Electrolytic capacitor and production method for electrolytic capacitor

Abstract

This electrolytic capacitor includes a capacitor element and a liquid component contained in a gap in the capacitor element. The capacitor element has: an anode foil that has a dielectric layer; a cathode foil; a separator that is interposed between the anode foil and the cathode foil; and a conductive polymer layer that is interposed between the anode foil and the cathode foil and is in contact with the separator. The liquid component includes a solvent and a solute. The solute includes a sugar alcohol, and the sugar alcohol is at least one sugar alcohol selected from the group consisting of xylitol and xylitol derivatives. The sugar alcohol content in the liquid component is 4-70 mass%.

Description

Electrolytic capacitor and method for manufacturing the same

[0001] The present disclosure relates to electrolytic capacitors and methods for manufacturing electrolytic capacitors.

[0002] Patent Document 1 proposes an electrolytic capacitor that includes a capacitor element and a liquid component, where the capacitor element includes an anode body having a dielectric layer on its surface and a conductive polymer that covers a portion of the dielectric layer, and the liquid component includes a sugar alcohol component and a polyalkylene glycol component, where the sugar alcohol component includes at least one selected from the group consisting of sugar alcohols having four or more hydroxy groups and derivatives thereof.

[0003] Patent Document 2 proposes an electrolytic capacitor including an anode body having a dielectric layer on its surface, a cathode body, and an electrolytic solution interposed between the anode body and the cathode body, wherein the electrolytic solution contains a first ester compound that is a condensate of boric acid and a sugar alcohol, and a second ester compound, wherein the second ester compound contains at least one of a condensate of boric acid and a monool compound and a condensate of boric acid and a polyol compound (excluding sugar alcohols), wherein the total amount of the boric acid and the sugar alcohol added to the entire electrolytic solution is 2% by mass or more and 10% by mass or less, and the amount of the second ester compound added to the entire electrolytic solution is 2% by mass or more and 10% by mass or less.

[0004] Patent Document 3 proposes "a solid electrolytic capacitor comprising: a capacitor element formed by placing an anode foil and a cathode foil opposite each other via a separator; a solid electrolyte layer made of a conductive polymer and formed within the capacitor element; and an electrolyte solution filled in voids within the capacitor element with the solid electrolyte layer formed therein and containing a tetravalent or higher sugar alcohol derivative, wherein the alkylene oxide group of the tetravalent or higher sugar alcohol derivative is an ethylene oxide group, a propylene oxide group, or both, and the viscosity of the electrolyte solution at 25°C is 209 mPa·s or less."

[0005] International Publication No. 2021 / 149751 Patent No. 7022910 Patent No. 7067059

[0006] A first aspect of the present disclosure relates to an electrolytic capacitor. The electrolytic capacitor includes a capacitor element and a liquid component contained in voids within the capacitor element. The capacitor element includes an anode foil having a dielectric layer, a cathode foil, a separator interposed between the anode foil and the cathode foil, and a conductive polymer layer interposed between the anode foil and the cathode foil and in contact with the separator. The liquid component includes a solvent and a solute. The solute includes a sugar alcohol, and the sugar alcohol is at least one selected from the group consisting of xylitol and xylitol derivatives. The sugar alcohol content in the liquid component is 4% by mass or more and 70% by mass or less.

[0007] A second aspect of the present disclosure relates to a method for manufacturing an electrolytic capacitor. The method includes the steps of: (a) preparing an anode foil having a dielectric layer, a cathode foil, and a separator; (b) applying a coating liquid containing a conductive polymer, a dopant, and a liquid medium to at least one surface selected from the surface of the dielectric layer and the surface of the cathode foil and into voids in the separator; (c) removing at least a portion of the liquid medium from the coating liquid to form a conductive polymer layer on the at least one surface and in the voids in the separator; (d) forming a capacitor element including the conductive polymer layer by disposing the separator between the anode foil and the cathode foil; and (e) impregnating the voids in the capacitor element with a liquid component, in this order. The liquid component includes a solvent and a solute. The solute includes a sugar alcohol, and the sugar alcohol is at least one selected from the group consisting of xylitol and xylitol derivatives. The content of the sugar alcohol in the liquid component is 4% by mass or more and 70% by mass or less.

[0008] According to the present disclosure, precipitation of sugar alcohols is suppressed during the manufacturing process of an electrolytic capacitor and within the completed electrolytic capacitor, thereby obtaining an electrolytic capacitor with excellent characteristics.

[0009] 1 is a side view schematically illustrating an electrolytic capacitor according to an embodiment of the present disclosure; 2 is an exploded perspective view schematically illustrating a capacitor element according to an embodiment of the present disclosure;

[0010] The problems in the prior art will be briefly described below.

[0011] Because sugar alcohols are solids, they are dissolved in a solvent and used as a solution. Although it depends on the type of solvent, sugar alcohols tend to precipitate at room temperature, and the tendency becomes greater the more sugar alcohol is used. If sugar alcohols precipitate during the manufacturing process of electrolytic capacitors, it becomes difficult to form a good conductive polymer layer. Furthermore, if sugar alcohols precipitate inside the completed electrolytic capacitor, the characteristics of the electrolytic capacitor may be reduced.

[0012] Hereinafter, embodiments according to the present invention will be described using examples, but the present invention 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 other materials may be applied as long as the invention according to the present disclosure can be implemented. In this specification, the expression "numerical value A to numerical value B" includes numerical value A and numerical value B and can be read as "numerical value A or more and numerical value B or less." In the following description, when lower and upper limits of numerical values ​​related to specific physical properties or conditions are exemplified, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit is not equal to or greater than the upper limit.

[0013] [Electrolytic Capacitor] An electrolytic capacitor according to a first aspect of the present disclosure includes a capacitor element and a liquid component contained in voids within the capacitor element.

[0014] The liquid component may be filled in at least a portion of the voids in the capacitor element. That is, the electrolytic capacitor according to the present disclosure is a solid-liquid hybrid electrolytic capacitor.

[0015] The capacitor element includes an anode foil having a dielectric layer, a cathode foil, a separator, and a conductive polymer layer. The separator is interposed between the anode foil and the cathode foil. The conductive polymer layer is interposed between the anode foil and the cathode foil and is in contact with the separator. The conductive polymer layer preferably contacts the anode foil, the cathode foil, and the separator over a sufficiently large contact area. This allows the conductive polymer layer to form a sufficient conductive path between the anode foil and the cathode foil, reducing the equivalent series resistance (ESR) of the electrolytic capacitor and improving reliability.

[0016] The liquid component includes a solvent and a solute. The solute includes a sugar alcohol. The sugar alcohol is at least one selected from the group consisting of xylitol and xylitol derivatives (hereinafter collectively referred to as "xylitol compound"). Therefore, hereinafter, "sugar alcohol" may be referred to as "xylitol compound."

[0017] Xylitol derivatives may be compounds in which some of the hydroxyl groups of xylitol are esterified, compounds in which some of the hydroxyl groups of xylitol are etherified, or compounds in which some of the hydroxyl groups of xylitol are anionized to form salts. However, the chemical structure of xylitol derivatives is not limited to these. The molar mass of the xylitol derivative may be in the range of 0.9 to 2 times the molar mass of xylitol (152.15 g / mol). The chemical formula of the xylitol derivative is the same as the chemical formula of xylitol (C ５ H ７ (OH) ５ ) can be used as a base, for example, C ５ H ７ (OH) ５-ａ X ａ (X may be an atom or group other than an OH group, and 1≦a≦4). X may be a halogen atom, an OM group (M is an alkali metal atom), OR (R is a hydrocarbon group having 5 or less carbon atoms, and at least one hydrogen atom of the hydrocarbon group may be substituted with a hydrophilic group such as a hydroxyl group or a carboxyl group, a halogen atom, or the like). It is preferable that X satisfies 1≦a≦3 or 1≦a≦2.

[0018] Among sugar alcohols, xylitol compounds have a low melting point and excellent solubility in solvents. By using a xylitol compound, even when a large amount of the xylitol compound is used, precipitation of the xylitol compound during the manufacturing process and in the completed electrolytic capacitor can be sufficiently suppressed.

[0019] Here, the use of a large amount of the xylitol compound refers to the case where the content of the xylitol compound in the liquid component is 4% by mass or more and 70% by mass or less. When these conditions are satisfied, the xylitol compound acts on the conductive polymer layer, increasing the contact area between the conductive polymer layer and the anode foil, the cathode foil, and the separator, and forming a sufficient conductive path between the anode foil and the cathode foil through the conductive polymer layer.

[0020] The greater the mass content of the xylitol compound in the liquid component, the greater the amount of the xylitol compound that can act on the conductive polymer layer. Except when the mass content of the xylitol compound in the liquid component is excessively high, the greater the mass content of the xylitol compound, the greater the contact area between the conductive polymer layer and the anode foil, the cathode foil, and the separator, and the conductive polymer layer forms a sufficient conductive path between the anode foil and the cathode foil.

[0021] In order to form a better conductive path between the anode foil and the cathode foil by the conductive polymer layer, the mass content of the xylitol compound in the liquid component is preferably 5 mass% or more, more preferably 7.5 mass% or more, may be 10 mass% or more, or may be 15 mass% or more.

[0022] On the other hand, in order to more reliably suppress the precipitation of xylitol compounds, the mass content of xylitol compounds in the liquid component is preferably 50 mass% or less, more preferably 30 mass% or less, and even more preferably 15 mass% or less.

[0023] The solute may further include at least one selected from the group consisting of an acid, a base, and an electrolyte salt. In this case, in order to more reliably suppress precipitation of the xylitol compound, the total mass content of all solutes in the liquid component is preferably 70 mass% or less, and more preferably 50 mass% or less.

[0024] The solvent preferably includes a first solvent, which is at least one selected from the group consisting of ethylene glycol, diethylene glycol, triethylene glycol, ethylene glycol condensates having a molecular weight of 250 or less, glycerin, γ-butyrolactone, and sulfolane.

[0025] The mass content of each component contained in the liquid component (and therefore the mass content of the xylitol compound) can be measured by various analytical methods such as gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS).

[0026] Next, the conductive polymer layer includes a conductive polymer and a dopant. The conductive polymer layer may also include a xylitol compound. In the conductive polymer layer, the ratio of the mass Ms of the sugar alcohol to the total mass Mp of the conductive polymer and the dopant (Ms / Mp) is, for example, 1 to 40, preferably 2 or more, and more preferably 5 to 20. When these conditions are satisfied, the contact area between the conductive polymer layer and the anode foil, the cathode foil, and the separator is likely to increase, and a sufficient conductive path is likely to be formed between the anode foil and the cathode foil by the conductive polymer layer.

[0027] The mass content of the xylitol compound in the conductive polymer layer may be greater than the mass contents of all other components in the conductive polymer layer. In this case, the ratio (Ms / Mp) may be greater than or equal to 1, greater than or equal to 5, greater than or equal to 7, or greater than or equal to 10. When the mass content of the xylitol compound in the conductive polymer layer is this high, the contact area between the conductive polymer layer and the anode foil, the cathode foil, and the separator can be significantly increased.

[0028] The mass content of the xylitol compound in the conductive polymer layer may be 50% by mass or more and 98% by mass or less, 60% by mass or more and 93% by mass or less, or 80% by mass or more and 93% by mass or less.

[0029] The conductive polymer layer is preferably formed on at least one surface selected from the surface of the dielectric layer and the surface of the cathode foil, and may also be formed within the voids of the separator (i.e., the inner walls of the separator's constituent material surrounding the voids of the separator). This allows a stronger conductive path to be formed between the anode foil and the cathode foil by the conductive polymer layer. The conductive polymer layer is preferably formed on at least the surface of the dielectric layer of the anode foil, and is preferably formed on both the surface of the dielectric layer and the surface of the cathode foil, and further formed within the voids of the separator.

[0030] <Method of Determining the Ratio (Ms / Mp)> The ratio (Ms / Mp) of the mass Ms of the sugar alcohol (xylitol compound) to the total mass Mp of the conductive polymer and the dopant can be determined, for example, by the following method.

[0031] (When the electrolytic capacitor does not contain liquid components) First, the cathode foil is separated from the capacitor element. A conductive polymer layer is attached to the cathode foil. Next, water-soluble components are removed from the cathode foil to which the conductive polymer layer is attached. The water-soluble components include xylitol compounds. Because the conductive polymer and dopant have different solubility in water than other water-soluble components, the conductive polymer and dopant can be separated from the other components using water.

[0032] For example, when a cathode foil is immersed in excess ion-exchanged water, the water-soluble components are thoroughly removed, and the foil is then dried, the dried cathode foil does not contain any water-soluble components (including xylitol compounds). Therefore, the mass of the water-soluble components can be measured from the dry mass of the cathode foil before and after the water-soluble components are removed.

[0033] Furthermore, the mass content of each component contained in the water-soluble component (and therefore the mass content of the xylitol compound) can be measured by various analytical methods such as gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS).

[0034] Furthermore, the cathode foil from which the water-soluble components have been removed can be subjected to thermal analysis using, for example, a differential scanning calorimeter, thereby measuring the mass content of the conductive polymer layer contained in the sample.

[0035] Using the above measurement results, the ratio (Ms / Mp) in the conductive polymer layer of the electrolytic capacitor containing no liquid component can be determined.

[0036] (When the electrolytic capacitor contains a liquid component) First, the cathode foil is separated from the capacitor element, and the liquid component is separated from the cathode foil. For example, the cathode foil is immersed in an excess of a solvent (e.g., ion-exchanged water) that has affinity for the liquid component, and the solvent is thoroughly removed. After drying, the dried cathode foil contains no liquid component. This allows for the production of a cathode foil having a conductive polymer layer that does not contain any liquid component.

[0037] Thereafter, in the same manner as in the case where the electrolytic capacitor does not contain any liquid component, the water-soluble component is removed from the cathode foil to which the conductive polymer layer is attached, and the cathode foil is dried. The sample is then subjected to thermal analysis using, for example, a differential scanning calorimeter, whereby the mass content of the conductive polymer layer contained in the sample can be measured.

[0038] On the other hand, the mass content of each component contained in the separated liquid component and water-soluble component (and therefore the mass content of the xylitol compound) can be measured by various analytical methods such as gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS).

[0039] Alternatively, the liquid component alone can be separated and analyzed to determine the mass content of each component contained in the liquid component.

[0040] Furthermore, by separating the cathode foil from the capacitor element and then drying it without washing, the mass content of the solvent contained in the liquid component in the cathode foil can be determined. The mass content of the solute contained in the liquid component in the cathode foil can be determined from the mass content of the solvent and the separately determined mass contents of each component contained in the liquid component.

[0041] Using the above measurement results, the ratio (Ms / Mp) in the conductive polymer layer of the electrolytic capacitor containing the liquid component can be determined.

[0042] Next, examples of components of the electrolytic capacitor according to the present disclosure will be further described, although the components of the electrolytic capacitor are not limited to the following examples.

[0043] (Anode Foil) Examples of anode foils include metal foils containing at least one valve metal such as titanium, tantalum, aluminum, and niobium. The anode foil may be a metal foil of a valve metal (e.g., aluminum foil). The anode foil may contain the valve metal in the form of an alloy containing the valve metal or a compound containing the valve metal. The thickness of the anode foil may be 15 μm or more and 300 μm or less. The surface of the anode foil may be roughened by etching or the like.

[0044] A dielectric layer is formed on the surface of the anode foil. The dielectric layer may be formed by chemically treating the anode foil. In this case, the dielectric layer may contain an oxide of a valve metal (e.g., aluminum oxide). Note that the dielectric layer may be formed of any dielectric other than an oxide of a valve metal as long as it functions as a dielectric.

[0045] In an electrolytic capacitor, the end surface of the anode foil does not necessarily have to be provided with a conductive polymer layer, but it is preferable that the end surface of the anode foil has a dielectric layer formed thereon.

[0046] (Cathode foil) The cathode foil is not particularly limited as long as it functions as a cathode. Examples of the cathode foil include metal foil (e.g., aluminum foil). The type of metal is not particularly limited, and may be a valve metal or an alloy containing a valve metal. The thickness of the cathode foil may be 15 μm or more and 300 μm or less. The surface of the cathode foil may be roughened or chemically treated as necessary.

[0047] The cathode foil may include a conductive coating layer. When the metal foil includes a valve metal, the coating layer may include carbon and at least one metal having a lower ionization tendency than the valve metal. This facilitates improving the acid resistance of the metal foil. When the metal foil includes aluminum, the coating layer may include at least one selected from the group consisting of carbon, nickel, titanium, tantalum, and zirconium. In particular, the coating layer may include nickel and / or titanium, which are low in cost and resistance.

[0048] The thickness of the coating layer may be 5 nm or more, 10 nm or more, or 200 nm or less. The coating layer may be formed by vapor deposition or sputtering of the above-mentioned metal on the metal foil. Alternatively, the coating layer may be formed by vapor deposition of a conductive carbon material on the metal foil or by applying a carbon paste containing a conductive carbon material. Examples of conductive carbon materials include graphite, hard carbon, soft carbon, carbon black, etc.

[0049] (Separator) A porous sheet can be used as the separator. Examples of porous sheets include woven fabric, nonwoven fabric, and microporous membrane. The thickness of the separator is not particularly limited and may be in the range of 10 μm to 300 μm. Examples of separator materials include cellulose, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, vinylon, nylon, aromatic polyamide, polyimide, polyamideimide, polyetherimide, rayon, and glass.

[0050] (Exterior Body) The exterior body includes a case and / or a sealing resin. There is no limitation thereto, and known cases and sealing resins may be used. The sealing resin may include a thermosetting resin. Examples of thermosetting resins include epoxy resins, phenolic resins, silicone resins, melamine resins, urea resins, alkyd resins, polyurethanes, polyimides, unsaturated polyesters, etc. The sealing resin may include a filler, a curing agent, a polymerization initiator, and / or a catalyst, etc.

[0051] An example of an electrolytic capacitor according to the present disclosure will be specifically described below with reference to the drawings. The components described above can be applied to the components of the example described below. The components of the example described below can be modified based on the above description. The matters described below may also be applied to the above-described embodiment. In the example described below, components that are not essential for the electrolytic capacitor of the present disclosure may be omitted.

[0052] Fig. 1 is a cross-sectional view schematically illustrating an example of an electrolytic capacitor 100 according to this embodiment. Fig. 2 is a schematic view showing a portion of a capacitor element 10 included in the electrolytic capacitor 100 in an exploded view.

[0053] Electrolytic capacitor 100 includes capacitor element 10, bottomed case 101 that houses capacitor element 10, sealing member 102 that closes the opening of bottomed case 101, seat plate 103 that covers sealing member 102, lead wires 104A and 104B that extend from sealing member 102 and pass through seat plate 103, and lead tabs 105A and 105B that connect the lead wires to electrodes of capacitor element 10. The vicinity of the open end of bottomed case 101 is drawn inward, and the open end is curled so as to be crimped to sealing member 102.

[0054] Capacitor element 10 is, for example, a wound body as shown in Fig. 1. The wound body includes anode foil 11 connected to lead tab 105A, cathode foil 12 connected to lead tab 105B, and separator 13. Capacitor element 10 (wound body) includes a conductive polymer layer (not shown).

[0055] The anode foil 11 and the cathode foil 12 are wound with a separator 13 interposed therebetween. The outermost periphery of the wound body is fixed with a stop tape 14. Note that Fig. 1 shows a partially unfolded state of the wound body before the outermost periphery is fixed.

[0056] The electrolytic capacitor may have at least one capacitor element, or may have a plurality of capacitor elements, and the number of capacitor elements included in the electrolytic capacitor may be determined depending on the application.

[0057] The electrolytic capacitor according to the present disclosure can be manufactured by the manufacturing method (I) according to the second aspect of the present disclosure, which will be described below. However, the electrolytic capacitor may also be manufactured by a method other than the manufacturing method (I).

[0058] A second aspect of the present disclosure relates to a method (I) for manufacturing an electrolytic capacitor. The method (I) includes, in order, the steps of: (a) preparing an anode foil having a dielectric layer, a cathode foil, and a separator; (b) applying a coating liquid containing a conductive polymer, a dopant, and a liquid medium to at least one surface selected from the surface of the dielectric layer and the surface of the cathode foil and into voids in the separator; (c) forming a conductive polymer layer on at least one surface and in the voids in the separator by removing at least a portion of the liquid medium from the coating liquid; (d) forming a capacitor element including the conductive polymer layer by disposing a separator between the anode foil and the cathode foil; and (e) impregnating the voids in the capacitor element with a liquid component.

[0059] <Step (a)> The step of preparing an anode foil, a cathode foil, and a separator each having a dielectric layer is not particularly limited. The materials for the anode foil, the cathode foil, and the separator are also not particularly limited. The materials already described may be used for the anode foil, the cathode foil, and the separator.

[0060] <Step (b)> The coating liquid used in step (b) may contain a sugar alcohol, and the sugar alcohol may be at least one selected from the group consisting of xylitol and xylitol derivatives (xylitol compound).

[0061] In step (b), the coating liquid may be applied to the surface of the dielectric layer and the separator, or to the surface of the cathode foil and the separator. Alternatively, the coating liquid may be applied to the surface of the dielectric layer, the surface of the cathode foil, and the separator. If necessary, the coating liquid is applied to the dielectric layers formed on both sides of the anode foil, and the coating liquid is applied to both sides of the cathode foil. A conductive polymer layer is formed at the location where the coating liquid is applied.

[0062] The coating liquid may be applied by any known method. For example, a coater may be used, the coating liquid may be sprayed, or the substrate may be immersed in the coating liquid. Examples of methods using a coater include gravure coating and die coating. In the gravure coating method, the coating liquid is applied to a transfer member such as a gravure roll, excess coating liquid is removed from the transfer member, and the coating liquid applied to the transfer member is then transferred to the anode foil, cathode foil, and separator, respectively, thereby forming a uniformly thick coating liquid layer on each of the anode foil, cathode foil, and separator. Methods for applying the coating liquid to the separator include impregnating the separator with the coating liquid. The coating liquid applied to the separator penetrates into the separator, forming a conductive polymer layer across the entire thickness of the separator. The viscosity of the coating liquid may be, for example, 10 mPa·s or more (or 100 mPa·s or more) and 200 mPa·s or less. In this case, the coating liquid can be easily applied to the anode foil, cathode foil, and separator, and can easily be impregnated into the separator. The viscosity of the coating liquid can be measured at room temperature (20°C) using a vibration viscometer (for example, VM-100A, manufactured by Sekonic Corporation).

[0063] The dopant may be doped into the conductive polymer. The dopant may be an anion having a negative charge, and the conductive polymer may be a cation having a positive charge. The ionized dopant and the conductive polymer may interact with each other through Coulomb force. The conductive polymer doped with the dopant may be dispersed in the coating liquid in the form of particles.

[0064] The liquid medium preferably contains water. The liquid medium may contain an organic compound that does not boil at 100°C under 1 atmosphere (hereinafter also referred to as "organic compound (C)"). As the organic compound (C), one type of compound may be used, or multiple types of compounds may be used. The organic compound (C) can be read as "at least one type of organic compound."

[0065] In this specification, unless otherwise specified, boiling point means the boiling point at 1 atmosphere. Examples of the organic compound (C) include organic compounds having a boiling point higher than 100°C. When the organic compound (C) has a boiling point, the boiling point may be 110°C or higher, 150°C or higher, or 200°C or higher, or 400°C or lower, 300°C or lower, 250°C or lower, or 200°C or lower. The boiling point may be in the range of 110°C to 400°C (e.g., 150°C to 350°C).

[0066] In a preferred example of production method (I), the water content in the coating liquid is preferably 40% by mass or more (e.g., 50% by mass or more), and after the conductive polymer layer is formed, a solution containing a xylitol compound or a liquid component (e.g., an electrolyte solution) can easily penetrate into the conductive polymer layer. When the organic compound (C) is used, the content of the organic compound (C) in the coating liquid may be 0% by mass or more and 10% by mass or less.

[0067] Water boils and evaporates at about 100°C at 1 atmosphere. On the other hand, the organic compound (C) is a compound that does not boil at 100°C at 1 atmosphere. Therefore, by heating the coating liquid at a temperature of 100°C or higher, at which the organic compound (C) does not boil or decompose, water can be removed from the coating liquid while the organic compound (C) remains. As a result, the organic compound (C) remains in the formed conductive polymer layer. In this case, a solution or liquid component (e.g., an electrolyte solution) containing a xylitol compound can then easily penetrate into the conductive polymer layer.

[0068] <Step (c)> In step (c), there is no limitation on the method for removing at least a portion of the liquid medium from the coating liquid. The liquid medium may be removed by heating and / or reducing pressure, and it is preferable to at least heat the coating liquid.

[0069] When heating is performed, it is preferable to remove a portion of the liquid medium by heating at a temperature of 100°C or higher. Heating at a temperature of 100°C or higher allows for rapid removal of water from the liquid medium. The heating temperature is preferably a temperature at which the organic compound (C) does not boil or decompose. When the organic compound (C) is a compound without a clear boiling point, it is preferable to heat at a temperature at which evaporation of the organic compound (C) is minimal and at which the organic compound (C) does not decompose. The heating temperature may be 100°C or higher, 120°C or higher, or 140°C or higher, and may be 200°C or lower, or 160°C or lower. The heating temperature may be in the range of 100°C to 200°C. The heating time is not particularly limited as long as it is a time that allows at least a portion of the liquid medium to be appropriately removed. An example heating time is in the range of 5 to 60 minutes.

[0070] When forming a conductive polymer layer on one member, heating may be performed two or more times within a predetermined temperature range (for example, a temperature in the range of 100°C to 200°C). For example, when forming a conductive polymer layer on dielectric layers formed on both sides of an anode foil, a coating liquid may be applied to one side and then heated, and then a coating liquid may be applied to the other side and then heated. A similar method can be applied when forming conductive polymer layers on both sides of a cathode foil.

[0071] An example of a typical electrolytic capacitor includes a wound assembly of an anode foil, a separator, and a cathode foil. Such an electrolytic capacitor includes a conductive polymer layer disposed within the wound assembly. The conductive polymer layer is formed by impregnating the wound assembly with a dispersion liquid containing a conductive polymer.

[0072] However, because dispersions containing conductive polymers have high viscosity, even if the dispersion is impregnated into a wound body, a sufficient conductive polymer layer may not be formed inside the wound body. Insufficient formation of the conductive polymer layer can cause a decrease in initial capacity, an increase in equivalent series resistance (ESR), a decrease in reliability, and the like. Furthermore, because sugar alcohols are solids, solutions in which sugar alcohols are dissolved in solvents have high viscosity. If a sugar alcohol is added to a dispersion containing a conductive polymer, it becomes even more difficult to form a sufficient conductive polymer layer inside the wound body.

[0073] On the other hand, the electrolytic capacitor manufacturing method (I) includes steps (b) and (c), in which a coating liquid is applied to at least one surface selected from the surface of the dielectric layer of the anode foil and the surface of the cathode foil, and the coating liquid is also applied to the voids of the separator. The coating liquid can be highly viscous because it contains a conductive polymer and a dopant. However, when the coating liquid is applied to the surface of the dielectric layer or the surface of the cathode foil, for example, using a coater, a sufficient amount of conductive polymer layer can be formed within the capacitor element. Similarly, the electrolytic capacitor manufacturing method (I) can form a sufficient amount of conductive polymer layer within the voids of the separator (more precisely, the inner wall formed of the separator material surrounding the voids) when the coating liquid is applied to the surface of the separator, for example, using a coater.

[0074] <Step (d)> In step (d), a conductive polymer layer is formed on at least one of the anode foil and the cathode foil and a separator, and then the separator is disposed between the anode foil and the cathode foil to form a capacitor element including the conductive polymer layer. This step also involves stacking the anode foil and the cathode foil with the separator interposed between them. Therefore, the capacitor element may also be referred to as a "laminate."

[0075] The method for forming the capacitor element (laminate) is not limited, and the capacitor element may be formed by a known method. The capacitor element may be a wound body. In this case, the wound body is formed by winding an anode foil, a cathode foil, and a separator so that the separator is disposed between the anode foil and the cathode foil. In the wound body, the anode foil, the cathode foil, and the separator are stacked in the radial direction of the wound body.

[0076] A capacitor element may be formed by stacking flat anode foils, flat cathode foils, and flat separators in one direction. For example, a plurality of anode foils, a plurality of cathode foils, and a plurality of separators may be stacked in one direction to form a stack capacitor element. In a typical stack, the anode and cathode foils are alternately arranged, with separators positioned between the anode and cathode foils.

[0077] After step (d) and before step (e), the capacitor element may be impregnated with a solution containing a sugar alcohol (xylitol compound) (hereinafter also referred to as a "xylitol solution") to impregnate the conductive polymer layer with the xylitol compound. This allows the conductive polymer layer to contain the xylitol compound. The solvent for the xylitol solution preferably contains at least water. 80% by mass or more, or even 90% by mass or more (preferably 100%) of the solvent for the xylitol solution may be water. The solvent for the xylitol solution may also contain an organic solvent. Examples of organic solvents that can be used include ethylene glycol, sulfolane, and γ-butyrolactone. The mass content of the xylitol compound in the xylitol solution is preferably 10% by mass to 70% by mass, and may be 15% by mass to 60% by mass.

[0078] There is no limitation on the method for impregnating the capacitor element with the xylitol solution. For example, the capacitor element may be impregnated with the xylitol compound by immersing at least a portion of the capacitor element in the xylitol solution. The step of immersing at least a portion of the capacitor element in the xylitol solution and the step of removing at least a portion of the solvent may be performed multiple times. The xylitol solution may be heated to 40°C to 90°C.

[0079] The total mass Mp of the conductive polymer and the dopant and the mass Ms of the xylitol compound in the conductive polymer layer can be controlled by controlling the concentrations of the conductive polymer and the dopant in the coating liquid and the concentration of the xylitol compound in the xylitol solution.

[0080] <Step (e)> There is no limitation on the method for impregnating the liquid component into the voids in the capacitor element. For example, the capacitor element may be impregnated with the liquid component by immersing at least a portion of the capacitor element in the liquid component.

[0081] The liquid component used in step (e) is the same as the liquid component described above, and includes a solvent and a solute. The solute includes a sugar alcohol, and the sugar alcohol is at least one selected from the group consisting of xylitol and xylitol derivatives (a xylitol compound). The mass content of the xylitol compound in the liquid component is 4% by mass or more and 70% by mass or less. This allows a solid-liquid hybrid electrolytic capacitor to be obtained. The liquid component may be an electrolyte solution containing an electrolyte salt in addition to the xylitol compound.

[0082] The xylitol compound used in step (e) has a low melting point among sugar alcohols and has excellent affinity for the conductive polymer layer, so a sufficient amount of sugar alcohol or xylitol compound can be contained in the voids in the capacitor element. The xylitol compound enhances the adhesive strength between the conductive polymer layers formed on each member, so that a strong conductive path can be formed between the anode foil and the cathode foil by the conductive polymer layer.

[0083] The above steps form a capacitor element containing a conductive polymer layer and a liquid component. The capacitor element is then encapsulated in an outer casing, if necessary. In this manner, an electrolytic capacitor is manufactured. Note that manufacturing method (I) may include other steps in addition to the above steps, if necessary.

[0084] As described above, in manufacturing method (I), a conductive polymer layer can be formed by combining a first conductive polymer layer formed on the surface of the dielectric layer of the anode foil and / or the surface of the cathode foil with a second conductive polymer layer formed in the voids of the separator. According to manufacturing method (I), a mixed region in which a portion of the first conductive polymer layer and a portion of the second conductive polymer layer are mixed can be formed at the boundary between the first conductive polymer layer and the second conductive polymer layer. In other words, the first conductive polymer layer and the second conductive polymer layer can be bonded to each other. Therefore, a strong conductive path is formed between the anode foil and the cathode foil by the conductive polymer layer, reducing the ESR of the electrolytic capacitor and significantly improving its reliability.

[0085] The first conductive polymer layer and the second conductive polymer layer may be composed of the same conductive polymer or may contain different conductive polymers. The first conductive polymer layer and the second conductive polymer layer may contain the same dopant or different dopants. The first conductive polymer layer formed on the anode foil (on the dielectric layer), the first conductive polymer layer formed on the cathode foil, and the second conductive polymer layer may be composed of the same conductive polymer or may contain different conductive polymers. The first conductive polymer layer formed on the anode foil (on the dielectric layer), the first conductive polymer layer formed on the cathode foil, and the second conductive polymer layer may contain the same dopant or different dopants.

[0086] When a first conductive polymer layer is formed on the surface of an anode foil (or cathode foil), the first conductive polymer layer is preferably formed on 80% or more (e.g., 90% or more) of the surface area on which the first conductive polymer layer is formed. The first conductive polymer layer is preferably formed on the entire surface of the electrode foil (anode foil, cathode foil) that contributes to the capacitance of the capacitor element. The area on which the second conductive polymer layer is formed on the separator is preferably 80% or more (e.g., 90% or more) of the separator's area, and may be formed on the entire separator. Here, the surface area of ​​the electrode foil (anode foil, cathode foil) refers to the area ignoring surface irregularities and can be calculated from the outline of the electrode foil. When the first conductive polymer is formed on both sides of the electrode foil, the surface area on which the first conductive polymer is formed is the sum of the areas of both sides.

[0087] The mass of the first conductive polymer layer per unit area is 0.01 mg / cm ２ or more, or 0.02 mg / cm ２ or more, and ２ or less than 0.3 mg / cm ２ The mass may be 0.1 mg / cm or less. ２ By setting the above, the conductive polymer layer can be formed more uniformly. When the first conductive polymer layer is formed on both sides of the electrode foil, the above mass per unit area is the mass of the layer formed on one side of the electrode foil.

[0088] The mass of the second conductive polymer layer per unit area is 0.02 mg / cm ２ or more, or 0.05 mg / cm ２ or more, and ２ or less than 1.0 mg / cm ２ The mass may be 0.3 mg / cm or less. ２ By doing so, the conductive polymer layer can be formed more uniformly.

[0089] The mass of the conductive polymer layer per unit area can be determined by the following method. First, five samples are prepared by cutting out a predetermined area from a member (electrode foil or separator) before the conductive polymer layer is formed, and the masses of the five samples are measured. Five samples are also prepared by cutting out the predetermined area from a member (electrode foil or separator) on which a conductive polymer layer has been formed, and the masses of the five samples are measured. The mass of the conductive polymer layer per unit area is determined using the predetermined area and the difference between the total mass of the five samples after the conductive polymer layer has been formed and the total mass of the five samples before the conductive polymer layer has been formed.

[0090] (Coating Liquid) Next, the coating liquid will be described in more detail. The coating liquid contains a conductive polymer, a dopant, and a liquid medium, and may contain a xylitol compound. The liquid medium preferably contains water, and further preferably contains an organic compound (C). If necessary, the coating liquid may contain other components. As the organic compound (C), an organic compound that is easily soluble in water can be preferably used. The organic compound (C) may be a compound that is miscible with water.

[0091] The coating liquid may contain sugar alcohols other than xylitol compounds. However, it is preferable that the majority of the sugar alcohols contained in the coating liquid are xylitol compounds. It is preferable that 80% by mass or more (even 90% by mass or more) of the sugar alcohols contained in the coating liquid are xylitol compounds. Examples of sugar alcohols other than xylitol compounds include mannitol, sorbitol, erythritol, and pentaerythritol.

[0092] Examples of the organic compound (C) include compounds used as organic solvents. Examples of the organic compound (C) include polyhydric alcohols (excluding sugar alcohols) having two or more hydroxyl groups. Water in which the organic compound (C) is dissolved can be used as a dispersion medium for the conductive polymer. From one perspective, the coating liquid is a dispersion liquid in which particles of a conductive polymer doped with a dopant are dispersed, and the dispersion medium can be water in which the organic compound (C) and / or a xylitol compound is dissolved.

[0093] Examples of the organic compound (C) include polyhydric alcohols (excluding sugar alcohols), sulfolane, γ-butyrolactone, boric acid esters, etc. The organic compound (C) may include at least one selected from the group consisting of polyhydric alcohols, sulfolane, γ-butyrolactone, and boric acid esters, or may be at least one of the above.

[0094] Examples of polyhydric alcohols include glycols, glycerins, etc. Examples of glycols include ethylene glycol, diethylene glycol, triethylene glycol, polyalkylene glycol (e.g., polyethylene glycol), polyoxyethylene polyoxypropylene glycol (ethylene oxide-propylene oxide copolymer), etc. Examples of glycerins include glycerin and polyglycerin, etc.

[0095] Examples of conductive polymers include polypyrrole, polythiophene, polyfuran, polyaniline, polyacetylene, and derivatives thereof. These derivatives include polymers with polypyrrole, polythiophene, polyfuran, polyaniline, and polyacetylene as their basic skeletons. For example, polythiophene derivatives include poly(3,4-ethylenedioxythiophene). These conductive polymers may be used alone or in combination. Furthermore, 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. One preferred example of a conductive polymer is poly(3,4-ethylenedioxythiophene) (PEDOT).

[0096] The conductive polymer is doped with a dopant. From the viewpoint of suppressing dedoping from the conductive polymer, it is preferable to use a polymer dopant as the dopant. Examples of polymer dopants include polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallylsulfonic acid, polyacrylic sulfonic acid, polymethacrylic sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, polyacrylic acid, and the like. These may be used alone or in combination of two or more. At least a portion of these may be added in the form of a salt. A preferred example of the dopant is polystyrene sulfonic acid (PSS).

[0097] In the electrolytic capacitor of the present disclosure, the dopant may be a dopant containing an acidic group or a polymeric dopant containing an acidic group. Examples of the acidic group include a sulfonic acid group and a carboxyl group. The polymeric dopant containing an acidic group is a polymer in which at least some of the constituent units contain an acidic group. Examples of such polymeric dopants include the polymeric dopants described above.

[0098] 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 conductive polymer layer.

[0099] The dopant may be polystyrene sulfonic acid, and the conductive polymer may be poly(3,4-ethylenedioxythiophene). That is, the conductive polymer doped with a dopant may be poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid.

[0100] When a conductive polymer doped with a dopant is used, the pH of the coating liquid is preferably less than 7.0, and may be 6.0 or less or 5.0 or less, in order to suppress dedoping of the dopant. The pH of the coating liquid may be 1.0 or more, or 2.0 or more.

[0101] The conductive polymer doped with a dopant may be present in the coating liquid in the form of particles. In the volume-based particle size distribution of the particles of the conductive polymer doped with a dopant, the mode of particle size may be 10 nm or more, or 20 nm or more, or may be 1000 nm or less, 500 nm or less, 200 nm or less, or 100 nm or less. The volume-based particle size distribution can be determined using a laser diffraction / scattering particle size distribution analyzer.

[0102] The mode of particle size of the conductive polymer particles doped with the dopant may be in the range of 20 nm to 200 nm (e.g., in the range of 20 nm to 100 nm). Furthermore, in the volume-based particle size distribution, the volume-based proportion of particles with particle sizes in the range of 20 nm to 100 nm may be 90% or more of the total. These ranges facilitate the formation of a conductive polymer layer containing the conductive polymer doped with the dopant in the pores of the members (electrode foil and separator).

[0103] The water content in the coating liquid may be 40% by mass or more, 50% by mass or more, 70% by mass or more, 73% by mass or more, 78% by mass or more, 80% by mass or more, 88% by mass or more, 90% by mass or more, or 95% by mass or more. The water content may be 98% by mass or less, 95% by mass or less, 90% by mass or less, or 80% by mass or less. The water content may be in the range of 40 to 98% by mass or more, 50 to 98% by mass, 80 to 98% by mass, or 70 to 98% by mass. In any of these ranges, the upper limit may be 95% by mass, 90% by mass, or 80% by mass.

[0104] The content of the xylitol compound and the organic compound (C) in the coating liquid may be 0% by mass or more, 1.0% by mass or more, 3.0% by mass or more, 5.0% by mass or more, or 10% by mass or more. The content may be 59.5% by mass or less, 45% by mass or less, 30% by mass or less, 25% by mass or less, 20% by mass or less, 15% by mass or less, or 10% by mass or less. The content may be in the range of 1 to 59.5% by mass, 3 to 59.5% by mass, or 5 to 59.5% by mass. In any of these ranges, the upper limit may be 45% by mass, 30% by mass, 25% by mass, 20% by mass, 15% by mass, or 10% by mass.

[0105] The total mass content of the conductive polymer and dopant in the coating liquid may be 0.5% by mass or more, or 1.0% by mass or more, and may be 4.0% by mass or less, 3.0% by mass or less, or 2.0% by mass or less. The content may be in the range of 0.5 to 4.0% by mass, or in the range of 1.0 to 4.0% by mass. In either of these ranges, the upper limit may be 3.0% by mass or 2.0% by mass. In terms of excellent physical properties and stability over time of the coating liquid, and a good balance between the ESR and cost of the electrolytic capacitor, the content is preferably in the range of 1.0 to 3.0%.

[0106] There are no particular limitations on the mass of the dopant contained in the coating liquid, and it may be in the range of 0.1 to 5 times (for example, in the range of 0.5 to 3 times) the mass of the conductive polymer contained in the coating liquid.

[0107] The mass content of the xylitol compound in the coating liquid is preferably 1 to 12 times, and more preferably 7 to 12 times, the total mass content of the conductive polymer and dopant in the coating liquid. Furthermore, in terms of excellent physical properties and stability over time of the coating liquid and a good balance between the ESR of the electrolytic capacitor and cost, the content is preferably in the range of 1.0 to 3.0%.

[0108] In the coating liquid, the ratio of water content:total content of the xylitol compound and the organic compound (C):total content of the conductive polymer and the dopant may be (40 to 98):(1.0 to 59.5):(0.5 to 4.0), or may be (69.5 to 98):(1.0 to 30):(0.5 to 4.0).

[0109] The above-mentioned water content, the total content of the xylitol compound and the organic compound (C), and the total content of the conductive polymer and the dopant can be combined in any desired manner as long as no contradiction occurs. One example of the coating liquid may satisfy one, two, three, or four of the following conditions (1) to (5), or may satisfy all of the conditions:

[0110] (1) The water content is in the range of 50 to 98% by mass (e.g., 73 to 95% by mass), the total content of the xylitol compound and the organic compound (C) is in the range of 3 to 30% by mass (e.g., 5 to 25% by mass), and the total content of the conductive polymer and the dopant is in the range of 0.5 to 4.0% by mass (e.g., 1.0 to 3.0% by mass). (2) The mass content of the xylitol compound in the coating liquid is 1 to 45 times, or even 7 to 20 times, the total mass content of the conductive polymer and the dopant in the coating liquid. (3) The organic compound (C) is a glycol (e.g., ethylene glycol). (4) The conductive polymer component includes poly(3,4-ethylenedioxythiophene) and polystyrene sulfonic acid. For example, the conductive polymer component may be composed of poly(3,4-ethylenedioxythiophene) and polystyrene sulfonic acid. (5) The pH of the coating liquid is in the range of 1.0 to 6.0 (e.g., 2.0 to 5.0). (6) The conductive polymer doped with a dopant is present in the coating liquid in the form of particles, and in the volume-based particle size distribution of the particles, the mode of particle size is in the range of 20 nm to 1000 nm (e.g., 20 nm to 200 nm or 20 nm to 100 nm). In the volume-based particle size distribution, the proportion (by volume) of particles having a particle size in the range of 20 nm to 1000 nm (e.g., 20 nm to 200 nm or 20 nm to 100 nm) of the total particles may be 90% or more.

[0111] (Liquid Component) The liquid component may be a solvent in which a solute is dissolved. The solute includes at least a xylitol compound. In this specification, the liquid component may be a component that is liquid at room temperature (25°C) or at the temperature at which the electrolytic capacitor is used.

[0112] The solvent used in the liquid component may be an organic solvent, an ionic liquid, or a protic solvent. Examples of the organic 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.

[0113] A polymer solvent may be used as the solvent. Examples of polymer solvents include polyalkylene glycol, polyalkylene glycol derivatives, and compounds in which at least one hydroxyl group in a polyhydric alcohol has been substituted with polyalkylene glycol (including derivatives). Specific examples of polymer 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. Further examples of polymer solvents include ethylene glycol-propylene glycol copolymers, ethylene glycol-butylene glycol copolymers, and propylene glycol-butylene glycol copolymers. One type of nonaqueous solvent may be used alone, or two or more types may be used in combination.

[0114] The liquid component may contain a basic component (base) and / or an acid component (acid) as a solute.

[0115] The acid component can be a polycarboxylic acid or a monocarboxylic acid. Examples of the polycarboxylic acid include aliphatic polycarboxylic acids (saturated polycarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, 1,6-decanedicarboxylic acid, and 5,6-decanedicarboxylic acid; unsaturated polycarboxylic acids such as maleic acid, fumaric acid, and itanoic acid), aromatic polycarboxylic acids (phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, and pyromellitic acid), and alicyclic polycarboxylic acids (cyclohexane-1,2-dicarboxylic acid and cyclohexene-1,2-dicarboxylic acid).

[0116] Examples of the monocarboxylic acid include aliphatic monocarboxylic acids (having 1 to 30 carbon atoms) ([saturated monocarboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, lauric acid, myristic acid, stearic acid, and behenic acid]; [unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, and oleic acid]), aromatic monocarboxylic acids (such as benzoic acid, cinnamic acid, and naphthoic acid), and oxycarboxylic acids (such as salicylic acid, mandelic acid, and resorcylic acid).

[0117] Among these, maleic acid, phthalic acid, benzoic acid, pyromellitic acid, and resorcylic acid are thermally stable and are therefore preferably used.

[0118] An inorganic acid may be used as the acid component. Typical examples of inorganic acids include phosphoric acid, phosphorous acid, hypophosphorous acid, alkyl phosphate esters, boric acid, fluoroboric acid, tetrafluoroboric acid, hexafluorophosphoric acid, benzenesulfonic acid, and naphthalenesulfonic acid. Alternatively, a composite compound of an organic acid and an inorganic acid may be used as the acid component. Examples of such composite compounds include borodiglycolic acid, borodisalic acid, and borodisalicylic acid.

[0119] The base component may be a compound having an alkyl-substituted amidine group, such as an imidazole compound, a benzimidazole compound, or an alicyclic amidine compound (a pyrimidine compound, an imidazoline compound). Specifically, 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, or 1-methylbenzimidazole is preferred. By using these, a capacitor with excellent impedance performance can be obtained.

[0120] The base component may be a quaternary salt of a compound having an alkyl-substituted amidine group. Examples of such base components include imidazole compounds, benzimidazole compounds, and alicyclic amidine compounds (pyrimidine compounds, imidazoline compounds) quaternized with an alkyl group or arylalkyl group having 1 to 11 carbon atoms. Specifically, 1-methyl-1,8-diazabicyclo[5,4,0]undecene-7, 1-methyl-1,5-diazabicyclo[4,3,0]nonene-5, 1,2,3-trimethylimidazolinium, 1,2,3,4-tetramethylimidazolinium, 1,2-dimethyl-3-ethyl-imidazolinium, 1,3,4-trimethyl-2-ethylimidazolinium, 1,3-dimethyl-2-heptylimidazolinium, 1,3-dimethyl-2-(3'heptyl)imidazolinium, 1,3-dimethyl-2-dodecylimidazolinium, 1,2,3-trimethyl-1,4,5,6-tetrahydropyrimidium, 1,3-dimethylimidazolium, 1-methyl-3-ethylimidazolium, 1,3-dimethylbenzimidazolium is preferred. By using these, a capacitor with excellent impedance performance can be obtained.

[0121] A tertiary amine may be used as the base component. Examples of tertiary amines include trialkylamines (trimethylamine, dimethylethylamine, methyldiethylamine, triethylamine, dimethyl-n-propylamine, dimethylisopropylamine, methylethyl-n-propylamine, methylethylisopropylamine, diethyl-n-propylamine, diethylisopropylamine, tri-n-propylamine, triisopropylamine, tri-n-butylamine, tri-tert-butylamine, etc.), and phenyl group-containing amines (dimethylphenylamine, methylethylphenylamine, diethylphenylamine, etc.). Among these, trialkylamines are preferred in terms of increasing conductivity, and it is more preferable to include at least one selected from the group consisting of trimethylamine, dimethylethylamine, methyldiethylamine, and triethylamine. Furthermore, secondary amines such as dialkylamines, primary amines such as monoalkylamines, and ammonia may be used as the base component.

[0122] The liquid component may contain a salt of an acid component and a base component. The salt may be an inorganic salt and / or an organic salt. An organic salt is a salt in which at least one of the anion and the cation contains an organic substance. Examples of organic salts that may be used include trimethylamine maleate, triethylamine borodisalicylate, ethyldimethylamine phthalate, mono-1,2,3,4-tetramethylimidazolinium phthalate, and mono-1,3-dimethyl-2-ethylimidazolinium phthalate.

[0123] To suppress dedoping of the dopant, the pH of the liquid component (L) may be less than 7.0 or 5.0 or less, or may be 1.0 or more, or 2.0 or more. The pH may be 1.0 or more and less than 7.0 (for example, in the range of 2.0 to 5.0).

[0124] The liquid component preferably contains a protic solvent. By using a protic solvent, it is possible to particularly swell the conductive polymer layer. In addition to the protic solvent, the liquid component may also contain a solvent other than the protic solvent.

[0125] The protic solvent may include at least one selected from the group consisting of glycols, glycerin, polyglycerin, and sugar alcohols, and may be composed of only one type of compound or may include multiple types of compounds.

[0126] <<Supplementary Note>> The above description of the embodiment discloses the following techniques.

[0127] (Technology 1) An electrolytic capacitor including a capacitor element and a liquid component contained in voids within the capacitor element, wherein the capacitor element includes: an anode foil having a dielectric layer; a cathode foil; a separator interposed between the anode foil and the cathode foil; and a conductive polymer layer interposed between the anode foil and the cathode foil and in contact with the separator; the liquid component includes a solvent and a solute; the solute includes a sugar alcohol, and the sugar alcohol is at least one selected from the group consisting of xylitol and xylitol derivatives; and the content of the sugar alcohol in the liquid component is 4% by mass or more and 70% by mass or less.

[0128] (Technology 2) The electrolytic capacitor according to Technology 1, wherein the content of the sugar alcohol in the liquid component is 50% by mass or less.

[0129] (Technology 3) The electrolytic capacitor according to Technology 1 or 2, wherein the solute further includes at least one selected from the group consisting of an acid, a base, and an electrolyte salt, and the content of the solute in the liquid component is 70 mass % or less.

[0130] (Technology 4) The electrolytic capacitor according to any one of Technologies 1 to 3, wherein the conductive polymer layer further contains at least one sugar alcohol selected from the group consisting of xylitol and xylitol derivatives.

[0131] (Technology 5) The electrolytic capacitor according to any one of Technologies 1 to 4, wherein the mass content of the sugar alcohol in the conductive polymer layer is 30 mass % or more and 98 mass % or less.

[0132] (Technology 6) The electrolytic capacitor according to any one of Technologies 1 to 5, wherein the conductive polymer layer is formed on at least one surface selected from a surface of the dielectric layer and a surface of the cathode foil, and is also formed in voids of the separator.

[0133] (Technology 7) The electrolytic capacitor according to any one of Technologies 1 to 6, wherein the solvent includes a first solvent, and the first solvent is at least one selected from the group consisting of ethylene glycol, diethylene glycol, triethylene glycol, an ethylene glycol condensate having a molecular weight of 250 or less, glycerin, γ-butyrolactone, and sulfolane.

[0134] (Technology 8) The electrolytic capacitor according to any one of Technologies 1 to 7, wherein the proportion of the first solvent in the solvent is 20 mass % or more.

[0135] (Technology 9) A capacitor element comprising: a step (a) of preparing an anode foil having a dielectric layer, a cathode foil, and a separator; a step (b) of applying a coating liquid containing a conductive polymer, a dopant, and a liquid medium to at least one surface selected from the surface of the dielectric layer and the surface of the cathode foil and into voids in the separator; a step (c) of forming a conductive polymer layer on the at least one surface and in voids in the separator by removing at least a part of the liquid medium from the coating liquid; a step (d) of forming a capacitor element comprising the conductive polymer layer by disposing the separator between the anode foil and the cathode foil; and a step (e) of impregnating voids in the capacitor element with a liquid component, in this order; the liquid component comprising a solvent and a solute; the solute comprising a sugar alcohol; and the sugar alcohol being at least one selected from the group consisting of xylitol and xylitol derivatives. The method for manufacturing an electrolytic capacitor, wherein the content of the sugar alcohol in the liquid component is 4% by mass or more and 70% by mass or less.

[0136] (Technology 10) The method for producing an electrolytic capacitor according to Technology 9, wherein the coating liquid contains the sugar alcohol.

[0137] (Technology 11) The method for producing an electrolytic capacitor according to Technology 9 or 10, further comprising, after the step (d) and before the step (e), a step of impregnating the capacitor element with a solution containing the sugar alcohol, thereby causing the conductive polymer layer to contain the sugar alcohol.

[0138] (Technology 12) The method for manufacturing an electrolytic capacitor according to any one of Techniques 9 to 11, wherein the conductive polymer layer includes a first conductive polymer layer formed on the at least one surface and a second conductive polymer layer formed in voids of the separator, and a mixed region in which a part of the first conductive polymer layer and a part of the second conductive polymer layer are mixed is present at the boundary between the first conductive polymer layer and the second conductive polymer layer.

[0139] [Examples] The present disclosure will be described in more detail below based on examples, but the present disclosure is not limited to these examples. In these examples, a plurality of electrolytic capacitors were produced and evaluated by the following method.

[0140] <Capacitor B1> An electrolytic capacitor was produced by the following method.

[0141] (a) Preparation of Components An aluminum foil (thickness: 100 μm) was subjected to an etching treatment to roughen the surface of the aluminum foil. The roughened surface of the aluminum foil was subjected to a chemical conversion treatment to form a dielectric layer. In this way, an anode foil having a dielectric layer formed on both sides was obtained.

[0142] Furthermore, an aluminum foil (thickness: 50 μm) was subjected to an etching treatment to roughen the surface of the aluminum foil, thereby obtaining a cathode foil.

[0143] A nonwoven fabric (thickness: 50 μm) was prepared as a separator. The nonwoven fabric was composed of 50% by mass of synthetic fibers (25% by mass of polyester fibers and 25% by mass of aramid fibers) and 50% by mass of cellulose, and contained polyacrylamide as a paper strength agent. The density of the nonwoven fabric was 0.35 g / cm. ３ It was.

[0144] (b) Preparation of Coating Liquid A dispersion liquid (commercially available) in which particles of polyethylenedioxythiophene (PEDOT) doped with polystyrene sulfonic acid (PSS) were dispersed in water was prepared as a coating liquid.

[0145] (c) Formation of a Conductive Polymer Layer Using a gravure coater, the coating liquid was applied to one side of the anode foil (surface of the dielectric layer). A drying treatment was then performed to form a conductive polymer layer on one side of the anode foil (surface of the dielectric layer). The drying treatment was performed by heating the anode foil coated with the coating liquid at 125°C for 5 minutes. Next, a conductive polymer layer was formed on the other side of the anode foil (surface of the dielectric layer) in the same manner.

[0146] Conductive polymer layers were formed on both sides of the cathode foil in the same manner as that used for forming the conductive polymer layers on both sides of the anode foil. Also, a conductive polymer layer was formed on the separator by applying the coating liquid to the separator and then performing a drying process in the same manner as that used for forming the conductive polymer layers on both sides of the anode foil.

[0147] (d) Preparation of Capacitor Element The anode foil, cathode foil, and separator were each cut to a predetermined size. Anode lead tabs and cathode lead tabs were connected to the anode foil and cathode foil, respectively. Next, the anode foil and cathode foil were wound with the separator interposed therebetween. At this time, the ends of the outer surface of the wound body were fixed with winding tape. Anode lead wires and cathode lead wires were connected to the ends of each lead tab protruding from the wound body, respectively. The obtained wound body was again subjected to chemical conversion treatment, and a dielectric layer was formed on the end surface of the anode foil. In this way, a capacitor element was obtained.

[0148] (e) Impregnation with Liquid Component An electrolyte solution (liquid component) was prepared by dissolving o-phthalic acid and triethylamine (base component) in a solvent at a total concentration of 25% by mass. The capacitor element was immersed in the electrolyte solution for 5 minutes in a reduced pressure atmosphere (40 kPa). This allowed the capacitor element to be impregnated with the electrolyte. The solvent used was a mixed solvent of ethylene glycol (EG) and sulfolane (SL) in a volume ratio of 50:50.

[0149] (f) Sealing of Capacitor Element The capacitor element impregnated with the electrolytic solution was sealed to produce an electrolytic capacitor as shown in Fig. 1. Then, aging was performed at 95°C for 90 minutes while applying a voltage. In this way, an electrolytic capacitor (Capacitor B1) was obtained.

[0150] <Capacitors A1 and A2> Electrolytic capacitors (Capacitors A1 and A2) were produced in the same manner as Capacitor B1, except that in the liquid component impregnation step (e), xylitol was dissolved in the liquid component at a mass content (CX) shown in Table 1. In addition, the total mass content of o-phthalic acid and triethylamine (base component) in the liquid component was 25 mass%.

[0151] (Measurement of Initial ESR) The ESR (mΩ) of the initial electrolytic capacitor after the aging was measured at a frequency of 100 kHz using an LCR meter. The measurement temperature was 20°C.

[0152]

[0153] The results in Table 1 show that the initial ESR is significantly reduced by including a xylitol compound in the liquid component so that the mass content is 4 mass % or more.

[0154] (Capacitors A3 to A12, Capacitors B2 to B9) Solid-liquid hybrid capacitors A3 to A12 and B2 to B9 were fabricated in the same manner as capacitor A1, except that xylitol was dissolved in the solvent of the liquid component shown in Table 2 at the mass content (CX) shown in Table 2. The capacitor elements were immersed in the liquid component in a reduced pressure atmosphere (40 kPa) for 5 minutes. This allowed the liquid component to be impregnated into the capacitor elements. Other than the above, electrolytic capacitors (capacitors A3 to A12, capacitors B2 to B9) were fabricated in the same manner as capacitor A1.

[0155] (Measurement of ESR after reliability test) A reliability test was performed on the electrolytic capacitors after the sealing process (after aging) of the capacitor elements in (f) above, in which they were stored in a thermostatic chamber at 145°C for 1,000 hours. The ESR of the electrolytic capacitors after the reliability test was measured. The measurement temperature was 20°C. The measurement results are shown in Table 2. In Table 2, the ESR values ​​after the reliability test for capacitors A3 to A12 and capacitors B2 to B9 are expressed as a ratio to the ESR of capacitor A3 after the reliability test.

[0156]

[0157] The results in Table 2 show that when the liquid component contains a sugar alcohol, particularly a xylitol compound, a solid-liquid hybrid electrolytic capacitor with a small ESR after reliability testing can be obtained.

[0158] These results are thought to be due to the suppression of sugar alcohol precipitation during the manufacturing process and in the finished electrolytic capacitor.

[0159] The present disclosure can be used in solid-liquid hybrid electrolytic capacitors.

[0160] 10: Capacitor element 11: Anode foil 12: Cathode foil 13: Separator 14: Winding tape 100: Electrolytic capacitor 101: Bottomed case 102: Sealing member 103: Seat plate 104A, 104B: Lead wire 105A, 105B: Lead tab

Claims

1. An electrolytic capacitor comprising a capacitor element and a liquid component contained in the air gap within the capacitor element, The aforementioned capacitor element is Anode foil having a dielectric layer, Cathode foil and A separator interposed between the anode foil and the cathode foil, It has a conductive polymer layer interposed between the anode foil and the cathode foil and in contact with the separator, The aforementioned liquid component comprises a solvent and a solute. The solute comprises a sugar alcohol, The sugar alcohol is at least one selected from the group consisting of xylitol and xylitol derivatives. An electrolytic capacitor in which the content of the sugar alcohol in the liquid component is 4% by mass or more and 70% by mass or less.

2. The electrolytic capacitor according to claim 1, wherein the content of the sugar alcohol in the liquid component is 50% by mass or less.

3. The solute further comprises at least one selected from the group consisting of acids, bases, and electrolyte salts. The electrolytic capacitor according to claim 1, wherein the content of the solute in the liquid component is 70% by mass or less.

4. The electrolytic capacitor according to claim 1, wherein the conductive polymer layer comprises at least one sugar alcohol selected from the group consisting of xylitol and xylitol derivatives.

5. The electrolytic capacitor according to claim 1, wherein the mass content of the sugar alcohol in the conductive polymer layer is 30% by mass or more and 98% by mass or less.

6. The electrolytic capacitor according to claim 1, wherein the conductive polymer layer is formed on at least one surface selected from the surface of the dielectric layer and the surface of the cathode foil, and is also formed within the void of the separator.

7. The solvent includes the first solvent, The electrolytic capacitor according to claim 1, wherein the first solvent is at least one selected from the group consisting of ethylene glycol, diethylene glycol, triethylene glycol, ethylene glycol condensates with a molecular weight of 250 or less, glycerin, γ-butyrolactone, and sulfolane.

8. The electrolytic capacitor according to claim 1, wherein the proportion of the first solvent in the solvent is 20% by mass or more.

9. Step (a) of preparing an anode foil having a dielectric layer, a cathode foil, and a separator, (b) A step of applying a coating solution containing a conductive polymer, a dopant, and a liquid medium to at least one surface selected from the surface of the dielectric layer and the surface of the cathode foil and into the void of the separator, (c) A step of forming a conductive polymer layer in the void of the separator and at least a portion of the liquid medium by removing it from the coating liquid, (d) A step of forming a capacitor element including the conductive polymer layer by arranging the separator between the anode foil and the cathode foil, (e) A step of filling the void within the capacitor element with a liquid component, This includes them in this order, The aforementioned liquid component comprises a solvent and a solute. The solute comprises a sugar alcohol, The sugar alcohol is at least one selected from the group consisting of xylitol and xylitol derivatives. A method for manufacturing an electrolytic capacitor, wherein the content of the sugar alcohol in the liquid component is 4% by mass or more and 70% by mass or less.

10. The method for manufacturing an electrolytic capacitor according to claim 9, wherein the coating liquid contains the sugar alcohol.

11. A method for manufacturing an electrolytic capacitor according to claim 9, further comprising the step of impregnating the capacitor element with a solution containing the sugar alcohol after step (d) and before step (e) to incorporate the sugar alcohol into the conductive polymer layer.

12. The conductive polymer layer includes a first conductive polymer layer formed on at least one surface and a second conductive polymer layer formed in the void of the separator. A method for manufacturing an electrolytic capacitor according to claim 9, wherein a mixed region exists at the boundary between the first conductive polymer layer and the second conductive polymer layer, in which a part of the first conductive polymer layer and a part of the second conductive polymer layer are mixed.