Solid electrolytic capacitor and manufacturing method

Abstract

Provided are a solid electrolytic capacitor in which ESR changes due to thermal shock are suppressed, and a method for manufacturing the solid electrolytic capacitor. The solid electrolytic capacitor includes an anode body, a cathode body, and an electrolyte layer. The anode body contains a valve action metal, and a dielectric film is formed on the surface of the anode body. The cathode body faces the anode body. The electrolyte layer is interposed between the positive electrode body and the negative electrode body, and contains an electrolyte solution and a conductive polymer. The electrolyte solution contains an aliphatic dicarboxylic acid having an acid dissociation constant (pKa) of 4.52 or more, and the D50 in the particle size distribution of the conductive polymer is 50 nm or less.

Description

Technical Field

[0001] The present invention relates to a solid electrolytic capacitor including an electrolytic solution and a conductive polymer in an electrolyte layer, and a manufacturing method thereof. Background Art

[0002] An electrolytic capacitor includes a valve action metal such as tantalum or aluminum as an anode foil and a cathode foil. The anode foil is surface-expanded by forming the valve action metal into a sintered body or an etched foil, etc., and has a dielectric coating layer on the surface after surface-expansion. This electrolytic capacitor can increase the specific surface area by the surface-expansion of the anode foil, and thus has a large electrostatic capacitance, meeting the requirement of high capacitance.

[0003] An electrolytic capacitor has an electrolytic solution interposed between the anode foil and the cathode foil. The electrolytic solution is in close contact with the uneven surface of the anode foil and functions as a true cathode. The contact area between the electrolytic solution and the dielectric coating of the anode foil increases. Therefore, the electrostatic capacitance of the electrolytic capacitor can be further increased, which is suitable for the high-capacity requirement with the recent increase in power. In the electrolytic solution, evaporation and volatilization that leak to the outside of the electrolytic capacitor occur over time. Therefore, the electrolytic capacitor dries out, and the electrostatic capacitance decreases over time, and the tangent of the loss angle (tanδ) increases over time, and finally the life is exhausted.

[0004] Therefore, among electrolytic capacitors, solid electrolytic capacitors using solid electrolytes have attracted attention. As solid electrolytes, manganese dioxide, 7,7,8,8-tetracyano-p-benzoquinodimethane (TCNQ) complexes are known. In recent years, solid electrolytic capacitors using conductive polymers derived from monomers having π-conjugated double bonds, such as poly(3,4-ethylenedioxythiophene) (PEDOT), which have a slow reaction rate and excellent adhesion to the dielectric coating, have been rapidly popularized. The conductive polymer uses an oxide compound such as a polyanion as a dopant and has a partial structure that functions as a dopant within the monomer molecule, showing high conductivity. Therefore, the solid electrolytic capacitor has the advantage of a low equivalent series resistance (ESR).

[0005] However, compared with an electrolytic capacitor having a solid electrolyte, the electrolytic capacitor having a solid electrolyte has insufficient repair effect on the defective part of the dielectric coating. Therefore, a so-called hybrid type electrolytic capacitor in which a conductive polymer is interposed between the anode foil and the cathode foil and the electrolytic solution is infiltrated has also attracted attention.

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2017-38010 Summary of the Invention

[0009] For example, in on-vehicle applications and power generation and transmission fields in cold regions, an electrolytic capacitor is sometimes rapidly heated from a low temperature such as -55°C to a high temperature such as 155°C, or conversely, rapidly cooled from a high temperature of 155°C to a low temperature of -55°C. This rapid temperature change is called a thermal shock.

[0010] The electrolytic capacitor that repeatedly undergoes thermal shock is liable to deteriorate in ESR due to the deterioration caused by the thermal shock. If the ESR increases, the electrolytic capacitor is liable to generate heat and its lifespan is shortened, and furthermore, a large ripple voltage occurs, etc., resulting in various effects.

[0011] The present invention is proposed to solve the above problems, and its object is to provide a solid electrolytic capacitor and a manufacturing method in which the change in ESR caused by thermal shock is suppressed.

[0012] To solve the above problems, the solid electrolytic capacitor of the present embodiment has: an anode body containing a valve action metal, with a dielectric film formed on the surface; a cathode body facing the anode body; and an electrolyte layer interposed between the anode body and the cathode body, containing an electrolytic solution and a conductive polymer, the electrolytic solution containing an aliphatic dicarboxylic acid with an acid dissociation constant pKa of 4.52 or more, and the D50 in the particle size distribution of the conductive polymer being 50 nm or less.

[0013] When the acid dissociation constant pKa is large, the withstand voltage of the solid electrolytic capacitor can be further increased, making it more suitable for on-vehicle applications and power generation and transmission applications. However, when the electrolytic solution contains an aliphatic dicarboxylic acid with an acid dissociation constant pKa of 4.52 or more, the change in ESR during repeated thermal shock becomes particularly large. On the other hand, when the electrolytic solution contains an aliphatic dicarboxylic acid with pKa of 4.52 or more, and the electrolyte layer contains a conductive polymer with a D50 in the particle size distribution of 50 nm or less, this change in ESR is suppressed.

[0014] The electrolyte layer may also contain a polyol. That is, this solid electrolytic capacitor contains an aliphatic dicarboxylic acid with an acid dissociation constant pKa of 4.52 or more in the electrolytic solution, contains a conductive polymer with a D50 in the particle size distribution of 50 nm or less in the electrolyte layer, and contains a polyol in the electrolyte layer. The change in ESR of this solid electrolytic capacitor is suppressed to be equivalent to that of a capacitor containing an aliphatic dicarboxylic acid with an acid dissociation constant pKa of 4.51 or less in the electrolytic solution.

[0015] The electrolyte layer may also be formed using a conductive polymer solution containing the conductive polymer and the polyol.

[0016] The polyol may also be included in an amount of 8 wt% or more and 50 wt% or less relative to the total amount of the conductive polymer liquid. Thereby, the change in ESR of the solid electrolytic capacitor is suppressed to be equivalent to that of a capacitor containing an aliphatic dicarboxylic acid having an acid dissociation constant pKa of 4.51 or less in the electrolyte. Further, the polyol may also be included in an amount of 8 wt% or more and 30 wt% or less relative to the total amount of the conductive polymer liquid. When limited to this range, the change in ESR of the solid electrolytic capacitor is suppressed better than that of a capacitor containing an aliphatic dicarboxylic acid having an acid dissociation constant pKa of 4.51 or less in the electrolyte.

[0017] The polyol may also be one or a mixture of two or more selected from polyethylene glycol, xylitol, and sorbitol. When these polyols are contained in the electrolyte layer, the change in ESR of the solid electrolytic capacitor is more suppressed than that of a capacitor containing an aliphatic dicarboxylic acid having an acid dissociation constant pKa of 4.51 or less in the electrolyte.

[0018] The aliphatic dicarboxylic acid may also be one or a mixture of two or more selected from the group of azelaic acid, suberic acid, and sebacic acid.

[0019] The electrolyte may also contain an aliphatic dicarboxylic acid having an acid dissociation constant pKa of 4.51 or less. Based on mixing an aliphatic dicarboxylic acid having an acid dissociation constant pKa of 4.52 or more and an aliphatic dicarboxylic acid having an acid dissociation constant pKa of 4.51 or less, when a conductive polymer having a D50 in the particle size distribution of 50 nm or less is contained in the electrolyte layer, the change in ESR during repeated thermal shock is further suppressed.

[0020] In addition, to solve the above problems, a method for manufacturing a solid electrolytic capacitor according to the present embodiment includes: a conductive polymer attachment step of attaching a conductive polymer liquid to an anode body having a dielectric film formed on its surface or a capacitor element facing the anode body and the cathode body and drying it; and an electrolyte infiltration step of infiltrating the electrolyte into the capacitor element after the conductive polymer attachment step. The conductive polymer liquid contains a conductive polymer having a D50 in the particle size distribution of 50 nm or less, and the electrolyte contains an aliphatic dicarboxylic acid having an acid dissociation constant pKa of 4.52 or more.

[0021] According to the present invention, even when repeatedly subjected to thermal shock, the change in ESR of the solid electrolytic capacitor is suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a graph showing the change in ESR of a solid electrolytic capacitor containing a conductive polymer having a D50 in the particle size distribution of 450 nm.

[0023] Figure 2 It is a graph showing the relationship with the change in ESR for Comparative Example 1, Example 1, and Example 2.

[0024] Figure 3 It is a graph showing the relationship with the change in ESR for Comparative Example 3, Examples 3 to 5.

[0025] Figure 4 It is a graph showing the relationship between the type of polyol and the change in ESR.

[0026] Figure 5 It is a graph showing the relationship between the addition amount of polyol and the change in ESR.

[0027] Figure 6 It is a graph showing the relationship with the change in ESR for Example 2, Reference Example 2, and Examples 15 to 17.

[0028] Figure 7 It is a graph showing the relationship with the change in ESR for Example 2, Reference Example 3, and Examples 18 to 20. Detailed Embodiments

[0029] Hereinafter, the solid electrolytic capacitor according to the embodiment will be described. In addition, the present invention is not limited to the embodiments described below.

[0030] (Solid Electrolytic Capacitor)

[0031] A solid electrolytic capacitor is a passive component that stores and discharges electric charges by obtaining capacitance through the dielectric polarization of a dielectric film. The solid electrolytic capacitor includes a capacitor element. The capacitor element includes an anode body, a cathode body, an electrolyte layer, and a separator. A dielectric film is formed on the surface of the anode foil. The anode body and the cathode body face each other with the dielectric film interposed therebetween. The electrolyte layer is interposed between the dielectric film of the anode body and the cathode body. The electrolyte layer is in close contact with the dielectric film of the anode body and functions as a true cathode. In addition, the electrolyte layer extends between the dielectric film and the cathode body to form a conduction path.

[0032] This solid electrolytic capacitor is a so-called hybrid type that includes an electrolytic solution and a conductive polymer. In the electrolyte layer, at least an electrolytic solution and a conductive polymer are contained. The separator separates the anode body and the cathode body to prevent short circuits and holds the electrolyte layer. When the conductive polymer can self-maintain the shape of the electrolyte layer and isolate the anode body and the cathode body, the separator can be removed from the solid electrolytic capacitor.

[0033] An anode body and a cathode body are alternately stacked with an electrolyte layer therebetween. In this stacked type, except for a flat type with the outer package omitted, for example, the capacitor element is covered with a laminated film, or a resin such as a heat-resistant resin or an insulating resin is molded, dip-coated, or printed, thereby performing sealing. Alternatively, the anode body and the cathode body are alternately stacked with an electrolyte layer therebetween and wound. In this wound type, for example, the capacitor element is stored in a bottomed cylindrical case. The opening of the case is sealed by riveting and using a sealing body.

[0034] After sealing the capacitor element, it is transferred to an aging process, and a DC voltage is applied to the solid electrolytic capacitor at a high temperature to repair the oxidized coating film damaged during the manufacturing process such as winding of the solid electrolytic capacitor. Thus, a finished product of the solid electrolytic capacitor is formed.

[0035] (Anode body)

[0036] The anode body is a foil body made of a valve-acting metal. In the wound type, the anode body is a long strip-shaped body formed by stretching the valve-acting metal. In the stacked type, the anode body is a sintered body obtained by forming a flat plate or powder and sintering it into a flat plate shape. The valve-acting metals are aluminum, tantalum, niobium, niobium oxide, titanium, hafnium, zirconium, zinc, tungsten, bismuth, antimony, etc. Regarding the anode body, the purity is preferably 99.9% or more, but it may also contain impurities such as silicon, iron, copper, magnesium, and zinc.

[0037] On one or both sides of the anode body, an enlarged surface layer is formed. The enlarged surface layer is a surface layer that has been processed to increase the surface area ratio to the projected area, and is an etched layer formed by etching the foil body, a sintered layer formed by attaching and sintering the powder of the valve-acting metal to the foil body, or a vapor deposition layer formed by vapor-depositing the valve-acting metal particles on the foil body. That is, the enlarged surface layer has a porous structure and is composed of tunnel-shaped holes, sponge-shaped holes, or voids between dense powders or particles.

[0038] The tunnel-shaped etched holes are holes dug in the foil thickness direction and may penetrate the foil body. Typically, the tunnel-shaped etched holes are formed by passing a direct current through an acidic aqueous solution containing halogen ions such as hydrochloric acid. Furthermore, the tunnel-shaped etched holes are enlarged in diameter by passing a direct current through an acidic aqueous solution such as nitric acid. Through the sponge-shaped etched holes, the enlarged surface layer becomes a sponge-shaped layer that connects and expands small voids in a spatial manner. The sponge-shaped etched holes are formed by passing an alternating current through an acidic aqueous solution containing halogen ions such as hydrochloric acid.

[0039] The sintered layer is produced by attaching powder of a valve-acting metal that is the same as or different from the foil body and sintering it. The powder is obtained by methods such as a pulverization method, a spraying method, a melt spinning method, a rotating disk method, a rotating electrode method, etc. The powder is made into a paste with a binder and a solvent, applied to the foil body, and dried. Then, it is sintered by heating in a vacuum or a reducing atmosphere, etc. The spraying method can be any one of a water spraying method, a gas spraying method, and a water gas spraying method. The vapor deposition layer is produced, for example, by a resistance heating type vapor deposition method or an electron beam heating type vapor deposition method. By heating a valve-acting metal that is the same as or different from the foil body using the heat of resistance or electron beam energy to evaporate it, and causing the vapor of the valve-acting metal particles to accumulate on the surface of the foil body to form the vapor deposition layer.

[0040] The dielectric coating is formed on the surface layer of the anode body along the unevenness of the diffusion layer. Typically, the dielectric coating is an oxide coating formed by anodizing the surface layer of the anode body. If the anode body is an aluminum foil, the dielectric coating is an aluminum oxide layer formed by oxidizing the surface layer of the anode body along the unevenness of the diffusion layer. The dielectric coating is formed by a chemical conversion treatment. In the chemical conversion treatment, a voltage is applied to the anode body in a chemical conversion solution with a desired breakdown voltage as the target. The chemical conversion solution is a solution that does not contain halogen ions, for example, a chemical conversion solution of phosphoric acid such as ammonium dihydrogen phosphate, a chemical conversion solution of boric acid such as ammonium borate, or a chemical conversion solution of adipic acid such as ammonium adipate.

[0041] (Cathode body)

[0042] The cathode body is a foil body formed by extending a valve-acting metal. The purity of the cathode foil is preferably 99% or more, but it may also contain impurities such as silicon, iron, copper, magnesium, and zinc. The foil body is a flat plate foil with a flat surface, or a diffusion layer is formed on the surface by surface area expansion. An oxide coating may also be formed intentionally or naturally in the diffusion layer. The intentional one may be to form a thin oxide coating of about 1 - 10 Vfs by a chemical conversion treatment. The natural oxide coating is formed by the reaction of the cathode foil with oxygen in the air.

[0043] In the case where the solid electrolytic capacitor is a stacked type, the cathode body is preferably a laminate of a metal layer and a carbon layer. The carbon layer of the cathode body is arranged facing the anode body. The carbon layer is formed by being made into a paste, coated on the electrolyte layer after forming the electrolyte layer on the anode body, and hardened by heating. The metal layer is, for example, a silver layer, and the metal layer is formed by being made into a paste, coated from above the carbon layer, and hardened by heating.

[0044] In addition, the cathode body may further have a stacked conductive layer. The conductive layer is a layer containing a conductive material and having a higher conductivity than the oxide film. The conductive layer is stacked on one or both sides of the cathode foil and is located on the outermost surface of the cathode body. Examples of the conductive material include titanium, zirconium, tantalum, niobium, their nitrides or carbides, aluminum carbide, carbon materials, and their composite materials or mixed materials. The conductive layer may also be stacked in multiple layers, and each layer may be a different layer. The conductive layer and the cathode body may have a crimped structure. After stacking the conductive layer, a stamping process is applied. Regarding the crimped structure, the conductive layer is pressed into the pores of the expanded layer, and the conductive layer deforms along the uneven surface of the expanded layer. The crimped structure improves the adhesion and fixity between the conductive layer and the cathode body, and reduces the ESR of the solid electrolytic capacitor.

[0045] (Electrolyte layer)

[0046] In the electrolyte of the electrolyte layer, as the anion component, it contains an aliphatic dicarboxylic acid with an acid dissociation constant pKa of 4.52 or more. When the acid dissociation constant pKa is large, the withstand voltage of the solid electrolytic capacitor can be further increased, making it more suitable for in-vehicle applications and power generation and transmission applications. In the aliphatic dicarboxylic acid, two hydrogens of the chain hydrocarbon are replaced by hydroxyl groups. Examples of the aliphatic dicarboxylic acid with an acid dissociation constant pKa of 4.52 or more include azelaic acid, suberic acid, and sebacic acid. It is also possible to include in the electrolyte of the electrolyte layer one or more mixtures selected from the group of azelaic acid, suberic acid, and sebacic acid. In addition, the acid dissociation constant pKa is a value measured in water at 25°C.

[0047] However, when an aliphatic dicarboxylic acid with an acid dissociation constant pKa of 4.52 or more is included, as the conductive polymer of the electrolyte layer, particles with a D50 of 50 nm or less in the particle size distribution are included in the electrolyte layer. The D50 in the particle size distribution is the median diameter in the volume particle size distribution obtained by a particle size distribution measuring device based on the dynamic light scattering method. Hereinafter, the D50 in the particle size distribution will be referred to as the median diameter. The particle size distribution of the conductive polymer is measured in a state where the conductive polymer is dispersed.

[0048] Here, when the acid dissociation constant of the aliphatic dicarboxylic acid contained in the electrolyte layer is pKa = 4.51 or less, even if the solid electrolytic capacitor is repeatedly subjected to thermal shock, the change in ESR is small. On the other hand, when the acid dissociation constant of the aliphatic dicarboxylic acid is pKa = 4.52 or more, the ESR deteriorates significantly. However, only when the electrolyte layer contains an aliphatic dicarboxylic acid with an acid dissociation constant pKa = 4.52 or more, the aliphatic dicarboxylic acid with an acid dissociation constant pKa = 4.52 or more and a conductive polymer with a median diameter of 50 nm or less coexist in the electrolyte layer. Thereby, the deterioration of the conductive polymer caused by thermal shock due to a rapid temperature change is suppressed, and the change in ESR is suppressed.

[0049] The following is speculation and not limited to this mechanism. The reason for the speculation that the change in ESR is suppressed is as follows. First, an aliphatic dicarboxylic acid with a large pKa is likely to precipitate at low temperatures due to its long straight-chain alkyl group. When the precipitated aliphatic dicarboxylic acid enters between the conductive polymer and the anode body and between the conductive polymer and the cathode body, the interfacial resistance between the conductive polymer and the anode body and the interfacial resistance between the conductive polymer and the cathode body increase. Therefore, it is considered that the ESR deterioration caused by thermal shock becomes larger when using an aliphatic dicarboxylic acid with a large pKa.

[0050] On the other hand, a conductive polymer with a D50 in the particle size distribution of 50 nm or less adheres tightly to the anode body and the cathode body. Therefore, even if an aliphatic dicarboxylic acid with an acid dissociation constant pKa = 4.52 or more precipitates at low temperatures, there is little room for the precipitated aliphatic dicarboxylic acid to enter between the conductive polymer and the anode body and between the conductive polymer and the cathode body. Therefore, even if the aliphatic dicarboxylic acid precipitates, it is difficult to increase the interfacial resistance between the conductive polymer and the anode body and the interfacial resistance between the conductive polymer and the cathode body.

[0051] Moreover, since the conductive polymer adheres tightly to the anode body and the cathode body, many conduction paths between the anode body and the electrolyte layer and between the cathode body and the electrolyte layer are formed. Therefore, even if the aliphatic dicarboxylic acid precipitates and there is an aliphatic dicarboxylic acid that can enter between the conductive polymer and the anode body and between the conductive polymer and the cathode body, considering the existence of many conduction paths, the influence of the increase in the interfacial resistance caused by this aliphatic dicarboxylic acid is only slight.

[0052] Therefore, it is speculated that only when the electrolyte layer contains an aliphatic dicarboxylic acid with an acid dissociation constant pKa = 4.52 or more and the aliphatic dicarboxylic acid with an acid dissociation constant pKa = 4.52 or more and a conductive polymer with a median diameter of 50 nm or less coexist in the electrolyte layer, the change in ESR of the solid electrolytic capacitor is suppressed.

[0053] In addition, when an aliphatic dicarboxylic acid with an acid dissociation constant pKa of 4.52 or more and an aliphatic dicarboxylic acid with an acid dissociation constant pKa of 4.51 or less are mixed in addition to the conductive polymer with a median diameter of 50 nm or less, compared with a solid electrolytic capacitor in which an aliphatic dicarboxylic acid with an acid dissociation constant pKa of 4.51 or less is included as the aliphatic dicarboxylic acid in the electrolyte layer, deterioration of the conductive polymer due to repeated thermal shock caused by a rapid temperature change is suppressed, and change in ESR is suppressed.

[0054] Therefore, in the electrolytic solution, as a further anionic component, it is preferable to contain an aliphatic dicarboxylic acid with an acid dissociation constant pKa of 4.51 or less. Examples of the aliphatic dicarboxylic acid with an acid dissociation constant pKa of 4.51 or less include succinic acid, glutaric acid, and pimelic acid. It is also possible to contain a mixture of one or more selected from the group of succinic acid, glutaric acid, and pimelic acid in the electrolytic solution of the electrolyte layer.

[0055] In the electrolyte layer, a polyhydric alcohol may also be contained. Examples of the polyhydric alcohol include polyethylene glycol, xylitol, sorbitol, 1-hexanol, ethylene glycol, diethylene glycol, triethylene glycol, polyoxyethylene glycol, glycerin, polyglycerin, polyoxyethylene glycerin, erythritol, mannitol, dipentaerythritol, pentaerythritol, or a combination of two or more thereof.

[0056] When an aliphatic dicarboxylic acid with an acid dissociation constant pKa of 4.52 or more, a conductive polymer with a median diameter of 50 nm or less, and a polyhydric alcohol coexist in the electrolyte layer, the change in ESR after repeated thermal shock is suppressed to the same level as that of a solid electrolytic capacitor having an aliphatic dicarboxylic acid with an acid dissociation constant pKa of 4.51 or less.

[0057] Among the polyhydric alcohols, polyethylene glycol with an average molecular weight of 300, xylitol, sorbitol, or a combination of two or more thereof is preferable. When these polyhydric alcohols are contained in the electrolyte layer, only when the electrolyte layer contains an aliphatic dicarboxylic acid with an acid dissociation constant pKa of 4.52 or more and a conductive polymer with a median diameter of 50 nm or less, the change in ESR is suppressed to a lower level compared with a solid electrolytic capacitor having an aliphatic dicarboxylic acid with an acid dissociation constant pKa of 4.51 or less, and it is possible to maintain an ESR close to that before receiving thermal shock.

[0058] (Electrolytic solution)

[0059] In the electrolytic solution, although not particularly limited, it may contain other known components. In addition to aliphatic dicarboxylic acids with an acid dissociation constant pKa of 4.52 or more, other types of anion components may also be contained in the electrolytic solution. As the organic acids that become other types of anion components, other carboxylic acids, phenols, and sulfonic acids can be cited. As the inorganic acids that become other types of anion components, boric acid, phosphoric acid, phosphorous acid, hypophosphorous acid, carbonic acid, silicic acid, etc. can be cited. As the composite compounds of organic acids and inorganic acids that become other types of anion components, boron disalicylate, boron dioxalate, boron diglycolate, boron dipropionate, boron disuccinate, boron diadipate, boron dinonadipate, boron dibenzoate, boron dimaleate, boron dilactate, boron dimalate, boron ditartrate, boron dicitrate, boron diphthalate, boron bis(2-hydroxy)isobutyrate, boron resorcinolate, boron dimethylsalicylate, boron dinaphthoate, boron mandelate, and boron bis(3-hydroxy)propionate, etc. can be cited.

[0060] In the electrolytic solution, in addition to the anion components, known cation components can also be contained. Regarding the solvent of the electrolytic solution, a protic organic polar solvent or an aprotic organic polar solvent can be cited, and they can be used alone or in combination of two or more types.

[0061] As the cation components, ammonium, quaternary ammonium, guanidinium, amine, sodium, potassium, etc. can be cited. As the quaternary ammonium, tetramethylammonium, triethylmethylammonium, tetraethylammonium, etc. can be cited. As the guanidinium, ethyldimethylimidazolinium, tetramethylimidazolinium, etc. can be cited. As the amine, primary amine, secondary amine, and tertiary amine can be cited. As the primary amine, methylamine, ethylamine, propylamine, etc. can be cited. As the secondary amine, dimethylamine, diethylamine, ethylmethylamine, dibutylamine, etc. can be cited. As the tertiary amine, trimethylamine, triethylamine, tributylamine, ethyldimethylamine, ethyldiisopropylamine, etc. can be cited.

[0062] As the protic organic solvents that become the solvent, monohydric alcohols, polyhydric alcohols, and oxy alcohol compounds, etc. can be cited. As the monohydric alcohols, ethanol, propanol, butanol, pentanol, hexanol, cyclobutanol, cyclopentanol, cyclohexanol, benzyl alcohol, etc. can be cited. As the polyhydric alcohols and oxy alcohol compounds, ethylene glycol, diethylene glycol, propylene glycol, glycerol, methyl cellosolve, ethyl cellosolve, methoxypropylene glycol, dimethoxypropanol, polyglycerol, polyethylene glycol, polyoxyethylene glycerol, polypropylene glycol, etc., which are alkylene oxide adducts of polyhydric alcohols, etc. can be cited.

[0063] As aprotic organic polar solvents that become solvents, sulfones, amides, lactones, cyclic amides, nitriles, sulfoxides, etc. can be cited as representatives. As sulfones, dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, sulfolane, 3-methyl sulfolane, 2,4-dimethyl sulfolane, etc. can be cited. As amides, N-methylformamide, N,N-dimethylformamide, N-ethylformamide, N,N-diethylformamide, N-methylacetamide, N,N-dimethylacetamide, N-ethylacetamide, N,N-diethylacetamide, etc. can be cited. As lactones and cyclic amides, γ-butyrolactone, γ-valerolactone, δ-valerolactone, N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, butylene carbonate, isobutylene carbonate, etc. can be cited. As nitriles, acetonitrile, 3-methoxypropionitrile, glutarodinitrile, etc. can be cited. As sulfoxides, dimethyl sulfoxide, etc. can be cited.

[0064] The capacitor element is impregnated with the electrolytic solution so that the electrolytic solution infiltrates into the voids inside the capacitor element. In order to make the electrolytic solution infiltrate into finer voids, a pressure reduction treatment or a pressure increase treatment can also be carried out as needed. The infiltration process can also be repeated multiple times. For example, the inside of the capacitor element can be depressurized, and the electrolytic solution can be injected into the inside of the capacitor element while pressurizing the electrolytic solution.

[0065] (Conductive polymer)

[0066] The conductive polymer contained in the electrolyte layer is a self-doped type doped by dopant molecules in the molecule or a conjugated polymer doped by external dopant molecules. The conjugated polymer is obtained by chemical oxidative polymerization or electrolytic oxidative polymerization of a monomer having a π-conjugated double bond or its derivative. By carrying out a doping reaction on the conjugated polymer, the conductive polymer exhibits high conductivity. That is, conductivity is exhibited by adding a small amount of a dopant such as an acceptor that easily accepts electrons or a donor that easily provides electrons to the conjugated polymer.

[0067] There is no particular limitation on the conjugated polymer, and known examples can be used. For example, polypyrrole, polythiophene, polyaniline, etc. can be cited. These conjugated polymers can be used alone, or two or more of them can be combined, and furthermore, they can be copolymers of two or more monomers.

[0068] Among the above conjugated polymers, conjugated polymers formed by polymerizing thiophene or its derivatives are preferred, and conjugated polymers formed by polymerizing 3,4-ethylenedioxythiophene (i.e., 2,3-dihydrothieno[3,4-b][1,4]dioxin), 3-alkylthiophene, 3-alkoxythiophene, 3-alkyl-4-alkoxythiophene, 3,4-alkylthiophene, 3,4-alkoxythiophene or their derivatives are preferred. As the thiophene derivatives, compounds selected from thiophenes having substituents at the 3- and 4-positions are preferred, and the substituents at the 3- and 4-positions of the thiophene ring may also form a ring together with the carbons at the 3- and 4-positions. The number of carbon atoms of the alkyl and alkoxy groups is preferably 1 to 16.

[0069] In particular, a polymer of 3,4-ethylenedioxythiophene called EDOT, that is, poly(3,4-ethylenedioxythiophene) called PEDOT is particularly preferred. In addition, it may be an alkylated ethylenedioxythiophene obtained by adding an alkyl group to 3,4-ethylenedioxythiophene. For example, methylated ethylenedioxythiophene (i.e., 2-methyl-2,3-dihydro-thieno[3,4-b][1,4]dioxin), ethylated ethylenedioxythiophene (i.e., 2-ethyl-2,3-dihydro-thieno[3,4-b][1,4]dioxin), etc. can be cited.

[0070] Regarding the dopant, there is no particular limitation, and known examples can be used. The dopant can be used alone or in combination of two or more. In addition, a polymer or a monomer can also be used. For example, as the dopant, polyanions, inorganic acids such as boric acid, nitric acid, and phosphoric acid, organic acids such as acetic acid, oxalic acid, citric acid, tartaric acid, squaric acid, rhodizonic acid, crotonic acid, salicylic acid, p-toluenesulfonic acid, 1,2-dihydroxy-3,5-benzenedisulfonic acid, methanesulfonic acid, trifluoromethanesulfonic acid, boron disalicylate, bisoxaloborate, sulfimide acid, dodecylbenzenesulfonic acid, propylnaphthalenesulfonic acid, butylnaphthalenesulfonic acid, etc. can be cited.

[0071] The polyanion is, for example, a substituted or unsubstituted polyalkylene, a substituted or unsubstituted polyalkenylene, a substituted or unsubstituted polyimide, a substituted or unsubstituted polyamide, a substituted or unsubstituted polyester, and a polymer composed only of structural units having an anionic group and a polymer composed of structural units having an anionic group and structural units not having an anionic group can be cited. Specifically, as the polyanion, polyvinylsulfonic acid, polystyrenesulfonic acid, polyallylsulfonic acid, polyacrylic acid sulfonic acid, polymethacrylic acid sulfonic acid, poly(2-acrylamide-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, polyacrylic acid, polymethacrylic acid, polymaleic acid, etc. can be cited.

[0072] Here, regarding the conductive polymer, for example, the electrolyte layer is filled by impregnating the conductive polymer liquid into the capacitor element. The conductive polymer liquid may also be applied or sprayed onto the dielectric coating of the anode body. The conductive polymer liquid is a liquid in which particles or powders of the conductive polymer are dispersed. In order to promote the impregnation of the conductive polymer liquid into the capacitor element, a pressure reduction treatment or a pressure application treatment may be performed as needed. The impregnation process may be repeated multiple times. After impregnating the conductive polymer liquid into the capacitor element, the dispersant is removed by a drying process.

[0073] The conductive polymer with a median diameter of 50 nm or less is obtained by oxidative polymerization. In chemical oxidative polymerization, as an example of a method for adjusting the median diameter of the conductive polymer to be smaller, the following method can be cited. PEDOT (PEDOT / PSS) doped with polystyrene sulfonic acid (PSS) in the conductive polymer is generally produced by emulsion polymerization. In emulsion polymerization, the colloidal particles of EDOT are further reduced by using a homogenizer to obtain PEDOT / PSS with a small particle size. In addition, the particle size of PEDOT / PSS is reduced by subjecting the polymerized PEDOT / PSS to a pulverization treatment using a high-pressure ultrasonic homogenizer. The homogenizer can be any of a high-pressure type, an ultrasonic type, or a type that combines both.

[0074] For example, in chemical oxidative polymerization, a solution containing a monomer that becomes a monomer unit of the conductive polymer and an oxidizing agent are mixed to cause a polymerization reaction. As the solvent, for example, water is used. As the oxidizing agent, as long as it is a compound that releases a dopant, any known oxidizing agent can be used, and trivalent iron salts such as iron(III) p-toluenesulfonate, iron(III) naphthalenesulfonate, and iron(III) anthraquinonesulfonate, or peroxydisulfates such as peroxydisulfuric acid, ammonium peroxydisulfate, and sodium peroxydisulfate can be used. Either a single compound or two or more compounds can be used. The polymerization temperature is not strictly limited and is generally in the range of 10 to 200 °C. The polymerization time is generally in the range of 10 minutes to 30 hours.

[0075] After the polymerization reaction is completed, residual monomers and impurities are removed by refining means such as ultrafiltration, cation exchange, and anion exchange. Regarding the solvent of the conductive polymer liquid, it is only necessary to disperse the conductive polymer, and water or a mixture of water and an organic solvent is preferred. As the organic solvent, polar solvents, alcohols, esters, hydrocarbons, carbonate compounds, ether compounds, chain ethers, heterocyclic compounds, nitrile compounds, etc. can be cited.

[0076] Examples of polar solvents include N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, etc. Examples of alcohols include methanol, ethanol, propanol, butanol, etc. Examples of esters include ethyl acetate, propyl acetate, butyl acetate, etc. Examples of hydrocarbons include hexane, heptane, benzene, toluene, xylene, etc. Examples of carbonate compounds include ethylene carbonate, propylene carbonate, etc. Examples of ether compounds include dioxane, diethyl ether, etc. Examples of chain ethers include ethylene glycol dialkyl ether, propylene glycol dialkyl ether, polyethylene glycol dialkyl ether, polypropylene glycol dialkyl ether, etc. Examples of heterocyclic compounds include 3-methyl-2-oxazolidinone, etc. Examples of nitrile compounds include acetonitrile, glutarodinitrile, methoxyacetonitrile, propionitrile, benzonitrile, etc.

[0077] The polyol filled in the electrolyte layer can also be added to the conductive polymer liquid and filled into the electrolyte layer together with the conductive polymer. Since the polyol has a high boiling point, it remains in the electrolyte layer after the conductive polymer liquid is infiltrated and dried. Preferably, the polyol is contained in a proportion of 8 wt% or more and 50 wt% or less based on the total amount of the conductive polymer liquid. When the polyol is contained in this range, the polyol contained in the electrolyte layer more effectively inhibits the deterioration of the conductive polymer and further inhibits the change in ESR.

[0078] Particularly preferably, the polyol is contained in a proportion of 8 wt% or more and 30 wt% or less based on the total amount of the conductive polymer liquid. When in this range, compared with the case where an anion component having an acid dissociation constant pKa = 4.51 or less is contained in the electrolyte solution, the change in ESR caused by repeated thermal shock can be more reduced. When the content ratio of the polyol increases to more than 30 wt% based on the total amount of the conductive polymer liquid, the inhibitory effect on the change in ESR obtained by containing the polyol is reduced to the same level as the case where an anion component having an acid dissociation constant pKa = 4.51 or less is contained in the electrolyte solution.

[0079] The pH of the conductive polymer liquid can also be adjusted with ammonia water. In addition, an organic binder, a surfactant, a dispersant, an antifoaming agent, a coupling agent, an antioxidant, an ultraviolet absorber, etc. can be added.

[0080] (Separator)

[0081] Regarding the separator, examples include cellulose such as kraft paper, abaca, Spanish papyrus, hemp, and synthetic fibers, as well as their mixed papers, polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and their derivatives, polytetrafluoroethylene resins, polyvinylidene fluoride resins, vinylon resins, aliphatic polyamides, semi-aromatic polyamides, fully aromatic polyamides, polyimide resins, polyethylene resins, polypropylene resins, trimethylpentene resins, polyphenylene sulfide resins, acrylic resins, polyvinyl alcohol resins, etc. These resins can be used alone or in combination.

[0082]

Examples

[0083] Hereinafter, the solid electrolytic capacitor of the examples will be described in more detail. In addition, the present invention is not limited to the examples described below.

[0084] (Examples 1 and 2)

[0085] Solid electrolytic capacitors of Example 1, Example 2, Comparative Example 1, and Comparative Example 2 were fabricated. First, aluminum foils were used to fabricate the anode body and the cathode body. The anode body was surface-expanded by an etching process.

[0086] Next, by immersing the anode body in an aqueous solution of adipic acid and applying a chemical conversion voltage, a dielectric film was formed. The cathode body was surface-expanded by an etching process. Leads were connected to the anode body and the cathode body, and the anode body and the cathode body were opposed to each other with a cellulose-based separator in between and wound. For the wound body, repair chemical conversion was performed by immersing it in an aqueous solution of ammonium dihydrogen phosphate for 30 minutes. Then, it was dried at 100 °C.

[0087] The wound body was immersed in a conductive polymer solution to attach the conductive polymer to the dielectric film of the anode body, the cathode body, and the separator. As the conductive polymer solution, particles of poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid were dispersed in water as the conductive polymer, and ethylene glycol was added. After the wound body was first immersed in the conductive polymer solution, the wound body was dried at 145 °C for 30 minutes. Further, the wound body was immersed in the conductive polymer solution for a second immersion, and after that, the wound body was dried at 150 °C for 30 minutes.

[0088] Here, in Comparative Example 1, a conductive polymer solution was used in which a conductive polymer with a median diameter of 450 nm was dispersed in a dispersant. In Comparative Example 2, a conductive polymer solution was used in which a conductive polymer with a median diameter of 168 nm was dispersed in a dispersant. In Example 1, a conductive polymer solution was used in which a conductive polymer with a median diameter of 47 nm was dispersed in a dispersant. In Example 2, a conductive polymer solution was used in which a conductive polymer with a median diameter of 10 nm was dispersed in a dispersant. The dispersant was water. The conductive polymer solution with a conductive polymer concentration of 2 wt% was adjusted to pH 4 with ammonia water and dispersed by an ultrasonic homogenizer to prepare a conductive polymer solution.

[0089] The particle size of the conductive polymer was measured using a particle size distribution measuring device. First, the pH-adjusted conductive polymer solution was diluted 100 times with water and ultrasonicated. The particle size was measured using this diluted aqueous solution and a particle size distribution measuring device (Nikkiso UPA-UT151).

[0090] Furthermore, an electrolyte solution was infiltrated into a wound body having an electrolyte layer formed of a conductive polymer. The solvent of the electrolyte solution was ethylene glycol. In the electrolyte solution, azelaic acid and ammonia were mixed such that the amount was 16 mmol per 100 g of the electrolyte solution. The anion component of the electrolyte solution was azelaic acid.

[0091] After forming the electrolyte layer with the conductive polymer and the electrolyte solution, the capacitor element was housed in a bottomed cylindrical outer packaging case. A sealing rubber was installed at the open end of the outer packaging case and sealed by riveting. Each solid electrolytic capacitor was subjected to an aging treatment by applying a voltage. Each solid electrolytic capacitor had a diameter of 6.3 mm and a height of 5.8 mm, a rated withstand voltage of 35 WV, and a capacitance of 47 μF.

[0092] In addition, solid electrolytic capacitors of Comparative Example 3 and Reference Examples 1 to 3 were also fabricated. Regarding the solid electrolytic capacitor of Comparative Example 3, suberic acid was used as the anion component of the electrolyte solution. Except for this, the solid electrolytic capacitor of Comparative Example 3 was fabricated by the same manufacturing method and manufacturing conditions as those of Example 1 and had the same structure. That is, the solid electrolytic capacitor of Comparative Example 3 used a conductive polymer with a median diameter of 450 nm.

[0093] The solid electrolytic capacitor of Reference Example 1 was produced by the same manufacturing method and manufacturing conditions as those of Example 1, except that pimelic acid was used as the anion component of the electrolyte, and the median diameter of the conductive polymer was 450 nm, and it had the same structure. The solid electrolytic capacitor of Reference Example 2 was produced by the same manufacturing method and manufacturing conditions as those of Example 1, except that glutaric acid was used as the anion component of the electrolyte, and the median diameter of the conductive polymer was 450 nm, and it had the same structure. The solid electrolytic capacitor of Reference Example 3 was produced by the same manufacturing method and manufacturing conditions as those of Example 1, except that succinic acid was used as the anion component of the electrolyte, and the median diameter of the conductive polymer was 450 nm, and it had the same structure.

[0094] In addition, the acid dissociation constant of azelaic acid is pKa = 4.55, the acid dissociation constant of suberic acid is pKa = 4.526, the acid dissociation constant of pimelic acid is pKa = 4.51, the acid dissociation constant of glutaric acid is pKa = 4.31, and the acid dissociation constant of succinic acid is pKa = 4.20.

[0095] (Thermal shock test 1)

[0096] By repeatedly applying thermal shock to the solid electrolytic capacitors of Example 1 and 2, Comparative Examples 1 to 3, and Reference Examples 1 to 3, the change in ESR after the thermal shock test was measured. The thermal shock test was as follows. First, the reflow heat during installation was applied to the solid electrolytic capacitor. After exposure to the reflow heat, the ESR of the solid electrolytic capacitor was measured. Using an LCR meter (manufactured by Agilent Technologies, E4980A), the AC current level was set to 1.0 Vrms, the measurement frequency was set to 100 kHz, and it was set to DC bias to measure the ESR. The ESR after exposure to the reflow heat was referred to as the initial ESR.

[0097] After measuring the initial ESR, the temperature environment of the solid electrolytic capacitor was repeatedly changed between high temperature and low temperature. The high temperature environment was 155 °C, and the low temperature environment was -55 °C. The solid electrolytic capacitor was exposed to the high temperature environment for 30 minutes, and then exposed to the low temperature environment for 30 minutes, and such a cycle was repeated for 150 hours. After the 150-hour thermal shock test, the ESR was measured again, and the percentage of the ESR after the thermal shock test relative to the initial ESR was calculated as the ESR change (ΔESR).

[0098] In Table 1 below, the results of the ESR change of the solid electrolytic capacitors of Comparative Examples 1 and 3 and Reference Examples 1 to 3 are shown. In addition, Figure 1 was produced based on Table 1 below, and it is a graph with the acid dissociation constant pKa on the horizontal axis and the ESR change on the vertical axis. In the figure, AzA represents azelaic acid.

[0099] (Table 1)

[0100]

[0101] As shown in Table 1 and Figure 1 as shown, the change in ESR after the thermal shock test of Reference Examples 1 to 3 containing an anion component with an acid dissociation constant pKa of 4.51 or less in the electrolytic solution was good. In contrast, the change in ESR after the thermal shock test of Comparative Examples 1 and 3 containing an anion component with an acid dissociation constant pKa of 4.52 or more became at least 1.7 times or more compared to Reference Examples 1 to 3, and the ESR deteriorated. Thus, it was confirmed that the ESR of the solid electrolytic capacitor containing an anion component with an acid dissociation constant pKa of 4.52 or more in the electrolytic solution deteriorated when repeatedly subjected to thermal shock.

[0102] On the other hand, the results of the change in ESR of the solid electrolytic capacitors of Comparative Example 1, Comparative Example 2, Example 1, and Example 2 are shown in Table 2 below. In addition, Figure 2 is made based on Table 2 below and is a graph showing the change in ESR of Comparative Example 1, Comparative Example 2, Example 1, and Example 2.

[0103] (Table 2)

[0104]

[0105] As shown in Table 2 and Figure 2 as shown, it was confirmed that when an anion component with an acid dissociation constant pKa of 4.52 or more was contained in the electrolytic solution and a conductive polymer with a median diameter of 50 nm or less was used in combination, the change in ESR of the solid electrolytic capacitor when repeatedly subjected to thermal shock became smaller.

[0106] (Examples 3 - 5)

[0107] Furthermore, solid electrolytic capacitors of Examples 3 to 5 were manufactured. Regarding the solid electrolytic capacitor of Example 3, suberic acid was used as the anion component of the electrolytic solution. In addition, the solid electrolytic capacitor of Example 3 was manufactured by the same manufacturing method and manufacturing conditions as Example 1 and had the same structure. That is, the solid electrolytic capacitor of Example 3 used a conductive polymer with a median diameter of 47 nm.

[0108] Regarding the solid electrolytic capacitor of Example 4, suberic acid was used as the anion component of the electrolytic solution, and a conductive polymer solution in which a conductive polymer with a median diameter of 10 nm was dispersed in a dispersant was used for manufacturing. In addition, the solid electrolytic capacitor of Example 4 was manufactured by the same manufacturing method and manufacturing conditions as Example 1 and had the same structure.

[0109] Regarding the solid electrolytic capacitor of Example 5, sebacic acid was used as the anion component of the electrolytic solution. In addition, the solid electrolytic capacitor of Example 5 was fabricated by the same manufacturing method and under the same manufacturing conditions as those of Example 1 and has the same structure. That is, the solid electrolytic capacitor of Example 5 uses a conductive polymer with a median diameter of 47 nm. In addition, the acid dissociation constant of sebacic acid is pKa = 4.59.

[0110] (Thermal Shock Test 2)

[0111] By repeatedly applying thermal shock to the solid electrolytic capacitors of these Examples 3 to 5, the change in ESR after the thermal shock test was measured. The content of the thermal shock test and the measurement conditions of ESR are the same as those of Comparative Examples 1 to 3 and Examples 1 to 3.

[0112] The results of the change in ESR of the solid electrolytic capacitors of Comparative Example 3 and Examples 3 to 5 are shown in Table 3 below. In addition, Figure 3 is made based on Table 3 below and is a graph showing the change in ESR of Comparative Example 3 and Examples 3 to 5.

[0113] (Table 3)

[0114]

[0115] As shown in Table 3 and Figure 3 it was confirmed that when suberic acid or sebacic acid is contained in the electrolytic solution and a conductive polymer with a median diameter of 50 nm or less is used in combination, the change in ESR when the solid electrolytic capacitor is repeatedly subjected to thermal shock becomes smaller. Suberic acid and sebacic acid, like azelaic acid, are anion components with an acid dissociation constant pKa = 4.52 or more. Therefore, it was confirmed that if an anion component with an acid dissociation constant pKa = 4.52 or more is contained in the electrolytic solution, regardless of the type of the anion component, by using a conductive polymer with a median diameter of 50 nm or less in combination, the change in ESR when the solid electrolytic capacitor is repeatedly subjected to thermal shock becomes smaller.

[0116] (Examples 6 - 12)

[0117] Furthermore, solid electrolytic capacitors of Examples 6 to 12 were fabricated. Examples 6 to 12 are different from Example 1 in that polyhydric alcohol was added to the conductive polymer solution and the electrolyte layer contains polyhydric alcohol. Regarding other structures, compositions, manufacturing methods, and manufacturing conditions, including the fact that the anion component is azelaic acid with an acid dissociation constant pKa = 4.52 or more and the median diameter of the conductive polymer is 47 nm, Examples 6 to 12 are the same as Example 1.

[0118] 1-Hexanol was added to the conductive polymer solution of Example 6. Ethylene glycol was added to the conductive polymer solution of Example 7. Diethylene glycol was added to the conductive polymer solution of Example 8. Glycerol was added to the conductive polymer solution of Example 9. Polyethylene glycol with an average molecular weight of 300 was added to the conductive polymer solution of Example 10. Sorbitol was added to the conductive polymer solution of Example 11. Xylitol was added to the conductive polymer solution of Example 12. The amount of polyol added to the conductive polymer solutions of Examples 6 to 12 was added in such a way that the conductive polymer solution adjusted to pH 4 became 8 wt%.

[0119] By repeatedly applying thermal shock to the solid electrolytic capacitors of these Examples 6 to 12, the change in ESR after the thermal shock test was measured. The content of the thermal shock test and the measurement conditions of ESR were the same as those of Comparative Example 1, Example 1, and Example 2.

[0120] The results of the change in ESR of the solid electrolytic capacitors of Examples 6 to 12 are shown in Table 4 below. In addition, Figure 4 is made based on Table 4 below and is a chart showing the change in ESR of Examples 6 to 12.

[0121] (Table 4)

[0122]

[0123] As shown in Table 4 and Figure 4 shown, Examples 6 to 12 further suppressed the change in ESR compared with Example 1. Moreover, Examples 6 to 12 had a smaller change in ESR compared with Reference Examples 1 to 3 with less change in ESR. Thus, it was confirmed that when an anion component having an acid dissociation constant pKa of 4.52 or more was included in the electrolytic solution, when the median diameter of the conductive polymer was made 50 nm or less, and further when a polyol was included in the electrolyte layer, the change in ESR could be reduced compared with when an anion component having an acid dissociation constant pKa of 4.51 or less was included in the electrolytic solution.

[0124] Moreover, almost no change in ESR was observed in Examples 10 to 12. That is, it was confirmed that when polyethylene glycol, xylitol, or sorbitol was included in the electrolyte layer, the change in ESR could be substantially suppressed even when the solid electrolytic capacitor was repeatedly subjected to thermal shock.

[0125] (Examples 13 - 14)

[0126] Furthermore, solid electrolytic capacitors of Example 13 and Example 14 were fabricated. In Example 13 and Example 14, similar to Example 7, ethylene glycol was added to the conductive polymer solution as a polyol. In Example 7, the amount of ethylene glycol was added such that the conductive polymer solution adjusted to pH 4 became 8 wt%. In contrast, the amount of ethylene glycol in Example 13 was added such that it became 30 wt% relative to the conductive polymer solution, and the amount of ethylene glycol in Example 14 was added such that it became 50 wt% relative to the conductive polymer solution. Regarding other structures, compositions, manufacturing methods, and manufacturing conditions, Example 13 and Example 14 were the same as Example 7.

[0127] By repeatedly applying thermal shock to these solid electrolytic capacitors of Example 13 and Example 14, the change in ESR after the thermal shock test was measured. The content of the thermal shock test and the measurement conditions of ESR were the same as those in Comparative Example 1, Example 1, and Example 2.

[0128] In Table 5 below, the results of the change in ESR of the solid electrolytic capacitors of Example 13 and Example 14 are shown together with Example 1 and Example 7. Additionally, Figure 5 is made based on Table 5 below and is a chart showing the relationship between the addition ratio of the polyol and the change in ESR.

[0129] (Table 5)

[0130]

[0131] As shown in Table 5 and Figure 5 it was confirmed that when the polyol was added in the range of 8 wt% or more and 50 wt% or less relative to the conductive polymer solution, the change in ESR when the solid electrolytic capacitor was repeatedly subjected to thermal shock became smaller. In particular, it was confirmed that when the polyol was added in the range of 8 wt% or more and 30 wt% or less relative to the conductive polymer solution, the change in ESR could be reduced compared to when the electrolyte contained an anion component with an acid dissociation constant pKa = 4.51 or less.

[0132] (Example 15 - 22)

[0133] Solid electrolytic capacitors of Example 15 to Example 22 were fabricated. In Example 15 to Example 22, in addition to azelaic acid with an acid dissociation constant pKa = 4.52 or more, an anion component with an acid dissociation constant pKa = 4.51 or less was added to the electrolyte layer. Regarding other structures, compositions, manufacturing methods, and manufacturing conditions, Example 15 to Example 22 were the same as Example 2.

[0134] In the electrolytes of Examples 15 to 17, an anion component and ammonia were mixed such that the amount became 16 mmol per 100 g of the electrolyte. The anion component is a mixture of azelaic acid and glutaric acid with an acid dissociation constant of pka = 4.31. The azelaic acid and glutaric acid in Example 15 were mixed at a molar ratio of 1:1. Regarding the azelaic acid and glutaric acid in Example 16, the amount of azelaic acid was made twice, i.e., mixed at a molar ratio of 2:1. Regarding the azelaic acid and glutaric acid in Example 17, the amount of azelaic acid was made three times, i.e., mixed at a molar ratio of 3:1.

[0135] In the electrolytes of Examples 18 to 20, an anion component and ammonia were mixed such that the amount became 16 mmol per 100 g of the electrolyte. The anion component is a mixture of azelaic acid and succinic acid with an acid dissociation constant of pka = 4.2. The azelaic acid and succinic acid in Example 18 were mixed at a molar ratio of 1:1. Regarding the azelaic acid and succinic acid in Example 19, the amount of azelaic acid was made twice, i.e., mixed at a molar ratio of 2:1. Regarding the azelaic acid and succinic acid in Example 20, the amount of azelaic acid was made three times, i.e., mixed at a molar ratio of 3:1.

[0136] Examples 21 and 22 are different from Example 2 in that the content of azelaic acid in the electrolyte is different. In Example 2, azelaic acid and ammonia were mixed such that the amount became 16 mmol per 100 g of the electrolyte. In contrast, in Example 21, azelaic acid and ammonia were mixed such that the amount became 12 mmol per 100 g of the electrolyte, and in Example 22, azelaic acid and ammonia were mixed such that the amount became 10.6 mmol per 100 g of the electrolyte.

[0137] By repeatedly applying thermal shock to the solid electrolytic capacitors of these Examples 15 and 22, the change in ESR after the thermal shock test was measured. The content of the thermal shock test and the measurement conditions of ESR are the same as those in Comparative Example 1, Example 1, and Example 2.

[0138] In Table 7 below, the results of the change in ESR of the solid electrolytic capacitors of Examples 15 to 22 are shown together with Example 2, Reference Example 2, and Reference Example 3. Additionally, Figure 6 and Figure 7 is made according to Table 6 below, Figure 6 is a graph showing the change in ESR of Example 2 and Examples 15 to 17, Figure 7 is a graph showing the change in ESR of Example 2 and Examples 18 to 20.

[0139] (Table 6)

[0140]

[0141] First, as shown in Table 6, compared with Example 2, Example 21 more effectively suppresses the change in ESR. Furthermore, compared with Example 21, Example 22 more effectively suppresses the change in ESR. Based on this result, it was confirmed that by reducing the amount of the anionic component with pKa = 4.52 or higher, even when repeatedly subjected to thermal shock, the change in ESR of the solid electrolytic capacitor is suppressed.

[0142] Furthermore, as shown in Table 6, Figure 6 and Figure 7 it was confirmed that when an anionic component with an acid dissociation constant of pKa = 4.51 or lower is added to the electrolyte layer in addition to azelaic acid with an acid dissociation constant of pKa = 4.52 or higher, even when the electrolytic capacitor is repeatedly subjected to thermal shock, the change in ESR can be substantially suppressed.

[0143] In particular, by comparing with Reference Example 2 and Reference Example 3, it was confirmed that although the aliphatic dicarboxylic acid with an acid dissociation constant of pKa = 4.52 or higher, which increases the change in ESR when repeatedly subjected to thermal shock, is contained in a large amount in the electrolyte solution, the change in ESR is more effectively suppressed compared to a capacitor containing an aliphatic dicarboxylic acid with an acid dissociation constant of pKa = 4.51 or lower in the electrolyte solution.

[0144] Here, when comparing Example 21, Example 17, and Example 20, it was confirmed that although the amount of azelaic acid with pKa = 4.52 or higher is the same, Example 17 and Example 20 further suppress the change in ESR compared to Example 21, and the suppression effect of the change in ESR is higher compared to Reference Example 2 and Reference Example 3. In addition, when comparing Example 22, Example 16, and Example 19, it was confirmed that although the amount of azelaic acid with pKa = 4.52 or higher is the same, Example 16 and Example 19 further suppress the change in ESR compared to Example 22, and the suppression effect of the change in ESR is higher compared to Reference Example 2 and Reference Example 3.

[0145] That is, it was confirmed that in addition to the reason of simply reducing the amount of the aliphatic dicarboxylic acid with an acid dissociation constant of pKa = 4.52 or higher, which increases the change in ESR when repeatedly subjected to thermal shock, the interaction between the aliphatic dicarboxylic acid with an acid dissociation constant of pKa = 4.52 or higher, the aliphatic dicarboxylic acid with an acid dissociation constant of pKa = 4.51 or lower, and the conductive polymer with a D50 of 50 nm or less in the particle size distribution contributes greatly to the suppression of the change in ESR.

[0146] It was confirmed that such deterioration due to repeated thermal shock does not occur in an electrolytic capacitor using only the electrolyte solution or a solid electrolytic capacitor using only the conductive polymer, and deterioration occurs only in a hybrid capacitor combining the conductive polymer and the electrolyte solution.

Claims

1. A solid electrolytic capacitor, characterized in that, Comprising: An anode body containing valve-acting metal and having a dielectric film formed on its surface; A cathode body facing the anode body; and An electrolyte layer interposed between the anode body and the cathode body, containing an electrolytic solution and a conductive polymer, The electrolytic solution contains an aliphatic dicarboxylic acid having an acid dissociation constant pKa of 4.52 or more, The D50 in the particle size distribution of the conductive polymer is 50 nm or less.

2. The solid electrolytic capacitor according to claim 1, wherein The electrolyte layer contains a polyhydric alcohol.

3. The solid electrolytic capacitor according to claim 1, wherein The electrolyte layer is formed using a conductive polymer solution containing the conductive polymer and a polyhydric alcohol.

4. The solid electrolytic capacitor according to claim 3, wherein The polyhydric alcohol is contained in a proportion of 8 wt% or more and 50 wt% or less relative to the total amount of the conductive polymer solution.

5. The solid electrolytic capacitor according to claim 3, wherein The polyhydric alcohol is contained in a proportion of 8 wt% or more and 30 wt% or less relative to the total amount of the conductive polymer solution.

6. The solid electrolytic capacitor according to any one of claims 2 to 5, wherein The polyhydric alcohol is one or a mixture of two or more selected from polyethylene glycol, xylitol, and sorbitol.

7. The solid electrolytic capacitor according to any one of claims 1 to 5, wherein The aliphatic dicarboxylic acid is one or a mixture of two or more selected from the group of azelaic acid, suberic acid, and sebacic acid.

8. The solid electrolytic capacitor according to any one of claims 1 to 5, wherein The electrolytic solution further contains an aliphatic dicarboxylic acid having an acid dissociation constant pKa of 4.51 or less.

9. A method for manufacturing a solid electrolytic capacitor, characterized in that, Including: A conductive polymer attaching step of attaching a conductive polymer solution to an anode body having a dielectric film formed on its surface or to a capacitor element facing the anode body and the cathode body and drying it; and An electrolytic solution impregnation step of impregnating the electrolytic solution into the capacitor element after the conductive polymer attaching step, The conductive polymer solution contains a conductive polymer having a D50 in the particle size distribution of 50 nm or less, The electrolytic solution contains an aliphatic dicarboxylic acid having an acid dissociation constant pKa of 4.52 or more.

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