Electrolytic capacitor and method for manufacturing the same

Abstract

This invention provides an electrolytic capacitor and a method for manufacturing the same that enhance the coating properties of conductive polymers, enabling higher capacitance. [Solution] The electrolytic capacitor includes a capacitor element 10. The capacitor element includes an anode 21 having a dielectric layer on its surface, and an electrolyte covering a portion of the dielectric layer. The electrolyte includes a conjugated polymer, a polymer dopant having anionic groups, and metal ions. The amount of metal ions is less than 1 equivalent per equivalent of the anionic groups.

Description

Technical Field

[0001] The present disclosure relates to an electrolytic capacitor and a method for manufacturing the same.

Background Art

[0002] As a small-sized and large-capacity capacitor with low ESR (equivalent series resistance), an electrolytic capacitor including an anode body having a dielectric layer on the surface and a solid electrolyte layer covering at least a part of the dielectric layer is regarded as promising. The solid electrolyte layer generally includes a conductive polymer containing a conjugated polymer and a dopant. The solid electrolyte layer is formed, for example, using a liquid dispersion containing a conductive polymer. In the liquid dispersion, a polymer type polyanion such as polystyrene sulfonic acid is generally widely used as a dopant.

[0003] Patent Document 1 provides a conductive polymer particle dispersion including a solvent mainly composed of water, fine particles of polythiophene having at least one selected from thiophenes and derivatives thereof as a polymerization unit, and a polyanion as a dopant, dispersed in the solvent, having a pH of 3 or more, and a concentration of iron content in an iron compound insoluble in the solvent of 450 ppm or less.

[0004] Patent Document 2 proposes a manufacturing method including a step of preparing a dispersion liquid by dispersing a thiophene as a monomer and a polyanion as a dopant in a solvent mainly composed of water to prepare a dispersion liquid, and a step of preparing a conductive polythiophene particle dispersion doped with a polyanion by mixing the dispersion liquid and an oxidizing agent to oxidatively polymerize the monomer. In Patent Document 2, it is proposed to use polystyrene sulfonic acid or the like as the polyanion, the hue of an aqueous solution in which the polyanion is dissolved in water so that the concentration is 2% has a Hazen color number measured by the APHA method of 10 or more and 1000 or less.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] International Publication No. 2014 / 155420 [Patent Document 2] International Publication No. 2014 / 155422 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Polymer dopants such as polystyrene sulfonic acid are highly effective in improving the conductivity of conductive polymers, which is advantageous in keeping the ESR of electrolytic capacitors low. On the other hand, because polymer dopants have high molecular weights, they are difficult to impregnate into the fine recesses of the dielectric layer. If the coverage of the dielectric layer by conductive polymers can be improved in electrolytic capacitors, further increases in capacitance will be possible. [Means for solving the problem]

[0007] One aspect of this disclosure is an electrolytic capacitor including a capacitor element, The capacitor element includes an anode having a dielectric layer on its surface and an electrolyte covering a portion of the dielectric layer. The electrolyte comprises a conjugated polymer, a polymer dopant having anionic groups, and a metal ion. The amount of the metal ion is less than 1 equivalent per equivalent of the anionic group, and the electrolytic capacitor includes an electrolytic capacitor element. The capacitor element includes an anode having a dielectric layer on its surface and an electrolyte covering a portion of the dielectric layer. The electrolyte comprises a conjugated polymer, a polymer dopant having anionic groups, and a metal ion. The present invention relates to an electrolytic capacitor in which the amount of the metal ion is less than 1 equivalent per equivalent of the anionic group.

[0008] Another aspect of this disclosure is a method for manufacturing an electrolytic capacitor including a capacitor element comprising an anode having a dielectric layer on its surface and an electrolyte covering a portion of the dielectric layer, A step of preparing a liquid mixture containing a conjugated polymer, a first polymer dopant having anionic groups, and a metal ion, The step includes applying the liquid mixture to the anode to form the electrolyte, The step of preparing the liquid mixture includes a substep of polymerizing the 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, The present invention relates to a method for manufacturing an electrolytic capacitor, comprising a substep of further mixing the metal ions with the first mixture to prepare the liquid mixture as a second mixture. [Effects of the Invention]

[0009] We can provide electrolytic capacitors with high capacitance and low ESR. Novel features of the present invention are described in the appended claims, but the present invention, both in terms of structure and content, and in conjunction with other objects and features of the present invention, will be better understood by the following detailed description in conjunction with the drawings. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic cross-sectional view of an electrolytic capacitor according to one embodiment of the present disclosure. [Figure 2] This is a schematic diagram illustrating the configuration of the capacitor element in Figure 1. [Modes for carrying out the invention]

[0011] The following describes embodiments of electrolytic capacitors relating to this disclosure with examples, but this disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be given as examples, but other numerical values ​​and materials may be applied as long as the effects of this disclosure are obtained. In this specification, the description "numerical value A to numerical value B" includes numerical value A and numerical value B, and can be read as "greater than or equal to numerical value A and less than or equal to numerical value B". In the following description, when lower and upper limits of numerical values ​​relating to specific physical properties or conditions are given as examples, either of the given lower limits and either of the given upper limits can be arbitrarily combined as long as the lower limit is not greater than or equal to the upper limit. When multiple materials are given as examples, one of them may be selected and used alone, or two or more may be used in combination.

[0012] Furthermore, this disclosure encompasses any combination of matters described in two or more claims, which may be arbitrarily selected from the multiple claims set forth in the attached claims. In other words, any combination of matters described in two or more claims, which may be arbitrarily selected from the multiple claims set forth in the attached claims, is possible, provided that no technical inconsistency arises.

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

[0014] It has been revealed that when forming the electrolyte of an electrolytic capacitor 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 for forming the electrolyte is usually formed by polymerizing a precursor of a conjugated polymer in the presence of a polymeric dopant. On the other hand, metal ions are usually added to the conductive polymer in the form of a salt of the polymeric dopant and the metal ions. Therefore, the amount of metal ions is small compared to the total amount of the polymeric dopant contained in the liquid mixture. More specifically, it is less than 1 equivalent relative to 1 equivalent of the anionic group of the polymeric dopant. In an electrolytic capacitor containing an electrolyte in such a state, the ESR can be suppressed to a low level and a high capacitance can be obtained. This is considered to be because the liquid mixture contains an appropriate amount of metal ions, which makes it easier for the liquid mixture to penetrate into the fine recesses of the dielectric layer, and the coating property of the dielectric layer by the conductive polymer is enhanced, resulting in an increase in capacitance and a decrease in tanδ. Also, since the polymeric dopant contains many anionic groups, it is considered that high conductivity of the conductive polymer can be obtained and the ESR of the electrolytic capacitor can be suppressed to a low level.

[0016] Note that it is also possible to perform the polymerization of the precursor using a salt of the polymeric dopant and the metal ions. However, when using the conductive polymer obtained by polymerization in the presence of the salt, the coating property of the dielectric layer by the conductive polymer becomes high, but the ESR tends to increase. When the polymeric dopant is used in the form of a salt, the amount of metal ions becomes more than 1 equivalent relative to 1 equivalent of the anionic group of the polymeric dopant. Therefore, it is considered that the increase in the amount of metal ions may reduce the conductivity of the electrolyte and increase the ESR.

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

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

[0019] (Anode Body) The anode body may include valve metals, alloys containing valve metals, and compounds containing valve metals. These materials can be used individually or in combination of two or more. As valve metals, aluminum, tantalum, niobium, and titanium are preferably used. An anode body with a porous surface can be obtained, for example, by roughening the surface of a substrate containing a valve metal (such as a foil or plate-shaped substrate) by etching. Alternatively, the anode body may be a molded body 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 through chemical conversion treatment or other means. The dielectric layer only needs to cover at least a portion of the anode body. Typically, the dielectric layer is formed on the surface of the anode body. Because the dielectric layer is formed on the porous surface of the anode body, it forms along the inner walls of pores and depressions (pits) on the anode body's surface.

[0021] The dielectric layer contains an oxide of the 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 these; any material that functions as a dielectric is acceptable. If the surface of the anode is porous, the dielectric layer is formed along the surface of the anode (including the inner walls of the pores).

[0022] (electrolyte) The electrolyte comprises a conjugated polymer, a polymer dopant having anionic groups, and metal ions. In the electrolyte, the conjugated polymer and polymer dopant constitute a conductive polymer, resulting in high conductivity. 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 part of the cathode in an 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 polypyrrole, polythiophene, polyaniline, polyfuran, polyacetylene, polyphenylene, polyphenylenevinylene, polyacene, and polythiophenevinylene as their basic skeletons. The above polymers only need to contain at least one monomer unit that constitutes the basic skeleton. The above polymers also include homopolymers, copolymers of two or more monomers, and derivatives thereof (such as substituted products having substituents). For example, polythiophene includes poly(3,4-ethylenedioxythiophene).

[0024] Conjugated polymers may be used individually or in combination of two or more types.

[0025] The weight-average molecular weight (Mw) of a conjugated polymer is not particularly limited, but is, for example, between 1,000 and 1,000,000.

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

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

[0028] Examples of the first dopant include polymers having multiple anionic groups. Such polymers include those containing monomer units having anionic groups. Examples of anionic groups include sulfonic acid groups and carboxyl groups. The first dopant may have one type of anionic group or two or more types of anionic groups.

[0029] In electrolytes, the anionic group of the first dopant can exist in acidic form (e.g., -SO3H for a sulfonic acid group) or anionic form (e.g., -SO3H for a sulfonic acid group). - The anionic group may be present in the electrolyte in at least one form selected from the group consisting of the anionic group, a carboxyl group, and a salt form. 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 near the electrolyte within the electrolytic capacitor. Such a salt is also included in the salt form described above. The anionic group of the first dopant may be present in the electrolyte in a form bonded to or interacting with a conjugated polymer system. In this specification, all of these forms may be simply referred to as the "anionic group," "sulfonic acid group," or "carboxyl group."

[0030] Specific examples of the first dopant having a carboxyl 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 high-molecular-weight 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), polyallyl sulfonic 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 secondary dopants 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 be used. For example, aromatic sulfonic acids (p-toluenesulfonic acid, naphthalenesulfonic acid, etc.) can be used to generate sulfonate ions. However, these are merely examples, and secondary dopants are 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 per 100 parts by mass of the conjugated polymer, and may also be 20 to 500 parts by mass or 50 to 200 parts by mass.

[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, per 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, per 100 parts by mass of the conjugated polymer.

[0034] (Metal ions) In electrolytes, when metal ions are not dissociated, a portion of the first dopant usually forms a salt with the metal ions. For example, if an electrolytic capacitor does not contain a liquid component, the metal ions are usually present in a state where they form a salt with the anionic group of the first dopant. If the electrolyte contains a second dopant, the metal ions may be present in a state where they form a salt with the anionic group of the second dopant. If the electrolytic capacitor does not contain a liquid component, a portion of the metal ions may be present in the electrolyte in a state where they form a salt with anions present in the vicinity of the electrolyte.

[0035] The amount of metal ions is less than 1 equivalent per equivalent of the anionic group of the first dopant. When the electrolyte contains such an amount of metal ions, it is possible to keep the ESR low while ensuring high impregnation of the liquid mixture used to form the electrolyte into the fine depressions of the dielectric layer. Furthermore, when a separator is used, it is thought that the permeability of the liquid mixture into the separator will also increase. High impregnation of the liquid mixture improves the coverage of the dielectric layer by the electrolyte, so high capacity can be obtained and tanδ can be kept low. The amount of metal ions per equivalent of the anionic group of the first dopant is, for example, 0.001 equivalents or more and less than 1. From the viewpoint of easily obtaining a higher capacitance, the amount of metal ions per equivalent of anionic group of the first dopant is preferably 0.005 equivalents or more and 0.95 equivalents or less, more preferably 0.01 equivalents or more (or 0.05 equivalents or more) and 0.95 equivalents or more, even more preferably 0.1 equivalents or more and 0.9 equivalents or less, and particularly preferably 0.3 equivalents or more and 0.5 equivalents or less. Within these ranges, from the viewpoint of obtaining a lower ESR, the amount of metal ions is preferably 0.9 equivalents or less, and more preferably 0.5 equivalents or less.

[0036] Alkali metal ions are preferred as the metal ions. This is because alkali metal ions have a high effect in improving the impregnation of the liquid mixture and cause fewer undesirable side reactions in the electrolytic capacitor. Lithium ions, sodium ions, or potassium ions are preferred as the alkali metal ions. The electrolyte may contain one metal ion, or a combination of two or more 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 an electrolyte can be determined by the following procedure: Remove the capacitor element from the electrolytic capacitor, disassemble it, and scrape out the electrolyte to obtain a sample. If liquid components are present, remove them using equipment such as a centrifuge. Identify the types of dopants and metal ions by analyzing the obtained sample using methods such as ion chromatography, capillary electrophoresis, and ICP (inductively coupled plasma) emission spectrometry. Take a portion of the sample, weigh it accurately, and determine the content of the dopants and metal ions. From the obtained content and the number of anionic groups in the dopant, the amount (equivalent) of metal ions per equivalent of anionic groups can be determined.

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

[0039] Examples of secondary cations include inorganic cations such as ammonium ions and organic cations derived from nitrogen-containing compounds. Examples of nitrogen-containing compounds corresponding to organic cations include amines (primary to tertiary amines, etc.), quaternary ammonium compounds (amidine compounds (including imidazole compounds), etc.), and amidinium compounds. Amines can 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 secondary cation, or a combination of two or more secondary cations.

[0041] (others) 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 of 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 C1 > C2. The second portion does not have to contain metal ions. The second portion does not have to contain both metal ions and secondary cations. The metal ion content C1 and C2 can be determined by measuring the distribution of metal ions in the portion filled in the recesses of the dielectric layer of the electrolyte and the portion covering the outside of the dielectric layer of the electrolyte, respectively, using a high-sensitivity EDS (energy-dispersive X-ray spectrometer), and confirming the magnitudes of C1 and C2.

[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 having a dielectric layer. The electrolyte is formed 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 may be performed once or repeated two or more times.

[0043] The liquid mixture can be prepared, for example, by 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 into the first mixture to prepare a liquid mixture as a second mixture.

[0044] If metal ions are present in the liquid mixture at the time of application to the anode having a dielectric layer, high impregnation can be obtained. Therefore, metal ions do not need to be present in the reaction system during the polymerization of the precursor. It is preferable that the amount of metal ions in the reaction system be small so that they do not affect the reaction system. In the reaction system, for example, the amount of metal ions may be 0.01 equivalents or less or 0.001 equivalents or less per equivalent of anionic groups of the first polymer dopant. In particular, it is preferable to carry out the polymerization of the precursor in the absence of metal ions.

[0045] Metal ions may be mixed into the first mixture in the form of a salt. When the salt is dissolved in a solvent and mixed into the first mixture, the metal ions may dissociate; however, this case is also included when the salt is mixed. For example, metal ions may be mixed into the first mixture in the form of a salt of the first dopant (specifically, the second polymer dopant) and the metal ion. The second polymer dopant is included in the first dopant described above, and the description of the first dopant can be found therein. The second polymer dopant may be used alone or in combination of two or more. The first polymer dopant included in the first mixture may be at least a part of the second polymer dopant, or it may be entirely different. When a second cation is used, it may be added to the first mixture or to a 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 other anions.

[0046] The first part may be formed using the liquid mixture containing metal ions obtained in this manner, and the second part may be formed using a liquid mixture prepared without using metal ions (for example, the first mixture). The first part may be formed by applying the liquid mixture once, or by applying it two or more times. Similarly, the second part may be formed by applying the liquid mixture for the second part once, or by applying it two or more times.

[0047] When multiple liquid mixtures are used to form an electrolyte, the composition of each liquid mixture (for example, the types and amounts of each monomer, dopant, metal ion, secondary cation, etc.) may be the same or different.

[0048] Examples of precursors for conjugated polymers used in liquid mixtures include the raw material monomers of the conjugated polymer, oligomers and prepolymers formed by linking multiple molecular chains of the raw material monomers. One precursor may be used, or two or more precursors may be used in combination.

[0049] The oxidizing agent may be added to the liquid mixture, or the oxidizing agent may be applied to the anode body before or after contacting the liquid mixture with the dielectric layer formed on the anode body. Examples of such oxidizing agents include Fe 3+ Examples of compounds capable of generating oxidizing agents include ferric sulfate, persulfates (such as sodium persulfate and ammonium persulfate), and hydrogen peroxide. The oxidizing agent may be used alone or in combination of two or more.

[0050] Liquid mixtures typically contain a solvent. Examples of solvents include water, organic solvents, and mixed solvents of water and organic solvents (such as water-soluble organic solvents).

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

[0052] (Cathole body) Similar to the anode, a metal foil may be used for the cathode. Preferably, the metal is a valve metal such as aluminum, tantalum, or niobium, or an alloy containing a valve metal. However, the metal constituting the cathode is not limited to these. The surface of the metal foil may be roughened as needed. The surface of the metal foil may be coated with a chemical conversion film, or a coating of a different metal (dissimilar metal) or nonmetal. Examples of dissimilar metals or nonmetals include metals such as titanium or nonmetals such as carbon.

[0053] (Separator) When a metal foil is used as the cathode, a separator may be placed between the metal foil and the anode. The separator is not particularly limited, and for example, nonwoven fabrics containing fibers of cellulose, polyethylene terephthalate, vinylon, or polyamide (e.g., aliphatic polyamide, aromatic polyamide such as aramid) may be used. In this disclosure, since the electrolyte is formed using a liquid mixture containing metal ions, high impregnation of the liquid mixture into the separator can be ensured. Therefore, even when the anode and cathode are stacked with a separator in between and the liquid mixture is applied to form the electrolyte, the electrolyte can be formed with high coverage.

[0054] (Liquid component) When electrolytic capacitors contain a liquid component, it is advantageous in achieving even higher capacitance. Furthermore, even when electrolytic capacitors are exposed to high temperatures, ESR changes can be kept low.

[0055] The liquid component contains a solvent. From the viewpoint of suppressing solvent volatilization, it is preferable that the solvent contains at least a polyhydric alcohol. In addition to polyhydric alcohols, sulfone compounds, lactone compounds, carbonate compounds, etc., may also be used. One solvent may be used, or two or more solvents may be used in combination.

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

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

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

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

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

[0062] The liquid component may contain a solute. Examples of solutes include acidic components and basic components.

[0063] Examples of acidic components 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 acid (tetrafluoroboric acid, etc.), or partial esters thereof), phosphorus-containing acids (phosphoric acid, halogenated phosphoric acid (hexafluorophosphoric acid, etc.), phosphonic acid, phosphinic acid, or partial esters thereof), nitric acid, and nitrous acid. Condensates of carboxylic acids and inorganic acids (boric acid, phosphoric acid, etc.) (borodisalicylic acid, borodiglycolic acid, borodisuoic acid, etc.) may also be used as acidic components. Aromatic sulfonic acids also include aromatic sulfonic acids having a hydroxyl group or a carboxyl group in addition to a sulfo group (oxyaromatic sulfonic acid (e.g., phenol-2-sulfonic acid), sulfoaromatic carboxylic acids (e.g., p-sulfobenzoic acid, 3-sulfophthalic acid, 5-sulfosalicylic acid), etc.). Furthermore, a polymeric acid component may 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, polyacryl sulfonic acid, polymethacrylic sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), and polyisoprene sulfonic acid. The liquid component may contain one acid component or two or more acid components.

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

[0065] The liquid component may contain acidic and basic components in a free state, in ionic form, or in salt form. The liquid component may also contain organic salts. Examples of organic salts include those in which at least one of the acidic and basic components is organic.

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

[0067] (others) Electrolytic capacitors may be wound-wound, chip-type, or multilayer-type. An electrolytic capacitor may have at least one capacitor element, or it may have multiple capacitor elements. For example, a solid electrolytic capacitor may have a multilayer structure of two or more capacitor elements, or it may have two or more wound-wound capacitor elements. The configuration or number of capacitor elements should be selected according to the type or application of the electrolytic capacitor.

[0068] The electrolytic capacitors of this disclosure will be described in more detail below based on embodiments. However, the electrolytic capacitors of this disclosure are not limited to the following embodiments.

[0069] Figure 1 is a schematic cross-sectional view of an electrolytic capacitor according to this embodiment, and Figure 2 is a schematic diagram showing a portion of the capacitor elements related to the electrolytic capacitor unfolded.

[0070] The electrolytic capacitor shown in Figure 1 comprises a capacitor element 10, a bottomed case 11 housing the capacitor element 10, a sealing member 12 closing the opening of the bottomed case 11, a base plate 13 covering the sealing member 12, lead wires 14A and 14B extending from the sealing member 12 and passing through the base plate 13, lead tabs 15A and 15B connecting 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] The capacitor element 10 is manufactured from a wound body as shown in Figure 2. The wound body is a semi-finished product of the capacitor element 10, in which a conductive polymer is not placed between the anode 21, which has a dielectric layer on its surface, and the cathode 22. The wound body is made by winding the anode 21, which is connected to a lead tab 15A, and the cathode 22, which is connected to a lead tab 15B, with a separator 23 in between. The outermost circumference of the wound body is fixed with a winding stopper tape 24. Note that Figure 2 shows a partially unfolded state of the wound body before the outermost circumference is fixed.

[0072] The anode body 21 comprises a metal foil with a roughened surface, and a dielectric layer is formed on the roughened surface. A capacitor element 10 is formed by attaching a conductive polymer to at least a portion of the surface of the dielectric layer. The capacitor element 10 is housed in an outer casing along with a liquid component (not shown).

[0073] The following describes an example of a manufacturing method for electrolytic capacitors. (i) Steps to prepare an anode 21 and a cathode 22 having a dielectric layer. The anode 21 and cathode 22 are made from metal foil formed from valve metal. In the case of the anode 21, the surface of the metal foil is roughened by etching or the like, creating multiple irregularities on the surface of the metal foil. Next, a dielectric layer is formed on the roughened surface of the metal foil by chemical conversion treatment or the like. The surface of the cathode 22 may also be roughened as needed.

[0074] (ii) Preparation of the coiled body A winding body is prepared by winding an anode 21 and a cathode 22 with a separator 23 in between. The separator 23 may be a nonwoven fabric mainly composed of synthetic cellulose or the like. A winding stopper tape 24 is placed on the outer surface of the cathode 22, which is located in the outermost layer of the winding body, to fix the end of the cathode 22. If necessary, the winding body is further treated with chemical conversion.

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

[0076] (iv) Process of sealing capacitor elements The capacitor element 10 is housed in the bottomed case 11 along with its liquid component so that the lead wires 14A and 14B are positioned on the opening side of the bottomed case 11. Next, the opening of the bottomed case 11 is closed with a sealing member 12 through which each lead wire passes, the open ends are crimped to the sealing member 12 and curled, and a base plate 13 is placed on the curled portion to complete the electrolytic capacitor as shown in Figure 1.

[0077] Although the above embodiments described wound electrolytic capacitors, the scope of application of the present invention is not limited to those described above. It can also be applied to other electrolytic capacitors, such as chip-type electrolytic capacitors that use a sintered metal body as the anode, and multilayer electrolytic capacitors that use a metal plate as the anode.

[0078] All of the features described herein can be combined in any way.

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

[0080] Fabrication of electrolytic capacitors A1-A14 and B1-B3 A wound electrolytic capacitor (10mm diameter x 10mm length) with a rated voltage of 25V and a rated capacitance of 330μF was fabricated. The specific manufacturing method of the electrolytic capacitor is described below.

[0081] (Preparation of the anode) A 100 μm thick aluminum foil was etched to roughen its surface. Subsequently, a dielectric layer was formed on the surface of the aluminum foil by a chemical conversion treatment. This treatment involved immersing the aluminum foil in an ammonium adipate solution and applying a voltage of 45 V. Afterward, the aluminum foil was cut to prepare the anode.

[0082] (Preparation of the cathode) A 50 μm thick aluminum foil was etched to roughen its surface. Then, the aluminum foil was cut to prepare the cathode.

[0083] (Preparation of coiled bodies) Anode lead tabs and cathode lead tabs were connected to the anode and cathode bodies, and the anode and cathode bodies were wound together with a separator, incorporating the lead tabs. Anode lead wires and cathode lead wires were connected to the ends of each lead tab protruding from the wound body. The fabricated wound body was subjected to another chemical conversion treatment to form a dielectric layer on the cut ends of the anode bodies. Next, the ends of the outer surface of the wound body were secured with winding tape to create the wound body. A cellulose nonwoven fabric was used as the separator.

[0084] (Preparation of liquid mixture) A mixed solution was prepared by dissolving 3,4-ethylenedioxythiophene (EDOT) and polystyrene sulfonic acid (PSS, weight-average molecular weight 100,000), the first polymer dopant, in deionized water. While stirring the mixed solution, iron(III) sulfate (oxidizing agent) dissolved in deionized water was added to carry out the polymerization reaction. After the reaction, the resulting reaction solution was dialyzed to remove unreacted monomers and excess oxidizing agent, yielding a polymer dispersion (first mixture) containing PSS-doped polyethylenedioxythiophene (PEDOT / PSS). At this time, the doping amount was adjusted so that EDOT was 0.5 equivalents for every 1 equivalent of PSS anionic groups. Note that in B1, the 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 added and mixed with an aqueous solution of the cation hydroxide shown in the table, or with aqueous ammonia. The hydroxide or ammonia was added in a ratio such that the cations shown in the table were in the amount shown in the table for every 1 equivalent of the anionic group of polystyrene sulfonic acid, and the pH was adjusted to approximately 2.0 to 3.5. In this way, liquid mixture (second mixture) A was prepared. Note that 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 such that 0.2 equivalents of ammonium ions were present for every 1 equivalent of anionic groups of polystyrene sulfonic acid, adjusting the pH to approximately 2.2. In this way, liquid mixture B was prepared.

[0087] (Formation of electrolytes) In a reduced-pressure atmosphere (40 kPa), the coiled body was immersed in a liquid mixture contained in a predetermined container for 5 minutes, and then the coiled body was removed from the liquid mixture. Next, the coiled body impregnated with the liquid mixture was dried in a 150°C drying oven for 20 minutes to form a conductive polymer layer that covers at least a portion of the dielectric layer. A capacitor element was formed in this way. In A12 and A13, the coiled body was immersed in liquid mixture A for 2 minutes, and then the coiled body was removed from the liquid mixture and dried in a 150°C drying oven for 20 minutes. After drying, the coiled body was immersed in liquid mixture B for 3 minutes in A12, and in the first mixture for 3 minutes in A13. In A14, the coiled body was immersed in the first mixture for 2 minutes, and then the coiled body was removed from the first mixture and dried in a 150°C drying oven for 20 minutes. In A14, the dried coiled body was immersed in liquid mixture A for 3 minutes. Subsequently, each capacitor element was removed from the liquid mixture and dried in a drying oven at 150°C for 20 minutes. In this way, the capacitor elements were formed.

[0088] (Preparation of liquid components) Ethyl glycol, used as a solvent, was mixed with phthalic acid, used as an acidic component, and triethylamine, used as a basic component, so that their concentrations in the liquid component were 5% by mass and 5% by mass, respectively. The liquid component was thus prepared.

[0089] (Assembly of electrolytic capacitors) The above-mentioned wound body, in which the electrolyte was formed, was immersed in the liquid component in a reduced-pressure atmosphere (40 kPa) for 5 minutes. This resulted in obtaining a capacitor element impregnated with the liquid component. The obtained capacitor element was sealed to complete an electrolytic capacitor as shown in Figure 1. Subsequently, an aging treatment was performed at 130°C for 2 hours while applying the rated voltage.

[0090] [Evaluation: Measurement of ESR and capacitance] Under conditions of 20°C, the initial capacitance (μF) at 120 Hz and the ESR at 100 kHz of each solid electrolytic capacitor were measured using a four-terminal LCR meter. 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] [Table 1]

[0093] [Table 2]

[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 of B3 with B1 and A1-A8). The rate of decrease in ESR and the rate of increase in capacitance are lower when using a liquid mixture containing metal ions compared to when using a liquid mixture containing ammonium ions (comparison of B3 with B2 and A6). When the amount of metal ions exceeds 1 equivalent, the effect of increasing capacitance and reducing ESR becomes smaller. In contrast, when the amount of metal ions is less than 1 equivalent, high capacitance can be obtained and the ESR can be kept low (comparison of B1 with A1-A9).

[0095] As shown in Table 2, when sodium ions or potassium ions are used as metal ions, excellent effects almost equivalent to those obtained with lithium ions can be obtained (comparison of A1 with A9 and A10). Even when the electrolyte contains ammonium ions, if metal ions are also included, a certain level of high capacitance can be secured and the ESR can be kept relatively low (comparison of B2 with A1 and A11). From the viewpoint of easily obtaining higher capacitance, when adding ammonium ions, it is more advantageous to add them to the second part than to the first part (comparison of A11 and A12). Also, when metal ions are present in greater quantities in the first part than in the second part, the capacitance tends to be higher and the ESR tends to be lower (comparison of A1 and A14). [Industrial applicability]

[0096] The electrolytic capacitors disclosed herein can be used in a variety of applications requiring high capacitance and low ESR. They are also suitable for use as hybrid electrolytic capacitors. However, the applications of electrolytic capacitors are not limited to these.

[0097] Although the present invention has been described in relation to preferred embodiments at present, such disclosure should not be interpreted restrictively. Various modifications and alterations will undoubtedly become apparent to those skilled in the art in the field to which the invention pertains by reading the above disclosure. Accordingly, the appended claims should be interpreted as encompassing all modifications and alterations without departing from the true spirit and scope of the invention. [Explanation of Symbols]

[0098] 10: Capacitor element 11: Case with bottom 12: Sealing member 13: Seat board 14A, 14B: Lead wires 15A, 15B: Lead tabs 21: Anode 22: Cathode 23: Separator 24: Retaining tape

Claims

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

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

3. The electrolytic capacitor according to claim 1 or 2, wherein the anionic group of the polymer dopant is contained in the electrolyte in at least one form selected from the group consisting of acids, anions, and salts with the metal ions.

4. The electrolytic capacitor according to any one of claims 1 to 3, wherein the metal ion is an alkali metal ion.

5. The electrolytic capacitor according to any one of claims 1 to 4, wherein the metal ion comprises at least one selected from the group consisting of lithium ions, sodium ions, and potassium ions.

6. The electrolytic capacitor according to any one of claims 1 to 5, 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. The electrolytic capacitor according to any one of claims 1 to 6, wherein the content C1 of the metal ions in the first portion and the content C2 of the metal ions in the second portion satisfy the condition C1 > C2.

8. The second part is the electrolytic capacitor according to claim 7, wherein the metal ions are not included.

9. An electrolytic capacitor according to any one of claims 1 to 8, 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 manufacturing an electrolytic capacitor including a capacitor element comprising an anode having a dielectric layer on its surface and an electrolyte covering a portion of the dielectric layer, A step of preparing a liquid mixture containing a conjugated polymer, a first polymer dopant having anionic groups, and a metal ion, The step includes applying the liquid mixture to the anode to form the electrolyte, The step of preparing the liquid mixture includes a substep of polymerizing the 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, A method for manufacturing an electrolytic capacitor, comprising the substep of further mixing the metal ions with the first mixture to prepare the liquid mixture as a second mixture.

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

13. The method for manufacturing 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.

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