Electrolytic capacitor and liquid component for electrolytic capacitor

Abstract

This electrolytic capacitor includes a capacitor element and a liquid component. The liquid component contains a solvent, a base component, a first acid component, a second acid component, and a third acid component. The total mass content of the base component, the first acid component, the second acid component, and the third acid component in the liquid component is 4.5-16.5%. The first acid component is a composite complex of an inorganic acid and an organic acid. The organic acid has a first aromatic ring, and at least one of a first carboxyl group and a first hydroxyl group that are bound to the first aromatic ring. The second acid component has a second aromatic ring, and a second carboxyl group and a second hydroxyl group that are bound to the second aromatic ring. The third acid component is boric acid. In the liquid component, the molar concentration Cb of the base component, the molar concentration Ca1 of the first acid component, the molar concentration Ca2 of the second acid component, and the molar concentration Ca3 of the third acid component satisfy the following relational expressions. 1.2≤(Ca1+Ca2+Ca3) / Cb≤7.5 0.4≤(Ca2+Ca3) / Ca1≤7.0

Description

Electrolytic capacitors and liquid components for electrolytic capacitors

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

[0002] Patent Document 1 describes an electrolytic capacitor comprising: a capacitor element configured by winding an anode foil and a cathode foil, each having a dielectric oxide film formed on its surface, with a separator interposed therebetween; a cylindrical metal case with a bottom that houses the capacitor element together with a driving electrolyte; and a sealing member that seals the opening of the metal case; wherein the separator has a conductive polymer containing an acid component as a dopant attached thereto; the driving electrolyte contains a solute containing an acid component and a base component, and a solvent; and the content of the solute in the driving electrolyte is 90% by weight. % or less, the solute contains, as the acid component, at least one organic acid selected from phthalic acid, trimellitic acid, pyromellitic acid, maleic acid, salicylic acid, benzoic acid, and resorcylic acid, and at least one inorganic acid selected from boric acid, hypophosphorous acid, naphthalenesulfonic acid, fluoroboric acid, phosphoric acid, and ethyl phosphate, or a composite compound of an organic acid and an inorganic acid, and the solute contains the acid component in a molar excess over the base component.

[0003] Patent Document 2 proposes a solid electrolytic capacitor characterized in that "a solid electrolyte layer is formed on a capacitor element formed by winding an anode electrode foil and a cathode electrode foil with a separator interposed therebetween using a conductive polymer dispersion in which conductive polymer particles are dispersed in a solvent, and the voids in the capacitor element on which the solid electrolyte layer is formed are filled with an electrolyte solution containing, as a solute, 1 to less than 9 wt % of a salt of borodisalicylic acid, which is a complex compound of an inorganic acid and an organic acid, and 20 wt % or more of ethylene glycol in a solvent."

[0004] Patent Document 3 describes an electrolytic capacitor comprising: a capacitor element constructed by winding an anode foil whose surface is roughened and formed with a dielectric oxide film and a cathode foil whose surface is roughened, with a conductive separator interposed therebetween that has been made conductive by adhering a conductive polymer therebetween; a cylindrical metal case with a bottom that houses the capacitor element together with a driving electrolyte solution that is composed of an organic solvent, a solute, and an additive; and a sealing member that seals the opening of the metal case; wherein the solute is composed of an acid component material and a base component material, and the acid component material has an organic carboxylic acid and an inorganic acid, and the organic carboxylic acid is selected from the group consisting of phthalic acid, trimellitic acid, and pyromellitic acid. The article proposes an electrolytic capacitor in which the inorganic acid is at least one of borodiglycolic acid, maleic acid, salicylic acid, benzoic acid, and resorcylic acid, and the inorganic acid is either boric acid, hypophosphorous acid, naphthalenesulfonic acid, hydrofluoric acid, phosphoric acid, or ethyl phosphate, or the material for the acid component is either borodiglycolic acid or borodisalicylic acid, which are composite compounds of organic and inorganic acids, and the material for the base component is a tertiary amine, and the acid component of the solute is in excess of the base component of the solute in terms of molar ratio, thereby suppressing the dopant, which is an acid contained in the conductive separator, from being de-doped into the driving electrolyte.

[0005] JP 2012-109635 A JP 2015-165550 A JP 2006-114540 A

[0006] One aspect of the present disclosure relates to an electrolytic capacitor. The electrolytic capacitor includes a capacitor element and a liquid component. The capacitor element includes an anode body having a dielectric layer on its surface and a conductive component covering a portion of the dielectric layer. The conductive component includes a conductive polymer. The liquid component includes a solvent, a base component, a first acid component, a second acid component, and a third acid component. The total mass content of the base component, the first acid component, the second acid component, and the third acid component in the liquid component is 4.5% or more and 16.5% or less. The first acid component is a composite complex of an inorganic acid and an organic acid. The organic acid has a first aromatic ring and at least one of a first carboxyl group and a first hydroxyl group bonded to the first aromatic ring. The second acid component has a second aromatic ring, a second carboxyl group bonded to the second aromatic ring, and a second hydroxyl group bonded to the second aromatic ring. The third acid component is boric acid. The molar concentration C of the base component in the liquid component ｂ , the molar concentration C of the first acid component ａ１ , the molar concentration C of the second acid component ａ２ and the molar concentration C of the third acid component ａ３ satisfies the following relation:

[0007] 1.2≦(C ａ１ +C ａ２ +C ａ３ ) / C ｂ ≦7.5 0.4≦(C ａ２ +C ａ３ ) / C ａ１≦7.0 Another aspect of the present disclosure relates to a liquid component for an electrolytic capacitor. The liquid component for an electrolytic capacitor includes a solvent, a base component, a first acid component, a second acid component, and a third acid component. The total mass content of the base component, the first acid component, the second acid component, and the third acid component in the liquid component is 4.5% or more and 16.5% or less. The first acid component is a composite complex of an inorganic acid and an organic acid. The organic acid has a first aromatic ring and at least one of a first carboxyl group and a first hydroxyl group bonded to the first aromatic ring. The second acid component has a second aromatic ring, a second carboxyl group bonded to the second aromatic ring, and a second hydroxyl group bonded to the second aromatic ring. The third acid component is boric acid. The molar concentration C of the base component in the liquid component is ｂ , the molar concentration C of the first acid component ａ１ , the molar concentration C of the second acid component ａ２ and the molar concentration C of the third acid component ａ３ satisfies the following relation:

[0008] 1.2≦(C ａ１ +C ａ２ +C ａ３ ) / C ｂ ≦7.5 0.4≦(C ａ２ +C ａ３ ) / C ａ１ ≦7.0 According to the present disclosure, it is possible to provide a highly durable electrolytic capacitor in which the changes in capacitance and equivalent series resistance (ESR) are small even after long-term use at high temperatures.

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

[0010] Electrolytic capacitors that include an anode body with a dielectric layer and a conductive polymer covering at least a portion of the dielectric layer are considered promising as small, high-capacity capacitors with low ESR. Electrolytic capacitors are often used for long periods of time in high-temperature environments. Electrolytic capacitors are required to exhibit minimal changes in capacitance and ESR after long-term use at high temperatures.

[0011] Hereinafter, embodiments of the present disclosure will be described using examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values, materials, etc. may be exemplified, but other numerical values, materials, etc. may be applied as long as the effects of the present disclosure are obtained. Note that components other than those characteristic of the present disclosure may be components of known secondary batteries. In this specification, when a "range from numerical value A to numerical value B" is mentioned, the range includes numerical value A and numerical value B. When multiple materials are exemplified, one may be selected from the materials and used alone, or two or more may be used in combination.

[0012] The electrolytic capacitor according to 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 component covering a portion of the dielectric layer, the conductive component including a conductive polymer. When an electrolytic capacitor including a conductive polymer as the conductive component is used at high temperatures for a long period of time, the capacitance and ESR change due to degradation of the conductive component. Degradation of the conductive component occurs, for example, when a dopant is dedoped from the conductive polymer, reducing the conductivity of the conductive component.

[0013] In contrast, impregnating a capacitor element with a liquid component containing an acid component and a base component suppresses deterioration of the conductive component. The acid component maintains the acidic atmosphere of the liquid component to suppress deterioration of the conductive component, and also plays a role in repairing the dielectric layer of the anode body. The base component enhances the dissociation of the ionic substance contained in the liquid component. From the viewpoint of enhancing the dissociation of the ionic substance, it is desirable that the base component have a small base dissociation constant pKb, and it is desirable that the acid component be contained in excess of the base component.

[0014] On the other hand, deterioration of the liquid component may also occur during long-term use at high temperatures. The deterioration of the liquid component progresses due to decomposition reactions and volatilization of the components contained in the liquid component. When the liquid component deteriorates, it becomes difficult to suppress the deterioration of the conductive component.

[0015] Therefore, it is desirable to find a liquid component composition that makes it difficult for the capacitance and ESR of an electrolytic capacitor to change when used at high temperatures for a long period of time. The liquid component (hereinafter also referred to as "liquid component (L)") contained in the electrolytic capacitor according to the present disclosure has a composition that meets such requirements.

[0016] The liquid component (L) contains a solvent, a base component, a first acid component, a second acid component, and a third acid component. The base component dissociates to generate a conjugate acid (cation). The base component promotes the dissociation of the acid components.

[0017] The first acid component is a main component that dissociates in the liquid component and behaves as an anion. The acid dissociation constant (pKa1) of the first acid component may be 0.3 to 1.5. When multiple acid dissociation constants exist, it is sufficient that the lowest acid dissociation constant satisfies the above requirement.

[0018] The base component and the first acid component may be introduced into the liquid component as an electrolyte salt. In this case, the second acid component and the third acid component are acid components contained in excess of the electrolyte salt (or the base component). The liquid component exhibits sufficient acidity by including the first acid component, the second acid component, and the third acid component.

[0019] The first acid component is a composite complex of an inorganic acid and an organic acid. The organic acid has a first aromatic ring and at least one of a first carboxyl group and a first hydroxyl group bonded to the first aromatic ring. The composite complex of an inorganic acid and an organic acid refers to a composite complex produced, for example, by an esterification reaction (dehydration reaction) between a hydroxyl group of an inorganic acid and a carboxyl group of an organic acid. The composite complex may have a C-O-B bond or a CO-O-B bond. For example, a composite complex of boric acid and an organic acid has boron and a ligand derived from the organic acid coordinated to the boron. The first acid component may have two or more ligands. Specifically, borodisalicylic acid, a composite complex, is produced by an esterification reaction (dehydration reaction) between boric acid (one molecule), an inorganic acid, and salicylic acid (two molecules), an organic acid.

[0020] The organic acid is not limited to salicylic acid, but may be any other aromatic organic acid having a first carboxyl group and a first hydroxyl group at the ortho position, two first carboxyl groups at the ortho position, or two first hydroxyl groups at the ortho position. Examples include dihydroxybenzoic acid, hydroxynaphthyl acid having one or more carboxyl groups and one or more hydroxyl groups, catechol, pyrogallol, and derivatives thereof. The derivative may have a functional group (e.g., a halogen atom) bonded to the first aromatic ring in addition to the carboxyl group and hydroxyl group. The inorganic acid is not limited to boric acid, but may also be phosphoric acid, phosphorous acid, hypophosphorous acid, phosphonic acid, etc. Since a phenolic hydroxyl group bonded to an aromatic ring exhibits acidity, an organic compound having a phenolic hydroxyl group may be considered an organic acid.

[0021] The first acid component has a high tendency to dissociate protons in water, is a sufficiently strong acid, can maintain the pH of the liquid component low, and has good heat resistance. However, in the liquid component, it has the tendency to dissociate into an inorganic acid and an organic acid due to a side reaction with the solvent or water. If the first acid component is reduced due to the side reaction, the pH of the liquid component increases, resulting in a decrease in the conductivity of the conductive component (i.e., an increase in ESR).

[0022] In contrast, the use of the second and third acid components makes it possible to stabilize the ESR over a long period of time. The second and third acid components have the effect of suppressing the dissociation of the first acid component into an inorganic acid and an organic acid.

[0023] The second acid component has a second aromatic ring, a second carboxyl group bonded to the second aromatic ring, and a hydroxyl group bonded to the second aromatic ring. The second acid component is an acid component that is not a composite complex of an inorganic acid and an organic acid. When the dissociability of the base component and the first acid component is sufficiently high, most of the second acid component remains stable without dissociating, and is prevented from behaving as an anion. Therefore, a decrease in the heat resistance of the electrolytic capacitor due to a hydration reaction of the anion of the second acid component with the foil (e.g., aluminum) constituting the anode body is prevented.

[0024] The second acid component is preferably a relatively strong acid so that a small amount can lower the pH of the liquid component. The acid dissociation constant pKa (pKa2) of the second acid component may be 2.0 to 3.0. When multiple acid dissociation constants exist, it is sufficient that the lowest acid dissociation constant satisfies the above requirement.

[0025] The third acid component is boric acid. When the dissociation between the base component and the first acid component is sufficiently high, most of the third acid component remains stable without dissociating, and is prevented from behaving as an anion. Furthermore, in the presence of the first acid component and the second acid component, the esterification reaction of the relatively weak third acid component is unlikely to proceed. Therefore, the acidity of the liquid component is replenished over the long term, and deterioration of the liquid component is prevented.

[0026] The total mass content of the base component, the first acid component, the second acid component, and the third acid component in the liquid component is 4.5% or more and 16.5% or less. By lowering the solute concentration in this manner, it becomes easier to maintain the low pKa anion in a sufficiently dissociated state.

[0027] Molar concentration C of the base component in the liquid component ｂ , the molar concentration C of the first acid component ａ１ , the molar concentration of the second acid component C ａ２ and the molar concentration C of the third acid component ａ３ satisfies the following relation:

[0028] 1.2≦(C ａ１ +C ａ２ +C ａ３ ) / C ｂ ≦7.5 0.4≦(C ａ２ +C ａ３ ) / C ａ１ ≦7.0 Furthermore, the above relational expression may be as follows.

[0029] 1.2≦(C ａ１ +C ａ２ +C ａ３ ) / C ｂ ≦3.5 0.4≦(C ａ２ +C ａ３ ) / C ａ１ ≦2.5 Molar concentration C of first acid component ａ１ and the molar concentration of the base component C ｂ may not be significantly different and may be roughly the same, and Cａ１ =C ｂ may be.

[0030] The total mass content of the base component and the first acid component in the liquid component may be, for example, 3% or more and 15% or less, or 8% or less.

[0031] The mass content of the second acid component in the liquid component may be 0.75% or more and 9% or less. The mass content of the second acid component in the liquid component may be 2.5% or less.

[0032] The mass content of the third acid component in the liquid component may be 0.75% or more and 3% or less. In order to maintain sufficient acidity for a longer period of time, the mass content of the third acid component in the liquid component is preferably equal to or less than the mass content of the second acid component in the liquid component.

[0033] In order to facilitate maintaining a state in which the low pKa anion of the first acid component is sufficiently dissociated, the total mass content of the second acid component and the third acid component in the liquid component is preferably 10% or less.

[0034] In the first acid component, the inorganic acid constituting the composite complex is, for example, boric acid. Furthermore, the organic acid constituting the composite complex is preferably, for example, an organic acid having two carboxyl groups located at ortho positions on the first aromatic ring, an organic acid having a carboxyl group and a hydroxyl group located at ortho positions on the first aromatic ring, or an organic acid having two hydroxyl groups located at ortho positions on the first aromatic ring. Such a first acid component is considered to be highly stable and resistant to deterioration. The organic acid constituting the composite complex may be salicylic acid.

[0035] The first acid component may include borodisalicylic acid, borodiphthalic acid, borodicatecholic acid, and derivatives thereof. The derivatives may have, in addition to a carboxyl group and a hydroxyl group, a functional group (e.g., a halogen atom) bonded to the first aromatic ring. Among these, borodisalicylic acid has high acidity and high stability, and exhibits excellent properties of suppressing deterioration of the conductive component over a long period of time. 50% or more, further 70% or more, and preferably 90% or more of the mass of the first acid component may be borodisalicylic acid.

[0036] The second acid component may contain hydroxybenzoic acid. The hydroxybenzoic acid may have one carboxyl group and one or two hydroxy groups. The positional relationship between the carboxyl group and the hydroxy group may be ortho, meta, or para, but it is preferable that the hydroxy group be at least at the ortho position of the carboxyl group. Among these, salicylic acid is preferred because it is easily available and exhibits excellent properties. Salicylic acid may account for 50% or more, further 70% or more, and preferably 90% or more of the mass of the second acid component.

[0037] From the viewpoint of enhancing the dissociation property of the first acid component, the base component is preferably an amine compound with a small base dissociation constant pKb. For example, a tertiary amine is preferred. The pKb of the base component is preferably 3.0 to 6.2, more preferably 3.0 to 5.0. Even when such a strong base component is used, when it is used in combination with the first acid component, the second acid component, and the third acid component, it is possible to maintain a low pH of the liquid component.

[0038] The tertiary amine may be a tri-C1-6 alkylamine. Specifically, trimethylamine, ethyldimethylamine, diethylmethylamine, triethylamine, diethylpropylamine, tripropylamine, tributylamine, trioctylamine, etc. are preferred. Among these, tri-C1-3 alkylamines are preferred, more preferably diethylmethylamine and ethyldimethylamine, and 50% or more, further 70% or more, preferably 90% or more of the mass of the base component may be tri-C1-3 alkylamines (particularly ethyldimethylamine, diethylmethylamine, etc.). In this specification, Cx-y means that the number of carbon atoms is x or more and y or less. For example, C1-4 alkyl means an alkyl group having 1 to 4 carbon atoms.

[0039] The base component may include a base component having a morpholine skeleton. The base component having a morpholine skeleton may be morpholine, N-alkylmorpholine (N-methylmorpholine, N-butylmorpholine, 4-isobutylmorpholine, etc.), N-hydroxyalkylmorpholine, etc. The number of carbon atoms in the alkyl group or alkyl moiety of the hydroxyalkyl group on the nitrogen atom of the morpholine may be 1 to 20 or 1 to 10. The alkyl moiety may be methyl or ethyl, but is preferably a C3-20 alkyl, or may be a C4-20 alkyl or C4-10 alkyl (butyl, etc.). The number of carbon atoms in the alkyl group or alkyl moiety of the hydroxyalkyl group on the nitrogen atom of the morpholine is preferably 1 to 4.

[0040] Preferred combinations of the base component and the first acid component include, for example, the following: As the second acid component, it is preferable to use, for example, salicylic acid.

[0041] Example 1: A liquid component containing diethylmethylamine as the base component and borodisalicylic acid as the first acid component, in a total amount of 3% by mass to 15% by mass. Example 2: A liquid component containing diethylmethylamine as the base component and 3-fluoro-borodicathecholic acid as the first acid component, in a total amount of 3% by mass to 15% by mass. The solvent for the liquid component preferably contains at least ethylene glycol as the first solvent component. Ethylene glycol is unlikely to volatilize when exposed to high temperatures, and is suitable for ensuring the effect of repairing the dielectric layer of the anode body.

[0042] The mass content of ethylene glycol in the liquid component is, for example, 15% or more and 80% or less, and may be 30% or more and 70% or less.

[0043] The solvent may further include at least one second solvent component selected from the group consisting of sulfolane, gamma-butyrolactone, polyethylene glycol, and glycerin. The second solvent component is resistant to volatilization when exposed to high temperatures, and polyethylene glycol and glycerin are suitable for ensuring the action of repairing the dielectric layer of the anode body.

[0044] In order to maintain a low viscosity of the liquid component, the weight average molecular weight (Mw) of polyethylene glycol is preferably 1,000 or less (for example, 150 to 1,000 or 200 to 600).

[0045] In this specification, the weight average molecular weight (Mw) is a value calculated as polystyrene measured by gel permeation chromatography (GPC), which is typically performed using a polystyrene gel column and a water / methanol (volume ratio 8 / 2) mobile phase.

[0046] The mass content of sulfolane in the liquid component is, for example, 0% or more and 35% or less, and may be 0% or more and 20% or less.

[0047] The mass content of gamma-butyrolactone in the liquid component is, for example, 0% or more and 48% or less, and may be 0% or more and 35% or less.

[0048] The mass content of polyethylene glycol in the liquid component is, for example, 0% or more and 45% or less, and may be 0% or more and 25% or less.

[0049] The mass content of glycerin in the liquid component is, for example, 0% or more and 67% or less, and may be 0% or more and 20% or less.

[0050] The solvent for the liquid component preferably contains at least ethylene glycol as a first solvent component and glycerin as a second solvent component, which is believed to have the effect of suppressing the esterification of boric acid and the hydration of salicylic acid.

[0051] The mass content of ethylene glycol in the liquid component may be less than the mass content of glycerin, but the mass content of glycerin in the liquid component is preferably 50% or less. Furthermore, from the viewpoint of sufficiently suppressing the esterification of boric acid and the hydration of salicylic acid, the mass content of glycerin in the liquid component is preferably 10% or more.

[0052] Preferred examples of the composition of the solvent contained in the liquid component include the following.

[0053] <Example 1> A liquid component containing 65% by mass to 75% by mass of ethylene glycol and 12% by mass to 17% by mass of sulfolane as solvents. <Example 2> A liquid component containing 20% ​​by mass to 40% by mass of ethylene glycol, 12% by mass to 17% by mass of sulfolane, and 25% by mass to 35% by mass of polyethylene glycol as solvents. <Example 3> A liquid component containing 60% by mass to 75% by mass of ethylene glycol and 5% by mass to 15% by mass of polyethylene glycol as solvents. <Example 4> A liquid component containing 60% by mass to 75% by mass of ethylene glycol and 5% by mass to 15% by mass of gamma-butyrolactone as solvents. <Example 5> A liquid component containing 20% ​​by mass to 30% by mass of ethylene glycol, 20% by mass to 30% by mass of gamma-butyrolactone, and 5% by mass to 15% by mass of polyethylene glycol as solvents. <Example 6> Example 7: A liquid component containing 15% to 30% by mass of ethylene glycol, 25% to 40% by mass of glycerin, and 10% to 20% by mass of sulfolane as solvents. Example 8: A liquid component containing 15% to 30% by mass of ethylene glycol, 25% to 40% by mass of glycerin, and 10% to 25% by mass of polyethylene glycol as solvents. The liquid component may contain a sugar alcohol. The sugar alcohol component includes sugar alcohols having four or more hydroxy groups and derivatives of such sugar alcohols. Examples of sugar alcohols include sorbitol, mannitol, erythritol, pentaerythritol, threitol, arabinitol, ribitol, xylitol, galactitol, rhamnitol, isomaltose, maltitol, lactitol, palatinose, and reduced forms thereof (for example, reduced palatinose).

[0054] The liquid component may further contain additives, such as additives having an antioxidant function, alkyl phosphate esters having a pH adjusting function, and nitro compounds suitable for conductive polymers.

[0055] The pH of the liquid component is preferably 6 or less, more preferably 4 or less, and may be 3.8 or less, or 3.6 or less. By setting the pH of the liquid component in this range, deterioration of the conductive component is easily suppressed. The pH is preferably 1.0 or more.

[0056] The electrolytic capacitor will be described in more detail below.

[0057] (Capacitor Element) The capacitor element includes at least an anode body having a dielectric layer on its surface, and a conductive component covering a portion of the dielectric layer.

[0058] (Anode Body) The anode body can contain a valve metal, an alloy containing a valve metal, a compound containing a valve metal, or the like. These materials can be used alone or in combination of two or more. Examples of preferred valve metals include aluminum, tantalum, niobium, and titanium. Anode bodies with porous surfaces can be obtained by roughening the surface of a substrate (such as a foil-shaped or plate-shaped substrate) containing a valve metal, for example, by etching. The anode body can also be a compact of particles containing a valve metal, or a sintered body thereof. The sintered body has a porous structure.

[0059] (Dielectric Layer) The dielectric layer is formed by anodizing the valve metal on the surface of the anode body by chemical conversion treatment or the like. The dielectric layer may be formed so as to cover at least a portion of the anode body. The dielectric layer is usually formed on the surface of the anode body. Since the dielectric layer is formed on the porous surface of the anode body, it is formed along the inner wall surfaces of holes and depressions (pits) on the surface of the anode body.

[0060] 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 The dielectric layer is not limited to this, and may be any layer that functions as a dielectric. When the surface of the anode body is porous, the dielectric layer is formed along the surface of the anode body (including the inner wall surfaces of the pores).

[0061] (Conductive Component) The conductive component includes, for example, a conductive polymer and a dopant. The conductive component is attached to cover a portion of the dielectric layer. The conductive component attached to the surface of the dielectric layer may be referred to as a solid electrolyte layer. The conductive component constitutes at least a portion of the cathode body in the electrolytic capacitor. The conductive component may further include an additive, if necessary.

[0062] Examples of conductive polymers include π-conjugated polymers, such as polypyrrole, polythiophene, polyfuran, polyaniline, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, and polythiophene vinylene. These may be used alone or in combination of two or more, or may be copolymers of two or more monomers.

[0063] In this specification, polypyrrole, polythiophene, polyfuran, polyaniline, etc. refer to polymers having polypyrrole, polythiophene, polyfuran, polyaniline, etc. as their basic skeletons, respectively. Therefore, polypyrrole, polythiophene, polyfuran, polyaniline, etc. may also include their respective derivatives. For example, polythiophene includes poly(3,4-ethylenedioxythiophene).

[0064] The dopant may be a polyanion. Specific examples of polyanions include polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallyl sulfonic acid, polyacrylic sulfonic acid, polymethacrylic sulfonic acid, poly(2-acrylamido-2-methylpropane sulfonic acid), polyisoprene sulfonic acid, and polyacrylic acid. These may be used alone or in combination of two or more. Furthermore, these may be polymers of a single monomer or copolymers of two or more monomers. Among these, polyanions derived from polystyrene sulfonic acid are preferred.

[0065] The conductive component can be formed, for example, by chemical polymerization and / or electrolytic polymerization of raw material monomers on the dielectric layer. Alternatively, the conductive component can be formed by contacting the dielectric layer with a solution in which the conductive component is dissolved or a dispersion in which the conductive component is dispersed in a liquid dispersion medium. The conductive component may be formed so as to cover at least a portion of the dielectric layer.

[0066] (Cathode body) As with the anode body, a metal foil may also be used for the cathode body. 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.

[0067] (Separator) When a metal foil is used for the cathode body, a separator may be disposed between the metal foil and the anode body. 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).

[0068] (Others) The electrolytic capacitor may be a wound type, a chip type, or a laminated type. The configuration of the capacitor element may be selected depending on the type of electrolytic capacitor.

[0069] The electrolytic capacitor may have at least one capacitor element, or may have a plurality of capacitor elements, and the number of capacitor elements included in the electrolytic capacitor may be determined depending on the application.

[0070] The electrolytic capacitor of the present disclosure will be described in more detail below based on embodiments, but the electrolytic capacitor of the present disclosure is not limited to the following embodiments.

[0071] FIG. 1 is a cross-sectional view of an electrolytic capacitor according to this embodiment, and FIG. 2 is a schematic view of a portion of a capacitor element of the electrolytic capacitor in an expanded form.

[0072] 1 includes a capacitor element 10, a bottomed case 11 that houses the capacitor element 10, a sealing member 12 that closes the opening of the bottomed case 11, a seat plate 13 that covers the sealing member 12, lead wires 14A and 14B that extend from the sealing member 12 and pass through the seat plate 13, lead tabs 15A and 15B that connect the lead wires to the electrodes of the capacitor element 10, and a liquid component (not shown). The open end of the bottomed case 11 is curled so as to be crimped to the sealing member 12.

[0073] Capacitor element 10 is produced from a wound body as shown in Fig. 2. The wound body is a semi-finished product of capacitor element 10, in which a conductive polymer is not disposed between anode body 21 and cathode body 22 having a dielectric layer on the surface. The wound body is formed by winding anode body 21 connected to lead tab 15A and cathode body 22 connected to lead tab 15B with separator 23 interposed therebetween. The outermost periphery of the wound body is fixed with stop tape 24. Note that Fig. 2 shows a state in which the wound body is partially unfolded before the outermost periphery is fixed.

[0074] Anode body 21 includes a metal foil having a roughened surface, and a dielectric layer is formed on the roughened surface. A conductive polymer is attached to at least a portion of the surface of the dielectric layer to form capacitor element 10. Capacitor element 10 is housed in an exterior case together with a liquid component (not shown).

[0075] An example of a method for manufacturing an electrolytic capacitor will now be described.

[0076] (i) Step of preparing anode body 21 and cathode body 22 having a dielectric layer Metal foil made of a valve metal is used as the raw material for anode body 21 and cathode body 22. In the case of anode body 21, the surface of the metal foil is roughened by etching or the like, and a plurality of projections and depressions are formed on the surface of the metal foil. Next, a dielectric layer is formed on the surface of the roughened metal foil by chemical conversion or the like. The surface of cathode body 22 may also be roughened as needed.

[0077] (ii) Preparation of Wound Body Anode body 21 and cathode body 22 are wound with separator 23 interposed therebetween to prepare a wound body. Separator 23 may be a nonwoven fabric containing synthetic cellulose or the like as a main component. Stop tape 24 is placed on the outer surface of cathode body 22, which is located in the outermost layer of the wound body, to fix the end of cathode body 22. If necessary, the wound body is further subjected to a chemical conversion treatment.

[0078] (iii) Step of forming capacitor element 10: For example, a dispersion of a conductive component is impregnated into the dielectric layer to form a film of the conductive component that covers at least a portion of the dielectric layer. This results in a capacitor element 10 in which the conductive component is disposed between the anode body 21 and the cathode body 22. The step of applying a dispersion of a conductive component to the surface of the dielectric layer may be repeated two or more times. Thereafter, the capacitor element 10 may be impregnated with a liquid component. This results in an electrolytic capacitor comprising the conductive component and the liquid component.

[0079] (iv) Step of sealing the capacitor element Capacitor element 10 is housed in bottomed case 11 together with the liquid component so that lead wires 14A and 14B are located on the opening side of bottomed case 11. Next, the opening of bottomed case 11 is sealed with sealing member 12 through which each lead wire passes, the open end is crimped to sealing member 12 and curled, and seat plate 13 is placed on the curled portion, completing the electrolytic capacitor as shown in FIG.

[0080] In the above embodiment, a wound-type electrolytic capacitor has been described, but the scope of application of the present invention is not limited to the above, and the present invention can also be applied to other electrolytic capacitors, such as chip-type electrolytic capacitors that use a metal sintered body as an anode body, and stacked-type electrolytic capacitors that use a metal plate as an anode body.

[0081] 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.

[0082] <<Fabrication of Electrolytic Capacitors A1 to A17 and B1 to B6>> Wound electrolytic capacitors (diameter 10 mm × length 10 mm) with a rated voltage of 25 V and a rated capacitance of 470 μF were fabricated. Specific methods for fabricating the electrolytic capacitors are described below.

[0083] (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 of 45 V thereto. The aluminum foil was then cut to prepare an anode body.

[0084] (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 the aluminum foil was cut to prepare a cathode body.

[0085] (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 again subjected to chemical conversion treatment, and a dielectric layer was formed on the cut end of the anode body.

[0086] (Preparation of a Dispersion of Conductive Component) 3,4-ethylenedioxythiophene and the polymer dopant polystyrene sulfonic acid (PSS, weight-average molecular weight 100,000) were dissolved in ion-exchanged water to prepare a mixed solution. Iron (III) sulfate (oxidant) dissolved in ion-exchanged water was added to the mixed solution while stirring, and a polymerization reaction was carried out. After the reaction, the resulting reaction solution was dialyzed to remove unreacted monomers and excess oxidant, yielding a dispersion (polymer dispersion) containing approximately 5% by mass of PSS-doped polyethylenedioxythiophene (PEDOT / PSS).

[0087] (Formation of Solid Electrolyte Layer) 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. The wound body impregnated with the polymer dispersion was then dried in a drying oven at 150°C for 20 minutes to form a solid electrolyte layer covering at least a portion of the dielectric layer. In this way, a capacitor element was formed.

[0088] (Preparation of Liquid Components) The solvents shown in Tables 1 to 3 were prepared. At this time, the solvent mixture was heated to 95°C while stirring, if necessary. The base component, first acid component, and second acid component shown in Tables 1 to 3 were added to the prepared solvents and mixed so that the concentrations (mass contents) in the liquid components were the values ​​shown in Tables 1 to 3. The concentrations (mass contents) of each solvent in the liquid component and the concentrations (mass contents) of other additives in the liquid component are shown in Tables 1 to 5. The liquid components were prepared in this manner.

[0089] The abbreviations in each table are as follows:

[0090] BS: borodisalicylic acid; FBC: 3-fluoroborodicatechol; PHTHA: phthalic acid (pKa = 2.89); EDMA: ethyldimethylamine (pKb = 3.72); MORPH: methylmorpholine (pKb = 6.04); TEA: triethylamine (pKb = 3.78); SalA: salicylic acid (pKa = 2.97); BA: boric acid; EG: ethylene glycol; SL: sulpholan; GBL: gamma-butyrolactone; PEG: polyethylene glycol (weight average molecular weight Mw = 300); GL: glycerin. (Assembly of Electrolytic Capacitor) The above-described wound body with a solid electrolyte layer formed thereon was immersed in the liquid component for 5 minutes in a reduced pressure atmosphere (40 kPa). This resulted in a capacitor element impregnated with the liquid component. The resulting capacitor element was sealed to complete the electrolytic capacitor shown in Figure 1. Thereafter, the capacitor was subjected to aging treatment at 130° C. for 2 hours while applying the rated voltage.

[0091] [Evaluation: Measurement of Capacitance and ESR] Using a four-terminal LCR meter, the capacitance (initial C0) and ESR at a frequency of 100 kHz (initial ESR (Z0)) of the electrolytic capacitor were measured in an environment of 20°C.

[0092] Next, the electrolytic capacitor was held at 145° C. for 1200 hours while applying the rated voltage, and the capacitance (C1) and ESR (Z1) were measured in a 20° C. environment using the same procedures as in the initial stage.

[0093] The capacitance reduction rate (ΔCap) was calculated as the ratio (C1 / C0) of the capacitance (C1) of the electrolytic capacitor after being held at 145° C. to the initial value (C0).

[0094] The increase rate of ESR (ΔESR) was calculated as the ratio (Z1 / Z0) of the ESR (Z1) of the electrolytic capacitor after being held at 145° C. to the initial value (Z0).

[0095] The evaluation results are shown in Tables 1 to 3.

[0096]

[0097]

[0098]

[0099] The electrolytic capacitor of the present disclosure can be used as a hybrid electrolytic capacitor. The electrolytic capacitor is particularly suited to applications requiring high durability, but the applications of the electrolytic capacitor are not limited to these.

[0100] 10: Capacitor element, 11: Bottomed case, 12: Sealing member, 13: Seat plate, 14A, 14B: Lead wires, 15A, 15B: Lead tabs, 21: Anode body, 22: Cathode body, 23: Separator, 24: Winding tape

Claims

1. A capacitor element and a liquid component, the capacitor element comprising an anode body having a dielectric layer on a surface thereof and a conductive component covering a portion of the dielectric layer, the conductive component comprising a conductive polymer, the liquid component comprising a solvent, a base component, a first acid component, a second acid component, and a third acid component, the total mass content of the base component, the first acid component, the second acid component, and the third acid component in the liquid component being 4.5% or more and 16.5% or less, the first acid component being a composite complex of an inorganic acid and an organic acid, the organic acid having a first aromatic ring, and at least one of a first carboxyl group and a first hydroxyl group bonded to the first aromatic ring, the second acid component having a second aromatic ring, a second carboxyl group bonded to the second aromatic ring, and a second hydroxyl group bonded to the second aromatic ring, the third acid component being boric acid, and a molar concentration C of the base component in the liquid component being 1. ｂ , the molar concentration C of the first acid component ａ１ , the molar concentration of the second acid component C ａ２ and the molar concentration C of the third acid component ａ３ satisfies the following relation: 1.2≦(C ａ１ +C ａ２ +C ａ３ ) / C ｂ ≦7.5 0.4≦(C ａ２ +C ａ３ ) / C ａ１ ≦7.0 Electrolytic capacitor.

2. The electrolytic capacitor according to claim 1, wherein the total mass content of the base component and the first acid component in the liquid component is 3% or more and 15% or less.

3. The electrolytic capacitor according to claim 2, wherein the total mass content of the base component and the first acid component in the liquid component is 8% or less.

4. The electrolytic capacitor according to claim 1, wherein the mass content of the second acid component in the liquid component is 0.75% or more and 9% or less.

5. The electrolytic capacitor according to claim 1, wherein the mass content of the second acid component in the liquid component is 2.5% or less.

6. The electrolytic capacitor according to claim 1, wherein the mass content of the third acid component in the liquid component is 0.75% or more and 3% or less.

7. The electrolytic capacitor according to claim 1, wherein the total mass content of the second acid component and the third acid component in the liquid component is 10% or less.

8. The electrolytic capacitor according to claim 1, wherein the mass content of the third acid component in the liquid component is equal to or less than the mass content of the second acid component in the liquid component.

9. The electrolytic capacitor of claim 1, wherein said first acid component comprises borodisalicylic acid.

10. The electrolytic capacitor according to claim 1, wherein the second acid component comprises at least one selected from the group consisting of hydroxybenzoic acid and derivatives thereof.

11. The electrolytic capacitor of claim 1, wherein the solvent comprises ethylene glycol as a first solvent component.

12. The electrolytic capacitor according to claim 11, wherein the mass content of the ethylene glycol in the liquid component is 15% or more and 80% or less.

13. The electrolytic capacitor of claim 11, wherein the solvent comprises at least one second solvent component selected from the group consisting of sulfolane, gamma-butyrolactone, polyethylene glycol, and glycerin.

14. The electrolytic capacitor of claim 1, wherein the solvent includes ethylene glycol as a first solvent component and glycerin as a second solvent component.

15. The electrolytic capacitor according to claim 14, wherein the mass content of said ethylene glycol in said liquid component is less than the mass content of said glycerin, and the mass content of said glycerin in said liquid component is 50% or less.

16. A liquid component comprising a solvent, a base component, a first acid component, a second acid component, and a third acid component, wherein a total mass content of the base component, the first acid component, the second acid component, and the third acid component in the liquid component is 4.5% or more and 16.5% or less, the first acid component is a composite complex of an inorganic acid and an organic acid, the organic acid has a first aromatic ring, and at least one of a first carboxyl group and a first hydroxyl group bonded to the first aromatic ring, the second acid component has a second aromatic ring, a second carboxyl group bonded to the second aromatic ring, and a second hydroxyl group bonded to the second aromatic ring, the third acid component is boric acid, and a molar concentration C of the base component in the liquid component is 1.5% or more and 1.5% or less. ｂ , the molar concentration C of the first acid component ａ１ , the molar concentration of the second acid component C ａ２ and the molar concentration C of the third acid component ａ３ satisfies the following relation: 1.2≦(C ａ１ +C ａ２ +C ａ３ ) / C ｂ ≦7.5 0.4≦(C ａ２ +C ａ３ ) / C ａ１ ≦7.0 Liquid component for electrolytic capacitors.

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