JP2003059773A - Electrolytic capacitor driving electrolyte and electrolytic capacitor using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrolytic capacitor driving electrolyte for enabling the utilization of an aluminum electrolytic capacitor having a low impedance, an improved low temperature characteristic expressed by the ratio of impedances at a low and an ordinary temperatures, and a good life characteristic. SOLUTION: The electrolytic capacitor driving electrolyte contains: (1) a solvent composed of 20-80 wt.% of an organic solvent and 80-20 wt.% of water, (2) at least one or more electrolytes selected from a carboxylic acid, a salt of a carboxylic acid, an inorganic acid and a salt of an inorganic acid, and (3) a chelate compound.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an electrolytic capacitor. More specifically, the present invention relates to an electrolytic solution for driving an aluminum electrolytic capacitor, which has low impedance, excellent low temperature characteristics, and good life characteristics.

[0002]

2. Description of the Related Art A capacitor is one of general electric parts and is widely used in various electric and electronic products, mainly for power supply circuits and noise filters for digital circuits.

Although there are various kinds of capacitors currently in use, the present invention is concerned with aluminum electrolytic capacitors, of which a typical one is a high-purity aluminum foil obtained by etching a surface area. The anode foil whose surface has been anodized to make it a dielectric, an aluminum cathode foil whose surface is etched and whose surface is etched, and a separator (isolate between the anode foil and the cathode foil). An element having a structure in which a laminated body composed of (paper) is wound up is impregnated with an electrolytic solution, the element is housed in a case (generally made of aluminum), and then sealed with an elastic sealing body. There are electrolytic capacitors other than such a wound structure.

In such an electrolytic capacitor, the characteristics of the electrolytic solution play a major factor in determining the performance of the electrolytic capacitor. Especially with the recent miniaturization of electrolytic capacitors,
Anode foils or cathode foils with a high etching rate have come to be used, and the resistivity of the capacitor body is high. Therefore, the electrolytic solution used for this is a high conductivity type with a low resistivity (specific resistance). Degrees are always required.

The electrolytic solution of the conventional electrolytic capacitors is composed of ethylene glycol (EG) as a main solvent and water up to about 10% by weight, and a carboxylic acid such as adipic acid or benzoic acid as an electrolyte. Alternatively, a solution of an ammonium salt thereof is generally used. With such an electrolytic solution, the specific resistance is about 1.5 Ω · m (150 Ω · cm).

In the capacitor, it is constantly required to lower the impedance (Z) in order to fully exhibit its performance. The impedance is determined by various factors. For example, the impedance decreases as the electrode area of the capacitor increases, so that the impedance of the large capacitor is naturally lowered. There is also an approach to improve the impedance by improving the separator. However, in a small capacitor, the specific resistance of the electrolytic solution is the controlling factor of impedance.

Recently, aproton-based (γ-butyrolactone, etc.) low specific resistance electrolytes have been developed (JP-A-62-62).
-145713, 62-145714, 62-1457
No. 15), a capacitor using an aprotic electrolyte solution is far inferior in impedance to a solid capacitor using an electronic conductor known as a low resistivity electrolyte.

The aluminum electrolytic capacitor has poor low temperature characteristics because it uses an electrolytic solution, and the ratio of the impedance at -40 ° C. to the impedance at 20 ° C. at 100 kHz (Z (-40 ° C.) / Z (20 The actual situation is that it is considerably large, about 40).

On the other hand, water used as a part of the solvent of the electrolytic solution of the aluminum electrolytic capacitor is a chemically active substance for the material of the anode foil and the cathode foil, and acts on the anode foil and the cathode foil ( The hydration reaction) usually tends to shorten the life of the electrolytic capacitor.

[0010]

SUMMARY OF THE INVENTION Therefore, the present invention provides a driving electrolytic cell for an aluminum electrolytic capacitor which has a low impedance and is excellent in low-temperature characteristics represented by an impedance ratio at low temperature and room temperature, and also has good life characteristics. The purpose is to provide a liquid.

It is also an object of the present invention to provide an electrolytic capacitor having a low impedance, improved low temperature characteristics and long life by using the electrolytic solution of the present invention.

[0012]

The electrolytic solution for driving an electrolytic capacitor according to the present invention comprises (1) a solvent composed of 20 to 80% by weight of an organic solvent and 80 to 20% by weight of water, and (2) At least one electrolyte selected from carboxylic acids, salts of carboxylic acids, inorganic acids and salts of inorganic acids, and (3) a chelate compound.

The chelate compound in the electrolytic solution of the present invention suppresses the hydration reaction of the aluminum electrode foil to prevent the deterioration of the electrode foil and thereby prolongs the life of the electrolytic capacitor. When the organic electrolyte of carboxylic acid or its salt and the inorganic electrolyte of inorganic acid or its salt are used together, the effect of further prolonging the life of the electrolytic capacitor is exhibited.

The electrolytic capacitor of the present invention is characterized by using the electrolytic solution of the present invention as the electrolytic solution.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION In the electrolytic solution for driving an electrolytic capacitor of the present invention, the solvent is composed of a mixture of an organic solvent and water.

As the organic solvent, a protic solvent and an aprotic solvent can be used. An alcohol compound can be given as an example of a typical proton-based solvent. Specific examples of the alcohol compound include monohydric alcohols such as ethyl alcohol, propyl alcohol and butyl alcohol, dihydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol and propylene glycol, and trihydric alcohols such as glycerin. Can be mentioned. Examples of aprotic solvents include intramolecularly polarized compounds such as lactone compounds such as γ-butyrolactone. The organic solvent is
One or more selected from a protic solvent and an aprotic solvent can be used. Plural kinds of protic solvents may be used, plural kinds of aprotic solvents may be used, and a mixed system of protic solvent and aprotic solvent may be used.

The electrolytic solution of the present invention contains water as a solvent in addition to the organic solvent. Thus, the solvent in the electrolytic solution of the present invention is a mixture of an organic solvent and water. In the present invention, by using such a mixed solvent, the freezing point of the solvent is lowered, thereby improving the impedance characteristics of the electrolytic solution at low temperature, and it is shown that the impedance ratio at low temperature and room temperature is small. It is possible to realize good low temperature characteristics. The content of water in the solvent is preferably 20 to 80% by weight, and the balance is an organic solvent. Whether the water content is less than 20% by weight or more than 80% by weight, the degree of depression of the freezing point of the electrolytic solution becomes insufficient, and it becomes difficult to obtain good low-temperature characteristics of the electrolytic capacitor. A more preferable amount of water in the solvent is 30 to 80% by weight, and the most preferable amount of water is 45 to 80% by weight.

As the electrolyte in the electrolytic solution, organic acid,
Particularly preferably, one or more selected from carboxylic acids, salts of carboxylic acids, inorganic acids and salts of inorganic acids can be used. What can be used as carboxylic acid,
Monocarboxylic acids represented by formic acid, acetic acid, propionic acid, butyric acid, p-nitrobenzoic acid, salicylic acid and benzoic acid, and oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, fumaric acid, maleic acid, phthalic acid. Acids and dicarboxylic acids represented by azelaic acid are included, and carboxylic acids having a functional group such as an OH group such as citric acid and oxybutyric acid can also be used. Examples of usable inorganic acids include phosphoric acid, phosphorous acid, hypophosphorous acid, boric acid, sulfamic acid and the like. As the salt of carboxylic acid or inorganic acid, ammonium salt, sodium salt, potassium salt and the like can be used, and among these, it is more preferable to use ammonium salt. In addition, when an inorganic acid or a salt thereof is used as the electrolyte, it is expected that the freezing point of the electrolytic solution will be lowered thereby, which is considered to contribute to the further improvement of the low temperature characteristics of the electrolytic solution.

The amount of electrolyte used in the electrolytic solution of the present invention depends on the characteristics required for the electrolytic solution, the type of solvent used,
It may be appropriately determined according to conditions such as the type of electrolyte used. However, generally speaking, the amount of the carboxylic acid or its salt is preferably about 3 to 30% by weight of the total weight of the electrolytic solution. If it is less than 3% by weight, the desired electric conductivity cannot be sufficiently ensured, and if it exceeds 30% by weight, the effect becomes saturated and it becomes difficult to dissolve in a solvent. The amount of the inorganic acid or its salt is preferably about 0.1 to 15% by weight of the total weight of the electrolytic solution. If the amount is less than 0.1% by weight, the desired conductivity cannot be sufficiently secured, If it exceeds, the effect will be saturated and it will be difficult to dissolve in a solvent. When the carboxylic acid or its salt is used in combination with the inorganic acid or its salt, it can be used within the above range.

The electrolytic solution of the present invention contains a chelate compound as an additive. The chelate compound used in the present invention is a compound which forms a cyclic structure containing a metal (known as a “chelate ring”) by being coordinated with a metal ion. A typical example of the chelate compound used in the present invention is ethylenediaminetetraacetic acid (EDT).
A), trans-1,2-diaminocyclohexane-
N, N, N ', N'-tetraacetic acid monohydrate (CyDTA),
Dihydroxyethylglycine (DHEG), ethylenediaminetetrakis (methylenephosphonic acid) (EDTP
O), diethylenetriamine-N, N, N ′, N ″,
N "-pentaacetic acid (DTPA), diaminopropanol tetraacetic acid (DPTA-OH), ethylenediamine diacetic acid (ED
DA), ethylenediamine-N, N'-bis (methylenephosphonic acid) hemihydrate (EDDPO), glycol ether diamine tetraacetic acid (GEDTA), hydroxyethylethylenediamine triacetic acid (EDTA-OH) and the like. The chelate compound may be used in any form of acid, salt, ester, anhydride and the like.

In the electrolytic solution of the present invention, the chelate compound is considered to suppress the hydration reaction of the aluminum electrode foil to prevent the deterioration of the electrode foil and contribute to the extension of the life of the electrolytic capacitor. In addition, there is an accompanying effect that the corrosion resistance is improved by adding the chelate compound. It is also possible to use the chelate compound as a mixture of two or more kinds.

The amount of the chelate compound added is preferably 0.01 to 3% by weight based on the total weight of the electrolytic solution. If the amount of the chelate compound added is less than 0.01% by weight, the effect of prolonging the life of the electrolytic capacitor can hardly be expected, and if it exceeds 3% by weight, the effect will be saturated and it will precipitate in the solution at low temperature. There is also a disadvantage that the deterioration of the characteristics is induced and the electrolyte itself becomes very expensive. The more preferable addition amount of the chelate compound is 0.05 to 3% by weight.

In the present invention, by using the above-mentioned electrolyte and additive together with the above-mentioned mixed solvent, the specific resistance of the electrolytic solution can be lowered to about 20 Ω · cm at 30 ° C., that is, an electrolytic capacitor having a low impedance can be obtained. Can be realized. As described above, the specific resistance obtained with a normal electrolytic solution is at most about 150 Ω · cm, so the effect of lowering impedance according to the present invention can be said to be remarkable.

The electrolytic solution of the present invention may contain components other than those mentioned above as additional additives, if necessary. Suitable additives include, for example, the following compounds as used by the present inventors in the invention contemporaneous with the present invention and separately patented.

(A) Gluconic acid and gluconolactone. This additive is generally used in an amount of 0.01 to 5% by weight based on the total weight of the electrolytic solution. If this additive is used, the life of the low impedance capacitor Al electrode foil is suppressed by the hydration reaction, thereby prolonging the life and electrolysis. It is possible to improve the low temperature characteristics of the capacitor and the corrosion resistance.

(B) Sugars such as glucose, fructose, xylose and galactose. Generally, it is preferable to add the saccharide in the range of 0.01 to 5% by weight. Such a saccharide can prevent the deterioration of the electrode foil by suppressing the hydration reaction of the aluminum electrode foil, and can promote the extension of the life of the electrolytic capacitor. When a carboxylic acid is used as the electrolyte, the saccharide is effective in suppressing its decomposition.

(C) Hydroxybenzyl alcohol (particularly 2-hydroxybenzyl alcohol), L-glutamic acid or a salt thereof (for example, Na, K, NH ₄ , amine and alkylammonium salts) and the like. This additive is generally
It is preferably added in the range of 0.01 to 5% by weight. Such additives prevent deterioration of the electrode foil by suppressing the hydration reaction of the aluminum electrode foil and contribute to prolonging the life of the electrolytic capacitor. (D) A nitro compound selected from nitrophenol, nitrobenzoic acid, dinitrobenzoic acid, nitroacetophenone and nitroanisole. This additive is generally used in an amount of 0.01 to 5% by weight, based on the total weight of the electrolyte, and when used, a significant hydrogen gas absorption effect is obtained.

The above-mentioned additives (a) to (d) can be used alone or in combination.

In addition to these additives, additives commonly used in the field of aluminum electrolytic capacitors or other electrolytic capacitors may be further added. Examples thereof include mannite and silane coupling agents. , Water-soluble silicone, polymer electrolyte, and the like.

The electrolytic solution of the present invention may further contain one or both of gluconic acid and gluconolactone. Gluconic acid and gluconolactone can exert effects of extending the life by suppressing the hydration reaction of the Al electrode foil of the low impedance capacitor, improving the low temperature characteristics of the electrolytic capacitor, and improving the corrosion resistance.

Further, according to the research conducted by the present inventors, when a carboxylic acid or a salt thereof and an inorganic acid or a salt of an inorganic acid are used together as an electrolyte, compared with the case where they are used alone, an electrolytic capacitor is used. It is also possible to obtain the effect of significantly extending the life of the. Moreover, in the conventional electrolytic capacitor, the inorganic acid-based electrolyte has been mainly used for medium to high voltage (160 to 500 V) type electrolytic capacitors because of problems such as electric conductivity. When using a combination of organic and inorganic electrolytes,
It can also be advantageously used in low voltage (less than 160V) type electrolytic capacitors.

The electrolytic solution of the present invention can be easily prepared by dissolving the electrolyte and the chelate compound in a solvent which is a mixture of an organic solvent and water. The above (a) to (d)
Even when the additional additive of 1 or other additives are used, they may be dissolved in a solvent.

The electrolytic capacitor of the present invention comprises an anode foil made of aluminum whose surface is oxidized and made into a dielectric, a cathode foil made of aluminum which faces the dielectricized surface of this anode foil, an anode foil and a cathode. A wound element composed of a separator (separator paper) interposed between the foil and the electrolytic solution is impregnated and sealed in a case, and the electrolytic solution of the present invention is used as the electrolytic solution. There is. As described above, since the electrolytic solution of the present invention is used, in this electrolytic capacitor, the effect of improving the low temperature characteristics by the mixed solvent of the organic solvent and water, the hydration reaction of the electrode foil by the addition of the chelate compound The effect of lowering the impedance can be achieved in addition to the effect of extending the life due to suppression.

[0034]

The present invention will be further described with reference to the following examples.
It goes without saying that the examples given here are intended to illustrate the invention and not to limit it.

[Comparative Examples 1 to 3 and Examples 1 to 20] Here, an aluminum electrolytic capacitor having a wound structure will be described as an example. First, an aluminum foil was electrochemically etched, anodized to form an oxide film on the surface, and then a lead tab for drawing out an electrode was attached to produce an aluminum anode foil. Next, another aluminum foil was also subjected to an electrochemical etching treatment, and then an electrode lead-out lead tab was accommodated to form an aluminum cathode foil. Next, a separator (separator paper) between the anode foil and cathode foil.
A capacitor element was made by sandwiching and winding. Then, the capacitor element is impregnated with the electrolyte solution whose composition is shown in Tables 1 to 4 and then housed in a bottomed aluminum case so that the lead tabs for leading out the electrode come out of the case. The electrolytic capacitor (10 WV-1000 μF) having a wound structure was produced by sealing with a sealing body.

The specific resistance values of the used electrolyte at 30 ° C. are shown in Tables 1 to 4. Further, the impedance ratio (Z ratio) expressed as the ratio of the impedance at low temperature (−40 ° C.) to the impedance at normal temperature (20 ° C.) of the manufactured electrolytic capacitor is 120 Hz and 100 kHz.
It was measured at. The measurement results are shown in Tables 1 to 4. Table 1 shows
The comparative example which used the electrolyte solution which does not contain a chelate compound additive is shown, and Tables 2-4 have shown the Example which used the electrolyte solution of this invention which added the chelate compound.

Furthermore, in order to evaluate the life characteristics of each electrolytic capacitor, the capacitors whose initial values of capacitance, tan δ and leakage current were measured were applied with a rated voltage at 105 ° C. and left for 1000 hours, and then these capacitors were again measured. The characteristic value was measured. The results are also shown in Tables 1 to 4.

[0038]

[Table 1]

[0039]

[Table 2]

[0040]

[Table 3]

[0041]

[Table 4]

From these results, it was found that the specific resistance of the electrolytic solution of the present invention was the same as that of the comparative example except for Example 5, and these specific resistance values were the same as those of the conventional general electrolytic solution. You can see that it is smaller than that. The specific resistance value of the electrolytic solution of Example 5 seems to be high only by looking at the data in Table 2, but since the specific resistance value of the conventional general electrolytic solution was about 150 Ω · cm as described above, It can be said that this is substantially comparable to an ordinary electrolytic capacitor and is at a practically sufficient level, and it is noted that it has realized a relatively low impedance in comparison with the conventional electrolytic capacitors. Therefore, the capacitor using the electrolytic solution of the present invention can realize a lower impedance than the conventional ones, and even if not, at least a low impedance equivalent to the conventional ones can be realized. it can.

Further, in the capacitor using the electrolytic solution of the present invention, it was found that the Z ratio was small, and in particular 100
It can be seen that the Z ratio at a high frequency of kHz is suppressed smaller than that of the comparative example. This indicates that the electrolytic capacitor using the electrolytic solution of the present invention exhibits good low temperature characteristics over a wide frequency range.

On the other hand, the examples of the present invention using the chelate compound additive showed stable characteristics even after 1000 hours at 105 ° C., and did not lead to destruction of the capacitor itself due to gas generation. For it,
In each of the capacitors of Comparative Examples using the electrolyte solution containing no chelate compound additive, the explosion-proof valve actuated due to the generation of gas long before 1000 hours, and the capacitors became unusable. From this, it is understood that according to the present invention, the life of the electrolytic capacitor can be easily extended.

[Examples 21 to 26] Using electrolytic solutions having the compositions shown in Table 5, electrolytic capacitors were prepared in the same manner as in the above examples, and various characteristics were measured. In these examples, the data for evaluating the life characteristics was measured at 105 ° C. after 5000 hours.

[0046]

[Table 5]

As described above, in Comparative Examples 1 to 3 using the electrolytic solution containing no chelate compound, 250
In the case of the capacitors of Examples 21 to 26, while none of them became usable by the time of ~ 500 hours,
Although the decrease in capacity was observed, it was still usable after 5000 hours had elapsed.

It should be further noted that one of Examples 21, 22 and 25 in which a carboxylic acid or its salt of an organic electrolyte and an inorganic acid of an inorganic electrolyte are used in combination, and one of the organic electrolyte or the inorganic electrolyte is used. Examples 23, 2 using only
Comparing 4 and 26, the former is 500 more than the latter.
That is, there is little decrease in capacity due to aging after 0 hours. From this, it is understood that the combined use of the organic electrolyte and the inorganic electrolyte in the present invention further improves the life characteristics of the electrolytic capacitor.

[0049]

As described above, according to the present invention, it is possible to use a highly reliable electrolytic capacitor having low impedance, excellent low temperature characteristics, and good life characteristics.

Claims (8)

[Claims] (1) 20 to 80% by weight of an organic solvent and 8
A solvent composed of 0 to 20% by weight of water, (2) at least one electrolyte selected from carboxylic acids, salts of carboxylic acids, inorganic acids and salts of inorganic acids, and (3) chelate compounds An electrolytic solution for driving an electrolytic capacitor, comprising: 2. The electrolytic solution for driving an electrolytic capacitor according to claim 1, wherein the organic solvent is at least one solvent selected from a protic solvent and an aprotic solvent. 3. The carboxylic acid and a salt of the carboxylic acid,
Formic acid, acetic acid, propionic acid, butyric acid, p-nitrobenzoic acid, salicylic acid, benzoic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, fumaric acid, maleic acid, phthalic acid, azelaic acid, citric acid and The electrolytic solution for driving an electrolytic capacitor according to claim 1 or 2, which is selected from oxybutyric acid and ammonium salts, sodium salts, potassium salts, amine salts and alkylammonium salts thereof. 4. The inorganic acid and the salt of the inorganic acid are phosphoric acid,
4. Phosphorous acid, hypophosphorous acid, boric acid and sulfamic acid and their ammonium salts, sodium salts, potassium salts, amine salts and alkylammonium salts, selected from any one of claims 1 to 3. Electrolytic solution for driving electrolytic capacitors. 5. The chelate compound is ethylenediaminetetraacetic acid, trans-1,2-diaminocyclohexane-N, N, N ′, N′-tetraacetic acid monohydrate, dihydroxyethylglycine, ethylenediaminetetrakis (methylenephosphonic acid). ), Diethylenetriamine-N, N,
N ', N ", N" -pentaacetic acid, diaminopropanoltetraacetic acid, ethylenediaminediacetic acid, ethylenediamine-N,
2. Selected from N'-bis (methylenephosphonic acid) hemihydrate, glycol ether diamine tetraacetic acid and hydroxyethyl ethylenediamine triacetic acid.
The electrolytic solution for driving the electrolytic capacitor according to any one of 1 to 4. 6. The total electrolyte weight is 0.01 to 0.01.
6. Containing 3% by weight of chelate compound.
The electrolytic solution for driving the electrolytic capacitor as described in any one of 1 above. 7. The electrolytic solution for driving an electrolytic capacitor according to any one of claims 1 to 6, further containing one or both of gluconic acid and gluconolactone. 8. An electrolytic capacitor comprising the electrolytic solution for driving an electrolytic capacitor according to claim 1 as an electrolytic solution.