Solid electrolytic capacitor

Abstract

This solid electrolytic capacitor includes at least one capacitor element which includes: an anode body that includes a porous part at least in a surface layer; a dielectric layer that covers at least a part of the surface of the anode body; and a solid electrolyte layer that covers at least a part of the dielectric layer. The solid electrolyte layer includes: a first portion that is filled in a void of the porous part in the anode body having the dielectric layer; and a second portion that protrudes from a main surface of the anode body having the dielectric layer. The first portion contains a self-doped conductive polymer, and also contains an antioxidant.

Description

solid electrolytic capacitor CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This disclosure claims the benefit of priority to Japanese Patent Application No. 2023-202858, filed on November 30, 2023, in the Japan Patent Office, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates to solid electrolytic capacitors.

[0003] A solid electrolytic capacitor includes, for example, a capacitor element and an exterior body that seals the capacitor element. The capacitor element includes, for example, a conductor (more specifically, an anode body), a dielectric layer formed on the surface of the conductor, and a solid electrolyte layer that covers at least a portion of the dielectric layer. The solid electrolyte layer is formed, for example, by chemical polymerization or electrolytic polymerization, or by using a treatment liquid (such as a liquid dispersion) containing a conductive polymer. The conductive polymer may, for example, be a self-doping conductive polymer or a non-self-doping conductive polymer (such as a conjugated polymer or a dopant).

[0004] Patent Document 1 proposes "a solid electrolytic capacitor comprising an anode body made of a valve metal, a dielectric layer formed on the anode body, and a solid electrolyte layer formed on the dielectric layer, wherein the solid electrolyte layer has: a first conductive polymer layer formed on the dielectric layer and heterogeneously doped with a monomolecular dopant; a block layer formed on the first conductive polymer layer; and a second conductive polymer layer formed on the block layer and made of a self-doping conductive polymer having a plurality of side chains with dopable functional groups, wherein the block layer blocks migration of the self-doping conductive polymer from the second conductive polymer layer to the first conductive polymer layer and / or migration of the self-doping conductive polymer from the second conductive polymer layer into pores of the porous anode body."

[0005] Patent Document 2 proposes a process for producing a capacitor, comprising: "a) preparing an electrode body (1) of an electrode material (2), wherein a dielectric (3) at least partially covers one surface (4) of the electrode material (2) under the formation of an anode body (5); b) introducing into at least a portion of the anode body (5) a dispersion comprising a dispersant, a heterogeneously doped conductive polymer, and counterions not covalently bonded to the heterogeneously doped conductive polymer; and c) at least partially removing the dispersant while obtaining a solid electrolyte (6) in a capacitor body, wherein a self-doped conductive polymer is further introduced into at least a portion of the anode body (5)."

[0006] JP 2023-13918 A JP 2015-532525 A

[0007] Self-doping conductive polymers are suitable for coating the surface of dielectric layers because of their small particle size and ease of impregnation into porous regions. However, compared with non-self-doping conductive polymers, self-doping conductive polymers have relatively low heat resistance, leaving room for improvement in terms of reliability.

[0008] One aspect of the present disclosure relates to a solid electrolytic capacitor including at least one capacitor element including: an anode body including a porous portion in at least a surface layer; a dielectric layer covering at least a portion of the surface of the anode body; and a solid electrolyte layer covering at least a portion of the dielectric layer, wherein the solid electrolyte layer has, in the anode body having the dielectric layer, a first portion filled in voids of the porous portion and a second portion protruding from a main surface of the anode body having the dielectric layer, and at least the first portion includes a self-doping conductive polymer and an antioxidant.

[0009] According to the present disclosure, the reliability of solid electrolytic capacitors can be improved. 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.

[0010] FIG. 1 is a cross-sectional schematic view of a solid electrolytic capacitor according to an embodiment of the present disclosure.

[0011] Hereinafter, embodiments of 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, materials, etc. may be exemplified, but other numerical values, materials, etc. may be applied as long as the effects of the present disclosure are obtained. Note that components other than those characteristic of the present disclosure may be components of known capacitors. In this specification, when a "range from numerical value A to numerical value B" is mentioned, the range includes numerical value A and numerical value B. When multiple materials are exemplified, one may be selected from the materials and used alone, or two or more may be used in combination.

[0012] The present disclosure also encompasses combinations of two or more features arbitrarily selected from the appended claims, i.e., two or more features arbitrarily selected from the appended claims can be combined unless a technical contradiction arises.

[0013] A "solid electrolytic capacitor" is an "electrolytic capacitor" that includes a solid electrolyte, and may be read simply as an "electrolytic capacitor," or "capacitor" may be read as a "capacitor."

[0014] An electrolytic capacitor according to an embodiment of the present disclosure includes a capacitor element. The form of the capacitor element is not particularly limited. The capacitor element includes an anode portion and a cathode portion. The capacitor element includes an anode body including a porous portion at least on its surface, a dielectric layer covering at least a portion of the surface of the anode body, and a solid electrolyte layer covering at least a portion of the dielectric layer. The anode body constitutes the anode portion. The solid electrolyte layer constitutes the cathode portion. The cathode portion may include a cathode extraction layer.

[0015] The solid electrolyte layer has a first portion and a second portion. The first portion is a portion that fills voids in the porous portion of the anode body, at least a portion of which has a dielectric layer. On the other hand, the second portion is a portion that protrudes from the main surface of the anode body that has the dielectric layer.

[0016] A part of the first portion may not fill the voids of the porous portion having the dielectric layer and may protrude from the main surface of the porous portion having the dielectric layer. That is, the first portion may have an inner layer filling the voids of the porous portion having the dielectric layer and an outer layer protruding from the main surface of the porous portion having the dielectric layer.

[0017] The second portion may be formed like a skin covering the anode body having the dielectric layer. A portion of the second portion may be filled into the voids of the porous portion having the dielectric layer. However, the volume ratio (Rv1) of the inner layer of the first portion to the entire first portion is greater than the volume ratio (Rv2) of the portion of the second portion that may be filled into the voids of the porous portion having the dielectric layer to the entire second portion. Rv1 is at least twice as large as Rv2.

[0018] At least the first portion contains a self-doped conductive polymer. Self-doped conductive polymers have small particle sizes and are easily impregnated into porous portions, so they can penetrate deep into the pores of the dielectric layer and cover a wider surface of the dielectric layer. This makes it easier to achieve high conductivity and high capacitance.

[0019] Repeated charging and discharging of solid electrolytic capacitors or exposure to high-temperature environments can result in reduced reliability. Specifically, the capacitance decreases and the ESR (equivalent series resistance) increases. This is thought to be due to oxidative degradation of the solid electrolyte layer and peeling of the solid electrolyte layer. Peeling of the solid electrolyte layer includes internal peeling within the solid electrolyte layer and interlayer peeling between the dielectric layer and the solid electrolyte layer. Oxidative degradation and peeling reduce the conductivity of the solid electrolyte layer and the conductivity between the dielectric layer and the solid electrolyte layer.

[0020] In contrast, when the first portion of the solid electrolyte layer contains a self-doped conductive polymer and an antioxidant, oxidative degradation and peeling of the conductive polymer are suppressed, and a decrease in capacity and an increase in ESR are suppressed. When a self-doped conductive polymer and an antioxidant are both present in the first portion, not only is oxidative degradation of the conductive polymer suppressed, but internal peeling and interlayer peeling of the solid electrolyte layer are also suppressed.

[0021] It is not clear why antioxidants not only prevent oxidative degradation of conductive polymers but also prevent internal peeling and delamination. It is thought that the improvement in the film quality of the solid electrolyte layer by antioxidants probably contributes to the prevention of internal peeling and delamination. It has also been found that antioxidants improve the strength of the solid electrolyte layer and improve the adhesion between the solid electrolyte layer and the dielectric layer. It is thought that this improvement in adhesion contributes to improved reliability.

[0022] The presence of the antioxidant in the first portion can be confirmed, for example, by TOF-SIMS (time-of-flight secondary ion mass spectrometry) of the cross section of the solid electrolyte layer. TOF-SIMS allows the presence of the antioxidant in any portion of the cross section of the solid electrolyte layer to be confirmed. Furthermore, by performing TOF-SIMS analysis of the cross section of the solid electrolyte layer at equal intervals along the thickness direction (depth direction) of the solid electrolyte layer, the distribution state of the antioxidant in the thickness direction of the solid electrolyte layer can be estimated. TOF-SIMS analysis may be performed at multiple locations (e.g., five locations) of the cross section of the solid electrolyte layer along the circumferential direction of the cross section of the anode body. In this case, the estimated concentrations of the antioxidant at multiple locations at the same depth of the solid electrolyte layer may be averaged.

[0023] A sample of the solid electrolyte layer used for analysis is prepared by embedding a solid electrolytic capacitor or capacitor element in acrylic resin, cutting the capacitor element at the center of its width in a direction parallel to its length to expose a cross section (e.g., a cross section as shown in Figure 1), and polishing it.

[0024] The second portion may not contain an antioxidant. If the second portion contains an antioxidant, the mass content of the antioxidant in the first portion is preferably higher than the mass content of the antioxidant in the second portion. The first portion, which is closer to the dielectric layer, has a greater impact on the reliability of the solid electrolytic capacitor than the second portion, which is farther from the dielectric layer. Therefore, by including a sufficient content of antioxidant in the first portion, the reliability of the solid electrolytic capacitor can be efficiently improved. Furthermore, by not including an antioxidant, which is an insulator, in the second portion, the ESR of the solid electrolytic capacitor can be maintained low and the capacitance extraction ability can be improved.

[0025] The mass content C1 of the antioxidant in the first portion and the mass content C2 of the antioxidant in the second portion may satisfy 0 < C2 / C1 < 1, 0 < C2 / C1 ≦ 0.5, or 0 < C2 / C1 ≦ 0.3.

[0026] The mass content C1 of the antioxidant in the first portion is not particularly limited, but from the viewpoint of enhancing the effect of the antioxidant and maintaining a small ESR, it is, for example, 0.1% to 20%, or may be 1% to 10%, or may be 3% to 5%, relative to the mass of the first portion.

[0027] The antioxidant preferably includes a water-soluble antioxidant. It is believed that the water-soluble antioxidant more significantly improves the film quality of the solid electrolyte layer and greatly improves the adhesion between the solid electrolyte layer and the dielectric layer. The water-soluble antioxidant dissolves in water contained in a dispersion or solution of the conductive polymer, which is a raw material for the solid electrolyte layer. The antioxidant dissolved in water can be widely and uniformly dispersed in the first portion, suppressing oxidative degradation of the conductive polymer throughout almost the entire first portion and improving film quality.

[0028] The first portion may further include a non-self-doping conductive polymer. Non-self-doping conductive polymers generally have higher heat resistance than self-doping conductive polymers. By using a highly impregnated self-doping conductive polymer and a non-self-doping conductive polymer in the first portion in combination, a solid electrolytic capacitor with high capacity, excellent heat resistance, and well-balanced performance can be realized.

[0029] The antioxidant contained in the first portion can also act on non-self-doping conductive polymers. Non-self-doping conductive polymers are prone to a decrease in conductivity due to oxidative degradation and dedoping of conjugated molecular chains. In contrast, the inclusion of an antioxidant in the first portion suppresses oxidative degradation and dedoping of non-self-doping conductive polymers. Therefore, when the solid electrolytic capacitor is repeatedly charged and discharged or exposed to a high-temperature environment, a decrease in capacitance and conductivity is suppressed, resulting in higher reliability.

[0030] Non-self-doping conductive polymers include, for example, conjugated polymers and polymer anions, and are available as dispersions or aqueous solutions in water.

[0031] The first portion may include a first layer covering at least a portion of the surface of the dielectric layer and a second layer covering at least a portion of the first layer, in which case the first layer may be in direct contact with the dielectric layer.

[0032] It is preferable that the mass content of the antioxidant in the second layer be higher than that in the first layer. The conductivity of the first layer, which is closer to the dielectric layer, has a greater impact on the reliability of the solid electrolytic capacitor than the conductivity of the second layer, which is farther from the dielectric layer. Because antioxidants are insulators, it is preferable that the amount of antioxidant contained in the first layer be relatively small. This allows the ESR of the solid electrolytic capacitor to be maintained low and also improves the capacitance extraction ability. On the other hand, by including a sufficient content of antioxidant in the second layer, the reliability of the solid electrolytic capacitor can be efficiently improved.

[0033] The mass content C1L of the antioxidant in the first layer and the mass content C2L of the antioxidant in the second layer may satisfy 0 < C1L / C2L < 1, 0 < C1L / C2L ≦ 0.5, or 0 < C1L / C2L ≦ 0.3.

[0034] The mass content C1 of the antioxidant in the first layer is not particularly limited, but from the viewpoint of enhancing the effect of the antioxidant and maintaining a small ESR, it is, for example, 0.1% to 20%, or may be 1% to 10%, or may be 3% to 5%, relative to the mass of the first layer.

[0035] The first layer may include a self-doped conductive polymer. In particular, when the first layer is a layer that is in direct contact with the dielectric layer, the first layer preferably includes a self-doped conductive polymer that has a small particle size and is easily impregnated into the porous portion.

[0036] The second layer may contain a non-self-doping conductive polymer. Non-self-doping conductive polymers generally have higher pressure resistance than self-doping conductive polymers. By covering the dielectric layer with the second layer containing a non-self-doping conductive polymer via the first layer, high pressure resistance can be obtained.

[0037] The mass content C2 of the antioxidant in the second layer is not particularly limited, but from the viewpoint of enhancing the effect of the antioxidant and maintaining a small ESR, it is, for example, 3% to 40%, or may be 5% to 35%, or may be 10% to 30%, relative to the mass of the second layer.

[0038] Preferred embodiments of the solid electrolyte layer according to the present invention include the following.

[0039] (First Aspect) A solid electrolyte layer comprising an anode body including a porous portion having a dielectric layer, the solid electrolyte layer having a first portion filled in voids of the porous portion and a second portion protruding from a main surface of the anode body having the dielectric layer, the first portion including a first layer covering at least a portion of a surface of the dielectric layer and a second layer covering at least a portion of the first layer, the first layer including a self-doping conductive polymer, and the second layer including a non-self-doping conductive polymer, the first layer not including an antioxidant, and the second layer including an antioxidant.

[0040] (Second Aspect) A solid electrolyte layer comprising an anode body including a porous portion having a dielectric layer, the solid electrolyte layer having a first portion filled in voids of the porous portion and a second portion protruding from a main surface of the anode body having the dielectric layer, the first portion including a first layer covering at least a portion of a surface of the dielectric layer and a second layer covering at least a portion of the first layer, the first layer including a self-doping conductive polymer, and the second layer including a non-self-doping conductive polymer, the second layer not including an antioxidant, and the first layer including an antioxidant.

[0041] (Third Aspect) A solid electrolyte layer comprising an anode body including a porous portion having a dielectric layer, the solid electrolyte layer having a first portion filled in voids of the porous portion and a second portion protruding from a main surface of the anode body having the dielectric layer, the first portion including a first layer covering at least a portion of a surface of the dielectric layer and a second layer covering at least a portion of the first layer, the first layer including a self-doping conductive polymer, the second layer including a non-self-doping conductive polymer, and the first layer and the second layer including an antioxidant. (Fourth Aspect) A solid electrolyte layer comprising an anode body including a porous portion having a dielectric layer, the solid electrolyte layer having a first portion filled in voids of the porous portion and a second portion protruding from a main surface of the anode body having the dielectric layer, the first portion including a first layer covering at least a portion of a surface of the dielectric layer and a second layer covering at least a portion of the first layer, the first layer including a self-doping conductive polymer, and the second layer including a non-self-doping conductive polymer, the first layer and the second layer including an antioxidant, the mass content of the antioxidant in the second layer being higher than the mass content of the antioxidant in the first layer.

[0042] The configuration of an example of an electrolytic capacitor according to the present disclosure will be described in more detail below. [Solid Electrolytic Capacitor] The capacitor element included in the solid electrolytic capacitor includes an anode portion and a cathode portion. The cathode portion includes a solid electrolyte layer. The solid electrolytic capacitor and capacitor element according to the present disclosure are characterized primarily by the solid electrolyte layer, and therefore the other components are not particularly limited. Components used in known solid electrolytic capacitors may be applied to each component.

[0043] (Capacitor Element) The anode portion of the capacitor element includes an anode body, a dielectric layer formed on at least a portion of the surface of the anode body, and a cathode portion formed on at least a portion of the surface of the dielectric layer.

[0044] (Anode Body) The anode body is made of a conductive material and may be a sheet-shaped anode foil, or a molded or sintered body of metal particles.

[0045] The conductive material constituting the anode body may include a valve metal, an alloy containing a valve metal, a compound containing a valve metal, etc. The anode body may include one of these materials or a combination of two or more of them. Preferred examples of the valve metal include aluminum, tantalum, niobium, and titanium.

[0046] The anode body has a porous portion at least on the surface layer thereof. The porous portion of the anode body has many fine voids. Due to this porous portion, the anode body has a finely uneven shape.

[0047] An anode body having a porous portion in its surface layer can be obtained, for example, by roughening the surface of a substrate (such as a sheet-like (e.g., foil-like, plate-like) substrate) containing a valve metal. The roughening may be performed, for example, by etching (electrolytic etching, chemical etching, etc.). Such an anode body (anode foil) has, for example, a core and porous portions formed on both surfaces of the core and integrated with the core.

[0048] The anode body may be a sintered body or a compact of particles containing a valve metal. The compact and sintered body are porous and may be a rectangular parallelepiped, a cube, or a similar shape. The sintered body may be, for example, a sintered body of particles containing tantalum.

[0049] The anode body may have an electrode lead portion (also referred to as an anode lead portion) including a first end and a cathode forming portion including a second end opposite the first end. A cathode portion including a solid electrolyte layer is formed on the surface of the cathode forming portion of the anode body. The anode lead portion is used, for example, for electrical connection with an external electrode on the anode side. An anode lead terminal may be connected to the anode lead portion.

[0050] (Anode Wire) When the anode body is a porous sintered body or a molded body, the anode portion may include an anode wire. The anode wire may be a metal wire. Examples of materials for the anode wire include the valve metals described above, copper, or copper alloys. A portion of the anode wire is embedded in the anode body, and the remaining portion protrudes outward from the end face of the anode body. The end of the anode wire protruding outward corresponds to the first end, and the end of the anode body opposite the first end corresponds to the second end.

[0051] (Dielectric Layer) The dielectric layer is formed so as to cover at least a portion of the surface of the anode body or the porous portion. The dielectric layer can be formed by a known method. The dielectric layer may be formed by oxidizing a valve metal on the surface of the anode body or the porous portion by chemical conversion treatment or the like. The dielectric layer has a fine uneven shape that conforms to the surface shape of the porous portion.

[0052] The dielectric layer contains an oxide of the valve metal. For example, when tantalum is used as the valve metal, the dielectric layer contains Ta. ２ O ５ When aluminum is used as the valve metal, the dielectric layer is Al ２ O ３ The dielectric layer is not limited to these examples, but may be any layer that functions as a dielectric.

[0053] (Cathode portion) The cathode portion includes at least a solid electrolyte layer covering at least a portion of the dielectric layer. The solid electrolyte layer is formed on the second end side of the anode body (in other words, the cathode-forming portion) via the dielectric layer. The cathode portion typically includes a solid electrolyte layer covering at least a portion of the dielectric layer and a cathode extraction layer covering at least a portion of the solid electrolyte layer.

[0054] (Solid Electrolyte Layer) In a capacitor element, the solid electrolyte layer is formed so as to cover at least a portion of the dielectric layer. The solid electrolyte layer has a first portion filling the voids of the porous portion in the anode body having the dielectric layer and a second portion protruding from the main surface of the anode body having the dielectric layer. As described above, the first portion contains a self-doping conductive polymer and an antioxidant. The first portion may further contain a non-self-doping conductive polymer.

[0055] (Antioxidant) An antioxidant is a component that has the effect of inactivating radicals generated by the involvement of oxygen. Antioxidants include components generally called antioxidants, as well as components called antidegradants, antiaging agents, radical chain inhibitors, peroxide decomposers, chain initiation inhibitors, light stabilizers, heat stabilizers (or heat stabilizers), metal deactivators, ultraviolet absorbers, weathering stabilizers, etc.

[0056] The antioxidant contains at least one selected from the group consisting of, for example, a hydroxy group, a nitrogen atom, an oxygen atom, a sulfur atom, and a phosphorus atom. Examples of such antioxidants include phenol-based antioxidants, amine-based antioxidants, phosphorus-based antioxidants, sulfur-based antioxidants, benzimidazole-based antioxidants, and carotenoid compounds. Among these, phenol-based antioxidants are preferred because of their high effectiveness.

[0057] The phenolic antioxidant has a phenolic hydroxy group. The phenolic antioxidant may be, for example, a monocyclic compound having only one aromatic ring with a phenolic hydroxy group, or a compound having multiple aromatic rings with phenolic hydroxy groups. Among these, a monocyclic compound having only one aromatic ring with a phenolic hydroxy group is preferred because it has a small molecular weight and can exhibit high effectiveness even in small amounts. Furthermore, a material with low insulating properties is preferred from the viewpoint of maintaining high conductivity of the solid electrolyte layer. Such a phenolic antioxidant may contain two or more phenolic hydroxy groups per molecule, or may contain three or more phenolic hydroxy groups. The upper limit of the number of phenolic hydroxy groups bonded to the aromatic ring can be selected depending on the size of the aromatic ring, and may be, for example, five or less, four or less, or three or less. Examples of such phenolic antioxidants include pyrogallol, catechol, gallic acid, and L-ascorbic acid. These antioxidants are also preferred because of their water solubility.

[0058] The aromatic ring having a phenolic hydroxy group may be a fused ring of an aromatic ring and a non-aromatic ring. The aromatic ring and the non-aromatic ring may each be either a hydrocarbon ring or a heterocycle. The non-aromatic ring may be a bridged ring. Examples of the aromatic ring include aromatic hydrocarbon rings having 6 to 20 carbon atoms (e.g., 6 to 14 or 6 to 10 carbon atoms) (e.g., benzene, naphthalene, phenanthrene, anthracene, etc.) and aromatic heterocycles having 5 to 20 members (e.g., 6 to 14 members) (e.g., furan, pyrrole, thiophene, imidazole, pyridine, pyrazine, quinoline, indole, benzimidazole, benzotriazole, purine, etc.). Examples of the fused ring of an aromatic ring and a non-aromatic ring include chromene, chromone, chroman, coumarin, 4H-chromen-4-one, and carbazole. Examples of the non-aromatic ring include alicyclic hydrocarbon rings having 5 to 14 (e.g., 5 to 10) carbon atoms (cyclopentane, cyclohexane, cyclooctane, etc.), bridged cyclic hydrocarbon rings having 6 to 20 (e.g., 6 to 14) carbon atoms (norbornane, norbornene, dicyclopentadiene, etc.), and 5- to 20-membered (e.g., 6- to 14-membered) non-aromatic heterocycles (tetrahydrofuran, dioxolane, dioxane, pyrrolidine, piperidine, morpholine, thiazine, etc.).

[0059] (Self-doped conductive polymer) A self-doped conductive polymer has, for example, a conjugated polymer skeleton and a functional group (such as an anionic group) that functions as a dopant and is directly or indirectly bonded to the skeleton by a covalent bond.

[0060] Examples of the anionic group include a sulfo group, a carboxy group, a phosphate group, and a phosphonate group. The self-doping conductive polymer may contain one type of anionic group or two or more types of anionic groups. From the viewpoint of easily ensuring higher conductivity of the self-doping conductive polymer, the self-doping conductive polymer may contain at least a sulfo group.

[0061] The anionic group of the self-doped conductive polymer may be contained in any form such as anion, acid, ester, salt, etc., or may be contained in a form that interacts with or is complexed with a component contained in the solid electrolyte layer. In this specification, all of these forms are simply referred to as anionic group.

[0062] Examples of conjugated polymers that constitute the skeleton of self-doping conductive polymers include polymers with a basic skeleton of a π-conjugated polymer (such as polypyrrole, polythiophene, polyaniline, polyfuran, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, and polythiophene vinylene). The polymers may contain at least one monomer unit that constitutes the basic skeleton. Examples of the polymers include homopolymers, copolymers of two or more monomers, and derivatives thereof (e.g., substituted products having substituents). For example, polythiophenes include poly(3,4-ethylenedioxythiophene). Self-doping conductive polymers have anionic groups in the skeleton of these conjugated polymers. The anionic groups may be directly introduced into the skeleton of the conjugated polymer or may be introduced via a linking group. Examples of the linking group include polyvalent groups (divalent groups) containing an alkylene group. Examples of the linking group include aliphatic polyvalent groups (divalent groups) such as alkylene groups, -R １ -X-R ２ - group (X is an oxygen element or a sulfur element, R １ and R ２ are the same or different and are alkylene groups.) The number of carbon atoms in each alkylene group contained in the linking group may be, for example, 1 or more and 10 or less, or 1 or more and 6 or less. The alkylene group may be linear or branched. The linking group may, for example, contain at least an alkylene group having 2 or more carbon atoms. The number of carbon atoms in such an alkylene group may be 2 or more (or 3 or more) and 10 or less, or 2 or more (or 3 or more) and 6 or less. For example, R １ is an alkylene group having 1 to 6 carbon atoms, and R ２ may be an alkylene group having 2 or more (or 3 or more) and 10 or less carbon atoms. However, the linking group is not limited to these.

[0063] The conjugated polymer constituting the skeleton of the self-doping conductive polymer may be polypyrrole, polythiophene, or polyaniline. From the viewpoint of easily obtaining high conductivity, etc., the self-doping conductive polymer is preferably a polymer having a conjugated polymer skeleton containing a repeating structure of monomer units corresponding to a thiophene compound and an anionic group introduced into this skeleton.

[0064] The thiophene compound includes a compound having a thiophene ring and capable of forming a repeating structure of the corresponding monomer unit, which can be linked at the 2- and 5-positions of the thiophene ring to form a repeating structure of the monomer unit.

[0065] The thiophene compound may have a substituent at, for example, at least one of the 3- and 4-positions of the thiophene ring. The substituent at the 3-position and the substituent at the 4-position may be linked to form a ring fused to the thiophene ring. Examples of the thiophene compound include thiophenes which may have a substituent at, at least one of the 3- and 4-positions, alkylenedioxythiophene compounds (C thiophenes such as ethylenedioxythiophene compounds), and the like. ２－４ Alkylenedioxythiophene compounds include compounds having a substituent on the alkylene group.

[0066] The substituents include alkyl groups (C such as methyl and ethyl groups) １－４ alkyl groups, alkoxy groups (C groups such as methoxy groups and ethoxy groups) １－４ alkoxy group, hydroxy group, hydroxyalkyl group (hydroxy C such as hydroxymethyl group) １－４ Preferred are, but not limited to, alkyl groups. When the thiophene compound has two or more substituents, the respective substituents may be the same or different. The thiophene ring (in the case of an alkylenedioxythiophene ring, at least one of the thiophene ring and the alkylene group) may have, as a substituent, the above-mentioned anionic group or a group containing an anionic group (for example, a sulfoalkyl group).

[0067] The self-doped conductive polymer may have a backbone of a conjugated polymer (such as PEDOT) containing a repeating structure of monomer units corresponding to at least a 3,4-ethylenedioxythiophene compound (such as 3,4-ethylenedioxythiophene (EDOT)). The backbone of the conjugated polymer containing a repeating structure of monomer units corresponding to at least EDOT may contain only monomer units corresponding to EDOT, or may contain, in addition to the monomer units, monomer units corresponding to a thiophene compound other than EDOT.

[0068] An example of a monomer unit for a self-doped conductive polymer is shown below.

[0069]

[0070] The weight average molecular weight (Mw) of the self-doping conductive polymer may be 1,000 or more and 1,000,000 or less, or may be 1,000 or more and 50,000 or less.

[0071] In this specification, the weight average molecular weight (Mw) is a value calculated as polystyrene measured by gel permeation chromatography (GPC), which is typically performed using a polystyrene gel column and a water / methanol (volume ratio 8 / 2) mobile phase.

[0072] (Non-self-doping conductive polymer) The non-self-doping conductive polymer includes, for example, a non-self-doping conjugated polymer (for example, a conjugated polymer having no anionic groups) and a dopant.

[0073] Examples of conjugated polymers include conjugated polymers (such as π-conjugated polymers) exemplified as conjugated polymers constituting the backbone of self-doping conductive polymers. Conjugated polymers may be used singly or in combination of two or more. From the viewpoint of easily ensuring high initial capacity, voltage resistance, and high heat resistance, non-self-doping conjugated polymers containing a repeating structure of thiophene compound monomer units may be used. Examples of thiophene compounds corresponding to the monomer units of non-self-doping conjugated polymers include the thiophene compounds described for the self-doping conductive polymers. Non-self-doping conjugated polymers may include conjugated polymers (such as PEDOT) containing a repeating structure of monomer units corresponding to at least a 3,4-ethylenedioxythiophene compound (such as EDOT). A conjugated polymer containing a repeating structure of at least a monomer unit corresponding to EDOT may contain only a monomer unit corresponding to EDOT, or may contain, in addition to the monomer unit, a monomer unit corresponding to a thiophene compound other than EDOT.

[0074] The dopant may be at least one selected from the group consisting of anions and polyanions (e.g., polymer anions). Examples of anions include sulfate ions, nitrate ions, phosphate ions, borate ions, organic sulfonate ions, and carboxylate ions. Examples of dopants that generate sulfonate ions include p-toluenesulfonic acid and naphthalenesulfonic acid. Polymer anions may be used to facilitate higher heat resistance, reliability, and voltage resistance. Examples of polymer anions containing sulfo groups include polymeric polysulfonic acids. Specific examples of polymer anions include polyvinylsulfonic acid, polystyrenesulfonic acid (PSS (including copolymers and substituted forms thereof)), polyallylsulfonic acid, polyacrylicsulfonic acid, polymethacrylicsulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprenesulfonic acid, polyestersulfonic acids (e.g., aromatic polyestersulfonic acids), and phenolsulfonic acid novolac resins. However, the dopant is not limited to these specific examples. The dopants may be used alone or in combination of two or more.

[0075] In the non-self-doping conductive polymer, the amount of the dopant may be 10 parts by mass or more and 1000 parts by mass or less, or 20 parts by mass or more and 500 parts by mass or less, relative to 100 parts by mass of the conjugated polymer.

[0076] (Method for forming a solid electrolyte layer) The step of forming a solid electrolyte layer so as to cover at least a portion of a dielectric layer includes, for example, a first step of forming a first portion and a second step of forming a second portion, and may further include a step of performing any processing between the first step and the second step.

[0077] (First step of forming first portion) The first step includes, for example, a step of forming a first layer containing a self-doping conductive polymer and a step of forming a second layer containing a non-self-doping conductive polymer.

[0078] (Step of forming first layer) In the step of forming the first layer, for example, the first layer may be formed using a treatment liquid (first treatment liquid) containing a self-doping conductive polymer. More specifically, the first treatment liquid containing a self-doping conductive polymer is applied to the dielectric layer to form the first layer. After the first treatment liquid is applied to the dielectric layer, it may be dried. If necessary, the application of the first treatment liquid to the dielectric layer and drying may be repeated two or more times.

[0079] The first treatment liquid contains, for example, a self-doping conductive polymer and a liquid medium. The first treatment liquid may contain one type of self-doping conductive polymer or two or more types of self-doping conductive polymer. The liquid medium is, for example, a medium that is liquid at room temperature (e.g., 20°C or higher and 35°C or lower). Examples of the liquid medium include water, an organic solvent, or a mixture thereof. Among these, water is preferably used.

[0080] The first treatment liquid may be a dispersion in which particles of a self-doping conductive polymer are dispersed in a liquid medium, or a solution in which a self-doping conductive polymer is dissolved in a liquid medium. Self-doping conductive polymers have relatively flexible polymer chains, and functional groups such as anionic groups are randomly positioned. Furthermore, self-doping conductive polymers have low polymer chain orientation and low crystallinity. Therefore, compared with non-self-doping conductive polymers, they are more easily dissolved in a liquid medium or dispersed in the form of fine particles. Therefore, the viscosity of the first treatment liquid is relatively low, making it easier to impregnate the voids in the porous portion with high permeability.

[0081] The concentration of the self-doping conductive polymer in the first treatment liquid may be 0.5% by mass or more and 5% by mass or less, or may be 1% by mass or more and 3% by mass or less.

[0082] The first treatment liquid may contain an antioxidant, but from the viewpoint of ensuring higher reliability, it is not necessary to contain an antioxidant. When the first treatment liquid contains an antioxidant, the concentration of the antioxidant in the first treatment liquid is preferably lower than the concentration of the antioxidant in the second treatment liquid described below. The concentration of the antioxidant in the first treatment liquid may be 5% by mass or less, less than 3% by mass, 1% by mass or less, or 0.1% by mass or less.

[0083] (Step of forming the second layer) In the step of forming the second layer, for example, the second layer may be formed using a treatment liquid (second treatment liquid) containing a non-self-doping conductive polymer. More specifically, the second layer is formed by applying the second treatment liquid containing the non-self-doping conductive polymer to the dielectric layer. After applying the second treatment liquid to the dielectric layer, the dielectric layer may be dried. If necessary, the application of the second treatment liquid to the dielectric layer and drying may be repeated two or more times.

[0084] The second treatment liquid contains, for example, a non-self-doping conductive polymer and a liquid medium. The second treatment liquid may be a dispersion liquid in which particles of the non-self-doping conductive polymer are dispersed in a liquid medium. The second treatment liquid may contain one type of self-doping conductive polymer, or two or more types. Examples of the liquid medium include water, an organic solvent, or a mixture thereof. Among these, water is preferably used.

[0085] The concentration of the non-self-doping conductive polymer in the second treatment liquid may be 0.5% by mass or more and 5% by mass or less, or may be 1% by mass or more and 3% by mass or less.

[0086] The second treatment liquid may contain an antioxidant. When the liquid medium of the second treatment liquid contains water, it is preferable to use a water-soluble antioxidant. The concentration of the antioxidant in the second treatment liquid may be appropriately controlled in accordance with the concentration of the non-self-doping conductive polymer in the second treatment liquid. The concentration of the antioxidant in the second treatment liquid may be, for example, 0.1% to 10% by mass, 1% to 5% by mass, or 3% to 5% by mass. The second treatment liquid may contain an antioxidant in an amount equal to or greater than the mass of the non-self-doping conductive polymer. It is estimated that a portion of the antioxidant volatilizes during the drying process of the treatment liquid. As a result, a second layer containing the antioxidant at a mass content of, for example, 3% to 40%, 5% to 35%, or 10% to 30% may be formed. The mass content of the antioxidant in the second layer is preferably higher than the mass content of the antioxidant in the first layer.

[0087] (Second step of forming the second portion) In the second step, for example, a treatment liquid (third treatment liquid) containing a non-self-doping conductive polymer is used to form the second portion covering at least a part of the first portion so as to extend beyond the main surface of the anode body having the dielectric layer. More specifically, the third treatment liquid containing the non-self-doping conductive polymer is applied to the dielectric layer to form the second portion. After applying the third treatment liquid to the first portion, it may be dried. If necessary, the application of the second treatment liquid to the first portion and drying may be repeated two or more times.

[0088] The third treatment liquid includes, for example, a non-self-doping conductive polymer and a liquid medium. The third treatment liquid may be a dispersion liquid in which particles larger in size than the non-self-doping conductive polymer used to form the second layer of the first portion are dispersed in a liquid medium. The third treatment liquid may include one type of self-doping conductive polymer, or may include two or more types. Examples of the liquid medium include water, an organic solvent, or a mixture thereof. Among these, water is preferably used.

[0089] The concentration of the non-self-doping conductive polymer in the third treatment liquid may be 0.5% by mass or more and 5% by mass or less, or 1% by mass or more and 3% by mass or less. Note that the non-self-doping conductive polymer contained in the third treatment liquid has a large particle size and is likely to have a high viscosity, so the concentration is preferably lower than that of the non-self-doping conductive polymer in the second treatment liquid. A non-self-doping conductive polymer with a large particle size is unlikely to fill the pores of the porous portion of the anode body, and is likely to form a skin-like film of the non-self-doping conductive polymer on the outside of the porous portion.

[0090] (Cathode Extraction Layer) The cathode extraction layer may include, for example, at least a first extraction layer in contact with the solid electrolyte layer and covering at least a portion of the solid electrolyte layer, and a second extraction layer covering at least a portion of the first extraction layer.

[0091] Examples of the first extraction layer include a layer containing conductive particles and metal foil. Examples of the conductive particles include at least one selected from conductive carbon and metal powder. The cathode extraction layer may include a layer containing metal powder (e.g., a metal particle-containing layer). The cathode extraction layer may be composed of, for example, a layer containing conductive carbon (a carbon layer) as the first extraction layer and a layer containing metal powder (e.g., a metal particle-containing layer) or metal foil as the second extraction layer.

[0092] When the cathode extraction layer includes a metal foil or a metal particle-containing layer, the entire cathode extraction layer may be composed of the metal foil or the metal particle-containing layer, or at least one of the first extraction layer and the second extraction layer may be composed of the metal particle-containing layer.

[0093] Examples of conductive carbon include graphite (artificial graphite, natural graphite, etc.).

[0094] The metal powder-containing layer serving as the second leader layer can be formed, for example, by laminating a metal powder-containing composition on the surface of the first leader layer. Examples of such second leader layers include metal particle-containing layers formed using a paste containing metal powder and a resin binder. While thermoplastic resins can be used as the resin binder, thermosetting resins such as imide resins and epoxy resins are preferred. To facilitate high conductivity of the second leader layer, silver-containing particles may be used as the metal powder. Examples of silver-containing particles include silver particles and silver alloy particles. The second leader layer may contain one type of silver-containing particle or a combination of two or more types. The silver particles may contain a small amount of impurities.

[0095] When a metal foil is used as the first lead layer, the type of metal is not particularly limited. It is preferable to use a valve metal (aluminum, tantalum, niobium, etc.) or an alloy containing a valve metal as the metal foil. If necessary, the surface of the metal foil may be roughened. The surface of the metal foil may be provided with a chemical conversion coating, or may be provided with a coating of a metal (dissimilar metal) or a nonmetal different from the metal constituting the metal foil. Examples of dissimilar metals and nonmetals include metals such as titanium and nonmetals such as carbon (e.g., conductive carbon).

[0096] The coating of the dissimilar metal or non-metal (for example, conductive carbon) may serve as a first lead layer, and the metal foil may serve as a second lead layer.

[0097] The cathode extraction layer is formed by a known method depending on its layer structure. For example, when the cathode extraction layer includes a metal foil as the first extraction layer or the second extraction layer, the first extraction layer or the second extraction layer is formed by laminating the metal foil so as to cover at least a portion of the solid electrolyte layer or the first extraction layer. The first extraction layer containing conductive particles is formed, for example, by applying a conductive paste or liquid dispersion containing conductive particles and, if necessary, a resin binder (e.g., a water-soluble resin, a curable resin, etc.) to the surface of the solid electrolyte layer. The second extraction layer containing metal powder is formed, for example, by applying a paste containing the metal powder and a resin binder to the surface of the first extraction layer. During the formation of the cathode extraction layer, drying treatment, heating treatment, etc. may be performed as necessary.

[0098] (Other) The solid electrolytic capacitor includes at least one capacitor element. The solid electrolytic capacitor may be a wound type, and may be either a chip type or a stacked type. For example, the solid electrolytic capacitor may include multiple stacked capacitor elements. The solid electrolytic capacitor may also include two or more wound capacitor elements. The configuration of the capacitor element may be selected depending on the type of solid electrolytic capacitor.

[0099] When a metal foil is used for the cathode extraction layer, a separator may be disposed between the metal foil and the anode foil serving as the anode body. The separator is not particularly limited, and may be, for example, a nonwoven fabric containing fibers of cellulose, polyethylene terephthalate, vinylon, or polyamide (e.g., aliphatic polyamide, aromatic polyamide such as aramid).

[0100] In the capacitor element, one end of a cathode lead terminal may be electrically connected to the cathode extraction layer. The cathode lead terminal is bonded to the cathode extraction layer via a conductive adhesive applied to the cathode extraction layer, for example. One end of an anode lead terminal may be electrically connected to the anode extraction portion of the anode body. The other end of the anode lead terminal and the other end of the cathode lead terminal are each extracted from the resin exterior body or the case. The other end of each terminal exposed from the resin exterior body or the case is used for soldering to a substrate on which the solid electrolytic capacitor is to be mounted, for example. Furthermore, instead of extracting a lead terminal, at least one end face of the anode portion and the cathode portion may be exposed from the outer surface of the sealing body and electrically connected to an external electrode.

[0101] The capacitor element is sealed using a resin outer casing or case. For example, the capacitor element and the resin material of the outer casing (e.g., uncured thermosetting resin and filler) may be placed in a mold, and the capacitor element may be sealed in the resin outer casing by transfer molding, compression molding, or the like. At this time, the other end portions of the anode lead terminal and the cathode lead terminal connected to the anode lead drawn from the capacitor element are exposed from the mold. Alternatively, the capacitor element may be housed in a bottomed case so that the other end portions of the anode lead terminal and the cathode lead terminal are positioned on the opening side of the bottomed case, and the opening of the bottomed case may be sealed with a sealant to form a solid electrolytic capacitor. The leads may be wire-shaped or frame-shaped (e.g., lead frame).

[0102] 1 is a cross-sectional schematic diagram of a solid electrolytic capacitor according to an embodiment of the present disclosure. Solid electrolytic capacitor 20 includes a capacitor element including an anode portion 6 and a cathode portion 7, an exterior body 11 that seals the capacitor element, an anode lead frame 13 electrically connected to anode portion 6, and a cathode lead frame 14 electrically connected to cathode portion 7.

[0103] The anode part 6 has an anode body 1 and an anode wire 2. A part of the anode wire 2 is embedded in the anode body 1, and the rest of the anode wire 2 protrudes outward from the outer surface of the anode body 1. A part of the anode lead frame 13 is joined to the protruding part of the anode wire 2 by welding or the like, and is electrically connected to it.

[0104] A dielectric layer 3 is formed on the surface of the anode body 1. The cathode portion 7 has a solid electrolyte layer 4 covering at least a portion of the dielectric layer 3, and a cathode extraction layer 5 covering at least a portion of the surface of the solid electrolyte layer 4. The cathode extraction layer 5 has a carbon layer formed so as to cover at least a portion of the surface of the solid electrolyte layer 4, and a metal particle-containing layer formed so as to cover at least a portion of the carbon layer. A portion of the cathode lead frame 14 is adhered to and electrically connected to the cathode extraction layer 5 via a conductive adhesive layer 8.

[0105] (Additional Notes) The above description discloses the following technologies. (Technology 1) A solid electrolytic capacitor including at least one capacitor element including an anode body including a porous portion at least in a surface layer thereof, a dielectric layer covering at least a portion of the surface of the anode body, and a solid electrolyte layer covering at least a portion of the dielectric layer, wherein the solid electrolyte layer has, in the anode body having the dielectric layer, a first portion filling voids in the porous portion and a second portion protruding from a main surface of the anode body having the dielectric layer, and at least the first portion containing a self-doping conductive polymer and an antioxidant. (Technology 2) The solid electrolytic capacitor according to Technology 1, wherein the mass content of the antioxidant in the first portion is higher than the mass content of the antioxidant in the second portion. (Technology 3) The solid electrolytic capacitor according to Technology 1 or 2, wherein the second portion does not contain the antioxidant. (Technology 4) The solid electrolytic capacitor according to any one of Technology 1 to 3, wherein the antioxidant contains a water-soluble antioxidant. (Technology 5) The solid electrolytic capacitor according to any one of Technologies 1 to 4, wherein the first portion further includes a non-self-doping conductive polymer. (Technology 6) The solid electrolytic capacitor according to Technology 5, wherein the non-self-doping conductive polymer includes a conjugated polymer and a polymer anion. (Technology 7) The solid electrolytic capacitor according to any one of Technologies 1 to 6, wherein the first portion includes a first layer covering at least a portion of the surface of the dielectric layer and a second layer covering at least a portion of the first layer, at least the second layer including the antioxidant, and wherein the mass content of the antioxidant in the second layer is higher than the mass content of the antioxidant in the first layer. (Technology 8) The solid electrolytic capacitor according to Technology 7, wherein the first layer does not include the antioxidant. (Technology 9) The solid electrolytic capacitor according to Technology 7 or 8, wherein the first layer includes the self-doping conductive polymer, and the second layer includes a non-self-doping conductive polymer.

[0106] EXAMPLES The present invention will be specifically described below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0107] Example 1 A capacitor element was fabricated in the following manner, and its characteristics were evaluated.

[0108] (1) Preparation of an anode body having a dielectric layer A tantalum sintered body (porous body) with a part 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.

[0109] (2) Formation of Solid Electrolyte Layer (2-1) First Step (Step of Forming First Layer) An aqueous dispersion (first treatment liquid) containing a self-doping polythiophene-based polymer was prepared. The concentration of the polythiophene-based polymer in the first treatment liquid was 1 to 3 mass %. As the self-doping polythiophene-based polymer, PEDOT (Mw: approximately 10,000) having a sulfo group bonded to the PEDOT skeleton via a linking group containing a butylene group was used.

[0110] Pyrogallol was dissolved as an antioxidant in a first treatment liquid in an amount of 30 mass % relative to the mass of the self-doping polythiophene polymer, and then the tantalum sintered compact prepared in (1) above was immersed in the first treatment liquid for about 30 to 60 seconds, and then the tantalum sintered compact was pulled out of the first treatment liquid. Next, the tantalum sintered compact pulled out of the first treatment liquid was heated (dried) at 140 to 180°C for 10 to 20 minutes, thereby forming a first layer.

[0111] (Step of forming the second layer) An aqueous dispersion (second treatment liquid) containing a non-self-doping conductive polymer (PSS-doped PEDOT) was prepared. The concentration of PSS-doped PEDOT in the second treatment liquid was 1 to 3 mass %. The tantalum sintered compact on which the first layer had been formed was immersed in the second treatment liquid for approximately 30 to 60 seconds, and then the tantalum sintered compact was pulled out of the second treatment liquid. Next, the tantalum sintered compact pulled out of the second treatment liquid was heated (dried) at 140 to 180°C for 10 to 20 minutes.

[0112] (2-2) Second Step: An aqueous dispersion (third treatment liquid) containing a non-self-doping conductive polymer (PSS-doped PEDOT) was prepared. The concentration of PSS-doped PEDOT in the third treatment liquid was 1 to 3 mass%. The tantalum sintered body on which the first and second layers (i.e., the first portion) had been formed was immersed in the third treatment liquid for approximately 30 to 60 seconds, and then the tantalum sintered body was removed from the third treatment liquid. Next, the tantalum sintered body removed from the third treatment liquid was heated (dried) at 140 to 180°C for 10 to 20 minutes. The immersion of the tantalum sintered body in the third treatment liquid and the above-mentioned drying were repeated multiple times to form the second portion of the solid electrolyte layer.

[0113] (3) Formation of Cathode Extraction Layer The tantalum sintered compact on which the solid electrolyte layer formed in (2) above was formed was immersed in a dispersion liquid in which graphite particles were dispersed in water, and then removed from the dispersion liquid and dried to form a carbon layer (first extraction layer) on the surface of the solid electrolyte layer. The drying was carried out at 180°C for 10 to 30 minutes.

[0114] Next, a silver paste containing silver particles and a binder resin (epoxy resin) was applied to the surface of the carbon layer and dried at 60 to 80°C for 20 to 40 minutes. The binder resin was then cured by heating at 180°C for 30 to 60 minutes, forming a metal particle-containing layer (second extraction layer). In this way, a cathode extraction layer composed of the carbon layer and the metal particle-containing layer was formed.

[0115] In this manner, a total of 30 capacitor elements A1 each including a cathode portion composed of a solid electrolyte layer and a cathode extraction layer were fabricated.

[0116] Example 2 In the step of forming the first layer, no antioxidant was dissolved in the first treatment liquid. Meanwhile, in the step of forming the second layer, 60 mass % of the antioxidant was dissolved in the second treatment liquid relative to the total mass of the PSS-doped PEDOT and the antioxidant. A total of 30 capacitor elements A2 were fabricated in the same manner as in Example 1.

[0117] Example 3 A total of 30 capacitor elements A3 were fabricated in the same manner as in Example 1, except that in the step of forming the second layer, 60 mass % of the antioxidant was dissolved in the second treatment liquid relative to the total mass of the PSS-doped PEDOT and the antioxidant.

[0118] Comparative Example 1 A total of 30 capacitor elements B1 were produced in the same manner as in Example 1, except that no antioxidant was dissolved in the first treatment liquid in the step of forming the first layer.

[0119] Capacitor element A1 contains an antioxidant only in the first layer of the first portion of the solid electrolyte layer. Capacitor element A2 contains an antioxidant only in the second layer of the first portion of the solid electrolyte layer. Capacitor element A3 contains an antioxidant in both the first and second layers of the first portion of the solid electrolyte layer. Capacitor element B1 does not contain an antioxidant in either the first or second layer of the first portion of the solid electrolyte layer.

[0120] [Evaluation] (Tape peeling test) Adhesion was evaluated using the cross-cut method (JIS K5600) specified in the JIS standard. The second treatment liquid of Example 2 was applied to the surface of a stainless steel foil (SUS), which was then heated (dried) at 140 to 180°C for 10 to 20 minutes to form a thin film A2 (5 μm thick) of PEDOT doped with PSS. A cutter knife was used to make a grid-like cut (1 mm intervals) in the resulting coating film.

[0121] In the same manner as described above, the second treatment liquid of Comparative Example 1 (Example 1) was applied to the surface of the SUS foil, and heated (dried) at 140 to 180°C for 10 to 20 minutes to form a thin film B1 (thickness 5 μm) of PEDOT doped with PSS.

[0122] Peel evaluation was performed based on the JIS-K5600 test standard. A peel test was performed by attaching adhesive tape (Cellotape manufactured by Nichiban Co., Ltd.) to thin films A2 and B1, then manually peeling the tape off. Most of thin film B1 peeled off from the SUS foil (JIS test result: Category 5). On the other hand, thin film A2 barely peeled off from the SUS foil, and the tape peeled off at the interface with thin film A2 (JIS test result: Category 1). These results confirm that the antioxidant significantly enhances the adhesion between the solid electrolyte layer and the dielectric layer.

[0123] (Single Film Heat Resistance Test) Thin Film A2 and Thin Film B1 were each heated at 125°C for 500 hours, and the electrical conductivity (S / cm) of the thin films was measured before and after heating using a Loresta-GP (MCP-T610 type in-line 4-point probe) manufactured by Nitto Seiko Analytech Co., Ltd. As a result, the electrical conductivity of Thin Film A2 and Thin Film B1 before heating was almost the same, but the electrical conductivity of Thin Film A2 after heating for 500 hours was 1.7 times that of Thin Film B1.

[0124] (1) Initial Characteristics (Capacitance (Cap)) The initial capacitance C0 (μF) of the capacitor element was measured at a frequency of 120 Hz using a four-terminal LCR meter in an environment of 20° C. Then, the average value for 30 capacitor elements was calculated.

[0125] (2) Initial Characteristics (ESR) The initial ESR (mΩ) of the capacitor element was measured at a frequency of 100 kHz using a four-terminal LCR meter in an environment of 20° C. Then, the average value for 30 capacitor elements was calculated.

[0126] (3) Reliability Test (After Charge and Discharge) An ON-OFF test in which charging to the rated voltage and discharging to 0 V was repeated 100,000 cycles at room temperature, and then the capacitance (Cap) and ESR (mΩ) were measured in the same manner as above, and the rate of change (ΔCap, ΔESR) relative to the initial characteristics was calculated.

[0127] (4) Reliability Test (After High-Temperature Load) The capacitor elements charged to the rated voltage were heated at 125°C for 100 hours, and then the capacitance (Cap) and ESR (mΩ) were measured in the same manner as above, and the rate of change (ΔCap, ΔESR) relative to the initial characteristics was calculated.

[0128] Table 1 shows the initial characteristics (standard values ​​with capacitor element B1 being 1.00) and the results of the reliability test.

[0129]

[0130] The solid electrolytic capacitor according to the present disclosure can suppress a decrease in capacitance and an increase in ESR when exposed to high temperatures. Furthermore, the solid electrolytic capacitor can suppress a decrease in capacitance when repeatedly charged and discharged. Therefore, the solid electrolytic capacitor according to the present disclosure is suitable for applications requiring high reliability.

[0131] 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.

[0132] 20: Solid electrolytic capacitor 1: Anode body 2: Anode wire 3: Dielectric layer 4: Solid electrolyte layer 5: Cathode lead layer 6: Anode portion 7: Cathode portion 8: Conductive adhesive layer 11: Outer case 13: Anode lead frame 14: Cathode lead frame

Claims

1. A solid electrolytic capacitor comprising at least one capacitor element including an anode body including a porous portion at least in a surface layer thereof, a dielectric layer covering at least a portion of the surface of the anode body, and a solid electrolyte layer covering at least a portion of the dielectric layer, wherein the solid electrolyte layer has, in the anode body having the dielectric layer, a first portion filled in the voids of the porous portion and a second portion protruding from a main surface of the anode body having the dielectric layer, and at least the first portion contains a self-doped conductive polymer and an antioxidant.

2. The solid electrolytic capacitor according to claim 1, wherein the mass content of the antioxidant in the first portion is higher than the mass content of the antioxidant in the second portion.

3. The solid electrolytic capacitor according to claim 1, wherein the second portion does not contain the antioxidant.

4. The solid electrolytic capacitor according to any one of claims 1 to 3, wherein the antioxidant includes a water-soluble antioxidant.

5. The solid electrolytic capacitor according to any one of claims 1 to 3, wherein the first portion further comprises a non-self-doping conductive polymer.

6. The solid electrolytic capacitor according to claim 5, wherein the non-self-doping conductive polymer comprises a conjugated polymer and a polymer anion.

7. The solid electrolytic capacitor according to claim 1 or 2, wherein the first portion includes a first layer covering at least a portion of a surface of the dielectric layer and a second layer covering at least a portion of the first layer, at least the second layer includes the antioxidant, and the mass content of the antioxidant in the second layer is higher than the mass content of the antioxidant in the first layer.

8. The solid electrolytic capacitor according to claim 7, wherein the first layer does not contain the antioxidant.

9. The solid electrolytic capacitor of claim 7, wherein the first layer comprises the self-doped conductive polymer, and the second layer comprises a non-self-doped conductive polymer.

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