Solid electrolytic capacitor having a conductive polymer compound and method for manufacturing the same

Abstract

The objective is to provide a solid electrolytic capacitor that has sufficient lifespan characteristics under high-temperature conditions. [Solution] A solid electrolytic capacitor is provided, having an anode foil, a cathode foil, and a separator between them, with an oxide film formed on their surfaces, and having an electrolyte portion in the gap between the anode foil and the cathode foil, wherein the electrolyte portion is composed of a solid electrolyte containing a conductive polymer compound, a polyanion dopant, an aromatic nitro compound having a polar group, and a secondary dopant as an optional swelling agent.

Description

[Technical Field]

[0001] The present invention relates to a solid electrolytic capacitor having a conductive polymer compound and a method for manufacturing the same. [Background technology]

[0002] Conventionally, solid electrolytic capacitors using conductive polymer compounds as solid electrolytes are known. Such capacitors can exhibit low ESR and excellent low-temperature characteristics.

[0003] Electrolytic capacitors (hybrid capacitors) that use a conductive polymer compound and an electrolyte as the electrolyte are also known. Such capacitors are advantageous in terms of, for example, the capacitance appearance rate in the initial capacitor characteristics and the film repairability.

[0004] Patent Document 1 describes a solid electrolytic capacitor using a conductive polymer compound as the electrolyte, and states that the polymerization solution used to form the conductive polymer on the electrode body by a chemical polymerization reaction during the manufacture of the capacitor contains a nitro compound. Representative examples of nitro compounds include p-nitrophenol.

[0005] Patent Document 2 describes a method for manufacturing a capacitor, comprising a step of forming a conductive polymer layer containing a thiophene derivative having alkoxy substituents at the 3rd and 4th positions as repeating units by chemical polymerization in an aqueous medium. It also states that this chemical polymerization can be carried out in a system in which a phenol derivative such as p-nitrophenol, p-cyanophenol, m-hydroxybenzoic acid, m-hydroxyphenol, or m-nitrophenol, or a nitrobenzene derivative such as nitrobenzoic acid or nitrobenzyl alcohol, is added to the aqueous medium containing the thiophene derivative or an oxidizing agent. According to Patent Document 2, the interaction between the thiophene derivative and the phenol derivative and the nitrobenzene derivative increases the polymerization rate, making it possible to form a conductive polymer layer with fewer polymerization cycles, thereby easily realizing a capacitor with excellent high-frequency characteristics and heat and moisture resistance.

[0006] Patent Document 3 describes a method for manufacturing a capacitor using a conductive polymer obtained by electrolytic polymerization using an electrolyte containing at least an alkyl phosphate ester, a phenol derivative, an aromatic sulfonate, and a polymerizable monomer as electrodes. The document states that the phenol derivative refers to phenol or an aromatic hydroxy compound having a substituent, and that substituents with high electron-withdrawing properties are preferred, with nitrophenol being the optimal choice.

[0007] Patent document 4 describes an electrolytic capacitor comprising an anode body having a dielectric layer formed on its surface, a solid electrolyte layer in contact with the dielectric layer and containing a conductive polymer, and an electrolyte. It states that the electrolyte may contain a nitro compound.

[0008] Patent Document 5 describes a solid electrolytic capacitor comprising an anode, a dielectric layer formed on the surface of the anode, a solid electrolyte layer covering at least a portion of the dielectric layer, and a cathode extraction layer covering at least a portion of the solid electrolyte layer, wherein the solid electrolyte layer contains a conductive polymer and a dopant, the dopant contains a compound having a benzene skeleton and at least one sulfo group bonded to the benzene skeleton, and the sulfate ions contained in the solid electrolyte layer are 1% by mass or less. The dopant contains a compound having a benzene skeleton and at least one sulfo group bonded to the benzene skeleton, and specific examples of this compound are given as 3-nitrosulfonic acid, 3,5-nitrodisulfonic acid, 2,4,6-trinitrobenzenesulfonic acid, etc.

[0009] Patent Document 6 describes an electrolytic capacitor in which a water-soluble first polymer and a water-dispersible second polymer are provided on the surface of the anode and the surface of the cathode, respectively, and the second polymer electrically connects the surface of the anode and the surface of the cathode, and a room-temperature solid substance is placed in a solvent that is solid at or below a first temperature and melts when heated to a second temperature or higher than the first temperature. The electrolyte may include nitrophthalic acid, trinitrophenol, hydroxynitrophenol, and hydroxynitrobenzoic acid, etc., with the room-temperature solid substance as the solvent. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Japanese Patent Publication No. 2004-228271 [Patent Document 2] Japanese Patent Application Publication No. 11-274006 [Patent Document 3] Japanese Patent Application Publication No. 06-267798 [Patent Document 4] Japanese Patent Publication No. 2023-169323 [Patent Document 5] Japanese Patent Publication No. 2023-058759 [Patent Document 6] Japanese Patent Application Laid-Open No. 2023-032518

Summary of the Invention

Problems to be Solved by the Invention

[0011] In conventional electrolytic capacitors containing a conductive polymer compound, there is a problem that the characteristics, particularly the life characteristics, are not sufficient under particularly severe high-temperature conditions (especially 120 to 200 °C or even 135 °C to 180 °C).

[0012] An object of the present disclosure is to provide an electrolytic capacitor that exhibits stable performance, particularly life characteristics, under high-temperature conditions.

Means for Solving the Problems

[0013] The present invention can solve the above problems by the following aspects. <Aspect 1> A solid electrolytic capacitor having an anode foil, a cathode foil, and a separator between them, on the surfaces of which an oxide film is formed, and having an electrolyte portion in the gap between the anode foil and the cathode foil, where the electrolyte portion is composed of a solid electrolyte containing a conductive polymer compound, a dopant that is a polyanion, an aromatic nitro compound having a polar group, and an optional secondary dopant, Solid electrolytic capacitor. <Aspect 2> The solid electrolytic capacitor according to Aspect 1, wherein the aromatic nitro compound has a hydroxy group or a carboxyl group. <Aspect 3> The solid electrolytic capacitor according to Aspect 1 or 2, wherein the aromatic nitro compound has a solubility of 0.01 g / 100 g aq or more. <Aspect 4> The solid electrolytic capacitor according to any one of Aspects 1 to 3, wherein the aromatic nitro compound is at least one selected from the group consisting of nitrophenol, nitrobenzoic acid or its salt, nitrosalicylic acid or its salt, and nitrobenzyl alcohol. <Aspect 5> A solid electrolytic capacitor according to any one of embodiments 1 to 4, wherein the content of the aromatic nitro compound is 0.5 to 100 parts by mass per 100 parts by mass of the total of the conductive polymer compound, the polyanion dopant and optional secondary dopant. <Aspect 6> A solid electrolytic capacitor according to any one of embodiments 1 to 5, wherein the ratio of the polyanion dopant to the conductive polymer compound in the solid electrolyte is 1:10 to 1:0.5. <Aspect 7> A solid electrolytic capacitor according to any one of embodiments 1 to 6, wherein the solid electrolyte comprises a secondary dopant, and the secondary dopant is at least one selected from the group consisting of glycerin, diglycerin, triglycerin, tetraglycerin, polyglycerin, polyglyceryl ether, diethylene glycol, triethylene glycol, and polyethylene glycol. <Aspect 8> A solid electrolytic capacitor according to any one of embodiments 1 to 7, wherein the conductive polymer compound and the polyanion dopant form fine particles. <Pattern 9> The solid electrolytic capacitor according to embodiment 8, wherein the aromatic nitro compound is localized on the surface of the fine particles and / or penetrates into the conductive polymer. <Aspect 10> The solid electrolytic capacitor according to embodiment 8, wherein the aromatic nitro compound is localized on the surface of the fine particles and / or penetrates into the conductive polymer, thereby being present between the fine particles and the oxide film of the anode foil. <Aspect 11> A solid electrolytic capacitor according to any one of embodiments 1 to 10, wherein the solid electrolyte further contains an amphoteric compound having an acidic group and a basic group in one molecule. <Aspect 12> The solid electrolytic capacitor according to embodiment 11, wherein the content of the amphoteric compound is 1 to 100 parts by mass with respect to 100 parts by mass of the total of the conductive polymer compound and the dopant. <Aspect 13> A solid electrolytic capacitor according to any one of embodiments 1 to 12, wherein the conductive polymer compound comprises polyethylenedioxythiophene. <Aspect 14> A solid electrolytic capacitor according to any one of embodiments 1 to 13, wherein the polyanion dopant contains polystyrene sulfonic acid. <Aspect 15> A solid electrolytic capacitor according to any one of embodiments 1 to 14, for use at temperatures of 100°C to 200°C. <Aspect 16> A method for manufacturing a solid electrolytic capacitor, (i) To provide a capacitor element comprising an anode foil, a cathode foil, and a separator between them, each having an oxide film formed on its surface, (ii) Prepare a dispersion of conductive polymer compounds containing fine particles composed of conductive polymer compounds and polyanion dopants, as well as optional secondary dopants. (iii) Adding an aromatic nitro compound having a polar group to the conductive polymer compound dispersion, (iv) Impregnate the capacitor element with the conductive polymer compound dispersion and dry it to form an electrolyte portion on the oxide film. Includes, After forming the electrolyte portion, the capacitor element is sealed in the case without adding any liquid substance. method. [Effects of the Invention]

[0014] According to this disclosure, it is possible to provide an electrolytic capacitor that has sufficient characteristics, particularly sufficient lifespan characteristics, under high-temperature conditions (especially 120-200°C, 125-190°C, or even 135-180°C). Furthermore, according to the present invention, it is possible to provide an electrolytic capacitor that suppresses the decrease in capacitance and increase in ESR at high temperatures, and reduces leakage current (LC) when stored at high temperatures. [Brief explanation of the drawing]

[0015] [Figure 1a] Figure 1a is a schematic cross-sectional view of a solid electrolytic capacitor according to one embodiment of the present disclosure. [Figure 1b] Figure 1b is a schematic perspective view of a capacitor element according to one embodiment of the present disclosure. [Figure 2] Figure 2 is a schematic cross-sectional view of the main part of a solid electrolytic capacitor. [Modes for carrying out the invention]

[0016] <<Solid electrolytic capacitor>> The solid electrolytic capacitor relating to this disclosure is It has an anode foil, a cathode foil, and a separator between them, with an oxide film formed on their surfaces, and an electrolyte portion in the void between the anode foil and the cathode foil. The electrolyte portion consists of a solid electrolyte containing a conductive polymer compound, a polyanion dopant, an aromatic nitro compound having a polar group, and an optional secondary dopant.

[0017] Conventional electrolytic capacitors containing conductive polymer compounds have a problem in that their characteristics (especially their lifespan characteristics) are insufficient, particularly under severe high-temperature conditions (especially 120-200°C, 125-190°C, or even 135-180°C).

[0018] Conventional hybrid capacitors, which are electrolytic capacitors using conductive polymer compounds, can exhibit good properties such as film repairability due to containing a sufficient amount of liquid to fill the capacitor void. However, it has been found that under high-temperature conditions (120-200°C, e.g., life tests at 135-180°C), deformation (abnormal appearance) and / or increased ESR occur due to increased internal pressure caused by the contained liquid. Furthermore, under high-temperature conditions, the liquid held in the capacitor may dry up, preventing it from maintaining sufficient properties. In addition, with regard to hybrid capacitors that contain an electrolyte, under high-temperature conditions, the electrolyte may deteriorate, or the concentration of the electrolyte due to solvent evaporation may promote ion activation, leading to a relative decrease in the conductivity mechanism of the electrode foil and conductive polymer.

[0019] On the other hand, while conventional solid electrolytic capacitors reduce or avoid the aforementioned problems associated with hybrid designs, their characteristics (lifetime characteristics), especially at high temperatures, were sometimes insufficient. For example, conventional solid electrolytic capacitors may have insufficient film repair characteristics, which can lead to peeling of the oxide film, etc. In conventional solid electrolytic capacitors, once such peeling occurs, it is considered difficult to repair or restore the film.

[0020] Therefore, there is a need for electrolytic capacitors that can operate stably even under high-temperature conditions.

[0021] In the present invention, a solid electrolytic capacitor having a conductive polymer compound and a dopant contains an aromatic nitro compound having a polar group in the solid electrolyte portion. Furthermore, the solid electrolytic capacitor of the present invention does not contain a liquid (e.g., electrolyte) that fills the voids of the capacitor elements, and even if a liquid is present, it is only in a relatively small amount as a secondary dopant, such as a swelling agent, present in the solid electrolyte. Due to these configurations, the solid electrolytic capacitor of the present invention can operate stably even under high temperature conditions (especially 120-200°C, 125-190°C, or even 135-180°C).

[0022] In conventional hybrid capacitors containing liquids such as electrolytes, as described above, the presence of liquids such as electrolytes could cause a significant decrease in performance under high-temperature conditions. Furthermore, in the case of conventional solid electrolytic capacitors, the gas pressure of hydrogen gas generated during film repair could cause delamination of the conductive polymer.

[0023] Although not limited to theory, according to the present invention, the electrolyte portion does not contain liquid or only contains a reduced amount of liquid in the solid electrolyte as a secondary dopant such as a swelling agent, thus avoiding or reducing the above-mentioned problems associated with hybrid electrolytic capacitors. In addition, because the solid electrolytic capacitor of the present invention contains an aromatic nitro compound having a polar group, it is believed that the peeling of the conductive polymer is suppressed in advance, and good characteristics are maintained even at high temperatures. In particular, according to the present invention, the aromatic nitro compound having a polar group is localized on the surface of the fine particles formed by the conductive polymer and the dopant and / or penetrates into the polymer, and is present at the interface between the conductive polymer compound-containing fine particles adhering to the surface of the capacitor components and the oxide film of the anode foil, thereby more effectively absorbing hydrogen gas, and thus maintaining the contact interface between the conductive polymer and the electrode foil in an optimal state.

[0024] According to one embodiment of the solid electrolytic capacitor of the present invention, by further including an amphoteric compound having both an acidic group and a basic group in one molecule, a solid electrolytic capacitor can be obtained that has superior characteristics with respect to at least one of the following: leakage current (LC) reduction, ESR stabilization, and capacitance reduction suppression effect, and in particular, particularly excellent characteristics can be obtained in the ultra-high temperature range (especially above 160°C).

[0025] Note that the present invention may contain a liquid substance such as a polyalkylene glycol as a secondary dopant, which is different from the functional liquid or electrolyte solution that coexists separately from the conventional solid electrolyte. This is because the secondary dopant of the present application is for swelling the solid electrolyte and has a different function. In particular, the capacitor of the present invention has a porosity of 40 to 85%, preferably 50 to 80%. In particular, the liquid occupancy in the capacitor element of the present invention is 10 to 50%, preferably 15 to 40%. These porosity and liquid occupancy can be calculated by the filling experiment of the capacitor element and the density values and weight measurement of the liquid and components. More specifically, it can be determined as follows.

[0026] (i) (Calculation of the volume of the voids in the element) Measure the impregnation weights before and after impregnating the capacitor element with a liquid having a density of 1 g / cm 3 , and calculate the total void volume (cm 3 ) of the capacitor element from these values (i.e., impregnation amount = total void volume). The total void volume can be, for example, 230 cm 3 to 250 cm 3 . (ii) (Calculation of the volume of the solid electrolyte) Calculate the density (g / cm 3 ) of the solid electrolyte from the density and content of each component (conductive polymer compound, dopant which is a polyanion, aromatic nitro compound having a polar group, and optional secondary dopant) constituting the solid electrolyte. Then, divide the filling amount (impregnation amount) (mg) of the solid electrolyte by the calculated density (g / cm 3 ) of the solid electrolyte to obtain the solid electrolyte occupied volume (cm 3 ). The filling amount of the solid electrolyte can be, for example, 70 mg to 100 mg. The solid electrolyte occupied volume (cm 3 ) can be 50 to 85 cm 3 , particularly 56 cm 3 to 81 cm 3 . (iii-a) (Calculation of the porosity of the solid electrolyte-filled element) The total void volume (cm 3) From the solid electrolyte occupied volume (cm³) obtained in (ii) above 3 Subtract the value from the total void volume (cm³) and use the resulting value to obtain the total void volume (cm³). 3 The void ratio (%) of the solid electrolyte-filled element is determined by dividing by ).

[0027] (iii-b) (Calculation of liquid volume in the element) Liquid volume (cm³) inside a capacitor element 3 ) is calculated by adding the amount of solid electrolyte filling (mg) to the density of the solid electrolyte (g / cm³) obtained in (ii) above. 3 It is obtained by dividing by ( ) and then multiplying by the percentage of liquid occupancy in the solid electrolyte. The percentage of liquid occupancy in the solid electrolyte can be, for example, 85-90%. In particular, the liquid in the solid electrolyte is composed of secondary dopants. (iv-b) (Converted to liquid occupancy rate in the element) The liquid occupancy rate (%) in the element is calculated using the liquid volume (cm³) in the element obtained in (iii-b) above. 3 ) is the total void volume (cm³) obtained in (i) above. 3 It can be found by dividing by ).

[0028] In one embodiment, the solid electrolytic capacitor of the present invention is used at a temperature of 120°C to 200°C, preferably 135°C to 180°C. This temperature in which the solid electrolytic capacitor of the present invention is used may be 125°C or higher, 130°C or higher, 140°C or higher, 150°C or higher, 160°C or higher, or 170°C or higher, and / or 200°C or lower, 195°C or lower, 190°C or lower, or 185°C or lower.

[0029] This disclosure also provides a method for obtaining a solid electrolytic capacitor having excellent properties, the method of which is: (i) To provide a capacitor element comprising an anode foil, a cathode foil, and a separator between them, each having an oxide film formed on its surface. (ii) Prepare a dispersion of conductive polymer compounds containing fine particles composed of conductive polymer compounds and polyanion dopants, as well as optional secondary dopants. (iii) Adding an aromatic nitro compound having a polar group to a dispersion of conductive polymer compounds, (iv) Impregnating the capacitor element with a conductive polymer compound dispersion and drying it to form an electrolyte portion on the oxide film. Includes, After forming the electrolyte portion, the capacitor element is sealed in the case without adding any liquid substances, such as functional liquids and electrolytes.

[0030] Conventionally, in the case of solid electrolytic capacitors containing conductive polymer compounds, methods of adding nitro compounds or their derivatives as additives during the synthesis of the conductive polymer compound are unsuitable for synthesis and polymerization that prioritizes the formation of fine particles.

[0031] In contrast, in the present invention, the nitro compound is added not during the synthesis of the conductive polymer, but after polymerization or even in a dispersion of the conductive polymer compound in which fine particles have already been formed. Therefore, polymerization or fine particle formation is not inhibited. Furthermore, by adding the compound after polymerization or fine particle formation, the aromatic nitro compound penetrates well into the surface and / or interior of the conductive polymer (especially the conductive polymer-containing fine particles). As a result, the aromatic nitro compound is well positioned at the interface between the conductive polymer and the film, improving peel prevention and / or film repair properties, and resulting in excellent high-temperature characteristics.

[0032] In particular, the electrolyte portion in the present invention is formed by placing a reaction inhibitor such as a nitro compound on the surface of a conductive polymer (e.g., PEDOT / PSS particles) in a dispersion of conductive polymers (e.g., PEDOT / PSS particles), and then adhering it to an electrode foil or separator by drying and solidifying to form a solid electrolyte.

[0033] The following describes in more detail each component of the embodiments of the invention relating to this disclosure.

[0034] <Electrolyte section> In the capacitor according to this disclosure, the electrolyte portion is composed of a solid electrolyte. As described above, the electrolyte portion of the present invention may contain a secondary dopant having a swelling effect (e.g., polyalkylene glycol), but even in that case, the electrolyte portion maintains a solid-like shape at least at room temperature. In particular, the term "solid electrolyte" in this disclosure includes not only a completely solid state but also a solid-like state having a certain degree of fluidity, such as a gel or paste.

[0035] The electrolyte is located in the void between the anode foil and the cathode foil. In this disclosure, "the void between the anode foil and the cathode foil" includes not only "the void between the anode foil and the separator and the void between the cathode foil and the separator," but also "the void between fibers within the separator." Furthermore, "the void between the anode foil and the cathode foil" also includes "the void in etching pits (recesses) formed on the surface of the anode foil or cathode foil by roughening through etching."

[0036] The electrolyte portion, composed of a solid electrolyte, is in at least partial contact with the oxide film formed on the surface of the anode foil. The electrolyte portion has a conductive polymer compound and a polyanion dopant, as well as optional secondary dopants, and further comprises an aromatic nitro compound having a polar group. In one embodiment, it may further contain an amphoteric compound having both an acidic and a basic group in one molecule.

[0037] The electrolyte portion may take various forms, for example, a continuous, uniform thick or thin layer, a film, or an aggregate of microparticles, or a network of microparticle chains. In particular, the electrolyte portion may take the form of a microparticle layer composed of microparticles containing a conductive polymer compound (and optionally a dopant).

[0038] The method for forming the electrolyte portion is not particularly limited, but it can be formed, for example, by immersion impregnation or vacuum impregnation. For example, an electrolyte portion can be formed in the void between the anode foil and cathode foil by filling the void with a dispersion liquid (conductive polymer compound dispersion) in which a conductive polymer compound and a dopant are dispersed in a dispersion medium, or a solution (conductive polymer compound solution) in which a conductive polymer compound is dissolved in a solvent, and then removing the dispersion medium or solvent from the void by heating or drying. In a preferred embodiment of the present invention, a conductive polymer compound dispersion is used.

[0039] The electrolyte portion is in at least partially direct contact with the oxide film of the anode foil, and at least partially direct contact with the metal surface and / or oxide film of the cathode foil.

[0040] (Aromatic nitro compounds with polar groups) The solid electrolyte relating to this disclosure includes an aromatic nitro compound having a polar group. The aromatic nitro compound having a polar group is an aromatic compound having a nitro group and other polar groups.

[0041] While there is no intention to limit this to theory, it is thought that the nitro group of aromatic nitro compounds with polar groups has the effect of improving the lifespan characteristics of solid electrolytic capacitors under high-temperature conditions by absorbing hydrogen gas generated during recombination reactions, etc.

[0042] Furthermore, although not limited to theory, aromatic nitro compounds having polar groups are thought to disperse more easily in compositions containing conductive polymers when forming solid electrolytes during the manufacturing process (particularly improving dispersibility as they dissolve more readily in conductive polymer dispersions) due to the presence of polar groups. In this case, the uniformity of the nitro compound in the formed electrolyte is improved, and as a result, the hydrogen gas absorption effect is thought to be effectively exerted. In particular, this is thought to improve the localization of the nitro compound at the interface between the conductive polymer and the film, which is important for preventing peeling and repairing the film.

[0043] Therefore, according to the present invention, in particular, an electrolytic capacitor with good characteristics can be obtained with a relatively small amount of nitro compound content.

[0044] In one embodiment, an aromatic nitro compound having a polar group may have a solubility of 0.01 g / 100 gaq or more at 15 to 25°C (particularly 25°C). Solubility can be measured by known methods.

[0045] The following solubility values ​​can be obtained for specific aromatic nitro compounds: Nitrophenol 1.6g / 100gaq (25℃) Nitrosalicylic acid 0.13g / 100gaq (16℃) Nitrobenzoic acid 0.02g / 100gaq (25℃) Nitrobenzyl alcohol 0.5g / 100gaq (20℃). For acidic aromatic nitro compounds with low solubility, reacting them with basic compounds such as ammonia can form cations and salts, making them readily soluble in water and thus increasing their solubility.

[0046] Examples of "polar groups" found in aromatic nitro compounds containing polar groups include hydroxyl groups, carboxyl groups, carbonyl groups, and amino groups.

[0047] Examples of aromatic nitro compounds having polar groups according to this disclosure include nitrophenol, nitroacetophenone, nitrobenzyl alcohol, nitrobenzoic acid, ammonium nitrobenzoate, amine nitrobenzoate salts, nitrobenzaldehyde, nitroanisole, nitrobenzene carboxylic acid, nitrobenzene dicarboxylic acid, nitrosalicylic acid, ammonium nitrosalicylate, amine nitrosalicyate salts, nitroaniline, nitroacetanilide, nitrophenylacetic acid, nitrocresol, dinitrobenzoic acid, methylnitrobenzoic acid, nitroterephthalic acid, and nitroisophthalic acid. These may be used individually or in combination of two or more.

[0048] The aromatic nitro compounds having a polar group according to this disclosure preferably have a hydroxyl group or a carboxyl group as the polar group. The aromatic nitro compounds having a hydroxyl group or a carboxyl group are preferably at least one selected from the group consisting of nitrophenol, nitrobenzoic acid, ammonium nitrobenzoate, amine nitrobenzoate salts, nitrosalicylic acid, ammonium nitrosalicylate, amine nitrosalicyate salts, and nitrobenzyl alcohol. By using these aromatic nitro compounds, a solid electrolytic capacitor can be obtained that has particularly good high-temperature characteristics (especially lifetime characteristics under high-temperature conditions), as well as a significant suppression of capacitance reduction, low ESR characteristics, and a stabilized tanδ.

[0049] Although not limited to theory, it is believed that by using aromatic nitro compounds having a hydroxyl group or a carboxyl group, the uniformity of the nitro compounds in the formed electrolyte is particularly improved, and as a result, the hydrogen gas absorption effect is exhibited more effectively. In this embodiment, it is thought that the nitro compounds are more likely to be localized at the interface between the conductive polymer contained in the electrolyte and the electrode and / or film. Furthermore, according to this embodiment, an electrolytic capacitor with good characteristics can be obtained with a very small amount of nitro compound content.

[0050] In one embodiment of the present disclosure, the aromatic nitro compound having a polar group does not have a sulfo group. When the aromatic nitro compound does not have a sulfo group, it is more preferable in terms of the stability of the capacitor characteristics and the lifespan of the device. Although not limited by theory, in this case it is thought that corrosion of the electrodes or deterioration of the separator caused by chemical reactions (oxidative degradation) with the electrodes (electrode metal such as aluminum) is suppressed.

[0051] In this disclosure, the content of the aromatic nitro compound having a polar group in the solid electrolyte may be 0.5 to 100 parts by mass per 100 parts by mass of the total of the conductive polymer compound, the polyanion dopant, and optional secondary dopant. This content may be 0.5 parts by mass or more, 1 part by mass or more, 2 parts by mass or more, 3 parts by mass or more, 4 parts by mass or more, 5 parts by mass or more, 6 parts by mass or more, 7 parts by mass or more, 9 parts by mass or more, or 10 parts by mass or more, and / or 100 parts by mass or less, 90 parts by mass or less, 80 parts by mass or less, 70 parts by mass or less, 60 parts by mass or less, 50 parts by mass or less, 40 parts by mass or less, 30 parts by mass or less, 25 parts by mass or less, 20 parts by mass or less, 19 parts by mass or less, 18 parts by mass or less, 17 parts by mass or less, 16 parts by mass or less, 15 parts by mass or less, 14 parts by mass or less, 13 parts by mass or less, 12 parts by mass or less, or 11 parts by mass or less. In one preferred embodiment, the content is 3 to 30 parts by mass, 4 to 25 parts by mass, or even 5 to 20 parts by mass.

[0052] Furthermore, in this disclosure, the content of the aromatic nitro compound having a polar group in the solid electrolyte may be 1 to 100 parts by mass per 100 parts by mass of the total of the conductive polymer compound and the polyanion dopant.

[0053] This content may be 2 parts by mass or more, 3 parts by mass or more, 4 parts by mass or more, 5 parts by mass or more, 6 parts by mass or more, 7 parts by mass or more, 9 parts by mass or more, or 10 parts by mass or more, and / or 100 parts by mass or less, 90 parts by mass or less, 80 parts by mass or less, 70 parts by mass or less, 60 parts by mass or less, 50 parts by mass or less, 40 parts by mass or less, 30 parts by mass or less, 25 parts by mass or less, 20 parts by mass or less, 19 parts by mass or less, 18 parts by mass or less, 17 parts by mass or less, 16 parts by mass or less, 15 parts by mass or less, 14 parts by mass or less, 13 parts by mass or less, 12 parts by mass or less, or 11 parts by mass or less.

[0054] In one embodiment of the present disclosure, the content of the aromatic nitro compound having a polar group in the solid electrolyte is relatively reduced to 1 to 10 parts by mass, 2 to 8 parts by mass, or even 3 to 6 parts by mass, per 100 parts by mass of the total of the conductive polymer compound and the polyanion dopant. The solid-state capacitor according to the present invention exhibits sufficient life characteristics under high-temperature conditions even with such a very low aromatic nitro compound content. In this case, material costs are reduced.

[0055] Although not limited by theory, aromatic nitro compounds with polar groups have relatively high dispersibility in solid electrolytes containing conductive polymers. Therefore, by being present between the conductive polymer contained in the solid electrolyte (particularly conductive polymer compound-containing fine particles adhering to the surface of the capacitor components) and the oxide film of the anode foil, they efficiently absorb hydrogen gas. Thus, it is thought that a solid electrolytic capacitor with sufficient lifespan characteristics can be obtained with only the minimum necessary amount of aromatic nitro compound.

[0056] When the content of aromatic nitro compounds is below the upper limit of the above range, excellent film repair is achieved by rapidly adsorbing hydrogen gas generated at the interface during the film repair reaction without inhibiting film repair on the electrode foil. This contributes to stress relief on the electrode foil surface, suppression of delamination between the electrode foil and the solid electrolyte, maintaining a good interfacial state, and / or suppression of the generation of microcracks due to penetration into the film surface, thereby achieving a further reduction in leakage current. Furthermore, the effects of alkalization by amino groups associated with the reduction of nitro groups generated during the hydrogen absorption reaction can be minimized, thereby suppressing film breakdown and / or dedoping of conductive polymer compounds.

[0057] Furthermore, when amphoteric compounds are added, the reduction in aromatic nitro compounds can mitigate or avoid undesirable effects caused by competition with amphoteric compounds due to excessive aromatic nitro compound content.

[0058] In one embodiment of the present disclosure, the polar group of the aromatic nitro compound has a molecular weight of 130 to 1000 or more specifically 130 to 500, and more particularly 130 to 250. By keeping the aromatic nitro compound from being excessively large, good dispersibility of the aromatic nitro compound in the solid electrolyte can be ensured.

[0059] (Modes of existence of aromatic nitro compounds) In one embodiment of the present disclosure, an aromatic nitro compound having a polar group is dispersed in a solid electrolyte.

[0060] Furthermore, in one embodiment of the present disclosure, an aromatic nitro compound having a polar group is present at the interface between the oxide film formed on the surface of the anode foil and the solid electrolyte, and / or at the interface between the anode foil and the solid electrolyte.

[0061] In one embodiment of the present disclosure, the conductive polymer compound and dopant constituting the solid electrolyte form fine particles, and the aromatic nitro compound having a polar group is localized on the surface of these fine particles and / or penetrates into the conductive polymer. In this case, it is believed that the hydrogen gas absorption effect is effectively exerted by promoting the localization of the aromatic nitro compound at the interface between the oxide film (or anode foil) and the solid electrolyte. Furthermore, this makes it possible to reduce the content of the aromatic nitro compound having a polar group, resulting in a reduction in material costs.

[0062] (Conductive polymer compound) The solid electrolyte contains a conductive polymer compound.

[0063] Examples of conductive polymer compounds include at least one selected from polythiophene, polypyrrole, and polyaninin, and their derivatives. The conductive polymer compound may be at least one of these. Preferably, the conductive polymer compound is a polymer of EDOT and its derivatives. Particularly preferred conductive polymer compounds are polyethylenedioxythiophene (PEDOT) (especially poly(3,4-ethylenedioxythiophene)).

[0064] (Dopant) The solid electrolyte further contains a polyanion dopant. Specific examples of polyanion dopants include aromatic sulfonic acids such as benzenesulfonic acid or its derivatives, naphthalenesulfonic acid or its derivatives, and anthraquinonesulfonic acid or its derivatives; polymeric sulfonic acids such as polystyrenesulfonic acid (PSS), sulfonated polyesters, phenolsulfonic acid novolac resins, and copolymers of styrenesulfonic acid with non-sulfonic monomers (such as methacrylic acid esters, acrylic acid esters, unsaturated hydrocarbon-containing alkoxysilane compounds or their hydrolysates); and chain-like sulfones such as methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid, and butanesulfonic acid. These may be used individually or in combination of two or more.

[0065] Polystyrene sulfonic acid (PSS) with a weight-average molecular weight of 10,000 to 1,000,000 is preferred.

[0066] In a particularly preferred embodiment, the solid electrolyte comprises polyethylenedioxythiophene (PEDOT) as a conductive polymer compound and polystyrene sulfonic acid (PSS) as a polyanion dopant.

[0067] The conductive polymer compound and the polyanion dopant may have a particulate shape. The average particle size of the fine particles composed of the conductive polymer compound and the polyanion dopant may be 1 nm to 1 μm or 1 nm to 600 nm, preferably in the range of 1 nm to 300 nm, or even more preferably in the range of 5 nm to 200 nm (e.g., 20 nm). The average particle size of the fine particles composed of the conductive polymer and the polyanion dopant can be determined, for example, from the particle size distribution by dynamic light scattering.

[0068] In the capacitor according to this disclosure, the proportion of the conductive polymer compound in the void between the anode foil and the cathode foil may be 0.5 vol% to 40 vol%, or even 1.0 vol% to 20 vol%.

[0069] In one embodiment, the solid electrolyte contains a high concentration of a polyanionic dopant, and the ratio of the conductive polymer compound to the dopant is 1:10 to 1:0.5, or more precisely, 1:8 to 1:1, 1:6 to 1:1, or even more precisely, 1:5 to 1:1.5. For example, the conductive polymer compound (e.g., PEDOT) may be present in 10 to 55% by mass, preferably 20 to 50% by mass, relative to the polyanionic dopant (e.g., PSS).

[0070] (Second Dopant) The solid electrolyte may contain a secondary dopant. The secondary dopant may act as an conductivity enhancer. The secondary dopant is a compound different from the polyanion dopant mentioned above. The secondary dopant may be a particle-penetrating liquid (particularly a liquid that penetrates conductive polymer-containing particles), and this liquid may penetrate and fill the inside of the particles (particularly conductive polymer-containing particles), moving the molecular chains of the conductive polymer, thereby promoting stacking of the conductive polymer particles, and consequently improving conductivity. Furthermore, the secondary dopant may have a swelling effect. That is, by containing a secondary dopant, the solid electrolyte constituting the electrolyte portion (for example, fine particles formed from a conductive polymer compound and a dopant) may swell, thereby expanding the internal space of the particles and further improving conductivity. Therefore, the secondary dopant is particularly a swelling agent. The secondary dopant may be a polar organic solvent or organic compound with a boiling point of 150°C or higher, or a liquid polymer compound without a boiling point, such as a polymer having a polyether structure, and may have a weight-average molecular weight of 100 to 10000 (measured by gel filtration chromatography). Specific examples of secondary dopants include glycerin, diglycerin, triglycerin, tetraglycerin, polyglycerin, polyglyceryl ether, diethylene glycol, triethylene glycol, and polyethylene glycol. These can function as solid electrolytes by being incorporated into conductive polymers. Unlike conventional functional liquids and electrolytes, the secondary dopant exists within a solid electrolyte.

[0071] In an exemplary embodiment, PSS acts as a counterion (Dope agent) that stabilizes the polarons (+holes) of PEDOT formed during the polymerization of EDOT (it is contained in the polymer). Furthermore, the conductivity is improved by adding a high-boiling point solvent such as PEG or glycerin as a secondary dopant to this particulate PEDOT / PSS. Although not limited by theory, this phenomenon is thought to be caused by the swelling of PEDOT / PSS particles (imagine a ball-like structure of PSS, with PEDOT partially attached to the threads of PSS) in a solvent, etc., forming a stacking (layered arrangement) inter-particle structure similar to the crystallization of PEDOT, thereby promoting electronic conductivity. The swollen PEDOT / PSS particles then solidify as a solid electrolyte.

[0072] In one embodiment, the mass content of the secondary dopant contained in the capacitor element according to the present disclosure may be 1 to 20 times, or even 1 to 10 times, the total amount of the dopants, which are conductive polymer compounds and polyaniline.

[0073] In one embodiment, the void occupancy rate of the secondary dopant in the capacitor element according to the present disclosure may be 30-50%, or even 36-42%. The void occupancy rate is calculated by the same method as the calculation of the liquid occupancy rate in the element described above.

[0074] (Amphoteric compounds) The solid electrolyte of the solid electrolytic capacitor according to this disclosure may further contain an amphoteric compound having both an acidic group and a basic group in one molecule.

[0075] By using a combination of an aromatic nitro compound having a polar group and an amphoteric compound, it is possible to provide a solid electrolytic capacitor that exhibits particularly excellent properties, such as superior leakage current suppression, even under ultra-high temperature conditions (e.g., above 160°C).

[0076] In one embodiment, the solid electrolytic capacitor of the present invention is suitable for use at temperatures of 100°C to 200°C or even 120°C to 190°C, and is preferably optimal for use at temperatures of 135°C to 180°C. The solid electrolytic capacitor of the present invention exhibits remarkable stability characteristics at temperatures of 160°C to 190°C, and is therefore particularly advantageous for applications in this temperature range.

[0077] While there is no intention to limit the theory, when aromatic nitro compounds and amphoteric compounds are used together, the polyanions contained in the dopants of the solid electrolyte are neutralized by the basic groups of the amphoteric compounds, suppressing the surface charge of the conductive polymer particles. This allows the amphoteric compounds, which contribute to the chemical conversion, to be positioned on the surface of the solid electrolyte, and furthermore, the nitro compounds, which have polar groups, are dispersed more uniformly on the solid electrolyte surface. As a result, in the repair of deteriorated coatings, the chemical conversion reaction by the amphoteric compounds is carried out more efficiently due to the hydrogen absorption effect of the nitro groups.

[0078] Furthermore, while the ionic groups of nitro compounds may cause some degradation of the coating at the electrode interface, when aromatic nitro compounds and amphoteric compounds are used together, the mechanism by which the amphoteric compounds further repair such degradation sites is thought to contribute to further improvement of properties.

[0079] An acidic group is generally defined as a group that, when dissolved in water, releases protons (H) + It is a group that either donates electrons or accepts electron pairs.

[0080] Examples of acidic groups include carboxyl groups, oxoacid groups such as phosphate groups, boric acid ester groups, and boric acid crosslinked products.

[0081] A basic group is generally defined as a group containing a proton (H + It is a base that receives or donates electron pairs.

[0082] The basic group may be at least one selected from an amino group, an amidine group, and a guanidino group.

[0083] Amphoteric compounds, in particular, can form twinned ions in aqueous solutions.

[0084] According to this disclosure, the number of nitrogen atoms N in one molecule of an amphoteric compound N and the number of carbon atoms N C Ratio N N / N C However, it may be between 0.125 and 0.65. This results in a solid electrolytic capacitor with better suppressed leakage current.

[0085] This ratio N N / N C It may be 0.15 or greater, 0.20 or greater, or 0.25 or greater, and / or 0.60 or less, or 0.55 or less.

[0086] In one embodiment of this disclosure, the isoelectric point of the amphoteric compound is between 2.0 and 10.0. Although there is no intention to limit the theory, in this case, it is thought that the balance between acidic and basic groups in the amphoteric compound is optimized, thereby avoiding the dedoping phenomenon of the conductive polymer compound and obtaining a sufficient film repair effect.

[0087] The isoelectric point may be 2.2 or higher, 2.4 or higher, or 2.6 or higher, and / or 9.0 or lower, 8.5 or lower, 8.0 or lower, or 7.5 or lower.

[0088] The amphoteric compound preferably has an isoelectric point in the range of 2.0 to 7.5, more preferably 2.5 to 7.0. In this case, the risk of dedoping of the conductive polymer can be effectively prevented.

[0089] In one embodiment of the present disclosure, the amphoteric compound has a molecular weight of 50 to 1000. By not having an excessively small amphoteric compound, a good film repair effect on the electrode foil can be ensured, especially when the amphoteric compound is present on or near the surface of conductive polymer fine particles. Furthermore, by not having an excessively large amphoteric compound, good dispersibility of the amphoteric compound in the solid electrolyte can be ensured.

[0090] Among the amphoteric compounds related to this disclosure, those having a carboxyl group as an acidic group and an amino group as a basic group include, for example, amino acids and their derivatives.

[0091] Preferred examples of amino acids as amphoteric compounds relating to this disclosure include glycine, glutamic acid, asparagine, alanine, serine, threonine, leucine, isoleucine, valine, proline, glutamine, aspartic acid, methionine, and aminooctanoic acid. These may be used individually or in combination.

[0092] In one embodiment, the amphoteric compound does not have a benzene ring, and in particular does not have a phenyl group. When the amphoteric compound does not have a benzene ring, particularly good chemical conversion ability can be ensured. In particular, when the amphoteric compound does not have a phenyl group, relatively high chemical conversion ability can be obtained by improving solubility in solvents such as water.

[0093] Furthermore, specific examples of amphoteric compounds having a carboxyl group as an acidic group and an amidine group as a basic group include water-soluble azo polymerization initiators having an amphoteric structure, particularly 2,2′-Azobis[N-(2-carboxyethyl)-2-methylpropionamidine]tetrahydrate (molecular weight 414.46) (the chemical formula is shown below). This substance is commercially available (Fujifilm Wako Pure Chemical Industries, Ltd., VA-057). [ka]

[0094] In this disclosure, the content of the amphoteric compound in the solid electrolyte may be 1 to 100 parts by mass per 100 parts by mass of the total of the conductive polymer compound and the polyanion dopant.

[0095] The content of the amphoteric compound in the solid electrolyte may be 1 part by mass or more, 2 parts by mass or more, 3 parts by mass or more, 4 parts by mass or more, or 5 parts by mass or more, and / or 90 parts by mass or less, 80 parts by mass or less, 70 parts by mass or less, 60 parts by mass or less, 50 parts by mass or less, 40 parts by mass or less, 30 parts by mass or less, 25 parts by mass or less, 20 parts by mass or less, 10 parts by mass or less, 9 parts by mass or less, or 8 parts by mass or less, based on 100 parts by mass of the total of the conductive polymer compound and the polyanion dopant.

[0096] Preferably, the content of the amphoteric compound in the solid electrolyte is 3 to 30 parts by mass, 4 to 28 parts by mass, or even 5 to 25 parts by mass, based on 100 parts by mass of the total of the conductive polymer compound and the polyanion dopant.

[0097] In one embodiment of the present disclosure, the content of the amphoteric compound in the solid electrolyte is relatively reduced to 1 to 10 parts by mass, 2 to 8 parts by mass, or even 3 to 6 parts by mass, per 100 parts by mass of the total of the conductive polymer compound and the polyanion dopant. In this case, particularly good results can be obtained in terms of reducing leakage current after reflow.

[0098] Exemplary embodiments of the present invention will be described in more detail with reference to the drawings. Note that these drawings and exemplary embodiments are not limiting to the present invention. The drawings are schematic diagrams and are not necessarily to scale.

[0099] <Configuration of electrolytic capacitor 1 according to the embodiment> Figures 1a and 1b are diagrams illustrating the solid electrolytic capacitor 1 according to the embodiment. Figure 1a is a cross-sectional view of the solid electrolytic capacitor 1, and Figure 1b is a perspective view of the capacitor element 20.

[0100] Figure 2 is a cross-sectional view of the main part of the electrolytic capacitor 1 according to the embodiment, illustrating the main part of the electrolytic capacitor 1.

[0101] The electrolytic capacitor 1 according to this embodiment is a wound-type electrolytic capacitor, and as shown in Figure 1a, comprises a bottomed cylindrical metal case 10, a capacitor element 20, and a sealing member 40.

[0102] The bottom of the metal case 10 is nearly circular in shape, and a valve (not shown) is provided near the center. Therefore, when the internal pressure rises, the valve can break, releasing the internal pressure to the outside. The side surfaces of the metal case 10 are erected almost perpendicularly to the outer edge of the bottom surface. The opening of the metal case 10 is sealed by a sealing member 40, and the two leads 29 and 30 of the capacitor element 20 are led out through a through-hole in the sealing member 40.

[0103] The capacitor element 20 is housed inside the metal case 10 and, as shown in Figures 1(b) and 2, comprises an anode foil 21, a cathode foil 23, and a separator 25 disposed between the anode foil 21 and the cathode foil 23, with the anode foil 21 and cathode foil 23 overlapping and wound together via the separator 25.

[0104] In the embodiment shown in Figure 2, the anode foil 21 and cathode foil 23 each have oxide films 22 and 24 on their surfaces, respectively. A solid electrolyte 26, composed of fine particles of a conductive polymer compound / dopant, is placed in contact with the oxide film 22 on the surface of the anode foil 21, forming a solid electrolyte.

[0105] <Anode foil> The capacitor relating to this disclosure includes an anode foil on which an oxide film is formed on its surface.

[0106] The anode foil may be formed from a valve metal such as aluminum, tantalum, or niobium.

[0107] The anode foil has an oxide film on its surface. For example, an oxide film can be formed on the surface of the anode foil by roughening the surface by etching according to known methods, expanding the surface by sintering fine particles, and then performing a chemical conversion treatment.

[0108] <Cathode Foil> The capacitor relating to this disclosure includes cathode foil.

[0109] The cathode foil, like the anode foil, may be formed from a valve metal such as aluminum, tantalum, or niobium. The cathode foil may also be formed from an aluminum alloy containing copper.

[0110] The cathode foil may have an oxide film formed on its surface. For example, the surface of the cathode foil may be roughened by etching, similar to the anode foil, and then an oxide film may be formed by natural oxidation. Alternatively, the cathode foil may be subjected to a chemical conversion treatment at a desired voltage (e.g., 2V), which may also form an oxide film.

[0111] <Separator> The capacitor relating to this disclosure may include a separator. The separator is disposed between the anode foil and the cathode foil.

[0112] Preferably, the separator is made of conductive polymer particles, cellulose fibers that are chemically compatible with water-soluble polymers, or synthetic resins such as nylon, PET, and PPS that have excellent heat resistance. For example, heat-resistant cellulose paper or heat-resistant flame-retardant paper can be used. More specifically, examples of separators include cellulose and mixed papers such as kraft, Manila hemp, esparto, hemp, and rayon; polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and their derivatives; polytetrafluoroethylene resins; polyvinylidene fluoride resins; vinylon resins; polyamide resins such as aliphatic polyamides, semi-aromatic polyamides, and fully aromatic polyamides; polyimide resins; polyethylene resins; polypropylene resins; trimethylpentene resins; polyphenylene sulfide resins; acrylic resins; and polyvinyl alcohol resins. These resins can be used individually or in mixtures.

[0113] <<Capacitor Manufacturing Method>> The method for manufacturing the solid electrolytic capacitors according to this disclosure is not particularly limited, but preferably they can be manufactured by the manufacturing method according to the present invention described below: (i) To provide a capacitor element comprising an anode foil, a cathode foil, and a separator between them, each having an oxide film formed on its surface. (ii) Prepare a dispersion of conductive polymer compounds containing fine particles composed of conductive polymer compounds and polyanion dopants, as well as optional secondary dopants. (iii) Adding an aromatic nitro compound having a polar group to a dispersion of conductive polymer compounds, (iv) Impregnating the capacitor element with a conductive polymer compound dispersion and drying it to form an electrolyte portion on the oxide film. Includes, After forming the electrolyte portion, the capacitor element is sealed in the case without adding any liquid substances, such as functional liquids and electrolytes.

[0114] For details on each component used in this manufacturing method (capacitor element, conductive polymer compound, dopant, secondary dopant, aromatic nitro compound having a polar group, etc.) and their suitable concentration ranges, please refer to the above description regarding electrolytic capacitors.

[0115] Conventionally, in the case of solid electrolytic capacitors made of conductive polymers, methods of adding nitro compounds or their derivatives as additives during the synthesis of conductive polymer compounds were unsuitable for synthesis and polymerization prioritizing the formation of fine particles.

[0116] In contrast, in step (iii) of the method for manufacturing a solid electrolytic capacitor according to this disclosure, the aromatic nitro compound is added to a dispersion of a conductive polymer compound in which fine particles have already been formed, rather than during the synthesis of the conductive polymer compound, so the formation of fine particles is not inhibited.

[0117] Furthermore, by adding an aromatic nitro compound when the conductive polymer is in a dispersion state (with a dispersion medium such as water) as fine particles, the nitro compound is localized on the surface of the fine particles and / or penetrates into the polymer, making it possible to provide a solid electrolytic capacitor with an effective hydrogen gas absorption effect.

[0118] The following describes each step in this manufacturing method.

[0119] <Process (i)> Step (i) provides a capacitor element comprising an anode foil, a cathode foil, and a separator between them, each having an oxide film formed on their surfaces. Step (i) is described exemplified below.

[0120] First, an aluminum foil is provided as the anode foil 21. After roughening the surface of the aluminum foil by a surface expansion treatment, a predetermined voltage of 2V to 500V is applied to the roughened surface of the aluminum foil to perform a chemical conversion treatment, thereby forming an oxide film 22 on the surface of the aluminum foil. Then, a capacitor element is fabricated comprising the anode foil 21 having the oxide film 22, a cathode foil 23, and a separator 25 disposed between the anode foil 21 and the cathode foil 23 (see Figure 1(b)). Specifically, the capacitor element 20 is fabricated by overlapping and winding the anode foil 21, which has an uneven surface (rough surface) and on which the oxide film 22 is formed, and the cathode foil 23, which has an uneven surface, via the separator 25. At this time, a lead 30 is connected to the anode foil 21 and a lead 29 is connected to the cathode foil 23.

[0121] Next, the capacitor element 20 is immersed in the chemical conversion solution in the chemical conversion solution tank, and a predetermined voltage (e.g., 100V) is applied between the anode lead 30 and the chemical conversion solution for 5 minutes. This operation repairs oxide film defects present at the edges of the anode foil 21 and any oxide film defects that may be present on the surface.

[0122] As the chemical conversion solution, an aqueous solution of adipic acid, ammonium adipate, boric acid, ammonium borate, phosphoric acid, ammonium dihydrogen phosphate, ammonium hydrogen phosphate, ammonium phosphate, ammonium glutarate, ammonium azelaate, ammonium tartrate, ammonium sebacate, ammonium pimephosphate, ammonium suberate, decanedicarboxylic acid, ammonium decanedicarboxylic acid, long-chain dicarboxylic acid, long-chain ammonium dicarboxylic acid, etc. can be used.

[0123] <Process (ii)> In step (ii), a dispersion of conductive polymer compounds is prepared, which contains fine particles composed of a conductive polymer compound and a polyanion dopant, as well as optional secondary dopants.

[0124] A conductive polymer compound dispersion can be produced, for example, by polymerizing a suspended monomer (e.g., PEDOT monomer) (radical polymerization or oxidative polymerization) to create a conductive polymer compound (e.g., PEDOT polymer) to which dopants and emulsifiers have been added, and then dispersing the conductive polymer compound in a predetermined dispersion medium. The average particle size of the conductive polymer compound can be adjusted by appropriately setting the polymerization reaction conditions (e.g., concentrations of initiators, monomers, polymerization aids, etc., reaction temperature, stirring conditions of the reaction solution, etc.). It can also be adjusted by known grinding treatments (e.g., stirring grinding, vibration grinding, etc.). Furthermore, the particle size can be made uniform by preparative filtration.

[0125] As a specific example of a method for preparing a conductive polymer compound dispersion, the preparation procedure (a) to (e) for a PEDOT / PSS fine particle dispersion is shown below: (a) Prepare a PEDOT / PSS fine particle dispersion (e.g., 2% by mass) using ethylenedioxythiophene (EDOT) monomer and polystyrene sulfonic acid (PSS). (b) Remove excess cationic and / or anionic components by ion exchange treatment. (c) The process is carried out using a rotary homogenizer or an ultrasonic homogenizer to produce microparticles. (d) Adjust the pH to 2-5 by neutralization treatment. (e) Add a high-boiling point compound to the PEDOT / PSS fine particle dispersion. This may improve conductivity.

[0126] Steps (a) through (e) may be carried out according to conventional methods.

[0127] The content of the conductive polymer compound in the conductive polymer compound dispersion or conductive polymer compound solution may be 0.1 to 10% by mass, 0.2 to 5% by mass, and particularly 0.5 to 3% by mass.

[0128] For dispersions of conductive polymer compounds, for example, water, protic solvents such as alcohols (e.g., methanol, ethanol, 1-propanol, butanol), and mixtures thereof can be used as dispersion media. For solutions of conductive polymer compounds, for example, water, protic solvents such as alcohols (e.g., methanol, ethanol, 1-propanol, butanol), and mixtures thereof can be used as solvents.

[0129] To further improve the conductive properties of the conductive polymer, at least one selected from, for example, glycerin, diglycerin, triglycerin, tetraglycerin, polyglycerin, polyglyceryl ether, diethylene glycol, triethylene glycol, and polyethylene glycol may be added to the conductive polymer dispersion as a secondary dopant. A solid electrolyte can be formed by drying and solidifying the conductive polymer dispersion. These additives function as a solid electrolyte by being incorporated into the conductive polymer.

[0130] <Step (iii)> In step (iii) of the method for manufacturing a solid electrolytic capacitor according to this disclosure, an aromatic nitro compound having a polar group is added to a dispersion of a conductive polymer compound. Details and preferred embodiments of the aromatic nitro compound having a polar group can be found in the above description relating to solid electrolytic capacitors.

[0131] The concentration of the aromatic nitro compound having a polar group in the conductive polymer compound dispersion may be 0.01 to 2.0% by mass, or even more precisely, 0.1% to 1.0% by mass, relative to the conductive polymer compound dispersion.

[0132] The content is preferably 0.1% by mass or more, 0.2% by mass or more, 0.3% by mass or more, or 0.4% by mass or more, and / or 1.0% by mass or less, 0.9% by mass or less, 0.7% by mass or less, 0.6% by mass or less, or 0.5% by mass or less.

[0133] More preferably, this content is 0.2% by mass to 8.0% by mass, or even more preferably 0.3% by mass to 0.6% by mass.

[0134] (Addition of amphoteric compounds) An amphoteric compound can be added during the preparation process of a conductive polymer compound dispersion. Preferably, the amphoteric compound according to this disclosure is added after the step of micronizing the conductive polymer compound and the dopant particles (particularly PEDOT / PSS particles) which are polyaniline. Preferably, the amphoteric compound according to this disclosure is added before the neutralization treatment described above.

[0135] The concentration of the amphoteric compound in the conductive polymer compound dispersion may be 0.01% to 3.0% by mass relative to the conductive polymer compound dispersion. This results in a solid electrolytic capacitor with better suppressed leakage current.

[0136] This content may be 0.02% by mass or more, 0.04% by mass or more, 0.06% by mass or more, 0.08% by mass or more, or 0.1% by mass or more, and / or 2.8% by mass or less, 2.6% by mass or less, 2.4% by mass or less, 2.2% by mass or less, 2.0% by mass or less, 1.8% by mass or less, 1.6% by mass or less, 1.4% by mass or less, 1.2% by mass or less, 1.0% by mass or less, 0.8% by mass or less, or 0.6% by mass or less.

[0137] Preferably, this content is 0.01% by mass to 2.0% by mass, or even more preferably 0.1% by mass to 0.5% by mass.

[0138] <Process (iv)> In step (iv) of the method for manufacturing a solid electrolytic capacitor according to the present disclosure, a conductive polymer compound dispersion is impregnated into a capacitor element and dried to form an electrolyte portion on an oxide film.

[0139] For example, a capacitor element is immersed in a conductive polymer compound dispersion or conductive polymer compound solution using an introduction tank. Then, the capacitor element is removed from the conductive polymer compound dispersion or solution and heat-treated to form an electrolyte between the anode foil and the cathode foil. This operation can be repeated multiple times, thereby increasing the amount of solid electrolyte packed in.

[0140] The electrolyte portion can be formed by an immersion impregnation method. Specifically, a conductive polymer compound dispersion (for example, a conductive polymer compound concentration of 2% by mass) is filled into an introduction tank, and then the capacitor element is immersed in the conductive polymer compound dispersion. Next, the capacitor element is removed from the introduction tank, and then the capacitor element is heat-treated. This allows a solid electrolyte to be introduced into the gap between the anode foil 21 and the cathode foil 23, thereby forming an electrolyte portion on the oxide film.

[0141] Furthermore, in order to increase the proportion of solid electrolyte in the voids, the number of repetitions of the above operation can be increased, and / or the polymer concentration in the conductive polymer compound dispersion can be increased. On the other hand, in order to decrease the proportion of solid electrolyte in the voids, the number of repetitions of the above operation can be decreased, and / or the polymer concentration in the conductive polymer compound dispersion can be decreased.

[0142] The impregnated capacitor elements may be dried at a temperature of 100°C to 180°C for 10 to 120 minutes. This drying process removes at least some of the liquid components contained in the solid electrolyte.

[0143] A solid electrolytic capacitor can be manufactured by enclosing a capacitor element having a solid electrolyte, manufactured through the above process, in a case. In the manufacturing method according to the present invention, the capacitor element is enclosed in a case without adding any liquid substance, such as a functional liquid (a liquid that does not contain an electrolyte) or an electrolyte solution, after the electrolyte portion has been formed.

[0144] This process (assembly and sealing process) is described exemplified below. In the assembly and sealing process, for example, the sealing member 40 is attached to the capacitor element 20, and after inserting the capacitor element 20 into the metal case 10, the metal case 10 is crimped near the open end of the metal case 10. As the sealing member 40, for example, isobutylene-isoprene rubber (IIR) can be used. Instead of isobutylene-isoprene rubber (IIR), rubber materials such as ethylene-propylene terpolymer (EPT), EPT-IIR blend rubber, silicone rubber, or rubber composite materials made by bonding resin and rubber such as phenolic resin (Bakelite), epoxy resin, or fluororesin can be used for sealing. Furthermore, the sealing rubber surface crimped using the sealing member can be coated with epoxy resin or the like by potting to enhance airtightness, sealing strength, and heat resistance. After that, an aging process is carried out by applying a predetermined voltage in a high-temperature atmosphere. This completes the solid electrolytic capacitor 1 according to the embodiment. [Examples]

[0145] Embodiments of the present invention will be described in more detail below with reference to examples. The following examples and comparative examples are not intended to limit the present invention.

[0146] <<Examples 1-8 and Comparative Examples 1-4>> In Examples 1-8 and Comparative Examples 1-4, the characteristics of solid electrolytic capacitors containing aromatic nitro compounds with polar groups were evaluated, as well as the characteristics of solid electrolytic capacitors containing amphoteric compounds in addition to aromatic nitro compounds with polar groups. In this experiment, the life characteristics were evaluated using a life test (load test).

[0147] In Examples 1-8 and Comparative Examples 1-4, solid electrolytic capacitors with a rating of 25V-330μF were fabricated. The characteristics of the reflow-processed capacitors were measured under a 25V load test at 135°C for 3000 hours.

[0148] <Example 1> (Manufacturing of solid electrolytic capacitors) In Example 1, nitrobenzyl alcohol was used as the aromatic nitro compound having a polar group. To manufacture a solid electrolytic capacitor, an aqueous solvent dispersion was prepared containing conductive polymer compound fine particles composed of 2.0% by mass of PEDOT and PSS and 15% by mass of triglycerin as a secondary dopant. 0.5% by mass of nitrobenzyl alcohol was added to this dispersion. Commercially available reagents were used.

[0149] This conductive polymer compound dispersion was impregnated into a capacitor element. Specifically, an aluminum anode foil and an aluminum cathode foil, each having a voltage-resistant coating corresponding to the capacitor's rated voltage, were wound together via a cellulose separator to create a capacitor element. The conductive polymer compound dispersion was then vacuum-impregnated into the element to form an electrolyte between the anode and cathode foils. After drying, a solid electrolytic capacitor according to Example 1 was obtained. The solid electrolytic capacitor according to Example 1 is characterized by the absence of liquid substances, such as functional liquids and electrolytes, added after the formation of the electrolyte. The capacitor of Example 1 had a porosity in the range of 50% to 80%, and the liquid occupancy rate within the capacitor element was in the range of 15% to 40% (the same applies to the following Examples and Comparative Examples).

[0150] (Initial values ​​and characteristics measured under a 135°C high-temperature load test) The characteristics of the solid electrolytic capacitor obtained according to Example 1 were measured after aging treatment and defined as the initial characteristics. Then, a reflow process was performed with a peak temperature of 260°C for a holding time of 10 seconds, followed by a high-temperature load test at 135°C and 25V, and the characteristics were measured after 3000 hours. Capacitance change (ΔC) at 120Hz, ESR value at 100kHz, tanδ at 120Hz, and 1-minute leakage current were measured. The results are shown in Table 1 below.

[0151] <Example 2> A solid electrolytic capacitor according to Example 2 was manufactured in the same manner as in Example 1, except that 0.1% by mass of glutamic acid as an amphoteric compound was added to the dispersion. The initial characteristics and characteristics after a 3000-hour high-temperature load test at 135°C following reflow were measured and evaluated. The results are shown in Table 1 below.

[0152] <Examples 3, 5, 7> Solid electrolytic capacitors according to Examples 3, 5, and 7 were manufactured in the same manner as in Example 1, except that the aromatic nitro compound having a polar group and its content were changed as shown in Table 1 below. The initial characteristics and the characteristics after a 3000-hour high-temperature load test at 135°C following reflow were measured and evaluated. The results are shown in Table 1 below.

[0153] <Examples 4, 6, 8> Solid electrolytic capacitors according to Examples 4, 6, and 8 were manufactured in the same manner as in Example 2, except that the aromatic nitro compound having a polar group and its content were changed as shown in Table 1 below. The initial characteristics and the characteristics after a 3000-hour high-temperature load test at 135°C following reflow were measured and evaluated. The results are shown in Table 1 below.

[0154] <Comparative Example 1> A solid electrolytic capacitor according to Comparative Example 1 was manufactured in the same manner as in Example 1, except that an aromatic nitro compound having a polar group was not added. The initial characteristics and the characteristics after a 3000-hour high-temperature load test at 135°C following reflow were measured and evaluated. The results are shown in Table 1 below.

[0155] <Comparative Example 2> A solid electrolytic capacitor according to Comparative Example 2 was manufactured in the same manner as in Example 1, except that 0.1% by mass of glutamic acid as an amphoteric compound was added to the dispersion without adding an aromatic nitro compound having a polar group. The initial characteristics were measured, and after reflow soldering, the characteristics were measured and evaluated after a 200-hour no-load test at 180°C. The results are shown in Table 1 below.

[0156] <Comparative Example 3> A solid electrolytic capacitor according to Comparative Example 3 was manufactured in the same manner as in Example 1, except that nitrobenzene, an aromatic nitro compound without polar groups, was added instead of nitrobenzyl alcohol. The initial characteristics and the characteristics after a 3000-hour high-temperature load test at 135°C following reflow were measured. The results are shown in Table 1 below.

[0157] <Comparative Example 4> A solid electrolytic capacitor according to Comparative Example 4 was manufactured in the same manner as in Example 1, except that nitrobenzene, an aromatic nitro compound without polar groups, was added instead of nitrobenzyl alcohol, and 0.1% by mass of glutamic acid as an amphoteric compound was added to the dispersion. The initial characteristics and the characteristics after a 3000-hour high-temperature load test at 135°C following reflow were measured. The results are shown in Table 1 below.

[0158] [Table 1]

[0159] As can be seen in Table 1, in all of Examples 1 to 8, which use aromatic nitro compounds with polar groups, volume reduction and ESR are well suppressed compared to Comparative Example 1, which does not contain either aromatic nitro compounds with polar groups or amphoteric compounds. In particular, Examples 1 to 6, which use nitrobenzyl alcohol, ammonium nitrobenzoate, and nitrophenol, show excellent suppression of volume reduction, ESR, and tanδ.

[0160] Furthermore, Examples 2, 4, 6, and 8, in which an amphoteric compound was further added to an aromatic nitro compound having a polar group, show better suppression of ESR while maintaining sufficient suppression of volume loss or further suppressing volume loss compared to the corresponding example in which only an aromatic nitro compound having a polar group was added.

[0161] <<Examples 9-16 and Comparative Examples 5-8>> In Examples 9-16 and Comparative Examples 5-8, the capacitors were manufactured and evaluated in the same manner as in Examples 1-8 and Comparative Examples 1-4, except that the life characteristics were evaluated by a shelf test (no-load standing test).

[0162] (Initial characteristics and characteristics measured during a 135°C no-load storage test) The characteristics of the obtained solid electrolytic capacitors were measured after aging and defined as the initial characteristics. Furthermore, after performing a reflow process with a peak temperature of 260°C and a holding time of 10 seconds, the characteristics were measured after 3000 hours of no-load standing at 135°C. Capacitance change at 120Hz, ESR value at 100kHz, tanδ at 120Hz, and 1-minute leakage current values ​​were measured. Details and results of Examples 9-20 and Comparative Examples 5-8 are shown in Table 2 below.

[0163] [Table 2]

[0164] Table 2 also confirmed the same trend observed in Table 1.

[0165] <<Examples 17-31 and Comparative Examples 9-11>> In Examples 17-31 and Comparative Examples 9-11, the characteristics of solid electrolytic capacitors containing aromatic nitro compounds with polar groups were evaluated (Life test), and the characteristics of solid electrolytic capacitors containing amphoteric compounds in addition to aromatic nitro compounds with polar groups were also evaluated. In these experimental examples, evaluations were performed using various concentrations of aromatic nitro compounds with polar groups.

[0166] In Examples 17-31 and Comparative Examples 9-11, solid electrolytic capacitors with a rating of 25V-330μF were fabricated. After aging, the characteristics were measured and recorded as the initial characteristics. Furthermore, the characteristics of the reflow-coated capacitors were measured after a 25V load test at 135°C for 3000 hours.

[0167] <Example 17> (Manufacturing of solid electrolytic capacitors) In Example 17, nitrobenzyl alcohol was used as the aromatic nitro compound having a polar group. To manufacture a solid electrolytic capacitor, an aqueous solvent dispersion was prepared containing conductive polymer compound fine particles composed of 2.0% by mass of PEDOT and PSS, and 15% by mass of diglycerin and tetraglycerin as secondary dopants in a molar ratio of 7:3. To this dispersion, 0.1% by mass of nitrobenzyl alcohol was added. Commercially available reagents were used.

[0168] This conductive polymer compound dispersion was impregnated into a capacitor element. Specifically, an aluminum anode foil and an aluminum cathode foil, each having a voltage-resistant coating corresponding to the capacitor's rated voltage, were wound together via a cellulose separator to create a capacitor element. The conductive polymer compound dispersion was then vacuum-impregnated into this element to form an electrolyte between the anode foil and the cathode foil. After drying, a solid electrolytic capacitor according to Example 17 was obtained.

[0169] (Characteristic measurement during 135°C high-temperature load test) The solid electrolytic capacitor obtained in Example 17 underwent aging treatment, and its initial characteristics were measured. Furthermore, after performing a reflow process with a peak temperature of 260°C and a holding time of 10 seconds, the characteristics were measured after 3000 hours of 135°C 25V load testing. Capacitance change at 120Hz, ESR value at 100kHz, tanδ at 120Hz, and leakage current over 2 minutes were measured. The results are shown in Table 3 below. The solid electrolytic capacitor in Example 17 showed sufficient initial characteristics (capacitance, tanδ, ESR, LC). The same was true for the other examples described below.

[0170] <Example 18> A solid electrolytic capacitor according to Example 18 was manufactured in the same manner as in Example 17, except that 0.2% by mass of nitrobenzyl alcohol was added. The initial characteristics and the characteristics after a 3000-hour high-temperature load test at 135°C following reflow were measured and evaluated. The results are shown in Table 3 below.

[0171] <Example 19> A solid electrolytic capacitor according to Example 19 was manufactured in the same manner as in Example 17, except that 0.5% by mass of nitrobenzyl alcohol was added. The initial characteristics and the characteristics after a 3000-hour high-temperature load test at 135°C following reflow were measured and evaluated. The results are shown in Table 3 below.

[0172] <Example 20> A solid electrolytic capacitor according to Example 20 was manufactured in the same manner as in Example 17, except that 0.1% by mass of alanine as an amphoteric compound was added to the dispersion. The initial characteristics and the characteristics after a 3000-hour high-temperature load test at 135°C following reflow were measured and evaluated. The results are shown in Table 3 below.

[0173] <Examples 21-24, 26-29, 31> Solid electrolytic capacitors according to Examples 21-24, 26-29, and 31 were manufactured in the same manner as in Example 17, except that the aromatic nitro compound having a polar group and its content were changed as shown in Table 3 below. The initial characteristics and characteristics after a 3000-hour high-temperature load test at 135°C following reflow were measured and evaluated. The results are shown in Table 3 below.

[0174] <Examples 25, 30> Solid electrolytic capacitors according to Examples 25 and 30 were manufactured in the same manner as in Example 20, except that the aromatic nitro compounds and amphoteric compounds having polar groups, and their content, were changed as shown in Table 3 below. The initial characteristics and the characteristics after a 3000-hour high-temperature load test at 135°C following reflow were measured and evaluated. The results are shown in Table 3 below.

[0175] <Comparative Example 9> A solid electrolytic capacitor according to Comparative Example 9 was manufactured in the same manner as in Example 17, except that an aromatic nitro compound having a polar group was not added. The initial characteristics and the characteristics after a 3000-hour high-temperature load test at 135°C following reflow were measured and evaluated. The results are shown in Table 3 below.

[0176] <Comparative Example 10> A solid electrolytic capacitor according to Comparative Example 10 was manufactured in the same manner as in Example 17, except that 0.1% by mass of glutamic acid as an amphoteric compound was added to the dispersion without adding an aromatic nitro compound having a polar group. The initial characteristics and the characteristics after a 3000-hour high-temperature load test at 135°C following reflow were measured and evaluated. The results are shown in Table 3 below.

[0177] <Comparative Example 11> A solid electrolytic capacitor according to Comparative Example 11 was manufactured in the same manner as in Example 17, except that 0.5% by mass of nitrobenzene, an aromatic nitro compound with a polar group, was added to the dispersion instead of nitrobenzyl alcohol. The initial characteristics and the characteristics after a 3000-hour high-temperature load test at 135°C following reflow were measured and evaluated. The results are shown in Table 3 below.

[0178] [Table 3]

[0179] In Table 3, in all of Examples 17 to 31, which used aromatic nitro compounds with polar groups, the volume reduction was well suppressed compared to Comparative Examples 9 and 11, which did not contain either aromatic nitro compounds with polar groups or amphoteric compounds. In particular, Examples 17 to 30, which used nitrobenzyl alcohol, ammonium nitrobenzoate, and nitrophenol, respectively, showed particularly good suppression of volume reduction, tanδ, and ESR.

[0180] Furthermore, the results in Table 3 show that improved properties can be obtained even with a relatively reduced amount of nitro compound added, around 0.1%. Moreover, it can be seen that particularly excellent improvements are observed when the amount of nitro compound added is around 0.5%.

[0181] Furthermore, Examples 20, 25, and 30, in which an amphoteric compound was further added to an aromatic nitro compound having a polar group, demonstrate that leakage current (LC) is reduced while maintaining sufficient capacity reduction and suppression of tanδ and ESR, compared to the corresponding example in which only an aromatic nitro compound having a polar group was added.

[0182] <<Examples 32-46 and Comparative Examples 12-14>> In Examples 32-46 and Comparative Examples 12-14, the capacitors were manufactured and evaluated in the same manner as in Examples 17-31 and Comparative Examples 9-11, except that the life characteristics were evaluated by a shelf test (no-load standing test).

[0183] (Initial characteristics and characteristics measured during a 135°C high-temperature no-load storage test) The obtained solid electrolytic capacitors were subjected to initial characteristics measurement after aging. Following a reflow process with a peak temperature of 260°C and a holding time of 10 seconds, the characteristics were measured after 3000 hours of no-load standing at 135°C. Capacitance change at 120Hz, ESR value at 100kHz, tanδ at 120Hz, and leakage current over 2 minutes were measured. Details and results of Examples 32-46 and Comparative Examples 12-14 are shown in Table 4 below. The solid electrolytic capacitor in Example 32 exhibited sufficient initial characteristics (capacitance, tanδ, ESR, LC). Similar results were observed in the other examples.

[0184] [Table 4]

[0185] Table 4 also showed the same trend as observed in Table 3 above.

[0186] <<Examples 47-51 and Comparative Examples 15 and 16>> In Examples 47-51 and Comparative Examples 15 and 16, the characteristics of solid electrolytic capacitors containing aromatic nitro compounds with polar groups were evaluated under even more severe high-temperature conditions (ultra-high temperature conditions) than those described above. In addition, the characteristics of solid electrolytic capacitors containing amphoteric compounds in addition to aromatic nitro compounds with polar groups were evaluated. For this test, epoxy resin was potted onto the sealing rubber surface of the sealing member to cover the sealing portion, so that the sealing member could withstand high temperatures of 180°C. This enhanced heat resistance by suppressing thermal degradation of the rubber member and preventing thermal oxidation.

[0187] In Examples 47-51 and Comparative Examples 15 and 16, solid electrolytic capacitors with a rating of 25V-330μF were fabricated. Initial characteristics were measured, and after reflow soldering, characteristics were measured after a 200-hour no-load test at 180°C.

[0188] <Example 47> (Manufacturing of solid electrolytic capacitors) In Example 47, nitrophenol was used as the aromatic nitro compound having a polar group. To manufacture a solid electrolytic capacitor, an aqueous solvent dispersion was prepared containing conductive polymer compound fine particles composed of 2.0% by mass of PEDOT and PSS and 15% by mass of triglycerin as a secondary dopant. 0.5% by mass of nitrophenol was added to this dispersion. Commercially available reagents were used.

[0189] This conductive polymer compound dispersion was impregnated into a capacitor element. Specifically, an aluminum anode foil and an aluminum cathode foil, each having a voltage-resistant coating corresponding to the capacitor's rated voltage, were wound together via a cellulose separator to create a capacitor element. The conductive polymer compound dispersion was then vacuum-impregnated into this element to form an electrolyte between the anode foil and the cathode foil. After drying, a solid electrolytic capacitor according to Example 47 was obtained.

[0190] (Initial characteristics and characteristics measured during 180°C no-load storage test) The characteristics of the solid electrolytic capacitor obtained in Example 47 were measured after aging treatment and defined as the initial characteristics. Furthermore, after performing a reflow with a peak temperature of 260°C and a holding time of 10 seconds, the characteristics were measured after 200 hours and 500 hours of no-load standing tests at 180°C. Capacitance change at 120 Hz, ESR value at 100 kHz, tanδ at 120 Hz, and leakage current over 2 minutes were measured. The results are shown in Table 5 below. The solid electrolytic capacitor in Example 47 showed sufficient initial characteristics (capacitance, tanδ, ESR, LC). The same was true for the other examples described below.

[0191] <Example 48> A solid electrolytic capacitor according to Example 48 was manufactured in the same manner as in Example 47, except that 0.1% by mass of glutamic acid as an amphoteric compound was added to the dispersion. The initial characteristics and characteristics after reflow and no-load standing tests at 180°C for 200 hours and 500 hours were measured and evaluated. The results are shown in Table 5 below.

[0192] <Examples 49-51> Solid electrolytic capacitors according to Examples 49-51 were manufactured in the same manner as in Example 48, except that the amphoteric compound and its content were changed as shown in Table 3 below. Initial characteristics were measured, and after reflow soldering, characteristics were measured and evaluated after 200 hours and 500 hours of no-load standing tests at 180°C. The results are shown in Table 5 below.

[0193] <Comparative Example 15> A solid electrolytic capacitor according to Comparative Example 15 was manufactured in the same manner as in Example 47, except that an aromatic nitro compound having a polar group was not added. The initial characteristics were measured, and after reflow soldering, the characteristics were measured and evaluated after 200 hours and 500 hours of no-load standing tests at 180°C. The results are shown in Table 5 below.

[0194] <Comparative Example 16> A solid electrolytic capacitor according to Comparative Example 16 was manufactured in the same manner as in Example 47, except that 0.5% by mass of glutamic acid as an amphoteric compound was added to the dispersion instead of adding an aromatic nitro compound having a polar group. The initial characteristics were measured, and after reflow soldering, the characteristics were measured and evaluated after 200 hours and 500 hours of no-load standing tests at 180°C. The results are shown in Table 5 below.

[0195] <Comparative Example 17> An electrolytic capacitor according to Comparative Example 17 was manufactured in the same manner as in Example 47, except that no aromatic nitro compounds having polar groups were added, and after forming the electrolyte and drying the capacitor element, 1500 parts by mass of diglycerin per 100 parts by mass of the total of the conductive polymer and polyanion dopant was impregnated into the voids of the element. The electrolytic capacitor of Comparative Example 17 is an electrolytic capacitor (solid-liquid hybrid electrolytic capacitor) that further contains a liquid substance in addition to the solid electrolyte. The obtained electrolytic capacitor was measured for initial characteristics, reflowed, and then its characteristics were measured and evaluated after 200 hours and 500 hours of no-load standing tests at 180°C. Appearance abnormalities (deformation) were evaluated by visual inspection. The results are shown in Table 5 below.

[0196] [Table 5]

[0197] In Table 5, in all of the examples using aromatic nitro compounds with polar groups, the decrease in volume and increase in ESR were well suppressed compared to Comparative Examples 15 and 16, in which aromatic nitro compounds with polar groups were not added.

[0198] Furthermore, Examples 47-51, which included an amphoteric compound, compared to Example 47, which did not contain an amphoteric compound, showed that even under ultra-high temperature conditions of 180°C, the suppression of ESR was maintained, the reduction in capacity was further suppressed, and the leakage current (LC) was significantly reduced. Comparing Examples 48, 50, and 51, Example 51, which used glycine as the amphoteric compound, showed particularly good suppression of capacity reduction, suppression of ESR increase, and reduction of leakage current. Comparing Examples 48 and 49, the addition of 0.5% glutamic acid showed better suppression of capacity reduction and reduction of leakage current than the addition of 0.1% glutamic acid.

[0199] In the 180°C 500-hour test, all of the examples showed good performance, with no abnormalities in appearance or significant increases in ESR. On the other hand, in Comparative Example 17, where liquid was added after the formation of the electrolyte, deformation of the appearance due to an increase in internal pressure was observed under the 180°C 500-hour conditions, and capacitor malfunction accompanied by a rapid increase in ESR occurred. [Explanation of Symbols]

[0200] 1. Solid electrolytic capacitor 10 Exterior 20 Capacitor elements 21 Anode foil 22, 24 Oxide film 23 Cathode foil 25 Separators 26 Solid electrolyte 29, 30 Lead 40 Sealing material

Claims

1. A solid electrolytic capacitor having an anode foil, a cathode foil, and a separator between them, with an oxide film formed on their surfaces, and having an electrolyte portion in the gap between the anode foil and the cathode foil, The electrolyte portion is composed of a solid electrolyte containing a conductive polymer compound, a polyanion dopant, an aromatic nitro compound having a polar group, and an optional secondary dopant. Solid electrolytic capacitor.

2. The solid electrolytic capacitor according to claim 1, wherein the aromatic nitro compound has a hydroxyl group or a carboxyl group.

3. The solid electrolytic capacitor according to claim 1 or 2, wherein the aromatic nitro compound has a solubility of 0.01 g / 100 gaq or more.

4. The solid electrolytic capacitor according to claim 1 or 2, wherein the aromatic nitro compound is at least one selected from the group consisting of nitrophenol, nitrobenzoic acid or a salt thereof, nitrosalicylic acid or a salt thereof, and nitrobenzyl alcohol.

5. The solid electrolytic capacitor according to claim 1 or 2, wherein the content of the aromatic nitro compound is 0.5 to 100 parts by mass with respect to 100 parts by mass of the total of the conductive polymer compound, the polyanion dopant and optional secondary dopant.

6. The solid electrolytic capacitor according to claim 1 or 2, wherein the ratio of the polyanion dopant to the conductive polymer compound in the solid electrolyte is 1:10 to 1:0.

5.

7. The solid electrolytic capacitor according to claim 1 or 2, wherein the solid electrolyte comprises a secondary dopant, and the secondary dopant is at least one selected from the group consisting of glycerin, diglycerin, triglycerin, tetraglycerin, polyglycerin, polyglyceryl ether, diethylene glycol, triethylene glycol, and polyethylene glycol.

8. The solid electrolytic capacitor according to claim 1 or 2, wherein the conductive polymer compound and the polyanion dopant form fine particles.

9. The solid electrolytic capacitor according to claim 8, wherein the aromatic nitro compound is localized on the surface of the fine particles and / or penetrates into the conductive polymer.

10. The solid electrolytic capacitor according to claim 8, wherein the aromatic nitro compound is localized on the surface of the fine particles and / or penetrates into the conductive polymer, thereby being present between the fine particles and the oxide film of the anode foil.

11. The solid electrolytic capacitor according to claim 1 or 2, wherein the solid electrolyte further contains an amphoteric compound having an acidic group and a basic group in one molecule.

12. The solid electrolytic capacitor according to claim 11, wherein the content of the amphoteric compound is 1 to 100 parts by mass with respect to 100 parts by mass of the total of the conductive polymer compound and the dopant.

13. The solid electrolytic capacitor according to claim 1 or 2, wherein the conductive polymer compound comprises polyethylenedioxythiophene.

14. The solid electrolytic capacitor according to claim 1 or 2, wherein the polyanion dopant comprises polystyrene sulfonic acid.

15. A solid electrolytic capacitor according to claim 1 or 2, for use at temperatures of 100°C to 200°C.

16. A method for manufacturing a solid electrolytic capacitor, (i) To provide a capacitor element comprising an anode foil, a cathode foil, and a separator between them, each having an oxide film formed on its surface. (ii) Prepare a dispersion of conductive polymer compounds containing fine particles composed of conductive polymer compounds and polyanion dopants, as well as optional secondary dopants. (iii) Adding an aromatic nitro compound having a polar group to the conductive polymer compound dispersion, (iv) Impregnating the capacitor element with the conductive polymer compound dispersion and drying it to form an electrolyte portion on the oxide film. Includes, After forming the electrolyte portion, the capacitor element is sealed in the case without adding any liquid substance. method.

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