Solid-state electrolytic capacitor element and solid-state electrolytic capacitor

Abstract

A solid-state electrolytic capacitor comprises: at least one capacitor element; and cladding that seals the capacitor element. The capacitor element includes: an anode body having a first end and a second end on the side opposite the first end; a dielectric layer that covers at least part of the anode body; and a cathode portion that covers at least part of the dielectric layer in a section of the anode body on the second end side. The cathode portion includes a solid-state electrolyte layer that covers at least part of the dielectric layer. The breaking strength of the solid-state electrolyte layer is 0.55-45 MPa.

Description

Solid electrolytic capacitor element and solid electrolytic capacitor

[0001] The present disclosure relates to a solid electrolytic capacitor element and a solid electrolytic capacitor.

[0002] The solid electrolytic capacitor includes, for example, a solid electrolytic capacitor element, an exterior body that seals the solid electrolytic capacitor element, and an external electrode 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 portion of the dielectric layer. The cathode portion includes a solid electrolyte layer containing a conductive polymer that covers at least a portion of the dielectric layer.

[0003] Patent Document 1 proposes a solid electrolytic capacitor comprising an anode, a dielectric layer provided on the surface of the anode, a first conductive polymer layer provided on the dielectric layer, a second conductive polymer layer provided on the first conductive polymer layer, a third conductive polymer layer provided on the second conductive polymer layer, and a cathode layer provided on the third conductive polymer layer, wherein the first conductive polymer layer is a conductive polymer film formed by polymerizing pyrrole or a derivative thereof, the second conductive polymer layer is a conductive polymer film formed by polymerizing thiophene or a derivative thereof, and the third conductive polymer layer is a conductive polymer film formed by polymerizing pyrrole or a derivative thereof.

[0004] JP 2010-278423 A

[0005] In solid electrolytic capacitors, the solid electrolytic capacitor element is usually encapsulated in an outer casing or the like. The encapsulation may involve molding a resin composition provided around the solid electrolytic capacitor element into a predetermined shape, or injecting a resin composition between the solid electrolytic capacitor and the outer casing and allowing it to solidify. In such cases, stress is applied to the solid electrolytic capacitor element during encapsulation, which can cause cracks in the solid electrolyte layer, damage the dielectric layer, and result in leakage current.

[0006] One aspect of the present disclosure relates to a solid electrolytic capacitor element including: an anode body having a first end and a second end opposite the first end; a dielectric layer covering at least a portion of the anode body; and a cathode portion covering at least a portion of the dielectric layer at a portion of the anode body on the second end side, wherein the cathode portion includes a solid electrolyte layer covering at least a portion of the dielectric layer, and the breaking strength of the solid electrolyte layer is 0.55 MPa or more and 45 MPa or less.

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

[0008] In a solid electrolytic capacitor, leakage current can be reduced.

[0009] 1A and 1B are schematic cross-sectional views of a solid electrolytic capacitor according to an embodiment of the present disclosure and a solid electrolytic capacitor according to another embodiment of the present disclosure.

[0010] The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

[0011] The solid electrolytic capacitor element is sealed with an outer casing. In the case of a resin outer casing, for example, the solid electrolytic capacitor element is surrounded by a resin composition and compression-molded or heated to harden the resin composition, thereby sealing the solid electrolytic capacitor element with the resin outer casing. Alternatively, the solid electrolytic capacitor element may be sealed by filling the space between the solid electrolytic capacitor element and the outer casing with a resin composition and solidifying it. Therefore, stress due to molding, hardening of the resin composition, filling, or solidification is applied to the solid electrolytic capacitor element. The inventors have found that stress applied during sealing is applied to the solid electrolyte layer, causing cracks and leakage current. The leakage current is thought to be caused by damage to the dielectric layer when cracks occur in the solid electrolyte layer.

[0012] In view of the above, (1) a solid electrolytic capacitor element according to one aspect of the present disclosure includes an anode body having a first end and a second end opposite the first end, a dielectric layer covering at least a portion of the anode body, and a cathode part covering at least a portion of the dielectric layer at a portion of the anode body on the second end side. The cathode part includes a solid electrolyte layer covering at least a portion of the dielectric layer. The solid electrolyte layer has a breaking strength of 0.55 MPa or more and 45 MPa or less.

[0013] In the present disclosure, by setting the breaking strength of the solid electrolyte layer within the above range, even if stress is applied to the solid electrolyte layer when sealing the solid electrolytic capacitor element with an exterior body, the occurrence of cracks can be reduced. Therefore, damage to the dielectric layer can be reduced. As a result, leakage current in the solid electrolytic capacitor can be reduced. Furthermore, an increase in leakage current due to sealing can be kept low.

[0014] (2) In the above (1), the minimum thickness of the solid electrolyte layer may be 1 μm or more.

[0015] (3) In the above (1) or (2), the average thickness of the solid electrolyte layer at the second end is t ｎ The average thickness of the solid electrolyte layer at the center in the direction parallel to the direction from the first end to the second end is t ｃ When t ｎ t ｃ Ratio to t ｎ / t ｃ may be 0.5 or more and 1.8 or less.

[0016] (4) In any one of the above (1) to (3), the solid electrolyte layer may contain a conjugated polymer, a dopant, and a water-soluble polymer.

[0017] (5) The present disclosure also includes a solid electrolytic capacitor including at least one solid electrolytic capacitor element according to any one of (1) to (4) above and an outer casing that seals the solid electrolytic capacitor element. In such a solid electrolytic capacitor, the high breaking strength of the solid electrolyte layer reduces cracks caused by stress when sealing the solid electrolytic capacitor element, thereby reducing damage to the dielectric layer and reducing leakage current. Furthermore, the increase in leakage current due to sealing can be kept low.

[0018] (6) In the above (5), the exterior body may contain a resin.

[0019] (7) In the above (5) or (6), the solid electrolytic capacitor may include a stack of two or more solid electrolytic capacitor elements.

[0020] The solid electrolytic capacitor element and solid electrolytic capacitor of the present disclosure, including the above (1) to (7), will be described in more detail below for each component, with reference to the drawings as necessary. To the extent that there is no technical contradiction, at least one of the above (1) to (7) may be combined with at least one of the elements described below. Hereinafter, the solid electrolytic capacitor element may be simply referred to as a capacitor element.

[0021] [Capacitor Element] (Anode Body) The anode body included in the capacitor element can contain a valve metal, an alloy containing a valve metal, a compound containing a valve metal, etc. The anode body can contain one of these materials or a combination of two or more of them. Preferred examples of the valve metal include aluminum, tantalum, niobium, and titanium.

[0022] The anode body may have a porous portion at least in its surface layer. An anode body having a porous surface can be obtained, for example, by roughening the surface of a substrate (such as a sheet-like (e.g., foil-like, plate-like) substrate) containing a valve metal by etching or the like. The roughening can be performed, for example, by etching or the like. The anode body may also be a compact or sintered body of particles containing a valve metal. Note that the entire anode body has a porous structure, and each of the compact and sintered body may be in a sheet-like shape, such as a rectangular parallelepiped, a cube, or a similar shape. When the anode body is in a sheet shape, the dielectric layer is more susceptible to damage by stress than when it is in a compact or sintered body. Even in such cases, according to the present disclosure, the rupture strength of the solid electrolyte layer is within the above range, thereby suppressing an increase in leakage current.

[0023] The anode body has a first end and a second end opposite the first end. The cathode section is formed on a portion of the anode body on the second end side via a dielectric. The portion of the anode body on the second end side where the cathode section is formed is sometimes called a cathode forming portion. The portion of the anode body on the first end side where the cathode section is not formed is sometimes called an anode lead section. An anode lead terminal is connected to the anode lead section.

[0024] (Dielectric Layer) The dielectric layer is formed so as to cover at least a portion of the anode body. 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 by chemical conversion treatment or the like. In the case of a dielectric layer formed on the surface of an anode body having a porous portion, the surface of the dielectric layer has a fine uneven shape corresponding to the surface shape of the porous portion.

[0025] The dielectric layer may be formed of a material that functions as a dielectric layer. Examples of such materials include oxides of valve metals. For example, when tantalum is used as the valve metal, the dielectric layer includes TaO, and when aluminum is used as the valve metal, the dielectric layer includes AlO. However, the dielectric layer is not limited to these specific examples.

[0026] (Cathode portion) The cathode portion includes at least a solid electrolyte layer that covers at least a portion of the dielectric layer. The solid electrolyte layer is formed on the second end side of the anode body with the dielectric layer interposed therebetween. The cathode portion typically includes a solid electrolyte layer and a cathode extraction layer that covers at least a portion of the solid electrolyte layer. The solid electrolyte layer and the cathode extraction layer are described below.

[0027] (Solid Electrolyte Layer) The solid electrolyte layer contains a conductive polymer. The conductive polymer contains, for example, a conjugated polymer and a dopant. The solid electrolyte layer may further contain an additive, if necessary.

[0028] Conjugated polymers include known conjugated polymers used in solid electrolytic capacitors, such as π-conjugated polymers. Examples of conjugated polymers include polymers with a basic skeleton of polypyrrole, polythiophene, polyaniline, polyfuran, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, and polythiophene vinylene. Of these, polymers with a basic skeleton of polypyrrole, polythiophene, or polyaniline are preferred. The above polymers need only contain at least one monomer unit constituting the basic skeleton. The monomer unit may also include a monomer unit having a substituent. The above polymers also include homopolymers and copolymers of two or more monomers. For example, polythiophenes include poly(3,4-ethylenedioxythiophene).

[0029] Among conjugated polymers, preferred are conjugated polymers containing monomer units corresponding to at least one selected from the group consisting of pyrrole compounds, thiophene compounds, and aniline compounds. Examples of pyrrole compounds include compounds having a pyrrole ring and capable of forming a repeating structure of the corresponding monomer units. Examples of thiophene compounds include compounds having a thiophene ring and capable of forming a repeating structure of the corresponding monomer units. These compounds can be linked at the 2- and 5-positions of the pyrrole ring or thiophene ring to form a repeating structure of the corresponding monomer units. Examples of aniline compounds include compounds having a benzene ring and at least one (preferably one) amino group bonded to the benzene ring and capable of forming a repeating structure of the corresponding monomer units. Aniline compounds can be linked, for example, to an amino group at the CH group (the CH group constituting the benzene ring) at the para-position relative to the amino group to form a repeating structure of the monomer units.

[0030] The pyrrole compound may have a substituent at, for example, at least one of the 3rd and 4th positions of the pyrrole ring. The thiophene compound may have a substituent at, 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 pyrrole ring or the thiophene ring. Examples of the pyrrole compound include pyrrole which may have a substituent at, for example, at least one of the 3rd and 4th positions. Examples of the thiophene compound include thiophene which may have a substituent at, for example, at least one of the 3rd and 4th positions, alkylenedioxythiophene compounds (C such as ethylenedioxythiophene compounds), etc. ２－４ Examples of the aniline compound include aniline which may have a substituent at at least one of the o-position and p-position relative to the amino group.

[0031] The substituents include alkyl groups (C such as methyl and ethyl groups) １－４ alkyl groups, alkoxy groups (C groups such as methoxy groups and ethoxy groups)１－４ alkoxy group, hydroxy group, hydroxyalkyl group (hydroxy C such as hydroxymethyl group) １－４ Preferred examples of the aryl group include, but are not limited to, alkyl groups, etc. When each of the pyrrole compound, the thiophene compound, and the aniline compound has two or more substituents, the substituents may be the same or different.

[0032] A conjugated polymer containing at least a monomer unit corresponding to pyrrole, or a conjugated polymer (such as PEDOT) containing at least a monomer unit corresponding to a 3,4-ethylenedioxythiophene compound (such as 3,4-ethylenedioxythiophene (EDOT)) may be used. A conjugated polymer containing at least a monomer unit corresponding to pyrrole may contain only a monomer unit corresponding to pyrrole, or may contain, in addition to the monomer unit, a monomer unit corresponding to a pyrrole compound other than pyrrole (such as a pyrrole having a substituent). A conjugated polymer containing at least a monomer unit corresponding to EDOT may contain only a monomer unit corresponding to EDOT, or may contain, in addition to the monomer unit, a monomer unit corresponding to a thiophene compound other than EDOT.

[0033] The solid electrolyte layer may contain one type of conjugated polymer or a combination of two or more types of conjugated polymers.

[0034] The weight average molecular weight (Mw) of the conjugated polymer is not particularly limited, but is, for example, 1,000 or more and 1,000,000 or less.

[0035] In this specification, the weight average molecular weight (Mw) is a value calculated as polystyrene measured by gel permeation chromatography (GPC), which is typically performed using a polystyrene gel column and a water / methanol (volume ratio 8 / 2) mobile phase.

[0036] The dopant may be, for example, at least one selected from the group consisting of anions and polyanions.

[0037] Examples of anions include, but are not limited to, sulfate ions, nitrate ions, phosphate ions, borate ions, organic sulfonate ions, carboxylate ions, etc. Examples of dopants that generate sulfonate ions include benzenesulfonic acid, p-toluenesulfonic acid, and naphthalenesulfonic acid.

[0038] Examples of the polyanion include a polymer anion, etc. The solid electrolyte layer may include, for example, a conjugated polymer including a monomer unit corresponding to a thiophene compound and a polymer anion.

[0039] Examples of polymer anions include polymers having multiple anionic groups. Such polymers include polymers containing monomer units having anionic groups. Examples of anionic groups include sulfonic acid groups and carboxy groups. It is preferable that the polymer anion has at least a sulfonic acid group.

[0040] In the solid electrolyte layer, the anionic group of the dopant may be contained in a free form, an anion form, or a salt form, or may be contained in a form bound to or interacting with the conjugated polymer. In this specification, all of these forms may be simply referred to as an "anionic group," "sulfonic acid group," "carboxy group," or the like.

[0041] Examples of polymer anions having sulfonic acid groups include polymeric polysulfonic acids. Specific examples of polymer anions include polyvinyl sulfonic acid, polystyrene sulfonic acid (including copolymers and substituted products having substituents), polyallylsulfonic acid, polyacrylic sulfonic acid, polymethacrylic sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, polyester sulfonic acids (such as aromatic polyester sulfonic acids), and phenolsulfonic acid novolac resins. However, the polymer anions are not limited to these specific examples.

[0042] The amount of the dopant contained in the solid electrolyte layer may be, for example, 10 parts by mass or more and 1,000 parts by mass or less, 20 parts by mass or more and 500 parts by mass or less, or 50 parts by mass or more and 200 parts by mass or less, relative to 100 parts by mass of the conjugated polymer.

[0043] The solid electrolyte layer may be a single layer or may be composed of multiple layers. When the solid electrolyte layer is composed of multiple layers, the conductive polymer contained in each layer may be the same or different. Furthermore, the dopant contained in each layer may be the same or different. A layer for improving adhesion may be interposed between the dielectric layer and the solid electrolyte layer.

[0044] Examples of additives include known additives added to solid electrolyte layers (e.g., coupling agents and silane compounds), known conductive materials other than conductive polymers, and water-soluble polymers. The solid electrolyte layer (or each layer constituting the solid electrolyte layer) may contain one of these additives or a combination of two or more. When the solid electrolyte layer is composed of multiple layers, the additives contained in each layer may be the same or different.

[0045] The conductive material as an additive may be, for example, at least one selected from the group consisting of conductive inorganic materials such as manganese dioxide and TCNQ complex salts.

[0046] Examples of water-soluble polymers include water-soluble polymer compounds having hydrophilic groups in the main chain or side chain. Polymer-type dopants are also included in the water-soluble polymers. Examples of hydrophilic groups that water-soluble polymers have include polyoxyalkylene chains, hydroxy groups, and acid groups (carboxy groups, sulfonic acid groups, etc.). As the water-soluble polymer, a component having lower electron-withdrawing properties than the dopant is usually used. Examples of such water-soluble polymers include water-soluble polymers having at least one selected from the group consisting of carboxy groups, hydroxy groups, and polyoxyalkylene chains. Water-soluble polymers that do not contain sulfonic acid groups may also be used. Examples of polyoxyalkylene chains include polyoxy C ２－３Examples of suitable water-soluble polymers include alkylene chains. The polyoxyalkylene chain may include at least a polyoxyethylene chain. Examples of suitable 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. The water-soluble polymer preferably has at least multiple carboxyl groups. Examples of suitable water-soluble polymers include polymeric polycarboxylic acids and resins with multiple carboxyl groups (water-soluble polyurethane resins, water-soluble polyamides, water-soluble polyimides, water-soluble acrylic resins, etc.). The use of a water-soluble polymer increases the breaking strength of the solid electrolyte layer and facilitates increasing the thickness and reducing thickness variation of the solid electrolyte layer. This further enhances the effect of reducing leakage current. It is also advantageous in terms of improving pressure resistance. From this perspective, when the solid electrolyte layer is composed of multiple layers, it is preferable that the second layer contains a water-soluble polymer. The first layer may or may not contain a water-soluble polymer.

[0047] Water-soluble acrylic resins also include, for example, acrylic polymer-type polycarboxylic acids. Examples of such polymer-type polycarboxylic acids include polyacrylic acid, polymethacrylic acid, and copolymers using at least one of acrylic acid and methacrylic acid (e.g., acrylic acid-methacrylic acid copolymers, copolymers of at least one selected from the group consisting of acrylic acid and methacrylic acid with other copolymerizable monomers, etc.). Examples of other copolymerizable monomers include acrylic acid esters (e.g., alkyl esters, hydroxyalkyl esters), methacrylic acid esters (e.g., alkyl esters, hydroxyalkyl esters), vinyl compounds (e.g., vinyl cyanide, olefins, aromatic vinyl compounds), and polycarboxylic acids having polymerizable unsaturated bonds (e.g., maleic acid, fumaric acid) or acid anhydrides thereof. The copolymers may contain one or more monomer units derived from other copolymerizable monomers.

[0048] As in the case of dopants, the carboxyl groups and sulfonic acid groups of the water-soluble polymer may be contained in the solid electrolyte layer (or each layer constituting the solid electrolyte layer) in a free form, an anion form, or a salt form. Furthermore, some of the carboxyl groups and sulfonic acid groups may be contained in the solid electrolyte layer (or each layer constituting the solid electrolyte 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 "carboxy groups," and all of these forms of sulfonic acid groups may be simply referred to as "sulfonic acid groups."

[0049] The Mw of the water-soluble polymer is, for example, 100 or more and 5 million or less (or 1 million or less), and may be 400 or more and 5 million or less (or 1 million or less).

[0050] The content of the water-soluble polymer in the solid electrolyte layer is, for example, 10% by mass or more and 70% by mass or less, or may be 25% by mass or more and 70% by mass or less, or may be 30% by mass or more and 70% by mass or less. When the content of the water-soluble polymer in the solid electrolyte layer is in such a range, the breaking strength of the solid electrolyte layer is more easily increased, and the effect of reducing leakage current is enhanced.

[0051] The content of the water-soluble polymer in the solid electrolyte layer can be determined using a sample of the solid electrolyte layer (hereinafter referred to as Sample A) taken from a cross-section of a sample for measuring the breaking strength described below. More specifically, the solid electrolyte layer is scraped from the cross-section, a predetermined amount of Sample A is taken, and its mass is measured. The water-soluble polymer is extracted from Sample A with water at 20°C to 40°C. The extract is concentrated, and the water-soluble polymer is identified by liquid chromatography-mass spectrometry (LC-MS) or gas chromatography-mass spectrometry (GC-MS). The concentration of the water-soluble polymer in the extract is determined using a calibration curve method. The content (mass) of the water-soluble polymer in the solid electrolyte layer is determined from this concentration and the mass of Sample A.

[0052] In the present disclosure, the rupture strength of the solid electrolyte layer is 0.55 MPa or more. When the solid electrolyte layer has such a high rupture strength, even if stress occurs when sealing the capacitor element with an exterior body, the occurrence of cracks in the solid electrolyte layer can be reduced, and leakage current can be kept low. From the viewpoint of further enhancing the effect of reducing leakage current in the solid electrolytic capacitor, the rupture strength of the solid electrolyte layer may be 0.59 MPa or more. The rupture strength of the solid electrolyte layer is 45 MPa or less. In this case, stress is easily distributed when bundling the anode lead portions of multiple capacitor elements. The rupture strength of the solid electrolyte layer may be 15 MPa or less, 5 MPa or less, or 2 MPa or less. When the rupture strength is within this range, a high stress distribution effect is easily achieved, and leakage current can be further suppressed. These lower and upper limits can be combined in any combination. The breaking strength of the solid electrolyte layer may be, for example, 0.55 MPa or more and 45 MPa or less (or 15 MPa or less), or 0.55 MPa or more and 5 MPa or less (or 2 MPa or less).

[0053] The solid electrolyte layer having the above-described breaking strength is formed by electrolytic polymerization. By adjusting the electrolytic polymerization conditions, a dense and more uniform solid electrolyte layer can be formed, ensuring high breaking strength.

[0054] The breaking strength is measured by the nanoindentation method in accordance with ISO 14577 using a sample with an exposed cross section of the solid electrolyte layer. A nanoindenter (e.g., a TI950 Triboindenter manufactured by Hysitron) is used for the measurement. More specifically, a diamond indenter is pressed into the cross section of the solid electrolyte layer of the sample in the indenter mode, and the strength at which the solid electrolyte layer breaks is measured. Measurements are performed at 20 points, and the median value is calculated. This median value is the breaking strength of the solid electrolyte layer. The measurement sample is prepared by embedding a solid electrolytic capacitor in acrylic resin, cutting the capacitor element at the center of the width direction in a direction parallel to the length direction, exposing the cross section, and polishing it. When measuring the breaking strength of the solid electrolyte layer in the state of a capacitor element, the measurement sample is prepared in the same manner as above, except that a capacitor element is used instead of a solid electrolytic capacitor.

[0055] The length direction of the capacitor element is a direction parallel to the direction from the first end to the second end of the anode body. The direction from the first end to the second end of the anode body is also referred to as the length direction of the anode body. The direction from the first end to the second end of the anode body is a direction connecting the center of the end face of the anode body on the first end side and the center of the end face on the second end side when the anode body is not bent. The length direction of the capacitor element is parallel to the length direction of the cathode portion or the solid electrolyte layer. The width direction of the capacitor element is parallel to the width direction of the cathode portion or the solid electrolyte. The width direction of the capacitor element is a direction perpendicular to both the length direction and thickness direction of the capacitor element (or the stacking direction of the layers constituting the capacitor element).

[0056] Generally, indicators of the strength or hardness of a resin molded product include, for example, tensile strength, flexural strength, indentation hardness, scratch hardness, and rebound hardness. In the present disclosure, leakage current in solid electrolytic capacitors tends to increase with the degree of cracking in the solid electrolyte layer. Hardness (e.g., indentation hardness or scratch hardness) evaluates the traces left when a certain pressure is applied (in other words, evaluates the degree of deformation within the range of plastic deformation), and therefore has little correlation with cracks that occur beyond the range of plastic deformation. Tensile strength or flexural strength is largely unrelated to the stress applied to the solid electrolyte layer during the manufacturing process of a solid electrolytic capacitor. In contrast, evaluation of fracture strength is believed to more easily reproduce effects similar to those applied to the solid electrolyte layer during the manufacturing process of a solid electrolytic capacitor. Therefore, the fracture strength of the solid electrolyte layer is believed to be highly correlated with the occurrence of cracks in the solid electrolyte layer.

[0057] In the present disclosure, the minimum thickness of the solid electrolyte layer is, for example, 1 μm or more, and may be 1.3 μm or more. When the minimum thickness is within this range, the rigidity of the solid electrolyte layer is improved, and damage to the dielectric layer can be further reduced. Therefore, the effect of reducing crack occurrence is enhanced. From the viewpoint of further reducing crack occurrence, the minimum thickness of the solid electrolyte layer is preferably 5 μm or more, more preferably 8 μm or more or 8.9 μm or more. From the viewpoint of ensuring high capacity, the minimum thickness of the solid electrolyte layer is, for example, 20 μm or less.

[0058] The solid electrolyte layer may have a first portion filling voids in the porous portion of the anode body having the dielectric layer and a second portion protruding from the main surface of the anode body having the dielectric layer, in which case the minimum thickness of the solid electrolyte layer is the minimum thickness of the second portion.

[0059] The thickness of the solid electrolyte layer is measured using a cross-sectional image of a sample prepared using the same procedure as for the sample for measuring the breaking strength. More specifically, in the cross-sectional image of the solid electrolyte layer of the sample, the distance from the main surface of the anode body having the dielectric layer to the surface of the solid electrolyte layer (in other words, the interface between the solid electrolyte layer and the cathode extraction layer) is measured as the thickness of the solid electrolyte layer. The thickness of the solid electrolyte layer is measured at any multiple locations (e.g., five locations), and the minimum of these measurements is taken as the minimum thickness of the solid electrolyte layer. The cross-sectional image of the sample is taken using, for example, a scanning electron microscope (SEM).

[0060] Generally, solid electrolyte layers are formed by chemical polymerization or electrolytic polymerization, or by using a liquid composition containing a conductive polymer. In the case of polymerization, it is difficult to control the polymerization conditions, and the thickness of the solid electrolyte layer is likely to vary. In the case of using a liquid composition containing a conductive polymer, the thickness of the solid electrolyte layer is likely to vary because the dopant and conjugated polymer contained in the liquid composition have high molecular weights, the liquid composition is a dispersion, or the liquid composition needs to be applied and dried multiple times. Depending on the method for forming the solid electrolyte layer, the thickness of the solid electrolyte layer near the end of the solid electrolyte layer on the first end side of the anode body or the end of the solid electrolyte layer on the second end side of the anode body is likely to be smaller than the thickness of the solid electrolyte layer at the center in the longitudinal direction of the cathode part.

[0061] In the present disclosure, electrolytic polymerization conditions and other factors are adjusted to form a dense solid electrolyte layer in order to increase fracture strength. This reduces thickness variation in the solid electrolyte layer, allowing the thickness of the solid electrolyte layer to be relatively large even near the edges. Therefore, when sealing the capacitor element with an exterior body, stress is prevented from concentrating in thin portions of the solid electrolyte layer, and stress is dispersed throughout the solid electrolyte layer, facilitating stress relaxation. As a result, the durability of the solid electrolyte layer is improved, and crack occurrence is further suppressed. Damage to the dielectric layer can be further reduced, further enhancing the effect of reducing leakage current.

[0062] The average thickness of the solid electrolyte layer at the second end is t ｎ The average thickness of the solid electrolyte layer at the center in the longitudinal direction of the solid electrolyte layer is t ｃ In this case, t ｎ t ｃ Ratio to t ｎ / t ｃ is, for example, 0.5 or more, may be 0.75 or more, 0.9 or more, or 0.97 or more. ｎ / t ｃ is, for example, 1.8 or less, and preferably 1.5 or less. ｎ / t ｃ When the ratio t is in this range, the solid electrolyte layer is likely to have high durability against stress applied thereto, and the effect of suppressing an increase in leakage current in the solid electrolytic capacitor is enhanced. These lower and upper limits can be arbitrarily combined. ｎ / t ｃ may be, for example, 0.5 or more (or 0.75 or more) and 1.8 or less, or 0.5 or more (or 0.75 or more) and 1.5 or less.

[0063] Thickness of the solid electrolyte layer t ｎ and t ｃ Each of the thicknesses t at the second end portion is determined in the same manner as in the case of the thickness of the solid electrolyte layer described above, using a cross-sectional image of a sample prepared in the same manner as the sample for measuring the breaking strength. ｎ The thickness t at the center is determined by measuring the thickness of the solid electrolyte layer formed in the portion extending from the end face on the second end side of the anode body to a distance of 0.9 mm from this end face at a plurality of locations (for example, five locations) and averaging the measured values. ｃ is determined by measuring the thickness of the solid electrolyte layer formed on the main surface of the anode body at multiple locations (for example, five locations) in a portion between a position 0.9 mm from the center of the solid electrolyte layer toward the first end and a position 0.9 mm from the center of the solid electrolyte layer toward the second end in the longitudinal direction and averaging the results. When the solid electrolytic capacitor includes multiple capacitor elements, the thickness of the solid electrolyte layer at the second end and the center of each capacitor element is measured at multiple locations in the same manner as above, and the thickness is averaged for all capacitor elements to determine tｎ and t ｃ is required.

[0064] When the solid electrolyte layer has a first portion and a second portion, at least one of the composition and film quality of the solid electrolyte layer may be different between the first portion and the second portion, or both the composition and film quality may be the same. When the solid electrolyte layer is composed of multiple layers, the first portion may be the first layer and the second portion may be the second layer. In this case, at least one of the composition and film quality may be different between the first layer and the second layer, or both the composition and film quality may be the same.

[0065] The electrolytic polymerization of the solid electrolyte layer can be carried out by applying a polymerization voltage to an anode foil having a dielectric layer while the anode foil is in contact with (e.g., immersed in) a polymerization liquid (liquid composition) containing a precursor of a conductive polymer. The polymerization voltage is applied via a power supply. The anode body typically has an insulating region in a predetermined region between the first end and the second end to ensure insulation between the cathode portion and the anode lead portion. The insulating region can be formed, for example, by attaching insulating tape to the surface of the anode body, impregnating a porous portion with an insulating material (e.g., insulating resin), or by a combination of these. The power supply is connected to such an insulating region, and a polymerization voltage is applied.

[0066] The liquid composition contains a precursor of a conductive polymer. The precursor of the conductive polymer contains at least a precursor of a conjugated polymer, and optionally a dopant. Examples of the precursor of the conjugated polymer include raw material monomers of the conjugated polymer, and oligomers and prepolymers in which multiple molecular chains of the raw material monomers are linked together. One type of precursor may be used, or two or more types may be used in combination. From the viewpoint of facilitating the attainment of higher orientation of the conjugated polymer and the formation of a dense solid electrolyte layer, it is preferable to use at least one type (particularly a monomer) selected from the group consisting of monomers and oligomers as the precursor.

[0067] The liquid composition usually contains a solvent, such as at least one solvent selected from the group consisting of water and organic solvents.

[0068] When a dopant, other conductive material, additive, etc. is used, it may be added to the liquid composition. Adjusting the concentration of the dopant in the liquid composition makes it easier to increase the orientation of the conjugated polymer in the solid electrolyte layer, making it easier to obtain a dense solid electrolyte layer. Using a liquid composition containing the above-mentioned water-soluble polymer as an additive can increase the breaking strength and reduce the variation in the thickness of the solid electrolyte layer, which is advantageous in further reducing leakage current. Prior to electropolymerization, a precoat layer containing a conductive material may be formed on the surface of the dielectric layer.

[0069] At least one of the Mw of the water-soluble polymer used and the concentration of the water-soluble polymer in the liquid composition may be adjusted. In this case, the water-soluble polymer appropriately increases the viscosity of the liquid mixture, and electrolytic polymerization proceeds slowly to obtain a dense solid electrolyte layer. It is also believed that the water-soluble polymer itself acts as a skeleton supporting the polymer film in the solid electrolyte layer, thereby increasing its strength.

[0070] The concentration of the water-soluble polymer in the liquid composition may be, for example, 1% by mass or more and 30% by mass or less, 1.5% by mass or more and 15% by mass or less, or 2% by mass or more and 15% by mass or less (or 10% by mass or less). When the concentration of the water-soluble polymer is in such a range, a higher breaking strength of the solid electrolyte layer is likely to be obtained, and the variation in thickness of the solid electrolyte layer is likely to be further reduced.

[0071] The liquid composition may contain an oxidizing agent, if necessary. The oxidizing agent may be applied to the anode foil having a dielectric layer before or after the liquid composition is brought into contact with the anode foil. Examples of such an oxidizing agent include Fe. ３＋ Examples of the oxidizing agent include compounds capable of generating oxidizing agent (such as ferric sulfate), persulfates (such as sodium persulfate and ammonium persulfate), and hydrogen peroxide. The oxidizing agent can be used alone or in combination of two or more.

[0072] In the electrolytic polymerization, the polymerization voltage is preferably less than 0.90 V, more preferably 0.87 V or less or 0.85 V or less. When the polymerization voltage is in this range, the polymerization proceeds slowly, the orientation of the conjugated polymer is likely to be enhanced, and a dense solid electrolyte layer is likely to be formed. Therefore, high breaking strength is likely to be ensured. The polymerization voltage may be 0.6 V or more. The polymerization voltage is set by using a reference electrode (silver / silver chloride electrode (Ag / Ag ＋ ) is the potential of the current feeder relative to

[0073] Electropolymerization may be performed in a bipolar system using two electrodes, an anode body with a dielectric layer formed on its surface, and a counter electrode; however, a tripolar system is preferred. Tripolar electropolymerization is performed using three electrodes: an anode body with a dielectric layer formed on its surface, an anode, a counter electrode, and a reference electrode. In tripolar electropolymerization, the use of a reference electrode allows precise control of the anode potential without being affected by changes in the natural potential of the counter electrode. Compared to bipolar electropolymerization, the tripolar system allows for more precise control of the electropolymerization reaction, resulting in enhanced orientation of the conjugated polymer formed by electropolymerization and the formation of a denser solid electrolyte layer. This is advantageous for increasing breaking strength. It also facilitates reducing variation in the thickness of the solid electrolyte layer.

[0074] The three-electrode electropolymerization is carried out in a state where an anode body, a counter electrode, and a reference electrode are immersed in the liquid composition. The counter electrode may be, but is not limited to, a Ti electrode. The reference electrode may be a silver / silver chloride electrode (Ag / Ag ＋ ) is preferably used.

[0075] The temperature at which the electropolymerization is carried out is, for example, 5°C or higher and 60°C or lower, and may be 15°C or higher and 35°C or lower.

[0076] (Cathode Extraction Layer) The cathode extraction layer may include at least a third layer that is in contact with the solid electrolyte layer and covers at least a portion of the solid electrolyte layer, and may also include a third layer and a fourth layer that covers the third layer. Examples of the third layer include a layer containing conductive particles and metal foil. Examples of the conductive particles include at least one selected from conductive carbon and metal powder. For example, the cathode extraction layer may be composed of a layer containing conductive carbon (also referred to as a carbon layer) as the third layer and a metal-containing layer (e.g., a layer containing metal powder or metal foil) as the fourth layer. When metal foil is used as the third layer, the cathode extraction layer may be composed of this metal foil.

[0077] Examples of conductive carbon include graphite (artificial graphite, natural graphite, etc.).

[0078] The fourth layer containing metal powder can be formed, for example, by laminating a composition containing metal powder on the surface of the third layer. An example of such a fourth layer is a metal paste layer formed using a composition containing metal powder such as silver particles and a resin (binder resin). While a thermoplastic resin can be used as the resin, it is preferable to use a thermosetting resin such as an imide resin or an epoxy resin.

[0079] When a metal foil is used as the third layer, the type of metal is not particularly limited. It is preferable to use a valve metal (aluminum, tantalum, niobium, etc.) or an alloy containing a valve metal as the metal foil. If necessary, the surface of the metal foil may be roughened. The surface of the metal foil may be provided with a chemical conversion coating, or may be provided with a coating of a metal (dissimilar metal) or a nonmetal different from the metal constituting the metal foil. Examples of dissimilar metals and nonmetals include metals such as titanium and nonmetals such as carbon (e.g., conductive carbon).

[0080] The coating of the dissimilar metal or non-metal (for example, conductive carbon) may serve as a third layer, and the metal foil may serve as a fourth layer.

[0081] (Separator) When a metal foil is used for the cathode extraction layer, a separator may be disposed between the metal foil and the anode foil. The separator is not particularly limited, and examples thereof include a nonwoven fabric containing fibers of cellulose, polyethylene terephthalate, vinylon, or polyamide (e.g., aliphatic polyamide, aromatic polyamide such as aramid).

[0082] (Others) The capacitor element may be, for example, a wound type, a laminated type, or a chip type. The configuration of the capacitor element may be selected depending on the type of solid electrolytic capacitor.

[0083] [Solid Electrolytic Capacitor] A solid electrolytic capacitor includes at least one capacitor element and an exterior body that seals the capacitor element. The solid electrolytic capacitor may include multiple capacitor elements. The solid electrolytic capacitor may be a wound type, a chip type, or a laminate type.

[0084] In the capacitor element, one end of a cathode lead terminal is electrically connected to the cathode extraction layer. One end of an anode lead terminal is electrically connected to the first portion of the anode foil. The other end of the anode lead terminal and the other end of the cathode lead terminal are each drawn out from the exterior housing. The other end of each lead terminal exposed from the exterior housing is used for soldering to a substrate on which the solid electrolytic capacitor is to be mounted, for example. Each lead terminal may be a lead wire or a lead frame.

[0085] The exterior body may be a resin exterior body or another exterior body. A resin composition may be injected between the exterior body and the capacitor element and solidified to seal the capacitor element. When the capacitor element is sealed by a resin exterior body or by injecting a resin composition between the exterior body and the capacitor element and solidifying it, stress is applied to the capacitor element, which makes it easy for cracks to occur in the solid electrolyte layer. In the present disclosure, even in such a case, the high fracture strength of the solid electrolyte layer reduces the occurrence of cracks and enables the leakage current to be kept low.

[0086] The solid electrolytic capacitor may include, for example, a stack of two or more capacitor elements. In the stack, the anode leads of each capacitor element are bundled and connected to a lead terminal. When the anode leads of multiple stacked capacitor elements are bundled, stress generated by the bundling is applied to the solid electrolyte layer near the end on the first end side. As a result, cracks are likely to occur near the end on the first end side of the solid electrolyte layer, and damage to the dielectric layer is also likely to occur. If the stack of capacitor elements in this state is sealed with an outer casing, cracks are likely to increase and damage to the dielectric layer is likely to increase, which in turn increases leakage current in the solid electrolytic capacitor. In the present disclosure, even in such cases, the high fracture strength of the solid electrolyte layer of each capacitor element reduces the occurrence of cracks. Therefore, leakage current can be effectively reduced.

[0087] The laminate may include, for example, two or more capacitor elements. As the number of capacitor elements increases, stress is likely to be applied to the solid electrolyte layer near the first end. Even in such cases, the present disclosure can reduce leakage current in the solid electrolytic capacitor.

[0088] The capacitor element is sealed using an outer casing. When a resin outer casing is used, for example, the capacitor element and the resin material of the outer casing (e.g., a resin composition containing an uncured thermosetting resin and a filler) may be placed in a mold, and the capacitor element may be sealed with the resin outer casing by transfer molding, compression molding, or the like. At this time, the other end portion of the anode lead terminal and the other end portion of the cathode lead terminal, which are drawn out from the capacitor element, are each exposed from the mold. Alternatively, the capacitor element may be housed in an outer casing, and a resin material (e.g., a resin composition containing an uncured thermosetting resin and a filler) may be injected between the outer casing and the capacitor element and solidified. For example, the capacitor element may be housed in a bottomed case such that the other end portion of the anode lead terminal and the other end portion of the cathode lead terminal are positioned on the opening side of the bottomed case, and a resin material may be injected into the case, the opening of the bottomed case may be sealed with a sealant, and the resin material may be solidified to form a solid electrolytic capacitor.

[0089] FIG. 1 is a cross-sectional view schematically illustrating the structure of a solid electrolytic capacitor according to an embodiment of the present disclosure. FIG. 1 is a cross-sectional schematic view of the solid electrolytic capacitor, taken along a direction parallel to both the length and thickness directions of a capacitor element 2. As shown in FIG. 1 , the solid electrolytic capacitor 1 includes a capacitor element 2, a resin outer casing 3 that seals the capacitor element 2, and an anode lead terminal 4 and a cathode lead terminal 5, at least a portion of which is exposed to the outside of the resin outer 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 outer casing 3 has a substantially rectangular parallelepiped outer shape, and the solid electrolytic capacitor 1 also has a substantially rectangular parallelepiped outer shape.

[0090] The capacitor element 2 includes an anode body 6, a dielectric layer 7 covering the anode body 6, and a cathode section 8 covering the dielectric layer 7. The cathode section 8 includes a solid electrolyte layer 9 covering the dielectric layer 7, and a cathode extraction layer 10 covering the solid electrolyte layer 9. The cathode extraction layer 10 includes a carbon layer 11 as a third layer covering the solid electrolyte layer 9, and a metal-containing layer 12 as a fourth layer covering the carbon layer 11. In the present disclosure, because the solid electrolyte layer 9 has high fracture strength, even if stress is applied when sealing the capacitor element 2 with the resin outer casing 3, the occurrence of cracks in the solid electrolyte layer 9 can be reduced, and damage to the dielectric layer can be reduced. Therefore, leakage current can be kept low.

[0091] The anode body 6 includes a region facing the cathode portion 8 and a region not facing the cathode portion 8. Of the region of the anode body 6 not facing the cathode portion 8, an insulating separation portion (insulating region) 13 is formed in a strip-like shape on the surface of the anode body 6 in a portion adjacent to the cathode portion 8, thereby restricting contact between the cathode portion 8 and the anode body 6. Of the region of the anode body 6 not facing the cathode portion 8, another portion is electrically connected to the anode lead terminal 4 by welding. The cathode lead terminal 5 is electrically connected to the cathode portion 8 via an adhesive layer 14 formed of a conductive adhesive.

[0092] 2 is a cross-sectional schematic diagram of a solid electrolytic capacitor according to another embodiment of the present disclosure. The solid electrolytic capacitor 21 includes a laminate L of a plurality of capacitor elements 22, a resin outer casing 3 that seals the laminate L, and an anode lead terminal 4 and a cathode lead terminal 5, at least a portion of which is exposed to the outside of the resin outer casing 3. Note that FIG. 2 shows the layout of the capacitor elements 22 in the length direction and thickness direction (stacking direction) D. Ｔ 2 is a schematic cross-sectional view of the solid electrolytic capacitor 21 in a direction parallel to the arrows .

[0093] In the laminate L, one first end e1 of the anode bodies 6 included in each capacitor element 22 is bundled and electrically connected to one end of the anode lead terminal 4 by welding. One end of the cathode lead terminal 5 is electrically connected to the cathode portion of the capacitor element 22 arranged on the outermost side of the laminate L (the lower end in the figure) via an adhesive layer 14 formed of a conductive adhesive. A portion of the other end side of the anode lead terminal 4 and a portion of the other end side of the cathode lead terminal 5 each extend to the outside from another main surface of the resin outer casing 3. For the other configuration of FIG. 2 , refer to the description of FIG. 1 . Note that the configuration of the capacitor element 22 is omitted in FIG. 2 . When the solid electrolytic capacitor 21 includes a laminate of capacitor elements 22, the first ends of the anode bodies 6 may be bundled together as shown in FIG. 2 . In this case, stress generated by bundling is applied to the solid electrolyte layer of the capacitor element 22 near the first end e1, which is likely to cause cracks. Even in such a case, in the present disclosure, the high breaking strength of the solid electrolyte layer can suppress the occurrence of cracks, and can prevent the cracks from becoming significant when sealing the laminate L with the resin outer casing 3. Therefore, an increase in leakage current can be reduced.

[0094] The length direction of anode body 6 or capacitor element 22 is a direction parallel to the direction from first end e1 to second end e2 when anode body 6 is not bent.

[0095] EXAMPLES The present invention will be specifically described below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0096] <Solid Electrolytic Capacitors E1 to E4 and R1> Solid electrolytic capacitors (solid electrolytic capacitors E1 to E4 and R1) including a laminate L of capacitor elements 22 as shown in Figure 2 were fabricated in the following manner, and their characteristics were evaluated. However, laminate L was a laminate of seven capacitor elements 22. The configuration of capacitor element 22 was the same as that of capacitor element 2 in Figure 1.

[0097] (1) Preparation of Anode Body 6 Both surfaces of an aluminum foil (thickness: 100 μm) serving as a substrate were roughened by etching to prepare an anode body 6 .

[0098] (2) Formation of Dielectric Layer 7 The cathode forming portion of the anode body 6 was immersed in a chemical conversion solution, and a DC voltage of 70 V was applied for 20 minutes to form a dielectric layer 7 containing aluminum oxide.

[0099] (3) Formation of Solid Electrolyte Layer 9 An insulating resist tape was attached to an area of ​​anode body 6 on which dielectric layer 7 was formed, between an area where a solid electrolyte layer was to be formed and an area where a solid electrolyte layer was not to be formed, thereby forming separation portion 13. Anode body 6 on which separation portion 13 was formed was immersed in a liquid composition containing a conductive material, taken out, and dried, thereby forming a precoat layer (not shown).

[0100] A polymerization solution containing pyrrole (a conjugated polymer monomer), naphthalenesulfonic acid (a dopant), and water was prepared. A three-electrode electropolymerization was performed using the resulting polymerization solution. More specifically, an anode body 6 with a precoat layer formed thereon, a counter electrode, and a reference electrode (a silver / silver chloride reference electrode) were immersed in the polymerization solution. A voltage was applied to the anode body 6 so that the potential of the anode body 6 relative to the reference electrode was the polymerization voltage value shown in Table 1. Electropolymerization was performed at 25°C to form a solid electrolyte layer 9. In addition to the polymerization voltage, at least one of the area of ​​the counter electrode and the amount of naphthalenesulfonic acid added was adjusted as necessary during electropolymerization. In the examples, a water-soluble polymer (polymer-type polycarboxylic acid) was added to the polymerization solution at the concentration shown in Table 1.

[0101] (4) Formation of Cathode Extraction Layer 10 Anode element 6 obtained in (3) above was immersed in a dispersion liquid in which graphite particles were dispersed in water, removed from the dispersion liquid, and then dried to form carbon layer 11 at least on the surface of solid electrolyte layer 9. Drying was performed at 150° C. for 30 minutes.

[0102] Next, a silver paste containing silver particles and a binder resin (epoxy resin) was applied to the surface of carbon layer 11, and the binder resin was cured by heating at 150°C for 30 minutes to form metal-containing layer (metal paste layer) 12. In this way, cathode extraction layer 10 composed of carbon layer 11 and metal paste layer 12 was formed, and cathode part 8 composed of solid electrolyte layer 9 and cathode extraction layer 10 was formed. In this manner, a plurality of capacitor elements 22 were produced.

[0103] (5) Assembly of Solid Electrolytic Capacitor A laminate L was produced by stacking seven of the capacitor elements 22 obtained in (4) above via conductive adhesive layers 14. The cathode portions 8 of the capacitor elements 22 located at the end of the laminate L in the stacking direction were joined to one end of the cathode lead terminal 5 with the conductive adhesive layer 14. One end of the anode bodies 6 protruding from each capacitor element 22 of the laminate L (i.e., the end of the anode lead portion) was bundled and joined to one end of the anode lead terminal 4 by laser welding. A total of 20 such laminates L were produced. Next, a resin outer casing 3 made of an insulating resin was formed around each laminate L by molding. At this time, the other end of the anode lead terminal 4 and the other end of the cathode lead terminal 5 were extended from the resin outer casing 3. In this manner, a total of 20 solid electrolytic capacitors were completed.

[0104] [Evaluation] The following evaluations were carried out using the capacitor elements or solid electrolytic capacitors obtained above. Regarding leakage current, evaluation was carried out on the solid electrolytic capacitor, and also on the capacitor element 22 obtained in (4) above, to which the cathode lead terminal 5 and the anode lead terminal 4 were joined in the same manner as in (5) above.

[0105] (a) Breaking Strength Using a solid electrolytic capacitor, the breaking strength (MPa) of the solid electrolyte layer was determined according to the procedure described above.

[0106] (b) Thickness of the solid electrolyte layer Using a solid electrolytic capacitor, the ratio t ｎ / t ｃ asked for.

[0107] (c) Leakage Current (LC) For each solid electrolytic capacitor, a 1 kΩ resistor was connected in series, and a rated voltage of 25 V was applied from a DC power supply for 1 minute. The leakage current (initial leakage current) (μA) was measured, and the average value for 20 solid electrolytic capacitors was calculated. Similarly to the solid electrolytic capacitor, the initial leakage current for each capacitor element was also measured, and the average value for the 20 capacitor elements was calculated. These average values ​​are shown in Table 1 below as the LC of the capacitor and the LC of the capacitor element, respectively.

[0108] The evaluation results are shown in Table 1. E1 to E4 are examples, and R1 is a reference example.

[0109]

[0110] As shown in Table 1, when the breaking strength of the solid electrolyte layer is less than 0.55 MPa, the leakage current is large in both the capacitor element and the solid electrolytic capacitor. While the leakage current in the capacitor element is 69.2 μA, the leakage current in the solid electrolytic capacitor is significantly higher at 994.9 μA. This is thought to be due to the solid electrolyte layer cracking due to the inability to withstand the large stress applied when the capacitor element is encapsulated in resin molding to form the resin outer casing 3, resulting in damage to the dielectric layer. When the solid electrolytic capacitor R1 was measured using transmission X-ray CT (computed tomography), it was confirmed that multiple relatively large cracks had formed in the solid electrolyte layer. A Zeiss Xradia 520 Versa was used for the transmission X-ray CT.

[0111] In contrast, in E1 to E4, the leakage current in the capacitor element was significantly lower than that of R1, at 7.6 μA or less, and the leakage current in the solid electrolytic capacitor was also very low, at 28.3 μA or less. This is thought to be because the high breaking strength of the solid electrolyte layer reduced the occurrence of cracks when sealing the capacitor element with a resin outer casing, thereby reducing damage to the dielectric layer. Furthermore, a larger minimum thickness of the solid electrolyte layer or the second portion can reduce the leakage current in the solid electrolytic capacitor (comparison of R1 and E4 with E1 to E3).

[0112] While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention.

[0113] According to the present disclosure, a solid electrolytic capacitor element and a solid electrolytic capacitor with reduced leakage current are provided, and therefore the solid electrolytic capacitor element and the solid electrolytic capacitor can be used in a variety of applications requiring high reliability.

[0114] 1, 21: Solid electrolytic capacitor 2, 22: Capacitor element 3: Resin exterior body 4: Anode lead terminal 5: Cathode lead terminal 6: Anode body 7: Dielectric layer 8: Cathode portion 9: Solid electrolyte layer 10: Cathode extraction layer 11: Carbon layer 12: Metal-containing layer (metal paste layer) 13: Separation portion (insulating region) 14: Adhesive layer L: Laminate e1: First end of anode body 6 e2: Second end of anode body 6 D Ｔ : Thickness of the capacitor element (or lamination direction) D Ｌ : Length direction of the capacitor element

Claims

1. An anode body having a first end portion and a second end portion opposite to the first end portion, a dielectric layer covering at least a part of the anode body, and a cathode portion covering at least a part of the dielectric layer in a portion on the second end side of the anode body, The cathode portion includes a solid electrolyte layer covering at least a part of the dielectric layer, The solid electrolyte capacitor element, wherein a breaking strength of the solid electrolyte layer is 0.55 MPa or more and 45 MPa or less.

2. The solid electrolyte capacitor element according to claim 1, wherein a minimum value of a thickness of the solid electrolyte layer is 1 μm or more.

3. When an average value of a thickness of the solid electrolyte layer at the second end portion is t ｎ and an average value of a thickness at a center of the solid electrolyte layer in a direction parallel to a direction from the first end portion toward the second end portion is t ｃ then, a ratio of t ｎ to t ｃ : t ｎ / t ｃ is 0.5 or more and 1.8 or less. The solid electrolyte capacitor element according to claim 1 or 2.

4. The solid electrolyte capacitor element according to claim 1 or 2, wherein the solid electrolyte layer includes a conjugated polymer, a dopant, and a water-soluble polymer.

5. A solid electrolyte capacitor including at least one solid electrolyte capacitor element according to claim 1 or 2 and an exterior body for encapsulating the solid electrolyte capacitor element.

6. The solid electrolyte capacitor according to claim 5, wherein the exterior body includes a resin.

7. The solid electrolyte capacitor according to claim 5, including a laminate of two or more of the solid electrolyte capacitor elements.