JP2006155928A - Nonaqueous electrolyte and electrochemical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte which has high safety and can sufficiently obtain mobility of carrier ions, and to provide an electrochemical device with excellent electrical characteristics. <P>SOLUTION: This nonaqueous electrolyte consists at least of lithium salt and cold molten salt, and assumes a liquid at normal temperature. The nonaqueous electrolyte contains 0.5 mol or more of lithium salt per 1L of the nonaqueous electrolyte and satisfies conditions represented by formula (1): 0.9η<SB>IL</SB>≤η<SB>EL</SB>≤1.5η<SB>IL</SB>[where η<SB>IL</SB>is viscosity of the cold molten salt and ηEL is viscosity the nonaqueous electrolyte] and Formula (2): 0.8 C<SB>IL</SB>≤C<SB>EL</SB>≤1.5C<SB>IL</SB>[where C<SB>IL</SB>is molar concentration of the cold molten salt and C<SB>EL</SB>is the sum of molar concentrations of the lithium salt and the and cold molten salt in the nonaqueous electrolyte] at 30°C. The electrochemical device using the nonaqueous electrolyte is obtained. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a non-aqueous electrolyte and an electrochemical device, and more particularly to a non-aqueous electrolyte containing at least a lithium salt and a room temperature molten salt and an electrochemical device using the same.

  In recent years, non-aqueous electrolyte batteries and electric double layers using various non-aqueous electrolytes that can obtain high energy density, such as power supplies for electronic devices, power storage power supplies, electric vehicle power supplies, etc., which have been improved in performance and size. Electrochemical devices such as capacitors have attracted attention.

In general, electrochemical devices such as non-aqueous electrolyte batteries and electric double layer capacitors have a non-aqueous electrolyte that exhibits a liquid at room temperature, in which a lithium salt or aliphatic ammonium salt that is solid at room temperature is dissolved in an organic solvent that is liquid at room temperature. (Non-aqueous electrolyte) ”is used.
Examples of the organic solvent used include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, propiolactone, valerolactone, tetrahydrofuran, dimethoxyethane, diethoxyethane, methoxyethoxyethane, and the like. Is mentioned.

  However, these organic solvents are generally volatile and highly flammable, and therefore are classified as flammable substances. Therefore, when such non-aqueous electrolytes are used in relatively large electrochemical devices, such as those used for power storage power supplies, electric vehicle power supplies, etc., they can be used safely during misuse or in high-temperature environments. There was a problem.

Therefore, it has been proposed to use a room temperature molten salt that exhibits a liquid at room temperature as a non-aqueous electrolyte for electrochemical devices that does not contain a combustible substance such as an organic solvent as a main component and is excellent in safety. For example, a nonaqueous electrolyte secondary battery has been proposed as an electrochemical device using lithium ions as carrier ions.
Room temperature molten salt is liquid at room temperature but has almost no volatility, and has flame retardancy or nonflammability, so it is high when used as an electrolyte for electrochemical devices such as non-aqueous electrolyte secondary batteries. An electrochemical device having safety can be obtained (see Patent Document 1, Patent Document 2, Patent Document 3, and Patent Document 4).

  However, such a non-aqueous electrolyte secondary battery has a drawback of being inferior in high rate charge / discharge characteristics and low temperature charge / discharge characteristics. The following factors can be cited as this cause. That is, the room temperature molten salt has a higher melting point and higher viscosity than a general non-aqueous electrolyte. For this reason, the mobility of lithium ions, which are carrier ions, is lower than that of a general non-aqueous electrolyte, and as a result, high rate charge / discharge characteristics and low-temperature charge / discharge characteristics are considered to deteriorate.

In addition, the normal temperature molten salt in the present invention refers to a salt that is at least partially liquid at normal temperature. The normal temperature is a temperature range in which the electrochemical device is assumed to normally operate, and the upper limit is about 100 ° C., in some cases about 60 ° C., and the lower limit is about −50 ° C., and in some cases about −20 ° C. .
On the other hand, an inorganic molten salt such as “Li ₂ CO ₃ —Na ₂ CO ₃ —K ₂ CO ₃ ” used for various electrodepositions as described in Non-Patent Document 1 has a melting point of 300 ° C. or higher. Most of them are not in a liquid state within a temperature range in which an electrochemical device is normally assumed to operate, and are not included in the room temperature molten salt in the present invention.

JP-A-4-349365 (refer to claim 1) JP-A-10-92467 (refer to claim 1) Japanese Patent Laid-Open No. 11-86905 (see paragraphs [0026] and [0032]) JP 11-260400 A (see paragraphs [0028] to [0031]) JP 2002-110230 A (refer to claim 1) Study Group for Molten Salt / Thermal Technology "Basics of Molten Salt / Thermal Technology", Agne Technology Center, 1993, 313p (ISBN 4-900041-24-6)

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a non-aqueous electrolyte that has high safety and can sufficiently obtain carrier ion mobility. Another object of the present invention is to provide an electrochemical device having excellent electrical characteristics.

In order to solve the above-mentioned problems, the invention described in claim 1 is a non-aqueous electrolyte which is composed of at least a lithium salt and a room temperature molten salt and exhibits a liquid at room temperature, and the non-aqueous electrolyte converts the lithium salt into a non-aqueous electrolyte 1. A nonaqueous electrolyte characterized by containing 0.5 mol or more per liter and satisfying both the conditions represented by the following formulas (1) and (2) at 30 ° C.
Formula (1) ... 0.9 η _IL ≤ η _EL ≤ 1.5 η _IL
[Where η _IL is the viscosity of the ambient temperature molten salt and η _EL is the viscosity of the non-aqueous electrolyte. ]
Formula (2) ... 0.8 C _IL ≤ C _EL ≤ 1.5 C _IL
[Wherein C _IL is the molar concentration of the ambient temperature molten salt, and C _EL is the sum of the molar concentrations of the lithium salt and the ambient temperature molten salt in the non-aqueous electrolyte. ]

  According to the first aspect of the invention, the non-aqueous electrolyte is composed of a room temperature molten salt as a main constituent, so that the room temperature molten salt is almost volatile while being liquid at room temperature, and is flame retardant or incombustible. Therefore, the non-aqueous electrolyte having high safety can be obtained. It should also be noted that when lithium salt is added to room temperature molten salt, the viscosity of the non-aqueous electrolyte increases, resulting in a decrease in ionic conductivity and mobility of lithium ions as carrier ions. Select a combination of salt species and room temperature molten salt species (and organic solvent species), and specify the specific conditions (the above formula (the above formula) for the sum of the viscosity of the nonaqueous electrolyte and the molar concentration of lithium salt and room temperature molten salt in the nonaqueous electrolyte. By controlling to satisfy the conditions 1) and (2), it is possible to suppress a decrease in ion conductivity and keep the mobility of lithium ions as carrier ions high.

The invention according to claim 2 is the nonaqueous electrolyte characterized in that the room temperature molten salt constituting the nonaqueous electrolyte has a quaternary ammonium organic cation.
The invention according to claim 3 is a nonaqueous electrolyte characterized in that the quaternary ammonium organic cation is an imidazolium cation having a skeleton represented by the following chemical formula (Formula 2).

  According to the invention of claim 2 and claim 3, the non-aqueous electrolyte has a lithium salt and the quaternary ammonium organic cation, in particular, a room temperature molten salt having an imidazolium cation having a skeleton represented by the chemical formula (Chemical Formula 2) By using this, the mobility of lithium ions in the non-aqueous electrolyte can be sufficiently obtained, and the above action can be effectively obtained.

The invention according to claim 4 is the nonaqueous electrolyte characterized in that the nonaqueous electrolyte is composed of a room temperature molten salt and a lithium salt composed of an anion composed of only a nonmetallic element.
According to the fourth aspect of the invention, by selecting the anion of the non-aqueous electrolyte from an anion consisting only of a non-metallic element, it becomes easy to form a room temperature molten salt having a low melting point, so that the above action is obtained more effectively. It becomes possible.

The invention according to claim 5 is an electrochemical device using the non-aqueous electrolyte.
According to the invention described in claim 5, since the electrolyte of the electrochemical device is composed of a non-aqueous electrolyte exhibiting sufficient ionic conductivity and mobility of lithium ions, the electrochemical characteristics of a non-aqueous electrolyte battery, an electric double layer capacitor, etc. The device can have excellent electrical characteristics.

  The best mode for carrying out the present invention will be described below, but the present invention is not limited to these descriptions.

The non-aqueous electrolyte in the present invention comprises a room temperature molten salt and a lithium salt as essential components, and in some cases, in addition to a lithium salt and a room temperature molten salt, an organic solvent that is liquid at room temperature may be added. is there. The content of the lithium salt in the nonaqueous electrolyte is 0.5 mol or more per liter of the nonaqueous electrolyte, and the viscosity of the nonaqueous electrolyte (η _EL ) and the sum of the molar concentrations of the lithium salt and the ambient temperature molten salt ( C _EL ) is appropriately determined depending on the combination of lithium salt species and room temperature molten salt species (and organic solvent species) so as to satisfy specific conditions (conditions represented by the above formulas (1) and (2)). .
In the present invention, the reason for limiting the content of the lithium salt in the non-aqueous electrolyte as described above is that the non-aqueous electrolyte having a lithium salt content of less than 0.5 mol, particularly an electrochemical such as a non-aqueous electrolyte battery. This is because it is difficult to obtain good characteristics (electric characteristics such as high rate charge / discharge characteristics and low temperature charge / discharge characteristics) when applied to a device.

Note that “a condition that is expressed by the expression (1)” corresponds to a condition that “0.9 ≦ η _EL / η _IL ≦ 1.5”, and “the expression (2) “Conditions to be expressed” corresponds to satisfying the condition of “0.8 ≦ C _EL / C _IL ≦ 1.5”. In the examples and comparative examples described later, “η _EL / η _IL ” and “C _EL / C _IL ” are indicated (see [Table 1] below).

The room temperature molten salt in the present invention desirably has a quaternary ammonium organic cation. Examples of the quaternary ammonium organic cation include imidazolium cation, tetraalkylammonium cation, pyridinium cation, pyrrolium cation, pyrazolium cation, pyrrolinium cation, pyrrolidinium cation, and piperidinium cation. Of these, imidazolium cations having a skeleton represented by the following chemical formula (Formula 3) are particularly desirable.

  Examples of the imidazolium cation include 1,3-dimethylimidazolium ion, 1-ethyl-3-methylimidazolium ion, 1-methyl-3-ethylimidazolium ion, 1-butyl as dialkylimidazolium cation. -3-methylimidazolium ion, etc., as the trialkylimidazolium cation, 1,2,3-trimethylimidazolium ion, 1,2-dimethyl-3-ethylimidazolium ion, 1,2-dimethyl-3- Examples thereof include, but are not limited to, propyl imidazolium ion and 1-butyl-2,3-dimethylimidazolium ion.

  Examples of the tetraalkylammonium cation include, but are not limited to, trimethylethylammonium ion, trimethylpropylammonium ion, trimethylhexylammonium ion, and tetrapentylammonium ion.

  Examples of the pyridinium cation include N-methylpyridinium ion, N-ethylpyridinium ion, N-propylpyridinium ion, N-butylpyridinium ion 1-ethyl-2-methylpyridinium, 1-butyl-4-methylpyridinium, 1-butyl Examples include -2,4-dimethylpyridinium, but are not limited thereto.

  Examples of the pyrrolium cation include 1,1-dimethylpyrrolium ion, 1-ethyl-1-methylpyrrolium ion, 1-methyl-1-propylpyrrolium ion, 1-butyl-1-methylpyrrolium ion, It is not limited to these.

Examples of the pyrazolium cation include 1,2-dimethylpyrazolium ion, 1-ethyl-2-methylpyrazolium ion, 1-propyl-2-methylpyrazolium ion, 1-butyl-2-methylpyrazolium ion, and the like. However, it is not limited to these.

Examples of the pyrrolium cation include 1,2-dimethylpyrrolium ion, 1-ethyl-2-methylpyrrolium ion, 1-propyl-2-methylpyrrolium ion, 1-butyl-2-methylpyrrolium ion, and the like. Although it is mentioned, it is not limited to these.

Examples of the pyrrolidinium cation include 1,1-dimethylpyrrolidinium ion, 1-ethyl-1-methylpyrrolidinium ion, 1-methyl-1-propylpyrrolidinium ion, 1-butyl-1-methylpyrrolidinium ion, and the like. However, it is not limited to these.

Examples of the piperidinium cation include 1,1-dimethylpiperidinium ion, 1-ethyl-1-methylpiperidinium ion, 1-methyl-1-propylpiperidinium ion, 1-butyl-1-methylpiperidinium ion, and the like. However, it is not limited to these.

  In addition, the normal temperature molten salt which has these quaternary ammonium organic substance cations may be used independently, and may be used in mixture of 2 or more types.

In the present invention, it is desirable to select the anion of the non-aqueous electrolyte from an anion consisting only of a non-metallic element. Examples of the anion consisting of the nonmetallic element include BF ₄ ⁻ , PF ₆ ⁻ , CF ₃ SO ₃ ⁻ , N (CF ₃ SO ₂ ) ₂ ⁻ , N (C ₂ F ₅ SO ₂ ) ₂ ⁻ , N (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ) ⁻ , C (CF ₃ SO ₂ ) ₃ ^— and C (C ₂ F ₅ SO ₂ ) ₃ ^— are preferably selected from one or more anions. However, it is not limited to these. These may be used alone or in combination of two or more. Further, the anion of the room temperature molten salt and the anion of the lithium salt may be the same or different.

The nonaqueous electrolyte in the present invention may be used by adding an organic solvent that is liquid at room temperature in addition to the lithium salt and the room temperature molten salt. Here, as said organic solvent, the organic solvent generally used for the electrolyte solution for nonaqueous electrolyte batteries can be used. Examples include, but are not limited to, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, propiolactone, valerolactone, tetrahydrofuran, dimethoxyethane, diethoxyethane, methoxyethoxyethane, and the like. Is not to be done. However, since these organic solvents are flammable as described above, if the addition amount is too large, the non-aqueous electrolyte may be flammable and sufficient safety may not be obtained, which is not preferable. Furthermore, if the amount of the organic solvent added is too large, the sum of the molar concentrations of the lithium salt and the ambient temperature molten salt in the non-aqueous electrolyte is less than 0.8 times the molar concentration of the ambient temperature molten salt. Cannot be obtained sufficiently, which is not preferable.
Moreover, the phosphate ester which is a flame-retardant solvent generally added to the electrolyte solution for nonaqueous electrolyte batteries can also be used. For example, trimethyl phosphate, triethyl phosphate, ethyl dimethyl phosphate, diethyl methyl phosphate, tripropyl phosphate, tributyl phosphate, tri (trifluoromethyl) phosphate, tri (trifluoroethyl) phosphate, triphosphate (Triperfluoroethyl) and the like may be mentioned, but are not limited thereto. These may be used alone or in combination of two or more.

  In addition, the nonaqueous electrolyte in the present invention may be used by solidifying the nonaqueous electrolyte into a gel by combining a polymer other than lithium salt and room temperature molten salt. Here, examples of the polymer include, for example, polyethylene oxide, polypropylene oxide, polyacrylonitrile, polymethyl methacrylate, polyvinylidene fluoride, various acrylic monomers, methacrylic monomers, acrylamide monomers, allyl monomers, and styrene monomers. Examples include, but are not limited to, polymers. These may be used alone or in combination of two or more.

  Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these descriptions.

Example 1
By dissolving 1 mol of LiPF ₆ in 1 liter of 1-butyl-3-methylimidazolium hexafluorophosphate (BMIPF ₆ ), a nonaqueous electrolyte a was obtained.

(Example 2)
Nonaqueous electrolyte b was obtained by mixing 1 mol of LiBF ₄ with 1 liter of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF ₄ ) and 0.25 liter of propylene carbonate (PC).

(Example 3)
By mixing 1 liter of lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) with 1 liter of 1-ethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide (EMITFSI) and 0.25 liter of PC, non-water An electrolyte c was obtained.

(Comparative Example 1)
The BMIPF ₆ 0.75 liters and PC0.25 liters, by dissolving 0.75 moles of LiPF _6, to obtain a non-aqueous electrolyte d.

(Comparative Example 2)
Nonaqueous electrolyte e was obtained by mixing 1 mol of LiBF ₄ with 1 liter of EMIBF ₄ .

(Comparative Example 3)
By dissolving 1 mol of LiTFSI in 1 liter of EMITFSI, a nonaqueous electrolyte f was obtained.

(Measurement of viscosity)
Viscosity measurement tests were performed on the nonaqueous electrolytes a to c of the present invention, the comparative nonaqueous electrolytes df, BMIPF ₆ , EMIBF ₄ , and EMITFSI. The viscosity at 30 ° C. was measured with a vibration viscometer (manufactured by Yamaichi Electronics Co., Ltd., model: VM-100, measurement probe model: L).

(Measurement of molar concentration)
The present invention the non-aqueous electrolyte a to c, compared nonaqueous electrolyte d-f, _and, for BMIPF _6, EMIBF 4, EMITFSI, was measured specific gravity. The specific gravity at 30 ° C. was measured using a pycnometer. From the obtained specific gravity, the sum of the molar concentrations of the room temperature molten salt and the lithium salt in the nonaqueous electrolyte and the room temperature molten salt was determined.

(Ion conductivity measurement)
The ionic conductivity was measured for the present nonaqueous electrolytes a to c, comparative nonaqueous electrolytes df, BMIPF ₆ , EMIBF ₄ , and EMITFSI. The ionic conductivity at 30 ° C. was measured using the AC impedance method.

The present invention non-aqueous electrolytes a to c, comparative non-aqueous electrolytes d to f, BMIPF ₆ , EMIBF ₄ , EMITFSI viscosity (η), molar concentration of room temperature molten salt, and molar concentration of lithium salt and normal temperature molten salt Table 1 shows (C) and ionic conductivity (σ).

As is clear from Table 1, the non-aqueous electrolytes a to c of the present invention all have substantially the same ionic conductivity (σ _EL ) as compared with the ionic conductivity (σ _IL ) of the room temperature molten salt which is a constituent component. ). On the other hand, it was found that the ionic conductivity (σ _EL ) of each of the comparative nonaqueous electrolytes d to f is lower than the ionic conductivity (σ _IL ) of the room temperature molten salt that is a constituent component.

(Battery performance test)
A lithium battery was produced as an electrochemical device using the nonaqueous electrolytes a to c of the present invention and the comparative nonaqueous electrolytes df. A cross-sectional view of a lithium battery according to the present invention is shown in FIG. The lithium battery according to the present invention includes a pole group 4 including a positive electrode 1, a negative electrode 2, and a separator 3, a nonaqueous electrolyte, and a metal resin composite film 5 as an exterior material.
The positive electrode 1 is formed by applying a positive electrode mixture 11 on a positive electrode current collector 12. The negative electrode 2 is formed by applying a negative electrode mixture 21 on a negative electrode current collector 22. The nonaqueous electrolyte is impregnated in the pole group 4. The metal resin composite film 5 covers the pole group 4 and is sealed on all four sides by heat welding.

Next, a method for manufacturing the lithium battery having the above configuration will be described. The positive electrode 1 was obtained as follows. First, LiCoO ₂ and acetylene black as a conductive agent are mixed, and further, an N-methyl-2-pyrrolidone solution of polyvinylidene fluoride is mixed as a binder, and this mixture is used as a positive electrode current collector 12 made of an aluminum foil. After coating on one side, it was dried and pressed so that the thickness of the positive electrode mixture 11 was 0.1 mm. The positive electrode 1 was obtained by the above process.
The negative electrode 2 was obtained as follows. First, Li _4/3 Ti _5/3 O _{4 as} a negative electrode active material and Ketjen black as a conductive agent are mixed, and further, an N-methyl-2-pyrrolidone solution of polyvinylidene fluoride is mixed as a binder. The mixture was applied to one side of the negative electrode current collector 22 made of copper foil, dried, and pressed so that the thickness of the negative electrode mixture 21 was 0.1 mm. The negative electrode 2 was obtained by the above process.
As the separator 3, a polyethylene microporous film was used. The pole group 4 was configured by making the positive electrode mixture 11 and the negative electrode mixture 21 face each other, placing the separator 3 therebetween, and laminating the positive electrode 1, the separator 3, and the negative electrode 2 in this order. Next, the electrode group 4 was impregnated with the non-aqueous electrolyte by immersing the electrode group 4 in the non-aqueous electrolyte. Furthermore, the pole group 4 was covered with the metal resin composite film 5, and the four sides were sealed by heat welding.

  Lithium batteries were prepared using the nonaqueous electrolytes a to c of the present invention and the comparative nonaqueous electrolytes df, respectively, as the electrolyte. These are designated as inventive batteries A to C and comparative batteries D to F, respectively.

(Initial discharge capacity test)
The initial discharge capacity test was performed on the batteries A to C of the present invention and the comparative batteries D to F. The test temperature was 20 ° C. The charging was a constant current charging with a current of 1 mA and a final voltage of 2.7 V. The discharge was a constant current discharge with a current of 1 mA and a final voltage of 1.2V. The obtained battery capacity was defined as the initial discharge capacity. The design capacities of the inventive batteries A to C and the comparative batteries D to F are all 10 mAh.

(High rate discharge test)
The inventive batteries A to C and the comparative batteries D to F were subjected to a high rate discharge test. A battery whose initial capacity was confirmed under the same conditions as in the initial discharge capacity test was charged under the same conditions, and then a constant current discharge with a current of 5 mA and a final voltage of 1.2 V was performed. The obtained battery capacity was defined as a high rate discharge capacity.

  Table 2 shows the results of the initial discharge capacity test and the high rate discharge test.

  As is clear from Table 2, the batteries A to C of the present invention exhibited performance superior to the comparative batteries D to F in both the initial discharge capacity and the high rate discharge capacity.

  As is clear from the above results, the nonaqueous electrolyte of the present invention has specific conditions (the conditions represented by the above formulas (1) and (2)) regarding the viscosity and the sum of the molar concentrations of the lithium salt and the room temperature molten salt. Therefore, the battery of the present invention using the same exhibits excellent performance. Furthermore, since the nonaqueous electrolyte of the present invention has flame retardancy, the battery of the present invention using the nonaqueous electrolyte has high safety.

  In this example, a lithium battery was used as an example of an electrochemical device. However, the nonaqueous electrolyte according to the present invention can be suitably applied to other electrochemical devices such as an electric double layer capacitor. .

  According to the present invention, it is possible to provide a non-aqueous electrolyte that is high in safety and sufficiently obtains carrier ion mobility, and an electrochemical device using the non-aqueous electrolyte has excellent electrical characteristics. Its availability is extremely significant.

It is sectional drawing of the lithium battery which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode 11 Positive electrode mixture 12 Positive electrode collector 2 Negative electrode 21 Negative electrode mixture 22 Negative electrode collector 3 Separator 4 Electrode group 5 Metal resin composite film

Claims (5)

A non-aqueous electrolyte comprising at least a lithium salt and a normal temperature molten salt and presenting a liquid at normal temperature, wherein the non-aqueous electrolyte contains 0.5 mol or more of a lithium salt per liter of the non-aqueous electrolyte, and at 30 ° C. A nonaqueous electrolyte characterized by satisfying both of the conditions represented by the following formulas (1) and (2):
Formula (1) ... 0.9 η _IL ≤ η _EL ≤ 1.5 η _IL
[Where η _IL is the viscosity of the ambient temperature molten salt and η _EL is the viscosity of the non-aqueous electrolyte. ]
Formula (2) ... 0.8 C _IL ≤ C _EL ≤ 1.5 C _IL
[Wherein C _IL is the molar concentration of the ambient temperature molten salt, and C _EL is the sum of the molar concentrations of the lithium salt and the ambient temperature molten salt in the non-aqueous electrolyte. ] The non-aqueous electrolyte according to claim 1, wherein the room temperature molten salt constituting the non-aqueous electrolyte has a quaternary ammonium organic cation. The nonaqueous electrolyte according to claim 2, wherein the quaternary ammonium organic cation is an imidazolium cation having a skeleton represented by the following chemical formula (Formula 1).

The nonaqueous electrolyte according to any one of claims 1 to 3, wherein the nonaqueous electrolyte is composed of a normal temperature molten salt and a lithium salt composed of an anion composed of only a nonmetallic element. The electrochemical device using the nonaqueous electrolyte as described in any one of Claims 1-4.

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