Electrolytic capacitor and method for manufacturing the same

Abstract

This electrolytic capacitor is provided with a capacitor element which comprises: a positive electrode body that has a dielectric layer on a surface thereof; and a conductive polymer that covers a part of the dielectric layer. The conductive polymer comprises a first monomer unit that corresponds to a 3, 4-ethylenedioxythiophene compound and a second monomer unit that corresponds to a 3, 4-dialkoxythiophene compound.

Description

Technical Field

[0001] The present disclosure relates to an electrolytic capacitor and a method for manufacturing the same.

Background Art

[0002] As a capacitor that is small, has a large capacitance, and has a low ESR (equivalent series resistance), an electrolytic capacitor including an anode body having a dielectric layer formed thereon and a conductive polymer covering at least a part of the dielectric layer is regarded as promising. As the conductive polymer, poly(3,4-ethylenedioxythiophene) (PEDOT) obtained by polymerizing 3,4-ethylenedioxythiophene (EDOT) is frequently used (Patent Document 1, Patent Document 2, etc.).

[0003] Note that Patent Document 3 proposes an electrolytic capacitor including a conductive polymer and a conductive auxiliary liquid, the conductive auxiliary liquid including a high-boiling organic solvent having a boiling point of 150°C or higher and an aromatic compound having at least one hydroxy group.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

[0005] The electrolytic capacitor according to the first aspect of the present disclosure includes a capacitor element including an anode body having a dielectric layer on its surface and a conductive polymer covering a part of the dielectric layer. The conductive polymer includes a first monomer unit corresponding to a 3,4-ethylenedioxythiophene compound and a second monomer unit corresponding to a 3,4-dialkoxythiophene compound.

[0006] The method for manufacturing an electrolytic capacitor according to the second aspect of the present disclosure includes a first step of preparing an anode body, a second step of forming a dielectric layer on the surface of the anode body, and a third step of treating the anode body on which the dielectric layer is formed with a treatment liquid containing a conductive polymer or a precursor thereof. The conductive polymer includes a first monomer unit corresponding to a 3,4-ethylenedioxythiophene compound and a second monomer unit corresponding to a 3,4-dialkoxythiophene compound. The precursor includes at least one of a 3,4-ethylenedioxythiophene compound and an oligomer of the 3,4-ethylenedioxythiophene compound, and at least one of a 3,4-dialkoxythiophene compound and an oligomer of the 3,4-dialkoxythiophene compound. Alternatively, the precursor is and includes an oligomer containing a first monomer unit corresponding to a 3,4-ethylenedioxythiophene compound and a second monomer unit corresponding to a 3,4-dialkoxythiophene compound.

[0007] According to the present disclosure, in an electrolytic capacitor using a conductive polymer containing a monomer unit corresponding to a 3,4-ethylenedioxythiophene compound, a high capacitance can be ensured.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0009] In an electrolytic capacitor using PEDOT or the like shown in the prior art, further increase in capacitance is required.

[0010] Polymers obtained by polymerizing 3,4-ethylenedioxythiophene compounds such as PEDOT exhibit relatively high conductivity, and thus are used as conductive polymers in electrolytic capacitors including a solid electrolyte layer (conductive polymer layer). However, even in electrolytic capacitors using such conductive polymers, further increase in capacitance is required.

[0011] According to one aspect of the present disclosure, a conductive polymer is used which includes a first monomer unit corresponding to a 3,4-ethylenedioxythiophene compound and a second monomer unit corresponding to a 3,4-dialkoxythiophene compound. By using such a conductive polymer, a higher capacitance can be ensured as compared with the case of using a conventional conductive polymer such as PEDOT. In addition, the dielectric loss tangent tanδ can be kept low, and the quality of the electrolytic capacitor can be made more stable. In an electrolytic capacitor using a conventional conductive polymer such as PEDOT, when the electrolytic capacitor is exposed to a high temperature, the ESR tends to increase. On the other hand, when a conductive polymer including the first monomer unit and the second monomer unit is used, the rate of change of the ESR when exposed to a high temperature can be reduced.

[0012] Note that, even if a conductive polymer including a 3-methoxythiophene unit or a 3,4-dimethylthiophene unit and the first monomer unit is used instead of the second monomer unit, the effect of improving the capacitance, the effect of reducing tanδ, or the effect of reducing the ESR change rate cannot be obtained.

[0013] By using a conductive polymer containing a first monomer unit and a second monomer unit, the reason why the capacitance is improved or the change rate of ESR when exposed to a high temperature is reduced is not clear, but it is presumed to be due to the following reasons. Since the dielectric layer is formed on the porous surface of the anode body, it is formed along the inner wall surfaces of the pores and depressions (pits) on the surface of the anode body. By including a second monomer unit in addition to the first monomer unit in the conductive polymer, the affinity for the dielectric layer is improved, and it is considered that the coating property of the dielectric layer with the conductive polymer is enhanced even in the pores and pits on the surface of the anode body. When forming the conductive polymer layer using a treatment liquid containing the conductive polymer, it is considered that the coating property can also be improved by enhancing the impregnation property into the pores and pits on the surface of the anode body due to the inclusion of the second monomer unit in the conductive polymer. Further, when the conductive polymer contains a second monomer unit in addition to the first monomer unit, it is considered that the conductivity of the conductive polymer contained in the capacitor element is improved by enhancing the orientation of the conductive polymer. By including a first monomer unit and a second monomer unit in the conductive polymer, it is considered that the dedoping of the dopant is suppressed and the thermal stability of the conductive polymer is enhanced. Thereby, it is considered that the high conductivity of the conductive polymer layer is maintained even after the electrolytic capacitor is exposed to a high temperature.

[0014] Hereinafter, the configuration of the electrolytic capacitor and the manufacturing method of the electrolytic capacitor will be described in more detail.

[0015] [Electrolytic Capacitor] The electrolytic capacitor includes a capacitor element. The electrolytic capacitor may further contain a liquid component.

[0016] (Co Capacitor Element) The capacitor element includes at least an anode body having a dielectric layer on the surface and a conductive polymer covering a part of the dielectric layer.

[0017] (Anode Body) The anode body can include valve-acting metals, alloys containing valve-acting metals, compounds containing valve-acting metals, etc. These materials can be used alone or in combination of two or more. As the valve-acting metal, for example, aluminum, tantalum, niobium, and titanium are preferably used. The anode body with a porous surface can be obtained, for example, by roughening the surface of a base material (such as a foil-shaped or plate-shaped base material) containing a valve-acting metal by etching or the like. Also, the anode body may be a molded body of particles containing a valve-acting metal or a sintered body thereof. Note that the sintered body has a porous structure.

[0018] (Dielectric layer) The dielectric layer is formed by anodizing the valve-acting metal on the surface of the anode body by a forming treatment or the like. The dielectric layer may be formed so as to cover at least a part 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 surface of the pores and depressions (pits) on the surface of the anode body.

[0019] The dielectric layer contains an oxide of the valve-acting metal. For example, when tantalum is used as the valve-acting metal, the dielectric layer contains Ta2O5, and when aluminum is used as the valve-acting metal, the dielectric layer contains Al2O3. Note that the dielectric layer is not limited to this, and any material that functions as a dielectric may be used. 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 surface of the pores and pits).

[0020] (Conductive polymer layer) The conductive polymer adheres so as to cover a part of the dielectric layer to form a conductive polymer layer. The conductive polymer constitutes at least a part of the cathode body in the electrolytic capacitor. The conductive polymer layer may further contain at least one of a dopant and an additive, if necessary. As the conductive polymer, those containing a first monomer unit corresponding to a 3,4-ethylenedioxythiophene compound and a second monomer unit corresponding to a 3,4-dialkoxythiophene compound are used.

[0021] Examples of the 3,4-ethylenedioxythiophene compound include EDOT or a substituted EDOT (specifically, EDOT having a substituent (first substituent)). Examples of the first substituent include a hydrocarbon group (an alkyl group (C 1-4 Alkyl groups (methyl, ethyl, etc.), cycloalkyl groups, aryl groups, aralkyl groups, etc.), alkoxy groups (C 1-4 Examples of the substituent include an alkoxy group (such as a methoxy group or an ethoxy group), an alkylthio group, a carbonyl group, a thiocarbonyl group, a sulfoxide group, a sulfonic acid group, a sulfonate group, an amino group, a formyl group, a carboxylic acid ester group (such as an acyloxy group or an alkoxycarbonyl group), an acyl group, a carboxy group, a carbonate group, a cyano group, an alkylsilyl group, an alkoxysilyl group, and a carboxylic acid amide group (such as an acylamino group). EDOT may have one or more of these substituents. When EDOT has a substituent, at least one of the alkyl group and the alkoxy group is preferred among these substituents.

[0022] The conductive polymer may contain one type of the first monomer unit, or may contain two or more types of the first monomer unit.

[0023] Examples of the 3,4-dialkoxythiophene compound include 3,4-dialkoxythiophene. Examples of the alkoxy group contained in the 3,4-dialkoxythiophene compound include C 1-4 Alkoxy groups are exemplified. 1-3 Alkoxy group or C 1-2 It may be an alkoxy group. The alkoxy group may be either linear or branched. Specific examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, an n-butoxy group, and a t-butoxy group. The alkoxy groups at the 3- and 4-positions of the thiophene ring may be the same or different.

[0024] The conductive polymer may contain one type of second monomer unit or may contain two or more types of second monomer units.

[0025] The amount of the second monomer unit in the conductive polymer is, for example, 0.005 parts by mass or more and 15 parts by mass or less, and may be 0.008 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the first monomer unit. When the amount of the second monomer unit is within such a range, a higher capacitance is likely to be obtained. From the viewpoint of obtaining a lower dielectric tangent tanδ and ESR, the amount of the second monomer unit is preferably 0.01 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the first monomer unit.

[0026] The conductive polymer may contain a third monomer unit other than the first monomer unit and the second monomer unit. From the viewpoint of easily ensuring a higher capacitance, the total molar ratio of the first monomer unit and the second monomer unit in the conductive polymer is preferably 90 mol% or more. The total molar ratio of the first monomer unit and the second monomer unit in the conductive polymer is 100 mol% or less.

[0027] As the dopant, for example, at least one selected from the group consisting of anions and polyanions is used.

[0028] Examples of the anion include, but are not particularly limited to, sulfate ion, nitrate ion, phosphate ion, borate ion, organic sulfonate ion, carboxylate ion, etc. Examples of the dopant that generates sulfonate ion include p-toluenesulfonic acid and naphthalenesulfonic acid.

[0029] Specific examples of the polyanion include polyvinylsulfonic acid, polystyrenesulfonic acid, polyallylsulfonic acid, polyacrylicsulfonic acid, polymethacrylicsulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprenesulfonic acid, and polyacrylic acid. These may be used alone or in combination of two or more. Also, these may be polymers of single monomers or copolymers of two or more monomers. Among them, a polyanion derived from polystyrenesulfonic acid is preferred.

[0030] The conductive polymer layer may be a single layer or may be composed of a plurality of layers. When the conductive polymer layer is composed of a plurality of layers, the composition of the conductive polymer contained in each layer (for example, the type and amount of each monomer, etc.) may be the same or different.

[0031] For the cathode body, similar to the anode body, a metal foil may be used. The type of metal is not particularly limited, but it is preferable to use a valve metal such as aluminum, tantalum, niobium or an alloy containing a valve metal. If necessary, the surface of the metal foil may be roughened. A formation film may be provided on the surface of the metal foil, or a film of a metal (dissimilar metal) or a non-metal different from the metal constituting the metal foil may be provided. Examples of the dissimilar metal or non-metal include metals such as titanium and non-metals such as carbon.

[0032] (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 for example, a non-woven fabric containing fibers of cellulose, polyethylene terephthalate, vinylon, polyamide (for example, aliphatic polyamide, aromatic polyamide such as aramid, etc.) may be used.

[0033] (Others) The electrolytic capacitor may be of a wound type, or may be either a chip type or a multilayer type. The configuration of the capacitor element may be selected according to the type of the electrolytic capacitor.

[0034] (Liquid component) When the electrolytic capacitor contains a liquid component, it is advantageous for ensuring a higher capacitance. In addition, the rate of change of ESR after exposing the electrolytic capacitor to a high temperature can be further reduced.

[0035] The liquid component contains a solvent. Examples of the solvent include sulfone compounds, lactone compounds, carbonate compounds, polyhydric alcohols, etc. The solvent may be used alone or in combination of two or more.

[0036] Examples of the sulfone compound include sulfolane, dimethyl sulfoxide, and diethyl sulfoxide. Examples of the lactone compound include γ-butyrolactone and γ-valerolactone. Examples of the carbonate compound include dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, and fluoroethylene carbonate.

[0037] From the viewpoint of more effectively suppressing the increase in the ESR change rate after exposing the electrolytic capacitor to high temperature, it is preferable to use a liquid component containing a polyhydric alcohol. The ratio of the polyhydric alcohol in the entire solvent contained in the liquid component is, for example, 50% by mass or more, and may be 75% by mass or more or 90% by mass or more. The ratio of the polyhydric alcohol in the entire solvent contained in the liquid component is 100% by mass or less.

[0038] Examples of the polyhydric alcohol include glycerin compounds, sugar alcohol compounds, and glycol compounds.

[0039] Examples of the glycerin compound include glycerin, polyglycerin (such as diglycerin and triglycerin), or derivatives thereof. The number of repetitions of the glycerin unit in polyglycerin is, for example, 2 or more and 20 or less, and may be 2 or more and 10 or less. Examples of the sugar alcohol compound include sugar alcohols (such as erythritol, mannitol, and pentaerythritol) or derivatives thereof. Examples of the derivative include alkylene oxide adducts (such as an adduct in which one alkylene oxide is added to one hydroxy group of glycerin, polyglycerin, or a sugar alcohol). Examples of the alkylene oxide adduct include C 2-4 Examples of the alkylene oxide adduct include ethylene oxide adducts.

[0040] Examples of the glycol compound include alkylene glycol (C 2-4Alkylene glycols (such as ethylene glycol, propylene glycol, etc.), polyalkylene glycols (poly C 2-4 Alkylene glycols (such as diethylene glycol, dipropylene glycol, triethylene glycol, polyethylene glycol, etc.), polyalkylene oxide adducts of sugar alcohols (such as glycerin, erythritol, mannitol, pentaerythritol, etc.) (poly C 2-4 Examples thereof include polyalkylene oxide adducts (such as polyethylene oxide adducts).

[0041] The weight average molecular weight (Mw) of the polyalkylene glycol or the polyalkylene oxide adduct of the sugar alcohol is, for example, 150 or more and 3000 or less, and may be 200 or more and 1000 or less. Mw is a value in terms of polystyrene measured by gel permeation chromatography (GPC). Note that GPC is usually measured using a polystyrene gel column and water / methanol (volume ratio 8 / 2) as the mobile phase.

[0042] (Solute) The liquid component may contain a solute. Examples of the solute include an acid component and a base component.

[0043] Examples of the acid component include carboxylic acids (such as aliphatic carboxylic acids, aromatic carboxylic acids (including polyvalent carboxylic acids such as phthalic acid and pyromellitic acid)), sulfur-containing acids (such as sulfuric acid, sulfonic acids (such as aliphatic sulfonic acids and aromatic sulfonic acids)), boron-containing acids (such as boric acid, halogenated boric acids (such as tetrafluoroboric acid), or partial esters thereof), phosphorus-containing acids (such as phosphoric acid, halogenated phosphoric acids (such as hexafluorophosphoric acid), phosphonic acids, phosphinic acids, or partial esters thereof), nitric acid, and nitrous acid. As the acid component, condensates of carboxylic acids and inorganic acids (such as boric acid and phosphoric acid) (such as borodisalicylic acid, borodiglycolic acid, and borodisuccinic acid) may be used. Aromatic sulfonic acids include aromatic sulfonic acids having a hydroxy group or a carboxy group in addition to a sulfo group (such as oxyaromatic sulfonic acids (such as phenol-2-sulfonic acid), sulfonaromatic carboxylic acids (such as p-sulfobenzoic acid, 3-sulfophthalic acid, and 5-sulfosalicylic acid)). The liquid component may contain one kind of acid component or two or more kinds of acid components.

[0044] Examples of the base component include ammonia, amines (specifically, primary amines, secondary amines, and tertiary amines), quaternary ammonium compounds, and amidinium compounds. The amines may be any of aliphatic, aromatic, and heterocyclic. Examples of the amines include trimethylamine, diethylamine, triethylamine, ethylenediamine, aniline, pyrrolidine, imidazole, 4-dimethylaminopyridine, and the like. Examples of the quaternary ammonium compounds include amidine compounds (including imidazole compounds). The liquid component may contain one kind of base component or two or more kinds of base components.

[0045] The liquid component may contain the acid component and the base component in a free state, respectively, or in the form of salts. The liquid component may contain organic salts. Examples of the organic salts include those in which at least one of the acid component and the base component is organic.

[0046] The pH of the liquid component is preferably 4 or less, and may be 3.8 or less, or 3.6 or less. When the pH of the liquid component is within such a range, deterioration of the conductive polymer is likely to be suppressed. The pH is preferably 1.0 or more.

[0047] The concentration of the solute in the liquid component is, for example, 0.1 mass% or more and 25 mass% or less, and may be 0.5 mass% or more and 15 mass% or less. When the concentration of the solute is within such a range, dedoping of the dopant is likely to be suppressed.

[0048] FIG. 1 is a schematic cross-sectional view of the electrolytic capacitor according to the present embodiment, and FIG. 2 is a schematic view showing a part of the capacitor element related to the same electrolytic capacitor developed.

[0049] Electrolytic capacitor 100 For example, includes a capacitor element 10, a bottomed case 101 that houses the capacitor element 10 and a liquid component (not shown), a sealing body 102 that closes the opening of the bottomed case 101, a seat plate 103 that covers the sealing body 102, lead wires 104A, 104B that are led out from the sealing body 102 and penetrate the seat plate 103, and lead tabs 105A, 105B that connect the lead wires and the electrodes of the capacitor element 10. The vicinity of the opening end of the bottomed case 101 is inwardly tapered, and the opening end is curled so as to be caulked to the sealing body 102.

[0050] The capacitor element 10 is, for example, a wound body as shown in FIG. 2. The wound body includes an anode body 11 connected to the lead tab 105A, a cathode body 12 connected to the lead tab 105B, and a separator 13. A conductive polymer layer (not shown) is formed on the anode body 11. And at least the conductive polymer layer of the capacitor element 10 may be impregnated with a liquid component.

[0051] The anode body 11 and the cathode body 12 are wound with the separator 13 interposed therebetween. The outermost periphery of the wound body is fixed by a winding tape 14. Note that FIG. 2 shows a partially developed state before stopping the outermost periphery of the wound body.

[0052] An electrolytic capacitor only needs to have at least one capacitor element, and it may also have a plurality of capacitor elements. The number of capacitor elements included in the electrolytic capacitor may be determined according to the application.

[0053] [Manufacturing Method of Electrolytic Capacitor] The electrolytic capacitor is manufactured by a manufacturing method including at least a step of preparing an anode body, a step of forming a dielectric layer, and a step of treating the anode body with a treatment liquid containing a conductive polymer or a precursor thereof.

[0054] Hereinafter, an example of the manufacturing method of the electrolytic capacitor will be described.

[0055] (i) Step of preparing the anode body 11 (first step) and step of forming the dielectric layer (second step) As the raw material of the anode body 11, a metal foil formed of a valve action metal is used. In the case of the anode body 11, the surface of the metal foil is roughened by an etching treatment or the like, and a plurality of irregularities are formed on the surface of the metal foil. The anode body 11 is thus prepared. Next, a dielectric layer is formed on the surface of the roughened metal foil by a forming treatment or the like.

[0056] (ii) Step of preparing the cathode body 12 As the raw material of the cathode body 12, a metal foil formed of a valve action metal is used. The surface of the cathode body 12 may be roughened if necessary.

[0057] (iii) Preparation of the wound body The anode body 11 and the cathode body 12 are wound through a separator 13 to prepare a wound body. A winding tape 14 is disposed on the outer surface of the cathode body 12 located on the outermost layer of the wound body to fix the end of the cathode body 12. If necessary, a forming treatment is further performed on the wound body.

[0058] (iv) Step of treating the anode body 11 with a treatment liquid (third step) In the third step, it is only necessary to bring the treatment liquid containing the conductive polymer or its precursor into contact with at least the dielectric layer. For example, the treatment liquid can be brought into contact with at least the dielectric layer by immersing the anode body on which the dielectric layer is formed in the treatment liquid, or by pouring the treatment liquid onto the anode body on which the dielectric layer is formed. By bringing the treatment liquid into contact with the dielectric layer, a film of the conductive polymer covering at least a part of the dielectric layer is formed. For example, when a wound body is used, by applying the treatment liquid to the wound body, a capacitor element 10 in which the conductive polymer is disposed between the anode body 11 and the cathode body 12 can be obtained.

[0059] When using a treatment liquid containing a precursor of the conductive polymer, it is preferable to immerse the anode body and polymerize the precursor by chemical polymerization or electrolytic polymerization to generate the conductive polymer. After the anode body is taken out of the treatment liquid, it is usually dried. When drying, the anode body may be heated as necessary. The anode body taken out of the treatment liquid may be washed as necessary prior to drying. In this way, the conductive polymer layer is formed.

[0060] When using a treatment liquid containing the conductive polymer, for example, the treatment liquid is brought into contact with at least the dielectric layer of the anode body and dried. In this way, the conductive polymer layer is formed. When drying, the anode body may be heated as necessary.

[0061] The treatment liquid is prepared by dissolving or dispersing the constituent components of the treatment liquid in a liquid medium. Examples of the constituent components include a conductive polymer or its precursor, a dopant, and an additive. For the conductive polymer and the dopant, reference can be made to the description of the conductive polymer layer.

[0062] Examples of the precursor of the conductive polymer include monomers and oligomers (including prepolymers) of the conductive polymer. The treatment liquid may contain one kind of precursor or two or more kinds of precursors. The precursor may contain at least one of a 3,4-ethylenedioxythiophene compound (first monomer) and its oligomer (first oligomer), and at least one of a 3,4-dialkoxythiophene compound (second monomer) and its oligomer (second oligomer). Alternatively, the precursor may contain an oligomer (third oligomer) containing a first monomer unit and a second monomer unit. The precursor may contain the third oligomer and at least one selected from the group consisting of the first monomer, the first oligomer, the second monomer, and the second oligomer. For each monomer or its unit, reference can be made to the description of the conductive polymer layer.

[0063] The ratio of each monomer or oligomer in the precursor may be determined so that the amount of the second monomer unit relative to 100 parts by mass of the first monomer unit in the conductive polymer is within the above range. For example, when the first monomer and the second monomer are used as the precursor, the amount of the second monomer relative to 100 parts by mass of the first monomer may be within the above range described as the amount of the second monomer unit relative to 100 parts by mass of the first monomer unit.

[0064] Examples of the liquid medium contained in the treatment liquid include water, organic media, and mixtures thereof. Examples of the organic medium include aliphatic alcohols, aliphatic ketones (such as acetone), nitriles (such as acetonitrile), amides (such as N,N-dimethylformamide), and sulfoxides (such as dimethyl sulfoxide). As the aliphatic alcohol, an aliphatic alcohol having 1 to 5 carbon atoms is preferred. The aliphatic alcohol may be either a monool or a polyol. Examples of the aliphatic monool include methanol, ethanol, propanol, and butanol. Examples of the aliphatic polyol include ethylene glycol and glycerin.

[0065] The treatment liquid can contain known additives used when forming the conductive polymer layer. As the additive, a silane compound may be used.

[0066] When using a treatment liquid containing a precursor of a conductive polymer, an oxidizing agent is used to polymerize the precursor. The oxidizing agent may be contained in the treatment liquid as an additive. Further, the oxidizing agent may be applied to the anode body before or after bringing the treatment liquid into contact with the anode body on which the dielectric layer is formed. Examples of such an oxidizing agent include sulfates, sulfonic acids or salts thereof. The oxidizing agent can be used alone or in combination of two or more.

[0067] Examples of the sulfate include salts of sulfuric acid or persulfuric acid such as ferric sulfate and sodium persulfate with metals. Examples of the metal constituting the salt include alkali metals (such as sodium and potassium), iron, copper, chromium, zinc, etc. The sulfonic acid or its salt has a function as a dopant in addition to the function as an oxidizing agent. As the sulfonic acid or its salt, the low-molecular sulfonic acid or its salt exemplified for the dopant is used.

[0068] The step of forming the conductive polymer layer by immersion in the treatment liquid and polymerization (or drying) may be performed once, or may be repeated a plurality of times. In each time, the conditions such as the composition and viscosity of the treatment liquid may be the same, or at least one condition may be changed.

[0069] (v) Liquid component impregnation step In this step, the capacitor element 10 may be impregnated with the liquid component. Thereby, an electrolytic capacitor having a conductive polymer and a liquid component is obtained. This step is performed after the third step. The liquid component may be impregnated into the capacitor element 10, for example, by accommodating the capacitor element 10 and the liquid component in a container, by immersing the capacitor element 10 in the liquid component, or by dropping the liquid component onto the capacitor element 10.

[0070] The liquid component is prepared prior to this step. The liquid component can be prepared by mixing the constituent components.

[0071] (vi) Step of sealing the capacitor element 10 The capacitor element 10 is housed in the bottomed case 101 such that the lead wires 104A and 104B are positioned on the opening side of the bottomed case 101. The bottomed case 101 also houses the liquid component. Next, the opening of the bottomed case 101 is closed with a sealing body 102 through which each lead wire passes, the opening end is caulked to the sealing body 102 and curled, and if a seat plate 103 is arranged on the curled portion, an electrolytic capacitor as shown in FIG. 1 is completed.

[0072] In the above embodiment, the wound type electrolytic capacitor has been described, but the application range of the present invention is not limited to the above, and it can also be applied to other electrolytic capacitors, for example, a chip type electrolytic capacitor using a sintered body of metal as the anode body, or a multilayer type electrolytic capacitor using a metal plate as the anode body.

[0073] [Examples] Hereinafter, the present invention will be specifically described based on examples and comparative examples, but the present invention is not limited to the following examples.

[0074] 《Fabrication of Electrolytic Capacitors E1 to E12 and C1 to C6》 [Manufacture of Electrolytic Capacitors] A wound type electrolytic capacitor (diameter 10 mm × L (length) 10 mm) with a rated voltage of 25 V and a rated capacitance of 330 μF was fabricated. The following describes the specific manufacturing method of the electrolytic capacitor.

[0075] (Preparation of Anode Body) An aluminum foil with a thickness of 100 μm was subjected to an etching treatment to roughen the surface of the aluminum foil. Thereafter, a dielectric layer was formed on the surface of the aluminum foil by a forming treatment. The forming treatment was performed by immersing the aluminum foil in an ammonium adipate solution and applying a voltage of 180 V thereto. Thereafter, the aluminum foil was cut to prepare an anode body.

[0076] (Preparation of the cathode body) An aluminum foil with a thickness of 50 μm was subjected to an etching treatment to roughen the surface of the aluminum foil. Then, the aluminum foil was cut to prepare a cathode body.

[0077] (Fabrication of the wound body) An anode lead tab and a cathode lead tab were connected to the anode body and the cathode body, respectively, and the anode body and the cathode body were wound through a separator while involving the lead tabs. An anode lead wire and a cathode lead wire were respectively connected to the ends of each lead tab protruding from the wound body. The fabricated wound body was subjected to a formation treatment again, and a dielectric layer was formed on the cut end of the anode body. Next, the end of the outer surface of the wound body was fixed with a winding tape to fabricate a wound body.

[0078] (Preparation of the polymer dispersion) The first monomer shown in Table 1 and, if necessary, other monomers (the second monomer or the third monomer) and polystyrene sulfonic acid (PSS, weight average molecular weight 100,000), which is a polymer dopant, were dissolved in ion-exchanged water to prepare a mixed solution. When other monomers were used, the amount of the other monomers was the amount shown in Table 1 with respect to 100 parts by mass of the first monomer.

[0079] While stirring the mixed solution, iron(III) sulfate (oxidizing agent) dissolved in ion-exchanged water was added to carry out a polymerization reaction. After the reaction, the obtained reaction solution was dialyzed to remove unreacted monomers and excess oxidizing agent, and a polymer dispersion containing a polymer containing a first monomer unit (and, if necessary, a second monomer unit or a third monomer unit) doped with about 5% by mass of PSS was obtained.

[0080] (Formation of the conductive polymer layer) In a reduced-pressure atmosphere (40 kPa), a winding body was immersed in a polymer dispersion contained in a predetermined container for 5 minutes, and then the winding body was pulled out from the polymer dispersion. Next, the winding body impregnated with the polymer dispersion was dried in a drying furnace at 150°C for 20 minutes to form a conductive polymer layer covering at least a part of the dielectric layer. In this way, a capacitor element was formed.

[0081] (Assembly of electrolytic capacitor) If necessary, together with the liquid components shown in Table 1, the capacitor element was housed in a case, and the opening of the case was sealed using a sealing body to complete an electrolytic capacitor as shown in Fig. 1. When using the liquid component, 200 mg of the liquid component was housed in the case, and in a reduced-pressure atmosphere (40 kPa), the capacitor element was impregnated with the liquid component over 5 minutes. Regarding the assembled electrolytic capacitor, an aging treatment was performed at 130°C for 2 hours while applying the rated voltage.

[0082] [Evaluation] (Measurement of capacitance, tanδ, and ESR) In an environment at 20°C, using an LCR meter, the initial capacitance (μF), tanδ, and ESR (mΩ) at a frequency of 100 kHz / Ω of the obtained electrolytic capacitor were measured. Also, in order to evaluate the long-term reliability, it was held at 145°C for 2000 hours while applying the rated voltage, and the increase rate of ESR (ΔESR) was confirmed. ΔESR was expressed as the ratio (Z / Z0 × 100%) of the ESR (Z) of the electrolytic capacitor after holding at 145°C to the initial ESR (Z0). ESR (Z) was measured in the same manner as in the case of the initial ESR using the electrolytic capacitor after holding at 145°C.

[0083] The evaluation results are shown in Table 1. In Table 1, E1 to E12 are examples, and C1 to C6 are comparative examples.

[0084]

Table 1

Industrial applicability

[0085] The electrolytic capacitor of the present disclosure can be used as a solid electrolytic capacitor or a hybrid electrolytic capacitor. The electrolytic capacitor is also suitable for applications that require high heat resistance. However, the applications of the electrolytic capacitor are not limited to these.

Description of Reference Numerals

[0086] 100: Electrolytic capacitor 101: Bottomed case 102: Sealing body 103: Base plate 104A, 104B: Lead wires 105A, 105B: Lead tabs 10: Capacitor element 11: Anode body 12: Cathode body 13: Separator 14: Winding tape

Claims

1. A capacitor element comprising an anode body having a dielectric layer on its surface and a conductive polymer covering a part of the dielectric layer, wherein the conductive polymer includes a first monomer unit corresponding to a 3,4-ethylenedioxythiophene compound and a second monomer unit corresponding to a 3,4-dialkoxythiophene compound, the conductive polymer further includes a polymeric dopant, and an amount of the second monomer unit in the conductive polymer is 0.008 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the first monomer unit. An electrolytic capacitor.

2. The electrolytic capacitor according to claim 1, further comprising a liquid component.

3. The electrolytic capacitor according to claim 2, wherein the liquid component includes at least one selected from the group consisting of a glycerin compound and a polyalkylene glycol compound.

4. The electrolytic capacitor according to claim 2 or 3, wherein the liquid component includes a solute.

5. An amount of the second monomer unit in the conductive polymer is 0.01 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the first monomer unit. The electrolytic capacitor according to any one of claims 1 to 4.

6. A first step of preparing an anode body, a second step of forming a dielectric layer on the surface of the anode body, and a third step of treating the anode body having the dielectric layer formed thereon with a treatment liquid containing a conductive polymer. The method for manufacturing an electrolytic capacitor, wherein the treatment liquid further includes a polymeric dopant, the conductive polymer includes a first monomer unit corresponding to a 3,4-ethylenedioxythiophene compound and a second monomer unit corresponding to a 3,4-dialkoxythiophene compound, and an amount of the second monomer unit in the conductive polymer is 0.008 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the first monomer unit.

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