanding layer into a sponge-like layer with fine, interconnected voids. These spongy etching pits are formed by passing an alternating current in an acidic aqueous solution containing halogen ions, such as hydrochloric acid.

[0042] The cathode body may have a natural oxide film or a thin oxide film of about 1 to 10 V formed by chemical conversion treatment. The natural oxide film is formed by the reaction of the cathode body with oxygen in the air.

[0043] (Separator) Examples of separators include cellulose papers such as kraft, Manila hemp, esparto, hemp, cotton, and rayon, and mixtures thereof; polyester-based resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and derivatives thereof; polytetrafluoroethylene-based resins, polyvinylidene fluoride-based resins, vinylon-based resins; polyamide-based resins such as aliphatic polyamides, semi-aromatic polyamides, and wholly aromatic polyamides; polyimide-based resins, polyethylene resins, polypropylene resins, trimethylpentene resins, polyphenylene sulfide resins, acrylic resins, and polyvinyl alcohol resins. These resins can be used alone or in combination.

[0044] (Capacitor element) A cylindrical wound body is prepared. Before winding, aluminum lead terminals are connected to the anode body and the cathode body by stitching, cold welding, ultrasonic welding, laser welding, or the like. The separators are overlapped so that one end protrudes beyond one end of the anode body and the cathode body. The protruding separator is wound first so that the core of the wound body is aligned with the short sides of the anode body and the cathode body, to prepare a winding core. Next, the winding core is used as a winding shaft to roll up the long sides of the anode body and the cathode body.

[0045] In an anode body with divided sections, the divided sections open first during winding, and multiple divided sections share the bending stress. This reduces the bending stress at each location and suppresses the occurrence of microcracks. The anode body is then wound with a smooth curve without bending. As microcracks are suppressed, an increase in leakage current is suppressed.

[0046] After the element formation process, a repair chemical formation process may be performed to repair defects in the bare metal portions of the valve metal exposed when the anode body and cathode body are cut to the desired width, as well as defects formed in the dielectric coating of the anode body due to physical stress such as winding. In the repair chemical formation process, the wound body is immersed in a chemical formation solution and a voltage is applied. The chemical formation solution may be a phosphoric acid-based chemical formation solution such as ammonium dihydrogen phosphate, a boric acid-based chemical formation solution such as ammonium borate, an adipic acid-based chemical formation solution such as ammonium adipate, or a chemical formation solution containing a mixture of boric acid and a dicarboxylic acid such as citric acid. The repair chemical formation voltage is preferably, for example, 0.1 to 1.2 times the chemical formation voltage applied to the anode body. Furthermore, the voltage application method during repair chemical formation may be appropriately selected from a method of applying a constant voltage from the start of repair chemical formation or a method of increasing the applied voltage stepwise at regular intervals.

[0047] (Electrolyte) The electrolyte is a mixed solution in which a solute is dissolved in a solvent and additives are added as needed. The solvent of the electrolyte is first water to adjust the moisture content in the capacitor element. Other solvents that can be mixed with water include protic organic polar solvents and aprotic organic polar solvents, which can be used alone or in combination of two or more.

[0048] Examples of the protic organic polar solvent include monohydric alcohols, polyhydric alcohols, and oxyalcohol compounds. Examples of the monohydric alcohols include ethanol, propanol, butanol, pentanol, hexanol, cyclobutanol, cyclopentanol, cyclohexanol, and benzyl alcohol. Examples of the polyhydric alcohols and oxyalcohol compounds include ethylene glycol, propylene glycol, diethylene glycol, glycerin, methyl cellosolve, ethyl cellosolve, methoxypropylene glycol, and dimethoxypropanol.

[0049] Representative examples of aprotic organic polar solvents include sulfones, amides, lactones, cyclic amides, and nitriles. Examples of sulfones include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, sulfolane, 3-methyl sulfolane, and 2,4-dimethyl sulfolane. Examples of amides include N-methylformamide, N,N-dimethylformamide, N-ethylformamide, N,N-diethylformamide, N-methylacetamide, N,N-dimethylacetamide, N-ethylacetamide, N,N-diethylacetamide, and hexamethylphosphoric amide. Examples of lactones and cyclic amides include γ-butyrolactone, γ-valerolactone, δ-valerolactone, N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, butylene carbonate, and isobutylene carbonate. Examples of nitriles include acetonitrile, 3-methoxypropionitrile, and glutaronitrile.

[0050] Among these, glycol compounds are preferred as the solvent for the electrolyte solution to be mixed with water. Glycol compounds are compounds in which hydrogen atoms bonded to two or more carbon atoms in an aliphatic hydrocarbon or cyclic aliphatic hydrocarbon are replaced with hydroxyl groups. Glycol compounds have a high boiling point of 150°C or higher. These glycol compounds improve the chemical conversion properties of the dielectric film, thereby reducing the ESR and improving the withstand voltage of electrolytic capacitors. Examples of glycol compounds include ethylene glycol, propylene glycol, diethylene glycol, and triethylene glycol. The electrolyte solution may contain one type of glycol compound solvent, or two or more types of glycol compound solvents. Furthermore, glycol compounds may be used alone or in combination with other glycol compounds.

[0051] The electrolyte also contains a solute. The solute is classified into an anion component and a cation component. The solute is typically a salt of an organic acid, a salt of an inorganic acid, or a salt of a complex compound of an organic acid and an inorganic acid, and is used alone or in combination of two or more. An acid that becomes an anion and a base that becomes a cation may be added separately to a solvent.

[0052] Examples of organic acids that serve as anionic components as solutes 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, 1-methylazelaic acid, undecanedioic acid, dodecanedioic acid, tridecanedioic acid, t-butyladipic acid, 11-vinyl-8-octadecenedioic acid, resorcylic acid, phloroglucinic acid, gallic acid, gentisic acid, protocatechuic acid, pyrocatechuic acid, trimellitic acid, and pyromellitic acid, as well as phenols and sulfonic acids.

[0053] Furthermore, 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 borodisalicylic acid, borodioxalic acid, borodiglycolic acid, borodimalonic acid, borodisuccinic acid, borodiadipic acid, borodiazelaic acid, borodibenzoic acid, borodimaleic acid, borodilactic acid, borodimalic acid, boroditartaric acid, borodicitric acid, borodiphthalic acid, borodi(2-hydroxy)isobutyric acid, borodiresorcylic acid, borodimethylsalicylic acid, borodinaphthoic acid, borodimandelic acid, and borodi(3-hydroxy)propionic acid, etc.

[0054] Furthermore, examples of at least one salt of an organic acid, an inorganic acid, or a complex compound of an organic acid and an inorganic acid include ammonium salts, quaternary ammonium salts, quaternized amidinium salts, amine salts, sodium salts, and potassium salts. Examples of quaternary ammonium ions of quaternary ammonium salts include tetramethylammonium, triethylmethylammonium, and tetraethylammonium. Examples of quaternized amidinium salts include ethyldimethylimidazolinium and tetramethylimidazolinium. Examples of amine salts include salts of primary amines, secondary amines, and tertiary amines. Examples of primary amines include methylamine, ethylamine, and propylamine. Examples of secondary amines include dimethylamine, diethylamine, ethylmethylamine, and dibutylamine. Examples of tertiary amines include trimethylamine, triethylamine, tributylamine, ethyldimethylamine, and ethyldiisopropylamine.

[0055] Preferably, 50 mol % or more of the cationic components in the electrolyte solution are amines. When 50 mol % or more of the cationic components are amines, the leakage current of the electrolytic capacitor can be further reduced. The amine is more preferably methylamine, dimethylamine, diethylamine, triethylamine, ethyldimethylamine, or a mixture of two or more of these, which can further reduce the leakage current of the electrolytic capacitor. In particular, when the amine is dimethylamine or diethylamine, the effect of reducing the leakage current of the electrolytic capacitor is significant.

[0056] The anion component in the electrolyte is preferably a carboxylic acid having a total of 12 or less carbon atoms in the molecule. Examples of carboxylic acids having a total of 12 or less carbon atoms in the molecule include adipic acid having 6 carbon atoms, suberic acid having 8 carbon atoms, azelaic acid having 9 carbon atoms, t-butyl adipic acid having 10 carbon atoms, 1-methylazelaic acid having 10 carbon atoms, sebacic acid having 10 carbon atoms, and 1,6-decanedicarboxylic acid having 12 carbon atoms. When the electrolyte contains a carboxylic acid having a total of 12 or less carbon atoms in the molecule, the leakage current of the electrolytic capacitor can be further reduced.

[0057] Furthermore, other additives can also be added to the electrolyte solution. Examples of additives include alkylene oxide adducts of polyhydric alcohols such as polyethylene glycol, complex compounds of boric acid and polysaccharides (mannite, sorbite, etc.), complex compounds of boric acid and polyhydric alcohols, boric acid esters, nitro compounds (o-nitrobenzoic acid, m-nitrobenzoic acid, p-nitrobenzoic acid, o-nitrophenol, m-nitrophenol, p-nitrophenol, p-nitrobenzyl alcohol, m-nitroacetophenone, etc.), and phosphate esters. These may be used alone or in combination of two or more.

[0058] It is also preferable to add a polyol compound having a branched chain in the main skeleton to the electrolyte solution as a pressure resistance improver, which can further reduce the leakage current of the electrolytic capacitor compared to polyol compounds having a linear skeleton such as polyethylene glycol.

[0059] Examples of polyol compounds having a branched chain include polyethylene glycol diglyceryl ether, polyethylene glycol triglyceryl ether, polypropylene glycol diglyceryl ether, polypropylene glycol triglyceryl ether, polyoxyethylene glycerin, polyoxypropylene glycerin, glycerin to which a propylene oxide polymer and an ethylene oxide polymer have been added, and diglycerin to which a propylene oxide polymer and an ethylene oxide polymer have been added.

[0060] It is particularly preferable that the polyol compound having a branched chain in the main skeleton is added to the electrolyte solution in an amount of 40 wt % or less based on the total amount of the electrolyte solution. If the amount added exceeds 40 wt %, the leakage current suppression effect will be equivalent to that of a polyol compound having a chain skeleton.

[0061] When a polyol compound having a branched chain in its main skeleton is added to the electrolytic solution as a pressure resistance improver, the solute concentration of the electrolytic solution is preferably 45 mmol or more and 100 mmol or less per 100 g of the electrolytic solution. When the solute concentration of the electrolytic solution is in this range, the leakage current of the electrolytic capacitor can be further reduced.

[0062] The capacitor element is immersed in the electrolyte solution, and the electrolyte solution is impregnated into the voids within the capacitor element. A depressurization or pressurization process may be performed as necessary to impregnate the electrolyte solution into smaller voids. The electrolyte solution impregnation process may be repeated multiple times. For example, the pressure inside the capacitor element may be reduced, and the electrolyte solution may be injected into the capacitor element while pressurizing the electrolyte solution.

[0063] (Case) The case that houses the capacitor element impregnated with the electrolyte is made of aluminum, an aluminum alloy containing manganese, or stainless steel, and is, for example, a cylindrical body with a bottom and an open end. A pressure release valve may be formed at the bottom of the case. A sealing body is attached to the opening of the case that houses the capacitor element. The sealing body is an elastic insulator such as a rubber plate, or a laminate of a hard substrate insulating plate such as a synthetic resin plate and an elastic insulator, and is crimped from the outside of the case. After the capacitor element is sealed in the case, the electrolytic capacitor undergoes an aging process to complete its production. In the aging process, a DC voltage is applied to the electrolytic capacitor to repair defects in the dielectric coating, etc.

[0064] The case may be a cylindrical body with one end closed and the other end open, or may be, for example, a laminate film. The case may also be formed by molding the element with a resin such as a heat-resistant resin or an insulating resin, or the case may be formed in the form of a thin film by dip-coating or printing the resin on the element.

[0065] The electrolytic capacitor and the manufacturing method of the present invention will be described in more detail below based on examples, but the present invention is not limited to the following examples.

[0066] (Examples 1 to 4) Electrolytic capacitors were fabricated in Examples 1 to 4 and Comparative Examples 1 to 3. The electrolytic capacitors in Examples 1 to 4 and Comparative Examples 1 to 3 have in common the anode body being a powder laminate foil, but differ in the moisture content in the capacitor element.

[0067] The anode foil is a long strip of aluminum foil. The anode body is a sintered anode body made of an aluminum substrate with a sintered layer made of sintered aluminum grains and a dielectric coating formed on the sintered layer. This sintered layer has a divided section.

[0068] The cathode body is a long strip of aluminum foil. The cathode body was surface-enlarged by AC etching. In the cathode body surface-enlarging process, an AC current was passed through the aluminum foil in an aqueous solution containing hydrochloric acid, forming a surface-enlarged layer consisting of spongy etching pits. In addition, an oxide film was formed on the foil surface of the cathode body by chemical conversion treatment. In the chemical conversion treatment of the cathode body, the cathode body was immersed in a phosphoric acid-based aqueous solution, and an oxide film of 1 V was formed by applying a voltage.

[0069] After connecting lead terminals to the anode body and cathode body, the anode body and cathode body having the same length and width were overlapped with a cellulose-based separator and wound together. The dimensions of the wound body consisting of the anode body, cathode body, and separator were 10 mm in diameter and 20 mm in height.

[0070] This wound body was impregnated with electrolyte solutions of different moisture contents in Examples 1 to 4 and Comparative Examples 1 to 3, taking into consideration the moisture content of the capacitor element. The electrolyte solutions were composed of water, ethylene glycol, azelaic acid, diethylamine, paranitrobenzyl alcohol, and a voltage-resistance improver. The voltage-resistance improver was a glycerin derivative in which a propylene oxide polymer and an ethylene oxide polymer were attached to the two hydroxyl groups of glycerin. The azelaic acid content was 4.0 wt% of the total electrolyte, the diethylamine content was 2.0 wt%, the paranitrobenzyl alcohol content was 1.0 wt%, and the voltage-resistance improver content was 17.0 wt% of the total electrolyte.

[0071] In Comparative Example 1, the water content was 0.0 wt % and the ethylene glycol content was 76 wt % relative to the total amount of the electrolyte, and the moisture content of the capacitor element was 0.6 wt %. In Comparative Example 2, the moisture content was increased from Comparative Example 1, and the water content was 3.0 wt % and the ethylene glycol content was 73.0 wt % relative to the total amount of the electrolyte, and the moisture content of the capacitor element was 3.1 wt %.

[0072] In Example 1, the water content was increased compared to Comparative Example 2, with 6.0 wt% water and 70.0 wt% ethylene glycol relative to the total amount of electrolyte, and the moisture content of the capacitor element was 5.4 wt%. In Example 2, the water content was increased compared to Example 1, with 7.0 wt% water and 69.0 wt% ethylene glycol relative to the total amount of electrolyte, and the moisture content of the capacitor element was 6.5 wt%. In Example 3, the water content was increased compared to Example 2, with 10.0 wt% water and 66.0 wt% ethylene glycol relative to the total amount of electrolyte, and the moisture content of the capacitor element was 8.3 wt%. In Example 4, the water content was increased compared to Example 3, with 20.0 wt% water and 56.0 wt% ethylene glycol relative to the total amount of electrolyte, and the moisture content of the capacitor element was 17.7 wt%.

[0073] In Comparative Example 3, the amount of water was increased compared to Example 4, with 30.0 wt % of water and 46.0 wt % of ethylene glycol relative to the total amount of the electrolyte, and the moisture content of the capacitor element was 28.7 wt %.

[0074] After the wound body was impregnated with the electrolyte to form the capacitor element, each capacitor element was housed in a case, and the opening of the case was sealed with a sealing member to complete the electrolytic capacitor. This electrolytic capacitor had a rated voltage of 450 V and a capacitance of 18 μF.

[0075] Furthermore, electrolytic capacitors of Comparative Examples 4 to 9 were fabricated. The electrolytic capacitors of Comparative Examples 4 to 9 differ from the electrolytic capacitors of Examples 1 to 4 and Comparative Examples 1 to 3 in that no powder layer was laminated on the anode body and the anode body was subjected to an etching process to enlarge the surface. The composition ratios of the electrolytic solutions of Comparative Examples 4 to 9 were the same as those of the corresponding electrolytic capacitors of Examples 1 to 4 and Comparative Examples 1 to 3. However, the electrolytic capacitors of Comparative Examples 4 to 9 had a capacitance of 15 μF.

[0076] In the electrolytic capacitors of Comparative Examples 4 to 9, the anode body was a long strip of aluminum foil. The anode body was immersed in an aqueous solution containing hydrochloric acid, and a direct current was passed through the anode body to form a surface-expanded layer consisting of tunnel-shaped etching pits. Next, the anode body was subjected to a chemical conversion treatment to form an oxide film on the surface layer of the anode body. In the chemical conversion treatment, the anode body was immersed in an ammonium borate aqueous solution and a voltage was applied. The powder layer was not laminated, and the anode body whose surface was expanded by etching was referred to as an etched foil.

[0077] The composition and composition ratio of the electrolyte solution in Comparative Example 4 were the same as those in Comparative Example 1, with the water content in the electrolyte solution being 0.0 wt % and the water content of the capacitor element being 1.0 wt %. The composition and composition ratio of the electrolyte solution in Comparative Example 5 were the same as those in Comparative Example 2, with the water content in the electrolyte solution being 3.0 wt % and the water content of the capacitor element being 3.6 wt %. The composition and composition ratio of the electrolyte solution in Comparative Example 6 were the same as those in Example 2, with the water content in the electrolyte solution being 7.0 wt % and the water content of the capacitor element being 7.0 wt %.

[0078] The composition and composition ratio of the electrolyte solution in Comparative Example 7 were the same as those in Example 3, with the water content in the electrolyte solution being 10.0 wt % and the water content of the capacitor element being 9.2 wt %. The composition and composition ratio of the electrolyte solution in Comparative Example 8 were the same as those in Example 4, with the water content in the electrolyte solution being 20.0 wt % and the water content of the capacitor element being 18.4 wt %. The composition and composition ratio of the electrolyte solution in Comparative Example 9 were the same as those in Comparative Example 3, with the water content in the electrolyte solution being 30.0 wt % and the water content of the capacitor element being 26.0 wt %.

[0079] The moisture content of the capacitor elements of Examples 1 to 4 and Comparative Examples 1 to 9 was measured by disassembling the electrolytic capacitor after fabricating it, measuring the amount of moisture contained in the liquid component extracted from the capacitor element, and regarding the liquid component extracted from the capacitor element as the electrolyte.

[0080] (Characteristics Tests of Examples 1 to 4) The specific resistance Rs [Ω cm] of the electrolytic solution and the leakage current Lc [μA] of the electrolytic capacitor were measured for the electrolytic capacitors of Examples 1 to 4, Comparative Examples 1 to 3, and Comparative Examples 4 to 9. The specific resistance was measured using an immersion-type electrical conductivity cell (MM-43X multi-water quality meter, manufactured by DKK-TOA Corporation) with the electrolytic solution at a liquid temperature of 30°C. The leakage current was measured after leaving the electrolytic capacitor in a temperature environment of 150°C for 500 hours, and then applying 450 V, and then measuring the current value 5 minutes later.

[0081] The measurement results of resistivity and leakage current are shown in Tables 1 and 2 below. The relationship between moisture content in the element (%) and leakage current (μA) for the powder laminated foil series of Examples 1 to 4 and Comparative Examples 1 to 3, in which the anode body is a powder laminated foil, and the etched foil series of Comparative Examples 4 to 9, in which the anode body is an etched foil, is shown in the graph of Figure 1. The moisture content in the element is the moisture content of the capacitor element. The powder laminated foil series is plotted with circles, and the etched foil series is plotted with triangles.

[0082] (Table 1)

[0083] (Table 2)

[0084] As shown in Table 2 above, among Comparative Examples 4 to 9, Comparative Examples 6 to 9, in which the moisture content in the element was increased, had good electrolytic solution resistivity. However, as shown in Table 2 above and FIG. 1 , the electrolytic capacitors of Comparative Examples 6 to 7, in which the electrolytic solution had good electrolytic solution resistivity, experienced a sharp increase in leakage current. The electrolytic capacitors of Comparative Examples 6 to 9 had an elemental moisture content, i.e., a moisture content of the capacitor element, of over 3.1%. Thus, when the anode body is an etched foil, an increase in the moisture content of the capacitor element tends to improve the electrolytic solution resistivity, but conversely, to cause a sharp increase in leakage current.

[0085] Next, as shown in Table 1, among Examples 1 to 4 and Comparative Examples 1 to 3, the electrolytic solutions of Examples 1 to 4 and Comparative Example 3, which had increased moisture content in the element, had good resistivity, similar to Comparative Examples 6 to 9. Moreover, from the viewpoint of leakage current, as shown in Table 1 above and Figure 1, in the electrolytic capacitors of Examples 1 to 4, when the moisture content in the element was increased to more than 3.1 wt%, the leakage current decreased sharply, in contrast to Comparative Examples 6 to 7, where the leakage current increased sharply.

[0086] That is, when the moisture content in the element was 3.1 wt% or less, the etched foils of Comparative Examples 4 and 5 had lower leakage current than the powder laminated foils of Comparative Examples 1 and 2. However, when the moisture content in the element exceeded 3.1 wt%, the leakage current of Examples 1 to 3, which were powder laminated foils, suddenly decreased, reversing the situation from the etched foils of Comparative Examples 4 and 5, which had a sharp increase in leakage current.

[0087] However, in Comparative Examples 8 and 9, in which the moisture content in the element was 17.7% or more, and Comparative Example 3, in which the moisture content in the element was 28.7%, the valve opened when a rated voltage treatment of 450 V was carried out after 90 hours had elapsed while the electrolytic capacitors were exposed to a temperature environment of 150°C, and the leakage current could not be measured.

[0088] In this way, by providing an anode body made of valve action metal powder and having a powder layer laminated on an anode foil, and by setting the moisture content of the capacitor element to 4 wt % or more and 20 wt % or less based on the electrolyte, it is possible to achieve both low resistivity of the electrolyte and low leakage current of the electrolytic capacitor.

[0089] (Examples 5-7) Electrolytic capacitors of Examples 5 to 7 were produced. The electrolytic capacitors of Examples 5 to 7 differed from Example 3 in the composition of the electrolytic solution. Other than the composition of the electrolytic solution, the electrolytic capacitors of Examples 5 to 7 had the same configuration as Example 3 and were produced by the same production method and under the same production conditions.

[0090] The entire amount of the cationic component contained in the electrolyte solution of Example 3 was diethylamine. In contrast, the electrolytic capacitors of Examples 5 to 7 were provided with electrolyte solutions containing both ammonia and diethylamine as cationic components. Table 3 below shows the compositions of the electrolyte solutions of Examples 5 to 7 and Example 3.

[0091] (Table 3)

[0092] The molecular weight of ammonia is 17.03 g / mol, and the molecular weight of diethylamine is 73.14 g / mol. In this case, the ratio (mol%) of diethylamine to the cationic components in the electrolyte solution of Example 5 is 25 mol%. The ratio (mol%) of diethylamine to the cationic components in the electrolyte solution of Example 6 is 50 mol%. The ratio (mol%) of diethylamine to the cationic components in the electrolyte solution of Example 7 is 75 mol%. The ratio (mol%) of diethylamine to the cationic components in the electrolyte solution of Example 3 is 100 mol%.

[0093] (Characteristics Tests of Examples 5 to 7 and Example 3) The leakage current Lc [μA] was measured for the electrolytic capacitors of Examples 5 to 7 and Example 3. The leakage current measurement method and conditions were the same as those of Examples 1 to 4. After the electrolytic capacitors were left in a temperature environment of 150° C. for 500 hours, the current value was measured 5 minutes after applying 450 V.

[0094] The measurement results of the leakage current are shown in Table 4 below. The relationship between the ratio (mol %) of diethylamine to the cationic components in the electrolyte and the leakage current Lc (μA) is shown in the graph of FIG.

[0095] (Table 4)

[0096] As shown in Table 4 above and Figure 2, it can be confirmed that the leakage current of the electrolytic capacitor decreases as the ratio of amines to the cationic components of the electrolyte solution increases. As shown in Examples 6, 7, and 3, when amines account for 50 mol % or more of the cationic components, the leakage current of the electrolytic capacitor falls within a low range.

[0097] (Examples 8-12) Electrolytic capacitors of Examples 8 to 12 were produced. The electrolytic capacitors of Examples 8 to 12 differ from Example 3 in the type of amine contained in the electrolytic solution. Other than the type of amine contained in the electrolytic solution, the electrolytic capacitors of Examples 8 to 12 had the same configuration as Example 3 and were produced using the same manufacturing method and conditions. The compositions of the electrolytic solutions provided in the electrolytic capacitors of Examples 8 to 12 are shown in Table 5 below.

[0098] (Table 5)

[0099] The moisture content of the capacitor element in Example 8 was 8.2%, the moisture content of the capacitor element in Example 9 was 8.7%, the moisture content of the capacitor element in Example 10 was 8.8%, the moisture content of the capacitor element in Example 11 was 8.3%, and the moisture content of the capacitor element in Example 12 was 8.8%.

[0100] (Characteristics Tests of Examples 8 to 12 and Example 3) The leakage current Lc [μA] was measured for the electrolytic capacitors of Examples 8 to 12 and Example 3. The leakage current measurement method and conditions were the same as those of Examples 1 to 4. After the electrolytic capacitors were left in a temperature environment of 150° C. for 500 hours, the current value was measured 5 minutes after applying 450 V.

[0101] The results of the leakage current measurements are shown in Table 6 below. The relationship between the series number (n) of various amines and the leakage current Lc (μA) is shown in the graph of Figure 3. In the table and figure, MA is methylamine, DMA is dimethylamine, DEA is diethylamine, TMA is trimethylamine, TEA is triethylamine, and EDMA is ethyldimethylamine.

[0102] (Table 6)

[0103] As shown in Table 6 and Figure 3, it was confirmed that the leakage current of electrolytic capacitors can be reduced regardless of the amine contained in the electrolyte. In particular, the leakage current was significantly reduced when amines with an amine series of 2, such as dimethylamine and diethylamine, were contained in the electrolyte.

[0104] (Examples 13-19) Electrolytic capacitors of Examples 13 to 19 were produced. The electrolytic capacitors of Examples 13 to 19 differ from Example 3 in the type of anion component, in other words, acid component, contained in the electrolytic solution. Other than the type of anion component contained in the electrolytic solution, the electrolytic capacitors of Examples 13 to 19 had the same configuration as Example 3 and were produced using the same production method and the same production conditions. The compositions of the electrolytic solutions provided in the electrolytic capacitors of Examples 13 to 19 are shown in Table 7 below.

[0105] (Table 7)

[0106] The electrolytic capacitors of Examples 13 to 19 and Example 3 having such electrolyte compositions contain carboxylic acids with different numbers of carbon atoms in the electrolytes. The adipic acid of Example 13 has a total of 6 carbon atoms in the molecule, the suberic acid of Example 14 has a total of 8 carbon atoms in the molecule, the azelaic acid of Example 3 has a total of 9 carbon atoms in the molecule, the t-butyl adipic acid of Example 15 has a total of 10 carbon atoms in the molecule, the 1-methylazelaic acid of Example 16 has a total of 10 carbon atoms in the molecule, the sebacic acid of Example 17 has a total of 10 carbon atoms in the molecule, the 1,6-decanedicarboxylic acid of Example 18 has a total of 12 carbon atoms in the molecule, and the 11-vinyl-8-octadecenedioic acid of Example 19 has a total of 20 carbon atoms in the molecule.

[0107] The moisture content of the capacitor element in Example 13 was 8.5%, the moisture content of the capacitor element in Example 14 was 8.3%, the moisture content of the capacitor element in Example 15 was 8.9%, the moisture content of the capacitor element in Example 16 was 8.1%, the moisture content of the capacitor element in Example 17 was 8.8%, the moisture content of the capacitor element in Example 18 was 8.7%, and the moisture content of the capacitor element in Example 19 was 8.2%.

[0108] (Characteristics Tests of Examples 13 to 19 and Example 2) The leakage current Lc [μA] was measured for the electrolytic capacitors of Examples 13 to 19 and Example 2. The leakage current measurement method and conditions were the same as those of Examples 1 to 4. After the electrolytic capacitors were left in a temperature environment of 150° C. for 500 hours, the current value was measured 5 minutes after applying 450 V.

[0109] The measurement results of the leakage current are shown in Table 8. The relationship between the total number of carbon atoms constituting the molecules of the cationic component contained in the electrolyte and the leakage current Lc (μA) is shown in the graph of FIG.

[0110] (Table 8)

[0111] As shown in Table 8 above and Figure 4, the electrolytic capacitors of Examples 13 to 18 and Example 2 have lower leakage currents than Example 19. The anion components in the electrolyte solutions used in the electrolytic capacitors of Examples 13 to 18 and Example 3 are carboxylic acids with a total carbon number of 12 or less in the molecular structure, whereas the anion component in Example 19 has a total carbon number of 20.

[0112] This confirmed that when the anion component in the electrolyte solution is a carboxylic acid having a total carbon number of 12 or less in the molecular structure, the leakage current of the electrolytic capacitor can be further reduced.

[0113] (Examples 20-21) Electrolytic capacitors of Examples 20 to 21 were produced. The electrolytic capacitors of Examples 20 to 21 differ from those of Example 3 and Comparative Example 7 in the type of additive added to the electrolytic solution. Other than the type of voltage resistance improver, the electrolytic capacitors of Examples 20 and 21 had the same configuration as Example 3 and were produced using the same manufacturing method and conditions. The moisture content of the capacitor elements in Examples 20 and 21 was both 8.1%.

[0114] In Example 3 and Comparative Example 7, a glycerin derivative in which a propylene oxide polymer and an ethylene oxide polymer are added to the positions of two hydroxyl groups of glycerin was added to the electrolyte solution as a pressure resistance improver. In contrast, in Example 20, polyoxyethylene glycerin was added to the electrolyte solution as a pressure resistance improver. In Example 21, polyethylene glycol was added to the electrolyte solution as a pressure resistance improver. The additives in Example 3, Comparative Example 7, and Example 20 were polyol compounds having a branched chain in the main skeleton. On the other hand, the additive in Example 21 was a polyol compound having a linear skeleton without a branched chain in the main skeleton.

[0115] (Characteristics Test of Examples 20 and 21) The leakage current Lc [μA] of the electrolytic capacitors of Examples 20 and 21 was measured. The measurement method and conditions for the leakage current Lc were the same as those in Example 3 and Comparative Example 7. The measurement results of the leakage current are shown in Table 9 below.

[0116] (Table 9)

[0117] As shown in Table 9 above, when the group of Examples 3 and 20 is compared with Example 21, Examples 3 and 20 have a lower leakage current than Example 21. The difference between the group of Examples 3 and 20 and Example 21 is the type of pressure resistance improver; the pressure resistance improver of Example 21 is a polyol compound having a chain skeleton, whereas the pressure resistance improvers of Examples 3 and 20 are polyol compounds having a branched chain in the main skeleton.

[0118] This confirmed that the low leakage current of an electrolytic capacitor can be further reduced by providing an anode body made of valve action metal powder and having a powder layer laminated on an anode foil, adjusting the moisture content of the capacitor element to 4 wt % or more and 20 wt % or less based on the electrolyte solution, and adding a polyol compound having a branched chain in its main skeleton to the electrolyte solution.

[0119] (Examples 22-24) Electrolytic capacitors of Examples 22 to 24 were fabricated. The electrolytic capacitors of Examples 22 to 24 contained the same type of glycerin derivative as the voltage resistance improver of Example 3, added to the electrolytic solution. However, Examples 3 and 22 to 24 differ in the amount of voltage resistance improver added. Other than the amount of voltage resistance improver added, the electrolytic capacitors of Examples 22 to 24 had the same configuration as Example 3 and were fabricated using the same manufacturing method and conditions. The moisture content of the capacitor element of Example 22 was 8.4%, and the moisture content of the capacitor elements of Examples 23 and 24 was both 8.5%.

[0120] The amount of the pressure resistance improver added in Example 3 was 17.0 wt % relative to the total amount of the electrolyte. In contrast, in Example 22, the pressure resistance improver was added in a proportion of 30.0 wt % relative to the total amount of the electrolyte. In Example 23, the pressure resistance improver was added in a proportion of 40.0 wt % relative to the total amount of the electrolyte. In Example 24, the pressure resistance improver was added in a proportion of 50.0 wt % relative to the total amount of the electrolyte.

[0121] (Characteristics Tests of Examples 22 to 24) The leakage current Lc [μA] of the electrolytic capacitors of Examples 22 to 24 was measured. The measurement method and conditions for the leakage current Lc were the same as those in Example 3 and Comparative Example 7. The measurement results of the leakage current are shown in Table 10 below.

[0122] (Table 10)

[0123] As shown in Table 10 above, when the group of Examples 3, 22, and 23 is compared with Example 24, Examples 3, 22, and 23 have a lower leakage current than Example 24. The difference between the group of Examples 3, 22, and 23 and Example 24 is the amount of the voltage resistance improver added; the amount of the voltage resistance improver added in Example 24 is more than 40 wt % with respect to the total amount of the electrolyte, whereas the amount of the voltage resistance improver added in Examples 3, 22, and 23 is 40 wt % or less with respect to the total amount of the electrolyte.

[0124] This confirmed that the low leakage current of an electrolytic capacitor can be further reduced by providing an anode body made of valve action metal powder and having a powder layer laminated on an anode foil, adjusting the moisture content of the capacitor element to 4 wt % or more and 20 wt % or less based on the electrolyte solution, adding a polyol compound having a branched chain in its main skeleton to the electrolyte solution, and setting the amount of this polyol compound added to 40 wt % or less of the total amount of the electrolyte solution.

[0125] (Examples 25-29) Electrolytic capacitors of Examples 25 to 29 were produced. The electrolytic capacitors of Examples 25 to 29 contained electrolytic solutions having the same compositions as those of Example 3. However, the solute concentrations of the electrolytic solutions of Examples 25 to 29 were different from those of Example 3. Other than the solute concentrations of the electrolytic solutions, the electrolytic capacitors of Examples 25 to 29 had the same configuration as those of Example 3, and were produced using the same production method and under the same production conditions.

[0126] The moisture content of the capacitor elements in Examples 25 and 28 was 8.2%, the moisture content of the capacitor elements in Examples 26 and 27 was 8.1%, and the moisture content of the capacitor element in Example 29 was 8.0%.

[0127] The solutes contained in the electrolyte of Example 3 were azelaic acid and diethylamine. The total amount of azelaic acid and diethylamine added in Example 3 was 48.61 mmol per 100 g of electrolyte. In contrast, the amount of solute added in Example 25 was 72.92 mmol per 100 g of electrolyte. The amount of solute added in Example 26 was 97.23 mmol per 100 g of electrolyte. The amount of solute added in Example 27 was 121.54 mmol per 100 g of electrolyte. The amount of solute added in Example 28 was 145.84 mmol per 100 g of electrolyte. The amount of solute added in Example 29 was 182.31 mmol per 100 g of electrolyte. The difference in solute concentration was adjusted by the amount of ethylene glycol added.

[0128] (Characteristics Tests of Examples 25 to 29) The leakage current Lc [μA] of the electrolytic capacitors of Examples 25 to 29 was measured. The measurement method and conditions for the leakage current Lc were the same as those in Example 3 and Comparative Example 7. The measurement results of the leakage current are shown in Table 11 below.

[0129] (Table 11)

[0130] As shown in Table 11 above, when comparing the group of Examples 3, 25, and 26 with the group of Examples 27 to 29, Examples 3, 25, and 26 have a lower leakage current than Examples 27 to 29. The difference between the group of Examples 3, 25, and 26 and the group of Examples 27 to 29 is the amount of solute added to the electrolyte; in the group of Examples 27 to 29, the amount of solute added to the electrolyte is more than 100 mmol / 100 g, while in the group of Examples 3, 25, and 26, the amount of solute added to the electrolyte is 45 mmol / 100 g or more and 100 mmol / 100 g or less.

[0131] As a result, it was confirmed that the low leakage current of an electrolytic capacitor can be further reduced by providing an anode body made of valve action metal powder and having a powder layer laminated on an anode foil, adjusting the moisture content of the capacitor element to 4 wt % or more and 20 wt % or less based on the electrolyte solution, adding a polyol compound having a branched chain in its main skeleton to the electrolyte solution, and further adjusting the solute content of the electrolyte solution to 45 mmol or more and 100 mmol or less per 100 g of the electrolyte solution.

Claims

1. An electrolytic capacitor comprising: an anode body having a dielectric film; a cathode body facing the anode body; a separator interposed between the anode body and the cathode body; an electrolytic solution containing moisture interposed between the anode body and the cathode body; and a capacitor element having the anode body, the cathode body, the separator, and the electrolytic solution, wherein the anode body comprises an anode foil made of a valve metal, and a powder layer made of valve metal powder and formed on the anode foil, and wherein the moisture content of the capacitor element is 4 wt % or more and 20 wt % or less based on the electrolytic solution.

2. The electrolytic capacitor according to claim 1, wherein the electrolyte contains cationic components, and 50 mol % or more of the cationic components are amines.

3. The electrolytic capacitor according to claim 2, wherein the amine is methylamine, dimethylamine, diethylamine, triethylamine, ethyldimethylamine, or a combination thereof.

4. The electrolytic capacitor according to claim 1, wherein the electrolyte contains a carboxylic acid having a total carbon number of 12 or less in the molecule.

5. The electrolytic capacitor according to claim 1, wherein the electrolyte contains a glycol compound.

6. The electrolytic capacitor according to any one of claims 1 to 5, wherein the capacitor element is a wound body formed by winding the strip-shaped anode body and cathode body, and the anode body has a plurality of dividing portions extending in the width direction of the strip and dividing the powder layer.

7. The electrolytic capacitor according to claim 1, wherein the moisture content of the capacitor element is the percentage of moisture extracted from the capacitor element based on the electrolyte.

8. The electrolytic capacitor according to claim 1, wherein the electrolyte solution contains a polyol compound having a branched chain in its main skeleton.

9. The electrolytic capacitor according to claim 8, wherein the polyol compound is 40 wt % or less of the total amount of the electrolyte solution.

10. The electrolytic capacitor according to claim 8, wherein the electrolyte contains a solute, and the amount of the solute is 45 mmol or more and 100 mmol or less per 100 g of the electrolyte.

11. A method for manufacturing an electrolytic capacitor, comprising: an element forming step of stacking an anode body having a dielectric film and a cathode body facing the anode body with a separator interposed therebetween to form a capacitor element; an impregnation step of impregnating the capacitor element with an electrolytic solution containing moisture; and an adjustment step of adjusting the moisture content of the capacitor element, wherein in the element forming step, the anode body, which is formed by forming a powder layer of valve action metal powder on an anode foil made of valve action metal, is stacked on the cathode body with the separator interposed therebetween, and in the adjustment step, the moisture content of the capacitor element is adjusted to between 4 wt % and 20 wt % based on the electrolytic solution.

12. The method for manufacturing an electrolytic capacitor according to claim 11, wherein the adjustment step is included in the impregnation step, and water is added to the electrolytic solution taking into account water contained during manufacturing or water volatilized from the electrolytic solution.

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