JP2006196390A - Ionic liquid composition and electrochemical device using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ionic liquid useful as an electrolyte and an electrolytic liquid of an electrochemical device such as a secondary battery, an electric double layer capacitor, a fuel cell, and a dye-sensitized solar cell. <P>SOLUTION: The ionic liquid composition is composed of a compound (A) as expressed by a general formula (1) (wherein, R<SB>1</SB>, R<SB>2</SB>of cation express each independently alkyl group of carbon number 1-4 and may form a ring-structure by two groups of R<SB>1</SB>, R<SB>2</SB>, X, Y of anion express each independently fluoroalkyl group of carbon number 1-4 and may form a ring-structure by two groups of X, Y) and a compound (B) as expressed by a general formula (2) (wherein, R<SB>3</SB>, R<SB>4</SB>express each independently alkyl group of carbon number 1-4 and may form a ring-structure by two groups of R<SB>3</SB>, R<SB>4</SB>). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ionic liquid composition and an electrochemical device using the same.

  An ionic liquid is generally defined as a salt that exhibits a liquid state near room temperature, has a low vapor pressure over a wide temperature range, is flame retardant and has excellent safety during use, and is composed only of ions and is high. Since the ionic conductivity is exhibited, the development of an electrochemical device to an electrolyte or an electrolytic solution is attempted.

  Regarding cation components of ionic liquids, imidazolium-based cations such as 1-ethyl-3-methylimidazolium or pyridinium-based cations such as 1-butylpyridinium have been mainly studied so far. Many ionic liquids combining various anions such as fluoroborate, hexafluorophosphate, trifluoromethane sulfate, and bis (trifluoromethylsulfonyl) imide have been synthesized (see, for example, Patent Document 1).

  For quaternary ammonium ionic liquids other than imidazolium and pyridinium, chain ammonium cations such as trimethylpropylammonium, trimethylbutylammonium and trimethylhexylammonium, or N-methyl-N-propylpyrrolidi An ionic liquid composed of a combination of a cyclic ammonium cation such as nium or N-methyl-N-propylpiperidinium and bis (trifluoromethylsulfonyl) imide has been reported (for example, see Patent Documents 2 and 3).

Furthermore, an art complex compound in which the dissociation property of conventional tetrafluoroborate and hexafluoroborate in an electrolytic solution is improved and the electrical conductivity is improved in an electrolyte lithium salt has been proposed (see, for example, Patent Document 4). ).
JP-A-11-307121 JP-A-11-297355 JP 2003-331918 A JP 2002-110235 A

  Cyclic amidinium cations such as imidazolium-based or pyridinium-based are characterized in that a liquid salt can be obtained relatively easily at around room temperature by combining with an appropriate anion species, and also exhibits high electrical conductivity. Although there is a disadvantage, the withstand voltage is low. For example, when an electrolyte for a lithium secondary battery is used, an imidazolium salt decomposes at a higher potential than lithium and is less stable, and when an electrolyte for an electric double layer capacitor is used, There is a problem that a sufficient operating voltage cannot be obtained due to poor chemical stability.

  Also, a chain ammonium cation such as trimethylpropylammonium or trimethylbutylammonium, or a cyclic such as N-methyl-N- (n-) propylpyrrolidinium, N-methyl-N- (n-) propylpiperidinium An ionic liquid in which an ammonium cation and bis (trifluoromethylsulfonyl) imide are combined has a problem that the electrochemical stability is good but the electrical conductivity is insufficient.

  Furthermore, in the state of the composition in which ionic liquids or ionic liquids are mixed with a room temperature solid salt, the electrical conductivity is improved, but the electrochemical stability is deteriorated, or the viscosity of the system is increased. There is a problem that electric conductivity is lowered, and it is difficult to achieve both electrochemical stability and electric conductivity.

  The present invention has been made in view of the above problems, and exhibits an electrolyte or electrolysis of an electrochemical device such as a secondary battery, an electric double layer capacitor, a fuel cell, and a dye-sensitized solar cell, which is liquid at room temperature. It is to provide an ionic liquid composition useful as a liquid.

  As a result of intensive studies on the problems as described above, the present inventors have found that a specific ionic liquid composition is liquid at room temperature and exhibits high electrochemical stability and electrical conductivity. It was found useful as an electrolyte and an electrolytic solution for chemical devices, and the present invention was completed.

  That is, this invention is an ionic liquid composition as shown to the following [1]-[5], and an electrochemical device using the same.

  [1] The following general formula (1)

(R ₁ and R ₂ of the cation each independently represent an alkyl group having 1 to 4 carbon atoms, and a ring structure may be formed by two groups of R ₁ and R ₂ , Independently, it represents a C1-C4 fluoroalkyl group, and a ring structure may be formed by two groups of X and Y.)
And the following general formula (2):

(In the formula, R ₃ and R ₄ each independently represents an alkyl group having 1 to 4 carbon atoms, and a ring structure may be formed by two groups of R ₃ and R _4. )
The ionic liquid composition characterized by consisting of the compound (B) represented by these.

  [2] The compound (A) represented by the general formula (1) and the compound (B) represented by the general formula (2) are (A) :( B) = 99: 1 to 30:70. The ionic liquid composition according to the above [1], which is contained within a range of (weight ratio).

  [3] The compound (A) represented by the general formula (1) is N-methyl-N- (n-) propylpyrrolidinium bis (trifluoromethylsulfonyl) imide. The ionic liquid composition according to [1] or [2].

  [4] The above [1] to [3], wherein the compound (B) represented by the general formula (2) is N-methyl-N-ethylpyrrolidinium difluoro (oxalato) borate. An ionic liquid composition according to any one of the above.

  [5] An electrochemical device comprising the ionic liquid composition according to any one of [1] to [4].

  Since the ionic liquid composition of the present invention exhibits a liquid state near room temperature and exhibits high electrical conductivity, it is an electrolyte for electrochemical devices such as secondary batteries, electric double layer capacitors, fuel cells, and dye-sensitized solar cells. Suitable as an electrolytic solution.

  The ionic liquid of the present invention means a salt that exhibits a liquid state near room temperature.

  The ionic liquid composition of the present invention comprises the compound (A) represented by the general formula (1) and the compound (B) represented by the general formula (2).

  In the compound (A) represented by the general formula (1), the cation component is represented by the following general formula (1a)

(In the formula, R ₁ and R ₂ each independently represent an alkyl group having 1 to 4 carbon atoms, and a ring structure may be formed by two groups of R ₁ and R _2. )
N, N-dialkylpyrrolidinium cation represented by the formula (1b):

(In the formula, X and Y each independently represent a fluoroalkyl group having 1 to 4 carbon atoms, and two groups of X and Y may form a ring structure.)
Is an imide anion represented by:

  In the compound (B) represented by the general formula (2), the cation component is represented by the following general formula (2a).

(In the formula, R ₃ and R ₄ each independently represents an alkyl group having 1 to 4 carbon atoms, and a ring structure may be formed by two groups of R ₃ and R _4. )
N, N-dialkylpyrrolidinium cation represented by the formula (2b):

It is a difluoro (oxalato) borate shown by these.

In the N, N-dialkylpyrrolidinium cation represented by the above general formula (1a) or general formula (2a), R _{1 to} R ₄ each independently represents an alkyl group having 1 to 4 carbon atoms. The Examples of the alkyl group having 1 to 4 carbon atoms include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, s-butyl group, and t-butyl group.

  Specific examples of the N, N-dialkylpyrrolidinium cation represented by the general formulas (1a) and (2a) include N, N-dimethylpyrrolidinium and N-methyl-N-ethylpyrrole. Examples include dinium, N-methyl-N- (n-) propylpyrrolidinium, N-methyl-N- (n-) butylpyrrolidinium, N-ethyl- (n-) propylpyrrolidinium, and the like. These may be used alone in each of the compound (A) represented by the general formula (1) or the compound (B) represented by the general formula (2), or two or more of them may be combined.

  For the imide anion represented by the above general formula (1b), a fluoroalkyl group having 1 to 4 carbon atoms is independently selected as X and Y. For example, bis (trifluoromethylsulfonyl) imide, bis (penta Fluoroethylsulfonyl) imide, bis (nonafluorobutanesulfonyl) imide, (trifluoromethylsulfonyl) (pentafluoroethylsulfonyl) imide, and the like. These may be used alone or in combination of two or more. .

  Regarding the ionic liquid composition of the present invention, the abundance ratio of the compound (A) represented by the general formula (1) and the compound (B) represented by the general formula (2) is particularly limited. However, it is preferable that (A) :( B) = 99: 1 to 30:70 (weight ratio), (A) :( B) = 90: 10 to 40:60 (weight ratio) It is particularly preferable that the range is If (B) is less than 1 part by weight, the effect on electrical conductivity may not be seen, and if it exceeds 70 parts by weight, melting and compatibility may not occur.

  In the present invention, the compound (A) represented by the general formula (1) is not particularly limited, but N is a liquid at room temperature alone from the viewpoint of electrochemical stability and electrical conductivity. -Methyl-N- (n-) propylpyrrolidinium bis (trifluoromethanesulfonylimide) is not particularly limited as the compound (B) represented by the general formula (2), but it is room temperature alone. Solid N-methyl-N-ethylpyrrolidinium difluoro (oxalato) borate is preferred. That is, as the ionic liquid composition of the present invention, an ionic liquid composition comprising these compounds is particularly preferable.

  The ionic liquid composition of the present invention exhibits a liquid state in a room temperature region and exhibits high electrical conductivity. Therefore, the chemistry of secondary batteries, electric double layer capacitors, fuel cells, dye-sensitized solar cells, etc. It can be used as an electrolyte and electrolyte for devices. In addition, when an electrochemical device is configured using the ionic liquid of the present invention, the basic components thereof include an ionic conductor, a negative electrode, a positive electrode, a current collector, a separator, a container, and the like. Can be used as is.

  As the ionic conductor, the ionic liquid composition itself of the present invention, the use of a mixture of several kinds of ionic liquids, or the case where a specific cation such as lithium is required, a specific cation is used. It is also possible to use the electrolyte having the electrolyte dissolved in the ionic composition liquid of the present invention, or to mix an ionic liquid composition with a general organic solvent. The concentration of the ionic liquid composition of the present invention when used as an electrolyte is not particularly limited, but is preferably 0.1 mol / l or more, more preferably 0.5 mol / l or more from the viewpoint of performance. Furthermore, by adding a gelling agent or a polymer to the ionic liquid, it is possible to use it in a pseudo-solid state.

  The organic solvent used in the ionic conductor is particularly suitable if it is mixed with the ionic liquid composition of the present invention and is stable in the operating voltage range of electrochemical devices such as secondary batteries and electric double layer capacitors. Among them, a solvent having a high dielectric constant, a low viscosity, and a high boiling point is preferable. Specific examples include ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, and sulfolane. These solvents may be used alone or in combination of two or more.

  When the ionic liquid composition of the present invention is used as an electrolyte for a lithium secondary battery, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium trifluorosulfuric acid, lithium bis (trifluoromethylsulfonyl) is used as a lithium salt. Imide, lithium perchlorate, etc. are added.

  Although it does not specifically limit as said negative electrode material, In the case of a lithium battery, the alloy of lithium metal and lithium and another metal is used. In the case of a lithium ion battery, a material using a phenomenon called an intercalator such as carbon, natural graphite, or metal oxide obtained by firing a polymer, an organic substance, pitch, or the like is used. In the case of an electric double layer capacitor, activated carbon, porous metal, conductive polymer, or the like is used.

As the positive electrode material is not particularly limited, a lithium battery and a lithium ion battery, for _{example, LiCoO 2, LiNiO 2, LiMnO} 2, lithium-containing oxides such as _{LiMn 2 O 4, TiO 2,} V 2 Oxides such as O ₅ and MoO ₃ , sulfides such as TiS ₂ and FeS, or conductive polymers such as polyacetylene, polyaniline, and polypyrrole are used. In the case of an electric double layer capacitor, activated carbon, porous metal oxide, porous metal, conductive polymer, or the like is used.

  Moreover, you may use the ionic composition of this invention as a reaction solvent for organic synthesis, extraction, and a separation solvent.

Examples Hereinafter, the effects of the ionic liquid composition of the present invention as an electrochemical device will be specifically described based on Examples and Comparative Examples, but the present invention is not limited to these Examples. .

  The viscosity was measured by an EL viscometer, and the electrical conductivity was measured at 25 ° C. by a two-terminal AC impedance method. The oxidation-reduction potential is measured at 25 ° C. using a saturated calomel (SCE) electrode as a reference electrode, a working electrode and a platinum electrode as a counter electrode, and a cyclic voltammogram is measured at a sweep rate of 50 mV / s. I asked for it.

Example 1
N-methyl-N-propylpyrrolidinium bis (trifluoromethanesulfonyl) imide and N-methyl-N-ethylpyrrolidinium difluoro (oxalato) borate are mixed at a weight ratio of 60:40 to obtain an ionic liquid composition Got. The viscosity was 52 mPa · s, the electric conductivity was 6.5 mS / cm, and the oxidation-reduction potential was −3.2 V and +2.8 V (potential window 6.0 V), respectively.

Examples 2-4
An ionic liquid composition as shown in Table 1 was prepared, and the viscosity, electrical conductivity, and oxidation-reduction potential were measured.

Comparative Example 1
Table 1 shows the viscosity, electrical conductivity, and oxidation-reduction potential of an ionic liquid composed of N-methyl-N-propylpyrrolidinium bis (trifluoromethanesulfonyl) imide alone belonging to the general formula (1) of the present invention. As is clear from Table 1, it can be seen that the electrical conductivity of Example 1 is higher than that of Comparative Example 1.

Comparative Example 2 to Comparative Example 5
The properties, melting point, viscosity, conductivity, and oxidation-reduction potential of the molten / non-molten salt as shown in Table 1 were measured. When a salt of a chain ammonium cation and a difluoro (oxalato) borate anion is used as in Comparative Example 2, the viscosity increases and good electrical conductivity cannot be obtained. Moreover, also when tetrafluoroborate anion is used like the comparative example 3, a viscosity rises and electrical conductivity falls rather than the case where it does not add. Comparative Example 4 shows the performance of 1-ethyl-3-methylimidazolium tetrafluoroborate, which is a typical ionic liquid, and although its electrical conductivity is excellent, its electrochemical stability is lower than that of the examples. It has become a thing. Furthermore, N-methyl-N-ethylpyrrolidinium described in Comparative Example 5 belonging to the general formula (2) of the present invention is solid at room temperature alone.

  Since the ionic liquid composition of the present invention exhibits a liquid state near room temperature and exhibits high electrical conductivity, it is an electrolyte for electrochemical devices such as secondary batteries, electric double layer capacitors, fuel cells, and dye-sensitized solar cells. Alternatively, it is useful as an electrolytic solution.

Claims (5)

The following general formula (1)

(In the formula, R ₁ and R ₂ of the cation each independently represent an alkyl group having 1 to 4 carbon atoms, and a ring structure may be formed by two groups of R ₁ and R ₂ , Y represents each independently a fluoroalkyl group having 1 to 4 carbon atoms, and a ring structure may be formed by two groups of X and Y.)
And the following general formula (2):

(In the formula, R ₃ and R ₄ each independently represents an alkyl group having 1 to 4 carbon atoms, and a ring structure may be formed by two groups of R ₃ and R _4. )
The ionic liquid composition characterized by consisting of the compound (B) represented by these. The compound (A) represented by the general formula (1) and the compound (B) represented by the general formula (2) are (A) :( B) = 99: 1 to 30:70 (weight ratio). The ionic liquid composition according to claim 1, wherein the ionic liquid composition is contained in the range of The compound (A) represented by the general formula (1) is N-methyl-N- (n-) propylpyrrolidinium bis (trifluoromethylsulfonyl) imide. 2. The ionic liquid composition according to 2. The compound (B) represented by the general formula (2) is N-methyl-N-ethylpyrrolidinium difluoro (oxalato) borate, according to any one of claims 1 to 3. The ionic liquid composition described. An electrochemical device comprising the ionic liquid composition according to any one of claims 1 to 4.