Electrolytic capacitor and method for producing same

Abstract

This electrolytic capacitor comprises a capacitor element. The capacitor element comprises: a positive electrode body that has a dielectric layer on the surface thereof; and an electrolyte that covers a part of the dielectric layer. The electrolyte contains a conjugated polymer, a polymer dopant that has an anionic group, and a metal ion. The amount of the metal ion is less than 1 equivalent per 1 equivalent of the anionic group.

Description

Electrolytic capacitor and its manufacturing method

[0001] The present disclosure relates to electrolytic capacitors and methods for manufacturing the same.

[0002] Electrolytic capacitors, which include an anode body having a dielectric layer on its surface and a solid electrolyte layer covering at least a portion of the dielectric layer, are considered promising as capacitors with small size, large capacity, and low ESR (equivalent series resistance). The solid electrolyte layer typically contains a conductive polymer that includes a conjugated polymer and a dopant. The solid electrolyte layer is formed, for example, using a liquid dispersion containing the conductive polymer. Polymer-type polyanions such as polystyrene sulfonate are commonly used as dopants in the liquid dispersion.

[0003] Patent Document 1 proposes a conductive polymer particle dispersion comprising a solvent containing water as a main component, and polythiophene particles dispersed in the solvent, the polythiophene particles having at least one polymer unit selected from thiophenes and their derivatives and containing a polyanion as a dopant, the dispersion having a pH of 3 or higher and containing an iron compound insoluble in the solvent with a concentration of 450 ppm or less.

[0004] Patent Document 2 proposes a method for producing a dispersion for forming a solid electrolyte layer, the method comprising the steps of: dispersing a thiophene as a monomer and a polyanion as a dopant in a solvent mainly composed of water to prepare a dispersion; and mixing the dispersion with an oxidizing agent to oxidatively polymerize the monomer to prepare a conductive polythiophene microparticle dispersion doped with the polyanion. Patent Document 2 proposes using, as the polyanion, polystyrene sulfonic acid or the like, in which the hue of an aqueous solution obtained by dissolving the polyanion in water to a concentration of 2% has a Hazen color scale of 10 or more and 1,000 or less, as measured by the APHA method.

[0005] International Publication No. WO 2014 / 155420 International Publication No. WO 2014 / 155422

[0006] Polymer dopants such as polystyrene sulfonic acid are highly effective in improving the conductivity of conductive polymers, which is advantageous for keeping the ESR of electrolytic capacitors low. However, due to their high molecular weight, polymer dopants are difficult to impregnate into minute recesses in the dielectric layer. In electrolytic capacitors, if the coverage of the dielectric layer by the conductive polymer can be improved, further increases in capacitance are possible.

[0007] One aspect of the present disclosure relates to an electrolytic capacitor including a capacitor element, wherein the capacitor element includes an anode body having a dielectric layer on a surface thereof and an electrolyte covering a portion of the dielectric layer, wherein the electrolyte includes a conjugated polymer, a polymer dopant having an anionic group, and a metal ion, and the amount of the metal ion is less than 1 equivalent relative to 1 equivalent of the anionic group.

[0008] Another aspect of the present disclosure relates to a method for producing an electrolytic capacitor including a capacitor element including an anode body having a dielectric layer on a surface thereof and an electrolyte covering a portion of the dielectric layer, the method comprising: preparing a liquid mixture containing a conjugated polymer, a first polymer dopant having anionic groups, and metal ions; and applying the liquid mixture to the anode body to form the electrolyte, wherein the step of preparing the liquid mixture comprises the substeps of polymerizing a precursor of the conjugated polymer in the presence of the first polymer dopant and an oxidizing agent to obtain a first mixture containing the conjugated polymer and the first polymer dopant; and further mixing the metal ions with the first mixture to prepare the liquid mixture as a second mixture.

[0009] The present invention provides an electrolytic capacitor having a high capacitance and a low ESR. The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

[0010] 1 is a schematic cross-sectional view of an electrolytic capacitor according to an embodiment of the present disclosure.

[0011] The following describes embodiments of the electrolytic capacitor according to the present disclosure using examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be used as examples. However, other numerical values ​​and materials may be used as long as the effects of the present disclosure are obtained. In this specification, the term "numerical value A to numerical value B" includes numerical value A and numerical value B and can be interpreted as "numerical value A or greater and numerical value B or less." In the following description, when lower and upper limits for specific physical properties or conditions are exemplified, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit is not greater than the upper limit. When multiple materials are exemplified, one of the materials may be selected and used alone, or two or more materials may be used in combination.

[0012] The present disclosure also encompasses combinations of two or more features arbitrarily selected from the appended claims, i.e., two or more features arbitrarily selected from the appended claims can be combined unless a technical contradiction arises.

[0013] "Electrolytic capacitor" may be read as "solid electrolytic capacitor", and "capacitor" may be read as "capacitor".

[0014] It has been revealed that when an electrolyte for an electrolytic capacitor is formed using a liquid mixture containing a conductive polymer that includes a conjugated polymer and a polymer dopant, the capacitor performance may be improved if the liquid mixture contains metal ions.

[0015] The conductive polymer contained in the liquid mixture used to form the electrolyte is typically formed by polymerizing a conjugated polymer precursor in the presence of a polymer dopant. Meanwhile, metal ions are typically added to the conductive polymer in the form of a salt of the polymer dopant and the metal ion. Therefore, the amount of metal ions in the liquid mixture is small compared to the total amount of polymer dopant. More specifically, it is less than one equivalent of the anionic groups in the polymer dopant. Electrolytic capacitors containing such electrolytes can achieve low ESR and high capacitance. This is believed to be because the liquid mixture contains an appropriate amount of metal ions, which facilitates penetration of the liquid mixture into the fine recesses of the dielectric layer, improving the coverage of the dielectric layer with the conductive polymer, thereby increasing capacitance and lowering tan δ. Furthermore, the polymer dopant contains many anionic groups, which is believed to provide high conductivity for the conductive polymer and thereby reducing the ESR of the electrolytic capacitor.

[0016] It is also possible to polymerize the precursor using a salt of a polymer dopant and a metal ion. However, when a conductive polymer obtained by polymerization in the presence of a salt is used, the coverage of the dielectric layer by the conductive polymer increases, but the ESR tends to increase. When the polymer dopant is used in a salt state, the amount of metal ions is greater than one equivalent per equivalent of the anionic group of the polymer dopant. Therefore, it is thought that an increase in the amount of metal ions reduces the conductivity of the electrolyte and increases the ESR.

[0017] The electrolytic capacitor will be described in more detail below.

[0018] [Electrolytic Capacitor] (Capacitor Element) The capacitor element included in the electrolytic capacitor includes at least an anode body having a dielectric layer on its surface, and an electrolyte covering a portion of the dielectric layer.

[0019] (Anode Body) The anode body can contain a valve metal, an alloy containing a valve metal, a compound containing a valve metal, or the like. These materials can be used alone or in combination of two or more. Examples of preferred valve metals include aluminum, tantalum, niobium, and titanium. Anode bodies with porous surfaces can be obtained by roughening the surface of a substrate (such as a foil-shaped or plate-shaped substrate) containing a valve metal, for example, by etching. The anode body can also be a compact of particles containing a valve metal, or a sintered body thereof. The sintered body has a porous structure.

[0020] (Dielectric Layer) The dielectric layer is formed by anodizing the valve metal on the surface of the anode body by chemical conversion treatment or the like. The dielectric layer may be formed so as to cover at least a portion of the anode body. The dielectric layer is usually formed on the surface of the anode body. Since the dielectric layer is formed on the porous surface of the anode body, it is formed along the inner wall surfaces of holes and depressions (pits) on the surface of the anode body.

[0021] The dielectric layer contains an oxide of a valve metal. For example, when tantalum is used as the valve metal, the dielectric layer contains Ta2O5, and when aluminum is used as the valve metal, the dielectric layer contains Al2O3. However, the dielectric layer is not limited to this and may be any material that functions as a dielectric. When the surface of the anode body is porous, the dielectric layer is formed along the surface of the anode body (including the inner wall surfaces of the pores).

[0022] (Electrolyte) The electrolyte contains a conjugated polymer, a polymer dopant having an anionic group, and metal ions. In the electrolyte, the conjugated polymer and the polymer dopant constitute a conductive polymer, which provides high conductivity of the electrolyte. The electrolyte attached to the surface of the dielectric layer may form a layer. Such an electrolyte layer is sometimes called a solid electrolyte layer or a conductive polymer layer. The electrolyte constitutes at least a portion of the cathode body in the electrolytic capacitor.

[0023] (Conjugated Polymers) Examples of conjugated polymers include known conjugated polymers used in electrolytic capacitors, such as π-conjugated polymers. Examples of conjugated polymers include polymers with a basic skeleton of polypyrrole, polythiophene, polyaniline, polyfuran, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, and polythiophene vinylene. The above polymers may contain at least one monomer unit constituting the basic skeleton. The above polymers also include homopolymers, copolymers of two or more monomers, and derivatives thereof (e.g., substituted products having substituents). For example, polythiophenes include poly(3,4-ethylenedioxythiophene).

[0024] The conjugated polymer may be used alone or in combination of two or more kinds.

[0025] The weight average molecular weight (Mw) of the conjugated polymer is not particularly limited, but is, for example, 1,000 or more and 1,000,000 or less.

[0026] In this specification, the weight average molecular weight (Mw) is a value calculated as polystyrene measured by gel permeation chromatography (GPC), which is typically performed using a polystyrene gel column and a water / methanol (volume ratio 8 / 2) mobile phase.

[0027] (Dopant) A polymer dopant (first dopant) having an anionic group is used as the dopant. By using the first dopant, dedoping from the conjugated polymer is less likely to occur, the ESR is easily kept low, and excellent capacitor performance can be stably obtained. If necessary, a second dopant other than the first dopant may be used as the electrolyte. Examples of the second dopant include a relatively low molecular weight anion.

[0028] The first dopant may be, for example, a polymer having a plurality of anionic groups. Such a polymer may include a polymer containing a monomer unit having an anionic group. Examples of the anionic group include a sulfonic acid group and a carboxyl group. The first dopant may have one type of anionic group, or may have two or more types of anionic groups.

[0029] In the electrolyte, the anionic group of the first dopant is in the form of an acid (e.g., a sulfonic acid group, -SO ３ H), anionic form (e.g., sulfonic acid group, -SO ３ － The first dopant may be contained in the electrolyte in at least one form selected from the group consisting of anionic groups, sulfonic acid groups, and salt forms. The salt form includes a form in which the anionic group and a metal ion form a salt. The anionic group may also form a salt with a cation present in the vicinity of the electrolyte in the electrolytic capacitor. Such a salt is also included in the above-mentioned salt form. The anionic group of the first dopant may be contained in the electrolyte in a form in which it is bonded to or interacts with the conjugated polymer. In this specification, all of these forms may be referred to simply as an "anionic group," a "sulfonic acid group," a "carboxy group," or the like.

[0030] Specific examples of the first dopant having a carboxy group include polyacrylic acid, polymethacrylic acid, and copolymers using at least one of acrylic acid and methacrylic acid. Examples of the first dopant having a sulfonic acid group include polymeric polysulfonic acid. Specific examples of the first dopant having a sulfonic acid group include polyvinyl sulfonic acid, polystyrene sulfonic acid (including copolymers and substituted products having substituents), polyallylsulfonic acid, polyacrylic sulfonic acid, polymethacrylic sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, polyester sulfonic acid (such as aromatic polyester sulfonic acid), and phenolsulfonic acid novolac resin. These are merely examples, and the first dopant is not limited to these.

[0031] Examples of the second dopant include sulfate ions, nitrate ions, phosphate ions, borate ions, organic sulfonate ions, and carboxylate ions. Compounds capable of generating these ions (e.g., acids, salts, etc.) may also be used. For example, compounds that generate sulfonate ions include aromatic sulfonic acids (e.g., p-toluenesulfonic acid, naphthalenesulfonic acid, etc.). However, these are merely examples, and the second dopant is not limited to these examples.

[0032] The amount of the first dopant contained in the electrolyte is, for example, 10 to 1000 parts by mass, or may be 20 to 500 parts by mass, or 50 to 200 parts by mass, relative to 100 parts by mass of the conjugated polymer.

[0033] The amount of the second dopant contained in the electrolyte is, for example, 10 parts by mass or less, and may be 5 parts by mass or less, relative to 100 parts by mass of the conjugated polymer. The amount of the second dopant contained in the electrolyte may be 1 part by mass or more, relative to 100 parts by mass of the conjugated polymer.

[0034] (Metal Ions) In an electrolyte in which the metal ions are not dissociated, a portion of the first dopant typically forms a salt with the metal ions. For example, when the electrolytic capacitor does not contain a liquid component, the metal ions typically form a salt with the anionic groups of the first dopant. When the electrolyte contains a second dopant, the metal ions may also form a salt with the anionic groups of the second dopant. When the electrolytic capacitor does not contain a liquid component, a portion of the metal ions may also form a salt with an anion present near the electrolyte.

[0035] The amount of metal ions is less than 1 equivalent relative to 1 equivalent of the anionic group of the first dopant. When the electrolyte contains such an amount of metal ions, the ESR can be kept low while ensuring high impregnation of the liquid mixture used to form the electrolyte into the fine recesses of the dielectric layer. Furthermore, when a separator is used, it is thought that the permeability of the liquid mixture into the separator is also improved. High impregnation of the liquid mixture improves the coverage of the electrolyte on the dielectric layer, thereby achieving high capacity and keeping tan δ low. The amount of metal ions relative to 1 equivalent of the anionic group of the first dopant is, for example, 0.001 equivalents or more but less than 1. From the viewpoint of easily obtaining a higher capacitance, the amount of metal ions relative to 1 equivalent of the anionic group of the first dopant is preferably 0.005 to 0.95 equivalents, more preferably 0.01 to 0.95 equivalents, even more preferably 0.1 to 0.9 equivalents, and particularly preferably 0.3 to 0.5 equivalents. Within these ranges, from the viewpoint of obtaining a lower ESR, the amount of metal ions is preferably 0.9 to 0.5 equivalents, more preferably 0.5 to 0.9 equivalents.

[0036] The metal ions are preferably alkali metal ions. This is because alkali metal ions are highly effective in increasing the impregnation of the liquid mixture and reduce undesired side reactions in the electrolytic capacitor. The alkali metal ions are preferably lithium ions, sodium ions, or potassium ions. The electrolyte may contain one type of metal ion or a combination of two or more types of metal ions. At least lithium ions may be used. If necessary, lithium ions may be combined with at least one of sodium ions and potassium ions.

[0037] The amount (equivalent) of metal ions per equivalent of anionic groups in the electrolyte can be determined by the following procedure: The capacitor element is removed from the electrolytic capacitor and disassembled, and the electrolyte is scraped out and used as a sample. If liquid components are present, they are removed using equipment such as a centrifuge. The obtained sample is analyzed using techniques such as ion chromatography, capillary electrophoresis, and ICP (inductively coupled plasma) atomic emission spectrometry to identify the types of dopant and metal ions. A portion of the sample is removed and accurately weighed to determine the dopant and metal ion content. The amount (equivalent) of metal ions per equivalent of anionic groups can be determined from the obtained content and the number of anionic groups in the dopant.

[0038] (Second Cation) The electrolyte may contain a cation (second cation) other than a metal ion (first cation). When the second cation is not dissociated in the electrolyte, the second cation usually forms a salt with an anion present in the vicinity of the electrolyte. For example, when the electrolytic capacitor does not contain a liquid component, the second cation may form a salt with an anionic group of the first dopant, may form a salt with an anionic group of the second dopant, or may form a salt with an anion other than these.

[0039] Examples of the second cation include inorganic cations such as ammonium ions, and organic cations derived from nitrogen-containing compounds. Examples of nitrogen-containing compounds corresponding to the organic cation include amines (primary to tertiary amines, etc.), quaternary ammonium compounds (amidine compounds (including imidazole compounds)), amidinium compounds, etc.). The amine may be aliphatic, aromatic, or heterocyclic. Examples of amines include trimethylamine, diethylamine, triethylamine, ethylenediamine, aniline, pyrrolidine, imidazole, and 4-dimethylaminopyridine.

[0040] The electrolyte may contain one type of second cation or a combination of two or more types.

[0041] (Other) The electrolyte may have the same composition throughout. Alternatively, the electrolyte layer may be formed to include a first portion on the dielectric layer side and a second portion covering the first portion. In this case, it is preferable that the first portion, which requires high permeability into fine recesses, be formed from a liquid mixture containing at least metal ions. In such an electrolyte, the metal ion content C1 in the first portion and the metal ion content C2 in the second portion satisfy the relationship C1 > C2. The second portion may not contain metal ions. The second portion may not contain both metal ions and the second cation. The metal ion contents C1 and C2 can be determined by defining the portion of the electrolyte filling the recesses of the dielectric layer and the portion of the electrolyte covering the outer side of the dielectric layer as the first portion and the second portion, respectively, and measuring the distribution of metal ions in each portion using a high-sensitivity EDS (energy dispersive X-ray spectroscope).

[0042] The electrolyte is formed by applying a liquid mixture containing a conjugated polymer, a first dopant (specifically, a first polymer dopant), and metal ions to an anode body having a dielectric layer. The electrolyte is formed so as to cover at least a portion of the dielectric layer. The liquid mixture may be a solution or a dispersion. The application of the liquid mixture to the anode body may be performed once, or may be repeated two or more times.

[0043] The liquid mixture can be prepared, for example, by going through a substep of polymerizing a precursor of a conjugated polymer in the presence of a first polymer dopant and an oxidizing agent to obtain a first mixture containing the conjugated polymer and the first polymer dopant, and a substep of further mixing metal ions with the first mixture to prepare a second mixture as a liquid mixture.

[0044] High impregnation can be achieved as long as the metal ions are present in the liquid mixture at the time of application to the anode body having a dielectric layer. Therefore, the metal ions do not need to be present in the reaction system during polymerization of the precursor. It is preferable that the amount of metal ions present in the reaction system is small so that the metal ions do not affect the reaction system. In the reaction system, for example, the amount of metal ions per equivalent of the anionic group of the first polymer dopant may be 0.01 equivalents or less, or 0.001 equivalents or less. It is particularly preferable to polymerize the precursor in the absence of metal ions.

[0045] The metal ions may be mixed into the first mixture in the form of a salt. When a salt is dissolved in a solvent or the like and mixed into the first mixture, the metal ions may be dissociated. This case is also included in the case of mixing in the form of a salt. For example, the metal ions may be mixed into the first mixture in the form of a salt of the first dopant (specifically, the second polymeric dopant). The second polymeric dopant is included in the first dopant described above, and the description of the first dopant can be referenced. The second polymeric dopant may be used alone or in combination of two or more. The first polymeric dopant contained in the first mixture may be the same as at least a portion of the second polymeric dopant or may be completely different from the second polymeric dopant. When a second cation is used, it may be added to the first mixture or to the liquid mixture. The second cation is added in the form of a salt as needed. The salt may be a salt with the first dopant, a salt with the second dopant, or a salt with another anion.

[0046] The thus obtained liquid mixture containing metal ions may be used to form a first portion, and a liquid mixture prepared without metal ions (e.g., the first mixture) may be used to form a second portion. The first portion may be formed by depositing the liquid mixture once, or by depositing it two or more times. Similarly, the second portion may be formed by depositing the liquid mixture for the second portion once, or by depositing it two or more times.

[0047] When multiple liquid mixtures are used to form the electrolyte, the compositions of the liquid mixtures (e.g., the types and amounts of each monomer, dopant, metal ion, second cation, etc.) may be the same or different.

[0048] Examples of precursors of conjugated polymers used in the liquid mixture include raw material monomers of conjugated polymers, oligomers and prepolymers in which multiple molecular chains of raw material monomers are linked together, etc. One type of precursor may be used, or two or more types may be used in combination.

[0049] The oxidizing agent may be added to the liquid mixture, or may be applied to the anode body on which the dielectric layer is formed before or after the liquid mixture is brought into contact with the anode body. ３＋ Examples of the oxidizing agent include compounds capable of generating ferric sulfate, persulfates (sodium persulfate, ammonium persulfate, etc.), and hydrogen peroxide. One type of oxidizing agent may be used alone, or two or more types may be used in combination.

[0050] The liquid mixture usually contains a solvent, such as water, an organic solvent, or a mixed solvent of water and an organic solvent (such as a water-soluble organic solvent).

[0051] When other conductive materials, additives, etc. are used, they may be added to the liquid mixture.

[0052] (Cathode Body) As with the anode body, a metal foil may be used for the cathode body. The metal is preferably a valve metal such as aluminum, tantalum, or niobium, or an alloy containing a valve metal. However, the metal constituting the cathode body is not limited to these. The surface of the metal foil may be roughened as necessary. The surface of the metal foil may be provided with a chemical conversion coating, or may be provided with a coating of a metal (dissimilar metal) or a nonmetal different from the metal constituting the metal foil. Examples of dissimilar metals or nonmetals include metals such as titanium and nonmetals such as carbon.

[0053] (Separator) When a metal foil is used for the cathode body, a separator may be disposed between the metal foil and the anode body. The separator is not particularly limited, and may be, for example, a nonwoven fabric containing fibers of cellulose, polyethylene terephthalate, vinylon, or polyamide (e.g., aliphatic polyamide, aromatic polyamide such as aramid). In the present disclosure, an electrolyte is formed using a liquid mixture containing metal ions, thereby ensuring high impregnation of the liquid mixture into the separator. Therefore, even when an electrolyte is formed by applying a liquid mixture to an anode body and a cathode body stacked with a separator interposed therebetween, an electrolyte can be formed with high coverage.

[0054] (Liquid Component) When an electrolytic capacitor contains a liquid component, it is advantageous in that a higher capacitance can be ensured and that the change in ESR can be kept low even when the electrolytic capacitor is exposed to high temperatures.

[0055] The liquid component contains a solvent. From the viewpoint of suppressing evaporation of the solvent, the solvent preferably contains at least a polyhydric alcohol. In addition to the polyhydric alcohol, a sulfone compound, a lactone compound, a carbonate compound, or the like may be used. The solvent may be used alone or in combination of two or more.

[0056] Examples of sulfone compounds include sulfolane, dimethyl sulfoxide, and diethyl sulfoxide. Examples of lactone compounds include γ-butyrolactone and γ-valerolactone. Examples of carbonate compounds include dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, and fluoroethylene carbonate.

[0057] The proportion of the polyhydric alcohol in the entire solvent contained in the liquid component is, for example, 50% by mass or more, or may be 75% by mass or more, and the proportion of the polyhydric alcohol in the entire solvent contained in the liquid component is 100% by mass or less.

[0058] Examples of polyhydric alcohols include glycerin compounds, sugar alcohol compounds, and glycol compounds.

[0059] Examples of glycerin compounds include glycerin, polyglycerin (diglycerin, triglycerin, etc.), and derivatives thereof. The number of repeating glycerin units in polyglycerin is, for example, 2 or more and 20 or less, and may be 2 or more and 10 or less. Examples of sugar alcohol compounds include sugar alcohols (erythritol, mannitol, pentaerythritol, etc.) or derivatives thereof. Examples of derivatives include alkylene oxide adducts (such as adducts in which one alkylene oxide is added to one hydroxy group of glycerin, polyglycerin, or sugar alcohol). Examples of alkylene oxide adducts include C ２－４ Alkylene oxide adducts (such as ethylene oxide adducts) are also included.

[0060] Examples of glycol compounds include alkylene glycols (C ２－４ Alkylene glycols (ethylene glycol, propylene glycol, etc.), polyalkylene glycols (polyC ２－４ alkylene glycols (diethylene glycol, dipropylene glycol, triethylene glycol, polyethylene glycol, etc.), polyalkylene oxide adducts (poly C) of sugar alcohols (glycerin, erythritol, mannitol, pentaerythritol, etc.) ２－４ alkylene oxide adducts (such as polyethylene oxide adducts), etc.

[0061] The solvent preferably contains one selected from the group consisting of polyhydric alcohols, particularly ethylene glycol, glycerin, diethylene glycol, triethylene glycol, and propylene glycol.

[0062] The liquid component may contain a solute, such as an acid component or a base component.

[0063] Examples of the acid component include carboxylic acids (aliphatic carboxylic acids, aromatic carboxylic acids (including polycarboxylic acids such as phthalic acid and pyromellitic acid), sulfur-containing acids (sulfuric acid, sulfonic acids (aliphatic sulfonic acids, aromatic sulfonic acids), etc.), boron-containing acids (boric acid, halogenated boric acids (such as tetrafluoroboric acid), or partial esters thereof), phosphorus-containing acids (phosphoric acid, halogenated phosphoric acids (such as hexafluorophosphoric acid), phosphonic acid, phosphinic acid, or partial esters thereof), nitric acid, and nitrous acid. Condensates of carboxylic acids and inorganic acids (such as boric acid and phosphoric acid) (borodisalicylic acid, borodiglycolic acid, borodisalic acid, etc.) may also be used as the acid component. Aromatic sulfonic acids include aromatic sulfonic acids having a hydroxy group or a carboxy group in addition to a sulfo group (oxyaromatic sulfonic acids (such as phenol-2-sulfonic acid), sulfoaromatic carboxylic acids (such as p-sulfobenzoic acid, 3-sulfophthalic acid, 5-sulfosalicylic acid), etc.). Furthermore, polymeric acid components may also be used. The polymeric acid component may include, for example, one or more selected from the group consisting of polyacrylic acid, polymethacrylic acid, polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallyl sulfonic acid, polyacrylsulfonic acid, polymethacrylsulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), and polyisoprene sulfonic acid. The liquid component may include one or more acid components.

[0064] Examples of the basic component include ammonia, amines (specifically, primary amines, secondary amines, and tertiary amines), quaternary ammonium compounds, and amidinium compounds. The amine may be aliphatic, aromatic, or heterocyclic. Examples of the amine include trimethylamine, diethylamine, triethylamine, ethylenediamine, aniline, pyrrolidine, imidazole, and 4-dimethylaminopyridine. Examples of the quaternary ammonium compound include amidine compounds (including imidazole compounds). The liquid component may contain one type of basic component, or two or more types.

[0065] The liquid component may contain the acid component and the base component in a free state, in the form of ions, or in the form of a salt. The liquid component may also contain an organic salt. Examples of organic salts include those in which at least one of the acid component and the base component is organic.

[0066] The concentration of the solute in the liquid component is, for example, 0.1% by mass to 25% by mass, and may be 0.5% by mass to 15% by mass. When the concentration of the solute is in this range, undoping of the dopant is easily suppressed.

[0067] (Other) The electrolytic capacitor may be a wound type, and may be either a chip type or a laminate type. The electrolytic capacitor may have at least one capacitor element, or may have multiple capacitor elements. For example, a solid electrolytic capacitor may have a laminate of two or more capacitor elements, or may have two or more wound capacitor elements. The configuration or number of capacitor elements may be selected depending on the type or application of the electrolytic capacitor.

[0068] The electrolytic capacitor of the present disclosure will be described in more detail below based on embodiments, but the electrolytic capacitor of the present disclosure is not limited to the following embodiments.

[0069] FIG. 1 is a cross-sectional view of an electrolytic capacitor according to this embodiment, and FIG. 2 is a schematic view of a portion of a capacitor element of the electrolytic capacitor in an expanded form.

[0070] 1 includes a capacitor element 10, a bottomed case 11 that houses the capacitor element 10, a sealing member 12 that closes the opening of the bottomed case 11, a seat plate 13 that covers the sealing member 12, lead wires 14A and 14B that extend from the sealing member 12 and pass through the seat plate 13, lead tabs 15A and 15B that connect the lead wires to the electrodes of the capacitor element 10, and a liquid component (not shown). The open end of the bottomed case 11 is curled so as to be crimped to the sealing member 12.

[0071] Capacitor element 10 is produced from a wound body as shown in Fig. 2. The wound body is a semi-finished product of capacitor element 10, in which a conductive polymer is not disposed between anode body 21 and cathode body 22 having a dielectric layer on the surface. The wound body is formed by winding anode body 21 connected to lead tab 15A and cathode body 22 connected to lead tab 15B with separator 23 interposed therebetween. The outermost periphery of the wound body is fixed with stop tape 24. Note that Fig. 2 shows a state in which the wound body is partially unfolded before the outermost periphery is fixed.

[0072] Anode body 21 includes a metal foil having a roughened surface, and a dielectric layer is formed on the roughened surface. A conductive polymer is attached to at least a portion of the surface of the dielectric layer to form capacitor element 10. Capacitor element 10 is housed in an exterior case together with a liquid component (not shown).

[0073] An example of a method for manufacturing an electrolytic capacitor is described below. (i) Step of preparing anode body 21 and cathode body 22 having a dielectric layer: Metal foil made of a valve metal is used as the raw material for anode body 21 and cathode body 22. In the case of anode body 21, the surface of the metal foil is roughened by etching or the like, and a plurality of projections and depressions are formed on the surface of the metal foil. Next, a dielectric layer is formed on the roughened surface of the metal foil by chemical conversion or the like. The surface of cathode body 22 may also be roughened as needed.

[0074] (ii) Preparation of Wound Body Anode body 21 and cathode body 22 are wound with separator 23 interposed therebetween to prepare a wound body. Separator 23 may be a nonwoven fabric containing synthetic cellulose or the like as a main component. Stop tape 24 is placed on the outer surface of cathode body 22, which is located in the outermost layer of the wound body, to fix the end of cathode body 22. If necessary, the wound body is further subjected to a chemical conversion treatment.

[0075] (iii) Step of forming capacitor element 10 For example, a liquid mixture containing the conjugated polymer, the first polymer dopant, and metal ions prepared by the above-described procedure is impregnated into the dielectric layer to form a conductive polymer film (electrolyte) that covers at least a portion of the dielectric layer. This results in a capacitor element 10 in which the conductive polymer (electrolyte) is disposed between the anode body 21 and the cathode body 22. The step of applying the liquid mixture to the surface of the dielectric layer may be repeated two or more times. When a liquid component is used, the liquid component is impregnated into the capacitor element 10 after the electrolyte is formed.

[0076] (iv) Step of sealing the capacitor element Capacitor element 10 is housed in bottomed case 11 together with the liquid component so that lead wires 14A and 14B are located on the opening side of bottomed case 11. Next, the opening of bottomed case 11 is sealed with sealing member 12 through which each lead wire passes, the open end is crimped to sealing member 12 and curled, and seat plate 13 is placed on the curled portion, completing the electrolytic capacitor as shown in FIG.

[0077] In the above embodiment, a wound-type electrolytic capacitor has been described, but the scope of application of the present invention is not limited to the above, and the present invention can also be applied to other electrolytic capacitors, such as chip-type electrolytic capacitors that use a metal sintered body as an anode body, and stacked-type electrolytic capacitors that use a metal plate as an anode body.

[0078] All of the features described herein may be combined in any combination.

[0079] EXAMPLES The present invention will be specifically described below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0080] <<Fabrication of Electrolytic Capacitors A1 to A14 and B1 to B3>> Wound electrolytic capacitors (diameter 10 mm x length 10 mm) with a rated voltage of 25 V and a rated capacitance of 330 μF were fabricated. Specific methods for fabricating the electrolytic capacitors are described below.

[0081] (Preparation of anode body) An aluminum foil having a thickness of 100 μm was subjected to an etching treatment to roughen the surface of the aluminum foil. Then, a dielectric layer was formed on the surface of the aluminum foil by chemical conversion treatment. The chemical conversion treatment was performed by immersing the aluminum foil in an ammonium adipate solution and applying a voltage of 45 V thereto. The aluminum foil was then cut to prepare an anode body.

[0082] (Preparation of Cathode Body) An aluminum foil having a thickness of 50 μm was subjected to an etching treatment to roughen the surface of the aluminum foil, and then the aluminum foil was cut to prepare a cathode body.

[0083] (Preparation of Wound Body) An anode lead tab and a cathode lead tab were connected to the anode body and the cathode body, respectively, and the anode body and the cathode body were wound around the lead tabs, with a separator interposed therebetween. An anode lead wire and a cathode lead wire were connected to the ends of each lead tab protruding from the wound body, respectively. The prepared wound body was again subjected to chemical conversion treatment, and a dielectric layer was formed on the cut end of the anode body. Next, the end of the outer surface of the wound body was fixed with a winding tape to prepare the wound body. A cellulose nonwoven fabric was used as the separator.

[0084] (Preparation of Liquid Mixture) 3,4-ethylenedioxythiophene (EDOT) and the first polymer dopant, polystyrene sulfonic acid (PSS, weight-average molecular weight 100,000), were dissolved in ion-exchanged water to prepare a mixed solution. Iron (III) sulfate (oxidant) dissolved in ion-exchanged water was added to the mixed solution while stirring, and a polymerization reaction was carried out. After the reaction, the resulting reaction solution was dialyzed to remove unreacted monomer and excess oxidant, yielding a polymer dispersion (first mixture) containing PSS-doped polyethylenedioxythiophene (PEDOT / PSS). The doping amount was adjusted so that 0.5 equivalents of EDOT were used per equivalent of anionic group in PSS. In B1, a lithium salt of PSS was used instead of PSS.

[0085] Polystyrene sulfonic acid (PSS, weight-average molecular weight 100,000), a second polymer dopant, was mixed with an aqueous solution of the hydroxide of the cation shown in the table, or with aqueous ammonia. The hydroxide or ammonia was added in a ratio such that the equivalent of the cation shown in the table was the equivalent shown in the table per equivalent of the anionic group of polystyrene sulfonic acid, and the pH was adjusted to approximately 2.0 to 3.5. In this manner, liquid mixture (second mixture) A was prepared. In addition, in B1, the first mixture was used as the liquid mixture.

[0086] Polystyrene sulfonic acid (PSS, weight-average molecular weight 100,000) and aqueous ammonia were added. The aqueous ammonia was added in a ratio of 0.2 equivalents of ammonium ions per equivalent of anionic groups of polystyrene sulfonic acid, and the pH was adjusted to approximately 2.2. In this way, liquid mixture B was prepared.

[0087] (Electrolyte Formation) The wound body was immersed in a liquid mixture contained in a designated container in a reduced pressure atmosphere (40 kPa) for 5 minutes, and then removed from the liquid mixture. The wound body impregnated with the liquid mixture was then dried in a drying oven at 150°C for 20 minutes to form a conductive polymer layer covering at least a portion of the dielectric layer. In this manner, capacitor elements were formed. For A12 and A13, the wound body was immersed in liquid mixture A for 2 minutes, then removed from the liquid mixture, and dried in a drying oven at 150°C for 20 minutes. After drying, the wound body was immersed in liquid mixture B for 3 minutes for A12, and in the first mixture for 3 minutes for A13. For A14, the wound body was immersed in the first mixture for 2 minutes, then removed from the first mixture, and dried in a drying oven at 150°C for 20 minutes. In the case of A14, the dried wound body was immersed in the liquid mixture A for 3 minutes. Then, the capacitor element of each example was taken out of the liquid mixture and dried in a drying oven at 150° C. for 20 minutes. In this way, the capacitor element was formed.

[0088] (Preparation of Liquid Component) Phthalic acid as an acid component and triethylamine as a base component were added to ethylene glycol as a solvent and mixed so that the concentrations in the liquid component were 5% by mass and 5% by mass, respectively. In this way, a liquid component was prepared.

[0089] (Assembly of Electrolytic Capacitor) The above-described wound body with the electrolyte formed thereon was immersed in a liquid component in a reduced pressure atmosphere (40 kPa) for 5 minutes. This resulted in a capacitor element impregnated with the liquid component. The resulting capacitor element was sealed to complete the electrolytic capacitor shown in FIG. 1. Subsequently, the element was subjected to an aging treatment at 130°C for 2 hours while applying the rated voltage.

[0090] [Evaluation: Measurement of ESR and Capacitance] The initial capacitance (μF) at a frequency of 120 Hz and the ESR at a frequency of 100 kHz of each solid electrolytic capacitor were measured using a four-terminal LCR meter in an environment of 20° C. The average values ​​for 20 solid electrolytic capacitors were then calculated.

[0091] The evaluation results are shown in Tables 1 and 2. In the tables, A1 to A14 are examples, and B1 to B3 are comparative examples.

[0092]

[0093]

[0094] As shown in Table 1, when an electrolyte is formed using a liquid mixture containing metal ions (specifically, lithium ions), the ESR decreases and the capacitance improves (comparison between B3 and B1 and A1 to A8). When a liquid mixture containing metal ions is used, the rate of decrease in ESR is lower and the rate of increase in capacitance is higher than when a liquid mixture containing ammonium ions is used (comparison between B3 and B2 and A6). When the amount of metal ions is one equivalent or more, the effect of increasing capacitance and the effect of reducing ESR become smaller. In contrast, when the amount of metal ions is less than one equivalent, a high capacitance can be obtained and the ESR can be kept low (comparison between B1 and A1 to A9).

[0095] As shown in Table 2, even when sodium ions or potassium ions are used as metal ions, excellent effects almost equivalent to those of lithium ions can be obtained (comparison of A1 with A9 and A10). Even when the electrolyte contains ammonium ions, if it also contains metal ions, a relatively high capacitance can be ensured and the ESR can be kept relatively low (comparison of B2 and A1 with A11). From the perspective of easily obtaining a higher capacitance, it is advantageous to add ammonium ions to the second portion rather than the first portion (comparison of A11 with A12). Furthermore, when metal ions are contained in a larger amount in the first portion than in the second portion, the capacitance tends to be higher and the ESR tends to be lower (comparison of A1 with A14).

[0096] The electrolytic capacitor of the present disclosure can be used in a variety of applications requiring high capacitance and low ESR, including as a hybrid electrolytic capacitor, but the applications of the electrolytic capacitor are not limited thereto.

[0097] While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention.

[0098] 10: Capacitor element 11: Bottomed case 12: Sealing member 13: Seat plate 14A, 14B: Lead wires 15A, 15B: Lead tabs 21: Anode body 22: Cathode body 23: Separator 24: Winding tape

Claims

1. 1. An electrolytic capacitor including a capacitor element, the capacitor element includes an anode body having a dielectric layer on a surface thereof, and an electrolyte covering a portion of the dielectric layer; the electrolyte includes a conjugated polymer, a polymer dopant having an anionic group, and a metal ion; The amount of the metal ion is less than 1 equivalent per equivalent of the anionic group.

2. 2. The electrolytic capacitor according to claim 1, wherein the amount of the metal ions is 0.005 equivalents or more and 0.95 equivalents or less per equivalent of the anionic group.

3. 2. The electrolytic capacitor according to claim 1, wherein the anionic group of the polymer dopant is contained in the electrolyte in at least one form selected from the group consisting of an acid, an anion, and a salt with the metal ion.

4. 2. The electrolytic capacitor of claim 1, wherein the metal ions are alkali metal ions.

5. 2. The electrolytic capacitor according to claim 1, wherein the metal ions include at least one selected from the group consisting of lithium ions, sodium ions, and potassium ions.

6. The electrolytic capacitor of claim 1 , wherein the electrolyte further comprises ammonium ions.

7. the electrolyte includes a first portion on the dielectric layer side and a second portion covering at least a part of the first portion, 2. The electrolytic capacitor according to claim 1, wherein a content C1 of the metal ions in the first portion and a content C2 of the metal ions in the second portion satisfy C1>C2.

8. The electrolytic capacitor of claim 7 , wherein the second portion is free of the metal ions.

9. The electrolytic capacitor of claim 1 further comprising a liquid component.

10. The electrolytic capacitor according to any one of claims 1 to 9, further comprising a separator.

11. A method for producing an electrolytic capacitor including a capacitor element including an anode body having a dielectric layer on a surface thereof and an electrolyte covering a portion of the dielectric layer, comprising the steps of: preparing a liquid mixture containing a conjugated polymer, a first polymer dopant having an anionic group, and metal ions; applying the liquid mixture to the anode body to form the electrolyte; The step of preparing the liquid mixture includes a sub-step of polymerizing a precursor of the conjugated polymer in the presence of the first polymer dopant and an oxidizing agent to obtain a first mixture containing the conjugated polymer and the first polymer dopant; and a sub-step of mixing the metal ions with the first mixture to prepare a second mixture in a liquid state.

12. The method for producing an electrolytic capacitor according to claim 11 , wherein the metal ions are mixed into the first mixture in the form of a salt of the metal ions and a second polymer dopant having an anionic group.

13. The method for producing an electrolytic capacitor according to claim 11 or 12, wherein the polymerization of the precursor is carried out in the absence of the metal ions.