Solid electrolytic capacitor and method for manufacturing the same

Abstract

This invention provides a solid electrolytic capacitor with suppressed leakage current and superior reliability. [Solution] The capacitor element included in a solid electrolytic capacitor includes an anode body having a porous portion on at least its surface, a dielectric layer, and a solid electrolyte layer. The solid electrolyte layer has a first portion filled in the voids of the porous portion in the anode body having the dielectric layer, and a second portion extending beyond the main surface of the anode body having the dielectric layer. The first portion includes an antioxidant component and also includes a solid electrolyte 2a and a solid electrolyte 2b covering at least a part of the solid electrolyte 2a. The solid electrolyte 2a includes a non-self-doped conductive polymer 2a. The solid electrolyte 2b includes a non-self-doped conductive polymer 2b. The conductivity C2a measured for the solid electrolyte 2a and the conductivity C2b measured for the solid electrolyte 2b are C2a

Description

[Technical Field]

[0001] This disclosure relates to a solid electrolytic capacitor and a method for manufacturing the same. [Background technology]

[0002] A solid electrolytic capacitor comprises, for example, a capacitor element and an outer casing that encloses the capacitor element. The capacitor element comprises, for example, a conductor (more specifically, an anode), a dielectric layer formed on the surface of the conductor, and a solid electrolyte layer covering 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 processing solution (such as a liquid dispersion) containing a conductive polymer. As the conductive polymer, for example, a self-doped conductive polymer or a non-self-doped conductive polymer (such as a conjugated polymer and dopants) is used.

[0003] Patent Document 1 proposes a capacitor comprising an electrode body (1) of an electrode material (2), wherein a dielectric (3) at least partially covers the surface (4) of the electrode material (2) to form an anode (5), and the anode (5) is at least partially coated with a solid electrolyte (6) comprising a heterogeneously doped conductive polymer, counterions that do not covalently bond with the heterogeneously doped conductive polymer, and a self-doped conductive polymer.

[0004] Patent Document 2 proposes a solid electrolytic capacitor comprising an anode made of valve metal, a dielectric layer formed on the anode, and a solid electrolyte layer formed on the dielectric layer, wherein the solid electrolyte layer comprises a first conductive polymer layer formed on the dielectric layer and heterogeneously doped with a single-molecule 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-doped conductive polymer having a plurality of side chains having dopeable functional groups, wherein the block layer blocks the movement of the self-doped conductive polymer from the second conductive polymer layer to the first conductive polymer layer, and / or the movement of the self-doped conductive polymer from the second conductive polymer layer into the pores of the porous anode. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Special Publication No. 2015-532525 [Patent Document 2] Japanese Patent Publication No. 2023-13918 [Overview of the project] [Problems that the invention aims to solve]

[0006] There is a need for solid electrolytic capacitors that exhibit suppressed capacity reduction even after repeated charging and discharging, possess high reliability, and have reduced leakage current. [Means for solving the problem]

[0007] A first aspect of this disclosure is a solid electrolytic capacitor comprising at least one capacitor element and an outer casing, The capacitor element includes an anode body having a porous portion in at least its 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. In the anode body having the dielectric layer, the solid electrolyte layer has a first portion filled in the voids of the porous portion and a second portion protruding from the main surface of the anode body having the dielectric layer. The first portion contains an antioxidant component and includes a solid electrolyte 2a and a solid electrolyte 2b that covers at least a part of the solid electrolyte 2a. The solid electrolyte 2a contains a non-self-doped conductive polymer 2a. The solid electrolyte 2b contains a non-self-doped conductive polymer 2b. Regarding the solid electrolytic capacitor, the conductivity C2a measured for the solid electrolyte 2a and the conductivity C2b measured for the solid electrolyte 2b satisfy C2a < C2b.

[0008] A second aspect of the present disclosure is a method for manufacturing a solid electrolytic capacitor including at least one capacitor element and an exterior body, The capacitor element includes an anode body having at least a porous portion on at least the surface layer, a dielectric layer covering at least a part of the surface of the anode body, and a solid electrolyte layer covering at least a part of the dielectric layer. In the anode body having the dielectric layer, the solid electrolyte layer has a first portion filled in the voids of the porous portion and a second portion protruding from the main surface of the anode body having the dielectric layer. The manufacturing method includes a step of forming the solid electrolyte layer. The step of forming the solid electrolyte layer includes a step of forming the first portion and a step of forming the second portion. The step of forming the first portion includes a step of forming the solid electrolyte 2a using a treatment liquid 2a containing a non-self-doped conductive polymer 2a, and a step of forming the solid electrolyte 2b using a treatment liquid 2b containing a non-self-doped conductive polymer 2b so as to cover at least a part of the solid electrolyte 2a. At least one of the treatment liquid 2a and the treatment liquid 2b further contains an antioxidant component. The treatment liquid 2a further contains a resistance component. The treatment liquid 2b either does not contain a resistance component or further contains a resistance component, and in the method for manufacturing a solid electrolytic capacitor, the concentration of the resistance component in the treatment liquid 2a is higher than the concentration of the resistance component in the treatment liquid 2b.

Advantages of the Invention

[0009] According to the present disclosure, high reliability of the solid electrolytic capacitor can be ensured and leakage current can be reduced.

Brief Description of the Drawings

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

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present disclosure will be described with 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 can be obtained. For components other than the characteristic parts of the present disclosure, components of known capacitors may be applied. In this specification, when it is said "the range of numerical value A to numerical value B", the range includes numerical value A and numerical value B. When a plurality of materials are exemplified, one of them may be selected and used alone, or two or more of them may be used in combination.

[0012] The present disclosure includes combinations of matters described in two or more claims arbitrarily selected from a plurality of claims described in the appended claims. That is, as long as no technical contradiction occurs, matters described in two or more claims arbitrarily selected from a plurality of claims described in the appended claims can be combined.

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

[0014] When the charge and discharge of a solid electrolytic capacitor are repeated or the solid electrolytic capacitor is exposed to a high-temperature environment, the reliability may decrease. Specifically, the capacitance may decrease or the ESR (equivalent series resistance) may increase. This is considered to be due to the oxidative degradation of the solid electrolyte layer or the peeling in the solid electrolyte layer. The peeling of the solid electrolyte layer includes internal peeling within the solid electrolyte layer and interfacial peeling between the dielectric layer and the solid electrolyte layer. Due to the oxidative degradation and peeling, the conductivity of the solid electrolyte layer and the conductivity between the dielectric layer and the solid electrolyte layer decrease.

[0015] The inventors have found that in a solid electrolytic capacitor, when the solid electrolyte layer contains an antioxidant, oxidative degradation of the conductive polymer is suppressed, and a decrease in capacitance and an increase in ESR are suppressed. However, it has been clarified that in such a solid electrolytic capacitor, sufficient reliability may not be obtained due to an increase in leakage current.

[0016] Technology (1) The solid electrolytic capacitor according to the first aspect of the present disclosure includes at least one capacitor element and an exterior body. The capacitor element includes an anode body including a porous portion at least on the surface layer, a dielectric layer covering at least a part of the surface of the anode body, and a solid electrolyte layer covering at least a part of the dielectric layer. The solid electrolyte layer has a first portion filled in 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. The first portion includes a solid electrolyte 2a containing an antioxidant component and having a conductivity C2a, and a solid electrolyte 2b covering at least a part of the solid electrolyte 2a and having a conductivity C2b. The solid electrolyte 2a includes a non-self-doped conductive polymer 2a. The solid electrolyte 2b includes a non-self-doped conductive polymer 2b. The conductivity C2a measured for the solid electrolyte 2a and the conductivity C2b measured for the solid electrolyte 2b satisfy C2a < C2b.

[0017] In the present disclosure, the first part includes a non-self-doped conductive polymer and an antioxidant component. In addition, as described above, the conductivities C2a and C2b of the solid electrolytes 2a and 2b constituting the first part satisfy C2a < C2b. As a result, the reduction in capacitance when charge and discharge are repeated is suppressed, and the leakage current can be reduced. In addition, a high withstand voltage property of the solid electrolytic capacitor can be obtained.

[0018] More specifically, in the present disclosure, since the first part contains an antioxidant component, it is considered that the oxidative degradation of the conductive polymer is suppressed, and internal peeling and interlayer peeling of the solid electrolyte are suppressed. As a result, it is considered that the reduction in capacitance when charge and discharge are repeated is suppressed, and high reliability can be obtained. On the other hand, when the first part contains an antioxidant, the film repairing property of the dielectric layer decreases, and the leakage current tends to increase. When the leakage current increases, the product failure rate due to the leakage current (also referred to as the leakage current failure rate) increases. In the present disclosure, the relationship between the conductivities of the solid electrolytes 2a and 2b is C2a < C2b. By providing the solid electrolyte 2a with a low conductivity on the side closer to the dielectric layer, the leakage current can be reduced and the withstand voltage property can be enhanced. In addition, the high-capacity can be maintained by the solid electrolyte 2b with a high conductivity, and it becomes easier to obtain high reliability. In addition, the equivalent series resistance (ESR) of the solid electrolytic capacitor can be kept low.

[0019] Note that the reason why the antioxidant not only suppresses the oxidative degradation of the conductive polymer but also suppresses the internal peeling and interlayer peeling of the solid electrolyte is not clear. Probably, the improvement of the film quality of the solid electrolyte layer by the antioxidant contributes to the suppression of the internal peeling and interlayer peeling. The finding that the strength of the solid electrolyte layer is improved and the adhesion between the solid electrolyte layer and the dielectric layer is improved by the antioxidant has also been obtained. Such an improvement in adhesion is considered to contribute to the improvement of reliability.

[0020] [[ID=_{11}]] Technology (2) In the above technology (1), the first part may include a first solid electrolyte covering at least a portion of the dielectric layer, and a second solid electrolyte covering at least a portion of the first solid electrolyte. The first solid electrolyte may contain a self-doped conductive polymer. The second solid electrolyte may include a solid electrolyte 2a covering at least a portion of the first solid electrolyte, and a solid electrolyte 2b. Self-doped conductive polymers are suitable for coating the surface of the dielectric layer because they have a small particle size and are easily impregnated into porous parts. By covering at least a portion of the dielectric layer with a first solid electrolyte containing a self-doped conductive polymer, a second solid electrolyte containing a non-self-doped conductive polymer and an antioxidant component is more easily formed. This makes it easier for the effects of the second solid electrolyte to be exhibited. As a result, higher reliability can be obtained, and leakage current can be further reduced.

[0021] Technology(3) In the above techniques (1) or (2), the conductivity C2b measured for a 5 μm thick thin film of the solid electrolyte 2b is preferably 200 S / cm or more. In this case, the solid electrolyte 2b allows for the maintenance of a higher capacitance, making it easier to obtain high reliability. In addition, the equivalent series resistance (ESR) of the solid electrolytic capacitor can be kept low.

[0022] Technology(4) In any one of the above technologies (1) to (3), the conductivity C2a measured for a 5 μm thick thin film of the solid electrolyte 2a is preferably 1 S / cm or less. By providing a solid electrolyte 2a with low conductivity on the side closer to the dielectric layer of the first portion, leakage current can be further reduced, and higher dielectric strength can be obtained.

[0023] Technology(5) In any one of the above technologies (1) to (4), the ratio of the average thickness T2b of the solid electrolyte 2b to the average thickness T2a of the solid electrolyte 2a (=T2b / T2a) is preferably 2 or more and 5 or less. In this case, it is easier to obtain higher capacitance and higher reliability while keeping leakage current low.

[0024] Technology(6) In any one of the above technologies (1) to (5), the second portion may or may not contain an antioxidant component. Preferably, the mass content of the antioxidant component in the first portion is higher than the mass content of the antioxidant component 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 further away from the dielectric layer. Therefore, by including an antioxidant in the first portion at a sufficient concentration, the reliability of the solid electrolytic capacitor can be efficiently improved.

[0025] Technology(7) In any one of the above technologies (1) to (6), it is preferable that the second portion does not contain the antioxidant component. In technology (6) or technology (7), by not including an antioxidant that is an insulator in the second portion, the ESR of the solid electrolytic capacitor can be kept low and the capacitance extraction performance is improved.

[0026] Technology(8) In any one of the above technologies (1) to (7), the first part preferably contains silicon. In the first part, the conductivity of solid electrolyte 2a and solid electrolyte 2b is different. The conductivity can be adjusted, for example, by the content of a resistive component such as a silane compound in the solid electrolyte. Therefore, by including silicon in the first part, the conductivity becomes lower compared to the case where silicon is not included, making it easier to reduce leakage current.

[0027] Technology(9) In the above technique (8), it is preferable that the mass content rate of silicon element in the solid electrolyte 2a is higher than that in the solid electrolyte 2b. In this case, the conductivity of each of the solid electrolytes 2a and 2b can be easily adjusted by a silane compound or the like, and the relationship of C2a < C2b can be satisfied. As a result, high reliability and leakage current suppression can be easily achieved simultaneously. Also, by analyzing the silicon element, the relationship of C2a < C2b can be easily confirmed.

[0028] Technique (10) The present disclosure also includes a method for manufacturing a solid electrolytic capacitor including at least one capacitor element and an exterior body. The capacitor element includes an anode body including a porous portion at least on the surface layer, a dielectric layer covering at least a part of the surface of the anode body, and a solid electrolyte layer covering at least a part of the dielectric layer. The solid electrolyte layer has a first portion filled in the voids of the porous portion and a second portion protruding from the main surface of the anode body having the dielectric layer in the anode body having the dielectric layer. The manufacturing method includes a step of forming the solid electrolyte layer. The step of forming the solid electrolyte layer includes a step of forming the first portion and a step of forming the second portion. The step of forming the first portion includes a step of forming a solid electrolyte 2a using a treatment liquid 2a containing a non-self-doping type conductive polymer 2a, and a step of forming a solid electrolyte 2b using a treatment liquid 2b containing a non-self-doping type conductive polymer 2b so as to cover at least a part of the solid electrolyte 2a. At least one of the treatment liquid 2a and the treatment liquid 2b further includes an antioxidant component. The treatment liquid 2a further includes a resistance component. The treatment liquid 2b does not include a resistance component or further includes a resistance component, and the concentration of the resistance component in the treatment liquid 2a is higher than the concentration of the resistance component in the treatment liquid 2b.

[0029] By such a manufacturing method, a solid electrolyte 2a and a solid electrolyte 2b in which the relationship of conductivity satisfies C2a < C2b are formed. Since the first portion includes the solid electrolyte 2a and the solid electrolyte 2b, leakage current is suppressed. In addition, since the first portion includes an antioxidant component, high reliability is obtained.

[0030] Technology(11) In the above technology (10), the resistive component may include a silane compound. By using a silane compound as the resistive component, the conductivity of the solid electrolyte 2a and solid electrolyte 2b can be easily adjusted while ensuring high capacitor performance.

[0031] Technology(12) In the above technology (10) or technology (11), the first portion may include a first solid electrolyte covering at least a portion of the dielectric layer, and a second solid electrolyte covering at least a portion of the first solid electrolyte. The second solid electrolyte includes a solid electrolyte 2a covering at least a portion of the first solid electrolyte, and a solid electrolyte 2b. The step of forming the first portion includes forming the first solid electrolyte using a first processing solution containing a self-doped conductive polymer. The step of forming the solid electrolyte 2a is performed so as to cover at least a portion of the first solid electrolyte. Because the first solid electrolyte containing the self-doped conductive polymer is formed prior to the formation of the second solid electrolyte, the inner surface of the porous material is more easily coated with the first solid electrolyte, and the second solid electrolyte containing a non-self-doped conductive polymer and antioxidant components is more easily formed. This makes it easier for the effects of the second solid electrolyte to be exhibited. As a result, higher reliability can be obtained and leakage current can be further reduced.

[0032] The solid electrolytic capacitor and its manufacturing method described herein will be explained in more detail below, including the above techniques (1) to (12), with reference to drawings as necessary. To the extent that it is not technically inconsistent, at least one of the above techniques (1) to (12) may be combined with at least one of the elements described below. Note that the figures are schematic representations, and the proportions of the dimensions (e.g., thickness) of each component may differ from those of actual components.

[0033] [Solid electrolytic capacitors] The solid electrolytic capacitor of this disclosure comprises a capacitor element. The solid electrolytic capacitor has at least one capacitor element. The solid electrolytic capacitor may have two or more capacitor elements.

[0034] (Capacitor element) The capacitor element includes an anode, a dielectric layer covering at least a portion of the surface of the anode, and a cathode portion covering at least a portion of the dielectric layer. The cathode portion includes a solid electrolyte layer covering at least a portion of the dielectric layer. The cathode portion may also include a cathode extraction layer covering at least a portion of the solid electrolyte layer.

[0035] (Anode) The anode body may include, for example, a valve metal, an alloy containing a valve metal, or a compound containing a valve metal. The anode body may contain one of these materials or a combination of two or more. Preferred valve metals include, for example, aluminum, tantalum, niobium, and titanium.

[0036] The anode body includes a porous region at least on its surface. This increases the surface area of ​​the anode body, allowing for higher capacitance.

[0037] An anode having a porous surface can be obtained, for example, by roughening the surface of a substrate containing a valve-acting metal (such as a sheet-like substrate (e.g., foil-like or plate-like substrate)) by etching. Surface roughening can be performed, for example, by etching.

[0038] An anode foil having a porous surface comprises, for example, a core and a porous portion integrated with the core. The porous portion may be formed on the surface of each of the two main surfaces of the anode foil.

[0039] The thickness of the anode foil is, for example, between 15 μm and 300 μm.

[0040] The anode body may be a porous molded body or a porous sintered body of particles containing valve metal. In both the porous molded body and the sintered body, the entire anode body typically has a porous structure. The molded body and the sintered body may be in sheet form, or they may be rectangular parallelepipeds, cubes, or similar shapes.

[0041] The anode body includes, for example, a cathode forming portion where a cathode portion (particularly a solid electrolyte layer) is formed via a dielectric layer, and an anode portion where no cathode portion is formed. A separation portion may be formed at the end of the anode portion on the cathode forming portion side to ensure insulation between the cathode portion and the anode portion. The portion of the anode portion where no separation portion is formed is sometimes called the anode lead portion. Anode lead terminals may be connected to the anode portion. The separation portion is formed of, for example, an insulating material (such as an insulating resin).

[0042] If the anode is a porous molded or sintered body, a portion of the metal lead member is embedded in the molded or sintered body.

[0043] (Dielectric layer) The dielectric layer is an insulating layer that functions as a dielectric. The dielectric layer may also be an oxide film. The surface of the dielectric layer has a fine uneven surface shape depending on the shape of the surface of the porous part of the anode body.

[0044] For example, a dielectric layer, which is an oxide film, may be formed on the surface of the anode by chemical conversion treatment. The chemical conversion treatment may be carried out, for example, by immersing the anode in a conversion solution and anodizing the surface of the anode. As the conversion solution, for example, a solution containing an acid such as phosphoric acid or adipic acid may be used. The oxide film may be formed using a gas-phase method, or by heating the anode in an oxygen-containing atmosphere and oxidizing the surface.

[0045] The dielectric layer may contain an oxide of the valve metal. For example, when tantalum is used as the valve metal, the dielectric layer contains Ta2O5, and when aluminum is used as the valve metal, the dielectric layer contains Al2O3. However, the dielectric layer is not limited to these specific examples.

[0046] (solid electrolyte layer) The solid electrolyte layer has a first portion and a second portion. The first portion is a part that fills the voids in the porous portion of the anode body, at least a part of which is a dielectric layer. The second portion, on the other hand, is a part that extends beyond the main surface of the anode body having a dielectric layer.

[0047] A portion of the first part may not be filled within the voids of the porous portion having the dielectric layer, but may protrude from the main surface of the porous portion having the dielectric layer. That is, the first part may have an inner layer filled within the voids of the porous portion having the dielectric layer, and an outer layer that protrudes from the main surface of the porous portion having the dielectric layer.

[0048] The second portion may be formed as a skin covering the anode body having a 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 of the inner layer of the first portion to the entire first portion (Rv1) is greater than the volume ratio of the portion of the second portion that can be filled into the voids of the porous portion having the dielectric layer to the entire second portion (Rv2). Rv1 is at least twice that of Rv2.

[0049] (Part 1) In this disclosure, the first portion of the solid electrolyte layer includes an antioxidant component. (Antioxidant component) Antioxidant components are ingredients that have the effect of inactivating radicals generated with the involvement of oxygen. Antioxidant components include not only those commonly called antioxidants, but also components called degradation inhibitors, anti-aging agents, radical chain inhibitors, peroxide decomposers, chain initiation inhibitors, light stabilizers, heat stabilizers (or heat-resistant stabilizers), metal deactivators, UV absorbers, and weather-resistant stabilizers.

[0050] Examples of antioxidant components include antioxidants containing at least one selected from the group consisting of a hydroxyl group, a nitrogen atom, an oxygen atom, a sulfur atom, and a phosphorus atom. Examples of such antioxidants include phenolic antioxidants, amine antioxidants, phosphorus antioxidants, sulfur antioxidants, benzimidazole antioxidants, and carotenoid compounds. Among these, phenolic antioxidants are preferred due to their high efficacy.

[0051] Phenolic antioxidants have phenolic hydroxyl groups. Phenolic antioxidants may be monocyclic compounds having only one aromatic ring with a phenolic hydroxyl group, or compounds having multiple aromatic rings with phenolic hydroxyl groups. Among these, monocyclic compounds having only one aromatic ring with a phenolic hydroxyl group are preferred because they have a small molecular weight and can exhibit high effectiveness in small amounts. Furthermore, from the viewpoint of maintaining high conductivity of the solid electrolyte layer, materials with low insulating properties are preferred. Such phenolic antioxidants may contain two or more phenolic hydroxyl groups in one molecule, or three or more. The upper limit of the number of phenolic hydroxyl groups bonded to the aromatic ring can be selected according to the size of the aromatic ring, for example, five or fewer, four or fewer, or three or fewer. Examples of such phenolic antioxidants include pyrogallol, catechol, gallic acid, and L-ascorbic acid. These are also preferred because they are water-soluble. It is preferable that the antioxidant component includes a water-soluble antioxidant. This is because it facilitates the uniform dispersion of antioxidants in aqueous treatment solutions containing non-self-doped conductive polymers.

[0052] The aromatic ring having a phenolic hydroxyl 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 crosslinking ring. Examples of aromatic rings include aromatic hydrocarbon rings with 6 to 20 carbon atoms (e.g., 6 to 14 or 6 to 10 carbon atoms) (benzene, naphthalene, phenanthrene, anthracene, etc.) and aromatic heterocycles with 5 to 20 members (e.g., 6 to 14 carbon atoms) (furan, pyrrole, thiophene, imidazole, pyridine, pyrazine, quinoline, indole, benzimidazole, benzotriazole, purine, etc.). Examples of fused rings of aromatic rings and non-aromatic rings include chromene, chromone, chroman, coumarin, 4H-chromene-4-one, and carbazole. Examples of non-aromatic rings include alicyclic hydrocarbon rings with 5 to 14 carbon atoms (e.g., 5 to 10 carbon atoms) such as cyclopentane, cyclohexane, and cyclooctane; bridging hydrocarbon rings with 6 to 20 carbon atoms (e.g., 6 to 14 carbon atoms) such as norbornane, norbornene, and dicyclopentadiene; and non-aromatic heterocycles with 5 to 20 members (e.g., 6 to 14 members) such as tetrahydrofuran, dioxolane, dioxane, pyrrolidine, piperidine, morpholine, and thiazine.

[0053] The antioxidant component may contain one of these antioxidants, or a combination of two or more.

[0054] The first part includes at least a solid electrolyte 2a and a solid electrolyte 2b covering at least a portion of the solid electrolyte 2a. The solid electrolyte 2a may cover at least a portion of the dielectric layer. The first part may further include a first solid electrolyte covering at least a portion of the dielectric layer. In this case, the first part includes a second solid electrolyte covering at least a portion of the first solid electrolyte. The second solid electrolyte includes a solid electrolyte 2a covering at least a portion of the first solid electrolyte and a solid electrolyte 2b.

[0055] The antioxidant component may be included in either the first solid electrolyte or the second solid electrolyte. From the viewpoint of obtaining higher reliability, it is preferable that at least the second solid electrolyte contains the antioxidant component. The antioxidant component may be included in both solid electrolyte 2a and solid electrolyte 2b, or in either one. The first solid electrolyte does not need to contain the antioxidant component.

[0056] The mass content of the antioxidant component in the first part may be 0.1% by mass or more and 40% by mass or less, 1% by mass or more and 35% by mass or less, or 10% by mass or more and 30% by mass or less. Having the mass content of the antioxidant component within this range ensures higher capacitance when the solid electrolytic capacitor is repeatedly charged and discharged, resulting in higher reliability.

[0057] In solid electrolytic capacitors, the distribution of antioxidant components in the solid electrolyte layer is determined by time-of-flight secondary ion mass spectrometry (TOF-SIMS). Depending on the target chemical species, either negative or positive mode may be used in the analysis. TOF-SIMS analysis is performed by etching the solid electrolyte layer from the outermost surface toward the anode (for example, from the outermost surface toward the anode).

[0058] (1st solid electrolyte) The first solid electrolyte includes, for example, a self-doped conductive polymer.

[0059] Self-doped conductive polymers, for example, have a conjugated polymer skeleton and functional groups (such as anionic groups) that function as dopants, directly or indirectly bonded to this skeleton by covalent bonds.

[0060] Examples of anionic groups include sulfo groups, carboxyl groups, phosphate groups, and phosphonic acid groups. Self-doped conductive polymers may contain one type of anionic group, or two or more types. From the viewpoint of easily ensuring higher conductivity of self-doped conductive polymers, self-doped conductive polymers may contain at least a sulfo group.

[0061] The anionic groups of a self-doped conductive polymer may be present in any form, such as anions, acids, esters, and salts, and may be present in a form that interacts with or is complexed with components contained in the solid electrolyte layer. In this specification, all of these forms are simply referred to as anionic groups.

[0062] Examples of conjugated polymers that constitute the backbone of self-doped conductive polymers include polymers with a π-conjugated polymer (such as polypyrrole, polythiophene, polyaniline, polyfuran, polyacetylene, polyphenylene, polyphenylenevinylene, polyacene, and polythiophenevinylene) as the basic backbone. The above polymers only need to contain at least one monomer unit that constitutes the basic backbone. The above polymers also include homopolymers, copolymers of two or more monomers, and derivatives thereof (such as substituted products having substituents). For example, polythiophene includes poly(3,4-ethylenedioxythiophene). Self-doped conductive polymers have anionic groups in the backbone of these conjugated polymers. The anionic groups may be directly introduced into the backbone of the conjugated polymer or introduced via linking groups. Preferred linking groups include polyvalent groups (divalent groups) containing alkylene groups. Examples of linking groups include aliphatic polyvalent groups (divalent groups, etc.) such as alkylene groups, -R 1 -XR 2 - group (X is an oxygen element or a sulfur element, R 1 and R 2These are identical or different alkylene groups. The number of carbon atoms in each alkylene group included in the linking group is, for example, 1 to 10, or 1 to 6. The alkylene group may be linear or branched. The linking group may contain, for example, at least an alkylene group with 2 or more carbon atoms. The number of carbon atoms in such an alkylene group may be 2 to 10 (or 3 to 10), or 2 to 6 (or 3 to 6). For example, R 1 is an alkylene group having 1 to 6 carbon atoms, and R 2 The linking group 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 backbone of the self-doped conductive polymer may be polypyrrole, polythiophene, or polyaniline. From the viewpoint of easily obtaining high conductivity, a polymer having a conjugated polymer backbone containing a repeating structure of monomer units corresponding to the thiophene compound, and an anionic group introduced into this backbone, is preferred as the self-doped conductive polymer.

[0064] Examples of thiophene compounds include compounds having a thiophene ring and capable of forming a repeating structure of the corresponding monomer unit. Thiophene compounds can form a repeating structure of monomer units by linking at the 2nd and 5th positions of the thiophene ring.

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

[0066] Examples of substituents include alkyl groups (such as C alkyl groups like methyl group, ethyl group, etc.), alkoxy groups (such as C alkoxy groups like methoxy group, ethoxy group, etc.), hydroxy group, hydroxyalkyl groups (such as hydroxy C alkyl groups like hydroxymethyl group, etc.), etc., but are not limited thereto. When the thiophene compound has two or more substituents, each substituent 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, etc.). 1-4 alkyl groups, etc.), alkoxy groups (such as C 1-4 alkoxy groups, etc.), hydroxy group, hydroxyalkyl groups (such as hydroxy C 1-4 alkyl groups, etc.), etc., but are not limited thereto. When the thiophene compound has two or more substituents, each substituent 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, etc.).

[0067] The self-doped conductive polymer may have a skeleton of a conjugated polymer (such as PEDOT) containing a repeating structure of monomer units corresponding to at least 3,4-ethylenedioxythiophene compounds (such as 3,4-ethylenedioxythiophene (EDOT), etc.). The skeleton 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 said monomer units, monomer units corresponding to thiophene compounds other than EDOT.

[0068] An example of the monomer unit of the self-doped conductive polymer is shown below. * represents a bond.

[0069]

Chemical formula

[0070] The weight average molecular weight (Mw) of the self-doped 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 the polystyrene-converted value measured by gel permeation chromatography (GPC). GPC is typically measured using a polystyrene gel column and water / methanol (volume ratio 8 / 2) as the mobile phase.

[0072] (Second solid electrolyte) The second solid electrolyte includes a solid electrolyte 2a covering at least a portion of the dielectric layer or the first solid electrolyte, and a solid electrolyte 2b covering at least a portion of the solid electrolyte 2a. The second solid electrolyte preferably contains a non-self-doped conductive polymer, and more preferably contains an antioxidant component. The inclusion of a non-self-doped conductive polymer in the second solid electrolyte makes it easier to obtain high conductivity. The inclusion of a non-self-doped conductive polymer and an antioxidant component in the second solid electrolyte suppresses oxidative degradation of the conductive polymer and inhibits delamination within the solid electrolyte and between layers, thereby maintaining high conductivity and obtaining high capacity.

[0073] (Non-self-doped conductive polymer) The non-self-doped conductive polymer includes, for example, a non-self-doped conjugated polymer (e.g., a conjugated polymer without anionic groups) and a dopant.

[0074] Solid electrolyte 2a includes a non-self-doped conductive polymer 2a. Solid electrolyte 2b includes a non-self-doped conductive polymer 2b. The non-self-doped conductive polymer 2a and the non-self-doped conductive polymer 2b may have the same type of conjugated polymer and dopant, and their respective molecular weights may be the same, or at least one of the conjugated polymer and dopant may have different types or molecular weights.

[0075] Examples of conjugated polymers included in non-self-doped conductive polymers include the conjugated polymers exemplified as conjugated polymers constituting the backbone of self-doped conductive polymers (such as π-conjugated polymers). Conjugated polymers may be used individually or in combination of two or more types. From the viewpoint of easily ensuring high initial capacity and voltage resistance, as well as high heat resistance, non-self-doped conjugated polymers containing repeating structures of monomer units of thiophene compounds may be used. Examples of thiophene compounds corresponding to the monomer units of non-self-doped conjugated polymers include the thiophene compounds described for self-doped conductive polymers. Non-self-doped conjugated polymers may include conjugated polymers (such as PEDOT) containing repeating structures of monomer units corresponding to at least 3,4-ethylenedioxythiophene compounds (such as EDOT). Conjugated polymers containing repeating structures of monomer units corresponding to at least EDOT may contain only the monomer units corresponding to EDOT, or they may contain monomer units corresponding to thiophene compounds other than EDOT in addition to the monomer units.

[0076] The dopant can be at least one selected from the group consisting of anions and polyanions (polymer anions, etc.). 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 from the viewpoint of easily obtaining higher heat resistance and reliability, as well as higher dielectric strength. Examples of polymer anions having a sulfo group include high molecular weight polysulfonic acid. Specific examples of polymer anions include polyvinylsulfonic acid, polystyrenesulfonic acid (PSS (including copolymers and substituted products having substituents)), polyallylsulfonic acid, polyacrylic sulfonic acid, polymethacrylatesulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprenesulfonic acid, polyestersulfonic acid (aromatic polyestersulfonic acid, etc.), and phenolsulfonic acid novolac resin. However, Dopants are not limited to these specific examples. Dopants may be used individually or in combination of two or more types.

[0077] The unself-doped conductive polymer (or each of the unself-doped conductive polymers 2a and 2b) contained in the second solid electrolyte preferably contains a conjugated polymer (unself-doped conjugated polymer) and a polymer anion. This is because it is easier to obtain high conductivity in the solid electrolyte layer, and because oxidative degradation of the conductive polymer is suppressed, higher reliability of the solid electrolytic capacitor can be obtained.

[0078] In a non-self-doped conductive polymer, the amount of dopant may be 10 to 1000 parts by mass, or 20 to 500 parts by mass, per 100 parts by mass of the conjugated polymer.

[0079] (conductivity) The conductivity C2a of the solid electrolyte 2a and the conductivity C2b of the solid electrolyte 2b satisfy C2a < C2b. When the first part contains an antioxidant component, the film restorability of the dielectric layer decreases and the leakage current increases. In the present disclosure, by having the solid electrolyte 2a with a low conductivity present on the side closer to the dielectric layer, the leakage current when the first part contains an antioxidant component can be greatly reduced.

[0080] The ratio of the conductivity C2a to the conductivity C2b (= C2a / C2b) is preferably 5 or more, more preferably 10 or more or 100 or more, and even more preferably 150 or more or 200 or more. When the ratio of each conductivity is within such a range, the leakage current can be further reduced by the solid electrolyte 2a with a low conductivity, and high withstand voltage characteristics can be ensured. Also, a higher capacitance is more easily obtained by the solid electrolyte 2b with a high conductivity.

[0081] The conductivity C2a is preferably 5 S / cm or less, more preferably 1 S / cm or less. When the conductivity C2a is within such a range, the leakage current can be further reduced and high withstand voltage characteristics can be obtained. The conductivity C2a may also be 0.01 S / cm or more.

[0082] The conductivity C2b is preferably 100 S / cm or more, more preferably 200 S / cm or more. When the conductivity C2b is within such a range, a higher capacitance is more easily obtained. The conductivity C2b may also be 1000 S / cm or less.

[0083] The conductivity of each solid electrolyte may be measured by, for example, preparing a thin film sample with the same composition as the solid electrolyte and measuring the conductivity using this sample. A more specific example of a conductivity measurement method is described below. First, a processing solution for forming the solid electrolyte is applied to the surface of a glass plate and dried by heating at a temperature of 140°C to 180°C for 10 to 20 minutes to form a thin film (5 μm thick) of the solid electrolyte. The conductivity (S / cm) of this thin film is measured using a Loresta-GP (MCP-T610 series 4-probe probe) manufactured by Nitto Seiko Analytech Co., Ltd., and this is taken as the conductivity of the solid electrolyte. The conductivity C2a and C2b of 5 μm thick thin films of each solid electrolyte are measured using a processing solution containing a conductive polymer for preparing solid electrolyte 2a or solid electrolyte 2b.

[0084] (Resistance component) Solid electrolytes 2a and 2b differ in conductivity as described above. The conductivity of each solid electrolyte can be adjusted by the composition of the solid electrolyte, but it can be easily adjusted by using a resistive component. Examples of resistive components include organic compounds and silane compounds. From the viewpoint of easier uniform dispersion in the solid electrolyte, relatively low molecular weight compounds are preferred for the resistive component. The molecular weight (or weight-average molecular weight) of the resistive component is preferably 3000 or less, and may be 2000 or less.

[0085] Silane compounds are readily available commercially as silane coupling agents and other similar products. Adding silane compounds to solid electrolytes can increase the resistance of the solid electrolyte and reduce delamination within the solid electrolyte.

[0086] As the silane compound, a compound having a silicon atom and four radicals covalently bonded to the silicon atom may be used. At least one of the four radicals may be a reactive functional group. Reactive functional groups may include epoxy groups, alkyl halides, amino groups, ureido groups, mercapto groups, isocyanate groups, polymerizable groups, etc. Examples of polymerizable groups include acryloyl groups, methacryloyl groups, vinyl groups, etc. At least one of the four radicals may be hydrolyzable. Hydrolyzable radicals may include, for example, alkoxy groups such as methoxy groups, ethoxy groups, and propoxy groups, halogen atoms such as chlorine atoms and bromine atoms, etc.

[0087] The reactive functional groups or hydrolyzable groups of the silane compound may interact with or bond to other components in the solid electrolyte (such as conductive polymers) or dielectric layers.

[0088] A silane coupling agent may be used as the silane compound. Preferred silane coupling agents include those having an epoxy group and those having an acrylic group.

[0089] Examples of silane coupling agents having an epoxy group include 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 3-glycidoxypropyltriethoxysilane.

[0090] Examples of silane coupling agents having an acrylic group include 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, and 3-acryloxypropyltrimethoxysilane (γ-acryloxypropyltrimethoxysilane).

[0091] Other 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, hydrochloride of N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane, 3-ureidopropyltriethoxysilane, 3-chloropropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, bis(triethoxysilylpropyl)tetrasulfide, 3-isocyanatopropyltriethoxysilane, and the like.

[0092] These resistance components (such as silane compounds) may be used alone or in combination of two or more.

[0093] (Silicon element) The first part may contain a silicon element. When using a silane compound to adjust the conductivity of a solid electrolyte, due to the silane compound, the solid electrolyte contains a silicon element. To confirm the presence of the silane compound or to confirm the relationship between the high and low conductivity between solid electrolytes, mapping of the silicon element may be used.

[0094] In the present disclosure, the conductivity of solid electrolyte 2a and solid electrolyte 2b satisfies the relationship of C2a < C2b. Therefore, it can be said that the mass content rate of the silicon element in solid electrolyte 2a is higher than that in solid electrolyte 2b.

[0095] The mass content rate of the silicon element in solid electrolyte 2a is preferably 1 mass% or more and 500 mass% or less, and more preferably 1 mass% or more and 100 mass% or less.

[0096] The ratio of the mass content of silicon element P2b in solid electrolyte 2b to the mass content of silicon element P2a in solid electrolyte 2a (=P2b / P2a) is less than 1, preferably 0.10 or less, and more preferably 0.01 or less. It is also preferable that P2b is 0 mass% (P2b / P2a ratio is 0).

[0097] The silicon elements in solid electrolytes 2a and 2b are determined by the following procedure. First, a cross-sectional image (including the porous portion) of the thickness direction of the anode body of the solid electrolytic capacitor or capacitor element is taken using a scanning electron microscope (SEM) or a transmission electron microscope (TEM). Next, elemental mapping is performed using energy dispersive X-ray spectroscopy (EDX) analysis with this image to obtain a map of silicon elements in the portion filled in the depressions of the porous part. Using the above image, solid electrolyte 2a and solid electrolyte 2b are distinguished by the difference in the distribution of silicon elements. For example, the two solid electrolytes can be distinguished by binarization of the image. In the elemental mapping, the region where the second metal is distributed among the metal oxide regions is identified and designated as the second dielectric layer. Within the metal oxide region, a region between the anode and the second dielectric layer where the first metal element is distributed and the second metal element is not distributed (below the detection limit of the second metal) is identified and designated as the first dielectric layer. From the above elemental mapping, the abundance ratio (mass content) of silicon element in solid electrolyte 2a and the abundance ratio (mass content) of silicon element in solid electrolyte 2b are determined.

[0098] (Thickness of solid electrolyte) The average thickness of the solid electrolyte 2b is preferably greater than the average thickness of the solid electrolyte 2a, as this allows for higher capacity and also helps to keep the ESR low. Furthermore, even if the average thickness of the solid electrolyte 2a is relatively small, its low conductivity ensures a reduction in leakage current, resulting in high dielectric strength.

[0099] The ratio of the average thickness T2b of the solid electrolyte 2b to the average thickness T2a of the solid electrolyte 2a (=T2b / T2a) is preferably greater than 1 and 10 or less, more preferably between 2 and 7, and even more preferably between 2 and 5. Having the ratio T2b / T2a within this range makes it easier to achieve high capacity and high reliability while keeping leakage current low.

[0100] The average thickness of each solid electrolyte can be determined using the cross-sectional image used to determine the mass content of silicon. More specifically, first, solid electrolyte 2a and solid electrolyte 2b are distinguished in the cross-sectional image as previously described. The average thickness is then determined by measuring the thickness at any 10 points in the cross-sectional image of each solid electrolyte and calculating the average value of these measurements.

[0101] (Second part) The second part may contain a self-doped conductive polymer or a non-self-doped conductive polymer. From the viewpoint of easily adjusting the thickness of the second part and easily obtaining high conductivity, it is preferable that the second part contains a non-self-doped conductive polymer. For details on the self-doped conductive polymer and the non-self-doped conductive polymer, please refer to the explanation in the first part.

[0102] The second part may or may not contain antioxidant components. However, it is preferable that the mass content of antioxidant components in the first part is higher than the mass content of antioxidant components in the second part. A low mass content of antioxidant components in the second part makes it easier to obtain high conductivity in the solid electrolyte layer, resulting in high initial capacitance and low initial ESR. The antioxidant component's effect of suppressing oxidative degradation of the conductive polymer is more easily exerted in the first part than in the second part. In this disclosure, the inclusion of antioxidant components in the first part provides high reliability for the solid electrolytic capacitor. It is also preferable that the second part does not contain antioxidant components. When the second part does not contain antioxidant components, this includes cases where the antioxidant components in the second part are below the detection limit.

[0103] (others) The solid electrolyte layer may contain additives. Examples of additives include known additives added to the solid electrolyte layer, known conductive materials other than conductive polymers (e.g., conductive inorganic materials such as manganese dioxide, TCNQ complex salts), etc. The solid electrolyte layer may contain one type of additive, or two or more types in combination.

[0104] (Formation of a solid electrolyte layer) The method for manufacturing a solid electrolytic capacitor according to this disclosure includes a step of forming a solid electrolyte layer. The step of forming the solid electrolyte layer includes a step of forming a first portion and a step of forming a second portion.

[0105] Each solid electrolyte is generally formed by using a processing solution (such as a solution or liquid dispersion) containing the constituent components of each solid electrolyte, or by in-situ polymerization (such as chemical polymerization or electrolytic polymerization) using a polymerization solution containing a precursor and dopant of a conjugated polymer. A combination of in-situ polymerization and a method using a liquid composition containing a conductive polymer may also be used. In in-situ polymerization, an oxidizing agent may be used as needed.

[0106] (Process for forming the first part) In this disclosure, the step of forming the first part includes the steps of forming a solid electrolyte 2a using a processing solution 2a containing a non-self-doped conductive polymer 2a, and forming a solid electrolyte 2b using a processing solution 2b containing a non-self-doped conductive polymer 2b so as to cover at least a portion of the solid electrolyte 2a. The step of forming the first part may also include the step of forming a first solid electrolyte using a first processing solution containing a self-doped conductive polymer. In this case, a second solid electrolyte is formed so as to cover at least a portion of the first solid electrolyte. The step of forming the second solid electrolyte includes the steps of forming the solid electrolyte 2a so as to cover at least a portion of the first electrolyte, and forming the solid electrolyte 2b.

[0107] (Step to form the first solid electrolyte) A first solid electrolyte is formed by applying a first treatment solution containing a self-doped conductive polymer to an anode having a dielectric layer. For example, the first treatment solution may be applied to the anode having a dielectric layer, or the self-doped conductive polymer can be attached to cover at least a portion of the dielectric layer by immersing the anode having a dielectric layer in the first treatment solution. By forming the first solid electrolyte containing the self-doped conductive polymer prior to the formation of the second solid electrolyte, the inner surface of the porous material is more easily coated with the first solid electrolyte, and the second solid electrolyte containing a non-self-doped conductive polymer and antioxidant components is more easily formed. This makes it easier for the effects of the second solid electrolyte to be exerted. After applying the first treatment solution to the anode, a drying process is usually performed. The application of the first treatment solution and drying may be repeated.

[0108] The first processing solution includes, for example, a liquid medium. The liquid medium may be water, an organic liquid medium, or a mixture thereof, depending on the type of self-doped conductive polymer. It is preferable to use water or a mixture of water and a water-soluble organic liquid medium. The organic liquid medium only needs to be liquid at the stage of forming the first solid electrolyte; for example, it is an organic medium that is liquid in a temperature range of at least 25°C to 35°C.

[0109] The first treatment solution may be a dispersion in which particles of self-doped conductive polymer are dispersed in a liquid medium, or it may be a solution in which the self-doped conductive polymer is dissolved in a liquid medium. Self-doped conductive polymers have relatively flexible polymer chains, and the positions of functional groups such as anionic groups are random. In addition, self-doped conductive polymers have low orientation of polymer chains and low crystallinity. Therefore, compared to non-self-doped conductive polymers, they are easier to dissolve in a liquid medium or dispersed in particulate form. As a result, the viscosity of the first treatment solution is relatively low, and it is easy to impregnate the voids in the porous part with high permeability.

[0110] The concentration of the self-doped conductive polymer in the first processing solution 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.

[0111] The first treatment solution may contain an antioxidant component. The thickness of the first solid electrolyte tends to be small, and the antioxidant component is most effective when incorporated into the second solid electrolyte. Therefore, if the first treatment solution contains an antioxidant component, it is preferable that the concentration of the antioxidant component in the first treatment solution is lower than the concentration of the antioxidant component in treatment solutions 2a and 2b described later.

[0112] The concentration of the antioxidant component in the first treatment solution may be 5% by mass or less, less than 3% by mass, 1% by mass or less, or 0.1% by mass or less. It is also preferable that the first treatment solution does not contain any antioxidant component.

[0113] The first treatment solution may contain a resistive component, but from the viewpoint of forming the second solid electrolyte more uniformly, it is preferable that it does not contain a resistive component.

[0114] (Step to form the second solid electrolyte) A solid electrolyte 2a is formed by applying a processing solution 2a containing a non-self-doped conductive polymer 2a to an anode having a dielectric layer or an anode on which a first solid electrolyte is formed (solid electrolyte 2a formation step). A solid electrolyte 2b is formed by applying a processing solution 2b containing a non-self-doped conductive polymer 2b to the anode on which the solid electrolyte 2a is formed (solid electrolyte 2b formation step). After applying each processing solution, a drying process may be performed. The application of the processing solution and the drying process may be repeated multiple times.

[0115] Each of the treatment solutions 2a and 2b contains, for example, a liquid medium. The liquid medium may be water, an organic liquid medium, or a mixture thereof, depending on the type of non-self-doped conductive polymer. It is preferable to use water or a mixture of water and a water-soluble organic liquid medium. The organic liquid medium only needs to be liquid at the stage of forming the solid electrolyte 2a and solid electrolyte 2b; for example, it is an organic medium that is liquid in a temperature range of at least 25°C to 35°C.

[0116] The concentration of the non-self-doped conductive polymer 2a in the processing solution 2a 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. The concentration of the non-self-doped conductive polymer 2b in the processing solution 2b may also be selected from a similar range.

[0117] Corresponding to the description of solid electrolytes 2a and 2b, it is preferable that at least one of the treatment solutions 2a and 2b contains an antioxidant component, and both may contain an antioxidant component. The antioxidant component contained in treatment solution 2a and the antioxidant component contained in treatment solution 2b may be the same or different. The concentrations (mass%) of the antioxidant components in treatment solution 2a and treatment solution 2b may be the same or different.

[0118] The concentration of the antioxidant component in the treatment liquid 2a or the treatment liquid 2b may be appropriately adjusted according to the concentration of the non-self-doped conductive polymer in each treatment liquid. The concentration of the antioxidant component in each treatment liquid may be 0.1% by mass or more and 10% by mass or less, or may be 1% by mass or more and 5% by mass or less. In addition, each treatment liquid may contain an antioxidant component in an amount equal to or more than the mass of the non-self-doped conductive polymer. A part of the antioxidant component is presumed to volatilize in the drying process of the treatment liquid. As a result, for example, the solid electrolyte 2a or the solid electrolyte 22 containing the antioxidant component can be formed at a mass content of 3% by mass or more and 40% by mass or less, or 10% by mass or more and 30% by mass or less. It is preferable that the mass content of the antioxidant component in each solid electrolyte is higher than the mass content of the antioxidant component in the first solid electrolyte.

[0119] In the present disclosure, the treatment liquid 2a further contains a resistance component. The treatment liquid 2b does not contain a resistance component or further contains a resistance component, and the concentration of the resistance component in the treatment liquid 2a is higher than the concentration of the resistance component in the treatment liquid 2b.

[0120] In the present disclosure, by having the concentration (mass%) of the resistance component in the treatment liquid 2a higher than the concentration (mass%) of the resistance component in the treatment liquid 2b, the conductivity of the solid electrolyte 2a and the solid electrolyte 2b can be adjusted to satisfy C2a < C2b. As described above, the resistance component preferably contains a silane compound.

[0121] The concentration of the resistance component (or silane compound) in the treatment liquid 2a is preferably 0.01% by mass or more and 10% by mass or less, and more preferably 0.1% by mass or more and 5% by mass or less. By having the concentration of the resistance component in the treatment liquid 2a within such a range, the conductivity of the solid electrolyte 2a can be suppressed to be relatively low, and the effect of reducing the leakage current can be easily obtained. In addition, high breakdown voltage resistance can be easily obtained.

[0122] The concentration of the resistive component (or silane compound) in the treatment solution 2b is preferably 1% by mass or less, and more preferably 0.01% by mass or less. If the treatment solution 2b contains a resistive component (or silane compound), the concentration may be, for example, 0.001% by mass. It is also preferable that the treatment solution 2b does not contain a resistive component (or silane compound). In these cases, a relatively high conductivity can be obtained in the solid electrolyte 2b. This makes it easier to obtain high initial capacity and low ESR.

[0123] The process of forming the solid electrolyte 2a is preferably carried out using a treatment solution 2a in the form of a solution or liquid dispersion, rather than by in-situ polymerization. This is because treatment solutions 2a in this form tend to stably contain antioxidant components and resistance components. Similarly, the process of forming the solid electrolyte 2b is also preferably carried out using a treatment solution 2b in the form of a solution or liquid dispersion, rather than by in-situ polymerization.

[0124] (Process for forming the second part) The second portion may be formed using a polymerization solution containing precursors and dopants of a non-self-doped conjugated polymer, but it is preferable to form it using a treatment solution (second treatment solution) containing a non-self-doped conductive polymer. Such a second treatment solution is, for example, a solution or liquid dispersion containing a non-self-doped conductive polymer. The second treatment solution includes, for example, a liquid medium.

[0125] The second processing solution is applied to the anode body on which the first portion has been formed, so that the second portion, which covers at least a part of the first portion, extends beyond the main surface of the anode body having a dielectric layer. The first portion may be dried after the second processing solution has been applied. If necessary, the application of the second processing solution to the first portion and drying may be repeated two or more times.

[0126] In the second treatment solution, the average particle size of the non-self-doped conductive polymer particles may be larger than the average particle size of the non-self-doped conductive polymer particles contained in treatment solution 2a or treatment solution 2b.

[0127] The liquid medium included in the second processing solution may be water, an organic liquid medium, or a mixture thereof, depending on the type of non-self-doped conductive polymer. It is preferable to use water or a mixture of water and a water-soluble organic liquid medium. The organic liquid medium only needs to be liquid at the stage of forming the second part; for example, it is an organic medium that is liquid in a temperature range of at least 25°C to 35°C.

[0128] The concentration of the unself-doped conductive polymer in the second processing solution may be 0.5% by mass or more and 5% by mass or 1% by mass or more and 3% by mass. However, the unself-doped conductive polymer contained in the second processing solution has a large particle size, which tends to increase the viscosity of the second processing solution. Therefore, it is preferable that the concentration of the unself-doped conductive polymer in the second processing solution is lower than the concentration of the unself-doped conductive polymer in processing solution 2a and processing solution 2b. Large particle sizes of the unself-doped conductive polymer are less likely to fill the pores of the porous portion of the anode body, and tend to form a skin-like film of the unself-doped conductive polymer on the outside of the porous portion.

[0129] (Cathode extraction layer) The cathode extraction layer comprises at least a first layer in contact with the solid electrolyte layer. The cathode extraction layer may also comprise a first layer and a second layer covering the first layer. Examples of the first layer include a layer containing conductive particles and a metal foil. Examples of conductive particles include at least one selected from conductive carbon and metal particles. For example, the cathode extraction layer may be composed of a layer containing conductive carbon as the first layer (also referred to as a carbon layer) and a layer containing metal particles or a metal foil as the second layer. If a metal foil is used as the first layer, the cathode extraction layer may be composed of this metal foil.

[0130] Examples of conductive carbon include graphite (artificial graphite, natural graphite, etc.). The carbon layer is formed, for example, using a paste or slurry containing conductive carbon and, if necessary, a binder (such as a binder resin).

[0131] A second layer containing metal particles can be formed, for example, by laminating a composition containing metal particles (such as metal powder) onto the surface of the first layer. Examples of such a second layer include a metal particle-containing layer (for example, a metal paste layer such as a silver paste layer) formed using a composition containing metal particles such as silver particles and a resin (binder resin).

[0132] Examples of binder resins used in carbon layers and metal particle-containing layers include thermoplastic resins and thermosetting resins. Thermosetting resins such as imide resins and epoxy resins are preferably used as binder resins.

[0133] When a metal foil is used as the first layer, the type of metal is not particularly limited. Preferably, the metal foil is a valve metal (such as aluminum, tantalum, or niobium) or an alloy containing a valve metal. The surface of the metal foil may be roughened as needed. The surface of the metal foil may be coated with a chemical conversion film, or a coating of a metal different from the metal constituting the metal foil (a dissimilar metal) or a nonmetal. Examples of dissimilar metals or nonmetals include metals such as titanium and nonmetals such as carbon (such as conductive carbon).

[0134] The above-mentioned dissimilar metal or nonmetal (for example, conductive carbon) coating may be used as the first layer, and the above-mentioned metal foil may be used as the second layer.

[0135] (Separator) When metal foil is used as the cathode lead layer, a separator may be placed between the metal foil and the anode (anode foil, etc.). The separator is not particularly limited, and for example, nonwoven fabrics containing fibers of cellulose, polyethylene terephthalate, vinylon, or polyamide (e.g., aliphatic polyamide, aromatic polyamide such as aramid) may be used.

[0136] (others) Solid electrolytic capacitors may be wound-wound, chip-type, or multilayer-type. For example, a solid electrolytic capacitor may include two or more multilayer-type capacitor elements. Alternatively, a solid electrolytic capacitor may include one wound-wound capacitor element or two or more wound-wound capacitor elements. The configuration of the capacitor elements is selected, for example, depending on the type of solid electrolytic capacitor.

[0137] In a capacitor element, one end of a cathode lead terminal is electrically connected to the cathode lead layer. The cathode lead terminal is joined to the cathode lead layer by, for example, applying a conductive adhesive to the cathode lead layer and bonding it to the cathode lead layer via this conductive adhesive. One end of an anode lead terminal is electrically connected to the anode portion of the anode body. The other end of the anode lead terminal and the other end of the cathode lead terminal are led out from the resin casing or case, respectively. The other ends of each terminal exposed from the resin casing or case are used for soldering to the substrate on which the solid electrolytic capacitor is to be mounted, etc.

[0138] The capacitor element is sealed using an outer casing (such as a resin outer casing) or a case. For example, the capacitor element and the resin material for the outer casing (e.g., uncured thermosetting resin and filler) may be placed in a mold, and the capacitor element may be sealed with the resin outer casing by a transfer molding method, compression molding method, or the like. In this case, the other ends of the anode lead terminal and cathode lead terminal connected to the anode lead drawn out from the capacitor element are exposed from the mold. Examples of thermosetting resins include epoxy resin.

[0139] Alternatively, a solid electrolytic capacitor may be formed by housing the capacitor element in a bottomed case such that the other ends of the anode lead terminal and cathode lead terminal are located on the opening side of the bottomed case, and then sealing the opening of the bottomed case with a sealing material. As the material for the bottomed case, metals such as aluminum, stainless steel, copper, iron, brass, or alloys thereof can be used.

[0140] Figure 1 is a schematic cross-sectional view of a solid electrolytic capacitor according to one embodiment of the present disclosure. The solid electrolytic capacitor 20 includes a capacitor element including an anode portion 6 and a cathode portion 7, an outer casing 11 that encloses the capacitor element, an anode lead frame 13 electrically connected to the anode portion 6, and a cathode lead frame 14 electrically connected to the cathode portion 7.

[0141] The anode section 6 comprises an anode body 1 and an anode wire 2. A portion of the anode wire 2 is embedded within the anode body 1, while the remaining portion protrudes outward from the outer surface of the anode body 1. A portion of the anode lead frame 13 is joined to this protruding portion of the anode wire 2 by welding or other means, and is electrically connected to it.

[0142] A dielectric layer 3 is formed on the surface of the anode 1. The cathode 7 has a solid electrolyte layer 4 that covers at least a portion of the dielectric layer 3, and a cathode extraction layer 5 that covers at least a portion of the surface of the solid electrolyte layer 4. The cathode extraction layer 5 has a carbon layer formed to cover at least a portion of the surface of the solid electrolyte layer 4, and a metal particle-containing layer formed to cover at least a portion of the carbon layer. A portion of the cathode lead frame 14 is bonded to the cathode extraction layer 5 via a conductive adhesive layer 8 and electrically connected.

[0143] [Examples] The present invention will be described below in detail based on examples and comparative examples, but the present invention is not limited to the following examples.

[0144] Example 1 Capacitor elements were fabricated and their characteristics evaluated according to the following procedure.

[0145] (1) Preparation of an anode having a dielectric layer As the anode, a tantalum sintered body (porous body) in which a portion of the anode wire was embedded was prepared. By anodizing the surface of this tantalum sintered body, a dielectric layer containing tantalum oxide was formed on the surface of the anode.

[0146] (2) Process for forming a solid electrolyte layer (2-1) Formation process of the first part (First solid electrolyte formation process) An aqueous dispersion (first treatment solution) containing a self-doped polythiophene polymer was prepared. The concentration of the polythiophene polymer in the first treatment solution was set to 1% by mass or more and 3% by mass or less. As the self-doped polythiophene polymer, PEDOT (Mw: approximately 10,000), which has a sulfo group attached to the PEDOT skeleton via a linking group containing a butylene group, was used.

[0147] The tantalum sintered body prepared in (1) above was immersed in the first processing solution for approximately 30 seconds to 60 seconds, and then the tantalum sintered body was removed from the first processing solution. Next, the tantalum sintered body removed from the first processing solution was heated (dried) at a temperature of 140°C to 180°C for 10 minutes to 20 minutes to form the first solid electrolyte.

[0148] (Formation process of solid electrolyte 2a) An aqueous dispersion (treatment solution 2a) containing an antioxidant (pyrogallol), a silane compound (3-glycidoxypropyltriethoxysilane), and a non-self-doped conductive polymer (PSS-doped PEDOT) was prepared. The concentration of PSS-doped PEDOT in treatment solution 2a was 1% by mass or more and 3% by mass or less. The concentration of pyrogallol in treatment solution 2a was 3% by mass. The concentration of the silane compound in treatment solution 2a was 1% by mass.

[0149] The tantalum sintered body on which the first solid electrolyte was formed was immersed in the treatment solution 2a for approximately 30 to 60 seconds, and then the tantalum sintered body was removed from the treatment solution 2a. Next, the tantalum sintered body removed from the treatment solution 2a was heated (dried) at a temperature of 140°C to 180°C for 10 to 20 minutes. In this way, a tantalum sintered body on which the solid electrolyte 2a was formed was obtained.

[0150] (Formation process of solid electrolyte 2b) An aqueous dispersion (treatment solution 2b) containing an antioxidant (pyrogallol) and a non-self-doped conductive polymer (PSS-doped PEDOT) was prepared. The aqueous dispersion (treatment solution 2b) did not contain any silane compounds. A tantalum sintered body on which solid electrolyte 2a was formed was immersed in treatment solution 2b. Solid electrolyte 2b was formed in the same manner as for solid electrolyte 2a, except for these steps. In this way, a second solid electrolyte having solid electrolyte 2a and solid electrolyte 2b was formed. Following the above procedure, a tantalum sintered body was formed in which a first portion having a first solid electrolyte and a second solid electrolyte was formed.

[0151] (2-2) Formation process of the second part An aqueous dispersion (second treatment solution) containing a non-self-doped conductive polymer (PSS-doped PEDOT) was prepared. The concentration of PSS-doped PEDOT in the second treatment solution was set to 1% by mass or more and 3% by mass or less. The tantalum sintered body with the first part formed was immersed in the second treatment solution for approximately 30 seconds or more and 60 seconds or less, and then the tantalum sintered body was removed from the second treatment solution. Next, the tantalum sintered body removed from the second treatment solution was heated (dried) at a temperature of 140°C or more and 180°C or less for a time of 10 minutes or more and 20 minutes or less. The second part of the solid electrolyte layer was formed by repeating the immersion of the tantalum sintered body in the second treatment solution and the above drying process multiple times.

[0152] (3) Formation of the cathode extraction layer The tantalum sintered body with the solid electrolyte layer obtained in (2) above was immersed in a dispersion of graphite particles dispersed in water, and after being removed from the dispersion, it was dried to form a carbon layer (first layer) on the surface of the solid electrolyte layer. Drying was carried out at 180°C for a period of 10 to 30 minutes.

[0153] 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 a temperature of 60°C to 80°C for 20 to 40 minutes. After that, the binder resin was cured by further heating at 180°C for 30 to 60 minutes, forming a metal particle-containing layer (second layer). In this way, a cathode extraction layer composed of the carbon layer and the metal particle-containing layer was formed.

[0154] Following the above procedure, a total of 60 capacitor elements E1, each including a cathode composed of a solid electrolyte layer and a cathode extraction layer, were fabricated.

[0155] Comparative Example 1 The entire second solid electrolyte was formed using an aqueous dispersion containing a non-self-doped conductive polymer (PSS-doped PEDOT). This aqueous dispersion contained neither antioxidants nor silane compounds. A total of 60 capacitor elements C1 were fabricated in the same manner as for capacitor element E1.

[0156] 《Reference example 1》 The entire second solid electrolyte was formed using only processing solution 2b. A total of 60 capacitor elements R1 were fabricated in the same manner as for capacitor element E1.

[0157] Comparative Example 2 Solid electrolyte 2a was formed in the same manner as in Example 1, except that treatment solution 2a without antioxidants was used. Solid electrolyte 2b was formed in the same manner as in Example 1, except that treatment solution 2b without antioxidants was used. A total of 60 capacitor elements C2 were fabricated in the same manner as in Example 1, except for these differences.

[0158] The capacitor element E1 contains an antioxidant in the second solid electrolyte of the first portion of the solid electrolyte layer, and a resistive component (silane compound) in the solid electrolyte 2a. The capacitor element C1 does not contain any antioxidants or resistive components (silane compounds) in the first portion of its solid electrolyte layer. The capacitor element R1 contains an antioxidant in the second solid electrolyte of the first portion of the solid electrolyte layer. However, the first portion does not contain a resistive component (silane compound). The capacitor element C2 contains a resistive component (silane compound) in the solid electrolyte 2a of the first portion of the solid electrolyte layer. The first portion does not contain antioxidants.

[0159] [evaluation] The following evaluations were performed on the capacitor elements of the examples, comparative examples, and reference examples, or on the thin films formed using processing solution 2a or processing solution 2b.

[0160] (1) Reliability testing Under 20°C conditions, the initial capacitance (μF) of capacitor elements at a frequency of 120 Hz was measured using a 4-terminal LCR meter. The average value C0 (μF) for 60 capacitor elements was then calculated.

[0161] For 20 capacitor elements, an ON-OFF test was repeated 10,000 times at 25°C, in which the element was charged to its rated voltage and then discharged to 0V. After that, the capacitance C1 (μF) was measured in the same manner as above, and the average value C1 (μF) was calculated. The capacitance reduction rate (%) of capacitance C1 relative to the initial capacitance C0 was calculated using the following formula. Capacity reduction rate (%)=(C1-C0) / C0×100

[0162] (2) Leakage current (LC) failure rate Twenty capacitor elements that had not undergone ON-OFF testing were connected in series with a 1kΩ resistor, and a voltage of 30V to 60V was applied from a DC power supply. The leakage current value (in amperes) was measured 40 seconds after the start of voltage application. An Agilent Technologies 4155B semiconductor parameter analyzer was used to measure the leakage current. The percentage of capacitor elements with a leakage current value of 100A or more out of the 20 capacitor elements was determined as the LC failure rate.

[0163] (3) Withstand voltage For 20 capacitor elements on which an ON - OFF test was not performed, a voltage was applied while increasing the voltage at a rate of 1.0 V / second, and the breakdown voltage (BVD: breakdown voltage) (unit: V) at which an overcurrent of 0.5 A flows was measured. The breakdown voltage resistance was expressed as a relative value when the BVD (V) of the solid electrolytic capacitor of Comparative Example 1 was set to 1.00. A larger value indicates higher breakdown voltage resistance.

[0164] (4) Mass content rate of silicon element in solid electrolyte 2a and solid electrolyte 2b For Example 1 and Comparative Example 2, the mass content rate of the silicon element in each solid electrolyte was determined by the procedure described above.

[0165] (5) Conductivity of solid electrolyte 2a and solid electrolyte 2b Using the treatment liquid 2a of Example 1, a thin film 2a (thickness 5 μm) of solid electrolyte 2a was formed by the procedure described above. A thin film 2b (thickness 5 μm) of solid electrolyte 2b was formed in the same manner as above, except that the treatment liquid 2b of Example 1 was used instead of the treatment liquid 2a. Then, the conductivity (S / cm) of each of the thin films 2a and 2b was measured by the procedure described above. As a result, the conductivity of the thin film 2a was 1 S / cm or less, and the conductivity of the thin film 2b was 200 S / cm or more.

[0166] The evaluation results are shown in Table 1. [[ID=IS]]

[0167]

Table 1

[0168] As shown in Table 1, when the second solid electrolyte in the first part contains a non - self - doped conductive polymer and an antioxidant component, the rate of capacity decrease when charge - discharge is repeated can be significantly reduced compared to the case where the antioxidant component is not included (comparison between C1 and R1). However, in R1, the LC failure rate increases significantly. On the other hand, by configuring the second solid electrolyte with solid electrolyte 2a and solid electrolyte 2b that satisfy the relationship of conductivity C2a < C2b, the LC failure rate can be significantly reduced (comparison between R1 and E1).

[0169] Even when the second solid electrolyte in the first part is composed of the solid electrolyte 2a and the solid electrolyte 2b that satisfy the relationship of conductivity C2a < C2b, when the first part does not contain an antioxidant component, the capacity reduction rate after repeated charge and discharge is large (C2). In contrast, in E1, in addition to the configuration of C2, since the first part contains an antioxidant component, the capacity reduction rate can be significantly reduced (comparison between C2 and E1). From the comparison between C1 and R1, when the first part contains an antioxidant component, the LC failure rate increases significantly. However, from the comparison between C2 and E1, since the second solid electrolyte contains the solid electrolyte 2a and the solid electrolyte 2b, the influence of the antioxidant component on the LC failure rate is suppressed low.

[0170] In addition, by configuring the second solid electrolyte in the first part with the solid electrolyte 2a and the solid electrolyte 2b that satisfy the relationship of conductivity C2a < C2b, high withstand voltage can be obtained (comparison between C1 and R1, and C2 and E1).

Industrial Applicability

[0171] The solid electrolytic capacitor according to the present disclosure can suppress a decrease in capacity when charge and discharge are repeated. In addition, in the solid electrolytic capacitor, the leakage current is reduced. Therefore, the solid electrolytic capacitor according to the present disclosure is suitable for applications that require high reliability and long life. However, the applications of electrolytic capacitors are not limited to these.

Explanation of Signs

[0172] 20: Solid electrolytic capacitor 1: Anode body 2: Anode wire 3: Dielectric layer 4: Solid electrolyte layer 5: Cathode lead-out layer 6: Anode part 7: Cathode part 8: Conductive adhesive layer 11: Outer package 13: Anode lead frame 14: Cathode lead frame

Claims

1. A solid electrolytic capacitor comprising at least one capacitor element and an outer casing, The capacitor element includes an anode body having a porous portion in at least its 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. 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 extending beyond the main surface of the anode body having the dielectric layer. The first portion includes an antioxidant component and a solid electrolyte 2a and a solid electrolyte 2b covering at least a portion of the solid electrolyte 2a, The solid electrolyte 2a includes a non-self-doped conductive polymer 2a. The solid electrolyte 2b includes a non-self-doped conductive polymer 2b. A solid electrolytic capacitor in which the conductivity C2a measured for the solid electrolyte 2a and the conductivity C2b measured for the solid electrolyte 2b satisfy the condition C2a < C2b.

2. The first portion comprises a first solid electrolyte covering at least a portion of the dielectric layer, and a second solid electrolyte covering at least a portion of the first solid electrolyte. The first solid electrolyte comprises a self-doped conductive polymer, The solid electrolytic capacitor according to claim 1, wherein the second solid electrolyte includes the solid electrolyte 2a covering at least a portion of the first solid electrolyte and the solid electrolyte 2b.

3. The solid electrolytic capacitor according to claim 1 or 2, wherein the conductivity C2b measured for the 5 μm thick thin film of the solid electrolyte 2b is 200 S / cm or more.

4. The solid electrolytic capacitor according to claim 1 or 2, wherein the conductivity C2a measured for a thin film of the solid electrolyte 2a with a thickness of 5 μm is 1 S / cm or less.

5. The solid electrolytic capacitor according to claim 1 or 2, wherein the ratio of the average thickness T2b of the solid electrolyte 2b to the average thickness T2a of the solid electrolyte 2a (= T2b / T2a) is 2 or more and 5 or less.

6. The second portion may not contain antioxidant components, or may contain antioxidant components. The solid electrolytic capacitor according to claim 1 or 2, wherein the mass content of the antioxidant component in the first portion is higher than the mass content of the antioxidant component in the second portion.

7. The second part is a solid electrolytic capacitor according to claim 1 or 2, wherein the antioxidant component is not included.

8. The first part comprises a silicon element, as described in claim 1 or 2.

9. The solid electrolytic capacitor according to claim 8, wherein the mass content of silicon element in the solid electrolyte 2a is higher than the mass content of silicon element in the solid electrolyte 2b.

10. A method for manufacturing a solid electrolytic capacitor, comprising at least one capacitor element and an outer casing, The capacitor element includes an anode body having a porous portion in at least its 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. 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 extending beyond the main surface of the anode body having the dielectric layer. The manufacturing method includes a step of forming the solid electrolyte layer, The step of forming the solid electrolyte layer includes the step of forming the first portion and the step of forming the second portion. The step of forming the first portion includes the steps of forming a solid electrolyte 2a using a processing solution 2a containing a non-self-doped conductive polymer 2a, and forming a solid electrolyte 2b using a processing solution 2b containing a non-self-doped conductive polymer 2b so as to cover at least a portion of the solid electrolyte 2a. At least one of the processing liquids 2a and 2b further contains an antioxidant component. The processing liquid 2a further contains a resistive component, The processing liquid 2b either does not contain a resistive component or further contains a resistive component. A method for manufacturing a solid electrolytic capacitor, wherein the concentration of the resistive component in the processing solution 2a is higher than the concentration of the resistive component in the processing solution 2b.

11. The method for manufacturing a solid electrolytic capacitor according to claim 10, wherein the resistive component includes a silane compound.

12. The first portion comprises a first solid electrolyte covering at least a portion of the dielectric layer, and a second solid electrolyte covering at least a portion of the first solid electrolyte. The second solid electrolyte comprises the solid electrolyte 2a covering at least a portion of the first solid electrolyte and the solid electrolyte 2b, The solid electrolytic capacitor according to claim 10 or 11, wherein the step of forming the first portion includes the step of forming the first solid electrolyte using a first processing solution containing a self-doped conductive polymer, and the step of forming the solid electrolyte 2a so as to cover at least a portion of the first solid electrolyte.

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