Electrolytic capacitor and method for producing same

Abstract

This capacitor element included in an electrolytic capacitor comprises: a positive electrode foil that has a porous part on at least a surface layer thereof and has a dielectric layer on the surface thereof; a negative electrode foil that has a conductive coating layer on the surface thereof; and a separator that is interposed between the positive electrode foil and the negative electrode foil and is made of a conductive polymer and a synthetic resin. The positive electrode foil has a plurality of tunnel-shaped pits in the porous part, and a dielectric layer is provided on the surface of the positive electrode foil including the inner surfaces of the plurality of pits. In at least a portion of the plurality of pits, at least a deep part of the tunnel-shaped pit is covered with a silane coupling agent.

Description

Electrolytic Capacitor and Method for Manufacturing the Same

[0001] The present disclosure relates to an electrolytic capacitor and a method for manufacturing the same.

[0002] A capacitor element included in an electrolytic capacitor includes, for example, an anode foil, a cathode foil, and a conductive polymer interposed between the anode foil and the cathode foil. From the viewpoint of ensuring high capacitance, an anode foil having a large number of pits (in other words, recesses) formed on the surface layer by etching or the like is used. In AC etching, sponge-like pits are formed, and in DC etching, tunnel-like pits are formed. On the surface of the anode foil, a dielectric layer containing a metal oxide is formed by a forming process in which the metal constituting the anode foil is oxidized.

[0003] Patent Document 1 proposes an aluminum alloy clad foil for a high-voltage anode in an electrolytic capacitor composed of three layers of an aluminum outer layer - an aluminum core layer - an aluminum outer layer, where (1) the thickness of the core layer is 2 to 30% of the clad foil thickness, (2) the tensile strength of the clad foil is 28 N / mm ２ or more, (3) the cubic orientation occupancy of the outer layer is 80% or more, and (4) there are no tunnel pits penetrating the core layer after DC electrolytic etching.

[0004] International Publication No. 2001 / 43150

[0005] In recent years, further improvement in the withstand voltage of electrolytic capacitors has been demanded.

[0006] The first aspect of this disclosure relates to an electrolytic capacitor including a capacitor element, wherein the capacitor element comprises: an anode foil having a porous portion at least on its surface and a dielectric layer on its surface; a cathode foil having a conductive coating layer on its surface; and a separator made of a conductive polymer and synthetic resin interposed between the anode foil and the cathode foil, wherein the anode foil has a plurality of tunnel-shaped pits in the porous portion, and the dielectric layer is provided on the surface of the anode foil including the inner surfaces of the plurality of pits, and at least the deep portion of the tunnel-shaped pits in at least a portion of the plurality of pits is coated with a silane coupling agent.

[0007] A second aspect of the present disclosure is a method for manufacturing an electrolytic capacitor including a capacitor element, the capacitor element comprising: an anode foil having a porous portion at least on its surface and a dielectric layer on its surface; a cathode foil having a conductive coating layer on its surface; and a separator made of a conductive polymer and synthetic resin interposed between the anode foil and the cathode foil, wherein the anode foil has a plurality of tunnel-shaped pits in the porous portion and the dielectric layer is provided on the surface of the anode foil including the inner surfaces of the plurality of tunnel-shaped pits, the manufacturing method comprising: a first step of preparing the anode foil having the dielectric layer; a second step of stacking the anode foil having the dielectric layer and the cathode foil via the separator to obtain an element precursor; and a third step, after the second step, applying a processing solution containing a silane coupling agent to the element precursor under reduced pressure to coat at least the inner surface of the deepest part of the plurality of tunnel-shaped pits with the silane coupling agent. The present invention relates to a method for manufacturing an electrolytic capacitor, comprising: a fourth step of attaching the conductive polymer to the element precursor after the third step to form the capacitor element; and

[0008] This invention provides electrolytic capacitors with excellent voltage resistance and a method for manufacturing the same.

[0009] This is a schematic cross-sectional view showing an electrolytic capacitor according to an embodiment of the present disclosure. This is a perspective view showing a portion of the winding unfolded.

[0010] While novel features of this disclosure are described in the attached claims, this disclosure, in conjunction with other purposes and features of this disclosure, will be better understood by the following detailed description accompanied by drawings, both in terms of its structure and content.

[0011] Anode foil with pits formed on it has a large surface area. In addition, a large capacitance can be obtained by filling the pits with conductive polymer. If the conductive polymer is filled to the depths of the pits, an even larger capacitance can be obtained. In electrolytic capacitors equipped with anode foil with tunnel-shaped pits, the capacitance attenuation rate is smaller, even when the oxide film, which is the dielectric layer, is formed at a high chemical conversion voltage, compared to electrolytic capacitors equipped with sponge-like pits obtained by AC etching. Therefore, high capacitance can be expected even in high-voltage products in electrolytic capacitors equipped with anode foil with tunnel-shaped pits.

[0012] Prior to filling the pits with conductive polymer, a dielectric layer is formed on the surface of the anode foil by a chemical conversion treatment. Because the tunnel-shaped pits are deep, oxygen supply is likely to be insufficient in the deeper parts during the chemical conversion treatment. As a result, variations in the thickness of the dielectric layer are likely to occur in the deeper parts of the tunnel-shaped pits, and defective areas not covered by the dielectric layer are likely to form. Therefore, when conductive polymer is filled into the deeper parts of the tunnel-shaped pits, leakage current flows in the defective areas of the dielectric layer, or defects occur in areas where the dielectric layer is thin, and leakage current flows in these areas. When a large leakage current flows, the incidence of short-circuit failures increases.

[0013] Technical (1) In view of the above, the electrolytic capacitor of the present disclosure includes a capacitor element. The capacitor element comprises an anode foil having a porous portion at least on its surface and a dielectric layer on its surface, a cathode foil having a conductive coating layer on its surface, and a separator made of a conductive polymer and synthetic resin interposed between the anode foil and the cathode foil. The anode foil has a plurality of tunnel-shaped pits in the porous portion, and the dielectric layer is provided on the surface of the anode foil, including the inner surfaces of the plurality of tunnel-shaped pits. In at least a portion of the plurality of tunnel-shaped pits, at least the deep portion of the tunnel-shaped pits is coated with a silane coupling agent.

[0014] According to the electrolytic capacitor of this disclosure, even if a defect occurs in the dielectric layer at the depth of the tunnel-shaped pit, it is covered by a silane coupling agent. Therefore, when the conductive polymer is filled to the depth of the tunnel-shaped pit, leakage current is suppressed even when a relatively high voltage is applied. Thus, excellent dielectric strength can be obtained. In addition, because the conductive polymer can be filled to the depth of the tunnel-shaped pit, a large capacitance can be easily obtained, and the equivalent series resistance (ESR) can be kept low.

[0015] The silane coupling agent can be attached to the inner wall of the tunnel-shaped pits by applying the silane coupling agent to the anode foil having a dielectric layer. In a simpler method, for example, the silane coupling agent can be attached to the inner wall of the tunnel-shaped pits of the anode foil by applying the silane coupling agent to an element precursor in which an anode foil having a dielectric layer and a cathode foil are stacked with a separator in between. However, since the silane coupling agent is a resistive component, it causes a decrease in the capacitance of the electrolytic capacitor and an increase in ESR. Therefore, it is preferable that the silane coupling agent is not attached to parts of the anode foil other than the inner wall of the tunnel-shaped pits. In the electrolytic capacitor of this disclosure, a coating layer is formed on the cathode foil and the separator is made of synthetic resin, so even when the silane coupling agent is applied to the element precursor, adhesion to the cathode foil and separator (more specifically, coupling) is suppressed, making it easier to obtain high capacitance and low ESR.

[0016] Technology (2) In Technology (1) above, the plurality of tunnel-shaped pits have an average depth D. The plurality of tunnel-shaped pits are divided into a shallow part from the entrance of the tunnel-shaped pit to the average depth D / 2 and a deep part from the deepest part of the tunnel-shaped pit to the average depth D / 2. In this case, it is preferable that the silane coupling agent is unevenly distributed in the deep part. The presence of the silane coupling agent in the deep part covers defects in the dielectric layer, resulting in high dielectric strength. On the other hand, a smaller amount of silane coupling agent in the shallow part results in higher capacitance and lower ESR. Furthermore, defects in the dielectric layer are less likely to occur in the shallow part of the tunnel-shaped pit compared to the deep part. Therefore, even if there is less silane coupling agent in the shallow part, it does not have a significant effect on the dielectric strength.

[0017] Technology (3) In Technology (2) described above, it is preferable that the average ratio of the silicon content Rs in the shallow part to the silicon content Rd in the deep part (= Rs / Rd) is 0 or more and 0.6 or less. In this case, it is easier to obtain higher capacitance and lower ESR while ensuring high dielectric strength. The silicon content Rs and Rd are content based on mass.

[0018] Technology (4) In any one of the above technologies (1) to (3), it is preferable that the coating layer of the cathode foil contains at least one selected from the group consisting of conductive carbon and titanium. When the coating layer of the cathode foil contains such components, the coupling bond of the silane coupling agent to the cathode foil can be suppressed when the silane coupling agent is applied to the device precursor. Therefore, it is advantageous in obtaining higher capacity and lower ESR.

[0019] Technology (5) In any one of the above technologies (1) to (4), it is preferable that the separator is a nonwoven fabric made of synthetic resin fibers. In electrolytic capacitors, paper separators are generally often used. Silane coupling agents readily bond to paper separators. When a separator made of a nonwoven fabric made of synthetic resin fibers is used, the coupling bond of the silane coupling agent to the separator when the silane coupling agent is applied to the element precursor can be suppressed. Therefore, it is advantageous in ensuring higher capacitance and lower ESR.

[0020] Technology (6) In Technology (5) above, it is preferable that the synthetic resin fiber is at least one selected from the group consisting of aramid fibers and polyester fibers. When a nonwoven fabric separator formed of such synthetic resin fibers is used, the coupling bond of the silane coupling agent to the separator can be further suppressed.

[0021] Technology (7) In any one of the above technologies (1) to (6), the electrolytic capacitor may further contain a liquid component. In this case, the liquid component increases the ionic conductivity, making it easier to obtain higher capacitance and lower ESR.

[0022] Technical Information (8) The present disclosure also includes a method for manufacturing an electrolytic capacitor. The electrolytic capacitor includes a capacitor element. The capacitor element comprises an anode foil having a porous portion on at least its surface and a dielectric layer on its surface, a cathode foil having a conductive coating layer on its surface, and a separator made of a conductive polymer and synthetic resin interposed between the anode foil and the cathode foil. The anode foil has a plurality of tunnel-shaped pits in the porous portion, and the dielectric layer is provided on the surface of the anode foil, including the inner surfaces of the plurality of tunnel-shaped pits. The manufacturing method comprises: a first step of preparing the anode foil having the dielectric layer; a second step of stacking the anode foil having the dielectric layer and the cathode foil via the separator to obtain an element precursor; a third step, after the second step, applying a processing solution containing a silane coupling agent to the element precursor under reduced pressure to coat the inner surface of at least the deepest part of the plurality of tunnel-shaped pits with the silane coupling agent; and a fourth step, after the third step, attaching the conductive polymer to the element precursor to form the capacitor element.

[0023] By coating at least the inner surface of the deepest part of the tunnel-shaped pit with a silane coupling agent, defects in the dielectric layer are covered by the silane coupling agent, and high voltage resistance of the electrolytic capacitor can be obtained even if the conductive polymer fills the deepest part of the tunnel-shaped pit. By forming a coating layer on the surface of the cathode foil and using a separator made of synthetic resin, the binding of the silane coupling agent to the cathode foil and separator is suppressed when the element precursor is treated with the silane coupling agent. In addition, the conductive polymer fills the deepest part of the tunnel-shaped pit. As a result, high capacitance and low ESR of the electrolytic capacitor can be obtained.

[0024] Technical (9) In the above technical (8), the third step preferably includes a substep (3-1) of applying the processing liquid to the element precursor under reduced pressure, and a substep (3-2) of washing the element precursor after the substep (3-1). The substep (3-2) removes the silane coupling agent from the opening side (mainly the shallow part) of the tunnel-shaped pit, resulting in the silane coupling agent being unevenly distributed in the deeper part. The silane coupling agent coating the inner surface of the deeper part provides high dielectric strength. The amount of silane coupling agent adhering to the inner surface of the shallow part is less than that of the deeper part, resulting in higher capacity and lower ESR.

[0025] Technology (10) In the above technology (8) or technology (9), in the second step, the element precursor is preferably a wound body in which the anode foil and cathode foil having the dielectric layer are wound with the separator in between. Even when a wound body is used, the inner surface of the deep part of the tunnel-shaped pit of the anode foil having the dielectric layer can be coated with a silane coupling agent.

[0026] The electrolytic capacitor and its manufacturing method described herein will be explained in more detail below, including techniques (1) to (10) described above, with reference to drawings as necessary. To the extent that it is not technically inconsistent, at least one of techniques (1) to (10) described above may be combined with at least one of the elements described below. Note that each figure is for illustrative purposes only, and the proportions of the dimensions (e.g., thickness) of each component may differ from those of actual components.

[0027] [Electrolytic Capacitor] The capacitor elements included in an electrolytic capacitor comprise an anode foil having a dielectric layer on its surface, a cathode foil having a coating layer on its surface, and a conductive polymer and separator interposed between the anode foil and the cathode foil. An electrolytic capacitor may have one capacitor element or two or more.

[0028] (Anode foil) The anode foil has a porous portion in at least its surface layer. The anode foil has a plurality of tunnel-shaped pits in the porous portion.

[0029] The anode foil contains a valve metal. Examples of valve metals include Al, Ta, and Nb. The anode foil may be a foil of a valve metal (e.g., Al), or a foil containing an alloy or compound containing a valve metal (e.g., Al).

[0030] For example, an anode foil having a porous portion on its surface is formed by etching the surface of a metal foil containing a valve-acting metal. Such an anode foil has a core and a porous portion continuous with the core. The porous portion is provided, for example, on both surfaces of the anode foil. From the viewpoint of ensuring capacity, the ratio of the thickness of the porous portion (thickness per side of the anode foil) to the total thickness of the anode foil may be 0.1 or more, or 0.2 or more. From the viewpoint of ensuring the core, the ratio of the thickness of the porous portion (thickness per side of the anode foil) to the total thickness of the anode foil may be 0.48 or less, or 0.45 or less.

[0031] The thickness of the porous portion is determined by measuring the thickness at 10 arbitrary points using a cross-sectional image of the anode foil in the capacitor element and calculating the average value of these measurements. The cross-sectional image of the anode foil is taken using a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0032] The total thickness of the anode foil may be 15 μm or more and 300 μm or less, or 50 μm or more and 250 μm or less.

[0033] The tunnel-shaped pits extend in the thickness direction of the porous section. In other words, the tunnel-shaped pits extend from the surface side to the core side of the porous section. Here, extending in the thickness direction of the porous section means that the direction in which the pits extend is either parallel to the thickness direction of the porous section or inclined at an angle of 80° or less. That is, the angle (acute angle) formed by the direction in which the tunnel-shaped pits extend and the thickness direction of the porous section is 0° or more and 80° or less, may be 0° or more and 40° or less, or 0° or more and 15° or less. This angle can be determined by measuring the above angle at any 10 points using cross-sectional images of the anode foil of the capacitor element obtained by SEM or TEM, and calculating the average value of these measurements.

[0034] From the viewpoint of facilitating coating of the inner surface of the deepest part of the pit with a silane coupling agent, the most frequent pore diameter of the tunnel-shaped pit is preferably 300 nm or larger. From the viewpoint of securing the surface area (capacity) of the anode foil, the upper limit of the most frequent pore diameter of the tunnel-shaped pit is preferably 2000 nm or less, and more preferably 1000 nm or less. The most frequent pore diameter of the tunnel-shaped pit is the most frequent pore diameter in the volume-based pore size distribution measured by a mercury porosimeter.

[0035] The average depth D of the multiple tunnel-shaped pits may be between 10 μm and 60 μm, or between 30 μm and 60 μm. When the average depth D is within this range, defects and areas with low thickness are likely to occur in the dielectric layer in the deeper parts. In this disclosure, high dielectric strength can be ensured by coating at least the inner surface of the deeper parts with a silane coupling agent. The part from the entrance of the tunnel-shaped pit to the average depth D / 2 is referred to as the shallow part, and the part from the deepest part of the tunnel-shaped pit to the average depth D / 2 is referred to as the deep part. The average depth D is the average depth per side of the anode foil.

[0036] The average depth D of the tunnel-shaped pits can be determined by measuring the depth of any 10 tunnel-shaped pits using cross-sectional images of the anode foil of the capacitor element obtained by SEM or TEM, and then calculating the average value of these measurements.

[0037] Examples of tunnel-shaped pits include columnar (e.g., cylindrical, rectangular prism, etc.), conical (e.g., conical, square pyramidal, etc.), and frustum-shaped (e.g., frustum-shaped cone, square frustum-shaped pyramidal, etc.). The tunnel-shaped pit may branch midway. In the porous portion of one surface layer, a part of the tunnel-shaped pit may extend to the core, and may further extend to the porous portion of the other surface layer.

[0038] (Dielectric layer) The anode foil has a dielectric layer on a portion of its surface, including the inner surfaces of a plurality of pits. The dielectric layer is formed, for example, by oxidizing the surface of the anode foil by a chemical conversion treatment.

[0039] The dielectric layer contains, for example, an oxide of the valve metal. For example, when aluminum is used as the valve metal, the dielectric layer is Al ２ O ３ This includes the following. Furthermore, the dielectric layer may be formed from a material that functions as a dielectric, not limited to an oxide of the valve metal.

[0040] The dielectric layer is typically formed on the surface of the anode foil. When the dielectric layer is formed on the surface of the porous portion of the anode foil, it is formed along the inner walls of the pores in the porous portion or the depressions (pits) on the surface of the anode foil.

[0041] (Silane coupling agent) Due to the depth of the tunnel-shaped pit, defects are likely to form in the deeper parts, such as areas where the dielectric layer is not formed or areas where the dielectric layer is thin. Not only in the defective areas, but also in areas where the dielectric layer is thin, stress is applied due to charging and discharging, making it easy for defects in the dielectric layer to occur. If the dielectric layer has defects, leakage current is likely to occur when conductive polymer is filled into the tunnel-shaped pit, and high dielectric strength cannot be obtained. In this disclosure, by covering at least a portion of the inner surface of at least the deep part of the tunnel-shaped pit with a silane coupling agent, defects in the dielectric layer are covered by the silane coupling agent, and high dielectric strength can be obtained.

[0042] Examples of the silane coupling agent include a silane coupling agent having at least one reactive functional group and at least one hydrolyzable functional group. The reactive functional group may be an epoxy group, a halogenated alkyl group, an amino group, a ureido group, a mercapto group, an isocyanate group, a polymerizable group, or the like. Examples of the polymerizable group include an acryloyl group, a methacryloyl group, a vinyl group, and the like. The hydrolyzable functional group may be, for example, an alkoxy group (such as a methoxy group, an ethoxy group, a propoxy group, etc.), a halogen atom (such as a chlorine atom, a bromine atom, etc.), or the like.

[0043] In an electrolytic capacitor, the reactive functional group or the functional group having hydrolyzability of the silane coupling agent may be in a free state or in an ionic state, and may interact or bond with other elements (preferably, a dielectric layer) or other components (preferably, a conductive polymer) contained in the electrolytic capacitor.

[0044] Preferred silane coupling agents include those having an epoxy group and those having an acrylic group. Examples of silane coupling agents having an epoxy group include 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 3-glycidoxypropyltriethoxysilane. Examples of silane coupling agents having an acrylic group include 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, and 3-acryloxypropyltrimethoxysilane (γ-acryloxypropyltrimethoxysilane). Other silane couplings include vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, p-styryltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-di Examples include methyl-butylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, hydrochloride of N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane, 3-ureidopropyltriethoxysilane, 3-chloropropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, bis(triethoxysilylpropyl)tetrasulfide, and 3-isocyanatetopropyltriethoxysilane. The electrolytic capacitor may contain one silane coupling agent or a combination of two or more.

[0045] In the porous portion of the anode foil, it is preferable that the silane coupling agent is unevenly distributed in the deep part of the tunnel-shaped pits. The deep part where defects are likely to occur in the dielectric layer is coated with the silane coupling agent, so that high breakdown voltage resistance can be obtained. In the shallow part where a dielectric layer with an appropriate thickness is relatively easily formed uniformly, even if the amount of the silane coupling agent per unit area is smaller than that in the deep part, leakage current is less likely to occur and high breakdown voltage resistance is less likely to be impaired. Also, since the amount of the silane coupling agent per unit area in the shallow part is smaller than that in the deep part, higher capacitance and lower ESR can be obtained.

[0046] The average of the ratio (=Rs / Rd) of the silicon content rate Rs in the shallow part to the silicon content rate Rd in the deep part is preferably 0 or more and 0.6 or less, more preferably 0 or more and 0.4 or less, and even more preferably 0 or more and 0.3 or less. When the ratio Rs / Rd is within such a range, higher capacitance and lower ESR are more likely to be obtained while ensuring high breakdown voltage resistance.

[0047] The silicon content rates Rs and Rd are obtained by the following procedure. First, a cross-sectional image in the thickness direction of the anode foil (a cross-sectional image including the porous part) is obtained by SEM or TEM, and using this image, elemental mapping by energy dispersive X-ray spectroscopy (EDX) analysis is performed to obtain a map of silicon elements in the porous part. From this map, the abundance ratio of silicon elements is determined for each of the shallow and deep parts of the pits.

[0048] (Conductive polymer) The conductive polymer includes, for example, a conjugated polymer and a dopant. The conductive polymer contacts at least a part of the silane coupling agent or the dielectric layer and also contacts at least a part of the coating layer of the cathode foil. The conductive polymer may be impregnated in a separator interposed between the anode foil and the cathode foil. The conductive polymer may form a layer. The conductive polymer is sometimes called a solid electrolyte. The conductive polymer constitutes at least a part of the cathode body in an electrolytic capacitor. The conductive polymer may further contain an additive as necessary.

[0049] (Conjugated Polymers) Examples of conjugated polymers include known conjugated polymers used in electrolytic capacitors, such as π-conjugated polymers. Examples of conjugated polymers include polymers with polypyrrole, polythiophene, polyaniline, polyfuran, polyacetylene, polyphenylene, polyphenylenevinylene, polyacene, and polythiophenevinylene as their basic skeleton. The above polymers only need to contain at least one monomer unit that constitutes the basic skeleton. The above polymers also include homopolymers, copolymers of two or more monomers, and derivatives thereof (such as substituted products having substituents). For example, polythiophene also includes poly(3,4-ethylenedioxythiophene) (PEDOT).

[0050] Conjugated polymers may be used individually or in combination of two or more types.

[0051] The weight-average molecular weight (Mw) of the conjugated polymer is not particularly limited, and is, for example, between 1,000 and 1,000,000.

[0052] In this specification, weight-average molecular weight (Mw) is a polysaccharide-converted value measured by gel permeation chromatography (GPC). GPC is typically performed using a polyhydroxymethacrylate gel column and an aqueous sodium nitrate solution as the mobile phase.

[0053] (Dopants) Examples of dopants include relatively low-molecular-weight anions and high-molecular-weight anions. Examples of anions include sulfate ions, nitrate ions, phosphate ions, borate ions, organic sulfonate ions, and carboxylate ions. Compounds that produce these anions are used as dopants. Examples of dopants that produce sulfonate ions include aromatic sulfonic acid compounds (such as p-toluenesulfonic acid and naphthalenesulfonic acid). Aromatic sulfonic acid compounds may have, for example, at least one selected from the group consisting of a carboxyl group and a hydroxyl group.

[0054] Examples of polymer anions include polyvinyl sulfonic acid, polystyrene sulfonic acid (PSS), polyallyl sulfonic acid, polyacrylic sulfonic acid, polymethacrylate sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, polyester sulfonic acid (such as aromatic polyester sulfonic acid), phenol sulfonic acid novolac resin, and polyacrylic acid. The polymer anion may be a polymer of a single monomer, a copolymer of two or more monomers, or a substituted product having substituents. Among these, polyanions derived from polystyrene sulfonic acid are preferred.

[0055] However, these dopants are merely examples and are not limited to them. A single dopant may be used alone, or two or more may be used in combination.

[0056] The Dopant's Mw is not particularly limited and may be between 1,000 and 1,000,000.

[0057] The amount of dopant contained in the conductive polymer may be 10 parts by mass or more and 1000 parts by mass or 20 parts by mass or more and 500 parts by mass per 100 parts by mass of the conjugated polymer.

[0058] (Cathode Foil) The cathode foil comprises a metal foil and a coating layer formed on the surface of the metal foil. The coating layer may be formed on one surface of the metal foil. From the viewpoint of suppressing the bonding of the silane coupling agent to the cathode foil, it is preferable that the coating layer is formed on both surfaces of the metal foil. In this case, even when the element precursor is treated with a silane coupling agent, the bonding of the silane coupling agent to the cathode foil is suppressed.

[0059] It is preferable to use a valve metal or an alloy of a valve metal as the metal constituting the metal foil. The valve metal may be at least one selected from the group consisting of aluminum, tantalum, and niobium. The surface of the metal foil may be roughened as needed. A chemical conversion coating may be provided on the surface of the metal foil.

[0060] The coating layer is conductive. The coating layer may be a non-metallic film (such as conductive carbon), or a film of a different metal (a dissimilar metal) from the metal constituting the metal foil. Examples of conductive carbon include carbon black and graphite. Titanium is preferred as the dissimilar metal. It is preferable that the coating layer contains at least one selected from the group consisting of conductive carbon and titanium. Such a coating layer has high conductivity in addition to being difficult for silane coupling agents to bond to. Therefore, it is advantageous in ensuring high capacitance and low ESR of electrolytic capacitors.

[0061] The coating layer may contain conductive particles such as conductive carbon or titanium and a binder. Examples of binders include resin binders such as thermosetting resins (epoxy resins, imide resins, etc.) and thermoplastic resins. The coating layer containing metals such as titanium may be a film formed by a vapor deposition method or other vapor deposition method. The coating layer can be formed by applying a slurry or paste containing conductive particles and a binder to the surface of a metal foil. The slurry or paste may contain a solvent (water, organic solvents, or a mixture thereof, etc.). After applying the slurry or paste, a drying treatment may be performed. Alternatively, the coating layer may be formed by depositing the metal constituting the coating layer onto the surface of the metal foil by a vapor deposition method.

[0062] The thickness of the coating layer is preferably 0.001 μm or more (or 0.01 μm or more) and 5.00 μm or less per surface of the metal foil, more preferably 0.01 μm or more (or 0.1 μm or more) and 4.00 μm or less, and even more preferably 0.1 μm or more and 3.00 μm or less. When the thickness of the coating layer is within this range, it is easier to suppress the bonding of the coupling agent to the cathode foil, and it is easier to obtain a higher capacitance.

[0063] The thickness of the cathode foil including the coating layer may be 20 μm or more and 100 μm or less, 20 μm or more and 60 μm or less, or 20 μm or more and 50 μm or less.

[0064] (Separator) In this disclosure, a separator made of synthetic resin is used. This reduces the increase in resistance caused by the silane coupling agent binding to the separator. A separator made of synthetic resin means a separator mainly composed of synthetic resin. The separator may contain known additives such as reinforcing materials and binders as needed. The content of synthetic resin in the separator is preferably 50% by mass or more, more preferably 75% by mass or more, and may be 90% by mass or more. The content of synthetic resin in the separator is 100% by mass or less.

[0065] Examples of separators include microporous membranes formed from synthetic resins, nonwoven fabrics formed from synthetic resin fibers, or laminates thereof. Examples of synthetic resins constituting the microporous membranes or fibers include polyamide resins, polyester resins, polyolefin resins, vinylon, acrylic resins, vinyl cyanide resins (such as polyacrylonitrile resins), polyurethane resins, and halogen-containing resins. As polyamide resins, aromatic polyamide resins are preferred, and aramid resins are more preferred. As polyester resins, polyalkylene arylates (such as polyethylene terephthalate and polybutylene terephthalate) and aromatic polyester resins are preferred. Examples of halogen-containing resins include vinyl halogenated resins and vinylidene halogenated resins containing vinyl halides such as vinyl chloride and vinylidene chloride as monomer units, and halogenated olefin resins (such as fluoroolefin resins such as polytetrafluoroethylene). The separator may contain one type of synthetic resin, or two or more types.

[0066] The separator preferably includes a layer of nonwoven fabric made of synthetic resin fibers, and more preferably a nonwoven fabric made of synthetic resin fibers. In particular, the synthetic resin fibers are preferably at least one selected from the group consisting of aramid fibers and polyester fibers. Separators using these nonwoven fabrics can ensure high ionic conductivity while ensuring insulation between the positive and negative electrodes. In addition, compared to conventional paper separators, the bonding of silane coupling agents is significantly suppressed, resulting in higher capacitance and lower ESR of the electrolytic capacitor.

[0067] The proportion of synthetic resin fibers in the fibers contained in the separator is preferably 50% by mass or more, more preferably 75% by mass or more, and even more preferably 90% by mass or more. All of the fibers contained in the separator may be synthetic resin fibers. Furthermore, in order to efficiently place the silane capligun agent deep inside the tunnel-shaped pit, if the fibers contained in the separator include cellulose fibers, the proportion of cellulose fibers is preferably 50% by mass or less, and more preferably 30% by mass or less. It is also preferable that the fibers contained in the separator do not include cellulose fibers.

[0068] The thickness of the separator may be 30 μm or more and 160 μm or less, or 40 μm or more and 80 μm or less.

[0069] (Electrolyte) The electrolytic capacitor of this disclosure may further contain a liquid component. The liquid component may be an electrolyte or a non-aqueous solvent. The electrolyte includes a non-aqueous solvent and an ionic substance (also called a solute) dissolved therein. The non-aqueous solvent may be an organic solvent or an ionic liquid.

[0070] Examples of non-aqueous solvents include polyol compounds such as ethylene glycol and polyethylene glycol, sulfone compounds such as sulfolane, lactone compounds such as γ-butyrolactone, ester compounds such as methyl acetate, carbonate compounds such as propylene carbonate, ether compounds such as 1,4-dioxane, and ketone compounds such as methyl ethyl ketone. The liquid component may contain one non-aqueous solvent or a combination of two or more.

[0071] The liquid component may contain an acid component (anion) and a base component (cation). A salt (solute) may be formed by the acid and base components. The acid component contributes to the film repair function.

[0072] Examples of acidic components include carboxylic acids, acids other than carboxylic acids that have a carbonyloxy bond (such as oxocarbonic acid and meldrumic acid) or their coordination compounds, phenolic compounds (such as picric acid, p-nitrophenol, pyrogallol, and catechol) or their coordination compounds, sulfur-containing acids (such as sulfuric acid, sulfonic acid (such as aromatic sulfonic acid), oxyaromatic sulfonic acid (such as phenol-4-sulfonic acid)), compounds having a sulfonyliimide bond, boron-containing acids (such as boric acid, halide boric acid (such as tetrafluoroboric acid), or partial esters thereof), phosphorus-containing acids (such as phosphoric acid, halide phosphoric acid (such as hexafluorophosphate), phosphonic acid, phosphinic acid, or partial esters thereof), and nitrogen-containing acids (such as nitric acid and nitrite). Examples of carboxylic acids include aliphatic carboxylic acids, organic carboxylic acids such as aromatic carboxylic acids, acid anhydrides of organic carboxylic acids, and coordination compounds of organic carboxylic acids. Examples of aromatic carboxylic acids include aromatic hydroxy acids (such as benzoic acid and salicylic acid), aromatic polycarboxylic acids (such as phthalic acid and pyromellitic acid), and sulfo-aromatic carboxylic acids (such as m-sulfobenzoic acid, 4-sulfophthalic acid, and 5-sulfosalicylic acid).

[0073] Examples of compounds containing a sulfonylimide bond include saccharin, 1,2-benzenedisulfonamide, cyclohexafluoropropane-1,3-bis(sulfonyl)imide, 4-methyl-N-[(4-methylphenyl)sulfonyl]benzenesulfonamide, dibenzenesulfonamide, trifluoromethanesulfonanilide, N-[(4-methylphenyl)sulfonyl]acetamide, benzenesulfonanilide, and N,N'-diphenylsulfamide.

[0074] Examples of the coordination compounds mentioned above include those comprising at least one central atom selected from the group consisting of boron, aluminum, and silicon, to which a carboxylic acid, an acid having a carbonyloxy bond, or a phenolic compound is bonded. Specific examples of coordination compounds include borodisalicylic acid, borodisuoic acid, borodiglycolic acid, borodigallic acid, borodicatechol, and borodipyrogallol.

[0075] The electrolyte may contain one type of acid component, or a combination of two or more types.

[0076] In the electrolyte, the acidic groups of the acidic component (carboxyl groups, sulfonic acid groups, phosphate groups, phosphonic acid groups, phenolic hydroxyl groups, etc.) may exist in any of the following forms: free form, salt form, anionic form, or form interacting with (compounding with) the conductive polymer. Each acidic group of the acidic component encompasses all of these forms.

[0077] Examples of basic components include ammonia, amines (specifically, primary amines, secondary amines, and tertiary amines), quaternary ammonium compounds, and amidinium compounds. The electrolyte may contain one of these basic components or a combination of two or more.

[0078] The amine may be aliphatic, aromatic, or heterocyclic. Examples of amines include dialkylamines (such as diethylamine), trialkylamines (such as trimethylamine, ethyldimethylamine, triethylamine (TEA), tri-n-butylamine (TBA), and dimethyl-n-octylamine (DMOA)), alkylenediamines (such as ethylenediamine), aromatic amines (such as aniline), and heterocyclic amines (such as pyrrolidine, imidazole compounds (such as imidazole (Imd), 1,2,3,4-tetramethylimidazolinium), pyridine (Pyr), 4-dimethylaminopyridine, and diazabicycloundecene (DBU)). Both aromatic amines and heterocyclic amines may be monocyclic or polycyclic (such as fused rings or cross-linked rings). Examples of quaternary ammonium compounds include amidine compounds (including imidazole compounds).

[0079] The electrolyte may contain basic components in free form, in cation form, or in salt form. All of these forms are sometimes collectively referred to as basic components.

[0080] From the viewpoint of suppressing dopant dedoping from conductive polymers (degradation of solid electrolytes), it is preferable that the liquid component contains more acidic components than basic components. Furthermore, since the acidic components contribute to the film repair function of the liquid component, it is also preferable that the liquid component contains more acidic components than basic components. The molar ratio of acidic components to basic components (acidic component / basic component) is, for example, 1.1 or higher. From the viewpoint of suppressing dopant dedoping from conductive polymers, the pH of the liquid component may be 7 or lower, 2 or higher, or 6 or lower.

[0081] (Other) Electrolytic capacitors may be wound type, chip type, or multilayer type. Electrolytic capacitors have at least one capacitor element. Electrolytic capacitors may have multiple capacitor elements. For example, an electrolytic capacitor may have a multilayer structure of two or more capacitor elements, or it may have two or more wound type capacitor elements. The configuration or number of capacitor elements may be selected depending on the type or application of the electrolytic capacitor.

[0082] An electrolytic capacitor comprises, for example, a capacitor element and an outer casing or case that houses the capacitor element. The capacitor element may be sealed with a resin outer casing or the like. If the electrolytic capacitor contains a liquid component, the capacitor element and the liquid component are housed in the case, and the opening of the case is sealed with a sealing member or the like. One end of the anode lead and the cathode lead of the capacitor element are electrically connected to the anode foil and cathode foil, respectively, with the other end extending outside the outer casing or case. The other end of each lead exposed from the outer casing or case is used for soldering to a substrate on which the electrolytic capacitor is to be mounted.

[0083] [Method for Manufacturing Electrolytic Capacitors] An electrolytic capacitor can be manufactured by a manufacturing method comprising, for example, a first step of preparing an anode foil having a dielectric layer, a second step of obtaining an element precursor, a third step of applying a processing solution containing a silane coupling agent to the element precursor under reduced pressure after the second step, and a fourth step of forming a capacitor element by attaching a conductive polymer to the element precursor after the third step. The capacitor element comprises, as described above, an anode foil having a porous portion at least on its surface and a dielectric layer on its surface, a cathode foil having a conductive coating layer on its surface, and a separator made of a conductive polymer and synthetic resin interposed between the anode foil and the cathode foil. The anode foil has a plurality of tunnel-shaped pits in its porous portion, and the dielectric layer is provided on the surface of the anode foil, including the inner surfaces of the plurality of tunnel-shaped pits. The following describes each step of the manufacturing method in more detail. For each component of the electrolytic capacitor, refer to the above description of the electrolytic capacitor.

[0084] (First step) In the first step, an anode foil having a porous portion at least on its surface is formed by etching a metal foil containing a valve metal (substep (1-1)). The etching process may be carried out by AC etching (AC electrolysis), but it is preferable to carry out at least by DC etching (DC electrolysis). When etching is carried out by DC etching, a porous portion having multiple tunnel-shaped pits is easily formed. The etching conditions are determined according to the thickness of the anode foil, the thickness of the porous portion, etc.

[0085] After substep (1-1), a dielectric layer is formed on the surface of the anode foil (substep (1-2)). The dielectric layer is formed, for example, by a chemical conversion treatment. The chemical conversion treatment may be carried out, for example, by immersing the anode foil in a chemical conversion solution and anodic oxidizing the surface of the anode foil. As the chemical conversion solution, for example, a solution containing an acid (such as phosphoric acid or adipic acid) may be used. The oxide film may be formed using a gas-phase method, or by heating the anode foil in an oxygen-containing atmosphere and oxidizing the surface.

[0086] In this way, an anode foil is obtained that has a porous portion at least on its surface and a dielectric layer on its surface. In such an anode foil, the dielectric layer is formed on the surface of the anode foil, including the inner surfaces of the multiple tunnel-shaped pits.

[0087] (Second step) The device precursor is formed by stacking an anode foil having a dielectric layer obtained in the first step and a cathode foil having a coating layer, with a separator in between.

[0088] The cathode foil having a coating layer may be obtained by forming a conductive coating layer on the surface of a metal foil prior to the second step, or a commercially available product may be used.

[0089] The device precursor may be, for example, a wound body in which an anode foil having a dielectric layer and a cathode foil having a coating layer are wound with a separator in between. Even when a wound body is used, according to this disclosure, the inner surface of the deepest part of the tunnel-shaped pit of the anode foil having the dielectric layer can be coated with a silane coupling agent. Alternatively, the device precursor may be a laminate in which an anode foil having a dielectric layer and a cathode foil having a coating layer are stacked with a separator in between. In the laminate, the anode foil and cathode foil may be stacked alternately with a separator in between. The cathode foil is stacked with the anode foil such that the coating layer faces the anode foil. The form of the device precursor is selected according to the type of electrolytic capacitor.

[0090] (Third step) In the third step, a silane coupling agent is applied to the device precursor. More specifically, under reduced pressure, a processing solution containing the silane coupling agent is applied to the device precursor obtained in the second step (substep (3-1)). This allows the processing solution to penetrate into the interior of the multiple tunnel-shaped pits. As a result, in at least a portion of the multiple tunnel-shaped pits, the inner surface of at least the deeper part of the tunnel-shaped pit can be coated with the silane coupling agent.

[0091] The treatment solution may consist solely of a silane coupling agent, or it may contain a silane coupling agent and a solvent. Examples of solvents include organic solvents and water. The treatment solution may contain one solvent or two or more solvents.

[0092] The concentration of the silane coupling agent in the treatment solution is preferably 0.1% by mass or more and 5.0% by mass or less, and more preferably 0.5% by mass or more and 3.0% by mass or less. When the concentration is within this range, the treatment solution easily penetrates into the tunnel-shaped pit, and the inner surface of the deeper parts is easily coated with the silane coupling agent.

[0093] The third step preferably includes a substep (3-2) for cleaning the element precursor after substep (3-1). Substep (3-2) removes the silane coupling agent from the opening side (mainly the shallow part) of the tunnel-shaped pit, resulting in the silane coupling agent being concentrated in the deeper part.

[0094] Cleaning can be carried out using, for example, water, organic solvents, and mixtures thereof. The cleaning solvent can be selected according to the type of silane coupling agent. The degree of uneven distribution of the silane coupling agent in the tunnel-shaped pit can be adjusted by the type of silane coupling agent, the cleaning solvent, the cleaning time, etc.

[0095] From the viewpoint of environmental and working conditions, cleaning is preferably performed by washing with water. The cleaning time is preferably 10 seconds to 1 hour, more preferably 30 seconds to 30 minutes, and even more preferably 1 minute to 15 minutes. When the cleaning time is within this range, higher capacity and lower ESR can be obtained while ensuring high voltage resistance.

[0096] After substep (3-1) and before substep (3-2), a drying treatment may be performed as needed. From the viewpoint of easily removing the silane coupling agent from the shallow parts, it is preferable to perform substep (3-2) immediately after substep (3-1) without performing a drying treatment.

[0097] Following substep (3-2), a drying treatment is performed. The drying temperature and drying time are selected according to, for example, the type of silane coupling agent and the type of solvent in the treatment solution. Drying may be carried out under atmospheric pressure or under reduced pressure. Drying may be carried out in the atmosphere of air or in an inert gas atmosphere (nitrogen gas, argon gas, etc.). For example, the drying temperature may be 110°C to 170°C, or 130°C to 160°C. The drying time may be, for example, 5 minutes to 24 hours, or 5 minutes to 10 hours (or 2 hours or less).

[0098] (Fourth step) After the third step, a conductive polymer is attached to the element precursor (specifically, the element precursor to which the silane coupling agent is attached) to form a capacitor element.

[0099] The conductive polymer may be formed, for example, by in-situ polymerization of a conjugated polymer precursor on a dielectric layer or on a dielectric layer to which a silane coupling agent has been applied, in the presence of a dopant. In in-situ polymerization, at least one of chemical polymerization and electrolytic polymerization can be used. For example, the conductive polymer is formed by immersing the device precursor obtained in the third step in a polymerization solution containing the conjugated polymer precursor, a dopant, and optionally an oxidizing agent, and polymerizing the precursor. As the oxidizing agent, for example, a known oxidizing agent can be used.

[0100] Alternatively, a conductive polymer (for example, a layer of conductive polymer) may be formed by bringing a processing solution containing a conductive polymer into contact with a dielectric layer or a dielectric layer to which a silane coupling agent has been applied. More specifically, a capacitor element can be formed by immersing the element precursor obtained in the third step in a processing solution containing a conductive polymer to adhere the conductive polymer to the element precursor. Examples of processing solutions include a solution in which a conductive polymer is dissolved and a dispersion in which a conductive polymer is dispersed. The conductive polymer used in these processing solutions can be obtained by polymerizing a conjugated polymer precursor in the presence of a dopant. Immersion in the processing solution may be performed once or multiple times. After immersing the element precursor in the processing solution, a drying treatment may be performed. Immersion in the processing solution and drying may be repeated.

[0101] Examples of precursors for conjugated polymers include the raw material monomers for the conjugated polymer, oligomers and prepolymers formed by linking multiple molecular chains of the raw material monomers. A single precursor may be used, or two or more precursors may be used in combination.

[0102] (Other) In the capacitor element, at an appropriate stage, one end of the cathode lead is electrically connected to the cathode foil, and one end of the anode lead is electrically connected to the anode foil. For example, an electrolytic capacitor can be obtained by housing the capacitor element with the connected leads and, if necessary, a liquid component in a case, and sealing the opening of the case with a sealing member. Alternatively, an electrolytic capacitor can be formed by sealing the capacitor element with the connected leads in a resin casing with the other ends of the leads extended. Each lead may be a lead wire or a lead frame.

[0103] Figure 1 is a schematic cross-sectional view of an electrolytic capacitor according to one embodiment of the present disclosure, and Figure 2 is a schematic diagram showing a part of the capacitor element relating to the electrolytic capacitor unfolded. However, the electrolytic capacitor of the present disclosure is not limited to the following embodiments. Furthermore, the components of the following embodiments may be arbitrarily combined with at least one of the above technologies (1) to (10) relating to the electrolytic capacitor of the present disclosure, or at least one of the above technologies (1) to (10) and the components described above.

[0104] The electrolytic capacitor 200 comprises, for example, a capacitor element 100, a bottomed case 211, a sealing member 212 that closes the opening of the bottomed case 211, a base plate 213 that covers the sealing member 212, lead wires 60A, 60B, and lead tabs 50A, 50B. The bottomed case 211 houses the capacitor element 100 and, if necessary, an electrolyte (not shown). The area near the opening end of the bottomed case 211 is tapered inward, and the opening end is curled so as to be crimped to the sealing member 212. The lead wires 60A, 60B are led out from the sealing member 212 and pass through the base plate 213. The lead tabs 50A, 50B connect the lead wires 60A, 60B to the electrodes of the capacitor element 100, respectively.

[0105] The capacitor element 100 is, for example, a wound body as shown in Figure 2. The wound body comprises an anode foil 10 connected to a lead tab 50A, a cathode foil 20 connected to a lead tab 50B, and a separator 30. The anode foil 10 and the cathode foil 20 are wound around the separator 30. The outermost circumference of the wound body is secured by a winding stopper tape 40. Note that Figure 2 shows the state in which a portion of the wound body is unfolded before securing the outermost circumference.

[0106] In the capacitor element 100, a dielectric layer (not shown) is formed on at least a portion of the surface of the anode foil 10. A separator 30 and a conductive polymer (not shown) are interposed between the anode foil 10 and the cathode foil 20. The conductive polymer is in contact with at least a portion of the dielectric layer. The conductive polymer is also in contact with at least a portion of the cathode foil 20. If the electrolytic capacitor 200 contains a liquid component, the liquid component is impregnated into the conductive polymer and the separator.

[0107] [Examples] The electrolytic capacitor and its manufacturing method according to the present disclosure will be described in detail below based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0108] 《Electrolytic Capacitors E1 to E4》 (A) Manufacturing of Electrolytic Capacitors Following the procedure below, wound electrolytic capacitors with a rated voltage of 250V, a diameter of 10.0 mm, and a length of 12.6 mm were manufactured.

[0109] (1) An aluminum foil (120 μm thick) that had undergone the first step of DC etching was prepared. The average etching depth was 45 μm per side. This average etching depth corresponds to the average thickness of the porous region formed on both surfaces of the aluminum foil. Observation by SEM revealed that numerous tunnel-shaped pits were formed in the porous region. The above average etching depth corresponds to the average depth D of the tunnel-shaped pits. The most frequent pore size of the tunnel-shaped pits was determined to be 420 nm from the volume-based pore size distribution using a mercury porosimeter.

[0110] A dielectric layer was formed by performing a chemical conversion treatment on the surface of the aluminum foil having the porous portion described above.

[0111] (2) Second Step An anode lead tab was attached to the anode foil obtained in the first step. A cathode lead tab was attached to the cathode foil. These anode foils and cathode foils were wound together via a separator to produce a winding element precursor. As the cathode foil, aluminum foil (thickness 40 μm) with titanium coating on both surfaces was used. The thickness of the titanium coating layer was 1.00 μm to 3.00 μm. As the separator, a nonwoven fabric of polyester fibers (density 0.4 g / cm³) was used. ３ A thickness of 60 μm was used.

[0112] (3) Step 3 The coiled body obtained in Step 2 was immersed in an aqueous solution containing a silane coupling agent at a concentration of 2.0% by mass, and the aqueous solution was impregnated into the coiled body under a reduced pressure atmosphere (40 kPa). 3-Glycidoxypropyltrimethoxysilane was used as the silane coupling agent.

[0113] The coiled material was removed from the aqueous solution and washed with water for the time shown in Table 1, if necessary. Then, it was dried at 150°C for 20 minutes.

[0114] (4) Fourth step A mixed solution was prepared by dissolving 3,4-ethylenedioxythiophene and poly(4-styrenesulfonic acid) (PSS, mass average molecular weight Mw 100,000, dopant) in deionized water. Next, while stirring the mixed solution, an oxidizing agent (ferrous sulfate (III) and ammonium persulfate) dissolved in deionized water was added to the mixed solution to carry out a polymerization reaction. After the polymerization reaction, the resulting reaction solution was dialyzed to remove unreacted monomers and excess oxidizing agent. As a result, poly(3,4-ethylenedioxythiophene) (PEDOT / PSS) doped with PSS was obtained as a polymer dispersion.

[0115] A coiled body was immersed in a polymer dispersion for 5 minutes in a reduced-pressure atmosphere (40 kPa), and then the coiled body was removed from the polymer dispersion. Next, the coiled body impregnated with the polymer dispersion was dried in a drying oven at 150°C for 20 minutes to deposit a conductive polymer inside the coiled body. In this way, a capacitor element was obtained.

[0116] (5) Assembly of electrolytic capacitors An electrolyte (liquid component) was prepared containing polyethylene glycol (PEG), sulfolane (SL), and 2-butyloctanedioate diethylamine (2BA) in a ratio of PEG:SL:2BA = 45:40:15.

[0117] The capacitor element was immersed in an electrolyte solution for 5 minutes under reduced pressure (40 kPa). This allowed the electrolyte solution to penetrate the capacitor element.

[0118] A total of 40 electrolytic capacitors, as shown in Figure 1, were fabricated by housing capacitor elements impregnated with electrolyte in a bottomed case and sealing the opening of the case with a sealing member. Subsequently, an aging process was performed at 95°C for 90 minutes while applying voltage. An elastic material containing butyl rubber was used as the sealing member.

[0119] (B) Evaluation (1) Initial Capacitance (Cap) and ESR For 20 electrolytic capacitors that had undergone aging treatment, the initial capacitance (in μF) was measured at a temperature of 20°C and a frequency of 120 Hz, and the ESR was measured at a frequency of 100 kHz. The average initial capacitance (Cap) and the average initial ESR were obtained by arithmetic mean of each measurement. Capacitance and ESR were measured using an LCR meter.

[0120] (2) Dielectric Strength (Breakdown Dielectric Strength) Of the electrolytic capacitors that underwent aging treatment, the dielectric strength was evaluated for the remaining 20 capacitors whose initial capacitance and ESR were measured. Specifically, voltage was applied to the electrolytic capacitors at a rate of 1.0 V / sec while boosting the voltage in an environment of 20°C, and the breakdown dielectric strength (BDV) (unit: V) at which an overcurrent of 0.5 A flows was measured.

[0121] Electrolytic capacitor C1 was manufactured and evaluated in the same manner as electrolytic capacitor E1, except that the third step was omitted.

[0122] 《Electrolytic Capacitor C2》 Separator: Paper separator (natural cellulose fiber nonwoven fabric, density 0.4 g / cm³) ３A material with a thickness of 60 μm was used. Otherwise, electrolytic capacitor C2 was fabricated and evaluated in the same manner as electrolytic capacitor E1.

[0123] 《Electrolytic Capacitor C3》 An aluminum etched foil (40 μm thick) was immersed in an adipic acid aqueous solution, and a voltage of 10 V was applied to form a chemical conversion film on the surface, thereby forming a cathode foil. Electrolytic capacitor C3 was fabricated and evaluated in the same manner as electrolytic capacitor E1, except that the resulting cathode foil was used.

[0124] The results are shown in Table 1. Electrolytic capacitors E1 to E4 are examples, and electrolytic capacitors C1 to C3 are comparative examples.

[0125]

[0126] As shown in Table 1, the withstand voltage was significantly improved in the examples compared to the comparative examples. In addition, relatively high capacitance and low ESR were obtained in the examples. In Examples 2 and 3, where water washing was performed after treatment with the silane coupling agent, relatively high withstand voltage was maintained, and higher capacitance and lower ESR were obtained compared to Example 1, where water washing was not performed. This is thought to be because in Examples 2 and 3, water washing removed the silane coupling agent from the shallow parts of the tunnel-shaped pits. In Comparative Examples 2 and 3, the ESR is thought to have increased compared to the examples because the silane coupling agent bonded to the cathode foil and separator. In addition, the withstand voltage was lower in Comparative Examples 2 and 3 compared to the examples. This is thought to be because in Comparative Examples 2 and 3, the silane coupling agent bonded to the cathode foil and separator, relatively reducing the proportion of silane coupling agent adhering to the pits of the anode foil.

[0127] Although the present invention has been described in relation to preferred embodiments at present, such disclosure should not be interpreted restrictively. Various modifications and alterations will undoubtedly become apparent to those skilled in the art in the field to which the invention pertains by reading the above disclosure. Accordingly, the appended claims should be interpreted as encompassing all modifications and alterations without departing from the true spirit and scope of the invention.

[0128] The electrolytic capacitors disclosed herein are suitable for applications requiring high voltage resistance. These electrolytic capacitors can also be used as hybrid electrolytic capacitors. However, the applications of electrolytic capacitors are not limited to these.

[0129] 200: Electrolytic capacitor 211: Bottomed case 212: Sealing material 213: Base plate 50A, 50B: Lead tab 60A, 60B: Lead wire 100: Capacitor element 10: Anode foil 20: Cathode foil 30: Separator 40: Winding tape

Claims

1. An electrolytic capacitor comprising a capacitor element, wherein the capacitor element comprises: an anode foil having a porous portion at least on its surface and a dielectric layer on its surface; a cathode foil having a conductive coating layer on its surface; and a separator made of a conductive polymer and synthetic resin interposed between the anode foil and the cathode foil, wherein the anode foil has a plurality of tunnel-shaped pits in the porous portion, and the dielectric layer is provided on the surface of the anode foil including the inner surfaces of the plurality of tunnel-shaped pits, and at least the deep portion of the plurality of tunnel-shaped pits is coated with a silane coupling agent.

2. The electrolytic capacitor according to claim 1, wherein the plurality of tunnel-shaped pits have an average depth D, the plurality of tunnel-shaped pits are divided into a shallow portion from the entrance of the tunnel-shaped pit to the average depth D / 2, and a deep portion from the deepest part of the tunnel-shaped pit to the average depth D / 2, and the silane coupling agent is unevenly distributed in the deep portion.

3. The electrolytic capacitor according to claim 2, wherein the average ratio of the silicon content Rs in the shallow part to the silicon content Rd in the deep part (= Rs / Rd) is 0 or more and 0.6 or less.

4. The electrolytic capacitor according to any one of claims 1 to 3, wherein the cathode foil comprises at least one selected from the group consisting of conductive carbon and titanium.

5. The electrolytic capacitor according to any one of claims 1 to 3, wherein the separator is a nonwoven fabric formed of synthetic resin fibers.

6. The electrolytic capacitor according to claim 5, wherein the synthetic resin fiber is at least one selected from the group consisting of aramid fibers and polyester fibers.

7. An electrolytic capacitor according to any one of claims 1 to 3, further comprising a liquid component.

8. A method for manufacturing an electrolytic capacitor including a capacitor element, wherein the capacitor element comprises: an anode foil having a porous portion on at least its surface and a dielectric layer on its surface; a cathode foil having a conductive coating layer on its surface; and a separator made of a conductive polymer and synthetic resin interposed between the anode foil and the cathode foil, wherein the anode foil has a plurality of tunnel-shaped pits in the porous portion and the dielectric layer is provided on the surface of the anode foil including the inner surfaces of the plurality of tunnel-shaped pits, and the manufacturing method comprises: a first step of preparing the anode foil having the dielectric layer; a second step of stacking the anode foil having the dielectric layer and the cathode foil via the separator to obtain an element precursor; and a third step, after the second step, applying a processing solution containing a silane coupling agent to the element precursor under reduced pressure to coat at least the inner surface of the deepest part of the plurality of tunnel-shaped pits with the silane coupling agent in at least a portion of the tunnel-shaped pits. A method for manufacturing an electrolytic capacitor, comprising: a fourth step of attaching the conductive polymer to the element precursor after the third step to form the capacitor element; 9. The method for manufacturing an electrolytic capacitor according to claim 8, wherein the third step comprises a substep (3-1) of applying the processing liquid to the element precursor under reduced pressure, and a substep (3-2) of washing the element precursor after the substep (3-1).

10. The method for manufacturing an electrolytic capacitor according to claim 8 or 9, wherein in the second step, the element precursor is a wound body obtained by winding the anode foil and the cathode foil, which have the dielectric layer, with the separator in between.

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