JP2013222866A - Electric double-layer capacitor electrolyte and electric double-layer capacitor using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a durable electric double-layer capacitor electrolyte that can enhance capability for eliminating a strong alkaline component generated on a surface of a cathode-side polarizable electrode or a surface of a drawing lead connected to the cathode-side polarizable electrode, and can prevent deterioration of sealing performance of a sealing body at high temperature of particularly 70°C or more.SOLUTION: An electric double-layer capacitor electrolyte contains aprotic solvent (A); quaternary ammonium salt (D) and 4-methoxy butyric acid. The content of 4-methoxy butyric acid is 0.001-0.1% by weight of a total weight of (A) and (D).

Description

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

Conventionally, an electric double layer in the electrolyte of the capacitor tetraethylammonium tetrafluoroborate (hereinafter, described as TEA · BF ₄₎ salts (e.g., Patent Document 1) is mainly used as an electrolyte, ethyl trimethylammonium tetrafluoroborate ( Hereinafter, ETMA · BF ₄ ) salts (for example, Patent Document 2) have also been studied. In recent years, new applications such as hybrid electric vehicles that are used for a long period of time from a low temperature to a high temperature and with a large current are spreading, and in such a field, long-term durability particularly at a high temperature of 70 ° C. or higher, There is a need for a reliable electric double layer capacitor. For this reason, it is an urgent need to develop an electrolytic solution that is a member constituting the same and that is chemically stable and can be used for a long period of time.

JP-A-63-173312 Special table 2008-508736

  When the quaternary ammonium salt described in Patent Document 1 or 2 is used, a strong alkali component generated on the surface of the cathode side polarizable electrode or the surface of the lead lead connected to the cathode side polarizable electrode causes There was a problem that the sealing performance was lowered. This problem becomes more prominent as the temperature is higher, and particularly at 70 ° C. or higher, the sealing performance is significantly deteriorated. On the other hand, there are known electrolytic solutions in which the sealing performance of the sealing body does not deteriorate. However, these electrolytic solutions have insufficient durability, and the rate of change in equivalent series resistance after the durability test is large.

An object of the present invention is to improve the ability to eliminate strong alkali components generated on the surface of the cathode-side polarizable electrode or the surface of the lead lead connected to the cathode-side polarizable electrode, particularly at a high temperature of 70 ° C. or higher. An object of the present invention is to provide a durable electric double layer capacitor electrolyte that can prevent the sealing performance of the sealing body from being lowered.

As a result of intensive studies to solve the above problems, the present inventors have arrived at the present invention. That is, the present invention contains an aprotic solvent (A), a quaternary ammonium salt (D) and 4-methoxybutyric acid, and the content of 4-methoxybutyric acid is in the total weight of (A) and (D). The electric double layer capacitor electrolyte solution is 0.001 to 0.1% by weight with respect to the electric double layer capacitor electrolyte solution.

The electric double layer capacitor using the electrolytic solution for an electric double layer capacitor of the present invention can prevent the sealing performance from being deteriorated at a high temperature of 70 ° C. or more, and has durability.

The present invention is described in detail below.
By using the electrolytic solution of the present invention, a strong alkali component is generated on the surface of the cathode-side polarizable electrode or the surface of the lead lead connected to the cathode-side polarizable electrode when a voltage is applied. The strong alkali component and 4-methoxybutyric acid react well at 70 ° C. or higher when a voltage is applied, and the reaction product dissolves in the electrolytic solution. Therefore, performance deterioration due to solid precipitation does not occur, and deterioration of the sealing performance of the sealing body can be prevented particularly at a high temperature of 70 ° C. or higher.
The electrolytic solution for an electric double layer capacitor of the present invention contains an aprotic solvent (A), a quaternary ammonium salt (D), and 4-methoxybutyric acid.

The content of 4-methoxybutyric acid is 0.001 to 0.1% by weight of the total amount of (A) and (D), preferably 0.01 to 0.08% by weight, and more preferably 0 0.03 to 0.06% by weight.
If it is less than 0.001% by weight, liquid leakage occurs, and if it exceeds 0.1% by weight, the durability of the electrolyte is lost.

Specific examples of the aprotic solvent (A) include the following. Two or more of these can be used in combination.
Ethers: chain ether [carbon number 2-6 (diethyl ether, methyl isopropyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, etc.); carbon number 7-12 (diethylene glycol diethyl ether, triethylene glycol dimethyl ether, etc.)], cyclic ether [C2-C4 (tetrahydrofuran, 3-dioxolane, 1,4-dioxane, etc.); C5-C18 (2-butyldioxane, crown ether, etc.)].
Amides: N, N-dimethylformamide, N, N-dimethylacetamide, N, N-dimethylpropionamide, hexamethylphosphorylamide, N-methylpyrrolidone and the like.
-Chain esters: methyl acetate, methyl propionate, etc.
Lactones: γ-butyrolactone (hereinafter abbreviated as GBL), α-acetyl-γ-butyrolactone, β-butyrolactone, γ-valerolactone, δ-valerolactone, and the like.
Nitriles: acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropionitrile, acrylonitrile, benzonitrile and the like.
Cyclic carbonates: Propylene carbonate (hereinafter abbreviated as PC), ethylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, etc. Chain carbonate esters: dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, etc. .
Sulfones: ethylpropylsulfone, ethylisopropylsulfone, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, and the like.
・ Nitro: Nitromethane, nitroethane, etc.
Benzenes: toluene, xylene, chlorobenzene, fluorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene and the like.
Heterocyclic class: N-methyl-2-oxazolidinone, 3,5-dimethyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, N-methylpyrrolidinone and the like.
Ketones: acetone, 2,5 hexanedione, cyclohexanone, etc.
-Phosphate esters: trimethyl phosphoric acid, triethyl phosphoric acid, tripropyl phosphoric acid and the like.

Among these, lactones, cyclic carbonates, chain carbonates, chain esters, nitriles, and sulfones are preferable, and γ-butyrolactone, propylene carbonate, dimethyl carbonate, ethylene carbonate, Sulfolane and acetonitrile are preferable, and γ-butyrolactone is most preferable.

Examples of the cation (B) of the quaternary ammonium salt (D) include chain alkyl ammonium, alicyclic ammonium, aromatic ammonium, and two or more mixed cations.

Examples of the chain alkylammonium include tetraalkylammonium, and specific examples include tetramethylammonium, ethyltrimethylammonium (hereinafter referred to as ETMA), diethyldimethylammonium (hereinafter referred to as DEDMA), triethylmethylammonium (hereinafter referred to as TEMA), Tetraethylammonium (hereinafter TEA), methyltri-n-propylammonium, tri-n-butylmethylammonium, ethyltri-n-butylammonium, tri-n-octylmethylammonium, ethyltri-n-octylammonium, and diethylmethyl-i -Propyl ammonium and the like. Preferred are ETMA, DEDMA, and TEMA from the viewpoint of steric hindrance in Hoffman decomposition.

Examples of alicyclic ammonium include pyrrolidinium, piperidinium, hexamethylene iminium, morpholinium, piperazinium and the like, and specific examples are as follows.
Pyrrolidinium N, N-dimethylpyrrolidinium, N-ethyl-N-methylpyrrolidinium, N, N-ethylpyrrolidinium, spiro- (1,1 ′)-bipyrrolidinium, and piperidine-1-spiro-1 'Pyrrolidinium etc.
Piperidinium N, N-dimethylpiperidinium, N-ethyl-N-methylpiperidinium, N, N-diethylpiperidinium, Nn-butyl-N-methylpiperidinium, N-ethyl-N- n-butyl piperidinium, spiro- (1,1 ′)-bipiperidinium and the like.

-Hexamethyleneiminium N, N-dimethylhexamethyleneiminium, N-ethyl-N-methylhexamethyleneiminium, N, N-diethylhexamethyleneiminium, etc.
Morpholinium N, N-dimethylmorpholinium, N-ethyl-N-methylmorpholinium, N-butyl-N-methylmorpholinium, N-ethyl-N-butylmorpholinium, and the like.
Piperazinium N, N, N ′, N′-tetramethylpiperazinium, N-ethyl-N, N ′, N′-trimethylpiperazinium, N, N′-diethyl-N, N′-dimethylpiperazi Ni, N, N, N′-triethyl-N′-methylpiperazinium and N, N, N ′, N′-tetraethylpiperazinium.

Examples of the aromatic ammonium include pyridinium, picolinium, quinolinium, bipyridinium and the like. Specific examples are as follows.
-Pyridinium N-methylpyridinium, N-ethylpyridinium, N-methyl-4-dimethylaminopyridinium, N-ethyl-4-dimethylaminopyridinium and the like. -Picolinium N-methylpicolinium and N-ethylpicolinium.

-Quinolinium N-methylquinolinium, N-ethylquinolinium, etc.
-Bipyridinium N-methyl-2,2'-bipyridinium and N-ethyl-2,2'-bipyridinium.

Of these, tetraalkylammonium is preferred because it reacts with alkali and undergoes Hoffman decomposition. From the viewpoint of steric hindrance in Hoffman decomposition, TEMA, DEDMA, and ETMA are more preferable. Particularly preferred are DEDMA and ETMA.

Specific examples of the quaternary ammonium salt (D) anion (C) include I ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , PCl ₆ ⁻ , BCl ₄ ⁻ , AsCl ₆ ⁻ , SbCl ₆ ⁻ and TaCl. ₆ ⁻ , NbCl ₆ ⁻ , PBr ₆ ⁻ , BBr ₄ ⁻ , AsBr ₆ ⁻ , AlBr ₄ ⁻ , TaBr ₆ ⁻ , NbBr ₆ ⁻ , SbF ₆ ⁻ , AlF ₄ ⁻ , ClO ₄ ⁻ , TaCl ₄ ⁻ , TaF ₆ ⁻ , NbF ₆ ⁻ , F (HF) _n ⁻ (wherein n represents a numerical value of 1 or more and 4 or less), N (RfSO ₃ ) ₂ ⁻ , C (RfSO ₃ ) ₃ ⁻ , RfSO ₃ ⁻ , RfCO ₂ ^- and the like.
^{_{N (RfSO 3) 2 -,}} C (RfSO 3) 3 -, RfSO 3 - or RfCO ₂ ^- Rf contained in the anions represented by represents a fluoroalkyl group having 1 to 12 carbon atoms, a trifluoromethyl group , Pentafluoroethyl group, heptafluoropropyl group and nonafluorobutyl group. Of these, a trifluoromethyl group, a pentafluoroethyl group, and a heptafluoropropyl group are preferable, a trifluoromethyl group and a pentafluoroethyl group are more preferable, and a trifluoromethyl group is particularly preferable.
Among the above anions (C), from the viewpoint of electrochemical stability, an anion represented by I ⁻ , BF ₄ ⁻ , PF ₆ ^— or N (RfSO ₃ ) ₂ ^— , more preferably I ⁻ , PF ₆ ^— or a counter anion represented by BF ₄ ^— , particularly preferably an anion represented by BF ₄ ^— .

Preferred examples of the quaternary ammonium salt (D), BF chain alkylammonium ₄ ^- is a salt. Preferable specific examples are ETMA · BF ₄ , DEDMA · BF ₄ , and TEMA · BF ₄ .

The water content in the electrolytic solution of the present invention is preferably 300 ppm or less, more preferably 100 ppm or less, particularly preferably 50 ppm or less based on the weight of the electrolytic solution from the viewpoint of electrochemical stability. Within this range, it is possible to suppress the deterioration in performance of the electrochemical capacitor over time.
The water content in the electrolytic solution can be measured by the Karl Fischer method (JIS K0113-1997, coulometric titration method).
Examples of the method for setting the water content in the electrolytic solution in the above range include a method using a sufficiently dried electrolyte (A) and a non-aqueous solvent sufficiently dehydrated in advance. Examples of the drying method include a method of drying by heating under reduced pressure (for example, heating at 150 ° C. under a reduced pressure of 2.7 kPa), evaporating and removing a trace amount of water contained therein, and recrystallization.

In addition to these, the electrolytic solution is heated and dehydrated under reduced pressure (for example, heated at 100 ° C. under reduced pressure of 13.3 kPa) to evaporate and remove a trace amount of water, molecular sieve (Nacalai Tesque) Manufactured, 3A 1/16, etc.), a method using a dehydrating agent such as activated alumina powder, and the like. These methods may be performed alone or in combination.

As a basic structure of the electric double layer capacitor, a separator is sandwiched between two polarizable electrodes and impregnated with an electrolytic solution. The main component of the polarizable electrode is preferably a carbonaceous material such as activated carbon, graphite, or polyacene organic semiconductor because it is electrochemically inert to the electrolyte and has an appropriate electrical conductivity. Thus, at least one of the positive electrode and the negative electrode is a carbonaceous material. A porous carbon material (for example, activated carbon) having a specific surface area of 10 m ² / g or more determined by the BET method by the nitrogen adsorption method is more preferable because of the large electrode interface where charges are accumulated. The specific surface area of the porous carbon material is selected in consideration of the target capacitance per unit area (F / m ² ) and the decrease in bulk density associated with the increase in the specific surface area. preferably it has a specific surface area determined is 30~2,500m ² / g by the BET method, since the electrostatic capacity per volume is large, the specific surface area is particularly preferably activated carbon 300~2,300m ² / g.

Examples of the electric double layer capacitor of the present invention include a coin type, a wound type, and a rectangular type. The electrolytic solution for an electric double layer capacitor of the present invention can be applied to any electric double layer capacitor.

  As sealing bodies for electric double layer capacitors, butyl rubber containing isoprene and isobutylene is generally used. Among them, butyl rubber to which alkylphenol formalin resin is added as a vulcanizing agent and peroxide as a vulcanizing agent are used. Added butyl rubber is preferred.

The electrolytic solution of the present invention can be prepared by a known method, and the concentration of the quaternary ammonium salt (D) in the electrolytic solution is preferably 0.5 to 2.0 mol / L, and 0.7 to 1. 7 mol / L is more preferable, and 0.8 to 1.5 mol / L is most preferable. When the concentration of (D) is 0.5 mol / L or more, the conductivity of the electrolytic solution is sufficient, and when it is 2.0 mol / L or less, the low-temperature characteristics are good and the economy is excellent.

The electrolytic solution of the present invention is used for an electric double layer capacitor. In particular, it is preferably used as an electric double layer capacitor for automobile applications. Since the deterioration of the sealing rubber at 70 ° C. or more can be suppressed, it can be used in an engine room where higher durability is required.
Also for power backup of various electronic devices, as a power storage device that replaces secondary batteries such as power storage elements used in combination with various power backup power sources and solar cells, and for power tools such as motor drive power supplies and power tools The present invention can be applied to power sources, particularly power sources for hybrid vehicles and electric vehicles that require long-term durability and reliability. Also in these applications, it can be used without leakage even at 70 ° C. or higher, and a capacitor with high durability and reliability can be provided.

Next, specific examples of the present invention will be described, but the present invention is not limited thereto. Hereinafter, “parts” means “parts by weight” unless otherwise specified.
In the following examples, ¹ H-NMR, ¹⁹ F-NMR, and ¹³ C-NMR were measured by the following methods.
Measurement conditions for ¹ H-NMR Instrument: AVANCE 300 (manufactured by Nippon Bruker Co., Ltd.), solvent: deuterated dimethyl sulfoxide, frequency: 300 MHz.
¹⁹ F-NMR measurement conditions Instrument: AL-300 (manufactured by JEOL Ltd.), solvent: deuterated dimethyl sulfoxide, frequency: 300 MHz
Measurement conditions for ¹³ C-NMR Instrument: AL-300 (manufactured by JEOL Ltd.), solvent: deuterated dimethyl sulfoxide, frequency: 300 MHz
Moreover, the silver ion content was quantified by the turbidimetric method with an atomic absorption spectrophotometer (Shimadzu Corporation AA-6200).

The purity of the quaternary ammonium salt (D) was quantified by the peak area obtained by high performance liquid chromatography (HPLC). HPLC measurement conditions are as follows.
Column: packed with polymer-coated filler, mobile phase: phosphate buffer (pH 2-3), flow rate: 0.5 ml / min, detector: UV, temperature: 40 ° C. (eg, instrument: mold) Name (LC-10A), manufacturer (Shimadzu Corporation), column: Develosil C30-UG (4.6 mmφ × 25 cm) manufacturer (Nomura Chemical), mobile phase: phosphoric acid concentration 10 mmol / l, sodium perchlorate concentration 100 mmol / L aqueous solution, flow rate: 0.8 ml / min, detector: UV (210 nm), injection volume: 20 μl, column temperature: 40 ° C.

Hereinafter, production examples of the present invention will be described. DEDMA · BF ₄ and TEMA · BF ₄ were prepared as solutions because they were difficult to handle as salts due to the properties of the compounds.

<Production Example 1><< Production of ETMA · BF ₄ salt >>
Synthesis of iodide salt 110 parts of N, N-dimethylethylamine (manufactured by Tokyo Chemical Industry Co., Ltd.) and 339 parts of acetone were charged into a glass beaker and uniformly dissolved. 234 parts of methyl iodide was slowly added dropwise while stirring the solution, and then stirring was continued at 30 ° C. for 3 hours. The precipitated white solid was filtered and dried at 80 ° C. under reduced pressure to obtain 322 parts of ethyltrimethylammonium iodide.

Preparation of AgBF ₄ solution A solution obtained by mixing 174 parts of silver oxide and 314 parts of a 42% by weight aqueous solution of borohydrofluoric acid was dehydrated at 100 ° C. under reduced pressure, and 825 parts of methanol was added to dissolve it. AgBF ₄ methanol A solution was obtained.

-Preparation of BF ₄ salt 1117 parts of AgBF ₄ methanol solution was slowly added dropwise to the above mixed solution of 322 parts of ethyltrimethylammonium iodide and 353 parts of methanol, and then filtered to collect the filtrate. The AgBF ₄ solution or mixed solution was added little by little to the collected filtrate to finely adjust the silver ion content in the solution to 10 ppm or less and the iodine ion content to 5 ppm or less, and then filtered to collect the filtrate.
The filtrate was desolvated at 80 ° C. under reduced pressure to obtain 262 parts of white crystals. Silver ions in the crystal were 10 ppm or less, and iodide ion content was 5 ppm or less. After adding 3000 parts of methanol to the crystal and dissolving at 60 ° C., the solution was cooled to −10 ° C. and allowed to stand for 12 hours for recrystallization. The precipitated crystals were filtered and dried under reduced pressure at 80 ° C. to obtain 124 parts of white crystals. As a result of analysis by ¹ H-NMR, ¹⁹ F-NMR and ¹³ C-NMR, this white crystal was an ETMA · BF ₄ salt. ^From the integral value of ¹ H-NMR, the purity was 99 mol%.

<Production Example 2><< Production of DEDMA · BF ₄ salt / GBL solution >>
Hereinafter, commercially available γ-butyrolactone (manufactured by Tokyo Chemical Industry) is distilled at 120 ° C. under a reduced pressure of 10 kPa to remove moisture and impurities, and is referred to as “purified γ-butyrolactone”.
261 parts of diethylmethylamine (manufactured by Tokyo Chemical Industry Co., Ltd.), 540 parts of dimethyl carbonate (manufactured by Tokyo Chemical Industry Co., Ltd.) and 720 parts of methanol (manufactured by Tokyo Chemical Industry Co., Ltd.) are charged and uniformly dissolved in a stainless steel autoclave with a reflux condenser. It was. Next, the temperature was raised to 130 ° C. The reaction was performed at a pressure of 0.8 MPa for 80 hours. 1H-NMR analysis of the reaction product revealed that diethyldimethylammonium monomethyl carbonate (S-0) was produced. 1174 parts of the resulting reaction mixture was placed in a flask, and 582 parts of a 42% pure borofluoric acid aqueous solution (manufactured by Wako Pure Chemical Industries, Ltd.) was gradually added dropwise over about 30 minutes at room temperature with stirring. Carbon dioxide gas was generated along with the dripping. The water content of this reaction solution was 17%. To the reaction solution, 648 parts of purified γ-butyrolactone was added, transferred to a simple distillation apparatus, decompressed to 120 ° C. and 10 kPa, and methanol and water were removed in 2 hours. 1178 parts of a yellowish brown transparent aqueous solution remained in the flask. To this solution was added 530 parts of methanol, the pressure was reduced to 120 ° C. and 10 kPa, and the water was removed by distilling off the methanol in 1 hour. This operation was repeated three times. As a result of ¹ H-NMR analysis of this liquid, the main component was diethyldimethylammonium tetrafluoroborate, and the purity was 98% from HPLC analysis. The water content of this solution was 0.1%.
To this solution was added 933 parts of isopropyl alcohol. The contents of DEDMA · BF ₄ , γ-butyrolactone and isopropyl alcohol in this solution were 25%, 31% and 44%, respectively. The crystals were allowed to stand in a −5 ° C. refrigerator for 10 hours, and the crystals were collected by filtration. To the crystal obtained by filtration, 530 parts of isopropyl alcohol was added, washed with reslurry, and filtered again. This operation was repeated three times to obtain washed crystals (S-1). The HF content generated by hydrolysis of BF _{4 as} an anion was about 40 ppm in the crystal (S-1). When a large amount of HF is contained in the crystal (S-1), the solvent is decomposed in the heat dehydration in the next step.
144 parts of crystals (S-1) were put in a 1000 ml container, and 573 parts of purified γ-butyrolactone was added. In order to further lower the water content by azeotropic distillation, 1% of isopropyl alcohol was added, and water and isopropyl alcohol were distilled off under reduced pressure at 60 ° C. to obtain 718 parts of a DEDMA · BF ₄ / GBL solution. The yield was 95%, and the purity was 99.7% from HPLC analysis. The moisture was 40 ppm. ^{From 1} H-NMR analysis, this DEDMA / GBL solution did not contain impurities such as GBL ring-opened products.

The HF content of the crystal (S-1) was measured by the following method.
2 parts of crystals (S-1) were uniformly dissolved in 8 parts of purified γ-butyrolactone and precisely weighed into a flask using an analytical balance. Cold water at 0 ° C. was added thereto to make a total of 100 ml. Bromothymol blue was added to this solution as an indicator, and titrated with a 1/10 normal aqueous sodium hydroxide solution. The point at which the solution turned blue-violet and lasted for 5 seconds was taken as the end point of the titration. The HF content of the crystal (S-1) was calculated by the following formula.
_{C (S-1) = (} 0.002 × A × F / S) × 10 6 / (C S / 100)
here,
C _(S-1) : HF content (ppm) in crystal (S-1)
A: Amount of sodium hydroxide aqueous solution required for titration (ml)
F: Factor of sodium hydroxide aqueous solution S: Weight of crystal (S-1) / GBL solution (g)
C _S : concentration of crystal (S-1) / GBL solution (wt%)

<Production Example 3><< Production of DEDMA · BF ₄ / PC Solution >>
Hereinafter, commercially available propylene carbonate (manufactured by Tokyo Chemical Industry Co., Ltd.) is distilled at 65 ° C. and 1.3 kPa under reduced pressure to remove moisture and impurities, and is referred to as “purified propylene carbonate”. 145 parts of the crystals (S-1) obtained in Production Example 2 are placed in a 500 ml container, 428 parts of purified propylene carbonate are added, water and isopropyl alcohol are distilled off under reduced pressure at 60 ° C., and 573 parts of DEDMA · BF are added. _{A 4} / PC solution was obtained. The yield was 95%, and the purity was 99.7% from HPLC analysis. The moisture was 40 ppm.

<Production Example 4><< Production of triethylmethylammonium tetrafluoroborate (TEMA.BF ₄ ) >>
In a stainless steel autoclave with a reflux condenser, 389 parts of triethylamine (manufactured by Tokyo Chemical Industry Co., Ltd.), 450 parts of dimethyl carbonate (manufactured by Tokyo Chemical Industry Co., Ltd.) and 211 parts of methanol (manufactured by Tokyo Chemical Industry Co., Ltd.) were charged and uniformly dissolved. Next, the temperature was raised to 110 ° C. The reaction was performed at a pressure of 0.8 MPa for 80 hours. ¹ H-NMR analysis of the reaction product revealed that triethylmethylammonium monomethyl carbonate was produced. 1002 parts of the obtained reaction mixture was placed in a flask, and 735 parts of a 42% pure borofluoric acid aqueous solution (manufactured by Wako Pure Chemical Industries, Ltd.) was gradually added dropwise over about 30 minutes at room temperature with stirring. Carbon dioxide gas was generated along with the dripping. The water content of this reaction solution was 17%. 904 parts of γ-butyrolactone was added to the reaction solution, transferred to a simple distillation apparatus, decompressed to 120 ° C. and 10 kPa, and methanol and water were removed in 2 hours. In the flask, 1644 parts of a yellowish brown transparent aqueous solution remained. 740 parts of methanol was added to this solution, the pressure was reduced to 120 ° C. and 10 kPa, and water was removed by distilling off the methanol in 1 hour. This operation was repeated three times. As a result of 1H-NMR analysis of this liquid, the main component was trimethylethylammonium tetrafluoroborate, and the purity was 98% from HPLC analysis. The water content of this solution was 0.1%.
To this solution, 1302 parts of isopropyl alcohol was added. The contents of TEMA · BF ₄ , γ-butyrolactone, and isopropyl alcohol in this solution were 25%, 31%, and 44%, respectively. The crystals were allowed to stand in a −5 ° C. refrigerator for 10 hours, and the crystals were collected by filtration. To the crystals obtained by filtration, 740 parts of isopropyl alcohol was added, and reslurry washing was performed, followed by filtration again. This operation was repeated three times to obtain washed crystals (S-2). 154 parts of crystals (S-2) were placed in a 1000 ml container, and 423 parts of γ-butyrolactone was added. In order to further reduce the water content by azeotropic distillation, 1% of isopropyl alcohol was added again, and water and isopropyl alcohol were distilled off under reduced pressure at 60 ° C. to obtain 576 parts of a TEMA · BF ₄ / GBL solution. The yield was 95%, and the purity was 99.7% from HPLC analysis. The moisture was 40 ppm. ^{From the 1} H-NMR analysis, this TEMA / PC solution did not contain impurities such as a ring-opened product of propylene carbonate.

<Production Example 5><< Production of DEDMA · PF ₆ >>
To 500 parts of diethyldimethylammonium monomethyl carbonate (S-0) obtained in Production Example 2, 183 parts of potassium hexafluorophosphate (manufactured by Tokyo Chemical Industry Co., Ltd.) was gradually added dropwise at 0 ° C. over about 30 minutes. Carbon dioxide gas was generated along with the dripping. After generation | occurrence | production of foam | bubble settled, the reaction liquid was moved to the rotary evaporator, and the whole quantity of solvent was removed. In the flask, 221 parts of a yellowish brown transparent liquid remained. When this liquid was analyzed by ¹ H-NMR, the main component was diethyldimethylammonium hexafluorophosphonate (hereinafter abbreviated as crude DEDMA.PF ₆ ).
In the Erlenmeyer flask, the prepared crude DEDMA. 100 parts of PF ₆ was dissolved in 150 parts of isopropyl alcohol. It was left to stand in a −10 ° C. refrigerator for 10 hours, crystallized, and collected by filtration. The crystals were placed in a 500 ml container, and water and isopropyl alcohol were distilled off under reduced pressure at 125 ° C. × 1.3 kPa. PF ₆ was obtained. The yield was 60%, and the purity was 99.1% from HPLC analysis.

<Production Example 6><< DEDMA. Production of C ₄ F ₉ SO ₃ >>
To 500 parts of diethyldimethylammonium monomethyl carbonate (S-0) obtained in Production Example 2, 361 parts of nonafluorobutanesulfonic acid (manufactured by Tokyo Chemical Industry Co., Ltd.) was gradually added dropwise at 0 ° C. over about 30 minutes. Carbon dioxide gas was generated along with the dripping. After generation | occurrence | production of foam | bubble settled, the reaction liquid was moved to the rotary evaporator, and the whole quantity of solvent was removed. In the flask, 322 parts of a tan transparent liquid remained. When this liquid was analyzed by ¹ H-NMR, the main component was diethyldimethylammonium nonafluorobutanesulfonate (hereinafter abbreviated as crude DEDMA.C ₄ F ₉ SO ₃ ).
In the Erlenmeyer flask, the prepared crude DEDMA. 100 parts of C ₄ F ₉ SO ₃ was dissolved in 150 parts of isopropyl alcohol. The crystals were deposited in a refrigerator at −40 ° C. for 10 hours, and collected by filtration. The crystals were placed in a 500 ml container, and water and isopropyl alcohol were distilled off under reduced pressure at 125 ° C. × 1.3 kPa. PF ₆ was obtained. The yield was 63%, and the purity was 99.3% from HPLC analysis.

Production Example 7 << Production of Spiro- (1,1 ')-bipyrrolidinium tetrafluoroborate (hereinafter abbreviated as SBP · BF ₄ ) >>
100 parts of pyrrolidine and 97 parts of potassium carbonate were charged into an autoclave coated with Teflon (registered trademark), 198 parts of 1,5-dichloropentane was added, and the reaction was performed at 90 ° C. for 8 hours. To this reaction solution, 294 parts of a 42% by weight aqueous borohydrofluoric acid solution was added dropwise at 25 ° C. over about 30 minutes. After the completion of the dropping and the generation of bubbles was stopped, the entire solvent was distilled off at 20 Torr and 100 ° C. to obtain 200 parts of a solid. This solid was crystallized twice using ethanol and isopropyl alcohol to obtain 155 parts of white crystals. As a result of analysis by ¹ H-NMR, ¹⁹ F-NMR and ¹³ C-NMR, the white crystals were SBP · BF ₄ .

<< Production Example 8 >><< Production of Tetraethylammonium Tetrafluoroborate (TEA · BF ₄ ) >>
Synthesis of iodide salt 102 parts of triethylamine (manufactured by Tokyo Chemical Industry Co., Ltd.) and 300 parts of acetone were charged into a glass beaker and dissolved uniformly. While stirring the solution, 171 parts of ethyl iodide was slowly added dropwise, and stirring was continued at 30 ° C. for 3 hours. The precipitated white solid was filtered and dried at 80 ° C. under reduced pressure to obtain 257 parts of tetraethylammonium iodide.

-Preparation of AgBF ₄ solution A solution obtained by mixing 116 parts of silver oxide and 209 parts of 42 wt% aqueous borofluoric acid solution at 100 ° C under reduced pressure was dissolved in 550 parts of methanol, and dissolved in AgBF ₄ methanol. A solution was obtained.

-Preparation of BF ₄ salt 745 parts of the above AgBF ₄ solution was slowly added dropwise to a mixed solution of 257 parts of tetraethylammonium iodide and 232 parts of methanol and filtered, and the filtrate was recovered. An AgBF ₄ solution or an iodide salt solution was added little by little to the filtrate to finely adjust the silver ion content in the solution to 10 ppm or less and the iodine ion content to 5 ppm or less, and then filtered to collect the filtrate. The filtrate was desolvated at 80 ° C. under reduced pressure to obtain 186 parts of white crystals. 300 parts of methanol was added to the crystal and dissolved at 30 ° C., then cooled to −5 ° C. and allowed to stand for 12 hours for recrystallization. The precipitated crystals were filtered and dried under reduced pressure at 80 ° C. to obtain 162 parts of white crystals. As a result of analysis by ¹ H-NMR, ¹⁹ F-NMR and ¹³ C-NMR, this white crystal was TEA · BF ₄ . ^From the integral value of ¹ H-NMR, the purity was 99%.

<Production Example 9><< Production of 1-ethyl-2,3-dimethylimidazolium tetrafluoroborate (EDMI · BF ₄ ) >>
A reaction flask equipped with a stirrer, thermometer, dropping funnel, reflux condenser, and nitrogen gas introducing agent was charged with a mixture of 31 parts ethylamine (70% aqueous solution) and 32 parts ammonia (28% aqueous solution) while stirring. Dissolved uniformly. While maintaining the temperature at 45 ° C. or lower, a mixed solution of 69 parts of glyoxal (40% aqueous solution) and 71 parts of acetaldehyde (30% aqueous solution) was dropped from the dropping funnel. Whether or not the mixture of glioxal and acetaldehyde was an enemy was carried out over 5 hours, and the reaction was carried out at 40 ° C. for 1 hour after completion of the dropwise addition. Next, dehydration was performed by gradually reducing the pressure from normal pressure to 5.0 kPa at a temperature of 80 ° C., followed by rough purification by simple distillation under the conditions of a temperature of 105 ° C. and a pressure of 1.0 kPa. Got. In a stainless steel autoclave with a reflux condenser, 100 parts of 1-ethyl-2-methylimidazole, 135 parts of dimethyl carbonate and 192 parts of methanol were charged and uniformly dissolved. Next, the temperature was raised to 130 ° C. The reaction was performed at a pressure of 0.8 kPa for 80 hours. ¹ H-NMR analysis of the reaction product revealed that 1-ethyl-2,3-dimethylimidazolium monomethyl carbonate was produced. 427 parts of the resulting reaction mixture was placed in a flask, and 207 parts of a borohydrofluoric acid aqueous solution (purity 42% by weight) was gradually added dropwise over about 30 minutes at room temperature with stirring. Carbon dioxide gas was generated during the dropping. After generation | occurrence | production of foam | bubble settled, the reaction liquid was moved to the rotary evaporator and the whole quantity of solvent was removed. In the flask, 82 parts of a tan transparent liquid remained. The obtained yellowish brown transparent liquid was crystallized using methanol and isopropyl alcohol to obtain a white solid. When this solid was analyzed by 1H-NMR, it was 1-ethyl-2,3-dimethylimidazolium tetrafluoroborate. ^From the integral value of ¹ H-NMR, the purity was 99 mol%.

Example 1
13.7 parts of ETMA · BF ₄ salt of Production Example 1 and 0.05 part of 4-methoxybutyric acid (manufactured by Nacalai Tesque) were uniformly dissolved in 86.3 parts of purified γ-butyrolactone (electrolyte concentration 0.9 mol / L). ) To obtain an electrolytic solution 1 of the present invention.

Example 2
13.3 parts of ETMA · BF ₄ salt of Production Example 1 and 0.05 part of 4-methoxybutyric acid were uniformly dissolved in 43.3 parts of purified γ-butyrolactone and 43.3 parts of purified propylene carbonate (electrolyte concentration of 0.1). 9 mol / L), an electrolytic solution 2 of the present invention was obtained.

Example 3
13.5 parts of ETMA · BF ₄ salt of Production Example 1 and 0.05 part of 4-methoxybutyric acid were uniformly dissolved in 58.0 parts of purified γ-butyrolactone and 28.5 parts of purified propylene carbonate (electrolyte concentration of 0.2%). 9 mol / L), an electrolytic solution 3 of the present invention was obtained.

Example 4
58.8 parts of the DEDMA · BF ₄ / GBL solution of Production Example 2 and 0.05 part of 4-methoxybutyric acid were uniformly dissolved in 41.2 parts of purified γ-butyrolactone (electrolyte concentration 0.9 mol / L). Inventive electrolyte 4 was obtained.

Example 5
57.2 parts of the DEDMA · BF ₄ / PC solution of Production Example 3 and 0.05 part of 4-methoxybutyric acid were uniformly dissolved in 42.8 parts of purified γ-butyrolactone (electrolyte concentration: 0.9 mol / L). Inventive electrolyte 5 was obtained.

Example 6
71.8 parts of the DEDMA · BF ₄ / GBL solution of Production Example 2 and 0.05 part of 4-methoxybutyric acid were uniformly dissolved in 28.2 parts of purified propylene carbonate (electrolyte concentration 0.9 mol / L), and the present invention. An electrolytic solution 6 was obtained.

Example 7
59.3 parts of the TEMA · BF ₄ salt / GBL solution of Production Example 7 and 0.05 part of 4-methoxybutyric acid were uniformly dissolved in 40.7 parts of purified γ-butyrolactone (electrolyte concentration: 0.9 mol / L). The electrolytic solution 7 of the present invention was obtained.

Example 8
57.7 parts of TEMA · BF ₄ salt / GBL solution of Production Example 3 and 0.05 part of 4-methoxybutyric acid were uniformly dissolved in 42.3 parts of purified propylene carbonate (electrolyte concentration 0.9 mol / L). Inventive electrolyte 8 was obtained.

Example 9
An electrolytic solution 9 of the present invention was obtained in the same manner as in Example 4 except that 0.1 part of 4-methoxybutyric acid was used instead of 0.05 part of 4-methoxybutyric acid.

Example 10
An electrolytic solution 10 of the present invention was obtained in the same manner as in Example 4 except that 0.001 part of 4-methoxybutyric acid was used instead of 0.05 part of 4-methoxybutyric acid.

Example 11
12.9 parts of ETMA · BF ₄ salt of Production Example 1 and 0.05 part of 4-methoxybutyric acid were uniformly dissolved in 87.1 parts of purified propylene carbonate (electrolyte concentration of 0.9 mol / L), and the electrolysis of the present invention. Liquid 11 was obtained.

Hereinafter, commercially available sulfolane (manufactured by Sumitomo Seika Co., Ltd.) is distilled under reduced pressure conditions at 120 ° C. and 0.7 kPa to remove moisture and impurities and is referred to as “purified sulfolane”.

Example 12
14.9 parts of the DEDMA · BF ₄ / GBL solution of Production Example 2 and 0.05 part of 4-methoxybutyric acid were uniformly dissolved in 85.1 parts of purified sulfolane (electrolyte concentration: 0.9 mol / L). Obtained electrolyte solution 12

Example 13
17.7 parts of SBP · BF ₄ salt of Production Example 7 and 0.05 part of 4-methoxybutyric acid were uniformly dissolved in 82.3 parts of purified propylene carbonate (electrolyte concentration of 0.9 mol / L), and the electrolysis of the present invention. Liquid 13 was obtained.

Example 14
19.2 parts of DEDMA · PF ₆ salt of Production Example 5 and 0.05 part of 4-methoxybutyric acid were uniformly dissolved in 80.8 parts of purified γ-butyrolactone (electrolyte concentration: 0.9 mol / L). An electrolytic solution 14 was obtained.

Example 15
30.7 parts of DEDMA · C ₄ F ₉ SO ₃ salt of Production Example 6 and 0.05 part of 4-methoxybutyric acid were uniformly dissolved in 69.3 parts of purified γ-butyrolactone (electrolyte concentration: 0.9 mol / L). The electrolytic solution 15 of the present invention was obtained.

Comparative Example 1
Comparative electrolyte solution 1 was obtained in the same manner as in Example 1 except that 0.05 part of 4-methoxybutyric acid was not added.

Comparative Example 2
12.9 parts of ETMA · BF ₄ salt of Production Example 1 and 0.0005 part of 4-methoxybutyric acid were uniformly dissolved in 87.1 parts of purified γ-butyrolactone (electrolyte concentration: 0.9 mol / L), and a comparative electrolytic solution 2 was obtained.

Comparative Example 3
12.9 parts of ETMA · BF ₄ salt of Production Example 1 and 0.15 part of 4-methoxybutyric acid are uniformly dissolved in 87.1 parts of purified γ-butyrolactone (electrolyte concentration: 0.9 mol / L), and a comparative electrolytic solution 3 was obtained.

Comparative Example 4
Comparative electrolyte solution 4 was obtained in the same manner as in Example 4 except that 0.05 part of 4-methoxybutyric acid was not added.

Comparative Example 5
Comparative electrolytic solution 5 was obtained in the same manner as in Example 5 except that 0.05 part of 4-methoxybutyric acid was not added.

Comparative Example 6
Comparative electrolytic solution 6 was obtained in the same manner as in Example 7 except that 0.05 part of 4-methoxybutyric acid was not added.

Comparative Example 7
Comparative electrolyte solution 7 was obtained in the same manner as in Example 13 except that 0.05 part of 4-methoxybutyric acid was not added.

Comparative Example 8
16.9 parts of TEA · BF ₄ salt of Production Example 8 was uniformly dissolved in 83.1 parts of purified γ-butyrolactone (electrolyte concentration: 0.9 mol / L) to obtain Comparative Electrolytic Solution 8.

Comparative Example 9
Comparative electrolyte solution 9 was obtained in the same manner as in Example 11 except that 0.05 part of 4-methoxybutyric acid was not added.

Comparative Example 10
Comparative electrolytic solution 10 was obtained in the same manner as in Example 12 except that 0.05 part of 4-methoxybutyric acid was not added.

Comparative Example 11
17.4 parts of EDMI · BF ₄ salt of Production Example 9 was uniformly dissolved in 82.6 parts of purified γ-butyrolactone (electrolyte concentration: 1.0 mol / L) to obtain a comparative electrolyte solution 11.

Comparative Example 12
Comparative electrolyte solution 12 was obtained in the same manner as in Example 14 except that 0.05 part of 4-methoxybutyric acid was not added.

Comparative Example 13
Comparative electrolytic solution 13 was obtained in the same manner as in Example 15 except that 0.05 part of 4-methoxybutyric acid was not added.

Using the electrolytic solutions 1 to 15 of the present invention and the comparative electrolytic solutions 1 to 13, a wound type electric double layer capacitor (diameter 17 mm, height 40 mm) was prepared, and the equivalent series resistance was obtained by the following method. Change rate and the sealing rubber surface of the sealing body were observed. These results are shown in Table 1.

(1) Sealing Rubber Surface of Sealing Body The state of the sealing rubber surface constituting the sealing body of the electric double layer capacitor after applying a voltage of 2.8 V to the electric double layer capacitor at 85 ° C. for 3000 hours was confirmed.
The number of test of the sealing rubber surface of the sealing body is eight.
The same experiment was conducted by changing the temperature from 85 ° C to 30 ° C.

(2) Rate of change of equivalent series resistance Equivalent series resistance (RE ₃₀₀₀ ) at 1 kHz of the electric double layer capacitor after applying a voltage of 2.8 V to the electric double layer capacitor at 85 ° C. for 3000 hours and 1 kHz before voltage application The ratio with respect to the equivalent series resistance (RE ₀ ) was calculated by the following formula, and this was taken as the rate of change of the equivalent series resistance. The equivalent series resistance was measured at −30 ° C. using an impedance analyzer (Solartron SI1253, SI1286). A smaller value of the rate of change means that performance deterioration with time is smaller and good charge / discharge characteristics can be maintained.
(Equivalent Series Resistance Change Rate) (%) = [(RE ₃₀₀₀ ) / (RE ₀ )] × 100
The same experiment was conducted by changing the temperature from 85 ° C to 30 ° C.

In Table 1, Example 1 and Comparative Examples 1 and 2, Examples 4 to 6, 9, 10 and Comparative Examples 4 to 5, and Example 7 and Comparative Example 6 and Example using the same solvent and the same kind of electrolyte were used. 13 and Comparative Example 7, Example 12 and Comparative Example 10, Example 14 and Comparative Example 12, Example 15 and Comparative Example 13 are compared, and the electric double layer capacitor of Comparative Example has an abnormal liquid leakage due to deterioration of the sealing rubber. However, no abnormality of liquid leakage was observed in the examples. There was no significant difference in the rate of change of the equivalent series resistance.
In Comparative Example 3 in which the content of 4-methoxybutyric acid exceeds 0.1% by weight, there was no abnormality of liquid leakage due to deterioration of the sealing rubber of the electric double layer capacitor as compared with Example 1, but the change in equivalent series resistance The rate was great.

That is, by using the electrolytic solution of the present invention, it is clear that the sealing performance of the sealing body of the electric double layer capacitor is excellent and the change rate of the equivalent series resistance is small, and a highly reliable electric double layer capacitor can be configured. is there.

The electric double layer capacitor produced using the electrolytic solution of the present invention is a power storage device that replaces secondary batteries such as power storage elements used in combination with memory backup for various electronic devices, various power backup power sources, and solar cells. As such, it can be applied to a power source for a power tool such as a motor driving power source and a power tool, particularly a hybrid vehicle and a power source for an electric vehicle that require long-term durability and reliability.

Claims (6)

The aprotic solvent (A) contains a quaternary ammonium salt (D) and 4-methoxybutyric acid, and the content of 4-methoxybutyric acid is 0.001 to the total weight of (A) and (D). Electrolytic solution for electric double layer capacitor which is 0.1% by weight. The electrolytic solution for an electric double layer capacitor according to claim 1, wherein the cation (B) of the quaternary ammonium salt (D) is a chain alkyl ammonium. The electrolytic solution for an electric double layer capacitor according to claim 1 or 2, wherein the cation (B) of the quaternary ammonium salt (D) is at least one selected from the group consisting of triethylmethylammonium, ethyltrimethylammonium, and diethyldimethylammonium. . Anion of quaternary ammonium salt (D) (C) is, BF ₄ ^- and electrolytic solution for an electric double layer capacitor according to any one of claims 1 to 3. The electric double layer capacitor which uses the electrolyte solution of any one of Claims 1-4. The electric double layer capacitor according to claim 5, which is used for automobiles.