Electrolyte solution

Abstract

The purpose of the present invention is to provide a novel electrolyte solution.　The electrolyte solution contains an isopropyl-tri(C1-2 alkyl)-ammonium salt.

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 electrolyte solutions, etc.: [1] An electrolyte solution containing an isopropyl tri C1-2 alkyl ammonium salt (having 1 to 2 carbon atoms). [2] The electrolyte solution according to [1], wherein the isopropyl tri C1-2 alkyl ammonium salt is one or more selected from isopropyl trimethyl ammonium salt, isopropyl triethyl ammonium salt, and isopropyl ethyl dimethyl ammonium salt. [3] The electrolyte solution according to [1] or [2], wherein the isopropyl tri C1-2 alkyl ammonium salt is isopropyl ethyl dimethyl ammonium salt. [4] The electrolyte solution according to any one of [1] to [3], wherein the ammonium salt is ammonium tetrafluoroborate. [5] The electrolyte solution according to any one of [1] to [4], wherein the electrolyte contains one or more non-aqueous solvents selected from gamma butyrolactone and acetonitrile. [6] The electrolyte solution according to [5], wherein the non-aqueous solvent contains at least acetonitrile. [7] The electrolyte solution according to any one of [1] to [6], containing 50 ppm or less of alkali metal cations (e.g., 0.1 to 50 ppm, 40 ppm or less, 0.1 to 30 ppm). [8] The electrolyte solution according to [7], wherein the alkali metal cations are sodium ions and / or potassium ions. [9] An electrolyte solution comprising an isopropyl tri-C1-2 alkyl ammonium salt, a non-aqueous solvent containing at least one selected from gamma-butyrolactone and acetonitrile, and 0.1 to 30 ppm of alkali metal cations.

[10] An electrolyte solution comprising an isopropyl tri-C1-2 alkyl ammonium salt, a non-aqueous solvent containing at least acetonitrile, and 0.1 to 30 ppm of alkali metal cations.

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

[10] , which is used for an electric double layer capacitor.

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

[11] .

[13] A method for suppressing capacity degradation when an electrolytic solution containing a quaternary ammonium salt and a non-aqueous solvent is used in an electric double layer capacitor, the method comprising adding an isopropyl tri-C1-2 alkyl ammonium salt to the electrolytic solution.

[14] An isopropyl tri-C1-2 alkyl ammonium salt.

[15] An ammonium salt selected from isopropyltrimethylammonium salt, isopropyltriethylammonium salt, and isopropylethyldimethylammonium salt.

[16] Isopropylethyldimethylammonium salt.

[17] The ammonium salt according to any one of

[14] to

[16] , which is ammonium tetrafluoroborate.

[18] The ammonium salt according to any one of

[14] to

[17] , which contains 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.

[19] An ammonium salt selected from isopropyltrimethylammonium salt, isopropyltriethylammonium salt, and isopropylethyldimethylammonium salt, which is ammonium tetrafluoroborate and contains 200 ppm or less of alkali metal cations.

[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 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 [isopropyltriC1-2 (having 1 to 2 carbon atoms) alkylammonium salt (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] Examples of the ammonium salt (1) include isopropyltrimethylammonium salt (e.g., isopropyltrimethylammonium tetrafluoroborate, etc.), isopropyltriethylammonium salt, isopropylethyldimethylammonium salt, isopropylmethyldiethylammonium salt, etc. In particular, from the viewpoint of reducing the capacity degradation of the electrolyte, isopropylethyldimethylammonium salt, etc. may be used. In addition, in electrochemical devices such as electric double layer capacitors, when a voltage is applied, a small amount of water present in the electrolyte is reduced together with oxygen to form OH in the vicinity of the negative electrode. － ions (hydroxide ions) are generated, and the electrolyte gradually becomes strongly alkaline. － Ions can corrode the resin, rubber, or metal of the sealing portion of the negative electrode, causing electrolyte leakage and reducing the reliability of the electrochemical device. The use of these ammonium salts (1) can suppress strong alkalinization, and in particular, compounds having two or more methyl groups can exhibit excellent alkalinization suppression effects. Specifically, isopropyltrimethylammonium salts (e.g., isopropyltrimethylammonium tetrafluoroborate), isopropylethyldimethylammonium salts (e.g., isopropylethyldimethylammonium tetrafluoroborate), etc. are preferred, with isopropyltrimethylammonium salts (e.g., isopropyltrimethylammonium tetrafluoroborate) being particularly preferred. Ammonium salts (1) having two or more methyl groups are likely to efficiently achieve both alkalinization suppression and improved voltage resistance, which are in a trade-off relationship.

[0020] The ammonium salt (1) may be used alone or in combination of two or more.

[0021] Ammonium salt (1) can be produced, for example, by a method including at least a step of reacting a tertiary amine having an isopropyl group with an alkyl halide to obtain a halide salt of isopropyltriC1-2 alkylammonium corresponding to ammonium salt (1). 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) that is 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 may be used 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, for example, involve mixing and reacting an acid or an alkali metal salt thereof, which constitutes the counterion of the target ammonium salt (1), in an arbitrary solvent.

[0022] 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).

[0023] 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.

[0024] When the electrolyte contains multiple types of alkali metal ions, the total amount of these ions is adjusted to fall within the above range.

[0025] The electrolyte may contain one or more electrolytes other than the ammonium salt (1), as long as the effects of the present invention are achieved.

[0026] 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.

[0027] As the other electrolytes, commercially available products may be used, or those produced by known methods may be used.

[0028] 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%.

[0029] 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.

[0030] 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 %.

[0031] The present invention also includes the above ammonium salt (1).

[0032] 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.

[0033] The non-aqueous solvent may be used alone or in combination of two or more.

[0034] The non-aqueous solvent may be a commercially available product, or may be further purified by any method before use.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] When the electrolyte contains multiple types of alkali metal ions, the total amount of these ions is adjusted to fall within the above range.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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 one that uses the above-mentioned electrolytic solution as the electrolyte, and its manufacturing method, etc., is not particularly limited. By using the above-mentioned electrolytic solution, the electric double layer capacitor is excellent in durability, with reduced capacity reduction (capacity degradation) and increased resistance. The above-mentioned electrolytic solution can be used over a wide temperature range, and can efficiently reduce capacity degradation, especially at low temperatures where degradation is particularly noticeable.

[0045] The present invention relates to a method for suppressing capacity degradation when an electrolytic solution containing a quaternary ammonium salt and a nonaqueous solvent is used in an electric double layer capacitor, and also includes a method of incorporating an isopropyl tri-C1-2 alkyl ammonium salt into the electrolytic solution. This method can suppress capacity degradation when measured over a wide temperature range (e.g., −40 to 80°C) during high-temperature or long-term use in an electric double layer capacitor. For example, this method may provide a ratio (capacity of the capacitor after 500 hours of voltage application / initial capacitance of the capacitor × 100) of 80% or more when measured at room temperature and 25% or more when measured at −30°C. In this method, the electrolytic solution, nonaqueous solvent, and isopropyl tri-C1-2 alkyl ammonium salt exemplified above can be used.

[0046] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0047] 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

[0048] 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.

[0049] 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.

[0050] 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

[0051] Na ＋ , and other alkali metal cations were analyzed by changing the standard to the target compound.

[0052] 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.

[0053] 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).

[0054] 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.

[0055] 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.

[0056] Synthesis Example 3: 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, thereby performing ion exchange. 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 performing dehydration. The resulting suspension was allowed to cool to room temperature, and the solid content was separated by suction filtration. The separated solid content was dispersed in n-butanol and washed by stirring at room temperature. After crushing and washing for 1 hour, the solid content was separated by suction filtration. The separated solid content was allowed to stand and dried under reduced pressure at 150°C to obtain isopropylethyldimethylammonium tetrafluoroborate.

[0057] 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.

[0058] Electrolyte Example 1: An electrolyte solution was prepared by dissolving isopropyltrimethylammonium tetrafluoroborate 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 manufactured using this solution are shown in Table 2.

[0059] 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.

[0060] Example 3: An electrolyte solution was prepared by dissolving the isopropylethyldimethylammonium 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.

[0061] Reference Example 1: Dimethylpyrrolidinium tetrafluoroborate 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 prepare an electrolyte solution at a concentration of 1.0 mol / L. The characteristics of an electric double layer capacitor manufactured using this solution are shown in Table 2.

[0062]

[0063]

[0064] 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.

[0065] Example 4: 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.

[0066] Example 5: 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.

[0067] Example 6: 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.

[0068] Example 7: 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.

[0069]

[0070] As shown in Table 3, the electrolyte solutions of Examples 4 to 7 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.

[0071] After storing for 500 hours as described in paragraph 0048 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 initially measured volume was taken as the amount of gas generated.

[0072] Synthesis Example 5: 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.

[0073] 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 5 was dissolved as an electrolyte in high-purity propylene carbonate to a concentration of 1.0 mol / L to prepare an electrolytic solution.

[0074] The amounts of gas generated were measured for the electrolyte solutions of Examples 2, 4 to 7 and Comparative Example 1, and the results are shown in Table 4.

[0075]

[0076] As shown in Table 4, the electrolyte solutions of Examples 2 and 4 to 7 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.

[0077] 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 containing isopropyltriC1-2 alkylammonium salt.

2. The electrolyte solution according to claim 1, wherein the isopropyltriC1-2 alkylammonium salt is at least one selected from the group consisting of isopropyltrimethylammonium salt, isopropyltriethylammonium salt and isopropylethyldimethylammonium salt.

3. The electrolyte according to claim 1, wherein the isopropyltriC1-2 alkylammonium salt is isopropylethyldimethylammonium salt.

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

5. The electrolyte solution according to claim 1 or 2, which contains at least one non-aqueous solvent selected from the group consisting of gamma-butyrolactone and acetonitrile.

6. The electrolyte according to claim 5, wherein the non-aqueous solvent contains at least acetonitrile.

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

8. The electrolyte according to claim 7, wherein the alkali metal cation is a sodium ion and / or a potassium ion.

9. An electrolyte solution containing an isopropyltriC1-2 alkylammonium salt, a non-aqueous solvent containing at least one selected from gamma-butyrolactone and acetonitrile, and 0.1 to 30 ppm of an alkali metal cation.

10. An electrolyte solution containing an isopropyltriC1-2 alkylammonium salt, a non-aqueous solvent containing at least acetonitrile, and 0.1 to 30 ppm of an alkali metal cation.

11. The electrolyte solution according to claim 1 or 9, which is for use in an electric double layer capacitor.

12. An electric double layer capacitor using the electrolyte solution according to claim 1 or 9 as the electrolyte solution.

13. A method for suppressing capacity degradation when an electrolyte containing a quaternary ammonium salt and a non-aqueous solvent is used in an electric double layer capacitor, comprising adding an isopropyl tri-C1-2 alkyl ammonium salt to the electrolyte.

Images