JP2008135693A - Electrolytic solution for aluminum electrolytic capacitor, and aluminum electrolytic capacitor using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolytic solution for an aluminum electrolytic capacitor, along with an aluminum electrolytic capacitor using the same, of which the specific conductivity of electrolytic solution at 30°C is kept at 4-25 mS/cm, with high spark voltage, and a capacitor member has no possibility of corrosion. <P>SOLUTION: The electrolytic solution contains electrolytic solution (C) consisting of anion (A) and cation (B) of alkyl phosphate which is represented by a specific chemical formula, and organic solvent (D). It is featured that the content of phosphorous acid contained in the electrolytic solution is 1 wt.% or less. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrolytic solution for an electrolytic capacitor and an electrolytic capacitor using the same.

2. Description of the Related Art In recent years, there has been a demand for an electrolytic solution that maintains the specific conductivity of the electrolytic solution at 4 mS / cm or higher and has a high spark voltage of the electrolytic solution as the operating voltage of an in-vehicle electrical power supply or digital home appliance increases.
Such an electrolytic solution for an aluminum electrolytic capacitor comprises a quaternary salt of a compound having an N, N, N′-substituted amidine group {for example, 1-methylimidazole, 1,2-dimethylimidazoline, etc.} and phthalic acid. An electrolyte solution containing an electrolyte and an organic solvent is known (Patent Document 1).
Moreover, the electrolyte solution containing the electrolyte comprised from tetrafluoroaluminate ion and the organic solvent is known (patent document 2).
International Publication No. 95/15572 Pamphlet JP 2003-142346 A

The former electrolyte has a problem that the spark voltage is too low.
Moreover, although the latter electrolyte solution has a high spark voltage, there is a problem that tetrafluoroaluminic acid is hydrolyzed to generate hydrogen fluoride and corrodes aluminum oxide that is an anode foil of the electrolytic capacitor.
The present invention uses an electrolytic solution for an aluminum electrolytic capacitor that maintains the specific conductivity of the electrolytic solution at 30 ° C. at 4 to 25 mS / cm, has a high spark voltage, and does not cause corrosion of the capacitor member, and the same. It is an object to provide an aluminum electrolytic capacitor.

As a result of intensive studies to solve the above problems, the present inventors have arrived at the present invention. That is, this invention contains the electrolyte (C) comprised from the anion (A) and cation (B) of the alkyl phosphate ester shown by the following general formula (1) or (2), and the organic solvent (D) An electrolytic solution in which the content of phosphoric acid contained in the electrolytic solution is 1% by weight or less, and an aluminum electrolytic capacitor using the electrolytic solution.

［式中、Ｒ^１は炭素数１〜１０のアルキル基、Ｒ^２は水素原子又は炭素数１〜１０のアルキル基である。］

[Wherein, R ¹ represents an alkyl group having 1 to 10 carbon atoms, and R ² represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. ]

  The electrolytic solution of the present invention maintains the specific conductivity of the electrolytic solution at 30 ° C. at 4 to 25 mS / cm, has a high spark voltage, and does not cause corrosion of the capacitor member.

<Anion (A) of alkyl phosphate ester>
The number of carbon atoms of the alkyl group (R ¹ , R ² ) is 1 to 10, preferably 1 to 8, more preferably 1 to 6, particularly preferably 1 to 4, from the viewpoints of specific conductivity and spark voltage. is there. Note that the smaller the carbon number, the higher the specific conductivity and the spark voltage.

Since phosphoric acid corrodes the capacitor member {particularly, the aluminum oxide foil that is the anode of the aluminum electrolytic capacitor}, the alkyl phosphate anion must have at least one alkyl group. With the use of a capacitor (including a load test at 125 ° C.), the alkyl phosphate anion (A) tends to hydrolyze to increase phosphoric acid. The anion represented by 2) is preferred, and more preferred is an anion in which R ¹ and R ² are both alkyl groups.

Phosphoric acid causing corrosion of the capacitor member (particularly aluminum oxide foil) is 1 wt% or less (hereinafter also referred to as wt%) with respect to the weight of the electrolytic solution, preferably 0.5 wt%. % Or less, more preferably 0.1 wt% or less. Within this range, even if the capacitor is used for a long period of time (including a long-term reliability test), an electrical failure (such as a short circuit due to corrosion of the electrode foil) is less likely to occur.

  The alkyl phosphate ester anion (A) includes (1) a monoanion and dianion of a monoalkyl phosphate ester and (2) a monoanion of a dialkyl phosphate ester.

(1) Monoalkyl phosphate ester {corresponding to alkyl phosphate ester anion (dianion) represented by general formula (1) and alkyl phosphate ester (R2 is hydrogen atom; monoanion) represented by general formula (2) . }
Monomethyl phosphate, monoethyl phosphate, monopropyl phosphate [mono (n-propyl) phosphate, mono (iso-propyl) phosphate], monobutyl phosphate [mono (n-butyl) phosphate, Mono (iso-butyl) phosphate ester and mono (tert-butyl) phosphate ester], monopentyl phosphate ester, monohexyl phosphate ester, monoheptyl phosphate ester, monooctyl phosphate ester [mono (2- Ethylhexyl) phosphate ester, etc.].

(2) Dialkyl phosphate ester {corresponds to the alkyl phosphate anion (monoanion) represented by the general formula (2). }
Dimethyl phosphate ester, diethyl phosphate ester, dipropyl phosphate ester [di (n-propyl) phosphate ester, di (iso-propyl) phosphate ester], dibutyl phosphate ester [di (n-butyl) phosphate ester, di (Iso-butyl) phosphate ester, and di (tert-butyl) phosphate ester], dipentyl phosphate ester, dihexyl phosphate ester, diheptyl phosphate ester, dioctyl phosphate ester [bis (2-ethylhexyl) phosphate ester, etc. ]etc.

The alkyl phosphate ester anion (A) may be used alone or in combination of two or more, or may be a mixture of a monoanion and a dianion.
Among these, a monoanion in which R1 and R2 are alkyl groups having 1 to 8 carbon atoms in general formula (2) is preferable, and dimethyl phosphate anion, diethyl phosphate anion, di (n-propyl) are more preferable. ) Phosphate anion, di (iso-propyl) phosphate anion, di (n-butyl) phosphate anion, di (iso-butyl) phosphate anion, di (tert-butyl) phosphate anion and Bis (2-ethylhexyl) phosphate anion.

  In general, industrially available alkyl phosphate ester is a mixture of monoalkyl phosphate ester, dialkyl phosphate ester, and trialkyl phosphate ester. In the present invention, as alkyl phosphate ester anion (A), It is preferable to use dialkyl phosphate esters. The method for obtaining the dialkyl phosphate anion is not particularly limited. By mixing an imidazolium salt {monomethyl carbonate, hydroxide salt, etc.] with a commercially available trialkyl phosphate ester, hydrolysis is performed. A method of obtaining a salt of an imidazolium cation and a dialkyl phosphate anion is preferred.

<Cation (B)>
As the cation (B), an amidinium cation (B1), a phosphonium cation, a quaternary ammonium cation, or the like can be used.
The amidinium cation (B1) includes (1) an imidazolinium cation and (2) an imidazolium cation.

(1) Imidazolinium cation 1,2,3,4-tetramethylimidazolinium, 1,3,4-trimethyl-2-ethylimidazolinium, 1,3-dimethyl-2,4-diethylimidazolinium 1,2-dimethyl-3,4-diethylimidazolinium, 1-methyl-2,3,4-triethylimidazolinium, 1,2,3,4-tetraethylimidazolinium, 1,2,3- Trimethylimidazolinium, 1,3-dimethyl-2-ethylimidazolinium, 1-ethyl-2,3-dimethylimidazolinium, 1,2,3-triethylimidazolinium, 4-cyano-1,2, 3-trimethylimidazolinium, 3-cyanomethyl-1,2-dimethylimidazolinium, 2-cyanomethyl-1,3-dimethylimidazolinium, 4-acetate Til-1,2,3-trimethylimidazolinium, 3-acetylmethyl-1,2-dimethylimidazolinium, 4-methylcarbooxymethyl-1,2,3-trimethylimidazolinium, 3-methylcarbooxy Methyl-1,2-dimethylimidazolinium, 4-methoxy-1,2,3-trimethylimidazolinium, 3-methoxymethyl-1,2-dimethylimidazolinium, 4-formyl-1,2,3- Trimethylimidazolinium, 3-formylmethyl-1,2-dimethylimidazolinium, 3-hydroxyethyl-1,2-dimethylimidazolinium, 4-hydroxymethyl-1,2,3-trimethylimidazolinium, 2 -Hydroxyethyl-1,3-dimethylimidazolinium and the like.

(2) Imidazolium cation 1,3-dimethylimidazolium, 1,3-diethylimidazolium, 1-ethyl-3-methylimidazolium, 1,2,3-trimethylimidazolium, 1,2,3,4- Tetramethylimidazolium, 1,3-dimethyl-2-ethylimidazolium, 1-ethyl-2,3-dimethyl-imidazolium, 1,2,3-triethylimidazolium, 1,2,3,4-tetraethylimidazolium Lithium, 1,3-dimethyl-2-phenylimidazolium, 1,3-dimethyl-2-benzylimidazolium, 1-benzyl-2,3-dimethyl-imidazolium, 4-cyano-1,2,3-trimethyl Imidazolium, 3-cyanomethyl-1,2-dimethylimidazolium, 2-cyanomethyl-1,3-dimethyl-imidazole Zorium, 4-acetyl-1,2,3-trimethylimidazolium, 3-acetylmethyl-1,2-dimethylimidazolium, 4-methylcarbooxymethyl-1,2,3-trimethylimidazolium, 3-methylcarbo Oxymethyl-1,2-dimethylimidazolium, 4-methoxy-1,2,3-trimethylimidazolium, 3-methoxymethyl-1,2-dimethylimidazolium, 4-formyl-1,2,3-trimethylimidazolium Rium, 3-formylmethyl-1,2-dimethylimidazolium, 3-hydroxyethyl-1,2-dimethylimidazolium, 4-hydroxymethyl-1,2,3-trimethylimidazolium, 2-hydroxyethyl-1, 3-dimethylimidazolium and the like.

  Examples of the phosphonium cation include a tetraalkylphosphonium cation {tetramethylphosphonium, tetraethylphosphonium, triethylmethylphosphonium, etc.} having an alkyl having 1 to 4 carbon atoms.

  Examples of the quaternary ammonium cation include tetraalkylammonium cations having 1 to 4 carbon atoms such as tetramethylammonium, tetraethylammonium and triethylmethylammonium.

  One or two or more amidinium cations may be used in combination. Of these, amidinium cation (B1) is preferable, 1,2,3,4-tetramethylimidazolinium cation, 1-ethyl-2,3-dimethylimidazolinium cation, 1-ethyl is more preferable. -3-methylimidazolium cation and 1-ethyl-2,3-dimethylimidazolium cation.

<Electrolyte (C)>
Examples of the combination of the alkyl phosphate anion (A) and the cation (B) include a monoanion and a monocation, a dianion and a monocation, a mixture of a monoanion and a dianion, and a monocation.

  As the electrolyte (C), 1,2,3,4-tetramethylimidazolinium monomethyl phosphate anion, 1,2,3,4-tetramethylimidazolinium dimethyl phosphate anion, 1,2 , 3,4-tetramethylimidazolinium / monoethyl phosphate anion, 1,2,3,4-tetramethylimidazolinium / diethyl phosphate anion, 1,2,3,4-tetramethylimidazolinium / Mono (n-propyl) phosphate anion, 1,2,3,4-tetramethylimidazolinium di (n-propyl) phosphate anion, 1,2,3,4-tetramethylimidazolinium Mono (iso-propyl) phosphate anion, 1,2,3,4-tetramethylimidazolinium di (iso-pro) Pyr) phosphate anion, 1,2,3,4-tetramethylimidazolinium mono (n-butyl) phosphate anion, 1,2,3,4-tetramethylimidazolinium di (n- Butyl) phosphate anion, 1,2,3,4-tetramethylimidazolinium mono (iso-butyl) phosphate anion, 1,2,3,4-tetramethylimidazolinium di (iso-) Butyl) phosphate anion, 1,2,3,4-tetramethylimidazolinium mono (tert-butyl) phosphate anion, 1,2,3,4-tetramethylimidazolinium di (tert-) Butyl) phosphate anion, 1,2,3,4-tetramethylimidazolinium mono (2-ethylhexyl) phosphate anion, 1, , 3,4-Tetramethylimidazolinium bis (2-ethylhexyl) phosphate anion, 1-ethyl-2,3-dimethylimidazolinium monoethylphosphate anion, 1-ethyl-2,3-dimethylimidazolinium・ Diethyl phosphate anion, 1-ethyl-3-methylimidazolium ・ Monoethyl phosphate anion, 1-ethyl-3-methylimidazolium ・ Diethyl phosphate anion, 1-ethyl-2,3-dimethylimidazolium monoethyl phosphate Anion, 1-ethyl-2,3-dimethylimidazolium • diethyl phosphate anion, and the like can be mentioned.

<Organic solvent (D)>
Examples of the organic solvent (D) include (1) alcohol, (2) ether, (3) amide, (4) oxazolidinone, (5) lactone, (6) nitrile, (7) carbonate, (8) sulfone, and (9 ) Other organic solvents are included.

(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 alcohol (glycerin, etc.), tetravalent or higher alcohol (hexitol, etc.), etc.

(2) Ether monoether (ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monophenyl ether, tetrahydrofuran, 3-methyltetrahydrofuran, etc.), diether (ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol monomethyl ether, diethylene glycol mono Ethyl ether), triether (diethylene glycol dimethyl ether, diethylene glycol diethyl ether, etc.), etc.

(3) 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, etc.

(4) Oxazolidinone N-methyl-2-oxazolidinone, 3,5-dimethyl-2-oxazolidinone, and the like.

(5) Lactone γ-butyrolactone (hereinafter referred to as GBL), α-acetyl-γ-butyrolactone, β-butyrolactone, γ-valerolactone, δ-valerolactone, and the like.

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

(7) Carbonate Ethylene carbonate, propion carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate and the like.

(8) Sulfone Sulfolane, dimethyl sulfoxide, dimethyl sulfone and the like.

(9) Other organic solvents 1,3-dimethyl-2-imidazolidinone, aromatic solvents (toluene, xylene, etc.) paraffin solvents (normal paraffin, isoparaffin, etc.), etc.

  One or two or more organic solvents may be used in combination. Among these, alcohol, lactone and sulfone are preferable, and γ-butyrolactone, sulfolane and ethylene glycol are more preferable.

  The content of the electrolyte (C) is preferably 5 to 70 wt%, particularly preferably 10 to 10 wt% based on the weight of the electrolyte (C) and the organic solvent (D) from the viewpoint of specific conductivity and solubility in an organic solvent. 40 wt%.

  The content of the organic solvent (D) is preferably 30 to 95 wt%, particularly preferably 60 to 90 wt% based on the weight of the electrolyte (C) and the organic solvent (D) from the viewpoint of specific conductivity.

  The electrolytic solution of the present invention preferably further contains water. When water is contained, the chemical property of the capacitor member {aluminum oxide foil or the like as the anode foil} {the property of forming an oxide film and repairing it if there is a defect portion on the surface of the anode foil} can be improved. On the other hand, when the content of water is large, hydrolysis of the alkyl phosphate anion tends to proceed, and phosphoric acid produced by hydrolysis corrodes the capacitor member. Therefore, when water is contained, the content of water is preferably 0.01 to 5 wt%, more preferably 0.05 to 1 wt%, particularly based on the weight of the electrolyte (C) and the organic solvent (D). Preferably it is 0.1-0.5 wt%. As for moisture, JIS K0113: 2005 “8. Karl Fischer titration method, 8.1 volumetric titration method” {corresponding international standard ISO760: 1978; the disclosure content disclosed therein is incorporated into the present application by reference. } Is measured in accordance with.

  The molar ratio (A / B) of the alkyl phosphate ester anion (A) to the cation (B) in the electrolyte (C) is a viewpoint of corrosion of the capacitor member {sealing rubber of aluminum electrolytic capacitor, aluminum oxide foil, etc.} Therefore, it is preferably 0.9 to 1.1, more preferably 0.95 to 1.05, and particularly preferably 0.98 to 1.02.

  If the ratio (A / B) is less than 1, the liquidity of the electrolytic solution becomes alkaline, and the butyl rubber that is the sealing rubber of the aluminum electrolytic capacitor is likely to deteriorate, resulting in problems such as leakage of the electrolytic solution from the capacitor. Is likely to occur. On the other hand, when the ratio (A / B) exceeds 1, the liquidity of the electrolytic solution becomes acidic, and the aluminum oxide foil of the anode is likely to be corroded, and as a result, problems such as short circuit are likely to occur.

  If necessary, various additives usually used in the electrolytic solution can be added to the electrolytic solution of the present invention. Examples of the additive include boric acid derivatives (for example, boric acid, complex compounds of boric acid and polysaccharides (mannitol, sorbit, etc.), complex compounds of boric acid and polyhydric alcohols (ethylene glycol, glycerin, etc.), etc. ), Nitro compounds (for example, o-nitrobenzoic acid, p-nitrobenzoic acid, m-nitrobenzoic acid, o-nitrophenol, p-nitrophenol, etc.). The addition amount is preferably 5 wt% or less, particularly preferably 2 wt% or less, based on the weight of the electrolyte (C) and the organic solvent (D), from the viewpoint of specific conductivity and solubility in the electrolytic solution.

  The electrolytic solution of the present invention is suitable for an aluminum electrolytic capacitor. The aluminum electrolytic capacitor is not particularly limited, and is, for example, a scraped aluminum electrolytic capacitor, in which a separator is provided between an anode (aluminum oxide foil) in which aluminum oxide is formed on the anode surface and a cathode aluminum foil. A capacitor formed by winding with an interposition is exemplified. The separator is impregnated with the electrolytic solution of the present invention as a driving electrolytic solution, and is housed in a bottomed cylindrical aluminum case together with a positive electrode, and then the aluminum case opening is sealed with a sealing rubber to form an aluminum electrolytic capacitor. be able to.

Next, specific examples of the present invention will be described, but the present invention is not limited thereto.
<Example 1>
By adding 2,4-dimethylimidazoline (0.1 mol) dropwise to a methanol solution (74 wt%) of dimethyl carbonate (0.2 mol) and stirring at 120 ° C. for 15 hours, 1,2,3,4- A methanol solution of tetramethylimidazolinium methyl carbonate salt was obtained.

  Methyl phosphate mixed ester (phosphoric acid about 1-3 wt%, monomethyl phosphate ester about 44-49 wt%, dimethyl phosphate ester about 44-49 wt%, trimethyl phosphate ester about 3-5 wt%) (AP-1; Daihachi (Chemical Industry Co., Ltd.) (0.1 mol) is added to a methanol solution of 1,2,3,4-tetramethylimidazolinium methyl carbonate salt (0.1 mol) to carry out a salt exchange reaction. A methanol solution of 3,4-tetramethylimidazolinium / methyl phosphate mixed ester anion was obtained. After the methanol was distilled by heating the above solution at a reduced pressure of 1.0 kPa or less and 50 ° C. until the distillation of methanol disappeared, the temperature was raised from 50 ° C. to 100 ° C. and heated for 30 minutes to obtain monomethyl carbonate ( HOCO2CH3), methanol and carbon dioxide (methanol and carbon dioxide are slightly generated by thermal decomposition of monomethyl carbonate. These are hereinafter abbreviated as by-products) to distill electrolyte (c1) {1,2 , 3,4-tetramethylimidazolinium / methylphosphoric acid mixed ester anion} was obtained. The yield is 98 wt% {1,2,3,4-tetramethylimidazolinium methyl carbonate salt (0.1 mol) based on the weight, and so on. }Met.

  25 g of the electrolyte (c1) was dissolved in 75 g of an organic solvent (d1) {γ-butyrolactone (manufactured by Mitsubishi Chemical Corporation)} to obtain an electrolytic solution of the present invention. The content of phosphoric acid contained in the electrolytic solution was 0.14 wt%. The water content was 0.1 wt%. }.

<Example 2>
Instead of methyl phosphate ester (AP-1), butyl phosphate mixed ester (mono (n-butyl) phosphate ester about 20 wt%, di (n-butyl) phosphate ester about 60 wt%, tri (n-butyl) phosphate The electrolyte (c2) {1,2,3,4-tetramethylimidazolinium-.about.20 wt% ester (DP-4; manufactured by Daihachi Chemical Industry Co., Ltd.) was used in the same manner as in Example 1. Butyl phosphate mixed ester anion} was obtained. The yield was 99 wt%.

  An electrolytic solution of the present invention was obtained by dissolving 25 g of the electrolyte (c2) in 75 g of the organic solvent (d1). The content of phosphoric acid contained in the electrolytic solution was 0.03 wt%.

<Example 3>
Instead of methyl phosphate ester (AP-1), 2-ethylhexyl phosphate mixed ester [mono (2-ethylhexyl) phosphate ester about 3 wt%, bis (2-ethylhexyl) phosphate ester about 95 wt%, tris (2-ethylhexyl ) Phosphate ester about 2 wt%] (DP-8R; manufactured by Daihachi Chemical Industry Co., Ltd.), and in the same manner as in Example 1, the electrolyte (c3) {1,2,3,4-tetramethylimidazo Rinium / 2-ethylhexyl phosphate mixed ester anion} was obtained. The yield was 99 wt%.

  An electrolytic solution of the present invention was obtained by dissolving 25 g of the electrolyte (c3) in 75 g of the organic solvent (d1). The phosphoric acid contained in the electrolytic solution was 0.01 wt%.

<Example 4>
Instead of methyl phosphate ester (AP-1), (iso-propyl) phosphate mixed ester [mono (iso-propyl) phosphate ester about 44-49 wt%, di (iso-propyl) phosphate ester about 44-49 wt% In the same manner as in Example 1, except that tri (iso-propyl) phosphate ester was about 3 to 5 wt% (PAP; manufactured by Nippon Chemical Industry Co., Ltd.), the electrolyte (c4) {1, 2, 3, 4-tetramethylimidazolinium / (iso-propyl) phosphate mixed ester anion} was obtained. The yield was 99 wt%.

  25 g of the electrolyte (c4) was dissolved in 75 g of the organic solvent (d1) to obtain the electrolytic solution of the present invention. The content of phosphoric acid contained in the electrolytic solution was 0.08 wt%.

<Example 5>
1,2,3,4-tetramethylimidazolinium methyl carbonate salt (0.1 mol) obtained by trimethyl phosphate (TMP: manufactured by Daihachi Chemical Industry Co., Ltd.) (0.1 mol) in the same manner as in Example 1. ), Methanol (0.3 mol) is added, and the mixture is stirred at 100 ° C. for 20 hours to hydrolyze trimethyl phosphate and carry out a salt exchange reaction. A methanol solution of tetramethylimidazolinium dimethyl phosphate monoanion was obtained. The solution was heated at a reduced pressure of 1.0 kPa or less at 50 ° C. until the distillation of methanol ceased to distill methanol, and then the temperature was raised from 50 ° C. to 100 ° C. and heated for 30 minutes to remove by-products. By distillation, an electrolyte (c5) {1,2,3,4-tetramethylimidazolinium dimethyl phosphate monoanion} was obtained. The yield was 99 wt%. The content of dimethyl phosphate monoanion in the anion was 99 mol%.

  25 g of the electrolyte (c5) was dissolved in 75 g of the organic solvent (d1) to obtain the electrolytic solution of the present invention. The content of phosphoric acid contained in the electrolytic solution was 0.14 wt%.

<Example 6>
The electrolyte (c6) {1,2,3,4-tetra is the same as in Example 5 except that triethyl phosphate (TEP: manufactured by Daihachi Chemical Industry Co., Ltd.) was used instead of trimethyl phosphate (TMP). Methylimidazolinium / diethyl phosphate monoanion} was obtained. The yield was 99 wt%. The content of diethyl phosphate monoanion in the anion was 99 mol%.

  An electrolytic solution of the present invention was obtained by dissolving 25 g of the electrolyte (c6) in 75 g of the organic solvent (d1). The content of phosphoric acid contained in the electrolytic solution was 0.12 wt%.

<Example 7>
Tri (n-propyl) phosphate (Triprop) instead of trimethyl phosphate (TMP)
The electrolyte (c7) {1,2,3,4-tetramethylimidazolinium di (n-propyl) phosphate mono ester was the same as in Example 5 except that yl Phosphate (manufactured by Aldrich) was used. Anion} was obtained. The yield was 99 wt%. The content of di (n-propyl) phosphate monoanion in the anion was 99 mol%.

  An electrolytic solution of the present invention was obtained by dissolving 25 g of the electrolyte (c7) in 75 g of the organic solvent (d1). The content of phosphoric acid contained in the electrolytic solution was 0.08 wt%.

<Example 8>
The electrolyte (c8) {1,2,3, except that tri (iso-propyl) phosphate (Tripropyl Phosphate: manufactured by Aldrich) was used instead of trimethyl phosphate (TMP). 4-tetramethylimidazolinium di (iso-propyl) phosphate monoanion} was obtained. The yield was 99 wt%. The content of di (iso-propyl) phosphate monoanion in the anion was 99 mol%.

  The electrolytic solution of the present invention was obtained by dissolving 25 g of the electrolyte (c8) in 75 g of the organic solvent (d1). The content of phosphoric acid contained in the electrolytic solution was 0.07 wt%.

<Example 9>
The electrolyte (c9) {1, 2, 2 was used in the same manner as in Example 5 except that tri (n-butyl) phosphate (TBP: manufactured by Daihachi Chemical Industry Co., Ltd.) was used instead of trimethyl phosphate (TMP). 3,4-tetramethylimidazolinium di (n-butyl) phosphate monoanion} was obtained. The yield was 99 wt%. The content of di (n-butyl) phosphate monoanion in the anion was 99 mol%.

  An electrolytic solution of the present invention was obtained by dissolving 25 g of the electrolyte (c9) in 75 g of the organic solvent (d1). The content of phosphoric acid contained in the electrolytic solution was 0.04 wt%.

<Example 10>
1-Ethylimidazole (0.1 mol) was added dropwise to a methanol solution (74% by weight) of dimethyl carbonate (0.1 mol), and the mixture was stirred at 120 ° C. for 15 hours to give 1-ethyl-3-methylimidazolium. A methanol solution of methyl carbonate salt was obtained.

  Triethyl phosphate (TEP; manufactured by Daihachi Chemical Industry Co., Ltd.) (0.1 mol) was added to a methanol solution of 1-ethyl-3-methylimidazolium methyl carbonate salt (0.1 mol), and water (0.3 mol) was added. Is added and the mixture is stirred at 100 ° C. for 20 hours to hydrolyze triethyl phosphate and perform a salt exchange reaction to obtain a methanol solution of 1-ethyl-3-methylimidazolium diethyl phosphate monoanion. It was. The solution was heated at a reduced pressure of 1.0 kPa or less at 50 ° C. until the distillation of methanol ceased to distill methanol, and then the temperature was raised from 50 ° C. to 100 ° C. and heated for 30 minutes to remove by-products. By distillation, an electrolyte (c10) {1-ethyl-3-methylimidazolium · diethyl phosphate monoanion} was obtained. The yield was 98 wt%. The content of diethyl phosphate in the anion was 99 mol%.

  An electrolytic solution of the present invention was obtained by dissolving 25 g of the electrolyte (c10) in 75 g of the organic solvent (d1). The content of phosphoric acid contained in the electrolytic solution was 0.12 wt%.

<Example 11>
Except for changing the 1,2,3,4-tetramethylimidazolinium / methylphosphoric acid mixed ester anion methanol solution at 100 ° C for 30 minutes (distillation of by-products) to 110 ° C for 3 hours. In the same manner as in Example 1, an electrolyte (c11) {1,2,3,4-tetramethylimidazolinium / methyl phosphate mixed ester anion} was obtained. The yield was 98 wt%.

  The electrolytic solution of the present invention was obtained by dissolving 25 g of the electrolyte (c11) in 75 g of the organic solvent (d1). The content of phosphoric acid contained in the electrolytic solution was 0.50 wt%.

<Comparative Example 1>
The electrolyte (HC1) {1,2,3,4-tetramethylimidazolinium o- is used in the same manner as in Example 1 except that o-phthalic acid is used in place of the methyl phosphate ester (AP-1). Phthalic acid} was obtained. The yield was 99 wt%.

  An electrolytic solution for comparison was obtained by dissolving 25 g of the electrolyte (HC1) in 75 g of the organic solvent (d1). The content of phosphoric acid contained in the electrolytic solution was not detected.

<Comparative example 2>
By adding 2,4-dimethylimidazoline (0.1 mol) dropwise to a methanol solution (74% by weight) of dimethyl carbonate (0.2 mol) and stirring at 120 ° C. for 15 hours, 1,2,3,4 -A methanol solution of tetramethylimidazolinium methyl carbonate salt was obtained.

  Methyl phosphoric acid mixed ester (AP-1; manufactured by Daihachi Chemical Industry Co., Ltd.) (0.1 mol) is added to a methanol solution of 1,2,3,4-tetramethylimidazolinium methyl carbonate salt (0.1 mol). Thus, a salt exchange reaction was performed to obtain a methanol solution of 1,2,3,4-tetramethylimidazolinium / methylphosphoric acid mixed ester monoanion. The above solution was heated at a reduced pressure of 1.0 kPa or less at 120 ° C. until the distillation of methanol was stopped, and methanol was distilled to obtain electrolyte (HC2) {1,2,3,4-tetramethylimidazolinium. -Methyl phosphate mixed ester monoanion} was obtained. The yield was 98 wt%.

  An electrolytic solution for comparison was obtained by dissolving 25 g of the electrolyte (HC2) in 75 g of the organic solvent (d1). The content of phosphoric acid contained in the electrolytic solution was 1.18 wt%.

  Using the electrolytic solutions obtained in Examples 1 to 11 and Comparative Examples 1 and 2, specific conductivity and spark voltage were measured, and the results are shown in Table 1.

Specific conductivity: Specific conductivity at 30 ° C. was measured using a conductivity meter CM-40S manufactured by Toa Denpa Kogyo Co., Ltd.

Spark voltage: A 10 cm 2 high-pressure chemical etching aluminum foil was used as the anode and a 10 cm 2 plain aluminum foil was used as the cathode, and the discharge voltage of the electrolyte was measured at 25 ° C when a constant current method (2 mA) was applied.

Phosphoric acid content: Performed using an ion chromatograph manufactured by Shimadzu Corporation.
Column: Shim-Pakk IC-A1
Mobile phase: Mixed solvent flow rate of 2.5 mM phthalic acid aqueous solution and 2.4 mM tris (hydroxymethyl) aminomethane (pH 4.0) aqueous solution Flow rate: 1.5 mL / min (trade name: Pump LP-6A, Shimadzu Corporation) Manufacturing)
Column oven (CTO-6AS): Temperature 40 ° C
Detector (CDD-6A): Polarity (+)

Content of dialkyl phosphate ester in anion: Measured using AL-300 type superconducting NMR apparatus manufactured by JEOL.
Sample preparation: To a 5 mmΦ NMR tube, 30 mg of sample, 0.3 ml of deuterated methanol, and 0.1 mL of triethylamine were added.
Measurement nuclide: 31P
Chemical shift of phosphoric acid diester: around -2 PPM, quintet

  Using the electrolytic solutions obtained in Examples 1 to 11 and Comparative Examples 1 and 2, a take-up type aluminum electrolytic capacitor (rated voltage 100 WV, capacitance 200 μF, size: Φ10 mm × L16 mm) was prepared.

The aluminum electrolytic capacitor thus prepared was subjected to a load test {leaving at 125 ° C for 500 hours}, and then the loss angle tangent (tan δ), leakage current (LC), and phosphoric acid content were measured. Are listed in Table 1. An evaluation result shows the average value of ten measurement results. Note that the tangent of loss angle (tan δ) and leakage current (LC) are JIS C5101-4: 1998 {corresponding international standard IEC60384-4: 1985; take in. The same applies below. }.
Further, in accordance with JIS C5101-4: 1998, the capacitance (C0) before the load test and the capacitance (C1) after the load test are measured, and the capacitance (ΔC) reduced by the load test is measured. The results are shown in Table 1. Further, from the phosphoric acid content (PO) before the load test and the phosphoric acid content (P1) after the load test, the amount of phosphoric acid (ΔP) increased by the load test was determined and shown in Table 1. .

  As is clear from Table 1, in the electrolytic solutions of the present invention (Examples 1 to 11), the specific electric conductivity of the electrolytic solution at 30 ° C. was maintained at 4 mS / cm or more and the spark voltage was sufficiently high. On the other hand, since the electrolyte obtained in Comparative Example 1 has a low spark voltage, the anode foil is short-circuited at a rated voltage of 100 WV, the capacitance change rate (ΔC) is remarkably increased, and the loss angle tangent (tan δ). ) And leakage current (LC) both increased significantly.

  When Examples 1 and 11 and Comparative Example 2 using methyl phosphate as an anion were compared in phosphoric acid content, in Comparative Example 2 having a high phosphoric acid content, the anode foil was short-circuited due to foil corrosion. As a result, the rate of change in capacitance (ΔC) increased remarkably, and the tangent of loss angle (tan δ) and leakage current (LC) both increased. On the other hand, in Examples 1 to 11 where the phosphoric acid content is low, the change rate of capacitance (ΔC), loss angle tangent (tan δ), and leakage current (LC) are both small and highly reliable. Capacitor could be created.

  The electrolyte solution containing di (n-butyl) phosphate anion obtained in Example 9 was an electrolyte solution containing mono (n-butyl) phosphate anion and di (n-butyl) phosphate anion Compared with Example 2), the amount of increase in phosphoric acid (ΔP) is small, and the rate of change in capacitance (ΔC), loss tangent (tan δ), and leakage current (LC) are further reduced. I was able to. Similarly, the electrolysis that includes the dimethyl phosphate anion obtained in Example 5 is an increase in phosphoric acid compared to the electrolyte solution (Example 1) that includes the monomethyl phosphate anion and the dimethyl phosphate anion. The amount (ΔP) was small, and the change rate of the capacitance (ΔC), loss angle tangent (tan δ), and leakage current (LC) could be further reduced. The same applies to the case where Example 4 and Example 8 are compared.

  By using the electrolytic solution of the present invention, it is possible to achieve both a high specific conductivity and a high spark voltage, and it is possible to realize an aluminum electrolytic capacitor that is free from corrosion of the capacitor member. Therefore, the market value of the electrolytic solution of the present invention is very large as the withstand voltage of the power source used in the market is increasing.

Claims (9)

An electrolyte containing an electrolyte (C) composed of an alkyl phosphate ester anion (A) and a cation (B) represented by the following general formula (1) or (2), and an organic solvent (D), An electrolytic solution, wherein the content of phosphoric acid contained in the electrolytic solution is 1% by weight or less.

[Wherein, R ¹ represents an alkyl group having 1 to 10 carbon atoms, and R ² represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. ] 2. The electrolytic solution according to claim 1, wherein, in the general formulas (1) and (2), R ¹ is an alkyl group having 1 to 4 carbon atoms, and R ² is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. The electrolytic solution according to claim 1, wherein the alkyl phosphate ester anion (A) is an anion represented by the general formula (2). Anion (A) is dimethyl phosphate anion, diethyl phosphate anion, di-iso-propyl phosphate anion, di-n-propyl phosphate anion, di-n-butyl phosphate anion, di-iso The electrolyte solution according to any one of claims 1 to 3, which is at least one selected from the group consisting of a -butyl phosphate ester anion and a di-ter-butyl phosphate anion.   The anion (A) is a monomethyl phosphate anion, a dimethyl phosphate anion, a monobutyl phosphate anion, a dibutyl phosphate anion, a mono (2-ethylhexyl) phosphate anion, and a bis (2-ethylhexyl) phosphate anion. The electrolytic solution according to claim 1, which is at least one selected from the group consisting of: The electrolyte according to any one of claims 1 to 5, wherein the cation (B) is an amidinium cation (B1). Cations (B) are 1,2,3,4-tetramethylimidazolinium cation, 1-ethyl-2,3-dimethylimidazolinium cation, 1-ethyl-3-methylimidazolium cation, and 1-ethyl. The electrolyte solution according to any one of claims 1 to 6, which is at least one selected from the group consisting of -2,3-dimethylimidazolium cations.   The electrolyte solution according to any one of claims 1 to 7, wherein the organic solvent (D) is at least one selected from the group consisting of γ-butyrolactone, sulfolane, and ethylene glycol. An aluminum electrolytic capacitor using the electrolytic solution according to claim 1.