JP2006190618A - Ionic liquid composition and electrochemical device containing same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ionic liquid useful as an electrolyte and an electrolytic solution 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 contains compounds B expressed by a salt compound 1 of N,N-dialkyl pyrrolidinium cation and bis (fluoroalkylsulfonyl) imide anion and a salt compound 2 of N,N-dialkyl pyrrolidinium cation and Z- [Z is one type of or at least two types of anions selected from a group comprising trifluoromethanesulfate, trifluoromethanecarboxylate, bis (trifluoromethanesulfonyl)imide, bis(pentafluoroethanesulfonyl)imide, tetrafluoroborate, and hexafluorophosphate] [however, the compounds A and B are not identical]. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ionic liquid composition and an electrochemical device comprising the same. The ionic liquid composition of the present invention is electrochemically stable and at the same time has high electrical conductivity, and is used for electrochemical devices such as secondary batteries, electric double layer capacitors, fuel cells, and dye-sensitized solar cells. Useful as electrolyte and electrolyte.

  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 it exhibits ionic conductivity, it has been developed as an electrochemical device to electrolytes and electrolytes.

  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 borate, hexafluorophosphate, trifluoromethane sulfate, and bis (trifluoromethylsulfonyl) imide have been synthesized (see, for example, Patent Document 1).

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

JP-A-11-307121 Japanese Patent No. 2981545 JP 2003-331918 A

  Cyclic amidinium cations such as the imidazolium cation and pyridinium cation described above can be easily obtained in the form of a liquid salt near normal temperature by combining with an appropriate anion species, and also exhibit high electrical conductivity. However, there is a drawback that 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.

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

  The present invention has been made in view of the above problems, and exhibits liquidity at room temperature, and also provides electrolytes and electrolysis of electrochemical devices such as secondary batteries, electric double layer capacitors, fuel cells, and dye-sensitized solar cells. It is to provide an ionic liquid composition useful as a liquid.

  As a result of intensive studies to solve the problems as described above, the present inventors have found that an ionic liquid composition containing a specific compound exhibits a liquid state at room temperature and has high electrochemical stability. The present inventors have found that it exhibits electrical conductivity and is useful as an electrolyte and an electrolytic solution for electrochemical devices, and has completed the present invention.

  That is, this invention is an ionic liquid composition as shown below, and an electrochemical device containing the same.

  [1] The following general formula (1)

（式中、カチオンのＲ_１、Ｒ_２は各々独立して炭素数１〜４のアルキル基を表し、Ｒ_１、Ｒ_２の２つの基により環構造を形成しても良い。アニオンのＸ、Ｙは各々独立して、炭素数１〜４のフルオロアルキル基を表し、また、Ｘ、Ｙの２つの基により環構造を形成していても良い。）
で表される化合物（Ａ）、及び下記一般式（２）

(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):

［式中、Ｒ_３、Ｒ_４は各々独立して炭素数１〜４のアルキル基を表し、Ｒ_３、Ｒ_４の２つの基により環構造を形成しても良い。Ｚはトリフルオロメタンスルフェート、トリフルオロメタンカルボキシレート、ビス（トリフルオロメタンスルホニル）イミド、ビス（ペンタフルオロエタンスルホニル）イミド、テトラフルオロボレート、及びヘキサフルオロホスフェートからなる群より選ばれる１種又は２種以上のアニオンである。］
で表される化合物（Ｂ）を含有してなるイオン性液体組成物［ただし、化合物（Ａ）と化合物（Ｂ）は同一ではない］。

[Wherein, R ₃ and R ₄ each independently represent 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 . Z is one or more selected from the group consisting of trifluoromethane sulfate, trifluoromethane carboxylate, bis (trifluoromethanesulfonyl) imide, bis (pentafluoroethanesulfonyl) imide, tetrafluoroborate, and hexafluorophosphate. Anion. ]
An ionic liquid composition comprising the compound (B) represented by the formula [However, the compound (A) and the compound (B) are not the same].

  [2] The composition of the compound (A) represented by the general formula (1) and the compound (B) represented by the general formula (2) is (A) / (B) = 99 to 50 in weight ratio. The ionic liquid composition as described in [1] above, which is in the range of 1 to 50.

  [3] The above-mentioned [1], wherein the compound (A) represented by the general formula (1) is N-methyl-N- (n-) propylpyrrolidinium bis (trifluoromethanesulfonyl) imide. ] Or the ionic liquid composition as described in [2].

  [4] In any one of the above [1] to [3], in the compound (B) represented by the general formula (2), the cation is N-methyl-N-ethylpyrrolidinium. The ionic liquid composition described.

  [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. Furthermore, the ionic composition liquid of the present invention is useful as a reaction solvent, extraction, and separation solvent for organic synthesis.

  Hereinafter, the present invention will be described in detail.

  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) [provided that the compound (A) and compound (B) are not the same. The cation component is an N, N-dialkylpyrrolidinium cation in the general formula (1) and the general formula (2), and the anion component is an imide anion in the general formula (1). And the general formula (2) is characterized by being an anion Z.

In the N, N-dialkylpyrrolidinium cation in the general formula (1) and the general formula (2), each of the substituents R _{1 to} R ₄ is independently an alkyl group having 1 to 4 carbon atoms. Specifically, N, N-dimethylpyrrolidinium, N-methyl-N-ethylpyrrolidinium, N-methyl-N- (n-) propylpyrrolidinium, N-methyl-N- (n- ) Butylpyrrolidinium, N-ethyl-N- (n-) propylpyrrolidinium, and the like. These may be used alone in each of the compound (A) or the compound (B), or two or more of them may be combined.

  In the imide anion in the general formula (1), X and Y are each independently a C 1-4 fluoroalkyl group, and specifically, bis (trifluoromethanesulfonyl) imide, bis ( And pentafluoroethanesulfonyl) imide, bis (nonafluorobutanesulfonyl) imide, and (trifluoromethanesulfonyl) (pentafluoroethanesulfonyl) imide. These may be used alone or in combination of two or more.

  The anion Z in the general formula (2) includes trifluoromethane sulfate, trifluoromethanecarboxylate, bis (trifluoromethanesulfonyl) imide, bis (pentafluoroethanesulfonyl) from the viewpoint of electrical conductivity and electrochemical stability. ) Imido, tetrafluoroborate and hexafluorophosphate are suitable, and these anions may be used alone or in combination of two or more.

  The compound (A) represented by the general formula (1) is not particularly limited. For example, N, N-dimethylpyrrolidinium bis (trifluoromethanesulfonylimide), N-methyl-N— Ethylpyrrolidinium bis (trifluoromethanesulfonylimide), N-methyl-N- (n-) propylpyrrolidinium bis (trifluoromethanesulfonylimide), N-methyl-N- (n-) butylpyrrolidinium -Bis (trifluoromethanesulfonylimide), N-ethyl-N- (n-) propylpyrrolidinium, bis (trifluoromethanesulfonylimide), etc. are mentioned. Of these, N-methyl-N- (n-) propylpyrrolidinium bis (trifluoromethanesulfonylimide), which exhibits a liquid state at room temperature alone, is particularly preferred from the viewpoints of electrochemical stability and electrical conductivity. It is mentioned as a thing.

  Moreover, as a cation component of the compound (B) represented by the said General formula (2), N-methyl-N-ethylpyrrolidinium is mentioned as a particularly suitable thing, As a compound (B), for example, N-methyl-N-ethylpyrrolidinium trifluoromethane sulfate, N-methyl-N-ethylpyrrolidinium trifluoromethanecarboxylate, N-methyl-N-ethylpyrrolidinium bis (trifluoromethanesulfonyl) imide N-methyl-N-ethylpyrrolidinium bis (pentafluoroethanesulfonyl) imide, N-methyl-ethylpyrrolidinium tetrafluoroborate, N-methyl-ethylpyrrolidinium hexafluorophosphate, etc. .

  In the present invention, an ionic liquid composition comprising these compounds or cationic components described above is particularly preferred.

  In the present invention, when the cation of the compound (A) represented by the general formula (1) and the cation of the compound (B) represented by the general formula (2) are the same, the compound (A) And the anion of the compound (B) are not the same, and the compound (A) and the compound (B) are composed of different compounds.

  In the ionic liquid composition of the present invention, the composition of the compound (A) represented by the general formula (1) and the compound (B) represented by the general formula (2) is in a weight ratio, (A) / (B) = 99 to 50/1 to 50, and more preferably (A) / (B) = 95 to 60/5 to 40. If the weight ratio of (B) is less than 1 part by weight, the electrical conductivity is low. On the other hand, if it exceeds 50 parts by weight, the electrical conductivity and electrochemical stability may be reduced, and melting and compatibility may not occur.

  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 constituted using the ionic liquid composition of the present invention, the basic constituent elements thereof include an ionic conductor, a negative electrode, a positive electrode, a current collector, a separator, a container and the like. You can use things as they are.

  As the ionic conductor, the ionic liquid composition of the present invention itself can be used. Further, several kinds of ionic liquids can be mixed and used. When a specific cation such as lithium is required, an electrolyte having the specific cation can be used after being dissolved in the ionic composition liquid of the present invention. Furthermore, it is also possible to mix and use a general organic solvent in the ionic liquid composition.

  Further, the concentration of the ionic liquid composition of the present invention when used as an electrolyte or an electrolytic solution is not particularly limited, but in view of performance, it is preferably 0.1 mol / l or more, more preferably Is used as 0.5 mol / l or more. 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 that can be used by mixing with the ionic liquid composition of the present invention is mixed with the ionic liquid composition of the present invention to operate an electrochemical device such as a secondary battery or an electric double layer capacitor. Any solvent may be used as long as it is stable in the voltage range. 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 trifluoromethane sulfate, lithium bis (trifluoromethanesulfonyl) is used as a lithium salt. Imide, lithium perchlorate, etc. are added.

  The negative electrode material is not particularly limited, but in the case of a lithium battery, lithium metal or an alloy of 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.

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

  Hereinafter, the effect 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 trifluoromethanesulfate are mixed at a weight ratio of 90:10 to prepare an ionic liquid composition. Obtained. The viscosity was 49 mPa · s, the electric conductivity was 5.8 mS / cm, and the oxidation-reduction potential was −3.2 V and +2.9 V (potential window 6.1 V), respectively. The results are shown in Table 1.

実施例２〜実施例４
表１に示すようなイオン性液体組成物を調製し、粘度、電気伝導率、酸化還元電位を測定した。結果を表１に併せて示す。

Example 2 to Example 4
An ionic liquid composition as shown in Table 1 was prepared, and the viscosity, electrical conductivity, and oxidation-reduction potential were measured. The results are also shown in Table 1.

Comparative Example 1
Viscosity, electrical conductivity, oxidation of ionic liquid consisting of N-methyl-N-propylpyrrolidinium bis (trifluoromethanesulfonyl) imide alone belonging to compound (A) represented by general formula (1) of the present invention The reduction potential is also shown in Table 1.

  As is clear from Table 1, the electrical conductivity of Example 1 is higher than that of Comparative Example 1.

Comparative Example 2 to Comparative Example 5
As shown in Table 1, the properties, melting point, viscosity, conductivity, and redox potential of the molten / non-molten salt were measured. The results are also shown in Table 1.

  In Comparative Example 2 and Comparative Example 3, a salt composition comprising N-methyl-N-propylpyrrolidinium bis (trifluoromethanesulfonyl) imide and a chain ammonium cation was used. In Comparative Example 4, a molten salt chain was formed. Although a composition comprising an ammonium cation and N-methyl-N-ethylpyrrolidinium bis (trifluoromethanesulfonyl) imide was used, as is apparent from Table 1, the viscosity increased and good electrical conductivity was obtained. Absent.

  In Comparative Example 5, 1-ethyl-3-methylimidazolium tetrafluoroborate, which is a typical ionic liquid, was used. As is apparent from Table 1, although the electrical conductivity is excellent, the electrochemical stability is Compared to the embodiment, it is low.

Comparative Example 6
N-methyl-N-ethylpyrrolidinium bis (trifluoromethanesulfonyl) imide belonging to compound (A) or compound (B) is a solid at room temperature (melting point: 64 to 68 ° C.), and measurement of electrochemical properties is It was difficult.

Comparative Example 7
N-methyl-N-ethylpyrrolidinium tetrafluoroborate belonging to the compound (B) is a room-temperature solid (melting point: 218 to 223 ° C.), and it was difficult to measure electrochemical properties.

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 independently represents 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):

[Wherein 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 . Z is one or more selected from the group consisting of trifluoromethane sulfate, trifluoromethane carboxylate, bis (trifluoromethanesulfonyl) imide, bis (pentafluoroethanesulfonyl) imide, tetrafluoroborate, and hexafluorophosphate. Anion. ]
An ionic liquid composition comprising the compound (B) represented by the formula [However, the compound (A) and the compound (B) are not the same]. The composition of the compound (A) represented by the general formula (1) and the compound (B) represented by the general formula (2) is (A) / (B) = 99-50 / 1 in weight ratio. The ionic liquid composition according to claim 1, wherein the ionic liquid composition is in the range of 50. The compound (A) represented by the general formula (1) is N-methyl-N- (n-) propylpyrrolidinium bis (trifluoromethanesulfonyl) imide. 2. The ionic liquid composition according to 2. The ionicity according to any one of claims 1 to 3, wherein in the compound (B) represented by the general formula (2), the cation is N-methyl-N-ethylpyrrolidinium. Liquid composition. An electrochemical device comprising the ionic liquid composition according to any one of claims 1 to 4.