JP2023097332A - Electrolyte for electrolytic capacitor and electrolytic capacitor - Google Patents

Abstract

To provide electrolyte for an electrolytic capacitor, in which the generation of hydrogen gas is suppressed in high-pressure use and which is prolonged in the life as a result, and an electrolytic capacitor.SOLUTION: Electrolyte for an electrolytic capacitor includes: a glycol-based solvent; a voltage resistance improver; and an anion component containing boric acid. The voltage resistance improver is included in an amount of 5 wt% or more with respect to a whole amount of the electrolyte for the electrolytic capacitor. Boric acid is included in the range of 8.5 wt% or less with respect to a whole amount of the electrolyte for the electrolytic capacitor. A ratio in a whole anion component in the electrolyte for the electrolytic capacitor. is 0.4 or more in a weight ratio. The electrolytic capacitor comprises a capacitor element into which the electrolyte for the electrolytic capacitor is impregnated. The capacitor element includes metal for a valve, and includes: a positive electrode foil in which a dielectric oxide film is formed on a front surface; and a negative electrode foil including the metal for the valve.SELECTED DRAWING: Figure 1

Description

The present invention relates to an electrolytic solution for electrolytic capacitors and an electrolytic capacitor containing the electrolytic solution.

Electrolytic capacitors have valve metals such as tantalum or aluminum as anode and cathode foils. The anode foil is expanded by forming a valve metal into a sintered body or an etched foil, and has a dielectric oxide film layer on the expanded surface. An electrolytic solution is interposed between the anode foil and the cathode foil. The electrolyte is in close contact with the uneven surface of the anode foil and functions as a true cathode.

The cathode foil of an electrolytic capacitor undergoes a dissolution reaction due to hydration, and this dissolution reaction generates hydrogen gas. That is, at the cathode foil of the electrolytic capacitor, hydrogen gas is generated according to the following chemical reaction formula (1). As for water, it is presumed that it is mixed in during the manufacturing process of the electrolytic capacitor.

Hydrogen gas increases the internal pressure of the electrolytic capacitor, which may cause swelling of the case that houses the capacitor element, swelling of the sealing body that seals the capacitor element, and opening of the pressure release valve provided in the electrolytic capacitor.

Therefore, it is conventionally known to subject the cathode foil to immersion treatment or chemical conversion treatment in an aqueous solution of phosphoric acid to coat the cathode foil with an oxide film, thereby protecting the valve action metal constituting the cathode foil from the electrolytic solution. (See Patent Document 1, for example).

JP 2010-219083

However, for example, in electrolytic capacitors for high-voltage applications with a rating of 550 V or more, even if an oxide film is formed on the cathode foil, if it is exposed to a high-temperature environment for a long time, the oxide film will deteriorate due to hydration. Experiments by the present inventors have revealed that the base metal, the valve action metal, is exposed. Since the oxide film of the cathode foil is thin, the base metal of the cathode foil is particularly likely to be exposed. That is, in an electrolytic capacitor for high voltage use, when exposed to a high temperature environment for a long time, the following chemical reaction formula (2) occurs in the cathode foil.

Then, even if the cathode foil is protected with an oxide film, deterioration of the oxide film causes a dissolution reaction of the valve action metal forming the cathode foil, generating hydrogen gas and shortening the life of the electrolytic capacitor.

The present invention has been proposed to solve the above problems, and its object is to provide an electrolytic solution for an electrolytic capacitor and an electrolytic capacitor that suppresses the generation of hydrogen gas in high-pressure applications and has a long life. .

In order to achieve the above objects, an electrolytic capacitor for electrolytic capacitors according to the present invention is an electrolytic solution for electrolytic capacitors used in electrolytic capacitors, comprising a glycol-based solvent and 5 wt % of the total amount of the electrolytic solution for electrolytic capacitors. The breakdown voltage improving agent contained above and an anion component containing boric acid are contained, and the boric acid is contained in an amount of 8.5 wt% or less with respect to the total amount of the electrolytic solution for electrolytic capacitors, and the electrolytic solution for electrolytic capacitors contains The weight ratio of the anion component to all the anion components is 0.4 or more.

Mannitol may be further included, and the content ratio B/A of the mannitol (B) to the boric acid (A) may be 0.4 or more in terms of weight ratio.

The amount of boric acid may be 5.5 wt % or more with respect to the total amount of the electrolytic solution for electrolytic capacitors.

The electrolytic solution for an electrolytic capacitor, a capacitor element impregnated with the electrolytic solution for an electrolytic capacitor, an anode foil contained in the capacitor element, containing a valve metal, and having a dielectric oxide film formed on its surface; An electrolytic capacitor including a cathode foil that is included in the capacitor element and contains a valve metal is also an aspect of the present invention.

According to the present invention, generation of hydrogen gas is suppressed, and the life of the electrolytic capacitor is extended.

It is a graph of each embodiment and a comparative example which shows the transition of the electric potential for 5 minutes after 1 minute passed from a steady state. It is a graph which shows the relationship between a boric-acid density|concentration and an electric potential. 4 is a graph showing the relationship between the ratio of mannitol to boric acid and potential. It is a graph showing the relationship between boric acid and ΔESR.

An electrolytic solution for an electrolytic capacitor and an electrolytic capacitor according to embodiments of the present invention will be described. In addition, this invention is not limited to embodiment described below.

(Electrolytic capacitor)
An electrolytic capacitor is a passive device that stores and discharges electric charge according to its capacitance. This electrolytic capacitor has a wound or laminated capacitor element. A capacitor element includes an anode foil, a cathode foil, a separator, and an electrolyte for an electrolytic capacitor (hereinafter referred to as electrolyte). A dielectric oxide film is formed on the surface of the anode foil. An oxide film is also formed on the surface of the cathode foil. A separator is interposed between the anode foil and the cathode foil. The electrolytic solution is impregnated in the capacitor element, closely adheres to the uneven surface of the dielectric oxide film of the anode foil, and functions as a true cathode.

The capacitor element is housed in a case and sealed with a sealing member. The case has a cylindrical shape with a bottom that accommodates the capacitor element, and is made of aluminum, for example. A pressure valve that opens when the pressure inside the case exceeds a predetermined value is formed at the bottom of the case. The sealing member is an elastic insulator such as a rubber plate, or a laminate of a rigid substrate insulating plate such as a synthetic resin plate and an elastic insulator, and is attached to the opening of the case by crimping to seal the opening of the case. . Lead terminals are connected to the anode foil and the cathode foil, and the lead terminals are electrically connected to external terminals. An external terminal is led out to the outside through a through hole of the sealing member.

(electrode foil)
The anode foil and the cathode foil are long foil bodies made of a valve metal. Valve metals include aluminum, tantalum, niobium, niobium oxide, titanium, hafnium, zirconium, zinc, tungsten, bismuth and antimony. The purity of the anode foil is desirably 99.9% or higher, and the purity of the cathode foil is desirably about 99% or higher. Impurities such as silicon, iron, copper, magnesium and zinc may be contained.

The anode foil is a sintered body obtained by sintering powder of a valve metal, or an etched foil obtained by subjecting a stretched foil to an etching treatment, and the surface of the anode foil is enlarged. The spreading structure consists of tunnel-like pits, spongy pits, or voids between dense particles. The tunnel-shaped pits may be dug leaving the deep part of the anode foil, or may be formed so as to penetrate the anode foil.

This expanded surface structure is typically formed by DC etching or AC etching in which a direct current or alternating current is applied in an acidic aqueous solution in which halogen ions such as hydrochloric acid are present. It is formed by depositing or sintering metal particles or the like on the core.

The dielectric oxide film is typically an oxide film formed on the surface layer of the anode foil, and if the anode foil is made of aluminum, it is aluminum oxide obtained by oxidizing the enlarged surface structure region. This dielectric oxide film is formed by a chemical conversion treatment in which a voltage is applied in a halogen ion-absent solution of adipic acid, boric acid, phosphoric acid, or the like.

The cathode foil may be a plain foil without an enlarged surface structure, or may have an enlarged surface structure by vapor deposition, sintering or etching in the same manner as the anode foil. A thin oxide film (about 1 to 10 V) may also be formed on the surface layer of the cathode foil by chemical conversion treatment. The oxide film of the cathode foil may be formed intentionally by chemical conversion treatment, or may be a natural oxide film naturally oxidized in the air. Furthermore, a layer made of metal nitride, metal carbide, metal carbonitride, or carbide may be formed on the oxide film.

The lead terminals are connected to the anode foil and the cathode foil by stitching, ultrasonic welding, or the like. The lead terminals are metal wires of aluminum or the like, and are responsible for electrical connection between the anode foil and the cathode foil and the outside by connecting to external terminals.

(Electrolyte)
(Glycol type)
The electrolytic solution is a mixed solution in which a solute is dissolved in a solvent, and a pressure resistance improver or other additives are added as necessary. As a solvent, a glycol-based solvent is used in order to cope with high-pressure applications. A glycol system is a compound having a structure in which the hydrogens bonded to two carbon atoms of an aliphatic hydrocarbon having two or more carbon atoms or a cycloaliphatic hydrocarbon are substituted one by one with a hydroxy group. and includes ethylene glycol, propylene glycol, diethylene glycol, methoxypropylene glycol, and the like. The electrolytic solution may contain one type of glycol-based solvent, or may contain two or more types of glycol-based solvents.

Furthermore, as a solvent, a glycol-based solvent may be used alone, or a glycol-based solvent may be used in combination with another solvent. Other types of solvents may be either protic polar solvents or aprotic polar solvents. Representative examples of protic polar solvents include monohydric alcohols, polyhydric alcohols, oxyalcohols, and water. Typical aprotic polar solvents include sulfones, amides, lactones, cyclic amides, nitriles, sulfoxides and the like.

Examples of monohydric alcohols include ethanol, propanol, butanol, pentanol, hexanol, cyclobutanol, cyclopentanol, cyclohexanol, and benzyl alcohol. Polyhydric alcohols and oxyalcohol compounds include glycerin, methyl cellosolve, ethyl cellosolve, dimethoxypropanol, and the like. Sulfone-based solvents include dimethylsulfone, ethylmethylsulfone, diethylsulfone, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, and the like. Examples of amides include N-methylformamide, N,N-dimethylformamide, N-ethylformamide, N,N-diethylformamide, N-methylacetamide, N,N-dimethylacetamide, N-ethylacetamide, N,N- diethylacetamide, hexamethylphosphoricamide and the like. Lactones and cyclic amides include γ-butyrolactone, γ-valerolactone, δ-valerolactone, N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, butylene carbonate and isobutylene carbonate. Nitrile-based solvents include acetonitrile, 3-methoxypropionitrile, glutaronitrile, and the like. The sulfoxide type includes dimethyl sulfoxide and the like.

(Boric acid)
The electrolyte contains boric acid as a solute. Boric acid is contained within the range of 8.5 wt% or less in the total amount of the electrolytic solution. By containing boric acid in the electrolyte in this range, even if the electrolytic capacitor is exposed to a high temperature environment for a long time as a high voltage application, the oxide film of the cathode foil is dissolved by the moisture in the electrolyte, and the cathode foil Dissolution of the underlying valve action metal, or both, is suppressed. When the dissolution of the oxide film of the cathode foil is suppressed, the valve-acting metal, which is the base metal of the cathode foil, is less likely to be exposed to the electrolyte, and the valve-acting metal reacts with the moisture contained in the electrolyte to generate hydrogen gas. phenomenon is suppressed. By suppressing the generation of hydrogen gas, the valve opening of the electrolytic capacitor is suppressed, and the life of the electrolytic capacitor is extended.

Preferably, boric acid is 8.0 wt% or less in the total amount of the electrolytic solution. When boric acid is contained in the electrolytic solution in this range, dissolution of the oxide film of the cathode foil due to moisture in the electrolytic solution, dissolution of the valve action metal, which is the base metal of the cathode foil, or both of these are particularly suppressed. .

However, when the amount of boric acid in the electrolytic solution is small, the ESR (equivalent series resistance) of the electrolytic capacitor exposed to a high-temperature environment for a long time deteriorates significantly. Therefore, when boric acid is contained within the range of 8.5 wt% or less in the total amount of the electrolytic solution, boric acid is contained so as to account for 0.4 or more in weight ratio among all anions contained in the electrolytic solution. . When boric acid accounts for 0.4 or more by weight in all anions, even if boric acid is 8.5 wt% or less in the total amount of the electrolyte, the ESR of the electrolytic capacitor exposed to a high temperature environment for a long time aggravation of More preferably, the proportion of boric acid is 5.5 wt % or more in the total amount of the electrolytic solution. If boric acid is 5.5 wt % or more in the total amount of the electrolytic solution, the ESR of the electrolytic capacitor can be further reduced.

Preferably, when boric acid is contained within the range of 8.5 wt% or less in the total amount of the electrolytic solution, boric acid is contained so as to account for 0.5 or more in weight ratio among all anions contained in the electrolytic solution. Let When boric acid accounts for 0.5 or more by weight in all anions, even if boric acid is 8.5 wt% or less in the total amount of the electrolyte, the ESR of the electrolytic capacitor exposed to a high temperature environment for a long time aggravation is greatly suppressed.

Examples of anions other than boric acid that can be contained in the electrolytic solution include organic acids, inorganic acids, and composite compounds of organic acids and inorganic acids. 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, Carboxylic acids such as 1,6-decanedicarboxylic acid, 1,7-octanedicarboxylic acid, azelaic acid, undecanedioic acid, dodecanedioic acid, tridecanedioic acid, t-butyladipic acid, 11-vinyl-8-octadecenedioic acid , phenols, and sulfonic acids. Examples of inorganic acids include phosphorous acid, hypophosphorous acid, carbonic acid, and silicic acid. Compound compounds of organic acids and inorganic acids include borodisalicylic acid, borodisalicylic acid, borodiglycolic acid, and the like.

The electrolytic solution preferably contains mannite together with boric acid. Boric acid and mannite may form a complex compound. With respect to boric acid and mannitol, the weight ratio B/A of mannitol to boric acid is preferably 0.4 or more, where the weight A of boric acid and the weight B of mannitol in the electrolytic solution are used. Both boric acid and mannite are included, and at this weight ratio, even if the electrolytic capacitor is exposed to a high temperature environment for a long time as a high voltage application, the oxide film formed on the cathode foil will dissolve in the electrolyte. are restrained from doing so.

Preferably, the content ratio B/A of mannitol to boric acid is 0.9 or more in weight ratio. When both boric acid and mannite are contained, and at this weight ratio, dissolution of the oxide film of the cathode foil, dissolution of the valve action metal, which is the base metal of the cathode foil, or both of these due to the moisture in the electrolytic solution Suppressed.

The electrolytic solution contains cations as well as anions as solutes. Cations include ammonium, quaternary ammonium, quaternary amidinium, amine, sodium, potassium and the like. Quaternary ammonium includes tetramethylammonium, triethylmethylammonium, tetraethylammonium and the like. Examples of quaternary amidiniums include ethyldimethylimidazolinium and tetramethylimidazolinium. Amines of the amine salt include primary amines, secondary amines, and tertiary amines. Examples of primary amines include methylamine, ethylamine and propylamine; examples of secondary amines include dimethylamine, diethylamine, ethylmethylamine and dibutylamine; examples of tertiary amines include trimethylamine, triethylamine, tributylamine and ethyldimethylamine; and ethyldiisopropylamine.

The anions and cations may be added to the electrolytic solution in the form of salts having ion dissociation properties, or the acid serving as the anion and the base serving as the cation may be separately added to the electrolytic solution as solute components. Anions and cations can be used either singly or in combination of two or more.

(Pressure resistance improver)
The electrolyte contains polyoxyalkylene polyols such as polyethylene glycol, polyglycerin, polyoxyethylene glycerin, and polypropylene glycol, colloidal silica, silicone oil, polyvinyl alcohol, and the like, as pressure resistance improvers. The breakdown voltage improving agent is contained in an amount of 5 wt % or more with respect to the total amount of the electrolytic solution. By containing these breakdown voltage improvers in this range, the breakdown voltage of the electrolytic capacitor can be increased to 650 V or higher.

(other additives)
Other additives can also be added to the electrolytic solution. Examples of the additive include phosphoric acid, phosphoric acid compounds such as phosphoric acid esters, and nitro compounds. Nitro compounds include o-nitrobenzoic acid, m-nitrobenzoic acid, p-nitrobenzoic acid, o-nitrophenol, m-nitrophenol, p-nitrophenol, p-nitrobenzene, o-nitrobenzene and m-nitrobenzene. etc. Nitro compounds have the ability to absorb hydrogen gas.

(separator)
The separator is interposed between the anode foil and the cathode foil to prevent short-circuiting between the anode foil and the cathode foil, and retains the electrolytic solution. Separators are made of cellulose such as kraft, manila hemp, esparto, hemp, rayon, and mixed paper thereof, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyester resins such as their derivatives, polytetrafluoroethylene resin, polyfluoride, etc. Polyamide resins such as vinylidene resins, vinylon resins, aliphatic polyamides, semi-aromatic polyamides, and wholly aromatic polyamides, polyimide resins, polyethylene resins, polypropylene resins, trimethylpentene resins, polyphenylene sulfide resins, acrylic resins, polyvinyl alcohol resins, etc., and these resins can be used singly or in combination.

(Example)
The present invention will be described in more detail below based on examples. In addition, the present invention is not limited to the following examples.

Electrolytic capacitors of Examples 1 to 5 and Comparative Examples 1 and 2 were produced as follows. The electrolytic capacitors of Examples 1 to 5 and Comparative Examples 1 and 2 have wound capacitor elements with a diameter of 10 mm and a height of 25 mm. Anode foils, cathode foils and separators are common to Examples 1 to 5 and Comparative Examples 1 and 2.

The anode foil is strip-shaped aluminum foil. The anode foil was subjected to a direct-current etching treatment to form surface-enlarging layers composed of tunnel-shaped etching pits on both sides of the foil. After forming the surface-enlarging layer, the anode foil was subjected to chemical conversion treatment for forming a dielectric oxide film on the surface of the surface-enlarging layer. The cathode foil is strip-shaped aluminum foil. The cathode foil was subjected to an alternating current etching treatment to form a surface enlarging layer composed of spongy etching pits on both sides of the foil.

In the AC etching treatment for the cathode foil, the cathode foil is immersed in an acidic aqueous solution containing hydrochloric acid at a liquid temperature of 25° C. and about 8% by weight of hydrochloric acid as the main electrolyte, and a current of 10 Hz and a current density of 0.14 A/cm ² is applied to the substrate. It was applied for 5 minutes to expand both sides of the aluminum foil. Then, the cathode foil was subjected to a chemical conversion treatment to form an oxide film on the surface of the surface enlarging layer. In the chemical conversion treatment of the cathode foil, after removing chlorine adhering during the AC etching treatment with an aqueous solution of phosphoric acid, a voltage of 10 V was applied in an aqueous solution of ammonium dihydrogen phosphate.

An aluminum tab-shaped lead terminal was ultrasonically connected to each of the anode foil and the cathode foil. A separator was interposed between the anode foil and the cathode foil and wound to form a capacitor element. As a separator, a Kraft separator was sandwiched and wound to form a capacitor element.

The electrolytic capacitors of Examples 1 to 5 and Comparative Examples 1 and 2 have different electrolytes. A capacitor element was impregnated with an electrolytic solution prepared as shown in Table 1 below, housed in a cylindrical case with a pressure valve formed on the bottom, and the opening of the cylindrical case was sealed with a sealing body to obtain the 5 and the electrolytic capacitors of Comparative Examples 1 and 2 were produced. A voltage of 300 V was applied to the produced electrolytic capacitor to perform re-formation (aging).

(Table 1)

As shown in Table 1, in the electrolytes of Examples 1 to 5 and Comparative Examples 1 and 2, a mixed solution of ethylene glycol and diethylene glycol is used as a solvent in order to support the high pressure of the electrolytic capacitor. Further, the electrolytic solutions of Examples 1 to 5 and Comparative Examples 1 and 2 contained boric acid and 1,6-decanedicarboxylic acid as anions, ammonia was blown in as cations, mannitol was added, and phosphorus was added as an additive. Acid and nitro compounds are added, and silicone oil is added as a pressure resistance improver.

According to the composition ratio shown in Table 1 of the electrolytic solutions of Examples 1 to 5 and Comparative Examples 1 and 2, the electrolytic solutions of Examples 1 to 5 and Comparative Examples 1 and 2 have the amount of boric acid and the amount of boric acid in all anions. The ratio of acid and mannite (B) to boric acid (A) are different as shown in Table 2 below. The total anion is the total amount of boric acid and 1,6-decanedicarboxylic acid.

(Table 2)

(Deterioration of cathode foil)
The electrolytic capacitors of Examples 1 to 5 and Comparative Examples 1 and 2 were left unloaded in a high temperature environment of 150° C. for 1500 hours. These electrolytic capacitors were disassembled, the cathode foil was washed with water, and the potential (E vs. Pt) transition of the cathode foil was measured. The potential started to be measured after 1 minute from the steady state. The results are shown in Table 3 and FIG. Table 1 shows the potential of the cathode foil 10 seconds after the start of measurement. FIG. 1 is a graph of each embodiment and a comparative example showing the potential transition for 5 minutes from the steady state through the start of measurement.

(Table 3)

As shown in Table 3 and FIG. 1, in Examples 1 to 4 and Comparative Example 2, the potential increased rapidly from the start of measurement and reached 2 V in less than 4 minutes. On the other hand, in Comparative Example 1, the potential was small from the start of the measurement, and the potential increased gradually thereafter, reaching only over 0 V even after 5 minutes. From this result, it can be seen that except for Examples 1 to 4 and Comparative Example 2, only Comparative Example 1 is in the conversion mode for repairing the oxide film of the cathode foil. In other words, in Examples 1 to 4 and Comparative Example 2, dissolution of the oxide film on the cathode foil is suppressed even when the electrolytic capacitor is left in a high temperature environment of 150° C. for 1500 hours. Therefore, the valve-acting metal, which is the base metal of the cathode foil, is less likely to be exposed to the electrolyte, suppressing the reaction between the valve-acting metal and moisture contained in the electrolyte, thereby suppressing the generation of hydrogen gas.

FIG. 2 is a graph showing the relationship between the boric acid concentration and the potential, with the vertical axis representing the potential and the horizontal axis representing the boric acid concentration. As shown in FIG. 2, when the boric acid concentration increases beyond the boric acid concentration of 8.5 wt. %, the potential is kept high 10 seconds after the start of measurement when the boric acid concentration decreases. That is, it can be confirmed that deterioration of the oxide film of the cathode foil is suppressed when the concentration of boric acid is 8.5 wt % or less.

As shown in FIGS. 1 and 2, when the boric acid concentration is 8.0 wt % or less, the potential rises particularly rapidly from the start of measurement. That is, it can be confirmed that deterioration of the oxide film of the cathode foil is particularly suppressed when the concentration of boric acid is 8.0 wt % or less.

FIG. 3 is a graph showing the relationship between the potential and the ratio of mannitol to boric acid, with the vertical axis representing the potential and the horizontal axis representing the ratio of mannitol to boric acid. As shown in FIG. 3, when the ratio of mannitol to boric acid was 0.4 or more, the potential of the cathode foil increased 10 seconds after the start of measurement, indicating that deterioration of the oxide film of the cathode foil was suppressed. can be confirmed. When the ratio of mannitol to boric acid is 0.9 or more, the potential of the cathode foil becomes particularly high 10 seconds after the start of measurement, and it can be confirmed that deterioration of the oxide film of the cathode foil is particularly suppressed.

Here, electrolytic capacitors of Example 6 and Comparative Example 3 having the electrolytic solutions having the composition ratios shown in Table 4 below were produced. The electrolytic capacitors of Example 6 and Comparative Example 3 were manufactured in the same configuration, by the same manufacturing method, and under the same conditions as in Examples 1 to 5, except that the composition of the electrolytic solution was different.

(Table 4)

According to the composition ratios of the electrolyte solutions of Example 6 and Comparative Example 3 as shown in Table 4, the electrolyte solutions of Example 6 and Comparative Example 3 are as shown in Table 5 below. It can be seen that the ratio of mannite (B) to boric acid (A) is the same, and only the amount of boric acid is different. The total anion is the total amount of boric acid and 1,6-decanedicarboxylic acid.

(Table 5)

Then, similarly to Examples 1 to 5 and Comparative Examples 1 and 2, the electrolytic capacitors of Example 6 and Comparative Example 3 were left unloaded in a high temperature environment of 150° C. for 1500 hours. These electrolytic capacitors were disassembled, the cathode foil was washed with water, and the potential (E vs. Pt) transition of the cathode foil was measured. The results are shown in Table 6 below and added to Figure 2 using diamond plots. Table 6, like Table 1, shows the potential of the cathode foil 10 seconds after the start of measurement.

(Table 6)

As can be seen from the plots corresponding to Example 6 and Comparative Example 3 in Table 6 and FIG. 2, Comparative Example 3, which has a high boric acid concentration, has a small potential 10 seconds after the start of measurement, and an example with a low boric acid concentration. 6 shows that the potential is kept high 10 seconds after the start of measurement. That is, from the difference in the results between Example 6 and Comparative Example 3, which are the same in composition ratios other than the concentration of boric acid, there is a close causal relationship between the concentration of boric acid and the deterioration of the oxide film of the cathode foil. If the concentration of boric acid is 8.5 wt % or less, it is more likely that deterioration of the oxide film of the cathode foil is suppressed.

In addition, electrolytic capacitors of Examples 7 and 8 having electrolytic solutions having composition ratios shown in Table 7 below were produced. The electrolytic capacitors of Examples 7 and 8 were manufactured in the same configuration, by the same manufacturing method, and under the same conditions as those of Examples 1 to 5, except that the composition of the electrolytic solution was different. Table 7 also includes Example 6 above.

(Table 7)

According to the composition ratios shown in Table 7 of the electrolytic solutions of Examples 7 and 8 and the preceding Example 6, the electrolytic solutions of Examples 6 to 8 have the amount of boric acid and the amount of boric acid in all anions as shown in Table 8 below. It can be seen that the ratio of boric acid to the boric acid (A) is the same, and only the ratio of mannite (B) to boric acid (A) is different. The total anion is the total amount of boric acid and 1,6-decanedicarboxylic acid.

(Table 8)

Then, similarly to Examples 1 to 5 and Comparative Examples 1 and 2, the electrolytic capacitors of Examples 6 to 8 were left unloaded in a high temperature environment of 150° C. for 1500 hours. These electrolytic capacitors were disassembled, the cathode foil was washed with water, and the transition of the potential (E vs. Pt) of the cathode foil was measured. The results are shown in Table 9 below and added to FIG. 3 using diamond plots. Table 9 shows the potential of the cathode foil 10 seconds after the start of measurement.

(Table 9)

From the plots of Examples 6 to 8 corresponding to 6 to 8 in Table 9 and FIG. 3, the higher the ratio of mannite (B) to boric acid (A), the higher the potential 10 seconds after the start of measurement. I understand. That is, from the difference in the results of Examples 6 to 8 in which the composition ratio other than the ratio of mannite (B) to boric acid (A) is the same, if the concentration of boric acid is 8.5 wt% or less It is more likely that deterioration of the oxide film of the cathode foil is further suppressed by increasing the ratio of mannite (B) to boric acid (A).

(Measurement of equivalent series resistance (ESR))
The ΔESR of the electrolytic capacitors of Examples 1 to 5 and Comparative Example 2 were measured. In the measurement of ΔESR, the initial ESR is measured before the electrolytic capacitor is placed in a high temperature environment, placed in a high temperature environment of 150 ° C. for 150 hours, the ESR is measured again, and after exposure to the high temperature environment for the initial ESR. was calculated as ΔESR. ESR was measured by connecting terminals of an LCR meter. The measurement conditions were an ambient temperature of 20° C., an AC voltage level of 1.0 Vrms sine wave, and a measurement frequency of 100 kHz.

ΔESR is shown in Table 10 below. The horizontal axis represents the ratio of boric acid to all anions in the electrolytic solution, and the vertical axis represents ΔESR. FIG. 4 shows the relationship between boric acid and ΔESR.
(Table 10)

As shown in Table 10 and FIG. 4, the ΔESR of the electrolytic capacitors of each example is kept low except for Comparative Example 2. That is, it can be seen that ΔESR is kept low when the ratio of boric acid to all anions is 0.4 or more. Thus, it was confirmed that even if the electrolytic capacitor was exposed to a high-temperature environment for a long time, the ESR was suppressed when the ratio of boric acid to all anions was 0.4 or more. In particular, when the ratio of boric acid to all anions is 0.5 or more, ΔESR is further suppressed.

In general, if boric acid is contained in the range of 8.5 wt% or less with respect to the total amount of the electrolyte, and the ratio of boric acid to the total anion components in the electrolyte is 0.4 or more in weight ratio, the electrolytic capacitor Although the ESR is good, it was confirmed that the generation of hydrogen gas can be suppressed and the life is extended.

(anti-voltage test)
The withstand voltages of the electrolytic capacitors of Example 9 and Reference Example shown in Table 11 and the electrolytic capacitor of Example 4 were measured. The electrolytic capacitors of Example 9 and Reference Example were manufactured in the same configuration, by the same manufacturing method, and under the same conditions as those of Examples 1 to 5, except that the composition of the electrolytic solution was different.

(Table 11)

As shown in Table 11, Example 4, Example 9 and Reference Example differ in the amount of polymer added as a pressure resistance improver. The electrolytic capacitors of Examples 4, 9 and Reference were placed in a constant temperature bath at 105° C. and subjected to a current density of 2 mA/pc. A voltage was applied at , and the voltage value immediately before the voltage dropped by 200 V or more was taken as the withstand voltage value. The withstand voltage measurement results are shown in Table 12 below.

(Table 12)

As shown in Table 12, the withstand voltage exceeded 650 V when the polymer contained in the electrolytic solution as a withstand voltage improving agent was 5.0 wt % or more. As a result, for high-pressure applications, boric acid is contained in the range of 8.5 wt% or less with respect to the total amount of the electrolyte, and the proportion of the total anion components in the electrolyte is 0.4 or more by weight. On the other hand, it was confirmed that it is preferable to include the breakdown voltage improving agent in an amount of 5 wt % or more with respect to the total amount of the electrolytic solution.

In this example, the deterioration of the cathode foil (dissolution of the oxide film) was verified by measuring the transition of the potential of the cathode foil used in the electrolytic capacitor after being left unloaded in a high-temperature environment. When using a cathode foil that does not have an oxide film intentionally formed, it is possible to verify the deterioration of the cathode foil by measuring the amount of hydrogen gas generated by the electrolytic capacitor after being left unloaded in a high-temperature environment, for example. is.

Claims (4)

An electrolytic solution for electrolytic capacitors used in electrolytic capacitors,
a glycol-based solvent;
A breakdown voltage improving agent contained in an amount of 5 wt% or more with respect to the total amount of the electrolytic solution for electrolytic capacitors;
an anionic component comprising boric acid;
including
The boric acid is
Containing 8.5 wt% or less with respect to the total amount of the electrolyte for electrolytic capacitors,
The weight ratio of all anion components in the electrolytic solution for an electrolytic capacitor is 0.4 or more;
An electrolytic solution for an electrolytic capacitor, characterized by: further comprising mannite;
The content ratio B/A of the mannitol (B) to the boric acid (A) is 0.4 or more by weight,
The electrolytic solution for an electrolytic capacitor according to claim 1, characterized by: The boric acid is 5.5 wt% or more with respect to the total amount of the electrolytic solution for the electrolytic capacitor,
The electrolytic solution for an electrolytic capacitor according to claim 1 or 2, characterized by: The electrolytic solution for electrolytic capacitors according to claims 1 to 3,
a capacitor element impregnated with the electrolytic solution for an electrolytic capacitor;
an anode foil included in the capacitor element, containing a valve metal, and having a dielectric oxide film formed on its surface;
a cathode foil included in the capacitor element and containing a valve metal;
to provide
An electrolytic capacitor characterized by:

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