Electrolytic capacitor and additive for liquid component of electrolytic capacitor

Abstract

This electrolytic capacitor includes a capacitor element and a liquid component. The capacitor element includes an anode body comprising a dielectric layer on the surface thereof, and a conductive polymer that covers a portion of the dielectric layer. The liquid component contains a solvent and an acid component. The acid component includes a carboxylic acid compound that has a first cyclic group having aromaticity, a second cyclic group having aromaticity, a linking group linking the first cyclic group and the second cyclic group, and at least one carboxy group directly or indirectly bonded to at least one of the first cyclic group and the second cyclic group.

Description

Additives for electrolytic capacitors and liquid components of electrolytic capacitors

[0001] The present disclosure relates to electrolytic capacitors and additives for liquid components of electrolytic capacitors.

[0002] Electrolytic capacitors are considered promising as capacitors with small size, large capacity, and low ESR (equivalent series resistance). The electrolytic capacitors include an anode body having a dielectric layer, a conductive polymer covering at least a portion of the dielectric layer, and an electrolyte. The conductive polymer includes, for example, a conjugated polymer and a dopant. The electrolyte is a liquid component such as a non-aqueous solvent or a solution in which a solute is dissolved in a non-aqueous solvent.

[0003] Patent Document 1 proposes an electrolytic capacitor including an anode body having a dielectric layer, a solid electrolyte layer in contact with the dielectric layer of the anode body, and an electrolytic solution, the electrolytic solution including a solvent and a solute, the solvent including a glycol compound, the solute including a carboxylic acid component and a base component, and the solute including 200 parts by mass or more of the carboxylic acid component per 100 parts by mass of the base component.

[0004] International Publication No. 2017 / 017947

[0005] A first aspect of the present disclosure relates to an electrolytic capacitor. The electrolytic capacitor includes a capacitor element and a liquid component. The capacitor element includes an anode body having a dielectric layer on its surface, and a conductive polymer covering a portion of the dielectric layer. The liquid component includes a solvent and an acid component. The acid component includes a carboxylic acid compound having a first cyclic group having aromaticity, a second cyclic group having aromaticity, a linking group connecting the first cyclic group and the second cyclic group, and at least one carboxy group directly or indirectly bonded to at least one of the first cyclic group and the second cyclic group.

[0006] A second aspect of the present invention relates to an additive for use in a liquid component of an electrolytic capacitor, the liquid component including a capacitor element containing a conductive polymer, the additive including a carboxylic acid compound having a first cyclic group having aromaticity, a second cyclic group having aromaticity, a linking group connecting the first cyclic group and the second cyclic group, and at least one carboxy group bonded directly or indirectly to at least one of the first cyclic group and the second cyclic group.

[0007] The fluctuation of the equivalent series resistance (ESR) over time in the electrolytic capacitor can be kept low.

[0008] 1 is a schematic cross-sectional view of an electrolytic capacitor according to an embodiment of the present disclosure;

[0009] Electrolytic capacitors are required to have little fluctuation in ESR even after long-term use.

[0010] Phthalic acid is used as the acid component of the liquid component of electrolytic capacitors because it is easier to reduce the pH of the liquid component than aliphatic carboxylic acids. However, the carboxyl group of phthalic acid is easily deactivated by esterification, causing the pH of the liquid component to increase over time. When the pH of the liquid component is high, the conductive polymer contained in the capacitor element is more likely to be de-doped than when the pH is low, causing a gradual decrease in the conductivity of the conductive polymer and an increase in the ESR over time. Furthermore, the ESR is also likely to increase when the electrolytic capacitor is exposed to relatively high temperatures (e.g., 60°C or higher).

[0011] In view of the above, (Technology 1) an electrolytic capacitor according to a first aspect of the present disclosure includes a capacitor element and a liquid component. The capacitor element includes an anode body having a dielectric layer on its surface, and a conductive polymer covering a portion of the dielectric layer. The liquid component includes a solvent and an acid component. The acid component includes a carboxylic acid compound having a first cyclic group having aromaticity, a second cyclic group having aromaticity, a linking group connecting the first cyclic group and the second cyclic group, and at least one carboxy group directly or indirectly bonded to at least one of the first cyclic group and the second cyclic group. In this specification, such a carboxylic acid compound is referred to as a "first carboxylic acid compound."

[0012] In the first carboxylic acid compound, multiple aromatic cyclic groups are linked via linking groups, and at least one carboxy group is directly or indirectly bonded to at least one cyclic group. Due to the moderate steric hindrance between the carboxy groups based on this structure, esterification of the carboxy groups in the first carboxylic acid compound is less likely to proceed than in phthalic acid. Furthermore, because multiple cyclic groups are linked via linking groups, they behave as a single compound, making it easier to achieve high acidity due to the charge distribution within the molecule. Furthermore, the first carboxylic acid compound has high affinity for conductive polymers due to the cyclic groups and carboxy groups. Therefore, by including the first carboxylic acid compound in the liquid component, a low pH of the liquid component can be stably maintained in the vicinity of the conductive polymer. Since the high conductivity of the conductive polymer can be stably maintained for a long period of time, the ESR can be suppressed over time even when the electrolytic capacitor is used for a long period of time. Furthermore, the electrolytic capacitor can maintain a relatively high capacity even when used for a long period of time. Furthermore, the first carboxylic acid compound stabilizes the pH of the liquid component, so that even when the electrolytic capacitor is exposed to a relatively high temperature (e.g., a temperature of 60°C or higher and 200°C or lower), the high conductivity of the conductive polymer is maintained, fluctuations in ESR are suppressed, and a decrease in capacity is suppressed.

[0013] (Technology 2) In the above (Technology 1), each of the first cyclic group and the second cyclic group may be a single ring or a fused ring. In this case, high acidity and higher affinity with the conductive polymer are easily obtained. Therefore, the low pH of the liquid component can be more stably maintained, and the high conductivity of the conductive polymer can be easily maintained.

[0014] (Technology 3) In the above (Technology 1) or (Technology 2), each of the first cyclic group and the second cyclic group may be 5-membered or more and 14-membered or less. In this case, it is easy to obtain a moderate effect due to the steric hindrance of the multiple carboxy groups, and it is easy to obtain a relatively high affinity for the conductive polymer. Therefore, it is easy to maintain the high conductivity of the conductive polymer, and it is easy to further suppress fluctuations in ESR over time.

[0015] (Technology 4) In any one of the above (Technology 1) to (Technology 3), the first cyclic group and the second cyclic group may be linked by a single bond. In this case, the first cyclic group and the second cyclic group are relatively easy to move, and a higher affinity with the conductive polymer is easily obtained. Therefore, the high conductivity of the conductive polymer is more easily maintained.

[0016] (Technology 5) In any one of the above (Technology 1) to (Technology 4), the at least one carboxy group may be located at an ortho position relative to the linking group. In this case, it is easy to bring the first carboxylic acid compound into close proximity with the conductive polymer while suppressing esterification, and it is easy to maintain the high conductivity of the conductive polymer.

[0017] (Technology 6) In any one of the above (Technology 1) to (Technology 5), the at least one carboxy group may be directly bonded to the first cyclic group or the second cyclic group. In this case, esterification of the carboxy group is further suppressed, the low pH of the liquid component can be more stably maintained for a long period of time, and fluctuations in ESR over time can be further suppressed.

[0018] (Technology 7) In any one of (Technology 1) to (Technology 6) above, the liquid component may further contain a base component. In this case, it is easy to maintain the dissociated state of the acid component and easy to maintain the high conductivity of the conductive polymer.

[0019] (Technology 8) In the above (Technology 7), the base component may have a conjugate acid with a pKa of 3.5 or more and 7.0 or less. In this case, esterification of the first carboxylic acid compound can be suppressed while maintaining the dissociation state of the acid component, and the high conductivity of the conductive polymer can be more easily maintained. In addition, high initial capacity and low ESR can be easily ensured, and high voltage resistance can be easily obtained.

[0020] In this specification, the acid dissociation constant (pKa) means the acid dissociation constant in water at a temperature of 25°C. The pKa of the conjugate acid of a base is the pKa of the cation of the base. When the conjugate acid of a base exhibits multiple pKa values, the lowest pKa (i.e., pKa １ ) shall mean

[0021] (Technology 9) In the above (Technology 7) or (Technology 8), the base component may contain a heterocyclic amine. In this case, esterification of the first carboxylic acid compound can be suppressed while maintaining the dissociated state of the acid component, making it easier to maintain the high conductivity of the conductive polymer. In addition, it is easier to ensure high initial capacity and low ESR, and to obtain high voltage resistance.

[0022] (Technology 10) In any one of the above (Technology 7) to (Technology 9), the equivalent ratio of the carboxylic acid compound to the base component may be 0.5 or more and 10 or less. In this case, it is easy to ensure a high degree of dissociation of the acid component, and it is also easy to suppress corrosion of the electrode.

[0023] (Technology 11) The present disclosure also includes an additive (additive for a liquid component of an electrolytic capacitor) used in a liquid component of an electrolytic capacitor including a capacitor element containing a conductive polymer and the liquid component. This additive includes a carboxylic acid compound, i.e., a first carboxylic acid compound, having a first cyclic group having aromaticity, a second cyclic group having aromaticity, a linking group connecting the first cyclic group and the second cyclic group, and at least one carboxy group bonded directly or indirectly to at least one of the first cyclic group and the second cyclic group. By using such an additive in the liquid component of an electrolytic capacitor containing a conductive polymer, the liquid component can be stably maintained at a low pH, and the high conductivity of the conductive polymer can be stably maintained over a long period of time. Therefore, even when the electrolytic capacitor is used for a long period of time, the fluctuation of the ESR over time can be suppressed.

[0024] The electrolytic capacitor and the liquid component additive for the electrolytic capacitor of the present disclosure will be described in more detail below, including the above (Technology 1) to (Technology 11). At least one selected from the components described below can be arbitrarily combined with at least one of the above (Technology 1) to (Technology 11) related to the electrolytic capacitor and the liquid component additive of the present disclosure, as long as such combination is technically possible.

[0025] (Additive for Liquid Component) The additive for liquid component of the present disclosure is used in the liquid component of an electrolytic capacitor. The electrolytic capacitor in which the additive is used includes, in addition to the liquid component, a capacitor element containing a conductive polymer.

[0026] The liquid component additive includes a first carboxylic acid compound. The first carboxylic acid compound has a first cyclic group having aromaticity, a second cyclic group having aromaticity, a linking group connecting the cyclic groups, and at least one carboxy group bonded directly or indirectly to at least one of the cyclic groups. In the case of phthalic acid, both of the two carboxy groups are easily esterified, which causes the pH of the liquid component to increase over time and the conductivity of the conductive polymer to decrease. In contrast, when a first carboxylic acid compound has two or more carboxy groups, even if one carboxy group is esterified, the remaining carboxy groups are unlikely to be esterified due to the steric hindrance of the cyclic groups. This makes it easier to maintain a low pH of the liquid component, maintain high conductivity of the conductive polymer, and further suppress fluctuations in ESR over time. Furthermore, even when the first carboxylic acid compound has one carboxy group, the steric hindrance of the cyclic group makes it difficult for the carboxy group to be esterified, making it easier to maintain a low pH of the liquid component.

[0027] The first cyclic group and the second cyclic group are at least partially aromatic. Each cyclic group may contain an aromatic ring in part or may be an aromatic group. Each cyclic group may be a hydrocarbon group or may contain a heteroatom. Examples of heteroatoms include at least one selected from the group consisting of an oxygen atom, a sulfur atom, and a nitrogen atom. Examples of single rings corresponding to the cyclic group include hydrocarbon rings (such as a benzene ring, an annulene ring other than a benzene ring, such as an [8]annulene ring, and a tropone ring), heterocycles (such as furan, thiophene, pyrrole, imidazole, and pyridine), and the like. The fused ring may be a fused ring of multiple aromatic rings, or a fused ring in which an aromatic ring and a non-aromatic ring are fused. Examples of the fused ring corresponding to the cyclic group include hydrocarbon rings (such as an indene ring, an indane ring, a naphthalene ring, a fluorene ring, an anthracene ring, and a phenanthrene ring), and heteroatom-containing fused rings (such as a benzofuran ring, a benzothiophene ring, a benzopyran ring, an indole ring, a benzimidazole ring, a quinoline ring, a xanthene ring, a carbazole ring, an adenine ring, and a guanine ring).

[0028] Each cyclic group may have from 5 to 14 members, from 6 to 14 members, or from 6 to 10 members.

[0029] When the cyclic group is a condensed ring, the linking group may be bonded to an aromatic ring or a non-aromatic ring.Similarly, the carboxy group may be bonded to an aromatic ring or a non-aromatic ring.From the viewpoint of easily obtaining a suitable steric hindrance, it is preferable that the linking group be bonded to an aromatic ring.From the same viewpoint, it is preferable that the carboxy group be bonded to an aromatic ring.

[0030] In the cyclic group, the position of the carboxy group may be, for example, the ortho position (the second position when the position of the linking group is the first position), the meta position (the third position), or the para position (the fourth position) relative to the linking group. It is also preferable that at least one of the carboxy groups is located in the ortho position relative to the linking group. A first carboxylic acid compound is also preferred in which the first cyclic group has a carboxy group at the ortho position relative to the linking group, and the second cyclic group has a carboxy group or a substituent (a first substituent (such as an alkoxy group) described below) at the ortho position relative to the linking group. In these cases, it is easy to bring the first carboxylic acid compound close to the conductive polymer while suppressing esterification of the carboxy group, and it is easier to maintain the high conductivity of the conductive polymer.

[0031] Examples of the linking group (first linking group) connecting the first cyclic group and the second cyclic group include a single bond or a chain group. The chain group also includes a chain group having a substituent (second substituent). From the viewpoint of further suppressing the progress of esterification and easily ensuring high acidity through moderate steric hindrance, it is preferable that the linking group is not a group that hinders the movement (rotation, etc.) of the first cyclic group and the second cyclic group, such as a double bond. The chain group may be a hydrocarbon group (specifically, an aliphatic hydrocarbon group) or a chain group containing a heteroatom (containing a heteroatom). In addition to the first cyclic group and the second cyclic group, the first carboxylic acid compound may further have an aromatic cyclic group (e.g., a third cyclic group, a fourth cyclic group). The valence of the chain group as a linking group is determined depending on the number of cyclic groups. The chain group may be divalent to tetravalent, or may be divalent or trivalent.

[0032] From the viewpoint of further suppressing the progress of esterification by a moderate steric hindrance and easily ensuring high acidity, the valence of the chain group as the linking group is preferably divalent. Examples of divalent hydrocarbon groups include alkylene (C such as methylene, ethylene, propylene, trimethylene, dimethylmethylene, 1,4-butanediyl, 1,1-dimethylethylene, and 1,2-dimethylethylene). １－６ Alkylene group (C １－４ alkylene groups, etc.), alkenylene (e.g., vinylene), ２－６ Alkenylene group (C ２－４ Depending on the number of cyclic groups in the first carboxylic acid compound, the linking group may be a trivalent or tetravalent group corresponding to the above-mentioned divalent hydrocarbon group. Examples of the chain group containing a hetero atom include a carbonyl group (-C(=O)-), a sulfur atom (-S-), an oxygen atom (-O-), an imino group (-N(-R)-), an oxyalkylene (oxy C such as oxyethylene and oxypropylene), and the like. ２－４ alkylene, etc.), a divalent group corresponding to a dialkyl ether (oxydi-C such as oxydiethylene group) ２－４ alkylene groups, etc.), polyoxyalkylenes (polyoxy C such as polyoxyethylene and polyoxypropylene) ２－４ Examples of such groups include divalent groups corresponding to dialkyl amines (such as divalent groups corresponding to dimethylamine and diethylamine), divalent groups corresponding to dialkyl sulfides, divalent groups corresponding to dialkylamines (such as divalent groups corresponding to dimethylamine and diethylamine), and divalent or trivalent groups corresponding to trialkylamines (such as divalent or trivalent groups corresponding to trimethylamine and triethylamine). R corresponds to the second substituent carried by the chain group.

[0033] Examples of the second substituent that the chain group has include alkyl groups (C groups such as methyl groups, ethyl groups, and isopropyl groups). １－４ alkyl groups, alkoxy groups (e.g., methoxy groups, ethoxy groups, propoxy groups, n-butoxy groups, tert-butoxy groups, etc.) １－４The number of second substituents is determined depending on the type and length of the chain group. The number of second substituents in the chain group may be 1 or more and 3 or less, or may be 1 or 2. The chain group may not have a second substituent. When the chain group has two or more second substituents, at least two of the second substituents may be the same, or all of the second substituents may be different.

[0034] From the viewpoint that the first cyclic group and the second cyclic group are relatively easy to move and a higher affinity with the conductive polymer is easily obtained, the linking group is preferably a single bond, an alkylene group (C １－２ The linking group is preferably a single bond, an alkylene group, a carbonyl group, an element atom, a sulfur atom, or an imino group.

[0035] In the electrolytic capacitor, the carboxy group of the first carboxylic acid compound may be in any of the following forms: a free form, a salt form, an anion form, or a form interacting (e.g., complexing) with a conductive polymer. In this specification, the carboxy group of the first carboxylic acid compound includes all of these forms.

[0036] The carboxy group may be directly bonded to at least one of the first cyclic group and the second cyclic group (in other words, without any other group). Alternatively, the carboxy group may be indirectly bonded to at least one of the first cyclic group and the second cyclic group (in other words, via another group (second linking group)). For example, the carboxy group may be bonded to the cyclic group via an aliphatic group (such as an alkylene group or an alkenylene group). Examples of the aliphatic group to which a carboxy group is bonded include carboxy alkyl groups (such as a carboxy C group, e.g., a carboxymethyl group or a carboxyethyl group). １－４ alkyl group, carboxyalkenyl group (carboxy C such as carboxyvinyl group) ２－４ From the viewpoint of easily maintaining a low pH of the liquid component, it is preferred that at least one of the carboxy groups is directly bonded to the first cyclic group or the second cyclic group.

[0037] From the viewpoint of further suppressing the progress of esterification, it is preferable that the first carboxylic acid compound has two or more carboxy groups. In this case, one cyclic group may have at least two carboxy groups. From the viewpoint of easily exerting the effect of steric hindrance by the cyclic groups, it is preferable that each cyclic group has at least one carboxy group.

[0038] The first carboxylic acid compound may have a substituent (first substituent) other than a carboxy group and an aliphatic group having a carboxy group on a cyclic group. Examples of the first substituent include at least one selected from the group consisting of a hydrocarbon group, an alkoxy group, an alkoxycarbonyl group, and an oxo group (═O). Examples of the hydrocarbon group include an aliphatic hydrocarbon group, an alicyclic hydrocarbon group (e.g., a cyclohexyl group), and an aromatic hydrocarbon group (e.g., a phenyl group). Examples of the aliphatic hydrocarbon group include an alkyl group (C such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, or a t-butyl group). １－４ alkyl groups, alkenyl groups (vinyl groups, allyl groups, etc.) ２－４ Alkenyl groups, etc.) and the like. Examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, an n-butoxy group, and a t-butoxy group (C １－４ Examples of the alkoxycarbonyl group include a methoxycarbonyl group, an ethoxycarbonyl group (C １－４ Examples of the first substituent include an alkoxy-carbonyl group and the like. Among these, the first substituent may be at least one selected from the group consisting of an aliphatic hydrocarbon group (such as an alkyl group) and an alkoxy group. The number of first substituents in one cyclic group is selected depending on, for example, the number of members of the cyclic group and the number of carboxy groups. The number of first substituents may be 1 to 6, or 1 to 4, or may be 1, 2, or 3. Furthermore, the first carboxylic acid compound may not have a first substituent other than a carboxy group (and an aliphatic group having a carboxy group) on the cyclic group. When one cyclic group has two or more first substituents, at least two of the first substituents may be the same, or all of the first substituents may be different.

[0039] The first carboxylic acid compound may include, for example, a compound represented by the following formula (I) or a compound represented by the following formula (i): Among the first carboxylic acid compounds, examples of compounds having a carboxy group at the ortho position of the linking group include compounds represented by the following formula (i):

[0040]

[0041] In formula (I), ring Z １ is a first cyclic group, and ring Z ２ is a second cyclic group, and A is a linking group (first linking group). B1 and B2 are each a linking group (second linking group), and x1 and x2 are each 0 or 1. n1 and n2 are the number of carboxy groups in the first cyclic group and the second cyclic group, respectively. R １ and R ２ m1 and m2 are the first substituents R １ and R ２ is the number of

[0042] In formula (i), ring Z １ａ is a first cyclic group, and ring Z ２ａ is a second cyclic group. ３ is a hydrogen atom, a carboxy group, or a first substituent. １ａ The number of carboxy groups in the second cyclic group Z is (p1+1). ２ａ The number of carboxy groups in R ３ When R is a carboxy group, it is (p2+1). q is the number of the first substituent R in the second cyclic group. ２ is the number of R ３ is the first substituent, the number of first substituents in the second cyclic group is ２ The number q and R ３ In formula (i), A, B1, B2, R １ , R ２ , x1, and x2 are the same as in formula (I).

[0043] In formula (I) or formula (i), the first linking group A is preferably a single bond. Alternatively, the first carboxylic acid compound may be a biphenyl compound in which the first linking group A is a single bond and the first cyclic group and the second cyclic group are benzene rings (in other words, phenyl groups). Such a compound is, for example, represented by the following formula (ia). The first carboxylic acid compound may include a compound represented by formula (ia).

[0044]

[0045] In formula (ia), B1, B2, R １ , R ２ , R ３ , x1, x2, m1, p1, p2, and q are the same as in formula (I). ３ is preferably a first substituent or a carboxy group.

[0046] For the groups or moieties and numbers in formula (I), formula (i) and formula (ia), reference can be made to the descriptions in the relevant sections above.

[0047] Examples of the first carboxylic acid compound include biphenyl-2,2'-dicarboxylic acid (DA), 4,4'-biphenyldicarboxylic acid, 2,6-biphenyldicarboxylic acid, 2-phenylbenzoic acid, 2'-methoxy-1,1'-biphenyl-2'-carboxylic acid (MPBA), and hydrogenated products thereof (such as bicyclohexyl-2,2'-dicarboxylic acid (BHDC)). However, these compounds are merely examples, and the first carboxylic acid compound is not limited to these compounds.

[0048] The first carboxylic acid compound may be used alone or in combination of two or more.

[0049] (Liquid Component) The liquid component contains a solvent and an acid component. The liquid component may further contain a base component.

[0050] (Solvent) The solvent contained in the liquid component may be a non-aqueous solvent. Examples of the non-aqueous solvent include sulfone compounds, lactone compounds, carbonate compounds, and alcohol compounds. The liquid component may contain one type of non-aqueous solvent or a combination of two or more types.

[0051] Among the aprotic polar solvents, sulfone compounds include cyclic sulfone compounds (such as sulfolane (SL)) and sulfoxide compounds (such as dimethyl sulfoxide and diethyl sulfoxide). Lactone compounds include γ-butyrolactone (GBL) and γ-valerolactone. Carbonate compounds include chain carbonates (such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate), and cyclic carbonates (such as ethylene carbonate, propylene carbonate, and fluoroethylene carbonate).

[0052] Among the non-aqueous solvents, alcohol compounds include monohydric alcohols and polyhydric alcohols. Examples of polyhydric alcohols include glycol compounds (alkylene glycols (ethylene glycol (EG), propylene glycol, etc.), polyalkylene glycols (polyethylene glycol (PEG), polypropylene glycol (PPG), polyethylene glycol-polypropylene glycol copolymers (PEG-PPG)), etc.), glycerin compounds (glycerin (GC), polyglycerin, etc.), sugar alcohol compounds, and alkylene oxide adducts thereof (ethylene oxide adducts, polyethylene oxide adducts, etc.).

[0053] From the viewpoint of being suitable for improving the conductivity of the conductive polymer, the non-aqueous solvent preferably contains at least a glycol compound. The non-aqueous solvent may contain a glycol compound and a sulfone compound (e.g., a cyclic sulfone compound such as SL), and may additionally contain a polyalkylene glycol (e.g., PEG).

[0054] The weight-average molecular weight Mw of the polyalkylene glycol may be 150 or more and 20,000 or less, or 200 or more and 20,000 or less. Within these ranges, the upper limit of the weight-average molecular weight Mw may be 5,000 or less, or 1,000 or less. When the weight-average molecular weight Mw is in such a range, not only is it easy to obtain high film repairability, but it is also easy to maintain the viscosity of the liquid component relatively low, which can increase the dissociation of the acid component and the base component.

[0055] In this specification, the weight average molecular weight (Mw) is a value calculated as polystyrene measured by gel permeation chromatography (GPC), which is typically performed using a polystyrene gel column and a water / methanol (volume ratio 8 / 2) mobile phase.

[0056] (Acid Component) The acid component includes the first carboxylic acid compound described above. For the first carboxylic acid compound, the description of the additives described above can be referred to. The liquid component may include an acid component other than the first carboxylic acid compound. Examples of such an acid component include a carboxylic acid compound other than the first carboxylic acid compound (a second carboxylic acid compound) and other acids.

[0057] (Second Carboxylic Acid Compound) The acid component may further contain a second carboxylic acid compound different from the first carboxylic acid compound. When the acid component contains the second carboxylic acid compound, the pH of the liquid component can be further reduced. Since the decrease in the conductivity of the conductive polymer is further suppressed, it is easier to further reduce the change in ESR over time.

[0058] Examples of the second carboxylic acid compound include carboxylic acids other than the first carboxylic acid compound, carboxylic acid anhydrides, and coordination compounds of carboxylic acids.

[0059] Examples of the carboxylic acid include aliphatic carboxylic acids and aromatic carboxylic acids. Examples of the aromatic carboxylic acid include aromatic hydroxy acids (such as benzoic acid, nitrobenzoic acid, and salicylic acid), aromatic polycarboxylic acids (such as phthalic acid and pyromellitic acid), and sulfoaromatic carboxylic acids (such as p-sulfobenzoic acid, 3-sulfophthalic acid, and 5-sulfosalicylic acid).

[0060] Examples of the coordination compound include a coordination compound having at least one central atom selected from the group consisting of boron, aluminum, and silicon, and an acid having a carbonyloxy bond bound to the central atom. Specific examples of the coordination compound include borodisalicylic acid, borodisalic acid, borodiglycolic acid, and borodigallic acid.

[0061] The acid component may contain one or more second carboxylic acid compounds. Among the second carboxylic acid compounds, aromatic carboxylic acids (such as phthalic acid, salicylic acid, benzoic acid, and nitrobenzoic acid) and the coordination compounds (such as borodisalicylic acid, borodisalic acid, and borodiglycolic acid) are preferred, and phthalic acid, salicylic acid, and borodisalicylic acid are particularly preferred.

[0062] In the liquid component, the carboxy group and other acid groups (such as sulfonic acid groups, phosphoric acid groups, and phosphonic acid groups) of the second carboxylic acid compound may each be in any of the following forms: free form, salt form, anionic form, or form interacting (e.g., complexing) with the conductive polymer. The carboxy group and other acid groups of the second carboxylic acid compound each include all of these forms.

[0063] (Other Acids) The acid component may include an acid other than the first carboxylic acid compound and the second carboxylic acid compound. Examples of such other acids include acids having a carbonyloxy bond other than carboxylic acid (such as oxocarbonic acid and Meldrum's acid) or coordination compounds thereof, phenolic compounds (such as picric acid, p-nitrophenol, pyrogallol, and catechol) or coordination compounds thereof, sulfur-containing acids (such as sulfuric acid, sulfonic acids (such as aromatic sulfonic acids), and oxyaromatic sulfonic acids (such as phenol-2-sulfonic acid)), compounds having a sulfonylimide bond, boron-containing acids (such as boric acid, halogenated boric acids (such as tetrafluoroboric acid), and partial esters thereof), phosphorus-containing acids (such as phosphoric acid, halogenated phosphoric acids (such as hexafluorophosphoric acid), phosphonic acids, phosphinic acids, and partial esters thereof (such as butyl phosphate)), and nitrogen-containing acids (such as nitric acid and nitrous acid).

[0064] Examples of compounds having a sulfonylimide bond include saccharin, 1,2-benzenedisulfonimide, cyclohexafluoropropane-1,3-bis(sulfonyl)imide, 4-methyl-N-[(4-methylphenyl)sulfonyl]benzenesulfonamide, dibenzenesulfonimide, trifluoromethanesulfonanilide, N-[(4-methylphenyl)sulfonyl]acetamide, benzenesulfonanilide, and N,N'-diphenylsulfamide.

[0065] Examples of the coordination compound include a coordination compound having at least one central atom selected from the group consisting of boron, aluminum, and silicon, and an acid or phenol compound having a carbonyloxy bond bound to the central atom. Specific examples of the coordination compound include borodicatechol and borodipyrogallol.

[0066] The acid component may contain one or more of the above-mentioned other acids.

[0067] (Other) The ratio of the first carboxylic acid compound in the acid component may be 20% by mass or more, 33% by mass or more, or 50% by mass or more. In this case, fluctuations in ESR over time can be further suppressed. The ratio of the first carboxylic acid compound in the acid component is 100% by mass or less. From the viewpoint of improving the film repairability of the dielectric layer, the ratio of the first carboxylic acid compound in the acid component may be 80% by mass or less.

[0068] The ratio of the first carboxylic acid compound in the acid component may be 20% by mass or more (or 33% by mass or more) and 100% by mass or less, 50% by mass or more and 100% by mass or less, 20% by mass or more (or 33% by mass or more) and 80% by mass or less, or 50% by mass or more and 80% by mass or less.

[0069] The mass ratio of the second carboxylic acid compound to the first carboxylic acid compound (=second carboxylic acid compound / first carboxylic acid compound) may be 0 / 100 or more and 80 / 20 or less, 20 / 80 or more and 67 / 33 or less, or 20 / 80 or more and 50 / 50 or less. When the mass ratio is within such a range, the effect of the first carboxylic acid compound is easily exerted, and fluctuations in high ESR over time can be further suppressed.

[0070] The concentration of the first carboxylic acid compound contained in the liquid component may be 1% by mass or more and 30% by mass or less, or 1% by mass or more and 20% by mass or less. From the viewpoint of further reducing the fluctuation of ESR over time, the concentration of the first carboxylic acid compound is preferably 1% by mass or more and 14% by mass or less, and more preferably 2% by mass or more and 12% by mass or less.

[0071] The above ratios, mass ratios, and concentrations are values ​​determined based on the mass of each acid when it is in its free form.

[0072] (Base Component) When the liquid component contains a base component, the dissociation property of the acid component such as the first carboxylic acid compound is enhanced, and the acid group such as a carboxy group can easily react with the conductive polymer, thereby easily obtaining higher conductivity of the conductive polymer.

[0073] Examples of the basic component include ammonia, amines (specifically, primary amines, secondary amines, and tertiary amines), quaternary ammonium compounds, and amidinium compounds. The liquid component may contain one type of basic component or two or more types.

[0074] The amine may be any of aliphatic, aromatic, and heterocyclic. Examples of the amine include dialkylamines (diethylamine, etc.), trialkylamines (trimethylamine, ethyldimethylamine, triethylamine (TEA), tri-n-butylamine (TBA), dimethyl-n-octylamine (DMOA), etc.), alkylenediamines (ethylenediamine, etc.), aromatic amines (aniline, etc.), and heterocyclic amines (pyrrolidine, imidazole compounds (imidazole (Imd), 1,2,3,4-tetramethylimidazolinium, etc.), pyridine (Pyr), 4-dimethylaminopyridine, diazabicycloundecene (DBU), etc.). Each of the aromatic amines and heterocyclic amines may be monocyclic or polycyclic (fused ring, bridged ring, etc.). Examples of the quaternary ammonium compound include amidine compounds (including imidazole compounds).

[0075] The base component may contain a heterocyclic amine. Examples of heterocyclic amines include 4- to 20-membered or 4- to 10-membered heterocyclic amines. The heterocyclic amine may have one or two or more nitrogen atoms constituting the heterocycle. The heterocycle may have one or two or more heteroatoms other than nitrogen atoms (oxygen atoms, sulfur atoms, etc.) as ring constituent atoms. The heterocycle may be saturated or unsaturated. The heterocyclic amine may be a secondary amine or a tertiary amine. Heterocyclic amines also include those having one or two or more substituents (e.g., hydroxy groups, amino groups or substituted amino groups, alkyl groups, alkoxy groups, hydroxyalkyl groups, etc.) on the heterocycle. Specific examples of heterocyclic amines include pyrrolidine, piperidine, piperazine, morpholine, N-alkylmorpholine, N-hydroxyalkylmorpholine, pyridine, pyridazine, pyrimidine, pyrazine, and 4-dimethylaminopyridine. Among heterocyclic amines, tertiary amines are preferred, and unsaturated tertiary amines are more preferred, from the viewpoint of easily adjusting the pKa of the conjugate acid to a suitable range. Furthermore, heterocyclic amines that do not have a free amino group are preferred, from the viewpoint of easily suppressing electrode corrosion while maintaining a high dedoping suppression effect due to the acid component. Among heterocyclic amines, pyridine, N-alkylmorpholine, and N-hydroxyalkylmorpholine are more preferred. The alkyl group or the alkyl moiety of the hydroxyalkyl group on the nitrogen atom of morpholine is C １－２０ The alkyl moiety may be linear or branched. From the viewpoint of easily adjusting the pKa of the conjugate acid to a suitable range, the alkyl moiety is preferably C ３－２０ Alkyl (propyl, isopropyl, n-butyl, isobutyl, etc.) is preferred, C ４－２０ Alkyl or C ４－１０N-alkylmorpholine and N-hydroxyalkylmorpholine (particularly N-alkylmorpholine) are preferred from the viewpoint of easily ensuring a high initial capacity and a low ESR and easily obtaining a high withstand voltage. Examples of N-alkylmorpholine include N-methylmorpholine, N-isopropylmorpholine, N-butylmorpholine, and N-isobutylmorpholine.

[0076] The base component may include a base (first base) whose conjugate acid has a pKa of 3.5 or more and 7.0 or less. The pKa of the conjugate acid of the first base may be 3.5 or more and 6.0 or less, or 3.5 or more and 5.5 or less. When the pKa is within such a range, esterification of the first carboxylic acid compound can be suppressed while maintaining the dissociation state of the acid component, making it easier to maintain the high conductivity of the conductive polymer. In addition, it is easier to ensure high initial capacity and low ESR, and to obtain high voltage resistance.

[0077] The liquid component may contain the base component in a free form, a cationic form, or a salt form, and all of these forms may be referred to as the base component.

[0078] The equivalent ratio of the first carboxylic acid compound to the base component (=first carboxylic acid compound / base component) may be 0.5 or more and 10 or less, 1.0 or more and 9.0 or less, or 1.3 or more and 8.9 or less. In this case, a high degree of dissociation of the first carboxylic acid compound can be ensured and corrosion of the electrode can be suppressed.

[0079] The equivalent ratio of the first carboxylic acid compound to the base component is (the total number of carboxy groups per molecule of the first carboxylic acid compound) / (OH groups that can be generated per molecule of the base component) － is the ratio of the total number of moles of

[0080] The equivalent ratio of the acid component to the base component (=acid component / base component) may be 0.5 or more and 15 or less, or 1.0 or more and 10 or less. The equivalent ratio of the acid component / base component may be selected from the above-mentioned numerical range described for the equivalent ratio of the first carboxylic acid compound / base component.

[0081] The equivalent ratio of the acid component to the base component is (the total number of acid groups per molecule of the acid component) / (OH groups that can be generated per molecule of the base component) － is the ratio of the total number of moles of

[0082] (Capacitor Element) The capacitor element included in the electrolytic capacitor includes an anode body having a dielectric layer on its surface and a conductive polymer covering at least a portion of the dielectric layer. The conductive polymer constitutes at least a portion of the cathode body of the capacitor element. The cathode body may further include a cathode extraction layer (e.g., a cathode foil).

[0083] (Anode Body) The anode body may contain a valve metal, an alloy containing a valve metal, or a compound containing a valve metal. These materials may be used alone or in combination of two or more. Preferred valve metals include aluminum, tantalum, niobium, and titanium.

[0084] The anode body is preferably an anode foil. The anode body preferably has a porous portion having pores at least in the surface layer. Anode bodies other than anode foil include a porous sintered body or a porous molded body of particles containing a valve metal.

[0085] The porous anode foil can be obtained by roughening the surface of a valve metal-containing substrate (e.g., a foil or plate-shaped substrate). The roughening can be performed by etching (e.g., electrolytic etching or chemical etching).

[0086] (Dielectric Layer) The dielectric layer is formed by anodizing the valve metal on the surface of the anode body. Anodization is performed, for example, by chemical conversion treatment. The dielectric layer is formed, for example, so as to cover at least a portion of the surface of the anode body.

[0087] The dielectric layer contains an oxide of the valve metal. For example, when tantalum is used as the valve metal, the dielectric layer contains Ta. ２ O ５ When aluminum is used as the valve metal, the dielectric layer contains Al ２ O ３However, the dielectric layer is not limited to this, and may be any layer that functions as a dielectric.

[0088] The dielectric layer is usually formed on the surface of the anode body. When the dielectric layer is formed on the surface of the porous portion of the anode body, the dielectric layer is formed along the inner wall surfaces of the pores in the porous portion and the depressions (pits) on the surface of the anode body.

[0089] (Conductive Polymer) The conductive polymer includes, for example, a conjugated polymer and a dopant. The conductive polymer may cover at least a portion of the dielectric layer. This embodiment includes a case where the conductive polymer is in contact with at least a portion of the dielectric layer. When the capacitor element includes an anode foil and a cathode foil, the conductive polymer may be interposed between these foils. In this case, the conductive polymer may be impregnated into a separator interposed between the anode foil and the cathode foil. The conductive polymer may be in contact with at least a portion of the cathode foil in addition to at least a portion of the dielectric layer. The conductive polymer may form a layer. The conductive polymer is sometimes called a solid electrolyte. The conductive polymer forms at least a portion of the cathode body in an electrolytic capacitor. The conductive polymer may further include an additive, if necessary.

[0090] (Conjugated Polymers) Examples of conjugated polymers include known conjugated polymers used in electrolytic capacitors, such as π-conjugated polymers. Examples of conjugated polymers include polymers with a basic skeleton of polypyrrole, polythiophene, polyaniline, polyfuran, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, and polythiophene vinylene. The above polymers may contain at least one monomer unit constituting the basic skeleton. The above polymers also include homopolymers, copolymers of two or more monomers, and derivatives thereof (e.g., substituted products having substituents). For example, polythiophenes include poly(3,4-ethylenedioxythiophene) (PEDOT).

[0091] The conjugated polymer may be used alone or in combination of two or more kinds.

[0092] The weight average molecular weight (Mw) of the conjugated polymer is not particularly limited and is, for example, 1,000 or more and 1,000,000 or less.

[0093] (Dopants) Examples of dopants include relatively low molecular weight anions and polymeric anions. Examples of anions include sulfate ions, nitrate ions, phosphate ions, borate ions, organic sulfonate ions, and carboxylate ions. Compounds that generate these anions are used as dopants. Examples of dopants that generate sulfonate ions include aromatic sulfonic acid compounds (such as paratoluenesulfonic acid and naphthalenesulfonic acid). The aromatic sulfonic acid compound may have at least one group selected from the group consisting of a carboxy group and a hydroxy group.

[0094] Examples of polymeric anions include polyvinyl sulfonic acid, polystyrene sulfonic acid (PSS), polyallylsulfonic acid, polyacrylic sulfonic acid, polymethacrylic sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, polyester sulfonic acid (such as aromatic polyester sulfonic acid), phenolsulfonic acid novolac resin, and polyacrylic acid. The polymeric anion may be a polymer of a single monomer, a copolymer of two or more monomers, or a substituted product having a substituent. Among these, polyanions derived from polystyrene sulfonic acid are preferred.

[0095] However, these dopants are merely examples and are not limited to these. One dopant may be used alone, or two or more dopants may be used in combination.

[0096] The conductive polymer may be formed, for example, by chemically polymerizing or electrolytically polymerizing a conjugated polymer precursor on a dielectric layer in the presence of a dopant. Alternatively, a conductive polymer (e.g., a conductive polymer layer) may be formed by contacting a solution in which the conductive polymer is dissolved or a dispersion in which the conductive polymer is dispersed with a dielectric layer. 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 raw material monomers for conjugated polymers, and 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.

[0097] The weight average molecular weight (Mw) of the dopant is not particularly limited and is, for example, 1,000 or more and 1,000,000 or less.

[0098] The amount of the dopant contained in the conductive polymer is, for example, 10 parts by mass or more and 1000 parts by mass or less, and may be 20 parts by mass or more and 500 parts by mass or less, relative to 100 parts by mass of the conjugated polymer.

[0099] (Cathode Extraction Layer) The cathode extraction layer may include, for example, a first layer covering at least a portion of the conductive polymer. The cathode extraction layer may include a first layer and a second layer covering the first layer. Examples of the first layer include a layer containing conductive particles and a metal foil (cathode foil). Examples of the conductive particles include at least one selected from conductive carbon and metal powder. For example, the cathode extraction layer may include a first layer containing conductive carbon (e.g., graphite) (also referred to as a carbon layer) and a second layer containing metal powder or a metal foil. When a metal foil is used as the first layer, the cathode extraction layer may be formed of this metal foil. The cathode extraction layer can be formed by a known method depending on the layer configuration.

[0100] The second layer containing metal powder can be formed, for example, by laminating a composition containing metal powder on the surface of the first layer. Examples of such a second layer include a metal paste layer (e.g., a silver paste layer) formed using a composition containing metal powder such as silver particles and a resin (binder resin). The resin may be a thermosetting resin such as an imide resin or an epoxy resin, or a thermoplastic resin.

[0101] When a metal foil is used as the first layer, the type of metal is not particularly limited, but it is preferable to use a valve metal such as aluminum, tantalum, or niobium, or an alloy containing a valve metal. If necessary, the surface of the metal foil may be roughened. The surface of the metal foil may be provided with a chemical conversion coating, or may be provided with a coating of a metal (dissimilar metal) or a nonmetal different from the metal constituting the metal foil. Examples of dissimilar metals and nonmetals include metals such as titanium and nonmetals such as carbon (e.g., conductive carbon).

[0102] The coating of the dissimilar metal or non-metal (for example, conductive carbon) may be the first layer, and the metal foil may be the second layer.

[0103] (Separator) A separator may be disposed between the cathode body (e.g., cathode foil) and the anode body (e.g., anode foil). The separator is not particularly limited, and may be, for example, a nonwoven fabric containing fibers of cellulose, polyethylene terephthalate, vinylon, or polyamide (e.g., aliphatic polyamide, aromatic polyamide such as aramid).

[0104] When the capacitor element includes a separator, the conductive polymer may be impregnated into the separator. The conductive polymer may be interposed between an anode body (e.g., an anode foil) and a cathode body (e.g., a cathode foil) and may be in contact with at least a portion of the dielectric layer and at least a portion of the cathode body. In the present disclosure, the combination of the conductive polymer with a liquid component containing a first carboxylic acid compound can maintain high conductivity of the conductive polymer, so that a decrease in ESR can be suppressed even in these embodiments.

[0105] (Other) The electrolytic capacitor may be a wound type, and may be either a chip type or a laminated type. The electrolytic capacitor has at least one capacitor element. The electrolytic capacitor may have multiple capacitor elements. For example, the electrolytic capacitor may have a laminate of two or more capacitor elements, or may have two or more wound capacitor elements. The configuration or number of capacitor elements may be selected depending on the type or application of the electrolytic capacitor.

[0106] In the capacitor element, one end of a cathode lead is electrically connected to the cathode extraction layer. One end of an anode lead is electrically connected to the anode body. The other end of the anode lead and the other end of the cathode lead are each drawn out from the exterior body or case. The other end of each lead exposed from the exterior body or case is used for soldering to a substrate on which the electrolytic capacitor is to be mounted, for example. Each lead may be a lead wire or a lead frame.

[0107] Fig. 1 is a cross-sectional schematic diagram of an electrolytic capacitor according to this embodiment, and Fig. 2 is a schematic diagram of a partially exploded capacitor element of the electrolytic capacitor. However, the electrolytic capacitor of the present disclosure is not limited to the following embodiments. Furthermore, the components of the following embodiments may be arbitrarily combined with at least one of the above-described (Technology 1) to (Technology 11) related to the electrolytic capacitor or liquid component additive of the present disclosure, or may be arbitrarily combined with at least one of the above-described (Technology 1) to (Technology 11) and the components described above.

[0108] The electrolytic capacitor includes, for example, a capacitor element 10, a bottomed case 101 that contains capacitor element 10 and a liquid component (not shown), a sealing member 102 that closes the opening of bottomed case 101, a seat plate 103 that covers sealing member 102, lead wires 104A and 104B that extend from sealing member 102 and pass through seat plate 103, and lead tabs 105A and 105B that connect the lead wires to electrodes of capacitor element 10. The vicinity of the open end of bottomed case 101 is drawn inward, and the open end is curled so as to be crimped to sealing member 102.

[0109] Capacitor element 10 is, for example, a wound body as shown in Fig. 2. The wound body includes anode foil 11 connected to lead tab 105A, cathode foil 12 connected to lead tab 105B, and separator 13. Anode foil 11 and cathode foil 12 are wound with separator 13 interposed therebetween. The outermost periphery of the wound body is fixed with stop tape 14. Note that Fig. 2 shows a partially unfolded state of the wound body before the outermost periphery is secured.

[0110] In capacitor element 10, a dielectric layer (not shown) is formed on at least a portion of the surface of anode foil 11. Separator 13 and a conductive polymer (not shown) are interposed between anode foil 11 and cathode foil 12. The conductive polymer is in contact with at least a portion of the dielectric layer. The conductive polymer is also in contact with at least a portion of cathode foil 12. The conductive polymer and separator are impregnated with a liquid component.

[0111] EXAMPLES The present invention will be specifically described below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0112] Examples 1 to 7 and Comparative Examples 1 to 3 Wound electrolytic capacitors (rated voltage 25 V, rated capacitance 330 μF) were fabricated and evaluated according to the following procedure.

[0113] (Preparation of anode body) An aluminum foil having a thickness of 100 μm was subjected to an etching treatment to roughen the surface of the aluminum foil. Then, a dielectric layer was formed on the surface of the aluminum foil by chemical conversion treatment. The chemical conversion treatment was performed by immersing the aluminum foil in an ammonium adipate solution and applying a voltage thereto. Then, the aluminum foil was cut into a size of 8 mm length x 120 mm width to prepare an anode body.

[0114] (Preparation of Cathode Body) An aluminum foil having a thickness of 50 μm was subjected to an etching treatment to roughen the surface of the aluminum foil, and then cut into a size of 8 mm length×120 mm width to prepare a cathode body.

[0115] (Preparation of Wound Body) An anode lead tab and a cathode lead tab were connected to the anode body and the cathode body, and the anode body and the cathode body were wound around the lead tabs, with a separator interposed therebetween, and the ends of the outer surface of the wound body were fixed with a winding tape to prepare a wound body. An anode lead wire and a cathode lead wire were connected to the ends of each lead tab protruding from the wound body, respectively. The prepared wound body was then subjected to a chemical conversion treatment again, and a dielectric layer was formed on the cut end of the anode body.

[0116] (Preparation of Polymer Dispersion Containing Conductive Polymer) 3,4-ethylenedioxythiophene and the polymer dopant poly(4-styrenesulfonic acid) (PSS, Mw: 100,000) were dissolved in ion-exchanged water to prepare a mixed solution. While stirring the mixed solution, an oxidizing agent (iron(III) sulfate and ammonium persulfate) dissolved in ion-exchanged water was added to carry out a polymerization reaction. After the reaction, the resulting reaction solution was dialyzed to remove unreacted monomers and excess oxidizing agent, yielding a polymer dispersion containing PSS-doped poly(3,4-ethylenedioxythiophene) (PEDOT / PSS) as the conductive polymer. The weight-average molecular weight (Mw) of the polymer dopant was measured under the conditions described above.

[0117] (Coating of the dielectric layer with a conductive polymer) The wound body was immersed in a polymer dispersion contained in a specified container in a reduced pressure atmosphere (40 kPa) for 5 minutes, and then removed from the polymer dispersion. Next, the wound body impregnated with the polymer dispersion was dried in a drying oven at 150°C for 20 minutes, and at least a portion of the dielectric layer was coated with the conductive polymer. In this way, a capacitor element was formed.

[0118] (Preparation of Liquid Component and Impregnation into Capacitor Element) Liquid components were prepared by mixing the salts and other acid components shown in Table 1 into a solvent so that the concentrations in the liquid component were the values ​​(% by mass) shown in Table 1. As the solvent, a mixed solvent of ethylene glycol, sulfolane, and polyethylene glycol in a volume ratio of 40:40:20 was used.

[0119] (Assembly of Electrolytic Capacitor) The capacitor element was immersed in the liquid component and placed in a reduced pressure atmosphere (40 kPa) for 5 minutes to allow the liquid component to be impregnated into the capacitor element.

[0120] The capacitor element impregnated with the liquid component was placed inside a bottomed case, with the lead wires positioned on the open side of the case. A sealing member (made of an elastic material containing butyl rubber as a rubber component) formed to allow the lead wires to pass through was placed above the capacitor element. The bottomed case was then drawn near the open end, and the open end was further curled to adhere to the sealing member. In this way, the capacitor element and liquid component were sealed inside the bottomed case. An electrolytic capacitor as shown in Figure 1 was completed by placing a seat plate on the curled portion. A total of 40 electrolytic capacitors were produced for each example. The produced electrolytic capacitors were then aged at 130°C for two hours while applying the rated voltage.

[0121] [Evaluation] The electrolytic capacitors prepared above were evaluated for capacitance change (Δcap) and ESR change (ΔESR) according to the following procedure.

[0122] For the 20 electrolytic capacitors after the aging treatment, the capacitance at a frequency of 120 Hz and the ESR value at a frequency of 100 kHz were measured using an LCR meter in an environment of 20°C, and the average values ​​(initial capacitance value: c0 (F), initial ESR value: r0 (Ω)) were calculated.

[0123] After measuring the initial capacitance value c0 and the initial ESR value r0, a high-temperature load test (accelerated test) was conducted. In the high-temperature load test (accelerated test), the electrolytic capacitor was held at 145°C for 750 hours with the rated voltage applied. For the electrolytic capacitor after the accelerated test, the average capacitance value (c1 (F)) and average ESR value (r1 (Ω)) after the accelerated test were determined in the same manner as in the measurement of the initial capacitance value and initial ESR value.

[0124] Using the obtained initial capacitance value (c0) and capacitance value after the accelerated test (c1), as well as the initial ESR value (r0) and ESR value after the accelerated test (r1), the capacitance change (Δcap) and ESR change (ΔESR) were calculated according to the following formula.

[0125] Δcap=c1 / c0 ΔESR=r1 / r0 The evaluation results for each electrolytic capacitor are shown in Table 1. In Table 1, A1 to A7 are examples, and B1 to B3 are comparative examples.

[0126]

[0127] As shown in Table 1, in the Examples, the ESR fluctuation after the accelerated test was suppressed and a high capacity was maintained compared to the Comparative Examples. Since the accelerated test was performed in a 145°C environment, the electrolytic capacitors of the Examples suppressed the ESR fluctuation and the capacity decrease in a high-temperature environment.

[0128] The electrolytic capacitor of the present disclosure can be used as a hybrid electrolytic capacitor. The electrolytic capacitor exhibits small variations in ESR over time and in high-temperature environments, and is highly reliable. Therefore, it is particularly suitable for applications requiring high reliability or long life. However, the applications of the electrolytic capacitor are not limited to these.

[0129] 100: Electrolytic capacitor 101: Bottomed case 102: Sealing member 103: Seat plate 104A, 104B: Lead wire 105A, 105B: Lead tab 10: Capacitor element 11: Anode foil 12: Cathode foil 13: Separator 14: Winding tape

Claims

1. An electrolytic capacitor comprising: a capacitor element; and a liquid component; the capacitor element comprises an anode body having a dielectric layer on a surface thereof; and a conductive polymer covering a portion of the dielectric layer; the liquid component comprises a solvent; and an acid component; and the acid component comprises a carboxylic acid compound having a first cyclic group having aromaticity, a second cyclic group having aromaticity, a linking group connecting the first cyclic group and the second cyclic group, and at least one carboxy group bonded directly or indirectly to at least one of the first cyclic group and the second cyclic group.

2. The electrolytic capacitor of claim 1, wherein each of the first cyclic group and the second cyclic group is a single ring or a fused ring.

3. The electrolytic capacitor according to claim 1 or 2, wherein each of the first cyclic group and the second cyclic group has 5 or more and 14 or less members.

4. The electrolytic capacitor according to claim 1 or 2, wherein the first cyclic group and the second cyclic group are linked by a single bond.

5. The electrolytic capacitor according to claim 1 or 2, wherein the at least one carboxy group is located in an ortho position relative to the linking group.

6. The electrolytic capacitor of claim 1 or 2, wherein the at least one carboxy group is directly bonded to the first cyclic group or the second cyclic group.

7. The electrolytic capacitor according to claim 1 or 2, wherein the liquid component further contains a base component.

8. The electrolytic capacitor according to claim 7, wherein the base component has a conjugate acid with a pKa of 3.5 or more and 7.0 or less.

9. The electrolytic capacitor of claim 7, wherein the base component comprises a heterocyclic amine.

10. The electrolytic capacitor according to claim 7, wherein the equivalent ratio of the carboxylic acid compound to the base component is 0.5 or more and 10 or less.

11. An additive for use in a liquid component of an electrolytic capacitor comprising a capacitor element including a conductive polymer and the liquid component, the additive comprising a carboxylic acid compound having a first cyclic group having aromaticity, a second cyclic group having aromaticity, a linking group connecting the first cyclic group and the second cyclic group, and at least one carboxy group bonded directly or indirectly to at least one of the first cyclic group and the second cyclic group.

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