Electrolytic capacitor and method for producing electrolytic capacitor

Abstract

This electrolytic capacitor comprises: a positive-electrode foil having a metal part and a dielectric layer formed on the surface of the metal part; a negative-electrode foil; a separator interposed between the positive-electrode foil and the negative-electrode foil; an electroconductive polymer layer formed on the surface of the dielectric layer, the electroconductive polymer layer containing an electroconductive polymer; and a positive-electrode lead connected to the positive-electrode foil. A portion of the positive-electrode foil (21) has an exposed region (21R) exposed from the electroconductive polymer layer (24). The positive-electrode lead (60) is electrically connected to the positive-electrode foil (21) by directly contacting the metal part (21a) in the exposed region (21R).

Description

Electrolytic capacitor and method for manufacturing the same

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

[0002] Conventionally, electrolytic capacitors have been known that include an anode foil, a cathode foil, and a separator interposed therebetween (see, for example, Patent Document 1). The electrolytic capacitor in Patent Document 1 has a conductive polymer layer formed on the surface of the anode foil, and an anode lead connected to the anode foil. The anode lead is drawn out of a case that houses the anode foil and functions as one of the external terminals of the electrolytic capacitor.

[0003] Special Publication No. 2019-516241

[0004] One aspect of the present disclosure relates to an electrolytic capacitor. The electrolytic capacitor includes an anode foil having a metal portion and a dielectric layer formed on the surface of the metal portion, a cathode foil, a separator interposed between the anode foil and the cathode foil, a conductive polymer layer formed on the surface of the dielectric layer and containing a conductive polymer, and an anode lead connected to the anode foil. A portion of the anode foil has an exposed region exposed from the conductive polymer layer. The anode lead is electrically connected to the anode foil by direct contact with the metal portion in the exposed region.

[0005] Another aspect of the present disclosure relates to a method for manufacturing an electrolytic capacitor including an anode foil having a metal portion and a dielectric layer formed on a surface of the metal portion, a cathode foil, and a separator, the method comprising: a coating liquid application step of applying a coating liquid containing a conductive polymer and a liquid medium to a surface of the dielectric layer of the anode foil; a polymer layer formation step of forming a conductive polymer layer containing the conductive polymer on the surface of the dielectric layer by removing at least a portion of the liquid medium from the coating liquid; a polymer layer removal step of removing a portion of the conductive polymer layer in the anode foil to form an exposed region in which the portion of the anode foil is exposed from the conductive polymer layer; and a lead connection step of electrically connecting the anode lead to the anode foil by directly contacting the metal portion in the exposed region with the anode lead.

[0006] According to the present disclosure, the equivalent series resistance (ESR) of an electrolytic capacitor can be reduced.

[0007] 1 is a side view schematically illustrating an example of an electrolytic capacitor according to the present disclosure; 2 is an exploded perspective view schematically illustrating a capacitor element; 3 is a front view showing a region where an anode foil and an anode lead are connected; and 4 is a cross-sectional view showing a region where an anode foil and an anode lead are connected.

[0008] The problems in the prior art will be briefly described below.

[0009] Generally, the anode foil and anode lead are each made of metal, with a conductive polymer layer interposed between them. Because the conductive polymer layer has lower conductivity than metal, the presence of the conductive polymer layer increases the connection resistance between the anode foil and anode lead, thereby increasing the equivalent series resistance (ESR) of the electrolytic capacitor.

[0010] The present disclosure provides an electrolytic capacitor capable of reducing ESR and a method for manufacturing an electrolytic capacitor.

[0011] The following describes examples of embodiments of an electrolytic capacitor and a method for manufacturing an electrolytic capacitor according to the present disclosure. However, the present disclosure is not limited to the examples described below. While the following description may use specific numerical values ​​and materials, other numerical values ​​and materials may be used as long as the effects of the present disclosure are obtained.

[0012] (Method for manufacturing an electrolytic capacitor) The method for manufacturing an electrolytic capacitor according to the present disclosure is a method for manufacturing an electrolytic capacitor including an anode foil having a metal portion and a dielectric layer formed on the surface thereof, a cathode foil, and a separator, and includes a coating liquid application step, a polymer layer formation step, a polymer layer removal step, and a lead connection step.

[0013] (Coating Liquid Application Step) In the coating liquid application step, a coating liquid containing a conductive polymer and a liquid medium is applied (or coated) to the surface of the dielectric layer of the anode foil. The conductive polymer may be dispersed in the coating liquid in the form of particles. The liquid medium may contain water and an organic compound. The organic compound may be a single compound or may be composed of multiple compounds. The method for applying (or coating) the coating liquid is not particularly limited and may be applied by a known method. For example, the coating liquid may be applied using a coater, the coating liquid may be sprayed, or the anode foil 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 attached to the transfer member is then transferred to each of the anode foil, cathode foil, and separator, thereby forming a coating liquid layer of uniform thickness on each of the anode foil, cathode foil, and 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, the cathode foil, and the separator, and can easily be impregnated into the separator. The viscosity of the coating liquid is measured at room temperature (20°C) using a vibration viscometer (for example, VM-100A, manufactured by Sekonic Corporation).

[0014] Examples of the organic compound may include at least one selected from the group consisting of polyhydric alcohols, sulfolane, γ-butyrolactone, and boric acid esters, and may be at least one of the organic compounds. The organic compound may include at least one selected from the group consisting of glycols, glycerols, sugar alcohols, sulfolane, γ-butyrolactone, and boric acid esters, and may be at least one of the organic compounds.

[0015] Examples of polyhydric alcohols include glycols, glycerins, and sugar alcohols. 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. Examples of sugar alcohols include mannitol, xylitol, sorbitol, erythritol, and pentaerythritol.

[0016] 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).

[0017] The conductive polymer may be 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, and polyacrylic acid. 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). The weight-average molecular weight of the dopant is not particularly limited. From the viewpoint of facilitating the formation of a homogeneous conductive polymer layer, the weight-average molecular weight of the dopant may be in the range of 1,000 to 100,000.

[0018] (Polymer Layer Formation Process) In the polymer layer formation process, at least a portion of the liquid medium (e.g., water) is removed from the coating liquid to form a conductive polymer layer containing a conductive polymer on the surface of the dielectric layer. The method for removing at least a portion of the liquid medium from the coating liquid is not particularly limited. For example, the removal may be performed by heating and / or reducing pressure, and preferably involves at least heating. When heating is performed, at least a portion of the liquid medium may be removed by heating at a temperature of 100°C or higher. This allows the water in the liquid medium to be removed quickly. The heating temperature is preferably a temperature at which the organic compound does not boil or decompose. When the organic compound does not have a clear boiling point, it is preferable to heat at a temperature at which the organic compound evaporates little and does not decompose.

[0019] (Polymer Layer Removal Process) In the polymer layer removal process, a portion of the conductive polymer layer is removed from a portion of the anode foil to form an exposed region in which the portion of the anode foil is exposed from the conductive polymer layer. When forming the exposed region, the conductive polymer layer may be removed, and a portion of the metal portion of the anode foil and / or the dielectric layer may also be removed. The method for removing the portion of the conductive polymer layer and / or the portion of the anode foil is not particularly limited. For example, removal using a router, removal by polishing, removal by laser light irradiation, or removal by application of ultrasonic waves may be used. Alternatively, the conductive polymer layer may be removed together with a portion of the anode foil by drilling a hole in the anode foil. In this case, the region where the metal portion is exposed on the inner surface of the hole becomes the exposed region. Alternatively, a portion of the conductive polymer layer may be removed by removing a portion of the anode foil by etching. In the exposed region, it is preferable that the metal portion is exposed from the conductive polymer layer.

[0020] (Lead Connection Process) In the lead connection process, the anode lead is electrically connected to the anode foil by directly contacting the metal portion in the exposed region with the anode lead. The anode lead may be made of a metal (e.g., aluminum, aluminum alloy, copper, or copper alloy). The anode lead may be connected to the anode foil by needle crimping. In needle crimping, a needle is pressed against the anode lead superimposed on the anode foil, and through-holes are formed in the anode foil and the anode lead, and a portion of the anode lead is passed through the hole in the anode foil, thereby mechanically and electrically connecting the anode foil and the anode lead. By forming an exposed region in the anode foil in advance in the polymer layer removal process, the metal portion and the anode lead can be directly contacted in the lead connection process. Because a conductive polymer layer with high electrical resistance is not interposed between the metal portion and the anode lead, the connection resistance between the metal portion and the anode lead can be reduced, thereby reducing the ESR of the electrolytic capacitor.

[0021] In the polymer layer removal step, a portion of the conductive polymer layer may be removed from both sides of the anode foil. In this case, exposed regions are formed on both sides of the anode foil, and when an anode lead is connected so as to contact both sides of the anode foil, the connection resistance between the anode foil and the anode lead can be further reduced. Note that in the polymer layer removal step, a portion of the conductive polymer layer may be removed from only one side of the anode foil.

[0022] As long as the metal portion and the anode lead are in direct contact in the exposed region, a conductive polymer layer may be interposed between a portion of the anode lead and the anode foil. Even if the entire anode lead is not in contact with the anode foil without a conductive polymer layer, there is a portion where the metal portion of the anode foil and the anode lead are in direct contact, thereby sufficiently reducing the connection resistance between the anode lead and the anode foil. Furthermore, the amount of conductive polymer layer removed can be reduced compared to when no conductive polymer layer is interposed between the entire anode lead and the anode foil. This reduces the burden of the removal work. Furthermore, because a conductive polymer layer is also formed in the region of the anode foil near the anode lead, adverse effects (such as a decrease in capacitance and an increase in ESR) caused by regions of the anode foil where no conductive polymer layer is formed can be suppressed. Note that a conductive polymer layer need not be interposed between the entire anode lead and the anode foil. If the area of ​​the region where the anode lead and the anode foil overlap as viewed in the thickness direction of the anode foil is S1 and the area of ​​the region of the anode foil from which the conductive polymer layer has been removed is S2, the ratio of the area S2 to the area S1 (S2 / S1) may be, for example, 0.1 or more and 3.0 or less. The ratio (S2 / S1) may be preferably 0.5 or more and 1.5 or less, and more preferably 0.9 or more and 1.1 or less. Note that if the ratio (S2 / S1) is less than 1.0, the conductive polymer layer is interposed between a portion of the anode lead and the anode foil.

[0023] The metal part may have a core part and a porous part having a lower density than the core part. In the polymer layer removal step, in a part of the anode foil, in addition to a part of the conductive polymer layer, at least a part of the porous part may be removed. The core part and the porous part can be formed, for example, by etching the surface of the metal foil. The porous part may have a large number of micropores extending in the thickness direction of the anode foil, or may have a large number of micropores formed in a sponge-like shape. Because the porous part has lower conductivity than the core part, removing at least a part of such a porous part allows the anode lead and the core part of the metal part to be in direct contact with each other, thereby further reducing the connection resistance between them.

[0024] (Electrolytic Capacitor) An electrolytic capacitor according to the present disclosure includes an anode foil, a cathode foil, a separator, a conductive polymer layer, and an anode lead.

[0025] The anode foil has a metal portion and a dielectric layer formed on the surface of the metal portion. Examples of the anode foil include metal foils containing at least a portion of a valve metal such as titanium, tantalum, aluminum, or niobium, and may be a valve metal foil (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 dielectric layer may be formed by chemical conversion treatment of the anode foil. In this case, the dielectric layer contains an oxide of the valve metal (e.g., aluminum oxide). Note that the dielectric layer may be composed of a dielectric other than an oxide of the valve metal, as long as it functions as a dielectric.

[0026] 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 or compound 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 subjected to a chemical conversion treatment as necessary. The cathode foil may have a conductive polymer layer containing a conductive polymer, or may not have such a conductive polymer layer. Examples of the conductive polymer may be the same as those described above. The composition of the conductive polymer layer of the cathode foil may be the same as or different from the composition of the conductive polymer layer of the anode foil.

[0027] 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 improves the acid resistance of the metal foil. When the metal foil includes aluminum, the coating layer may include at least one metal 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.

[0028] 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 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, and carbon black.

[0029] The separator is interposed between the anode foil and the cathode foil. 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 10 μm or more and 300 μm or less. Examples of separator materials include cellulose, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, vinylon, nylon, aromatic polyamide, polyimide, polyamideimide, polyetherimide, rayon, and glass. The separator may have a conductive polymer layer containing a conductive polymer, or may not have such a conductive polymer layer. Examples of conductive polymers may be the same as those described above. The composition of the conductive polymer layer of the separator may be the same as or different from the composition of the conductive polymer layer of the anode foil.

[0030] The conductive polymer layer is formed on the surface of the dielectric layer and contains a conductive polymer. Examples of the conductive polymer are as described above. The conductive polymer layer is not formed on a portion of the anode foil. That is, the portion of the anode foil has an exposed region that is exposed from the conductive polymer layer. In the exposed region, it is preferable that a metal portion is exposed from the conductive polymer layer.

[0031] The anode lead is connected to the anode foil. Specifically, the anode lead is connected to the anode foil by directly contacting the metal portion in the exposed region. This reduces the connection resistance between the metal portion and the anode lead, thereby reducing the ESR of the electrolytic capacitor. The anode lead may be made of a metal (e.g., aluminum, an aluminum alloy, copper, or a copper alloy). The anode lead may be connected to the anode foil by needle crimping.

[0032] The metal portion may be exposed from the conductive polymer layer on both sides of the anode foil. In this case, exposed regions are formed on both sides of the anode foil, and when an anode lead is connected so as to contact both sides of the anode foil, the connection resistance between the anode foil and the anode lead can be further reduced. Note that the metal portion may be exposed from the conductive polymer layer on only one side of the anode foil.

[0033] The metal portion may have a core portion and a porous portion having a lower density than the core portion. The thickness of the porous portion in a portion of the anode foil may be smaller than the thickness of the porous portion in the remaining portion of the anode foil. Since the conductivity of the porous portion is lower than that of the core portion, the smaller thickness of such a porous portion can reduce the connection resistance between the portion of the anode foil and the anode lead. Note that the configuration described in this paragraph also includes cases where the portion of the anode foil does not have a porous portion.

[0034] A conductive polymer layer may be interposed between a portion of the anode lead and the anode foil. Even with this configuration, the technique of the present disclosure can sufficiently reduce the connection resistance between the anode lead and the anode foil, thereby reducing the ESR of the electrolytic capacitor.

[0035] As described above, according to the present disclosure, the ESR of the electrolytic capacitor can be reduced by bringing the metal portion and the anode lead into direct contact in the exposed region formed in a part of the anode foil.

[0036] An example of an electrolytic capacitor and a method for manufacturing an electrolytic capacitor according to the present disclosure will be described in detail below with reference to the drawings. The components and steps described above can be applied to the components and steps of the example electrolytic capacitor and method for manufacturing an electrolytic capacitor described below. The components and steps of the example electrolytic capacitor and method for manufacturing an electrolytic capacitor described below can be modified based on the above description. Furthermore, the matters described below may be applied to the above-described embodiment. Among the components and steps of the example electrolytic capacitor and method for manufacturing an electrolytic capacitor described below, components and steps that are not essential to the electrolytic capacitor and method for manufacturing an electrolytic capacitor according to the present disclosure may be omitted. Note that the diagrams shown below are schematic and do not accurately reflect the shapes and numbers of actual components.

[0037] 1 to 3 , an electrolytic capacitor 10 of this embodiment includes a capacitor element 20, a bottomed case 30 that houses the capacitor element 20, a sealing member 40 that closes the opening of the bottomed case 30, a seat plate 50 that covers the sealing member 40, lead wires 61 and 71 that extend from the sealing member 40 and pass through the seat plate, and lead tabs 62 and 72 that connect the lead wires to electrodes of the capacitor element 20. The vicinity of the open end of the bottomed case 30 is drawn inward, and the open end is curled so as to clamp the sealing member 40. One lead wire 61 and one lead tab 62 form an anode lead 60, and the other lead wire 71 and other lead tab 72 form a cathode lead 70.

[0038] The capacitor element 20 is, for example, a wound body as shown in FIG. 2 . The wound body includes an anode foil 21 connected to the lead tab 62 of the anode lead 60, a cathode foil 22 connected to the lead tab 72 of the cathode lead 70, and a separator 23 interposed between the anode foil 21 and the cathode foil 22. As shown in FIGS. 3A and 3B , the anode foil 21 includes a metal portion 21 a having a core portion and a porous portion (neither of which are shown), and a dielectric layer (not shown) formed on the surface of the metal portion 21 a. The density of the porous portion is lower than the density of the core portion. A conductive polymer layer 24 containing a conductive polymer is formed on the surface of the dielectric layer.

[0039] The electrolytic capacitor 10 may include a liquid component (e.g., an electrolyte solution) impregnated in the capacitor element 20. Examples of the liquid component include a nonaqueous solvent and an electrolyte solution. The electrolyte solution may be a mixture of a nonaqueous solvent and an ionic substance (a solute, e.g., an organic salt) dissolved therein. The nonaqueous solvent may be an organic solvent or an ionic liquid. Examples of nonaqueous solvents include polyhydric alcohols such as ethylene glycol and propylene glycol, cyclic sulfones such as sulfolane, lactones such as γ-butyrolactone, 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. Polymer solvents may also be used as the nonaqueous solvent. Examples of polymer solvents include polyalkylene glycols, 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, 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. The nonaqueous solvents may be used singly or in combination of two or more.

[0040] Examples of organic salts include trimethylamine maleate, triethylamine borodisalicylate, ethyldimethylamine phthalate, mono 1,2,3,4-tetramethylimidazolinium phthalate, mono 1,3-dimethyl-2-ethylimidazolinium phthalate, etc. In this specification, the liquid component may be a component that is liquid at room temperature (25°C) or a component that is liquid at the temperature at which the electrolytic capacitor is used.

[0041] The anode foil 21 and the cathode foil 22 are wound with a separator 23 interposed therebetween. The outermost periphery of the wound body is fixed with a stop tape 25. Note that Fig. 2 shows a partially unfolded state of the wound body before the outermost periphery is fixed.

[0042] 3A and 3B , a portion of the anode foil 21 has exposed regions 21R on both sides, where the metal portion 21a (more specifically, the core of the metal portion 21a) is exposed from the conductive polymer layer 24. In the exposed regions 21R, the lead tab 62 of the anode lead 60 is in direct contact with the metal portion 21a, thereby mechanically and electrically connecting the anode lead 60 to the anode foil 21. The anode lead 60 is connected to the anode foil 21 by needle crimping. Therefore, a portion of the lead tab 62 penetrates the metal portion 21a and is in direct contact with both sides of the metal portion 21a.

[0043] There are almost no porous portions in exposed region 21R, and therefore the thickness of the porous portions in exposed region 21R is smaller than the thickness of the porous portions in the portions of anode foil 21 other than exposed region 21R.

[0044] In this embodiment, the conductive polymer layer 24 is not interposed between the lead tab 62 of the anode lead 60 and the anode foil 21, but the conductive polymer layer 24 may be interposed between a part of the anode lead 60 and the anode foil 21.

[0045] (Method for Manufacturing Electrolytic Capacitor) Next, a method for manufacturing the electrolytic capacitor 10 of this embodiment will be described. The manufacturing method includes a coating liquid application step, a polymer layer formation step, a polymer layer removal step, and a lead connection step.

[0046] In the coating liquid application step, a coating liquid containing a conductive polymer and a liquid medium is applied to the surface of the dielectric layer of the anode foil 21. In this embodiment, the coating liquid is applied to the surface of the dielectric layer by gravure coating, but the method is not limited to this.

[0047] In the polymer layer forming step, at least a portion of the liquid medium is removed from the coating liquid to form a conductive polymer layer 24 containing a conductive polymer on the surface of the dielectric layer. In this embodiment, the removal is performed by heating under a reduced pressure atmosphere, but the present invention is not limited to this.

[0048] In the polymer layer removal step, a portion of the conductive polymer layer 24 is removed from both surfaces of a portion of the anode foil 21, thereby forming an exposed region 21R in which the portion of the anode foil 21 is exposed from the conductive polymer layer 24. More specifically, in the polymer layer removal step of this embodiment, in the portion of the anode foil 21, not only the portion of the conductive polymer layer 24 but also substantially the entire porous portion of the metal portion 21a is removed. Here, "substantially the entirety" means that 90% or more, 95% or more, or 99% or more of the porous portion is removed.

[0049] In the lead connection step, the metal portion 21a (specifically, the core portion of the metal portion 21a) in the exposed region 21R is brought into direct contact with the lead tab 62 of the anode lead 60, and the anode lead 60 is connected to the anode foil 21 by needle crimping. In this embodiment, the conductive polymer layer 24 is removed in the polymer layer removal step so that the conductive polymer layer 24 is not interposed between the anode lead 60 and the anode foil 21. However, the conductive polymer layer 24 may be interposed between a part of the anode lead 60 and the anode foil 21.

[0050] <<Supplementary Note>> The above description of the embodiment discloses the following techniques.

[0051] (Technology 1) An electrolytic capacitor comprising: an anode foil having a metal portion and a dielectric layer formed on a surface of the metal portion; a cathode foil; a separator interposed between the anode foil and the cathode foil; a conductive polymer layer formed on the surface of the dielectric layer and containing a conductive polymer; and an anode lead connected to the anode foil, wherein a part of the anode foil has an exposed region exposed from the conductive polymer layer, and the anode lead is in direct contact with the metal portion in the exposed region, thereby being electrically connected to the anode foil.

[0052] (Technology 2) The electrolytic capacitor according to Technology 1, wherein the metal portion is exposed from the conductive polymer layer on both sides of the anode foil.

[0053] (Technology 3) The electrolytic capacitor according to Technology 1 or 2, wherein the metal portion has a core portion and a porous portion having a lower density than the core portion, and the thickness of the porous portion in the portion of the anode foil is smaller than the thickness of the porous portion in the portion other than the portion of the anode foil.

[0054] (Technology 4) The electrolytic capacitor according to any one of Technologies 1 to 3, wherein the conductive polymer layer is interposed between a part of the anode lead and the anode foil.

[0055] (Technology 5) A method for manufacturing an electrolytic capacitor including an anode foil having a metal portion and a dielectric layer formed on a surface of the metal portion, a cathode foil, and a separator, the method comprising: a coating liquid applying step of applying a coating liquid containing a conductive polymer and a liquid medium to a surface of the dielectric layer of the anode foil; a polymer layer forming step of forming a conductive polymer layer containing the conductive polymer on the surface of the dielectric layer by removing at least a portion of the liquid medium from the coating liquid; a polymer layer removing step of removing a portion of the conductive polymer layer in a portion of the anode foil to form an exposed region in which the portion of the anode foil is exposed from the conductive polymer layer; and a lead connecting step of electrically connecting the anode lead to the anode foil by directly contacting the metal portion in the exposed region with the anode lead.

[0056] (Technology 6) The method for manufacturing an electrolytic capacitor according to Technology 5, wherein in the polymer layer removing step, a part of the conductive polymer layer is removed from both sides of the anode foil.

[0057] (Technology 7) The method for manufacturing an electrolytic capacitor according to Technology 5 or 6, wherein the conductive polymer layer is interposed between a part of the anode lead and the anode foil.

[0058] (Technology 8) The method for manufacturing an electrolytic capacitor according to any one of Technologies 5 to 7, wherein the metal portion has a core portion and a porous portion having a lower density than the core portion, and in the polymer layer removing step, in the part of the anode foil, not only the part of the conductive polymer layer but also at least a part of the porous portion is removed.

[0059] For the anode foils to which an anode lead was connected (hereinafter also referred to as anode foils with leads) of the following Examples, Comparative Examples, and Reference Examples 1 and 2, the connection resistance between the anode foil and the anode lead was measured, and the ESR of the electrolytic capacitors fabricated using each anode foil was also measured.

[0060] Example: 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 then subjected to a chemical conversion treatment to form a dielectric layer. In this manner, an anode foil having a dielectric layer formed on both sides was obtained.

[0061] A dispersion (commercially available) of polystyrene sulfonic acid (PSS)-doped polyethylenedioxythiophene (PEDOT) particles dispersed in water was prepared, and ethylene glycol and water were added to the dispersion to obtain a coating liquid.

[0062] The coating liquid was applied to one side of the anode foil (the surface of the dielectric layer) using a gravure coater. The coating was then dried to form a conductive polymer layer on the other side of the anode foil (the surface of the dielectric layer). A conductive polymer layer was then formed on the other side of the anode foil (the surface of the dielectric layer) in the same manner.

[0063] By forming a punch hole in the anode foil on which the conductive polymer layer was formed, part of the conductive polymer layer and part of the anode foil (specifically, the dielectric layer and the porous portion) were removed from a part of the anode foil, and an exposed region in which the core of the metal portion was exposed was formed on the inner surface of the punch hole.

[0064] The lead tab of the anode lead was placed on the exposed region, and the lead tab was brought into direct contact with the core of the metal part of the anode foil by needle crimping, thereby electrically connecting the anode lead to the anode foil.

[0065] After obtaining the anode foil with leads in this manner, the connection resistance between the anode lead and the anode foil was measured using a four-terminal measurement method. The connection resistance measured in this example was 0.55 mΩ.

[0066] An electrolytic capacitor was fabricated using the leaded anode foil of this example. The ESR of this electrolytic capacitor was 9.62 mΩ. The ESR was measured at a frequency of 100 kHz / Ω using an LCR meter.

[0067] Comparative Example: Anode foils with leads were fabricated using the same process as in the example, except that the step of forming punch holes in the anode foil with a conductive polymer layer formed thereon was not performed. The connection resistance between the anode lead and the anode foil in the comparative example was 2.07 mΩ. The ESR of the electrolytic capacitor fabricated using the comparative example anode foil with leads was 11.31 mΩ.

[0068] Reference Example 1 Anode foils with leads were fabricated using the same process as in the Examples, except that the step of forming a conductive polymer layer on the surface of the dielectric layer was omitted. The connection resistance between the anode lead and the anode foil in the lead-attached anode foil of Reference Example 1 was 0.52 mΩ. The ESR of the electrolytic capacitor fabricated using the lead-attached anode foil of Reference Example 1 was 200.5 mΩ.

[0069] Reference Example 2: Anode foils with leads were fabricated using the same process as in Example 1, except that the step of forming a conductive polymer layer on the surface of the dielectric layer and the step of forming punch holes were not performed. The connection resistance between the anode lead and the anode foil in the anode foil with leads of Reference Example 2 was 0.57 mΩ. The ESR of an electrolytic capacitor fabricated using the anode foil with leads of Reference Example 1 was 208.3 mΩ.

[0070] As described above, the leaded anode foil of the Example had a significantly lower connection resistance between the anode lead and the anode foil than the leaded anode foil of the Comparative Example. Accordingly, the ESR of the Example electrolytic capacitor was also significantly lower than the ESR of the Comparative Example electrolytic capacitor. Therefore, it can be said that the Example is superior.

[0071] The present disclosure can be used for an electrolytic capacitor and a method for manufacturing an electrolytic capacitor.

[0072] 10: Electrolytic capacitor 20: Capacitor element 21: Anode foil 21a: Metal part 21R: Exposed area 22: Cathode foil 23: Separator 24: Conductive polymer layer 25: Winding tape 30: Bottomed case 40: Sealing member 50: Seat plate 60: Anode lead 61: Lead wire 62: Lead tab 70: Cathode lead 71: Lead wire 72: Lead tab

Claims

1. An electrolytic capacitor comprising: an anode foil having a metal portion and a dielectric layer formed on a surface of the metal portion; a cathode foil; a separator interposed between the anode foil and the cathode foil; a conductive polymer layer formed on the surface of the dielectric layer and containing a conductive polymer; and an anode lead connected to the anode foil, wherein a part of the anode foil has an exposed region exposed from the conductive polymer layer, and the anode lead is in direct contact with the metal portion in the exposed region, thereby electrically connected to the anode foil.

2. The electrolytic capacitor according to claim 1, wherein the metal portion is exposed from the conductive polymer layer on both sides of the anode foil.

3. The electrolytic capacitor according to claim 1 or 2, wherein the metal portion has a core and a porous portion having a lower density than the core, and the thickness of the porous portion in the portion of the anode foil is smaller than the thickness of the porous portion in the other portion of the anode foil.

4. The electrolytic capacitor according to claim 1 or 2, wherein the conductive polymer layer is interposed between a portion of the anode lead and the anode foil.

5. A method for producing an electrolytic capacitor comprising an anode foil having a metal portion and a dielectric layer formed on a surface of the metal portion, a cathode foil, and a separator, the method comprising: a coating liquid applying step of applying a coating liquid containing a conductive polymer and a liquid medium to a surface of the dielectric layer of the anode foil; a polymer layer forming step of forming a conductive polymer layer containing the conductive polymer on the surface of the dielectric layer by removing at least a part of the liquid medium from the coating liquid; a polymer layer removing step of removing a part of the conductive polymer layer in a part of the anode foil to form an exposed region in which the part of the anode foil is exposed from the conductive polymer layer; and a lead connecting step of electrically connecting the anode lead to the anode foil by directly contacting the metal portion in the exposed region with the anode lead.

6. The method for producing an electrolytic capacitor according to claim 5, wherein in the polymer layer removing step, a portion of the conductive polymer layer is removed from both sides of the anode foil.

7. The method for producing an electrolytic capacitor according to claim 5 or 6, wherein the conductive polymer layer is interposed between a portion of the anode lead and the anode foil.

8. The method for manufacturing an electrolytic capacitor according to claim 5 or 6, wherein the metal portion has a core and a porous portion having a lower density than the core, and in the polymer layer removal step, in the part of the anode foil, in addition to the part of the conductive polymer layer, at least a part of the porous portion is removed.

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