JP2015019015A - Electrolyte for electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrolyte for electrolytic capacitor having sufficient electrical conductivity and spark generation voltage, and capable of suppressing precipitation and temporal separation of crystal under low temperature.SOLUTION: An electrolyte for electrolytic capacitor contains (a) a polar solvent, and (b) a compound or its salt shown by formula (1). (HOOC-X-O-(AO)-Y-COOH ...(1)). (In the formula (1), X and Y are a hydrocarbon group of 2-5C, respectively. AO is an oxyalkylene group of 2-4C. n is an average addition mol number of the oxyalkylene group of 2-4C, and is 1-100).

Description

  The present invention relates to an electrolytic solution for an electrolytic capacitor.

  In aluminum electrolytic capacitors, solidification of the electrolyte in the electrolyte may cause a decrease in conductivity and a decrease in spark generation voltage, and the separation of the electrolyte component is an industrial productivity of supplying a certain quality product during capacitor production. This may be a problem. Therefore, the aluminum electrolytic capacitor is required to be used stably in a wide temperature range from about −40 ° C. to a temperature exceeding 100 ° C.

Also, aluminum electrolytic capacitors are required to have a high spark generation voltage so that they can be used stably without causing short puncture even in applications where high voltage is applied, such as digital equipment and in-vehicle equipment.
As an electrolytic solution used for an aluminum electrolytic capacitor, a polar solvent mainly composed of ethylene glycol or γ-butyrolactone, an inorganic acid such as boric acid, a dibasic acid such as adipic acid or maleic acid or a salt thereof as an electrolyte Electrolytic solutions are known. However, an electrolytic solution using these acids as an electrolyte has a problem of low spark generation voltage although it has high conductivity.

  As a method for improving the spark generation voltage of an electrolytic solution, a method of adding a nonionic polyalkylene glycol derivative such as polyethylene glycol to an electrolytic solution containing an electrolyte is known. However, since such a polyalkylene glycol derivative exhibits little electrical conductivity, it has an effect of improving the spark generation voltage, but has a problem of reducing electrical conductivity.

  In addition, an electrolytic solution using an electrolyte having a high spark generation voltage has been reported as a method for improving the spark generation voltage without greatly reducing the electrical conductivity. A method using butyloctanedioic acid (for example, Patent Document 1) and a method using 5,6-decanedicarboxylic acid (for example, Patent Document 2) have been reported. The electrolyte using such a carboxylic acid is effective in improving the spark generation voltage. However, since the solubility of the carboxylic acid in a polar solvent is low, it may crystallize and precipitate at a low temperature.

  A method using a diester compound of polyethylene glycol and adipic acid (for example, Patent Document 3), a method using a diester compound of polyethylene glycol and an aliphatic dibasic acid having a branched chain (for example, Patent Document 4), etc. are reported. In addition, since electrolytes using these diester compounds have high solubility in polar solvents, crystallization at low temperatures can be suppressed. However, an electrolytic solution using such a diester compound has a higher effect of improving the spark generation voltage than an aliphatic dibasic acid such as adipic acid, but the ester bond is hydrolyzed with time and the electrolytic solution is Sometimes separated.

  Although a method using polyoxyethylene diglycolic acid (for example, Patent Document 5) and a method using polyoxypropylene diglycolic acid (for example, Patent Document 6) have been reported, the spark generation voltage was not sufficient.

Japanese Patent Publication No. 60-13293 Japanese Patent Publication No. 63-15738 JP 2004-128275 A JP 2007-126611 A JP-A-60-176218 Japanese Patent Laid-Open No. 06-61100

  As described above, an electrolytic solution for electrolytic capacitors that has a sufficient spark generation voltage and can suppress the precipitation of crystals at a low temperature and separation over time has not yet been obtained.

  The subject of this invention is providing the electrolyte solution for electrolytic capacitors which has sufficient electroconductivity and a spark generation voltage, and can suppress the precipitation of a crystal | crystallization at low temperature and a temporal separation.

The present invention is as follows.
(1) An electrolytic solution for electrolytic capacitors, comprising component (a) and component (b).
(A) Polar solvent (b) Compound represented by formula (1) or a salt thereof

HOOC-X-O- (AO) _n -Y-COOH (1)

(In Formula (1), X and Y are respectively a C2-C5 hydrocarbon group.
AO is an oxyalkylene group having 2 to 4 carbon atoms.
n is the average addition mole number of a C2-C4 oxyalkylene group, and is 1-100. )

(2) In said Formula (1), the ratio of the C3-C4 oxyalkylene group which occupies for (AO) _n is 30-85 mol%.

(3) Further, (c) an aliphatic dibasic acid having 5 to 12 carbon atoms or a salt thereof is contained.

  The electrolytic solution for an electrolytic capacitor of the present invention has sufficient conductivity and spark generation voltage, and can suppress crystal precipitation and separation over time at a low temperature, so that the capacitor can be used stably in a wide temperature range. be able to.

(Electrolytic solution for electrolytic capacitors)
In an electrolytic capacitor, a valve metal in which an insulating oxide film is formed on the surface of a metal such as aluminum or tantalum is used as an anode electrode, and the oxide film is used as a dielectric. An electrolytic solution is brought into contact with the surface of the oxide film, and a current collecting electrode is disposed. The electrolytic solution for the electrolytic capacitor contacts the dielectric and acts as a cathode.

((A) Polar solvent)
As the polar solvent used in the present invention, a solvent having polarity, particularly a solvent generally known as an organic solvent or water can be used. Preferably, monohydric alcohols such as ethanol and propanol, dihydric alcohols such as ethylene glycol, propylene glycol, diethylene glycol, 1,3-butanediol and 1,4-butanediol, trihydric alcohols such as glycerin, ethylene glycol monomethyl ether And ether solvents such as diethylene glycol diethyl ether, lactone solvents such as γ-butyrolactone, amide solvents such as N-methylformamide, water, and the like. A solvent may be used independently and may mix and use 2 or more types.

  As the polar solvent, a mixture of water and a polar organic solvent is preferable, a mixture of water and a dihydric alcohol or a trihydric alcohol is more preferable, and a mixture of ethylene glycol and water is more preferable.

((B) a compound represented by the formula (1) or a salt thereof)
Since the compound represented by the formula (1) has a hydrocarbon group and a polyoxyalkylene group adjacent to the carboxyl group, it exhibits high solubility in a polar solvent and expresses a high spark generation voltage. Furthermore, the compound represented by the formula (1) is chemically stable without decomposition such as hydrolysis, and separation is suppressed.

  X and Y in formula (1) are each a hydrocarbon group having 2 to 5 carbon atoms, and may be the same or different. X and Y may be linear or branched and may be saturated or unsaturated. Specific examples include linear hydrocarbon groups such as ethylene group, propylene group, butylene group, and pentylene group, and branched hydrocarbon groups.

  When the carbon number of X and Y is smaller than 2, the spark generation voltage is insufficient, and when it is larger than 5, the solubility in the electrolyte solvent is lowered. From this viewpoint, the number of carbon atoms of X and Y is particularly preferably 2 to 4. X and Y are preferably straight-chain hydrocarbon groups and / or saturated hydrocarbon groups.

  Specifically, X and Y are preferably an ethylene group, a propylene group, a butylene group, and a pentylene group.

  AO in Formula (1) is one or more oxyalkylene groups having 2 to 4 carbon atoms. When AO is 2 or more types, it may be added in a block shape or may be added in a random shape. AO is particularly preferably a triblock adduct in the order of an oxyalkylene group having 3 to 4 carbon atoms, an oxyalkylene group having 2 carbon atoms, and an oxyalkylene group having 3 to 4 carbon atoms.

  N in Formula (1) is an average addition mole number of the C2-C4 oxyalkylene group AO, and is 1-100. When n is smaller than 1, the solubility in a polar solvent decreases. From this viewpoint, n is preferably 8 or more, more preferably 10 or more, and particularly preferably 15 or more. Moreover, when n is larger than 100, sufficient conductivity cannot be obtained. From this viewpoint, n is preferably 80 or less, more preferably 70 or less, and particularly preferably 50 or less.

When the total number of repeating units of (AO) _n is 100 mol%, the proportion of the oxyalkylene group having 3 to 4 carbon atoms in (AO) _n is improved in sparking voltage and solubility in polar solvents. From the viewpoint, it is preferably 30 mol% or more, and preferably 85 mol% or less. The balance in this case is an oxyalkylene group having 2 carbon atoms.

  The molecular weight of the compound represented by the formula (1) is preferably 500 to 5000, and more preferably 600 to 3000. By setting the molecular weight to 500 or more, the fire generation voltage is further improved. Moreover, the specific resistance of electrolyte solution is suppressed and electrical conductivity becomes high by making this molecular weight 5000 or less.

  The compound represented by the formula (1) can be used as it is, but is preferably used as a salt with ammonia or an amine compound from the viewpoint of improving the solubility in its own solvent and improving the conductivity of the electrolytic solution. . Examples of amine compounds include primary amines such as N-butylamine and monoethanolamine, secondary amines such as diethanolamine, tertiary amines such as triethylamine, triethanolamine, dimethylaminoethanol, and N-methyldiethanolamine, ethylenediamine, diethylenetriamine, and triamine. Examples thereof include polyalkylene polyamines such as ethylene tetramine and tetraethylene pentamine, and alkylene oxide adducts of polyalkylene polyamines, which may be used alone or in admixture of two or more. Ammonia is preferred.

(Component (c))
It is preferable to add the following (c) component to the electrolyte solution of this invention from the point of electrical conductivity improvement.

  Component (c) is an aliphatic dibasic acid having 5 to 12 carbon atoms or a salt thereof. Examples of aliphatic dibasic acids having 5 to 12 carbon atoms include linear aliphatic dibasic acids such as glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, and dodecanedioic acid, and branched chains. The aliphatic dibasic acid which has is mentioned. As for carbon number of the acid of a component (c), 6-10 are still more preferable.

  Although the aliphatic dibasic acid having 5 to 12 carbon atoms can be used as it is, it is used as a salt with ammonia or an amine compound from the viewpoint of improving the solubility in its own solvent and improving the conductivity of the electrolytic solution. It is preferable. Examples of amine compounds include primary amines such as N-butylamine and monoethanolamine, secondary amines such as diethanolamine, tertiary amines such as triethylamine, triethanolamine, dimethylaminoethanol, and N-methyldiethanolamine, ethylenediamine, diethylenetriamine, and triamine. Examples thereof include polyalkylene polyamines such as ethylene tetramine and tetraethylene pentamine, and alkylene oxide adducts of polyalkylene polyamines, which may be used alone or in admixture of two or more. Ammonia is preferred.

(Composition ratio)
In the electrolytic solution of the present invention, when the weight ratio of the component (a) is a and the weight ratio of the component (b) is b, a + b is 100 parts by weight. At this time, the weight ratio b is preferably 0.1 parts by weight or more, thereby improving the conductivity of the electrolytic solution. From this viewpoint, the weight ratio b is preferably 1 part by weight or more, and more preferably 3 parts by weight or more. Further, the weight ratio b is preferably 50 parts by weight or less, which can reduce the viscosity of the electrolyte and facilitate handling. From this viewpoint, the weight ratio b is preferably 40 parts by weight or less, and more preferably 30 parts by weight or less.

  When component (a) is a mixture of water and a polar organic solvent, the weight ratio of water is preferably 0.1 to 30% by weight when the total amount of both is 100% by weight. More preferably, the content is 0.5 to 10% by weight.

  When the weight ratio of the component (c) in the electrolytic solution of the present invention is c, from the above viewpoint, the weight ratio c is preferably 0.1 parts by weight or more, more preferably 0.5 parts by weight or more. The above is particularly preferable. The weight ratio c is preferably 20 parts by weight or less, more preferably 10 parts by weight or less, and particularly preferably 8 parts by weight or less. However, a + b = 100 parts by weight.

  Moreover, b / c in the electrolytic solution of the present invention is preferably 50/50 to 99.9 / 0.1, more preferably 60/40 to 97/3, and particularly preferably 65/35 to 95/5.

(Additive)
Various additives can be added to the electrolytic solution of the present invention for the purpose of reducing leakage current, improving spark generation voltage, gas absorption, and the like. Examples of additives include phosphoric acid compounds, boric acid compounds, polyhydric alcohols, nitro compounds, polyvinyl alcohol, polyethylene glycol, polypropylene glycol, polyoxyethylene polyoxypropylene glycol random copolymers and block copolymers And the like.

Hereinafter, the present invention will be described in more detail with reference to examples.
[Example 1]
Table 1 shows compound g represented by the formula (1). Table 2 shows the composition of an electrolytic solution using (a) a polar solvent, (b) an ammonium salt of compound g represented by formula (1), and (c) an ammonium salt of sebacic acid. Table 4 shows the presence or absence of crystal precipitation when the electrolyte solution was left at -40 ° C for 1 hour, the specific resistance, the spark generation voltage, and the presence or absence of separation when left at 25 ° C for 3 months. The weight ratio of ethylene glycol was 83.0 parts by weight, and the weight ratio of water was 4.0 parts by weight.

  In addition, the presence or absence of crystal precipitation when left at -40 ° C. for 1 hour, the specific resistance, the spark generation voltage, and the presence or absence of separation when left at 25 ° C. for 3 months were evaluated according to the following criteria.

<Evaluation of Presence of Crystal Precipitation>
The presence or absence of crystal precipitation when the electrolyte solution 50 g was put in a glass bottle and allowed to stand for 1 hour in a -40 ° C. constant temperature bath was evaluated according to the following criteria.
○: Crystal does not precipitate and is uniform ×: Crystal is precipitated

<Measurement of specific resistance>
Specific resistance was measured as an index of electrical conductivity. It means that electrical conductivity is so low that a specific resistance is large. The specific resistance at 30 ° C. of the electrolytic solution was measured with an electric conductivity meter (CM-60S manufactured by Toa Radio Industry Co., Ltd.) and evaluated according to the following criteria.
○: Specific resistance is less than 2500 Ω · cm ×: Specific resistance is 2500 Ω · cm or more

<Measurement of spark generation voltage>
Put 700 g of electrolyte in a 1 L capacity stainless steel container, immerse aluminum foil with a purity of 99.99% or more cut into 60 mm × 10 mm, connect a DC power supply, and measure the spark generation voltage of the electrolyte at 25 ° C. Evaluation based on the criteria. The results are shown in Table 2.
○: Spark generation voltage improvement is 400V or more ×: Spark generation voltage improvement is less than 400V

<Evaluation of presence or absence of separation when left at 25 ° C. for 3 months>
The following criteria evaluated the presence or absence of the crystal | crystallization precipitation when putting electrolyte solution 50g into a glass bottle, and leaving still for 3 months with a 25 degreeC thermostat.
○: Uniform without separation ×: Separated

[Examples 2 to 6]
Table 2 shows the composition of an electrolytic solution using (a) a polar solvent, (b) an ammonium salt of compounds h, i, j, k, and m represented by formula (1) (see Table 1) and an ammonium salt of sebacic acid. Shown in In the same manner as in Example 1, the presence or absence of crystal precipitation when left at -40 ° C for 1 hour, the specific resistance, the spark generation voltage, and the presence or absence of separation when left at 25 ° C for 3 months were evaluated. The results are shown in Table 4.

[Comparative Examples 1-6]
The composition of the electrolytic solution using (a) a polar solvent, an ammonium salt of compounds s, t, u (see Table 1) or an ammonium salt of compounds p, q, r and (c) an ammonium salt of sebacic acid. Table 3 shows. In Table 3, p is sebacic acid, q is butyloctanedioic acid, and r is HOOC- (CH ₂ ) ₄ —COO— (CH ₂ CH ₂ O) ₉ —CO— (CH ₂ ). ₄ -COOH. In Comparative Examples 1, 2, and 3, the weight ratio of ethylene glycol was 75.5 parts by weight, and the weight ratio of water was 7.0 parts by weight. In Comparative Examples 4, 5, and 6, the weight ratio of ethylene glycol was 83.0 parts by weight, and the weight ratio of water was 4.0 parts by weight.

  In the same manner as in Example 1, the presence or absence of crystal precipitation when left at -40 ° C for 1 hour, the specific resistance, the spark generation voltage, and the presence or absence of separation when left at 25 ° C for 3 months were evaluated. The results are shown in Table 4. When crystal precipitation was observed in the evaluation of the presence or absence of crystal precipitation, the specific resistance, the spark generation voltage, and the presence or absence of separation when left at 25 ° C. for 3 months were not evaluated.

  From the results of Tables 2 and 4, it can be seen that the electrolytes of Examples 1 to 6 are uniform without crystals being precipitated at low temperatures. Moreover, it turns out that the electrolyte solution of Examples 1-6 shows a high spark generation voltage improvement, showing sufficient electroconductivity. Furthermore, it turns out that the electrolyte solution of Examples 1-6 is uniform, without isolate | separating with time.

On the other hand, since Comparative Example 1 and Comparative Example 2 did not use the compound represented by the formula (1) of the present invention, crystals were precipitated in the electrolytic solution at a low temperature.
In Comparative Example 3, since the compound represented by the formula (1) of the present invention was not used, the electrolytic solution separated over time.
In Comparative Example 4 and Comparative Example 5, since the number of carbon atoms of the hydrocarbon group adjacent to the carboxyl group of the compound represented by the formula (1) is smaller than the range of the present invention, the spark generation voltage is insufficient.
In Comparative Example 6, the specific resistance is large because the added mole number of the oxyalkylene group of the compound represented by the formula (1) is larger than the range of the present invention.

Claims (3)

An electrolytic solution for an electrolytic capacitor comprising the component (a) and the component (b).
(A) Polar solvent (b) Compound represented by formula (1) or a salt thereof

HOOC-X-O- (AO) _n -Y-COOH (1)

(In Formula (1), X and Y are respectively a C2-C5 hydrocarbon group.
AO is an oxyalkylene group having 2 to 4 carbon atoms.
n is the average addition mole number of a C2-C4 oxyalkylene group, and is 1-100. ) 2. The electrolytic solution for an electrolytic capacitor according to claim 1, wherein a ratio of the oxyalkylene group having 3 to 4 carbon atoms in (AO) _n in the formula (1) is 30 to 85 mol%.   (C) The electrolytic solution for electrolytic capacitors according to claim 1, comprising an aliphatic dibasic acid having 5 to 12 carbon atoms or a salt thereof.