JP2006236829A - Ionic liquid, nonaqueous electrolyte for electricity accumulation device and electricity accumulation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ionic liquid having viscosity lower than that of an ionic liquid containing, as constituents, tetrafluoborate anions or hexafluorophosphoric acid anions, and hardly causing hydrolysis. <P>SOLUTION: This ionic liquid is represented by formula (1) or (4) and having a melting point below 50°C. In the formulas, R<SP>1</SP>-R<SP>4</SP>are different types of 1-5C alkyl groups or alkoxyalkyl groups represented by R'-O-(CH<SB>2</SB>)<SB>n</SB>(R' is a methyl or ethyl group and n is an integer of 1 to 4); and any two groups of R<SP>1</SP>to R<SP>4</SP>may form a ring along with X; however, at least one of R<SP>1</SP>to R<SP>4</SP>is an alkoxyalkyl group; X is a nitrogen atom or a phosphorous atom; R<SB>F</SB>is a 1-4C perfluoroalkyl group; (a) is an integer of 1 to 4; and (b) is an integer of 1 to 6 (when (a) and (b) are each not smaller than 2, R<SB>F</SB>s may be identical or different from one another; and R<SB>F</SB>s may form a ring along with a boron atom or a phosphorous atom by being bonded to one another). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ionic liquid, a nonaqueous electrolytic solution for an electricity storage device, and an electricity storage device.

  An ionic liquid composed of an onium cation having an alkoxyalkyl group and a tetrafluoroborate or hexafluorophosphate anion has (1) no or very low vapor pressure, and (2) noncombustibility or flame retardancy. , (3) having high ionic conductivity, (4) higher decomposition voltage than water, (5) wider liquid temperature range than water, (6) capable of handling in the atmosphere, (7) until then In recent years, it has been found that it is suitable as an electrolytic solution (solvent) for an electric double layer capacitor, a lithium ion battery or the like because of various advantages such as having a wider potential window than a known ionic liquid (Patent Document 1). : International Publication No. 02/076924 Pamphlet).

The tetrafluoroborate anion and hexafluorophosphate anion constituting this ionic liquid have the property of being easily hydrolyzed by water present in the system. When these anions are hydrolyzed, hydrogen fluoride is generated. As a result, the electric capacity, charge / discharge efficiency, withstand voltage, etc. of the capacitor and battery are reduced, and the capacitor and battery are expanded by gas generation. Problems arise. Although reducing the water present in the system is usually performed, it is difficult to completely remove moisture adhering to the capacitor such as the electrode active material or the battery constituent member. For this reason, the water content in the electrolytic solution is usually only about several tens of ppm, and it is difficult to completely prevent the hydrolysis.
It is also known that when an electricity storage device using an electrolyte salt having each of the above anions is repeatedly charged and discharged with a large current of 30 C or more at a C rate, a reversible capacity decrease caused by ion association occurs. ing.

  Furthermore, the ionic liquid has a relatively high viscosity, and when used as an electrolytic solution for an electric double layer capacitor or a lithium ion battery, it is diluted with an electrolyte solvent so that the internal resistance does not increase. Is generally reduced. As the electrolyte solvent, an organic solvent such as propylene carbonate is often used. However, since the organic solvent has flammability, the ionic liquid itself has no vapor pressure, as described above, is nonflammable, or Even if it has the property of being flame retardant, its advantage cannot be fully utilized.

From the viewpoint of preventing hydrolysis of an anionic component, an electrolyte salt composed of a fluoroborate anion having a perfluoroalkyl group or a fluorophosphate anion has been developed (Patent Document 2: JP-A-2002-63934, Patent Document 3: Japanese Patent Laid-Open No. 2002-100403, Patent Document 4: Japanese Patent Laid-Open No. 2002-151361, etc.).
In addition, an ionic liquid composed of an ammonium cation having an alkoxyalkyl group and a perfluoroethyl trifluoroborate anion has a lower viscosity than an ionic liquid composed of the cation and a tetrafluoroborate anion. This has also been reported (see Non-Patent Document 1).
However, this ionic liquid is not only insufficient in terms of viscosity, but it cannot be said that the characteristics of capacitors and batteries using the ionic liquid as an electrolytic solution are practically satisfactory.

International Publication No. 02/076924 Pamphlet JP 2002-63934 A JP 2002-100403 A JP 2002-151361 A Chemistry Letters, Vol. 33, no. 7, 886-887, 2004

  The present invention has been made in view of such circumstances, and has a lower viscosity than an ionic liquid containing a tetrafluoroborate anion or a hexafluorophosphate anion as its constituent component and hardly causes hydrolysis. It is an object of the present invention to provide an ionic liquid, a nonaqueous electrolytic solution for an electrical storage device, and an electrical storage device using the nonaqueous electrolytic solution.

  As a result of intensive studies in order to achieve the above object, the present inventor has found that the ionic liquid represented by the following formulas (1) and (4), preferably formulas (2), (3), (5), ( The ionic liquid represented by 6) has a lower viscosity than an ionic liquid containing a tetrafluoroborate anion or a hexafluorophosphate anion as a constituent component thereof, and hardly causes hydrolysis, and includes this ionic liquid. It has been found that electric storage devices such as electric double layer capacitors and secondary batteries using electrolytes have low internal resistance, high rated voltage, and excellent durability and cycle characteristics during large current charge / discharge. The present invention has been completed.

〔式中、Ｒ¹〜Ｒ⁴は互いに同一もしくは異種の炭素数１〜５のアルキル基、またはＲ′−Ｏ−（ＣＨ₂）_n−で表されるアルコキシアルキル基（Ｒ′はメチル基またはエチル基を示し、ｎは１〜４の整数である。）を示し、これらＲ¹、Ｒ²、Ｒ³およびＲ⁴のいずれか２個の基がＸと共に環を形成していてもよい。ただし、Ｒ¹〜Ｒ⁴の内少なくとも１つは上記アルコキシアルキル基である。Ｘは窒素原子またはリン原子を示し、Ｒ_Fは、炭素数１〜４のパーフルオロアルキル基を示し、ａは１〜４の整数である（なお、ａが２以上の場合、Ｒ_Fは互いに同一でも異なっていてもよく、またＲ_Fが相互に結合してホウ素原子と共に環を形成していてもよい。）。〕
２． 下記一般式（２）で示されることを特徴とする１のイオン液体、

〔式中、Ｘは窒素原子またはリン原子を示し、Ｒ′は、メチル基またはエチル基を示し、ｎは１〜４の整数である。Ｒ_Fは、炭素数１〜４のパーフルオロアルキル基を示し、ａは１〜４の整数である（なお、ａが２以上の場合、Ｒ_Fは互いに同一でも異なっていてもよく、またＲ_Fが相互に結合してホウ素原子と共に環を形成していてもよい。）。ただし、Ｘが窒素原子、Ｒ′がメチル基、Ｒ_Fがペンタフルオロエチル基、ｎが２、ａが１のものを除く。〕
３． 下記一般式（３）で示されることを特徴とする１のイオン液体、

〔式中、Ｘは窒素原子またはリン原子を示し、Ｒ¹は炭素数１〜５のアルキル基を示し、Ｒ′は、メチル基またはエチル基を示し、ｍは４または５の整数であり、ｎは１〜４の整数である。Ｒ_Fは、炭素数１〜４のパーフルオロアルキル基を示し、ａは１〜４の整数を示す（なお、ａが２以上の場合、Ｒ_Fは互いに同一でも異なっていてもよく、またＲ_Fが相互に結合してホウ素原子と共に環を形成していてもよい。）。〕
４． 下記一般式（４）で示され、融点が５０℃以下であることを特徴とするイオン液体、

〔式中、Ｒ¹〜Ｒ⁴は互いに同一もしくは異種の炭素数１〜５のアルキル基、またはＲ′−Ｏ−（ＣＨ₂）_n−で表されるアルコキシアルキル基（Ｒ′はメチル基またはエチル基を示し、ｎは１〜４の整数である。）を示し、これらＲ¹、Ｒ²、Ｒ³およびＲ⁴のいずれか２個の基がＸと共に環を形成していてもよい。ただし、Ｒ¹〜Ｒ⁴の内少なくとも１つは上記アルコキシアルキル基である。Ｘは窒素原子またはリン原子を示し、Ｒ_Fは、炭素数１〜４のパーフルオロアルキル基を示し、ｂは１〜６の整数である（なお、ｂが２以上の場合、Ｒ_Fは互いに同一でも異なっていてもよく、またＲ_Fが相互に結合してリン原子と共に環を形成していてもよい。）。〕
５． 下記一般式（５）で示されることを特徴とする４のイオン液体、

〔式中、Ｘは窒素原子またはリン原子を示し、Ｒ′は、メチル基またはエチル基を示し、ｎは１〜４の整数である。Ｒ_Fは、炭素数１〜４のパーフルオロアルキル基を示し、ｂは１〜６の整数である（なお、ｂが２以上の場合、Ｒ_Fは互いに同一でも異なっていてもよく、またＲ_Fが相互に結合してリン原子と共に環を形成していてもよい。）。〕
６． 下記一般式（６）で示されることを特徴とする４のイオン液体、

〔式中、Ｘは窒素原子またはリン原子を示し、Ｒ¹は炭素数１〜５のアルキル基を示し、Ｒ′は、メチル基またはエチル基を示し、ｍは４または５の整数であり、ｎは１〜４の整数である。Ｒ_Fは、炭素数１〜４のパーフルオロアルキル基を示し、ｂは１〜４の整数を示す（なお、ｂが２以上の場合、Ｒ_Fは互いに同一でも異なっていてもよく、またＲ_Fが相互に結合してリン原子と共に環を形成していてもよい。）。〕
７． ２〜６のいずれかのイオン液体のみからなることを特徴とする蓄電デバイス用非水電解液、
８． ２〜６のいずれかのイオン液体を含むことを特徴とする蓄電デバイス用非水電解液、
９． ７または８の蓄電デバイス用非水電解質を用いて構成された蓄電デバイス、
１０． 電気二重層キャパシタまたはリチウムイオン電池である９の蓄電デバイス
を提供する。 That is, the present invention
1. An ionic liquid represented by the following general formula (1) and having a melting point of 50 ° C. or lower,

[Wherein, R ^{1 to} R ⁴ are the same or different alkyl groups having 1 to 5 carbon atoms, or an alkoxyalkyl group represented by R′—O— (CH ₂ ) _n — (R ′ is a methyl group or Represents an ethyl group, and n represents an integer of 1 to 4.), and any two groups of R ¹ , R ² , R ³ and R ⁴ may form a ring together with X. However, at least one of R ^{1 to} R ⁴ is the alkoxyalkyl group. X represents a nitrogen atom or a phosphorus atom, R _F represents a perfluoroalkyl group having 1 to 4 carbon atoms, a is an integer of 1 to 4 (in the case where a is 2 or more, R _F is mutually They may be the same or different, and R _F may be bonded to each other to form a ring with a boron atom.) ]
2. 1 ionic liquid characterized by being represented by the following general formula (2):

[Wherein, X represents a nitrogen atom or a phosphorus atom, R ′ represents a methyl group or an ethyl group, and n is an integer of 1 to 4. R _F represents a perfluoroalkyl group having 1 to 4 carbon atoms, a is an integer of 1 to 4 (in the case where a is 2 or more, R _F may be the same or different from each other, and R _F may be bonded to each other to form a ring together with the boron atom.) Provided that X is a nitrogen atom, R ′ is a methyl group, R _F is a pentafluoroethyl group, n is 2, and a is 1. ]
3. 1 ionic liquid characterized by being represented by the following general formula (3):

[In the formula, X represents a nitrogen atom or a phosphorus atom, R ¹ represents an alkyl group having 1 to 5 carbon atoms, R ′ represents a methyl group or an ethyl group, m is an integer of 4 or 5, n is an integer of 1-4. R _F represents a perfluoroalkyl group having 1 to 4 carbon atoms, a represents an integer of 1 to 4 (in the case where a is 2 or more, R _F may be the same or different from each other, and R _F may be bonded to each other to form a ring together with the boron atom.) ]
4). An ionic liquid represented by the following general formula (4) and having a melting point of 50 ° C. or lower;

[Wherein, R ^{1 to} R ⁴ are the same or different alkyl groups having 1 to 5 carbon atoms, or an alkoxyalkyl group represented by R′—O— (CH ₂ ) _n — (R ′ is a methyl group or Represents an ethyl group, and n represents an integer of 1 to 4.), and any two groups of R ¹ , R ² , R ³ and R ⁴ may form a ring together with X. However, at least one of R ^{1 to} R ⁴ is the alkoxyalkyl group. X represents a nitrogen atom or a phosphorus atom, R _F represents a perfluoroalkyl group having 1 to 4 carbon atoms, b is an integer of 1 to 6 (in the case where b is 2 or more, R _F is mutually They may be the same or different, and R _F may be bonded to each other to form a ring together with the phosphorus atom). ]
5. 4 ionic liquids represented by the following general formula (5):

[Wherein, X represents a nitrogen atom or a phosphorus atom, R ′ represents a methyl group or an ethyl group, and n is an integer of 1 to 4. R _F represents a perfluoroalkyl group having 1 to 4 carbon atoms, and b is an integer of 1 to 6 (in addition, when b is 2 or more, R _F may be the same as or different from each other, and R _F may be bonded to each other to form a ring together with the phosphorus atom.) ]
6). 4 ionic liquids represented by the following general formula (6):

[In the formula, X represents a nitrogen atom or a phosphorus atom, R ¹ represents an alkyl group having 1 to 5 carbon atoms, R ′ represents a methyl group or an ethyl group, m is an integer of 4 or 5, n is an integer of 1-4. R _F represents a perfluoroalkyl group having 1 to 4 carbon atoms, and b represents an integer of 1 to 4 (in addition, when b is 2 or more, R _F may be the same as or different from each other, and R _F may be bonded to each other to form a ring together with the phosphorus atom.) ]
7). A non-aqueous electrolyte for an electricity storage device, characterized by comprising only one of the ionic liquids of 2 to 6,
8). A nonaqueous electrolytic solution for an electricity storage device, comprising any one of 2 to 6 ionic liquids,
9. An electricity storage device configured using the non-aqueous electrolyte for electricity storage device according to 7 or 8,
10. Nine electric storage devices which are electric double layer capacitors or lithium ion batteries are provided.

According to the present invention, (a) lower viscosity than organic ionic liquids having a conventional alkoxyalkyl group, (b) high ionic conductivity, (c) hardly generate hydrogen fluoride by hydrolysis (D) An ionic liquid having characteristics such as a wide potential window and (e) a wide liquid temperature region can be provided.
The electrolytic solution for an electricity storage device made of the ionic liquid has a low viscosity and does not need to be diluted with an organic solvent, or can be used with a very small amount of dilution, and thus has high safety. In addition, since the liquid temperature range is wide, crystallization is difficult even at low temperatures.
An electric storage device using the electrolytic solution for the electric storage device has a small internal resistance, and thus is not only suitable for large current charge / discharge but also excellent in cycle characteristics in large current charge / discharge. In addition, as described above, the amount of the organic solvent used in the electrolytic solution can be suppressed as much as possible, so that the safety is excellent and the electrolytic solution is less prone to hydrolysis. Difficult to cause problems such as gas generation. Further, since the liquid temperature range of the electrolytic solution is wide, the temperature characteristics, particularly the charge / discharge characteristics at a low temperature, are also excellent.

Hereinafter, the present invention will be described in more detail.
[1] First Ionic Liquid The first ionic liquid according to the present invention is represented by the general formula (1) and has a melting point of 50 ° C. or lower.
(1) Cationic component In formula (1), examples of the alkyl group having 1 to 5 carbon atoms include a methyl group, an ethyl group, a propyl group, a 2-propyl group, a butyl group, and a pentyl group. Examples of the alkoxyalkyl group represented by R′—O— (CH ₂ ) _n — include a methoxy or ethoxymethyl group, a methoxy or ethoxyethyl group, a methoxy or ethoxypropyl group, and a methoxy or ethoxybutyl group.
In addition, as a compound in which any two groups of R ¹ , R ² , R ³ and R ⁴ together with X form a ring, when a nitrogen atom is employed for X, an aziridine ring, an azetidine ring, A quaternary ammonium salt having a pyrrolidine ring, a piperidine ring, or the like. On the other hand, when X employs a phosphorus atom, a quaternary phosphonium salt having a pentamethylenephosphine (phosphorinane) ring or the like can be used.

In particular, a quaternary ammonium cation having at least one methoxyethyl group in which R ′ is a methyl group and n is 2 is preferable as a substituent.
(A) As a substituent, a quaternary cation represented by the following formula (7) having a methyl group, two ethyl groups, and an alkoxyalkyl group; (B) As a substituent, an ethyl group, two methyl groups, And a quaternary cation represented by the following formula (8) having an alkoxyalkyl group (provided that when the anion component is pentafluoroethyl trifluoroborate, in formulas (7) and (8), X is a nitrogen atom, R ′ Is a methyl group and n is 2), (C) a methyl group as a substituent, a pyrrolidine ring (in the ionic liquid of the above formula (3), R ¹ is CH ₃ , m is 4, X is a nitrogen atom) And quaternary cations represented by the following formula (9) having an alkoxyethyl group can be preferably used. Among them, a quaternary cation having a pyrrolidine ring represented by the following formula (9) is preferable because it easily forms a low-viscosity ionic liquid.

(2) Anion component The anion component constituting the first ionic liquid is a fluoroborate anion having a perfluoroalkyl group R _F having 1 to 4 carbon atoms represented by [(R _F ) _a BF _4−a ] ^−. is there.
Examples of the perfluoroalkyl group having 1 to 4 carbon atoms include a trifluoromethyl group, a pentafluoroethyl group, a heptafluoropropyl group, and a nonafluorobutyl group.

Specific examples of the anion include trifluoromethyl trifluoroborate, bis (trifluoromethyl) difluoroborate, tris (trifluoromethyl) fluoroborate, tetrakis (trifluoromethyl) borate, pentafluoroethyl trifluoroborate, bis ( Pentafluoroethyl) difluoroborate, tris (pentafluoroethyl) fluoroborate, tetrakis (pentafluoroethyl) borate, heptafluoropropyltrifluoroborate, bis (heptafluoropropyl) difluoroborate, tris (heptafluoropropyl) fluoroborate, tetrakis (Heptafluoropropyl) borate, nonafluorobutyl trifluoroborate, bis (nonafluorobutyl) difluoroborate, tri (Nonafluorobutyl) fluoroborate, trifluoromethylpentafluoroethyl difluoroborate, bis (trifluoromethyl) pentafluoroethylfluoroborate, tris (trifluoromethyl) pentafluoroethylborate, trifluoromethylbis (pentafluoroethyl) fluoro Borate, bis (trifluoromethyl) bis (pentafluoroethyl) borate, trifluoromethyltris (pentafluoroethyl) fluoroborate, tetrakis (pentafluoroethyl) borate, perfluoro (B, B-tetramethylene) difluoroborate, per Fluoro [bis (B, B-tetramethylene) borate], perfluoro (B, B-pentamethylene) difluoroborate, perfluoro [bis (B, B-penta Styrene) borate], and the like.
Considering the simplicity of synthesis and cost, and the small size and asymmetry required when used as an electric double layer capacitor electrolyte salt, trifluoromethyl trifluoroborate or pentafluoroethyl trifluoroborate is preferable.

These anion components can be produced by a known method. For example, perfluoroalkyl trifluoroborate is R.I. D. Chambers et al. , J .; Am. Chem. Soc. , 82, 5298 (1960), M.M. Ue et al. , J .; Fluorine Chem. 127-131, 123 (2003), G.M. A. Molander and B.M. P. They can be synthesized by methods described in literature such as Hoag, Organometallics, 3313-3315, 22 (2003). Bis (trifluoromethyl) difluoroborate is described in G.I. Pawellke et al. , J .; Organomet. Chem. , 178, 1 (1979). Other anions can also be obtained by applying these methods.
As a suitable 1st ionic liquid in this invention, what is shown by a following formula is mentioned, for example.

(3) Manufacturing method The manufacturing method of the first ionic liquid is not particularly limited, and a known method can be used. For example, a method in which a halogen salt of a quaternary onium cation having an alkoxyalkyl group and a metal salt of a fluoroboric acid anion having a perfluoroalkyl group are mixed and produced by a salt exchange reaction (salt exchange method), a quaternary onium cation A direct quaternization method or the like in which a precursor and a fluoroborate anion precursor having a perfluoroalkyl group are reacted can be used. Of these, the salt exchange method is preferred because of the ease of reaction.

In the fluoroboric acid anion metal salt having a perfluoroalkyl group used in the salt exchange method, suitable metals include alkali metals such as lithium, sodium and potassium.
On the other hand, examples of the method for synthesizing a halogen salt of a quaternary onium cation having an alkoxyalkyl group used in the salt exchange method include the following methods.
In the case of a quaternary ammonium salt, a tertiary amine and an alkyl halide are mixed and heated as necessary to obtain a quaternary ammonium halide salt.
In the case of a quaternary phosphonium salt, a tertiary phosphine and an alkyl halide are mixed and heated as necessary to obtain a quaternary phosphonium halide salt. In addition, when using compounds with low reactivity, such as alkoxymethyl halide and alkoxyethyl halide, it is preferable to make it react under pressure using an autoclave.
As the halogen of the halogen salt, any of fluorine, chlorine, bromine and iodine can be used without limitation, but chlorine, bromine and iodine are preferred from the viewpoint of easy salt exchange.

  The salt exchange reaction is generally performed in a solvent. The solvent is not particularly limited, and halogenated hydrocarbons such as chloroform and dichloromethane; ethers such as diisopropyl ether, diethyl ether, tetrahydrofuran, and 1,4-dioxane; ketones such as acetone and methyl ethyl ketone; Esters such as ethyl acetate and isopropyl acetate; Nitriles such as acetonitrile; Alcohols such as methanol, ethanol, isopropyl alcohol and tert-butyl alcohol; Amides such as dimethylformamide and dimethylacetamide; Sulphoxides such as dimethyl sulfoxide An organic solvent and water are mentioned. Among these, acetone, methyl ethyl ketone, acetonitrile, methanol, ethanol, isopropyl alcohol, tert-butyl alcohol, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, water, and the like are fluoroboric acid anion metal salts and alkoxyalkyls having perfluoroalkyl groups as raw materials. Since the solubility of the quaternary onium cation halogen salt having a group is high, it is preferably used.

The conditions for the salt exchange reaction are not particularly limited, and the temperature conditions may be any of heating, room temperature, and cooling, and the pressure conditions may be any of pressure, reduced pressure, and normal pressure. . In general, the reaction proceeds sufficiently under conditions of normal pressure and room temperature, and the reaction is completed within a few minutes to 10 hours.
The concentration of each raw material in the reaction solution during the salt exchange reaction is not particularly limited, and may be set as appropriate in consideration of the solubility of each raw material in the solvent used. However, if the concentration is too low, the reaction efficiency is poor, and if it is too high, the raw material may not dissolve in the solvent. Therefore, generally, the total content of the quaternary onium cation halogen salt and the fluoroborate anion metal salt in the reaction solution It is preferable to carry out the reaction in an amount of 3 to 50% by mass, preferably 5 to 30% by mass.

  After completion of the reaction, the by-product inorganic salt may be removed and the target product may be isolated. For example, after extracting an inorganic salt with water, a method for removing the solvent, a method for removing the solvent after precipitating and filtering the inorganic salt, dissolving the inorganic salt and crystallizing the target organic salt. An appropriate method such as a filtering method can be used. In addition, when the isolated ionic liquid contains moisture, the moisture may be removed by performing concentration, azeotropic dehydration, or the like as necessary.

[2] Second Ionic Liquid The second ionic liquid according to the present invention is represented by the above general formula (4) and has a melting point of 50 ° C. or lower.
(1) Cation component The cation component is as described in the first ionic liquid, but in the second ionic liquid, as a substituent of the cation component of the formula (4), a methyl group, two ethyl Even in the case of a quaternary cation having a group and an alkoxyalkyl group, or a quaternary cation having an ethyl group, two methyl groups, and an alkoxyalkyl group, X, R ′, n, and the anion component are not limited.

(2) Anion component The anion component constituting the second ionic liquid is a fluorophosphate anion having a C 1-4 perfluoroalkyl group R _F represented by [(R _F ) _b PF _6-b ] ^- It is.
Here, the C1-C4 perfluoroalkyl group is the same as that of the said 1st ionic liquid.

Specific examples of this anion include trifluoromethyl pentafluorophosphate, bis (trifluoromethyl) tetrafluorophosphate, tris (trifluoromethyl) trifluorophosphate, pentafluoroethyl pentafluorophosphate, bis (pentafluoroethyl) tetrafluoro. Phosphate, tris (pentafluoroethyl) trifluorophosphate, pentafluoroethyltrifluoromethyltetrafluorophosphate, pentafluoroethylbis (trifluoromethyl) trifluorophosphate, bis (pentafluoroethyl) trifluoromethyltrifluorophosphate, heptafluoro Propylpentafluorophosphate, bis (heptafluoropropyl) tetrafluorophosphate, tri (Heptafluoropropyl) trifluorophosphate, trifluoromethyl heptafluoropropyl tetrafluorophosphate, trifluoromethylbis (heptafluoropropyl) trifluorophosphate, bis (trifluoromethyl) heptafluoropropyl trifluorophosphate, bis (trifluoromethyl ) Bis (heptafluoropropyl) difluorophosphate, tris (trifluoromethyl) bis (heptafluoropropyl) fluorophosphate, pentafluoroethyl heptafluoropropyl tetrafluorophosphate, bis (pentafluoroethyl) heptafluoropropyl trifluorophosphate, tris ( Pentafluoroethyl) heptafluoropropyl difluorophosphate, pentafluoro Tilbis (heptafluoropropyl) trifluorophosphate, pentafluoroethyl trifluoromethyl heptafluoropropyl trifluorophosphate, bis (pentafluoroethyl) trifluoromethyl heptafluoropropyl difluorophosphate, bis (pentafluoroethyl) bis (trifluoromethyl) Heptafluoropropyl fluorophosphate, pentafluoroethyl bis (trifluoromethyl) heptafluoropropyl difluorophosphate, pentafluoroethyl tris (trifluoromethyl) heptafluoropropyl fluorophosphate, pentafluoroethyltetrakis (trifluoromethyl) heptafluoropropyl phosphate, Pentafluoroethyl trifluoromethyl bis (heptafluoro Propyl) difluorophosphate and the like.
Among these, in consideration of the ease of synthesis and cost, and the small molecular diameter required for use as an electric double layer capacitor electrolyte salt, the total number of carbon atoms of R _F is 6 or less. preferable.

  As a suitable 2nd ionic liquid in this invention, what is shown by a following formula is mentioned, for example.

(3) Manufacturing method The second ionic liquid can also be manufactured by applying a known method. For example, N.I. Ignat'ev et al. , J .; Fluorine. Chem. , 103, 57 (2000), and a fluorophosphorane having a perfluoroalkyl group obtained by applying the method described above, and a fluoride of a quaternary onium cation can be produced.
Similarly to the borate production method, it can also be produced by a salt exchange reaction between a halogen salt of a quaternary onium cation having an alkoxyalkyl group and a metal salt of a fluorophosphate anion having a perfluoroalkyl group. (Salt exchange method).

The first and second ionic liquids of the present invention described above are (1) low viscosity, (2) have high ionic conductivity, and (3) hydrolysis compared to conventional organic ionic liquids. Therefore, it has various advantages such as (4) having a wide potential window and (5) a wide liquid temperature range.
In particular, when an ionic liquid is used as a nonaqueous electrolytic solution for an electricity storage device, if the potential window is narrow, the electrolyte and the electrolytic solution may be oxidatively decomposed or reductively decomposed along with charge / discharge. The imidazolium-based ionic liquid cannot be used in a lithium ion secondary battery system because of its narrow potential window, but the ionic liquid of the present invention having a wide potential window can also be used in a lithium ion secondary battery.

  Considering the use of the non-aqueous electrolyte for the electricity storage device, the viscosity at 25 ° C. of the first and second ionic liquids is preferably 200 mPa · s or less, more preferably 100 mPa · s or less, and more preferably 50 mPa · s or less. Even more preferred. By setting it as the viscosity of this range, in the electrical storage device using the electrolyte solution which consists only of an ionic liquid, the increase in internal resistance etc. can be suppressed and the cycling characteristics in large current charging / discharging can be improved. The viscosity is not particularly limited as long as a measuring instrument calibrated with a standard solution for calibration of a viscometer specified in JIS Z8809 is used, and the viscosity can be measured using a rotary, vibration or capillary type viscometer. it can. The viscosity of the present invention uses a Brookfield type rotational viscometer (trade name “Digital Rheometer DV-III”, manufactured by Brookfield) as a viscometer, and the spindle and rotational speed depend on the viscosity of the electrolyte. It is a value that is appropriately selected and measured at 25 ° C.

  Moreover, although melting | fusing point of the ionic liquid of this invention is 50 degrees C or less, when the use of the nonaqueous electrolyte for electrical storage devices is considered, 25 degrees C or less is preferable and 15 degrees C or less is more preferable. When an ionic liquid having a melting point higher than 25 ° C. is used as the non-aqueous electrolyte, there is a possibility that it is solidified at a low temperature or precipitated in an organic solvent. When such solidification of the electrolytic solution or precipitation in the electrolytic solution occurs, the ionic conductivity of the electrolytic solution decreases, and the possibility that the amount of electricity that can be taken out decreases. For this reason, the lower the melting point, the better, and the lower limit is not particularly limited.

[3] Nonaqueous Electrolyte for Electricity Storage Device The nonaqueous electrolyte for an electricity storage device according to the present invention (hereinafter abbreviated as nonaqueous electrolyte) is (1) the first or second ionic liquid (hereinafter, referred to as “nonaqueous electrolyte”). These are simply composed of only ionic liquid) or (2) contain the ionic liquid.
Here, the electricity storage device refers to a device or element that can store electricity chemically, physically, or physicochemically, such as a secondary battery such as a lithium ion battery, an electric double layer capacitor, an electrolytic capacitor, etc. These devices can be charged and discharged.
The non-aqueous electrolyte containing an ionic liquid used in these electricity storage devices includes (2a) a non-aqueous electrolyte containing an ionic liquid and an organic solvent and no ionic conductive salt, and (2b) an ionic liquid and an ionic conductivity. Examples thereof include a nonaqueous electrolytic solution containing a salt and not containing an organic solvent, (2c) a nonaqueous electrolytic solution containing an ionic liquid, an organic solvent and an ionic conductive salt.

The organic solvent is not particularly limited as long as it can dissolve an ionic liquid or an ion conductive salt and is stable in the operating voltage range of the electricity storage device.
Specific examples include dibutyl ether, 1,2-dimethoxyethane, 1,2-ethoxymethoxyethane, methyl diglyme, methyl triglyme, methyl tetraglyme, ethyl glyme, ethyl diglyme, butyl diglyme, glycol ethers ( Chain ethers such as ethyl cellosolve, ethyl carbitol, butyl cellosolve, butyl carbitol); tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4,4-dimethyl-1,3-dioxane, etc. Cyclic ethers; Lactones such as γ-butyrolactone, γ-valerolactone, δ-valerolactone, 3-methyl-1,3-oxazolin-2-one; N-methylformamide, N, N-dimethylformamide, N- Methylacetamide, N-methylpyrrolidi Amides such as ethylene; carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, ethylene carbonate, styrene carbonate, vinylene carbonate; imidazolidinones such as 1,3-dimethyl-2-imidazolidinone, Or the fluorine-type solvent etc. by which the hydrogen atom or alkyl group of these various organic solvents was substituted by the fluoroalkyl group etc. are mentioned. These non-aqueous organic solvents can be used singly or in combination of two or more.

  Among them, those having a large dielectric constant, a wide electrochemical stability range and a wide use temperature range, and excellent safety are preferable. For example, a mixed solvent containing ethylene carbonate or propylene carbonate as a main component, or ethylene carbonate or propylene carbonate. It is preferable to use at least one solvent selected from vinylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, fluorinated propylene carbonate, and fluorinated γ-butyrolactone.

  In the case of the electrolytic solution containing the ionic liquid and the organic solvent (the above (2a) and (2c)), the content of the ionic liquid in the electrolytic solution is preferably 5 to 90% by mass, and more preferably 10 to 80% by mass. If the content is less than 5% by mass, the internal resistance increases, and as a result, energy loss may increase. On the other hand, when the content exceeds 90% by mass, when an ionic liquid having a low solubility and a relatively high melting point is used, it may be precipitated at a low temperature, resulting in problems such as a decrease in device stability. However, since the ionic liquid of the present invention is more soluble in organic solvents than the electrolyte salt that is usually used and has a melting point of 25 ° C. or less (a wide liquid temperature range), the ionic liquid concentration is made higher than usual. However, the precipitation hardly occurs at low temperatures.

Examples of the ion conductive salt include various known ion conductive materials such as alkali metal salts and quaternary ammonium salts that are generally used in power storage devices such as lithium secondary batteries, lithium ion secondary batteries, and electric double layer capacitors. Salt can be used. By using these ion conductive salt and an ionic liquid in combination, crystallization of the ion conductive salt and dendrite formation of the metal can be prevented. When using an ion conductive salt, the concentration in the non-aqueous electrolyte is usually about 5 to 40% by mass.
The non-aqueous electrolyte of the present invention uses a low-viscosity ionic liquid as described above, and is excellent in safety because it does not use an organic solvent or only uses a very small amount.

[4] Power Storage Device The power storage device according to the present invention is configured using the above-described nonaqueous electrolyte for a power storage device.
The basic structure of the electricity storage device is such that a positive electrode and a negative electrode are opposed to each other via a separator and impregnated with a non-aqueous electrolyte. In the present invention, as the non-aqueous electrolyte, the electricity storage of the present invention described above is used. Use non-aqueous electrolyte for devices.

In the case of a lithium secondary battery and a lithium ion secondary battery, the positive electrode active material contained in the positive electrode is a composite oxide of lithium and a transition metal such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , MnO ₂ , Transition metal oxides such as V ₂ O ₅ , transition metal sulfides such as MoS ₂ and TiS, conductive polymer compounds such as polyacetylene, polyacene, polyaniline, polypyrrole and polythiophene, poly (2,5-dimercapto-1, Disulfide compounds such as 3,4-thiadiazole) are used.
Negative electrode active materials contained in the negative electrode include lithium metals, lithium alloys such as lithium aluminum alloys, carbonaceous materials that can occlude and release lithium, cokes such as graphite, phenolic resin, and furan resin, carbon fiber, and glassy carbon. Pyrolytic carbon, activated carbon, etc. are used.

In the case of an electric double layer capacitor, a pair of polarizable electrodes is used as the positive electrode and the negative electrode.
As the material constituting the polarizable electrode, a carbonaceous substance is preferably used because it is electrochemically inert to the non-aqueous electrolyte and has a suitable conductivity. In particular, activated carbon is optimal because the area of the electrode interface where charges accumulate is large.
In the case of an electrolytic capacitor, an aluminum foil having an insulating alumina layer formed on the surface by anodic oxidation or the like is used for the positive electrode, and an aluminum foil is used for the negative electrode. These aluminum foils are usually subjected to an etching process in order to increase the surface area and increase the capacitance.

  Examples of conductive aids used when creating an electrode using an electrode active material include carbon black such as acetylene black and ketjen black, natural graphite, thermally expanded graphite, carbon fiber, ruthenium oxide, titanium oxide, and aluminum. Metal fibers such as nickel are used. Among these, acetylene black and ketjen black that can ensure desired conductivity with a small amount of blend are preferable. In addition, although a conductive support agent is normally mix | blended about 5-50 mass% with respect to an electrode active material, it is more preferable to mix | blend 10-30 mass%.

Various known binders can be used as the binder used together with the conductive assistant. For example, polytetrafluoroethylene, polyvinylidene fluoride, carboxymethyl cellulose, fluoroolefin copolymer cross-linked polymer, polyvinyl alcohol, polyacrylic acid, polyimide, petroleum pitch, coal pitch, phenol resin and the like can be mentioned.
Various known separators can be used as the separator. Specific examples include paper, polypropylene, polyethylene, glass fiber separators, and the like.

  In the non-aqueous electrolyte of the present invention, either one of the positive and negative electrodes is a polarizable electrode used in an electric double layer capacitor, and the other is an active material that can insert and desorb lithium ions used in a lithium ion battery. The present invention can also be applied to a hybrid type electricity storage device as a material electrode.

  Since the electricity storage device according to the present invention described above is configured using the non-aqueous electrolyte of the present invention, (1) it is suitable for large current charge / discharge because of its low internal resistance, (2) large current charge / discharge (3) High safety because it can reduce the amount of organic solvent used to zero or as much as possible, (4) Excellent charge / discharge characteristics at low temperatures, (5) Mixing of moisture Even if there is, there are various advantages such as reduced capacity and less generation of gas.

  EXAMPLES Hereinafter, although a synthesis example, an Example, and a comparative example are given and this invention is demonstrated more concretely, this invention is not limited to the following Example.

[1] Ionic liquid [Synthesis Example 1] Synthesis of ionic liquid (38)

Pyrrolidine (Kanto Chemical Co., Inc.) 88 ml and 2-methoxyethyl chloride (Kanto Chemical Co., Ltd.) 50 ml were stirred in a flask equipped with a condenser and reacted for 24 hours under reflux. After the reaction, the reaction solution was allowed to cool and the precipitated crystals were filtered off. The filtrate was distilled under reduced pressure to obtain 41 g of N- (2-methoxyethyl) -pyrrolidine.
20 g of N- (2-methoxyethyl) -pyrrolidine was dissolved in 200 ml of tetrahydrofuran (Wako Pure Chemical Industries, Ltd.), and 13.5 ml of methyl iodide (Wako Pure Chemical Industries, Ltd.) was added with stirring under ice cooling. . After 30 minutes, the ice bath was removed and the mixture was stirred overnight at room temperature. The precipitated crystals were separated by filtration, washed, and recrystallized from acetonitrile (Wako Pure Chemical Industries, Ltd.)-Tetrahydrofuran system to obtain 38 g of N- (2-methoxyethyl) -N-methylpyrrolidinium iodine salt.
15.0 g of N- (2-methoxyethyl) -N-methylpyrrolidinium iodine salt is dissolved in chloroform (Wako Pure Chemical Industries, Ltd.) and stirred under ice cooling with silver tetrafluoroborate (Tokyo Chemical Industry). 10.8 g) was added and stirred for 18 hours. After completion of the stirring, the crystals were filtered off and the solvent was distilled off from the filtrate under reduced pressure to obtain 12.4 g of ionic liquid (38) <N- (2-methoxyethyl) -N-methylpyrrolidinium tetrafluoroborate>. Obtained. The viscosity of the ionic liquid (38) was 145 mPa · s (25 ° C.).

[Synthesis Example 2] Synthesis of ionic liquid (17)

The intermediate N- (2-methoxyethyl) -N-methylpyrrolidinium iodine salt was obtained in the same manner as in Synthesis Example 1.
15.0 g of N- (2-methoxyethyl) -N-methylpyrrolidinium iodine salt is dissolved in chloroform and stirred under ice-cooling with potassium pentafluoroethyl trifluoroborate (the aforementioned reference M. Ue et al. , J. Fluorine Chem., 128-131, 123 (2003)) (12.5 g) was added and stirred for 18 hours. After completion of the stirring, the crystals were filtered off, the solvent was distilled off from the filtrate under reduced pressure, and the ionic liquid (17) <N- (2-methoxyethyl) -N-methylpyrrolidinium pentafluoroethyl trifluoroborate> 17. 4 g was obtained. The viscosity of the ionic liquid (17) was 15 mPa · s (25 ° C.).

[2] Electric double layer capacitor Using the ionic liquids obtained in Synthesis Examples 1 and 2 as an electrolytic solution, electric double layer capacitors were respectively produced by the following procedure.
[Example 1]
Activated carbon (MSP-20, manufactured by Kansai Thermochemical Co., Ltd.) obtained by subjecting a phenol resin-derived carbon material to alkali activation treatment as an active material, and HS-100 (manufactured by Denki Kagaku Kogyo Co., Ltd.) as conductive carbon, PVDF (Aldrich, weight average molecular weight 534,000) as binder resin, N-methylpyrrolidone (hereinafter referred to as NMP) as coating solvent, active material: conductive carbon: binder resin: NMP = 90: 5: The mixture was made into a paste by mixing at a ratio of 5: 230 (mass ratio) to prepare a polarizable electrode composition.
The paste-like polarizable electrode composition was applied to both sides of an aluminum current collector foil (30CB, manufactured by Nippon Electric Power Industry Co., Ltd.), dried at 80 ° C. for 4 hours, and then rolled to obtain a polarizable electrode. It was.
Next, cells were assembled by laminating polarizable electrodes via a cellulose separator (TF40-35, manufactured by Nippon Kogyo Paper Industries Co., Ltd.), and an aluminum laminate (Dai Nippon Printing Co., Ltd., outer layer: 6-nylon / thickness). 25 μm, gas barrier layer: soft aluminum / thickness 40 μm, inner layer: polypropylene + modified polypropylene / 30 μm + 15 μm), and then impregnated by injecting and impregnating an electrolytic solution consisting only of the ionic liquid (17) of Synthesis Example 2. After sealing, the electric double layer capacitor cell 1 was obtained.

[Comparative Example 1]
An electric double layer capacitor cell 2 was produced in the same manner as in Example 1 except that the electrolytic solution consisting only of the ionic liquid (38) of Synthesis Example 1 was injected as the electrolytic solution.

<Capacitor cell evaluation>
The electric double layer capacitor cells 1 and 2 obtained in Example 1 and Comparative Example 1 were subjected to a charge / discharge test according to current density and a cycle charge / discharge test under the following conditions.
(1) Charging / discharging test according to current density In a 25 ° C. environment, charging / discharging was performed at a setting of a constant current of 1, 5, 10, 20 mA / cm ² and a charging / discharging voltage of 0 to 3.0 V, respectively. The capacitance per active material mass was calculated from the amount of discharge energy of the current density and the active material mass used in the cell. The results are shown in FIG.
(2) Cycle charge / discharge test Cycle charge / discharge in a 25 ° C environment with current density: 10 mA / cm ² constant current, charge / discharge voltage: 2.0 to 3.0 V, no constant voltage charge, and no pause. The amount of discharge energy for each cycle was measured. In addition, the cell after 10,000 cycles of charge / discharge was disassembled, the electrolyte solution was collected, and the fluorine ion concentration in the electrolyte solution was measured by ion chromatography (in addition, the fluorine ion concentration in the electrolyte solution before the charge / discharge test was The water content in the electrolyte before the start of the test was measured by the same method and measured with a Karl Fischer moisture meter (manufactured by Kyoto Electronics Industry Co., Ltd.). FIG. 2 shows the results of the discharge energy maintenance rate with the initial discharge energy amount being 100%, and Table 1 shows the fluorine ion concentration in the electrolytic solution.

As shown in FIG. 1, in the capacitor cell 1 of Example 1 using only the ionic liquid of the present invention as the electrolyte, even when the current density is increased, there is little decrease in the capacitance per mass of the active material. It can be seen that the large current discharge characteristics are superior to the capacitor cell 2 of 1.
Further, as shown in FIG. 2, not only the discharge energy amount but also the cycle charge / discharge characteristics, the capacitor cell 1 of Example 1 has a high retention rate, and the cycle characteristics are superior to the capacitor cell 2 of Comparative Example 1. .
Furthermore, as shown in Table 1, it can be seen that the amount of fluorine ions generated by the decomposition of anions is small.
As described above, when only an ionic liquid is used as an electrolytic solution, it is superior to a conventional electrolytic solution containing only an ionic liquid, and not only can an electric double layer capacitor having the same performance as a normal organic electrolytic solution be obtained. From the viewpoint of safety, it can be seen that the ionic liquid of the present invention can be a useful electrolyte for an electricity storage device.

6 is a graph showing charging / discharging test results by current density of capacitor cells 1 and 2 produced in Example 1 and Comparative Example 1. 6 is a graph showing cycle charge / discharge test results of capacitor cells 1 and 2 produced in Example 1 and Comparative Example 1.

Claims (10)

An ionic liquid represented by the following general formula (1) and having a melting point of 50 ° C. or lower.

[Wherein, R ^{1 to} R ⁴ are the same or different alkyl groups having 1 to 5 carbon atoms, or an alkoxyalkyl group represented by R′—O— (CH ₂ ) _n — (R ′ is a methyl group or Represents an ethyl group, and n represents an integer of 1 to 4.), and any two groups of R ¹ , R ² , R ³ and R ⁴ may form a ring together with X. However, at least one of R ^{1 to} R ⁴ is the alkoxyalkyl group. X represents a nitrogen atom or a phosphorus atom, R _F represents a perfluoroalkyl group having 1 to 4 carbon atoms, a is an integer of 1 to 4 (in the case where a is 2 or more, R _F is mutually They may be the same or different, and R _F may be bonded to each other to form a ring with a boron atom.) ] It is shown by following General formula (2), The ionic liquid of Claim 1 characterized by the above-mentioned.

[Wherein, X represents a nitrogen atom or a phosphorus atom, R ′ represents a methyl group or an ethyl group, and n is an integer of 1 to 4. R _F represents a perfluoroalkyl group having 1 to 4 carbon atoms, a is an integer of 1 to 4 (in the case where a is 2 or more, R _F may be the same or different from each other, and R _F may be bonded to each other to form a ring together with the boron atom.) Provided that X is a nitrogen atom, R ′ is a methyl group, R _F is a pentafluoroethyl group, n is 2, and a is 1. ] It is shown by the following general formula (3), The ionic liquid according to claim 1 characterized by things.

[In the formula, X represents a nitrogen atom or a phosphorus atom, R ¹ represents an alkyl group having 1 to 5 carbon atoms, R ′ represents a methyl group or an ethyl group, m is an integer of 4 or 5, n is an integer of 1-4. R _F represents a perfluoroalkyl group having 1 to 4 carbon atoms, a represents an integer of 1 to 4 (in the case where a is 2 or more, R _F may be the same or different from each other, and R _F may be bonded to each other to form a ring together with the boron atom.) ] An ionic liquid represented by the following general formula (4) and having a melting point of 50 ° C. or lower.

[Wherein, R ^{1 to} R ⁴ are the same or different alkyl groups having 1 to 5 carbon atoms, or an alkoxyalkyl group represented by R′—O— (CH ₂ ) _n — (R ′ is a methyl group or Represents an ethyl group, and n represents an integer of 1 to 4.), and any two groups of R ¹ , R ² , R ³ and R ⁴ may form a ring together with X. However, at least one of R ^{1 to} R ⁴ is the alkoxyalkyl group. X represents a nitrogen atom or a phosphorus atom, R _F represents a perfluoroalkyl group having 1 to 4 carbon atoms, b is an integer of 1 to 6 (in the case where b is 2 or more, R _F is mutually They may be the same or different, and R _F may be bonded to each other to form a ring together with the phosphorus atom). ] The ionic liquid according to claim 4, which is represented by the following general formula (5).

[Wherein, X represents a nitrogen atom or a phosphorus atom, R ′ represents a methyl group or an ethyl group, and n is an integer of 1 to 4. R _F represents a perfluoroalkyl group having 1 to 4 carbon atoms, and b is an integer of 1 to 6 (in addition, when b is 2 or more, R _F may be the same as or different from each other, and R _F may be bonded to each other to form a ring together with the phosphorus atom.) ] It is shown by following General formula (6), The ionic liquid of Claim 4 characterized by the above-mentioned.

[In the formula, X represents a nitrogen atom or a phosphorus atom, R ¹ represents an alkyl group having 1 to 5 carbon atoms, R ′ represents a methyl group or an ethyl group, m is an integer of 4 or 5, n is an integer of 1-4. R _F represents a perfluoroalkyl group having 1 to 4 carbon atoms, and b represents an integer of 1 to 4 (in addition, when b is 2 or more, R _F may be the same as or different from each other, and R _F may be bonded to each other to form a ring together with the phosphorus atom.) ]   A nonaqueous electrolytic solution for an electricity storage device, comprising only the ionic liquid according to any one of claims 2 to 6.   A nonaqueous electrolytic solution for an electricity storage device, comprising the ionic liquid according to claim 2.   An electricity storage device comprising the nonaqueous electrolyte for an electricity storage device according to claim 7 or 8. The electrical storage device according to claim 9, which is an electric double layer capacitor or a lithium ion battery.

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