JP6641685B2 - Flame retardant non-aqueous electrolyte and lithium ion secondary battery - Google Patents

Description

  The present invention relates to a flame-retardant non-aqueous electrolyte used for a lithium ion secondary battery and a lithium ion secondary battery using the same.

2. Description of the Related Art In recent years, higher voltage and higher energy density of lithium ion secondary batteries have been developed and widely used mainly for consumer use. In addition, applications for electric vehicles and power storage devices have been attempted, and the size of lithium ion secondary batteries has been increasing.
As the non-aqueous solvent used in the non-aqueous electrolyte of such a lithium ion secondary battery, a carbonate solvent such as ethylene carbonate and diethyl carbonate, which easily dissolves a lithium salt and is not easily electrolyzed, is used.
In addition, there is a report that thermal stability is improved by using only a lithium salt and a glyme compound as an electrolytic solution. It is believed that when an alkali metal salt and glyme are mixed, the oxygen part in the glyme structure coordinates with the metal ion to form a complex, thereby improving the oxidation resistance and thermal stability of the electrolyte. (Patent Document 1).

JP 2010-73489 A

Electrolyte solutions that use carbonate solvents such as ethylene carbonate and diethyl carbonate achieve high energy densities for lithium ion secondary batteries, but have poor flame retardancy due to the presence of carbonate-based solvents, causing abnormal overheating of batteries. There was a risk of fire at times.
In Patent Literature 1, the oxidation resistance and the thermal stability are improved by forming a complex of a glyme-based compound and a lithium salt, and a carbonate-based solvent is not included, which contributes to the nonflammability of the electrolytic solution. . However, since a low-viscosity carbonate-based solvent was not used, the viscosity of the electrolytic solution increased, and the rate characteristics at high current decreased. The problem was to develop a technology for reducing the viscosity of the electrolyte while ensuring non-combustibility and realizing high rate characteristics.
In view of the above circumstances, the present invention has been made to solve these problems of the prior art. Even when a complex of a lithium salt and a glyme compound is used as an electrolyte, a flame retardant having excellent nonflammability and rate characteristics is provided. It is an object of the present invention to provide a non-aqueous electrolyte having a neutral property and a lithium ion secondary battery using the same.

The present inventors have conducted intensive studies to solve the above problems, and as a result, have found that it is effective to dilute a complex of a lithium salt and a glyme compound with an ionic liquid, and have completed the present invention. That is, the present invention for solving the above problems is as follows.
(1) A non-aqueous electrolyte comprising (A) a chain ether compound represented by the following general formula (I), (B) a lithium salt, and (C) an ionic liquid.

（一般式（Ｉ）中、Ｒ_１およびＲ_３は総炭素数１〜４のアルキル基を示し、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く、ｎは１〜５の整数である。）
（２）前記一般式（Ｉ）で表される鎖状エーテル化合物のｎが２〜４であることを特徴とする、（１）に記載の非水電解液。
（３）前記一般式（Ｉ）で表される鎖状エーテル化合物のＲ_１がメチル基であることを特徴とする、（１）または（２）に記載の非水電解液。
（４）前記（Ｂ）リチウム塩が、下記一般式（ＩＩ）で表される構造である（１）〜（３）のいずれか一項に記載の非水電解液。

(In the general formula (I), R ₁ and R ₃ each represent an alkyl group having 1 to 4 carbon atoms, and R ₂ represents an alkylene having 2 to 4 carbon atoms constituting a main chain having 2 to 4 carbon atoms. Represents a group, and may have a substituent, and n is an integer of 1 to 5.)
(2) The non-aqueous electrolyte according to (1), wherein n of the chain ether compound represented by the general formula (I) is 2 to 4.
(3) The non-aqueous electrolyte according to (1) or (2), wherein R ₁ of the chain ether compound represented by the general formula (I) is a methyl group.
(4) The non-aqueous electrolyte according to any one of (1) to (3), wherein the (B) lithium salt has a structure represented by the following general formula (II).

（一般式（ＩＩ）中、ｌ、ｍは、それぞれ０〜５の整数を示す。）
（５）前記（Ｂ）リチウム塩が、リチウムビス（フルオロスルホニル）イミド又はリチウムビス（トリフルオロメチルスルホニル）イミドであることを特徴とする（１）〜（４）のいずれか一項に記載の非水電解液。
（６）（Ｃ）イオン性液体のカチオンが、鎖状四級アンモニウムカチオン、ピペリジニウムカチオン、ピロリジニウムカチオン、及びイミダゾリウムカチオンからなる群より選択される少なくとも一種であることを特徴とする、（１）〜（５）のいずれか一項に記載の非水電解液。
（７）（Ｃ）イオン性液体のアニオンが、Ｎ（Ｃ_４Ｆ_９ＳＯ_２）_２ ⁻、ＣＦ_３ＳＯ_３ ⁻、Ｎ（ＳＯ_２Ｆ）_２ ⁻、Ｎ（ＳＯ_２ＣＦ_３）_２ ⁻、及びＮ（ＳＯ_２ＣＦ_２ＣＦ_３）_２ ⁻からなる群より選択される少なくとも一種であることを特徴とする、（１）〜（６）のいずれかに記載の非水電解液。
（８）前記（１）〜（７）のいずれか一項に記載の非水電解液を用いてなるリチウムイオン二次電池。

(In the general formula (II), l and m each represent an integer of 0 to 5.)
(5) The method according to any one of (1) to (4), wherein the lithium salt (B) is lithium bis (fluorosulfonyl) imide or lithium bis (trifluoromethylsulfonyl) imide. Non-aqueous electrolyte.
(6) The cation of the ionic liquid (C) is at least one selected from the group consisting of a chain quaternary ammonium cation, a piperidinium cation, a pyrrolidinium cation, and an imidazolium cation. , (1) to (5).
(7) The anion of (C) the ionic liquid is N (C ₄ F ₉ SO ₂ ) ₂ ⁻ , CF ₃ SO ₃ ⁻ , N (SO ₂ F) ₂ ⁻ , N (SO ₂ CF ₃ ) ₂ ⁻ , And N (SO ₂ CF ₂ CF ₃ ) ₂ ^—, which is at least one selected from the group consisting of: (1) to (6).
(8) A lithium ion secondary battery using the non-aqueous electrolyte according to any one of (1) to (7).

  The non-aqueous electrolyte containing (A) the chain ether compound represented by the general formula (I), (B) a lithium salt, and (C) an ionic liquid according to the present invention has the flame retardancy and discharge of the electrolyte. It is compatible as a non-aqueous electrolyte component for an energy device, particularly a lithium ion secondary battery, while maintaining both capacity retention rates.

  The chain ether compound used in the present invention is represented by the following general formula (I).

（一般式（Ｉ）中、Ｒ_１およびＲ_３は総炭素数１〜４のアルキル基を示し、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く、ｎは１〜５の整数である。）
Ｒ_１およびＲ_３として表される置換基を有していてもよい総炭素１〜４のアルキル基は特に制限はないが、具体的には、メチル基、エチル基、ｎ−プロピル基、ｓｅｃ−プロピル基、ｎ−ブチル基、ｓｅｃ−ブチル基、ｔｅｒｔ−ブチル基等の無置換アルキル基、モノフルオロメチル基、トリフルオロメチル基、ペンタフルオロエチル基等のフルオロアルキル基、トリクロロメチル基、２−クロロエチル基、ペンタクロロエチル基等の置換アルキル基の他、ニトリル基、ケトン基、アルケニル基等で置換された置換アルキル基を挙げることができる。
Ｒ_１又はＲ_３が総炭素数５以上のアルキル基では、リチウム塩との錯体が高粘度となり非水電解液が低イオン導電率となりやすいため、Ｒ_１又はＲ_３としては、置換又は無置換のメチル基、エチル基、プロピル基、ブチル基であることが好ましく、置換又は無置換のメチル基、エチル基であることがより好ましい。
前記一般式（Ｉ）において、Ｒ_２は置換基を有していてもよい総炭素数が２〜４のアルキレン基であり、その主鎖を構成する炭素数は２〜４であり、好ましくは主鎖を構成する炭素数が２のものである。
また、Ｒ_２は、総炭素数が２〜４であれば置換されていてもよい（総炭素数は、置換基を有する場合には、該置換基の炭素原子も含む数である）。総炭素数が５以上では、イオン導電率が不十分となりやすい傾向がある。なお、前記置換基としては、アルキル基、フッ素、塩素等のハロゲン基、アリル基、アリール基、エーテル基、エステル基、カルボキシル基、ニトリル基等が挙げられる。
Ｒ_２として好適な基としては、エチレン基、トリメチレン基、テトラメチレン基等の無置換アルキレン基、イソプロピレン基、イソブチレン基等のアルキル置換アルキレン基、１、１−ジフルオロエチレン基等のフルオロアルキレン基、テトラクロロエチレン基、１，２−ジクロロエチレン基、１，１−ジクロロエチレン基等のクロロアルキレン基等を挙げることができる。
上記一般式（Ｉ）において、ｎは１〜５の整数を示し、好ましくはｎは２〜４の整数である。ｎが０又は１であると、リチウム塩との組み合わせによりそのリチウム塩との錯体が高粘度となり非水電解液が低イオン導電率となる場合がある。また、ｎが６以上になると、２分子以上のリチウム塩と錯体を形成しやすくなり、非水電解液の粘度が高くなる傾向があり非水電解液が低イオン導電率となりやすい傾向がある。
前記一般式（Ｉ）で表される鎖状エーテル化合物において、Ｒ_１がメチル基であり、Ｒ_２がエチレン基であり、ｎが３であることが、低粘度化できる傾向がある点で好ましい。

(In the general formula (I), R ₁ and R ₃ each represent an alkyl group having 1 to 4 carbon atoms, and R ₂ represents an alkylene having 2 to 4 carbon atoms constituting a main chain having 2 to 4 carbon atoms. Represents a group, and may have a substituent, and n is an integer of 1 to 5.)
The alkyl group of 1 to 4 carbon atoms which may have a substituent represented by R ₁ and R ₃ is not particularly limited, but specifically, a methyl group, an ethyl group, an n-propyl group, a sec An unsubstituted alkyl group such as -propyl group, n-butyl group, sec-butyl group and tert-butyl group; a fluoroalkyl group such as a monofluoromethyl group, a trifluoromethyl group and a pentafluoroethyl group; a trichloromethyl group; In addition to a substituted alkyl group such as -chloroethyl group and pentachloroethyl group, a substituted alkyl group substituted with a nitrile group, a ketone group, an alkenyl group, and the like can be given.
When R ₁ or R ₃ is an alkyl group having a total carbon number of 5 or more, the complex with the lithium salt has a high viscosity and the non-aqueous electrolyte tends to have low ionic conductivity. Therefore, R ₁ or R ₃ is substituted or unsubstituted. Of methyl, ethyl, propyl and butyl groups, and more preferably a substituted or unsubstituted methyl group and ethyl group.
In the general formula (I), R ₂ is an alkylene group having a total of 2 to 4 carbon atoms which may have a substituent, and the number of carbon atoms constituting a main chain thereof is 2 to 4; The main chain has 2 carbon atoms.
Further, R ₂ may be substituted as long as the total number of carbon atoms is 2 to 4 (the total number of carbon atoms is the number including carbon atoms of the substituent when having a substituent). When the total carbon number is 5 or more, the ionic conductivity tends to be insufficient. Examples of the substituent include an alkyl group, a halogen group such as fluorine and chlorine, an allyl group, an aryl group, an ether group, an ester group, a carboxyl group, a nitrile group, and the like.
Suitable groups as R ₂ include unsubstituted alkylene groups such as ethylene group, trimethylene group and tetramethylene group, alkyl-substituted alkylene groups such as isopropylene group and isobutylene group, and fluoroalkylene groups such as 1,1-difluoroethylene group. And chloroalkylene groups such as tetrachloroethylene group, 1,2-dichloroethylene group and 1,1-dichloroethylene group.
In the general formula (I), n represents an integer of 1 to 5, and preferably n is an integer of 2 to 4. When n is 0 or 1, the complex with the lithium salt may have high viscosity due to the combination with the lithium salt, and the non-aqueous electrolyte may have low ionic conductivity. When n is 6 or more, a complex is easily formed with two or more lithium salts, the viscosity of the non-aqueous electrolyte tends to increase, and the non-aqueous electrolyte tends to have low ionic conductivity.
In the chain ether compound represented by the general formula (I), it is preferable that R ₁ is a methyl group, R ₂ is an ethylene group, and n is 3 in that the viscosity can be reduced. .

  The chain ether compound used in the present invention preferably has high purity, and preferably does not contain water. The purification method is not particularly limited. Along with the dehydration treatment, the chain ether compound often contains a catalyst and an unreacted substance at the time of synthesis. For example, after removing an acidic catalyst with an adsorbent and filtering off, the unreacted substance is heated and / or reduced in pressure. A method of purifying by distillation is exemplified. Incidentally, examples of the acid adsorbent include Kyoward 500SH manufactured by Kyowa Chemical Industry Co., Ltd. and hydrotalcites manufactured by Wako Pure Chemical Industries, Ltd. Further, in order to further purify the chain ether compound, distillation under reduced pressure can be performed.

As the lithium salt (B) used in the present invention, a compound represented by the following general formula (II) can be used. Further, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiCF ₃ SO ₃ , LiSbF ₆ and Li (C ₂ F ₅ SO ₂ ) ₂ can be used, but lithium which is stable in the operating voltage range of a lithium battery or a lithium ion battery can be used. The salt is not particularly limited as long as it is a salt. These lithium salts can be used alone or in combination of two or more.

（一般式（ＩＩ）中、ｌ、ｍはそれぞれ０〜５の整数を示す。）
一般式（ＩＩ）で表される化合物のなかでは、リチウムビス（フルオロスルホニル）イミド、リチウムビス（トリフルオロメチルスルホニル）イミドが好ましい。

(In the general formula (II), l and m each represent an integer of 0 to 5.)
Among the compounds represented by the general formula (II), lithium bis (fluorosulfonyl) imide and lithium bis (trifluoromethylsulfonyl) imide are preferable.

The complex of the (A) chain ether compound represented by the general formula (I) and the (B) lithium salt used in the present invention can be obtained by mixing both.
Assuming that the number of moles of the chain ether compound represented by the general formula (I) is A and the number of moles of the lithium salt is B, the mixing molar ratio A / B is 0.5 ≦ (A / B) ≦ 2. Preferably, 0.7 ≦ (A / B) ≦ 1.4 is more preferable, and 0.9 ≦ (A / B) ≦ 1.0 is even more preferable. If this ratio is less than 0.5, the viscosity will increase, the rate characteristics will decrease, and the impregnation properties of the separator and the electrode will decrease, and the battery performance may not be fully exhibited. If this ratio exceeds 2, the probability of the presence of a chain ether compound that does not form a complex increases, and the oxidation resistance of the electrolytic solution tends to decrease.
In the production of the above complex, the treatment temperature and time are not particularly limited. In general, under stirring, at a temperature equal to or lower than the boiling point of the chain ether compound to be used, the chain ether compound and the lithium salt are mixed, and the treatment is completed in several minutes to several hours. The processing temperature may be adjusted.
The completion of the treatment and the confirmation of the mixture can be confirmed by confirming the viscosity. It can be confirmed that there is no change in viscosity after a certain time.
The viscosity of the complex is preferably 200,000 mPa · s or less, more preferably 3000 mPa · s or less. Here, the viscosity refers to a viscosity at 30 ° C. measured using a viscoelasticity measuring device (“Physica MCR301” manufactured by ANTON Paar Corporation). The viscosity can be adjusted to the above range by appropriately selecting a chain ether compound or a lithium salt and adjusting the mixing ratio of the chain ether compound and the lithium salt.

The ionic liquid (C) used in the present invention can be mixed with a complex of (A) a chain ether compound and (B) a lithium salt, and is in a liquid state at room temperature (25 ° C.). There is no particular limitation as long as it is nonflammable and stable in the operating voltage range of the lithium ion secondary battery. From the viewpoint of improving the rate characteristics, the viscosity (25 ° C.) is preferably 120 cP or less, and 1-butyl-3-methylimidazolium bis (fluorosulfonyl) imide, 1-butyl-3-methylimidazolium bis (trifluoromethane Sulfonyl) imide, 1-butyl-3-methylimidazolium tricyanomethane, 1-butyl-3-methylimidazolium trifluoroacetate, N-butyl-N-methylpyrrolidinium bis (trifluoromethanesulfonyl) imide, 1-butyl-3-methylimidazolium trifluoroacetate Butylpyridinium bis (fluorosulfonyl) imide, 1,3-diallylimidazolium bis (trifluoromethanesulfonyl) imide, 1-ethyl-3-methylimidazolium bis (fluorosulfonyl) imide, 1-ethyl-3-methylimidazolium bis (bird (Fluoromethylsulfonyl) imide, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium trifluoroacetate, 1-ethyl-3-methylimidazolium trifluoromethylsulfonate, 1-ethyl -3-methylpyridinium bis (fluorosulfonyl) imide, 1-ethylpyridinium bis (fluorosulfonyl) imide, 1-hexyl-3-methylimidazolium bis (fluorosulfonyl) imide, 1-hexyl-3-methylimidazolium bis ( Trifluoromethylsulfonyl) imide, N-hexylpyridinium bis (trifluoromethylsulfonyl) imide, 1-methyl-3-octylimidazolium bis (trifluoromethylsulfonyl) imide, N-methyl-N- Propylpyrrolidinium bis (fluorosulfonyl) imide, N-methyl-N-propylpyrrolidinium bis (trifluoromethanesulfonyl) imide, 1-propyl-2,3,5-trimethylpyrazolium bis (trifluoromethanesulfonyl) Examples include imide, triethyloctylphosphonium bis (trifluoromethanesulfonyl) imide, triethylpentylphosphonium bis (trifluoromethanesulfonyl) imide, N, N, N-trimethyl-N-propylammoniumbis (trifluoromethanesulfonyl) imide and the like. It is not limited to these.
(C) The cationic component of the ionic liquid contains at least one selected from the group consisting of a chain quaternary ammonium cation, a piperidinium cation, a pyrrolidinium cation and an imidazolium cation, and N (C ^{_{4 F 9 SO 2) 2 -}} , CF 3 SO 3 -, N (SO 2 F) 2 -, N (SO 2 CF 3) 2 - and _{N (SO 2 CF 2 CF 3} ) 2 - selected from the group consisting of The ionic liquid containing at least one is relatively low in viscosity, and an ionic liquid containing N (SO ₂ F) ₂ ⁻ is particularly preferable from the viewpoint of improving the rate characteristics. These ionic liquids may be used alone or in a combination of two or more.

The lithium ion secondary battery of the present invention is characterized by using the above-described non-aqueous electrolyte of the present invention. For example, a negative electrode and a positive electrode are arranged to face each other with a separator interposed therebetween, and It can be obtained by injecting a water electrolyte.
Examples of the positive electrode active material contained in the positive electrode include composite oxides of lithium and a transition metal such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , and LiFePO ₄ , and transition metal oxides such as MnO ₂ and V ₂ O _5. , Transition metal sulfides such as MoS ₂ , TiS, conductive polymer compounds such as polyacetylene, polyacene, polyaniline, polypyrrole, polythiophene, and disulfide compounds such as poly (2,5-dimercapto-1,3,4-thiadiazole) Are used.
As the negative electrode active material contained in the negative electrode, lithium metal, lithium alloy such as lithium aluminum alloy, lithium titanate, carbonaceous material capable of inserting and extracting lithium, graphite, phenol resin, coke such as furan resin, carbon fiber, Glassy carbon, pyrolytic carbon, activated carbon and the like are used.

When producing an electrode using the electrode active material, it is preferable to use a conductive aid together with a binder, as the conductive aid used, acetylene black, carbon black such as Ketjen black, natural graphite, thermal expansion graphite, Metal fibers such as carbon fiber, conductive carbon, ruthenium oxide, titanium oxide, aluminum, and nickel are used. Among these, acetylene black and Ketjen black, which can secure desired conductivity with a small amount of blending, are preferable.
In addition, the conductive assistant is usually blended in an amount of about 0.5 to 50% by mass, more preferably 1 to 30% by mass, based on the electrode active material.

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

  Although various known separators can be used for the separator, it is preferable to use a material that is stable with respect to the electrolytic solution and has excellent liquid retaining properties. Specifically, it is preferable to use a polyolefin porous membrane containing polyethylene, polypropylene, or the like; a nonwoven fabric containing polyolefin fibers (polyethylene fiber, polypropylene fiber, or the like), glass fiber, cellulose fiber, polyimide fiber, or the like. Among these, a nonwoven fabric is preferable as the separator from the viewpoint of being stable with respect to the electrolytic solution and having excellent liquid retention properties, and at least one selected from the group consisting of polyolefin fibers, glass fibers, cellulose fibers, and polyimide fibers. Is more preferable, but is not limited thereto.

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 group, or a structure in which these electrode groups are sealed in an exterior body.
The lithium ion secondary battery of the present invention is not particularly limited, but is used as a paper battery, a button battery, a coin battery, a stacked battery, a cylindrical battery, a square battery, and the like.

Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited to these Examples.
(Purification example 1)
Purification of chain ether compound (1)
Triethylene glycol butyl methyl ether (manufactured by Wako Pure Chemical Industries, Ltd.) is subjected to dehydration treatment with Molecular Sieves 4A (manufactured by Wako Pure Chemical Industries, Ltd.), followed by vacuum distillation to obtain a chain ether compound (1). Was. The purity was confirmed by gas chromatography to be 99.9%.

(Purification example 2)
Purification of chain ether compound (2)
Diethylene glycol ethyl methyl ether (manufactured by Wako Pure Chemical Industries, Ltd.) was subjected to dehydration treatment using Molecular Sieves 4A (manufactured by Wako Pure Chemical Industries, Ltd.), followed by vacuum distillation to obtain a chain ether compound (2). The purity was confirmed by gas chromatography to be 99.9%.

(Example 1)
0.66 g (3.0 mmol) of the chain ether compound (A) of the component (A) obtained in Purification Example 1 was mixed with lithium bis (fluorosulfonyl) imide (manufactured by Nippon Shokubai Co., Ltd.) as a lithium salt of the component (B). ) Was added and diluted with 4.05 g of N-methyl-N-propylpyrrolidinium bis (fluorosulfonyl) imide as the ionic liquid of the component (C), and diluted under an argon atmosphere at room temperature. For 24 hours to obtain a colorless and transparent non-aqueous electrolyte (1).

(Example 2)
0.86 g (3.0 mmol) of lithium bis (trifluorosulfonyl) imide (manufactured by Nippon Shokubai Co., Ltd.) as a lithium salt was added to 0.66 g (3.0 mmol) of the chain ether compound (1) obtained in Purification Example 1. Was added and diluted with 4.05 g of N-methyl-N-propylpyrrolidinium bis (fluorosulfonyl) imide, and the mixture was stirred at room temperature for 24 hours under an argon atmosphere to obtain a colorless and transparent nonaqueous electrolyte solution (2). Was.

(Example 3)
To 0.66 g (3.0 mmol) of the chain ether compound (1) obtained in Purification Example 1, 0.56 g (3.0 mmol) of lithium bis (fluorosulfonyl) imide (manufactured by Nippon Shokubai Co., Ltd.) as a lithium salt. In addition, 4.31 g of N-methyl-N-propylpyrrolidinium bis (trifluoromethanesulfonyl) imide was added and diluted, and the mixture was stirred at room temperature for 24 hours under an argon atmosphere to obtain a colorless and transparent nonaqueous electrolyte (3). Was.

(Example 4)
To 0.45 g (3.0 mmol) of the chain ether compound (2) obtained in Purification Example 2, 0.56 g (3.0 mmol) of lithium bis (fluorosulfonyl) imide (manufactured by Nippon Shokubai Co., Ltd.) as a lithium salt was added. In addition, 4.05 g of N-methyl-N-propylpyrrolidinium bis (fluorosulfonyl) imide was added for dilution, and the mixture was stirred at room temperature for 24 hours under an argon atmosphere to obtain a colorless and transparent nonaqueous electrolyte (4). .

(Comparative Example 1)
0.56 g (3.0 mmol) of lithium bis (fluorosulfonyl) imide (manufactured by Nippon Shokubai Co., Ltd.) as a lithium salt was added to 0.66 g (3.0 mmol) of the chain ether compound (1) obtained in Purification Example 1. In addition, the mixture was stirred at room temperature for 24 hours under an argon atmosphere to obtain a colorless and transparent non-aqueous electrolyte (5).

(Comparative Example 2)
0.56 g (3.0 mmol) of lithium bis (fluorosulfonyl) imide (manufactured by Nippon Shokubai Co., Ltd.) as a lithium salt was added to 0.66 g (3.0 mmol) of the chain ether compound (1) obtained in Purification Example 1. In addition, 2.25 g of a 3: 7 mixed solution (volume ratio) of ethylene carbonate and ethyl methyl carbonate was added for dilution, and the mixture was stirred at room temperature for 24 hours under an argon atmosphere to obtain a colorless and transparent nonaqueous electrolyte (6). .

(Non-aqueous electrolyte flammability test evaluation method)
(Flammability test)
1.5 cm ^{3 of} each of the nonaqueous electrolytes (1) to (6) obtained above was impregnated into a glass filter (GA-100 manufactured by Toyo Roshi Kaisha, Ltd.) cut to a width of 3.0 cm and a length of 13.0 cm. After that, the test flame was brought close to the end of the glass filter, and the time from approaching the flame to the start of combustion was measured.

(Preparation of positive electrode for lithium ion secondary battery)
Lithium iron phosphate (manufactured by Sigma-Aldrich Japan GK), conductive carbon ("DENKA BLACK" manufactured by Denki Kagaku Kogyo Co., Ltd.) as a positive electrode active material, polyvinylidene fluoride as a binder resin, and N-methyl as a coating solvent Pyrrolidone (hereinafter, NMP) is mixed into a paste by mixing active material: conductive carbon: binder resin: NMP at a ratio of 91: 5: 4: 29 (mass ratio), and after drying, 8.8 mg / cm ² is obtained. It was applied to an aluminum current collector foil ("20CB" manufactured by Nippon Denki Industrial Co., Ltd.) to be applied, dried at 80 ° C. for 4 hours, and then rolled to obtain a positive electrode for a lithium ion secondary battery.

(Preparation of negative electrode for lithium ion secondary battery)
Lithium titanate (manufactured by Sigma-Aldrich Japan GK), conductive carbon ("Denka Black" manufactured by Denki Kagaku Kogyo Co., Ltd.) as a negative electrode active material, polyvinylidene fluoride as a binder resin, and N-methylpyrrolidone as a coating solvent (Hereinafter, NMP) was mixed at a ratio of active material: conductive carbon: binder resin: NMP = 92: 4: 4: 32 (mass ratio) to form a paste, and after drying, 9.2 mg / cm ² was applied. The negative electrode was applied to an aluminum current collector foil ("20CB" manufactured by Nippon Denki Co., Ltd.), dried at 80 ° C. for 4 hours, and then rolled to obtain a negative electrode for a lithium ion secondary battery.

(Production of coin-type lithium ion secondary battery)
A circular positive electrode having a diameter of 9 mm was allowed to stand on a coin can (lower part), and the nonaqueous electrolytes (1) to (4) of Examples 1 to 4 and the nonaqueous electrolytes (5) of Comparative Examples 1 and 2 were used. (6) was dropped and impregnated, a separator ("Celgard # 2300", Celgard Co., Ltd., three-layer (PP / PE / PP) separator) was placed, and fixed with a gasket. After dropping the nonaqueous electrolytes (5) and (6) of (1) to (4) and Comparative Examples 1 and 2, a circular negative electrode having a diameter of 14 mm was placed so as to face the positive electrode, and a spacer and a coin can (top) ) Was placed and caulked to obtain a CR2016 type coin battery (diameter 20 mm, height 1.6 mm).

(Evaluation of lithium ion secondary battery)
The battery was charged to 2.7 V with a current corresponding to the positive electrode capacity of 0.1 C, and then charged at 2.7 V until the current reached 0.01 C. Discharge was performed up to 0.7 V at a current corresponding to 0.1 C of the positive electrode capacity, and the initial (initial) discharge capacity was measured. The battery was charged again to 2.7 V with a current corresponding to 0.1 C, and charged at 2.7 V until the current reached 0.01 C. Discharge was performed up to 0.7 V at a current corresponding to 2.0 C of the positive electrode capacity, and the discharge capacity at a high current was measured. The initial measurement was performed at 25 ° C. The results are shown in Table 1. The discharge capacity was indicated by an index with the initial (initial) discharge capacity of Comparative Example 1 being 100. Further, the discharge capacity retention ratio was determined by the following equation.
Discharge capacity retention ratio (%) = discharge capacity at 2.0 C (mAh) / discharge capacity at 0.1 C (mAh)

The electrolytes of the non-aqueous electrolytes (1) to (4) of Examples 1 to 4 were 10 times shorter than the non-aqueous electrolytes (5) and (6) of Comparative Examples 1 and 2 until the start of combustion. Flame-retardant for as long as seconds.
Further, as shown in Table 1, the non-aqueous electrolytes (1) to (4) of Examples 1 to 4 had a better discharge capacity retention ratio than the non-aqueous electrolyte (5) of Comparative Example 1. is there. Although the battery performance of the non-aqueous electrolyte (6) of Comparative Example 2 is comparable to that of the battery, the non-aqueous electrolytes (1) to (4) of Examples 1 to 4 are preferable in consideration of the flammability of the electrolyte. I understand.
The electrolyte solution obtained by diluting the complex of the chain ether compound and the lithium salt of the present invention with an ionic liquid achieves both the flame retardancy of the electrolyte solution and the discharge capacity retention ratio, and is suitable for use in energy devices, particularly lithium ion secondary batteries. It is suitable as a water electrolyte component.

Claims (5)

(A) and chain ether compounds represented by the following general formula (I), and (B) a lithium salt, a nonaqueous electrolytic solution diluted with (C) an ionic liquid,
(B) the lithium salt is lithium bis (fluorosulfonyl) imide,
(C) The non-aqueous electrolytic solution, wherein the anion of the ionic liquid is N (SO ₂ F) ₂ ⁻ .

(In the general formula (I), R ₁ and R ₃ each represent an alkyl group having 1 to 4 carbon atoms, and R ₂ represents an alkylene having 2 to 4 carbon atoms constituting a main chain having 2 to 4 carbon atoms. Represents a group, and may have a substituent, and n is an integer of 1 to 5.)   The non-aqueous electrolyte according to claim 1, wherein n of the chain ether compound represented by the general formula (I) is 2 to 4. 3. The non-aqueous electrolyte according to claim ₁ , wherein R ₁ of the chain ether compound represented by the general formula (I) is a methyl group. 4.   (C) the cation of the ionic liquid is at least one selected from the group consisting of a chain quaternary ammonium cation, a piperidinium cation, a pyrrolidinium cation, and an imidazolium cation. Item 4. The non-aqueous electrolyte according to any one of Items 1 to 3. A lithium ion secondary battery using the non-aqueous electrolyte according to claim 1.