Electrolytic capacitor and its manufacturing method

Abstract

Disclosed is an electrolytic capacitor comprising a capacitor element 10. The capacitor element 10 comprises: an electrode group 20 including a foil anode body 21 having a dielectric layer on a surface thereof, a foil cathode body 22, and a separator 23; and an electrolyte layer in contact with the anode body 21, the cathode body 22, and the separator 23. The electrolyte layer contains a hydroxyl-containing compound that is at least one compound selected from the group consisting of sugars and polyalcohols and that has a melting point of 50℃ or more, and an electrically conductive polymer. The hydroxyl-containing compound is present more in the periphery of the capacitor element than in the center of the capacitor element 10.

Description

[Technical field]

[0001] The present disclosure relates to electrolytic capacitors and methods for manufacturing the same. [Background technology]

[0002] Capacitors used in electronic devices are required to have a large capacity and a small equivalent series resistance (ESR) value in the high frequency range. As a capacitor with a large capacity and low ESR, electrolytic capacitors using conductive polymers such as polypyrrole, polythiophene, polyfuran, and polyaniline are promising. Patent Document 1 discloses a method of impregnating a capacitor element formed by winding an anode foil and a cathode foil with a separator therebetween with a dispersion containing a conductive polymer and a solvent. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2008-10657 A Summary of the Invention [Problem to be solved by the invention]

[0004] Currently, there is a demand for electrolytic capacitors with higher characteristics (particularly high voltage resistance and high reliability). In this situation, one of the objects of the present disclosure is to provide an electrolytic capacitor with high characteristics and a manufacturing method thereof. [Means for solving the problem]

[0005] One aspect of the present disclosure relates to a method for producing an electrolytic capacitor, which includes an electrolytic capacitor including a foil-shaped anode body having a dielectric layer on a surface thereof and a foil-shaped cathode body, and includes the steps of: (i) forming a capacitor element precursor by winding or laminating a separator and the anode body and the cathode body facing each other with the separator interposed therebetween; (ii) disposing, inside the capacitor element precursor, at least one compound containing a hydroxyl group, selected from the group consisting of sugars and polyhydric alcohols, and having a melting point of 50° C. or higher; and (iii) forming, inside the capacitor element precursor that has been subjected to the step (ii), a conductive polymer layer containing a conductive polymer, the step (ii) comprising impregnating the capacitor element precursor with an aqueous treatment liquid containing the hydroxyl group-containing compound. The method includes a step (ii-a) and a step (ii-b) of disposing the hydroxyl group-containing compound inside the capacitor element precursor by drying the impregnated aqueous treatment liquid, and the step (iii) includes a step (iii-a) of impregnating the capacitor element precursor that has been subjected to the step (ii) with an aqueous dispersion containing the conductive polymer, and a step (iii-b) of drying the impregnated aqueous dispersion to form the conductive polymer layer, and the drying in the step (ii-b) is performed at a predetermined temperature, and the predetermined temperature is a temperature that is equal to or higher than the boiling point of the aqueous treatment liquid under a pressure at which the drying in the step (ii-b) is performed and is lower than the melting point of the hydroxyl group-containing compound under a pressure at which the drying in the step (ii-b) is performed.

[0006] Another aspect of the present disclosure relates to a method for producing an electrolytic capacitor, which includes a porous anode body having a dielectric layer on its surface, and includes a step (I) of disposing a hydroxyl-containing compound, which is at least one compound selected from the group consisting of sugars and polyhydric alcohols and has a melting point of 50° C. or higher, on the surface of the anode body, and a step (II) of forming a conductive polymer layer containing a conductive polymer on the anode body that has been subjected to the step (I). The step (I) includes a step (Ia) of impregnating the anode body with an aqueous treatment solution containing the hydroxyl-containing compound, and a step (Ib) of drying the impregnated aqueous treatment solution to remove the hydroxyl-containing compound. and a step (Ib) of disposing a conductive polymer on a surface of the anode body, the step (II) comprising: a step (II-a) of impregnating the anode body that has been subjected to the step (I) with an aqueous dispersion containing a conductive polymer; and a step (II-b) of drying the impregnated aqueous dispersion to form the conductive polymer layer on the anode body, the drying in the step (Ib) being performed at a predetermined temperature, the predetermined temperature being a temperature that is equal to or higher than the boiling point of the aqueous treatment liquid under a pressure at which the drying in the step (Ib) is performed and that is lower than the melting point of the hydroxyl group-containing compound under a pressure at which the drying in the step (Ib) is performed.

[0007] Another aspect of the present disclosure relates to an electrolytic capacitor, which includes a capacitor element, the capacitor element including an electrode group including a foil-shaped anode body having a dielectric layer on its surface, a foil-shaped cathode body, and a separator, and an electrolyte layer in contact with the anode body, the cathode body, and the separator, the electrode group being a wound body formed by winding the anode body and the cathode body facing each other with the separator interposed therebetween, or a laminate formed by laminating the anode body and the cathode body facing each other with the separator interposed therebetween, the electrolyte layer containing at least one compound selected from the group consisting of sugars and polyhydric alcohols, the hydroxyl group-containing compound having a melting point of 50° C. or higher, and a conductive polymer, the hydroxyl group-containing compound being unevenly distributed in the peripheral portion of the capacitor element rather than in the center portion of the capacitor element.

[0008] Another aspect of the present disclosure relates to an electrolytic capacitor including a capacitor element, the capacitor element including a porous anode body having a dielectric layer on its surface, a cathode layer, and an electrolyte layer disposed between the anode body and the cathode layer, the capacitor element including at least one compound selected from the group consisting of sugars and polyhydric alcohols, a hydroxyl-containing compound having a melting point of 50° C. or higher, and a conductive polymer, the hydroxyl-containing compound being unevenly distributed in the periphery of the anode body relative to the center of the anode body. Effect of the Invention

[0009] According to the present disclosure, an electrolytic capacitor with excellent characteristics can be obtained. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view illustrating a schematic example of an electrolytic capacitor according to the present disclosure. [Diagram 2] FIG. 2 is a diagram illustrating a schematic view of a portion of the electrolytic capacitor illustrated in FIG. [Diagram 3]FIG. 2 is a cross-sectional view illustrating a schematic diagram of a portion of another example of an electrolytic capacitor according to the present disclosure. [Figure 4] FIG. 1 shows the results of an example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] In the following, the embodiment of the present disclosure will be described with examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be exemplified, but other numerical values ​​and materials may be applied as long as the effects of the present disclosure are obtained. In the following description, the melting point is a value at 1 atmosphere unless otherwise specified. In addition, the viscosity is a value at room temperature (25°C) and 1 atmosphere unless otherwise specified.

[0012] As a result of their investigation, the inventors of the present application have found that an electrolytic capacitor having excellent characteristics can be obtained by disposing a conductive polymer on a capacitor element precursor by a specific method. The present disclosure is based on this new finding.

[0013] The electrolytic capacitor of the present disclosure may be a first electrolytic capacitor described below, or a second electrolytic capacitor described below, which will be described below.

[0014] [First electrolytic capacitor] The first electrolytic capacitor is an electrolytic capacitor including a capacitor element. The capacitor element includes an electrode group including a foil-shaped anode body having a dielectric layer on the surface, a foil-shaped cathode body, and a separator, and an electrolyte layer in contact with the anode body, the cathode body, and the separator. The electrode group may be a wound body formed by winding the anode body, the cathode body, and the separator so that the separator is disposed between the anode body and the cathode body. Alternatively, the electrode group may be a laminate formed by folding the anode body, the cathode body, and the separator in a zigzag shape so that the separator is disposed between the anode body and the cathode body. The electrolyte layer contains a hydroxyl group-containing compound, which is at least one compound selected from the group consisting of sugars and polyhydric alcohols and has a melting point of 50° C. or higher, and a conductive polymer. Hereinafter, the hydroxyl group-containing compound may be referred to as a "hydroxyl group-containing compound (C)". The hydroxyl-containing compound (C) is unevenly distributed in the peripheral portion of the capacitor element rather than in the central portion of the capacitor element.

[0015] The electrolyte layer of the first electrolytic capacitor contains a hydroxyl group-containing compound (C). The hydroxyl group-containing compound (C) improves the adhesion of the conductive polymer by its hydroxyl group. As a result, good characteristics (particularly low ESR) can be achieved. The improved adhesion of the conductive polymer increases the stability of the electrolyte layer, and the reliability of the electrolytic capacitor can be improved.

[0016] The peripheral portion of the capacitor element is prone to defects in the dielectric layer (oxide film) of the anode body. By disposing a hydroxyl-containing compound (C) having multiple hydroxyl groups in this portion, defects in the dielectric layer are easily repaired. As a result, a highly reliable electrolytic capacitor is obtained. Specifically, an electrolytic capacitor with high breakdown voltage and low short circuiting is obtained.

[0017] Furthermore, by distributing the hydroxyl group-containing compound (C) unevenly in the peripheral portion of the capacitor element, it is possible to distribut the conductive polymer unevenly in the peripheral portion, i.e., it is possible to form a thick conductive polymer layer in the peripheral portion.

[0018] The electrode group of the first electrolytic capacitor is not particularly limited, and a known electrode group may be used. For example, the electrode group that is a wound body may be an electrode group used in a general wound electrolytic capacitor. Similarly, the electrode group that is a laminate may be an electrode group used in a general laminate electrolytic capacitor. For example, the electrode group that is a laminate includes a foil-shaped anode body, a foil-shaped cathode body, and a separator that are stacked and folded in a zigzag pattern to stack them. At this time, the foil-shaped anode body and the foil-shaped cathode body are arranged so that the separator is present between them. Examples of the foil-shaped anode body, the foil-shaped cathode body, and the separator will be described later.

[0019] (Hydroxy group-containing compound (C)) The hydroxyl-containing compound (C) contained in the electrolyte layer of the first electrolytic capacitor will be described below. The hydroxyl-containing compound (C) is at least one compound selected from the group consisting of sugars and polyhydric alcohols, and has a melting point of 50°C or higher. The melting point of the hydroxyl-containing compound (C) is preferably higher than the temperature at which the capacitor is used. The melting point of the hydroxyl-containing compound (C) may be in the range of 80°C to 300°C (for example, in the range of 120°C to 300°C).

[0020] Examples of sugars include glucose, etc. Examples of polyhydric alcohols include mannitol, sorbitol, xylitol, pentaerythritol, and trimethylolpropane, etc. Note that mannitol, sorbitol, xylitol, pentaerythritol, etc. may be called sugar alcohols. The hydroxyl group-containing compound may be a sugar alcohol.

[0021] The number of hydroxyl groups contained in the hydroxyl-containing compound (C) may be in the range of 2 to 12 (for example, in the range of 3 to 6). Usually, the hydroxyl-containing compound (C) is a water-soluble compound.

[0022] From another perspective, the hydroxyl-containing compound contained in the electrolyte layer of the first electrolytic capacitor may be an organic compound (e.g., a non-polymer organic compound) containing multiple hydroxyl groups (-OH) bonded to a carbon atom and having a melting point within the above range. The molecular weight of the organic compound and the number of hydroxyl groups contained in the organic compound may each be within the above ranges exemplified for the hydroxyl-containing compound.

[0023] The hydroxyl group-containing compound (C) 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 to 150°C, that of mannitol is about 165 to 169°C, that of sorbitol is about 93 to 95°C, that of xylitol is about 92 to 97°C, that of pentaerythritol is about 257 to 260°C, and that of trimethylolpropane is about 56 to 58°C. Note that the melting points of these substances may vary depending on the structure (stereoisomer). Glucose, mannitol, and pentaerythritol are preferred because they have high melting points.

[0024] (conductive polymer) The conductive polymer used in the first electrolytic capacitor will be described below. Examples of the conductive polymer include polypyrrole, polythiophene, polyfuran, polyaniline, polyacetylene, and derivatives thereof. The derivatives include polymers having polypyrrole, polythiophene, polyfuran, polyaniline, and polyacetylene as a basic skeleton. For example, a derivative of polythiophene includes poly(3,4-ethylenedioxythiophene). These conductive polymers may be used alone or in combination. The conductive polymer may be a copolymer of two or more monomers. The weight-average molecular weight of the conductive polymer is not particularly limited, and may be in the range of 1,000 to 100,000, for example. A preferred example of the conductive polymer is poly(3,4-ethylenedioxythiophene) (PEDOT).

[0025] A dopant may be added to the conductive polymer. From the viewpoint of suppressing dedoping from the conductive polymer, it is preferable to use a polymer dopant. Examples of polymer dopants include polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallyl sulfonic acid, polyacryl sulfonic acid, polymethacryl sulfonic acid, poly(2-acrylamido-2-methylpropane sulfonic acid), polyisoprene sulfonic acid, polyacrylic acid, and the like. These may be used alone or in combination of two or more. These may be added in the form of a salt. The polymer dopant may exist in the electrolyte in the form of an anion in which a cation (e.g., a proton) is dissociated from at least a part of the acidic group. A preferred example of the dopant is polystyrene sulfonic acid (PSS).

[0026] The weight-average molecular weight of the dopant is not particularly limited, but may be in the range of 1,000 to 100,000 in order to facilitate the formation of a homogeneous electrolyte layer.

[0027] The conductive polymer may be poly(3,4-ethylenedioxythiophene) doped with polystyrenesulfonic acid.

[0028] The electrode group of the first electrolytic capacitor may be a wound body. In this case, the electrolyte layer preferably has unevenly distributed portions where the hydroxyl-containing compound is unevenly distributed at both ends of the wound body in the winding axis direction and at the outermost periphery of the wound body. Defects in the dielectric layer (oxide film) of the anode body are likely to occur at both ends of the wound body in the winding axis direction and at the outermost periphery of the wound body. By unevenly distributing the hydroxyl-containing compound (C) in these portions, it is possible to promote repair of defects in the dielectric layer.

[0029] The anode body and cathode body of the first electrolytic capacitor usually have a rectangular planar shape. In this case, the vicinity of both ends of the winding body in the winding axis direction can be regarded as the vicinity of the long sides of the rectangular anode body and cathode body.

[0030] The electrode group of the first electrolytic capacitor may be a laminate. In this case, the electrolyte layer has an uneven distribution part where the hydroxyl-containing compound is unevenly distributed in a part in contact with the peripheral part of the anode body. Since defects of the dielectric layer (oxide film) of the anode body are likely to occur in the peripheral part of the anode body, it is preferable to unevenly distribute the hydroxyl-containing compound (C) in these parts.

[0031] The electrolyte layer of the first electrolytic capacitor may contain a nonaqueous solvent or a nonaqueous electrolyte. Hereinafter, the nonaqueous solvent and the nonaqueous electrolyte contained in the electrolyte layer may be collectively referred to as "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 during use of the first electrolytic capacitor. A preferred example of the liquid component (L) is a liquid in which the hydroxyl group-containing compound (C) is substantially insoluble.

[0032] The non-aqueous solvent may be an organic solvent or an ionic liquid. Examples of the non-aqueous solvent include polyhydric alcohols 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.

[0033] Also, a polymer-based solvent may be used as the non-aqueous solvent. Examples of polymer-based solvents include polyalkylene glycol, derivatives of polyalkylene glycol, and compounds in which at least one hydroxyl group in a polyhydric alcohol is substituted with polyalkylene glycol (including derivatives). Specifically, examples of polymer-based solvents include 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, and polybutylene glycol. Examples of polymer-based solvents further include ethylene glycol-propylene glycol copolymers, ethylene glycol-butylene glycol copolymers, and propylene glycol-butylene glycol copolymers. The non-aqueous solvent may be used alone or in a mixture of two or more.

[0034] The liquid component (L) may contain an acid component and a base component. Examples of the acid component include maleic acid, phthalic acid, benzoic acid, pyromellitic acid, and resorcylic acid. Examples of the base component include 1,8-diazabicyclo[5,4,0]undecene-7, 1,5-diazabicyclo[4,3,0]nonene-5, 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.

[0035] The nonaqueous electrolyte contains a nonaqueous solvent and a solute (e.g., an organic salt) dissolved therein. Examples of the nonaqueous solvent constituting the nonaqueous electrolyte include the examples of the nonaqueous solvent described above. Examples of the solute include inorganic salts and organic salts. An organic salt is a salt in which at least one of the anion and the cation contains an organic substance. Examples of the organic salt include trimethylamine maleate, triethylamine borodisalicylate, ethyldimethylamine phthalate, mono-1,2,3,4-tetramethylimidazolinium phthalate, mono-1,3-dimethyl-2-ethylimidazolinium phthalate, and the like.

[0036] In order to suppress dedoping of the dopant, the pH of the liquid component (L) may be less than 7, or may be 5 or less.

[0037] (Anode body) The anode body can be a metal foil having a dielectric layer formed on its surface. The type of metal constituting the metal foil is not particularly limited. In terms of ease of forming the dielectric layer, examples of metals constituting the metal foil include valve metals such as aluminum, tantalum, niobium, and titanium, and alloys of valve metals. A preferred example is aluminum and an aluminum alloy. Usually, 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.

[0038] (cathode body) A metal foil can be used for the cathode body. The type of metal constituting the metal foil is not particularly limited. Examples of metals constituting the metal foil include metals having valve action, such as aluminum, tantalum, niobium, and titanium, and alloys of metals having valve action. A preferred example is aluminum and an aluminum alloy. In addition, a chemical conversion film may be provided on the surface of the cathode body, and a coating of a metal (heterogeneous metal) or a nonmetal different from the metal constituting the cathode body may be provided. Examples of the heterogeneous metal or nonmetal include metals such as titanium and nonmetals such as carbon.

[0039] (Separator) The separator may be a sheet-like material that can be impregnated with an electrolyte, for example, a sheet-like material that has insulating properties and can be impregnated with an electrolyte. The separator may be a woven fabric, a nonwoven fabric, or a porous membrane. Examples of the separator material include cellulose, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, vinylon, nylon, aromatic polyamide, polyimide, polyamideimide, polyetherimide, rayon, and glass.

[0040] The electrolyte of the electrolytic capacitor of the present disclosure contains a hydroxyl group-containing compound (C). This hydroxyl group-containing compound (C) can improve the strength of the separator. In conventional electrolytic capacitors, when a separator with low strength (for example, a separator made of natural cellulose fibers such as Manila hemp or esparto) is used, the characteristics of the capacitor, such as the withstand voltage, may be reduced. By using the hydroxyl group-containing compound (C), such a reduction in characteristics can be suppressed. The effect of reinforcing the separator can be obtained regardless of the type of separator.

[0041] [Second electrolytic capacitor] The second electrolytic capacitor is an electrolytic capacitor including a capacitor element. The capacitor element includes a porous anode body having a dielectric layer on its surface, a cathode layer, and an electrolyte layer disposed between the anode body and the cathode layer. The capacitor element includes a hydroxyl-containing compound having a melting point of 50°C or higher, which is at least one compound selected from the group consisting of sugars and polyhydric alcohols, and a conductive polymer. The hydroxyl-containing compound is unevenly distributed in the peripheral portion of the anode body rather than in the center portion of the anode body. The hydroxyl-containing compound used in the second electrolytic capacitor may be any of the compounds exemplified for the hydroxyl-containing compound of the first electrolytic capacitor. Therefore, the hydroxyl-containing compound used in the second electrolytic capacitor may also be referred to as "hydroxyl-containing compound (C)".

[0042] The porous anode body may be columnar (e.g., cylindrical or prismatic) or plate-shaped. The porous anode body is usually a sintered body formed by sintering, as described later. These porous anode bodies are prone to chipping at the periphery. In the second electrolytic capacitor, the hydroxyl-containing compound (C) is disposed at the periphery of the porous anode body, thereby preventing chipping at the periphery. Therefore, an electrolytic capacitor with excellent characteristics is obtained. In addition, the hydroxyl-containing compound (C) is present at the periphery of the anode body (i.e., near the interface between the electrolyte layer and the anode body of the second electrolytic capacitor). Therefore, the effects described in the first electrolytic capacitor are obtained.

[0043] Furthermore, by distributing the hydroxyl group-containing compound (C) unevenly in the peripheral portion of the anode body, it is possible to distribut the conductive polymer unevenly in the peripheral portion, i.e., it is possible to form a thick conductive polymer layer in the peripheral portion.

[0044] The hydroxyl-containing compound (C) used in the second electrolytic capacitor may be at least one selected from the group consisting of glucose, mannitol, sorbitol, xylitol, pentaerythritol, and trimethylolpropane.

[0045] The electrolyte layer of the second electrolytic capacitor may be a solid electrolyte layer. The electrolyte layer may be formed using a manganese compound or a conductive polymer. The conductive polymer may be the conductive polymer described in relation to the electrolyte layer of the first electrolytic capacitor. For example, the conductive polymer may be poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid.

[0046] An electrolyte layer (e.g., a solid electrolyte layer) containing a conductive polymer may be formed by polymerizing a raw material monomer on the dielectric layer of the anode body. Alternatively, it may be formed by applying a liquid containing a conductive polymer to the dielectric layer of the anode body. The electrolyte layer may be composed of one layer, or may be composed of two or more layers made of different materials.

[0047] The anode body, cathode layer, and electrolyte layer of the second electrolytic capacitor are not particularly limited except for matters related to the hydroxyl group-containing compound (C). For example, the anode body, cathode layer, and electrolyte layer of the second electrolytic capacitor may be formed using materials and techniques used in known electrolytic capacitors including porous anode bodies. The anode body and cathode layer of the second electrolytic capacitor are described below.

[0048] The porous anode body may be, for example, a porous sintered body obtained by sintering material particles containing a valve metal. The anode body may be in the shape of a rectangular parallelepiped. Examples of the valve metal include titanium (Ti), tantalum (Ta), and niobium (Nb). The material particles may be made of an alloy containing a valve metal. For example, an alloy containing a valve metal and silicon, vanadium, boron, or the like may be used. The valve metal alloy contains a valve metal as a main component, for example, 50 atomic % or more of the valve metal. Also, material particles made of a compound containing a valve metal and a typical element such as nitrogen may be used. One type of material particle may be used alone, or two or more types may be mixed and used.

[0049] The anode body has a dielectric layer on its surface. Therefore, the electrolyte layer is in contact with the dielectric layer of the anode body. The dielectric layer is formed, for example, by subjecting the sintered body to a chemical conversion treatment and growing an oxide film on the surface of the sintered body.

[0050] The cathode layer has a current collecting function. The cathode layer is formed, for example, of a conductive material. The cathode layer may be a conductive layer formed to cover the electrolyte layer. The cathode layer may include a carbon layer formed to cover the electrolyte layer, and a metal paste layer formed on the carbon layer. The carbon layer may include a conductive carbon material such as graphite and a resin. The metal paste layer may include metal particles (for example, silver particles) and a resin.

[0051] As examples of the method of the present disclosure for manufacturing an electrolytic capacitor, the first and second manufacturing methods are described below. According to these manufacturing methods, the electrolytic capacitor of the present disclosure can be manufactured. The matters described for the electrolytic capacitor of the present disclosure can be applied to the manufacturing methods below, so duplicated explanations may be omitted. For example, the components of the electrolytic capacitor of the present disclosure (anode body, cathode body or cathode layer, separator, and components of the electrolyte layer) have been described above, so duplicated explanations may be omitted. Specifically, the hydroxyl group-containing compound (C), conductive polymer, separator, and liquid component (L) have been described above, so duplicated explanations may be omitted. In addition, the matters described below can be applied to the electrolytic capacitor of the present disclosure described above.

[0052] [First manufacturing method of electrolytic capacitor] According to a first manufacturing method, the above-mentioned first electrolytic capacitor can be manufactured. The first manufacturing method is a method for manufacturing an electrolytic capacitor including a foil-shaped anode body having a dielectric layer on its surface, and a foil-shaped cathode body. This first manufacturing method includes the following steps (i) to (iii).

[0053] (Process ( i ) ) 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 that face each other with the separator interposed therebetween. The capacitor element precursor is a pre-formed composite material before an electrolyte layer is formed. Capacitor It is an element.

[0054] The foil-shaped anode body may be formed by a known method. For example, first, a metal foil, which is the raw material of the anode body, is prepared, and the surface of the metal foil is roughened. The roughening can be performed, for example, by etching using a direct current electrolysis method or an alternating current electrolysis method. Next, a dielectric layer is 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 surface of the metal foil is oxidized by the chemical conversion treatment of the metal foil, thereby forming a dielectric layer, which is an oxide film. In this manner, the anode body is formed.

[0055] If necessary, lead terminals for electrical connection are connected to the anode body and the cathode body.

[0056] When the first electrolytic capacitor is a wound type capacitor, for example, a capacitor element precursor can be formed by winding together a foil-shaped anode body, a foil-shaped cathode body, and a separator such that the separator is disposed between the anode body and the cathode body.

[0057] When the capacitor element is a laminated capacitor, for example, a capacitor element precursor can be formed by folding a foil-shaped anode body, a foil-shaped cathode body, and a separator together in a zigzag pattern such that the separator is disposed between the anode body and the cathode body.

[0058] (Step (ii)) Step (ii) is a step of disposing a hydroxyl-containing compound (hydroxyl-containing compound (C)), which is at least one compound selected from the group consisting of sugars and polyhydric alcohols and has a melting point of 50°C or higher, inside the capacitor element precursor. Step (ii) may be a step of precipitating the hydroxyl-containing compound (C) inside the capacitor element precursor. Therefore, in the following description, "disposing" may be read as "precipitating".

[0059] The step (ii) includes a step (ii-a) and a step (ii-b). The step (ii-a) is a step of impregnating the capacitor element precursor with an aqueous treatment liquid containing a hydroxyl group-containing compound (C).

[0060] Step (ii-a) can be carried out, for example, by immersing the capacitor element precursor in an aqueous treatment liquid. There is no limitation on the immersion time, and it may be 1 minute or more and less than 20 minutes. The entire capacitor element precursor may be immersed in the aqueous treatment liquid, or only a part of the capacitor element precursor may be immersed in the aqueous treatment liquid. For example, only 50% or less of the capacitor element precursor in the longitudinal direction (axial direction in the case of a wound body) may be immersed in the aqueous treatment liquid.

[0061] Step (ii-a) may be carried out at room temperature or at a temperature other than room temperature (e.g., a temperature higher than room temperature) and may be carried out under atmospheric pressure or in an environment other than atmospheric pressure (e.g., under reduced pressure).

[0062] The aqueous treatment liquid is a treatment liquid containing water. The amount of water contained in the liquid (solvent) constituting the aqueous treatment liquid is, for example, in the range of 50 to 100 mass %. Usually, the hydroxyl group-containing compound (C) is dissolved in the aqueous treatment liquid. That is, the aqueous treatment liquid may be a solution in which the hydroxyl group-containing compound (C) is dissolved. In a typical example, the aqueous treatment liquid is an aqueous solution of the hydroxyl group-containing compound (C).

[0063] The content (concentration) of the hydroxyl-containing compound (C) in the aqueous treatment liquid (e.g., an aqueous solution of the hydroxyl-containing compound (C)) may be in the range of 3 to 50% by mass (e.g., in the range of 5 to 15% by mass). The aqueous treatment liquid may contain components other than the hydroxyl-containing compound (C) as necessary.

[0064] The aqueous treatment liquid may contain a macromolecule (polymer), but preferably does not contain a macromolecule. For example, the aqueous treatment liquid may not contain a conductive polymer. The aqueous treatment liquid that does not contain a macromolecule has a low viscosity, which facilitates impregnation into the capacitor element precursor. Here, the macromolecule means a polymer having a weight average molecular weight of 1000 or more.

[0065] Step (ii-b) is a step of disposing the hydroxyl-containing compound (C) inside the capacitor element precursor by drying the impregnated aqueous treatment liquid. Step (ii-b) may be performed under atmospheric pressure or under an environment other than atmospheric pressure (e.g., reduced pressure).

[0066] The drying in step (ii-b) is carried out at a predetermined temperature (T). The predetermined temperature (T) is a temperature equal to or higher than the boiling point of the aqueous treatment liquid under the pressure at which the drying in step (ii-b) is carried out (for example, 100°C or higher, 120°C or higher, or 125°C or higher), and is a temperature lower than the melting point of the hydroxyl-containing compound (C) under the pressure at which the drying in step (ii-b) is carried out. Note that since the change in melting point due to pressure is small, the melting point of the hydroxyl-containing compound (C) at 1 atmosphere can be regarded as the melting point of the hydroxyl-containing compound (C) under the pressure at which the drying in step (ii-b) is carried out.

[0067] As a result of the investigation, the inventors of the present application found that the drying conditions in step (ii-b) can cause the hydroxyl group-containing compound (C) to be unevenly distributed in the peripheral portion of the capacitor element precursor rather than in the center of the capacitor element precursor. Therefore, the hydroxyl group-containing compound (C) can be unevenly distributed in the peripheral portion of the capacitor element manufactured by this manufacturing method. The peripheral portion of the capacitor element is prone to defects in the dielectric layer (oxide film) of the anode body. By disposing the hydroxyl group-containing compound (C) having multiple hydroxyl groups in this portion, defects in the dielectric layer are easily repaired. As a result, a highly reliable electrolytic capacitor can be obtained. Specifically, an electrolytic capacitor with high breakdown voltage and less susceptible to short circuits can be obtained.

[0068] If necessary, step (ii) may be repeated to increase the amount of the hydroxyl group-containing compound (C) precipitated.

[0069] (Step (iii)) Step (iii) is a step of forming a conductive polymer layer containing a conductive polymer inside the capacitor element precursor that has been subjected to step (ii). The conductive polymer layer is a layer that can become the electrolyte layer of the first electrolytic capacitor.

[0070] Step (iii) includes steps (iii-a) and (iii-b). Step (iii-a) is a step of impregnating the capacitor element precursor that has been subjected to step (ii) with an aqueous dispersion containing a conductive polymer.

[0071] Step (iii-a) can be carried out, for example, by immersing the capacitor element precursor in the aqueous dispersion. The immersion time is not limited and may be from 1 second to 30 minutes. The entire capacitor element precursor may be immersed in the aqueous dispersion, or only a portion of the capacitor element precursor may be immersed in the aqueous dispersion. For example, only 50% or less of the capacitor element precursor in the longitudinal direction (axial direction in the case of a wound body) may be immersed in the aqueous dispersion.

[0072] Step (iii-a) may be carried out at room temperature or at a temperature other than room temperature (e.g., a temperature higher than room temperature) and may be carried out under atmospheric pressure or in an environment other than atmospheric pressure (e.g., under reduced pressure).

[0073] The aqueous dispersion is a treatment liquid containing water. The amount of water contained in the aqueous liquid (dispersion medium) constituting the aqueous dispersion is, for example, in the range of 2 to 100 mass %. The aqueous liquid may be water. The conductive polymer is dispersed in the aqueous liquid. That is, the aqueous dispersion is a suspension in which the conductive polymer is dispersed in the aqueous liquid.

[0074] The content (concentration) of the conductive polymer in the aqueous dispersion may be in the range of 0.1 to 20% by mass (for example, in the range of 0.5 to 3% by mass).

[0075] The viscosity of the 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 (for example, in the range of 1 mPa·s to 25 mPa·s). The lower the viscosity of the aqueous dispersion, the easier it is to impregnate the capacitor element precursor.

[0076] The aqueous dispersion preferably does not contain the above-mentioned hydroxyl-containing compound (C). By not adding the hydroxyl-containing compound (C), the viscosity of the aqueous dispersion can be reduced. Even if the aqueous dispersion contains the hydroxyl-containing compound (C), it is preferable to contain it in a range such that the viscosity of the aqueous dispersion is a certain value or less (for example, 40 mPa s or less, 25 mPa s or less).

[0077] As described above, a dopant may be added to the conductive polymer, and the aqueous dispersion may contain components other than the conductive polymer and the dopant, as necessary.

[0078] Step (iii-b) is a step of forming a conductive polymer layer by drying the impregnated aqueous dispersion. Typically, the conductive polymer layer contains a conductive polymer as a main component.

[0079] There is no particular limitation on the method for drying the aqueous dispersion. Step (iii-b) may be performed under atmospheric pressure or under an environment other than atmospheric pressure (e.g., reduced pressure). In step (iii-b), at least heating is usually performed. The heating temperature in step (iii-b) is selected from the following (1) and / or (2): Conditions may be satisfied. (1) The heating temperature in step (iii-b) is a temperature that is equal to or higher than the boiling point of the aqueous dispersion under the pressure at which the drying in step (iii-b) is performed and is a temperature that is lower than the melting point of the hydroxyl group-containing compound (C) under the pressure at which the drying in step (iii-b) is performed. (2) The heating temperature in step (iii-b) is higher than the heating temperature in step (ii-b).

[0080] In order to realize high characteristics (e.g., low ESR), it is necessary to increase the content of the conductive polymer in the electrolyte layer. For this, it is important to increase the adhesiveness of the conductive polymer. As one method for increasing the adhesiveness of the conductive polymer, it is considered to add a polyhydric alcohol or the like to an aqueous dispersion of the conductive polymer. However, when a polyhydric alcohol or the like is added to the aqueous dispersion, there is a problem that the viscosity of the aqueous dispersion increases, making it difficult to impregnate the aqueous dispersion. In the manufacturing method of the present disclosure, first, a treatment is performed with an aqueous treatment liquid containing a hydroxyl group-containing compound (C), and then the aqueous dispersion is impregnated. Therefore, the impregnation with the aqueous dispersion is easy. In addition, by disposing the hydroxyl group-containing compound (C) in advance in the capacitor element precursor, it is possible to firmly fix the conductive polymer to be impregnated thereafter. As a result, an electrolytic capacitor with high characteristics can be manufactured.

[0081] In this manner, the electrolyte layer is formed, that is, the capacitor element including the electrolyte layer is formed.

[0082] The capacitor element obtained as described above can be used to manufacture the electrolytic capacitors (first and second electrolytic capacitors) of the present disclosure. There is no particular limitation on the method for manufacturing the electrolytic capacitor using the capacitor element, and a known method may be applied. For example, the capacitor element may be placed in a case and sealed.

[0083] [Second manufacturing method of electrolytic capacitor] According to the second manufacturing method, the second electrolytic capacitor can be manufactured. The second manufacturing method is a method for manufacturing an electrolytic capacitor including a porous anode body having a dielectric layer on its surface. The second manufacturing method includes steps (I) and (II).

[0084] (Process (I)) Step (I) is a step of disposing, on the surface of the anode body, at least one compound selected from the group consisting of sugars and polyhydric alcohols, a hydroxyl-containing compound (C) having a melting point of 50° C. or higher. The porous anode body having a dielectric layer on its surface can be one described in the second electrolytic capacitor.

[0085] Step (I) includes steps (Ia) and (Ib). Step (Ia) is a step of impregnating an aqueous treatment liquid containing a hydroxyl group-containing compound (C) into an anode body. Step (Ia) can be carried out under the same conditions as step (ii-a), except that an anode body is used instead of a capacitor element precursor. For example, the aqueous treatment liquid can be the aqueous treatment liquid described in step (ii-a).

[0086] In step (Ib), the hydroxyl group-containing compound is removed by drying the impregnated aqueous treatment liquid. (C) is placed on the surface of the anode body. The drying in step (Ib) is carried out at a predetermined temperature. The predetermined temperature is a temperature equal to or higher than the boiling point of the aqueous treatment liquid under the pressure at which the drying in step (Ib) is carried out and is lower than the melting point of the hydroxyl group-containing compound (C) under the pressure at which the drying in step (Ib) is carried out. The drying in step (Ib) can be carried out under the same conditions as those for the drying described in step (ii-b).

[0087] (Step (II)) Step (II) is a step of forming a conductive polymer layer containing a conductive polymer on the anode body that has been subjected to step (I) (on the dielectric layer of the anode body).

[0088] Step (II) includes steps (II-a) and (II-b). Step (II-a) is a step of impregnating an aqueous dispersion containing a conductive polymer into the anode body that has been subjected to step (I). Step (II-a) can be performed under the same conditions as step (iii-a), except that the anode body is used instead of the capacitor element precursor. For example, the aqueous dispersion can be the aqueous dispersion described in step (iii-a).

[0089] When the conductive polymer is dispersed in a dispersion medium in the form of particles, the average particle size of the particles may be in the range of 0.1 μm to 0.5 μm. If the average particle size of the particles is in this range, the particles can easily penetrate into the inside of the anode body. Here, the average particle size is defined as the median diameter (D 50 The median diameter can be determined, for example, by using a laser diffraction / scattering type particle size distribution measuring device.

[0090] Step (II-b) is a step of forming a conductive polymer layer on the anode body by drying the impregnated aqueous dispersion. The drying in step (II-b) can be performed under the same conditions as those described in step (iii-b). For example, the heating temperature in step (II-b) may satisfy the following (1) and / or (2). (1) The heating temperature in step (II-b) is a temperature that is equal to or higher than the boiling point of the aqueous dispersion under the pressure at which the drying in step (II-b) is performed and is a temperature that is lower than the melting point of the hydroxyl group-containing compound (C) under the pressure at which the drying in step (II-b) is performed. (2) The heating temperature in step (II-b) is higher than the heating temperature in step (Ib).

[0091] In this way, a conductive polymer layer (electrolyte layer) formed on the anode body (on the dielectric layer) is obtained. Thereafter, a cathode layer is formed on the conductive polymer layer (electrolyte layer). The cathode layer can be formed, for example, by applying a material constituting the cathode layer onto the electrolyte layer. In this way, a capacitor element is obtained. An electrolytic capacitor (second electrolytic capacitor) can be manufactured using this capacitor element. There is no particular limitation on the method for manufacturing an electrolytic capacitor using the capacitor element, and a known method can be applied.

[0092] In the following, an example of the electrolytic capacitor according to the present disclosure will be specifically described with reference to the drawings, but the electrolytic capacitor of the present disclosure is not limited to the following drawings. The above-mentioned components can be applied to the components of the example electrolytic capacitor described below. In addition, the components of the example electrolytic capacitor described below can be modified based on the above description. In addition, the matters described below may be applied to the above embodiment. Note that the same reference numerals may be used for similar parts, and duplicated descriptions may be omitted.

[0093] (Embodiment 1) In embodiment 1, an example of a first electrolytic capacitor will be described. Fig. 1 shows a schematic cross-section of an example of an electrolytic capacitor 100 of embodiment 1. Fig. 2 shows a schematic view in which a part of a capacitor element included in the electrolytic capacitor 100 shown in Fig. 1 is developed.

[0094] 1, electrolytic capacitor 100 includes, for example, capacitor element 10, bottomed case 11 that houses capacitor element 10, sealing member 12 that closes the opening of bottomed case 11, seat plate 13 that covers sealing member 12, lead wires 14A and 14B that are led out from sealing member 12 and pass through seat plate 13, and lead tabs 15A and 15B (not shown) that connect lead wires 14A and 14B to electrodes of capacitor element 10. Capacitor element 10 is housed in bottomed case 11. When capacitor element 10 contains a liquid component (L), liquid component (L) is also housed in bottomed case 11. The vicinity of the open end of bottomed case 11 is drawn inward, and the open end is curled so as to crimp sealing member 12.

[0095] Capacitor element 10 includes an anode body 21 having a dielectric layer on its surface, a cathode body 22, and a separator 23 disposed therebetween. These constitute an electrode group (wound body) 20. Capacitor element 10 includes an electrolyte layer (not shown) disposed between anode body 21 and cathode body 22. Anode body 21 and cathode body 22 are wound with separator 23 disposed therebetween. The outermost periphery of the wound body is fixed by a stop tape 24. Note that FIG. 2 shows a partially unfolded state of the wound body before the outermost periphery is fixed.

[0096] The electrolyte layer has unevenly distributed portions where the hydroxyl-containing compound (C) is unevenly distributed at both ends of the wound body in the winding axis direction and at the outermost periphery of the wound body.

[0097] (Embodiment 2) An example of a capacitor element included in the second electrolytic capacitor will be described in the second embodiment. Fig. 3 is a schematic cross-sectional view of a capacitor element 210 of the electrolytic capacitor according to the second embodiment. Capacitor element 210 includes an anode portion 220 and a cathode portion 230. Anode portion 220 includes an anode body 221 and an anode wire 222. Anode body 221 includes a dielectric layer 221a formed on the surface. A portion of anode wire 222 is embedded in anode body 221. Cathode portion 230 has an electrolyte layer (e.g., a solid electrolyte layer) 231 covering at least a portion of dielectric layer 221a, and a cathode layer 232 covering electrolyte layer 231.

[0098] The anode wire 222 is made of a conductive material. The material of the anode wire 222 is not particularly limited, and may be the valve metals described above or other metals (copper, aluminum, aluminum alloy, etc.).

[0099] In one example of the production of the anode part 220, first, a part of the anode wire 222 is embedded in metal powder (raw material of the anode body 221), and the powder is pressure-molded into a rectangular parallelepiped shape. Next, the powder is sintered. In this manner, the anode body 221 is obtained before the dielectric layer 221a is formed. There is no limitation on the method for forming the dielectric layer 221a, and it may be formed by a known method. The dielectric layer 221a may be formed by immersing the anode body 221 in a chemical conversion solution and anodizing the surface of the anode body 221. Alternatively, the dielectric layer 221a may be formed by heating the anode body 221 in an atmosphere containing oxygen.

[0100] There is no limitation on the method for forming the electrolyte layer 231 and the cathode layer 232, and they may be formed by the above-mentioned method or a known method.

[0101] The capacitor element 210 is connected to a lead wire and sealed with an insulating material (e.g., insulating resin) as necessary. There is no limitation to these, and known techniques can be applied. In this manner, the second electrolytic capacitor is obtained. EXAMPLES

[0102] In the following, the embodiments of the present disclosure will be described in more detail with reference to examples. In these examples, a number of electrolytic capacitors (capacitors A1, A2 and capacitors C1 to C4) were fabricated and evaluated. The manufacturing and evaluation methods of these capacitors will be described below. In the description of the manufacturing method of the comparative capacitor, conditions different from the above-mentioned conditions of steps (ii) and (iii) may be used, but for convenience, these will also be described as steps (ii) and (iii).

[0103] [Preparation of capacitor A1] 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 by the following procedure.

[0104] (Preparation of the cathode body) For the cathode body, an Al foil (aluminum foil) with a thickness of 50 μm was used.

[0105] (Preparation of the anode body) An Al foil with a thickness of 120 μm was prepared. This Al foil was subjected to DC etching treatment to roughen the surface. Subsequently, the Al foil was subjected to formation treatment to form a dielectric layer (thickness: approximately 70 nm), thereby obtaining the anode body. The dielectric layer was formed by immersing the Al foil in an ammonium adipate solution and performing formation treatment at 70 °C for 5 hours while applying a voltage of 50 V to the Al foil. Thereafter, the anode body was cut to a predetermined size to prepare the anode body of capacitor A1.

[0106] (Fabrication of the wound body (process (i))) An anode lead tab and a cathode lead tab to which lead wires were connected were respectively connected to the prepared anode body and cathode body. Then, the anode body and the cathode body were wound with a separator sandwiched therebetween, and the outer surface was fixed with a winding tape. As the separator, a non-woven fabric made of aramid (aromatic polyamide fiber), which is a synthetic fiber, was used. In this way, a wound body (precursor of the capacitor element) was fabricated. The fabricated wound body was immersed in an ammonium adipate solution, and formation treatment was performed again at 70 °C for 60 minutes while applying a voltage of 50 V to the anode body, thereby forming a dielectric layer mainly on the end face of the anode body.

[0107] (Preparation of the aqueous treatment liquid) By dissolving mannitol in ion-exchanged water, an aqueous mannitol solution with a concentration of 10 mass% was prepared. When the viscosity of the obtained aqueous mannitol solution was measured, it was 5 mPa·s or less.

[0108] (Preparation of the aqueous dispersion) A mixed solution of 3,4-ethylenedioxythiophene and polystyrenesulfonic acid as a dopant was prepared by dissolving them in ion-exchanged water. While stirring the obtained mixed solution, iron (III) sulfate (oxidant) 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 oxidant, and a dispersion (aqueous dispersion) containing poly(3,4-ethylenedioxythiophene) doped with about 5% by mass of polystyrenesulfonic acid (PSS) was obtained. In the following, poly(3,4-ethylenedioxythiophene) doped with about 5% by mass of polystyrenesulfonic acid (PSS) may be referred to as "PEDOT:PSS". In addition, a dispersion in which PEDOT:PSS is dispersed may be referred to as "PEDOT:PSS dispersion". Using this PEDOT:PSS dispersion, an aqueous dispersion with a PEDOT:PSS concentration of 2% by mass was prepared. The viscosity of the resulting dispersion was measured and found to be 25 mPa·s.

[0109] (Step (ii)) First, an aqueous treatment liquid was placed in a container. Next, the wound body (capacitor element precursor) was immersed in the aqueous treatment liquid in the container for 5 minutes at room temperature under atmospheric pressure. At this time, the wound body was immersed in the aqueous treatment liquid from the side to which the lead tab was not connected (this is the same for other immersion steps described below). Then, the wound body was lifted up from the aqueous treatment liquid. In this way, the aqueous treatment liquid was impregnated into the wound body. Next, the wound body was dried at 125°C for 30 minutes in a drying furnace with a pressure of 1 atmosphere, thereby drying the aqueous treatment liquid. In this way, mannitol, which is a hydroxyl group-containing compound (C), was placed inside the wound body.

[0110] When the wound body was unfolded and the electrolyte layer was observed, mannitol was found to be unevenly distributed and precipitated at locations corresponding to both ends of the wound body in the axial direction and at a location corresponding to the outermost periphery of the wound body. That is, the electrolyte layer had unevenly distributed portions where mannitol was unevenly distributed at both ends of the wound body in the axial direction and at the outermost periphery of the wound body.

[0111] (Step (iii)) First, an aqueous dispersion was placed in a container. Next, the wound body was immersed in the aqueous dispersion in the container for 15 minutes at room temperature in a reduced pressure atmosphere (40 kPa), and then the wound body was pulled out of the aqueous dispersion. In this way, the aqueous dispersion was impregnated into the wound body. Next, the wound body was dried at 150°C for 30 minutes in a drying furnace with a pressure of 1 atmosphere. This allowed the aqueous dispersion to dry. In this way, a conductive polymer layer was formed.

[0112] (Electrolyte Impregnation) The wound body that had undergone step (iii) was impregnated with an electrolytic solution at room temperature under atmospheric pressure. As the electrolytic solution, a solution was used in which polyethylene glycol, γ-butyrolactone, sulfolane, and mono(ethyldimethylamine) phthalate (solute) were mixed in a mass ratio of polyethylene glycol:γ-butyrolactone:sulfolane:mono(ethyldimethylamine) phthalate = 25:25:25:25. In this way, a capacitor element including an electrolyte layer was obtained. This capacitor element was sealed to complete an electrolytic capacitor. Thereafter, an aging treatment was performed at 130°C for 2 hours while applying the rated voltage. In this way, a capacitor A1 was obtained.

[0113] [Capacitor A2] Capacitor A2 was fabricated under the same conditions as Capacitor A1, except that the separator was changed to a natural cellulose fiber.

[0114] [Capacitor C1] Capacitor C1 was produced under the same conditions as capacitor A1, except that step (ii) was not performed and the conditions of step (iii) were changed.

[0115] In step (iii) of the capacitor C1, an aqueous dispersion was prepared by dissolving mannitol in the PEDOT:PSS dispersion described in the preparation of the capacitor A1. The concentration of PEDOT:PSS in the aqueous dispersion was 2% by mass, and the concentration of mannitol was 10% by mass. The viscosity of the resulting dispersion was measured to be 45 mPa s.

[0116] This aqueous dispersion was used for impregnation under the same conditions as in step (iii) of capacitor A1. Next, the wound body was dried in a drying oven at 60°C for 30 minutes, and then at 125°C for 15 minutes. This dried the aqueous dispersion. In this way, a conductive polymer layer was formed. Thereafter, capacitor C1 was produced using the same process as capacitor A1.

[0117] [Capacitor C2] Capacitor C2 was produced under the same conditions as capacitor A1, except that the drying temperature in step (ii) and the drying temperature and time in step (iii) were changed. In step (ii) of the capacitor C2, drying was performed at 180° C. for 30 minutes. In step (iii) of the capacitor C2, drying was performed at 60° C. for 30 minutes, followed by drying at 125° C. for 15 minutes.

[0118] [Capacitor C3] Capacitor C3 was produced under the same conditions as capacitor C2, except that step (ii) was not performed.

[0119] [Capacitor C4] Capacitor C4 was fabricated under the same conditions as capacitor C2, except for the separator, which was made of natural cellulose fiber.

[0120] (Evaluation of distribution of mannitol) For the wound body (capacitor element precursor before step (ii)) produced in step (i) of capacitor A1, the end face in the axial direction of the wound body was visually observed. A photograph of the end face is shown in FIG. 4(a). In addition, for capacitor A1 and capacitor C2, the end faces of the wound bodies after step (ii) were each performed were visually observed. Photographs of these end faces are shown in FIG. 4(b) and FIG. 4(c). As shown in FIG. 4, when step (ii) of capacitor A1 was performed, mannitol was unevenly distributed as white on the end face of the wound body. This precipitate was present at both ends of the wound body. On the other hand, after step (ii) of capacitor C2, such uneven distribution was not observed.

[0121] Furthermore, the above three wound bodies were disassembled and the electrolyte held in the separator was observed. In the electrolyte after the step (ii) of the capacitor A1, mannitol was unevenly distributed in the portions corresponding to both ends of the wound body in the winding axis direction and in the portion corresponding to the outermost portion of the wound body. On the other hand, in the electrolyte after the step (ii) of the capacitor C2, no such uneven distribution was observed.

[0122] The steps up to step (ii) were carried out in the same manner as in the preparation of each of the above capacitors. The wound body (capacitor element precursor) that had undergone step (ii) was then disassembled to examine the distribution of mannitol in the electrolyte layer. Specifically, mannitol was identified using a micro FT-IR analyzer (Nicolet-iN10 manufactured by ThermoFisher). Regarding the distribution ratio of mannitol, first, Capacitor Element end and Capacitor The element was cut into two parts, one at the center and the other at the center, and the mannitol attached to each part was extracted with a water solvent. Next, the dry weight of the mannitol present in each part was calculated. From this dry weight, the distribution ratio of mannitol was calculated. Similarly, the same method as the preparation method for each of the above capacitors was carried out up to step (iii), and the distribution ratio of mannitol in the electrolyte layer was calculated.

[0123] (Evaluation of characteristics) The equivalent series resistance (ESR) of the electrolytic capacitor prepared as described above was measured. The ESR was measured using a four-terminal LCR meter in an environment of 20°C. In addition, a voltage was applied to the electrolytic capacitor while increasing it at a rate of 1.0 V / sec, and the breakdown voltage at which an overcurrent of 0.5 A flows was measured.

[0124] In addition, 30 pieces of each of the six types of capacitors mentioned above were made, and the rated voltage of 35V was applied in an environment of 150°C, and the presence or absence of short circuits was confirmed after 60 minutes had elapsed. Then, an evaluation was made of how many of the 30 capacitors were short-circuited.

[0125] The measurement results and some of the manufacturing conditions for the electrolytic capacitor are shown in Table 1. In Table 1, "PEDOT:PSS mixture" means that the aqueous dispersion contains PEDOT:PSS and mannitol.

[0126] [Table 1]

[0127] The drying temperature in the step (ii-b) of the condensers A1 and A2 is equal to or higher than the boiling point of the aqueous treatment liquid. The melting point of mannitol is about 165 to 169°C. Therefore, the drying temperature in the step (ii-b) of the condensers A1 and A2 is equal to or higher than the boiling point of the aqueous treatment liquid and lower than the melting point of mannitol (hydroxyl group-containing compound (C)). On the other hand, the drying temperature in the step (ii-b) of the condensers C2 and C4 is higher than the melting point of mannitol (hydroxyl group-containing compound (C)).

[0128] A lower ESR value is preferable. The ESR value is preferably 20 mΩ or less (for example, in the range of 3 to 20 mΩ), and more preferably 12 mΩ or less (for example, in the range of 3 to 12 mΩ). A higher breakdown voltage is preferable, and is preferably 75 V or more (for example, in the range of 75 to 100 V). A smaller number of short circuits is preferable.

[0129] As shown in Table 1, the capacitors A1 and A2 of the present disclosure were good in ESR, breakdown voltage, and number of short circuits. The reason for the low ESR is believed to be that the electrolyte layer contains mannitol (hydroxyl group-containing compound (C)). The reason for the low breakdown voltage and number of short circuits is believed to be that mannitol is unevenly distributed at both ends of the wound body in the winding axis direction and at the outermost periphery of the wound body.

[0130] Comparing capacitor C2, which uses a synthetic fiber separator, with capacitor C3, which uses a natural fiber separator, the breakdown voltage and number of short circuits in capacitor C3, which uses a natural fiber separator, were significantly worse. On the other hand, there was no significant difference between capacitors A1 and A2. This is thought to be because the separator is reinforced by carrying out step (ii). [Industrial Applicability]

[0131] The present disclosure can be used for an electrolytic capacitor and a manufacturing method thereof. [Explanation of symbols]

[0132] 10, 210 Capacitor element 20 electrode groups 21, 221 Anode body 22 Cathode body 23 Separator 100 Electrolytic capacitor 221a Dielectric layer 222 Anode Wire 230 Cathode 231 Electrolyte layer 232 Cathode Layer

Claims

1. A method for manufacturing an electrolytic capacitor including a foil-shaped anode body having a dielectric layer on a surface thereof and a foil-shaped cathode body, comprising the steps of: (i) forming a capacitor element precursor by winding or stacking a separator and the anode body and the cathode body facing each other with the separator therebetween; (ii) disposing at least one compound selected from the group consisting of sugars and sugar alcohols, which is a hydroxyl group-containing compound having a melting point of 50° C. or higher, inside the capacitor element precursor; and (iii) forming a conductive polymer layer containing a conductive polymer inside the capacitor element precursor that has been subjected to the step (ii), The step (ii) a step (ii-a) of impregnating the capacitor element precursor with an aqueous treatment liquid containing the hydroxyl group-containing compound; and (ii-b) a step of disposing the hydroxyl-containing compound inside the capacitor element precursor by drying the impregnated aqueous treatment liquid, the number of hydroxyl groups contained in the hydroxyl group-containing compound is in the range of 2 to 12; The step (iii) A step (iii-a) of impregnating the capacitor element precursor that has been subjected to the step (ii) with an aqueous dispersion containing the conductive polymer; and (iii-b) forming the conductive polymer layer by drying the impregnated aqueous dispersion, The drying in the step (ii-b) is carried out at a predetermined temperature, the predetermined temperature is a temperature that is equal to or higher than the boiling point of the aqueous treatment liquid under the pressure at which the drying in the step (ii-b) is performed, and is a temperature that is lower than the melting point of the hydroxyl group-containing compound under the pressure at which the drying in the step (ii-b) is performed.

2. A method for producing an electrolytic capacitor including a porous anode body having a dielectric layer on a surface thereof, comprising the steps of: A step (I) of disposing at least one compound selected from the group consisting of sugars and sugar alcohols, which is a hydroxyl group-containing compound having a melting point of 50° C. or higher, on a surface of the anode body; and step (II) of forming a conductive polymer layer containing a conductive polymer on the anode body that has been subjected to step (I), The step (I) a step (I-a) of impregnating the anode body with an aqueous treatment liquid containing the hydroxyl group-containing compound; and (I-b) disposing the hydroxyl group-containing compound on the surface of the anode body by drying the impregnated aqueous treatment liquid, The step (II) A step (II-a) of impregnating the anode body having undergone the step (I) with an aqueous dispersion containing the conductive polymer; and a step (II-b) of forming the conductive polymer layer on the anode body by drying the impregnated aqueous dispersion, the number of hydroxyl groups contained in the hydroxyl group-containing compound is in the range of 2 to 12; The drying in the step (I-b) is carried out at a predetermined temperature, The method for manufacturing an electrolytic capacitor, wherein the predetermined temperature is a temperature equal to or higher than the boiling point of the aqueous treatment liquid under the pressure at which the drying in the step (I-b) is performed, and is a temperature lower than the melting point of the hydroxyl group-containing compound under the pressure at which the drying in the step (I-b) is performed.

3. The method according to claim 1 or 2, wherein the viscosity of the aqueous dispersion is in the range of 1 to 100 Pa·s.

4. The method according to any one of claims 1 to 3, wherein the aqueous treatment liquid is polymer-free.

5. The method according to any one of claims 1 to 4, wherein the hydroxyl group-containing compound is at least one selected from the group consisting of glucose, mannitol, sorbitol, xylitol, and pentaerythritol.

6. The method according to any one of claims 1 to 5, wherein the conductive polymer is poly(3,4-ethylenedioxythiophene) doped with polystyrenesulfonic acid.

7. 1. An electrolytic capacitor including a capacitor element, The capacitor element is an electrode group including a foil-shaped anode body having a dielectric layer on a surface thereof, a foil-shaped cathode body, and a separator; an electrolyte layer in contact with the anode body, the cathode body, and the separator; the electrode group is a wound body formed by winding the separator and the anode body and the cathode body that face each other with the separator in between, or a laminate formed by stacking the separator and the anode body and the cathode body that face each other with the separator in between, the electrolyte layer contains at least one compound selected from the group consisting of sugars and sugar alcohols, a hydroxyl group-containing compound having a melting point of 50° C. or higher, and a conductive polymer; the number of hydroxyl groups contained in the hydroxyl group-containing compound is in the range of 2 to 12; The hydroxyl-containing compound is unevenly distributed in a peripheral portion of the capacitor element rather than in a central portion of the capacitor element.

8. the electrode group is the wound body, 8. The electrolytic capacitor according to claim 7, wherein the electrolyte layer has unevenly distributed portions in which the hydroxyl group-containing compound is unevenly distributed at both ends of the wound body in the winding axis direction and at an outermost periphery of the wound body.

9. the electrode group is the laminate, 8. The electrolytic capacitor according to claim 7, wherein the electrolyte layer has an uneven distribution portion in which the hydroxyl group-containing compound is unevenly distributed, in a portion in contact with a peripheral edge portion of the anode body.

10. The electrolytic capacitor according to any one of claims 7 to 9, wherein the electrolyte layer contains a non-aqueous solvent or a non-aqueous electrolyte solution.

11. 1. An electrolytic capacitor including a capacitor element, The capacitor element includes a porous anode body having a dielectric layer on a surface thereof, a cathode layer, and an electrolyte layer disposed between the anode body and the cathode layer; The capacitor element includes at least one compound selected from the group consisting of sugars and sugar alcohols, the hydroxyl group-containing compound having a melting point of 50° C. or higher, and a conductive polymer; the number of hydroxyl groups contained in the hydroxyl group-containing compound is in the range of 2 to 12; The hydroxyl-containing compound is unevenly distributed in a peripheral portion of the anode body rather than in a central portion of the anode body.

12. 12. The electrolytic capacitor according to claim 7, wherein the hydroxyl group-containing compound is at least one selected from the group consisting of glucose, mannitol, sorbitol, xylitol, and pentaerythritol.

13. The electrolytic capacitor according to any one of claims 7 to 12, wherein the conductive polymer is poly(3,4-ethylenedioxythiophene) doped with polystyrenesulfonic acid.

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