JPWO2016084792A1 - Ionic liquid, its production method and its use - Google Patents

Abstract

An ionic liquid having a low melting point obtained by using a molecule having high ion conductivity, a method for producing the ionic liquid, and various uses of the ionic liquid. An onium salt having a melting point of 50 ° C. or higher and an alkali metal salt having a melting point of 50 ° C. or higher are mixed, and the melting point of both the original onium salt and the alkali metal salt is higher. A method for producing an ionic liquid having a low melting point of 100 ° C. or lower. The ionic liquid obtained by this production method is suitably used as an electrolyte for secondary batteries. [Selection figure] None

Description

This application is based on the patent application and Japanese Patent Application No. 2014-242571 for which it applied in Japan, The indication is included in this specification by reference.
The present invention relates to an ionic liquid obtained by mixing an alkali metal salt and an onium salt, a production method thereof, and an application thereof.

  Ionic liquids can be used as battery electrolytes with unique characteristics that are different from conventional electrolyte systems, and as solvents with low environmental impact in organic / inorganic reactions, catalytic reactions, biochemical reactions, and liquid-liquid extraction separations. Possibilities are being considered. For example, a secondary battery using an electrolytic solution containing an ionic liquid made of a compound having a low melting point made of an onium salt as a solvent and an alkali metal salt dissolved in the solvent is known.

  Patent Document 1 discloses a lithium secondary battery including a non-aqueous electrolyte containing a lithium salt. This nonaqueous electrolytic solution contains an ionic liquid containing a bis (fluorosulfonyl) imide anion as an anionic component. This ionic liquid is liquid at room temperature and is used as a solvent.

  Patent Document 2 includes an ionic liquid having a melting point of 50 ° C. or less, a compound that is reduced and decomposed at a noble potential from the ionic liquid, and a lithium salt, A secondary battery using the same is disclosed.

JP 2007-207675 A JP 2004-146346 A

  The ionic liquid in the prior art has a low melting point of the compound itself, and generally has a tendency of low molecular symmetry, so that it is not necessarily high that ion conductivity is high. In view of this, an object of the present invention is to provide an ionic liquid having a low melting point obtained by using a molecule having high ion conductivity, a method for producing the ionic liquid, and various uses of the ionic liquid.

As a result of intensive studies by the present inventors, the present invention having the following contents was completed.
The production method of the present invention is characterized by mixing an onium salt having a melting point of 50 ° C. or more and an alkali metal salt having a melting point of 50 ° C. or more. In the production method of the present invention, the original onium salt and An ionic liquid having a melting point lower than 100 ° C. and lower than the melting point of both alkali metal salts is obtained.
The alkali metal salt is preferably a lithium salt.
The onium cation in the onium salt is preferably a quaternary ammonium cation, a pyrrolidinium cation, a piperidinium cation or an imidazolium cation.

で表される第四級アンモニウムカチオンである。但し、４つのＲ^１は好ましくは各々独立に炭素数１又は２のアルキル基である。The onium cation is preferably the following formula (1)

A quaternary ammonium cation represented by However, the four R ¹ are preferably each independently an alkyl group having 1 or 2 carbon atoms.

で表されるピロリジニウムカチオン又はピペリジニウムカチオンである。但し、ｎは４又は５である。２つのＲ^２は好ましくは各々独立に炭素数１又は２のアルキル基であるか、あるいは、２つのＲ^２が結合して炭素数４又は５のアルキレン基を形成している。Separately, preferably, the onium cation is represented by the following formula (2):

A pyrrolidinium cation or a piperidinium cation represented by the formula: However, n is 4 or 5. Two R ² are preferably each independently an alkyl group having 1 or 2 carbon atoms, or two R ² are bonded to form an alkylene group having 4 or 5 carbon atoms.

で表されるイミダゾリウムカチオンである。但し、Ｚは好ましくは水素原子又はメチル基であり、２つのＲ^３は好ましくは各々独立に炭素数１又は２のアルキル基である。Separately, preferably, the onium cation is represented by the following formula (3):

It is an imidazolium cation represented by. However, Z is preferably a hydrogen atom or a methyl group, and the two R ³ are preferably each independently an alkyl group having 1 or 2 carbon atoms.

When mixing, the ratio of the molar amount (M _A ) of the alkali metal salt to the molar amount (M _O ) of the onium salt is preferably such that M _A / M _O is in the range of 1/9 to 7/3.

  An ionic liquid obtained by the production method described above is also an embodiment of the present invention. In other words, the ionic liquid of the present invention is composed of a mixture of an onium salt having a melting point of 50 ° C. or higher and an alkali metal salt having a melting point of 50 ° C. or higher, and the melting points of both the original onium salt and the alkali metal salt. And a melting point of 100 ° C. or lower. This ionic liquid preferably contains no solvent. Here, the solvent refers to a compound of the above mixture having a melting point of less than 50 ° C.

  The ionic liquid of the present invention is useful as a battery electrolyte, an organic reaction solvent, or an extraction solvent, and a device having the ionic liquid is also an embodiment of the present invention.

According to the present invention, an ionic liquid having a melting point lower than the melting point of each component can be obtained by mixing two or more components of the electrolyte. According to the present invention, an ionic liquid using an onium salt that does not become an ionic liquid as a single substance can be provided. Generally, onium salts with a high melting point have low molecular weight, good molecular symmetry, excellent crystallinity, and excellent ionic conductivity when dissolved in a solvent. It was difficult to make an ionic liquid by itself. Moreover, since onium salts having a high melting point are difficult to dissolve alkali metal salts at room temperature, it has been considered difficult to use them as secondary batteries that can be driven at room temperature.
According to the present invention, an ionic liquid having a low melting point can be obtained even if the onium salt itself used as a raw material has a high melting point. The ionic liquid thus obtained tends to have a low viscosity due to the low molecular weight of the cation used, and is a molten salt with a low melting point, so that, for example, high ionic conductivity exceeding 1 mS / cm at room temperature is achieved. Can do. The molten salt obtained by the present invention can be kept in a liquid state even at a low temperature of 0 ° C. or lower depending on the mixed composition.
The secondary battery using the ionic liquid obtained by the present invention as an electrolytic solution has good rate characteristics even at room temperature because the electrolytic solution exhibits low viscosity and high ionic conductivity, and no solvent is used. Therefore, it is non-volatile, flame retardant, and excellent in safety.

It is an example of the measurement output by a DSC apparatus. The measurement output of a linear sweep voltammetry about the ionic liquid of an Example is represented. It is sectional drawing which shows the structure of the coin-type battery of an Example. The discharge rate test result about the secondary battery of an Example is represented.

  The present invention will be described below with reference to the drawings as appropriate. The drawings are referred to for illustrative purposes and the invention is not limited to the description of the drawings.

In the present invention, an onium salt and an alkali metal salt are mixed.
In the present invention, an onium salt having a melting point of 50 ° C. or higher is used, and an alkali metal salt having a melting point of 50 ° C. or higher is used. An ionic liquid is a liquid salt composed of ions (anions and cations). In the present invention, an ionic liquid having a melting point of 100 ° C. or lower is called an ionic liquid. The melting point of the ionic liquid is preferably 65 ° C. or lower, more preferably 30 ° C. or lower. The ionic liquid obtained by the present invention has a melting point lower than the melting point of the used onium salt and lower than the melting point of the used alkali metal.

(Onium salt)
In the present invention, an onium salt having a melting point of 50 ° C. or higher is used. Preferably, the molecular weight (formula) of the onium cation moiety is 150 or less. In general, small molecules tend to have low viscosity and high conductivity, but small molecules and high molecular structure symmetry tend to increase crystallinity when solidified. Therefore, the melting point with a single onium salt is high. Therefore, mixing an onium salt with a small molecular weight to make an ionic liquid is effective for lowering the viscosity of the obtained ionic liquid, improving conductivity, and the like. From this viewpoint, the melting point of the onium salt is 50 ° C. or higher, preferably 55 ° C. or higher, more preferably 90 ° C. or higher, and further preferably 150 ° C. or higher. The upper limit of the melting point of the onium salt is not particularly limited, and examples thereof include 400 ° C. The molecular weight (formula) of the onium cation moiety is preferably 150 or less, more preferably 120 or less. The lower limit of the molecular weight (formula) is not particularly limited, and is, for example, 70.

  The cation in the onium salt is preferably a quaternary ammonium cation, a pyrrolidinium cation, a piperidinium cation or an imidazolium cation.

The quaternary ammonium cation is preferably a cation represented by the above formula (1). In the formula (1), four R ^{1 s} are each independently an alkyl group having 1 or 2 carbon atoms, and preferably all four R ^{1 s} are the same alkyl group because of the high symmetry of the molecular structure.

The pyrrolidinium cation and the piperidinium cation are preferably cations represented by the above formula (2). In Formula (2), the case where n = 4 is a pyrrolidinium cation, and the case where n = 5 is a piperidinium cation. Two R ^{2 s} in the formula (2) are each independently an alkyl group having 1 or 2 carbon atoms, or two R ² are bonded to form an alkylene group having 4 or 5 carbon atoms. The two R ² are preferably the same alkyl group because of the high symmetry of the molecular structure.

The imidazolium cation is preferably a cation represented by the above formula (3). Z in Formula (3) is a hydrogen atom or a methyl group. Two R ³ in the formula (3) are each independently an alkyl group having 1 or 2 carbon atoms. Preferably two R ³ are the same alkyl group because of the high symmetry of the molecular structure.

  More specific examples of these suitable onium cations include, but are not limited to, tetramethylammonium cation, ethyltrimethylammonium cation, diethyldimethylammonium cation, triethylmethylammonium cation, tetraethylammonium cation, dimethylpyrrolidinium cation, ethylmethyl Pyrrolidinium cation, diethyl pyrrolidinium cation, dimethyl piperidinium cation, ethyl methyl piperidinium cation, diethyl piperidinium cation, dimethyl imidazolium cation, trimethyl imidazolium cation, azonia spiro [4.4] cation, azonia spiro [4 .5] cations, azonia spiro [5,5] cations, and the like.

The anion in the onium salt is not particularly limited and is not limited to F ⁻ , Cl ⁻ , Br ⁻ , I ⁻ , N (FSO ₂ ) ₂ ⁻ , N (FSO ₂ ) (CF ₃ SO ₂ ) ⁻ , N ( ^{_{CF 3 SO 2) 2 -,}} N (CF 3 CF 2 SO 2) 2 -, N (C 2 H 5 SO 2) 2 -, CF 3 SO 3 -, CF 3 CF 2 SO 3 -, PF 6 -, BF ₄ ⁻ , ClO ₄ ⁻ , AsF ₆ ^{− and the} like can be mentioned.
And among these azoniaspiro [4.4] nonane cation or diethyl dimethyl ammonium _{^{cation, N (FSO 2) 2 -}} , N (CF 3 SO 2) 2 -, BF 4 - combination of one and, selected from melt It is preferable because the viscosity of the salt can be further lowered.

  For obtaining the onium salt, a commercially available product may be used, or a conventionally known production method may be appropriately referred to. For example, a desired onium cation halide as described in Examples below, etc. May be mixed with an alkali metal salt of a desired anion under an aqueous solution, and then the desired onium salt may be extracted with an organic solvent. When an onium salt is obtained by synthesis, it may be purified by a recrystallization method or the like, or dried under reduced pressure.

(Alkali metal salt)
Examples of the alkali metal cation in the alkali metal salt include a lithium cation, a sodium cation, and a potassium cation. In the present invention, an alkali metal salt having a melting point of 50 ° C. or higher is used. The melting point of ordinary alkali metal salts is 50 ° C. or higher, and these can be used without any particular limitation.

As anions, F ⁻ , Cl ⁻ , Br ⁻ , I ⁻ , N (FSO ₂ ) ₂ ⁻ , N (FSO ₂ ) (CF ₃ SO ₂ ) ⁻ , N (CF ₃ SO ₂ ) ₂ ⁻ , N (CF ^{_{3 CF 2 SO 2) 2 -}} , N (C 2 H 5 SO 2) 2 -, CF 3 SO 3 -, CF 3 CF 2 SO 3 -, PF 6 -, BF 4 -, ClO 4 -, AsF 6 - Etc. Among _{^{these, N (FSO 2) 2 -}} , N (CF 3 SO 2) 2 -, BF 4 - are preferably mentioned from the viewpoint to be lowered more the viscosity of the molten salt.

  As the alkali metal salt, a commercially available product or the like may be used as it is, or it may be produced by appropriately referring to conventional techniques.

(Mixing process)
In the present invention, the above-described onium salt and alkali metal salt are mixed to obtain an ionic liquid. In the mixing, the onium salt and the metal salt may be chemically brought into contact with each other, and for example, dry mixing or wet mixing using an appropriate solvent may be used. In the case of wet mixing, the solvent is preferably distilled off after mixing. In the present invention, by mixing, a mixture having a lower melting point than the original onium salt, a lower melting point than the original alkali metal salt, and a melting point of 100 ° C. or less is obtained. Non-limiting examples of specific mixing steps are described in the examples below.

The preferred range for the ratio of both salts in obtaining a low melting point ionic liquid by mixing an onium salt and an alkali metal salt is as follows. The ratio of the molar amount (M _A ) of the alkali metal salt and the molar amount (M _O ) of the onium salt is preferably such that M _A / M _O is 1/9 to 7/3. Within the above range, the inventors have found that the melting point of the mixture is effectively reduced.

  In the present invention, two or more onium salts and / or alkali metal salts may be mixed. In other words, for example, a “ternary” ionic liquid can be obtained by mixing two kinds of onium salts and one kind of alkali metal salt.

(Ionic liquid)
The ionic liquid thus obtained is also an embodiment of the present invention. In other words, the ionic liquid of the present invention is composed of a mixture of an onium salt having a melting point of 50 ° C. or higher and an alkali metal salt having a melting point of 50 ° C. or higher, and the melting points of both the original onium salt and the alkali metal salt. And a melting point of 100 ° C. or lower. The ionic liquid of the present invention preferably does not contain a solvent. Here, the “solvent” refers to a substance other than the above mixture and having a melting point of less than 50 ° C. By not containing a solvent, the advantages of the ionic liquid itself can be more effectively demonstrated.

  In addition to the above-mentioned mixture of onium salt and alkali metal, the ionic liquid of the present invention may contain other components, though not necessarily preferable. Examples of such other components include, but are not limited to, acetonitrile, ethylene carbonate, sulfolane, tetraethylene glycol dimethyl ether, and vinylene carbonate. The proportion of the salt formed by mixing the onium salt and the alkali metal salt in the ionic liquid of the present invention is preferably 80% by mass or more, and more preferably 90% by mass or more. Most preferably, the ionic liquid consists only of a mixture of the above-described onium salt and alkali metal salt.

In the present invention, the ionic liquid is preferably used alone or mixed with a solvent as the battery electrolyte or electrolyte. The battery may be a primary battery or a secondary battery, for example, a lithium ion battery. The solvent that can be used is not particularly limited, and examples thereof include known nonaqueous organic solvents such as ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, dimethoxyethane, methyl acetate, and methyl formate. Non-limiting examples. In the present invention, the ionic liquid described above may be used as the electrolyte, or a gel electrolyte in which this is fixed with a polymer matrix. For the specific structure of the battery such as a lithium ion secondary battery, the prior art can be referred to as appropriate. For example, the positive electrode, the negative electrode, the separator, etc. of the battery may be used as they are, or the battery Examples of the shape include a cylindrical shape, a square shape, a coin shape, and a film shape. More specifically, examples of the negative electrode material include lithium metal and alloys thereof, carbon materials and polymer materials that can be doped / undoped with lithium, lithium intercalation compounds such as metal oxides, and the like. Examples thereof include composite oxides of lithium and transition metals such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , and LiMnO ₂ , polymer materials, and the like. Examples of the separator include a porous film made of a polymer material such as polyethylene and polypropylene. As a material of the current collector, for example, copper, aluminum, stainless steel, titanium, nickel, tungsten steel, carbon material and the like are used, and the shape thereof includes foil, net, nonwoven fabric, punched metal and the like. In the examples described later, examples of manufacturing coin-type batteries are given.

  In the present invention, the ionic liquid can be used as a solvent for various organic synthesis reactions. The above-mentioned ionic liquid has low solubility in water. For example, a two-phase reaction field composed of an aqueous phase and an ionic liquid can be constructed. In the present invention, the ionic liquid described above may be used for the construction of a three-phase reaction field composed of a low polarity organic solvent / water / room temperature molten salt. This is because the ionic liquid is hardly soluble in an organic solvent having low polarity such as toluene, ethyl acetate, diethyl ether and the like. In the present invention, an ionic liquid may be used as a reaction solvent and then used as an extraction solvent for separation and purification.

  In the present invention, the above-described ionic liquid may be used as an extraction solvent for separation and purification in an organic synthesis reaction. For example, when the reaction solvent is distilled off from the reaction mixture using a metal catalyst, and ether and ionic liquid are added to the resulting residue, the reaction product is held in the ether phase, and the metal catalyst is held in the ionic liquid. be able to. When a two-phase system is formed in this way, the product and catalyst can be separated and purified very easily. In the present invention, the above ionic liquid may be used as an electrolytic solution for plating. The ionic liquid obtained in the present invention is suitable because it has high heat resistance, a wide temperature range in the liquid state, and high ionic conductivity. In addition, in the present invention, the ionic liquid may be used as a capacitor electrolyte such as an electric double layer capacitor, an electrorheological fluid, a heat storage medium, a catalyst, or the like.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited at all by this Example.

The following abbreviations are used in the following description of the compounds used in the examples.
LiFSI: lithium bis (fluorosulfonyl) imide LiTFSI: lithium bis (fluoromethanesulfonyl) imide SBP-FSI: 5-azoniaspiro [4,4] nonanebis (fluorosulfonyl) imide SBP-BF4: 5-azoniaspiro [4,4] nonane Tetrafluoroborate SBP-TFSI: 5-azoniaspiro [4,4] nonanebis (trifluoromethanesulfonyl) imide TMA-FSI: tetramethylammonium bis (fluorosulfonyl) imide DMI-FSI: dimethylimidazolium bis (fluorosulfonyl) imide DEDMA- FSI: Diethyldimethylammonium bis (fluorosulfonyl) imide DEDMA-TFSI: Diethyldimethylammonium bis (trifluoromethanesulfonyl) Imide DMI-FSI: dimethyl imidazolium bis (fluorosulfonyl) imide

Example 1
In this example, an ionic liquid obtained by mixing LiFSI and SBP-FSI was manufactured as follows (molar ratio, 3: 7).

<Preparation of 5-azoniaspiro [4,4] nonanebis (fluorosulfonyl) imide (SBP-FSI)>
50 g (0.309 mol) of SBP-Cl (5-azoniaspiro [4.4] nonane chloride) produced by a known method was charged into a 500 ml four-necked flask purged with argon and dissolved in 150 g of pure water. Thereto, 67.8 g (0.309 mol) of potassium bis (fluorosulfonyl) imide (KFSI) manufactured by Mitsubishi Materials Electronic Chemical Co., Ltd. was added, stirred at 70 ° C. for 30 minutes, and then cooled to room temperature. Thereto, 120 g of ethyl acetate was added, and the synthesized SBP-FSI was extracted into the organic layer. The liquid mixture was transferred to 1 L and a separatory funnel, and washing was repeated 5 times with 150 g of pure water in the separatory funnel. The organic layer after washing, that is, an ethyl acetate solution of SBP-FSI was transferred to 300 ml, a four-necked flask, and ethyl acetate was distilled off under reduced pressure at 350 mmHg. Next, the pressure was returned to normal pressure, 100 g of isopropyl alcohol was added and recrystallization was performed to obtain SBP-FSI isopropyl alcohol wet crystals. This wet crystal was dried at 10 mmHg and 80 ° C. for 8 hours in a vacuum dryer installed in a dry room controlled at a dew point of −40 ° C. or lower to obtain 75.5 g of SBP-FSI (yield: 80 %).
The synthesized SBP-FSI was identified using NMR.
SBP-FSI
¹ H-NMR (CD3OD, TMS, 300.4MHz) δ2.22 (m, 8H), δ3.55 (m, 8H)
¹⁹ F-NMR (CD3CN, CFCl3,470.6 MHz): δ 56.6 (s, 2F)

<Preparation of ionic liquid>
In a dry room controlled at a dew point of -40 ° C. or lower, 200 ml of LiFSI powder manufactured by Nippon Shokubai Co., Ltd., 14.52 g (0) in a four-necked flask so that the molar ratio of LiFSI to SBP-FSI is 3: 7. .181 mol) and 55.48 g (0.776 mol) of the synthesized SBP-FSI powder were added and gently stirred at room temperature. The mixed powder gradually changed into a liquid state immediately after the start of stirring, and after stirring overnight, a LiFSI-SBP-FSI ionic liquid (room temperature molten salt) was obtained as a uniform colorless transparent liquid.

<Viscosity measurement>
An E-type viscometer manufactured by Tokimec Co., Ltd. was used. First, the viscometer was calibrated with JS50 standard solution. Then, the thermostat was set to 25 ° C., 1 ml of the sample was injected into the apparatus, and the viscosity of the sample at 25 ° C. was measured.

<Melting point measurement>
A differential scanning calorimetry DSC apparatus Exstar 6000 manufactured by Seiko Instruments Inc. was used. Samples 1 to 5 mg were placed in a SUS316 container and sealed in a dry room controlled at a dew point of −40 ° C. or lower. The measurement conditions were that the temperature was maintained at 30 ° C. for 3 minutes, and then the temperature was raised to 400 ° C. at 10 ° C./min. FIG. 1 shows an output example from the DSC apparatus.
A liquid at 30 ° C. or lower is held in a −20 ° C. constant temperature bath for 24 hours, and in the case of holding a liquid, it is determined that it is lower than −20 ° C. (indicated in the table below as “<−20”), When the liquid was not retained, it was determined to be −20 ° C. to 30 ° C. (denoted as “<30” in the table described later).

(Examples 2 to 18)
As in Example 1, ionic liquids were produced and evaluated using other compounds. In addition, the viscosity measurement was not performed about what is solid at 25 degreeC. Even such an ionic liquid can enjoy the effects of the present invention depending on the temperature range to be used, and therefore is within the scope of the present invention. The raw materials used in the production of each ionic liquid are as follows. In addition, what was manufactured by the well-known method was used for the halide of onium cation.
LiTFSI: Nippon Solvay Co., Ltd. KTFSI: Mitsubishi Materials Electronics Chemical Co., Ltd.

Table 1 shows the measurement results of the melting point of a single electrolyte before mixing.

The measurement results of the ionic liquid in each example are shown in the following tables. Tables 2 to 6 show the measurement results of LiFSI-onium FSI ionic liquid.

Table 7 shows the measurement results for the LiTFSI-onium FSI ionic liquid.

Table 8 shows the measurement results of LiTFSI-onium TFSI ionic liquid.

Table 9 shows the measurement results of LiFSI-onium BF4 ionic liquid.

Tables 10 to 11 show the measurement results of the ternary ionic liquid.

<Linear sweep voltammetry measurement>
The potential window of the ionic liquid of Example 2 was measured by linear sweep voltammetry in the following manner.

(Reduction side potential window measurement)
Linear sweep voltammetry on the ionic liquid reduction side was measured using an electrochemical measurement system “HZ-5000” manufactured by Hokuto Denko in a thermostatic chamber at 25 ° C. ± 1 ° C. The measurement was performed using a triode cell (counter electrode: Li, reference electrode: Li, working electrode: Ni). The area of the working electrode was 0.8 cm ² and the voltage sweep rate was 1 mV / s. The measurement results are shown in FIG. A curve indicated by reference numeral 11 is a measurement result on the reduction side.

(Oxidation side potential window measurement)
Linear sweep voltammetry on the ionic liquid oxidation side was measured using an electrochemical measurement system “HZ-5000” manufactured by Hokuto Denko in a thermostatic chamber at 25 ° C. ± 1 ° C. The measurement was performed using a three-electrode cell (counter electrode: Li, reference electrode: Li, working electrode: carbon black). The area of the working electrode was 0.8 cm ² and the voltage sweep rate was 1 mV / s. The measurement results are shown in FIG. A curve indicated by reference numeral 12 is the measurement result on the oxidation side.

  As shown in FIG. 2, the ionic liquid of the present invention was confirmed to be electrochemically stable, with no decomposition observed over a wide range of potentials.

<Production of secondary battery>
(Preparation of positive electrode)
173 g of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ which is a positive electrode active material, 7.79 g of acetylene black (trade name Denka Black, manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive material, carbon fiber (Showa Denko KK) (Product name VGCF) 3.89g, PVdF 9.73g as binder, N-methyl-2-pyrrolidone (NMP) 130g as a dispersion medium, each mixed with a mixer, positive electrode coating with a solid content of 60% A liquid was prepared. This coating solution was coated on an aluminum foil having a thickness of 20 μm with a coating machine, dried at 80 ° C., and then subjected to a roll press treatment to obtain a positive electrode having a positive electrode active material weight of 7.4 mg / cm ² .

(Preparation of negative electrode)
123 g of graphite as a negative electrode active material, 1.28 g of acetylene black (trade name Denka Black, manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive material, 12.8 g of carboxymethyl cellulose (CMC) as a binder, and styrene butadiene rubber (SBR) 12.8 g and 105 g of pure water as a dispersion medium were mixed with a mixer to prepare a negative electrode coating liquid having a solid content of 55%. This coating solution was coated on a copper foil having a thickness of 18 μm with a coating machine, dried at 80 ° C., and then subjected to a roll press treatment to obtain a negative electrode having a negative electrode active material weight of 3.4 mg / cm ² .

(Coin type battery)
The battery was evaluated using a 2032 standard stainless steel coin cell manufactured by Hosen Co., Ltd. A cross-sectional view of the manufactured coin-type battery 10 is shown in FIG. For the positive electrode 1, a positive electrode prepared in a dry room controlled at a dew point of −40 ° C. or lower was punched to φ14. Next, the prepared negative electrode 2 was punched into φ16. The positive electrode 1 has a positive electrode current collector 1a, and the negative electrode 2 has a negative electrode current collector 2a. Similarly, a polyethylene separator 7 was punched into φ19, and a negative electrode 2, a separator 7, a gasket 6, a positive electrode 1, and a stainless steel spacer (1 mm) leaf spring were combined in this order. Thereto was injected 0.4 μl of the ionic liquid obtained in each of the above examples as the electrolytic solution 3, and then the electrolytic solution was impregnated under reduced pressure at −0.09 MPa for 1 hour. These power generation elements were housed in a stainless steel case (consisting of a positive electrode case 4 and a negative electrode case 5). The positive electrode case 4 and the negative electrode case 5 serve as a positive electrode terminal and a negative electrode terminal. A gasket 6 made of polypropylene is interposed between the positive electrode case 4 and the negative electrode case 5 to ensure sealing and insulation between the positive electrode case 4 and the negative electrode case 5. Thereafter, the cell was sealed with a caulking machine to obtain a secondary battery cell for evaluation.

(Charge / discharge cycle test)
Using a charge / discharge test apparatus, the upper limit voltage is regulated to 4.2V, the lower limit voltage is set to 2.7V, the initial charge is performed at a 0.1C time rate, and the initial discharge is performed at a 0.1C time rate. The charge / discharge cycle by 1C discharge was repeated 50 cycles. Compared with the initial 1C discharge capacity, the capacity retention rate at the 50th cycle was determined.

(Discharge rate test)
Using a charge / discharge test apparatus, the upper limit voltage is regulated to 4.2V, the lower limit voltage is regulated to 2.7V, the charge is regulated to a 0.1C time rate, and the discharge rate is 0.1C, 0.2C, 0.5C. 1C, 2C, 3C, 5C, and 10C were specified, and the expression capacity at the time of rapid discharge was confirmed.

The ionic liquid used in the secondary battery of each example is as follows.
Secondary battery Ionic liquid Example 19 Example 1
Example 20 Example 2
Example 21 Example 3
Example 22 Example 6
Example 23 Example 7
Example 24 Example 8
Example 25 Example 9
Example 26 Example 11
Example 27 Example 12
Example 28 Example 13
Example 29 Example 14
Example 30 Example 15
Example 31 Example 17

Table 12 shows the charge / discharge cycle test results.

  The lithium ion secondary battery using the ionic liquid of the present invention can obtain a cycle capacity retention ratio and a better discharge capacity equivalent to those at 20 ° C. driving at a battery driving temperature of 60 ° C.

FIG. 4 shows the discharge rate test results at 20 ° C. for the secondary batteries of Examples 19-21.
The lithium ion secondary battery using the ionic liquid of the present invention can exhibit a good discharge capacity in 1C rate discharge at 20 ° C. In comparison between Examples 19, 20, and 21, the best rate characteristics are obtained with the battery of Example 21. Compared with the battery of Example 19 using the ionic liquid of Example 1 having a low viscosity, the rate characteristics of the ionic liquid of Example 3 having a high molar ratio of the Li salt having a high viscosity can be obtained. The ionic liquid of the present invention is useful as an electrolytic solution for a secondary battery that is driven with good durability and rate characteristics in a wide temperature range from room temperature to medium temperature.

1: Positive electrode 1a: Positive electrode current collector 2: Negative electrode 2a: Negative electrode current collector 3: Electrolyte solution 4: Positive electrode case 5: Negative electrode case 6: Gasket 7: Separator 10: Coin type battery 11: Reduction-side linear sweep voltammetry Measurement result 12: Measurement result of linear sweep voltammetry on the oxidation side

Claims (11)

  An onium salt having a melting point of 50 ° C. or higher and an alkali metal salt having a melting point of 50 ° C. or higher are mixed and lower than the melting points of both the original onium salt and the alkali metal salt and 100 ° C. The manufacturing method of the ionic liquid which has the following melting | fusing point.   The process according to claim 1, wherein the alkali metal salt is a lithium salt.   The production method according to claim 1 or 2, wherein the onium cation in the onium salt is a quaternary ammonium cation, a pyrrolidinium cation, a piperidinium cation, or an imidazolium cation. The onium cation in the onium salt is represented by the following formula (1)

3. The production method according to claim 1, wherein the four R ^{1 s} are each independently a quaternary ammonium cation represented by C 1 or C 2 alkyl group. The onium cation in the onium salt is represented by the following formula (2)

(However, n is 4 or 5, and two R ² are each independently an alkyl group having 1 or 2 carbon atoms, or two R ² are bonded to form an alkylene group having 4 or 5 carbon atoms. The production method according to claim 1, wherein the pyrrolidinium cation or piperidinium cation is represented by the formula: The onium cation in the onium salt is represented by the following formula (3)

(Wherein Z is a hydrogen atom or a methyl group, and two R ^{3 s} are each independently an alkyl group having 1 or 2 carbon atoms) 3. The production according to claim 1 or 2, Method. The ratio M _A / M _O between the molar amount (M _A ) of the alkali metal salt and the molar amount (M _O ) of the onium salt in the mixing is 1/9 to 7/3. The manufacturing method of 1 item | term.   It consists of a mixture of an onium salt having a melting point of 50 ° C. or more and an alkali metal salt having a melting point of 50 ° C. or more, and has a melting point lower than the melting point of both the original onium salt and the alkali metal salt and not more than 100 ° C. Having ionic liquid.   The ionic liquid according to claim 8, which contains no substance having a melting point lower than 50 ° C other than the mixture.   The ionic liquid according to claim 8 or 9, which is a battery electrolyte, an organic reaction solvent, an extraction solvent or a capacitor electrolyte.   A secondary battery having the ionic liquid according to claim 8 or 9 as an electrolytic solution.

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