JP2010146740A - Electrolytic solution - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide electrolytic solution with well-balanced properties of a boiling point and viscosity (solubility) holding a high oxidation resistance. <P>SOLUTION: The electrolytic solution comprises a solvent for dissolving electrolytic salt (I), which includes fluorinated linear ether with a boiling point of 90°C or higher, represented by an expression (A): Rf-O-R (where Rf denotes a fluorinated alkyl group with two or three carbon atoms, and R denotes an alkyl group with 4 to 6 carbon atoms) and non-fluorinated cyclic carbonate (B), and electrolytic salt (II). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrolytic solution suitable for an electrochemical device such as a lithium ion secondary battery and a novel fluorine-containing chain ether used therefor.

  As solvents for dissolving electrolyte salts for electrochemical devices such as lithium ion secondary batteries, carbonates such as ethylene carbonate, propylene carbonate, and dimethyl carbonate are widely used.

  Hydrocarbon ethers are known to have the effect of improving the rate characteristics of lithium ion secondary batteries, but on the other hand, they have a problem of low oxidation resistance.

  Therefore, attempts have been made to use fluorine-containing ethers in order to improve oxidation resistance. Furthermore, hydrocarbon solvents also have problems in terms of safety (nonflammability and flame retardancy), and in order to increase such safety, it has been proposed to add a fluorinated chain ether.

Fluorine-containing chain ether takes a structure of R ¹ -O-R ^2, R ¹ and the type R ² is either a fluorine-containing alkyl group, either one is a fluorine-containing alkyl group of R ¹ and R ² Divided into types.

Type of fluorine-containing chain ether R ¹ and R ² are both a fluorine-containing alkyl group of the former are those low compatibility low addition dissolving an electrolyte salt with other solvents, electrolytes for secondary batteries The liquid solvent is not always sufficient when aiming at further heat resistance and oxidation resistance.

As the type of fluorine-containing chain ether in which only ^{one of the} latter R ¹ and R ² is a fluorine-containing alkyl group, those described in Patent Documents 1 to 6 are known.

Patent Document 1 includes a general formula:
^{R 1 -O- (R 3 -O)} n -R 2
(R ^{1 to} R ³ are the same or different and are a C ^{1 to} C ⁶ linear or branched monovalent or divalent hydrocarbon group, or a linear or branched monovalent or divalent group containing one or more fluorine atoms. In which at least one of R ^{1 to} R ³ contains one or more fluorine atoms), specifically, HCF ₂ CF ₂ —O—C ₄ H ₉ is exemplified.

Patent Document 2 discloses a fluorine-containing chain ether represented by the formula: C _m F _{2m + 1} —O—C _n H _{2n + 1} (m = 2 to 8, n = 1 to 5), Specific examples include C ₃ F ₇ —O—CH ₃ and C ₃ F ₇ —O—C ₂ H ₅ .

Patent Document 3 shows the formula: R ¹ —O—R ² (R ¹ is an alkyl group having 2 or less carbon atoms or a halogen-substituted alkyl group, and R ² is a halogen-substituted alkyl group having 2 to 10 carbon atoms). Fluorine-containing chain ethers are described, and pentafluoropropyl methyl ether is used in the examples.

Patent Document 4 discloses a fluorine-containing chain ether represented by the formula: C _n F _m OR (R is an alkyl group, n is 1 to 10, m is 2n + 1, and the H / F ratio is 2/3 or less). Specific examples include C ₄ F ₉ —O—CH ₃ and C ₄ F ₉ —O—C ₂ H ₅ .

Patent Document 5 discloses a fluorine-containing chain ether represented by the formula: CF ₃ CH ₂ —O—C _n H 2 _{n + 1} (n = 1 to 2). As a specific example, CF ₃ CH ₂ -O-C ₂ H ₅ is mentioned.

Patent Document 6 discloses the formula: R ¹ —ORf ¹ (wherein R ¹ is an optionally branched alkyl group having 1 to 4 carbon atoms, Rf ¹ is a fluorinated alkyl having 5 to 10 carbon atoms). fluorine-containing chain ether is shown represented by _{group), C 6 F 13 -O-} CH 3 and _{C 6 F 13 -O-C 2} H 5 are exemplified as specific examples.

JP-A-8-37024 Japanese Patent Laid-Open No. 11-307123 Japanese Patent No. 3218982 JP 2001-93572 A JP 2002-343424 A JP 2006-49037 A

  The fluorine-containing chain ether of the type in which only one of those specifically described in Patent Documents 1 to 6 is a fluorine-containing alkyl group has relatively high oxidation resistance, but improves the solubility of the electrolyte salt, In order to keep the viscosity low, the carbon number tends to be reduced. However, when the number of carbon atoms is reduced, the boiling point is lowered and the flammability is also lowered, so that use at a recently required high temperature (90 ° C. or higher) is limited. On the other hand, if the boiling point is to be raised, the number of carbon atoms must be increased, so that the solubility becomes low and the viscosity becomes high.

For example, HCF ₂ CF ₂ —O—C ₄ H ₉ (carbon number 6) described in Patent Document 1, C ₆ F ₁₃ —O—CH ₃ (carbon number 7) and C ₆ F ₁₃ — described in Patent Document 6 are used. In O—C ₂ H ₅ (carbon number 8), the boiling point exceeds 90 ° C., but the solubility is low and the viscosity is high.

On the other hand, C ₃ F ₇ —O—CH ₃ (carbon number 4), C ₃ F ₇ —O—C ₂ H ₅ (carbon number 5) described in Patent Document 2, and pentafluoropropylmethyl described in Patent Document 3 ether (4 carbon _{atoms), CF 3 CH 2 -O-} C 2 H 5 described in Patent Document 5 (4 carbon atoms), although a high viscosity is low solubility, becomes lower than a boiling point of 90 ° C. .

  As a result of intensive research on these points, the present inventors have limited the number of carbon atoms on the fluorine-containing alkyl group side, and by combining the adjustment of the carbon number on the alkyl group side with a branched structure, the narrowness is limited. A range of fluorine-containing chain ethers has been found to have a good balance between boiling point and viscosity (solubility) while maintaining high oxidation resistance, and the present invention has been completed.

That is, the present invention
(I) (A) Formula (A):
Rf-O-R
(Wherein Rf is a fluorine-containing alkyl group having 2 or 3 carbon atoms, R is an alkyl group having 4 to 6 carbon atoms) and has a boiling point of 90 ° C. or higher, and (B) The present invention relates to a solvent for dissolving an electrolyte salt containing a fluorinated cyclic carbonate, and (II) an electrolyte solution containing an electrolyte salt.

  In the formula (A), R is preferably a C 4-6 alkyl group containing a branched chain from the viewpoint of lower viscosity.

  Further, the boiling point of the fluorine-containing chain ether (A) is preferably 90 ° C. or higher from the viewpoint of good storage test results at a high temperature (90 ° C. or higher).

More specifically, the fluorine-containing chain ether (A) includes HCF ₂ CF ₂ —O—CH ₂ CH ₂ CH ₂ CH ₃ , HCF ₂ CF ₂ —O—CH ₂ CH (CH ₃ ) ₂ and HCF _2. At least one selected from the group consisting of CF ₂ —O—CH ₂ C (CH ₃ ) ₃ is particularly preferred because it has a boiling point of 90 ° C. or higher and low viscosity.

  As the non-fluorinated cyclic carbonate (B), at least one selected from the group consisting of ethylene carbonate, vinylene carbonate, propylene carbonate, and fluoroethylene carbonate is preferable from the viewpoint of good cycle characteristics.

  In the electrolyte salt dissolving solvent (I), the fluorine-containing chain ether (A) is contained in an amount of 1 to 60% by volume and the non-fluorinated cyclic carbonate (B) is contained in an amount of 5 to 50% by volume based on the whole solvent (I). It is preferable from the viewpoint of good cycle characteristics and load characteristics.

  The electrolyte salt-dissolving solvent (I) includes, as other electrolyte salt-dissolving solvent (C), a fluorine-containing chain ether (C1) other than the fluorine-containing chain ether (A), a fluorine-containing ester (C2), It may contain at least one solvent selected from the group consisting of fluorine carbonate (C3), fluorine-containing lactone (C4), and non-fluorine chain carbonate (C5).

One electrolyte salt (II) is preferably one or more of LiPF ₆ , LiBF ₄ , LiN (SO ₂ CF ₃ ) ₂ , and LiN (SO ₂ CF ₂ CF ₃ ) ₂ .

  Such an electrolytic solution of the present invention is particularly useful for a lithium ion secondary battery, and by using the electrolytic solution of the present invention, an electrochemical device, a lithium ion secondary battery, specifically, a positive electrode, a negative electrode, and A lithium ion secondary battery including a separator can be provided.

  According to the present invention, it is possible to provide a solvent for dissolving an electrolyte salt with a good balance between boiling point and viscosity (solubility) while maintaining high oxidation resistance. In addition, phase separation does not occur even at low temperatures, and flame retardancy is achieved. In addition, it is possible to provide an electrolytic solution suitable for an electrochemical device such as a lithium ion secondary battery having excellent nonflammability, high solubility of electrolyte salt, large discharge capacity, and excellent charge / discharge cycle characteristics.

  The electrolytic solution of the present invention contains an electrolyte salt dissolving solvent (I) and an electrolyte salt (II) having a specific composition. Hereinafter, each component will be described.

(I) Solvent for dissolving electrolyte salt The solvent (I) for dissolving electrolyte salt used in the present invention has the formula (A):
Rf-O-R
(Wherein Rf is a fluorine-containing alkyl group having 2 or 3 carbon atoms, R is an alkyl group having 4 to 6 carbon atoms), and the fluorine-containing chain ether (A) having a boiling point of 90 ° C. or higher and non-fluorine A cyclic carbonate (B).

(A) Fluorinated chain ether In the formula (A), the fluorinated alkyl group Rf is a fluorinated alkyl group having 2 or 3 carbon atoms, specifically, CF ₃ CF ₂ —, HCF ₂ CF ₂ —, H ₂ CFCF ₂ —, CH ₃ CF ₂ —, CF ₃ CFH—, CF ₃ CH ₂ —, HCF ₂ CFH—, HCF ₂ CH ₂ —, H ₂ CFCFH—, and H ₂ CFCH ₂ —.

When the number of fluorine atoms (fluorine content) decreases, the effects of fluorination, that is, the effect of improving oxidation resistance, the effect of improving flame retardancy, etc. tend to decrease. From these points, preferably _{CF 3 CF 2 -, HCF 2} CF 2 -, H 2 CFCF 2 -, CH 3 CF 2 -, CF 3 CFH-, CF 3 CH 2 - and the like. Further, those containing HCF ₂ — or CF ₃ CF ₂ — at the end are excellent in polarizability and can give a fluorine-containing chain ether having a high boiling point (100 ° C. or higher), so that HCF ₂ CF ₂ — and CF are particularly suitable. ₃ CF ₂ - is preferred.
In the formula (A), the alkyl group R is an alkyl group having 4 to 6 carbon atoms.

The alkyl group of 4 carbon atoms, for example, addition of CH ₂ CH ₂ CH ₂ CH ₃ is a straight-chain alkyl _{groups, -CH 2 CH 2 C (CH} 3) H 2, -CH 2 CH 2 C (CH 3) ₂ H, -CH ₂ CH ₂ C (CH ₃ ) ₃ , -CH ₂ C (CH ₃ ) HCH ₃ , -CH ₂ C (CH ₃ ) ₂ CH ₃ , -C (CH ₃ ) HCH ₂ CH ₃ ,- branched chain alkyl groups such as _{C (CH 3) 2 CH 2} CH 3 and the like.

The alkyl group of 5-6 carbon atoms, for example _{-CH 2 CH 2 CH (CH 3} ) 2, -CH 2 CH 2 C (CH 3) 3, -CH (CH 3) CH 2 CH 2 CH 3, - _{C (CH 3) 2 CH 2} CH 2 CH 3, -CH (CH 3) CH (CH 3) CH 2 CH 3, -CH (CH 3) CH (CH 3) CH 3, -CH 2 C (CH 3 _{) 2 CH 3, -CH 2 C} (CH 3) 2 branched chain alkyl groups such as _{CH 2 CH 3; -CH 2 CH} 2 CH 2 CH 2 CH 3, -CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 And a straight chain alkyl group.

Among these alkyl groups R, CH ₂ CH ₂ CH ₂ CH ₃ is preferable from the viewpoint of solubility, and —CH ₂ CH (CH ₃ ) ₂ , − from the point that viscosity is lowered and solubility is increased. Branched alkyl groups such as CH ₂ CH ₂ CH (CH ₃ ) ₂ and —CH ₂ CH ₂ C (CH ₃ ) ₃ are preferred, and in particular, —CH ₂ CH (CH ₃ ) ₂ has a boiling point of 90 ° C. or higher and has a viscosity. Since it is low, the storage test results and load characteristics are good.

  When the total carbon number of the fluorine-containing chain ether (A) is less than 6, the boiling point of the fluorine-containing ether becomes too low, and when the total carbon number exceeds 8, the solubility of the electrolyte salt decreases, The compatibility with the solvent also begins to have an adverse effect, and the rate characteristic is reduced because the viscosity increases. In particular, when Rf has 2 or 3 carbon atoms and R contains a branched chain and has 4 to 6 carbon atoms, it is advantageous in that it has a high boiling point and excellent viscosity and rate characteristics.

  Moreover, since the fluorine-containing chain ether (A) contains a fluorine atom, the electrolyte solution of the present invention containing the fluorine-containing chain ether (A) has improved nonflammability.

  More preferably, the fluorine content of the fluorine-containing chain ether (A) is 5% by mass or more, more preferably 10% by mass or more, particularly preferably 15% by mass or more, and the upper limit is 60% by mass, further 40% by mass. Is preferred. When it has a fluorine content in this range, it is particularly excellent in the balance between incombustibility and compatibility. In the present invention, the fluorine content is a value calculated by {(number of fluorine atoms × 19) / molecular weight} × 100 (%).

Preferable specific fluorine-containing chain ether (A) is HCF ₂ CF ₂ —O—CH ₂ CH ₂ CH ₂ CH ₃ (boiling point: 91.0 ° C., viscosity from the viewpoint of good battery characteristics and storage characteristics. : 0.81 mPa · s), HCF ₂ CF ₂ —O—CH ₂ CH (CH ₃ ) ₂ (boiling point: 91.7 ° C., viscosity: 0.76 mPa · s), and HCF ₂ CF ₂ —O—CH ₂ C (CH ₃ ) ₃ (boiling point: 99.0 ° C., viscosity: 0.70 mPa · s) is preferred.

  Content of a fluorine-containing chain | strand-shaped ether (A) is 1-60 volume% as content with respect to the whole solvent (I). If the amount is too large, the solubility of the electrolyte salt may decrease, and layer separation may occur. If the amount is too small, the low temperature characteristics (low temperature stability) will decrease, and the flame retardancy will also decrease. The balance of battery characteristics is lost. A preferred upper limit is 40% by volume from the viewpoint of good compatibility with other solvents and solubility of the electrolyte salt, and a preferred lower limit is 5% by volume from the viewpoint of maintaining low temperature characteristics and maintaining flame retardancy. Is 20% by volume.

(B) Non-fluorinated cyclic carbonate Among non-fluorinated cyclic carbonates (B), ethylene carbonate (EC), vinylene carbonate (VC), propylene carbonate (PC), and fluoroethylene carbonate (FEC) have a high dielectric constant, In addition, the solubility of the electrolyte salt is particularly excellent, which is preferable for the electrolytic solution of the present invention. Moreover, when using a graphite-type material for a negative electrode, a stable film can also be formed on a negative electrode. Butylene carbonate, vinyl ethylene carbonate, and the like can also be used.

  Content of a non-fluorine-type cyclic carbonate (B) is 5-50 volume% as content with respect to the whole solvent (I). In the solvent (I) system used in the present invention, if the amount of the non-fluorinated cyclic carbonate (B) is excessive, it may be contained in a low temperature atmosphere (for example, −30 to −20 ° C.) such as a winter outdoor temperature or a freezer room temperature. Fluorine chain ether (A) causes layer separation. In this respect, the preferable upper limit is 40% by volume, and further 30% by volume. On the other hand, when the amount is too small, the solubility of the electrolyte salt (II) of the solvent is lowered, and a desired electrolyte concentration (0.8 mol / liter or more) cannot be achieved.

(C) Solvent for dissolving other electrolyte salt In the present invention, the solvent for dissolving electrolyte salt (I) is a fluorine-containing chain other than the above-mentioned fluorine-containing chain ether (A) as another solvent for dissolving electrolyte salt (C). And at least one solvent selected from the group consisting of a fluorinated ether (C1), a fluorinated ester (C2), a fluorinated carbonate (C3), a fluorinated lactone (C4), and a non-fluorinated chain carbonate (C5). May be.

  However, it is necessary to make it the combination and quantity which do not prevent the solution of the subject of this invention.

(C1) Fluorinated chain ether other than the fluorinated chain ether (A) The fluorinated chain ether (C1) includes a fluorinated chain ether (C1) in which both alkyl groups are both fluorinated alkyl groups. -1) and a fluorine-containing ether (C1-2) in which only one alkyl group is a fluorine-containing alkyl group and does not satisfy the formula (A).

Examples of the fluorine-containing chain ether (C1-1) in which both alkyl groups are fluorine-containing alkyl groups include, for example, the formula (C1-1):
Rf ¹ -O-Rf ²
Wherein Rf ¹ and Rf ² are the same or different, Rf ¹ is a fluorine-containing alkyl group having 3 to 6 carbon atoms, and Rf ² is a fluorine-containing alkyl group having 2 to 6 carbon atoms. Examples include chain ethers. Specific examples of the fluorine-containing chain ether (C1-1) include HCF ₂ CF ₂ CH ₂ OCF ₂ CFHCF ₃ , CF ₃ CF ₂ CH ₂ OCF ₂ CFHCF ₃ , HCF ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H, CF ₃ CF ₂ CH ₂ OCF ₂ CF ₂ H and the like can be exemplified.

  When the fluorine-containing chain ether (C1) is blended, the effects of improving nonflammability and oxidation resistance can be expected.

  As the fluorine-containing ether (C1-2) in which only one alkyl group is a fluorine-containing alkyl group and does not satisfy the formula (A), fluorine-containing chain ethers described in Patent Documents 1 to 6 are shown together with specific examples. can give.

  When blending the fluorine-containing chain ether (C1-2), an effect of improving load characteristics can be expected.

(C2) Fluorine-containing ester As the fluorine-containing ester (C2), the formula (C2):
Rf ³ COORf ⁴
(Wherein Rf ³ is a fluorine-containing alkyl group having 1 to 2 carbon atoms, Rf ⁴ is a fluorine-containing alkyl group having 1 to ⁴ carbon atoms), the flame-retardant property is high, and other solvents From the viewpoint of good compatibility and oxidation resistance.

Examples of Rf ³ include CF _3- , CF ₃ CF _2- , HCF ₂ CF _2- , HCF _2- , CH ₃ CF _2- , CF ₃ CH _2- and the like, among them CF _3- , CF ₃ CF ₂ - are particularly preferred from the viewpoint that the rate characteristics favorable.

The Rf ^4, for example _{-CF 3, -CF 2 CF 3,} -CH (CF 3) 2, -CH 2 CF 3, -CH 2 CH 2 CF 3, -CH 2 CF 2 CFHCF 3, -CH 2 C ₂ F ₅ , —CH ₂ CF ₂ CF ₂ H, —CH ₂ CH ₂ C ₂ F ₅ , —CH ₂ CF ₂ CF ₃ , —CH ₂ CF ₂ CF ₂ CF _{3 and the} like can be exemplified, and in particular, —CH ₂ CF ₃ , —CH (CF ₃ ) ₂ —CH ₂ C ₂ F ₅ , and —CH ₂ CF ₂ CF ₂ H are particularly preferable from the viewpoint of good compatibility with other solvents.

Specific examples of the fluorine-containing ester (C2) include, for example, CF ₃ C (═O) OCH ₂ CF ₃ , CF ₃ C (═O) OCH ₂ CH ₂ CF ₃ , and CF ₃ C (═O) OCH ₂ C _2. One or more of F ₅ , CF ₃ C (═O) OCH ₂ CF ₂ CF ₂ H, CF ₃ C (═O) OCH (CF ₃ ) _{2 and the} like can be exemplified, and among them, CF ₃ C (= _{O) OCH 2 C 2 F 5} , CF 3 C (= O) OCH 2 CF 2 CF 2 H, CF 3 C (= O) OCH 2 CF 3, CF 3 C (= O) OCH (CF 3) 2 is In view of good compatibility with other solvents and rate characteristics, it is particularly preferable.

  When blending the fluorinated ester (C2), the effect of improving oxidation resistance can be expected.

(C3) Fluorinated carbonate Examples of the fluorinated carbonate (C3) include a fluorinated chain carbonate (C3-1) and a fluorinated cyclic carbonate (C3-2).

As the fluorine-containing chain carbonate (C3-1), for example, formula (C3-1):
Rf ⁵ OCOORf ⁶
(Wherein Rf ⁵ and Rf ⁶ are the same or different, and the fluorine-containing alkyl group having 1 to 4 carbon atoms) has high flame retardancy and good rate characteristics and oxidation resistance. It is preferable from the point.

Rf ⁵ or as the Rf ^6, for example _{-CF 3, -CF 2 CF 3,} -CH (CF 3) 2, CF 3 CH 2 -, C 2 F 5 CH 2 -, HCF 2 CF 2 CH 2 -, CF ₂ CFHCF ₂ CH ₂ — and the like can be exemplified, among which CF ₃ CH ₂ — and C ₂ F ₅ CH ₂ — are particularly preferable from the viewpoints of high flame retardancy and good rate characteristics and oxidation resistance.

Specific examples of the fluorine-containing chain carbonate (C3-1) include, for example, CF ₃ CH ₂ OCOOCH ₂ CF ₃ , CF ₃ CF ₂ CH ₂ OCOOCH ₂ CF ₂ CF ₃ , CF ₃ CF ₂ CH ₂ OCOOCH ₃ , and CF _3. One or two or more kinds of fluorine-containing chain carbonates such as CH ₂ OCOOCH ₃ can be exemplified, among which CF ₃ CH ₂ OCOOCH ₂ CF ₃ and CF ₃ CF ₂ CH ₂ OCOOCH ₂ CF ₂ CF ₃ are suitable for viscosity. The flame retardancy, compatibility with other solvents, and rate characteristics are particularly preferable. Further, for example, compounds described in JP-A-06-21992, JP-A-2000-327634, JP-A-2001-256983 and the like can also be exemplified.

  When blending the fluorine-containing chain carbonate (C3-1), an effect of improving oxidation resistance can be expected.

（式中、Ｘ¹〜Ｘ⁴は同じかまたは異なり、いずれも−Ｈ、−Ｆ、−ＣＦ₃、−ＣＦ₂Ｈ、−ＣＦＨ₂、−ＣＦ₂ＣＦ₃、−ＣＨ₂ＣＦ₃または−ＣＨ₂ＯＣＨ₂ＣＦ₂ＣＦ₃；ただし、Ｘ¹〜Ｘ⁴の少なくとも１つは−Ｆ、−ＣＦ₃、−ＣＦ₂ＣＦ₃、−ＣＨ₂ＣＦ₃または−ＣＨ₂ＯＣＨ₂ＣＦ₂ＣＦ₃である）
で示されるものである。 The fluorine-containing cyclic carbonate (C3-2) is, for example, a formula (C3-2):

(Wherein, X ^{1 to} X ⁴ are the same or different, and all are —H, —F, —CF ₃ , —CF ₂ H, —CFH ₂ , —CF ₂ CF ₃ , —CH ₂ CF ₃ or —CH ₂ OCH ₂ CF ₂ CF ₃ ; provided that at least one of X ^{1 to} X ⁴ is —F, —CF ₃ , —CF ₂ CF ₃ , —CH ₂ CF _3, or —CH ₂ OCH ₂ CF ₂ CF ₃ . )
It is shown by.

X ¹ to X ⁴ _{are, -H, -F, -CF 3,} -CF 2 H, -CFH 2, -CF 2 CF 3, a -CH ₂ CF ₃ or _{-CH 2 OCH 2 CF 2 CF 3} , -F, -CF ₃ , and -CH ₂ CF ₃ are preferred from the viewpoint of good dielectric constant and viscosity and excellent compatibility with other solvents.

In Formula (C3-2), when at least one of X ^{1 to} X ⁴ is —F, —CF ₃ , —CF ₂ CF ₃ , —CH ₂ CF _3, or —CH ₂ OCH ₂ CF ₂ CF ₃ , H, -F, -CF ₃ , -CF ₂ H, -CFH ₂ , -CF ₂ CF ₃ , -CH ₂ CF ₃ or -CH ₂ OCH ₂ CF ₂ CF ₃ are only in one place of X ^{1 to} X ⁴ Or may be substituted at a plurality of locations. Among these, from the point that the dielectric constant and oxidation resistance are good, the number of substitution sites is preferably 1 to 2.

  The fluorine content of the fluorine-containing cyclic carbonate (C3-2) is preferably 20 to 50% by mass and more preferably 30 to 50% by mass from the viewpoint of good dielectric constant and oxidation resistance.

  Among the fluorine-containing cyclic carbonates (C3-2), the lithium in the present invention is particularly advantageous in that it has excellent characteristics such as a high dielectric constant and a high withstand voltage, and also has good solubility in electrolyte salts and a reduction in internal resistance. From the viewpoint of improving the characteristics as an ion secondary battery, the following is preferable.

などがあげられる。 As the fluorine-containing cyclic carbonate (C3-2) having high withstand voltage and good solubility of the electrolyte salt, for example,

Etc.

なども使用できる。 In addition, as the fluorine-containing cyclic carbonate (C3-2),

Etc. can also be used.

  By including the fluorine-containing cyclic carbonate (C3-2), effects such as an action of increasing the dielectric constant, oxidation resistance, and improvement of ion conductivity can be obtained.

（式中、Ｘ⁵〜Ｘ¹⁰は同じかまたは異なり、いずれも−Ｈ、−Ｆ、−Ｃｌ、−ＣＨ₃または含フッ素アルキル基；ただし、Ｘ⁵〜Ｘ¹⁰の少なくとも１つは含フッ素アルキル基である）
で示される含フッ素ラクトンがあげられる。 (C4) Fluorine-containing lactone As the fluorine-containing lactone (C4), for example, the formula (C4):

(In the formula, X ^{5 to} X ¹⁰ are the same or different and all are —H, —F, —Cl, —CH ₃ or a fluorine-containing alkyl group; provided that at least one of X ^{5 to} X ¹⁰ is a fluorine-containing alkyl. Base)
The fluorine-containing lactone shown by these is mention | raise | lifted.

Examples of the fluorine-containing alkyl group in X ^{5 to} X ¹⁰ include —CFH ₂ , —CF ₂ H, —CF ₃ , —CH ₂ CF ₃ , —CF ₂ CF ₃ , —CH ₂ CF ₂ CF ₃ , —CF (CF ₃ ) _{2 and the} like are mentioned, and —CH ₂ CF ₃ and —CH ₂ CF ₂ CF ₃ are preferred from the viewpoint of high oxidation resistance and an effect of improving safety.

If at least one Tsuga含fluoroalkyl group ^{X 5 ~X 10, -H, -F} , -Cl, -CH 3 or a fluorine-containing alkyl group is substituted only at one place of the X ⁵ to X ¹⁰ Alternatively, a plurality of locations may be substituted. Preferably, the number of the electrolyte salt is 1 to 3 and preferably 1 to 2 from the viewpoint of good solubility of the electrolyte salt.

Although the substitution position of the fluorine-containing alkyl group is not particularly limited, X ⁷ and / or X ⁸ is preferably a fluorine-containing alkyl group, particularly —CH ₂ CF ₃ , particularly X ⁷ or X ⁸ because the synthesis yield is good. it is preferably -CH ₂ CF ₂ CF _3. X ^{5 to} X ¹⁰ other than the fluorine-containing alkyl group are —H, —F, —Cl or —CH ₃ , and —H is particularly preferable from the viewpoint of good solubility of the electrolyte salt.

（式中、ＡおよびＢはいずれか一方がＣＸ¹⁶Ｘ¹⁷（Ｘ¹⁶およびＸ¹⁷は同じかまたは異なり、いずれも−Ｈ、−Ｆ、−Ｃｌ、−ＣＦ₃、−ＣＨ₃または水素原子がハロゲン原子で置換されていてもよくヘテロ原子を鎖中に含んでいてもよいアルキレン基）であり、他方は酸素原子；Ｒｆ³はエーテル結合を有していてもよい含フッ素アルキル基または含フッ素アルコキシ基；Ｘ¹¹およびＸ¹²は同じかまたは異なり、いずれも−Ｈ、−Ｆ、−Ｃｌ、−ＣＦ₃または−ＣＨ₃；Ｘ¹³〜Ｘ¹⁵は同じかまたは異なり、いずれも−Ｈ、−Ｆ、−Ｃｌまたは水素原子がハロゲン原子で置換されていてもよくヘテロ原子を鎖中に含んでいてもよいアルキル基；ｎ＝０または１）
で示される含フッ素ラクトン（Ｃ４−１）などもあげられる。 Examples of the fluorine-containing lactone (C4) include those represented by the formula (C4-1):

(In the formula, either one of A and B is CX ¹⁶ X ¹⁷ (X ¹⁶ and X ¹⁷ are the same or different, and each is —H, —F, —Cl, —CF ₃ , —CH ₃ or a hydrogen atom) An alkylene group which may be substituted with a halogen atom and may contain a hetero atom in the chain), the other is an oxygen atom; Rf ³ is a fluorine-containing alkyl group or fluorine-containing group which may have an ether bond An alkoxy group; X ¹¹ and X ¹² are the same or different, and all are —H, —F, —Cl, —CF ₃ or —CH ₃ ; X ^{13 to} X ¹⁵ are the same or different, and both are —H, — F, -Cl or an alkyl group in which a hydrogen atom may be substituted with a halogen atom and may contain a hetero atom in the chain; n = 0 or 1)
And a fluorine-containing lactone (C4-1) represented by

（式中、Ａ、Ｂ、Ｒｆ³、Ｘ¹¹、Ｘ¹²およびＸ¹³は式（Ｃ４−１）と同じである）
で示される５員環構造が、合成が容易である点、化学的安定性が良好な点から好ましくあげられ、さらには、ＡとＢの組合せにより、式：

（式中、Ｒｆ³、Ｘ¹¹、Ｘ¹²、Ｘ¹³、Ｘ¹⁶およびＸ¹⁷は式（Ｃ４−１）と同じである）
で示される含フッ素ラクトンと、
式：

（式中、Ｒｆ³、Ｘ¹¹、Ｘ¹²、Ｘ¹³、Ｘ¹⁶およびＸ¹⁷は式（Ｃ４−１）と同じである）
で示される含フッ素ラクトンがある。 As the fluorine-containing lactone (C4) represented by the formula (C4-1), the formula:

(In the formula, A, B, Rf ³ , X ¹¹ , X ¹² and X ¹³ are the same as those in formula (C4-1)).
Is preferable from the viewpoint that synthesis is easy and chemical stability is good, and further, a combination of A and B gives a formula:

^{(Wherein, Rf 3, X 11, X} 12, X 13, X 16 and X ¹⁷ are the same as the formula (C4-1))
A fluorine-containing lactone represented by
formula:

(In the formula, Rf ³ , X ¹¹ , X ¹² , X ¹³ , X ¹⁶ and X ¹⁷ are the same as those in formula (C4-1)).
There is a fluorine-containing lactone represented by

が好ましい。 Among these, the point that the excellent characteristics such as high dielectric constant and high withstand voltage can be exhibited especially, and the characteristics as the electrolytic solution in the present invention are improved in that the solubility of the electrolyte salt and the reduction of internal resistance are good. From

Is preferred.

なども使用できる。 Other,

Etc. can also be used.

  By including the fluorine-containing lactone (C4), effects such as improvement of ionic conductivity, improvement of safety, and improvement of stability at high temperatures can be obtained.

(C5) Non-fluorine chain carbonate As the non-fluorine chain carbonate (C5), for example, CH ₃ CH ₂ OCOOCH ₂ CH ₃ (diethyl carbonate: DEC), CH ₃ CH ₂ OCOOCH ₃ (ethyl methyl carbonate: EMC) ), CH ₃ OCOOCH ₃ (dimethyl carbonate: DMC), CH ₃ OCOOCH ₂ CH ₂ CH ₃ (methylpropyl carbonate) and other hydrocarbon chain carbonates. Of these, DEC, EMC, and DMC are preferred because of their high boiling point, low viscosity, and good low temperature characteristics.

  By including the non-fluorinated chain carbonate (C5), the effect of improving the load characteristics due to the low temperature characteristics and viscosity reduction can be obtained.

(D) Other additives In the present invention, the components (A) to (B), and if necessary, the volume ratio of the component (C) are not destroyed, and incombustible (flame retardant) within the range not impairing the effects of the present invention. ) Other additives such as an agent, a surfactant, a high dielectric additive, a cycle characteristic and rate characteristic improver and an overcharge inhibitor may be blended.

  Examples of the incombustible (incombustible) agent for improving incombustibility and flame retardancy include phosphate esters. Ignition can be prevented at a compounding amount of 1 to 10% by volume in the solvent (I) for dissolving the electrolyte salt.

  Examples of phosphate esters include fluorine-containing alkyl phosphate esters, non-fluorine-based alkyl phosphate esters, and aryl phosphate esters. However, fluorine-containing alkyl phosphate esters contribute to the incombustibility of electrolytes in a small amount. It is preferable because of its non-flammable effect.

  Examples of the fluorine-containing alkyl phosphate ester include fluorine-containing dialkyl phosphate esters described in JP-A No. 11-233141, cyclic alkyl phosphate esters described in JP-A No. 11-283669, and fluorine-containing trialkyl phosphate esters. Examples thereof include alkyl phosphate esters.

For the purpose of improving flame retardancy, flame retardants such as (CH ₃ O) ₃ P═O and (CF ₃ CH ₂ O) ₃ P═O can also be added.

  Further, the surfactant may be blended in order to improve capacity characteristics and rate characteristics.

  As the surfactant, any of a cationic surfactant, an anionic surfactant, a nonionic surfactant, and an amphoteric surfactant may be used, but the fluorine-containing surfactant has good cycle characteristics and rate characteristics. It is preferable from the point.

For example, the formula:
Rf ⁷ COO ^- M ⁺
(Wherein Rf ⁷ is a fluorine-containing alkyl group which may contain an ether bond having 3 to 10 carbon atoms; M ⁺ is Li ⁺ , Na ⁺ , K ⁺ or NHR ′ ₃ ⁺ (R ′ is the same or different) , Each of which is H or an alkyl group having 1 to 3 carbon atoms).
Rf ⁸ SO ₃ ^- M ⁺
(Wherein Rf ⁸ is a fluorine-containing alkyl group which may contain an ether bond having 3 to 10 carbon atoms; M ⁺ is Li ⁺ , Na ⁺ , K ⁺ or NHR ′ ₃ ⁺ (R ′ is the same or different) Are preferably H or an alkyl group having 1 to 3 carbon atoms).

  The blending amount of the surfactant is preferably 0.01 to 2% by mass with respect to the entire electrolyte salt dissolving solvent (I) from the viewpoint of reducing the surface tension of the electrolytic solution without reducing the charge / discharge cycle characteristics. .

  Examples of the high dielectric additive include sulfolane, methyl sulfolane, γ-butyrolactone, γ-valerolactone, acetonitrile, propionitrile and the like.

  Examples of the overcharge preventing agent include hexafluorobenzene, fluorobenzene, cyclohexylbenzene, dichloroaniline, toluene and the like.

  Examples of the cycle characteristic and rate characteristic improver include methyl acetate, ethyl acetate, tetrahydrofuran, 1,4-dioxane and the like.

  The electrolyte salt dissolving solvent (I) can be prepared by mixing and uniformly dissolving the components (A) to (B) and, if necessary, the components (C) to (D).

(II) Electrolyte salt Examples of the electrolyte salt (II) used in the electrolyte solution of the present invention include LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiPF ₆ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) _{2 and the} like, and LiPF ₆ , LiBF ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ or a combination thereof is particularly preferable from the viewpoint of good cycle characteristics.

  The concentration of the electrolyte salt (II) is required to be 0.8 mol / liter or more, further 1.0 mol / liter or more in order to achieve the required battery characteristics. The upper limit is usually 1.5 mol / liter although it depends on the organic solvent (I) for dissolving the electrolyte salt.

  The electrolytic solution of the present invention described above includes, for example, electrolytic capacitors, electric double layer capacitors, batteries charged / discharged by charge transfer of ions, solid display elements such as electroluminescence, sensors such as current sensors and gas sensors, etc. Can be used for

  Among them, it is preferable to use as a positive electrode, a negative electrode, a separator, and a lithium ion secondary battery including the electrolytic solution of the present invention. In particular, the positive electrode active material used for the positive electrode is a cobalt-based composite oxide, nickel. Because at least one selected from the group consisting of manganese-based complex oxides, manganese-based complex oxides, iron-based complex oxides, and vanadium-based complex oxides provides a secondary battery with high energy density and high output. preferable.

An example of the cobalt-based composite oxide is LiCoO ₂ , an example of the nickel-based composite oxide is LiNiO ₂ , and an example of the manganese-based composite oxide is LiMnO ₂ . In addition, a CoNi composite oxide represented by LiCo _x Ni _1-x O ₂ (0 <x <1) or a CoMn composite oxide represented by LiCo _x Mn _1-x O ₂ (0 <x <1) _{and, LiNi x Mn 1-x O} 2 (0 <x <1), and complex oxides of NiMn represented by _{LiNi x Mn 2-x O 4} (0 <x <2), LiNi 1-xy Co x Mn A NiCoMn composite oxide represented by _y O ₂ (0 <x <1, 0 <y <1, 0 <x + y <1) may be used. In these lithium-containing composite oxides, a part of metal elements such as Co, Ni, and Mn may be substituted with one or more metal elements such as Mg, Al, Zr, Ti, and Cr. .

In addition, examples of the iron-based composite oxide include LiFeO ₂ and LiFePO ₄ , and examples of the vanadium-based composite oxide include V ₂ O ₅ .

  As the positive electrode active material, among the above complex oxides, a nickel complex oxide or a cobalt complex oxide is preferable because the capacity can be increased. In particular, in a small lithium ion secondary battery, it is desirable to use a cobalt-based composite oxide from the viewpoint of high energy density and safety.

  In the present invention, particularly when used in a large-sized lithium ion secondary battery for a hybrid vehicle or a distributed power source, a high output is required. Therefore, the particles of the positive electrode active material are mainly secondary particles. It is preferable to contain 0.5 to 7.0% by volume of fine particles having an average particle diameter of 40 μm or less and an average primary particle diameter of 1 μm or less.

  By containing fine particles having an average primary particle diameter of 1 μm or less, the contact area with the electrolytic solution is increased, and the diffusion of lithium ions between the electrode and the electrolytic solution can be accelerated, and the output performance can be improved. .

Examples of the negative electrode active material used for the negative electrode in the present invention include carbon materials, and also include metal oxides and metal nitrides into which lithium ions can be inserted. Examples of carbon materials include natural graphite, artificial graphite, pyrolytic carbons, cokes, mesocarbon microbeads, carbon fibers, activated carbon, and pitch-coated graphite. Metal oxides capable of inserting lithium ions include tin and Examples of the metal compound containing silicon include tin oxide and silicon oxide. Examples of the metal nitride include Li _2.6 Co _0.4 N.

  The separator that can be used in the present invention is not particularly limited, and is a microporous polyethylene film, a microporous polypropylene film, a microporous ethylene-propylene copolymer film, a microporous polypropylene / polyethylene bilayer film, a microporous polypropylene / polyethylene / Examples thereof include a polypropylene three-layer film.

  In addition, since the electrolytic solution of the present invention is nonflammable, it is particularly useful as an electrolytic solution for the above-described hybrid vehicle and a large-sized lithium ion secondary battery for a distributed power source. It is also useful as a non-aqueous electrolyte solution.

  Next, the present invention will be described with reference to synthesis examples and examples, but the present invention is not limited to these examples.

  The structural analysis of the fluorine-containing chain ether (A) was performed by NMR analysis and IR analysis, and the boiling point and viscosity were measured by the following method.

(NMR analysis)
Uses AC-300 manufactured by BRUKER.
¹⁹ F-NMR:
Measurement conditions: 282 MHz (trichlorofluoromethane = 0 ppm)
¹ H-NMR:
Measurement conditions: 300 MHz (tetramethylsilane = 0 ppm)

(boiling point)
The top temperature during atmospheric distillation is measured and the value is taken as the boiling point.

(Measurement of viscosity)
Using a vibration viscometer SV-10 manufactured by AND, the value at 25 ° C. is the viscosity.

Synthesis Example 1 (Fluorine-containing chain ether A1)
The inside of the stainless steel 3 L autoclave system was evacuated, potassium hydroxide (31 g: 0.55 mol) and butanol (406 g: 5.48 mol) were inhaled, and vacuum-nitrogen substitution was performed 10 times at room temperature. After evacuating the system, tetrafluoroethylene was injected at a pressure of 0.1 MPa, and the reaction system was heated to 45 ° C. After the internal temperature reached 45 ° C., tetrafluoroethylene was gradually added so that the reaction pressure was maintained at 0.3 to 0.8 MPa. The internal temperature was adjusted to maintain 45 to 90 ° C. When the amount of tetrafluoroethylene added reached 0.6 equivalent, the supply was stopped, and stirring was continued until no pressure drop of tetrafluoroethylene was observed. After completion of the reaction, the autoclave was returned to room temperature, and unreacted tetrafluoroethylene was blown. The reaction product was washed with water five times to obtain 255 g (1.47 mol) of crude fluoroether corresponding to a conversion rate of 45% of tetrafluoroethylene.

The product ^{19 F-NMR, 1 H-} NMR fluorine-containing chain ether was analyzed by analytical A1:
HCF ₂ CF ₂ —O—CH ₂ CH ₂ CH ₂ CH ₃
It was confirmed.

¹⁹ F-NMR :( acetone): - 92.90~-92.89ppm (2F ), - 138.55ppm~-139.85 (2F)
¹ H-NMR: (acetone): 1.06 (6H), 1.26 (2H), 2.16 (1H), 6.02 (1H)
The fluorine-containing chain ether A1 had a fluorine content of 43.64% by mass (calculated value), a boiling point of 90 ° C., and a viscosity of 0.81 mPa · s.

Synthesis Example 2 (Fluorine-containing chain ether A2)
Potassium hydroxide (143 g: 2.55 mol) and isobutanol (401 g: 5.35 mol) were placed in a 3 L autoclave made of stainless steel, and vacuum-nitrogen substitution was performed 10 times at room temperature. After evacuating the system, tetrafluoroethylene was injected at a pressure of 0.1 MPa, and the reaction system was heated to 50 ° C. After the internal temperature reached 50 ° C., tetrafluoroethylene was gradually added so that the reaction pressure was maintained at 0.3 to 0.8 MPa. The internal temperature was adjusted to maintain 45 to 90 ° C. When the amount of tetrafluoroethylene added reached 535 g of 1.0 equivalent, the supply was stopped, and stirring was continued until no pressure drop of tetrafluoroethylene was observed. After completion of the reaction, the autoclave was returned to room temperature, and unreacted tetrafluoroethylene was blown. The reaction product was washed with water 5 times to obtain 726 g (4.13 mol) of crude fluoroether corresponding to a conversion rate of tetrafluoroethylene of 78%.

  Next, 726 g of the obtained crude fluoroether was purified by distillation to obtain 99.9% pure fluoroether with a yield of 97%.

Was the product was analyzed by ^{19 F-NMR, 1 H-} NMR analysis, the fluorine-containing chain ether A2:
HCF ₂ CF ₂ —O—CH ₂ CH (CH ₃ ) ₂
It was confirmed that.

¹⁹ F-NMR: (acetone): −92.755 to −92.800 ppm (2F), −137.705 ppm to −137.969 (2F)
¹ H-NMR :( acetone): 0.635-0.835ppm (6H), 1.656-1.681ppm (1H), 3.244-3.607ppm (2H), 5.19-5.438ppm ( 1H)
The fluorine-containing chain ether A2 had a fluorine content of 43.64% by mass (calculated value), a boiling point of 91.7 ° C., and a viscosity of 0.76 mPa · s.

Example 1
A solvent (I) for dissolving the electrolyte salt was prepared by mixing the fluorine-containing chain ether A1 / ethylene carbonate / ethyl methyl carbonate synthesized in Synthesis Example 1 at a ratio of 40/20/40% by volume. LiPF ₆ as an electrolyte salt was added to the solvent (I) so as to have a concentration of 1 mol / liter, and the mixture was sufficiently stirred at 25 ° C. to produce the electrolytic solution of the present invention.

Examples 2-9 and Comparative Examples 1-2
Using the electrolyte salt dissolving solvent (I) and electrolyte salt (II) having the composition shown in Table 1, the electrolyte solution of the present invention was produced in the same manner as in Example 1.

  In addition, each compound used by the Example and the comparative example is as follows.

(A) Fluorine-containing chain ether A1: HCF ₂ CF ₂ —O—CH ₂ CH ₂ CH ₂ CH ₃ (Synthesis Example 1)
A2: HCF ₂ CF ₂ —O—CH ₂ CH (CH ₃ ) ₂ (Synthesis Example 2)
A3: HCF ₂ CF ₂ CH ₂ —O—CH ₃ (boiling point: 34.0 ° C., viscosity: 0.72 mPa · s)
A4: HCF ₂ CF ₂ CH ₂ —O—CH ₂ CH ₃ (boiling point: 57.0 ° C., viscosity: 0.68 mPa · s)
(B) Non-fluorinated cyclic carbonate B1: Ethylene carbonate (EC)
B2: Propylene carbonate (PC)
(C) Other solvent for dissolving electrolyte salt C5a: ethyl methyl carbonate (EMC)
C5b: Dimethyl carbonate (DMC)
C5c: Diethyl carbonate (DEC)

Test example (charge / discharge characteristics)
(Production of cylindrical battery)
A positive electrode active material obtained by mixing LiCoO ₂ , carbon black, and polyvinylidene fluoride (manufactured by Kureha Chemical Co., Ltd., trade name KF-1000) at 92/3/5 (mass% ratio) is dispersed in N-methyl-2-pyrrolidone. Then, the slurry is applied uniformly on a positive electrode current collector (aluminum foil having a thickness of 15 μm), dried to form a positive electrode mixture layer, and then compression-molded with a roller press and then cut. The lead body was then welded to produce a strip-shaped positive electrode.

  Separately, styrene-butadiene rubber dispersed with distilled water is added to artificial graphite powder (manufactured by Hitachi Chemical Co., Ltd., trade name MAG-D) so that the solid content becomes 6% by mass, and mixed with a disperser. After applying the slurry in a uniform manner on a negative electrode current collector (copper foil having a thickness of 10 μm), drying, forming a negative electrode mixture layer, and then compression molding with a roller press machine and cutting, It dried and welded the lead body and produced the strip | belt-shaped negative electrode.

  Next, the belt-like positive electrode was overlapped with the belt-like negative electrode through a microporous polyethylene film (separator) having a thickness of 20 μm and wound in a spiral shape to obtain a laminated electrode body having a spiral winding structure. In that case, it wound so that the rough surface side of the positive electrode current collector could be the outer peripheral side. Thereafter, the electrode body was filled in a bottomed cylindrical battery case having an outer diameter of 18 mm, and the positive and negative lead bodies were welded.

  Next, the electrolyte solutions prepared in Examples and Comparative Examples were injected into the battery case, and after the electrolyte solution sufficiently penetrated into the separator, etc., sealed, precharged, and aged, a cylindrical lithium secondary battery was obtained. Produced.

  These batteries were evaluated for discharge capacity and storage characteristics by the following methods. The results are shown in Table 1.

(Discharge capacity)
When the charge / discharge current is indicated by C, measurement was performed under the following charge / discharge measurement conditions with 1800 mA as 1C. The evaluation is performed using an index with the result of the discharge capacity of Comparative Example 1 as 100.0.

Charging / Discharging Condition Charging: Holds charging current to 1 / 10C at 0.5C and 4.35V (CC / CV charging)
Discharge: 1.0C, 2.5Vcut (CC discharge)

(Storage characteristics)
Regarding charging, the battery was charged at 1.0C and 4.35V under the above conditions until the charging current became 1 / 10C, and discharged to 3.0V at a current equivalent to 1.0C to obtain the discharge capacity. Subsequently, the battery was charged at 0.5C, 4.35V until the charging current became 1 / 10C, placed in a constant temperature bath at 85 ° C., and taken out after 10 hours. Then, after leaving at room temperature for 4 hours, it was discharged to 3.0 V at 1.0 C. As the storage characteristics, the change in the discharge capacity calculated by the following formula was observed.

Storage characteristics (%) = 1C discharge capacity before storage (mAh) / 1C discharge capacity after storage (mAh) × 100

  In addition, when there is much generation | occurrence | production of gas, in order to discharge | release gas, the cleavage vent provided in the battery will act | operate.

  Regarding the discharge capacity, the capacities of Examples 1 to 9 are higher than those of Comparative Examples 1 and 2. Further, in the storage characteristics test, the comparative advantages 1 and 2 generated a gas at the time of storage because the boiling point was low, and the cleavage vent was activated, whereas in Examples 1 to 9, the boiling point was high (90 ° C. or higher). It was considered that the cleavage vent did not work because no boiling occurred and no gas was generated.

Claims (12)

(I) (A) Formula (A):
Rf-O-R
(Wherein Rf is a fluorine-containing alkyl group having 2 or 3 carbon atoms, R is an alkyl group having 4 to 6 carbon atoms) and has a boiling point of 90 ° C. or higher, and (B) A solvent for dissolving an electrolyte salt containing a fluorine-based cyclic carbonate, and an electrolyte solution containing (II) an electrolyte salt. The electrolytic solution according to claim 1, wherein in formula (A), R is a C 4-6 alkyl group containing a branched chain. The fluorine-containing chain ether (A) is HCF ₂ CF ₂ —O—CH ₂ CH ₂ CH ₂ CH ₃ , HCF ₂ CF ₂ —O—CH ₂ CH (CH ₃ ) ₂ and HCF ₂ CF ₂ —O—CH. The electrolytic solution according to claim 1 or 2, which is at least one selected from the group consisting of ₂ C (CH ₃ ) ₃ . The electrolyte solution according to any one of claims 1 to 3, wherein the non-fluorinated cyclic carbonate (B) is at least one selected from the group consisting of ethylene carbonate, vinylene carbonate, and propylene carbonate. The electrolyte salt dissolving solvent (I) contains 1 to 60% by volume of the fluorine-containing chain ether (A) and 5 to 50% by volume of the non-fluorinated cyclic carbonate (B) with respect to the entire solvent (I). The electrolyte solution in any one of Claims 1-4. As other electrolyte salt dissolving solvent (C), fluorine-containing chain ether (C1), fluorine-containing ester (C2), fluorine-containing carbonate (C3), fluorine-containing lactone (other than the above-mentioned fluorine-containing chain ether (A)) The electrolytic solution according to any one of claims 1 to 5, comprising at least one solvent selected from the group consisting of C4) and non-fluorine chain carbonate (C5). Electrolytic solution according to any one of claims 1 to 6 electrolyte salt (II) is LiPF ₆ or LiBF _4. The electrolyte salt (II) is at least one electrolyte salt selected from the group consisting of LiN (SO ₂ CF ₃ ) ₂ and LiN (SO ₂ CF ₂ CF ₃ ) _2. Electrolyte of description. It is an object for lithium ion secondary batteries, The electrolyte solution in any one of Claims 1-8. An electrochemical device comprising the electrolytic solution according to claim 1. A lithium ion secondary battery comprising the electrolytic solution according to claim 1. The lithium ion secondary battery according to claim 11, further comprising a positive electrode, a negative electrode, and a separator.