Capacitor element, solid electrolytic capacitor, and method for manufacturing capacitor element

Abstract

A capacitor element according to the present disclosure comprises: a porous anode body having a plurality of hole parts; a dielectric layer covering the inner surfaces of the plurality of hole parts; and a solid electrolyte layer covering the dielectric layer. The thickness of the solid electrolyte layer in the plurality of hole parts increases from the outer surface toward the center part of the anode body.

Description

Capacitor element, solid electrolytic capacitor, and method for manufacturing capacitor element

[0001] The present invention relates to a capacitor element, a solid electrolytic capacitor, and a method for manufacturing the capacitor element. More specifically, the present invention relates to a capacitor element including a porous anode body having a plurality of holes, a solid electrolytic capacitor including the capacitor element, and a method for manufacturing the capacitor element.

[0002] A solid electrolytic capacitor includes, for example, a capacitor element and an exterior body that seals the capacitor element. The capacitor element includes, for example, an anode body, a dielectric layer that covers the anode body, and a solid electrolyte layer that covers the dielectric layer. In the capacitor element, the solid electrolyte layer usually contains a conductive polymer.

[0003] Patent Document 1 below describes a capacitor element in which a conductive polymer formed by chemical oxidative polymerization is used as the solid electrolyte, and the thickness of the conductive polymer layer in the center of the capacitor element is set to 0.02 μm (20 nm) or more and 0.14 μm (140 nm) or less. Patent Document 1 also describes a capacitor element in which the conductive polymer film thickness is made thicker near the outer surface than near the center. Patent Document 1 also describes that by configuring the capacitor element as described above, insulation of the conductive polymer layer due to heat inside the capacitor element is suppressed, and as a result, deterioration of the ESR (equivalent series resistance) in the solid electrolytic capacitor can be suppressed.

[0004] The following Patent Document 2 describes a solid electrolyte layer configured as a laminated structure of two layers with different properties in a solid electrolytic capacitor in order to simultaneously suppress insulation deterioration of the dielectric layer and suppress an increase in ESR. The following Patent Document 2 also describes that a first layer, which is one layer of the laminated structure, includes a first conductive polymer doped with a monomolecular dopant and a second conductive polymer consisting of a self-doping conductive polymer having a plurality of side chains with dopable functional groups, and that the other layer, which is the second layer, includes a third conductive polymer doped with a polymer dopant.

[0005] Patent No. 3228323 Patent No. 6952921

[0006] As described above, Patent Documents 1 and 2 mainly discuss how the conductive polymer layer can be formed to achieve a low ESR in a solid electrolytic capacitor. However, these documents do not discuss how the conductive polymer layer can be formed to provide a solid electrolytic capacitor with excellent reliability (e.g., capacitance retention rate) and voltage resistance.

[0007] Therefore, an object of the present disclosure is to provide a solid electrolytic capacitor having excellent reliability and voltage resistance, a capacitor element used in the solid electrolytic capacitor, and a method for manufacturing the capacitor element.

[0008] One aspect of the present invention relates to a capacitor element including: a porous anode body having a plurality of holes; a dielectric layer covering inner surfaces of the plurality of holes; and a solid electrolyte layer covering the dielectric layer, wherein a thickness of the solid electrolyte layer in the plurality of holes increases from an outer surface of the anode body toward a center thereof.

[0009] Another aspect of the present invention relates to a solid electrolytic capacitor including the above capacitor element and an exterior body that seals the capacitor element.

[0010] Yet another aspect of the present invention relates to a method for manufacturing a capacitor element, including: a first step of forming a dielectric layer so as to cover inner surfaces of a plurality of holes in a porous anode body having a plurality of holes; and a second step of forming a solid electrolyte layer so as to cover the dielectric layer, wherein the solid electrolyte layer includes a conductive polymer layer, and the second step includes: a first substep of immersing the anode body in a conductive polymer solution containing a conductive polymer at a first atmospheric pressure; a second substep of exposing the anode body after the first substep to a pressure higher or lower than the first atmospheric pressure; and a third substep of drying the anode body after the second substep to form the conductive polymer layer.

[0011] According to the present disclosure, it is possible to provide a solid electrolytic capacitor having excellent reliability and withstand voltage, a capacitor element used in the solid electrolytic capacitor, and a method for manufacturing the capacitor element.

[0012] 1 is a schematic cross-sectional view of a solid electrolytic capacitor according to an embodiment of the present disclosure;

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

[0014] In the following description, when lower and upper limits of numerical values ​​relating to specific physical properties, conditions, etc. are exemplified, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit is not equal to or greater than the upper limit. When multiple materials are exemplified, one of them can be selected and used alone, or two or more can be used in combination, unless otherwise specified.

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

[0016] [Solid Electrolytic Capacitor] A solid electrolytic capacitor according to an embodiment of the present disclosure includes a capacitor element and an exterior body that seals the capacitor element. The solid electrolytic capacitor according to an embodiment of the present disclosure includes at least one capacitor element. Examples of solid electrolytic capacitors include tantalum electrolytic capacitors and aluminum electrolytic capacitors. A tantalum electrolytic capacitor includes an anode body, which will be described later, containing tantalum as a valve metal, and a dielectric layer, such as Ta, formed on the anode body. ２ O ５In a tantalum electrolytic capacitor, the anode body is usually made of a sintered body of tantalum particles. In an aluminum electrolytic capacitor, the anode body contains aluminum as a valve metal, and an aluminum dielectric layer is formed on the anode body. ２ O ３ In aluminum electrolytic capacitors, the anode body is usually made of aluminum foil.

[0017] <Capacitor Element> A capacitor element according to an embodiment of the present disclosure includes a porous anode body having a plurality of holes, a dielectric layer covering the inner surfaces of the plurality of holes, and a solid electrolyte layer covering the dielectric layer. As described above, in a capacitor element including a porous anode body having a plurality of holes, a dielectric layer is typically formed so as to cover the outer surface of the anode body in addition to the inner surfaces of the plurality of holes, and a solid electrolyte layer is also formed so as to cover the dielectric layer. A capacitor element according to an embodiment of the present disclosure includes a cathode portion. The cathode portion includes a solid electrolyte layer and a cathode extraction layer covering at least a portion of the solid electrolyte layer. In a capacitor element according to an embodiment of the present disclosure, the thickness of the solid electrolyte layer in the plurality of holes increases from the outer surface of the anode body toward the center.

[0018] In a capacitor element, current tends to concentrate on the outer surface of the anode body. Furthermore, the thicker the solid electrolyte layer, the larger the cross-sectional area through which electricity flows, resulting in a lower resistance. Therefore, if the solid electrolyte layer is thick near the entrances of the multiple holes (on the outer surface of the anode body), the current value increases. Therefore, a solid electrolytic capacitor equipped with such a capacitor element tends to have poor voltage resistance.

[0019] Furthermore, in a capacitor element, if the solid electrolyte layer is formed thinly deep inside the multiple holes (toward the center of the anode body), it is thought that not only will it be difficult to extract sufficient capacity from inside the multiple holes, but it will also be difficult to maintain the extractable capacity sufficiently over a long period of time. Therefore, a solid electrolytic capacitor including such a capacitor element is likely to have poor reliability.

[0020] However, in the capacitor element according to the embodiment of the present disclosure, the thickness of the solid electrolyte layer in the holes increases from the outer surface of the anode body toward the center. That is, the solid electrolyte layer is formed thin near the entrances of the holes (toward the outer surface of the anode body) and thick deep inside the holes (toward the center of the anode body). Therefore, a solid electrolytic capacitor including the capacitor element according to the embodiment of the present disclosure has excellent reliability and voltage resistance.

[0021] (Anode Body) The anode body may contain a valve metal, an alloy containing a valve metal, a compound containing a valve metal, or the like. These materials may be used alone or in combination. Examples of the valve metal include aluminum, tantalum, niobium, and titanium. In the capacitor element according to the embodiment of the present disclosure, as described above, the anode body is configured as a porous anode body having a plurality of pores. The porous anode body may have a porous portion formed therein, including a plurality of pores opening from the outer surface toward the center. The porous portion can be formed by roughening the outer surface of a substrate (e.g., a foil-shaped or plate-shaped substrate) containing a valve metal by etching or the like. The porous anode body may be a compact of particles containing a valve metal, or a sintered body thereof. The sintered body has a porous structure. Therefore, a sintered body having a porous structure may have a porous portion throughout its entirety. In the capacitor element according to the embodiment of the present disclosure, the anode body is preferably configured as a sintered body (e.g., a tantalum sintered body). As explained above, the sintered body can be entirely porous, and therefore the solid electrolyte layer can be formed deep inside the porous portion, allowing the capacitance of such a capacitor element to be fully utilized.

[0022] (Dielectric Layer) The dielectric layer is formed, for example, by subjecting an anode body containing a valve metal to chemical conversion treatment (anodization treatment). The dielectric layer is an insulating layer that functions as a dielectric. In the capacitor element according to the embodiment of the present disclosure, as described above, the dielectric layer covers the inner surfaces of the multiple holes. As described above, the dielectric layer also typically covers the outer surface of the anode body. That is, the dielectric layer typically covers the outer surface of the anode body and the inner surfaces of the multiple holes.

[0023] The dielectric layer includes an oxide of the valve metal. For example, if tantalum is used as the valve metal, the dielectric layer may include an oxide of Ta. ２ O ５ When aluminum is used as the valve metal, the dielectric layer contains Al ２ O ３ The dielectric layer is not limited to the above, and any material can be used as long as it functions as a dielectric and has insulating properties.

[0024] (Cathode Section) The cathode section may be formed so as to cover at least a portion of the dielectric layer. As described above, the cathode section includes a solid electrolyte layer covering the dielectric layer and a cathode extraction layer covering the solid electrolyte layer. That is, the cathode section may be formed so as to cover the dielectric layer with the solid electrolyte layer. Furthermore, the cathode extraction layer may be formed so as to cover the solid electrolyte layer.

[0025] The solid electrolyte layer is a conductive polymer layer containing a conductive polymer, such as a self-doping conductive polymer or a non-self-doping conductive polymer.

[0026] Self-doping conductive polymers have small particle sizes. Therefore, in a conductive polymer solution containing a self-doping conductive polymer (hereinafter referred to as a first conductive polymer solution), the self-doping conductive polymer is sufficiently dissolved. Therefore, the first conductive polymer solution has a low viscosity. Therefore, when a conductive polymer layer is formed using the first conductive polymer solution, the first conductive polymer solution can be sufficiently permeated into the interior of the multiple holes. This makes it easier to form a sufficient coating of the self-doping conductive polymer on the inner surfaces of the multiple holes. On the other hand, because the self-doping conductive polymer has a small particle size, the conductive polymer layer formed using the first conductive polymer solution tends to be thin.

[0027] The particle size of the non-self-doping conductive polymer is large. Therefore, the non-self-doping conductive polymer is not necessarily sufficiently dissolved in a conductive polymer solution containing the non-self-doping conductive polymer (hereinafter referred to as the second conductive polymer solution). Therefore, the viscosity of the second conductive polymer solution is high. Therefore, when a conductive polymer layer is formed using the second conductive polymer solution, the second conductive polymer solution is unlikely to penetrate into the interior of the multiple holes, but a thick coating can be formed near the entrances of the multiple holes (on the outer surface of the anode body) due to the large particle size of the non-self-doping conductive polymer.

[0028] A self-doping conductive polymer has, for example, a conjugated polymer skeleton and a functional group (such as an anionic group) that is directly or indirectly bonded to the skeleton by a covalent bond and functions as a dopant.

[0029] Examples of the anionic group include a sulfo group, a carboxyl group, a phosphate group, and a phosphonate group. The self-doping conductive polymer may contain one or more types of anionic group, or may contain two or more types. From the viewpoint of increasing conductivity, the self-doping conductive polymer preferably has at least a sulfo group as the anionic group.

[0030] The anionic group may be present in any form, such as a free form, an ester form, or a salt form, or may be present in a form that interacts with or is complexed with a component contained in the first solid electrolyte layer and the second solid electrolyte layer. In this specification, all of these forms are simply referred to as an anionic group.

[0031] Examples of conjugated polymers that constitute the backbone of self-doping conductive polymers include polymers with a π-conjugated polymer as the basic backbone. Examples of π-conjugated polymers include polypyrrole, polythiophene, polyaniline, polyfuran, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, and polythiophene vinylene. The above polymers may 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 (e.g., substituted products having substituents). For example, polythiophenes include poly(3,4-ethylenedioxythiophene). Self-doping conductive polymers have anionic groups in the backbone of these conjugated polymers. The anionic groups may be introduced directly into the backbone of the conjugated polymer or via a linking group. The linking group is preferably a polyvalent group (e.g., a divalent group) containing an alkylene group. Examples of the linking group include aliphatic polyvalent groups (e.g., divalent groups) such as alkylene groups, -R １ -X-R ２ - group (X is an oxygen element or a sulfur element, R １ and R ２ are alkylene groups which may be the same or different.) The number of carbon atoms in each alkylene group contained in the linking group is, for example, 1 or more and 10 or less. The number of carbon atoms may be 1 or more and 6 or less. The alkylene group may be linear or branched. The linking group may, for example, contain at least an alkylene group having 2 or more carbon atoms. The number of carbon atoms in such an alkylene group may be 2 or more (or 3 or more) and 10 or less, or 2 or more (or 3 or more) and 6 or less. For example, R １ is an alkylene group having 1 to 6 carbon atoms, and R ２may 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 the above.

[0032] The conjugated polymer constituting the skeleton of the self-doping conductive polymer may be polypyrrole, polythiophene, or polyaniline. From the viewpoint of increasing conductivity, the self-doping conductive polymer is preferably a polymer having a conjugated polymer skeleton containing a repeating structure of monomer units corresponding to a thiophene compound and an anionic group introduced into the skeleton.

[0033] The thiophene compound includes a compound having a thiophene ring and capable of forming a repeating structure of the corresponding monomer unit, which can be linked at the 2- and 5-positions of the thiophene ring to form a repeating structure of the monomer unit.

[0034] The thiophene compound may have a substituent at, for example, at least one of the 3-position and the 4-position of the thiophene ring. The substituent at the 3-position and the substituent at the 4-position may be linked to each other to form a ring fused to the thiophene ring. Examples of the thiophene compound include thiophenes which may have a substituent at, at least one of the 3-position and the 4-position, alkylenedioxythiophene compounds (C thiophenes such as ethylenedioxythiophene compounds), and the like. ２－４ Alkylenedioxythiophene compounds include compounds having a substituent on the alkylene group.

[0035] Examples of the substituent include alkyl groups (C such as methyl and ethyl groups). １－４ alkyl groups, alkoxy groups (C groups such as methoxy groups and ethoxy groups) １－４ alkoxy group, hydroxy group, hydroxyalkyl group (hydroxy C such as hydroxymethyl group) １－４Preferably, an anionic group or a group containing an anionic group (e.g., an alkyl group) is used. However, the substituent is not limited to these. When the thiophene compound has two or more substituents, the respective substituents may be the same or different. The thiophene ring (in the case of an alkylenedioxythiophene ring, at least one of the thiophene ring and the alkylene group) may have, as a substituent, the above-mentioned anionic group or a group containing an anionic group (e.g., a sulfoalkyl group).

[0036] The self-doping conductive polymer may have a backbone of a conjugated polymer (such as PEDOT) containing a repeating structure of monomer units corresponding to at least a 3,4-ethylenedioxythiophene compound (such as 3,4-ethylenedioxythiophene (EDOT)). The backbone of the conjugated polymer containing a repeating structure of monomer units corresponding to EDOT may contain only monomer units corresponding to EDOT, or may contain, in addition to the monomer units, monomer units corresponding to a thiophene compound other than EDOT.

[0037] The weight average molecular weight (Mw) of the self-doping conductive polymer may be 1,000 or more and 1,000,000 or less, or may be 1,000 or more and 50,000 or less.

[0038] In this specification, the weight average molecular weight (Mw) of the self-doping conductive polymer is a polystyrene-equivalent value measured by gel permeation chromatography (GPC), which is usually performed using a polystyrene gel column and water / methanol (volume ratio 8 / 2) as the mobile phase.

[0039] The non-self-doping conductive polymer includes, for example, a conjugated polymer (a non-self-doping conjugated polymer (for example, a conjugated polymer having no anionic groups)) and a dopant.

[0040] Examples of conjugated polymers include conjugated polymers (e.g., π-conjugated polymers) exemplified as conjugated polymers constituting the backbone of self-doping conductive polymers. Conjugated polymers may be used singly or in combination of two or more. From the viewpoint of easily ensuring high initial capacity, high voltage resistance, and high heat resistance, non-self-doping conjugated polymers containing a repeating structure of thiophene compound monomer units may be used. Examples of thiophene compounds corresponding to the monomer units of non-self-doping conjugated polymers include the thiophene compounds described for the self-doping conductive polymers. Non-self-doping conjugated polymers may include conjugated polymers (e.g., PEDOT) containing at least a repeating structure of monomer units corresponding to a 3,4-ethylenedioxythiophene compound (e.g., EDOT). Conjugated polymers containing at least a repeating structure of monomer units corresponding to EDOT may contain only monomer units corresponding to a compound other than EDOT, or may contain, in addition to the monomer units, monomer units corresponding to a thiophene compound other than EDOT.

[0041] The dopant may be at least one selected from the group consisting of anions and polyanions (e.g., polymer anions). Examples of anions include sulfate ions, nitrate ions, phosphate ions, borate ions, organic sulfonate ions, and carboxylate ions. Examples of dopants that generate sulfonate ions include p-toluenesulfonic acid and naphthalenesulfonic acid. Polymer anions may be used to facilitate improved heat resistance, reliability, and voltage resistance. Examples of polymer anions having sulfo groups include polymeric polysulfonic acids. Specific examples of polymer anions include polyvinylsulfonic acid, polystyrenesulfonic acid (PSS (including copolymers and substituted forms having substituents)), polyallylsulfonic acid, polyacrylicsulfonic acid, polymethacrylicsulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprenesulfonic acid, polyestersulfonic acids (e.g., aromatic polyestersulfonic acids), and phenolsulfonic acid novolac resins. However, the dopant is not limited to the above. The dopants may be used alone or in combination of two or more.

[0042] In the capacitor element according to the embodiment of the present disclosure, the solid electrolyte layer preferably contains both a self-doping conductive polymer and a non-self-doping conductive polymer as the conductive polymer. The solid electrolyte layer preferably includes a first conductive polymer layer containing a self-doping conductive polymer and a second conductive polymer layer containing a non-self-doping conductive polymer, with the first conductive polymer layer being disposed between the dielectric layer and the second conductive polymer layer. The above-described configuration of the solid electrolyte layer allows the solid electrolyte layer to be formed with sufficient thickness deep inside the holes (toward the center of the anode body), while preventing the solid electrolyte film from being excessively thick near the entrances of the holes (toward the outer surface of the anode body). Therefore, a solid electrolytic capacitor including such a capacitor element has even better reliability and voltage resistance.

[0043] As described above, when the solid electrolyte layer is formed by laminating the second conductive polymer layer on the first conductive polymer layer, the thickness L of the first conductive polymer layer is 1 / 2 mm or less at any cross section along the thickness direction of the solid electrolyte layer inside the plurality of holes. ＰＬ１ is the thickness L of the second conductive polymer layer ＰＬ２ It is preferable that the thickness of the first conductive polymer layer is thinner than L ＰＬ１ is preferably 5 nm or more and 15 nm or less, and the thickness L ＰＬ２ The thickness L is preferably greater than 5 nm and not greater than 55 nm. ＰＬ１ and thickness L ＰＬ２ When the thickness L of the first conductive polymer layer is within the above range, a solid electrolytic capacitor including such a capacitor element will have even better reliability and voltage resistance. ＰＬ１ and the thickness L of the second conductive polymer layer ＰＬ２ can be measured as follows. First, a solid electrolytic capacitor is disassembled to remove the capacitor element, and an image of any cross section of the capacitor element is obtained using a scanning electron microscope (SEM). Next, the image is used to measure the thickness of the first conductive polymer layer and the second conductive polymer layer at any 10 points. The measured values ​​obtained for each of the first conductive polymer layer and the second conductive polymer layer are then arithmetically averaged. The first conductive polymer layer and the second conductive polymer layer can be confirmed by SEM-EDX (energy dispersive X-ray spectroscopy) analysis.

[0044] In the capacitor element according to the embodiment of the present disclosure, the thickness L of the solid electrolyte layer from the outer surface of the anode body to 50 μm in the plurality of holes ＳＥＥ is preferably 15 nm or more, more preferably 17 nm or more, and even more preferably 20 nm or more. ＳＥＥ When the thickness L of the solid electrolyte layer is within the above range, the reliability of a solid electrolytic capacitor including such a capacitor element is further improved. ＳＥＥ is preferably 45 nm or less, more preferably 43 nm or less, and even more preferably 40 nm or less.ＳＥＥ When the thickness L of the solid electrolyte layer in the plurality of holes is within the range of 50 μm from the outer surface of the anode body, the solid electrolyte layer has a thickness L of 50 μm from the outer surface of the anode body. ＳＥＥ As explained above, the thickness L of the solid electrolyte layer can be determined by observing the cross section of the capacitor element using an SEM. ＳＥＥ can be determined by measuring the thickness at any 10 points on an SEM image and calculating the arithmetic average of the measured values.

[0045] In the capacitor element according to the embodiment of the present disclosure, the thickness of the solid electrolyte layer in the plurality of holes from the center side of the anode body to 300 μm is set to L ＳＥＣ Then, L ＳＥＥ L for ＳＥＣ The ratio (L ＳＥＣ / L ＳＥＥ ) is preferably greater than 1.0, more preferably 1.1 or greater, and even more preferably 1.3 or greater. ＳＥＣ / L ＳＥＥ may be 3.0 or less, 1.8 or less, or 1.5 or less. ＳＥＣ / L ＳＥＥ When the thickness L of the solid electrolyte layer is within the above range, the reliability of a solid electrolytic capacitor including such a capacitor element is further improved. ＳＥＣ is preferably 30 nm or more, more preferably 35 nm or more, and even more preferably 55 nm or more. ＳＥＣ The thickness L of the solid electrolyte layer in the plurality of holes from the center of the anode body to 300 μm may be 200 nm or less, 100 nm or less, or 70 nm or less. ＳＥＣ As explained above, the thickness L of the solid electrolyte layer can be determined by observing the cross section of the capacitor element using an SEM. ＳＥＣ can be determined by measuring the thickness at any 10 points on an SEM image and calculating the arithmetic average of the measured values.

[0046] The cathode extraction layer includes a carbon layer covering at least a portion of the outer surface of the solid electrolyte layer and a silver paste layer covering the carbon layer. The silver paste layer does not necessarily need to be formed so as to cover the entire outer surface of the carbon layer, but only needs to be formed so as to cover at least a portion of the outer surface of the carbon layer. The carbon layer may be formed using, for example, a conductive carbon material (such as graphite). The silver paste layer may be formed, for example, using a composition containing silver powder and a binder resin (such as an epoxy resin). The configuration of the cathode extraction layer is not limited to the above and may be any configuration that has a current collecting function.

[0047] <Exterior Body> The exterior body is configured to cover the entire capacitor element according to the embodiment of the present disclosure. The exterior body is preferably a resin exterior body. As a material for the resin exterior body, for example, epoxy resin can be used.

[0048] A specific configuration of a solid electrolytic capacitor according to an embodiment of the present disclosure will be described below with reference to Figures 1 and 2. Figure 1 is a schematic cross-sectional view of a solid electrolytic capacitor according to an embodiment of the present disclosure, and Figure 2 is an enlarged cross-sectional view schematically showing region II in Figure 1. In the following description, the dielectric layer covering at least a portion of the outer surface of the anode body will be referred to as a first dielectric layer 7a, the dielectric layer covering at least a portion of the inner surface of each of the plurality of holes will be referred to as a second dielectric layer 7b, the solid electrolyte layer covering at least a portion of the outer surface of the first dielectric layer 7a will be referred to as a first solid electrolyte layer 9a, and the solid electrolyte layer covering at least a portion of the outer surface of the second dielectric layer 7b will be referred to as a second solid electrolyte layer 9b.

[0049] 1, solid electrolytic capacitor 1 includes capacitor element 2, resin outer casing 3 that seals capacitor element 2, and anode terminal 4 and cathode terminal 5, at least a portion of which is exposed to the outside of resin outer casing 3. Anode terminal 4 and cathode terminal 5 may be made of a metal such as copper or a copper alloy. Resin outer casing 3 has a substantially rectangular parallelepiped outer shape, and solid electrolytic capacitor 1 also has a substantially rectangular parallelepiped outer shape. The resin outer casing 3 may be made of, for example, epoxy resin.

[0050] The capacitor element 2 includes an anode body 6 having a porous portion 6a including a plurality of pores 6a1 opening from the outer surface toward the center, a first dielectric layer 7a covering at least a portion of the outer surface S1 of the anode body 6, a second dielectric layer 7b covering at least a portion of the inner surface S2 of each of the plurality of pores 6a1, a first solid electrolyte layer 9a covering at least a portion of the outer surface of the first dielectric layer 7a, and a second solid electrolyte layer 9b covering at least a portion of the outer surface of the second dielectric layer 7b. The capacitor element 2 includes a cathode portion 8, which includes the first solid electrolyte layer 9a, a second solid electrolyte layer 9b, and a cathode extraction layer 10 covering at least the first solid electrolyte layer 9a. In the illustrated example, the cathode extraction layer 10 includes a carbon layer 11 as a first layer and a silver paste layer 12 as a second layer. The first solid electrolyte layer 9a and the second solid electrolyte layer 9b are conductive polymer layers containing a conductive polymer, and the conductive polymer layers contain the conductive polymer described above.

[0051] The anode body 6 includes a region facing the cathode portion 8 (hereinafter simply referred to as the facing region) and a region not facing the cathode portion 8 (hereinafter simply referred to as the non-facing region). In the non-facing region, an insulating separation layer 13 is formed in a strip shape on one end side adjacent to the cathode portion 8 so as to cover the outer surface (exposed surface) of the anode body 6, thereby restricting contact between the cathode portion 8 and the anode body 6. In the non-facing region, an anode terminal 4 is electrically connected by welding to the other end side not adjacent to the cathode portion 8. The cathode terminal 5 is electrically connected to the cathode portion 8 via an adhesive layer 14 formed of a conductive adhesive.

[0052] The main surface 4S of the anode terminal 4 and the main surface 5S of the cathode terminal 5 are exposed on the same side of the resin outer casing 3. That is, the main surface 4S of the anode terminal 4 and the main surface 5S of the cathode terminal 5 constitute exposed surfaces. These exposed surfaces are used for soldering to a substrate (not shown) on which the solid electrolytic capacitor 1 is to be mounted.

[0053] Carbon layer 11 may be made of any material as long as it is conductive, such as a conductive carbon material (such as graphite). Silver paste layer 12 may be made of a composition containing silver powder and a binder resin (such as an epoxy resin). The configuration of cathode extraction layer 10 is not limited to this, and may be any material that has a current collecting function.

[0054] The first solid electrolyte layer 9a is formed so as to cover at least a portion of the outer surface of the first dielectric layer 7a, and the second solid electrolyte layer 9b is formed so as to cover at least a portion of the outer surface of the second dielectric layer 7b. As shown in Fig. 2, the first dielectric layer 7a is formed along the outer surface S1 of the anode body, and the second dielectric layer 7b is formed along the inner surfaces S2 of each of the plurality of holes 6a1 in the porous portion 6a. As shown in Fig. 2, the thickness of the second solid electrolyte layer 9b increases from the outer surface to the center of the anode body 6 inside at least one of the plurality of holes 6a1.

[0055] [Method for Manufacturing Capacitor Element] A method for manufacturing a capacitor element according to an embodiment of the present disclosure includes a first step of forming a dielectric layer so as to cover inner surfaces of a plurality of holes in a porous anode body having a plurality of holes, and a second step of forming a solid electrolyte layer so as to cover the dielectric layer. In the method for manufacturing a capacitor element according to an embodiment of the present disclosure, the solid electrolyte layer includes a conductive polymer layer.

[0056] In the method for manufacturing a capacitor element according to an embodiment of the present disclosure, the second step includes a first substep of immersing the anode body in a conductive polymer solution containing a conductive polymer at a first atmospheric pressure, a second substep of exposing the anode body after the first substep to a pressure higher or lower than the first atmospheric pressure, and a third substep of drying the anode body after the second substep to form a conductive polymer layer.

[0057] <First Step> In the first step, the dielectric layer covering the inner surfaces of the holes in the porous anode body having a plurality of holes can be formed by various known methods. The dielectric layer can be formed by oxidizing the valve metal on the inner surfaces of the holes in the anode body by chemical conversion treatment or the like. For example, the dielectric layer may be formed by immersing the porous anode body having a plurality of holes in a chemical conversion solution and applying a voltage. By performing the first step, the dielectric layer can be formed so as to cover the inner surfaces of the holes. When forming the dielectric layer as described above, a dielectric layer is usually also formed on the outer surface of the anode body. In this case, the dielectric layer can be formed by oxidizing the valve metal on the outer surface of the anode body.

[0058] <Second Step> In the first substep of the second step, the anode body is immersed in a conductive polymer solution containing a conductive polymer at a first atmospheric pressure. By performing the first substep, the conductive polymer solution can be applied to the dielectric layer covering the inner surfaces of the plurality of holes. The first atmospheric pressure can be, for example, atmospheric pressure. As the conductive polymer, a self-doping conductive polymer or a non-self-doping conductive polymer as described above can be used. As the conductive polymer, a self-doping conductive polymer may be used alone, a non-self-doping conductive polymer may be used alone, or a combination of a self-doping conductive polymer and a non-self-doping conductive polymer may be used. In the first substep, the conductive polymer solution is usually also applied to the dielectric layer formed on the outer surface of the anode body.

[0059] In the second substep of the second process, the anode body after the first substep is exposed to a pressure higher or lower than the first atmospheric pressure. When the anode body is exposed to a pressure higher than the first atmospheric pressure, the conductive polymer solution can be pushed deep into the multiple holes at high pressure. When the anode body is exposed to a pressure lower than the first atmospheric pressure, the conductive polymer solution can be drawn deep into the multiple holes at low pressure. That is, when the second substep is performed, a pressure difference with atmospheric pressure can cause a portion of the conductive polymer solution adhering to the dielectric layer to move deep into the multiple holes. Specifically, a portion of the conductive polymer solution adhering to the dielectric layer can be moved deep into the multiple holes so that the amount of the conductive polymer solution adhering to the central part of the anode body is greater than that on the outer surface side of the anode body.

[0060] The pressure to which the anode body after the first step is exposed may be 0.1 times or more, 0.3 times or more, 0.5 times or more, or 0.9 times or more of the first atmospheric pressure. The pressure to which the anode body after the first step is exposed may be 2 times or less, 1.5 times or less, 1.3 times or less, or 1.1 times or less of the first atmospheric pressure. When the anode body after the first step is exposed to a pressure lower than the first atmospheric pressure, the upper limit of the pressure is less than 1 time the first atmospheric pressure, and when the anode body after the first step is exposed to a pressure higher than the first atmospheric pressure, the lower limit of the pressure is more than 1 time the first atmospheric pressure.

[0061] The second step is preferably performed by exposing the anode body to a pressure lower than the first atmospheric pressure and then exposing it to the first atmospheric pressure again. Performing the second step in this manner not only allows the conductive polymer solution to be drawn deep into the multiple holes at low pressure, but also allows the conductive polymer solution to be pushed even deeper into the multiple holes due to the pressure difference between the low pressure and atmospheric pressure. This allows the amount of conductive polymer solution to be further increased inside the multiple holes, closer to the center of the anode body than to the outer surface of the anode body. When the second step is performed as described above, the time required for the anode body to be transferred from a pressure lower than the first atmospheric pressure back to the first atmospheric pressure (hereinafter referred to as the transfer time) is preferably relatively short. The transfer time is preferably 60 seconds or less, more preferably 30 seconds or less, and even more preferably 15 seconds or less. The lower limit of the transfer time is typically 5 seconds. By setting the transfer time within the above range, the amount of conductive polymer solution to be further increased inside the multiple holes, closer to the center of the anode body than to the outer surface of the anode body.

[0062] In the third substep of the second step, the anode body after the second substep is dried. This allows a solid electrolyte layer to be formed in the plurality of holes so that the thickness increases from the outer surface of the anode body toward the center. The drying temperature for the anode body can be 100°C or higher and 200°C or lower. The drying time for the anode body can be 5 minutes or higher and 60 minutes or lower.

[0063] In order to form a solid electrolyte layer having a desired thickness so as to cover the inner surfaces of the plurality of holes, the second step and the third step may be repeated multiple times in the second process.

[0064] In the method for manufacturing a capacitor element according to an embodiment of the present disclosure, it is preferable to use a combination of a first conductive polymer solution containing a self-doping conductive polymer and a second conductive polymer solution containing a non-self-doping conductive polymer as the conductive polymer solution. Note that the self-doping conductive polymer and the non-self-doping conductive polymer may be the same as those exemplified above.

[0065] When the first conductive polymer solution and the second conductive polymer solution are used in combination as described above, it is preferable that in the second step, the first substep through the third substep are performed using the first conductive polymer solution to form a first conductive polymer layer so as to cover the inner surfaces of the plurality of holes in the anode body, and then the first substep through the third substep are performed using the second conductive polymer solution to form a second conductive polymer layer on the first conductive polymer layer. Regardless of whether the first conductive polymer solution or the second conductive polymer solution is used, the second step and the third step may be repeated multiple times. Furthermore, by performing the first substep through the third substep as described above, the first conductive polymer layer and the second conductive polymer layer may also be laminated in this order on the outer surface of the anode body.

[0066] (Additional Notes) The above description discloses the following technologies: (Technology 1) A capacitor element comprising: a porous anode body having a plurality of holes; a dielectric layer covering the inner surfaces of the plurality of holes; and a solid electrolyte layer covering the dielectric layer, wherein the thickness of the solid electrolyte layer in the plurality of holes increases from the outer surface of the anode body toward the center. (Technology 2) A thickness L of the solid electrolyte layer in the plurality of holes from the outer surface of the anode body to 50 μm is ＳＥＥ The capacitor element according to the first aspect of the present invention has a thickness L of the solid electrolyte layer of 20 nm or more. ＳＥＥ The capacitor element according to Technology 1 or 2, wherein the thickness L of the first conductive polymer layer is 40 nm or less. (Technology 4) The capacitor element according to any one of Technology 1 to 3, wherein the solid electrolyte layer has a first conductive polymer layer containing a self-doping conductive polymer and a second conductive polymer layer containing a non-self-doping conductive polymer, and the first conductive polymer layer is disposed between the dielectric layer and the second conductive polymer layer. (Technology 5) In any cross section along the thickness direction of the solid electrolyte layer, the thickness L of the first conductive polymer layer is ＰＬ１ is the thickness L of the second conductive polymer layer ＰＬ２ The capacitor element according to Technology 4, wherein the thickness L of the first conductive polymer layer is thinner than ＰＬ１is 5 nm or more and 15 nm or less, and the thickness L of the second conductive polymer layer ＰＬ２ is greater than 5 nm and not greater than 55 nm. (Technology 7) A solid electrolytic capacitor comprising the capacitor element according to any one of Technologies 1 to 6 and an exterior body sealing the capacitor element. (Technology 8) A method for manufacturing a capacitor element, comprising: a first step of forming a dielectric layer so as to cover inner surfaces of a plurality of holes in a porous anode body having a plurality of holes; and a second step of forming a solid electrolyte layer so as to cover the dielectric layer, wherein the solid electrolyte layer includes a conductive polymer layer, and the second step comprises: a first substep of immersing the anode body in a conductive polymer solution containing a conductive polymer at a first atmospheric pressure; a second substep of exposing the anode body after the first substep to a pressure higher or lower than the first atmospheric pressure; and a third substep of drying the anode body after the second substep to form the conductive polymer layer. (Technology 9) A method for manufacturing a capacitor element according to Technology 8, wherein the second substep is performed by exposing the anode body to a pressure lower than the first atmospheric pressure and then exposing it to the first atmospheric pressure again. (Technology 10) The method for manufacturing a capacitor element according to Technology 8 or 9, wherein in the second step, the first sub-step to the third sub-step are performed using a first conductive polymer solution containing a self-doping conductive polymer to form a first conductive polymer layer so as to cover inner surfaces of the plurality of holes in the anode body, and then the first sub-step to the third sub-step are performed using a second conductive polymer solution containing a non-self-doping conductive polymer to form a second conductive polymer layer so as to cover the first conductive polymer layer.

[0067] While the present invention has been described in terms of presently preferred embodiments, such disclosure should not be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention.

[0068] Hereinafter, the present disclosure will be specifically described based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0069] Example 1 (1) Preparation of Anode Body A tantalum sintered body (porous body) with a portion of an anode lead embedded therein was prepared as the anode body. The tantalum sintered body had a rectangular parallelepiped shape. A portion of the anode lead was embedded in one end face of the tantalum sintered body. That is, the anode lead was provided so as to protrude outward from one end of the tantalum sintered body. The anode body was anodized in a phosphoric acid aqueous solution (phosphoric acid concentration: 0.010% by mass) to form a dielectric layer covering at least a portion of the outer surface of the anode body and at least a portion of the inner surface of each of the multiple holes contained in the porous portion. The anodization was performed under the condition of applying a DC voltage of 70 V for 20 minutes.

[0070] (2) Formation of a Solid Electrolyte Layer An aqueous dispersion (first conductive polymer solution) containing a polythiophene-based polymer as a self-doping conductive polymer was prepared. The concentration of the polythiophene-based polymer in the first conductive polymer solution was 1 to 3% by mass. The self-doping polythiophene-based polymer used was PEDOT (Mw: approximately 10,000) having a sulfo group bonded to the PEDOT skeleton via a linking group containing a butylene group.

[0071] A tantalum sintered compact on which a dielectric layer had been formed (hereinafter referred to as a tantalum sintered compact with a dielectric layer) was immersed in a first conductive polymer solution under atmospheric pressure (0.1 MPa (1 atm)) for approximately 30 to 60 seconds, and then the tantalum sintered compact with a dielectric layer was pulled out of the first conductive polymer solution. The tantalum sintered compact with the first conductive polymer solution attached was then exposed to reduced pressure (0.01 MPa (0.1 atm)) and then exposed to atmospheric pressure again for 10 seconds. Next, the tantalum sintered compact after being exposed to atmospheric pressure again was heated (dried) at 140 to 180°C for 10 to 20 minutes, thereby forming a first conductive polymer layer on at least a portion of the outer surface of the dielectric layer. In other words, a tantalum sintered compact with a first conductive polymer layer was obtained. The target thickness was obtained by repeating this operation three times.

[0072] An aqueous dispersion (second conductive polymer solution) containing PEDOT doped with PSS (hereinafter referred to as PEDOT / PSS) was prepared as a non-self-doping conductive polymer. The concentration of PEDOT / PSS in the second conductive polymer solution was 1 to 3% by mass.

[0073] The tantalum sintered compact with the first conductive polymer layer was immersed in the second conductive polymer solution under atmospheric pressure for approximately 30 to 60 seconds, and then the tantalum sintered compact with the first conductive polymer layer was pulled out of the second conductive polymer solution. The tantalum sintered compact with the second conductive polymer solution attached was then exposed to reduced pressure (0.01 MPa (0.1 atm)) and then exposed to atmospheric pressure again for 10 seconds. Next, the tantalum sintered compact after being exposed to atmospheric pressure again was heated (dried) at 140 to 180°C for 10 to 20 minutes, thereby forming a second conductive polymer layer on at least a portion of the outer surface of the first conductive polymer layer. This formed a solid electrolyte layer in which the first conductive polymer layer and the second conductive polymer layer were laminated in this order on at least a portion of the outer surface of the tantalum sintered compact and on at least a portion of the inner surface of each of the multiple pores contained in the porous portion. This operation was repeated four times to obtain the desired thickness.

[0074] The thicknesses of the solid electrolyte layer formed on at least a portion of the inner surface of each of the plurality of holes included in the porous portion were measured on the outer surface side and the central portion (anode wire side) of the anode body, and were found to be 20 nm and 35 nm, respectively. The thickness of the solid electrolyte layer on the outer surface side of the anode body was broken down as follows: the first conductive polymer layer was 5 nm and the second conductive polymer layer was 10 nm. The thickness of the solid electrolyte layer on the central portion of the anode body was broken down as follows: the first conductive polymer layer was 15 nm and the second conductive polymer layer was 25 nm. The results are shown in Table 1 below. The thicknesses of the solid electrolyte layer, the first conductive polymer layer, and the second conductive polymer layer on the outer surface side and the central portion of the anode body were measured according to the methods described in the above embodiments.

[0075] (3) Formation of Cathode Extraction Layer A dispersion of graphite particles dispersed in water was applied to at least a portion of the outer surface of the solid electrolyte layer, followed by drying, thereby forming a carbon layer primarily on at least a portion of the outer surface of the solid electrolyte layer. Drying was carried out at 130 to 180°C for 10 to 30 minutes. Next, a silver paste containing silver particles and a binder resin (epoxy resin) was applied to at least a portion of the outer surface of the carbon layer, and the binder resin was then thermally cured to form a silver paste layer on at least a portion of the outer surface of the carbon layer. The binder resin was thermally cured at 150 to 200°C for 10 to 60 minutes. This resulted in a cathode extraction layer primarily composed of a carbon layer and a silver paste layer formed on at least a portion of the outer surface of the solid electrolyte layer. In this manner, a capacitor element according to Example 1 was obtained.

[0076] (4) Fabrication of a Solid Electrolytic Capacitor After attaching an anode terminal (anode lead frame) and a cathode terminal (cathode lead frame) to the capacitor element, the entire capacitor element was encapsulated with a resin encapsulant so that the anode terminal and the cathode terminal were exposed, and the remaining portions of the anode terminal and the cathode terminal were also encapsulated with a resin encapsulant. In this manner, a solid electrolytic capacitor (tantalum electrolytic capacitor) according to Example 1 was obtained. Specifically, a solid electrolytic capacitor such as that shown in FIG. 1 was obtained. The anode terminal was attached by welding the anode terminal to the anode lead of the capacitor element, and the cathode terminal was attached by connecting the cathode terminal to the cathode extraction layer of the capacitor element with a conductive adhesive.

[0077] [Example 2] A solid electrolytic capacitor according to Example 2 was obtained in the same manner as Example 1, except that on the outer surface side of the anode body, the solid electrolyte layer was 40 nm thick, the first conductive polymer layer was 10 nm thick, and the second conductive polymer layer was 30 nm thick, and further on the center side of the anode body, the solid electrolyte layer was 55 nm thick, the first conductive polymer layer was 15 nm thick, and the second conductive polymer layer was 40 nm thick. In Example 2, the first conductive polymer layer was formed by repeating the operation described in Example 1 four times, and the second conductive polymer layer was formed by repeating the operation described in Example 1 seven times.

[0078] Example 3 A solid electrolytic capacitor according to Example 3 was obtained in the same manner as Example 1, except that on the outer surface side of the anode body, the solid electrolyte layer was 50 nm thick, the first conductive polymer layer was 10 nm thick, and the second conductive polymer layer was 40 nm thick, and further on the center side of the anode body, the solid electrolyte layer was 70 nm thick, the first conductive polymer layer was 15 nm thick, and the second conductive polymer layer was 55 nm thick. In Example 3, the first conductive polymer layer was formed by repeating the operation described in Example 1 four times, and the second conductive polymer layer was formed by repeating the operation described in Example 1 ten times.

[0079] Example 4 A solid electrolytic capacitor according to Example 4 was obtained in the same manner as Example 1, except that on the outer surface side of the anode body, the solid electrolyte layer was 10 nm thick, the first conductive polymer layer was 5 nm thick, and the second conductive polymer layer was 5 nm thick, and further on the center side of the anode body, the solid electrolyte layer was 30 nm thick, the first conductive polymer layer was 10 nm thick, and the second conductive polymer layer was 20 nm thick. In Example 4, the first conductive polymer layer was formed by repeating the operation described in Example 1 three times, and the second conductive polymer layer was formed by repeating the operation described in Example 1 three times.

[0080] Example 5 A solid electrolytic capacitor according to Example 5 was obtained in the same manner as Example 1, except that the solid electrolyte layer was composed only of a second conductive polymer layer (a layer containing a non-self-doping conductive polymer), and the thickness of the solid electrolyte layer (second conductive polymer layer) on the outer surface side of the anode body was 30 nm and the thickness of the solid electrolyte layer (second conductive polymer layer) on the center side of the anode body was 45 nm. In Example 5, the second conductive polymer layer was formed by repeating the operation described in Example 1 eight times.

[0081] Example 6 A solid electrolytic capacitor according to Example 6 was obtained in the same manner as Example 1, except that the solid electrolyte layer was composed only of a first conductive polymer layer (a layer containing a self-doping conductive polymer), and the thickness of the solid electrolyte layer (first conductive polymer layer) was 25 nm on the outer surface side of the anode body and 35 nm on the center side of the anode body. In Example 6, the first conductive polymer layer was formed by repeating the operation described in Example 1 ten times.

[0082] Comparative Example 1 A solid electrolytic capacitor according to Comparative Example 1 was obtained in the same manner as in Example 1, except that on the outer surface side of the anode body, the solid electrolyte layer was 25 nm thick, the first conductive polymer layer was 10 nm thick, and the second conductive polymer layer was 15 nm thick, and further on the center side of the anode body, the solid electrolyte layer was 10 nm thick, the first conductive polymer layer was 5 nm thick, and the second conductive polymer layer was 5 nm thick. In Comparative Example 1, the first conductive polymer layer was formed by repeating the operation described in Example 1 three times, except that exposure to reduced pressure was not performed, and the second conductive polymer layer was formed by repeating the operation described in Example 1 six times, except that exposure to reduced pressure was not performed.

[0083] Comparative Example 2 A solid electrolytic capacitor according to Comparative Example 2 was obtained in the same manner as in Example 1, except that on the outer surface side of the anode body, the solid electrolyte layer was 45 nm thick, the first conductive polymer layer was 10 nm thick, and the second conductive polymer layer was 35 nm thick, and further on the center side of the anode body, the solid electrolyte layer was 10 nm thick, the first conductive polymer layer was 5 nm thick, and the second conductive polymer layer was 5 nm thick. In Comparative Example 2, the first conductive polymer layer was formed by repeating the operation described in Example 1 three times, except that exposure to reduced pressure was not performed, and the second conductive polymer layer was formed by repeating the operation described in Example 1 four times, except that exposure to reduced pressure was not performed.

[0084]

[0085] <Evaluation> ・Reliability Initial capacitance C ０ (μF) vs. capacitance C after processing under specified conditions １(μF) ratio (C １ / C ０ ) was used to evaluate the reliability of the solid electrolytic capacitors according to each example (Examples 1 to 6 and Comparative Examples 1 and 2). In other words, the closer the calculated value is to 1, the higher the reliability of the solid electrolytic capacitor. ０ The value measured at a temperature of 20°C and a frequency of 120 Hz was used. １ The capacitance C was measured at a frequency of 120 Hz after applying a rated voltage (35 V) for 500 hours at a temperature of 125°C. ０ and C １ was measured using a four-terminal LCR meter. ０ and C １ was calculated by arithmetically averaging the measurements obtained for 10 solid electrolytic capacitors. The reliability evaluation results for the solid electrolytic capacitors of each example are shown in Table 2 below. Breakdown voltage A 1 kΩ resistor was connected in series to the solid electrolytic capacitor of each example. Next, for the solid electrolytic capacitors of each example after application of the rated voltage, a voltage was applied while increasing at a rate of 1.0 V / sec, and the breakdown voltage (V) was measured when an overcurrent of 0.5 A flowed. The breakdown voltage was calculated by arithmetically averaging the measurements obtained for the 10 solid electrolytic capacitors. The breakdown voltage of the solid electrolytic capacitors of each example is shown in Table 2 below. In Table 2 below, breakdown voltage is simply referred to as "breakdown voltage."

[0086]

[0087] It can be seen from Table 2 that the solid electrolytic capacitors according to each example (Examples 1 to 6) all exhibited high reliability evaluation values ​​exceeding 0.50, and also exhibited high withstand voltage values ​​exceeding 70 V. This shows that the thickness of the solid electrolyte layer formed on at least a portion of the inner surfaces of the plurality of holes increases from the outer surface of the anode body toward the center, thereby providing the solid electrolytic capacitor with excellent reliability and withstand voltage.

[0088] The solid electrolytic capacitor according to the present disclosure can be used in applications where excellent reliability (particularly, capacitance retention rate) and voltage resistance are required.

[0089] 1: Solid electrolytic capacitor 2: Capacitor element 3: Resin exterior body 4: Anode terminal 4S: Main surface of anode terminal 5: Cathode terminal 5S: Main surface of cathode terminal 6: Anode body 6a: Porous portion 6a1: Hole portion 7a: First dielectric layer 7b: Second dielectric layer 8: Cathode portion 9a: First solid electrolyte layer 9b: Second solid electrolyte layer 10: Cathode extraction layer 11: Carbon layer 12: Silver paste layer 13: Separation layer 14: Adhesive layer S1: Outer surface of anode body S2: Inner surface of hole portion

Claims

1. A capacitor element comprising: a porous anode body having a plurality of holes; a dielectric layer covering the inner surfaces of the plurality of holes; and a solid electrolyte layer covering the dielectric layer, wherein the thickness of the solid electrolyte layer in the plurality of holes increases from the outer surface of the anode body toward the center.

2. The thickness L of the solid electrolyte layer from the outer surface of the anode body to 50 μm in the plurality of holes ＳＥＥ The capacitor element according to claim 1 , wherein the thickness of the first and second electrodes is 15 nm or more.

3. The thickness L of the solid polymer layer ＳＥＥ The capacitor element according to claim 1 or 2, wherein the thickness of the first and second electrodes is 45 nm or less.

4. The capacitor element according to claim 1 or 2, wherein the solid electrolyte layer comprises a first conductive polymer layer containing a self-doping conductive polymer and a second conductive polymer layer containing a non-self-doping conductive polymer, and the first conductive polymer layer is disposed between the dielectric layer and the second conductive polymer layer.

5. In any cross section along the thickness direction of the solid electrolyte layer, the thickness L of the first conductive polymer layer ＰＬ１ is the thickness L of the second conductive polymer layer ＰＬ２ The capacitor element of claim 4 , wherein the thickness is less than 100 μm.

6. Thickness L of the first conductive polymer layer ＰＬ１ is 5 nm or more and 15 nm or less, and the thickness L of the second conductive polymer layer ＰＬ２ The capacitor element according to claim 5 , wherein the average particle size is greater than 5 nm and equal to or less than 55 nm.

7. A solid electrolytic capacitor comprising the capacitor element according to claim 1 or 2 and an exterior body that seals the capacitor element.

8. A method for manufacturing a capacitor element, comprising: a first step of forming a dielectric layer so as to cover inner surfaces of a plurality of pores in a porous anode body having the pores; and a second step of forming a solid electrolyte layer so as to cover the dielectric layer, wherein the solid electrolyte layer includes a conductive polymer layer, and the second step comprises: a first sub-step of immersing the anode body in a conductive polymer solution containing a conductive polymer at a first atmospheric pressure; a second step of exposing the anode body after the first sub-step to a pressure higher or lower than the first atmospheric pressure; and a third sub-step of drying the anode body after the second sub-step to form the conductive polymer layer.

9. The method for manufacturing a capacitor element according to claim 8, wherein the second step is carried out by exposing the anode body to a pressure lower than the first atmospheric pressure and then exposing it to the first atmospheric pressure again.

10. A method for manufacturing a capacitor element as described in claim 8 or 9, wherein in the second step, the first sub-step through the third sub-step are carried out using a first conductive polymer solution containing a self-doping conductive polymer to form a first conductive polymer layer so as to cover the inner surfaces of the plurality of holes in the anode body, and then the first sub-step through the third sub-step are carried out using a second conductive polymer solution containing a non-self-doping conductive polymer to form a second conductive polymer layer so as to cover the first conductive polymer layer.

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