Electrolyte solution

Abstract

The purpose of the present invention is to provide a novel electrolyte solution.　The electrolyte solution contains a quaternary ammonium salt having at least one group selected from among branched aliphatic hydrocarbon groups and alicyclic hydrocarbon groups.

Description

electrolyte

[0001] The present invention relates to an electrolyte solution and the like.

[0002] An electric double-layer capacitor (EDLC) is an energy storage device that stores electricity by utilizing the phenomenon in which ions in an electrolyte form an electric double layer due to physical adsorption between the electrolyte and an electrode when an electric field is applied to the electrolyte. Compared to secondary batteries such as lithium-ion batteries, which generate electricity through chemical reactions, electric double-layer capacitors have a faster charge / discharge rate and are therefore widely used in, for example, uninterruptible power supplies (UPS). In recent years, as societal demands for environmental and energy efficiency have become increasingly stringent, EDLCs have recently been increasingly used in a wide range of applications, including energy regeneration from automobiles, auxiliary power, temporary storage of power from wind power generation, and power supply for devices such as copiers when they resume from standby mode. EDLCs are therefore one of the most popular energy storage devices.

[0003] Furthermore, in recent years, there has been an increasing demand for improved output density and energy density of electrochemical devices such as batteries and capacitors, and from the viewpoint of voltage resistance, organic electrolyte solutions (non-aqueous electrolyte solutions) are increasingly being used rather than aqueous electrolyte solutions.

[0004] As an organic electrolyte, for example, Patent Document 1 discloses a non-aqueous electrolyte containing N-ethyl-N-methylpyrrolidinium tetrafluoroborate or the like.

[0005] Japanese Patent Application Laid-Open No. 2014-241347

[0006] An object of the present invention is to provide a novel electrolyte solution.

[0007] Another object of the present invention is to provide an electrolyte solution having excellent durability.

[0008] The present inventors have conducted extensive research into electrolytes containing ammonium salts and have found that, among quaternary ammonium salts, the use of a specific ammonium salt results in superior durability. After further intensive research, they have completed the present invention.

[0009] That is, the present invention relates to the following electrolytes, etc.: [1] An electrolyte containing a quaternary ammonium salt having at least one selected from a branched aliphatic hydrocarbon group and an alicyclic hydrocarbon group. [2] The electrolyte according to [1], wherein the branched aliphatic hydrocarbon group is a C3 to C10 (3 to 10 carbon atoms) branched alkyl group. [3] The electrolyte according to [1] or [2], wherein the branched aliphatic hydrocarbon group is a C3 to C5 branched alkyl group. [4] The electrolyte according to any one of [1] to [3], wherein the branched aliphatic hydrocarbon group is selected from an isopropyl group, a sec-butyl group, an isobutyl group, a tert-butyl group, a 2-pentyl group, a 3-pentyl group, and a 3-methyl-2-butyl group. [5] The electrolyte according to any one of [1] to [4], wherein the alicyclic hydrocarbon group is a C3 to C10 cycloalkyl group. [6] The electrolyte according to any one of [1] to [5], wherein the alicyclic hydrocarbon group is a C3 to C7 cycloalkyl group. [7] The electrolyte solution according to any one of [1] to [4], wherein the quaternary ammonium salt is a mono C3-C6 branched alkyl tri-linear C1-C4 alkyl ammonium salt. [8] The electrolyte solution according to any one of [1] to [4] and [7], wherein the quaternary ammonium salt is an isopropyl tri-linear C1-C4 alkyl ammonium salt. [9] The electrolyte solution according to any one of [1] to [8], wherein the quaternary ammonium salt has two or more methyl groups (or contains one or more selected from a quaternary ammonium salt having at least one branched aliphatic hydrocarbon group and two or more (two or three) methyl groups, and a quaternary ammonium salt having at least one alicyclic hydrocarbon group and two or more (two or three) methyl groups).

[10] The electrolyte solution according to any one of [1] to [9], which contains one or more non-aqueous solvents selected from propylene carbonate, ethylene carbonate, butylene carbonate, sulfolane, methyl sulfolane, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, gamma butyrolactone, and acetonitrile.

[11] The electrolyte solution according to any one of [1] to

[10] , wherein the non-aqueous solvent contains one or more non-aqueous solvents selected from gamma butyrolactone and acetonitrile.

[12] The electrolyte solution according to any one of [1] to

[11] , wherein the quaternary ammonium salt is a mono C3-C6 branched alkyl tri-linear C1-C4 alkyl ammonium salt, and the non-aqueous solvent contains one or more selected from gamma butyrolactone and acetonitrile.

[13] The electrolyte solution according to any one of [1] to

[12] , wherein the quaternary ammonium salt is ammonium tetrafluoroborate.

[14] The electrolyte solution according to any one of [1] to

[13] , wherein the electrolyte contains 50 ppm or less of an alkali metal cation (e.g., 0.1 to 50 ppm, 40 ppm or less, 0.1 to 30 ppm).

[15] The electrolyte solution according to

[14] , wherein the alkali metal cation is sodium ion and / or potassium ion.

[16] The electrolyte solution according to any one of [1] to

[15] , wherein the electrolyte is for use in an electric double layer capacitor.

[17] An electric double layer capacitor comprising the electrolyte solution according to any one of [1] to

[16] .

[18] A quaternary ammonium salt having at least one selected from a branched aliphatic hydrocarbon group and an alicyclic hydrocarbon group.

[19] The quaternary ammonium salt according to

[18] , wherein the branched aliphatic hydrocarbon group is a C3 to C10 branched alkyl group.

[20] A quaternary ammonium salt selected from isopropyltrimethylammonium salt, isopropyltriethylammonium salt, isopropylethyldimethylammonium salt, sec-butyltrimethylammonium salt, sec-butylethyldimethylammonium salt, diisopropyldimethylammonium salt, 3-pentyltrimethylammonium salt, isopropyl-n-propyldimethylammonium salt, isobutyltrimethylammonium salt, isobutylethyldimethylammonium salt, 2-pentyltrimethylammonium salt, 3-methyl-2-butyltrimethylammonium salt, cyclopentyltrimethylammonium salt, and cyclohexyltrimethylammonium salt.

[21] Isopropylethyldimethylammonium salt and sec-butyltrimethylammonium salt.

[22] The quaternary ammonium salt according to any one of

[18] to

[21] , wherein the ammonium salt is ammonium tetrafluoroborate.

[23] The ammonium salt according to any one of

[18] to

[22] , containing 300 ppm or less (e.g., 0.1 to 300 ppm) [e.g., 200 ppm or less (e.g., 0.1 to 200 ppm), 150 ppm or less (e.g., 0.1 to 150 ppm)] of alkali metal cations.

[24] A quaternary ammonium salt selected from isopropyltrimethylammonium salt, isopropyltriethylammonium salt, isopropylethyldimethylammonium salt, sec-butyltrimethylammonium salt, sec-butylethyldimethylammonium salt, diisopropyldimethylammonium salt, 3-pentyltrimethylammonium salt, isopropyl-n-propyldimethylammonium salt, isobutyltrimethylammonium salt, isobutylethyldimethylammonium salt, 2-pentyltrimethylammonium salt, 3-methyl-2-butyltrimethylammonium salt, cyclopentyltrimethylammonium salt, and cyclohexyltrimethylammonium salt, wherein the ammonium salt of the quaternary ammonium salt is ammonium tetrafluoroborate, and the quaternary ammonium salt contains 300 ppm or less of an alkali metal cation.

[25] A method for producing a quaternary ammonium salt according to any one of

[18] to

[24] , comprising at least a step of reacting a tertiary amine corresponding to the quaternary ammonium salt (a tertiary amine having a branched aliphatic hydrocarbon group and / or an alicyclic hydrocarbon group) with an alkyl halide to obtain a halide salt of the quaternary ammonium (a quaternary ammonium having at least one group selected from a branched aliphatic hydrocarbon group and an alicyclic hydrocarbon group).

[0010] According to the present invention, a novel electrolyte solution can be provided. Such an electrolyte solution can reduce capacity degradation and therefore exhibit excellent durability.

[0011] According to another aspect of the present invention, the capacity degradation of the electrolyte can be reduced in terms of the capacity value over a wide temperature range (for example, −40 to 80° C.).

[0012] According to another aspect of the present invention, the capacity degradation of the electrolyte can be reduced even at low temperatures (for example, about −40° C. to 0° C.) where degradation is more pronounced. An electrolyte that has deteriorated due to high temperature or long-term use is likely to experience significant capacity degradation, particularly when used at low temperatures. However, according to another aspect of the present invention, the capacity degradation of the electrolyte can be reduced even when such an electrolyte is used at low temperatures.

[0013] According to another aspect of the present invention, an electrolyte solution with reduced capacity degradation can be provided, and therefore an electric double layer capacitor with excellent durability in which a decrease in capacity (capacity degradation) and an increase in resistance are reduced over a long period of time can be provided.

[0014] According to another aspect of the present invention, alkalinization due to moisture in the electrolyte can be suppressed, thereby suppressing leakage from an electric double layer capacitor. Although there is a trade-off between improving the withstand voltage, which contributes to reducing capacity degradation of the electrolyte, and suppressing alkalinization, according to another aspect of the present invention, both improving the withstand voltage and suppressing alkalinization can be efficiently achieved.

[0015] According to another aspect of the present invention, gas generation due to decomposition of the electrolyte can be suppressed, and swelling of the electric double layer capacitor can be suppressed.

[0016] The electrolytic solution of the present invention usually contains an electrolyte.

[0017] Electrolyte The electrolyte contains a specific electrolyte [a quaternary ammonium salt having at least one selected from a branched aliphatic hydrocarbon group and an alicyclic hydrocarbon group (hereinafter, sometimes simply referred to as "ammonium salt (1)")].

[0018] In the ammonium salt (1), examples of the counter ion of the ammonium cation include PF ６ － , tetrafluoroborate (BF ４ － ), AsF ６ － , N(CF ３ SO ２ ) ２ － , SbF ６ － , RfSO ３- (Rf is a fluoroalkyl group having 1 to 8 carbon atoms), and preferably BF ４ － may be.

[0019] In the ammonium salt (1), the number of branched aliphatic hydrocarbon groups and / or alicyclic hydrocarbon groups may be at least one, or may be two or more (e.g., three or four). From the viewpoint of reducing capacity degradation of the electrolyte solution, the number of branched aliphatic hydrocarbon groups is preferably one or two, and more preferably one.

[0020] Examples of branched aliphatic hydrocarbon groups include branched saturated aliphatic hydrocarbon groups (for example, C3 to C10 branched alkyl groups) and branched unsaturated aliphatic hydrocarbon groups (for example, C3 to C10 branched alkenyl groups).

[0021] Examples of the branched aliphatic hydrocarbon group include, from the viewpoint of reducing capacity degradation of the electrolyte, C3 to C10 branched alkyl groups (e.g., 2-ethylhexyl group, isooctyl group), and preferably C3 to C5 branched alkyl groups (e.g., isopropyl group, sec-butyl group, isobutyl group, tert-butyl group, 2-pentyl group, 3-pentyl group, 3-methyl-2-butyl group, etc.).

[0022] The branched aliphatic hydrocarbon group is preferably branched at the carbon atom adjacent to the nitrogen atom of the ammonium salt. The branched aliphatic hydrocarbon group may have one branch or two or more branches.

[0023] Examples of the alicyclic hydrocarbon group include saturated alicyclic hydrocarbon groups (for example, C3 to C10 cycloalkyl groups) and unsaturated alicyclic hydrocarbon groups (for example, C3 to C10 cycloalkenyl groups).

[0024] Examples of saturated alicyclic hydrocarbon groups include C3 to C10 cycloalkyl groups (e.g., cycloheptyl group, cyclooctyl group), C3 to C10 cycloalkyl C1 to C4 alkyl groups (e.g., cyclohexylmethyl group), and from the viewpoint of reducing capacity degradation of the electrolyte, preferred are C3 to C7 cycloalkyl groups (e.g., cyclopropyl group, cyclobutyl group, cyclopentyl group, cyclohexyl group, cycloheptyl group).

[0025] Representative examples of the ammonium salt (1) include mono C3-C6 branched alkyl tri-straight-chain C1-C4 alkyl ammonium salts [for example, isopropyl tri-straight-chain C1-C4 alkyl ammonium salts (for example, isopropyl trimethyl ammonium salts such as isopropyl trimethyl ammonium tetrafluoroborate, isopropyl triethyl ammonium salt, isopropyl ethyl dimethyl ammonium salt, isopropyl-n-propyl dimethyl ammonium salt, isopropyl methyl di-n-propyl ammonium salt, isopropyl diethyl-n-propyl ammonium salt, isopropyl ethyl methyl-n-propyl ammonium salt], isobutyl tri-straight-chain C1-C4 alkyl ammonium salts (for example, isobutyl trimethyl ammonium salt, isobutyl ethyl dimethyl ammonium salt, isobutyl triethyl ammonium salt, isobutyl n-butyl dimethyl ammonium salt), sec-butyl tri-straight-chain C1-C4 alkyl ammonium salts (for example, sec-butyl trimethyl ammonium salt, sec-butyl ethyl dimethyl ammonium salt), tert-butyl tri-straight-chain C1-C4 alkyl ammonium salt (e.g., tert-butyltrimethylammonium salt, tert-butylethyldimethylammonium salt, tert-butyltriethylammonium salt, tert-butyl-n-propyldimethylammonium salt, tert-butyl-n-butyldimethylammonium salt), 3-pentyltri straight-chain C1-C4 alkylammonium salt (e.g., 3-pentyltrimethylammonium salt), 2-pentyltri straight-chain C1-C4 alkylammonium salt (e.g., 2-pentyltrimethylammonium salt), 3-methyl-2-butyltri straight-chain C1-C4 alkylammonium salt di-C3-C6 branched alkyl di-linear C1-C4 alkyl ammonium salts (e.g., diisopropyldimethylammonium salt, diisopropyldiethylammonium salt, diisopropylethylmethylammonium salt, diisopropylmethyl-n-propylammonium salt, isobutyl-tert-butyldimethylammonium salt, di-tert-butyldimethylammonium salt), mono-C3-C7 cycloalkyl tri-linear C1-C4 alkyl ammonium salts (e.g.,In electrochemical devices such as electric double layer capacitors, when a voltage is applied, the small amount of water present in the electrolyte is reduced together with oxygen to form OH, － ions (hydroxide ions) are generated, and the electrolyte gradually becomes strongly alkaline. －The ions corrode the resin, rubber, or metal of the sealing part of the negative electrode, causing leakage of the electrolyte and reducing the reliability of the electrochemical device. The use of these ammonium salts (1) can suppress strong alkalization, and among them, quaternary ammonium salts having at least one branched aliphatic hydrocarbon group and two or more (two or three) methyl groups [e.g., mono C3-C6 branched alkyl dimethyl mono linear C1-C4 alkyl ammonium salts (e.g., isopropylethyl dimethyl ammonium salt, sec-butylethyl dimethyl ammonium salt, isopropyl-n-propyl dimethyl ammonium salt, isobutylethyl dimethyl ammonium salt), mono C3-C6 branched alkyl trimethyl ammonium salts (e.g., isopropyl trimethyl ammonium salt, sec-butyl trimethyl ammonium salt, 3-pentyl trimethyl ammonium salt, isobutyl trimethyl ammonium salt, 2-pentyl trimethyl ammonium salt), di C3-C6 branched alkyl dimethyl ammonium salts (e.g., diisopropyl dimethyl ammonium salt), 3-methyl Preferred are quaternary ammonium salts having at least one alicyclic hydrocarbon group and two or more (two or three) methyl groups [e.g., mono C3-C7 cycloalkyltrimethylammonium salts (e.g., cyclopentyltrimethylammonium salt, cyclohexyltrimethylammonium salt)], and more preferred are isopropylethyldimethylammonium salt, sec-butyltrimethylammonium salt, sec-butylethyldimethylammonium salt, diisopropyldimethylammonium salt, 3-pentyltrimethylammonium salt, isopropyl-n-propyldimethylammonium salt, isobutyltrimethylammonium salt, isobutylethyldimethylammonium salt, 2-pentyltrimethylammonium salt, 3-methyl-2-butyltrimethylammonium salt, cyclopentyltrimethylammonium salt, and cyclohexyltrimethylammonium salt. Ammonium salts (1) having two or more methyl groups are likely to efficiently achieve both improved voltage resistance, which contributes to reducing capacity degradation, and alkalinity suppression, which are in a trade-off relationship.

[0026] The ammonium salt (1) may be used alone or in combination of two or more.

[0027] Ammonium salt (1) can be produced, for example, by a method including at least a step of reacting a tertiary amine having a branched aliphatic hydrocarbon group and / or an alicyclic hydrocarbon group with an alkyl halide to obtain a halide salt of a quaternary ammonium having at least one group selected from a branched aliphatic hydrocarbon group and an alicyclic hydrocarbon group, which corresponds to ammonium salt (1). The halide salt may be reacted with a counter ion of the desired ammonium salt (1) to perform salt exchange.

[0028] The electrolyte may or may not contain an alkali metal cation. The alkali metal cation content in the ammonium salt (1) may be, for example, 300 ppm or less (e.g., 0.1 ppm to 300 ppm), 200 ppm or less (e.g., 0.1 ppm to 200 ppm), or 150 ppm or less (e.g., 0.1 ppm to 150 ppm).

[0029] Examples of alkali metal cations include lithium ions, sodium ions, and potassium ions, and are preferably sodium ions and potassium ions, more preferably potassium ions. The alkali metal cations may be one type or two or more types.

[0030] When the electrolyte contains multiple types of alkali metal ions, the total amount of these ions is adjusted to fall within the above range.

[0031] The electrolytic solution may contain one or more electrolytes other than the ammonium salt (1), as long as the effects of the present invention are achieved.

[0032] Examples of other electrolytes include quaternary ammonium salts that do not belong to the category of ammonium salts (1). Examples of such ammonium salts include tetraalkylammonium salts that do not belong to the category of ammonium salts (1), pyrrolidinium salts, spiro-type quaternary ammonium salts, morpholinium salts, imidazolinium salts, pyrimidinium salts, piperazinium salts, piperidinium salts, pyridinium salts, and imidazolium salts. Note that the counter ion of the ammonium cation in such ammonium salts is not particularly limited, and examples thereof include those exemplified above.

[0033] As the other electrolytes, commercially available products may be used, or those produced by known methods may be used.

[0034] When another electrolyte is used, the proportion of the ammonium salt (1) in the total amount of the ammonium salt (1) and the other electrolyte may be, for example, 10 mol% or more, 30 mol% or more, 50 mol% or more, 70 mol% or more, 90 mol% or more, 95 mol% or more, 99 mol% or more, or may be substantially 100 mol%.

[0035] When another electrolyte is used, the upper limit of the proportion of the ammonium salt (1) in the total amount of the ammonium salt (1) and the other electrolyte is not particularly limited, and may be, for example, 99 mol% or less, 95 mol% or less, 90 mol% or less, 85 mol% or less, or 80 mol% or less.

[0036] The proportion of the ammonium salt (1) in the total amount of the ammonium salt (1) and other electrolytes may be selected by appropriately combining these ranges (upper and lower limits), and may be, for example, 10 to 90 mol %.

[0037] The present invention also includes the above ammonium salt (1).

[0038] Solvent The electrolyte may contain a solvent. The solvent may typically contain a non-aqueous solvent. Examples of non-aqueous solvents include carbonate-based solvents (e.g., propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate), sulfur-containing solvents (e.g., sulfolane, methyl sulfolane, and mixed solvents of these with ethyl methyl sulfone), phosphate-based solvents (e.g., triethyl phosphate), lactone-based solvents (e.g., gamma butyrolactone), and nitrile-based solvents (e.g., acetonitrile). From the viewpoint of reducing capacity degradation of the electrolyte, gamma butyrolactone, acetonitrile, and the like are preferred. In electrochemical devices such as electric double layer capacitors, gases such as carbon dioxide can be generated by oxidation and hydrolysis reactions that occur near the electrodes when voltage is applied. This can cause deterioration and reduced reliability of the electrochemical device, and can also cause the device to appear swollen. In the electrolyte solution of the present invention, the generation of this gas can be efficiently suppressed by using a sulfur-containing solvent, a phosphate ester solvent, a lactone solvent, or a nitrile solvent, with lactone solvents being preferred and lactone solvents being more preferred. Specifically, gamma-butyrolactone and acetonitrile are preferred, with acetonitrile being particularly preferred.

[0039] The non-aqueous solvent may be used alone or in combination of two or more.

[0040] The non-aqueous solvent may be a commercially available product, or may be further purified by any method before use.

[0041] Electrolyte The electrolyte may or may not contain an alkali metal cation. Examples of the alkali metal cation include those exemplified above, and preferably sodium ions, potassium ions, etc., and more preferably potassium ions. The alkali metal cation may be one type or two or more types.

[0042] The content of alkali metal cations in the electrolytic solution is not particularly limited, and may be, for example, 0.1 ppm or more (e.g., 1 ppm or more, 5 ppm or more, 7 ppm or more), preferably 10 ppm or more (e.g., 12 ppm or more, 15 ppm or more, 18 ppm or more, 20 ppm or more, 25 ppm or more). From the viewpoint of durability, the electrolytic solution preferably contains alkali metal cations at a predetermined ratio, and the lower limit of the alkali metal cation content in the electrolytic solution may be, for example, 3 ppm or more, 5 ppm or more, etc.

[0043] The upper limit of the alkali metal cation content in the electrolyte is not particularly limited, and may be, for example, 70 ppm or less (e.g., 65 ppm or less, 60 ppm or less), 55 ppm or less (e.g., 50 ppm or less, 45 ppm or less), 40 ppm or less (e.g., 35 ppm or less), or 30 ppm or less (e.g., 25 ppm or less). In Patent Document 1, the durability of the electrolyte is achieved by adjusting the alkali metal cation content in the electrolyte. However, in the present invention, durability can be efficiently improved by using ammonium salt (1) without relying on adjusting the alkali metal cation content. In the present invention, further adjustment of the alkali metal cation content may make it easier to improve durability.

[0044] The content of alkali metal cations in the electrolyte may be selected by appropriately combining these ranges (upper and lower limits), and may be, for example, 0.1 to 30 ppm.

[0045] When the electrolyte contains multiple types of alkali metal ions, the total amount of these ions is adjusted to fall within the above range.

[0046] The method for producing an electrolyte solution having an alkali metal cation content within the above range is not particularly limited. For example, the alkali metal cation content in the electrolyte solution may be adjusted by adjusting the alkali metal cation content in the nonaqueous solvent and / or electrolyte, which are raw materials for the electrolyte solution, or an alkali metal salt may be added separately to the electrolyte solution. Among these, a method of adjusting the alkali metal cation content in the electrolyte solution by adjusting the alkali metal cation content in the electrolyte is preferred. For example, the alkali metal cation content in the electrolyte used in the electrolyte solution is preferably 0.1 to 300 ppm, more preferably 0.5 to 120 ppm. In particular, the alkali metal cation content in the ammonium salt (1) is preferably 0.1 to 300 ppm (e.g., 0.1 to 200 ppm), more preferably 0.5 to 120 ppm. Examples of methods for adjusting the alkali metal cation content in an electrolyte such as ammonium salt (1) include using an alkali metal salt during salt exchange in the production of an electrolyte of ammonium salt (1) and controlling the equivalent number of reagents; dissolving the electrolyte in a solvent (poor solvent) that has low solubility for alkali metal salts, and filtering the resulting electrolyte solution to remove the alkali metal salt that did not dissolve in the poor solvent. These methods typically produce an electrolyte such as ammonium salt (1) containing 0.1 ppm to 300 ppm of alkali metal cations. The resulting electrolyte such as ammonium salt (1) can be dissolved in a high-purity (e.g., purity of about 99.99% or higher) non-aqueous solvent to give an electrolyte concentration of, for example, about 0.1 to 3 mol / L, thereby producing an electrolyte solution having an alkali metal cation content of 0.1 to 30 ppm.

[0047] The amount of alkali metal cations contained in the electrolyte and the electrolytic solution can be measured by a known method such as ion chromatography. For example, when measuring by ion chromatography, the conditions described in the Examples can be used.

[0048] The concentration of the ammonium salt (1) in the electrolytic solution is preferably 0.1 to 3 mol / L, particularly preferably 0.8 to 2.5 mol / L, from the viewpoints of easily improving the conductivity of the electrolytic solution, easily suppressing an increase in the internal resistance of an electric double layer capacitor produced using the electrolytic solution, and easily using the electrolytic solution even at low temperatures because salt is less likely to precipitate in the electrolytic solution even at low temperatures.

[0049] The electrolytic solution of the present invention may contain one or more components other than the above components (electrolyte, non-aqueous solvent, and alkali metal cation) as long as the effects of the present invention are achieved.

[0050] A typical electrolyte solution of the present invention is, for example, an electrolyte solution containing a quaternary ammonium salt having at least one group selected from a branched aliphatic hydrocarbon group and an alicyclic hydrocarbon group, and containing at least one nonaqueous solvent selected from carbonate-based solvents (e.g., propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate), sulfur-containing solvents (e.g., sulfolane, methyl sulfolane, and mixed solvents of these with ethyl methyl sulfone), phosphate-based solvents (e.g., triethyl phosphate), lactone-based solvents (e.g., gamma butyrolactone), and nitrile-based solvents (e.g., acetonitrile). The electrolytic solution of the present invention may preferably be an electrolytic solution containing at least one selected from quaternary ammonium salts such as isopropyltrimethylammonium salt, isopropyltriethylammonium salt, isopropylethyldimethylammonium salt, sec-butyltrimethylammonium salt, sec-butylethyldimethylammonium salt, diisopropyldimethylammonium salt, 3-pentyltrimethylammonium salt, isopropyl-n-propyldimethylammonium salt, isobutyltrimethylammonium salt, isobutylethyldimethylammonium salt, 2-pentyltrimethylammonium salt, 3-methyl-2-butyltrimethylammonium salt, cyclopentyltrimethylammonium salt, and cyclohexyltrimethylammonium salt, and at least one selected from non-aqueous solvents such as sulfolane, methylsulfolane, gamma butyrolactone, and acetonitrile.The electrolytic solution of the present invention is preferably at least one selected from quaternary ammonium salts, such as isopropylethyldimethylammonium salt, sec-butyltrimethylammonium salt, sec-butylethyldimethylammonium salt, diisopropyldimethylammonium salt, 3-pentyltrimethylammonium salt, isopropyl-n-propyldimethylammonium salt, isobutyltrimethylammonium salt, isobutylethyldimethylammonium salt, 2-pentyltrimethylammonium salt, 3-methyl-2-butyltrimethylammonium salt, cyclopentyltrimethylammonium salt, and cyclohexyltrimethylammonium salt, and at least one selected from non-aqueous solvents, such as propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, sulfolane, methylsulfolane, gamma butyrolactone, and acetonitrile. The electrolytic solution of the present invention may preferably be an electrolytic solution containing at least one quaternary ammonium salt selected from isopropylethyldimethylammonium salt, sec-butyltrimethylammonium salt, sec-butylethyldimethylammonium salt, diisopropyldimethylammonium salt, 3-pentyltrimethylammonium salt, isopropyl-n-propyldimethylammonium salt, isobutyltrimethylammonium salt, isobutylethyldimethylammonium salt, 2-pentyltrimethylammonium salt, 3-methyl-2-butyltrimethylammonium salt, cyclopentyltrimethylammonium salt, and cyclohexyltrimethylammonium salt, and at least one non-aqueous solvent selected from gamma-butyrolactone and acetonitrile.

[0051] The electrolytic solution of the present invention can be suitably used for, for example, electric double layer capacitors. The present invention also encompasses electric double layer capacitors that use the electrolytic solution of the present invention as the electrolyte. The electric double layer capacitor of the present invention may be any capacitor that uses the above-described electrolytic solution as the electrolyte, and its manufacturing method, etc., is not particularly limited. By using the above-described electrolytic solution, the electric double layer capacitor is improved in durability by reducing a decrease in capacity (capacity degradation) and an increase in resistance. The above-described electrolytic solution can be used over a wide temperature range (e.g., −40 to 80°C), and can efficiently reduce capacity degradation even at low temperatures where degradation is particularly noticeable.

[0052] The present invention also encompasses a method for producing ammonium salt (1), which includes at least a step of reacting a tertiary amine (a tertiary amine having a branched aliphatic hydrocarbon group and / or an alicyclic hydrocarbon group) corresponding to the quaternary ammonium salt (ammonium salt (1)) with an alkyl halide to obtain a halide salt of the quaternary ammonium (a quaternary ammonium having at least one group selected from a branched aliphatic hydrocarbon group and an alicyclic hydrocarbon group). The halide salt may be reacted with a counterion of the target ammonium salt (1) to perform salt exchange. The alkyl group in the alkyl halide used in this step may generally be an alkyl group present in the target ammonium salt (1), but not present in the tertiary amine used in this step. For example, when the target ammonium salt (1) is an isopropyltrimethylammonium salt, isopropyldimethylamine may be used as the tertiary amine and methyl chloride as the alkyl halide. Known organic chemistry techniques may be used for the reaction of the tertiary amine with the alkyl halide and for the salt exchange. The salt exchange method may be, for example, a method in which an acid consisting of a counter ion of the target ammonium salt (1) or an alkali metal salt thereof is mixed in an arbitrary solvent and reacted.

[0053] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0054] Evaluation of Electric Double Layer Capacitor Characteristics (Method of Producing Capacitor) An element (3 cm x 5 cm: 5 sheets laminated) was produced using the following materials, and after vacuum drying at 150°C for 15 hours, it was impregnated with an electrolyte (amount of electrolyte: 0.1 cc / F) to produce a laminate cell (electric double layer capacitor). The produced electric double layer capacitor was subjected to an aging treatment for 24 hours with 2.7 V applied at room temperature, and the initial capacity was measured at room temperature and -30°C. Electrodes: Sheet electrodes manufactured by Japan Gore-Tex (Japan Gore LLC) Electrolytic paper (separator): TF4050 manufactured by Nippon Kodoshi Kogyo Electrolyte: Each electrolyte solution produced in each example and comparative example

[0055] The electric double layer capacitor was stored at 65° C. for 500 hours while a voltage of 2.7 V was applied, and the capacity was then measured at room temperature and −30° C., and the rate of capacity deterioration from the initial capacity was calculated.

[0056] Quantitative analysis of alkali metal cations Quantitative analysis of potassium ions: Measurements were performed using ion chromatography. Column: Dionex Ion Pac CS14 φ4 × 250 mm (Nippon Dionex Co., Ltd.) Detection method: Conductivity Suppressor: CSRS300 (product name, Nippon Dionex Co., Ltd.) Suppressor current: 35 mA Mobile phase: 0.010 M methanesulfonic acid solution Regenerant: Ultrapure water (2 mL / min) Mobile phase flow rate: 1.0 mL / min Column temperature: 30°C Cell temperature: 35°C Sample injection volume: 25 μL Measurement method: A standard (0.1 ppm potassium solution) and a sample solution (approximately 500 mg of sample diluted to 50 mL with ultrapure water) were analyzed, and the content was calculated using the following formula based on the peaks obtained.

[0057] Potassium ion (K ＋ ) content (ppm) = K in sample solution ＋ Peak area x 0.1 x 50 / sample amount (mg) / K in standard solution ＋ Peak area x 1000

[0058] Na ＋ , and other alkali metal cations were analyzed by changing the standard to the target compound.

[0059] The electrolyte salt (ammonium salt) and K in the electrolyte solution in each example and reference example ＋ and Na ＋ The contents are shown in Table 1.

[0060] The electrolyte solutions used in the Examples and Comparative Examples were prepared as follows: The gamma-butyrolactone used in the Examples and Comparative Examples was high-purity gamma-butyrolactone (purity of 99.9% or more).

[0061] Electrolyte Synthesis Example 1: Isopropyldimethylamine and acetone were charged into a pressure vessel, and methyl chloride was blown into the pressure vessel and reacted at 110°C for 8 hours while stirring. The precipitated solid was filtered and dried under reduced pressure at 80°C to obtain isopropyltrimethylammonium chloride salt. Isopropyltrimethylammonium chloride salt and potassium fluoroborate were subjected to ion exchange in an acetone solution, and the precipitated solid (potassium chloride) was filtered to obtain an isopropyltrimethylammonium tetrafluoroborate / acetone solution. The solvent was removed from the obtained solution to obtain crystals. 2-Propanol was added to the crystals and dissolved at 80°C, then cooled to 5°C and allowed to stand for 12 hours to allow recrystallization. The precipitated crystals were filtered and dried under reduced pressure at 80°C to obtain white isopropyltrimethylammonium tetrafluoroborate crystals.

[0062] Synthesis Example 2: Isopropylethyldimethylammonium tetrafluoroborate was obtained in the same manner as in Synthesis Example 1, except that methyl chloride was changed to ethyl chloride.

[0063] Synthesis Example 3: sec-butylamine, potassium carbonate, and chloroform were charged into a pressure vessel, and methyl chloride was blown into the pressure vessel and reacted at 110°C for 16 hours with stirring. The precipitated solid was filtered and dried under reduced pressure at 80°C to obtain a mixture of sec-butyltrimethylammonium chloride salt and potassium chloride. The resulting mixture and potassium fluoroborate were subjected to ion exchange in an acetone solution, and the precipitated solid (potassium chloride) was filtered to obtain a sec-butyltrimethylammonium tetrafluoroborate / acetone solution. The solvent was removed from the resulting solution to obtain crystals. 2-Propanol was added to the crystals and dissolved at 80°C, then cooled to 5°C and allowed to stand for 12 hours to allow recrystallization. The precipitated crystals were filtered and dried under reduced pressure at 80°C to obtain white sec-butyltrimethylammonium tetrafluoroborate.

[0064] Synthesis Example 4: Dimethylpyrrolidinium tetrafluoroborate was obtained according to the method described in Example 1 of JP-B-8-31401, except that dimethylpyrrolidinium bromide was used instead of 1-ethyl-1-methylpyrrolidinium bromide. The obtained dimethylpyrrolidinium tetrafluoroborate was recrystallized according to the method described in Production Example 2 of Patent Document 1, to obtain dimethylpyrrolidinium tetrafluoroborate.

[0065] Electrolyte Example 1: An electrolyte solution was prepared by dissolving the isopropyltrimethylammonium tetrafluoroborate obtained in Synthesis Example 1 as an electrolyte in high-purity gamma-butyrolactone (GBL) at room temperature in a dry atmosphere with a dew point of −40° C. to a concentration of 1.0 mol / L. The characteristics of an electric double layer capacitor produced using this electrolyte are shown in Table 2.

[0066] Example 2: An electrolyte solution was prepared by dissolving the isopropylethyldimethylammonium tetrafluoroborate obtained in Synthesis Example 2 as an electrolyte in high-purity gamma-butyrolactone at room temperature in a dry atmosphere with a dew point of −40° C. to a concentration of 1.0 mol / L. The characteristics of an electric double layer capacitor produced using this solution are shown in Table 2.

[0067] Example 3: An electrolyte solution was prepared by dissolving the sec-butyltrimethylammonium tetrafluoroborate obtained in Synthesis Example 3 as an electrolyte in high-purity gamma-butyrolactone at room temperature in a dry atmosphere with a dew point of −40° C. to a concentration of 1.0 mol / L. The characteristics of an electric double layer capacitor produced using this solution are shown in Table 2.

[0068] Reference Example 1: Dimethylpyrrolidinium tetrafluoroborate obtained in Synthesis Example 4 was dissolved as an electrolyte in high-purity gamma-butyrolactone at room temperature in a dry atmosphere with a dew point of −40° C. to a concentration of 1.0 mol / L to prepare an electrolyte solution. The characteristics of an electric double layer capacitor produced using this solution are shown in Table 2.

[0069]

[0070]

[0071] Among the examples in Patent Document 1, the example using N-ethyl-N-methylpyrrolidinium tetrafluoroborate was able to most effectively reduce the capacity degradation of the electrolyte solution, but N,N-dimethylpyrrolidinium tetrafluoroborate, which has a similar structure to this example, was used in Reference Example 1. As shown in Table 2, the electrolyte solutions of Examples 1 to 3 achieved initial capacities equivalent to that of Reference Example 1. Moreover, the electrolyte solutions of Examples 1 to 3 were able to efficiently maintain a high initial capacity, and furthermore, were able to efficiently maintain this capacity over a wide range of temperatures. On the other hand, in Reference Example 1, the durability of the electrolyte solution was significantly worse when measured at −30°C. Note that the alkali metal cation contents in the electrolyte solutions of Examples 1 to 3 and Reference Example 1 were all within the range described in Patent Document 1, but despite the similar alkali metal cation contents, Examples 1 to 3 had better durability than Reference Example 1.

[0072] In order to examine the rate of change in capacitance in low-temperature measurements for a quaternary ammonium salt having two branched aliphatic hydrocarbon groups, the following Synthesis Example 5 and Example 4 were carried out.

[0073] Synthesis Example 5: Diisopropylamine, potassium carbonate, and chloroform were charged into a pressure vessel, and methyl chloride was blown into the pressure vessel and reacted at 110°C for 16 hours with stirring. The precipitated solid was filtered and dried under reduced pressure at 80°C to obtain a mixture of diisopropyldimethylammonium chloride salt and potassium chloride. The resulting mixture was subjected to ion exchange with potassium borofluoride in an acetone solution, and the precipitated solid (potassium chloride) was filtered to obtain a diisopropyldimethylammonium tetrafluoroborate / acetone solution. The solvent was removed from the resulting solution to obtain crystals. 2-Propanol was added to the crystals and dissolved at 80°C, then cooled to 5°C and allowed to stand for 12 hours to allow recrystallization. The precipitated crystals were filtered and dried under reduced pressure at 80°C to obtain white diisopropyldimethylammonium tetrafluoroborate.

[0074] Example 4: An electrolyte solution was prepared by dissolving diisopropyldimethylammonium tetrafluoroborate as an electrolyte in high-purity gamma-butyrolactone at room temperature in a dry atmosphere with a dew point of -40°C to a concentration of 1.0 mol / L. The characteristics of an electric double layer capacitor manufactured using this solution were evaluated at -30°C, and the capacitance change rate was comparable to that of Example 1. Note that the K in the electrolyte solution of Example 4 ＋ is 12.8 ppm, Na ＋ is 0.0 ppm, K in the ammonium salt of Synthesis Example 5 ＋ and Na ＋ The total was 75.3 ppm.

[0075] Synthesis Example 6: Isopropyldimethylamine, propyl chloride, and acetone were charged into a pressure vessel and reacted at 110°C for 24 hours with stirring. The precipitated solid was filtered and dried under reduced pressure at 80°C to obtain isopropyl-n-propyldimethylammonium chloride salt. Isopropyl-n-propyldimethylammonium chloride salt and potassium borofluoride were subjected to ion exchange in an acetone solution, and the precipitated solid (potassium chloride) was filtered to obtain an isopropyltrimethylammonium tetrafluoroborate / acetone solution. The solvent was removed from the resulting solution to obtain crystals. 2-Propanol was added to the crystals and dissolved at 115°C, then cooled to 5°C and allowed to stand for 12 hours to allow recrystallization. The precipitated crystals were filtered and dried under reduced pressure at 80°C to obtain white crystals of isopropyl-n-propyldimethylammonium tetrafluoroborate.

[0076] Synthesis Example 7: Isopropyldimethylamine and acetone were charged into a pressure vessel, and ethyl chloride was blown into the pressure vessel and reacted at 110°C for 8 hours with stirring. The precipitated solid was filtered and dried under reduced pressure at 80°C to obtain isopropylethyldimethylammonium chloride salt. Isopropylethyldimethylammonium chloride salt was mixed with an aqueous tetrafluoroboric acid solution, and the mixture was heated at 110°C by blowing nitrogen into the mixture to distill off hydrochloric acid and water, and ion exchange was performed. n-Butanol was added to the reaction solution, and the mixture was heated in an oil bath at 150°C to distill off a portion of the n-butanol, thereby dehydrating the mixture. The resulting suspension was allowed to cool to room temperature, and the solid was separated by suction filtration. The separated solid was dispersed in n-butanol and washed by stirring at room temperature. After crushing and washing for 1 hour, the solid was separated by suction filtration. The separated solid was allowed to stand and dried under reduced pressure at 150°C to obtain isopropylethyldimethylammonium tetrafluoroborate. The resulting isopropylethyldimethylammonium tetrafluoroborate was analyzed by ion chromatography and found to contain 0.79 ppm of sodium ions and 3.21 ppm of potassium ions, totaling 4.00 ppm.

[0077] Example 5: An electrolyte solution was prepared by dissolving the isopropyl n-propyldimethylammonium tetrafluoroborate obtained in Synthesis Example 6 as an electrolyte in high-purity gamma-butyrolactone at room temperature in a dry atmosphere with a dew point of −40° C. to a concentration of 1.0 mol / L. The characteristics of an electric double layer capacitor produced using this solution are shown in Table 3.

[0078] Example 6: An electrolyte solution was prepared by dissolving the isopropyltrimethylammonium tetrafluoroborate obtained in Synthesis Example 1 as an electrolyte in high-purity propylene carbonate (PC) at room temperature in a dry atmosphere with a dew point of −40° C. to a concentration of 1.0 mol / L. The characteristics of an electric double layer capacitor produced using this solution are shown in Table 3.

[0079] Example 7: An electrolyte solution was prepared by dissolving the isopropylethyldimethylammonium tetrafluoroborate obtained in Synthesis Example 2 as an electrolyte in high-purity propylene carbonate at room temperature in a dry atmosphere with a dew point of −40° C. to a concentration of 1.0 mol / L. The characteristics of an electric double layer capacitor produced using this solution are shown in Table 3.

[0080] Example 8: An electrolyte solution was prepared by dissolving the isopropyltrimethylammonium tetrafluoroborate obtained in Synthesis Example 1 as an electrolyte in high-purity acetonitrile (AN) at room temperature in a dry atmosphere with a dew point of −40° C. to a concentration of 1.0 mol / L. The characteristics of an electric double layer capacitor produced using this solution are shown in Table 3.

[0081] Example 9: An electrolyte solution was prepared by dissolving the isopropylethyldimethylammonium tetrafluoroborate obtained in Synthesis Example 2 as an electrolyte in high-purity acetonitrile at room temperature in a dry atmosphere with a dew point of −40° C. to a concentration of 1.0 mol / L. The characteristics of an electric double layer capacitor produced using this solution are shown in Table 3.

[0082] Example 10: An electrolyte solution was prepared by dissolving the isopropylethyldimethylammonium tetrafluoroborate obtained in Synthesis Example 7 as an electrolyte in high-purity gamma-butyrolactone at room temperature in a dry atmosphere with a dew point of −40° C. to a concentration of 1.0 mol / L. ＋is 0.55 ppm, Na ＋ The characteristics of the electric double layer capacitor manufactured using this are shown in Table 3.

[0083]

[0084] As shown in Table 3, the electrolyte solutions of Examples 5 to 10 were also able to efficiently maintain a high initial capacity, and furthermore, were able to efficiently maintain this capacity during measurements over a wide range of temperatures.

[0085] After storing for 500 hours as described in paragraph 0055 above, the laminated cell that had expanded due to gas generation was placed in a measuring cylinder filled with water and the volume was measured. The increase in volume from the initial volume was taken as the amount of gas generated.

[0086] Synthesis Example 8: N,N,N-triethylmethylammonium chloride salt and potassium borofluoride were subjected to ion exchange in an acetone solution, and the precipitated solid (potassium chloride) was filtered to obtain an N,N,N-triethyl-N-methylammonium tetrafluoroborate / acetone solution. The solvent was removed from the obtained solution to obtain crystals. 2-Propanol was added to the crystals and the solution was dissolved at 115°C, then cooled to 5°C and allowed to stand for 12 hours to perform recrystallization. The precipitated crystals were filtered and dried under reduced pressure at 80°C to obtain white crystals of N,N,N-triethyl-N-methylammonium tetrafluoroborate.

[0087] Comparative Example 1: At room temperature in a dry atmosphere with a dew point of −40° C., N,N,N-triethyl-N-methylammonium tetrafluoroborate obtained in Synthesis Example 8 was dissolved as an electrolyte in high-purity propylene carbonate to a concentration of 1.0 mol / L to prepare an electrolyte solution.

[0088] The amounts of gas generated were measured for the electrolyte solutions of Examples 2, 6 to 9 and Comparative Example 1, and the results are shown in Table 4.

[0089]

[0090] As shown in Table 4, the electrolyte solutions of Examples 2 and 6 to 9 were able to suppress gas generation after voltage application, compared to the electrolyte solution of Comparative Example 1, which used N,N,N-triethyl-N-methylammonium tetrafluoroborate used in the examples of Patent Document 1.

[0091] According to the present invention, a novel electrolytic solution can be provided. The electrolytic solution of the present invention has excellent durability.

Claims

1. An electrolyte solution containing a quaternary ammonium salt having at least one group selected from a branched aliphatic hydrocarbon group and an alicyclic hydrocarbon group.

2. The electrolyte according to claim 1, wherein the branched aliphatic hydrocarbon group is a C3 to C10 branched alkyl group.

3. The electrolyte according to claim 1, wherein the branched aliphatic hydrocarbon group is a C3 to C5 branched alkyl group.

4. The electrolyte solution according to claim 1, wherein the branched aliphatic hydrocarbon group is selected from the group consisting of an isopropyl group, a sec-butyl group, an isobutyl group, a tert-butyl group, a 2-pentyl group, a 3-pentyl group, and a 3-methyl-2-butyl group.

5. The electrolyte according to claim 1, wherein the alicyclic hydrocarbon group is a C3 to C10 cycloalkyl group.

6. The electrolyte according to claim 1, wherein the alicyclic hydrocarbon group is a C3 to C7 cycloalkyl group.

7. The electrolyte according to claim 1, wherein the quaternary ammonium salt is a mono C3-C6 branched alkyl tri-straight chain C1-C4 alkyl ammonium salt.

8. The electrolyte according to claim 1, wherein the quaternary ammonium salt is an isopropyltristraight-chain C1-C4 alkylammonium salt.

9. The electrolyte solution according to claim 1 or 2, wherein the quaternary ammonium salt contains one or more selected from the group consisting of quaternary ammonium salts having at least one branched aliphatic hydrocarbon group and two or more methyl groups, and quaternary ammonium salts having at least one alicyclic hydrocarbon group and two or more methyl groups.

10. The electrolyte solution according to claim 1 or 2, which contains one or more non-aqueous solvents selected from the group consisting of propylene carbonate, ethylene carbonate, butylene carbonate, sulfolane, methyl sulfolane, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, gamma butyrolactone, and acetonitrile.

11. The electrolyte solution according to claim 10, wherein the non-aqueous solvent contains at least one selected from the group consisting of gamma-butyrolactone and acetonitrile.

12. The electrolyte solution according to claim 1 or 2, wherein the quaternary ammonium salt is a mono C3-C6 branched alkyl tri-linear C1-C4 alkyl ammonium salt, and the non-aqueous solvent contains at least one solvent selected from the group consisting of gamma-butyrolactone and acetonitrile.

13. The electrolyte according to claim 1 or 2, wherein the quaternary ammonium salt is ammonium tetrafluoroborate.

14. The electrolyte according to claim 1 or 2, containing 50 ppm or less of alkali metal cations.

15. The electrolyte according to claim 14, wherein the alkali metal cation is sodium ion and / or potassium ion.

16. The electrolyte solution according to claim 1 or 2, which is for use in an electric double layer capacitor.

17. An electric double layer capacitor using the electrolyte solution according to claim 1 or 2 as the electrolyte solution.

18. A quaternary ammonium salt having at least one group selected from a branched aliphatic hydrocarbon group and an alicyclic hydrocarbon group.

19. The quaternary ammonium salt according to claim 18, wherein the branched aliphatic hydrocarbon group is a C3 to C10 branched alkyl group.

20. A quaternary ammonium salt selected from isopropyltrimethylammonium salt, isopropyltriethylammonium salt, isopropylethyldimethylammonium salt, sec-butyltrimethylammonium salt, sec-butylethyldimethylammonium salt, diisopropyldimethylammonium salt, 3-pentyltrimethylammonium salt, isopropyl-n-propyldimethylammonium salt, isobutyltrimethylammonium salt, isobutylethyldimethylammonium salt, 2-pentyltrimethylammonium salt, 3-methyl-2-butyltrimethylammonium salt, cyclopentyltrimethylammonium salt, and cyclohexyltrimethylammonium salt.

21. Isopropylethyldimethylammonium salts and sec-butyltrimethylammonium salts.

22. The quaternary ammonium salt according to claim 18 or 19, wherein the ammonium salt is ammonium tetrafluoroborate.

23. The quaternary ammonium salt according to claim 18 or 19, containing 300 ppm or less of alkali metal cations.

24. A quaternary ammonium salt selected from isopropyltrimethylammonium salt, isopropyltriethylammonium salt, isopropylethyldimethylammonium salt, sec-butyltrimethylammonium salt, sec-butylethyldimethylammonium salt, diisopropyldimethylammonium salt, 3-pentyltrimethylammonium salt, isopropyl-n-propyldimethylammonium salt, isobutyltrimethylammonium salt, isobutylethyldimethylammonium salt, 2-pentyltrimethylammonium salt, 3-methyl-2-butyltrimethylammonium salt, cyclopentyltrimethylammonium salt, and cyclohexyltrimethylammonium salt, wherein the ammonium salt of the quaternary ammonium salt is ammonium tetrafluoroborate, and the quaternary ammonium salt contains 300 ppm or less of an alkali metal cation.

25. A method for producing a quaternary ammonium salt according to claim 18, which comprises at least the step of reacting a tertiary amine corresponding to the quaternary ammonium salt with an alkyl halide to obtain a halide salt of the quaternary ammonium.

Images