Solid electrolytic capacitor and method for manufacturing the same

Abstract

The present invention includes at least one solid-electrolyte capacitor element that includes: a sheet-shaped anode body having a porous section on the surface; a dielectric layer that covers at least a part of the porous section; and a cathode section that covers at least a part of the dielectric layer. The cathode section includes a solid-electrolyte layer that covers at least a part of the dielectric layer. The solid-electrolyte layer includes: a first layer that includes a first electroconductive polymer covering at least a part of the dielectric layer; and a second layer that includes a second electroconductive polymer covering at least a part of the first layer. The first layer has an inner layer filled into the voids of the porous section having the dielectric layer, and an outer layer protruding from the main surface of the porous section having the dielectric layer. A solid-electrolyte capacitor is provided that uses a solid-electrolyte capacitor having a thickness Tm of the outer layer protruding from the main surface of 1 µm or more, whereby it is possible to mitigate reduction of capacitance when repeatedly used.

Description

Technical Field

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

Background Art

[0002] A solid electrolytic capacitor includes a solid electrolytic capacitor element, a resin exterior or a case that seals the solid electrolytic capacitor element, and an external electrode that is electrically connected to the solid electrolytic capacitor element. The solid electrolytic capacitor element includes an anode body, a dielectric layer formed on the surface of the anode body, and a cathode portion that covers at least a part of the dielectric layer. The cathode portion includes a solid electrolyte layer containing a conductive polymer that covers at least a part of the dielectric layer.

[0003] The solid electrolyte layer may be composed of a plurality of layers. For example, Patent Document 1 discloses a solid electrolytic capacitor including an anode conductor made of a valve action metal of a porous body, a dielectric layer formed on the surface of the anode conductor, and a solid electrolyte layer composed of a conductive polymer layer formed on the surface of the dielectric layer. The solid electrolyte layer is composed of a first solid electrolyte layer formed on the surface of the dielectric layer and a second solid electrolyte layer formed on the surface of the first solid electrolyte layer, and at least one continuous or discontinuous layer made of an amine compound exists between the first solid electrolyte layer and the second solid electrolyte layer and within the second solid electrolyte layer.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

[0005] The solid electrolytic capacitor according to the first aspect of the present disclosure includes a sheet-like anode body having a porous portion on the surface layer, a dielectric layer that covers at least a part of the porous portion, A cathode portion covering at least a part of the dielectric layer, It includes at least one solid electrolytic capacitor element, The cathode portion includes a solid electrolyte layer covering at least a portion of the dielectric layer, The solid electrolyte layer includes a first layer containing a first conductive polymer covering at least a portion of the dielectric layer, and a second layer containing a second conductive polymer covering at least a portion of the first layer. The first layer comprises an inner layer filled in the voids of the porous portion and an outer layer disposed outside the main surface of the porous portion. The thickness Tm of the outer layer is 1.3 μm or more. Furthermore, the outer layer is positioned outside the main surface and the end face of the porous portion, and when the thickness of the outer layer positioned outside the end face is Te, the ratio of the thickness Tm to the thickness Te is 13 or more.

[0006] A method for manufacturing a solid electrolytic capacitor according to the second aspect of this disclosure comprises a sheet-like anode having a porous portion on its surface, A dielectric layer covering at least a portion of the porous portion, A cathode portion covering at least a part of the dielectric layer, A method for manufacturing a solid electrolytic capacitor, comprising at least one solid electrolytic capacitor element including, The cathode portion includes a solid electrolyte layer covering at least a portion of the dielectric layer, The solid electrolyte layer includes a first layer containing a first conductive polymer covering at least a portion of the dielectric layer, and a second layer containing a second conductive polymer covering at least a portion of the first layer. before With one main surface of the porous portion facing vertically upward, the treatment solution containing the first conductive polymer is applied to the main surface, and then ,before The process includes the step of applying the treatment liquid to the other main surface of the porous portion with the other main surface facing vertically upward, and drying it to form the first layer.

[0007] According to this disclosure, it is possible to provide a solid electrolytic capacitor and a method for manufacturing the same that can reduce the decrease in capacitance when used repeatedly. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic cross-sectional view of a solid electrolytic capacitor according to one embodiment of the present disclosure. [Figure 2] Figure 2 is an enlarged view of the region enclosed by the solid line α in Figure 1. [Modes for carrying out the invention]

[0009] Before describing the embodiments, the problems of the prior art are briefly outlined below. The solid electrolyte layer of a solid electrolytic capacitor expands or contracts due to charging, discharging, or heat, which easily reduces its adhesion to the dielectric layer and makes delamination more likely. In particular, when the solid electrolyte layer consists of multiple layers, the degree of expansion or contraction differs among the layers, which reduces adhesion between the layers as well, making delamination more likely.

[0010] A solid electrolyte layer can be formed, for example, by applying a processing solution containing a conductive polymer to an anode body including a porous portion having a dielectric layer. When forming a layer (first layer) containing a conductive polymer (first conductive polymer) that covers at least a portion of the dielectric layer using such a processing solution, a method of immersing the anode body including the porous portion having a dielectric layer in the processing solution is usually employed from the viewpoint of ensuring high productivity. However, in the case of immersion, the amount of processing solution adhering to the porous portion is small, so the first layer is formed in a state where it is filled in the voids (sometimes called pits) of the porous portion, and hardly formed on the main surface of the porous portion. In this state, even if a layer (second layer) containing a conductive polymer (second conductive polymer) is formed to cover at least a portion of the first layer, there are few contact points between the first layer and the second layer. Therefore, when each layer expands or contracts due to repeated use or exposure to high temperatures of the solid electrolytic capacitor, delamination is likely to occur because sufficient adhesion between the layers cannot be maintained. In addition, the dielectric layer and the first layer may delaminate due to the expansion or contraction of the first layer. The second layer may be formed on the surface of the dielectric layer that is not covered by the first layer. In such conditions, the expansion and contraction of the second layer may cause delamination between the dielectric layer and the second layer. In these cases, it is difficult to ensure sufficient adhesion between the dielectric layer and the solid electrolyte layer. When delamination occurs between the dielectric layer and the solid electrolyte layer, or between the layers constituting the solid electrolyte layer, the capacitor performance deteriorates, such as a decrease in capacitance or an increase in equivalent series resistance (ESR).

[0011] In view of the above, in the solid electrolytic capacitor of this disclosure, the solid electrolyte layer includes a first layer and a second layer, the first layer having an inner layer filled in the voids of a porous portion having a dielectric layer and an outer layer disposed on the outside of the main surface of the porous portion having a dielectric layer, and the thickness Tm of the outer layer disposed on the outside of the main surface. is 1.3μ It is m or greater.

[0012] The first layer as described above can be formed by applying a treatment liquid (first treatment liquid) containing a first conductive polymer to one main surface of a porous portion having a dielectric layer with the one main surface facing vertically upward, and then applying the first treatment liquid to the other main surface with the other main surface facing vertically upward and drying it.

[0013] By applying the treatment liquid with the main surface of the porous portion having the dielectric layer facing vertically upward, unlike the case of conventional immersion, while filling the voids in the porous portion with the first conductive polymer, the amount of the first treatment liquid applied on the main surface can be increased. Since a large amount of the first conductive polymer can be adhered to the main surface, the thickness Tm 1.3μ of the outer layer disposed outside the main surface can be increased to m or more. Since the contact points between the first layer and the second layer can be increased, the adhesion between the first layer and the second layer is improved. Also, since the voids are filled with the first conductive polymer and a large amount of the first conductive polymer adheres to the porous portion having the dielectric layer, the adhesion between the dielectric layer and the first layer is improved. Therefore, even when the solid electrolytic capacitor is repeatedly used and the layers constituting the solid electrolyte layer repeatedly expand and contract, the delamination between the layers is reduced, and the delamination between the dielectric layer and the solid electrolyte layer is reduced. As a result, the decrease in capacitance is reduced. Also, an increase in ESR can be reduced. Since excellent capacitor performance is maintained even when the solid electrolytic capacitor is repeatedly used, the reliability of the solid electrolytic capacitor can be enhanced.

[0014] By improving the adhesion between the first layer and the second layer and between the dielectric layer and the solid electrolyte layer, even when the solid electrolytic capacitor is exposed to high temperature and the layers constituting the solid electrolyte layer expand or contract, the delamination between the layers is reduced, and the delamination between the dielectric layer and the solid electrolyte layer is reduced. Therefore, also in this case, the decrease in capacitance can be reduced and the increase in ESR can be reduced. Thus, since the solid electrolytic capacitor exhibits excellent heat resistance, from this viewpoint as well, the reliability of the solid electrolytic capacitor can be enhanced.

[0015] The sheet-shaped anode body has a pair of main surfaces that occupy most of the surface of the anode body and end surfaces located at the ends of the main surfaces. The main surfaces and the end surfaces form the sheet-shaped outer shape of the anode body. The sheet-shaped anode body has a porous portion in its surface layer. The solid electrolyte layer is formed at least in a portion where the porous portion of the anode body is formed. Among the solid electrolyte layers, the first layer that covers at least a part of the dielectric layer is divided into an inner layer that is a portion existing inside the main surface (or end surface) with the main surface (or end surface) of the porous portion where the dielectric layer is formed as a boundary, and an outer layer that is a portion protruding outward from the main surface (or end surface). The inner layer is in a state of being filled in the voids of the porous portion where the dielectric layer is formed.

[0016] In the step of forming the first layer, the state in which the main surface of the porous portion having the dielectric layer faces vertically upward means that the main surface of the porous portion having the dielectric layer to which the first treatment liquid is applied faces the upper side in the vertical direction. It is not necessarily required that the main surface is perpendicular to the vertical direction, but from the viewpoint of equalizing the amount of the first treatment liquid held on the entire main surface, when the first treatment liquid is applied, it is preferable that the main surface is in a state perpendicular to the vertical direction or the main surface is at 80° or more and 100° or less with respect to the vertical direction.

[0017] Hereinafter, the solid electrolytic capacitor and its manufacturing method of the present disclosure will be described more specifically with reference to the drawings as necessary.

[0018] [Solid electrolytic capacitor] The solid electrolytic capacitor element included in the solid electrolytic capacitor includes a sheet-shaped anode body having a porous portion in its surface layer, a dielectric layer covering at least a part of the porous portion, and a cathode portion covering at least a part of the dielectric layer. Hereinafter, the solid electrolytic capacitor element may be simply referred to as a capacitor element.

[0019] (Anode body) The anode body may include valve metals, alloys containing valve metals, and compounds containing valve metals. These materials may be used individually or in combination of two or more. As valve metals, aluminum, tantalum, niobium, and titanium are preferably used.

[0020] The anode body is sheet-shaped. This includes foil-shaped and plate-shaped forms as well.

[0021] The anode body has an anode extraction portion and a cathode forming portion. A cathode portion containing a solid electrolyte layer is formed on the surface of the cathode forming portion of the anode body.

[0022] The anode body has a porous portion on its surface. The porous portion may be formed not only on the surface of the anode body but also on parts other than the surface. The anode body may have the porous portion on the surface of, for example, at least a part of the surface of the cathode forming portion, or on the surface of the entire cathode forming portion. The porous portion may also be formed on the surface of the anode extraction portion. An anode body having a porous portion on its surface is formed, for example, by roughening the surface of a substrate containing a valve metal (specifically, a sheet-like substrate). An anode body having a porous portion on the surface of the cathode forming portion is formed, for example, by roughening the surface of the portion of the substrate corresponding to the cathode forming portion. Roughening can be performed, for example, by etching (e.g., electrolytic etching).

[0023] (Dielectric layer) The dielectric layer is an insulating layer that functions as a dielectric. The dielectric layer is formed by anodizing the valve metal on the surface of the anode body through chemical conversion treatment or the like. The dielectric layer only needs to be formed to cover at least a portion of the porous portion of the anode body. The dielectric layer is usually formed on the surface of the anode body. Therefore, the dielectric layer is formed along the irregularities on the surface of the anode body and the inner walls of the voids in the porous portion.

[0024] The dielectric layer is formed, for example, on at least a portion of the surface of the cathode forming portion of the anode body. The dielectric layer may also be formed on at least a portion of the surface of the anode extraction portion of the anode body, if necessary.

[0025] The dielectric layer contains an oxide of the valve metal. For example, when tantalum is used as the valve metal, the dielectric layer contains Ta2O5, and when aluminum is used as the valve metal, the dielectric layer contains Al2O3. Note that the dielectric layer is not limited to these examples; it can be formed from any material that functions as a dielectric.

[0026] (Cathode part) The cathode portion includes at least a solid electrolyte layer covering at least a portion of the dielectric layer. The cathode portion is usually formed on the surface of the cathode forming portion of the anode body via the dielectric layer. The cathode portion usually comprises a solid electrolyte layer and a cathode extraction layer covering at least a portion of the solid electrolyte layer. The solid electrolyte layer and the cathode extraction layer will be described below.

[0027] (solid electrolyte layer) The solid electrolyte layer is formed to cover the dielectric layer. The solid electrolyte layer does not necessarily need to cover the entire dielectric layer (entire surface); it is sufficient if it is formed to cover at least a portion of the dielectric layer. The solid electrolyte layer includes a first layer containing a first conductive polymer that covers at least a portion of the dielectric layer, and a second layer containing a second conductive polymer that covers at least a portion of the first layer. If there is a region on the dielectric layer where the first layer is not formed, the second layer may be formed on the dielectric layer in this region. The second layer may be a single layer or may consist of multiple layers.

[0028] Each of the first conductive polymer and the second conductive polymer may, for example, include a conjugated polymer. Each of the first conductive polymer and the second conductive polymer may optionally contain a dopant. Each of the first and second layers may optionally contain additives.

[0029] The first layer has a different composition from at least the layers of the second layer that are in contact with the first layer. "Different composition" includes cases where at least one component selected from the group consisting of conjugated polymers, dopants, and additives contained in each layer is different, or where the content of the components in each layer is different. If the second layer includes multiple layers, the composition of each layer may be different or the same. The layers of the second layer that are not in contact with the first layer may have the same composition as the first layer or a different composition.

[0030] The distinction between the first and second layers can be made, for example, by electron probe microanalyzer (EPMA) analysis of a cross-sectional image. For instance, by performing EPMA analysis at equal intervals on a cross-sectional image of the solid electrolyte layer, the boundary between the first and second layers can be determined from the difference in the wavelength of characteristic X-rays at each measurement point.

[0031] The first layer consists of an inner layer filled in the voids of the porous portion having a dielectric layer, and the main surface and end surface of the porous portion where the dielectric layer is formed. Located on the outside It has an outer layer. The inner layer can improve the adhesion between the first layer and the porous part. The outer layer can improve the adhesion between the first layer and the second layer. As a result, the adhesion between the porous part and the second layer is improved, which can suppress the decrease in capacitance when the solid electrolytic capacitor is used repeatedly or when the solid electrolytic capacitor is exposed to high temperatures.

[0032] The thickness Tm of the outer layer, which is located outside the main surface of the porous part on which the dielectric layer is formed, is , 1.3μThe thickness Tm is m or greater, preferably 2 μm or greater, and may be 2.3 μm or greater, 2.5 μm or greater, or 2.8 μm or greater. Having Tm within this range improves adhesion between the outer layer and the second layer, and suppresses delamination between the first and second layers. Therefore, it is possible to suppress the decrease in capacitance when solid electrolytic capacitors are repeatedly used or exposed to high temperatures. There is no particular upper limit to the thickness Tm. For example, the thickness Tm may be 20 μm or less. When the thickness Tm is within this range, the expansion of the solid electrolyte layer during drying can be reduced, thus further stabilizing the capacitor performance.

[0033] The first layer is formed as described above by applying a treatment solution containing the first conductive polymer to the main surface of the porous portion having the dielectric layer, with the main surface facing vertically upward, and then drying it. Located on the outside Compared to the thickness Tm of the outer layer, the end face Located on the outside The outer layer thickness Te is small. Because the thickness Te is smaller than the thickness Tm, even if a large amount of treatment liquid is applied to the main surface, gas can easily escape from the edges. This makes it easier to fill the inside of the voids with the treatment liquid, further improving the adhesion between the porous part and the first layer.

[0034] The ratio of thickness Tm to thickness Te (=Tm / Te) is 13 or less. It is above, The ratio Tm / Te may be 15 or greater, or 20 or greater. When the ratio Tm / Te is within this range, higher adhesion between the porous portion and the first layer is more easily obtained. There is no particular upper limit to the ratio Tm / Te. The thickness Te may be, for example, 0 μm or greater than 0 μm. The thickness Te may be, for example, 0.5 μm or less, or 0.1 μm or less. These lower and upper limits can be combined arbitrarily.

[0035] Thickness Tm and thickness Te are the average thickness of the outer layer of the first layer measured in a cross-sectional image of the solid electrolyte layer at a predetermined location in the capacitor element. The average thickness of the outer layer is the average value of the thickness of the outer layer measured on the main surface or end surface at any multiple locations. The thickness of the outer layer is measured using the roughness curve of the main surface or end surface of the porous portion where the dielectric layer is formed as a reference of 0 mm thickness. The cross-sectional image of the solid electrolyte layer is acquired, for example, by a scanning electron microscope, for regions including at least the interface between the porous portion and the first layer and the interface between the first layer and the second layer. The roughness curve showing the main surface or end surface of the porous portion is derived by image analysis of the acquired cross-sectional image. The roughness curve is specified in JIS B 0601:2013. The measurement locations for the outer layer thickness are, for example, 10 locations for the outer layer thickness on the main surface, and for example, 4 locations for the outer layer thickness on the end surface.

[0036] To measure the thickness Tm or Te, a sample (Sample A) obtained by the following procedure can be used. First, a solid electrolytic capacitor or capacitor element is embedded in a curable resin and the curable resin is cured. By polishing or cross-section polishing the cured material, a cross section parallel to the thickness direction of the solid electrolyte layer and perpendicular to the length direction of the capacitor element is exposed. The cross section is one that passes through the center of the solid electrolyte layer in a direction parallel to the length direction of the capacitor element. In this way, a sample for measurement (Sample A) is obtained.

[0037] The direction from the anode extraction end of the anode body to the cathode formation end is referred to as the length direction of the anode body or capacitor element. The length of the solid electrolyte layer is the length in the direction parallel to the length direction of the capacitor element. The direction from the anode extraction end of the anode body to the cathode formation end is the direction parallel to the straight line connecting the center of the anode extraction end face of the anode body and the center of the cathode formation end face of the anode body.

[0038] Examples of conjugated polymers included in the first and second conductive polymers include known conjugated polymers used in solid electrolytic capacitors, such as π-conjugated polymers. Examples of conjugated polymers include polymers with polypyrrole, polythiophene, polyaniline, polyfuran, polyacetylene, polyphenylene, polyphenylenevinylene, polyacene, and polythiophenevinylene as their basic skeletons. Of these, polymers with polypyrrole, polythiophene, or polyaniline as their basic skeletons are preferred. The polymer only needs to contain at least one monomer unit that constitutes the basic skeleton. Monomer units include monomer units having substituents. The above polymers include, for example, homopolymers and copolymers of two or more monomers. For example, polythiophene includes poly(3,4-ethylenedioxythiophene).

[0039] Each of the first conductive polymer and the second conductive polymer may contain one type of conjugated polymer, or a combination of two or more types.

[0040] Preferably, each conductive polymer contains a conjugated polymer that includes monomer units corresponding to the thiophene compound. Such conjugated polymers expand and contract greatly during charging and discharging, making them prone to delamination between the porous portion and the first layer, or between the first layer and the second layer. However, according to this disclosure, since the first layer has an inner layer and the outer layer of the first layer is thick, high adhesion can be obtained, so even when such a conjugated polymer is used, delamination between the porous portion and the first layer, and between the first layer and the second layer can be suppressed. Therefore, solid electrolytic capacitors can be repeatedly... Used This further suppresses the decrease in capacitance in certain cases. It also ensures high voltage resistance.

[0041] Examples of thiophene compounds include compounds having a thiophene ring and capable of forming a repeating structure of the corresponding monomer unit. Thiophene compounds may, for example, have substituents at least one of the 3rd and 4th positions of the thiophene ring. The substituent at the 3rd position and the substituent at the 4th position may be linked to form a ring fused to the thiophene ring. Examples of thiophene compounds include thiophenes having 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 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 While alkyl groups are preferred, the polymer is not limited to these. In particular, a conjugated polymer (such as PEDOT) containing monomer units corresponding to at least a 3,4-ethylenedioxythiophene compound (such as 3,4-ethylenedioxythiophene (EDOT)) is preferred. The conjugated polymer containing at least a monomer unit corresponding to EDOT may contain only the monomer unit corresponding to EDOT, or it may contain monomer units corresponding to thiophene compounds other than EDOT in addition to the monomer unit.

[0042] The weight-average molecular weight (Mw) of a conjugated polymer is not particularly limited, but is, for example, between 1,000 and 1,000,000.

[0043] In this specification, the weight-average molecular weight (Mw) is the polystyrene-converted value measured by gel permeation chromatography (GPC). GPC is typically measured using a polystyrene gel column and water / methanol (volume ratio 8 / 2) as the mobile phase.

[0044] Each of the first conductive polymer and the second conductive polymer may further contain a dopant. Examples of dopants include at least one selected from the group consisting of anions and polyanions.

[0045] Examples of anions include sulfate ions, nitrate ions, phosphate ions, borate ions, organic sulfonate ions, and carboxylate ions. Examples of dopants that produce sulfonate ions include benzenesulfonic acid, p-toluenesulfonic acid, and naphthalenesulfonic acid.

[0046] Examples of polyanions include high-molecular-weight polysulfonic acids and high-molecular-weight polycarboxylic acids. Examples of high-molecular-weight polysulfonic acids include polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallyl sulfonic acid, polyacrylic sulfonic acid, polymethacrylic sulfonic acid, or derivatives thereof. Examples of high-molecular-weight polycarboxylic acids include polyacrylic acid, polymethacrylic acid, or derivatives thereof. Derivatives include substituted products with substituents, partially esterified products, copolymers containing sulfonic acid units or carboxylic acid units and other monomer units. Polyanions also include polyester sulfonic acid and phenol sulfonic acid novolac resins. However, polyanions are not limited to these.

[0047] From the viewpoint of easily suppressing dedoping, it is advantageous to use dopants with relatively high electron-withdrawing properties (e.g., sulfonate ions, polymer-type polysulfonic acid). From the viewpoint of easily ensuring high conductivity of the solid electrolyte layer, it is also preferable to use sulfonate ions or polymer-type polysulfonic acid as dopants.

[0048] Polymer-type dopants generally have large molecular sizes and are difficult to fill into the voids of porous parts. However, according to this disclosure, the first layer is formed by applying a treatment solution containing the first conductive polymer to the main surface of the porous part having the dielectric layer, with the main surface facing vertically upward, and then drying it, as described above. Therefore, even if the first conductive polymer contains a polymer-type dopant, a relatively large amount of the first conductive polymer can be filled into the voids of the porous part, ensuring high adhesion between the porous part and the first layer. Furthermore, because the polymer-type dopant is included in the first layer, even when the solid electrolytic capacitor is exposed to high temperatures, the degradation of the first conductive polymer is suppressed, and high heat resistance is obtained.

[0049] Anions and polyanions may each be present in the form of salts in each layer constituting the solid electrolyte. In each layer, each anion and polyanion may form a complex with a conjugated polymer. For example, sulfonic acid groups may exist in each layer in a free form (-SO3H) and anionic form (-SO3H). - They may be present in the form of a free form (-COOH) or a salt, or in a form bonded to or interacting with a conjugated polymer. In this specification, all of these forms of sulfonic acid groups may be simply referred to as "sulfonic acid groups". Similarly, in each layer, the carboxyl group may be present in the free form (-COOH), the anionic form (-COOH) - They may be present in the form of carboxyl groups, or as salts, or in a form bonded to or interacting with a conjugated polymer system. In this specification, all of these forms of carboxyl groups may be simply referred to as "carboxyl groups."

[0050] The amount of dopant contained in each layer constituting the solid electrolyte layer is, for example, 10 to 1000 parts by mass per 100 parts by mass of the conjugated polymer, and may also be 20 to 500 parts by mass or 50 to 200 parts by mass.

[0051] Each layer constituting the solid electrolyte layer may contain additives as needed. Examples of additives include known additives added to the solid electrolyte layer (e.g., coupling agents, silane compounds), known conductive materials other than conductive polymers, and water-soluble polymers. Each layer constituting the solid electrolyte layer may contain one of these additives, or a combination of two or more.

[0052] Examples of conductive materials used as additives include at least one selected from the group consisting of conductive inorganic materials such as manganese dioxide and TCNQ complex salts.

[0053] Examples of water-soluble polymers include water-soluble polymer compounds having hydrophilic groups in their main chain or side chains. Polymer-type dopants are also included in water-soluble polymers. Examples of hydrophilic groups in water-soluble polymers include polyoxyalkylene chains, hydroxyl groups, and acidic groups (carboxyl groups, sulfonic acid groups, etc.). As water-soluble polymers, components with lower electron-withdrawing properties than dopants are usually used. Examples of such water-soluble polymers include water-soluble polymers having at least one selected from the group consisting of carboxyl groups, hydroxyl groups, and polyoxyalkylene chains. Examples of water-soluble polymers include at least one selected from the group consisting of polyalkylene glycol compounds, water-soluble polyurethanes, water-soluble polyamides, water-soluble polyimides, water-soluble acrylic resins, and polyvinyl alcohols. Using water-soluble polymers is advantageous in reducing leakage current and improving pressure resistance because it is easier to reduce variations in the thickness of the solid electrolyte layer. From this viewpoint, it is preferable that the second layer contains a water-soluble polymer. The first layer may or may not contain a water-soluble polymer.

[0054] Each of the carboxyl groups and sulfonic acid groups of a water-soluble polymer may be present in each layer constituting the solid electrolyte layer in a free form, anionic form, or salt form, as in the case of a dopant. Furthermore, some of each of the carboxyl groups and sulfonic acid groups may be present in each layer in a form bonded to or interacting with a conjugated polymer. In this specification, all of these forms of carboxyl groups may be simply referred to as "carboxyl groups," and all of these forms of sulfonic acid groups may be simply referred to as "sulfonic acid groups."

[0055] A layer to enhance adhesion may be interposed between the dielectric layer and the first layer (or solid electrolyte layer) as needed. Between the first layer and the second layer, and between each layer constituting the second layer, at least one selected from the group consisting of surface modifiers (such as surfactants), cationic agents, and anionic agents may be interposed as needed.

[0056] The average of the combined thickness of the outer layer of the first layer and the second layer is, for example, 5 μm or more and 20 μm or less, and may be 10 μm or more and 15 μm or less. The combined thickness of the outer layer of the first layer and the second layer is the thickness of the portion that extends outward from the main surface of the anode body having the dielectric layer of the solid electrolyte layer. The average of this combined thickness is determined in the same manner as for the thickness Tm of the outer layer.

[0057] (Formation of a solid electrolyte layer) When manufacturing the solid electrolytic capacitor of this disclosure, the first layer is formed using a processing solution (first processing solution) containing the first conductive polymer as described above. In the process of forming the first layer, first, the first processing solution is applied to one main surface of the porous portion having the dielectric layer, with one main surface facing vertically upward. Next, the other main surface of the porous portion having the dielectric layer is faced vertically upward, and the first processing solution is applied to the other main surface in this state. Then, the coating film of the formed first processing solution is dried. This forms the inner and outer layers on both main surface sides. By applying the first processing solution with the main surface facing vertically upward, a large amount of the first conductive polymer adheres to the anode, thereby improving the adhesion between the dielectric layer and the first layer, and the adhesion between the first layer and the second layer. On the end face side of the anode having the dielectric layer, the first processing solution applied to the main surface wraps around through the surface and voids of the porous portion, and the first layer is formed when the coating film dries in this state. Therefore, the thickness Te of the outer layer formed on the end face of the anode body tends to be smaller than the thickness Tm of the outer layer on the main surface.

[0058] In the process of forming the first layer, a large amount of the first conductive polymer can be attached to the anode without repeatedly applying the first treatment solution to the same main surface and drying it. Generally, when forming a solid electrolyte layer by immersing the anode in a treatment solution containing a conductive polymer, the conductive polymer attached to the anode expands as the immersion and drying are repeated, resulting in significant variations in the thickness of the formed solid electrolyte layer, which easily affects capacitor performance. In the manufacturing of solid electrolytic capacitors according to this disclosure, the number of drying cycles in the process of forming the first layer can be reduced compared to conventional methods, thereby reducing variations in the thickness of the solid electrolyte layer and ensuring excellent capacitor performance. For example, a large amount of the first conductive polymer can be attached to the anode even if the number of times the first treatment solution is applied and dried for each main surface is, for example, two times or less, or even just once. After applying the first treatment solution to one main surface, the coating film of the first treatment solution formed on one main surface may be dried before applying the first treatment solution to the other main surface, but it is preferable not to dry it. This is because it reduces the number of drying cycles and further reduces variations in the thickness of the solid electrolyte layer.

[0059] The application of the first treatment solution can be performed with each main surface of the porous portion having the dielectric layer facing vertically upward. The application of the first treatment solution to each main surface may be performed by at least one selected from the group consisting of dropping, dispensing (e.g., spraying, dispensing by a dispenser, etc.), and transfer. Such a method is advantageous in increasing the thickness Tm of the outer layer on the main surface.

[0060] The first treatment solution is prepared by dispersing or dissolving its constituent components in a liquid medium. Examples of constituent components include a first conductive polymer (conjugated polymer, dopant, etc.) and additives. The first treatment solution may also be prepared by polymerizing a precursor of a conjugated polymer (monomer, etc.) in a liquid medium, optionally in the presence of a dopant. For the first conductive polymer and additives, please refer to the description of the first layer (or second layer) above. Generally, when forming a solid electrolyte layer by immersion using a dispersion of conductive polymer, it is difficult to improve the adhesion between the dielectric layer and the solid electrolyte layer because the conductive polymer particles contained in the dispersion do not easily fill the voids in the porous portion. According to this disclosure, even when a dispersion containing the first conductive polymer is used as the first treatment solution, the first treatment solution is applied to the main surface with the main surface facing vertically upward, making it easy to penetrate into the voids in the porous portion and easy to fill the voids with the first conductive polymer. Therefore, the inner layer of the first layer within the void ensures high adhesion between the dielectric layer and the first layer.

[0061] The first treatment solution may contain one type of conjugated polymer, or a combination of two or more types. The first treatment solution may contain one type of dopant, or a combination of two or more types. The first treatment solution may contain one type of additive, or a combination of two or more types.

[0062] Examples of liquid media used in the first treatment solution include water and organic media. The liquid media only needs to be liquid at least at the temperature at which the first treatment solution is applied to the porous part, and may be liquid at room temperature (e.g., 20°C to 35°C). Examples of organic media include aliphatic alcohols, aliphatic ketones (such as acetone), nitriles (such as acetonitrile and benzonitrile), amides (such as N,N-dimethylformamide), and sulfoxides (such as dimethyl sulfoxide). The aliphatic alcohol may be either a monool or a polyol. The first treatment solution may contain one type of liquid media, or a combination of two or more types.

[0063] The concentration of the first conductive polymer in the first processing solution is, for example, 0.5% by mass or more and 5% by mass or less, and may also be 1% by mass or more and 4% by mass or less, or 1% by mass or more and 3.5% by mass or less. This concentration range facilitates the penetration of the first conductive polymer into the porous portion while allowing a large amount of the first conductive polymer to adhere to the first main surface.

[0064] The average particle size of the first conductive polymer in the first processing solution is, for example, 100 nm to 600 nm, and may also be 200 nm to 500 nm. When the average particle size is within this range, it is difficult to fill the pits of the porous portion with the first conductive polymer using the immersion method, but in this disclosure, the packing efficiency of the first conductive polymer into the pits can be improved.

[0065] The average particle diameter of the first conductive polymer is the cumulative 50% particle diameter (median diameter) in the volume-based particle size distribution measured using a dynamic light scattering particle size distribution analyzer for the particles of the first conductive polymer in the first processing solution. For example, the DLS-8000 light scattering photometer manufactured by Otsuka Electronics Co., Ltd. is used as the dynamic light scattering particle size distribution analyzer.

[0066] The application of the first treatment liquid to the porous portion may be carried out under reduced pressure or under increased pressure. In these cases, it is advantageous for the first treatment liquid to quickly penetrate into the voids. If necessary, the application of the first treatment liquid to the porous portion may be carried out under atmospheric pressure.

[0067] Drying after applying the first treatment solution to the main surface may be carried out, for example, under heating or under reduced pressure. The drying temperature and pressure should be determined according to the type of liquid medium contained in the first treatment solution.

[0068] The second layer is formed by treating the anode body (specifically the cathode-forming portion) on which the first layer is formed with a treatment solution (second treatment solution) containing a second conductive polymer or a precursor of a conjugated polymer. For example, the second layer is formed by applying the second treatment solution containing the second conductive polymer to the anode body on which the first layer is formed, and then drying the coating film of the second treatment solution. The application of the second treatment solution to the anode body and drying may be repeated multiple times as needed. Alternatively, the anode body (specifically the cathode-forming portion) on which the first layer is formed may be immersed in the second treatment solution containing a precursor of a conjugated polymer and, optionally, a dopant, and the precursor may be polymerized by chemical polymerization or electropolymerization to form the second layer containing the conjugated polymer and, optionally, a dopant of the second conductive polymer. The polymerized anode body is washed and dried as needed. Polymerization may be performed multiple times as needed.

[0069] In the step of forming the second layer, the anode body on which the first layer has been formed may be brought into contact with the second processing solution so as to cover at least the first layer. For example, the second layer may be formed in the same manner as in the step of forming the first layer, except that the second processing solution is used instead of the first processing solution. Alternatively, the second layer may be formed using the second processing solution by utilizing conventional methods for forming a solid electrolyte layer, such as immersion, injection, or coating (spray coating, printing, etc.). These methods may be combined as needed.

[0070] The second treatment solution is prepared by dissolving or dispersing its components in a liquid medium. Examples of components include conjugated polymers or their precursors, dopants, and additives. For details on each component, please refer to the description of the second layer (or first layer) above.

[0071] The second treatment solution may contain one type of conjugated polymer, or a combination of two or more types.

[0072] Examples of precursors of conjugated polymers include monomers, oligomers, and prepolymers of conjugated polymers. The second treatment solution may contain one precursor or two or more precursors.

[0073] When a second treatment solution containing a conjugated polymer precursor is used, an oxidizing agent is used to polymerize the precursor. The oxidizing agent may be included in the second treatment solution as an additive. Alternatively, the oxidizing agent may be applied to the first layer before or after contacting the anode body, on which the first layer is formed, with the second treatment solution. Such an oxidizing agent may be 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 can be used individually or in combination of two or more.

[0074] The second treatment solution may contain one dopant, or a combination of two or more dopants. The second treatment solution may contain one additive, or a combination of two or more additives.

[0075] (Cathode extraction layer) The cathode extraction layer may be a single-layer structure or a multi-layer structure. Examples of the cathode extraction 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 powder. The cathode extraction layer may include, for example, a layer containing conductive carbon (also called a carbon layer) covering the solid electrolyte layer and a layer containing metal powder or metal foil covering the carbon layer. The cathode extraction layer may consist of a metal foil covering the solid electrolyte layer.

[0076] Examples of conductive carbon include graphite (artificial graphite, natural graphite, etc.). The carbon layer can be formed by immersing an anode body having a solid electrolyte layer in a dispersion containing conductive carbon, or by applying a paste containing conductive carbon to the surface of the solid electrolyte layer. The dispersion and paste can be prepared, for example, by dispersing conductive carbon in an aqueous liquid medium.

[0077] Examples of metal powders include silver particles and silver alloy particles. A layer containing metal powder can be formed, for example, by laminating a paste containing metal powder onto the surface of a base layer (specifically, a carbon layer). The paste is prepared, for example, by mixing metal powder with a resin (binder resin) and, if necessary, a liquid medium. While thermoplastic resins can be used as the resin, it is preferable to use thermosetting resins such as imide resins and epoxy resins.

[0078] The type of metal constituting the metal foil is not particularly limited. Preferably, the metal foil uses 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 provided with a chemical conversion coating, or a coating of a metal different from the metal constituting the metal foil (a dissimilar metal) or a nonmetal. Examples of dissimilar metals include titanium. Examples of nonmetals include carbon (such as conductive carbon). The cathode extraction layer may be composed of a coating of a dissimilar metal or a nonmetal (e.g., conductive carbon) covering the solid electrolyte layer, and a metal foil covering the coating.

[0079] (Separator) When a metal foil is used as the cathode lead layer, a separator may be placed between the metal foil and the anode. The separator is not particularly limited, and may be a nonwoven fabric containing fibers of cellulose, polyethylene terephthalate, vinylon, or polyamide (e.g., aliphatic polyamide, aromatic polyamide such as aramid).

[0080] (others) Solid electrolytic capacitors may be wound-wound, chip-type, or multilayer-type. A solid electrolytic capacitor may contain at least one capacitor element, or it may contain multiple capacitor elements. For example, a solid electrolytic capacitor may comprise a stack of two or more capacitor elements. If a solid electrolytic capacitor contains multiple capacitor elements, each capacitor element may be, for example, wound-wound or multilayer-type. The configuration of the capacitor elements should be selected according to the type of solid electrolytic capacitor.

[0081] In a capacitor element, one end of the cathode lead is electrically connected to the cathode lead-out layer. One end of the anode lead is electrically connected to the anode body. The other end of the anode lead and the other end of the cathode lead are led out from the resin casing or case, respectively. The other ends of each lead exposed from the resin casing or case are used for soldering to the substrate on which the solid electrolytic capacitor is to be mounted. Each lead may be a lead wire or a lead frame.

[0082] The capacitor element is sealed using a resin casing or case. 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 end of the anode lead and the other end of the cathode lead that are drawn out from the capacitor element are exposed from the mold. Alternatively, the capacitor element may be housed in a bottomed case such that the other end of the anode lead and the other end of the cathode lead are located on the opening side of the bottomed case, and a solid electrolytic capacitor may be formed by sealing the opening of the bottomed case with a sealing body.

[0083] Figure 1 is a schematic cross-sectional view of a solid electrolytic capacitor according to one embodiment of the present disclosure. Figure 2 is an enlarged conceptual view of the region enclosed by the solid line α in Figure 1.

[0084] The solid electrolytic capacitor 1 comprises a capacitor element 11, a resin casing 12 that encloses the capacitor element 11, and an anode terminal 13 and a cathode terminal 14 that are exposed to the outside of the resin casing 12, respectively. The capacitor element 11 includes a sheet-like anode body 2 having a porous portion on its surface, a dielectric layer 3 that covers at least a portion of the porous portion of the anode body 2, and a cathode portion 15 that covers at least a portion of the dielectric layer 3. The portion of the anode body 2 where the cathode portion 15 is formed is the cathode forming portion, and the portion where the cathode portion 15 is not formed is the anode lead portion. The anode terminal 13 is electrically connected to the end of the anode body 2 on the anode lead portion side. The cathode terminal 14 is electrically connected to the cathode portion 15. The resin casing 12 has a substantially rectangular parallelepiped shape, and as a result, the solid electrolytic capacitor 1 also has a substantially rectangular parallelepiped shape.

[0085] The anode 2 and the cathode 15 are opposite each other via a dielectric layer 3. The cathode 15 has a solid electrolyte layer 4 covering the dielectric layer 3 and a cathode extraction layer 5 covering the solid electrolyte layer 4. The cathode extraction layer 5 in the illustrated example has a two-layer structure and includes a carbon layer 5a in contact with the solid electrolyte layer 4 and a metal paste layer 5b covering the surface of the carbon layer 5a.

[0086] In the anode lead-out portion of the anode body 2 protruding from the cathode portion 15, an insulating separation portion 16 is formed in the region on the cathode portion 15 side, covering the surface of the anode body 2 in a strip shape, thereby restricting contact between the cathode portion 15 and the anode body 2. The end of the anode body 2 protruding from the cathode portion 15 is electrically connected to one end 13a of the anode terminal 13 by welding or the like. On the other hand, the cathode lead-out layer 5 formed on the outermost layer of the cathode portion 15 is electrically connected to one end 14a of the cathode terminal 14 via a conductive adhesive 17 (for example, a mixture of thermosetting resin and metal particles). The other end 13b of the anode terminal 13 and the other end 14b of the cathode terminal 14 are each led out from different sides of the resin casing 12 and extend in an exposed state to one of the main flat surfaces (the bottom surface in Figure 1). The exposed parts of each terminal on this flat surface are used for soldering to a substrate (not shown) on which the electrolytic capacitor 1 is to be mounted.

[0087] The dielectric layer 3 is formed on a portion of the surface of the conductive material constituting the anode 2. The dielectric layer 3 is formed, for example, by anodizing the surface of the conductive material constituting the anode 2. Therefore, as shown in Figure 2, the dielectric layer 3 is formed along the surface of the porous portion of the anode 2 (including the inner wall surface of the voids).

[0088] The first layer 4a, which contains the first conductive polymer, is formed to cover the dielectric layer 3, and the second layer 4b, which contains the second conductive polymer, is formed to cover the first layer 4a. The first layer 4a consists of an inner layer 104a filled in the voids of the porous portion having the dielectric layer 3, and the main surface Sm or end surface of the porous portion having the dielectric layer 3. Located on the outside It has an outer layer 104b. In this disclosure, the main surface Sm of the porous portion having the dielectric layer 3 Located on the outside Since the thickness of the outer layer 104b can be increased, the adhesion between the dielectric layer 3 and the first layer 4a, and the adhesion between the first layer 4a and the second layer 4b can be improved.

[0089] [Examples] The present invention will be described in detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0090] 《Solid electrolytic capacitor element A1》 The capacitor element 11 (solid electrolytic capacitor element A1) of the solid electrolytic capacitor 1 shown in Figure 1 was fabricated according to the following procedure, and its characteristics were evaluated.

[0091] (1) Preparation of Anode 2 Both surfaces of the aluminum foil substrate (thickness: 100 μm) were roughened by etching. In this way, a sheet-like anode body 2 having a porous surface layer was fabricated.

[0092] (2) Formation of dielectric layer 3 The cathode-forming portion of the anode body 2 was immersed in a chemical conversion solution, and a DC voltage of 70V was applied for 20 minutes. In this way, a dielectric layer 3 containing aluminum oxide was formed on the surface of the porous portion of the anode body 2.

[0093] (3) Formation of the first layer 4a The anode body 2 having the dielectric layer 3 obtained in (2) above was placed on a flat surface with one main surface of the anode body 2 facing vertically upward, and 2 μl of the first treatment solution was dropped onto one main surface of the anode body 2. Next, the anode body 2 was inverted so that the other main surface was facing vertically upward. In this state, 2 μl of the first treatment solution was dropped onto the other main surface of the anode body 2, and it was dried at 120°C for 5 to 10 minutes. In this way, 2 μl of the first treatment solution was dropped onto each side to form a first layer 4a containing the first conductive polymer so as to cover the surface of the dielectric layer 3. As the first treatment solution, an aqueous dispersion containing conductive polymers (poly-3,4-ethylenedioxythiophene (PEDOT) and polystyrene sulfonic acid (PSS)) at a concentration of 2% by mass (average particle size of conductive polymer in the dispersion: 400 nm) was used.

[0094] (4) Formation of the second layer 4b The anode body 2 having the first layer 4a obtained in (3) above was immersed in the second treatment solution, removed, and then dried at 120°C for 10 to 30 minutes. By repeating the immersion in the second treatment solution and drying process alternately two more times, a second layer 4b containing the second conductive polymer was formed so as to cover the surface of the first layer 4a. As the second treatment solution, an aqueous dispersion containing conductive polymers (PEDOT and PSS derivatives) at a concentration of 4% by mass (average particle size of conductive polymers in the dispersion: 600 nm) was used.

[0095] In this way, the solid electrolyte layer 4, including the first layer 4a and the second layer 4b, was formed to cover the surface of the dielectric layer 3.

[0096] (5) Formation of cathode extraction layer 5 The anode body 2 having the solid electrolyte layer 4 obtained in (4) above was immersed in a dispersion of graphite particles dispersed in water, and after being removed from the dispersion, it was dried to form a carbon layer 5a on the surface of at least the second layer 4b. Drying was carried out at 130-180°C for 10-30 minutes.

[0097] Next, a silver paste containing silver particles and a binder resin (epoxy resin) was applied to the surface of the carbon layer 5a, and the binder resin was cured by heating at 150-200°C for 10-60 minutes to form a metal paste layer 5b. In this way, a cathode extraction layer 5 composed of the carbon layer 5a and the metal paste layer 5b was formed. In this manner, a total of 20 capacitor elements A1 were fabricated.

[0098] Solid electrolytic capacitor element A2 In (3) of solid electrolytic capacitor A1, 1 μl of the first treatment solution was dropped onto each side. Capacitor element A2 was fabricated in the same manner as capacitor element A1.

[0099] Solid electrolytic capacitor element A3 In (3) of the solid electrolytic capacitor A1, 0.5 μl of the first treatment solution was dropped onto each side. Capacitor element A3 was fabricated in the same manner as capacitor element A1.

[0100] (6) Evaluation The following evaluations were performed using capacitor elements (A1 to A3).

[0101] (a) Measurement of the thickness of the outer layer 104b In the procedure described above, in the first layer 4a of the solid electrolyte layer 4 in each capacitor element, the main surface of the porous portion Located on the outside Outer layer thickness Tm and end face Located on the outside The thickness Te of the outer layer was determined. Then, the average value was calculated by averaging it across 20 capacitor elements.

[0102] (b) Capacitance and ESR Under 20°C conditions, the initial capacitance (μF) of each capacitor element at a frequency of 120 Hz and the initial ESR (mΩ) at a frequency of 100 kHz were measured using a 4-terminal LCR meter. The average values ​​for all 20 capacitor elements were then calculated.

[0103] Next, an accelerated test was performed in a 70°C environment by applying the rated voltage to the capacitor element for 20 seconds, then stopping the voltage application for 20 seconds, and repeating this process 10,000 times. The capacitance and ESR after the accelerated test were measured in a 20°C environment using the same procedure as for the initial capacitance and ESR, and the average values ​​for 20 capacitor elements were calculated. The capacitance and ESR in the accelerated test were expressed as ratios to the initial capacitance and ESR, respectively, which were set to 100%.

[0104] 《Solid electrolytic capacitor element B1》 The first layer was formed by immersion in the first processing solution. More specifically, the anode body 2 having the dielectric layer 3 was immersed in the first processing solution, removed, and dried at 120°C for 5 to 10 minutes. By repeating the immersion in the first processing solution and drying process alternately two more times, a first layer containing the first conductive polymer was formed so as to cover the dielectric layer 3. Except for these steps, a total of 20 capacitor elements were fabricated and evaluated in the same manner as in Example 1.

[0105] Solid electrolytic capacitor element B2 In (3) of solid electrolytic capacitor A1, 0.2 μl of the first treatment solution was dropped onto each side. Capacitor element B2 was fabricated and evaluated in the same manner as capacitor element A1.

[0106] The evaluation results are shown in Table 1. In Table 1, A1 to A3 are Examples 1 to 3, and B1 and B2 are Comparative Examples 1 and 2.

[0107] [Table 1]

[0108] As shown in Table 1, in Comparative Example 1, where the first layer was formed by immersion, the capacitance after the accelerated test decreased significantly, and the ESR also increased significantly. Similarly, in Comparative Example 2, the capacitance after the accelerated test decreased significantly, and the ESR also increased significantly. In contrast, in Examples 1 to 3, both the decrease in capacitance and the increase in ESR after the accelerated test were kept low compared to Comparative Examples 1 and 2. In Comparative Example 1, almost no outer layer was formed on the main surface of the anode, and there was almost no difference in the thickness of the outer layer between the main surface and the end surface. Similarly, in Comparative Example 2, although the dropping process was the same as in Examples 1 to 3, the amount dropped was small, and similar to Comparative Example 1, almost no outer layer was formed on the main surface of the anode, and there was almost no difference in the thickness of the outer layer between the main surface and the end surface. In contrast, in Examples 1 to 3, the thickness of the outer layer was larger on the main surface of the anode. Furthermore, because the first treatment liquid is applied to the main surface with the main surface facing vertically upward, and because gas can easily escape from the end face, it is thought that a relatively large amount of the first treatment liquid fills the voids in the porous section. As a result, the adhesion between the first and second layers is improved by the outer layer, and the adhesion between the inner and outer layers is also improved. Consequently, the adhesion between the dielectric layer and the solid electrolyte layer is improved, which is thought to have resulted in the excellent capacitor performance described above, even after accelerated testing under harsh conditions. [Industrial applicability]

[0109] According to this disclosure, the decrease in capacitance during repeated use can be reduced, thereby providing a high-quality solid electrolytic capacitor with excellent reliability. Therefore, solid electrolytic capacitors can be used in a variety of applications. [Explanation of symbols]

[0110] 1: Solid electrolytic capacitor, 2: Anode body, 3: Dielectric layer, 4: Solid electrolyte layer, 4a: First layer, 104a: Inner layer, 104b: Outer layer, 4b: Second layer, 5: Cathode lead layer, 5a: Carbon layer, 5b: Metal paste layer, 11: Capacitor element, 12: Resin casing, 13: Anode terminal, 13a: One end of anode terminal, 13b: Other end of anode terminal, 14: Cathode terminal, 14a: One end of cathode terminal, 14b: Other end of cathode terminal, 15: Cathode part, 16: Separation part, 17: Conductive adhesive, Sm: Main surface of anode body

Claims

1. A sheet-like anode body having a porous portion on its surface, A dielectric layer covering at least a portion of the porous portion, A cathode portion covering at least a part of the dielectric layer, It includes at least one solid electrolytic capacitor element, The cathode portion includes a solid electrolyte layer covering at least a portion of the dielectric layer, The solid electrolyte layer comprises a first layer containing a first conductive polymer covering at least a portion of the dielectric layer, and a second layer containing a second conductive polymer covering at least a portion of the first layer, wherein the first layer has an inner layer filled in the voids of the porous portion and an outer layer disposed outside the main surface of the porous portion. The thickness Tm of the outer layer is 1.3 μm or more. The outer layer is positioned outside the main surface and the end surface of the porous portion. A solid electrolytic capacitor in which, when the thickness of the outer layer disposed on the outside of the end face is Te, the ratio of the thickness Tm to the thickness Te is 13 or more.

2. The first conductive polymer includes a conjugated polymer, The solid electrolytic capacitor according to claim 1, wherein the conjugated polymer comprises monomer units corresponding to the thiophene compound.

3. A method for manufacturing a solid electrolytic capacitor as described in claim 1, A sheet-like anode body having a porous portion on its surface, A dielectric layer covering at least a portion of the porous portion, A cathode portion covering at least a part of the dielectric layer, A method for manufacturing a solid electrolytic capacitor, comprising at least one solid electrolytic capacitor element including, The cathode portion includes a solid electrolyte layer covering at least a portion of the dielectric layer, A method for manufacturing a solid electrolytic capacitor, comprising the steps of forming the first layer by applying a processing solution containing the first conductive polymer to one main surface of the porous portion with one main surface of the porous portion facing vertically upward, and then applying the processing solution to the other main surface of the porous portion with the other main surface of the porous portion facing vertically upward, and drying.

4. The method for manufacturing a solid electrolytic capacitor according to claim 3, wherein the processing solution is applied to each of the one main surface and the other main surface by at least one selected from the group consisting of dropping, dispensing, and transfer.

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