JP6143410B2 - Electrochemical device and non-aqueous electrolyte for electrochemical device - Google Patents

Description

The present invention relates to an electrochemical device including a nonaqueous solvent in which the content of a specific compound is reduced, and a nonaqueous electrolytic solution containing an electrolyte salt. The present invention also relates to a non-aqueous electrolyte used for an electrochemical device. Furthermore, the present invention relates to 4-fluoroalkyl- (1,3) -dioxolan-2-one having a reduced content of a specific compound.

As non-aqueous electrolytes for electrochemical devices such as lithium ion secondary batteries, generally used are electrolytes such as LiPF ₆ and LiBF ₄ dissolved in non-aqueous solvents such as ethylene carbonate, propylene carbonate, and dimethyl carbonate. Has been.

However, since hydrocarbon-based solvents have low oxidation resistance, battery performance may be reduced when stored at high temperature or cycled at a high voltage. Various additives have also been proposed, but are not sufficient to suppress deterioration.

Patent Document 1 discloses that a nonaqueous electrolytic solution containing trifluoromethylethylene carbonate is specifically excellent in low-temperature characteristics, long-term stability, and cycle characteristics. However, Patent Document 1 does not describe impurities of the compound. Moreover, in a non-aqueous electrolyte secondary battery using such a non-aqueous electrolyte, the discharge capacity may decrease when the battery is left in a high temperature environment or repeatedly charged and discharged.

JP 2009-76467 A

An object of the present invention is to provide an electrochemical device excellent in high temperature storage characteristics and high voltage cycle characteristics, and a non-aqueous electrolyte used therein. Another object of the present invention is to provide 4-fluoroalkyl- (1,3) -dioxolan-2-one with a reduced content of a specific compound.

As a result of various studies to solve the above problems, the present inventors have found that the above problems can be solved by using a non-aqueous solvent having a reduced specific impurity content, and the present invention has been completed. I came to let you.

（式中、Ｒｆは、−ＣＦ_３、−ＣＨ_２ＣＦ_３、又は、−ＣＨ_２ＣＦ_２ＣＦ_３である）で示される４−フルオロアルキル−（１，３）−ジオキソラン−２−オンを含有し、かつ、
下記（Ｉ）で示される化合物を、前記４−フルオロアルキル−（１，３）−ジオキソラン−２−オンに対して５０００ｐｐｍ以下含有することを特徴とする、電気化学デバイスに関する。
（Ｉ）一般式（２）：

（式中、Ｒｆは前記同様である）で示される化合物。 That is, the present invention is an electrochemical device comprising a positive electrode, a negative electrode, and a nonaqueous electrolytic solution containing a nonaqueous solvent and an electrolyte salt,
The non-aqueous solvent is represented by the general formula (1):

(Wherein Rf is —CF ₃ , —CH ₂ CF ₃ , or —CH ₂ CF ₂ CF ₃ ), and contains 4-fluoroalkyl- (1,3) -dioxolan-2-one And
The present invention relates to an electrochemical device comprising a compound represented by the following (I) in an amount of 5000 ppm or less based on the 4-fluoroalkyl- (1,3) -dioxolan-2-one.
(I) General formula (2):

(Wherein Rf is the same as defined above).

The content of 4-fluoroalkyl- (1,3) -dioxolan-2-one is preferably 0.01 to 60% by weight in the non-aqueous solvent.

It is preferable that the electrochemical device is a lithium ion secondary battery.

（式中、Ｒｆは、−ＣＦ_３、−ＣＨ_２ＣＦ_３、又は、−ＣＨ_２ＣＦ_２ＣＦ_３である）で示される４−フルオロアルキル−（１，３）−ジオキソラン−２−オンを含有し、かつ、
下記（Ｉ）で示される化合物を、前記４−フルオロアルキル−（１，３）−ジオキソラン−２−オンに対して５０００ｐｐｍ以下含有することを特徴とする、電気化学デバイス用非水電解液に関する。
（Ｉ）一般式（２）：

（式中、Ｒｆは前記同様である）で示される化合物。 The present invention also provides a non-aqueous electrolyte for an electrochemical device containing a non-aqueous solvent and an electrolyte salt,
The non-aqueous solvent is represented by the general formula (1):

(Wherein Rf is —CF ₃ , —CH ₂ CF ₃ , or —CH ₂ CF ₂ CF ₃ ), and contains 4-fluoroalkyl- (1,3) -dioxolan-2-one And
The present invention relates to a nonaqueous electrolytic solution for electrochemical devices, which contains a compound represented by the following (I) in an amount of 5000 ppm or less based on the 4-fluoroalkyl- (1,3) -dioxolan-2-one.
(I) General formula (2):

(Wherein Rf is the same as defined above).

（式中、Ｒｆは、−ＣＦ_３、−ＣＨ_２ＣＦ_３、又は、−ＣＨ_２ＣＦ_２ＣＦ_３である）で示される４−フルオロアルキル−（１，３）−ジオキソラン−２−オンであって、
下記（Ｉ）で示される化合物を５０００ｐｐｍ以下含有する４−フルオロアルキル−（１，３）−ジオキソラン−２−オンに関する。
（Ｉ）一般式（２）：

（式中、Ｒｆは前記同様である）で示される化合物。 Furthermore, the present invention relates to a general formula (1):

(Wherein Rf is —CF ₃ , —CH ₂ CF ₃ , or —CH ₂ CF ₂ CF ₃ ), which is 4-fluoroalkyl- (1,3) -dioxolan-2-one. And
The present invention relates to 4-fluoroalkyl- (1,3) -dioxolan-2-one containing 5000 ppm or less of the compound represented by the following (I).
(I) General formula (2):

(Wherein Rf is the same as defined above).

The present invention can provide an electrochemical device excellent in high-temperature storage characteristics and cycle characteristics, and a nonaqueous electrolytic solution used therefor. In addition, the present invention can provide 4-fluoroalkyl- (1,3) -dioxolan-2-one with a reduced content of a specific compound.

（式中、Ｒｆは、−ＣＦ_３、−ＣＨ_２ＣＦ_３、又は、−ＣＨ_２ＣＦ_２ＣＦ_３である）で示される４−フルオロアルキル−（１，３）−ジオキソラン−２−オンを含有し、かつ、
下記（Ｉ）で示される化合物を、前記４−フルオロアルキル−（１，３）−ジオキソラン−２−オンに対して５０００ｐｐｍ以下含有することを特徴とする。
（Ｉ）一般式（２）：

（式中、Ｒｆは前記同様である）で示される化合物（以下、化合物（Ｉ）ということもある）。 The electrochemical device of the present invention comprises a positive electrode, a negative electrode, and a nonaqueous electrolytic solution containing a nonaqueous solvent and an electrolyte salt,
The non-aqueous solvent is represented by the general formula (1):

(Wherein Rf is —CF ₃ , —CH ₂ CF ₃ , or —CH ₂ CF ₂ CF ₃ ), and contains 4-fluoroalkyl- (1,3) -dioxolan-2-one And
The compound represented by the following (I) is contained in an amount of 5000 ppm or less based on the 4-fluoroalkyl- (1,3) -dioxolan-2-one.
(I) General formula (2):

(Wherein Rf is the same as above) (hereinafter also referred to as compound (I)).

The content of 4-fluoroalkyl- (1,3) -dioxolan-2-one is preferably 0.01 to 60% by weight in the non-aqueous solvent. As the amount of 4-fluoroalkyl- (1,3) -dioxolan-2-one increases, the discharge capacity tends to decrease, and the allowable upper limit is 60% by weight. 4-Fluoroalkyl- (1,3) -dioxolan-2-one can exert its effect in a relatively small amount. A preferable upper limit is 30% by weight or less, and an effective lower limit is preferably 0.1% by weight or more, and more preferably 0.5% by weight or more. In the present invention, 4-fluoroalkyl- (1,3) -dioxolan-2-one can be used as a solvent or an additive.

4-Fluoroalkyl- (1,3) -dioxolan-2-one can be usually synthesized by reacting the compound represented by the general formula (2) (compound (I)) with triphosgene. Therefore, depending on the purification method, the compound (I), which is a raw material, may remain as an impurity. Thus, since the compound (I) is an impurity generated in the synthesis of 4-fluoroalkyl- (1,3) -dioxolan-2-one represented by the general formula (1), the general formula (1) Rf in the inside and Rf in the general formula (2) are the same.

である。 When Rf is —CF ₃ , the compound represented by the general formula (1) is 4-trifluoromethyl- (1,3) -dioxolan-2-one. In this case, compound (I) is

It is.

である。 When Rf is —CH ₂ CF ₃ , the compound represented by the general formula (1) is 4- (2,2,2-trifluoroethyl- (1,3) -dioxolan-2-one. In this case, compound (I) is

It is.

である。 When Rf is —CH ₂ CF ₂ CF ₃ , the compound represented by the general formula (1) is 4- (2,2,3,3,3-pentafluoropropyl)-(1,3) -dioxolane— 2-on. In this case, compound (I) is

It is.

Content of compound (I) is 5000 ppm or less with respect to 4-fluoroalkyl- (1,3) -dioxolan-2-one, Preferably it is 3500 ppm or less, More preferably, it is 2500 ppm or less. When the compound (I) is contained in an amount of more than 5000 ppm, the discharge characteristics after storage at high temperatures tend to decrease significantly.

Moreover, since the compound (I) is a dialcohol, it easily reacts with Li, and as a result, the capacity of the battery decreases. Moreover, since the HOMO energy of compound (I) obtained by molecular activation calculation is higher than that of 4-fluoroalkyl- (1,3) -dioxolan-2-one, the oxidation resistance is weak. Therefore, it is considered that when the voltage is increased, it is decomposed and becomes a cause of deterioration. From these facts, it is considered that the lower the content of compound (I) in the non-aqueous solvent, the less the deterioration of the storage characteristics of the battery.

As described above, compound (I) is an impurity contained in 4-fluoroalkyl- (1,3) -dioxolan-2-one. Therefore, by purifying 4-fluoroalkyl- (1,3) -dioxolan-2-one in advance, the content of compound (I) in the non-aqueous solvent is within the above range (4-fluoroalkyl- (1, 3) 5000 ppm or less with respect to -dioxolan-2-one). Here, ppm is based on weight, and 5000 ppm or less with respect to 4-fluoroalkyl- (1,3) -dioxolan-2-one means 4-fluoroalkyl- (1,3) -dioxolane-2-one. It indicates that it is 0.5 parts by weight or less with respect to 100 parts by weight of ON.

As a purification method of 4-fluoroalkyl- (1,3) -dioxolan-2-one, for example, a method of rectification using a distillation column having a theoretical plate number of 10 or more can be mentioned. Specific examples include a method of rectifying under normal pressure using a 10-stage Older show.

As the main component of the non-aqueous solvent, any known one can be used as the solvent for the non-aqueous electrolyte secondary battery. For example, alkylene carbonate such as ethylene carbonate, propylene carbonate, butylene carbonate; dialkyl carbonate such as dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, ethyl methyl carbonate (preferably an alkyl group having 1 to 4 carbon atoms); tetrahydrofuran, Cyclic ethers such as 2-methyltetrahydrofuran; Chain ethers such as dimethoxyethane and dimethoxymethane; Cyclic carboxylic acid ester compounds such as γ-butyrolactone and γ-valerolactone; Chains such as methyl acetate, methyl propionate and ethyl propionate Examples thereof include carboxylic acid esters. Two or more of these may be used in combination.

One preferable non-aqueous solvent is mainly composed of alkylene carbonate and dialkyl carbonate. Among them, a mixed solvent containing 20 to 45% by volume of an alkylene carbonate having an alkylene group having 2 to 4 carbon atoms and 55 to 80% by volume of a dialkyl carbonate having an alkyl group having 1 to 4 carbon atoms. However, it is preferable because the electric conductivity of the electrolytic solution is high, and the cycle characteristics and high current discharge characteristics are high.

Examples of the alkylene carbonate having an alkylene group having 2 to 4 carbon atoms include ethylene carbonate, propylene carbonate, and butylene carbonate. Among these, ethylene carbonate or propylene carbonate is preferable.

Examples of the dialkyl carbonate having an alkyl group having 1 to 4 carbon atoms include dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, ethyl methyl carbonate, methyl-n-propyl carbonate, and ethyl-n-propyl carbonate. It is done. Among these, dimethyl carbonate, diethyl carbonate, or ethyl methyl carbonate is preferable.

Another example of the preferred non-aqueous solvent is one containing 60% by volume or more, preferably 85% by volume or more of an organic solvent selected from ethylene carbonate, propylene carbonate, γ-butyrolactone, and γ-valerolactone. An electrolytic solution in which a lithium salt is dissolved in this non-aqueous solvent causes less solvent evaporation and liquid leakage even when used at high temperatures. Among them, a mixture containing 5 to 45% by volume of ethylene carbonate and 55 to 95% by volume of γ-butyrolactone, or a solvent containing 30 to 60% by volume of ethylene carbonate and 40 to 70% by volume of propylene carbonate has cycle characteristics and large current discharge. This is preferable because the balance of characteristics and the like is good.

Still another example of a preferable non-aqueous solvent includes a phosphorus-containing organic solvent. Examples of the phosphorus-containing organic solvent include trimethyl phosphate, triethyl phosphate, dimethyl ethyl phosphate, methyl diethyl phosphate, ethylene methyl phosphate, and ethylene ethyl phosphate. When the phosphorus-containing organic solvent is contained in the nonaqueous solvent so as to be 10% by volume or more, the flammability of the electrolytic solution can be reduced. In particular, the content of the phosphorus-containing organic solvent is 10 to 80% by volume, and the other components are mainly dissolved in a non-aqueous solvent selected from γ-butyrolactone, γ-valerolactone, alkylene carbonate, and dialkyl carbonate. It is preferable to use an electrolyte because the balance between cycle characteristics and large current discharge characteristics is improved.

Furthermore, it is preferable to contain 8% by weight or less of a cyclic carbonate having a carbon-carbon unsaturated bond in the molecule in the non-aqueous solvent, and more preferably 0.01 to 8% by weight. When it is contained in this range, side reactions at the negative electrode of 4-fluoroalkyl- (1,3) -dioxolan-2-one can be suppressed, and storage characteristics and battery cycle characteristics can be further improved, which is preferable. . If the amount of cyclic carbonate added exceeds 8% by weight, battery characteristics after storage may be deteriorated. The lower limit is preferably 0.1% by weight or more, and the upper limit is preferably 3% by weight or less.

Examples of the cyclic carbonate having a carbon-carbon unsaturated bond in the molecule include vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, 4,5-dimethyl vinylene carbonate, 4,5-diethyl vinylene carbonate, fluoro vinylene carbonate, trifluoro Vinylene carbonate compounds such as methyl vinylene carbonate; 4-vinylethylene carbonate, 4-methyl-4-vinylethylene carbonate, 4-ethyl-4-vinylethylene carbonate, 4-n-propyl-4-vinylene ethylene carbonate, 5-methyl -4-vinylethylene carbonate, 4,4-divinylethylene carbonate, 4,5-divinylethylene carbonate, 4,4-dimethyl-5-methyleneethylene carbonate, 4,4 Vinyl ethylene carbonate compounds such as diethyl 5-methylene ethylene carbonate. Of these, vinylene carbonate, 4-vinylethylene carbonate, 4-methyl-4-vinylethylene carbonate or 4,5-divinylethylene carbonate, particularly vinylene carbonate or 4-vinylethylene carbonate are preferred. Two or more of these may be used in combination.

Furthermore, the non-aqueous solvent used in the present invention includes the general formula (3):
^{Rf 1 -O-Rf 2 (3} )
(Wherein Rf ¹ and Rf ² are the same or different and each represents an alkyl group having 1 to 10 carbon atoms or a fluoroalkyl group having 1 to 10 carbon atoms; provided that at least one is a fluoroalkyl group) Can be contained. However, it is preferable to contain a total of 5000 ppm or less of the compounds represented by the following (I ′) and (II ′), which are impurities of the fluorine-containing ether, with respect to the fluorine-containing ether.
(I ′) Fluorine-containing unsaturated compound (hereinafter sometimes referred to as compound (I ′))
(II ′) General formula (4):
Rf ¹ OH (4)
(Wherein Rf ¹ is the same as above)
A hydroxyl group-containing compound represented by formula (hereinafter also referred to as compound (II ′)).

Specific examples of the fluorine-containing ether represented by the general formula (3) include, for example, HCF ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H, CF ₃ CF ₂ CH ₂ OCF ₂ CF ₂ H, and HCF ₂ CF ₂ CH _{2. OCF 2 CFHCF 3, CF 3 CF} 2 CH 2 OCF 2 CFHCF 3, C 6 F 13 OCH 3, C 6 F 13 OC 2 H 5, C 8 F 17 OCH 3, C 8 F 17 OC 2 H 5, CF 3 CFHCF ₂ CH (CH ₃ ) OCF ₂ CFHCF ₃ , HCF ₂ CF ₂ OCH (C ₂ H ₅ ) ₂ , HCF ₂ CF ₂ OC ₄ H ₉ , HCF ₂ CF ₂ OCH ₂ CH (C ₂ H ₅ ) ₂ , HCF ₂ CF ₂ OCH ₂ CH (CH ₃ ) _{2 and the} like. Among these, it consists of HCF ₂ CF ₂ OCH ₂ CF ₂ CF ₂ H and HCF ₂ CF ₂ CH ₂ OCF ₂ CFHCF ₃ in terms of oxidation resistance and compatibility with electrolyte salts such as LiPF _6. One or more compounds selected from the group are preferable, and HCF ₂ CF ₂ OCH ₂ CF ₂ CF ₂ H is more preferable.

The content of the fluorinated ether represented by the general formula (3) is preferably 40% by weight or less, more preferably 3 to 40% by weight in the non-aqueous solvent.

The fluorine-containing unsaturated compound (I ′) is derived from a by-product generated when the fluorine-containing ether represented by the general formula (3) is synthesized. Specifically, hydrogen fluoride (HF) is eliminated from the fluorine-containing ether represented by the general formula (3) to form an unsaturated bond. More specifically, for _{example, (I'-1) CF 2} = CFCH 2 OCF 2 CF 2 H, (I'-2) HCF 2 CF = CHOCF 2 CF 2 H, (I'-3) CF 2 = _{CFCH 2 OCF 2 CFHCF 3, (} I'-4) HCF 2 CF 2 CH 2 OCF = CFCF 3, (I'-5) HCF 2 CF 2 CH 2 OCF 2 CF = CF 2, (I'-6) HCF ₂ CF = CHOCF ₂ CFHCF ₃ can be mentioned.

Moreover, as a hydroxyl-containing compound (II '), it originates from the raw material at the time of synthesize | combining the fluorine-containing ether shown by General formula (3), General formula (4):
Rf ¹ OH (4)
It is shown by. Here, the Rf ^1, the general formula (3) and can include the same, specifically, may be mentioned _{(II'-1) HCF 2 CF} 2 CH 2 OH.

Specifically, the fluorine-containing ether represented by the general formula (3) is HCF ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H,
Fluorine-containing unsaturated compound (I ′)
(I′-1) CF ₂ ═CFCH ₂ OCF ₂ CF ₂ H, and
(I′-2) HCF ₂ CF═CHOCF ₂ CF ₂ H
And
The hydroxyl group-containing compound (II ′)
(II′-1) HCF ₂ CF ₂ CH ₂ OH
Or a combination of
The fluorine-containing ether represented by the general formula (3) is HCF ₂ CF ₂ CH ₂ OCF ₂ CFHCF ₃ ,
Fluorine-containing unsaturated compound (I ′)
(I′-3) CF ₂ ═CFCH ₂ OCF ₂ CFHCF ₃ ,
(I′-4) HCF ₂ CF ₂ CH ₂ OCF═CFCF ₃ ,
_{(I'-5) HCF 2 CF} 2 CH 2 OCF 2 CF = CF 2 , and,
(I′-6) HCF ₂ CF═CHOCF ₂ CFHCF ₃
And
The hydroxyl group-containing compound (II ′)
(II′-1) HCF ₂ CF ₂ CH ₂ OH
A combination is preferred.

Compounds (I ′) and (II ′) are impurities contained in the fluorinated ether. Therefore, when the fluorine-containing ether represented by the general formula (3) is used, the content of the compounds (I ′) and (II ′) in the non-aqueous solvent is reduced by purifying the fluorine-containing ether in advance. Within the above range (a total of 5000 ppm or less with respect to the fluorinated ether). Here, ppm is based on weight, and 5000 ppm or less with respect to the fluorinated ether indicates 0.5 parts by weight or less with respect to 100 parts by weight of the fluorinated ether.

As an upper limit of content of compound (I '), (II'), it is preferable that it is 3500 ppm or less in total with respect to the said fluorine-containing ether, and it is more preferable that it is 2000 ppm or less. When the total amount of the compounds (I ′) and (II ′) is more than 5000 ppm, the cycle deterioration tends to increase when the discharge characteristics after high-temperature storage are lowered or the voltage is increased. Among the compounds (I ′) and (II ′), particularly when Rf ¹ OH (compound (II ′)) remains, it easily reacts with Li, so that the capacity tends to decrease. Further, since the fluorine-containing unsaturated compound (I ′) has a double bond, when many of these remain, there is a tendency that they easily react with moisture and the like in the electrolytic solution and decompose.

In the present invention, it is preferable to use a non-aqueous solvent containing the compound represented by the general formula (1) and the compound represented by the general formula (3) because safety can be improved and a high voltage can be obtained.

In addition, the nonaqueous solvent may contain other useful compounds, for example, conventionally known additives, dehydrating agents, deoxidizing agents, and overcharge preventing agents as necessary.

Additives include carbonate compounds such as fluoroethylene carbonate, trifluoropropylene carbonate, phenylethylene carbonate, and erythritan carbonate; succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride Acids, diglycolic anhydride, cyclohexanedicarboxylic anhydride, cyclopentanetetracarboxylic dianhydride, and carboxylic anhydrides such as phenylsuccinic anhydride; ethylene sulfite, 1,3-propane sultone, 1,4 -Sulfur-containing compounds such as butane sultone, methyl methanesulfonate, busulfan, sulfolane, sulfolene, dimethyl sulfone, and tetramethylthiuram monosulfide; 1-methyl-2-pyrrolidinone, 1-methyl-2-pi Nitrogen-containing compounds such as lidone, 3-methyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, and N-methylsuccinimide; such as heptane, octane, cycloheptane, and fluorobenzene A hydrocarbon compound etc. are mentioned. When these are contained in a non-aqueous solvent in an amount of 0.1 to 5% by weight, capacity retention characteristics and cycle characteristics after high-temperature storage are improved.

As the overcharge inhibitor, aromatic compounds such as cyclohexylbenzene, biphenyl, alkylbiphenyl, terphenyl, terphenyl partial hydride, t-butylbenzene, t-amylbenzene, diphenyl ether, benzofuran, and dibenzofuran; Partially fluorinated products of the aromatic compounds such as fluorobiphenyl; fluorine-containing anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, and 2,6-difluoroanisole, and the like can be given. When these are contained in a non-aqueous solvent in an amount of 0.1 to 5% by weight, rupture / ignition of the battery can be suppressed during overcharge or the like.

As an electrolyte salt used in the present invention, any salt can be used, but a lithium salt is preferable. Examples of the lithium salt include inorganic lithium salts such as LiClO ₄ , LiPF ₆ , and LiBF ₄ ; LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN ( CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiPF ₄ (CF ₃ ) ₂ , LiPF ₄ (C ₂ F ₅ ) ₂ , LiPF ₄ (CF ₃ SO ₂ ) ₂ LiPF ₄ (C ₂ F ₅ SO ₂ ) ₂ , LiBF ₂ (CF ₃ ) ₂ , LiBF ₂ (C ₂ F ₅ ) ₂ , LiBF ₂ (CF ₃ SO ₂ ) ₂ , and LiBF ₂ (C ₂ F ₅ Fluorine-containing organic acid lithium salts such as SO ₂ ) _{2 and the} like can be mentioned, and these can be used alone or in combination of two or more. Of these, LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ or LiN (C ₂ F ₅ SO ₂ ) ₂ , particularly LiPF ₆ or LiBF ₄ are preferred. When an inorganic lithium salt such as LiPF ₆ or LiBF ₄ and a fluorine-containing organic lithium salt such as LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ or LiN (C ₂ F ₅ SO ₂ ) ₂ are used in combination, This is preferable because deterioration after storage at high temperature is reduced.

When the non-aqueous solvent contains 55% by volume or more of γ-butyrolactone, LiBF ₄ preferably accounts for 50% by weight or more of the entire lithium salt. The lithium salt, LiBF ₄ is 50 to 95 _{wt%, LiPF 6, LiCF 3 SO} 3, LiN (CF 3 SO 2) 2, and _lithium salts selected from the group consisting of _{LiN (C 2 F 5 SO 2} ) 2 Is preferably 5 to 50% by weight.

The lithium salt concentration in the electrolytic solution is preferably 0.5 to 3 mol / liter. Outside this range, the electrical conductivity of the electrolytic solution tends to be low, and the battery performance tends to deteriorate.

Examples of the electrochemical device of the present invention include a lithium ion secondary battery and an electric double layer capacitor. Hereinafter, the configuration of the lithium ion secondary battery will be described.

Materials for the negative electrode constituting lithium ion secondary batteries include carbonaceous materials capable of occluding and releasing lithium, such as organic pyrolysis products under various pyrolysis conditions, artificial graphite, and natural graphite; tin oxide, silicon oxide Metal oxide materials that can occlude and release lithium, such as lithium metal, and various lithium alloys can be used. Two or more of these negative electrode material amounts may be mixed and used.

Carbonaceous materials that can occlude and release lithium include artificial graphite or purified natural graphite produced by high-temperature treatment of graphitizable pitch obtained from various raw materials, or surface treatment of these graphite with pitch or other organic substances. Those obtained by carbonization after application are preferred.

The negative electrode may be manufactured by a conventional method. For example, a method of adding a binder, a thickener, a conductive material, a solvent, and the like to the negative electrode material to form a slurry, applying the slurry to the current collector, drying, and pressing to increase the density can be given.

As the binder, any material can be used as long as it is a material that is safe with respect to the solvent and the electrolyte used in manufacturing the electrode. Examples thereof include polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, styrene / butadiene rubber, isoprene rubber, butadiene rubber, ethylene-acrylic acid copolymer, and ethylene-methacrylic acid copolymer.

Examples of the thickener include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, and casein.

Examples of the conductive material include metal materials such as copper and nickel; carbon materials such as graphite and carbon black.

Examples of the material for the negative electrode current collector include copper, nickel, and stainless steel. Of these, copper foil is preferred from the viewpoint of easy processing into a thin film and cost.

The material of the positive electrode constituting the battery is particularly preferably a lithium-containing transition metal composite oxide that produces a high voltage. For example, Formula (1): Li _a Mn _2-b M ¹ _b O ₄ 9 ≦ a; 0 ≦ b ≦ 1.5; M ¹ is Fe, Co, Ni, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Lithium-manganese spinel composite oxide represented by formula (2): LiNi _1-c M ² _c O ₂ (wherein 0 ≦ c ≦ 0., At least one metal selected from the group consisting of Ge). 5; M ² is at least one selected from the group consisting of Fe, Co, Mn, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge Lithium-nickel composite oxide represented by _1-d M ³ _d O ₂ (where 0 ≦ d ≦ 0.5; M ³ is Fe, Ni, Mn, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B , Ga, In, Si, and at least one metal selected from the group consisting of Ge) are preferable.

Specifically, LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiNi _0.8 Co _0.15 Al _0.05 O ₂ , or LiNi _1/3 Co _1/3 Mn _1/3 O ₂ is preferable from the viewpoint of providing a lithium secondary battery having high energy density and high output.

In addition, positive electrode actives such as LiFePO ₄ , LiNi _0.8 Co _0.2 O ₂ , Li _1.2 Fe _0.4 Mn _0.4 O ₂ , LiNi _0.5 Mn _0.5 O ₂ , LiV ₃ O _6, etc. It may be a substance.

The compounding amount of the positive electrode active material is preferably 50 to 99% by mass, more preferably 80 to 99% by mass of the positive electrode mixture, from the viewpoint of high battery capacity.

In the present invention, particularly when used in a large-sized lithium ion secondary battery for a hybrid vehicle or a distributed power source, a high output is required. Therefore, the particles of the positive electrode active material are mainly secondary particles, and the secondary It is preferable to contain 0.5 to 7.0% by volume of fine particles having an average particle diameter of 40 μm or less and an average primary particle diameter of 1 μm or less. By containing fine particles having an average primary particle diameter of 1 μm or less, the contact area with the electrolytic solution is increased, and the diffusion of lithium ions between the electrode and the electrolytic solution can be accelerated, and the output performance can be improved. .

As the binder for the positive electrode, the same one as that for the negative electrode can be used, and any material can be used as long as it is a safe material for the solvent and the electrolytic solution used in manufacturing the electrode. Examples thereof include polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, styrene / butadiene rubber, isoprene rubber, butadiene rubber, ethylene-acrylic acid copolymer, and ethylene-methacrylic acid copolymer.

Moreover, the same thing as a negative electrode can be used also about the thickener of a positive electrode, and carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, ethylcellulose, polyvinyl alcohol, an oxidized starch, a phosphorylated starch, casein etc. are mentioned.

Examples of the conductive material include carbon materials such as graphite and carbon black.

Examples of the material for the positive electrode current collector include metals such as aluminum, titanium, and tantalum, and alloys thereof. Of these, aluminum or an alloy thereof is preferable.

The material and shape of the separator used in the lithium ion secondary battery of the present invention are arbitrary as long as they are stable in the electrolyte and excellent in liquid retention. A porous sheet or non-woven fabric made of polyolefin such as polyethylene and polypropylene is preferred.

The shape of the battery is arbitrary, and examples thereof include a cylindrical shape, a square shape, a laminate shape, a coin shape, and a large size. In addition, the shape and structure of a positive electrode, a negative electrode, and a separator can be changed and used according to the shape of each battery.

（式中、Ｒｆは、−ＣＦ_３、−ＣＨ_２ＣＦ_３、又は、−ＣＨ_２ＣＦ_２ＣＦ_３である）で示される４−フルオロアルキル−（１，３）−ジオキソラン−２−オンを含有し、かつ、
下記（Ｉ）で示される化合物を、前記４−フルオロアルキル−（１，３）−ジオキソラン−２−オンに対して５０００ｐｐｍ以下含有することを特徴とする、電気化学デバイス用非水電解液に関する。
（Ｉ）一般式（２）：

（式中、Ｒｆは前記同様である）で示される化合物。 Furthermore, the present invention is a non-aqueous electrolyte for an electrochemical device containing a non-aqueous solvent and an electrolyte salt,
The non-aqueous solvent is represented by the general formula (1):

(Wherein Rf is —CF ₃ , —CH ₂ CF ₃ , or —CH ₂ CF ₂ CF ₃ ), and contains 4-fluoroalkyl- (1,3) -dioxolan-2-one And
The present invention relates to a nonaqueous electrolytic solution for electrochemical devices, which contains a compound represented by the following (I) in an amount of 5000 ppm or less based on the 4-fluoroalkyl- (1,3) -dioxolan-2-one.
(I) General formula (2):

(Wherein Rf is the same as defined above).

The nonaqueous solvent, the electrolyte salt, and the addition amount of each used in the nonaqueous electrolytic solution for electrochemical devices of the present invention are the same as described above.

（式中、Ｒｆは、−ＣＦ_３、−ＣＨ_２ＣＦ_３、又は、−ＣＨ_２ＣＦ_２ＣＦ_３である）で示される４−フルオロアルキル−（１，３）−ジオキソラン−２−オンであって、
下記（Ｉ）で示される化合物を５０００ｐｐｍ以下含有する４−フルオロアルキル−（１，３）−ジオキソラン−２−オンに関する。
（Ｉ）一般式（２）：

（式中、Ｒｆは前記同様である）で示される化合物。 Furthermore, the present invention relates to a general formula (1):

(Wherein Rf is —CF ₃ , —CH ₂ CF ₃ , or —CH ₂ CF ₂ CF ₃ ), which is 4-fluoroalkyl- (1,3) -dioxolan-2-one. And
The present invention relates to 4-fluoroalkyl- (1,3) -dioxolan-2-one containing 5000 ppm or less of the compound represented by the following (I).
(I) General formula (2):

(Wherein Rf is the same as defined above).

In the formulas (1) and (2), when Rf is —CF ₃ group, 4-trifluoromethane containing (trifluoromethyl) ethane-1,2-diol (compound (I-1)) at 5,000 ppm or less. Methyl- (1,3) -dioxolan-2-one. In the formulas (1) and (2), when Rf is —CH ₂ CF ₃ , 2,2,2-trifluoroethylethane-1,2-diol (compound (I-2)) is added at 5000 ppm. It becomes 4- (2,2,2-trifluoroethyl)-(1,3) -dioxolan-2-one contained below. Further, when Rf is —CH ₂ CF ₂ CF ₃ , the composition contains 5000 ppm or less of 2,2,3,3,3-pentafluoropropylethane-1,2-diol (compound (I-3)). -(2,2,3,3,3-pentafluoropropyl)-(1,3) -dioxolan-2-one.

An electrochemical device comprising a non-aqueous solvent containing 4-fluoroalkyl- (1,3) -dioxolan-2-one containing 5000 ppm or less of the compound (I) and a non-aqueous electrolyte containing an electrolyte salt It has excellent storage characteristics and high voltage cycle characteristics.

The said compound (I) is 5000 ppm or less with respect to 4-fluoroalkyl- (1,3) -dioxolan-2-one, Preferably it is 3500 ppm or less, More preferably, it is 2500 ppm or less. When the compound (I) is contained in an amount of more than 5000 ppm, the discharge characteristics after high-temperature storage tend to decrease, or the cycle deterioration tends to increase when the voltage is increased. The definition of ppm is the same as described above.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited only to such examples.

Synthesis Example 1 4-trifluoromethyl- (1,3) -dioxolan-2-one Synthetic glass 1 L 4-neck flask was equipped with a mechanical stirrer, Dimroth, and dropping funnel. Under an ice bath, 400 mL of isopropyl ether (IPE) was placed in a reaction vessel, and 133 g (0.45 mol) of triphosgene was dissolved in (trifluoromethyl) ethane-1,2-diol (compound (I-1 )) Was added in an amount of 222 g (1.71 mol). Next, 170 g (1.68 mol) of triethylamine was added dropwise, and the mixture was stirred at room temperature for 1 hour. The reaction solution was quenched by adding 600 mL of pure water, separated, and the organic layer was washed with 600 mL of 1N aqueous hydrochloric acid, separated, washed with 600 mL of pure water, and then separated. Secard KW (manufactured by Shinagawa Kasei Co., Ltd.) and magnesium sulfate were added to the obtained organic layer for deoxidation and dehydration. The filtrate was collected by suction filtration and purified under normal pressure using a 10-stage distillation purification tower. About 5% of the first fraction was discarded, and almost equal amounts were sampled in the order of distillation to obtain rectified fractions A, B, and C having different contents of compound (I-1).

Fractions A to C were gas chromatographed (manufactured by Shimadzu Corporation, GC-17A; column: DB624 (Length 60, ID 0.32, Film 1.8 μm); increased from 50 ° C. to 250 ° C. at 10 ° C./min. Temperature; both the injection and detector (FID) are 250 ° C.), and the purity of 4-trifluoromethyl- (1,3) -dioxolan-2-one and the 4-trimethyl compound (I-1) The content relative to fluoromethyl- (1,3) -dioxolan-2-one was determined. The results are shown in Table 1.

Synthesis Example 2 4- (2,2,2-trifluoroethyl)-(1,3) -dioxolan-2-one Synthetic glass 1 L 4-neck flask was equipped with a mechanical stirrer, Dimroth, and dropping funnel. In an ice bath, 400 mL of isopropyl ether (IPE) is placed in a reaction vessel, and 133 g (0.45 mol) of triphosgene is dissolved in 2,2,2-trifluoroethylethane-1,2-diol (compound 246 g (1.71 mol) of (I-2)) was added. Next, 170 g (1.68 mol) of triethylamine was added dropwise, and the mixture was stirred at room temperature for 1 hour. The reaction solution was quenched by adding 600 mL of pure water, separated, and the organic layer was washed with 600 mL of 1N aqueous hydrochloric acid, separated, washed with 600 mL of pure water, and then separated. Secard KW (manufactured by Shinagawa Kasei Co., Ltd.) and magnesium sulfate were added to the obtained organic layer for deoxidation and dehydration. The filtrate was collected by suction filtration and purified under normal pressure using a 10-stage distillation purification tower. About 5% of the first fraction was discarded, and approximately equal amounts were sampled in the order of distillation to obtain rectified fractions D, E, and F having different contents of compound (I-2).

Fractions D to F were gas chromatographed (manufactured by Shimadzu Corporation, GC-17A; column: DB624 (Length 60, ID 0.32, Film 1.8 μm); increased from 50 ° C. to 250 ° C. at 10 ° C./min. Temperature; both the injection and detector (FID) are 250 ° C.), and the purity of 4- (2,2,2-trifluoroethyl)-(1,3) -dioxolan-2-one and the compound ( The content of I-2) with respect to 4- (2,2,2-trifluoroethyl)-(1,3) -dioxolan-2-one was determined. The results are shown in Table 2.

Synthesis Example 3 4- (2,2,3,3,3-pentafluoropropyl)-(1,3) -dioxolan-2-one Synthetic glass 1 L 4-neck flask was charged with a mechanical stirrer, Dimroth, and dropping funnel. Attached. In an ice bath, 400 mL of isopropyl ether (IPE) is placed in a reaction vessel, and 133 g (0.45 mol) of triphosgene is dissolved in 2,2,3,3,3-pentafluoropropylethane-1,2. -331.8g (1.71 mol) of diol (compound (I-3)) was put. Next, 170 g (1.68 mol) of triethylamine was added dropwise, and the mixture was stirred at room temperature for 1 hour. The reaction solution was quenched by adding 600 mL of pure water, separated, and the organic layer was washed with 600 mL of 1N aqueous hydrochloric acid, separated, washed with 600 mL of pure water, and then separated. Secard KW (manufactured by Shinagawa Kasei Co., Ltd.) and magnesium sulfate were added to the obtained organic layer for deoxidation and dehydration. The filtrate was collected by suction filtration and purified under normal pressure using a 10-stage distillation purification tower. About 5% of the first fraction was discarded, and approximately equal amounts were sampled in the order of distillation to obtain rectified G, H, and I having different contents of compound (I-3).

Fractions G to I were gas chromatographed (manufactured by Shimadzu Corporation, GC-17A; column: DB624 (Length 60, ID 0.32, Film 1.8 μm); increased from 50 ° C. to 250 ° C. at 10 ° C./min. The purity of 4- (2,2,3,3,3-pentafluoropropyl)-(1,3) -dioxolan-2-one by measuring at a temperature of 250 ° C. for both injection and detector (FID), And content with respect to 4- (2,2,3,3,3-pentafluoropropyl)-(1,3) -dioxolan-2-one of compound (I-3) was determined. The results are shown in Table 3.

Example 1
Under a dry argon atmosphere, 97 parts by weight of a mixture of ethylene carbonate and ethyl methyl carbonate (volume ratio 3: 7) was added 3 parts by weight of 4-trifluoromethyl- (1,3) -dioxolan-2-one of rectification C. Then, LiPF ₆ which was sufficiently dried and dissolved was dissolved at a ratio of 1 mol / liter to obtain an electrolytic solution.

(Production of coin-type battery)
Positive electrode in which LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , carbon black, and polyvinylidene fluoride (made by Kureha Chemical Co., Ltd., trade name KF-7200) are mixed at 92/3/5 (mass% ratio). A positive electrode mixture slurry was prepared by dispersing the active material in N-methyl-2-pyrrolidone to form a slurry. The obtained positive electrode mixture slurry is uniformly applied on an aluminum current collector, dried to form a positive electrode mixture layer (thickness 50 μm), and then compression molded by a roller press machine to form a positive electrode laminate. Manufactured. The positive electrode laminate was punched into a diameter of 1.6 mm with a punching machine to produce a circular positive electrode.

Separately, styrene-butadiene rubber dispersed with distilled water was added to artificial graphite powder so as to have a solid content of 6% by mass, and mixed with a disperser to form a slurry. A negative electrode current collector (thickness 10 μm) On the copper foil) and dried to form a negative electrode mixture layer, followed by compression molding with a roller press machine, and punched into a diameter of 1.6 mm with a punching machine to produce a circular negative electrode did.

The above-mentioned circular positive electrode is opposed to the positive electrode and the negative electrode through a microporous polyethylene film (separator) having a thickness of 20 μm, the electrolytic solution is injected, and the electrolytic solution sufficiently permeates the separator, and then sealed. Precharging and aging were performed to produce a coin-type lithium secondary battery.

(Measurement of battery characteristics)
The coin-type lithium secondary battery was examined for high voltage cycle characteristics and high temperature storage characteristics in the following manner.

Charge / Discharge Condition Charging: Holds the charge current at 1 / 10C at 0.5C and 4.3V (CC / CV charge)
Discharge: 0.5C 3.0Vcut (CC discharge)

(High voltage cycle characteristics)
Regarding the cycle characteristics, the charge / discharge cycle performed under the above charge / discharge conditions (charging at 1.0 C at a predetermined voltage until the charging current becomes 1/10 C and discharging to 3.0 V at a current equivalent to 1 C) is 1 The discharge capacity after 5 cycles and the discharge capacity after 100 cycles are measured. For the cycle characteristics, the value obtained by the following formula is used as the capacity retention rate. The results are shown in Table 4.

(High temperature storage characteristics)
For high-temperature storage characteristics, charge / discharge is performed under the above charge / discharge conditions (charge at 1.0C at a predetermined voltage until the charge current becomes 1 / 10C and discharge to 3.0V at a current equivalent to 1C). The capacity was examined. Then, it charged again on said charging conditions, and preserve | saved for one day in a 85 degreeC thermostat. The battery after storage was discharged at 25 ° C. under the above discharge conditions to a discharge end voltage of 3 V, the remaining capacity was measured, and after charging under the above charge conditions, the discharge was stopped at a constant current under the above discharge conditions. The recovery capacity was measured by discharging to a voltage of 3V. Table 4 shows the recovery capacity when the discharge capacity before storage is 100.

Example 2
Example except that 4-trifluoromethyl- (1,3) -dioxolan-2-one of rectification C was changed to 4-trifluoromethyl- (1,3) -dioxolan-2-one of rectification B A battery was prepared and tested in the same manner as in Example 1.

Example 3
The 4-trifluoromethyl- (1,3) -dioxolan-2-one of rectification C is converted to 4- (2,2,2-trifluoroethyl)-(1,3) -dioxolane-2 of rectification F. A battery was prepared and tested in the same manner as in Example 1 except that it was turned on.

Example 4
The 4-trifluoromethyl- (1,3) -dioxolan-2-one of rectification C is converted to 4- (2,2,2-trifluoroethyl)-(1,3) -dioxolane-2 of rectification E. A battery was prepared and tested in the same manner as in Example 1 except that it was turned on.

Example 5
The 4-trifluoromethyl- (1,3) -dioxolan-2-one of rectification C is converted to 4- (2,2,3,3,3-pentafluoropropyl)-(1,3) of rectification I. A battery was prepared and tested in the same manner as in Example 1 except that -dioxolan-2-one was used.

Example 6
4-Trifluoromethyl- (1,3) -dioxolan-2-one of rectification C is converted to 4- (2,2,3,3,3-pentafluoropropyl)-(1,3) of rectification H. A battery was prepared and tested in the same manner as in Example 1 except that -dioxolan-2-one was used.

Comparative Example 1
Example 1 except that 4-trifluoromethyl- (1,3) -dioxolan-2-one of rectification C was changed to 4-trifluoromethyl- (1,3) -dioxolan-2-one of rectification A A battery was fabricated and tested in the same manner as described above.

Comparative Example 2
The 4-trifluoromethyl- (1,3) -dioxolan-2-one of rectified C is converted into 4-trifluoromethyl- (1,3) -dioxolan-2-one of rectified C to compound (I-1 ) Was added at a rate of 10,000 ppm, and a battery was produced and tested in the same manner as in Example 1.

Comparative Example 3
4-Trifluoromethyl- (1,3) -dioxolan-2-one from rectification C is converted to 4- (2,2,2-trifluoroethyl)-(1,3) -dioxolane-2-one from rectification D A battery was produced and tested in the same manner as in Example 1 except that the battery was turned on.

Comparative Example 4
The 4-trifluoromethyl- (1,3) -dioxolan-2-one of rectification C is converted to 4- (2,2,2-trifluoroethyl)-(1,3) -dioxolane-2 of rectification F. A battery was prepared and tested in the same manner as in Example 1 except that the compound (I-2) was added to the ON at a ratio of 10,000 ppm.

Comparative Example 5
4-trifluoromethyl- (1,3) -dioxolan-2-one of rectification C is converted to 4- (2,2,3,3,3-pentafluoropropyl)-(1,3)-of rectification G A battery was prepared and tested in the same manner as in Example 1 except that dioxolan-2-one was used.

Comparative Example 6
The 4-trifluoromethyl- (1,3) -dioxolan-2-one of rectification C is converted to 4- (2,2,3,3,3-pentafluoropropyl)-(1,3) of rectification I. A battery was produced and tested in the same manner as in Example 1 except that the compound (I-3) was added to dioxolan-2-one at a rate of 10,000 ppm.

From the comparison of Examples 1 to 6 and Comparative Examples 1 to 6 in Table 4, the storage characteristics at high temperatures and the high voltage cycle characteristics are improved by reducing the content of the compound (I) in the nonaqueous solvent to 5000 ppm or less. I understand that. Further, from comparison between Examples 1, 3, 5 and Examples 2, 4, 6, it can be seen that the characteristics are further improved by setting the content of compound (I) in the nonaqueous solvent to 2500 ppm or less. .

Claims (3)

An electrochemical device comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte containing a non-aqueous solvent and an electrolyte salt,
The non-aqueous solvent is represented by the general formula (1):

(Wherein Rf is —CF ₃ , —CH ₂ CF ₃ , or —CH ₂ CF ₂ CF ₃ ), and contains 4-fluoroalkyl- (1,3) -dioxolan-2-one And
Containing 5000 ppm or less of the compound represented by the following (I) with respect to the 4-fluoroalkyl- (1,3) -dioxolan-2-one ;
The electrochemical device , wherein the content of 4-fluoroalkyl- (1,3) -dioxolan-2-one is 0.01 to 30% by weight in the non-aqueous solvent .
(I) General formula (2):

(Wherein Rf is the same as defined above). Electrochemical device, the electrochemical device according to claim 1 Symbol mounting a lithium ion secondary battery. A non-aqueous electrolyte for an electrochemical device comprising a non-aqueous solvent and an electrolyte salt,
The non-aqueous solvent is represented by the general formula (1):

(Wherein Rf is —CF ₃ , —CH ₂ CF ₃ , or —CH ₂ CF ₂ CF ₃ ), and contains 4-fluoroalkyl- (1,3) -dioxolan-2-one And
Containing 5000 ppm or less of the compound represented by the following (I) with respect to the 4-fluoroalkyl- (1,3) -dioxolan-2-one ;
The content of 4-fluoroalkyl- (1,3) -dioxolan-2-one is 0.01 to 30% by weight in the non-aqueous solvent, for electrochemical devices Non-aqueous electrolyte.
(I) General formula (2):

(Wherein Rf is the same as defined above).