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

Abstract

This capacitor element comprises a positive electrode, a dielectric layer, and a negative electrode unit including a solid electrolyte layer and a negative electrode lead-out layer. The solid electrolyte layer includes an ionic liquid, and includes a first solid electrolyte and a second solid electrolyte layer. The first solid electrolyte includes a self-doped conductive polymer. The second solid electrolyte layer includes a solid electrolyte 2A, a solid electrolyte 2B, and a solid electrolyte 2C. Among a first interface between the first solid electrolyte and the solid electrolyte 2A, a second interface between the solid electrolyte 2A and the solid electrolyte 2B, a third interface between the solid electrolyte 2B and the solid electrolyte 2C, and a fourth interface between the solid electrolyte 2C and the negative-electrode lead-out layer, the distribution quantity of the ionic liquid is greatest at the second interface or the third interface.

Description

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

[0001] The present disclosure relates to a solid electrolytic capacitor element, a solid electrolytic capacitor, and a method for manufacturing a solid electrolytic capacitor element.

[0002] The 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 formed on the surface of the anode body, and a solid electrolyte layer that covers at least a portion of the dielectric layer. The solid electrolyte layer is formed, for example, by chemical polymerization or electrolytic polymerization, or by using a liquid dispersion containing particles of a conductive polymer (such as a conjugated polymer and a dopant).

[0003] Patent Document 1 proposes a method for forming an electrolytic capacitor, the method including: preparing an anode, the anode having a dielectric thereon, the anode including a sintered powder, the powder having a powder charge of at least 45,000 μFV / g; and applying a first slurry to form a first conductive polymer layer covering at least a portion of the dielectric, the first slurry including a polyanion and a conductive polymer, the weight ratio of the polyanion to the polymer being greater than 3, and the conductive polymer and the polyanion forming conductive particles having an average particle size of 20 nm or less.

[0004] Japanese Patent Application Laid-Open No. 2021-532584

[0005] The method using a liquid dispersion containing conductive polymer particles does not require precise control of the polymerization reaction as in chemical polymerization or electrolytic polymerization, and allows for relatively easy formation of a solid electrolyte layer. Furthermore, since it is relatively easy to increase the thickness of the solid electrolyte layer, it is easy to increase the voltage resistance of the solid electrolytic capacitor. However, in solid electrolytic capacitors, the film repairability of the dielectric layer is low, making it prone to leakage current. Furthermore, the low film repairability of the dielectric layer limits the level of voltage resistance that can be achieved.

[0006] A first aspect of the present disclosure includes an anode body having a porous portion at least in a surface layer thereof; a dielectric layer formed on at least a portion of the surface of the porous portion; and a cathode portion including a solid electrolyte layer covering at least a portion of the dielectric layer and a cathode extraction layer covering at least a portion of the solid electrolyte layer, wherein the solid electrolyte layer includes an ionic liquid and includes: a first solid electrolyte covering at least a portion of the dielectric layer; and a second solid electrolyte layer covering at least a portion of the first solid electrolyte, wherein the first solid electrolyte includes a self-doping conductive polymer, and the second solid electrolyte layer includes a solid electrolyte 2A covering at least a portion of the first solid electrolyte, a solid electrolyte 2B covering at least a portion of the solid electrolyte 2A, and a solid electrolyte 2C covering at least a portion of the solid electrolyte 2B, The present invention relates to a solid electrolytic capacitor element in which the amount of distribution of the ionic liquid is greatest at the second interface or the third interface among a first interface between the first solid electrolyte and the solid electrolyte 2A, a second interface between the solid electrolyte 2A and the solid electrolyte 2B, a third interface between the solid electrolyte 2B and the solid electrolyte 2C, and a fourth interface between the solid electrolyte 2C and the cathode extraction layer.

[0007] A second aspect of the present disclosure relates to a solid electrolytic capacitor including at least one of the above-described solid electrolytic capacitor elements and an exterior body that seals the solid electrolytic capacitor element.

[0008] A third aspect of the present disclosure is a method for manufacturing a solid electrolytic capacitor element including an anode body having a porous portion at least on a surface thereof, a dielectric layer formed on at least a portion of the surface of the porous portion, a solid electrolyte layer covering at least a portion of the dielectric layer, and a cathode portion including a cathode extraction layer covering at least a portion of the solid electrolyte layer, the method comprising: a first step of preparing the anode body having the dielectric layer on the surface of the porous portion; a second step of forming the solid electrolyte layer so as to cover at least a portion of the dielectric layer; and a third step of forming the cathode extraction layer so as to cover at least a portion of the solid electrolyte layer, the second step comprising: a first substep of forming a first solid electrolyte covering at least a portion of the dielectric layer using a first treatment liquid containing a self-doping conductive polymer; a second substep of forming a solid electrolyte 2A covering at least a portion of the first solid electrolyte using a liquid dispersion 2A containing a conductive polymer 2A; and a third substep of forming a solid electrolyte 2B covering at least a portion of the solid electrolyte 2A using a liquid dispersion 2B containing a conductive polymer 2B. and a fourth substep of forming a solid electrolyte 2C covering at least a portion of the solid electrolyte 2B using a liquid dispersion 2C containing a conductive polymer 2C, wherein the second step further includes at least one of a fifth substep, between the second substep and the third substep, of applying a second treatment liquid containing an ionic liquid to the surface of the solid electrolyte 2A and drying the liquid dispersion 2C, and a sixth substep, between the third substep and the fourth substep, of applying a third treatment liquid containing an ionic liquid to the surface of the solid electrolyte 2B and drying the solid electrolyte 2B. The method for producing a solid electrolytic capacitor element relates to a method for producing a solid electrolytic capacitor element, wherein the distribution amount of the ionic liquid is greatest at the second interface or the third interface among a first interface between the first solid electrolyte and the solid electrolyte 2A, a second interface between the solid electrolyte 2A and the solid electrolyte 2B, a third interface between the solid electrolyte 2B and the solid electrolyte 2C, and a fourth interface between the solid electrolyte 2C and the cathode extraction layer.

[0009] In the solid electrolytic capacitor, leakage current can be suppressed and excellent voltage resistance can be ensured.

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

[0011] The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

[0012] When a solid electrolyte layer is formed by in-situ polymerization, such as chemical polymerization or electrolytic polymerization, additives (such as Fe-based oxidizers) remaining in the solid electrolyte layer during polymerization can contribute to a decrease in voltage resistance. In contrast, a method using a liquid dispersion containing a conductive polymer can reduce the contamination of additives during polymerization and facilitate the creation of a thicker solid electrolyte layer, which is advantageous for improving voltage resistance. However, as applications become more diverse, solid electrolytic capacitors are required to further improve their voltage resistance. Furthermore, the dielectric layer of solid electrolytic capacitors has low film repairability, resulting in a low effect of suppressing leakage current.

[0013] In view of the above, (1) a solid electrolytic capacitor element according to a first aspect of the present disclosure includes an anode body having a porous portion at least in a surface layer thereof, a dielectric layer formed on at least a portion of the porous portion, and a cathode portion including a solid electrolyte layer covering at least a portion of the dielectric layer and a cathode extraction layer covering at least a portion of the solid electrolyte layer. The solid electrolyte layer includes an ionic liquid and includes a first solid electrolyte covering at least a portion of the dielectric layer and a second solid electrolyte layer covering at least a portion of the first solid electrolyte. The first solid electrolyte includes a self-doping conductive polymer. The second solid electrolyte layer includes at least a solid electrolyte 2A covering at least a portion of the first solid electrolyte, a solid electrolyte 2B covering at least a portion of the solid electrolyte 2A, and a solid electrolyte 2C covering at least a portion of the solid electrolyte 2B. Among the interface between the first solid electrolyte and the solid electrolyte 2A (first interface), the interface between the solid electrolyte 2A and the solid electrolyte 2B (second interface), the interface between the solid electrolyte 2B and the solid electrolyte 2C (third interface), and the interface between the solid electrolyte 2C and the cathode extraction layer (fourth interface), the amount of ionic liquid distributed at the second interface or the third interface is the largest. This state of distribution of ionic liquid is the state of distribution in an initial solid electrolytic capacitor. The initial solid electrolytic capacitor is an aged solid electrolytic capacitor or, if it is a commercially available product, an unused solid electrolytic capacitor.

[0014] Such a solid electrolyte layer is formed, for example, by a manufacturing method including a step of preparing an anode body having a dielectric layer (step 1), a step of forming a solid electrolyte layer (step 2), and a step of forming a cathode extraction layer (step 3). Step 2 includes a first substep of forming a first solid electrolyte, a second substep of forming a solid electrolyte 2A, a third substep of forming a solid electrolyte 2B, and a fourth substep of forming a solid electrolyte 2C. In Step 2, the solid electrolyte layer is formed by performing at least one of a fifth substep between the second and third substeps of applying a treatment liquid containing an ionic liquid to the surface of solid electrolyte 2A and drying the treatment liquid, and a sixth substep between the third and fourth substeps of applying a treatment liquid containing an ionic liquid to the surface of solid electrolyte 2B and drying the treatment liquid.

[0015] By performing drying in the fifth or sixth substep, the ionic liquid can be distributed so that the amount of distribution is maximized at the second or third interface among the first to fourth interfaces in the initial solid electrolytic capacitor. The ionic liquid also penetrates into the inner portions, specifically the solid electrolyte 2A or 2B, the first solid electrolyte, and the dielectric layer, before drying. Because the first solid electrolyte and the dielectric layer are typically very thin, the ionic liquid is retained at the above interfaces and is primarily retained in the solid electrolyte 2A or 2B. In the solid electrolyte layer, the amount of ionic liquid distributed in the solid electrolyte 2A or 2B can be maximized. In this way, by retaining a large amount of ionic liquid in the second solid electrolyte layer, which occupies a large portion of the solid electrolyte layer, the ionic liquid can moderately increase the resistance of the second solid electrolyte layer. Furthermore, by retaining a large amount of ionic liquid relatively close to the dielectric layer, even if defects such as cracks occur in the dielectric layer, the ionic liquid can repair them, ensuring high film repairability. The increased resistance of the second solid electrolyte layer and the improved film repairability of the dielectric layer due to the ionic liquid result in improved voltage resistance and reduced leakage current in the solid electrolytic capacitor. Furthermore, the low abundance of ionic liquid in the solid electrolyte 2C or in the portion of the solid electrolyte layer outside the solid electrolyte 2C (such as the interface between the solid electrolyte 2C and the cathode extraction layer, the cathode extraction layer, etc.) ensures high conductivity in the solid electrolyte 2C or in the portion outside the solid electrolyte 2C. Furthermore, high adhesion between the solid electrolyte layer and the cathode extraction layer can be ensured. This allows the equivalent series resistance (ESR) of the solid electrolytic capacitor to be kept low, while also ensuring high capacitance.

[0016] Even if the fifth and sixth substeps are omitted and a substep of applying a treatment solution containing an ionic liquid to the first solid electrolyte and drying it is performed between the first and second substeps, the effect of suppressing leakage current can be achieved to some extent, but it is difficult to ensure sufficient voltage resistance. Even if the ionic liquid is applied in such a substep, the ionic liquid is present at the first interface between the first solid electrolyte and the second solid electrolyte layer, the extremely thin first solid electrolyte and dielectric layer, and the pores of the porous portion of the anode body, and is almost absent in the second solid electrolyte layer, which occupies most of the solid electrolyte layer. Therefore, it is thought that the effect of the ionic liquid in increasing the resistance of the solid electrolyte layer is hardly achieved, and the effect of improving voltage resistance and the effect of suppressing leakage current are not achieved. Furthermore, the presence of a large amount of ionic liquid in the pores of the porous portion of the anode body may inhibit the formation of the second solid electrolyte inside the anode body. Furthermore, even if the fifth and sixth substeps are not performed and a substep of applying a treatment liquid containing an ionic liquid to the solid electrolyte 2C or a portion of the solid electrolyte layer outside the solid electrolyte 2C and drying it is performed after the fourth substep, it becomes difficult to suppress leakage current, and if a large amount of ionic liquid is distributed at the interface between the solid electrolyte layer and the cathode extraction layer, the interfacial resistance becomes large, resulting in an increase in ESR and a decrease in capacitance.

[0017] (2) In the above (1), the second solid electrolyte layer may contain a conjugated polymer and a dopant.

[0018] (3) In the above (1) or (2), the amount of the ionic liquid distributed at the second interface may be the largest among the first interface, the second interface, the third interface, and the fourth interface.

[0019] (4) In any one of the above (1) to (3), in the solid electrolyte layer, the distribution amount of the ionic liquid may be maximum in the solid electrolyte 2A or the solid electrolyte 2B.

[0020] (5) In any one of the above (1) to (4), the ionic liquid may be hydrophilic.

[0021] (6) In any one of the above (1) to (5), the ionic liquid is HSO ４ － It may contain ions.

[0022] (7) A solid electrolytic capacitor according to a second aspect of the present disclosure includes at least one solid electrolytic capacitor element according to any one of (1) to (6) above, and an exterior body that seals the solid electrolytic capacitor element.

[0023] (8) The present disclosure also includes a method for manufacturing a solid electrolytic capacitor element. The solid electrolytic capacitor element includes an anode body having a porous portion at least on its surface, a dielectric layer formed on at least a portion of the surface of the porous portion, and a cathode portion including a solid electrolyte layer covering at least a portion of the dielectric layer and a cathode extraction layer covering at least a portion of the solid electrolyte layer. The method for manufacturing a solid electrolytic capacitor element includes: a first step of preparing the anode body having the dielectric layer on the surface of the porous portion; a second step of forming the solid electrolyte layer so as to cover at least a portion of the dielectric layer; and a third step of forming the cathode extraction layer so as to cover at least a portion of the solid electrolyte layer. The second step includes: a first substep of forming a first solid electrolyte covering at least a portion of the dielectric layer using a first treatment liquid containing a self-doping conductive polymer; a second substep of forming a solid electrolyte 2A covering at least a portion of the first solid electrolyte using a liquid dispersion 2A containing a conductive polymer 2A; a third substep of forming a solid electrolyte 2B covering at least a portion of the solid electrolyte 2A using a liquid dispersion 2B containing a conductive polymer 2B; and a fourth substep of forming a solid electrolyte 2C covering at least a portion of the solid electrolyte 2B using a liquid dispersion 2C containing a conductive polymer 2C. The second step further includes at least one of a fifth substep of applying a second treatment liquid containing an ionic liquid to the surface of the solid electrolyte 2A and drying the applied second treatment liquid between the second and third substeps, and a sixth substep of applying a third treatment liquid containing an ionic liquid to the surface of the solid electrolyte 2B and drying the applied third treatment liquid between the third and fourth substeps. In the solid electrolytic capacitor element, the amount of the ionic liquid distributed is greatest at the second interface or the third interface among a first interface between the first solid electrolyte and the solid electrolyte 2A, a second interface between the solid electrolyte 2A and the solid electrolyte 2B, a third interface between the solid electrolyte 2B and the solid electrolyte 2C, and a fourth interface between the solid electrolyte 2C and the cathode extraction layer.

[0024] (9) In the above (8), the average particle diameter Da of the conductive polymer 2A, the average particle diameter Db of the conductive polymer 2B, and the average particle diameter Dc of the conductive polymer 2C may satisfy Da≦Db<Dc.

[0025] (10) In the above (8) or (9), none of the first treatment liquid, the liquid dispersion 2A, the liquid dispersion 2B, and the liquid dispersion 2C may contain an ionic liquid.

[0026] (11) In any one of the above (8) to (10), neither the second treatment liquid nor the third treatment liquid may contain a conductive polymer.

[0027] The solid electrolytic capacitor element and its manufacturing method, as well as the solid electrolytic capacitor and its manufacturing method according to the present disclosure, will be described in more detail below, including the above (1) to (11). At least one of the above (1) to (11) may be combined with at least one of the elements described below, provided that this is not technically inconsistent.

[0028] [Solid Electrolytic Capacitor] The solid electrolytic capacitor element included in the solid electrolytic capacitor includes an anode body, a dielectric layer formed on the surface of the anode body, and a cathode portion covering at least a portion of the dielectric layer. The anode body constitutes the anode portion. Hereinafter, the solid electrolytic capacitor element may be simply referred to as a capacitor element. In the present disclosure, there are no particular limitations on the components other than the solid electrolyte layer, and components used in known solid electrolytic capacitors may be applied.

[0029] (Capacitor Element) (Anode Portion) The anode portion includes an anode body. The anode portion may include an anode body and an anode wire.

[0030] (Anode Body) The anode body may contain 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 of them. Preferred examples of the valve metal include aluminum, tantalum, niobium, and titanium.

[0031] The anode body has a porous portion at least on the surface thereof, which has many fine pores in the porous portion, and the porous portion gives the anode body a finely uneven shape.

[0032] An anode body having a porous portion in its surface layer can be obtained, for example, by roughening the surface of a substrate (such as a sheet-like (e.g., foil-like, plate-like) substrate) containing a valve metal. The roughening may be performed, for example, by etching (such as electrolytic etching or chemical etching). Such an anode body has, for example, a core and porous portions formed on both surfaces of the core and integrally with the core.

[0033] The anode body may be a porous compact or a porous sintered body (e.g., a sintered body of a porous compact) of particles containing a valve metal. Each of the compact and the sintered body may be in the form of a sheet, a rectangular parallelepiped, a cube, or a similar shape. The porous sintered body may be, for example, a porous sintered body containing tantalum.

[0034] (Anode Wire) When the anode body is a porous sintered body or a porous molded body, the anode portion may include an anode wire. The anode wire may be a wire made of a metal. Examples of materials for the anode wire include the valve metals listed above, copper, or a copper alloy. A portion of the anode wire is embedded in the anode body, and the remaining portion protrudes outward from the end face of the anode body.

[0035] (Dielectric Layer) The dielectric layer is formed, for example, so as to cover at least a portion of the surface of the anode body (more specifically, the porous portion). The dielectric layer is an insulating layer that functions as a dielectric. The dielectric layer is formed by anodizing a valve metal on the surface of the anode body using a chemical conversion treatment or the like. Because the dielectric layer is formed on the porous surface of the anode body, the surface of the dielectric layer has a fine uneven shape that follows the shape of the porous portion.

[0036] The dielectric layer contains an oxide of the valve metal. For example, when tantalum is used as the valve metal, the dielectric layer contains Ta. ２ O ５ When aluminum is used as the valve metal, the dielectric layer contains Al ２ O３ The dielectric layer is not limited to these examples, but may be any layer that functions as a dielectric.

[0037] (Cathode portion) The cathode portion is formed so as to cover at least a portion of the dielectric layer formed on the surface of the anode body. The cathode portion includes at least a solid electrolyte layer covering at least a portion of the dielectric layer. The cathode portion may include, for example, a solid electrolyte layer covering at least a portion of the dielectric layer and a cathode extraction layer covering at least a portion of the solid electrolyte layer. Components of the cathode portion will be described below.

[0038] (Solid Electrolyte Layer) The solid electrolyte layer includes a first solid electrolyte covering at least a portion of the dielectric layer and a second solid electrolyte layer covering at least a portion of the first solid electrolyte. The solid electrolyte layer includes an ionic liquid.

[0039] (First Solid Electrolyte) The first solid electrolyte includes a self-doping conductive polymer. The self-doping conductive polymer has, for example, a conjugated polymer skeleton and a functional group (such as an anionic group) that functions as a dopant and is directly or indirectly bound to the skeleton by a covalent bond.

[0040] Self-doping conductive polymers typically contain anionic groups. Examples of anionic groups include sulfo groups, carboxy groups, phosphate groups, and phosphonate groups. In the solid electrolyte layer, the anionic groups of the self-doping conductive polymer may be present in any form, such as anionic, free, ester, or salt, or may be present in a form that interacts with or is complexed with a component contained in the solid electrolyte layer. In this specification, all of these forms are simply referred to as anionic groups.

[0041] The self-doping conductive polymer may contain one or more types of anionic groups. From the viewpoint of easily ensuring higher conductivity of the self-doping conductive polymer, the self-doping conductive polymer may contain at least a sulfo group.

[0042] The skeleton of the self-doping conductive polymer can be said to be composed of a conjugated polymer. The number of anionic groups contained in the self-doping conductive polymer is, for example, 1 to 3, or alternatively, 1 to 2, or even 1, per molecule of the conjugated polymer constituting the skeleton of the self-doping conductive polymer.

[0043] Conjugated polymers constituting the backbone of self-doping conductive polymers include, for example, polymers having a basic skeleton of polypyrrole, polythiophene, polyaniline, polyfuran, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, and polythiophene vinylene. The above polymers may contain at least one monomer unit constituting the basic skeleton. 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 directly introduced into the backbone of the conjugated polymer or may be introduced via a linking group. 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 -X-R ２ - group (X is an oxygen element or a sulfur element, R １ and R ２ are the same or different and are alkylene groups.) The number of carbon atoms in each alkylene group contained in the linking group may be, for example, 1 or more and 10 or less, or 1 or more and 6 or less. The alkylene group may be linear or branched. The linking group may, for example, contain at least an alkylene group having 2 or more carbon atoms. The number of carbon atoms in such an alkylene group may be 2 or more (or 3 or more) and 10 or less, or 2 or more (or 3 or more) and 6 or less. For example, R １ is an alkylene group having 1 to 6 carbon atoms, and R 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 these.

[0044] The conjugated polymer constituting the backbone of the self-doping conductive polymer may be polypyrrole, polythiophene, or polyaniline. From the viewpoint of easily obtaining high conductivity and stability, the self-doping conductive polymer is preferably a polymer having a backbone of a conjugated polymer containing a monomer unit corresponding to a thiophene compound and an anionic group introduced into the backbone.

[0045] 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.

[0046] The thiophene compound may have a substituent at, for example, at least one of the 3- and 4-positions of the thiophene ring. The substituent at the 3-position and the substituent at the 4-position may be linked to form a ring fused to the thiophene ring. Examples of the thiophene compound include thiophenes which may have a substituent at, at least one of the 3- and 4-positions, alkylenedioxythiophene compounds (C thiophenes such as ethylenedioxythiophene compounds), and the like. ２－４ Alkylenedioxythiophene compounds include compounds having a substituent on the alkylene group.

[0047] The substituents include alkyl groups (C such as methyl and ethyl groups) １－４ alkyl groups, alkoxy groups (C groups such as methoxy groups and ethoxy groups) １－４ alkoxy group, hydroxy group, hydroxyalkyl group (hydroxy C such as hydroxymethyl group) １－４Preferred are, but not limited to, alkyl groups. When the thiophene compound has two or more substituents, the respective substituents may be the same or different. The thiophene ring (in the case of an alkylenedioxythiophene ring, at least one of the thiophene ring and the alkylene group) may have, as a substituent, the above-mentioned anionic group or a group containing an anionic group (for example, a sulfoalkyl group).

[0048] The self-doped conductive polymer may have a backbone of a conjugated polymer (such as PEDOT) containing at least a monomer unit corresponding to a 3,4-ethylenedioxythiophene compound (such as 3,4-ethylenedioxythiophene (EDOT)). The backbone of the conjugated polymer containing at least a monomer unit corresponding to EDOT may contain only a monomer unit corresponding to EDOT, or may contain, in addition to the monomer unit, a monomer unit corresponding to a thiophene compound other than EDOT.

[0049] The weight average molecular weight (Mw) of the self-doping conductive polymer is not particularly limited, but is, for example, 1,000 to 1,000,000, or may be 1,000 to 100,000, or may be 5,000 to 50,000.

[0050] In this specification, the weight average molecular weight (Mw) is a value calculated as polystyrene measured by gel permeation chromatography (GPC), which is typically performed using a polystyrene gel column and a water / methanol (volume ratio 8 / 2) mobile phase.

[0051] The first solid electrolyte is formed using a treatment liquid (first treatment liquid) containing a self-doping conductive polymer. The first treatment liquid contains a self-doping conductive polymer and a liquid medium. The liquid medium is, for example, a medium that is liquid at room temperature (e.g., 20°C or higher and 35°C or lower). The first treatment liquid may be a liquid dispersion in which particles of the self-doping conductive polymer are dispersed in the liquid medium, or a solution in which the self-doping conductive polymer is dissolved in the liquid medium. Self-doping conductive polymers have relatively flexible polymer chains, and the positions of functional groups such as anionic groups are random. In addition, the polymer chains are less oriented and have low crystallinity. Therefore, compared to non-self-doping conductive polymers, they are more easily dissolved in a liquid medium or dispersed in the form of fine particles. Therefore, the first treatment liquid can be easily impregnated into the pores of the porous portion with high permeability. From the viewpoint of impregnating the pores of the porous portion with high permeability, it is preferable that the conductive polymer concentration in the first treatment liquid is low. The first solid electrolyte formed is, for example, a continuous or discontinuous ultrathin film. Therefore, adding an ionic liquid to the first solid electrolyte increases the film repairability of the dielectric layer to a certain extent, making it possible to suppress leakage current. However, since the first solid electrolyte is only a small portion of the innermost part of the solid electrolyte layer, even if a large amount of ionic liquid is present in the first solid electrolyte or at the interface (first interface) between the first solid electrolyte and the second solid electrolyte layer, it is difficult to obtain the effect of increasing the resistance of the solid electrolyte layer, and it is difficult to ensure high voltage resistance.

[0052] The first solid electrolyte may contain a non-self-doping conductive polymer (such as a conjugated polymer and a dopant). However, in the case of a non-self-doping conductive polymer, the conjugated polymer and the dopant tend to interact with each other, resulting in larger particles of the conductive polymer. Therefore, when the first treatment liquid contains a non-self-doping conductive polymer, its permeability into the pores of the porous portion tends to decrease. From this perspective, the ratio of the self-doping conductive polymer to the total amount of the conductive polymers constituting the first solid electrolyte (the total amount of the self-doping conductive polymer, the conjugated polymer, and the dopant) is, for example, 75% by mass or more, and may even be 90% by mass or more. The ratio of the self-doping conductive polymer to the total amount of the conductive polymers constituting the first solid electrolyte is 100% by mass or less. The conductive polymer constituting the first solid electrolyte may be composed solely of a self-doping conductive polymer.

[0053] (Second Solid Electrolyte Layer) The second solid electrolyte layer typically contains a non-self-doping conductive polymer (such as a conjugated polymer and a dopant). The second solid electrolyte layer may contain an additive, if necessary. A large amount of the ionic liquid may be contained in the second solid electrolyte layer.

[0054] The second solid electrolyte layer includes a solid electrolyte 2A that covers at least a portion of the first solid electrolyte, a solid electrolyte 2B that covers at least a portion of the solid electrolyte 2A, and a solid electrolyte 2C that covers at least a portion of the solid electrolyte 2B. Each solid electrolyte may be a continuous or discontinuous layer. By being composed of these solid electrolytes, the second solid electrolyte layer is layered as a whole.

[0055] Among the solid electrolytes constituting the second solid electrolyte layer, adjacent solid electrolytes (e.g., solid electrolyte 2A and solid electrolyte 2B, solid electrolyte 2B and solid electrolyte 2C) may have different compositions. "Different compositions" includes cases where the components contained in each solid electrolyte (e.g., at least one selected from the group consisting of conjugated polymers, dopants, and additives) are different, or cases where the contents of components contained in each layer are different. When each solid electrolyte includes multiple layers, the compositions of each layer are typically the same. When each solid electrolyte includes multiple layers, a flocculant (e.g., a cationic component, or a cationic component and an anionic component) may be present between adjacent layers. Furthermore, a flocculant may be present between the first solid electrolyte and the second solid electrolyte layer, and between adjacent solid electrolytes constituting the second solid electrolyte layer.

[0056] The first solid electrolyte and the second solid electrolyte layer, and the solid electrolytes constituting the second solid electrolyte layer can be distinguished, for example, by analyzing a cross-sectional image using an electron probe microanalyzer (EPMA). For example, EPMA analysis is performed at equal intervals on a cross-sectional image of the entire solid electrolyte layer, and the boundary between the first solid electrolyte and the second solid electrolyte layer and the boundary between adjacent solid electrolytes constituting the second solid electrolyte layer can be determined from the difference in wavelength of characteristic X-rays at each measurement point.

[0057] Examples of the conductive polymer (such as a non-self-doping conductive polymer) contained in the second solid electrolyte layer or each solid electrolyte constituting the second solid electrolyte layer include a conjugated polymer (such as a non-self-doping conjugated polymer (e.g., a conjugated polymer having no anionic group)) and a dopant.

[0058] Examples of conjugated polymers include those exemplified as conjugated polymers constituting the main skeleton of the self-doping conductive polymer of the first solid electrolyte. Conjugated polymers may be used singly or in combination of two or more. From the viewpoint of easily ensuring higher voltage resistance, non-self-doping conjugated polymers containing monomer units of thiophene compounds 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 polymer. Non-self-doping conjugated polymers may include conjugated polymers (e.g., PEDOT) containing at least monomer units corresponding to 3,4-ethylenedioxythiophene compounds (e.g., EDOT). Conjugated polymers containing at least 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 thiophene compounds other than EDOT.

[0059] 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 also be used to facilitate higher stability and higher 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 thereof)), polyallylsulfonic acid, polyacrylicsulfonic acid, polymethacrylicsulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprenesulfonic acid, polyestersulfonic acids (e.g., aromatic polyestersulfonic acids), and phenolsulfonic acid novolac resins. However, the dopant is not limited to these specific examples. The dopants may be used alone or in combination of two or more.

[0060] In the second solid electrolyte layer or in each solid electrolyte constituting the second solid electrolyte layer, the amount of the dopant is, for example, 10 parts by mass or more and 1,000 parts by mass or less, and may be 20 parts by mass or more and 500 parts by mass or less, relative to 100 parts by mass of the conjugated polymer.

[0061] The second solid electrolyte layer and each solid electrolyte constituting the second solid electrolyte layer may contain a self-doping conductive polymer in addition to a non-self-doping conductive polymer. The self-doping conductive polymer may be selected from the self-doping conductive polymers described for the first solid electrolyte, for example. From the viewpoint of easily ensuring higher voltage resistance, the ratio of the non-self-doping conductive polymer (conjugated polymer and dopant) to the total conductive polymer contained in the solid electrolyte constituting the second solid electrolyte layer and each solid electrolyte constituting the second solid electrolyte layer may be, for example, 75% by mass or more, or even 90% by mass or more. The ratio of the non-self-doping conductive polymer (conjugated polymer and dopant) to the total conductive polymer contained in the solid electrolyte constituting the second solid electrolyte layer and each solid electrolyte constituting the second solid electrolyte layer is 100% by mass or less. The conductive polymer contained in the solid electrolyte constituting the second solid electrolyte layer and each solid electrolyte constituting the second solid electrolyte layer may be composed solely of a non-self-doping conductive polymer (conjugated polymer and dopant).

[0062] (Ionic Liquid) The ionic liquid contained in the solid electrolyte layer is synonymous with a salt in a molten state (molten salt), and is an ionic substance that is liquid at 25°C, for example.

[0063] Examples of cations constituting ionic liquids include cations of nitrogen-containing heterocycles (imidazolium, pyrrolidinium, piperidinium, pyridinium, morpholinium, etc.), ammonium, phosphonium, sulfonium, and derivatives thereof (e.g., substituted compounds having a substituent such as an alkyl group). The cation may be an organic cation.

[0064] The anions that make up the ionic liquid include hydrogen sulfate ions (HSO ４ － ), sulfate ions (SO ４ ２－ , -SO ４ － ), carboxylate anion (-COO － ), nitrate anion, sulfonate anion (-SO ３ － ), phosphonate anion (PO ３ ２－, -HPO ３ － ) and the like. Acids capable of generating these anions include sulfuric acid, sulfuric acid monoesters (methyl sulfate, etc.), carboxylic acids (acetic acid, lactic acid, benzoic acid, trifluoromethane acetic acid, etc.), nitric acid, sulfonic acids (methanesulfonic acid, trifluoromethanesulfonic acid, bis(trifluoromethylsulfonyl)imide anion, etc.), phosphonic acids (diethylphosphonic acid, etc.), or derivatives thereof (e.g., substituted compounds having a substituent such as an alkyl group, a halogenated alkyl group, or a halogen atom). The anion may contain a fluorine atom. Examples of fluorine atom-containing anions include the above-mentioned trifluoromethane acetic acid, trifluoromethanesulfonic acid, bis(trifluoromethylsulfonyl)imide anion, and derivatives thereof.

[0065] From the viewpoint of easily ensuring the hydrophilicity of the ionic liquid, the ionic liquid is preferably a hydrogen sulfate ion (HSO ４ － ), and sulfate ions (SO ４ ２－ , -SO ４ － It is preferable that the ionic liquid contains at least one anion selected from the group consisting of hydrogen sulfate ion (HSO ４ － ) is preferably included. When a hydrophilic ionic liquid containing hydrogen sulfate ions or the like is used, the permeability into the solid electrolyte is enhanced and the ionic liquid is easily retained between the particles of the conductive polymer that constitutes the solid electrolyte. Furthermore, hydrophilic ionic liquids are easily able to retain water, and the water contained in the ionic liquid is likely to improve the repairability of damage to the dielectric layer. By retaining such an ionic liquid between the particles of the conductive polymer in the solid electrolyte relatively close to the dielectric layer, high film repairability of the dielectric layer can be ensured. Furthermore, by retaining the ionic liquid in the inner portion of the second solid electrolyte layer, high voltage resistance can be ensured without impairing adhesion to the cathode extraction layer or conductivity between the solid electrolyte layer and the cathode extraction layer. Therefore, while suppressing leakage current, better voltage resistance can be ensured, and ESR can be kept low, resulting in high capacitance.

[0066] Specific examples of ionic liquids include 1-butyl-3-methylimidazolium hydrogensulfate, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, and 1-ethyl-3-methylimidazolium diethylphosphonic acid. Among these specific examples, hydrophilic ionic liquids include 1-butyl-3-methylimidazolium hydrogensulfate, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, and 1-ethyl-3-methylimidazolium diethylphosphonic acid. However, ionic liquids are not limited to these specific examples.

[0067] The amount of ionic liquid distributed at the second or third interface is the largest among the first to fourth interfaces. The amount of ionic liquid distributed at the second interface and the amount of ionic liquid distributed at the third interface may be approximately the same. This case is also encompassed by the present invention. By distributing a large amount of ionic liquid at the second or third interface, it is possible to suppress leakage current to a low level while ensuring high voltage resistance, as described above. In particular, when the amount of ionic liquid distributed at the second interface is the largest among the first to fourth interfaces, higher film repairability is obtained, which makes it possible to further reduce leakage current and ensure higher voltage resistance.

[0068] In the solid electrolyte layer, the distribution amount of the ionic liquid may be greatest in solid electrolyte 2A or solid electrolyte 2B. As described above, in the second solid electrolyte layer, which occupies most of the solid electrolyte layer, a large amount of ionic liquid is retained in the inner portion, thereby ensuring high voltage resistance and suppressing leakage current. In addition, high adhesion and conductivity between the cathode extraction layer and the solid electrolyte layer can be ensured, thereby suppressing ESR to a low level and ensuring high capacitance. The distribution amounts of the ionic liquid in solid electrolyte 2A and solid electrolyte 2B may be approximately the same. Such cases are also encompassed by the present invention.

[0069] The solid electrolyte layer and each solid electrolyte constituting the solid electrolyte layer may contain additives as needed. Examples of additives include known additives added to solid electrolyte layers (e.g., coupling agents, silane compounds), and known conductive materials other than conductive polymers. The solid electrolyte layer or each solid electrolyte may contain one of these additives or a combination of two or more of them. Examples of conductive materials used as additives include at least one selected from the group consisting of conductive inorganic materials such as manganese dioxide and TCNQ complex salts.

[0070] (Formation of Solid Electrolyte Layer) In the above-described method for manufacturing a capacitor element, the second step (forming a solid electrolyte layer) includes, for example, the first to fourth substeps and at least one of the fifth and sixth substeps. The second step forms a solid electrolyte layer. Prior to the second step, the first step prepares an anode body having a dielectric layer on the surface of a porous portion. For the first step, the description of the anode body and the dielectric layer can be referred to. The second to fourth substeps form a second solid electrolyte layer. The second solid electrolyte layer and each solid electrolyte constituting the second solid electrolyte layer can be formed using a liquid dispersion in which a conductive polymer is dispersed in a liquid medium. The liquid dispersions used to form solid electrolytes 2A, 2B, and 2C in the second solid electrolyte layer are referred to as liquid dispersions 2A, 2B, and 2C, respectively. The conductive polymers contained in liquid dispersions 2A, 2B, and 2C are referred to as conductive polymers 2A, 2B, and 2C, respectively.

[0071] (First Substep) In the first substep, a first solid electrolyte is formed covering at least a part of the dielectric layer using a first treatment liquid containing a self-doping conductive polymer. For example, the first solid electrolyte is formed by applying the first treatment liquid so as to cover at least a part of the dielectric layer and drying it.

[0072] The first treatment liquid may be applied to the dielectric layer, for example, by immersing the anode body on which the dielectric layer has been formed in the first treatment liquid or by pouring the first treatment liquid into the anode body on which the dielectric layer has been formed. The application is not limited to impregnation or pouring, and known coating methods (e.g., spray coating) or printing methods may also be used. These methods may be combined as necessary.

[0073] The application and drying of the first treatment liquid may be performed once or may be repeated alternately multiple times. For the self-doping type conductive polymer and the additive, the above description of the first solid electrolyte or the solid electrolyte layer can be referred to.

[0074] The self-doping conductive polymer can be obtained, for example, by polymerizing (e.g., oxidatively polymerizing) a precursor of the self-doping conductive polymer in a liquid medium. The precursor can be at least one selected from the group consisting of a monomer constituting the self-doping conductive polymer, an oligomer in which several monomers are linked together, and a prepolymer. If necessary, at least one of another conjugated polymer and a dopant may be present when producing the self-doping conductive polymer.

[0075] Examples of liquid media used in the polymerization of self-doping conductive polymers include water and organic liquid media. The liquid medium is, for example, a medium that is liquid at room temperature (a temperature of 20°C or higher and 35°C or lower). Examples of organic liquid media include monohydric alcohols (methanol, ethanol, propanol, etc.), polyhydric alcohols (ethylene glycol, glycerin, etc.), and aprotic polar solvents (N,N-dimethylformamide, dimethyl sulfoxide, acetonitrile, acetone, benzonitrile, etc.). One type of liquid medium may be used alone, or two or more types may be used in combination.

[0076] The first treatment liquid is prepared by dispersing or dissolving the components of the first treatment liquid, such as a self-doping conductive polymer and an additive, in a liquid medium.

[0077] Examples of liquid media used in the first treatment liquid include water and organic media. The liquid medium may be liquid at least at the temperature at which the first treatment liquid is applied to the porous portion, and may be liquid at room temperature (e.g., 20°C or higher and 35°C or lower). Examples of organic media include aliphatic alcohols, aliphatic ketones (e.g., acetone), nitriles (e.g., acetonitrile, benzonitrile), amides (e.g., N,N-dimethylformamide), and sulfoxides (e.g., dimethyl sulfoxide). The aliphatic alcohol may be either a monool or a polyol. The first treatment liquid may contain one type of liquid medium or a combination of two or more types.

[0078] When the first treatment liquid contains a particulate self-doping conductive polymer, the particles of the self-doping conductive polymer may have an average particle size of 100 nm or less, 50 nm or less, or less than 10 nm, from the viewpoint of facilitating filling of the pores of the porous portion. The lower limit of the average particle size is not particularly limited, but is, for example, 0.5 nm or more.

[0079] The average particle size of the self-doping conductive polymer referred to here is the cumulative 50% particle size (median) in the volume-based particle size distribution. The average particle size of the self-doping conductive polymer can be determined from the volume-based particle size distribution by dynamic light scattering (DLS). Specifically, it is measured using an aqueous dispersion (e.g., a first treatment liquid) containing particles of the self-doping conductive polymer with a dynamic light scattering particle size distribution measuring device. As a particle size distribution measuring device using the dynamic light scattering method, for example, a DLS-8000 light scattering photometer manufactured by Otsuka Electronics Co., Ltd. is used.

[0080] The first treatment liquid may contain one or more self-doping conductive polymers, and may contain one or more additives.

[0081] The concentration of the self-doping conductive polymer in the first treatment liquid is, for example, 0.5% by mass to 4% by mass, or may be 1% by mass to 4% by mass, which makes it easy to adhere the self-doping conductive polymer to a wide area on the surface of the dielectric layer while allowing the self-doping conductive polymer to penetrate into minute recesses on the surface of the dielectric layer.

[0082] When the first treatment liquid contains an ionic liquid, the conductive polymer aggregates due to the action of the anions of the ionic liquid, the viscosity of the first treatment liquid increases significantly, and the permeability of the first treatment liquid into the fine recesses of the porous portion tends to decrease. Therefore, it is preferable that the first treatment liquid does not contain an ionic liquid. Note that when the first treatment liquid does not contain an ionic liquid, this includes cases where the ionic liquid is below the detection limit in the first treatment liquid.

[0083] The drying of the first treatment liquid applied to the dielectric layer may be performed, for example, under heating or under reduced pressure, and the drying temperature, pressure, and time are determined depending on, for example, the type of liquid medium contained in the first treatment liquid.

[0084] (Second Substep) In the second substep, a solid electrolyte 2A is formed to cover at least a portion of the first solid electrolyte. More specifically, for example, a liquid dispersion (liquid dispersion 2A) containing the conductive polymer 2A that constitutes the solid electrolyte 2A is applied to the surface of the first solid electrolyte, followed by drying, thereby forming the solid electrolyte 2A. If necessary, the application of the liquid dispersion 2A and drying may be repeated multiple times.

[0085] After the first substep and prior to the second substep, a flocculant (e.g., a cation, or a cation and an anion) may be applied to the surface of the first solid electrolyte, if necessary. Furthermore, when the liquid dispersion 2A is applied multiple times in the second substep, a flocculant may be applied to the surface of the already formed solid electrolyte 2A prior to the application of the liquid dispersion 2A, if necessary.

[0086] The liquid dispersion 2A may be applied in the same manner as in the case of the first treatment liquid, for example, by applying the liquid dispersion 2A to the surface of the first solid electrolyte or the surface of the already formed solid electrolyte 2A by using at least one method selected from immersion, pouring, coating, and printing.

[0087] The conductive polymer 2A used in the liquid dispersion 2A can be obtained by polymerizing a precursor of a conjugated polymer in the presence of a dopant. Examples of the precursor of the conjugated polymer include raw material monomers of the conjugated polymer, and oligomers and prepolymers formed by linking multiple molecular chains of the raw material monomers. One type of precursor may be used, or two or more types may be used in combination. The liquid dispersion 2A is prepared by dispersing the conductive polymer 2A in a liquid medium. The liquid dispersion 2A may contain an additive. For details about the conjugated polymer, dopant, and additive, please refer to the explanations for the second solid electrolyte layer or the solid electrolyte layer above. The liquid medium used in the liquid dispersion 2A may be selected from the liquid media described for the first treatment liquid.

[0088] Liquid dispersion 2A may contain one type of conjugated polymer or a combination of two or more types. Liquid dispersion 2A may contain one type of dopant or a combination of two or more types. Liquid dispersion 2A may contain one type of additive or a combination of two or more types.

[0089] The concentration of the conductive polymer 2A in the liquid dispersion 2A is, for example, 1% by mass to 5% by mass, or may be 1% by mass to 4% by mass. When the concentration is in this range, the liquid dispersion 2A can easily penetrate into the pores of the porous portion, and the conductive polymer 2A can easily be highly filled.

[0090] In the liquid dispersions 2A to 2C, the average particle diameter Da of the conductive polymer 2A, the average particle diameter Db of the conductive polymer 2B, and the average particle diameter Dc of the conductive polymer 2C may satisfy Da≦Db<Dc, and preferably satisfy Da<Db<Dc. Having a small average particle diameter of the conductive polymer in the liquid dispersion forming the inner solid electrolyte allows the conductive polymer to be densely packed into the pores of the porous portion and the recesses on the surface of the first solid electrolyte, which is advantageous for forming a second solid electrolyte layer with more uniform film quality. Furthermore, having a large average particle size of the conductive polymer in the liquid dispersion forming the outer solid electrolyte makes it easier to increase the thickness of the solid electrolyte layer. This is therefore advantageous for ensuring higher voltage resistance.

[0091] The average particle diameter Da of the conductive polymer 2A in the liquid dispersion 2A is, for example, 10 to 400 nm, or may be 20 to 300 nm, or 20 to 100 nm (or 50 nm). An average particle diameter within this range is advantageous in improving the filling of the conductive polymer 2A into the pores of the porous portion or the recesses on the surface of the first solid electrolyte. The average particle diameter of the conductive polymer 2A can be determined by the same procedure as for the average particle diameter of the self-doping conductive polymer.

[0092] When an ionic liquid is contained in the liquid dispersion 2A, the conductive polymer aggregates due to the action of the anions of the ionic liquid, the viscosity of the liquid dispersion 2A increases significantly, and the permeability of the liquid dispersion 2A into the fine recesses of the porous portion tends to decrease. Therefore, it is preferable that the liquid dispersion 2A does not contain an ionic liquid. Note that when the liquid dispersion 2A does not contain an ionic liquid, this includes cases where the ionic liquid is below the detection limit in the liquid dispersion 2A.

[0093] The drying of the liquid dispersion 2A after application may be carried out, for example, under heating or under reduced pressure. The drying temperature, pressure, and time are determined, for example, depending on the type of liquid medium contained in the liquid dispersion 2A.

[0094] (Third Substep) In the third substep, a solid electrolyte 2B is formed to cover at least a portion of the solid electrolyte 2A. More specifically, for example, a liquid dispersion (liquid dispersion 2B) containing the conductive polymer 2B that constitutes the solid electrolyte 2B is applied to the surface of the solid electrolyte 2A and then dried, thereby forming the solid electrolyte 2B. If necessary, the application of the liquid dispersion 2B and drying may be repeated multiple times.

[0095] In the third sub-step, when the liquid dispersion 2B is applied multiple times, a flocculant may be applied to the surface of the already formed solid electrolyte 2B prior to the application of the liquid dispersion 2B, as necessary.

[0096] The liquid dispersion 2B may be applied in the same manner as in the case of the first treatment liquid, for example, by applying the liquid dispersion 2B to the surface of the solid electrolyte 2A or the surface of the already formed solid electrolyte 2B by at least one method selected from immersion, pouring, coating, and printing.

[0097] The conductive polymer 2B used in the liquid dispersion 2B can be obtained in the same manner as for the conductive polymer 2A. The liquid dispersion 2B is prepared in the same manner as for the liquid dispersion 2A. The liquid dispersion 2B may contain an additive. For the conjugated polymer, dopant, and additive, refer to the explanation for the second solid electrolyte layer or the solid electrolyte layer above. The liquid medium used in the liquid dispersion 2B may be selected from the liquid media described for the first treatment liquid.

[0098] Liquid dispersion 2B may contain one type of conjugated polymer or a combination of two or more types. Liquid dispersion 2B may contain one type of dopant or a combination of two or more types. Liquid dispersion 2B may contain one type of additive or a combination of two or more types.

[0099] The concentration of the conductive polymer 2B in the liquid dispersion 2B is, for example, 1% by mass or more and 5% by mass or less, and may be 1% by mass or more and 4% by mass or less. When the concentration is in this range, the liquid dispersion 2B can easily penetrate into the recesses on the surface of the solid electrolyte 2A, and the conductive polymer 2B can easily be highly filled. Furthermore, the solid electrolyte 2B having a certain thickness can easily be obtained.

[0100] The average particle diameter Db of the conductive polymer 2B in the liquid dispersion 2B is equal to or larger than Da (it may be larger than Da) and smaller than Dc. The average particle diameter Db of the conductive polymer 2B is determined by the same procedure as in the case of the average particle diameter of the self-doping conductive polymer.

[0101] For the same reasons as in the case of Liquid Dispersion 2A, Liquid Dispersion 2B preferably does not contain ionic liquid (its content is below the detection limit).

[0102] The drying of the liquid dispersion 2B after application may be carried out, for example, under heating or under reduced pressure. The drying temperature, pressure, and time are determined, for example, depending on the type of liquid medium contained in the liquid dispersion 2B.

[0103] (Fourth Substep) In the fourth substep, a solid electrolyte 2C is formed to cover at least a portion of the solid electrolyte 2B. More specifically, for example, a liquid dispersion (liquid dispersion 2C) containing the conductive polymer 2C that constitutes the solid electrolyte 2C is applied to the surface of the solid electrolyte 2B and then dried, thereby forming the solid electrolyte 2C. If necessary, the application of the liquid dispersion 2C and drying may be repeated multiple times.

[0104] In the fourth sub-step, when the liquid dispersion 2C is applied multiple times, if necessary, a flocculant may be applied to the surface of the already formed solid electrolyte 2C prior to the application of the liquid dispersion 2C.

[0105] The application of the liquid dispersion 2C may be carried out in the same manner as in the case of the first treatment liquid, for example, by applying the liquid dispersion 2C to the surface of the solid electrolyte 2B or the surface of the already formed solid electrolyte 2C by using at least one method selected from immersion, pouring, coating, and printing.

[0106] The conductive polymer 2C used in the liquid dispersion 2C can be obtained in the same manner as for the conductive polymer 2A. The liquid dispersion 2C is prepared in the same manner as for the liquid dispersion 2A. The liquid dispersion 2C may contain an additive. For the conjugated polymer, dopant, adhesive component, and additive, refer to the explanation for the second solid electrolyte layer or the solid electrolyte layer described above. The liquid medium used in the liquid dispersion 2C may be selected from the liquid media described for the first treatment liquid.

[0107] Liquid dispersion 2C may contain one type of conjugated polymer or a combination of two or more types. Liquid dispersion 2C may contain one type of dopant or a combination of two or more types. Liquid dispersion 2C may contain one type of additive or a combination of two or more types.

[0108] The concentration of the conductive polymer 2C in the liquid dispersion 2C is, for example, 1% by mass to 10% by mass, and may be 1% by mass to 4% by mass. By having the concentration in this range, it is easier to obtain a solid electrolyte 2C having a more uniform film quality and a certain thickness.

[0109] The average particle diameter Dc of the conductive polymer 2C in the liquid dispersion 2C is 200 nm or more and 800 nm or less, and may be 300 nm or more and 600 nm or less. The average particle diameter of the conductive polymer 2C is determined by the same procedure as that for the average particle diameter of the self-doping conductive polymer.

[0110] For the same reasons as in the case of Liquid Dispersion 2A, Liquid Dispersion 2C preferably does not contain ionic liquid (its content is below the detection limit).

[0111] Drying after application of the liquid dispersion 2C may be carried out, for example, under heating or under reduced pressure. The drying temperature, pressure, and time are determined, for example, depending on the type of liquid medium contained in the liquid dispersion 2C. If necessary, drying may be carried out at an elevated temperature or in multiple stages.

[0112] (Fifth Substep) In the fifth substep, between the second and third substeps, a treatment liquid (second treatment liquid) containing an ionic liquid is applied to the surface of the solid electrolyte 2A and dried. The fifth substep allows the ionic liquid to penetrate the solid electrolyte 2A and adhere to the surface of the solid electrolyte 2A. By forming the solid electrolyte 2B on the surface of the solid electrolyte 2A in this state in the third substep, a relatively large amount of ionic liquid can be distributed at the interface (second interface) between the solid electrolyte 2A and the solid electrolyte 2B. Furthermore, a large amount of ionic liquid can be retained in the solid electrolyte 2A. This improves the voltage resistance of the solid electrolytic capacitor. By retaining a large amount of ionic liquid at the second interface or the solid electrolyte 2A, which are located relatively close to the dielectric layer, high film repairability of the dielectric layer can be ensured, enhancing the effect of suppressing leakage current.

[0113] The second treatment liquid may contain, for example, an ionic liquid and a liquid medium. The liquid medium used for the second treatment liquid may be selected from the liquid media exemplified for the first treatment liquid or the liquid dispersion 2A. Depending on the type of ionic liquid, it is preferable to use a liquid medium that is compatible with the ionic liquid. If a conductive polymer is contained in the second treatment liquid, the conductive polymer tends to aggregate due to the action of the anions of the ionic liquid, significantly increasing the viscosity of the second treatment liquid and reducing its permeability into the solid electrolyte 2A. Therefore, it is preferable that the second treatment liquid does not contain a conductive polymer (such as a conjugated polymer or a dopant). When the second treatment liquid does not contain a conductive polymer, this includes cases where the conductive polymer is below the detection limit in the second treatment liquid.

[0114] The second treatment liquid may be applied to the surface of the solid electrolyte 2A by, for example, at least one method selected from immersion, pouring, coating, and printing, similar to the case of the first treatment liquid. From the viewpoint of easily ensuring high voltage resistance, it is preferable that the ionic liquid be applied so as to cover the entire surface of the underlying solid electrolyte 2A (or the entire surface of the cathode-forming portion of the anode body).

[0115] The concentration of the ionic liquid in the second treatment liquid is, for example, 1% by mass or more and 50% by mass or less, and may be 2.5% by mass or more and 25% by mass or less (or 20% by mass or less). Within these ranges, the lower limit may be 5% by mass or more or 10% by mass or more. When the concentration of the ionic liquid is in such a range, it is possible to distribute a large amount of the ionic liquid at the second interface, and it is easy to retain a large amount of the ionic liquid in the solid electrolyte 2A.

[0116] After the second treatment liquid is applied to the surface of the solid electrolyte 2A, a drying process is performed. This drying may be performed, for example, under heating or reduced pressure. The drying temperature and pressure are determined, for example, depending on the type of liquid medium and ionic liquid contained in the second treatment liquid. The drying process allows a large amount of ionic liquid to be distributed at the second interface and allows a large amount of ionic liquid to be retained in the solid electrolyte 2A.

[0117] (Sixth Substep) In the sixth substep, between the third and fourth substeps, a third treatment liquid containing an ionic liquid is applied to the surface of the solid electrolyte 2B and dried. At least one of the fifth and sixth substeps may be performed, or both may be performed.

[0118] In the sixth substep, the ionic liquid penetrates the solid electrolyte 2B and adheres to the surface of the solid electrolyte 2B. By forming the solid electrolyte 2C on the surface of the solid electrolyte 2B in this state in the fourth substep, a relatively large amount of ionic liquid can be distributed at the interface (third interface) between the solid electrolyte 2B and the solid electrolyte 2C. Furthermore, a large amount of ionic liquid can be retained in the solid electrolyte 2B. This improves the voltage resistance of the solid electrolytic capacitor. By retaining a large amount of ionic liquid at the third interface or the solid electrolyte 2B, which are located relatively close to the dielectric layer, high film repairability of the dielectric layer can be ensured, and the effect of suppressing leakage current can be enhanced.

[0119] The third treatment liquid may contain, for example, an ionic liquid and a liquid medium. The liquid medium used for the third treatment liquid may be selected from the liquid media exemplified for the first treatment liquid or the liquid dispersion 2A. Depending on the type of ionic liquid, it is preferable to use a liquid medium that is compatible with the ionic liquid. For the same reasons as in the case of the second treatment liquid, it is preferable that the third treatment liquid does not contain (below the detection limit of) a conductive polymer (such as a conjugated polymer or a dopant).

[0120] When the fifth and sixth substeps are performed, the compositions of the second and third treatment liquids may be the same or different. For example, the type of ionic liquid in the second and third treatment liquids may be the same or different. The concentration of the ionic liquid in the second and third treatment liquids may be the same or different. The type of liquid medium in the second and third treatment liquids may be the same or different.

[0121] The third treatment liquid may be applied to the surface of the solid electrolyte 2B by, for example, at least one method selected from immersion, pouring, coating, and printing, similar to the case of the first treatment liquid. From the viewpoint of easily ensuring high voltage resistance, it is preferable that the ionic liquid be applied so as to cover the entire surface of the underlying solid electrolyte 2B (or the entire surface of the cathode-forming portion of the anode body).

[0122] The concentration of the ionic liquid in the third treatment solution may be selected from the concentrations described for the ionic liquid in the second treatment solution. When the concentration of the ionic liquid is in this range, a large amount of the ionic liquid can be distributed at the third interface, and a large amount of the ionic liquid can be easily retained in the solid electrolyte 2B.

[0123] After the third treatment liquid is applied to the surface of the solid electrolyte 2B, a drying process is performed. This drying may be performed, for example, under heating or reduced pressure. The drying temperature and pressure are determined, for example, depending on the type of liquid medium and ionic liquid contained in the third treatment liquid. The drying process allows a large amount of ionic liquid to be distributed at the third interface and allows a large amount of ionic liquid to be retained in the solid electrolyte 2B.

[0124] In this manner, the solid electrolyte layer is formed.

[0125] From the viewpoints of ensuring high adhesion between the solid electrolyte 2C and the cathode extraction layer (or a part thereof) and suppressing an increase in interfacial resistance at the interface therebetween (the fourth interface), it is preferable not to apply an ionic liquid (e.g., a treatment liquid containing an ionic liquid) to the surface of the solid electrolyte 2C. Therefore, the amount of the ionic liquid distributed at the fourth interface is significantly smaller than the amount of the ionic liquid distributed at the second interface or the third interface, and may be below the detection limit.

[0126] Furthermore, applying an ionic liquid to the surface of the first solid electrolyte can improve the film repairability of the dielectric layer to a certain extent and suppress leakage current. However, since the first solid electrolyte is only a small portion of the innermost part of the solid electrolyte layer, even if the ionic liquid is present in large amounts at the first solid electrolyte or at the interface (first interface) between the first solid electrolyte and the second solid electrolyte layer (more specifically, the solid electrolyte 2A), it is difficult to obtain the effect of increasing the resistance of the solid electrolyte layer. In addition, the ionic liquid tends to reduce the permeability of the liquid dispersion 2A into the pores of the porous portion. Therefore, from the viewpoint of ensuring higher voltage resistance, it is not necessary to apply an ionic liquid (or a treatment liquid containing an ionic liquid) to the first solid electrolyte prior to the second substep.

[0127] (Cathode Extraction Layer) The cathode extraction layer may include, for example, a first layer that is in contact with the solid electrolyte layer and covers at least a portion of the solid electrolyte layer. The cathode extraction layer may include a first layer and a second layer that covers the first layer. Examples of the first layer include a layer containing conductive particles and metal foil. Examples of the conductive particles include at least one selected from conductive carbon and metal powder. For example, the cathode extraction layer may include a first layer containing conductive carbon (also referred to as a carbon layer) and a second layer containing metal powder or metal foil. When metal foil is used as the first layer, the cathode extraction layer may be formed of this metal foil. The cathode extraction layer can be formed by a known method depending on the layer configuration.

[0128] Examples of conductive carbon include graphite (artificial graphite, natural graphite, etc.).

[0129] The second layer containing metal powder can be formed, for example, by laminating a composition containing metal powder on the surface of the first layer. Examples of such a second layer include a metal paste layer (e.g., a silver paste layer) formed using a composition containing metal powder such as silver particles and a resin (binder resin). While a thermoplastic resin can be used as the resin, it is preferable to use a thermosetting resin such as an imide resin or an epoxy resin.

[0130] When a metal foil is used as the first layer, the type of metal is not particularly limited, but it is preferable to use a valve metal such as aluminum, tantalum, or niobium, or an alloy containing a valve metal. If necessary, the surface of the metal foil may be roughened. The surface of the metal foil may be provided with a chemical conversion coating, or may be provided with a coating of a metal (dissimilar metal) or a nonmetal different from the metal constituting the metal foil. Examples of dissimilar metals and nonmetals include metals such as titanium and nonmetals such as carbon (e.g., conductive carbon).

[0131] The coating of the dissimilar metal or non-metal (for example, conductive carbon) may be the first layer, and the metal foil may be the second layer.

[0132] The method for manufacturing a capacitor element includes a third step of forming a cathode extraction layer so as to cover at least a portion of the solid electrolyte layer. The method for manufacturing a capacitor element may include, for example, a step of forming a cathode extraction layer (e.g., a first layer) that covers at least a portion of the solid electrolyte layer.

[0133] (Other) A solid electrolytic capacitor includes at least one capacitor element and an exterior body that seals the capacitor element. A solid electrolytic capacitor may include two or more capacitor elements. A solid electrolytic capacitor may be a wound type, and may be either a chip type or a stacked type. For example, a solid electrolytic capacitor may include two or more wound capacitor elements, or may include two or more stacked capacitor elements. The configuration of the capacitor elements may be selected depending on the type of solid electrolytic capacitor.

[0134] In the capacitor element, one end of the cathode lead is electrically connected to the cathode extraction layer. One end of the anode lead is electrically connected to the anode body. The other end of the anode lead and the other end of the cathode lead are each drawn out from the resin exterior body or the case. The other end of each lead exposed from the resin exterior body or the case is used for soldering to a substrate on which the solid electrolytic capacitor is to be mounted. Each lead may be a lead wire or a lead frame.

[0135] The solid electrolytic capacitor can be obtained, for example, by a manufacturing method including a step of forming at least one capacitor element by a manufacturing method including steps 1, 2, and 3, and a step of sealing the at least one solid electrolytic capacitor element with an exterior body. For example, when manufacturing a solid electrolytic capacitor including two or more stacked capacitor elements, the manufacturing method further includes a step of stacking the two or more capacitor elements prior to the sealing step. Then, in the sealing step, the two or more stacked capacitor elements are sealed with an exterior body.

[0136] The exterior body also includes a case. The exterior body may include a resin. For example, the capacitor element and the resin material of the exterior body (e.g., an uncured thermosetting resin and a filler) may be placed in a mold, and the capacitor element may be sealed in the resin exterior body by transfer molding, compression molding, or the like. At this time, the other end of the anode lead and the other end of the cathode lead drawn out from the capacitor element are exposed from the mold. Alternatively, the capacitor element may be housed in a bottomed case such that the other end of the anode lead and the other end of the cathode lead are positioned on the opening side of the bottomed case, and the opening of the bottomed case may be sealed with a sealant to form a solid electrolytic capacitor.

[0137] The solid electrolytic capacitor may further include a case disposed on the exterior of the resinous outer casing, as needed. Examples of resin materials constituting the case include thermoplastic resins and compositions containing thermoplastic resins. Examples of metal materials constituting the case include metals such as aluminum, copper, and iron, and alloys thereof (including stainless steel and brass).

[0138] Fig. 1 is a schematic cross-sectional view of a solid electrolytic capacitor according to one embodiment of the present disclosure. The solid electrolytic capacitor 100 in Fig. 1 includes a capacitor element 110, an outer casing 150, an anode lead terminal 210, and a cathode lead terminal 220. The outer casing 150 is disposed so as to cover a portion of the anode lead terminal 210, a portion of the cathode lead terminal 220, and the capacitor element 110.

[0139] The capacitor element 110 includes an anode portion 111, a dielectric layer 114, and a cathode portion 115. The anode portion 111 includes an anode body 113 and an anode wire 112. The anode body 113 is a porous sintered body in the shape of a rectangular parallelepiped, and a dielectric layer 114 is formed on the surface thereof. A portion of the anode wire 112 protrudes from one end face of the anode body 113 toward the front surface 100f of the solid electrolytic capacitor 100. The other portion of the anode wire 112 is embedded in the anode body 113.

[0140] Cathode section 115 includes solid electrolyte layer 116 disposed so as to cover at least a portion of dielectric layer 114, and cathode extraction layer 117 formed on solid electrolyte layer 116. Cathode extraction layer 117 includes, for example, a carbon layer formed on solid electrolyte layer 116 and a metal particle layer formed on the carbon layer. The metal particle layer is, for example, a metal paste layer (e.g., a silver paste layer) formed using a metal paste.

[0141] As described above, the solid electrolyte layer 116 includes an ionic liquid and a first solid electrolyte covering at least a portion of the dielectric layer 114, and a second solid electrolyte layer covering at least a portion of the first solid electrolyte. The first solid electrolyte includes a self-doping conductive polymer. The second solid electrolyte layer includes at least a solid electrolyte 2A covering at least a portion of the first solid electrolyte, a solid electrolyte 2B covering at least a portion of the solid electrolyte 2A, and a solid electrolyte 2C covering at least a portion of the solid electrolyte 2B. The cathode portion 115 includes a layer covering at least a portion of the solid electrolyte 2C. The interfaces between the first solid electrolyte and the solid electrolyte 2A, the solid electrolyte 2A and the solid electrolyte 2B, the solid electrolyte 2B and the solid electrolyte 2C, and the solid electrolyte 2C and the layer covering at least a portion of the solid electrolyte 2C are designated as first to fourth interfaces, respectively. Among these interfaces, the second or third interface has the largest distribution of the ionic liquid. This allows for high voltage resistance while suppressing leakage current. From the viewpoint of obtaining a higher effect, the distribution amount of the ionic liquid in the solid electrolyte 2A or the solid electrolyte 2B in the solid electrolyte layer 116 may be maximum.

[0142] The anode lead terminal 210 includes an anode terminal portion 211 and a wire connection portion 212. The anode terminal portion 211 is exposed on the bottom surface 100b of the solid electrolytic capacitor 100. The wire connection portion 212 is connected to the anode wire 112. The cathode lead terminal 220 includes a cathode terminal portion 221 and a connection portion 222. The cathode terminal portion 221 is exposed on the bottom surface 100b of the solid electrolytic capacitor 100. The connection portion 222 is electrically connected to the cathode extraction layer 117 (cathode portion 115) by a conductive layer 141.

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

[0144] Examples 1 and 2 and Comparative Examples 1 and 2 Solid electrolytic capacitors were fabricated in the following manner, and their characteristics were evaluated.

[0145] (1) Preparation of an anode body having a dielectric layer A tantalum sintered body (porous body) with a part of an anode wire embedded therein was prepared as an anode body. The surface of this tantalum sintered body was anodized to form a dielectric layer containing tantalum oxide on the surface of the anode body.

[0146] (2) Formation of the First Solid Electrolyte An aqueous dispersion (first treatment liquid) containing a self-doping polythiophene-based polymer was prepared. The concentration of the polythiophene-based polymer in the first treatment liquid was 1 to 4% by mass. The polythiophene-based polymer particles were very small, with a particle diameter of less than 10 nm. The self-doping polythiophene-based polymer used was PEDOT (Mw: approximately 10,000) with a sulfo group bonded to the PEDOT skeleton via a linking group containing a butylene group.

[0147] The tantalum sintered compact prepared in (1) above was immersed in the first treatment liquid for about 30 to 60 seconds, and then pulled out of the dispersion liquid. Next, the tantalum sintered compact pulled out of the dispersion liquid was heated at 140 to 180°C for 10 to 20 minutes to form a first solid electrolyte.

[0148] (3) Formation of Second Solid Electrolyte Layer (a) Formation of Solid Electrolyte 2A A solid electrolyte 2A was formed using a liquid dispersion 2A. Specifically, a tantalum sintered body on which a first solid electrolyte had been formed was first immersed in the liquid dispersion 2A for approximately 30 to 60 seconds, and then the tantalum sintered body was pulled out of the liquid dispersion 2A. Next, the tantalum sintered body pulled out of the liquid dispersion 2A was heated at 140 to 180°C for 10 to 20 minutes to form a solid electrolyte 2A. As the liquid dispersion 2A, an aqueous dispersion (average particle size of the conductive polymer in the dispersion: 20 to 30 nm) containing a conductive polymer 2A (PSS-doped PEDOT) at a concentration of 1 to 4 mass% was used.

[0149] (b) Formation of Solid Electrolyte 2B A solid electrolyte 2B was formed using the liquid dispersion 2B. Specifically, first, the tantalum sintered body on which the solid electrolyte 2A had been formed was immersed in the liquid dispersion 2B for approximately 30 to 60 seconds, and then the tantalum sintered body was pulled out of the liquid dispersion 2B. Next, the tantalum sintered body pulled out of the liquid dispersion 2B was heated at 140 to 180°C for 10 to 20 minutes to form the solid electrolyte 2B. As the liquid dispersion 2B, an aqueous dispersion (average particle size of the conductive polymer in the dispersion: 20 to 300 nm) containing the conductive polymer 2B (PSS-doped PEDOT) at a concentration of 1 to 4 mass% was used.

[0150] (c) Formation of Solid Electrolyte 2C A solid electrolyte 2C was formed using liquid dispersion 2C. Specifically, the tantalum sintered body on which solid electrolyte 2B had been formed was first immersed in liquid dispersion 2C for approximately 30 to 60 seconds, and then the tantalum sintered body was pulled out of liquid dispersion 2C. Next, the tantalum sintered body pulled out of liquid dispersion 2C was heated at 60 to 100°C for 10 to 20 minutes, and then further heated at 140 to 180°C for 10 to 20 minutes to form solid electrolyte 2C. As liquid dispersion 2C, an aqueous dispersion (average particle size of the conductive polymer in the dispersion: 300 to 500 nm) containing a conductive polymer 2C (PSS-doped PEDOT) at a concentration of 1 to 4 mass% and an adhesive component was used.

[0151] In this manner, a second solid electrolyte layer containing solid electrolytes 2A to 2C was formed, and a solid electrolyte layer composed of the first solid electrolyte and the second solid electrolyte layer was formed.

[0152] (4) Application of Ionic Liquid In the step of forming the solid electrolyte layer, the tantalum sintered body on which the solid electrolyte had been formed was immersed in a treatment solution containing an ionic liquid under reduced pressure for approximately 10 to 20 minutes. After the pressure was returned to atmospheric pressure, the tantalum sintered body was further immersed for approximately 5 to 10 minutes, and then removed from the treatment solution. Next, the tantalum sintered body removed from the treatment solution was dried by heating at 100 to 150°C for 10 to 30 minutes. As the treatment solution containing an ionic liquid, a solution in which 1-butyl-2-methyl-imidazolium hydrogen sulfate was dissolved in pure water at a concentration of 20% by mass was used. The timing of application of the treatment solution is shown in Table 1. In Comparative Example 1, the treatment solution containing an ionic liquid was not applied.

[0153] (5) Formation of Cathode Extraction Layer The tantalum sintered compact on which the solid electrolyte layer had been formed was immersed in a dispersion liquid in which graphite particles had been dispersed in water, and after being removed from the dispersion liquid, was dried to form a carbon layer (first layer) on the surface of the solid electrolyte layer. The drying was carried out at 180°C for 10 to 30 minutes.

[0154] Next, a silver paste containing silver particles and a binder resin (epoxy resin) was applied to the surface of the carbon layer, dried at 60 to 80°C for 20 to 40 minutes, and then heated at 180°C for 30 to 60 minutes to harden the binder resin, forming a metal paste layer (second layer). In this way, a cathode extraction layer composed of the carbon layer and the metal paste layer was formed. In this way, a capacitor element including a cathode portion composed of a solid electrolyte layer and a cathode extraction layer was produced.

[0155] (6) Assembly of a Solid Electrolytic Capacitor The cathode extraction layer of the capacitor element obtained in (5) above was joined to one end of the cathode lead terminal with a conductive adhesive. The anode body protruding from the capacitor element was joined to one end of the anode lead terminal by laser welding.

[0156] Next, a resin outer casing made of insulating resin was formed around the capacitor element by transfer molding. At this time, the other end of the anode lead terminal and the other end of the cathode lead terminal were extended from the outer casing. In this way, a total of 20 solid electrolytic capacitors were completed.

[0157] Comparative Example 3 A total of 20 solid electrolytic capacitors were produced in the same manner as in Example 1, except that the solid electrolyte layer was formed in the following manner and no treatment liquid containing an ionic liquid was applied.

[0158] A solid electrolyte layer (inner layer) was formed on the surface of the dielectric layer of the tantalum sintered compact by chemical polymerization using the following procedure: First, a polymerization solution was prepared by dissolving ferric p-toluenesulfonate (oxidizing agent) and 3,4-ethylenedioxythiophene (EDOT) in ethanol.

[0159] The tantalum sintered body having the dielectric layer was immersed in the polymerization solution for about 3 to 10 seconds. Next, after the tantalum sintered body was removed from the reaction solution, it was heated at 210°C for 3 minutes to polymerize the EDOT. In this way, a solid electrolyte layer (inner layer) containing a conductive polymer including PEDOT was formed.

[0160] Next, solid electrolyte 2C (outer layer) was formed using liquid dispersion 2C. The formation of solid electrolyte 2C was carried out in the same manner as in (c) of (3) of Example 1, except that the tantalum sintered body forming the inner solid electrolyte layer was used. In this manner, a solid electrolyte layer having an inner layer and an outer layer was formed.

[0161] <Evaluation> The solid electrolytic capacitors obtained in the examples and comparative examples were evaluated as follows.

[0162] (1) Initial Capacitance and ESR The initial capacitance (μF) at a frequency of 120 Hz and the initial ESR (mΩ) at a frequency of 100 kHz of the solid electrolytic capacitors were measured using a four-terminal LCR meter at 20°C. The average values ​​for 20 solid electrolytic capacitors were then calculated. The initial capacitance and ESR were expressed as relative values, with the capacitance and ESR of Comparative Example 3 set at 100.

[0163] (2) Leakage Current (LC) A 1 kΩ resistor was connected in series to each solid electrolytic capacitor, and a rated voltage of 35 V was applied from a DC power supply for 1 minute. The leakage current (μA) was measured and the average value of 20 solid electrolytic capacitors was calculated. The leakage current was expressed as a relative value, with the leakage current of Comparative Example 3 being set to 100.

[0164] (3) Voltage Withstand Property A voltage was applied to the solid electrolytic capacitor while increasing it at a rate of 1.0 V / sec, and the breakdown voltage (V) at which an overcurrent of 0.5 A flows was measured. The voltage withstand property was expressed as a relative value when the breakdown voltage (V) of the solid electrolytic capacitor of Comparative Example 3 was set to 100. A larger value indicates a higher voltage withstand property.

[0165] The evaluation results are shown in Table 1. In Table 1, E1 and E2 are Examples 1 and 2, and C1 to C3 are Comparative Examples 1 to 3.

[0166]

[0167] As shown in Table 1, the solid electrolytic capacitor C1, which did not contain an ionic liquid, had improved voltage resistance but increased leakage current compared to the solid electrolytic capacitor C3, which had a solid electrolyte layer including an inner layer formed by chemical polymerization and an outer layer formed using a liquid dispersion. Furthermore, in the capacitor C2, in which a treatment liquid containing an ionic liquid was applied and dried between the first and second substeps (i.e., the case in which the distribution amount of ionic liquid was greatest at the first interface among the first to fourth interfaces), leakage current was significantly reduced, but voltage resistance was lower than that of capacitor C1, and the improvement in voltage resistance was limited. Furthermore, the ESR of capacitor C2 was not significantly different from that of capacitor C1.

[0168] In contrast, in E2, in which a treatment liquid containing an ionic liquid was applied between the third and fourth substeps and then dried (i.e., the distribution amount of the ionic liquid was greatest at the third interface among the first to fourth interfaces), high voltage resistance was ensured while the leakage current was kept low. Furthermore, in E1, in which a treatment liquid containing an ionic liquid was applied between the second and third substeps and then dried (i.e., the distribution amount of the ionic liquid was greatest at the second interface among the first to fourth interfaces), the leakage current was also low and even higher voltage resistance was ensured.

[0169] While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention.

[0170] In the present disclosure, a solid electrolytic capacitor can ensure high voltage resistance and suppress leakage current to a low level. Therefore, the solid electrolytic capacitor can be used in a variety of applications, including applications requiring high voltage resistance and high reliability. However, the applications of the solid electrolytic capacitor are not limited to these.

[0171] 100: Solid electrolytic capacitor 110: Capacitor element 113: Anode body 114: Dielectric layer 116: Solid electrolyte layer

Claims

1. an anode body having a porous portion at least on a surface layer; a dielectric layer formed on at least a portion of the surface of the porous portion; a cathode portion including a solid electrolyte layer covering at least a portion of the dielectric layer and a cathode extraction layer covering at least a portion of the solid electrolyte layer, the solid electrolyte layer includes a first solid electrolyte containing an ionic liquid and covering at least a portion of the dielectric layer, and a second solid electrolyte layer covering at least a portion of the first solid electrolyte, the first solid electrolyte comprises a self-doped conductive polymer; the second solid electrolyte layer includes a solid electrolyte 2A covering at least a portion of the first solid electrolyte, a solid electrolyte 2B covering at least a portion of the solid electrolyte 2A, and a solid electrolyte 2C covering at least a portion of the solid electrolyte 2B, a first interface between the first solid electrolyte and the solid electrolyte 2A, a second interface between the solid electrolyte 2A and the solid electrolyte 2B, a third interface between the solid electrolyte 2B and the solid electrolyte 2C, and a fourth interface between the solid electrolyte 2C and the cathode extraction layer, the second interface being the largest, or the third interface being the largest.

2. The solid electrolytic capacitor element according to claim 1 , wherein the second solid electrolyte layer contains a conjugated polymer and a dopant.

3. 3 . The solid electrolytic capacitor element according to claim 1 , wherein a distribution amount of the ionic liquid is greatest at the second interface among the first interface, the second interface, the third interface, and the fourth interface.

4. 3. The solid electrolytic capacitor element according to claim 1, wherein in the solid electrolyte layer, a distribution amount of the ionic liquid is maximum in the solid electrolyte 2A or the solid electrolyte 2B.

5. The solid electrolytic capacitor element according to claim 1 , wherein the ionic liquid is hydrophilic.

6. The ionic liquid is HSO ４ － The solid electrolytic capacitor element according to claim 1 or 2, which contains ions.

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

8. A method for manufacturing a solid electrolytic capacitor element including an anode body having a porous portion at least in a surface layer thereof, a dielectric layer formed on at least a part of a surface of the porous portion, and a cathode portion including a solid electrolyte layer covering at least a part of the dielectric layer and a cathode extraction layer covering at least a part of the solid electrolyte layer, a first step of preparing the anode body having the dielectric layer on the surface of the porous portion; a second step of forming the solid electrolyte layer so as to cover at least a portion of the dielectric layer; a third step of forming the cathode extraction layer so as to cover at least a portion of the solid electrolyte layer; Including, The second step comprises: a first sub-step of forming a first solid electrolyte covering at least a portion of the dielectric layer using a first treatment liquid including a self-doped conductive polymer; A second sub-step of forming a solid electrolyte 2A covering at least a part of the first solid electrolyte using a liquid dispersion 2A containing a conductive polymer 2A; a third sub-step of forming a solid electrolyte 2B covering at least a part of the solid electrolyte 2A using a liquid dispersion 2B containing a conductive polymer 2B; and a fourth sub-step of forming a solid electrolyte 2C covering at least a part of the solid electrolyte 2B using a liquid dispersion 2C containing a conductive polymer 2C, The second step further comprises: at least one of a fifth substep between the second substep and the third substep of applying a second treatment liquid containing an ionic liquid to a surface of the solid electrolyte 2A and drying the same, and a sixth substep between the third substep and the fourth substep of applying a third treatment liquid containing an ionic liquid to a surface of the solid electrolyte 2B and drying the same; a first interface between the first solid electrolyte and the solid electrolyte 2A, a second interface between the solid electrolyte 2A and the solid electrolyte 2B, a third interface between the solid electrolyte 2B and the solid electrolyte 2C, and a fourth interface between the solid electrolyte 2C and the cathode extraction layer, the second interface or the third interface having the ionic liquid therein being maximum.

9. 9. The method for producing a solid electrolytic capacitor element according to claim 8, wherein an average particle diameter Da of the conductive polymer 2A, an average particle diameter Db of the conductive polymer 2B, and an average particle diameter Dc of the conductive polymer 2C satisfy Da≦Db<Dc.

10. The method for producing a solid electrolytic capacitor element according to claim 8 or 9, wherein none of the first treatment liquid, the liquid dispersion 2A, the liquid dispersion 2B, and the liquid dispersion 2C contains an ionic liquid.

11. The method for producing a solid electrolytic capacitor element according to claim 8 , wherein neither the second treatment liquid nor the third treatment liquid contains a conductive polymer.