JP2011236161A - Ionic liquid, method for producing the same, power storage device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrochemically stable ionic liquid having excellent organic compound solubility.SOLUTION: The ionic liquid is composed of oxazolidine cation, wherein an alkyl/methoxyalkyl group (R) is substituted for the N position, and an anion (X-) including halogen, and is represented by general formula (1).

Description

  The present invention relates to an oxazolidine-based ionic liquid, a manufacturing method thereof, and a power storage device using the ionic liquid.

  Ionic liquids have various properties such as flame retardancy, ion conductivity, non-volatility, high polarity, solubility, etc., and are used as a special reaction medium and as a solubilizer for hardly soluble substances in the field of synthetic organic chemistry. At the same time, it is used as a specific catalyst such as a phase transfer catalyst such as crown ether. In addition, ionic liquids can be used in non-aqueous electrolyte materials for secondary batteries such as capacitors and lithium-ion batteries, and electronic device-related fields such as dye-sensitized solar cells, field effect transistors, organic memories, and organic actuators. In recent years, it has attracted attention.

  Various compounds are known as ionic liquids. A typical example is an imidazole compound disclosed in Patent Document 1 below, and this compound is expected to be used as an electrolytic solution for a power storage device such as a capacitor or a secondary battery. Up to now, propylene carbonate (PC) has often been used as an electrolytic solution for a power storage device, but when comparing this propylene carbonate and the imidazole compound, the latter is more heat resistant ( It is said to be excellent in that it has a high decomposition temperature) and contributes to an increase in battery capacity of a power storage device having a non-aqueous electrolyte.

JP 2005-515168 A

  However, since the imidazole compound disclosed in Patent Document 1 has a skeletal structure containing two N (nitrogen) in the five-membered ring and having an unsaturated double bond, it is electrochemically attacked. There is a drawback that it is easy (not electrochemically stable). For this reason, when it uses as electrolyte solution for electrical storage apparatuses, there exists a problem that the upper limit voltage of an electrical storage apparatus cannot fully be raised.

  In addition, since the imidazole compound has only N in the five-membered ring except for C, it is poor in polarity and has a slightly low ability as an ionic liquid for dissolving an organic compound.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an ionic liquid which is electrochemically stable and has an excellent ability to dissolve an organic compound, a method for producing the same, and the like. .

In order to solve the above problems, the present invention includes an oxazolidine cation in which an alkyl group or a methoxyalkyl group (R) is substituted at the N-position, and an anion (X ⁻ ) containing a halogen, which has the following general formula: An ionic liquid represented by (1) (Claim 1).

  Since the ionic liquid of the present invention has no double bond in the five-membered ring, it is resistant to electrochemical attack and exhibits higher stability. Further, since not only N but also O is present in the five-membered ring, the polarity is high and the ability to dissolve an organic compound is excellent.

Preferable examples of the halogen-containing anion (X ⁻ ) include any one of Br ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , and N (SO ₂ CF ₃ ) ₂ ⁻ .

  Moreover, this invention is an electrical storage apparatus containing the said ionic liquid as electrolyte solution (Claim 3).

  According to the present invention, the upper limit voltage of the power storage device can be increased by using the ionic liquid having high electrochemical stability as the electrolytic solution for the power storage device, and the capacity is increased and the energy density is increased. Can be achieved. Moreover, since the solubility of the organic compound by the said ionic liquid is high, salts, such as lithium salt, can be dissolved easily or the density | concentration of the salt to dissolve can be raised.

The present invention also relates to a method for producing an ionic liquid, wherein N-methyloxazolidine is mixed with the alkyl halide having the alkyl group or methoxyalkyl group, and the temperature condition is 50 ° C. or higher and 100 ° C. or lower. A step of obtaining a salt compound having an N-methyloxazolidine cation in which the alkyl group or methoxyalkyl group of R is substituted at the N-position and a halogen anion, and the salt compound, and the X ⁻ And an anion exchange reaction at room temperature using an alkali salt or acid reagent contained as a counter anion (Claim 4).

  Here, the temperature condition of 50 ° C. or more and 100 ° C. or less is set because the reaction rate is slow when the temperature is less than 50 ° C., and it takes a long time until the reaction is completed, so the yield tends to be low. On the other hand, when the temperature exceeds 100 ° C., the raw material or product is partially decomposed to lower the purity, or the raw material exceeds the boiling point of the raw material and part is lost outside the reaction system, resulting in a decrease in yield. For reasons.

  According to the production method of the present invention, the ionic liquid can be appropriately produced with high purity and high yield.

  As described above, according to the present invention, it is possible to provide an ionic liquid which is electrochemically stable and has an excellent ability to dissolve an organic compound, and a method for producing the ionic liquid.

  Further, by using the ionic liquid as an electrolytic solution for a power storage device, the performance of the power storage device can be effectively improved.

It is a table | surface which shows the basic physical property of the ionic liquid of an Example and a comparative example. It is a table | surface which shows the evaluation result of the coin battery which used the ionic liquid of the Example and the comparative example as electrolyte solution.

<Ionic liquid>
First, an ionic liquid according to an embodiment of the present invention will be described. The ionic liquid according to this embodiment is composed of a cation represented by the following general formula (1) and an anion (X ⁻ ).

As shown in the general formula (1), the cation has oxazolidine as a main structure, and the N-position substituent (R) is an alkyl group having 5 to 7 carbon atoms; C _n H _{2n +1} (n = 5 to 7), or a methoxyalkyl group having 3 to 4 methylene groups (4 to 5 carbon atoms); CH ₃ O (CH ₂ ) _m (m = 3 to 4) Have.

The anion (X ⁻ ) is an anion containing halogen, and preferred examples thereof include a bromine anion (Br ⁻ ), a boron tetrafluoride anion (BF ₄ ⁻ ), a phosphorous hexafluoride anion (PF ₆ ⁻ ), and a trifluoro. And lomethanesulfonyl anion (N (SO ₂ CF ₃ ) ₂ ⁻ ). In the following, the chemical formulas of trifluoromethanesulfonyl anion; N (SO ₂ CF ₃₎ to a _2, omitting denoted as NTf _2.

  The inventor of the present application has confirmed that the ionic liquid having the above structure has high electrochemical stability and excellent ability to dissolve organic compounds.

  For example, an imidazole compound that has been attracting attention as an ionic liquid in recent years has characteristics such as excellent heat resistance, but is susceptible to electrochemical attack because of the presence of an unsaturated double bond in the five-membered ring. (It is not electrochemically stable). On the other hand, the oxazolidine-based ionic liquid according to the present embodiment has a high resistance to electrochemical attack and is higher because there is no double bond in the five-membered ring as shown in the general formula (1). It shows stability.

  In addition, since the imidazole compound has only N except for C in the five-membered ring, the polarity is poor and the ability to dissolve the organic compound is somewhat low. However, the oxazolidine-based ionic liquid according to the present embodiment is Since not only N but also O is present in the ring, there are advantages of high polarity and higher ability to dissolve organic compounds.

  The ionic liquid of this embodiment having such properties can be suitably used as an electrolytic solution for a power storage device such as a capacitor or a secondary battery. That is, by using the ionic liquid of the present embodiment that is excellent in electrochemical stability as the electrolytic solution, the upper limit voltage of the power storage device can be increased, and the performance of the power storage device can be further improved.

<Example>
Next, specific examples of the ionic liquid according to the above embodiment will be described as examples of the present invention.

(I) Production of ionic liquid As examples, 15 types of ionic liquids having different substituents (R) and anions (X ⁻ ) in the general formula (1) were produced. The synthesis scheme is shown below.

That is, in order to synthesize the ionic liquids of the examples, first, N-methyloxazolidine (1) is used as a starting material, this is mixed with an alkyl halide (RBr), and stirred at 70 ° C. for 24 hours. . Examples of the halogenated alkyl include an alkyl group represented by C _n H _{2n + 1} (n = 5 to 7) or a methoxyalkyl group represented by CH ₃ O (CH ₂ ) _m (m = 3 to 4). A compound of either (R) and halogen (Br in this case) was used. By mixing and stirring this alkyl halide (RBr) with N-methyloxazolidine (1) as described above, an N-methyloxazolidine cation in which the alkyl group or methoxyalkyl group (R) is substituted at the N-position Various salt compounds (2a to 2e) having halogen anions (Br ⁻ ) were obtained.

Next, an anion exchange reaction is carried out at room temperature for 24 hours using the salt compounds (2a to 2e) and various alkali salts or acid reagents (MX) containing the target counter anion (X ⁻ ). Thus, various oxazolidium salts (3a-3e, 4a-4e, 5a-5e) were synthesized. As MX, any one of LiNTf ₂ , HBF ₄ , and KPF ₆ was used. That is, the counter anion (X ⁻ ) here is any of NTf ₂ ⁻ , BF ₄ ⁻ , and PF ₆ ⁻ .

Here, a more detailed procedure of the above synthesis scheme is shown as an experimental item. Each compound was identified by ¹ H-NMR analysis.

(Ii) Experimental items • N-pentyl-N-methyloxazolidinium bromide (2a)
Under a nitrogen atmosphere, N-methyl-1,3-oxazolidine (1) (8.0 g, 92 mmol) and 1-bromopentane (13.87 g, 92 mmol) were mixed and heated and stirred for 24 hours at 70 ° C. After vacuum drying at 100 ° C. for 2 hours, the mixture was allowed to cool to room temperature. The obtained crude product was recrystallized from 2-propanol-tetrahydrofuran to obtain 2a as a pale yellow solid (12.15 g, 56%).
Mp90-93 ° C; ¹ H-NMR (270 MHz, CDCl ₃ , TMS) δ5.23 (2H, s), 4.52 (2H, t, J = 7.4 Hz), 4.04-4.22 (2H, m), 3.75- 3.92 (2H, m), 3.47 (3H, s), 1.78-1.83 (2H, brm), 1.33-1.45 (4H, m), 0.93 (3H, t, J = 7.3 Hz).
・ N-hexyl bromide-N-methyloxazolidinium (2b)
Under a nitrogen atmosphere, N-methyl-1,3-oxazolidine (1) (10.0 g, 115 mmol) and 1-bromohexane (18.95 g, 115 mmol) were mixed and heated and stirred for 24 hours at 70 ° C. After vacuum drying at 100 ° C. for 2 hours, the mixture was allowed to cool to room temperature. The resulting crude product was purified by alumina column chromatography (elution solvent: acetonitrile) and then vacuum dried at 100 ° C. for 2 hours to obtain 2b as a brown liquid (19.58 g, 67%).
¹ H-NMR (270 MHz, CDCl ₃ , TMS) δ5.22 (2H, s), 4.52 (2H, t, J = 7.4 Hz), 4.03-4.22 (2H, m), 3.74-3.90 (2H, m ), 3.47 (3H, s), 1.71-1.86 (2H, brm), 1.26-1.45 (6H, m), 0.91 (3H, t, J = 7.3 Hz).
・ N-Heptyl-N-methyloxazolidinium bromide (2c)
In the same manner as 2b, N-methyl-1,3-oxazolidine (1) (10.0 g, 115 mmol) and 1-bromoheptane (20.56 g, 115 mmol) are reacted, and 2c is a brown liquid (21.35 g, 70 %).
¹ H-NMR (270 MHz, CDCl ₃ , TMS) δ5.23 (2H, s), 4.51 (2H, t, J = 7.4 Hz), 4.05-4.17 (2H, m), 3.78-3.86 (2H, m ), 3.47 (3H, s), 1.73-1.86 (2H, brm), 1.21-1.45 (8H, m), 0.90 (3H, t, J = 7.0 Hz).
・ N-methyl-N- (3-methoxy) propyloxazolidinium bromide (2d)
In the same manner as 2a, N-methyl-1,3-oxazolidine (1) (8.0 g, 92 mmol) is reacted with 1-bromo-3-methoxypropane (14.05 g, 92 mmol) to give 2d a brown solid ( 13.62 g, 62%).
Mp78-80 ° C; ¹ H-NMR (270 MHz, CDCl ₃ , TMS) δ 5.28 (1H, d, J = 5.4 Hz), 5.20 (1H, d, J = 5.4 Hz), 4.46-4.56 (2H, m), 4.08-4.14 (2H, m), 3.90-3.97 (2H, m), 3.54 (2H, t, J = 5.4 Hz), 3.50 (3H, s), 3.34 (3H, s), 2.10-2.20 (2H, m).
・ N-methyl-N- (4-methoxy) butyloxazolidinium bromide (2e)
In the same manner as 2b, N-methyl-1,3-oxazolidine (1) (4.17 g, 48 mmol) is reacted with 1-bromo-4-methoxybutane (8.0 g, 48 mmol) to give 2e a brown liquid ( 10.66 g, 87%).
¹ H-NMR (270 MHz, CDCl ₃ , TMS) δ5.25 (1H, d, J = 5.4 Hz), 5.22 (1H, d, J = 5.4 Hz), 4.49-4.55 (2H, m), 4.04- 4.21 (2H, m), 3.85-3.92 (2H, m), 3.52 (3H, s), 3.51 (2H, t, J = 5.4 Hz), 3.34 (3H, s), 1.87 -1.99 (2H, m) , 1.66-1.76 (2H, m).
N-pentyl-N-methyloxazolidinium bis (trifluorosulfonyl) imide (3a)
N-pentyl-N-methyloxazolidinium bromide (2a) (0.30 g, 1.3 mmol) and lithium bis (trifluorosulfonyl) imide (0.36 g, 1.3 mmol) were dissolved in water (1.4 mL) . After stirring at room temperature for 24 hours, the mixture was extracted with dichloromethane (3 × 3 mL). The organic layer was washed with water (1 × 3 mL) and then dried over anhydrous magnesium sulfate. After the solvent was distilled off, the crude product was purified by alumina column chromatography (elution solvent: acetonitrile). The obtained product was vacuum-dried at 100 ° C. for 2 hours to obtain 3a as a brown liquid (0.39 g, 70%).
¹ H-NMR (270 MHz, CDCl ₃ , TMS) δ4.82 (2H, s), 4.40 (2H, t, J = 8.0 Hz), 3.61-3.80 (2H, m), 3.33-3.47 (2H, m ), 3.21 (3H, s), 1.70-1.81 (2H, brm), 1.35-1.44 (4H, m), 0.93 (3H, t, J = 7.0 Hz).
N-hexyl-N-methyloxazolidinium bis (trifluorosulfonyl) imide (3b)
N-hexyl bromide-N-methyloxazolidinium (2b) (0.30 g, 1.2 mmol) and lithium bis (trifluorosulfonyl) imide (0.34 g, 1.2 mmol) were dissolved in water (1.4 mL) . Synthesis was performed by the same method as 3a to obtain 3b as a colorless liquid (0.28 g, 52%).
¹ H-NMR (270 MHz, CDCl ₃ , TMS) δ4.83 (2H, s), 4.40 (2H, t, J = 8.0 Hz), 3.65-3.82 (2H, m), 3.40-3.47 (2H, m ), 3.21 (3H, s), 1.70-1.80 (2H, brm), 1.32-1.40 (6H, m), 0.91 (3H, t, J = 6.9 Hz).
N-heptyl-N-methyloxazolidinium bis (trifluorosulfonyl) imide (3c)
N-heptyl-N-methyloxazolidinium bromide (2c) (0.30 g, 1.1 mmol) and lithium bis (trifluorosulfonyl) imide (0.32 g, 1.1 mmol) were dissolved in water (1.4 mL) . Synthesis was performed by the same method as 3a to obtain 3c as a colorless liquid (0.35 g, 67%).
¹ H-NMR (270 MHz, CDCl ₃ , TMS) δ4.84 (2H, s), 4.41 (2H, t, J = 7.8 Hz), 3.67-3.85 (2H, m), 3.42-3.48 (2H, m ), 3.21 (3H, s), 1.70-1.83 (2H, brm), 1.24-1.42 (6H, m), 0.90 (3H, t, J = 6.8 Hz).
N-methyl-N- (3-methoxy) propyloxazolidinium bis (trifluorosulfonyl) imide (3d)
N-methyl-N- (3-methoxy) propyloxazolidinium bromide (2d) (4.0 g, 17 mmol) and lithium bis (trifluorosulfonyl) imide (4.78 g, 17 mmol) were mixed with water (10 mL ). Synthesis was performed by the same method as 3a to obtain 3d as a colorless liquid (6.07 g, 83%).
¹ H-NMR (270 MHz, CDCl ₃ , TMS) δ4.85 (2H, s), 4.39-4.45 (2H, m), 3.73-3.82 (2H, m), 3.59-3.66 (2H, m), 3.50 (2H, t, J = 5.4 Hz), 3.34 (3H, s), 3.20 (3H, s), 2.00-2.11 (2H, m).
N-methyl-N- (4-methoxy) butyloxazolidinium bis (trifluorosulfonyl) imide (3e)
N-methyl-N- (4-methoxy) butyloxazolidinium bromide (2e) (8.0 g, 32 mmol) and lithium bis (trifluorosulfonyl) imide (9.04 g, 32 mmol) were mixed with water (20 mL ). Synthesis was performed in the same manner as 3a to obtain 3e as a colorless liquid (11.29 g, 70%).
¹ H-NMR (270 MHz, CDCl ₃ , TMS) δ4.82 (2H, s), 4.37-4.43 (2H, m), 3.69-3.77 (2H, m), 3.49 (2H, m), 3.44 (2H , t, J = 5.4 Hz), 3.38 (3H, s), 3.20 (3H, s), 1.86-2.00 (2H, m), 1.63-1.72 (2H, m).
N-pentyl-N-methyloxazolidinium = tetrafluoroborate (4a)
N-pentyl-N-methyloxazolidinium bromide (2a) (0.90 g, 3.8 mmol) and 50 wt% tetrafluoroboric acid aqueous solution (0.66 g, 1.3 mmol) were dissolved in water (3 mL). . After stirring at room temperature for 24 hours, the mixture was extracted with ethyl acetate (3 × 5 mL). The extracted organic layer was dried over anhydrous magnesium sulfate, and then the solvent was distilled off. The resulting crude product was purified by alumina column chromatography (elution solvent: acetonitrile). The obtained product was vacuum-dried at 100 ° C. for 2 hours to obtain 4a as a yellow liquid (0.61 g, 66%).
¹ H-NMR (270 MHz, CDCl ₃ , TMS) δ4.89 (2H, s), 4.41 (2H, t, J = 7.8 Hz), 3.70-3.83 (2H, m), 3.38-3.53 (2H, m ), 3.24 (3H, s), 1.69-1.79 (2H, brm), 1.25-1.42 (4H, m), 0.90 (3H, t, J = 6.8 Hz).
N-hexyl-N-methyloxazolidinium = tetrafluoroborate (4b)
N-hexyl bromide-N-methyloxazolidinium (2b) (10.0 g, 39.7 mmol) and 50 wt% tetrafluoroboric acid aqueous solution (7.25 g, 39.7 mmol) were dissolved in water (20 mL). . Synthesis was performed by the same method as 4a to obtain 4b as a yellow liquid (7.23 g, 70%).
¹ H-NMR (270 MHz, CDCl ₃ , TMS) δ4.89 (2H, s), 4.41 (2H, t, J = 7.8 Hz), 3.70-3.83 (2H, m), 3.38-3.53 (2H, m ), 3.24 (3H, s), 1.69-1.79 (2H, brm), 1.25-1.42 (6H, m), 0.90 (3H, t, J = 6.8 Hz).
N-heptyl-N-methyloxazolidinium = tetrafluoroborate (4c)
N-heptyl-N-methyloxazolidinium bromide (2c) (8.0 g, 30 mmol) and 50 wt% tetrafluoroboric acid aqueous solution (5.27 g, 30.0 mmol) were dissolved in water (20 mL). . Synthesis was performed in the same manner as 4a to obtain 4c as a yellow liquid (4.24 g, 52%).
¹ H-NMR (270 MHz, CDCl ₃ , TMS) δ4.89 (2H, s), 4.41 (2H, t, J = 7.8 Hz), 3.70-3.83 (2H, m), 3.38-3.53 (2H, m ), 3.24 (3H, s), 1.69-1.79 (2H, brm), 1.25-1.42 (8H, m), 0.90 (3H, t, J = 6.8 Hz).
N-pentyl-N-methyloxazolidinium = hexafluorophosphate (5a)
N-heptyl-N-methyloxazolidinium bromide (2a) (0.90 g, 3.8 mmol) and potassium hexafluorophosphate (0.66 g, 3.8 mmol) were dissolved in water (3 mL). After stirring at room temperature for 24 hours, the mixture was extracted with dichloromethane (3 × 3 mL). The organic layer was washed with water (1 × 3 mL) and then dried over anhydrous magnesium sulfate. After the solvent was distilled off, recrystallization from dichloromethane-hexane gave 5a as a pale yellow solid (0.61 g, 66%).
Mp94-96 ° C; ¹ H-NMR (270 MHz, CDCl ₃ , TMS) δ4.82 (2H, s), 4.42 (2H, t, J = 8.6 Hz), 3.70-3.77 (2H, m), 3.42- 3.50 (2H, m), 3.21 (3H, s), 1.70-1.83 (2H, brm), 1.36-1.42 (4H, m), 0.92 (3H, t, J = 7.0 Hz).
N-hexyl-N-methyloxazolidinium = hexafluorophosphate (5b)
N-hexyl-N-methyloxazolidinium bromide (2b) (0.30 g, 1.2 mmol) and potassium hexafluorophosphate (0.22 g, 1.2 mmol) were dissolved in water (3 mL). Synthesis was performed by the same method as 5a to obtain 5b as a white solid (0.25 g, 67%).
Mp67-70 ° C; ¹ H-NMR (270 MHz, CDCl ₃ , TMS) δ4.81 (2H, s), 4.41 (2H, t, J = 7.1 Hz), 3.69-3.80 (2H, m), 3.40- 3.52 (2H, m), 3.20 (3H, s), 1.69-1.82 (2H, brm), 1.32-1.45 (6H, m), 0.91 (3H, t, J = 7.0 Hz).
N-heptyl-N-methyloxazolidinium = hexafluorophosphate (5c)
N-heptyl-N-methyloxazolidinium bromide (2c) (0.30 g, 1.1 mmol) and potassium hexafluorophosphate (0.21 g, 1.1 mmol) were dissolved in water (3 mL). Synthesis was performed by the same method as 5a to obtain 5c as a white solid (0.20 g, 54%).
Mp67-70 ° C; ¹ H-NMR (270 MHz, CDCl ₃ , TMS) δ4.80 (2H, s), 4.39 (2H, t, J = 7.1 Hz), 3.69-3.80 (2H, m), 3.38- 3.50 (2H, m), 3.20 (3H, s), 1.69-1.82 (2H, brm), 1.25-1.42 (8H, m), 0.90 (3H, t, J = 6.8 Hz).
N-methyl-N- (3-methoxy) propyloxazolidinium = hexafluorophosphate (5d)
N-methyl-N- (3-methoxy) propyloxazolidinium bromide (2d) (4.0 g, 17 mmol) and potassium hexafluorophosphate (3.01 g, 17 mmol) were dissolved in water (20 mL). . Synthesis was performed by the same method as 5a to obtain 5d as a white solid (2.49 g, 49%).
Mp45-47 ° C; ¹ H-NMR (270 MHz, CDCl ₃ , TMS) δ4.85 (2H, s), 4.39-4.45 (2H, m), 3.73-3.82 (2H, m), 3.59-3.66 (2H , m), 3.50 (2H, t, J = 5.4 Hz), 3.34 (3H, s), 3.20 (3H, s), 2.00-2.11 (2H, m).

(Iii) Characteristics of each ionic liquid Among various oxazolidium salts (3a to 3e, 4a to 4e, 5a to 5e) obtained by the above-described synthesis scheme, NTf ₂ ⁻ (= N (SO ₂ CF ₃ ) ₂ ⁻ ) is used. Five types of salts as anions, that is, N-pentyl-N-methyloxazolidinium = bis (trifluorosulfonyl) imide (3a), N-hexyl-N-methyloxazolidinium = bis (trifluorosulfonyl) ) Imide (3b), N-heptyl-N-methyloxazolidinium = bis (trifluorosulfonyl) imide (3c), N-methyl-N- (3-methoxy) propyloxazolidinium = bis (trifluoro) Sulfonyl) imide (3d), and N-methyl-N- (4-methoxy) butyloxazolidinium bis (trifluorosulfonyl) imide (3e) ) Were used as the ionic liquids of Examples 1 to 5, respectively, and experiments were conducted to measure the reductive decomposition potential, the oxidative decomposition potential, the potential window, and the thermal decomposition temperature (Td) for each of these Examples.

  The reduction (oxidation) decomposition potential is a potential difference (V) generated during the reduction (oxidation) reaction of a certain compound. The larger the absolute value, the less the compound is reduced (oxidized). . The potential window is a difference (total absolute value) between the reductive decomposition potential and the oxidative decomposition potential. The thermal decomposition temperature (Td) is a thermal decomposition starting temperature (° C.) measured using a commercially available thermogravimetric / differential thermal analyzer (TG / DTA).

  In comparative examples for comparison with Examples 1 to 5, imidazole ionic liquid (Comparative Example 1) and propylene carbonate (Comparative Example 2) were used as conventional ionic liquids. The compound name of the imidazole-based ionic liquid in Comparative Example 1 is 1-ethyl-3-methylimidazolium midazole tetrafluoroborate, and the compound name of propylene carbonate in Comparative Example 2 is propylene carbonate / tetraethylammonium tetra. It is a fluoroborate.

  The results of measuring the reductive decomposition potential, the oxidative decomposition potential, the potential window, and the thermal decomposition temperature (Td) using the above Examples and Comparative Examples are shown in FIG. The reductive decomposition potential and the oxidative decomposition potential are based on Ag / AgCl = 0V. As shown in FIG. 1, in any of the ionic liquids of Examples 1 to 5, the absolute values of the reductive decomposition potential and the oxidative decomposition potential were different from those of Comparative Examples 1 and 2 (imidazole ionic liquid and propylene carbonate). As a result, there is a considerable increase in the value of the potential window. That is, it was found that the ionic liquids of Examples 1 to 5 were less oxidized / reduced than Comparative Examples 1 and 2, and were excellent in electrochemical stability.

  Moreover, about thermal decomposition temperature (Td), the thermal decomposition temperature of Examples 1-4 is high compared with Comparative Examples 1 and 2, and has shown the outstanding heat resistance. Moreover, about Example 5, when compared with the comparative example 1 (imidazole type | system | group ionic liquid), although thermal decomposition temperature has fallen a little, when compared with the comparative example 2 (propylene carbonate), heat The decomposition temperature is significantly increased, and sufficient heat resistance is improved.

  As described above, it was found that the ionic liquids of Examples 1 to 5 were excellent in electrochemical stability as compared with Comparative Examples 1 and 2, and had sufficient performance with respect to heat resistance.

In the experiment of FIG. 1, five kinds of oxazolidium salts (3a to 3e) having NTf ₂ ⁻ as an anion are used as Examples 1 to 5, and the reduction decomposition potential, the oxidation decomposition potential, the potential window, and the thermal decomposition temperature (Td ) Was measured, but the electrochemical characteristics of the other oxazolidium salts (4a to 4e, 5a to 5e) having BF ₄ ⁻ and PF ₆ ⁻ as anions are the same as in FIG. It is thought that the result of is obtained.

(Iv) Characteristics when used in a power storage device Next, when the ionic liquid of the example is used as an electrolytic solution for a power storage device, it is confirmed how much performance improvement is seen in the power storage device. The experiment was conducted. In this experiment, a coin battery of model CR2032 was used as the power storage device, and the ionic liquids (3b, 3c) of Examples 2 and 3 were used as the electrolyte of the coin battery. The positive and negative electrodes of the CR2032 coin battery are both activated carbon (manufactured by Kureha).

Using the coin battery as described above, the upper limit voltage (V), initial discharge capacity (mAh / g), and energy density (Wh / kg) were measured. The upper limit voltage is a voltage at which the electrolyte begins to decompose, and the measurement was performed by gradually increasing the voltage applied to the coin battery and specifying the voltage when the slope of the charging curve changed. Moreover, after charging to the measured upper limit voltage, the initial discharge capacity was measured. Specifically, after charging to the upper limit voltage with a constant current of 1 mA, the battery was discharged to 0 V with a constant current of 1 mA, and the discharge capacity at the first cycle was measured as the initial discharge capacity. The energy density is energy obtained per weight, and is obtained by 1/2 × (initial discharge capacity) × (upper limit voltage) ² ÷ (weight of coin battery). The weight of the CR2032 coin battery used in this experiment is 4 g.

  The measurement results of the above experiment are shown in FIG. In FIG. 2, the upper limit voltage, initial discharge capacity, and energy density were measured for the coin battery using the ionic liquids of Examples 2 and 3 as the electrolyte, and Comparative Examples 1 and 2 (imidazole-based ionic liquid and The same measurement was performed on a coin battery using an ionic liquid of propylene carbonate.

  According to FIG. 2, when the ionic liquids of Examples 2 and 3 are used as the electrolyte solution for the coin battery, the upper limit voltage and the discharge capacity are compared with the case of using the ionic liquids of Comparative Examples 1 and 2. It can be seen that all values of energy density are rising. In particular, the energy density is about 3.5 times that of the case where propylene carbonate (Comparative Example 2), which is the current mainstream, is used, and an imidazole ionic liquid (Comparative Example 1) is obtained. ), It can be seen that the energy density is twice or more.

  That is, as shown in FIG. 1, the ionic liquids of Examples 2 and 3 have a considerably large potential window value and superior electrochemical stability as compared with the ionic liquids of Comparative Examples 1 and 2. By using the ionic liquids of Examples 2 and 3 as the electrolytic solution, the operating voltage (upper limit voltage) of the coin battery is increased. As a result, the capacity of the battery is increased and the energy density is significantly increased. It is thought that it was obtained.

  In FIG. 2, the upper limit voltage, discharge capacity, and energy density were measured for the coin battery using the ionic liquids (3b, 3c) of Examples 2 and 3 as the electrolytic solution. For example, even when the ionic liquids (3a, 3d, 3e) of other Examples 1, 4, and 5 are used as the electrolytic solution, it is naturally considered that the same performance improvement as in FIG. 2 can be obtained. It is considered that the same results can be obtained when the oxazolidium salts (4a to 4e, 5a to 5e) according to the other examples are used.

Claims (4)

An ionic liquid represented by the following general formula (1), comprising an oxazolidine cation in which an alkyl group or a methoxyalkyl group (R) is substituted at the N-position, and an anion (X ⁻ ) containing a halogen.

_2. The ionic liquid according to claim 1, wherein the halogen-containing anion (X ⁻ ) is any one of Br ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , and N (SO ₂ CF ₃ ) ₂ ⁻ .   A power storage device comprising the ionic liquid according to claim 1 or 2 as an electrolytic solution. A method for producing an ionic liquid according to claim 1, comprising:
By mixing N-methyloxazolidine and the alkyl halide having the alkyl group of R or the methoxyalkyl group, and reacting under a temperature condition of 50 ° C. or more and 100 ° C. or less, the alkyl group or methoxyalkyl group of the R Obtaining a salt compound having an N-methyloxazolidine cation substituted at the N-position and a halogen anion;
A method for producing an ionic liquid comprising the step of performing an anion exchange reaction at room temperature using the salt compound and an alkali salt or acid reagent containing X ⁻ as a counter anion.

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