JP2001102260A - Electrolyte for electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrolytic capacitor which has low impedance characteristic can be used in 100V specification, and has high reliability at 125 deg.C. SOLUTION: In an electrolyte, a quaternary cyclic amidinum salt of benzoic acid is dissolved in a mixed solvent of γ-butyrolactone and ethylene glycol, colloidal silica and alkyl phosphoric acid having a 3-8C alkyl group are added, and dinitrophenol is added in the range of 0.01-4 wt.%. Since such an electrolyte is used, an electrolytic capacitor which has low impedance characteristic, stability of breakdown voltage characteristic or the like at 125 deg.C and satisfactory liquid leakage characteristic and can be used in 100V specification can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolytic capacitor, in particular, having a low impedance characteristic and capable of 100V specification.
Further, the present invention relates to an electrolytic capacitor having high reliability at 125 ° C.

[0002]

2. Description of the Related Art An electrolytic capacitor generally has a structure as shown in FIG. That is, a high-purity aluminum foil formed in a belt shape is chemically or electrochemically etched to enlarge the surface, and the expanded aluminum foil is subjected to a chemical conversion treatment in a chemical conversion solution such as an ammonium borate aqueous solution. The anode foil 2 having an oxide film layer formed on the surface of the aluminum foil and the cathode foil 3 having the same high-purity aluminum foil as the expanded foil are separated by a separator 8.
To form a capacitor element. In addition,
As shown in FIG. 2, an anode tab 4 and a cathode tab 5 are electrically connected to the anode foil 2 and the cathode foil 3 by electrical means, respectively. Wire 6 and cathode lead 7 are connected. The capacitor element 1 is impregnated with a driving electrolytic solution, and is housed in a metal bottomed outer case 10 having a bottom. Further, a sealing body 9 made of elastic rubber is housed at the open end of the outer case 10, and the open end of the outer case 10 is caulked to seal, thereby forming an electrolytic capacitor.

[0003]

In recent years, there has been an increasing demand for the use of electrolytic capacitors in the fields of vehicles and exchanges. In the on-vehicle field, it is a high-temperature specification, and in the exchange field, it is a long-life specification. In both cases, high reliability at 125 ° C. is required. In this field, low impedance characteristics and 100 V specification must be satisfied.

Heretofore, as an electrolytic solution of 100 V and 125 ° C., an electrolytic solution using ethylene glycol as a solvent and ammonium benzoate as a solute has been used. I do not endure. In addition, as the conventional electrolytic solution for electrolytic capacitors having low impedance characteristics, γ-butyrolactone is used as a solvent, and an electrolytic solution using a phthalate or maleate of a quaternized cyclic amidinium as a solute is used. Withstand voltage is low and cannot meet 100V specification. Therefore, using γ-butyrolactone as a main solvent and using a quaternized cyclic amidinium salt of benzoic acid as a solute,
By adding silica particles or a phosphoric acid compound, which is known to have a withstand voltage improving effect, a withstand voltage characteristic of 100 V can be obtained. However, this electrolyte has problems such as a decrease in withstand voltage during a life test and the occurrence of leakage, and cannot satisfy high reliability at 125 ° C. In particular, in the electrolytic solution using a quaternized cyclic amidinium salt, there is a problem that leakage occurs, but with an electrolyte using γ-butyrolactone as a solvent and a quaternized cyclic amidinium salt of benzoic acid as a solute, This liquid leakage characteristic tends to deteriorate. As described above, in reality, it has not been possible to obtain an electrolytic capacitor that can satisfy the above-mentioned requirements.

Accordingly, the present invention is intended to improve this disadvantage, has low impedance characteristics, is capable of 100 V specification, and has stability such as withstand voltage characteristics at 125 ° C. and good liquid leakage characteristics. An object of the present invention is to provide an electrolytic capacitor having high reliability characteristics.

[0006]

According to the present invention, a quaternized cyclic amidinium salt of benzoic acid is dissolved in a mixed solvent of γ-butyrolactone and ethylene glycol, and colloidal silica and an alkyl phosphate represented by the formula (2) are dissolved. And dinitrophenol in the range of 0.01 to 4% by weight.

Embedded image

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of an aluminum electrolytic capacitor has the same structure as that of the prior art, as shown in FIGS. The capacitor element 1 is formed by winding an anode foil 2 and a cathode foil 3 with a separator 8 interposed therebetween. As shown in FIG. 2, an anode tab 4 and a cathode tab 5 are connected to the anode foil 2 and the cathode foil 3, respectively. The anode tab 4 and the cathode tab 5 are made of aluminum, and are composed of a flat portion connected to each foil and a round bar portion continuous with the flat portion. The round bar portion has an anode lead wire 6 and a cathode lead wire 7 respectively. Is connected. The respective foils and the electrode tabs are mechanically connected by a stitch method, ultrasonic welding, or the like.

The anode foil 2 is formed by chemically or electrochemically etching an aluminum foil having a purity of 99% or more in an acidic solution and expanding the surface of the aluminum foil, followed by a chemical conversion treatment in an aqueous solution of ammonium borate or ammonium adipate. And use an anodic oxide film layer formed on the surface.

[0009] Further, as the cathode foil, a foil obtained by etching an aluminum foil having a purity of 99% or more to enlarge the surface is used. As the cathode tab 5, an anodized film made of aluminum oxide formed on the surface by a chemical conversion treatment using an aqueous solution of ammonium borate, an aqueous solution of ammonium phosphate, or an aqueous solution of ammonium adipate is used.

[0010] The capacitor element 1 configured as described above
Is impregnated with an electrolytic solution for driving an electrolytic capacitor. Using a mixed solvent of γ-butyrolactone and ethylene glycol as an electrolytic solution, dissolving a quaternized cyclic amidinium salt of benzoic acid, adding colloidal silica and an alkyl phosphoric acid represented by the following formula (4), and further adding 0.01% An electrolytic solution to which about 4% by weight of dinitrophenol is added is used.

As a low-impedance electrolytic solution using γ-butyrolactone as a solvent, ethylene glycol is used as a secondary solvent in order to obtain a high-pressure 100V specification, and the chemical conversion of the electrolytic solution is improved. The content of ethylene glycol in the mixed solvent is 5 to 30 wt%, preferably 10 to 20 wt%. If the content is less than this range, the leakage current characteristics of the electrolytic capacitor will be reduced, and if it exceeds this range, the impedance characteristics will be reduced.

In this mixed solvent, a quaternized cyclic amidinium salt of benzoic acid is dissolved as a solute. The content of the quaternized cyclic amidinium salt of benzoic acid in the electrolyte is 5 to 30 watts.
When the amount is less than t%, preferably 10 to 20% by weight, the impedance characteristic is deteriorated. When the amount exceeds this range, the withstand voltage characteristic is deteriorated.

The quaternized cyclic amidinium ion serving as the cation component is a cation obtained by quaternizing a cyclic compound having an N, N, N'-substituted amidine group.
Examples of the cyclic compound having an N′-substituted amidine group include the following compounds. Imidazole monocyclic compound (1-
Methylimidazole, 1-phenylimidazole, 1,
2-dimethylimidazole, 1-ethyl-2-methylimidazole, 1,2-dimethylimidazole, 1,2,2
Imidazole homologs such as 4-trimethylimidazole, 1-ethyl-2,3-dimethylimidazole, 1,2,3,4-tetramethylimidazole, 1-methyl-2
Oxyalkyl derivatives such as -oxymethylimidazole and 1-methyl-2-oxyethylimidazole, nitro derivatives such as 1-methyl-4 (5) -nitroimidazole, 1,2-dimethyl-5 (4) -aminoimidazole and the like Aminoderivatives), benzimidazole compounds (1
-Methylbenzimidazole, 1-methyl-2-benzimidazole, 1-methyl-5 (6) -nitrobenzimidazole, etc., compounds having a 2-imidazoline ring (1-methylimidazoline, 1,2-dimethylimidazoline, 1 , 2,4-trimethylimidazoline, 1-methyl-2-phenylimidazoline, 1-ethyl-2-methyl-imidazoline, 1,4-dimethyl-2-ethylimidazoline, 1-methyl-2-ethoxymethylimidazoline, etc.), Compound having a tetrahydropyrimidine ring (1
-Methyl-1,4,5,6-tetrahydropyrimidine,
1,2-dimethyl-1,4,5,6-tetrahydropyrimidine, 1,5-diazabicyclo [4,3,0] nonene-5, and the like. Among them, quaternized amidinium such as 1-ethyl-2,3-dimethylimidazole and 1,2,3,4-tetramethylimidazole is preferred.

Then, colloidal silica and an alkyl phosphoric acid represented by the formula (2) are added. The electrolytic solution having the above configuration has a high conductivity and a withstand voltage characteristic of 100 V. Here, the colloidal silica is dispersed in a dispersion solvent and added as a colloid solution. The alkyl group of the alkyl phosphoric acid represented by Chemical Formula ₂ , R ₁ and R ₂ have 3 to 8 carbon atoms. If it is less than 3, the alkylphosphoric acid is hydrolyzed at high temperatures, and the withstand voltage characteristic is reduced. If it exceeds 8, the impedance characteristic is reduced. Therefore, high reliability at 125 ° C. cannot be obtained with an alkyl phosphoric acid having an alkyl group having less than 3 carbon atoms, such as diethyl phosphate.

The content of colloidal silica in the electrolyte is as follows:
2 to 12 wt%, preferably 4 to 8 wt%, if less than this range, the withstand voltage decreases, and if it exceeds this range, the impedance characteristics deteriorate. The content of the alkyl phosphoric acid in the electrolyte is 1 to 10 wt%, preferably 2 to 6 wt%,
Below this range, the withstand voltage decreases, and beyond this range, both the impedance characteristics and the withstand voltage characteristics decrease.

Then, 0.01 to 4% by weight of dinitrophenol is added. This can prevent liquid leakage. Outside of this range, the liquid leakage characteristics deteriorate.

The capacitor element 1 impregnated with the electrolytic solution as described above is accommodated in an outer case 10 made of aluminum having a bottomed cylindrical shape, and lead wires 6 and 7 are led out to the open end of the outer case 10. The sealing of the electrolytic capacitor is performed by inserting a sealing member 9 made of butyl rubber having a hole and crimping the end of the outer case 10.

The above-described electrolytic capacitor of the present invention has low impedance characteristics, is capable of 100 V specification,
Good stability such as withstand voltage characteristics at ℃ and good liquid leakage characteristics.

Here, the reason why the liquid leakage property is good in the present invention is considered to be as follows. In general, the mechanism by which the electrolyte in which the quaternized cyclic amidinium salt is dissolved leaks from the cathode lead portion is considered as follows. That is, in the conventional electrolytic capacitor,
Since the spontaneous immersion potential of the cathode lead shows a more noble potential than the spontaneous immersion potential of the cathode electrode foil, when left unloaded, a local battery is composed of the cathode lead and the cathode foil. A cathode current flows, and in a DC load state, more cathode current flows in the cathode lead wire than in the cathode foil. As described above, in both cases of load and no load, a cathode current flows through the cathode lead, and as a result, a reduction reaction of dissolved oxygen or hydrogen ions occurs on the cathode lead side, and a round bar of the cathode tab is formed. Hydrogen ions are generated at the interface between the electrolyte and the connection part.

Then, when the hydroxyl ions are generated in this manner, the quaternized cyclic amidinium is hydrolyzed,
Combines with hydroxyl ions, resulting in secondary amines. Further, when hydroxyl ions are generated and become basic at pH = 7 or more, γ-butyrolactone as a solvent is combined with hydroxyl ions by a hydrolysis reaction to form γ-hydroxybutyric acid. This reduces the hydroxyl ions and the basicity. Thus, when the basicity decreases, the secondary amine generated by the hydrolysis reaction of the quaternized cyclic amidinium becomes the quaternized cyclic amidinium again,
This quaternized cyclic amidinium has no volatility and is highly hygroscopic, so the quaternized cyclic amidinium regenerated between the round bar portion of the cathode lead wire and the sealing member absorbs moisture and becomes a liquid leakage state. Become. The above is inferred from the results of analysis that the liquid leakage is composed of most of water and quaternized cyclic amidinium.

[0021] Also, in the electrolytic solution using quaternized amidinium salt of γ-butyrolactone and benzoic acid, a liquid leakage state occurs due to the above-described reaction. Further, in this electrolyte, the pH must be increased in order to increase the electric conductivity, and therefore, the concentration of hydroxide ions in the electrolyte is increased, and the amount of the quaternized cyclic amidinium regenerated as a whole is increased. It seems that the leaked state became worse and the liquid leakage state became worse.

However, in the present invention, 0.01 to 4
It is thought that the reaction was caused by the reaction between the dinitrophenol and hydroxide ions because of the addition of dinitrophenol in an amount of about 10% by weight. The condition is improved.

Furthermore, when the external connection part on the anode side and the external connection part on the cathode side come into contact with each other when no load is left, if the anode lead wire is made of aluminum or the like which is more noble than the cathode foil, the anode side The local battery is composed of the lead wire and the cathode foil,
A reduction reaction of dissolved oxygen or hydrogen ions occurs near the lead wire. As a result, hydroxide ions are generated on the anode side, causing deterioration in sealing accuracy. However, the generation of hydroxide ions is also suppressed on the anode side as described above, and therefore, the leakage state is improved.

For the above reasons, in the present invention, even when γ-butyrolactone is used as a solvent and a quaternized cyclic amidinium salt of benzoic acid is used as a solute,
It is considered that liquid leakage was prevented under both load and no load.

As described above, the quaternized cyclic amidinium salt of benzoic acid is dissolved in the mixed solvent of γ-butyrolactone and ethylene glycol of the present invention, and the colloidal silica and the alkylphosphorus having an alkyl group having 3 to 8 carbon atoms are dissolved. Add the acid,
Further, by using an electrolytic solution to which dinitrophenol is added in the range of 0.01 to 4% by weight, it has a low impedance characteristic, can be used in a 100 V specification, and has a low impedance of 1 V.
An electrolytic capacitor having good stability of withstand voltage characteristics at 25 ° C. and good liquid leakage characteristics is realized.

[0026]

Next, embodiments of the present invention will be described in detail. As shown in FIG. 1, the capacitor element 1 is formed by winding an anode foil 2 and a cathode foil 3 with a separator 8 interposed therebetween. As shown in FIG. 2, an anode tab 4 and a cathode tab 5 are connected to the anode foil 2 and the cathode foil 3, respectively. The anode tab 4 and the cathode tab 5 are made of high-purity aluminum, and include a flat portion connected to each foil and a round bar portion continuous with the flat portion. The round bar portion has an anode lead wire 6 and a cathode bar, respectively. Lead wire 7 is connected. The respective foils and the electrode tabs are mechanically connected by a stitch method, ultrasonic welding, or the like.

The anode electrode foil 2 is obtained by chemically or electrochemically etching an aluminum foil having a purity of 99.9% in an acidic solution and expanding the surface thereof, and then performing a chemical conversion treatment in an aqueous solution of ammonium adipate. An anodic oxide film layer is formed on the surface.

As the cathode foil, a foil obtained by etching an aluminum foil having a purity of 99.9% and expanding the surface was used. Then, an anodic oxide film made of aluminum oxide was formed on the surface of the cathode tab by a chemical conversion treatment using an ammonium phosphate aqueous solution.

The capacitor element 1 configured as described above
Is impregnated with an electrolytic solution for driving an electrolytic capacitor. As an electrolyte, benzoic acid (1-ethyl-2,3-dimethylimidazolium) salt (20 wt%) is dissolved as a solute in a mixed solvent of γ-butyrolactone (62 wt%) and ethylene glycol (11 wt%), and colloidal. Silica (5
wt.) and dioctyl phosphate (2 wt.%) were used.

Capacitor element 1 impregnated with this electrolyte
Is housed in an outer case 10 made of aluminum having a bottomed cylindrical shape, and lead wires 6 and 7
The sealing of the electrolytic capacitor is performed by inserting a sealing member 9 made of butyl rubber having a through-hole for leading out, and caulking the end of the outer case 10.

With respect to Examples and Comparative Examples in which dinitrophenol was added to the electrolytic solution of the electrolytic capacitor configured as described above, and the electrolytic capacitors of Conventional Examples 1 and 2, the initial characteristics and the load at 125 ° C. for 1000 hours were not measured. The load characteristics were evaluated. Here, as the electrolyte of Conventional Example 1, ethylene glycol (90 wt%) and ammonium benzoate (10 wt%), and as the electrolyte of Conventional Example 2, γ-butyrolactone (83 wt%), maleic acid (10 wt%),
Triethylamine (7 wt%) was used. The rating of the electrolytic capacitor is 100 WV-56 μF. Table 1 shows the specifications and initial characteristics of these electrolytic capacitors.
The results of the 125 ° C. load and no load test are shown in (Table 2). Here, the amount of addition in (Table 1) is the amount of addition to 100 parts of the electrolytic solution. In addition, in order to evaluate the liquid leakage characteristics, 100
Using an electrolytic capacitor of WV-4.7 μF (6.3φ-11L), which is a strict condition for a liquid leakage evaluation test 85
The liquid leakage state was determined under the conditions of ℃ / 85% for 3000 hours. The results are shown in (Table 3).

[0032]

[Table 1]

[0033]

[Table 2]

[0034]

[Table 3]

As is clear from Table 1, in the embodiment, a capacitor having a low tan δ is obtained. In addition, as is clear from (Table 2) and (Table 3), 125 ° C.
It can be seen that the characteristics after the load and no-load tests are stable, high reliability at 125 ° C. has been obtained, and no liquid leakage has occurred. In contrast, in Conventional Example 1, the initial ta
n δ is high, and in Conventional Example 2, tan δ significantly increases in both the 125 ° C. load and no-load tests. The amount of dinitrophenol added is 0.01 to 4% by weight.
In the comparative examples out of the range, liquid leakage occurs, and high reliability cannot be obtained.

[0036]

According to the present invention, a quaternized cyclic amidinium salt of benzoic acid is dissolved in a mixed solvent of γ-butyrolactone and ethylene glycol, and colloidal silica and an alkyl phosphoric acid represented by the formula (1) are added. Further, an electrolytic solution to which dinitrophenol is added in the range of 0.01 to 4% by weight is used. With the electrolytic capacitor using the electrolytic solution of the present invention as described above, low impedance characteristics, 100 V specifications, stability of withstand voltage characteristics at 125 ° C., and good liquid leakage characteristics can be realized.

[Brief description of the drawings]

FIG. 1 is an internal sectional view showing a structure of an electrolytic capacitor.

FIG. 2 is an exploded perspective view showing the structure of the capacitor element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Capacitor element 2 Anode foil 3 Cathode foil 4 Anode tab 5 Cathode tab 6 Anode lead wire 7 Cathode lead wire 8 Separator 9 Sealing body 10 Outer case

Claims (1)

[Claims] 1. A quaternized cyclic amidinium salt of benzoic acid is dissolved in a mixed solvent of γ-butyrolactone and ethylene glycol, colloidal silica and an alkyl phosphoric acid represented by the formula (1) are added, and dinitrophenol is further added. In an amount of 0.01 to 4% by weight. Embedded image