JP2010277960A - Nonaqueous electrolyte solution and lithium ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hardly volatile nonaqueous electrolyte solution having low viscosity, which can be used as an electrolyte solution for a lithium ion battery. <P>SOLUTION: The nonaqueous electrolyte solution contains chain ether represented by general formula (I), and lithium salt as an electrolyte. In the general formula (I), R<SB>1</SB>and R<SB>3</SB>are each alkyl group with the total number of carbons of 1 to 4 which may have a substituent, and R<SB>1</SB>and R<SB>3</SB>never become the same group at the same time. R<SB>2</SB>is an alkylene group with the number of carbons from 2 to 4 constituting the main chain and the total number of carbons from 2 to 4 which may have the substituent, and n is an integer of 2 to 6. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte for a lithium ion secondary battery and a lithium ion secondary battery.

2. Description of the Related Art In power storage devices such as lithium primary batteries and lithium secondary batteries that have been widely used in recent years, charging and discharging are performed by movement of lithium ions.
Accompanying the miniaturization and high performance of portable devices in which these electricity storage devices are used, energy storage devices are required to have higher energy density.

  In these batteries, an electrolytic solution in which a lithium salt is dissolved in an organic solvent is used. As the organic solvent, a polar solvent such as propylene carbonate, ethylene carbonate, and γ-butyrolactone, or an organic solvent such as dimethyl carbonate is used. ing.

  Since these organic solvents are volatile and flammable, they also have environmental impacts, ignition problems during overheating, and the like.

  As one of methods for solving the above problems, a method using a so-called room temperature molten salt has also been proposed. That is, a room temperature molten salt is a compound that is dissociable into ions but is a liquid at room temperature, and since it is non-volatile, there is no risk of ignition. Therefore, the room temperature molten salt is used as a solvent and lithium salt is melted at room temperature. There has been proposed a method for reducing environmental problems and safety problems caused by volatile organic solvents by dissolving in a salt (see, for example, Patent Document 1).

  In addition, ether complex salts having an ether compound having a specific structure as a ligand have been proposed and reported to exhibit low volatility (for example, see Non-Patent Document 1), and the ether complex salt is used as an electrolytic solution. It can also be used.

JP 2004-43407 A JP 2005-126339 A

Journal of Chemical Physics, Vol. 117, P: 5929 (2002)

However, when the above-mentioned room temperature molten salt is used as the electrolyte, and graphite that is conventionally used as the negative electrode active material of a lithium ion battery, the room temperature molten salt is decomposed or cations constituting the room temperature molten salt are inserted between the graphite layers. There was a problem that the layered structure of graphite was destroyed. Moreover, there were few kinds of room temperature molten salts having a melting point lower than 0 ° C., and there were problems that there were few room temperature molten salts that could be used even at temperatures lower than 0 ° C.
In addition, the ether complex salt has a high viscosity, poor impregnation into electrodes or separators, and poor handling in the battery manufacturing process.

In view of the above-mentioned conventional problems, an object of the present invention is to provide a low-viscosity and hardly volatile non-aqueous electrolyte.
Another object of the present invention is to provide a lithium ion secondary battery that is excellent in low temperature characteristics, has a low risk of ignition, and is highly safe.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a mixture of a chain ether having a specific structure with an asymmetric structure and a lithium salt is a low-viscosity liquid even at room temperature. The invention has been completed. That is, the present invention for solving the above problems is as follows.

(1) A nonaqueous electrolytic solution comprising a chain ether represented by the following general formula (I) and a lithium salt as an electrolyte.

（一般式（Ｉ）中、Ｒ_１及びＲ_３は、置換基を有していてもよい総炭素数１〜４のアルキル基を示し、Ｒ_１及びＲ_３が同時に同じ基となることはない。Ｒ_２は、主鎖を構成する炭素数が２〜４である総炭素数２〜４のアルキレン基を示し、置換基を有していてもよい。ｎは２〜６の整数である。）

(In general formula (I), R ₁ and R ₃ represent an alkyl group having 1 to 4 carbon atoms which may have a substituent, and R ₁ and R ₃ are not the same group at the same time. R ₂ represents a C 2-4 alkylene group having 2 to 4 carbon atoms constituting the main chain, and may have a substituent, and n is an integer of 2 to 6. )

(2) The nonaqueous electrolytic solution according to (1), wherein the lithium salt has a structure represented by the following general formula (II).

（一般式（ＩＩ）中、ｎ、ｍは０〜５の整数を示す。）

(In general formula (II), n and m represent integers of 0 to 5.)

(3) The nonaqueous electrolytic solution according to (1) or (2), wherein the lithium salt represented by the general formula (II) is bis (trifluoromethanesulfonyl) amidolithium.

(4) The lithium salt is at least one selected from the group consisting of LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiSbF ₆ , LiN (C ₂ F ₅ SO ₂ ) ₂ and LiClO _4. (1) Nonaqueous electrolyte solution.

(5) In the chain ether represented by the general formula (I), R ₁ is a methyl group, R ₂ is an ethylene group, n is 3, and R ₃ is an ethyl group, n-propyl. The nonaqueous electrolytic solution according to any one of (1) to (4), which is at least one selected from a group and an n-butyl group.

(6) In the chain ether represented by the general formula (I), R ₁ is a methyl group, R ₂ is an ethylene group, n is 4, and R ₃ is an ethyl group. The nonaqueous electrolytic solution according to any one of (1) to (4), which is characterized in that

(7) The molar ratio A / B between the chain ether (A) represented by the general formula (I) and the lithium salt (B) is 0.5 to 2, (1) The nonaqueous electrolytic solution according to any one of to (6).

(8) The non-aqueous electrolyte according to (7), wherein the molar ratio A / B is 1.

(9) A lithium ion secondary battery using the nonaqueous electrolytic solution according to any one of (1) to (8).

According to the present invention, it is possible to provide a low-viscosity, hardly volatile non-aqueous electrolyte that can be used as an electrolyte for a lithium ion battery.
In addition, according to the present invention, it is possible to provide a highly safe lithium ion secondary battery having excellent low temperature characteristics and low risk of ignition.

  The nonaqueous electrolytic solution of the present invention is characterized by containing a chain ether represented by the following general formula (I) and a lithium salt as an electrolyte.

（一般式（Ｉ）中、Ｒ_１及びＲ_３は、置換基を有していてもよい総炭素数１〜４のアルキル基を示し、Ｒ_１及びＲ_３が同時に同じ基となることはない。Ｒ_２は、主鎖を構成する炭素数が２〜４である総炭素数２〜４のアルキレン基を示し、置換基を有していてもよい。ｎは２〜６の整数である。）

(In general formula (I), R ₁ and R ₃ represent an alkyl group having 1 to 4 carbon atoms which may have a substituent, and R ₁ and R ₃ are not the same group at the same time. R ₂ represents a C 2-4 alkylene group having 2 to 4 carbon atoms constituting the main chain, and may have a substituent, and n is an integer of 2 to 6. )

(Chain ether)
The chain ether according to the present invention is represented by the general formula (I). In the general formula (I), R ₁ and R ₃ each have 1 to 4 carbon atoms which may have a substituent. The alkyl group is not simultaneously represented by the same group. Examples of the substituent include a halogenon group such as fluorine and chlorine, a nitrile group, a ketone group, and an alkenyl group.

  The chain ether represented by the general formula (I) has an asymmetric structure, and the asymmetric structure tends to have a low melting point and a low viscosity.

Specific examples of the optionally substituted alkyl group having 1 to 4 carbon atoms represented by R ₁ or R ₃ include a methyl group, an ethyl group, an n-propyl group, a sec-propyl group, n -Unsubstituted alkyl group such as butyl group, sec-butyl group, tert-butyl group; fluoroalkyl group such as monofluoromethyl group, trifluoromethyl group, pentafluoroethyl group; trichloromethyl group, 2-chloroethyl group, penta A chloroalkyl group such as a chloroethyl group;

When the number of carbon atoms too large, a strong tendency to viscosity increases, in the R ₁ or R ₃ is C 5 or greater alkyl group having a carbon becomes high viscosity and low ion conductivity, which is also object of the present invention, It becomes difficult to obtain a non-aqueous electrolyte with good viscosity and ionic conductivity. Therefore, R ₁ and R ₃ are preferably a methyl group, an ethyl group, a propyl group, or a butyl group, and more preferably a methyl group or an ethyl group.

In the general formula (I), R ₂ may have a substituent, the total number of carbon atoms is an alkylene group having 2 to 4 carbon atoms constituting the main chain is 2 to 4. The compound having 1 carbon in the main chain in R ₂ has a low stability and tends not to be obtained as a stable compound near room temperature. On the other hand, when the number of carbon atoms in the main chain is 5 or more, not only the chemical stability is lowered but also the ionic conductivity tends to be lowered. R ₂ is particularly preferably one having 2 carbon atoms constituting the main chain.

R ₂ may be substituted if the total carbon number is 2 to 4 (the total carbon number is the number including the carbon atom of the substituent when it has a substituent). If the total number of carbon atoms is 5 or more, the ionic conductivity tends to be insufficient. Examples of the substituent include a halogen group such as an alkyl group, fluorine, and chlorine, an allyl group, an aryl group, an ether group, an ester group, a carboxyl group, and a nitrile group.

R ₂ is preferably an unsubstituted alkylene group such as an ethylene group, trimethylene group or tetramethylene group; an alkyl-substituted alkylene group such as an isopropylene group or isobutylene group, a tetrafluoroethylene group or a 1,1-difluoroethylene group. And fluoroalkylene groups such as hexafluorotrimethylene group; chloroalkylene groups such as tetrachloroethylene group, 1,2-dichloroethylene group and 1,1-dichloroethylene group.

  In the said general formula (I), n shows the integer of 2-6. When n is 1, the flame retardancy effect tends to be hardly obtained. On the other hand, when n exceeds 6, the viscosity of the non-aqueous electrolyte tends to increase, and the permeability of the non-aqueous electrolyte to the electrode tends to decrease. In addition, the ionic conductivity tends to be low and the rate characteristics tend to decrease. By setting n to 2 to 6, the number of oxygen atoms in the ether that can interact with the ion conductive salt increases, so that the melting point tends to be low.

In the chain ether represented by the general formula (I), R ₁ is a methyl group, R ₂ is an ethylene group, n is 3, and R ₃ is an ethyl group, an n-propyl group, and It is preferable that at least one selected from n-butyl groups can reduce the viscosity, and even when combined with various lithium salts, it tends to be liquid at room temperature.

In the chain ether represented by the general formula (I), R ₁ is a methyl group, R ₂ is an ethylene group, n is n = 4, and R ₃ is an ethyl group. Is preferable in terms of lowering the viscosity.

  Specific examples of the chain ether represented by the general formula (I) according to the present invention include the following compounds.

  The production method of the chain ether represented by the general formula (I) is not particularly limited, but can be obtained by reacting an alcohol with a halide in the presence of a strong base. Examples of strong bases include NaH and alkyl lithium. Examples of alcohols include triethylene glycol monomethyl ether, tetraethylene glycol monomethyl ether, and pentaethylene glycol monomethyl ether. Examples of the halide include bromoethane, 1-bromopropane, 1-bromobutane, 1-bromopropene, 1-bromobutene, iodoethane, 1-iodopropane, 1-iodopropene, 1-iodobutane, 1-iodobutene and the like. .

  The higher the boiling point or flash point of the ether constituting the electrolytic solution is preferable because the risk of ignition when used as a lithium battery or a lithium ion battery tends to decrease. Therefore, the chain ether used in the present invention preferably has a boiling point of 100 ° C. or higher, and more preferably 200 ° C. or higher.

(Electrolytes)
The nonaqueous electrolytic solution of the present invention contains a lithium salt as an electrolyte. The lithium salt is not particularly limited as long as it is a stable lithium salt within the operating voltage range of a lithium battery or a lithium ion battery, but a lithium salt having a structure represented by the following general formula (II) is preferable.

（一般式（ＩＩ）中、ｎ、ｍは０〜５の整数を示す。）

(In general formula (II), n and m represent integers of 0 to 5.)

Specific examples of the lithium salt used in the present invention include lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiClO ₄ ), and lithium trifluoromethanesulfonate. (LiCF ₃ SO ₃ ) and the like. In particular, those represented by the formula (II), lithium bis (trifluoromethanesulfonyl) amide _{(LiN (SO 2 CF 3)} 2), lithium bis (pentafluoroethane sulfonyl) amide (LiN _(SO 2 _{C 2} F ₅ ) ₂ ) and the like.
These lithium salts can be used singly or in combination of two or more.

In addition, when the melting point of the mixture of the chain ether and the lithium salt is higher than room temperature and is solid at room temperature (about 25 ° C.), it can be used by dissolving in an organic solvent.
Even if the mixture of the chain ether and the lithium salt is liquid at room temperature, an organic solvent may be added for the purpose of lowering the viscosity and improving the lithium battery characteristics.

The organic solvent is not particularly limited as long as it can dissolve a lithium salt and is stable in the operating voltage range of a lithium battery or a lithium ion battery.
Specific examples of the organic solvent include lactones such as γ-butyrolactone, γ-valerolactone, δ-valerolactone, 3-methyl-1,3-oxazolin-2-one; N-methylformamide, N, N-dimethyl Amides such as formamide, N-methylacetamide, N-methylpyrrolidinone; carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, ethylene carbonate, styrene carbonate, vinylene carbonate; 1,3-dimethyl-2- Examples thereof include imidazolidinones such as imidazolidinone or fluorine-based solvents in which hydrogen atoms or alkyl groups of these various organic solvents are substituted with fluoroalkyl groups.
These non-aqueous organic solvents may be used individually by 1 type, and 2 or more types may be mixed and used for them.

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

  The method for producing the non-aqueous electrolyte of the present invention is not particularly limited, but there is a method for producing the mixture by reacting the chain ether (A) and the lithium salt (B) at a specific mixing ratio. It is preferable because of the ease of reaction.

  The mixing molar ratio A / B of the chain ether (A) and the lithium salt (B) is preferably 0.8 ≦ (A / B) ≦ 5, and 0.5 ≦ (A / B) ≦ 2. More preferably, 1 is more preferable. If this ratio is less than 0.5, the viscosity becomes high, impregnation into the separator and the electrode is lowered, and the battery performance may not be sufficiently exhibited. If this ratio exceeds 2, the concentration of the lithium salt is lowered, the ionic conductivity is lowered, and the battery performance may be lowered.

In the production of the electrolytic solution, the reaction temperature and time are not particularly limited. Generally, under stirring, the chain ether, lithium salt, and, if necessary, an organic solvent are mixed at a temperature below the boiling point of the starting chain ether to be used, and the reaction is completed within a few minutes to several hours. In the invention, the reaction time and the reaction temperature may be adjusted as appropriate.
In addition, confirmation that reaction was completed and the mixture was obtained can be performed by viscosity confirmation. This can be confirmed by no change in viscosity after a certain time.

  The electrolytic solution preferably has a viscosity of 200000 mPa · s or less, and more preferably 3000 mPa · s. Here, the viscosity refers to a viscosity at 30 ° C. measured using a viscoelasticity measuring device (“Physica MCR301” manufactured by ANTON Paar Co., Ltd.). Viscosity can be controlled within the above range by appropriately selecting a chain ether or a lithium salt, adjusting a mixing ratio of the chain ether and the lithium salt, or adding an organic solvent to the electrolytic solution.

<Lithium ion secondary battery>
The lithium ion secondary battery of the present invention is characterized by using the non-aqueous electrolyte solution of the present invention described above. For example, a negative electrode and a positive electrode are arranged to face each other via a separator, and the non-aqueous electrolyte of the present invention is used. It can be obtained by injecting a water electrolyte.

Examples of the positive electrode active material included in the positive electrode include composite oxides of lithium and transition metals such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , and LiMn ₂ O ₄ , transition metal oxides such as MnO ₂ and V ₂ O ₅ , MoS _2, transition metal sulfides such as TiS, polyacetylene, polyacene, polyaniline, polypyrrole, conductive polymer compounds such as polythiophene, poly (2,5-dimercapto-1,3,4-thiadiazole) disulfide compounds such like are used It is done.

  As the negative electrode active material contained in the negative electrode, lithium alloys such as lithium metal and lithium aluminum alloy, carbonaceous materials capable of occluding and releasing lithium, cokes such as graphite, phenolic resin, and furan resin, carbon fiber, glassy carbon, Pyrolytic carbon, activated carbon, etc. are used.

When producing an electrode for a charging device using an electrode active material, it is preferable to use a conductive aid together with a binder. Examples of the conductive aid used include carbon black such as acetylene black and ketjen black, natural graphite, and the like. Further, metal fibers such as thermally expanded graphite, carbon fiber, conductive carbon, ruthenium oxide, titanium oxide, aluminum, and 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 0.5-50 mass% with respect to an electrode active material, it is more preferable to mix | blend 1-30 mass%.

Various publicly known binders can be used as the binder used together with the conductive aid when producing the electrode for the charging device.
For example, polytetrafluoroethylene, polyvinylidene fluoride, carboxymethyl cellulose, fluoroolefin copolymer crosslinked polymer, styrene-butadiene copolymer, polyacrylonitrile, polyvinyl alcohol, polyacrylic acid, polyimide, petroleum pitch, coal pitch, phenol resin, etc. Is mentioned.
In the production of the charging device electrode, it is also preferable to use a coating solvent such as N-methylpyrrolidone, N, N-dimethylformamide, dimethylacetamide, water, and alcohols.

  Various known separators can also be used as the separator used in the charging device. Specific examples include paper, polypropylene, polyethylene, glass fiber separators, and the like.

  However, when the electrolyte solution has a high viscosity, the use of polypropylene or polyethylene may deteriorate the wettability, so the surface of the polypropylene or polyethylene porous body is made of silane and a pulling agent or resin. By using the treated separator, the wettability to the separator can be improved.

  Although the structure of the lithium ion secondary battery of the present invention is not particularly limited, usually, a positive electrode and a negative electrode, and a separator provided as necessary, are wound into a flat spiral to form a wound electrode group, In general, these are laminated as a flat plate to form a laminated electrode plate group, or the electrode plate group is enclosed in an exterior body.

  The lithium ion secondary battery of the present invention is not particularly limited, but is used as a paper-type battery, a button-type battery, a coin-type battery, a laminated battery, a cylindrical battery, a rectangular battery, or the like.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

(Synthesis Example 1)
~ Synthesis of chain ether (1) ~

  4 g (0.1 mol) of sodium hydride (purity 60%, balance 40% is mineral oil) (manufactured by Wako Pure Chemical Industries, Ltd.) was dissolved in 20 ml of dimethylformamide (manufactured by Wako Pure Chemical Industries, Ltd.), then 8 0.2 g (0.05 mol) of triethylene glycol monomethyl ether (manufactured by Sigma Aldrich Japan Co., Ltd.) dissolved in 100 ml of dimethylformamide (manufactured by Wako Pure Chemical Industries, Ltd.) was added dropwise. Subsequently, 5.45 g (0.05 mol) of bromoethane (manufactured by Tokyo Chemical Industry Co., Ltd.) dissolved in 100 ml of dimethylformamide (manufactured by Wako Pure Chemical Industries, Ltd.) was added dropwise and reacted at room temperature for 24 hours. Subsequently, 100 mL of pure water was added, extracted 5 times with 100 mL of chloroform (manufactured by Wako Pure Chemical Industries, Ltd.), and purified by distillation to obtain 7.65 g of a colorless and transparent liquid.

When the structure was identified using NMR (“AL400” manufactured by JEOL Ltd.) using tetramethylsilane as a reference substance, ¹ H-NMR: δ 3.65-3.47 ppm (m, 14H), 3.36 ppm ( s, 3H), 1.19 ppm (t, 3H).

(Synthesis Example 2)
~ Synthesis of chain ether (2) ~

Synthesis was performed in the same manner as in Synthesis Example 1 except that 6.15 g (0.05 mol) of 1-bromopropane (manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of bromoethane. When the structure was identified in the same manner as in Synthesis Example 1, ¹ H-NMR: δ 3.66-3.53 ppm (m, 14H), 3.41 ppm (m, 2H), 3.37 ppm (s, 3H), 1 .83 (m, 2H) 0.90 ppm (t, 3H).

(Synthesis Example 3)
~ Synthesis of chain ether (3) ~

Synthesis was conducted in the same manner as in Synthesis Example 1 except that 6.85 g (0.05 mol) of 1-bromobutane (manufactured by Wako Pure Chemical Industries, Ltd.) was used instead of chloroethane. When the structure was identified in the same manner as in Synthesis Example 1, ¹ H-NMR: δ 3.65-3.53 ppm (m, 14H), 3.43 ppm (m, 2H), 3.40 ppm (s, 3H), 0 92 ppm (t, 3H).

(Synthesis Example 4)
~ Synthesis of chain ether (4) ~

Synthesis was performed in the same manner as in Synthesis Example 1 except that 10.4 g of tetraethylene glycol monomethyl ether (manufactured by Wako Pure Chemical Industries, Ltd.) was used instead of triethylene glycol monomethyl ether. When the structure was identified in the same manner as in Synthesis Example ^{1, 1 H-NMR: δ} 3.64-3.48ppm (m, 18H), 3.18ppm (s, 3H), 1.19ppm (t, 3H) met It was.

[Example 1]
To 2.88 g (0.015 mol) of the chain ether (1) synthesized in Synthesis Example 1, 4.31 g (0.015 mol) of lithium bis (trifluoromethanesulfonyl) amide (Morita Chemical Co., Ltd.) was used as the lithium salt. In addition, the mixture was stirred at room temperature under an argon atmosphere for 24 hours to obtain a colorless and transparent nonaqueous electrolytic solution (1).

[Example 2]
To the chain ether (2) synthesized in Synthesis Example 2 (3.09 g, 0.015 mol), 4.31 g (0.015 mol) of lithium bis (trifluoromethanesulfonyl) amide was added as a lithium salt, and the mixture was added at room temperature under an argon atmosphere. The mixture was stirred for 24 hours to obtain a colorless and transparent nonaqueous electrolytic solution (2).

[Example 3]
To 3.30 g (0.015 mol) of the chain ether (3) synthesized in Synthesis Example 3, 4.31 g (0.015 mol) of lithium bis (trifluoromethanesulfonyl) amide was added as a lithium salt at room temperature under an argon atmosphere. The mixture was stirred for 24 hours to obtain a colorless and transparent non-aqueous electrolyte (3).

[Example 4]
To the chain ether (4) synthesized in Synthesis Example 4 (3.54 g, 0.015 mol), 4.31 g (0.015 mol) of lithium bis (trifluoromethanesulfonyl) amide was added as a lithium salt at room temperature under an argon atmosphere. The mixture was stirred for 24 hours to obtain a colorless and transparent nonaqueous electrolytic solution (4).

[Example 5]
1.43 g (0.015 mol) of lithium tetrafluoroborate as a lithium salt was added to 3.54 g (0.015 mol) of the chain ether (4) synthesized in Synthesis Example 1, and the mixture was stirred at room temperature for 24 hours under an argon atmosphere. A colorless and transparent nonaqueous electrolytic solution (5) was obtained.

[Comparative Example 1]
To 4.85 g (17 mmol) of lithium bis (trifluoromethanesulfonyl) imide, 3.03 g (17 mmol) of triethylene glycol dimethyl ether (manufactured by Tokyo Chemical Industry Co., Ltd.) was added and stirred at room temperature for 24 hours under an argon atmosphere. A colorless and transparent liquid was obtained and used as a nonaqueous electrolytic solution (6).

[Comparative Example 2]
To 4.85 g (17 mmol) of lithium bis (trifluoromethanesulfonyl) imide, 3.77 g (17 mmol) of tetraethylene glycol dimethyl ether (manufactured by Tokyo Chemical Industry Co., Ltd.) was added and stirred at room temperature for 24 hours under an argon atmosphere. A colorless and transparent liquid was obtained, and this was designated as a nonaqueous electrolytic solution (7).

[Comparative Example 3]
1.59 g (17 mmol) of lithium tetrafluoroborate was added to 3.77 (17 mmol) of tetraethylene glycol dimethyl ether, and the mixture was stirred at 40 ° C. for 24 hours in an argon atmosphere at room temperature. As a result, a white solid was obtained.

<Evaluation of electrolyte>
(Measurement of melting point)
For the non-aqueous electrolytes (1) to (5) of Examples 1 to 5 and the electrolytes (6) and (7) of Comparative Examples 1 and 2, a differential calorimetric analyzer (“DDS-220” manufactured by Seiko Instruments Inc.) ) Was measured from −150 ° C. to 100 ° C. at 10 ° C./min.

(Measurement of viscosity)
About the non-aqueous electrolytes (1) to (5) of Examples 1 to 5 and the non-aqueous electrolytes (6) and (7) of Comparative Examples 1 and 2, viscoelasticity measuring device ("Physica MCR301" manufactured by ANTON Paar Co., Ltd.) )) Was used to measure the viscosity at 30 ° C. The results are shown in Table 1.

(Measurement of ionic conductivity)
For the non-aqueous electrolytes (1) to (5) of Examples 1 to 5 and the non-aqueous electrolytes (6) and (7) of Comparative Examples 1 and 2, an electric conductivity meter (“CG511B” manufactured by Toa DKK) was used. Used to measure the ionic conductivity at 30 ° C. The results are shown in Table 1.

[Example 6]
(Preparation of positive electrode for lithium ion secondary battery)
Lithium manganate (manufactured by Aldrich) as a positive electrode active material, conductive carbon (“Denka Black” manufactured by Denki Kagaku Kogyo Co., Ltd.), polyvinylidene fluoride (“PVDF # 1120” manufactured by Kureha Co., Ltd.) as a binder resin, N-methylpyrrolidone (hereinafter referred to as NMP) as a working solvent is mixed in a ratio of active material: conductive carbon: binder resin: NMP = 94: 3: 3: 28 (weight ratio) to form a paste, and aluminum It apply | coated to electric foil (Nippon Electric Power Co., Ltd. make "20CB"), after making it dry at 80 degreeC for 4 hours, it rolled and obtained the positive electrode for lithium ion secondary batteries.

(Production of lithium ion secondary battery)
Metal lithium having a thickness of 1 mm was used as the counter electrode, and the positive electrode obtained as described above was used as the working electrode, and both electrodes were opposed to each other via a separator (“Celguard # 2300” manufactured by Celguard Co., Ltd.). Using the nonaqueous electrolytic solution (1) prepared in Example 1, a lithium ion secondary battery was produced by a usual method.

(Evaluation of lithium ion secondary battery)
The counter electrode (lithium electrode) was charged to 4.2 V with a current corresponding to 0.1 C.
Discharge was performed up to 2.5 V with a current corresponding to 0.1 C with respect to the lithium electrode, and the initial (initial) discharge capacity was measured. The initial measurement was performed at 25 ° C. After performing this two cycles, the temperature was lowered to 0 ° C. and the same measurement was performed to measure the discharge capacity. The results are shown in Table 2.

[Comparative Example 4]
A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 6 except that the nonaqueous electrolytic solution used in Comparative Example 1 was used. The results are shown in Table 2.

As shown in Table 1, the non-aqueous electrolytes of Examples 1 to 3 have a low melting point, and the non-aqueous electrolytes of Examples 4 and 5 have a melting point of −150 ° C. or in a supercooled state. It can be seen that the liquid state is stable over a wide range of temperatures. When a symmetrical ether compound is used, when lithium bis (trifluoromethanesulfonyl) imide is used as the lithium salt (Comparative Example 2), it is liquid at room temperature, but when lithium tetrafluoroborate is used ( Comparative Example 3) was a solid. In contrast, when an ether compound with an asymmetric structure is used, even if lithium tetrafluoroborate is used, it is liquid at room temperature, and by using an asymmetric structure ether, a liquid can be obtained even when combined with various lithium salts. I found out that
Further, as can be seen from Example 6 and Comparative Example 4, it can be seen that the lithium ion secondary battery using the non-aqueous electrolyte of the present invention is also excellent in low temperature characteristics.

Claims (9)

A nonaqueous electrolytic solution comprising a chain ether represented by the following general formula (I) and a lithium salt as an electrolyte.

(In general formula (I), R ₁ and R ₃ represent an alkyl group having 1 to 4 carbon atoms which may have a substituent, and R ₁ and R ₃ are not the same group at the same time. R ₂ represents a C 2-4 alkylene group having 2 to 4 carbon atoms constituting the main chain, and may have a substituent, and n is an integer of 2 to 6. ) The non-aqueous electrolyte according to claim 1, wherein the lithium salt has a structure represented by the following general formula (II).

(In general formula (II), n and m represent integers of 0 to 5.) 3. The nonaqueous electrolytic solution according to claim 1, wherein the lithium salt represented by the general formula (II) is bis (trifluoromethanesulfonyl) amidolithium. The lithium salt is at least one selected from the group consisting of LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiSbF ₆ , LiN (C ₂ F ₅ SO ₂ ) ₂ and LiClO _4. The non-aqueous electrolyte described. In the chain ether represented by the general formula (I), R ₁ is a methyl group, R ₂ is an ethylene group, n is 3, and R ₃ is an ethyl group, an n-propyl group, and The nonaqueous electrolytic solution according to claim 1, wherein the nonaqueous electrolytic solution is at least one selected from n-butyl groups. In the chain ether represented by the general formula (I), R ₁ is a methyl group, R ₂ is an ethylene group, n is 4, and R ₃ is an ethyl group. The non-aqueous electrolyte of any one of Claims 1-4.   The molar ratio A / B between the chain ether (A) represented by the general formula (I) and the lithium salt (B) is 0.5 to 2, The non-aqueous electrolyte solution according to claim 1.   The non-aqueous electrolyte according to claim 7, wherein the molar ratio A / B is 1.   The lithium ion secondary battery which uses the nonaqueous electrolyte solution of any one of Claims 1-8.