Method for manufacturing electrolytic capacitor having conductive polymer

Abstract

The purpose of the present invention is to provide a capacitor manufacturing method which includes impregnating a capacitor element with a conductive polymer-containing liquid in a plurality of stages, the method achieving a sufficient characteristic improvement effect in each impregnation stage. The present invention relates to a method for manufacturing an electrolytic capacitor comprising: an anode foil with an oxide film formed on a surface thereof; a cathode foil; and a solid electrolyte portion in a gap between the anode foil and the cathode foil, the solid electrolyte portion containing a conductive polymer. The method comprises (i) providing a capacitor element having an anode foil with an oxide film formed on a surface thereof, and a cathode foil; (ii) impregnating the capacitor element with a first conductive polymer-containing liquid containing 15 mass% or less of an organic solvent having a boiling point or a decomposition temperature of 150°C or higher, and drying the capacitor element to form a solid electrolyte portion precursor in a gap between the anode foil and the cathode foil; and (iii) impregnating the capacitor element, having the solid electrolyte portion precursor formed therein, with a second conductive polymer-containing liquid containing 20 mass% or more of an organic solvent having a boiling point or a decomposition temperature of 150°C or more, and drying the capacitor element to form a solid electrolyte portion in the gap between the anode foil and the cathode foil.

Description

Method for manufacturing electrolytic capacitors having conductive polymers

[0001] The present invention relates to a method for manufacturing an electrolytic capacitor having a conductive polymer.

[0002] (Electrolytic capacitors having conductive polymers) Conventionally, solid electrolytic capacitors using conductive polymer compounds as solid electrolytes have been known. Such capacitors can exhibit low ESR and excellent low-temperature characteristics. Furthermore, by using a solid, heat-resistant conductive polymer as the electrolyte, such capacitors can be provided with high reliability.

[0003] The use of various additives has been investigated to improve the properties of electrolytic capacitors containing conductive polymers (conductive polymer compounds).

[0004] Patent Document 1 describes a method for producing an electrolytic capacitor, in which a capacitor element is impregnated with a dispersion of a conductive polymer, followed by a drying operation at least once to form a conductive polymer layer on the capacitor element, and then the capacitor element is impregnated with a high-boiling organic solvent having a boiling point of 150°C or higher or a solution containing 20% ​​by mass or more but less than 100% by mass of a high-boiling organic solvent having a boiling point of 150°C or higher, followed by a drying operation at least once.

[0005] Patent Document 2 describes a method for producing a solid electrolytic capacitor, in which a dielectric oxide film is formed on the surface of an electrode body made of a porous valve metal, and then the electrode body is immersed in a solution for forming a metal oxide semiconductor layer having a concentration of less than 30% by weight to form a metal oxide semiconductor layer as a conductive precoat layer on the dielectric oxide film. This formation process is performed at most twice, and then a step of immersing the electrode body in a solution containing a heterocyclic compound and a derivative thereof and a step of immersing the electrode body in a solution containing an oxidizing agent and a dopant having an electrode potential higher than the oxidation potential of the heterocyclic compound and a derivative thereof are alternately repeated multiple times to form a conductive polymer electrolyte layer by chemical oxidative polymerization.

[0006] Patent Document 3 describes a method for manufacturing a capacitor, which includes a step of forming a solid electrolyte layer on the surface of a dielectric layer, and describes that a film formation process is repeated two or more times, in which a conductive polymer solution containing a π-conjugated conductive polymer, a polyanion, and a solvent is applied to the dielectric layer of the capacitor substrate, and the solution is dried to form a conductive polymer film, and that the conductive polymer solution used in at least one film formation process from the second time onwards is a high-viscosity solution having a higher viscosity than the conductive polymer solution used in the first film formation process.

[0007] JP 2014-82392 A JP 9-213575 A JP 2010-87401 A

[0008] When a capacitor element is impregnated with a conductive polymer-containing liquid (e.g., a dispersion), the impregnation can be performed in multiple steps (e.g., two steps) to improve the capacitor characteristics compared to a single impregnation with the same total amount of conductive polymer. When a capacitor element is impregnated with a dispersion containing a conductive polymer in multiple steps, conventional methods sometimes result in insufficient improvement in the capacitor characteristics at each impregnation step.

[0009] The present invention aims to provide a method for manufacturing a capacitor that includes impregnating a capacitor element with a conductive polymer-containing liquid in multiple stages, which method can achieve sufficient characteristic improvement effects in each impregnation stage.

[0010] The above-described problems associated with the present disclosure can be solved by the following aspects of the invention according to the present disclosure: <Aspect 1> A method for manufacturing an electrolytic capacitor having an anode foil and a cathode foil each having an oxide film formed on its surface, and having a solid electrolyte portion containing a conductive polymer in a gap between the anode foil and the cathode foil, the method comprising: (i) providing a capacitor element including an anode foil each having an oxide film formed on its surface and a cathode foil, (ii) impregnating the capacitor element with a first conductive polymer-containing liquid containing 15 mass % or less of an organic solvent having a boiling point or decomposition temperature of 150°C or higher, and drying the liquid to form a solid electrolyte portion precursor in the gap between the anode foil and the cathode foil, and (iii) impregnating the capacitor element with the solid electrolyte portion precursor formed therein with a second conductive polymer-containing liquid containing 15 mass % or more of an organic solvent having a boiling point or decomposition temperature of 150°C or higher, and drying the liquid to form a solid electrolyte portion in the gap between the anode foil and the cathode foil. <Aspect 2> The method of Aspect 1, wherein the first conductive polymer-containing liquid contains 2 to 15 mass % of the organic solvent having a boiling point or decomposition temperature of 150°C or higher, and / or the second conductive polymer-containing liquid contains 15 to 45 mass % of the organic solvent having a boiling point or decomposition temperature of 150°C or higher. <Aspect 3> The method of Aspect 1 or 2, wherein the second conductive polymer-containing liquid contains more than 20 mass % of the organic solvent having a boiling point or decomposition temperature of 150°C or higher. <Aspect 4> The method of any one of Aspects 1 to 3, wherein the organic solvent having a boiling point or decomposition temperature of 150°C or higher comprises at least one selected from glycerin, diglycerin, polyglycerin, ethylene glycol, diethylene glycol, polyethylene glycol, and derivatives thereof. <Aspect 5> The method of any one of Aspects 1 to 4, wherein the conductive polymer content in each of the first conductive polymer-containing liquid and the second conductive polymer-containing liquid is 0.5 to 5 mass %. Aspect 6 The method according to any one of Aspects 1 to 5, wherein the conductive polymers contained in the first conductive polymer-containing liquid and the second conductive polymer-containing liquid are polythiophene and derivatives thereof.<Aspect 7> The method according to any one of Aspects 1 to 6, wherein the first conductive polymer-containing liquid and the second conductive polymer-containing liquid both contain fine particles composed of a conductive polymer compound and an optional dopant. <Aspect 8> The method according to Aspect 7, wherein the dopant is polystyrene sulfonic acid. <Aspect 9> The method according to any one of Aspects 1 to 8, wherein the electrolytic capacitor is a solid electrolytic capacitor. <Aspect 10> The method according to any one of Aspects 1 to 9, further comprising impregnating a space between the anode foil and the cathode foil of the capacitor element having the solid electrolyte portion with a liquid substance.

[0011] According to the method of the present disclosure, in a capacitor manufacturing method that includes impregnating a capacitor element with a conductive polymer-containing liquid in multiple stages, a method can be provided that can achieve a sufficient characteristic improvement effect in each impregnation stage.

[0012] Fig. 1a is a cross-sectional schematic diagram of an electrolytic capacitor according to one embodiment of the present disclosure. Fig. 1b is a perspective schematic diagram of a capacitor element according to one embodiment of the present disclosure. Fig. 2 is a cross-sectional schematic diagram of a main part of an electrolytic capacitor. Fig. 3 is a graph showing the capacitance increase ratio of each of Examples and Comparative Examples. Fig. 4 is a graph showing the ESR reduction ratio of each of Examples and Comparative Examples.

[0013] <<Electrolytic Capacitor>> The invention according to the present disclosure is a method for manufacturing an electrolytic capacitor having an anode foil and a cathode foil each having an oxide film formed on its surface, and having a solid electrolyte portion containing a conductive polymer in a gap between the anode foil and the cathode foil. The method includes: (i) providing a capacitor element including an anode foil each having an oxide film formed on its surface and a cathode foil; (ii) impregnating the capacitor element with a first conductive polymer-containing liquid containing 15 mass % or less of an organic solvent having a boiling point or decomposition temperature of 150°C or higher, and drying the liquid to form a solid electrolyte portion precursor in the gap between the anode foil and the cathode foil; and (iii) impregnating the capacitor element with the solid electrolyte portion precursor formed therein with a second conductive polymer-containing liquid containing 15 mass % or more of an organic solvent having a boiling point or decomposition temperature of 150°C or higher, and drying the liquid to form a solid electrolyte portion in the gap between the anode foil and the cathode foil.

[0014] The characteristics of the resulting capacitor can be improved by adding an additive (an organic solvent having a boiling point or decomposition temperature of 150° C. or higher) to the conductive polymer-containing liquid. Without intending to be limited by theory, it is believed that such an additive added to the conductive polymer-containing liquid promotes proper alignment (and rearrangement) of the conductive polymer and / or conductive polymer-containing fine particles impregnated in the capacitor element, thereby improving the capacitor characteristics.

[0015] When a capacitor element is impregnated with a conductive polymer-containing liquid (particularly a dispersion liquid), the impregnation can be performed in multiple steps, thereby improving the capacitor characteristics compared to a single impregnation with the same total amount of conductive polymer.

[0016] In conventional methods, the effect of improving the capacitor characteristics obtained at each stage of such multi-stage impregnation may be insufficient.

[0017] The present inventors have found that by optimizing the amount of additive in each of the conductive polymer-containing liquids used in the multi-stage impregnation, it is possible to obtain a sufficient effect of improving the properties in each impregnation stage.

[0018] That is, in the present invention, the first conductive polymer-containing liquid contains, as an additive, 15 mass % or less of an organic solvent having a boiling point or decomposition temperature of 150°C or higher, and the second conductive polymer dispersion contains, as an additive, 15 mass % or more of an organic solvent having a boiling point or decomposition temperature of 150°C or higher, thereby making it possible to obtain a sufficient characteristic improvement effect at each impregnation stage.

[0019] In particular, according to the present invention, the capacity increase rate can be maximized by using an organic solvent having a boiling point or decomposition temperature of 150°C or higher as an additive in the first impregnation at a concentration of 15% by mass or less. Also, according to the present invention, the ESR reduction effect can be maximized by using an organic solvent having a boiling point or decomposition temperature of 150°C or higher as an additive in the second impregnation at a concentration of 15% by mass or more.

[0020] While not intending to be limited by theory, it is believed that by using an additive amount of 15% by mass or less in the first impregnation, the additive effect (neutralizing the hydrophobicity of the conductive polymer to promote impregnation) can be obtained while suppressing the impregnation of the conductive polymer into the capacitor element due to the presence of the additive itself. In particular, by using a relatively small amount of additive in the first impregnation, an appropriate amount of voids can be secured within the capacitor element, leaving space for the conductive polymer-containing liquid to enter during the second impregnation, thereby ensuring a certain level of conductivity. Furthermore, it is believed that using an additive amount of 15% by mass or more in the second impregnation promotes rearrangement of the conductive polymer (especially its fine particles) in the solid electrolyte precursor already formed in the capacitor element and the conductive polymer (especially its fine particles) that will form the newly impregnated solid electrolyte, thereby improving capacitor characteristics.

[0021] According to the present invention, by setting the concentration of the organic solvent having a boiling point or decomposition temperature of 150°C or higher and used in the first impregnation to 15% by mass or less, and by setting the concentration of the organic solvent having a boiling point or decomposition temperature of 150°C or higher and used in the second impregnation to 15% by mass or more, when the amount of conductive polymer in the element is the same, the conductive polymer film will be more stable than when produced by one impregnation, thereby reducing variations in characteristics and enabling stable production. Furthermore, by dividing the liquid into two, the amount of conductive polymer in the liquid is less than in the liquid for one impregnation, which makes it possible to suppress aggregation of the conductive polymer, and it is expected that the shelf life of the dispersion will be extended.

[0022] The drawings are used to explain in more detail exemplary embodiments of the present invention, but these drawings and exemplary embodiments are not intended to limit the present invention. The drawings are schematic and are not necessarily drawn to scale.

[0023] 1a and 1b are diagrams shown to explain the electrolytic capacitor 1 according to the embodiment. Fig. 1a is a cross-sectional view of the electrolytic capacitor 1, and Fig. 1b is a perspective view of a capacitor element 20.

[0024] FIG. 2 is a cross-sectional view of a main part of the electrolytic capacitor 1 according to the embodiment, which is shown for explaining the main part of the electrolytic capacitor 1 according to the embodiment.

[0025] The electrolytic capacitor 1 according to the embodiment is a wound-type electrolytic capacitor, and as shown in FIG. 1 a, includes a cylindrical metal case 10 with a bottom, a capacitor element 20, and a sealing member 40.

[0026] The bottom of the metal case 10 is substantially circular, with a valve (not shown) located near the center. This allows the valve to break and release the internal pressure to the outside when the internal pressure increases. The side of the metal case 10 extends vertically from the outer edge of the bottom. The opening of the metal case 10 is sealed with a sealing member 40, and two leads 29 and 30 of the capacitor element 20 extend to the outside through a through-hole provided in the sealing member 40.

[0027] Capacitor element 20 is housed inside metal case 10, and as shown in FIGS. 1(b) and 2, includes anode foil 21, cathode foil 23, and separator 25 disposed between anode foil 21 and cathode foil 23, with anode foil 21 and cathode foil 23 overlapping and wound with separator 25 interposed therebetween.

[0028] In the embodiment shown in Fig. 2, anode foil 21 and cathode foil 23 have oxide films (dielectric layers) 22 and 24 on their surfaces, respectively. A solid electrolyte composed of conductive polymer compound / dopant fine particles 26 is disposed so as to contact oxide film 22 on the surface of anode foil 21, thereby forming a solid electrolyte portion. In addition, in the embodiment shown in Fig. 2, liquid substance 27 containing a liquid substance is introduced between anode foil 21 and cathode foil 23, and liquid substance 27 is present so as to surround solid electrolyte composed of conductive polymer compound 26.

[0029] <<Method for manufacturing capacitor>> A method for manufacturing a capacitor according to the present invention is a method for manufacturing an electrolytic capacitor having an anode foil and a cathode foil each having an oxide film formed on its surface, and having a solid electrolyte portion containing a conductive polymer in a gap between the anode foil and the cathode foil, and includes the steps of: (i) providing a capacitor element including an anode foil each having an oxide film formed on its surface and a cathode foil (capacitor element providing step); (ii) impregnating the capacitor element with a first conductive polymer-containing liquid containing 15 mass % or less of an organic solvent having a boiling point or decomposition temperature of 150°C or higher, and drying the liquid to form a solid electrolyte portion precursor in the gap between the anode foil and the cathode foil (first impregnation step); and (iii) impregnating the capacitor element, on which the solid electrolyte portion precursor has been formed, with a second conductive polymer-containing liquid containing 15 mass % or more of an organic solvent having a boiling point or decomposition temperature of 150°C or higher, and drying the liquid to form a solid electrolyte portion in the gap between the anode foil and the cathode foil (second impregnation step).

[0030] Each step of this manufacturing method will be described below.

[0031] <Capacitor Element Providing Step> (i) In the capacitor element providing step, a capacitor element is provided that includes an anode foil having an oxide film formed on the surface thereof and a cathode foil.

[0032] To provide an example of step (i), first, an aluminum foil is provided as anode foil 21. After the surface of the aluminum foil is roughened by a surface-expanding treatment, a predetermined voltage of 2 V to 500 V 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. A capacitor element is then fabricated, including anode foil 21 having oxide film 22, cathode foil 23, and a separator 25 disposed between anode foil 21 and cathode foil 23 (see FIG. 1( b )). Specifically, capacitor element 20 is fabricated by overlapping and winding anode foil 21 having a textured surface (rough surface) on which oxide film 22 is formed and cathode foil 23 having a textured surface, via separator 25. At this time, lead 30 is connected to anode foil 21, and lead 29 is connected to cathode foil 23.

[0033] Next, capacitor element 20 is immersed in the chemical conversion solution in a chemical conversion solution tank, and a predetermined voltage (e.g., 100 V) is applied between anode lead 30 and the chemical conversion solution for 5 minutes. This operation repairs defects in the oxide film present at the edge of anode foil 21 and defects in the oxide film that may be present on the surface.

[0034] As the chemical conversion liquid, a chemical conversion liquid (for example, 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 pimelate, ammonium suberate, decanedicarboxylic acid, ammonium decanedicarboxylate, long-chain dicarboxylic acid, ammonium long-chain dicarboxylate, or the like) can be used.

[0035] <Anode Foil> The capacitor according to the present disclosure includes an anode foil having an oxide film formed on the surface thereof.

[0036] The anode foil may be formed from a valve metal such as aluminum, tantalum, or niobium.

[0037] The anode foil has an oxide film on its surface, which can be formed, for example, by roughening the surface by etching according to a known method and then subjecting the surface to a chemical conversion treatment.

[0038] Cathode Foil A capacitor according to the present disclosure includes a cathode foil.

[0039] The cathode foil, like the anode foil, may be made of a valve metal such as aluminum, tantalum, niobium, etc. The cathode foil may also be made of an aluminum alloy containing copper.

[0040] 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 in the same manner as the anode foil, and then the 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., 2 V), thereby forming the oxide film.

[0041] <Separator> A capacitor according to the present disclosure may include a separator disposed between the anode foil and the cathode foil.

[0042] The separator is preferably made of cellulose fiber, which is chemically compatible with conductive polymer particles and water-soluble polymers, or a synthetic resin, such as nylon, PET, or PPS, which has excellent heat resistance. For example, heat-resistant cellulose paper or heat-resistant flame-retardant paper can be used. More specifically, examples of the separator 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 derivatives thereof, 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 alone or in combination.

[0043] <First Impregnation Step> In the first impregnation step (ii) according to the production method of the present invention, the capacitor element is impregnated with a first conductive polymer-containing liquid and dried to form a solid electrolyte precursor in the gap between the anode foil and the cathode foil (particularly on the oxide film).

[0044] The solid electrolyte precursor can be formed, for example, by a dipping impregnation method. That is, for example, a conductive polymer-containing liquid (e.g., a dispersion liquid with 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-containing liquid. Next, the capacitor element is removed from the introduction tank and subjected to a heat treatment. This allows the solid electrolyte precursor to be introduced into the gap between the anode foil and the cathode foil, and the solid electrolyte precursor can be formed on the oxide film.

[0045] (First Conductive Polymer-Containing Liquid) The first conductive polymer-containing liquid used in the first impregnation step is a liquid containing a conductive polymer, and contains 15 mass % or less of an organic solvent having a boiling point or decomposition temperature of 150° C. or higher as an additive.

[0046] The first conductive polymer-containing liquid may be a conductive polymer dispersion or a conductive polymer solution, and may particularly be a conductive polymer dispersion.

[0047] In the present invention, the "organic solvent" refers to an organic compound that is liquid at room temperature (25°C) by itself, and is a compound different from the conductive polymer compound and the dopant that is optionally added.

[0048] The content of the conductive polymer in the first conductive polymer-containing liquid may be 0.1 to 10 mass %, 0.2 to 5 mass %, and particularly 0.5 to 3 mass %.

[0049] Examples of the dispersion medium for the conductive polymer dispersion include protic solvents such as water, alcohols (e.g., methanol, ethanol, 1-propanol, and butanol), and mixtures thereof. The content of the dispersion medium (particularly water) in the conductive polymer dispersion may be 50 to 99% by mass, 55 to 90% by mass, or even 60 to 80% by mass.

[0050] As the solvent for the conductive polymer solution, for example, protic solvents such as water, alcohols (for example, methanol, ethanol, 1-propanol, butanol), and mixtures thereof can be used.

[0051] The conductive polymer-containing liquid may contain an aromatic nitro compound.

[0052] (Additives) As described above, the first conductive polymer-containing liquid contains an organic solvent having a boiling point or decomposition temperature of 150° C. or higher (particularly, an organic solvent having a boiling point of 150° C. or higher).

[0053] Examples of such organic solvents having a boiling point or decomposition temperature of 150° C. or higher include glycerin, diglycerin, and polyglycerin, glycol compounds such as ethylene glycol, diethylene glycol, and other polyethylene glycols, and derivatives thereof, γ-butyrolactone, butanediol, dimethyl sulfoxide, sulfolane, N-methylpyrrolidone, dimethyl sulfolane, and polyethylene glycol, and derivatives thereof. These may be used alone or in combination of two or more.

[0054] The content of the organic solvent having a boiling point or decomposition temperature of 150°C or higher in the first conductive polymer-containing liquid is 15% by mass or less. This content may be 1% by mass or more, 2% by mass or more, 3% by mass or more, 4% by mass or more, 5% by mass or more, or 6% by mass or more, and / or may be less than 15% by mass, 14% by mass or less, 13% by mass or less, 12% by mass or less, or 11% by mass or less. This content is preferably 1 to 15% by mass, 1 to 14% by mass, more preferably 2 to 13% by mass, and particularly preferably 7 to 12% by mass. In one embodiment, this content is 1 to 10% by mass, 1 to 8% by mass, or even 2 to 6% by mass. In one embodiment, the content of the organic solvent having a boiling point or decomposition temperature of 150°C or higher in the first conductive polymer-containing liquid is lower than the content of the organic solvent having a boiling point or decomposition temperature of 150°C or higher in the second conductive polymer-containing liquid. In this case, more desirable properties may be obtained.

[0055] The additive (an organic solvent with a boiling point or decomposition temperature of 150°C or higher) added to the conductive polymer-containing solution may exist as a liquid substance between the anode foil and the cathode foil after the capacitor is manufactured. In this case, the conductivity of the conductive polymer compound may be further improved. In addition, in this case, the characteristics of the capacitor may also be improved, resulting in low ESR (low resistance) and high capacity, and the improved conductivity may also have the effect of delaying deterioration (extending life). While not intending to be limited by theory, it is believed that when the additive is added to the conductive polymer-containing solution, it is absorbed into the fine particles of the conductive polymer compound, promoting the formation of an array structure of the conductive polymer compound, resulting in improved conductivity.

[0056] (Conductive polymer) The conductive polymer (conductive polymer compound) may be at least one selected from polythiophene, polypyrrole, polyaniline, and derivatives thereof. The conductive polymer compound may be at least one of these. Preferably, the conductive polymer compound is a polymer of EDOT or a derivative thereof. A particularly preferred conductive polymer compound is polyethylenedioxythiophene (PEDOT) (particularly poly(3,4-ethylenedioxythiophene)).

[0057] (Dopant) The solid electrolyte may further contain a dopant. The dopant may be a polyanion. Specific examples of 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 polyester, phenolsulfonic acid novolac resin, and copolymers of styrenesulfonic acid and non-sulfonic acid monomers (such as methacrylic acid esters, acrylic acid esters, unsaturated hydrocarbon-containing alkoxysilane compounds, or their hydrolysates); and chain sulfones such as methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid, and butanesulfonic acid. These may be used alone or in combination of two or more.

[0058] The polystyrene sulfonic acid (PSS) preferably has a weight average molecular weight of 10,000 to 1,000,000.

[0059] In a particularly preferred embodiment, the solid electrolyte comprises polyethylenedioxythiophene (PEDOT) as the conductive polymer and polystyrene sulfonic acid (PSS) as the dopant.

[0060] (Fine Particles) The conductive polymer in the conductive polymer-containing liquid may be present in the form of fine particles. In a preferred embodiment, the first conductive polymer-containing liquid contains fine particles composed of a conductive polymer compound and an optional dopant. The average particle size of the fine particles composed of the conductive polymer compound and the dopant may be 1 nm to 600 nm, preferably 1 nm to 300 nm, or even 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 dopant can be determined, for example, from particle size distribution by dynamic light scattering.

[0061] The method for preparing the conductive polymer compound dispersion is not particularly limited, and may be a conventional method. As a specific example, the conductive polymer compound dispersion may be prepared according to the following preparation procedures (a) to (e) for a PEDOT / PSS microparticle dispersion: (a) Using ethylenedioxythiophene (EDOT) monomer and polystyrene sulfonic acid (PSS), a PEDOT / PSS microparticle dispersion (e.g., 2% by mass) is prepared. (b) Excess cation components and / or anion components are removed by ion exchange treatment. (c) Microparticulation treatment is performed using a rotary homogenizer or ultrasonic homogenizer. (d) The pH is adjusted to 2 to 5 by neutralization treatment. (e) A high-boiling-point compound is added to the PEDOT / PSS microparticle dispersion. This may improve conductivity.

[0062] (Solid Electrolyte Portion Precursor) As a result of the first impregnation step, a solid electrolyte portion precursor is formed between the anode foil and the cathode foil of the capacitor element.

[0063] <Second Impregnation Step> In the second impregnation step (iii) of the production method according to the present invention, the capacitor element having the solid electrolyte portion precursor obtained as a result of the first impregnation step is impregnated with a second conductive polymer-containing liquid, and then dried to form a solid electrolyte portion in the gap between the anode foil and the cathode foil (particularly on the oxide film).

[0064] For details of the second impregnation step, the description of the first impregnation step above can be referred to. For example, with regard to the components of the conductive polymer-containing liquid, the impregnation method, the dispersion medium, the solvent, the conductive polymer, and the organic solvent having a boiling point or decomposition temperature of 150°C or higher, the description of the first impregnation step above and the description of the first conductive polymer-containing liquid can be referred to.

[0065] The organic solvent having a boiling point or decomposition temperature of 150°C or higher contained as an additive in the second conductive polymer-containing liquid may be the same as or different from the organic solvent having a boiling point or decomposition temperature of 150°C or higher contained in the first conductive polymer-containing liquid.

[0066] The content of the conductive polymer in the second conductive polymer-containing liquid may be 0.1 to 10 mass %, 0.2 to 5 mass %, and particularly 0.5 to 3 mass %.

[0067] When the second conductive polymer-containing liquid is a conductive polymer dispersion, the content of the dispersion medium (particularly water) in the conductive polymer dispersion may be 30 to 85 mass %, 40 to 80 mass %, or even 50 to 75 mass %.

[0068] The second conductive polymer-containing liquid contains a conductive polymer and 15% by mass or more of an organic solvent having a boiling point or decomposition temperature of 150° C. or higher. The content of the additive in the second conductive polymer-containing liquid may be 15 to 50% by mass, further 15 to 45% by mass, and particularly 20 to 45% by mass. In one embodiment, the content is greater than 15% by mass. This content may also be 16% by weight or more, 17% by weight or more, 18% by weight or more, 19% by weight or more, 20% by weight or more, more than 20% by weight, 21% by weight or more, 22% by weight or more, 23% by weight or more, 24% by weight or more, 25% by weight or more, 26% by weight or more, 27% by weight or more, 28% by weight or more, 29% by weight or more, or 30% by weight or more, and / or 60% by weight or less, 58% by weight or less, 56% by weight or less, 54% by weight or less, 52% by weight or less, 50% by weight or less, or 48% by weight or less. In one embodiment, this content is 16 to 50% by weight, 18 to 48% by weight, 20 to 45% by weight, or even 30 to 45% by weight. In one embodiment, the content of the organic solvent having a boiling point or decomposition temperature of 150°C or higher in the second conductive polymer-containing liquid is greater than the content of the organic solvent having a boiling point or decomposition temperature of 150°C or higher in the first conductive polymer-containing liquid, and in this case, more desirable properties can be obtained.

[0069] (Solid Electrolyte Portion) As a result of the second impregnation step, a solid electrolyte portion is formed. The solid electrolyte portion is made of a solid electrolyte. The solid electrolyte portion includes a conductive polymer.

[0070] The solid electrolyte portion is present in the gap between the anode foil and the cathode foil. In this disclosure, the "gap between the anode foil and the cathode foil" includes not only the "gap between the anode foil and the separator and the gap between the cathode foil and the separator" but also the "gap between the fibers in the separator." Furthermore, the "gap between the anode foil and the cathode foil" also includes the "gap in the etching pits (recesses) formed in the surface of the anode foil or the cathode foil by roughening through etching."

[0071] The solid electrolyte portion is at least partially in contact with the oxide film formed on the surface of the anode foil, and includes a conductive polymer compound and an optional dopant.

[0072] The solid electrolyte portion may have various forms, such as a continuous, uniform thick or thin layer, a membrane (film), or an aggregate of fine particles or a network of fine particle chains. The solid electrolyte portion is particularly in the form of a fine particle layer composed of fine particles containing a conductive polymer (and optionally a dopant).

[0073] In particular, the solid electrolyte portion is in at least partial direct contact with the oxide film of the anode foil, and is in at least partial direct contact with the metal surface and / or the oxide film of the cathode foil.

[0074] The solid electrolyte portion containing the conductive polymer compound may be formed by polymerizing a monomer by so-called "in-situ polymerization."

[0075] In the capacitor according to the present disclosure, the proportion of the conductive polymer compound in the gap between the anode foil and the cathode foil may be 0.5 vol % to 40 vol %, or even 1.0 vol % to 20 vol %.

[0076] <Liquid Material> The method according to the present disclosure may further include impregnating a liquid material between the anode foil and the cathode foil of a capacitor element having a solid electrolyte portion. In the resulting electrolytic capacitor, the liquid material is preferably present between the anode foil and the cathode foil. The liquid material may be present particularly so as to surround the solid electrolyte (particularly the conductive polymer compound-containing fine particles) that constitute the solid electrolyte portion.

[0077] From the viewpoint of film repair, an electrically neutral and polar liquid substance (solvent) is preferable. This solvent is less susceptible to repulsion due to the surface charge of the PEDOT / PSS particles, so it penetrates into the interior and even migrates to the outside of the particles. Furthermore, the supply of oxygen-containing polar solvents allows for highly efficient film formation. Examples of such solvents include proton-based high-boiling polar solvents with boiling points of 150°C or higher, such as ethylene glycol, diethylene glycol, triethylene glycol, glycerin, and their derivatives, as well as polymer solutions of polyethylene glycol, polyalkylene glycol, polyglycerin, polyoxyalkylene polyglyceryl ether, and their derivatives.

[0078] In the capacitor according to the present disclosure, the proportion of the liquid substance in the gap between the anode foil and the cathode foil may be 10 vol% to 99 vol%, particularly 50 vol% to 99 vol%, or even 70 vol% to 99 vol%.

[0079] The liquid substance is not particularly limited, and may include, for example, an organic solvent, particularly a polymeric organic solvent. The liquid substance may include, for example, water, a hydrophilic polymer compound, a component having a hydroxyl group, such as polyoxyalkylene and its derivatives (polyglycerin), water-soluble polyurethane, water-soluble polyester, water-soluble polyamide, water-soluble polyimide, water-soluble polyacrylic, water-soluble polyacrylamide, water-soluble silicone, polyvinyl alcohol, polyacrylic acid, or a mixture thereof.

[0080] In particular, components of the liquid material include glycol compounds such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, and other polyethylene glycols and their derivatives, glycerin and diglycerin and their derivatives, γ-butyrolactone, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, and dimethylformamide. These may be used alone or in combination of two or more. Of these, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, other polyethylene glycols, and their derivatives are preferred, with ethylene glycol and diethylene glycol being most preferred. When ethylene glycol and / or diethylene glycol is used as the liquid material, an electrolytic capacitor with particularly good reflow characteristics can be obtained.

[0081] The liquid substance is, for example, a liquid capable of retaining the acid component and the base component, and in particular a solvent in which the acid component and the base component as solutes can be dissolved.

[0082] In particular, the liquid material contains glycol compounds (particularly ethylene glycol and / or diethylene glycol) in a total amount of 30% to 99%, 50 to 95%, or even 60% to 80% by weight. In one particular embodiment, the liquid material contains glycol compounds (particularly ethylene glycol and / or diethylene glycol) in a total amount of 90% to 100%, 90 to 99.9%, or even 95% to 99.5% by weight.

[0083] (Water) The liquid substance may contain water.

[0084] When the liquid substance present in the gap between the anode foil and the cathode foil contains "water," it is possible to obtain particularly favorable effects in terms of reducing the defect density of the oxide film and reducing leakage current.

[0085] The water content may be 0 to 10% by mass, preferably 0.1 to 10% by mass, and more preferably 0.5 to 5% by mass, relative to the liquid substance. When the water content is within this range, the oxide film defect repair effect can be sufficiently obtained, and adverse effects caused by an excessive water content (such as expansion of the capacitor that can occur when used for a long period of time in a high-temperature environment) can be avoided or suppressed.

[0086] In particular, when the electrolytic capacitor contains a liquid substance, the electrolytic capacitor can be called a hybrid electrolytic capacitor.

[0087] <Liquid Material Injection Step> The method for manufacturing an electrolytic capacitor according to the present disclosure may optionally include the step of injecting a liquid material into the capacitor element (particularly into the gap between the anode foil and the cathode foil). For details of the liquid material, see the above description of the electrolytic capacitor.

[0088] In one embodiment, a liquid substance is introduced into the above-described capacitor element having the solid electrolyte portion formed therein, so that the liquid substance is present between the anode foil and the cathode foil.

[0089] The liquid substance introduced in this manner can permeate the formed solid electrolyte portion, thereby further improving the conductivity of the conductive polymer compound. In this case, the characteristics of the capacitor may also be improved, resulting in low ESR (low resistance) and high capacity, and the improved conductivity may also result in delayed deterioration (longer life). Without intending to be limited by theory, it is believed that the liquid substance (e.g., a high-boiling point compound such as ethylene glycol) that permeates the solid electrolyte portion is absorbed by the fine particles of the conductive polymer compound, thereby promoting the formation of an array structure of the conductive polymer compound and, as a result, improving the conductivity.

[0090] In this step, for example, the liquid material 27 is introduced into the gap between the anode foil 21 and the cathode foil 23 so as to surround the solid electrolyte and so that the proportion of the liquid material 27 in the gap is within the range of 10 vol % to 99 vol %.

[0091] When the liquid substance is filled by the immersion impregnation method, the liquid substance may be introduced into the voids by filling an introduction tank with the liquid substance and then immersing the capacitor element in the liquid substance.

[0092] The liquid substance may include an acid component and a base component.

[0093] The acid component includes organic acids, inorganic acids, and complex compounds thereof.

[0094] Examples of organic acids include carboxylic acids, phenols, and sulfonic acids. Examples of carboxylic acids include formic acid, phthalic acid, isophthalic acid, terephthalic acid, salicylic acid, sulfosalicylic acid, maleic acid, adipic acid, benzoic acid, tricarboxylic acid, enanthic acid, malonic acid, 1,6-decanedicarboxylic acid, 1,7-octanedicarboxylic acid, azelaic acid, resorcylic acid, phloroglucinic acid, gallic acid, and citric acid.

[0095] Examples of inorganic acids include boric acid, phosphoric acid, phosphorous acid, hypophosphorous acid, carbonic acid, and silicic acid.

[0096] Examples of the composite compound of an organic acid and an inorganic acid include borodisalicylic acid, borodisoxalic acid, and borodiglycolic acid.

[0097] The above-described acid components may be used alone or in combination of two or more.

[0098] The acid component is contained in an amount of, for example, 0.01% by mass to 15% by mass relative to the liquid substance.

[0099] The base component may be one or more selected from amines, amidines, and ammonia, and is preferably an amine.

[0100] The base component may be contained in an amount of 0.01% by mass to 15% by mass relative to the liquid substance.

[0101] (Aromatic Nitro Compound) The liquid material of the electrolytic capacitor according to the present disclosure may contain an aromatic nitro compound. The aromatic nitro compound is an aromatic compound having a nitro group. The aromatic nitro compound can improve the pressure resistance and heat resistance of the capacitor by absorbing hydrogen gas generated by a re-chemical conversion reaction or the like.

[0102] When an aromatic nitro compound is used, the proportion of the aromatic nitro compound in the liquid substance may be 0.5% to 10% by weight, 0.5% to 5% by weight, or even 1% to 5% by weight.

[0103] The aromatic nitro compound may be at least one selected from the group consisting of nitrophenol, nitroacetophenone, nitrobenzyl alcohol, nitrobenzoic acid, nitrobenzaldehyde, nitroanisole, nitrobenzenecarboxylic acid, nitrobenzenedicarboxylic acid, nitroaniline, nitroacetanilide, nitrophenylacetic acid, nitrocresol, dinitrobenzoic acid, methylnitrobenzoic acid, nitroterephthalic acid, and nitroisophthalic acid. These may be used alone or in combination of two or more.

[0104] Preferably, the aromatic nitro compound is at least one selected from the group consisting of nitrophenol, nitroacetophenone, nitrobenzyl alcohol, nitrobenzoic acid, and nitrobenzaldehyde. The aromatic nitro compound is particularly preferably nitroacetophenone.

[0105] <Other Post-Processes> An electrolytic capacitor can be manufactured by sealing the capacitor element having the solid electrolyte (and optionally a liquid substance) manufactured through the above-described processes in a case. This process (assembly and sealing process) is described below as an example.

[0106] In the assembly and sealing process, for example, the sealing member 40 is attached to the capacitor element 20, and the capacitor element 20 is inserted into the metal case 10. The metal case 10 is then crimped near the open end of the metal case 10. The sealing member 40 can be, for example, isobutylene-isoprene rubber (IIR). Instead of isobutylene-isoprene rubber (IIR), rubber materials such as ethylene-propylene terpolymer (EPT), EPT-IIR blend rubber, and silicone rubber, as well as rubber composite materials made by bonding rubber with resins such as phenolic resin (Bakelite), epoxy resin, and fluororesin, can also be used. Subsequently, an aging process is optionally performed by applying a predetermined voltage in a high-temperature atmosphere. This completes the electrolytic capacitor 1 according to the embodiment.

[0107] The 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.

[0108] <<Examples 1-1 to 1-2 and Comparative Examples 1-1 to 1-4>> In Examples 1-1 to 1-2 and Comparative Examples 1-1 to 1-4, solid electrolytic capacitors were fabricated with various additive concentrations in the conductive polymer-containing liquid used during impregnation, and the capacitor characteristics were evaluated.

[0109] (Production of Solid Electrolytic Capacitor) A solid electrolytic capacitor rated at 25 V and 330 μF was produced by impregnating a capacitor element with a conductive polymer-containing liquid in two stages.

[0110] The capacitor element was fabricated by winding an aluminum anode foil and an aluminum cathode foil, each having a pressure-resistant coating corresponding to the rated voltage of the capacitor, with a cellulose separator interposed therebetween.

[0111] The conductive polymer-containing liquid used was a water-solvent dispersion containing conductive polymer compound fine particles composed of 2.0 mass % in total of PEDOT and PSS and additives. The reagents used were commercially available.

[0112] The materials used in the impregnation step are as follows: Conductive polymer compound: PEDOT Dopant: PSS Organic solvent as an additive having a boiling point or decomposition temperature of 150° C. or higher (diglycerin and polyglycerin) Water as a dispersion medium

[0113] In Examples 1-1 and 1-2 and Comparative Examples 1-1 to 1-4, as shown in Table 1 below, the amount of additive in the second conductive polymer-containing liquid used in the second impregnation was kept constant (40 mass%), and the first conductive polymer-containing liquid used in the first impregnation was changed to various values ​​(4 mass%, 12 mass%, 18 mass%, 19 mass%, 20 mass%, 23 mass%), and a plurality of series of solid electrolytic capacitors were manufactured.

[0114] The capacitance (μF) at 120 Hz and the ESR (mΩ) at 100 kHz of the obtained capacitor were measured using an LCR meter. The obtained measurements were compared with the measurements of a capacitor manufactured in the same manner as above except that the second impregnation was not performed, and the capacitance increase rate and the ESR reduction rate were calculated.

[0115] The results are shown in Table 1 below and in FIGS.

[0116] The evaluation of the capacity increase effect in Table 1 was based on the capacity increase ratio compared to a capacitor that had been subjected to only the first impregnation, and was performed according to the following criteria: (++) The capacity increase ratio was 2.00 times or more. (+) The capacity increase ratio was 1.10 times or more and less than 2.00 times. (-) The capacity increase ratio was less than 1.10 times.

[0117] The evaluation of the ESR reduction effect in Table 1 was based on the ESR reduction effect compared to a capacitor that had been subjected to only the first impregnation, and was performed according to the following criteria: (+++) The ESR reduction ratio was 0.40 times or less. (++) The ESR reduction ratio was more than 0.40 times and 0.60 times or less. (+) The ESR reduction ratio was more than 0.60 times and 0.80 times or less. (-) The ESR reduction ratio was more than 0.80 times.

[0118] In Figure 3, the content of the additive used in the first impregnation is plotted on the horizontal axis, and the capacity increase rate (times) is plotted on the vertical axis. That is, Figure 3 shows how much capacity increase effect was obtained by the second impregnation relative to the amount of additive used in the first impregnation shown on the horizontal axis.

[0119] In Fig. 4, the horizontal axis represents the content of the additive used in the first impregnation, and the vertical axis represents the ESR reduction rate (times). That is, Fig. 4 shows how much of an ESR reduction effect was obtained by the second impregnation relative to the amount of additive used in the first impregnation, as shown on the horizontal axis.

[0120] Examples 2-1 to 2-2 and Comparative Examples 2-1 to 2-3 In Examples 2-1 to 2-2 and Comparative Examples 2-1 to 2-3, capacitors were manufactured and their characteristics were evaluated in the same manner as in Example 1-1 above, except that a series of dispersions were prepared in which the additive concentration in the conductive polymer-containing liquid used in the first impregnation was various values ​​(9 mass%, 12 mass%, 18 mass%, 19 mass%, and 20 mass%), and the additive amount in the second conductive polymer-containing liquid used in the second impregnation was 20 mass%. The results are shown in Table 1 below and in FIGS. 3 and 4.

[0121] Examples 3-1 to 3-2 and Comparative Examples 3-1 to 3-2 In Examples 3-1 to 3-2 and Comparative Examples 3-1 to 3-2, capacitors were manufactured and their characteristics were evaluated in the same manner as in Example 1-1, except that a series of dispersions were prepared in which the additive concentration in the conductive polymer-containing liquid used in the first impregnation was varied (11 mass%, 15 mass%, 19 mass%, and 20 mass%), and the additive amount in the second conductive polymer-containing liquid used in the second impregnation was 15 mass%. The results are shown in Table 1 below and in FIGS. 3 and 4.

[0122] Comparative Examples 4-1 to 4-6 In Comparative Examples 4-1 to 4-6, a series of dispersions were prepared in which the additive concentration in the conductive polymer-containing liquid used in the first impregnation was varied (9 mass%, 12 mass%, 18 mass%, 19 mass%, 20 mass%, and 21 mass%), and the additive amount in the second conductive polymer-containing liquid used in the second impregnation was 10 mass%, except that capacitors were manufactured and their characteristics were evaluated in the same manner as in Example 1-1. The results are shown in Table 1 below and in FIGS. 3 and 4.

[0123]

[0124] As can be seen from Table 1 and Figure 3, there was a tendency that the lower the content of the additive in the first impregnation, the higher the capacity increase effect. Also, it can be seen that when the content of the additive in the first impregnation exceeds 15 mass%, the capacity increase effect by the second impregnation is hardly observed.

[0125] Furthermore, as can be seen from Table 1 and Figure 4, it was confirmed that the higher the content of the additive in the second test, the greater the ESR reduction effect. In particular, when the content of the additive in the first test was relatively low and the content of the additive in the second test was relatively high, a particularly large ESR reduction effect was obtained.

[0126] REFERENCE SIGNS LIST 1 electrolytic capacitor 10 metal case 20 capacitor element 21 anode foil 22, 24 oxide film 23 cathode foil 25 separator 26 solid electrolyte 27 liquid substance 29, 30 lead 40 sealing member

Claims

1. A method for manufacturing an electrolytic capacitor having an anode foil and a cathode foil with an oxide film formed on their surfaces, and having a solid electrolyte portion containing a conductive polymer in a gap between the anode foil and the cathode foil, the method comprising: (i) providing a capacitor element including an anode foil with an oxide film formed on its surface and a cathode foil; (ii) impregnating the capacitor element with a first conductive polymer-containing liquid containing 15% by mass or less of an organic solvent having a boiling point or decomposition temperature of 150°C or higher, and drying the liquid to form a solid electrolyte portion precursor in the gap between the anode foil and the cathode foil; and (iii) impregnating the capacitor element with the solid electrolyte portion precursor formed therein with a second conductive polymer-containing liquid containing 15% by mass or more of an organic solvent having a boiling point or decomposition temperature of 150°C or higher, and drying the liquid to form a solid electrolyte portion in the gap between the anode foil and the cathode foil.

2. The method according to claim 1, wherein the first conductive polymer-containing liquid contains 2 to 15 mass % of the organic solvent having a boiling point or decomposition temperature of 150°C or higher, and / or the second conductive polymer-containing liquid contains 15 to 45 mass % of the organic solvent having a boiling point or decomposition temperature of 150°C or higher.

3. The method according to claim 1 or 2, wherein the second conductive polymer-containing liquid contains more than 20 mass % of the organic solvent having a boiling point or decomposition temperature of 150°C or higher.

4. The method according to claim 1 or 2, wherein the organic solvent having a boiling point or decomposition temperature of 150°C or higher comprises at least one selected from the group consisting of glycerin, diglycerin, polyglycerin, ethylene glycol, diethylene glycol, polyethylene glycol, and derivatives thereof.

5. The method according to claim 1 or 2, wherein the content of the conductive polymer in each of the first conductive polymer-containing liquid and the second conductive polymer-containing liquid is 0.5 to 5 mass %.

6. The method according to claim 1 or 2, wherein the conductive polymer contained in the first conductive polymer-containing liquid and the second conductive polymer-containing liquid is polythiophene or a derivative thereof.

7. The method according to claim 1 or 2, wherein the first conductive polymer-containing liquid and the second conductive polymer-containing liquid both contain fine particles composed of a conductive polymer compound and an optional dopant.

8. The method of claim 7, wherein the dopant is polystyrene sulfonic acid.

9. The method according to claim 1 or 2, wherein the electrolytic capacitor is a solid electrolytic capacitor.

10. The method according to claim 1 or 2, further comprising impregnating a liquid substance between the anode foil and the cathode foil of the capacitor element having the solid electrolyte portion.

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