JP6676303B2 - Electrolyte for electrolytic capacitors - Google Patents

Description

  The present invention relates to an electrolytic solution for an electrolytic capacitor and an electrolytic capacitor using the same. Specifically, the present invention relates to an electrolytic solution suitable for an aluminum electrolytic capacitor.

  Conventionally, an electrolytic capacitor represented by an aluminum electrolytic capacitor has a sealed case in which an anode provided with a dielectric, a cathode for collecting current and a separator holding an electrolytic solution disposed between the anode and the cathode are sealed. It has a structure housed in the inside, and a wound type or a laminated type is widely known.

Here, for the purpose of increasing the withstand voltage, a solution in which polyethylene glycol is added to the electrolyte has been proposed as the electrolyte used. (For example, Patent Document 1).

JP-A-62-268121

However, polyethylene glycol is easily solidified at a low temperature, the temperature range in which an electrolytic capacitor can be used is narrow, and it cannot be used in cold regions.
An object of the present invention is to provide an electrolytic capacitor that can be driven even in a cold region because it is hard to be solidified even at a low temperature in a high voltage region and has a sufficient withstand voltage.

The present inventors have studied to achieve the above object, and as a result, have reached the present invention.
That is, the present invention comprises, as essential components, an alkylene oxide adduct of a polyhydric alcohol (a) (A), an electrolyte (B) and a polar solvent (C), and the weight of (A) / (C). The ratio is 5/95 to 40/60, the 4- to 6-valent polyhydric alcohol (a) is sorbitol and / or mannitol, and the alkylene oxide is ethylene oxide alone. An electrolytic solution; and an electrolytic capacitor using the same.

  The electrolytic capacitor of the present invention does not solidify even at a low temperature, for example, −30 ° C., and has an effect that the withstand voltage is sufficiently high.

The electrolytic solution for an electrolytic capacitor of the present invention contains, as essential components, an alkylene oxide adduct (A) of a polyhydric alcohol (a) having 4 to 6 valences, an electrolyte (B) and a polar solvent (C), and further comprises (A) / The weight ratio of (C) is 5/95 to 40/60.

The alkylene oxide adduct (A) of the present invention is an alkylene oxide adduct of a polyhydric alcohol (a) having 4 to 6 valences. Examples of the alkylene oxide include ethylene oxide, propylene oxide, and butylene oxide, and may be used alone or in combination of two or more.
As the type of the alkylene oxide to be added, ethylene oxide is preferable from the viewpoint of easy penetration into the electrode.
When ethylene oxide is used in combination with other alkylene oxides, it is preferable that 70 mol% or more of the alkylene oxide is ethylene oxide, and more preferably 85 mol% or more, from the viewpoint of facilitating penetration into the electrode. . When 70 mol% or more of the alkylene oxide is ethoxide, there is an effect of increasing the withstand voltage.

Examples of the 4- to 6-valent polyhydric alcohol (a) include a tetrahydric alcohol such as pentaerythritol; a pentahydric alcohol such as xylitol; and a hexahydric alcohol such as sorbitol, mannitol, and dipentaerythritol.
Among them, (a) is preferably a hexahydric polyhydric alcohol, more preferably sorbitol and mannitol, and most preferably sorbitol.
On the other hand, an alkylene oxide adduct of a monohydric to trihydric alcohol is solidified at a low temperature, and thus is difficult to use as an electrolyte.
The average number of moles of the alkylene oxide added to the polyhydric alcohol (a) is preferably from 12 to 42 mol, and more preferably from 18 to 30 mol.
If the average number of added moles is less than 12 moles, the effect of increasing the withstand voltage is weak, and if it exceeds 42 moles, the viscosity becomes too high, so that it becomes difficult to soak the electrolyte into the separator when assembling the capacitor.

The number average molecular weight of the alkylene oxide adduct (A) of the polyhydric alcohol (a) having 4 to 6 valences is preferably from 1,000 to 2,200, more preferably from 1,000 to 1,500, from the viewpoint of conductivity. It is. If it is less than 1,000, the effect of increasing the withstand voltage is weak, and if it exceeds 2,200, it becomes difficult to impregnate the electrolyte into the separator when assembling the capacitor.

As a method for synthesizing the alkylene oxide adduct (A) of a polyhydric alcohol having 4 to 6 valences, it is general to react ethylene oxide or propylene oxide with the polyhydric alcohol in the presence of a potassium hydroxide or sodium hydroxide catalyst. is there.
In the aluminum electrolytic capacitor application of this application, since metal ions cause a short circuit of the capacitor, potassium or sodium must be reduced to 10 ppm or less, preferably 1 ppm or less by an adsorption treatment or the like.

The type of the electrolyte (B) of the present invention is not particularly limited as long as it is an electrolyte usually used for an electrolytic solution for an electrolytic capacitor. The electrolyte (B) is composed of a cation component (B1) and an anion component (B2). .

Examples of the cation component (B1) include ammonia cations; cations of secondary amines such as dimethylamine, ethylmethylamine and diethylamine; cations of tertiary amines such as trimethylamine and triethylamine; tetramethylammonium, 1,2,3,4- There are quaternary ammonium cations such as tetramethyl imidazolinium and 1-ethyl-2,3-methyl imidazolinium, which may be used alone or in combination of two or more. Of these, ammonia cations and secondary amines are preferred, and ammonia cations are more preferred.

The anionic component (B2) includes carboxylic acids such as adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, 1,6-decanedicarboxylic acid, 1,10-decanedicarboxylic acid, maleic acid, phthalic acid, and citraconic acid. Anions; phosphate anions such as phosphate anions and phosphate esters; borate anions; and borate derivative anions.
Among them, a carboxylate anion is preferred, and an aliphatic carboxylate anion having 4 to 12 carbon atoms is more preferred.
The anions may be used alone or in combination of two or more.

The polar solvent (C) of the present invention is not particularly limited as long as it is a polar solvent usually used for an electrolytic solution for an electrolytic capacitor. Examples thereof include (1) alcohol, (2) amide, (3) lactone, and (4) nitrile. , (5) sulfone and (6) other polar organic solvents.

(1) Alcohol Monohydric alcohol (methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, diacetone alcohol, benzyl alcohol, amino alcohol, furfuryl alcohol, etc.), dihydric alcohol (ethylene glycol, propylene glycol, diethylene glycol, hexylene) Glycol, etc.), trihydric alcohols (eg, glycerin), and tetravalent or higher alcohols (eg, hexitol).

(2) Amide formamide (N-methylformamide, N, N-dimethylformamide, N-ethylformamide, N, N-diethylformamide, etc.), acetamide (N-methylacetamide, N, N-dimethylacetamide, N-ethylacetamide , N, N-diethylacetamide, etc.), propionamide (N, N-dimethylpropionamide, etc.), pyrrolidone (N-methylpyrrolidone, N-ethylpyrrolidone, etc.), hexamethylphosphorylamide and the like.

(3) Lactone γ-butyrolactone, α-acetyl-γ-butyrolactone, β-butyrolactone, γ-valerolactone, δ-valerolactone and the like.

(4) Nitrile Acetonitrile, propionitrile, butyronitrile, acrylonitrile, methacrylonitrile, benzonitrile and the like.

(5) Sulfone sulfolane, dimethyl sulfoxide, ethyl methyl sulfone and the like.

(6) Other organic solvents 1,3-dimethyl-2-imidazolidinone and the like.

    These polar solvents (C) may be used alone or in combination of two or more. Of these, alcohols and lactones are preferred, ethylene glycol and γ-butyrolactone are more preferred, and ethylene glycol is most preferred.

The weight ratio (A) / (C) between the alkylene oxide adduct (A) and the polar solvent (C) in the electrolytic solution of the present invention is 5/95 to 40/60, and 7/90 to 30/70 is More preferred.
When the weight ratio (A) / (C) is less than 5/95, the withstand voltage becomes insufficient. On the other hand, when the weight ratio exceeds 40/60, the viscosity becomes high. It becomes difficult to seep.

If necessary, various additives commonly used for the electrolytic solution can be added to the electrolytic solution of the present invention.
For the purpose of absorbing hydrogen gas generated slightly during driving, for example, nitro compounds such as o-nitrobenzoic acid, p-nitrobenzoic acid, m-nitrobenzoic acid, o-nitrophenol, p-nitrophenol, etc. Is added. Further, boric acid or the like is added to increase the withstand voltage. The amount of addition is preferably 5% by weight or less, particularly preferably 0.1 to 2% by weight, based on the weight of the electrolytic solution, from the viewpoint of specific conductivity and solubility in the electrolytic solution.

The electrolytic solution for an electrolytic capacitor of the present invention is most suitable for an aluminum electrolytic capacitor.
The aluminum electrolytic capacitor is not particularly limited, and is, for example, a wound electrolytic capacitor in which a separator is interposed between an anode (aluminum oxide foil) having aluminum oxide formed on the anode surface and a cathode aluminum foil. And then wound and wound.
Impregnating the separator of the present invention as a driving electrolyte into a separator, storing it in a cylindrical aluminum case with a bottom together with the positive and negative electrodes, and then closing the opening of the aluminum case with a sealing rubber to constitute an electrolytic capacitor. Can be.

  Next, specific examples of the present invention will be described, but the present invention is not limited thereto.

Hereinafter, the present invention will be further described with reference to Examples and Comparative Examples, but the present invention is not limited thereto. Hereinafter, unless otherwise specified,% means% by weight and part means parts by weight. Example 4 below is a reference example.

Production Example 1
1.1 parts by weight (0.02 mol) of potassium hydroxide is added to 182 parts by weight (1 mol) of hexavalent sorbitol (a-1), and 880 parts by weight (20 mol) of ethylene oxide is reacted at 170 ° C. to obtain a pressure equilibrium. When it reached, it was the end point. Thereafter, potassium hydroxide was reduced to 1 ppm or less using KYOWARD 600 and KYOWARD 700 (manufactured by Kyowa Chemical Industry Co., Ltd.) as adsorbents to remove potassium hydroxide. Proton nuclear magnetic resonance (H-NMR) chart and hydroxyl value confirmed that 20 mol ethylene oxide adduct of sorbitol (A-1) was obtained.

Production Example 2
The reaction was carried out in the same manner as in Production Example 1 except that the number of reaction parts of ethylene oxide was changed to 1320 parts by weight (30 mol), to obtain a 30 mol ethylene oxide adduct of sorbitol (A-2).

Production Example 3
Except that sorbitol was changed to 182 parts by weight (1 mol) of hexavalent mannitol (a-2), a 20 mol ethylene oxide adduct of mannitol (A-3) was obtained in the same manner as in Production Example 1.

Production Example 4
Except that 880 parts by weight (20 mol) of ethylene oxide was changed to 528 parts by weight (12 mol) of ethylene oxide and 472 parts by weight (8 mol) of propylene oxide, the same procedure as in Production Example 1 was carried out to add 12 mol of ethylene oxide of sorbitol and 8 mol of propylene oxide. A product (A-4) was obtained.

Comparative Production Example 1
Except that sorbitol was changed to 92 parts by weight (1 mol) of trivalent glycerin (a'-1), a glycerin ethylene oxide 20 mol adduct (A'-1) was obtained in the same manner as in Production Example 1.

Example 1
The sorbitol ethylene oxide 20 mol adduct (A-1) and ethylene glycol (B-1) were mixed in the blending parts (parts by weight) shown in Table 1. Thereafter, 8 parts by weight of 1,6-decanedicarboxylic acid was added to 100 parts by weight of the solution, and 1 part by weight of ammonia gas was blown thereinto to be dissolved while neutralizing, whereby an electrolytic solution of Example 1 was obtained. pH was 6.9.

Examples 2 to 4, Comparative Examples 1 to 3
According to the number of parts (parts by weight) described in Table 1, the same operation as in Example 1 was performed to obtain electrolyte solutions of Examples 2 and 3 and Comparative Examples 1 to 3.

Using the electrolyte solutions obtained in Examples 1 to 4 and Comparative Examples 1 to 3, the state at a low temperature (−30 ° C.) was visually observed by the method described below, and the results of measuring the electrical conductivity are shown in Table 1. Described.

[State of electrolyte at -30 ° C]
The electrolytic solution was placed in a transparent glass bottle, left in a constant temperature bath at -30 ° C for 24 hours, and the glass bottle was tilted at -30 ° C, visually observed, and evaluated according to the following criteria.
：: transparent, no precipitate, and fluid when tilted. △: slightly turbid, but uniform as a whole and fluid when tilted. ×: solidified as a whole.

[Measurement of conductivity]
The conductivity (mS / cm) at 30 ° C. was measured using a conductivity meter CM-40S (manufactured by Toa Denpa Kogyo Co., Ltd.).

[Measurement of withstand voltage]
When a constant current (2 mA) was applied at 25 ° C. using a 10 cm ² high-purity chemically etched aluminum foil for the anode and a 10 cm ² plain aluminum foil for the cathode, a drop in voltage (short) was observed. The voltage value at the time of reading was read and regarded as the withstand voltage. The measurement was performed using a GP650-05R manufactured by Takasago Seisakusho as a DC stabilized power supply.

The electrolyte solutions of Examples 1 to 4 of the present invention were transparent even at −30 ° C., had no deposits, had fluidity, and had high conductivity.
On the other hand, the electrolyte solution of Comparative Example 1 using an alkylene oxide adduct of a trihydric alcohol was completely solidified at −30 ° C., and the weight ratio of (A) / (C) was lower than the lower limit. The electrolyte solution was solidified as a whole and had a low withstand voltage. On the other hand, the electrolyte solution of Comparative Example 2 in which the weight ratio of (A) / (C) was equal to or more than the upper limit had low conductivity.

Since the electrolytic solution of the present invention is an electrolytic capacitor that does not solidify even at low temperatures and can be driven even in a cold region, it can be suitably used for outdoor use, for example, for use in vehicles.

Claims (4)

Alkylene oxide adducts of polyhydric alcohols (a) (A), electrolytes (B) and polar solvents (C) are essential components, and the weight ratio of (A) / (C) is 5 / 95- 40/60, wherein the 4- to 6-valent polyhydric alcohol (a) is sorbitol and / or mannitol, and wherein the alkylene oxide is ethylene oxide alone.   2. The electrolytic solution for an electrolytic capacitor according to claim 1, wherein the average addition mole number of the alkylene oxide of (A) is 12 to 42.   The electrolytic solution for an electrolytic capacitor according to claim 1 or 2, wherein the weight average molecular weight of (A) is 1,000 to 2,200.   An electrolytic capacitor using the electrolytic solution for an electrolytic capacitor according to claim 1.