Cathode body and electrolytic capacitor and method for manufacturing cathode body and electrolytic capacitor

Abstract

To provide a cathode body capable of suppressing generation of hydrogen gas, and an electrolytic capacitor including the cathode body.SOLUTION: A cathode body includes a cathode foil composed of valve action metal, and a carbon layer which is stacked on the cathode foil and contains a carbon material. As for the carbon material, by analysis by X-ray photoelectron spectroscopy, a peak P1 derived from a C-O bond of an O1 s spectrum, a peak P2 derived from an O-C=O bond of the O1 s spectrum, and a peak P3 derived from a C=O bond of the O1 s spectrum are detected. A ratio of the total value of an area ratio [COO] of the peak P2 and an area ratio [C=O] of the peak P3 to an area ratio [C-O] of the peak P1 is ([COO]+[C=O]) / [C-O]<2.0.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a cathode body provided in an electrolytic capacitor, the electrolytic capacitor, and methods for manufacturing the cathode body and the electrolytic capacitor. [Background technology]

[0002] Electrolytic capacitors have anode and cathode foils made of valve metals such as tantalum or aluminum. The anode foil is enlarged by shaping the valve metal into a sintered or etched foil, and the enlarged surface is coated with a dielectric film. An electrolyte is interposed between the anode and cathode foils. The electrolyte is in close contact with the uneven surface of the anode foil and functions as the true cathode.

[0003] The electrolyte repairs deteriorated or damaged parts of the dielectric film formed on the anode foil due to leakage current. However, when the dielectric film is repaired by leakage current, hydrogen gas is generated. That is, when the film is repaired by leakage current on the anode side, an anodic reaction occurs, as shown in the following chemical reaction formula (1). When the film is repaired by leakage current on the cathode side, a cathodic reaction occurs, as shown in the following chemical reaction formula (2), in which electrons generated in the anodic reaction are received and hydrogen ions are reduced. The atomic hydrogen generated in chemical reaction formula (2) combines as shown in the following chemical reaction formula (3), generating hydrogen gas.

[0004] TIFF2025121729000002.tif30162

[0005] Hydrogen gas increases the internal pressure of the electrolytic capacitor, which may cause the bulging of the case housing the capacitor element, the bulging of the sealing cap that seals the capacitor element, or the opening of the pressure release valve installed in the electrolytic capacitor. When leakage current increases on the anode side and charge movement on the anode side electrode surface becomes intense, the reaction rate on the cathode side also increases in accordance with Faraday's law, and the amount of hydrogen gas generated on the cathode side increases.

[0006] In particular, in recent years, electrolytic capacitors for medium- to high-voltage applications (100 V or higher) have been required to have even higher capacitance. In other words, there is also a need to reduce the thickness of the dielectric film while maintaining the withstand voltage. However, reducing the thickness of the dielectric film tends to increase leakage current, which leads to problems such as increased generation of hydrogen gas.

[0007] Nitro compounds are sometimes added to the electrolyte. Nitro compounds are reduced on the cathode side and react with hydrogen ions. Therefore, nitro compounds suppress the generation of hydrogen gas. However, depending on the type of nitro compound, they can reduce the withstand voltage of the electrolytic capacitor, so the amount that can be used is limited. In addition, nitro compounds are reduced on the cathode side over time, and their hydrogen gas suppression performance decreases. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent Publication No. 2017-34030 Summary of the Invention [Problem to be solved by the invention]

[0009] A new means for more effectively suppressing hydrogen gas generation is desired for electrolytic capacitors. The present invention has been proposed to solve the above-mentioned problems, and an object of the present invention is to provide a cathode body capable of suppressing hydrogen gas generation, an electrolytic capacitor including the cathode body, and methods for manufacturing the cathode body and the electrolytic capacitor. [Means for solving the problem]

[0010] In order to achieve the above object, the cathode body of the electrolytic capacitor of the present embodiment includes a cathode foil made of a valve action metal and a carbon layer laminated on the cathode foil and containing a carbon material, wherein a peak P1 derived from a C-O bond in an O1s spectrum, a peak P2 derived from an O-C=O bond in the O1s spectrum, and a peak P3 derived from a C=O bond in the O1s spectrum are detected from the carbon material by X-ray photoelectron spectroscopy analysis, and the ratio of the area ratio [CO] of peak P1 to the sum of the area ratio [COO] of peak P2 and the area ratio [C=O] of peak P3 satisfies ([COO] + [C=O]) / [CO] < 2.0.

[0011] Furthermore, the peak P1 derived from a C-O bond in the O1s spectrum may appear in a range of 533 eV or more, the peak P2 derived from an O-C=O bond in the O1s spectrum may appear in a range of 530 eV or more and 533 eV or less, and the peak P3 derived from a C=O bond in the O1s spectrum may appear in a range of 530 eV or more and 533 eV or less.

[0012] In order to solve the above-described problems, the electrolytic capacitor of the present embodiment includes the cathode body, an anode body having a dielectric coating and facing the cathode body, and an electrolyte interposed between the cathode body and the anode body.

[0013] In order to solve the above-described problems, the method for manufacturing a cathode body of an electrolytic capacitor according to the present embodiment includes a surface functional group adjusting step of adjusting the amount of surface functional groups of a carbon material, and a carbon layer laminating step of forming a carbon layer containing the carbon material on a cathode foil made of a valve action metal. In the surface functional group adjusting step, a peak P1 derived from a C-O bond in an O1s spectrum, a peak P2 derived from an O-C=O bond in an O1s spectrum, and a peak P3 derived from a C=O bond in an O1s spectrum are detected by analyzing the carbon material using X-ray photoelectron spectroscopy, and the ratio of the area ratio [CO] of peak P1 to the sum of the area ratio [COO] of peak P2 and the area ratio [C=O] of peak P3 is adjusted to satisfy ([COO] + [C=O]) / [CO] < 2.0.

[0014] The peak P1 derived from a C-O bond in the O1s spectrum may appear in a range of 533 eV or more, the peak P2 derived from an O-C=O bond in the O1s spectrum may appear in a range of 530 eV or more and 533 eV or less, and the peak P3 derived from a C=O bond in the O1s spectrum may appear in a range of 530 eV or more and 533 eV or less.

[0015] In order to solve the above-described problems, the method for manufacturing an electrolytic capacitor according to the present embodiment includes the steps of: fabricating a cathode body; fabricating an anode body having a dielectric coating; and interposing an electrolyte between the cathode body and the anode body. [Effects of the Invention]

[0016] According to the present invention, the generation of hydrogen gas can be suppressed by controlling the functional groups in the carbon layer mounted on the cathode body. [Brief explanation of the drawings]

[0017] [Figure 1] 1 shows the results of analysis of the carbon material of Example 1 by X-ray photoelectron spectroscopy. [Figure 2] 1 shows the results of analysis of the carbon material of Example 2 by X-ray photoelectron spectroscopy. [Figure 3] 1 shows the results of analysis of the carbon material of Example 3 by X-ray photoelectron spectroscopy. [Figure 4] 1 shows the results of analysis of the carbon material of Comparative Example 1 by X-ray photoelectron spectroscopy. [Figure 5] 1 shows the results of analysis of the carbon material of Comparative Example 2 by X-ray photoelectron spectroscopy. [Figure 6] 1 shows the results of analysis of the carbon material of Comparative Example 3 by X-ray photoelectron spectroscopy. [Figure 7] 1 is a graph showing the volume change over time of the electrolytic capacitors of Examples 1 to 3 and Comparative Examples 1 to 4. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, a cathode body and an electrolytic capacitor according to embodiments of the present invention, and a method for manufacturing the cathode body and the electrolytic capacitor will be described. However, the present invention is not limited to the embodiments described below.

[0019] (cathode body) The cathode body is an electrode disposed on the cathode side of the electrolytic capacitor. The electrolytic capacitor in which this cathode body is disposed is a passive element that obtains capacitance by the dielectric polarization action of a dielectric film and stores and discharges electric charge. Examples of electrolytic capacitors include electrolytic capacitors that use an electrolytic solution and so-called hybrid electrolytic capacitors that contain a conductive polymer and an electrolytic solution.

[0020] The cathode body includes a cathode foil made of a valve metal, such as aluminum, tantalum, niobium, niobium oxide, titanium, hafnium, zirconium, zinc, tungsten, bismuth, or antimony. The purity of the cathode foil is preferably 99% or higher, but it may contain impurities such as silicon, iron, copper, magnesium, or zinc.

[0021] For example, the cathode foil may be made of an aluminum material having a temper code of H as defined in JIS standard H0001, known as an H material, or an aluminum material having a temper code of O as defined in JIS standard H0001, known as an O material. Use of a highly rigid metal foil made of an H material can suppress deformation of the cathode foil due to press working of the carbon material applied to the cathode body, which is performed to bond the cathode foil and the carbon material to each other, as described below.

[0022] The cathode foil is made of a valve metal stretched into a foil shape. The surface of the cathode foil may be subjected to a surface-expanding treatment. The surface-expanding layer of the cathode foil is formed by electrolytic etching, chemical etching, sandblasting, or the like, or by depositing or sintering metal particles or the like onto the metal foil. Examples of electrolytic etching include direct current etching and alternating current etching. In chemical etching, the metal foil is immersed in an acid solution or alkaline solution. The formed surface-expanding layer is a layer region having tunnel-shaped etching pits or spongy etching pits dug from the foil surface toward the foil core. The etching pits may be formed so as to penetrate the cathode foil.

[0023] An oxide film may be formed intentionally or naturally on the surface-expanding layer. A natural oxide film is formed by the cathode foil reacting with oxygen in the air, while a chemical conversion film is a thin oxide film of about 1 to 10 V that is intentionally formed by chemical conversion treatment in which a voltage is applied in a solution that does not contain halogen ions, such as an aqueous solution of adipic acid or boric acid. If the metal foil is, for example, aluminum foil, the oxide film formed by this method is aluminum oxide, which is formed by oxidizing the surface of the surface-expanding layer.

[0024] When the cathode foil is assembled into an electrolytic capacitor, a lead terminal is connected to the cathode foil, and the lead terminal is electrically and mechanically connected by cold welding, ultrasonic welding, laser welding, or the like.

[0025] The cathode body has a laminated structure of the cathode foil and a carbon layer. That is, the carbon layer is laminated on the anode foil. The carbon layer is laminated on one or both sides of the cathode foil and is located as the outermost layer of the cathode body. The carbon layer contains a carbon material. In addition to the carbon material, the carbon layer may also contain a metal such as titanium, or a metal nitride or metal carbide such as titanium nitride, titanium carbide, or aluminum carbide. Multiple carbon layers may be laminated.

[0026] The carbon material may be fibrous carbon, carbon powder, or a mixture thereof. It may also be fibrous carbon or carbon powder that has been subjected to a porous treatment, such as an activation treatment or an opening treatment to form pores. Examples of carbon powder include activated carbon derived from natural plant tissues such as coconut husks, synthetic resins such as phenols, and fossil fuels such as coal, coke, and pitch; carbon blacks such as ketjen black, acetylene black, and channel black; carbon nanohorns; amorphous carbon; natural graphite; artificial graphite; graphitized ketjen black; and mesoporous carbon. Examples of fibrous carbon include carbon nanotubes and carbon nanofibers. Carbon nanotubes may be single-walled carbon nanotubes, which have a single graphene sheet, or multi-walled carbon nanotubes (MWCNTs), which have two or more graphene sheets coaxially rolled together to form multiple tube walls.

[0027] The carbon material is attached to the cathode foil by coating, vapor deposition, heat treatment, etc. In the coating method, a slurry containing the carbon material, binder, and solvent is applied to the cathode body by a slurry casting method, doctor blade method, spray atomization method, etc., and dried, and the cathode foil and the carbon layer are adhered to each other by pressing as needed. In the heat treatment, powder of the carbon material is attached to the surface of the cathode foil and sintered.

[0028] This carbon material has surface functional groups on its surface. As surface functional groups, the carbon material has at least a hydroxyl group which is a C-O bond, a carboxyl group which is an O-C=O bond, a lactone group or an acid anhydride, and a carbonyl group which is a C=O bond. The hydroxyl group is confirmed as a C-O bond in an O1s spectrum analysis using X-ray photoelectron spectroscopy.

[0029] The amount of these surface functional groups on a carbon material can be adjusted by calcining the carbon material in a reducing atmosphere or by treating it with a reagent that reduces only the desired surface functional groups. A reducing atmosphere is an atmosphere containing little or no oxygen, low-oxidizing gas, or steam, such as nitrogen, argon, or hydrogen. For example, calcining in a reducing atmosphere converts O-C=O bonds into CO gas and decarbonizes them, reducing the amount of surface functional groups containing O-C=O bonds.

[0030] The amount of these surface functional groups on the carbon material can be adjusted by treating it with a reagent that reduces only the desired surface functional groups. Examples of reducing agents that can be used include hydrogen, sodium borohydride, and lithium aluminum hydride. When sodium borohydride is used, only the carbonyl groups of the surface functional groups contained in the carbon material are selectively reduced, resulting in a decrease in the amount of surface functional groups containing C=O bonds.

[0031] The amount of surface functional groups on this carbon material is adjusted as follows. That is, this carbon material is analyzed by X-ray photoelectron spectroscopy. When the O1s spectrum is subjected to waveform separation, a peak P1 derived from a C-O bond in the O1s spectrum, a peak P2 derived from an O-C=O bond in the O1s spectrum, and a peak P3 derived from a C=O bond in the O1s spectrum are detected. The peak P1 derived from a C-O bond in the O1s spectrum appears in the range of 533 eV or higher. The peak P2 derived from an O-C=O bond in the O1s spectrum appears in the range of 530 eV or higher and 533 eV or lower. The peak P3 derived from a C=O bond in the O1s spectrum appears in the range of 530 eV or higher and 533 eV or lower.

[0032] The area ratio of peak P1 derived from a C-O bond in the O1s spectrum is defined as [CO]. The area ratio of peak P2 derived from an O-C=O bond in the O1s spectrum is defined as [COO]. The area ratio of peak P3 derived from a C=O bond in the O1s spectrum is defined as [C=O]. In this case, the ratio of the area ratio of peak P1 [CO] to the sum of the area ratio of peak P2 [COO] and the area ratio of peak P3 [C=O] is less than 2.0.

[0033] That is, the amount of surface functional groups on the carbon material is adjusted to satisfy the following mathematical formula (1): In other words, the total amount of surface functional groups containing O-C=O bonds, which are in a more advanced oxidation state than surface functional groups containing C-O bonds, and surface functional groups containing C=O bonds is reduced until at least the following mathematical formula (1) is satisfied.

[0034] ([COO] + [C=O]) / [CO] < 2.0 (Equation 1) [COO] is the area ratio of peak P2 due to the O-C=O bond in the O1s spectrum, [C=O] is the area ratio of peak P3 due to the C=O bond in the O1s spectrum, and [CO] is the area ratio of peak P1 due to the C-O bond in the O1s spectrum.

[0035] By laminating a carbon layer containing a carbon material that satisfies the above formula (Equation 1) on the cathode body, the amount of hydrogen gas generated in the electrolytic capacitor is reduced. Although this mechanism is speculative and not limited to this mechanism, the mechanism by which hydrogen gas generation is suppressed by satisfying the above formula (Equation 1) is thought to be as follows.

[0036] First, on the cathode side, in addition to the reduction reaction of hydrogen ions shown in the above chemical reaction formula (2), the reduction reaction of dissolved oxygen shown in the following chemical reaction formula (4) can occur. When the cathodic reaction that reduces dissolved oxygen occurs predominantly, the cathodic reaction that reduces hydrogen ions is suppressed. TIFF2025121729000003.tif11162

[0037] Furthermore, surface functional groups that have become highly oxidized are susceptible to reduction reactions, such as when OC=O bonds become HC=O bonds or C-OH bonds. This reduction reaction acts to suppress the reduction reaction of dissolved oxygen in the electrolyte. When the reduction reaction of dissolved oxygen is dominant, the reduction reaction of hydrogen ions becomes sluggish, but when the reduction reaction of dissolved oxygen is suppressed, the reduction reaction of hydrogen ions becomes more likely to occur. This makes it easier for hydrogen gas to be generated.

[0038] Conversely, if the amount of oxidized surface functional groups is reduced, the reduction reaction caused by the surface functional groups of the carbon material is reduced, making it less likely to inhibit the reduction reaction of dissolved oxygen. As a result, the reduction reaction of dissolved oxygen suppresses the reduction reaction of hydrogen ions, thereby suppressing the generation of hydrogen gas. Furthermore, by satisfying the above formula (Mathematical Formula 1), the effect of suppressing the generation of hydrogen gas becomes significant.

[0039] (electrolytic capacitor) An electrolytic capacitor is constructed by housing a capacitor element including this cathode body in a case and sealing the case opening with a sealing member. 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. The case is crimped to bend and crush the opening inward, thereby tightly sealing the sealing member. The sealing member is formed, for example, from a resin plate containing a resin such as phenolic resin, or an elastic material such as rubber.

[0040] The capacitor element includes an anode body and a separator in addition to a cathode body. The capacitor element also includes an electrolyte that fills the voids in the capacitor element and the separator. The anode body has a dielectric coating on its surface. The electrolyte is interposed between the anode body and the cathode body and is in close contact with the dielectric coating.

[0041] (anode body) The anode body is made of a valve metal foil with a dielectric coating formed on its surface. The purity of the valve metal for the anode foil is preferably 99.9% or higher, but impurities such as silicon, iron, copper, magnesium, and zinc may be present. The anode foil can be produced as a compact formed from valve metal powder, a sintered compact formed from a compact, an etched foil formed from rolled foil that has been etched, or a sintered compact formed from rolled foil with valve metal powder molded and sintered.

[0042] The surface-expanding structure is formed by tunnel-like pits, spongy pits, or voids between densely packed powder particles. The surface-expanding structure is typically formed by direct current etching or alternating current etching, which applies direct current or alternating current in an acidic aqueous solution containing halogen ions, such as hydrochloric acid, or by vapor deposition or sintering of metal particles or the like on the core. The cathode foil may also be etched to have the surface-expanding structure.

[0043] The dielectric film is typically an oxide film formed on the surface of the anode foil. For example, if the anode foil is an aluminum foil, the dielectric film is aluminum oxide obtained by oxidizing the surface-expanding structure. The dielectric film is formed by chemical conversion treatment in which a voltage is applied in an aqueous solution of adipic acid, boric acid, phosphoric acid, or the like. Alternatively, a thin dielectric film (approximately 1 to 10 V) may be formed on the surface of the cathode foil by chemical conversion treatment, as needed. Furthermore, the dielectric film may be produced by a vapor deposition method, a sol-gel method, a liquid-phase deposition method, or the like. Alternatively, the dielectric film may be a layer formed by molding oxidized valve metal powder onto the foil surface.

[0044] (separator) Examples of materials for the separator include cellulose papers such as kraft, Manila hemp, esparto, hemp, 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.

[0045] The separator may be fibrillated by generating thin fibers that branch off from the surface of the original fibers, such as fibrillated cellulose. The fibrillation can be achieved, for example, by beating. The fibrillated fibers are entangled with each other using the fibrillated thin fibers, improving the strength of the separator. This allows the separator to be made thinner. Reducing the separator thickness allows for larger anode and cathode bodies per unit volume, improving the capacitance of the electrolytic capacitor.

[0046] (electrolyte) The electrolyte is an electrolyte in which a solute is dissolved in a solvent, and additives are added as needed. 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 sulfoxides.

[0047] Examples of monohydric alcohols include ethanol, propanol, butanol, pentanol, hexanol, cyclobutanol, cyclopentanol, cyclohexanol, benzyl alcohol, etc. Examples of polyhydric alcohols and oxyalcohol compounds include ethylene glycol, propylene glycol, glycerin, methyl cellosolve, ethyl cellosolve, methoxypropylene glycol, dimethoxypropanol, etc.

[0048] 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. Examples of sulfoxides include dimethyl sulfoxide.

[0049] The solute contained in the electrolytic solution includes anionic and cationic components, and is typically an organic acid or a salt thereof, an inorganic acid or a salt thereof, or a salt of a complex compound of an organic acid and an inorganic acid, and may be used alone or in combination of two or more.

[0050] Examples of organic acids that serve as anionic 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, resorcylic acid, phloroglucinic acid, gallic acid, gentisic acid, protocatechuic acid, pyrocatechuic acid, trimellitic acid, pyromellitic acid, undecanedioic acid, dodecanedioic acid, tridecanedioic acid, t-butyladipic acid, and 11-vinyl-8-octadecenedioic acid, as well as phenols and sulfonic acids.

[0051] 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.

[0052] Examples of the cationic component include ammonium, quaternary ammonium, quaternized amidinium, amine, sodium, potassium, etc. Examples of the quaternary ammonium include tetramethylammonium, triethylmethylammonium, tetraethylammonium, etc. Examples of the quaternized amidinium include ethyldimethylimidazolinium, tetramethylimidazolinium, etc. Examples of the amine include primary amine, secondary amine, and tertiary amine. Examples of the primary amine include methylamine, ethylamine, propylamine, etc. Examples of the secondary amine include dimethylamine, diethylamine, ethylmethylamine, dibutylamine, etc. Examples of the tertiary amine include trimethylamine, triethylamine, tributylamine, ethyldimethylamine, ethyldiisopropylamine, etc.

[0053] The anions and cations may be added to the electrolytic solution in the form of ionically dissociable salts, or an acid that becomes the anion and a base that becomes the cation may be added to the electrolytic solution separately as solute components. The anions and cations may be used alone or in combination of two or more.

[0054] Glycol compounds are preferred as the solvent for the electrolyte. 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, reducing the ESR and improving the withstand voltage of electrolytic capacitors. Examples of glycol compounds include ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, and polyoxyethylene glycol. The electrolyte may contain one type of glycol compound solvent, or two or more types of glycol compound solvents. Furthermore, glycol compounds may be used alone as the solvent, or may be combined with other glycol compounds.

[0055] Furthermore, other additives can be added to the electrolyte. Examples of additives include complex compounds of boric acid and polysaccharides (e.g., mannitol, sorbitol), complex compounds of boric acid and polyhydric alcohols, borate esters, nitro compounds, phosphate esters, and colloidal silica. These may be used alone or in combination of two or more. Nitro compounds suppress the generation of hydrogen gas in the electrolytic capacitor. Examples of nitro compounds include o-nitrobenzoic acid, m-nitrobenzoic acid, p-nitrobenzoic acid, o-nitrophenol, m-nitrophenol, and p-nitrophenol.

[0056] The electrolyte is impregnated into the voids within the capacitor element by immersing the capacitor element in the electrolyte. A depressurization or pressurization process may be performed as necessary to impregnate the electrolyte into smaller voids. The electrolyte impregnation process may be repeated multiple times. For example, the pressure inside the capacitor element may be reduced, and the electrolyte may be injected into the capacitor element while pressurizing the electrolyte.

[0057] When using a gel electrolyte in an electrolytic capacitor, polyvinyl alcohol may be added to the electrolyte solution to increase viscosity, or the electrolyte may be composed of an electrolyte solution and a polymer with a three-dimensional network structure that holds the electrolyte solution. The three-dimensional network structure polymer is formed by crosslinking the polymer formed by polymerizing the monomer using a monomer that forms the main chain of the gel network, a polymerization initiator for polymerizing the monomer, and a crosslinking agent for crosslinking the polymer.

[0058] (Manufacturing method) (wound type) An example of a manufacturing method for an electrolytic capacitor is as follows: First, in the anode formation step, a surface expansion layer is formed on one or both sides of an anode foil, and a dielectric film is formed on the surface expansion layer by chemical conversion treatment.

[0059] The cathode side includes a surface functional group adjusting step and a cathode forming step. In the surface functional group adjusting step, a treatment is performed to adjust the amount of surface functional groups of the carbon material. The cathode forming step includes a cathode foil forming step and a carbon layer laminating step. In the cathode foil forming step, a surface enlarging layer is formed on one or both sides of the cathode foil as needed, and an oxide film is formed on the surface. In the carbon layer laminating step, a carbon layer containing a carbon material is laminated on the cathode foil. An anode lead and a cathode lead are electrically and mechanically connected to the anode body and the cathode body.

[0060] In the element formation process, long anode and cathode bodies are wound with a separator interposed therebetween to produce a cylindrical wound body. The separator is overlapped so that one end protrudes beyond one end of the anode and cathode bodies. The protruding separator is wound first so that the core of the wound body is aligned with the short sides of the anode and cathode bodies to produce a winding core. Then, the anode and cathode bodies are wound by rolling up the long sides of the anode and cathode bodies using the winding core as a winding shaft.

[0061] In the impregnation step, the capacitor element is immersed in an electrolyte solution to impregnate the voids within the capacitor element with the electrolyte solution. A depressurization or pressurization process may be performed as necessary to impregnate the electrolyte solution into smaller voids. The electrolyte impregnation step 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.

[0062] The capacitor element is housed in an outer case with one end closed and the other end open, and the capacitor element is sealed in the outer case with a sealing member. The sealing member is made of 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 outer case. A pressure valve is formed at the bottom of the case, which opens when the pressure inside the case exceeds a predetermined value. After the capacitor element is sealed in the outer 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 such as the bare metal portion of the valve metal exposed when the anode body was cut and defects in the dielectric coating that occurred during the element formation process, and to form a dielectric coating.

[0063] (Laminated type) In the element formation process for stacked electrolytic capacitors, flat anode foils and cathode bodies are stacked with a separator between them. After the stack is impregnated with an electrolyte, the capacitor element is covered with a laminate film. Alternatively, the element is encapsulated by molding, dip-coating, or printing with a resin such as a heat-resistant resin or an insulating resin. Finally, a voltage application process is carried out, similar to that for wound-type capacitors. [Example]

[0064] The cathode body and electrolytic capacitor of the present invention will be described in more detail below based on examples, but the present invention is not limited to the examples described below.

[0065] (Example) Cathode bodies were fabricated in Examples 1 to 3 and Comparative Examples 1 to 4, and electrolytic capacitors were fabricated using each cathode body. Each carbon material to be contained in the carbon layer was prepared in Examples 1 to 3 and Comparative Examples 1 to 3. In Comparative Example 4, no carbon layer was laminated on the cathode body.

[0066] In Example 1, carbon black was used as the carbon material, in Example 2, carbon black was used as the carbon material, in Example 3, Ketjen black was used as the carbon material, in Comparative Example 1, carbon black was used as the carbon material, in Comparative Example 2, a mixture of aluminum carbide and carbon (Al4C3+C) was used as the carbon material, and in Comparative Example 3, carbon nanotubes (CNTs) were used, and they were prepared so that the amount of surface functional groups was different.

[0067] The carbon materials of Examples 1 to 3 and Comparative Examples 1 to 3 were analyzed by X-ray photoelectron spectroscopy. For X-ray photoelectron spectroscopy, an X-ray photoelectron spectrometer (manufactured by Kratos Analytical, model number ESCA-3400, control software Vision Instrument Manager) was used. Each carbon material was placed on a sample stage, and spectrum measurement was performed by narrow scan measurement. Magnesium Kα radiation (Mg-Kα) was used as the X-ray source, and the carbon material was irradiated with X-rays to obtain an O1s spectrum (526 to 540 eV). Other narrow scan conditions were an acceleration voltage of 10 kV, an emission current of 15 mA, a pass energy of 75 eV, a step voltage of 0.05 eV, and 35 accumulations.

[0068] Vision Processing was used as the waveform analysis software for the O1s spectrum. The Shirley method was used for background subtraction to separate the O1s spectrum into background and signal. Charge correction was performed on the O1s spectrum by correcting the peak-top binding energy of the C1s spectrum (280–300 eV) obtained under the same measurement conditions as the O1s spectrum to 284.8 eV. A Gaussian-Lorentzian mixed function (70% Gaussian function ratio) was used for peak fitting to approximate individual peaks. For peak fitting, the full width half maximum (FWHM) of the C1s spectrum was set to 1.5–1.9 eV, and the FWHM of the O1s spectrum was set to 2.0–2.5 eV. In all of the spectra of Examples 1 to 3 and Comparative Examples 1 to 3, the FWHM of each peak obtained by waveform separation of the same spectrum was set to the same value, and peak fitting was performed.

[0069] 1 to 6 show the analysis results of Examples 1 to 3 and Comparative Examples 1 to 3 by X-ray photoelectron spectroscopy. FIG. 1 shows the analysis results of the carbon material of Example 1 by X-ray photoelectron spectroscopy. FIG. 2 shows the analysis results of the carbon material of Example 2 by X-ray photoelectron spectroscopy. FIG. 3 shows the analysis results of the carbon material of Example 3 by X-ray photoelectron spectroscopy. FIG. 4 shows the analysis results of the carbon material of Comparative Example 1 by X-ray photoelectron spectroscopy. FIG. 5 shows the analysis results of the carbon material of Comparative Example 2 by X-ray photoelectron spectroscopy. FIG. 6 shows the analysis results of the carbon material of Comparative Example 3 by X-ray photoelectron spectroscopy.

[0070] In the figure, S is the measured O1s spectrum, Wc is the synthetic waveform, P1 is the peak due to the C-O bond, P2 is the peak due to the O-C=O bond, P3 is the peak due to the C=O bond, and P4 is the peak due to the H2O bond.

[0071] The numerical values of the analysis results by X-ray photoelectron spectroscopy are as shown in Table 1 below. (Table 1) TIFF2025121729000004.tif136161

[0072] In Examples 1 to 3 and Comparative Examples 1 to 3, electrolytic capacitors were produced using cathode bodies in which a carbon layer containing the carbon material shown in Table 1 was laminated on a cathode foil. In Comparative Example 4, an electrolytic capacitor was produced using a cathode foil without a carbon layer.

[0073] The cathode foils in Examples 1 to 3 and Comparative Examples 1 to 4 were aluminum foils measuring 3 cm x 4 cm. Except for Comparative Example 3, the aluminum foils were subjected to an AC etching treatment, and a surface-enlarging layer consisting of spongy etching pits was formed on both sides of the foil. In the AC etching treatment, the cathode foils were immersed in an acidic aqueous solution containing approximately 8% by weight of hydrochloric acid as the main electrolyte at a liquid temperature of 25°C, and an AC current of 10 Hz and a current density of 0.14 A / cm was applied. 2 A current of 1000kJ / cm2 was applied to the substrate for about 5 minutes to enlarge both surfaces of the aluminum foil. Then, the aluminum foil was subjected to a chemical conversion treatment to form a dielectric film on the surface of the surface-enlarging layer.

[0074] A carbon layer was laminated on the cathode foils of Examples 1 to 3 and Comparative Examples 1 to 3. Except for Comparative Example 2, a carbon material shown in Table 1 above, styrene butadiene rubber (SBR) as a binder, and an aqueous solution of carboxymethyl cellulose sodium (CMC-Na) as a dispersant-containing aqueous solution were mixed and kneaded in a composition ratio of 84:6:10 to prepare a slurry for the carbon layer.

[0075] This slurry was uniformly applied to the cathode foil. The slurry was then heated and dried to volatilize the solvent. In Example 1, the cathode body was further subjected to press working. In the press working, the cathode body was sandwiched between press rollers, and a linear press pressure of 5.38 kN / cm was applied to fix the carbon layer onto the cathode foil. The linear press pressure was applied using a press machine manufactured by Takumi Giken Co., Ltd. The diameter of the press rollers was 180 mm, the press width was 130 mm, and the cathode body was transported once at 3 m / min.

[0076] The carbon layer of Comparative Example 2 has a two-layer structure in which a carbon layer is formed on the surface of an aluminum carbide layer. First, the surface of an aluminum foil is coated with carbon particles, and the aluminum foil coated with carbon particles is heat-treated in a hydrocarbon atmosphere. This heat treatment carbonizes the surface of the aluminum foil, forming an aluminum carbide layer.

[0077] The anode element was common to Examples 1 to 3 and Comparative Examples 1 to 4. A 3 cm x 4 cm aluminum foil was used as the anode foil. The aluminum foil was subjected to a DC etching process to form a surface-enlarging layer consisting of tunnel-shaped etching pits. The DC etching process involved a first step to form pits and a second step to enlarge the pits. In the first step, the aluminum foil was electrochemically etched with a DC current in an aqueous solution containing chloride ions. In the second step, the pits formed in the aluminum foil after the first step were enlarged by electrochemical etching with a DC current in an aqueous solution containing nitrate ions.

[0078] After forming the surface-expanding layer, the anode foil was subjected to chemical conversion treatment to form a dielectric film on the surface of the surface-expanding layer. Specifically, a voltage of 558 V was applied in a chemical conversion solution of 70 wt % boric acid at a liquid temperature of 85°C.

[0079] Aluminum tab-shaped lead terminals were ultrasonically connected to the anode foil and cathode body, respectively. A stack was then fabricated by sandwiching the anode foil between two cathode bodies with a separator interposed between them. A 4 cm x 5 cm kraft separator was used as the separator. Prior to stacking, the rear side of the cathode body, opposite the side facing the anode foil across the separator, was covered with insulating resin.

[0080] The laminate of the anode foil, cathode body, and separator was impregnated with an electrolyte solution. The electrolyte solution contained ethylene glycol as a solvent and azelaic acid salt as a solute. After impregnation with the electrolyte solution, the laminate of the anode foil, cathode body, and separator was sealed with a laminate material. The lead terminals connected to the anode foil and cathode body were extended outside the laminate material. In this way, a laminate cell electrolytic capacitor was fabricated. The laminate material was made of aluminum with a thickness of 110 μm.

[0081] After the laminate cells were prepared, they were subjected to an aging treatment in which a voltage of 450 V was applied for 120 minutes at room temperature (25°C). As a result, electrolytic capacitors with a rated voltage of 401 V according to Examples 1 to 3 and Comparative Examples 1 to 4 were prepared.

[0082] (Hydrogen gas generation test) A DC voltage of 401 V was applied to the electrolytic capacitors of Examples 1 to 3 and Comparative Examples 1 to 4 for 2000 hours at a temperature of 105°C, and the amount of gas generated was measured at each elapsed time. The amount of gas generated was measured by the swelling amount (volume change; ml) of the laminate cell. The swelling amount of the laminate cell was measured by Archimedes' method. That is, the volume of liquid displaced by the laminate cell was measured by measuring the weight increase when the laminate cell was immersed in water.

[0083] The measurement results of the hydrogen gas generation test are shown in Fig. 7. Fig. 7 is a graph showing the volume change over time of the electrolytic capacitors of Examples 1 to 3 and Comparative Examples 1 to 4.

[0084] 7, there is a large difference in the volume change after 2000 hours between the groups of Comparative Examples 1 to 4 and the groups of Examples 1 to 3. In other words, it can be confirmed that a large amount of hydrogen gas is generated in the groups of Comparative Examples 1 to 4, whereas hydrogen gas generation is suppressed in the groups of Examples 1 to 3.

[0085] Furthermore, Comparative Example 4 is an electrolytic capacitor using a cathode body without a carbon layer, but it is clear that the electrolytic capacitors of Comparative Examples 1 to 3 generate a large amount of hydrogen gas despite having a carbon layer on the cathode body. On the other hand, it is confirmed that the electrolytic capacitors of Examples 1 to 3 suppress hydrogen gas generation despite having a carbon layer on the cathode body, just like Comparative Examples 1 to 3.

[0086] As shown in Table 1 above, the cathode bodies of Comparative Examples 1 to 3 have a ratio of the sum of the area ratio [COO] of peak P2 derived from an O-C=O bond in the O1s spectrum and the area ratio [C=O] of peak P3 derived from a C=O bond in the O1s spectrum to the area ratio [CO] of peak P1 derived from a C-O bond in the O1s spectrum, such that ([COO] + [C=O]) / [CO] > 2.0. That is, the cathode bodies of Comparative Examples 1 to 3 have carbon layers containing a carbon material with many surface functional groups in an oxidized state.

[0087] On the other hand, in the cathode bodies of Examples 1 to 3, as shown in Table 1 above, the ratio of the sum of the area ratio [COO] of peak P2 derived from an O-C=O bond in the O1s spectrum and the area ratio [C=O] of peak P3 derived from a C=O bond in the O1s spectrum to the area ratio [CO] of peak P1 derived from a C-O bond in the O1s spectrum is ([COO]+[C=O]) / [CO]<2.0. That is, the cathode bodies of Examples 1 to 3 are provided with a carbon layer containing a carbon material with few surface functional groups in an oxidized state.

[0088] As a result, it was confirmed that the amount of hydrogen gas generated can be suppressed not only by the cathode body including a carbon layer, but also by the carbon material contained in the carbon layer, where the ratio of the area ratio [CO] of peak P1 resulting from CO bonds in the O1s spectrum to the sum of the area ratio [COO] of peak P2 resulting from O-C=O bonds in the O1s spectrum and the area ratio [C=O] of peak P3 resulting from C=O bonds in the O1s spectrum is ([COO]+[C=O]) / [CO]<2.0, as determined by analysis using X-ray photoelectron spectroscopy.

Claims

1. A cathode body of an electrolytic capacitor, a cathode foil made of a valve metal; a carbon layer including a carbon material laminated on the cathode foil; Equipped with The carbon material is By analysis by X-ray photoelectron spectroscopy, a peak P1 derived from a C—O bond in the O1s spectrum, a peak P2 derived from an O—C═O bond in the O1s spectrum, and a peak P3 derived from a C═O bond in the O1s spectrum were detected. a ratio of the sum of the area ratio [COO] of the peak P2 and the area ratio [C=O] of the peak P3 to the area ratio [C-O] of the peak P1 is ([COO]+[C=O]) / [C-O]<2.0; A cathode body characterized by:

2. The peak P1 due to the C—O bond in the O1s spectrum appears in the range of 533 eV or higher, The peak P2 derived from the O—C═O bond in the O1s spectrum appears in the range of 530 eV or more and 533 eV or less, the peak P3 derived from a C═O bond in the O1s spectrum appears in the range of 530 eV or more and 533 eV or less; The cathode body according to claim 1 ,

3. The cathode body according to claim 1 or 2; an anode body having a dielectric coating and facing the cathode body; an electrolyte interposed between the cathode body and the anode body; To have An electrolytic capacitor characterized by:

4. a surface functional group adjusting step of adjusting the amount of surface functional groups of the carbon material; a carbon layer lamination step of forming a carbon layer containing the carbon material on a cathode foil made of a valve metal; Including, In the surface functional group adjusting step, By analyzing the carbon material by X-ray photoelectron spectroscopy, a peak P1 derived from a C—O bond in the O1s spectrum, a peak P2 derived from an O—C═O bond in the O1s spectrum, and a peak P3 derived from a C═O bond in the O1s spectrum are detected; adjusting the ratio of the area ratio [C-O] of the peak P1 to the sum of the area ratio [COO] of the peak P2 and the area ratio [C=O] of the peak P3 to satisfy ([COO]+[C=O]) / [C-O]<2.0; 2. A method for manufacturing a cathode body of an electrolytic capacitor, comprising:

5. The peak P1 due to the C—O bond in the O1s spectrum appears in the range of 533 eV or higher, The peak P2 derived from the O—C═O bond in the O1s spectrum appears in the range of 530 eV or more and 533 eV or less, the peak P3 derived from a C═O bond in the O1s spectrum appears in the range of 530 eV or more and 533 eV or less; 5. The method for manufacturing a cathode body of an electrolytic capacitor according to claim 4,

6. a step of producing the cathode body according to claim 4 or 5; preparing an anode body having a dielectric coating; interposing an electrolyte between the cathode body and the anode body; To have A method for manufacturing an electrolytic capacitor, comprising:

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