JP7375540B2 - solid electrolytic capacitor - Google Patents

Description

The present invention relates to a hybrid type solid electrolytic capacitor that uses both a solid electrolyte and an electrolytic solution.

Electrolytic capacitors that use valve metals such as tantalum or aluminum can achieve small size and large capacitance by making the valve metal as the anode side counter electrode into a sintered body or etched foil, etc., and expanding the surface of the dielectric material. You can get In particular, solid electrolytic capacitors, which have a dielectric oxide film covered with a solid electrolyte, have characteristics such as being small, large capacitance, and low equivalent series resistance, as well as being easy to chip and suitable for surface mounting. , is essential for making electronic devices smaller, more sophisticated, and lower in cost.

However, compared to liquid electrolytic capacitors in which the capacitor element is impregnated with an electrolytic solution, solid electrolytic capacitors have a poor ability to repair defects in the anodic oxide film, which is a dielectric, and there is a risk that leakage current may increase. Therefore, a so-called hybrid type solid electrolytic capacitor was proposed in which a solid electrolyte layer is formed on a capacitor element in which an anode foil and a cathode foil are opposed to each other with a separator interposed between them, and the gap in the capacitor element is impregnated with a driving electrolyte. (For example, see Patent Document 1).

Compared to a solid electrolytic capacitor using only a solid electrolyte, a hybrid type solid electrolytic capacitor has an increased capacitance (Cap) and a decreased equivalent series resistance (ESR). Furthermore, the leakage current of a hybrid type solid electrolytic capacitor is reduced because repair of defective portions of the dielectric oxide film is promoted by the action of the electrolytic solution.

Japanese Patent Application Publication No. 2006-114540

Not only in hybrid type solid electrolytic capacitors but also in cases where only a liquid or only a solid is used as an electrolyte, if halogen ions (particularly chlorine ions) are mixed into the electrolytic capacitor, the anode foil will corrode. More specifically, chlorine ions have a dissolving effect on the dielectric oxide film, and if this dissolving action exceeds the electrolyte's ability to repair defects in the dielectric oxide film, the product characteristics of the capacitor will deteriorate. Eventually, it will no longer function as an electrolytic capacitor. For this reason, measures are being taken to reduce the amount of chlorine ions unique to materials such as electrode foils, separators, and sealing bodies as much as possible, and to prevent chlorine ions from being mixed in during the manufacturing process. It is difficult to reduce the amount of chlorine ions to zero.

Based on previous findings, it has been found that increasing the water content of the electrolytic solution or using γ-butyrolactone as a solvent can suppress the dissolution effect of the dielectric oxide film caused by chlorine ions. However, increasing the moisture content in a solid electrolytic capacitor may adversely affect the reflow characteristics, deteriorate the adhesion between the electrode foil and the solid electrolyte layer (deteriorate the solid electrolyte layer), and increase the ESR. Furthermore, when ethylene glycol is used as a solvent, the electrical conductivity of the conductive polymer is improved by changing the higher order structure of the conductive polymer and reorienting the crystal structure of the polymer chains, but in the case of γ-butyrolactone, the electrical conductivity of the conductive polymer is improved. Such an effect cannot be obtained. Therefore, when γ-butyrolactone is used as a solvent, the product properties are worse than when ethylene glycol is used.

The present invention was proposed to solve the above problems, and its purpose is to provide a hybrid type solid electrolytic capacitor that can suppress corrosion reactions even if chlorine ions are mixed in.

The solid electrolytic capacitor of the present invention includes a capacitor element made of an anode foil and a cathode foil facing each other via a separator, a solid electrolyte layer formed in the capacitor element, and a solid electrolyte layer formed in the capacitor element. an electrolytic solution filled in a void in the capacitor element in which a 2,4-dihydroxybenzoic acid, 2,6-dihydroxybenzoic acid, 3,5-dihydroxybenzoic acid is formed. , 2,4,6-trihydroxybenzoic acid and 3,4,5-trihydroxybenzoic acid, and ethylene glycol.

The electrolyte includes 2,4-dihydroxybenzoic acid, 2,6-dihydroxybenzoic acid, 3,5-dihydroxybenzoic acid, 2,4,6-trihydroxybenzoic acid, and 3,4,5-trihydroxybenzoic acid. It may further contain an acid different from the above.

The different acids may be benzoic acid, salicylic acid, phthalic acid, azelaic acid, adipic acid or borodisalicylic acid.

The electrolytic solution contains a base, and the 2,4-dihydroxybenzoic acid, 2,6-dihydroxybenzoic acid, 3,5-dihydroxybenzoic acid, 2,4,6-trihydroxybenzoic acid, and 3,4,5-dihydroxybenzoic acid. - The molar concentration of the one or more acids selected from trihydroxybenzoic acid may be higher than the molar concentration of the base.

The electrolytic solution contains a base, and the 2,4-dihydroxybenzoic acid, 2,6-dihydroxybenzoic acid, 3,5-dihydroxybenzoic acid, 2,4,6-trihydroxybenzoic acid, and 3,4,5-dihydroxybenzoic acid. - The total molar concentration of one or more acids selected from trihydroxybenzoic acid and the different acid may be higher than the molar concentration of the base.

selected from the 2,4-dihydroxybenzoic acid, 2,6-dihydroxybenzoic acid, 3,5-dihydroxybenzoic acid, 2,4,6-trihydroxybenzoic acid and 3,4,5-trihydroxybenzoic acid One or more acids may be contained in a total amount of 0.1 wt% or more based on the total amount of the electrolyte.

The electrolytic solution contains the 2,6-dihydroxybenzoic acid, the 2,4,6-trihydroxybenzoic acid, or both, Alternatively, both may be contained in a total amount of 0.1 wt% or more based on the total amount of the electrolyte.

The electrolyte includes the 2,6-dihydroxybenzoic acid, the 2,4,6-trihydroxybenzoic acid, or both, the different acid is azelaic acid, the 2,6-dihydroxybenzoic acid, the 2,4,6-trihydroxybenzoic acid, or both. 2,4,6-trihydroxybenzoic acid or both may be contained in a total amount of 0.05 wt% or more based on the total amount of the electrolyte.

The moisture content of the electrolytic solution may be 0.01 wt% or more and 5 wt% or less.

The electrolytic solution may further contain γ-butyrolactone.

The electrolytic solution may further contain at least one solvent selected from sulfolane, 3-methylsulfolane, and 2,4-dimethylsulfolane.

According to the present invention, it is possible to improve the chlorine ion resistance of a solid electrolytic capacitor that uses both a solid electrolyte and an electrolytic solution, and to suppress corrosion reactions caused by chlorine ions.

Hereinafter, solid electrolytic capacitors according to embodiments of the present invention will be described. Note that the present invention is not limited to the embodiments described below.

(1. Overall composition)
The solid electrolytic capacitor according to this embodiment is a so-called hybrid type in which a solid electrolyte layer and an electrolyte are used together. The capacitor element includes an anode foil, a cathode foil, a separator, a solid electrolyte layer, and an electrolyte. The anode foil and the cathode foil face each other with a separator in between. The surface of the anode foil is enlarged, and a dielectric oxide film layer is formed on the enlarged surface. The surface of the cathode foil may be enlarged as necessary, and a dielectric oxide film layer may be formed thereon. The solid electrolyte layer is interposed between the anode foil and the cathode foil and is in close contact with the dielectric oxide film layer. The electrolytic solution fills the void of the capacitor element, which is composed of the anode foil, the cathode foil, the separator, and the solid electrolyte layer.

An example of a method for manufacturing this solid electrolytic capacitor is roughly as follows. First, as a first step, a capacitor element is formed by winding an anode foil and a cathode foil with an oxide film layer formed on the surface with a separator interposed therebetween, and a repair chemical conversion is applied to this capacitor element. Subsequently, as a second step, a solid electrolyte layer is formed on the capacitor element. In this step, a capacitor element is impregnated with a dispersion containing conductive polymer particles or powder and a solvent. Thereafter, as a third step, this capacitor element is immersed in an electrolytic solution to fill the void within the capacitor element with the electrolytic solution. Then, as a fourth step, the capacitor element is inserted into the outer case, a sealing rubber is attached to the open end, and the capacitor is sealed by crimping, followed by aging to form a solid electrolytic capacitor.

(2. Electrode foil)
The anode foil and the cathode foil are long foil bodies made of valve metal. Valve metals include aluminum, tantalum, niobium, niobium oxide, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. The purity is preferably 99.9% or more for the anode foil, and about 99% or more for the cathode foil, but impurities such as silicon, iron, copper, magnesium, and zinc may be contained.

The anode foil and the cathode foil have a porous structure on the surface as a sintered body obtained by sintering valve metal powder, or an etched foil obtained by etching a stretched foil. The porous structure consists of tunnel-like pits, cavernous pits, or voids between closely packed powders. The porous structure is typically formed by direct current etching or alternating current etching in which direct current or alternating current is applied in an acidic aqueous solution containing halogen ions such as hydrochloric acid, or by depositing or sintering metal particles on the core. It is formed by

The dielectric oxide film layer is typically a film formed on the surface layer of the anode foil, and if the anode foil is made of aluminum, it is an aluminum oxide layer in which the porous structure region is oxidized. This dielectric oxide film layer is formed by chemical conversion treatment in which a voltage is applied in an aqueous solution of adipic acid, boric acid, phosphoric acid, or the like. Furthermore, a thin dielectric oxide film (approximately 1 to 10 V) may be formed on the surface layer of the cathode foil by chemical conversion treatment if necessary, and a layer consisting of metal nitride, metal carbide, or metal carbonitride may be formed by vapor deposition. It is also possible to use a material formed by or a material containing carbon on the surface.

(3. Separator)
Separators can be made of cellulose such as kraft, Manila hemp, esparto, hemp, rayon, and mixed papers thereof, polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and their derivatives, polytetrafluoroethylene resins, and polyfluoride. Polyamide resins such as vinylidene resin, vinylon resin, aliphatic polyamide, semi-aromatic polyamide, fully aromatic polyamide, polyimide resin, polyethylene resin, polypropylene resin, trimethylpentene resin, polyphenylene sulfide resin, acrylic resin, polyvinyl alcohol Examples include resins, and these resins can be used alone or in combination.

(4. Solid electrolyte layer)
The solid electrolyte layer is a conductive polymer that incorporates a dopant. The dopant plays a role in exhibiting conductivity. Examples of the conductive polymer include polypyrrole, polythiophene, polyfuran, polyaniline, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, polythiophene vinylene, and derivatives thereof. These may be used alone, two or more types may be combined, or a copolymer of two or more types of monomers may be used.

Dopants include vinylsulfonic acid, styrenesulfonic acid, allylsulfonic acid, acrylsulfonic acid, methacrylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, isoprenesulfonic acid, acrylic acid, benzenesulfonic acid, naphthalenesulfonic acid, and anthraquinone. Examples include anions such as sulfonic acid or derivatives thereof. These may be used alone or in combination of two or more. Moreover, these may be polymers of a single monomer or copolymers of two or more types of monomers.

The solvent for dispersing the conductive polymer may be any solvent in which conductive polymer particles or powder can be dispersed; for example, a protic solvent may be used, and specific examples include water and ethylene glycol. Ethylene glycol is one of the solvents of the electrolytic solution, and even if it remains in the capacitor element, it does not become an impurity, and it has been found that among the electrical properties of the product, in particular, ESR can be reduced, so it is preferable.

When impregnating the capacitor element with the dispersion liquid, depressurization treatment or pressurization treatment may be performed as necessary to promote impregnation. The impregnation step may be repeated multiple times. The solvent of the conductive polymer dispersion is removed by evaporation by drying, if necessary. Heat drying or reduced pressure drying may be performed as necessary. Furthermore, in order to improve the impregnation properties and conductivity of the conductive polymer, various additives may be added to the conductive polymer dispersion or neutralization may be performed by adding cations.

(5. Electrolyte)
In the electrolytic solution impregnation process, depressurization treatment or pressurization treatment is performed as necessary. An acid (hereinafter referred to as a specific acid) that suppresses corrosion reactions caused by chlorine ions is added to this electrolytic solution. Specific acids include 2,6-dihydroxybenzoic acid, 2,4-dihydroxybenzoic acid, 3,5-dihydroxybenzoic acid, and 2,4,6-dihydroxybenzoic acid represented by the following structural formulas (Chemical Formula 1) to (Chemical Formula 5). -trihydroxybenzoic acid or 3,4,5-trihydroxybenzoic acid, and one or more of these are added to the electrolyte.

2,6-dihydroxybenzoic acid and 2,4,6-trihydroxybenzoic acid, which have hydroxyl groups at both ortho positions relative to the carboxylic acid group, are effective in suppressing corrosion reactions even when a large amount of chlorine ions are mixed in. It is particularly preferable because it is expensive. In addition, the specific acids represented by the above structural formulas (Chemical Formulas 1) to (Chemical Formulas 5) are preferably contained in a total amount of 1.5 wt% or more based on the total amount of the electrolytic solution, and if the total content is 1.5 wt% or more, With various compositions of solid electrolytic capacitors, reduction in withstand voltage can be suppressed in a wide range of ways.

These specific acids may behave as a main anion component in the electrolytic solution, or may also serve as an anion component along with other main anion components. The acid serving as an anion component in the electrolytic solution is supplied by ionic dissociation of an organic acid, an inorganic acid, a composite compound of an organic acid and an inorganic acid, or a salt thereof. Two or more types of anion components including a specific acid may be combined.

Examples of organic acids include oxalic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, maleic acid, adipic acid, benzoic acid, toluic acid, enanthic acid, malonic acid, Examples include carboxylic acids such as 1,6-decanedicarboxylic acid, 1,7-octanedicarboxylic acid, azelaic acid, undecanedioic acid, dodecanedioic acid, and tridecanedioic acid, phenols, and sulfonic acids. In addition, examples of inorganic acids include boric acid, phosphoric acid, phosphorous acid, hypophosphorous acid, carbonic acid, and silicic acid. Examples of complex compounds of organic acids and inorganic acids include borodisalicylic acid, borodisoxalic acid, borodiglycolic acid, borodismalonic acid, borodisuccinic acid, borodiadipic acid, borodiazelaic acid, borodisbenzoic acid, borodismaleic acid, borodisilactic acid, borodimalic acid, Examples include boroditartaric acid, borodicitric acid, borodiphthalic acid, borodi(2-hydroxy)isobutyric acid, borodiresorcic acid, borodimethylsalicylic acid, borodinaphthoic acid, borodimandelic acid, and borodi(3-hydroxy)propionic acid.

Furthermore, a specific acid may be added as an additive to adjust the properties of the electrolyte. That is, it is sufficient that the specific acid exists in the electrolyte. Further, an additive other than the specific acid may be added to the electrolytic solution. Other additives include polyethylene glycol, complex compounds of boric acid and polysaccharides (such as mannitol and sorbitol), complex compounds of boric acid and polyhydric alcohols, boric acid esters, and nitro compounds (o-nitrobenzoic acid). , m-nitrobenzoic acid, p-nitrobenzoic acid, o-nitrophenol, m-nitrophenol, p-nitrophenol, p-nitrobenzyl alcohol, etc.), phosphoric acid esters, and the like. These may be used alone or in combination of two or more.

Among the above additives, polyethylene glycol and complex compounds of boric acid and polysaccharides are added for the purpose of improving withstand voltage, nitro compounds are added for the purpose of gas absorption in capacitors, and moisture resistance is improved. It is preferable to add a phosphoric acid ester for this purpose.

As the anion component, other acids added to the electrolytic solution together with the specific acid may be general acids, such as the aforementioned organic acids, inorganic acids, or composite compounds of organic acids and inorganic acids. Among these, benzoic acid, salicylic acid, phthalic acid, azelaic acid, adipic acid and borodisalicylic acid are preferred.

In addition, the specific acid is added in a concentration exceeding the equimolar amount of a base that becomes a cation component in the electrolytic solution, or the specific acid and other acids in the electrolytic solution are added in a concentration exceeding the equimolar amount of the base. It is also possible to use an electrolyte with excess acid. The reason is unknown, but if the electrolyte has an excess of acid, even if a small amount of specific acid is added to the electrolyte, it will have high chlorine ion resistance and will be able to suppress the drop in withstand voltage due to chlorine ions. can. It has been found that when the electrolytic solution has an excess of acid, sufficient chlorine ion resistance is exhibited even when the specific acid is present in a total amount of 0.1 wt % or more based on the total amount of the electrolytic solution. Preferably, when the specific acid is an excessively acidic electrolyte, the total amount of the specific acid is 0.3 wt% or more, particularly preferably 0.5 wt% or more, based on the total amount of the electrolyte, and the amount of the specific acid added is increased. As a result, chloride ion resistance improves.

Furthermore, if 2,6-dihydroxybenzoic acid, 2,4,6-trihydroxybenzoic acid, or both, which have hydroxyl groups at both ortho positions based on the carboxylic acid group, are added, even if the acid is not excessive, these Chloride ion resistance is exhibited even when the specific acid is added in a total amount of 0.1 wt% or more based on the total amount of the electrolyte. Furthermore, when azelaic acid is used as the other acid serving as the anion component and 2,6-dihydroxybenzoic acid, 2,4,6-trihydroxybenzoic acid, or both are used as the specific acid, the amount of these specific acids added. can be kept in an extremely small amount, such as a total of 0.05 wt% or more, and exhibits sufficient chlorine ion resistance.

Other salts that supply anionic components and cationic components in the electrolytic solution include ammonium salts, amine salts, quaternary ammonium salts, quaternized amidinium salts, amine salts, sodium salts, potassium salts, and the like. Examples of the amine in the amine salt include primary amines, secondary amines, and tertiary amines. Primary amines include methylamine, ethylamine, propylamine, etc. Secondary amines include dimethylamine, diethylamine, ethylmethylamine, dibutylamine, etc. Tertiary amines include trimethylamine, triethylamine, tripropylamine, tributylamine, Examples include ethyldimethylamine and ethyldiisopropylamine. Further, examples of the quaternary ammonium ion of the quaternary ammonium salt include tetramethylammonium, triethylmethylammonium, and tetraethylammonium. Examples of quaternized amidinium salts include ethyldimethylimidazolinium and tetramethylimidazolinium. At least one of these cationic components is added to the electrolytic solution.

Contains ethylene glycol as a solvent for the electrolyte. It is known that an electrolytic solution using ethylene glycol as a solvent has lower chloride ion resistance than an electrolytic solution using γ-butyrolactone as a solvent. When ethylene glycol is used as a solvent, chlorine ion resistance can be improved with a specific acid and corrosion reactions caused by chlorine ions can be suppressed without increasing the moisture content of the electrolytic solution. Furthermore, since a low moisture content can be achieved, it has the effect of suppressing deterioration of reflow characteristics and deterioration of the solid electrolyte layer. Furthermore, it is possible to suppress the reduction in initial equivalent series resistance (ESR) and the deterioration of capacitance (ΔCap) over time due to ethylene glycol.

Of course, the effect of inhibiting the corrosion reaction of chlorine ions by the specific acid works well even with solvents other than ethylene glycol. Such other solvents include protic organic polar solvents and aprotic organic polar solvents, which may be used alone or in combination of two or more.

As the protic organic polar solvent, monohydric alcohols, polyhydric alcohols, oxyalcohol compounds, etc. may be used. Examples of monohydric alcohols include ethanol, propanol, butanol, pentanol, hexanol, cyclobutanol, cyclopentanol, cyclohexanol, benzyl alcohol, and the like. Examples of polyhydric alcohols and oxyalcohol compounds include ethylene glycol, propylene glycol, glycerin, methyl cellosolve, ethyl cellosolve, methoxypropylene glycol, dimethoxypropanol, and the like.

As the aprotic organic polar solvent, sulfone type, amide type, lactone type, cyclic amide type, nitrile type, oxide type, etc. may be used. Examples of the sulfone type include dimethylsulfone, ethylmethylsulfone, diethylsulfone, sulfolane, 3-methylsulfolane, and 2,4-dimethylsulfolane. Amides include N-methylformamide, N,N-dimethylformamide, N-ethylformamide, N,N-diethylformamide, N-methylacetamide, N,N-dimethylacetamide, N-ethylacetamide, N,N- Examples include diethylacetamide and hexamethylphosphoric amide. Examples of lactones and cyclic amides include γ-butyrolactone, γ-valerolactone, δ-valerolactone, N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, butylene carbonate, isobutylene carbonate, and the like. Examples of nitriles include acetonitrile, 3-methoxypropionitrile, glutaronitrile, and the like. Examples of oxides include dimethyl sulfoxide and the like.

The moisture content of the electrolytic solution having the above structure is preferably 0.01 wt% or more and 5 wt% or less. If the moisture content is less than 0.01 wt%, the repairability of the oxide film may deteriorate and leakage current may increase. Furthermore, if the moisture content exceeds 5 wt%, water may evaporate during reflow and the electrolytic capacitor may swell. Note that the water in the electrolyte includes both water intentionally contained in the electrolyte and water unintentionally contained due to the manufacturing environment or manufacturing method.

Hereinafter, the solid electrolytic capacitor of the present invention will be explained in more detail based on Examples. Note that the present invention is not limited to the following examples.

(6. Voltage resistance characteristics due to addition of various specific acids)
Electrolytes of Examples 1 to 5 and Comparative Examples 1 to 3 shown in Table 1 below were prepared. Table 1 also shows the specific resistance (Rs) of each electrolytic solution.

As shown in Table 1, 2,6-dihydroxybenzoic acid represented by the above structural formula (Chemical formula 1) was added to the electrolytic solution of Example 1. 2,4-dihydroxybenzoic acid represented by the above structural formula (Chemical formula 2) was added to the electrolytic solution of Example 2. 3,5-dihydroxybenzoic acid represented by the above structural formula (Chemical formula 3) was added to the electrolytic solution of Example 3. 2,4,6-trihydroxybenzoic acid represented by the above structural formula (Chemical formula 4) was added to the electrolytic solution of Example 4. 3,4,5-trihydroxybenzoic acid represented by the above structural formula (Chemical formula 5) was added to the electrolytic solution of Example 5.

To the electrolytic solution of Comparative Example 1, 2,5-dihydroxybenzoic acid represented by the following chemical formula (Chemical formula 6), which is a structural isomer of Examples 1 to 3 but differs in the position of the hydroxyl group, was added. Furthermore, 3,4-dihydroxybenzoic acid represented by the following chemical formula (Chemical formula 7), which is a structural isomer of Examples 1 to 3 but has a different position of the hydroxyl group, was added to the electrolyte solution of Comparative Example 2. . In addition, 2,3-dihydroxybenzoic acid represented by the following chemical formula (Chemical formula 8), which is a structural isomer of Examples 1 to 3 but has a different hydroxyl group position, was added to the electrolyte solution of Comparative Example 3. .

All of the electrolytes of Examples 1 to 5 and Comparative Examples 1 to 3 contain ethylene glycol as a solvent. All of these electrolytes contain triethylamine. The electrolytic solutions of Examples 1 to 5 and the electrolytic solutions of Comparative Examples 1 to 3 contain the acids shown in Table 1 as anion components of solutes. The specific acids added to the electrolytes of Examples 1 to 5 and the acids added to the electrolytes of Comparative Examples 1 to 3 and triethylamine were equimolar. The specific acids added to the electrolytes of Examples 1 to 5 and the acids added to the electrolytes of Comparative Examples 1 to 3 were also equimolar.

Further, in all of the electrolytes of Examples 1 to 5 and Comparative Examples 1 to 3, a total of 3.5 wt% of phosphoric acid ester and p-nitrobenzoic acid were added to the total amount of the electrolyte. The moisture content in the electrolytic solution was adjusted to 0.5 wt% in the electrolytic solutions of Examples 1 to 5 and Comparative Examples 1 to 3.

A constant current of 10 mA/cm ² was applied to the electrolytic solutions of Examples 1 to 5 and Comparative Examples 1 to 3 at 25° C. using aluminum foil as an electrode foil. Then, the voltage increase curve over time was examined, and the voltage at which a spike or scintillation was first observed in the voltage increase curve was defined as the withstand voltage. Measurements were performed while changing the amount of chlorine ions added to 0 (not added), 2, 4, 6, 8, and 10 ppm. The results are shown in Table 2 below. In Table 2, the withstand voltage when no chlorine ions were added was taken as the reference value, and the withstand voltages when each amount of chlorine ions were added were expressed as a percentage of the reference value.

As shown in Table 2, even when the amount of chlorine ions increased in the electrolytic solutions of Examples 1 to 5, the withstand voltage remained within a favorable range compared to the electrolytic solutions of Comparative Examples 1 to 3. In particular, the withstand voltage of the electrolytes of Examples 1 and 4, in which 2,6-dihydroxybenzoic acid and 2,4,6-dihydroxybenzoic acid were added, hardly decreased even when the amount of chlorine ions increased. Ta. From the above results, it was confirmed that Examples 1 to 5 had high chlorine ion resistance and suppressed corrosion reactions.

(7. Withstand voltage characteristics of electrolyte containing specific acid and mixed solvent)
Electrolytes of Example 6 and Example 7 shown in Table 3 below were prepared.

As shown in Table 3, the electrolytic solution of Example 6 used a mixed solution of equal amounts of ethylene glycol and γ-butyrolactone as a solvent. Further, in the electrolytic solution of Example 7, a mixed solution of ethylene glycol, γ-butyrolactone, and sulfolane was used as a solvent. The total amount of γ-butyrolactone and sulfolane is equivalent to ethylene glycol. The electrolyte solutions of Examples 6 and 7 are the same as the electrolyte solution of Example 1 in other compositions and moisture percentages, such as using 2,6-dihydroxybenzoic acid as the specific acid. The electrolytes of Examples 6 and 7 were tested for withstand voltage characteristics in relation to the amount of chlorine ions in the same manner as Examples 1 to 5 and Comparative Examples 1 to 3. compared with the results. The results are shown in Table 4 below. In Table 4, the withstand voltage when no chlorine ions were added was taken as the reference value, and the withstand voltage when each amount of chlorine ions was added was expressed as a percentage of the reference value.

As shown in Table 4, the specific acid acts effectively and chloride ion It was confirmed that even if the amount increased, the corrosion reaction was suppressed.

(8. Voltage resistance characteristics depending on the amount of specific acid added)
Electrolytes of Examples 8 to 11 shown in Table 5 below were prepared.

As shown in Table 5, 2,6-dihydroxybenzoic acid represented by the above structural formula (Chemical formula 1) was added to the electrolyte solutions of Examples 8 to 11. However, Examples 8 to 11 differ in the amount of 2,6-dihydroxybenzoic acid added. In addition, it contains ethylene glycol as a solvent, triethylamine is included, 2,6-dihydroxybenzoic acid and triethylamine are added in equal moles, and phosphoric acid ester and p-nitrobenzoic acid are added to the total amount of electrolyte. The electrolytic solutions of Examples 8 to 11 have this in common in that a total of 3.5 wt% is added.

The electrolytes of Examples 8 to 11 were tested for withstand voltage characteristics in relation to the amount of chlorine ions in the same manner as in Examples 1 to 5 and Comparative Examples 1 to 3. However, in Examples 10 and 11, tests were also conducted in which the amount of chlorine ions added was 15, 20, and 30 ppm. The results are shown in Table 6 below. In Table 6, the withstand voltage when no chlorine ions were added was taken as the reference value, and the withstand voltage when each amount of chlorine ions was added was expressed as a percentage of the reference value.

As shown in Table 6, with respect to the electrolytes of Examples 9 to 11 in which 1.5 wt% or more of the specific acid was added, the withstand voltage hardly decreased even when the amount of chlorine ions increased. That is, it was confirmed that when the specific acid was contained in an amount of 1.5 wt% or more based on the entire electrolytic solution, the chlorine ion resistance performance was further improved dramatically. From the above results, it was confirmed that Examples 8 to 11 had high chlorine ion resistance and suppressed corrosion reactions.

(9-1. Voltage resistance characteristics of combinations of different acids 1)
Electrolytes of Examples 12 to 14 shown in Table 5 below were prepared.

As shown in Table 7, in addition to the 2,6-dihydroxybenzoic acid represented by the above structural formula (Chemical formula 1), benzoic acid was added to the electrolytes of Examples 12 to 14 as an anion component of the solute. . Furthermore, Examples 12 to 14 differ in the amount of 2,6-dihydroxybenzoic acid added. In Examples 12 to 14, 2,6-dihydroxybenzoic acid and benzoic acid were added in equimolar amounts, and triethylamine was added in an equimolar amount with respect to the total molar amount of 2,6-dihydroxybenzoic acid and benzoic acid. ing. In addition, phosphoric acid ester and p-nitrobenzoic acid are added in a total of 3.5 wt% based on the total amount of the electrolyte. The moisture content was adjusted to 0.5 wt%.

The electrolytic solutions of Examples 11 to 14 were tested for withstand voltage characteristics in relation to the amount of chlorine ions in the same manner as in Examples 1 to 5 and Comparative Examples 1 to 3. However, in Examples 12 to 14, tests were also conducted in which the amount of chlorine ions added was 15, 20, and 30 ppm. The results are shown in Table 8 below. In Table 8, the withstand voltage when no chlorine ions were added was taken as the reference value, and the withstand voltage when each amount of chlorine ions was added was expressed as a percentage of the reference value.

As shown in Table 8, it was confirmed that even when the specific acid was used together with benzoic acid, the effect of maintaining voltage resistance against chlorine ions was maintained. Further, regarding the electrolytes of Examples 12 to 14 in which 1.5 wt% or more of the specific acid was added, even when other acids were added, the withstand voltage hardly decreased even when the amount of chlorine ions increased. That is, it was confirmed that when the specific acid was contained in an amount of 1.5 wt% or more based on the entire electrolytic solution, the chlorine ion resistance performance was further improved dramatically, regardless of the presence of other acids. From the above results, it was confirmed that Examples 12 to 14 had high chlorine ion resistance and suppressed corrosion reactions.

(9-2. Voltage resistance characteristics of combinations of different acids 2)
Electrolytes of Examples 15 to 18 shown in Table 9 below were prepared.

As shown in Table 9, the electrolytic solutions of Examples 15 to 18 differ from the electrolytic solutions of Examples 11 to 14 in that equimolar amounts of azelaic acid were added to 2,6-dihydroxybenzoic acid. Other cationic components, additives, amounts added, and moisture content are the same as in the electrolytes of Examples 11 to 14.

The electrolytic solutions of Examples 15 to 18 were tested for withstand voltage characteristics in relation to the amount of chlorine ions in the same manner as in Examples 1 to 5 and Comparative Examples 1 to 3. However, in Examples 16 to 18, tests were also conducted in which the amount of chlorine ions added was 15, 20, and 30 ppm. The results are shown in Table 10 below. In Table 10, the withstand voltage when no chlorine ions were added was taken as the reference value, and the withstand voltage when each amount of chlorine ions was added was expressed as a percentage of the reference value.

As shown in Table 10, it was confirmed that even when the specific acid was used together with another acid, azelaic acid, the effect of maintaining voltage resistance against chlorine ions was maintained. Further, regarding the electrolytes of Examples 16 to 18 in which 1.5 wt % or more of the specific acid was added, even when other acids were added, the withstand voltage hardly decreased even when the amount of chlorine ions increased. That is, it was confirmed that when the specific acid was contained in an amount of 1.5 wt% or more based on the entire electrolytic solution, the chlorine ion resistance performance was further improved dramatically, regardless of the presence of other acids. From the above results, it was confirmed that Examples 15 to 18 had high chlorine ion resistance and suppressed corrosion reactions.

(10. Voltage resistance characteristics due to specific acid in excess acid state)
The electrolytic solutions of Examples 19 to 23 and the electrolytic solutions of Comparative Examples 4 and 5 shown in Table 11 below were prepared.

As shown in Table 11, ammonium benzoate was added as a solute to the electrolytes of Examples 19 to 23 and the electrolytes of Comparative Examples 4 and 5. Further, 2,6-dihydroxybenzoic acid represented by the above structural formula (Chemical formula 1) was added to the electrolytes of Examples 19 to 23 as a specific acid. Ammonium benzoate has an anion component and a cation component in a 1:1 ratio, but by further adding 2,6-dihydroxybenzoic acid, Examples 19 to 23 produced an electrolyte with an excess of anion components, that is, an excess of acid. It becomes.

Furthermore, Examples 19 to 23 differ in the degree of excess acid. That is, in the electrolytic solution of Example 19, 0.1 wt% of 2,6-dihydroxybenzoic acid was added to the total amount of the electrolytic solution. In the electrolytic solution of Example 20, 0.3 wt% of 2,6-dihydroxybenzoic acid was added to the total amount of the electrolytic solution. In the electrolytic solution of Example 22, 1 wt % of 2,6-dihydroxybenzoic acid was added to the total amount of the electrolytic solution. In the electrolytic solution of Example 23, 3 wt% of 2,6-dihydroxybenzoic acid was added to the total amount of the electrolytic solution. Note that in Comparative Example 5, the amount of ammonium benzoate was increased compared to Comparative Example 4.

In addition, a total of 3.5 wt% of phosphoric acid ester and p-nitrobenzoic acid were added to the electrolyte solutions of Examples 19 to 23 and Comparative Examples 4 and 5 based on the total amount of the electrolyte solution. There is.

The electrolytic solutions of Examples 19 to 23 and the electrolytic solutions of Comparative Examples 4 and 5 were tested for withstand voltage characteristics in relation to the amount of chlorine ions. I did the same. The results are shown in Table 12 below. In Table 12, the withstand voltage when no chlorine ions were added was taken as the reference value, and the withstand voltage when each amount of chlorine ions was added was expressed as a percentage of the reference value.

As shown in Table 12, it was confirmed that the corrosion inhibiting effect against chlorine ions was exerted even when the electrolytic solution contained a specific acid and the electrolytic solution was excessively acidic. Furthermore, in the electrolytic solutions of Examples 19 to 23, less than 1.5 wt% of the specific acid was added to the entire electrolytic solution, but if the electrolytic solution was too acidic, the addition of a small amount of the specific acid would be difficult. However, it was confirmed that the withstand voltage hardly decreases even if the amount of chlorine ions increases. The amount of the specific acid added is preferably 0.1 wt% or more, more preferably 0.3 wt% or more, particularly preferably 0.5 wt% or more, and as the amount of the specific acid added increases, the chloride ion resistance improves. It was confirmed that the corrosion reaction suppression effect was improved.

(11. Voltage resistance characteristics with equimolar acid/base)
Electrolytes of Examples 24 to 31 and Comparative Example 6 shown in Table 13 below were prepared.

As shown in Table 13, 2,6-dihydroxybenzoic acid represented by the above structural formula (Chemical formula 1) was added to the electrolytes of Examples 24 to 31. Additionally, azelaic acid was added as an anionic component of the solute. However, Examples 24 to 31 differ in the amount of 2,6-dihydroxybenzoic acid added. In the electrolyte solution of Example 25, the amount of 2,6-dihydroxybenzoic acid added was 0.1 wt% with respect to the total amount of the electrolyte solution, and in the electrolyte solution of Example 29, the amount of 2,6-dihydroxybenzoic acid added was 0.1 wt% with respect to the total amount of the electrolyte solution. is 1.3 wt% based on the total amount of electrolyte solution, and in the electrolyte solutions of Examples 25 to 29, the amount of 2,6-dihydroxybenzoic acid added is 0.1 wt% or more based on the total amount of electrolyte solution. It is less than .5wt%. Further, the electrolytic solution of Example 24 differs in that the amount of 2,6-dihydroxybenzoic acid added is a very small amount of 0.05 wt% based on the total amount of the electrolytic solution.

As a cation component, ammonia was added to the electrolyte solutions of Examples 24 to 31 in an amount equal to the total molar amount of 2,6-dihydroxybenzoic acid and azelaic acid. In addition, a total of 3.5 wt% of phosphoric acid ester and p-nitrobenzoic acid were added to the electrolyte solutions of Examples 24 to 31 based on the total amount of the electrolyte solution. The electrolytic solution of Comparative Example 6 had the same types of solvent and additives as Examples 24 to 31, except that no specific acid was added, and the acid-base ratio was also equimolar.

The electrolytes of Examples 24 to 31 and Comparative Example 6 were tested for withstand voltage characteristics in relation to the amount of chlorine ions in the same manner as in Examples 1 to 5 and Comparative Examples 1 to 3. The results are shown in Table 14 below. In Table 14, the withstand voltage when no chlorine ions were added was taken as the reference value, and the withstand voltage when each amount of chlorine ions was added was expressed as a percentage of the reference value.

As shown in Table 14, the electrolytes of Examples 29 and 31 have a withstand voltage higher than that of Comparative Example 6 in terms of total chlorine ion content, but when the amount of 2,6-dihydroxybenzoic acid added is 0.1 wt% or more, It was confirmed that the electrolytic solutions of certain Examples 25 to 29 also had voltage resistance characteristics superior to those of Comparative Example 6. That is, by selecting 2,6-dihydroxybenzoic acid and 2,4,6-trihydroxybenzoic acid, which have hydroxyl groups at both ortho positions with respect to the carboxylic acid group, as specific acids, the acid base in the electrolyte becomes acidic. Even if it is not excessive but equimolar, if the amount of the specific acid added is 0.1 wt% or more, the chlorine ion resistance will improve as the amount of the specific acid added increases, and the effect of inhibiting corrosion reactions will improve. It was confirmed that

Furthermore, the electrolytic solution of Example 24 exceeded the withstand voltage characteristics of the electrolytic solutions of Comparative Examples 1 to 6 even when the amount of 2,6-dihydroxybenzoic acid added was 0.05 wt%. That is, by selecting 2,6-dihydroxybenzoic acid and 2,4,6-trihydroxybenzoic acid, which have hydroxyl groups at both ortho positions based on the carboxylic acid group, as specific acids and adding azelaic acid, electrolysis can be performed. Even if the acid bases in the solution are equimolar and not in excess, if the amount of the specific acid added is more than a trace amount of 0.05 wt%, the chloride ion resistance will decrease as the amount of the specific acid added increases. It was confirmed that the corrosion reaction suppression effect was improved.

Claims (11)

A solid electrolytic capacitor containing 30 ppm or less of chlorine ions,
A capacitor element comprising an anode foil and a cathode foil facing each other with a separator interposed therebetween;
a solid electrolyte layer made of a conductive polymer and formed within the capacitor element;
an electrolytic solution filled in a void in the capacitor element in which the solid electrolyte layer is formed;
Equipped with
The electrolyte is
one or more acids selected from 2,6-dihydroxybenzoic acid, 3,5-dihydroxybenzoic acid and 2,4,6-trihydroxybenzoic acid;
46.1 wt% or more of ethylene glycol in the electrolyte;
including;
A solid electrolytic capacitor featuring: The electrolyte is
further comprising an acid different from 2,6-dihydroxybenzoic acid, 3,5-dihydroxybenzoic acid and 2,4,6-trihydroxybenzoic acid;
The solid electrolytic capacitor according to claim 1, characterized in that: the different acids are benzoic acid, salicylic acid, phthalic acid, azelaic acid, adipic acid or borodisalicylic acid;
The solid electrolytic capacitor according to claim 2, characterized in that: The electrolyte solution contains a base,
the molar concentration of one or more acids selected from 2,6-dihydroxybenzoic acid, 3,5-dihydroxybenzoic acid and 2,4,6-trihydroxybenzoic acid is higher than the molar concentration of the base;
The solid electrolytic capacitor according to claim 1, characterized in that: The electrolyte solution contains a base,
The total molar concentration of the different acid and one or more acids selected from 2,6-dihydroxybenzoic acid, 3,5-dihydroxybenzoic acid, and 2,4,6-trihydroxybenzoic acid is equal to the molar concentration of the base. higher than the concentration,
The solid electrolytic capacitor according to claim 2 or 3, characterized in that: The one or more acids selected from 2,6-dihydroxybenzoic acid, 3,5-dihydroxybenzoic acid, and 2,4,6-trihydroxybenzoic acid have a total content of 0.1 wt% based on the total amount of the electrolytic solution. Including more than
The solid electrolytic capacitor according to claim 4 or 5, characterized in that: The electrolytic solution contains the 2,6-dihydroxybenzoic acid, the 2,4,6-trihydroxybenzoic acid, or both,
The 2,6-dihydroxybenzoic acid, the 2,4,6-trihydroxybenzoic acid, or both contain a total of 0.1 wt% or more based on the total amount of the electrolyte;
The solid electrolytic capacitor according to claim 1, characterized in that: The electrolytic solution contains the 2,6-dihydroxybenzoic acid, the 2,4,6-trihydroxybenzoic acid, or both,
the different acid is azelaic acid,
The 2,6-dihydroxybenzoic acid, the 2,4,6-trihydroxybenzoic acid, or both contain a total of 0.05 wt% or more based on the total amount of the electrolyte;
The solid electrolytic capacitor according to claim 2, characterized in that: The moisture content of the electrolyte is 0.01 wt% or more and 5 wt% or less,
The solid electrolytic capacitor according to any one of claims 1 to 8, characterized by: The electrolyte further contains γ-butyrolactone;
The solid electrolytic capacitor according to any one of claims 1 to 9, characterized by: The electrolyte further contains at least one solvent selected from sulfolane, 3-methylsulfolane, and 2,4-dimethylsulfolane;
The solid electrolytic capacitor according to any one of claims 1 to 10, characterized by: