JP2006210259A - Nonaqueous electrolytic solution - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolyte excelling in ion conductivity and electrochemical stability, in relation to a nonaqueous electrolytic solution used for primary and secondary lithium batteries, a dye-sensitized solar cell, an electric double-layer capacitor or the like. <P>SOLUTION: In this nonaqueous electrolytic solution containing a salt having anions represented by formula (1): Rf<SB>1</SB>SO<SB>2</SB>N<SP>-</SP>SO<SB>2</SB>Rf<SB>2</SB>(Rf<SB>1</SB>and Rf<SB>2</SB>are each a 1-12C perfluoroalkyl group) (for instance, (CF<SB>3</SB>SO<SB>2</SB>)<SB>2</SB>N<SP>-</SP>), the content of anions represented by formula (2): R<SB>1</SB>SO<SB>2</SB>N<SP>-</SP>SO<SB>2</SB>R<SB>2</SB>(R<SB>1</SB>and R<SB>2</SB>are each independently a 1-12C fluoroalkyl group, and either or both of R<SB>1</SB>and R<SB>2</SB>is/are each a fluoroalkyl group containing at least one hydrogen atom) (for instance, CF<SB>2</SB>HSO<SB>2</SB>N<SP>-</SP>SO<SB>2</SB>CF<SB>3</SB>) is not more than 50 ppm with respect to the anions represented by formula (1). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrochemical device such as a primary or secondary lithium battery, a dye-sensitized solar cell, an electric double layer capacitor, a display element, an electrodeposition bath, or a non-aqueous electrolyte that can be used as a chemical synthesis medium. About.

  Lithium primary batteries, lithium secondary batteries, electrolytic capacitors, electric double layer capacitors, electrochromic display elements that have been widely used in recent years, or dye-sensitized types that have been studied for various practical applications in the future As a non-aqueous electrolyte solution in an electrochemical device such as a solar battery, an electrolyte was dissolved in an organic solvent such as ethylene carbonate, propylene carbonate, dimethoxyethane, γ-butyrolactone, N, N-dimethylformamide, tetrahydrofuran, or acetonitrile. Solutions have been used. However, since the organic solvent used in these electrolyte solutions is volatile and is a dangerous substance itself, there are problems in long-term reliability, durability, and safety.

Accordingly, it has been proposed and variously studied to apply a salt (ionic liquid) that is liquid at room temperature as an electrolyte without using an organic solvent as an electrolyte. For example, an onium salt composed of 1-methyl-3-ethylimidazolium cation and bistrifluoromethanesulfonic acid amide anion (CF ₂ HSO ₂ N ^— SO ₂ CF ₃ ) is liquid at ambient temperature and has high ionic conductivity ( 8.8 mScm ⁻¹ ) (see Patent Document 1). The salt has an excellent electrochemical stability characteristic that it is not oxidized at a potential of 5.2 V or less with respect to Li ⁺ / Li. However, it has been widely used as an electrolyte solution for Li secondary batteries, an electrolyte solution obtained by dissolving lithium hexafluorophosphate in a propylene carbonate solvent, and a propylene carbonate solvent used as an electrolyte solution for capacitors. Since the electrochemical stability is inferior to that of an electrolytic solution in which a quaternary ammonium tetrafluoroboron salt is dissolved, further improvement in electrochemical stability is desired.

  In addition, as an electrolytic solution exhibiting high electrical conductivity, an electrolytic solution for an electric double layer capacitor using a salt composed of a quaternary ammonium cation and a bistrifluoromethanesulfonic acid amide anion as an electrolyte has also been proposed (for example, a patent) Reference 2). However, according to the study by the present inventors, this electrolytic solution shows good performance when a glassy carbon electrode is used, but a porous carbon electrode such as activated carbon that is actually used in an electrochemical capacitor or the like is used. If so, it was found that there was a problem with electrochemical stability.

JP-A-8-259543 JP-A-7-272882

  Under such a background, in the field of electrochemical devices using an electrolyte, a method for obtaining higher electrochemical stability is one of the problems. Therefore, an object of the present invention is to provide an electrolyte having good ion conductivity and electrochemical stability.

The present inventors have intensively studied to solve the above problems. And CF ₂ HSO ₂ N ^— SO ₂ CF ₃ contained as an impurity in a salt having CF ₃ SO ₂ N ^— SO ₂ CF ₃ as an anion has an extremely large influence on electrochemical stability and thermal stability. As a result of further finding out and finding out, the present invention was completed. That is, the present invention provides the following formula (1):
Rf ₁ SO ₂ N ^— SO ₂ Rf ₂ (1)
(In the above formula, Rf ₁ and Rf ₂ are each independently a C 1-12 perfluoroalkyl group)
A nonaqueous electrolytic solution containing a salt having an anion represented by the following formula (2), which is contained in the nonaqueous electrolytic solution:
R ₁ SO ₂ N ^— SO ₂ R ₂ (2)
(In the above formula, R ₁ and R ₂ are each independently a fluoroalkyl group having 1 to 12 carbon atoms, and either or both of R ₁ and R ₂ are fluoroalkyls containing at least one hydrogen atom) Base)
The amount of the anion represented by the formula (1) is 50 ppm or less with respect to the anion represented by the formula (1).

A compound having a group represented by Rf ₁ SO ₂ — (for example, CF ₃ SO ₂ —) (or a raw material thereof) is usually obtained by fluorinating a corresponding hydride (for example, CH ₃ SO ₂ —). However, during the fluorination, an impurity (for example, CF ₂ HSO ₂ —) in which hydrogen atoms remain without being completely fluorinated is contained, and this is mixed in the electrolytic solution as it is to remain. It is considered that the hydrogen atom contained in the material deteriorates electrochemical stability and thermal stability. In the electrolytic solution of the present invention, the above problem is solved by minimizing the proportion of the electrolyte (salt) in which such hydrogen atoms remain.

  According to the electrochemical device using the electrolytic solution of the present invention, it is possible to solve the problem of deterioration of device characteristics over time due to the electrolysis and thermal decomposition of impurities on the electrode surface.

The electrolytic solution of the present invention has the following formula (1)
Rf ₁ SO ₂ N ^— SO ₂ Rf ₂ (1)
(In the above formula, Rf ₁ and Rf ₂ are each independently a C 1-12 perfluoroalkyl group)
A nonaqueous electrolytic solution containing a salt having an anion represented by

In the above formula (1), Rf ₁ and Rf ₂ are both a C 1-12 perfluoroalkyl group, that is, a fully fluorinated alkyl group, and neither of them has a hydrogen atom. The anion represented by the above formula (1) is not particularly limited as long as the above formula is satisfied. However, the larger the ion, the smaller the electric conductivity of the electrolyte solution, and the better the electric conductivity. Are preferably a perfluoroalkyl group having 1 to 5 carbon atoms, and Rf ₁ and Rf ₂ (hereinafter sometimes simply referred to as Rf without limitation). Specific examples of such anions include bistrifluoromethanesulfonic acid imide, trifluoromethanesulfonic acid pentafluoroethanesulfonic acid imide, and bispentafluoroethanesulfonic acid imide. Of these, bistrifluoromethanesulfonic acid imide (CF ₃ SO ₂ N ^— SO ₂ CF ₃ ) is most preferable because it is the smallest and relatively inexpensive.

  The counter anion for the anion is not particularly limited, and a known cation in the electrolyte of the non-aqueous electrolyte can be combined, but an organic onium ion is preferred because of its high electrical conductivity and high potential resistance. Specifically, triethylmethylammonium, diethyldimethylammonium, trimethylpropylammonium, N-methylethylpyrrolidinium, N-methylpropylpyrrolidinium, 1-methyl-3-ethylimidazolium and the like are preferably used.

The non-aqueous electrolyte of the present invention has the following formula (2)
R ₁ SO ₂ N ^— SO ₂ R ₂ (2)
(In the above formula, R ₁ and R ₂ are each independently a fluoroalkyl group having 1 to 12 carbon atoms, and either or both of R ₁ and R ₂ are fluoroalkyls containing at least one hydrogen atom) Base)
The amount of the anion represented by the formula (1) is 50 ppm or less with respect to the anion represented by the formula (1). The content is on a molar basis.

  An anion having a hydrogen atom represented by the above formula (2) is inferior in electrochemical stability and thermal stability to the fully fluorinated anion represented by the above formula (1). It is presumed that when it is used in an electrochemical device, it decomposes first, and this decomposition generates a reaction product that is more easily decomposed, resulting in deterioration of electrochemical and thermal characteristics.

Specific examples of the anion represented by the formula ^{_{(2), CF 2 HSO 2}} N - SO 2 CF 3, (CF 2 HSO 2) 2 N -, C 2 F 4 HSO 2 N - SO 2 C 2 F ₅ or the like.

Usually, the salt having an anion represented by the formula (1) is synthesized using RfSO ₂ -X (X is a halogen atom such as fluorine, chlorine or bromine, the same shall apply hereinafter) as a raw material. Here, in RfSO ₂ -X, RSO ₂ -X (R is a C 1-12 fluoroalkyl group containing at least one hydrogen atom) that is not completely fluorinated is present as an impurity. It is considered that this reacts in the same manner as RfSO ₂ -X, and the component represented by the formula (2) is mixed.

  The method for obtaining the electrolytic solution not containing the anion component represented by the formula (2) is not particularly limited. As described above, the component is an impurity in the salt having the anion represented by the formula (1). As it comes in. For this reason, the method of reducing the ratio of the anion shown by Formula (2) contained in the salt which has an anion shown by Formula (1) is common. However, it is usually difficult to recrystallize a salt having an anion represented by the formula (1). It is also difficult to remove by adsorption with activated carbon or the like. Therefore, it is preferable to prevent such impurities from being mixed in the process of synthesizing the salt having an anion represented by the formula (1).

As described above, in the representative method of the salt having an anion represented by the formula (1), first, R′SO ₂ —X (where R ′ is a hydrocarbon group having 1 to 12 carbon atoms) is fluorinated to give Rf producing ₁ SO ₂ -F.

Then as the first method, and the _Rf 1 _SO 2 -F, anhydrous ammonia and ^M + · F ^- to (M is lithium, sodium, alkali metals such as potassium) is reacted with, _(Rf 1 SO ₂ ) There is a method for obtaining ₂ N ⁻ · M ⁺ .

The second method is to synthesize Rf ₁ SO ₂ —NH ₂ from the above Rf ₁ SO ₂ —F and ammonia, then react this with alkali metal alcoholate, and then add Rf ₂ SO ₂ —F to add Rf ₂ SO ₂ —F. there are SO ₂ Rf ₂ · ^{M +} method of obtaining ^- ₁ SO ₂ N.

  In addition, since the alkali metal salt is obtained by the above method, the organic onium cation may be exchanged as described above by a salt exchange method or the like as necessary.

As can be understood from this process, Rf ₁ SO ₂ -F (and Rf ₂ SO ₂ -F) are as pure as possible, that is, RSO ₂ -X (R contains at least one hydrogen atom). It is effective to use one having a small amount of mixing of (C1-C12 fluoroalkyl group). When performing synthesis by the step, after synthesized RfSO ₂ -F by fluorinating a R'SO ₂ -X, although the _RSO 2 -X contained as impurities may be removed by purification processes such as distillation, It is simpler and more economical to set the reaction conditions more strictly so that hydrogen atoms that have not been fluorinated remain.

  On the other hand, the anion component represented by the formula (2) is not usually mixed into the electrolytic solution of the present invention through a route other than the impurities derived from the salt having the anion represented by the formula (1). Therefore, if the amount of the anion component represented by the formula (2) contained in the salt having an anion represented by the formula (1) is controlled by the method as described above, the electrolytic solution of the present invention can be easily obtained. be able to.

The ratio of the anion component represented by the formula (2) contained in the salt having an anion represented by the formula (1) can be determined by the following method. That is, it is possible to dissolve the salt in a suitable deuterated solvent and measure H-NMR or F-NMR. In the H-NMR spectrum, it is detected as a multiple peak coupling with F in the vicinity of 6.1 to 6.5 ppm with respect to 0 ppm of chemical shift of the methyl group of tetramethylsilane. In F-NMR, if it is a CF ₂ H group, it is detected as a multiplet that is coupled to H from −120 to −187 ppm if it is CFH to −181 to −187 ppm. The impurity content can be quantified by measuring the ratio of the main component peak in the F-NMR spectrum. The H-NMR spectrum can be quantified by weighing and adding an appropriate reference substance.

  Many of the salts having an anion represented by the above formula (1) are so-called room temperature molten salts (also called ionic liquids) that are liquid near room temperature, and therefore the room temperature molten salt is used as an electrolytic solution as it is ( That is, it is possible to use an electrolyte alone without using a solvent, but it is more preferable to dissolve in a non-aqueous solvent to obtain an electrolytic solution. As the non-aqueous solvent, a known organic solvent can be employed without particular limitation as a solvent in the non-aqueous electrolyte. Usually, the organic solvent to be used is selected from the electrochemical stability of the organic solvent and the solubility of the electrolyte salt. The organic solvent may be used alone or in combination of two or more. Examples of suitable organic solvents include chain ethers (diethyl ether, dipropyl ether, methyl isobutyl ether, ethylene glycol dimethyl ether, etc.) and cyclic ethers (tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1, 3-dioxalane, etc.), amides (N, N-dimethylformamide, N-methylpyrrolidone, etc.), carboxylic acid esters (methyl acetate, ethyl acetate, etc.), lactones (γ-butyrolactone, etc.) and nitriles (acetonitrile, pro Pionitrile, 3-methoxypropionitrile, etc.) and carbonates (dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, etc.) chain carbonates, ethylene carbonate, propylene carbonate Cyclic carbonate) and sulfoxides (dimethyl sulfoxide, sulfolane, 3-methyl sulfonium run, etc.). Of these, carbonates, sulfoxides, and ethers are preferable.

  When the organic solvent as described above is blended in the nonaqueous electrolytic solution of the present invention, the ratio of the electrolyte (salt) and the organic solvent is not particularly limited, and is appropriately set according to the use of the nonaqueous electrolyte. In general, the electrolyte concentration may be set to 0.1 to 2.0 mol / L.

  Moreover, in addition to the said electrolyte (salt) and an organic solvent, you may add the other component well-known as a mixing | blending component of nonaqueous electrolyte in the range which does not impair the effect of this invention in the electrolyte solution of this invention.

  The non-aqueous electrolyte of the present invention is used as a primary or secondary lithium battery, dye-sensitized solar cell, electric double layer capacitor, display element or other electrochemical device, or as an electrodeposition bath or chemical synthesis medium, respectively. It can be used by known means.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further in detail, this invention is not limited to these. Each physical property was measured by the following method.

(1) NMR measurement method 0.5 g of a sample was dissolved in 0.75 ml of deuterated acetonitrile, and ¹ H and ¹⁹ F nuclei were measured by JEOL nuclear magnetic resonance apparatus JNM-LA500. The number of scans was 200 times for both ¹ H and ¹⁹ F nuclei. The peak position of ¹ H was based on the residual hydrogen peak of deuterated acetonitrile solvent as 2.07 ppm. The peak position of ¹⁹ F showed a chemical shift when the peak of 1,4-bistrifluoromethylbenzene was −64.00 ppm with the external reference.

(2) Measurement of charge / discharge characteristics Electrochemical capacitors were produced as follows, and the charge / discharge characteristics were evaluated. Electrochemical capacitor electrodes (aluminum foil 30 μm, activated carbon layer 150 μm, electrostatic capacity 16 F / CC) purchased from Hosen Co., Ltd. were cut into 100 mm ² in a glove box with a humidity of −80 ° C. or less, and then 180 ° C. for 24 hours. It dried at the reduced pressure of 1 Pa or less. Next, the two electrodes were placed opposite to each other through a separator that had been dried at 180 ° C. for 24 hours under a reduced pressure of 1 Pa or less to produce an electrode element. Next, the electrode element was placed in an aluminum laminate cell and impregnated with an electrolyte under reduced pressure. The electrochemical capacitor produced by this method was applied with a constant current to a predetermined voltage (2.0 V or 2.5 V) at 0.5 mA in an environment of 25 ° C. for 2 hours, and then applied at 0.25 mA. Constant current discharge was performed to 0V. Thereafter, the internal resistance was measured by an alternating current double-ended method at a frequency of 1 KHz to obtain an initial resistance value. Next, a predetermined voltage (2.0 V or 2.5 V) is applied in an environment of 80 ° C. and held for 100 hours, and then a constant current discharge is performed to 0 V at 0.25 mA, and then the internal resistance is AC 2 at a frequency of 1 KHz. A value obtained by measuring by the end method and dividing the value by the initial resistance value was calculated as the rate of increase in internal resistance.

Example 1
While stirring 229.0 g of commercially available methylsulfonyl chloride in 4 L of 2M aqueous potassium fluoride solution, the mixture was stirred at 50 ° C. for 1 hour. The organic layer was separated and dried over sodium sulfate to obtain 125.4 g of methylsulfonyl fluoride. The obtained methylsulfonyl fluoride was placed in an electrochemical cell for electrolytic fluorination containing liquid hydrogen fluoride and subjected to electrolytic fluorination at 5.3 V for 10 days. After completion of the reaction, 156.4 g of gaseous trifluorosulfonyl fluoride was separated and collected using a dry ice-ethanol cryogen.

  A stainless steel autoclave was charged with 300 ml of acetonitrile and 91.4 g of potassium fluoride, and cooled with dry ice-ethanol to introduce 7.0 g of anhydrous ammonia. Subsequently, 121.4 g of the trifluorosulfonyl fluoride synthesized above was introduced and returned to room temperature with stirring. Then, it heated at 40 degreeC and hold | maintained for 1 hour. Thereafter, the reaction solution was dried under reduced pressure to obtain 227.2 g of bistrifluoromethanesulfonic acid amide (TFSI) -potassium salt. Next, 226.2 g of this TFSI-potassium salt was added to 98% concentrated sulfuric acid and dissolved by heating. Thereafter, vacuum distillation was performed to obtain 185.2 g of TFSI-hydride. The obtained TFSI-hydride was dissolved in pure water, reacted with 25 g of lithium carbonate, excess lithium carbonate was filtered off, and the filtrate was concentrated to obtain 185.4 g of TFSI-lithium salt.

  75.8 g of commercially available special grade triethylmethylammonium (TEMA) chloride was dissolved in 500 ml of ultrapure water, 147.5 g of TFSI-lithium salt obtained by the above method was added thereto, and after stirring for 10 minutes, 200 ml of commercially available special grade methylene chloride was added. The mixture was allowed to stand for salt exchange for a time. After standing, 300 ml of commercially available special grade methylene chloride was added, and the methylene chloride layer and the aqueous layer were separated. To the resulting methylene chloride layer, 250 ml of ultrapure water was added and stirred to separate the aqueous layer. Further, 250 ml of ultrapure water was added to the obtained methylene chloride layer and stirred to separate the aqueous layer. This was done a total of 5 times. The resulting methylene chloride layer was dried under reduced pressure at 60 mmHg and 35 ° C. to obtain 187.9 g of a TEMA-TFSI salt. This TEMA-TFSI salt was measured by NMR, but no signal was detected in the vicinity of 6.3 ppm of the H-NMR spectrum and in the vicinity of -125.1 ppm of the F-NMR spectrum.

  59.5 g of the obtained TEMA-TFSI salt was dissolved in 62.4 g of ethyl methyl carbonate to prepare an ethyl methyl carbonate solution of 1.5 mol / L TEMA-TFSI salt. An electrochemical capacitor was prepared using this electrolytic solution, and charge / discharge characteristics at a predetermined voltage of 2.5 V were measured. As a result, the rate of increase in internal resistance was 108.1%.

Comparative Example 1
A TEMA-TFSI salt was obtained in the same manner as in Example 1 using a commercially available bistrifluoromethanesulfonic acid amide-lithium salt. When this TEMA-TFSI salt was measured by NMR, a triplet peak was observed at 6.32 ppm in the H-NMR spectrum, and a doublet signal was detected at -125.1 ppm in the F-NMR spectrum. These peaks were estimated to be CF ₂ H of CF ₂ HSO ₂ N ^— SO ₂ CF ₃ , and were present at 2014 ppm with respect to TFSI as the main component from the peak area ratio.

  An electrochemical capacitor was produced in the same manner as in Example 1 using the above TEMA-TFSI salt, and charge / discharge characteristics were measured. As a result, the rate of increase in internal resistance was 145.2%.

Example 2
An electrochemical capacitor was prepared using an electrolyte obtained by dissolving 58.5 g of the TEMA-TFSI salt produced in Example 1 and 1.0 g of the TEMA-TFSI salt produced in Comparative Example 1 in 62.4 g of ethyl methyl carbonate, The charge / discharge characteristics were measured. As a result, the internal resistance increase rate was 106.8%.

When the TEMA-TFSI salt obtained by the above mixing was measured by NMR, a triplet peak was observed at 6.32 ppm of the H-NMR spectrum, and a doublet signal was detected at -125.1 ppm of the F-NMR spectrum. These peaks were estimated as CF ₂ H of CF ₂ HSO ₂ N ^— SO ₂ CF ₃ , and were present at 37 ppm with respect to TFSI as the main component from the peak area ratio.

Comparative Example 2
An electrochemical capacitor was prepared using an electrolyte obtained by dissolving 56.5 g of the TEMA-TFSI salt produced in Example 1 and 3.0 g of the TEMA-TFSI salt produced in Comparative Example 1 in 62.4 g of ethyl methyl carbonate, The charge / discharge characteristics were measured. As a result, the rate of increase in internal resistance was 125.3%.

When the TEMA-TFSI salt obtained by the above mixing was measured by NMR, a triplet peak was observed at 6.32 ppm of the H-NMR spectrum, and a doublet signal was detected at -125.1 ppm of the F-NMR spectrum. These peaks were estimated as CF ₂ H of CF ₂ HSO ₂ N ^— SO ₂ CF ₃ , and 97 ppm was present with respect to the main component bistrifluoromethanesulfonic acid amide from the peak area ratio.

  The electrolytic solution compositions and the evaluation results of the internal resistance increase rate in Examples 1 and 2 and Comparative Examples 1 and 2 are listed in Table 1 below.

Example 3
95.4 g of commercially available special grade 1-methyl-3-ethylimidazolium (EMI) bromide was dissolved in 500 ml of ultrapure water, and 147.9 g of TFSI-lithium salt produced in the same manner as in Example 1 was added thereto, followed by stirring for 10 minutes. Later, 200 ml of commercially available special grade methylene chloride was added and the mixture was allowed to stand for 1 hour for salt exchange. After standing, 300 ml of commercially available special grade methylene chloride was added, and the methylene chloride layer and the aqueous layer were separated. To the resulting methylene chloride layer, 250 ml of ultrapure water was added and stirred to separate the aqueous layer. Further, 250 ml of ultrapure water was added to the obtained methylene chloride layer and stirred to separate the aqueous layer. This was done a total of 5 times. The obtained methylene chloride layer was dried under reduced pressure at 60 mmHg and 35 ° C. to obtain 176.9 g of an EMI-TFSI salt. This EMI-TFSI salt was measured by NMR, but no signal was detected in the vicinity of 6.3 ppm of the H-NMR spectrum and in the vicinity of -125.1 ppm of the F-NMR spectrum.

  55.7 g of the obtained EMI-TFSI salt was dissolved in 62.4 g of ethyl methyl carbonate to prepare an ethyl methyl carbonate solution of 1.5 mol / L of EMI-TFSI salt. An electrochemical capacitor was prepared using this electrolytic solution, and charge / discharge characteristics at a predetermined voltage of 2.0 V were measured. As a result, the rate of increase in internal resistance was 108.7%.

Comparative Example 3
An EMI-TFSI salt was obtained in the same manner as in Example 3 using a commercially available bistrifluoromethanesulfonic acid amide-lithium salt. When this EMI-TFSI salt was measured by NMR, a triplet peak was observed at 6.32 ppm in the H-NMR spectrum, and a doublet signal was detected at -125.1 ppm in the F-NMR spectrum. These peaks were estimated as CF ₂ H of CF ₂ HSO ₂ N ^— SO ₂ CF ₃ , and were found to be 2160 ppm with respect to TFSI as the main component from the peak area ratio.

  The electrochemical capacitor was produced using the said EMI-TFSI salt, and the charge / discharge characteristic was measured. As a result, the rate of increase in internal resistance was 172.9%.

Example 4
An electrochemical capacitor was prepared using an electrolytic solution obtained by dissolving 54.7 g of the EMI-TFSI salt produced in Example 3 and 1.0 g of the EMI-TFSI salt produced in Comparative Example 3 in 62.4 g of ethyl methyl carbonate, The charge / discharge characteristics were measured. As a result, the rate of increase in internal resistance was 109.4%.

When the EMI-TFSI salt obtained by the above mixing was measured by NMR, a triplet peak was observed at 6.32 ppm in the H-NMR spectrum, and a doublet signal was detected at -125.1 ppm in the F-NMR spectrum. These peaks were estimated as CF ₂ H of CF ₂ HSO ₂ N ^— SO ₂ CF ₃ , and were present at 42 ppm relative to TFSI as the main component from the peak area ratio.

Comparative Example 4
An electrochemical capacitor was produced using an electrolytic solution obtained by dissolving 53.7 g of the EMI-TFSI salt produced in Example 3 and 2.0 g of the EMI-TFSI salt produced in Comparative Example 3 in 62.4 g of ethyl methyl carbonate, The charge / discharge characteristics were measured. As a result, the internal resistance increase rate was 131.6%.

When the EMI-TFSI salt obtained by the above mixing was measured by NMR, a triplet peak was observed at 6.32 ppm in the H-NMR spectrum, and a doublet signal was detected at -125.1 ppm in the F-NMR spectrum. These peaks were estimated to be CF ₂ H of CF ₂ HSO ₂ N ^— SO ₂ CF ₃ , and were present at 68 ppm with respect to TFSI as the main component from the peak area ratio.

  The electrolytic solution composition and the evaluation results of the rate of increase in internal resistance in Examples 3 and 4 and Comparative Examples 3 and 4 are shown in Table 2 below.

As shown in Tables 1 and 2, when the ratio of impurities that are not completely fluorinated in the electrolytic solution is 50 ppm or less with respect to the electrolyte that is completely fluorinated, the rate of increase in internal resistance is 110. It can be seen that it is extremely suppressed as compared with the case where the content is 50% or more.

Claims (2)

Following formula (1)
Rf ₁ SO ₂ N ^— SO ₂ Rf ₂ (1)
(In the above formula, Rf ₁ and Rf ₂ are each independently a C 1-12 perfluoroalkyl group)
A nonaqueous electrolytic solution containing a salt having an anion represented by the following formula (2), which is contained in the nonaqueous electrolytic solution:
R ₁ SO ₂ N ^— SO ₂ R ₂ (2)
(In the above formula, R ₁ and R ₂ are each independently a fluoroalkyl group having 1 to 12 carbon atoms, and either or both of R ₁ and R ₂ are fluoroalkyls containing at least one hydrogen atom) Base)
The amount of the anion represented by the formula (1) is 50 ppm or less with respect to the anion represented by the above formula (1). An electrochemical device using the nonaqueous electrolytic solution according to claim 1.