Production method for solid electrolytic capacitor, and solid electrolytic capacitor

Abstract

This production method for a solid electrolytic capacitor includes: a first step, in which an anode body is prepared; a second step, in which a dielectric layer is formed on at least some of the surfaces of the anode body; a third step, in which the surface of the dielectric layer is precoated with an electroconductive material; and a fourth step, in which the anode body including the precoated dielectric layer is immersed in a polymerization solution to conduct electrolytic polymerization and form an electroconductive polymer. The polymerization solution includes a thiophene compound and a polymer dopant. The production method further includes: a first silane treatment step, in which between the second step and the third step, the anode body including the dielectric layer is treated with a first silane compound; and / or a second silane treatment step, in which between the third step and the fourth step, the anode body including the precoated dielectric layer is treated with a second silane compound.

Description

Method for manufacturing a solid electrolytic capacitor and solid electrolytic capacitor

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

[0002] Electrolytic capacitors are used in a variety of electronic devices because they have a low equivalent series resistance (ESR) and excellent frequency characteristics. Electrolytic capacitors typically consist of a capacitor element comprising an anode and a cathode. The anode contains a porous anode body, and a dielectric layer is formed on the surface of the anode body. The dielectric layer is in contact with the electrolyte. Solid electrolytic capacitors use solid electrolytes such as conductive polymers. Solid electrolytes are formed by in-situ polymerization, such as chemical polymerization or electrolytic polymerization, or by using a solution or dispersion containing a conductive polymer. In the case of in-situ polymerization, a pre-coat layer may be formed prior to the polymerization.

[0003] Patent Document 1 proposes a method for manufacturing a solid electrolytic capacitor, comprising: a dielectric film layer formation step of forming a dielectric film layer on the surface of an anode body made of a valve metal; a pre-coat layer formation step of forming a conductive pre-coat layer on the dielectric film layer; and an electrolytic polymerization step of immersing the element intermediate having the pre-coat layer formed thereon in an electrolytic polymerization solution and supplying power from a power supply point where an external electrode is in contact with or close to the element intermediate to form a conductive polymer layer on the pre-coat layer by electrolytic polymerization, wherein the power supply point is provided on the ridge line between two adjacent faces of the element intermediate.

[0004] Japanese Patent Publication No. 2014-192231

[0005] When forming solid electrolytes by electrolytic polymerization, controlling the polymerization reaction is difficult, and it can be challenging to ensure high conductivity of the solid electrolyte. Therefore, it is difficult to improve initial properties such as capacitance and ESR.

[0006] A first aspect of this disclosure relates to a method for manufacturing a solid electrolytic capacitor, comprising: a first step of preparing an anode; a second step of forming a dielectric layer on at least a portion of the surface of the anode; a third step of pre-coating the surface of the dielectric layer with a conductive material; and a fourth step of immersing the anode having the pre-coated dielectric layer in a polymerization solution to perform electrolytic polymerization and form a conductive polymer, wherein the polymerization solution comprises a thiophene compound and a polymer dopant, and the manufacturing method further comprises at least one of a first silane treatment step between the second step and the third step, in which the anode having the dielectric layer is treated with a first silane compound, and a second silane treatment step between the third step and the fourth step, in which the anode having the pre-coated dielectric layer is treated with a second silane compound.

[0007] A second aspect of this disclosure relates to a solid electrolytic capacitor comprising: an anode having a dielectric layer on at least a portion of its surface; a conductive material covering at least a portion of the surface of the dielectric layer; and a conductive polymer formed by electrolytic polymerization to cover at least a portion of the surface of the conductive material, wherein the conductive polymer comprises a conjugated polymer containing monomer units corresponding to a thiophene compound and a polymer dopant, and a silane compound is present between the dielectric layer and the conductive material, and between the conductive material and the conductive polymer.

[0008] According to this disclosure, a solid electrolytic capacitor with excellent initial characteristics and a method for manufacturing the same can be provided.

[0009] This is a schematic cross-sectional view of a solid electrolytic capacitor according to one embodiment of the present disclosure.

[0010] Novel features of the present invention are described in the appended claims, but the present invention, both in terms of structure and content, and in conjunction with other objects and features of the present invention, will be better understood by the following detailed description in conjunction with the drawings.

[0011] When forming conductive polymers by electropolymerization, controlling the polymerization reaction is crucial to obtaining an electropolymerized film with excellent film quality. However, when using thiophene compounds as raw materials, forming a high-quality electropolymerized film is technically difficult. To facilitate smooth electropolymerization and achieve more uniform electropolymerization on the dielectric layer, a conductive material is sometimes pre-coated onto the surface of the dielectric layer prior to electropolymerization. Patent Document 1 describes pre-coating with a conductive polymer formed by chemical polymerization. However, it has become clear that when a conductive polymer is formed by electropolymerization after pre-coating, the packing density in the depressions on the surface of the anode body having a dielectric layer may be low. If the packing density of the conductive polymer (solid electrolyte) in the aforementioned depressions is low, areas with few contact points (in other words, low adhesion) occur within the solid electrolyte and between the dielectric layer and the solid electrolyte, making it difficult to obtain high conductivity. Therefore, it is difficult to extract high capacity from the initial stage and difficult to keep the ESR low.

[0012] Conventionally, the technique of performing electropolymerization as in-situ polymerization using pyrrole is well known. However, even when performing electropolymerization of thiophene compounds in a manner similar to that using pyrrole, it is difficult to obtain a solid electrolyte of sufficient quality to function as the cathode body of an electrolytic capacitor.

[0013] Technology (1) In view of the above, the method for manufacturing a solid electrolytic capacitor of the present disclosure includes: a first step of preparing an anode body; a second step of forming a dielectric layer on at least a part of the surface of the anode body; a third step of pre-coating a conductive material on the surface of the dielectric layer; and a fourth step of immersing the anode body having the pre-coated dielectric layer in a polymerization solution to perform electrolytic polymerization and form a conductive polymer. The polymerization solution includes a thiophene compound and a polymer dopant. The manufacturing method further includes at least one of a first silane treatment step between the second step and the third step, in which the anode body having the dielectric layer is treated with a first silane compound, and a second silane treatment step between the third step and the fourth step, in which the anode body having the pre-coated dielectric layer is treated with a second silane compound.

[0014] According to this disclosure, as described above, treatment with a silane compound is performed at least one of the following: (A) before pre-coating, and (B) after pre-coating and before electrolytic polymerization. When treatment with a silane compound is performed in (A), the conductive material to be pre-coated on the anode body having a dielectric layer becomes more easily absorbed, and a wide area of ​​the surface, including the inner surface of fine depressions on the surface, can be covered with the conductive material. When treatment with a silane compound is performed in (B), the polymerization solution becomes more easily absorbed on the anode body having a dielectric layer, and the polymerization solution can spread throughout the entire surface. Therefore, in both cases (A) and (B), electrolytic polymerization as in-situ polymerization can proceed smoothly. Furthermore, by using a thiophene compound and a polymer dopant, a conductive polymer (solid electrolyte) with excellent film quality can be formed even when electrolytic polymerization is performed as in-situ polymerization. As a result, the conductive polymer can be filled even into the deep depressions of the anode body having a dielectric layer, and high adhesion between the dielectric layer and the solid electrolyte can be obtained, so that the interfacial resistance can be kept low. In addition, high conductivity of the solid electrolyte can be obtained due to the excellent film quality. As a result, high capacitance can be obtained in the initial stages of solid electrolytic capacitor development, while keeping the ESR low. Thus, according to this disclosure, a solid electrolytic capacitor with excellent initial characteristics can be obtained.

[0015] Technology (2) In the above technology (1), the manufacturing method preferably includes at least the first silane treatment step. Performing the silane treatment before pre-coating makes it easier to obtain a higher capacitance.

[0016] Technology (3) In technology (1) or (2) above, the manufacturing method may include both the first silane treatment step and the second silane treatment step. In this case, the effect of improving capacitance is significant.

[0017] Technology (4) In any one of the above technologies (1) to (3), the conductive material may include a self-doped conductive polymer. In this case, the self-doped conductive polymer easily adheres thinly and uniformly to the surface of the dielectric layer. Furthermore, unlike when pre-coating is performed by chemical polymerization as in-situ polymerization, in the case of a self-doped conductive polymer, dissolution into the polymerization solution of the electrolytic polymerization is less likely to occur. Therefore, the polymerization reaction of the electrolytic polymerization proceeds more easily after pre-coating, and a more uniform electrolytic polymerized film is more easily formed.

[0018] Technology (5) In any one of the above technologies (1) to (4), the polymer dopant may contain a plurality of sulfonic acid groups. In this case, higher conductivity can be obtained for the conductive polymer formed by electrolytic polymerization. In addition, since dedoping of the conductive polymer is easily suppressed, degradation of the conductive polymer can be suppressed.

[0019] Technology (6) In any one of the above technologies (1) to (5), the solid electrolytic capacitor may include an anode portion having an anode body and an anode wire in which a portion is embedded in the anode body. The anode body is preferably a molded body of particles containing a valve metal, or a sintered body of the molded body. In this case, the depth of the recess in the anode body having a dielectric layer tends to be deep. In this disclosure, the conductive polymer can be filled to the depth of such recess, and since high adhesion between the dielectric layer and the solid electrolyte can be obtained, the interfacial resistance can be kept low.

[0020] Technical (7) The present disclosure also includes solid electrolytic capacitors. The solid electrolytic capacitor of the present disclosure comprises an anode having a dielectric layer on at least a portion of its surface, a conductive material covering at least a portion of the surface of the dielectric layer, and a conductive polymer formed by electrolytic polymerization to cover at least a portion of the surface of the conductive material. The conductive polymer includes a conjugated polymer containing monomer units corresponding to a thiophene compound and a polymer dopant. A silane compound is present between the dielectric layer and the conductive material, and between the conductive material and the conductive polymer, at least one of the two.

[0021] The presence of the silane compound at the above position enhances the impregnation of the conductive material for pre-coating and the polymerization solution for electrolytic polymerization into the anode body with a dielectric layer, allowing electrolytic polymerization to proceed smoothly. Furthermore, electrolytic polymerization forms a conductive polymer (solid electrolyte) containing a conjugated polymer with monomer units corresponding to the thiophene compound and a polymer dopant. As a result, an electrolytic polymerized film with excellent film quality is obtained despite containing a conjugated polymer with monomer units corresponding to the thiophene compound. Moreover, despite using a polymer dopant, the conductive polymer (solid electrolyte) can be highly filled into the recesses of the anode body with a dielectric layer. As a result, the adhesion between the dielectric layer and the conductive polymer is enhanced, interfacial resistance is kept low, and high conductivity of the solid electrolyte is obtained due to the excellent film quality. Consequently, excellent initial characteristics (capacitance and ESR, etc.) of the solid electrolytic capacitor are obtained.

[0022] Technology (8) In the above technology (7), it is preferable that the silane compound is present at least between the dielectric layer and the conductive material. In this case, a higher capacitance is more easily obtained.

[0023] Technology (9) In Technology (7) or Technology (8) above, the conductive material preferably contains a self-doped conductive polymer. In this case, the polymerization reaction of electropolymerization proceeds more easily, making it easier to form a more uniform electropolymerized film.

[0024] Technology (10) In any one of the above technologies (7) to (9), the solid electrolytic capacitor may include an anode portion having an anode body and an anode wire in which a portion is embedded in the anode body. The anode body is preferably a molded body of particles containing a valve metal, or a sintered body of the molded body. In this case, the depth of the recess in the anode body having a dielectric layer tends to be deep. In this disclosure, the conductive polymer can be filled to the depth of such recess, and since high adhesion between the dielectric layer and the solid electrolyte can be obtained, the interfacial resistance can be kept low.

[0025] The solid electrolytic capacitor and its manufacturing method described herein will be explained in more detail below, including techniques (1) to (10) described above, with reference to drawings as necessary. To the extent that it is not technically inconsistent, at least one of techniques (1) to (10) described above may be combined with at least one of the elements described below. Note that each figure is for illustrative purposes only, and the proportions of the dimensions (e.g., thickness) of each component may differ from those of the actual components.

[0026] [Method for Manufacturing a Solid Electrolytic Capacitor] The method for manufacturing a solid electrolytic capacitor according to the present disclosure includes a first step of preparing an anode, a second step of forming a dielectric layer, a third step of pre-coating a conductive material, and a fourth step of forming a conductive polymer by electrolytic polymerization. The manufacturing method further includes at least one of a first silane treatment step between the second and third steps, and a second silane treatment step between the third and fourth steps.

[0027] (First step) The anode body typically has a porous portion at least on its surface. The anode body has multiple fine pits or pores in its porous portion. Therefore, the anode body has a surface with fine irregularities. This shape makes it easier to obtain a large surface area for the anode body, thus making it easier to secure a larger capacitance.

[0028] The anode may contain valve metals, alloys containing valve metals, and compounds containing valve metals. The anode may contain one of these materials or a combination of two or more. As valve metals, aluminum, tantalum, niobium, and titanium are preferably used. The anode preferably contains at least tantalum.

[0029] In the first step, an anode body (sometimes referred to as an anode foil) having a porous portion on its surface is prepared by roughening a sheet-like metal substrate, such as a metal foil. The first step may include a substep of roughening the metal foil. Roughening may be performed by etching, for example. By roughening, a porous portion is formed on the surface, and at the same time, a metal core integrated with the porous portion is formed on the inner part of the metal foil. Etching may be performed by applying an electric current, for example, or by chemical etching. The thickness of the sheet-like substrate (such as a metal foil) is, for example, 15 μm to 300 μm.

[0030] The anode body may be a porous molded body of particles containing valve metal or a porous sintered body thereof. In both the porous molded body and the sintered body, the entire anode body typically has a porous structure. The molded body and the sintered body may be in sheet form, or they may be rectangular parallelepipeds, cubes, or similar shapes. Such an anode body may be formed, for example, by pressure molding valve metal particles into a desired shape, or by further sintering a pressure-molded body.

[0031] One end of a lead member (such as an anode lead terminal) is connected to the anode body. If the anode body is an anode foil, the lead member (such as an anode lead terminal) may be connected to the anode foil by welding or other means.

[0032] If the anode body is a porous molded or sintered body, a portion of a metal lead member (such as a lead wire) may be embedded in the molded or sintered body. The lead wire is also called an anode wire. The anode wire may be a metal wire. Examples of materials for the anode wire include the valve metal mentioned above, copper, or copper alloys. A portion of the anode wire is embedded in the anode body, and the remaining portion protrudes outward from the end face of the anode body. A solid electrolytic capacitor may include an anode section comprising such an anode body and an anode wire with a portion embedded in the anode body. Such an anode section may be prepared in the first step.

[0033] The anode body is divided into, for example, a first part including a first end and a second part including a second end opposite to the first end. The first and second ends are the ends of the anode body in the longitudinal direction. A cathode (particularly a conductive polymer) is formed in the second part via a dielectric layer. For this reason, the second part is sometimes called the cathode-forming part. No cathode is formed in the first part. A separation section may be formed at the end of the first part on the second part side to ensure insulation between the first part and the cathode. The part of the first part in which the separation section is not formed is sometimes called the anode section (or anode lead section). Anode lead terminals may be connected to the anode section. The separation section is formed of, for example, an insulating material (such as insulating resin). In the case of an anode wire, the end of the anode wire protruding outward from the anode body corresponds to the first end, and the end of the anode body opposite to the first end corresponds to the second end.

[0034] (Second step) In the second step, a dielectric layer is formed on at least a portion of the surface of the anode. The dielectric layer is an insulating layer that functions as a dielectric. The dielectric layer may be an oxide film. The surface of the dielectric layer has a fine uneven shape depending on the shape of the surface of the porous part of the anode.

[0035] For example, a dielectric layer, which is an oxide film, may be formed on the surface of the anode by chemical conversion treatment. The chemical conversion treatment may be carried out, for example, by immersing the anode in a conversion solution and anodizing the surface of the anode. As the conversion solution, for example, a solution containing an acid such as phosphoric acid or adipic acid may be used. The oxide film may be formed using a gas-phase method, or by heating the anode in an oxygen-containing atmosphere and oxidizing the surface.

[0036] The dielectric layer may contain an oxide of the valve metal. For example, when tantalum is used as the valve metal, the dielectric layer may contain Ta ２ O ５ It includes. When aluminum is used as the valve metal, the dielectric layer is Al ２ O ３ This includes, however, dielectric layers are not limited to these specific examples.

[0037] (Step 3) In Step 3, a conductive material is pre-coated on the surface of the dielectric layer. As a result, a pre-coated layer of the conductive material is formed on the surface of the dielectric layer.

[0038] In Step 3, a pre-coated layer is formed by attaching a conductive material to the surface of the dielectric layer. For example, the pre-coated layer may be formed by immersing an anode body having a dielectric layer in a liquid mixture containing a conductive material, taking it out, and drying it. The pre-coated layer may also be formed by applying the liquid mixture to the surface of the dielectric layer and drying it.

[0039] Examples of the conductive material include inorganic conductive materials such as manganese dioxide and conductive polymers. The conductive material may be used alone as one kind or in combination of two or more kinds. When a conductive polymer is used, the affinity with the conductive polymer formed in Step 4 is high, and an electrolytic polymerization film excellent in film quality is formed. When the pre-coated layer is formed of a conductive polymer, it may be formed by in-situ polymerization such as chemical polymerization, or a liquid mixture (solution or dispersion) containing a conductive polymer may be used.

[0040] From the viewpoint of allowing electrolytic polymerization to proceed more smoothly in Step 4, it is preferable to perform pre-coating using a liquid mixture containing a conductive polymer. As the conductive polymer, a self-doped conductive polymer may be used, a non-self-doped conductive polymer may be used, or a combination thereof may be used. The non-self-doped conductive polymer includes, for example, a conjugated polymer and a dopant. It is preferable to use a conductive material containing a self-doped conductive polymer for pre-coating. This is because the liquid mixture containing the self-doped conductive polymer has a relatively low viscosity, and a thinner and more uniform pre-coated layer can be formed on a wider range of surfaces including the inner wall surface of the fine recesses of the anode body having the dielectric layer. In Step, 4, since electrolytic polymerization proceeds on such a pre-coated layer, the fine recesses can be highly filled with the conductive polymer formed by electrolytic polymerization.

[0041] Self-doped conductive polymers have a conjugated polymer backbone and a functional group that functions as a dopant introduced into this backbone. The functional group may be directly bonded to the backbone or indirectly bonded via a linking group. Examples of functional groups that function as dopants include anionic groups. An anionic group is a group that becomes negatively charged by dissociation of a cation. The anionic group may be at least one selected from the group consisting of a sulfonic acid group, a phosphoric acid group, a phosphonic acid group, and a carboxyl group, and a preferred example of the anionic group is a sulfonic acid group. In a solid electrolytic capacitor, the anionic group may be in a free form, in a salt form (such as a salt with an inorganic base or an organic base), in an anionic form, or may interact or complex with components contained in the solid electrolytic capacitor. In some cases, all these forms are simply referred to as an anionic group, a sulfonic acid group, etc.

[0042] The number of functional groups (such as anionic groups) that function as dopants may be 0.2 or more and 3 or less, 0.5 or more and 2 or less, 0.5 or more and 1 or less, or 1 or less per monomer unit of the conjugated polymer backbone.

[0043] Examples of conjugated polymers that constitute the backbone include polymers containing monomer units corresponding to thiophene compounds, pyrrole compounds, aniline compounds, etc. The polymer may be a homopolymer or a copolymer. The self-doped conductive polymer may be, for example, a conductive polymer in which a sulfonic acid group is bonded to the backbone of poly(3,4-ethylenedioxythiophene) (PEDOT) via a linking group. The linking group may be a hydrocarbon chain (such as an alkylene group), or may 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 (such as functional groups) other than the functional group that functions as a dopant may be bonded to the backbone of the conjugated polymer.

[0044] The weight-average molecular weight Mw of the self-doped conductive polymer may be between 1,000 and 1,000,000, or between 1,000 and 500,000. When the Mw of the self-doped conductive polymer is within this range, the self-doped conductive polymer can easily penetrate into the depressions on the surface of the anode body having a dielectric layer, allowing for a thin and more uniform pre-coating of many areas of the dielectric layer surface, including the depressions.

[0045] The precoat may use one type of conductive polymer (such as a self-doped conductive polymer), or two or more types in combination.

[0046] The conjugated polymer constituting the backbone of the conductive polymer for pre-coating and the conjugated polymer formed by electrolytic polymerization may be of the same type or of different types.

[0047] To facilitate the penetration of the conductive material into the recesses, the concentration of the conductive material (such as a self-doped conductive polymer) in the pre-coating liquid mixture may be 3% by mass or more and 40% by mass or 5% by mass or more and 30% by mass or less.

[0048] (Fourth step) In the fourth step, a conductive polymer (solid electrolyte) is formed by electrolytic polymerization. The formed conductive polymer (solid electrolyte) may be in a layered form (sometimes referred to as a conductive polymer layer or a solid electrolyte layer).

[0049] Electropolymerization is carried out, for example, by immersing an anode body (more specifically, the cathode-forming portion of the anode body) having a dielectric layer pre-coated with a conductive material in a polymerization solution for electropolymerization. Electropolymerization may also be carried out in a two-electrode system using the anode body and a counter electrode. Alternatively, electropolymerization may be carried out in a three-electrode system using the anode body, 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 conductive polymer in the fine depressions on the surface of the anode body with the dielectric layer can be further increased.

[0050] The polymerization solution contains a thiophene compound and a polymer dopant. The thiophene compound is a precursor of the conjugated polymer that constitutes the conductive polymer. When electropolymerization is performed with the cathode forming portion of the anode body immersed in the polymerization solution, the polymerization reaction of the thiophene compound proceeds in the presence of the polymer dopant, and a conductive polymer containing a conjugated polymer with the thiophene compound as monomer units and the polymer dopant is formed on the surface of the pre-coated dielectric layer. In the resulting conductive polymer, the polymer dopant and the conjugated polymer may interact or be complexed.

[0051] Examples of thiophene compounds include compounds having a thiophene ring and capable of forming a repeating structure of monomer units corresponding to the thiophene compound. Thiophene compounds include not only single molecules (monomers) but also oligomers in which multiple monomer units corresponding to the thiophene compound are linked together. As a precursor of a conjugated polymer, it is preferable to use at least a thiophene compound that is a monomer.

[0052] Thiophene compounds 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. Thiophene compounds also include compounds having substituents. The substituents 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 fused to the thiophene ring. Examples of thiophene compounds include thiophenes which may have substituents at least one of the 3rd and 4th positions, alkylenedioxythiophene compounds (such as ethylenedioxythiophene compounds), and C ２－４ Examples include alkylenedioxythiophene compounds. Alkylenedioxythiophene compounds also include those having substituents on the alkylene group. Substituents on thiophene compounds include alkyl groups (such as methyl and ethyl groups). １－４ Alkyl groups (such as alkyl groups), alkoxy groups (such as methoxy groups and ethoxy groups), etc. 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 thiophene compound has two or more substituents, each substituent may be the same or different.

[0053] Among 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.

[0054] The precursor (thiophene compound) may be used alone or in combination of two or more types.

[0055] Thiophene compounds generally have a higher polymerization potential than pyrrole compounds, making in-situ polymerization by electropolymerization technically difficult. However, using thiophene compounds in which electron-donating groups, such as alkylenedioxythiophene or alkoxy groups, are substituted on the thiophene ring can lower the polymerization potential. Therefore, the polymerization reaction of thiophene compounds can proceed rapidly even in the presence of polymer dopants. As a result, despite the use of polymer dopants, the conjugated polymer and polymer dopant can be more uniformly dispersed, allowing for high-density filling of fine depressions on the pre-coated dielectric surface.

[0056] Electropolymerization is generally carried out using monomolecule dopants such as toluenesulfonic acid or naphthalenesulfonic acid. This is because polymerization can be performed in a state where the conjugated polymer precursor and the dopant are relatively uniformly 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 difficult to form a conductive polymer layer that functions sufficiently as a cathode. In this disclosure, by combining a thiophene compound with a polymer dopant, high film-forming properties of the conductive polymer are obtained, and an electropolymerized film with excellent film quality is formed.

[0057] Examples of the polymer dopant include, for example, polymers having a plurality of anionic groups. Examples of such polymers include polymers containing monomer units having anionic groups.

[0058] Examples of the anionic group include a sulfonic acid group, a carboxy group, etc. In the polymerization solution or the conductive polymer to be formed, the anionic group may be contained in a free form, anionic form, or salt form. In the conductive polymer, the anionic group may be contained in a form bonded or interacting with the conjugated polymer. In this specification, all these forms may be simply referred to as "anionic group", "sulfonic acid group", or "carboxy group".

[0059] The polymerization solution may contain one kind of polymer dopant or may contain a combination of two or more kinds.

[0060] 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.

[0061] 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 conductive polymer can be ensured, and dedoping from the conductive polymer is easily suppressed.

[0062] 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 may be a copolymer containing the monomer unit M １ and other monomer units.

[0063] Specific examples of polymer anions having a sulfonic acid group include, for example, polyvinyl sulfonic acid, polystyrene sulfonic acid (including copolymers and substituted products), polyallyl sulfonic acid, polyacryl sulfonic acid, polymethacrylate sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, polyester sulfonic acid, and phenolsulfonic acid novolac resin. However, polymer anions having a sulfonic acid group are not limited to these.

[0064] 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 pre-coated dielectric 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 conductive polymer, the Mw of the polymer dopant is preferably 10,000 or more.

[0065] The polymer dopant contained in the polymerization solution or conductive polymer (or 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 precursor (such as a thiophene compound).

[0066] Polymerization solutions typically contain a solvent. Examples of solvents include water and organic solvents. Water and organic solvents may be used in combination.

[0067] The polymerization solution may contain other conductive materials, additives, etc.

[0068] The polymerization solution may contain an oxidizing agent as needed. The oxidizing agent may be applied to an anode body having a pre-coated dielectric layer. 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.

[0069] 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 ).

[0070] In electropolymerization, the voltage applied to the anode (polymerization voltage) is, for example, 0.6V to 1.5V. From the viewpoint of easily achieving high filling in the voids of the pre-coated porous portion and easily ensuring relatively high crystallinity of the solid electrolyte, 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 recesses. Note that in three-electrode electropolymerization, the polymerization voltage is applied to the reference electrode (silver / silver chloride electrode (Ag / Ag)). ＋ This is the potential of the anode relative to the given polarity.

[0071] The temperature at which electrolytic polymerization is carried out may be between 5°C and 60°C, or between 15°C and 35°C.

[0072] (Silane Treatment Step) The manufacturing method of the present disclosure further comprises 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 body having a dielectric layer with a first silane compound between the second and third steps. The second silane treatment step is a step of treating an anode body having a pre-coated dielectric layer with a second silane compound between the third and fourth steps. The first silane treatment step increases the impregnation of the conductive material for pre-coating into the anode body having a dielectric layer. The second silane treatment step increases the impregnation of the polymerization solution into the anode body having a dielectric layer. Therefore, despite the use of a thiophene compound and a polymer dopant, electrolytic polymerization, which is in-situ polymerization, proceeds smoothly in the fourth step. As a result, high adhesion between the dielectric layer and the conductive polymer is obtained, and a conductive polymer with excellent film quality is obtained by electrolytic polymerization.

[0073] The manufacturing method of the present disclosure preferably includes at least a first silane treatment step. Performing the silane treatment before pre-coating yields a higher initial capacitance. Both the first silane treatment step and the second silane treatment step may be performed. When both silane treatments are performed, the initial capacitance can be significantly improved.

[0074] Each silane treatment step is carried out by depositing a liquid mixture containing each silane compound onto the surface of, for example, an anode having a dielectric layer or an anode having a pre-coated dielectric layer. In other words, each silane treatment step may include a first substep of depositing a liquid mixture containing each silane compound. After this first substep, a second substep of drying the liquid mixture may be performed as needed. In other words, each silane treatment step may include the first substep, or it may include the first substep and the second substep.

[0075] 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.

[0076] The coating may be performed by immersing an anode body having a dielectric layer or an anode body having a pre-coated dielectric layer in a liquid mixture, or by coating these anode bodies with the liquid mixture using a known coating method.

[0077] 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).

[0078] The first silane compound and the second silane compound 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 step (type of silane compound, type of solvent, concentration of silane compound, etc.) may be the same or different.

[0079] Each silane compound may be a compound having a silicon atom and four radicals covalently bonded to the silicon atom. 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.

[0080] The reactive functional groups or hydrolyzable groups of the 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.

[0081] A silane coupling agent may be used as the silane compound. Silane coupling agents are readily available and easier to apply uniformly.

[0082] 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. These may be used individually or in combination of two or more.

[0083] 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.

[0084] By going through the first to fourth steps and at least one of the first silane treatment step and the second silane treatment step, an electrolytic capacitor is obtained that includes a capacitor element comprising an anode, a dielectric layer, and a cathode. The cathode contains at least a conductive polymer.

[0085] (Fifth step) The cathode portion may have a conductive polymer and a cathode extraction layer in contact with the conductive polymer. In this case, the method for manufacturing a solid electrolytic capacitor of the present disclosure may further include a step of forming a cathode extraction layer (fifth step).

[0086] The cathode extraction layer comprises at least a first layer in contact with a conductive polymer. The cathode extraction layer may also comprise a first layer and a second layer covering the first layer. Examples of the first layer include a layer containing conductive particles and a metal foil. Examples of conductive particles include at least one selected from conductive carbon and metal particles. For example, the cathode extraction layer may be composed of a layer containing conductive carbon as the first layer (also referred to as a carbon layer) and a layer containing metal particles or a metal foil as the second layer. If a metal foil is used as the first layer, the cathode extraction layer may be composed of this metal foil.

[0087] Examples of conductive carbon include graphite (artificial graphite, natural graphite, etc.). The carbon layer is formed, for example, by applying a paste or slurry containing conductive carbon and, if necessary, a binder (such as a binder resin) to the surface of a conductive polymer. Alternatively, the carbon layer may be formed by immersing the anode body on which the conductive polymer is formed in a slurry containing conductive carbon, removing it, and drying it. Alternatively, the carbon layer may be formed by coating the surface of the conductive polymer with a paste containing conductive carbon using a known coating method.

[0088] 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). The metal particle-containing layer may also be formed, for example, by coating the surface of the first layer with a paste containing metal particles using a known coating method.

[0089] 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.

[0090] 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).

[0091] 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.

[0092] The metal foil is laminated onto the underlying layer.

[0093] Furthermore, when using metal foil as the cathode lead layer, a separator may be placed between the metal foil and the anode (anode foil, etc.). The separator is not particularly limited, and for example, nonwoven fabrics containing fibers of cellulose, polyethylene terephthalate, vinylon, or polyamide (e.g., aliphatic polyamide, aromatic polyamide such as aramid) may be used.

[0094] When metal foil is used as the cathode extraction layer, for example, a capacitor element is formed by laminating or winding an anode body (such as an anode foil) on which a conductive polymer is formed and the metal foil constituting the cathode extraction layer, with a separator in between.

[0095] 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 it to the cathode lead layer via this conductive adhesive.

[0096] (Sixth step) The method for manufacturing a solid electrolytic capacitor may include a step of sealing the capacitor element (sixth step). The capacitor element is sealed using a resin casing or case.

[0097] For example, the capacitor element and the resin material for the casing (e.g., uncured thermosetting resin and filler) may be placed in a mold, and the capacitor element may be sealed with the resin casing by a transfer molding method, compression molding method, or the like. In this case, the other ends of the anode lead terminal and cathode lead terminal connected to the anode lead drawn out from the capacitor element are exposed from the mold. Examples of thermosetting resins include epoxy resin.

[0098] Alternatively, a solid electrolytic capacitor may be formed by housing the capacitor element in a bottomed case such that the other ends of the anode lead terminal and cathode lead terminal are located on the opening side of the bottomed case, and then sealing the opening of the bottomed case with a sealing material. As the material for the bottomed case, metals such as aluminum, stainless steel, copper, iron, brass, or alloys thereof can be used.

[0099] The other end of the anode lead member and the other end of the cathode lead terminal are drawn out from the resin casing or case, respectively. The other ends of the lead members or lead terminals exposed from the resin casing or case are used for soldering connections to the circuit board on which the solid electrolytic capacitor is to be mounted.

[0100] [Solid Electrolytic Capacitor] The solid electrolytic capacitor of this disclosure comprises an anode having a dielectric layer on at least a portion of its surface, a conductive material covering at least a portion of the surface of the dielectric layer, and a conductive polymer formed by electrolytic polymerization to cover at least a portion of the surface of the conductive material. The conductive polymer includes a conjugated polymer containing monomer units corresponding to a thiophene compound and a polymer dopant. A silane compound is present between the dielectric layer and the conductive material, and between the conductive material and the conductive polymer, at least one of these.

[0101] From the viewpoint of obtaining higher capacitance, it is preferable that the silane compound is present at least between the dielectric layer and the conductive material. Furthermore, when the silane compound is present both between the dielectric layer and the conductive material, and between the conductive material and the conductive polymer, a very high capacitance can be obtained while keeping the ESR low.

[0102] Such solid electrolytic capacitors can be manufactured by the manufacturing method described above. For details on the components of a solid electrolytic capacitor, please refer to the description of the manufacturing method.

[0103] The distribution of silane compounds can be determined, for example, by electron probe microanalyzer (EPMA) analysis of cross-sectional images that allow observation of the thickness direction (or stacking direction) of a solid electrolytic capacitor or capacitor element. In EPMA analysis, silane compounds are detected as silicon elements.

[0104] The silane compound may be present in the dielectric layer or in the conductive material.

[0105] The silicon content in the dielectric layer may be 5% by mass or more and 20% by mass or 10% by mass or more and 15% by mass or less.

[0106] The silicon content in the conductive material may be 5% by mass or more and 20% by mass or less, or 10% by mass or more and 15% by mass or less.

[0107] (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.

[0108] 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 (anode lead frame) 4 and a cathode lead terminal (cathode lead frame) 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.

[0109] The capacitor element 2 comprises an anode portion 6, a dielectric layer 7 covering the anode portion 6, and a cathode portion 8 covering the dielectric layer 7.

[0110] The anode section 6 comprises an anode body 6a and an anode wire 6b. A portion of the anode wire 6b is embedded within the anode body 6a, while the remaining portion protrudes outward from the outer surface of the anode body 6a. A portion of the anode lead frame 4 is joined to this protruding portion of the anode wire 6b by welding or other means, and is electrically connected to it.

[0111] The cathode 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 6a is a porous sintered body (for example, a sintered body made of tantalum particles sintered together) obtained by sintering a molded body of valve-acting metal particles such as Ta. The entire anode 6a corresponds to a porous portion. The solid electrolyte layer 9 contains S element and, in a porous anode 6a having a dielectric layer 7, has a first portion filled in the voids of the porous portion and a second portion that protrudes from the main surface of the anode 6. The second portion is divided into portion A on the side of the first portion and portion B on the opposite side from the first portion.

[0112] The cathode lead layer 10 may consist of a carbon particle-containing layer (first layer) covering at least a portion of the solid electrolyte layer 9, and a metal-containing layer (second layer) covering at least a portion of the first layer. Such a cathode lead 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 lead 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). The cathode lead terminal 5 is electrically connected to the cathode portion 8 via an adhesive layer 14 formed of a conductive adhesive.

[0113] [Examples] The solid electrolytic capacitor or its manufacturing method according to the present disclosure will be described below in detail based on examples and comparative examples, but the solid electrolytic capacitor or its manufacturing method according to the present disclosure is not limited to the following examples.

[0114] (Solid electrolytic capacitor E1) A solid electrolytic capacitor E1 was fabricated according to the following procedure, and its characteristics were evaluated.

[0115] (1) Preparation of the anode body (anode section) (first step) An anode section was prepared, comprising a tantalum sintered body (porous body) as the anode body and an anode wire in which part of the anode body is embedded.

[0116] (2) Formation of dielectric layer (second step) The anode was immersed in a chemical conversion solution and anodized by applying a DC voltage of 70 V for 20 minutes. In this way, a dielectric layer containing tantalum oxide was formed on the surface of the anode.

[0117] (3) First silane treatment step The anode portion on which the dielectric layer of the anode 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.

[0118] (4) Formation of pre-coat layer (third step) The anode portion having the pre-coated dielectric layer obtained in (3) above was immersed in a liquid mixture containing a self-doped conductive polymer and water as a solvent, and then removed and dried to form a pre-coat layer. As the self-doped 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 to the ethylenedioxy portion of EDOT was used. The concentration of the self-doped conductive polymer in the liquid mixture was 10% by mass.

[0119] (5) Second Silane Treatment Step The anode portion having the pre-coated dielectric layer obtained in (4) above was immersed in a solution containing 3-glycidoxypropyltriethoxysilane at a concentration of 1.0% by mass (solvent: IPA), removed, and dried. Drying was carried out at 130°C for 30 minutes.

[0120] (6) Formation of conductive polymer by electrolytic polymerization (Fourth step) 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 using the obtained polymerization solution in a three-electrode system. More specifically, the anode portion of the anode body having the silane-treated precoat layer obtained in (5) above, the counter electrode, and the reference electrode (silver / silver chloride reference electrode) were immersed in the polymerization solution. A voltage was applied to the anode body so that the potential of the anode body relative to the reference electrode was 1.1V, and electrolytic polymerization was carried out at 25°C to form a conductive polymer.

[0121] (7) Formation of cathode extraction layer (5th step) The anode portion of the anode section, on which the conductive polymer 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 (1st layer) on the surface of at least 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. Alternatively, drying may be carried out at a temperature of 100°C to 200°C for a time of 10 to 40 minutes.

[0122] 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). The heating may also be performed at a temperature of 150°C to 220°C. In this way, a cathode extraction layer composed of the first and second layers was formed, and a cathode portion containing a conductive polymer and the cathode extraction layer was formed. A capacitor element was fabricated in the manner described above.

[0123] (8) Assembly of the solid electrolytic capacitor The cathode portion of the capacitor element obtained in (7) above and one end of the cathode lead terminal were joined with an adhesive layer of conductive adhesive. One end of the anode wire protruding from the capacitor element and one end of the anode lead terminal were joined by laser welding.

[0124] Next, a resin casing made of insulating resin was 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 were extended from the resin casing. In this way, the solid electrolytic capacitor E1 was completed. A total of 20 solid electrolytic capacitors E1 were manufactured in the same manner as described above.

[0125] (Solid electrolytic capacitor E2) Except for not performing the second silane treatment step, a total of 20 solid electrolytic capacitors E2 were manufactured in the same manner as solid electrolytic capacitor E1.

[0126] (Solid electrolytic capacitor E3) A total of 20 solid electrolytic capacitors E3 were manufactured in the same manner as solid electrolytic capacitor E1, except that the first silane treatment step was omitted.

[0127] (Solid electrolytic capacitor C1) A total of 20 solid electrolytic capacitors C1 were manufactured in the same manner as solid electrolytic capacitor E1, except that the first and second silane treatment steps were omitted.

[0128] (Evaluation) For the solid electrolytic capacitors obtained in the examples and comparative examples, the initial characteristics, specifically the initial capacitance and initial ESR, were measured using the following procedure.

[0129] Under conditions of 20°C, the initial capacitance (μF) at 120 Hz and the initial ESR (mΩ) at 100 kHz of each solid electrolytic capacitor were measured using a four-terminal LCR meter. The initial capacitance and ESR were then measured for 20 solid electrolytic capacitors, and the average values ​​were calculated. The capacitance and ESR of solid electrolytic capacitors E1 to E3 are shown as relative values, with the average value of solid electrolytic capacitor C1 set to 100.

[0130] The evaluation results are shown in Table 1. Solid electrolytic capacitors E1 to E3 are solid electrolytic capacitors according to this disclosure, and solid electrolytic capacitor C1 is a comparative example.

[0131]

[0132] As shown in Table 1, the solid electrolytic capacitors E1 to E3 of this disclosure, which have undergone at least one of the first silane treatment step and the second silane treatment step, show improved initial capacitance and reduced initial ESR compared to solid electrolytic capacitor C1. The effect of improving capacitance and reducing ESR by performing the first silane treatment step is greater than that of performing the second silane treatment step (comparison between E2 and E3). Furthermore, by performing both the first and second silane treatment steps, a very large capacitance can be obtained while keeping the ESR low (comparison between E1 and C1, E2 and E3).

[0133] The above example uses a self-doped conductive polymer as the precoat. On the other hand, when precoating is performed by in-situ polymerization using chemical polymerization, the precoat layer contains a large amount of low-molecular-weight components. In this disclosure, even in such cases, the initial properties are improved by silane treatment. From the viewpoint of ensuring a higher improvement in initial properties, it is preferable to use a self-doped conductive polymer as the precoat.

[0134] Furthermore, when electrolytic polymerization was carried out using EDOT and aromatic sulfonic acid as a dopant, it was difficult to make it function as a solid electrolytic capacitor, even under the same conditions as electrolytic capacitors E1 to E3. This is thought to be due to the low film-forming ability of the conductive polymer.

[0135] 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.

[0136] According to this disclosure, a solid electrolytic capacitor with excellent initial characteristics (such as capacitance and ESR) can be obtained. Therefore, the solid electrolytic capacitor and its manufacturing method according to this disclosure can be used in a variety of applications. However, the applications of the solid electrolytic capacitor and its manufacturing method are not limited to these.

[0137] 1: Solid electrolytic capacitor 2: Capacitor element 3: Resin casing 4: Anode lead terminal (anode lead frame) 5: Cathode lead terminal (cathode lead frame) 6: Anode section 6a: Anode body 6b: Anode wire 7: Dielectric layer 8: Cathode section 9: Solid electrolyte layer 10: Cathode lead layer 14: Adhesive layer

Claims

1. A method for manufacturing a solid electrolytic capacitor, comprising: a first step of preparing an anode; a second step of forming a dielectric layer on at least a portion of the surface of the anode; a third step of pre-coating a conductive material on the surface of the dielectric layer; and a fourth step of immersing the anode having the pre-coated dielectric layer in a polymerization solution to perform electrolytic polymerization and form a conductive polymer, wherein the polymerization solution comprises a thiophene compound and a polymer dopant, and the manufacturing method further comprises at least one of a first silane treatment step between the second step and the third step, in which the anode having the dielectric layer is treated with a first silane compound, and a second silane treatment step between the third step and the fourth step, in which the anode having the pre-coated dielectric layer is treated with a second silane compound.

2. A method for manufacturing a solid electrolytic capacitor according to claim 1, comprising at least the first silane treatment step.

3. A method for manufacturing a solid electrolytic capacitor according to claim 1 or 2, comprising both the first silane treatment step and the second silane treatment step.

4. The method for manufacturing a solid electrolytic capacitor according to claim 1 or 2, wherein the conductive material includes a self-doped conductive polymer.

5. The method for producing a solid electrolytic capacitor according to claim 1 or 2, wherein the polymer dopant comprises a plurality of sulfonic acid groups.

6. A method for manufacturing a solid electrolytic capacitor according to claim 1 or 2, wherein the solid electrolytic capacitor comprises an anode portion having an anode body and an anode wire in which a portion is embedded in the anode body, and the anode body is a molded body of particles containing a valve-acting metal, or a sintered body of the molded body.

7. A solid electrolytic capacitor comprising: an anode having a dielectric layer on at least a portion of its surface; a conductive material covering at least a portion of the surface of the dielectric layer; and a conductive polymer formed by electrolytic polymerization to cover at least a portion of the surface of the conductive material, wherein the conductive polymer comprises a conjugated polymer containing monomer units corresponding to a thiophene compound and a polymer dopant, and a silane compound is present between the dielectric layer and the conductive material, and between the conductive material and the conductive polymer.

8. The solid electrolytic capacitor according to claim 7, wherein at least the silane compound is present between the dielectric layer and the conductive material.

9. The solid electrolytic capacitor according to claim 7 or 8, wherein the conductive material comprises a self-doped conductive polymer.

10. The solid electrolytic capacitor according to claim 7 or 8, comprising an anode portion having the anode body and an anode wire partially embedded in the anode body, wherein the anode body is a molded body of particles containing a valve-acting metal, or a sintered body of the molded body.

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