Solid electrolytic capacitor element and solid electrolytic capacitor

Abstract

A solid electrolytic capacitor element according to the present invention comprises an anode body, a dielectric layer formed on a surface of the anode body, and a cathode part covering at least a portion of the dielectric layer. The cathode part is provided with a solid electrolyte layer covering at least a portion of the dielectric layer. When a solid electrolyte constituting the solid electrolyte layer is subjected to thermogravimetric analysis by increasing the temperature to 180ºC, holding at 180ºC for 20 minutes, and cooling from 180ºC to 30ºC, and then increasing the temperature from 30ºC to 260ºC at a rate of 20ºC / min, a weight reduction rate of the solid electrolyte is 3% or less.

Description

[Technical Field]

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

[0002] The solid electrolytic capacitor includes a solid electrolytic capacitor element, a resin outer casing or case that seals the solid electrolytic capacitor element, and external electrodes 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 that covers at least a portion of the dielectric layer and contains a conductive polymer and a dopant.

[0003] Patent Document 1 proposes a method for manufacturing a solid electrolytic capacitor, which includes the steps of forming a preliminary conductive layer on a valve metal having a dielectric oxide film formed thereon, and forming a conductive polymer layer on the preliminary conductive layer by electrolytic polymerization using an electrolytic polymerization solution for forming a conductive polymer. The electrolytic polymerization solution for forming a conductive polymer contains a polymerizable monomer and a compound represented by a specific formula as a supporting electrolyte dissolved in a solvent. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-175424 Summary of the Invention [Problem to be solved by the invention]

[0005] Solid electrolytic capacitors are sometimes exposed to high-temperature environments, so high thermal stability is required for solid electrolytic capacitors and solid electrolytic capacitor elements. [Means for solving the problem]

[0006] A first aspect of the present disclosure provides a fuel cell comprising: an anode body; a dielectric layer formed on a surface of the anode body; and a cathode portion covering at least a portion of the dielectric layer, the cathode portion includes a solid electrolyte layer covering at least a portion of the dielectric layer, The present invention relates to a solid electrolytic capacitor element in which the solid electrolyte constituting the solid electrolyte layer has a weight loss rate of 3% or less when heated to 180°C, held at 180°C for 20 minutes, cooled from 180°C to 30°C, and then heated from 30°C to 260°C at a rate of 20°C / min, as determined by thermogravimetric analysis.

[0007] A second aspect of the present disclosure provides a fuel cell comprising: an anode body; a dielectric layer formed on a surface of the anode body; and a cathode portion covering at least a portion of the dielectric layer, the cathode portion includes a solid electrolyte layer covering at least a portion of the dielectric layer, the solid electrolyte layer contains a conductive polymer and a dopant component, the dopant component includes an aromatic compound having an electron-withdrawing functional group and an electron-donating functional group on an aromatic ring; the aromatic compound has, as the electron-withdrawing functional groups, at least a first functional group: a sulfo group and a second functional group: a carboxy group, and, as the electron-donating functional group, a third functional group: at least one selected from the group consisting of a hydroxy group and an alkoxy group; The present invention relates to a solid electrolytic capacitor element in which, in one molecule of the aromatic compound, when the number of the first functional groups is n1, the number of the second functional groups is n2, and the number of the third functional groups is n3, n1≧1, n2≧1, n3≧1, and (n1+n2+n3)≧4.

[0008] A third aspect of the present disclosure relates to a solid electrolytic capacitor including at least one of the above solid electrolytic capacitor elements. [Effects of the Invention]

[0009] It is possible to provide a solid electrolytic capacitor element having excellent thermal stability and a solid electrolytic capacitor including the same. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic cross-sectional view of a solid electrolytic capacitor according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

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

[0012] When air penetrates into a solid electrolytic capacitor, the moisture or oxygen in the air can decompose the dopant components or oxidize the conductive polymer, resulting in a decrease in the conductivity of the solid electrolyte layer. This decrease in the conductivity of the solid electrolyte layer can lead to a decrease in the performance of the solid electrolytic capacitor, such as an increase in the equivalent series resistance (ESR) or a decrease in capacitance. The decomposition of dopant components and the oxidative degradation of conductive polymers are particularly pronounced in high-temperature environments. Depending on the application, solid electrolytic capacitors are sometimes used in high-temperature environments. Furthermore, solid electrolytic capacitors are generally soldered to a substrate through a reflow process that exposes them to high temperatures. If the dopant components are prone to decomposition, a large amount of gas is generated during the reflow process, reducing the airtightness and reliability of the solid electrolytic capacitor. Therefore, there is a need for solid electrolytic capacitor elements and solid electrolytic capacitors that exhibit excellent thermal stability by suppressing the decomposition of dopant components and the oxidative degradation of conductive polymers, even in high-temperature environments.

[0013] In view of the above, in the solid electrolytic capacitor element according to the first aspect of the present disclosure, the solid electrolyte constituting the solid electrolyte layer has a weight loss rate of 3% or less when heated to 180°C, held at 180°C for 20 minutes, cooled from 180°C to 30°C, and then heated from 30°C to 260°C at a rate of 20°C / min, as determined by thermogravimetric analysis.

[0014] According to the first aspect of the present disclosure, the weight loss rate of the solid electrolyte is as low as 3% or less, thereby suppressing gas generation under heating conditions equivalent to those in a reflow process. This suppresses the loss of airtightness of the solid electrolytic capacitor during the reflow process. Even when exposed to a high-temperature environment, gas generation is suppressed and high airtightness is ensured, thereby minimizing fluctuations in capacitor performance. Furthermore, in the solid electrolytic capacitor element and solid electrolytic capacitor, degradation of the solid electrolyte is suppressed even when exposed to a high-temperature environment, thereby minimizing a decrease in capacitance or an increase in ESR. Therefore, the solid electrolytic capacitor element and solid electrolytic capacitor achieve high thermal stability and ensure high reliability. According to the present disclosure, the weight loss rate can be suppressed to 2.5% or less, or 2% or less, and even to less than 1%, or 0.8% or less (or 0.5% or less).

[0015] In the solid electrolytic capacitor element of the first aspect, the solid electrolyte layer may use a dopant component containing an aromatic compound having an electron-withdrawing functional group and, optionally, an electron-donating functional group on an aromatic ring. Here, in this aromatic compound, when the number of electron-withdrawing functional groups in one molecule of the aromatic compound is m1 and the number of electron-donating functional groups is m2, (m1-m2) ≥ 2. Such an aromatic compound may be referred to as dopant IA.

[0016] When a dopant has two or more electron-withdrawing functional groups in its aromatic ring, it tends to be strongly coordinated to the conductive polymer, and dedoping tends to be suppressed even in a high-temperature environment, making it easier to ensure high conductivity of the solid electrolyte layer. On the other hand, the electron-donating functional group has the effect of capturing oxygen radicals. When a dopant has an electron-donating functional group, the dopant, which is coordinated to the conductive polymer due to the action of the electron-withdrawing functional group, can have the electron-donating functional group present in the vicinity of the conductive polymer. The electron-donating functional group can capture oxygen radicals in the vicinity of the conductive polymer, so that oxidative degradation of the conductive polymer can be effectively reduced even in a high-temperature environment. However, when the electron density of the aromatic ring, particularly the electron density of the carbon atom substituted with the electron-withdrawing functional group, is low, high When the dopant IA is used, the number m1 of electron-withdrawing functional groups and the number m2 of electron-donating functional groups satisfy (m1-m2) ≥ 2, so that excellent dedoping can be achieved even when the dopant IA has an electron-donating functional group. restraint This effectively reduces the decrease in capacitance or the increase in ESR even when the solid electrolytic capacitor element is exposed to a high-temperature environment, thereby ensuring high thermal stability and high reliability of the solid electrolytic capacitor element and the solid electrolytic capacitor.

[0017] In a solid electrolytic capacitor element according to a second aspect of the present disclosure, the solid electrolyte layer uses a dopant component containing an aromatic compound having, on an aromatic ring, a first functional group (a sulfo group), a second functional group (a carboxy group), and a third functional group (at least one selected from the group consisting of a hydroxy group and an alkoxy group). In this aromatic compound, where n1 is the number of first functional groups, n2 is the number of second functional groups, and n3 is the number of third functional groups in one molecule of the aromatic compound, the relationships n1≧1, n2≧1, n3≧1, and (n1+n2+n3)≧4 are satisfied. Such an aromatic compound is sometimes referred to as dopant IB.

[0018] In this specification, dopant IA and dopant IB may be collectively referred to simply as the first dopant. Also, at least one selected from the group consisting of dopant IA and dopant IB may be referred to as the first dopant. In a first aspect, the first dopant is at least dopant IA, and in a second aspect, the first dopant is at least dopant IB.

[0019] According to a second aspect of the present disclosure, the dopant IB is a compound having an electron-withdrawing first functional group and a second functional group on an aromatic ring (such as a benzene ring or a naphthalene ring). This facilitates strong coordination with a conductive polymer and suppresses dedoping even in high-temperature environments, thereby ensuring high conductivity of the solid electrolyte layer. Furthermore, due to this structure, the dopant IB has excellent hydrolysis resistance and is suppressed from decomposition in high-temperature environments. Therefore, the dopant IB exhibits high thermal stability. In the dopant IB, the total number of the first to third functional groups (= n1 + n2 + n3) is 4 or greater. That is, the number of at least one of the first to third functional groups is 2 or greater. When the number of at least one of the first functional group and the second functional group is 2 or greater, even higher thermal stability of the dopant IB is easily ensured. Furthermore, the dopant IB has an electron-donating third functional group in addition to the first and second functional groups. The third functional group has the ability to capture oxygen radicals. When the dopant IB is coordinated to the conductive polymer through the action of the first and second functional groups, a third functional group can be present near the conductive polymer. The third functional group can capture oxygen radicals near the conductive polymer, effectively reducing oxidative degradation of the conductive polymer even in high-temperature environments. When the number of third functional groups is two or more, the oxygen radical capturing effect is enhanced, further enhancing the effect of reducing oxidative degradation of the conductive polymer. Thus, in this disclosure, the use of a dopant component containing the dopant IB reduces decomposition of the dopant component and oxidative degradation of the conductive polymer in high-temperature environments. Therefore, excellent thermal stability can be ensured for solid electrolytic capacitor elements and solid electrolytic capacitors. Furthermore, the excellent hydrolysis resistance of the dopant IB makes the solid electrolyte layer less susceptible to moisture even in high-temperature environments. This can also improve the moisture resistance of solid electrolytic capacitor elements and solid electrolytic capacitors.

[0020] Furthermore, according to the second aspect of the present disclosure, decomposition of the dopant component is suppressed, thereby reducing the amount of gas generated during the reflow process. The solid electrolyte layer included in such a solid electrolytic capacitor exhibits a small weight loss rate under heating conditions equivalent to those of the reflow process. For example, thermogravimetric analysis shows that the solid electrolyte constituting the solid electrolyte layer exhibits a weight loss rate of 3% or less when heated to 180°C, held at 180°C for 20 minutes, cooled from 180°C to 30°C, and then heated from 30°C to 260°C at a rate of 20°C / min. Thus, according to the present disclosure, gas generation under heating conditions equivalent to those of the reflow process is suppressed, thereby preventing a decrease in the airtightness of the solid electrolytic capacitor during the reflow process. Even when exposed to a high-temperature environment, gas generation is suppressed, ensuring high airtightness and suppressing oxidative degradation of the conductive polymer, thereby reducing a decrease in capacitance or an increase in ESR. This ensures high reliability of the solid electrolytic capacitor element and the solid electrolytic capacitor. According to the present disclosure, the weight loss rate can be suppressed to 2.5% or less, or 2% or less, and can also be suppressed to less than 1%, or 0.8% or less (or 0.5% or less), thereby ensuring excellent reliability of the solid electrolytic capacitor.

[0021] The weight loss rate of the solid electrolyte can be determined using thermogravimetric analysis according to the following procedure. First, a solid electrolytic capacitor element is removed from the solid electrolytic capacitor, and a solid electrolyte sample is prepared by scraping off the solid electrolyte layer. The sample is placed in a thermogravimetric analyzer, heated from room temperature (20°C to 35°C) to 180°C, held at 180°C for 20 minutes, cooled from 180°C to 30°C, and the weight of the cooled sample, w0, is measured. Next, the sample is heated from 30°C to 260°C at a rate of 20°C / min using the thermogravimetric analyzer, and the weight of the sample after heating, w1, is measured. The weight loss of the sample, Δw (= w0 - w1), when heated from 30°C to 260°C is determined, and the ratio (%) of Δw to w0, which is set to 100%, is calculated to determine the weight loss rate of the solid electrolyte layer. All of these thermogravimetric analyses are performed under a nitrogen gas flow. As the thermogravimetric analyzer, for example, a simultaneous differential thermal and thermogravimetric analyzer (NEXTA STA300) manufactured by Hitachi High-Tech Science Corporation is used.

[0022] Hereinafter, the solid electrolytic capacitor and solid electrolytic capacitor element (hereinafter sometimes simply referred to as capacitor element) of the present disclosure will be described in more detail with reference to the drawings as necessary.

[0023] [Solid electrolytic capacitor] A solid electrolytic capacitor includes one or more capacitor elements. It is sufficient that the solid electrolyte layer of at least one of the capacitor elements included in the solid electrolytic capacitor contains a first dopant. It is preferable that the solid electrolyte layers of 50% or more of the capacitor elements included in the solid electrolytic capacitor contain the first dopant, more preferably that the solid electrolyte layers of 75% or more of the capacitor elements contain the first dopant, and even more preferably that the solid electrolyte layers of all of the capacitor elements contain the first dopant.

[0024] (Capacitor element) (anode body) The anode body can contain a valve metal, an alloy containing a valve metal, a compound containing a valve metal, or the like. These materials can be used alone or in combination of two or more. Examples of preferred valve metals include aluminum, tantalum, niobium, and titanium. Anode bodies with porous surfaces can be obtained by roughening the surface of a substrate (such as a foil-shaped or plate-shaped substrate) containing a valve metal, for example, by etching. Surface roughening can be achieved, for example, by etching. The anode body may also be a compact of particles containing a valve metal, or a sintered body thereof. The sintered body has a porous structure.

[0025] (dielectric layer) The dielectric layer is an insulating layer that functions as a dielectric and is formed so as to cover at least a portion of the surface of the anode body. The dielectric layer is formed by anodizing the valve metal on the surface of the anode body using a chemical conversion treatment or the like. The dielectric layer may be formed so as to cover at least a portion of the anode body. The dielectric layer is usually formed on the surface of the anode body. Since the dielectric layer is formed on the porous surface of the anode body, it is formed along the inner wall surfaces of the holes and pits on the surface of the anode body.

[0026] The dielectric layer contains an oxide of a 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. However, the dielectric layer is not limited to these, and any layer that functions as a dielectric may be used.

[0027] (cathode) The cathode section includes at least a solid electrolyte layer that covers at least a portion of the dielectric layer. The cathode section is usually formed on at least a portion of the surface of the anode body via a dielectric layer. The cathode section may include 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.

[0028] (Solid electrolyte layer) The solid electrolyte layer is formed on the surface of the anode body via the dielectric layer so as to cover the dielectric layer. The solid electrolyte layer does not necessarily have to cover the entire dielectric layer (the entire surface), but only needs to cover at least a portion of the dielectric layer. The solid electrolyte layer constitutes at least a portion of the cathode part of the solid electrolytic capacitor.

[0029] The solid electrolyte layer includes a conductive polymer and a dopant component.

[0030] (conductive polymer) The conductive polymer may be a known conductive polymer used in solid electrolytic capacitors, such as a π-conjugated conductive polymer. Examples of conductive polymers include polymers with a basic skeleton of polypyrrole, polythiophene, polyaniline, polyfuran, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, and polythiophene vinylene. Among these, polymers with a basic skeleton of polypyrrole, polythiophene, or polyaniline are preferred. The above polymers include homopolymers, copolymers of two or more monomers, and derivatives thereof (e.g., substituted products having substituents). For example, polythiophenes include poly(3,4-ethylenedioxythiophene).

[0031] The conductive polymers may be used alone or in combination of two or more.

[0032] The weight average molecular weight (Mw) of the conductive polymer is not particularly limited, but is, for example, 1,000 or more and 1,000,000 or less.

[0033] In this specification, the weight-average molecular weight (Mw) is a value calculated as polystyrene measured by gel permeation chromatography (GPC), which is usually performed using a polystyrene gel column and water / methanol (volume ratio 8 / 2) as the mobile phase.

[0034] (dopant component) The dopant component may contain at least a first dopant, and may further contain a second dopant other than the first dopant, as necessary. The ratio of the first dopant in the dopant component is, for example, 50% by mass or more, 75% by mass or more, 90% by mass or more, or 95% by mass or more. The ratio of the first dopant in the dopant component is 100% by mass or less. The dopant component may be composed of only the first dopant. Furthermore, the ratio of dopant IA in the dopant component may be within the above range. The ratio of dopant IB in the dopant component may be within the above range. In a first aspect, the dopant component may be composed of only dopant IA. In a second aspect, the dopant component may be composed of only dopant IB.

[0035] (First dopant) Examples of the aromatic ring contained in the first dopant include a benzene ring, a naphthalene ring, an anthracene ring, and a phenanthrene ring. The number of carbon atoms in the aromatic ring is, for example, 6 to 20, or may be 6 to 14, or may be 6 to 10. In the case of a benzene ring or a naphthalene ring, the molecular size is relatively small, and the molecules of the first dopant are easily brought into close proximity to the conductive polymer, and the positions of the multiple electron-withdrawing functional groups are also easily brought into close proximity. Therefore, the first dopant is easily tightly coordinated to the conductive polymer, and the high conductivity of the solid electrolyte layer is more easily ensured.

[0036] The first dopant has a plurality of functional groups on an aromatic ring. The plurality of functional groups includes at least an electron-withdrawing functional group. The plurality of functional groups may further include an electron-donating functional group. The first dopant has two or more electron-withdrawing functional groups in one molecule.

[0037] Examples of electron-withdrawing functional groups include sulfo, carboxy, nitro, cyano, aldehyde, acyl, tosyl, and halogen atoms (fluoro, chloro, bromo, and iodo groups). Among the electron-withdrawing functional groups, sulfo (first functional group) and carboxy (second functional group) are preferred from the viewpoint of obtaining higher capacitor performance.

[0038] The electron-donating functional group (third functional group) is preferably a hydroxy group or an alkoxy group. When the first dopant has multiple third functional groups, each third functional group may be either a hydroxy group or an alkoxy group. The number of carbon atoms in the alkoxy group is, for example, 1 to 10, or may be 1 to 6. From the viewpoint of easily obtaining a higher oxygen radical scavenging effect, each third functional group is preferably a hydroxy group or an alkoxy group having 1 to 4 carbon atoms. The alkoxy group may be either linear or branched. Specific examples of the alkoxy group include, but are not limited to, a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, an n-butoxy group, an isobutoxy group, a sec-butoxy group, a tert-butoxy group, a hexyloxy group, a 2-ethyl-hexyloxy group, and an octoxy group.

[0039] In the solid electrolyte layer, the sulfo group, which is the first functional group, exists in the free form (-SO3H) and the anion form (-SO3 - ), or in the form of a salt, or may be contained in a form bound to or interacting with a conductive polymer. In this specification, all of these forms of sulfo groups may be simply referred to as "sulfo groups." Similarly, in the solid electrolyte layer, the carboxy group may be contained in a free form (-COOH), an anion form (-COO - ), or a salt form, or may be contained in a form bonded to or interacting with the conductive polymer. In this specification, all of these forms of carboxy groups may be simply referred to as a "carboxy group." Furthermore, the hydroxy of the third functional group (in other words, a phenolic hydroxy group) may be contained in a free form (-OH), an anion form (-O - The salt may be a salt of a sulfonate anion or a carboxylate anion with either an organic base (organic amine, organic ammonium, etc.) or an inorganic base (metal hydroxide, ammonia, etc.).

[0040] When the first dopant has two or more first functional groups, at least some of the first functional groups may be included in the same form, or all of the first functional groups may be included in different forms. When the first dopant has two or more second functional groups, at least some of the two or more second functional groups may be included in the same form, or all of the second functional groups may be included in different forms. When the first dopant has two or more third functional groups, at least some of the two or more third functional groups may be included in the same form, or all of the third functional groups may be included in different forms.

[0041] In the dopant IA, the number m1 of electron-withdrawing functional groups in one molecule is m1≧2, or may be m1≧3, or may be m1≧4. The upper limit of the number m1 can be determined depending on the number of carbon atoms in the aromatic ring. The number m1 may be m1≦6, or may be m1≦4. These upper and lower limit values ​​can be combined in any manner.

[0042] In the first dopant (specifically, dopant IA or dopant IB), the number n1 of the first functional groups is, for example, n1≧1 and may be n1≧2. The number n2 of the second functional groups is, for example, n2≧1 and may be n2≧2. When at least one of n1≧2 and n2≧2 is satisfied, the thermal stability of the first dopant can be further improved. When n1≧2, a stronger binding strength of the first dopant to the conductive polymer is obtained, thereby suppressing dedoping even in high-temperature environments, which is more advantageous in ensuring high conductivity of the solid electrolyte layer. When n2≧2, the hydrolysis resistance of the first dopant can be further improved, further enhancing the effect of suppressing decomposition of the first dopant even in high-temperature environments. This is therefore advantageous in further improving the thermal stability of the solid electrolyte layer.

[0043] In dopant IA, the number m2 of electron-donating functional groups (or the number n3 of third functional groups) in one molecule is determined according to the number m1 of electron-withdrawing functional groups so as to satisfy the relationship (m1-m2)≧2. The number m2 (or n3) may be m2 (or n3)≦1. When the types and numbers of electron-withdrawing functional groups are the same, the weight loss rate tends to be lower when the number m2 of electron-donating functional groups (or the number n3 of third functional groups) is 1 or greater than that when the number m2 (or n3) is 0. From the viewpoint of further reducing the weight loss rate, dopant IA preferably has an electron-donating functional group (m2 (or n3)≧1), and m2 (or n3)=1 may be used.

[0044] The dopant IB may have first to third functional groups in an aromatic ring (e.g., the above-mentioned aromatic rings such as a benzene ring and a naphthalene ring) such that the numbers of the functional groups, n1, n2, and n3, satisfy the following conditions: n1≧1, n2≧1, n3≧1, and (n1+n2+n3)≧4. In the dopant IB, the upper limit of (n1+n2+n3) can be determined depending on the number of carbon atoms in the aromatic ring. For example, when the aromatic ring is a benzene ring, (n1+n2+n3)≦6, and when the aromatic ring is a naphthalene ring, (n1+n2+n3)≦8. Regardless of the type of aromatic ring, (n1+n2+n3)≦6 may also be satisfied.

[0045] In the dopant IB, the number n3 of the third functional groups satisfies n3 ≧ 1, and may also satisfy n3 ≧ 2. When n3 ≧ 2, the effect of capturing oxygen radicals is further enhanced, which is more advantageous from the viewpoint of suppressing oxidative degradation of the conductive polymer.

[0046] When the first dopant has a first functional group, the position of the first functional group on the aromatic ring is not particularly limited. When the first dopant has a naphthalene ring as the aromatic ring, it is preferable that the first functional group be located at at least one selected from the group consisting of the 2-, 3-, 6-, and 7-positions of the naphthalene ring. In this case, the first dopant is more likely to come into close proximity with the conductive polymer, which is advantageous in terms of increasing the conductivity of the solid electrolyte layer.

[0047] In the first dopant, the positions of the first functional group and the second functional group in the aromatic ring (such as a benzene ring or a naphthalene ring) are not particularly limited. When the first dopant has a benzene ring as the aromatic ring, the position of the second functional group in the benzene ring may be any of the o-position, m-position, and p-position relative to the first functional group. When the second functional group is located in the m-position relative to the first functional group in the benzene ring, this is preferred because it makes it easier to obtain higher hydrolysis resistance of the first dopant. When the first dopant has two or more first functional groups, it is preferred that the second functional group be located in the m-position relative to at least one first functional group. When the first dopant has two or more second functional groups, it is preferred that at least one second functional group be located in the m-position relative to the first functional group.

[0048] When the first dopant has a first functional group and an electron-donating functional group (or a third functional group), the position of the electron-donating functional group (or the third functional group) in the aromatic ring (such as a benzene ring or a naphthalene ring) is not particularly limited. When the first dopant has a benzene ring as the aromatic ring, the position of the electron-donating functional group (or the third functional group) in the benzene ring may be any of the o-position, m-position, and p-position relative to the first functional group. When the electron-donating functional group (or the third functional group) is located in the o-position or m-position relative to the first functional group, it is more likely to capture oxygen radicals in closer proximity to the conductive polymer, which is thought to further enhance the effect of suppressing oxidative degradation of the conductive polymer. The position of the electron-donating functional group (or the third functional group) may be in the o-position or p-position relative to the first functional group. In this case, it is easy to introduce each functional group into the benzene ring, and it is easy to balance the high hydrolysis resistance provided by the electron-withdrawing functional groups (first and second functional groups) with the high oxygen radical scavenging effect provided by the electron-donating functional group (or third functional group), which is advantageous in further improving the thermal stability of the solid electrolyte layer.

[0049] The first dopant having a naphthalene ring as the aromatic ring may be at least one selected from the group consisting of aromatic compounds in which the number m1 of electron-withdrawing functional groups is m1≧4, aromatic compounds in which the number n1 of sulfo groups is n1≧2 and the number n2 of carboxy groups is n2=0, and dopant IB (e.g., aromatic compounds in which the number m2 (or n3) of electron-donating functional groups is m2≧1). These compounds tend to achieve a lower weight loss rate. From a similar perspective, dopant IA having a naphthalene ring as the aromatic ring may be any dopant IA other than 6,8-disulfo-2-naphthoic acid, 5,7-disulfo-2-naphthoic acid, 3,6-disulfo-1-naphthoic acid, 4,8-disulfo-2-naphthoic acid, and 3,7-disulfo-2-naphthoic acid. These disulfonaphthoic acids have no substituents other than two sulfo groups and one carboxy group.

[0050] The first dopant may have a first substituent other than the electron-withdrawing functional group and the electron-donating functional group (e.g., the first to third functional groups) as needed. The first dopant may also be a compound having a non-aromatic ring Z fused to an aromatic ring (e.g., a benzene ring, a naphthalene ring, etc.). In a first dopant having such a structure, among the carbon atoms constituting the aromatic ring (e.g., the carbon atoms at positions 1 to 6 of the benzene ring), two carbon atoms that are not substituted with the electron-withdrawing functional group and the electron-donating functional group (e.g., the first to third functional groups) are connected by an aliphatic chain. The aliphatic chain may be saturated or unsaturated. The first dopant may have one or more second substituents on the aliphatic chain. In addition to the electron-withdrawing functional group and the electron-donating functional group (such as the first to third functional groups), compounds having such a first substituent and compounds in which ring Z, which may have a second substituent, is condensed with an aromatic ring (such as a benzene ring or a naphthalene ring) are also included in the first dopant (or dopant IA or dopant IB).

[0051] Examples of the first substituent that the first dopant may have on the aromatic ring (such as a benzene ring or a naphthalene ring) include hydrocarbon groups. In dopant IB, the first substituent may be an electron-donating group other than the third functional group, or an electron-withdrawing group other than the first and second functional groups. However, from the viewpoint of easily achieving the effects of the first to third functional groups in a balanced manner, a hydrocarbon group is preferred. The hydrocarbon group may be any of aliphatic, alicyclic, and aromatic. From the viewpoint of easy coordination with the conductive polymer, the hydrocarbon group is preferably an aliphatic hydrocarbon group. The carbon number of the aliphatic hydrocarbon group is, for example, 1 to 10, and may be 1 to 6 or 1 to 4. The aliphatic hydrocarbon group may be either saturated or unsaturated. Examples of the aliphatic hydrocarbon group include an alkyl group, an alkenyl group, and a dienyl group.

[0052] The number n4 of first substituents may be determined depending on the number of carbon atoms in the aromatic ring and the number of electron-withdrawing functional groups and electron-donating functional groups. The number n4 of first substituents is, for example, 0 to 6, and may be 0 to 4. When the first dopant has a benzene ring as the aromatic ring, the number n4 of first substituents is 0, 1, or 2. When the first dopant has two or more first substituents, at least two of the first substituents may be the same, or all of them may be different. From the viewpoint of easily achieving a balanced effect of the electron-withdrawing functional group and the electron-donating functional group (e.g., the first to third functional groups), it is also preferable that the first dopant does not have a first substituent.

[0053] When the first dopant contains ring Z, examples of the second substituent that the first dopant may have on the aliphatic chain constituting ring Z include the groups described for the electron-withdrawing functional group, the groups described for the first to third functional groups, and the groups described for the first substituent. The number n5 of second substituents in the first dopant may be 1 or may be 2 or more. When the first dopant has two or more second substituents, some of the second substituents may be the same, or all of the second substituents may be different.

[0054] From the viewpoint of facilitating the approach of the first dopant to the conductive polymer, it is preferable that the first dopant does not have the non-aromatic ring Z as described above.

[0055] The dopant component may include one type of first dopant or may include two or more types of first dopants. The dopant component may include one type of dopant IA or may include two or more types of dopants IA. The dopant component may include one type of dopant IB or may include two or more types of dopants IB. The dopant component may include at least one type of dopant IB and at least one type of dopant IA that is not included in dopant IB.

[0056] (Second dopant) The second dopant may be any dopant other than the first dopant, and may be, for example, at least one selected from the group consisting of anions and polyanions.

[0057] 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 p-toluenesulfonic acid and naphthalenesulfonic acid.

[0058] Examples of polyanions include polymeric polysulfonic acids and polymeric polycarboxylic acids. Polymeric polysulfonic acids include polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallyl sulfonic acid, polyacrylic sulfonic acid, and polymethacrylic sulfonic acid. Polymeric polycarboxylic acids include polyacrylic acid and polymethacrylic acid. Polyanions also include polyester sulfonic acid and phenol sulfonic acid novolac resin. However, polyanions are not limited to these.

[0059] The anion and the polyanion may each be contained in the solid electrolyte layer in the form of a salt. In the solid electrolyte layer, the anion and the polyanion may each bind to or interact with the conductive polymer to form a conductive polymer complex together with the conductive polymer.

[0060] The dopant component may include one type of second dopant, or may include two or more types of second dopants.

[0061] As described above, in the solid electrolytic capacitor element of the present disclosure, the weight loss rate of the solid electrolyte as determined by thermogravimetric analysis can be kept low. The weight loss rate of the solid electrolyte can be adjusted by, for example, the type of dopant, the ratio of the dopant to the conductive polymer, and the polymerization conditions for forming the conductive polymer (e.g., the polymerization potential of the electrolytic polymerization, the concentration of the conductive polymer precursor and the concentration of the dopant in the treatment solution used for polymerization).

[0062] (others) The amount of the dopant component contained in the solid electrolyte layer is, for example, 10 to 1000 parts by mass, or may be 20 to 500 parts by mass, or 50 to 200 parts by mass, relative to 100 parts by mass of the conductive polymer.

[0063] 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 composition of the dopant component contained in each layer may be the same or different. When the solid electrolyte layer is composed of multiple layers, it is sufficient that at least one layer contains the first dopant.

[0064] The solid electrolyte layer may further contain, as necessary, known additives and known conductive materials other than conductive polymers, such as at least one selected from the group consisting of conductive inorganic materials such as manganese dioxide and TCNQ complex salts. A layer for enhancing adhesion may be interposed between the dielectric layer and the solid electrolyte layer.

[0065] The solid electrolyte layer is formed, for example, by polymerizing a conductive polymer precursor and a dopant component on a dielectric layer using a treatment liquid. Polymerization can be performed by at least one of chemical polymerization and electrolytic polymerization. Examples of conductive polymer precursors include at least one selected from the group consisting of monomers, oligomers, and prepolymers. Each of the oligomers and prepolymers has a structure in which multiple monomer units are linked together. One precursor may be used, or two or more precursors may be used in combination. The solid electrolyte layer may be formed by applying a treatment liquid (e.g., a dispersion or solution) containing a conductive polymer and a dopant component to a dielectric layer and then drying the resulting layer. Examples of the dispersion medium (or solvent) include water, an organic solvent, or a mixture thereof. The treatment liquid may further contain other components such as additives.

[0066] When using a treatment solution containing a conductive polymer precursor and a dopant component, an oxidizing agent is used to polymerize the precursor as needed. The first dopant may be used as the oxidizing agent, but an oxidizing agent other than the first dopant may also be used. The oxidizing agent may be included in the treatment solution as an additive. The oxidizing agent may also be applied to the anode body on which the dielectric layer has been formed before or after contacting the treatment solution with the anode body. Examples of such oxidizing agents include sulfates, sulfonic acids, and their salts. The oxidizing agents may be used alone or in combination of two or more. Examples of sulfates include salts of sulfuric acid and metals, such as ferric sulfate and sodium persulfate, and salts of sulfates such as persulfates. Examples of metals constituting the salts include alkali metals (sodium, potassium, etc.), iron, copper, chromium, and zinc. Sulfonic acids and their salts function not only as oxidizing agents but also as dopants. Examples of sulfonic acids and their salts include low-molecular-weight sulfonic acids and their salts, such as those exemplified for the second dopant. Examples of oxidizing agents include Fe. 3+Compounds capable of generating oxidizing agent (such as ferric sulfate), persulfates (such as sodium persulfate and ammonium persulfate), hydrogen peroxide, etc. may also be used. The oxidizing agent may be used alone or in combination of two or more.

[0067] The process of forming a solid electrolyte layer by immersion in a treatment solution and polymerization (or drying) may be performed once or may be repeated multiple times, with the conditions, such as the composition and viscosity of the treatment solution, remaining the same each time, or at least one of the conditions may be changed.

[0068] From the viewpoint of easy control of the properties of the solid electrolyte, it is preferable to form the solid electrolyte layer by electrolytic polymerization. Electrolytic polymerization can be carried out by applying a polymerization voltage while the anode body having a dielectric layer is in contact with (e.g., immersed in) a treatment solution containing a precursor of a conductive polymer and a dopant component. The polymerization voltage is applied via a power supply.

[0069] In the electrolytic polymerization, the polymerization voltage is, for example, 1 V or more and 3.5 V or less (or 3 V or less), and may be 2 V or more and 3.5 V or less (or 3 V or less). The polymerization voltage is set by the voltage applied to a reference electrode (silver / silver chloride electrode (Ag / Ag + ) is the potential of the current source relative to

[0070] In the treatment liquid, the ratio of the dopant component to the conductive polymer precursor is, for example, 0.1 mol or more and 0.75 mol or less, and may be 0.4 mol or more and 0.75 mol or less, per 1 mol of the monomer unit of the conductive polymer.

[0071] The temperature at which 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.

[0072] (Cathode extraction layer) The cathode extraction layer may include at least a first 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 first layer and a second layer that covers the first layer. Examples of the first layer include a layer containing conductive particles and metal foil. Examples of the conductive particles include at least one selected from conductive carbon and metal powder. For example, the cathode extraction layer may be formed of a first layer containing conductive carbon and a second layer containing metal powder or metal foil. When metal foil is used as the first layer, the cathode extraction layer may be formed of this metal foil.

[0073] The first layer containing conductive carbon can be formed, for example, by immersing an anode body having a dielectric layer on which a solid electrolyte layer has been formed in a dispersion liquid containing conductive carbon, or by applying a paste containing conductive carbon to the surface of the solid electrolyte layer. Examples of the conductive carbon include graphites such as artificial graphite and natural graphite. Examples of the dispersion liquid and paste include a mixture in which conductive carbon is dispersed in an aqueous liquid medium.

[0074] The second layer containing metal powder can be formed, for example, by laminating a composition containing metal powder on the surface of the first layer. For example, a metal paste layer formed using a composition containing metal powder such as silver particles and a resin (binder resin) can be used as the second layer. Thermoplastic resins can also be used as the resin, but it is preferable to use thermosetting resins such as imide resins and epoxy resins.

[0075] When a metal foil is used as the first layer, the type of metal is not particularly limited, but it is preferable to use a valve metal such as aluminum, tantalum, or niobium, or an alloy containing a valve metal. If necessary, the surface of the metal foil may be roughened by etching or the like. 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 non-metal different from the metal constituting the metal foil. Examples of dissimilar metals and non-metals include metals such as titanium and non-metals such as carbon (e.g., conductive carbon).

[0076] The coating of the dissimilar metal or non-metal (for example, conductive carbon) may be the first layer, and the metal foil may be the second layer.

[0077] The thickness of each of the first layer and the second layer is, for example, 0.1 μm or more and 100 μm or less, or may be 0.5 μm or more and 50 μm or less, or may be 1 μm or more and 20 μm or less.

[0078] (separator) When a metal foil is used for the cathode extraction layer, a separator may be disposed between the metal foil and the anode body. The separator is not particularly limited, and may be, for example, a nonwoven fabric containing fibers of cellulose, polyethylene terephthalate, vinylon, or polyamide (e.g., aliphatic polyamide, aromatic polyamide such as aramid).

[0079] (others) The solid electrolytic capacitor may be a wound type, and may be either a chip type or a laminate type. The solid electrolytic capacitor may include two or more capacitor elements. For example, the solid electrolytic capacitor may include a laminate of two or more capacitor elements. The solid electrolytic capacitor may include two or more wound capacitor elements. The configuration of the capacitor elements may be selected depending on the type of solid electrolytic capacitor.

[0080] In the capacitor element, one end of a cathode terminal is electrically connected to the cathode extraction layer. drawer A conductive adhesive is applied to the layer, and the cathode is attached via the conductive adhesive. drawer The anode body is electrically connected to one end of an anode terminal. The other end of the anode terminal and the other end of the cathode terminal are each drawn out from the resin exterior body or the case. The other end of each terminal exposed from the resin exterior body or the case is connected to the substrate on which the solid electrolytic capacitor is to be mounted. Board and It is used for soldering connections, etc.

[0081] The capacitor element is sealed using a resin outer casing or case. For example, the capacitor element and the resin material of the outer casing (e.g., uncured thermosetting resin and filler) may be placed in a mold, and the capacitor element may be sealed in the resin outer casing by transfer molding, compression molding, or the like. At this time, the other end portions of the anode terminal and cathode terminal connected to the anode lead drawn from the capacitor element are exposed from the mold. Alternatively, the capacitor element may be placed in a bottomed case so that the other end portions of the anode terminal and cathode terminal are positioned on the opening side of the bottomed case, and the opening of the bottomed case may be sealed with a sealant to form a solid electrolytic capacitor.

[0082] Fig. 1 is a cross-sectional view schematically illustrating the structure of a solid electrolytic capacitor according to an embodiment of the present disclosure. As shown in Fig. 1, solid electrolytic capacitor 1 includes a capacitor element 2, a resin outer casing 3 that seals capacitor element 2, and an anode terminal 4 and a cathode terminal 5, at least a portion of which is exposed to the outside of resin outer casing 3. Anode terminal 4 and cathode terminal 5 may be made of a metal such as copper or a copper alloy. Resin outer casing 3 has a substantially rectangular parallelepiped outer shape, and solid electrolytic capacitor 1 also has a substantially rectangular parallelepiped outer shape.

[0083] The capacitor element 2 includes an anode body 6, a dielectric layer 7 covering the anode body 6, and a cathode body 8 covering the dielectric layer 7. The cathode body 8 includes a solid electrolyte layer 9 covering the dielectric layer 7 and a cathode extraction layer 10 covering the solid electrolyte layer 9, constituting the cathode section described above. In the illustrated example, the cathode extraction layer 10 includes a carbon layer 11 as a first layer and a metal paste layer 12 as a second layer. According to the present disclosure, the weight loss rate of the solid electrolyte constituting the solid electrolyte layer 9 is 3% or less. Alternatively, the solid electrolyte layer 9 includes a conductive polymer and a dopant component including a first dopant (e.g., dopant IB). This configuration allows the capacitor element 2 and the solid electrolytic capacitor 1 to exhibit high thermal stability. Furthermore, the high reliability of the capacitor element 2 and the solid electrolytic capacitor 1 can be ensured.

[0084] The anode body 6 includes a region facing the cathode body 8 and a region not facing the cathode body 8. Of the region of the anode body 6 not facing the cathode body 8, an insulating separation layer 13 is formed in a strip-like shape on the surface of the anode body 6 in a portion adjacent to the cathode body 8, thereby restricting contact between the cathode body 8 and the anode body 6. Another part of the region of the anode body 6 not facing the cathode body 8 is electrically connected to the anode terminal 4 by welding. The cathode terminal 5 is electrically connected to the cathode body 8 via an adhesive layer 14 formed of a conductive adhesive.

[0085] Principal surfaces 4S and 5S of anode terminal 4 and cathode terminal 5 are exposed from the same surface of resin outer casing 3. These exposed surfaces are used for soldering to a substrate (not shown) on which solid electrolytic capacitor 1 is to be mounted.

[0086] [Example] 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.

[0087] <Solid electrolytic capacitor A1> A solid electrolytic capacitor 1 (solid electrolytic capacitor A1) shown in FIG. 1 was fabricated in the following manner, and its characteristics were evaluated.

[0088] (1) Preparation of anode body 6 Anode body 6 was produced by roughening both surfaces of an aluminum foil (thickness: 100 μm) used as a substrate by etching.

[0089] (2) Formation of dielectric layer 7 The other end of the anode body 6 was immersed in a chemical conversion solution, and a direct current voltage of 70 V was applied for 20 minutes to form a dielectric layer 7 containing aluminum oxide.

[0090] (3) Formation of solid electrolyte layer 9 An aqueous solution containing pyrrole monomer and 4-hydroxy-5-sulfoisophthalic acid (dopant component) was prepared. The monomer concentration in this aqueous solution was 0.5 mol / L, and the concentration of 4-hydroxy-5-sulfoisophthalic acid was 0.3 mol / L. The 4-hydroxy-5-sulfoisophthalic acid used is represented by the following formula:

[0091] [ka]

[0092] The anode body 6 on which the dielectric layer 7 was formed in (2) above and a counter electrode were immersed in the obtained aqueous solution, and electrolytic polymerization was carried out at 25°C and a polymerization voltage of 3 V (polymerization potential relative to the silver reference electrode), thereby forming a solid electrolyte layer 9.

[0093] (4) Formation of cathode body 8 Anode body 6 having solid electrolyte layer 9 formed thereon 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 130 to 180°C for 10 to 30 minutes.

[0094] 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 to 200°C for 10 to 60 minutes, thereby forming metal paste layer 12. In this way, cathode body 8 composed of carbon layer 11 and metal paste layer 12 was formed. Capacitor element 2 was fabricated in the manner described above.

[0095] (5) Assembly of solid electrolytic capacitor 1 Cathode body 8 of capacitor element 2 obtained in (4) above was joined to one end of cathode terminal 5 with adhesive layer 14 of a conductive adhesive. One end of anode body 6 protruding from capacitor element 2 was joined to one end of anode terminal 4 by laser welding. Next, a resin outer casing 3 made of insulating resin was formed around the capacitor element 2 by molding. At this time, the other end of the anode terminal 4 and the other end of the cathode terminal 5 were left pulled out from the resin outer casing 3. In this way, the solid electrolytic capacitor A1 was completed. In the same manner as above, a total of 20 solid electrolytic capacitors A1 were produced.

[0096] (6) Evaluation The solid electrolytic capacitors were evaluated as follows. (a) Rate of change of ESR and capacitance Using a four-terminal LCR meter at 20°C, the initial capacitance (μF) of each solid electrolytic capacitor was measured at a frequency of 120 Hz, and the initial ESR (mΩ) at a frequency of 100 kHz was also measured. The average values ​​(initial capacitance: c0, initial ESR: r0) for the 20 solid electrolytic capacitors were then calculated.

[0097] The solid electrolytic capacitors were then reflowed at 260°C for 3 minutes. After the reflow process, an accelerated test was performed by applying the rated voltage to the solid electrolytic capacitors at 145°C for 500 hours. The capacitance and ESR were then measured at 20°C using the same procedure as for the initial capacitance and ESR, and the average values ​​for 20 solid electrolytic capacitors (capacitance after accelerated test: c1, ESR after accelerated test: r1) were calculated. The change in capacitance due to the accelerated test (= c1 - c0) was calculated, and the ratio (%) of the change in capacitance to the average initial capacitance (c0) was calculated as the capacitance change rate (ΔCap). The change in ESR due to the accelerated test (= r1 - r0) was calculated, and the ratio (%) of the change in ESR to the average initial ESR (r0) was calculated as the ESR change rate (ΔESR).

[0098] (b) Weight loss rate of the solid electrolyte layer upon heating A sample of the solid electrolyte was taken from the solid electrolyte layer of the capacitor element 2 removed from the solid electrolytic capacitor 1 according to the procedure already described, and the weight loss rate of this sample was determined.

[0099] <Solid electrolytic capacitor A2> A capacitor element and a solid electrolytic capacitor A2 were fabricated and evaluated in the same manner as the solid electrolytic capacitor A1, except that in (3) of the solid electrolytic capacitor A1, 4-hydroxy-5-sulfoisophthalic acid was replaced with 3-hydroxy-6,8-disulfo-2-naphthoic acid represented by the following formula. [ka]

[0100] <Solid electrolytic capacitor A3> A capacitor element and a solid electrolytic capacitor A3 were fabricated and evaluated in the same manner as the solid electrolytic capacitor A1, except that in (3) of the solid electrolytic capacitor A1, 4-hydroxy-5-sulfoisophthalic acid was replaced with 5-sulfoisophthalic acid represented by the following formula.

[0101] [ka]

[0102] <Solid electrolytic capacitor B1> A capacitor element and a solid electrolytic capacitor B1 were fabricated and evaluated in the same manner as the solid electrolytic capacitor A1, except that in (3) of the solid electrolytic capacitor A1, 5-sulfosalicylic acid represented by the following formula was used instead of 4-hydroxy-5-sulfoisophthalic acid.

[0103] [ka]

[0104] <Solid electrolytic capacitor B2> A capacitor element and a solid electrolytic capacitor B2 were fabricated and evaluated in the same manner as the solid electrolytic capacitor A1, except that in (3) of the solid electrolytic capacitor A1, 2-naphthalenesulfonic acid represented by the following formula was used instead of 4-hydroxy-5-sulfoisophthalic acid.

[0105] [ka]

[0106] Table 1 shows the evaluation results for the solid electrolytic capacitors A1 to A3, B1, and B2.

[0107] [Table 1]

[0108] As shown in Table 1, in the examples in which the weight loss rate of the solid electrolyte was 3% or less, the changes in capacitance and ESR after the reflow treatment of the solid electrolytic capacitor were significantly reduced compared to the comparative examples in which the weight loss rate exceeded 3%.

[0109] <Solid electrolytic capacitors A4 to A6> Capacitor elements and solid electrolytic capacitors A4 to A6 were fabricated in the same manner as solid electrolytic capacitor A1, except that in (3) of solid electrolytic capacitor A1, 4-hydroxy-5-sulfoisophthalic acid was replaced with the dopant components shown in Table 2. Using the capacitor elements or solid electrolytic capacitors, evaluations of (6)(a) and (b) were performed, and the rate of decrease in airtightness in (c) below was also evaluated.

[0110] (c) Airtightness reduction rate After reflow processing, the solid electrolytic capacitor was cooled to 25°C. The reflow processing was performed under the following conditions: a peak temperature of 260°C, a holding time at the peak temperature of 10 seconds, and a holding time of 140 seconds at 220°C or higher. After performing the reflow processing and cooling to 25°C three times in total, the solid electrolytic capacitor was immersed in Fluorinert (a fluorine-based inert liquid, manufactured by 3M) heated to 120°C for 30 seconds. At this time, the generation of bubbles from the solid electrolytic capacitor was checked. A total of 20 solid electrolytic capacitors were evaluated, and the number of solid electrolytic capacitors that generated bubbles was evaluated as the rate of decrease in airtightness.

[0111] <Solid electrolytic capacitor B3> In (3) of the solid electrolytic capacitor A1, the dopant component shown in Table 2 was used instead of 4-hydroxy-5-sulfoisophthalic acid. The concentration of the dopant component in the aqueous solution was 0.5 mol / L. The polymerization voltage for electrolytic polymerization was 4 V (polymerization potential relative to the silver reference electrode). Apart from these, a capacitor element and a solid electrolytic capacitor B3 were fabricated in the same manner as the solid electrolytic capacitor A1. Using the capacitor element or the solid electrolytic capacitor, evaluations (6)(a) and (b) were performed, and the above (c) The rate of decrease in airtightness was evaluated.

[0112] The evaluation results for solid electrolytic capacitors A4 to A6 and B3 are shown in Table 2. Table 2 also shows the results of similar evaluations for solid electrolytic capacitors A1, A3, B1 and B2.

[0113] [Table 2]

[0114] As shown in Table 2, when the weight loss rate of the solid electrolyte is 3% or less, the changes in capacitance and ESR after the solid electrolytic capacitor is reflow processed are significantly reduced compared to when the weight loss rate exceeds 3%.

[0115] When the weight loss rate of the solid electrolyte exceeded 3%, the airtightness significantly decreased when exposed to high temperatures (B1 to B3). When the dopant component satisfied (m1 - m2) ≥ 2, the weight loss rate of the solid electrolyte tended to be 3% or less (comparison of A1, A3 to A6 with B1 to B3). Furthermore, when the dopant component had an electron-donating functional group (or a third functional group), the weight loss rate of the solid electrolyte tended to be even lower (comparison of A1 with A3). However, the weight loss rate of the solid electrolyte was not only dependent on the type of dopant component, but was also significantly affected by the polymerization conditions of the solid electrolyte (comparison of A3 with B3).

[0116] 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. Accordingly, the appended claims should be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention. [Industrial Applicability]

[0117] According to the present disclosure, a solid electrolytic capacitor element and a solid electrolytic capacitor having excellent thermal stability are provided. Furthermore, the deterioration of the airtightness of the solid electrolytic capacitor during the reflow process can be suppressed. Therefore, the solid electrolytic capacitor element and the solid electrolytic capacitor can be used in various applications requiring high reliability. [Explanation of symbols]

[0118] 1: solid electrolytic capacitor, 2: capacitor element, 3: resin outer casing, 4: anode terminal, 4S: main surface of anode terminal, 5: cathode terminal, 5S: main surface of cathode terminal, 6: anode body, 7: dielectric layer, 8: cathode body, 9: solid electrolyte layer, 10: cathode lead layer, 11: carbon layer, 12: metal paste layer, 13: separation layer, 14: adhesive layer

Claims

1. an anode body, a dielectric layer formed on a surface of the anode body, and a cathode portion covering at least a portion of the dielectric layer, the cathode portion includes a solid electrolyte layer covering at least a portion of the dielectric layer, the solid electrolyte layer contains a conductive polymer and a dopant component, the dopant component includes an aromatic compound having a plurality of functional groups on an aromatic ring; the plurality of functional groups includes an electron-withdrawing functional group and may or may not include an electron-donating functional group; In one molecule of the aromatic compound, when the number of the electron-withdrawing functional groups is m1 and the number of the electron-donating functional groups is m2, (m1-m2)≧2; a solid electrolytic capacitor element in which the solid electrolyte constituting the solid electrolyte layer has a weight loss rate of 3% or less when heated to 180°C, held at 180°C for 20 minutes, cooled from 180°C to 30°C, and then heated from 30°C to 260°C at a rate of 20°C / min, as determined by thermogravimetric analysis.

2. The solid electrolytic capacitor element according to claim 1 , wherein m2≦1 is satisfied.

3. 3. The solid electrolytic capacitor element according to claim 1, wherein the aromatic compound has at least one first functional group: a sulfo group as the electron-withdrawing functional group.

4. an anode body, a dielectric layer formed on a surface of the anode body, and a cathode portion covering at least a portion of the dielectric layer, the cathode portion includes a solid electrolyte layer covering at least a portion of the dielectric layer, the solid electrolyte layer contains a conductive polymer and a dopant component, the dopant component includes an aromatic compound having an electron-withdrawing functional group and an electron-donating functional group on an aromatic ring; the aromatic compound has, as the electron-withdrawing functional groups, at least a first functional group: a sulfo group and a second functional group: a carboxy group, and, as the electron-donating functional group, a third functional group: at least one selected from the group consisting of a hydroxy group and an alkoxy group; In one molecule of the aromatic compound, when the number of the first functional groups is n1, the number of the second functional groups is n2, and the number of the third functional groups is n3, n1≧1, n2≧1, n3≧1, and (n1+n2+n3)≧4 are satisfied; a solid electrolytic capacitor element in which the solid electrolyte constituting the solid electrolyte layer has a weight loss rate of 3% or less when heated to 180°C, held at 180°C for 20 minutes, cooled from 180°C to 30°C, and then heated from 30°C to 260°C at a rate of 20°C / min, as determined by thermogravimetric analysis.

5. the aromatic compound has a benzene ring as the aromatic ring, 5. The solid electrolytic capacitor element according to claim 4, wherein the second functional group is located at the m-position relative to the first functional group.

6. The solid electrolytic capacitor element according to claim 4 or 5, which satisfies at least one of n1≧2 and n2≧2.

7. The solid electrolytic capacitor element according to any one of claims 4 to 6, wherein n3≧2 is satisfied.

8. 8. The solid electrolytic capacitor element according to claim 4, wherein the alkoxy group has 1 to 4 carbon atoms.

9. the aromatic compound has a benzene ring as the aromatic ring, 9. The solid electrolytic capacitor element according to claim 3, wherein the electron-donating functional group is located at the o-position or p-position relative to the first functional group.

10. The solid electrolytic capacitor element according to any one of claims 3 to 8, wherein the aromatic compound has a naphthalene ring as the aromatic ring, and at least the first functional group is located at at least one position selected from the group consisting of the 2-position, the 3-position, the 6-position, and the 7-position of the naphthalene ring.

11. 11. The solid electrolytic capacitor element according to claim 1, wherein the weight loss rate is 2.5% or less.

12. A solid electrolytic capacitor comprising at least one solid electrolytic capacitor element according to any one of claims 1 to 11.

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