Electrolytic capacitor

Abstract

This electrolytic capacitor contains a positive electrode body with a porous section, a dielectric layer formed on at least a part of the surface of the porous section, and a solid electrolyte layer that covers at least a part of the dielectric layer. The solid electrolyte layer contains a first electroconductive polymer that includes units of a first monomer. The first monomer is at least one selected from the group consisting of compounds represented by formula (I). In formula (I), m is an integer from 0 to 10, X is O or S, and R1 is a linear or branched alkyl group.

Description

electrolytic capacitor CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This disclosure claims the benefit of priority to Japanese Patent Application No. 2024-051299, filed on March 27, 2024, in the Japan Patent Office, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates to electrolytic capacitors.

[0003] As a method for forming a solid electrolyte layer of an electrolytic capacitor, a method of polymerizing a monomer on the surface of a dielectric layer has been proposed.

[0004] Patent Document 1 discloses a solid electrolytic capacitor characterized in that "a capacitor element has an anode made of a porous body of a valve metal selected from tantalum, niobium, and aluminum, and a dielectric layer made of an oxide film of the valve metal, the capacitor element being formed with a monomer mixture of 2,3-dihydro-thieno[3,4-b][1,4]dioxine and 2-alkyl-2,3-dihydro-thieno[3,4-b][1,4]dioxine in a molar ratio of 0.05:1 to 1:0.1 in the presence of an organic sulfonic acid, to form a layer of a conductive polymer containing the organic sulfonic acid as a dopant, and the conductive polymer is used as a solid electrolyte."

[0005] Patent No. 5093915

[0006] Currently, there is a demand for improved reliability in electrolytic capacitors (e.g., reduced leakage current, improved voltage resistance, etc.) In this situation, one of the objects of the present disclosure is to provide an electrolytic capacitor with improved characteristics.

[0007] One aspect of the present disclosure provides an anode body including a porous portion; a dielectric layer formed on at least a portion of the surface of the porous portion; and a solid electrolyte layer covering at least a portion of the dielectric layer, wherein the solid electrolyte layer includes a first conductive polymer including a unit of a first monomer, and the first monomer is represented by the following formula (I):

[0008]

[0009] wherein in formula (I), m is an integer of 0 to 10, X is O or S, and R1 is a linear or branched alkyl group.

[0010] According to the present disclosure, an electrolytic capacitor with excellent characteristics can be obtained.

[0011] It is a cross-sectional view that shows typically the electrolytic capacitor according to the embodiment 1. It is a cross-sectional view that shows typically a part of the electrolytic capacitor shown in FIG.

[0012] The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

[0013] Below, embodiments according to the present disclosure will be described 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 exemplified, but other numerical values ​​and other materials may be applied as long as the invention according to the present disclosure can be implemented. In this specification, the expression "numerical value A to numerical value B" includes numerical value A and numerical value B and can be read as "numerical value A or more and numerical value B or less." In the following description, when lower and upper limits of numerical values ​​related to specific physical properties or conditions are exemplified, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit is not equal to or greater than the upper limit.

[0014] An electrolytic capacitor according to one embodiment of the present disclosure (hereinafter also referred to as "capacitor (C)") includes an anode body having a porous portion, a dielectric layer formed on at least a portion of the surface of the porous portion, and a solid electrolyte layer covering at least a portion of the dielectric layer. An electrolytic capacitor including a solid electrolyte layer may also be referred to as a "solid electrolytic capacitor." Note that "capacitor" may also be read as "capacitor."

[0015] The porous portion is provided in at least a surface layer portion of the anode body. The entire anode body may be a porous portion. The capacitor (C) may have an anode wire having an embedded portion embedded in the anode body and a protruding portion protruding outside the anode body.

[0016] Hereinafter, the smallest unit of an electrolytic capacitor including an anode body, a dielectric layer, and a solid electrolyte layer may be referred to as a “capacitor element.” The term “capacitor (C)” is a concept that encompasses both electrolytic capacitors and capacitor elements.

[0017] An electrolytic capacitor (or capacitor element) is divided into an anode portion and a cathode portion. The anode body constitutes the anode portion. The solid electrolyte layer constitutes the cathode portion. The anode portion and the cathode portion are insulated by a dielectric layer. The cathode portion includes at least the solid electrolyte layer and may also include a cathode extraction layer.

[0018] The anode section includes an anode body and may further include an anode wire. The anode body may be a porous sintered body or a metal foil with a porous surface.

[0019] The dielectric layer is formed on at least a portion of the surface of the anode body. The dielectric layer is formed, for example, by subjecting the anode body to a chemical conversion treatment and growing an oxide film on the surface of the anode body. In the chemical conversion treatment, the surface of the anode body may be anodized by immersing the anode body in a chemical conversion solution. The oxide film may also be formed using a gas phase method such as atomic layer deposition (ALD). The surface of the anode body may also be oxidized by heating the anode body in an oxygen-containing atmosphere.

[0020] The solid electrolyte layer is disposed between a dielectric layer formed on the surface of the anode body and a cathode extraction layer. Here, the solid electrolyte layer includes a first conductive polymer including a unit of a first monomer. Note that the "unit" in "unit of the first monomer" refers to the smallest unit of a structural portion derived from the first monomer in the polymer. Hereinafter, the "unit" of a monomer in a polymer is defined in the same sense regardless of the type of polymer and the type of monomer.

[0021] The first monomer has the following formula (I):

[0022]

[0023] wherein, in formula (I), m is an integer of 0 to 10, X is O (oxygen atom) or S (sulfur atom), and R1 is a linear or branched alkyl group. The compound represented by formula (I) is also a derivative of 3,4-ethylenedioxythiophene. Hereinafter, "3,4-ethylenedioxythiophene" may be abbreviated as "EDOT."

[0024] When the first conductive polymer contained in the solid electrolyte layer contains units of the first monomer, the characteristics of the electrolytic capacitor are improved. In particular, the leakage current of the electrolytic capacitor is significantly reduced, and the withstand voltage characteristics are significantly improved. This improvement in characteristics is likely due to the fact that the units of the first monomer improve the orientation of the first conductive polymer, thereby improving the film quality of the solid electrolyte layer. Furthermore, it is thought that a change in the orientation of the first conductive polymer makes it more difficult for current to flow between the electrodes. Because atom X of the first monomer has electron-donating properties, there is a possibility that an interaction occurs between the thiophene skeleton of one molecule and atom X of another molecule.

[0025] In the first conductive polymer, only one type of first monomer may be used alone, or multiple types of first monomers may be combined. The units of the first monomer may constitute the entirety of the units constituting the first conductive polymer. The units of the first monomer may constitute, for example, 1 mol % or more, 10 mol % or more, or 20 mol % or more of the units constituting the first conductive polymer. The units of the first monomer may constitute, for example, 99 mol % or less, 90 mol % or less, or 80 mol % or less of the units constituting the first conductive polymer.

[0026] In formula (I), m is preferably an integer of 1 or greater; for example, m may be an integer of 1 to 5, or may be an integer of 1 to 3. For example, when X is O (oxygen atom), the first monomer is preferably an alkoxyalkyl-EDOT, and when X is S (sulfur atom), the first monomer is preferably an alkylthioalkyl-EDOT. It is believed that the structural stability of the first monomer unit is enhanced by the atom X being bonded to the carbon atom of the ethylene group via an alkylene group.

[0027] In formula (I), X is preferably O (oxygen atom) in terms of ease of synthesis.

[0028] In formula (I), R1 may have 1 to 10 carbon atoms, or may be an alkyl group having 1 to 6 carbon atoms. When R1 has 5 or more carbon atoms, the withstand voltage characteristics of the electrolytic capacitor are particularly likely to be improved.

[0029] For example, in formula (I), when m=1 and X=O (oxygen atom), the first monomer is represented by the following formula (II):

[0030]

[0031] The first monomer is alkoxymethyl-3,4-ethylenedioxythiophene (alkoxymethyl-EDOT) represented by the formula (I). That is, the first monomer may contain at least one selected from the group consisting of alkoxymethyl-EDOT. 50 mol % or more of the first monomer may be alkoxymethyl-EDOT, or 70 mol % or more of the first monomer may be alkoxymethyl-EDOT.

[0032] R1 in formula (II) is defined the same as R1 in formula (I) and is a linear or branched alkyl group, and the number of carbon atoms in such an alkyl group may be 1 to 10 or 1 to 6. That is, the first monomer may be an alkoxymethyl-EDOT in which R1 has 1 to 6 carbon atoms (more specifically, at least one selected from the group of alkoxymethyl-EDOT in which R1 has 1 to 6 carbon atoms). 50 mol % or more of the first monomer may be an alkoxymethyl-EDOT in which R1 has 1 to 6 carbon atoms, or 70 mol % or more of the first monomer may be an alkoxymethyl-EDOT in which R1 has 1 to 6 carbon atoms.

[0033] Specific preferred examples of the first monomer include, but are not limited to, methoxymethyl-EDOT in which R1 in formula (II) is a methyl group, ethoxymethyl-EDOT in which R1 in formula (II) is an ethyl group, butoxymethyl-EDOT in which R1 in formula (II) is a butyl group, and hexoxymethyl-EDOT in which R1 in formula (II) is a hexyl group. However, it is more preferable that the first monomer in these preferred specific examples accounts for 50 mol % or more, and even more preferably 70 mol % or more, of the first monomer.

[0034] The first conductive polymer may further include a unit of a second monomer. The first conductive polymer may be a copolymer of the first monomer and the second monomer, or a mixture of a polymer containing the first monomer and a polymer containing the second monomer. The first conductive polymer may be a copolymer of the first monomer and the second monomer, and a mixture of at least one of a polymer containing the first monomer and a polymer containing the second monomer.

[0035] The second monomer may be, for example, a compound represented by the following formula (III):

[0036]

[0037] and 3,4-ethylenedioxythiophene (EDOT) represented by the following formula (IV):

[0038]

[0039] The EDOT and alkyl-EDOT have a chemical structure suitable for forming a copolymer or a polymer mixture with the first monomer.

[0040] R2 in formula (IV) may be, for example, an alkyl group having 1 to 10 carbon atoms, but is preferably an alkyl group having 1 to 6 carbon atoms. That is, at least a portion of the alkyl-EDOT may be an alkyl-EDOT in which R2 has 1 to 6 carbon atoms (more specifically, at least one selected from the group of alkyl-EDOTs in which R2 has 1 to 6 carbon atoms). 50 mol % or more of the alkyl-EDOT may be an alkyl-EDOT in which R2 has 1 to 6 carbon atoms, or 70 mol % or more of the alkyl-EDOT may be an alkyl-EDOT in which R2 has 1 to 6 carbon atoms.

[0041] The number of carbon atoms in R2 in formula (IV) may be, for example, in the range of 1 to 4 or in the range of 2 to 4, or may be 2 or 3, or may be 3 or 4.

[0042] The second monomer may contain only EDOT or alkyl-EDOT, or may contain both EDOT and alkyl-EDOT. The alkyl-EDOT may contain multiple types of alkyl-EDOT with different R2.

[0043] The total of the units of the first monomer and the units of the second monomer may constitute, for example, 70 mol % or more, 90 mol % or more, or 95 mol % or more of the units constituting the first conductive polymer, and the total of the units of the first monomer and the units of the second monomer may constitute 100% of the units constituting the first conductive polymer.

[0044] The molar ratio (U1 / U2) of the units of the first monomer (U1) to the units of the second monomer (U2) contained in the first conductive polymer is, for example, in the range of 0.01 to 100, and may be in the range of 0.1 to 10, or in the range of 0.25 to 4, or in the range of 0.3 to 3.5. By using the units of the first monomer (U1) and the units of the second monomer (U2) in such a range in combination, it is possible to improve the capacitance, reduce leakage current, and also improve the withstand voltage characteristics.

[0045] The solid electrolyte layer may include a first solid electrolyte layer and a second solid electrolyte layer covering at least a portion of the first solid electrolyte layer. The first solid electrolyte layer covers at least a portion of the dielectric layer. The second solid electrolyte layer is formed on the first solid electrolyte layer using the first solid electrolyte layer as a base layer. However, a portion of the second solid electrolyte layer may adhere to the surface of the dielectric layer. The first conductive polymer is preferably contained at least in the first solid electrolyte layer. A first conductive polymer containing a unit of the first monomer is considered to have a high affinity with the dielectric layer.

[0046] The first solid electrolyte layer may be formed, for example, by chemical polymerization (in situ polymerization) in which a polymerization liquid containing a first monomer is brought into contact with the dielectric layer and the first monomer is polymerized on the surface of the dielectric layer. The polymerization liquid used in the chemical polymerization may contain, for example, a component that acts as an oxidizing agent and a material that generates a low-molecular-weight dopant (e.g., an organic sulfonic acid metal salt). Therefore, the first solid electrolyte layer may contain a low-molecular-weight dopant. The molecular weight of the low-molecular-weight dopant may be, for example, 500 or less.

[0047] The low molecular weight dopant is a general term for dopants other than polymer dopants, and examples thereof include organic sulfonic acids such as p-toluenesulfonic acid and naphthalenesulfonic acid, and salts and complexes of organic sulfonic acids.

[0048] Specific examples of the first conductive polymer include poly(alkoxyalkyl-EDOT) doped with organic sulfonate anions (low-molecular-weight dopant), a copolymer of EDOT and alkoxyalkyl-EDOT doped with organic sulfonate anions, a copolymer of alkyl-EDOT and alkoxyalkyl-EDOT doped with organic sulfonate anions, a copolymer of alkyl-EDOT, EDOT, and alkyl-EDOT doped with organic sulfonate anions, etc. More specific examples include polymers doped with organic sulfonate anions and containing at least one unit (e.g., ethoxymethyl-EDOT) selected from the group of alkoxymethyl-EDOTs in which R1 has 1 to 6 carbon atoms.

[0049] The first solid electrolyte layer may include a first conductive polymer and a silicon-containing component. The inclusion of the silicon-containing component in the first solid electrolyte layer is thought to further facilitate change in the orientation of the first conductive polymer containing units of the first monomer, thereby further significantly reducing leakage current and further significantly improving withstand voltage characteristics of the electrolytic capacitor.

[0050] The silicon-containing component may be derived from, for example, a silane coupling agent. The silane coupling agent is a silane compound having a hydrolyzable group (e.g., an alkoxy group). The silane compound preferably has an epoxy group or an acrylic group, since this is advantageous for reducing ESR and increasing capacity. As the silane coupling agent, only one type of silane coupling agent may be used, or two or more types of silane coupling agents may be used in combination.

[0051] Examples of silane compounds (silane coupling agents) having an epoxy group include 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane (γ-glycidoxypropyltrimethoxysilane), 3-glycidoxypropylmethyldiethoxysilane, and 3-glycidoxypropyltriethoxysilane.

[0052] Examples of silane compounds (silane coupling agents) having an acrylic group include 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, and 3-acryloxypropyltrimethoxysilane (γ-acryloxypropyltrimethoxysilane).

[0053] Other examples of silane coupling agents 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- dimethyl-butylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane hydrochloride, 3-ureidopropyltriethoxysilane, 3-chloropropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, bis(triethoxysilylpropyl)tetrasulfide, 3-isocyanatopropyltriethoxysilane, and the like.

[0054] The second solid electrolyte layer includes a second conductive polymer. Examples of the second conductive polymer include polypyrrole, polythiophene, polyaniline, and derivatives thereof. The derivative means a polymer having a conductive polymer as a basic skeleton. For example, an example of a polythiophene derivative includes poly(3,4-ethylenedioxythiophene) (hereinafter also referred to as "PEDOT"). These may be used alone or in combination.

[0055] The second conductive polymer is preferably different from the first conductive polymer. The second conductive polymer preferably includes a unit of a third monomer. The third monomer may be the second monomer, for example, 3,4-ethylenedioxythiophene (EDOT). The polymer of EDOT is poly(3,4-ethylenedioxythiophene) (PEDOT).

[0056] The second solid electrolyte layer may contain a polymer dopant. The second solid electrolyte layer is formed on the first solid electrolyte layer using the first solid electrolyte layer as a base layer, making it suitable for use with a polymer dopant. The polymer dopant contributes to further improving the withstand voltage characteristics of the electrolytic capacitor.

[0057] Examples of the polymer dopant include polymers such as polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallylsulfonic acid, polyacrylic sulfonic acid, polymethacrylic sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, aromatic polyester sulfonic acid, and phenolsulfonic acid novolac resin, as well as salts and complexes of these polymers.

[0058] A preferred example of the second conductive polymer is PEDOT doped with polystyrene sulfonate (PSS) anions as a polymer dopant (ie, PEDOT / PSS).

[0059] In the electrolytic capacitor according to the present disclosure, the components other than the solid electrolyte layer are not particularly limited, and components used in known electrolytic capacitors may be applied. These components will be further described below.

[0060] (Anode Body) Valve metals can be used as the material for the anode body. Examples of valve metals that can be used include titanium (Ti), tantalum (Ta), niobium (Nb), aluminum (Al), and alloys containing these. An anode body having a porous portion may be formed by sintering particles of the material (e.g., particles of a valve metal). Alternatively, an anode body having a porous portion may be formed by etching the surface of a metal foil. The dielectric layer formed on the surface of the anode body may be formed by subjecting the surface of the anode body to a chemical conversion treatment. There are no limitations on the method of chemical conversion treatment, and known chemical conversion treatment methods may be applied.

[0061] Capacitors that use a sintered body (e.g., a tantalum sintered body) as an anode body typically do not include a separator. In separator-free capacitors, the gap between the anode body and the cathode extraction layer is narrow, making it particularly important to suppress leakage current. Therefore, it is particularly preferable that the solid electrolyte layer of a separator-free capacitor have the above-described configuration.

[0062] (Anode Wire) When the anode body is a sintered body, the anode portion may include an anode wire. The anode wire may be a wire made of a metal. Examples of materials for the anode wire include the valve metals described above and copper. A portion of the anode wire is embedded in the anode body, and the remaining portion protrudes from the end face of the anode body.

[0063] (Solid Electrolyte Layer) The solid electrolyte layer already described may be applied.

[0064] (Cathode extraction layer) The cathode extraction layer is a conductive layer and is disposed so as to cover at least a portion of the solid electrolyte layer (or the second solid electrolyte layer). The cathode extraction layer may include a carbon layer formed on the solid electrolyte layer and a metal paste layer formed on the carbon layer. The carbon layer may be formed of a conductive carbon material such as graphite and a resin. The metal paste layer may be formed of metal particles (e.g., silver particles) and a resin, for example, a known silver paste.

[0065] (Cathode Lead Terminal and Anode Lead Terminal) The lead terminals (cathode lead terminal and anode lead terminal) are not particularly limited, and known lead terminals may be used. A portion of the cathode lead terminal is electrically connected to the cathode extraction layer. For example, the portion may be connected to the cathode extraction layer via a conductive layer (e.g., a silver paste layer) or the like.

[0066] (Exterior Body) The exterior body is not limited, and a known exterior body may be used. The exterior body may be composed of at least one material selected from the group consisting of a resin composition, a film, and a case. An example exterior body is arranged around the capacitor element so that the capacitor element is not exposed on the surface of the electrolytic capacitor. Furthermore, the example exterior body is arranged so as to cover a portion of the anode lead frame and a portion of the cathode lead frame. The resin composition used as the exterior body may contain a resin (insulating resin) and an insulating filler.

[0067] (Manufacturing Method) Next, an example of a method for manufacturing an electrolytic capacitor will be described. The manufacturing method for an electrolytic capacitor according to this embodiment is a method for manufacturing an electrolytic capacitor including an anode body having a porous portion and a dielectric layer formed on at least a portion of the surface of the porous portion. Hereinafter, this manufacturing method may be referred to as "manufacturing method (M)."

[0068] The manufacturing method (M) includes steps (i) and (ii) in this order. As described below, the manufacturing method (M) including steps (i) and (ii) can form a solid electrolyte layer including a first solid electrolyte layer and a second solid electrolyte layer. The first solid electrolyte layer includes a first conductive polymer including units of a first monomer and may include a silicon-containing component. The use of the first conductive polymer including units of the first monomer reduces leakage current and improves voltage resistance.

[0069] The first solid electrolyte layer is preferably formed by, for example, chemical polymerization (in situ polymerization). In this case, the first solid electrolyte layer can be formed more uniformly on the surface of the intricate porous portion. This allows for a reduction in ESR and an improvement in capacity. Furthermore, by adding a silane compound to the polymerization solution that forms the first solid electrolyte layer and forming the second solid electrolyte layer, the withstand voltage can be increased.

[0070] Steps (i) and (ii) are described below.

[0071] (Step (i)) Step (i) is a step of forming a first solid electrolyte layer covering at least a portion of the dielectric layer. The first solid electrolyte layer includes a first conductive polymer. Step (i) includes a step (ia) of supplying a polymerization liquid (reaction liquid) containing a first monomer and a silane compound to the surface of the dielectric layer, and a step (ib) of polymerizing the first monomer (and other monomers (e.g., second monomers) if any) in the supplied polymerization liquid to form a first conductive polymer, thereby forming the first solid electrolyte layer.

[0072] The polymerization liquid may satisfy the following condition (1): (1) The proportion of the first monomer in the total monomers in the polymerization liquid is 25 mol % or more, or 50 mol % or more, and 90 mol % or less, or 75 mol % or less.

[0073] The polymerization liquid may satisfy the following conditions (2) and / or (3). For example, the polymerization liquid may satisfy both conditions (2) and (3). In these cases, the polymerization liquid may further satisfy condition (1).

[0074] (2) The total proportion of the first monomer and the second monomer in the total monomers in the polymerization liquid is in the range of 80 to 100 mol %, 90 to 100 mol %, or 95 to 100 mol % (for example, 100 mol %).

[0075] (3) In the polymerization liquid, the molar ratio of the first monomer to the second monomer may be in the range of 0.1 to 10, or may be in the range of 0.25 to 4.

[0076] The silane compound may be a silane coupling agent. In the reaction liquid, the value X of (mass of the silane compound) / (total mass of the monomer, mass of the oxidizing agent, and mass of the liquid medium of the polymerization liquid) may be 0.05 or more, 0.10 or more, 0.15 or more, or 0.20 or more, and may be 0.40 or less, 0.30 or less, or 0.20 or less. The value X may be in the range of 0.05 to 0.40, 0.05 to 0.30, or 0.10 to 0.30. By setting the value X in these ranges, a capacitor with low ESR, high withstand voltage, and low leakage current is likely to be obtained.

[0077] The liquid medium (solvent) of the reaction solution is not particularly limited, and any liquid medium that allows polymerization to proceed without problems may be used. The liquid medium may be water, a mixture of water and a non-aqueous solvent, or a non-aqueous solvent. Examples of non-aqueous solvents include organic solvents and ionic liquids. Specific examples of non-aqueous solvents include alcohols such as methanol, ethanol, propanol, butanol, ethylene glycol, and propylene glycol; amides such as formaldehyde, N-methylacetamide, N,N-dimethylformamide, and N-methyl-2-pyrrolidone; esters such as methyl acetate; ethers such as 1,4-dioxane; and ketones such as methyl ethyl ketone.

[0078] Polymerization of the monomer may be carried out by chemical polymerization. When chemical polymerization is carried out, the polymerization solution contains an oxidizing agent. As the oxidizing agent, an oxidizing agent capable of polymerizing the monomer may be used, and a known oxidizing agent may be used. Examples of the oxidizing agent include sulfuric acid, hydrogen peroxide, and organic sulfonic acid metal salts. Examples of metal ions of organic sulfonic acid metal salts include iron (III), copper (II), chromium (VI), cerium (IV), manganese (VII), and zinc (II).

[0079] As the organic metal sulfonate, an aromatic metal sulfonate is preferred, and examples thereof include metal toluenesulfonate, metal naphthalenesulfonate, metal tetralinsulfonate, metal alkylbenzenesulfonate, and metal alkoxybenzenesulfonate. Aromatic metal sulfonates function not only as an oxidizing agent but also as a dopant, eliminating the need for a separate dopant. Furthermore, because aromatic metal sulfonates function excellently as dopants, they can form high-quality conductive polymers. Iron(III) p-toluenesulfonate is particularly preferred, as it produces conductive polymers with excellent conductivity and heat resistance.

[0080] The polymerization liquid may contain other components as necessary. For example, the polymerization liquid may contain a low molecular weight dopant. Examples of the low molecular weight dopant added to the reaction liquid include the low molecular weight dopants already described. The use of a low molecular weight dopant makes it easier for the polymerization liquid to penetrate into the porous portion.

[0081] Step (ia) can be carried out by bringing the dielectric layer on the surface of the anode body into contact with the polymerization liquid. For example, the anode body may be immersed in the polymerization liquid, thereby supplying the polymerization liquid to the surface of the dielectric layer.

[0082] Step (ib) can be carried out by causing a polymerization reaction in a state where the dielectric layer on the surface of the anode body is in contact with the polymerization solution. The polymerization reaction may be caused by leaving the polymerization solution to stand, or a treatment for accelerating the reaction may be carried out. For example, a heat treatment may be carried out. A first solid electrolyte layer is formed by step (ib).

[0083] (Step (ii)) Step (ii) is a step of forming a second solid electrolyte layer covering at least a portion of the first solid electrolyte layer. The second solid electrolyte layer includes a second conductive polymer. The second solid electrolyte layer may include a second conductive polymer and a dopant. The second conductive polymer may be the same as or different from the first conductive polymer. In a preferred example, the first conductive polymer is a copolymer of a first monomer and a second monomer, and the second conductive polymer is a polymer of the second monomer doped with a polymeric dopant. Such a second conductive polymer may be, for example, poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid (PEDOT / PSS).

[0084] Step (ii) may be performed by a known method for forming a solid electrolyte layer of an electrolytic capacitor. Step (ii) may include steps (ii-a) and (ii-b) in this order. Step (ii-a) is a step of applying a dispersion containing a second conductive polymer and a dispersion medium to the first solid electrolyte layer. Step (ii-b) is a step of forming a second solid electrolyte layer by removing at least a portion of the dispersion medium from the applied dispersion.

[0085] Step (ii-a) can be performed by contacting the first solid electrolyte layer formed on the dielectric layer with a dispersion liquid. For example, the first solid electrolyte layer may be immersed in the dispersion liquid, or the dispersion liquid may be applied to the first solid electrolyte layer. In step (ii-b), the method for removing at least a portion of the dispersion medium from the dispersion liquid applied to the first solid electrolyte layer is not limited, and known methods may be used. For example, the dispersion medium may be removed by heating and / or reducing pressure. Note that the formation step including steps (ii-a) and (ii-b) may be repeated multiple times. Repeating this formation step allows the second solid electrolyte layer to be thicker.

[0086] The dispersion medium of the dispersion liquid is not limited, and may be water or a mixture of water and an organic solvent. The dispersion liquid may contain a dopant. The second conductive polymer may be dispersed in the dispersion medium in the form of particles.

[0087] There are no particular limitations on the concentration of the second conductive polymer in the dispersion, and the concentration may be in the range of 0.5 to 5.0 mass % (for example, 1.0 to 3.0 mass %).

[0088] In this manner, a solid electrolyte layer including a first solid electrolyte layer and a second solid electrolyte layer is formed. Thereafter, steps necessary for manufacturing an electrolytic capacitor are performed. These steps are not particularly limited, and known steps for manufacturing electrolytic capacitors may be performed. For example, first, a cathode extraction layer is formed so as to cover at least a portion of the solid electrolyte layer (more specifically, the second solid electrolyte layer). In this manner, a capacitor element is obtained. Next, lead terminals are connected to the capacitor element. For example, an anode lead terminal is electrically connected to the anode body or anode wire, and a cathode lead terminal is electrically connected to the cathode extraction layer. Next, a portion of the lead terminal and the capacitor element are encapsulated in an exterior case. In this manner, a solid electrolytic capacitor is obtained.

[0089] Next, an example of a method for manufacturing an electrolytic capacitor will be specifically described with reference to the drawings. The above description can be applied to the example described below. The example described below can be modified based on the above description. The matters described below may also be applied to the above-described embodiment. In the embodiment described below, components that are not essential to the electrolytic capacitor of the present disclosure may be omitted. Note that, for ease of understanding, the following figures may show shapes that differ from the actual shapes.

[0090] (Embodiment 1) A cross-sectional view of an example of a capacitor (C) of embodiment 1 is shown schematically in Fig. 1. The capacitor (solid electrolytic capacitor) 100 of Fig. 1 includes a capacitor element 110, an outer casing 150, an anode lead terminal 210, and a cathode lead terminal 220. The outer casing 150 is disposed so as to cover a portion of the anode lead terminal 210, a portion of the cathode lead terminal 220, and the capacitor element 110.

[0091] The capacitor element 110 includes an anode portion 111, a dielectric layer 114, and a cathode portion 115. The anode portion 111 includes an anode body 113 and an anode wire 112. The anode body 113 is a porous sintered body in the shape of a rectangular parallelepiped, and a dielectric layer 114 is formed on the surface. A portion of the anode wire 112 protrudes from one end face of the anode body 113 toward the front surface 100f of the electrolytic capacitor 100. The other portion of the anode wire 112 is embedded in the anode body 113.

[0092] Cathode section 115 includes solid electrolyte layer 116 disposed so as to cover at least a portion of dielectric layer 114, and cathode extraction layer 117 formed on solid electrolyte layer 116. Cathode extraction layer 117 includes, for example, a carbon layer formed on solid electrolyte layer 116 and a metal particle layer formed on the carbon layer. The metal particle layer is, for example, a metal paste layer (e.g., a silver paste layer) formed using a metal paste.

[0093] The anode lead terminal 210 includes an anode terminal portion 211 and a wire connection portion 212. The anode terminal portion 211 is exposed on the bottom surface 100b of the electrolytic capacitor 100 (see FIG. 2 ). The wire connection portion 212 is connected to the anode wire 112. The cathode lead terminal 220 includes a cathode terminal portion 221 and a connection portion 222. The cathode terminal portion 221 is exposed on the bottom surface 100b of the electrolytic capacitor 100. The connection portion 222 is electrically connected to the cathode extraction layer 117 (cathode portion 115) by a conductive layer 141.

[0094] FIG. 2 is a schematic enlarged view of the anode body 113, the dielectric layer 114, and the solid electrolyte layer 116. Referring to FIG. 2, the anode body 113 has a porous portion 113a on at least its surface. The dielectric layer 114 is formed on the surface of the porous portion 113a. The solid electrolyte layer 116 includes a first solid electrolyte layer 116a and a second solid electrolyte layer 116b. The first solid electrolyte layer 116a is formed on the dielectric layer 114. The second solid electrolyte layer 116b is formed on the first solid electrolyte layer 116a. That is, the first solid electrolyte layer 116a and the second solid electrolyte layer 116b are stacked in this order on the dielectric layer 114.

[0095] The solid electrolyte layer 116 of the capacitor 100 is formed by the method described above. Specifically, a first solid electrolyte layer 116a is formed in step (i), and a second solid electrolyte layer 116b is formed in step (ii). The first solid electrolyte layer 116a includes a first conductive polymer and may include a silicon-containing component. The second solid electrolyte layer 116b includes a second conductive polymer.

[0096] (Additional Note) The above description discloses the following technology: (Technology 1) An anode body including an anode body having a porous portion, a dielectric layer formed on at least a part of the surface of the porous portion, and a solid electrolyte layer covering at least a part of the dielectric layer, wherein the solid electrolyte layer includes a first conductive polymer including a unit of a first monomer, and the first monomer is represented by the following formula (I):

[0097]

[0098] In the electrolytic capacitor according to the first technique, m is an integer of 1 to 5, X is O, and R1 has 1 to 10 carbon atoms. (Technology 3) The first monomer is at least one selected from the group consisting of compounds represented by the following formula (II):

[0099]

[0100] The electrolytic capacitor according to Technology 1 or 2, wherein the first monomer is at least one selected from the group consisting of alkoxymethyl-3,4-ethylenedioxythiophenes, wherein R1 has 1 to 6 carbon atoms. (Technology 4) The electrolytic capacitor according to any one of Technology 1 to 3, wherein the first monomer is at least one selected from the group consisting of alkoxymethyl-3,4-ethylenedioxythiophenes, wherein R1 has 1 to 6 carbon atoms. (Technology 5) The electrolytic capacitor according to any one of Technology 1 to 4, wherein the first conductive polymer further contains units of a second monomer, and the second monomer contains at least one selected from the group consisting of 3,4-ethylenedioxythiophene and alkyl-3,4-ethylenedioxythiophene. (Technology 6) The electrolytic capacitor according to Technology 5, wherein the molar ratio (U1 / U2) of the units of the first monomer (U1) to the units of the second monomer (U2) contained in the first conductive polymer is in the range of 0.01 to 100. (Technology 7) The electrolytic capacitor according to any one of Techniques 1 to 6, wherein the solid electrolyte layer includes: a first solid electrolyte layer; and a second solid electrolyte layer covering at least a portion of the first solid electrolyte layer, and at least the first solid electrolyte layer includes the first conductive polymer. (Technology 8) The electrolytic capacitor according to Technique 7, wherein the first solid electrolyte layer includes a low-molecular-weight dopant. (Technology 9) The electrolytic capacitor according to Technique 8, wherein the first conductive polymer is doped with an organic sulfonate anion as the low-molecular-weight dopant and includes at least one unit selected from the group consisting of alkoxymethyl-3,4-ethylenedioxythiophenes in which R2 has 1 to 6 carbon atoms. (Technology 10) The electrolytic capacitor according to any one of Techniques 7 to 9, wherein the first solid electrolyte layer includes the first conductive polymer and a silicon-containing component. (Technology 11) The electrolytic capacitor according to Technique 10, wherein the silicon-containing component is derived from a silane coupling agent. (Technology 12) The electrolytic capacitor according to any one of Technologies 7 to 11, wherein the second solid electrolyte layer includes a second conductive polymer different from the first conductive polymer, the second conductive polymer includes units of a third monomer, and the third monomer includes 3,4-ethylenedioxythiophene.(Technology 13) The electrolytic capacitor according to Technology 12, wherein the second solid electrolyte layer contains a polymer dopant. (Technology 14) The electrolytic capacitor according to Technology 13, wherein the second conductive polymer contains poly(3,4-ethylenedioxythiophene) doped with polystyrenesulfonate anions as the polymer dopant.

[0101] EXAMPLES The electrolytic capacitor according to the present disclosure will be described in more detail with reference to examples. In each of the following examples, a plurality of electrolytic capacitors (n=40) were fabricated and evaluated.

[0102] (Capacitors A1 to A7, B1) Each capacitor was fabricated by the following procedure. First, a tantalum sintered body (porous body) with a portion of an anode wire embedded therein was prepared as an anode body. The surface of this tantalum sintered body was anodized to form a dielectric layer containing tantalum oxide on the surface of the anode body.

[0103] <First Solid Electrolyte Layer> Next, a first solid electrolyte layer was formed on the surface of the dielectric layer by chemical polymerization. First, a polymerization solution was prepared. The polymerization solution was prepared by adding ferric p-toluenesulfonate (oxidizer), 3-acryloxypropyltrimethoxysilane (silane compound), and monomers to ethanol (liquid medium) and mixing them.

[0104] Only the first monomer was used in Example 1 (Capacitor A1), only the second monomer was used in Comparative Example 1 (Capacitor B1), and a mixture of the first and second monomers was used in Capacitors A2 to A7 of Examples 2 to 7. The molar fractions of the first and second monomers (U1 / U2) in the polymerization liquid were adjusted to the values ​​shown in Table 1.

[0105] In capacitors A1 to A7 of Examples 1 to 7, the first monomer used was ethoxymethyl-EDOT, which is represented by formula (II) and where R1 is an ethyl group. In capacitor A8 of Example 8, the first monomer used was butoxymethyl-EDOT, which is represented by formula (II) and where R1 is a butyl group. In capacitor A9 of Example 9, the first monomer used was hexoxymethyl-EDOT, which is represented by formula (II) and where R1 is a hexyl group.

[0106] In capacitors A2 to A9 and B1, 3,4-ethylenedioxythiophene (EDOT) was used as the second monomer, and the value X was calculated by dividing the mass of the silane compound by the sum of the mass of the monomer, the mass of the oxidizing agent, and the mass of the liquid medium of the reaction solution.

[0107]

[0108] Next, the tantalum sintered body was immersed in the polymerization liquid for about 3 to 10 seconds. Next, after the tantalum sintered body was pulled out of the polymerization liquid, it was heated at 210°C for 3 minutes to polymerize the monomer. In this way, a first solid electrolyte layer containing a first conductive polymer and a silicon-containing component was formed.

[0109] <Second Solid Electrolyte Layer> In capacitors A1, A2, A4, A6, A8, A9, and B1 of Examples 1, 2, 4, 6, 8, and 9 and Comparative Example 1, a second solid electrolyte layer was formed using a dispersion liquid of a second conductive polymer. Specifically, a tantalum sintered compact was first immersed in the dispersion liquid of the second conductive polymer for approximately 3 to 10 seconds, and then the tantalum sintered compact was pulled out of the dispersion liquid. Next, the tantalum sintered compact pulled out of the dispersion liquid was heated at 180°C for 20 minutes to form a second solid electrolyte layer. PEDOT / PSS was used as the second conductive polymer.

[0110] Next, a cathode extraction layer was formed on the second conductive polymer layer. In this manner, a capacitor element was formed. Next, lead terminals were connected to the capacitor element. Next, a portion of the lead terminal and the capacitor element were sealed with an exterior body. In this manner, electrolytic capacitors (capacitors A1 to A9, B1) were produced.

[0111] The capacitors obtained as described above were subjected to aging treatment for 90 minutes at 120° C. and a rated voltage of 35 V. Next, the capacitors that had undergone the aging treatment were left at room temperature for at least 1 hour, and then the capacitance (Cap), the defect rate of leakage current (LC), and the withstand voltage characteristics were measured by the following methods.

[0112] [Evaluation] (Leakage Current (LC)) For each of the 40 capacitors produced, a voltage of 35 V was applied between the anode lead terminal and the cathode lead terminal, and the leakage current (LC) after 120 seconds was measured and the median value was calculated. Table 1 shows the relative values ​​when the LC value of Sample B1 of Comparative Example 1 was set to 100. The smaller the value, the smaller the leakage current, and the better the performance of the electrolytic capacitor.

[0113] (Capacitance (Cap)) For each of the 40 capacitors produced, the capacitance (Cap) was measured at a frequency of 120 Hz using a four-terminal LCR meter, and the average value was calculated. Table 1 shows the relative values ​​when the Cap value of Sample B1 of Comparative Example 1 is set to 100. The larger the value, the larger the capacitance and the better the performance of the electrolytic capacitor.

[0114] (Voltage Withstanding Characteristics (Vbd)) For each of the 40 capacitors produced, a voltage was applied to the capacitor while increasing the voltage at a rate of 1.0 V / second, and the voltage when an overcurrent of 0.5 A flowed was measured and averaged. Table 1 shows the relative values ​​when the Vbd value of capacitor B1 of Comparative Example 1 is set to 100. The larger the value, the better the voltage withstanding characteristics and the better the performance of the electrolytic capacitor.

[0115] As shown in Table 1, compared to capacitor B1, capacitors A1 to A9 exhibited a significant decrease in LC and a significant improvement in withstand voltage characteristics. In particular, when a copolymer of a first monomer and a second monomer was used as the first conductive polymer, a tendency for the capacitance to improve was observed. The U1 / U2 ratio was particularly excellent in the range of 0.3 to 3.5, for example. Furthermore, in Example 9, in which R1 had 5 or more carbon atoms (6 carbon atoms), the withstand voltage characteristics were particularly significantly improved.

[0116] While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes 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 changes and modifications that do not depart from the true spirit and scope of the invention.

[0117] The electrolytic capacitor according to the present disclosure has low leakage current, high voltage resistance, and high reliability. Such an electrolytic capacitor is suitable for use in connection with electronic circuits, and can suppress malfunctions of the electronic circuits. However, the applications of the electrolytic capacitor are not limited to these.

[0118] 100: Electrolytic capacitor 113: Anode body 113a: Porous portion 114: Dielectric layer 116: Solid electrolyte layer 116a: First solid electrolyte layer 116b: Second solid electrolyte layer

Claims

1. An anode body having a porous portion; a dielectric layer formed on at least a portion of the surface of the porous portion; and a solid electrolyte layer covering at least a portion of the dielectric layer, wherein the solid electrolyte layer includes a first conductive polymer including a unit of a first monomer, and the first monomer is represented by the following formula (I): wherein in formula (I), m is an integer of 0 to 10, X is O or S, and R1 is a linear or branched alkyl group.

2. The electrolytic capacitor according to claim 1, wherein m is an integer of 1 to 5, X is O, and R1 has 1 to 10 carbon atoms.

3. The first monomer has the following formula (II):

2. The electrolytic capacitor according to claim 1, wherein the alkoxymethyl-3,4-ethylenedioxythiophene is at least one selected from the group consisting of alkoxymethyl-3,4-ethylenedioxythiophenes represented by the formula:

4. The electrolytic capacitor according to claim 1, wherein the first monomer is at least one selected from the group consisting of alkoxymethyl-3,4-ethylenedioxythiophenes in which R1 has 1 to 6 carbon atoms.

5. The electrolytic capacitor according to claim 1, wherein the first conductive polymer further comprises units of a second monomer, and the second monomer comprises at least one selected from the group consisting of 3,4-ethylenedioxythiophene and alkyl-3,4-ethylenedioxythiophene.

6. The electrolytic capacitor according to claim 5, wherein the molar ratio (U1 / U2) of the units of the first monomer (U1) to the units of the second monomer (U2) contained in the first conductive polymer is in the range of 0.01 to 100.

7. The electrolytic capacitor according to claim 1, wherein the solid electrolyte layer includes: a first solid electrolyte layer; and a second solid electrolyte layer covering at least a portion of the first solid electrolyte layer, and at least the first solid electrolyte layer includes the first conductive polymer.

8. The electrolytic capacitor of claim 7, wherein the first solid electrolyte layer includes a small molecule dopant.

9. The electrolytic capacitor according to claim 8, wherein the first conductive polymer is doped with an organic sulfonate anion as the low-molecular-weight dopant, and R1 includes at least one unit selected from the group consisting of alkoxymethyl-3,4-ethylenedioxythiophene having 1 to 6 carbon atoms.

10. The electrolytic capacitor according to claim 7, wherein the first solid electrolyte layer comprises the first conductive polymer and a silicon-containing component.

11. The electrolytic capacitor of claim 10, wherein the silicon-containing component is derived from a silane coupling agent.

12. The electrolytic capacitor according to claim 7, wherein the second solid electrolyte layer contains a second conductive polymer different from the first conductive polymer, the second conductive polymer contains units of a third monomer, and the third monomer contains 3,4-ethylenedioxythiophene.

13. The electrolytic capacitor of claim 12, wherein the second solid electrolyte layer comprises a polymeric dopant.

14. The electrolytic capacitor of claim 13, wherein the second conductive polymer comprises poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonate anions as the polymer dopant.

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