Electrolytic capacitor and method of manufacturing the same

Abstract

An electrolytic capacitor includes a capacitor element. The capacitor element comprises: a separator; a foil-shaped anode and a foil-shaped cathode facing each other with the separator interposed therebetween; and an electrolyte layer in contact with the anode, cathode, and separator. The electrolyte layer contains a first conductive polymer and a first compound having a melting point of 50°C or higher, which is at least one compound selected from the group consisting of sugars and polyols. The electrolyte layer has a localized portion where the first compound is localized.

Description

Technical Field

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

[0002] Capacitors used in electronic devices are required to have high capacitance and low equivalent series resistance (ESR) in high-frequency regions. Electrolytic capacitors using conductive polymers such as polypyrrole, polythiophene, polyfuran, and polyaniline are promising high-capacity, low-ESR capacitors. Patent Document 1 discloses a method in which a dispersion containing a conductive polymer and a solvent is impregnated into a capacitor element formed by winding an anode foil and a cathode foil with a separator interposed therebetween.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2008-10657 Summary of the Invention

[0006] Problems to be solved by the invention

[0007] In order to achieve better characteristics (particularly lower ESR), it is necessary to increase the amount of the conductive polymer filled between the anode foil and the cathode foil.

[0008] Under such circumstances, one object of the present invention is to provide an electrolytic capacitor with high characteristics and a method for manufacturing the same.

[0009] Means for solving problems

[0010] One aspect of the present invention relates to a method for manufacturing an electrolytic capacitor. The method includes: step (i) forming a capacitor element precursor comprising a separator, and a foil-shaped anode and a foil-shaped cathode facing each other with the separator interposed therebetween; step (ii) placing a first compound having a melting point of 50°C or higher, which is at least one compound selected from the group consisting of sugars and polyols, within the capacitor element precursor; and step (iii) forming a first layer containing a first conductive polymer within the capacitor element precursor that has undergone step (ii). Step (iii) includes step (iii-a) impregnating the capacitor element precursor that has undergone step (ii) with a first aqueous dispersion containing the first conductive polymer; and step (iii-b) drying the impregnated first aqueous dispersion to form the first layer.

[0011] Another aspect of the present invention relates to an electrolytic capacitor. The electrolytic capacitor includes a capacitor element comprising a separator, a foil-shaped anode body and a foil-shaped cathode body facing each other with the separator interposed therebetween, and an electrolyte layer in contact with the anode body, the cathode body, and the separator. The electrolyte layer contains a first compound having a melting point of 50°C or higher, which is at least one compound selected from the group consisting of sugars and polyols, and a first conductive polymer. The electrolyte layer has a localized portion in which the first compound is unevenly distributed.

[0012] Effects of the Invention

[0013] According to the present invention, an electrolytic capacitor with high characteristics can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a cross-sectional view schematically showing an example of the electrolytic capacitor of the present invention.

[0015] Figure 2 It is schematically represented Figure 1 A diagram of a portion of an electrolytic capacitor is shown.

[0016] Figure 3 This is a cross-sectional view schematically showing a portion of an example of a capacitor element included in the electrolytic capacitor of the present invention.

[0017] Figure 4 This is a cross-sectional view schematically showing a portion of another example of a capacitor element included in the electrolytic capacitor of the present invention. DETAILED DESCRIPTION

[0018] Hereinafter, embodiments of the present invention will be described with examples, but the present invention is not limited to the examples described below. In the following description, specific numerical values ​​and materials are sometimes illustrated, but other numerical values ​​and materials may also be applied as long as the effects of the present invention can be obtained. It should be noted that, in the following description, unless otherwise specified, the melting point is the value under 1 atmosphere. In addition, unless otherwise specified, the viscosity is the value at room temperature (25°C) and 1 atmosphere.

[0019] As a result of their research, the inventors of the present application have discovered that an electrolytic capacitor with high performance can be obtained by filling a capacitor element precursor with a conductive polymer using a specific method. The present invention is based on this new finding.

[0020] (Electrolytic Capacitors)

[0021] The electrolytic capacitor of the present invention is an electrolytic capacitor including a capacitor element. The capacitor element includes a separator, a foil-shaped anode body and a foil-shaped cathode body facing each other with the separator interposed therebetween, and an electrolyte layer in contact with the anode body, the cathode body, and the separator. The electrolyte layer contains a first compound having a melting point of 50°C or higher, which is at least one compound selected from the group consisting of sugars and polyols, and a first conductive polymer. The electrolyte layer has a localized portion in which the first compound is localized. The electrolytic capacitor of the present invention can be the first electrolytic capacitor described below or the second electrolytic capacitor described below. The first electrolytic capacitor and the second electrolytic capacitor have different electrolyte layers. However, in the example of the embodiment, embodiments belonging to both the first electrolytic capacitor and the second electrolytic capacitor are included.

[0022] The electrolyte layer of the first electrolytic capacitor has a localized portion where the first compound is localized in at least one portion selected from the group consisting of a portion in contact with the anode body, a portion in contact with the cathode body, and a portion in contact with the separator.

[0023] The localized portion containing the first compound may be located in at least a portion of the portion in contact with the anode body, or in at least a portion of the portion in contact with the cathode body, or in at least a portion of the portion in contact with the separator, or in at least a portion of two or more portions thereof (for example, all portions).

[0024] The electrolyte layer of the second electrolytic capacitor includes a second layer formed on at least a portion of the surfaces of the anode and cathode bodies and containing a second conductive polymer, and a first layer formed at least on the second layer and containing a first conductive polymer. Furthermore, the electrolyte layer of the second electrolytic capacitor includes a localized portion in which the first compound is localized, at least in a portion of the interface contacting the first and second layers.

[0025] The first compound present in the aforementioned localized portion utilizes its hydroxyl groups to improve the fixability of the first conductive polymer. As a result, excellent properties (particularly low ESR) can be achieved. Furthermore, the improved fixability of the first conductive polymer enhances the stability of the electrolyte layer, thereby improving the reliability of the electrolytic capacitor. Furthermore, by localizing the first compound, the conductive polymer layer in this portion can be formed thicker.

[0026] The electrolyte layer of the first electrolytic capacitor can be formed from the first compound and the first conductive polymer, or from these and other substances. The electrolyte layer of the second electrolytic capacitor can be formed from the first compound and the first and second conductive polymers, or from these and other substances. As described later, the electrolyte layer of the electrolytic capacitor of the present invention can be an electrolyte layer (mixed electrolyte layer) containing a conductive polymer and a liquid component (non-aqueous solvent or non-aqueous electrolyte) described later. As the first and second conductive polymers (and dopants added thereto) and the liquid component, substances used in known electrolyte layers of electrolytic capacitors can be used.

[0027] The electrolyte layer of the electrolytic capacitor of the present invention is a layer containing the aforementioned conductive polymer as a primary component (e.g., a content of 50% by mass or greater). It should be noted that if the electrolyte layer contains a liquid component, the liquid component is not taken into account when calculating the content of the conductive polymer in the electrolyte layer.

[0028] (First Compound)

[0029] The first compound contained in the electrolyte layer of the electrolytic capacitor of the present invention is described below. The first compound is at least one compound selected from the group consisting of sugars and polyols, and has a melting point of 50°C or higher. The melting point of the first compound is preferably higher than the temperature at which the capacitor is used. The melting point of the first compound can be in the range of 80°C to 300°C (e.g., 120°C to 300°C).

[0030] Examples of sugars include glucose. Examples of polyols include mannitol, sorbitol, xylitol, pentaerythritol, and trimethylolpropane. It should be noted that mannitol, sorbitol, xylitol, pentaerythritol, and the like are sometimes referred to as sugar alcohols. The first compound may also be a sugar alcohol.

[0031] The number of hydroxyl groups contained in the first compound may be in the range of 2 to 12 (eg, in the range of 2 to 4). Usually, the first compound is a water-soluble compound.

[0032] From another perspective, an organic compound containing a plurality of hydroxyl groups (-OH) bonded to carbon atoms (e.g., an organic compound that is not a polymer) and having a melting point within the above-mentioned range may also be used as the first compound. The molecular weight of the organic compound and the number of hydroxyl groups contained in the organic compound may each be within the above-mentioned ranges exemplified for the first compound.

[0033] The first compound may be at least one selected from the group consisting of glucose, mannitol, sorbitol, xylitol, pentaerythritol, and trimethylolpropane. The melting point of glucose is about 146-150°C, the melting point of mannitol is about 165-169°C, the melting point of sorbitol is about 93-95°C, the melting point of xylitol is about 92-97°C, the melting point of pentaerythritol is about 257-260°C, and the melting point of trimethylolpropane is about 56-58°C. It should be noted that these substances sometimes fluctuate in melting point due to differences in structure (stereoisomers). Glucose, mannitol, and pentaerythritol are preferred because of their high melting points.

[0034] (First conductive polymer)

[0035] The first conductive polymer (conductive polymer) used in the electrolytic capacitor of the present invention is described below. Examples of the first conductive polymer include polypyrrole, polythiophene, polyfuran, polyaniline, polyacetylene and their derivatives. The derivatives include polymers with polypyrrole, polythiophene, polyfuran, polyaniline and polyacetylene as basic skeletons. For example, polythiophene derivatives include poly(3,4-ethylenedioxythiophene) and the like. These conductive polymers can be used alone or in combination. In addition, the first conductive polymer can also be a copolymer of two or more monomers. The weight average molecular weight of the first conductive polymer is not particularly limited, for example, it can be in the range of 1000 to 100000. A preferred example of the first conductive polymer is poly(3,4-ethylenedioxythiophene) (PEDOT).

[0036] A dopant can be added to the first conductive polymer. From the viewpoint of suppressing dedoping from the first conductive polymer, a polymer dopant is preferably used. Examples of polymer dopants include polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallyl sulfonic acid, polyacryloyl sulfonic acid, polymethacryloyl sulfonic acid, poly(2-acrylamide-2-methylpropane sulfonic acid), polyisoprene sulfonic acid, polyacrylic acid, etc. They can be used alone or in combination of two or more. They can be added in the form of a salt. The polymer dopant can exist in the electrolyte in the form of an anion in which a cation (such as a proton) is dissociated from at least a portion of the acidic group. A preferred example of a dopant is polystyrene sulfonic acid (PSS).

[0037] The weight average molecular weight of the dopant is not particularly limited, but can be set in the range of 1,000 to 100,000 from the viewpoint of facilitating the formation of a uniform electrolyte layer.

[0038] The first conductive polymer may be poly(3,4-ethylenedioxythiophene) doped with polystyrenesulfonic acid.

[0039] The polymers exemplified for the first conductive polymer can be used as the second conductive polymer forming the second layer of the second electrolytic capacitor. The first conductive polymer and the second conductive polymer may be the same or different.

[0040] The second layer of the electrolyte layer of the second electrolytic capacitor may contain a second compound having a melting point of 50°C or higher, which is at least one compound selected from the group consisting of sugars and polyols. The compounds exemplified for the first compound can be used as the second compound. The first and second compounds may be the same or different.

[0041] When the above-mentioned second layer contains the second compound, the second layer may have a partial portion in which the second compound is partial in at least one portion selected from a group consisting of a portion in contact with the anode body, a portion in contact with the cathode body, and a portion in contact with the separator.

[0042] The electrolyte layer of the electrolytic capacitor of the present invention may contain a non-aqueous solvent or a non-aqueous electrolyte solution. Hereinafter, the non-aqueous solvent and the non-aqueous electrolyte solution contained in the electrolyte layer may be collectively referred to as the "liquid component (L)." The liquid component (L) may be a substance that is liquid at room temperature (25°C) or a substance that is liquid at the temperature at which the electrolytic capacitor is used. A preferred example of the liquid component (L) is a liquid that does not substantially dissolve the first compound.

[0043] The non-aqueous solvent may be an organic solvent or an ionic liquid. Examples of non-aqueous solvents include polyols such as ethylene glycol and propylene glycol, cyclic sulfones such as sulfolane (SL), lactones such as γ-butyrolactone (γBL), amides such as N-methylacetamide, N,N-dimethylformamide, and N-methyl-2-pyrrolidone, esters such as methyl acetate, carbonate compounds such as propylene carbonate, ethers such as 1,4-dioxane, ketones such as methyl ethyl ketone, and formaldehyde.

[0044] In addition, a polymer solvent can also be used as a non-aqueous solvent. In the example of a polymer solvent, at least one of the hydroxyl groups in the polyalkylene glycol, the derivative of the polyalkylene glycol, and the polyol is substituted with a compound of polyalkylene glycol (including derivatives) etc. Specifically, in the example of a polymer solvent, polyethylene glycol (PEG), polyethylene glycol glyceryl ether, polyethylene glycol diglyceryl ether, polyethylene glycol sorbitol ether, polypropylene glycol, polypropylene glycol glyceryl ether, polypropylene glycol diglyceryl ether, polypropylene glycol sorbitol ether, polybutylene glycol etc. are included. In the example of a polymer solvent, a copolymer of ethylene glycol-propylene glycol, a copolymer of ethylene glycol-butylene glycol, a copolymer of propylene glycol-butylene glycol etc. are also included. One non-aqueous solvent can be used alone or two or more can be mixed.

[0045] The liquid component (L) may contain an acid component and an alkali component. Examples of the acid component include maleic acid, phthalic acid, benzoic acid, pyromellitic acid, and resorcinic acid. Examples of the alkali component include 1,8-diazabicyclo[5,4,0]undec-7-ene, 1,5-diazabicyclo[4,3,0]non-5-ene, 1,2-dimethylimidazolinium, 1,2,4-trimethylimidazoline, 1-methyl-2-ethyl-imidazoline, 1,4-dimethyl-2-ethylimidazoline, 1-methyl-2-heptylimidazoline, 1-methyl-2-(3'heptyl)imidazoline, 1-methyl-2-dodecylimidazoline, 1,2-dimethyl-1,4,5,6-tetrahydropyrimidine, 1-methylimidazole, and 1-methylbenzimidazole.

[0046] The non-aqueous electrolyte comprises a non-aqueous solvent and a solute (e.g., an organic salt) dissolved therein. Examples of non-aqueous solvents forming the non-aqueous electrolyte include the aforementioned examples of non-aqueous solvents. Examples of solutes include inorganic salts and organic salts. The so-called organic salt is a salt in which at least one of the anion and the cation contains an organic substance. Examples of organic salts include trimethylamine maleate, triethylamine boronate disalicylate, ethyldimethylamine phthalate, mono-1,2,3,4-tetramethylimidazolinium phthalate, and mono-1,3-dimethyl-2-ethylimidazolinium phthalate.

[0047] In order to suppress dedoping of the dopant, the pH of the liquid component (L) may be set to less than 7, or may be set to 5 or less.

[0048] The capacitor element of the electrolytic capacitor of the present invention may be a wound capacitor element or a stacked capacitor element. In one example of a wound capacitor element, a foil-shaped anode body, a foil-shaped cathode body, and a separator are wound together, with a separator disposed between the anode body and the cathode body. In one example of a stacked capacitor element, a foil-shaped anode body, a foil-shaped cathode body, and a separator are folded into a zigzag shape, with a separator disposed between the anode body and the cathode body.

[0049] The anode body, cathode body, and separator of the electrolytic capacitor of the present invention are not particularly limited, and known members can be used. Specific examples of these will be described below.

[0050] (Anode)

[0051] The anode body has a dielectric layer on its surface. A metal foil having a dielectric layer formed on its surface can be used as the anode body. The type of metal forming the metal foil is not particularly limited. From the perspective of ease of forming the dielectric layer, examples of metals forming the metal foil include valve metals such as aluminum, tantalum, niobium, and titanium, as well as alloys of valve metals. A preferred example is aluminum and aluminum alloys. Typically, the surface of the anode body is roughened, and the dielectric layer is formed on the roughened surface. The electrolyte layer is in contact with the dielectric layer of the anode body.

[0052] (Cathode)

[0053] A metal foil can be used as the cathode body. The type of metal forming the metal foil is not particularly limited. Examples of metals forming the metal foil include metals having valve functions such as aluminum, tantalum, niobium, and titanium, and alloys of metals having valve functions. A preferred example is aluminum and aluminum alloys. In addition, a chemically generated covering film can be provided on the surface of the cathode body, and a film of a metal (heterogeneous metal) or a non-metallic film different from the metal forming the cathode body can also be provided. Examples of heterogeneous metals and non-metals include metals such as titanium and non-metals such as carbon.

[0054] (Spacer)

[0055] A sheet-like material that can be impregnated with an electrolyte can be used as the separator. For example, a sheet-like material that is insulating and can be impregnated with an electrolyte can be used. The separator can be a woven fabric, a non-woven fabric, or a porous membrane. Examples of separator materials include cellulose, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, vinylon, nylon, aromatic polyamide, polyimide, polyamideimide, polyetherimide, rayon, and glass.

[0056] The electrolyte of the electrolytic capacitor of the present invention contains a first compound. The first compound can improve the strength of the spacer. If a weak spacer (for example, a spacer formed from cellulose-based natural fibers) is used, there is a case where characteristics such as withstand voltage are reduced. By using the first compound, such a reduction in characteristics can be suppressed. It should be noted that the effect of strengthening the spacer can be achieved regardless of the type of spacer.

[0057] (Method for Manufacturing Electrolytic Capacitor)

[0058] An example of the method of the present invention for manufacturing an electrolytic capacitor is described below. According to this manufacturing method, the electrolytic capacitor of the present invention can be manufactured. Since the matters described for the electrolytic capacitor of the present invention can be applied to the following manufacturing method, repeated descriptions are sometimes omitted. For example, since the constituent elements of the electrolytic capacitor of the present invention (constituent elements of the anode body, cathode body, separator, and electrolyte layer) have been described above, repeated descriptions are sometimes omitted. Specifically, since the first and second compounds, the first and second conductive polymers, the separator and the liquid component (L) have been described above, repeated descriptions are sometimes omitted. In addition, the matters described below can be applied to the above-mentioned electrolytic capacitor of the present invention.

[0059] An example of a production method for producing an electrolytic capacitor is described below. This production method includes steps (i) to (iii).

[0060] (Process (i))

[0061] Step (i) is a step of forming a capacitor element precursor including a separator and a foil-shaped anode body and a foil-shaped cathode body facing each other with the separator interposed therebetween. The capacitor element precursor is a capacitor element before the electrolyte layer is formed.

[0062] The foil-shaped anode body can be formed using known methods. For example, first, a metal foil serving as the raw material for the anode body is prepared, and the surface of the metal foil is roughened. Roughening can be performed, for example, by etching using direct current electrolysis or alternating current electrolysis. A dielectric layer is then formed on the roughened surface of the metal foil. The dielectric layer can be formed, for example, by subjecting the metal foil to a chemical conversion treatment. The chemical conversion treatment of the metal foil oxidizes the surface of the metal foil, thereby forming the dielectric layer as an oxide film. The anode body is formed by the above-described operation.

[0063] Note that, as necessary, lead terminals for electrical connection are connected to the anode body and the cathode body.

[0064] When the first electrolytic capacitor is a wound type capacitor, for example, a capacitor element precursor can be formed by winding a foil-shaped anode body, a foil-shaped cathode body, and a separator together. In this case, the anode body and the cathode body are wound with a separator interposed therebetween.

[0065] In the case of a laminated capacitor, the capacitor element precursor can be formed by, for example, bending a foil-shaped anode body, a foil-shaped cathode body, and a separator together in a zigzag shape. In this case, the anode body and the cathode body are bent so that the separator is disposed between them.

[0066] (Step (ii))

[0067] Step (ii) is a step of placing a first compound having a melting point of 50°C or higher, which is at least one compound selected from the group consisting of sugars and polyols, within the capacitor element precursor. Step (ii) may also be a step of precipitating the first compound within the capacitor element precursor. Therefore, in the following description, "placement" may be referred to as "precipitation."

[0068] Step (ii) includes step (ii-a) and step (ii-b). Step (ii-a) is a step of impregnating the capacitor element precursor with the first aqueous treatment liquid containing the first compound.

[0069] Step (ii-a) can be performed, for example, by immersing the capacitor element precursor in a first aqueous treatment liquid. The immersion time is not limited and can be 1 minute or more and less than 20 minutes. The entire capacitor element precursor can be immersed in the first aqueous treatment liquid, or only a portion of the capacitor element precursor can be immersed in the first aqueous treatment liquid. For example, only a portion of the capacitor element precursor in the longitudinal direction (axial direction in the case of a wound body) of 50% or less can be immersed in the first aqueous treatment liquid.

[0070] Step (ii-a) can be carried out at room temperature or at a temperature other than room temperature (e.g., a temperature higher than room temperature). In addition, step (ii-a) can be carried out at atmospheric pressure or at an environment other than atmospheric pressure (e.g., under reduced pressure).

[0071] The first aqueous treatment liquid is a treatment liquid containing water. The amount of water contained in the liquid (solvent) forming the first aqueous treatment liquid is, for example, in the range of 50 to 100% by mass. Typically, the first compound is dissolved in the first aqueous treatment liquid. In other words, the first aqueous treatment liquid can be a solution in which the first compound is dissolved. In a typical example, the first aqueous treatment liquid is an aqueous solution of the first compound.

[0072] The content (concentration) of the first compound in the first aqueous treatment liquid (eg, aqueous solution of the first compound) may be in the range of 3 to 50% by mass (eg, 5 to 15% by mass). The first aqueous treatment liquid may contain components other than the first compound as needed.

[0073] The first aqueous treatment liquid may not contain a macromolecule (polymer). For example, the first aqueous treatment liquid may not contain a first conductive macromolecule. The first aqueous treatment liquid without a macromolecule has a low viscosity, making it easier to infiltrate the capacitor element precursor. Here, the so-called macromolecule refers to a polymer with a weight-average molecular weight of 1000 or more.

[0074] Step (ii-b) is a step of configuring the first compound inside the capacitor element precursor by drying the impregnated first aqueous treatment liquid. Drying is usually performed by heating. Step (ii-b) can be performed under atmospheric pressure or under an environment other than atmospheric pressure (e.g., under reduced pressure). The drying temperature in step (ii-b) can be a temperature above the melting point of the first compound. In addition, it can also be a temperature above the boiling point of the first aqueous treatment liquid under the pressure of the drying step (ii-b) (e.g., above 100°C). In a preferred example, the drying temperature in step (ii-b) is a temperature above the boiling point of the first aqueous treatment liquid under the pressure of the drying step (ii-b) (e.g., above 100°C), and is a temperature above the melting point and below the boiling point of the first compound under the pressure of the drying step (ii-b). By drying at a temperature above the melting point of the first compound, the permeability of the first compound to the capacitor element precursor can be improved.

[0075] It should be noted that step (ii) may be repeated as needed. By repeating step (ii), the amount of the precipitated first compound can be increased.

[0076] Alternatively, step (ii) may be performed by impregnating the capacitor element precursor with the melt of the first compound while raising the temperatures of the first compound and the capacitor element precursor to a temperature equal to or higher than the melting point of the first compound.

[0077] (Process (iii))

[0078] Step (iii) is a step of forming a first layer containing a first conductive polymer within the capacitor element precursor that has undergone step (ii). Hereinafter, the first layer formed in step (iii) may be referred to as "first layer (CL1)." The first layer (CL1) is a layer that can serve as the electrolyte layer of the first electrolytic capacitor. Furthermore, the first layer (CL1) is a layer that can serve as the first layer of the electrolyte layer of the second electrolytic capacitor.

[0079] Step (iii) includes step (iii-a) and step (iii-b). Step (iii-a) is a step of impregnating the capacitor element precursor after step (ii) with the first aqueous dispersion containing the first conductive polymer.

[0080] Step (iii-a) can be performed, for example, by immersing the capacitor element precursor in a first aqueous dispersion. The immersion time is not limited and can be from 1 second to 30 minutes. The entire capacitor element precursor can be immersed in the first aqueous dispersion, or only a portion of the capacitor element precursor can be immersed in the first aqueous dispersion. For example, only a portion of the capacitor element precursor in the longitudinal direction (axial direction in the case of a wound body) of 50% or less can be immersed in the first aqueous dispersion.

[0081] Step (iii-a) can be carried out at room temperature or at a temperature other than room temperature (e.g., a temperature higher than room temperature). In addition, step (iii-a) can be carried out at atmospheric pressure or at an environment other than atmospheric pressure (e.g., under reduced pressure).

[0082] The first aqueous dispersion is a treatment liquid containing water. The amount of water contained in the aqueous liquid (dispersion medium) forming the first aqueous dispersion is, for example, in the range of 2 to 100% by mass. The aqueous liquid can be water. The first conductive polymer is dispersed in the aqueous liquid. In other words, the first aqueous dispersion is a suspension in which the first conductive polymer is dispersed in the aqueous liquid.

[0083] The content (concentration) of the first conductive polymer in the first aqueous dispersion can be in the range of 0.1 to 20% by mass (eg, in the range of 0.5 to 3% by mass).

[0084] The viscosity of the first aqueous dispersion may be in the range of 1 mPa·s to 100 mPa·s, or in the range of 1 mPa·s to 40 mPa·s (eg, 1 mPa·s to 25 mPa·s). The lower the viscosity of the first aqueous dispersion, the easier it is to impregnate the capacitor element precursor.

[0085] The first aqueous dispersion preferably does not contain the aforementioned first compound. By not adding the first compound, the viscosity of the first aqueous dispersion can be reduced. Even when the first aqueous dispersion contains the first compound, it is preferably included within a range where the viscosity of the first aqueous dispersion is below a certain value (e.g., 40 mPa·s or less, 25 mPa·s or less).

[0086] As described above, a dopant may be added to the first conductive polymer. In addition, the first aqueous dispersion may contain components other than the first conductive polymer and the dopant, as needed.

[0087] Step (iii-b) is a step of drying the impregnated first aqueous dispersion to form the first layer (CL1). When step (X), described below, is not performed (i.e., when manufacturing the first electrolytic capacitor), the first layer (CL1) is in contact with the separator. In this case, the first layer (CL1) may also be in contact with the anode and / or cathode. Typically, the first layer (CL1) comprises the first conductive polymer as its main component.

[0088] The method for drying the first aqueous dispersion is not particularly limited. Drying can be carried out in at least one atmosphere selected from a dry atmosphere, a reduced pressure atmosphere, and a heated atmosphere, and usually at least heating is performed. In a preferred example, the heating temperature in step (iii-b) is a temperature above the boiling point of the first aqueous dispersion under the pressure of the drying of step (iii-b) (for example, above 100°C), and a temperature below the melting point of the first compound under the pressure of the drying of step (iii-b). Alternatively, the heating temperature in step (iii-b) is a temperature above the boiling point of the first aqueous dispersion under the pressure of the drying of step (iii-b) (for example, above 100°C), and a temperature above the melting point of the first compound under the pressure of the drying of step (iii-b) and below the boiling point.

[0089] In order to achieve high characteristics (such as low ESR), it is necessary to increase the content of the conductive polymer in the electrolyte layer. To this end, it is important to improve the fixability of the conductive polymer. As one of the methods to improve the fixability of the conductive polymer, it is conceivable to add a polyol or the like to the aqueous dispersion of the conductive polymer. However, if a polyol or the like is added to the aqueous dispersion, the viscosity of the aqueous dispersion increases, thereby causing the problem that the impregnation of the aqueous dispersion becomes difficult. In the manufacturing method of the present invention, first, after being treated with a first aqueous treatment liquid containing a first compound, the first aqueous dispersion is impregnated. Therefore, the impregnation of the first aqueous dispersion is easy. In addition, by pre-arranging the first compound in the capacitor element precursor, the first conductive polymer impregnated thereafter can be firmly fixed. As a result, an electrolytic capacitor with high characteristics can be manufactured.

[0090] As examples of the manufacturing method of the present invention, a first manufacturing method (M1) and a second manufacturing method (M2) are described below. The first manufacturing method (M1) can be used to manufacture a first electrolytic capacitor, and the second manufacturing method (M2) can be used to manufacture a second electrolytic capacitor.

[0091] In the first production method (M1), the first compound is disposed on at least a portion of at least one surface (S1) selected from the surface of the anode body, the surface of the cathode body, and the surface of the separator.

[0092] In the first manufacturing method (M1), in step (ii-a), the first aqueous treatment liquid can be impregnated into the capacitor element precursor so that the first aqueous treatment liquid contacts at least a portion of at least one surface (S1) selected from the group consisting of the surface of the anode body, the surface of the cathode body, and the surface of the separator. Subsequently, in step (ii-b), the first compound can be arranged on at least a portion of the at least one surface (S1) by drying the impregnated first aqueous treatment liquid. According to this configuration, step (iii) is performed in a state where the first compound is separated from at least a portion of the surface (S1) to form the first layer (CL1). The formed first layer (CL1) has a localized portion in which the first compound is localized in at least a portion of at least one portion selected from the group consisting of the portion in contact with the anode body, the portion in contact with the cathode body, and the portion in contact with the separator. Therefore, the first conductive polymer in the first layer (CL1) is fixed by the first compound. Step (ii-a) can be performed by treating the capacitor element precursor with the first aqueous treatment liquid after assembling the capacitor element precursor and before impregnating the conductive polymer with the aqueous dispersion.

[0093] (Process (X))

[0094] The second manufacturing method (M2) may further include a step (X) between steps (i) and (ii). Step (X) includes steps (Xa) and (Xb). Step (Xa) is a step of impregnating the capacitor element precursor with a second aqueous dispersion containing a second conductive polymer. Step (Xb) is a step of drying the impregnated second aqueous dispersion to form a second layer containing a second conductive polymer on at least a portion of the surface of the anode and cathode bodies. Hereinafter, this second layer may be referred to as "second layer (CL2)". The second layer (CL2) is a conductive polymer layer.

[0095] Step (Xa) and step (Xb) are performed in the same manner as step (iii-a) and step (iii-b), respectively, except that a second conductive polymer is used instead of the first conductive polymer. For example, a second aqueous dispersion can be prepared in the same manner as the first aqueous dispersion, except that a second conductive polymer is used instead of the first conductive polymer. As described above, the second conductive polymer may be the same as or different from the first conductive polymer. Furthermore, the conditions for carrying out step (iii) may be the same as or different from those for carrying out step (X).

[0096] In one example, the average particle size of the second conductive polymer can be made smaller than the average particle size of the first conductive polymer. Here, the average particle size is the volume-based median diameter (D 50 For example, the median diameter (D 50The average particle size of the first conductive polymer can be in the range of 0.1 μm to 0.5 μm. The average particle size of the second conductive polymer can be in the range of 0.01 μm to 0.2 μm. Within these ranges, the average particle size of the second conductive polymer can be smaller than the average particle size of the first conductive polymer.

[0097] In the manufacturing method (M2), in the step (ii), the first compound is disposed on the second layer (CL2).

[0098] In the manufacturing method (M2), in step (ii-a), the first aqueous treatment liquid can be impregnated into the capacitor element precursor that has undergone step (X), and in step (ii-b), the impregnated first aqueous treatment liquid can be dried, thereby configuring the first compound on the surface of the second layer (CL2). According to this configuration, step (iii) is performed in a state where the first compound is precipitated on the surface of the second layer (CL2) to form the first layer (CL1). Therefore, the electrolyte layer of the second electrolytic capacitor has a partial portion where the first compound is partial in contact with at least a portion of the interface between the first layer (CL1) and the second layer (CL2). According to this configuration, the conductive polymer can be firmly fixed at the interface between the first layer (CL1) and the second layer (CL2).

[0099] In manufacturing method (M2), the second aqueous dispersion may contain a second compound having a melting point of 50°C or higher, which is at least one compound selected from the group consisting of sugars and polyols. In this case, the viscosity of the second aqueous dispersion increases, resulting in poor permeability. However, by subsequently performing steps (ii) and (iii), the filling rate of the first conductive polymer can be increased. Consequently, an electrolytic capacitor with high performance can be obtained.

[0100] Manufacturing method (M2) may further include step (Y) of disposing a second compound having a melting point of 50° C. or higher, which is at least one compound selected from the group consisting of sugars and polyols, inside the capacitor element precursor between steps (i) and (X).

[0101] (Process (Y))

[0102] Process (Y) includes process (Ya) and process (Yb). Process (Ya) is a process for impregnating a second aqueous treatment liquid containing a second compound into a capacitor element precursor so that the second aqueous treatment liquid is contacted with at least a portion of at least one surface (S2) selected from a group consisting of the surface of the anode body, the surface of the cathode body, and the surface of the separator. Process (Yb) is a process for configuring the second compound on at least a portion of at least one surface (S2) by drying the impregnated second aqueous treatment liquid. Except for using the second compound instead of the first compound, process (Ya) and process (Yb) can be performed in the same manner as process (ii-a) and process (ii-b), respectively. For example, except for using the second compound instead of the first compound, the second aqueous treatment liquid can be prepared in the same manner as the first aqueous treatment liquid. As described above, the second compound may be the same as or different from the first compound. In addition, the implementation conditions of process (ii) may be the same as or different from those of process (Y).

[0103] In the production method of the present invention, drying in step (iii-b) can be performed at a temperature equal to or higher than the melting point of the first compound. Depending on the drying conditions, the first compound disposed in step (ii) can be melted, further improving the fixation properties of the first compound.

[0104] Similarly, when the production method of the present invention includes step (Y) and step (X), drying in step (Xb) can be performed at a temperature equal to or higher than the melting point of the second compound.

[0105] In the manufacturing method of the present invention, step (iii) can be repeated multiple times. In order to achieve higher characteristics (such as low ESR), it is preferred to increase the content of the first conductive polymer contained in the electrolyte layer. By repeatedly performing step (iii) multiple times, the content of the first conductive polymer can be increased. The number of repetitions of the repeated step (iii) is not particularly limited. The number of times step (iii) is implemented in the manufacturing method of the present invention can be in the range of 1 to 5 (for example, in the range of 2 to 3). When step (iii) is repeated, the multiple steps (iii) can be the same or different. For example, the preparation conditions (components and concentration, etc.) and drying conditions of the first aqueous dispersion in each step (iii) can be the same or different.

[0106] Likewise, when the production method of the present invention includes step (X), step (X) may be repeated a plurality of times.

[0107] The first layer (CL1) and the second layer (CL2) can be used directly as an electrolyte layer. Alternatively, the above-mentioned liquid component (L) can be impregnated into the first layer (CL1) and the second layer (CL2) to form an electrolyte layer. In the case of repeating step (iii) multiple times, the liquid component (L) can be impregnated after all these steps are completed. The impregnation of the liquid component (L) can be, for example, by immersing the capacitor element precursor after step (iii) in the liquid component (L).

[0108] At least a portion of the first compound precipitated on the surface of the capacitor element precursor component (e.g., the anode body) in step (ii) dissolves in the first aqueous dispersion during the treatment in step (iii-a). A portion of the first compound that did not dissolve in the first aqueous dispersion remains on the surface precipitated in step (ii). Furthermore, most of the portion of the first compound that dissolved in the first aqueous dispersion remains near the surface. As a result, a portion of the first compound is concentrated near the surface.

[0109] The first compound present near the surface helps to fix the first conductive polymer to the surface. Therefore, according to the above-mentioned manufacturing method, the amount of the first conductive polymer contained in the electrolyte layer can be increased, thereby achieving high characteristics (such as low ESR). In addition, since the stability of the electrolyte layer can be improved, a highly reliable electrolytic capacitor can be obtained.

[0110] When step (iii) is repeated, it is particularly important to prevent the first conductive polymer, which has been filled into the capacitor element precursor in the previous step (iii), from falling out during the impregnation step (iii-a). Therefore, when step (iii) is repeated, it is particularly important to perform step (ii).

[0111] The electrolyte layer is formed by the above-described operation. That is, the capacitor element including the electrolyte layer is formed by the above-described operation.

[0112] The capacitor element obtained as described above can be used to manufacture the electrolytic capacitor of the present invention (the first and second electrolytic capacitors). The method for manufacturing an electrolytic capacitor using the capacitor element is not particularly limited, and known methods can be applied. For example, the capacitor element can be placed in a housing and sealed.

[0113] Below, an example of an electrolytic capacitor of the present invention is described in detail with reference to the accompanying drawings. However, the electrolytic capacitor of the present invention is not limited to the following drawings. The above-mentioned components can be applied as the components of the electrolytic capacitor of the example described below. In addition, the components of the electrolytic capacitor of the example described below can be changed based on the above description. In addition, the matters described below can also be applied to the above-mentioned embodiment. It should be noted that the same symbols are sometimes used for the same parts, and repeated descriptions are omitted.

[0114] (Implementation 1)

[0115] In the first embodiment, an example of the electrolytic capacitor of the present invention will be described. Figure 1 A cross section of an example of electrolytic capacitor 100 according to Embodiment 1 is schematically shown. Figure 2 Indicates that Figure 1 FIG. 1 is a schematic diagram showing a partially expanded portion of a capacitor element included in electrolytic capacitor 100 .

[0116] like Figure 1 As shown, the electrolytic capacitor 100 includes, for example: a capacitor element 10, a bottomed casing 11 that accommodates the capacitor element 10, a sealing member 12 that blocks the opening of the bottomed casing 11, a seat plate 13 that covers the sealing member 12, leads 14A and 14B that extend from the sealing member 12 and pass through the seat plate 13, and lead connectors 15A and 15B (not shown) that connect the leads 14A and 14B to the electrodes of the capacitor element 10. The capacitor element 10 is accommodated in the bottomed casing 11. When the capacitor element 10 contains a liquid component (L), the liquid component (L) is also accommodated in the bottomed casing 11. The opening end of the bottomed casing 11 is necked inward, and the opening end of the bottomed casing 11 is crimped so as to be riveted to the sealing member 12.

[0117] The capacitor element 10 includes a foil-shaped anode body 21 having a dielectric layer on its surface, a foil-shaped cathode body 22, and a separator 23 and an electrolyte layer (not shown) disposed therebetween. The anode body 21 and the cathode body 22 are wound with the separator 23 disposed therebetween. The outermost periphery of the wound body is fixed by a winding fixing tape 24. Figure 2 The diagram shows a partially unwound state before the outermost periphery of the wound body is fixed.

[0118] Figure 3 A cross-sectional view schematically shows a portion of an example of a capacitor element included in the first electrolytic capacitor. Figure 3Capacitor element 10a includes an anode body 21, a cathode body 22, an electrolyte layer 31 disposed therebetween, and a separator (not shown). Dielectric layer 21a is formed on the surface of anode body 21. Electrolyte layer 31 includes a first conductive polymer and a first compound. As described above, electrolyte layer 31 includes a localized portion of the first compound (not shown). Electrolyte layer 31 may also include the aforementioned liquid component (L).

[0119] Figure 4 A cross-sectional view schematically shows a portion of an example of a capacitor element included in the second electrolytic capacitor. Figure 4 The capacitor element 10b includes an anode body 21, a cathode body 22, an electrolyte layer 41 disposed therebetween, and a separator (not shown). The electrolyte layer 41 includes a second layer 41b and a first layer 41a formed at least on the second layer 41b. Figure 4 The configuration of the electrolyte layer shown is an example, and the present invention is not limited to Figure 4 The first layer 41a comprises a first conductive polymer. The second layer 41b comprises a second conductive polymer. As described above, the electrolyte layer 41 comprises a localized portion (not shown) of the first compound. The electrolyte layer 41 may also comprise the aforementioned liquid component (L).

[0120] Example

[0121] Hereinafter, the embodiments of the present invention will be described in further detail using examples. In this example, a plurality of electrolytic capacitors (capacitors A1 to A7 and capacitors C1 to C6) were produced and evaluated. The manufacturing method and evaluation method of these capacitors are described below. It should be noted that in the description of the method for producing the capacitors of the comparative example, conditions different from those of the above-mentioned steps (ii) and (iii) are sometimes used, but for convenience, they are also described as steps (ii) and (iii).

[0122] [Fabrication of Capacitor A1]

[0123] Capacitor A1 is a wound-type electrolytic capacitor (diameter 10 mm×length 10 mm) with a rated voltage of 35 V and a rated capacitance of 270 μF. Capacitor A1 was produced using the following steps.

[0124] (Preparation of cathode body)

[0125] As the cathode body, an Al foil (aluminum foil) having a thickness of 50 μm was used.

[0126] (Preparation of anode body)

[0127] Prepare a 120μm thick Al foil. Roughen the surface by DC etching. Then, chemically convert the Al foil to form a dielectric layer (thickness: approximately 70nm), thereby obtaining an anode body. The Al foil is immersed in an ammonium adipate solution and subjected to a chemical conversion treatment at 70°C for 5 hours while applying a voltage of 50V. This forms the dielectric layer. The anode body is then cut to the specified size, thereby preparing the anode body for capacitor A1.

[0128] (Production of wound body (step (i)))

[0129] The anode lead connector and cathode lead connector, each connected to a lead, are connected to the prepared anode and cathode bodies, respectively. Thereafter, the anode and cathode bodies are wound with a separator sandwiched therebetween, and the outer surfaces are fixed with a winding fixing tape. A non-woven fabric made of aramid (aromatic polyamide fiber), which is a synthetic fiber, is used as a separator. A wound body (capacitor element precursor) is produced by the above operation. The produced wound body is immersed in an ammonium adipate solution, and while applying a voltage of 50 V to the anode body, a chemical conversion treatment is performed again at 70°C for 60 minutes, thereby forming a dielectric layer mainly on the end face of the anode body.

[0130] (Preparation of the first aqueous treatment solution)

[0131] Mannitol was dissolved in ion-exchanged water to prepare a mannitol aqueous solution having a concentration of 10% by mass. The viscosity of the obtained mannitol aqueous solution was measured to be 5 mPa·s or less.

[0132] (Preparation of the first aqueous dispersion)

[0133] A mixed solution of 3,4-ethylenedioxythiophene and polystyrenesulfonic acid as a dopant is prepared by dissolving them in ion-exchanged water. While stirring the resulting mixed solution, iron (III) sulfate (oxidant) dissolved in ion-exchanged water is added to allow a polymerization reaction to proceed. After the reaction, the resulting reaction solution is dialyzed to remove unreacted monomers and excess oxidant, yielding a dispersion (first aqueous dispersion) containing poly(3,4-ethylenedioxythiophene) doped with approximately 5% by mass of polystyrenesulfonic acid (PSS). Hereinafter, poly(3,4-ethylenedioxythiophene) doped with approximately 5% by mass of polystyrenesulfonic acid (PSS) may be referred to as "PEDOT:PSS." Furthermore, a dispersion containing PEDOT:PSS may be referred to as a "PEDOT:PSS dispersion." This PEDOT:PSS dispersion is used to prepare a first aqueous dispersion having a PEDOT:PSS concentration of 2% by mass. The viscosity of the obtained dispersion was measured and found to be 25 mPa·s.

[0134] (Step (ii))

[0135] First, place the first aqueous treatment liquid in a container. Then, immerse the wound body (capacitor element precursor) in the first aqueous treatment liquid in the container at room temperature and atmospheric pressure for 5 minutes. At this time, immerse the wound body in the first aqueous treatment liquid from the side where the lead connector is not connected (the same applies to the other immersion steps described below). Thereafter, lift the wound body from the first aqueous treatment liquid. Operate as described above to allow the first aqueous treatment liquid to penetrate into the wound body. Then, dry the wound body at 180°C in a drying oven for 30 minutes to dry the first aqueous treatment liquid. Operate as described above to place the first compound inside the wound body.

[0136] (Process (iii))

[0137] First, place the first aqueous dispersion in a container. Then, at room temperature and under a reduced pressure atmosphere (40 kPa), immerse the wound body in the first aqueous dispersion in the container for 15 minutes, and thereafter, lift the wound body out of the first aqueous dispersion. By operating as described above, the first aqueous dispersion is impregnated into the wound body. Then, in a drying oven, dry the wound body at 60°C for 30 minutes, and then at 125°C for 15 minutes. Thus, the first aqueous dispersion is dried. By operating as described above, the first layer (conductive polymer layer) is formed.

[0138] (Impermeation of electrolyte)

[0139] The wound body that has undergone step (iii) is impregnated with an electrolyte at room temperature and atmospheric pressure. A solution in which polyethylene glycol, γ-butyrolactone, cyclopentane and mono(ethyldimethylamine)phthalate (solute) are mixed in a mass ratio of polyethylene glycol: γ-butyrolactone: cyclopentane: mono(ethyldimethylamine)phthalate = 25:25:25:25 is used as the electrolyte. By operating as described above, a capacitor element including an electrolyte layer is obtained. The capacitor element is sealed to complete the electrolytic capacitor. Thereafter, an aging treatment is performed at 150°C for 1 hour while applying the rated voltage. By operating as described above, capacitor A1 is obtained.

[0140] [Capacitor A2]

[0141] Capacitor A2 was produced under the same conditions as capacitor A1 except that the spacer was changed. A nonwoven fabric of cellulose-based natural fibers was used as the spacer.

[0142] [Capacitor A3]

[0143] Capacitor A3 was produced by the same method as capacitor A1 except that step (X) was performed. Step (X) was performed as follows.

[0144] The PEDOT:PSS dispersion described in the fabrication of capacitor A1 was used as the second aqueous dispersion. This second aqueous dispersion was impregnated and dried under the same conditions as in step (iii) of capacitor A1 to form the second layer (conductive polymer layer). This process proceeded to step (X). Subsequently, steps (ii) and (iii) were performed under the same conditions as capacitor A1 to form the first layer on the second layer. Subsequently, capacitor A3 was fabricated using the same process as capacitor A1.

[0145] [Capacitor A4]

[0146] Capacitor A4 was produced by the same method as capacitor A1 except that the above-mentioned step (X) was performed. Step (X) was performed as follows.

[0147] Mannitol was dissolved in the PEDOT:PSS dispersion described in the preparation of capacitor A1 to prepare a second aqueous dispersion. The PEDOT:PSS concentration in the second aqueous dispersion was set to 2% by mass, and the mannitol concentration was set to 10% by mass. The viscosity of the resulting dispersion was measured and found to be 45 mPa·s.

[0148] This second aqueous dispersion was impregnated and dried under the same conditions as in step (iii) of capacitor A1 to form the second layer (conductive polymer layer). This process proceeded to step (X). Subsequently, steps (ii) and (iii) were performed under the same conditions as in capacitor A1 to form the first layer on the second layer. Subsequently, capacitor A4 was produced using the same process as in capacitor A1.

[0149] [Capacitor A5]

[0150] Capacitor A5 was produced under the same conditions as those for capacitor A1, except that step (iii) of capacitor A1 was performed twice continuously under the same conditions.

[0151] [Capacitor A6]

[0152] Capacitor A6 was produced by the same method as capacitor A1 except that another step (iii) was performed after step (iii). Specifically, capacitor A6 was produced by the following method.

[0153] The same process as for capacitor A1 was followed until step (iii) of capacitor A1. Then, another step (iii) was performed. The same second aqueous dispersion (containing PEDOT:PSS and mannitol) used in the production of capacitor A4 was used as the first aqueous dispersion. This dispersion was used for impregnation and drying under the same conditions as step (iii) of capacitor A1. Then, capacitor A6 was produced using the same process as capacitor A1.

[0154] [Capacitor A7]

[0155] Capacitor A7 was fabricated using the same method as capacitor A1, except that steps (Y) and (X) were performed. Steps (Y) and (X) were performed under the same conditions as steps (ii) and (iii) of capacitor A1, respectively. After forming the second layer in this manner, steps (ii) and (iii) were performed under the same conditions as capacitor A1 to form the first layer on the second layer. Subsequently, capacitor A7 was fabricated using the same process as capacitor A1.

[0156] [Capacitor C1]

[0157] A capacitor C1 was produced under the same conditions as those of the capacitor A1 except that step (ii) was not performed.

[0158] [Capacitor C2]

[0159] Capacitor C1 was produced under the same conditions as capacitor A1, except that step (ii) was not performed and the dispersion used in step (iii) was changed. The same second aqueous dispersion (a dispersion containing PEDOT:PSS and mannitol) as the second aqueous dispersion used in the production of capacitor A4 was used as the dispersion in step (iii).

[0160] [Capacitor C3]

[0161] Capacitor C3 was produced under the same conditions as capacitor A1 except that step (ii) was not performed and the spacer was different. As the spacer, a spacer made of the same natural fiber as that used in capacitor A2 was used.

[0162] [Capacitor C4]

[0163] Capacitor C4 was produced under the same conditions as capacitor A1 except that step (ii) was not performed and step (iii) was performed twice continuously.

[0164] [Capacitor C5]

[0165] Capacitor C5 was fabricated under the same conditions as capacitor A1, except that step (ii) was not performed and that step (iii) was performed under conditions different from those of step (iii) of capacitor A1, followed by step (iii) being performed under the same conditions as step (iii) of capacitor A1. The first step (iii) was performed under the same conditions as step (iii) of capacitor A1, except that the second aqueous dispersion (a dispersion containing PEDOT:PSS and mannitol) used in the fabrication of capacitor A4 was used.

[0166] [Capacitor C6]

[0167] Capacitor C6 was produced under the same conditions as capacitor A1, except that step (ii) was not performed and that step (iii) was performed under the same conditions as step (iii) of capacitor A1, but then under different conditions. A second step (iii) was performed under the same conditions as step (iii) of capacitor A1, except that the second aqueous dispersion (a dispersion containing PEDOT:PSS and mannitol) used in the production of capacitor A4 was used.

[0168] (Evaluation of filling status)

[0169] In the process of manufacturing the above-mentioned capacitor, after completing the final step (iii), the extent to which the conductive polymer is filled in the capacitor element is visually evaluated. Specifically, the extent to which the conductive polymer is filled on the side of the capacitor element precursor connected to the lead tab is visually determined. Excellent filling is rated S, excellent filling is rated A, and insufficient filling is rated B.

[0170] It should be noted that the identification of the first compound (and the second compound described later) in the electrolyte layer and its distribution in the electrolyte layer can be studied, for example, using the following method. For the identification of the first compound, a microscopic FT-IR analysis device (Nicolet-iN10 manufactured by ThermoFisher) can be used. Regarding the distribution of the first compound, first, the electrolyte layer (capacitor element) is cut into multiple parts, and the first compound present in each part is extracted with an aqueous solvent. Then, the extracted first compound is quantified, thereby determining the distribution of the first compound in each part.

[0171] (Evaluation of characteristics)

[0172] The equivalent series resistance (ESR) of the electrolytic capacitors fabricated as described above was measured. ESR was measured at 20°C using a four-terminal LCR meter. ESR was measured at the initial value immediately after fabrication and after the electrolytic capacitors were exposed to high temperatures (145°C for 250 hours). The reliability evaluation value F was then calculated using the following formula as an indicator of reliability.

[0173] Reliability evaluation value F = (ESR value after high temperature storage) / (initial ESR value)

[0174] The breakdown voltage of capacitors A1, A2, and C3 was also measured. Specifically, the voltage was applied while increasing at a rate of 1.0 V / second, and the breakdown voltage was measured when an overcurrent of 0.5 A flowed. The measurement results and a portion of the electrolytic capacitor manufacturing conditions are shown in Table 1. Note that in Table 1, the term "PEDOT:PSS mixture" refers to an aqueous dispersion containing PEDOT:PSS and mannitol.

[0175] [Table 1]

[0176]

[0177] As described above, drying in steps (ii-b) and (Yb) was performed at 180°C for 30 minutes. Furthermore, drying in steps (iii-b) and (Xb) was performed at 60°C for 30 minutes and at 125°C for 15 minutes. As described above, the viscosity of the mannitol aqueous solution was 5 mPa·s or less, the viscosity of the PEDOT:PSS dispersion was 25 mPa·s, and the viscosity of the dispersion containing PEDOT:PSS and mannitol was 45 mPa·s. Mannitol has a melting point of approximately 165-169°C.

[0178] The ESR value is preferably low. The ESR value is preferably 15 mΩ or less (e.g., in the range of 10 to 15 mΩ), more preferably 12 mΩ or less (e.g., in the range of 8 to 12 mΩ). The breakdown voltage is preferably high, preferably 70 V or more (e.g., in the range of 70 to 90 V). The reliability evaluation value F is preferably small. The evaluation value F is preferably 1.3 or less (e.g., in the range of 1 to 1.3), more preferably 1.2 or less (e.g., in the range of 1 to 1.2).

[0179] As shown in Table 1, the electrolytic capacitors (capacitors A1 to A7) of the present invention manufactured by the manufacturing method of the present invention using steps (ii) and (iii) exhibited high characteristics. Capacitor A7, which had steps (Y) and (X), exhibited particularly high characteristics.

[0180] Comparing capacitors C1 and C3, manufactured without step (ii), shows that the breakdown voltage decreases when using a natural fiber spacer (a weak spacer) without step (ii). On the other hand, comparing capacitors A1 and A2, manufactured with step (ii), shows high breakdown voltage regardless of the type of spacer used.

[0181] Comparing capacitors A3 and A4, capacitor A4 has a lower reliability evaluation value F. This is presumably because capacitor A4 has localized portions of the first compound near the surfaces of the anode and cathode foils, resulting in improved thermal stability.

[0182] Industrial applicability

[0183] The present invention can be applied to an electrolytic capacitor and a method for manufacturing the same.

[0184] Description of Reference Numerals

[0185] 10, 10a, 10b capacitor element, 21 anode body, 22 cathode body, 23 separator, 31, 41 electrolyte layer, 41a first layer, 41b second layer, 100 electrolytic capacitor.

Claims

1. A method for manufacturing an electrolytic capacitor, comprising: Step (i) of forming a capacitor element precursor including a separator, and a foil-shaped anode body and a foil-shaped cathode body facing each other with the separator interposed therebetween; Step (ii) of placing a first compound having a melting point of 50° C. or higher, which is at least one compound selected from the group consisting of sugars and polyols, inside the capacitor element precursor; as well as Step (iii) of forming a first layer containing a first conductive polymer inside the capacitor element precursor after the step (ii), The step (ii) comprises: Step (ii-a), impregnating the capacitor element precursor with a first aqueous treatment liquid containing the first compound and excluding the first conductive polymer; and Step (ii-b) of disposing the first compound inside the capacitor element precursor by drying the impregnated first aqueous treatment liquid. In the step (ii-a), the first aqueous treatment liquid is impregnated into the capacitor element precursor so that the first aqueous treatment liquid contacts at least a portion of at least one surface selected from the group consisting of the surface of the anode body, the surface of the cathode body, and the surface of the separator. In the step (ii-b), the first compound is arranged on at least a portion of the at least one surface by drying the impregnated first aqueous treatment liquid. The step (iii) comprises: step (iii-a) of impregnating the capacitor element precursor having undergone step (ii) and in which the first compound has been deposited on at least a portion of the at least one surface with a first aqueous dispersion containing the first conductive polymer; and Step (iii-b) is to form the first layer by drying the impregnated first aqueous dispersion.

2. The manufacturing method according to claim 1, wherein The first aqueous dispersion does not contain the first compound.

3. The manufacturing method according to claim 1, wherein In the electrolyte layer that is in contact with the anode body, the cathode body, and the separator and includes the first layer, the content of the conductive polymer is 50% by mass or more.

4. The manufacturing method according to claim 1, wherein The process further includes step (X) between step (i) and step (ii), The step (X) comprises: Step (Xa), impregnating the capacitor element precursor with a second aqueous dispersion containing a second conductive polymer; and Step (Xb) of drying the impregnated second aqueous dispersion to form a second layer containing the second conductive polymer on at least a portion of the surface of the anode body and the cathode body, In the step (ii-a), the capacitor element precursor having undergone the step (X) is impregnated with the first aqueous treatment liquid. In the step (ii-b), the first compound is arranged on the surface of the second layer by drying the impregnated first aqueous treatment liquid.

5. The manufacturing method according to claim 4, wherein: The second aqueous dispersion contains a second compound having a melting point of 50° C. or higher, which is at least one compound selected from the group consisting of sugars and polyols.

6. The manufacturing method according to claim 4, wherein: A step (Y) is further included between the step (i) and the step (X), wherein a second compound having a melting point of 50° C. or higher, which is at least one compound selected from the group consisting of sugars and polyols, is disposed inside the capacitor element precursor. The process (Y) comprises: step (Ya) of impregnating the capacitor element precursor with a second aqueous treatment liquid containing the second compound so that the second aqueous treatment liquid contacts at least a portion of at least one surface selected from the group consisting of a surface of the anode body, a surface of the cathode body, and a surface of the separator; and In step (Yb), the second compound is arranged on at least a portion of the at least one surface by drying the impregnated second aqueous treatment liquid.

7. The manufacturing method according to claim 1, wherein: The drying temperature in the step (ii-b) is a temperature equal to or higher than the melting point of the first compound.

8. The manufacturing method according to claim 1, wherein: The step (iii) is repeated multiple times.

9. The manufacturing method according to claim 1, wherein: The viscosity of the first aqueous dispersion is in the range of 1 mPa·s to 100 mPa·s.

10. The manufacturing method according to claim 1, wherein: The first aqueous treatment liquid does not contain a polymer.

11. The manufacturing method according to claim 1, wherein: The first compound is at least one selected from the group consisting of glucose, mannitol, sorbitol, xylitol, pentaerythritol, and trimethylolpropane.

12. The manufacturing method according to claim 1, wherein: The first conductive polymer is poly(3,4-ethylenedioxythiophene) doped with polystyrenesulfonic acid.

13. An electrolytic capacitor manufactured by the manufacturing method according to any one of claims 1 to 12, The electrolytic capacitor comprises a capacitor element, The capacitor element comprises: Spacers, a foil-shaped anode body and a foil-shaped cathode body facing each other with the separator interposed therebetween, and an electrolyte layer in contact with the anode body, the cathode body, and the separator, The electrolyte layer contains a first conductive polymer and a first compound having a melting point of 50° C. or higher, which is at least one compound selected from the group consisting of sugars and polyols. The electrolyte layer has a localized portion where the first compound is localized.

14. An electrolytic capacitor, Is an electrolytic capacitor containing capacitor elements, The capacitor element comprises: Spacers, a foil-shaped anode body and a foil-shaped cathode body facing each other with the separator interposed therebetween, and an electrolyte layer in contact with the anode body, the cathode body, and the separator, The electrolyte layer contains a first conductive polymer and a first compound having a melting point of 50° C. or higher, which is at least one compound selected from the group consisting of sugars and polyols. The electrolyte layer has a localized portion where the first compound is localized. The content of the conductive polymer in the electrolyte layer is 50% by mass or more.

15. The electrolytic capacitor according to claim 13 or 14, wherein: The electrolyte layer has a localized portion where the first compound is localized in at least one portion selected from the group consisting of a portion in contact with the anode body, a portion in contact with the cathode body, and a portion in contact with the separator.

16. The electrolytic capacitor according to claim 13 or 14, wherein: The electrolyte layer includes a second layer formed on at least a portion of the surface of the anode body and the cathode body and containing a second conductive polymer, and a first layer formed at least on the second layer and containing the first conductive polymer. The electrolyte layer has a localized portion where the first compound is localized in at least a portion of a portion in contact with an interface between the first layer and the second layer.

17. The electrolytic capacitor according to claim 16, wherein The second layer contains a second compound having a melting point of 50° C. or higher, which is at least one compound selected from the group consisting of sugars and polyols.

18. The electrolytic capacitor according to claim 17, wherein The second layer has a localized portion where the second compound is localized in at least one portion selected from the group consisting of a portion in contact with the anode body, a portion in contact with the cathode body, and a portion in contact with the separator.

19. The electrolytic capacitor according to claim 13 or 14, wherein: The first compound is at least one selected from the group consisting of glucose, mannitol, sorbitol, xylitol, pentaerythritol, and trimethylolpropane.

20. The electrolytic capacitor according to claim 13 or 14, wherein The first conductive polymer is poly(3,4-ethylenedioxythiophene) doped with polystyrenesulfonic acid.

21. The electrolytic capacitor according to claim 13 or 14, wherein The electrolyte layer contains a non-aqueous solvent or a non-aqueous electrolyte solution.

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