Solid electrolytic capacitor and method for manufacturing solid electrolytic capacitor

Abstract

This solid electrolytic capacitor comprises: an anode foil that has a porous part in a surface layer; a dielectric layer that covers at least a part of the surface of the anode foil; a first conductive polymer layer that covers at least a part of the surface of the dielectric layer; and a second conductive polymer layer that covers at least a part of the surface of the first conductive polymer layer. The first conductive polymer layer contains a self-doped first conductive polymer. The second conductive polymer layer is formed by electrolytic polymerization and contains a non-self-doped second conductive polymer. Elemental silicon is present in at least a part of the space between the dielectric layer and the second conductive polymer layer.

Description

Solid electrolytic capacitor and method for manufacturing a solid electrolytic capacitor Cross-reference of related applications

[0001] This disclosure claims priority rights to Japanese Patent Application No. 2025-26191, filed with the Japan Patent Office on February 20, 2025, and the entirety of the said patent application is incorporated herein by reference.

[0002] This disclosure relates to a solid electrolytic capacitor and a method for manufacturing the same.

[0003] Patent Document 1 proposes a method for manufacturing a solid electrolytic capacitor, in which a conductive polyaniline layer, a chemically polymerized conductive polymer layer, and an electrolytically polymerized conductive polymer layer are sequentially formed on a valve metal having a dielectric oxide film formed on its surface. The method is characterized by applying a polyaniline solution, obtained by dissolving a polyaniline derivative (a) having sulfonic acid groups and a silane coupling agent (b) in a mixed solvent (c) of water and an alcohol having 1 to 3 carbon atoms, to the dielectric oxide film surface of the valve metal, drying it to form a conductive polyaniline layer, and then sequentially forming a chemically polymerized conductive polymer layer and an electrolytically polymerized conductive polymer layer on the conductive polyaniline layer.

[0004] Patent Document 2 proposes a solid electrolytic capacitor comprising a solid electrolyte layer on a dielectric oxide film provided on a valve-acting metal surface, wherein the dielectric oxide film surface is coated with a compound of a specific formula containing silicon, and a conductive polymer layer is formed thereon.

[0005] Japanese Patent Publication No. 2008-53479 Japanese Patent Publication No. 2009-32895

[0006] A first aspect of this disclosure relates to a solid electrolytic capacitor comprising: an anode foil having a porous portion on its surface; a dielectric layer covering at least a portion of the surface of the anode foil; a first conductive polymer layer covering at least a portion of the surface of the dielectric layer; and a second conductive polymer layer covering at least a portion of the surface of the first conductive polymer layer, wherein the first conductive polymer layer comprises a self-doped first conductive polymer, the second conductive polymer layer is formed by electrolytic polymerization and comprises a non-self-doped second conductive polymer, and silicon is present in at least a portion between the dielectric layer and the second conductive polymer layer.

[0007] A second aspect of this disclosure is a method for manufacturing a solid electrolytic capacitor, comprising: a first step of preparing an anode foil having a porous portion on its surface; a second step of forming a dielectric layer on at least a portion of the surface of the anode foil; a third step of forming a first conductive polymer layer containing a self-doped first conductive polymer on the surface of the dielectric layer; and a fourth step of forming a second conductive polymer layer containing a non-self-doped second conductive polymer containing a conjugated polymer and a dopant on the surface of the first conductive polymer layer, wherein in the fourth step, the anode foil having the dielectric layer on which the first conductive polymer layer is formed is immersed in a polymerization solution containing a precursor of the conjugated polymer and the dopant and electropolymerized to produce the second conductive polymer, thereby forming the second conductive polymer layer, and the manufacturing method is The present invention relates to a method for manufacturing a solid electrolytic capacitor, further comprising at least one of the following: a first silane treatment step, after the second step and before the third step, in which the anode foil having the dielectric layer is treated with a first silane compound; and a second silane treatment step, after the third step and before the fourth step, in which the anode foil having the dielectric layer on which the first conductive polymer layer is formed is treated with a second silane compound.

[0008] A third aspect of this disclosure relates to a method for manufacturing a solid electrolytic capacitor, comprising: a first step of preparing an anode foil having a porous portion on its surface; a second step of forming a dielectric layer on at least a portion of the surface of the anode foil; a third step of applying a processing solution containing a third silane compound and a self-doped first conductive polymer to the surface of the dielectric layer to form a first conductive polymer layer containing silicon elements derived from the third silane compound and the first conductive polymer; and a fourth step of forming a second conductive polymer layer on the surface of the first conductive polymer layer, the second conductive polymer layer being formed by electrolytic polymerization in the fourth step while the anode foil having the dielectric layer on which the first conductive polymer layer is formed is immersed in a polymerization solution containing a precursor of the conjugated polymer and the dopant to produce the second conductive polymer.

[0009] According to this disclosure, a solid electrolytic capacitor having high initial capacitance and excellent voltage withstand characteristics can be provided.

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

[0011] While novel features of the present invention are described in the appended claims, the present invention, both in terms of its structure and content, will be better understood by the following detailed description in conjunction with the drawings, along with other objects and features of the present invention.

[0012] This disclosure aims to provide a solid electrolytic capacitor having high initial capacitance and excellent voltage withstand characteristics.

[0013] In solid electrolytic capacitors having a solid electrolyte layer, it is advantageous to be able to form the solid electrolyte layer uniformly in order to ensure high initial characteristics such as high initial capacitance. The solid electrolyte layer is formed, for example, by in-situ polymerization using a polymerization solution containing a conductive polymer precursor. Alternatively, the solid electrolyte layer can also be formed using a liquid dispersion containing a conductive polymer. The anode foil of a solid electrolytic capacitor has a porous surface to obtain higher capacitance. In in-situ polymerization, chemical polymerization makes it easy to densely fill the voids in the porous part with solid electrolyte, but the thickness of the solid electrolyte layer varies greatly. When using a liquid dispersion, it is relatively easy to make the thickness of the solid electrolyte layer uniform, but the filling of the voids in the porous part is low. In solid electrolytic capacitors with solid electrolyte layers formed by such conventional methods, it is difficult to obtain high conductivity, and the effect of improving initial capacitance is insufficient.

[0014] Electropolymerization is technically challenging due to the difficulty in controlling the polymerization reaction. While solid electrolyte layers formed by electropolymerization exhibit relatively high conductivity due to increased crystallinity of the solid electrolyte, they have low dielectric strength.

[0015] Technology (1) In view of the above, a solid electrolytic capacitor according to the first aspect of the present disclosure comprises: an anode foil having a porous portion on its surface; a dielectric layer covering at least a portion of the surface of the anode foil; a first conductive polymer layer covering at least a portion of the surface of the dielectric layer; and a second conductive polymer layer covering at least a portion of the surface of the first conductive polymer layer. The first conductive polymer layer contains a self-doped first conductive polymer. The second conductive polymer layer is formed by electrolytic polymerization and contains a non-self-doped second conductive polymer. At least a portion between the dielectric layer and the second conductive polymer layer contains silicon.

[0016] The silicon element originates from the silane compound used in the manufacturing process. In this disclosure, the presence of silicon element in at least a portion between the dielectric layer and the second conductive polymer layer enhances the impregnation of the processing solution for forming the first conductive polymer layer and the polymerization solution for forming the second conductive polymer layer into the anode foil, which is a base material with a dielectric layer. As a result, the first and second conductive polymers can be highly packed into the voids in the porous portion of the anode foil, allowing for more uniform formation of the first and second conductive polymer layers. In addition, forming the second conductive polymer layer by electrolytic polymerization enhances the crystallinity of the second conductive polymer layer. These factors result in high adhesion between the solid electrolyte layer containing the first and second conductive polymer layers and the dielectric layer, reducing interfacial resistance. Although resistance increases in the areas where silicon element is present, high conductivity of the second conductive polymer is obtained. Therefore, high initial capacitance can be ensured while improving the voltage withstand characteristics. The high conductivity of the second conductive polymer also helps to suppress the initial equivalent series resistance (ESR). High adhesion is achieved between the solid electrolyte layer and the dielectric layer, and a second conductive polymer layer with excellent film quality is formed by electrolytic polymerization. Therefore, even after repeated charging and discharging, degradation of the conductive polymer and delamination between the solid electrolyte layer and the dielectric layer, as well as within the solid electrolyte layer, are suppressed, thus maintaining high capacity.

[0017] Technology (2) In Technology (1) above, it is preferable that the silicon element is present between the first conductive polymer layer and the second conductive polymer layer. In this case, the adhesion between the first conductive polymer layer and the second conductive polymer layer is increased, and the filling rate into the voids of the porous portion of the second conductive polymer is increased. Therefore, a higher initial capacity is more easily obtained. In addition, since the surface of the first conductive polymer layer is treated with a silane compound, the second conductive polymer layer is formed more uniformly with high adhesion. As the uniformity of the second conductive polymer layer is increased, the flow of large localized currents is suppressed, and thus a higher dielectric strength can be obtained.

[0018] Technology (3) In Technology (1) or Technology (2) described above, the silicon element may be present between the dielectric layer and the first conductive polymer layer. In this case, higher dielectric strength characteristics can be obtained.

[0019] Technology (4) In any one of the above technologies (1) to (3), the first conductive polymer layer may contain the silicon element. In this case, higher dielectric strength can be obtained while ensuring a high initial capacitance.

[0020] Technology (5) In any one of the above technologies (1) to (4), the silicon element is derived from a silane compound. The silicon element may also exist as a silane compound or as a hydrolysis product (including hydrolysis condensates) of a silane compound.

[0021] Technology (6) In any one of the above technologies (1) to (5), the first conductive polymer may have a conjugated polymer skeleton containing a repeating structure of a first monomer unit corresponding to a first thiophene compound, and an anionic group introduced into the conjugated polymer skeleton. A processing solution containing such a first conductive polymer has relatively low viscosity and easily penetrates an anode foil having a dielectric layer. Therefore, it is easy to form a more uniform second conductive polymer layer by electropolymerization. The second conductive polymer may contain a conjugated polymer containing a repeating structure of a second monomer unit corresponding to a second thiophene compound, and a polymer dopant. Conventionally, the technique of performing electropolymerization as in-situ polymerization using pyrrole is well known. However, electropolymerization of thiophene compounds is technically difficult, but the second conductive polymer layer containing the above second conductive polymer has excellent film quality and high conductivity is easily obtained. Therefore, such a second conductive polymer is advantageous for obtaining high voltage withstand characteristics while ensuring high initial capacity.

[0022] Technology (7) In any one of the above technologies (1) to (6), the anode foil preferably contains aluminum. Even in this case, according to the present disclosure, high voltage withstand characteristics can be obtained while maintaining a higher initial capacitance of the solid electrolytic capacitor.

[0023] Technical (8) A method for manufacturing a solid electrolytic capacitor according to a second aspect of the present disclosure comprises: a first step of preparing an anode foil having a porous portion on its surface; a second step of forming a dielectric layer on at least a part of the surface of the anode foil; a third step of forming a first conductive polymer layer containing a self-doped first conductive polymer on the surface of the dielectric layer; and a fourth step of forming a second conductive polymer layer containing a non-self-doped second conductive polymer containing a conjugated polymer and a dopant on the surface of the first conductive polymer layer. In the fourth step, the anode foil having the dielectric layer on which the first conductive polymer layer is formed is immersed in a polymerization solution containing a precursor of the conjugated polymer and the dopant, and electropolymerization is performed to produce the second conductive polymer, thereby forming the second conductive polymer layer. Furthermore, the manufacturing method further comprises at least one of the following: a first silane treatment step, after the second step and before the third step, in which the anode foil having the dielectric layer is treated with a first silane compound; and a second silane treatment step, after the third step and before the fourth step, in which the anode foil having the dielectric layer on which the first conductive polymer layer is formed is treated with a second silane compound.

[0024] When the first silane treatment step is performed, the treatment solution containing the first conductive polymer easily penetrates the anode foil equipped with a dielectric layer, allowing a wide area of ​​the anode foil surface, including the inner surface of the fine voids in the porous portion, to be covered with the first conductive polymer layer. When the second silane treatment step is performed, the polymerization solution easily penetrates the anode foil equipped with a dielectric layer, allowing the polymerization solution to spread across the entire surface of the first conductive polymer layer. Therefore, in either case, electrolytic polymerization as in-situ polymerization can proceed smoothly, and a second conductive polymer layer with excellent film quality can be formed. As a result, the first and second conductive polymers can be highly packed into the voids of the porous portion. High adhesion between the dielectric layer and the solid electrolyte layer can be obtained, so the interfacial resistance can be kept low. In addition, the high crystallinity of the second conductive polymer provides high conductivity to the second conductive polymer layer. Solid electrolytes formed by electrolytic polymerization tend to have low dielectric strength due to their high crystallinity and conductivity. In this disclosure, the silane treatment process described above ensures that silicon elements derived from the first or second silane compound are present in at least a portion of the space between the dielectric layer and the second conductive polymer layer. Therefore, while ensuring relatively high conductivity of the solid electrolyte layer, the dielectric strength can be enhanced by the silicon elements (more specifically, the silane compound or its derived components (such as hydrolysates)). As a result, according to this disclosure, high dielectric strength can be obtained in a solid electrolytic capacitor while ensuring high initial capacitance.

[0025] Technology (9) In the above technology (8), it is preferable that the manufacturing method includes the second silane treatment step. In this case, a higher initial capacitance and higher dielectric strength can be obtained.

[0026] Technical (10) A method for manufacturing a solid electrolytic capacitor according to a third aspect of the present disclosure comprises: a first step of preparing an anode foil having a porous portion on its surface; a second step of forming a dielectric layer on at least a part of the surface of the anode foil; a third step of applying a processing solution containing a third silane compound and a self-doped first conductive polymer to the surface of the dielectric layer to form a first conductive polymer layer containing silicon elements derived from the third silane compound and the first conductive polymer; and a fourth step of forming a second conductive polymer layer on the surface of the first conductive polymer layer, containing a conjugated polymer and a non-self-doped second conductive polymer containing a dopant. In the fourth step, the anode foil having the dielectric layer on which the first conductive polymer layer is formed is immersed in a polymerization solution containing a precursor of the conjugated polymer and the dopant, and electropolymerization is performed to produce the second conductive polymer, thereby forming the second conductive polymer layer.

[0027] In the third step, a first conductive polymer layer is formed using a processing solution containing a third silane compound and a first conductive polymer. This allows the processing solution to easily penetrate the anode foil equipped with a dielectric layer, enabling the first conductive polymer layer to cover a wide area of ​​the anode foil surface, including the inner surface of the fine voids in the porous portion. The formation of the first conductive polymer layer containing silicon elements derived from the third silane compound allows the polymerization solution to spread across the entire surface of the first conductive polymer layer in the fourth step. Therefore, electrolytic polymerization can proceed smoothly in the fourth step, and a second conductive polymer layer with excellent film quality can be formed. As a result, the first and second conductive polymers can be highly packed into the voids of the porous portion. High adhesion is obtained between the dielectric layer and the solid electrolyte layer, and between the first conductive polymer layer and the second conductive polymer layer, thus keeping interfacial resistance low. Furthermore, the high crystallinity of the second conductive polymer provides high conductivity to the second conductive polymer layer. Solid electrolytes formed by electrolytic polymerization tend to have low dielectric strength due to their high crystallinity and conductivity. In this disclosure, silicon elements derived from a third silane compound are present in the first conductive polymer layer. Therefore, while ensuring high conductivity of the solid electrolyte layer, the dielectric strength can be enhanced by the silicon elements. As a result, a solid electrolytic capacitor can be obtained that has high initial capacitance while also having high dielectric strength.

[0028] Technology (11) In any one of the above technologies (8) to (10), it is preferable that the anode foil contains aluminum. Even in this case, according to the present disclosure, high voltage withstand characteristics can be obtained while maintaining a higher initial capacitance of the solid electrolytic capacitor.

[0029] The solid electrolytic capacitor and its manufacturing method described herein will be explained in more detail below, including the above technologies (1) to (11). At least one of the components described below can be arbitrarily combined with at least one of the above technologies (1) to (11) of this disclosure, insofar as it is technically possible to combine them. Note that the figures are schematic representations, and the proportions of the dimensions (e.g., thickness) of each component may differ from those of the actual components.

[0030] The following descriptions may include examples of embodiments of the Disclosure, but the Disclosure is not limited to these examples. The following descriptions may include specific numerical values ​​and materials, but other numerical values ​​and materials may be used as long as the effects of the Disclosure are achieved. In the following descriptions, when lower and upper limits of numerical values ​​relating to specific physical properties or conditions are given as examples, any combination of either of the given lower limits and either of the given upper limits may be used, as long as the lower limit does not exceed the upper limit. When multiple materials are given as examples, one may be selected and used alone, or two or more may be used in combination.

[0031] [Solid Electrolytic Capacitor] The solid electrolytic capacitor of this disclosure comprises at least one capacitor element. The capacitor element comprises an anode foil having a porous portion on its surface, a dielectric layer covering at least a portion of the surface of the anode foil, and a cathode portion covering at least a portion of the surface of the dielectric layer. The cathode portion comprises a solid electrolyte layer covering at least a portion of the surface of the dielectric layer. The cathode portion may further comprise a cathode extraction layer covering at least a portion of the solid electrolyte layer.

[0032] The solid electrolytic capacitor of this disclosure comprises a first conductive polymer layer covering at least a portion of the surface of a dielectric layer, and a second conductive polymer layer covering at least a portion of the surface of the first conductive polymer layer. The entirety of the first conductive polymer layer and the second conductive polymer layer may be referred to as the solid electrolyte layer in this specification. In this disclosure, the first conductive polymer layer contains a self-doped first conductive polymer. The second conductive polymer layer is formed by electrolytic polymerization and contains a non-self-doped second conductive polymer. At least a portion of the space between the dielectric layer and the second conductive polymer layer contains silicon. With this configuration, high initial capacitance and high dielectric strength are obtained.

[0033] The silicon element originates from silane compounds used in the manufacturing process of capacitor elements. In solid electrolytic capacitors, the silicon element may be included, for example, as a silane compound, or as a hydrolysate of a silane compound.

[0034] The silicon element may be present (a) between the dielectric layer and the first conductive polymer layer, or (b) between the first conductive polymer layer and the second conductive polymer layer. The silicon element may (c) be contained in the first conductive polymer layer. The silicon element may be present at two or more positions selected from these (a) to (c). Among these, when the silicon element is present at the position of (b), it is preferable because a higher initial capacitance and higher breakdown voltage characteristics can be obtained. For the same reason, it is also preferable when the silicon element is present at the position of (c), or at the positions of (b) and (c).

[0035] The distribution state of the silicon element can be determined, for example, by electron probe microanalyzer (EPMA) analysis of a cross-sectional image capable of observing the thickness direction (or stacking direction) of a solid electrolytic capacitor or capacitor element.

[0036] (Anode foil) The anode foil has a porous portion on its surface layer. The anode foil has a plurality of fine pits or pores in the porous portion. Therefore, the surface of the anode foil has a fine uneven shape. Such a shape makes it easier to obtain a large surface area of the anode foil, so it is easier to secure a larger capacitance.

[0037] The anode foil may contain, for example, a valve metal, an alloy containing a valve metal, and a compound containing a valve metal. The anode foil may contain one of these materials or a combination of two or more. As the valve metal, aluminum, niobium, and titanium are preferably used. Among these, it is preferable for the anode foil to contain aluminum. In this case, it is inexpensive, high conductivity can be easily obtained, and foil processing is easy.

[0038] The porous portion is formed, for example, by roughening the surface of a sheet-like base material containing a valve metal. The roughening is performed, for example, by an etching treatment or the like.

[0039] The thickness of the anode foil is, for example, 15 μm or more and 3 cm or less.

[0040] One end of a lead member (such as an anode lead terminal) is connected to the anode foil. The connection may be made, for example, by welding or the like.

[0041] The anode foil is, for example, divided into a first portion including a first end portion and a second portion including a second end portion opposite to the first end portion. The first end portion and the second end portion are both end portions in the length direction of the anode foil. A cathode portion (especially a solid electrolyte layer) is formed on the second portion via a dielectric layer. Therefore, the second portion may be called a cathode formation portion. The cathode portion is not formed on the first portion. A separation portion for ensuring insulation between the first portion and the cathode portion may be formed at an end of the first portion on the side of the second portion. A portion of the first portion where the separation portion is not formed may be called an anode portion (or an anode lead-out portion). An anode lead terminal may be connected to the anode portion. Note that the separation portion is formed of, for example, an insulating material (such as an insulating resin).

[0042] (Dielectric layer) The dielectric layer is an insulating layer that functions as a dielectric. The surface of the dielectric layer has a fine uneven shape according to the shape of the surface of the porous portion of the anode foil.

[0043] The dielectric layer may be formed, for example, by subjecting the anode foil to a forming treatment or by a vapor phase method.

[0044] The dielectric layer may be, for example, an oxide film containing a valve action metal. For example, when aluminum is used as the valve action metal, the dielectric layer contains Al ２ O ３ However, the dielectric layer is not limited to such specific examples.

[0045] (Solid electrolyte layer) (First conductive polymer layer) The first conductive polymer layer contains a self-doped first conductive polymer. The processing solution containing the first conductive polymer for forming the first conductive polymer layer has a relatively low viscosity. By using such a processing solution, a thin and more uniform first conductive polymer layer can be formed on a wider surface, including the inner wall surface of fine recesses in the anode foil having a dielectric layer. Furthermore, since electrolytic polymerization for forming the second conductive polymer can be carried out on the surface of the first conductive polymer layer, the first and second conductive polymers can be highly packed even in fine recesses. As a result, high adhesion can be obtained between the dielectric layer and the solid electrolyte layer, and between the first conductive polymer layer and the second conductive polymer layer, while interfacial resistance can be kept relatively low.

[0046] The first conductive polymer has a conjugated polymer skeleton and functional groups that function as dopants introduced into this skeleton. The functional groups may be directly bonded to the skeleton or indirectly bonded via linking groups.

[0047] Examples of conjugated polymers that constitute the backbone include polymers containing monomer units corresponding to thiophene compounds, pyrrole compounds, aniline compounds, and the like. These polymers also include homopolymers, copolymers of two or more monomers, and derivatives thereof (such as substituted products with substituents).

[0048] The conjugated polymer constituting the backbone of the first conductive polymer and the conjugated polymer contained in the second conductive polymer formed by electrolytic polymerization may be of the same type or of different types.

[0049] Examples of functional groups that function as dopants include anionic groups. Anionic groups are groups that acquire a negative charge upon cation dissociation. Anionic groups may be at least one selected from the group consisting of sulfonic acid groups, phosphoric acid groups, phosphonic acid groups, and carboxyl groups, and a preferred example of an anionic group is a sulfonic acid group. In solid electrolytic capacitors, anionic groups may be in free form, in salt form (salt with an inorganic base, salt with an organic base, etc.), in anionic form, or may interact with or complex with components contained in the solid electrolytic capacitor. All of these forms are sometimes simply referred to as anionic groups or sulfonic acid groups.

[0050] The number of functional groups (e.g., anionic groups) that function as dopants may be 0.2 to 3, 0.5 to 2, 0.5 to 1, 1, or less than 1 per monomer unit of the conjugated polymer skeleton.

[0051] The linking group may be a hydrocarbon chain (such as an alkylene group), and may also contain an oxyalkylene group or a poly(oxyalkylene) group. The alkylene group contained in the linking group may be linear or branched. Other atomic groups (e.g., functional groups) besides the functional group that functions as a dopant may be bonded to the backbone of the conjugated polymer.

[0052] The first conductive polymer may have a conjugated polymer backbone containing a repeating structure of monomer units (first monomer units) corresponding to a thiophene compound (first thiophene compound), and an anionic group introduced into this conjugated polymer backbone. Such a first conductive polymer has high conductivity and, when forming a second conductive polymer by electropolymerization using a thiophene compound (second thiophene compound), it has high affinity with the second conductive polymer and readily exhibits high adhesion. Therefore, a higher initial capacity is easily obtained. As the first conductive polymer, for example, a conductive polymer in which sulfonic acid groups are bonded to a poly(3,4-ethylenedioxythiophene) (PEDOT) backbone via linking groups is preferred.

[0053] The weight-average molecular weight (Mw) of the first conductive polymer may be between 1,000 and 1,000,000, or between 1,000 and 500,000. When the Mw of the first conductive polymer is within this range, the first conductive polymer can easily penetrate into the depressions on the surface of the anode foil having a dielectric layer, allowing for a thin and more uniform coating of many areas of the dielectric layer's surface, including the depressions.

[0054] The first conductive polymer layer may contain one type of first conductive polymer, or it may contain two or more types.

[0055] (Second conductive polymer layer) The second conductive polymer layer contains a non-self-doped second conductive polymer. The second conductive polymer and the second conductive polymer layer are formed by electropolymerization. The second conductive polymer contains a conjugated polymer and a dopant.

[0056] Examples of conjugated polymers include polymers containing monomer units corresponding to thiophene compounds, pyrrole compounds, aniline compounds, and the like. These polymers also include homopolymers, copolymers of two or more monomers, and their derivatives (such as substituted products with substituents).

[0057] As the dopant, at least one selected from the group consisting of anions and polyanions is used. Examples of anions include sulfate ions, nitrate ions, phosphate ions, borate ions, organic sulfonate ions, and carboxylate ions, but are not particularly limited. Examples of dopants that generate sulfonate ions include p-toluenesulfonic acid and naphthalenesulfonic acid.

[0058] The second conductive polymer preferably comprises a conjugated polymer containing a repeating structure of monomer units (second monomer units) corresponding to a thiophene compound (second thiophene compound), and a polymer dopant.

[0059] Examples of secondary thiophene compounds include compounds having a thiophene ring and capable of forming a repeating structure of monomer units corresponding to the secondary thiophene compound.

[0060] The second thiophene compound can be linked at the 2nd and 5th positions of the thiophene ring to form a repeating structure of the first monomer unit, thereby enabling the formation of a polymer in which the π electron cloud is spread throughout the entire molecule. The second thiophene compound also includes compounds having substituents. The substituent may be located, for example, at least one of the 3rd and 4th positions of the thiophene ring. The substituent at the 3rd position and the substituent at the 4th position may be linked to form a ring that condenses with the thiophene ring. Examples of thiophene compounds include thiophenes which may have substituents at least one of the 3rd and 4th positions, alkylenedioxythiophene compounds (such as ethylenedioxythiophene compounds), and C ２－４ Examples include alkylenedioxythiophene compounds. Alkylenedioxythiophene compounds also include those having substituents on the alkylene group. Substituents on the second thiophene compound include alkyl groups (such as methyl and ethyl groups). １－４ Alkyl groups, etc.), alkoxy groups (such as methoxy groups and ethoxy groups) １－４ Alkoxy groups, hydroxyl groups, hydroxyalkyl groups (such as hydroxymethyl groups and other hydroxyC groups) １－４ Preferably, substituents are alkyl groups, etc. However, substituents are not limited to these examples. If the second thiophene compound has two or more substituents, each substituent may be the same or different.

[0061] Among secondary thiophene compounds, using 3,4-ethylenedioxythiophene compounds (especially monomers) makes it easier to ensure higher conductivity in the resulting conductive polymer. Hereinafter, 3,4-ethylenedioxythiophene may be referred to as EDOT, and poly(3,4-ethylenedioxythiophene) as PEDOT.

[0062] The conjugated polymer may contain one type of second monomer unit, or it may contain two or more types.

[0063] Thiophene compounds generally have a higher polymerization potential than pyrrole compounds, making in-situ polymerization by electropolymerization technically difficult. Using a secondary thiophene compound in which an electron-donating group, such as alkylenedioxythiophene or an alkoxy group, is substituted on the thiophene ring, the polymerization potential can be reduced. Therefore, the polymerization reaction of the secondary thiophene compound can proceed rapidly. Furthermore, this polymerization reaction can proceed rapidly even in the presence of a polymer dopant. As a result, even when using a polymer dopant, the conjugated polymer and the polymer dopant can be more uniformly dispersed, allowing for high-density filling of fine depressions on the surface of the dielectric layer where the first conductive polymer layer is formed.

[0064] Electropolymerization is generally carried out using monomolecule dopants such as toluenesulfonic acid or naphthalenesulfonic acid. This is because polymerization can be performed in a relatively uniform state where the conjugated polymer precursor and the dopant are mixed. However, in the case of thiophene compounds, even when combined with such monomolecule dopants, the resulting conductive polymer has low film-forming properties, making it technically difficult to form a conductive polymer layer that exhibits high functionality as a cathode. Contrary to this common technical understanding, when a secondary thiophene compound is combined with a polymer dopant, the electropolymerization reaction as in-situ polymerization can proceed smoothly. As a result, high film-forming properties of the conductive polymer can be obtained, and an electropolymerized film with excellent film quality can be formed.

[0065] Examples of polymer dopants include polymers having multiple anionic groups. Such polymers include polymers containing monomer units having anionic groups.

[0066] Examples of anionic groups include sulfonic acid groups and carboxyl groups. In the polymerization solution or the resulting conductive polymer, anionic groups may be present in free form, anionic form, or salt form. In the conductive polymer, anionic groups may be present in a form bonded to or interacting with the conjugated polymer system. In this specification, all of these forms may be simply referred to as "anionic group," "sulfonic acid group," or "carboxyl group."

[0067] Examples of the polymer dopant having a carboxy group include, for example, polyacrylic acid, polymethacrylic acid, and copolymers using at least one of acrylic acid and methacrylic acid. However, the polymer dopant having a carboxy group is not limited to only these examples.

[0068] As the polymer dopant, it is preferable to use at least a polymer dopant having a sulfonic acid group. Among them, it is preferable to use a polymer dopant containing a plurality of sulfonic acid groups. In this case, higher conductivity of the second conductive polymer can be ensured, and dedoping from the second conductive polymer is easily suppressed.

[0069] Examples of the polymer dopant having a sulfonic acid group include those containing a monomer unit M １ corresponding to an organic sulfonic acid compound. The organic sulfonic acid compound may be any of aliphatic, alicyclic, aromatic, and heterocyclic. The polymer dopant may be a homopolymer containing only the monomer unit M １ or a copolymer containing the monomer unit M １ and other monomer units.

[0070] Specific examples of the polymeric anion having a sulfonic acid group include, for example, polyvinyl sulfonic acid, polystyrene sulfonic acid (including copolymers and substituents having substituents, etc.), polyallyl sulfonic acid, polyacrylic sulfonic acid, polymethacrylic sulfonic acid, poly(2-acrylamido-2-methylpropane sulfonic acid), polyisoprene sulfonic acid, polyester sulfonic acid, and phenol sulfonic acid novolak resin. However, the polymeric anion having a sulfonic acid group is not limited to only these.

[0071] The second conductive polymer may contain one kind of polymer dopant or may contain a combination of two or more kinds.

[0072] The weight-average molecular weight Mw of the polymer dopant may be 1,000 or more, or 500,000 or less. From the viewpoint of improving the filling ability into fine depressions on the surface of the dielectric layer having the first conductive polymer layer, the Mw of the polymer dopant may be 100,000 or less. From the viewpoint of easily ensuring higher film formation ability of the second conductive polymer, the Mw of the polymer dopant is preferably 10,000 or more.

[0073] The polymer dopant contained in the second conductive polymer (or second conductive polymer layer) may be 10 to 1000 parts by mass, or 50 to 200 parts by mass, per 100 parts by mass of the conjugated polymer. The amount of polymer dopant in the polymerization solution used for electrolytic polymerization can also be selected from a similar range.

[0074] (Cathode Extraction Layer) The cathode extraction layer comprises at least a first layer in contact with the solid electrolyte layer. The cathode extraction layer may also comprise a first layer and a second layer covering the first layer. Examples of the first layer include a layer containing conductive particles and a metal foil. Examples of conductive particles include at least one selected from conductive carbon and metal particles. For example, the cathode extraction layer may be composed of a layer containing conductive carbon as the first layer (also referred to as a carbon layer) and a layer containing metal particles or a metal foil as the second layer. When a metal foil is used as the first layer, the cathode extraction layer may be composed of this metal foil.

[0075] Examples of conductive carbon include graphite (artificial graphite, natural graphite, etc.).

[0076] A second layer containing metal particles can be formed, for example, by laminating a composition containing metal particles (such as metal powder) onto the surface of the first layer. An example of such a second layer is a metal particle-containing layer formed using a composition (such as a paste) containing metal particles such as silver particles and a resin (binder resin).

[0077] Examples of binder resins used in carbon layers and metal particle-containing layers include thermoplastic resins and thermosetting resins. Thermosetting resins such as imide resins and epoxy resins are preferably used as binder resins.

[0078] When a metal foil is used as the first layer, the type of metal is not particularly limited. Preferably, the metal foil is a valve metal (such as aluminum, tantalum, or niobium) or an alloy containing a valve metal. The surface of the metal foil may be roughened as needed. The surface of the metal foil may be coated with a chemical conversion film, or a coating of a metal different from the metal constituting the metal foil (a dissimilar metal) or a nonmetal. Examples of dissimilar metals or nonmetals include metals such as titanium and nonmetals such as carbon (such as conductive carbon).

[0079] The above-mentioned dissimilar metal or nonmetal (for example, conductive carbon) coating may be used as the first layer, and the above-mentioned metal foil may be used as the second layer. The metal foil is laminated onto the underlying layer.

[0080] Furthermore, when using metal foil as the cathode lead layer, a separator may be placed between the metal foil and the anode foil. The separator is not particularly limited, and for example, nonwoven fabrics containing fibers of cellulose, polyethylene terephthalate, vinylon, or polyamide (e.g., aliphatic polyamides, aromatic polyamides such as aramids) may be used.

[0081] When metal foil is used as the cathode extraction layer, for example, a capacitor element is formed by laminating or winding the anode foil, on which a solid electrolyte layer is formed, and the metal foil constituting the cathode extraction layer via a separator.

[0082] For example, one end of a cathode lead terminal is electrically connected to the cathode lead layer. The cathode lead terminal is joined to the cathode lead layer by, for example, applying a conductive adhesive to the cathode lead layer and bonding the cathode lead terminal to the cathode lead layer via this conductive adhesive.

[0083] (Other) Solid electrolytic capacitors may be wound type, chip type, or multilayer type. Solid electrolytic capacitors comprise at least one capacitor element. For example, a solid electrolytic capacitor may include two or more multilayer capacitor elements. A solid electrolytic capacitor may also include one wound type capacitor element or two or more wound type capacitor elements. The configuration of the capacitor elements is selected, for example, according to the type of solid electrolytic capacitor.

[0084] [Method for Manufacturing Solid Electrolytic Capacitors] A method for manufacturing a solid electrolytic capacitor according to the second or third aspect of the present disclosure comprises a first step of preparing an anode foil, a second step of forming a dielectric layer, a third step of forming a first conductive polymer layer, and a fourth step of forming a second conductive polymer layer. The manufacturing method according to the second aspect further comprises at least one of a first silane treatment step using a first silane compound and a second silane treatment step using a second silane compound. The manufacturing method according to the third aspect uses a treatment solution containing a third silane compound and a first conductive polymer in the third step. In this disclosure, at least one of the first silane treatment step and the second silane treatment step may be combined with a third step using a treatment solution containing a third silane compound and a first conductive polymer. The manufacturing method according to the present disclosure may further include a fifth step of forming a cathode extraction layer.

[0085] The following provides a more detailed explanation of each step. For information on the components of a solid electrolytic capacitor, please refer to the above explanation of each component.

[0086] (First step) In the first step, an anode foil having a porous portion on its surface is prepared. Such an anode foil is prepared, for example, by roughening a sheet-like metal substrate such as a metal foil.

[0087] The first step may include a substep of roughening the metal foil. Roughening may be performed, for example, by etching. Roughening forms a porous portion on the surface layer, and at the same time, a metal core integrated with the porous portion is formed on the inside of the metal foil.

[0088] Etching may be performed, for example, by applying an electric current, or by chemical etching.

[0089] The thickness of the sheet-like substrate (such as metal foil) is, for example, 15 μm to 300 μm.

[0090] (Second step) In the second step, a dielectric layer is formed on at least a portion of the surface of the anode foil having a porous portion obtained in the first step.

[0091] For example, a dielectric layer, which is an oxide film, may be formed on the surface of the anode foil by chemical conversion treatment. The chemical conversion treatment may be carried out, for example, by immersing the anode foil in a chemical conversion solution and anodic oxidizing the surface of the anode foil. As the chemical conversion solution, for example, a solution containing an acid such as phosphoric acid or adipic acid may be used.

[0092] The dielectric layer may be formed using a vapor phase method. For example, it may be formed by heating the anode foil in an oxygen-containing atmosphere to oxidize the surface.

[0093] (Third step) In the third step, a first conductive polymer layer is formed on the surface of the dielectric layer.

[0094] In the third step, a first conductive polymer layer containing a self-doped first conductive polymer is formed. For example, a treatment solution containing the first conductive polymer is used to form the first conductive polymer layer. In the manufacturing method relating to the third aspect, a treatment solution containing a third silane compound and the first conductive polymer is used. For example, a liquid mixture (solution or dispersion) containing the first conductive polymer (and, if necessary, the third silane compound) is used as the treatment solution.

[0095] The first conductive polymer layer may be formed, for example, by immersing an anode foil having a dielectric layer in the above-mentioned processing solution, removing it, and drying it. Alternatively, the first conductive polymer layer may be formed by applying the above-mentioned processing solution to the surface of the dielectric layer and drying it. Because the first conductive polymer layer has a high affinity with the second conductive polymer formed in the fourth step, an electrolytic polymerized film (second conductive polymer layer) with excellent film quality is formed.

[0096] The processing solution may contain one type of first conductive polymer, or it may contain two or more types.

[0097] To facilitate the penetration of the first conductive polymer into the recesses, the concentration of the first conductive polymer in the treatment solution may be 1% by mass or more and 5% by mass or 2% by mass or more and 4% by mass or less.

[0098] As the third silane compound, a compound having a silicon atom and four radicals covalently bonded to the silicon atom may be used. At least one of the four radicals may be a reactive functional group. Reactive functional groups may include epoxy groups, alkyl halides, amino groups, ureido groups, mercapto groups, isocyanate groups, polymerizable groups, etc. Examples of polymerizable groups include acryloyl groups, methacryloyl groups, vinyl groups, etc. At least one of the four radicals may be hydrolyzable. Hydrolyzable radicals may include, for example, alkoxy groups such as methoxy groups, ethoxy groups, and propoxy groups, or halogen atoms such as chlorine atoms and bromine atoms.

[0099] The reactive functional groups or hydrolyzable groups of the third silane compound may interact with or bond with other components (such as conductive polymers) contained in the precoat layer or electrolytic polymerization film, or with the dielectric layer, etc.

[0100] A silane coupling agent may be used as the third silane compound. Silane coupling agents are readily available and easier to apply uniformly.

[0101] Preferred silane coupling agents include those having an epoxy group and those having an acrylic group. Examples of silane coupling agents having an epoxy group include 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 3-glycidoxypropyltriethoxysilane. Examples of silane coupling agents having an acrylic group include 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, and 3-acryloxypropyltrimethoxysilane (γ-acryloxypropyltrimethoxysilane). Other silane couplings include vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, p-styryltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-di Examples include methyl-butylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, hydrochloride of N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane, 3-ureidopropyltriethoxysilane, 3-chloropropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, bis(triethoxysilylpropyl)tetrasulfide, and 3-isocyanatetopropyltriethoxysilane.

[0102] The treatment solution may contain one or more third silane compounds (such as the silane coupling agent mentioned above).

[0103] The concentration of the third silane compound in the treatment solution may be 0.1% by mass or more and 0.5% by mass or less, or 0.2% by mass or more and 0.4% by mass or less.

[0104] The processing solution typically contains a liquid medium. For example, a medium that is fluid at 25°C and can be removed by drying is used as the liquid medium. Examples of liquid media include water and organic liquid media. Water and organic liquid media may be used in combination.

[0105] The processing solution may, if necessary, contain conductive materials other than the first conductive polymer, additives, etc.

[0106] (Fourth step) In the fourth step, a second conductive polymer (and a second conductive polymer layer) is formed by electrolytic polymerization. The third and fourth steps form a solid electrolyte layer comprising a first conductive polymer layer and a second conductive polymer layer.

[0107] Electropolymerization is carried out, for example, by immersing an anode foil (more specifically, the cathode-forming portion of the anode foil) having an electrolytic layer on which a first conductive polymer layer is formed, in a polymerization solution for electropolymerization. Electropolymerization may also be carried out in a two-electrode system using the anode foil and a counter electrode. Alternatively, electropolymerization may be carried out in a three-electrode system using the anode foil, a counter electrode, and a reference electrode. Performing electropolymerization in a three-electrode system allows for more precise control of the polymerization reaction compared to the two-electrode system, resulting in the formation of an electropolymerized film with superior film quality. Furthermore, the packing density of the second conductive polymer in the fine depressions on the surface of the anode foil having a dielectric layer can be further increased.

[0108] The polymerization solution contains a precursor and dopant of the conjugated polymer. The precursor includes not only single molecules (monomers) but also oligomers, which are chains of multiple monomer units. It is preferable to use at least monomers as the precursor of the conjugated polymer. For example, a polymerization solution containing a thiophene compound and a polymer dopant may be used. The polymerization solution may contain one precursor or two or more precursors. The polymer may contain one dopant or two or more dopants.

[0109] When electrolytic polymerization is performed with the cathode-forming portion of the anode foil immersed in the polymerization solution, the polymerization reaction of the conjugated polymer precursor proceeds in the presence of the dopant, and a second conductive polymer layer containing a second conductive polymer including the conjugated polymer and a polymer dopant is formed on the surface of the dielectric layer on which the first conductive polymer layer is formed. In the second conductive polymer, the dopant and the conjugated polymer may interact or be compounded.

[0110] The concentration of the precursor in the polymerization solution may be 0.5% by mass or more and 3.0% by mass or less, or 1.0% by mass or more and 2.0% by mass or less.

[0111] Polymerization solutions typically contain a solvent. Examples of solvents include water and organic solvents. Water and organic solvents may be used in combination.

[0112] The polymerization solution may contain other conductive materials, additives, etc.

[0113] The polymerization solution may contain an oxidizing agent as needed. The oxidizing agent may be applied to the anode foil having a dielectric layer on which the first conductive polymer layer is formed. As an oxidizing agent, Fe ３＋ Examples of compounds capable of generating oxidizing agents include ferric sulfate, persulfates (such as sodium persulfate and ammonium persulfate), and hydrogen peroxide. The oxidizing agent may be used alone or in combination of two or more.

[0114] For the counter electrode, a Ti electrode is used, but is not limited to this. For the reference electrode, a silver / silver chloride electrode (Ag / Ag) is used. ＋ It is preferable to use ).

[0115] In electropolymerization, the voltage applied to the anode foil (polymerization voltage) is, for example, 0.9V to 1.5V. From the viewpoint of easily achieving high filling in the recesses and ensuring relatively high crystallinity of the second conductive polymer, the polymerization voltage may be 1.0V to 1.2V. Performing electropolymerization in a three-electrode system with such a polymerization voltage can further improve the filling of the recesses. Note that in three-electrode electropolymerization, the polymerization voltage is set by the reference electrode (silver / silver chloride electrode (Ag / Ag) ＋ This is the potential of the anode foil relative to )).

[0116] The temperature at which electrolytic polymerization is carried out may be between 5°C and 60°C, or between 15°C and 35°C.

[0117] (Silane Treatment Step) A manufacturing method relating to a second aspect of this disclosure includes at least one of a first silane treatment step and a second silane treatment step. The first silane treatment step is a step of treating an anode foil having a dielectric layer with a first silane compound after the second step and before the third step. The second silane treatment step is a step of treating an anode foil having a dielectric layer on which a first conductive polymer layer has been formed with a second silane compound after the third step and before the fourth step. The first silane treatment step increases the impregnation of the first conductive polymer and the coating by the first conductive polymer into the anode foil having a dielectric layer. The second silane treatment step increases the impregnation of the polymerization solution into the anode foil having a dielectric layer on which the first conductive polymer layer has been formed. As a result, electrolytic polymerization, which is in-situ polymerization, proceeds smoothly in the fourth step. This provides high adhesion between the dielectric layer and the solid electrolyte layer and between the first conductive polymer layer and the second conductive polymer layer, and the electrolytic polymerization forms a second conductive polymer layer with excellent film quality.

[0118] Either the first silane treatment step or the second silane treatment step may be performed, or both may be performed. The manufacturing method relating to the second aspect preferably includes the second silane treatment step. In this case, a higher initial capacitance can be obtained. In addition, a higher withstand voltage characteristic can be obtained. An even greater effect can be obtained when the second silane treatment step is performed but the first silane treatment step is omitted.

[0119] Each silane treatment step is carried out by adhering a liquid mixture containing each silane compound to the surface of, for example, an anode foil having a dielectric layer or an anode foil having a dielectric layer on which a first conductive polymer layer is formed. In other words, each silane treatment step may include the step of adhering a liquid mixture containing each silane compound. After this step, a step of drying the liquid mixture may be performed as needed.

[0120] The liquid mixture may contain a first silane compound (or a second silane compound) and a solvent. Examples of solvents include organic solvents and water. Organic solvents and water may be used in combination. The liquid mixture may contain one solvent or two or more solvents.

[0121] The liquid mixture may be applied by immersing an anode foil having a dielectric layer or an anode foil having a dielectric layer on which a first conductive polymer layer is formed in the liquid mixture, or by coating these anode foils with the liquid mixture using a known coating method.

[0122] The drying temperature and drying time may be selected depending on the type of silane compound and the type of solvent. Drying may be carried out under atmospheric pressure or under reduced pressure. Drying may be carried out in air or in an inert gas atmosphere (such as nitrogen or argon).

[0123] The first and second silane compounds may be the same or different. Each silane compound may be used alone or in combination of two or more. The composition of the liquid mixture used in each silane treatment step (type of silane compound, type of solvent, concentration of silane compound, etc.) may be the same or different. Each silane compound can be selected from the compounds exemplified for the third silane compound.

[0124] The concentration of the first silane compound (or second silane compound) in the liquid mixture may be 0.2% by mass or more and 2.0% by mass or less, or 0.5% by mass or more and 1.0% by mass or less.

[0125] (Step 5) In Step 5, a cathode extraction layer is formed so as to cover the solid electrolyte layer (such as the second conductive polymer layer). The cathode extraction layer can be formed by known methods according to the layer configuration described for the cathode extraction layer.

[0126] If the cathode extraction layer includes a carbon layer, the carbon layer is formed, for example, by applying a paste or slurry containing conductive carbon and, optionally, a binder (such as a binder resin) to the surface of the solid electrolyte layer (such as a second conductive polymer layer). Alternatively, the carbon layer may be formed by immersing the anode foil on which the solid electrolyte layer (such as a second conductive polymer layer) is formed in a slurry containing conductive carbon, removing it, and drying it. Furthermore, the carbon layer may be formed by coating the surface of the solid electrolyte layer (such as a second conductive polymer layer) with a paste containing conductive carbon using a known coating method.

[0127] If the cathode extraction layer has a metal particle-containing layer, the metal particle-containing layer may be formed, for example, by coating the surface of the first layer (such as a carbon layer) of the cathode extraction layer with a paste containing metal particles using a known coating method.

[0128] If the cathode extraction layer includes a metal foil, at least a portion of the cathode extraction layer is formed by laminating the metal foil onto the underlying layer. Alternatively, the anode foil on which the solid electrolyte layer is formed and the metal foil constituting the cathode extraction layer may be laminated or wound together via a separator.

[0129] The solid electrolytic capacitors of this disclosure can be used in a variety of applications requiring high capacitance or high voltage withstand characteristics. However, the applications of solid electrolytic capacitors are not limited to these.

[0130] Figure 1 is a schematic cross-sectional view showing the structure of a solid electrolytic capacitor according to one embodiment of the present disclosure. As shown in Figure 1, the solid electrolytic capacitor 1 comprises a capacitor element 2, a resin casing 3 that encloses the capacitor element 2, and an anode lead terminal 4 and a cathode lead terminal 5, at least a portion of which are exposed to the outside of the resin casing 3. The anode lead terminal 4 and the cathode lead terminal 5 can be made of a metal such as copper or a copper alloy. The resin casing 3 has a substantially rectangular parallelepiped shape, and the solid electrolytic capacitor 1 also has a substantially rectangular parallelepiped shape.

[0131] The capacitor element 2 comprises an anode foil 6 made of Al foil, a dielectric layer 7 covering the anode foil 6, and a cathode portion 8 covering the dielectric layer 7. The cathode portion 8 comprises a solid electrolyte layer 9 covering the dielectric layer 7 and a cathode extraction layer 10 covering the solid electrolyte layer 9. The anode foil 6 has porous portions formed on both surface layers by etching or the like. The solid electrolyte layer 9 contains S element and, in the anode foil 6 having the dielectric layer 7, has a first portion filled in the voids of the porous portion and a second portion extending beyond the main surface of the anode foil. The second portion is divided into portion A on the side of the first portion and portion B on the opposite side of the first portion.

[0132] The cathode extraction layer 10 may consist of a carbon particle-containing layer (first layer) 11 covering at least a portion of the solid electrolyte layer 9, and a metal-containing layer (second layer) 12 covering at least a portion of the first layer. Such a cathode extraction layer 10 is used when portion B of the second part does not contain carbon particles. When portion B contains carbon particles, the carbon particle-containing layer is not particularly necessary, and the cathode extraction layer 10 may be composed of a metal-containing layer. Such a metal-containing layer may be a layer containing metal powder (such as a metal paste layer).

[0133] The anode foil 6 includes a region facing the cathode portion 8 and a region that does not face it. In the region of the anode foil 6 that does not face the cathode portion 8, an insulating separation portion 13 is formed in a strip-like manner to cover the surface of the anode foil 6 adjacent to the cathode portion 8, thereby restricting contact between the cathode portion 8 and the anode foil 6. In the other portion of the region of the anode foil 6 that does not face the cathode portion 8, it is electrically connected to the anode lead terminal 4 by welding. The cathode lead terminal 5 is electrically connected to the cathode portion 8 via an adhesive layer 14 formed of a conductive adhesive.

[0134] [Examples] The solid electrolytic capacitor or its manufacturing method according to the present disclosure will be described in detail below based on examples, comparative examples and reference examples, but the solid electrolytic capacitor or its manufacturing method according to the present disclosure is not limited to the following examples.

[0135] Example 1: Capacitor elements were fabricated and their characteristics evaluated according to the following procedure.

[0136] (1) Preparation of anode foil (first step) Anode foil was prepared by roughening both surfaces of an aluminum foil (thickness: 130 μm) by etching. The thickness of the porous portion formed on both surfaces of the anode foil was 50 μm each.

[0137] (2) Formation of dielectric layer (second step) The cathode formation portion of the anode foil was immersed in a chemical conversion solution, and a DC voltage of 70V was applied for 20 minutes to form a dielectric layer containing aluminum oxide.

[0138] An anode foil having a dielectric layer was divided into a region where a solid electrolyte is formed (second portion) and a region where a solid electrolyte is not formed (first portion). A separation was then formed between the first portion and the second portion by attaching an insulating resist tape.

[0139] (3) First silane treatment step The cathode-forming portion of the anode foil on which the separation portion obtained in (2) above was formed was immersed in a solution containing 3-glycidoxypropyltriethoxysilane at a concentration of 0.5% by mass (solvent: isopropyl alcohol (IPA)), removed, and dried. Drying was carried out at 130°C for 30 minutes.

[0140] (4) Formation of the first conductive polymer layer (third step) The cathode forming portion of the anode foil, which has the silane-treated dielectric layer obtained in (3) above, was immersed in a liquid dispersion containing a self-doped first conductive polymer and water as a solvent, and then removed and dried to form the first conductive polymer layer. As the first conductive polymer, a PEDOT-based conductive polymer containing monomer units corresponding to a compound in which a (3-sulfo-n-butoxy)methyl group is introduced into the ethylenedioxy portion of EDOT was used. The concentration of the first conductive polymer in the liquid dispersion was 4% by mass.

[0141] (5) Second Silane Treatment Step The cathode-forming portion of the anode foil, which has a dielectric layer on which the first conductive polymer layer obtained in (4) above is formed, was immersed in a solution containing 3-glycidoxypropyltriethoxysilane at a concentration of 0.5% by mass (solvent: isopropyl alcohol (IPA)), removed, and dried. Drying was carried out at 130°C for 30 minutes.

[0142] (6) Formation of the second conductive polymer layer by electrolytic polymerization (Step 4) EDOT monomer and polystyrene sulfonic acid (PSS, Mw: 100,000) as a polymer dopant were dissolved in deionized water to prepare a mixed solution. A polymerization solution was prepared by adding iron(III) sulfate (oxidizing agent) dissolved in deionized water while stirring the mixed solution. Electrolytic polymerization was carried out in a trielectrode using the obtained polymerization solution. More specifically, an anode foil having the first conductive polymer layer that had been treated with silane as obtained in (5) above, a counter electrode, and a reference electrode (silver / silver chloride reference electrode) were immersed in the polymerization solution. A voltage was applied to the anode foil so that the potential of the anode foil relative to the reference electrode was 1.1V, and electrolytic polymerization was carried out at 25°C to form a second conductive polymer (second conductive polymer layer). In this way, a solid electrolyte layer containing the first conductive polymer layer and the second conductive polymer layer was formed.

[0143] (7) Formation of cathode extraction layer (5th step) The anode foil on which the second conductive polymer layer obtained in (6) above was formed was immersed in a dispersion of graphite particles dispersed in water, and after being removed from the dispersion, it was dried to form a carbon layer (first layer) on at least the surface of the solid electrolyte layer. Drying was carried out at a temperature of 130°C to 180°C for a time of 10 to 30 minutes.

[0144] Next, a silver paste containing silver particles and a binder resin (epoxy resin) was applied to the surface of the first layer, and the binder resin was cured by heating at a temperature of 150°C to 200°C for a time of 10 to 60 minutes to form a metal particle-containing layer (second layer). In this way, a cathode extraction layer composed of the first and second layers was formed, and a cathode portion including a solid electrolyte layer and a cathode extraction layer was formed. A capacitor element was fabricated in the manner described above. A total of 20 capacitor elements were fabricated in the same manner as described above.

[0145] (8) Assembly of Solid Electrolytic Capacitors Solid electrolytic capacitors are manufactured, for example, by the following procedure: The cathode portion of the capacitor element obtained in (7) above and one end of the cathode lead terminal are joined with an adhesive layer of conductive adhesive. One end of the anode foil protruding from the capacitor element and one end of the anode lead terminal are joined by laser welding.

[0146] Next, a resin casing made of insulating resin is formed around the capacitor element by molding. At this time, the other end of the anode lead terminal and the other end of the cathode lead terminal are extended from the resin casing. In this way, a solid electrolytic capacitor is manufactured.

[0147] Example 2: A total of 20 capacitor elements were manufactured in the same manner as in Example 1, except that the first silane treatment step was omitted.

[0148] Example 3: A total of 20 capacitor elements were manufactured in the same manner as in Example 1, except that the second silane treatment step was omitted.

[0149] Comparative Example 1: A total of 20 capacitor elements were manufactured in the same manner as in Example 1, except that the first and second silane treatment steps were omitted.

[0150] 《Reference Example 1》 An aqueous dispersion (liquid dispersion) containing a non-self-doped conductive polymer (PSS-doped PEDOT) was prepared. The concentration of PSS-doped PEDOT in the aqueous dispersion was set to 1% by mass or more and 3% by mass or less. In Comparative Example 1, instead of performing the electrolytic polymerization in the fourth step, a second conductive polymer layer was formed using the above aqueous dispersion. More specifically, an anode foil having the first conductive polymer layer was immersed in the above aqueous dispersion for about 30 seconds or more and 60 seconds or less, and then the anode foil was removed from the aqueous dispersion. Next, the anode foil removed from the aqueous dispersion was heated (dried) at a temperature of 140°C or more and 180°C or less for 10 minutes or more and 20 minutes or less. By repeating the immersion of the anode foil in the aqueous dispersion and the above drying multiple times, a second conductive polymer layer was formed. In this way, a solid electrolyte layer including the first conductive polymer layer and the second conductive polymer layer using the aqueous dispersion was formed. Aside from these, a total of 20 capacitor elements were fabricated using the same procedure as in Comparative Example 1.

[0151] 《Evaluation》 The capacitor elements obtained in the examples, comparative examples, and reference examples were evaluated as follows.

[0152] (1) Initial capacitance Under conditions of 20°C, the initial capacitance (μF) of each capacitor element at a frequency of 120 Hz was measured using a four-terminal LCR meter, and the average value of 20 values ​​was calculated.

[0153] (2) After measuring the capacitance at the initial stage of voltage withstand characteristics, a voltage was applied to the capacitor element while boosting it at a rate of 1.0 V / s, and the breakdown voltage (BVD) (unit: V) at which an overcurrent of 2 mA flows was measured.

[0154] Table 1 shows the evaluation results for the examples, comparative examples, and reference examples. In Table 1, E1 to E3 are Examples 1 to 3. C1 is Comparative Example 1, and R1 is Reference Example 1. The capacitance and withstand voltage characteristics (BVD) of each capacitor element are shown as relative values ​​with the average value at C1 set to 100.

[0155]

[0156] As shown in Table 1, in Reference Example R1, which uses a liquid dispersion, higher dielectric strength is obtained compared to Comparative Example C1, which uses electrolytic polymerization, but the initial capacitance is low. In C1, even after 60,000 charge-discharge cycles following moisture absorption and reflow treatment of the solid electrolytic capacitor, the capacitance hardly decreases from the initial value, and high charge-discharge characteristics are obtained. In contrast, in R1, after 60,000 charge-discharge cycles following moisture absorption and reflow treatment of the solid electrolytic capacitor, almost no capacitance is obtained. This is thought to be because in R1, the packing rate of the conductive polymer into the voids of the porous part is low, and as charge-discharge cycles are repeated, deterioration of the conductive polymer, delamination between the dielectric layer and the solid electrolyte layer, and delamination within the solid electrolyte layer occur, resulting in a decrease in conductivity.

[0157] In C1, a high initial capacity is obtained compared to R1, but the voltage withstand characteristics are low. In contrast, in Examples E1 to E3, an initial capacity equal to or higher than that of C1 is obtained, and voltage withstand characteristics are obtained despite the use of electropolymerization. From the viewpoint of ensuring higher voltage withstand characteristics, a second silane treatment is preferable (comparison of E2 with E1 and E3). In other words, it is preferable that silicon elements are present between the first conductive polymer layer and the second conductive polymer layer.

[0158] Furthermore, when the second silane treatment is performed, the silane compound also permeates the first conductive polymer layer. This first conductive polymer layer contains silicon. Therefore, even when the first conductive polymer layer contains silicon, the same or similar effects as E2 can be obtained.

[0159] Although the present invention has been described in relation to preferred embodiments at present, such disclosure should not be interpreted restrictively. Various modifications and alterations will undoubtedly become apparent to those skilled in the art in the field to which the invention pertains by reading the above disclosure. Accordingly, the appended claims should be interpreted as encompassing all modifications and alterations without departing from the true spirit and scope of the invention.

[0160] 1: Solid electrolytic capacitor 2: Capacitor element 3: Resin casing 4: Anode lead terminal 5: Cathode lead terminal 6: Anode foil 7: Dielectric layer 8: Cathode section 9: Solid electrolyte layer 10: Cathode lead layer 11: First layer 12: Second layer 13: Separation section 14: Adhesive layer

Claims

1. A solid electrolytic capacitor comprising: an anode foil having a porous portion on its surface; a dielectric layer covering at least a portion of the surface of the anode foil; a first conductive polymer layer covering at least a portion of the surface of the dielectric layer; and a second conductive polymer layer covering at least a portion of the surface of the first conductive polymer layer, wherein the first conductive polymer layer contains a self-doped first conductive polymer, the second conductive polymer layer is formed by electrolytic polymerization and contains a non-self-doped second conductive polymer, and silicon is present in at least a portion between the dielectric layer and the second conductive polymer layer.

2. The solid electrolytic capacitor according to claim 1, wherein the silicon element is present between the first conductive polymer layer and the second conductive polymer layer.

3. The solid electrolytic capacitor according to claim 1, wherein the silicon element is present between the dielectric layer and the first conductive polymer layer.

4. The solid electrolytic capacitor according to claim 1, wherein the first conductive polymer layer contains the silicon element.

5. The solid electrolytic capacitor according to any one of claims 1 to 4, wherein the silicon element is derived from a silane compound.

6. The solid electrolytic capacitor according to any one of claims 1 to 4, wherein the first conductive polymer comprises a conjugated polymer skeleton including a repeating structure of first monomer units corresponding to a first thiophene compound, and an anionic group introduced into the conjugated polymer skeleton, and the second conductive polymer comprises a conjugated polymer including a repeating structure of second monomer units corresponding to a second thiophene compound, and a polymer dopant.

7. The solid electrolytic capacitor according to any one of claims 1 to 4, wherein the anode foil comprises aluminum.

8. A method for manufacturing a solid electrolytic capacitor, comprising: a first step of preparing an anode foil having a porous portion on its surface; a second step of forming a dielectric layer on at least a part of the surface of the anode foil; a third step of forming a first conductive polymer layer containing a self-doped first conductive polymer on the surface of the dielectric layer; and a fourth step of forming a second conductive polymer layer containing a non-self-doped second conductive polymer containing a conjugated polymer and a dopant on the surface of the first conductive polymer layer, wherein in the fourth step, the anode foil having the dielectric layer on which the first conductive polymer layer is formed is immersed in a polymerization solution containing a precursor of the conjugated polymer and the dopant and electropolymerized to produce the second conductive polymer, thereby forming the second conductive polymer layer, and the manufacturing method is as follows: A method for manufacturing a solid electrolytic capacitor, further comprising: a first silane treatment step of treating the anode foil having the dielectric layer with a first silane compound after the second step and before the third step; and a second silane treatment step of treating the anode foil having the dielectric layer on which the first conductive polymer layer is formed with a second silane compound after the third step and before the fourth step.

9. A method for manufacturing a solid electrolytic capacitor according to claim 8, comprising the second silane treatment step.

10. A method for manufacturing a solid electrolytic capacitor, comprising: a first step of preparing an anode foil having a porous portion on its surface; a second step of forming a dielectric layer on at least a portion of the surface of the anode foil; a third step of applying a processing solution containing a third silane compound and a self-doped first conductive polymer to the surface of the dielectric layer to form a first conductive polymer layer containing silicon elements derived from the third silane compound and the first conductive polymer; and a fourth step of forming a second conductive polymer layer on the surface of the first conductive polymer layer, the second conductive polymer layer being formed by electropolymerizing the anode foil having the dielectric layer on which the first conductive polymer layer is formed, while immersed in a polymerization solution containing a precursor of the conjugated polymer and the dopant, thereby generating the second conductive polymer.

11. The method for manufacturing a solid electrolytic capacitor according to any one of claims 8 to 10, wherein the anode foil contains aluminum.

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