Electrolytic capacitor and production method for electrolytic capacitor

Abstract

This electrolytic capacitor includes: an anode having a dielectric layer on the surface thereof; a cathode; a porous insulating layer that is formed on at least one electrode selected from the group consisting of the anode and the cathode, and that is disposed between the anode and the cathode; and an electrolyte disposed in a gap of the insulating layer.

Description

Electrolytic capacitor and method for manufacturing the same

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

[0002] While electrolytic capacitors that include a wound body of an anode foil, a separator, and a cathode foil are known, electrolytic capacitors that do not use a separator have also been proposed.

[0003] Claim 1 of Patent Document 1 (Japanese Patent No. 5072857) describes "a method for manufacturing an electrolytic capacitor, comprising the steps of: forming an anode member in which a first conductive polymer layer is coated on the surface of a first metal foil; forming a cathode member in which a second conductive polymer layer is coated on the surface of a second metal foil; connecting a first lead tab terminal to the anode member; connecting a second lead tab terminal to the cathode member; winding the anode member and the cathode member without any intervening space therebetween; and, after the winding step, forming a third conductive polymer layer by polymerization in the gap between the anode member and the cathode member."

[0004] Patent No. 5072857

[0005] One aspect of the present disclosure relates to an electrolytic capacitor including an anode having a dielectric layer on a surface thereof, a cathode, a porous insulating layer formed on at least one electrode selected from the group consisting of the anode and the cathode and disposed between the anode and the cathode, and an electrolyte disposed in the pores of the insulating layer.

[0006] Another aspect of the present disclosure relates to a method for manufacturing an electrolytic capacitor including an anode having a dielectric layer on its surface and a cathode. The method includes the steps of: (i) forming a porous insulating layer on at least one electrode selected from the group consisting of the anode and the cathode; and (ii) stacking the anode and the cathode so that the insulating layer is disposed between the anode and the cathode. The method further includes the step of (a) disposing an electrolyte in the pores of the insulating layer.

[0007] According to the present disclosure, an electrolytic capacitor capable of achieving high capacitance can be obtained.

[0008] Fig. 1 is a side view schematically illustrating an example of an electrolytic capacitor according to an embodiment of the present disclosure. Fig. 2 is an exploded perspective view schematically illustrating an example of a capacitor element included in the electrolytic capacitor shown in Fig. 1. Fig. 3 is a cross-sectional view schematically illustrating an example of a portion of the laminate structure of the capacitor element. Fig. 4 is a schematic view for explaining an example of an electrospinning method.

[0009] The problems in the prior art will be briefly described below.

[0010] To increase the capacity of electrolytic capacitors using separators, the separators must be made thinner. However, thinner separators make them more difficult to handle, making them more susceptible to short circuits and increasing the difficulty of manufacturing electrolytic capacitors. On the other hand, not using a separator poses problems such as reduced voltage resistance and reduced reliability at high temperatures.

[0011] The present disclosure provides a new electrolytic capacitor that can achieve high capacitance.

[0012] The following describes embodiments of the present invention 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 term "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. In the following description, when examples of components or methods are listed, only one of the listed examples may be used, or multiple of the listed examples may be used in combination, unless otherwise specified.

[0013] (Electrolytic Capacitor) The electrolytic capacitor according to this embodiment may be referred to below as an "electrolytic capacitor (C)." The electrolytic capacitor (C) includes an anode having a dielectric layer on its surface, a cathode, a porous insulating layer, and an electrolyte disposed in the voids of the insulating layer. The porous insulating layer is formed on at least one electrode selected from the group consisting of an anode and a cathode, and is disposed between the anode and the cathode. The at least one electrode may be referred to below as an "electrode (E)" or "at least one electrode (E)." The porous insulating layer formed on the electrode (E) may be referred to below as an "insulating layer (L)."

[0014] The insulating layer (L) functions as an insulating layer in place of a separator. Because the insulating layer (L) is formed on the electrode (E), it is easy to handle even if it is thin. Therefore, it can be made thinner than a separator. By using a thin insulating layer (L), it is possible to increase the capacitance per unit volume. In other words, the electrolytic capacitor (C) can have a high capacitance.

[0015] The electrolytic capacitor of Patent Document 1, which does not have a separator between the anode and cathode, is prone to a decrease in withstand voltage and a decrease in reliability. On the other hand, the electrolytic capacitor (C) has an insulating layer (L) between the anode and cathode. Therefore, the electrolytic capacitor (C) can suppress a decrease in withstand voltage and a decrease in reliability.

[0016] The electrolytic capacitor (C) does not usually include a separator. However, the electrolytic capacitor (C) may include a separator. For example, an insulating layer may be formed on only one side of the electrode (E), with a separator disposed on the other side. In this specification, the term "separator" refers to a porous insulating film that is treated as a component that exists independently of the electrode. Examples of separators include nonwoven fabrics and microporous membranes. The insulating layer (L) formed by depositing fibers has a structure different from that of known nonwoven fabrics used as separators.

[0017] The insulating layer (L) may be attached to the dielectric layer of the anode, or may be attached to the cathode. The insulating layer (L) may be attached to the dielectric layer and integrated with the anode, or may be attached to the cathode and integrated with the cathode. Being integrated with the electrode (E) makes the insulating layer (L) easier to handle. Here, "integrated" means a state in which it can be handled as a single member in the manufacturing process. The insulating layer (L) may be formed only on the anode, only on the cathode, or on both the anode and the cathode.

[0018] The capacitor element of the electrolytic capacitor (C) may include a wound body formed by winding an anode and a cathode. In this case, the anode and the cathode are stacked in the radial direction of the wound body. The electrolytic capacitor (C) may also include a laminate in which the anode and the cathode are stacked. For example, the capacitor element of the electrolytic capacitor (C) may include a stacked-type laminate formed by stacking flat anodes and flat cathodes in one direction. For example, a laminate may be formed by stacking multiple anodes and multiple cathodes in one direction. In this case, the anodes and cathodes are arranged alternately.

[0019] The region of the electrode (E) on which the insulating layer (L) is formed may be selected depending on the form of the electrolytic capacitor (C). Depending on the form of the capacitor element, the insulating layer (L) is formed on one or both sides of the electrode (E). The insulating layer (L) is usually formed on both sides of the electrode (E). The insulating layer (L) may be formed on 90% or more (e.g., 95% or more) of the area of ​​both sides of the electrode (E). However, it is preferable that the insulating layer (L) is not formed in the portion where a lead or the like is connected. Furthermore, for electrodes (E) arranged at both ends of a laminated laminate, the insulating layer (L) may be formed only on the surface on the adjacent electrode side.

[0020] In the capacitor element, it is preferable that the electrodes on which the insulating layer (L) is not formed do not protrude outward beyond the insulating layer (L). For example, it is preferable that the width (length in the short direction) of the electrodes on which the insulating layer (L) is not formed is smaller than the width of the insulating layer (L). This configuration can suppress short-circuiting of the electrodes.

[0021] The insulating layer (L) may include fibers deposited on at least one electrode (E). The insulating layer (L) may be composed solely of the fibers or may contain the fibers as a main component. The content of the fibers in the material constituting the insulating layer (L) may be 50% by mass or more, 80% by mass or more, 90% by mass or more, or 95% by mass or more.

[0022] The average diameter of the fibers constituting the insulating layer (L) may be 0.05 μm or more, 0.1 μm or more, 0.3 μm or more, or 0.5 μm or more, or 2.0 μm or less, 1.5 μm or less, 1.0 μm or less, or 0.6 μm or less. The average diameter of the fibers may be in the range of 0.1 to 1.5 μm. The lower and / or upper limits of this range may be replaced with the above-mentioned lower and / or upper limits as long as the lower limit does not exceed the upper limit. By setting the average diameter of the fibers to 0.1 μm or more, the insulating layer can be made denser, improving its voltage resistance. By setting the average diameter of the fibers to 1.5 μm or less, it becomes easier to form a structure in which the fibers are intricately layered, improving the voltage resistance of the insulating layer.

[0023] The average fiber diameter is determined by arithmetically averaging the diameters of 30 randomly selected fibers. The diameter of each fiber is determined by measuring the diameter at one randomly selected location. When the cross section of the fiber is not circular, the diameter of the fiber is the equivalent circle diameter calculated from the area of ​​the cross section of the fiber.

[0024] The fibers constituting the insulating layer (L) are not particularly limited. Materials that are insulating and stable within the electrolytic capacitor can be used. The fibers may be polymeric. Examples of fiber materials include various insulating polymers. Examples of fiber materials include polyacrylonitrile, fluoropolymers (such as polyvinylidene fluoride), polyurethane, polyethylene oxide, polyvinyl alcohol, poly-L-lactic acid, nylon 6, polyethylene terephthalate, polystyrene, polymethyl methacrylate, polypropylene, polysulfone, polyethersulfone, polycaprolactone, polyimide, and cellulose-based polymers. Cellulose-based polymers include cellulose and cellulose derivatives. Examples of cellulose-based polymers include cellulose, alkyl cellulose, and cellulose acetate. The fibers constituting the insulating layer (L) may be composed of at least one material selected from the group consisting of polyacrylonitrile and polyvinylidene fluoride. Polyacrylonitrile and polyvinylidene fluoride are easily spun by electrospinning. By using these fibers, it is possible to particularly improve the properties of the electrolytic capacitor (C).

[0025] The insulating layer (L) may contain a material other than fibers or may be composed of a material other than fibers. Examples of insulating layers (L) composed of materials other than fibers include insulating layers formed by depositing a polymer or a composition containing a polymer on the electrode (E). The method for depositing the polymer on the electrode (E) is not particularly limited. For example, a porous insulating layer (L) may be formed by spraying a coating liquid containing a polymer. The polymer may be any of the polymers exemplified as the fiber material.

[0026] The thickness of the insulating layer (L) may be 0.5 μm or more, 3 μm or more, 5 μm or more, 10 μm or more, or 20 μm or more, or 50 μm or less, 30 μm or less, 20 μm or less, or 10 μm or less. The thickness of the insulating layer (L) may be in the range of 0.5 to 30 μm. The lower and / or upper limits of this range may be replaced with the above lower and / or upper limits as long as the lower limit does not exceed the upper limit. By making the insulating layer (L) 0.5 μm or more, it is possible to increase the dielectric strength and reduce the leakage current. By making the insulating layer (L) 30 μm or less, it is particularly easy to achieve high capacity.

[0027] The insulating layer (L) is usually formed so that its thickness is as uniform as possible. The thickness of the insulating layer (L) can be measured using an image of a cross section of the electrode (E) on which the insulating layer (L) is formed.

[0028] The anode and cathode may each include a metal foil. Examples of metal foils are described below. The cathode may include a metal foil and another layer formed on the surface of the metal foil. Examples of the other layer include a conductive layer made of a material different from the metal foil.

[0029] The anode and cathode of the electrolytic capacitor (C) face each other with an insulating layer (L) interposed therebetween. The arrangement of the anode and cathode is not particularly limited. The anode and cathode may be wound. That is, the electrolytic capacitor (C) may include a wound body in which the anode and cathode are wound.

[0030] (Method for manufacturing electrolytic capacitor) The manufacturing method according to this embodiment may be referred to as "manufacturing method (M)" below. According to the manufacturing method (M), the electrolytic capacitor (C) can be manufactured. However, the electrolytic capacitor (C) may also be manufactured by a method other than the manufacturing method (M). The matters described for the electrolytic capacitor (C) may also be applied to the manufacturing method (M), and therefore, redundant explanations may be omitted. The matters described for the manufacturing method (M) may also be applied to the electrolytic capacitor (C).

[0031] The manufacturing method (M) is a method for manufacturing an electrolytic capacitor including an anode and a cathode having a dielectric layer on their surfaces. The manufacturing method (M) includes a step (i) of forming a porous insulating layer (insulating layer (L)) on at least one electrode (electrode (E)) selected from the group consisting of an anode and a cathode, and a step (ii) of stacking the anode and the cathode so that the insulating layer (L) is disposed between them. The manufacturing method (M) further includes a step (a) of disposing an electrolyte in the voids of the insulating layer (L).

[0032] (Step (i)) The method for forming the insulating layer (L) in step (i) is not particularly limited. As described above, the porous insulating layer (L) may be formed by spraying a coating liquid containing a polymer. Alternatively, in step (i), the insulating layer (L) may be formed by depositing fibers on at least one electrode (E). For example, in step (i), fibers may be deposited on at least one electrode (E) by electrospinning. In step (i), the insulating layer (L) can be formed so as to adhere to the electrode (E). By adhering the insulating layer (L) to the electrode (E), the electrode (E) and the insulating layer (L) can be handled as a single integrated member in step (ii).

[0033] When forming the insulating layer (L) by electrospinning, a higher surface conductivity of the electrode (E) facilitates increased adhesion of fibers to the electrode (E). Therefore, from the viewpoint of increasing adhesion of the insulating layer (L) to the electrode (E), the electrode (E) may serve as the cathode. When forming the insulating layer (L) by electrospinning, fibers can be deposited on the electrode (E) by ejecting a polymer solution from a nozzle. The polymer in the polymer solution may be any of the polymers described above. The solvent for the polymer solution is not limited, and known solvents used in electrospinning may be used depending on the type of polymer. Examples of solvents include water and organic solvents. Examples of organic solvents include alcohol, acetone, dichloromethane, dimethylformamide, dimethylacetamide, tetrahydrofuran, and dimethyl sulfoxide. The solvent may be used alone or in combination. The polymer solution may contain additives (e.g., known additives).

[0034] The concentration of the polymer solution is not limited and may be selected depending on the fiber to be formed. The physical properties of the formed fiber (e.g., fiber diameter) can be varied by changing the conditions for electrospinning (e.g., nozzle diameter, applied voltage, solvent type, polymer solution concentration, etc.). The concentration of the polymer solution may be 5% by mass or more, 10% by mass or more, or 15% by mass or more, or 20% by mass or less, 15% by mass or less, or 10% by mass or less.

[0035] In step (i), an insulating layer (L) may be formed on a large conductive sheet, and then the conductive sheet may be cut to form the electrode (E). In this case, the width of the insulating layer (L) is usually equal to the width of the electrode (E). The conductive sheet is a sheet that becomes an anode or a cathode by cutting. Therefore, a metal foil on which a dielectric layer is formed, or a metal foil, etc., is used as the conductive sheet.

[0036] A dielectric layer is formed on the surface of the anode used in step (i). The dielectric layer may be formed by a known method (e.g., chemical conversion treatment). The surface of the anode is usually made porous. The surface of the cathode may also be made porous. By making these surfaces porous, the surface area of ​​the electrode can be increased. Furthermore, by making the surface of the electrode (E) porous, the adhesion of the insulating layer (L) to the electrode (E) can be improved. The method for making the surface of the electrode porous is not limited, and a known method may be used. For example, the surface of the electrode may be made porous by etching.

[0037] (Step (ii)) In step (ii), the method for stacking the anode and the cathode is not particularly limited, and a known method may be used. In step (ii), the anode and the cathode may be stacked by winding the anode and the cathode. Alternatively, in step (ii), flat anodes may be stacked in one direction.

[0038] (Step (a)) Step (a) is a step of disposing an electrolyte in the voids of the insulating layer (L). Step (a) can also be considered as a step of disposing an electrolyte between the anode and the cathode. By disposing the electrolyte between the anode and the cathode, the electrolyte is disposed in the voids of the insulating layer (L).

[0039] The step (a) of disposing the electrolyte in the voids of the insulating layer (L) may be performed simultaneously with the step (ii) of forming the insulating layer (L), but is usually performed after the insulating layer (L) is formed. When the electrolyte contains a conductive polymer (solid electrolyte), the conductive polymer may be disposed in the voids of the insulating layer (L) before forming a wound body (or laminate) of the anode and cathode. In this case, the conductive polymer may be disposed in the insulating layer (L) by applying a liquid containing the conductive polymer to the insulating layer (L) and then drying it. Then, a wound body (or laminate) of the anode and cathode is formed.

[0040] The conductive polymer may be disposed in the voids of the insulating layer (L) after forming a wound body (or laminate) of the anode and the cathode. In this case, the wound body (or laminate) may be impregnated with a liquid containing the conductive polymer and then dried, thereby disposing the conductive polymer in the insulating layer (L).

[0041] When the electrolyte includes an electrolytic solution, the electrolytic solution may be disposed in the voids of the insulating layer (L) after forming a wound body (or laminate) of the anode and the cathode. For example, the electrolytic solution may be disposed in the insulating layer (L) by impregnating the wound body (or laminate) with the electrolytic solution. The impregnation of the electrolytic solution may be performed before or after the wound body (or laminate) is housed in the exterior case.

[0042] In this manner, a capacitor element containing an electrolyte is formed. An electrolytic capacitor is manufactured using the formed capacitor element. For example, an electrolytic capacitor is obtained by housing the capacitor element in an outer casing. Steps other than those described above are not particularly limited, and steps used in known manufacturing methods may be used.

[0043] Examples of components used in the electrolytic capacitor (C) are described below. However, the components used in the electrolytic capacitor (C) are not limited to the examples described below. Components other than those specific to the electrolytic capacitor (C) are not particularly limited, and known components may be used.

[0044] (Anode) Examples of the anode include a metal foil containing at least one valve metal such as titanium, tantalum, aluminum, and niobium. The anode may be a metal foil of a valve metal (e.g., aluminum foil). The anode may contain the valve metal in the form of an alloy containing the valve metal or a compound containing the valve metal. The surface of the anode may be roughened by etching or the like. That is, the surface of the anode may be made porous. The thickness of the anode may be 15 μm or more, or 50 μm or more, and may be 300 μm or less, or 100 μm or less. When the capacitor element is a wound element, the anode has a strip shape.

[0045] A dielectric layer is formed on the surface of the anode. The dielectric layer may be formed by chemically treating the anode. 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.

[0046] (Cathode) A conductive sheet can be used for the cathode, and a metal foil (e.g., aluminum foil) may also be used. The metal constituting the metal foil may be a valve metal or an alloy containing a valve metal. The surface of the cathode may be roughened by etching or the like. That is, the surface of the cathode may be made porous. The thickness of the cathode may be 15 μm or more, or 50 μm or more, and may be 300 μm or less, or 100 μm or less. When the capacitor element is a wound element, the cathode has a strip shape.

[0047] (Electrolyte) The electrolyte is disposed between the anode and the cathode (for example, in the voids of the insulating layer (L)). A solid electrolyte (for example, a conductive polymer) and / or an electrolytic solution may be used as the electrolyte. The electrolytic capacitor (C) preferably contains a conductive polymer and an electrolytic solution. The electrolytic capacitor (C) may contain a conductive polymer and a liquid component disposed between the anode and the cathode. The liquid component may be an electrolytic solution or a non-aqueous solvent used in the electrolytic solution. When an insulating layer (L) is used, using a conductive polymer and an electrolytic solution as the electrolyte is preferable because it reduces the ESR while easily achieving high reliability and high voltage resistance of the electrolytic capacitor.

[0048] 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).

[0049] The conductive polymer may be doped with a dopant. From the viewpoint of suppressing dedoping from the conductive polymer, a polymer dopant may be used 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).

[0050] The dopant may be polystyrene sulfonic acid, and the conductive polymer may be poly(3,4-ethylenedioxythiophene). That is, the conductive polymer may be poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid.

[0051] When a conductive polymer is disposed between an anode and a cathode, a liquid containing the conductive polymer may be used, as described above. The liquid medium is not particularly limited. Examples of the liquid medium include water, organic solvents (alcohol, ethylene glycol), and mixed solvents thereof. The liquid containing the conductive polymer may be a dispersion liquid in which conductive polymer particles are dispersed in a liquid whose main component is water (content: 50% by mass or more).

[0052] The content of the conductive polymer in the liquid containing the conductive polymer 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.

[0053] The electrolytic solution is not particularly limited, and may be a known electrolytic solution used in electrolytic capacitors. The electrolytic solution may contain a non-aqueous solvent and a solute (e.g., an organic salt) dissolved in the non-aqueous solvent.

[0054] 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.

[0055] The non-aqueous solvent may contain a polymer 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 non-aqueous solvent may be used alone, or two or more types may be used in combination.

[0056] Examples of solutes include inorganic salts and organic salts. Organic salts are salts in which at least one of the anion and cation contains an organic compound. Examples of organic salts include trimethylamine maleate, triethylamine borodisalicylate, ethyldimethylamine phthalate, mono-1,2,3,4-tetramethylimidazolinium phthalate, and mono-1,3-dimethyl-2-ethylimidazolinium phthalate.

[0057] (Exterior Body) The capacitor element is housed in an exterior body. The exterior body is not particularly limited, and a known exterior body may be used.

[0058] An example of 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. Furthermore, the components of the example described below can be modified based on the above description. Furthermore, the matters described below may be applied to the above embodiment. Furthermore, in the example described below, components that are not essential for the electrolytic capacitor according to the present disclosure may be omitted.

[0059] (Embodiment 1) 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 expanded form. The electrolytic capacitor 100 is a wound-type capacitor including a wound body.

[0060] 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 open end of bottomed case 101 is curled inward.

[0061] An example of a capacitor element 10 is shown schematically in FIG. 2. Capacitor element 10 is a wound body formed by winding an anode (anode foil) 11 and a cathode (cathode foil) 12. A porous insulating layer 21 is formed on the anode 11 and the cathode 12, or on either the anode 11 or the cathode 12. FIG. 2 shows an example in which insulating layer 21 is formed on both sides of cathode 12. Insulating layer 21 is integral with cathode 12 and is wound together with cathode 12. The outermost periphery of the wound body is fixed with stop tape 14. Note that FIG. 2 shows a state in which capacitor element 10 is partially unfolded before the outermost periphery of the wound body is secured.

[0062] A portion of capacitor element 10 is shown schematically in Fig. 3. Note that although Fig. 3 shows anode 11, cathode 12, and insulating layer 21 as flat members, within capacitor element 10, anode 11, cathode 12, and insulating layer 21 are curved.

[0063] As shown in FIG. 3 , the capacitor element 10 includes an anode 11, a cathode 12, an insulating layer 21 (insulating layer (L)), and an electrolyte (not shown). A dielectric layer 11a is formed on the surface of the anode 11. The insulating layer 21 and the electrolyte are disposed between the anode 11 (more specifically, the dielectric layer 11a on the surface of the anode 11) and the cathode 12. The electrolyte is disposed between the anode 11 and the cathode 12 (for example, in the voids in the insulating layer 21). The insulating layer 21 is formed on the anode 11 and / or the cathode 12. As described above, the surfaces of the anode 11 and / or the cathode 12 may be porous.

[0064] An apparatus for performing the electrospinning method is not particularly limited. An example of an apparatus 200 for performing the electrospinning method is schematically shown in FIG. 4. The apparatus 200 includes a syringe 201 having a conductive nozzle 201a and a power supply 202. A polymer solution 211 is placed in the syringe 201. A high voltage is applied between the nozzle 201a and an electrode 221 (anode or cathode) by the power supply 202. Fibers 212 are formed by ejecting the polymer solution 211 from the nozzle 201a. The formed fibers 212 are deposited on the electrode 221 to form a porous insulating layer. By increasing the number of nozzles 201a, it is possible to simultaneously deposit a large number of fibers 212.

[0065] (Additional Note) The above description discloses the following techniques.

[0066] (Technology 1) An electrolytic capacitor comprising: an anode having a dielectric layer on a surface thereof; a cathode; a porous insulating layer formed on at least one electrode selected from the group consisting of the anode and the cathode and disposed between the anode and the cathode; and an electrolyte disposed in voids of the insulating layer.

[0067] (Technology 2) The electrolytic capacitor according to Technology 1, wherein the insulating layer is attached to at least one of the dielectric layer and the cathode.

[0068] (Technology 3) The electrolytic capacitor according to Technology 1 or 2, wherein the insulating layer includes fibers deposited on the at least one electrode.

[0069] (Technology 4) The electrolytic capacitor according to Technology 3, wherein the average diameter of the fibers is 0.1 μm or more and 1.5 μm or less.

[0070] (Technology 5) The electrolytic capacitor according to Technology 3 or 4, wherein the fibers are made of a polymer.

[0071] (Technology 6) The electrolytic capacitor according to Technology 3 or 4, wherein the fibers are made of at least one material selected from the group consisting of polyacrylonitrile and polyvinylidene fluoride.

[0072] (Technology 7) The electrolytic capacitor according to any one of Technologies 1 to 6, wherein the insulating layer has a thickness of 0.5 μm or more and 30 μm or less.

[0073] (Technology 8) The electrolytic capacitor according to any one of Technologies 1 to 7, wherein the anode and the cathode are each a metal foil.

[0074] (Technology 9) The electrolytic capacitor according to any one of Technologies 1 to 8, including a wound body in which the anode and the cathode are wound.

[0075] (Technology 10) The electrolytic capacitor according to any one of Technologies 1 to 8, including a laminate in which the anode and the cathode are laminated.

[0076] (Technology 11) A method for manufacturing an electrolytic capacitor including an anode having a dielectric layer on a surface thereof and a cathode, the method comprising: (i) forming a porous insulating layer on at least one electrode selected from the group consisting of the anode and the cathode; and (ii) stacking the anode and the cathode such that the insulating layer is disposed between the anode and the cathode; and further comprising: (a) disposing an electrolyte in voids in the insulating layer.

[0077] (Technology 12) The manufacturing method according to Technology 11, wherein in the step (i), the insulating layer is formed by depositing fibers on the at least one electrode.

[0078] (Technology 13) The manufacturing method according to Technology 12, wherein in the step (i), the fibers are deposited on the at least one electrode by an electrospinning method.

[0079] (Technology 14) The manufacturing method according to any one of Techniques 11 to 13, wherein in the step (ii), the anode and the cathode are stacked by winding them together.

[0080] The present disclosure will be described in more detail below based on examples, but the present disclosure is not limited to the examples described below. In these examples, a plurality of electrolytic capacitors were fabricated and evaluated. In these examples, parallel plate capacitors including one anode and one cathode were fabricated.

[0081] (Capacitor A1) An electrolytic capacitor (capacitor A1) was produced by the following method.

[0082] (1) Preparation of anode foil: Aluminum foil (thickness: 100 μm) was etched to roughen (porous) the surface of the aluminum foil. The roughened aluminum foil surface was subjected to a chemical conversion treatment to form a dielectric layer. Next, the aluminum foil with the dielectric layer formed thereon was cut into 20 mm square pieces. In this way, an anode foil with a dielectric layer formed on both sides was obtained.

[0083] (2) Preparation of Cathode Foil Aluminum foil (thickness: 50 μm) was etched to roughen (porousize) the surface of the aluminum foil, thereby obtaining a cathode foil. Next, a porous insulating layer was formed on the cathode foil (aluminum foil) by depositing fibers on the surface using an electrospinning method. A polyacrylonitrile solution was used as the polymer solution for the electrospinning method. An aprotic polar solvent was used as the solvent for the polymer solution. Using this polymer solution, a porous insulating layer (thickness: 15 μm) made of polyacrylonitrile fibers was formed on the cathode foil. Next, the cathode foil with the insulating layer formed on it was cut into 22 mm squares. In this way, a cathode foil with an insulating layer formed on one side was obtained.

[0084] (3) Assembly of electrolytic capacitors The porous insulating layer of the cathode foil is coated with a film having a surface density of 0.3 mg / cm ２ The conductive polymer dispersion was dropped onto the foil so that the thickness of the conductive polymer dispersion was 100 μm. The anode foil and cathode foil were then stacked with the insulating layer sandwiched between them to form a laminate. The laminate was then dried at 150°C for 20 minutes, thereby disposing the conductive polymer between the anode foil and the cathode foil. At this time, the conductive polymer was disposed in the voids in the insulating layer. Poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrene sulfonate (PSS) was used as the conductive polymer. The dispersion medium for the conductive polymer dispersion was a liquid obtained by adding 5% by mass of ethylene glycol to water.

[0085] Next, the laminate was impregnated with an electrolyte solution to place the electrolyte in the voids of the insulating layer. The electrolyte solution was prepared by dissolving 5-sulfosalicylic acid and triethylamine in ethylene glycol (solvent) to a total concentration of 25% by mass. The equivalent ratio of 5-sulfosalicylic acid to triethylamine was 2.0. The electrolytic capacitor thus fabricated was aged to obtain a parallel-plate capacitor A1. Aging was performed by applying a rated voltage to the capacitor for 30 minutes.

[0086] Three capacitors A1 were fabricated, and the capacitance (Cap) at 120 Hz, the equivalent series resistance (ESR) at 100 kHz, and the leakage current (LC) were measured for each. The evaluation results of the three cells were then arithmetically averaged.

[0087] (Capacitor A2) Capacitor A2 was fabricated using the same method and conditions as Capacitor A1, except that the polymer solution used in the electrospinning process and the thickness of the insulating layer were changed. In the fabrication of Capacitor A2, a polyvinylidene fluoride solution was used as the polymer solution. An aprotic polar solvent was used as the solvent for the polymer solution. By using this polymer solution, a porous insulating layer (thickness: 10 μm) made of polyvinylidene fluoride fibers was formed on the cathode foil. Three Capacitors A2 were fabricated and evaluated in the same manner as Capacitor A1.

[0088] (Capacitor C1) Capacitor A2 was fabricated using the same method and conditions as capacitor A1, except that a separator was used instead of an insulating layer. That is, in capacitor C1, no insulating layer was formed on the cathode, and a separator was placed between the anode and cathode. A nonwoven fabric (thickness: 50 μm) made of cellulose was used as the separator. Three capacitors C1 were fabricated and evaluated in the same manner as capacitor A1.

[0089] Table 1 shows some of the manufacturing conditions and evaluation results for each capacitor. The numerical values ​​of the evaluation results are the arithmetic mean values ​​of the evaluation results for three capacitors. The evaluation results in Table 1 are shown as relative values, with the evaluation result for capacitor C1 set at 1.00. "Insulator" in Table 1 refers to an insulator disposed between the anode and cathode. A large capacitance is preferable, and small ESR and leakage current are preferable.

[0090]

[0091] Capacitors A1 and A2 are electrolytic capacitors (C) according to the present disclosure. Capacitor C1 is a comparative example. As shown in Table 1, capacitors A1 and A2 had large capacitance and small ESR and leakage current. The increase in capacitance is believed to be due to the increased amount of conductive polymer filled in the porous anode due to the thin insulating layer. The decrease in ESR is believed to be due to the insulating layer being thinner than the separator. When a wound (or laminated) capacitor element is formed using the insulating layer used in capacitors A1 and A2, the thin insulating layer allows for an increase in capacitance per volume.

[0092] The present disclosure can be used for electrolytic capacitors.

[0093] 10: Capacitor element 11: Anode 11a: Dielectric layer 12: Cathode 21: Porous insulating layer 100: Electrolytic capacitor

Claims

1. An electrolytic capacitor comprising: an anode having a dielectric layer on a surface thereof; a cathode; a porous insulating layer formed on at least one electrode selected from the group consisting of the anode and the cathode and disposed between the anode and the cathode; and an electrolyte disposed in the voids of the insulating layer.

2. The electrolytic capacitor of claim 1, wherein said insulating layer is attached to at least one of said dielectric layer and said cathode.

3. The electrolytic capacitor of claim 1 or 2, wherein the insulating layer comprises fibers deposited on the at least one electrode.

4. The electrolytic capacitor according to claim 3, wherein the average diameter of the fibers is 0.1 μm or more and 1.5 μm or less.

5. The electrolytic capacitor of claim 3, wherein the fibers are made of a polymer.

6. The electrolytic capacitor according to claim 3, wherein the fibers are made of at least one material selected from the group consisting of polyacrylonitrile and polyvinylidene fluoride.

7. The electrolytic capacitor according to claim 1 or 2, wherein the thickness of the insulating layer is 0.5 μm or more and 30 μm or less.

8. The electrolytic capacitor according to claim 1 or 2, wherein the anode and the cathode are each a metal foil.

9. The electrolytic capacitor according to claim 1 or 2, comprising a wound body in which the anode and the cathode are wound.

10. The electrolytic capacitor according to claim 1 or 2, comprising a laminate in which the anode and the cathode are laminated.

11. A method for manufacturing an electrolytic capacitor including an anode having a dielectric layer on its surface and a cathode, the method comprising: (i) forming a porous insulating layer on at least one electrode selected from the group consisting of the anode and the cathode; and (ii) stacking the anode and the cathode so that the insulating layer is disposed between the anode and the cathode; and further comprising: (a) disposing an electrolyte in voids in the insulating layer.

12. The method of claim 11, wherein in step (i), the insulating layer is formed by depositing fibers on the at least one electrode.

13. The method of claim 12, wherein in step (i), the fibers are deposited on the at least one electrode by electrospinning.

14. The manufacturing method according to claim 11 or 12, wherein in step (ii), the anode and the cathode are stacked by winding them together.

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