Electrolytic capacitor and additive for liquid component of electrolytic capacitor

Abstract

This electrolytic capacitor comprises a capacitor element and a liquid component. The capacitor element includes an anode body that has a dielectric layer on the surface thereof, and a conductive polymer that covers a part of the dielectric layer. The liquid component includes a solvent and an acid component. The acid component includes a carboxylic acid compound (excluding 2,5-dicarboxyfuran compound and 2-carboxyfuran compound) which has a heterocycle and at least one carboxy group that is directly or indirectly bonded to the heterocycle.

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 electrolyte solution for an electrolytic capacitor used in an electrolytic capacitor, which is formed by winding a pair of electrodes via a conductive separator (E) having a conductive polymer layer (F) containing a dopant agent (H) formed on the surface thereof, and impregnating the space between the electrodes with an electrolyte solution to form a capacitor element housed in a case, the electrolyte solution being characterized in that the acid component (D) is in excess in the molar ratio of the acid component (D) to the base component (C) that are electrolyte components contained in the electrolyte solution for an electrolytic capacitor.

[0004] Patent Document 2 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.

[0005] Patent Document 3 proposes an electrolyte solution for a hybrid electrolytic capacitor that contains a carboxylic acid anion (A) represented by a specific formula and a solvent (B), in which the solvent (B) contains at least a polyalkylene glycol (b) having a number average molecular weight of 200 or more and 20,000 or less.

[0006] JP 2006-108650 A International Publication No. 2017 / 017947 JP 2023-95765 A

[0007] A first aspect of the present disclosure relates to an electrolytic capacitor including a capacitor element and a liquid component, wherein the capacitor element includes an anode body having a dielectric layer on a surface thereof, and a conductive polymer covering a portion of the dielectric layer, and the liquid component includes a solvent and an acid component, and the acid component includes a carboxylic acid compound (excluding 2,5-dicarboxyfuran compounds and 2-carboxyfuran compounds) having a heterocycle and at least one carboxy group bonded directly or indirectly to the heterocycle.

[0008] A second aspect of the present disclosure relates to an additive for use in a liquid component of an electrolytic capacitor comprising a capacitor element and a liquid component, the additive comprising a carboxylic acid compound (excluding 2,5-dicarboxyfuran compounds and 2-carboxyfuran compounds) having a heterocycle and at least one carboxy group bonded directly or indirectly to the heterocycle.

[0009] The fluctuation of the equivalent series resistance (ESR) over time in the electrolytic capacitor can be kept low.

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

[0011] Electrolytic capacitors are required to have little fluctuation in equivalent series resistance (ESR) even after long-term use.

[0012] 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).

[0013] 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 (excluding 2,5-dicarboxyfuran compounds and 2-carboxyfuran compounds) having a heterocycle and at least one carboxy group directly or indirectly bonded to the heterocycle. In this specification, such a carboxylic acid compound is referred to as a first carboxylic acid compound.

[0014] In the first carboxylic acid compound, a carboxy group is directly or indirectly bonded to a heterocycle. Therefore, compared to phthalic acid, the first carboxylic acid compound is more likely to have a charge imbalance due to the heteroatom in the ring structure, making it easier to achieve high acidity and less susceptible to esterification. Furthermore, the first carboxylic acid compound has a heterocycle, which gives it a high affinity for conductive polymers. 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 over 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, by stabilizing the pH of the liquid component with the first carboxylic acid compound, the high conductivity of the conductive polymer is maintained, fluctuations in ESR are suppressed, and a decrease in capacity is suppressed, even when the electrolytic capacitor is exposed to relatively high temperatures (e.g., temperatures of 60°C or higher and 200°C or lower).

[0015] (Technology 2) In the above (Technology 1), the heteroatom constituting the heterocycle may include at least one selected from the group consisting of a sulfur atom and a nitrogen atom. In this case, higher affinity with the conductive polymer can be ensured, and the low pH of the liquid component can be more stably maintained, making it easier to maintain the high conductivity of the conductive polymer.

[0016] (Technology 3) In the above (Technology 2), the heterocycle may contain one or two heteroatoms, including the heteroatom. In this case, the electronic state of the first carboxylic acid compound makes it difficult for the carboxy group to be further esterified. Furthermore, the bias in the charge of the first carboxylic acid compound makes it easier to maintain a low pH of the liquid component. Therefore, the low pH of the liquid component can be more stably maintained for a long period of time, and fluctuations in ESR can be further suppressed.

[0017] (Technology 4) In the above (Technology 2) or (Technology 3), the carboxylic acid compound may not have the at least one carboxy group on an atom adjacent to the heteroatom among the atoms constituting the hetero ring. In this case, esterification of the carboxy group is more likely to be suppressed, and fluctuations in ESR can be further suppressed even when the electrolytic capacitor is used for a long period of time.

[0018] (Technology 5) In the above (Technology 1), the heteroatom constituting the hetero ring may include an oxygen atom. In this case, the amount of ESR fluctuation during long-term use of the electrolytic capacitor can be kept relatively low.

[0019] (Technology 6) In the above (Technology 5), the first carboxylic acid compound may satisfy the following requirement (i) or requirement (ii):

[0020] (i) The heterocycle has no unsaturated bond or has one unsaturated bond.

[0021] (ii) The carboxylic acid compound does not have the at least one carboxy group on an atom adjacent to the oxygen atom constituting the heterocycle.

[0022] In this case, the electron and charge state of the first carboxylic acid compound can be easily optimized, esterification of the carboxy group can be further suppressed, and the low pH of the liquid component can be more easily maintained stably.

[0023] (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.

[0024] (Technology 8) In the above (Technology 7), 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.

[0025] (Technology 9) The present disclosure also encompasses an additive (additive for a liquid component of an electrolytic capacitor) used in the liquid component of an electrolytic capacitor comprising a capacitor element containing a conductive polymer and the liquid component. This additive comprises a carboxylic acid compound (excluding 2,5-dicarboxyfuran compounds and 2-carboxyfuran compounds) having a heterocycle and at least one carboxy group bonded directly or indirectly to the heterocycle, i.e., a first carboxylic acid compound. By using such an additive in the liquid component of an electrolytic capacitor containing a conductive polymer, the low pH of the liquid component can be stably maintained, and the high conductivity of the conductive polymer can be stably maintained over an extended period of time. Therefore, fluctuations in ESR can be kept low even when the electrolytic capacitor is used for an extended period of time.

[0026] 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 9). At least one selected from the components described below can be arbitrarily combined with at least one of the above (Technology 1) to (Technology 9) related to the electrolytic capacitor and the liquid component additive of the present disclosure, as long as such combination is technically possible.

[0027] (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.

[0028] The liquid component additive includes a first carboxylic acid compound. The first carboxylic acid compound has a heterocycle and at least one carboxy group directly or indirectly bonded to the heterocycle. 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, in the case of a first carboxylic acid compound, when two or more carboxy groups are directly or indirectly bonded to the heterocycle, even if one carboxy group is esterified, the remaining carboxy groups are unlikely to be esterified due to the distribution of electrons and charges in the first carboxylic acid compound. This makes it easier to maintain a low pH of the liquid component, maintains high conductivity of the conductive polymer, and further suppresses fluctuations in ESR over time. Furthermore, even when one carboxy group is directly or indirectly bonded to the heterocycle, esterification of the carboxy group is unlikely to proceed due to charge imbalance and electron localization in the heterocycle.

[0029] At least one carboxy group may be bonded directly to the heterocycle (in other words, without any other group). At least one carboxy group may be bonded indirectly to the heterocycle (in other words, via another group (linking group)). When the first carboxylic acid compound has two or more carboxy groups indirectly bonded to the heterocycle, at least two carboxy groups may be bonded to the heterocycle via one linking group, or each carboxy group may be bonded via one linking group. For example, a carboxy group may be bonded to the cyclic group via an aliphatic group (such as an alkylene group, an alkenylene group, or a trivalent group corresponding thereto). Examples of the aliphatic group to which a carboxy group is bonded include carboxyalkyl groups (carboxy C groups such as a carboxymethyl group, a dicarboxymethyl group, a carboxyethyl group, and a 1,2-dicarboxyethyl group). １－４ Alkyl group (monocarboxy or dicarboxy C １－４ alkyl group, etc.), carboxyalkenyl group (carboxy vinyl group, etc.) ２－４ Alkenyl group (monocarboxy or dicarboxy C ２－４ alkenyl groups, etc.).

[0030] In the electrolytic capacitor, the carboxy group directly or indirectly bonded to the heterocycle may be in any of the following forms: a free form, a salt form, an anion form, or a form interacting (complexed, etc.) with a conductive polymer. In this specification, the carboxy group directly or indirectly bonded to the heterocycle includes all of these forms.

[0031] The first carboxylic acid compound may have a substituent other than a carboxy group (and a linking group having a carboxy group) on the heterocycle. Examples of the 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, and a tert-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 substituent include an alkoxy-carbonyl group. Among these, the substituent may be at least one selected from the group consisting of an aliphatic hydrocarbon group (such as an alkyl group) and a carboxyalkyl group. The number of substituents in the heterocycle is selected depending on, for example, the number of members in the heterocycle, the type of heteroatom, the number of carboxy groups, etc. The number of substituents may be 1 or more and 3 or less, or may be 1 or 2. The heterocycle may have a substituent on a carbon atom or a heteroatom. In addition, the first carboxylic acid compound may not have a substituent on the heterocycle other than a carboxy group (and a linking group having a carboxy group).

[0032] The heteroatom constituting the heterocycle is, for example, at least one selected from the group consisting of a sulfur atom, a nitrogen atom, and an oxygen atom. The heterocycle may contain one heteroatom constituting the heterocycle, or may contain two or more heteroatoms constituting the heterocycle. The number of heteroatoms in the heterocycle may be, for example, three or less. The number of heteroatoms in the heterocycle is preferably one or two, depending on the number of members of the heterocycle.

[0033] The heterocycle may be 4 to 12 membered, 5 to 10 membered, 5 to 8 membered, or 5 or 6 membered. The heterocycle may be saturated or unsaturated.

[0034] The heterocycle may be a monocycle, a bridged ring, or a fused ring. Each ring constituting the bridged ring or fused ring may be a heterocycle, or some of the rings may be hydrocarbon rings and the remaining rings may be heterocycles. Examples of heterocycles that are bridged rings or fused rings include sulfur atom-containing rings (benzothiophene, benzothiazole, dibenzothiophene, 5,5-dioxide, etc.), nitrogen atom-containing rings (indole, benzimidazole, benzoxazole, purine, quinuclidine, 1,4-diazabicyclooctane, etc.), and oxygen atom-containing rings (benzofuran, etc.).

[0035] The heterocycle may contain at least one heteroatom selected from the group consisting of a sulfur atom and a nitrogen atom as a heteroatom constituting the heterocycle. Such a heterocycle may contain, for example, one or two heteroatoms. The heterocycle may contain at least one heteroatom selected from the group consisting of a sulfur atom and a nitrogen atom, and an oxygen atom as heteroatoms constituting the heterocycle.

[0036] Examples of heterocycles (e.g., monocycles) containing a sulfur atom include tetrahydrothiophene, thiophene, tetrahydrothiopyran, dithiolane (e.g., 1,3-dithiolane, 1,2-dithiolane), thiazole, thiazine, tetrahydrothiopyran, thiopyran, dithiane (e.g., 1,3-dithiane), tetramethylene sulfoxide, sulfolane, sulfolene, etc. Examples of heterocycles (e.g., monocycles) containing a nitrogen atom include pyrrolidine, pyrrole, imidazole, imidazoline, oxazole, morpholine, pyridine, etc.

[0037] Examples of the first carboxylic acid compound having a sulfur atom-containing ring as described above include 3,4-thiophenedicarboxylic acid, 3-thiophenecarboxylic acid, 2,5-thiophenedicarboxylic acid, 2-thiophenecarboxylic acid, 2,5-dimethyl-3-thiophenecarboxylic acid, 3-thiophenemalonic acid, 3-carboxylic acid-tetrahydrothiophene, 1,3-dithiolane-2-carboxylic acid, 1,3-dithiane-2-carboxylic acid, thiazole-4-carboxylic acid, and 2-methylthiazole-4-carboxylic acid. Examples of the first carboxylic acid compound having a nitrogen atom-containing ring include 2-carboxyimidazole and 1-methylimidazole-4-carboxylic acid. However, these compounds are merely examples, and the first carboxylic acid compound having a sulfur atom-containing ring or a nitrogen atom-containing ring is not limited to these compounds. One type of first carboxylic acid compound may be used alone, or two or more types may be used in combination.

[0038] When the heteroatom constituting the heterocycle includes at least one selected from the group consisting of a sulfur atom and a nitrogen atom, the first carboxylic acid compound may or may not have a carboxy group on an atom adjacent to at least one heteroatom among the atoms constituting the heterocycle.

[0039] For example, the first carboxylic acid compound may include a compound having a thiophene ring and represented by the following formula (I), or may include a compound represented by the following formula (Ia): Furthermore, hydrogenated compounds corresponding to these formulas (such as tetrahydrothiophene compounds) may also be used.

[0040]

[0041] In formula (I), X1 is a linking group, and p1 is 0 or 1. n1 is an integer of 1 or more, and may be an integer of 1 to 3, or may be 1 or 2. When p1 is 0, n1 is 1. q1 is an integer of 1 to 4, and may be an integer of 1 to 3, or may be 1 or 2. n1×q1 represents the number of carboxy groups directly or indirectly bonded to the thiophene ring, and is an integer of 1 or more, and may be an integer of 1 to 3. n1×q1 is preferably 1 or 2, and more preferably 2.

[0042] In formula (Ia), X2 and X3 each represent a linking group, and p2 and p3 each represent 0 or 1. n2 is an integer of 1 or greater, and may be an integer of 1 to 3, or may be 1 or 2. When p2 is 0, n2 is 1. q2 is 0 or 1. When q2 is 0, position 4 of the thiophene ring is a hydrogen atom or a substituent R. When q2 is 1 and p3 is 0, n3 is 1. When q2 is 1 and p3 is 1, n3 is an integer of 1 or greater, and may be an integer of 1 to 3, or may be 1 or 2. (n2 + n3 × q2) represents the number of carboxy groups directly or indirectly bonded to the thiophene ring, and is an integer of 1 or greater, and may be an integer of 1 to 3, or may be 1 or 2.

[0043] Among the compounds represented by formula (I) or formula (Ia), for example, compounds represented by the following formula (IA), (IB), or (IC) (particularly, compounds represented by formula (IA) or (IC)) are preferred. A compound represented by the following formula (ID) may also be used. Furthermore, hydrogenated compounds corresponding to these formulas (such as tetrahydrothiophene compounds) may also be used.

[0044]

[0045] The compound represented by formula (IA) is a 3,4-thiophenedicarboxylic acid compound, and the compound represented by formula (IB) is a 2,5-thiophenedicarboxylic acid compound. The compound represented by formula (IC) is a thiophene aliphatic carboxylic acid compound, and the compound represented by formula (ID) is a 3-thiophenecarboxylic acid compound. Examples of hydrogenated products of the compound represented by formula (ID) include 3-carboxylic acid-tetrahydrothiophene compounds.

[0046] Also usable are 1,3-dithiolane compounds and 1,3-dithiane compounds corresponding to formula (IC) or formula (ID). Examples of the 1,3-dithiolane compound include a compound of formula (IC) in which the thiophene ring is a 1,3-dithiolane ring and the —X1-(COOH)n1 group is bonded to the 2-position of the 1,3-dithiolane ring, and a compound of formula (ID) in which the thiophene ring is a 1,3-dithiolane ring and the carboxy group is bonded to the 2-position of the 1,3-dithiolane ring (for example, a 1,3-dithiolane-2-carboxylic acid compound). Examples of the 1,3-dithiane compound include a compound in which the thiophene ring of formula (IC) is a 1,3-dithiane ring and the —X1-(COOH)n1 group is bonded to the 2-position of the 1,3-dithiane ring, and a compound in which the thiophene ring of formula (ID) is a 1,3-dithiane ring and the carboxy group is bonded to the 2-position of the 1,3-dithiane ring (for example, a 1,3-dithiane-2-carboxylic acid compound).

[0047] The heterocycle may contain an oxygen atom as a heteroatom constituting the heterocycle. Such a heterocycle (oxygen atom-containing ring) may contain, for example, one or two heteroatoms. However, the first carboxylic acid compound does not include 2,5-dicarboxyfuran compounds and 2-carboxyfuran compounds.

[0048] The first carboxylic acid compound having an oxygen atom-containing ring may satisfy the following requirement (i) or requirement (ii).

[0049] (i) The heterocycle has no unsaturated bond or has one unsaturated bond.

[0050] (ii) The first carboxylic acid compound does not have a carboxy group on an atom adjacent to the oxygen atom constituting the heterocycle.

[0051] Examples of heterocycles (for example, monocycles) containing an oxygen atom include tetrahydrofuran, furan, tetrahydropyran, dioxolane, and dioxane.

[0052] Examples of the first carboxylic acid compound having an oxygen atom-containing ring as described above include 3-carboxyfuran, 3,4-dicarboxyfuran, and 2,5-dimethyl-3-furancarboxylic acid. However, these compounds are merely examples, and the first carboxylic acid compound having an oxygen atom-containing ring is not limited to these compounds. The first carboxylic acid compound may contain one of these compounds or a combination of two or more of them.

[0053] For example, the first carboxylic acid compound may include a compound represented by the following formula (II) having a furan ring.

[0054]

[0055] Formula (II) is the same as Formula (Ia), except that the thiophene ring in Formula (Ia) is changed to a furan ring. For each symbol, refer to the explanation of Formula (Ia).

[0056] Among the compounds represented by formula (II), compounds represented by the following formula (IIA) or (IID) are preferred.

[0057]

[0058] The compound represented by formula (IIA) is a 3,4-dicarboxyfuran compound, and the compound represented by formula (IID) is a 3-carboxyfuran compound. The compounds represented by these formulas satisfy the above requirement (ii).

[0059] In these formulas, R is the above-mentioned substituent that the heterocycle may have. m, m1, and m2 each represent the number of substituents R in the thiophene ring or furan ring. m is an integer of 0 to 3. When the heterocycle (more specifically, the thiophene ring or furan ring, etc.) has two or more substituents R, at least two of the substituents may be the same, or all of the substituents may be different. m1 is 0, 1, or 2. m2 is an integer of 0 to 3.

[0060] A first carboxylic acid compound (compound 1a) having two or more (preferably two) carboxy groups may be combined with a first carboxylic acid compound (compound 1b) having one carboxy group. For example, compound 1a may be used as a salt with a base component, and compound 1b may be used as a free acid component. For example, a thiophenedicarboxylic acid compound may be combined with at least one selected from the group consisting of thiophenecarboxylic acid, imidazolecarboxylic acid compound, and carboxyfuran compound.

[0061] The mass ratio of compound 1b to compound 1a (=mass of compound 1b / mass of compound 1a) may be 0 / 100 or more and 75 / 25 or less, or 0 / 100 or more and 50 / 50 or less. When the mass ratio 1b / 1a is in such a range, the effect of maintaining a low pH of the liquid component is further enhanced, which is advantageous in further suppressing fluctuations in ESR over time.

[0062] (Liquid Component) The liquid component contains a solvent and an acid component. The liquid component may further contain a base component.

[0063] (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.

[0064] 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).

[0065] 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.).

[0066] 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).

[0067] (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.

[0068] (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.

[0069] 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.

[0070] 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).

[0071] 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.

[0072] 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.

[0073] 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.

[0074] (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).

[0075] 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.

[0076] 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.

[0077] The acid component may contain one or more of the above-mentioned other acids.

[0078] (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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] The above ratios, mass ratios, and concentrations are values ​​determined based on the mass of each acid when it is in its free form.

[0083] (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.

[0084] 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.

[0085] 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), N-methylmorpholine (MMP), N-butylmorpholine, and N-isobutylmorpholine). 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).

[0086] 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.

[0087] 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.

[0088] 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

[0089] 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.

[0090] 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

[0091] (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).

[0092] (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.

[0093] 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.

[0094] 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).

[0095] (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.

[0096] 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 ３ However, the dielectric layer is not limited to this, and may be any layer that functions as a dielectric.

[0097] 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.

[0098] (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.

[0099] (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).

[0100] The conjugated polymer may be used alone or in combination of two or more kinds.

[0101] 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.

[0102] In this specification, the weight average molecular weight (Mw) is a value calculated as polysaccharide as measured by gel permeation chromatography (GPC). GPC is usually performed using a polyhydroxymethacrylate gel column and an aqueous sodium nitrate solution as the mobile phase.

[0103] (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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] (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.

[0110] 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.

[0111] 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).

[0112] 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.

[0113] (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).

[0114] 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.

[0115] (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.

[0116] 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.

[0117] Fig. 1 is a cross-sectional schematic diagram of an electrolytic capacitor according to this embodiment, and Fig. 2 is a schematic diagram showing a portion of a capacitor element of the electrolytic capacitor in an exploded view. 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 9) 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 9) and the components described above.

[0118] 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.

[0119] 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.

[0120] 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.

[0121] 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.

[0122] Examples 1 to 6 and Comparative Examples 1 to 4 Wound electrolytic capacitors (rated voltage 25 V, rated capacitance 330 μF) were fabricated and evaluated according to the following procedure.

[0123] (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.

[0124] (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.

[0125] (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.

[0126] (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.

[0127] (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.

[0128] (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.

[0129] (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.

[0130] 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.

[0131] [Evaluation] The electrolytic capacitors prepared above were evaluated for capacitance change (Δcap) and ESR change (ΔESR) according to the following procedure.

[0132] 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.

[0133] 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 1,500 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.

[0134] 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.

[0135] Δcap=c1 / c0 ΔESR=r1 / r0 The evaluation results for each electrolytic capacitor are shown in Table 1. In Table 1, A1 to A6 are examples, and B1 to B4 are comparative examples.

[0136]

[0137] As shown in Table 1, in the examples using a liquid component containing a first carboxylic acid compound, the fluctuation in ESR was suppressed to a low level even after a long-term accelerated test, compared to the comparative examples. In the examples, it can be said that the fluctuation in ESR over time is suppressed, and the fluctuation in ESR in a high-temperature environment is also suppressed. Furthermore, in the examples, the decrease in capacity due to the accelerated test is also suppressed, compared to the comparative examples.

[0138] 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.

[0139] 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, wherein 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 comprising a solvent and an acid component, and the acid component comprising a carboxylic acid compound (excluding 2,5-dicarboxyfuran compounds and 2-carboxyfuran compounds) having a heterocycle and at least one carboxy group bonded directly or indirectly to the heterocycle.

2. The electrolytic capacitor according to claim 1, wherein the heteroatom constituting the hetero ring includes at least one type selected from the group consisting of a sulfur atom and a nitrogen atom.

3. The electrolytic capacitor of claim 2, wherein the heterocycle includes one or two heteroatoms including the heteroatom.

4. The electrolytic capacitor according to claim 2, wherein the carboxylic acid compound does not have the at least one carboxy group on an atom adjacent to the heteroatom among the atoms constituting the hetero ring.

5. The electrolytic capacitor according to claim 1, wherein the heteroatom constituting the hetero ring includes an oxygen atom.

6. The electrolytic capacitor according to claim 5, wherein the carboxylic acid compound satisfies the following requirement (i) or requirement (ii): (i) the heterocycle has no unsaturated bond or has one unsaturated bond, and (ii) the carboxylic acid compound does not have the at least one carboxy group on an atom adjacent to the oxygen atom constituting the heterocycle.

7. The electrolytic capacitor according to any one of claims 1 to 6, wherein the liquid component further contains a base component.

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

9. An additive for use in a liquid component of an electrolytic capacitor comprising a capacitor element containing a conductive polymer and the liquid component, the additive for the liquid component of an electrolytic capacitor comprising a carboxylic acid compound (excluding 2,5-dicarboxyfuran compounds and 2-carboxyfuran compounds) having a heterocycle and at least one carboxy group bonded directly or indirectly to the heterocycle.

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