JP2010097802A - Electrolytic solution - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolytic solution that improves the oxidation resistance and rate characteristics and enhances safety, while maintaining the characteristics of a fluorine-containing chain carbonate. <P>SOLUTION: The electrolytic solution contains an electrolyte salt and a solvent that dissolve an electrolyte salt that may have a fluorine-containing chain carbonate, expressed by formula: R<SP>a</SP>CF<SB>2</SB>-OCOOR<SP>b</SP>(wherein R<SP>a</SP>is H, F, Cl or an alkyl group that may contain a fluorine atom with a carbon number of 1-3; R<SP>b</SP>is an alkyl group that may have a fluorine atom with a carbon number of 1-7). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrolytic solution containing a fluorine-containing chain carbonate excellent in oxidation resistance and an electrolyte salt.

  Carbonates such as ethylene carbonate, propylene carbonate, and dimethyl carbonate are used as electrolyte salt solvents for electrochemical devices such as lithium secondary batteries, solar batteries, radical batteries, and capacitors. However, there is a problem that the flash point is low and the combustibility is high, so there is a risk of ignition explosion due to overcharging and overheating, and the output is lowered because the viscosity is high and the conductivity at low temperature is low.

  Further, in the lithium secondary battery, an increase in the withstand voltage of the electrolytic solution is required to increase the capacity. Furthermore, in the capacitor, it is desirable that both the negative electrode and the positive electrode are hard carbon, and particularly, it is desirable that they can be stably used at 3 V or more, but conventionally used solvents for electrolyte salts such as propylene carbonate and dimethyl carbonate. Then, since the decomposition of the electrolyte occurs at 3 V or more, it cannot be used.

In order to solve the problem, it has been proposed to use a fluorinated chain carbonate obtained by fluorinating a chain carbonate. For example, a fluorine-containing chain carbonate typified by a carbonate (Patent Document 1) represented by R ¹ CH ₂ OCOOCH ₂ R ² (R ¹ and R ² are different and may be substituted with a fluorine atom) Proposed.

Further, in Patent Document 2, as a chain carbonate having excellent flame retardancy, low temperature characteristics, withstand voltage, high electrolyte salt solubility, and excellent compatibility with hydrocarbon solvents, a general formula:
^{(HCX 1 X 2) - (} CF 2) n - (CH 2) m -O-COO-
(Wherein X ¹ and X ² are the same or different and H or F; n is an integer of 0 to 10; m is an integer of 0 to 5; provided that when X ¹ = X ² = H, n is 0. Is not proposed), but there is no specific example of m = 0.

JP-A-6-219992 International Publication No. 2006/088009 Pamphlet

  An object of the present invention is to provide an electrolytic solution that further improves the oxidation resistance and rate characteristics while maintaining the characteristics of the conventional fluorine-containing chain carbonate, and increases the safety.

In general, fluorine-containing chain carbonates were considered to be inferior in oxidation resistance. However, the present inventors have found that all of the conventional fluorine-containing chain carbonates represented by Patent Documents 1 and 2 are carbonate groups —OCOO—. The fluoroalkyl group to be bonded is linked by a methylene group —CH ₂ —, and when this methylene group is replaced with a difluoromethylene group (—CF ₂ —), the oxidation resistance is unexpectedly improved and the viscosity is low. In addition, the excellent flame retardancy, low-temperature characteristics, and withstand voltage of conventional fluorine-containing chain carbonates are based on fluoroalkyl groups, and further improve the solubility of electrolyte salts and phase with hydrocarbon solvents. The inventors have found that the effect of improving solubility can be maintained, and have completed the present invention.

That is, the present invention provides the formula (1):
R ^a CF ₂ —OCOOR ^b (1)
(In the formula, R ^a is H, F, Cl or an alkyl group which may have a fluorine atom having 1 to 3 carbon atoms; R ^b is an alkyl which may have a fluorine atom having 1 to 7 carbon atoms; The present invention relates to an electrolyte solution containing a solvent (I) for dissolving an electrolyte salt containing the fluorine-containing chain carbonate (1) represented by the formula (III) and an electrolyte salt (II).

  The present invention also relates to an electrochemical device including the electrolytic solution of the present invention and a lithium secondary battery including the electrolytic solution of the present invention.

  According to the present invention, oxidation resistance is further maintained while maintaining the characteristics of conventional fluorine-containing chain carbonates such as flame retardancy, low temperature characteristics, withstand voltage, solubility of electrolyte salts and compatibility with hydrocarbon solvents. It is possible to provide an electrolytic solution that improves the safety and rate characteristics and increases the safety.

  The electrolytic solution of the present invention includes an electrolyte salt dissolving solvent (I) containing a fluorine-containing chain carbonate (1) containing a specific fluoroalkyl group and an electrolyte salt (II).

The fluorine-containing chain carbonate (1) contained in the electrolyte salt-dissolving solvent (I) used in the present invention has the formula (1):
R ^a CF ₂ —OCOOR ^b (1)
(In the formula, R ^a is H, F, Cl or an alkyl group which may have a fluorine atom having 1 to 3 carbon atoms; R ^b is an alkyl which may have a fluorine atom having 1 to 7 carbon atoms; Group).

As R ^a , the formula (1a):
(HCX ¹ X ² )-(1a)
(Wherein X ¹ and X ² are the same or different and H or F) is a fluoroalkyl group terminated with a site represented by the solubility of the electrolyte salt and the compatibility with the hydrocarbon solvent. It is preferable in terms of improvement.

Furthermore, the fluorine content of R ^a CF ₂ — is 40% by mass or more and 82.7% by mass (all hydrogen atoms are replaced by fluorine atoms) or less, and further 40.9 to 82.7% by mass. It is preferable from the viewpoint of good viscosity reduction and flash point improvement at low temperatures.

Specific examples of R ^a —CF ₂ — in the fluorine-containing chain carbonate (1) represented by the formula (1) include, for example, FCF ₂ —, HCF ₂ —, ClCF ₂ —, CH ₃ CF ₂ —, HCF ₂ CF _{2 -, H 2 CFCF 2 -} , CH 3 CHFCF 2 -, HCF 2 CHFCF 2 -, H 2 CFCH 2 CF 2 -, HCFClCF 2 CF 2 -, HCF 2 CFClCF 2 -, CH 3 CH 2 CF 2 -, CH ₃ CH ₂ CH ₂ CF ₂ — and the like can be preferably exemplified. However, since the viscosity tends to be high if there is a branch of —CH ₃ or —CF ₃ , the number is less (one) or more preferably zero.

R ^b of the fluorine-containing chain carbonate (1) is an alkyl group having 1 to 7 carbon atoms or a fluoroalkyl group.

Examples of the alkyl group having 1 to 7 carbon atoms include linear alkyl groups such as CH ₃ —, CH ₃ CH ₂ —, CH ₃ CH ₂ CH ₂ —, CH ₃ CH ₂ CH ₂ CH ₂ —; CH ₃ CH _{(CH 3) -, (CH} 3) 2 CH-, CH 3 CH (CH 3) CH 2 -, CH 3 CH 2 CH (CH 3) -, (CH 3) 2 CHCH 2 -, (C 2 H 5 ) ₂ CHCH ₂ —, branched chain alkyl groups such as (C ₂ H ₅ ) ₂ CH— and the like, and linear alkyl groups are preferred because of their low viscosity.

などを好ましくあげることができる。ただし、−ＣＨ₃や−ＣＦ₃という分岐を有していると粘性が高くなりやすいため、その数は少ない（１個）かゼロの方がより好ましい。 Examples of the fluoroalkyl group having 1 to 7 carbon atoms include those exemplified for R ^a CF ₂ —, H ₂ CF—, CH ₃ CF ₂ CH ₂ —, HCF ₂ CH ₂ CH ₂ —, CH ₃ CHFCH ₂ —, H ₂ CFCH ₂ CH _2- , HCF ₂ CHFCH _2- , H ₂ CFCF ₂ CH _2- , HCFClCF ₂ CH _2- , HCF ₂ CFClCH _2- , CH ₃ CHFCH ₂ CHFCH _2- , CH ₃ CF ₂ CH ₂ CF ₂ CH _2- , HCF ₂ CH ₂ CF ₂ CH ₂ CH _2- , HCF ₂ CHFCF ₂ CHFCH _2- , H ₂ CFCF ₂ CFHCF ₂ CH _2- , H ₂ CFCF ₂ CHFCF ₂ CH _2- , H ₂ CFCH ₂ CHFCH _{2 CH 2 -, HCF 2 CFClCF 2} CFClCH 2 -, HCFClCF 2 CFClCF 2 CH 2 -,

Etc. can be preferably given. However, since the viscosity tends to be high if there is a branch of —CH ₃ or —CF ₃ , the number is less (one) or more preferably zero.

The combination of R ^a and R ^b is ^{a case} where R ^a is a fluorine atom or an alkyl group which may have a fluorine atom having 1 to 3 carbon atoms, and R ^b is an alkyl group having 1 to 3 carbon atoms. From the viewpoint of low viscosity.

  Preferred specific examples of the fluorine-containing chain carbonate (1) are shown below, but are not limited thereto.

As a synthesis method, the formula (1b):
R ^a CF ₂ —O ^— M ⁺ (M is an alkali metal atom)
And R ^b -O-M ⁺ (M represents an alkali metal atom)
A method of subjecting the fluoroalcohol represented by the formula (wherein R ^a and R ^b are the same as described above) to the next reaction can be exemplified.

(1) React with phosgene such as COCl ₂ , COF ₂ and triphosgene under basic conditions.
(2) Formula (1c) in the presence or absence of a base catalyst:
R ¹ OCOOR ² (1c)
(Wherein R ¹ and R ² are the same or different and both are alkyl groups, preferably methyl groups or ethyl groups) and reacted with a compound represented by the method while distilling off by-produced alcohol (methanol or ethanol). Advance the reaction.
(3) Formula (1d) in the presence or absence of a base catalyst:
R ³ OCOOR ⁴ (1d)
(Wherein R ³ and R ⁴ are the same or different and are aryl groups, preferably phenyl groups).
(4) Formula (Ie) under basic or non-basic conditions:
ClCOOR ⁵ (1e)
(Wherein R ⁵ is an alkyl group, preferably a methyl group or an ethyl group), and the reaction proceeds while distilling off by-produced alcohol (methanol or ethanol).
(5) R ^a CF ₂ -OM ⁺ or R ^b -OM ⁺ is reacted in the presence of an equivalent or excess amount of phosgene or trichlorophosgene to give the formula (1e):
ClCOOCF ₂ R ^a
Or ClCOOR ^b
Is obtained in two steps, each of which is reacted with a different type of fluorinated alcohol.

When R ^a and R ^b are different types of groups, the above method (3) may be used, or synthesis may be performed in two stages using the methods (3) and (4).

A linear carbonate in which R ^b is a CF ₃ -terminal fluoroalkyl group can be synthesized by the same reaction as described above, but is particularly preferably synthesized by the method (3), (4) or (5).

  In the present invention, as the electrolyte salt dissolving solvent (I), in addition to the specific fluorine-containing chain carbonate (1), other electrolyte salt dissolving solvent (2) is used alone or in combination. May be.

  Other electrolyte salt dissolving solvents (2) include non-fluorinated solvents such as hydrocarbon carbonate solvents, nitrile solvents, lactone solvents, ester solvents, and fluorine-containing solvents other than fluorine-containing chain carbonates (1). It may be a system solvent.

  Examples of the non-fluorine solvent include ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane. , Methyl formate, methyl acetate, methyl propionate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, acetonitrile, dimethyl sulfoxide, methyl pyrrolidone, etc., especially in terms of improving dielectric constant, oxidation resistance, and electrochemical stability To ethylene carbonate, propylene carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, 1,3-dioxolane, and acetonitrile are preferred.

  Examples of the fluorine-containing solvent other than the fluorine-containing chain carbonate (1) include, for example, JP-A-6-219992, JP-A-10-149840, JP-A-2001-256983 and JP-A-2000-327634. In particular, fluorine-containing carbonates described in JP-A-6-219992 and JP-A-2001-256984, JP-A-6-176768, and JP-A-8-37024. The fluorine-containing ethers described in JP-A-11-307123 and JP-A-2000-294281 are preferred.

（式中、Ｒｆ⁵はフッ素含有率が１０〜７６質量％である含フッ素エーテル基、含フッ素アルコキシ基または炭素数２以上の含フッ素アルキル基；Ｘ⁵およびＸ⁶は同じかまたは異なり、いずれもＨ、Ｆ、Ｃｌ、ＣＦ₃またはＣＨ₃；Ｘ⁷は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）で示される環状カーボネートが好ましい。 In addition, it is desirable to use a fluorine-containing cyclic carbonate as another electrolyte salt-dissolving solvent (2) for a capacitor application that requires a particularly high withstand voltage. Furthermore, the formula (3):

(In the formula, Rf ⁵ is a fluorine-containing ether group, fluorine-containing alkoxy group or fluorine-containing alkyl group having 2 or more carbon atoms having a fluorine content of 10 to 76% by mass; X ⁵ and X ⁶ are the same or different, H, F, Cl, CF ₃ or CH ₃ ; X ⁷ is an alkyl group in which H, F, Cl or a hydrogen atom may be substituted with a halogen atom, and a hetero atom may be included in the chain) The cyclic carbonates shown are preferred.

As a specific example of a particularly preferable cyclic carbonate that can be used in combination, for example, in the formula (3), X ⁵ = X ⁶ = X ⁷ = H and Rf ⁵ is CF _3- , CF ₃ CF ₂ CH _2- , HCF _{2 CF 2 CH 2 -, CF 3} CF (CF 3) CH 2 -, CF 3 CH (CF 3) CH 2 -, CF 3 CF 2 CF 2 CF 2 CH 2 -, CF 3 CH 2 OCH 2 -, H ( Examples thereof include fluorine-containing cyclic carbonates such as CF ₂ ) ₂ CH ₂ OCH ₂ —, CF ₃ OCH ₂ —, CF ₃ CF ₂ CH ₂ OCH ₂ —, and FCH ₂ CF ₂ CH ₂ OCH ₂ —.

  By the way, fluorine-containing ethers are useful because they have excellent nonflammability-improving effects, but have low compatibility with non-fluorinated electrolyte salt dissolving solvents, especially hydrocarbon carbonates such as ethylene carbonate and diethylene carbonate. When a certain amount or more was mixed with the electrolyte salt dissolving solvent, it sometimes separated into two layers. However, when a fluorine-containing chain carbonate including a specific fluorine-containing chain carbonate (1) coexists, a uniform solution of these three components can be easily formed. This is presumed that the fluorine-containing chain carbonate acts as a compatibilizing agent for compatibilizing the fluorine-containing ether and the solvent for dissolving the non-fluorine electrolyte salt. Therefore, the fluorine-containing chain carbonate (1) and the electrolyte In the electrolytic solution containing the salt (II), the solvent for dissolving the non-fluorinated electrolyte salt, and the fluorine-containing ether, further improvement in incombustibility can be expected.

  The amount of the other electrolyte salt dissolving solvent (2) to be mixed is 1% by mass or more, preferably 10% by mass or more, particularly 20% by mass or more in the total electrolyte salt dissolving solvent. The upper limit is preferably 98% by mass, preferably 90% by mass, and particularly 80% by mass from the viewpoints of flame retardancy, low temperature characteristics, and withstand voltage.

  In particular, a capacitor can cope with a large current density, so that the electrolyte salt concentration in the electrolytic solution is preferably as high as possible. From this point of view, hydrocarbon solvents excellent in electrolyte salt solubility, particularly fluorine-containing carbonates other than the above-mentioned fluorine-containing chain carbonates of the present invention, propylene carbonate, γ-butyrolactone, acetonitrile, 1,3-dioxolane, etc. It is preferable to use together.

Further, when the operating voltage is increased particularly for capacitors, the fluorine-containing chain carbonate of the present invention itself has a high oxidation resistance, and therefore other solvents and electrolyte salts to be combined preferably have a high oxidation resistance. From this viewpoint, the other solvent is preferably a fluorine-containing carbonate other than the above-described fluorine-containing chain carbonate of the present invention, propylene carbonate, and γ-butyrolactone, and among the electrolyte salts described later, the anion is BF ₄ ⁻ , A salt which is PF ₆ ⁻ , AsF ₆ ⁻ or SbF ₆ ⁻ is preferred.

  Next, the electrolyte salt (II) which is the other component of the electrolytic solution of the present invention will be described.

  Examples of the electrolyte salt (II) that can be used in the present invention include conventionally known metal salts, liquid salts (ionic liquids), inorganic polymer salts, organic polymer salts, and the like.

  These electrolyte salts are particularly suitable compounds depending on the intended use of the electrolytic solution. Next, suitable electrolyte salts are illustrated for each application, but are not limited to the illustrated specific examples. In other applications, the following exemplified electrolyte salts can be used as appropriate.

  First, as the metal salt of the lithium secondary battery, various organic metal salts such as boron anion type, oxygen anion type, nitrogen anion type, carbon anion type, and phosphorus anion type can be used. Is preferably used.

Specific examples of the oxygen anion type include CF ₃ SO ₃ Li, C ₄ F ₉ SO ₃ Li, C ₈ F ₁₇ SO ₃ Li, CH ₃ SO ₃ Li, C ₆ H ₅ SO ₃ Li, and LiSO ₃ C. ₂ F ₄ SO ₃ Li, CF ₃ CO ₂ Li, C ₆ H ₅ CO ₂ Li, Li ₂ C ₄ O ₄ or the like may be used, and in particular, CF ₃ SO ₃ Li, C ₄ F ₉ SO ₃ Li, C It is preferable to use ₈ F ₁₇ SO ₃ Li.

Nitrogen anion types include (CF ₃ SO ₂ ) ₂ NLi (TFSI), (C ₂ F ₅ SO ₂ ) ₂ NLi (BETI), (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ) NLi, (CF ₃ SO ₂ ) (C ₈ F ₁₇ SO ₂ ) NLi, (CF ₃ CO) ₂ NLi, (CF ₃ CO) (CF ₃ CO ₂ ) NLi, ((CF ₃ ) ₂ CHOSO ₂ ) ₂ NLi, (C ₂ F ₅ CH ₂ OSO ₂ ) ₂ NLi or the like may be used, and (CF ₃ SO ₂ ) ₂ NLi (TFSI) or (C ₂ F ₅ SO ₂ ) ₂ NLi (BETI) is particularly preferable.

As the inorganic metal salt, LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiClO _{4 and the} like can be used, and it is particularly preferable to use LiPF ₆ , LiBF ₄ .

For capacitors, the organometallic salt is (Me) _x (Et) _y N (Me is methylene, Et is ethylene, x and y are the same or different and are integers from 0 to 4 and x + y = 4) The quaternary ammonium salts shown, specifically Et ₄ NBF ₄ , Et ₄ NClO ₄ , Et ₄ NPF ₆ , Et ₄ NAsF ₆ , Et ₄ NSbF ₆ , Et ₄ NCF ₃ SO ₃ , Et ₄ N (CF ₃ SO _{2) 2 N, Et 4 NC} 4 F 9 SO 3, Et 3 MeBF 4, Et 3 MeClO 4, Et 3 MePF 6, Et 3 MeAsF 6, Et 3 MeSbF 6, Et 3 MeCF 3 SO 3, Et 3 Me ( CF ₃ SO ₂ ) ₂ N, Et ₃ MeC ₄ F ₉ SO ₃ may be used, and Et ₄ NBF ₄ , Et ₄ NPF ₆ , Et ₄ NSbF ₆ , and Et ₄ NAsF ₆ are particularly preferable.

As the inorganic metal salt, LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ , LiClO ₄ , NaPF ₆ , NaBF ₄ , NaAsF ₆ , NaClO ₄ , KPF ₆ , KBF ₄ , KAsF ₆ , KClO _4, etc. can be used. in _{particular, LiPF 6, LiBF 4, LiSbF} 6, LiAsF 6, NaPF 6, it is preferable to use a NaBF _4.

などが例示できる。 For dye-sensitized solar cells, R ⁶ R ⁷ R ⁸ R ⁹ NI (R ^{6 to} R ⁹ are the same or different and are alkyl groups having 1 to 3 carbon atoms), LiI, NaI, KI,

Etc. can be exemplified.

  When a liquid salt is used as the electrolyte salt (II), organic and inorganic anions and polyalkylimidazolium cations, N-alkylpyridinium cations, tetrasalts are used for lithium secondary batteries, capacitors, and dye-sensitized solar cells. Examples thereof include salts with alkylammonium cations and tetraalkylphosphonium cations, and 1,3-dialkylimidazolium salts are particularly preferred.

Examples of polyalkylimidazolium cations include 1,3-dialkylimidazolium cations such as 1-ethyl-3-methylimidazolium cation (EMI ⁺ ) and 1-butyl-3-methylimidazolium cation (BMI ⁺ ); Trialkylimidazolium cations such as 2-dimethyl-3-propylimidazolium cation (DMPI ⁺ ) are preferred.

Preferred inorganic anions include, for example, AlCl ₄ ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , I ^{− and the} like, and organic anions include, for example, CH ₃ COO ⁻ , CF ₃ COO ⁻ , C ₃ F ₇ COO ⁻ , CF ₃ SO ₃ ⁻ , C ₄ F ₉ SO ₃ ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ , (C ₂ F ₅ SO ₂ ) ₂ N ^{− and the} like can be mentioned.

Specific examples include EMIAlCl ₄ , EMIBF ₄ , EMIPF ₆ , EMIAsF ₆ , EMII, EMICH ₃ COO, EMCF ₃ COO, EMIC ₃ F ₇ COO, EMCF ₃ SO ₃ , EMIC ₄ F ₉ SO ₃ , EMI (CF ₃ SO ₂ ) ₂ N, EMI (C ₂ F ₅ SO ₂ ) ₂ N, BMIAlCl ₄ , BMIBF ₄ , BMIPF ₆ , BMIAsF ₆ , BMII, BMICH ₃ COO, BMICF ₃ COO, BMIC ₃ F ₇ COO, BMICF ₃ SO ₃ , BMIC ₄ F ₉ SO ₃ , BMI (CF ₃ SO ₂ ) ₂ N, BMI (C ₂ F ₅ SO ₂ ) ₂ N, DMPIAlCl ₄ , DMPIBF ₄ , DMPIPF ₆ , DMPIAsF ₆ , DMPII, DMPICH ₃ COO, DMPICF ₃ COO , DMPIC ₃ F ₇ COO, DMPICF ₃ SO ₃ , DMPIC Examples thereof include ₄ F ₉ SO ₃ , DMPI (CF ₃ SO ₂ ) ₂ N, DMPI (C ₂ F ₅ SO ₂ ) ₂ N, and the like.

  In particular, iodides such as EMII, BMII, and DMPII are suitable for dye-sensitized solar cells.

  The amount of electrolyte salt (II) blended varies depending on the required current density, application, type of electrolyte salt, etc., but 0.1 part by mass or more with respect to 100 parts by mass of the specific fluoroalkyl group-containing chain carbonate (1), Further, it is preferably 1 part by mass or more, particularly 5 parts by mass or more, 200 parts by mass or less, more preferably 100 parts by mass or less, and particularly preferably 50 parts by mass or less.

  The electrolytic solution of the present invention is prepared by dissolving the electrolyte salt (II) in the fluoroalkyl group-containing chain carbonate (1) or the electrolyte salt dissolving solvent (I) containing the carbonate (1).

  The electrolytic solution of the present invention may be combined with a polymer material that dissolves or swells in the solvent used in the electrolytic solution of the present invention to form a gel (plasticized) gel electrolytic solution.

  Examples of such a polymer material include conventionally known polyethylene oxide and polypropylene oxide, modified products thereof (Japanese Patent Laid-Open Nos. 8-222270 and 2002-140405); polyacrylate polymers, polyacrylonitrile, and polyvinylidene fluoride. , Fluororesins such as vinylidene fluoride-hexafluoropropylene copolymer (Japanese Patent Publication No. 4-506726, Japanese Patent Publication No. 8-507407, Japanese Patent Laid-Open No. 10-294131); Examples thereof include composites with resins (Japanese Patent Laid-Open Nos. 11-35765 and 11-86630). In particular, it is desirable to use polyvinylidene fluoride or a vinylidene fluoride-hexafluoropropylene copolymer.

  In addition, ion conductive compounds described in JP-A-2006-114401 can also be used.

（式中、Ｒｆは架橋性官能基を有していてもよいフルオロエーテル基；Ｒ¹⁰はＲｆと主鎖を結合する基または結合手）で示される側鎖にフルオロエーテル基を有するエーテル単位；
ＦＡＥは、式（５ｂ）：

（式中、Ｒｆａは水素原子、架橋性官能基を有していてもよい含フッ素アルキル基；Ｒ¹¹はＲｆａと主鎖を結合する基または結合手）で示される側鎖に含フッ素アルキル基を有するエーテル単位；
ＡＥは、式（５ｃ）：

（式中、Ｒ¹³は水素原子、架橋性官能基を有していてもよいアルキル基、架橋性官能基を有していてもよい脂肪族環式炭化水素基または架橋性官能基を有していてもよい芳香族炭化水素基；Ｒ¹²はＲ¹³と主鎖を結合する基または結合手）で示されるエーテル単位；
Ｙは、式（５ｄ−１）〜（５ｄ−３）：

の少なくとも１種を含む単位；
ｎは０〜２００の整数；ｍは０〜２００の整数；ｐは０〜１００００の整数；ｑは１〜１００の整数；ただしｎ＋ｍは０ではなく、Ｄ１、ＦＡＥ、ＡＥおよびＹの結合順序は特定されない）；
ＡおよびＢは同じかまたは異なり、水素原子、フッ素原子および／または架橋性官能基を含んでいてもよいアルキル基、フッ素原子および／または架橋性官能基を含んでいてもよいフェニル基、−ＣＯＯＨ基、−ＯＲ¹⁴（Ｒ¹⁴は水素原子またはフッ素原子および／または架橋性官能基を含んでいてもよいアルキル基）、エステル基またはカーボネート基（ただし、Ｄの末端が酸素原子の場合は−ＣＯＯＨ基、−ＯＲ¹⁴、エステル基およびカーボネート基ではない）］で表される側鎖に含フッ素基を有する非晶性含フッ素ポリエーテル化合物である。 This ion conductive compound has the formula (4):
A- (D) -B (4)
[Wherein D represents the formula (5):
-(D1) _n- (FAE) _m- (AE) _p- (Y) _q- (5)
(Where D1 is the formula (5a):

(Wherein, Rf good fluoroether group which may have a crosslinkable functional group; R ¹⁰ is a group or a bond that binds the Rf main chain) ether unit having a fluoroether group in its side chain represented by;
FAE has the formula (5b):

(Wherein, Rfa is hydrogen atom, a crosslinkable functional group which may have a fluorine-containing alkyl group; R ¹¹ is a group or a bond that binds the Rfa main chain) a fluorine-containing alkyl group in its side chain represented by Ether units having:
AE is the formula (5c):

(Wherein R ¹³ has a hydrogen atom, an alkyl group which may have a crosslinkable functional group, an aliphatic cyclic hydrocarbon group which may have a crosslinkable functional group, or a crosslinkable functional group. An aromatic hydrocarbon group which may be substituted; R ¹² is an ether unit represented by R ¹³ and a group or a bond which bonds the main chain;
Y represents formulas (5d-1) to (5d-3):

A unit comprising at least one of
n is an integer from 0 to 200; m is an integer from 0 to 200; p is an integer from 0 to 10000; q is an integer from 1 to 100; provided that n + m is not 0, and the bonding order of D1, FAE, AE and Y is Not specified);
A and B are the same or different and are a hydrogen atom, a fluorine atom and / or an alkyl group which may contain a crosslinkable functional group, a phenyl group which may contain a fluorine atom and / or a crosslinkable functional group, -COOH A group, —OR ¹⁴ (R ¹⁴ is a hydrogen atom or a fluorine atom and / or an alkyl group which may contain a crosslinkable functional group), an ester group or a carbonate group (provided that —COOH when D is terminated with an oxygen atom) Group, —OR ¹⁴ , not an ester group and a carbonate group)], and an amorphous fluorine-containing polyether compound having a fluorine-containing group in the side chain.

  In the present invention, a surfactant can be blended as necessary. The compounding amount of the surfactant is 5% by mass or less, more preferably 3% by mass or less, based on the total amount of the solvent (I) from the viewpoint of reducing the surface tension of the electrolytic solution without reducing the charge / discharge cycle characteristics. In particular, 0.05 to 2% by mass is preferable.

  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.

  You may mix | blend another additive with the electrolyte solution of this invention as needed. Examples of other additives include metal oxides and glass.

  In addition, it is preferable that the electrolyte solution of this invention does not freeze at low temperature (for example, 0 degreeC or -20 degreeC), or electrolyte salt precipitates. Specifically, the viscosity at 0 ° C. is preferably 100 mPa · sec or less, more preferably 30 mPa · sec or less, and particularly preferably 15 mPa · sec or less. Furthermore, specifically, the viscosity at −20 ° C. is preferably 100 mPa · sec or less, more preferably 40 mPa · sec or less, and particularly preferably 15 mPa · sec or less.

  The electrolyte solution of the present invention can simultaneously improve flame resistance, low temperature characteristics, withstand voltage, solubility of electrolyte salt and compatibility with hydrocarbon solvents, and further improve oxidation resistance to generate gas. Can be reduced and energy efficiency can be improved, so that it is suitable as an electrolyte for an electrochemical device.

  That is, this invention relates also to the electrochemical device provided with said electrolyte solution. Examples of electrochemical devices include lithium secondary batteries, capacitors (electrolytic double layer capacitors), radical batteries, solar cells (particularly dye-sensitized solar cells), fuel cells, various electrochemical sensors, electrochromic elements, It is particularly suitable for lithium secondary batteries and electrolytic double layer capacitors. A high-capacity electric double layer capacitor is required to have a withstand voltage of 3.0 V or more, but the electric double layer capacitor of the present invention sufficiently satisfies the requirement.

  The electrolyte solution of the present invention is suitable for a lithium secondary battery from the viewpoint of improving capacity and rate characteristics, and can provide a lithium secondary battery including a positive electrode, a negative electrode, a separator, and the electrolyte solution of the present invention.

  The positive electrode active material used for the positive electrode is not particularly limited, but at least selected from the group consisting of cobalt-based composite oxides, nickel-based composite oxides, manganese-based composite oxides, iron-based composite oxides, and vanadium-based composite oxides. When using 1 type, it is preferable from becoming a high output lithium secondary battery with a high energy density.

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 . LiCo _x Ni _1-x O ₂ (0 <x <1), LiCo _x Mn _1-x O ₂ (0 <x <1), LiNi _x Mn _1-x O ₂ (0 <x <1), _{LiNi x Mn 2-x O 4} (0 <x <2), CoNi represented by _{LiNi 1-xy Co x Mn y} O 2 (0 <x <1,0 <y <1,0 <x + y <1) , CoMn, NiMn, and NiCoMn composite oxides 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 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 secondary battery for a hybrid vehicle or a distributed power source, a high output is required, so the particles of the positive electrode active material are mainly secondary particles, and the secondary particles It is preferable to contain 0.5 to 7.0% by volume of fine particles having an average particle size of 40 μm or less and an average primary particle size 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 include silicon and titanium, such as tin oxide, silicon oxide, and lithium titanate. Examples of the metal nitride include Li _2.6 Co _0.4 N.

  As a combination of the positive electrode active material and the negative electrode active material, the positive electrode active material is lithium cobaltate and the negative electrode active material is graphite. The positive electrode active material is nickel-based composite oxide and the negative electrode active material is graphite. This is preferable.

  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, a film in which an aramid resin is coated on a separator made to prevent a short circuit caused by Li dentlite and improve safety, or a film in which a resin containing polyamideimide and an alumina filler is coated on a separator Etc.

  In addition, since the electrolytic solution of the present invention is nonflammable, it is particularly useful as an electrolytic solution for a hybrid lithium battery or a large lithium secondary battery for a distributed power source. It is also useful as a non-aqueous electrolytic solution for electrolytic capacitors, electrolytic double layer capacitors, and particularly, electric double layer capacitors having a withstand voltage of 3.5 V or more.

  In addition, the electrolytic solution of the present invention can be used for, for example, electrolytic capacitors, solid display elements such as electroluminescence, sensors such as current sensors, and the like. In addition, the electrolytic solution of the present invention can also be used as an ionic conductor of an antistatic coating material.

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

In addition, the measuring method employ | adopted by this invention is as follows.
NMR: AC-300 manufactured by BRUKER is used.

¹⁹ F-NMR:
Measurement conditions: 282 MHz (trichlorofluoromethane = 0 ppm)
¹ H-NMR:
Measurement conditions: 300 MHz (tetramethylsilane = 0 ppm)
IR:
Measure at room temperature with a Fourier transform infrared spectrophotometer 1760X manufactured by Perkin Elmer.

Synthesis example 1
A dry ice / acetone reflux tube was attached to the top of a 200 ml glass three-necked flask equipped with a stirrer, and after sufficient nitrogen substitution, the flask was immersed in a dry ice / methanol bath. 150 ml of diglyme and 58 g of spray-dried potassium fluoride were added thereto, and 66 g of COF ₂ gas was introduced with stirring. After the introduction, the mixture was stirred for 10 minutes, and then 108 g of Cl-COOC ₂ H ₅ was added dropwise, and gradually returned to room temperature with stirring. After stirring at room temperature for 1 hour, the target product was obtained by distillation (yield 62%).

This product was analyzed by ¹⁹ F-NMR and ¹ H-NMR analysis and confirmed to be FCF ₂ OCOOC ₂ H ₅ (A1).
¹⁹ F-NMR: (neat): -82 to -87 ppm (3F)
¹ H-NMR: (neat): 4.1 to 4.5 ppm (2H), 1.6 to 1.9 ppm (3H)
The obtained FCF ₂ OCOOC ₂ H ₅ (A1) was blended with LiPF ₆ as an electrolyte salt to a concentration of 1 mol / liter to prepare an electrolytic solution. When the withstand voltage of this electrolyte was examined, the withstand voltage was 6.4V.

(Measurement method of withstand voltage)
Electrolytic solution was applied to a three-electrode voltage measuring cell (working electrode, counter electrode: platinum (where the area ratio of the counter electrode and working electrode is 5: 1), reference electrode: Ag, HS cell manufactured by Hosen Co., Ltd.) Then, the potential is pulled at 3 mV / sec with a potentiostat, and the range where the decomposition current does not flow more than 0.1 mA is defined as the withstand voltage (V).

In addition, FPF ₂ OCOOC ₂ H ₅ (A1) is mixed with LiPF ₆ , LiN (SO ₂ C ₂ F ₅ ) ₂ and tetraethylammonium tetrafluoroborate [(C ₂ H ₅ ) ₄ NBF ₄ ] at room temperature. They were added so as to be mol / liter, stirred sufficiently, and visually observed for solubility, all were uniformly dissolved.

Synthesis example 2
A dry ice / acetone reflux tube was attached to the top of a 200 ml glass three-necked flask equipped with a stirrer, and after sufficient nitrogen substitution, the flask was immersed in a dry ice / methanol bath. 150 ml of diglyme and 58 g of spray-dried potassium fluoride were added thereto, and 39 g of C ₂ H ₅ COCl was introduced with stirring. After the introduction, the mixture was stirred for 2 hours, 54 g of Cl-COOC ₂ H ₅ was added dropwise, and the temperature was gradually returned to room temperature with stirring. After stirring at room temperature for 2 hours, the target product was obtained by distillation (yield 54%).

This product was analyzed by ¹⁹ F-NMR and ¹ H-NMR analysis and confirmed to be CH ₃ CF ₂ OCOOC ₂ H ₅ (A2).
¹⁹ F-NMR: (neat): −124 to −128 ppm (2F)
¹ H-NMR: (neat): 4.1 to 4.5 ppm (2H), 1.6 to 2.2 ppm (3H), 1.1 to 1.4 ppm (3H)
The obtained CH ₃ CF ₂ OCOOC ₂ H ₅ (A2) was blended with LiPF ₆ as an electrolyte salt to a concentration of 1 mol / liter to prepare an electrolyte solution. With respect to this electrolytic solution, when the withstand voltage was examined in the same manner as in Synthesis Example 1, the withstand voltage was 6.3V.

In addition, LiPF ₆ , LiN (SO ₂ C ₂ F ₅ ) _2, and 4 ethylammonium tetrafluoroborate [(C ₂ H ₅ ) ₄ NBF ₄ ] were added to CH ₃ CF ₂ OCOOC ₂ H ₅ (A2) at room temperature, respectively. When 1 mol / liter was added, the mixture was sufficiently stirred, and the solubility was visually observed.

Example 1
As an electrolyte salt, a solvent obtained by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC) and FCF ₂ OCOOC ₂ H ₅ (A1) obtained in Synthesis Example 1 at 30/50/20 (volume ratio) is used. LiPF ₆ was blended to a concentration of 1 mol / liter to prepare an electrolytic solution. With respect to this electrolytic solution, a charge / discharge test (discharge capacity, rate characteristics, overcharge characteristics) was examined. The results are shown in Table 1.

Example 2
Ethylene carbonate (EC), ethyl methyl carbonate (EMC), FCF ₂ OCOOC ₂ H ₅ (A1) obtained in Synthesis Example 1 and HCF ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H in 20/40/10/30 (volume) Ratio) was mixed with LiPF ₆ as an electrolyte salt to a concentration of 1 mol / liter to prepare an electrolytic solution. With respect to this electrolytic solution, a charge / discharge test (discharge capacity, rate characteristics, overcharge characteristics) was examined. The results are shown in Table 1.

Example 3
The solvent was obtained by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and CH ₃ CF ₂ OCOOC ₂ H ₅ (A2) obtained in Synthesis Example 2 at 30/50/20 (volume ratio). An electrolyte was prepared by blending LiPF ₆ as a salt to a concentration of 1 mol / liter. With respect to this electrolytic solution, a charge / discharge test (discharge capacity, rate characteristics, overcharge characteristics) was examined. The results are shown in Table 1.

Example 4
Ethylene carbonate (EC), ethyl methyl carbonate (EMC), CH ₃ CF ₂ OCOOC ₂ H ₅ (A2) obtained in Synthesis Example 2 and HCF ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H were added to 20/40/10/30. An electrolyte solution was prepared by blending LiPF ₆ as an electrolyte salt to a concentration of 1 mol / liter in a solvent obtained by mixing (volume ratio). With respect to this electrolytic solution, a charge / discharge test (discharge capacity, rate characteristics, overcharge characteristics) was examined. The results are shown in Table 1.

Comparative Example 1
A solvent obtained by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at 30/70 (volume ratio) was mixed with LiPF ₆ as an electrolyte salt to a concentration of 1 mol / liter, and an electrolyte solution. Was prepared. With respect to this electrolytic solution, a charge / discharge test (discharge capacity, rate characteristics, overcharge characteristics) was examined. The results are shown in Table 1.

[Charge / discharge test]
A coin battery was actually made and the battery characteristics were evaluated.

(Preparation of positive electrode)
A positive electrode active material prepared by mixing LiCoO ₂ , carbon black, and polyvinylidene fluoride (manufactured by Kureha Chemical Co., Ltd., trade name KF-1000) at 90/3/7 (mass% ratio) is dispersed in N-methyl-2-pyrrolidone. Then, the slurry was applied uniformly on a positive electrode current collector (aluminum foil having a thickness of 15 μm), dried, and then punched into a disc having a diameter of 13.0 mm to produce a positive electrode.

(Preparation of negative electrode)
To artificial graphite powder (manufactured by Hitachi Chemical Co., Ltd., trade name MAG-D), styrene-butadiene rubber dispersed with distilled water is added to a solid content of 6% by mass and mixed with a disperser to form a slurry. Was applied uniformly on a negative electrode current collector (copper foil having a thickness of 10 μm), dried, and then punched into a disc having a diameter of 13.0 mm to produce a negative electrode.

(Production of coin-type lithium secondary battery)
The positive electrode is housed in a stainless steel can that also serves as a positive electrode current collector, and a polyethylene separator having a diameter of 17 mm (manufactured by Celgard Co., Ltd., trade name Celguard 3501) is layered thereon, and the negative electrode is further placed thereon. Impregnate with electrolyte. The can body and a sealing plate serving also as a negative electrode current collector were caulked and sealed through an insulating gasket to produce a coin-type lithium secondary battery.

(Discharge capacity)
When the charge / discharge current is indicated by C, measurement is performed under the following charge / discharge measurement conditions with 3.5 mA as 1C. The evaluation is performed using an index with the result of the discharge capacity of Comparative Example 1 as 100.
Charge / Discharge Condition Charging: Holds the charge current at 1 / 10C at 0.5C / 4.2V (CC / CV charge)
Discharge: 1C 2.5Vcut (CC discharge)

(Rate characteristics)
Regarding charging, the battery was charged under the above conditions at 0.5C and 4.2V until the charging current became 1 / 10C, and discharged at a current equivalent to 0.3C to 2.5V to obtain the discharge capacity. Subsequently, the battery was charged at 0.5 C and 4.2 V until the charging current became 1/10 C, and discharged at a current equivalent to 5 C until it reached 2.5 V, and the discharge capacity was determined. The rate characteristics were evaluated from the ratio of the discharge capacity at 5C and the above discharge capacity at 0.3C. For the rate characteristic, a value obtained by the following calculation formula is described as the rate characteristic.
Rate characteristic (%) = 5C discharge capacity (mAh) /0.3C discharge capacity (mAh) × 100

(Overcharge characteristics)
Cylindrical batteries were produced in the following manner using the electrolytic solutions of the examples and comparative examples.

A positive electrode active material prepared by mixing LiCoO ₂ , carbon black, and polyvinylidene fluoride (manufactured by Kureha Chemical Co., Ltd., trade name KF-1000) at 90/3/7 (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.

  The cylindrical lithium secondary battery is discharged to 3.0 V at a current value equivalent to 1 CmA, overcharged at a current value equivalent to 1 CmA with 12 V as the upper limit voltage, and the presence or absence of ignition / rupture 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.

Claims (7)

Formula (1):
R ^a CF ₂ —OCOOR ^b (1)
(In the formula, R ^a is H, F, Cl or an alkyl group which may have a fluorine atom having 1 to 3 carbon atoms; R ^b is an alkyl which may have a fluorine atom having 1 to 7 carbon atoms; An electrolytic solution containing an electrolyte salt-dissolving solvent (I) and an electrolyte salt (II) containing the fluorine-containing chain carbonate (1). In the fluorine-containing chain carbonate (1), R ^a is represented by the formula (1a):
(HCX ¹ X ² )-(1a)
^2. The electrolytic solution according to claim 1, which is a fluoroalkyl group having a terminal represented by (wherein X ¹ and X ² are the same or different and are H or F). The electrolytic solution according to claim 1 or 2, wherein, in the fluorine-containing chain carbonate (1), R ^a CF ₂ -is a fluoroalkyl group having a fluorine content of 40 to 82.7% by mass. The electrolyte solution according to any one of claims 1 to 3, wherein the electrolyte salt dissolving solvent (I) contains at least one carbonate selected from the group consisting of cyclic carbonates and non-fluorine chain carbonates. The electrolyte solution according to any one of claims 1 to 4, wherein the solvent (I) for dissolving the electrolyte salt contains a fluorinated ether. An electrochemical device comprising the electrolytic solution according to claim 1. A lithium secondary battery comprising the electrolytic solution according to claim 1.