Electrolytic capacitor and liquid component for electrolytic capacitors

Abstract

This electrolytic capacitor includes a capacitor element and a liquid component. The capacitor element includes a conductive component. The conductive component includes a conductive polymer. The liquid component includes a solvent, a base component, a first acid component, and a second acid component. The total mass content of the base component, the first acid component, and the second acid component in the liquid component is 3% to 15% inclusive. The base dissociation constant pKb of the base component is more than 4.75 and equal to or less than 7.00. The first acid component has a first aromatic ring and two or more first carboxyl groups that are bonded to the first aromatic ring. The second acid component has a second aromatic ring, and a second carboxyl group and a hydroxyl group which are bonded to the second aromatic ring. The mass content Ma1 of the first acid component, the mass content Ma2 of the second acid component, and the mass content Mb of the base component in the liquid component satisfy the following relational expressions. 1.5 ≤ (Ma1 + Ma2) / Mb ≤ 3.0 0.8 ≤ Ma1 / Ma2 ≤ 6.0

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 proposes "an electrolytic capacitor comprising a capacitor element and a liquid component, the capacitor element comprising an anode body having a dielectric layer on its surface and a conductive polymer component covering a portion of the dielectric layer, the liquid component comprising a first solvent, a base component, and an acid component, the first solvent being at least one selected from the group consisting of polyols and derivatives thereof, and the base component comprising a first base whose conjugate acid has an acid dissociation constant of 5 or more and 10 or less and which has no boiling point or a boiling point of 100°C or higher."

[0003] Patent Document 2 proposes "a solid electrolytic capacitor comprising an anode foil on which a dielectric layer is formed, and a cathode foil, wherein a solid electrolyte and an electrolytic solution are contained in a gap between the anode foil and the cathode foil, wherein the electrolytic solution contains a solvent and a solute, the solute contains an acid component and a base component, and the base component contains an amine having a morpholine skeleton."

[0004] Patent Document 3 proposes "an electrolyte (A) for an electrolytic capacitor impregnated into gaps in a solid electrolyte layer (J) formed in an electrolytic capacitor element, the electrolyte (A) being a salt of a cation (b) of a basic compound (B) and an anion (c) of an acidic compound (C), the pKa of a conjugate acid of the basic compound (B) being 14.0 or less, and the boiling point of the basic compound (B) being 90°C or more, and the basic compound (B) being a predetermined alkylene oxide adduct of ammonia (B1) or a predetermined alkylene oxide adduct of an amine (B2) described below."

[0005] International Publication No. 2022 / 044636 International Publication No. 2022 / 255057 Japanese Patent Application Laid-Open No. 2016-15365

[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, and the liquid component includes a solvent, a base component, a first acid component, and a second acid component. The total mass content of the base component, the first acid component, and the second acid component in the liquid component is 3% or more and 15% or less. The base component has a base dissociation constant pKb greater than 4.75 and less than 7.00. The first acid component has a first aromatic ring and two or more first carboxyl groups 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 hydroxyl group bonded to the second aromatic ring. The mass content Ma1 of the first acid component, the mass content Ma2 of the second acid component, and the mass content Mb of the base component in the liquid component satisfy the following relationship: 1.5≦(Ma1+Ma2) / Mb≦3.0 0.8≦Ma1 / Ma2≦6.0 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, and a second acid component. The total mass content of the base component, the first acid component, and the second acid component in the liquid component is 3% or more and 15% or less. The base component has a base dissociation constant pKb greater than 4.75 and less than 7.00. The first acid component has a first aromatic ring and two or more first carboxyl groups 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 hydroxyl group bonded to the second aromatic ring. The mass content Ma1 of the first acid component, the mass content Ma2 of the second acid component, and the mass content Mb of the base component in the liquid component satisfy the following relationship: 1.5≦(Ma1+Ma2) / Mb≦3.0 0.8≦Ma1 / Ma2≦6.0 According to the present disclosure, it is possible to provide an electrolytic capacitor with high durability that exhibits small changes in capacitance and equivalent series resistance (ESR) after long-term use at high temperatures.

[0007] 1 is a schematic cross-sectional view of an electrolytic capacitor according to an embodiment of the present disclosure.

[0008] 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.

[0009] 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.

[0010] 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.

[0011] In contrast, impregnating a capacitor element with a liquid component containing an acid component and a base component inhibits deterioration of the conductive component. The acid component maintains the acidic atmosphere of the liquid component to inhibit 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 ionic substances contained in the liquid component. From the viewpoint of maintaining the acidic atmosphere of the liquid component, it is desirable that the base dissociation constant pKb of the base component is not too small, and it is desirable that the acid component be contained in excess of the base component.

[0012] 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.

[0013] 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.

[0014] The liquid component (L) contains a solvent, a base component, a first acid component, and a second acid component, and the total mass content of the base component, the first acid component, and the second acid component in the liquid component is 3% or more and 15% or less.

[0015] The base component and the first acid component may be introduced into the liquid component (L) as an electrolyte salt. In this case, the second acid component can be said to be an acid component contained in excess of the electrolyte salt (or the base component). Thus, the liquid component exhibits sufficient acidity.

[0016] The base dissociation constant pKb of the base component is greater than 4.75 and less than or equal to 7, and may be greater than or equal to 5.0 and less than or equal to 7. In other words, the base component is not too basic, but has a moderate base strength. The base component dissociates to produce a moderate amount of conjugate acid (cation). The base component promotes the dissociation of the second acidic component.

[0017] In this specification, the base dissociation constant (pKb) means the base dissociation constant in water at a temperature of 25° C. When a base component exhibits multiple pKb values, the lowest pKb should be greater than 4.75 and equal to or less than 7.00.

[0018] The first acid component has a first aromatic ring and two or more first carboxyl groups bonded to the first aromatic ring. The first acid component may have two or more first aromatic rings. The first acid component is a main component that dissociates in the liquid component (L) and behaves as an anion. If the first acid component is too acidic, it is likely to undergo a hydration reaction with the foil (e.g., aluminum) constituting the anode body, reducing the heat resistance of the electrolytic capacitor. Therefore, it is desirable for the first acid component to exhibit moderate acidity.

[0019] Furthermore, when the base dissociation constant pKb of the base component is greater than 4.75 and less than 7.00, the dissociability of the first acid component decreases (the base component is less likely to generate cations), which increases the decomposition of the first acid component (particularly the carboxyl group) through side reactions and makes it easier for the first acid component to decrease. When the first acid component decreases, the pH of the liquid component (L) increases, leading to a decrease in the conductivity of the conductive component (i.e., an increase in ESR).

[0020] In contrast to this, by using a second acid component which can lower the pH of the liquid component (L) in a small amount and which suppresses side reactions, it becomes possible to stabilize the ESR for a long period of time.

[0021] 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 a hydroxy acid different from the first acid component and functions favorably when the dissociation property between the base component and the first acid component is low. However, if the amount of the second acid component is too large, the second acid component behaves as an anion and undergoes a hydration reaction with the foil (e.g., aluminum) constituting the anode body, thereby reducing the heat resistance of the electrolytic capacitor. Therefore, it is important to balance the amount used.

[0022] Specifically, in the liquid component (L), the mass content Mb of the base component, the mass content Ma1 of the first acid component, and the mass content Ma2 of the second acid component satisfy the following relationship: 1.5≦(Ma1+Ma2) / Mb≦3.0 0.8≦Ma1 / Ma2≦6.0 The total mass content of the base component and the first acid component in the liquid component (L) may be, for example, 2% or more and 13% or less. The total mass content of the base component and the first acid component in the liquid component may be 8% or less.

[0023] The mass content of the second acid component in the liquid component (L) may be 0.5% or more and 6% or less, or 2.5% or less.

[0024] The second acid component is preferably a relatively strong acid so that a small amount can lower the pH of the liquid component (L). However, the acid dissociation constant pKa (pKa2) of the second acid component is preferably greater than the acid dissociation constant (pKa1) of the first acid component. pKa2 may be 2.0 to 3.5. pKa2 / pKa1 may be within the range of 1.02≦pKa2 / pKa1≦2.72. When multiple acid dissociation constants are present, it is sufficient that the lowest acid dissociation constant satisfies the above requirement.

[0025] In the first acid component, the two first carboxyl groups are preferably located at the ortho-position relative to each other, which is considered to be highly stable and resistant to deterioration.

[0026] The first acid component may include at least one selected from the group consisting of phthalic acid, trimellitic acid, pyromellitic acid, and derivatives thereof. These first acid components have moderate acidity and high stability, and exhibit 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 at least one selected from the group consisting of phthalic acid, trimellitic acid, pyromellitic acid, and derivatives thereof.

[0027] The derivatives of phthalic acid, trimellitic acid, and pyromellitic acid are not particularly limited, but may be compounds in which a substituent other than a carboxyl group is bonded to the benzene ring constituting each acid. The number of substituents is not particularly limited, and may be any number expressed by the formula: number of substituents = 6 - n (n is the number of carboxyl groups bonded to the benzene ring). Examples of the substituent include an alkyl group having 1 to 4 carbon atoms, a halogenated alkyl group having 1 to 4 carbon atoms, a halogen atom, an alkyl group having 1 to 4 carbon atoms and an ether group, and a methoxy group.

[0028] 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.

[0029] The base component may include a first base component having a morpholine skeleton, or may include a second base component of a polyoxyalkylene alkylamine type.

[0030] The first base component 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 may be 1 to 10. The alkyl moiety may be methyl or ethyl, but is preferably a C3-20 alkyl, and may also be a C4-20 alkyl or C4-10 alkyl (butyl, etc.). From the viewpoint of easily adjusting the degree of dissociation of the first base component within an appropriate range, 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. The first base component may account for 50% or more, further 70% or more, preferably 90% or more by mass of the base component.

[0031] The second base component may be a tertiary amine having at least one polyoxyalkylene alkyl group bonded to the nitrogen atom. The alkyl chain of the polyoxyalkylene alkyl group may be a C3-20 alkyl chain, a C4-20 alkyl chain, or a C4-10 alkyl chain. The polyoxyalkylene chain of the polyoxyalkylene alkyl group may be a polyoxyethylene chain, a polyoxypropylene chain, or the like, and the number of repeating oxyalkylene groups may be 3 to 12. The second base component may have an alkyl group bonded to the nitrogen atom. The alkyl group is preferably a C3-20 alkyl group, and may be a C4-20 alkyl group or a C4-10 alkyl group.

[0032] In this specification, Cx-y means that the number of carbon atoms is x or more and y or less. For example, C3-20 alkyl means an alkyl group having 3 to 20 carbon atoms.

[0033] 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.

[0034] Example 1: Liquid component (L) containing methylmorpholine as a base component and phthalic acid as a first acid component in a total amount of 2% by mass to 13% by mass. Example 2: Liquid component (L) containing isobutylmorpholine as a base component and phthalic acid as a first acid component in a total amount of 2% by mass to 13% by mass. Example 3: Liquid component (L) containing methylmorpholine as a base component and borodicatecholic acid as a first acid component in a total amount of 2% by mass to 13% by mass. Example 4: Liquid component (L) containing {CH ３ CH ２ (-OCH ２ CH ２ -) ３} ２ -N-(CH ２ ) ７ CH ３ and a liquid component (L) containing phthalic acid as a first acid component in a total amount of 2% by mass to 13% by mass. The solvent of the liquid component (L) preferably contains at least ethylene glycol as a first solvent component. Ethylene glycol is unlikely to volatilize when exposed to high temperatures and is suitable for ensuring the function of repairing the dielectric layer of the anode body.

[0035] The mass content of ethylene glycol in the liquid component (L) is, for example, 15% or more and 77% or less, and may be 30% or more and 70% or less.

[0036] 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.

[0037] When the viscosity of the liquid component (L) is to be kept low, the weight average molecular weight (Mw) of the polyethylene glycol is preferably 1,000 or less (for example, 150 to 1,000 or 200 to 600).

[0038] 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.

[0039] The mass content of sulfolane in the liquid component (L) is, for example, 0% or more and 45% or less, and may be 0% or more and 30% or less.

[0040] The mass content of gamma-butyrolactone in the liquid component (L) is, for example, 0% or more and 50% or less, and may be 0% or more and 35% or less.

[0041] The mass content of polyethylene glycol in the liquid component (L) is, for example, 0% or more and 50% or less, and may be 0% or more and 20% or less.

[0042] The mass content of glycerin in the liquid component (L) is, for example, 0% or more and 75% or less, and may be 0% or more and 50% or less.

[0043] The solvent is preferably one or two selected from the group consisting of sulfolane, γ-butyrolactone, polyethylene glycol, and glycerin. Preferred examples of the solvent contained in the liquid component include the following.

[0044] Example 1: Liquid component (L) 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: Liquid component (L) 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: Liquid component (L) 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: Liquid component (L) 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: Liquid component (L) 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. The liquid component (L) may contain a sugar alcohol. The sugar alcohol component includes sugar alcohols having four or more hydroxy groups and derivatives of such sugar alcohols, such as sorbitol, mannitol, erythritol, pentaerythritol, threitol, arabinitol, ribitol, xylitol, galactitol, rhamnitol, isomaltose, maltitol, lactitol, palatinose, and reduced forms thereof (e.g., reduced palatinose).

[0045] The liquid component (L) 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.

[0046] The pH of the liquid component (L) 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.

[0047] The electrolytic capacitor will be described in more detail below.

[0048] (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.

[0049] (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.

[0050] (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.

[0051] 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).

[0052] (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.

[0053] 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.

[0054] 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).

[0055] 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.

[0056] 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.

[0057] (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.

[0058] (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).

[0059] (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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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).

[0066] An example of a method for manufacturing an electrolytic capacitor will now be described.

[0067] (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.

[0068] (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.

[0069] (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.

[0070] (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.

[0071] 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.

[0072] 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.

[0073] <<Preparation of Electrolytic Capacitors A1 to A38 and B1 to B15>> Wound electrolytic capacitors (diameter 10 mm × length 10 mm) with a rated voltage of 25 V and a rated capacitance of 270 μF were prepared. Specific methods for producing the electrolytic capacitors are described below.

[0074] (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.

[0075] (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.

[0076] (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.

[0077] (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).

[0078] (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.

[0079] (Preparation of Liquid Components) The solvents shown in Tables 1 to 5 were prepared. At this time, the solvent mixture was heated to 95°C while stirring, if necessary. The electrolyte salts (salts of a base component and a first acid component) and second acid components shown in Tables 1 to 5 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 5. The concentrations (mass contents) of each solvent in the liquid component and the concentrations (mass contents) of other additives in the liquid component are also shown in Tables 1 to 5. The liquid components were prepared in this manner.

[0080] The abbreviations in each table are as follows:

[0081] EG: ethylene glycol SL: sulfolane GB: gamma-butyrolactone PEG: polyethylene glycol (weight average molecular weight Mw=300) GL: glycerin PE / PP: polyethylene-polypropylene copolymer The base dissociation constants pKb of the base components are as follows:

[0082] Methylmorpholine pKb = 6.04, isobutylmorpholine pKb = 5.99, N-butylmorpholine pKb = 5.99, triethylamine pKb = 3.78 (Assembly of Electrolytic Capacitor) The above-described wound body with a solid electrolyte layer formed thereon was immersed in the liquid component in a reduced pressure atmosphere (40 kPa) for 5 minutes. 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. Subsequently, an aging treatment was performed at 130°C for 2 hours while applying the rated voltage.

[0083] [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.

[0084] Next, the electrolytic capacitor was held at 145° C. for 1000 hours while applying the rated voltage, and the capacitance (C1) and ESR (Z1) were measured in a 25° C. environment using the same procedures as in the initial stage.

[0085] 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).

[0086] 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).

[0087] The evaluation results are shown in Tables 1 to 5.

[0088]

[0089]

[0090]

[0091]

[0092]

[0093] 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.

[0094] 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, wherein the capacitor element comprises an anode body having a dielectric layer on a surface thereof, and a conductive component covering a portion of the dielectric layer, wherein the conductive component comprises a conductive polymer, wherein the liquid component comprises a solvent, a base component, a first acid component, and a second acid component, wherein the total mass content of the base component, the first acid component, and the second acid component in the liquid component is 3% or more and 15% or less, wherein the base component has a base dissociation constant pKb greater than 4.75 and less than 7.00, wherein the first acid component has a first aromatic ring and two or more first carboxyl groups bonded to the first aromatic ring, and 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 mass content Ma1 of the first acid component, the mass content Ma2 of the second acid component, and the mass content Mb of the base component in the liquid component satisfy the following relational expressions: 1.5≦(Ma1+Ma2) / Mb≦3.0 0.8≦Ma1 / Ma2≦6.0 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 2% or more and 13% 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 0.5% or more and 6% 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 of claim 1, wherein the acid dissociation constant pKa of the second acid component is greater than the acid dissociation constant of the first acid component.

7. The electrolytic capacitor according to claim 1, wherein in the first acid component, the two first carboxyl groups are located in ortho positions relative to each other.

8. The electrolytic capacitor according to claim 1, wherein the first acid component includes at least one selected from the group consisting of phthalic acid, trimellitic acid, pyromellitic acid, and derivatives thereof.

9. The electrolytic capacitor of claim 1, wherein the second acid component comprises a hydroxybenzoic acid.

10. The electrolytic capacitor according to claim 1, wherein the base component includes a first base component having a morpholine skeleton.

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 77% or less.

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

14. A liquid component for an electrolytic capacitor comprising a solvent, a base component, a first acid component, and a second acid component, wherein a total mass content of the base component, the first acid component, and the second acid component in the liquid component is 3% or more and 15% or less, the base component has a base dissociation constant pKb greater than 4.75 and equal to or less than 7, the first acid component has a first aromatic ring and two or more first carboxyl groups 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 hydroxyl group bonded to the second aromatic ring, and a mass content Ma1 of the first acid component, a mass content Ma2 of the second acid component, and a mass content Mb of the base component in the liquid component satisfy the following relationship: 1.5≦(Ma1+Ma2) / Mb≦3.0 0.8≦Ma1 / Ma2≦6.0.

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