Liquid component for electrolytic capacitor, electrolytic capacitor, and method for manufacturing same

Abstract

This liquid component, which is used in an electrolytic capacitor containing a conductive polymer, includes a nonaqueous solvent and a dicarboxylic acid compound. The dicarboxylic acid compound includes: component (A), an aromatic dicarboxylic acid; and component (B), a monoester in which one carboxy group of an aromatic dicarboxylic acid is esterified with an aliphatic group having a hydroxy group.

Description

Liquid component for electrolytic capacitor, electrolytic capacitor and method for manufacturing the same

[0001] The present disclosure relates to a liquid component for an electrolytic capacitor, an electrolytic capacitor, and a method for producing the same.

[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 foil with a dielectric layer, a cathode foil, and a conductive polymer and electrolyte interposed between the anode foil and the cathode foil. The electrolyte can be a liquid component such as a solution in which a solute is dissolved in a non-aqueous solvent or a non-aqueous solvent.

[0003] Patent Document 1 proposes an electrolytic capacitor having a capacitor element including an anode body having a dielectric layer formed on the surface thereof, a solid electrolyte layer provided on the dielectric layer and containing a conductive polymer and a polymer dopant, and an electrolyte solution impregnated in the capacitor element and containing a polyhydric alcohol and a borate ester.

[0004] International Publication No. 2017 / 073062

[0005] A first aspect of the present disclosure relates to a liquid component for an electrolytic capacitor. The liquid component for an electrolytic capacitor is a liquid component used in an electrolytic capacitor containing a conductive polymer. The liquid component includes a non-aqueous solvent and a dicarboxylic acid compound. The dicarboxylic acid compound includes: component (A): an aromatic dicarboxylic acid; and component (B): a monoester in which one carboxy group of the aromatic dicarboxylic acid is esterified with an aliphatic group having a hydroxy group.

[0006] A second aspect of the present disclosure relates to an electrolytic capacitor comprising the liquid component described above and a capacitor element including an anode foil having a dielectric layer, a cathode foil disposed opposite the dielectric layer, and a conductive polymer interposed between the anode foil and the cathode foil.

[0007] A third aspect of the present disclosure relates to a method for manufacturing an electrolytic capacitor, the method including the steps of: preparing a capacitor element including an anode foil having a dielectric layer, a cathode foil, and a conductive polymer interposed between the anode foil and the cathode foil; housing the capacitor element together with the liquid component in a case and sealing the case; and heating the sealed assembly obtained in the sealing step at a temperature of 130°C or higher for 10 minutes or longer.

[0008] The present disclosure provides highly reliable electrolytic capacitors and liquid components for use in electrolytic capacitors.

[0009] 1 is a schematic cross-sectional view of an electrolytic capacitor according to an embodiment of the present disclosure;

[0010] Liquid components used in electrolytic capacitors containing conductive polymers include, for example, an acid component and a nonaqueous solvent. For example, when only component (A): an aromatic dicarboxylic acid is used as the acid component, the low pH of the liquid component initially facilitates high conductivity of the conductive polymer. However, a reaction (esterification reaction) between the nonaqueous solvent containing hydroxyl groups and component (A) may proceed, resulting in a decrease in the amount of the acid component (A). This reaction is more likely to occur at high temperatures. For example, ripple current during use of an electrolytic capacitor can cause self-heating, leading to the esterification reaction. Furthermore, the esterification reaction can also occur when an electrolytic capacitor is used in a high-temperature environment (e.g., temperatures above 140°C (e.g., temperatures between 140°C and 160°C)). The decrease in component (A) increases the pH of the liquid component, which reduces the conductivity of the conductive polymer due to dedoping and increases the equivalent series resistance (ESR). Furthermore, the reaction (esterification reaction) between the nonaqueous solvent containing hydroxyl groups and component (A) generates water, increasing the amount of water contained in the liquid component. If the amount of moisture in the electrolytic capacitor increases, the swelling of the electrolytic capacitor may become significant when the electrolytic capacitor is exposed to high temperatures (for example, temperatures of 200°C or higher (temperatures of 200°C or higher and 300°C or lower)).

[0011] In view of the above, (Technology 1) a liquid component according to a first aspect of the present disclosure is used in an electrolytic capacitor containing a conductive polymer. The liquid component includes a non-aqueous solvent and a dicarboxylic acid compound. The dicarboxylic acid compound includes a dicarboxylic acid and a monoester in which one carboxy group of the dicarboxylic acid is esterified with an aliphatic group having a hydroxy group.

[0012] In the liquid component according to the first aspect, for example, the dicarboxylic acid compound includes component (A): an aromatic dicarboxylic acid; and component (B): a monoester in which one carboxy group of the aromatic dicarboxylic acid is esterified with an aliphatic group having a hydroxy group.

[0013] In the present disclosure, the combination of a dicarboxylic acid and a monoester (more specifically, component (A) and component (B)) as described above ensures high reliability of electrolytic capacitors. This is explained in more detail below. The use of the liquid component of the present disclosure can suppress the decrease of component (A) in the liquid component. This is because, even as the reaction (esterification reaction) between a nonaqueous solvent having a hydroxy group and component (A) proceeds, a hydrolysis reaction between water in the liquid component and component (B) occurs in parallel to the reaction, producing component (A). Furthermore, electrolytic capacitors may experience self-heating due to ripple current during use, or may be used in high-temperature environments. Even in the presence of such thermal influences, the present disclosure contains a certain concentration of component (A) in the liquid component, thereby maintaining a low pH of the liquid component. This suppresses deterioration of the conductive polymer (such as due to dedoping), maintaining high conductivity. As a result, an increase in ESR can be suppressed. Furthermore, since the water generated by the reaction (esterification reaction) between the nonaqueous solvent having a hydroxy group and component (A) is used in the hydrolysis reaction with component (B), an increase in the water content in the liquid component can be suppressed, which can also suppress swelling when the electrolytic capacitor is exposed to high temperatures (e.g., temperatures of 200°C or higher and 300°C or lower) during reflow treatment or the like.

[0014] (Technology 2) In the above (Technology 1), the aromatic dicarboxylic acid of component (A) and the aromatic dicarboxylic acid of component (B) may be the same or different. When the aromatic dicarboxylic acids of both components are the same, the equilibrium reaction between component (A) and component (B) is less likely to be biased, which is advantageous because the pH is stable and the water content is more likely to be reduced stably.

[0015] (Technology 3) In the above (Technology 1) or (Technology 2), the aromatic dicarboxylic acid of the component (A) and the aromatic dicarboxylic acid of the component (B) may each be phthalic acid. When the aromatic dicarboxylic acids of both components are phthalic acid, the equilibrium reaction between the component (A) and the component (B) is less likely to be biased, which is advantageous because the pH is stable and the water content is more likely to be reduced stably.

[0016] (Technology 4) In any one of the above (Technology 1) to (Technology 3), the nonaqueous solvent may contain at least an aliphatic diol. In this case, moisture is likely to be generated by esterification with component (A). In the present disclosure, even in such a case, by using component (B), moisture is consumed by the hydrolysis reaction. Therefore, an increase in the amount of moisture in the liquid component can be suppressed. Therefore, swelling when the electrolytic capacitor is exposed to high temperatures can be suppressed while maintaining the high conductivity of the conductive polymer.

[0017] (Technology 5) In the above (Technology 4), the aliphatic diol is an alkylene glycol having 2 to 6 carbon atoms, and a polyC having 15 or less repeating oxyalkylene groups. ２－４ The liquid component may contain at least one selected from the group consisting of alkylene glycols. When these aliphatic diols are contained, moisture is easily generated by esterification with component (A). In the present disclosure, even in such a case, moisture is consumed by the hydrolysis reaction by using component (B). Therefore, an increase in the moisture content in the liquid component can be suppressed. Therefore, swelling of the electrolytic capacitor when exposed to high temperatures can be suppressed while maintaining the high conductivity of the conductive polymer.

[0018] (Technology 6) In any one of the above (Technology 1) to (Technology 5), the molar ratio (B / A) of component (B) to component (A) may be 0.05 or more and 0.5 or less. When the molar ratio B / A is in this range, an increase in ESR can be suppressed, and swelling of the electrolytic capacitor when exposed to high temperatures can be suppressed. Furthermore, excessive loss of water content due to the hydrolysis reaction between water in the liquid component and component (B) can be suppressed, thereby maintaining the film repairability of the dielectric layer and suppressing an increase in leakage current.

[0019] (Technology 7) In any one of the above (Technology 1) to (Technology 5), the dicarboxylic acid compound may further include component (C): a diester in which two carboxy groups of an aromatic dicarboxylic acid are esterified with an aliphatic group having a hydroxy group. A hydrolysis reaction of components (B) and (C) occurs to produce component (A), thereby maintaining the high conductivity of the conductive polymer and further suppressing an increase in ESR. Furthermore, the hydrolysis reaction further reduces the water content, further reducing swelling when the electrolytic capacitor is exposed to high temperatures (e.g., temperatures of 200°C or higher and 300°C or lower).

[0020] (Technology 8) In the above (Technology 7), the molar ratio (C / A) of component (C) to component (A) may be 0.01 or more and 0.10 or less. When the molar ratio C / A is within this range, an increase in ESR can be suppressed, and swelling of the electrolytic capacitor when exposed to high temperatures can be suppressed. Furthermore, excessive loss of water content due to the hydrolysis reaction between the water in the liquid component and component (B) can be suppressed. Therefore, the film repairability of the dielectric layer can be maintained, and an increase in leakage current can be suppressed.

[0021] The above molar ratios B / A and C / A are values ​​in the liquid component collected from the initial electrolytic capacitor.

[0022] In this specification, the initial electrolytic capacitor refers to an electrolytic capacitor after aging or break-in charging and discharging, or an unused electrolytic capacitor if it is a commercially available product.

[0023] (Technology 9) In any one of the above (Technology 1) to (Technology 8), the aliphatic group having a hydroxy group is a hydroxyalkyl group or -R(-O-R) ｍ It may also be —OH (where R is an alkylene group, and m is the number of repeating oxyalkylene groups and is an integer of 1 or greater). In this case, the hydrolysis reaction of component (B) or component (C) produces alkylene glycol or polyalkylene glycol together with component (A). These glycols have high film repair properties for the dielectric layer and are more effective in suppressing leakage current.

[0024] (Technology 10) In the above (Technology 9), the hydroxyalkyl group has 2 to 6 carbon atoms, and the -R(-O-R) ｍ In the —OH group, R may be an alkylene group having 2 to 4 carbon atoms, and m may be an integer of 1 to 14. In this case, a higher film repair effect of the dielectric layer can be obtained, and leakage current can be further suppressed.

[0025] (Technology 11) In any one of (Technology 1) to (Technology 10) above, the liquid component may further contain a base component. The molar ratio of the base component to the dicarboxylic acid compound (base component / dicarboxylic acid compound) may be 1 or less. In this case, the degree of dissociation of the dicarboxylic acid compound can be increased, and the film repairability of the dielectric layer can be improved.

[0026] (Technology 12) In the above (Technology 11), the base component may have a conjugate acid with a pKa of 10 or less. In this case, it is easier to maintain the high degree of dissociation of the dicarboxylic acid compound and the high conductivity of the conductive polymer.

[0027] 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 component is the pKa of the cation of the base component. When the conjugate acid of a base component exhibits multiple pKa values, the lowest pKa (i.e., pKa1) is meant.

[0028] (Technology 13) The electrolytic capacitor of the present disclosure includes the liquid component according to any one of (Technology 1) to (Technology 12) above, and a capacitor element. The capacitor element may include an anode foil having a dielectric layer, a cathode foil disposed opposite the dielectric layer, and a conductive polymer interposed between the anode foil and the cathode foil. Because the electrolytic capacitor includes the liquid component, an increase in ESR can be suppressed, and swelling of the electrolytic capacitor when exposed to high temperatures can be suppressed.

[0029] (Technology 14) The present disclosure also includes a method for manufacturing an electrolytic capacitor. The method for manufacturing an electrolytic capacitor may include the steps of: preparing a capacitor element including an anode foil having a dielectric layer, a cathode foil, and a conductive polymer interposed between the anode foil and the cathode foil; housing the capacitor element in a case together with the liquid component described in any one of (Technology 1) to (Technology 13) above and sealing the case; and heating the sealed product obtained in the sealing step at a temperature of 130°C or higher for 10 minutes or longer. The heating step facilitates the hydrolysis reaction of component (B) or component (C), reducing the water content and further suppressing swelling when the electrolytic capacitor is exposed to high temperatures (e.g., temperatures of 200°C or higher and 300°C or lower).

[0030] The liquid component, electrolytic capacitor, and manufacturing method thereof of the present disclosure will be described in more detail below, including the above (Technology 1) to (Technology 14). At least one selected from the components described below can be arbitrarily combined with at least one of the above (Technology 1) to (Technology 14) relating to the liquid component, electrolytic capacitor, or manufacturing method thereof of the present disclosure, as long as such combination is technically possible.

[0031] [Liquid Component] The liquid component includes a solvent and an acid component. The liquid component may further include a base component. The liquid component may include other components as needed. More specifically, the liquid component of the present disclosure includes a non-aqueous solvent and a dicarboxylic acid compound.

[0032] (Non-aqueous solvent) Examples of the non-aqueous solvent include protic solvents and aprotic solvents. Examples of the non-aqueous solvent include organic solvents having a hydroxy group, sulfone compounds, lactone compounds, carbonate compounds, ether compounds, etc. The liquid component may contain one type of non-aqueous solvent or a combination of two or more types.

[0033] In the organic solvent having a hydroxy group, the hydroxy group may be an alcoholic hydroxy group. The use of an organic solvent having an alcoholic hydroxy group can improve the film repairability of the dielectric layer. In particular, the non-aqueous solvent preferably contains an aliphatic diol (first solvent).

[0034] (First Solvent) Examples of the aliphatic diol include alkylene glycols and polyalkylene glycols. Among these, it is preferred that the liquid component contains at least one selected from the group consisting of alkylene glycols having 2 to 6 carbon atoms and polyalkylene glycols having 15 or less repeating oxyalkylene groups.

[0035] The number of carbon atoms in the alkylene glycol may be 2 or more and 6 or less, or 2 or more and 4 or less. The alkylene moiety of the alkylene glycol may be linear or branched. Specific examples of alkylene glycols include ethylene glycol (EG), propylene glycol, trimethylene glycol, tetramethylene glycol, and 1,6-hexanediol.

[0036] The polyalkylene glycol is, for example, HO-R(-O-R) ｍ It is represented by -OH. Here, R is an alkylene group, and m represents the number of repetitions of the oxyalkylene group. The oxyalkylene group in the entire polyalkylene glycol, including the -O-R- portion of the HO-R- group portion, is represented by (m+1). (m+1) may be 15 or less, 12 or less, or 10 or less. (m+1) is 2 or more.

[0037] From the viewpoint of easily obtaining a higher film repairability of the dielectric layer, among polyalkylene glycols, poly C ２－４Alkylene glycol is preferred, polyC ２－３ Alkylene glycol is more preferred. Specific examples of polyalkylene glycol include polyethylene glycol, polypropylene glycol, polyoxyethylene-polyoxypropylene copolymer, etc. Polyethylene glycol includes polyethylene glycols such as diethylene glycol (DEG) and triethylene glycol, in which the number of repeating oxyalkylene groups (m+1) falls within the above range.

[0038] (Second Solvent) Among the non-aqueous solvents (second solvents) other than the first solvent, examples of organic solvents having a hydroxy group include monohydric alcohols and polyols other than aliphatic diols. Examples of monohydric alcohols include aliphatic alcohols (C 100, C 110, C 120, C 130, C 150, C 160, C 170, C 180, C 190, C 200, C 250, C 300, C 400, C 500, C 600, C 700, C 800, C 900, C 190, C 210, C 310, C 410, C 510, C 610, C 190, C 190, C 210, C 190, C 210, C 190, C 2 ６－１８ Examples of polyols include glycerin compounds (glycerin (SGC), polyglycerin, etc.), sugar alcohol compounds, and alkylene oxide adducts thereof (ethylene oxide adducts, polyethylene oxide adducts, etc.).

[0039] Examples of sulfone compounds include cyclic sulfone compounds (such as sulfolane (SL)) and sulfoxide compounds (such as dimethyl sulfoxide and diethyl sulfoxide). Examples of lactone compounds include γ-butyrolactone (GBL) and γ-valerolactone. Examples of carbonate compounds include linear carbonates (such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate) and cyclic carbonates (such as ethylene carbonate, propylene carbonate, and fluoroethylene carbonate). Examples of ether compounds include alkyl ethers of the above-mentioned aliphatic diols, monohydric alcohols, and polyols. In the ether compounds, some or all of the hydroxy groups may be etherified.

[0040] (Others) From the viewpoint of ensuring higher film repairability, the proportion of the aliphatic diol in the entire non-aqueous solvent may be, for example, 30% by mass or more, or 50% by mass or more, and the proportion of the aliphatic diol in the entire non-aqueous solvent is 100% by mass or less.

[0041] (Dicarboxylic Acid Compound) The dicarboxylic acid compound includes component (A) and component (B). The dicarboxylic acid compound may further include component (C). The dicarboxylic acid compound may also include a dicarboxylic acid compound (component (D)) other than components (A) to (C).

[0042] (Component (A)) Component (A) is an aromatic dicarboxylic acid. Component (A) is, for example, represented by the following formula (A).

[0043] HOOC-X-COOH (A) X is an aromatic divalent group. The aromatic divalent group represented by X also includes an aromatic divalent group having a substituent (first substituent). Examples of the first substituent include a halogen atom.

[0044] Examples of the aromatic divalent group represented by X include an arylene group (such as phenylene, tolylene, or naphthylene), and a bisarylene group (such as a divalent group corresponding to biphenyl, a diphenylalkane (such as diphenylmethane or 2,2-diphenylpropane), diphenyl ether, or diphenyl sulfide). The number of carbon atoms in the aromatic divalent group may be 6 or more and 20 or less, or 6 or more and 14 or less.

[0045] Specific examples of component (A) include phthalic acid (ortho-form), isophthalic acid (meta-form), terephthalic acid (para-form), 2,3-naphthalenedicarboxylic acid, 2,4-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and biphenyldicarboxylic acid. However, component (A) is not limited to these specific examples.

[0046] The liquid component may contain one type of component (A) or a combination of two or more types.

[0047] (Component (B)) Component (B) is a monoester having a structure in which one carboxy group of the aromatic dicarboxylic acid of component (A) is esterified with an aliphatic group having a hydroxy group. Combining component (A) with component (B) ensures high reliability of the electrolytic capacitor. In addition, swelling of the electrolytic capacitor when exposed to high temperatures (for example, temperatures of 200°C or higher and 300°C or lower) can be suppressed.

[0048] For the aromatic dicarboxylic acid corresponding to component (B), the description of the aromatic dicarboxylic acid of component (A) can be referred to. The aromatic dicarboxylic acid of component (A) and the aromatic dicarboxylic acid corresponding to component (B) may be the same or different. Both the aromatic dicarboxylic acid of component (A) and the aromatic dicarboxylic acid of component (B) may be phthalic acid.

[0049] Component (B) can be considered a monoester formed by esterifying one carboxy group of an aromatic dicarboxylic acid with one hydroxy group of an aliphatic diol. Therefore, the aliphatic group having a hydroxy group corresponds to the portion of the aliphatic diol excluding one hydroxy group. For the aliphatic diol, please refer to the description of the aliphatic diol (first solvent) described as a non-aqueous solvent.

[0050] Examples of the aliphatic group having a hydroxy group include a hydroxyalkyl group, -R(-O-R) ｍ -OH, etc. Here, R is an alkylene group, and m is the number of repetitions of the oxyalkylene group, and m is an integer of 1 or more.

[0051] The hydroxyalkyl group corresponds to the alkylene glycol described above. The number of carbon atoms in the hydroxyalkyl group may be 2 or more and 6 or less, or 2 or more and 4 or less. The alkyl portion of the hydroxyalkyl group may be linear or branched. Specific examples of the hydroxyalkyl group include a hydroxyethyl group, a 2-hydroxy-1-methyl-ethyl group, a 3-hydroxy-n-propyl group, a 4-hydroxy-n-butyl group, and a 6-hydroxy-n-hexyl group.

[0052] -R(-O-R) ｍThe -OH group corresponds to polyalkylene glycol. The alkylene group represented by R may be an alkylene group having 2 to 4 carbon atoms (an alkylene group having 2 or 3 carbon atoms), such as an ethylene group or a propylene group. The number of repeats m of the oxyalkylene group may be within the range determined from the above-mentioned range of (m+1). For example, m may be an integer of 1 to 14. -R(-O-R) ｍ In the —OH group, at least two of the alkylene groups R may be the same (for example, all the same), or all may be different.

[0053] Component (B) includes, for example, a compound represented by the following formula (B).

[0054] HOOC-X-COO-R ２ (B) For X, see the explanation for formula (A). ２ is -R ２ａ -OH group or the above-mentioned -R-(O-R) ｍ -OH group. ２ａ The —OH group corresponds to the hydroxyalkyl group described above.

[0055] Specific examples of component (B) are hydroxyethyl phthalate and hydroxyethyl 2,3-naphthalenedicarboxylate. Component (B) may also include hydroxy C corresponding to these hydroxyethyl esters. ３－６ Alkyl esters (e.g., hydroxy C ３－４ alkyl esters), and the hydroxyethyl portion of these hydroxyethyl esters is -R(-O-R) ｍ However, component (B) is not limited to these specific examples.

[0056] The liquid component may contain one type of component (B) or a combination of two or more types.

[0057] The molar ratio (B / A) of component (B) to component (A) may be 0.01 or more, 0.02 or more, or even 0.05 or more. When the molar ratio B / A is within this range, an increase in ESR after high-temperature storage and swelling of the electrolytic capacitor when exposed to high temperatures can be further suppressed. The molar ratio B / A may be 1.00 or less, or 0.70 or less. When the molar ratio B / A is within this range, excessive loss of water content due to the hydrolysis reaction between the water in the liquid component and component (B) is suppressed. Therefore, the film repairability of the dielectric layer can be maintained and an increase in leakage current can be suppressed. From the viewpoint of maintaining higher film repairability of the dielectric layer and further suppressing an increase in leakage current, the molar ratio B / A is preferably 0.50 or less.

[0058] The molar ratio B / A may be 0.01 or more and 1.00 or less (or 0.70 or less), 0.02 or more and 1.00 or less (or 0.70 or less), 0.05 or more and 1.00 or less (or 0.70 or less), 0.01 or more and 0.50 or less, 0.02 or more and 0.50 or less, or 0.05 or more and 0.50 or less.

[0059] (Component (C)) Component (C) is a diester having a structure in which two carboxy groups of the aromatic dicarboxylic acid of component (A) are esterified with an aliphatic group having a hydroxy group. By combining component (A) with components (B) and (C), it is possible to further suppress the increase in ESR after exposure to high temperatures and the swelling of the electrolytic capacitor when exposed to high temperatures.

[0060] For the aromatic dicarboxylic acid corresponding to component (C), the explanation for the aromatic dicarboxylic acid of component (A) can be referred to. The aromatic dicarboxylic acid of component (A) and the aromatic dicarboxylic acid corresponding to component (C) may be the same or different. The aromatic dicarboxylic acid corresponding to component (B) and the aromatic dicarboxylic acid corresponding to component (C) may be the same or different. The aromatic dicarboxylic acid of component (A), the aromatic dicarboxylic acid corresponding to component (B), and the aromatic dicarboxylic acid corresponding to component (C) may all be the same. All of the aromatic dicarboxylic acids of each of components (A) to (C) may be phthalic acid.

[0061] Component (C) can also be considered a diester in which each of the two carboxy groups of the aromatic dicarboxylic acid is esterified with one hydroxy group of the aliphatic diol. Therefore, the aliphatic group having a hydroxy group corresponds to the portion of the aliphatic diol excluding one hydroxy group. For the aliphatic diol, please refer to the description of the aliphatic diol (first solvent) described as a non-aqueous solvent.

[0062] For the aliphatic group having a hydroxy group, the description of component (B) can be referred to.

[0063] Component (C) includes, for example, a compound represented by the following formula (C):

[0064] R ２ -OOC-X-COO-R ２ (C) For X, see the explanation for formula (A). ２ For details, see the explanation for formula (B). ２ is -R ２ａ -OH group or the above-mentioned -R-(O-R) ｍ -OH group. ２ａ The —OH group corresponds to the hydroxyalkyl group described above. In formula (C), the R ２ may be the same or different.

[0065] Specific examples of component (C) are di(hydroxyethyl) phthalate and di(hydroxyethyl) 2,3-naphthalenedicarboxylate. Component (C) may also be di(hydroxyethyl) esters corresponding to these di(hydroxyethyl) esters. ３－６ alkyl) esters (e.g., di(hydroxy C ３－４ di(hydroxyethyl) esters), and the hydroxyethyl portion of these di(hydroxyethyl) esters is -R(-O-R) ｍ However, component (C) is not limited to these specific examples.

[0066] The liquid component may contain one type of component (C) or a combination of two or more types.

[0067] The molar ratio (C / A) of component (C) to component (A) may be 0.001 or more and 0.150 or less, or 0.01 or more and 0.10 or less (or 0.010 or more and 0.100 or less). When the molar ratio C / A is within this range, an increase in ESR can be suppressed, and swelling of the electrolytic capacitor when exposed to high temperatures can be suppressed. Furthermore, excessive loss of water content due to the hydrolysis reaction between the water in the liquid component and component (B) can be suppressed. Therefore, the film repairability of the dielectric layer can be maintained, and an increase in leakage current can be suppressed.

[0068] (Others) Examples of component (D) include aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, and esters of these dicarboxylic acids (monoesters, diesters). The esters may have a structure in which the carboxy group of the dicarboxylic acid is esterified with an aliphatic group having a hydroxy group, as in component (B) or (D). The liquid component may contain one type of component (D) or a combination of two or more types.

[0069] In the liquid component, the carboxy group of the dicarboxylic acid compound may be in any of the following forms: a free form, a salt form, an anion form, or a form interacting with (complexing with) the conductive polymer. The carboxy group of the dicarboxylic acid compound includes all of these forms.

[0070] In this specification, the dicarboxylic acid compound includes components (A), (B), (C), and (D). The total amount of components (A) to (C) may be 50% by mass or more, 75% by mass or more, or 90% by mass or more of the total dicarboxylic acid compound. The total amount of components (A) to (C) may be 100% by mass or less of the total dicarboxylic acid compound. The dicarboxylic acid compound may consist solely of components (A) to (C) (or components (A) and (B)). When the total amount of components (A) to (C) is within this range, higher reliability of the electrolytic capacitor is likely to be achieved. Furthermore, swelling when the electrolytic capacitor is exposed to high temperatures (e.g., temperatures of 200°C or higher and 300°C or lower) can be further suppressed. The above ratios are values ​​determined based on the mass when the carboxy groups are in a free form.

[0071] (Acid Component) The acid component contained in the liquid component includes components having a carboxy group, such as component (A) and component (B). Of component (D), the component having a carboxy group is also included in the acid component. The acid component further includes carboxylic acid compounds (other carboxylic acid compounds) other than component (A), component (B), and component (D) and other acids. The liquid component may contain at least one selected from the group consisting of other carboxylic acid compounds and other acids.

[0072] Examples of other carboxylic acid compounds include carboxylic acids other than components (A), (B) and (D) (other carboxylic acids), and coordination compounds of carboxylic acids.

[0073] Examples of other carboxylic acids include aliphatic carboxylic acids and aromatic carboxylic acids. Examples of aliphatic carboxylic acids include aliphatic monocarboxylic acids, aliphatic polycarboxylic acids, and aliphatic hydroxycarboxylic acids. Examples of aromatic carboxylic acids include aromatic hydroxy acids (benzoic acid, nitrobenzoic acid, salicylic acid, etc.), aromatic polycarboxylic acids other than component (A) (trimellitic acid, pyromellitic acid, etc.), and sulfoaromatic carboxylic acids (p-sulfobenzoic acid, 3-sulfophthalic acid, 5-sulfosalicylic acid, etc.).

[0074] 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.

[0075] Examples of other acids include acids having a carbonyloxy bond other than carboxylic acids (such as oxocarbonic acids 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), 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), or partial esters thereof), phosphorus-containing acids (such as phosphoric acid, halogenated phosphoric acids (such as hexafluorophosphoric acid), phosphonic acid, phosphinic acid, or partial esters thereof (such as butyl phosphate)), and nitrogen-containing acids (such as nitric acid and nitrous acid).

[0076] In the liquid component, the carboxyl group and other acid groups (sulfonic acid group, phosphate group, phosphonic acid group, etc.) of the acid component may each be in any form, such as a free form, a salt form, an anion form, or a form interacting (e.g., complexing) with a conductive polymer. The carboxyl group and other acid groups of the acid component each include all of these forms.

[0077] The proportion of the dicarboxylic acid compounds (components (A) to (D)) in the total acid components may be 50% by mass or more, 75% by mass or more, or 90% by mass or more. The proportion of the dicarboxylic acid compounds (components (A) to (D)) in the total acid components is 100% by mass or less. The acid components may be composed solely of dicarboxylic acid compounds. When the proportion of the dicarboxylic acid compounds is within this range, electrode corrosion is suppressed, and it is easy to obtain the high effects of components (A) to (C). The above proportions are values ​​for the liquid component collected from an initial electrolytic capacitor.

[0078] The concentration of the acid component 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, the concentration being the value in the liquid component collected from the initial electrolytic capacitor.

[0079] The concentration of component (A) in the liquid component may be 1% by mass or more and 20% by mass or less, or 5% by mass or more and 15% by mass or less, the concentration being the value in the liquid component collected from the initial electrolytic capacitor.

[0080] The above ratios and concentrations are values ​​determined based on the mass of acid groups such as carboxy groups in a free form.

[0081] (Base Component) When the liquid component contains a base component, the dissociation of acid components such as dicarboxylic acid compounds is enhanced, making it easier for acid groups such as carboxy groups to act on the conductive polymer, thereby making it easier to obtain higher conductivity of the conductive polymer.

[0082] 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.

[0083] 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).

[0084] 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, from the viewpoint of easily suppressing electrode corrosion while maintaining a high dedoping suppression effect due to the acid component, the heterocyclic amine is preferably a compound having no free amino group. 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.

[0085] The base component may include a base (first base) whose conjugate acid has a pKa of 10 or less. The pKa of the conjugate acid of the first base may be 3.5 or more and 10.0 or less, or 3.5 or more and 7.5 or less. When the pKa is within this range, esterification of component (A) is easily suppressed while maintaining the dissociated state of the acid component, and the high conductivity of the conductive polymer is more easily maintained.

[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 molar ratio of the base component to the dicarboxylic acid compound (base component / dicarboxylic acid compound) may be 1 or less, 0.1 to 1.0, 0.2 to 0.9, or 0.3 to 0.8. In this case, a high degree of dissociation of the dicarboxylic acid compound can be ensured, and higher conductivity of the conductive polymer can be easily ensured. Furthermore, corrosion of the electrode can be suppressed.

[0088] 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, 1.0 or more and 10 or less, or 1.0 or more and 9.0 or less.

[0089] 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) － The ratio is the sum of the moles of

[0090] [Electrolytic Capacitor] The electrolytic capacitor of the present disclosure includes the above-described liquid component and a capacitor element.

[0091] (Capacitor Element) The capacitor element includes an anode body having a dielectric layer and a solid electrolyte in contact with the dielectric layer. The solid electrolyte includes a conductive polymer. The solid electrolyte (or 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). The solid electrolyte (or conductive polymer) may be interposed between the anode body (e.g., an anode foil) and the cathode foil. For example, the capacitor element may include an anode foil having a dielectric layer, a cathode foil arranged to face the dielectric layer, and a solid electrolyte (or conductive polymer) interposed between the anode foil and the 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, and preferably has a porous portion having pores at least on the surface thereof.

[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, for example, so as to cover at least a portion of the surface of the anode body.

[0096] The dielectric layer includes, for example, an oxide of a valve metal. For example, when tantalum is used as the valve metal, the dielectric layer includes Ta. ２ O ５ When aluminum is used as the valve metal, the dielectric layer contains Al ２ O ３ The dielectric layer is not limited to these, 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] (Solid Electrolyte) The conductive polymer constituting the solid electrolyte includes, for example, a conjugated polymer and a dopant. The solid electrolyte (or conductive polymer) covers, for example, at least a portion of the dielectric layer. This embodiment includes a case where the solid electrolyte (or 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 solid electrolyte (or conductive polymer) may be interposed between these foils. The solid electrolyte (or 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 solid electrolyte (or conductive polymer) may form a layer. The solid electrolyte may further include an additive in addition to the conductive polymer, as necessary.

[0099] When the capacitor element includes a separator, the separator is interposed between the anode foil and the cathode foil. In this case, the separator may be impregnated with a solid electrolyte (or a conductive polymer). The solid electrolyte (or a conductive polymer) may be interposed between the anode body (e.g., anode foil) and the cathode body (e.g., 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.

[0100] (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).

[0101] The conjugated polymer may be used alone or in combination of two or more kinds.

[0102] 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.

[0103] In this specification, the weight average molecular weight (Mw) is a value calculated as polystyrene measured by gel permeation chromatography (GPC). GPC is usually performed using a polystyrene gel column and water / methanol (volume ratio 8 / 2) as the mobile phase.

[0104] (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.

[0105] 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.

[0106] 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.

[0107] 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 solid electrolyte 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.

[0108] The Mw of the dopant is not particularly limited and is, for example, 1,000 or more and 1,000,000 or less.

[0109] 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.

[0110] (Cathode Extraction Layer) The cathode extraction layer may include, for example, a first layer covering at least a portion of the solid electrolyte. 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.

[0111] 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.

[0112] 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 dielectric layer, or may be provided with a coating of a metal (heterogeneous metal) or a nonmetal different from the metal constituting the metal foil. Examples of heterogeneous metals and nonmetals include metals such as titanium and nonmetals such as carbon (e.g., conductive carbon).

[0113] 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.

[0114] (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 examples thereof include nonwoven fabrics containing fibers. Examples of materials that may be used for the fibers include nonwoven fabrics containing fibers of cellulose, polyethylene terephthalate, vinylon, and polyamide (e.g., aliphatic polyamides, aromatic polyamides such as aramid).

[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] [Method for Manufacturing Electrolytic Capacitor] The electrolytic capacitor is manufactured by a manufacturing method including, for example, a step of housing a capacitor element together with the liquid component in a case and sealing the case. The manufacturing method may further include a step of preparing the capacitor element. The manufacturing method may further include a step of preparing the liquid component. The step of preparing the capacitor element and the step of preparing the liquid component may each be performed prior to the sealing step.

[0118] The capacitor element is fabricated according to the description of the components of the capacitor element. The liquid component is prepared by dissolving the components, such as the dicarboxylic acid compound, the acid component, and the base component, in a solvent (non-aqueous solvent).

[0119] In the sealing step, the capacitor element is housed in a case together with the liquid component, and then the opening of the case is sealed with a sealing material or the like.

[0120] The manufacturing method of the present disclosure may further include a step of heating the sealed product obtained in the sealing step. In the heating step, the sealed product may be sealed at a temperature of 130°C or higher. The heating temperature may be 130°C or higher and 150°C or lower. The heating time may be 10 minutes or longer, or 10 minutes or longer and 60 minutes or shorter. Such a heating step facilitates the hydrolysis reaction of component (B) or component (C). Therefore, even if moisture is generated in the electrolytic capacitor due to the reaction (esterification reaction) between the nonaqueous solvent having a hydroxy group and component (A), the amount of moisture can be reduced by the hydrolysis reaction. Therefore, swelling of the electrolytic capacitor when exposed to high temperatures (e.g., temperatures of 200°C or higher and 300°C or lower) can be further suppressed.

[0121] 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 14) related to the liquid component, electrolytic capacitor, or manufacturing method thereof of the present disclosure, or may be arbitrarily combined with at least one of the above-described (Technology 1) to (Technology 14) and the components described above.

[0122] 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.

[0123] 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.

[0124] 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 solid electrolyte (e.g., a conductive polymer) (not shown) are interposed between anode foil 11 and cathode foil 12. The solid electrolyte is in contact with at least a portion of the dielectric layer. The solid electrolyte is also in contact with at least a portion of cathode foil 12. The solid electrolyte and separator are impregnated with a liquid component.

[0125] 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.

[0126] Examples 1 to 10 and Comparative Examples 1 and 2 Wound electrolytic capacitors (diameter 10 mm, length 10 mm) with a rated voltage of 25 V and a rated capacitance of 560 μF were fabricated and evaluated according to the following procedure.

[0127] (Preparation of anode foil) An aluminum foil with a thickness of 120 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. The aluminum foil was then cut into a size of 6 mm length x 200 mm width to prepare an anode foil.

[0128] (Preparation of Cathode Foil) 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 6 mm length×220 mm width to prepare a cathode foil.

[0129] (Preparation of Wound Body) An anode lead tab and a cathode lead tab were connected to the anode foil and the cathode foil, and the anode foil and the cathode foil were wound around the lead tabs, with a separator interposed therebetween. The wound body was then prepared by fixing the ends of the outer surface of the wound body with a winding tape. An anode lead wire and a cathode lead wire were connected to the ends of each lead tab, 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.

[0130] (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 poly(3,4-ethylenedioxythiophene) doped with PSS (PEDOT / PSS) as the conductive polymer. The Mw of the polymer dopant is the value measured under the conditions described above.

[0131] (Coating of the dielectric layer with a conductive polymer) The wound body was immersed in a polymer dispersion contained in a designated container in a reduced pressure atmosphere (40 kPa) for 5 minutes, and then removed from the polymer dispersion. The wound body impregnated with the polymer dispersion was then dried in a drying oven at 150°C for 20 minutes, and the conductive polymer was attached so as to cover at least a portion of the dielectric layer. In this way, a capacitor element was formed. In the capacitor element, a separator and a conductive polymer were interposed between the anode foil and the cathode foil.

[0132] (Preparation of Liquid Component) A liquid component was prepared by dissolving the salt of component (A) and morpholine, and components (A) to (C) shown in Table 1, in a mixed solvent of ethylene glycol, polyethylene glycol (Mw 300), and sulfolane. The mass ratio of ethylene glycol (EG), polyethylene glycol (PEG), and sulfolane (SL) in the solvent was EG:PEG:SL = 30:20:50, assuming the total solvent volume to be 100. The amounts of each component were adjusted so that the salt concentration in the liquid component was 13% by mass and the total concentration of components (A) to (C) was approximately 10% by mass. The pH of the prepared liquid component was approximately 4.0 ± 0.5. In Comparative Example 2, a boric acid ester was used instead of components (A) to (C). The boric acid ester used was a polycondensate of boric acid with a mixture of triethylene glycol monomethyl ether and diethylene glycol.

[0133] (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.

[0134] 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 manner, 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 fabricated for each example. The fabricated electrolytic capacitors were heat-treated at 135°C for 60 minutes, followed by aging treatment by heating at 105°C for 60 minutes while applying a voltage of 31.3 V.

[0135] (Evaluation) (a) Reliability After the aging treatment, the initial leakage current X0 (LC) and the initial equivalent series resistance Y0 (ESR) of the electrolytic capacitor were measured.

[0136] Next, to evaluate reliability, the electrolytic capacitors were held at 145°C for 1000 hours with the rated voltage (25V) applied, and the change in leakage current (ΔLC) and the change in ESR (ΔESR) were confirmed.

[0137] ΔLC was expressed as the ratio (X / X) of LC (X) after holding at 145° C. to the initial value (X). The leakage current was measured after 120 seconds at room temperature after applying a voltage of 25 V between the anode and cathode bodies of the electrolytic capacitor.

[0138] ΔESR was expressed as the ratio (Y / Y0) of ESR (Y) after holding at 145° C. to the initial value (Y0). The ESR was measured at a frequency of 100 kHz for the electrolytic capacitor using an LCR meter in a room temperature environment.

[0139] (b) Measurement of swelling amount of electrolytic capacitors For ten electrolytic capacitors after the aging treatment, the maximum distance α1 from the bottom of the case to the top surface of the sealing member was measured using a microgauge. The electrolytic capacitors were then heated to 200°C and left for five minutes, and the maximum distance α2 from the bottom of the case to the top surface of the sealing member after heating was measured. For each capacitor, the swelling amount was calculated by subtracting α1 from α2, and the average value (mm) of the ten capacitors was calculated and evaluated according to the following criteria.

[0140] A: The swelling amount is 0.17 mm or less.

[0141] B: The swelling amount is more than 0.17 mm and 0.25 mm or less.

[0142] C: The swelling amount is more than 0.25 mm and 0.30 mm or less.

[0143] D: The swelling amount exceeds 0.30 mm.

[0144] The evaluation results are shown in Table 1. Table 1 also shows the molar ratio (B / A) of component (B) to component (A) and the molar ratio (C / A) of component (C) to component (A). In Table 1, E1 to E10 represent working examples, and C1 and C2 represent comparative examples.

[0145]

[0146] As shown in Table 1, in Comparative Example C2, which used a liquid component containing a borate ester, the leakage current after the reliability test was more than seven times higher than the initial value. Furthermore, in Comparative Example C1, which used only component (A) as the acid component, the ΔESR after the reliability test was large. In contrast, in Examples E1 to E10, which used a liquid component containing components (A) and (B), the ΔLC after the reliability test was significantly reduced compared to the comparative example, and relatively low ΔESR values ​​were obtained. Furthermore, in Examples E1 to E10, the swelling of the electrolytic capacitor when exposed to high temperatures (200°C) was also reduced compared to Comparative Example C1. In Examples E8 to E10, which used a liquid component containing components (A) to (C), the ΔESR after the reliability test was further reduced compared to Example E3, which contained components (A) and (B), and the swelling of the electrolytic capacitor when exposed to high temperatures (200°C) was also further reduced.

[0147] The liquid component of the present disclosure is useful for electrolytic capacitors (e.g., hybrid capacitors) that include a capacitor element containing a conductive polymer, but applications of the electrolytic capacitor are not limited to these.

[0148] 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. A liquid component for an electrolytic capacitor including a conductive polymer, the liquid component comprising a non-aqueous solvent and a dicarboxylic acid compound, the dicarboxylic acid compound comprising: component (A): an aromatic dicarboxylic acid; and component (B): a monoester in which one carboxy group of the aromatic dicarboxylic acid is esterified with an aliphatic group having a hydroxy group.

2. The liquid component for an electrolytic capacitor according to claim 1, wherein the aromatic dicarboxylic acid of the component (A) is the same as the aromatic dicarboxylic acid of the component (B).

3. The liquid component for an electrolytic capacitor according to claim 1 or 2, wherein the aromatic dicarboxylic acid of the component (A) and the aromatic dicarboxylic acid of the component (B) are each phthalic acid.

4. The liquid component for an electrolytic capacitor according to claim 1 or 2, wherein the non-aqueous solvent contains at least an aliphatic diol.

5. The aliphatic diol is an alkylene glycol having 2 to 6 carbon atoms, and a polyC having 15 or less repeating oxyalkylene groups. ２－４ The liquid component for an electrolytic capacitor according to claim 4 , comprising at least one selected from the group consisting of alkylene glycols.

6. The liquid component for an electrolytic capacitor according to claim 1 or 2, wherein the molar ratio (B / A) of said component (B) to said component (A) is 0.05 or more and 0.5 or less.

7. The liquid component for an electrolytic capacitor according to claim 1, wherein the dicarboxylic acid compound further comprises: Component (C): a diester in which two carboxy groups of an aromatic dicarboxylic acid are esterified with an aliphatic group having a hydroxy group.

8. The liquid component for an electrolytic capacitor according to claim 7, wherein the molar ratio (C / A) of said component (C) to said component (A) is 0.01 or more and 0.10 or less.

9. The aliphatic group having a hydroxy group is a hydroxyalkyl group or -R(-O-R) ｍ 8. The liquid component for an electrolytic capacitor according to claim 1, wherein R is an alkylene group, and m is an integer of 1 or more, and represents the number of repetitions of the oxyalkylene group.

10. The hydroxyalkyl group has 2 to 6 carbon atoms, and the -R(-O-R) ｍ 10. The liquid component for an electrolytic capacitor according to claim 9, wherein in the --OH group, R is an alkylene group having 2 to 4 carbon atoms, and m is an integer of 1 to 14.

11. The liquid component for an electrolytic capacitor according to claim 1 or 7, further comprising a base component, and the molar ratio of the base component to the dicarboxylic acid compound (base component / dicarboxylic acid compound) is 1 or less.

12. The liquid component for an electrolytic capacitor according to claim 11, wherein the base component has a conjugate acid with a pKa of 10 or less.

13. An electrolytic capacitor comprising the liquid component according to claim 1 or 7 and a capacitor element, the capacitor element having an anode foil having a dielectric layer, a cathode foil arranged so as to face the dielectric layer, and a conductive polymer interposed between the anode foil and the cathode foil.

14. A method for producing an electrolytic capacitor, comprising the steps of: preparing a capacitor element comprising an anode foil having a dielectric layer, a cathode foil, and a conductive polymer interposed between the anode foil and the cathode foil; housing the capacitor element together with the liquid component according to claim 1 or 7 in a case and sealing it; and heating the sealed product obtained in the sealing step at a temperature of 130°C or higher for 10 minutes or longer.

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