Electrolytic capacitor

Abstract

To provide an electrolytic capacitor that can simultaneously suppress an increase in leakage current and an increase in ESR.SOLUTION: An electrolytic capacitor includes a capacitor element and a liquid component, the capacitor element includes a long anode foil (11), a long cathode foil (12), a long separator (13) interposed between the anode foil and the cathode foil, a first conductive polymer layer (P1), and a second conductive polymer layer (P2), the anode foil, the cathode foil, and the separator are wound up in the longitudinal direction of a long shape to form a wound body, the anode foil includes a porous portion at least a part of its surface covered with a dielectric layer (DL1), the cathode foil is disposed opposite the dielectric layer, the separator includes a fibrous material, the first conductive polymer layer covers at least a part of the surface of the dielectric layer in the porous portion, the second conductive polymer layer covers at least a part of the surface of the fibrous material in the separator, the first conductive polymer layer and the second conductive polymer layer include a first conductive polymer and a second conductive polymer, respectively.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an electrolytic capacitor. [Background technology]

[0002] An electrolytic capacitor, for example, includes a capacitor element and an electrolyte. The capacitor element typically includes an anode foil having a dielectric layer, a cathode foil facing the dielectric layer, and a separator interposed between the anode foil and the cathode foil. Among such electrolytic capacitors, those containing a liquid component (e.g., an electrolytic solution) filling the voids in the capacitor element and a conductive polymer interposed between the anode foil and the cathode foil are known. In other words, electrolytic capacitors with a solid-liquid electrolyte are known.

[0003] Patent Document 1 describes an electrolytic capacitor including a capacitor element including an anode foil having a dielectric layer on its surface, a cathode foil, a separator interposed between the anode foil and the cathode foil, a hydroxyl-containing compound, and a conductive polymer. Patent Document 1 also describes that the separator in the electrolytic capacitor includes synthetic fibers and cellulosic fibers, and the hydroxyl-containing compound is at least one compound (excluding polymers) selected from the group consisting of sugars and polyhydric alcohols. Patent Document 1 also describes that the conductive polymer and the hydroxyl-containing compound are attached to the surface and interior of the separator, and the hydroxyl-containing compound is unevenly distributed in the separator. Patent Document 1 also describes that an electrolytic capacitor configured as described above can achieve high capacitance and reduced ESR (equivalent series resistance). That is, Patent Document 1 describes an electrolytic capacitor that can achieve both high capacitance and suppressed ESR increase.

[0004] Patent Document 2 describes an electrolytic capacitor including an anode body having a dielectric layer, a solid electrolyte layer in contact with the dielectric layer of the anode body, and an electrolytic solution, the electrolytic solution containing a solvent and a solute. Patent Document 2 also describes that in the electrolytic capacitor, the solvent uses a solvent containing a glycol compound, and the solute uses a solute containing 200 parts by mass or more of a carboxylic acid component per 100 parts by mass of a base component. Patent Document 2 also describes that an electrolytic capacitor configured as described above has excellent voltage resistance characteristics and heat resistance and can maintain a low ESR. That is, Patent Document 2 describes an electrolytic capacitor that can achieve both excellent voltage resistance characteristics and heat resistance and suppress an increase in ESR.

[0005] Patent Document 3 describes an electrolytic capacitor including a capacitor element having an electrode foil, with a conductive polymer layer formed on the electrode foil. Patent Document 3 describes that in the electrolytic capacitor, 90% or more of the area of ​​one main surface of the electrode foil is covered with the conductive polymer layer, and that the conductive polymer layer includes a first conductive polymer layer containing a first conductive polymer component, and a second conductive polymer layer covering a portion of the first conductive polymer layer and containing a second conductive polymer component. Patent Document 3 also describes that an electrolytic capacitor configured as described above can achieve a reduction in ESR. That is, Patent Document 3 describes an electrolytic capacitor that can achieve suppression of ESR increase. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2022-117355 [Patent Document 2] International Publication No. 2017 / 017947 [Patent Document 3] International Publication No. 2020 / 158780 Summary of the Invention [Problem to be solved by the invention]

[0007] In recent years, there has been an increasing demand for electrolytic capacitors that include a liquid component as an electrolyte and a conductive polymer layer to simultaneously suppress an increase in leakage current and an increase in ESR.

[0008] However, in any of the publicly known documents, including Patent Documents 1 to 3, there has not yet been sufficient research into how to simultaneously suppress an increase in leakage current and an increase in ESR for electrolytic capacitors that have a liquid component as an electrolyte and a conductive polymer layer.

[0009] Therefore, the present disclosure provides an electrolytic capacitor that can suppress both an increase in leakage current and an increase in ESR. [Means for solving the problem]

[0010] One aspect of the present invention is an electrolytic capacitor including a capacitor element and a liquid component, wherein the capacitor element includes an elongated anode foil, an elongated cathode foil, an elongated separator interposed between the anode foil and the cathode foil, and a first conductive polymer layer and a second conductive polymer layer interposed between the anode foil and the cathode foil, the anode foil, the cathode foil, and the separator are wound up in the longitudinal direction of the elongated shape to form a wound body, the anode foil has a porous portion at least a part of a surface of which is covered with a dielectric layer, the cathode foil is disposed so as to face the dielectric layer, the separator contains a fibrous material, and the The electrolytic capacitor relates to: a first conductive polymer layer covering at least a portion of the surface of the dielectric layer in the porous portion; a second conductive polymer layer covering at least a portion of the surface of the fiber material in the separator; the first conductive polymer layer containing a first conductive polymer; and the second conductive polymer layer containing a second conductive polymer; the content of the first conductive polymer in the porous portion is greater than the content of the second conductive polymer; the content of the second conductive polymer in the separator is greater than the content of the first conductive polymer; and the electrical conductivity of the first conductive polymer layer is lower than the electrical conductivity of the second conductive polymer layer. [Effects of the Invention]

[0011] According to the present disclosure, it is possible to provide an electrolytic capacitor that can suppress both an increase in leakage current and an increase in ESR. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic diagram of a capacitor element according to an embodiment of the present disclosure, in a partially developed state. [Figure 2] 1 is an enlarged schematic cross-sectional view showing a main part of a capacitor element according to an embodiment of the present disclosure. [Figure 3] FIG. 2 is a schematic diagram showing the inside of a separator of a capacitor element according to an embodiment of the present disclosure. [Figure 4]10A and 10B are cross-sectional schematic views illustrating modified examples of capacitor elements according to embodiments of the present disclosure. [Figure 5] FIG. 1 is a cross-sectional schematic view of an electrolytic capacitor according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0013] The following describes embodiments of the present disclosure using examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be used as examples, but other numerical values, materials, etc. may be applied as long as the effects of the present disclosure are obtained. Note that known components may be applied to components characteristic of the present disclosure. In this specification, when a "range between numerical value A and numerical value B" is mentioned, the range includes numerical value A and numerical value B.

[0014] In the following description, when lower and upper limits of numerical values ​​relating to specific physical properties, conditions, etc. 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. When multiple materials are exemplified, one of them can be selected and used alone, or two or more can be used in combination, unless otherwise specified.

[0015] The present disclosure encompasses any combination of two or more claims arbitrarily selected from the appended claims, i.e., any combination of two or more claims arbitrarily selected from the appended claims may be combined unless a technical contradiction arises.

[0016] [Electrolytic capacitor] An electrolytic capacitor according to an embodiment of the present disclosure includes a capacitor element and a liquid component. In the electrolytic capacitor according to an embodiment of the present disclosure, the capacitor element includes a long anode foil, a long cathode foil, a long separator interposed between the anode foil and the cathode foil, and a first conductive polymer layer and a second conductive polymer layer interposed between the anode foil and the cathode foil.

[0017] In the electrolytic capacitor according to the embodiment of the present disclosure, an anode foil, a cathode foil, and a separator are wound in the longitudinal direction of an elongated shape to form a wound body, the anode foil has a porous portion at least a part of the surface of which is covered with a dielectric layer, the cathode foil is disposed so as to face the dielectric layer, and the separator includes a fibrous material.

[0018] In an electrolytic capacitor according to an embodiment of the present disclosure, a first conductive polymer layer covers at least a portion of the surface of the dielectric layer in the porous portion, and a second conductive polymer layer covers at least a portion of the surface of the fibrous material in the separator. In an electrolytic capacitor according to an embodiment of the present disclosure, the first conductive polymer layer includes a first conductive polymer, and the second conductive polymer layer includes a second conductive polymer, and the content of the first conductive polymer in the porous portion is greater than the content of the second conductive polymer, and the content of the second conductive polymer in the separator is greater than the content of the first conductive polymer. In an electrolytic capacitor according to an embodiment of the present disclosure, the electrical conductivity of the first conductive polymer layer is lower than the electrical conductivity of the second conductive polymer layer.

[0019] In the electrolytic capacitor according to the embodiment of the present disclosure, it is important that a first conductive polymer layer containing a first conductive polymer covers at least a portion of the surface of the dielectric layer in the porous portion, and a second conductive polymer layer containing a second conductive polymer covers at least a portion of the surface of the fibrous material in the separator, and that the content of the first conductive polymer in the porous portion is greater than the content of the second conductive polymer, and that the content of the second conductive polymer in the separator is greater than the content of the first conductive polymer, and that the electrical conductivity of the first conductive polymer layer is lower than the electrical conductivity of the second conductive polymer layer. The reasons for this are explained below.

[0020] In the capacitor element of an electrolytic capacitor, as described above, in order to increase the capacitance, a porous portion is formed on at least one main surface of the anode foil, and a dielectric layer is formed to cover at least a portion of the porous portion. The solid electrolyte, such as a conductive polymer, sufficiently covers the dielectric layer inside the multiple holes in the porous portion, thereby forming a sufficient conductive path between the anode foil and the cathode foil, thereby reducing the ESR of the electrolytic capacitor.

[0021] On the other hand, if a defect such as a crack occurs in the dielectric layer, leakage current will occur at the defect. If the solid electrolyte, such as a conductive polymer, placed near the defect in the dielectric layer has low conductivity, the leakage current generated at the defect can be reduced. Therefore, by using a low-conductivity conductive polymer for the solid electrolyte, leakage current in an electrolytic capacitor can be reduced. However, if the solid electrolyte between the anode foil and cathode foil is entirely made of a low-conductivity conductive polymer, the conductivity of the conductive path between the anode foil and cathode foil will be low, resulting in a high ESR of the electrolytic capacitor.

[0022] In the electrolytic capacitor according to the embodiment of the present disclosure, a first conductive polymer layer containing a first conductive polymer covers at least a portion of the surface of the dielectric layer in the porous portion, and a second conductive polymer layer containing a second conductive polymer covers at least a portion of the surface of the fibrous material in the separator, the content of the first conductive polymer in the porous portion is greater than the content of the second conductive polymer, and the content of the second conductive polymer in the separator is greater than the content of the first conductive polymer, so that the electrical conductivity of the first conductive polymer layer is lower than that of the second conductive polymer layer. That is, in the electrolytic capacitor according to the embodiment of the present disclosure, the dielectric layer in the porous portion of the anode foil is mainly covered by the first conductive polymer layer, and the surface of the fibrous material in the separator is mainly covered by the second conductive polymer layer. Therefore, by disposing a first conductive polymer layer with low electrical conductivity on the surface of the dielectric layer (i.e., near the defective portion of the dielectric layer), it is possible to suppress leakage current that occurs in the defective portion, and also to dispose a second conductive polymer layer with higher electrical conductivity than the first conductive polymer layer in the conductive path between the anode foil and the cathode foil, thereby suppressing an increase in ESR of the electrolytic capacitor.

[0023] Furthermore, for example, when the electrical conductivity of the first conductive polymer layer is made lower than that of the second conductive polymer layer by lowering the degree of polymerization of the first conductive polymer contained in the first conductive polymer layer compared to the degree of polymerization of the second conductive polymer contained in the second conductive polymer layer, the size of the first conductive polymer contained in the first conductive polymer layer is smaller than that of the second conductive polymer contained in the second conductive polymer layer, allowing the first conductive polymer layer to sufficiently penetrate into the multiple pores in the porous portion. On the other hand, the second conductive polymer is larger, making it difficult for it to penetrate into the multiple pores in the porous portion. Therefore, a sufficient conductive path can be formed between the anode foil and the cathode foil by the conductive polymer layers (the first conductive polymer layer and the second conductive polymer layer), thereby reducing the ESR of the electrolytic capacitor. On the other hand, the second conductive polymer layer, which has a high electrical conductivity, is unlikely to be disposed near defects in the dielectric layer inside the multiple pores, thereby suppressing an increase in leakage current.

[0024] <Capacitor element> As described above, a capacitor element according to an embodiment of the present disclosure includes a long anode foil, a long cathode foil, a long separator interposed between the anode foil and the cathode foil, and a first conductive polymer layer and a second conductive polymer layer interposed between the anode foil and the cathode foil. In the capacitor element according to an embodiment of the present disclosure, the anode foil, the cathode foil, and the separator are wound in the longitudinal direction of the long shape to form a wound body. The anode foil, the cathode foil, the separator, the first conductive polymer layer, and the second conductive polymer layer will be described below.

[0025] (anode foil) Examples of the anode foil 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. As described above, the anode foil has a porous portion, at least a portion of whose surface is covered with a dielectric layer. The porous portion has a plurality of holes drilled from the main surface of the anode foil toward the center. The porous portion can be formed, for example, by etching the surface of the anode foil. The porous portion may be formed on only one main surface of the anode foil, or on both main surfaces of the anode foil. It is preferable that the porous portion be formed on both main surfaces of the anode foil.

[0026] As described above, in the anode foil, at least a portion of the surface of the porous portion is covered with a dielectric layer. The porous portion has an outer surface that constitutes the main surface of the anode foil and an inner surface that constitutes the inner walls of the multiple holes. Therefore, in the anode foil, at least a portion of the outer and inner surfaces of the porous portion are covered with a dielectric layer. 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.

[0027] (cathode foil) The cathode foil is not particularly limited as long as it functions as a cathode. Examples of the cathode foil include metal foils (e.g., aluminum foils). The type of metal contained in the metal foil is not particularly limited. The metal 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. Similar to the anode foil, the cathode foil may have a porous portion on at least a portion of its surface. The porous portion can be formed, for example, by etching the surface of the cathode foil. The porous portion may be formed on only one main surface of the cathode foil, or on both main surfaces of the cathode foil. In the cathode foil, the porous portion may also have an outer surface that constitutes the main surface of the cathode foil and an inner surface that constitutes the inner walls of the multiple holes.

[0028] A dielectric layer may also be formed on at least a portion of the porous portion of the cathode foil. At least a portion of the outer surface and inner surface of the porous portion of the cathode foil may also be covered with a dielectric layer. That is, the cathode foil may also be subjected to a chemical conversion treatment.

[0029] The cathode foil may include a conductive coating layer. When the metal foil includes a valve metal, the coating layer may include at least one of carbon and a 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 terms of emphasizing low cost and low resistance, the coating layer may include at least one of nickel and titanium.

[0030] The thickness of the coating layer may be 5 nm or more, or 10 nm or more. The thickness of the coating layer may be 200 nm or less. The coating layer may be formed by vapor deposition or sputtering the above-mentioned metal onto the metal foil. Alternatively, the coating layer may be formed by vapor deposition of a conductive carbon material onto 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.

[0031] (separator) The separator includes a fibrous material. The separator may be a porous sheet including the fibrous material. By including the fibrous material in the separator, sufficient voids can be formed inside the separator. This allows the second conductive polymer layer to sufficiently penetrate into the separator. In this case, a good conductive path can be formed between the separator and the first conductive polymer layer formed to cover the surface of the dielectric layer of the anode foil. Furthermore, if the first conductive polymer layer is also formed to cover the surface of the cathode foil, a good conductive path can also be formed between the separator and this first conductive polymer layer. In this case, a good conductive path can be formed connecting the surface of the dielectric layer of the anode foil to the surface of the cathode foil via the separator. Therefore, the ESR of the electrolytic capacitor can be further reduced.

[0032] Examples of the separator include woven fabric and nonwoven fabric. The thickness of the separator is not particularly limited and may be in the range of 10 μm to 300 μm. Examples of materials for the separator include cellulose, polyethylene terephthalate, polybutylene terephthalate, polyphenyl sulfide, vinylon, nylon, aromatic polyamide, polyimide, polyamideimide, polyetherimide, rayon, and glass.

[0033] (Conductive polymer layer) The first conductive polymer layer includes a first conductive polymer. Examples of the first conductive polymer include polypyrrole, polythiophene, polyfuran, polyaniline, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, polythiophene vinylene, and derivatives thereof. These may be used alone or in combination of two or more. The first conductive polymer may also be a copolymer of two or more monomers.

[0034] In this specification, polypyrrole, polythiophene, polyfuran, polyaniline, etc. refer to polymers having polypyrrole, polythiophene, polyfuran, polyaniline, etc. as their basic skeletons, respectively. Therefore, polypyrrole, polythiophene, polyfuran, polyaniline, etc. also include their derivatives. For example, polythiophene includes poly(3,4-ethylenedioxythiophene).

[0035] The first conductive polymer may further contain a dopant. The dopant may be a polymer dopant. The polymer dopant may be a polyanion. Specific examples of polyanions include polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallylsulfonic acid, polyacrylic sulfonic acid, polymethacrylic sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprenesulfonic acid, and polyacrylic acid. These may be used alone or in combination of two or more. These may be polymers of a single monomer or copolymers of two or more monomers. The polymer dopant preferably has a sulfonic acid group. As the polymer dopant, a polyanion derived from polystyrene sulfonic acid is preferably used.

[0036] The weight average molecular weight Mw of the first conductive polymer is preferably 100 to 3,000, more preferably 300 to 2,500, and even more preferably 500 to 2,000.

[0037] (Second conductive polymer layer) The second conductive polymer layer includes a second conductive polymer. The second conductive polymer is not particularly limited and may be the same conductive polymer as the first conductive polymer. The second conductive polymer may also include the same dopant as the first conductive polymer. That is, the second conductive polymer may include a polyanion as a dopant.

[0038] The degree of polymerization of the second conductive polymer is preferably higher than that of the first conductive polymer. In other words, the degree of polymerization of the first conductive polymer is preferably lower than that of the second conductive polymer. In such a case, the electrical conductivity of the first conductive polymer is lower than that of the second conductive polymer, making it easier to adjust the electrical conductivity of the first conductive polymer layer to be lower than that of the second conductive polymer layer.

[0039] The weight average molecular weight Mw of the second conductive polymer is preferably 300 to 5,000, more preferably 500 to 4,000, and even more preferably 1,000 to 3,000.

[0040] In the electrolytic capacitor according to the embodiment of the present disclosure, as described above, the electrical conductivity of the first conductive polymer layer is lower than the electrical conductivity of the second conductive polymer layer. The electrical conductivities of the first conductive polymer layer and the second conductive polymer layer can be measured by the four-probe method in accordance with JIS K 7194:1994.

[0041] The electrical conductivity of the first conductive polymer layer is preferably 100 S / cm to 500 S / cm, more preferably 150 S / cm to 450 S / cm, and even more preferably 200 S / cm to 400 S / cm. The electrical conductivity of the second conductive polymer layer is preferably 300 S / cm to 800 S / cm, more preferably 350 S / cm to 750 S / cm, and even more preferably 400 S / cm to 700 S / cm.

[0042] When both the first conductive polymer and the second conductive polymer contain a dopant, the doping rate of the dopant in the first conductive polymer is preferably lower than that of the dopant in the second conductive polymer. This allows the size of the first conductive polymer to be reduced, allowing the first conductive polymer layer containing the first conductive polymer to more fully penetrate into the multiple pores in the porous portion. In this case, the electrical conductivity of the first conductive polymer is lower than that of the second conductive polymer, making it easier to adjust the electrical conductivity of the first conductive polymer layer to be lower than that of the second conductive polymer layer. The doping rate of the first conductive polymer can be calculated using the masses of the monomers and dopant that will constitute the first conductive polymer, as well as the mass of the solid content (first conductive polymer and dopant) after the polymerization reaction. The doping rate of the second conductive polymer can be calculated in the same manner as the doping rate of the first conductive polymer.

[0043] When the doping rate of the second conductive polymer is taken as 100%, the doping rate of the first conductive polymer is preferably 50% to 95%, more preferably 55% to 90%, and even more preferably 60% to 85%.

[0044] The first conductive polymer preferably contains a first polymer dopant having a sulfonic acid group as a dopant, and the second conductive polymer preferably contains a second polymer dopant having a sulfonic acid group as a dopant. In this case, the weight-average molecular weight Mw1 of the first polymer dopant is preferably smaller than the weight-average molecular weight Mw2 of the second polymer dopant. In this case, the electrical conductivity of the first conductive polymer can be made lower than that of the second conductive polymer. This makes it easier to adjust the electrical conductivity of the first conductive polymer layer to be lower than that of the second conductive polymer layer. The weight-average molecular weight Mw1 of the first polymer dopant and the weight-average molecular weight Mw2 of the second polymer dopant can be measured by gel permeation chromatography (GPC) or electrospray ionization mass spectrometry (ESI-MS).

[0045] When both the first polymer dopant and the second polymer dopant have sulfonic acid groups, the degree of sulfonation of the first polymer dopant is preferably smaller than the degree of sulfonation of the second polymer dopant. In this case, the electrical conductivity of the first conductive polymer can be made lower than that of the second conductive polymer. This makes it easier to adjust the electrical conductivity of the first conductive polymer layer to be lower than that of the second conductive polymer layer. The degrees of sulfonation of the first polymer dopant and the second polymer dopant can be determined by a combination of NMR analysis, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and X-ray fluorescence analysis.

[0046] Both the first conductive polymer layer and the second conductive polymer layer preferably contain an alkaline component. Examples of alkaline components include ammonia, ethanolamine, triethanolamine, dimethylamine, diethylamine, triethylamine, morpholine, and imidazole. The content of the alkaline component in the first conductive polymer layer is preferably greater than the content of the alkaline component in the second conductive polymer layer. In this case, the electrical conductivity of the first conductive polymer layer can be made lower than the electrical conductivity of the second conductive polymer layer. This also facilitates penetration of the first conductive polymer layer into the multiple pores in the porous portion of the anode foil. This also facilitates penetration of the first conductive polymer layer into the multiple pores in the porous portion of the cathode foil.

[0047] Both the first conductive polymer layer and the second conductive polymer layer preferably contain an organic solvent having a boiling point of 150°C or higher (hereinafter also referred to as a high-boiling-point solvent). In this case, the content of the high-boiling-point solvent in the first conductive polymer layer is preferably smaller than the content of the high-boiling-point solvent in the second conductive polymer layer. Examples of high-boiling-point solvents include ethylene glycol and propylene glycol. The high-boiling-point solvent can enhance the orientation of the conductive polymer in the conductive polymer dispersion for forming the conductive polymer layer. That is, the greater the content of the high-boiling-point solvent in the conductive polymer layer, the higher the orientation of the conductive polymer in the conductive polymer layer. Furthermore, the higher the orientation of the conductive polymer, the higher the electrical conductivity of the conductive polymer layer. Therefore, by making the content of the high-boiling-point solvent in the first conductive polymer layer smaller than the content of the high-boiling-point solvent in the second conductive polymer layer, it becomes easier to adjust the electrical conductivity of the first conductive polymer layer to be lower than that of the second conductive polymer layer.

[0048] The first conductive polymer layer preferably contains a water-soluble polymer compound. Examples of water-soluble polymer compounds include polyvinyl alcohol (PVA) and polyvinylpyrrolidone (PVP). When the first conductive polymer layer contains a water-soluble polymer compound, the electrical conductivity of the first conductive polymer layer can be reduced. Furthermore, the voltage resistance can be improved. Furthermore, the adhesion of the first conductive polymer layer to the porous portions of the anode foil and the cathode foil can be improved.

[0049] The first conductive polymer layer and the second conductive polymer layer preferably form a conductive path connecting the dielectric layer of the anode foil to the cathode foil via a separator. As described above, when the cathode foil has a porous portion on at least a part of its surface and a dielectric layer is formed on at least a part of the surface (outer surface and inner surface) of the porous portion, the first conductive polymer layer and the second conductive polymer layer preferably form a conductive path connecting the dielectric layer of the anode foil to the dielectric layer of the cathode foil via a separator.

[0050] The first conductive polymer layer and the second conductive polymer layer preferably form a conductive path connecting the dielectric layer of the anode foil to the cathode foil via the separator. The conductive path is preferably formed so as to continuously connect the surface of the dielectric layer of the anode foil to the surface of the cathode foil. This further reduces the ESR of the electrolytic capacitor. The first conductive polymer layer and the second conductive polymer layer preferably contact the anode foil, the cathode foil, and the separator over a sufficiently large area. This forms a better conductive path in the electrolytic capacitor, thereby further reducing the ESR. As described above, when the cathode foil has a porous portion on at least a portion of its surface and a dielectric layer is formed on at least a portion of the surface (outer surface and inner surface) of the porous portion, the first conductive polymer layer and the second conductive polymer layer preferably form a conductive path connecting the dielectric layer of the anode foil to the dielectric layer of the cathode foil via the separator.

[0051] As described above, a capacitor element according to an embodiment of the present disclosure includes an elongated anode foil, an elongated cathode foil, and an elongated separator interposed between the anode foil and the cathode foil. As shown in Fig. 1 , in capacitor element 10 according to an embodiment of the present disclosure, anode foil 11, cathode foil 12, and separator 13 are wound in the longitudinal direction of the elongated shape to form a wound body.

[0052] 1, the wound body includes anode foil 11 connected to lead tab (anode lead) 105A, cathode foil 12 connected to lead tab (cathode lead) 105B, and separator 13. Capacitor element 10 includes a first conductive polymer layer and a second conductive polymer layer (not shown). Lead wire 104A is connected to lead tab (anode lead) 105A, and lead wire 104B is connected to lead tab (cathode lead) 105B.

[0053] The anode foil 11 and the cathode foil 12 are wound up with a separator 13 interposed therebetween to form a wound body. The outermost periphery of this wound body is fixed with a stop tape 14. Note that Fig. 1 shows a partially unfolded state before the outermost periphery is fixed with the stop tape 14.

[0054] 1, the wound body has a first end face E1 and a second end face E2 aligned in the winding axis direction A. As described above, capacitor element 10 has lead tab (anode lead) 105A connected to anode foil 11 and lead tab (cathode lead) 105B connected to cathode foil 12. As shown in FIG. 1, in capacitor element 10, lead tab (anode lead) 105A and lead tab (cathode lead) 105B protrude from first end face E1 of the wound body.

[0055] In the capacitor element according to the embodiment of the present disclosure, for example, as shown in FIGS. 2 and 3, a first conductive polymer layer P1 and a second conductive polymer layer P2 may be formed.

[0056] Specifically, the first conductive polymer layer P1 may be formed so as to cover the surface of the dielectric layer DL1 formed on the surface of the anode foil 11 and the surface of the cathode foil 12, and the second conductive polymer layer P2 may be formed so as to cover the surface of the fibers F contained in the separator 13.

[0057] Furthermore, from the viewpoint of forming a good conductive path from the anode foil 11 to the cathode foil 12 via the separator, at least a portion of the second conductive polymer layer P2 covering the fibers F of the separator 13 may be in contact with at least a portion of the first conductive polymer layer P1 covering the surface of the dielectric layer DL1 and at least a portion of the first conductive polymer layer P1 covering the surface of the cathode foil 12.

[0058] In the capacitor element according to the embodiment of the present disclosure, the second conductive polymer layer may be formed in at least one of the dielectric layer, the cathode foil, and the separator, biased toward a portion closer to the second end face than to the first end face of the wound body. For example, as shown in FIG. 4 , when the end face from which the lead tabs (anode lead) 105A and the lead tabs (cathode lead) 105B protrude is defined as the first end face E1 and the opposite end face is defined as the second end face E2, the second conductive polymer layer P2 may be formed biased toward a portion closer to the second end face E2. That is, the second conductive polymer layer P2 may be formed biased toward a portion away from the lead tabs (anode lead) 105A and the lead tabs (cathode lead) 105B. On the other hand, the first conductive polymer layer P1 may be formed over the entire surface from the first end face E1 to the second end face E2. 2 and 3, in a region close to the second end face E2, the first conductive polymer layer P1 is formed so as to cover the surface of the dielectric layer DL1 formed on the surface of the anode foil 11 and the surface of the cathode foil 12, and the second conductive polymer layer P2 is formed so as to cover the surface of the fibers F contained in the separator 13, and the second conductive polymer layer P2 is not present in the separator 13 in a region close to the first end face E1. Also, as shown in FIG. 4, a lead wire 104A may be connected to the lead tab (anode lead) 105A, and a lead wire 104B may be connected to the lead tab (cathode lead) 105B.

[0059] (exterior body) The capacitor element may be covered with an exterior body. The exterior body includes at least one of a case and a sealing resin. The case and sealing resin are not limited, and known cases and sealing resins can be used. The sealing resin may include a thermosetting resin. Examples of thermosetting resins include epoxy resin, phenolic resin, silicone resin, melamine resin, urea resin, alkyd resin, polyurethane resin, polyimide resin, and unsaturated polyester resin. The sealing resin may include at least one selected from the group consisting of a filler, a curing agent, a polymerization initiator, and a catalyst.

[0060] <Liquid ingredients> The liquid component includes a nonaqueous solvent and an electrolyte. The electrolyte can be a nonaqueous electrolyte containing a nonaqueous solvent and a solute dissolved in the nonaqueous solvent. The nonaqueous solvent and solute can be any of the nonaqueous solvents and solutes used in various known electrolytic capacitors. The liquid component can be a component that is liquid at room temperature (25°C) or at the temperature at which the electrolytic capacitor is used.

[0061] The non-aqueous solvent may be an organic solvent or an ionic liquid.

[0062] Examples of organic solvents include glycol compounds, sulfone compounds, and lactone compounds. Examples of glycol compounds include ethylene glycol (EG), diethylene glycol (DEG), triethylene glycol (TEG), and propylene glycol (PG). Examples of sulfone compounds include sulfolane (SL), dimethyl sulfoxide (DMSO), and diethyl sulfoxide (DESO). Examples of lactone compounds include γ-butyrolactone (GBL), γ-valerolactone (GVL), and the like.

[0063] Examples of organic solvents include carbonate compounds and monohydric, trihydric or higher alcohols. Examples of carbonate compounds include dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), and fluoroethylene carbonate (FEC). Examples of monohydric, trihydric or higher alcohols include glycerin and polyglycerin. These may be used alone or in combination of two or more.

[0064] Regarding organic solvents, if a group consisting of glycol compounds, sulfone compounds, and lactone compounds is defined as Group 1, and a group consisting of carbonate compounds and monohydric or trihydric or higher alcohols is defined as Group 2, the organic solvents belonging to Group 1 preferably account for more than 50 mass%, more preferably 60 mass% or more, and preferably 70 mass% or more of the organic solvents. All of the organic solvents may be organic solvents belonging to Group 1. That is, the organic solvents belonging to Group 1 may be the main solvent, and the organic solvents belonging to Group 2 may be the auxiliary solvent.

[0065] The liquid component preferably contains at least one organic solvent selected from the group consisting of glycol compounds, sulfone compounds, and lactone compounds. When the liquid component contains at least one of these compounds, the re-chemical conversion of the dielectric layer by the acid component contained in the liquid component can be carried out efficiently. Furthermore, since the liquid component contains a glycol compound, protons (H + ) (specifically, the proton (H +) can be easily provided. That is, the affinity with the conductive polymer layer can be improved. Furthermore, since sulfone compounds and lactone compounds are aprotic, the liquid component containing at least one of a sulfone compound and a lactone compound can suppress the liquid component from reacting with the acid component (e.g., esterification reaction). That is, the stability of the liquid component can be improved even in a high-temperature environment (e.g., an environment of 145°C). This can stabilize the characteristics of the electrolytic capacitor.

[0066] When the liquid component contains at least one organic solvent selected from the group consisting of glycol compounds, sulfone compounds, and lactone compounds, the proportion of glycol compounds in the liquid component is preferably 40% by mass to 80% by mass, the proportion of sulfone compounds in the liquid component is preferably 20% by mass to 60% by mass, and the proportion of lactone compounds in the liquid component is preferably 40% by mass to 80% by mass. By containing glycol compounds, sulfone compounds, and lactone compounds in the above numerical ranges, re-chemical conversion of the dielectric layer by the acid component contained in the liquid component can be carried out more efficiently.

[0067] From the viewpoint of donating protons to the conductive polymer, the liquid component may contain compounds other than glycol compounds, such as glycerin and polyglycerin.

[0068] The liquid component may contain water. The water content in the liquid component may be 0.1% by mass or more and 6.0% by mass or less, 0.2% by mass or more and 4.0% by mass or less, or 0.5% by mass or more and 2.0% by mass or less. By including water in the liquid component in the above range, the repairability of the dielectric layer by the liquid component can be improved. Furthermore, when the electrolytic capacitor is used at high temperatures (for example, when used at 145°C), fluctuations in the ESR value can be suppressed. Note that sulfone compounds have excellent hydrolysis resistance, and therefore, when the liquid component contains a sulfone compound as described above, the hydrolysis resistance of the liquid component can be improved.

[0069] In the electrolytic capacitor according to the embodiment of the present disclosure, the liquid component contains, as solutes, cationic and anionic components. Examples of the cationic component include a base component (base), and examples of the anionic component include an acid component (acid). The proportion of the solute in the liquid component is preferably 70% by mass or less, and more preferably 50% by mass or less.

[0070] Examples of the base component include ammonia and N-alkylmorpholine, etc. As the N-alkylmorpholine, it is preferable to use N-methylmorpholine.

[0071] 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-ethylimidazoline, 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, the electrolytic capacitor can be made to have excellent impedance characteristics.

[0072] The base component may be a quaternary salt of a compound having an alkyl-substituted amidine group. Examples of such a base component 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; and 1,3-dimethylbenzimidazolium are preferred. By using these materials, the electrolytic capacitor can be made to have excellent impedance characteristics.

[0073] Tertiary amines may be used as the base component. Examples of tertiary amines include trialkylamines and phenyl group-containing amines. Examples of trialkylamines include trimethylamine, dimethylethylamine, methyldiethylamine, triethylamine, dimethyl-n-propylamine, dimethylisopropylamine, methylethyl-n-propylamine, methylethylisopropylamine, diethyl-n-propylamine, diethylisopropylamine, tri-n-propylamine, triisopropylamine, tri-n-butylamine, and tri-tert-butylamine. Examples of phenyl group-containing amines include dimethylphenylamine, methylethylphenylamine, and diethylphenylamine. From the viewpoint of increasing conductivity, trialkylamines are preferably used, and among trialkylamines, it is preferable to use at least one selected from the group consisting of trimethylamine, dimethylethylamine, methyldiethylamine, and triethylamine. Examples of the base component may include secondary amines such as dialkylamines, primary amines such as monoalkylamines, and ammonia.

[0074] A heterocyclic amine may be used as the base component. Examples of the heterocyclic amine include morpholines, and examples of the morpholines include morpholine and morpholine derivatives. Specific examples include morpholine, N-alkylmorpholine, and N-hydroxyalkylmorpholine. Examples of the N-alkylmorpholine include N-methylmorpholine, N-butylmorpholine, and 4-isobutylmorpholine. Furthermore, examples of the heterocyclic amine that can be used include pyridine and imidazole.

[0075] The acid component may be at least one selected from the group consisting of aromatic carboxylic acids, aliphatic carboxylic acids, and salts thereof. The aromatic carboxylic acids and aliphatic carboxylic acids may be polycarboxylic acids or monocarboxylic acids. The aliphatic polycarboxylic acids may be saturated polycarboxylic acids or unsaturated polycarboxylic acids. Examples of saturated polycarboxylic acids include 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-decanecarboxylic acid. Examples of unsaturated polycarboxylic acids include maleic acid, fumaric acid, and itaconic acid. Examples of aromatic polycarboxylic acids include phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, pyromellitic acid, and benzoic acid. The phthalic acid may be o-phthalic acid. Examples of aromatic monocarboxylic acids include salicylic acid.

[0076] The polycarboxylic acid also includes alicyclic polycarboxylic acids, such as cyclohexane-1,2-dicarboxylic acid and cyclohexene-1,2-dicarboxylic acid.

[0077] Examples of monocarboxylic acids include aliphatic monocarboxylic acids and aromatic monocarboxylic acids. In this specification, the term "aromatic monocarboxylic acid" encompasses hydroxycarboxylic acids. Examples of aliphatic monocarboxylic acids include saturated monocarboxylic acids and unsaturated monocarboxylic acids. Examples of saturated monocarboxylic acids include 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. Examples of unsaturated monocarboxylic acids include acrylic acid, methacrylic acid, and oleic acid. Examples of aromatic monocarboxylic acids include benzoic acid, cinnamic acid, and naphthoic acid. Examples of hydroxycarboxylic acids include salicylic acid, mandelic acid, and resorcylic acid.

[0078] The aromatic carboxylic acid is preferably at least one selected from the group consisting of o-phthalic acid, salicylic acid, and benzoic acid, and the aliphatic carboxylic acid is preferably at least one selected from the group consisting of adipic acid, azelaic acid, and sebacic acid.

[0079] An inorganic acid may be used as the acid component. 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 dicarboxylic acid derivatives such as borodiglycolic acid, borodisalic acid, and borodisalicylic acid.

[0080] The liquid component may contain a salt of an acid component and a base component. The salt may be an inorganic salt 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 include trimethylamine maleate, triethylamine borodisalicylate, ethyldimethylamine phthalate, mono-1,2,3,4-tetramethylimidazolinium phthalate, and mono-1,3-dimethyl-2-ethylimidazolinium phthalate. The organic salt may be an amine salt of a long-chain dibasic carboxylic acid. An example of an amine salt of a long-chain dibasic carboxylic acid is diethylamine 2-butyloctanedioate (2BA).

[0081] The ionic liquid is synonymous with a salt in a molten state (molten salt), and is an ionic substance that is liquid at 25°C, for example.

[0082] Examples of cations that constitute ionic liquids include cations of nitrogen-containing heterocycles (imidazolium, pyrrolidinium, piperidinium, pyridinium, morpholinium, etc.), ammonium, phosphonium, sulfonium, and derivatives thereof (e.g., substituted compounds having a substituent such as an alkyl group). The cation may be an organic cation.

[0083] The anions that make up ionic liquids include hydrogen sulfate ions (HSO4 - ), sulfate ions (SO4 2- , -SO4 - ), carboxylate anion (-COO - ), nitrate anion, sulfonate anion (-SO3 - ), phosphonate anion (PO3 2- , -HPO3 - ) and the like. Acids capable of generating these anions include sulfuric acid, sulfuric acid monoesters (such as methyl sulfate), carboxylic acids (such as acetic acid, lactic acid, benzoic acid, and trifluoromethaneacetic acid), nitric acid, sulfonic acids (such as methanesulfonic acid, trifluoromethanesulfonic acid, and the bis(trifluoromethylsulfonyl)imide anion), phosphonic acids (such as diethylphosphonic acid), and derivatives thereof (e.g., substituted compounds having a substituent such as an alkyl group, a halogenated alkyl group, or a halogen atom). The anion may contain a fluorine atom. Examples of fluorine atom-containing anions include the above-mentioned trifluoromethaneacetic acid, trifluoromethanesulfonic acid, and the bis(trifluoromethylsulfonyl)imide anion, as well as derivatives thereof.

[0084] Specific examples of ionic liquids include 1-butyl-3-methylimidazolium hydrogen sulfate, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, and 1-ethyl-3-methylimidazolium diethylphosphonate.

[0085] The liquid component may contain a polymer compound. Examples of the polymer compound include polyalkylene glycol, polyalkylene glycol derivatives, and compounds in which at least one hydroxyl group of a polyhydric alcohol is substituted with polyalkylene glycol (including derivatives). Specific examples include polyethylene glycol (PEG), polyethylene glycol glyceryl ether, polyethylene glycol diglyceryl ether, polyethylene glycol sorbitol ether, polypropylene glycol, polypropylene glycol diglyceryl ether, polypropylene glycol sorbitol ether, and polybutylene glycol.

[0086] The polyalkylene glycol may be a copolymer (a random copolymer, a block copolymer, a random block copolymer, or the like), such as a copolymer of ethylene glycol and propylene glycol, a copolymer of ethylene glycol and butylene glycol, or a copolymer of propylene glycol and butylene glycol.

[0087] The polymer compound may be a copolymer having ethylene oxide (EO) units and propylene oxide (PO) units. The copolymer includes a copolymer of EO and PO (EO-PO copolymer) and its derivatives. These may be used alone or in combination. The copolymer may be crosslinked with a crosslinking agent. Examples of the derivative include an EO-PO copolymer in which the hydroxyl group (—OH) normally present at its terminal is replaced with an acrylic group (O—CO—CH═CH). The molar ratio of EO units to PO units, based on 1 mole of the entire EO-PO copolymer, is preferably EO:PO=0.9:0.1 to 0.5:0.5. In other words, the EO-PO copolymer preferably contains at least the same amount of EO units as PO units. This prevents the EO-PO copolymer contained in the liquid component from permeating through the sealing member (e.g., sealing rubber) in an electrolytic capacitor in which a capacitor element is housed in a closed-end case and the opening of the closed-end case is sealed with a sealing member (e.g., sealing rubber).

[0088] In the electrolytic capacitor according to the embodiment of the present disclosure, the weight-average molecular weight Mw of the polymer compound may be 200 or more, 300 or more, 400 or more, or 500 or more. The weight-average molecular weight Mw of the polymer compound may be 5000 or less, 4000 or less, 3000 or less, 2000 or less, or 1000 or less.

[0089] The weight average molecular weight Mw of the polymer compound can be measured by GPC.

[0090] A specific configuration of an electrolytic capacitor according to an embodiment of the present disclosure will now be described with reference to Fig. 5. Fig. 5 is a cross-sectional view that schematically illustrates an electrolytic capacitor 100 according to an embodiment of the present disclosure.

[0091] Electrolytic capacitor 100 includes capacitor element 10, bottomed case 101 that houses capacitor element 10, sealing member 102 (e.g., a sealing rubber) that closes the opening of bottomed case 101, seat plate 103 that covers sealing member 102, seat plate 103 that is disposed outside bottomed case 101 so as to cover sealing member 102 from the opening side of bottomed case 101, a pair of lead wires 104A and 104B that extend from sealing member 102 and pass through seat plate 103, and a pair of lead tabs 105A and 105B that connect each of the pair of lead wires 104A and 104B to electrodes of the capacitor element (e.g., an anode foil 11 and a cathode foil 12, which will be described later). The vicinity of the open end of bottomed case 101 is drawn to be recessed inward, and the open end of bottomed case 101 is curled to be crimped to sealing member 102. In the example shown in FIG. 5, lead wire 104A is connected to an electrode of the capacitor element via lead tab 105A, and lead wire 104B is connected to an electrode of the capacitor element via lead tab 105B.

[0092] In electrolytic capacitor 100 according to one embodiment of the present disclosure, the capacitor element is configured as shown in FIGS.

[0093] The sealing member 102 is formed of an elastic material containing a rubber component. Examples of rubber components that can be used include butyl rubber (IIR), nitrile rubber (NBR), ethylene propylene rubber, ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), isoprene rubber (IR), Hypalon (trademark) rubber, silicone rubber, and fluororubber. The sealing member 102 may contain fillers such as carbon black and silica.

[0094] The electrolytic capacitor according to the present disclosure may include at least one capacitor element, or may include multiple capacitor elements, the number of capacitor elements being determined appropriately depending on the application.

[0095] [Manufacturing method of electrolytic capacitors] (b) applying a first conductive polymer dispersion, in which a first conductive polymer and a dopant are dispersed in a liquid medium, to a surface of the dielectric layer and at least one main surface of the cathode foil; (c) forming a first conductive polymer layer on the one surface by removing at least a portion of the liquid medium from the first conductive polymer dispersion; (d) applying a second conductive polymer dispersion, in which a second conductive polymer and a dopant are dispersed in a liquid medium, to voids in the separator; (e) forming a second conductive polymer layer in the voids of the separator by removing at least a portion of the liquid medium from the second conductive polymer dispersion; (f) forming a capacitor element by disposing the separator between the anode foil and the cathode foil; and (g) filling voids in the capacitor element with a liquid component containing a cation component and an anion component. In the method for manufacturing an electrolytic capacitor according to the embodiment of the present disclosure, the steps (a) to (g) are preferably performed in this order.

[0096] <(a) Process> The process for preparing the anode foil, cathode foil, and separator having a dielectric layer is not particularly limited. The materials for the anode foil, cathode foil, and separator are also not particularly limited. For example, the above-described materials can be used as the anode foil, cathode foil, and separator.

[0097] <(b) Process> In step (b), the first conductive polymer dispersion may be applied to the surface of the dielectric layer, or to at least one of the main surfaces of the cathode foil. Alternatively, the first conductive polymer dispersion may be applied to the surface of the dielectric layer and to at least one of the main surfaces of the cathode foil. When dielectric layers are formed on both main surfaces of the anode foil, the first conductive polymer dispersion may be applied to the surfaces of the dielectric layers formed on both main surfaces of the anode foil. Alternatively, the first conductive polymer dispersion may be applied to both main surfaces of the cathode foil. A first conductive polymer layer is formed at the location where the first conductive polymer dispersion is applied.

[0098] Examples of methods for applying the first conductive polymer dispersion include coating. Coating can be carried out by various known methods. Examples of coating include coating using a coater, spray coating, and coating by immersing the object to be coated in the first conductive polymer dispersion. Examples of coating using a coater include gravure coating and die coating. Note that the liquid medium can be, for example, water.

[0099] <(c) Process> In step (c), the method for removing at least a portion of the liquid medium from the first conductive polymer dispersion is not particularly limited. The liquid medium is preferably removed by at least heating. The liquid medium may be removed by heating under reduced pressure. When the liquid medium is water, the liquid medium is preferably removed by heating the liquid medium to 100°C or higher.

[0100] When the electrolytic capacitor is a wound-type electrolytic capacitor 100 as shown in FIG. 4, the first conductive polymer layer can be formed by impregnating a capacitor element 10 configured as a wound body as shown in FIG. 1 with the first conductive polymer dispersion, and then heating the capacitor element 10 at a predetermined temperature.

[0101] <(d) Process> In step (d), a second conductive polymer dispersion is applied to the voids of the separator. The second conductive polymer dispersion can be applied to the voids of the separator by the same method as that used to apply the first conductive polymer dispersion.

[0102] <(e) Process> In step (e), at least a portion of the liquid medium is removed from the second conductive polymer dispersion in the same manner as in step (c), thereby forming a second conductive polymer layer in the voids of the separator.

[0103] <(f) Process> In step (f), a first conductive polymer layer is formed on the surface of the dielectric layer and on at least one main surface of the cathode foil, a second conductive polymer layer is formed in the voids of the separator, and then a separator is placed between the anode foil and the cathode foil to form a capacitor element (specifically, a capacitor element including a conductive polymer layer). This step is also a step in which the anode foil and the cathode foil are stacked with the separator interposed therebetween.

[0104] In the method for manufacturing an electrolytic capacitor according to the present disclosure, the capacitor element is preferably manufactured to form a wound body as shown in Fig. 1. In the wound body as shown in Fig. 1, the anode foil, the cathode foil, and the separator are stacked in the radial direction of the wound body.

[0105] <(g) Process> The method for filling the voids in the capacitor element with the liquid component is not particularly limited. For example, the voids in the capacitor element may be filled with the liquid component by impregnating at least a portion of the capacitor element with a liquid component containing a cation component and an anion component. Note that the cation component and the anion component may be those described above.

[0106] As described above, steps (a) through (g) are performed to form a capacitor element having a first conductive polymer layer, a second conductive polymer layer, and a liquid component containing a cation component and an anion component. If necessary, the capacitor element is then encapsulated in an exterior body (case). In this manner, an electrolytic capacitor according to an embodiment of the present disclosure is manufactured.

[0107] Although the above describes an example in which a first conductive polymer layer is formed on the surface of the dielectric layer and at least one main surface of the cathode foil, and a second conductive polymer layer is formed on the separator, before the anode foil and the cathode foil are stacked together with a separator interposed therebetween, the example in which the first conductive polymer layer and the second conductive polymer layer are formed is not limited to this. The first conductive polymer layer and the second conductive polymer layer may be formed after the anode foil and the cathode foil are stacked together with a separator interposed therebetween. For example, after obtaining a wound body in which the anode foil and the cathode foil are stacked together with a separator interposed therebetween, the first conductive polymer layer may be formed by immersing the second end surface E2 (see FIG. 4) of the wound body in a first conductive polymer dispersion, and the second conductive polymer layer may be formed by immersing the second end surface E2 (see FIG. 4) of the wound body in a second conductive polymer dispersion. In this case, if the size of the first conductive polymer is smaller than the size of the second conductive polymer, the first conductive polymer dispersion will be impregnated closer to the first end face E1 (see Figure 4) than the second conductive polymer dispersion, and the second conductive polymer layer will be formed biased toward the second end face E2 side than the first conductive polymer layer.

[0108] (Addendum) The above description discloses the following techniques. (Technology 1) An electrolytic capacitor comprising a capacitor element and a liquid component, the capacitor element includes an elongated anode foil, an elongated cathode foil, an elongated separator interposed between the anode foil and the cathode foil, and a first conductive polymer layer and a second conductive polymer layer interposed between the anode foil and the cathode foil; the anode foil, the cathode foil, and the separator are wound in the longitudinal direction of the elongated shape to form a wound body, the anode foil has a porous portion at least a part of the surface of which is covered with a dielectric layer; the cathode foil is disposed opposite the dielectric layer; the separator includes a fibrous material; the first conductive polymer layer covers at least a portion of the surface of the dielectric layer within the porous portion; the second conductive polymer layer covers at least a portion of the surface of the fibrous material in the separator; the first conductive polymer layer includes a first conductive polymer; the second conductive polymer layer includes a second conductive polymer, In the porous portion, the content of the first conductive polymer is greater than the content of the second conductive polymer; In the separator, the content of the second conductive polymer is greater than the content of the first conductive polymer, the electrical conductivity of the first conductive polymer layer is lower than the electrical conductivity of the second conductive polymer layer; Electrolytic capacitor. (Technology 2) the first conductive polymer layer further covers at least a portion of the surface of the cathode foil; the first conductive polymer layer and the second conductive polymer layer form a conductive path that connects the dielectric layer to the cathode foil via the separator. The electrolytic capacitor according to claim 1. (Technology 3) the wound body has a first end surface and a second end surface aligned in a winding axis direction, the second conductive polymer layer is formed in the separator so as to be biased toward a portion closer to the second end face of the wound body than to the first end face of the wound body; The electrolytic capacitor according to claim 1. (Technology 4) the capacitor element has an anode lead connected to the anode foil and a cathode lead foil connected to the cathode foil, the anode lead and the cathode lead protrude from the first end surface of the wound body. The electrolytic capacitor according to claim 3. (Technology 5) The degree of polymerization of the first conductive polymer is lower than the degree of polymerization of the second conductive polymer. The electrolytic capacitor according to any one of the first to fourth aspects. (Technology 6) the first conductive polymer and the second conductive polymer both contain a dopant; a doping rate of the dopant in the first conductive polymer is lower than a doping rate of the dopant in the second conductive polymer; 6. The electrolytic capacitor according to any one of the first to fifth aspects. (Technology 7) the first conductive polymer includes a first polymer dopant having a sulfonic acid group; the second conductive polymer includes a second polymer dopant having a sulfonic acid group; The weight average molecular weight Mw1 of the first polymer dopant is smaller than the weight average molecular weight Mw2 of the second polymer dopant; The electrolytic capacitor according to any one of the first to sixth aspects. (Technology 8) The sulfonation degree of the first polymeric dopant is less than the sulfonation degree of the second polymeric dopant; The electrolytic capacitor according to Art. 7. (Technology 9) the first conductive polymer layer and the second conductive polymer layer both contain an alkali component; the content of the alkaline component in the first conductive polymer layer is greater than the content of the alkaline component in the second conductive polymer layer; The electrolytic capacitor according to any one of the first to eighth aspects. (Technology 10) the first conductive polymer layer and the second conductive polymer layer both contain an organic solvent having a boiling point of 150° C. or higher, the content of the organic solvent in the first conductive polymer layer is smaller than the content of the organic solvent in the second conductive polymer layer; The electrolytic capacitor according to any one of the first to ninth aspects. (Technology 11) the first conductive polymer layer further contains a water-soluble polymer compound; The electrolytic capacitor according to any one of the first to tenth aspects.

[0109] While the present invention has been described with respect to presently preferred embodiments, such disclosure should not be interpreted as limiting. Various variations and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all variations and modifications that do not depart from the true spirit and scope of the invention. [Example]

[0110] Hereinafter, the present disclosure will be specifically described based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0111] [Example 1] An electrolytic capacitor with a rated voltage of 35V was fabricated as follows.

[0112] (A) Preparation of components (A-1) Anode foil An aluminum foil having a thickness of 100 μm was subjected to an etching treatment to roughen the surface of the aluminum foil, and the roughened surface of the aluminum foil was subjected to a chemical conversion treatment to form a dielectric layer, thereby obtaining an anode foil.

[0113] (A-2) Cathode foil An aluminum foil having a thickness of 50 μm was subjected to an etching treatment to roughen the surface of the aluminum foil, thereby obtaining a cathode foil.

[0114] (A-3) Separator A nonwoven fabric (50 μm thick) 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.

[0115] (B) Preparation of conductive polymer dispersion (B-1) Preparation of First Conductive Polymer Dispersion A mixed solution was prepared by dissolving 3,4-ethylenedioxythiophene (3,4-ethylenedioxythiophene derivative) with alkyl groups introduced as substituents and poly(4-styrenesulfonic acid) (PSS, weight-average molecular weight Mw 100,000, dopant) in ion-exchanged water. Next, while stirring this mixed solution, an oxidizing agent (iron(III) sulfate and ammonium persulfate) dissolved in ion-exchanged water was added to the mixed solution to carry out a polymerization reaction. After the polymerization reaction, the resulting reaction solution was filtered (dialyzed) to remove unreacted monomer and excess oxidizing agent. To the filtered reaction solution, ammonia, an alkaline component, ethylene glycol, and polyacrylic acid were added to obtain a dispersion containing 2% by mass of the PSS-doped poly(3,4-ethylenedioxythiophene) derivative as a first conductive polymer dispersion. The first conductive polymer dispersion was adjusted to contain 5% by mass of ethylene glycol and 0.5% by mass of polyacrylic acid. The alkali component was adjusted to 0.9 equivalents per equivalent of PSS-doped poly(3,4-ethylenedioxythiophene) derivative. Ethylene glycol is an organic solvent with a boiling point of 150°C or higher, and polyacrylic acid is a water-soluble polymer compound.

[0116] (B-2) Preparation of second conductive polymer dispersion A mixed solution was prepared by dissolving 3,4-ethylenedioxythiophene and poly(4-styrenesulfonic acid) (PSS, weight-average molecular weight Mw 100,000, dopant) in ion-exchanged water. Next, while stirring this mixed solution, an oxidizing agent (iron(III) sulfate and ammonium persulfate) dissolved in ion-exchanged water was added to the mixed solution to carry out a polymerization reaction. After the polymerization reaction, the resulting reaction solution was filtered (dialyzed) to remove unreacted monomer and excess oxidizing agent. Ethylene glycol was added to the filtered reaction solution to obtain a dispersion containing 2% by mass of PSS-doped poly(3,4-ethylenedioxythiophene) (PEDOT / PSS) as a second conductive polymer dispersion. The ethylene glycol content of this second conductive polymer dispersion was adjusted to 10% by mass.

[0117] (C) Formation of a conductive polymer layer (C-1) Formation of the first conductive polymer layer Using a gravure coater, the first conductive polymer dispersion was applied to both sides of the anode foil so as to cover the dielectric layer. A drying treatment was then performed to form a first conductive polymer layer on both sides of the anode foil so as to cover the dielectric layer. Similarly, a first conductive polymer layer was formed on both sides of the cathode foil in the same manner.

[0118] (C-2) Formation of the second conductive polymer layer The separator was immersed in the second conductive polymer dispersion contained in a predetermined container in a reduced pressure atmosphere (40 kPa) for 5 minutes, and then the separator impregnated with the second conductive polymer dispersion was dried in a drying oven at 150°C for 20 minutes to form a second conductive polymer layer so as to cover at least a portion of the surface of the fiber material in the separator.

[0119] (D) Preparation of the roll The anode foil, cathode foil, and separator were each cut to have predetermined planar dimensions. An anode lead tab was connected to the anode foil, and a cathode lead tab was connected to the cathode foil. Next, the anode foil and cathode foil were wound with the separator interposed therebetween to obtain a wound body. At this time, the end of the outer surface of the wound body was fixed with a winding tape. An anode lead wire was connected to the end of the anode lead tab, and a cathode lead wire was connected to the end of the cathode lead tab.

[0120] (E) Impregnation of liquid components An electrolyte solution (liquid component) containing polyethylene glycol (PEG), sulfolane (SL), and 2-butyloctanedioic acid diethylamine (2BA) in a ratio of PEG:SL:2BA = 45:40:15 was prepared, and the capacitor element was immersed in the electrolyte solution for 5 minutes in a reduced pressure atmosphere (40 kPa), thereby impregnating the capacitor element with the electrolyte.

[0121] The capacitor element according to Example 1 was sealed to produce an electrolytic capacitor as shown in FIG. 1. Then, an aging treatment was performed at 95°C for 90 minutes while applying a voltage. In this way, the electrolytic capacitor according to Example 1 was obtained. Note that an elastic member containing butyl rubber as a rubber component was used as the sealing member for sealing the capacitor element. Note that 60 electrolytic capacitors were produced. The same applies to the following examples.

[0122] [Comparative Example 1] An electrolytic capacitor according to Comparative Example 1 was produced in the same manner as in Example 1, except that a second conductive polymer layer was formed on the anode foil and the cathode foil.

[0123] Comparative Example 2 An electrolytic capacitor according to Comparative Example 2 was produced in the same manner as in Example 1, except that a first conductive polymer layer was formed so as to cover at least a portion of the fibrous material in the separator.

[0124] Comparative Example 3 An electrolytic capacitor according to Comparative Example 3 was produced in the same manner as in Example 1, except that a second conductive polymer layer was formed on the anode foil and the cathode foil, and a first conductive polymer layer was formed so as to cover at least a portion of the fibers in the separator.

[0125] <Evaluation> <Measurement of capacitance, ESR, and leakage current> For each electrolytic capacitor according to Example 1 and Comparative Examples 1 to 3, the capacitance (unit: μF) was measured at a frequency of 120 Hz and the ESR (unit: mΩ) was measured at a frequency of 100 kHz using an LCR meter. The measurement temperature was 20°C. Measurements of the capacitance and initial ESR were taken for 20 samples each, and the arithmetic mean of the obtained measurements was calculated. The arithmetic mean was used as the capacitance and ESR values ​​for the electrolytic capacitor according to each example. A 1 kΩ resistor was connected in series to each electrolytic capacitor according to each example, and a rated voltage of 35 V was applied for 120 seconds from a DC power supply, after which the leakage current (unit: μA) was measured. The arithmetic mean of the measurements of the 20 samples was used as the leakage current value for the electrolytic capacitor according to each example. The capacitance, ESR, and leakage current (LC) for each electrolytic capacitor according to each example are shown in Table 1 below.

[0126] [Table 1]

[0127] Table 1 shows that the electrolytic capacitor of Example 1 had a low ESR value of 10.7 mΩ and a low leakage current (LC) value of 3.0 μA. In contrast, the electrolytic capacitor of Comparative Example 1 had a low ESR value of 10.8 mΩ but a high leakage current (LC) value of 6.6 μA. The electrolytic capacitor of Comparative Example 2 had a low leakage current (LC) value of 3.1 μA but a high ESR value of 13.7 mΩ. The electrolytic capacitor of Comparative Example 3 had a high ESR value of 14.1 mΩ and a high leakage current (LC) value of 6.2 μA. The electrolytic capacitor of Example 1 had the highest capacitance (271 μF). [Industrial Applicability]

[0128] The electrolytic capacitor according to the present disclosure can be used in applications where both suppression of an increase in leakage current and suppression of an increase in ESR are required. [Explanation of symbols]

[0129] 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, the capacitor element includes an elongated anode foil, an elongated cathode foil, an elongated separator interposed between the anode foil and the cathode foil, and a first conductive polymer layer and a second conductive polymer layer interposed between the anode foil and the cathode foil; the anode foil, the cathode foil, and the separator are wound in the longitudinal direction of the elongated shape to form a wound body, the anode foil has a porous portion at least a part of the surface of which is covered with a dielectric layer; the cathode foil is disposed opposite the dielectric layer; the separator includes a fibrous material; the first conductive polymer layer covers at least a portion of the surface of the dielectric layer within the porous portion; the second conductive polymer layer covers at least a portion of a surface of the fibrous material in the separator; the first conductive polymer layer includes a first conductive polymer, the second conductive polymer layer includes a second conductive polymer, In the porous portion, the content of the first conductive polymer is greater than the content of the second conductive polymer; In the separator, the content of the second conductive polymer is greater than the content of the first conductive polymer, the electrical conductivity of the first conductive polymer layer is lower than the electrical conductivity of the second conductive polymer layer; Electrolytic capacitor.

2. the first conductive polymer layer further covers at least a portion of the surface of the cathode foil; the first conductive polymer layer and the second conductive polymer layer form a conductive path that connects the dielectric layer to the cathode foil via the separator; 2. The electrolytic capacitor according to claim 1.

3. the wound body has a first end surface and a second end surface aligned in a winding axis direction, the second conductive polymer layer is formed biasedly in a portion of the separator closer to the second end face than to the first end face of the wound body.

2. The electrolytic capacitor according to claim 1.

4. the capacitor element has an anode lead connected to the anode foil and a cathode lead connected to the cathode foil, the anode lead and the cathode lead protrude from the first end surface of the wound body.

4. The electrolytic capacitor according to claim 3.

5. the degree of polymerization of the first conductive polymer is lower than the degree of polymerization of the second conductive polymer; 3. The electrolytic capacitor according to claim 1.

6. the first conductive polymer and the second conductive polymer both contain a dopant; a doping rate of the dopant in the first conductive polymer is lower than a doping rate of the dopant in the second conductive polymer; 3. The electrolytic capacitor according to claim 1.

7. the first conductive polymer includes a first polymer dopant having a sulfonic acid group; the second conductive polymer includes a second polymer dopant having a sulfonic acid group; The weight average molecular weight Mw1 of the first polymer dopant is smaller than the weight average molecular weight Mw2 of the second polymer dopant; 3. The electrolytic capacitor according to claim 1.

8. The sulfonation degree of the first polymer dopant is less than the sulfonation degree of the second polymer dopant; 8. The electrolytic capacitor according to claim 7.

9. the first conductive polymer layer and the second conductive polymer layer both contain an alkali component; the content of the alkaline component in the first conductive polymer layer is greater than the content of the alkaline component in the second conductive polymer layer; 3. The electrolytic capacitor according to claim 1.

10. the first conductive polymer layer and the second conductive polymer layer both contain an organic solvent having a boiling point of 150° C. or higher, the content of the organic solvent in the first conductive polymer layer is smaller than the content of the organic solvent in the second conductive polymer layer; 3. The electrolytic capacitor according to claim 1.

11. the first conductive polymer layer further contains a water-soluble polymer compound; 3. The electrolytic capacitor according to claim 1.

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