JP6897264B2 - Electrolyte, electrochemical device, lithium ion secondary battery and module - Google Patents

Description

The present invention relates to electrolytes, electrochemical devices, lithium ion secondary batteries and modules.

With the recent weight reduction and miniaturization of electrical products, the development of electrochemical devices such as lithium ion secondary batteries having high energy density is being promoted. Further, as the application fields of electrochemical devices such as lithium ion secondary batteries expand, improvement of characteristics is required. Especially in the future, when lithium-ion secondary batteries are used for automobiles, improvement of battery characteristics will become more and more important.

Lithium-ion secondary batteries are required to have various characteristics such as initial capacity, rate characteristics, cycle characteristics, high-temperature storage characteristics, low-temperature characteristics, continuous charging characteristics, self-discharge characteristics, and overcharge prevention characteristics. A method of incorporating various additives into the electrolytic solution for improvement is being studied.

For example, Patent Document 1 describes a dicarboxylic acid diester (provided that Shu) in an electrolytic solution prepared by dissolving a lithium salt in a solvent mainly composed of at least one non-aqueous solvent selected from the group consisting of carbonic acid ester, ether and lactone. An electrolytic solution characterized by containing 0.1 to 5% by weight of an acid diester (excluding an acid diester and a succinic acid diester) or a derivative thereof with respect to the above solvent is described.

JP-A-2002-376673

However, there is a need to further improve the properties of electrochemical devices. In particular, the conventional electrochemical device using an electrolytic solution has room for improvement in terms of gas generation and capacity reduction during a cycle.

The present invention has been made in view of the above situation, and provides an electrolytic solution capable of suppressing gas generation and capacity decrease generated during a cycle of an electrochemical device, and an electrochemical device including the electrolytic solution. With the goal.

The present inventors have found that an electrolytic solution containing a compound having a specific structure can suppress gas generation and volume reduction that occur during the cycle of an electrochemical device, and have arrived at the present invention.

（式中、Ｒ^１及びＲ^４は、同一又は異なって、直鎖若しくは分岐鎖の炭素数１〜４のアルキル基、又は、直鎖若しくは分岐鎖の炭素数２〜６のアルケニル基であり、前記アルキル基及びアルケニル基は、１個以上のフッ素原子により置換されていてもよい。Ｒ^２及びＲ^３は、同一又は異なって、−Ｈ、−Ｆ、直鎖若しくは分岐鎖の炭素数１〜４のアルキル基、又は、直鎖若しくは分岐鎖の炭素数２〜６のアルケニル基であり、前記アルキル基及びアルケニル基は、１個以上のフッ素原子により置換されていてもよい。ただし、Ｒ^２及びＲ^３の少なくとも一方は、−Ｆ、前記アルキル基又はアルケニル基である。式中の波線はシス配置又はトランス配置のいずれかを示す。）で示される化合物（１−１）、及び、
下記一般式（１−２）：

（式中、Ｒ^５及びＲ^６は、同一又は異なって、直鎖又は分岐鎖の炭素数１〜１２のアルキレン基であり、前記アルキレン基は、１個以上のフッ素原子により置換されていてもよく、１個以上の二重結合を含んでいてもよい。）で示される化合物（１−２）からなる群より選択される少なくとも１種の化合物（１）を含むことを特徴とする電解液である。 That is, the present invention describes a solvent and the following general formula (1-1):

(In the formula, R ¹ and R ⁴ are the same or different alkyl groups having 1 to 4 carbon atoms in the linear or branched chain, or alkenyl groups having 2 to 6 carbon atoms in the linear or branched chain. The alkyl group and alkenyl group may be substituted with one or more fluorine atoms. R ² and R ³ are the same or different, and have 1 to 1 carbon atoms in the -H, -F, linear or branched chain. 4 alkyl group, or a straight or branched chain alkenyl group having 2 to 6 carbon atoms, said alkyl and alkenyl groups may be substituted by one or more fluorine atoms. However, R ² And ^{at least one of R 3} is -F, said alkyl group or alkenyl group. Wavy lines in the formula indicate either cis or trans configuration), and compound (1-1).
The following general formula (1-2):

(In the formula, R ⁵ and R ⁶ are the same or different alkylene groups having 1 to 12 carbon atoms in the linear or branched chain, even if the alkylene group is substituted with one or more fluorine atoms. An electrolytic solution characterized by containing at least one compound (1) selected from the group consisting of the compound (1-2) represented by (may contain one or more double bonds). Is.

In the electrolytic solution of the present invention, it is preferable that at least one ^{of R 2} and R ^{3 in the above general formula (1-1) is −H or −F.}

The content of the compound (1) is preferably 0.0001 to 10% by mass with respect to the solvent.

The electrolytic solution of the present invention preferably further contains an electrolyte salt.

The present invention is also an electrochemical device characterized by comprising the above-mentioned electrolytic solution. The present invention is also a lithium ion secondary battery characterized by comprising the above electrolytic solution.
The present invention is also a module comprising the electrochemical device or the lithium ion secondary battery.

By having the above-mentioned structure, the electrolytic solution of the present invention can suppress gas generation and capacity decrease that occur during the cycle of the electrochemical device. The electrochemical device provided with the electrolytic solution has suppressed gas generation and capacity reduction that occur during the cycle.

Hereinafter, the present invention will be specifically described.

（式中、Ｒ^１及びＲ^４は、同一又は異なって、直鎖若しくは分岐鎖の炭素数１〜４のアルキル基、又は、直鎖若しくは分岐鎖の炭素数２〜６のアルケニル基であり、前記アルキル基及びアルケニル基は、１個以上のフッ素原子により置換されていてもよい。Ｒ^２及びＲ^３は、同一又は異なって、−Ｈ、−Ｆ、直鎖若しくは分岐鎖の炭素数１〜４のアルキル基、又は、直鎖若しくは分岐鎖の炭素数２〜６のアルケニル基であり、前記アルキル基及びアルケニル基は、１個以上のフッ素原子により置換されていてもよい。ただし、Ｒ^２及びＲ^３の少なくとも一方は、−Ｆ、前記アルキル基又は前記アルケニル基である。式中の波線はシス配置又はトランス配置のいずれかを示す。）で示される化合物（１−１）、及び、下記一般式（１−２）：

（式中、Ｒ^５及びＲ^６は、同一又は異なって、直鎖又は分岐鎖の炭素数１〜１２のアルキレン基であり、前記アルキレン基は、１個以上のフッ素原子により置換されていてもよく、１個以上の二重結合を含んでいてもよい。）で示される化合物（１−２）からなる群より選択される少なくとも１種の化合物（１）を含む。 The electrolytic solution of the present invention has the following general formula (1-1):

(In the formula, R ¹ and R ⁴ are the same or different alkyl groups having 1 to 4 carbon atoms in the linear or branched chain, or alkenyl groups having 2 to 6 carbon atoms in the linear or branched chain. The alkyl group and alkenyl group may be substituted with one or more fluorine atoms. R ² and R ³ are the same or different, and have 1 to 1 carbon atoms in the -H, -F, linear or branched chain. 4 alkyl group, or a straight or branched chain alkenyl group having 2 to 6 carbon atoms, said alkyl and alkenyl groups may be substituted by one or more fluorine atoms. However, R ² And ^{at least one of R 3} is -F, the alkyl group or the alkenyl group. The wavy line in the formula indicates either the cis or trans configuration), and the compound (1-1). The following general formula (1-2):

(In the formula, R ⁵ and R ⁶ are the same or different alkylene groups having 1 to 12 carbon atoms in the linear or branched chain, even if the alkylene group is substituted with one or more fluorine atoms. It often comprises at least one compound (1) selected from the group consisting of the compounds (1-2) represented by (which may contain one or more double bonds).

The compound (1-1) represented by the general formula (1-1) is preferable because it can further suppress gas generation and capacity reduction that occur during the cycle of the electrochemical device.
^{In R 1} , R ² , R ³ and R ⁴ of the general formula (1-1), the carbon number of the alkyl group is preferably 1 to 3 and more preferably 1 or 2, respectively. ..
Specific examples of the alkyl group include CH _3- , CH ₃ CH _2- , CF _3- , CF ₃ CF _2- and the like. Among them, at least one selected from the group consisting of _{CH 3} − and CH ₃ CH _{2 − is preferable.}

^{In R 1} , R ² , R ³ and R ⁴ of the general formula (1-1), the carbon number of the alkenyl group is preferably 2 to 4, and more preferably 2 or 3, respectively. ..
Specific examples of the alkenyl group include CH ₂ = CH −, CH ₂ = _{CH CH 2} −, CF ₃ CH = CH − and the like. Among _them, CH 2 = CH- and _{CH 2} = CHCH 2 - at least one member selected from the group consisting of is preferred.

It is more preferable that at least one ^{of R 2} and R ³ in the above general formula (1-1) is −H or −F because the gas generation and capacity decrease that occur during the cycle of the electrochemical device can be further suppressed. It is more preferable that at least one of R ² and R ^{3 is −F.}
Further, from the viewpoint of suppressing gas generation and capacity decrease, ^{it is also preferable that one of R 2} and R ³ is −F and the other is −H.

Specific examples of the compound (1-1) represented by the general formula (1-1) include compounds represented by the following formulas (A1) to (A4).

The compound (1-2) represented by the general formula (1-2) is preferable in that the gas generation generated during the cycle of the electrochemical device can be further suppressed.
In the general formula (1-2), the alkylene group preferably has 1 to 8 carbon atoms, more preferably 1 to 6 carbon atoms, and even more preferably 1 to 4 carbon atoms.
In ^{R 5} and ^{R 6} in the general formula (1-2), the alkylene _{group, -CH 2 CH 2 -, -} CH 2 -, - CH 2 CH 2 CH 2 -, - CH 2 CHFCH 2 -, - CH ₂ CF ₂ CH ₂ −, −CH ₂ CH (CF ₃ ) CH ₂ − and the like can be mentioned. Among them, at least one selected from the group consisting of _{−CH 2} CH ₂ − and −CH ₂ CH ₂ CH _{2 − is preferable, and −CH 2} CH ₂ − is more preferable.

Specific examples of the compound (1-2) represented by the general formula (1-2) include a compound represented by the following formula (A5).

The above compounds (1) are represented by the formulas (A1), (A2), formulas (A3), formulas (A4) and formulas (A5) because the gas generation and capacity reduction that occur during the cycle of the electrochemical device can be further suppressed. At least one selected from the group consisting of the compounds represented by the formula (A1), (A2) and (A3) is more preferable, and at least one selected from the group consisting of the compounds represented by the formula (A3) is more preferable. At least one selected from the group consisting of the compounds represented by (A1) and (A2) is more preferable.

The content of compound (1) is preferably 0.0001 to 10% by mass with respect to the solvent. When the content of the compound (1) is in the above range, gas generation and volume reduction that occur during the cycle of the electrochemical device can be further suppressed. The content of the compound (1) is more preferably 0.01% by mass or more, further preferably 0.1% by mass or more, and particularly preferably 0.5% by mass or more with respect to the solvent. Further, 7% by mass or less is more preferable, 5% by mass or less is further preferable, and 3% by mass or less is particularly preferable.

The compound (1) can be synthesized by a conventionally known method. For example, the above compound (A1) can be synthesized by the method described in Japanese Patent Publication No. 62-500299.

The electrolytic solution of the present invention contains a solvent.

The solvent preferably contains carbonate.
The solvent can include cyclic carbonate or chain carbonate.
The cyclic carbonate may be a non-fluorinated cyclic carbonate or a fluorinated cyclic carbonate.
The chain carbonate may be a non-fluorinated chain carbonate or a fluorinated chain carbonate.
The solvent preferably contains at least one selected from the group consisting of non-fluorinated saturated cyclic carbonate, fluorinated saturated cyclic carbonate, fluorinated chain carbonate and non-fluorinated chain carbonate.

Examples of the non-fluorinated saturated cyclic carbonate include non-fluorinated saturated cyclic carbonate having an alkylene group having 2 to 4 carbon atoms.

Among them, at least one selected from the group consisting of ethylene carbonate, propylene carbonate, and butylene carbonate is preferable as the non-fluorinated saturated cyclic carbonate in that the dielectric constant is high and the viscosity is preferable.

As the non-fluorinated saturated cyclic carbonate, one type may be used alone, or two or more types may be used in combination in any combination and ratio.

The content of the non-fluorinated saturated cyclic carbonate is preferably 5 to 80% by volume, more preferably 20 to 50% by volume, and further preferably 30 to 40% by volume with respect to the solvent. preferable.

Examples of the non-fluorinated chain carbonate include CH ₃ OCOOCH ₃ (dimethyl carbonate: DMC), CH ₃ CH ₂ OCOOCH ₂ CH ₃ (diethyl carbonate: DEC), and CH ₃ CH ₂ OCOOCH ₃ (ethyl methyl carbonate: EMC). ), CH ₃ OCOOCH ₂ CH ₂ CH ₃ (methylpropyl carbonate), methylbutyl carbonate, ethylpropyl carbonate, ethylbutyl carbonate and other hydrocarbon-based chain carbonates. Among them, at least one selected from the group consisting of ethyl methyl carbonate, diethyl carbonate and dimethyl carbonate is preferable.

As the non-fluorinated chain carbonate, one type may be used alone, or two or more types may be used in combination in any combination and ratio.

The content of the non-fluorinated chain carbonate is preferably 20 to 95% by volume, more preferably 50 to 80% by volume, and further preferably 60 to 70% by volume with respect to the solvent. preferable.

The solvent preferably contains at least one selected from the group consisting of the non-fluorinated chain carbonate and the non-fluorinated cyclic carbonate, and both the non-fluorinated chain carbonate and the non-fluorinated cyclic carbonate. It is more preferable to include. An electrolytic solution containing a solvent having this composition can be suitably used for an electrochemical device used at a relatively low voltage.

The solvent preferably contains the non-fluorinated saturated cyclic carbonate and the non-fluorinated chain carbonate in a total amount of 20 to 100% by volume, more preferably 30 to 95% by volume, and 50 to 90% by volume. Is even more preferable.

When the electrolytic solution contains both the non-fluorinated chain carbonate and the non-fluorinated cyclic carbonate, the volume ratio of the non-fluorinated cyclic carbonate to the non-fluorinated chain carbonate is 5/95 to 95. / 5 is preferable, 10/90 or more is more preferable, 20/80 or more is further preferable, 30/70 or more is particularly preferable, 90/10 or less is more preferable, and 60/40 or less is further preferable.

When the solvent contains at least one selected from the group consisting of the non-fluorinated chain carbonate and the non-fluorinated cyclic carbonate, the electrolytic solution of the present invention contains the fluorinated saturated cyclic carbonate as an additive. You can also do it. In this case, the content of the fluorinated saturated cyclic carbonate is preferably 0.1 to 5% by mass with respect to the solvent.

The solvent may contain at least one selected from the group consisting of non-fluorinated saturated cyclic esters and non-fluorinated chain esters.

Examples of the non-fluorinated saturated cyclic ester include a non-fluorinated saturated cyclic carbonate having an alkylene group having 2 to 4 carbon atoms.

Specific examples of the non-fluorinated saturated cyclic carbonate having an alkylene group having 2 to 4 carbon atoms include β-propiolactone, γ-butyrolactone, and δ-valerolactone. Of these, γ-butyrolactone and δ-valerolactone are particularly preferable from the viewpoint of improving the degree of lithium ion dissociation and improving the load characteristics.

As the non-fluorinated saturated cyclic ester, one type may be used alone, or two or more types may be used in combination in any combination and ratio.

Examples of the non-fluorinated chain ester include methyl acetate, ethyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate and the like.

Of these, ethyl propionate and propyl propionate are preferable, and ethyl propionate is particularly preferable.

As the non-fluorinated chain ester, one type may be used alone, or two or more types may be used in combination in any combination and ratio.

The non-fluorinated saturated cyclic ester is preferably 0 to 90% by volume, more preferably 0.001 to 90% by volume, still more preferably 1 to 60% by volume, based on the solvent. It is particularly preferably 5 to 40% by volume.
The non-fluorinated chain ester is preferably 0 to 90% by volume, more preferably 0.001 to 90% by volume, still more preferably 1 to 60% by volume, based on the solvent. It is particularly preferably 5 to 40% by volume.
The total amount of the non-fluorinated saturated cyclic ester and the non-fluorinated chain ester is preferably 0 to 90% by volume, more preferably 1 to 60% by volume, and 5 to 40% by volume with respect to the solvent. It is more preferably%.

The fluorinated saturated cyclic carbonate is a saturated cyclic carbonate to which a fluorine atom is added. Specifically, the following general formula (A):

（式中、Ｘ^１〜Ｘ^４は同じか又は異なり、それぞれ−Ｈ、−ＣＨ_３、−Ｃ_２Ｈ_５、−Ｆ、エーテル結合を有してもよいフッ素化アルキル基、又は、エーテル結合を有してもよいフッ素化アルコキシ基を表す。ただし、Ｘ^１〜Ｘ^４の少なくとも１つは、−Ｆ、エーテル結合を有してもよいフッ素化アルキル基、又は、エーテル結合を有してもよいフッ素化アルコキシ基である。）で示される化合物が挙げられる。上記フッ素化アルキル基とは、−ＣＦ_３、−ＣＦ_２Ｈ、−ＣＨ_２Ｆ等である。

(In the formula, X ^{1 to} X ⁴ are the same or different, and each has an -H, -CH ₃ , -C ₂ H ₅ , -F, a fluorinated alkyl group which may have an ether bond, or an ether bond. a represents an even better fluorinated alkoxy group. provided that at least one of X ¹ to X ⁴ are, -F, good fluorinated alkyl group which may have an ether bond, or may have an ether bond It is a good fluorinated alkoxy group.). The fluorinated alkyl group is -CF ₃ , -CF ₂ H, -CH ₂ F, or the like.

When the above-mentioned fluorinated saturated cyclic carbonate is contained, when the electrolytic solution of the present invention is applied to a high-voltage lithium ion secondary battery or the like, the oxidation resistance of the electrolytic solution is improved, and stable and excellent charge / discharge characteristics can be obtained.
In the present specification, the “ether bond” is a bond represented by −O−.

The electrolytic solution of the present invention preferably contains the above-mentioned fluorinated saturated cyclic carbonate because it can be suitably used even under a high voltage.

Dielectric constant, the oxidation resistance is good point, X ¹ one to X ⁴ or two, -F, good fluorinated alkyl group which may have an ether bond, or may have an ether bond It is preferably a fluorinated alkoxy group.

Decrease in viscosity at low temperatures, increased flash point, since the more can be expected to improve the solubility of an electrolyte salt, X ¹ to X ⁴ are, -H, -F, a fluorinated alkyl group (a), an ether bond It is preferably an alkyl fluorinated group (b) or an alkoxy fluorinated group (c).

The fluorinated alkyl group (a) is obtained by substituting at least one hydrogen atom of the alkyl group with a fluorine atom. The fluorinated alkyl group (a) preferably has 1 to 20 carbon atoms, more preferably 1 to 17 carbon atoms, further preferably 1 to 7 carbon atoms, and particularly preferably 1 to 5 carbon atoms.
If the carbon number is too large, the low temperature characteristics may be deteriorated or the solubility of the electrolyte salt may be lowered. If the carbon number is too small, the solubility of the electrolyte salt may be lowered, the discharge efficiency may be lowered, and further, the solubility of the electrolyte salt may be lowered. Increased viscosity may be seen.

Among the above fluorinated alkyl groups (a), those having 1 carbon atom include CFH _2- , CF ₂ H-, and CF _3- . In particular, CF ₂ H − or CF ₃ − is preferable in terms of high temperature storage characteristics.

Among the above fluorinated alkyl groups (a), those having 2 or more carbon atoms are selected from the following general formula (a-1):
R ¹ − R ² − (a-1)
(In the formula, R ¹ is an alkyl group having 1 or more carbon ^{atoms which may have a fluorine atom; R 2} is an alkylene group having 1 to 3 carbon atoms which may have a fluorine atom; however, R ¹ and The ^{alkyl fluorinated group represented by (at least one of R 2} has a fluorine atom) can be preferably exemplified from the viewpoint of good solubility of the electrolyte salt.
In addition, R ¹ and R ² may further have other atoms other than carbon atom, hydrogen atom and fluorine atom.

R ¹ is an alkyl group having 1 or more carbon atoms which may have a fluorine atom. As R 1, a linear or branched alkyl group having ^{1 to 16 carbon atoms is preferable.} The ^{number of carbon atoms of R 1} is more preferably 1 to 6, and even more preferably 1 to 3.

As R ¹ , specifically, as a linear or branched alkyl group, CH ₃ −, CH ₃ CH ₂ −, CH ₃ CH ₂ CH ₂ −, CH ₃ CH ₂ CH ₂ CH ₂ −,

And so on.

When R ¹ is a linear alkyl group having a fluorine atom, CF _3- , CF ₃ CH _2- , CF ₃ CF _2- , CF ₃ CH ₂ CH _2- , CF ₃ CF ₂ CH _2- , CF ₃ CF ₂ CF _2- , CF ₃ CH ₂ CF _2- , CF ₃ CH ₂ CH ₂ CH _2- , CF ₃ CF ₂ CH ₂ CH _2- , CF ₃ CH ₂ CF ₂ CH _2- , CF ₃ CF ₂ CF ₂ CH ₂ −, CF ₃ CF ₂ CF ₂ CF ₂ −, CF ₃ CF ₂ CH ₂ CF ₂ −, CF ₃ CH ₂ CH ₂ CH ₂ CH ₂ −, CF ₃ CF ₂ CH ₂ CH ₂ CH ₂ − , CF ₃ CH ₂ CF ₂ CH ₂ CH ₂ −, CF ₃ CF ₂ CF ₂ CH ₂ CH ₂ −, CF ₃ CF ₂ CF ₂ CF ₂ CH ₂ −, CF ₃ CF ₂ CH ₂ CF ₂ CH ₂ −, CF ₃ CF ₂ CH ₂ CH ₂ CH ₂ CH ₂ −, CF ₃ CF ₂ CF ₂ CF ₂ CH ₂ CH ₂ −, CF ₃ CF ₂ CH ₂ CF ₂ CH ₂ CH ₂ −, HCF ₂ −, HCF ₂ CH ₂ − , HCF ₂ CF ₂ −, HCF ₂ CH ₂ CH ₂ −, HCF ₂ CF ₂ CH ₂ −, HCF ₂ CH ₂ CF ₂ −, HCF ₂ CF ₂ CH ₂ CH ₂ −, HCF ₂ CH ₂ CF ₂ CH ₂ − , HCF ₂ CF ₂ CF ₂ CF _2- , HCF ₂ CF ₂ CH ₂ CH ₂ CH _2- , HCF ₂ CH ₂ CF ₂ CH ₂ CH _2- , HCF ₂ CF ₂ CF ₂ CF ₂ CH _2- , HCF ₂ CF ₂ CF ₂ CF ₂ CH ₂ CH _2- , FCH _2- , FCH ₂ CH _2- , FCH ₂ CF _2- , FCH ₂ CF ₂ CH _2- , FCH ₂ CF ₂ CF _2- , CH ₃ CF ₂ CH _2- , CH ₃ CF ₂ CF ₂ −, CH ₃ CF ₂ CH ₂ CF ₂ −, CH ₃ CF ₂ CF ₂ CF ₂ −, CH ₃ CH ₂ CF ₂ CF ₂ −, CH ₃ CF ₂ CH ₂ CF ₂ CH ₂ − , CH ₃ CF ₂ CF ₂ CF ₂ CH ₂ −, CH ₃ CF ₂ CF ₂ CH ₂ CH ₂ −, CH ₃ CH ₂ CF ₂ CF ₂ CH ₂ −, CH ₃ CF ₂ CH ₂ CF ₂ CH ₂ CH ₂ −, CH ₃ CF ₂ CH ₂ CF ₂ CH ₂ CH _2- , HCFClCF ₂ CH _2- , HCF ₂ CFClCH _2- , HCF ₂ CFClCF ₂ CFClCH _2- , HCFClCF ₂ CFClCF ₂ CH _2- and the like can be mentioned.

When R ¹ is a branched-chain alkyl group having a fluorine atom,

Etc. are preferably mentioned. However, _{if it has a branch of CH 3-} or CF _3- , the viscosity tends to be high, so the number is more preferably small (1) or zero.

R ² is an alkylene group having 1 to 3 carbon atoms which may have a fluorine atom. R ² may be linear or branched. An example of the smallest structural unit constituting such a linear or branched alkylene group is shown below. R ² is composed of these alone or in combination.

(I) Linear minimum structural unit:
_{-CH 2 -, - CHF -,} - CF 2 -, - CHCl -, - CFCl -, - CCl 2 -

(Ii) Branched chain minimum structural unit:

Among the above examples, it is preferable that the unit is composed of a Cl-free structural unit because the dehydrochloric acid reaction by a base does not occur and it is more stable.

When R ² is linear, it is composed of only the linear minimum structural unit described above, and among them, −CH ₂ −, _{−CH 2} CH ₂ − or −CF ₂₋ is preferable. _{-CH 2-} or -CH ₂ CH ₂ --is more preferable from the viewpoint that the solubility of the electrolyte salt can be further improved.

When R ² is in the form of a branched chain, it contains at least one of the above-mentioned minimum structural units in the form of a branched chain, and the general formula-(CX ^a X ^b )-(X ^a is H, F). , CH ₃ or CF ₃ ; X ^b is CH ₃ or CF _3. However, when X ^b is CF ₃ , X ^a is H or CH ₃ ). These can further improve the solubility of the electrolyte salt in particular.

Preferred alkyl fluorinated groups (a) include, for example, CF ₃ CF _2- , HCF ₂ CF _2- , H ₂ CFCF _2- , CH ₃ CF _2- , CF ₃ CHF-, CH ₃ CF _2- , CF ₃ CF. ₂ CF _2- , HCF ₂ CF ₂ CF _2- , H ₂ CFCF ₂ CF _2- , CH ₃ CF ₂ CF _2- ,

And so on.

The fluorinated alkyl group (b) having an ether bond is one in which at least one hydrogen atom of the alkyl group having an ether bond is replaced with a fluorine atom. The fluorinated alkyl group (b) having an ether bond preferably has 2 to 17 carbon atoms. If the number of carbon atoms is too large, the viscosity of the fluorinated saturated cyclic carbonate becomes high, and the number of fluorine-containing groups increases, so that the solubility of the electrolyte salt decreases due to the decrease in the dielectric constant and the compatibility with other solvents. May be seen to decrease. From this viewpoint, the number of carbon atoms of the fluorinated alkyl group (b) having an ether bond is more preferably 2 to 10, and even more preferably 2 to 7.

The alkylene group constituting the ether portion of the fluorinated alkyl group (b) having an ether bond may be a linear or branched alkylene group. An example of the smallest structural unit constituting such a linear or branched alkylene group is shown below.

(I) Linear minimum structural unit:
_{-CH 2 -, - CHF -,} - CF 2 -, - CHCl -, - CFCl -, - CCl 2 -

(Ii) Branched chain minimum structural unit:

The alkylene group may be composed of these minimum structural units alone, and may be linear (i) or branched chain (ii) or linear (i) and branched chain (ii). It may be composed of combinations. Preferred specific examples will be described later.

Among the above examples, it is preferable that the unit is composed of a Cl-free structural unit because the dehydrochloric acid reaction by a base does not occur and it is more stable.

As a fluorinated alkyl group (b) having a more preferable ether bond, the general formula (b-1):
R ^3- (OR ⁴ ) _n1- (b-1)
(In the formula, R ³ may have a fluorine atom, preferably an alkyl group having 1 to 6 carbon atoms; R ⁴ may have a fluorine atom, preferably an alkylene having 1 to 4 carbon atoms. group; n1 is an integer of 1 to 3; provided that at least one of ^{R 3} and ^{R 4} include those represented by and has a fluorine atom).

Examples of R ³ and R ⁴ include the following, and these can be appropriately combined to form a fluorinated alkyl group (b) having an ether bond represented by the above general formula (b-1). , Not limited to these.

(1) As R ³ , the general formula: X ^c ₃ C- (R ⁵ ) _{n 2-} (three X ^c are the same or different, and all are H or F; R ⁵ is a fluorine atom having 1 to 5 carbon atoms. An alkylene group that may have; n2 is preferably an alkyl group represented by 0 or 1).

When n2 is 0, examples of ^{R 3} include CH _3- , CF _3- , HCF _2-, and H _{2 CF-.}

As a specific example when n2 is 1, assuming that R ³ is linear, CF ₃ CH _2- , CF ₃ CF _2- , CF ₃ CH ₂ CH _2- , CF ₃ CF ₂ CH _2- , CF ₃ CF ₂ CF _2- , CF ₃ CH ₂ CF _2- , CF ₃ CH ₂ CH ₂ CH _2- , CF ₃ CF ₂ CH ₂ CH _2- , CF ₃ CH ₂ CF ₂ CH _2- , CF ₃ CF ₂ CF ₂ CH ₂ −, CF ₃ CF ₂ CF ₂ CF ₂ −, CF ₃ CF ₂ CH ₂ CF ₂ −, CF ₃ CH ₂ CH ₂ CH ₂ CH ₂ −, CF ₃ CF ₂ CH ₂ CH ₂ CH ₂ −, CF ₃ CH ₂ CF ₂ CH ₂ CH ₂ −, CF ₃ CF ₂ CF ₂ CH ₂ CH ₂ −, CF ₃ CF ₂ CF ₂ CF ₂ CH ₂ −, CF ₃ CF ₂ CH ₂ CF ₂ CH ₂ −, CF ₃ CF ₂ CH ₂ CH ₂ CH ₂ CH _2- , CF ₃ CF ₂ CF ₂ CF ₂ CH ₂ CH _2- , CF ₃ CF ₂ CH ₂ CF ₂ CH ₂ CH _2- , HCF ₂ CH _2- , HCF ₂ CF _2- , HCF ₂ CH ₂ CH _2- , HCF ₂ CF ₂ CH _2- , HCF ₂ CH ₂ CF _2- , HCF ₂ CF ₂ CH ₂ CH _2- , HCF ₂ CH ₂ CF ₂ CH _2- , HCF ₂ CF ₂ CF ₂ CF _2- , HCF ₂ CF ₂ CH ₂ CH ₂ CH _2- , HCF ₂ CH ₂ CF ₂ CH ₂ CH _2- , HCF ₂ CF ₂ CF ₂ CF ₂ CH _2- , HCF ₂ CF ₂ CF ₂ CF ₂ CH ₂ CH _2- , FCH ₂ CH _2- , FCH ₂ CF _2- , FCH ₂ CF ₂ CH _2- , CH ₃ CF _2- , CH ₃ CH _2- , CH ₃ CF ₂ CH _2- , CH ₃ CF ₂ CF _2- , CH ₃ CH ₂ CH _2- , CH ₃ CF ₂ CH ₂ CF _2- , CH ₃ CF ₂ CF ₂ CF _2- , CH ₃ CH ₂ CF ₂ CF _2- , CH ₃ CH ₂ CH ₂ CH _2- , CH ₃ CF ₂ CH ₂ CF ₂ CH ₂ −, CH ₃ CF ₂ CF ₂ CF ₂ CH ₂ −, CH ₃ CF ₂ CF ₂ CH ₂ CH ₂ −, CH ₃ CH ₂ CF ₂ CF ₂ CH ₂ −, CH ₃ CF ₂ CH ₂ CF ₂ Examples thereof include CH ₂ CH ₂ −, CH ₃ CH ₂ CF ₂ CF ₂ CH ₂ CH ₂ −, CH ₃ CF ₂ CH ₂ CF ₂ CH ₂ CH _{2 −.}

n2 is 1, and as R ³ is branched, the

And so on.

However, _{if it has a branch of CH 3} − or CF ₃ −, the viscosity tends to be high, so that R ³ is linear is more preferable.

^{(2) In − (OR 4} ) _n1 − of the above general formula (b-1), n1 is an integer of 1 to 3, preferably 1 or 2. When n1 = 2 or 3, R ⁴ may be the same or different.

As ^{a preferable specific example of R 4} , the following linear or branched chain can be exemplified.

As those _{linear, -CH 2 -, - CHF -} , - CF 2 -, - CH 2 CH 2 -, - CF 2 CH 2 -, - CF 2 CF 2 -, - CH 2 CF 2 -, -CH ₂ CH ₂ CH _2- , -CH ₂ CH ₂ CF _2- , -CH ₂ CF ₂ CH _2- , -CH ₂ CF ₂ CF _2- , -CF ₂ CH ₂ CH _2- , -CF ₂ CF ₂ CH _2- , −CF ₂ CH ₂ CF _2- , −CF ₂ CF ₂ CF _2-, etc. can be exemplified.

As a branched chain,

And so on.

The fluorinated alkoxy group (c) is obtained by substituting at least one hydrogen atom of the alkoxy group with a fluorine atom. The fluorinated alkoxy group (c) preferably has 1 to 17 carbon atoms. More preferably, it has 1 to 6 carbon atoms.

The fluorinated alkoxy group (c) has a general formula: X ^d ₃ C- (R ⁶ ) _n3- O- (three X ^d are the same or different, and H or F; R ⁶ is preferably the number of carbon atoms. alkylene group which may have 1 to 5 fluorine atoms; n3 is 0 or 1; with the proviso that one of the three X ^d is a fluorinated alkoxy group represented by contains fluorine atom) are particularly preferred.

Specific examples of the fluorinated alkoxy group (c), a fluorinated alkoxy group terminal oxygen atom is bonded to an alkyl group exemplified as R ¹ in formula (a-1) can be mentioned.

The fluorine content of the fluorinated alkyl group (a), the fluorinated alkyl group (b) having an ether bond, and the fluorinated alkoxy group (c) in the fluorinated saturated cyclic carbonate is preferably 10% by mass or more. If the fluorine content is too low, the effect of lowering the viscosity at low temperature and the effect of raising the flash point may not be sufficiently obtained. From this viewpoint, the fluorine content is more preferably 12% by mass or more, and further preferably 15% by mass or more. The upper limit is usually 76% by mass.
The fluorine content of the fluorinated alkyl group (a), the fluorinated alkyl group (b) having an ether bond, and the fluorinated alkoxy group (c) is determined by {(the number of fluorine atoms) based on the structural formula of each group. It is a value calculated by × 19) / formula amount of each group} × 100 (%).

Further, from the viewpoint of good dielectric constant and oxidation resistance, the fluorine content of the entire fluorinated saturated cyclic carbonate is preferably 10% by mass or more, more preferably 15% by mass or more. The upper limit is usually 76% by mass.
The fluorine content of the fluorinated saturated cyclic carbonate is determined by {(number of fluorine atoms × 19) / molecular weight of the fluorinated saturated cyclic carbonate} × 100 (%) based on the structural formula of the fluorinated saturated cyclic carbonate. It is a calculated value.

Specific examples of the fluorinated saturated cyclic carbonate include the following.

As a specific example of a fluorinated saturated cyclic carbonate in which at least one of ^{X 1 to} X ^{4 is -F,}

等が挙げられる。これらの化合物は、耐電圧が高く、電解質塩の溶解性も良好である。

And so on. These compounds have a high withstand voltage and good solubility of electrolyte salts.

other,

Etc. can also be used.

As a specific example of the fluorinated saturated cyclic carbonate in which at least one of ^{X 1 to} X ^{4 is a fluorinated alkyl group (a) and the rest are all −H,}

And so on.

Specific Example of Fluorinated Saturated Cyclic Carbonate in which at least one of X ^{1 to} X ⁴ is a fluorinated alkyl group (b) having an ether bond or a fluorinated alkoxy group (c), and the rest are all −H. as,

And so on.

Among them, the fluorinated saturated cyclic carbonate is preferably any of the following compounds.

As the fluorinated saturated cyclic carbonate, fluoroethylene carbonate, difluoroethylene carbonate or trifluoromethylethylene carbonate is more preferable.

The fluorinated saturated cyclic carbonate is not limited to the specific examples described above. Further, the above-mentioned fluorinated saturated cyclic carbonate may be used alone or in combination of two or more in any combination and ratio.

The content of the fluorinated saturated cyclic carbonate is preferably 5 to 80% by volume, more preferably 20 to 50% by volume, and even more preferably 30 to 40% by volume with respect to the solvent.

The fluorinated chain carbonate has the general formula (B):
Rf ² OCOOR ⁶ (B)
(In the formula, Rf ² is a fluorinated alkyl group ^{having 1 to 7 carbon atoms, and R 6} is an alkyl group which may contain a fluorine atom having 1 to 7 carbon atoms.) Can be mentioned.

The electrolytic solution of the present invention preferably contains the above-mentioned fluorinated chain carbonate because it can be suitably used even under a high voltage.

Rf ² is a fluorinated alkyl group having 1 to 7 carbon atoms, and R ⁶ is an alkyl group which may contain a fluorine atom having 1 to 7 carbon atoms.
The above-mentioned fluorinated alkyl group is obtained by substituting at least one hydrogen atom of the alkyl group with a fluorine atom. When R ⁶ is an alkyl group containing a fluorine atom, it becomes a fluorinated alkyl group.
Rf ² and R ⁶ preferably have 2 to 7 carbon atoms, and more preferably 2 to 4 carbon atoms in that they have low viscosities.
If the carbon number is too large, the low temperature characteristics may be deteriorated or the solubility of the electrolyte salt may be lowered. If the carbon number is too small, the solubility of the electrolyte salt may be lowered, the discharge efficiency may be lowered, and further, the solubility of the electrolyte salt may be lowered. Increased viscosity may be seen.

Examples of the fluorinated alkyl group having 1 carbon atom include CFH _2- , CF ₂ H-, CF _3- and the like. In particular, CF ₂ H − or CF ₃ − is preferable in terms of high temperature storage characteristics.

Examples of the fluorinated alkyl group having 2 or more carbon atoms include the following general formula (d-1):
R ¹ − R ² − (d-1)
(In the formula, R ¹ is an alkyl group having 1 or more carbon ^{atoms which may have a fluorine atom; R 2} is an alkylene group having 1 to 3 carbon atoms which may have a fluorine atom; however, R ¹ and The ^{alkyl fluorinated group represented by (at least one of R 2} has a fluorine atom) can be preferably exemplified from the viewpoint of good solubility of the electrolyte salt.
In addition, R ¹ and R ² may further have other atoms other than carbon atom, hydrogen atom and fluorine atom.

R ¹ is an alkyl group having 1 or more carbon atoms which may have a fluorine atom. As R ¹ , a linear or branched alkyl group having 1 to 6 carbon atoms is preferable. The ^{number of carbon atoms of R 1} is more preferably 1 to 6, and even more preferably 1 to 3.

As R ¹ , specifically, as a linear or branched alkyl group, CH ₃ −, CH ₃ CH ₂ −, CH ₃ CH ₂ CH ₂ −, CH ₃ CH ₂ CH ₂ CH ₂ −,

And so on.

When R ¹ is a linear alkyl group having a fluorine atom, CF _3- , CF ₃ CH _2- , CF ₃ CF _2- , CF ₃ CH ₂ CH _2- , CF ₃ CF ₂ CH _2- , CF ₃ CF ₂ CF _2- , CF ₃ CH ₂ CF _2- , CF ₃ CH ₂ CH ₂ CH _2- , CF ₃ CF ₂ CH ₂ CH _2- , CF ₃ CH ₂ CF ₂ CH _2- , CF ₃ CF ₂ CF ₂ CH ₂ −, CF ₃ CF ₂ CF ₂ CF ₂ −, CF ₃ CF ₂ CH ₂ CF ₂ −, CF ₃ CH ₂ CH ₂ CH ₂ CH ₂ −, CF ₃ CF ₂ CH ₂ CH ₂ CH ₂ − , CF ₃ CH ₂ CF ₂ CH ₂ CH ₂ −, CF ₃ CF ₂ CF ₂ CH ₂ CH ₂ −, CF ₃ CF ₂ CF ₂ CF ₂ CH ₂ −, CF ₃ CF ₂ CH ₂ CF ₂ CH ₂ −, CF ₃ CF ₂ CH ₂ CH ₂ CH ₂ CH ₂ −, CF ₃ CF ₂ CF ₂ CF ₂ CH ₂ CH ₂ −, CF ₃ CF ₂ CH ₂ CF ₂ CH ₂ CH ₂ −, HCF ₂ −, HCF ₂ CH ₂ − , HCF ₂ CF ₂ −, HCF ₂ CH ₂ CH ₂ −, HCF ₂ CF ₂ CH ₂ −, HCF ₂ CH ₂ CF ₂ −, HCF ₂ CF ₂ CH ₂ CH ₂ −, HCF ₂ CH ₂ CF ₂ CH ₂ − , HCF ₂ CF ₂ CF ₂ CF _2- , HCF ₂ CF ₂ CH ₂ CH ₂ CH _2- , HCF ₂ CH ₂ CF ₂ CH ₂ CH _2- , HCF ₂ CF ₂ CF ₂ CF ₂ CH _2- , HCF ₂ CF ₂ CF ₂ CF ₂ CH ₂ CH _2- , FCH _2- , FCH ₂ CH _2- , FCH ₂ CF _2- , FCH ₂ CF ₂ CH _2- , FCH ₂ CF ₂ CF _2- , CH ₃ CF ₂ CH _2- , CH ₃ CF ₂ CF ₂ −, CH ₃ CF ₂ CH ₂ CF ₂ −, CH ₃ CF ₂ CF ₂ CF ₂ −, CH ₃ CH ₂ CF ₂ CF ₂ −, CH ₃ CF ₂ CH ₂ CF ₂ CH ₂ − , CH ₃ CF ₂ CF ₂ CF ₂ CH ₂ −, CH ₃ CF ₂ CF ₂ CH ₂ CH ₂ −, CH ₃ CH ₂ CF ₂ CF ₂ CH ₂ −, CH ₃ CF ₂ CH ₂ CF ₂ CH ₂ CH ₂ −, CH ₃ CF ₂ CH ₂ CF ₂ CH ₂ CH _2- , HCFClCF ₂ CH _2- , HCF ₂ CFClCH _2- , HCF ₂ CFClCF ₂ CFClCH _2- , HCFClCF ₂ CFClCF ₂ CH _2- and the like can be mentioned.

When R ¹ is a branched-chain alkyl group having a fluorine atom,

Etc. are preferably mentioned. However, _{if it has a branch of CH 3-} or CF _3- , the viscosity tends to be high, so the number is more preferably small (1) or zero.

R ² is an alkylene group having 1 to 3 carbon atoms which may have a fluorine atom. R ² may be linear or branched. An example of the smallest structural unit constituting such a linear or branched alkylene group is shown below. R ² is composed of these alone or in combination.

(I) Linear minimum structural unit:
_{-CH 2 -, - CHF -,} - CF 2 -, - CHCl -, - CFCl -, - CCl 2 -

(Ii) Branched chain minimum structural unit:

Among the above examples, it is preferable that the unit is composed of a Cl-free structural unit because the dehydrochloric acid reaction by a base does not occur and it is more stable.

When R ² is linear, it is composed of only the linear minimum structural unit described above, and among them, −CH ₂ −, _{−CH 2} CH ₂ − or −CF ₂₋ is preferable. _{-CH 2-} or -CH ₂ CH ₂ --is more preferable from the viewpoint that the solubility of the electrolyte salt can be further improved.

When R ² is in the form of a branched chain, it contains at least one of the above-mentioned minimum structural units in the form of a branched chain, and the general formula-(CX ^a X ^b )-(X ^a is H, F). , CH ₃ or CF ₃ ; X ^b is CH ₃ or CF _3. However, when X ^b is CF ₃ , X ^a is H or CH ₃ ). These can further improve the solubility of the electrolyte salt in particular.

Specific preferred alkyl fluorinated groups include, for example, CF ₃ CF _2- , HCF ₂ CF _2- , H ₂ CFCF _2- , CH ₃ CF _2- , CF ₃ CH _2- , CF ₃ CF ₂ CF. _2- , HCF ₂ CF ₂ CF _2- , H ₂ CFCF ₂ CF _2- , CH ₃ CF ₂ CF _2- ,

And so on.

Among them, as the fluorinated alkyl groups of ^{Rf 2} and R ⁶ _{, CF 3-} , CF ₃ CF _2- , (CF ₃ ) ₂ CH-, CF ₃ CH _2- , C ₂ F ₅ CH _2- , CF ₃ CF ₂ CH _2- , HCF ₂ CF ₂ CH _2- , CF ₃ CFHCF ₂ CH _2- , CFH _2- , CF ₂ H- are preferable, and they have high flame retardancy and good rate characteristics and oxidation resistance. , CF ₃ CH _2- , CF ₃ CF ₂ CH _2- , HCF ₂ CF ₂ CH _2- , CFH _2- , CF ₂ H- are more preferable.

When R ⁶ is an alkyl group containing no fluorine atom, it is an alkyl group having 1 to 7 carbon atoms. R ⁶ preferably has 1 to 4 carbon atoms, and more preferably 1 to 3 carbon atoms in that it has a low viscosity.

Examples of the alkyl group containing no fluorine atom include CH ₃ −, CH ₃ CH ₂ −, (CH ₃ ) ₂ CH −, C ₃ H ₇ − and the like. _{Of these, CH 3} − and CH ₃ CH ₂ − are preferable because of their low viscosity and good rate characteristics.

The fluorinated chain carbonate preferably has a fluorine content of 20 to 70% by mass. When the fluorine content is in the above range, the compatibility with the solvent and the solubility of the salt can be maintained. The fluorine content is more preferably 30% by mass or more, further preferably 35% by mass or more, further preferably 60% by mass or less, still more preferably 50% by mass or less.
In the present invention, the fluorine content is determined based on the structural formula of the fluorinated chain carbonate.
{(Number of fluorine atoms x 19) / Molecular weight of fluorinated chain carbonate} x 100 (%)
It is a value calculated by.

The fluorinated chain carbonate is preferably one of the following compounds in terms of low viscosity.

The content of the fluorinated chain carbonate is preferably 20 to 95% by volume, more preferably 50 to 80% by volume, and even more preferably 60 to 70% by volume with respect to the solvent.

The solvent preferably contains at least one selected from the group consisting of the fluorinated chain carbonate and the fluorinated cyclic carbonate, and may contain both the fluorinated chain carbonate and the fluorinated cyclic carbonate. More preferred. An electrolytic solution containing a solvent having this composition can be suitably used for an electrochemical device used at a relatively high voltage.

The solvent preferably contains the fluorinated saturated cyclic carbonate and the fluorinated chain carbonate in a total amount of 10 to 100% by volume. In total, the content is more preferably 20% by volume or more, further preferably 30% by volume or more, particularly preferably 40% by volume or more, further preferably 95% by volume or less, further preferably 90% by volume or less, and 85% by volume. Volume% or less is particularly preferable.

When the solvent contains both the fluorinated chain carbonate and the fluorinated cyclic carbonate, the volume ratio of the fluorinated cyclic carbonate to the fluorinated chain carbonate is preferably 5/95 to 95/5. 10/90 or more is more preferable, 20/80 or more is further preferable, 30/70 or more is particularly preferable, 80/20 or less is more preferable, and 60/40 or less is further preferable.

The solvent preferably contains a fluorinated chain ester because it can be suitably used even under a high voltage. The fluorinated chain ester has the following general formula:
Rf ³¹ COORf ³²
In the formula, the ^{fluorinated chain ester represented by (Rf 31} is a fluorinated alkyl group ^{having 1 to 4 carbon atoms and Rf 32} is an alkyl group which may contain a fluorine atom having 1 to 4 carbon atoms) is another solvent. It is preferable from the viewpoint of good compatibility with and oxidation resistance.

Examples of Rf ³¹ _{include HCF 2-} , CF _3- , CF ₃ CF _2- , HCF ₂ CF _2- , CH ₃ CF _2- , CF ₃ CH _2-, and the like, and among them, HCF _2- and CF ₃ -, CF ₃ CF _2- , and CF ₃ CH _2- are particularly preferable because they have good viscosity and oxidation resistance.

Examples of Rf ³² _{include CH 3-} , C ₂ H _5- , CF _3- , CF ₃ CF _2- , (CF ₃ ) ₂ CH-, CF ₃ CH _2- , CF ₃ CH ₂ CH _2- , CF. ₃ CFHCF ₂ CH ₂ −, C ₂ F ₅ CH ₂ −, CF ₂ HCF ₂ CH ₂ −, C ₂ F ₅ CH ₂ CH ₂ −, CF ₃ CF ₂ CH ₂ −, CF ₃ CF ₂ CF ₂ CH ₂ − Etc., and among them, CH ₃ −, C ₂ H ₅ −, CF ₃ CH ₂ −, and CF ₃ CH ₂ CH ₂ − are particularly preferable because they have good compatibility with other solvents.

Specific examples of the fluorinated chain ester include CF ₃ CH ₂ C (= O) OCH ₃ , HCF ₂ C (= O) OCH ₃ , CF ₃ C (= O) OCH ₂ CH ₂ CF ₃ , CF. ₃ C (= O) OCH ₂ C ₂ F ₅ , CF ₃ C (= O) OCH ₂ CF ₂ CF ₂ H, CF ₃ C (= O) OCH ₂ CF ₃ , CF ₃ C (= O) OCH (CF) ₃ ) One type or two or more types such as _{2 can be exemplified, and among them, CF 3} CH ₂ C (= O) OCH ₃ , HCF ₂ C (= O) OCH ₃ , CF ₃ C (= O) OCH ₂ C ₂ F ₅ , CF ₃ C (= O) OCH ₂ CF ₂ CF ₂ H, CF ₃ C (= O) OCH ₂ CF ₃ , CF ₃ C (= O) OCH (CF ₃ ) ₂ are phases with other solvents. It is particularly preferable because of its good solubility and rate characteristics.

The content of the fluorinated chain ester is preferably 5 to 90% by volume, more preferably 10 to 70% by volume, based on the solvent.

The solvent may also contain at least one fluorinated carbonate selected from the group consisting of the fluorinated chain carbonate and the fluorinated cyclic carbonate, and the fluorinated chain ester. An electrolytic solution containing a solvent having this composition can be suitably used for an electrochemical device used at a relatively high voltage.

When the solvent contains the fluorinated carbonate and the fluorinated chain ester, it is preferable to contain the fluorinated carbonate and the fluorinated chain ester in a total amount of 10 to 100% by volume. In total, the content is more preferably 20% by volume or more, further preferably 30% by volume or more, particularly preferably 40% by volume or more, further preferably 95% by volume or less, further preferably 90% by volume or less, and 85% by volume. Volume% or less is particularly preferable.

When the solvent contains the fluorinated carbonate and the fluorinated chain ester, the volume ratio of the fluorinated carbonate to the fluorinated chain ester is preferably 5/95 to 95/5, and 10/90. The above is more preferable, 20/80 or more is further preferable, 30/70 or more is particularly preferable, and 90/10 or less is more preferable.

The solvent is preferably a non-aqueous solvent, and the electrolytic solution of the present invention is preferably a non-aqueous electrolytic solution.

The electrolytic solution of the present invention preferably further contains an electrolyte salt. As the electrolyte salt, in addition to lithium salt, ammonium salt and metal salt, liquid salt (ionic liquid), inorganic polymer type salt, organic polymer type salt and the like can be used in the electrolyte solution. Any one can be used.

As the electrolyte salt of the electrolytic solution for a lithium ion secondary battery, a lithium salt is preferable.
Any of the above lithium salts can be used, and specific examples thereof include the following. For _{example, LiPF 6, LiBF 4, LiClO} 4, LiAlF 4, LiSbF 6, inorganic lithium salts LiTaF 6, LiWF ₇ and the like;
Lithium tungstic acid salts such as LiWOF _5;
HCO ₂ Li, CH ₃ CO ₂ Li, CH ₂ FCO ₂ Li, CHF ₂ CO ₂ Li, CF ₃ CO ₂ Li, CF ₃ CH ₂ CO ₂ Li, CF ₃ CF ₂ CO ₂ Li, CF ₃ CF ₂ CF ₂ Lithium carboxylic acid salts such as CO ₂ Li, CF ₃ CF ₂ CF ₂ CF ₂ CO _{2 Li;}
FSO ₃ Li, CH ₃ SO ₃ Li, CH ₂ FSO ₃ Li, CHF ₂ SO ₃ Li, CF ₃ SO ₃ Li, CF ₃ CF ₂ SO ₃ Li, CF ₃ CF ₂ CF ₂ SO ₃ Li, CF ₃ CF ₂ CF ₂ CF ₂ SO ₃ Li and other lithium sulfonic acid salts;
LiN (FCO) ₂ , LiN (FCO) (FSO ₂ ), LiN (FSO ₂ ) ₂ , LiN (FSO ₂ ) (CF ₃ SO ₂ ), LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO) ₂ ) ₂ , Lithium imide salts such as lithium cyclic 1,2-perfluoroethanedisulfonylimide, lithium cyclic 1,3-perfluoropropanedisulfonylimide, LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂₎ ;
Lithiummethide salts such as LiC (FSO ₂ ) ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) _3;
Lithium oxalate borate salts such as lithium difluorooxalate borate and lithium bis (oxalate) borate;
Lithium oxalate phosphate salts such as lithium tetrafluorooxalat phosphate, lithium difluorobis (oxalate) phosphate, lithium tris (oxalat) phosphate, lithium difluorophosphate;
Other formulas: LiPF _a (C _n F _{2n + 1} ) _6-a (in the formula, a is an integer of 0 to 5 and n is an integer of 1 to 6) (for example, 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 ₃ CF ₃ , LiBF ₃ C ₂ F ₅ , LiBF Fluorine-containing organics such as ₃ C ₃ F ₇ , LiBF ₂ (CF ₃ ) ₂ , LiBF ₂ (C ₂ F ₅ ) ₂ , LiBF ₂ (CF ₃ SO ₂ ) ₂ , LiBF ₂ (C ₂ F ₅ SO ₂ ) _2. Lithium salts; etc.

Among them, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiTaF ₆ , FSO ₃ Li, CF ₃ SO ₃ Li, LiN (FSO ₂ ) ₂ , LiN (FSO ₂ ) (CF ₃ SO ₂ ), LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , Lithium cyclic 1,2-perfluoroethanedisulfonylimide, Lithium cyclic 1,3-perfluoropropanedisulfonylimide, LiC (FSO ₂ ) ₃ , LiC (CF ₃₎ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , Lithium Bis (Oxalato) Borate, Lithium Difluorooxalato Borate, Lithium Tetrafluorooxarat Phosphate, Lithium Difluorobis (Oxalato) Phosphate, LiBF ₃ CF ₃ , LiBF ₃ C ₂ F ₅ , LiPF ₃ (CF ₃ ) ₃ , LiPF ₃ (C ₂ F ₅ ) ₃ , LiPO ₂ F _2, etc. improve output characteristics, high rate charge / discharge characteristics, high temperature storage characteristics, cycle characteristics, etc. It is particularly preferable because it is effective.

These lithium salts may be used alone or in combination of two or more. A preferable example in which two or more types are used in combination is a combination of LiPF ₆ and LiBF ₄ , LiPF ₆ and FSO ₃ Li, or the like, which has the effect of improving load characteristics and cycle characteristics.

_{In this case, the blending amount of LiBF 4} or FSO ₃ Li with respect to 100% by mass of the entire electrolytic solution is not limited and is arbitrary as long as the effect of the present invention is not significantly impaired, but is usually 0 with respect to the electrolytic solution of the present invention. It is 0.01% by mass or more, preferably 0.1% by mass or more, and usually 30% by mass or less, preferably 20% by mass or less.

Another example is the combined use of an inorganic lithium salt and an organic lithium salt, and the combined use of both has an effect of suppressing deterioration due to high temperature storage. Organolithium salts include CF ₃ SO ₃ Li, LiN (FSO ₂ ) ₂ , LiN (FSO ₂ ) (CF ₃ SO ₂ ), LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , Lithium Cyclic 1,2-Perfluoroethanedisulfonylimide, Lithium Cyclic 1,3-Perfluoropropanedisulfonylimide, LiC (FSO ₂ ) ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO) ₂ ) ₃ , Lithium bisoxalatoborate, Lithium difluorooxalatobolate, Lithium tetrafluorooxalatophosphate, Lithium difluorobisoxarat phosphate, LiBF ₃ CF ₃ , LiBF ₃ C ₂ F ₅ , LiPF ₃ (CF ₃ ) ₃ , LiPF ₃ (C ₂ F ₅ ) _3, etc. are preferable. In this case, the ratio of the organolithium salt to 100% by mass of the entire electrolytic solution is preferably 0.1% by mass or more, particularly preferably 0.5% by mass or more, and preferably 30% by mass or less, particularly. It is preferably 20% by mass or less.

The concentration of these lithium salts in the electrolytic solution is not particularly limited as long as the effects of the present invention are not impaired. The total molar concentration of lithium in the electrolytic solution is preferably 0.3 mol / L or more, more preferably 0.4 mol / L, from the viewpoint of keeping the electric conductivity of the electrolytic solution in a good range and ensuring good battery performance. As mentioned above, it is more preferably 0.5 mol / L or more, preferably 3 mol / L or less, more preferably 2.5 mol / L or less, still more preferably 2.0 mol / L or less.

If the total molar concentration of lithium is too low, the electrical conductivity of the electrolyte may be insufficient, while if the concentration is too high, the electrical conductivity may decrease due to the increase in viscosity, resulting in poor battery performance. May be done.

As the electrolyte salt of the electrolytic solution for the electric double layer capacitor, an ammonium salt is preferable.
Examples of the ammonium salt include the following (IIa) to (IIe).
(IIa) Tetraalkyl Quaternary Ammonium Salt General Formula (IIa):

（式中、Ｒ^１ａ、Ｒ^２ａ、Ｒ^３ａ及びＲ^４ａは同じか又は異なり、いずれも炭素数１〜６のエーテル結合を含んでいてもよいアルキル基；Ｘ⁻はアニオン）
で示されるテトラアルキル４級アンモニウム塩が好ましく例示できる。また、このアンモニウム塩の水素原子の一部又は全部がフッ素原子及び／又は炭素数１〜４の含フッ素アルキル基で置換されているものも、耐酸化性が向上する点から好ましい。

(In the formula, R ^1a , R ^2a , R ^3a and R ^4a are the same or different, and all of them may contain an ether bond having 1 to 6 carbon atoms; X ⁻ is an anion).
The tetraalkyl quaternary ammonium salt represented by is preferably exemplified. Further, it is also preferable that a part or all of the hydrogen atoms of this ammonium salt are substituted with a fluorine atom and / or a fluorine-containing alkyl group having 1 to 4 carbon atoms from the viewpoint of improving oxidation resistance.

As a specific example, the general formula (IIa-1):

（式中、Ｒ^１ａ、Ｒ^２ａ及びＸ⁻は前記と同じ；ｘ及びｙは同じか又は異なり０〜４の整数で、かつｘ＋ｙ＝４）
で示されるテトラアルキル４級アンモニウム塩、一般式（ＩＩａ−２）：

(In the equation, R ^1a , R ^2a and X ⁻ are the same as above; x and y are the same or different integers from 0 to 4, and x + y = 4).
Tetraalkyl quaternary ammonium salt represented by, general formula (IIa-2):

（式中、Ｒ^５ａは炭素数１〜６のアルキル基；Ｒ^６ａは炭素数１〜６の２価の炭化水素基；Ｒ^７ａは炭素数１〜４のアルキル基；ｚは１又は２；Ｘ⁻はアニオン）
で示されるアルキルエーテル基含有トリアルキルアンモニウム塩、
等が挙げられる。アルキルエーテル基を導入することにより、粘性の低下を図ることができる。

(In the formula, R ^5a is an alkyl group having 1 to 6 carbon atoms; R ^6a is a divalent hydrocarbon group having 1 to 6 carbon atoms; R ^7a is an alkyl group having 1 to 4 carbon atoms; z is 1 or 2; X ^- is an anion)
Alkyl ether group-containing trialkylammonium salt, indicated by
And so on. By introducing an alkyl ether group, the viscosity can be reduced.

The anion X ⁻ may be an inorganic anion or an organic anion. The inorganic anions such as _{^{AlCl 4 -, BF 4 -,}} PF 6 -, AsF 6 -, TaF 6 -, I -, SbF 6 - and the like. Examples of the organic anion include bisoxalatoborate anion, difluorooxalatoborate anion, tetrafluorooxalatophosphate anion, difluorobisoxalatphosphate anion, CF ₃ COO ⁻ , CF ₃ SO ₃ ⁻ , (CF ₃ SO ₂ ). ₂ N ⁻ , (C ₂ F ₅ SO ₂ ) ₂ N ^{− and the} like can be mentioned.

Among these, from the oxidation resistance and ion dissociation viewpoint of _{^{good, BF 4 -, PF 6 -}} , AsF 6 -, SbF 6 - are preferred.

Suitable specific examples of the tetraalkyl quaternary ammonium salt include 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 MeNBF 4, Et 3 MeNClO 4, Et 3 MeNPF 6, Et 3 MeNAsF 6, Et 3 MeNSbF 6, Et 3 MeNCF 3 SO 3, Et _{3 MeN (CF 3 SO 2)} 2 N, may be used _{Et 3 MeNC 4 F 9 SO 3} , in _{particular, Et 4 NBF 4, Et 4} NPF 6, Et 4 NSbF 6, Et 4 NAsF 6, Et 3 MeNBF 4 , N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium salt and the like.

(IIb) Spiro ring bipyrrolidinium salt General formula (IIb-1):

（式中、Ｒ^８ａ及びＲ^９ａは同じか又は異なり、いずれも炭素数１〜４のアルキル基；Ｘ⁻はアニオン；ｎ１は０〜５の整数；ｎ２は０〜５の整数）
で示されるスピロ環ビピロリジニウム塩、一般式（ＩＩｂ−２）：

(In the formula, R ^8a and R ^9a are the same or different, and both are alkyl groups having 1 to 4 carbon atoms; X ⁻ is an anion; n1 is an integer of 0 to 5; n2 is an integer of 0 to 5).
Spiro ring bipyrrolidinium salt represented by, general formula (IIb-2):

（式中、Ｒ^１０ａ及びＲ^１１ａは同じか又は異なり、いずれも炭素数１〜４のアルキル基；Ｘ⁻はアニオン；ｎ３は０〜５の整数；ｎ４は０〜５の整数）
で示されるスピロ環ビピロリジニウム塩、又は、一般式（ＩＩｂ−３）：

(In the formula, R ^10a and R ^11a are the same or different, and both are alkyl groups having 1 to 4 carbon atoms; X ⁻ is an anion; n3 is an integer of 0 to 5; n4 is an integer of 0 to 5).
Spiro ring bipyrrolidinium salt represented by, or general formula (IIb-3):

（式中、Ｒ^１２ａ及びＲ^１３ａは同じか又は異なり、いずれも炭素数１〜４のアルキル基；Ｘ⁻はアニオン；ｎ５は０〜５の整数；ｎ６は０〜５の整数）
で示されるスピロ環ビピロリジニウム塩が好ましく挙げられる。また、このスピロ環ビピロリジニウム塩の水素原子の一部又は全部がフッ素原子及び／又は炭素数１〜４の含フッ素アルキル基で置換されているものも、耐酸化性が向上する点から好ましい。

(In the formula, R ^12a and R ^13a are the same or different, and both are alkyl groups having 1 to 4 carbon atoms; X ⁻ is an anion; n5 is an integer of 0 to 5; n6 is an integer of 0 to 5).
The spiro ring bipyrrolidinium salt represented by is preferably mentioned. Further, it is also preferable that a part or all of the hydrogen atoms of the spiro ring bipyrrolidinium salt are substituted with fluorine atoms and / or fluorine-containing alkyl groups having 1 to 4 carbon atoms from the viewpoint of improving oxidation resistance.

Preferred specific examples of anion X ⁻ are the same as in the case of (IIa). Among them, high dissociative, terms the internal resistance is low under a high _{voltage, BF 4 -, PF 6 -} , (CF 3 SO 2) 2 N- or _{(C 2 F 5 SO 2)} 2 N- is preferable.

等が挙げられる。 Preferred specific examples of the spiro ring bipyrrolidinium salt include, for example,

And so on.

This spiro ring bipyrrolidinium salt is excellent in solvent solubility, oxidation resistance, and ionic conductivity.

(IIc) Imidazole salt general formula (IIc):

（式中、Ｒ^１４ａ及びＲ^１５ａは同じか又は異なり、いずれも炭素数１〜６のアルキル基；Ｘ⁻はアニオン）
で示されるイミダゾリウム塩が好ましく例示できる。また、このイミダゾリウム塩の水素原子の一部又は全部がフッ素原子及び／又は炭素数１〜４の含フッ素アルキル基で置換されているものも、耐酸化性が向上する点から好ましい。

(In the formula, R ^14a and R ^15a are the same or different, and both are alkyl groups having 1 to 6 carbon atoms; X ⁻ is an anion).
The imidazolium salt represented by is preferably exemplified. Further, it is also preferable that a part or all of the hydrogen atoms of this imidazolium salt are substituted with fluorine atoms and / or fluorine-containing alkyl groups having 1 to 4 carbon atoms from the viewpoint of improving oxidation resistance.

Preferred specific examples of anion X ⁻ are the same as in (IIa).

As a preferable specific example, for example

等が挙げられる。

And so on.

This imidazolium salt is excellent in that it has low viscosity and good solubility.

(IId): N-alkylpyridinium salt general formula (IId):

（式中、Ｒ^１６ａは炭素数１〜６のアルキル基；Ｘ⁻はアニオン）
で示されるＮ−アルキルピリジニウム塩が好ましく例示できる。また、このＮ−アルキルピリジニウム塩の水素原子の一部又は全部がフッ素原子及び／又は炭素数１〜４の含フッ素アルキル基で置換されているものも、耐酸化性が向上する点から好ましい。

(In the formula, R ^16a is an alkyl group having 1 to 6 carbon atoms; X ⁻ is an anion)
The N-alkylpyridinium salt represented by is preferably exemplified. Further, it is also preferable that a part or all of the hydrogen atoms of this N-alkylpyridinium salt are substituted with fluorine atoms and / or fluorine-containing alkyl groups having 1 to 4 carbon atoms from the viewpoint of improving oxidation resistance.

Preferred specific examples of anion X ⁻ are the same as in (IIa).

As a preferable specific example, for example

等が挙げられる。

And so on.

This N-alkylpyridinium salt is excellent in that it has low viscosity and good solubility.

(IIe) N, N-dialkylpyrrolidinium salt General formula (IIe):

（式中、Ｒ^１７ａ及びＲ^１８ａは同じか又は異なり、いずれも炭素数１〜６のアルキル基；Ｘ⁻はアニオン）
で示されるＮ，Ｎ−ジアルキルピロリジニウム塩が好ましく例示できる。また、このＮ，Ｎ−ジアルキルピロリジニウム塩の水素原子の一部又は全部がフッ素原子及び／又は炭素数１〜４の含フッ素アルキル基で置換されているものも、耐酸化性が向上する点から好ましい。

(In the formula, R ^17a and R ^18a are the same or different, and both are alkyl groups having 1 to 6 carbon atoms; X ⁻ is an anion).
The N, N-dialkylpyrrolidinium salt represented by is preferably exemplified. Further, the oxidation resistance is also improved when a part or all of the hydrogen atoms of the N, N-dialkylpyrrolidinium salt are substituted with fluorine atoms and / or fluorine-containing alkyl groups having 1 to 4 carbon atoms. It is preferable from the point of view.

Preferred specific examples of anion X ⁻ are the same as in (IIa).

As a preferable specific example, for example

等が挙げられる。

And so on.

This N, N-dialkylpyrrolidinium salt is excellent in that it has low viscosity and good solubility.

Of these ammonium salts, (IIa), (IIb) and (IIc) are preferable in terms of good solubility, oxidation resistance and ionic conductivity, and further.

（式中、Ｍｅはメチル基；Ｅｔはエチル基；Ｘ⁻、ｘ、ｙは式（ＩＩａ−１）と同じ）
が好ましい。

(In the formula, Me is a methyl group; Et is an ethyl group; X ⁻ , x, y are the same as in formula (IIa-1))
Is preferable.

Further, a lithium salt may be used as the electrolyte salt for the electric double layer capacitor. Examples of the lithium _{salt, LiPF 6, LiBF 4, LiN} (FSO 2) 2, LiAsF 6, LiSbF 6, LiN (SO 2 C 2 H 5) 2 is preferred.
Magnesium salts may be used to further improve the volume. As the magnesium salt, for example, Mg (ClO ₄ ) ₂ , Mg (OOC ₂ H ₅ ) _{2, and the} like are preferable.

When the electrolyte salt is the above-mentioned ammonium salt, the concentration is preferably 0.7 mol / liter or more. If it is less than 0.7 mol / liter, not only the low temperature characteristics deteriorate, but also the initial internal resistance may increase. The concentration of the electrolyte salt is more preferably 0.9 mol / liter or more.
The upper limit of the concentration is preferably 2.0 mol / liter or less, and more preferably 1.5 mol / liter or less in terms of low temperature characteristics.
When the ammonium salt is triethylmethylammonium tetrafluoroborate (TEMABF ₄ ), its concentration is preferably 0.7 to 1.5 mol / liter in terms of excellent low temperature characteristics.
Further, in the case of spirobipyrrolidinium tetrafluoride (SBPBF ₄ ), it is preferably 0.7 to 2.0 mol / liter.

（式中、Ｒ^ａ及びＲ^ｂは、それぞれ独立して、水素原子、シアノ基（ＣＮ）、ハロゲン原子、アルキル基、又は、アルキル基の少なくとも一部の水素原子をハロゲン原子で置換した基を表す。ｎは１〜１０の整数を表す。）

（式中、Ｒ^ｃは、水素原子、ハロゲン原子、アルキル基、アルキル基の少なくとも一部の水素原子をハロゲン原子で置換した基、又は、ＮＣ−Ｒ^ｃ１−Ｘ^ｃ１−（Ｒ^ｃ１はアルキレン基、Ｘ^ｃ１は酸素原子又は硫黄原子を表す。）で表される基を表す。Ｒ^ｄ及びＲ^ｅは、それぞれ独立して、水素原子、ハロゲン原子、アルキル基、又は、アルキル基の少なくとも一部の水素原子をハロゲン原子で置換した基を表す。ｍは１〜１０の整数を表す。）

（式中、Ｒ^ｆ、Ｒ^ｇ、Ｒ^ｈ及びＲ^ｉは、それぞれ独立して、シアノ基（ＣＮ）を含む基、水素原子（Ｈ）、ハロゲン原子、アルキル基、又は、アルキル基の少なくとも一部の水素原子をハロゲン原子で置換した基を表す。ただし、Ｒ^ｆ、Ｒ^ｇ、Ｒ^ｈ及びＲ^ｉのうち少なくとも１つはシアノ基を含む基である。ｌは１〜３の整数を表す。）
これにより、電気化学デバイスの高温保存特性を向上させることができる。上記ニトリル化合物を単独で用いてもよく、２種以上を任意の組み合わせ及び比率で併用してもよい。 The electrolytic solution of the present invention may contain at least one selected from the group consisting of nitrile compounds represented by the following general formulas (1a), (1b) and (1c).

(In the formula, ^Ra and R ^b are independent hydrogen atoms, cyano groups (CN), halogen atoms, alkyl groups, or groups in which at least a part of the hydrogen atoms of the alkyl group are replaced with halogen atoms. Represents. N represents an integer of 1 to 10.)

(In the formula, R ^c is a hydrogen atom, a halogen atom, an alkyl group, a group in which at least a part of the hydrogen atom of the alkyl group is replaced with a halogen atom, or NC-R ^c1- X ^c1- (R ^c1 is an alkylene group). , X ^c1 is .R ^d and R ^e represents a group represented by an oxygen atom or a sulfur atom.) are each independently a hydrogen atom, a halogen atom, an alkyl group, or at least a portion of the alkyl group Represents a group in which the hydrogen atom of is replaced with a halogen atom. M represents an integer of 1 to 10.)

(In the formula, R ^f , R ^g , R ^h and ^Ri are each independently at least one of a group containing a cyano group (CN), a hydrogen atom (H), a halogen atom, an alkyl group, or an alkyl group. the part hydrogen atoms represents a group obtained by substituting a halogen atom. However, at least one of ^{R f,} R ^g, R ^h and R ⁱ is a group containing a cyano group .l represents an integer of 1 to 3 .)
This makes it possible to improve the high temperature storage characteristics of the electrochemical device. The above nitrile compounds may be used alone, or two or more thereof may be used in any combination and ratio.

In the above general formula (1a), ^Ra and R ^b independently use a hydrogen atom, a cyano group (CN), a halogen atom, an alkyl group, or at least a part of the hydrogen atom of the alkyl group as a halogen atom. It is a substituted group.
Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom. Of these, a fluorine atom is preferable.
The alkyl group preferably has 1 to 5 carbon atoms. Specific examples of the alkyl group include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group and the like.
Examples of the group in which at least a part of the hydrogen atom of the alkyl group is replaced with a halogen atom include a group in which at least a part of the hydrogen atom of the above-mentioned alkyl group is replaced with the above-mentioned halogen atom.
When R ^a and R ^b are an alkyl group or a group in which at least a part of hydrogen atoms of the alkyl group is substituted with a halogen atom, ^Ra and R ^b are bonded to each other to form a ring structure (for example, cyclohexane ring). ) May be formed.
R ^a and R ^b are preferably hydrogen atoms or alkyl groups.

In the above general formula (1a), n is an integer of 1 to 10. When n is 2 or more, n pieces of R ^a may be the same for all, it may be at least partially different. The same applies to ^{R b.} n is preferably an integer of 1 to 7, and more preferably an integer of 2 to 5.

As the nitrile compound represented by the general formula (1a), dinitrile and tricarbonitrile are preferable.
Specific examples of dinitrile include malononitrile, succinonitrile, glutaronitrile, adiponitrile, pimeronitrile, suberonitrile, azeranitrile, sebaconitrile, undecandinitrile, dodecandinitrile, methylmalononitrile, ethylmalononitrile, isopropylmalononitrile, and tert-butyl Marononitrile, methylsuccinonitrile, 2,2-dimethylsuccinonitrile, 2,3-dimethylsuccinonitrile, 2,3,3-trimethylsuccinonitrile, 2,2,3,3-tetramethylsuccinonitrile , 2,3-diethyl-2,3-dimethylsuccinonitrile, 2,2-diethyl-3,3-dimethylsuccinonitrile, bicyclohexyl-1,1-dicarbonitrile, bicyclohexyl-2,2-di Carbonitrile, bicyclohexyl-3,3-dicarbonitrile, 2,5-dimethyl-2,5-hexanedicarbonitrile, 2,3-diisobutyl-2,3-dimethylsuccinonitrile, 2,2-diisobutyl- 3,3-Dimethylsuccinonitrile, 2-methylglutaronitrile, 2,3-dimethylglutaronitrile, 2,4-dimethylglutaronitrile, 2,2,3,3-tetramethylglutaronitrile, 2, 2,4,4-tetramethylglutaronitrile, 2,2,3,4-tetramethylglutaronitrile, 2,3,3,4-tetramethylglutaronitrile, 1,4-dicyanopentane, 2,6 Examples thereof include −dicyanoheptane, 2,7-dicyanooctane, 2,8-dicyanononane, and 1,6-dicyanodecane. Of these, particularly preferred are succinonitrile, glutaronitrile, and adiponitrile.
Specific examples of the tricarbonitrile include pentantricarbonitrile, propantricarbonitrile, 1,3,5-hexanetricarbonitrile, 1,3,6-hexanetricarbonitrile, heptanetricarbonitrile, 1,2. , 3-Propanetricarbonitrile, 1,3,5-pentanetricarbonitrile and the like, and particularly preferable one is 1,3,6-hexanetricarbonitrile.

In the above general formula (1b), R ^c is a hydrogen atom, a halogen atom, an alkyl group, a group in which at least a part of hydrogen atoms of the alkyl group is replaced with a halogen atom, or NC-R ^c1- X ^c1- (R). ^c1 is an alkylene group, X ^c1 is an oxygen atom or a sulfur atom), and R ^d and ^Re are independently hydrogen atoms, halogen atoms, alkyl groups, or alkyl groups. It is a group in which at least a part of hydrogen atoms are replaced with halogen atoms.
Examples of the halogen atom, the alkyl group, and the group in which at least a part of the hydrogen atom of the alkyl group is replaced with the halogen atom include those exemplified by the above general formula (1a).
The ^{NC-R c1 -X} c1 - in ^{R c1} is an alkylene group. As the alkylene group, an alkylene group having 1 to 3 carbon atoms is preferable.
It is preferable that R ^c , R ^d and ^Re are independently hydrogen atoms, halogen atoms, alkyl groups, or groups in which at least a part of the hydrogen atoms of the alkyl groups are substituted with halogen atoms.
At ^{least one of R c} , R ^d and ^Re is preferably a halogen atom or a group in which at least a part of the hydrogen atom of the alkyl group is replaced with a halogen atom, and at least a fluorine atom or an alkyl group. More preferably, it is a group in which some hydrogen atoms are replaced with fluorine atoms.
When R ^d and ^Re are an alkyl group or a group in which at least a part of hydrogen atoms of the alkyl group is substituted with a halogen atom, R ^d and ^Re are bonded to each other to form a ring structure (for example, cyclohexane ring). ) May be formed.

In the above general formula (1b), m is an integer of 1 to 10. When m is 2 or more, ^{all m R ds} may be the same, or at least a part thereof may be different. The same applies to the R ^e. For m, an integer of 2 to 7 is preferable, and an integer of 2 to 5 is more preferable.

Examples of the nitrile compound represented by the general formula (1b) include acetonitrile, propionitrile, butyronitrile, isobutyronitrile, valeronitrile, isovaleronitrile, lauronitrile, 2-methylbutyronitrile, trimethylacetonitrile, and hexanenitrile. , Cyclopentancarbonitrile, cyclohexanecarbonitrile, fluoroacetonitrile, difluoroacetonitrile, trifluoroacetonitrile, 2-fluoropropionitrile, 3-fluoropropionitrile, 2,2-difluoropropionitrile, 2,3-difluoropropio Nitrile, 3,3-difluoropropionitrile, 2,2,3-trifluoropropionitrile, 3,3,3-trifluoropropionitrile, 3,3'-oxydipropionitrile, 3,3'-thiodipro Examples thereof include pionitrile and pentafluoropropionitrile. Of these, 3,3,3-trifluoropropionitrile is particularly preferred.

In the general formula ^{(1c), R f, R} g, R h and ^{R i} are each independently, a group containing a cyano group (CN), a hydrogen atom, a halogen atom, an alkyl group, or at least an alkyl group It is a group in which some hydrogen atoms are replaced with halogen atoms.
Examples of the halogen atom, the alkyl group, and the group in which at least a part of the hydrogen atom of the alkyl group is replaced with the halogen atom include those exemplified by the above general formula (1a).
Examples of the group containing a cyano group include a cyano group and a group in which at least a part of hydrogen atoms of an alkyl group is replaced with a cyano group. Examples of the alkyl group in this case include those exemplified for the above general formula (1a).
^{R f,} R g, at least one of ^{R h} and ^{R i} is a group containing a cyano group. Preferably is that R ^{f, R g,} at least two of R ^h and R ⁱ is a group containing a cyano group, more preferably, is that R ^h and R ⁱ is a group containing a cyano group .. When R ^h and R ⁱ are groups containing a cyano group, R ^f and R ^g are preferably hydrogen atoms.

In the above general formula (1c), l is an integer of 1 to 3. When l is 2 or more, ^{all l R fs} may be the same, or at least a part thereof may be different. The same applies to ^{R g.} l is preferably an integer of 1 to 2.

Examples of the nitrile compound represented by the general formula (1c) include 3-hexendinitrile, mucononitrile, maleonitrile, fumaronitrile, acrylonitrile, methacrylonitrile, crotononitrile, 3-methylcrotononitrile, and 2-methyl-2-. Butenenitrile, 2-pentenenitrile, 2-methyl-2-pentenenitrile, 3-methyl-2-pentenenitrile, 2-hexenenitrile and the like are exemplified, and 3-hexenedinitrile and mucononitrile are preferable, and 3-hexenedinitrile is particularly preferable. Nitrile is preferred.

The content of the nitrile compound is preferably 0.2 to 7% by mass with respect to the electrolytic solution. As a result, the high-voltage storage characteristics and safety of the electrochemical device can be further improved. The lower limit of the total content of the nitrile compounds is more preferably 0.3% by mass, further preferably 0.5% by mass. The upper limit is more preferably 5% by mass, further preferably 2% by mass, and particularly preferably 0.5% by mass.

The electrolytic solution of the present invention may further contain the compound (2) represented by the general formula (2).

（式中、Ａ^ａ＋は金属イオン、水素イオン又はオニウムイオン。ａは１〜３の整数、ｂは１〜３の整数、ｐはｂ／ａ、ｎ^２３は１〜４の整数、ｎ^２１は０〜８の整数、ｎ^２２は０又は１、Ｚ^２１は遷移金属、周期律表のＩＩＩ族、ＩＶ族又はＶ族の元素。
Ｘ^２１は、Ｏ、Ｓ、炭素数１〜１０のアルキレン基、炭素数１〜１０のハロゲン化アルキレン基、炭素数６〜２０のアリーレン基又は炭素数６〜２０のハロゲン化アリーレン基（アルキレン基、ハロゲン化アルキレン基、アリーレン基、及び、ハロゲン化アリーレン基はその構造中に置換基、ヘテロ原子を持っていてもよく、またｎ^２２が１でｎ^２３が２〜４のときにはｎ^２３個のＸ^２１はそれぞれが結合していてもよい）
Ｌ^２１は、ハロゲン原子、シアノ基、炭素数１〜１０のアルキル基、炭素数１〜１０のハロゲン化アルキル基、炭素数６〜２０のアリール基、炭素数６〜２０のハロゲン化アリール基（アルキレン基、ハロゲン化アルキレン基、アリーレン基、及び、ハロゲン化アリーレン基はその構造中に置換基、ヘテロ原子を持っていてもよく、またｎ^２１が２〜８のときにはｎ^２１個のＬ^２１はそれぞれが結合して環を形成してもよい）又は−Ｚ^２３Ｙ^２３。
Ｙ^２１、Ｙ^２２及びＺ^２３は、それぞれ独立でＯ、Ｓ、ＮＹ^２４、炭化水素基又はフッ素化炭化水素基。Ｙ^２３及びＹ^２４は、それぞれ独立でＨ、Ｆ、炭素数１〜１０のアルキル基、炭素数１〜１０のハロゲン化アルキル基、炭素数６〜２０のアリール基又は炭素数６〜２０のハロゲン化アリール基（アルキル基、ハロゲン化アルキル基、アリール基及びハロゲン化アリール基はその構造中に置換基、ヘテロ原子を持っていてもよく、Ｙ^２３又はＹ^２４が複数個存在する場合にはそれぞれが結合して環を形成してもよい）） General formula (2):

(In the formula, A ^{a +} is a metal ion, a hydrogen ion or an onium ion. A is an integer of 1 to 3, b is an integer of 1 to 3, p is b / a, n ²³ is an integer of 1 to 4, and n ²¹ is. An integer of 0 to 8, n ²² is 0 or 1, Z ²¹ is a transition metal, and an element of group III, IV or V of the periodic table.
X ²¹ is O, S, an alkylene group having 1 to 10 carbon atoms, a halogenated alkylene group having 1 to 10 carbon atoms, an arylene group having 6 to 20 carbon atoms, or a halogenated arylene group having 6 to 20 carbon atoms (alkylene group). , The alkylene group halide, the arylene group, and the arylene halide group may have a substituent or a heteroatom in the structure, and ^{when n 22} is 1 and n ²³ is 2 to 4, n ²³ . X ²¹ may be combined with each other)
L ²¹ is a halogen atom, a cyano group, an alkyl group having 1 to 10 carbon atoms, an alkyl halide group having 1 to 10 carbon atoms, an aryl group having 6 to 20 carbon atoms, and an aryl halide group having 6 to 20 carbon atoms ( The alkylene group, the halogenated alkylene group, the arylene group, and the halogenated arylene group may have a substituent or a hetero atom in the structure, and ^{when n 21} is 2 to 8, n ²¹ L ^21s may be present. Each may combine to form a ring) or -Z ²³ Y ²³ .
Y ²¹ , Y ²² and Z ²³ are independently O, S, NY ²⁴ , hydrocarbon groups or fluorinated hydrocarbon groups, respectively. Y ²³ and Y ²⁴ are independently H, F, an alkyl group having 1 to 10 carbon atoms, an alkyl halide group having 1 to 10 carbon atoms, an aryl group having 6 to 20 carbon atoms, or a halogen having 6 to 20 carbon atoms. The aryl group (alkyl group, alkyl halide group, aryl group and aryl halide group may have a substituent and a hetero atom in the structure, respectively, when a plurality of ^{Y 23} or Y ^{24 are present, respectively.} May combine to form a ring))

A ^{a +} includes lithium ion, sodium ion, potassium ion, magnesium ion, calcium ion, barium ion, cesium ion, silver ion, zinc ion, copper ion, cobalt ion, iron ion, nickel ion, manganese ion, titanium ion, etc. Lead ion, chromium ion, vanadium ion, ruthenium ion, ittrium ion, lanthanoid ion, actinoid ion, tetrabutylammonium ion, tetraethylammonium ion, tetramethylammonium ion, triethylmethylammonium ion, triethylammonium ion, pyridinium ion, imidazolium ion , Hydrogen ion, tetraethylphosphonium ion, tetramethylphosphonium ion, tetraphenylphosphonium ion, triphenylsulfonium ion, triethylsulfonium ion and the like.

When used in applications such as electrochemical devices, A ^{a +} is preferably lithium ion, sodium ion, magnesium ion, tetraalkylammonium ion, or hydrogen ion, and lithium ion is particularly preferable. ^{The cation valence a of} A a + is an integer of 1-3. If it is larger than 3, the crystal lattice energy becomes large, which causes a problem that it becomes difficult to dissolve in a solvent. Therefore, 1 is more preferable when solubility is required. The valence b of the anion is also an integer of 1 to 3, and 1 is particularly preferable. The constant p representing the ratio of cations and anions is inevitably determined by the ratio b / a of the valences of both.

Next, the ligand portion of the general formula (2) will be described. ^{In the present specification, the organic or inorganic moiety bound to Z 21} in the general formula (2) is referred to as a ligand.

Z ²¹ is preferably Al, B, V, Ti, Si, Zr, Ge, Sn, Cu, Y, Zn, Ga, Nb, Ta, Bi, P, As, Sc, Hf or Sb, and Al. , B or P is more preferable.

X ²¹ represents O, S, an alkylene group having 1 to 10 carbon atoms, a halogenated alkylene group having 1 to 10 carbon atoms, an arylene group having 6 to 20 carbon atoms, or a halogenated arylene group having 6 to 20 carbon atoms. These alkylene groups and arylene groups may have substituents and heteroatoms in their structures. Specifically, instead of hydrogen on the alkylene group and the arylene group, a halogen atom, a chain or cyclic alkyl group, an aryl group, an alkenyl group, an alkoxy group, an aryloxy group, a sulfonyl group, an amino group, a cyano group, and a carbonyl group. It may have a group, an acyl group, an amide group, or a hydroxyl group as a substituent, or it may have a structure in which nitrogen, sulfur, or oxygen is introduced instead of carbon on alkylene and arylene. Further, when n ²² is 1 and n ²³ is 2 to 4, n ²³ X ^21s may be bonded to each other. Such examples include ligands such as ethylenediaminetetraacetic acid.

L ²¹ is a halogen atom, a cyano group, an alkyl group having 1 to 10 carbon atoms, an alkyl halide group having 1 to 10 carbon atoms, an aryl group having 6 to 20 carbon atoms, an aryl halide group having 6 to 20 carbon atoms, or the like. -Z ²³ Y ²³ (Z ²³ and Y ²³ will be described later). ^{Similar to X 21} , the alkyl group and aryl group here may also have a substituent and a hetero atom in the structure, and ^{when n 21} is 2 to 8, n ²¹ L ^21s are each. They may be combined to form a ring. As L ²¹ , a fluorine atom or a cyano group is preferable. This is because, in the case of a fluorine atom, the solubility and dissociation degree of the salt of the anionic compound are improved, and the ionic conductivity is improved accordingly. In addition, the oxidation resistance is improved, which can suppress the occurrence of side reactions.

Y ²¹ , Y ²² and Z ²³ independently represent O, S, NY ²⁴ , a hydrocarbon group or a fluorinated hydrocarbon group. Y ²¹ and Y ²² are preferably O, S or NY ²⁴ , and more preferably O. A characteristic of compound (2) is that Y ²¹ and Y ²² bind to Z ²¹ in the same ligand, so that these ligands form a chelate structure with ^{Z 21.} Due to the effect of this chelate, the heat resistance, chemical stability, and hydrolysis resistance of this compound are improved. The constant n ^{22 in} this ligand is 0 or 1, but in particular, when it is 0, the chelating ring becomes a five-membered ring, so that the chelating effect is most strongly exerted and the stability is increased, which is preferable.
In the present specification, the fluorinated hydrocarbon group is a group in which at least one hydrogen atom of the hydrocarbon group is replaced with a fluorine atom.

Y ²³ and Y ²⁴ are independent of each other and have H, F, an alkyl group having 1 to 10 carbon atoms, an alkyl halide group having 1 to 10 carbon atoms, an aryl group having 6 to 20 carbon atoms, or an aryl group having 6 to 20 carbon atoms. It is an aryl halide group, and these alkyl groups and aryl groups may have a substituent or a hetero atom in the structure, and ^{when a plurality of Y 23} or Y ²⁴ are present, each of them is bonded. May form a ring.

^{Further, the constant n 23} related to the number of ligands described above is an integer of 1 to 4, preferably 1 or 2, and more preferably 2. ^{Further, the constant n 21} related to the number of ligands described above is an integer of 0 to 8, preferably an integer of 0 to 4, and more preferably 0, 2 or 4. Further, it is preferable that ^{n 21} is 2 ^{when n 23} is 1, and ^{n 21} is 0 when n ^{23 is 2.}

In the general formula (2), the alkyl group, the alkyl halide group, the aryl group, and the aryl halide group include those having other functional groups such as a branch, a hydroxyl group, and an ether bond.

（式中、Ａ^ａ＋、ａ、ｂ、ｐ、ｎ^２１、Ｚ^２１及びＬ^２１は上述したとおり）で示される化合物、又は、一般式：

（式中、Ａ^ａ＋、ａ、ｂ、ｐ、ｎ^２１、Ｚ^２１及びＬ^２１は上述したとおり）で示される化合物であることが好ましい。 The general formula of compound (2) is:

(In the formula, A ^{a +} , a, b, p, n ²¹ , Z ²¹ and L ²¹ are as described above), or a general formula:

(In the formula, A ^{a +} , a, b, p, n ²¹ , Z ²¹ and L ²¹ are as described above).

で示されるリチウムビス（オキサラト）ボレート（ＬＩＢＯＢ）、下記式：

で示されるリチウムジフルオロオキサラトボレート（ＬＩＤＦＯＢ）等が挙げられる。 Examples of the compound (2) include lithium oxalatoborate salts, which have the following formula:

Lithium bis (oxalate) borate (LIBOB) represented by, the following formula:

Examples thereof include lithium difluorooxalatoborate (LIDFOB) represented by.

で示されるリチウムジフルオロオキサラトホスファナイト（ＬＩＤＦＯＰ）、下記式：

で示されるリチウムテトラフルオロオキサラトホスファナイト（ＬＩＴＦＯＰ）、下記式：

で示されるリチウムビス（オキサラト）ジフルオロホスファナイト等が挙げられる。 The compound (2) also includes the following formula:

Lithium difluorooxalatphosphanite (LIDFOP) represented by, the following formula:

Lithium tetrafluorooxalatphosphanite (LITFOP) represented by, the following formula:

Examples thereof include lithium bis (oxalate) difluorophosphanite represented by.

The content of the compound (2) is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, and 10% by mass, based on the above solvent, because further excellent cycle characteristics can be obtained. % Or less is preferable, and 3% by mass or less is more preferable.

The electrolytic solution of the present invention may further contain polyethylene oxide having a weight average molecular weight of 2000 to 4000 and having -OH, -OCOOH, or -COOH at the end.
By containing such a compound, the stability of the electrode interface can be improved and the characteristics of the electrochemical device can be improved.
Examples of the polyethylene oxide include polyethylene oxide monool, polyethylene oxide carboxylic acid, polyethylene oxide diol, polyethylene oxide dicarboxylic acid, polyethylene oxide triol, and polyethylene oxide tricarboxylic acid. These may be used alone or in combination of two or more.
Among them, a mixture of polyethylene oxide monool and polyethylene oxide diol and a mixture of polyethylene carboxylic acid and polyethylene dicarboxylic acid are preferable in that the characteristics of the electrochemical device are improved.

If the weight average molecular weight of the polyethylene oxide is too small, it may be easily oxidatively decomposed. The weight average molecular weight is more preferably 3000 to 4000.
The weight average molecular weight can be measured by polystyrene conversion by a gel permeation chromatography (GPC) method.

The content of the polyethylene oxide ^{is preferably 1 × 10 -6} to 1 × 10 ⁻² mol / kg in the electrolytic solution. If the content of the polyethylene oxide is too high, the characteristics of the electrochemical device may be impaired.
The content of the polyethylene oxide ^{is more preferably 5 × 10-6} mol / kg or more.

The electrolytic solution of the present invention may further contain an unsaturated cyclic carbonate, an overcharge inhibitor, other known auxiliaries and the like. As a result, deterioration of the characteristics of the electrochemical device can be suppressed.

Examples of unsaturated cyclic carbonates include vinylene carbonates, ethylene carbonates substituted with a substituent having an aromatic ring or a carbon-carbon double bond or a carbon-carbon triple bond, phenyl carbonates, vinyl carbonates, and allyl carbonates. Examples include catechol carbonates.

Examples of vinylene carbonates include vinylene carbonate, methylvinylene carbonate, 4,5-dimethylvinylene carbonate, phenylvinylene carbonate, 4,5-diphenylvinylene carbonate, vinylvinylene carbonate, 4,5-divinylvinylene carbonate, allylvinylene carbonate, 4 , 5-Diallyl vinylene carbonate, 4-fluorovinylene carbonate, 4-fluoro-5-methylvinylene carbonate, 4-fluoro-5-phenylvinylene carbonate, 4-fluoro-5-vinylvinylene carbonate, 4-allyl-5-fluoro Examples include vinylene carbonate and the like.

Specific examples of ethylene carbonates substituted with a substituent having an aromatic ring or a carbon-carbon double bond or a carbon-carbon triple bond include vinyl ethylene carbonate, 4,5-divinylethylene carbonate, and 4-methyl-5. Vinyl ethylene carbonate, 4-allyl-5-vinylethylene carbonate, ethynylethylene carbonate, 4,5-dietinylethylene carbonate, 4-methyl-5-ethynylethylene carbonate, 4-vinyl-5-ethynylethylene carbonate, 4-allyl -5-Ethynylethylene carbonate, phenylethylene carbonate, 4,5-diphenylethylene carbonate, 4-phenyl-5-vinylethylene carbonate, 4-allyl-5-phenylethylene carbonate, allylethylene carbonate, 4,5-diallylethylene carbonate , 4-Methyl-5-allylethylene carbonate, 4-methylene-1,3-dioxolan-2-one, 4,5-dimethylene-1,3-dioxolan-2-one and the like.

Among them, the unsaturated cyclic carbonates include vinylene carbonate, methylvinylene carbonate, 4,5-dimethylvinylene carbonate, vinylvinylene carbonate, 4,5-vinylvinylene carbonate, allylvinylene carbonate, 4,5-diallylvinylene carbonate, and vinyl. Ethylene carbonate, 4,5-divinylethylene carbonate, 4-methyl-5-vinylethylene carbonate, allylethylene carbonate, 4,5-diallylethylene carbonate, 4-methyl-5-allylethylene carbonate, 4-allyl-5-vinyl Preferables are ethylene carbonate, ethynyl ethylene carbonate, 4,5-dietinyl ethylene carbonate, 4-methyl-5-ethynyl ethylene carbonate, and 4-vinyl-5-ethynyl ethylene carbonate. Further, vinylene carbonate, vinylethylene carbonate, and ethynylethylene carbonate are particularly preferable because they form a more stable interfacial protective film.

The molecular weight of the unsaturated cyclic carbonate is not particularly limited and is arbitrary as long as the effects of the present invention are not significantly impaired. The molecular weight is preferably 50 or more and 250 or less. Within this range, the solubility of the unsaturated cyclic carbonate in the electrolytic solution can be easily ensured, and the effect of the present invention can be sufficiently exhibited. The molecular weight of the unsaturated cyclic carbonate is more preferably 80 or more, and more preferably 150 or less.

The method for producing the unsaturated cyclic carbonate is not particularly limited, and a known method can be arbitrarily selected for production.

As the unsaturated cyclic carbonate, one type may be used alone, or two or more types may be used in combination in any combination and ratio.

The content of the unsaturated cyclic carbonate is not particularly limited and is arbitrary as long as the effects of the present invention are not significantly impaired. The content of the unsaturated cyclic carbonate is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, and further preferably 0.1% by mass or more in 100% by mass of the solvent in the present invention. The content is preferably 5% by mass or less, more preferably 4% by mass or less, and further preferably 3% by mass or less. Within the above range, the electrochemical device using the electrolytic solution is likely to exhibit a sufficient effect of improving the cycle characteristics, the high temperature storage characteristics are lowered, the amount of gas generated is increased, and the discharge capacity retention rate is lowered. It is easy to avoid such a situation.

As the unsaturated cyclic carbonate, in addition to the non-fluorinated unsaturated cyclic carbonate as described above, a fluorinated unsaturated cyclic carbonate can also be preferably used.
Fluorinated unsaturated cyclic carbonates are cyclic carbonates having unsaturated bonds and fluorine atoms. The number of fluorine atoms contained in the fluorinated unsaturated cyclic carbonate is not particularly limited as long as it is 1 or more. Among them, the number of fluorine atoms is usually 6 or less, preferably 4 or less, and one or two are most preferable.

Examples of the fluorinated unsaturated cyclic carbonate include a fluorinated vinylene carbonate derivative, a fluorinated ethylene carbonate derivative substituted with an aromatic ring or a substituent having a carbon-carbon double bond, and the like.

Examples of the fluorinated vinylene carbonate derivative include 4-fluorovinylene carbonate, 4-fluoro-5-methylvinylene carbonate, 4-fluoro-5-phenylvinylene carbonate, 4-allyl-5-fluorovinylene carbonate, and 4-fluoro-5-. Examples include vinyl vinylene carbonate and the like.

Examples of the fluorinated ethylene carbonate derivative substituted with a substituent having an aromatic ring or a carbon-carbon double bond include 4-fluoro-4-vinylethylene carbonate, 4-fluoro-4-allylethylene carbonate, and 4-fluoro-5. -Vinylethylene carbonate, 4-fluoro-5-allylethylene carbonate, 4,4-difluoro-4-vinylethylene carbonate, 4,4-difluoro-4-allylethylene carbonate, 4,5-difluoro-4-vinylethylene carbonate , 4,5-Difluoro-4-allylethylene carbonate, 4-fluoro-4,5-divinylethylene carbonate, 4-fluoro-4,5-diallylethylene carbonate, 4,5-difluoro-4,5-divinylethylene carbonate , 4,5-Difluoro-4,5-diallylethylene carbonate, 4-fluoro-4-phenylethylene carbonate, 4-fluoro-5-phenylethylene carbonate, 4,4-difluoro-5-phenylethylene carbonate, 4,5 −Difluoro-4-phenylethylene carbonate and the like can be mentioned.

Among them, as the fluorinated unsaturated cyclic carbonate, 4-fluorovinylene carbonate, 4-fluoro-5-methylvinylene carbonate, 4-fluoro-5-vinylvinylene carbonate, 4-allyl-5-fluorovinylene carbonate, 4- Fluoro-4-vinylethylene carbonate, 4-fluoro-4-allylethylene carbonate, 4-fluoro-5-vinylethylene carbonate, 4-fluoro-5-allylethylene carbonate, 4,4-difluoro-4-vinylethylene carbonate, 4,4-Difluoro-4-allylethylene carbonate, 4,5-difluoro-4-vinylethylene carbonate, 4,5-difluoro-4-allylethylene carbonate, 4-fluoro-4,5-divinylethylene carbonate, 4- Fluoro-4,5-diallylethylene carbonate, 4,5-difluoro-4,5-divinylethylene carbonate, 4,5-difluoro-4,5-diallylethylene carbonate form a stable interface protection film, so that it is more effective. It is preferably used.

The molecular weight of the fluorinated unsaturated cyclic carbonate is not particularly limited and is arbitrary as long as the effects of the present invention are not significantly impaired. The molecular weight is preferably 50 or more and 500 or less. Within this range, it is easy to secure the solubility of the fluorinated unsaturated cyclic carbonate in the electrolytic solution.

The method for producing the fluorinated unsaturated cyclic carbonate is not particularly limited, and a known method can be arbitrarily selected for production. The molecular weight is more preferably 100 or more, and more preferably 200 or less.

As the fluorinated unsaturated cyclic carbonate, one type may be used alone, or two or more types may be used in combination in any combination and ratio. The content of the fluorinated unsaturated cyclic carbonate is not particularly limited and is arbitrary as long as the effects of the present invention are not significantly impaired. The content of the fluorinated unsaturated cyclic carbonate is usually preferably 0.01% by mass or more, more preferably 0.1% by mass or more, still more preferably 0.2% by mass or more in 100% by mass of the electrolytic solution. Further, it is preferably 5% by mass or less, more preferably 4% by mass or less, and further preferably 3% by mass or less. Within this range, the electrochemical device using the electrolytic solution is likely to exhibit a sufficient effect of improving the cycle characteristics, the high temperature storage characteristics are lowered, the amount of gas generated is increased, and the discharge capacity retention rate is lowered. It is easy to avoid such a situation.

In the electrolytic solution of the present invention, an overcharge inhibitor can be used in order to effectively suppress the explosion and ignition of the battery when the electrochemical device using the electrolytic solution is in a state of overcharging or the like. ..

Examples of the overcharge inhibitor include aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, and partially hydrides of terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; 2-fluorobiphenyl, Partial fluorides of the above aromatic compounds such as o-cyclohexylfluorobenzene and p-cyclohexylfluorobenzene; 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, 3,5-difluoroanisole and the like. Benzene-containing anisole compounds and the like can be mentioned. Among them, aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, a partially hydride of terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether and dibenzofuran are preferable. These may be used alone or in combination of two or more. When two or more kinds are used in combination, in particular, a combination of cyclohexylbenzene and t-butylbenzene or t-amylbenzene, a partially hydride of biphenyl, alkylbiphenyl, tarphenyl, or tarphenyl, cyclohexylbenzene, t-butylbenzene, Overcharge prevention characteristics and high temperature storage characteristics are to be used in combination with at least one selected from oxygen-free aromatic compounds such as t-amylbenzene and at least one selected from oxygen-containing aromatic compounds such as diphenyl ether and dibenzofuran. It is preferable from the viewpoint of the balance of.

Other known auxiliaries can be used in the electrolytic solution of the present invention. Other auxiliaries include carbonate compounds such as erythritan carbonate, spiro-bis-dimethylene carbonate, methoxyethyl-methyl carbonate; succinic acid anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, anhydrous. Sulfonic acid anhydrides such as itaconic acid, diglycolic acid anhydride, cyclohexanedicarboxylic acid anhydride, cyclopentanetetracarboxylic acid dianhydride and phenylsuccinic acid anhydride; 2,4,8,10-tetraoxaspiro [5.5] ] Undecane, 3,9-divinyl-2,4,8,10-tetraoxaspiro [5.5] Spiro compounds such as undecane; ethylenesulfite, 1,3-propanesulton, 1-fluoro-1,3- Propane sulton, 2-fluoro-1,3-propane sulton, 3-fluoro-1,3-propane sulton, 1-propen-1,3-sulton, 1-fluoro-1-propen-1,3-sulton, 2 -Fluoro-1-propen-1,3-sulton, 3-fluoro-1-propen-1,3-sulton, 1,4-butane sulton, 1-buten-1,4-sulton, 3-buten-1,4 -Sulton, methyl fluorosulfonate, ethyl fluorosulfonate, methyl methanesulfonate, ethyl methanesulfonate, busulfane, sulfolene, diphenylsulfone, N, N-dimethylmethanesulfonamide, N, N-diethylmethanesulfonamide, vinylsulfone Methyl acid, ethyl vinyl sulfonate, allyl vinyl sulfonate, propargyl vinyl sulfonate, methyl allyl sulfonate, ethyl allyl sulfonate, allyl allyl sulfonate, propargyl allyl sulfonate, 1,2-bis (vinyl sulfonate) ethane Sulfur-containing compounds such as 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone and N-methylsuccinimide and the like. Compounds; trimethyl sulfonate, triethyl sulfonate, triphenyl phosphite, trimethyl phosphate, triethyl phosphate, triphenyl phosphate, dimethyl methyl phosphonate, diethyl ethyl phosphonate, dimethyl vinyl phosphonate, diethyl vinyl phosphonate, Phosphoric compounds such as ethyl diethylphosphonoacetate, methyl dimethylphosphinate, ethyl diethylphosphinate, trimethylphosphine oxide, triethylphosphine oxide; hep Examples thereof include hydrocarbon compounds such as tan, octane, nonane, decane and cycloheptane, and fluorine-containing aromatic compounds such as fluorobenzene, difluorobenzene, hexafluorobenzene and benzotrifluoride. These may be used alone or in combination of two or more. By adding these auxiliaries, the capacity retention characteristics and cycle characteristics after high temperature storage can be improved.

The blending amount of the other auxiliary agents is not particularly limited and is arbitrary as long as the effects of the present invention are not significantly impaired. The other auxiliary agent is preferably 0.01% by mass or more and 5% by mass or less in 100% by mass of the electrolytic solution. Within this range, the effects of other auxiliaries are likely to be sufficiently exhibited, and it is easy to avoid situations such as deterioration of battery characteristics such as high load discharge characteristics. The blending amount of the other auxiliary agent is more preferably 0.1% by mass or more, further preferably 0.2% by mass or more, still more preferably 3% by mass or less, still more preferably 1% by mass or less. ..

The electrolytic solution of the present invention contains a cyclic carboxylic acid ester, an ether compound, a nitrogen-containing compound, a boron-containing compound, an organosilicon-containing compound, a non-flammable (flame retardant) agent, a surfactant, as long as the effects of the present invention are not impaired. Additives such as high dielectricing additives, cycle property and rate property improvers may be further contained.

Examples of the cyclic carboxylic acid ester include those having a total carbon atom number of 3 to 12 in the structural formula. Specific examples thereof include gamma-butyrolactone, gamma-valerolactone, gamma caprolactone, and epsilon caprolactone. Of these, gamma-butyrolactone is particularly preferable from the viewpoint of improving the characteristics of the electrochemical device due to the improvement in the degree of lithium ion dissociation.

The blending amount of the cyclic carboxylic acid ester as an additive is usually 0.1% by mass or more, more preferably 1% by mass or more, based on 100% by mass of the solvent. Within this range, the electrical conductivity of the electrolytic solution can be improved, and the large-current discharge characteristics of the electrochemical device can be easily improved. The blending amount of the cyclic carboxylic acid ester is preferably 10% by mass or less, more preferably 5% by mass or less. By setting the upper limit in this way, the viscosity of the electrolytic solution is set to an appropriate range, the decrease in electrical conductivity is avoided, the increase in negative electrode resistance is suppressed, and the large current discharge characteristics of the electrochemical device are set to a good range. Make it easier.

Further, as the cyclic carboxylic acid ester, a fluorinated cyclic carboxylic acid ester (fluorinated lactone) can also be preferably used. Examples of the fluorine-containing lactone include the following formula (C):

(In the formula, X ^{15 to} X ²⁰ are the same or different, all of which are -H, -F, -Cl, -CH ₃ or fluorinated alkyl groups; where at least one of ^{X 15 to} X ^{20 is alkyl fluorinated.} Is the basis)
Fluorine-containing lactones indicated by.

Examples of the fluorinated alkyl group in X ^{15 to} X ²⁰ _{include -CFH 2} , -CF ₂ H, -CF ₃ , -CH ₂ CF ₃ , -CF ₂ CF ₃ , -CH ₂ CF ₂ CF ₃ , -CF. (CF ₃ ) _{2 and the like are mentioned, and -CH 2} CF ₃ and -CH ₂ CF ₂ CF ₃ are preferable from the viewpoint of high oxidation resistance and safety improving effect.

If ^{at least one of X 15 to} X ²⁰ is a fluorinated alkyl group, then the -H, -F, -Cl, -CH ₃ or fluorinated alkyl group is replaced with only one location ^{, X 15 to} X ^20. It may be replaced with a plurality of places. It is preferably 1 to 3 locations, more preferably 1 to 2 locations from the viewpoint of good solubility of the electrolyte salt.

But it is not fluorinated alkyl group substituted position particularly limited to, since the synthesis yields ^{good, X 17} and / or ^{X 18} is, in particular ^{X 17} or ^{X 18} is a fluorinated alkyl group, inter alia _-CH 2 CF ₃ , -CH ₂ CF ₂ CF ₃ is preferable. ^{X 15 to} X ²⁰ other than the fluorinated alkyl group are −H, −F, −Cl or CH ₃ , and −H is particularly preferable from the viewpoint of good solubility of the electrolyte salt.

As the fluorine-containing lactone, in addition to those represented by the above formula, for example, the following formula (D):

(In the formula, either A or B is CX ²⁶ X ²⁷ (X ²⁶ and X ²⁷ are the same or different, and both have -H, -F, -Cl, -CF ₃ , -CH ₃ or a hydrogen atom. An alkylene group that may be substituted with a halogen atom or may contain a heteroatom in the chain), while the other is an oxygen atom; Rf ¹² may have an ether bond fluorinated alkyl group or fluorinated. Alkane groups; X ²¹ and X ²² are the same or different, both -H, -F, -Cl, -CF ₃ or CH ₃ ; X ^23- X ²⁵ are the same or different, both -H, -F , -Cl or an alkyl group in which the hydrogen atom may be substituted with a halogen atom or a hetero atom may be contained in the chain; n = 0 or 1)
Fluorine-containing lactones and the like shown by are also mentioned.

The fluorine-containing lactone represented by the formula (D) includes the following formula (E):

(In the equation, A, B, Rf ¹² , X ²¹ , X ²² and X ²³ are the same as in equation (D))
The 5-membered ring structure represented by (1) is preferably cited from the viewpoint of easy synthesis and good chemical stability. Further, depending on the combination of A and B, the following formula (F):

(In the equation, Rf ¹² , X ²¹ , X ²² , X ²³ , X ²⁶ and X ²⁷ are the same as in equation (D))
Fluorine-containing lactone represented by and the following formula (G):

(In the equation, Rf ¹² , X ²¹ , X ²² , X ²³ , X ²⁶ and X ²⁷ are the same as in equation (D))
There is a fluorine-containing lactone indicated by.

Among these, excellent characteristics such as high dielectric constant and high withstand voltage can be exhibited in particular, and in addition, the characteristics as an electrolytic solution in the present invention are improved in that the solubility of the electrolyte salt and the reduction of internal resistance are good. From

等が挙げられる。
フッ素化環状カルボン酸エステルを含有させることにより、イオン伝導度の向上、安全性の向上、高温時の安定性向上といった効果が得られる。

And so on.
By containing the fluorinated cyclic carboxylic acid ester, effects such as improvement of ionic conductivity, improvement of safety, and improvement of stability at high temperature can be obtained.

As the ether compound, a chain ether having 3 to 10 carbon atoms and a cyclic ether having 3 to 6 carbon atoms are preferable.
Chain ethers having 3 to 10 carbon atoms include diethyl ether, di-n-butyl ether, dimethoxymethane, methoxyethoxymethane, diethoxymethane, dimethoxyethane, methoxyethoxyethane, diethoxyethane, and ethylene glycol di-n-propyl. Examples thereof include ether, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether.

Further, as the ether compound, fluorinated ether can also be preferably used.
The fluorinated ether has the following general formula (I):
Rf ^3- O-Rf ⁴ (I)
(In the formula, Rf ³ and Rf ⁴ are the same or different, and are an alkyl group having 1 to 10 carbon atoms or a fluorinated alkyl group having 1 to 10 carbon atoms. However, at least one of ^{Rf 3} and Rf ^{4 is fluorine.} Alkylated group.)
Fluorinated ether (I) represented by. By containing the fluorinated ether (I), the flame retardancy of the electrolytic solution is improved, and the stability and safety at high temperature and high voltage are improved.

In the above general formula (I), ^{at least one of Rf 3} and Rf ⁴ may be a fluorinated alkyl group having 1 to 10 carbon atoms, but the electrolytic solution is flame-retardant, stable at high temperature and high voltage, and safe. From the viewpoint of further improving the properties, ^{it is preferable that both Rf 3} and Rf ⁴ are fluorinated alkyl groups having 1 to 10 carbon atoms. In this case, Rf ³ and Rf ⁴ may be the same or different from each other.
Among them, Rf ³ and Rf ⁴ are the same or different, Rf ³ is a fluorinated alkyl group having 3 to 6 carbon atoms, and Rf ⁴ is a fluorinated alkyl group having 2 to 6 carbon atoms. More preferred.

If ^{the total carbon number of Rf 3} and Rf ⁴ is too small, the boiling point of the fluorinated ether becomes too low, and if ^{the carbon number of Rf 3} or Rf ⁴ is too large, the solubility of the electrolyte salt decreases, and other solvents The compatibility with the solvent also begins to be adversely affected, and the viscosity increases, so that the rate characteristics decrease. When ^{the carbon number of Rf 3} is 3 or 4, and ^{the carbon number of Rf 4} is 2 or 3, it is advantageous in that it is excellent in boiling point and rate characteristics.

The fluorinated ether (I) preferably has a fluorine content of 40 to 75% by mass. When the fluorine content is in this range, the balance between nonflammability and compatibility becomes particularly excellent. It is also preferable from the viewpoint of good oxidation resistance and safety.
The lower limit of the fluorine content is more preferably 45% by mass, further preferably 50% by mass, and particularly preferably 55% by mass. The upper limit is more preferably 70% by mass, further preferably 66% by mass.
The fluorine content of the fluorinated ether (I) is {(number of fluorine atoms × 19) / molecular weight of the fluorinated ether (I)} × 100 (%) based on the structural formula of the fluorinated ether (I). ) Is the value calculated by.

The Rf ^3, for _{example, CF 3 CF 2 CH 2 -} , CF 3 CFHCF 2 -, HCF 2 CF 2 CF 2 -, HCF 2 CF 2 CH 2 -, CF 3 CF 2 CH 2 CH 2 -, CF 3 CFHCF ₂ CH ₂ −, HCF ₂ CF ₂ CF ₂ CF ₂ −, HCF ₂ CF ₂ CF ₂ CH ₂ −, HCF ₂ CF ₂ CH ₂ CH ₂ −, HCF ₂ CF (CF ₃ ) CH ₂ − and the like can be mentioned. As Rf ⁴ , for example, -CH ₂ CF ₂ CF ₃ , -CF ₂ CFHCF ₃ , -CF ₂ CF ₂ CF ₂ H, -CH ₂ CF ₂ CF ₂ H, -CH ₂ CH ₂ CF ₂ CF ₃ , -CH ₂ CF ₂ CFHCF ₃ , -CF ₂ CF ₂ CF ₂ CF ₂ H, -CH ₂ CF ₂ CF ₂ CF ₂ H, -CH ₂ CH ₂ CF ₂ CF ₂ H, -CH ₂ CF (CF ₃ ) Examples thereof include CF ₂ H, -CF ₂ CF ₂ H, -CH ₂ CF ₂ H, and -CF ₂ CH _3.

Specific examples of the fluorinated ether (I) 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, 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 can be mentioned.

_{Among them, those containing HCF 2-} or CF ₃ CFH- at one end or both ends are excellent in polarity and can give fluorinated ether (I) having a high boiling point. The boiling point of the fluorinated ether (I) is preferably 67 to 120 ° C. It is more preferably 80 ° C. or higher, and even more preferably 90 ° C. or higher.

Examples of such fluorinated ether (I) include CF ₃ CH ₂ OCF ₂ CFHCF ₃ , CF ₃ CF ₂ CH ₂ OCF ₂ CFHCF ₃ , HCF ₂ CF ₂ CH ₂ OCF ₂ CFHCF ₃ , HCF ₂ CF ₂ CH. ₂ OCH ₂ CF ₂ CF ₂ H, CF ₃ CFHCF ₂ CH ₂ OCF ₂ CFHCF ₃ , HCF ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H, CF ₃ CF ₂ CH ₂ OCF ₂ CF ₂ H, etc. The above can be mentioned.
_{Among them, HCF 2} CF ₂ CH ₂ OCF ₂ CFHCF ₃ (boiling point 106 ° C) and CF ₃ CF ₂ CH are advantageous in that they have a high boiling point, compatibility with other solvents, and solubility of electrolyte salts. Selected from the group consisting of ₂ OCF _{2 CFHCF 3} (boiling point 82 ° C), HCF ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H (boiling point 92 ° C) and CF ₃ CF ₂ CH ₂ OCF ₂ CF ₂ H (boiling point 68 ° C). at least it is at least one that is _preferably selected from the group consisting of _{HCF 2 CF 2 CH 2 OCF 2} CFHCF 3 ( boiling point 106 ° C.) and _{HCF 2 CF 2 CH 2 OCF 2} CF 2 H ( boiling point 92 ° C.) It is more preferable that it is one kind.

Examples of the cyclic ether having 3 to 6 carbon atoms include 1,3-dioxane, 2-methyl-1,3-dioxane, 4-methyl-1,3-dioxane, 1,4-dioxane and the like, and fluorinated compounds thereof. Can be mentioned. Among them, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol-n-propyl ether, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether have high solvation ability to lithium ions and improve the degree of ion dissociation. Of the above, dimethoxymethane, diethoxymethane, and ethoxymethoxymethane are particularly preferable because they have low viscosity and give high ionic conductivity.

Examples of the nitrogen-containing compound include nitriles, fluorine-containing nitriles, carboxylic acid amides, fluorine-containing carboxylic acid amides, sulfonic acid amides, and fluorine-containing sulfonic acid amides. Further, 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxadiridinone, 1,3-dimethyl-2-imidazolidinone, N-methylsuccinimide and the like can also be used. However, the nitrile compounds represented by the general formulas (1a), (1b) and (1c) are not included in the nitrogen-containing compounds.

Examples of the boron-containing compound include borate esters such as trimethylborate and triethylborate, borate ether, and alkyl borate.

Examples of the organosilicon-containing compound include (CH ₃ ) ₄ -Si, (CH ₃ ) ₃ -Si-Si (CH ₃ ) _{3, and the} like.

Examples of the non-flammable (flame retardant) agent include phosphoric acid esters and phosphazene compounds. Examples of the phosphoric acid ester include a fluorine-containing alkyl phosphoric acid ester, a non-fluorine-based alkyl phosphoric acid ester, and an aryl phosphoric acid ester. Of these, a fluorine-containing alkyl phosphate is preferable because it can exert a non-combustible effect even in a small amount.

Specific examples of the fluorine-containing alkyl phosphate ester include the fluorine-containing dialkyl phosphoric acid ester described in JP-A-11-233141 and the cyclic alkyl phosphate ester described in JP-A-11-283669. , Or, a fluorine-containing trialkyl phosphoric acid ester and the like can be mentioned.

Examples of the non-flammable (flame retardant) agent include (CH ₃ O) ₃ P = O, (CF ₃ CH ₂ O) ₃ P = O, (HCF ₂ CH ₂ O) ₃ P = O, (CF ₃ CF _2). CH ₂ ) ₃ P = O, (HCF ₂ CF ₂ CH ₂ ) ₃ P = O and the like are preferable.

The surfactant may be any of a cationic surfactant, an anionic surfactant, a nonionic surfactant, and an amphoteric surfactant, but the fluorine atom is good in cycle characteristics and rate characteristics. It is preferable that it contains.

Examples of such a surfactant containing a fluorine atom include the following formula (3):
Rf ⁵ COO ⁻ M ⁺ (3)
(Wherein, Rf ⁵ is a fluorine-containing alkyl group which may contain an ether bond having 3 to 10 carbon atoms; ^{M +} is ^{Li +,} Na +, ^{K +} or NHR _'3 ⁺ (R' are the same or different , Both are H or alkyl groups with 1 to 3 carbon atoms)
Fluorine-containing carboxylate represented by and the following formula (4):
Rf ⁶ SO ₃ ^- M ⁺ (4)
(Wherein, Rf ⁶ is a fluorine-containing alkyl group which may contain an ether bond having 3 to 10 carbon atoms; ^{M +} is ^{Li +,} Na +, ^{K +} or NHR _'3 ⁺ (R' are the same or different , Both are H or alkyl groups with 1 to 3 carbon atoms)
A fluorine-containing sulfonate represented by is preferable.

The content of the surfactant is preferably 0.01 to 2% by mass in the electrolytic solution from the viewpoint that the surface tension of the electrolytic solution can be reduced without deteriorating the charge / discharge cycle characteristics.

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

Examples of the cycle property and rate property improving agent include methyl acetate, ethyl acetate, tetrahydrofuran, 1,4-dioxane and the like.

Further, the electrolytic solution of the present invention may be further combined with a polymer material to form a gel-like (plasticized) gel electrolytic solution.

Examples of such polymer materials include conventionally known polyethylene oxides and polypropylene oxides and modified products thereof (Japanese Patent Laid-Open Nos. 8-222270 and 2002-100405); polyacrylate-based polymers, polyacrylonitrile, and polyvinylidene fluoride. , Fluororesin such as vinylidene fluoride-hexafluoropropylene copolymer (Japanese Patent Laid-Open No. 4-506726, Japanese Patent Application Laid-Open No. 8-507407, Japanese Patent Application Laid-Open No. 10-294131); Examples thereof include a composite with a resin (Japanese Patent Laid-Open No. 11-35765, Japanese Patent Application Laid-Open No. 11-86630) and the like. In particular, it is desirable to use polyvinylidene fluoride or vinylidene fluoride-hexafluoropropylene copolymer as a polymer material for a gel electrolyte.

In addition, the electrolytic solution of the present invention may also contain the ionic conductive compound described in Japanese Patent Application No. 2004-301934.

This ionic conductive compound has the formula (J) :.
A- (D) -B (J)
[In the formula, D is the formula (2-1):
− (D1) _n − (FAE) _m − (AE) _p − (Y) _q − (2-1)
(In the formula, D1 is the formula (2a):

(Wherein, Rf is a fluorine-containing ether group which may have a crosslinkable functional group; groups R ¹⁰ couples Rf main chain or a bond)
An ether unit having a fluorine-containing ether group in the side chain indicated by;
FAE is the formula (2b):

(Wherein, Rfa is hydrogen atom, a crosslinkable good fluorinated alkyl group optionally having a functional group; R ¹¹ couples Rfa main chain group or a bond)
An ether unit having an alkyl fluorinated group in the side chain indicated by;
AE is the formula (2c):

(In the formula, 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. May be aromatic hydrocarbon group; R ¹² is a group or bond that binds the main chain to ^{R 13)}
Ether unit indicated by;
Y is the formula (2d-1) to (2d-3):

Units containing 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; where n + m is not 0 and the combination order of D1, FAE, AE and Y is Not specified);
A and B are the same or different, an alkyl group which may contain a hydrogen atom, a fluorine atom and / or a crosslinkable functional group, a phenyl group which may contain a fluorine atom and / or a crosslinkable functional group, -COOH. A group, -OR (R is an alkyl group that may contain a hydrogen or fluorine atom and / or a crosslinkable functional group), an ester group or a carbonate group (provided that D is an oxygen atom, a -COOH group, -OR, not ester or carbonate group)]
It is an amorphous fluorine-containing polyether compound having a fluorine-containing group in the side chain represented by.

If necessary, other additives may be added to the electrolytic solution of the present invention. Examples of other additives include metal oxides, glass and the like.

The electrolytic solution of the present invention preferably has a hydrogen fluoride (HF) content of 5 to 200 ppm. By containing HF, film formation of compound (1) and the above-mentioned additives can be promoted. If the HF content is too low, the film forming ability on the negative electrode tends to decrease, and the characteristics of the electrochemical device tend to deteriorate. Further, if the HF content is too large, the oxidation resistance of the electrolytic solution tends to decrease due to the influence of HF. Even if the electrolytic solution of the present invention contains HF in the above range, it does not reduce the high-temperature storage recovery capacity rate of the electrochemical device.
The content of HF is more preferably 10 ppm or more, further preferably 20 ppm or more. The content of HF is also more preferably 100 ppm or less, further preferably 80 ppm or less, and particularly preferably 50 ppm or less.
The content of HF can be measured by the neutralization titration method.

The electrolytic solution of the present invention may be prepared by any method using the above-mentioned components.

The electrolytic solution of the present invention can be suitably applied to an electrochemical device such as a lithium ion secondary battery or an electric double layer capacitor. An electrochemical device provided with such an electrolytic solution of the present invention is also one of the present inventions.

Electrochemical devices include lithium ion secondary batteries, capacitors (electric double-layer capacitors), radical batteries, solar cells (particularly dye-sensitized solar cells), fuel cells, various electrochemical sensors, electrochromic elements, and electrochemical switching. Examples thereof include elements, aluminum electrolytic capacitors, tantalum electrolytic capacitors and the like, and lithium ion secondary batteries and electric double layer capacitors are suitable.
A module including the above electrochemical device is also one of the present inventions.

The present invention is also a lithium ion secondary battery comprising the electrolytic solution of the present invention.
The lithium ion secondary battery may include a positive electrode, a negative electrode, and the above-mentioned electrolytic solution.

<Positive electrode>
The positive electrode is composed of a positive electrode active material layer containing a positive electrode active material and a current collector.

The positive electrode active material is not particularly limited as long as it can electrochemically occlude and release lithium ions, but for example, a substance containing lithium and at least one transition metal is preferable. Specific examples include a lithium-containing transition metal composite oxide and a lithium-containing transition metal phosphoric acid compound. Among them, as the positive electrode active material, a lithium-containing transition metal composite oxide that produces a high voltage is particularly preferable.

The transition metal of the lithium-containing transition metal composite oxide is preferably V, Ti, Cr, Mn, Fe, Co, Ni, Cu or the like, and specific examples thereof include a lithium-cobalt composite oxide such _{as LiCoO 2 or LiNiO 2.} Lithium-nickel composite oxides, _{lithium-manganese composite oxides such as LiMnO 2} , LiMn ₂ O ₄ , Li ₂ MnO _4, etc., and some of the transition metal atoms that are the main components of these lithium transition metal composite oxides are Na. Replaced with other elements such as K, B, F, Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Si, Nb, Mo, Sn, W And so on. Specific examples of the substituted ones include, for example, LiNi _0.5 Mn _0.5 O ₂ , LiNi _0.85 Co _0.10 Al _0.05 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O. ₂ , LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , LiNi _0.33 Co _0.33 Mn _0.33 O ₂ , LiNi _0.45 Co _0.10 Al _0.45 O ₂ , LiMn _{1. 8} Al _0.2 O ₄ , LiMn _1.5 Ni _0.5 O _{4, and the} like can be mentioned.

Among them, as the lithium-containing transition metal composite oxide, LiMn _1.5 Ni _0.5 O ₄ and LiNi _0.5 Co _0.2 Mn _0.3 O ₂ have high energy densities even when the voltage is high. LiNi _0.6 Co _0.2 Mn _0.2 O ₂ is preferable.

The transition metal of the lithium-containing transition metal phosphoric acid compound is preferably V, Ti, Cr, Mn, Fe, Co, Ni, Cu or the like, and specific examples thereof include, for example, LiFePO ₄ , Li ₃ Fe ₂ (PO ₄ ). _3. Iron phosphates such as _{LiFeP 2} O _{7 , cobalt phosphates such as LiCoPO 4} , and some of the transition metal atoms that are the main constituents of these lithium transition metal phosphate compounds are Al, Ti, V, Cr, Mn. , Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, Si and the like substituted with other elements.

Examples of the lithium-containing transition metal composite oxide include, for example.
Formula: Li _a Mn _2-b M ¹ _b O ₄ (in the formula, 0.9 ≦ a; 0 ≦ b ≦ 1.5; M ¹ is Fe, Co, Ni, Cu, Zn, Al, Sn, Cr, Lithium-manganese spinel composite oxide represented by (at least one metal selected from the group consisting of V, Ti, Mg, Ca, Sr, B, Ga, In, Si and Ge),
Formula: LiNi _1-c M ² _c O ₂ (in the formula, 0 ≦ c ≦ 0.5; M ² is Fe, Co, Mn, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, A lithium-nickel composite oxide represented by (at least one metal selected from the group consisting of Sr, B, Ga, In, Si and Ge), or
Formula: LiCo _1-d M ³ _d O ₂ (in the formula, 0 ≦ d ≦ 0.5; M ³ is Fe, Ni, Mn, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Examples thereof include a lithium-cobalt composite oxide represented by (at least one metal selected from the group consisting of Sr, B, Ga, In, Si and Ge).

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

Other positive electrode active materials include 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 , and LiV _3. O _{6 and the} like can be mentioned.

Further, it is preferable to include lithium phosphate in the positive electrode active material because the continuous charging characteristics are improved. The use of lithium phosphate is not limited, but it is preferable to use a mixture of the above-mentioned positive electrode active material and lithium phosphate. The lower limit of the amount of lithium phosphate used is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, still more preferably 0.5% by mass, based on the total of the positive electrode active material and lithium phosphate. % Or more, and the upper limit is preferably 10% by mass or less, more preferably 8% by mass or less, and further preferably 5% by mass or less.

Further, a substance having a composition different from that attached to the surface of the positive electrode active material may be used. Surface adhering substances include aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, bismuth oxide and other oxides, lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate. , Sulfates such as aluminum sulfate, carbonates such as lithium carbonate, calcium carbonate, magnesium carbonate, carbon and the like.

These surface-adhering substances are, for example, dissolved or suspended in a solvent and impregnated with the positive electrode active material and dried, or after the surface-adhering substance precursor is dissolved or suspended in the solvent and impregnated with the positive electrode active material. It can be attached to the surface of the positive electrode active material by a method of reacting by heating or the like, a method of adding to the positive electrode active material precursor and firing at the same time, or the like. When carbon is attached, a method of mechanically attaching the carbon substance later in the form of activated carbon or the like can also be used.

The amount of the surface adhering substance is preferably 0.1 ppm or more, more preferably 1 ppm or more, still more preferably 10 ppm or more, and the upper limit is preferably 20% or less, more preferably 20% or less, in terms of mass with respect to the positive electrode active material. Is used at 10% or less, more preferably 5% or less. The surface adhering substance can suppress the oxidation reaction of the electrolytic solution on the surface of the positive electrode active material and improve the battery life, but if the adhering amount is too small, the effect is not sufficiently exhibited and is often present. If it is too much, the resistance may increase because it blocks the ingress and egress of lithium ions.

Examples of the shape of the particles of the positive electrode active material include a mass, a polyhedron, a spherical shape, an elliptical spherical shape, a plate shape, a needle shape, and a columnar shape as conventionally used. Further, the primary particles may be aggregated to form secondary particles.

The tap density of the positive electrode active material is preferably 0.5 g / cm ³ or more, more preferably 0.8 g / cm ³ or more, and further preferably 1.0 g / cm ³ or more. When the tap density of the positive electrode active material is less than the above lower limit, the amount of the dispersion medium required for forming the positive electrode active material layer increases, and the required amount of the conductive material and the binder increases, so that the positive electrode to the positive electrode active material layer is formed. The filling rate of the active material is restricted, and the battery capacity may be restricted. By using the composite oxide powder having a high tap density, a high density positive electrode active material layer can be formed. Generally, the larger the tap density is, the more preferable it is, and there is no particular upper limit. However, if it is too large, the diffusion of lithium ions using the electrolytic solution as a medium in the positive electrode active material layer becomes rate-determining, and the load characteristics may be easily deteriorated. The upper limit is preferably 4.0 g / cm ³ or less, more preferably 3.7 g / cm ³ or less, and further preferably 3.5 g / cm ³ or less.
^{In the present invention, the tap density is the powder packing density (tap density) g / cm 3} when 5 to 10 g of positive electrode active material powder is placed in a 10 ml glass graduated cylinder and tapped 200 times with a stroke of about 20 mm. Ask as.

The median diameter d50 of the particles of the positive electrode active material (secondary particle diameter when the primary particles are aggregated to form secondary particles) is preferably 0.3 μm or more, more preferably 0.5 μm or more, still more preferable. Is 0.8 μm or more, most preferably 1.0 μm or more, and preferably 30 μm or less, more preferably 27 μm or less, still more preferably 25 μm or less, and most preferably 22 μm or less. If it falls below the above lower limit, a high tap density product may not be obtained, and if it exceeds the upper limit, it takes time to diffuse lithium in the particles, which causes deterioration of battery performance or preparation of a positive electrode of the battery, that is, an active material. When a conductive material, a binder, or the like is slurried with a solvent and applied in a thin film form, problems such as streaks may occur. Here, by mixing two or more kinds of the positive electrode active materials having different median diameters d50, the filling property at the time of producing the positive electrode can be further improved.

In the present invention, the median diameter d50 is measured by a known laser diffraction / scattering particle size distribution measuring device. When LA-920 manufactured by HORIBA is used as the particle size distribution meter, a 0.1 mass% sodium hexametaphosphate aqueous solution is used as the dispersion medium used in the measurement, and the measured refractive index is set to 1.24 after ultrasonic dispersion for 5 minutes. Is measured.

When the primary particles are aggregated to form secondary particles, the average primary particle diameter of the positive electrode active material is preferably 0.05 μm or more, more preferably 0.1 μm or more, still more preferably 0. It is 2 μm or more, and the upper limit is preferably 5 μm or less, more preferably 4 μm or less, still more preferably 3 μm or less, and most preferably 2 μm or less. If it exceeds the above upper limit, it is difficult to form spherical secondary particles, which adversely affects the powder filling property and greatly reduces the specific surface area, so that there is a high possibility that the battery performance such as output characteristics is deteriorated. is there. On the contrary, if it is less than the above lower limit, problems such as inferior reversibility of charge / discharge may occur because the crystal is usually underdeveloped.

In the present invention, the primary particle size is measured by observation using a scanning electron microscope (SEM). Specifically, in a photograph at a magnification of 10000, the longest value of the intercept by the left and right boundary lines of the primary particles with respect to the horizontal straight line is obtained for any 50 primary particles, and the average value is taken. Be done.

BET specific surface area of the positive electrode active material is preferably 0.1 m ² / g or more, more preferably 0.2 m ² / g or more, still more preferably 0.3 m ² / g or more, and the upper limit is preferably ^{50 m} 2 / It is g or less, more preferably 40 m ² / g or less, still more preferably 30 m ² / g or less. If the BET specific surface area is smaller than this range, the battery performance tends to deteriorate, and if it is large, the tap density does not easily increase, and a problem may easily occur in the coatability when forming the positive electrode active material layer.

In the present invention, the BET specific surface area is large after pre-drying the sample at 150 ° C. for 30 minutes under nitrogen flow using a surface area meter (for example, a fully automatic surface area measuring device manufactured by Okura Riken Co., Ltd.). It is defined by the value measured by the nitrogen adsorption BET 1-point method by the gas flow method using a nitrogen helium mixed gas accurately adjusted so that the value of the relative pressure of nitrogen with respect to the atmospheric pressure is 0.3.

When the lithium ion secondary battery of the present invention is used as a large lithium ion secondary battery for a hybrid vehicle or a distributed power source, high output is required. Therefore, the particles of the positive electrode active material are mainly secondary particles. Is preferable.
The particles of the positive electrode active material preferably 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 size 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 made faster, and as a result, the battery Output performance can be improved.

As a method for producing the positive electrode active material, a general method is used as a method for producing an inorganic compound. In particular, various methods can be considered for producing a spherical or elliptical spherical active material. For example, the raw material of a transition metal is dissolved or pulverized and dispersed in a solvent such as water, and the pH is adjusted while stirring. A method of obtaining an active material by preparing and recovering a spherical precursor, drying the precursor as necessary, _{adding a Li source such as LiOH, Li 2} CO ₃ , or LiNO ₃ and firing at a high temperature can be mentioned. ..

For the production of the positive electrode, the positive electrode active material may be used alone, or two or more kinds having different compositions may be used in any combination or ratio. In this case, a preferable combination is LiCoO ₂ and _{LiMn 2} O ₄ such as _{LiNi 0.33} Co _0.33 Mn _0.33 O _2, or a combination in which a part of this Mn is replaced with another transition metal or the like. Alternatively, a combination with LiCoO ₂ or a part of this Co substituted with another transition metal or the like can be mentioned.

The content of the positive electrode active material is preferably 50 to 99% by mass, more preferably 80 to 99% by mass of the positive electrode active material layer in terms of high battery capacity. The content of the positive electrode active material in the positive electrode active material layer is preferably 80% by mass or more, more preferably 82% by mass or more, and particularly preferably 84% by mass or more. The upper limit is preferably 99% by mass or less, more preferably 98% by mass or less. If the content of the positive electrode active material in the positive electrode active material layer is low, the electric capacity may be insufficient. On the contrary, if the content is too high, the strength of the positive electrode may be insufficient.

The positive electrode active material layer preferably further contains a binder, a thickener, and a conductive material.
As the binder, any material can be used as long as it is a material that is safe for the solvent and electrolytic solution used in electrode production, and for example, polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, and fragrance. Resin-based polymer such as group polyamide, chitosan, alginic acid, polyacrylic acid, polyimide, cellulose, nitrocellulose; SBR (styrene-butadiene rubber), isoprene rubber, butadiene rubber, fluororubber, NBR (acrylonitrile-butadiene rubber), ethylene -Rubber polymer such as propylene rubber; styrene-butadiene-styrene block copolymer or hydrogen additive thereof; EPDM (ethylene-propylene-diene ternary copolymer), styrene-ethylene-butadiene-styrene copolymer, Thermoplastic elastomeric polymers such as styrene / isoprene / styrene block copolymer or hydrogenated products thereof; syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene / vinyl acetate copolymer, propylene / α-olefin Soft resinous polymer such as copolymer; Fluorine-based polymer such as polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride copolymer, tetrafluoroethylene / ethylene copolymer; alkali metal ion (particularly lithium ion) Examples thereof include a polymer composition having ionic conductivity of the above. These may be used alone or in any combination and ratio of two or more.

The content of the binder is usually 0.1% by mass or more, preferably 1% by mass or more, more preferably 1.5% by mass or more, as the proportion of the binder in the positive electrode active material layer, and also. It is usually 80% by mass or less, preferably 60% by mass or less, more preferably 40% by mass or less, and most preferably 10% by mass or less. If the proportion of the binder is too low, the positive electrode active material cannot be sufficiently retained, the mechanical strength of the positive electrode is insufficient, and the battery performance such as cycle characteristics may be deteriorated. On the other hand, if it is too high, it may lead to a decrease in battery capacity and conductivity.

Examples of the thickener include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein and salts thereof. One type may be used alone, or two or more types may be used in any combination and ratio.

The ratio of the thickener to the active material is usually 0.1% by mass or more, preferably 0.2% by mass or more, more preferably 0.3% by mass or more, and usually 5% by mass or less, preferably 3%. It is in the range of mass% or less, more preferably 2 mass% or less. Below this range, the coatability may be significantly reduced. If it exceeds, the ratio of the active material to the positive electrode active material layer decreases, which may cause a problem that the capacity of the battery decreases and a problem that the resistance between the positive electrode active materials increases.

As the conductive material, a known conductive material can be arbitrarily used. Specific examples include metal materials such as copper and nickel, graphite (graphite) such as natural graphite and artificial graphite, carbon black such as acetylene black, and carbon materials such as amorphous carbon such as needle coke. It should be noted that one of these may be used alone, or two or more thereof may be used in any combination and ratio. The conductive material is usually 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 1% by mass or more, and usually 50% by mass or less, preferably 30% by mass in the positive electrode active material layer. It is used so as to contain% or less, more preferably 15% by mass or less. If the content is lower than this range, the conductivity may be insufficient. On the contrary, if the content is higher than this range, the battery capacity may decrease.

As the solvent for forming the slurry for forming the positive electrode active material layer, the positive electrode active material, the conductive material, the binder, and the thickener used as necessary can be dissolved or dispersed. The type of solvent is not particularly limited, and either an aqueous solvent or an organic solvent may be used. Examples of the aqueous solvent include water, a mixed medium of alcohol and water, and the like. Examples of the organic solvent include aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene and methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; and ketones such as acetone, methyl ethyl ketone and cyclohexanone. Classes; esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine, N, N-dimethylaminopropylamine; ethers such as diethyl ether, propylene oxide and tetrahydrofuran (THF); N-methylpyrrolidone (NMP) , Amides such as dimethylformamide and dimethylacetamide; aprotonic polar solvents such as hexamethylphosphalamide and dimethylsulfoxide can be mentioned.

Examples of the material of the current collector for the positive electrode include metals such as aluminum, titanium, tantalum, stainless steel and nickel, or metal materials such as alloys thereof; carbon materials such as carbon cloth and carbon paper. Of these, metal materials, especially aluminum or alloys thereof, are preferable.

Examples of the shape of the current collector include metal foil, metal cylinder, metal coil, metal plate, metal thin film, expanded metal, punch metal, foamed metal, etc. in the case of metal material, and carbon plate, carbon in the case of carbon material. Examples include a thin film and a carbon column. Of these, a metal thin film is preferable. The thin film may be formed in a mesh shape as appropriate. The thickness of the thin film is arbitrary, but is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and usually 1 mm or less, preferably 100 μm or less, more preferably 50 μm or less. If the thin film is thinner than this range, the strength required as a current collector may be insufficient. On the contrary, if the thin film is thicker than this range, the handleability may be impaired.

It is also preferable that the surface of the current collector is coated with a conductive auxiliary agent from the viewpoint of reducing the electrical contact resistance between the current collector and the positive electrode active material layer. Examples of the conductive auxiliary agent include carbon and precious metals such as gold, platinum, and silver.

The ratio of the thickness of the current collector to the positive electrode active material layer is not particularly limited, but the value of (thickness of the positive electrode active material layer on one side immediately before the electrolyte injection) / (thickness of the current collector) is 20. It is preferably less than or equal to, more preferably 15 or less, most preferably 10 or less, and preferably 0.5 or more, more preferably 0.8 or more, and most preferably 1 or more. If it exceeds this range, the current collector may generate heat due to Joule heat during high current density charging / discharging. Below this range, the volume ratio of the current collector to the positive electrode active material may increase and the capacity of the battery may decrease.

The positive electrode may be produced by a conventional method. For example, the above-mentioned binder, thickener, conductive material, solvent, etc. are added to the above-mentioned positive electrode active material to form a slurry-like positive electrode mixture, which is applied to a current collector, dried, and then pressed to obtain a high density. There is a method of densifying.

The high density can be achieved by a hand press, a roller press, or the like. The density of the positive electrode active material layer is preferably 1.5 g / cm ³ or more, more preferably 2 g / cm ³ or more, further preferably 2.2 g / cm ³ or more, and preferably 5 g / cm ³ or less. The range is more preferably 4.5 g / cm ³ or less, still more preferably 4 g / cm ³ or less. If it exceeds this range, the permeability of the electrolytic solution to the vicinity of the current collector / active material interface decreases, and the charge / discharge characteristics particularly at a high current density may decrease, so that high output may not be obtained. If it is lower than that, the conductivity between the active materials decreases, the battery resistance increases, and high output may not be obtained.

When the electrolytic solution of the present invention is used, it is preferable that the area of the positive electrode active material layer is larger than the outer surface area of the battery outer case from the viewpoint of enhancing the stability at high output and high temperature. Specifically, the total area of the electrode areas of the positive electrode with respect to the surface area of the exterior of the secondary battery is preferably 15 times or more, and more preferably 40 times or more in terms of area ratio. The outer surface area of the battery outer case is the total area calculated from the vertical, horizontal, and thickness dimensions of the case part filled with power generation elements excluding the protruding part of the terminal in the case of a bottomed square shape. Say. In the case of a bottomed cylindrical shape, the geometric surface area approximates the case portion filled with the power generation element excluding the protruding portion of the terminal as a cylinder. The total electrode area of the positive electrode is the geometric surface area of the positive electrode mixture layer facing the mixture layer containing the negative electrode active material, and in a structure in which the positive electrode mixture layer is formed on both sides via a current collector foil. , Refers to the sum of the areas calculated separately for each surface.

The thickness of the positive electrode plate is not particularly limited, but from the viewpoint of high capacity and high output, the thickness of the mixture layer obtained by subtracting the metal foil thickness of the core material is preferable as the lower limit with respect to one side of the current collector. Is 10 μm or more, more preferably 20 μm or more, and preferably 500 μm or less, more preferably 450 μm or less.

Further, a substance having a composition different from that attached to the surface of the positive electrode plate may be used. Surface adhering substances include aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, bismuth oxide and other oxides, lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate. , Sulfates such as aluminum sulfate, carbonates such as lithium carbonate, calcium carbonate, magnesium carbonate, carbon and the like.

<Negative electrode>
The negative electrode is composed of a negative electrode active material layer containing a negative electrode active material and a current collector.

The negative electrode active material is a carbonaceous material that can occlude and release lithium such as thermal decomposition products of organic substances and artificial graphite and natural graphite under various thermal decomposition conditions; and occludes and releases lithium such as tin oxide and silicon oxide. Possible metal oxide materials; lithium metals; various lithium alloys; lithium-containing metal composite oxide materials and the like can be mentioned. Two or more kinds of these negative electrode active materials may be mixed and used.

As a carbonaceous material capable of storing and releasing lithium, artificial graphite or purified natural graphite produced by high-temperature treatment of easy-to-graphite pitch obtained from various raw materials, or surface treatment of these graphites with pitch or other organic substances. It is preferable that the material is obtained by carbonizing after applying the above-mentioned material, and the natural graphite, the artificial graphite, the artificial carbonaceous substance, and the carbonaceous material and the negative electrode active material layer obtained by heat-treating the artificial graphite material at least once in the range of 400 to 3200 ° C. A carbonaceous material composed of at least two or more types of graphite having different crystalline properties and / or having an interface in which the different crystalline carbonaceous materials are in contact, the negative electrode active material layer has at least two or more different orientations. A material selected from a carbonaceous material having an interface in contact with the graphite is more preferable because it has a good balance between initial irreversible capacitance and high current density charge / discharge characteristics. In addition, one of these carbon materials may be used alone, or two or more of these carbon materials may be used in any combination and ratio.

As the carbonaceous material obtained by heat-treating the above-mentioned artificial carbonaceous substance and artificial graphite substance at least once in the range of 400 to 3200 ° C., coal-based coke, petroleum-based coke, coal-based pitch, petroleum-based pitch, and these pitches are oxidized. Treated, needle coke, pitch coke and partially graphitized carbon agents, furnace black, acetylene black, thermal decomposition products of organic substances such as pitch carbon fibers, carbonizable organic substances and their carbonized products, or carbonizable Examples thereof include solutions in which various organic substances are dissolved in low molecular weight organic solvents such as benzene, toluene, xylene, quinoline, and n-hexane, and carbonized products thereof.

As the metal material used as the negative electrode active material (excluding lithium titanium composite oxide), if lithium can be stored and released, lithium alone, a single metal and alloy forming a lithium alloy, or oxidation thereof. It may be any compound such as a substance, a carbide, a nitride, a silicide, a sulfide or a phosphor, and is not particularly limited. The elemental metal and alloy forming the lithium alloy are preferably materials containing group 13 and group 14 metal / semi-metal elements, and more preferably aluminum, silicon and tin (hereinafter abbreviated as "specific metal element"). ) Is a simple substance metal and an alloy or compound containing these atoms. One of these may be used alone, or two or more thereof may be used in any combination and ratio.

As the negative electrode active material having at least one atom selected from the specific metal element, the metal simple substance of any one specific metal element, the alloy consisting of two or more specific metal elements, or one type or two or more specific types are specified. Alloys consisting of metal elements and other one or more metal elements, compounds containing one or more specific metal elements, and oxides, carbides, nitrides, and silicates of the compounds. , Compound compounds such as sulfides or phosphates. By using these metal simple substances, alloys or metal compounds as the negative electrode active material, it is possible to increase the capacity of the battery.

In addition, a compound in which these composite compounds are complicatedly bonded to several kinds of elements such as elemental metals, alloys or non-metal elements can also be mentioned. Specifically, for example, in silicon and tin, an alloy of these elements and a metal that does not act as a negative electrode can be used. For example, in the case of tin, it is possible to use a complex compound containing 5 to 6 kinds of elements in combination with a metal that acts as a negative electrode other than tin and silicon, a metal that does not act as a negative electrode, and a non-metal element. it can.

Specifically, Si alone, SiB ₄ , SiB ₆ , Mg ₂ Si, Ni ₂ Si, TiSi ₂ , MoSi ₂ , CoSi ₂ , NiSi ₂ , CaSi ₂ , CrSi ₂ , Cu ₆ Si, FeSi ₂ , MnSi ₂ , NbSi ₂ , _{TaSi 2} , VSi ₂ , WSi ₂ , ZnSi ₂ , SiC, Si ₃ N ₄ , Si ₂ N ₂ O, SiO _v (0 <v ≦ 2), LiSiO or tin alone, SnSiO ₃ , LiSnO, Mg ₂ Sn, SnO _w (0 <w ≦ 2) can be mentioned.
Further, a composite material containing Si or Sn as the first constituent element and the second and third constituent elements in addition to the first constituent element can be mentioned. The second constituent element is, for example, at least one of cobalt, iron, magnesium, titanium, vanadium, chromium, manganese, nickel, copper, zinc, gallium and zirconium. The third constituent element is, for example, at least one of boron, carbon, aluminum and phosphorus.
In particular, since high battery capacity and excellent battery characteristics can be obtained, as the metal material, silicon or tin alone (may contain a trace amount of impurities), SiO _v (0 <v ≦ 2), SnO _w (0). ≦ w ≦ 2), Si—Co—C composite material, Si—Ni—C composite material, Sn—Co—C composite material, Sn—Ni—C composite material are preferable.

The lithium-containing metal composite oxide material used as the negative electrode active material is not particularly limited as long as it can store and release lithium, but a material containing titanium and lithium is preferable from the viewpoint of high current density charge / discharge characteristics. More preferably, a lithium-containing composite metal oxide material containing titanium is preferable, and a composite oxide of lithium and titanium (hereinafter, abbreviated as "lithium titanium composite oxide") is preferable. That is, it is particularly preferable to use a lithium-titanium composite oxide having a spinel structure contained in the negative electrode active material for an electrolytic solution battery because the output resistance is greatly reduced.

The lithium-titanium composite oxide has a general formula:
Li _x Ti _y M _z O ₄
[In the formula, M represents at least one element selected from the group consisting of Na, K, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn and Nb. ]
It is preferably a compound represented by.
Among the above compositions,
(I) 1.2 ≦ x ≦ 1.4, 1.5 ≦ y ≦ 1.7, z = 0
(Ii) 0.9 ≦ x ≦ 1.1, 1.9 ≦ y ≦ 2.1, z = 0
(Iii) 0.7 ≦ x ≦ 0.9, 2.1 ≦ y ≦ 2.3, z = 0
This structure is particularly preferable because it has a good balance of battery performance.

Particularly preferred representative compositions of the compounds are Li _4/3 Ti _5/3 O ₄ for (i), Li ₁ Ti ₂ O ₄ for (ii), and Li _4/5 Ti _11/5 O for (iii). It is _4. As for the structure of Z ≠ 0, for example, Li _4/3 Ti _4/3 Al _1/3 O ₄ is preferable.

The negative electrode active material layer preferably further contains a binder, a thickener, and a conductive material.

Examples of the binder include the same binders that can be used for the positive electrode described above. The ratio of the binder to the negative electrode active material is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, particularly preferably 0.6% by mass or more, and preferably 20% by mass or less, 15% by mass. It is more preferably mass% or less, further preferably 10 mass% or less, and particularly preferably 8 mass% or less. If the ratio of the binder to the negative electrode active material exceeds the above range, the ratio of the binder whose amount does not contribute to the battery capacity increases, which may lead to a decrease in the battery capacity. Further, if it falls below the above range, the strength of the negative electrode may decrease.

In particular, when a rubber-like polymer typified by SBR is contained in the main component, the ratio of the binder to the negative electrode active material is usually 0.1% by mass or more, preferably 0.5% by mass or more. , 0.6% by mass or more, and usually 5% by mass or less, preferably 3% by mass or less, and further preferably 2% by mass or less. When a fluoropolymer represented by polyvinylidene fluoride is contained in the main component, the ratio to the negative electrode active material is usually 1% by mass or more, preferably 2% by mass or more, and further 3% by mass or more. It is preferable, and usually it is 15% by mass or less, preferably 10% by mass or less, and further preferably 8% by mass or less.

Examples of the thickener include the same thickeners that can be used for the positive electrode described above. The ratio of the thickener to the negative electrode active material is usually 0.1% by mass or more, preferably 0.5% by mass or more, further preferably 0.6% by mass or more, and usually 5% by mass or less. It is preferably 3% by mass or less, and more preferably 2% by mass or less. If the ratio of the thickener to the negative electrode active material is less than the above range, the coatability may be significantly reduced. On the other hand, if it exceeds the above range, the ratio of the negative electrode active material to the negative electrode active material layer decreases, which may cause a problem that the capacity of the battery decreases and an increase in resistance between the negative electrode active materials.

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

As the solvent for forming the slurry for forming the negative electrode active material layer, the negative electrode active material, the binder, and the thickener and the conductive material used as needed can be dissolved or dispersed. The type of solvent is not particularly limited, and either an aqueous solvent or an organic solvent may be used.
Examples of the aqueous solvent include water, alcohol and the like, and examples of the organic solvent include N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, methylethylketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N, N-. Examples thereof include dimethylaminopropylamine, tetrahydrofuran (THF), toluene, acetone, diethyl ether, dimethylacetamide, hexamethylphosphalamide, dimethyl sulfoxide, benzene, xylene, quinoline, pyridine, methylnaphthalene and hexane.

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

The thickness of the current collector is usually 1 μm or more, preferably 5 μm or more, and usually 100 μm or less, preferably 50 μm or less. If the thickness of the negative electrode current collector is too thick, the capacity of the entire battery may be reduced too much, and conversely, if it is too thin, handling may be difficult.

The negative electrode may be manufactured by a conventional method. For example, there is a method in which the above-mentioned binder, thickener, conductive material, solvent and the like are added to the above-mentioned negative electrode material to form a slurry, which is applied to a current collector, dried and then pressed to increase the density. .. When an alloy material is used, a method of forming a thin film layer (negative electrode active material layer) containing the above-mentioned negative electrode active material by a method such as a vapor deposition method, a sputtering method, or a plating method is also used.

The electrode structure when the negative electrode active material is converted into an electrode is not particularly limited, but the density of the negative electrode active material existing on the current collector ^{is preferably 1 g · cm -3} or more, and 1.2 g · cm ^-3 or more. Is more preferable, 1.3 g · cm ^-3 or more is particularly preferable, 2.2 g · cm ^-3 or less is preferable, 2.1 g · cm ^-3 or less is more preferable, and 2.0 g · cm ^-3 or less is more preferable. More preferably, 1.9 g · cm ^-3 or less is particularly preferable. If the density of the negative electrode active material existing on the current collector exceeds the above range, the negative electrode active material particles are destroyed, the initial irreversible capacity is increased, and the electrolytic solution near the current collector / negative electrode active material interface is increased. High current density charge / discharge characteristics may deteriorate due to a decrease in permeability. On the other hand, if it falls below the above range, the conductivity between the negative electrode active materials may decrease, the battery resistance may increase, and the capacity per unit volume may decrease.

The thickness of the negative electrode plate is designed according to the positive electrode plate to be used and is not particularly limited, but the thickness of the mixture layer after subtracting the metal foil thickness of the core material is usually 15 μm or more, preferably 20 μm or more. , More preferably 30 μm or more, and usually 300 μm or less, preferably 280 μm or less, more preferably 250 μm or less.

Further, a substance having a composition different from that attached to the surface of the negative electrode plate may be used. Surface adhering substances include aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, bismuth oxide and other oxides, lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate. , Sulfates such as aluminum sulfate, carbonates such as lithium carbonate, calcium carbonate, magnesium carbonate and the like.

<Separator>
The lithium ion secondary battery of the present invention preferably further includes a separator.
The material and shape of the separator are not particularly limited as long as they are stable in the electrolytic solution and have excellent liquid retention properties, and known ones can be used. Among them, resins, glass fibers, inorganic substances, etc., which are formed of a material stable to the electrolytic solution of the present invention, are used, and a porous sheet or a non-woven fabric-like material having excellent liquid retention property is used. preferable.

As the material of the resin and the glass fiber separator, for example, polyolefins such as polyethylene and polypropylene, aromatic polyamides, polytetrafluoroethylene, polyether sulfone, glass filters and the like can be used. These materials, such as polypropylene / polyethylene two-layer film and polypropylene / polyethylene / polypropylene three-layer film, may be used alone or in any combination and ratio of two or more. Among them, the separator is preferably a porous sheet or a non-woven fabric made of a polyolefin such as polyethylene or polypropylene because it has good permeability of the electrolytic solution and a good shutdown effect.

The thickness of the separator is arbitrary, but is usually 1 μm or more, preferably 5 μm or more, more preferably 8 μm or more, and usually 50 μm or less, preferably 40 μm or less, further preferably 30 μm or less. If the separator is too thin than the above range, the insulating property and mechanical strength may decrease. Further, if it is too thick than the above range, not only the battery performance such as rate characteristics may be deteriorated, but also the energy density of the electrolytic solution battery as a whole may be lowered.

Further, when a porous material such as a porous sheet or a non-woven fabric is used as the separator, the porosity of the separator is arbitrary, but is usually 20% or more, preferably 35% or more, still more preferably 45% or more. Further, it is usually 90% or less, preferably 85% or less, and further preferably 75% or less. If the porosity is too small than the above range, the film resistance tends to increase and the rate characteristics tend to deteriorate. On the other hand, if it is larger than the above range, the mechanical strength of the separator tends to decrease, and the insulating property tends to decrease.

The average pore size of the separator is also arbitrary, but is usually 0.5 μm or less, preferably 0.2 μm or less, and usually 0.05 μm or more. If the average pore diameter exceeds the above range, a short circuit is likely to occur. Further, if it falls below the above range, the film resistance may increase and the rate characteristics may deteriorate.

On the other hand, as the inorganic material, for example, oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates such as barium sulfate and calcium sulfate are used, and those having a particle shape or a fiber shape are used. Used.

As the form, a thin film such as a non-woven fabric, a woven cloth, or a microporous film is used. As the thin film shape, a thin film having a pore diameter of 0.01 to 1 μm and a thickness of 5 to 50 μm is preferably used. In addition to the above-mentioned independent thin film shape, a separator formed by forming a composite porous layer containing the above-mentioned inorganic particles on the surface layer of the positive electrode and / or the negative electrode by using a resin binder can be used. For example, alumina particles having a 90% particle size of less than 1 μm may be formed on both sides of the positive electrode by using a fluororesin as a binder to form a porous layer.

<Battery design>
The electrode group has a laminated structure in which the positive electrode plate and the negative electrode plate are formed through the separator, and a structure in which the positive electrode plate and the negative electrode plate are spirally wound through the separator. Either may be used. The ratio of the volume of the electrode group to the internal volume of the battery (hereinafter referred to as the electrode group occupancy rate) is usually 40% or more, preferably 50% or more, and usually 90% or less, preferably 80% or less. ..

When the electrode group occupancy rate is less than the above range, the battery capacity becomes small. Further, if it exceeds the above range, the void space is small, and the internal pressure rises due to the expansion of the member due to the high temperature of the battery and the increase of the vapor pressure of the liquid component of the electrolyte, and the charge / discharge repetition performance as a battery. In some cases, various characteristics such as high temperature storage may be deteriorated, and a gas discharge valve that releases internal pressure to the outside may operate.

The current collecting structure is not particularly limited, but in order to more effectively improve the charge / discharge characteristics of the high current density by the electrolytic solution of the present invention, it is necessary to use a structure that reduces the resistance of the wiring portion and the joint portion. preferable. When the internal resistance is reduced in this way, the effect of using the electrolytic solution of the present invention is particularly well exhibited.

When the electrode group has the above-mentioned laminated structure, a structure formed by bundling the metal core portions of each electrode layer and welding them to the terminals is preferably used. When the area of one electrode becomes large, the internal resistance becomes large. Therefore, it is also preferably used to reduce the resistance by providing a plurality of terminals in the electrode. In the case where the electrode group has the above-mentioned wound structure, the internal resistance can be reduced by providing a plurality of lead structures on the positive electrode and the negative electrode and bundling them in the terminals.

The material of the outer case is not particularly limited as long as it is a substance stable to the electrolytic solution used. Specifically, a nickel-plated steel plate, stainless steel, aluminum or aluminum alloy, metals such as magnesium alloy, or a laminated film (laminated film) of resin and aluminum foil is used. From the viewpoint of weight reduction, aluminum or aluminum alloy metal or laminated film is preferably used.

In the outer case using metals, the metals are welded together by laser welding, resistance welding, or ultrasonic welding to form a sealed and sealed structure, or the above metals are used to form a caulking structure via a resin gasket. Things can be mentioned. Examples of the outer case using the above-mentioned laminated film include a case in which resin layers are heat-sealed to form a sealed and sealed structure. In order to improve the sealing property, a resin different from the resin used for the laminate film may be interposed between the resin layers. In particular, when the resin layer is heat-sealed via the current collecting terminal to form a closed structure, the metal and the resin are bonded to each other. Resin is preferably used.

The shape of the lithium ion secondary battery of the present invention is arbitrary, and examples thereof include a cylindrical type, a square type, a laminated type, a coin type, and a large size. The shapes and configurations of the positive electrode, the negative electrode, and the separator can be changed and used according to the shape of each battery.

A module including the lithium ion secondary battery of the present invention is also one of the present inventions.

Further, the positive electrode, the negative electrode, and the above-mentioned electrolytic solution are provided, the positive electrode includes a positive electrode current collector and a positive electrode active material layer containing a positive electrode active material, and the positive electrode active material is characterized by containing Mn. The lithium ion secondary battery is also one of the preferred embodiments. Since the positive electrode active material layer containing the positive electrode active material containing Mn is provided, the lithium ion secondary battery is more excellent in high temperature storage characteristics.

_{As the positive electrode active material containing Mn, LiMn 1.5} Ni _0.5 O ₄ and LiNi _0.5 Co _0.2 Mn ₀ can be provided because a lithium ion secondary battery having high energy density and high output can be provided. _.3 O ₂ and LiNi _0.6 Co _0.2 Mn _0.2 O ₂ are preferable.

The content of the positive electrode active material in the positive electrode active material layer is preferably 80% by mass or more, more preferably 82% by mass or more, and particularly preferably 84% by mass or more. The upper limit is preferably 99% by mass or less, more preferably 98% by mass or less. If the content of the positive electrode active material in the positive electrode active material layer is low, the electric capacity may be insufficient. On the contrary, if the content is too high, the strength of the positive electrode may be insufficient.

The positive electrode active material layer may further contain a conductive material, a thickener and a binder.

As the binder, any material can be used as long as it is a material that is safe against the solvent and electrolytic solution used in the manufacture of the electrode. For example, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene can be used. , SBR (Styrene-butadiene rubber), isoprene rubber, butadiene rubber, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, polyethylene terephthalate, polymethylmethacrylate, polyimide, aromatic polyamide, cellulose, nitrocellulose, NBR (Acrylonitrile-butadiene rubber), fluororubber, ethylene-propylene rubber, styrene / butadiene / styrene block copolymer or hydrogen additive thereof, EPDM (ethylene / propylene / diene ternary copolymer), styrene / ethylene / butadiene / Ethylene copolymer, styrene / isoprene / styrene block copolymer or hydrogen additive thereof, syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene / vinyl acetate copolymer, propylene / α-olefin copolymer , Fluorinated polyvinylidene fluoride, tetrafluoroethylene / ethylene copolymer, polymer composition having ionic conductivity of alkali metal ions (particularly lithium ions) and the like. In addition, as these substances, 1 type may be used alone, and 2 or more types may be used together in arbitrary combinations and ratios.

The content of the binder is usually 0.1% by mass or more, preferably 1% by mass or more, more preferably 1.5% by mass or more, as the proportion of the binder in the positive electrode active material layer, and also. It is usually 80% by mass or less, preferably 60% by mass or less, more preferably 40% by mass or less, and most preferably 10% by mass or less. If the proportion of the binder is too low, the positive electrode active material cannot be sufficiently retained, the mechanical strength of the positive electrode is insufficient, and the battery performance such as cycle characteristics may be deteriorated. On the other hand, if it is too high, it may lead to a decrease in battery capacity and conductivity.

Examples of the thickener include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein and salts thereof. One type may be used alone, or two or more types may be used in any combination and ratio.

The ratio of the thickener to the active material is usually 0.1% by mass or more, preferably 0.2% by mass or more, more preferably 0.3% by mass or more, and usually 5% by mass or less, preferably 3%. It is in the range of mass% or less, more preferably 2 mass% or less. Below this range, the coatability may be significantly reduced. If it exceeds, the ratio of the active material to the positive electrode active material layer decreases, which may cause a problem that the capacity of the battery decreases and a problem that the resistance between the positive electrode active materials increases.

As the conductive material, a known conductive material can be arbitrarily used. Specific examples include metal materials such as copper and nickel, graphite (graphite) such as natural graphite and artificial graphite, carbon black such as acetylene black, and carbon materials such as amorphous carbon such as needle coke. It should be noted that one of these may be used alone, or two or more thereof may be used in any combination and ratio. The conductive material is usually 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 1% by mass or more, and usually 50% by mass or less, preferably 30% by mass in the positive electrode active material layer. It is used so as to contain% or less, more preferably 15% by mass or less. If the content is lower than this range, the conductivity may be insufficient. On the contrary, if the content is higher than this range, the battery capacity may decrease.

The positive electrode current collector is preferably made of a valve metal or an alloy thereof because the high temperature storage characteristics are further improved. Examples of the valve metal include aluminum, titanium, tantalum, and chromium. It is more preferable that the positive electrode current collector is made of aluminum or an alloy of aluminum.

Since the high temperature storage characteristics of the lithium ion secondary battery are further improved, the portion of the portion electrically connected to the positive electrode current collector that comes into contact with the electrolytic solution is also made of a valve metal or an alloy thereof. It is preferably configured. In particular, the battery outer case and the parts of the lead wires and safety valves housed in the battery outer case that are electrically connected to the positive electrode current collector and that come into contact with the non-aqueous electrolytic solution are made of valve metal or. It is preferably composed of the alloy. Stainless steel coated with a valve metal or an alloy thereof may be used.

The method for producing the positive electrode is as described above. For example, the above-mentioned binder, thickener, conductive material, solvent and the like are added to the above-mentioned positive electrode active material to prepare a slurry-like positive electrode mixture, which is used as described above. Examples thereof include a method in which the film is applied to a positive electrode current collector, dried, and then pressed to increase the density.

The configuration of the negative electrode is as described above.

The electric double layer capacitor may include a positive electrode, a negative electrode, and the above-mentioned electrolytic solution.
In the electric double layer capacitor, at least one of the positive electrode and the negative electrode is a polarizable electrode, and the following electrodes described in detail in JP-A-9-7896 can be used as the polarizable electrode and the non-polarizing electrode.

The polarizable electrode mainly composed of activated carbon used in the present invention preferably contains an activated carbon having a large specific surface area and a conductive agent such as carbon black that imparts electron conductivity. The polar electrode can be formed by various methods. For example, a polarized electrode made of activated carbon and carbon black can be formed by mixing activated carbon powder, carbon black, and a phenolic resin, and firing and activating them in an inert gas atmosphere and a steam atmosphere after press molding. Preferably, the polarizing electrode is bonded to the current collector with a conductive adhesive or the like.

Alternatively, activated carbon powder, carbon black and a binder can be kneaded in the presence of alcohol to form a sheet and dried to obtain a polar electrode. For this binder, for example, polytetrafluoroethylene is used. Alternatively, activated carbon powder, carbon black, a binder and a solvent may be mixed to form a slurry, and this slurry may be coated on a metal foil of a current collector and dried to form a polar electrode integrated with the current collector. it can.

A polarization electrode mainly composed of activated carbon may be used for both electrodes to form an electric double layer capacitor, but a configuration using a non-polarizing electrode on one side, for example, a positive electrode mainly composed of a battery active material such as a metal oxide and activated carbon. A configuration that combines a negative electrode of a polarization electrode mainly composed of, a negative electrode mainly composed of a carbon material capable of reversibly storing and desorbing lithium ions, or a negative electrode mainly composed of a lithium metal or a lithium alloy and a portion mainly composed of activated carbon. A configuration in combination with a polar positive electrode is also possible.

Further, a carbonaceous material such as carbon black, graphite, expanded graphite, porous carbon, carbon nanotube, carbon nanohorn, or Ketjen black may be used instead of or in combination with activated carbon.

The non-polarizing electrode is preferably mainly composed of a carbon material capable of occluding and desorbing lithium ions reversibly, and a carbon material in which lithium ions are occluded is used for the electrode. In this case, a lithium salt is used as the electrolyte. According to the electric double layer capacitor of this configuration, a higher withstand voltage exceeding 4V can be obtained.

The solvent used for preparing the slurry in the preparation of the electrode is preferably one in which a binder is dissolved, and N-methylpyrrolidone, dimethylformamide, toluene, xylene, isophorone, methyl ethyl ketone, ethyl acetate, methyl acetate, and phthal are used according to the type of the binder. Dimethyl acetate, ethanol, methanol, butanol or water are appropriately selected.

Examples of the activated carbon used for the polar electrode include a phenol resin-based activated carbon, a palm-based activated carbon, and a petroleum coke-based activated carbon. Of these, petroleum coke-based activated carbon or phenol resin-based activated carbon is preferably used because a large capacity can be obtained. Further, the activated carbon activation treatment method includes a steam activation treatment method, a molten KOH activation treatment method, and the like, and it is preferable to use the activated carbon by the molten KOH activation treatment method in that a larger capacity can be obtained.

Preferred conductive agents used for the polarization electrode include carbon black, Ketjen black, acetylene black, natural graphite, artificial graphite, metal fiber, conductive titanium oxide, and ruthenium oxide. The mixing amount of the conductive agent such as carbon black used for the polar electrode is 1 to 1 in the total amount with activated carbon because good conductivity (low internal resistance) is obtained and the capacity of the product decreases if it is too large. It is preferably 50% by mass.

As the activated carbon used for the polar electrode, activated carbon having an average particle size of 20 μm or less and a specific surface area of 1500 to 3000 m ² / g is used so that an electric double layer capacitor having a large capacity and low internal resistance can be obtained. Is preferable. Further, as preferable carbon materials for forming an electrode mainly composed of a carbon material capable of reversibly occluding and releasing lithium ions, natural graphite, artificial graphite, graphitized mesocarbon globules, graphitized whiskers, and air layer Examples thereof include a calcined product of grown carbon fiber, a furfuryl alcohol resin, and a calcined product of novolak resin.

The current collector may be chemically or electrochemically corrosion resistant. Stainless steel, aluminum, titanium or tantalum can be preferably used as the current collector of the polar electrode mainly composed of activated carbon. Of these, stainless steel or aluminum is a particularly preferable material in terms of both characteristics and price of the obtained electric double layer capacitor. Stainless steel, copper or nickel is preferably used as the current collector of the electrode mainly composed of a carbon material capable of reversibly occluding and releasing lithium ions.

Further, in order to store lithium ions in advance in a carbon material capable of reversibly storing and releasing lithium ions, (1) powdered lithium is mixed with a carbon material capable of reversibly storing and releasing lithium ions. Method of leaving, (2) A lithium foil is placed on an electrode formed of a carbon material and a binder that can reversibly store and release lithium ions, and this electrode is placed in a state of being in electrical contact with the electrode as a lithium salt. A method of ionizing lithium by immersing it in an electrolytic solution in which lithium ions are dissolved and incorporating lithium ions into a carbon material. (3) Formed by a carbon material and a binder capable of reversibly storing and releasing lithium ions. The electrode is placed on the minus side, the lithium metal is placed on the plus side, and the lithium salt is immersed in a non-aqueous electrolyte solution as an electrolyte, and an electric current is applied to electrochemically incorporate lithium into the carbon material in an ionized state. There is a way.

As the electric double layer capacitor, a wound type electric double layer capacitor, a laminated type electric double layer capacitor, a coin type electric double layer capacitor and the like are generally known, and the above electric double layer capacitor can also be of these types. ..

For example, in a wound electric double layer capacitor, a positive electrode and a negative electrode composed of a laminate of a current collector and an electrode layer are wound via a separator to produce a wound element, and the wound element is made of aluminum. It is assembled by putting it in a case such as, filling it with an electrolytic solution, preferably a non-aqueous electrolytic solution, and then sealing it with a rubber sealing body.

As the separator, a conventionally known material and composition can be used. For example, polyethylene porous film, polypropylene fiber, glass fiber, non-woven fabric of cellulose fiber and the like can be mentioned.

Further, by a known method, a laminated electric double layer capacitor in which a sheet-shaped positive electrode and a negative electrode are laminated via an electrolytic solution and a separator, or a coin type positive electrode and a negative electrode are formed into a coin type via an electrolytic solution and a separator by fixing with a gasket. It can also be a configured coin-type electric double layer capacitor.

The electrolytic solution of the present invention is useful as an electrolytic solution for a large lithium ion secondary battery for a hybrid vehicle or a distributed power source, or for an electric double layer capacitor.

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

The compounds in Tables 1 and 2 used as additives in Examples and Comparative Examples are as follows.

[Characteristics of 4.9V class lithium ion secondary battery]
Examples 1-12, Comparative Examples 1-5
(Preparation of non-aqueous electrolyte solution)
_{LiPF 6} as a lithium salt was dissolved in a mixed organic solvent consisting of 30% by volume of fluoroethylene carbonate, 60% by volume of 2,2,2-trifluoroethylmethyl carbonate and 10% by volume of methyl difluoroacetate at a concentration of 1 mol / L. Further, as the electrolyte solution additive, A1 to A5 in Examples and B1 to B4 in Comparative Examples were dissolved in the electrolyte solution at the ratios shown in Table 1 to prepare a non-aqueous electrolyte solution.

(Preparation of positive electrode 1)
_{Using LiNi 0.5} Mn _1.5 O ₄ as the positive electrode active material, acetylene black as the conductive material, and N-methyl-2-pyrrolidone dispersion of polyvinylidene fluoride (PVdF) as the binder, the active material, the conductive material, A positive electrode mixture slurry mixed so that the solid content ratio of the binder was 92/3/5 (mass ratio) was prepared. The obtained positive electrode mixture slurry was uniformly applied onto an aluminum foil current collector having a thickness of 20 μm, dried, and then compression-molded by a press to obtain a positive electrode.

(Preparation of negative electrode)
Artificial graphite powder as negative electrode active material, aqueous dispersion of sodium carboxylmethylcellulose as thickener (concentration of sodium carboxymethylcellulose 1% by mass), aqueous dispersion of styrene-butadiene rubber as binder (concentration of styrene-butadiene rubber 50) By mass%), the active material, thickener, and binder have a solid content ratio of 97.6 / 1.2 / 1.2 (mass ratio) and are mixed in an aqueous solvent to form a slurry. The negative electrode mixture slurry was prepared. It was uniformly applied to a copper foil having a thickness of 20 μm, dried, and then compressed and formed by a press to obtain a negative electrode.

(Manufacturing of lithium ion secondary battery)
The negative electrode, the positive electrode and the polyethylene separator manufactured as described above were laminated in this order of the negative electrode, the separator and the positive electrode to prepare a battery element. After inserting this battery element into a bag made of a laminated film in which both sides of an aluminum sheet (thickness 40 μm) are coated with a resin layer while projecting the positive electrode and negative electrode terminals, an electrolyte having the composition shown in Table 1 is inserted. Each of the liquids was injected into a bag and vacuum-sealed to prepare a sheet-shaped lithium ion secondary battery.

(High temperature cycle characterization test)
The secondary battery manufactured above is sandwiched between plates and pressurized, and at 60 ° C., constant current-constant voltage charging up to 4.9V with a current equivalent to 0.5C (hereinafter referred to as CC / CV charging). (.) (0.1C cut), then discharged to 3V with a constant current of 0.5C, this was set as one cycle, and this was repeated until 200 cycles were reached. Then, the cycle capacity retention rate after 200 cycles at 60 ° C. was determined by the following formula.
(Discharge capacity after 200 cycles) ÷ (Initial discharge capacity) x 100 = Cycle capacity retention rate (%)
In addition, after the battery was sufficiently cooled, the volume was measured by the Archimedes method, and the amount of gas generated from the volume change before and after the cycle test was determined. The results are shown in Table 1.

[Characteristics of 4.4V class lithium ion secondary battery]
Examples 13 to 24, Comparative Examples 6 to 10
(Preparation of non-aqueous electrolyte solution)
_{LiPF 6} as a lithium salt was dissolved at a concentration of 1 mol / L in a mixed organic solvent composed of 30% by volume of ethylene carbonate, 40% by volume of ethylmethyl carbonate and 30% by volume of dimethyl carbonate. Further, as the electrolyte solution additive, A1 to A5 in Examples and B1 to B4 in Comparative Examples were dissolved in the electrolyte solution at the ratios shown in Table 2 to prepare a non-aqueous electrolyte solution.

(Preparation of positive electrode 2)
_{LiNi 0.5} Mn _0.3 Co _0.2 O ₂ was used as the positive electrode active material, acetylene black was used as the conductive material, and N-methyl-2-pyrrolidone dispersion of polyvinylidene fluoride (PVdF) was used as the binder, and the active material was used. , A positive electrode mixture slurry mixed so that the solid content ratio of the conductive material and the binder was 92/3/5 (mass ratio) was prepared. The obtained positive electrode mixture slurry was uniformly applied onto an aluminum foil current collector having a thickness of 20 μm, dried, and then compression-molded by a press to obtain a positive electrode.

(Preparation of negative electrode)
Artificial graphite powder as negative electrode active material, aqueous dispersion of sodium carboxylmethylcellulose as thickener (concentration of sodium carboxymethylcellulose 1% by mass), aqueous dispersion of styrene-butadiene rubber as binder (concentration of styrene-butadiene rubber 50) By mass%), the active material, thickener, and binder have a solid content ratio of 97.6 / 1.2 / 1.2 (mass ratio) and are mixed in an aqueous solvent to form a slurry. The negative electrode mixture slurry was prepared. It was uniformly applied to a copper foil having a thickness of 20 μm, dried, and then compressed and formed by a press to obtain a negative electrode.

(Manufacturing of lithium ion secondary battery)
The negative electrode, the positive electrode and the polyethylene separator manufactured as described above were laminated in this order of the negative electrode, the separator and the positive electrode to prepare a battery element.
After inserting this battery element into a bag made of a laminated film in which both sides of an aluminum sheet (thickness 40 μm) are coated with a resin layer while projecting the positive electrode and negative electrode terminals, an electrolyte having the composition shown in Table 2 is inserted. Each of the liquids was injected into a bag and vacuum-sealed to prepare a sheet-shaped lithium ion secondary battery.

(High temperature cycle characterization test)
The secondary battery manufactured above is sandwiched between plates and pressurized, and at 60 ° C., constant current-constant voltage charging up to 4.4V with a current equivalent to 0.5C (hereinafter referred to as CC / CV charging). After (0.1 C cut), the battery was discharged to 3 V with a constant current of 0.5 C, which was set as one cycle, and this was repeated until 200 cycles were reached. Then, the cycle capacity retention rate after 200 cycles at 60 ° C. was determined by the following formula.
(Discharge capacity after 200 cycles) ÷ (Initial discharge capacity) x 100 = Cycle capacity retention rate (%)
In addition, after the battery was sufficiently cooled, the volume was measured by the Archimedes method, and the amount of gas generated from the volume change before and after the cycle test was determined.

Claims (5)

Solvent and
The following general formula (1-1):

(In the formula, R ¹ and R ⁴ are the same or different alkyl groups having 1 to 4 carbon atoms in the linear or branched chain, or alkenyl groups having 2 to 6 carbon atoms in the linear or branched chain. The alkyl group and alkenyl group may be substituted with one or more fluorine atoms. R ² and R ³ are the same or different, and have 1 to 1 carbon atoms in the -H, -F, linear or branched chain. 4 alkyl group, or a straight or branched chain alkenyl group having 2 to 6 carbon atoms, said alkyl and alkenyl groups may be substituted by one or more fluorine atoms. However, R ² And at least one of ^{R 3} is −F . The wavy line in the formula indicates either the cis configuration or the trans configuration), and the compound (1-1) represented by the formula (1-1), and the following general formula (1-2). :

(In the formula, R ⁵ and R ⁶ are the same or different alkylene groups having 1 to 12 carbon atoms in the linear or branched chain, even if the alkylene group is substituted with one or more fluorine atoms. Well, at least one compound (1) selected from the group consisting of the compounds (1-2) represented by (may contain one or more double bonds).
A lithium ion secondary battery comprising an electrolytic solution comprising. The lithium ion secondary battery according to claim 1, wherein at least one ^{of R 2} and R ³ in the general formula (1-1) is −H or −F. The lithium ion secondary battery according to claim 1 or 2, wherein the content of the compound (1) is 0.0001 to 10% by mass with respect to the solvent. The lithium ion secondary battery according to claim 1, 2 or 3 , wherein the electrolytic solution further contains an electrolyte salt. Module comprising: a lithium ion secondary battery請Motomeko 1, 2, 3 or 4, wherein.