JP2012094491A - Nonaqueous electrolyte flame-resistant solvent and flame-resistant electrolyte and nonflammable electrolyte containing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flame-resistant solvent for nonaqueous electrolytes which exhibits a high degree of flame resistance, high electrolyte dissolving power, and excellent ion conductivity, and to provide a flame-resistant nonaqueous electrolyte and a nonflammable nonaqueous electrolyte containing the flame-resistant solvent.SOLUTION: The present invention relates to a flame-resistant solvent for nonaqueous electrolytes which is characterized in that [1] a fluorine-containing phosphoric ester expressed by a general formula (1) below (where, Rf, Rf, and Rfrespectively represent independently of each other a straight-chained or branched alkyl group having a carbon number 1-5 or a straight-chained or branched fluorine-containing alkyl group having a carbon number 1-5, at least one of Rfto Rfrepresenting a fluorine-containing alkyl group) has [2] at least one kind of fluorine-containing solvent selected from the group consisting of fluorine-containing ether, fluorine-containing ester, and fluorine-containing carbonate coexisting therein when put into use, and to a flame-resistant nonaqueous electrolyte and a nonflammable nonaqueous electrolyte containing the flame-resistant solvent.

Description

  The present invention relates to a flame retardant solvent for a non-aqueous electrolyte used in electrochemical energy conversion devices such as non-aqueous secondary batteries, capacitors and electrolytic capacitors. More specifically, a flame retardant solvent for non-aqueous electrolytes excellent in physical properties such as solubility and viscosity of the electrolyte and flame retardancy by mixing a fluorine-containing phosphate ester and a specific fluorine-containing solvent, The present invention relates to a flame retardant non-aqueous electrolyte and a non-flammable non-aqueous electrolyte having no flash point.

  Electrochemical energy conversion devices such as non-aqueous secondary batteries, capacitors, and electrolytic capacitors are used in various applications such as notebook PCs and mobile phones, backup power supplies, and smoothing of power supply circuits.

  In particular, non-aqueous secondary batteries have high output density and high energy density, and have recently attracted attention as power storage power sources and electric vehicle power sources.

Known non-aqueous secondary batteries include lithium secondary batteries, lithium ion secondary batteries, magnesium secondary batteries, and magnesium ion secondary batteries. For example, in the case of a lithium secondary battery or a lithium ion secondary battery, a material containing a lithium-containing transition metal oxide as a main constituent is used for the positive electrode, and metallic lithium or a lithium alloy is used for the negative electrode, or In some cases, a material mainly composed of a carbonaceous material typified by graphite is used. These are referred to as a lithium secondary battery and a lithium ion secondary battery, respectively. The positive electrode and the negative electrode are provided via a separator, and a non-aqueous electrolyte is filled between the positive electrode and the negative electrode as a medium in which Li ions move. As this non-aqueous electrolyte, an electrolyte such as lithium hexafluorophosphate (LiPF ₆ ) dissolved in a high dielectric constant organic solvent such as ethylene carbonate or dimethyl carbonate is widely used. Here, these organic solvents are volatile and flammable, and are classified as flammable substances. Thus, a non-aqueous electrolyte using a flammable liquid as a solvent and a non-aqueous secondary battery using this non-aqueous electrolyte are regarded as a “flammable liquid” during production, transportation and storage. When a secondary battery using an aqueous electrolyte and a non-aqueous electrolyte is produced in a factory, transported, or stored, it must be handled with an explosion-proof or fire-proof facility. For this reason, especially for the use of large non-aqueous secondary batteries such as power storage power sources and electric vehicle power sources, the electrolyte is flame retardant or self-extinguishing non-flammable non-aqueous electrolyte, A non-flammable non-aqueous electrolyte that does not have flammability even in the vapor phase is desired.

  For the purpose of making such a non-aqueous electrolyte flame-retardant, it has been studied to use a fluorine-containing phosphate as a solvent (Patent Documents 1 to 3, Non-Patent Document 1). Since the fluorine-containing phosphate ester has both a chemical flame-retarding effect due to phosphorus atoms and a flame-retarding function due to suffocation due to fluorine atoms, it can be highly flame-retardant. However, the electrolytic solution containing the fluorine-containing phosphate has a drawback that the characteristics as an electrolytic solution such as ionic conductivity are deteriorated. In particular, when the electrolytic solution is used in a secondary battery for an electric vehicle, the ionic conductivity is an important characteristic that affects the rapid charge / discharge performance and so on.

  In addition, in non-aqueous electrolytes containing these fluorine-containing phosphates, no investigation has been made on the flammability in the vapor phase.

On the other hand, as solvents other than the fluorine-containing phosphate ester that may be flame retardant, fluorine-containing ethers (Patent Documents 4 and 5), fluorine-containing esters (Patent Documents 6 and 7), and fluorine-containing carbonate (Patent Document 8) , 9) and the like have been proposed. However, these fluorine-containing solvents are not sufficient in flame retarding performance and have drawbacks that it is difficult to dissolve an electrolyte salt such as LiPF ₆ .

JP-A-8-88023 JP 2007-141760 A JP 2007-258067 A Japanese Patent Laid-Open No. 9-097627 JP-A-11-26015 JP-A-6-20719 JP-A-10-116627 Japanese Patent Laid-Open No. 7-6786 JP 2007-305352 A

J. Electrochemical Soc., 150, A161 (2003)

  The present invention has been made in view of these problems. That is, a flame retardant solvent for a non-aqueous electrolyte that exhibits a high degree of flame retardancy, a high electrolyte dissolving power, and good ion conductivity, a flame retardant non-aqueous electrolyte containing the same and a non-aqueous electrolyte containing the same An object is to provide a flammable non-aqueous electrolyte.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors showed high flame retardancy by using a mixture of a fluorine-containing phosphate ester and a specific fluorine-containing solvent, and dissolved the electrolyte. The present invention was completed by finding that the non-aqueous electrolyte has high ionic conductivity and high ionic conductivity. That is, the present invention relates to the following gist.

(1) [1] The following general formula (1)

(Wherein Rf ¹ , Rf ² and Rf ³ each independently represents a linear or branched alkyl group having 1 to 6 carbon atoms or a linear or branched fluorine-containing alkyl group having 1 to 6 carbon atoms. And at least one of Rf ^{1 to} Rf ³ represents a fluorine-containing alkyl group.)
In the fluorine-containing phosphate ester represented by
[2] The following general formula (2)
Rf ⁴ ORf ⁵ (2)
(In the formula, Rf ⁴ and Rf ⁵ each independently represent a linear or branched alkyl group having 1 to 6 carbon atoms or a linear or branched fluorine-containing alkyl group having 1 to 6 carbon atoms; Rf ⁴ And at least one of Rf ⁵ represents a fluorine-containing alkyl group.)
A fluorine-containing ether represented by the following general formula (3)

(In the formula, Rf ⁶ represents a fluorine atom or a linear or branched fluorine-containing alkyl group having 1 to 3 carbon atoms. Rf ⁷ represents a linear or branched alkyl group having 1 to 6 carbon atoms or 1 to 1 carbon atoms. 6 represents a linear or branched fluorine-containing alkyl group.)
And the following general formula (4)

(Wherein Rf ⁸ and Rf ⁹ each independently represent a linear or branched alkyl group having 1 to 6 carbon atoms or a linear or branched fluorine-containing alkyl group having 1 to 6 carbon atoms. Rf ⁸ and Rf ^At least one of ⁹ represents a fluorine-containing alkyl group.)
A flame retardant solvent for a non-aqueous electrolyte, which is used in the presence of at least one fluorine-containing solvent selected from the group consisting of fluorine-containing carbonates.

(2) In the general formula (1), Rf ¹ , Rf ² and Rf ³ are each independently a methyl group, an ethyl group, a 2,2-difluoroethyl group, a 2,2,2-trifluoroethyl group, 2 The non-aqueous solution according to (1), which is at least one selected from the group consisting of 2,2,3,3-tetrafluoropropyl group and 2,2,3,3,3-pentafluoropropyl group Flame retardant solvent for electrolyte.

(3) The fluorine-containing phosphoric acid ester of the general formula (1) is tris (2,2-difluoroethyl) phosphate, tris (2,2,2-trifluoroethyl) phosphate, tris (2,2) , 3,3-tetrafluoropropyl), tris phosphate (2,2,3,3,3-pentafluoropropyl), bis (2,2-difluoroethyl phosphate) 2,2,2-trifluoroethyl phosphate, Bis (2,2,2-trifluoroethyl) phosphate 2,2-difluoroethyl, bis (2,2,2-trifluoroethyl phosphate) 2,2,3,3-tetrafluoropropyl, bisphosphate (2,2,2-trifluoroethyl) methyl, bis (2,2,2-trifluoroethyl) ethyl phosphate and bis (2,2,3,3-tetrafluoropropyl) 2,2,2 -Trifluoroethyl And wherein the at least one selected from Ranaru group (1) or (2) a flame retardant solvent for non-aqueous electrolyte according.

(4) In the general formula (2), Rf ⁴ represents 2,2-difluoroethyl group, 2,2,2-trifluoroethyl group, 2,2,3,3-tetrafluoropropyl group, and 2,2, One or more selected from the group consisting of 3,3,3-pentafluoropropyl groups, and Rf ⁵ is a difluoromethyl group, 1,1,2,2-tetrafluoroethyl group, and 1,1,2, The flame retardancy for a non-aqueous electrolyte according to any one of (1) to (3), which is at least one selected from the group consisting of 3,3,3-hexafluoropropyl groups solvent.

(5) In General Formula (3), Rf ⁶ is at least one selected from the group consisting of a fluorine atom, a difluoromethyl group, a trifluoromethyl group, and a heptafluoropropyl group, and Rf ⁷ is a methyl group, an ethyl group, From the group consisting of 2,2-difluoroethyl group, 2,2,2-trifluoroethyl group, 2,2,3,3-tetrafluoropropyl group and 2,2,3,3,3-pentafluoropropyl group The flame-retardant solvent for a non-aqueous electrolyte according to any one of (1) to (3), which is one or more selected.

(6) In the general formula (4), Rf ⁸ and Rf ⁹ are each independently a methyl group, an ethyl group, a 2,2-difluoroethyl group, a 2,2,2-trifluoroethyl group, 2,2,3. Any one of (1) to (3), which is at least one selected from the group consisting of 1,2,3-tetrafluoropropyl group and 2,2,3,3,3-pentafluoropropyl group A flame retardant solvent for a non-aqueous electrolyte described in 1.

(7) The amount of the fluorine-containing solvent of the general formulas (2) to (4) to the fluorine-containing phosphate ester of the general formula (1) is 0.2 to 5 times in volume ratio (1 The flame-retardant solvent for non-aqueous electrolytes of any one of (6)-(6).

(8) A flame retardant non-aqueous electrolysis comprising a lithium salt and / or a magnesium salt as an electrolyte and the flame retardant solvent according to any one of (1) to (7) as a solvent. liquid.

(9) A flame retardant comprising a lithium salt and / or a magnesium salt as an electrolyte, and containing 3 to 80% by volume of the flame retardant solvent according to any one of (1) to (7). Non-aqueous electrolyte.

(10) The flame retardant solvent according to any one of (1) to (7), comprising a lithium salt and / or a magnesium salt as an electrolyte, and a fluorine-containing phosphate ester and a fluorine-containing solvent as a flame retardant solvent. And a cyclic carbonate and a non-fluorine chain carbonate as a solvent.

(11) The nonaqueous electrolytic solution according to (10), wherein the fluorine-containing solvent is a fluorine-containing ether having a fluorine content of 60% by weight or more in the fluorine-containing ether represented by the general formula (2). The non-flammable non-aqueous electrolyte is characterized in that the abundance of the fluorine-containing ether is 0.3 to 5 times by volume with respect to the non-fluorinated chain carbonate.

(12) The nonaqueous electrolytic solution according to (10), wherein (1,1,2,2-tetrafluoroethyl) 2,2,2-trifluoroethyl ether or (1,1 , 2,2-tetrafluoroethyl) 2,2,3,3-tetrafluoropropyl ether present in a volume ratio of 0.3 to 5 times that of non-fluorinated chain carbonate, non-flammable Non-aqueous electrolyte.

(13) The nonaqueous electrolytic solution according to (10), wherein at least part of the cyclic carbonate is fluoroethylene carbonate.

(14) The non-flammable non-aqueous electrolyte according to (11) or (12), wherein at least a part of the cyclic carbonate is fluoroethylene carbonate.

  According to the present invention, a flame-retardant solvent for non-aqueous electrolytes exhibiting high flame retardancy, high electrolyte solubility, and good ionic conductivity, and flame-retardant non-aqueous electrolysis containing the same Liquids and non-flammable non-aqueous electrolytes can be provided.

The graph which shows the relationship between the temperature of a nonaqueous electrolyte measured in Examples 13-15 and Comparative Example 9, and ionic conductivity. It is a schematic cross section which shows the structure of the lithium secondary battery of the coin-type cell used in Examples 16-19 and the comparative example 10. FIG.

The flame retardant solvent for non-aqueous electrolyte of the present invention contains a fluorine-containing phosphate ester represented by the general formula (1) as a first component. In the general formula (1), Rf ¹ , Rf ² and Rf ³ each independently represent a linear or branched alkyl group having 1 to 6 carbon atoms or a linear or branched fluorine-containing alkyl group having 1 to 6 carbon atoms. And at least one of Rf ^{1 to} Rf ³ is a fluorine-containing alkyl group. Examples of the linear or branched alkyl group having 1 to 6 carbon atoms include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, n-pentyl group and n- Hexyl group and the like, and examples of the linear or branched fluorine-containing alkyl group having 1 to 6 carbon atoms include trifluoromethyl group, 2,2-difluoroethyl group, 2,2,2-trifluoroethyl group, 2 , 2,3,3-tetrafluoropropyl group, 2,2,3,3,3-pentafluoropropyl group, hexafluoroisopropyl group, 2,2,3,3,4,4,5,5-octafluoro A pentyl group, 2,2,3,3,4,4,5,5,5-nonafluoropentyl group, 3,3,4,4,5,5,6,6,6-nonafluorohexyl group, etc. Can be mentioned. Examples of such a fluorine-containing phosphate ester include tris phosphate (trifluoromethyl), tris phosphate (2,2-difluoroethyl), tris phosphate (2,2,2-trifluoroethyl), and phosphoric acid. (2,2,3,3-tetrafluoropropyl), tris phosphate (2,2,3,3,3-pentafluoropropyl), tris phosphate (hexafluoroisopropyl), tris phosphate (2,2, 3,3,4,4,5,5-octafluoropentyl), tris phosphate (2,2,3,3,4,4,5,5,5-nonafluoropentyl), tris phosphate (3,3 3,4,4,5,5,6,6,6-nonafluorohexyl), bis (2,2-difluoroethyl) phosphate 2,2,2-trifluoroethyl, bis (2,2, 2-trifluoroethyl) methyl Bis (2,2,2-trifluoroethyl) ethyl phosphate, bis (2,2,2-trifluoroethyl phosphate) 2,2-difluoroethyl phosphate, bis (2,2,2-trifluorophosphate) Ethyl) 2,2,3,3-tetrafluoropropyl, bis (2,2,3,3-tetrafluoropropyl) 2,2,2-trifluoroethyl phosphate and bis (2,2,2-phosphate) Trifluoroethyl) (2,2,3,3-tetrafluoropropyl) methyl and the like. Among these fluorine-containing phosphate esters, tris phosphate (2,2,2-trifluoroethyl), tris phosphate (2,2,3,3-tetrafluoropropyl), tris phosphate (2,2,3) , 3,3-pentafluoropropyl), bis (2,2-difluoroethyl) phosphate 2,2,2-trifluoroethyl, bis (2,2,2-trifluoroethyl) phosphate 2,2-difluorophosphate Ethyl, bis (2,2,2-trifluoroethyl) phosphate 2,2,3,3-tetrafluoropropyl and bis (2,2,3,3-tetrafluoropropyl) phosphate 2,2,2- Trifluoroethyl is preferred in terms of physical properties such as flame retardancy and viscosity, and ion conductivity.

  The flame retardant solvent for the non-aqueous electrolyte of the present invention is used by mixing the fluorine-containing phosphate and the second fluorine-containing solvent. The second fluorinated solvent is a group consisting of a fluorinated ether represented by the general formula (2), a fluorinated ester represented by the general formula (3), and a fluorinated carbonate represented by the general formula (4). It is at least 1 sort chosen from more.

In General Formula (2), Rf ⁴ and Rf ⁵ are each independently a linear or branched alkyl group having 1 to 6 carbon atoms or a linear or branched fluorine-containing alkyl group having 1 to 6 carbon atoms. , Rf ⁴ and Rf ⁵ are fluorine-containing alkyl groups. Examples of the linear or branched alkyl group having 1 to 6 carbon atoms include, for example, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group, n-pentyl group and An n-hexyl group etc. can be mentioned. Examples of the linear or branched fluorine-containing alkyl group having 1 to 6 carbon atoms include fluoromethyl group, difluoromethyl group, trifluoromethyl group, 1,1-difluoroethyl group, 2,2-difluoroethyl group, 2,2 , 2-trifluoroethyl group, 1,1,2,2-tetrafluoroethyl group, 3,3,3-trifluoropropyl group, 2,2,3,3-tetrafluoropropyl group, hexafluoroisopropyl group, 1,1,2,3,3,3-hexafluoropropyl group, 4,4,4-trifluorobutyl group and 3,3,4,4,5,5,6,6,6-nonafluorohexyl group Etc. Among these, in particular, Rf ⁴ is 2,2-difluoroethyl group, 2,2,2-trifluoroethyl group, 2,2,3,3-tetrafluoropropyl group, and 2,2,3,3, Selected from one of 3-pentafluoropropyl groups and Rf ⁵ is a difluoromethyl group, 1,1,2,2-tetrafluoroethyl group and 1,1,2,3,3,3-hexa It is preferable from the viewpoint of physical properties such as viscosity and ion conductivity to be selected from one of fluoropropyl groups. Examples of such fluorine-containing ethers include difluoromethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2-difluoroethyl ether, 1,1,2, 2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2- Tetrafluoroethyl-2,2,3,3,3-pentafluoropropyl ether and 1,1,2,3,3,3-hexafluoropropyl-2,2,2-trifluoroethyl ether and the like or a mixture thereof Can be mentioned.

In the general formula (3), Rf ⁶ is a fluorine atom or a linear or branched fluorinated alkyl group having 1 to 3 carbon atoms, Rf ⁷ is a linear or branched alkyl group having 1 to 6 carbon atoms Or it is a C1-C6 linear or branched fluorine-containing alkyl group. Examples of the linear or branched fluorine-containing alkyl group having 1 to 3 carbon atoms as Rf ⁶ include a difluoromethyl group, a trifluoromethyl group, a pentafluoroethyl group, and a heptafluoropropyl group, and a carbon as Rf ⁷ Examples of the linear or branched alkyl group having 1 to 6 or the linear or branched fluorine-containing alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, Isobutyl group, t-butyl group, n-hexyl group, 2,2-difluoroethyl group, 2,2,2-trifluoroethyl group, 3,3,3-trifluoropropyl group, 2,2,3,3 -Tetrafluoropropyl group, 2,2,3,3,3-pentafluoropropyl group, hexafluoroisopropyl group, 4,4,4-trifluorobutyl group and 3 3,4,4,5,5,6,6,6- nonafluorohexyl group, and the like. Among these, in particular, Rf ⁶ is selected from one of a fluorine atom, a difluoromethyl group, a trifluoromethyl group, or a heptafluoropropyl group, and Rf ⁷ is a methyl group, an ethyl group, or 2,2-difluoro. The viscosity is selected from the group consisting of ethyl group, 2,2,2-trifluoroethyl group, 2,2,3,3-tetrafluoropropyl group and 2,2,3,3,3-pentafluoropropyl group From the viewpoint of physical properties such as ionic conductivity. Examples of such a fluorine-containing ester include methyl trifluoroacetate, ethyl trifluoroacetate, 2,2-difluoroethyl trifluoroacetate, 2,2,2-trifluoroethyl trifluoroacetate, 2,2, trifluoroacetic acid, and the like. 3,3-tetrafluoropropyl, 2,2,3,3,3-pentafluoropropyl trifluoroacetate, ethyl 1,1,2,2-tetrafluoropropionate, 1,1,2,2-tetrafluoropropion Acid 2,2,2-trifluoroethyl, 1,1,2,2-tetrafluoropropionic acid 2,2,3,3-tetrafluoropropyl, 1,1,2,2,3,3,4,4 , Ethyl 4-nonafluoropentanoate and 1,1,2,2,3,3,4,4,4-nonafluoropentanoic acid 2,2,2-trifluoroethyl and the like And a mixture of these.

In the general formula (4), Rf ⁸ and Rf ⁹ each independently represent a linear or branched alkyl group having 1 to 6 carbon atoms or a linear or branched fluorine-containing alkyl group having 1 to 6 carbon atoms. , Rf ⁸ and Rf ⁹ are fluorine-containing alkyl groups. Examples of the linear or branched alkyl group having 1 to 6 carbon atoms include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group and n-hexyl group. Examples of the linear or branched fluorine-containing alkyl group having 1 to 6 carbon atoms include a fluoromethyl group, a difluoromethyl group, a trifluoromethyl group, a 1,1-difluoroethyl group, a 2,2-difluoroethyl group, 2 , 2,2-trifluoroethyl group, 1,1,2,2-tetrafluoroethyl group, 3,3,3-trifluoropropyl group, 2,2,3,3-tetrafluoropropyl group, hexafluoroisopropyl Group, 1,1,2,3,3,3-hexafluoropropyl group, 4,4,4-trifluorobutyl group, 2,2,3,3,4,4,5,5-octafluorope Til group, 2,2,3,3,4,4,5,5,5-nonafluoropentyl group, 3,3,4,4,5,5,6,6,6-nonafluorohexyl group, etc. Can be mentioned. Among these, in particular, Rf ⁸ and Rf ⁹ are each independently a methyl group, ethyl group, 2,2-difluoroethyl group, 2,2,2-trifluoroethyl group, 2,2,3,3-tetra It is preferable in terms of physical properties such as viscosity and ionic conductivity to be selected from a fluoropropyl group and a 2,2,3,3,3-pentafluoropropyl group. Examples of such a fluorinated carbonate include methyl-2,2-difluoroethyl carbonate, methyl-2,2,2-trifluoroethyl carbonate, methyl-2,2,3,3-tetrafluoropropyl carbonate, ethyl- 2,2,2-trifluoroethyl carbonate, bis (2,2-difluoroethyl) carbonate, bis (2,2,2-trifluoroethyl) carbonate, bis (2,2,3,3-tetrafluoropropyl) Carbonate, bis (2,2,3,3,3-pentafluoropropyl) carbonate, 2,2-difluoroethyl-2,2,2-trifluoroethyl carbonate and 2,2,3,3-tetrafluoropropyl- List 2,2,2-trifluoroethyl carbonate, etc. or mixtures thereof It can be.

  The fluorine-containing phosphate ester of the general formula (1), the fluorine-containing ether of the general formula (2), the fluorine-containing ester of the general formula (3), and the fluorine-containing carbonate of the general formula (4) are all highly purified. It is desirable that the content of protic compounds such as water, acid and alcohol is less than 50 ppm, preferably less than 30 ppm.

  The flame retardant solvent for a non-aqueous secondary battery of the present invention is used by allowing the fluorine-containing phosphoric acid ester of the general formula (1) to coexist with the fluorine-containing solvent of the general formulas (2) to (4). In this case, the amount of the fluorine-containing solvent represented by the general formulas (2) to (4) is 0.2 to 5 times by volume with respect to the fluorine-containing phosphate ester. If the amount used is less than 0.2 times, physical properties such as viscosity and properties such as ionic conductivity may not be sufficient, and if it exceeds 5 times, the solubility and flame retardancy of the electrolyte may not be sufficient. is there.

  Moreover, although the flame-retardant solvent for non-aqueous electrolytes of this invention can also be used in the combination of the said flame-retardant solvent only, it is more preferable to mix and use with another solvent. At this time, the ratio of the total of the fluorine-containing phosphate ester of the general formula (1) and the fluorine-containing solvent of the general formulas (2) to (4) to the entire electrolyte solvent is in the range of 3 to 80% by volume ratio. It is preferable in terms of flame retardancy and electrolyte characteristics.

  When the total amount of the fluorine-containing phosphate ester and the fluorine-containing solvent is less than 3%, the non-flammable electrolyte has insufficient flame retardancy, and when it exceeds 80%, the electrochemical performance such as ionic conductivity decreases. Since there is a case, it is not preferable.

Examples of other solvents to be mixed include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, and fluoroethylene carbonate, cyclic esters such as γ-butyrolactone, γ-valerolactone, and propiolactone, and dimethyl carbonate. Non-fluorine chain carbonates such as diethyl carbonate, ethyl methyl carbonate and diphenyl carbonate, chain esters such as methyl acetate and methyl butyrate, ethers such as diisopropyl ether, tetrahydrofuran, dioxolane, dimethoxyethane, diethoxyethane and methoxyethoxyethane And nitriles such as acetonitrile and benzonitrile.
Among these, it is preferable in terms of viscosity and ionic conductivity to use a combination of cyclic carbonates such as ethylene carbonate and fluoroethylene carbonate and non-fluorine chain carbonates such as dimethyl carbonate and diethyl carbonate. At this time, if fluoroethylene carbonate is used for at least a part of the cyclic carbonate, the non-aqueous electrolyte can be made flame-retardant or non-flammable with a wider range of compositions, and the solubility of the electrolyte is sufficiently maintained even at low temperatures. This is particularly preferable because it can be performed.

  On the other hand, non-fluorine chain carbonates such as dimethyl carbonate have a flash point and generate flammable vapors even at low temperatures. When such a non-fluorine chain carbonate is used, as the flame retardant solvent, the fluorine-containing phosphate ester of the general formula (1) is used as the first component, and the formula (2) is used as the second component. The use of a fluorinated ether having a fluorine content of 60% by weight or more of the fluorinated ether is particularly preferred in order to make the electrolyte non-flammable. Since the fluorine-containing ether of the general formula (2) having a fluorine content of 60% by weight or higher has a high vapor pressure and is nonflammable, it forms a non-flammable atmosphere even in the presence of non-fluorine chain carbonate. Furthermore, it is considered that a non-flammable atmosphere is formed in a wide temperature range due to the coexistence effect with the fluorine-containing phosphate ester which is a high-temperature incombustible solvent. The abundance of the fluorinated ether is 0.3 to 5 times that of the non-fluorinated chain carbonate. When the amount of the fluorinated ether is less than 0.3 times, the electrolytic solution may have a flash point. When the amount of the fluorinated ether is more than 5 times, the solubility of the electrolyte is lowered and precipitation occurs at a low temperature. May invite.

As the electrolyte salt constituting the nonaqueous electrolytic solution of the present invention, lithium salt, magnesium salt and the like which are stable in a wide potential region can be used. Examples of the electrolyte salt include LiBF ₄ , LiPF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ). ₃ , Mg (ClO ₄ ) ₂ , Mg (CF ₃ SO ₃ ) ₂ , Mg (N (CF ₃ SO ₂ ) ₂ ) _{2 and the} like. These may be used alone or in combination of two or more. In order to improve the high rate charge / discharge characteristics of the battery, the concentration of the electrolyte salt in the non-aqueous electrolyte is preferably in the range of 0.2 to 2.5 mol / L.

The non-aqueous secondary battery using the non-aqueous electrolyte of the present invention comprises at least a positive electrode, a negative electrode, and a separator. As the negative electrode material, metallic lithium, a lithium alloy, a carbon material that can be doped / undoped with lithium ions, or the like is used. As the positive electrode material, a composite oxide of lithium and transition metal such as LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiFeO ₂ , LiFePO ₄ or the like is usually used. As the separator, a microporous film or the like is used, and as a material, a polyolefin resin such as polyethylene or a fluorine resin such as polyvinylidene fluoride is used. As the shape and form of the non-aqueous secondary battery, a cylindrical type, a square type, a coin type, a card type and the like are usually selected.

  Hereinafter, the present invention will be described in detail using examples, but the present invention is not limited to the examples.

Examples 1-4, Comparative Examples 1-5 Solubility of electrolyte Bis (2,2,2-trifluoroethyl) 2,2,3,3-tetrafluoropropyl phosphate and 1,1,2,2-tetra Fluoroethyl-2,2,2-trifluoroethyl ether was mixed at a volume ratio of 1: 1. LiPF ₆ was added to this mixed solution and dissolved by stirring at 20 ° C. for 6 hours. After insoluble LiPF ₆ was filtered off, the LiPF ₆ concentration was determined by ¹⁹ F-NMR analysis of the solution. A similar procedure is used for bis (2,2,2-trifluoroethyl) phosphate 2,2,3,3-tetrafluoropropyl and 1,1,2,2-tetrafluoroethyl-2,2-difluoroethyl ether. 1: 1 mixture, bis (2,2,2-trifluoroethyl) 2,2,3,3-tetrafluoropropyl phosphate and 1,1,2,2-tetrafluoroethyl-2,2,3 About 1: 1 mixture of 3-tetrafluoropropyl ether, 1: 1 mixture of bis (2,2,2-trifluoroethyl) phosphate 2,2,3,3-tetrafluoropropyl and ethyl trifluoroacetate Was also implemented. In addition, as a comparative example, the same operation was performed for each compound with a single solvent, and the solubility of LiPF ₆ was examined. The results are shown in Table 1.

The solvent in which the fluorine-containing phosphate ester of the present invention is mixed with another fluorine-containing solvent is surprisingly fluorinated phosphoric acid, despite the presence of a large amount of fluorine-containing solvent that hardly dissolves LiPF _6. It was confirmed that the solubility of the electrolyte was equal to or higher than that of the ester alone.

Examples 5 to 9 and Comparative Example 6 Viscosity Viscosity of a mixture of the fluorinated phosphate ester and each fluorine-based solvent was measured in a thermostatic bath at 20 ° C. using an Ubbelohde viscometer. The results are shown in Table 2.

  It was confirmed that the solvent in which the fluorine-containing phosphate ester of the present invention coexists with other fluorine-containing solvents has a significantly lower viscosity than the fluorine-containing phosphate ester single solvent.

Examples 10 to 12 and Comparative Examples 7 to 8 Flame retardance of electrolyte solution Bis (2,2,2-trifluoroethyl) 2,2,3,3-tetrafluoropropyl phosphate (15% by volume), 1, 1 mol of LiPF ₆ is added to a mixed liquid of 1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (15% by volume), ethylene carbonate (35% by volume) and dimethyl carbonate (35% by volume). The nonaqueous electrolytic solution dissolved at a concentration of / L was defined as electrolytic solution a. Bis (2,2,2-trifluoroethyl) phosphate 2,2,3,3-tetrafluoropropyl (15% by volume), 1,1,2,2-tetrafluoroethyl-2,2-difluoroethyl ether A nonaqueous electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1 mol / L in a mixed solution of (15% by volume), ethylene carbonate (35% by volume) and dimethyl carbonate (35% by volume) was defined as an electrolytic solution b. Bis (2,2,2-trifluoroethyl) phosphate 2,2,3,3-tetrafluoropropyl (15% by volume), ethyl trifluoroacetate (15% by volume), ethylene carbonate (35% by volume) and dimethyl A non-aqueous electrolyte obtained by dissolving LiPF ₆ at a concentration of 1 mol / L in a mixed solution of carbonate (35% by volume) was used as an electrolyte c. In addition, a non-aqueous electrolyte obtained by dissolving LiPF ₆ at a concentration of 1 mol / L in a mixed solution of ethylene carbonate (50% by volume) and dimethyl carbonate (50% by volume) is an electrolyte d, 1, 1, 2, 2. - tetrafluoroethyl 2,2-difluoroethyl ether (30 vol%), a mixture of ethylene carbonate (35 vol%) and dimethyl carbonate (35 vol%), and the LiPF ₆ was dissolved at a concentration of 1 mol / L The nonaqueous electrolytic solution was designated as electrolytic solution e. Using these non-aqueous electrolytes, flame retardancy was tested by the following method.

  0.25 ml of non-aqueous electrolyte was poured into a glass filter paper having a diameter of 21 mm, and a flame of an alcohol lamp was applied from a distance of 8 cm and held for 10 seconds to check for combustion. This test was repeated 5 times to determine the combustion probability. The results are shown in Table 3.

  It was confirmed that the electrolytic solution containing a solvent in which the fluorinated phosphate ester of the present invention coexists with another fluorinated solvent exhibits an excellent flame retardant effect of the electrolytic solution.

Examples 13 to 15 and Comparative Example 9 Ionic Conductivity of Nonaqueous Electrolytic Solution As electrolytic solution a of Example 10, electrolytic solution b of Example 11, electrolytic solution c of Example 12, and comparative electrolytic solution, bisphosphate LiPF ₆ was added to a mixture of (2,2,2-trifluoroethyl) 2,2,3,3-tetrafluoropropyl (30% by volume), ethylene carbonate (35% by volume) and dimethyl carbonate (35% by volume). About the non-aqueous electrolyte f dissolved so that it might become a density | concentration of 1 mol / L, the ion conductivity in each temperature was measured using the electrical conductivity meter (Kyoto Electronics CM-117 type | mold). The results are shown in FIG.

  It was confirmed that the electrolytic solution containing a solvent in which the fluorinated phosphate ester of the present invention and another fluorinated solvent coexist showed improved and improved ionic conductivity.

Examples 16 to 19, Comparative Example 10
As the electrolytic solution a of Example 10, the electrolytic solution b of Example 11, the electrolytic solution c of Example 12, and the electrolytic solution of Example 19, bis (2,2,2-trifluoroethyl) phosphate 2,2, 3,3-tetrafluoropropyl (20% by volume), 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (10% by volume), ethylene carbonate (60% by volume) and dimethyl A non-aqueous electrolyte obtained by dissolving LiPF ₆ at a concentration of 1 mol / L in a mixed solution of carbonate (10% by volume) using the electrolytic solution g and the electrolytic solution f of Comparative Example 9 by the following method was used. The test was conducted.

Preparation of non-aqueous secondary battery Lithium cobaltate (LiCoO ₂ ) is used as a positive electrode active material, and carbon black is used as a conductive auxiliary agent, and polyvinylidene fluoride (PVDF) is used as a binder. LiCoO ₂ : carbon black: PVDF = 85: 7 : 8 was blended and slurried with 1-methyl-2-pyrrolidone was applied on an aluminum current collector with a certain film thickness and dried to obtain a positive electrode.

  Natural negative graphite is used as a negative electrode active material, PVDF is blended as a binder so that graphite: PVDF = 9: 1, and slurried using 1-methyl-2-pyrrolidone is placed on a copper current collector. It apply | coated with the fixed film thickness, it was made to dry and the negative electrode was obtained.

  As the separator, an inorganic filler-impregnated polyolefin porous membrane was used.

  Using the above components, a lithium secondary battery using a coin-type cell having the structure shown in FIG. 2 was produced. In the lithium secondary battery, a positive electrode 1 and a negative electrode 4 are arranged opposite to each other with a separator 6 interposed therebetween, a stainless steel leaf spring 5 is installed on a negative electrode stainless steel cap 3, and a laminate including the negative electrode 4, the separator 6, and the positive electrode 1 is coin-shaped. Stored in the cell. After injecting the electrolyte solution of the present invention into this laminate, the gasket 7 was placed, and then the cap 2 made of a positive electrode stainless steel was put on and a coin type cell case was caulked.

Charge / Discharge Test The lithium ion secondary battery prepared by the above method was charged at a constant current of 25 ° C. with a charging current of 0.1 C and a maximum voltage of 4.2 V, and subsequently with a discharging current of 0.1 C. It discharged until it became 0V. After performing this operation three times, a constant current-constant voltage charge of 4.2 V was performed at a charging current of 5 C under a constant temperature condition of 25 ° C., and a constant current discharge was performed to a final voltage of 3.0 V with a discharging current of 5 C. . In the above test, the discharge capacity of 0.1 C was set as the initial discharge capacity, and the discharge capacity when discharged at 5 C was compared as the ratio of the 5 C discharge capacity to the initial discharge capacity. The results are shown in Table 4.

  It was confirmed that an electrolytic solution containing a solvent in which a chain carbonate and a cyclic carbonate coexist as a fluorine-containing phosphate ester and a fluorine-containing solvent of the present invention and a non-fluorine-based organic solvent exhibit good battery characteristics.

Examples 20-28, Comparative Examples 11-12
Bis (2,2,2-trifluoroethyl) phosphate 2,2,3,3-tetrafluoropropyl (20% by volume), 1,1,2,2-tetrafluoroethyl-2,2,2-triphosphate A non-aqueous electrolyte obtained by dissolving LiPF ₆ at a concentration of 1 mol / L in a mixed solution of fluoroethyl ether (10% by volume), ethylene carbonate (55% by volume), and dimethyl carbonate (15% by volume) is referred to as electrolyte h. did. Bis (2,2,2-trifluoroethyl) phosphate 2,2,3,3-tetrafluoropropyl (20% by volume), 1,1,2,2-tetrafluoroethyl-2,2,2-triphosphate A non-aqueous electrolyte obtained by dissolving LiPF ₆ at a concentration of 1 mol / L in a mixed solution of fluoroethyl ether (10% by volume), ethylene carbonate (60% by volume), and ethyl methyl carbonate (10% by volume) is used as an electrolyte. i.

Bis (2,2,2-trifluoroethyl) phosphate 2,2,3,3-tetrafluoropropyl (10% by volume), 1,1,2,2-tetrafluoroethyl-2,2,2-triphosphate A non-aqueous electrolyte solution prepared by dissolving LiPF ₆ at a concentration of 1 mol / L in a mixed solution of fluoroethyl ether (20% by volume), ethylene carbonate (60% by volume) and diethyl carbonate (10% by volume) was used as an electrolyte j. did. Bis (2,2,2-trifluoroethyl) phosphate 2,2,3,3-tetrafluoropropyl (20% by volume), 1,1,2,2-tetrafluoroethyl-2,2,3,3 -A nonaqueous electrolytic solution prepared by dissolving LiPF ₆ at a concentration of 1 mol / L in a mixed solution of tetrafluoropropyl ether (10 vol%), ethylene carbonate (50 vol%) and dimethyl carbonate (10 vol%) k. Bis (2,2,2-trifluoroethyl) phosphate 2,2,3,3-tetrafluoropropyl (20% by volume), 1,1,2,2-tetrafluoroethyl-2,2,2-triphosphate A nonaqueous electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1 mol / L in a mixed solution of fluoroethyl ether (10% by volume), ethylene carbonate (35% by volume) and dimethyl carbonate (35% by volume) did. Bis (2,2,2-trifluoroethyl) phosphate 2,2,3,3-tetrafluoropropyl (20% by volume), 1,1,2,2-tetrafluoroethyl-2,2,2-triphosphate A non-aqueous electrolyte obtained by dissolving LiPF ₆ at a concentration of 1 mol / L in a mixed solution of fluoroethyl ether (10% by volume), ethylene carbonate (35% by volume), and ethyl methyl carbonate (35% by volume) is an electrolyte m. It was. Bis (2,2,2-trifluoroethyl) phosphate 2,2,3,3-tetrafluoropropyl (20% by volume), 1,1,2,2-tetrafluoroethyl-2,2,2-triphosphate A non-aqueous electrolyte obtained by dissolving LiPF ₆ at a concentration of 1 mol / L in a mixed solution of fluoroethyl ether (10% by volume), fluoroethylene carbonate (50% by volume) and dimethyl carbonate (20% by volume) is an electrolyte n. It was. Bis (2,2,2-trifluoroethyl) phosphate 2,2,3,3-tetrafluoropropyl (10% by volume), 1,1,2,2-tetrafluoroethyl-2,2,2-triphosphate LiPF ₆ was dissolved at a concentration of 1 mol / L in a mixed solution of fluoroethyl ether (20% by volume), fluoroethylene carbonate (25% by volume), ethylene carbonate (25% by volume) and dimethyl carbonate (20% by volume). The non-aqueous electrolyte was designated as electrolyte o. LiPF ₆ was added to a mixture of 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (30% by volume), ethylene carbonate (35% by volume) and dimethyl carbonate (35% by volume). A nonaqueous electrolytic solution in which was dissolved at a concentration of 1 mol / L was used as an electrolytic solution p. Using these nonaqueous electrolytic solutions, the electrolytic solution f of Comparative Example 10 and the electrolytic solution g of Example 19, the flash point was measured by the following method.

  For the flash point measurement, a method according to the flash point measurement method of the Fire Service Act was selected, and a setter type flash point tester RT-1 (manufactured by ERDCO Engineering Corporation) was used. The RT-1 tester was heated to a predetermined temperature, and when the temperature became constant, 4 ml of an electrolytic solution was injected. After 2 minutes, the test flame was observed while looking inside the switch, and the presence or absence of ignition was observed. This was carried out with the temperature at which the electrolyte solution boiled as the upper limit, and the case where it did not ignite to the boiling temperature was judged as having no flash point.

  The results are shown in Table 5.

  In the electrolytic solution containing the solvent in which the fluorine-containing phosphate ester, the fluorine-containing ether and the non-fluorine chain carbonate of the present invention coexist, the volume ratio of the fluorine-containing ether to the non-fluorine chain carbonate is 0.3 or more. Was confirmed to be a non-flammable non-aqueous electrolyte.

  The flame retardant solvent for non-aqueous electrolyte solution of the present invention exhibits high flame retardancy, high solubility of electrolyte, and good ionic conductivity. Useful as.

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Positive electrode stainless cap 3 Negative electrode stainless steel cap 4 Negative electrode 5 Stainless steel leaf spring 6 Inorganic filler impregnation polyolefin porous separator 7 Gasket

Claims (14)

[1] The following general formula (1)
(Wherein Rf ¹ , Rf ² and Rf ³ each independently represents a linear or branched alkyl group having 1 to 6 carbon atoms or a linear or branched fluorine-containing alkyl group having 1 to 6 carbon atoms. And at least one of Rf ^{1 to} Rf ³ represents a fluorine-containing alkyl group.)
In the fluorine-containing phosphate ester represented by
[2] The following general formula (2)
Rf ⁴ ORf ⁵ (2)
(In the formula, Rf ⁴ and Rf ⁵ each independently represent a linear or branched alkyl group having 1 to 6 carbon atoms or a linear or branched fluorine-containing alkyl group having 1 to 6 carbon atoms; Rf ⁴ And at least one of Rf ⁵ represents a fluorine-containing alkyl group.)
A fluorine-containing ether represented by the following general formula (3)
(In the formula, Rf ⁶ represents a fluorine atom or a linear or branched fluorine-containing alkyl group having 1 to 3 carbon atoms. Rf ⁷ represents a linear or branched alkyl group having 1 to 6 carbon atoms or 1 to 1 carbon atoms. 6 represents a linear or branched fluorine-containing alkyl group.)
And the following general formula (4)
(Wherein Rf ⁸ and Rf ⁹ each independently represent a linear or branched alkyl group having 1 to 6 carbon atoms or a linear or branched fluorine-containing alkyl group having 1 to 6 carbon atoms. Rf ⁸ and Rf ^At least one of ⁹ represents a fluorine-containing alkyl group.)
A flame retardant solvent for a non-aqueous electrolyte, which is used in the presence of at least one fluorine-containing solvent selected from the group consisting of fluorine-containing carbonates. In the general formula (1), Rf ¹ , Rf ² and Rf ³ are each independently a methyl group, an ethyl group, a 2,2-difluoroethyl group, a 2,2,2-trifluoroethyl group, 2,2, 2. The non-aqueous electrolyte solution according to claim 1, which is at least one selected from the group consisting of a 3,3-tetrafluoropropyl group and a 2,2,3,3,3-pentafluoropropyl group. Flame retardant solvent.   The fluorine-containing phosphate ester of the general formula (1) is tris phosphate (2,2-difluoroethyl), tris phosphate (2,2,2-trifluoroethyl), tris phosphate (2,2,3,3). 3-tetrafluoropropyl), tris (2,2,3,3,3-pentafluoropropyl) phosphate, bis (2,2-difluoroethyl) phosphate 2,2,2-trifluoroethyl, bisphosphate (2,2,2-trifluoroethyl) 2,2-difluoroethyl, bis (2,2,2-trifluoroethyl) phosphate 2,2,3,3-tetrafluoropropyl, bis (2, 2,2-trifluoroethyl) methyl, bis (2,2,2-trifluoroethyl) ethyl phosphate and bis (2,2,3,3-tetrafluoropropyl) 2,2,2-trifluorophosphate Consisting of ethyl Flame retardant solvent for non-aqueous electrolyte according to claim 1 or claim 2, characterized in that at least one selected from the. In the general formula (2), Rf ⁴ represents 2,2-difluoroethyl group, 2,2,2-trifluoroethyl group, 2,2,3,3-tetrafluoropropyl group, and 2,2,3,3. , 3-pentafluoropropyl group, and Rf ⁵ is a difluoromethyl group, 1,1,2,2-tetrafluoroethyl group, and 1,1,2,3,3. The flame retardant solvent for a non-aqueous electrolyte according to any one of claims 1 to 3, wherein the flame retardant solvent is one or more selected from the group consisting of 1,3-hexafluoropropyl groups. In the general formula (3), Rf ⁶ is at least one selected from the group consisting of a fluorine atom, a difluoromethyl group, a trifluoromethyl group and a heptafluoropropyl group, and Rf ⁷ is a methyl group, an ethyl group, 2, 2 1 selected from the group consisting of a difluoroethyl group, a 2,2,2-trifluoroethyl group, a 2,2,3,3-tetrafluoropropyl group and a 2,2,3,3,3-pentafluoropropyl group The flame retardant solvent for a non-aqueous electrolyte according to any one of claims 1 to 3, wherein the flame retardant solvent is a species or more. In the general formula (4), Rf ⁸ and Rf ⁹ are each independently methyl group, ethyl group, 2,2-difluoroethyl group, 2,2,2-trifluoroethyl group, 2,2,3,3- 4. The method according to claim 1, which is at least one selected from the group consisting of a tetrafluoropropyl group and a 2,2,3,3,3-pentafluoropropyl group. 5. Flame retardant solvent for non-aqueous electrolyte.   The amount of the fluorine-containing solvent represented by the general formulas (2) to (4) to the fluorine-containing phosphate ester represented by the general formula (1) is 0.2 to 5 times in volume ratio. Item 7. A flame retardant solvent for a non-aqueous electrolyte solution according to any one of items 6.   A flame retardant nonaqueous electrolytic solution comprising a lithium salt and / or a magnesium salt as an electrolyte, and the flame retardant solvent according to any one of claims 1 to 7 as a solvent.   A flame retardant non-aqueous solution comprising a lithium salt and / or a magnesium salt as an electrolyte, and containing 3 to 80% by volume of the flame retardant solvent according to any one of claims 1 to 7. Electrolytic solution.   A lithium salt and / or magnesium salt as an electrolyte, and a flame retardant solvent according to any one of claims 1 to 7 comprising a fluorine-containing phosphate ester and a fluorine-containing solvent as a flame retardant solvent, A nonaqueous electrolytic solution comprising a cyclic carbonate and a non-fluorine chain carbonate as a solvent.   The nonaqueous electrolytic solution according to claim 10, wherein the fluorine-containing solvent is a fluorine-containing ether having a fluorine content of 60% by weight or more in the fluorine-containing ether represented by the general formula (2), and A non-flammable non-aqueous electrolyte characterized in that the abundance of the fluorinated ether is 0.3 to 5 times by volume with respect to the non-fluorinated chain carbonate.   The nonaqueous electrolytic solution according to claim 10, wherein (1,1,2,2-tetrafluoroethyl) 2,2,2-trifluoroethyl ether or (1,1,2,2) is used as the fluorine-containing solvent. Non-flammable non-aqueous electrolysis characterized in that 2-tetrafluoroethyl) 2,2,3,3-tetrafluoropropyl ether is present in a volume ratio of 0.3 to 5 times that of non-fluorinated chain carbonate liquid.   The nonaqueous electrolytic solution according to claim 10, wherein at least a part of the cyclic carbonate is fluoroethylene carbonate.   The nonflammable nonaqueous electrolytic solution according to claim 11 or 12, wherein at least a part of the cyclic carbonate is fluoroethylene carbonate.