Electrolytic capacitors

Abstract

This electrolytic capacitor comprises: a capacitor element that contains a conductive polymer; and a liquid component. The liquid component contains: a first anion component that has a carbonyloxy bond; and a second anion component that does not have a carbonyloxy bond, while having a sulfonyl imide bond.

Description

Technical Field

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

Background Art

[0002] As a capacitor that is small, has a large capacitance, and has a low ESR (equivalent series resistance), an electrolytic capacitor including a capacitor element containing a conductive polymer and an electrolytic solution is regarded as promising. As the electrolytic solution, liquid components such as a non-aqueous solvent or a solution in which a solute is dissolved in a non-aqueous solvent are used.

[0003] Patent Document 1 proposes using an electrolytic solution containing a solvent containing a glycol compound and a solute containing an acid component and a base component in an electrolytic capacitor. Here, the solute contains more acid components than base components by mass ratio, and the acid components include aromatic compounds having hydroxy.

[0004] Patent Document 2 proposes using a driving electrolytic solution composed of an organic solvent, a solute, and an additive in an electrolytic capacitor. Patent Document 2 describes that the solute is composed of a material of an acid component and a material of a base component, the material of the acid component has an organic carboxylic acid such as phthalic acid and an inorganic acid such as boric acid, and the acid component is in excess of the base component in molar ratio.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

[0006] An electrolytic capacitor relating to one aspect of this disclosure comprises a capacitor element containing a conductive polymer and a liquid component. The liquid component comprises a first anionic component having a carbonyloxy bond and a second anionic component that does not have a carbonyloxy bond but has a sulfonylime bond.

[0007] According to this disclosure, it is possible to provide electrolytic capacitors with low initial ESR and minimal ESR fluctuation. [Brief explanation of the drawing]

[0008] [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]

[0009] Depending on the type of acid component in the liquid component of an electrolytic capacitor, the film repairability of the dielectric layer may decrease, or the conductivity of the conductive polymer may decrease. Therefore, it can be difficult to maintain a low equivalent series resistance (ESR) or ensure stable capacitor performance.

[0010] In electrolytic capacitors containing conductive polymer capacitor elements, carboxylic acids such as phthalic acid are sometimes used as the anionic component in the liquid component. Because carboxylic acids exhibit a suitable pH, they have the effect of forming the anode and have excellent film repair properties, thus maintaining the effect of suppressing leakage current. On the other hand, the carbonyloxy bond (-C(=O)-O-) is prone to side reactions with solvents, etc., which reduces the amount of the anionic component and causes the pH of the liquid component to fluctuate, resulting in fluctuations in the conductivity of the conductive polymer and thus fluctuations in ESR.

[0011] Sometimes, anionic components with a lower pH than carboxyl groups, such as sulfonic acid or its derivatives, are used as the liquid component. Lowering the pH of the liquid component makes it easier to maintain the high conductivity of the conductive polymer, thus making it easier to keep the ESR low. However, using anionic components with a low pH can lead to excessive oxidation of the anode, reducing the film's repairability and making the electrodes more susceptible to corrosion, thus degrading capacitor performance.

[0012] Thus, with conventional electrolytic capacitors, it has been difficult to ensure stable capacitor performance (for example, suppressing ESR fluctuations during long-term use) while maintaining a low initial ESR.

[0013] In view of the above, the electrolytic capacitor of this disclosure uses a liquid component comprising a first anionic component having a carbonyloxy bond and a second anionic component having a sulfonylime bond but lacking a carbonyloxy bond. By using such a liquid component, excellent film repairability of the dielectric layer can be ensured, and the high conductivity of the conductive polymer can be maintained. Furthermore, electrode corrosion can be reduced. Therefore, stable capacitor performance can be ensured while keeping the initial ESR low. More specifically, fluctuations in ESR during long-term use can be kept low. In addition, leakage current can be suppressed by ensuring excellent film repairability of the dielectric layer.

[0014] The first anionic component has a carbonyloxy bond (-C(=O)-O-) and exhibits anionic properties. The second anionic component does not have a carbonyloxy bond, exhibits anionic properties, and has a sulfonylimide bond (-S(=O)2-NH-). The sulfonylimide bond in the second anionic component may be a sulfonylamide group (-S(=O)2-NH2).

[0015] The electrolytic capacitors of this disclosure will be described in more detail below.

[0016] (Liquid component) The liquid component contains a first anionic component and a second anionic component, and usually a solvent. The liquid component may also contain other anionic components (third anionic component), cationic components, additives, etc., as needed.

[0017] (First anion component) Examples of the first anionic component include acids having a carbonyloxy bond and derivatives of acids having a carbonyloxy bond that exhibit anionic properties.

[0018] Acids containing a carbonyloxy bond include, for example, carboxylic acids, oxocarbonic acids, and meldrumic acids. Examples of oxocarbonic acids include delta acids, squalaneic acids, croconic acids, rhodizonic acids, and heptagonic acids. Examples of carboxylic acids include aliphatic carboxylic acids and aromatic carboxylic acids. Acids containing a carbonyloxy bond also include sulfo-aromatic carboxylic acids. Examples of sulfo-aromatic carboxylic acids include p-sulfobenzoic acid, 3-sulfophthalic acid, and 5-sulfosalicylic acid. Among these, aromatic carboxylic acids (especially aromatic hydroxy acids and aromatic polycarboxylic acids) are preferred due to their high stability. Specifically, aromatic carboxylic acids can include benzoic acid, phthalic acid, pyromellitic acid, and salicylic acid. Among these, phthalic acid, salicylic acid, and benzoic acid are preferred.

[0019] Preferred acids having a carbonyloxy bond that constitutes the derivative are hydroxy acids and polycarboxylic acids (such as dicarboxylic acids). Examples of hydroxy acids include aliphatic hydroxy acids (glycolic acid, lactic acid, tartonic acid, hydroxybutyric acid, malic acid, citric acid, etc.) and aromatic hydroxy acids (salicylic acid, hydroxybenzoic acid, mandelic acid, benzyl acid, gallic acid, etc.). Examples of polycarboxylic acids include aliphatic polycarboxylic acids (oxalic acid, malonic acid, succinic acid, adipic acid, maleic acid, etc.) and aromatic polycarboxylic acids (such as phthalic acid).

[0020] Examples of the derivative include coordination compounds of acids having a carbonyloxy bond. Examples of such coordination compounds include coordination compounds in which at least one central atom selected from the group consisting of boron, aluminum, and silicon is bonded to an acid having a carbonyloxy bond. The coordination compound may have at least a structure in which an oxygen group of the carbonyloxy bond of the acid is coordinated to the central atom. When the acid has two or more carbonyloxy bonds, the coordination compound may have a structure in which oxygen groups of at least two carbonyloxy bonds are each coordinated to the central atom. When the acid has a hydroxy group, the coordination compound may have a structure in which an oxygen atom derived from the hydroxy group and an oxygen group of the carbonyloxy bond are coordinated to the central atom.

[0021] Specific examples of the coordination compound include, but are not limited to, borodisalicylate, borodisulfonate, borodiglycolate, and borodigallate.

[0022] The liquid component may contain one kind of the first anion component or may contain a combination of two or more kinds. Among the first anion components, phthalic acid, salicylic acid, benzoic acid, borodisalicylate, borodisulfonate, borodiglycolate (particularly, phthalic acid, salicylic acid, borodisalicylate), etc. are preferable.

[0023] In an electrolytic capacitor, the anionic group of the first anion component may be contained in any form such as an anion such as carboxylate anion (-COO - ), a free acid (-COOH, etc.), and a salt. Further, the coordination compound may exhibit anionic properties in a state where the carbonyloxy bond portion is coordinated to the central atom. These forms may be collectively referred to as an anionic group.

[0024] (The second anion component) The second anionic component commonly has a sulfonylimide bond -S(=O)2-NH-. Examples of such second anionic components include those having -S(=O)2-NH-, -S(=O)2-NH-C(=O)-, -NH-S(=O)2-NH-, or -S(=O)2-NH-S(=O)2-. Such second anionic components can form sulfonylimide anions. The second anionic component may have a cyclic structure containing a sulfonylimide bond, or it may have a chain-like structure. The cyclic structure may have an aromatic ring or the like fused to it. In addition, at least one of the sulfonyl group and the imide group may have a ring (aromatic ring, aliphatic ring, or heterocycle, etc.).

[0025] Specific examples of secondary anionic components include, but are not limited to, saccharin (pKa: 1.6), 1,2-benzenedisulfonamide (pKa: -1.1), cyclohexafluoropropane-1,3-bis(sulfonyl)imide (pKa: -7.8), 4-methyl-N-[(4-methylphenyl)sulfonyl]benzenesulfonamide (pKa: -0.5), dibenzenesulfonamide (pKa: -1.1), trifluoromethanesulfonanilide (pKa: 4.35), N-[(4-methylphenyl)sulfonyl]acetamide (pKa: 7.9), benzenesulfonanilide (pKa: 8.5), and N,N'-diphenylsulfamide (pKa: 5.4).

[0026] From the viewpoint of effectively maintaining a low pH in the liquid component, the acid dissociation constant pKa of the second anionic component in the form of a free acid is preferably 5.0 or less. When the pKa is 5.0 or less, the second anionic component dissociates easily, and the pH of the liquid component is easily lowered. When the pH of the liquid component is low, dedoping is less likely to occur, and the high conductivity of the conductive polymer is easily maintained stably. On the other hand, if the pH of the liquid component is too low, the metal parts (e.g., electrodes) in contact with the liquid component in the electrolytic capacitor may corrode. From the viewpoint of suppressing such corrosion, the pKa of the second anion in the form of a free acid is preferably higher than -2.0, and more preferably higher than -1.0.

[0027] In this specification, the acid dissociation constant (pKa) refers to the acid dissociation constant in water at a temperature of 25°C. If the anionic component in the form of a free acid exhibits multiple pKas, the highest pKa (i.e., pKa 1) is referred to.

[0028] The pKa of the second anionic component in the form of a free acid can be adjusted, for example, by controlling the electron distribution state at the imide group of the sulfonylimide group. For example, when an electron-donating group such as a phenyl group or a tolyl group is bonded to the imide group, the pKa tends to be high. When a sulfonyl group is bonded to one bond of the imide group and an electron-withdrawing group such as a sulfonyl group or a carbonyl group is bonded to the other, the pKa tends to be low. The sulfonyl group bonded to the imide group may have either an electron-donating or electron-withdrawing group bonded to it, but when an electron-withdrawing group is bonded to the sulfonyl group, the pKa tends to be lower compared to when an electron-donating group is bonded. For example, when a hydrocarbon group having a fluorine atom, such as a fluoroalkyl group, is bonded to the sulfonyl group, the effect of reducing pKa is enhanced. It is preferable to select the second anionic component taking these factors into consideration.

[0029] When the second anionic component has -S(=O)2-NH-C(=O)- or -S(=O)2-NH-S(=O)2-, it is preferable that the second anionic component has an electron-donating group attached to at least one of the sulfonyl group and the carbonyl group, or at least one of the two sulfonyl groups. When the second anionic component has -S(=O)2-NH- (where neither a carbonyl group nor a sulfonyl group is attached to NH), it is preferable that the second anionic component has an electron-donating group attached to the imide group and an electron-withdrawing group attached to the sulfonyl group. Among these, saccharin (pKa: 1.6), 4-methyl-N-[(4-methylphenyl)sulfonyl]benzenesulfonamide (pKa: -0.5), trifluoromethanesulfonanilide (pKa: 4.35), etc. are preferred from the viewpoint of having a moderate pKa and being readily available.

[0030] The liquid component may contain one type of secondary anionic component, or a combination of two or more types.

[0031] In electrolytic capacitors, the anionic group of the second anionic component is the sulfonylimid anion (-S(=O)2-N + It may be present in any form, such as -), free acid (-S(=O)2-NH-), or salt. These forms together are sometimes referred to as anionic groups.

[0032] The amount of the second anionic component is preferably 3 parts by mass or more, and more preferably 5 parts by mass or more (or 10 parts by mass or more), per 100 parts by mass of the first anionic component. When the amount of the second anionic component is within this range, even if the first anionic component disappears due to side reactions, etc., it is easier to maintain a low pH of the liquid component and reduce the decrease in conductivity of the conductive polymer. From the viewpoint of increasing the effect of suppressing fluctuations in ESR, the amount of the second anionic component per 100 parts by mass of the first anionic component is more preferably 12.5 parts by mass or more (or 25 parts by mass or more), and even more preferably 18 parts by mass or more (or 35 parts by mass or more). The amount of the second anionic component is, for example, 250 parts by mass or less (or 120 parts by mass or less), and may also be 230 parts by mass or less (or 115 parts by mass or less), or 227 parts by mass or less, per 100 parts by mass of the first anionic component. When the amount of the second anionic component is within this range, the film repair effect of the dielectric layer by the first anionic component is easily obtained. These upper and lower limits can be combined arbitrarily. However, the amount of each anionic component should be determined by converting it to free acid, not anions or salts.

[0033] (Third anion component) The liquid component may, if necessary, contain an anionic component other than the first and second anionic components (a third anionic component). Examples of third anionic components include phenol compounds (picric acid, p-nitrophenol, pyrogallol, catechol, etc.), coordination compounds of phenol compounds (borodicatechol, borodipyrogallol, etc.), sulfur-containing acids (sulfuric acid, sulfonic acid (aromatic sulfonic acid, etc.), oxyaromatic sulfonic acid (phenol-2-sulfonic acid, etc.)), boron-containing acids (boric acid, halide boric acid (tetrafluoroboric acid, etc.), or partial esters thereof), phosphorus-containing acids (phosphoric acid, halide phosphoric acid (hexafluorophosphate, etc.), phosphonic acid, phosphinic acid, or partial esters thereof), nitrogen-containing acids (nitric acid, nitrite, etc.), and p-nitrobenzene. The liquid component may contain one third anionic component, or two or more in combination.

[0034] The third anionic component may be present in the liquid component in an anionic form, a free form, or a salt form. All of these forms are sometimes collectively referred to as the third anionic component.

[0035] The amount of the third anionic component is, for example, 30 parts by mass or less (or 15 parts by mass or less) per 100 parts by mass of the first anionic component, and may also be 20 parts by mass or less (or 10 parts by mass or less). If the liquid component contains the third anionic component, it may be 0.1 parts by mass or more per 100 parts by mass of the first anion. It is also preferable that the liquid component does not contain the third anionic component. When the liquid component does not contain the third anionic component, this includes cases where the third anionic component or its traces in the liquid component are below the detection limit. However, the amount of the third anionic component is determined by converting it to free acid, not anions or salts.

[0036] (solvent) Examples of solvents include sulfone compounds, lactone compounds, carbonate compounds, and polyhydric alcohols. The liquid component may contain one solvent or a combination of two or more solvents.

[0037] Examples of sulfone compounds include sulfolane (SL), dimethyl sulfoxide, and diethyl sulfoxide. Examples of lactone compounds include γ-butyrolactone (GBL) and γ-valerolactone. Examples of carbonate compounds include dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, and fluoroethylene carbonate.

[0038] Examples of polyhydric alcohols include glycerol compounds, sugar alcohol compounds, and glycol compounds.

[0039] 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).

[0040] Examples of glycol compounds include alkylene glycol (C 2-4 Alkylene glycols (ethylene glycol (EG), propylene glycol, etc.), polyalkylene glycols (polyC) 2-4 Polyalkylene oxide adducts (polyC) of alkylene glycols (such as diethylene glycol, dipropylene glycol, triethylene glycol, polyethylene glycol (PEG), etc.) and sugar alcohols (such as glycerin, erythritol, mannitol, and pentaerythritol). 2-4Examples include alkylene oxide adducts (such as polyethylene oxide adducts).

[0041] The weight-average molecular weight (Mw) of polyalkylene glycols or polyalkylene oxide adducts of sugar alcohols is, for example, between 150 and 3000, and may also be between 200 and 1000. Mw is a polystyrene-converted value measured by gel permeation chromatography (GPC). GPC is typically performed using a polystyrene gel column and water / methanol (volume ratio 8 / 2) as the mobile phase.

[0042] (Cationic component) The liquid component may contain the cationic component in the form of a cation, in the form of a free substance, or in the form of a salt. All of these forms are sometimes collectively referred to as the cationic component.

[0043] Examples of cationic components include ammonia, amines (specifically, primary, secondary, and tertiary amines), quaternary ammonium compounds, and amidinium compounds. The amine may be aliphatic, aromatic, or heterocyclic. Examples of amines include trimethylamine, diethylamine, ethyldimethylamine, triethylamine, ethylenediamine, aniline, pyrrolidine, imidazole (such as 1,2,3,4-tetramethylimidazolinium), and 4-dimethylaminopyridine. Examples of quaternary ammonium compounds include amidine compounds (including imidazole compounds). The liquid component may contain one cationic component or a combination of two or more.

[0044] The molar ratio of the total amount of anionic components to the cationic components (= anionic component / cationic component) may be, for example, 0.5 or more, or 1 or more. From the viewpoint of suppressing dedoping and ensuring high conductivity of conductive polymers, it is preferable to use an excess of anionic components relative to cationic components. The molar ratio of the total amount of anionic components to the cationic components is preferably 1.1 or more, and may be 1.5 or more. The molar ratio of the total amount of anionic components to the cationic components may be, for example, 50 or less, or 20 or less. These lower and upper limits can be combined arbitrarily.

[0045] The molar ratio of the first anionic component to the cationic component (= first anionic component / catenic component) is preferably 1 or greater, more preferably 1.1 or greater, and may also be 1.5 or greater. When the molar ratio is within this range, fluctuations in the pH of the liquid component are easily suppressed, and the high conductivity of the conductive polymer is easily maintained. From the viewpoint of ensuring higher film repairability, the above molar ratio is preferably 10 or less, and more preferably 5 or less. These lower and upper limits can be combined arbitrarily.

[0046] The total concentration of anionic and cationic components in the liquid component is, for example, 0.1% by mass or more and 30% by mass or less, and may also be 0.5% by mass or more and 25% by mass or less, or 0.5% by mass or more and 15% by mass or less. When the total concentration of anionic and cationic components is within this range, dopant dedoping is easily suppressed. However, the amount of each anionic component is determined by converting it to free acid, and the amount of cationic component is determined by converting it to free base.

[0047] The pH of the liquid component is preferably 6 or less, more preferably 4 or less, and may be 3.8 or less, or 3.6 or less. Setting the pH of the electrolyte within this range makes it easier to suppress the degradation of the conductive polymer component. A pH of 1.0 or higher is preferred.

[0048] Furthermore, the components contained in the liquid component can be identified using infrared absorption spectroscopy, ultraviolet-visible absorption spectroscopy, gas chromatography-mass spectroscopy, liquid chromatography-mass spectroscopy, magnetic resonance spectroscopy, etc., using the liquid component collected from the electrolytic capacitor. It is preferable to collect the liquid component from an early-stage electrolytic capacitor. An early-stage electrolytic capacitor refers to an electrolytic capacitor after break-in charging and discharging, or, in the case of a commercially available product, an unused electrolytic capacitor. Quantitative analysis of the components contained in the liquid component can be performed using the calibration curve method, etc., in the analytical methods described above.

[0049] (Capacitor element) Capacitor elements include conductive polymers. Capacitor elements typically include at least an anode having a dielectric layer on its surface and a conductive polymer covering a portion of the dielectric layer.

[0050] (Anode) 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.

[0051] (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.

[0052] 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).

[0053] (conductive polymer) The conductive polymer includes, for example, a conjugated polymer and a dopant. The conductive polymer is attached so as to cover a portion of the dielectric layer. The conductive polymer attached to the surface of the dielectric layer may form a layer. The conductive polymer is sometimes called a solid electrolyte. The conductive polymer constitutes at least a portion of the cathode in the electrolytic capacitor. The conductive polymer may further contain additives as needed.

[0054] (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).

[0055] Conjugated polymers may be used individually or in combination of two or more types.

[0056] 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.

[0057] 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.

[0058] (Dopant) Examples of dopants include relatively low-molecular-weight anions and high-molecular-weight anions. Examples of anions include sulfate ions, nitrate ions, phosphate ions, borate ions, organic sulfonate ions, and carboxylate ions. Compounds that produce these anions are used as dopants. Examples of dopants that produce sulfonate ions include p-toluenesulfonic acid and naphthalenesulfonic acid.

[0059] Examples of polymer anions include polyvinyl sulfonic acid, polystyrene sulfonic acid, 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), phenol sulfonic acid novolac resin, and polyacrylic acid. The polymer anion may be a polymer of a single monomer, a copolymer of two or more monomers, or a substituted product having substituents. Among these, polyanions derived from polystyrene sulfonic acid are preferred.

[0060] However, these dopants are merely examples and are not limited to them. A dopant may be used alone or in combination of two or more types.

[0061] Conductive polymers can be formed, for example, by chemical polymerization and / or electrochemical polymerization of a conjugated polymer precursor on a dielectric layer in the presence of a dopant. Alternatively, they can be formed by contacting a dielectric layer with a solution in which the conductive polymer is dissolved or a dispersion in which the conductive polymer is dispersed. The conductive polymer used in these solutions or dispersions can be obtained by polymerizing a conjugated polymer precursor in the presence of a dopant. Examples of conjugated polymer precursors include the raw material monomers of the conjugated polymer, oligomers and prepolymers in which multiple molecular chains of the raw material monomers are linked together. One type of precursor may be used, or two or more types may be used in combination.

[0062] The amount of dopant contained in the conductive polymer 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.

[0063] (Cathole body) Similar to the anode, a metal foil may be used for the cathode. While the type of metal is not particularly limited, it is preferable to use a valve metal or an alloy containing a valve metal, such as aluminum, tantalum, or niobium. 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 a nonmetal. Examples of dissimilar metals or nonmetals include metals such as titanium and nonmetals such as carbon.

[0064] (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 may be a nonwoven fabric containing fibers of cellulose, polyethylene terephthalate, vinylon, or polyamide (e.g., aliphatic polyamide, aromatic polyamide such as aramid).

[0065] (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, an 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.

[0066] All of the features described herein can be combined in any way.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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).

[0072] 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. (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. (iii) Steps to form the capacitor element 10 For example, a liquid mixture containing a conductive polymer is impregnated into a dielectric layer to form a film of the conductive polymer that covers at least a portion of the dielectric layer. This yields a capacitor element 10 in which the conductive polymer 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. (iv) Step of impregnating with liquid components Prior to impregnation with the liquid component, the liquid component is prepared. The liquid component is prepared by dissolving anionic components, and optionally cationic components or additives, in a solvent. The prepared liquid component is then impregnated into a capacitor element having a conductive polymer. The specific method of impregnation is not particularly limited. For example, immersion or liquid injection may be used. (v) Process of sealing the capacitor element 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.

[0073] 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.

[0074] [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.

[0075] Fabrication of electrolytic capacitors A1-A22 and B1-B13 A wound electrolytic capacitor (Φ (diameter) 8 mm × L (length) 10 mm) with a rated voltage of 35 V and a rated capacitance of 150 μF was fabricated. The specific manufacturing method of the electrolytic capacitor is described below.

[0076] (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 60 V. Afterward, the aluminum foil was cut to prepare the anode.

[0077] (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.

[0078] (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 separators, 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.

[0079] (Preparation of liquid mixture) A mixed solution was prepared by dissolving 3,4-ethylenedioxythiophene (EDOT) and the dopant polystyrene sulfonic acid (PSS, weight-average molecular weight 100,000) in deionized water. Iron(III) sulfate (oxidizing agent) dissolved in deionized 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 monomers and excess oxidizing agent, yielding a polymer dispersion containing polyethylenedioxythiophene (PEDOT / PSS) doped with approximately 5% by mass of PSS.

[0080] (Formation of solid electrolytes) In a reduced-pressure atmosphere (40 kPa), a wound material was immersed in a liquid mixture contained in a designated container for 5 minutes, and then the wound material was removed from the liquid mixture. Next, the wound material impregnated with the liquid mixture was dried in a drying oven at 150°C for 20 minutes, and at least a portion of the dielectric layer was coated with a conductive polymer (solid electrolyte). A capacitor element was formed in this manner.

[0081] (Preparation of liquid components) A mixed solvent was prepared by combining each solvent in the volume ratios shown in Tables 1-3. An electrolyte salt composed of the anionic and cationic components shown in Tables 1-3 was added to this mixed solvent, and additional anionic components shown in Tables 1-3 were added separately as needed and mixed. The amount of each component added was adjusted so that the concentrations of the anionic and cationic components constituting the electrolyte salt, as well as any separately added anionic components, in the liquid component matched the values ​​shown in Tables 1-3. The total volume of these electrolyte salts and separately added anionic components, plus the solvent, was 100% by mass. The liquid component was prepared in this manner.

[0082] (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.

[0083] [Evaluation: Measurement of ESR and leakage current] Under 20°C conditions, the initial ESR of each electrolytic capacitor at a frequency of 100kHz was measured using a 4-terminal LCR meter. The average value for 20 electrolytic capacitors was then calculated.

[0084] Next, an accelerated test was conducted by placing the electrolytic capacitors in a constant temperature chamber at 140°C and maintaining them under the rated voltage for 1000 hours. After the accelerated test, the ESR of the electrolytic capacitors was measured in the same manner as above under a 20°C environment, and the average value for 20 electrolytic capacitors was calculated. The ratio of the average ESR after the accelerated test to the average ESR after the initial test (ESR change rate) was calculated and used as an indicator of ESR fluctuation during long-term use.

[0085] After the accelerated testing, the rated voltage was applied to the electrolytic capacitor in a 20°C environment, and the leakage current value was measured after 120 seconds.

[0086] The evaluation results are shown in Tables 1-3. In Tables 1-3, A1-A22 are examples, and B1-B13 are comparative examples. The results for each example are expressed as relative values, with the result of B1 set to 100. The numbers below each anion or cation in Tables 1-3 represent the concentration in the liquid component. The number in parentheses next to the second anion is the pKa of the second anion.

[0087] [Table 1]

[0088] [Table 2]

[0089] [Table 3]

[0090] As shown in Table 3, when only the first anion component was used without the second anion component, and when both the second and third anion components were used without the first anion component, the leakage current after the accelerated test increased, and the rate of change of ESR due to the accelerated test also became large in both cases. In contrast, as shown in Tables 1 and 2, when both the first and second anion components were used, the leakage current could be kept relatively low even after the accelerated test, and the ESR rate of change due to the accelerated test was also large. R change A low capacitance ratio resulted in stable capacitor performance. Furthermore, in this embodiment, the initial ESR was also kept low. [Industrial applicability]

[0091] The electrolytic capacitors of this disclosure can be used as hybrid electrolytic capacitors. Electrolytic capacitors are particularly suitable for applications requiring high reliability. However, the applications of electrolytic capacitors are not limited to these. [Explanation of symbols]

[0092] 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. A capacitor element containing a conductive polymer and a liquid component, The aforementioned liquid component comprises a first anionic component having a carbonyloxy bond and a second anionic component that does not have a carbonyloxy bond but has a sulfonylimide bond, in an electrolytic capacitor.

2. The electrolytic capacitor according to claim 1, wherein the acid dissociation constant pKa of the second anionic component in the form of a free acid is 5.0 or less.

3. The electrolytic capacitor according to claim 1 or 2, wherein the amount of the second anionic component in the liquid component is 3 parts by mass or more and 250 parts by mass or less per 100 parts by mass of the first anionic component.

4. The electrolytic capacitor according to claim 1 or 2, wherein the liquid component further comprises a cationic component.

5. The electrolytic capacitor according to claim 4, wherein the molar ratio of the first anion component in the liquid component to the cation component is 1 or more and 10 or less.

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