JP2008021560A - Nonaqueous electrolyte - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte useful for an electrolyte for a lithium secondary battery, incombustible, high in solubility of an electrolyte salt, high in discharge capacity, and excellent in charge discharge cycle characteristics. <P>SOLUTION: The nonaqueous electrolyte contains an organic solvent (II) containing 0.5-30 vol.% fluorine-containing phosphate (I) represented by O=P(CH<SB>2</SB>Rf)<SB>3</SB>, and an electrolyte salt (III). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a nonflammable electrolyte solution suitable for a lithium secondary battery.

  As a solvent for dissolving an electrolyte salt for a lithium secondary battery, cyclic carbonates such as ethylene carbonate and propylene carbonate, and chain carbonates such as diethyl carbonate and ethyl methyl carbonate are used. However, since these hydrocarbon carbonates have a low flash point and high combustibility, there is a risk of ignition or explosion due to overcharging or overheating. In particular, large lithium secondary batteries for hybrid vehicles and distributed power sources are important issues for ensuring safety.

  In order to prevent such ignition and explosion, it has been proposed to add a flame retardant or an incombustible agent. One such additive is an alkyl phosphate ester.

  Examples of the electrolyte solution for a lithium secondary battery to which an alkyl phosphate ester is added include those disclosed in Patent Documents 1 to 3. Although the trimethyl phosphate used in these documents makes the electrolyte flame-retardant (not flammable but ignited), it has not yet imparted non-flammability (a property that does not ignite).

（式中、ｎおよびｍは１または２でｎ＋ｍ＝３；Ｒ¹はアルキル基またはハロゲン化アルキル基など；Ｒ²はメチル、エチルまたはハロゲン化アルキル基）で示されるリン酸エステルを有機溶媒に対して５〜１００質量％配合するときに難燃性が向上すると記載されており、ハロゲン化アルキル基含有リン酸エステルの具体例として、ジ(２，２，２−トリフルオロエチル)−メタンホスホネート、ジ(２，２，２−トリフルオロエチル)−エタンホスホネート、ジ（２，２，３，３，３−ペンタフルオロ−ｎ−プロピル）−メタンホスホネート、ジメチル−パーフルオロエタンホスホネートがあげられている。 In Patent Document 4, the formula:

(Wherein n and m are 1 or 2 and n + m = 3; R ¹ is an alkyl group or a halogenated alkyl group, etc .; R ² is a methyl, ethyl or halogenated alkyl group) On the other hand, it is described that the flame retardancy is improved when blended in an amount of 5 to 100% by mass. As a specific example of the halogenated alkyl group-containing phosphate ester, di (2,2,2-trifluoroethyl) -methanephosphonate Di (2,2,2-trifluoroethyl) -ethanephosphonate, di (2,2,3,3,3-pentafluoro-n-propyl) -methanephosphonate, dimethyl-perfluoroethanephosphonate Yes.

  However, the amount of nonflammability (non-ignitability) obtained is 50% by mass or more of the organic solvent (Table 1), and nonflammability is achieved only when a large amount is blended. Also, the capacity retention rate is below 90%, and the cycle characteristics are degraded.

  Patent Document 5 describes that a special fluorine-containing phosphoric acid derivative having a ring structure containing a phosphorus atom is used as a flame retardant, but this flame retardant is also incorporated in a large amount of 50% by mass or more of an organic solvent. Incombustibility has been achieved for the first time (Table 1). The capacity retention rate is also about 85%, and the cycle characteristics are degraded.

Japanese Patent Laid-Open No. 04-184870 Japanese Patent Laid-Open No. 08-022839 Japanese Patent Application Laid-Open No. 11-238652 JP-A-11-233141 JP-A-11-283669

  The present invention is intended to solve such conventional problems, and provides a non-aqueous electrolyte solution that is nonflammable, has high solubility of electrolyte salt, has a large discharge capacity, and is excellent in charge / discharge cycle characteristics. With the goal.

（式中、Ｒｆ¹、Ｒｆ²およびＲｆ³は同じかまたは異なり、いずれも炭素数１〜３の含フッ素アルキル基）で示される含フッ素リン酸エステル（Ｉ）を０．５〜３０体積％含む有機溶媒（ＩＩ）と電解質塩（ＩＩＩ）を含む非水系電解液に関する。 That is, the present invention
Formula (I):

(Wherein Rf ¹ , Rf ² and Rf ³ are the same or different, and all are fluorine-containing alkyl groups having 1 to 3 carbon atoms) 0.5 to 30% by volume of fluorine-containing phosphate ester (I) represented by The present invention relates to a nonaqueous electrolytic solution containing an organic solvent (II) and an electrolyte salt (III).

  According to the present invention, a non-aqueous electrolyte solution that is non-flammable and flame retardant, which is useful as an electrolyte solution for a lithium secondary battery, has high electrolyte salt solubility, a large discharge capacity, and excellent charge / discharge cycle characteristics. Can be provided.

  In the present specification, “nonflammability” means a property that does not ignite in an ignition test (Test Example 6) described later, and “flame retardant” refers to ignition / ignition in a flame retardant test (Test Example 5) described later. The nature that does not rupture.

In the present invention, the fluorine-containing phosphate (I) added to achieve incombustibility is a compound represented by the formula (I). When Rf ¹ , Rf ² and Rf ³ have more than 4 carbon atoms, the viscosity becomes high and the compatibility becomes unfavorable. Rf ¹ , Rf ² and Rf ³ preferably have 2 carbon atoms.

In the formula (I), Rf ¹ , Rf ² and Rf ³ can be preferably exemplified by CF _3- , CF ₃ CF _2- , CF ₃ CH _2- , HCF ₂ CF ₂ -or CF ₃ CFHCF _2- From the viewpoint of high salt solubility and high compatibility with other solvents, at least one of Rf ¹ , Rf ² and Rf ³ , and all of them are preferably HCF ₂ CF ₂ —. Specifically, from the point that nonflammability can be achieved with a small amount, the viscosity is low, and the compatibility is good, Rf ¹ , Rf ^2, and Rf ³ are all CF ₃ CF ₂ — 2,2,3,3,3-pentafluoropropyl, Rf ¹ , Rf ² and Rf ³ are all HCF ₂ CF ₂ — tri2,2,3,3-tetrafluoropropyl phosphate, Rf ¹ , Preferred are tri-2,2,2-trifluoroethyl phosphate and the like in which both Rf ² and Rf ³ are CF ₃ —, and particularly tri-2,2,3,3,3-pentafluoropropyl phosphate, triphosphate phosphate 2,2,3,3-tetrafluoropropyl is preferable, and tri-2,2,3,3-tetrafluoropropyl phosphate is particularly preferable.

The fluorine-containing phosphate ester (I) is added in an amount of 0.5 to 30% by volume in the electrolyte salt dissolving organic solvent (II). When the amount is too large, the solubility of the electrolyte salt is lowered and the compatibility is lowered. When the amount is too small, the incombustibility becomes insufficient. The preferable upper limit is 25% by volume, and further 20% by volume, although it depends on the types of Rf ¹ , Rf ² and Rf ³ . The lower limit is preferably 1% by volume. In particular, when Rf ¹ , Rf ² and Rf ³ are a perfluoroalkyl group or a hydrofluoroalkyl group in which one or two fluorine atoms of the perfluoroalkyl group are substituted with a hydrogen atom, nonflammability is achieved at 20% by volume or less. Can be achieved.

  Examples of the organic solvent (II) for dissolving the electrolyte salt in the electrolytic solution of the present invention include hydrocarbon carbonates that may contain fluorine atoms, ethers that may contain fluorine atoms, and lactones that may contain fluorine atoms. One type or two or more types such as a nitrile which may contain a fluorine atom may be employed.

  Examples of hydrocarbon carbonates that may contain fluorine atoms include cyclic carbonates and / or chain carbonates, and these are most used in electrolyte solutions for lithium secondary batteries. Examples of the cyclic carbonate include ethylene carbonate, vinylene carbonate, propylene carbonate, butylene carbonate, and vinyl ethylene carbonate. Examples of the chain carbonate include diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate.

Moreover, when the fluorinated hydrocarbon carbonate is contained, the addition amount of the fluorine-containing phosphate (I) can be further reduced due to the flame retarding action of fluorine atoms. Examples of the fluorinated hydrocarbon carbonate include compounds described in JP-A-6-21992, JP-A-2000-327634, JP-A-2001-256983, etc. Among them, 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 3,3,3-trifluoropropyl carbonate are preferred.

  The ether which may contain a fluorine atom may be a non-fluorine ether or a fluorine-containing ether. Examples of non-fluorine ethers include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,4-dioxane, 1,3-dioxolane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and the like.

The fluorine-containing ether has both an effect of making the electrolyte flame-retardant and an effect of improving low-temperature characteristics. Examples of the fluorine-containing ether include Japanese Patent Application Laid-Open No. 08-037024, Japanese Patent Application Laid-Open No. 09-097627, Japanese Patent Application Laid-Open No. 11-026015, Japanese Patent Application Laid-Open No. 2000-294281, Japanese Patent Application Laid-Open No. 2001-052737, and Japanese Patent Application Laid-Open No. -307123 etc. can illustrate the compound described. Above all, formula (1):
Rf ⁴ -O-Rf ⁵
(Wherein Rf ⁴ and Rf ⁵ are the same or different, both of which are fluorine-containing alkyl groups having 2 to 4 carbon atoms). The compatibility is also preferable from the viewpoint of good compatibility. Specifically, HCF ₂ CF ₂ CH ₂ OCF ₂ CFHCF ₃ and HCF ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H are preferable.

  The addition amount of the fluorine-containing ether is 70% by volume or less, usually 60% by volume or less, preferably 55% by volume or less in the organic solvent (II) from the viewpoint of imparting flame retardancy.

  Examples of the lactone which may contain a fluorine atom include γ-butyrolactone and γ-valerolactone.

  Examples of the nitrile which may contain a fluorine atom include acetonitrile and propionitrile.

  In addition, hexafluorobenzene, fluorobenzene, toluene and the like can be used in an amount of up to 3% by volume for the purpose of improving the cycle characteristics of the electrolytic solution.

  Among these, an organic solvent containing a hydrocarbon cyclic carbonate as an essential component and further containing a hydrocarbon chain carbonate is preferable from the viewpoint of good solubility, compatibility and low temperature characteristics of the electrolyte salt.

  Specifically, an organic solvent for dissolving an electrolyte salt containing ethylene carbonate and / or vinylene carbonate in an amount of 3 to 40% by volume and diethyl carbonate, ethyl methyl carbonate or dimethyl carbonate in a proportion of 40 to 96% by volume. Is preferred. When ethylene carbonate and / or vinylene carbonate is 3 to 40% by volume, particularly 3 to 25% by volume, the compatibility and the low temperature characteristics are preferable. In addition, when adding 10 volume% or more of fluorine-containing phosphate ester (I) and improving nonflammability, chain carbonate is further added to ethylene carbonate and / or vinylene carbonate in the same amount as ethylene carbonate and / or vinylene carbonate. From the viewpoint of increasing the compatibility, it is preferable to use a large amount in combination.

Examples of the electrolyte salt (III) used in the electrolytic solution of the present invention include LiPF ₆ , LiBF ₄ , LiN (O ₂ SCF ₃ ) ₂ , LiN (O ₂ SC ₂ F ₅ ) _{2 and the} like. For a lithium secondary battery, LiPF ₆ and LiBF ₄ are preferable.

  The concentration of the electrolyte salt (III) needs 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 (II) for dissolving the electrolyte salt.

The nonaqueous electrolytic solution of the present invention is particularly excellent as an electrolytic solution for a lithium secondary battery. In this case, 3 to 40% by volume of ethylene carbonate and / or vinylene carbonate and 1 of diethyl carbonate, ethyl methyl carbonate, or dimethyl carbonate. Electrolyte containing 40-96 vol% of seeds or two or more and tri-2,2,3,3,3-pentafluoropropyl phosphate or 1-20 vol% of tri-2,2,3,3-tetrafluoropropyl phosphate A non-aqueous electrolyte solution containing LiPF ₆ or LiBF ₄ at a concentration of 0.8 mol / liter or more in the organic solvent for salt dissolution is suitable, particularly ethylene carbonate and / or vinylene carbonate 3 to 25% by volume, diethyl carbonate, One or more of ethyl methyl carbonate or dimethyl carbonate LiPF ₆ or LiBF ₄ at a concentration of 0.8 mol / liter or more in an electrolyte salt-dissolving organic solvent containing 55 to 96% by volume and 1 to 20% by volume of tri-2,2,3,3-tetrafluoropropyl phosphate. A nonaqueous electrolytic solution containing is preferable.

  Since the electrolyte of the present invention is nonflammable, it is useful as an electrolyte for large lithium secondary batteries for hybrid vehicles and distributed power supplies, but also for electrolytes for aluminum electrolytic capacitors and electric double layer capacitors. It is also useful as a non-aqueous electrolyte such as an electrolyte.

  Next, the present invention will be specifically described based on examples, but the present invention is not limited to such examples.

Example 1
An electrolyte salt dissolving solvent is prepared by mixing tri2,2,3,3,3-pentafluoropropyl phosphate / ethylene carbonate / diethyl carbonate in a 20/30/50 vol% ratio, and for dissolving the electrolyte salt. adding LiPF ₆ in a solvent at a concentration of 1.0 mole / liter, sufficiently stirred at 25 ° C., to produce the electrolytic solution of the present invention.

Example 2
An electrolyte salt dissolving solvent was prepared by mixing tri2,2,3,3-tetrafluoropropyl phosphate / ethylene carbonate / diethyl carbonate at a ratio of 10/30/60% by volume. LiPF ₆ was added to a concentration of 1.0 mol / liter, and the mixture was sufficiently stirred at 25 ° C. to produce the electrolytic solution of the present invention.

Example 3
An electrolyte salt dissolving solvent was prepared by mixing tri 2,2,3,3-tetrafluoropropyl phosphate / ethylene carbonate / diethyl carbonate in a 20/20/60 vol% ratio. LiPF ₆ was added to a concentration of 1.0 mol / liter, and the mixture was sufficiently stirred at 25 ° C. to produce the electrolytic solution of the present invention.

Example 4
An electrolyte salt dissolving solvent was prepared by mixing tri2,2,3,3-tetrafluoropropyl phosphate / ethylene carbonate / diethyl carbonate at a ratio of 30/10/60% by volume. LiPF ₆ was added to a concentration of 1.0 mol / liter, and the mixture was sufficiently stirred at 25 ° C. to produce the electrolytic solution of the present invention.

Example 5
An electrolyte salt dissolving solvent was prepared by mixing tri2,2,3,3-tetrafluoropropyl phosphate / ethylene carbonate / diethyl carbonate in a ratio of 20/10/70% by volume. LiPF ₆ was added to a concentration of 1.0 mol / liter, and the mixture was sufficiently stirred at 25 ° C. to produce the electrolytic solution of the present invention.

Example 6
An electrolyte salt dissolving solvent was prepared by mixing tri2,2,3,3-tetrafluoropropyl phosphate / ethylene carbonate / diethyl carbonate at a ratio of 10/20/70% by volume. LiPF ₆ was added to a concentration of 1.0 mol / liter, and the mixture was sufficiently stirred at 25 ° C. to produce the electrolytic solution of the present invention.

Example 7
An electrolyte salt dissolving solvent was prepared by mixing tri 2,2,3,3-tetrafluoropropyl phosphate / ethylene carbonate / diethyl carbonate at a ratio of 5/30/65% by volume. LiPF ₆ was added to a concentration of 1.0 mol / liter, and the mixture was sufficiently stirred at 25 ° C. to produce the electrolytic solution of the present invention.

Example 8
An electrolyte salt dissolving solvent is prepared by mixing tri2,2,3,3,3-pentafluoropropyl phosphate / ethylene carbonate / diethyl carbonate at a ratio of 20/40/40% by volume. adding LiPF ₆ in a solvent at a concentration of 1.0 mole / liter, sufficiently stirred at 25 ° C., to produce the electrolytic solution of the present invention.

Example 9
A solvent for dissolving an electrolyte salt was prepared by mixing tri2,2,3,3-tetrafluoropropyl phosphate / vinylene carbonate / diethyl carbonate at a ratio of 10/30/60% by volume. LiPF ₆ was added to a concentration of 1.0 mol / liter, and the mixture was sufficiently stirred at 25 ° C. to produce the electrolytic solution of the present invention.

Example 10
A solvent for dissolving an electrolyte salt was prepared by mixing tri2,2,3,3-tetrafluoropropyl phosphate / vinylene carbonate / diethyl carbonate at a ratio of 10/30/60% by volume. LiBF ₄ was added to a concentration of 1.0 mol / liter, and the mixture was sufficiently stirred at 25 ° C. to produce the electrolytic solution of the present invention.

Comparative Example 1
Ethylene carbonate / diethyl carbonate was mixed at a ratio of 40/60% by volume to prepare an electrolyte salt dissolving solvent, and LiPF ₆ was added to the electrolyte salt dissolving solvent to a concentration of 1.0 mol / liter, The solution was sufficiently stirred at 25 ° C. to produce a comparative electrolyte.

Comparative Example 2
An electrolyte salt dissolving solvent was prepared by mixing triethyl phosphate / ethylene carbonate / diethyl carbonate at a ratio of 10/30/60% by volume, and LiPF ₆ was added at a concentration of 1.0 mol / liter to the electrolyte salt dissolving solvent. Then, the mixture was sufficiently stirred at 25 ° C. to produce a comparative electrolyte.

Comparative Example 3
Mixing tri 2,2,3,3,3-pentafluoropropyl phosphate / ethylene carbonate / diethyl carbonate at a ratio of 35/30/35% by volume to prepare a solvent for dissolving the electrolyte salt. LiPF ₆ was added to the solvent so as to have a concentration of 1.0 mol / liter, and the mixture was sufficiently stirred at 25 ° C. to attempt to produce a comparative electrolyte, but an electrolyte salt was deposited.

Comparative Example 4
A solvent for dissolving an electrolyte salt is prepared by mixing tri2,2,3,3,3-pentafluoropropyl phosphate / ethylene carbonate / diethyl carbonate in a 35/10/55 volume% ratio. LiPF ₆ was added to the solvent so as to have a concentration of 1.0 mol / liter, and the mixture was sufficiently stirred at 25 ° C. to attempt to produce a comparative electrolyte, but an electrolyte salt was deposited.

Test Example 1 (Solubility of electrolyte salt)
6 ml of the electrolytic solution produced in each of Examples 1 to 10 and Comparative Examples 1 to 4 is taken out into a 9 ml sample bottle, allowed to stand at 25 ° C. for 8 hours, and the state of the liquid is visually observed. The results are shown in Table 1.
(Evaluation criteria)
○: A uniform solution.
(Triangle | delta): Electrolyte salt precipitates.
X: The liquid is separated into layers.

Test example 2 (low temperature stability)
6 ml of the electrolytic solution produced in each of Examples 1 to 10 and Comparative Examples 1 to 4 is taken out into a 9 ml sample bottle, and the state after standing in a freezer at −20 ° C. for 8 hours is visually observed. The results are shown in Table 1.
(Evaluation criteria)
○: A uniform solution.
(Triangle | delta): Electrolyte salt precipitates.
X: The liquid solidifies.

Test Example 3 (Ionic conductivity)
The ion conductivity of Examples 1 and 2 and Comparative Example 1 was examined by the following method. The results are shown in Table 2.
(Test method)
The ion conductivity is measured at room temperature by the AC four-terminal method. The impedance measurement apparatus uses SI1280B manufactured by Toyo Technica Co., Ltd., and the frequency is in the range of 10 ⁴ Hz to 10 ¹ Hz.

Test example 4 (charge / discharge characteristics)
A coin-type lithium secondary battery was produced by the following method.
(Preparation of positive electrode)
A positive electrode active material prepared by mixing LiCoO ₂ , carbon black, and polyvinylidene fluoride (made by Kureha Chemical Co., Ltd., trade name KF-1000) at 85/6/9 (mass% ratio) is dispersed in N-methyl-2-pyrrolidone. The slurry was applied uniformly on a positive electrode current collector (aluminum foil having a thickness of 20 μm), dried, and then punched into a disk having a diameter of 12.5 mm to produce a positive electrode.
(Preparation of negative electrode)
Styrene-butadiene rubber dispersed with distilled water is added to artificial graphite powder (manufactured by Temcal Co., Ltd., trade name KS-44) so that the solid content becomes 6% by mass, and mixed with a disperser to form a slurry. Was uniformly coated on a negative electrode current collector ((aluminum foil having a thickness of 18 μm), dried, and then punched into a disk having a diameter of 12.5 mm to produce a negative electrode.
(Preparation of separator)
A separator made of polyethylene having a diameter of 14 mm (manufactured by Celgard Co., Ltd., trade name Celgard 3501) was impregnated with the electrolytic solution produced in the above Example or Comparative Example.
(Production of coin-type lithium secondary battery)
The positive electrode is housed in a stainless steel can body that also serves as a positive electrode current collector, and the negative electrode is placed thereon via the separator, and the can body and a sealing plate that also serves as the negative electrode current collector are insulated. The coin-type lithium secondary battery was manufactured by caulking and sealing through a gasket.
(Charge / discharge test)
The discharge capacity after 50 cycles is measured under the following charge / discharge measurement conditions. The evaluation is performed using an index with the result of Comparative Example 1 as 100. The results are shown in Table 2.
Charging / discharging voltage: 2.5-4.2V
Charge: Hold constant voltage until charge current becomes 1/10 at 0.5C, 4.2V Discharge: 1C

Test Example 5 (Flame retardance test)
The flame retardancy of the electrolyte was examined by the following method. The results are shown in Table 2.
(Sample preparation)
A positive electrode and a negative electrode produced in the same manner as in Test Example 4 are cut into rectangles of 50 mm × 100 mm, and a polyethylene separator (manufactured by Celgard Co., Ltd., trade name Celgard 3501) is sandwiched between them to form a laminate. After welding an aluminum foil having a width of 5 mm and a length of 150 mm as a lead wire to the positive electrode and the negative electrode, this laminate is immersed in the electrolytic solution produced in the above example or comparative example, and then sealed with a laminator to produce a laminate cell. .
(Test method)
The laminate cell is subjected to the following three types of flame retardancy tests.
[Nail penetration test]
After charging the laminate cell to 4.3 V, a 3 mm diameter nail is passed through the laminate cell and examined for ignition or rupture of the laminate cell.
[Overcharge test]
The laminate cell is charged for 24 hours at a rate of 10 hours, and the presence or absence of ignition of the laminate cell is examined.
[Short-circuit test]
After charging the laminate cell to 4.3 V, the positive electrode and the negative electrode are short-circuited with a copper wire, and the presence or absence of ignition of the laminate cell is examined.

  In any of the tests, the case where there is no ignition (rupture) is indicated by ◯, and the case where ignition (explosion) is indicated by x.

Test Example 6 (Ignition test)
The nonflammability (non-ignition property) of the electrolyte was examined by the following method. The results are shown in Table 2.
(Sample preparation)
A strip of cellulose paper (width 15 mm, length 320 mm, thickness 0.04 mm) is sufficiently immersed in the electrolytic solution produced in the above-mentioned example or comparative example and then taken out to obtain a sample.
(Test method)
The sample is fixed on a metal table, and a lighter is brought close to one end of the sample and held for 1 second to check for ignition. In case of ignition, measure how long the sample burns. The test is performed three times and an average value is taken.

Claims (8)

Formula (I):

(Wherein Rf ¹ , Rf ² and Rf ³ are the same or different, and all are fluorine-containing alkyl groups having 1 to 3 carbon atoms) 0.5 to 30% by volume of fluorine-containing phosphate ester (I) represented by A nonaqueous electrolytic solution containing an organic solvent (II) and an electrolyte salt (III). In the fluorine-containing phosphate ester (I), Rf ¹ , Rf ² and Rf ³ are the same or different in the formula (I), and all of them are CF ₃ —, CF ₃ CF ₂ —, CF ₃ CH ₂ —, HCF _2. The nonaqueous electrolytic solution according to claim 1, which is CF ₂ — or CF ₃ CFHCF ₂ —. Fluorine-containing phosphate ester (I) is tri (2,2,3,3,3-pentafluoropropyl) phosphate in which Rf ¹ , Rf ² and Rf ³ are all CF ₃ CF ₂ — in formula (I) The non-aqueous electrolyte solution according to claim 2. The fluorine-containing phosphate ester (I) is tri-2,2,3,3-tetrafluoropropyl phosphate in which Rf ¹ , Rf ² and Rf ³ are all HCF ₂ CF ₂ — in the formula (I) The non-aqueous electrolyte solution according to claim 2. The organic solvent (II) is one or more of hydrocarbon-based carbonates optionally containing fluorine atoms, lactones optionally containing fluorine atoms, or ethers optionally containing fluorine atoms. The non-aqueous electrolyte solution in any one of 1-4. The non-aqueous electrolyte solution according to claim 1, wherein the electrolyte salt (III) is LiPF ₆ , LiBF ₄ , LiN (O ₂ SCF ₃ ) ₂ or LiN (O ₂ SC ₂ F ₅ ) ₂ . 3 to 40% by volume of ethylene carbonate and / or vinylene carbonate, 40 to 96% by volume of one or more of diethyl carbonate, ethyl methyl carbonate or dimethyl carbonate, and tri-2,2,3,3,3-pentaphosphate An electrolyte salt-dissolving organic solvent containing 1 to 20% by volume of fluoropropyl or tri2,2,3,3-tetrafluoropropyl phosphate contains LiPF ₆ or LiBF ₄ at a concentration of 0.8 mol / liter or more. Aqueous electrolyte. The nonaqueous electrolytic solution according to claim 1, which is an electrolytic solution for a lithium secondary battery.